137 results on '"Low MJ"'
Search Results
2. Germ cell defects and hematopoietic hypersensitivity to gamma- interferon in mice with a targeted disruption of the Fanconi anemia C gene
- Author
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Whitney, MA, primary, Royle, G, additional, Low, MJ, additional, Kelly, MA, additional, Axthelm, MK, additional, Reifsteck, C, additional, Olson, S, additional, Braun, RE, additional, Heinrich, MC, additional, Rathbun, RK, additional, Bagby, GC, additional, and Grompe, M, additional
- Published
- 1996
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3. Somatostatin secreted by islet delta-cells fulfills multiple roles as a paracrine regulator of islet function.
- Author
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Hauge-Evans AC, King AJ, Carmignac D, Richardson CC, Robinson IC, Low MJ, Christie MR, Persaud SJ, Jones PM, Hauge-Evans, Astrid C, King, Aileen J, Carmignac, Danielle, Richardson, Carolyn C, Robinson, Iain C A F, Low, Malcolm J, Christie, Michael R, Persaud, Shanta J, and Jones, Peter M
- Abstract
Objective: Somatostatin (SST) is secreted by islet delta-cells and by extraislet neuroendocrine cells. SST receptors have been identified on alpha- and beta-cells, and exogenous SST inhibits insulin and glucagon secretion, consistent with a role for SST in regulating alpha- and beta-cell function. However, the specific intraislet function of delta-cell SST remains uncertain. We have used Sst(-/-) mice to investigate the role of delta-cell SST in the regulation of insulin and glucagon secretion in vitro and in vivo.Research Design and Methods: Islet morphology was assessed by histological analysis. Hormone levels were measured by radioimmunoassay in control and Sst(-/-) mice in vivo and from isolated islets in vitro.Results: Islet size and organization did not differ between Sst(-/-) and control islets, nor did islet glucagon or insulin content. Sst(-/-) mice showed enhanced insulin and glucagon secretory responses in vivo. In vitro stimulus-induced insulin and glucagon secretion was enhanced from perifused Sst(-/-) islets compared with control islets and was inhibited by exogenous SST in Sst(-/-) but not control islets. No difference in the switch-off rate of glucose-stimulated insulin secretion was observed between genotypes, but the cholinergic agonist carbamylcholine enhanced glucose-induced insulin secretion to a lesser extent in Sst(-/-) islets compared with controls. Glucose suppressed glucagon secretion from control but not Sst(-/-) islets.Conclusions: We suggest that delta-cell SST exerts a tonic inhibitory influence on insulin and glucagon secretion, which may facilitate the islet response to cholinergic activation. In addition, delta-cell SST is implicated in the nutrient-induced suppression of glucagon secretion. [ABSTRACT FROM AUTHOR]- Published
- 2009
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4. In vivo evidence for inverse agonism of Agouti-related peptide in the central nervous system of proopiomelanocortin-deficient mice.
- Author
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Tolle V, Low MJ, Tolle, Virginie, and Low, Malcolm J
- Abstract
Objective: Melanocyte-stimulating hormone (MSH) peptides processed from proopiomelanocortin (POMC) regulate energy homeostasis by activating neuronal melanocortin receptor (MC-R) signaling. Agouti-related peptide (AgRP) is a naturally occurring MC-R antagonist but also displays inverse agonism at constitutively active melanocortin-4 receptor (MC4-R) expressed on transfected cells. We investigated whether AgRP functions similarly in vivo using mouse models that lack all neuronal MSH, thereby precluding competitive antagonism of MC-R by AgRP.Research Design and Methods: Feeding and metabolic effects of the MC-R agonist melanotan II (MTII), AgRP, and ghrelin were investigated after intracerebroventricular injection in neural-specific POMC-deficient (Pomc(-/-)Tg/+) and global POMC-deficient (Pomc(-/-)) mice. Gene expression was quantified by RT-PCR.Results: Hyperphagic POMC-deficient mice were more sensitive than wild-type mice to the anorectic effects of MTII. Hypothalamic melanocortin-3 (MC3)/4-R mRNAs in POMC-deficient mice were unchanged, suggesting increased receptor sensitivity as a possible mechanism for the heightened anorexia. AgRP reversed MTII-induced anorexia in both mutant strains, demonstrating its ability to antagonize MSH agonists at central MC3/4-R, but did not produce an acute orexigenic response by itself. The action of ghrelin was attenuated in Pomc(-/-)Tg/+ mice, suggesting decreased sensitivity to additional orexigenic signals. However, AgRP induced delayed and long-lasting modifications of energy balance in Pomc(-/-)Tg/+, but not glucocorticoid-deficient Pomc(-/-) mice, by decreasing oxygen consumption, increasing the respiratory exchange ratio, and increasing food intake.Conclusions: These data demonstrate that AgRP can modulate energy balance via a mechanism independent of MSH and MC3/4-R competitive antagonism, consistent with either inverse agonist activity at MC-R or interaction with a distinct receptor. [ABSTRACT FROM AUTHOR]- Published
- 2008
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5. Cyclic AMP regulates somatostatin mRNA accumulation in primary diencephalic cultures and in transfected fibroblast cells
- Author
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Montminy, MR, primary, Low, MJ, additional, Tapia-Arancibia, L, additional, Reichlin, S, additional, Mandel, G, additional, and Goodman, RH, additional
- Published
- 1986
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6. The homeodomain transcription factor Six3 regulates hypothalamic Pomc expression and its absence from POMC neurons induces hyperphagia and mild obesity in male mice.
- Author
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Yu H, Chiang A, Rubinstein M, and Low MJ
- Subjects
- Animals, Female, Male, Mice, Eating, Energy Metabolism, Mice, Inbred C57BL, Nerve Tissue Proteins metabolism, Nerve Tissue Proteins genetics, Homeodomain Proteins metabolism, Homeodomain Proteins genetics, Hyperphagia metabolism, Hypothalamus metabolism, Mice, Knockout, Neurons metabolism, Obesity metabolism, Obesity genetics, Pro-Opiomelanocortin metabolism, Pro-Opiomelanocortin genetics
- Abstract
Objective: Proopiomelanocortin (POMC) neurons release potent anorexigenic neuropeptides, which suppress food intake and enhance energy expenditure via melanocortin receptors. Although the importance of central melanocortin in physiological regulation is well established, the underlying genetic mechanisms that define the functional identity of melanocortin neurons and maintain hypothalamic Pomc expression remain to be fully determined. In this study, we investigate the functional significance of Six3, a transcriptional regulator notably expressed in embryonic and adult mouse POMC neurons, in the regulation of hypothalamic Pomc expression and downstream physiological consequences., Methods: We first evaluated the expression of Six3 in the developing and adult hypothalamus by double fluorescence in situ hybridization. Next, we assessed POMC immunoreactivity in mutant mice selectively lacking Six3 from Pomc-expressing neurons and quantified Pomc mRNA levels in a tamoxifen-inducible Six3 knockout mouse model activated at embryonic E9.5 days. We also determined glucose and insulin sensitivity, daily food intake, body composition and body weight in adult male and female mice lacking Six3 specifically from POMC neurons. Lastly, we assessed the physiological consequences of ablating Six3 from POMC neurons in adult mice., Results: Six3 and Pomc were co-expressed in mouse hypothalamic neurons during development and adulthood. Mouse embryos deficient in Six3 showed reduced Pomc expression in the developing hypothalamus. Targeted deletion of Six3 specifically from POMC neurons resulted in decreased hypothalamic Pomc expression, increased daily food intake, enhanced glucose sensitivity and mild obesity in male but not in female mice. Finally, conditional removal of Six3 from POMC neurons in adult mice led to a reduction in hypothalamic POMC immunoreactivity with no significant effects in body weight or food intake., Conclusions: Altogether, our results demonstrate that Six3 plays an essential role in the early establishment of POMC neuron identity and the maintenance of physiological levels of hypothalamic Pomc expression. In addition, our study demonstrates that the functional significance of Six3 expression in POMC neurons is sexually dimorphic and age-dependent., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier GmbH.. All rights reserved.)
- Published
- 2024
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7. A mammalian tripartite enhancer cluster controls hypothalamic Pomc expression, food intake, and body weight.
- Author
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Rojo D, Hael CE, Soria A, de Souza FSJ, Low MJ, Franchini LF, and Rubinstein M
- Subjects
- Animals, Mice, Female, Male, Mice, Transgenic, Humans, Transcription Factors metabolism, Transcription Factors genetics, Mammals metabolism, Mammals genetics, Pro-Opiomelanocortin metabolism, Pro-Opiomelanocortin genetics, Enhancer Elements, Genetic, Hypothalamus metabolism, Eating genetics, Eating physiology, Body Weight, Zebrafish genetics, Zebrafish metabolism
- Abstract
Food intake and energy balance are tightly regulated by a group of hypothalamic arcuate neurons expressing the proopiomelanocortin ( POMC) gene. In mammals, arcuate-specific POMC expression is driven by two cis -acting transcriptional enhancers known as nPE1 and nPE2. Because mutant mice lacking these two enhancers still showed hypothalamic Pomc mRNA, we searched for additional elements contributing to arcuate Pomc expression. By combining molecular evolution with reporter gene expression in transgenic zebrafish and mice, here, we identified a mammalian arcuate-specific Pomc enhancer that we named nPE3, carrying several binding sites also present in nPE1 and nPE2 for transcription factors known to activate neuronal Pomc expression, such as ISL1, NKX2.1, and ERα. We found that nPE3 originated in the lineage leading to placental mammals and remained under purifying selection in all mammalian orders, although it was lost in Simiiformes (monkeys, apes, and humans) following a unique segmental deletion event. Interestingly, ablation of nPE3 from the mouse genome led to a drastic reduction (>70%) in hypothalamic Pomc mRNA during development and only moderate (<33%) in adult mice. Comparison between double (nPE1 and nPE2) and triple (nPE1, nPE2, and nPE3) enhancer mutants revealed the relative contribution of nPE3 to hypothalamic Pomc expression and its importance in the control of food intake and adiposity in male and female mice. Altogether, these results demonstrate that nPE3 integrates a tripartite cluster of partially redundant enhancers that originated upon a triple convergent evolutionary process in mammals and that is critical for hypothalamic Pomc expression and body weight homeostasis., Competing Interests: Competing interests statement:The authors declare no competing interest.
- Published
- 2024
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8. Ultra-thin light-weight laser-induced-graphene (LIG) diffractive optics.
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Lee Y, Low MJ, Yang D, Nam HK, Le TD, Lee SE, Han H, Kim S, Vu QH, Yoo H, Yoon H, Lee J, Sandeep S, Lee K, Kim SW, and Kim YJ
- Abstract
The realization of hybrid optics could be one of the best ways to fulfill the technological requirements of compact, light-weight, and multi-functional optical systems for modern industries. Planar diffractive lens (PDL) such as diffractive lenses, photonsieves, and metasurfaces can be patterned on ultra-thin flexible and stretchable substrates and be conformally attached on top of arbitrarily shaped surfaces. In this review, we introduce recent research works addressed to the design and manufacturing of ultra-thin graphene optics, which will open new markets in compact and light-weight optics for next-generation endoscopic brain imaging, space internet, real-time surface profilometry, and multi-functional mobile phones. To provide higher design flexibility, lower process complexity, and chemical-free process with reasonable investment cost, direct laser writing (DLW) of laser-induced-graphene (LIG) is actively being applied to the patterning of PDL. For realizing the best optical performances in DLW, photon-material interactions have been studied in detail with respect to different laser parameters; the resulting optical characteristics have been evaluated in terms of amplitude and phase. A series of exemplary laser-written 1D and 2D PDL structures have been actively demonstrated with different base materials, and then, the cases are being expanded to plasmonic and holographic structures. The combination of these ultra-thin and light-weight PDL with conventional bulk refractive or reflective optical elements could bring together the advantages of each optical element. By integrating these suggestions, we suggest a way to realize the hybrid PDL to be used in the future micro-electronics surface inspection, biomedical, outer space, and extended reality (XR) industries., (© 2023. The Author(s).)
- Published
- 2023
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9. The G209R mutant mouse as a model for human PCSK1 polyendocrinopathy.
- Author
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Shakya M, Gahlot S, Martin NK, Arunagiri A, Martin MG, Arvan P, Low MJ, and Lindberg I
- Abstract
PCSK1 encodes an enzyme required for prohormone maturation into bioactive peptides. A striking number of SNPs and rare mutations in PCSK1 are associated with a range of clinical phenotypes. Infants bearing two copies of a catalytically inactivating mutation, such as G209R, exhibit life-threatening chronic diarrhea and subsequently develop systemic endocrinopathies. Using CRISPR/Cas9 technology, we have engineered a mouse model bearing a G209R missense mutation in exon 6 of the murine Pcsk1 locus. Most pups homozygous for the G209R mutation succumbed by day 2, and surviving pups were severely dwarfed. In homozygous (but not heterozygous) pups, blood glucose levels were significantly lower, accompanied by elevated plasma insulin-like immunoreactivity and accumulation of large quantities of unprocessed proinsulin in the pancreas. Peptide hormone processing was also aberrant in G209R mouse pituitary, with mature ACTH levels markedly reduced in homozygotes, accompanied by a significant accumulation of POMC. We also observed a significant reduction in PC1/3 protein in the brains of G209R homozygous mice by Western blotting, while PC2 levels remained unaffected. Most likely due to the continued presence of PC2, pituitary and brain levels of α-MSH were not impaired. Analysis of intestinal cell types indicated a modest reduction of enteroendocrine cells in G209R homozygotes. We suggest that the G209R Pcsk1 mouse model recapitulates many of the dramatic neonatal deficiencies of human patients with this homozygous mutation., (© The Author(s) 2022. Published by Oxford University Press on behalf of the Endocrine Society. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)
- Published
- 2022
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10. Developmental single-cell transcriptomics of hypothalamic POMC neurons reveal the genetic trajectories of multiple neuropeptidergic phenotypes.
