Socs1 deficiency enhances hepatic insulin signaling

Gene expression analysis of SOCS, STAT and PIAS genes in lung cancer patients

One of the most devastating diseases with the highest prevalence and mortality rate worldwide is lung cancer. Non-small cell lung cancer (NSCLC) is the subtype of lung cancer in 85% of cases. In this work, the expression levels of the STAT, SOCS and PIAS family genes involved in angiogenesis, proliferation and differentiation were examined. Using QRT-PCR technique, the expression level of STAT3 gene was assessed and tumor tissue samples had higher expression than normal tissue. In addition, the histological grade of adenocarcinoma was associated with the increase in STAT3 gene expression. The expression of the SOCS1 and SOCS2 genes in tumors was measured to be 0.58-fold and 0.36-fold lower than in healthy samples adjacent to the tumor, but this reduction in expression was not significant. In addition, when examining the relationship between the expression of SOCS1 and 2 and the clinical features of tumor samples, there was a significant decrease in the expression of the SOCS1 and 2 genes in the adenocarcinoma subtype. Compared to neighboring tumor samples, the expression of PIAS1 in the tumors was not different with controls. Our research revealed that tissue samples from adenocarcinoma had higher levels of STAT3 expression. Taken together, the mentioned genes can be suggested as possible targets for further studies in NSCLC.

Cytokine-inducible SH2 domain containing protein contributes to regulation of adiposity, food intake, and glucose metabolism

The cytokine-inducible SH2 domain containing protein (CISH) is the founding member of the suppressor of cytokine signaling (SOCS) family of negative feedback regulators and has been shown to be a physiological regulator of signaling in immune cells. This study sought to investigate novel functions for CISH outside of the immune system. Mice deficient in CISH were generated and analyzed using a range of metabolic and other parameters, including in response to a high fat diet and leptin administration. CISH knockout mice possessed decreased body fat and showed resistance to diet-induced obesity. This was associated with reduced food intake, but unaltered energy expenditure and microbiota composition. CISH ablation resulted in reduced basal expression of the orexigenic Agrp gene in the arcuate nucleus (ARC) region of the brain. Cish was basally expressed in the ARC, with evidence of co-expression with the leptin receptor (Lepr) gene in Agrp-positive neurons. CISH-deficient mice also showed enhanced leptin responsiveness, although Cish expression was not itself modulated by leptin. CISH-deficient mice additionally exhibited improved insulin sensitivity on a high-fat diet, but not glucose tolerance despite reduced body weight. These data identify CISH as an important regulator of homeostasis through impacts on appetite control, mediated at least in part by negative regulation of the anorexigenic effects of leptin, and impacts on glucose metabolism.

Identification of Key Genes and Immune Infiltrate in Nonalcoholic Steatohepatitis: A Bioinformatic Analysis

BACKGROUND

Nonalcoholic steatohepatitis (NASH) can progress to cirrhosis and hepatic carcinoma and is closely associated with changes in the neurological environment. The discovery of new biomarkers would aid in the treatment of NASH.

METHODS

Data GSE89632 were downloaded from the Gene Expression Omnibus (GEO) database, and R package "limma" was used to identify differentially expressed genes (DEGs) for NASH vs. normal tissues. The STRING database was used to construct a protein-protein interaction (PPI) network, and the Cytoscape software program (Version 3.80) was used to visualize the PPI network and identify key genes. The immune infiltration of NASH was determined using the R package "CIBERSORT".

RESULTS

We screened 41 DEGs. GO and KEGG enrichment analyses of the DEGs revealed the enrichment of pathways related to NAFLD steatosis and inflammation. A PPI network analysis was also performed on the DEGs, and seven genes (MYC, CXCL8, FOS, SOCS1, SOCS3, IL6, and PTGS2) were identified as hub genes. An immune infiltration assessment revealed that macrophages M2, memory resting CD4+ T cells, and γΔ T cells play important roles in the immune microenvironment of NASH, which may be mediated by the seven identified hub genes.

SOCS1 favors the epithelial-mesenchymal transition in melanoma, promotes tumor progression and prevents antitumor immunity by PD-L1 expression

Silencing of SOCS1 protein with shRNAi lentivirus (shR-SOCS1) led to partial reversion of the tumorigenic phenotype of B16F10-Nex2 melanoma cells. SOCS1 silencing inhibited cell migration and invasion as well as in vitro growth by cell cycle arrest at S phase with increased cell size and nuclei. Down-regulation of SOCS1 decreased the expression of epidermal growth factor receptor, Ins-Rα, and fibroblast growth factor receptors. The present work aimed at analyzing the SOCS1 cell signaling and expression of proteins relevant to tumor development. An RNA microarray analysis of B16F10-Nex2 melanoma cells with SOCS1 silenced by shRNAi-SOCS1 was undertaken in comparison with cells transduced with the empty vector. Among 609 differentially expressed genes, c-Kit, Met and EphA3 cytokine/tyrosine-kinase (TK) receptors were down regulated. A significant decrease in the expression of TK receptors, the phosphorylation of mediators of ERK1/2 and p38 pathways and STAT3 (S727) were observed. Subcutaneous immunization with shR-SOCS1-transduced viable tumor cells rendered protection against melanoma in a syngeneic model, with decreased expression of PD-L1 and of matrix metallo-proteinases (MMPs) and CD-10 in those cells. The present work shows the role of SOCS1 in murine melanoma development and the potential of SOCS1-silenced tumor cells in raising an effective anti-melanoma immune response.

