SOCS-3 is an insulin-induced negative regulator of insulin signaling

SOCS2 Binds to and Regulates EphA2 through Multiple Mechanisms

Suppressors of cytokine signaling (SOCS) proteins inhibit signaling by serving as substrate receptors for the Cullin5-RING E3 ubiquitin ligase (CRL5) and through a variety of CRL5-independent mechanisms. CRL5, SOCS2 and SOCS6 are implicated in suppressing transformation of epithelial cells. We identified cell proteins that interact with SOCS2 and SOCS6 using two parallel proteomics techniques: BioID and Flag affinity purification mass spectrometry. The receptor tyrosine kinase ephrin type-A receptor 2 (EphA2) was identified as a SOCS2-interacting protein. SOCS2-EphA2 binding requires the SOCS2 SH2 domain and EphA2 activation loop autophosphorylation, which is stimulated by Ephrin A1 (EfnA1) or by phosphotyrosine phosphatase inhibition. Surprisingly, EfnA1-stimulated EphA2-SOCS2 binding is delayed until EphA2 has been internalized into endosomes. This suggests that SOCS2 binds to EphA2 in the context of endosomal membranes. We also found that SOCS2 overexpression decreases steady state levels of EphA2, consistent with increased EphA2 degradation. This effect is indirect: SOCS2 induces EfnA1 expression, and EfnA1 induces EphA2 down-regulation. Other RTKs have been reported to bind, and be regulated by, over-expressed SOCS proteins. Our data suggest that SOCS protein over-expression may regulate receptor tyrosine kinases through indirect and direct mechanisms.

Mechanisms of inflammatory responses and development of insulin resistance: how are they interlinked?

Background

Insulin resistance (IR) is one of the major hallmark for pathogenesis and etiology of type 2 diabetes mellitus (T2DM). IR is directly interlinked with various inflammatory responses which play crucial role in the development of IR. Inflammatory responses play a crucial role in the pathogenesis and development of IR which is one of the main causative factor for the etiology of T2DM.

Methods

A comprehensive online English literature was searched using various electronic search databases. Different search terms for pathogenesis of IR, role of various inflammatory responses were used and an advanced search was conducted by combining all the search fields in abstracts, keywords, and titles.

Results

We summarized the data from the searched articles and found that inflammatory responses activate the production of various pro-inflammatory mediators notably cytokines, chemokines and adipocytokines through the involvement of various transcriptional mediated molecular pathways, oxidative and metabolic stress. Overnutrition is one of the major causative factor that contributes to induce the state of low-grade inflammation due to which accumulation of elevated levels of glucose and/or lipids in blood stream occur that leads to the activation of various transcriptional mediated molecular and metabolic pathways. This results in the induction of various pro-inflammatory mediators that are decisively involved to provoke the pathogenesis of tissue-specific IR by interfering with insulin signaling pathways. Once IR is developed, it increases oxidative stress in β-cells of pancreatic islets and peripheral tissues which impairs insulin secretion, and insulin sensitivity in β-cells of pancreatic islets and peripheral tissues, respectively. Moreover, we also summarized the data regarding various treatment strategies of inflammatory responses-induced IR.

Conclusions

In this article, we have briefly described that how pro-inflammatory mediators, oxidative stress, transcriptional mediated molecular and metabolic pathways are involved in the pathogenesis of tissues-specific IR. Moreover, based on recent investigations, we have also described that to counterfeit these inflammatory responses is one of the best treatment strategy to prevent the pathogenesis of IR through ameliorating the incidences of inflammatory responses.

Possible Integrative Actions of Leptin and Insulin Signaling in the Hypothalamus Targeting Energy Homeostasis

Obesity has emerged as one of the most burdensome conditions in modern society. In this context, understanding the mechanisms controlling food intake is critical. At present, the adipocyte-derived hormone leptin and the pancreatic β-cell-derived hormone insulin are considered the principal anorexigenic hormones. Although leptin and insulin signal transduction pathways are distinct, their regulation of body weight maintenance is concerted. Resistance to the central actions of leptin or insulin is linked to the emergence of obesity and diabetes mellitus. A growing body of evidence suggests a convergence of leptin and insulin intracellular signaling at the insulin-receptor-substrate-phosphatidylinositol-3-kinase level. Moreover, numerous factors mediating the pathophysiology of leptin resistance, a hallmark of obesity, such as endoplasmic reticulum stress, protein tyrosine phosphatase 1B, and suppressor of cytokine signaling 3 also contribute to insulin resistance. Recent studies have also indicated that insulin potentiates leptin-induced signaling. Thus, a greater understanding of the overlapping functions of leptin and insulin in the central nervous system is vital to understand the associated physiological and pathophysiological states. This mini-review focuses on the cross talk and integrative signaling of leptin and insulin in the regulation of energy homeostasis in the brain.

The impact of insulin resistance on the kidney and vasculature

Insulin resistance is a systemic disorder that affects many organs and insulin-regulated pathways. The disorder is characterized by a reduced action of insulin despite increased insulin concentrations (hyperinsulinaemia). The effects of insulin on the kidney and vasculature differ in part from the effects on classical insulin target organs. Insulin causes vasodilation by enhancing endothelial nitric oxide production through activation of the phosphatidylinositol 3-kinase pathway. In insulin-resistant states, this pathway is impaired and the mitogen-activated protein kinase pathway stimulates vasoconstriction. The action of insulin on perivascular fat tissue and the subsequent effects on the vascular wall are not fully understood, but the hepatokine fetuin-A, which is released by fatty liver, might promote the proinflammatory effects of perivascular fat. The strong association of salt-sensitive arterial hypertension with insulin resistance indicates an involvement of the kidney in the insulin resistance syndrome. The insulin receptor is expressed on renal tubular cells and podocytes and insulin signalling has important roles in podocyte viability and tubular function. Renal sodium transport is preserved in insulin resistance and contributes to the salt-sensitivity of blood pressure in hyperinsulinaemia. Therapeutically, renal and vascular insulin resistance can be improved by an integrated holistic approach aimed at restoring overall insulin sensitivity and improving insulin signalling.

Adipokines in nonalcoholic fatty liver disease

Since the discovery of adipose tissue as a higly active endocrine tissue, adipokines, peptides produced by adipose tissue and exerting autocrine, paracrine and endocrine function, have gained increasing interest in various obesity-related diseases, including nonalcoholic fatty liver disease (NAFLD). Data regarding the association between NAFLD and circulating leptin and adiponectin levels are generally well documented: leptin levels increase, whereas adiponectin levels decrease, by increasing the severity of NAFLD. Data regarding other adipokines in histologically confirmed NAFLD populations are inconclusive (e.g., resistin, visfatin, retinol-binding protein-4, chemerin) or limited (e.g., adipsin, obestatin, omentin, vaspin etc.). This review summarizes evidence on the association between adipokines and NAFLD. The first part of the review provides general consideration on the interplay between adipokines and NAFLD, and the second part provides evidence on specific adipokines possibly involved in NAFLD pathogenesis. A thorough insight into the pathophysiologic mechanisms linking adipokines with NAFLD may result in the design of studies investigating the combined adipokine use as noninvasive diagnostic markers of NAFLD and new clinical trials targeting the treatment of NAFLD.

