Search

The aims of this work were to evaluate thyroid hormone receptor-alpha (TR alpha), TR alpha 1, and TR alpha 2 mRNA gene expression and TR alpha 1:TR alpha 2 ratio, identified as candidate factors for explaining regional differences between human adipose tissue depots. TR alpha, TR alpha 1, and TR alpha 2 mRNA levels, and the gene expressions of arginine-serine-rich, splicing factor 2 (SF2), heterogeneous nuclear ribonucleoprotein H1 (hnRNP H1), heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1), and Spot 14 (S14) were evaluated in 76 paired adipose tissue samples obtained from a population of 38 women who varied widely in terms of obesity and body fat distribution. Gene expression for these factors was also studied in stromal-vascular cells (SVCs) and mature adipocytes (MAs) from eight paired fat depots. TR alpha gene and TR alpha 1 mRNA expression were increased 1.46-fold (P = 0.006) and 1.80-fold (P < 0.0001), respectively, in subcutaneous (SC) vs. visceral fat. These differences in gene expression levels were most significant in the obese group, in which the TR alpha 1:TR alpha 2 ratio was 2.24-fold (P < 0.0001) higher in SC vs. visceral fat. S14 gene expression was also increased by 2.42-fold (P < 0.0001) and correlated significantly with TR alpha and TR alpha 1 gene expression and with the TR alpha 1:TR alpha 2 ratio. In agreement with these findings, hnRNP A1:SF2 ratio was decreased by 1.39-fold (P = 0.001). TR alpha and S14 levels were 2.1-fold (P < 0.0001) and 112.4-fold (P < 0.0001), respectively, higher in MAs than in SVCs from both fat depots. In summary, genes for TR-alpha, their upstream regulators, and downstream effectors were differentially expressed in SC vs. omental (OM) adipose tissue. Our findings suggest that TR alpha1 could contribute to SC adipose tissue expandability in obese subjects.

The article discusess the role of FUN14 domain-containing protein 1 in contributing to cardiac function. Topics discussed include its role in the communication between mitochondria and the endoplasmic reticulum; prevention of heart failure; and analysis of mitochondrial-associated endoplasmic reticulum membranes.

Mitochondrial fusion and fission is a dynamic process critical for the maintenance of mitochondrial function and cell viability. During excitotoxicity neuronal mitochondria are fragmented, but the mechanism underlying this process is poorly understood. Here, we show that Mfn2 is the only member of the mitochondrial fusion/fission machinery whose expression is reduced in in vitro and in vivo models of excitotoxicity. Whereas in cortical primary cultures, Drp1 recruitment to mitochondria plays a primordial role in mitochondrial fragmentation in an early phase that can be reversed once the insult has ceased, Mfn2 downregulation intervenes in a delayed mitochondrial fragmentation phase that progresses even when the insult has ceased. Downregulation of Mfn2 causes mitochondrial dysfunction, altered calcium homeostasis, and enhanced Bax translocation to mitochondria, resulting in delayed neuronal death. We found that transcription factor MEF2 regulates basal Mfn2 expression in neurons and that excitotoxicity-dependent degradation of MEF2 causes Mfn2 downregulation. Thus, Mfn2 reduction is a late event in excitotoxicity and its targeting may help to reduce excitotoxic damage and increase the currently short therapeutic window in stroke. [ABSTRACT FROM AUTHOR]

Background: p38 MAPK activity plays an important role in several steps of the osteoblast lineage progression through activation of osteoblast-specific transcription factors and it is also essential for the acquisition of the osteoblast phenotype in early development. Although reports indicate p38 signalling plays a role in early skeletal development, its specific contributions to adult bone remodelling are still to be clarified. Methodology/Principal Findings: We evaluated osteoblast-specific deletion of p38α to determine its significance in early skeletogenesis, as well as for bone homeostasis in adult skeleton. Early p38α deletion resulted in defective intramembranous and endochondral ossification in both calvaria and long bones. Mutant mice showed reduction of trabecular bone volume in distal femurs, associated with low trabecular thickness. In addition, knockout mice also displayed decreased femoral cortical bone volume and thickness. Deletion of p38α did not affect osteoclast function. Yet it impaired osteoblastogenesis and osteoblast maturation and activity through decreased expression of osteoblast-specific transcription factors and their targets. Furthermore, the inducible Cre system allowed us to control the onset of p38α disruption after birth by removal of doxycycline. Deletion of p38α at three or eight weeks postnatally led to significantly lower trabecular and cortical bone volume after 6 or 12 months. Conclusions: Our data demonstrates that, in addition to early skeletogenesis, p38α is essential for osteoblasts to maintain their function in mineralized adult bone, as bone anabolism should be sustained throughout life. Moreover, our data also emphasizes that clinical development of p38 inhibitors should take into account their potential bone effects. [ABSTRACT FROM AUTHOR]

