Suppressor of cytokine signaling 3 is induced by angiotensin II in heart and isolated cardiomyocytes, and participates in desensitization

Genetic deletion of Mas receptor in FVB/N mice impairs cardiac use of glucose and lipids

Angiotensin-(1-7) is a biologically active product of the renin-angiotensin system cascade and exerts inhibitory effects on inflammation, vascular and cellular growth mechanisms signaling through the G protein-coupled Mas receptor. The major purpose of the present study was to investigate the use of glucose and fatty acids by cardiac tissue in Mas knockout mice models. Serum levels of glucose, lipids, and insulin were measured in Mas-deficient and wild-type FVB/N mice. To investigate the cardiac use of lipids, the lipoprotein lipase, the gene expression of peroxisome proliferator-activated receptor alpha; carnitine palmitoyltransferase I and acyl-CoA oxidase were evaluated. To investigate the cardiac use of glucose, the insulin signaling through Akt/GLUT4 pathway, glucose-6-phosphate (G-6-P) and fructose-6-phosphate (F-6-P) glycolytic intermediates, in addition to ATP, lactate and the glycogen content were measured. Despite normal body weight, cholesterol and insulin, Mas-Knockout mice presented hyperglycemia and hypertriglyceridemia, impaired insulin signaling, through reduced phosphorylation of AKT and decreased translocation of GLUT4 in response to insulin, with subsequent decrease of the cardiac G-6-P and F-6-P. Lactate production and glycogen content were not altered in Mas-KO hearts. Mas-KO presented reduced cardiac lipoprotein lipase activity and decreased translocation of CD36 in response to insulin. The expression of peroxisome proliferator-activated receptor alpha and carnitine palmitoyltransferase I genes were lower in Mas-KO animals compared to wild-type animals. The ATP content of Mas-KO hearts was smaller than in wild-type. The present results suggest that genetic deletion of Mas produced a devastating effect on cardiac use of glucose and lipids, leading to lower energy efficiency in the heart.

SOCS3 as a future target to treat metabolic disorders

The suppressors of cytokine signaling (SOCS) are a group of eight proteins responsible for preventing excessive cytokine signaling. Among this protein family, SOCS3 has received special attention. SOCS3 expression is important to control certain allergy autoimmune diseases. Furthermore, SOCS3 expression is elevated in obesity and it is involved in the inhibition of leptin and insulin signaling, two important hormones involved in the control of energy metabolism. Therefore, increased SOCS3 expression in obese individuals is associated with several metabolic disorders, including reduced energy expenditure, increased food intake and adiposity, and insulin and leptin resistance. In addition, recent studies found that SOCS3 expression regulates energy and glucose homeostasis in several metabolic conditions, such as pregnancy, caloric restriction, and refeeding. Importantly, attenuation of SOCS3 expression in most cases improves leptin and insulin sensitivity, leading to beneficial metabolic effects. This review aims to discuss the role of SOCS3 in the control of blood glucose levels as well as in energy homeostasis. The development of pharmacological compounds to inhibit SOCS3 activity and/or expression may represent a promising therapeutic approach to treat type 2 diabetes mellitus, obesity, and other metabolic imbalances.

Cross-Talk Between Insulin Signaling and G Protein-Coupled Receptors

Diabetes is a major risk factor for the development of heart failure. One of the hallmarks of diabetes is insulin resistance associated with hyperinsulinemia. The literature shows that insulin and adrenergic signaling is intimately linked to each other; however, whether and how insulin may modulate cardiac adrenergic signaling and cardiac function remains unknown. Notably, recent studies have revealed that insulin receptor and β2 adrenergic receptor (β2AR) forms a membrane complex in animal hearts, bringing together the direct contact between 2 receptor signaling systems, and forming an integrated and dynamic network. Moreover, insulin can drive cardiac adrenergic desensitization via protein kinase A and G protein-receptor kinases phosphorylation of the β2AR, which compromises adrenergic regulation of cardiac contractile function. In this review, we will explore the current state of knowledge linking insulin and G protein-coupled receptor signaling, especially β-adrenergic receptor signaling in the heart, with emphasis on molecular insights regarding its role in diabetic cardiomyopathy.

