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Query: UMLS:C0028754 (obesity)
 124,988 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Evidence demonstrates that exogenous nitric oxide (NO) and the NO produced by inducible nitric oxide synthase (iNOS) can induce insulin resistance in muscle. Here, we investigated whether this insulin resistance could be mediated by S-nitrosation of proteins involved in early steps of the insulin signal transduction pathway. Exogenous NO donated by S-nitrosoglutathione (GSNO) induced in vitro and in vivo S-nitrosation of the insulin receptor beta subunit (IRbeta) and protein kinase B/Akt (Akt) and reduced their kinase activity in muscle. Insulin receptor substrate (IRS)-1 was also rapidly S-nitrosated, and its expression was reduced after chronic GSNO treatment. In two distinct models of insulin resistance associated with enhanced iNOS expression-diet-induced obesity and the ob/ob diabetic mice-we observed enhanced S-nitrosation of IRbeta/IRS-1 and Akt in muscle. Reversal of S-nitrosation of these proteins by reducing iNOS expression yielded an improvement in insulin action in both animal models. Thus, S-nitrosation of proteins involved in insulin signal transduction is a novel molecular mechanism of iNOS-induced insulin resistance.
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PMID:S-nitrosation of the insulin receptor, insulin receptor substrate 1, and protein kinase B/Akt: a novel mechanism of insulin resistance. 1579 33

Studies of diabetic vascular disease have traditionally used murine models of type 1 diabetes and genetic models of type 2 diabetes. Because the majority of patients with type 2 diabetes have diet induced obesity, we sought to study the effect of diabetes on arterial disease in a mouse model of diet induced obesity/diabetes. C57Bl/6 mice fed a high-fat diet for 9 weeks developed type 2 diabetes characterized by elevated body weight, hyperglycemia, and hyperinsulinemia. Arteries from diabetic mice exhibited a marked decrease in endothelium-dependent vasodilation, a modest decrease in endothelium independent vasodilation, and an increase in sensitivity to adrenergic vasoconstricting agents. Insulin stimulated protein kinase B (akt) and endothelial nitric oxide synthase (eNOS) phosphorylation were preserved in arteries from diabetic mice; however, eNOS protein dimers were markedly diminished. Arterial nitrotyrosine staining indicated that increased levels of peroxynitrite contributed to eNOS dimer disruption in the diabetic mice. The abnormal vasomotion was not an acute response to the high-fat diet, as short term high-fat diet feeding had no effect on endothelium dependent dilation. A trend toward smaller neointimal lesions was noted in high-fat diet fed mice after femoral artery wire denudation injury. In summary, disrupted eNOS dimer formation rather than impaired insulin mediated eNOS phosphorylation contributed to the endothelial dysfunction in diet induced obese/diabetic mice. The lack of an increase in neointimal formation indicates that additional diabetes associated parameters (such as hyperlipidemia and atherosclerotic vascular disease) may need to be present to increase neointimal formation in this model.
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PMID:Diabetes induces endothelial dysfunction but does not increase neointimal formation in high-fat diet fed C57BL/6J mice. 1610 22

An elevated circulating level of the adipocyte-derived satiety hormone leptin is an independent risk factor for cardiovascular disease. Because thrombus formation is a major cause of acute coronary events and leptin was shown previously to facilitate ADP-induced platelet aggregation, we chose to define the signaling events involved in leptin-mediated platelet activation. Using pharmacological, biochemical, and cell biological approaches, we show that leptin-induced platelet activation required activation of a signaling cascade that included the long form of the leptin receptor, three kinases [Janus kinase 2 (JAK2), phosphatidylinositol 3-kinase (PI3K), and protein kinase B (PKB/Akt)], the insulin receptor substrate-1 (IRS-1), and the major human platelet cAMP phosphodiesterase phosphodiesterase 3A (PDE3A). Moreover, we identify a role for an intraplatelet LEPR/JAK2/IRS-1/PI3K/PKB/PDE3A molecular complex that allows for the selective leptin-mediated activation of platelets. Our data demonstrate that leptin promotes platelet activation, provides a mechanistic basis for the prothrombotic effect of this hormone, and identifies a potentially novel therapeutic avenue to limit obesity-associated cardiovascular disease.
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PMID:Leptin-mediated activation of human platelets: involvement of a leptin receptor and phosphodiesterase 3A-containing cellular signaling complex. 1588 25

