4PS/insulin receptor substrate (IRS)-2 is the alternative substrate of the insulin receptor in IRS-1-deficient mice

Deletion of IRS-1 leads to growth failure and insulin resistance with downregulation of liver and muscle insulin signaling in rats

Insulin receptor substrate (IRS)-1 and IRS-2 are major molecules that transduce signals from insulin and insulin-like growth factor-I receptors. The physiological functions of these proteins have been intensively investigated in mice, while little is known in other animals. Our previous study showed that the disruption of IRS-2 impairs body growth but not glucose tolerance or insulin sensitivity in rats, which led us to hypothesize that IRS-1 plays more pivotal roles in insulin functions than IRS-2. Here, we created IRS-1 knockout (KO) rats to elucidate the physiological roles of IRS-1 in rats. The body weight of IRS-1 KO rats at birth was lower than that of wild-type (WT) littermates, and postnatal growth of IRS-1 KO rats was severely impaired. Compared with WT rats, IRS-1 KO rats displayed insulin resistance but maintained euglycemia because of compensatory hyperinsulinemia. In addition, despite the increased activity of insulin-stimulated IRS-2-associated phosphatidylinositol-3 kinase (PI3K), insulin-induced phosphorylation of the kinases downstream of PI3K was suppressed in the liver and skeletal muscle of IRS-1 KO rats. Taken together, these results indicate that in rats, IRS-1 is essential for normal growth and the glucose-lowering effects of insulin. IRS-1 appears to be more important than IRS-2 for insulin functions in rats.

Phosphorylation Codes in IRS-1 and IRS-2 Are Associated with the Activation/Inhibition of Insulin Canonical Signaling Pathways

Insulin receptor substrates 1 and 2 (IRS-1 and IRS-2) are signaling adaptor proteins that participate in canonical pathways, where insulin cascade activation occurs, as well as in non-canonical pathways, in which phosphorylation of substrates is carried out by a diverse array of receptors including integrins, cytokines, steroid hormones, and others. IRS proteins are subject to a spectrum of post-translational modifications essential for their activation, encompassing phosphorylation events in distinct tyrosine, serine, and threonine residues. Tyrosine residue phosphorylation is intricately linked to the activation of the insulin receptor cascade and its interaction with SH2 domains within a spectrum of proteins, including PI3K. Conversely, serine residue phosphorylation assumes a different function, serving to attenuate the effects of insulin. In this review, we have identified over 50 serine residues within IRS-1 that have been reported to undergo phosphorylation orchestrated by a spectrum of kinases, thereby engendering the activation or inhibition of different signaling pathways. Furthermore, we delineate the phosphorylation of over 10 distinct tyrosine residues at IRS-1 or IRS-2 in response to insulin, a process essential for signal transduction and the subsequent activation of PI3K.

The strategic involvement of IRS in cancer progression

Insulin Receptor Substrate (IRS), an intracellular molecule devoid of an intrinsic kinase activity, is activated upon binding to IR which thereby works as a scaffold, organizing all signaling complexes and initiating the signaling process downstream. The level of IRS proteins and their stability in the cell is mostly maintained through the phosphorylation status of their tyrosine and serine residues. IRS is positively regulated by phosphorylation of its Tyr residues whereas a Ser residue phosphorylation attenuates it, although there exist some exceptions as well. Other post-translational modifications like O-linked glycosylation, N-linked glycosylation and acetylation also play a prominent role in IRS regulation. Since the discovery of the Warburg effect, people have been curious to find out all possible signaling networks and molecules that could lead to cancer and no doubt, the insulin signaling pathway is identified as one such pathway, which is highly deregulated in cancers. Eminent studies reveal that IRS is a pertinent regulator of cancer and is highly overexpressed in the five most commonly occurring cancers namely- Prostate, Ovarian, Breast, Colon and Lung cancers. IRS1 and IRS2 family members are actively involved in the progression, invasion and metastasis of these cancers. Recently, less studied IRS4 has also emerged as a contributor in ovarian, breast, colorectal and lung cancer, but no such studies related to IRS4 are found in Prostate cancer. The involvement of other IRS family members in cancer is still undiscovered and so paves the way for further exploration. This review is a time-lapse study of IRSs in the context of cancer done over the past two decades and it highlights all the major discoveries made till date, in these cancers from the perspective of IRS.

Insulin Regulation of Hepatic Lipid Homeostasis

The incidence of obesity, insulin resistance, and type II diabetes (T2DM) continues to rise worldwide. The liver is a central insulin-responsive metabolic organ that governs whole-body metabolic homeostasis. Therefore, defining the mechanisms underlying insulin action in the liver is essential to our understanding of the pathogenesis of insulin resistance. During periods of fasting, the liver catabolizes fatty acids and stored glycogen to meet the metabolic demands of the body. In postprandial conditions, insulin signals to the liver to store excess nutrients into triglycerides, cholesterol, and glycogen. In insulin-resistant states, such as T2DM, hepatic insulin signaling continues to promote lipid synthesis but fails to suppress glucose production, leading to hypertriglyceridemia and hyperglycemia. Insulin resistance is associated with the development of metabolic disorders such as cardiovascular and kidney disease, atherosclerosis, stroke, and cancer. Of note, nonalcoholic fatty liver disease (NAFLD), a spectrum of diseases encompassing fatty liver, inflammation, fibrosis, and cirrhosis, is linked to abnormalities in insulin-mediated lipid metabolism. Therefore, understanding the role of insulin signaling under normal and pathologic states may provide insights into preventative and therapeutic opportunities for the treatment of metabolic diseases. Here, we provide a review of the field of hepatic insulin signaling and lipid regulation, including providing historical context, detailed molecular mechanisms, and address gaps in our understanding of hepatic lipid regulation and the derangements under insulin-resistant conditions. © 2023 American Physiological Society. Compr Physiol 13:4785-4809, 2023.

Aging modulated by the Drosophila insulin receptor through distinct structure-defined mechanisms

Mutations of the Drosophila melanogaster insulin/IGF signaling system slow aging, while also affecting growth and reproduction. To understand this pleiotropy, we produced an allelic series of single codon substitutions in the Drosophila insulin receptor, InR. We generated InR substitutions using homologous recombination and related each to emerging models of receptor tyrosine kinase structure and function. Three mutations when combined as trans-heterozygotes extended lifespan while retarding growth and fecundity. These genotypes reduced insulin-stimulated Akt phosphorylation, suggesting they impede kinase catalytic domain function. Among these genotypes, longevity was negatively correlated with egg production, consistent with life-history trade-off theory. In contrast, one mutation (InR353) was located in the kinase insert domain, a poorly characterized element found in all receptor tyrosine kinases. Remarkably, wild-type heterozygotes with InR353 robustly extended lifespan without affecting growth or reproduction and retained capacity to fully phosphorylate Akt. The Drosophila insulin receptor kinase insert domain contains a previously unrecognized SH2 binding motif. We propose the kinase insert domain interacts with SH2-associated adapter proteins to affect aging through mechanisms that retain insulin sensitivity and are independent of reproduction.

