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Background: From their initial, accidental discovery 50 years ago, the highly conserved Heat Shock Proteins (HSPs) continue to exhibit fundamental roles in the protection of cell integrity. Meanwhile, in the midst of an obesity epidemic, research demonstrates a key involvement of low grade inflammation, and mitochondrial dysfunction amongst other mechanisms, in the pathology of insulin resistance and type 2 diabetes mellitus (T2DM). In particular, tumor necrosis factor alpha (TNFα), endoplasmic reticulum (ER) and oxidative stress all appear to be associated with obesity and stimulate inflammatory kinases such as c jun amino terminal kinase (JNK), inhibitor of NF-κβ kinase (IKK) and protein kinase C (PKC) which in turn, inhibit insulin signaling. Mitochondrial dysfunction in skeletal muscle has also been proposed to be prominent in the pathogenesis of T2DM either by reducing the ability to oxidize fatty acids, leading to the accumulation of deleterious lipid species in peripheral tissues such as skeletal muscle and liver, or by altering the cellular redox state. Since HSPs act as molecular chaperones and demonstrate crucial protective functions in stressed cells, we and others have postulated that the manipulation of HSP expression in metabolically relevant tissues represents a therapeutic avenue for obesity-induced insulin resistance., Scope of Review: This review summarizes the literature from both animal and human studies, that has examined how HSPs, particularly the inducible HSP, Heat Shock Protein 72 (Hsp72) alters glucose homeostasis and the possible approaches to modulating Hsp72 expression. A summation of the role of chemical chaperones in metabolic disorders is also included., Major Conclusions: Targeted manipulation of Hsp72 or use of chemical chaperiones may have clinical utility in treating metabolic disorders such as insulin resistance and T2DM.

Background: Costimulatory cascades such as the CD40L-CD40 dyad enhance immune cell activation and inflammation during atherosclerosis. Here, we tested the hypothesis that CD40 directly modulates traits of the metabolic syndrome in diet-induced obesity in mice., Methods and Results: To induce the metabolic syndrome, wild-type or CD40(-/-) mice consumed a high-fat diet for 20 weeks. Unexpectedly, CD40(-/-) mice exhibited increased weight gain, impaired insulin secretion, augmented accumulation of inflammatory cells in adipose tissue, and enhanced proinflammatory gene expression. This proinflammatory and adverse metabolic phenotype could be transplanted into wild-type mice by reconstitution with CD40-deficient lymphocytes, indicating a major role for CD40 in T or B cells in this context. Conversely, therapeutic activation of CD40 signaling by the stimulating antibody FGK45 abolished further weight gain during the study, lowered glucose levels, improved insulin sensitivity, and suppressed adipose tissue inflammation. Mechanistically, CD40 activation decreased the expression of proinflammatory cytokines in T cells but not in B cells or macrophages. Finally, repopulation of lymphocyte-free Rag1(-/-) mice with CD40(-/-) T cells provoked dysmetabolism and inflammation, corroborating a protective role of CD40 on T cells in the metabolic syndrome. Finally, levels of soluble CD40 showed a positive association with obesity in humans, suggesting clinical relevance of our findings., Conclusions: We present the surprising finding that CD40 deficiency on T cells aggravates whereas activation of CD40 signaling improves adipose tissue inflammation and its metabolic complications. Therefore, positive modulation of the CD40 pathway might describe a novel therapeutic concept against cardiometabolic disease., (© 2014 American Heart Association, Inc.)

Induction of heat shock protein (HSP)72 protects against obesity-induced insulin resistance, but the underlying mechanisms are unknown. Here, we show that HSP72 plays a pivotal role in increasing skeletal muscle mitochondrial number and oxidative metabolism. Mice overexpressing HSP72 in skeletal muscle (HSP72Tg) and control wild-type (WT) mice were fed either a chow or high-fat diet (HFD). Despite a similar energy intake when HSP72Tg mice were compared with WT mice, the HFD increased body weight, intramuscular lipid accumulation (triacylglycerol and diacylglycerol but not ceramide), and severe glucose intolerance in WT mice alone. Whole-body VO2, fatty acid oxidation, and endurance running capacity were markedly increased in HSP72Tg mice. Moreover, HSP72Tg mice exhibited an increase in mitochondrial number. In addition, the HSP72 coinducer BGP-15, currently in human clinical trials for type 2 diabetes, also increased mitochondrial number and insulin sensitivity in a rat model of type 2 diabetes. Together, these data identify a novel role for activation of HSP72 in skeletal muscle. Thus, the increased oxidative metabolism associated with activation of HSP72 has potential clinical implications not only for type 2 diabetes but also for other disorders where mitochondrial function is compromised., (© 2014 by the American Diabetes Association.)

