The mechanism of insulin-induced signal transduction mediated by the insulin receptor substrate family

Association between insulin receptor substrate 1 gene polymorphism rs1801278 and gestational diabetes mellitus: an updated meta- analysis

OBJECTIVES

we performed this meta- analysis to investigate the impact of insulin receptor substrate 1 (IRS1) gene rs1801278 on susceptibility to gestational diabetes mellitus (GDM).

METHODS

The pooled odds ratio (OR) and 95% confidence interval (95% CI) were calculated, and p value is used to determine statistical significance. Sensitivity analysis was performed under three models (dominant, recessive and allele model), and the pooled ORs and 95%CI were calculated. Funnel plots and Begger's regression test were employed to test the publication bias.

RESULTS

The meta-analysis included 4777 participants (2116 cases and 2661 controls). The IRS1 rs1801278 (C/T) were not significant associated with GDM risk under the dominant and allele models, OR (95%CI) = 1.22 (0.88-1.70) and 1.24 (0.91-1.68), respectively (both p values were more than 0.05). But we also found the IRS1 rs1801278 (C/T) were significant associated with GDM risk under the recessive model, OR (95%CI) = 0.37 (0.16-0.86), p = 0.030. Our results showed that none of the studies affected the quality of the pooled OR. We also found no significant publication bias existed in this meta study for three genetic models, PTT + CT vs. CC = 0.445; PCC+CT vs. TT= 0.095; PC vs. T = 0.697.

CONCLUSION

this meta-analysis indicated that IRS1 rs1801278 (C/T) was associated with the GDM risk under the recessive model but was not associated with the GDM risk under dominant and allele models.

DACH1 regulates macrophage activation and tumour progression in hypopharyngeal squamous cell carcinoma

Dachshund family transcription factor 1 (DACH1) has been shown to exhibit a tumour-suppressive role in a number of human cancers. However, the role of DACH1 in hypopharyngeal squamous cell carcinoma (HPSCC) and its function in the tumour microenvironment (TME) are still not clear. Crosstalk between cancer cells and tumour-associated macrophages (TAMs) mediates tumour progression in HPSCC. The expression of DACH1, CD86 and CD163 was detected in 71 matched HPSCC-non-cancerous tissue pairs using quantitative real-time polymerase chain reaction and IHC analysis. Cell proliferation, migration and invasion were monitored by colony formation, Transwell and EdU incorporation assays. ChIP-qPCR and dual-luciferase reporter assays were applied to verify the targeting relationships between DACH1 and IGF-1. Stably transfected HPSCC cells were co-cultured with MΦ macrophages to assess macrophage polarization and secretory signals. DACH1 was decreased in HPSCC tissues and was indicative of a poor prognosis for HPSCC patients. Decreased DACH1 expression in HPSCC was associated with fewer CD86+ TAMs and more CD163+ TAMs. Knockdown of DACH1 inhibited the proliferation, migration and invasion of FaDu cells via Akt/NF-κB/MMP2/9 signalling. Additionally, DACH1 was found to directly bind to the promoter region of IGF-1 to downregulate the secretion of IGF-1, which inhibited TAMs polarization through the IGF-1R/JAK1/STAT3 axis. Furthermore, in nude mice, the effects of DACH1 inhibition on tumour progression and M2-like TAMs polarization were confirmed. These findings suggest that IGF-1 is a critical downstream effector of DACH1 that suppresses cell migration and invasion and inhibits TAMs polarization. DACH1 could be a therapeutic target and prognostic marker for HPSCC.

Serotonin transporter-deficient mice display enhanced adipose tissue inflammation after chronic high-fat diet feeding

Introduction

Serotonin is involved in leukocyte recruitment during inflammation. Deficiency of the serotonin transporter (SERT) is associated with metabolic changes in humans and mice. A possible link and interaction between the inflammatory effects of serotonin and metabolic derangements in SERT-deficient mice has not been investigated so far.

Methods

SERT-deficient (Sert -/-) and wild type (WT) mice were fed a high-fat diet, starting at 8 weeks of age. Metabolic phenotyping (metabolic caging, glucose and insulin tolerance testing, body and organ weight measurements, qPCR, histology) and assessment of adipose tissue inflammation (flow cytometry, histology, qPCR) were carried out at the end of the 19-week high-fat diet feeding period. In parallel, Sert -/- and WT mice received a control diet and were analyzed either at the time point equivalent to high-fat diet feeding or as early as 8-11 weeks of age for baseline characterization.

Results

After 19 weeks of high-fat diet, Sert -/- and WT mice displayed similar whole-body and fat pad weights despite increased relative weight gain due to lower starting body weight in Sert -/-. In obese Sert -/- animals insulin resistance and liver steatosis were enhanced as compared to WT animals. Leukocyte accumulation and mRNA expression of cytokine signaling mediators were increased in epididymal adipose tissue of obese Sert -/- mice. These effects were associated with higher adipose tissue mRNA expression of the chemokine monocyte chemoattractant protein 1 and presence of monocytosis in blood with an increased proportion of pro-inflammatory Ly6C+ monocytes. By contrast, Sert -/- mice fed a control diet did not display adipose tissue inflammation.

Discussion

Our observations suggest that SERT deficiency in mice is associated with inflammatory processes that manifest as increased adipose tissue inflammation upon chronic high-fat diet feeding due to enhanced leukocyte recruitment.