Association of Polymorphisms in STRA6 and RARRES2 Genes with Type 2 Diabetes in Southern Han Chinese

Stimulated by retinoic acid gene homolog 6 (STRA6) and retinoic acid receptor responder 2 (RARRES2) are candidate genes involved in the pathogenesis of type 2 diabetes mellitus (T2DM). Three tag-SNPs in STRA6 and one in RARRES2 gene were selected and genotyped with TaqMan or PCR-RFLP method in 603 populations (571 patients with T2D versus 632 control subjects) in Southern Han Chinese. We estimated the interactions between T2DM risk and genetic variants in the STRA6 and RARRES2 genes using polymerase chain reaction. Rs736118 in STRA6 gene were significantly associated with T2DM occurrence in the recessive genetic model. The genotype of rs974456 was significantly associated with T2DM in the dominant genetic model correlated to sex, MBI, and triglyceride. However, the association of other SNPs with T2DM was not found. Furthermore, smoking history and other factors may be independent risk factors for the incidence of T2DM. This study suggested that a role of STRA6 polymorphism could also be of value in predicting the risk of T2DM while RARRES2 polymorphism could not predict the risk of T2DM.

Central leptin resistance and hypothalamic inflammation are involved in letrozole-induced polycystic ovary syndrome rats

Accumulating evidence indicates that leptin acts as an important mediator in energy homeostasis and reproduction. Since dysfunction of reproduction and metabolism are major characteristics of polycystic ovarian syndrome (PCOS), the role of leptin in pathogenesis of PCOS needs further research. Many studies have shown that central leptin resistance existed in obesity rats through leptin intracerebroventricular (icv) injection; however, central leptin resistance in PCOS rats has not been reported. This study aimed to investigate whether there was a state of central leptin resistance in PCOS rats, as well as explore the possible association of hypothalamic inflammation with central leptin resistance. First, letrozole was used to induce the PCOS model, 24 h food intake, 24 h body weight changes and the expression of p-STAT3 were determined following leptin or artificial cerebrospinal fluid (aCSF) icv injection in rats. Second, we further evaluated the expressions of IL-1β, IL-6, TNF-α, p-IKKβ, NF-κB, p-NF-κB, IκBα, p-IκBα and SOCS3 in hypothalamus. The results showed that 24 h food intake and body weight were decreased, while the expression of p-STAT3 was increased in control group rats following leptin icv injection compared with aCSF icv injection; however, both of them showed no significant difference in PCOS rats. Furthermore, inflammatory markers were upregulated in the hypothalami of PCOS rats. Taken together, our data indicated that there was a state of chronic low-grade inflammation in hypothalamus which might be the possible mechanism for central leptin resistance in PCOS rats.

Impact of anti-inflammatory nutrients on obesity-associated metabolic-inflammation from childhood through to adulthood

Obesity-related metabolic conditions such as insulin resistance (IR), type 2 diabetes and CVD share a number of pathological features, one of which is metabolic-inflammation. Metabolic-inflammation results from the infiltration of immune cells into the adipose tissue, driving a pro-inflammatory environment, which can induce IR. Furthermore, resolution of inflammation, an active process wherein the immune system counteracts pro-inflammatory states, may be dysregulated in obesity. Anti-inflammatory nutritional interventions have focused on attenuating this pro-inflammatory environment. Furthermore, with inherent variability among individuals, establishing at-risk populations who respond favourably to nutritional intervention strategies is important. This review will focus on chronic low-grade metabolic-inflammation, resolution of inflammation and the putative role anti-inflammatory nutrients have as a potential therapy. Finally, in the context of personalised nutrition, the approaches used in defining individuals who respond favourably to nutritional interventions will be highlighted. With increasing prevalence of obesity in younger people, age-dependent biological processes, preventative strategies and therapeutic options are important to help protect against development of obesity-associated co-morbidities.

Epigenetic associations of type 2 diabetes and BMI in an Arab population

Background

The prevalence of type 2 diabetes (T2D) and obesity has dramatically increased within a few generations, reaching epidemic levels. In addition to genetic risk factors, epigenetic mechanisms triggered by changing environment are investigated for their role in the pathogenesis of these complex diseases. Epigenome-wide association studies (EWASs) have revealed significant associations of T2D, obesity, and BMI with DNA methylation. However, populations from the Middle East, where T2D and obesity rates are highest worldwide, have not been investigated so far.

Methods

We performed the first EWAS in an Arab population with T2D and BMI and attempted to replicate 47 EWAS associations previously reported in Caucasians. We used the Illumina Infinium HumanMethylation450 BeadChip to quantify DNA methylation in whole blood DNA from 123 subjects of 15 multigenerational families from Qatar. To investigate the effect of differing genetic background and environment on the epigenetic associations, we further assessed the effect of replicated loci in 810 twins from UK.

Results

Our EWAS suggested a novel association between T2D and cg06721411 (DQX1; p value = 1.18 × 10⁻⁹). We replicated in the Qatari population seven CpG associations with BMI (SOCS3, p value = 3.99 × 10⁻⁶; SREBF1, p value = 4.33 × 10⁻⁵; SBNO2, p value = 5.87 × 10⁻⁵; CPT1A, p value = 7.99 × 10⁻⁵; PRR5L, p value = 1.85 × 10⁻⁴; cg03078551, intergenic region on chromosome 17; p value = 1.00 × 10⁻³; LY6G6E, p value = 1.10 × 10⁻³) and one with T2D (TXNIP, p value = 2.46 × 10⁻⁵). All the associations were further confirmed in the UK cohort for both BMI and T2D. Meta-analysis increased the significance of the observed associations and revealed strong heterogeneity of the effect sizes (apart from CPT1A), although associations at these loci showed concordant direction in the two populations.

Conclusions

Our study replicated eight known CpG associations with T2D or BMI in an Arab population. Heterogeneity of the effects at all loci except CPT1A between the Qatari and UK studies suggests that the underlying mechanisms might depend on genetic background and environmental pressure. Our EWAS results provide a basis for comparison with other ethnicities.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-016-0177-6) contains supplementary material, which is available to authorized users.

Vitamin A Transport and Cell Signaling by the Retinol-Binding Protein Receptor STRA6

Vitamin A, retinol, circulates in blood bound to retinol binding protein (RBP). In some tissues, the retinol-RBP complex (holo-RBP) is recognized by a membrane receptor, termed STRA6, which mediates uptake of retinol into cells. Recent studies have revealed that, in addition to serving as a retinol transporter, STRA6 is a ligand-activated cell surface signaling receptor that, upon binding of holo-RBP activates JAK/STAT signaling, culminating in the induction of STAT target genes. It has further been shown that retinol transport and cell signaling by STRA6 are critically interdependent and that both are coupled to intracellular vitamin A metabolism. The molecular mechanism of action of STRA6 and its associated machinery is beginning to be revealed, but further work is needed to identify and characterize the complete range of genes and associated signaling cascades that are regulated by STRA6 in different tissues. An understanding of STRA6 is clinically relevant, as for example, it has been shown to be hyper- activated in obese animals, leading to insulin resistance. A potential role for STRA6 in other pathologies, including cancer, awaits further investigation.

