Cardiovascular disease is the leading cause of death in people with type 2 diabetes and is linked to insulin resistance even in the absence of diabetes. Here we show that mice with combined deficiency of the insulin receptor and insulin-like growth factor 1 (IGF-1) receptor in cardiac and skeletal muscle develop early-onset dilated cardiomyopathy and die from heart failure within the first month of life despite having a normal glucose homeostasis. Mice lacking the insulin receptor show impaired cardiac performance at 6 months, and mice lacking the insulin receptor plus one Igf1r allele have slightly increased mortality. By contrast, mice lacking the IGF-1 receptor or the IGF-1 receptor plus one Ir allele appear normal. Morphological characterization and oligonucleotide array analysis of gene expression demonstrate that prior to development of these physiological defects, mice with combined deficiency of both insulin and IGF-1 receptors have a coordinated down-regulation of genes encoding components of the electron transport chain and mitochondrial fatty acid beta-oxidation pathways and altered expression of contractile proteins. Thus, while neither the insulin receptor nor IGF-1 receptor in muscle is critical for glucose homeostasis during the first month of life, signaling from these receptors, particularly the insulin receptor, is required for normal cardiac metabolism and function.

Diabetes mellitus is a complex metabolic disorder accompanied by alterations in cellular physiology, metabolism, and gene expression. These alterations can be primary (due to loss of direct insulin action) or secondary (due to the metabolic perturbations associated with the disease). To dissect and quantitate these two separate effects, we compared the skeletal muscle gene-expression profiles of muscle insulin receptor knockout (MIRKO) mice and their Lox controls in the basal, streptozotocin-induced diabetic, and insulin-treated diabetic states. Pure deficiency of insulin action as present in the MIRKO mouse results in regulation of 130 genes, with down-regulation of NSF (N-ethylmaleimide-sensitive fusion protein) and VAMP-2 (vesicle-associated membrane protein 2), stearoyl CoA desaturase 1, and cAMP-specific phosphodiesterase 4B, as well as up-regulation of some signaling-related genes, such as Akt2, and the fatty-acid transporter CD36. In diabetes, additional transcriptional mechanisms are activated, resulting in alterations in expression of approximately 500 genes, including a highly coordinated down-regulation of genes of the mitochondrial electron-transport chain and one of the mammalian homologues of the histone deacetylase Sir2, which has been implicated in the link between nutrition and longevity. These distinct pathways of direct and indirect regulation of gene expression provide insights into the complex mechanisms of transcriptional control in diabetes and areas of potential therapeutic targeting.

Mice with a fat-specific insulin receptor knock-out (FIRKO) exhibit a polarization of white adipose tissue into two populations of cells, one small (diameter <50 m) and one large (diameter >100 m), accompanied by changes in insulin-stimulated glucose uptake, triglyceride synthesis, and lipolysis. To characterize these subclasses of adipocytes, we have used a proteomics approach in which isolated adipocytes from FIRKO and control (IR lox/lox) mice were separated by size, fractionated into cytosolic and membrane subfractions, and analyzed by sucrose gradient, SDS-PAGE, and mass spectrometry. A total of 27 alterations in protein expression at key steps in lipid and energy metabolism could be defined, which were coordinately regulated by adipocyte cell size, impaired insulin signaling, or both. Nine proteins, including vimentin, EH-domain-containing protein 2, elongation factor 2, glucose-regulated protein 78, transketolase, and succinyl-CoA transferase were primarily affected by presence or absence of insulin signaling, whereas 21 proteins, including myosin non-muscle form A, annexin 2, annexin A6, and Hsp47 were regulated in relation to adipocyte size. Of these 27 alterations in protein expression, 14 changes correlated with altered levels of mRNA, whereas the remaining 13 were the result of changes in protein translation or turnover. These data suggest an intrinsic heterogeneity in adipocytes with differences in protein expression patterns caused by transcriptional and post-transcriptional alterations related to insulin action and cellular lipid accumulation.Adipose tissue plays a central role in the pathogenesis of diabetes and obesity. White adipose tissue provides the primary site of energy storage in the body and also serves as an important endocrine cell through secretion of hormones such as leptin, adiponectin (ACRP30), tumor necrosis factor ␣, resistin, and other cytokines (1). Brown adipose tissue is the major site of energy expenditure through expression of uncoupling protein 1 and its role in thermogenesis (2).Insulin signaling plays an important role in lipid storage and the process of adipogenesis for both white and brown adipocytes. The loss of insulin action selectively in adipose tissue in mice with a fat-specific insulin receptor knock-out (FIRKO) 1 leads to profound changes in adipocyte function, including changes in glucose metabolism, lipid metabolism, and protein expression (3). FIRKO mice have reduced fat mass and are protected against age-and diet-related obesity and its associated metabolic abnormalities, including glucose intolerance. In addition, these mice have increased longevity, despite normal or increased food intake (4). Adipose tissue-specific insulin receptor knock-out in FIRKO mice also causes heterogeneity of white adipose tissue with polarization into small (diameter Ͻ50 m) and large (diameter Ͼ150 m) subclasses of adipocytes (3). Western blot analysis of candidate molecules reveals changes in the expression of several key adipocyte proteins, such as ACRP30, fatty acid synthase...