A crowd-sourcing approach for the construction of species-specific cell signaling networks

Motivation: Animal models are important tools in drug discovery and for understanding human biology in general. However, many drugs that initially show promising results in rodents fail in later stages of clinical trials. Understanding the commonalities and differences between human and rat cell signaling networks can lead to better experimental designs, improved allocation of resources and ultimately better drugs.

Results: The sbv IMPROVER Species-Specific Network Inference challenge was designed to use the power of the crowds to build two species-specific cell signaling networks given phosphoproteomics, transcriptomics and cytokine data generated from NHBE and NRBE cells exposed to various stimuli. A common literature-inspired reference network with 220 nodes and 501 edges was also provided as prior knowledge from which challenge participants could add or remove edges but not nodes. Such a large network inference challenge not based on synthetic simulations but on real data presented unique difficulties in scoring and interpreting the results. Because any prior knowledge about the networks was already provided to the participants for reference, novel ways for scoring and aggregating the results were developed. Two human and rat consensus networks were obtained by combining all the inferred networks. Further analysis showed that major signaling pathways were conserved between the two species with only isolated components diverging, as in the case of ribosomal S6 kinase RPS6KA1. Overall, the consensus between inferred edges was relatively high with the exception of the downstream targets of transcription factors, which seemed more difficult to predict.

Contact:ebilal@us.ibm.com or gustavo@us.ibm.com.

Supplementary information:Supplementary data are available at Bioinformatics online.

JAK-STAT and the renin-angiotensin system: The role of the JAK-STAT pathway in blood pressure and intrarenal renin-angiotensin system regulation

The renin-angiotensin system (RAS) plays important roles in blood pressure control and tissue disease. An inappropriate local angiotensin II elevation in the kidneys leads to the development of hypertension, tissue damage and chronic injury. Studies have demonstrated that the JAK-STAT pathway mediates angiotensin II-triggered gene transcription. The JAK-STAT pathway in turn, acting as an amplifying system, contributes to further intrarenal RAS activation. These observations prompt the suggestion that the JAK-STAT pathway may be of importance in elucidating the mechanisms RAS-associated tissue injury. Accordingly, this review provides a brief overview of the interactions between the JAK-STAT pathway and the RAS, specifically the RAS expressed in the kidneys.

STAT transcription in the ischemic heart

All seven STAT proteins are expressed in the heart, and in this review we will focus on their contribution to cardiac physiology and to ischemic heart disease and its consequences. A substantial literature has focused on the roles of STAT1 and STAT3 in ischemic heart disease, where, at least in the acute phase, they appear to have a yin-yang relationship. STAT1 contributes to the loss of irreplaceable cardiac myocytes both by increasing apoptosis and by reducing cardioprotective autophagy. In contrast, STAT3 is cardioprotective, since STAT3-deficient mice have larger infarcts following ischemic injury, and a number of cardioprotective agents have been shown to act, at least partly, through STAT3 activation. STAT3 is also absolutely required for preconditioning—a process where periods of brief ischemia protect against a subsequent or previous prolonged ischemic episode. Prolonged activation of STAT3, however, is strongly implicated in the post-infarction remodeling of the heart which leads to heart failure, where, possibly together with STAT5, it augments activation of the renin-angiotensin system.

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.

Arrestins in the cardiovascular system

Of the four mammalian arrestins, only the β-arrestins (βarrs; Arrestin2 and -3) are expressed throughout the cardiovascular system, where they regulate, as either desensitizers/internalizers or signal transducers, several G-protein-coupled receptors (GPCRs) critical for cardiovascular homeostasis. The cardiovascular roles of βarrs have been delineated at an accelerated pace via a variety of techniques and tools, such as knockout mice, siRNA knockdown, artificial or naturally occurring polymorphic GPCRs, and availability of new βarr "biased" GPCR ligands. This chapter summarizes the current knowledge of cardiovascular arrestin physiology and pharmacology, addressing the individual cardiovascular receptors affected by βarrs in vivo, as well as the individual cell types, tissues, and organs of the cardiovascular system in which βarr effects are exerted; for example, cardiac myocyte or fibroblast, vascular smooth muscle, adrenal gland and platelet. In the broader scope of cardiovascular βarr pharmacology, a discussion of the βarr "bias" of certain cardiovascular GPCR ligands is also included.