Suppressor of Cytokine Signaling-3 (SOCS-3) Induces Proprotein Convertase Subtilisin Kexin Type 9 (PCSK9) Expression in Hepatic HepG2 Cell Line

The suppressor of cytokine signaling (SOCS) proteins are negative regulators of the JAK/STAT pathway activated by proinflammatory cytokines, including the tumor necrosis factor-α (TNF-α). SOCS3 is also implicated in hypertriglyceridemia associated to insulin resistance. Proprotein convertase subtilisin kexin type 9 (PCSK9) levels are frequently found to be positively correlated to insulin resistance and plasma very low density lipoprotein (VLDL) triglycerides concentrations. The present study aimed to investigate the possible role of TNF-α and JAK/STAT pathway on de novo lipogenesis and PCSK9 expression in HepG2 cells. TNF-α induced both SOCS3 and PCSK9 in a concentration-dependent manner. This effect was inhibited by transfection with siRNA anti-STAT3, suggesting the involvement of the JAK/STAT pathway. Retroviral overexpression of SOCS3 in HepG2 cells (HepG2(SOCS3)) strongly inhibited STAT3 phosphorylation and induced PCSK9 mRNA and protein, with no effect on its promoter activity and mRNA stability. Consistently, siRNA anti-SOCS3 reduced PCSK9 mRNA levels, whereas an opposite effect was observed with siRNA anti-STAT3. In addition, HepG2(SOCS3) express higher mRNA levels of key enzymes involved in the de novo lipogenesis, such as fatty-acid synthase, stearoyl-CoA desaturase (SCD)-1, and apoB. These responses were associated with a significant increase of SCD-1 protein, activation of sterol regulatory element-binding protein-1c (SREBP-1), accumulation of cellular triglycerides, and secretion of apoB. HepG2(SOCS3) show lower phosphorylation levels of insulin receptor substrate 1 (IRS-1) Tyr(896) and Akt Ser(473) in response to insulin. Finally, insulin stimulation produced an additive effect with SOCS3 overexpression, further inducing PCSK9, SREBP-1, fatty acid synthase, and apoB mRNA. In conclusion, our data candidate PCSK9 as a gene involved in lipid metabolism regulated by proinflammatory cytokine TNF-α in a SOCS3-dependent manner.

Methylation and microRNA-mediated epigenetic regulation of SOCS3

Epigenetic gene silencing of several genes causes different pathological conditions in humans, and DNA methylation has been identified as one of the key mechanisms that underlie this evolutionarily conserved phenomenon associated with developmental and pathological gene regulation. Recent advances in the miRNA technology with high throughput analysis of gene regulation further increased our understanding on the role of miRNAs regulating multiple gene expression. There is increasing evidence supporting that the miRNAs not only regulate gene expression but they also are involved in the hypermethylation of promoter sequences, which cumulatively contributes to the epigenetic gene silencing. Here, we critically evaluated the recent progress on the transcriptional regulation of an important suppressor protein that inhibits cytokine-mediated signaling, SOCS3, whose expression is directly regulated both by promoter methylation and also by microRNAs, affecting its vital cell regulating functions. SOCS3 was identified as a potent inhibitor of Jak/Stat signaling pathway which is frequently upregulated in several pathologies, including cardiovascular disease, cancer, diabetes, viral infections, and the expression of SOCS3 was inhibited or greatly reduced due to hypermethylation of the CpG islands in its promoter region or suppression of its expression by different microRNAs. Additionally, we discuss key intracellular signaling pathways regulated by SOCS3 involving cellular events, including cell proliferation, cell growth, cell migration and apoptosis. Identification of the pathway intermediates as specific targets would not only aid in the development of novel therapeutic drugs, but, would also assist in developing new treatment strategies that could successfully be employed in combination therapy to target multiple signaling pathways.

Lutein dietary supplementation attenuates streptozotocin-induced testicular damage and oxidative stress in diabetic rats

Background

Diabetes mellitus with the successive generation of reactive oxygen species signifies a major risk factor for testicular dysfunction. Antioxidant supplements are one of the best options to prevent such disorder. In the present study, lutein as dietary supplement has been used to explore its potential protective effects against diabetes-induced oxidative stress in testicular cells.

Methods

Diabetes was induced using a single IP injection of streptozotocin (STZ). Lutein was mixed with rat chow powder and supplemented to diabetic rats for 5 weeks. Serum testosterone levels were estimated. In testicular cells, thiobarbituric acid reactive substances (TBARS), total sulfhydryl groups (T-GSH), non-protein sulfhydryl groups (NP-SH), superoxide dismutase (SOD) and catalase (CAT) activities were measured. Pro-inflammatory mediators like tumor necrosis factor α (TNF-α) and interleukin 1β (IL-1β) were measured in the testis. Nucleic acids and total protein (TP) levels were also estimated in testicular cells. Histopathological changes were evaluated in testis.

Results

Serum testosterone level was significantly decreased in diabetic animals compared to controls. Diabetes markedly reduced T-GSH, NP-SH, CAT and SOD, while TBARS, TNF-α and IL-1β levels were increased in the diabetic testis compared to non-diabetic controls. Lutein supplementation, significantly and dose dependently increased the serum testosterone level. The elevated TBARS levels were significantly decreased compared to diabetic group, while the decreased levels of T-GSH and NP-SH and activities of CAT and SOD were found increased by lutein treatments in dose dependent manner. Lutein pretreatment also inhibited the TNF-α and IL-1β levels compared to diabetic group. The decreased values of nucleic acids and total protein in diabetic group were also significantly increased in lutein supplemented groups. The histopathological evaluation revealed protection the damaged testicular cells in the diabetic rats by lutein supplementation.

Conclusion

These findings showed that lutein has potential beneficial effects in diabetes-induced testicular damage, probably through its antioxidant and anti-inflammatory properties.

Interleukin-6 CpG Methylation and Body Weight Correlate Differently in Type 2 Diabetes Patients Compared to Obese and Lean Controls

BACKGROUND/AIMS

Diabetes mellitus type 2 (DMT2) is accompanied by systemic low-grade inflammation with elevated levels of interleukin-6 (IL-6), which is encoded by a gene (IL-6) previously shown to be regulated by DNA methylation. We investigated seven CpG sites in IL-6 in individuals with DMT2, obese individuals and lean controls. Further, the DMT2 group received the glucagon-like peptide 1 agonist liraglutide.

METHODS

Blood samples were taken at the beginning of the study and after 4 months. The DNA methylation was assessed using pyrosequencing.