- Author
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Yu H, Rubinstein M, and Low MJ
- Subjects
- Animals, Mice, Pro-Opiomelanocortin metabolism, RNA-Seq, Single-Cell Analysis, Hypothalamus metabolism, Neurons metabolism, Phenotype, Transcriptome
- Abstract
Proopiomelanocortin (POMC) neurons of the hypothalamic arcuate nucleus are essential to regulate food intake and energy balance. However, the ontogenetic transcriptional programs that specify the identity and functioning of these neurons are poorly understood. Here, we use single-cell RNA-sequencing (scRNA-seq) to define the transcriptomes characterizing Pomc -expressing cells in the developing hypothalamus and translating ribosome affinity purification with RNA-sequencing (TRAP-seq) to analyze the subsequent translatomes of mature POMC neurons. Our data showed that Pomc -expressing neurons give rise to multiple developmental pathways expressing different levels of Pomc and unique combinations of transcription factors. The predominant cluster, featured by high levels of Pomc and Prdm12 transcripts, represents the canonical arcuate POMC neurons. Additional cell clusters expressing medium or low levels of Pomc mature into different neuronal phenotypes featured by distinct sets of transcription factors, neuropeptides, processing enzymes, cell surface, and nuclear receptors. We conclude that the genetic programs specifying the identity and differentiation of arcuate POMC neurons are diverse and generate a heterogeneous repertoire of neuronal phenotypes early in development that continue to mature postnatally., Competing Interests: HY, MR, ML No competing interests declared, (© 2022, Yu et al.)
- Published
- 2022
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11. Adult-born proopiomelanocortin neurons derived from Rax-expressing precursors mitigate the metabolic effects of congenital hypothalamic proopiomelanocortin deficiency.
- Author
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Surbhi, Wittmann G, Low MJ, and Lechan RM
- Subjects
- Animals, Eye Proteins genetics, Homeodomain Proteins genetics, Mice, Mice, Inbred C57BL, Mice, Knockout, Mice, Transgenic, Transcription Factors genetics, Adrenal Insufficiency metabolism, Eye Proteins metabolism, Homeodomain Proteins metabolism, Hypothalamus metabolism, Neurons metabolism, Obesity metabolism, Pro-Opiomelanocortin deficiency, Pro-Opiomelanocortin metabolism, Transcription Factors metabolism
- Abstract
Objective: Proopiomelanocortin (POMC) neurons of the hypothalamic arcuate nucleus are essential regulators of energy balance. Selective loss of POMC production in these cells results in extreme obesity and metabolic comorbidities. Neurogenesis occurs in the adult hypothalamus, but it remains uncertain whether functional POMC neurons emerge in physiologically significant numbers during adulthood. Here, we tested whether Rax-expressing precursors generate POMC neurons in adult mice and rescue the metabolic phenotype caused by congenital hypothalamic POMC deficiency., Methods: Initially, we identified hypothalamic Rax-expressing cell types using wild-type and Rax-CreERT2:Ai34D mice. Then we generated compound Rax-CreERT2:ArcPomc
loxTB/loxTB mice in which endogenous hypothalamic Pomc expression is silenced, but can be restored by tamoxifen administration selectively in neurons derived from Rax+ progenitors. The number of POMC neurons generated by Rax+ progenitors in adult mice and their axonal projections was determined. The metabolic effects of these neurons were assessed by measuring food intake, bodyweight, and body composition, along with glucose and insulin levels., Results: We found that Rax is expressed by tanycytes and a previously unrecognized cell type in the hypothalamic parenchyma of adult mice. Rax+ progenitors generated ~10% of the normal adult hypothalamic POMC neuron population within two weeks of tamoxifen treatment. The same rate and steady state of POMC neurogenesis persisted from young adult to aged mice. These new POMC neurons established terminal projections to brain regions that were involved in energy homeostasis. Mice with Rax+ progenitor-derived POMC neurons had reduced body fat mass, improved glucose tolerance, increased insulin sensitivity, and decreased bodyweight in proportion to the number of new POMC neurons., Conclusions: These data demonstrate that Rax+ progenitors generate POMC neurons in sufficient numbers during adulthood to mitigate the metabolic abnormalities of hypothalamic POMC-deficient mice. The findings suggest that adult hypothalamic neurogenesis is a robust phenomenon in mice that can significantly impact energy homeostasis., (Copyright © 2021 The Authors. Published by Elsevier GmbH.. All rights reserved.)- Published
- 2021
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12. Mice lacking PC1/3 expression in POMC-expressing cells do not develop obesity.
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Shakya M, Gahlot S, White A, Verchere CB, Low MJ, and Lindberg I
- Abstract
Pro-opiomelanocortin (POMC) neurons form an integral part of the central melanocortin system regulating food intake and energy expenditure. Genetic and pharmacological studies have revealed that defects in POMC synthesis, processing, and receptor signaling lead to obesity. It is well established that POMC is extensively processed by a series of enzymes, including prohormone convertases PC1/3 and PC2, and that genetic insufficiency of both PC1/3 and POMC is strongly associated with obesity risk. However, whether PC1/3-mediated POMC processing is absolutely tied to body weight regulation is not known. To investigate this question, we generated a Pomc-CreER T2; Pcsk1 lox/lox mouse model in which Pcsk1 is specifically and temporally knocked out in POMC-expressing cells of adult mice by injecting tamoxifen at eight weeks of age. We then measured the impact of Pcsk1 deletion on POMC cleavage to ACTH and α-MSH, and on body weight. In whole pituitary, POMC cleavage was significantly impacted by the loss of Pcsk1, while hypothalamic POMC-derived peptide levels remained similar in all genotypes. However, intact POMC levels were greatly elevated in Pomc-CreER T2; Pcsk1 lox/lox mice. Males expressed two-fold greater levels of pituitary PC1/3 protein than females, consistent with their increased POMC cleavage. Past studies show that mice with germline removal of PC1/3 do not develop obesity, while mice expressing mutant PC1/3 forms do develop obesity. We conclude that obesity pathways are not disrupted by PC1/3 loss solely in POMC-expressing cells, further disfavoring the idea that alterations in POMC processing underlie obesity in PCSK1 deficiency., (© The Author(s) 2021. Published by Oxford University Press on behalf of the Endocrine Society. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)
- Published
- 2021
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13. Decreased sensitivity to the anorectic effects of leptin in mice that lack a Pomc-specific neural enhancer.
- Author
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Na ES, Lam DD, Yokosawa E, Adams JM, Olson DP, and Low MJ
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- Animals, Hypothalamus metabolism, Male, Mice, Mice, Knockout, Neurons metabolism, Appetite Depressants pharmacology, Body Weight drug effects, Eating drug effects, Enhancer Elements, Genetic, Hypothalamus drug effects, Leptin pharmacology, Neurons drug effects, Pro-Opiomelanocortin genetics
- Abstract
Enhancer redundancy has been postulated to provide a buffer for gene expression against genetic and environmental perturbations. While work in Drosophila has identified functionally overlapping enhancers, work in mammalian models has been limited. Recently, we have identified two partially redundant enhancers, nPE1 and nPE2, that drive proopiomelanocortin gene expression in the hypothalamus. Here we demonstrate that deletion of nPE1 produces mild obesity while knockout of nPE2 has no discernible metabolic phenotypes. Additionally, we show that acute leptin administration has significant effects on nPE1 knockout mice, with food intake and body weight change significantly impacted by peripheral leptin treatment. nPE1 knockout mice became less responsive to leptin treatment over time as percent body weight change increased over 2 week exposure to peripheral leptin. Both Pomc and Agrp mRNA were not differentially affected by chronic leptin treatment however we did see a decrease in Pomc and Agrp mRNA in both nPE1 and nPE2 knockout calorie restricted mice as compared to calorie restricted PBS-treated WT mice. Collectively, these data suggest dynamic regulation of Pomc by nPE1 such that mice with nPE1 knockout become less responsive to the anorectic effects of leptin treatment over time. Our results also support our earlier findings in which nPE2 may only be critical in adult mice that lack nPE1, indicating that these neural enhancers work synergistically to influence metabolism., Competing Interests: The authors have declared that no competing interests exist.
- Published
- 2020
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14. Hypothalamic POMC deficiency increases circulating adiponectin despite obesity.
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Yu H, Chhabra KH, Thompson Z, Jones GL, Kiran S, Shangguan G, and Low MJ
- Subjects
- Adiponectin deficiency, Adiponectin metabolism, Adipose Tissue metabolism, Animals, Caloric Restriction, Disease Models, Animal, Female, Melanocortins metabolism, Metabolism, Inborn Errors metabolism, Mice, Mice, Knockout, Peptides, Cyclic pharmacology, Pro-Opiomelanocortin genetics, Signal Transduction drug effects, Sympathetic Nervous System metabolism, alpha-MSH analogs & derivatives, alpha-MSH pharmacology, Adiponectin blood, Arcuate Nucleus of Hypothalamus metabolism, Neurons metabolism, Obesity blood, Pro-Opiomelanocortin deficiency
- Abstract
Objective: The steep rise in the prevalence of obesity and its related metabolic syndrome have become a major worldwide health concerns. Melanocortin peptides from hypothalamic arcuate nucleus (Arc) POMC neurons induce satiety to limit food intake. Consequently, Arc Pomc-deficient mice (ArcPomc
-/- ) exhibit hyperphagia and obesity. Previous studies demonstrated that the circulating levels of adiponectin, a protein abundantly produced and secreted by fat cells, negatively correlate with obesity in both rodents and humans. However, we found that ArcPomc-/- mice have increased circulating adiponectin levels despite obesity. Therefore, we investigated the physiological function and underlying mechanisms of hypothalamic POMC in regulating systemic adiponectin levels., Methods: Circulating adiponectin was measured in obese ArcPomc-/- mice at ages 4-52 weeks. To determine whether increased adiponectin was a direct result of ArcPomc deficiency or a secondary effect of obesity, we examined plasma adiponectin levels in calorie-restricted mice with or without a history of obesity and in ArcPomc-/- mice before and after genetic restoration of Pomc expression in the hypothalamus. To delineate the mechanisms causing increased adiponectin in ArcPomc-/- mice, we determined sympathetic outflow to adipose tissue by assessing epinephrine, norepinephrine, and tyrosine hydroxylase protein levels and measured the circulating adiponectin in the mice after acute norepinephrine or propranolol treatments. In addition, adiponectin mRNA and protein levels were measured in discrete adipose tissue depots to ascertain which fat depots contributed the most to the high level of adiponectin in the ArcPomc-/- mice. Finally, we generated compound Adiopoq-/- :ArcPomc-/- mice and compared their growth, body composition, and glucose homeostasis to the individual knockout mouse strains and their wild-type controls., Results: Obese ArcPomc-/- female mice had unexpectedly increased plasma adiponectin compared to wild-type siblings at all ages greater than 8 weeks. Despite chronic calorie restriction to achieve normal body weights, higher adiponectin levels persisted in the ArcPomc-/- female mice. Genetic restoration of Pomc expression in the Arc or acute treatment of the ArcPomc-/- female mice with melanotan II reduced adiponectin levels to control littermate values. The ArcPomc-/- mice had defective thermogenesis and decreased epinephrine, norepinephrine, and tyrosine hydroxylase protein levels in their fat pads, indicating reduced sympathetic outflow to adipose tissue. Injections of norepinephrine into the ArcPomc-/- female mice reduced circulating adiponectin levels, whereas injections of propranolol significantly increased adiponectin levels. Despite the beneficial effects of adiponectin on metabolism, the deletion of adiponectin alleles in the ArcPomc-/- mice did not exacerbate their metabolic abnormalities., Conclusion: In summary, to the best of our knowledge, this study provides the first evidence that despite obesity, the ArcPomc-/- mouse model has high circulating adiponectin levels, which demonstrated that increased fat mass is not necessarily correlated with hypoadiponectinemia. Our investigation also found a previously unknown physiological pathway connecting POMC neurons via the sympathetic nervous system to circulating adiponectin, thereby shedding light on the biological regulation of adiponectin., (Copyright © 2020 The Author(s). Published by Elsevier GmbH.. All rights reserved.)- Published
- 2020
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15. The transcriptional regulator PRDM12 is critical for Pomc expression in the mouse hypothalamus and controlling food intake, adiposity, and body weight.