Depletion of suppressor of cytokine signaling-1a causes hepatic steatosis and insulin resistance in zebrafish

Suppressor of cytokine signaling-1a (SOCS1a) is a member of the suppressor of cytokine signaling family, a group of related molecules that mediate the negative regulation of the JAK-STAT pathway. Here, we depleted SOCS1a using the transcription activator-like (TAL) effector nuclease (TALEN) technique to understand its physiological roles in zebrafish. Although elevated levels of JAK-STAT5 activation and erythropoiesis have been observed in socs1a-deficient zebrafish, these animals exhibited normal growth during the early stages. Socs1a-deficient zebrafish began to grow slowly with certain mortalities after 20 days postfertilization (dpf), whereas the heterozygous socs1a-deficient zebrafish exhibited enhanced somatic growth. Decreased adiposity, hepatic steatosis, and insulin resistance were observed in our socs1a-deficient adult zebrafish, which is similar to the lipodystrophy phenotypes observed in mammals. Comparative transcriptomic analyses revealed elevated levels of gluconeogenesis, lipolysis, and hypoxia-inducible response and decreased activities of lipogenesis and glycolysis in the hepatocytes of socs1a-deflicient adult zebrafish. Evident mitochondrial dysfunction has also been observed in hepatocytes from socs1a-deficient zebrafish. Taken together, our results suggest that the negative regulatory roles of SOCS1a on JAK-STAT5 signaling may be involved in the suppression of the erythropoiesis and growth hormone activities, which was also reflected in the enhanced somatic growth performance observed in the heterozygous socs1a-deficient fish. The differences in the effects caused by SOCS1a depletion on insulin sensitivity, lipid metabolism, and inflammatory responses between zebrafish and mammalian models observed here may reflect differences between the functional mechanisms of SOCS members in terrestrial mammals and aquatic teleosts.

SOCS proteins in regulation of receptor tyrosine kinase signaling

Receptor tyrosine kinases (RTKs) are a family of cell surface receptors that play critical roles in signal transduction from extracellular stimuli. Many in this family of kinases are overexpressed or mutated in human malignancies and thus became an attractive drug target for cancer treatment. The signaling mediated by RTKs must be tightly regulated by interacting proteins including protein-tyrosine phosphatases and ubiquitin ligases. The suppressors of cytokine signaling (SOCS) family proteins are well-known negative regulators of cytokine receptors signaling consisting of eight structurally similar proteins, SOCS1-7, and cytokine-inducible SH2-containing protein (CIS). A key feature of this family of proteins is the presence of an SH2 domain and a SOCS box. Recent studies suggest that SOCS proteins also play a role in RTK signaling. Activation of RTK results in transcriptional activation of SOCS-encoding genes. These proteins associate with RTKs through their SH2 domains and subsequently recruit the E3 ubiquitin machinery through the SOCS box, and thereby limit receptor stability by inducing ubiquitination. In a similar fashion, SOCS proteins negatively regulate mitogenic signaling by RTKs. It is also evident that RTKs can sometimes bypass SOCS regulation and SOCS proteins can even potentiate RTKs-mediated mitogenic signaling. Thus, apart from negative regulation of receptor signaling, SOCS proteins may also influence signaling in other ways.

Suppressor of cytokine signalling (SOCS) proteins as guardians of inflammatory responses critical for regulating insulin sensitivity

Overactivation of immune pathways in obesity is an important cause of insulin resistance and thus new approaches aimed to limit inflammation or its consequences may be effective for treating Type 2 diabetes. The SOCS (suppressors of cytokine signalling) are a family of proteins that play an essential role in mediating inflammatory responses in both immune cells and metabolic organs such as the liver, adipose tissue and skeletal muscle. In the present review we discuss the role of SOCS1 and SOCS3 in controlling immune cells such as macrophages and T-cells and the impact this can have on systemic inflammation and insulin resistance. We also dissect the mechanisms by which SOCS (1-7) regulate insulin signalling in different tissues including their impact on the insulin receptor and insulin receptor substrates. Lastly, we discuss the important findings from SOCS whole-body and tissue-specific null mice, which implicate an important role for these proteins in controlling insulin action and glucose homoeostasis in obesity.

