Human insulin receptor substrate-1 (IRS-1) polymorphism G972R causes IRS-1 to associate with the insulin receptor and inhibit receptor autophosphorylation

Insulin Receptor Substrate 1 Gly972Arg (rs1801278) Polymorphism Is Associated with Obesity and Insulin Resistance in Kashmiri Women with Polycystic Ovary Syndrome

Background: Polycystic ovary syndrome (PCOS) is commonly associated with metabolic abnormalities such as hyperinsulinemia, insulin resistance and obesity. The genetic variants of genes regulating insulin action, expression and regulation are suggested as possible factors involved in development and severity of clinical manifestations in PCOS. Aim: We investigated whether IRS-1Gly972Arg (rs1801278) polymorphism is associated with increased risk of PCOS in Kashmiri women. The correlation of various clinical, metabolic and hormonal markers with rs1801278 single nucleotide polymorphism was analyzed. The genotypic−phenotypic association of clinical manifestations of PCOS with the tested genetic variant was also assessed. Results: There were no significant differences in allele frequency (OR = 0.87, CI = 0.59−1.29, χ2 = 0.456, p = 0.499) or genotypic distribution (χ2 = 3.73, p = 0.15) between PCOS women and controls. No significant association was also found in the dominant (OR = 1.63, χ2 = 0.377, p = 0.53), recessive (OR = 0.79, χ2 = 1.01, p = 0.31) or heterozygote vs. homozygote (OR = 1.34, χ2 = 1.53, p = 0.22) genotype model analysis. The genotype−phenotype correlation analysis showed that the Arg allele was significantly associated with increased central adiposity markers hip circumference (p = 0.012), and body adiposity index BAI (p = 0.002) in the recessive model in PCOS women. The two-hour glucose (p = 0.04) and insulin resistance marker HOMA (p = 0.44) were significantly higher in Arg allele carriers. The androgen excess markers dehydroepiandrosterone sulfate DHEAS (p = 0.02), Ferriman−Gallwey score (p = 0.012), prevalence of acne, alopecia and hirsutism (all p < 0.01) were significantly elevated in the wild-type GG genotype. Conclusions:IRS-1Gly972Arg genetic variant does not increase the risk of PCOS in Kashmiri women. However, this polymorphism is associated with clinical manifestations of insulin resistance, obesity and hyperandrogenism, suggesting its possible role in variable phenotypic manifestations of PCOS.

Phase separation of insulin receptor substrate 1 drives the formation of insulin/IGF-1 signalosomes

As a critical node for insulin/IGF signaling, insulin receptor substrate 1 (IRS-1) is essential for metabolic regulation. A long and unstructured C-terminal region of IRS-1 recruits downstream effectors for promoting insulin/IGF signals. However, the underlying molecular basis for this remains elusive. Here, we found that the C-terminus of IRS-1 undergoes liquid-liquid phase separation (LLPS). Both electrostatic and hydrophobic interactions were seen to drive IRS-1 LLPS. Self-association of IRS-1, which was mainly mediated by the 301–600 region, drives IRS-1 LLPS to form insulin/IGF-1 signalosomes. Moreover, tyrosine residues of YXXM motifs, which recruit downstream effectors, also contributed to IRS-1 self-association and LLPS. Impairment of IRS-1 LLPS attenuated its positive effects on insulin/IGF-1 signaling. The metabolic disease-associated G972R mutation impaired the self-association and LLPS of IRS-1. Our findings delineate a mechanism in which LLPS of IRS-1-mediated signalosomes serves as an organizing center for insulin/IGF-1 signaling and implicate the role of aberrant IRS-1 LLPS in metabolic diseases.

Pathophysiological Role of Genetic Factors Associated With Gestational Diabetes Mellitus

Gestational Diabetes Mellitus (GDM) is a highly prevalent maternal pathology characterized by maternal glucose intolerance during pregnancy that is, associated with severe complications for both mother and offspring. Several risk factors have been related to GDM; one of the most important among them is genetic predisposition. Numerous single nucleotide polymorphisms (SNPs) in genes that act at different levels on various tissues, could cause changes in the expression levels and activity of proteins, which result in glucose and insulin metabolism dysfunction. In this review, we describe various SNPs; which according to literature, increase the risk of developing GDM. These SNPs include: (1) those associated with transcription factors that regulate insulin production and excretion, such as rs7903146 (TCF7L2) and rs5015480 (HHEX); (2) others that cause a decrease in protective hormones against insulin resistance such as rs2241766 (ADIPOQ) and rs6257 (SHBG); (3) SNPs that cause modifications in membrane proteins, generating dysfunction in insulin signaling or cell transport in the case of rs5443 (GNB3) and rs2237892 (KCNQ1); (4) those associated with enzymes such as rs225014 (DIO2) and rs9939609 (FTO) which cause an impaired metabolism, resulting in an insulin resistance state; and (5) other polymorphisms, those are associated with growth factors such as rs2146323 (VEGFA) and rs755622 (MIF) which could cause changes in the expression levels of these proteins, producing endothelial dysfunction and an increase of pro-inflammatory cytokines, characteristic on GDM. While the pathophysiological mechanism is unclear, this review describes various potential effects of these polymorphisms on the predisposition to develop GDM.

Differential expression of insulin receptor substrate-1(IRS-1) in visceral and subcutaneous adipose depots of morbidly obese subjects undergoing bariatric surgery in a tertiary care center in north India; SNP analysis and correlation with metabolic profile

BACKGROUND

/aim: Abdominal obesity and associated metabolic consequences are a burgeoning problem in Asian Indians and studying their genetic predisposition is important. This study is aimed at assessing variations in Insulin receptor substrate-1 (IRS-1), its expression at regional fat-depots (visceral and subcutaneous) in morbidly obese patients, and correlation with genotype-phenotype traits.

METHODS

Gene expression of IRS-1 in paired adipose tissue from 35 morbidly obese subjects (BMI) > 40 kg/m²) with co-morbidities and 15 controls (BMI<25 kg/m²), undergoing bariatric/elective abdominal surgery, respectively was determined by quantitative real time PCR. Genotyping of IRS-1Gly972Arg (n = 436) (rs 1801278) was performed by PCR-RFLP. Metabolic parameters were assessed. Full length sequencing of IRS-1 was performed to identify known/novel variations.

RESULTS

A marked reduction in IRS-1 expression was observed in visceral as compared to subcutaneous adipose tissue of morbidly obese subjects (p = 0.02). Homozygous variant of IRS-1 Gly972Arg was absent and there was no association with obesity or insulin resistance. A salient finding of this study was identification of two new variants in IRS-1 gene, representing G > A (codon 1102) encoding Glu > Lys and a deletion of (A) at codon 658 in morbidly obese subjects with insulin resistance.

CONCLUSIONS

Observation of a substantially lower expression of IRS-1 for first time in visceral adipose tissue of morbidly obese subjects is suggestive of predictive role of IRS-1 expression in insulin responsiveness of visceral adipose tissue. New variants in IRS-1, a non-synonymous mutation and a deletion should be evaluated further for their role in development of obesity and/orT2DM.