- Author
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Hael CE, Rojo D, Orquera DP, Low MJ, and Rubinstein M
- Subjects
- Animals, Carrier Proteins genetics, Female, Male, Mice, Mice, Inbred C57BL, Mice, Transgenic, Nerve Tissue Proteins genetics, Pregnancy, Pro-Opiomelanocortin metabolism, Adiposity, Body Weight, Carrier Proteins metabolism, Eating, Hypothalamus metabolism, Nerve Tissue Proteins metabolism, Pro-Opiomelanocortin genetics
- Abstract
Objective: Regulation of food intake and energy balance depends on a group of hypothalamic neurons that release anorexigenic melanocortins encoded by the Pomc gene. Although the physiological importance of central melanocortins is well appreciated, the genetic program that defines the functional identity of melanocortin neurons and assures high levels of hypothalamic Pomc expression is only beginning to be understood. This study assessed whether the transcriptional regulator PRDM12, identified as a highly expressed gene in adult mouse POMC neurons, plays an important role in the identity and function of melanocortin neurons., Methods: We first determined the cellular distribution of PRDM12 in the developing hypothalamus. Then we studied mutant mice with constitutively inactivated Prdm12 to evaluate possible changes in hypothalamic Pomc expression. In addition, we characterized conditional mutant mice specifically lacking Prdm12 in ISL1-positive or POMC neurons during development. Finally, we measured food intake, body weight progression up to 16 weeks of age, adiposity, and glucose tolerance in adult mice lacking Prdm12 selectively from POMC neurons., Results: PRDM12 co-expressed with POMC in mouse hypothalamic neurons from early development to adulthood. Mice lacking Prdm12 displayed greatly reduced Pomc expression in the developing hypothalamus. Selective ablation of Prdm12 from ISL1 neurons prevented hypothalamic Pomc expression. The conditional ablation of Prdm12 limited to POMC neurons greatly reduced Pomc expression in the developing hypothalamus and in adult mice led to increased food intake, adiposity, and obesity., Conclusions: Altogether, our results demonstrate that PRDM12 plays an essential role in the early establishment of hypothalamic melanocortin neuron identity and the maintenance of high expression levels of Pomc. Its absence in adult mice greatly impairs Pomc expression and leads to increased food intake, adiposity, and obesity., (Copyright © 2020 The Author(s). Published by Elsevier GmbH.. All rights reserved.)
- Published
- 2020
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16. Nuclear transcriptional changes in hypothalamus of Pomc enhancer knockout mice after excessive alcohol drinking.
- Author
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Zhou Y, Liang Y, Low MJ, and Kreek MJ
- Subjects
- Animals, Arginine Vasopressin metabolism, Binge Drinking metabolism, Enkephalins genetics, Enkephalins metabolism, Ethanol pharmacology, Hypothalamus drug effects, Male, Mice, Mice, Inbred C57BL, Oxytocin metabolism, Pro-Opiomelanocortin metabolism, Protein Precursors genetics, Protein Precursors metabolism, Receptors, Opioid, mu genetics, Receptors, Opioid, mu metabolism, Transcriptome, Binge Drinking genetics, Enhancer Elements, Genetic genetics, Hypothalamus metabolism, Pro-Opiomelanocortin genetics
- Abstract
Persistent alterations of proopiomelanocortin (Pomc) and mu-opioid receptor (Oprm1) activity and stress responses after alcohol are critically involved in vulnerability to alcohol dependency. Gene transcriptional regulation altered by alcohol may play important roles. Mice with genome-wide deletion of neuronal Pomc enhancer1 (nPE1
-/- ), had hypothalamic-specific partial reductions of beta-endorphin and displayed lower alcohol consumption, compared to wildtype littermates (nPE1+/+ ). We used RNA-Seq to measure steady-state nuclear mRNA transcripts of opioid and stress genes in hypothalamus of nPE1+/+ and nPE1-/- mice after 1-day acute withdrawal from chronic excessive alcohol drinking or after water. nPE1-/- had lower basal Pomc and Pdyn (prodynorphin) levels compared to nPE1+/+ , coupled with increased basal Oprm1 and Oprk1 (kappa-opioid receptor) levels, and low alcohol drinking increased Pomc and Pdyn to the basal levels of nPE1+/+ in the water group, without significant effects on Oprm1 and Oprk1. In nPE1+/+ , excessive alcohol intake increased Pomc and Oprm1, with no effect on Pdyn or Oprk1. For stress genes, nPE1-/- had lowered basal Oxt (oxytocin) and Avp (arginine vasopressin) that were restored by low alcohol intake to basal levels of nPE1+/+ . In nPE1+/+ , excessive alcohol intake decreased Oxt and Avpi1 (AVP-induced protein1). Functionally examining the effect of pharmacological blockade of mu-opioid receptor, we found that naltrexone reduced excessive alcohol intake in nPE1+/+ , but not nPE1-/- . Our results provide evidence relevant to the transcriptional profiling of the critical genes in mouse hypothalamus: enhanced opioid and reduced stress gene transcripts after acute withdrawal from excessive alcohol may contribute to altered reward and stress responses., (© 2019 John Wiley & Sons Ltd and International Behavioural and Neural Genetics Society.)- Published
- 2019
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17. Reduced Stability and pH-Dependent Activity of a Common Obesity-Linked PCSK1 Polymorphism, N221D.
- Author
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Jarvela TS, Shakya M, Bachor T, White A, Low MJ, and Lindberg I
- Subjects
- Animals, Endoplasmic Reticulum Stress, Enzyme Stability, Female, Glucose Intolerance, Humans, Hydrogen-Ion Concentration, Hypothalamus metabolism, Male, Mice, Neuropeptide Y metabolism, Pituitary Gland metabolism, Polymorphism, Single Nucleotide, Pro-Opiomelanocortin metabolism, Proprotein Convertase 1 genetics, Sex Characteristics, alpha-MSH metabolism, Obesity genetics, Proprotein Convertase 1 metabolism
- Abstract
Common mutations in the human prohormone convertase (PC)1/3 gene (PCKSI) are linked to increased risk of obesity. Previous work has shown that the rs6232 single-nucleotide polymorphism (N221D) results in slightly decreased activity, although whether this decrease underlies obesity risk is not clear. We observed significantly decreased activity of the N221D PC1/3 enzyme at the pH of the trans-Golgi network; at this pH, the mutant enzyme was less stable than wild-type enzyme. Recombinant N221D PC1/3 also showed enhanced susceptibility to heat stress. Enhanced susceptibility to tunicamycin-induced endoplasmic reticulum stress was observed in AtT-20/PC2 cell clones in which murine PC1/3 was replaced by human N221D PC1/3, as compared with wild-type human PC1/3. However, N221D PC1/3-expressing AtT-20/PC2 clones processed proopiomelanocortin to α-MSH similarly to wild-type PC1/3. We also generated a CRISPR-edited mouse line expressing the N221D mutation in the PCKSI gene. When homozygous N221D mice were fed either a standard or a high-fat diet, we found no increase in body weight compared with their wild-type sibling controls. Sexual dimorphism was observed in pituitary ACTH for both genotypes, with females exhibiting lower levels of pituitary ACTH. In contrast, hypothalamic α-MSH content for both genotypes was higher in females compared with males. Hypothalamic corticotropin-like intermediate peptide content was higher in wild-type females compared with wild-type, but not N221D, males. Taken together, these data suggest that the increased obesity risk linked to the N221D allele in humans may be due in part to PC1/3-induced loss of resilience to stressors rather than strictly to decreased enzymatic activity on peptide precursors., (Copyright © 2019 Endocrine Society.)
- Published
- 2019
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18. The Homeodomain Transcription Factor NKX2.1 Is Essential for the Early Specification of Melanocortin Neuron Identity and Activates Pomc Expression in the Developing Hypothalamus.
- Author
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Orquera DP, Tavella MB, de Souza FSJ, Nasif S, Low MJ, and Rubinstein M
- Subjects
- Animals, Body Weight physiology, Female, Gene Expression Regulation, Developmental physiology, Hypothalamus embryology, Hypothalamus metabolism, Male, Mice, Mice, Inbred C57BL, Mice, Transgenic, Melanocortins metabolism, Neurogenesis physiology, Neurons metabolism, Pro-Opiomelanocortin metabolism, Thyroid Nuclear Factor 1 metabolism
- Abstract
Food intake is tightly regulated by a group of neurons present in the arcuate nucleus of the hypothalamus, which release Pomc -encoded melanocortins, the absence of which induces marked hyperphagia and early-onset obesity. Although the relevance of hypothalamic POMC neurons in the regulation of body weight and energy balance is well appreciated, little is known about the transcription factors that establish the melanocortin neuron identity during brain development and its phenotypic maintenance in postnatal life. Here, we report that the transcription factor NKX2.1 is present in mouse hypothalamic POMC neurons from early development to adulthood. Electromobility shift assays showed that NKX2.1 binds in vitro to NKX binding motifs present in the neuronal Pomc enhancers nPE1 and nPE2 and chromatin immunoprecipitation assays detected in vivo binding of NKX2.1 to nPE1 and nPE2 in mouse hypothalamic extracts. Transgenic and mutant studies performed in mouse embryos of either sex and adult males showed that the NKX motifs present in nPE1 and nPE2 are essential for their transcriptional enhancer activity. The conditional early inactivation of Nkx2.1 in the ventral hypothalamus prevented the onset of Pomc expression. Selective Nkx2.1 ablation from POMC neurons decreased Pomc expression in adult males and mildly increased their body weight and adiposity. Our results demonstrate that NKX2.1 is necessary to activate Pomc expression by binding to conserved canonical NKX motifs present in nPE1 and nPE2. Therefore, NKX2.1 plays a critical role in the early establishment of hypothalamic melanocortin neuron identity and participates in the maintenance of Pomc expression levels during adulthood. SIGNIFICANCE STATEMENT Food intake and body weight regulation depend on hypothalamic neurons that release satiety-inducing neuropeptides, known as melanocortins. Central melanocortins are encoded by Pomc , and Pomc mutations may lead to hyperphagia and severe obesity. Although the importance of central melanocortins is well appreciated, the genetic program that establishes and maintains fully functional POMC neurons remains to be explored. Here, we combined molecular, genetic, developmental, and functional studies that led to the discovery of NKX2.1, a transcription factor that participates in the early morphogenesis of the developing hypothalamus, as a key player in establishing the early identity of melanocortin neurons by activating Pomc expression. Thus, Nkx2.1 adds to the growing list of genes that participate in body weight regulation and adiposity., (Copyright © 2019 the authors.)
- Published
- 2019
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19. Selective Restoration of Pomc Expression in Glutamatergic POMC Neurons: Evidence for a Dynamic Hypothalamic Neurotransmitter Network.
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Jones GL, Wittmann G, Yokosawa EB, Yu H, Mercer AJ, Lechan RM, and Low MJ
- Subjects
- Animals, Female, Glutamic Acid metabolism, Male, Mice, Mice, Inbred C57BL, Obesity metabolism, Arcuate Nucleus of Hypothalamus metabolism, Energy Metabolism physiology, Neurons metabolism, Neurotransmitter Agents metabolism, Pro-Opiomelanocortin metabolism
- Abstract
Hypothalamic POMC deficiency leads to obesity and metabolic deficiencies, largely due to the loss of melanocortin peptides. However, POMC neurons in the arcuate nucleus (ARC) are comprised of glutamatergic and GABAergic subpopulations. The developmental program, relative proportion and function of these two subpopulations are unresolved. To test whether glutamatergic POMC neurons serve a distinct role in maintaining energy homeostasis, we activated Pomc expression Cre- dependently in Vglut2 -expressing neurons of mice with conditionally silenced Pomc alleles. The Vglut2 - Pomc restored mice had normal ARC Pomc mRNA levels, POMC immunoreactivity, as well as body weight and body composition at age 12 weeks. Unexpectedly, the cumulative total of Vglut2
+ glutamatergic- and Gad67+ GABAergic - Pomc neurons detected by in situ hybridization (ISH) exceeded 100% in both Vglut2 - Pomc restored and control mice, indicating that a subpopulation of Pomc neurons must express both neuronal markers. Consistent with this hypothesis, triple ISH of C57BL/6J hypothalami revealed that 35% of ARC Pomc neurons were selectively Gad67+ , 21% were selectively Vglut2+ , and 38% expressed both Gad67 and Vglut2 . The single Gad67+ and Vglut2+ Pomc neurons were most prevalent in the rostral ARC, while the Vglut2/Gad67+ dual-phenotype cells predominated in the caudal ARC. A lineage trace using Ai9-tdTomato reporter mice to label fluorescently all Vglut2 -expressing neurons showed equal numbers of tdTomato+ and tdTomato- POMC immunoreactive neurons. Together, these data suggest that POMC neurons exhibit developmental plasticity in their expression of glutamatergic and GABAergic markers, enabling re-establishment of normal energy homeostasis in the Vglut2 - Pomc restored mice.- Published
- 2019
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20. Hypothalamic POMC or MC4R deficiency impairs counterregulatory responses to hypoglycemia in mice.