Insulin resistance and obesity are central components of the metabolic syndrome which has become the leading cause of cardiovascular morbidity and mortality worldwide. Direct interactions of the beta (3)-adrenoceptor system with adipocyte signaling and function in humans remain poorly understood. However, this might have important consequences for the regulation of energy homeostasis and insulin resistance in states of hyperinsulinemia and sympatho-adrenergic overactivity. We therefore investigated beta (3)-adrenoceptor-mediated effects on insulin signaling and glucose uptake in mammary adipocytes of healthy women that underwent breast reduction surgery. Glucose uptake was strongly induced by insulin stimulation. This was paralleled by robust induction of insulin receptor kinase activity, insulin receptor substrate-1-associated phosphatidylinositol-3 kinase activity, and protein kinase B phosphorylation. Treatment with the beta (3)-adrenoceptor-selective agonist CL316,243 alone, neither induced alterations in the early insulin signaling cascade nor changed the basal level of glucose uptake. By contrast, pretreatment with the beta (3)-adrenoceptor agonist inhibited the insulin-induced insulin receptor substrate-1-associated phosphatidylinositol-3 kinase activity by 50 % and protein kinase B phosphorylation by 40 % without affecting insulin receptor kinase activity upstream. However, on the functional level insulin-induced glucose uptake remained unchanged by beta (3)-adrenoceptor stimulation. Our data demonstrate an insulin receptor-independent negative influence of beta (3)-adrenoceptor stimulation on proximal insulin signaling. This inhibition is apparently dissociated from glucose uptake in human adipocytes.
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PMID:The beta3-adrenergic agonist CL316,243 inhibits insulin signaling but not glucose uptake in primary human adipocytes. 1615 74

Glucose transport into muscle is the initial process in glucose clearance and is uniformly defective in insulin-resistant conditions of obesity, metabolic syndrome, and Type II diabetes mellitus. Insulin regulates glucose transport by activating insulin receptor substrate-1 (IRS-1)-dependent phosphatidylinositol 3-kinase (PI3K) which, via increases in PI-3,4,5-triphosphate (PIP(3)), activates atypical protein kinase C (aPKC) and protein kinase B (PKB/Akt). Here, we review (i) the evidence that both aPKC and PKB are required for insulin-stimulated glucose transport, (ii) abnormalities in muscle aPKC/PKB activation seen in obesity and diabetes, and (iii) mechanisms for impaired aPKC activation in insulin-resistant conditions. In most cases, defective muscle aPKC/PKB activation reflects both impaired activation of IRS-1/PI3K, the upstream activator of aPKC and PKB in muscle and, in the case of aPKC, poor responsiveness to PIP(3), the lipid product of PI3K. Interestingly, insulin-sensitizing agents (e.g., thiazolidinediones, metformin) improve aPKC activation by insulin in vivo and PIP3 in vitro, most likely by activating 5'-adenosine monophosphate-activated protein kinase, which favorably alters intracellular lipid metabolism. Differently from muscle, aPKC activation in the liver is dependent on IRS-2/PI3K rather than IRS-1/PI3K and, surprisingly, the activation of IRS-2/PI3K and aPKC is conserved in high-fat feeding, obesity, and diabetes. This conservation has important implications, as continued activation of hepatic aPKC in hyperinsulinemic states may increase the expression of sterol regulatory element binding protein-1c, which controls genes that increase hepatic lipid synthesis. On the other hand, the defective activation of IRS-1/PI3K and PKB, as seen in diabetic liver, undoubtedly and importantly contributes to increases in hepatic glucose output. Thus, the divergent activation of aPKC and PKB in the liver may explain why some hepatic actions of insulin (e.g., aPKC-dependent lipid synthesis) are increased while other actions (e.g., PKB-dependent glucose metabolism) are diminished. This may explain the paradox that the liver secretes excessive amounts of both very low density lipoprotein triglycerides and glucose in Type II diabetes. Previous reviews from our laboratory that have appeared in the Proceedings have provided essentials on phospholipid-signaling mechanisms used by insulin to activate several protein kinases that seem to be important in mediating the metabolic effects of insulin. During recent years, there have been many new advances in our understanding of how these lipid-dependent protein kinases function during insulin action and why they fail to function in states of insulin resistance. The present review will attempt to summarize what we believe are some of the more important advances.
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PMID:Insulin-sensitive protein kinases (atypical protein kinase C and protein kinase B/Akt): actions and defects in obesity and type II diabetes. 1617 27