Insulin receptor substrate-1 G972R single nucleotide polymorphism in Egyptian patients with chronic hepatitis C virus infection and type 2 diabetes mellitus

Background

Insulin receptor substrate-1 (IRS1) plays a critical role in insulin signaling. IRS-1 gene polymorphism with glycine to arginine substitution (GGG ↔ AGG substitutions) in codon 972 (G972R) (rs1801278) is a common polymorphism of the IRS-1 gene, which may have a pathogenic role in the development of type 2 diabetes mellitus (type 2 DM) due to insulin resistance and impaired insulin secretion. In hepatitis C virus infection (HCV), the IRS proteins might be counter-regulated by degradation, differential expression, or modification by phosphorylation in cells expressing HCV core protein, which inhibits the interactions of IRS-1 with both the insulin receptor and the downstream effectors of IRS-1. The present retrospective case–control study aimed to evaluate IRS-1 G972R (rs 1801278) SNP in Egyptian patients with HCV and type 2 DM, two hundred and two subjects including 100 males and 102 females The present work is a retrospective case–control study aimed to detect IRS-1 G972R (rs 1801278) SNP in Egyptian patients with chronic HCV infection and DM. The subjects were divided into the control group (group I) which included 50 apparently healthy volunteers of comparable age, gender, and socioeconomic status to patients; group II included 50 type 2 diabetic patients without chronic hepatitis C infection; group III included 52 chronic HCV-infected patients without type 2 diabetes mellitus; and group IV included 50 chronic hepatitis C-infected patients with type 2 diabetes mellitus. IRS-1 G972R (rs 1801278) genotyping was done by using polymerase chain reaction (PCR-RFLP) technique with restriction enzymes BstNI.

Results

HOMA-IR and QUICKI index was significantly higher in the patient groups (groups II, III, and IV) than controls (P < 0.001, P = 0.019, and P < 0.001 respectively). There was a significant increase in minor allele (A) in groups II, III, and IV than controls (P = 0.007, P = 0.017, and P = 0.007 respectively). There was increased frequency of mutant allele (A) than wild allele (G) of IRS-1 G972R polymorphism in type 2 diabetic patients with BMI < 25 kg/m2. The DM patients without HCV infection (group II), HCV patients without DM (group III), and HCV patients with DM (group IV) showed a significant decrease in GG genotypes and a significant increase in AA genotypes than the controls (P = 0.017, P = 0.019, and P = 0.009 respectively). Body mass index and waist to hip ratio were significantly higher in DM patients without chronic hepatitis C infection (group II) and in HCV patients with type 2 diabetes (group IV) than controls, in hepatitis C patients with type 2 diabetes (group IV) than controls, and in group IV than group III (P < 0.001).

Conclusion

IRS-1 G972R (rs 1801278) polymorphism might be a contributing risk factor for the development of type 2 DM. The mutant allele (A) of IRS-1 suggests the role of this SNP as risk factors for type 2 diabetes mellitus even in subjects with normal body weight. The increase of body mass index may be an independent risk factor for the development of type 2 diabetes mellitus.

The putative etiology and prevention of autism

Since the initial psychological report by Leo Kanner in 1943, relatively little formal biochemical/neurological research on the cause of autism, other than peripheral searches for genomic mutations, had been carried until the end of the 20th century. As a result of studies on twin sets and the conclusion that autism was largely a hereditary defect, numerous investigations have sought various genetic faults in particular. However, such studies were able to reveal a plausible etiology for this malady in only a small percentage of instances. Key bio-molecular characteristics of this syndrome have been uncovered when the potential roles of the glia were studied in depth. Findings related to biochemical deficiencies appearing early in the newborn, such as depressed IGF-1 (insulin-like growth factor #1) in neurogenesis/myelination, are becoming emphasized in many laboratories. Progress leading to timely diagnoses and subsequent prevention of central nervous system dysconnectivity now seems plausible. The tendency for an infant to develop autism may currently be determinable and preventable before irreversible psychosocial disturbances become established. These discussions about glial function will be inter-spersed with comments about their apparent relevance to autism. The concluding portion of this presentation will be a detailed review and summation of this diagnosis and prevention proposition.

The Importance of Precision Medicine in Type 2 Diabetes Mellitus (T2DM): From Pharmacogenetic and Pharmacoepigenetic Aspects

BACKGROUND

Type 2 Diabetes Mellitus (T2DM) is a worldwide disorder as the most important challenges of health-care systems. Controlling the normal glycaemia greatly profit long-term prognosis and gives explanation for early, effective, constant, and safe intervention.

MATERIAL AND METHODS

Finding the main genetic and epigenetic profile of T2DM and the exact molecular targets of T2DM medications can shed light on its personalized management. The comprehensive information of T2DM was earned through the genome-wide association study (GWAS) studies. In the current review, we represent the most important candidate genes of T2DM like CAPN10, TCF7L2, PPAR-γ, IRSs, KCNJ11, WFS1, and HNF homeoboxes. Different genetic variations of a candidate gene can predict the efficacy of T2DM personalized strategy medication.

RESULTS

SLCs and AMPK variations are considered for metformin, CYP2C9, KATP channel, CDKAL1, CDKN2A/2B and KCNQ1 for sulphonylureas, OATP1B, and KCNQ1 for repaglinide and the last but not the least ADIPOQ, PPAR-γ, SLC, CYP2C8, and SLCO1B1 for thiazolidinediones response prediction.

CONCLUSION

Taken everything into consideration, there is an extreme need to determine the genetic status of T2DM patients in some known genetic region before planning the medication strategies.

A Missense Mutation in IRS1 is Associated with the Development of Early-Onset Type 2 Diabetes

There could be an overlap of monogenic diabetes and early-onset type 2 diabetes mellitus. Precise diagnosis of early-onset diabetes has proven valuable for understanding the mechanism of diabetes and selecting optimal therapy. The majority of maturity onset diabetes of the young (MODY) pathogenic genes in China is still unknown. In this study, a family with suspected MODY was enrolled. Whole-exome sequencing (WES) was used to analyze the variants of the proband. Variants were filtered according to their frequency, location, functional consequences, and bioinformatics software. Candidate pathogenic variants were validated by Sanger sequencing and tested for cosegregation in other members of the family and nonrelated healthy controls. KEGG (Kyoto Encyclopedia of Genes and Genomes) and PPI (protein-protein interaction) analysis were conducted using the DAVID (Database for Annotation, Visualization, and Integrated Discovery) and the STRING online analysis tools for the candidate pathogenic gene. A total of 123291 variants including 105344 SNPs and 17947 InDels were found in WES. A likely pathogenic rare missense heterozygous mutation in diabetes genes (c.2137C > T, p.His713Tyr in IRS1) was identified, which was a cosegregate in this family and not in nonrelated healthy controls. The position of the mutation in the aminoacid sequence of the gene is highly conserved among the species. 2 significantly enriched KEGG pathways were identified including bta04930, type II diabetes mellitus (GCK, INS, PDX1, ABCC8, and IRS1), and bta04910, insulin signaling pathway (GCK, INS, and IRS1). PPI analysis displayed that IRS1 interacts with 3 known pathogenic proteins including INS, KCNJ11, and GCK. We conclude that WES could be an initial option for genetic testing in patients with early-onset diabetes. IRS1 p.His713Tyr is implicated as a possible pathogenic mutation in monogenic diabetes, which might require further validation, and the precise molecular mechanism underlying the influence of IRS1 p.His713Tyr on the development of diabetes remains to be determined in the further prospective studies.