Pioglitazone does not improve insulin signaling in mice with GH over-expression

Type 2 diabetes and obesity are very serious health problems in both developed and developing countries. An increased level of GH is known to promote insulin resistance. Transgenic (Tg) mice over-expressing bovine GH are short-living and characterized, among other traits, by hyperinsulinemia and increased insulin resistance in comparison with normal (N) mice. Pioglitazone (PIO) is a member of the thiazolidinediones - a group of insulin-sensitizing drugs that are selective agonists of peroxisome proliferator-activated receptor gamma (PPARγ). The aim of the study was to analyze the effects of PIO on the insulin-signaling pathway in Tg and N mice. Plasma levels of insulin and glucose as well as hepatic levels of proteins involved in insulin signaling were analyzed by ELISA or western blot methods. Treatment with PIO decreased plasma level of glucose in N mice only. Similarly, PIO increased insulin sensitivity (expressed as the relative insulin sensitivity index; RISI) only in N mice. In the liver, PIO decreased the phosphorylation of insulin receptor substrate-1 (IRS1) at a serine residue (Ser(307)-pS-IRS1), which inhibits insulin action, and had a tendency to increase tyrosine phosphorylation of IRS2 (Tyr-pY-IRS2) only in N mice but did not affect either of these parameters in Tg mice. Levels of total and phosphorylated mammalian target of rapamycin were increased in Tg mice. Moreover, the level of AKT2 was decreased by PIO in N mice only. In conclusion, the lack of improvement of insulin sensitivity in insulin-resistant Tg mice during PIO treatment indicates that chronically elevated GH levels can inhibit the beneficial effects of PIO on insulin signaling.

Polymorphisms in the SOCS7 gene and glucose homeostasis traits

Background

SOCS7 is a member of the suppressor of cytokine signaling family of proteins and is expressed in skeletal muscle and islets. SOCS7 deficient mice develop islet hyperplasia in the setting of increased insulin sensitivity and normal glucose tolerance. The objective of this study was to determine if variants in SOCS7 play a role in variation of glucose and insulin levels and the development of type 2 diabetes (T2DM).

Results

Five SOCS7 tagging SNPs were genotyped in diabetic and nondiabetic Old Order Amish. A case–control study was performed in T2DM (n = 145) and normal glucose tolerant (n = 358) subjects. Nominal associations were observed with T2DM and the minor alleles for rs8068600 (P = 0.01) and rs8074124 (P = 0.04); however, only rs8068600 remained significant after Bonferroni adjustment for multiple comparisons (P = 0.01). Among nondiabetic Amish (n = 765), no significant associations with glucose or insulin traits including fasting or 2 hour glucose and insulin from the oral glucose tolerance test, insulin or glucose area under the curve, Matsuda Index or HOMA-IR were found for any of the SNPs.

Conclusion

In conclusion, genetic variants in the SOCS7 gene do not impact variation in glucose homeostasis traits and only minimally impact risk of T2DM in the Old Order Amish. Our study was not able to address whether rare variants that potentially impact gene function might influence T2DM risk.

Reduced Socs3 expression in adipose tissue protects female mice against obesity-induced insulin resistance

AIMS/HYPOTHESIS

Inflammation in obesity increases the levels of the suppressor of cytokine signalling-3 (SOCS3) protein in adipose tissue, but the physiological importance of this protein in regulating whole-body insulin sensitivity in obesity is not known.

METHODS

We generated Socs3 floxed (wild-type, WT) and Socs3 aP2 (also known as Fabp4)-Cre null (Socs3 AKO) mice. Mice were maintained on either a regular chow or a high-fat diet (HFD) for 16 weeks during which time body mass, adiposity, glucose homeostasis and insulin sensitivity were assessed.

RESULTS

The HFD increased SOCS3 levels in adipose tissue of WT but not Socs3 AKO mice. WT and Socs3 AKO mice had similar body mass and adiposity, assessed using computed tomography (CT) imaging, irrespective of diet or sex. On a control chow diet there were no differences in insulin sensitivity or glucose tolerance. When fed a HFD, female but not male Socs3 AKO mice had improved glucose tolerance as well as lower fasting glucose and insulin levels compared with WT littermates. Hyperinsulinaemic-euglycaemic clamps and positron emission tomography (PET) imaging demonstrated that improved insulin sensitivity was due to elevated adipose tissue glucose uptake. Increased insulin-stimulated glucose uptake in adipose tissue was associated with enhanced levels and activating phosphorylation of insulin receptor substrate-1 (IRS1).

CONCLUSIONS/INTERPRETATION

These data demonstrate that inhibiting SOCS3 production in adipose tissue of female mice is effective for improving whole-body insulin sensitivity in obesity.