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Tooke BP, Yu H, Adams JM, Jones GL, Sutton-Kennedy T, Mundada L, Qi NR, Low MJ, and Chhabra KH
- Subjects
- Animals, Epinephrine metabolism, Glucagon metabolism, Homeostasis, Male, Mice, Mice, Inbred C57BL, Mice, Inbred NOD, Pro-Opiomelanocortin deficiency, Pro-Opiomelanocortin genetics, Receptor, Melanocortin, Type 4 deficiency, Receptor, Melanocortin, Type 4 genetics, Hypoglycemia metabolism, Hypothalamus metabolism, Pro-Opiomelanocortin metabolism, Receptor, Melanocortin, Type 4 metabolism
- Abstract
Objective: Life-threatening hypoglycemia is a major limiting factor in the management of diabetes. While it is known that counterregulatory responses to hypoglycemia are impaired in diabetes, molecular mechanisms underlying the reduced responses remain unclear. Given the established roles of the hypothalamic proopiomelanocortin (POMC)/melanocortin 4 receptor (MC4R) circuit in regulating sympathetic nervous system (SNS) activity and the SNS in stimulating counterregulatory responses to hypoglycemia, we hypothesized that hypothalamic POMC as well as MC4R, a receptor for POMC derived melanocyte stimulating hormones, is required for normal hypoglycemia counterregulation., Methods: To test the hypothesis, we induced hypoglycemia or glucopenia in separate cohorts of mice deficient in either POMC or MC4R in the arcuate nucleus (ARC) or the paraventricular nucleus of the hypothalamus (PVH), respectively, and measured their circulating counterregulatory hormones. In addition, we performed a hyperinsulinemic-hypoglycemic clamp study to further validate the function of MC4R in hypoglycemia counterregulation. We also measured Pomc and Mc4r mRNA levels in the ARC and PVH, respectively, in the streptozotocin-induced type 1 diabetes mouse model and non-obese diabetic (NOD) mice to delineate molecular mechanisms by which diabetes deteriorates the defense systems against hypoglycemia. Finally, we treated diabetic mice with the MC4R agonist MTII, administered stereotaxically into the PVH, to determine its potential for restoring the counterregulatory response to hypoglycemia in diabetes., Results: Stimulation of epinephrine and glucagon release in response to hypoglycemia or glucopenia was diminished in both POMC- and MC4R-deficient mice, relative to their littermate controls. Similarly, the counterregulatory response was impaired in association with decreased hypothalamic Pomc and Mc4r expression in the diabetic mice, a phenotype that was not reversed by insulin treatment which normalized glycemia. In contrast, infusion of an MC4R agonist in the PVH restored the counterregulatory response in diabetic mice., Conclusion: In conclusion, hypothalamic Pomc as well as Mc4r, both of which are reduced in type 1 diabetic mice, are required for normal counterregulatory responses to hypoglycemia. Therefore, enhancing MC4R function may improve hypoglycemia counterregulation in diabetes., (Copyright © 2018 The Authors. Published by Elsevier GmbH.. All rights reserved.)
- Published
- 2019
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21. Electrical stimulation of renal nerves for modulating urine glucose excretion in rats.
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Jiman AA, Chhabra KH, Lewis AG, Cederna PS, Seeley RJ, Low MJ, and Bruns TM
- Abstract
Background: The role of the kidney in glucose homeostasis has gained global interest. Kidneys are innervated by renal nerves, and renal denervation animal models have shown improved glucose regulation. We hypothesized that stimulation of renal nerves at kilohertz frequencies, which can block propagation of action potentials, would increase urine glucose excretion. Conversely, we hypothesized that low frequency stimulation, which has been shown to increase renal nerve activity, would decrease urine glucose excretion., Methods: We performed non-survival experiments on male rats under thiobutabarbital anesthesia. A cuff electrode was placed around the left renal artery, encircling the renal nerves. Ureters were cannulated bilaterally to obtain urine samples from each kidney independently for comparison. Renal nerves were stimulated at kilohertz frequencies (1-50 kHz) or low frequencies (2-5 Hz), with intravenous administration of a glucose bolus shortly into the 25-40-min stimulation period. Urine samples were collected at 5-10-min intervals, and colorimetric assays were used to quantify glucose excretion and concentration between stimulated and non-stimulated kidneys. A Kruskal-Wallis test was performed across all stimulation frequencies (α = 0.05), followed by a post-hoc Wilcoxon rank sum test with Bonferroni correction (α = 0.005)., Results: For kilohertz frequency trials, the stimulated kidney yielded a higher average total urine glucose excretion at 33 kHz (+ 24.5%; n = 9) than 1 kHz (- 5.9%; n = 6) and 50 kHz (+ 2.3%; n = 14). In low frequency stimulation trials, 5 Hz stimulation led to a lower average total urine glucose excretion (- 40.4%; n = 6) than 2 Hz (- 27.2%; n = 5). The average total urine glucose excretion between 33 kHz and 5 Hz was statistically significant ( p < 0.005). Similar outcomes were observed for urine flow rate, which may suggest an associated response. No trends or statistical significance were observed for urine glucose concentrations., Conclusion: To our knowledge, this is the first study to investigate electrical stimulation of renal nerves to modulate urine glucose excretion. Our experimental results show that stimulation of renal nerves may modulate urine glucose excretion, however, this response may be associated with urine flow rate. Future work is needed to examine the underlying mechanisms and identify approaches for enhancing regulation of glucose excretion., Competing Interests: Competing interestsRJS has received research support from and/or has served as an advisor or consultant to Ethicon Endo-Surgery/Johnson & Johnson, Orexigen, Novo Nordisk, Daiichi Sankyo, Janssen/Johnson & Johnson, Novartis, Paul Hastings Law Firm, Zafgen, MedImmune, Sanofi, Kallyope, and Scohia., (© The Author(s) 2018.)
- Published
- 2018
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22. Hypothalamic ER-associated degradation regulates POMC maturation, feeding, and age-associated obesity.
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Kim GH, Shi G, Somlo DR, Haataja L, Song S, Long Q, Nillni EA, Low MJ, Arvan P, Myers MG Jr, and Qi L
- Subjects
- Animals, Axons, Cysteine chemistry, Feeding Behavior, Female, Green Fluorescent Proteins metabolism, Humans, Inflammation, Intracellular Signaling Peptides and Proteins, Leptin blood, Male, Mice, Mice, Inbred C57BL, Mutation, Neurons metabolism, Phenylalanine chemistry, Pro-Opiomelanocortin genetics, Proteins metabolism, Sulfhydryl Compounds, Ubiquitin chemistry, Ubiquitin-Protein Ligases metabolism, Ubiquitination, Endoplasmic Reticulum pathology, Endoplasmic Reticulum-Associated Degradation, Hypothalamus pathology, Obesity pathology, Pro-Opiomelanocortin metabolism
- Abstract
Pro-opiomelanocortin (POMC) neurons function as key regulators of metabolism and physiology by releasing prohormone-derived neuropeptides with distinct biological activities. However, our understanding of early events in prohormone maturation in the ER remains incomplete. Highlighting the significance of this gap in knowledge, a single POMC cysteine-to-phenylalanine mutation at position 28 (POMC-C28F) is defective for ER processing and causes early onset obesity in a dominant-negative manner in humans through an unclear mechanism. Here, we report a pathologically important role of Sel1L-Hrd1, the protein complex of ER-associated degradation (ERAD), within POMC neurons. Mice with POMC neuron-specific Sel1L deficiency developed age-associated obesity due, at least in part, to the ER retention of POMC that led to hyperphagia. The Sel1L-Hrd1 complex targets a fraction of nascent POMC molecules for ubiquitination and proteasomal degradation, preventing accumulation of misfolded and aggregated POMC, thereby ensuring that another fraction of POMC can undergo normal posttranslational processing and trafficking for secretion. Moreover, we found that the disease-associated POMC-C28F mutant evades ERAD and becomes aggregated due to the presence of a highly reactive unpaired cysteine thiol at position 50. Thus, this study not only identifies ERAD as an important mechanism regulating POMC maturation within the ER, but also provides insights into the pathogenesis of monogenic obesity associated with defective prohormone folding.
- Published
- 2018
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23. 17α-estradiol acts through hypothalamic pro-opiomelanocortin expressing neurons to reduce feeding behavior.
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Steyn FJ, Ngo ST, Chen VP, Bailey-Downs LC, Xie TY, Ghadami M, Brimijoin S, Freeman WM, Rubinstein M, Low MJ, and Stout MB
- Subjects
- Animals, Arcuate Nucleus of Hypothalamus drug effects, Arcuate Nucleus of Hypothalamus metabolism, Behavior, Animal drug effects, Eating drug effects, Hypothalamus metabolism, Leptin metabolism, Mice, Transgenic, Neurons metabolism, Obesity metabolism, Pro-Opiomelanocortin metabolism, Estradiol pharmacology, Feeding Behavior drug effects, Hypothalamus drug effects, Neurons drug effects, Pro-Opiomelanocortin pharmacology
- Abstract
Weight loss is an effective intervention for diminishing disease burden in obese older adults. Pharmacological interventions that reduce food intake and thereby promote weight loss may offer effective strategies to reduce age-related disease. We previously reported that 17α-estradiol (17α-E2) administration elicits beneficial effects on metabolism and inflammation in old male mice. These observations were associated with reduced calorie intake. Here, we demonstrate that 17α-E2 acts through pro-opiomelanocortin (Pomc) expression in the arcuate nucleus (ARC) to reduce food intake and body mass in mouse models of obesity. These results confirm that 17α-E2 modulates appetite through selective interactions within hypothalamic anorexigenic pathways. Interestingly, some peripheral markers of metabolic homeostasis were also improved in animals with near complete loss of ARC Pomc transcription. This suggests that 17α-E2 might have central and peripheral actions that can beneficially affect metabolism cooperatively or independently., (© 2017 The Authors. Aging Cell published by the Anatomical Society and John Wiley & Sons Ltd.)
- Published
- 2018
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24. Gastrin Induces Nuclear Export and Proteasome Degradation of Menin in Enteric Glial Cells.
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Sundaresan S, Meininger CA, Kang AJ, Photenhauer AL, Hayes MM, Sahoo N, Grembecka J, Cierpicki T, Ding L, Giordano TJ, Else T, Madrigal DJ, Low MJ, Campbell F, Baker AM, Xu H, Wright NA, and Merchant JL
- Subjects
- Active Transport, Cell Nucleus, Animals, Cells, Cultured, Cyclic AMP-Dependent Protein Kinases metabolism, Duodenal Neoplasms enzymology, Duodenal Neoplasms genetics, Duodenal Neoplasms pathology, Duodenum drug effects, Duodenum pathology, Gastrinoma enzymology, Gastrinoma genetics, Gastrinoma pathology, Gastrins genetics, Gene Expression Regulation, Glial Fibrillary Acidic Protein metabolism, Humans, Hyperplasia, Mice, Inbred C57BL, Mice, Knockout, Neuroglia drug effects, Proteasome Inhibitors pharmacology, Proteolysis, Proto-Oncogene Proteins genetics, Proton Pump Inhibitors pharmacology, Receptor, Cholecystokinin B metabolism, Receptors, Somatostatin genetics, Receptors, Somatostatin metabolism, Time Factors, Ubiquitination, Duodenum metabolism, Gastrins metabolism, Neuroglia enzymology, Proteasome Endopeptidase Complex metabolism, Proto-Oncogene Proteins metabolism
- Abstract
Background & Aims: The multiple endocrine neoplasia, type 1 (MEN1) locus encodes the nuclear protein and tumor suppressor menin. MEN1 mutations frequently cause neuroendocrine tumors such as gastrinomas, characterized by their predominant duodenal location and local metastasis at time of diagnosis. Diffuse gastrin cell hyperplasia precedes the appearance of MEN1 gastrinomas, which develop within submucosal Brunner's glands. We investigated how menin regulates expression of the gastrin gene and induces generation of submucosal gastrin-expressing cell hyperplasia., Methods: Primary enteric glial cultures were generated from the VillinCre:Men1
FL/FL :Sst-/- mice or C57BL/6 mice (controls), with or without inhibition of gastric acid by omeprazole. Primary enteric glial cells from C57BL/6 mice were incubated with gastrin and separated into nuclear and cytoplasmic fractions. Cells were incubated with forskolin and H89 to activate or inhibit protein kinase A (a family of enzymes whose activity depends on cellular levels of cyclic AMP). Gastrin was measured in blood, tissue, and cell cultures using an ELISA. Immunoprecipitation with menin or ubiquitin was used to demonstrate post-translational modification of menin. Primary glial cells were incubated with leptomycin b and MG132 to block nuclear export and proteasome activity, respectively. We obtained human duodenal, lymph node, and pancreatic gastrinoma samples, collected from patients who underwent surgery from 1996 through 2007 in the United States or the United Kingdom., Results: Enteric glial cells that stained positive for glial fibrillary acidic protein (GFAP+) expressed gastrin de novo through a mechanism that required PKA. Gastrin-induced nuclear export of menin via cholecystokinin B receptor (CCKBR)-mediated activation of PKA. Once exported from the nucleus, menin was ubiquitinated and degraded by the proteasome. GFAP and other markers of enteric glial cells (eg, p75 and S100B), colocalized with gastrin in human duodenal gastrinomas., Conclusions: MEN1-associated gastrinomas, which develop in the submucosa, might arise from enteric glial cells through hormone-dependent PKA signaling. This pathway disrupts nuclear menin function, leading to hypergastrinemia and associated sequelae., (Copyright © 2017 AGA Institute. Published by Elsevier Inc. All rights reserved.)- Published
- 2017
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25. Reduced renal sympathetic nerve activity contributes to elevated glycosuria and improved glucose tolerance in hypothalamus-specific Pomc knockout mice.