RESULTS

Methylation levels at the CpG sites -664, -628 and +13 at the first sampling time point (T1) and at -666 and -664 at the second sampling time point (T2) correlated negatively with initial body weight in the DMT2 group. We found positive correlations for the obese and the lean control group. In the obese group, CpG +27 methylation at T1 correlated with initial body weight (r = 0.685; p = 0.014). In the lean group, CpG -664 at T1 (r = 0.874; p = 0.005) and CpG -628 at T2 (r = 0.632; p = 0.050) correlated with initial body weight.

CONCLUSION

These findings are an informative basis for further studies to elucidate epigenetic mechanisms underlying DMT2. Additionally, our results might provide starting points for the development of biomarkers for prevention and therapy strategies.

Sodium salicylate reduced insulin resistance in the retina of a type 2 diabetic rat model

Sodium salicylate has been reported to reduce markers of diabetic retinopathy in a type 1 rat model. Because rates of type 2 diabetes are on the rise, we wanted to determine whether salicylate could improve insulin resistance in a type 2 rat model, as well as improve retinal function. We treated lean and obese BBZDR/Wor type 2 diabetic rats with salicylate in their chow for 2 months. Prior to salicylate treatment, rats underwent an electroretinogram to measure retinal function. After 2 months of treatment, rats underwent an additional electroretinogram prior to sacrifice. In addition to the animal model, we also treated retinal endothelial cells (REC) and rat Müller cells with salicylate and performed the same analyses as done for the rat retinal lysates. To investigate the role of salicylate in insulin signaling, we measured TNFα and caspase 3 levels by ELISA, as well as performed Western blotting for insulin receptor substrate 1, insulin receptor, SOCS3, and pro- and anti-apoptotic markers. Data demonstrated that salicylate significantly improved retinal function, as well as reduced TNFα and SOCS3-induced insulin resistance in all samples. Overall, results suggest that salicylate is effective in reducing insulin resistance in the retina of type 2 diabetic rat models.

Signaling by retinol and its serum binding protein

Vitamin A, retinol, circulates in blood bound to retinol-binding protein (RBP) which, in turn, associates with transthyretin (TTR) to form a retinol-RBP-TTR ternary complex. At some tissues, retinol-bound (holo-) RBP is recognized by a membrane protein termed STRA6, which transports retinol from extracellular RBP into cells and, concomitantly, activates a JAK2/STAT3/5 signaling cascade that culminates in induction of STAT target genes. STRA6-mediated retinol transport and cell signaling are critically inter-dependent, and they both require the presence of cellular retinol-binding protein 1 (CRBP1), an intracellular retinol acceptor, as well as a retinol-metabolizing enzyme such as lecithin:retinol acyltransferase (LRAT). STRA6 thus functions as a "cytokine signaling transporter" which couples vitamin A homeostasis and metabolism to cell signaling, thereby regulating gene transcription. Recent studies provided molecular level insights into the mode of action of this unique protein.

Signalling Networks Governing Metabolic Inflammation

Low-grade inflammation is an established pathological condition that contributes to the development of obesity, insulin resistance and type 2 diabetes. Metabolic inflammation is dependent on multiple signalling events. In an overnutrition state, canonical inflammatory pathways are induced by inflammatory cytokines and lipid species. They can also be triggered through inflammasome activation as well as through cellular stress provoked by the unfolded protein response at the endoplasmic reticulum as well as by reactive oxygen species. In this chapter, we summarize the current knowledge about signalling events within the cell and describe how they impact on metabolic inflammation and whole-body metabolism. We particularly highlight the interplay between different signalling pathways that link low-grade inflammation responses to the inactivation of the insulin receptor pathway, ultimately leading to insulin resistance, a hallmark of type 2 diabetes.

Leptin in nonalcoholic fatty liver disease: a narrative review

Leptin, the first described adipokine, interplays with hepatic metabolism. The aim of this review was to summarize available data on the association between leptin and nonalcoholic fatty liver disease (NAFLD). Leptin has a potential dual action on NAFLD experimental models, exerting a possible anti-steatotic, but also a proinflammatory and profibrogenic action. Observational clinical studies have shown higher or similar leptin levels between simple steatosis and nonalcoholic steatohepatitis (NASH) compared with controls. Interventional studies showed that circulating leptin diminishes together with body mass index after successful weight loss following lifestyle modifications or bariatric surgery. Studies providing evidence for the effect of other medications on leptin levels in NAFLD populations are limited and of low power. Data from small studies claim that recombinant leptin administration had a possibly beneficial effect on steatosis, but not fibrosis, in NAFLD patients with hypoleptinemia. Although the aforementioned dual leptin action has not yet been validated in humans, leptin administration in NAFLD patients with normoleptinemia or hyperleptinemia is discouraged. Further well-controlled studies in cautiously selected populations are needed to elucidate whether leptin has any prognostic and therapeutic role in NAFLD patients.

Macrophages, immunity, and metabolic disease

Chronic, low-grade adipose tissue inflammation is a key etiological mechanism linking the increasing incidence of type 2 diabetes (T2D) and obesity. It is well recognized that the immune system and metabolism are highly integrated, and macrophages, in particular, have been identified as critical effector cells in the initiation of inflammation and insulin resistance. Recent advances have been made in the understanding of macrophage recruitment and retention to adipose tissue and the participation of other immune cell populations in the regulation of this inflammatory process. Here we discuss the pathophysiological link between macrophages, obesity, and insulin resistance, highlighting the dynamic immune cell regulation of adipose tissue inflammation. We also describe the mechanisms by which inflammation causes insulin resistance and the new therapeutic targets that have emerged.

[Control of insulin signalisation and action by the Grb14 protein]

The action of insulin on metabolism and cell growth is mediated by a specific receptor tyrosine kinase, which, through phosphorylation of several substrates, triggers the activation of two major signaling pathways, the phosphatidylinositol 3-kinase (PI3-K)/Akt pathway and the Ras/extracellular signal-regulated kinase (ERK) pathway. Insulin-induced activation of the receptor and downstream signaling is also subjected to a negative feedback control involving several mechanisms, among which the interaction of the insulin receptor and its substrates with inhibitory proteins. After summarizing the major mechanisms underlying the activation and attenuation of insulin signaling, this review focuses on its control by the Grb14 adaptor protein. Grb14 has been identif-ied as an inhibitor of insulin signaling and action, and is involved in insulin resistance associated with type 2 diabetes and obesity. Studies on the molecular mechanism of action of Grb14 have shown that, through interaction with the activated insulin receptor, Grb14 inhibits its catalytic activity and the activation of downstream signaling. However, the consequences of Grb14 gene invalidation are complex and tissue-specific, and some effects of Grb14 on insulin signaling appear to be linked to its interaction with effector proteins downstream the insulin receptor. Pharmacological inhibition of Grb14 should allow to enhance insulin sensitivity and improve energy homeostasis in insulin-resistant states.

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.