Molecular and Pathological Events Involved in the Pathogenesis of Diabetes-Associated Nonalcoholic Fatty Liver Disease

Diabetes mellitus is a rising epidemic in most part of the world and is often associated with multiple organ disorders such as kidney, liver, and cardiovascular diseases. Liver is a major metabolic hub, and the metabolic disorders associated with diabetes result in liver dysfunctions culminating in spectrum of liver diseases such as fatty liver disorders, cirrhosis, and hepatocellular carcinoma. The intervention strategies to prevent diabetes-associated liver injury require an overall understanding of the key factors and molecular pathways which can be strategically targeted. The present review focuses on some of the key aspects of fatty acid metabolism, fetuin-A regulation, inflammatory pathways, and genetic factors associated with insulin resistance, dyslipidemia, hyperglycemia, oxidative stress, and so on involved in the nexus between diabetes and liver injury. Further recent interventions, pharmacological target, and newer therapeutic agents are discussed briefly for the better clinical management of diabetes-associated hepatic disorders.

Characterization of Plasma Membrane Localization and Phosphorylation Status of Organic Anion Transporting Polypeptide (OATP) 1B1 c.521 T>C Nonsynonymous Single-Nucleotide Polymorphism

PURPOSE

Membrane transport protein organic anion transporting polypeptide (OATP) 1B1 mediates hepatic uptake of many drugs (e.g. statins). The OATP1B1 c.521 T > C (p. V174A) polymorphism has reduced transport activity. Conflicting in vitro results exist regarding whether V174A-OATP1B1 has reduced plasma membrane localization; no such data has been reported in physiologically relevant human liver tissue. Other potential changes, such as phosphorylation, of the V174A-OATP1B1 protein have not been explored. Current studies characterized the plasma membrane localization of V174A-OATP1B1 in genotyped human liver tissue and cell culture and compared the phosphorylation status of V174A- and wild-type (WT)-OATP1B1.

METHODS

Localization of V174A- and WT-OATP1B1 were determined in OATP1B1 c.521 T > C genotyped human liver tissue (n = 79) by immunohistochemistry and in transporter-overexpressing human embryonic kidney (HEK) 293 and HeLa cells by surface biotinylation and confocal microscopy. Phosphorylation and transport of OATP1B1 was determined using ³²P-orthophosphate labeling and [³H]estradiol-17β-glucuronide accumulation, respectively.

RESULTS

All three methods demonstrated predominant plasma membrane localization of both V174A- and WT-OATP1B1 in human liver tissue and in cell culture. Compared to WT-OATP1B1, the V174A-OATP1B1 has significantly increased phosphorylation and reduced transport.

CONCLUSIONS

We report novel findings of increased phosphorylation, but not impaired membrane localization, in association with the reduced transport function of the V174A-OATP1B1.

The Role of Genetic Polymorphism in the Formation of Arterial Hypertension, Type 2 Diabetes and their Comorbidity

BACKGROUND

Hereditary component plays a significant role in the formation of insulin resistance (IR) - one of the pathogenetic links of arterial hypertension (AH) and type 2 diabetes mellitus (DM2). However, the genetic predisposition to IR can not be realized and does not manifest itself clinically in the absence of appropriate factors of the environment (excessive nutrition, low physical activity, etc.).

OBJECTIVE

The review summarizes the results of studies which describe the contribution of genetic polymorphism to the formation and progression of AH, DM2 and their comorbidity in various populations.

RESULTS

In many studies, it has been established that genetic polymorphism of candidate genes is influenced by the formation, course and complication of AH and DM2. According to research data, the modulating effect of polymorphism of some genetic markers of AH and DM2 on metabolism and hemodynamics has been established. The results of numerous studies have shown a higher frequency of occurrence of AH and DM2, as well as their more severe course with adverse genetic polymorphisms. At the same time, the role of genetic polymorphism in the formation of AH and DM2 differs in different populations.

CONCLUSION

Contradictory data on the influence of gene polymorphisms on the formation of AH and DM2 in different populations, as well as a small number of studies on the combined effects of several polymorphisms on the formation of comorbidity, determine the continuation of research in this direction.

The role of insulin receptor substrate 1 gene polymorphism Gly972Arg as a risk factor for ischemic stroke among Indonesian subjects

OBJECTIVE

The identification of new genetic-associated risk factor of ischemic stroke could improves strategies for stroke prevention. This study aims to identify insulin receptor substrate 1 (IRS-1) gene polymorphism Gly972Arg as the risk factor for ischemic stroke among Indonesian subjects. The case-control study was conducted by matching the gender and race on 85 cases of patients with ischemic stroke and 86 healthy non-stroke control subjects. Ischemic stroke was established by the complete neurology examination and brain computed tomography scan or magnetic resonance imaging. Polymerase chain reaction-Restriction Fragment Length Polymorphism was performed to analyze IRS-1 gene Gly972Arg genotype.

RESULTS

There were 85 ischemic stroke cases and 86 control subjects. The distribution of nucleotide IRS-1 gene polymorphism Gly972Arg in the ischemic stroke vs health controls for GG were 32.2% vs 41.5%, for GR were 16% vs 7.6%, and for RR were 0.5% vs 1.9%. IRS-1 gene polymorphism Gly972Arg was found as significant risk factor for ischemic stroke [odds ratio of 2.6 (1.27-5.27); CI 95%, p = 0.008]. Conclusively, the IRS-1 gene polymorphism Gly972Arg should be considered as an important factor in the prevention and treatment of ischemic stroke.

IRS-1 genetic polymorphism (r.2963G>A) in type 2 diabetes mellitus patients associated with insulin resistance

Background

Insulin receptor substrate (IRS) molecules are key mediators in insulin signaling. Several polymorphisms in the IRS genes have been identified, but only the Gly to Arg 972 substitution of IRS-1 seems to have a pathogenic role in the development of type 2 diabetes mellitus (T2DM). Many polymorphisms described in IRS-1 gene, especially Gly972Arg substitution, are shown to be associated with insulin resistance (IR) in T2DM.

Subjects and methods

This prospective case-control study was performed during the period from November 2014 to May 2015. All patients were selected from the Department of Internal Medicine and were screened for eligibility for this study. Subjects were divided into two groups: first group consisted of 100 T2DM patients; second group consisted of 120 nondiabetic controls. First group was further divided into two subgroups: 66 IR patients and 34 insulin-sensitive (IS) patients (homeostatic model assessment [HOMA] was performed). Restriction fragment length polymorphism (RFLP) was performed using specific primers for scanning single-nucleotide polymorphisms (SNPs) such as Gly972Arg (rs1801278 SNP).

Results

Taking GG genotype and G allele as references, GA, GA+AA genotypes and A allele showed significantly higher frequency in the T2DM group when compared to the control group, with higher risk to develop T2DM in healthy controls. Taking GG as a reference, rs1801278GA+AA genotype and A allele showed significantly higher proportion in IR when compared to IS, with higher risk to develop IR in T2DM patients. Logistic regression analysis showed that higher FBG, fasting plasma insulin (FPI), HOMA-IR, GA+AA genotypes were associated with higher risk to develop IR in univariable analysis.

Conclusion

IRS-1 genetic factor may be a significant genetic determinant for IR in T2DM patients during severe/acute-phase hyperglycemia.

Risk Factors for the Development of Nonalcoholic Fatty Liver Disease/Nonalcoholic Steatohepatitis, Including Genetics

Nonalcoholic fatty liver disease is emerging as the most common cause of chronic liver disease worldwide. This trend is, in part, secondary, to the growing incidence of obesity, type 2 diabetes, and metabolic syndrome. Other risk factors include age, gender, race/ethnicity, genetic predisposition, and polycystic ovarian disease. With the introduction of genome-wide association studies, genetic mutations contributing to inherited susceptibility to steatosis have been identified, which hold keys to future improvement in diagnosis and management. This article expands on the aforementioned risk factors and summarizes the current available data on genetic and environmental factors associated with this common entity.