Suppressors of cytokine signaling (SOCS) proteins and JAK/STAT pathways: regulation of T-cell inflammation by SOCS1 and SOCS3

Various cytokines are involved in the regulation of the immune system and inflammation. Dysregulation of cytokine signaling can cause a variety of diseases, including allergy, autoimmune diseases, inflammation, and cancer. Most cytokines use the so-called janus kinase/signal transducer and activator of transcription pathway, and this pathway is negatively regulated by suppressors of cytokine signaling (SOCS) proteins. SOCS proteins bind to janus kinase and to certain cytokine receptors and signaling molecules, thereby suppressing further signaling events. Studies have shown that SOCS proteins are key physiological regulators of inflammation. Recent studies have also demonstrated that SOCS1 and SOCS3 are important regulators of adaptive immunity.

Impaired dipsogenic and renal response to repetitive intracerebroventricular angiotensin II (AngII) injections in rats

The role of the central nervous system (CNS) in the control of blood pressure and hydrosaline homeostasis has been demonstrated by several studies. While circulating angiotensin II (AngII) tends to retain sodium by a direct renal action as well as through aldosterone release, stimulation of brain AngII receptors has been reported to induce natriuresis. Repetitive intracerebroventricular AngII injection was recently demonstrated to be capable of leading to desensitisation of the dipsogenic effect of AngII stimuli. The aim of the current study was to investigate a possible central desensitisation to AngII stimuli by observing the effects of a low-concentration solution of AngII on the dipsogenic and natriuretic mechanisms in conscious rats, compared with appropriate age-matched 0.15 M NaCl-injected subjects, as evaluated by lithium clearance. The present report confirmed earlier reports on the potent natriuretic and dipsogenic effects of central AngII receptor stimulation. Natriuresis is mediated by a decrease in sodium reabsorption in the proximal and post-proximal tubule segments of the nephron. The current findings lend further support to the idea that AngII, in the CNS, is instrumental in the regulation of body fluid homeostasis. The magnitude of the dipsogenic and renal response to AngII was significantly decreased by repetitive stimulus.

Hypothalamic SOCS-3 expression and the effect of intracerebroventricular angiotensin II injection on water intake and renal sodium handling in SHR

In rats, the acute central dipsogenic and natriuretic action of angiotensin II (AngII) seems to be independent of the hemodynamic effects of the peptide; however, in genetically hypertensive models, this relationship has not yet been investigated. It has been demonstrated that AngII induces the suppressor of cytokine signaling (SOCS-3) expression in the brain that, in turn, modulates further activation of the pathway, leading to desensitization to AngII stimuli with regard to its dipsogenic effect. This study investigates age-related Janus kinase (JAK-2) and SOCS-3 hypothalamic expression, by immunoblotting, and the involvement of SOCS-3 expression in urinary sodium handling and dipsogenic response in spontaneously hypertensive rats (SHR), compared with age-matched Wistar-Kyoto (WKy) rats. The intracerebroventricular (i.c.v.) application of AngII significantly enhanced the dipsogenic response, reduced C(Cr), and reciprocally promoted increased absolute and fractional rates of excretion of sodium in WKy rats. The central AngII-induced dipsogenic effect in WKy and SHR was significantly attenuated by prior i.c.v. administration of DUP753. In addition, the magnitude of the dipsogenic and renal response to AngII was significantly attenuated in age-matched SHR. Blocking of hypothalamic SOCS-3 expression by an antisense oligonucleotide resulted in partial reversal of the refractory nature of AngII in thirst responses in SHR. The altered centrally applied AngII response in SHR associated with increased hypothalamic JAK-2/SOCS-3 expression may suggest that abnormal regulation of the central angiotensin pathways may contribute to dysfunction of water-electrolyte homeostasis in SHR.