GST T1, M1, and IRS-1 G972R Genetic Variants Association to Gestational Diabetes Mellitus (GDM) in Egyptian Women: Linkage to Maternal Hyperglycemia

BACKGROUND

Gestational Diabetes Mellitus (GDM) shares in part the pathogenic mechanisms of multiple genetic interactions. Some of the T2D susceptibility genes are encountered in association with GDM.

OBJECTIVE

We aimed to investigate GST T1, M1, and G972R IRS-I gene polymorphisms with the risk of developing GDM.

METHODS

In this randomized case-control study, pregnant women with GDM were genotyped by PCR analysis for glutathione s-transferase-T1, M1 variant polymorphisms. RFLP was done for the G972R IRS 1 gene. Their newborns were additionally assayed for the whole of the clinical, laboratory, and genetic aspects.

RESULTS

The T allele IRS-1rs1801278 TT genotype was more frequently detected in GDM mothers in comparison to healthy control ones [for TT homozygous variant; OR(CI 95%): 2.05(1.09-3.87, p: 0.025)]. Furthermore, GST T1 null was significantly presented in GDM mothers than those of control mothers [OR (CI95%: 0.29 (0.084-1.02), p:0.04]. Added to the significant correlation of glycemic indices to clinical parameters of infants born to GDM, the M1-null genotype of GST was significantly correlated (p<0.05) to abnormal values of respiratory rates and 1 minute-APGAR score noted for extra NICU care.

CONCLUSION

Our results suggested that GST T1null and IRS-1 TT genotypic variants were claimed for GDM development among Egyptian women with a possible impact on their newly born infants.

Role of mitochondria in pathogenesis of type 2 diabetes mellitus

Type 2 diabetes mellitus (T2DM) is global health problem. An estimated 425 million people in the world had diabetes in 2017. It is a major cause of morbidity and mortality worldwide. Although, pathogenesis of T2DM and its complications have been focus of medical research for long, much remains to be learned. A better understanding of molecular pathogenesis is essential for more effective preventive and therapeutic interventions. Role of mitochondria in pathogenesis of metabolic problems such as obesity, metabolic syndrome, and T2DM is the focus of many recent research studies. Mitochondrial dysfunction contributes to the oxidative stress and systemic inflammation leading to insulin resistance (IR). Mitochondria are also essential for pancreatic beta cell insulin secretion. Hence, mitochondria are important players in the pathogenesis of T2DM. In this article, pathogenesis of T2DM is examined from a mitochondrial perspective.

Neuregulin-1 triggers GLUT4 translocation and enhances glucose uptake independently of insulin receptor substrate and ErbB3 in neonatal rat cardiomyocytes

During stress conditions such as pressure overload and acute ischemia, the myocardial endothelium releases neuregulin-1β (NRG-1), which acts as a cardioprotective factor and supports recovery of the heart. Recently, we demonstrated that recombinant human (rh)NRG-1 enhances glucose uptake in neonatal rat ventricular myocytes via the ErbB2/ErbB4 heterodimer and PI3Kα. The present study aimed to further elucidate the mechanism whereby rhNRG-1 activates glucose uptake in comparison to the well-established insulin and to extend the findings to adult models. Combinations of rhNRG-1 with increasing doses of insulin did not yield any additive effect on glucose uptake measured as ³H-deoxy-d-glucose incorporation, indicating that the mechanisms of the two stimuli are similar. In c-Myc-GLUT4-mCherry-transfected neonatal rat cardiomyocytes, rhNRG-1 increased sarcolemmal GLUT4 by 16-fold, similar to insulin. In contrast to insulin, rhNRG-1 did not phosphorylate IRS-1 at Tyr⁶¹², indicating that IRS-1 is not implicated in the signal transmission. Treatment of neonatal rats with rhNRG-1 induced a signaling response comparable with that observed in vitro, including increased ErbB4-pTyr¹²⁸⁴, Akt-pThr³⁰⁸ and Erk1/2-pThr²⁰²/Tyr²⁰⁴. In contrast, in adult cardiomyocytes rhNRG-1 only increased the phosphorylation of Erk1/2 without having any significant effect on Akt and AS160 phosphorylation and glucose uptake, suggesting that rhNRG-1 function in neonatal cardiomyocytes differs from that in adult cardiomyocytes. In conclusion, our results show that similar to insulin, rhNRG-1 can induce glucose uptake by activating the PI3Kα-Akt-AS160 pathway and GLUT4 translocation. Unlike insulin, the rhNRG-1-induced effect is not mediated by IRS proteins and is observed in neonatal, but not in adult rat cardiomyocytes.

The influence of the lack of insulin receptor substrate 2 (IRS2) on the thyroid gland

Involvement of IRS2 in the proliferative effects of IGF-I of follicular thyroid cells has been described, but there are no evidences for in vivo participation of IRS2. This study aimed to analyse the in vivo relevance of IRS2 in the proliferation and apoptosis of thyroid cells by immunocytochemical studies for PCNA, Ki67, and active-caspase-3 in thyroid cells of IRS2 knockout (IRS2-KO) mice, jointly to TUNEL assay. Thyroid hormones were lower in IRS2-KO mice than in their wild-type (WT) counterparts. Increases in the area, perimeter and diameter of thyroid follicles of IRS2-KO mice were observed, which also showed increased proliferation rate of follicular cells and decreased percentage of apoptotic cells that was more evident in the central than in the marginal region of the gland. Sex-related differences were also found, since the follicular epithelium height was higher in male than in female mice. The percentage of proliferating cells showed significant changes in male but not in female mice, and apoptotic cells were more abundant in female than in male IRS2-KO animals, without significant differences between WT-animals. Therefore, our results suggest that IRS2 could be involved in the maintenance of thyroid cells population and in the normal physiology of the thyroid gland.