Implication of inflammatory signaling pathways in obesity-induced insulin resistance

Obesity is characterized by the development of a low-grade chronic inflammatory state in different metabolic tissues including adipose tissue and liver. This inflammation develops in response to an excess of nutrient flux and is now recognized as an important link between obesity and insulin resistance. Several dietary factors like saturated fatty acids and glucose as well as changes in gut microbiota have been proposed as triggers of this metabolic inflammation through the activation of pattern-recognition receptors (PRRs), including Toll-like receptors (TLR), inflammasome, and nucleotide oligomerization domain (NOD). The consequences are the production of pro-inflammatory cytokines and the recruitment of immune cells such as macrophages and T lymphocytes in metabolic tissues. Inflammatory cytokines activate several kinases like IKKβ, mTOR/S6 kinase, and MAP kinases as well as SOCS proteins that interfere with insulin signaling and action in adipocytes and hepatocytes. In this review, we summarize recent studies demonstrating that PRRs and stress kinases are important integrators of metabolic and inflammatory stress signals in metabolic tissues leading to peripheral and central insulin resistance and metabolic dysfunction. We discuss recent data obtained with genetically modified mice and pharmacological approaches suggesting that these inflammatory pathways are potential novel pharmacological targets for the management of obesity-associated insulin resistance.

Macrophage deletion of SOCS1 increases sensitivity to LPS and palmitic acid and results in systemic inflammation and hepatic insulin resistance

OBJECTIVE

Macrophage secretion of proinflammatory cytokines contributes to the pathogenesis of obesity-related insulin resistance. An important regulator of inflammation is the suppressor of cytokine signaling-1 (SOCS1), which inhibits the JAK-STAT and toll-like receptor-4 (TLR4) pathways. Despite the reported role of SOCS1 in inhibiting insulin signaling, it is surprising that a SOCS1 polymorphism that increases SOCS1 promoter activity is associated with enhanced insulin sensitivity despite obesity. In the current study, we investigated the physiological role of myeloid and lymphoid cell SOCS1 in regulating inflammation and insulin sensitivity.

RESEARCH DESIGN AND METHODS

We used mice generated by crossing SOCS1 floxed mice with mice expressing Cre recombinase under the control of the LysM-Cre promoter (SOCS1 LysM-Cre). These mice have deletion of SOCS1 in macrophages and lymphocytes. We assessed macrophage inflammation using flow cytometry and serum cytokine levels using Bioplex assays. We then measured insulin sensitivity using glucose tolerance tests and the euglycemic-hyperinsulinemic clamp. Using bone marrow-derived macrophages, we tested the effects of SOCS1 deletion in regulating responses to the TLR4 ligands: lipopolysaccharide (LPS) and palmitic acid.

RESULTS

SOCS1 LysM-Cre mice had increased macrophage expression of CD11c, enhanced sensitivity to LPS, and palmitic acid and increased serum concentrations of tumor necrosis factor-α, interleukin-6, and monocyte chemoattractant protein. Increased inflammation was associated with impaired glucose tolerance and hyperinsulinemia as a result of reduced hepatic but not skeletal muscle insulin sensitivity.

CONCLUSIONS

The expression of SOCS1 in hematopoietic cells protects mice against systemic inflammation and hepatic insulin resistance potentially by inhibiting LPS and palmitate-induced TLR4 signaling in macrophages.

Role of SOCS-1 Gene on Melanoma Cell Growth and Tumor Development

Melanoma is the most aggressive form of skin cancer, and its incidence has increased dramatically over the years. The murine B16F10 melanoma in syngeneic C57Bl/6 mice has been used as a highly aggressive model to investigate tumor development. Presently, we demonstrate in the B16F10-Nex2 subclone that silencing of SOCS-1, a negative regulator of Jak/Stat pathway, leads to reversal of the tumorigenic phenotype and inhibition of melanoma cell metastasis. SOCS-1 silencing with short hairpin RNA affected tumor growth and cell cycle regulation with arrest at the S phase with large-sized nuclei, reduced cell motility, and decreased melanoma cell invasion through Matrigel. A clonogenic assay showed that SOCS-1 acted as a modulator of resistance to anoikis. In addition, downregulation of SOCS-1 decreased the expression of epidermal growth factor receptor (mainly the phosphorylated-R), Ins-Rα, and fibroblast growth factor receptor. In vivo, silencing of SOCS-1 inhibited subcutaneous tumor growth and metastatic development in the lungs. Because SOCS-1 is expressed in most melanoma cell lines and bears a relation with tumor invasion, thickness, and stage of disease, the present results on the effects of SOCS-1 silencing in melanoma suggest that this regulating protein can be a target of cancer therapy.

Suppressor of cytokine signaling 1 regulates embryonic myelopoiesis independently of its effects on T cell development

Suppressor of cytokine signaling 1 (SOCS1) has been shown to play important roles in the immune system. It acts as a key negative regulator of signaling via receptors for IFNs and other cytokines controlling T cell development, as well as Toll receptor signaling in macrophages and other immune cells. To gain further insight into SOCS1, we have identified and characterized the zebrafish socs1 gene, which exhibited sequence and functional conservation with its mammalian counterparts. Initially maternally derived, the socs1 gene showed early zygotic expression in mesodermal structures, including the posterior intermediate cell mass, a site of primitive hematopoiesis. At later time points, expression was seen in a broad anterior domain, liver, notochord, and intersegmental vesicles. Morpholino-mediated knockdown of socs1 resulted in perturbation of specific hematopoietic populations prior to the commencement of lymphopoiesis, ruling out T cell involvement. However, socs1 knockdown also lead to a reduction in the size of the developing thymus later in embryogenesis. Zebrafish SOCS1 was shown to be able to interact with both zebrafish Jak2a and Stat5.1 in vitro and in vivo. These studies demonstrate a conserved role for SOCS1 in T cell development and suggest a novel T cell-independent function in embryonic myelopoiesis mediated, at least in part, via its effects on receptors using the Jak2-Stat5 pathway.