- Author
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Chhabra KH, Morgan DA, Tooke BP, Adams JM, Rahmouni K, and Low MJ
- Subjects
- Animals, Arcuate Nucleus of Hypothalamus metabolism, Diabetes Mellitus, Experimental, Female, Glucose metabolism, Glucose Tolerance Test, Glucose Transporter Type 2 metabolism, Glycosuria metabolism, Glycosuria urine, Insulin metabolism, Insulin Resistance physiology, Kidney metabolism, Male, Mice, Mice, Knockout, Mice, Obese, Obesity metabolism, Pro-Opiomelanocortin genetics, Pro-Opiomelanocortin metabolism, Glycosuria physiopathology, Hypothalamus metabolism, Kidney innervation, Pro-Opiomelanocortin deficiency, Sympathetic Nervous System physiology
- Abstract
Objective: Hypothalamic arcuate nucleus-specific pro-opiomelanocortin deficient (ArcPomc
-/- ) mice exhibit improved glucose tolerance despite massive obesity and insulin resistance. We demonstrated previously that their improved glucose tolerance is due to elevated glycosuria. However, the underlying mechanisms that link glucose reabsorption in the kidney with ArcPomc remain unclear. Given the function of the hypothalamic melanocortin system in controlling sympathetic outflow, we hypothesized that reduced renal sympathetic nerve activity (RSNA) in ArcPomc-/- mice could explain their elevated glycosuria and consequent enhanced glucose tolerance., Methods: We measured RSNA by multifiber recording directly from the nerves innervating the kidneys in ArcPomc-/- mice. To further validate the function of RSNA in glucose reabsorption, we denervated the kidneys of WT and diabetic db/db mice before measuring their glucose tolerance and urine glucose levels. Moreover, we performed western blot and immunohistochemistry to determine kidney GLUT2 and SGLT2 levels in either ArcPomc-/- mice or the renal-denervated mice., Results: Consistent with our hypothesis, we found that basal RSNA was decreased in ArcPomc-/- mice relative to their wild type (WT) littermates. Remarkably, both WT and db/db mice exhibited elevated glycosuria and improved glucose tolerance after renal denervation. The elevated glycosuria in obese ArcPomc-/- , WT and db/db mice was due to reduced renal GLUT2 levels in the proximal tubules. Overall, we show that renal-denervated WT and diabetic mice recapitulate the phenotype of improved glucose tolerance and elevated glycosuria associated with reduced renal GLUT2 levels observed in obese ArcPomc-/- mice., Conclusion: Hence, we conclude that ArcPomc is essential in maintaining basal RSNA and that elevated glycosuria is a possible mechanism to explain improved glucose tolerance after renal denervation in drug resistant hypertensive patients., (Copyright © 2017 The Authors. Published by Elsevier GmbH.. All rights reserved.)- Published
- 2017
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26. Lorcaserin improves glycemic control via a melanocortin neurocircuit.
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Burke LK, Ogunnowo-Bada E, Georgescu T, Cristiano C, de Morentin PBM, Valencia Torres L, D'Agostino G, Riches C, Heeley N, Ruan Y, Rubinstein M, Low MJ, Myers MG, Rochford JJ, Evans ML, and Heisler LK
- Subjects
- Animals, Benzazepines metabolism, Body Weight drug effects, Diabetes Mellitus, Type 2 drug therapy, Disease Models, Animal, Eating drug effects, Energy Metabolism drug effects, Glucose metabolism, Glucose Tolerance Test, Homeostasis physiology, Humans, Insulin Resistance physiology, Melanocortins pharmacology, Mice, Mice, Transgenic, Obesity drug therapy, Receptors, Melanocortin drug effects, Weight Loss drug effects, Benzazepines pharmacology, Blood Glucose drug effects, Receptor, Serotonin, 5-HT2C drug effects
- Abstract
Objective: The increasing prevalence of type 2 diabetes (T2D) and associated morbidity and mortality emphasizes the need for a more complete understanding of the mechanisms mediating glucose homeostasis to accelerate the identification of new medications. Recent reports indicate that the obesity medication lorcaserin, a 5-hydroxytryptamine (5-HT, serotonin) 2C receptor (5-HT
2C R) agonist, improves glycemic control in association with weight loss in obese patients with T2D. Here we evaluate whether lorcaserin has an effect on glycemia without body weight loss and how this effect is achieved., Methods: Murine models of common and genetic T2D were utilized to probe the direct effect of lorcaserin on glycemic control., Results: Lorcaserin dose-dependently improves glycemic control in mouse models of T2D in the absence of reductions in food intake or body weight. Examining the mechanism of this effect, we reveal a necessary and sufficient neurochemical mediator of lorcaserin's glucoregulatory effects, brain pro-opiomelanocortin (POMC) peptides. To clarify further lorcaserin's therapeutic brain circuit, we examined the receptor target of POMC peptides. We demonstrate that lorcaserin requires functional melanocortin4 receptors on cholinergic preganglionic neurons (MC4RChAT ) to exert its effects on glucose homeostasis. In contrast, MC4RChAT signaling did not impact lorcaserin's effects on feeding, indicating a divergence in the neurocircuitry underpinning lorcaserin's therapeutic glycemic and anorectic effects. Hyperinsulinemic-euglycemic clamp studies reveal that lorcaserin reduces hepatic glucose production, increases glucose disposal and improves insulin sensitivity., Conclusions: These data suggest that lorcaserin's action within the brain represents a mechanistically novel treatment for T2D: findings of significance to a prevalent global disease., (Copyright © 2017 The Authors. Published by Elsevier GmbH.. All rights reserved.)- Published
- 2017
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27. Hypothalamic-specific proopiomelanocortin deficiency reduces alcohol drinking in male and female mice.
- Author
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Zhou Y, Rubinstein M, Low MJ, and Kreek MJ
- Subjects
- Adrenal Insufficiency genetics, Alcohol Drinking drug therapy, Alcohol Drinking genetics, Animals, Ethanol pharmacology, Female, Genotype, Hypothalamus drug effects, Hypothalamus metabolism, Male, Mice, Mice, Knockout, Naltrexone pharmacology, Obesity genetics, Pro-Opiomelanocortin genetics, Pro-Opiomelanocortin metabolism, Adrenal Insufficiency metabolism, Alcohol Drinking metabolism, Obesity metabolism, Pro-Opiomelanocortin deficiency
- Abstract
Opioid receptor antagonist naltrexone reduces alcohol consumption and relapse in both humans and rodents. This study investigated whether hypothalamic proopiomelanocortin (POMC) neurons (producing beta-endorphin and melanocortins) play a role in alcohol drinking behaviors. Both male and female mice with targeted deletion of two neuronal Pomc enhancers nPE1 and nPE2 (nPE-/-), resulting in hypothalamic-specific POMC deficiency, were studied in short-access (4-h/day) drinking-in-the-dark (DID, alcohol in one bottle, intermittent access (IA, 24-h cycles of alcohol access every other day, alcohol vs. water in a two-bottle choice) and alcohol deprivation effect (ADE) models. Wild-type nPE+/+ exposed to 1-week DID rapidly established stable alcohol drinking behavior with more intake in females, whereas nPE-/- mice of both sexes had less intake and less preference. Although nPE-/- showed less saccharin intake and preference than nPE+/+, there was no genotype difference in sucrose intake or preference in the DID paradigm. After 3-week IA, nPE+/+ gradually escalated to high alcohol intake and preference, with more intake in females, whereas nPE-/- showed less escalation. Pharmacological blockade of mu-opioid receptors with naltrexone reduced intake in nPE+/+ in a dose-dependent manner, but had blunted effects in nPE-/- of both sexes. When alcohol was presented again after 1-week abstinence from IA, nPE+/+ of both sexes displayed significant increases in alcohol intake (ADE or relapse-like drinking), with more pronounced ADE in females, whereas nPE-/- did not show ADE in either sex. Our results suggest that neuronal POMC is involved in modulation of alcohol 'binge' drinking, escalation and 'relapse', probably via hypothalamic-mediated mechanisms, with sex differences., (© 2016 John Wiley & Sons Ltd and International Behavioural and Neural Genetics Society.)
- Published
- 2017
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28. Reprogramming the body weight set point by a reciprocal interaction of hypothalamic leptin sensitivity and Pomc gene expression reverts extreme obesity.
- Author
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Chhabra KH, Adams JM, Jones GL, Yamashita M, Schlapschy M, Skerra A, Rubinstein M, and Low MJ
- Abstract
Objective: A major challenge for obesity treatment is the maintenance of reduced body weight. Diet-induced obese mice are resistant to achieving normoweight once the obesogenic conditions are reversed, in part because lowered circulating leptin leads to a reduction in metabolic rate and a rebound of hyperphagia that defend the previously elevated body weight set point. Because hypothalamic POMC is a central leptin target, we investigated whether changes in circulating leptin modify Pomc expression to maintain normal energy balance in genetically predisposed obese mice., Methods: Mice with reversible Pomc silencing in the arcuate nucleus (ArcPomc (-/-)) become morbidly obese eating low-fat chow. We measured body composition, food intake, plasma leptin, and leptin sensitivity in ArcPomc (-/-) mice weight-matched to littermate controls by calorie restriction, either from weaning or after developing obesity. Pomc was reactivated by tamoxifen-dependent Cre recombinase transgenes. Long acting PASylated leptin was administered to weight-reduced ArcPomc (-/-) mice to mimic the super-elevated leptin levels of obese mice., Results: ArcPomc (-/-) mice had increased adiposity and leptin levels shortly after weaning. Despite chronic calorie restriction to achieve normoweight, ArcPomc (-/-) mice remained moderately hyperleptinemic and resistant to exogenous leptin's effects to reduce weight and food intake. However, subsequent Pomc reactivation in weight-matched ArcPomc (-/-) mice normalized plasma leptin, leptin sensitivity, adiposity, and food intake. In contrast, extreme hyperleptinemia induced by PASylated leptin blocked the full restoration of hypothalamic Pomc expression in calorie restricted ArcPomc (-/-) mice, which consequently regained 30% of their lost body weight and attained a metabolic steady state similar to that of tamoxifen treated obese ArcPomc (-/-) mice., Conclusions: Pomc reactivation in previously obese, calorie-restricted ArcPomc (-/-) mice normalized energy homeostasis, suggesting that their body weight set point was restored to control levels. In contrast, massively obese and hyperleptinemic ArcPomc (-/-) mice or those weight-matched and treated with PASylated leptin to maintain extreme hyperleptinemia prior to Pomc reactivation converged to an intermediate set point relative to lean control and obese ArcPomc (-/-) mice. We conclude that restoration of hypothalamic leptin sensitivity and Pomc expression is necessary for obese ArcPomc (-/-) mice to achieve and sustain normal metabolic homeostasis; whereas deficits in either parameter set a maladaptive allostatic balance that defends increased adiposity and body weight.
- Published
- 2016
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29. Essential function of the transcription factor Rax in the early patterning of the mammalian hypothalamus.
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Orquera DP, Nasif S, Low MJ, Rubinstein M, and de Souza FSJ
- Subjects
- Animals, Body Patterning, Embryonic Development genetics, Eye Proteins genetics, Gene Expression Regulation, Developmental, Homeodomain Proteins genetics, Mice, Mice, Knockout, Transcription Factors genetics, Eye Proteins physiology, Homeodomain Proteins physiology, Hypothalamus embryology, Transcription Factors physiology
- Abstract
The hypothalamus is a region of the anterior forebrain that controls basic aspects of vertebrate physiology, but the genes involved in its development are still poorly understood. Here, we investigate the function of the homeobox gene Rax/Rx in early hypothalamic development using a conditional targeted inactivation strategy in the mouse. We found that lack of Rax expression prior to embryonic day 8.5 (E8.5) caused a general underdevelopment of the hypothalamic neuroepithelium, while inactivation at later timepoints had little effect. The early absence of Rax impaired neurogenesis and prevented the expression of molecular markers of the dorsomedial hypothalamus, including neuropeptides Proopiomelanocortin and Somatostatin. Interestingly, the expression domains of genes expressed in the ventromedial hypothalamus and infundibulum invaded dorsal hypothalamic territory, showing that Rax is needed for the proper dorsoventral patterning of the developing medial hypothalamus. The phenotypes caused by the early loss of Rax are similar to those of eliminating the expression of the morphogen Sonic hedgehog (Shh) specifically from the hypothalamus. Consistent with this similarity in phenotypes, we observed that Shh and Rax are coexpressed in the rostral forebrain at late head fold stages and that loss of Rax caused a downregulation of Shh expression in the dorsomedial portion of the hypothalamus., (Copyright © 2016 Elsevier Inc. All rights reserved.)
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- 2016
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30. Not All Mice Are the Same: Standardization of Animal Research Data Presentation.
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Omary MB, Cohen DE, El-Omar EM, Jalan R, Low MJ, Nathanson MH, Peek RM Jr, and Turner JR
- Subjects
- Animals, Guidelines as Topic, Humans, Mice, Quality Control, Reproducibility of Results, Species Specificity, Biomedical Research standards, Editorial Policies, Gastroenterology standards, Models, Animal, Periodicals as Topic standards
- Published
- 2016
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31. Somatostatin triggers rhythmic electrical firing in hypothalamic GHRH neurons.
