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Insulin receptor (InsR) signaling through transcription factor FoxO1 is important in the development of hypothalamic neuron feeding circuits, but knowledge about underlying mechanisms is limited. To investigate the role of InsR/FoxO1 signaling in the development and maintenance of these circuits, we surveyed the pool of hypothalamic neurons expressing Pomc mRNA in different mouse models of impaired hypothalamic InsR signaling. InsR ablation in the entire hypothalamus did not affect Pomc-neuron number at birth, but resulted in a 25% increase, most notably in the middle arcuate nucleus region, in young adults. Selective restoration of InsR expression in POMC neurons in these mice partly reversed the abnormality, resulting in a 10% decrease compared to age-matched controls. To establish whether FoxO1 signaling plays a role in this process, we examined POMC neuron number in mice with POMC-specific deletion of FoxO1, and detected a 23% decrease in age-matched animals, consistent with a cell-autonomous role of InsR/FoxO1 signaling in regulating POMC neuron number, distinct from its established role to activate Pomc transcription. These changes in Pomc cells occurred in the absence of marked changes in humoral factors or hypothalamic NPY neurons. [ABSTRACT FROM AUTHOR]

We present a consolidated view of the complexity and challenges of designing studies for measurement of energy metabolism in mouse models, including a practical guide to the assessment of energy expenditure, energy intake and body composition and statistical analysis thereof. We hope this guide will facilitate comparisons across studies and minimize spurious interpretations of data. We recommend that division of energy expenditure data by either body weight or lean body weight and that presentation of group effects as histograms should be replaced by plotting individual data and analyzing both group and body-composition effects using analysis of covariance (ANCOVA). [ABSTRACT FROM AUTHOR]

Weight-loss independent mechanisms may play an important role in the improvement of glucose homeostasis after Roux-en-Y gastric bypass (RYGB). The objective of this analysis was to determine whether RYGB causes greater improvement in glucostatic parameters as compared with laparoscopic adjustable gastric banding (LAGB) or low calorie diet (LCD) after equivalent weight loss and independent of enteral nutrient passage. Study 1 recruited participants without type 2 diabetes mellitus (T2DM) who underwent LAGB (n = 8) or RYGB (n = 9). Study 2 recruited subjects with T2DM who underwent LCD (n = 7) or RYGB (n = 7). Insulin-supplemented frequently-sampled intravenous glucose tolerance test (fsIVGTT) was performed before and after equivalent weight reduction. MINMOD analysis of insulin sensitivity (Si), acute insulin response to glucose (AIRg) and C-peptide (ACPRg) response to glucose, and insulin secretion normalized to the degree of insulin resistance (disposition index (DI)) were analyzed. Weight loss was comparable in all groups (7.8 ± 0.4%). In Study 1, significant improvement of Si, ACPRg, and DI were observed only after LAGB. In Study 2, Si, ACPRg, and plasma adiponectin increased significantly in the RYGB-DM group but not in LCD. DI improved in both T2DM groups, but the absolute increase was greater after RYGB (258.2 ± 86.6 vs. 55.9 ± 19.9; P < 0.05). Antidiabetic medications were discontinued after RYGB contrasting with 55% reduction in the number of medications after LCD. No intervention affected fasting glucagon-like peptide (GLP)-1, peptide YY (PYY) or ghrelin levels. In conclusion, RYGB produced greater improvement in Si and DI compared with diet at equivalent weight loss in T2DM subjects. Such a beneficial effect was not observed in nondiabetic subjects at this early time-point. [ABSTRACT FROM AUTHOR]

A major component of obesity-related insulin resistance is the establishment of a chronic inflammatory state with invasion of white adipose tissue by mononuclear cells. This results in the release of pro-inflammatory cytokines, which in turn leads to insulin resistance in target tissues such as skeletal muscle and liver. To determine the role of insulin action in macrophages and monocytes in obesity-associated insulin resistance, we conditionally inactivated the insulin receptor (IR) gene in myeloid lineage cells in mice (IRΔmyel-mice). While these animals exhibit unaltered glucose metabolism on a normal diet, they are protected from the development of obesity-associated insulin resistance upon high fat feeding. Euglycemic, hyperinsulinemic clamp studies demonstrate that this results from decreased basal hepatic glucose production and from increased insulin-stimulated glucose disposal in skeletal muscle. Furthermore, IRΔmyel-mice exhibit decreased concentrations of circulating tumor necrosis factor (TNF) α and thus reduced c-Jun Nterminal kinase (JNK) activity in skeletal muscle upon high fat feeding, reflecting a dramatic reduction of the chronic and systemic low-grade inflammatory state associated with obesity. This is paralleled by a reduced accumulation of macrophages in white adipose tissue due to a pronounced impairment of matrix metalloproteinase (MMP) 9 expression and activity in these cells. These data indicate that insulin action in myeloid cells plays an unexpected, critical role in the regulation of macrophage invasion into white adipose tissue and in the development of obesity-associated insulin resistance. [ABSTRACT FROM AUTHOR]