Antidiabetic Potential of Green Seaweed Enteromorpha prolifera Flavonoids Regulating Insulin Signaling Pathway and Gut Microbiota in Type 2 Diabetic Mice

This study aimed to investigate the antidiabetic activity of water-ethanol extract of green macroalgae Enteromorpha prolifera (EPW) and its flavonoid-rich fraction less than 3 kDa (EPW3) in type 2 diabetic mice induced by streptozotocin and a high-sucrose/high-fat diet. The major active compounds were identified using ultra-performance liquid chromatography coupled with quadrupole-time-of-flight-tandem mass spectrometry. Quantitative gene expression analysis of the insulin signaling pathway was performed. The effects of EPW3 on gut microflora in diabetic mice were analyzed by high-throughput 16S rRNA gene sequencing. The results showed EPW3 treatment decreased the fasting blood glucose, improved oral glucose tolerance, and protected against liver and kidney injury with reduced inflammation in diabetic mice. The active principle of EPW3 revealed hypoglycemic effect as indicated by activation of the IRS1/PI3K/AKT and inhibition of the JNK1/2 insulin pathway in liver. Furthermore, the treatment significantly enriched the abundance of Lachnospiraceae and Alisties, which were positive correlation of metabolic phenotypes. These findings indicated that EPW3 possessed great therapeutic potential as adjuvant therapy for type 2 diabetes.

Polarization of macrophages in the tumor microenvironment is influenced by EGFR signaling within colon cancer cells

Epidermal growth factor receptor (EGFR) is a target of colon cancer therapy, but the effects of this therapy on the tumor microenvironment remain poorly understood. Our in vivo studies showed that cetuximab, an anti-EGFR monoclonal antibody, effectively inhibited AOM/DSS-induced, colitis-associated tumorigenesis, downregulated M2-related markers, and decreased F4/80+/CD206+ macrophage populations. Treatment with conditioned medium of colon cancer cells increased macrophage expression of the M2-related markers arginase-1 (Arg1), CCL17, CCL22, IL-10 and IL-4. By contrast, conditioned medium of EGFR knockout colon cancer cells inhibited expression of these M2-related markers and induced macrophage expression of the M1-related markers inducible nitric oxide synthase (iNOS), IL-12, TNF-α and CCR7. EGFR knockout in colon cancer cells inhibited macrophage-induced promotion of xenograft tumor growth. Moreover, colon cancer-derived insulin-like growth factor-1 (IGF-1) increased Arg1 expression, and treatment with the IGF1R inhibitor AG1024 inhibited that increase. These results suggest that inhibition of EGFR signaling in colon cancer cells modulates cytokine secretion (e.g. IGF-1) and prevents M1-to-M2 macrophage polarization, thereby inhibiting cancer cell growth.

Nonalcoholic Fatty liver disease, diabetes, obesity, and hepatocellular carcinoma

Diabetes and obesity are associated with nonalcoholic fatty liver disease (NAFLD) and an increased incidence of hepatocellular carcinoma (HCC). NAFLD is the commonest cause of chronic liver disease. HCC can develop in NAFLD patients even without cirrhosis, suggesting an association between the metabolic process and HCC and raising a concern that many cancers could be missed given high NAFLD prevalence and screening limitations. The increasing prevalence of these conditions and lack of effective treatments necessitate a better understanding of their connection. This article defines the known interrelationships and common pathways between NAFLD, diabetes, obesity and HCC and possible chemoprevention strategies.

Hepatitis C virus infection and type 1 and type 2 diabetes mellitus

Hepatitis C virus (HCV) infection and diabetes mellitus are two major public health problems that cause devastating health and financial burdens worldwide. Diabetes can be classified into two major types: type 1 diabetes mellitus (T1DM) and T2DM. T2DM is a common endocrine disorder that encompasses multifactorial mechanisms, and T1DM is an immunologically mediated disease. Many epidemiological studies have shown an association between T2DM and chronic hepatitis C (CHC) infection. The processes through which CHC is associated with T2DM seem to involve direct viral effects, insulin resistance, proinflammatory cytokines, chemokines, and other immune-mediated mechanisms. Few data have been reported on the association of CHC and T1DM and reports on the potential association between T1DM and acute HCV infection are even rarer. A small number of studies indicate that interferon-α therapy can stimulate pancreatic autoimmunity and in certain cases lead to the development of T1DM. Diabetes and CHC have important interactions. Diabetic CHC patients have an increased risk of developing cirrhosis and hepatocellular carcinoma compared with non-diabetic CHC subjects. However, clinical trials on HCV-positive patients have reported improvements in glucose metabolism after antiviral treatment. Further studies are needed to improve prevention policies and to foster adequate and cost-effective programmes for the surveillance and treatment of diabetic CHC patients.

Relationship between melatonin receptor 1B and insulin receptor substrate 1 polymorphisms with gestational diabetes mellitus: a systematic review and meta-analysis

Studies have investigated the relationship between genetic variants and risk of gestational diabetes mellitus (GDM). However, the results remain inconclusive. The aim of this study was to investigate the association of rs10830963 and rs1387153 variants in melatonin receptor 1B (MTNR1B) and rs1801278 variant in insulin receptor substrate 1 (IRS1) with GDM susceptibility. Electronic database of PubMed, Medline, Embase, and CNKI (China National Knowledge Infrastructure) were searched for relevant studies between 2005 and 2014. The odds ratio (OR) with its 95% confidence interval (CI) were employed to estimate the association. Total ten case-control studies, including 3428 GDM cases and 4637 healthy controls, met the inclusion criteria. Our results showed a significant association between the three genetic variants and GDM risk, rs10830963 with a P-value less than 0.0001, rs1387153 with a P-value of 0.0002, and rs1801278 with a P-value of 0.001. Furthermore, all the genetic models in these three polymorphisms were associated with increased risks of GDM as well (P< = 0.009). In conclusion, our study found that the genetic polymorphisms rs10830963 and rs1387153 in MTNR1B and rs1801278 in IRS1 were associated with an increased risk of developing GDM. However, further studies with gene-gene and gene-environmental interactions should be considered.