It has been two decades since the discovery that pro-inflammatory cytokines are expressed in obesity. This initial work was the catalyst for the now-accepted paradigm that nutrient overload promotes inflammation and links the metabolic and immune systems, where inflammation may be pathological. However, inflammation is an adaptive and, importantly, an energy-consuming process. Indeed, the rapid mobilization of stored energy reserves by cytokines such as the interleukins, is critical to mounting any successful inflammatory response. Thus, the role of the interleukins in metabolism and energy homeostasis is more complex than first thought and recent evidence is mounting that, for several interleukins, although excess production is negative, blockade or insufficiency is equally undesirable., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

A lack of physical activity is linked to the development of many chronic diseases. It is now well established that the immune system and inflammation play a central role in the development of numerous chronic metabolic diseases including insulin resistance, type 2 diabetes, atherosclerosis, nonalcoholic fatty liver disease, and specific types of cancer. Physical exercise elicits potent anti-inflammatory effects that are likely to account for many of the salutary actions of regular exercise on chronic metabolic diseases. Here we review the anti-inflammatory and immunomodulatory mechanisms by which the beneficial effects of exercise on chronic metabolic diseases may be mediated., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Obesity and resistance to insulin are closely associated with the development of low-grade inflammation. Interleukin 6 (IL-6) is linked to obesity-associated inflammation; however, its role in this context remains controversial. Here we found that mice with an inactivated gene encoding the IL-6Rα chain of the receptor for IL-6 in myeloid cells (Il6ra(Δmyel) mice) developed exaggerated deterioration of glucose homeostasis during diet-induced obesity, due to enhanced resistance to insulin. Tissues targeted by insulin showed increased inflammation and a shift in macrophage polarization. IL-6 induced expression of the receptor for IL-4 and augmented the response to IL-4 in macrophages in a cell-autonomous manner. Il6ra(Δmyel) mice were resistant to IL-4-mediated alternative polarization of macrophages and exhibited enhanced susceptibility to lipopolysaccharide (LPS)-induced endotoxemia. Our results identify signaling via IL-6 as an important determinant of the alternative activation of macrophages and assign an unexpected homeostatic role to IL-6 in limiting inflammation.

Increased heat shock protein (HSP) 72 expression in skeletal muscle prevents obesity and glucose intolerance in mice, although the underlying mechanisms of this observation are largely unresolved. Herein we show that HSP72 is a critical regulator of stress-induced mitochondrial triage signaling since Parkin, an E3 ubiquitin ligase known to regulate mitophagy, was unable to ubiquitinate and control its own protein expression or that of its central target mitofusin (Mfn) in the absence of HSP72. In wild-type cells, we show that HSP72 rapidly translocates to depolarized mitochondria prior to Parkin recruitment and immunoprecipitates with both Parkin and Mfn2 only after specific mitochondrial insult. In HSP72 knockout mice, impaired Parkin action was associated with retention of enlarged, dysmorphic mitochondria and paralleled by reduced muscle respiratory capacity, lipid accumulation, and muscle insulin resistance. Reduced oxygen consumption and impaired insulin action were recapitulated in Parkin-null myotubes, confirming a role for the HSP72-Parkin axis in the regulation of muscle insulin sensitivity. These data suggest that strategies to maintain HSP72 may provide therapeutic benefit to enhance mitochondrial quality and insulin action to ameliorate complications associated with metabolic diseases, including type 2 diabetes.

The lack of physical activity and overnutrition in our modern lifestyle culminates in what we now experience as the current obesity and diabetes pandemic. Medical research performed over the past 20 years identified chronic low-grade inflammation as a mediator of these metabolic disorders. Hence, finding therapeutic strategies against this underlying inflammation and identifying molecules implicated in this process is of significant importance. Following the observation of an increased plasma concentration of interleukin-6 (IL-6) in obese patients, this protein, known predominantly as a pro-inflammatory cytokine, came into focus. In an attempt to clarify its importance, several studies implicated IL-6 as a co-inducer of the development of obesity-associated insulin resistance, which precedes the development of type 2 diabetes. However, the identification of IL-6 as a myokine, a protein produced and secreted by skeletal muscle to fulfil paracrine or endocrine roles in the insulin-sensitizing effects following exercise, provides a contrasting and hence paradoxical identity of this protein in the context of metabolism. We review here the literature considering the complex, pleiotropic role of IL-6 in the context of metabolism in health and disease.

Obesity is now recognised as a low grade, chronic inflammatory disease that is linked to a myriad of disorders including cancer, cardiovascular disease and type 2 diabetes (T2D). With respect to T2D, work in the last decade has revealed that cells of the immune system are recruited to white adipose tissue beds (WAT), where they can secrete cytokines to modulate metabolism within WAT. As many of these cytokines are known to impair insulin action, blocking the recruitment of immune cells has been purported to have therapeutic utility for the treatment of obesity-induced T2D. As inflammation is critical for host defence, and energy consuming in nature, the blockade of inflammatory processes may, however, result in unwanted complications. In this review, we outline the immunological changes that occur within the WAT with respect to systemic glucose homeostasis. In particular, we focus on the role of major immune cell types in regulating nutrient homeostasis and potential initiating stimuli for WAT inflammation.