Etanercept restores normal insulin signal transduction in β2-adrenergic receptor knockout mice

Background

Inhibition of TNFα protects the retina against diabetic-like changes in rodent models. The mechanism by which TNFα induces deleterious retinal changes is not known. Previously, we have shown that TNFα can inhibit normal insulin signal transduction, leading to increased apoptosis in both retinal endothelial cells (REC) and Müller cells. Additionally, β2-adrenergic receptor knockout mice (β2KO) have increased TNFα levels and decreased insulin receptor activity. In this study, we hypothesized that inhibition of TNFα in β2KO mice would increase normal insulin signaling, leading to improved retinal function.

Methods

C57BL6 or β2KO mice were left untreated or treated with etanercept (0.3 mg/kg subcutaneously, 3× a week) for 2 months. Electroretinogram analyses were done before treatment was initiated and after two months of treatment with etanercept on all mice. Western blot or ELISA analyses were done on whole retinal lysates from all four groups of mice for TNFα, suppressor of cytokine signaling 3 (SOCS3), insulin receptor, and apoptotic proteins.

Results

Etanercept significantly reduced TNFα levels in β2KO mice, leading to increased insulin receptor phosphorylation on tyrosine 1150/1151. SOCS3 levels were increased in β2KO mice, which were reduced after etanercept treatment. Pro-apoptotic proteins were reduced in etanercept-treated β2KO mice. Etanercept improved ERG amplitudes in β2KO mice.

Conclusions

Inhibition of TNFα by etanercept protects the retina likely through reduced TNFα-mediated insulin resistance, leading to reduced apoptosis.

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 normalizes insulin signaling in the diabetic rat retina through reduction in tumor necrosis factor α and suppressor of cytokine signaling 3

Dysfunctional insulin signaling is a key component of type 2 diabetes. Little is understood of the effects of systemic diabetes on retinal insulin signaling. A number of agents are used to treat patients with type 2 diabetes to normalize glucose levels and improve insulin signaling; however, little has been done to investigate the effects of these agents on retinal insulin signal transduction. We hypothesized that pioglitazone, a peroxisome proliferator-activated receptor γ (PPARγ) agonist, would normalize retinal insulin signal transduction through reduced tumor necrosis factor α (TNFα) and suppressor of cytokine signaling 3 (SOCS3) activities in whole retina and retinal endothelial cells (REC) and Müller cells. To test this hypothesis, we used the BBZDR/Wor type 2 diabetic rat model, as well as REC and Müller cells cultured in normoglycemia and hyperglycemic conditions, to investigate the effects of pioglitazone on TNFα, SOCS3, and downstream insulin signal transduction proteins. We also evaluated pioglitazone's effects on retinal function using electroretinogram and markers of apoptosis. Data demonstrate that 2 months of pioglitazone significantly increased electroretinogram amplitudes in type 2 diabetic obese rats, which was associated with improved insulin receptor activation. These changes occurred in both REC and Müller cells treated with pioglitazone, suggesting that these two cell types are key to insulin resistance in the retina. Taken together, these data provide evidence of impaired insulin signaling in type 2 diabetes rats, which was improved by increasing PPARγ activity. Further investigations of PPARγ actions in the retina may provide improved treatment options.

NUCKS is a positive transcriptional regulator of insulin signaling

Although much is known about the molecular players in insulin signaling, there is scant information about transcriptional regulation of its key components. We now find that NUCKS is a transcriptional regulator of the insulin signaling components, including the insulin receptor (IR). Knockdown of NUCKS leads to impaired insulin signaling in endocrine cells. NUCKS knockout mice exhibit decreased insulin signaling and increased body weight/fat mass along with impaired glucose tolerance and reduced insulin sensitivity, all of which are further exacerbated by a high-fat diet (HFD). Genome-wide ChIP-seq identifies metabolism and insulin signaling as NUCKS targets. Importantly, NUCKS is downregulated in individuals with a high body mass index and in HFD-fed mice, and conversely, its levels increase upon starvation. Altogether, NUCKS is a physiological regulator of energy homeostasis and glucose metabolism that works by regulating chromatin accessibility and RNA polymerase II recruitment to the promoters of IR and other insulin pathway modulators.

Mechanisms for the adverse effects of late gestational increases in maternal cortisol on the heart revealed by transcriptomic analyses of the fetal septum

We have previously shown in sheep that 10 days of modest chronic increase in maternal cortisol resulting from maternal infusion of cortisol (1 mg/kg/day) caused fetal heart enlargement and Purkinje cell apoptosis. In subsequent studies we extended the cortisol infusion to term, finding a dramatic incidence of stillbirth in the pregnancies with chronically increased cortisol. To investigate effects of maternal cortisol on the heart, we performed transcriptomic analyses on the septa using ovine microarrays and Webgestalt and Cytoscape programs for pathway inference. Analyses of the transcriptomic effects of maternal cortisol infusion for 10 days (130 day cortisol vs 130 day control), or ∼25 days (140 day cortisol vs 140 day control) and of normal maturation (140 day control vs 130 day control) were performed. Gene ontology terms related to immune function and cytokine actions were significantly overrepresented as genes altered by both cortisol and maturation in the septa. After 10 days of cortisol, growth factor and muscle cell apoptosis pathways were significantly overrepresented, consistent with our previous histologic findings. In the term fetuses (∼25 days of cortisol) nutrient pathways were significantly overrepresented, consistent with altered metabolism and reduced mitochondria. Analysis of mitochondrial number by mitochondrial DNA expression confirmed a significant decrease in mitochondria. The metabolic pathways modeled as altered by cortisol treatment to term were different from those modeled during maturation of the heart to term, and thus changes in gene expression in these metabolic pathways may be indicative of the fetal heart pathophysiologies seen in pregnancies complicated by stillbirth, including gestational diabetes, Cushing's disease and chronic stress.

Intravitreal injection of IGFBP-3 restores normal insulin signaling in diabetic rat retina

Diabetes-induced changes in growth factor binding protein 3 (IGFBP-3) and tumor necrosis factor alpha (TNFα) have been linked to decreased insulin receptor signaling in diabetic retinopathy. Our previous studies in retinas of diabetic rats have shown that Compound 49b, a novel β-adrenergic receptor agonist, prevented diabetic changes by increasing IGFBP-3 and decreasing TNFα, thus restoring insulin signaling and protection against diabetic retinopathy. The current study was designed to determine whether boosted expression of IGFBP-3 NB (a non-IGF-1 binding form of IGFBP-3) alone is sufficient to mimic the full actions of Compound 49b in protecting against diabetic retinopathy, as well as testing whether IGFBP-3 NB is linked to a restoration of normal insulin signal transduction. Two months after initiation of streptozotocin-induced diabetes, rats received a single intravitreal injection of IGFBP-3 NB plasmid in the right eye. Four days after injection, electroretinogram (ERG) analyses were performed prior to sacrifice. Whole retinal lysates from control, diabetic, diabetic + control plasmid, and diabetic+ IGFBP-3 NB were analyzed for IGFBP-3, TNFα, suppressor of cytokine signaling 3 (SOCS3), and insulin receptor signaling partners using Western blotting or ELISA. Data show that a single intraocular injection of IGFBP-3 NB in diabetic animals significantly reduced TNFα levels, concomitant with reductions in IRS-1^Ser307, SOCS3, and pro-apoptotic markers, while restoring insulin receptor phosphorylation and increasing anti-apoptotic marker levels. These cellular changes were linked to restoration of retinal function. Our findings establish IGFBP-3 as a pivotal regulator of the insulin receptor/TNFα pathway and a potential therapeutic target for diabetic retinopathy.