Deletion of Nck1 attenuates hepatic ER stress signaling and improves glucose tolerance and insulin signaling in liver of obese mice

Obesity has been shown to create stress in the endoplasmic reticulum (ER), and that initiates the activation of the unfolded protein response (UPR). This has been reported to cause insulin resistance in selective tissues through activation of the inositol-requiring enzyme 1α (IRE1α)-c-Jun NH(2)-terminal kinase (JNK) pathway, which results in the phosphorylation of the insulin receptor substrate-1 (IRS-1) at an inhibitory site and blocks insulin receptor signaling. In this study, we report that the Src homology domain-containing adaptor protein Nck1, previously shown to modulate the UPR, is of functional importance in obesity-induced ER stress signaling and inhibition of insulin actions. We have examined obese Nck1(-/-) and Nck1(+/+) mice for glucose tolerance, insulin sensitivity, and signaling as well as for ER stress markers and IRS-1 phosphorylation at Ser(307). Our findings show that obese Nck1-deficient mice display improved glucose disposal accompanied by enhanced insulin signaling in liver. This correlates with attenuated IRE1α and JNK activation and IRS-1 phosphorylation at Ser(307) compared with obese wild-type mice. Consistent with our in vivo data, we report that downregulation of Nck1 using siRNA in HepG2 cells results in decreased thapsigargin-induced IRE1α activation and signaling and IRS-1 phosphorylation at Ser(307), whereas it markedly enhances insulin signaling. Overall, in liver and in cultured cells, we show that depletion of Nck1 attenuates the UPR signal and its inhibitory action on insulin signaling. Taken all together, our findings implicate Nck1 in regulating the UPR, which secondary to obesity impairs glucose homeostasis and insulin actions.

Liver-specific suppressor of cytokine signaling-3 deletion in mice enhances hepatic insulin sensitivity and lipogenesis resulting in fatty liver and obesity

Obesity is associated with chronic inflammation and contributes to the development of insulin resistance and nonalcoholic fatty liver disease. The suppressor of cytokine signaling-3 (SOCS3) protein is increased in inflammation and is thought to contribute to the pathogenesis of insulin resistance by inhibiting insulin and leptin signaling. Therefore, we studied the metabolic effects of liver-specific SOCS3 deletion in vivo. We fed wild-type (WT) and liver-specific SOCS3 knockout (SOCS3 LKO) mice either a control diet or a high-fat diet (HFD) for 6 weeks and examined their metabolic phenotype. We isolated hepatocytes from WT and SOCS3 LKO mice and examined the effects of tumor necrosis factor α and insulin on Akt phosphorylation and fatty acid metabolism and lipogenic gene expression. Hepatocytes from control-fed SOCS3 LKO mice were protected from developing tumor necrosis factor α-induced insulin resistance but also had increased lipogenesis and expression of sterol response element-binding protein-1c target genes. Lean SOCS3 LKO mice fed a control diet had enhanced hepatic insulin sensitivity; however, when fed an HFD, SOCS3 LKO mice had increased liver fat, inflammation, and whole-body insulin resistance. SOCS3 LKO mice fed an HFD also had elevated hypothalamic SOCS3 and fatty acid synthase expression and developed greater obesity due to increased food intake and reduced energy expenditure.

CONCLUSION

Deletion of SOCS3 in the liver increases liver insulin sensitivity in mice fed a control diet but paradoxically promotes lipogenesis, leading to the development of nonalcoholic fatty liver disease, inflammation, and obesity.

High glucose induces suppression of insulin signalling and apoptosis via upregulation of endogenous IL-1beta and suppressor of cytokine signalling-1 in mouse pancreatic beta cells