Insulin resistance is often associated with obesity. We tested whether augmentation of triglyceride synthesis in adipose tissue by transgenic overexpression of the diacylglycerol aclytransferase-1 (Dgat1) gene causes obesity and/or alters insulin sensitivity. Male FVB mice expressing the aP2-Dgat1 had threefold more Dgat1 mRNA and twofold greater DGAT activity levels in adipose tissue. After 30 weeks of age, these mice had hyperglycemia, hyperinsulinemia, and glucose intolerance on a high-fat diet but were not more obese than wild-type littermates. Compared with control littermates, Dgat1 transgenic mice were both insulin and leptin resistant and had markedly elevated plasma free fatty acid levels. Adipocytes from Dgat1 transgenic mice displayed increased basal and isoproterenol-stimulated lipolysis rates and decreased gene expression for fatty acid uptake. Muscle triglyceride content was unaffected, but liver mass and triglyceride content were increased by 20 and 300%, respectively. Hepatic insulin signaling was suppressed, as evidenced by decreased phosphorylation of insulin receptor-beta (Tyr(1,131)/Tyr(1,146)) and protein kinase B (Ser473). Gene expression data suggest that the gluconeogenic enzymes, glucose-6-phosphatase and phosphoenolpyruvate carboxykinase, were upregulated. Thus, adipose overexpression of Dgat1 gene in FVB mice leads to diet-inducible insulin resistance, which is secondary to redistribution of fat from adipose tissue to the liver in the absence of obesity.
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PMID:Whole-body insulin resistance in the absence of obesity in FVB mice with overexpression of Dgat1 in adipose tissue. 1630 52

Loss of brain melanocortin receptors (Mc3rKO and Mc4rKO) causes increased adiposity and exacerbates diet-induced obesity (DIO). Little is known about how Mc3r or Mc4r genotype, diet, and obesity affect insulin sensitivity. Insulin resistance, assessed by insulin and glucose tolerance tests, Ser(307) phosphorylation of insulin receptor substrate 1, and activation of protein kinase B, was examined in control and DIO wild-type (WT), Mc3rKO and Mc4rKO C57BL/6J mice. Mc4rKO mice were hyperphagic and had increased metabolic efficiency (weight gain per kilojoule consumed) relative to WT; both parameters increased further on high-fat diet. Obesity of Mc3rKO was more dependent on fat intake, involving increased metabolic efficiency. Fat mass of DIO Mc3rKO and Mc4rKO was similar, although Mc4rKO gained weight more rapidly. Mc4rKO develop hepatic insulin resistance and severe hepatic steatosis with obesity, independent of diet. DIO caused further deterioration of insulin action in Mc4rKO of either sex and, in male Mc3rKO, compared with controls, associated with increased fasting insulin, severe glucose intolerance, and reduced insulin signaling in muscle and adipose tissue. DIO female Mc3rKO exhibited very modest perturbations in glucose metabolism and insulin sensitivity. Consistent with previous data suggesting impaired fat oxidation, both Mc3rKO and Mc4rKO had reduced muscle oxidative metabolism, a risk factor for weight gain and insulin resistance. Energy expenditure was, however, increased in Mc4rKO compared with Mc3rKO and controls, perhaps due to hyperphagia and metabolic costs associated with rapid growth. In summary, DIO affects insulin sensitivity more severely in Mc4rKO compared with Mc3rKO, perhaps due to a more positive energy balance.
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PMID:Diet-genotype interactions in the development of the obese, insulin-resistant phenotype of C57BL/6J mice lacking melanocortin-3 or -4 receptors. 1646 8