Liver X receptor activator downregulates angiotensin II type 1 receptor expression through dephosphorylation of Sp1

Atherosclerosis is considered to be a combined disorder of lipid metabolism and chronic inflammation. Recent studies have reported that liver X receptors (LXRs) are involved in lipid metabolism and inflammation and that LXR agonists inhibit atherogenesis. In contrast, angiotensin II is well known to accelerate atherogenesis through activation of the angiotensin II type 1 receptor (AT1R). To better understand the mechanism of LXR on the prevention of atherogenesis, we examined whether activation of LXR affects AT1R expression in vascular smooth muscle cells. T0901317, a synthetic LXR ligand, decreased AT1R mRNA and protein expression with a peak reduction at 6 hours and 12 hours of incubation, respectively. A well-established ligand of LXR, 22-(R)-hydroxycholesterol, also suppressed AT1R expression. The downregulation of AT1R by T0901317 required de novo protein synthesis. AT1R gene promoter activity measured by luciferase assay revealed that the DNA segment between -61 bp and +25 bp was sufficient for downregulation. Luciferase construct with a mutation in Sp1 binding site located in this segment lost its response to T0901317. T0901317 decreased Sp1 serine phosphorylation. Although preincubation of vascular smooth muscle cells with T0901317 for 30 minutes had no effect on angiotensin II-induced extracellular signal-regulated kinase phosphorylation, phosphorylation of extracellular signal-regulated kinase by angiotensin II was markedly suppressed after 6 hours of preincubation. These results indicate that the suppression of AT1R may be one of the important mechanisms by which LXR ligands exert antiatherogenic effects.

Resistin induces insulin resistance, but does not affect glucose output in rat-derived hepatocytes

AIM

The aim of the present study was to observe the effects of resistin on insulin sensitivity and glucose output in rat-derived hepatocytes.

METHODS

The rat hepatoma cell line H4IIE was cultured and stimulated with resistin; supernant glucose and glycogen content were detected. The insulin receptor substrate (IRS)-1 and IRS-2, protein kinase B/Akt, glycogen synthase kinase-3beta(GSK-3 beta), the suppressor of cytokine signaling 3 (SOCS-3) protein content, as well as the phosphorylation status were assessed by Western blotting. Specific antisense oligodeoxynucleotides directed against SOCS-3 were used to knockdown SOCS-3.

RESULTS

Resistin induced insulin resistance, but did not affect glucose output in rat hepatoma cell line H4IIE. Resistin attenuated multiple effects of insulin, including insulin-stimulated glycogen synthesis and phosphorylation of IRS, protein kinase B/Akt, as well as GSK-3beta. Resistin treatment markedly induced the gene and protein expression of SOCS-3, a known inhibitor of insulin signaling. Furthermore, a specific antisense oligodeoxynucleotide directed against SOCS-3 treatment prevented resistin from antagonizing insulin action.

CONCLUSION

The major function of resistin on liver is to induce insulin resistance. SOCS-3 induction may contribute to the resistin-mediated inhibition of insulin signaling in H4IIE hepatocytes.

[Insulin and angiotensin II signaling pathways cross-talk: implications with the association between diabetes mellitus, arterial hypertension and cardiovascular disease]

Insulin (Ins) and angiotensin II (AII) play pivotal roles in the control of two vital and closely related systems: the metabolic and the circulatory, respectively. A failure in the proper action of each of these hormones results, to a variable degree, in the development of two highly prevalent and commonly overlapping diseases--diabetes mellitus (DM) and hypertension (AH). In recent years, a series of studies has revealed a tight connection between the signal transduction pathways that mediate Ins and AII actions in target tissues. This molecular cross-talk occurs at multiple levels and plays an important role in phenomena that range from the action of anti-hypertensive drugs to cardiac hypertrophy and energy acquisition by the heart. At the extracellular level, the angiotensin-converting enzyme controls AII synthesis but also interferes with Ins signaling through the proper regulation of AII and the accumulation of bradykinin. At an early intracellular level, AII, acting through JAK-2/IRS-1/PI3-kinase, JNK and ERK, may induce the serine phosphorylation and inhibition of key elements of the Ins-signaling pathway. Finally, by inducing the expression of the regulatory protein SOCS-3, AII may impose a late control on the Ins signal. This review will focus on the main advances obtained in this field and will discuss the implications of this molecular cross-talk in the common clinical association between DM and AH.

