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Dietary methionine restriction (MR) produces an integrated series of biochemical and physiological responses that improve biomarkers of metabolic health, limit fat accretion, and enhance insulin sensitivity. Using transcriptional profiling to guide tissue-specific evaluations of molecular responses to MR, we report that liver and adipose tissue are the primary targets of a transcriptional program that remodeled lipid metabolism in each tissue. The MR diet produced a coordinated downregulation of lipogenic genes in the liver, resulting in a corresponding reduction in the capacity of the liver to synthesize and export lipid. In contrast, the transcriptional response in white adipose tissue (WAT) involved a depot-specific induction of lipogenic and oxidative genes and a commensurate increase in capacity to synthesize and oxidize fatty acids. These responses were accompanied by a significant change in adipocyte morphology, with the MR diet reducing cell size and increasing mitochondrial density across all depots. The coordinated transcriptional remodeling of lipid metabolism between liver and WAT by dietary MR produced an overall reduction in circulating and tissue lipids and provides a potential mechanism for the increase in metabolic flexibility and enhanced insulin sensitivity produced by the diet. Diabetes 62:3362-3372, 2013, Changes in dietary macronutrient composition (protein, carbohydrate, fat) are perceived through nutrient-sensing systems that affect overall energy balance through adaptive changes in behavior and peripheral metabolism. Diets lacking an essential [...]

Previous studies have demonstrated that Fyn knockout (FynKO) mice on a standard chow diet display increased glucose clearance and whole-body insulin sensitivity associated with decreased adiposity resulting from increased fatty acid use and energy expenditure. Surprisingly, however, despite a similar extent of adipose tissue (AT) mass accumulation on a high-fat diet, the FynKO mice remained fully glucose tolerant and insulin sensitive. Physiologic analyses demonstrated that the FynKO mice had a combination of skewed AT expansion into the subcutaneous compartment rather than to the visceral depot, reduced AT inflammation associated with reduced T-cell and macrophage infiltration, and increased proportion of anti-inflammatory M2 macrophages. These data demonstrate that Fyn is an important regulator of whole-body integrative metabolism that coordinates AT expansion, inflammation, and insulin sensitivity in states of nutrient excess. These data further suggest that inhibition of Fyn function may provide a novel target to prevent AT inflammation, insulin resistance, and the dyslipidemia components of the metabolic syndrome., Obesity is the single greatest predictor of the development of type 2 diabetes and has become a global pandemic with 475 million people worldwide affected and with 42% of the [...]

Type 2 diabetes involves insulin resistance and β-cell failure leading to inadequate insulin secretion. An important component of β-cell failure is cell loss by apoptosis. Apoptosis repressor with caspase recruitment domain (ARC) is an inhibitor of apoptosis that is expressed in cardiac and skeletal myocytes and neurons. ARC possesses the unusual property of antagonizing both the extrinsic (death receptor) and intrinsic (mitochondria/endoplasmic reticulum [ER]) cell death pathways. Here we report that ARC protein is abundant in cells of the endocrine pancreas, including >99.5% of mouse and 73% of human β-cells. Using genetic gain- and loss-of-function approaches, our data demonstrate that ARC inhibits β-cell apoptosis elicited by multiple inducers of cell death, including ER stressors tunicamycin, thapsigargin, and physiological concentrations of palmitate. Unexpectedly, ARC diminishes the ER stress response, acting distal to protein kinase RNA-like ER kinase (PERK) and inositol-requiring protein 1α, to suppress C/EBP homologous protein (CHOP) induction. Depletion of ARC in isolated islets augments palmitate-induced apoptosis, which is dramatically rescued by deletion of CHOP. These data demonstrate that ARC is a previously unrecognized inhibitor of apoptosis in β-cells and that its protective effects are mediated through suppression of the ER stress response pathway. Diabetes 62:183-193, 2013, Hyperglycemia in type 2 diabetes is mediated by insulin resistance and β-cell failure, the latter leading to inadequate insulin secretion relative to the degree of insulin resistance. β-Cell failure results [...]