Insulin has a major anabolic function leading to storage of lipidic and glucidic substrates. All its effects result from insulin binding to a specific membrane receptor which is expressed at a high level on the 3 insulin target tissues: liver, adipose tissue and muscles. The insulin receptor exhibits a tyrosine-kinase activity which leads, first, to receptor autophosphorylation and then to tyrosine phosphorylation of substrates proteins, IRS proteins in priority. This leads to the formation of macromolecular complexes close to the receptor. The two main transduction pathways are the phosphatidylinositol 3 kinase pathway activating protein kinase B which is involved in priority in metabolic effects, and the MAP kinase pathway involved in nuclear effects, proliferation and differentiation. However, in most cases, a specific effect of insulin requires the participation of the two pathways in a complex interplay which could explain the pleiotropy and the specificity of the insulin signal. The negative control of the insulin signal can result from hormone degradation or receptor dephosphorylation. However, the major negative control results from phosphorylation of serine/threonine residues on the receptor and/or IRS proteins. This phosphorylation is activated in response to different signals involved in insulin resistance, hyperinsulinism, TNFalpha or increased free fatty acids from adipose tissue, which are transformed inside the cell in acyl-CoA. A deleterious role for molecules issued from the adipose tissue is postulated in the resistance to insulin of the liver and muscles present in type 2 diabetes, obesity and metabolic syndrome.
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PMID:[Insulin signaling: mechanisms altered in insulin resistance]. 1659 3

Nonesterified fatty acids are acutely liberated during lipolysis and are chronically elevated in pathological conditions such as insulin resistance, hypertension, and obesity, which are known risk factors for atherosclerosis. The present study was designed to investigate the effects of oleic acid (OA), an 18-carbon cis-monosaturated fatty acid on proliferation of vascular smooth muscle cells (VSMC). Incubation of a rat VSMC (A10 cells) with OA (50 microM) resulted in an increase of cells entering the S phase of the cell cycle. In consistent with the effects on cell cycle distribution, OA stimulated VSMC proliferation in a dose-dependent manner. The mitogenic effect of OA was significantly reduced by pretreatment of LY294002 (5 microM) or wortmannin (1 microM), potent, and specific inhibitors of phosphatidylinositol 3-kinase (PI3K). OA also induced activation of Akt/protein kinase B (PKB) in a time-dependent manner. OA-induced activation of Akt/PKB was inhibited by either LY294002 or wortmannin. Taken together, these experiments show that the enhanced phosphorylation of Akt/PKB by OA is dependent on PI3K and suggest that this signaling event may be important for the regulation of OA-induced VSMC proliferation.
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PMID:Oleic acid enhances vascular smooth muscle cell proliferation via phosphatidylinositol 3-kinase/Akt signaling pathway. 1662 93

Epidemiologic studies show a positive association between obesity and cancer risk. In addition to increased body adiposity and secretion of fat-derived hormones, obesity is also linked to insulin resistance, type 2 diabetes, and chronic inflammation. We used the fatless A-ZIP/F-1 transgenic mouse to dissociate the relative role of each of these underlying factors in the development of cancer. These mice are unique in that they do not have white fat but do develop type 2 diabetes. In two cancer models, the classic two-stage skin carcinogenesis protocol and the C3(1)/T-Ag transgenic mouse mammary tumor model, A-ZIP/F-1 mice displayed higher tumor incidence, tumor multiplicity, and decreased tumor latency than wild-type mice. We examined circulating levels of adipokines, growth factors, and cytokines. As expected, adipokines (i.e., leptin, adiponectin, and resistin) were undetectable or found at very low levels in the blood of fatless mice. However, insulin, insulin-like growth factor-I, growth hormone, vascular endothelial growth factor, and proinflammatory Th2 cytokines, such as interleukin (IL)-1beta, IL-4, and IL-6, were elevated in A-ZIP/F-1 mice. Additionally, we examined multiple phosphorylated proteins (i.e., protein kinase B/Akt and ErbB2/HER-2 kinase) associated with cancer development. Results show that many of these phosphorylated proteins were activated specifically in the A-ZIP/F-1 skin but not in the wild-type skin. These findings suggest that adipokines are not required for the promotion of tumor development and thus contradict the epidemiologic data linking obesity to carcinogenesis. We postulate that insulin resistance and inflammation are responsible for the positive correlation with cancer observed in A-ZIP/F-1 mice.
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PMID:Accelerated tumor formation in a fatless mouse with type 2 diabetes and inflammation. 1670 76


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