Jak/STAT/SOCS signaling circuits and associated cytokine-mediated inflammation and hypertrophy in the heart

Cytokines are important mediators of cardiac disease. Accumulating evidence indicates that members of the interleukin-6 family of cytokines promote cardiac hypertrophy through the activation of the Janus kinase-signal transducer and activator of transcription (Jak/STAT) pathway. Aberrant Jak/STAT signaling may promote progression from hypertrophy to heart failure. Suppressor of cytokine signaling (SOCS) proteins are underexplored, negative regulators of Jak/STAT signaling. SOCS proteins may also interact with other inflammatory pathways known to affect cardiac function. A better understanding of the therapeutic potential of these proteins may lead to the controlled progression of heart failure and the limitation of myocardial depression. This review summarizes the cardiophysiological effect of the IL-6 cytokine family, outlines the mechanistic pathway of Jak/STAT signaling, explores the regulatory role of SOCS proteins in the heart, and discusses the potential of using SOCS proteins clinically.

Tumor necrosis factor-alpha activates signal transduction in hypothalamus and modulates the expression of pro-inflammatory proteins and orexigenic/anorexigenic neurotransmitters

Tumor necrosis factor-alpha (TNF-alpha) is known to participate in the wastage syndrome that accompanies cancer and severe infectious diseases. More recently, a role for TNF-alpha in the pathogenesis of type 2 diabetes mellitus and obesity has been shown. Much of the regulatory action exerted by TNF-alpha upon the control of energy stores depends on its action on the hypothalamus. In this study, we show that TNF-alpha activates canonical pro-inflammatory signal transduction pathways in the hypothalamus of rats. These signaling events lead to the transcriptional activation of an early responsive gene and to the induction of expression of cytokines and a cytokine responsive protein such as interleukin-1beta, interleukin-6, interleukin-10 and suppressor of cytokine signalling-3, respectively. In addition, TNF-alpha induces the expression of neurotransmitters involved in the control of feeding and thermogenesis. Thus, TNF-alpha may act directly in the hypothalamus inducing a pro-inflammatory response and the modulation of expression of neurotransmitters involved in energy homeostasis.

Electrophysiological characterization of left ventricular myocytes from obese Sprague-Dawley rat

OBJECTIVE

Obesity is a complex multifactorial disease that is often associated with cardiac arrhythmias. Various animal models have been used extensively to study the effects of obesity on physiological functions, but, to our knowledge, no study related to ionic membrane currents has been performed on isolated cardiac myocytes. Therefore, we examined the electrophysiological characteristics of four ionic currents from isolated left ventricular myocytes of a high-energy (HE)-induced obesity rat model.

RESEARCH METHODS AND PROCEDURES

Male Sprague-Dawley rats were fed with either a control diet or a diet containing 33% kcal as fat (HE) for 14 weeks starting at 6 weeks of age. Voltage-clamp experiments were performed on ventricular myocytes. Leptin receptor (ObR) expression was measured using ObR enzyme-linked immunosorbent assay.

RESULTS

In the HE group, rats designated as obese did not develop a cardiac hypertrophy, either at the organ level or at the cellular level. Densities and kinetics of the L-type calcium current, the transient outward potassium current, the delayed rectifier potassium current, and the sodium-calcium exchange current (I(NCX)) were not significantly different between control and obese rats. A down-regulation of ObR expression was evidenced in the heart of obese rats compared with controls. Acute exposure (5 minutes) of leptin (100 nM) did not induce a significant modification in the current densities either in control or in obese rats, except for I(NCX) density measured in control rats.

DISCUSSION

The absence of effect of leptin on I(NCX) in obese rats could be a potential arrhythmogenic substrate in obesity.

Alteration in erythropoietin-induced cardioprotective signaling by postinfarct ventricular remodeling