IGF-I shares structural homology and in vitro metabolic activity with insulin. Laboratory models suggest that IGF-I and its binding proteins IGFBP-1 and IGFBP-2 have potentially beneficial effects on diabetes risk, whereas IGFBP-3 may have adverse effects. We therefore conducted a prospective nested case-control investigation of incident diabetes (n = 742 case subjects matched 1:1 to control subjects) and its associations with IGF-axis protein levels in the Nurses' Health Study, a cohort of middle-aged women. The median time to diabetes was 9 years. Statistical analyses were adjusted for multiple risk factors, including insulin and C-reactive protein. Diabetes risk was fivefold lower among women with baseline IGFBP-2 levels in the top versus bottom quintile (odds ratio [[OR].sub.q5-q1] = 0.17 [95% CI 0.08-0.35]; P trend < 0.0001) and was also negatively associated with IGFBP-1 levels ([OR.sub.q5-q1] = 0.37 [0.180.73]; P trend = 0.0009). IGFBP-3 was positively associated with diabetes ([OR.sub.q5-q1] = 2.05 [1.20-3.51]; P trend = 0.002). Diabetes was not associated with total IGF-I levels, but free IGF-I and diabetes had a significant association that varied (P interaction = 0.003) by insulin levels above the median ([OR.sub.q5-q1] = 0.48 [0.26-0.90]; P trend = 0.0001) versus below the median ([OR.sub.q5-q1] = 2.52 [1.056.06]; P trend < 0.05). Thus, this prospective study found strong associations of incident diabetes with baseline levels of three IGFBPs and free IGF-I, consistent with hypotheses that the IGF axis might influence diabetes risk. Diabetes 61:2248-2254, 2012, Increasing evidence suggests that the insulin-like growth factor (IGF) axis may play a role in glucose homeostasis (1). IGF-I shares structural homology and downstream signaling pathways with insulin, and like [...]

OBJECTIVE--Previous studies have demonstrated that mice fed a high-fat diet (HFD) develop insulin resistance with proinflammatory macrophage infiltration into white adipose tissue. Concomitantly, adipocytes undergo programmed cell death with the loss of the adipocyte-specific lipid droplet protein perilipin, and the dead/dying adipocytes are surrounded by macrophages that are organized into crown-like structures. This study investigated whether adipocyte cell death provides the driving signal for macrophage inflammation or if inflammation induces adipocyte cell death. RESEARCH DESIGN AND METHODS--Two knockout mouse models were used: granulocyte/monocyte-colony stimulating factor (GM-CSF)-null mice that are protected against HFD-induced adipose tissue inflammation and cyclophilin D (CyP-D)-null mice that are protected against adipocyte cell death. Mice were fed for 4-14 weeks with a 60% HFD, and different markers of cell death and inflammation were analyzed. RESULTS--HFD induced a normal extent of adipocyte cell death in GM-CSF-null mice, despite a marked reduction in adipose tissue inflammation. Similarly, depletion of macrophages by clodronate treatment prevented HFD-induced adipose tissue inflammation without any affect on adipocyte cell death. However, CyP-D deficiency strongly protected adipocytes from HFD-induced cell death, without affecting adipose tissue inflammation. CONCLUSIONS--These data demonstrate that HFD-induced adipocyte cell death is an intrinsic cellular response that is CyP-D dependent but is independent of macrophage infiltration/ activation. Diabetes 60:2134-2143, 2011, Multiple studies in mice have demonstrated that a high-fat diet (HFD) results in an adipose tissue inflammatory response that consists of dynamic changes in adipose tissue macrophages, neutrophils, mast cells, [...]