Expression of brown adipose tissue (BAT) associated proteins like uncoupling protein 1 (UCP1) in inguinal WAT (iWAT) has been suggested to alter iWAT metabolism. The aim of this study was to investigate the role of interleukin-6 (IL-6) in exercise training and cold exposure-induced iWAT UCP1 expression. The effect of daily intraperitoneal injections of IL-6 (3 ng/g) in C57BL/6 mice for 7 days on iWAT UCP1 expression was examined. In addition, the expression of UCP1 in iWAT was determined in response to 3 days of cold exposure (4°C) and 5 weeks of exercise training in wild type (WT) and whole body IL-6 knockout (KO) mice. Repeated injections of IL-6 in C57BL/6 mice increased UCP1 mRNA but not UCP1 protein content in iWAT. Cold exposure increased iWAT UCP1 mRNA content similarly in IL-6 KO and WT mice, while exercise training increased iWAT UCP1 mRNA in WT mice but not in IL-6 KO mice. Additionally, a cold exposure-induced increase in iWAT UCP1 protein content was blunted in IL-6 KO mice, while UCP1 protein content in iWAT was lower in both untrained and exercise trained IL-6 KO mice than in WT mice. In conclusion, repeated daily increases in plasma IL-6 can increase iWAT UCP1 mRNA content and IL-6 is required for an exercise training-induced increase in iWAT UCP1 mRNA content. In addition IL-6 is required for a full induction of UCP1 protein expression in response to cold exposure and influences the UCP1 protein content iWAT of both untrained and exercise trained animals.

The contracting muscle has been shown to act as an endocrine organ, secreting "myokines" that participate in tissue crosstalk. In this issue of Cell Metabolism, Roberts et al. (2014) identify BAIBA as a contraction-induced myokine that results in browning of white adipose tissue and increases fat oxidation in the liver., (Copyright © 2014 Elsevier Inc. All rights reserved.)

During immune responses, T cells are subject to clonal competition, which leads to the predominant expansion of high-affinity clones; however, there is little understanding of how this process is controlled. We found here that the transcription factor IRF4 was induced in a manner dependent on affinity for the T cell antigen receptor (TCR) and acted as a dose-dependent regulator of the metabolic function of activated T cells. IRF4 regulated the expression of key molecules required for the aerobic glycolysis of effector T cells and was essential for the clonal expansion and maintenance of effector function of antigen-specific CD8(+) T cells. Thus, IRF4 is an indispensable molecular 'rheostat' that 'translates' TCR affinity into the appropriate transcriptional programs that link metabolic function with the clonal selection and effector differentiation of T cells.

Circulating interleukin (IL)-18 is elevated in obesity, but paradoxically causes hypophagia. We hypothesized that IL-18 may attenuate high-fat diet (HFD)-induced insulin resistance by activating AMP-activated protein kinase (AMPK). We studied mice with a global deletion of the α-isoform of the IL-18 receptor (IL-18R(-/-)) fed a standard chow or HFD. We next performed gain-of-function experiments in skeletal muscle, in vitro, ex vivo, and in vivo. We show that IL-18 is implicated in metabolic homeostasis, inflammation, and insulin resistance via mechanisms involving the activation of AMPK in skeletal muscle. IL-18R(-/-) mice display increased weight gain, ectopic lipid deposition, inflammation, and reduced AMPK signaling in skeletal muscle. Treating myotubes or skeletal muscle strips with IL-18 activated AMPK and increased fat oxidation. Moreover, in vivo electroporation of IL-18 into skeletal muscle activated AMPK and concomitantly inhibited HFD-induced weight gain. In summary, IL-18 enhances AMPK signaling and lipid oxidation in skeletal muscle implicating IL-18 in metabolic homeostasis.

Obesity and type 2 diabetes are now the most prevalent metabolic diseases in the Western world and the development of new strategies to treat these metabolic diseases is most warranted. Obesity results in a state of chronic low-grade inflammation in metabolically active tissues such as the liver, adipose tissue, brain and skeletal muscle. Work in our laboratory has focussed on the role of the cytokine interleukin-6 (IL)-6 and other IL-6-like cytokines that signal through the gp130 receptor complex. We have focussed on the role of blocking IL-6 trans-signalling to prevent inflammation on the one hand, and activating membrane-bound signalling to promote insulin sensitivity on the other hand. Since the cloning of the IL-6 gene nearly 30  years ago, a pattern has emerged associating IL-6 with a number of diseases associated with inflammation including rheumatoid arthritis (RA), Crohn's disease and several cancers. Accordingly, tocilizumab, an IL-6 receptor-inhibiting monoclonal antibody, is now useful for the treatment of RA. However, this may not be the most optimal strategy to block inflammation associated with IL-6 and may result in unwanted side effects that, paradoxically, could actually promote metabolic disease., (© 2013 John Wiley & Sons Ltd.)

p32 [also known as HABP1 (hyaluronan-binding protein 1), gC1qR (receptor for globular head domains complement 1q) or C1qbp (complement 1q-binding protein)] has been shown previously to have both mitochondrial and non-mitochondrial localization and functions. In the present study, we show for the first time that endogenous p32 protein is a mitochondrial protein in HeLa cells under control and stress conditions. In defining the impact of altering p32 levels in these cells, we demonstrate that the overexpression of p32 increased mitochondrial fibrils. Conversely, siRNA-mediated p32 knockdown enhanced mitochondrial fragmentation accompanied by a loss of detectable levels of the mitochondrial fusion mediator proteins Mfn (mitofusin) 1 and Mfn2. More detailed ultrastructure analysis by transmission electron microscopy revealed aberrant mitochondrial structures with less and/or fragmented cristae and reduced mitochondrial matrix density as well as more punctate ER (endoplasmic reticulum) with noticeable dissociation of their ribosomes. The analysis of mitochondrial bioenergetics showed significantly reduced capacities in basal respiration and oxidative ATP turnover following p32 depletion. Furthermore, siRNA-mediated p32 knockdown resulted in differential stress-dependent effects on cell death, with enhanced cell death observed in the presence of hyperosmotic stress or cisplatin treatment, but decreased cell death in the presence of arsenite. Taken together, our studies highlight the critical contributions of the p32 protein to the morphology of mitochondria and ER under normal cellular conditions, as well as important roles of the p32 protein in cellular metabolism and various stress responses.