Insulin receptor substrate-1 (IRS-1) Gly927Arg: correlation with gestational diabetes mellitus in Saudi women

Pregnant women with gestational diabetes mellitus (GDM) and type 2 diabetes mellitus (T2DM) share a common pathophysiology associated with similar risk factors. Genetic variants used to determine the risk of developing T2DM might also be associated with the prevalence of GDM. The aim of the present study was to scrutinize the relationship between the G972R polymorphism of the insulin receptor substrate-1 (IRS-1) gene with GDM in the Saudi female population. This is a case-control study that monitored 500 Saudi women. Subjects with GDM (n = 200) were compared with non-GDM (n = 300) controls. We opted to evaluate rs1801278 polymorphism in the IRS1 gene, which plays a critical role in the insulin-signaling pathway. Genotyping was performed with the Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) method. The frequency of the rs1801278 polymorphism was significantly higher in women with GDM than in women with non-GDM (for TT + CT versus CC: P = 0.02). Additionally, there was a significant increase in the frequency of the Arg-encoding mutant allele from GDM to non-GDM (for T versus C: P = 0.01). Our results suggest that the rs1801278 polymorphism in the IRS-1 gene is involved in the occurrence of GDM in the Saudi population.

Association study of a common variant near IRS1 with type 2 diabetes mellitus in Chinese Han population

The insulin receptor substrate-1 (IRS1) plays an important role in insulin signaling. A recent genome-wide association study identified rs2943641C>T as a susceptibility locus for type 2 diabetes mellitus (T2DM) in Caucasian patients. Therefore, we determined whether this common variant near IRS1 is also associated with the risk of T2DM and T2DM-related phenotypes in a Chinese Han population. A total of 2,290 unrelated Chinese Han individuals residing in Beijing were recruited in this study, including 1177 T2DM patients and 1113 subjects with normal glucose tolerance (control group). The single nucleotide polymorphism (SNP) was genotyped using a MassARRAY iPLEX system. The frequency of risk allele C was 0.929 in the control group and 0.939 in patients with T2DM. We found no association between the C allele of rs2943641 and T2DM in a recessive model [OR 1.14, 95 % confidence interval (CI) 0.89-1.45, P = 0.298], or after adjusting for sex, age, and body mass index (BMI) (OR 1.10, 95 % CI 0.85-1.43, P = 0.301). Analysis of the clinical features of the control subjects with normal glucose tolerance revealed that the 30-min plasma glucose level during a 75-g oral glucose tolerance test was significantly different between the CC and CT+TT genotypes (P = 0.017). Linear regression analysis showed that the 30-min plasma glucose levels was significantly and positively associated with the CC genotype after adjusting for sex, age, and BMI (β = 0.065, 95 % CI 0.009-0.654, P = 0.044). In addition, a potential association between this SNP and increased waist circumference (β = 1.337, 95 % CI -0.179 to 2.853, P = 0.084) was observed with adjustment for the sex and age. Our study was not able to demonstrate the association between rs2943641 near IRS1 and T2DM in a Chinese Han population. However, this SNP may be associated with postprandial hyperglycemia.

Estrogen therapy attenuates adiposity markers in spontaneously hypertensive rats

Ovarian hormones modulate the metabolism of adipose cells and present a protective effect against hypertension. The aim of this study was to compare the effect of estradiol on adiposity markers in spontaneously hypertensive rats. Ovariectomized spontaneously hypertensive rats treated with estradiol (5 μg/100 g/day), three weeks after ovariectomy, presented decreased blood pressure and insulin levels and increased hepatic glycogen content. Periuterine or mesenteric adipocytes from treated animals were smaller as compared to vehicle treated group, whereas no differences were observed in relation to the number of cells. Basal rates of glycerol release were higher only in periuterine adipocytes of treated rats. The increment of glycerol release over basal values in response to isoproterenol was 400% and 440%, 283% and 330% for vehicle and estradiol treated periuterine and mesenteric adipocytes, respectively. The estradiol treated group was more sensitive to insulin inhibition of isoproterenol-stimulated lipolysis than the control animals. The lipoprotein lipase activity decreased after treatment, only in periuterine adipose tissue. Estradiol administration increased basal and insulin-stimulated rates of glucose transport in adipocytes of both sites, although the values obtained by periuterine were higher than those observed for mesenteric adipocytes. Both adipose tissues from treated animals exhibited a decreased expression of the peroxisome proliferator-activated receptor-γ, but an increased expression of peroxisome proliferator-activated receptor-α in liver. These findings suggest that estrogen administration attenuates adiposity markers of spontaneously hypertensive rats as a result of the decreased expression levels of peroxisome proliferator-activated receptor-γ in adipose tissue and increased expression of peroxisome proliferator-activated receptor-α in liver.