Chronic hyperglycemia and inflammatory cytokines disrupt and/or attenuate signal transduction pathways that promote normal beta-cell survival, leading to the destruction of endocrine pancreas in type 2 diabetes. There is convincing evidence that autocrine insulin signalling exerts protective anti-apoptotic effects on beta cells. Suppressors of cytokine signalling (SOCS) were induced by several cytokines and inhibit insulin-initiated signal transduction. The aim of this study was to investigate whether high glucose can influence endogenous interleukin-1beta (IL-1beta) and SOCS expression thus affecting insulin signalling and survival in insulin-producing mouse pancreatic beta cells (betaTC-6). Results showed that prolonged exposure of betaTC-6 cells to increased glucose concentrations resulted in significant inhibition of insulin-induced tyrosine phosphorylation of the insulin receptor (IR), and insulin receptor substrate-2 (IRS-2) as well as PI3-kinase activation. These changes were accompanied by impaired activation of the anti-apoptotic signalling protein Akt and annulment of Akt-mediated suppression of the Forkhead family of transcription factors (FoxO) activation. Glucose-induced attenuation of IRS-2/Akt-mediated signalling was associated with increased IL-1beta expression. Enhanced endogenous IL-1beta specifically induced mRNA and protein expression of SOCS-1 in betaTC-6 cells. Inhibition of SOCS-1 expression by SOCS-1-specific small interfering RNA restored IRS-2/PI3K-mediated Akt phosphorylation suppressed by high glucose. The upregulation of endogenous cytokine signalling and FoxO activation were accompanied by enhanced caspase-3 activation and increased susceptibility of cells to apoptosis. These results indicated that glucose-induced endogenous IL-1beta expression increased betaTC-6 cells apoptosis by inhibiting, at least in part, IRS-2/Akt-mediated signalling through SOCS-1 upregulation.

Functional SOCS1 polymorphisms are associated with variation in obesity in whites

AIMS/HYPOTHESIS

The suppressor of cytokine signalling 1 (SOCS1) is a natural inhibitor of cytokine and insulin signalling pathways and may also play a role in obesity. In addition, SOCS1 is considered a candidate gene in the pathogenesis of both type 1 diabetes (T1D) and type 2 diabetes (T2D). The objective was to perform mutation analysis of SOCS1 and to test the identified variations for association to T2D-related quantitative traits, T2D or T1D.

METHODS

Mutation scanning was performed by direct sequencing in 27 white Danish subjects. Genotyping was carried out by TaqMan allelic discrimination. A total of more than 8100 individuals were genotyped.

RESULTS

Eight variations were identified in the 5' untranslated region (UTR) region. Two of these had allele frequencies below 1% and were not further examined. The six other variants were analysed in groups of T1D families (n = 1461 subjects) and T2D patients (n = 1430), glucose tolerant first-degree relatives of T2D patients (n = 212) and normal glucose tolerant (NGT) subjects. The rs33977706 polymorphism (-820G > T) was associated with a lower body mass index (BMI) (p = 0.004). In a second study (n = 4625 NGT subjects), significant associations of both the rs33977706 and the rs243330 (-1656G > A) variants to obesity were found (p = 0.047 and p = 0.015) respectively. The rs33977706 affected both binding of a nuclear protein to and the transcriptional activity of the SOCS1 promoter, indicating a relationship between this polymorphism and gene regulation.

CONCLUSIONS/INTERPRETATION

This study demonstrates that functional variations in the SOCS1 promoter may associate with alterations in BMI in the general white population.

Increased glucose production in mice overexpressing human fructose-1,6-bisphosphatase in the liver

Increased endogenous glucose production (EGP) predominantly from the liver is a characteristic feature of type 2 diabetes, which positively correlates with fasting hyperglycemia. Gluconeogenesis is the biochemical pathway shown to significantly contribute to increased EGP in diabetes. Fructose-1,6-bisphosphatase (FBPase) is a regulated enzyme in gluconeogenesis that is increased in animal models of obesity and insulin resistance. However, whether a specific increase in liver FBPase can result in increased EGP has not been shown. The objective of this study was to determine the role of upregulated liver FBPase in glucose homeostasis. To achieve this goal, we generated human liver FBPase transgenic mice under the control of the transthyretin promoter, using insulator sequences to flank the transgene and protect it from site-of-integration effects. This resulted in a liver-specific model, as transgene expression was not detected in other tissues. Mice were studied under the following conditions: 1) at two ages (24 wk and 1 yr old), 2) after a 60% high-fat diet, and 3) when bred to homozygosity. Hemizygous transgenic mice had an approximately threefold increase in total liver FBPase mRNA with concomitant increases in FBPase protein and enzyme activity levels. After high-fat feeding, hemizygous transgenics were glucose intolerant compared with negative littermates (P < 0.02). Furthermore, when bred to homozygosity, chow-fed transgenic mice showed a 5.5-fold increase in liver FBPase levels and were glucose intolerant compared with negative littermates, with a significantly higher rate of EGP (P < 0.006). This is the first study to show that FBPase regulates EGP and whole body glucose homeostasis in a liver-specific transgenic model. Our homozygous transgenic model may be useful for testing human FBPase inhibitor compounds with the potential to treat patients with type 2 diabetes.