Type 2 Diabetes (T2D) is a highly prevalent chronic metabolic disease with strong co-morbidity with obesity and cardiovascular diseases. There is growing evidence supporting the notion that a crosstalk between mitochondria and the insulin signaling cascade could be involved in the etiology of T2D and insulin resistance. In this study we investigated the molecular basis of this crosstalk by using systems biology approaches. We combined, filtered, and interrogated different types of functional interaction data, such as direct protein-protein interactions, co-expression analyses, and metabolic and signaling dependencies. As a result, we constructed the mitochondria-insulin (MITIN) network, which highlights 286 genes as candidate functional linkers between these two systems. The results of internal gene expression analysis of three independent experimental models of mitochondria and insulin signaling perturbations further support the connecting roles of these genes. In addition, we further assessed whether these genes are involved in the etiology of T2D using the genome- wide association study meta-analysis from the DIAGRAM consortium, involving 8,130 T2D cases and 38,987 controls. We found modest enrichment of genes associated with T2D amongst our linker genes (p = 0.0549), including three already validated T2D SNPs and 15 additional SNPs, which, when combined, were collectively associated to increased fasting glucose levels according to MAGIC genome wide meta-analysis (p = 8.12x10-5 ). This study highlights the potential of combining systems biology, experimental, and genome-wide association data mining for identifying novel genes and related variants that increase vulnerability to complex diseases. [ABSTRACT FROM AUTHOR]

Aims Mitofusin-2 (Mfn2) expression is dysregulated in vascular proliferative disorders and its overexpression attenuates the proliferation of vascular smooth muscle cells (VSMCs) and neointimal lesion development after balloon angioplasty. We sought to gain insight into the mechanisms that control Mfn2 expression in VSMCs. Methods and results We cloned and characterized 2 kb of the 5′-flanking region of the human Mfn2 gene. Its TATA-less promoter contains a CpG island. In keeping with this, 5′-rapid amplification of cDNA ends revealed six transcriptional start sites (TSSs), of which TSS2 and TSS5 were the most frequently used. The strong CpG island was found to be non-methylated under conditions characterized by large differences in Mfn2 gene expression. The proximal Mfn2 promoter contains six putative Sp1 motifs. Sp1 binds to the Mfn2 promoter and its overexpression activates the Mfn2 promoter in VSMCs. Chemical inhibition of Sp1 reduced Mfn2 expression, and Sp1 silencing reduced transcriptional activity of the Mfn2 promoter. In keeping with this view, Sp1 and Mfn2 mRNA levels were down-regulated in the aorta early after an atherogenic diet in apolipoprotein E-knockout mice or in VSMCs cultured in the presence of low serum. Conclusion Sp1 is a key factor in maintaining basal Mfn2 transcription in VSMCs. Given the anti-proliferative actions of Mfn2, Sp1-induced Mfn2 transcription may represent a mechanism for prevention of VSMC proliferation and neointimal lesion and development. [ABSTRACT FROM PUBLISHER]