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Osterstock G, Mitutsova V, Barre A, Granier M, Fontanaud P, Chazalon M, Carmignac D, Robinson IC, Low MJ, Plesnila N, Hodson DJ, Mollard P, and Méry PF
- Subjects
- Animals, Female, G Protein-Coupled Inwardly-Rectifying Potassium Channels antagonists & inhibitors, Hypothalamus metabolism, Male, Mice, Mice, Knockout, Patch-Clamp Techniques, Action Potentials physiology, Growth Hormone-Releasing Hormone metabolism, Hypothalamus physiology, Somatostatin physiology
- Abstract
Hypothalamic growth hormone-releasing hormone (GHRH) neurons orchestrate body growth/maturation and have been implicated in feeding responses and ageing. However, the electrical patterns that dictate GHRH neuron functions have remained elusive. Since the inhibitory neuropeptide somatostatin (SST) is considered to be a primary oscillator of the GH axis, we examined its acute effects on GHRH neurons in brain slices from male and female GHRH-GFP mice. At the cellular level, SST irregularly suppressed GHRH neuron electrical activity, leading to slow oscillations at the population level. This resulted from an initial inhibitory action at the GHRH neuron level via K(+) channel activation, followed by a delayed, sst1/sst2 receptor-dependent unbalancing of glutamatergic and GABAergic synaptic inputs. The oscillation patterns induced by SST were sexually dimorphic, and could be explained by differential actions of SST on both GABAergic and glutamatergic currents. Thus, a tripartite neuronal circuit involving a fast hyperpolarization and a dual regulation of synaptic inputs appeared sufficient in pacing the activity of the GHRH neuronal population. These "feed-forward loops" may represent basic building blocks involved in the regulation of GHRH release and its downstream sexual specific functions.
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- 2016
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32. Hypothalamic POMC Deficiency Improves Glucose Tolerance Despite Insulin Resistance by Increasing Glycosuria.
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Chhabra KH, Adams JM, Fagel B, Lam DD, Qi N, Rubinstein M, and Low MJ
- Subjects
- Agouti-Related Protein pharmacology, Animals, Blood Glucose drug effects, Blotting, Western, Epinephrine metabolism, Glucose Tolerance Test, Glucose Transporter Type 2 metabolism, Glycosuria, Renal metabolism, Hypothalamus metabolism, Injections, Intraventricular, Mice, Mice, Knockout, Norepinephrine metabolism, Obesity metabolism, Peptides, Cyclic pharmacology, Pro-Opiomelanocortin deficiency, Pro-Opiomelanocortin metabolism, Receptors, Melanocortin agonists, Receptors, Melanocortin antagonists & inhibitors, alpha-MSH analogs & derivatives, alpha-MSH pharmacology, Arcuate Nucleus of Hypothalamus metabolism, Blood Glucose metabolism, Glucose Transporter Type 2 genetics, Glycosuria, Renal genetics, Insulin Resistance genetics, Kidney metabolism, Obesity genetics, Pro-Opiomelanocortin genetics, Sympathetic Nervous System metabolism
- Abstract
Hypothalamic proopiomelanocortin (POMC) is essential for the physiological regulation of energy balance; however, its role in glucose homeostasis remains less clear. We show that hypothalamic arcuate nucleus (Arc)POMC-deficient mice, which develop severe obesity and insulin resistance, unexpectedly exhibit improved glucose tolerance and remain protected from hyperglycemia. To explain these paradoxical phenotypes, we hypothesized that an insulin-independent pathway is responsible for the enhanced glucose tolerance. Indeed, the mutant mice demonstrated increased glucose effectiveness and exaggerated glycosuria relative to wild-type littermate controls at comparable blood glucose concentrations. Central administration of the melanocortin receptor agonist melanotan II in mutant mice reversed alterations in glucose tolerance and glycosuria, whereas, conversely, administration of the antagonist Agouti-related peptide (Agrp) to wild-type mice enhanced glucose tolerance. The glycosuria of ArcPOMC-deficient mice was due to decreased levels of renal GLUT 2 (rGLUT2) but not sodium-glucose cotransporter 2 and was associated with reduced renal catecholamine content. Epinephrine treatment abolished the genotype differences in glucose tolerance and rGLUT2 levels, suggesting that reduced renal sympathetic nervous system (SNS) activity is the underlying mechanism for the observed glycosuria and improved glucose tolerance in ArcPOMC-deficient mice. Therefore, the ArcPOMC-SNS-rGLUT2 axis is potentially an insulin-independent therapeutic target to control diabetes., (© 2016 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered.)
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- 2016
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33. Sex difference in physical activity, energy expenditure and obesity driven by a subpopulation of hypothalamic POMC neurons.
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Burke LK, Doslikova B, D'Agostino G, Greenwald-Yarnell M, Georgescu T, Chianese R, Martinez de Morentin PB, Ogunnowo-Bada E, Cansell C, Valencia-Torres L, Garfield AS, Apergis-Schoute J, Lam DD, Speakman JR, Rubinstein M, Low MJ, Rochford JJ, Myers MG, Evans ML, and Heisler LK
- Abstract
Objective: Obesity is one of the primary healthcare challenges of the 21st century. Signals relaying information regarding energy needs are integrated within the brain to influence body weight. Central among these integration nodes are the brain pro-opiomelanocortin (POMC) peptides, perturbations of which disrupt energy balance and promote severe obesity. However, POMC neurons are neurochemically diverse and the crucial source of POMC peptides that regulate energy homeostasis and body weight remains to be fully clarified., Methods: Given that a 5-hydroxytryptamine 2c receptor (5-HT2CR) agonist is a current obesity medication and 5-HT2CR agonist's effects on appetite are primarily mediated via POMC neurons, we hypothesized that a critical source of POMC regulating food intake and body weight is specifically synthesized in cells containing 5-HT2CRs. To exclusively manipulate Pomc synthesis only within 5-HT2CR containing cells, we generated a novel 5-HT 2C R (CRE) mouse line and intercrossed it with Cre recombinase-dependent and hypothalamic specific reactivatable Pomc (NEO) mice to restrict Pomc synthesis to the subset of hypothalamic cells containing 5-HT2CRs. This provided a means to clarify the specific contribution of a defined subgroup of POMC peptides in energy balance and body weight., Results: Here we transform genetically programed obese and hyperinsulinemic male mice lacking hypothalamic Pomc with increased appetite, reduced physical activity and compromised brown adipose tissue (BAT) into lean, healthy mice via targeted restoration of Pomc function only within 5-HT2CR expressing cells. Remarkably, the same metabolic transformation does not occur in females, who despite corrected feeding behavior and normalized insulin levels remain physically inactive, have lower energy expenditure, compromised BAT and develop obesity., Conclusions: These data provide support for the functional heterogeneity of hypothalamic POMC neurons, revealing that Pomc expression within 5-HT2CR expressing neurons is sufficient to regulate energy intake and insulin sensitivity in male and female mice. However, an unexpected sex difference in the function of this subset of POMC neurons was identified with regard to energy expenditure. We reveal that a large sex difference in physical activity, energy expenditure and the development of obesity is driven by this subpopulation, which constitutes approximately 40% of all POMC neurons in the hypothalamic arcuate nucleus. This may have broad implications for strategies utilized to combat obesity, which at present largely ignore the sex of the obese individual.
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- 2016
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34. Rapid Glucocorticoid Feedback Inhibition of ACTH Secretion Involves Ligand-Dependent Membrane Association of Glucocorticoid Receptors.
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Deng Q, Riquelme D, Trinh L, Low MJ, Tomić M, Stojilkovic S, and Aguilera G
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- Animals, Calcium Signaling, Cells, Cultured, Corticotropin-Releasing Hormone, Feedback, Physiological, Female, Ligands, Male, Phosphorylation, Rats, Sprague-Dawley, src-Family Kinases metabolism, Adrenocorticotropic Hormone metabolism, Corticosterone administration & dosage, Corticotrophs metabolism, Glucocorticoids metabolism, Receptors, Glucocorticoid metabolism
- Abstract
The hypothesis that rapid glucocorticoid inhibition of pituitary ACTH secretion mediates a feedforward/feedback mechanism responsible for the hourly glucocorticoid pulsatility was tested in cultured pituitary cells. Perifusion with 30 pM CRH caused sustained the elevation of ACTH secretion. Superimposed corticosterone pulses inhibited CRH-stimulated ACTH release, depending on prior glucocorticoid clearance. When CRH perifusion started after 2 hours of glucocorticoid-free medium, corticosterone levels in the stress range (1 μM) caused a delayed (25 min) and prolonged inhibition of CRH-stimulated ACTH secretion, up to 60 minutes after corticosterone withdrawal. In contrast, after 6 hours of glucocorticoid-free medium, basal corticosterone levels inhibited CRH-stimulated ACTH within 5 minutes, after rapid recovery 5 minutes after corticosterone withdrawal. The latter effect was insensitive to actinomycin D but was prevented by the glucocorticoid receptor antagonist, RU486, suggesting nongenomic effects of the classical glucocorticoid receptor. In hypothalamic-derived 4B cells, 10 nM corticosterone increased immunoreactive glucocorticoid receptor content in membrane fractions, with association and clearance rates paralleling the effects on ACTH secretion from corticotrophs. Corticosterone did not affect CRH-stimulated calcium influx, but in AtT-20 cells, it had biphasic effects on CRH-stimulated Src phosphorylation, with early inhibition and late stimulation, suggesting a role for Src phosphorylation on the rapid glucocorticoid feedback. The data suggest that the nongenomic/membrane effects of classical GR mediate rapid and reversible glucocorticoid feedback inhibition at the pituitary corticotrophs downstream of calcium influx. The sensitivity and kinetics of these effects is consistent with the hypothesis that pituitary glucocorticoid feedback is part of the mechanism for adrenocortical ultradian pulse generation.
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- 2015
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35. Gene expression profiling reveals a possible role for somatostatin in the innate immune response of the liver.
- Author
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Adams JM and Low MJ
- Abstract
Somatostatin is a neuropeptide hormone that inhibits pituitary growth hormone (GH) release. Using microarray analysis of gene expression in the livers of wildtype control and somatostatin knockout mice, we have previously identified a panel of genes whose GH-dependent and sexually dimorphic expression patterns are significantly altered by the absence of somatostatin (1). Here, we provide methodological and analytical details of that study, the raw data of which is deposited in the Gene Expression Omnibus as data set GSE56520. In addition, we performed further gene ontology analysis of the data and found that the differential expression of a second subset of genes in the livers of somatostatin-knockout mice versus wildtype controls is likely independent of GH signaling and involved in the innate immune response.
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- 2015
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36. Islet 1 specifies the identity of hypothalamic melanocortin neurons and is critical for normal food intake and adiposity in adulthood.
- Author
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Nasif S, de Souza FS, González LE, Yamashita M, Orquera DP, Low MJ, and Rubinstein M
- Subjects
- Adiposity genetics, Animals, Base Sequence, Cell Differentiation genetics, Cell Differentiation physiology, Eating genetics, Female, Gene Expression Regulation, Developmental, Gene Knockdown Techniques, Hyperphagia genetics, Hyperphagia physiopathology, Hypothalamus cytology, Hypothalamus embryology, Hypothalamus metabolism, LIM-Homeodomain Proteins genetics, Male, Mice, Knockout, Mice, Transgenic, Microscopy, Fluorescence, Molecular Sequence Data, Neurons cytology, Obesity genetics, Obesity physiopathology, Pro-Opiomelanocortin genetics, Protein Binding, Reverse Transcriptase Polymerase Chain Reaction, Sequence Homology, Nucleic Acid, Transcription Factors genetics, Zebrafish embryology, Zebrafish metabolism, Adiposity physiology, Eating physiology, LIM-Homeodomain Proteins metabolism, Neurons metabolism, Pro-Opiomelanocortin metabolism, Transcription Factors metabolism
- Abstract
Food intake and body weight regulation depend on proper expression of the proopiomelanocortin gene (Pomc) in a group of neurons located in the mediobasal hypothalamus of all vertebrates. These neurons release POMC-encoded melanocortins, which are potent anorexigenic neuropeptides, and their absence from mice or humans leads to hyperphagia and severe obesity. Although the pathophysiology of hypothalamic POMC neurons is well understood, the genetic program that establishes the neuronal melanocortinergic phenotype and maintains a fully functional neuronal POMC phenotype throughout adulthood remains unknown. Here, we report that the early expression of the LIM-homeodomain transcription factor Islet 1 (ISL1) in the developing hypothalamus promotes the terminal differentiation of melanocortinergic neurons and is essential for hypothalamic Pomc expression since its initial onset and throughout the entire lifetime. We detected ISL1 in the prospective hypothalamus just before the onset of Pomc expression and, from then on, Pomc and Isl1 coexpress. ISL1 binds in vitro and in vivo to critical homeodomain binding DNA motifs present in the neuronal Pomc enhancers nPE1 and nPE2, and mutations of these sites completely disrupt the ability of these enhancers to drive reporter gene expression to hypothalamic POMC neurons in transgenic mice and zebrafish. ISL1 is necessary for hypothalamic Pomc expression during mouse and zebrafish embryogenesis. Furthermore, conditional Isl1 inactivation from POMC neurons impairs Pomc expression, leading to hyperphagia and obesity. Our results demonstrate that ISL1 specifies the identity of hypothalamic melanocortin neurons and is required for melanocortin-induced satiety and normal adiposity throughout the entire lifespan.
- Published
- 2015
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37. Conditional expression of Pomc in the Lepr-positive subpopulation of POMC neurons is sufficient for normal energy homeostasis and metabolism.