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.

Genetic factors that affect nonalcoholic fatty liver disease: A systematic clinical review

AIM: To investigate roles of genetic polymorphisms in non-alcoholic fatty liver disease (NAFLD) onset, severity, and outcome through systematic literature review.

METHODS: The authors conducted both systematic and specific searches of PubMed through December 2015 with special emphasis on more recent data (from 2012 onward) while still drawing from more historical data for background. We identified several specific genetic polymorphisms that have been most researched and, at this time, appear to have the greatest clinical significance on NAFLD and similar hepatic diseases. These were further investigated to assess their specific effects on disease onset and progression and the mechanisms by which these effects occur.

RESULTS: We focus particularly on genetic polymorphisms of the following genes: PNPLA3, particularly the p. I148M variant, TM6SF2, particularly the p. E167K variant, and on variants in FTO, LIPA, IFNλ4, and iron metabolism, specifically focusing on HFE, and HMOX-1. We discuss the effect of these genetic variations and their resultant protein variants on the onset of fatty liver disease and its severity, including the effect on likelihood of progression to cirrhosis and hepatocellular carcinoma. While our principal focus is on NAFLD, we also discuss briefly effects of some of the variants on development and severity of other hepatic diseases, including hepatitis C and alcoholic liver disease. These results are briefly discussed in terms of clinical application and future potential for personalized medicine.

CONCLUSION: Polymorphisms and genetic factors of several genes contribute to NAFLD and its end results. These genes hold keys to future improvements in diagnosis and management.

Genetic Factors That Affect Risk of Alcoholic and Nonalcoholic Fatty Liver Disease

Genome-wide association studies and candidate gene studies have informed our understanding of factors contributing to the well-recognized interindividual variation in the progression and outcomes of alcoholic liver disease and nonalcoholic fatty liver disease. We discuss the mounting evidence for shared modifiers and common pathophysiological processes that contribute to development of both diseases. We discuss the functions of proteins encoded by risk variants of genes including patatin-like phospholipase domain-containing 3 and transmembrane 6 superfamily member 2, as well as epigenetic factors that contribute to the pathogenesis of alcoholic liver disease and nonalcoholic fatty liver disease. We also discuss important areas of future genetic research and their potential to affect clinical management of patients.

Lack of association between the insulin receptor substrates-1 Gly972Arg polymorphism and type-2 diabetes mellitus among Saudis from Eastern Saudi Arabia

Objectives:

To investigate the association between the insulin receptor substrate-1 (IRS1) Gly972Arg polymorphism and type-2 diabetes mellitus (T2DM) among Saudis from Eastern Saudi Arabia.

Methods:

This study was conducted between May and December 2014 at King Fahad Hospital of the University, Al-Khobar, Kingdom of Saudi Arabia. In a case-control study design, a total of 143 subjects (age range: 35-73 years) comprising 74 healthy controls and 69 patients with T2DM were examined. Blood samples were collected from subjects and subjected to genomic DNA extraction and chemical analysis. The IRS1 Gly972Arg polymorphism was then genotyped using the standard polymerase chain reaction-restriction fragment length polymorphism technique.

Results:

Eight out of 74 (10.8%) of the control group carried at least one copy of the mutated allele. The frequency (8.7%) of the IRS1 variant was also found in the diabetic group. Logistic regression analysis showed an adjusted odds ratio of 1.04, 95% confidence interval 0.28 - 3.95, and a p-value of 0.94.

Conclusion:

We failed to find any association between the IRS1 Gly972Arg polymorphism and T2DM.

Genetic background in nonalcoholic fatty liver disease: A comprehensive review

In the Western world, nonalcoholic fatty liver disease (NAFLD) is considered as one of the most significant liver diseases of the twenty-first century. Its development is certainly driven by environmental factors, but it is also regulated by genetic background. The role of heritability has been widely demonstrated by several epidemiological, familial, and twin studies and case series, and likely reflects the wide inter-individual and inter-ethnic genetic variability in systemic metabolism and wound healing response processes. Consistent with this idea, genome-wide association studies have clearly identified Patatin-like phosholipase domain-containing 3 gene variant I148M as a major player in the development and progression of NAFLD. More recently, the transmembrane 6 superfamily member 2 E167K variant emerged as a relevant contributor in both NAFLD pathogenesis and cardiovascular outcomes. Furthermore, numerous case-control studies have been performed to elucidate the potential role of candidate genes in the pathogenesis and progression of fatty liver, although findings are sometimes contradictory. Accordingly, we performed a comprehensive literature search and review on the role of genetics in NAFLD. We emphasize the strengths and weaknesses of the available literature and outline the putative role of each genetic variant in influencing susceptibility and/or progression of the disease.

Central obesity, type 2 diabetes and insulin: exploring a pathway full of thorns

The prevalence of type 2 diabetes (T2D) is rapidly increasing. This is strongly related to the contemporary lifestyle changes that have resulted in increased rates of overweight individuals and obesity. Central (intra-abdominal) obesity is observed in the majority of patients with T2D. It is associated with insulin resistance, mainly at the level of skeletal muscle, adipose tissue and liver. The discovery of macrophage infiltration in the abdominal adipose tissue and the unbalanced production of adipocyte cytokines (adipokines) was an essential step towards novel research perspectives for a better understanding of the molecular mechanisms governing the development of insulin resistance. Furthermore, in an obese state, the increased cellular uptake of non-esterified fatty acids is exacerbated without any subsequent β-oxidation. This in turn contributes to the accumulation of intermediate lipid metabolites that cause defects in the insulin signaling pathway. This paper examines the possible cellular mechanisms that connect central obesity with defects in the insulin pathway. It discusses the discrepancies observed from studies organized in cell cultures, animal models and humans. Finally, it emphasizes the need for therapeutic strategies in order to achieve weight reduction in overweight and obese patients with T2D.

A rare co-segregation-mutation in the insulin receptor substrate 1 gene in one Chinese family with ankylosing spondylitis

Ankylosing spondylitis (AS; MIM 106300) is a common rheumatic disease with strong genetic components affecting approximately 0.3% of the population. The exact genetic mechanism of AS remains elusive. Our previous study showed that AS could be transmitted in an autosomal dominant inheritance mode and a 6-cM candidate region located on the chromosome 2q36.1-36.3 was mapped in a Chinese family. Mutation screening was conducted within the candidate region in the family and other AS by sequencing, and the novel mutation will be further validated in other AS families, sporadic cases and healthy controls by mass spectrometry. We identified a rare non-synonymous mutation (Arg580Gly) in insulin receptor substrate 1 (IRS1) co-segregated with disease phenotype in patients of the family, which was not found in other AS families, sporadic patients and healthy controls. In the study, we found a rare non-synonymous mutation in IRS1 co-segregation in one Chinese family with AS, which indicated a new candidate disease causative gene for AS.

IRS1 gene polymorphisms Gly972Arg and Ala513Pro are not associated with insulin resistance and type 2 diabetes risk in non-obese Turkish population

Insulin receptor substrate 1 (IRS1), plays a critical role in insulin signaling and its control has an important place in the development of insulin resistance. The tyrosine phosphorylation of IRS1 serves as docking molecules for downstream effectors such as Phosphatidylinositol 3-kinase and phosphotyrosine phosphatase-2. We focused on the Gly972Arg and Ala513Pro variants of the IRS1 gene, since these specific allelic variants are located near the Tyr-Met-X-Met (YMXM) motifs around Tyr987 and Tyr612. Thus, we aimed to investigate the effects of Gly972Arg/Ala513Pro polymorphisms in IRS1 gene on development of insulin resistance and the risk of type 2 diabetes in a non-obese Turkish population. This work included 306 individuals comprising 178 subjects with type 2 diabetes and 128 healthy subjects matched for body mass index. Gly972Arg/Ala513Pro polymorphisms had no effect on type 2 diabetes risk and its phenotypes (P > 0.05). Although IRS1 gene and its variants are associated with type 2 diabetes and insulin resistance in several studies worldwide, our data showed that there is no association between Gly972Arg and Ala513Pro variants in IRS1 and disease in Turkish population.