LKB1 phosphorylates members of the AMP-activated protein kinase (AMPK) family. LKB1 and AMPK in the skeletal muscle are believed to regulate not only fuel oxidation during exercise but also exercise capacity. LKB1 was also required to prevent diaphragm fatigue, which was shown to affect exercise performance. Using mice expressing dominant negative (DN) mutants of LKB1 and AMPK, specifically in the skeletal muscle but not in the heart, we investigated the roles of LKB1 and AMPK activity in exercise performance and the effects of these kinases on the characteristics of respiratory and locomotive muscles. In the diaphragm and gastrocnemius, both AMPK-DN and LKB1-DN mice showed complete loss of AMPKα2 activity, and LKB1-DN mice showed a reduction in LKB1 activity. Exercise capacity was significantly reduced in LKB1-DN mice, with a marked reduction in oxygen consumption and carbon dioxide production during exercise. The diaphragm from LKB1-DN mice showed an increase in myosin heavy chain IIB and glycolytic enzyme expression. Normal respiratory chain function and CPT I activity were shown in the isolated mitochondria from LKB1-DN locomotive muscle, and the expression of genes related to fiber type, mitochondria function, glucose and lipid metabolism, and capillarization in locomotive muscle was not different between LKB1-DN and AMPK-DN mice. We concluded that LKB1 in the skeletal muscle contributes significantly to exercise capacity and oxygen uptake during exercise. LKB1 mediated the change of fiber-type distribution in the diaphragm independently of AMPK and might be responsible for the phenotypes we observed.

Aims/hypothesis: While it is well known that diet-induced obesity causes insulin resistance, the precise mechanisms underpinning the initiation of insulin resistance are unclear. To determine factors that may cause insulin resistance, we have performed a detailed time-course study in mice fed a high-fat diet (HFD)., Methods: C57Bl/6 mice were fed chow or an HFD from 3 days to 16 weeks and glucose tolerance and tissue-specific insulin action were determined. Tissue lipid profiles were analysed by mass spectrometry and inflammatory markers were measured in adipose tissue, liver and skeletal muscle., Results: Glucose intolerance developed within 3 days of the HFD and did not deteriorate further in the period to 12 weeks. Whole-body insulin resistance, measured by hyperinsulinaemic-euglycaemic clamp, was detected after 1 week of HFD and was due to hepatic insulin resistance. Adipose tissue was insulin resistant after 1 week, while skeletal muscle displayed insulin resistance at 3 weeks, coinciding with a defect in glucose disposal. Interestingly, no further deterioration in insulin sensitivity was observed in any tissue after this initial defect. Diacylglycerol content was increased in liver and muscle when insulin resistance first developed, while the onset of insulin resistance in adipose tissue was associated with increases in ceramide and sphingomyelin. Adipose tissue inflammation was only detected at 16 weeks of HFD and did not correlate with the induction of insulin resistance., Conclusions/interpretation: HFD-induced whole-body insulin resistance is initiated by impaired hepatic insulin action and exacerbated by skeletal muscle insulin resistance and is associated with the accumulation of specific bioactive lipid species.

Intrauterine nutrition can program metabolism, creating stable changes in physiology that may have significant health consequences. The mechanism underlying these changes is widely assumed to involve epigenetic changes to the expression of metabolic genes, but evidence supporting this idea is limited. Here we have performed the first study of the epigenomic consequences of exposure to maternal obesity and diabetes. We used a mouse model of natural-onset obesity that allows comparison of genetically identical mice whose mothers were either obese and diabetic or lean with a normal metabolism. We find that the offspring of obese mothers have a latent metabolic phenotype that is unmasked by exposure to a Western-style diet, resulting in glucose intolerance, insulin resistance and hepatic steatosis. The offspring show changes in hepatic gene expression and widespread but subtle alterations in cytosine methylation. Contrary to expectation, these molecular changes do not point to metabolic pathways but instead reside in broadly developmental ontologies. We propose that, rather than being adaptive, these changes may simply produce an inappropriate response to suboptimal environments; maladaptive phenotypes may be avoidable if postnatal nutrition is carefully controlled.