OBJECTIVE--Phosphatidylinositol-4-phosphate-5-kinase (PI4P5K) has been proposed to facilitate regulated exocytosis and specifically insulin secretion by generating phosphatidylinositol-4,5bisphosphate ([PIP.sub.2]). We sought to examine the role of the isoform of PI4P5K in glucohomeostasis and insulin secretion. RESEARCH DESIGN AND METHODS--The response of PI4P5K[α-/-] mice to glucose challenge and a type 2-like diabetes-inducing high-fat diet was examined in vivo. Glucose-stimulated responses and PI4P5K[α.sup.-/-] pancreatic islets and [β-cells were characterized in culture. RESULTS--We show that PI4P5Kα.sup.-/-] mice exhibit increased first-phase insulin release and improved glucose clearance, and resist high-fat diet-induced development of type 24ike diabetes and obesity. PI4P5[α.sup.-/-] pancreatic islets cultured in vitro exhibited decreased numbers of insulin granules docked at the plasma membrane and released less insulin under quiescent conditions, but then secreted similar amounts of insulin on glucose stimulation. Stimulation-dependent [PIP.sub.2] depletion occurred on the plasma membrane of the PI4P5K[α.sup-/-] pancreatic β-cells, accompanied by a near-total loss of cortical F-actin, which was already decreased in the PI4P5K[α.sup.-/-] [β-cells under resting conditions. CONCLUSIONS--Our findings suggest that PI4P5Kα plays a complex role in restricting insulin release from pancreatic β-cells through helping to maintain plasma membrane [PIP.sub.2] levels and integrity of the actin cytoskeleton under both basal and stimulatory conditions. The increased first-phase glucose-stimulated release of insulin observed on the normal diet may underlie the partial protection against the elevated serum glucose and obesity seen in type 2 diabetes-like model systems. Diabetes 60:454-463, 2011, Failure of pancreatic β-cells to release adequate amounts of insulin contributes to the onset of type 2 diabetes and obesity (1). Elevated serum glucose transported into pancreatic β-cells is metabolized [...]

OBJECTIVE--Previous studies have demonstrated that the VAMP8 protein plays a complex role in the control of granule secretion, transport vesicle trafficking, phagocytosis, and endocytosis. The present study was aimed to investigate the role of VAMP8 in mediating GLUT4 trafficking and therefore insulin action in mice. RESEARCH DESIGN AND METHODS--Physiological parameters were measured using Oxymax indirect calorimetry system in 12-week-old VAMP8 null mice. Dynamic analysis of glucose homeostasis was assessed using euglycemic-hyperinsulinemic clamp coupled with tracer radioactively labeled 2-deoxyglucose. Insulin stimulated GLUT4 protein expressions on muscle cell surface were examined by immunofluorescence microscopy. RESULTS--VAMP8 null mice display reduced adiposity with increased energy expenditure despite normal food intake and reduced spontaneous locomotor activity. In parallel, the VAMP8 null mice also had fasting hypoglycemia (84 ± 11 vs. 115 ± 4) and enhanced glucose tolerance with increased insulin sensitivity due to increases in both basal and insulin-stimulated glucose uptake in skeletal muscle (0.19 ± 0.04 vs. 0.09 ± 0.01 mmol/kg/min during basal, 0.6 ± 0.04 vs. 0.31 ± 0.06 mmol/kg/min during clamp in red-gastrocnemius muscle, P < 0.05). Consistent with a role for VAMP8 in the endocytosis of the insulin-responsive GLUT4, sarcolemma GLUT4 protein levels were increased in both the basal and insulin-stimulated states without any significant change in the total amount of GLUT4 protein or related facilitative glucose transporters present in skeletal muscle, GLUT1, GLUT3, and GLUT11. CONCLUSIONS--These data demonstrate that, in the absence of VAMP8, the relative subcellular distribution of GLUT4 is altered, resulting in increased sarcolemma levels that can account for increased glucose clearance and insulin sensitivity. Diabetes 60:30-38, 2011, Insulin-stimulated glucose uptake in muscle and adipose tissue is mediated by the insulin-responsive GLUT isoform GLUT4 (1). In the basal state, ~95% of the GLUT4 protein is sequestered in intracellular [...]