Genetic predisposition in NAFLD and NASH: impact on severity of liver disease and response to treatment

Liver fat deposition related to systemic insulin resistance defines non-alcoholic fatty liver disease (NAFLD) which, when associated with oxidative hepatocellular damage, inflammation, and activation of fibrogenesis, i.e. non-alcoholic steatohepatitis (NASH), can progress towards cirrhosis and hepatocellular carcinoma. Due to the epidemic of obesity, NAFLD is now the most frequent liver disease and the leading cause of altered liver enzymes in Western countries. Epidemiological, familial, and twin studies provide evidence for an element of heritability of NAFLD. Genetic modifiers of disease severity and progression have been identified through genome-wide association studies. These include the Patatin-like phosholipase domain-containing 3 (PNPLA3) gene variant I148M as a major determinant of inter-individual and ethnicity-related differences in hepatic fat content independent of insulin resistance and serum lipid concentration. Association studies confirm that the I148M polymorphism is also a strong modifier of NASH and progressive hepatic injury. Furthermore, a few large multicentre case-control studies have demonstrated a role for genetic variants implicated in insulin signalling, oxidative stress, and fibrogenesis in the progression of NAFLD towards fibrosing NASH, and confirm that hepatocellular fat accumulation and insulin resistance are key operative mechanisms closely involved in the progression of liver damage. It is now important to explore the molecular mechanisms underlying these associations between gene variants and progressive liver disease, and to evaluate their impact on the response to available therapies. It is hoped that this knowledge will offer further insights into pathogenesis, suggest novel therapeutic targets, and could help guide physicians towards individualised therapy that improves clinical outcome.

Metabolic syndrome and insulin resistance: underlying causes and modification by exercise training

Metabolic syndrome (MS) is a collection of cardiometabolic risk factors that includes obesity, insulin resistance, hypertension, and dyslipidemia. Although there has been significant debate regarding the criteria and concept of the syndrome, this clustering of risk factors is unequivocally linked to an increased risk of developing type 2 diabetes and cardiovascular disease. Regardless of the true definition, based on current population estimates, nearly 100 million have MS. It is often characterized by insulin resistance, which some have suggested is a major underpinning link between physical inactivity and MS. The purpose of this review is to: (i) provide an overview of the history, causes and clinical aspects of MS, (ii) review the molecular mechanisms of insulin action and the causes of insulin resistance, and (iii) discuss the epidemiological and intervention data on the effects of exercise on MS and insulin sensitivity.

PKA and GAB2 play central roles in the FSH signaling pathway to PI3K and AKT in ovarian granulosa cells

Controlled maturation of ovarian follicles is necessary for fertility. Follicles are restrained at an immature stage until stimulated by FSH secreted by pituitary gonadotropes. FSH acts on granulosa cells within the immature follicle to inhibit apoptosis, promote proliferation, stimulate production of steroid and protein hormones, and induce ligand receptors and signaling intermediates. The phosphoinositide 3-kinase (PI3K)/AKT (protein kinase B) pathway is a pivotal signaling corridor necessary for transducing the FSH signal. We report that protein kinase A (PKA) mediates the actions of FSH by signaling through multiple targets to activate PI3K/AKT. PKA uses a route that promotes phosphorylation of insulin receptor substrate-1 (IRS-1) on Tyr(989), a canonical binding site for the 85-kDa regulatory subunit of PI3K that allosterically activates the catalytic subunit. PI3K activation leads to activation of AKT through phosphorylation of AKT on Thr(308) and Ser(473). The adaptor growth factor receptor bound protein 2-associated binding protein 2 (GAB2) is present in a preformed complex with PI3K heterodimer and IRS-1, it is an A-kinase anchoring protein that binds the type I regulatory subunit of PKA, and it is phosphorylated by PKA on Ser(159). Overexpression of GAB2 enhances FSH-stimulated AKT phosphorylation. GAB2, thus, seems to coordinate signals from the FSH-stimulated rise in cAMP that leads to activation of PI3K/AKT. The ability of PKA to commandeer IRS-1 and GAB2, adaptors that normally integrate receptor/nonreceptor tyrosine kinase signaling into PI3K/AKT, reveals a previously unrecognized route for PKA to activate a pathway that promotes proliferation, inhibits apoptosis, enhances translation, and initiates differentiation of granulosa cells.

Regulation of insulin sensitivity by serine/threonine phosphorylation of insulin receptor substrate proteins IRS1 and IRS2

The insulin receptor substrate proteins IRS1 and IRS2 are key targets of the insulin receptor tyrosine kinase and are required for hormonal control of metabolism. Tissues from insulin-resistant and diabetic humans exhibit defects in IRS-dependent signalling, implicating their dysregulation in the initiation and progression of metabolic disease. However, IRS1 and IRS2 are regulated through a complex mechanism involving phosphorylation of >50 serine/threonine residues (S/T) within their long, unstructured tail regions. In cultured cells, insulin-stimulated kinases (including atypical PKC, AKT, SIK2, mTOR, S6K1, ERK1/2 and ROCK1) mediate feedback (autologous) S/T phosphorylation of IRS, with both positive and negative effects on insulin sensitivity. Additionally, insulin-independent (heterologous) kinases can phosphorylate IRS1/2 under basal conditions (AMPK, GSK3) or in response to sympathetic activation and lipid/inflammatory mediators, which are present at elevated levels in metabolic disease (GRK2, novel and conventional PKCs, JNK, IKKβ, mPLK). An emerging view is that the positive/negative regulation of IRS by autologous pathways is subverted/co-opted in disease by increased basal and other temporally inappropriate S/T phosphorylation. Compensatory hyperinsulinaemia may contribute strongly to this dysregulation. Here, we examine the links between altered patterns of IRS S/T phosphorylation and the emergence of insulin resistance and diabetes.

The Gly(972)Arg variant of human IRS1 gene is associated with variation in glomerular filtration rate likely through impaired insulin receptor signaling

The objective of this study is to identify and characterize the genetic variants related to the glomerular filtration rate (GFR) linkage on 2q37. Of the positional candidate genes, we selected IRS1 and resequenced its 2-kb promoter region and exons for sequence variants in 32 subjects. A total of 11 single nucleotide polymorphisms (SNPs) were identified. To comprehensively cover the 59-kb-long intron-1, eight additional tagging SNPs were selected from the HapMap. All the 19 SNPs were genotyped by TaqMan Assay in the entire data set (N = 670; 39 families). Association analyses between the SNPs and GFR and type 2 diabetes-related traits were performed using the measured genotype approach. Of the SNPs examined for association, only the Gly(972)Arg variant of IRS1 exhibited a significant association with GFR (P = 0.0006) and serum triglycerides levels (P = 0.003), after accounting for trait-specific covariate effects. Carriers of Arg972 had significantly decreased GFR values. Gly(972)Arg contributed to 26% of the linkage signal on 2q. Expression of IRS1 mutant Arg972 in human mesangial cells significantly reduced the insulin-stimulated phosphorylation of IRS1 and Akt kinase. Taken together, the data provide the first evidence that genetic variation in IRS1 may influence variation in GFR probably through impaired insulin receptor signaling.