G protein-coupled receptor signaling is mediated by three main mechanisms of action; these are the classical pathway, β-arrestin scaffold signaling, and the transactivation of protein-tyrosine kinase receptors such as those for EGF and PDGF. Recently, it has been demonstrated that G protein-coupled receptors can also mediate signals via transactivation of serine/threonine kinase receptors, most notably the transforming growth factor-β receptor family. Atherosclerosis is characterized by the development of lipid-laden plaques in blood vessel walls. Initiation of plaque development occurs via low density lipoprotein retention in the neointima of vessels due to binding with modified proteoglycans secreted by vascular smooth muscle cells. Here we show that transactivation of protein-tyrosine kinase receptors is mediated by matrix metalloproteinase triple membrane bypass signaling. In contrast, serine/threonine kinase receptor transactivation is mediated by a cytoskeletal rearrangement-Rho kinase-integrin system, and both protein-tyrosine kinase and serine/threonine kinase receptor transactivation concomitantly account for the total proteoglycan synthesis stimulated by thrombin in vascular smooth muscle. This work provides evidence of thrombin-mediated proteoglycan synthesis and paves the way for a potential therapeutic target for plaque development and atherosclerosis.

According to the "membrane sensor" hypothesis, the membrane's physical properties and microdomain organization play an initiating role in the heat shock response. Clinical conditions such as cancer, diabetes and neurodegenerative diseases are all coupled with specific changes in the physical state and lipid composition of cellular membranes and characterized by altered heat shock protein levels in cells suggesting that these "membrane defects" can cause suboptimal hsp-gene expression. Such observations provide a new rationale for the introduction of novel, heat shock protein modulating drug candidates. Intercalating compounds can be used to alter membrane properties and by doing so normalize dysregulated expression of heat shock proteins, resulting in a beneficial therapeutic effect for reversing the pathological impact of disease. The membrane (and lipid) interacting hydroximic acid (HA) derivatives discussed in this review physiologically restore the heat shock protein stress response, creating a new class of "membrane-lipid therapy" pharmaceuticals. The diseases that HA derivatives potentially target are diverse and include, among others, insulin resistance and diabetes, neuropathy, atrial fibrillation, and amyotrophic lateral sclerosis. At a molecular level HA derivatives are broad spectrum, multi-target compounds as they fluidize yet stabilize membranes and remodel their lipid rafts while otherwise acting as PARP inhibitors. The HA derivatives have the potential to ameliorate disparate conditions, whether of acute or chronic nature. Many of these diseases presently are either untreatable or inadequately treated with currently available pharmaceuticals. Ultimately, the HA derivatives promise to play a major role in future pharmacotherapy.

FTY720 is a sphingosine-1-phosphate analog that has been shown to inhibit ceramide synthesis in vitro. Because ceramide accumulation in muscle is associated with insulin resistance, we aimed to examine whether FTY720 would prevent muscle ceramide accumulation in high fat-fed mice and subsequently improve glucose homeostasis. Male C57Bl/6 mice were fed either a chow or high fat-diet (HFD) for 6 wk, after which they were treated with vehicle or FTY720 (5 mg/kg) daily for a further 6 wk. The ceramide content of muscle was examined and insulin action was assessed. Whereas the HFD increased muscle ceramide, this was prevented by FTY720 treatment. This was not associated with alterations in the expression of genes involved in sphingolipid metabolism. Interestingly, the effects of FTY720 on lipid metabolism were not limited to ceramide because FTY720 also prevented the HFD-induced increase in diacylglycerol and triacylglycerol in muscle. Furthermore, the increase in CD36 mRNA expression induced by fat feeding was prevented in muscle of FTY720-treated mice. This was associated with an attenuation of the HFD-induced increase in palmitate uptake and esterification. In addition, FTY720 improved glucose homeostasis as demonstrated by a reduction in plasma insulin, an improvement in whole-body glucose tolerance, an increase in insulin-stimulated glucose uptake, and Akt phosphorylation in muscle. In conclusion, FTY720 exerts beneficial effects on muscle lipid metabolism that prevent lipid accumulation and improve glucose tolerance in high fat-fed mice. Thus, FTY720 and other compounds that target sphingosine-1-phosphate signaling may have therapeutic potential in treating insulin resistance.

The sphingolipids sphingosine-1-phosphate (S1P) and ceramide are important bioactive lipids with many cellular effects. Intracellular ceramide accumulation causes insulin resistance, but sphingosine kinase 1 (SphK1) prevents ceramide accumulation, in part, by promoting its metabolism into S1P. Despite this, the role of SphK1 in regulating insulin action has been largely overlooked. Transgenic (Tg) mice that overexpress SphK1 were fed a standard chow or high-fat diet (HFD) for 6 weeks before undergoing several metabolic analyses. SphK1 Tg mice fed an HFD displayed increased SphK activity in skeletal muscle, which was associated with an attenuated intramuscular ceramide accumulation compared with wild-type (WT) littermates. This was associated with a concomitant reduction in the phosphorylation of c-jun amino-terminal kinase, a serine threonine kinase associated with insulin resistance. Accordingly, skeletal muscle and whole-body insulin sensitivity were improved in SphK1 Tg, compared with WT mice, when fed an HFD. We have identified that the enzyme SphK1 is an important regulator of lipid partitioning and insulin action in skeletal muscle under conditions of increased lipid supply.