- Author
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Lam DD, Attard CA, Mercer AJ, Myers MG Jr, Rubinstein M, and Low MJ
- Subjects
- Animals, Blood Glucose metabolism, Female, Glucose Tolerance Test, Hypothalamus metabolism, Insulin metabolism, Leptin metabolism, Mice, Mice, Knockout, Motor Activity physiology, Pro-Opiomelanocortin genetics, Receptors, Leptin genetics, Energy Metabolism physiology, Homeostasis physiology, Neurons metabolism, Pro-Opiomelanocortin metabolism, Receptors, Leptin metabolism
- Abstract
Peptides derived from the proopiomelanocortin (POMC) precursor are critical for the normal regulation of many physiological parameters, and POMC deficiency results in severe obesity and metabolic dysfunction. Conversely, augmentation of central nervous system melanocortin function is a promising therapeutic avenue for obesity and diabetes but is confounded by detrimental cardiovascular effects including hypertension. Because the hypothalamic population of POMC-expressing neurons is neurochemically and neuroanatomically heterogeneous, there is interest in the possible dissociation of functionally distinct POMC neuron subpopulations. We used a Cre recombinase-dependent and hypothalamus-specific reactivatable PomcNEO allele to restrict Pomc expression to hypothalamic neurons expressing leptin receptor (Lepr) in mice. In contrast to mice with total hypothalamic Pomc deficiency, which are severely obese, mice with Lepr-restricted Pomc expression displayed fully normal body weight, food consumption, glucose homeostasis, and locomotor activity. Thus, Lepr+ POMC neurons, which constitute approximately two-thirds of the total POMC neuron population, are sufficient for normal regulation of these parameters. This functional dissociation approach represents a promising avenue for isolating therapeutically relevant POMC neuron subpopulations.
- Published
- 2015
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38. Somatostatin is essential for the sexual dimorphism of GH secretion, corticosteroid-binding globulin production, and corticosterone levels in mice.
- Author
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Adams JM, Otero-Corchon V, Hammond GL, Veldhuis JD, Qi N, and Low MJ
- Subjects
- Animals, Corticosterone blood, Female, Growth Hormone genetics, Male, Mice, Mice, Inbred C57BL, Mice, Knockout, RNA, Messenger genetics, RNA, Messenger metabolism, Sex Characteristics, Somatostatin genetics, Transcortin genetics, Corticosterone metabolism, Growth Hormone metabolism, Somatostatin metabolism, Transcortin metabolism
- Abstract
Distinct male and female patterns of pituitary GH secretion produce sexually differentiated hepatic gene expression profiles, thereby influencing steroid and xenobiotic metabolism. We used a fully automated system to obtain serial nocturnal blood samples every 15 minutes from cannulated wild-type (WT) and somatostatin knockout (Sst-KO) mice to determine the role of SST, the principal inhibitor of GH release, in the generation of sexually dimorphic GH pulsatility. WT males had lower mean and median GH values, less random GH secretory bursts, and longer trough periods between GH pulses than WT females. Each of these parameters was feminized in male Sst-KO mice, whereas female Sst-KO mice had higher GH levels than all other groups, but GH pulsatility was unaffected. We next performed hepatic mRNA profiling with high-density microarrays. Male Sst-KO mice exhibited a globally feminized pattern of GH-dependent mRNA levels, but female Sst-KO mice were largely unaffected. Among the differentially expressed female-predominant genes was Serpina6, which encodes corticosteroid-binding globulin (CBG). Increased CBG was associated with elevated diurnal peak plasma corticosterone in unstressed WT females and both sexes of Sst-KO mice compared with WT males. Sst-KO mice also had exaggerated ACTH and corticosterone responses to acute restraint stress. However, consistent with their lack of phenotypic signs of excess glucocorticoids, cerebrospinal fluid concentrations of free corticosterone in Sst-KO mice were not elevated. In summary, SST is necessary for the prolonged interpulse troughs that define masculinized pituitary GH secretion. SST also contributes to sexual dimorphism of the hypothalamic-pituitary-adrenal axis via GH-dependent regulation of hepatic CBG production.
- Published
- 2015
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39. Partially redundant enhancers cooperatively maintain Mammalian pomc expression above a critical functional threshold.
- Author
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Lam DD, de Souza FS, Nasif S, Yamashita M, López-Leal R, Otero-Corchon V, Meece K, Sampath H, Mercer AJ, Wardlaw SL, Rubinstein M, and Low MJ
- Subjects
- Animals, Conserved Sequence, Female, Gene Expression Regulation, Developmental, Mammals genetics, Mice, Neurons metabolism, Phylogeny, Pregnancy, Pro-Opiomelanocortin deficiency, Pro-Opiomelanocortin genetics, Embryonic Development genetics, Enhancer Elements, Genetic genetics, Evolution, Molecular, Pro-Opiomelanocortin biosynthesis, Regulatory Sequences, Nucleic Acid genetics
- Abstract
Cell-specific expression of many genes is conveyed by multiple enhancers, with each individual enhancer controlling a particular expression domain. In contrast, multiple enhancers drive similar expression patterns of some genes involved in embryonic development, suggesting regulatory redundancy. Work in Drosophila has indicated that functionally overlapping enhancers canalize development by buffering gene expression against environmental and genetic disturbances. However, little is known about regulatory redundancy in vertebrates and in genes mainly expressed during adulthood. Here we study nPE1 and nPE2, two phylogenetically conserved mammalian enhancers that drive expression of the proopiomelanocortin gene (Pomc) to the same set of hypothalamic neurons. The simultaneous deletion of both enhancers abolished Pomc expression at all ages and induced a profound metabolic dysfunction including early-onset extreme obesity. Targeted inactivation of either nPE1 or nPE2 led to very low levels of Pomc expression during early embryonic development indicating that both enhancers function synergistically. In adult mice, however, Pomc expression is controlled additively by both enhancers, with nPE1 being responsible for ∼80% and nPE2 for ∼20% of Pomc transcription. Consequently, nPE1 knockout mice exhibit mild obesity whereas nPE2-deficient mice maintain a normal body weight. These results suggest that nPE2-driven Pomc expression is compensated by nPE1 at later stages of development, essentially rescuing the earlier phenotype of nPE2 deficiency. Together, these results reveal that cooperative interactions between the enhancers confer robustness of Pomc expression against gene regulatory disturbances and preclude deleterious metabolic phenotypes caused by Pomc deficiency in adulthood. Thus, our study demonstrates that enhancer redundancy can be used by genes that control adult physiology in mammals and underlines the potential significance of regulatory sequence mutations in common diseases.
- Published
- 2015
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40. 5-HT obesity medication efficacy via POMC activation is maintained during aging.
- Author
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Burke LK, Doslikova B, D'Agostino G, Garfield AS, Farooq G, Burdakov D, Low MJ, Rubinstein M, Evans ML, Billups B, and Heisler LK
- Subjects
- Aging drug effects, Animals, Female, Humans, Male, Mice, Mice, Inbred C57BL, Mice, Knockout, Pro-Opiomelanocortin genetics, Treatment Outcome, Aging metabolism, Fenfluramine therapeutic use, Obesity drug therapy, Pro-Opiomelanocortin metabolism, Serotonin metabolism, Selective Serotonin Reuptake Inhibitors therapeutic use
- Abstract
The phenomenon commonly described as the middle-age spread is the result of elevated adiposity accumulation throughout adulthood until late middle-age. It is a clinical imperative to gain a greater understanding of the underpinnings of age-dependent obesity and, in turn, how these mechanisms may impact the efficacy of obesity treatments. In particular, both obesity and aging are associated with rewiring of a principal brain pathway modulating energy homeostasis, promoting reduced activity of satiety pro-opiomelanocortin (POMC) neurons within the arcuate nucleus of the hypothalamus (ARC). Using a selective ARC-deficient POMC mouse line, here we report that former obesity medications augmenting endogenous 5-hydroxytryptamine (5-HT) activity d-fenfluramine and sibutramine require ARC POMC neurons to elicit therapeutic appetite-suppressive effects. We next investigated whether age-related diminished ARC POMC activity therefore impacts the potency of 5-HT obesity pharmacotherapies, lorcaserin, d-fenfluramine, and sibutramine and report that all compounds reduced food intake to a comparable extent in both chow-fed young lean (3-5 months old) and middle-aged obese (12-14 months old) male and female mice. We provide a mechanism through which 5-HT anorectic potency is maintained with age, via preserved 5-HT-POMC appetitive anatomical machinery. Specifically, the abundance and signaling of the primary 5-HT receptor influencing appetite via POMC activation, the 5-HT2CR, is not perturbed with age. These data reveal that although 5-HT obesity medications require ARC POMC neurons to achieve appetitive effects, the anorectic efficacy is maintained with aging, findings of clinical significance to the global aging obese population.
- Published
- 2014
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41. Glucose rapidly induces different forms of excitatory synaptic plasticity in hypothalamic POMC neurons.
- Author
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Hu J, Jiang L, Low MJ, and Rui L
- Subjects
- Animals, Cells, Cultured, Hypothalamus metabolism, Male, Mice, Neurons cytology, Excitatory Postsynaptic Potentials, Glucose metabolism, Hypothalamus cytology, Neuronal Plasticity, Neurons metabolism, Pro-Opiomelanocortin metabolism
- Abstract
Hypothalamic POMC neurons are required for glucose and energy homeostasis. POMC neurons have a wide synaptic connection with neurons both within and outside the hypothalamus, and their activity is controlled by a balance between excitatory and inhibitory synaptic inputs. Brain glucose-sensing plays an essential role in the maintenance of normal body weight and metabolism; however, the effect of glucose on synaptic transmission in POMC neurons is largely unknown. Here we identified three types of POMC neurons (EPSC(+), EPSC(-), and EPSC(+/-)) based on their glucose-regulated spontaneous excitatory postsynaptic currents (sEPSCs), using whole-cell patch-clamp recordings. Lowering extracellular glucose decreased the frequency of sEPSCs in EPSC(+) neurons, but increased it in EPSC(-) neurons. Unlike EPSC(+) and EPSC(-) neurons, EPSC(+/-) neurons displayed a bi-phasic sEPSC response to glucoprivation. In the first phase of glucoprivation, both the frequency and the amplitude of sEPSCs decreased, whereas in the second phase, they increased progressively to the levels above the baseline values. Accordingly, lowering glucose exerted a bi-phasic effect on spontaneous action potentials in EPSC(+/-) neurons. Glucoprivation decreased firing rates in the first phase, but increased them in the second phase. These data indicate that glucose induces distinct excitatory synaptic plasticity in different subpopulations of POMC neurons. This synaptic remodeling is likely to regulate the sensitivity of the melanocortin system to neuronal and hormonal signals.
- Published
- 2014
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42. Temporal changes in nutritional state affect hypothalamic POMC peptide levels independently of leptin in adult male mice.
- Author
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Mercer AJ, Stuart RC, Attard CA, Otero-Corchon V, Nillni EA, and Low MJ
- Subjects
- Animals, Body Weight drug effects, Diet, Eating drug effects, Leptin pharmacology, Male, Mice, Mice, Inbred C57BL, Mice, Transgenic, Pro-Opiomelanocortin genetics, Time Factors, Hypothalamus metabolism, Leptin metabolism, Nutritional Status physiology, Pro-Opiomelanocortin metabolism
- Abstract
Hypothalamic proopiomelanocortin (POMC) neurons constitute a critical anorexigenic node in the central nervous system (CNS) for maintaining energy balance. These neurons directly affect energy expenditure and feeding behavior by releasing bioactive neuropeptides but are also subject to signals directly related to nutritional state such as the adipokine leptin. To further investigate the interaction of diet and leptin on hypothalamic POMC peptide levels, we exposed 8- to 10-wk-old male POMC-Discosoma red fluorescent protein (DsRed) transgenic reporter mice to either 24-48 h (acute) or 2 wk (chronic) food restriction, high-fat diet (HFD), or leptin treatment. Using semiquantitative immunofluorescence and radioimmunoassays, we discovered that acute fasting and chronic food restriction decreased the levels of adrenocorticotropic hormone (ACTH), α-melanocyte-stimulating hormone (α-MSH), and β-endorphin in the hypothalamus, together with decreased DsRed fluorescence, compared with control ad libitum-fed mice. Furthermore, acute but not chronic HFD or leptin administration selectively increased α-MSH levels in POMC fibers and increased DsRed fluorescence in POMC cell bodies. HFD and leptin treatments comparably increased circulating leptin levels at both time points, suggesting that transcription of Pomc and synthesis of POMC peptide products are not modified in direct relation to the concentration of plasma leptin. Our findings indicate that negative energy balance persistently downregulated POMC peptide levels, and this phenomenon may be partially explained by decreased leptin levels, since these changes were blocked in fasted mice treated with leptin. In contrast, sustained elevation of plasma leptin by HFD or hormone supplementation did not significantly alter POMC peptide levels, indicating that enhanced leptin signaling does not chronically increase Pomc transcription and peptide synthesis.
- Published
- 2014
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43. Constitutive TLR4 signalling in intestinal epithelium reduces tumor load by increasing apoptosis in APC(Min/+) mice.