Inputs and outputs of insulin receptor

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

The role of suppressors of cytokine signalling in human neoplasms

Suppressors of cytokine signalling 1-7 (SOCS1-7) and cytokine-inducible SH2-containing protein (CIS) are a group of intracellular proteins that are well known as JAK-STAT and several other signalling pathways negative feedback regulators. More recently several members have been identified as tumour suppressors and dysregulation of their biological roles in controlling cytokine and growth factor signalling may contribute to the development of many solid organ and haematological malignancies. This review explores their biological functions and their possible tumour suppressing role in human neoplasms.

Leptin regulation of Hsp60 impacts hypothalamic insulin signaling

Type 2 diabetes is characterized by insulin resistance and mitochondrial dysfunction in classical target tissues such as muscle, fat, and liver. Using a murine model of type 2 diabetes, we show that there is hypothalamic insulin resistance and mitochondrial dysfunction due to downregulation of the mitochondrial chaperone HSP60. HSP60 reduction in obese, diabetic mice was due to a lack of proper leptin signaling and was restored by leptin treatment. Knockdown of Hsp60 in a mouse hypothalamic cell line mimicked the mitochondrial dysfunction observed in diabetic mice and resulted in increased ROS production and insulin resistance, a phenotype that was reversed with antioxidant treatment. Mice with a heterozygous deletion of Hsp60 exhibited mitochondrial dysfunction and hypothalamic insulin resistance. Targeted acute downregulation of Hsp60 in the hypothalamus also induced insulin resistance, indicating that mitochondrial dysfunction can cause insulin resistance in the hypothalamus. Importantly, type 2 diabetic patients exhibited decreased expression of HSP60 in the brain, indicating that this mechanism is relevant to human disease. These data indicate that leptin plays an important role in mitochondrial function and insulin sensitivity in the hypothalamus by regulating HSP60. Moreover, leptin/insulin crosstalk in the hypothalamus impacts energy homeostasis in obesity and insulin-resistant states.

SOCS3, a Major Regulator of Infection and Inflammation

In this review, we describe the role of suppressor of cytokine signaling-3 (SOCS3) in modulating the outcome of infections and autoimmune diseases as well as the underlying mechanisms. SOCS3 regulates cytokine or hormone signaling usually preventing, but in some cases aggravating, a variety of diseases. A main role of SOCS3 results from its binding to both the JAK kinase and the cytokine receptor, which results in the inhibition of STAT3 activation. Available data also indicate that SOCS3 can regulate signaling via other STATs than STAT3 and also controls cellular pathways unrelated to STAT activation. SOCS3 might either act directly by hampering JAK activation or by mediating the ubiquitination and subsequent proteasome degradation of the cytokine/growth factor/hormone receptor. Inflammation and infection stimulate SOCS3 expression in different myeloid and lymphoid cell populations as well as in diverse non-hematopoietic cells. The accumulated data suggest a relevant program coordinated by SOCS3 in different cell populations, devoted to the control of immune homeostasis in physiological and pathological conditions such as infection and autoimmunity.

Midkine, a potential link between obesity and insulin resistance

Obesity is associated with increased production of inflammatory mediators in adipose tissue, which contributes to chronic inflammation and insulin resistance. Midkine (MK) is a heparin-binding growth factor with potent proinflammatory activities. We aimed to test whether MK is associated with obesity and has a role in insulin resistance. It was found that MK was expressed in adipocytes and regulated by inflammatory modulators (TNF-α and rosiglitazone). In addition, a significant increase in MK levels was observed in adipose tissue of obese ob/ob mice as well as in serum of overweight/obese subjects when compared with their respective controls. In vitro studies further revealed that MK impaired insulin signaling in 3T3-L1 adipocytes, as indicated by reduced phosphorylation of Akt and IRS-1 and decreased translocation of glucose transporter 4 (GLUT4) to the plasma membrane in response to insulin stimulation. Moreover, MK activated the STAT3-suppressor of cytokine signaling 3 (SOCS3) pathway in adipocytes. Thus, MK is a novel adipocyte-secreted factor associated with obesity and inhibition of insulin signaling in adipocytes. It may provide a potential link between obesity and insulin resistance.

Mitochondrial reactive oxygen species as a mystery voice in hepatitis C

There are several lines of evidence suggesting that oxidative stress is present in hepatitis C to a greater degree than in other inflammatory liver diseases and is closely related to disease progression. The main production site of reactive oxygen species (ROS) is assumed to be mitochondria, which concept is supported by evidence that hepatitis C virus (HCV) core protein is directly associated with them. The detoxification of ROS also is an important function of the cellular redox homeostasis system. These results draw our attention to how HCV-induced mitochondrial ROS production is beyond redox regulation and affects the disease progression and development of hepatocellular carcinoma (HCC) in chronic hepatitis C. On the other hand, HCV-related chronic liver diseases are characterized by metabolic alterations such as insulin resistance, hepatic steatosis and/or iron accumulation in the liver. These metabolic disorders also are relevant to the development of HCC in HCV-related chronic liver diseases. Here, we review the mechanisms by which HCV increases mitochondrial ROS production and offer new insights as to how mitochondrial ROS are linked to metabolic disorders such as insulin resistance, hepatic steatosis and hepatic iron accumulation that are observed in HCV-related chronic liver diseases.

Suppressors of cytokine signaling (SOCS) and type 2 diabetes

The suppressors of cytokine signaling (SOCS) proteins are originally identified as negative regulators of cytokine-activated Janus kinase/signal transducers and activators of transcription signaling pathway, but increasing evidence reveals that SOCS proteins play an important role in the development of type 2 diabetes involving regulation of the insulin signaling and pancreatic β-cell function, and that SOCS are promising to be the targets for the treatment of type 2 diabetes. In this review, we focus on the emerging role for SOCS and the potential drugs targeting SOCS for type 2 diabetes.

Insulin receptor signaling in normal and insulin-resistant states

In the wake of the worldwide increase in type-2 diabetes, a major focus of research is understanding the signaling pathways impacting this disease. Insulin signaling regulates glucose, lipid, and energy homeostasis, predominantly via action on liver, skeletal muscle, and adipose tissue. Precise modulation of this pathway is vital for adaption as the individual moves from the fed to the fasted state. The positive and negative modulators acting on different steps of the signaling pathway, as well as the diversity of protein isoform interaction, ensure a proper and coordinated biological response to insulin in different tissues. Whereas genetic mutations are causes of rare and severe insulin resistance, obesity can lead to insulin resistance through a variety of mechanisms. Understanding these pathways is essential for development of new drugs to treat diabetes, metabolic syndrome, and their complications.

