Hypoglycemia, hypoglycemia unawareness, and impaired counterregulation are major challenges to the intensive management of type 1 diabetes. While the counterregulatory response to hypoglycemia is predominantly determined by the degree and duration of hypoglycemia, there is now evidence that insulin per se may influence the counterregulatory response to hypoglycemia. To define the role of insulin action in the central nervous system in regulating the counterregulatory response to hypoglycemia, mice with a brain/neuron-specific insulin receptor knockout (NIRKO) and littermate controls were subjected to 90-min hyperinsulinemic (20 mU x kg(-1) x min(-1)) -hypoglycemic (approximately 1.5 mmol/l) clamps. In response to hypoglycemia, epinephrine levels rose 5.7-fold in controls but only 3.5-fold in NIRKO mice. Similarly, in response to hypoglycemia, norepinephrine levels rose threefold in controls, but this response was almost completely absent in NIRKO mice. In contrast, glucagon and corticosterone responses to hypoglycemia were similar in both groups. Thus, insulin action in the brain is critical for full activation of the sympathoadrenal response to hypoglycemia, and altered neural insulin signaling could contribute to defective glucose counterregulation in diabetes.

Intestinal glucagon-like peptide-1 (GLP-1) is a hormone released into the hepatoportal circulation that stimulates pancreatic insulin secretion. GLP-1 also acts as a neuropeptide to control food intake and cardiovascular functions, but its neural role in glucose homeostasis is unknown. We show that brain GLP-1 controlled whole-body glucose fate during hyperglycemic conditions. In mice undergoing a hyperglycemic hyperinsulinemic clamp, icv administration of the specific GLP-1 receptor antagonist exendin 9-39 (Ex9) increased muscle glucose utilization and glycogen content. This effect did not require muscle insulin action, as it also occurred in muscle insulin receptor KO mice. Conversely, icv infusion of the GLP-1 receptor agonist exendin 4 (Ex4) reduced insulin-stimulated muscle glucose utilization. In hyperglycemia achieved by i.v. infusion of glucose, icv Ex4, but not Ex9, caused a 4-fold increase in insulin secretion and enhanced liver glycogen storage. However, when glucose was infused intragastrically, icv Ex9 infusion lowered insulin secretion and hepatic glycogen levels, whereas no effects of icv Ex4 were observed. In diabetic mice fed a high-fat diet, a 1-month chronic i.p. Ex9 treatment improved glucose tolerance and fasting glycemia. Our data show that during hyperglycemia, brain GLP-1 inhibited muscle glucose utilization and increased insulin secretion to favor hepatic glycogen stores, preparing efficiently for the next fasting state.

Both environmental and genetic factors play important roles in the development of the metabolic syndrome. To elucidate how these factors interact under normal conditions, C57Bl/6 (B6) and 129S6/SvEvTac (129) mice were placed on a low-fat or high-fat diet. Over 18 weeks, the 129 strain developed features of the metabolic syndrome, notably obesity, hyperinsulinemia, and glucose intolerance only on the high-fat diet; the B6 strain on the other hand developed these features on both diets. High-fat feeding of both strains led to decreased serum triglycerides, hepatic steatosis, and hypercholesterolemia; however, B6 mice developed worse steatosis and a larger increase in LDL cholesterol. Both B6 background and high-fat feeding increased sterol regulatory element-binding protein-1c (SREBP-1c), a key regulator of lipogenic gene transcription, and its downstream targets. Stearoyl-CoA desaturase 1 (SCD1), an enzyme that regulates monounsaturated fatty acid (MUFA) synthesis, was also increased at the mRNA and enzyme activity levels by both high-fat feeding and B6 background. Furthermore, lipid analysis revealed increased hepatic triglycerides and MUFAs in B6 and high-fat-fed mice. Thus, dietary fat and genetic background act through SREBP-1c and SCD1 to affect hepatic lipid metabolism contributing to the development of the metabolic syndrome.

Mice with muscle-specific knockout of the Glut4 glucose transporter (muscle-G4KO) are insulin resistant and mildly diabetic. Here we show that despite markedly reduced glucose transport in muscle, muscle glycogen content in the fasted state is increased. We sought to determine the mechanism(s). Basal glycogen synthase activity is increased by 34% and glycogen phosphorylase activity is decreased by 17% (P

There are many theories of aging and parameters that influence lifespan, including genetic instability, telomerase activity and oxidative stress. The role of caloric restriction, metabolism and insulin and insulin-like growth factor-1 signaling in the process of aging is especially well conserved throughout evolution. These latter factors interact with each other, the former factors and histone deacetylases of the SIR family in a complex interaction to influence lifespan.

Insulin resistance, obesity, diabetes, dyslipidemia and nonalcoholic fatty liver are components of the metabolic syndrome, a disease complex that is increasing at epidemic rates in westernized countries. Although proinflammatory cytokines have been suggested to contribute to the development of these disorders, the molecular mechanism of the development of this syndrome is poorly understood. In this study, we show that expression of suppressor of cytokine signaling SOCS-1 and SOCS-3 is increased in livers of obese insulin-resistant animals, and that adenoviral-mediated overexpression of SOCS-1 or SOCS-3 in liver causes insulin resistance through down-regulation of tyrosine phosphorylation of insulin receptor substrate (IRS) proteins. Moreover, the increased SOCS-1 and SOCS-3 also cause a prominent up-regulation of the key regulator of fatty acid synthesis in liver, sterol regulatory element binding protein (SREBP)-1. Conversely, inhibition of SOCS-1 and SOCS-3 in livers of obese diabetic db/db mice by antisense treatment modestly improves insulin sensitivity, but completely normalizes the increased expression of SREBP-1. The latter leads to dramatic amelioration of hepatic steatosis and hypertriglyceridemia. Promoter activity analysis reveals that expression of SOCS-1 or SOCS-3 with SOCS-3 being more potent enhances SREBP-1c expression, while it is inhibited by expression of STAT3. This STAT3-mediated inhibition of SREBP-1c expression is antagonized by co-expression of SOCS proteins. Moreover, db/db mice display decreased STAT3 phosphorylation in liver that is normalized by antisense treatment of SOCS proteins. These data suggest that obese subjects in the persistent inflammatory states, such as elevated circulating tumor necrosis factor-alpha, may have down-regulated STAT3-mediated signaling by increased SOCS proteins, leading to up-regulation of SREBP-1c expression and increased fatty acid synthesis in liver. Thus, SOCS proteins play an important role in pathogenesis of the metabolic syndrome by concordantly modulating cytokine signaling and insulin signaling.