MiR-7-5p inhibits thyroid cell proliferation by targeting the EGFR/MAPK and IRS2/PI3K signaling pathways

The aberrant expression of miRNAs is often correlated to tumor development. MiR-7-5p is a recently discovered downregulated miRNA in thyroid papillary carcinoma (PTC). The goal of this project was to characterize its functional role in thyroid tumorigenesis and to identify the targeted modulated pathways. MiR-7-5p overexpression following transfection in TPC1 and HT-ori3 cells decreased proliferation of the two thyroid cell lines. Analysis of global transcriptome modifications showed that miR-7-5p inhibits thyroid cell proliferation by modulating the MAPK and PI3K signaling pathways which are both necessary for normal thyroid proliferation and play central roles in PTC tumorigenesis. Several effectors of these pathways are indeed targets of miR-7-5p, among which EGFR and IRS2, two upstream activators. We confirmed the upregulation of IRS2 and EGFR in human PTC and showed the existence of a negative correlation between the decreased expression of miR-7-5p and the increased expression of IRS2 or EGFR. Our results thus support a tumor-suppressor activity of miR-7-5p. The decreased expression of miR-7-5p during PTC tumorigenesis might give the cells a proliferative advantage and delivery of miR-7-5p may represent an innovative approach for therapy.

New Regions With Molecular Alterations in a Rare Case of Insulinomatosis: Case Report With Literature Review

Insulinomatosis is characterized by monohormonality of multiple macro-tumors and micro-tumors that arise synchronously and metachronously in all regions of the pancreas, and often recurring hypoglycemia. One of the main characteristics of insulinomatosis is the presence of insulin-expressing monohormonal endocrine cell clusters that are exclusively composed of proliferating insulin-positive cells, are less than 1 mm in size, and show solid islet-like structure. It is presumed that insulinomatosis affects the entire population of β-cells. With regards to molecular genetics, this phenomenon is not related to mutation in MEN1 gene and is more similar to sporadic benign insulinomas, however, at the moment molecular genetics of this disease remains poorly investigated. NGS sequencing was performed with a panel of 409 cancer-related genes. Results of sequencing were analyzed by bioinformatic algorithms for detecting point mutations and copy number variations. DNA copy number variations were detected that harbor a large number of genes in insulinoma and fewer genes in micro-tumors. qPCR was used to confirm copy number variations at ATRX, FOXL2, IRS2 and CEBPA genes. Copy number alterations involving FOXL2, IRS2, CEBPA and ATRX genes were observed in insulinoma as well as in micro-tumors samples, suggesting that alterations of these genes may promote malignization in the β-cells population.

A Maternal High-Fat Diet Induces DNA Methylation Changes That Contribute to Glucose Intolerance in Offspring

Scope: Overnutrition in utero is a critical contributor to the susceptibility of diabetes by programming, although the exact mechanism is not clear. In this paper, we aimed to study the long-term effect of a maternal high-fat (HF) diet on offspring through epigenetic modifications. Procedures: Five-week-old female C57BL6/J mice were fed a HF diet or control diet for 4 weeks before mating and throughout gestation and lactation. At postnatal week 3, pups continued to consume a HF or switched to a control diet for 5 weeks, resulting in four groups of offspring differing by their maternal and postweaning diets. Results: The maternal HF diet combined with the offspring HF diet caused hyperglycemia and insulin resistance in male pups. Even after changing to the control diet, male pups exposed to the maternal HF diet still exhibited hyperglycemia and glucose intolerance. The livers of pups exposed to a maternal HF diet had a hypermethylated insulin receptor substrate 2 (Irs2) gene and a hypomethylated mitogen-activated protein kinase kinase 4 (Map2k4) gene. Correspondingly, the expression of the Irs2 gene decreased and that of Map2k4 increased in pups exposed to a maternal HF diet. Conclusion: Maternal overnutrition programs long-term epigenetic modifications, namely, Irs2 and Map2k4 gene methylation in the offspring liver, which in turn predisposes the offspring to diabetes later in life.

Insulin Substrate Receptor (IRS) proteins in normal and malignant hematopoiesis

The insulin receptor substrate (IRS) proteins are a family of cytoplasmic proteins that integrate and coordinate the transmission of signals from the extracellular to the intracellular environment via transmembrane receptors, thus regulating cell growth, metabolism, survival and proliferation. The PI3K/AKT/mTOR and MAPK signaling pathways are the best-characterized downstream signaling pathways activated by IRS signaling (canonical pathways). However, novel signaling axes involving IRS proteins (noncanonical pathways) have recently been identified in solid tumor and hematologic neoplasm models. Insulin receptor substrate-1 (IRS1) and insulin receptor substrate-2 (IRS2) are the best-characterized IRS proteins in hematologic-related processes. IRS2 binds to important cellular receptors involved in normal hematopoiesis (EPOR, MPL and IGF1R). Moreover, the identification of IRS1/ABL1 and IRS2/JAK2V617F interactions and their functional consequences has opened a new frontier for investigating the roles of the IRS protein family in malignant hematopoiesis. Insulin receptor substrate-4 (IRS4) is absent in normal hematopoietic tissues but may be expressed under abnormal conditions. Moreover, insulin receptor substrate-5 (DOK4) and insulin receptor substrate-6 (DOK5) are linked to lymphocyte regulation. An improved understanding of the signaling pathways mediated by IRS proteins in hematopoiesis-related processes, along with the increased development of agonists and antagonists of these signaling axes, may generate new therapeutic approaches for hematological diseases. The scope of this review is to recapitulate and review the evidence for the functions of IRS proteins in normal and malignant hematopoiesis.

Two Novel Susceptibility Loci for Prostate Cancer in Men of African Ancestry

Prostate cancer incidence is 1.6-fold higher in African Americans than in other populations. The risk factors that drive this disparity are unknown and potentially consist of social, environmental, and genetic influences. To investigate the genetic basis of prostate cancer in men of African ancestry, we performed a genome-wide association meta-analysis using two-sided statistical tests in 10 202 case subjects and 10 810 control subjects. We identified novel signals on chromosomes 13q34 and 22q12, with the risk-associated alleles found only in men of African ancestry (13q34: rs75823044, risk allele frequency = 2.2%, odds ratio [OR] = 1.55, 95% confidence interval [CI] = 1.37 to 1.76, P = 6.10 × 10-12; 22q12.1: rs78554043, risk allele frequency = 1.5%, OR = 1.62, 95% CI = 1.39 to 1.89, P = 7.50 × 10-10). At 13q34, the signal is located 5' of the gene IRS2 and 3' of a long noncoding RNA, while at 22q12 the candidate functional allele is a missense variant in the CHEK2 gene. These findings provide further support for the role of ancestry-specific germline variation in contributing to population differences in prostate cancer risk.

