Insulin and insulin-like growth factor 1 (IGF1) are ubiquitous growth factors that regulate proliferation in most mammalian tissues including pancreatic islets. To explore the specificity of insulin receptors in compensatory ␤-cell growth, we examined two models of insulin resistance. In the first model, we used liverspecific insulin receptor knockout (LIRKO) mice, which exhibit hyperinsulinemia without developing diabetes due to a compensatory increase in ␤-cell mass. LIRKO mice, also lacking functional insulin receptors in ␤-cells (␤IRKO/LIRKO), exhibited severe glucose intolerance but failed to develop compensatory islet hyperplasia, together leading to early death. In the second model, we examined the relative significance of insulin versus IGF1 receptors in islet growth by feeding high-fat diets to ␤IRKO and ␤-cell-specific IGF1 receptor knockout (␤IGFRKO) mice. Although both groups on the high-fat diet developed insulin resistance, ␤IRKO, but not ␤IG-FRKO, mice exhibited poor islet growth consistent with insulinstimulated phosphorylation, nuclear exclusion of FoxO1, and reduced expression of Pdx-1. Together these data provide direct genetic evidence that insulin/FoxO1/Pdx-1 signaling is one pathway that is crucial for islet compensatory growth response to insulin resistance.␤-cell growth ͉ compensatory hyperplasia ͉ ␤-cell apoptosis I nsulin resistance is a common feature of type 2 diabetes, obesity, and hyperlipidemias (1). In patients with type 2 diabetes and mouse models of diabetes and obesity, the ␤-cells compensate for the insulin resistance by increasing their mass (2, 3). One of these models, the liver-specific insulin receptor knockout (LIRKO) mouse, manifests severe insulin resistance and glucose intolerance, but the mutants do not become overtly diabetic due, in part, to a significant increase in ␤-cell mass (4). Although lineage tracing experiments in normal mice and studies in cyclin D2 knockouts indicate that ␤-cell replication is a major mechanism for regeneration of adult ␤-cells (5, 42), the signals that induce ␤-cell replication are not fully defined.Insulin and IGFI and the proteins in their signaling pathways regulate cell growth and function (6), but their specificity in modulating ␤-cell proliferation is not fully explored. Thus, ␤-cellspecific insulin receptor (␤IRKO) (7), IGF1 receptor knockout (␤IGFRKO) (8, 9), or double mutants (10) surprisingly exhibited normal growth and development of ␤-cells consistent with data from global knockouts of insulin receptor or IGF1 receptor genes (11). Mice with global knockout of IRS1 (12, 13) or IRS2 genes (12, 14) also do not manifest defects in the development of islet cells, whereas overexpression of Akt in ␤-cells promotes an increase in cell size (15). Together these studies indicate that insulin/IGF1 signaling is not critical for early development and growth of ␤-cells.Our follow-up studies showed that ␤IRKO, but not ␤IGFRKO, mice developed an age-dependent decrease in ␤-cell mass and a susceptibility to develop overt diabetes (7,16,17). F...

In record time, microRNAs (miRNAs) have acquired the respected stature of important natural regulators of global gene expression. Multiple studies have demonstrated that a large number of miRNAs are under the control of various metabolic stimuli, including nutrients, hormones, and cytokines. Conversely, it is now well recognized that miRNAs control metabolism, thereby generating a bidirectional functional link, which perturbs energy homeostasis in case of disconnection in the miRNA-metabolism interplay. A challenging road lies ahead for defining the role of miRNAs in the pathogenesis of diseases such as diabetes and for establishing their usefulness as new medications and clinically reliable biomarkers.

Summary Although infections with virulent pathogens often induce a strong inflammatory reaction, what drives the increased immune response to pathogens compared to non-pathogenic microbes is poorly understood. One possibility is that the immune system senses the level of threat from a microorganism and augments the response accordingly. Here, focussing on cytotoxic necrotizing factor 1 (CNF1), an Escherichia coli-derived effector molecule, we showed the host indirectly sensed the pathogen by monitoring for the effector that modified RhoGTPases. CNF1 modified Rac2, which then interacted with the innate immune adaptors IMD and Rip1-Rip2 in flies and mammalian cells, respectively to drive an immune response. This response was protective and increased the ability of the host to restrict pathogen growth, thus defining a mechanism of effector-triggered immunity that contributes to how metazoans defend against microbes with pathogenic potential.