BACKGROUND: Rad (Ras associated with diabetes) GTPase is a prototypic member of a new subfamily of Ras-related GTPases with unique structural features, although its physiological role remains largely unknown. In the present study, we characterized the Rad function in vascular smooth muscle cells (VSMCs) and the influence of adenovirus-mediated Rad (Ad-Rad) gene delivery on vascular remodeling after experimental angioplasty. METHODS AND RESULTS: We documented for the first time that neointimal formation using balloon-injured rat carotid arteries was associated with a significant increase in Rad expression as determined by immunohistochemistry and quantitative real-time reverse-transcriptase polymerase chain reaction. The levels of Rad expression in VSMCs were highly induced by platelet-derived growth factor and tumor necrosis factor-alpha. Morphometric analyses 14 days after injury revealed significantly diminished neointimal formation in the Ad-Rad-treated carotid arteries compared with Ad-GFP or PBS controls, whereas the mutated form of Rad GTPase, which can bind GDP but not GTP, increased neointimal formation. Overexpression of Rad significantly inhibited the attachment and migration of VSMCs. In addition, Rad expression dramatically reduced the formation of focal contacts and stress fibers in VSMCs by blocking the Rho/ROK signaling pathway. CONCLUSIONS: Our data clearly identified Rad GTPase as a novel and critical mediator that inhibits vascular lesion formation. Manipulation of the Rad signaling pathway may provide new therapeutic approaches that will limit vascular pathological remodeling.

Insulin resistance is a cardinal feature of normal pregnancy and excess growth hormone (GH) states, but its underlying mechanism remains enigmatic. We previously found a significant increase in the p85 regulatory subunit of phosphatidylinositol kinase (PI 3-kinase) and striking decrease in IRS-1-associated PI 3-kinase activity in the skeletal muscle of transgenic animals overexpressing human placental growth hormone. Herein, using transgenic mice bearing deletions in p85alpha, p85beta, or insulin-like growth factor-1, we provide novel evidence suggesting that overexpression of p85alpha is a primary mechanism for skeletal muscle insulin resistance in response to GH. We found that the excess in total p85 was entirely accounted for by an increase in the free p85alpha-specific isoform. In mice with a liver-specific deletion in insulin-like growth factor-1, excess GH caused insulin resistance and an increase in skeletal muscle p85alpha, which was completely reversible using a GH-releasing hormone antagonist. To understand the role of p85alpha in GH-induced insulin resistance, we used mice bearing deletions of the genes coding for p85alpha or p85beta, respectively (p85alpha (+/-) and p85beta(-/-)). Wild type and p85beta(-/-) mice developed in vivo insulin resistance and demonstrated overexpression of p85alpha and reduced insulin-stimulated PI 3-kinase activity in skeletal muscle in response to GH. In contrast, p85alpha(+/-)mice retained global insulin sensitivity and PI 3-kinase activity associated with reduced p85alpha expression. These findings demonstrated the importance of increased p85alpha in mediating skeletal muscle insulin resistance in response to GH and suggested a potential role for reducing p85alpha as a therapeutic strategy for enhancing insulin sensitivity in skeletal muscle.

Pten (phosphatase with tensin homology), a dual-specificity phosphatase, is a negative regulator of the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway. Pten regulates a vast array of biological functions including growth, metabolism, and longevity. Although the PI3K/Akt pathway is a key determinant of the insulin-dependent increase in glucose uptake into muscle and adipose cells, the contribution of this pathway in muscle to whole-body glucose homeostasis is unclear. Here we show that muscle-specific deletion of Pten protected mice from insulin resistance and diabetes caused by high-fat feeding. Deletion of muscle Pten resulted in enhanced insulin-stimulated 2-deoxyglucose uptake and Akt phosphorylation in soleus but, surprisingly, not in extensor digitorum longus muscle compared to littermate controls upon high-fat feeding, and these mice were spared from developing hyperinsulinemia and islet hyperplasia. Muscle Pten may be a potential target for treatment or prevention of insulin resistance and diabetes.

A defect in Klotho gene expression in mice accelerates the degeneration of multiple age-sensitive traits. Here, we show that overexpression of Klotho in mice extends life span. Klotho protein functions as a circulating hormone that binds to a cell-surface receptor and represses intracellular signals of insulin and insulin-like growth factor 1 (IGF1), an evolutionarily conserved mechanism for extending life span. Alleviation of aging-like phenotypes in Klotho-deficient mice was observed by perturbing insulin and IGF1 signaling, suggesting that Klotho-mediated inhibition of insulin and IGF1 signaling contributes to its anti-aging properties. Klotho protein may function as an anti-aging hormone in mammals.