MicroRNA-494, upregulated by tumor necrosis factor-α, desensitizes insulin effect in C2C12 muscle cells

Chronic inflammation is fundamental for the induction of insulin resistance in the muscle tissue of vertebrates. Although several miRNAs are thought to be involved in the development of insulin resistance, the role of miRNAs in the association between inflammation and insulin resistance in muscle tissue is poorly understood. Herein, we investigated the aberrant expression of miRNAs by conducting miRNA microarray analysis of TNF-α-treated mouse C₂C₁₂ myotubes. We identified two miRNAs that were upregulated and six that were downregulated by a >1.5-fold change compared to normal cells. Among the findings, qRT-PCR analysis confirmed that miR-494 is consistently upregulated by TNF-α-induced inflammation. Overexpression of miR-494 in CHO_IR/IRS1 and C₂C₁₂ myoblasts suppressed insulin action by down-regulating phosphorylations of GSK-3α/β, AS160 and p70S6K, downstream of Akt. Moreover, overexpression of miR-494 did not regulate TNF-α-mediated inflammation . Among genes bearing the seed site for miR-494, RT-PCR analysis showed that the expression of Stxbp5, an inhibitor of glucose transport, was downregulated following miR-494 inhibition. In contrast, the expression of PTEN decreased in the cells analyzed, thus showing that both positive and negative regulators of insulin action may be simultaneously controlled by miR-494. To investigate the overall effect of miR-494 on insulin signaling, we performed a PCR array analysis containing 84 genes related to the insulin signaling pathway, and we observed that 25% of genes were downregulated (P<0.05) and 11% were upregulated (P<0.05). These results confirm that miR-494 might contribute to insulin sensitivity by positive and negative regulation of the expression of diverse genes. Of note, PCR array data showed downregulation of Slc2A4, a coding gene for Glut4. Altogether, the present study concludes that the upregulation of miR-494 expression by TNF-α-mediated inflammation exacerbates insulin resistance. Therefore, we suggest that miR-494 could prove an important target for the diagnosis and therapy of inflammation-mediated insulin resistance in muscle.

Effect of combined prescription and separate prescription of promoting blood circulation and removing blood stasis traditional Chinese medicine on expression of SOCS-3 and SREBP-1c in diabetic fatty liver in rats

AIM: To investigate the effect of promoting blood circulation and removing blood stasis traditional Chinese medicine on the expression of suppressors of cytokine signaling protein-3 (SOCS-3) and sterol regulatory element binding protein-1c (SREBP-1c) in diabetic fatty liver in rats and to explore potential mechanisms involved.

METHODS: Fifty healthy male Sprague-Dawley rats were randomly divided into five groups: a normal group, a model group, a promoting blood circulation group (salvia miltiorrhiza, rhizoma ligustici, wallichii), a removing blood stasis group (leech, lumbricus), and a combination group (salvia miltiorrhiza, rhizoma ligustici, wallichii, leech, lumbricus). Diabetes was induced with streptozocin (50 mg/kg i.p.) in all the groups except for the normal group. The three treatment groups were intragastrically treated with Chinese traditional medicine which can promote blood circulate and/or remove stasis once a day for 12 wk. Triglyceride (TG) and cholesterol (TC) were measured using biochemical methods. The expression of SOCS-3 and SREBP-1c mRNAs was determined by RT-PCR.

RESULTS: Compared to the normal group, the levels of TG and TC were significantly increased in the model group (6.80 mmol/L ± 0.19 mmol/L, 5.36 mmol/L ± 0.24 mmol/L, 5.37 mmol/L ± 0.25 mmol/L, 5.01 mmol/L ± 0.22 mmol/L vs 3.55 mmol/L ± 0.28 mmol/L, all P < 0.05; 2.26 mmol/ ± 0.27 mmol/L, 1.83 mmol/L ± 0.25 mmol/L, 1.82 mmol/L ± 0.23 mmol/L, 1.58 mmol/L ± 0.19 mmol/L vs 1.35 mmol/L ± 0.16 mmol/L, all P < 0.05); however, the levels of TG and TC were significantly lower in each drug intervention group than in the model group (5.36 mmol/L ± 0.24 mmol/L, 5.37 mmol/L ± 0.25 mmol/L, 5.01 mmol/L ± 0.22 mmol/L vs 6.80 mmol/L ± 0.19 mmol/L, all P < 0.05; 1.83 mmol/L ± 0.25mmol/L, 1.82 mmol/L ± 0.23 mmol/L, 1.58 mmol/L ± 0.19 mmol/L vs 2.21 mmol/L ± 0.21 mmol/L, all P < 0.05). The levels of TG and TC were significantly higher in the promoting blood circulation group and removing blood stasis group than in the combination group (5.01 mmol/L ± 0.22 mmol/L vs 5.36 mmol/L ± 0.24 mmol/L, 5.37 mmol/L ± 0.25 mmol/L, both P < 0.05; 1.58 mmol/L ± 0.19 mmol/L vs 1.83 mmol/L ± 0.25 mmol/L, 1.82 mmol/L ± 0.23 mmol/L, both P < 0.05). There was no significant change in the levels of TG and TC between the promoting blood circulation group and removing blood stasis group. Compared to the model group, liver steatosis was significantly reduced in each drug intervention group; however, liver steatosis was significantly more serious in the promoting blood circulation group and removing blood stasis group than in the combination group. Compared to the normal group, the expression of SOCS-3 and SREBP-1c mRNAs was significantly increased in the model group (0.885 ± 0.227, 0.778 ± 0.005, 0.633 ± 0.678, 0.475 ± 0.012 vs 0.189 ± 0.002, all P < 0.05; 0.861 ± 0.020, 0.751 ± 0.003, 0.600 ± 0.005, 0.382 ± 0.014 vs 0.176 ± 0.001, all P < 0.05). However, the expression of SOCS-3 and SREBP-1c mRNAs was significantly lower in each drug intervention group than in the model group (0.778 ± 0.005, 0.633 ± 0.678, 0.475 ± 0.012 vs 0.885 ± 0.227, both P < 0.05; 0.751 ± 0.003, 0.600 ± 0.005, 0.382 ± 0.014 vs 0.861 ± 0.020, both P < 0.05). The expression of SOCS-3 and SREBP-1c mRNAs was significantly higher in the promoting blood circulation group and removing blood stasis group than in the combination group (0.751 ± 0.003, 0.600 ± 0.005 vs 0.382 ± 0.014, both P < 0.05; 0.778 ± 0.005, 0.633 ± 0.678 vs 0.475 ± 0.012, both P < 0.05).