OBJECTIVE--The study objective was to evaluate the possible role of the macrophage molecule CD 14 in insulin resistance. RESEARCH DESIGN AND METHODS--The effects of re-combinant human soluble CD14 (rh-sCD14) on insulin sensitivity (clamp procedure) and adipose tissue gene expression were evaluated in wild-type (WT) mice, high fat-fed mice, ob/ob mice, and CD14 knockout (KO) mice. We also studied WT mice grafted with bone marrow stem cells from WT donor mice and CD14 KO mice. Finally, CD 14 was evaluated in human adipose tissue and during differentiation of human preadipocytes. RESULTS--rh-sCD14 led to increased insulin action in WT mice, high-fat-fed mice, and ob/ob mice, but not in CD14 KO mice, in parallel to a marked change in the expression of 3,479 genes in adipose tissue. The changes in gene families related to lipid metabolism were most remarkable. WT mice grafted with bone marrow stem cells from WT donor mice became insulin resistant after a high-fat diet. Conversely, WT mice grafted with cells from CD14 KO mice resisted the occurrence of insulin resistance in parallel to decreased mesenteric adipose tissue inflammatory gene expression. Glucose intolerance did not worsen in CD14 KO mice grafted with bone marrow stem cells from high fat-fed WT mice when compared with recipient KO mice grafted with cells from CD14 KO donor mice. CD14 gene expression was increased in whole adipose tissue and adipocytes from obese humans and further increased after tumor necrosis factor-α. CONCLUSIONS--CD14 modulates adipose tissue inflammatory activity and insulin resistance. [ABSTRACT FROM AUTHOR]

Summary: Background: Mammalian DOR was discovered as a gene whose expression is misregulated in muscle of Zucker diabetic rats. Because no DOR loss-of-function mammalian models are available, we analyze here the in vivo function of DOR by studying flies mutant for Drosophila DOR (dDOR). Results: We show that dDOR is a novel coactivator of ecdysone receptor (EcR) that is needed during metamorphosis. dDOR binds EcR and is required for maximal EcR transcriptional activity. In the absence of dDOR, flies display a number of ecdysone loss-of-function phenotypes such as impaired spiracle eversion, impaired salivary gland degradation, and pupal lethality. Furthermore, dDOR knockout flies are lean. We find that dDOR expression is inhibited by insulin signaling via FOXO. Conclusion: This work uncovers dDOR as a novel EcR coactivator. It also establishes a mutual antagonistic relationship between ecdysone and insulin signaling in the fly fat body. Furthermore, because ecdysone signaling inhibits insulin signaling in the fat body, this also uncovers a feed-forward mechanism whereby ecdysone potentiates its own signaling via dDOR. [Copyright &y& Elsevier]

The aims of this work were to evaluate thyroid hormone receptor-α (TRα), TRα1, and TRα2 mRNA gene expression and TRα1:TRα2 ratio, identified as candidate factors for explaining regional differences between human adipose tissue depots. TRα, TRα1, and TRα2 mRNA levels, and the gene expressions of arginine–serine-rich, splicing factor 2 (SF2), heterogeneous nuclear ribonucleoprotein H1 (hnRNP H1), heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1), and Spot 14 (S14) were evaluated in 76 paired adipose tissue samples obtained from a population of 38 women who varied widely in terms of obesity and body fat distribution. Gene expression for these factors was also studied in stromal-vascular cells (SVCs) and mature adipocytes (MAs) from eight paired fat depots. TRα gene and TRα1 mRNA expression were increased 1.46-fold (P = 0.006) and 1.80-fold (P < 0.0001), respectively, in subcutaneous (SC) vs. visceral fat. These differences in gene expression levels were most significant in the obese group, in which the TRα1:TRα2 ratio was 2.24-fold (P < 0.0001) higher in SC vs. visceral fat. S14 gene expression was also increased by 2.42-fold (P < 0.0001) and correlated significantly with TRα and TRα1 gene expression and with the TRα1:TRα2 ratio. In agreement with these findings, hnRNP A1:SF2 ratio was decreased by 1.39-fold (P = 0.001). TRα and S14 levels were 2.1-fold (P < 0.0001) and 112.4-fold (P < 0.0001), respectively, higher in MAs than in SVCs from both fat depots. In summary, genes for TR-α, their upstream regulators, and downstream effectors were differentially expressed in SC vs. omental (OM) adipose tissue. Our findings suggest that TRα1 could contribute to SC adipose tissue expandability in obese subjects. [ABSTRACT FROM AUTHOR]