Diabetes, obesity, and cancer affect upward of 15% of the world's population. Interestingly, all three diseases juxtapose dysregulated intracellular signaling with altered metabolic state. Exactly which genetic factors define stable metabolic set points in vivo remains poorly understood. Here, we show that hedgehog signaling rewires cellular metabolism. We identify a cilium-dependent Smo-Ca(2+)-Ampk axis that triggers rapid Warburg-like metabolic reprogramming within minutes of activation and is required for proper metabolic selectivity and flexibility. We show that Smo modulators can uncouple the Smo-Ampk axis from canonical signaling and identify cyclopamine as one of a new class of "selective partial agonists," capable of concomitant inhibition of canonical and activation of noncanonical hedgehog signaling. Intriguingly, activation of the Smo-Ampk axis in vivo drives robust insulin-independent glucose uptake in muscle and brown adipose tissue. These data identify multiple noncanonical endpoints that are pivotal for rational design of hedgehog modulators and provide a new therapeutic avenue for obesity and diabetes., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Aims/hypothesis: Although skeletal muscle insulin resistance has been associated with activation of c-Jun N-terminal kinase (JNK), whether increased JNK activity causes insulin resistance in this organ is not clear. In this study we examined the metabolic consequences of isolated JNK phosphorylation in muscle tissue., Methods: Plasmids containing genes encoding a wild-type JNK1 (WT-JNK) or a JNK1/JNKK2 fusion protein (rendering JNK constitutively active; CA-Jnk) were electroporated into one tibialis anterior (TA) muscle of C57Bl/6 mice, with the contralateral TA injected with an empty vector (CON) to serve as a within-animal control., Results: Overproduction of WT-JNK resulted in a modest (~25%) increase in phosphorylation (Thr(183)/Tyr(185)) of JNK, but no differences were observed in Ser(307) phosphorylation of insulin receptor substrate 1 (IRS-1) or total IRS-1 protein, nor in insulin-stimulated glucose clearance into the TA muscle when comparing WT-JNK with CON. By contrast, overexpression of CA-Jnk, which markedly increased the phosphorylation of CA-JNK, also increased serine phosphorylation of IRS-1, markedly decreased total IRS-1 protein, and decreased insulin-stimulated phosphorylation of the insulin receptor (Tyr(1361)) and phosphorylation of Akt at (Ser(473) and Thr(308)) compared with CON. Moreover, overexpression of CA-Jnk decreased insulin-stimulated glucose clearance into the TA muscle compared with CON and these effects were observed without changes in intramuscular lipid species., Conclusions/interpretation: Constitutive activation of JNK in skeletal muscle impairs insulin signalling at the level of IRS-1 and Akt, a process which results in the disruption of normal glucose clearance into the muscle.

Background: Numerous molecular and biochemical changes have been linked with the cardioprotective effects of exercise, including increases in antioxidant enzymes, heat shock proteins, and regulators of cardiac myocyte proliferation. However, a master regulator of exercise-induced protection has yet to be identified. Here, we assess whether phosphoinositide 3-kinase (PI3K) p110α is essential for mediating exercise-induced cardioprotection, and if so, whether its activation independent of exercise can restore function of the failing heart., Methods and Results: Cardiac-specific transgenic (Tg) mice with elevated or reduced PI3K(p110α) activity (constitutively active PI3K [caPI3K] and dominant negative PI3K, respectively) and non-Tg controls were subjected to 4 weeks of exercise training followed by 1 week of pressure overload (aortic-banding) to induce pathological remodeling. Aortic-banding in untrained non-Tg controls led to pathological cardiac hypertrophy, depressed systolic function, and lung congestion. This phenotype was attenuated in non-Tg controls that had undergone exercise before aortic-banding. Banded caPI3K mice were protected from pathological remodeling independent of exercise status, whereas exercise provided no protection in banded dominant negative PI3K mice, suggesting that PI3K is necessary for exercise-induced cardioprotection. Tg overexpression of heat shock protein 70 could not rescue the phenotype of banded dominant negative PI3K mice, and deletion of heat shock protein 70 from banded caPI3K mice had no effect. Next, we used a gene therapy approach (recombinant adeno-associated viral vector 6) to deliver caPI3K expression cassettes to hearts of mice with established cardiac dysfunction caused by aortic-banding. Mice treated with recombinant adeno-associated viral 6-caPI3K vectors had improved heart function after 10 weeks., Conclusions: PI3K(p110α) is essential for exercise-induced cardioprotection and delivery of caPI3K vector can improve function of the failing heart.

Follistatin is essential for skeletal muscle development and growth, but the intracellular signaling networks that regulate follistatin-mediated effects are not well defined. We show here that the administration of an adeno-associated viral vector expressing follistatin-288aa (rAAV6:Fst-288) markedly increased muscle mass and force-producing capacity concomitant with increased protein synthesis and mammalian target of rapamycin (mTOR) activation. These effects were attenuated by inhibition of mTOR or deletion of S6K1/2. Furthermore, we identify Smad3 as the critical intracellular link that mediates the effects of follistatin on mTOR signaling. Expression of constitutively active Smad3 not only markedly prevented skeletal muscle growth induced by follistatin but also potently suppressed follistatin-induced Akt/mTOR/S6K signaling. Importantly, the regulation of Smad3- and mTOR-dependent events by follistatin occurred independently of overexpression or knockout of myostatin, a key repressor of muscle development that can regulate Smad3 and mTOR signaling and that is itself inhibited by follistatin. These findings identify a critical role of Smad3/Akt/mTOR/S6K/S6RP signaling in follistatin-mediated muscle growth that operates independently of myostatin-driven mechanisms.

