Insulin and insulin-like growth factor 1 (IGF-1) act as antiapoptotic hormones. We found that, unexpectedly, double-knockout (DKO) cells that lacked both insulin and IGF-1 receptors (IR and IGF1R, respectively) were resistant to apoptosis induced through either the intrinsic or the extrinsic pathway. This resistance to apoptosis was associated with decreased abundance of the proapoptotic protein Bax and increases in abundance of the antiapoptotic proteins Bcl-2, Bcl-xL, XIAP, and Flip. These changes in protein abundance involved primarily posttranscriptional mechanisms. Restoration of IR or IGF1R to DKO cells also restored their sensitivity to apoptosis. Notably, expression of a catalytically inactive mutant form of the IR also restored susceptibility to apoptosis. Thus, IR and IGF1R have bidirectional roles in the control of cell survival and can be viewed as dependence receptors. Insulin and IGF-1 binding stimulates receptor tyrosine kinase activity and blocks apoptosis, whereas unliganded IR and IGF1R, acting through a mechanism independent of their catalytic activity, exert a permissive effect on cell death.

Type 2 diabetes is characterized by insulin resistance and pancreatic β cell dysfunction, the latter possibly caused by a defect in insulin signaling in β cells. Inhibition of class IA phosphatidylinositol 3-kinase (PI3K), using a mouse model lacking the pik3r1 gene specifically in β cells and the pik3r2 gene systemically (βDKO mouse), results in glucose intolerance and reduced insulin secretion in response to glucose. β cells of βDKO mice had defective exocytosis machinery due to decreased expression of soluble N-ethylmaleimide attachment protein receptor (SNARE) complex proteins and loss of cell-cell synchronization in terms of Ca(2+) influx. These defects were normalized by expression of a constitutively active form of Akt in the islets of βDKO mice, preserving insulin secretion in response to glucose. The class IA PI3K pathway in β cells in vivo is important in the regulation of insulin secretion and may be a therapeutic target for type 2 diabetes.

The brain is the most cholesterol-rich organ in the body, most of which comes from in situ synthesis. Here we demonstrate that in insulin-deficient diabetic mice, there is a reduction in expression of the major transcriptional regulator of cholesterol metabolism, SREBP-2, and its downstream genes in the hypothalamus and other areas of the brain, leading to a reduction in brain cholesterol synthesis and synaptosomal cholesterol content. These changes are due, at least in part, to direct effects of insulin to regulate these genes in neurons and glial cells and can be corrected by intracerebroventricular injections of insulin. Knockdown of SREBP-2 in cultured neurons causes a decrease in markers of synapse formation and reduction of SREBP-2 in the hypothalamus of mice using shRNA results in increased feeding and weight gain. Thus, insulin and diabetes can alter brain cholesterol metabolism, and this may play an important role in the neurologic and metabolic dysfunction observed in diabetes and other disease states.

Diabetic nephropathy (DN) is the leading cause of renal failure in the world. It is characterized by albuminuria and abnormal glomerular function and is considered a hyperglycemic "microvascular" complication of diabetes, implying a primary defect in the endothelium. However, we have previously shown that human podocytes have robust responses to insulin. To determine whether insulin signaling in podocytes affects glomerular function in vivo, we generated mice with specific deletion of the insulin receptor from their podocytes. These animals develop significant albuminuria together with histological features that recapitulate DN, but in a normoglycemic environment. Examination of "normal" insulin-responsive podocytes in vivo and in vitro demonstrates that insulin signals through the MAPK and PI3K pathways via the insulin receptor and directly remodels the actin cytoskeleton of this cell. Collectively, this work reveals the critical importance of podocyte insulin sensitivity for kidney function.

Obesity is associated with insulin resistance in metabolic tissues such as adipose, liver, and muscle, but it is unclear whether nonclassical target tissues, such as those of the reproductive axis, are also insulin resistant. To determine if the reproductive axis maintains insulin sensitivity in obesity in vivo, murine models of diet-induced obesity (DIO) with and without intact insulin signaling in pituitary gonadotrophs were created. Diet-induced obese wild-type female mice (WT DIO) were infertile and experienced a robust increase in luteinizing hormone (LH) after gonadotropin-releasing hormone (GnRH) or insulin stimulation. By contrast, both lean and obese mice with a pituitary-specific knockout of the insulin receptor (PitIRKO) exhibited reproductive competency, indicating that insulin signaling in the pituitary is required for the reproductive impairment seen in DIO and that the gonadotroph maintains insulin sensitivity in a setting of peripheral insulin resistance.