IRS1 and IRS2: molecular characterization, tissue expression and transcriptional regulation by insulin in yellow catfish Pelteobagrus fulvidraco

The insulin receptor substrate (IRS) proteins, in particular, IRS1 and IRS2, are the key downstream players of insulin signaling pathway and the regulation of lipid metabolism. In the present study, two genes of IRS (IRS1 and IRS2) were isolated and characterized from yellow catfish Pelteobagrus fulvidraco. Their molecular characterizations, tissue expressions, and transcriptional levels by insulin both in vivo and in vitro were determined. The validated complementary DNAs encoding for IRS1 and IRS2 were 3693 and 3177 bp in length, encoding proteins of 1230 and 1058 amino acid residues, respectively. Similarly to mammals, amino acid sequence alignment revealed that IRSs contained an N-terminal pleckstrin homology (PH) domain, a phosphotyrosine-binding (PTB) domain, and several C-terminal multiple sites of tyrosine phosphorylation. Both IRS1 and IRS2 were widely expressed across the ten tissues (liver, white muscle, spleen, brain, gill, mesenteric fat, anterior intestine, heart, mid-kidney, and ovary), but at the variable levels. Insulin injection at 1 μg/g in vivo significantly stimulated the messenger RNA (mRNA) expression of IRS2, but not IRS1 mRNA expression levels in the liver of yellow catfish after 48 h. In hepatocytes of yellow catfish, insulin incubation significantly stimulated the IRS1 (at a 1000 nM insulin group) and IRS2 (at both 100 and 1000 nM insulin groups) mRNA expressions, which indicated that IRS2 was more sensitive than IRS1 to insulin stimulation in the liver of yellow catfish, and IRS2 played a more important role in mediating insulin's effects on the liver metabolism. The present study serves to increase our understanding into the function of IRS in fish.

Animal models for assessing the impact of natural products on the aetiology and metabolic pathophysiology of Type 2 diabetes

Type 2 diabetes mellitus is a complex and heterogeneous disorder which in its most common manifestation arises from insulin resistance and later insulin insufficiency. Type 2 diabetes is characterised by impaired insulin sensitivity and diagnosed as hyperglycaemia. Because of its cardiovascular consequences, Type 2 diabetes represents one of the world's leading causes of mortality and morbidity. Drug discovery and development are required to produce better ways to prevent, treat and manage diabetes and its complications. Diabetes is a human, not an animal disease, so animals do not get Type 2 diabetes. However there are animal models which are variously suitable for the investigation of new agents for the treatment of Type 2 diabetes. In this Review we have examined the various models that are available for the study of natural products with a focus on models (genetic, nutritional and spontaneous) for the metabolic abnormities of diabetes. These models are also relevant to the investigation of Western medicines for the treatment of diabetes. A suitable experimental model plays an important role in drug discovery for translational studies leading to increased understanding of the molecular basis and management of diabetes.

IRS-2 Partially Compensates for the Insulin Signal Defects in IRS-1-/- Mice Mediated by miR-33

Insulin signaling is coordinated by insulin receptor substrates (IRSs). Many insulin responses, especially for blood glucose metabolism, are mediated primarily through Irs-1 and Irs-2. Irs-1 knockout mice show growth retardation and insulin signaling defects, which can be compensated by other IRSs in vivo; however, the underlying mechanism is not clear. Here, we presented an Irs-1 truncated mutated mouse (Irs-1-/-) with growth retardation and subcutaneous adipocyte atrophy. Irs-1-/- mice exhibited mild insulin resistance, as demonstrated by the insulin tolerance test. Phosphatidylinositol 3-kinase (PI3K) activity and phosphorylated Protein Kinase B (PKB/AKT) expression were elevated in liver, skeletal muscle, and subcutaneous adipocytes in Irs-1 deficiency. In addition, the expression of IRS-2 and its phosphorylated version were clearly elevated in liver and skeletal muscle. With miRNA microarray analysis, we found miR-33 was down-regulated in bone marrow stromal cells (BMSCs) of Irs-1-/- mice, while its target gene Irs-2 was up-regulated in vitro studies. In addition, miR-33 was down-regulated in the presence of Irs-1 and which was up-regulated in fasting status. What's more, miR-33 restored its expression in re-feeding status. Meanwhile, miR-33 levels decreased and Irs-2 levels increased in liver, skeletal muscle, and subcutaneous adipocytes of Irs-1-/- mice. In primary cultured liver cells transfected with an miR-33 inhibitor, the expression of IRS-2, PI3K, and phosphorylated-AKT (p-AKT) increased while the opposite results were observed in the presence of an miR-33 mimic. Therefore, decreased miR-33 levels can up-regulate IRS-2 expression, which appears to compensate for the defects of the insulin signaling pathway in Irs-1 deficient mice.

IRS2 silencing increases apoptosis and potentiates the effects of ruxolitinib in JAK2V617F-positive myeloproliferative neoplasms

The recurrent V617F mutation in JAK2 (JAK2^V617F) has emerged as the primary contributor to the pathogenesis of myeloproliferative neoplasms (MPN). However, the lack of complete response in most patients treated with the JAK1/2 inhibitor, ruxolitinib, indicates the need for identifying pathways that cooperate with JAK2. Activated JAK2 was found to be associated with the insulin receptor substrate 2 (IRS2) in non-hematological cells. We identified JAK2/IRS2 binding in JAK2^V617F HEL cells, but not in the JAK2^WT U937 cell line. In HEL cells, IRS2 silencing decreased STAT5 phosphorylation, reduced cell viability and increased apoptosis; these effects were enhanced when IRS2 silencing was combined with ruxolitinib. In U937 cells, IRS2 silencing neither reduced cell viability nor induced apoptosis. IRS1/2 pharmacological inhibition in primary MPN samples reduced cell viability in JAK2^V617F-positive but not JAK2^WT specimens; combination with ruxolitinib had additive effects. IRS2 expression was significantly higher in CD34⁺ cells from essential thrombocythemia patients compared to healthy donors, and in JAK2^V617F MPN patients when compared to JAK2^WT. Our data indicate that IRS2 is a binding partner of JAK2^V617F in MPN. IRS2 contributes to increased cell viability and reduced apoptosis in JAK2-mutated cells. Combined pharmacological inhibition of IRS2 and JAK2 may have a potential clinical application in MPN.

Animal models for diabetes: Understanding the pathogenesis and finding new treatments

Diabetes mellitus is a lifelong, metabolic disease that is characterised by an inability to maintain normal glucose homeostasis. There are several different forms of diabetes, however the two most common are Type 1 and Type 2 diabetes. Type 1 diabetes is caused by the autoimmune destruction of pancreatic beta cells and a subsequent lack of insulin production, whilst Type 2 diabetes is due to a combination of both insulin resistance and an inability of the beta cells to compensate adequately with increased insulin release. Animal models are increasingly being used to elucidate the mechanisms underlying both Type 1 and Type 2 diabetes as well as to identify and refine novel treatments. However, a wide range of different animal models are currently in use. The majority of these models are suited to addressing certain specific aspects of diabetes research, but may be of little use in other studies. All have pros and cons, and selecting an appropriate model for addressing a specific question is not always a trivial task and will influence the study results and their interpretation. Thus, as the number of available animal models increases it is important to consider the potential roles of these models in the many different aspects of diabetes research. This review gathers information on the currently used experimental animal models of both Type 1 and Type 2 diabetes and evaluates their advantages and disadvantages for research purposes and details the factors that should be taken into account in their use.