Duchenne muscular dystrophy (DMD) is a severe and progressive muscle wasting disorder caused by mutations in the dystrophin gene that result in the absence of the membrane-stabilizing protein dystrophin. Dystrophin-deficient muscle fibres are fragile and susceptible to an influx of Ca(2+), which activates inflammatory and muscle degenerative pathways. At present there is no cure for DMD, and existing therapies are ineffective. Here we show that increasing the expression of intramuscular heat shock protein 72 (Hsp72) preserves muscle strength and ameliorates the dystrophic pathology in two mouse models of muscular dystrophy. Treatment with BGP-15 (a pharmacological inducer of Hsp72 currently in clinical trials for diabetes) improved muscle architecture, strength and contractile function in severely affected diaphragm muscles in mdx dystrophic mice. In dko mice, a phenocopy of DMD that results in severe spinal curvature (kyphosis), muscle weakness and premature death, BGP-15 decreased kyphosis, improved the dystrophic pathophysiology in limb and diaphragm muscles and extended lifespan. We found that the sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase (SERCA, the main protein responsible for the removal of intracellular Ca(2+)) is dysfunctional in severely affected muscles of mdx and dko mice, and that Hsp72 interacts with SERCA to preserve its function under conditions of stress, ultimately contributing to the decreased muscle degeneration seen with Hsp72 upregulation. Treatment with BGP-15 similarly increased SERCA activity in dystrophic skeletal muscles. Our results provide evidence that increasing the expression of Hsp72 in muscle (through the administration of BGP-15) has significant therapeutic potential for DMD and related conditions, either as a self-contained therapy or as an adjuvant with other potential treatments, including gene, cell and pharmacological therapies.

During the past decade, skeletal muscle has been identified as a secretory organ. Accordingly, we have suggested that cytokines and other peptides that are produced, expressed and released by muscle fibres and exert either autocrine, paracrine or endocrine effects should be classified as myokines. The finding that the muscle secretome consists of several hundred secreted peptides provides a conceptual basis and a whole new paradigm for understanding how muscles communicate with other organs, such as adipose tissue, liver, pancreas, bones and brain. However, some myokines exert their effects within the muscle itself. Thus, myostatin, LIF, IL-6 and IL-7 are involved in muscle hypertrophy and myogenesis, whereas BDNF and IL-6 are involved in AMPK-mediated fat oxidation. IL-6 also appears to have systemic effects on the liver, adipose tissue and the immune system, and mediates crosstalk between intestinal L cells and pancreatic islets. Other myokines include the osteogenic factors IGF-1 and FGF-2; FSTL-1, which improves the endothelial function of the vascular system; and the PGC-1α-dependent myokine irisin, which drives brown-fat-like development. Studies in the past few years suggest the existence of yet unidentified factors, secreted from muscle cells, which may influence cancer cell growth and pancreas function. Many proteins produced by skeletal muscle are dependent upon contraction; therefore, physical inactivity probably leads to an altered myokine response, which could provide a potential mechanism for the association between sedentary behaviour and many chronic diseases.

Exercise increases the expression of the prototypical myokine IL-6, but the precise mechanism by which this occurs has yet to be identified. To mimic exercise conditions, C2C12 myotubes were mechanically stimulated via electrical pulse stimulation (EPS). We compared the responses of EPS with the pharmacological Ca(2+) carrier calcimycin (A23187) because contraction induces marked increases in cytosolic Ca(2+) levels or the classical IκB kinase/NFκB inflammatory response elicited by H(2)O(2). We demonstrate that, unlike H(2)O(2)-stimulated increases in IL-6 mRNA, neither calcimycin- nor EPS-induced IL-6 mRNA expression is under the transcriptional control of NFκB. Rather, we show that EPS increased the phosphorylation of JNK and the reporter activity of the downstream transcription factor AP-1. Furthermore, JNK inhibition abolished the EPS-induced increase in IL-6 mRNA and protein expression. Finally, we observed an exercise-induced increase in both JNK phosphorylation and IL-6 mRNA expression in the skeletal muscles of mice after 30 min of treadmill running. Importantly, exercise did not increase IL-6 mRNA expression in skeletal muscle-specific JNK-deficient mice. These data identify a novel contraction-mediated transcriptional regulatory pathway for IL-6 in skeletal muscle.