Fusion and fission of mitochondria regulate their morphology and distribution. Mitofusin-2 (Mfn2) is a mitochondrial protein involved in such fusion. Recent observations indicate that Mfn2 is a multifunctional protein that participates in cell proliferation and metabolism and that it is required for normal endoplasmic reticulum morphology. In relation to the metabolic role of Mfn2, alterations in activity have been reported to modify cell respiration, substrate oxidation, and oxidative phosphorylation subunit expression in cultured nonmuscle and muscle cells. Mfn2 expression in skeletal muscle is subject to regulation and conditions characterized by reduced mitochondrial activity, such as obesity or type 2 diabetes, and are associated with repressed Mfn2. In contrast, cold-exposure treatment with β3-adrenergic agonists or exercise induce the expression of this gene in muscle. Estrogen-related receptor-α transcription factor is a key regulator of Mfn2 transcription and recruits peroxisome proliferator-activated receptor γ coactivator (PGC)-1β and PGC-1α. These 2 nuclear coactivators are potent, positive regulators of Mfn2 expression in muscle cells, and ablation of PGC-1β causes Mfn2 downregulation in skeletal muscle and in the heart. We propose that PGC-1β is a regulator of normal expression of Mfn2 in muscle, whereas PGC-1α participates in the stimulation of Mfn2 expression under a variety of conditions characterized by enhanced energy expenditure. [ABSTRACT FROM AUTHOR]

Background: There is no evidence to date on whether transcriptional regulators are able to shift the balance between mitochondrial fusion and fission events through selective control of gene expression. Methodology/Principal Findings: Here, we demonstrate that reduced mitochondrial size observed in knock-out mice for the transcriptional regulator PGC-1β is associated with a selective reduction in Mitofusin 2 (Mfn2) expression, a mitochondrial fusion protein. This decrease in Mfn2 is specific since expression of the remaining components of mitochondrial fusion and fission machinery were not affected. Furthermore, PGC-1β increases mitochondrial fusion and elongates mitochondrial tubules. This PGC-1β-induced elongation specifically requires Mfn2 as this process is absent in Mfn2-ablated cells. Finally, we show that PGC-1β increases Mfn2 promoter activity and transcription by coactivating the nuclear receptor Estrogen Related Receptor α (ERRα). Conclusions/Significance: Taken together, our data reveal a novel mechanism by which mammalian cells control mitochondrial fusion. In addition, we describe a novel role of PGC-1β in mitochondrial physiology, namely the control of mitochondrial fusion mainly through Mfn2. [ABSTRACT FROM AUTHOR]

Mitofusin 2 (Mfn2) is a mitochondrial membrane protein that participates in mitochondrial fusion and regulates mitochondrial metabolism in mammalian cells. Here, we show that Mfn2 gene expression is induced in skeletal muscle and brown adipose tissue by conditions associated with enhanced energy expenditure, such as cold exposure or β3-adrenergic agonist treatment. In keeping with the role of peroxisome proliferator-activated receptor-γ coactivator (PGC)-1α on energy expenditure, we demonstrate a stimulatory effect of PGC-1α on Mfn2 mRNA and protein expression in muscle cells. PGC-1α also stimulated the activity of the Mfn2 promoter, which required the integrity of estrogen-related receptor-1α (ERRα-binding elements located at -413/-398. ERRα also activated the transcriptional activity of the Mfn2 promoter, and the effects were synergic with those of PGC-α. Mfn2 loss of function reduced the stimulatory effect of PGC-1α on mitochondrial membrane potential. Exposure to cold substantially increased Mfn2 gene expression in skeletal muscle from heterozygous Mfn2 knock-out mice, which occurred in the presence of higher levels of PGC-1α mRNA compared with control mice. Our results indicate the existence of a regulatory pathway involving PGC-1α, ERRα, and Mfn2. Alterations in this regulatory pathway may participate in the pathophysiology of insulin-resistant conditions and type 2 diabetes. [ABSTRACT FROM AUTHOR]