Upregulation of the insulin receptor and type I insulin-like growth factor receptor are early events in hepatocarcinogenesis

The molecular mechanisms underlying the development of hepatocellular carcinoma (HCC) are not yet fully understood. Preneoplastic foci of altered hepatocytes regularly precede HCC in various species. The predominant earliest type of foci of altered hepatocytes, the glycogen storage focus (GSF), shows an excess of glycogen (glycogenosis) in the cytoplasm. During progression from GSF to HCC, the stored glycogen is gradually reduced, resulting in complete loss in basophilic HCC. We have previously shown that in N-nitrosomorpholine-induced hepatocarcinogenesis, insulin receptor substrate (IRS-1) is strongly expressed in GSF and reduced during progression to HCC, thus correlating with the glycogen content. In the present study, we observed increased levels of insulin receptor, IGF-I receptor (IGF-IR), IRS-2, and mitogen-activated kinase/extracellular regulated kinase-1 in GSF, following the same pattern of expression as IRS-1. We conclude that the abundance of IRS-1, IRS-2, and mitogen-activated kinase/extracellular regulated kinase-1 coincides with a concerted upregulation of both IR and IGF-IR induced by the hepatocarcinogen. Our data suggest that in early hepatocellular preneoplasia, the upregulation of IR elicits glycogenosis through IRS-1 and/or IRS-2, whereas the increased level of the IGF-IR may lead to the increased cell proliferation previously reported in GSF. Therefore, the concerted upregulation of both IR and IGF-IR may represent initial events in hepatocarcinogenesis.

NASH and HCC

Primary liver cancer is the fifth most common malignancy worldwide and the third leading cause of cancer mortality. Non-alcoholic fatty liver disease is the most common cause of chronic liver disease in the United States encompassing a spectrum of entities marked by hepatic steatosis in the absence of significant alcohol consumption. Although simple steatosis follows a generally benign course, the more aggressive form, non-alcoholic steatohepatitis, can progress to cirrhosis and result in complications including hepatocellular carcinoma. A significant number of cases of hepatocellular carcinoma remain cryptogenic without known underlying chronic liver disease. It is increasingly recognized that non-alcoholic steatohepatitis likely accounts for a substantial portion of cryptogenic hepatocellular carcinoma.

Glucose transporter 4 and insulin receptor substrate-1 messenger RNA expression in omental and subcutaneous adipose tissue in women

Insulin receptor substrate-1 (IRS-1) and glucose transporter 4 (GLUT4) expression may provide an indirect reflection of the capacity of adipocytes to respond to insulin stimulation. We examined messenger RNA (mRNA) expression of these genes in omental and subcutaneous adipose tissue of women. Paired omental and subcutaneous adipose tissue samples were obtained from 36 women (age, 47 +/- 5 years; body mass index, 28.0 +/- 5.4 kg/m(2)) undergoing gynecologic surgeries. Total adiposity and visceral adiposity were assessed by dual-energy x-ray absorptiometry and computed tomography. The GLUT4 and IRS-1 mRNA expression levels were both significantly higher in subcutaneous compared with omental adipose tissue. A negative correlation was observed between body fat percentage and subcutaneous adipose tissue GLUT4 (r = -0.39, P < .05) and IRS-1 (r = -0.30, P < .08) mRNA abundance. However, in omental fat, only GLUT4 mRNA was inversely associated with body fat percentage (r = -0.53, P < .001). Moreover, the homeostasis model assessment of insulin resistance index was associated with mRNA expression of subcutaneous GLUT4 (r = -0.56, P < .001), subcutaneous IRS-1 (r = -0.51, P < .01), and omental GLUT4 (r = -0.54, P < .001), but not omental IRS-1. Interestingly, plasma adiponectin was only associated with subcutaneous GLUT4 (r = 0.48, P < .01) and IRS-1 (r = 0.48, P < .05) mRNA expression. The GLUT4 protein, unlike mRNA expression, was higher in omental than in subcutaneous adipose tissue. However, abdominal obesity-related differences in protein or mRNA expression were similar. Omental IRS-1 expression was low and unaffected by visceral obesity. In contrast, omental and subcutaneous GLUT4 as well as subcutaneous IRS-1 were reduced in visceral obesity. This divergent pattern of expression may reflect a lower capacity of omental adipose tissue to respond to insulin stimulation at all adiposity levels.

The Etiology of Steroid Cataract

Steroid-induced posterior subcapsular cataracts (PSCs) exhibit three main distinctive characteristics: (i) association only with steroids possessing glucocorticoid activity, (ii) involvement of aberrant migrating lens epithelial cells, and (iii) a central posterior location. The first characteristic suggests a key role for glucocorticoid receptor activation and subsequent changes to the transcription of specific genes. Glucocorticoid receptor activation is associated in many cell types with proliferation, suppressed differentiation, a reduced susceptibility to apoptosis, altered transmembrane transport, and enhancement of reactive oxygen species activity. Glucocorticoids may be capable of inducing changes to the transcription of genes in lens epithelial cells that are related to many of these cellular processes. This review examines the various mechanisms that have been proposed to account for the development of PSC in the context of recent DNA array studies. Additionally, given that the glucocorticoid receptor can also engender wide-ranging indirect activities, glucocorticoids could also indirectly affect the lens through the responses of other cells within the ocular compartment and/or through effects on cells at more remote locations. These indirect mechanisms, which, for example, could be mediated through alterations to the intraocular levels of growth factors that normally orchestrate lens development and maintain lens homeostasis, are also discussed. Although the mechanism of steroid cataract induction remains unknown, glucocorticoid-induced gene transcription events in lens epithelial cells, and also other intraocular or systemic cells, likely interact to generate steroid cataracts. Finally, although evidence for glucocorticoid-protein adduct formation in the lens is inconclusive, the generation of such adducts cannot yet be discounted as a contributing factor and must necessarily be retained in discussions of the etiology of steroid cataract.