Skeletal muscle insulin resistance: role of inflammatory cytokines and reactive oxygen species

The cardiometabolic syndrome (CMS), with its increased risk for cardiovascular disease (CVD), nonalcoholic fatty liver disease (NAFLD), and chronic kidney disease (CKD), has become a growing worldwide health problem. Insulin resistance is a key factor for the development of the CMS and is strongly related to obesity, hyperlipidemia, hypertension, type 2 diabetes mellitus (T2DM), CKD, and NAFLD. Insulin resistance in skeletal muscle is particularly important since it is normally responsible for more than 75% of all insulin-mediated glucose disposal. However, the molecular mechanisms responsible for skeletal muscle insulin resistance remain poorly defined. Accumulating evidence indicates that low-grade chronic inflammation and oxidative stress play fundamental roles in the development of insulin resistance, and inflammatory cytokines likely contribute to the link between inflammation, oxidative stress, and skeletal muscle insulin resistance. Understanding the mechanisms by which skeletal muscle tissue develops resistance to insulin will provide attractive targets for interventions, which may ultimately curb this serious problem. This review is focused on the effects of inflammatory cytokines and oxidative stress on insulin signaling in skeletal muscle and consequent development of insulin resistance.

LCAT-null mice develop improved hepatic insulin sensitivity through altered regulation of transcription factors and suppressors of cytokine signaling

We previously reported that LCAT-deficient mice develop not only low HDL-cholesterol but also hypertriglyceridemia, hepatic triglyceride (TG) overproduction, and, unexpectedly, improved hepatic insulin sensitivity and reduced hepatic TG content. Here, we examined the mechanistic links underlying this apparent paradox. The LDL receptor-deficient (Ldlr)(-/-)xLcat(-/-) mouse model and age- and sex-matched Ldlr(-/-)xLcat(+/+) littermates, both in C57Bl/6 background, were employed. Studies of hepatic insulin signal transduction showed an upregulation of hepatic Irs2 mRNA level (5.3-fold, P = 0.02), IRS-2 protein mass level (1.5-fold, P = 0.009) and pIRS-2 (1.8-fold. P = 0.02) in the Ldlr(-/-)xLcat(-/-) mice. There was a 1.2-fold increase in pAkt (P = 0.03) with a nonsignificant change in total Akt. We observed a significant shift in its downstream transcription factor FoxO-1 to the cytosolic compartment (2.3-fold increase in cytosolic/nuclear ratio, P = 0.04). We also observed a significant 3.1-fold increase in nuclear abundance of FoxA-2 mass (P = 0.017) and a 1.5-fold upregulation of its coactivator PGC-1beta (P = 0.002), the coordinated actions of which promotes hepatic TG production and beta-oxidation. Increased hepatic insulin signaling in the Ldlr(-/-)xLcat(-/-) mice was associated with an upregulation of the Tcfe3 gene (1.7-fold, P = 0.024), a selective downregulation of the Socs-1 gene by 60% (P = 0.01), and no change in PTP-1B protein mass. These data suggest that LCAT deficiency induces complex alterations in hepatic signal transduction cascades, which explain, at least in part, the observed enhanced insulin signaling in association with hepatic TG overproduction and reduced hepatic TG content.

The dual function of hepatic SOCS3 in insulin resistance in vivo

Inflammation associates with insulin resistance, which dysregulates nutrient homeostasis and leads to diabetes. The suppressor of cytokine signaling 3 (SOCS3), which is induced by pro-inflammatory cytokines, such as TNFalpha and IL-6, has been implicated in inflammation-mediated insulin resistance in the liver and adipocytes. However, no genetic evidence has been provided for the involvement of SOCS3 on insulin resistance. Here, we generated hepatocyte-specific SOCS3-deficient (L-SOCS3 cKO) mice and examined insulin sensitivity. Being consistent with a previous idea, the loss of SOCS3 in the liver apparently improved insulin sensitivity. However, unexpectedly, L-SOCS3 cKO mice exhibited obesity and systemic insulin resistance with age. Insulin signaling was rather suppressed in muscles, suggesting that deletion of the SOCS3 gene in the liver modulates insulin sensitivity in other organs. Anti-inflammatory reagent, sodium salicylate, partial improved insulin resistance of aged L-SOCS3 cKO mice, suggesting that enhanced inflammatory status is associated with the phenotype of these mice. STAT3 was hyperactivated and acute-phase proteins were elevated in L-SOCS3 cKO mice liver, which were reduced by sodium salicylate treatment. We conclude that hepatic SOCS3 is a mediator of insulin resistance in the liver; however, lack of SOCS3 in the liver promotes systemic insulin resistance by mimicking chronic inflammation.