The primary gene mutated in Charcot-Marie-Tooth type 2A is mitofusin-2 (Mfn2). Mfn2 encodes a mitochondrial protein that participates in the maintenance of the mitochondrial network and that regulates mitochondrial metabolism and intracellular signaling. The potential for regulation of human Mfn2 gene expression in vivo is largely unknown. Based on the presence of mitochondrial dysfunction in insulin-resistant conditions, we have examined whether Mfn2 expression is dysregulated in skeletal muscle from obese or nonobese type 2 diabetic subjects, whether muscle Mfn2 expression is regulated by body weight loss, and the potential regulatory role of tumor necrosis factor (TNF)α or interleukin-6. We show that mRNA concentration of Mfn2 is decreased in skeletal muscle from both male and female obese subjects. Muscle Mfn2 expression was also reduced in lean or in obese type 2 diabetic patients. There was a strong negative correlation between the Mfn2 expression and the BMI in nondiabetic and type 2 diabetic subjects. A positive correlation between the Mfn2 expression and the insulin sensitivity was also detected in nondiabetic and type 2 diabetic subjects. To determine the effect of weight loss on Mfn2 mRNA expression, six morbidly obese subjects were subjected to weight loss by bilio-pancreatic diversion. Mean expression of muscle Mfn2 mRNA increased threefold after reduction in body weight, and a positive correlation between muscle Mfn2 expression and insulin sensitivity was again detected. In vitro experiments revealed an inhibitory effect of TNFα or interleukin-6 on Mfn2 expression in cultured cells. We conclude that body weight loss upregulates the expression of Mfn2 mRNA in skeletal muscle of obese humans, type 2 diabetes downregulates the expression of Mfn2 mRNA in skeletal muscle, Mfn2 expression in skeletal muscle is directly proportional to insulin sensitivity and is inversely proportional to the BMI, TNFα and interleukin-6 downregulate Mfn2 expression and may participate in the dysregulation of Mfn2 expression in obesity or type 2 diabetes, and the in vivo modulation of Mfn2 mRNA levels is an additional level of regulation for the control of muscle metabolism and could provide a molecular mechanism for alterations in mitochondrial function in obesity or type 2 diabetes. Diabetes 54: 2685-2693, 2005 [ABSTRACT FROM AUTHOR]

Mitochondrial impairment is hypothesized to contribute to the pathogenesis of insulin resistance. Mitofusin (Mfn) proteins regulate the biogenesis and maintenance of the mitochondrial network, and when inactivated, cause a failure in the mitochondrial architecture and decreases in oxidative capacity and glucose oxidation. Exercise increases muscle mitochondrial content, size, oxidative capacity and aerobic glucose oxidation. To address if Mfn proteins are implicated in these exercise-induced responses, we measured Mfn1 and Mfn2 mRNA levels, pre-, post-, 2 and 24 h post-exercise. Additionally, we measured the expression levels of transcriptional regulators that control mitochondrial biogenesis and functions, including PGC-1α, NRF-1, NRF-2 and the recently implicated ERRα. We show that Mfn1, Mfn2, NRF-2 and COX IV mRNA were increased 24 h post-exercise, while PGC-1α and ERRα mRNA increased 2 h post-exercise. Finally, using in vitro cellular assays, we demonstrate that Mfn2 gene expression is driven by a PGC-1α programme dependent on ERRα. The PGC-1α/ERRα-mediated induction of Mfn2 suggests a role of these two factors in mitochondrial fusion. Our results provide evidence that PGC-1α not only mediates the increased expression of oxidative phosphorylation genes but also mediates alterations in mitochondrial architecture in response to aerobic exercise in humans. [ABSTRACT FROM AUTHOR]

The article presents a research report on disrupted circadian oscillations in type 2 diabetes are linked to altered rhythmic mitochondrial metabolism in skeletal muscle. Topics include identify bidirectional communication between mitochondrial function and rhythmic gene expression, processes that are disturbed in diabetes; and Inner-mitochondria disruption altered core-clock gene expression and free-radical production, phenomena that were restored by resveratrol treatment.