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.

Glucose regulates Foxo1 through insulin receptor signaling in the pancreatic islet beta-cell

Glucose controls islet beta-cell mass and function at least in part through the phosphatidylinositol 3-kinase (PI3K)/Akt pathway downstream of insulin signaling. The Foxo proteins, transcription factors known in other tissues to be negatively regulated by Akt activation, affect proliferation and metabolism. In this study, we tested the hypothesis that glucose regulates Foxo1 activity in the beta-cell via an autocrine/paracrine effect of released insulin on its receptor. Mouse insulinoma cells (MIN6) were starved overnight for glucose (5 mmol/l) then refed with glucose (25 mmol/l), resulting in rapid Foxo1 phosphorylation (30 min, P < 0.05 vs. untreated). This glucose response was demonstrated to be time (0.5-2 h) and dose (5-30 mmol/l) dependent. The use of inhibitors demonstrated that glucose-induced Foxo1 phosphorylation was dependent upon depolarization, calcium influx, and PI3K signaling. Additionally, increases in glucose concentration over a physiological range (2.5-20 mmol/l) resulted in nuclear to cytoplasmic translocation of Foxo1. Phosphorylation and translocation of Foxo1 following glucose refeeding were eliminated in an insulin receptor knockdown cell line, indicating that the glucose effects are mediated primarily through the insulin receptor. Activity of Foxo1 was observed to increase with decreased glucose concentrations, assessed by an IGF binding protein-1 promoter luciferase assay. Starvation of MIN6 cells identified a putative Foxo1 target, Chop, and a Chop-promoter luciferase assay in the presence of cotransfected Foxo1 supported this hypothesis. The importance of these observations was that nutritional alterations in the beta-cell are associated with changes in Foxo1 transcriptional activity and that these changes are predominantly mediated through glucose-stimulated insulin secretion acting through its own receptor.

On the role of IRS2 in the regulation of functional beta-cell mass

The proper regulation of blood glucose homeostasis in mammals requires an adequate relation between the capacity to produce insulin and metabolic demand. Insulin receptor substrate proteins (IRS) are signalling intermediates that are required to keep this balance because they are needed for insulin action in target tissues but also for insulin production in pancreatic beta-cells. The total functional beta-cell mass in an individual sets the limit of how much insulin can be produced at a given time. It can change adaptively to meet demand and studies in vivo indicate that the regulation of beta-cell mass involves IRS2, while IRS1 is only required for proper insulin production in beta-cells. Overexpression studies in isolated islets have shown that IRS2, but not IRS1 or Shc, is sufficient to induce proliferation of beta-cells and to protect against d-glucose-induced apoptosis. In light of the finding that many growth factors can regulate Irs2 in islets, this signalling intermediate could balance capacity for insulin production with demand. This review summarizes observations in mouse models and in primary beta-cells and proposes a new hypothetical model of how IRS2 might control beta-cell mass.

A novel regulation of IRS1 (insulin receptor substrate-1) expression following short term insulin administration

Reduced insulin-mediated glucose transport in skeletal muscle is a hallmark of the pathophysiology of T2DM (Type II diabetes mellitus). Impaired intracellular insulin signalling is implicated as a key underlying mechanism. Attention has focused on early signalling events such as defective tyrosine phosphorylation of IRS1 (insulin receptor substrate-1), a major target for the insulin receptor tyrosine kinase. This is required for normal induction of signalling pathways key to many of the metabolic actions of insulin. Conversely, increased serine/threonine phosphorylation of IRS1 following prolonged insulin exposure (or in obesity) reduces signalling capacity, partly by stimulating IRS1 degradation. We now show that IRS1 levels in human muscle are actually increased 3-fold following 1 h of hyperinsulinaemic euglycaemia. Similarly, transient induction of IRS1 (3-fold) in the liver or muscle of rodents occurs following feeding or insulin injection respectively. The induction by insulin is also observed in cell culture systems, although to a lesser degree, and is not due to reduced proteasomal targeting, increased protein synthesis or gene transcription. Elucidation of the mechanism by which insulin promotes IRS1 stability will permit characterization of the importance of this novel signalling event in insulin regulation of liver and muscle function. Impairment of this process would reduce IRS1 signalling capacity, thereby contributing to the development of hyperinsulinaemia/insulin resistance prior to the appearance of T2DM.

Liver disease in patients with diabetes mellitus

Diabetes mellitus is a growing health concern in our society. In addition to the well-known cardiovascular, renal, and ophthalmologic complications of diabetes, liver-related complications occur commonly and are often underrecognized. The ensuing article will review the relationship between diabetes mellitus and two common liver diseases: chronic hepatitis C and nonalcoholic fatty liver disease. The association with diabetes and cirrhosis, acute liver failure, hepatocellular carcinoma, and outcomes following orthotopic liver transplantation will also be discussed.