Effects of pioglitazone on suppressor of cytokine signaling 3 expression: potential mechanisms for its effects on insulin sensitivity and adiponectin expression

Pioglitazone is widely used for the treatment of diabetic patients with insulin resistance. The mechanism of pioglitazone to improve insulin sensitivity is not fully understood. Recent studies have shown that the induction of suppressor of cytokine signaling 3 (SOCS3) is related to the development of insulin resistance. Here, we examined whether the insulin-sensitizing effect of pioglitazone affects the SOCS induction. In db/db mice and high-fat-fed mice, expression of SOCS3 mRNA in fat tissue was increased compared with that in lean control mice, and pioglitazone suppressed SOCS3 levels. In 3T3-L1 adipocytes, mediators of insulin resistance such as tumor necrosis factor-alpha (TNF-alpha), interleukin-6, growth hormone, and insulin increased SOCS3 expression, which was partially inhibited by pioglitazone. The ability of pioglitazone to suppress SOCS3 induction by TNF-alpha was greatly augmented by peroxisome proliferator-activated receptor gamma overexpression. SOCS3 overexpression and tyrphostin AG490, a Janus kinase 2 inhibitor, or dominant-negative STAT3 expression partially inhibited adiponectin secretion and was accompanied by decreased STAT3 phosphorylation. Conversely, pioglitazone increased adiponectin secretion and STAT3 phosphorylation in fat tissue of db/db mice and in 3T3-L1 adipocytes. These results suggest that pioglitazone exerts its effect to improve whole-body insulin sensitivity in part through the suppression of SOCS3, which is associated with the increase in STAT3 phosphorylation and adiponectin production in fat tissue.

Tumor necrosis factor alpha-induced skeletal muscle insulin resistance involves suppression of AMP-kinase signaling

Elevated levels of tumor necrosis factor (TNFalpha) are implicated in the development of insulin resistance, but the mechanisms mediating these chronic effects are not completely understood. We demonstrate that TNFalpha signaling through TNF receptor (TNFR) 1 suppresses AMPK activity via transcriptional upregulation of protein phosphatase 2C (PP2C). This in turn reduces ACC phosphorylation, suppressing fatty-acid oxidation, increasing intramuscular diacylglycerol accumulation, and causing insulin resistance in skeletal muscle, effects observed both in vitro and in vivo. Importantly even at pathologically elevated levels of TNFalpha observed in obesity, the suppressive effects of TNFalpha on AMPK signaling are reversed in mice null for both TNFR1 and 2 or following treatment with a TNFalpha neutralizing antibody. Our data demonstrate that AMPK is an important TNFalpha signaling target and is a contributing factor to the suppression of fatty-acid oxidation and the development of lipid-induced insulin resistance in obesity.

SOCS proteins and caveolin-1 as negative regulators of endocrine signaling

Recently, a new class of regulatory molecules has emerged; these molecules, termed SOCS proteins, function as suppressors of cytokine signaling. SOCS proteins negatively regulate the Janus kinase signal transducer and activator of transcription (JAK-STAT) signaling cascade. Interestingly, it appears that other proteins, such as caveolin-1, can also function as suppressors of cytokine signaling by inhibiting the kinase activity of JAK family members. This might result from the ability of caveolin-1 to function as a broad-spectrum kinase inhibitor through the caveolin-scaffolding domain.

SOCS1: a potent and multifaceted regulator of cytokines and cell-mediated inflammation

Suppressor of cytokine signalling-1 (SOCS1), as the name implies, is a protein that functions as a negative regulator of cytokine signalling. Initially characterized for its ability to inhibit JAK phosphorylation and function, SOCS1 also targets proteins for degradation by the proteosome machinery. The expression of SOCS1 can be regulated at the transcription, translation and protein level. Despite the broad spectrum of cytokines that can induce SOCS1 expression and/or be inhibited by SOCS1 in vitro, the use of genetically modified mice has revealed a more specific role for SOCS1 in vivo including a critical role in the regulation of IFNgamma signalling. In addition, SOCS1 has a complex role in T cell activation, and studies have revealed significant roles for SOCS1 in the regulation of IL-4, IL-12 and IL-15 in vivo. Interestingly, SOCS1 action is not limited to the regulation of the classical JAK/STAT-signalling pathway, because SOCS1 also inhibits cytokines like insulin and toll-like receptor signal transduction, neither of which activates the JAK/STAT pathway. Evidence is emerging for a role for aberrant SOCS1 expression in human disease, particularly in a number of malignancies.

Deletion of SOCS7 leads to enhanced insulin action and enlarged islets of Langerhans

NIDDM is characterized by progressive insulin resistance and the failure of insulin-producing pancreatic beta cells to compensate for this resistance. Hyperinsulinemia, inflammation, and prolonged activation of the insulin receptor (INSR) have been shown to induce insulin resistance by decreasing INSR substrate (IRS) protein levels. Here we describe a role for SOCS7 in regulating insulin signaling. Socs7-deficient mice exhibited lower glucose levels and prolonged hypoglycemia during an insulin tolerance test and increased glucose clearance in a glucose tolerance test. Six-month-old Socs7-deficient mice exhibited increased growth of pancreatic islets with mildly increased fasting insulin levels and hypoglycemia. These defects correlated with increased IRS protein levels and enhanced insulin action in cells lacking SOCS7. Additionally, SOCS7 associated with the INSR and IRS1--molecules that are essential for normal regulation of insulin action. These data suggest that SOCS7 is a potent regulator of glucose homeostasis and insulin signaling.