Postinfarct remodeling impairs mechanisms of ischemic preconditioning. We examined whether myocardial response to activation of the erythropoietin (EPO) receptor is modified by postinfarct remodeling. Four weeks after induction of myocardial infarction (MI) by coronary ligation in post-MI group (post-MI) or a sham operation in sham group (sham), rat hearts were isolated and subjected to 25-min global ischemia/2-h reperfusion. Infarct size was expressed as a percentage of risk area (i.e., left ventricle) from which scarred infarct was excluded (%I/R). The heart weight was 15% larger in post-MI, but there was no intergroup difference in plasma EPO levels or myocardial EPO receptor levels. EPO infusion (5 U/ml) significantly reduced %I/R from 59.9 +/- 4.1 to 36.2 +/- 4.2 in sham and from 58.1 +/- 5.0 to 35.2 +/- 4.0 in post-MI. This EPO-induced protection was sensitive to a phosphatidylinositol 3-kinase (PI3K) inhibitor, 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (LY294002), in sham. However, neither LY294002 nor wortmannin inhibited the EPO-induced protection in post-MI. Phosphorylation of Janus kinase 2 by EPO was attenuated and phosphorylation of Akt was not detected in post-MI. A guanylyl cyclase inhibitor, 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one, and a mitochondrial ATP-sensitive K(+) channel (mitoK(ATP) channel) blocker, 5-hydroxydecanoate, inhibited EPO-induced protection in both sham and post-MI. Suppressor of cytokine signaling (SOCS)-1 protein level was higher by 50% in post-MI than in sham, although SOCS-3 levels were similar. These findings suggest that postinfarct remodeling disrupts cellular signaling from the EPO receptor to PI3K, presumably by increased SOCS-1. However, in the remodeled myocardium, lack of PI3K/Akt activation by the EPO receptor seems to be compensated by a mechanism upstream of the guanylyl cyclase-mitoK(ATP) channel pathway to achieve EPO-induced protection.

The multi-faceted cross-talk between the insulin and angiotensin II signaling systems

Insulin and angiotensin II are hormones that play pivotal roles in the control of two vital and closely related systems, the metabolic and the circulatory systems, respectively. A failure in the proper action of each of these hormones results, to a variable degree, in the development of two highly prevalent and commonly overlapping diseases-diabetes mellitus and hypertension. In recent years, a series of studies has revealed a tight connection between the signal transduction pathways that mediate insulin and angiotensin II actions in target tissues. This molecular cross-talk occurs at multiple levels and plays an important role in phenomena that range from the action of anti-hypertensive drugs to cardiac hypertrophy and energy acquisition by the heart. At the extracellular level, the angiotensin-converting enzyme controls angiotensin II synthesis but also interferes with insulin signaling through the proper regulation of angiotensin II and through the accumulation of bradykinin. At an early intracellular level, angiotensin II, acting through JAK-2/IRS-1/PI3-kinase, JNK and ERK, may induce the serine phosphorylation and inhibition of key elements of the insulin-signaling pathway. Finally, by inducing the expression of the regulatory protein SOCS-3, angiotensin II may impose a late control on the insulin signal. This review will focus on the main advances obtained in this field and will discuss the implications of this molecular cross-talk in the common clinical association between diabetes mellitus and hypertension.

Mechanisms underlying the diminished sensitivity to prolactin negative feedback during lactation: reduced STAT5 signaling and up-regulation of cytokine-inducible SH2 domain-containing protein (CIS) expression in tuberoinfundibular dopaminergic neurons

Hyperprolactinaemia during lactation is a consequence of the sucking stimulus and in part due to reduced prolactin (PRL) negative feedback. To date, the mechanisms involved in this diminished sensitivity to PRL feedback are unknown but may involve changes in PRL signal transduction within tuberoinfundibular dopaminergic (TIDA) neurons. Therefore, we investigated signal transducers and activators of transcription (STAT) 5 signaling in the TIDA neurons of lactating rats. Dual-label confocal immunofluorescence studies were used to determine the intracellular distribution of STAT5 within TIDA neurons in the dorsomedial arcuate nucleus. In lactating rats with pups removed for 16 h, injection of ovine PRL significantly (P < 0.05) increased the STAT5 nuclear/cytoplasmic ratio compared with vehicle-treated mothers. In contrast, ovine PRL injection did not increase the STAT5 nuclear/cytoplasmic ratio in lactating mothers with pups, demonstrating that PRL signal transduction through STAT5 is reduced in TIDA neurons in the presence of pups. To investigate possible mechanisms involved in reduced PRL signaling, we examined the expression of suppressors of cytokine signaling (SOCS) proteins. Northern analysis on whole hypothalamus showed that CIS (cytokine-inducible SH2 domain-containing protein), but not SOCS1 or SOCS3, mRNA expression was significantly (P < 0.01) up-regulated in suckled lactating rats. Semiquantitative RT-PCR on arcuate nucleus micropunches also showed up-regulation of CIS transcripts. Immunofluorescence studies demonstrated that CIS is expressed in all TIDA neurons in the dorsomedial arcuate nucleus, and the intensity of CIS staining in these neurons is significantly (P < 0.05) increased in lactating rats with sucking pups. Together, these results support the hypothesis that loss of sensitivity to PRL-negative feedback during lactation is a result of increased CIS expression in TIDA neurons.