OBJECTIVE--The sites of insulin action in the central nervous system that regulate glucose metabolism and energy expenditure are incompletely characterized. We have shown that mice with hypothalamic deficiency (L1) of insulin receptors (InsRs) fail to regulate hepatic glucose production (HGP) in response to insulin. RESEARCH DESIGN AND METHODS--To distinguish neurons that mediate insulin's effects on HGP from those that regulate energy homeostasis, we used targeted knock-ins to express InsRs in agouti-related protein (AgRP) or proopiomelanocortin (POMC) neurons of L1 mice. RESULTS--Restoration of insulin action in AgRP neurons normalized insulin suppression of HGP. Surprisingly, POMC-specific InsR knock-in increased energy expenditure and locomotor activity, exacerbated insulin resistance and increased HGP, associated with decreased expression of the ATP-sensitive K[sup +] channel (K[sub ATP] channel) sulfonylurea receptor 1 subunit, and decreased inhibitory synaptic contacts on POMC neurons. CONCLUSIONS--The contrasting phenotypes of InsR knockins in POMC and AgRP neurons suggest a branched-pathway model of hypothalamic insulin signaling in which InsR signaling in AgRP neurons decreases HGP, whereas InsR activation in POMC neurons promotes HGP and activates the melanocortinergic energy expenditure program. Diabetes 59:337-346, 2010 [ABSTRACT FROM AUTHOR]

Reduced food intake brings about an adaptive decrease in energy expenditure that contributes to the recidivism of obesity after weight loss. Insulin and leptin inhibit food intake through actions in the central nervous system that are partly mediated by the transcription factor FoxO1. We show that FoxO1 ablation in pro-opiomelanocortin (Pomc)-expressing neurons in mice (here called Pomc-Foxo1−/− mice) increases Carboxypeptidase E (Cpe) expression, resulting in selective increases of α-melanocyte–stimulating hormone (α-Msh) and carboxy-cleaved β-endorphin, the products of Cpe-dependent processing of Pomc. This neuropeptide profile is associated with decreased food intake and normal energy expenditure in Pomc-Foxo1−/− mice. We show that Cpe expression is downregulated by diet-induced obesity and that FoxO1 deletion offsets the decrease, protecting against weight gain. Moreover, moderate Cpe overexpression in the arcuate nucleus phenocopies features of the FoxO1 mutation. The dissociation of food intake from energy expenditure in Pomc-Foxo1−/− mice represents a model for therapeutic intervention in obesity and raises the possibility of targeting Cpe to develop weight loss medications. [ABSTRACT FROM AUTHOR]

Ciliary neurotrophic factor (CNTF) exerts anorectic effects by overcoming leptin resistance via activation of hypothalamic neurons. However, the exact site of CNTF action in the hypothalamus has not yet been identified. Using Cre-loxP-mediated recombination in vivo, we have selectively ablated the common cytokine signaling chain gp130, which is required for functional CNTF signaling, in proopiomelanocortin (POMC)-expressing neurons. POMC-specific gp130 knockout mice exhibit unaltered numbers of POMC cells and normal energy homeostasis under standard and high fat diet. Endotoxin (LPS) and stress-induced anorexia and adrenocorticotropin regulation were unaffected in these animals. Strikingly, the anorectic effect of centrally administered CNTF was abolished in POMC-specific gp130 knockout mice. Correspondingly, in these animals, CNTF failed to activate STAT3 phosphorylation in POMC neurons and to induce c-Fos expression in the paraventricular nucleus. These data reveal POMC neurons as a critical site of CNTF action in mediating its anorectic effect. [ABSTRACT FROM AUTHOR]

Cerebral insulin receptors play an important role in regulation of energy homeostasis and development of neurodegeneration. Accordingly, type 2 diabetes characterized by insulin resistance is associated with an increased risk of developing Alzheimer's disease. Formation of neurofibrillary tangles, which contain hyperphosphorylated tau, represents a key step in the pathogenesis of neurodegenerative diseases. Here, we directly addressed whether peripheral hyperinsulinemia as one feature of type 2 diabetes can alter in vivo cerebral insulin signaling and tau phosphorylation. Peripheral insulin stimulation rapidly increased insulin receptor tyrosine phosphorylation, mitogen-activated protein kinase and phosphatidylinositol (PI) 3-kinase pathway activation, and dose-dependent tau phosphorylation at Ser202 in the central nervous system. Phospho-FoxO1 and PI-3,4,5-phosphate immunostainings of brains from insulin-stimulated mice showed neuronal staining throughout the brain, not restricted to brain areas without functional blood-brain barrier. Importantly, in insulin-stimulated neuronal/brain-specific insulin receptor knockout mice, cerebral insulin receptor signaling and tau phosphorylation were completely abolished. Thus, peripherally injected insulin directly targets the brain and causes rapid cerebral insulin receptor signal transduction and site-specific tau phosphorylation in vivo, revealing new insights into the linkage of type 2 diabetes and neurodegeneration. [ABSTRACT FROM AUTHOR]