Causal drift, robust signaling, and complex disease

The phenotype of many regulatory circuits in which mutations can cause complex, polygenic diseases is to some extent robust to DNA mutations that affect circuit components. Here I demonstrate how such mutational robustness can prevent the discovery of genetic disease determinants. To make my case, I use a mathematical model of the insulin signaling pathway implicated in type 2 diabetes, whose signaling output is governed by 15 genetically determined parameters. Using multiple complementary measures of a parameter's importance for this phenotype, I show that any one disease determinant that is crucial in one genetic background will be virtually irrelevant in other backgrounds. In an evolving population that drifts through the parameter space of this or other robust circuits through DNA mutations, the genetic changes that can cause disease will vary randomly over time. I call this phenomenon causal drift. It means that mutations causing disease in one (human or non-human) population may have no effect in another population, and vice versa. Causal drift casts doubt on our ability to infer the molecular mechanisms of complex diseases from non-human model organisms.

Decreased gene expressions of insulin signal molecules in canine hyperadrenocorticism

Hyperadrenocorticism (HAC) is a common endocrine disorder in dogs, in which excess glucocorticoid causes insulin resistance. Disturbance of insulin action may be caused by multiple factors, including transcriptional modulation of insulin signal molecules which lie downstream of insulin binding to insulin receptors. In this study, gene expressions of insulin signal molecules were examined using neutrophils of the HAC dogs (the untreated dogs and the dogs which had been treated with trilostane). Insulin receptor substrate (IRS)-1, IRS-2, phosphatidylinositol 3-kinase (PI3-K), protein kinase B/Akt kinase (Akt)-2 and protein kinase C (PKC)-lambda were analyzed in the HAC dogs and compared with those from normal dogs. The IRS-1 gene expressions decreased by 37% and 35% of the control dogs in the untreated and treated groups, respectively. The IRS-2 gene expressions decreased by 61% and 72%, the PI3-K gene expressions decreased by 47% and 55%, and the Akt-2 gene expressions decreased by 45% and 56% of the control dogs, similarly. Collectively, gene expressions of insulin signal molecules are suppressed in the HAC dogs, which may partially contribute to the induction of insulin resistance.

Insulin receptor substrate 2-mediated phosphatidylinositol 3-kinase signaling selectively inhibits glycogen synthase kinase 3β to regulate aerobic glycolysis

Insulin receptor substrate 1 (IRS-1) and IRS-2 are cytoplasmic adaptor proteins that mediate the activation of signaling pathways in response to ligand stimulation of upstream cell surface receptors. Despite sharing a high level of homology and the ability to activate PI3K, only Irs-2 positively regulates aerobic glycolysis in mammary tumor cells. To determine the contribution of Irs-2-dependent PI3K signaling to this selective regulation, we generated an Irs-2 mutant deficient in the recruitment of PI3K. We identified four tyrosine residues (Tyr-649, Tyr-671, Tyr-734, and Tyr-814) that are essential for the association of PI3K with Irs-2 and demonstrate that combined mutation of these tyrosines inhibits glucose uptake and lactate production, two measures of aerobic glycolysis. Irs-2-dependent activation of PI3K regulates the phosphorylation of specific Akt substrates, most notably glycogen synthase kinase 3β (Gsk-3β). Inhibition of Gsk-3β by Irs-2-dependent PI3K signaling promotes glucose uptake and aerobic glycolysis. The regulation of unique subsets of Akt substrates by Irs-1 and Irs-2 may explain their non-redundant roles in mammary tumor biology. Taken together, our study reveals a novel mechanism by which Irs-2 signaling preferentially regulates tumor cell metabolism and adds to our understanding of how this adaptor protein contributes to breast cancer progression.

Inputs and outputs of insulin receptor

The insulin receptor (IR) is an important hub in insulin signaling and its activation is tightly regulated. Upon insulin stimulation, IR is activated through autophosphorylation, and consequently phosphorylates several insulin receptor substrate (IRS) proteins, including IRS1-6, Shc and Gab1. Certain adipokines have also been found to activate IR. On the contrary, PTP, Grb and SOCS proteins, which are responsible for the negative regulation of IR, are characterized as IR inhibitors. Additionally, many other proteins have been identified as IR substrates and participate in the insulin signaling pathway. To provide a more comprehensive understanding of the signals mediated through IR, we reviewed the upstream and downstream signal molecules of IR, summarized the positive and negative modulators of IR, and discussed the IR substrates and interacting adaptor proteins. We propose that the molecular events associated with IR should be integrated to obtain a better understanding of the insulin signaling pathway and diabetes.

Developmental programming by maternal insulin resistance: hyperinsulinemia, glucose intolerance, and dysregulated lipid metabolism in male offspring of insulin-resistant mice

Maternal obesity and gestational diabetes mellitus (GDM) are associated with obesity and diabetes risk in offspring. We tested whether maternal insulin resistance, which frequently coexists with GDM and obesity, could independently contribute to dysregulation of offspring metabolism. Female mice haploinsufficient for insulin receptor substrate-1 (IRS1-het) are hyperinsulinemic and insulin resistant during pregnancy, despite normal plasma glucose and body weight, and thus serve as a model of isolated maternal insulin resistance. Wild-type (WT) offspring of IRS1-het dams insulin resistance-exposed [IR-exposed] were compared with WT offspring of WT dams. Despite no differences in adiposity, male IR-exposed pups were glucose intolerant (P = 0.04) and hyperinsulinemic (1.3-fold increase, P = 0.02) by 1 month of age and developed progressive fasting hyperglycemia. Moreover, male IR-exposed pups challenged with high-fat diet exhibited insulin resistance. Liver lipidomic analysis of 3-week-old IR-exposed males revealed increases in the 16:1n7 fraction of several lipid classes, suggesting increased Scd1 activity. By 6 months of age, IR-exposed males had increased lipid accumulation in liver as well as increased plasma refed fatty acids, consistent with disrupted lipid metabolism. Our results indicate that isolated maternal insulin resistance, even in the absence of hyperglycemia or obesity, can promote metabolic perturbations in male offspring.

CCCTC-binding factor mediates effects of glucose on beta cell survival

OBJECTIVES

Pancreatic islet β-cell survival is paramount for regulation of insulin activity and for maintaining glucose homeostasis. Recently, Pax6 has been shown to be essential for many vital functions in β-cells, although many molecular mechanisms of its homeostasis in β-cells remain unclear. The present study investigates novel effects of glucose- and insulin-induced CCCTC-binding factor (CTCF) activity on Pax6 gene expression as well as for subsequent effects of insulin-activated signalling pathways, on β-cell proliferation.

MATERIALS AND METHODS

Pancreatic β-TC-1-6 cells were cultured in DMEM and stimulated with high concentrations of glucose (5-125 mm); cell viability was assessed by MTT assay. Effects of CTCF on Pax6 were evaluated in the high glucose-induced environment and CTCF/Erk-suppressed cells, by promoter reporter and western blotting analyses.

RESULTS

Increases in glucose and insulin concentrations upregulated CTCF and consequently downregulated Pax6 in β-cell survival and proliferation. Knocking-down CTCF directly affected Pax6 transcription through CTCF binding and blocked the response to glucose. Altered Erk activity mediated effects of CTCF on controlling Pax6 expression, which partially regulated β-cell proliferation.

CONCLUSIONS

CTCF functioned as a molecular mediator between insulin-induced upstream Erk signalling and Pax6 expression in these pancreatic β-cells. This pathway may contribute to regulation of β-cell survival and proliferation.