Optimisation of glycaemic control during episodes of severe/acute hyperglycaemia in patients with type 2 diabetes mellitus

BACKGROUND

Patients with type 2 diabetes mellitus (T2DM) are frequently admitted to the hospital with severe or acute hyperglycaemia secondary to an acute illness or disease. Uncontrolled glycaemia is a significant problem during severe or acute hyperglycaemia.

OBJECTIVE

This study sought to identify demographic, clinical, and genetic factors that may contribute to increased insulin resistance or worsening of glycaemic control in patients with T2DM.

SETTING

This prospective cohort study included 156 patients with T2DM and severe or acute hyperglycaemia who were treated with insulin at any medical ward of the National University of Malaysia Medical Centre.

METHOD

Insulin resistance was determined using the homeostatic model assessment-insulin resistance index. Glycaemic control during the episode of hyperglycaemia was assessed as the degree to which the patient achieved the target glucose levels. The polymerase chain reaction-restriction fragment length polymorphism method was used to identify polymorphisms in insulin receptor substrate (IRS) genes.

MAIN OUTCOME MEASURE

Identification of possible predictors (demographic, clinical, or genetic) for insulin resistance and glycaemic control during severe/acute hyperglycaemia.

RESULTS

A polymorphism in IRS1, r.2963 G>A (p.Gly972Arg), was a significant predictor of both insulin resistance [odds ratios (OR) 4.48; 95 % confidence interval (CI) 1.2-16.7; P = 0.03) and worsening of glycaemic control (OR 6.04; 95 % CI 0.6-64.6; P = 0.02). The use of loop diuretics (P < 0.05) and antibiotics (P < 0.05) may indirectly predict worsening of insulin resistance or glycaemic control in patients with severe/acute hyperglycaemia.

CONCLUSION

Clinical and genetic factors contribute to worsening of insulin resistance and glycaemic control during severe/acute hyperglycaemia in patients with T2DM. Early identification of factors that may influence insulin resistance and glycaemic control may help to achieve optimal glycaemic control during severe/acute hyperglycaemia.

Effect of genetic polymorphisms on the development of secondary failure to sulfonylurea in egyptian patients with type 2 diabetes

OBJECTIVE

This study investigated the possibility that genetic factors, such as polymorphism of K inward rectifier subunit (Kir6.2), E23K, and Arg(972) polymorphism of insulin receptor sub-strate-1 (IRS-1), may predispose patients to sulfonylurea failure.

METHODS

A total of 100 unrelated Egyptian patients with type 2 diabetes were recruited. They were divided into two equal groups: group I consisted of patients with secondary failure to sulfonylurea (hemoglobin A(1c) ≥ 8% despite sulfonylurea therapy) while group II consisted of patients whose condition was controlled with oral therapy.

RESULTS

Of all the patients, 45% and 14% were carriers of the K allele and Arg(972) variants respectively. The frequency of the K allele was 34% among patients with diabetes that was controlled with oral therapy and 56% among patients with secondary failure to sulfonylurea. The frequency of the Arg(972) IRS-1 variant was 6% among patients with diabetes controlled with oral therapy and 22% among patients with secondary failure.

CONCLUSION

The E23K variant of the Kir6.2 gene and Arg(972) IRS-1 variants are associated with increased risk for secondary failure to sulfonylurea.

Association study of IRS1 gene polymorphisms with type 2 diabetes in south Indians

BACKGROUND AND OBJECTIVES

The insulin receptor substrate-1 (IRS1) gene is a candidate gene for type 2 diabetes. The aim of this study was to investigate the association of the IRS1 gene polymorphisms Gly972Arg and Ala513Pro with type 2 diabetes in an Asian Indian population in south India.

METHODS

A total of 2,148 subjects (1,187 normal glucose-tolerant [NGT] and 961 type 2 diabetes subjects) were randomly selected from the Chennai Urban Rural Epidemiology Study. The IRS1 gene polymorphisms Gly972Arg and Ala513Pro were genotyped in these subjects using polymerase chain reaction-restriction fragment length polymorphism, and a few variants were confirmed by direct sequencing.

RESULTS

The frequency of the "A" allele of the Gly972Arg(G→A) single nucleotide polymorphism was similar between the NGT and diabetes subjects (2%). There was no significant difference in the genotypic frequency between the NGT and type 2 diabetes group (P = 0.25). When the study subjects were stratified based on body mass index (BMI) as per World Health Organization Asia Pacific guidelines as nonobese (BMI <25 kg/m(2)) and obese (BMI ≥25 kg/m(2)), neither the allelic frequency (nonobese, P = 0.44; obese, P = 0.37) nor the genotypic frequency (nonobese, P = 0.29; obese, P = 0.35) was significantly different between the NGT and type 2 diabetes groups. The Ala513Pro polymorphism was first genotyped in 500 NGT and 500 type 2 diabetes subjects. None of these subjects carried the Ala513Pro or the Pro513Pro genotype. Hence, the Ala513Pro polymorphism was not genotyped further.

CONCLUSION

The IRS1 gene variants Gly972Arg and Ala513Pro are not associated with type 2 diabetes in this south Indian population.

Predisposition for borderline personality disorder with comorbid major depression is associated with that for polycystic ovary syndrome in female Japanese population

Polycystic ovary syndrome (PCOS) is a common lifestyle-related endocrinopathy in women of reproductive age and is associated with several mental health problems. We examined the genotypic distributions of IRS-1 Gly972Arg and CYP11B2 -344T/C, which were previously described as influencing PCOS, and assayed the serum levels of interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-α), in a set of female patients with borderline personality disorder (BPD) with comorbid major depressive disorder (MDD) (n = 50) and age-matched control subjects (n = 100), to investigate the predisposition for BPD with MDD. The results showed that the patients were more frequently IRS-1 972Arg variant allele carriers (P = 0.013; OR 6.68; 95% CI = 1.30-34.43) and homozygous for the CYP11B2 -344C variant allele (P = 0.022; OR = 3.32; 95% CI = 1.18-9.35) than the control subjects. The IL-6 level was significantly higher in the patients than in the controls (P < 0.0001). There was no significant difference in the serum TNF-α level between patients with BPD with MDD and the healthy comparison group (P = 0.5273). In conclusion, the predisposition for BPD with MDD is associated with that for PCOS, in the female Japanese population. An elevated serum IL-6 level is considered to be a possible biomarker of BPD with MDD.

Insulin-like growth factor axis gene polymorphisms and clinical outcomes in pancreatic cancer

BACKGROUND & AIMS

Insulin-like growth factor (IGF)-axis mediated signaling pathways play an important role in pancreatic cancer development and progression. We examined whether IGF-axis gene variants are associated with clinical outcomes in pancreatic cancer.

METHODS

We retrospectively genotyped 41 single-nucleotide polymorphisms from 10 IGF-axis genes in 333 patients with localized pancreatic adenocarcinoma and validated the findings in 373 patients with advanced disease. Associations between genotype and overall survival (OS) were evaluated using multivariable Cox proportional hazard regression models.