A backcross model of New Zealand obese mice (NZO) with the lean, atherosclerosis-resistant SJL strain was established to locate genes responsible for obesity, insulin resistance, and type 2 diabetes-like hyperglycemia. In male NZO x F1 backcross mice, a major susceptibility locus for the development of hyperglycemia and hypoinsulinemia (Nidd/SJL) was identified on chromosome 4 between the markers D4Mit278 and D4Mit232, 10-28 cM distal of the previously described Nidd1 locus. The diabetogenic allele has presumably been contributed by the SJL genome, and it appeared to be responsible for approximately 60% of the total prevalence of hyperglycemia. The presence of Nidd/SJL did not alter body weight or weight gain by week 12. Thereafter, it was associated with reduced weight gain or weight loss, presumably as a consequence of decompensated hyperglycemia. In all male backcross mice, the prevalence of hyperglycemia at week 22 increased with the body weight at week 12, suggesting that the development of hyperglycemia was dependent on the degree of obesity. In the absence of Nidd/SJL, mice weighing <50 g at week 12 did not develop hyperglycemia by week 22. In contrast, in animals carrying the diabetogenic allele, the prevalence of hyperglycemia was 20 and 64% when the 12-week weight was <45 and 45-50 g, respectively. These data are consistent with the conclusion that Nidd/SJL represents a diabetes gene that lowers the obesity threshold for the development of hyperglycemia and hypoinsulinemia. [ABSTRACT FROM AUTHOR]

Multiple hormones controlling energy homeostasis regulate the expression of neuropeptide Y (NPY) and agouti-related peptide (AgRP) in the arcuate nucleus of the hypothalamus. Nevertheless, inactivation of the genes encoding NPY and/or AgRP has no impact on food intake in mice. Here we demonstrate that induced selective ablation of AgRP-expressing neurons in adult mice results in acute reduction of feeding, demonstrating direct evidence for a critical role of these neurons in the regulation of energy homeostasis. [ABSTRACT FROM AUTHOR]

Insulin and leptin control food intake in part by regulating the transcription of orectic and anorectic neuropeptides in the hypothalamus. Activation of insulin receptor signaling results in nuclear exclusion of the transcription factor forkhead box-containing protein of the O subfamily (FoxO)-1, while Leptin activates the signal transducer and activator of transcription 3 (Stat3). We have previously shown that FoxO1 and Star3 exert opposing actions on the expression of Agrp and Pomc, resulting in activation of Agrp and inhibition of Pomc transcription. We reported that hypothalamic adenoviral delivery of constitutively nuclear FoxO1 blunted leptin's effect to acutely reduce food intake and body weight. However, it remains unclear whether chronic changes in hypothalamic FoxO1 activity affect the physiological regulation of energy homeostasis by insulin and leptin. To investigate the role of hypothalamic FoxO1 signaling in a genetic system, we inactivate the Foxol gene specifically in Pomc neurons in vivo, using cre/loxP technology in mice. Pomc-Foxo-/- mice were born at normal Mendelian ratios and had normal appearance at birth. Body weight in Pomc-specific Foxo1 knockout and wild type control animals was similar until 6-8 weeks of age, but subsequently both female and male mutant mice exhibited significantly reduced body weight compared to their wild type littermates. At 11 weeks, Pomc-Foxo-/- mice were significantly leaner (20.3±0.57 vs. 22.4±0.73 g in WT controls, P≤0.05). Importantly, reduced body weight in female mutant mice was accompanied by marked reduction of body fat content (7.0±1.05 vs. 3.7±0.43 %, P≤0.01 at wk. 14 in WT. vs. Pomc-Foxo-/females, respectively). While food intake under steady state conditions appeared unaltered, both female and male mice with Pomc-specific FoxOl-deficiency showed a blunted refeeding response to a 24h fast (88±5 vs. 73±4 mg/g/6h, P≤0.05; at wk.18, in WT. vs. Pomc-Foxo-/- males, respectively). These data are consistent with the hypothesis that FoxO1 is a critical player in hypothalamic Pomc neurons regulating energy homeostasis. Further physiologic analyses of Pomc-Foxo-/- mice are underway. ADA-Funded Research [ABSTRACT FROM AUTHOR]