SRC Homology 2 Domain Binding Sites in Insulin, IGF-1 and FGF receptor mediated signaling networks reveal an extensive potential interactome

Specific peptide ligand recognition by modular interaction domains is essential for the fidelity of information flow through the signal transduction networks that control cell behavior in response to extrinsic and intrinsic stimuli. Src homology 2 (SH2) domains recognize distinct phosphotyrosine peptide motifs, but the specific sites that are phosphorylated and the complement of available SH2 domains varies considerably in individual cell types. Such differences are the basis for a wide range of available protein interaction microstates from which signaling can evolve in highly divergent ways. This underlying complexity suggests the need to broadly map the signaling potential of systems as a prerequisite for understanding signaling in specific cell types as well as various pathologies that involve signal transduction such as cancer, developmental defects and metabolic disorders. This report describes interactions between SH2 domains and potential binding partners that comprise initial signaling downstream of activated fibroblast growth factor (FGF), insulin (Ins), and insulin-like growth factor-1 (IGF-1) receptors. A panel of 50 SH2 domains screened against a set of 192 phosphotyrosine peptides defines an extensive potential interactome while demonstrating the selectivity of individual SH2 domains. The interactions described confirm virtually all previously reported associations while describing a large set of potential novel interactions that imply additional complexity in the signaling networks initiated from activated receptors. This study of pTyr ligand binding by SH2 domains provides valuable insight into the selectivity that underpins complex signaling networks that are assembled using modular protein interaction domains.

IL-4 engagement of the type I IL-4 receptor complex enhances mouse eosinophil migration to eotaxin-1 in vitro

Background

Previous work from our laboratory demonstrated that IL-4Rα expression on a myeloid cell type was responsible for enhancement of Th2-driven eosinophilic inflammation in a mouse model of allergic lung inflammation. Subsequently, we have shown that IL-4 signaling through type I IL-4 receptors on monocytes/macrophages strongly induced activation of the IRS-2 pathway and a subset of genes characteristic of alternatively activated macrophages. The direct effect(s) of IL-4 and IL-13 on mouse eosinophils are not clear. The goal of this study was determine the effect of IL-4 and IL-13 on mouse eosinophil function.

Methods

Standard Transwell chemotaxis assay was used to assay migration of mouse eosinophils and signal transduction was assessed by Western blotting.

Results

Here we determined that (i) mouse eosinophils express both type I and type II IL-4 receptors, (ii) in contrast to human eosinophils, mouse eosinophils do not chemotax to IL-4 or IL-13 although (iii) pre-treatment with IL-4 but not IL-13 enhanced migration to eotaxin-1. This IL-4-mediated enhancement was dependent on type I IL-4 receptor expression: γC-deficient eosinophils did not show enhancement of migratory capacity when pre-treated with IL-4. In addition, mouse eosinophils responded to IL-4 with the robust tyrosine phosphorylation of STAT6 and IRS-2, while IL-13-induced responses were considerably weaker.

Conclusions

The presence of IL-4 in combination with eotaxin-1 in the allergic inflammatory milieu could potentiate infiltration of eosinophils into the lungs. Therapies that block IL-4 and chemokine receptors on eosinophils might be more effective clinically in reducing eosinophilic lung inflammation.

Association between IRS-2 G1057D polymorphism and risk of gastric cancer

AIM: To investigate the relationship between insulin receptor substrate-2 (IRS-2) G1057D polymorphism and the risk of gastric cancer (GC) in a Chinese population.

METHODS: A case-control study with 197 GC patients and 156 age- and sex- matched control subjects was conducted. The genotypes of polymorphism were assessed by polymerase chain reaction-restriction fragment length polymorphism.

RESULTS: The genotype frequencies of IRS-2 G1057D polymorphism in cases were obviously different from those in the control group (P = 0.031). Compared with GG genotype carriers, the risk for GC was significantly higher (adjusted odds ratio = 2.32, 95% CI: 1.03-5.23, P = 0.042) in the individuals with the IRS-2 DD genotype. Furthermore, stratified analysis was performed based on age, sex, smoking status and residence, but no significant difference between the two groups was found. In addition, no significant association between genotypes and clinicopathological features was observed either.

CONCLUSION: This study demonstrates that IRS-2 G1057D is involved in susceptibility to GC, although further large-sample studies are still needed.

Membrane localization of insulin receptor substrate-2 (IRS-2) is associated with decreased overall survival in breast cancer

Recent studies have identified a role for insulin receptor substrate-2 (IRS-2) in promoting motility and metastasis in breast cancer. However, no published studies to date have examined IRS-2 expression in human breast tumors. We examined IRS-2 expression by immunohistochemistry (IHC) in normal breast tissue, benign breast lesions, and malignant breast tumors from the institutional pathology archives and a tumor microarray from a separate institution. Three distinct IRS-2 staining patterns were noted: diffusely cytoplasmic, punctate cytoplasmic, and localized to the cell membrane. The individual and pooled datasets were analyzed for associations of IRS-2 staining pattern with core clinical parameters and clinical outcomes. Univariate analysis revealed a trend toward decreased overall survival (OS) with IRS-2 membrane staining, and this association became significant upon multivariate analysis (P = 0.01). In progesterone receptor negative (PR-) tumors, in particular, IRS-2 staining at the membrane correlated with significantly worse OS than other IRS-2 staining patterns (P < 0.001). When PR status and IRS-2 staining pattern were evaluated in combination, PR- tumors with IRS-2 at the membrane were associated with a significantly decreased OS when compared with all other combinations (P = 0.002). Evaluation of IRS-2 staining patterns could potentially be used to identify patients with PR- tumors who would most benefit from aggressive treatment.

Ginkgo biloba extract enhances glucose tolerance in hyperinsulinism-induced hepatic cells

Ginkgo biloba, an herbal medication, is capable of lowering glucose, fat, and lipid peroxide in diabetic patients. In the current study, we tested the hypothesis that Ginkgo biloba extract (GBE) prevented hyperinsulinism-induced glucose intolerance in hepatocytes. We investigated the effects of GBE on glucose consumption, glucokinase activity, and mRNA levels of key genes in glucose metabolism and the insulin signaling pathway. To better show its efficacy, we included a control group that was treated with rosiglitazone, a type of thiazolidinedione (TZD). The data indicated that GBE repressed glucose uptake under normal conditions, while it dramatically improved glucose tolerance under insulin-resistant conditions. Furthermore, after analyzing gene expression, we suggest that GBE chiefly exerts its effects by stimulating IRS-2 transcription. It should be noted that, unlike rosiglitazone, GBE did not stimulate excessive glucose uptake as it improved glucose tolerance. It is said that GBE treatment could avoid drug-induced obesity. Our data suggest that GBE has the potential to prevent insulin resistance and is a promising anti-diabetic drug.