Proteomic analysis on insulin signaling in human hematopoietic cells: identification of CLIC1 and SRp20 as novel downstream effectors of insulin

Insulin/IGF-I-dependent signals play important roles for the regulation of proliferation, differentiation, metabolism, and autophagy in various cells, including hematopoietic cells. Although the early protein kinase activation cascade has been intensively studied, the whole picture of intracellular signaling events has not yet been clarified. To identify novel downstream effectors of insulin-dependent signals in relatively early phases, we performed high-resolution two-dimensional electrophoresis (2-DE)-based proteomic analysis using human hematopoietic cells 1 h after insulin stimulation. We identified SRp20, a splicing factor, and CLIC1, an intracellular chloride ion channel, as novel downstream effectors besides previously reported effectors of Rho-guanine nucleotide dissociation inhibitor 2 and glutathione S-transferase-pi. Reduction in SRp20 was confirmed by one-dimensional Western blotting. Moreover, MG-132, a proteasome inhibitor, prevented this reduction. By contrast, upregulation of CLIC1 was not observed in one-dimensional Western blotting, unlike the 2-DE results. As hydrophilic proteins were predominantly recovered in 2-DE, the discrepancy between the 1-DE and 2-DE results may indicate a certain qualitative change of the protein. Indeed, the nuclear localization pattern of CLIC1 was remarkably changed by insulin stimulation. Thus insulin induces the proteasome-dependent degradation of SRp20 as well as the subnuclear relocalization of CLIC1.

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.

Aging is associated with decreased pancreatic acinar cell regeneration and phosphatidylinositol 3-kinase/Akt activation

BACKGROUND & AIMS

The effects of aging on pancreatic acinar cell proliferation have not been clearly defined. Phosphatidylinositol 3-kinase (PI3K)-mediated phosphorylation of Akt is a critical step for proliferation of various cell types and insulin secretion from pancreatic endocrine cells; however, its role in acinar cell proliferation is not known. The purpose of this study was to (1) delineate the effects of aging on pancreatic regeneration after partial pancreatectomy (Px) and (2) define the involvement of the PI3K/Akt pathway in pancreatic regeneration.

METHODS

Following partial Px, pancreatic regeneration and activation of the PI3K pathway were compared in young and aged mice. Activation of the PI3K/Akt pathway was evaluated by Akt phosphorylation (pAkt). The role of the PI3K pathway in pancreatic regeneration after partial Px was assessed by effects of a pharmacologic PI3K inhibitor wortmannin or small interfering RNA (siRNA) to the p85alpha regulatory subunit. To confirm further the critical role of the PI3K/Akt pathway in pancreatic acinar cell proliferation, IGF-1-mediated cell proliferation was determined in cultured acinar cells pretreated with wortmannin or p85alpha siRNA.

RESULTS

Pancreatic regeneration and pAkt expression after partial Px were significantly decreased with aging. Treatment with wortmannin or p85alpha siRNA reduced pancreatic regeneration after partial Px. The IGF-1-mediated cell proliferation in vitro was completely blocked by wortmannin or p85alpha siRNA but not by the MEK/ERK inhibitor PD98059.

CONCLUSIONS

PI3K/Akt activation plays a critical role in the regeneration of pancreatic acini after resection. Furthermore, pancreatic regeneration is markedly attenuated in the aged pancreas most likely because of decreased PI3K/Akt activation.

Liver-specific Protein-tyrosine Phosphatase 1B (PTP1B) Re-expression Alters Glucose Homeostasis of PTP1B–/–Mice

Protein-tyrosine phosphatase 1B (PTP1B) is an important negative regulator of insulin and leptin signaling in vivo. Mice lacking PTP1B (PTP1B-/- mice) are hyper-responsive to insulin and leptin and resistant to diet-induced obesity. The tissue(s) that mediate these effects of global PTP1B deficiency remain controversial. We exploited the high degree of hepatotropism of adenoviruses to assess the role of PTP1B in the liver. Liver-specific re-expression of PTP1B in PTP1B-/- mice led to marked attenuation of their enhanced insulin sensitivity. This correlated with, and was probably caused by, decreased insulin-stimulated tyrosyl phosphorylation of the insulin receptor (IR) and IR substrate 2-associated phosphatidylinositide 3-kinase activity. Analysis using phospho-specific antibodies for the IR revealed preferential dephosphorylation of Tyr-1162/1163 compared with Tyr-972 by PTP1B in vivo. Our findings show that the liver is a major site of the peripheral action of PTP1B in regulating glucose homeostasis.

Regulated membrane trafficking of the insulin-responsive glucose transporter 4 in adipocytes

Since the discovery of insulin roughly 80 yr ago, much has been learned about how target cells receive, interpret, and respond to this peptide hormone. For example, we now know that insulin activates the tyrosine kinase activity of its cell surface receptor, thereby triggering intracellular signaling cascades that regulate many cellular processes. With respect to glucose homeostasis, these include the function of insulin to suppress hepatic glucose production and to increase glucose uptake in muscle and adipose tissues, the latter resulting from the translocation of the glucose transporter 4 (GLUT4) to the cell surface membrane. Although simple in broad outline, elucidating the molecular intricacies of these receptor-signaling pathways and membrane-trafficking processes continues to challenge the creative ingenuity of scientists, and many questions remain unresolved, or even perhaps unasked. The identification and functional characterization of specific molecules required for both insulin signaling and GLUT4 vesicle trafficking remain key issues in our pursuit of developing specific therapeutic agents to treat and/or prevent this debilitating disease process. To this end, the combined efforts of numerous research groups employing a range of experimental approaches has led to a clearer molecular picture of how insulin regulates the membrane trafficking of GLUT4.