RESULTS

IGF1 *8470T>C, IGF1R IVS2+46329T>C, IGFBP3 A32G, IRS1 G972R in patients with localized disease; IGF1R IVS20-3431A>G, IGF1R T766T, IGFBP3-202A>C, IRS1 IVS1+4315C>G, IRS1 G972R in patients with advanced disease; and IGF1R T766T, IGF2R L252V, IGFBP3 -202A>C, IRS1 IVS1+4315C>G, IRS1 G972R, IRS2 IVS1+5687T>C in all patients were significantly associated with OS (P<or=.007). Two haplotypes containing the variant allele of either IRS1 G972R or IVS1-10949G>A, and an IRS2 haplotype predicted worse OS (P<or=.002). A significant correlation between increased number of unfavorable genotypes and decreased OS was observed; patients with 0-1 (n=247), 2 (n=237), 3 (n=145), 4 (n=60), and 5-8 (n=17) unfavorable genotypes had median survival time of 24.2, 16.4, 14.4, 9.6, and 7.4 months, respectively (P<.001). Several single-nucleotide polymorphisms of IGF1R, IGF2R, and IRS1 gene were significantly associated with tumor response to therapy and disease stage.

CONCLUSIONS

These data suggest that individual genetic variations in the IGF axis pathway may predict worse survival in patients with pancreatic cancer. This information may identify population subgroups that could benefit from IGF(1)R-targeted agents.

Polymorphisms of the insulin receptor and the insulin receptor substrates genes in polycystic ovary syndrome: a Mendelian randomization meta-analysis

Polycystic ovary syndrome (PCOS) is a heterogeneous condition with unknown aetiology which is considered to be the most common endocrine disorder in women of reproductive age. In this work we investigated the association of insulin receptor (IotaNSR) and insulin receptor substrates (IRSs) polymorphisms with the risk of developing PCOS. The meta-analysis of eleven studies (889 cases, 1303 controls) yielded a significant association for IRS-1 Gly972Arg (G972R) polymorphism concerning the GR vs. GG genotype (OR: 1.77, 95% CI: 1.28, 2.45), with no between-studies heterogeneity. Concerning IotaNSR His1058 C/T, the meta-analysis of eight studies (795 cases, 576 controls) found no significant evidence for association with PCOS (OR for the TT+CT vs. CC comparison equal to 1.28 with 95% CI: 0.88, 1.85) and a moderate between studies variability (I(2)=44.6%). No evidence for publication bias was found in these meta-analyses. Following a multivariate Mendelian randomization approach, the overall OR was unaffected but the overall mean difference of fasting insulin levels between carriers of GR and RR genotypes in controls was significant (2.18, 95% CI: 0.36, 4.01). These results suggest that IRS-1 Gly972Arg polymorphism is significantly associated with the risk of developing PCOS and that this association is primarily mediated by increasing the levels of fasting insulin. The particular polymorphism is located in a region nearby two phosphorylation sites that interact physically with INSR and PI 3-kinase and there is enough evidence from the literature suggesting that the Arg972 variant is associated with decreased PI 3-kinase activity and impaired insulin-stimulated signaling.

Association of Gly972Arg polymorphism of IRS1 gene with type 2 diabetes mellitus in lean participants of a national health survey in Mexico: a candidate gene study

Type 2 diabetes mellitus (T2D) is a main public health problem in the Mexican population. It is characterized by insulin resistance in peripheral tissues and a relative deficiency in the pancreatic beta-cell functions. Diverse single nucleotide polymorphisms (SNPs) of the IRS1 gene have been associated with insulin resistance and T2D risk. The aim of this study was to identify the association between known IRS1 polymorphisms (Pro512Ala, Asn1137Asp, Gly972Arg, and Arg158Pro) in a sample of diabetic patients compared with healthy controls selected from Mexico's 2000 National Health Survey, both with normal body mass index (BMI). We identified 444 diabetes cases that were age matched with the same number of controls. Genotypic and allelic frequencies were evaluated, and conditional logistic regression was used to evaluate the association between the SNPs and diabetes risk. Of the 4 SNPs studied, only Gly972Arg showed significant differences between cases and controls, with allele frequency of 2.6% in controls as compared with 7.9% in cases. Subjects with at least 1 copy of the Gly972Arg polymorphism of the IRS1 gene showed a greater risk for diabetes, with a crude odds ratio of 3.26 (95% confidence interval, 2.00-5.33); after adjusting for BMI, age, family history of T2D, and sex, the odds ratio was 2.91 (95% confidence interval, 1.73-4.90). Our results suggest the participation of Gly972Arg polymorphism of IRS1 in the genetic susceptibility to TD2 in Mexican population. The restriction of including only participants with normal BMI might increase the power to detect genetic determinants of T2D.

O-linked N-acetylglucosamine modification of insulin receptor substrate-1 occurs in close proximity to multiple SH2 domain binding motifs

Insulin receptor substrate-1 (IRS-1) is a highly phosphorylated adaptor protein critical to insulin and IGF-1 receptor signaling. Ser/Thr kinases impact the metabolic and mitogenic effects elicited by insulin and IGF-1 through feedback and feed forward regulation at the level of IRS-1. Ser/Thr residues of IRS-1 are also O-GlcNAc-modified, which may influence the phosphorylation status of the protein. To facilitate the understanding of the functional effects of O-GlcNAc modification on IRS-1-mediated signaling, we identified the sites of O-GlcNAc modification of rat and human IRS-1. Tandem mass spectrometric analysis of IRS-1, exogenously expressed in HEK293 cells, revealed that the C terminus, which is rich in docking sites for SH2 domain-containing proteins, was O-GlcNAc-modified at multiple residues. Rat IRS-1 was O-GlcNAc-modified at Ser(914), Ser(1009), Ser(1036), and Ser(1041). Human IRS-1 was O-GlcNAc-modified at Ser(984) or Ser(985), at Ser(1011), and possibly at multiple sites within residues 1025-1045. O-GlcNAc modification at a conserved residue in rat (Ser(1009)) and human (Ser(1011)) IRS-1 is adjacent to a putative binding motif for the N-terminal SH2 domains of p85alpha and p85beta regulatory subunits of phosphatidylinositol 3-kinase and the tyrosine phosphatase SHP2 (PTPN11). Immunoblot analysis using an antibody generated against human IRS-1 Ser(1011) GlcNAc further confirmed the site of attachment and the identity of the +203.2-Da mass shift as beta-N-acetylglucosamine. The accumulation of IRS-1 Ser(1011) GlcNAc in HEPG2 liver cells and MC3T3-E1 preosteoblasts upon inhibition of O-GlcNAcase indicates that O-GlcNAcylation of endogenously expressed IRS-1 is a dynamic process that occurs at normal glucose concentrations (5 mm). O-GlcNAc modification did not occur at any known or newly identified Ser/Thr phosphorylation sites and in most cases occurred simultaneously with phosphorylation of nearby residues. These findings suggest that O-GlcNAc modification represents an additional layer of posttranslational regulation that may impact the specificity of effects elicited by insulin and IGF-1.

Genetic variants associated with insulin resistance and metabolic syndrome in young Asian Indians with myocardial infarction

BACKGROUND

The objective of this study was to assess whether an association exists between the metabolic syndrome and polymorphisms in genes involved in insulin resistance in young Asian Indian patients presenting with acute myocardial infarction (AMI).

METHODS

The study population comprised 467 patients who were 45 years or younger. The National Cholesterol Education Program Adult Treatment Panel III (NCEP ATP III) and the International Diabetes Federation (IDF) definitions were used to assess the prevalence of metabolic syndrome. We examined the genotype and allele frequencies of the IRS-I G972R, PPAR-gamma P12A, KCNJ11 E23K, and TNF-alpha -308G/A polymorphisms in relation to the metabolic syndrome determined by both definitions.