Mutations of the Wilms tumor 1 gene (WT1) in older patients with primary cytogenetically normal acute myeloid leukemia: a Cancer and Leukemia Group B study

We previously reported the adverse prognostic impact of Wilms tumor 1 gene (WT1) mutations in younger adult cytogenetically normal acute myeloid leukemia (CN-AML). Here, we investigated 243 older (> or = 60 years) primary CN-AML patients. WT1 mutated (WT1mut) patients (7%) had FLT3-ITD more frequently (P < .001), lower hemoglobin (P = .01), higher white blood cell count (P = .03) and percentage blood blasts (P = .03), and a shorter overall survival (P = .08) than WT1 wild-type (WT1wt) patients. Comparing older and younger WT1mut patients, they had similar pretreatment characteristics and outcome. By contrast, among WT1wt CN-AML, younger patients had a significantly better outcome. A WT1 mutation-associated gene-expression signature, reported here for the first time, included CD96, a leukemia stem cell-specific marker, and genes involved in gene regulation (eg, MLL, PML, and SNRPN) and in proliferative and metabolic processes (eg, INSR, IRS2, and PRKAA1), supporting the role of mutated WT1 in deregulating multiple homeostatic processes. Our results indicate that WT1mut CN-AML represents a distinct entity with poor treatment response across age groups. This study has been registered at www.clinicaltrials.gov as #NCT00900224.

Expression and function of the insulin receptor substrate proteins in cancer

The Insulin Receptor Substrate (IRS) proteins are cytoplasmic adaptor proteins that function as essential signaling intermediates downstream of activated cell surface receptors, many of which have been implicated in cancer. The IRS proteins do not contain any intrinsic kinase activity, but rather serve as scaffolds to organize signaling complexes and initiate intracellular signaling pathways. As common intermediates of multiple receptors that can influence tumor progression, the IRS proteins are positioned to play a pivotal role in regulating the response of tumor cells to many different microenvironmental stimuli. Limited studies on IRS expression in human tumors and studies on IRS function in human tumor cell lines and in mouse models have provided clues to the potential function of these adaptor proteins in human cancer. A general theme arises from these studies; IRS-1 and IRS-4 are most often associated with tumor growth and proliferation and IRS-2 is most often associated with tumor motility and invasion. In this review, we discuss the mechanisms by which IRS expression and function are regulated and how the IRS proteins contribute to tumor initiation and progression.

Glucose effects on beta-cell growth and survival require activation of insulin receptors and insulin receptor substrate 2

Insulin and insulin-like growth factor I (IGF-I) are ubiquitous hormones that regulate growth and metabolism of most mammalian cells, including pancreatic beta-cells. In addition to being an insulin secretagogue, glucose regulates proliferation and survival of beta-cells. However, it is unclear whether the latter effects of glucose occur secondary to autocrine activation of insulin signaling proteins by secreted insulin. To examine this possibility we studied the effects of exogenous glucose or insulin in beta-cell lines completely lacking either insulin receptors (betaIRKO) or insulin receptor substrate 2 (betaIRS2KO). Exogenous addition of either insulin or glucose activated proteins in the insulin signaling pathway in control beta-cell lines with the effects of insulin peaking earlier than glucose. Insulin stimulation of betaIRKO and betaIRS2KO cells led to blunted activation of phosphatidylinositol 3-kinase and Akt kinase, while surprisingly, glucose failed to activate either kinase but phosphorylated extracellular signal-regulated kinase. Control beta-cells exhibited low expression of IGF-1 receptors compared to compensatory upregulation in betaIRKO cells. The signaling data support the slow growth and reduced DNA and protein synthesis in betaIRKO and betaIRS2KO cells in response to glucose stimulation. Together, these studies provide compelling evidence that the growth and survival effects of glucose on beta-cells require activation of proteins in the insulin signaling pathway.

Serine kinases of insulin receptor substrate proteins

Signaling of insulin and insulin-like growth factor-I (IGF-1) at target tissues is essential for growth, development and for normal homeostasis of glucose, fat, and protein metabolism. Control over this process is therefore tightly regulated. It can be achieved by a negative-feedback control mechanism, whereby downstream components inhibit upstream elements along the insulin and IGF-1 signaling pathway or by signals from other pathways that inhibit insulin/IGF-1 signaling thus leading to insulin/IGF-1 resistance. Phosphorylation of insulin receptor substrates (IRS) proteins on serine residues has emerged as a key step in these control processes both under physiological and pathological conditions. The list of IRS kinases is growing rapidly, concomitant with the list of potential Ser/Thr phosphorylation sites in IRS proteins. Here we review a range of conditions that activate IRS kinases to phosphorylate IRS proteins on selected domains. The specificity of this reaction is discussed and its characteristic as an "array" phosphorylation is suggested. Finally, its implications on insulin/IGF-1 signaling, insulin/IGF-1 resistance and diabetes, an emerging epidemic of the twenty-first century are outlined.

Overexpression of Akt1 upregulates glycogen synthase activity and phosphorylation of mTOR in IRS-1 knockdown HepG2 cells

Insulin receptor substrate (IRS) proteins are important docking proteins in mediating the insulin signaling cascade. We have investigated the effect of short interfering RNA (siRNA) mediated knockdown of IRS-1 on insulin signaling cascade in primary human hepatocellular carcinoma HepG2 cell line and HepG2 cells overexpressing Akt1/PKB-alpha (HepG2-CA-Akt/PKB). IRS-1 knockdown in both cell lines resulted in reduction of insulin stimulated Akt1 phosphorylation at Ser 473. In parental HepG2 cells, IRS-1 knockdown resulted in reduction (ca. 50%) in the basal level of phosphorylated mTOR (Ser 2448) irrespective of insulin treatment. In contrast, HepG2-CA-Akt/PKB cells showed an upregulation in the basal level of phosphorylated mTOR (Ser 2448) (ca. 40%). Insulin mediated phosphorylation of mTOR was reduced. IRS-1 knockdown also reduced the cell proliferation of parental HepG2 cells by ca. 30% in the presence/absence of insulin, whereas in HepG2-CA-Akt/PKB the cell proliferation was reduced by 15% and treatment of insulin further reduced it to ca. 50% (vs. control). IRS-1 knockdown also reduced the glycogen synthase (GS) activity in parental HepG2 cells, however, it was upregulated in HepG2-CA-Akt/PKB cells. These results suggest that knockdown of IRS-1 abolished basal as well as insulin mediated phosphorylation/activity of proteins involved in cell proliferation or glycogen metabolism in the parental Hep2 cells. IRS-1 knockdown in cells overexpressing constitutively active Akt1/PKB-alpha either did not change or upregulated the basal levels of phosphorylated/active proteins. However, insulin mediated response was either not altered or downregulated in these cells.

Mechanisms involved in the nutritional regulation of mRNA translation: features of the avian model

Abstract:Insulin and amino acids are key factors in regulating protein synthesis. The mechanisms of their action have been widely studied for several years. The insulin signal is mediated by the activation of intracellular kinases such as phosphatidylinositol–3'kinase and the mammalian target of rapamycin (mTOR), affecting the phosphorylation of some major effectors involved in the regulation of translation initiation, i.e. p70 S6 kinase (p70S6K) and the translational repressor eukaryotic initiation factor 4E binding protein (4E-BP1). The amino acid–induced signalling cascade also originates from mTOR and promotes p70S6K and 4E–BP1 activation. However, the mechanisms of regulation are complex and little understood, especiallyin vivo. Elucidating these mechanisms is important for both fundamental physiology and nutritional applications, i.e. better control of the use of nutrients and optimisation of dietary amino acid supplies in various physiological and physiopathological situations. In comparative physiology, the chicken is an interesting model to gain better understanding of the nutritional regulation of mRNA translation because of the very high rates of muscle growth and protein synthesis, and the unusual features compared with mammals. In the present review we provide an overview of the roles of insulin and amino acids as regulators of protein synthesis in both mammals and avian species.