Activation of AMPK in rat hypothalamus participates in cold-induced resistance to nutrient-dependent anorexigenic signals

The exposure of homeothermic animals to a cold environment leads to a powerful activation of orexigenic signalling which is accompanied by molecular and functional resistance to insulin-induced inhibition of feeding. Recent evidence suggests that AMPK participates in nutrient-dependent control of satiety and adiposity. The objective of the present study was to evaluate the effect of cold exposure upon the molecular activation of AMPK signalling in the hypothalamus of rats. Immunoblotting demonstrated that cold exposure per se is sufficient for inducing, on a time-dependent basis, the molecular activation of the serine/threonine kinase AMP-activated protein kinase (AMPK) and inactivation of the acetyl-CoA carboxylase (ACC). These molecular phenomena were accompanied by resistance to nutrient-induced inactivation of AMPK and activation of ACC. Moreover, cold-exposure led to a partial inhibition of a feeding-induced anorexigenic response, which was paralleled by resistance to insulin-induced suppression of feeding. Finally, cold exposure significantly impaired insulin-induced inhibition of AMPK through a mechanism dependent on the molecular cross-talk between phosphatidylinositol-3(PI3)-kinase/Akt and AMPK. In conclusion, increased feeding during cold exposure results, at least in part, from resistance to insulin- and nutrient-dependent anorexigenic signalling in the hypothalamus.

Suppressors of cytokine signaling in health and disease

Cytokines consist of a large family of secreted proteins, including pro-inflammatory agents, growth hormone and erythropoietin, that utilize the Janus kinase (JAK) signal transducer and activator of transcription (STAT) signal transduction pathway to mediate many of their key physiologic and pathologic actions. These actions include cytokine-mediated inflammation, immunoregulation, hematopoiesis and growth. The JAK-STAT pathway is regulated by several processes, among which negative feedback regulation by the suppressors of cytokine signaling (SOCS), members of a family of eight proteins, is particularly important. Each cytokine induces one or more specific SOCS proteins that in turn down-regulate the signal initiated by the cytokine. Through their impact on the cytokine-activated JAK-STAT pathway, the SOCS proteins are involved in many diseases that come to the attention of the pediatric nephrologist. For example, an increase in the expression of SOCS-2 and -3 may be a cause of growth hormone resistance and thus may contribute to the growth retardation that affects children with chronic renal failure. Because of their obvious biologic importance, the SOCS proteins have been the subject of intense research that includes the development of strategies to utilize these proteins to control cytokine-induced JAK/STAT signal transduction for therapeutic purposes.

Suppressors of Cytokine Signaling Regulate Angiotensin II-Activated Janus Kinase-Signal Transducers and Activators of Transcription Pathway in Renal Cells

Suppressors of cytokine signaling (SOCS) family is constituted by cytokine-inducible proteins that modulate receptor signal transduction via tyrosine kinases, mainly the Janus kinase-signal transducers and activators of transcription (JAK-STAT) pathway. Differential SOCS expression was noted in renal cells that were incubated with inflammatory stimuli, but the role of SOCS in the pathogenesis of renal diseases is not yet well defined. Because angiotensin II (Ang II) plays a key role in renal disease, SOCS proteins were studied as a novel mechanism involved in the negative regulation of Ang II-mediated processes. Systemic Ang II infusion for 3 d increased the renal mRNA expression of SOCS-3 and SOCS-1. SOCS protein synthesis was found in glomerular mesangial area and tubules. In cultured mesangial cells and tubular epithelial cells, Ang II induced a rapid and transient SOCS-3 and SOCS-1 expression in parallel with JAK2 and STAT1 activation. In both cell types, overexpression of SOCS proteins prevented the STAT activation in response to Ang II. SOCS expression observed in Ang II-infused rats and in Ang II-stimulated cells was significantly inhibited by treatment with AT(1) but not AT(2) receptor antagonist and was attenuated in mesangial cells from AT(1a)-deficient mice, demonstrating the implication of AT(1) in those responses. In SOCS-3 knockdown studies, antisense oligonucleotides inhibited the expression of SOCS-3 and increased the Ang II-induced STAT activation and c-Fos/c-Jun expression, then resulting in a more severe renal damage. These results suggest that SOCS proteins may act as negative regulators of Ang II signaling in renal cells and implicate SOCS as important modulators of renal damage.