BACKGROUND/AIMS: CEL-MODY is a monogenic form of diabetes and exocrine pancreatic insufficiency due to mutations in the carboxyl-ester lipase (CEL) gene. We aimed to investigate endocrine and exocrine pancreatic function in CEL knockout mice (CELKO). METHODS: A knockout mouse model with global targeted deletion of CEL was investigated physiologically and histopathologically, and compared to littermate control CEL+/+ mice at 7 and 12 months on normal chow and high-fat diets (HFD), i.e. 42 and 60% fat by calories. RESULTS: CELKO+/+ and -/- mice showed normal growth and development and normal glucose metabolism on a chow diet. Female CEL-/- mice on 60% HFD, on the other hand, had increased random blood glucose compared to littermate controls (p = 0.02), and this was accompanied by a reduction in glucose tolerance that did not reach statistical significance. In these mice there was also islet hyperplasia, however, α- and β-islet cells appeared morphologically normal and pancreatic exocrine function was also normal. CONCLUSION: Although we observed mild glucose intolerance in female mice with whole-body knockout of CEL, the full phenotype of human CEL-MODY was not reproduced, suggesting that the pathogenic mechanisms involved are more complex than a simple loss of CEL function. and IAP.

OBJECTIVE: Type 2 diabetes and obesity are increasingly affecting human populations around the world. Our goal was to identify early molecular signatures predicting genetic risk to these metabolic diseases using two strains of mice that differ greatly in disease susceptibility. RESEARCH DESIGN AND METHODS: We integrated metabolic characterization, gene expression, protein-protein interaction networks, RT-PCR, and flow cytometry analyses of adipose, skeletal muscle, and liver tissue of diabetes-prone C57BL/6NTac (B6) mice and diabetes-resistant 129S6/SvEvTac (129) mice at 6 weeks and 6 months of age. RESULTS: At 6 weeks of age, B6 mice were metabolically indistinguishable from 129 mice, however, adipose tissue showed a consistent gene expression signature that differentiated between the strains. In particular, immune system gene networks and inflammatory biomarkers were upregulated in adipose tissue of B6 mice, despite a low normal fat mass. This was accompanied by increased T-cell and macrophage infiltration. The expression of the same networks and biomarkers, particularly those related to T-cells, further increased in adipose tissue of B6 mice, but only minimally in 129 mice, in response to weight gain promoted by age or high-fat diet, further exacerbating the differences between strains. CONCLUSIONS: Insulin resistance in mice with differential susceptibility to diabetes and metabolic syndrome is preceded by differences in the inflammatory response of adipose tissue. This phenomenon may serve as an early indicator of disease and contribute to disease susceptibility and progression.

Pubertal onset, initiated by pulsatile gonadotropin-releasing hormone (GnRH), only occurs in a favorable, anabolic hormonal milieu. Anabolic factors that may signal nutritional status to the hypothalamus include the growth factors insulin and IGF-1. It is unclear which hypothalamic neuronal subpopulation these factors affect to ultimately regulate GnRH neuron function in puberty and reproduction. We examined the direct role of the GnRH neuron in growth factor regulation of reproduction using the Cre/lox system. Mice with the IR or IGF-1R deleted specifically in GnRH neurons were generated. Male and female mice with the IR deleted in GnRH neurons displayed normal pubertal timing and fertility, but male and female mice with the IGF-1R deleted in GnRH neurons experienced delayed pubertal development with normal fertility. With IGF-1 administration, puberty was advanced in control females, but not in females with the IGF-1R deleted in GnRH neurons, in control males, or in knockout males. These mice exhibited developmental differences in GnRH neuronal morphology but normal number and distribution of neurons. These studies define the role of IGF-1R signaling in the coordination of somatic development with reproductive maturation and provide insight into the mechanisms regulating pubertal timing in anabolic states.

Phosphoinositide 3-kinase (PI3K) plays a critical role in tumorigenesis, and the PI3K p85 regulatory subunit exerts both positive and negative effects on signaling. Expression of Pik3r1, the gene encoding p85, is decreased in human prostate, lung, ovarian, bladder, and liver cancers, consistent with the possibility that p85 has tumor suppressor properties. We tested this hypothesis by studying mice with a liver-specific deletion of the Pik3r1 gene. These mice exhibited enhanced insulin and growth factor signaling and progressive changes in hepatic pathology, leading to the development of aggressive hepatocellular carcinomas with pulmonary metastases. Liver tumors that arose exhibited markedly elevated levels of phosphatidylinositol (3,4,5)-trisphosphate, along with Akt activation and decreased PTEN expression, at both the mRNA and protein levels. Together, these results substantiate the concept that the p85 subunit of PI3K has a tumor-suppressive role in the liver and possibly other tissues.

Obesity develops when energy intake exceeds energy expenditure. Although most current obesity therapies are focused on reducing calorific intake, recent data suggest that increasing cellular energy expenditure (bioenergetics) may be an attractive alternative approach. This is especially true for adaptive thermogenesis - the physiological process whereby energy is dissipated in mitochondria of brown fat and skeletal muscle in the form of heat in response to external stimuli. There have been significant recent advances in identifying the factors that control the development and function of these tissues, and in techniques to measure brown fat in human adults. In this article, we integrate these developments in relation to the classical understandings of cellular bioenergetics to explore the potential for developing novel anti-obesity therapies that target cellular energy expenditure.