Age-related hearing loss (ARHL) is the most common sensory deficit in the elderly. The disease has a multifactorial etiology with both environmental and genetic factors involved being largely unknown. SLC7A8/SLC3A2 heterodimer is a neutral amino acid exchanger. Here, we demonstrated that SLC7A8 is expressed in the mouse inner ear and that its ablation resulted in ARHL, due to the damage of different cochlear structures. These findings make SLC7A8 transporter a strong candidate for ARHL in humans. Thus, a screening of a cohort of ARHL patients and controls was carried out revealing several variants in SLC7A8, whose role was further investigated by in vitro functional studies. Significant decreases in SLC7A8 transport activity was detected for patient's variants (p.Val302Ile, p.Arg418His, p.Thr402Met and p.Val460Glu) further supporting a causative role for SLC7A8 in ARHL. Moreover, our preliminary data suggest that a relevant proportion of ARHL cases could be explained by SLC7A8 mutations. [ABSTRACT FROM AUTHOR]

A precise balance between protein degradation and synthesis is essential to preserve skeletal muscle mass. Here, we found that TP53INP2, a homolog of the Drosophila melanogaster DOR protein that regulates autophagy in cellular models, has a direct impact on skeletal muscle mass in vivo. Using different transgenic mouse models, we demonstrated that muscle-specific overexpression of Tp53inp2 reduced muscle mass, while deletion of Tp53inp2 resulted in muscle hypertrophy. TP53INP2 activated basal autophagy in skeletal muscle and sustained p62-independent autophagic degradation of ubiquitinated proteins. Animals with muscle-specific overexpression of Tp53inp2 exhibited enhanced muscle wasting in streptozotocin-induced diabetes that was dependent on autophagy; however, TP53INP2 ablation mitigated experimental diabetes-associated muscle loss. The overexpression or absence of TP53INP2 did not affect muscle wasting in response to denervation, a condition in which autophagy is blocked, further indicating that TP53INP2 alters muscle mass by activating autophagy. Moreover, TP53INP2 expression was markedly repressed in muscle from patients with type 2 diabetes and in murine models of diabetes. Our results indicate that TP53INP2 negatively regulates skeletal muscle mass through activation of autophagy. Furthermore, we propose that TP53INP2 repression is part of an adaptive mechanism aimed at preserving muscle mass under conditions in which insulin action is deficient. [ABSTRACT FROM AUTHOR]

Abstract: Human heteromeric amino acid transporters (HATs) play key roles in renal and intestinal re-absorption, cell redox balance and tumor growth. These transporters are composed of a heavy and a light subunit, which are connected by a disulphide bridge. Heavy subunits are the two type II membrane N-glycoproteins rBAT and 4F2hc, while L-type amino acid transporters (LATs) are the light and catalytic subunits of HATs. We tested the expression of human 4F2hc and rBAT as well as seven light subunits in the methylotrophic yeast Pichia pastoris. 4F2hc and the light subunit LAT2 showed the highest expression levels and yields after detergent solubilization. Co-transformation of both subunits in Pichia cells resulted in overexpression of the disulphide bridge-linked 4F2hc/LAT2 heterodimer. Two sequential affinity chromatography steps were applied to purify detergent-solubilized heterodimers yielding ∼1mg of HAT from 2l of cell culture. Our results indicate that P. pastoris is a convenient system for the expression and purification of human 4F2hc/LAT2 for structural studies. [Copyright &y& Elsevier]

Expression of the glucose transporter GLUT1 is high in proliferating and tumour cells. Conditions in which the transcriptional activity of GLUT1 promoter are maximal are characterized by the operation of activators such as Sp1 and inhibitors as Sp3. Here, we have identified an element at -67/-60 (C8 box) in the rat GLUT1 promoter to which nuclear factors bind in a proliferation-dependent manner. Competition studies with a series of mutated oligonucleotides suggest that these nuclear factors are different in the proliferative state and after confluence. The C8 element does not bind any of the known factors defined in databases. Mutation of the C8 sequence enhanced transcriptional activity of the GLUT1 promoter in 10T1/2 fibroblasts and in L6E9 myoblasts but not in myotubes. Furthermore, the functional activity of the C8 box is maximal in the presence of serum. In summary, we have identified a novel inhibitory element, C8 box, in the rat GLUT1 promoter that operates in a proliferation-dependent manner. In keeping with this view, serum enhances the inhibitory activity of the C8 box, suggesting that this is regulated by growth factors. [Copyright &y& Elsevier]

Details the screening of differentially expressed genes in skeletal muscle from obese Zucker rats. Isolation of the fzo homologue mitofusin 2; Demonstration that Mfn2 expression is crucial to the maintenance of teh morphology and operation of the mitochondrial network and in mitochondrial metabolism.