Impaired IRS-1/PI3-kinase signaling in patients with HCV: a mechanism for increased prevalence of type 2 diabetes

Patients with hepatitis C virus (HCV) infection have a greater risk of developing type 2 diabetes mellitus. However, the mechanism of this association is unclear. In this study, we examined the potential defects in upstream insulin signaling pathways in liver specimens obtained from nonobese/nondiabetic subjects with HCV infection. Fasting liver biopsy specimens were obtained from 42 HCV-infected subjects and 10 non-HCV-infected subjects matched for age and body mass index. Liver tissues were exposed to insulin and examined for the contents and phosphorylation/activation status of the upstream insulin signaling molecules by immunoprecipitation and Western blot analysis. HCV infection resulted in a trend toward a 2-fold to 3-fold increase in insulin receptor (IR) and insulin receptor substrate (IRS)-1 contents when compared with non-HCV. In contrast, insulin-stimulated IRS-1 tyrosine phosphorylation was decreased by 2-fold in HCV-infected subjects compared with non-HCV-infected subjects (P <.05). The observed reductions in IRS-1 tyrosine phosphorylation were accompanied by a 3.4-fold decrease in IRS-1/p85 phosphatidylinositol 3-kinase (PI3-kinase) association and a 2.5-fold decrease in IRS-1-associated PI3-kinase enzymatic activity (P <.05 vs. non-HCV). This was accompanied by a marked reduction in insulin-stimulated Akt phosphorylation without any alterations in mitogen-activated protein kinase (MAPK) phosphorylation. Cellular contents of the hepatic p85 subunit of PI3-kinase were comparable between HCV-infected and non-HCV-infected subjects. In conclusion, we found that (1). HCV infection leads to a postreceptor defect in IRS-1 association with the IR and (2). insulin signaling defects in hepatic IRS-1 tyrosine phosphorylation and PI3-kinase association/activation may contribute to insulin resistance, which leads to the development of type 2 diabetes mellitus in patients with HCV infection.

The adipocyte plasma membrane caveolin functional/structural organization is necessary for the efficient endocytosis of GLUT4

It is well established that insulin stimulation of glucose uptake requires the translocation of intracellular localized GLUT4 protein to the cell surface membrane. This plasma membrane-redistributed GLUT4 protein was partially co-localized with caveolin as determined by confocal fluorescent microscopy but was fully excluded from lipid rafts based upon Triton X-100 extractability. Cholesterol depletion with methyl-beta-cyclodextrin, filipin, or cholesterol oxidase resulted in an insulin-independent increase in the amount of plasma membrane-localized GLUT4 that was fully reversible by cholesterol replenishment. This basal accumulation of cell surface GLUT4 occurred due to an inhibition of GLUT4 endocytosis. However, this effect was not specific since cholesterol extraction also resulted in a dramatic inhibition of clathrin-mediated endocytosis as assessed by transferrin receptor internalization. To functionally distinguish between caveolin- and clathrin-dependent endocytic processes, we took advantage of a dominant-interfering caveolin 1 mutant (Cav1/S80E) that specifically disrupts caveolae organization. Expression of Cav1/S80E, but not the wild type (Cav1/WT) or Cav1/S80A mutant, inhibited cholera toxin B internalization without any significant effect on transferrin receptor endocytosis. In parallel, Cav1/S80E expression increased the amount of plasma membrane-localized GLUT4 protein in an insulin-independent manner. Although Cav1/S80E also decreased GLUT4 endocytosis, the extent of GLUT4 internalization was only partially reduced ( approximately 40%). In addition, expression of Cav1/WT and Cav1/S80A enhanced GLUT4 endocytosis by approximately 20%. Together, these data indicate that the endocytosis of GLUT4 requires clathrin-mediated endocytosis but that the higher order structural organization of plasma membrane caveolin has a significant influence on this process.

Plasma adiponectin plays an important role in improving insulin resistance with glimepiride in elderly type 2 diabetic subjects

OBJECTIVE

We investigated the effect of glimepiride, a third-generation sulfonylurea hypoglycemic agent, on insulin resistance in elderly patients with type 2 diabetes, in connection with plasma adiponectin and 8-epi-prostagrandin F2alpha (8-epi-PGF2alpha), an oxidative stress marker.

RESEARCH DESIGN AND METHODS

A total of 17 elderly patients with type 2 diabetes received 12 weeks of treatment with glimepiride. Homeostasis assessment model of insulin resistance (HOMA-IR), homeostasis assessment model of beta-cell function, HbA(1c), C-peptide in 24-h pooled urine (urine CPR), and plasma concentrations of 8-epi-PGF2alpha, tumor necrosis factor-alpha (TNF-alpha), plasminogen activator inhibitor type 1, and adiponectin were measured at various times. The metabolic clearance rate of glucose (MCR-g) was also assessed by a hyperinsulinemic-euglycemic clamp.

RESULTS

After 8 weeks of glimepiride treatment, significant reductions were observed in HbA(1c) (from 8.4 +/- 1.9 to 6.9 +/- 1.0%), HOMA-IR (from 2.54 +/- 2.25 to 1.69 +/- 0.95%), and plasma TNF-alpha concentrations (from 4.0 +/- 2.0 to 2.6 +/- 2.5 pg/ml). MCR-g was significantly increased from 3.92 +/- 1.09 to 5.73 +/- 1.47 mg. kg(-1). min(-1). Plasma adiponectin increased from 6.61 +/- 3.06 to 10.2 +/- 7.14 micro g/ml. In control subjects, who maintained conventional treatment, no significant changes were observed in any of these markers.

CONCLUSIONS

Glimepiride remarkably improved insulin resistance, suggested by a significant reduction in HOMA-IR, an increase in MCR-g, and a reduction in HbA(1c) without changing extrapancreatic beta-cell function and urine CPR. Increased plasma adiponectin and decreased plasma TNF-alpha may underlie the improvement of insulin resistance with glimepiride.