- Author
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Li Y, Teo WL, Low MJ, Meijer L, Sanderson I, Pettersson S, and Greicius G
- Subjects
- Adenomatous Polyposis Coli Protein genetics, Adenomatous Polyposis Coli Protein metabolism, Animals, Caspase 3 metabolism, Cell Transformation, Neoplastic genetics, Cell Transformation, Neoplastic metabolism, Cells, Cultured, Colorectal Neoplasms genetics, Colorectal Neoplasms metabolism, Colorectal Neoplasms pathology, Cyclooxygenase 2 metabolism, Female, Humans, Immunoblotting, Immunohistochemistry, Interferon-beta metabolism, Intestinal Mucosa pathology, Male, Mice, Mice, Inbred C57BL, Mice, Mutant Strains, Mice, Transgenic, Organoids cytology, Organoids metabolism, Reverse Transcriptase Polymerase Chain Reaction, Toll-Like Receptor 4 genetics, Tumor Burden genetics, Apoptosis, Intestinal Mucosa metabolism, Signal Transduction, Toll-Like Receptor 4 metabolism
- Abstract
The microbial pattern-recognizing Toll-like receptors (TLRs) are major signal transducers known to shape and influence the postnatal maturation of host intestinal epithelium. Perturbations in this intricate host-microbe cross-talk have been reported to be associated with uncontrolled epithelial cell growth and thus potential cancer development by mechanisms which are largely unknown. We therefore generated transgenic mice carrying a constitutively active TLR4 (CD4-TLR4) linked to an intestinal epithelial cell-specific promoter. Ex vivo analysis of transgenic crypt-villus organoid cultures revealed an increased proliferative capacity and a lowered cyclooxygenase 2 (Cox-2) expression in these organoids compared with wild-type control cultures. Introducing the CD4-TLR4 transgene into APC(Min/+) mice (CD4-TLR4-APC(Min/+)), a model of colorectal carcinoma, resulted in a dramatic drop in tumor load as compared with control APC(Min/+) mice. Intestinal tumors from CD4-TLR4-APC(Min/+) mice displayed reduced Cox-2 protein, elevated interferon β expression and increased caspase-3 activity, which correlated with increased apoptosis in vivo. Thus, our data reveal that host microbiota-mediated signal transduction via TLR4 in intestinal epithelial cells is far more complex than what is previously reported.
- Published
- 2014
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44. Enhancer turnover and conserved regulatory function in vertebrate evolution.
- Author
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Domené S, Bumaschny VF, de Souza FS, Franchini LF, Nasif S, Low MJ, and Rubinstein M
- Subjects
- Animals, Animals, Genetically Modified, Computational Biology, Conserved Sequence genetics, Immunohistochemistry, In Situ Hybridization, Mutation genetics, Neurons metabolism, Zebrafish, Enhancer Elements, Genetic genetics, Evolution, Molecular, Gene Expression Regulation genetics, Pro-Opiomelanocortin genetics, Vertebrates genetics, Zebrafish Proteins genetics
- Abstract
Mutations in regulatory regions including enhancers are an important source of variation and innovation during evolution. Enhancers can evolve by changes in the sequence, arrangement and repertoire of transcription factor binding sites, but whole enhancers can also be lost or gained in certain lineages in a process of turnover. The proopiomelanocortin gene (Pomc), which encodes a prohormone, is expressed in the pituitary and hypothalamus of all jawed vertebrates. We have previously described that hypothalamic Pomc expression in mammals is controlled by two enhancers-nPE1 and nPE2-that are derived from transposable elements and that presumably replaced the ancestral neuronal Pomc regulatory regions. Here, we show that nPE1 and nPE2, even though they are mammalian novelties with no homologous counterpart in other vertebrates, nevertheless can drive gene expression specifically to POMC neurons in the hypothalamus of larval and adult transgenic zebrafish. This indicates that when neuronal Pomc enhancers originated de novo during early mammalian evolution, the newly created cis- and trans-codes were similar to the ancestral ones. We also identify the neuronal regulatory region of zebrafish pomca and confirm that it is not homologous to the mammalian enhancers. Our work sheds light on the process of gene regulatory evolution by showing how a locus can undergo enhancer turnover and nevertheless maintain the ancestral transcriptional output.
- Published
- 2013
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45. Central dopamine D2 receptors regulate growth-hormone-dependent body growth and pheromone signaling to conspecific males.
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Noaín D, Pérez-Millán MI, Bello EP, Luque GM, Casas Cordero R, Gelman DM, Peper M, Tornadu IG, Low MJ, Becú-Villalobos D, and Rubinstein M
- Subjects
- Analysis of Variance, Animals, Benzamides pharmacokinetics, Body Size drug effects, Body Size genetics, Body Weight drug effects, Body Weight genetics, Case-Control Studies, Catatonia chemically induced, Catatonia metabolism, Dopamine Antagonists pharmacology, Eating drug effects, Eating genetics, Eating physiology, Female, Haloperidol pharmacology, Insulin-Like Growth Factor I metabolism, Intermediate Filament Proteins genetics, Male, Mice, Mice, Inbred C57BL, Mice, Transgenic, Nerve Tissue Proteins genetics, Nestin, Oligodeoxyribonucleotides, Antisense pharmacology, Pheromones urine, Pituitary Gland drug effects, Prolactin genetics, Protein Binding drug effects, Protein Binding genetics, Proteins metabolism, Radioimmunoassay, Receptors, Dopamine D2 deficiency, Receptors, Dopamine D2 genetics, Social Dominance, Territoriality, Tritium pharmacokinetics, Body Size physiology, Growth Hormone metabolism, Pituitary Gland metabolism, Prolactin metabolism, Receptors, Dopamine D2 metabolism
- Abstract
Competition between adult males for limited resources such as food and receptive females is shaped by the male pattern of pituitary growth hormone (GH) secretion that determines body size and the production of urinary pheromones involved in male-to-male aggression. In the brain, dopamine (DA) provides incentive salience to stimuli that predict the availability of food and sexual partners. Although the importance of the GH axis and central DA neurotransmission in social dominance and fitness is clearly appreciated, the two systems have always been studied unconnectedly. Here we conducted a cell-specific genetic dissection study in conditional mutant mice that selectively lack DA D2 receptors (D2R) from pituitary lactotropes (lacDrd2KO) or neurons (neuroDrd2KO). Whereas lacDrd2KO mice developed a normal GH axis, neuroDrd2KO mice displayed fewer somatotropes; reduced hypothalamic Ghrh expression, pituitary GH content, and serum IGF-I levels; and exhibited reduced body size and weight. As a consequence of a GH axis deficit, neuroDrd2KO adult males excreted low levels of major urinary proteins and their urine failed to promote aggression and territorial behavior in control male challengers, in contrast to the urine taken from control adult males. These findings reveal that central D2Rs mediate a neuroendocrine-exocrine cascade that controls the maturation of the GH axis and downstream signals that are critical for fitness, social dominance, and competition between adult males.
- Published
- 2013
- Full Text
- View/download PDF
46. Lipocalin 2 performs contrasting, location-dependent roles in APCmin tumor initiation and progression.
- Author
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Reilly PT, Teo WL, Low MJ, Amoyo-Brion AA, Dominguez-Brauer C, Elia AJ, Berger T, Greicius G, Pettersson S, and Mak TW
- Subjects
- Acute-Phase Proteins deficiency, Acute-Phase Proteins genetics, Animals, Apoptosis physiology, Disease Progression, Female, Genes, APC, Intestinal Neoplasms genetics, Lipocalin-2, Lipocalins genetics, Male, Mice, Mice, Inbred C57BL, Oncogene Proteins deficiency, Oncogene Proteins genetics, Acute-Phase Proteins biosynthesis, Intestinal Neoplasms metabolism, Intestinal Neoplasms pathology, Lipocalins biosynthesis, Oncogene Proteins biosynthesis
- Abstract
Evidence that lipocalin 2 (LCN2) is oncogenic has grown in recent years and comes from both animal models and expression analysis from a variety of human cancers. In the intestine, LCN2 is overexpressed in colitis patients and its overexpression is a negative prognostic indicator in colorectal cancer. Functionally, LCN2 has a number of different activities that may contribute to its oncogenic potential, including increasing matrix metalloproteinase activity, control of iron availability and stimulating inflammation. In this report, we examined APCmin intestinal tumorigenesis in an LCN2-deficient background. We found that the loss of LCN2 increased tumor multiplicity specifically in the duodenum, suggesting a potential tumor-suppressive activity. Concurrently, however, LCN2 increased the average small intestinal tumor size particularly in the distal small intestine. We found that this increase was correlated to tumor iron(II) content, suggesting that an iron-scavenging role is important for LCN2 oncogenic activity in the intestine.
- Published
- 2013
- Full Text
- View/download PDF
47. Unraveling the central proopiomelanocortin neural circuits.
- Author
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Mercer AJ, Hentges ST, Meshul CK, and Low MJ
- Abstract
Central proopiomelanocortin (POMC) neurons form a potent anorexigenic network, but our understanding of the integration of this hypothalamic circuit throughout the central nervous system (CNS) remains incomplete. POMC neurons extend projections along the rostrocaudal axis of the brain, and can signal with both POMC-derived peptides and fast amino acid neurotransmitters. Although recent experimental advances in circuit-level manipulation have been applied to POMC neurons, many pivotal questions still remain: how and where do POMC neurons integrate metabolic information? Under what conditions do POMC neurons release bioactive molecules throughout the CNS? Are GABA and glutamate or neuropeptides released from POMC neurons more crucial for modulating feeding and metabolism? Resolving the exact stoichiometry of signals evoked from POMC neurons under different metabolic conditions therefore remains an ongoing endeavor. In this review, we analyze the anatomical atlas of this network juxtaposed to the physiological signaling of POMC neurons both in vitro and in vivo. We also consider novel genetic tools to further characterize the function of the POMC circuit in vivo. Our goal is to synthesize a global view of the POMC network, and to highlight gaps that require further research to expand our knowledge on how these neurons modulate energy balance.
- Published
- 2013
- Full Text
- View/download PDF
48. Mouse models in gastroenterology research.
- Author
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Low MJ
- Subjects
- Animals, Gastrointestinal Diseases, Genetic Engineering, Humans, Mice, Mice, Inbred C3H, Mice, Inbred C57BL, Mice, Transgenic, Biomedical Research, Disease Models, Animal, Gastroenterology
- Published
- 2012
- Full Text
- View/download PDF
49. Obesity-programmed mice are rescued by early genetic intervention.
- Author
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Bumaschny VF, Yamashita M, Casas-Cordero R, Otero-Corchón V, de Souza FS, Rubinstein M, and Low MJ
- Subjects
- Adipose Tissue metabolism, Adipose Tissue pathology, Animals, Disease Models, Animal, Hyperphagia genetics, Hyperphagia metabolism, Hyperphagia pathology, Hyperphagia physiopathology, Hyperphagia prevention & control, Hypothalamus metabolism, Hypothalamus pathology, Mice, Mice, Knockout, Neurons metabolism, Neurons pathology, Obesity genetics, Obesity metabolism, Pro-Opiomelanocortin genetics, Pro-Opiomelanocortin metabolism, Adipose Tissue physiopathology, Adiposity, Eating, Hypothalamus physiopathology, Obesity physiopathology, Obesity prevention & control
- Abstract
Obesity is a chronic metabolic disorder affecting half a billion people worldwide. Major difficulties in managing obesity are the cessation of continued weight loss in patients after an initial period of responsiveness and rebound to pretreatment weight. It is conceivable that chronic weight gain unrelated to physiological needs induces an allostatic regulatory state that defends a supranormal adipose mass despite its maladaptive consequences. To challenge this hypothesis, we generated a reversible genetic mouse model of early-onset hyperphagia and severe obesity by selectively blocking the expression of the proopiomelanocortin gene (Pomc) in hypothalamic neurons. Eutopic reactivation of central POMC transmission at different stages of overweight progression normalized or greatly reduced food intake in these obesity-programmed mice. Hypothalamic Pomc rescue also attenuated comorbidities such as hyperglycemia, hyperinsulinemia, and hepatic steatosis and normalized locomotor activity. However, effectiveness of treatment to normalize body weight and adiposity declined progressively as the level of obesity at the time of Pomc induction increased. Thus, our study using a novel reversible monogenic obesity model reveals the critical importance of early intervention for the prevention of subsequent allostatic overload that auto-perpetuates obesity.
- Published
- 2012
- Full Text
- View/download PDF
50. Positive selection of co-opted mobile genetic elements in a mammalian gene: If you can't beat them, join them.
- Author
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Franchini LF, de Souza FS, Low MJ, and Rubinstein M
- Abstract
The proopiomelanocortin (Pomc) gene encodes a prepropeptide with essential functions in the response to stress and energy balance, which is expressed in the pituitary and hypothalamus of vertebrate animals. Neuronal expression of Pomc is controlled by two distal enhancers named nPE1 and nPE2. Using transgenic mice, we observed that both enhancers drive identical expression patterns in the mammalian hypothalamus, starting at embryonic day 10.5, when endogenous Pomc expression commences. This overlapping enhancer activity is maintained throughout hypothalamic development and into adulthood. We also found that nPE1 and nPE2 were exapted as neuronal enhancers into the POMC locus after the sequential insertion of two unrelated retroposons. Thus, nPE1 and nPE2 are functional analogs and represent an authentic first example of convergent molecular evolution of cell-specific transcriptional enhancers. In this Commentary we discuss the following questions that remain unanswered: (1) how does transcriptional control of POMC operate in hypothalamic neurons of non-mammalian vertebrates? (2) What evolutionary forces are maintaining two discrete neuronal POMC enhancers under purifying selection for the last ~100 million years in all placental mammals? (3) What is the contribution of MaLRs to genome evolution?
- Published
- 2012
- Full Text
- View/download PDF
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