RESULTS

The metabolic syndrome as defined by the NCEP ATP III criteria was found in 282 (60.4%) patients, and in 278 (59.5%) patients according to the IDF criteria. This gave only a moderate level of agreement of 79% between the two definitions (Cohen's kappa = 0.554). No association was found between the IRS-I G972R, PPAR-gamma P12A, and KCNJ11 E23K, or TNF-alpha -308G/A polymorphic variants and the metabolic syndrome, or its components, for either definition.

CONCLUSION

Although the metabolic syndrome is a common finding in young Asian Indian patients with AMI, there was only a moderate level of agreement between the NCEP ATP III and IDF definitions of the syndrome. Our findings do not support a role for any of the polymorphic variant alleles in the four insulin resistance-related genes examined in the etiology of insulin resistance and reinforces the notion of a multifactorial etiology for the metabolic syndrome.

Insulin receptor substrates (IRSs) and breast tumorigenesis

Insulin receptor substrate (IRS)-1 and IRS-2 are adaptor proteins in the insulin-like growth factor I (IGF-I)/IGF-I receptor (IGF-IR) pathway that mediate cell proliferation, migration, and survival. In addition to their role as scaffolding proteins in the cytoplasm, they are able to translocate into the nucleus and regulate gene transcription. IRS levels are developmentally and hormonally regulated in the normal mammary gland and both are essential for normal mammary gland bud formation and lactation. Both IRS-1 and IRS-2 are transforming oncogenes, and induce transformation and metastasis in vitro and in vivo. In breast cancer IRSs have unique functions, with IRS-1 being mainly involved in cell proliferation and survival, whereas IRS-2 has clear roles in cell migration and metastasis. In this review we will discuss the roles of IRSs in mammary gland development and breast cancer.

The genetics of gestational diabetes mellitus: evidence for relationship with type 2 diabetes mellitus

Gestational diabetes is a major public health problem because of its prevalence, its associated complications during pregnancy, and its increased risk for type 2 diabetes later in life. Insulin resistance is one of many physiological changes occurring during pregnancy, and when insulin resistance is accompanied by pancreatic beta-cell insufficiency, gestational diabetes may develop. Several lines of evidence suggest that gestational diabetes shares a common etiology with type 2 diabetes and support the hypothesis that gestational diabetes serves as a window to reveal a predisposition to type 2 diabetes. Pregnancy is an environmental stressor that may catalyze the progression to a diabetic state in genetically predisposed women; therefore, identification of these women during pregnancy could decrease the occurrence of type 2 diabetes through targeted prevention. This review presents an overview of the genetics of gestational diabetes, focusing on human association studies with candidate genes common to both type 2 diabetes and gestational diabetes.

Vascular risk factors in South Asians

South Asians originate from the Indian sub-continent (India, Pakistan, Bangladesh, Sri Lanka and Nepal) and represent one fifth of the world's population. Several studies suggested that South Asians have an increased risk of developing coronary heart disease (CHD) when compared with European populations. We review the role of traditional and emerging risk factors in the increased CHD risk in South Asians. The high prevalence of insulin resistance and type 2 diabetes mellitus in South Asians may be a major cause for their elevated vascular risk. However, other established and emerging risk factors are also overrepresented in South Asians. Large-scale prospective studies could determine the relative contribution of established and emerging vascular risk factors in South Asians. There is an urgent need for trials in South Asians that will evaluate clinical outcomes following treatment of these risk factors.

Transgenic mice overexpressing human G972R IRS-1 show impaired insulin action and insulin secretion

Molecular scanning of human insulin receptor substrate (Irs) genes revealed a single lrs1 prevalent variant, a glycine to arginine change at codon 972 (G972R); previous in vitro studies had demonstrated that the presence of this variant results in an impaired activation of the insulin signalling pathway, while human studies gave controversial results regarding its role in the pathogenesis of insulin resistance and related diseases. To address in vivo impact of this IRS-1 variant on whole body glucose homeostasis and insulin signalling, we have generated transgenic mice overexpressing it (Tg972) and evaluated insulin action in the liver, skeletal muscle and adipose tissue and assessed glucose homeostasis both under a normal diet and a high-fat diet. We found that Tg972 mice developed age-related glucose and insulin intolerance and hyperglycaemia, with insulin levels comparatively low. Glucose utilization and insulin signalling were impaired in all key insulin target tissues in Tg972 mice. There were no differences in pancreatic morphology between Tg972 and wild-type mice, however when insulin secretion was evaluated in isolated islets, it was significantly reduced in Tg972 mice islets at any glucose concentration tested. Under a high-fat diet, Tg972 mice had increased body and adipose tissue weight, and were more prone to develop diet-induced glucose and insulin intolerance. So, we believe that Tg972 mice may represent a useful model to elucidate the interaction between genetic and environmental factors in insulin resistance pathogenesis. Furthermore, they may become an important tool to test novel tailored therapies.

Dietary fat, genes and insulin sensitivity

Both insulin resistance and dyslipidaemia are determined by genetic and environmental factors. Depending on their expression and their function, gene variants may influence either insulin action or dyslipidaemia. The purpose of this review was to give some examples from recent studies of gene variants that influence insulin signalling and the interaction between gene and diet to predispose insulin resistance. Recent findings indicate a major role for genetic susceptibility to the insulin resistance syndrome. Nutrition also plays an important role in the development and progression of the condition. Genetic background may interact with habitual dietary fat composition, affecting predisposition to the insulin resistance syndrome and individual responsiveness to changes in dietary fat intake. Due to the complex nature of gene-environment interactions, therefore, therapeutic dietary therapy may require a 'personalized' nutrition approach in the future. Although results have not always been consistent, gene variants that affect primary insulin action or dyslipidaemia, and particularly their interaction with the environment, are important modulators of glucose metabolism and insulin resistance syndrome.

The cerebrocortical response to hyperinsulinemia is reduced in overweight humans: a magnetoencephalographic study

Animal studies have shown that the brain is an insulin-responsive organ and that central nervous insulin resistance induces obesity and disturbances in glucose metabolism. In humans, insulin effects in the brain are poorly characterized. We used a magnetoencephalography approach during a two-step hyperinsulinemic euglycemic clamp to (i) assess cerebrocortical insulin effects in humans, (ii) compare these effects between 10 lean and 15 obese subjects, and (iii) test whether the insulin receptor substrate (IRS)-1 Gly972Arg polymorphism in the insulin-signaling cascade modifies these effects. Both spontaneous and stimulated (mismatch negativity) cortical activity were assessed. In lean humans, stimulated cortical activity (P = 0.046) and the beta and theta band of spontaneous cortical activity (P = 0.01 and 0.04) increased with insulin infusion relative to saline. In obese humans, these effects were suppressed. Moreover, the insulin effect on spontaneous cortical activity correlated negatively with body mass index and percent body fat (all r < -0.4; all P < 0.05) and positively with insulin sensitivity of glucose disposal (theta band, r = 0.48, P = 0.017). Furthermore, insulin increased spontaneous cortical activity (beta band) in carriers of wild-type IRS-1, whereas, in carriers of the 972Arg allele, this insulin effect was absent (P = 0.01). We conclude that, in lean humans, insulin modulates cerebrocortical activity, and that these effects are diminished in obese individuals. Moreover, cerebrocortical insulin resistance is found in individuals with the Gly972Arg polymorphism in IRS-1, which is considered a type 2 diabetes risk gene.