Amino acids are nutrients responsible for mammalian target of rapamycin (mTOR) regulation in mammalian cells. The mTOR protein is mainly known for its role in regulating cell growth, notably via protein synthesis. In addition to amino acids, mTOR is regulated by insulin via a phosphatidylinositol 3-kinase (PI 3-kinase)-dependent pathway. mTOR mediates crosstalk between amino acids and insulin signaling. We show that in freshly isolated rat adipocytes, insulin stimulates the phosphorylation of mTOR on serine 2448, a protein kinase B (PKB) consensus phosphorylation site. This site is also phosphorylated by amino acids, which in contrast to insulin do not activate PKB. Moreover, insulin and amino acids have an additive effect on mTOR phosphorylation, indicating that they act via two independent pathways. Importantly, amino acids, notably leucine, permit insulin to stimulate PKB when PI 3-kinase is inhibited. They also rescue glucose transport and the mTOR pathway. Further, leucine alone can improve insulin activation of PKB in db/db mice. Our results define the importance of amino acids in insulin signaling and reveal leucine as a key amino acid in disease situations associated with insulin-resistance in adipocytes.

No abstract

OBJECTIVEA major determinant of the progression from insulin resistance to the development of overt type 2 diabetes is a failure to mount an appropriate compensatory β-cell hyperplastic response to maintain normoglycemia. We undertook the present study to directly explore the significance of the cell cycle protein cyclin D2 in the expansion of β-cell mass in two different models of insulin resistance.RESEARCH DESIGN AND METHODSWe created compound knockouts by crossing mice deficient in cyclin D2 (D2KO) with either the insulin receptor substrate 1 knockout (IRS1KO) mice or the insulin receptor liver-specific knockout mice (LIRKO), neither of which develops overt diabetes on its own because of robust compensatory β-cell hyperplasia. We phenotyped the double knockouts and used RT-qPCR and immunohistochemistry to examine β-cell mass.RESULTSBoth compound knockouts, D2KO/LIRKO and D2KO/IRS1KO, exhibited insulin resistance and hyperinsulinemia and an absence of compensatory β-cell hyperplasia. However, the diabetic D2KO/LIRKO group rapidly succumbed early compared with a relatively normal lifespan in the glucose-intolerant D2KO/IRS1KO mice.CONCLUSIONSThis study provides direct genetic evidence that cyclin D2 is essential for the expansion of β-cell mass in response to a spectrum of insulin resistance and points to the cell-cycle protein as a potential therapeutic target that can be harnessed for preventing and curing type 2 diabetes.

The intrauterine environment of the fetus is a preeminent actor in long-term health. Indeed, mounting evidence shows that maternal malnutrition increases the risk of type 2 diabetes (T2D) in progeny. Although the consequences of a disturbed prenatal environment on the development of the pancreas are known, the underlying mechanisms are poorly defined. In rats, restriction of protein during gestation alters the development of the endocrine pancreas and favors the occurrence of T2D later in life. Here we evaluate the potential role of perturbed microRNA (miRNA) expression in the decreased b-cell mass and insulin secretion characterizing progeny of pregnant dams fed a low-protein (LP) diet. miRNA profiling shows increased expression of several miRNAs, including miR-375, in the pancreas of fetuses of mothers fed an LP diet. The expression of miR-375 remains augmented in neoformed islets derived from fetuses and in islets from adult (3-month-old) progeny of mothers fed an LP diet. miR-375 regulates the proliferation and insulin secretion of dissociated islet cells, contributing to the reduced b-cell mass and function of progeny of mothers fed an LP diet. Remarkably, miR-375 normalization in LP-derived islet cells restores b-cell proliferation and insulin secretion. Our findings suggest the existence of a developmental memory in islets that registers intrauterine protein restriction. Hence, pancreatic failure after in utero malnutrition could result from transgenerational transmission of miRNA misexpression in b-cells.

The pancreatic islets of Langerhans, and especially the insulin-producing beta cells, play a central role in the maintenance of glucose homeostasis. Alterations in the expression of multiple proteins in the islets that contribute to the maintenance of islet function are likely to underlie the pathogenesis of types 1 and 2 diabetes. To identify proteins that constitute the islet proteome, we provide the first comprehensive proteomic characterization of pancreatic islets for mouse, the most commonly used animal model in diabetes research. Using strong cation exchange fractionation coupled with reversed phase LC-MS/MS we report the confident identification of 17,350 different tryptic peptides covering 2612 proteins having at least two unique peptides per protein. The data set also identified approximately 60 post-translationally modified peptides including oxidative modifications and phosphorylation. While many of the identified phosphorylation sites corroborate those previously known, the oxidative modifications observed on cysteinyl residues reveal potentially novel information suggesting a role for oxidative stress in islet function. Comparative analysis with 15 available proteomic data sets from other mouse tissues and cells revealed a set of 133 proteins predominantly expressed in pancreatic islets. This unique set of proteins, in addition to those with known functions such as peptide hormones secreted from the islets, contains several proteins with as yet unknown functions. The mouse islet protein and peptide database accessible at (http://ncrr.pnl.gov), provides an important reference resource for the research community to facilitate research in the diabetes and metabolism fields.