Gender difference in the effect of intrauterine malnutrition on the central anorexigenic action of insulin in adult rats

OBJECTIVE

We evaluated whether insulin hypophagia and hypothalamic signaling are affected in adult rats exposed to intrauterine undernutrition.

METHODS

Pregnant rats ate ad libitum throughout pregnancy and lactation (control, C) or 50% of control intake in the first 2 wk of pregnancy (restricted, R). Four-month-old C and R progeny received insulin or vehicle intracerebroventricular injections for evaluation of 24-h food intake, hypothalamic insulin receptor (IR), and IR substrate-1 (IRS-1) protein content and tyrosine phosphorylation, pp185 phosphorylation, and IRS-1 association with phosphatidylinositol 3-kinase (PI3-K).

RESULTS

With respect to males, R males had normal body composition and insulin-induced hypophagia. IR protein levels were lower but IR phosphorylation was higher in R than in C males. IRS-1 levels and phosphorylation were similar between C and R males, insulin stimulated an IRS-1/PI3-K association in C but not in R males, and pp185 phosphorylation was higher in R than in C males. For females, body fat and serum leptin were elevated in R females. Insulin inhibited food intake in C but not in R females. Insulin-induced IR phosphorylation and protein levels of IR and IRS-1 were higher in R than in C females. However, IRS-1 and pp185 phosphorylation and IRS-1/PI3-K association were significantly stimulated by insulin in C but not in R females.

CONCLUSIONS

Female adult rats exposed to intrauterine undernutrition had increased adiposity, marked impairment of hypothalamic insulin signaling, and loss of insulin-induced hypophagia. These disturbances were less severe or even absent in male progeny. The findings show that female progeny are more susceptible than their male siblings to the effects of maternal malnutrition.

Saturated fatty acids inhibit induction of insulin gene transcription by JNK-mediated phosphorylation of insulin-receptor substrates

JNKs are attractive targets for treatment of obesity and type-2 diabetes. A sustained increase in JNK activity was observed in dietary and genetic models of obesity in mice, whereas JNK deficiency prevented obesity-induced insulin resistance. A similar insulin-sensitizing effect was seen upon treatment of obese mice with JNK inhibitors. We now demonstrate that treatment with the saturated fatty acid palmitic acid results in sustained JNK activation and insulin resistance in primary mouse hepatocytes and pancreatic beta-cells. In the latter, palmitic acid treatment inhibits glucose-induced insulin gene transcription, in part, by interfering with autocrine insulin signaling through phosphorylation of insulin-receptor substrates 1 and 2 at sites that interfere with binding to activated insulin receptors. This mechanism may account for the induction of central insulin resistance by free fatty acids.

Chronic exposure to ketone bodies impairs glucose uptake in adult cardiomyocytes in response to insulin but not vanadate: the role of PI3-K

There is a strong positive correlation between insulin resistance and cardiac diseases. We have already shown that chronic exposure to the ketone body beta-hydroxybutyrate (OHB) decreases insulin-mediated activation of protein kinase B (PKB) and glucose uptake in cardiomyocytes. To gain further insights into the mechanism underlying ketone body-induced insulin resistance, we examined whether OHB alters activation of the insulin-signaling cascade and whether the insulinomimetic agent vanadate could bypass insulin resistance and stimulate glucose uptake in these cells. Cardiomyocytes were incubated with 5 mM OHB, 50 microM vanadate or both for 16 h before the measurement of glucose uptake or the activation of insulin-signaling molecules. While chronic exposure to OHB did not alter insulin- or vanadate-mediated activation of the insulin receptor, it suppressed insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation in response to both agonists. Furthermore, this treatment decreased by 54 and 36% the phosphorylation of the p85 regulatory subunit of phosphatidylinositol 3-kinase (PI3-K) and PKB in response to insulin, whereas it did not alter vanadate-mediated activation of these enzymes. Although insulin did not significantly stimulate p38MAPK phosphorylation, vanadate increased it by 3.8-fold. Furthermore, chronic exposure to OHB potentiated vanadate's action, resulting in a 250% increase in enzyme activation compared to control cells. Though OHB induced a 2.1-fold increase of basal ERK1/2 phosphorylation, inhibition of this enzyme with the MEK inhibitor PD98059 demonstrated that ERK1/2 did not participate in OHB-induced insulin resistance. In conclusion, ketone bodies promote insulin resistance probably through decreased activation of the PI3-K/PKB signaling cascade. Furthermore, vanadate can bypass insulin resistance and stimulate glucose uptake in OHB-treated cardiomyocytes.

Resveratrol inhibits insulin responses in a SirT1-independent pathway

Resveratrol mimics calorie restriction to extend lifespan of Caenorhabditis elegans, yeast and Drosophila, possibly through activation of Sir2 (silent information regulator 2), a NAD+-dependent histone deacetylase. In the present study, resveratrol is shown to inhibit the insulin signalling pathway in several cell lines and rat primary hepatocytes in addition to its broad-spectrum inhibition of several signalling pathways. Resveratrol effectively inhibits insulin-induced Akt and MAPK (mitogen-activated protein kinase) activation mainly through disruption of the interactions between insulin receptor substrates and its downstream binding proteins including p85 regulatory subunit of phosphoinositide 3-kinase and Grb2 (growth factor receptor-bound protein 2). The inhibitory effect of resveratrol on insulin signalling is also demonstrated at mRNA level, where resveratrol reverses insulin effects on phosphoenolpyruvate carboxykinase, glucose-6-phosphatase, fatty acid synthase and glucokinase. In addition, RNA interference experiment shows that the inhibitory effect of resveratrol on insulin signalling pathway is not weakened in cells with reduced expression of SirT1, the mammalian counterpart of Sir2. These observations raise the possibility that resveratrol may additionally modulate lifespan through inhibition of insulin signalling pathway, independently of its activation of SirT1 histone deacetylase. Furthermore, the present study may help to explain a wide range of biological effects of resveratrol, and provides further insight into the molecular basis of calorie restriction.

Intake of trans fatty acid–rich hydrogenated fat during pregnancy and lactation inhibits the hypophagic effect of central insulin in the adult offspring

OBJECTIVE

Using rats we examined whether maternal intake of hydrogenated fat rich in trans fatty acids affects brain fatty acid profile, hypothalamic content of insulin receptor and insulin receptor substrate-1 proteins, and the hypophagic effect of centrally administered insulin in 3-mo-old male progeny.

METHODS

Throughout pregnancy and lactation, Wistar rats ate isocaloric/normolipidic diets with soybean oil (control) or soybean oil-derived hydrogenated fat (trans diet) as a fat source. Upon weaning, the trans offspring continued on the trans diet (trans group) or were switched to a control diet (trans-control group).