CONCLUSION: Both combined prescription and separate prescription of promoting blood circulation and removing blood stasis traditional Chinese medicine can alleviate fatty liver in rats possibly by decreasing the expression of SOCS-3 and SREBP-1c mRNAs. Combined prescription is better than separate prescription in alleviating fatty liver.

The renin-angiotensin system in adipose tissue and its metabolic consequences during obesity

Obesity is a worldwide disease that is accompanied by several metabolic abnormalities such as hypertension, hyperglycemia and dyslipidemia. The accelerated adipose tissue growth and fat cell hypertrophy during the onset of obesity precedes adipocyte dysfunction. One of the features of adipocyte dysfunction is dysregulated adipokine secretion, which leads to an imbalance of pro-inflammatory, pro-atherogenic versus anti-inflammatory, insulin-sensitizing adipokines. The production of renin-angiotensin system (RAS) components by adipocytes is exacerbated during obesity, contributing to the systemic RAS and its consequences. Increased adipose tissue RAS has been described in various models of diet-induced obesity (DIO) including fructose and high-fat feeding. Up-regulation of the adipose RAS by DIO promotes inflammation, lipogenesis and reactive oxygen species generation and impairs insulin signaling, all of which worsen the adipose environment. Consequently, the increase of circulating RAS, for which adipose tissue is partially responsible, represents a link between hypertension, insulin resistance in diabetes and inflammation during obesity. However, other nutrients and food components such as soy protein attenuate adipose RAS, decrease adiposity, and improve adipocyte functionality. Here, we review the molecular mechanisms by which adipose RAS modulates systemic RAS and how it is enhanced in obesity, which will explain the simultaneous development of metabolic syndrome alterations. Finally, dietary interventions that prevent obesity and adipocyte dysfunction will maintain normal RAS concentrations and effects, thus preventing metabolic diseases that are associated with RAS enhancement.

JAK-STAT signaling and myocardial glucose metabolism

JAK-STAT signaling occurs in virtually every tissue of the body, and so does glucose metabolism. In this review, we summarize the regulation of glucose metabolism in the myocardium and ponder whether JAK-STAT signaling participates in this regulation. Despite a paucity of data directly pertaining to cardiac myocytes, we conclude that JAK-STAT signaling may contribute to the development of insulin resistance in the myocardium in response to various hormones and cytokines.

Enhanced lipid oxidation and maintenance of muscle insulin sensitivity despite glucose intolerance in a diet-induced obesity mouse model

BACKGROUND

Diet-induced obesity is a rising health concern which can lead to the development of glucose intolerance and muscle insulin resistance and, ultimately, type II diabetes mellitus. This research investigates the associations between glucose intolerance or muscle insulin resistance and tissue specific changes during the progression of diet-induced obesity.

METHODOLOGY

C57BL/6J mice were fed a normal or high-fat diet (HFD; 60% kcal fat) for 3 or 8 weeks. Disease progression was monitored by measurements of body/tissue mass changes, glucose and insulin tolerance tests, and ex vivo glucose uptake in intact muscles. Lipid metabolism was analyzed using metabolic chambers and ex vivo palmitate assays in intact muscles. Skeletal muscle, liver and adipose tissues were analyzed for changes in inflammatory gene expression. Plasma was analyzed for insulin levels and inflammatory proteins. Histological techniques were used on muscle and liver cryosections to assess metabolic and morphological changes.

PRINCIPAL FINDINGS/CONCLUSIONS

A rapid shift in whole body metabolism towards lipids was observed with HFD. Following 3 weeks of HFD, elevated total lipid oxidation and an oxidative fiber type shift had occurred in the skeletal muscle, which we propose was responsible for delaying intramyocellular lipid accumulation and maintaining muscle's insulin sensitivity. Glucose intolerance was present after three weeks of HFD and was associated with an enlarged adipose tissue depot, adipose tissue inflammation and excess hepatic lipids, but not hepatic inflammation. Furthermore, HFD did not significantly increase systemic or muscle inflammation after 3 or 8 weeks of HFD suggesting that early diet-induced obesity does not cause inflammation throughout the whole body. Overall these findings indicate skeletal muscle did not contribute to the development of HFD-induced impairments in whole-body glucose tolerance following 3 weeks of HFD.

Novel roles for insulin receptor (IR) in adipocytes and skeletal muscle cells via new and unexpected substrates

The insulin signaling pathway regulates whole-body glucose homeostasis by transducing extracellular signals from the insulin receptor (IR) to downstream intracellular targets, thus coordinating a multitude of biological functions. Dysregulation of IR or its signal transduction is associated with insulin resistance, which may culminate in type 2 diabetes. Following initial stimulation of IR, insulin signaling diverges into different pathways, activating multiple substrates that have roles in various metabolic and cellular processes. The integration of multiple pathways arising from IR activation continues to expand as new IR substrates are identified and characterized. Accordingly, our review will focus on roles for IR substrates as they pertain to three primary areas: metabolism/glucose uptake, mitogenesis/growth, and aging/longevity. While IR functions in a seemingly pleiotropic manner in many cell types, through these three main roles in fat and skeletal muscle cells, IR multi-tasks to regulate whole-body glucose homeostasis to impact healthspan and lifespan.

Correlation of insulin resistance, beta cell function and insulin sensitivity with serum sFas and sFasL in newly diagnosed type 2 diabetes

Pancreatic beta cell dysfunction and reduced insulin sensitivity are fundamental factors associated with glucotoxicity, lipotoxicity and oxidative stress in type 2 diabetic patients (T2DM). Diabetic milieu can induce apoptosis in several types of cells. The aim of present study was to compare circulating soluble apoptotic markers (sFas and sFas-L) with HOMA-IR, HOMA-%S, HOMA-%B in the serum of newly diagnosed T2DM and healthy subjects. For this study, 94 T2DM and 60 healthy subjects were enroled and evaluated for various parameters. Biochemical quantifications were performed with Syncron CX5 auto-analyzer. The levels of serum sFas-L, TNF-α and IL-6 were estimated by flowcytometry. The fasting serum insulin and sFas quantified by ELISA. HOMA-IR, HOMA-%S and HOMA-%B were calculated with HOMA calculator v2.2.2. The levels of TC, TG, LDL-C, VLDL-C were augmented and HDL declined significantly (P < 0.001) in diabetics. The levels of serum insulin, TNF-α, IL-6, sFas, HOMA-IR were raised (P < 0.001) and sFas-L, HOMA-%S and HOMA-%B were decreased significantly (P < 0.001) in T2DM subjects than healthy. In diabetics, serum sFas was positively correlated with HOMA-IR (r = 0.720, P < 0.001) and negatively with HOMA-%B (r = -0.642, P < 0.001) significantly while serum sFasL was negatively correlated with HOMA-IR (r = -0.483, P < 0.001) and positively with HOMA-%B (r = 0.466, P < 0.001) significantly. Further, the multivariate stepwise regression analysis shows that HOMA-IR contributes significantly to the variance of sFas and sFasL. Our findings suggest that the pancreatic beta cell dysfunction along with increased insulin resistance appears to be associated with apoptotic markers.