Suppressor of cytokine signaling-3 Provides a novel interface in the cross-talk between angiotensin II and insulin signaling systems

Angiotensin II inhibits insulin-induced activation of phosphatidylinositol 3-kinase through a mechanism, at least in part, dependent on serine phosphorylation of the insulin receptor and insulin receptor substrates (IRS)-1/2. Recent evidence shows that suppressor of cytokine signaling-3 (SOCS-3) is induced by insulin and angiotensin II and participates in the negative control of further stimulation of each of these signaling systems independently. In the present study, we evaluated the interaction of angiotensin II-induced SOCS-3 with the insulin signaling pathway in the heart of living rats. A single iv dose of angiotensin II promotes a significant increase of SOCS-3 in heart, an effect that lasts up to 180 min. Once induced, SOCS-3 interacts with the insulin receptor, JAK-2, IRS-1, and IRS-2. The inhibition of SOCS-3 expression by a phosphorthioate-modified antisense oligonucleotide partially restores angiotensin II-induced inhibition of insulin-induced insulin receptor, IRS-1 and IRS-2 tyrosine phosphorylation, and IRS-1 and IRS-2 association with p85-phosphatidylinositol 3-kinase and [Ser473] phosphorylation of Akt. Moreover, the inhibition of SOCS-3 expression partially reverses angiotensin II-induced inhibition of insulin-stimulated glucose transporter-4 translocation to the cell membrane. These results are reproduced in isolated cardiomyocytes. Thus, SOCS-3 participates, as a late event, in the negative cross-talk between angiotensin II and insulin, producing an inhibitory effect on insulin-induced glucose transporter-4 translocation.

Cold-induced PGC-1alpha expression modulates muscle glucose uptake through an insulin receptor/Akt-independent, AMPK-dependent pathway

Peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) participates in control of expression of genes involved in adaptive thermogenesis, muscle fiber type differentiation, and fuel homeostasis. The objective of the present study was to evaluate the participation of cold-induced PGC-1alpha expression in muscle fiber type-specific activity of proteins that belong to the insulin-signaling pathway. Rats were exposed to 4 degrees C for 4 days and acutely treated with insulin in the presence or absence of an antisense oligonucleotide to PGC-1alpha. Cold exposure promoted a significant increase of PGC-1alpha and uncoupling protein-3 protein expression in type I and type II fibers of gastrocnemius muscle. In addition, cold exposure led to higher glucose uptake during a hyperinsulinemic clamp, which was accompanied by higher expression and membrane localization of GLUT4 in both muscle fiber types. Cold exposure promoted significantly lower insulin-induced tyrosine phosphorylation of the insulin receptor (IR) and Ser473 phosphorylation of acute transforming retrovirus thymoma (Akt) and an insulin-independent increase of Thr172 phosphorylation of adenosine 5'-monophosphate-activated protein kinase (AMPK). Inhibition of PGC-1alpha expression in cold-exposed rats by antisense oligonucleotide treatment diminished glucose clearance rates during a hyperinsulinemic clamp and reduced expression and membrane localization of GLUT4. Reduction of PGC-1alpha expression resulted in no modification of insulin-induced tyrosine phosphorylation of the IR and Ser473 phosphorylation of Akt. Finally, reduction of PGC-1alpha resulted in lower Thr172 phosphorylation of AMPK. Thus cold-induced hyperexpression of PGC-1alpha participates in control of skeletal muscle glucose uptake through a mechanism that controls GLUT4 expression and subcellular localization independent of the IR and Akt activities but dependent on AMPK.