RESULTS

Compared with control rats, trans rats had lower brain levels of eicosapentaenoic acid. Compared with trans rats, trans-control rats had increased levels of total polyunsaturated fatty acids and arachidonic acid and decreased levels of trans fatty acids, saturated fatty acids, and monounsaturated fatty acids. Insulin receptor and insulin receptor substrate-1 levels were significantly lower (44% and 38%, respectively) in trans than in control rats. In trans-control rats, insulin receptor was 26% lower (P < 0.05), whereas insulin receptor substrate-1 was 50% lower, than in control rats. Insulin decreased 24-h feeding in control (27%) and trans (38%) rats but failed to do so in trans-control rats. The latter group had increased serum glucose levels.

CONCLUSIONS

The data suggest that the early (intrauterine/perinatal) exposure to hydrogenated fat rich in trans fatty acids programmed the hypothalamic feeding control mechanisms. As young adults, only trans-control animals showed loss of insulin-induced hypophagia, indicating that the mismatch between early and later nutritional environments was relevant. However, the trans group also showed signs of altered appetite signaling mechanisms, suggesting that the early adaptations may have deleterious consequences later in life.

Chronic kidney disease causes defects in signaling through the insulin receptor substrate/phosphatidylinositol 3-kinase/Akt pathway: implications for muscle atrophy

Complications of chronic kidney disease (CKD) include depressed responses to insulin/IGF-1 and accelerated muscle proteolysis as a result of activation of caspase-3 and the ubiquitin-proteasome system. Experimentally, proteolysis in muscle cells occurs when there is suppression of phosphatidylinositol 3-kinase (PI3-K) activity. Postreceptor signaling through the insulin receptor substrate (IRS)/PI3-K/Akt pathway was evaluated in muscles of acidotic, CKD and pair-fed control rats under physiologic conditions and in response to a dose of insulin that quickly stimulated the pathway. Basal IRS-1-associated PI3-K activity was suppressed by CKD; IRS-2-associated PI3-K activity was increased. The basal level of activated Akt in CKD muscles also was low, indicating that the higher IRS-2-associated PI3-K activity did not compensate for the reduced IRS-1-associated PI3-K activity. Insulin treatment overcame this abnormality. The low IRS-1-associated PI3-K activity in muscle was not due to a decrease in IRS-1 protein, but there was a higher amount of the PI3-K p85 subunit protein without a concomitant increase in the p110 catalytic subunit, offering a potential explanation for the lower IRS-1-associated PI3-K activity. Eliminating the acidosis of CKD partially corrected the decrease in basal IRS-1-associated PI3-K activity and protein degradation in muscle. It is concluded that in CKD, acidosis and an increase in the PI3-K p85 subunit are mechanisms that contribute to suppression of PI3-K activity in muscle, and this leads to accelerated muscle proteolysis.

Association of Gly972Arg variant of insulin receptor substrate-1 with metabolic features in women with polycystic ovary syndrome

OBJECTIVE

To examine the prevalence and the effects of Gly972Arg (G972A) variant of insulin receptor substrate-1 (IRS-1) in women with polycystic ovary syndrome (PCOS).

DESIGN

Controlled clinical study.

SETTING

An academic clinical research center.

PATIENT(S)

Sixty women with PCOS and 60 control women matched for age.

INTERVENTION(S)

Biometric measures, metabolic and hormonal measures, genetic analyses.

MAIN OUTCOME MEASURE(S)

Serum androgens, glucose, and insulin were measured. Blood leukocytes were used for genetic analyses.

RESULT(S)

The G972A variant was encountered more often in women with PCOS. The G972A carriers were more obese than their counterparts, had higher fasting insulin levels, and were more insulin-resistant. However, androgen levels did not differ on the basis of IRS-1 genotype.

CONCLUSION(S)

We observed that the G972A variant of IRS-1 was more prevalent in women with PCOS, and that it had important metabolic effects without having a direct effect on the androgen levels. However, the G972A variant of IRS-1 may modulate reproduction by lowering sex hormone-binding globulin in both healthy women and women with PCOS.

Ghrelin improves renal function in mice with ischemic acute renal failure

Growth hormone and IGF-1 have been suggested to have tissue-protective effects. Ghrelin is a stomach-derived growth hormone secretagogue. The effects of ghrelin on ischemia/reperfusion-induced renal failure in mice were examined. Ischemic acute renal failure was induced by bilateral renal artery clamping for 45 min and reperfusion for 24 h. Ghrelin (100 microg/kg mouse) or vehicle was injected subcutaneously six times before surgery and three times after surgery every 8 h. Twenty-four hours after reperfusion, the right kidney was isolated and perfused. Acetylcholine (ACh)- and adrenomedullin-induced endothelium-dependent vasorelaxation of renal vessels significantly improved in ghrelin-pretreated mice (%Delta renal perfusion pressure by 10(-7) M ACh -63.5 +/- 3.7 versus -41.2 +/- 5.5%; P < 0.05). This change was associated with significant increases of nitric oxide release in the kidneys of ghrelin-treated mice (10(-7) M ACh 35.5 +/- 5.8 versus 16.9 +/- 3.5 fmol/g kidney per min; P < 0.05). Serum concentration of urea nitrogen (53 +/- 7 versus 87 +/- 15 mg/dl; P < 0.05) and renal injury score were significantly lower in the ghrelin group (2.5 +/- 0.8 versus 5.3 +/- 1.5; P < 0.01). Tubular apoptotic index was significantly lower in the ghrelin group (5 +/- 5 versus 28 +/- 4; P < 0.05). Furthermore, the survival rate after the 60-min ischemic period was higher in the ghrelin group (80 versus 20%; P < 0.05). Ghrelin treatment significantly increased the serum level of IGF-1. However, such renal protective effects of ghrelin on ischemia/reperfusion injury were not observed in insulin receptor substrate-2 knockout mice. These results suggest that ghrelin may protect the kidneys from ischemia/reperfusion injury and that this effect is related to an improvement of endothelial function through an IGF-1-mediated pathway.

Overexpression of insulin receptor substrate-2 in human and murine hepatocellular carcinoma

De-regulations in insulin and insulin-like growth factor (IGF) pathways may contribute to hepatocellular carcinoma. Although intracellular insulin receptor substrate-2 (IRS-2) is the main effector of insulin signaling in the liver, its role in hepatocarcinogenesis is unknown. Here, we show that IRS-2 was overexpressed in two murine models of hepatocarcinogenesis: administration of diethylnitrosamine and hepatic overexpression of SV40 large T antigen. In both models, IRS-2 overexpression was detected in preneoplastic lesions and at higher levels in tumoral nodules. IRS-2 overexpression associated with IGF-2 and IRS-1 overexpression and with GSK-3beta inhibition. Increased expression of IRS-2 was also detected in human hepatocellular carcinoma specimens and hepatoma cell lines. In murine and human hepatoma cells, IRS-2 protein induction associated with increased IRS-2 mRNA levels. The functionality of IRS-2 was demonstrated in Hep 3 B cells, in which IRS-2 tyrosine phosphorylation and its association with phosphatidylinositol-3 kinase were induced by IGF-2. Moreover, down-regulation of IRS-2 expression increased apoptosis in these cells. In conclusion, we demonstrate that IRS-2 is overexpressed in human and murine hepatocellular carcinoma. The emergence of IRS-2 overexpression at preneoplastic stages during experimental hepatocarcinogenesis and its protective effect against apoptosis suggest that IRS-2 contributes to liver tumor progression.