The disruption of Munc18c binding to syntaxin 4 impairs insulin-stimulated GLUT4 vesicle translocation in 3T3L1 adipocytes. To investigate the physiological function and requirement for Munc18c in the regulation of GLUT4 translocation and glucose homeostasis in vivo, we used homologous recombination to generate Munc18c-knockout (KO) mice. Homozygotic disruption of the Munc18c gene resulted in early embryonic lethality, whereas heterozygous KO mice (Munc[18c.sup.-/+]) had normal viability. Munc[18c.sup.-/+] mice displayed significantly decreased insulin sensitivity in an insulin tolerance test and a >50% reduction in skeletal muscle insulin-stimulated GLUT4 translocation when compared with wild-type (WT) mice. Furthermore, glucose-stimulated insulin secretion was significantly reduced in islets isolated from Munc[18c.sup.-/+] mice compared with those from WT mice. Despite the defects in insulin action and secretion, Munc[18c.sup.-/+] mice demonstrated the ability to clear glucose to the same level as WT mice in a glucose tolerance test when fed a normal diet. However, after consuming a high-fat diet for only 5 weeks, the Munc[18c.sup.-/+] mice manifested severely impaired glucose tolerance compared with high-fat-fed WT mice. Taken together, these data suggest that the reduction of Munc18c protein in the Munc[18c.sup.-/+] mice results in impaired insulin sensitivity with a latent increased susceptibility for developing severe glucose intolerance in response to environmental perturbations such as intake of a high-calorie diet rich in fat and carbohydrate., Glucose homeostasis is maintained by a series of regulated vesicle exocytosis events in several cell types and tissues. Vesicle exocytosis entails the pairing of a vesicle-associated membrane protein (VAMP) v-SNARE [...]

Four overlapping DNA fragments spanning 32 kb containing the human GLUT4 facilitative glucose-transporter gene were isolated and characterized. The sequence of the GLUT4 gene ([unkeyable]6.3 kb) and 2.0 kb of [...]

It has been 2 years since the current editorial board accepted stewardship of the premier journal of the American Diabetes Association (ADA), Diabetes. We believe this is an appropriate time [...]

Caveolae are plasma membrane subdomain regions that appear important for the regulation of several tyrosine kinase signaling events including the tyrosine phosphorylation of c-Cb1 and activation of GTP binding proteins [...]

It has been well established that the heterotrimeric GTP binding proteins Gq/11 function as a signal transducer that is activated by cell surface G protein coupled receptors (GPCRs). Gq/11 has [...]

Previous studies have suggested that t-SNARE protein (Syntaxin 4) and the v-SNARE proteins (VAMP2 and VAMP3/Cellubrevin) may play distinct roles in the regulation of GLUT4 vesicle translocation. To investigate the [...]

The 5'end of the GLUT4 glucose transporter promoter contains a consensus Myocyte Enhancer Factor 2 (MEF2) binding site which is essential for the tissue-specific and hormonal/metabolic regulation of the GLUT4 [...]

256-OR Insulin recruits Glut4 vesicles from intracellular stores to plasma membrane in muscle and adipose tissue. This complex trafficking process is mediated by specific interactions between several SNARE proteins, including [...]

Insulin recruits Glut4 vesicles from intracellular stores to the plasma membrane (PM) in muscle and adipose tissue. This complex trafficking process is mediated by specific interactions between several SNARE proteins, [...]

Recently we have demonstrated that Munc18c functions at a post-plasma membrane docking step in the insulin-stimulated translocation of GLUT4/IRAP-containing vesicles in 3T3L1 adipocytes (Thurmond et al., Mol Cell Biol, 20:379, [...]

In order to study the translocation of GLUT4 vesicles in skeletal muscle, we have prepared and characterized transgenic mice expressing a GLUT4-enhanced Green Fluorescent Protein (GLUT4-eGFP) fusion under the control [...]

Previous studies have suggested that timeric GTP binding proteins may play an important role in the regulation of GLUT4 translocation in adipocytes (Kishi et al., J Biol Chem 271:26561-26568, 1996). [...]

Insulin stimulates GLUT4 vesicle translocation from intracellular storage sites to the plasma membrane in 3T3L1 adipocytes through a VAMP2 and syntaxin 4 dependent mechanism. Munc 18c, a mammalian homolog of [...]

Insulin-stimulated translocation of GLUT4 containing vesicles requires specific interactions between the v-SNARE, VAMP2 and the t-SNARE, syntaxin 4. However, insulin does not directly affect these or any other SNARE-like molecules [...]