In the present study, we have examined whether IKKβ [IκB (inhibitor of nuclear factor κB) kinase β] plays a role in feedback inhibition of the insulin signalling cascade. Insulin induces the phosphorylation of IKKβ, in vitro and in vivo, and this effect is dependent on intact signalling via PI3K (phosphoinositide 3-kinase), but not PKB (protein kinase B). To test the hypothesis that insulin activates IKKβ as a means of negative feedback, we employed a variety of experimental approaches. First, pharmacological inhibition of IKKβ via BMS-345541 did not potentiate insulin-induced IRS1 (insulin receptor substrate 1) tyrosine phosphorylation, PKB phosphorylation or 2-deoxyglucose uptake in differentiated 3T3-L1 adipocytes. BMS-345541 did not prevent insulin-induced IRS1 serine phosphorylation on known IKKβ target sites. Secondly, adenovirus-mediated overexpression of wild-type IKKβ in differentiated 3T3-L1 adipocytes did not suppress insulin-stimulated 2-deoxyglucose uptake, IRS1 tyrosine phosphorylation, IRS1 association with the p85 regulatory subunit of PI3K or PKB phosphorylation. Thirdly, insulin signalling was not potentiated in mouse embryonic fibroblasts lacking IKKβ. Finally, insulin treatment of 3T3-L1 adipocytes did not promote the recruitment of IKKβ to IRS1, supporting our findings that IKKβ, although activated by insulin, does not promote direct serine phosphorylation of IRS1 and does not contribute to the feedback inhibition of the insulin signalling cascade.

The role of the cytokine interleukin-6 (IL-6) in metabolic homeostasis is the subject of conjecture. Recent work in Nature Medicine (Ellingsgaard et al., 2011) demonstrates that IL-6 released from skeletal muscle during exercise mediates crosstalk between insulin-sensitive tissues, intestinal L cells, and pancreatic islets to adapt to changes in insulin demand., (Copyright © 2012 Elsevier Inc. All rights reserved.)

Obesity is associated with a state of chronic low grade inflammation that plays an important role in the development of insulin resistance. Tumor progression locus 2 (Tpl2) is a serine/threonine mitogen activated protein kinase kinase kinase (MAP3K) involved in regulating responses to specific inflammatory stimuli. Here we have used mice lacking Tpl2 to examine its role in obesity-associated insulin resistance. Wild type (wt) and tpl2(-/-) mice accumulated comparable amounts of fat and lean mass when fed either a standard chow diet or two different high fat (HF) diets containing either 42% or 59% of energy content derived from fat. No differences in glucose tolerance were observed between wt and tpl2(-/-) mice on any of these diets. Insulin tolerance was similar on both standard chow and 42% HF diets, but was slightly impaired in tpl2(-/-) mice fed the 59% HFD. While gene expression markers of macrophage recruitment and inflammation were increased in the white adipose tissue of HF fed mice compared with standard chow fed mice, no differences were observed between wt and tpl2(-/-) mice. Finally, a HF diet did not increase Tpl2 expression nor did it activate Extracellular Signal-Regulated Kinase 1/2 (ERK1/2), the MAPK downstream of Tpl2. These findings argue that Tpl2 does not play a non-redundant role in obesity-associated metabolic dysfunction.

Background: Obesity and type 2 diabetes (T2DM) are associated with increased circulating free fatty acids and triacylglycerols. However, very little is known about specific molecular lipid species associated with these diseases. In order to gain further insight into this, we performed plasma lipidomic analysis in a rodent model of obesity and insulin resistance as well as in lean, obese and obese individuals with T2DM., Methodology/principal Findings: Lipidomic analysis using liquid chromatography coupled to mass spectrometry revealed marked changes in the plasma of 12 week high fat fed mice. Although a number of triacylglycerol and diacylglycerol species were elevated along with of a number of sphingolipids, a particularly interesting finding was the high fat diet (HFD)-induced reduction in lysophosphatidylcholine (LPC) levels. As liver, skeletal muscle and adipose tissue play an important role in metabolism, we next determined whether the HFD altered LPCs in these tissues. In contrast to our findings in plasma, only very modest changes in tissue LPCs were noted. To determine when the change in plasma LPCs occurred in response to the HFD, mice were studied after 1, 3 and 6 weeks of HFD. The HFD caused rapid alterations in plasma LPCs with most changes occurring within the first week. Consistent with our rodent model, data from our small human cohort showed a reduction in a number of LPC species in obese and obese individuals with T2DM. Interestingly, no differences were found between the obese otherwise healthy individuals and the obese T2DM patients., Conclusion: Irrespective of species, our lipidomic profiling revealed a generalized decrease in circulating LPC species in states of obesity. Moreover, our data indicate that diet and adiposity, rather than insulin resistance or diabetes per se, play an important role in altering the plasma LPC profile.

ERα is expressed in macrophages and other immune cells known to exert dramatic effects on glucose homeostasis. We investigated the impact of ERα expression on macrophage function to determine whether hematopoietic or myeloid-specific ERα deletion manifests obesity-induced insulin resistance in mice. Indeed, altered plasma adipokine and cytokine levels, glucose intolerance, insulin resistance, and increased adipose tissue mass were observed in animals harboring a hematopoietic or myeloid-specific deletion of ERα. A similar obese phenotype and increased atherosclerotic lesion area was displayed in LDL receptor-KO mice transplanted with ERα(-/-) bone marrow. In isolated macrophages, ERα was necessary for repression of inflammation, maintenance of oxidative metabolism, IL-4-mediated induction of alternative activation, full phagocytic capacity in response to LPS, and oxidized LDL-induced expression of ApoE and Abca1. Furthermore, we identified ERα as a direct regulator of macrophage transglutaminase 2 expression, a multifunctional atheroprotective enzyme. Our findings suggest that diminished ERα expression in hematopoietic/myeloid cells promotes aspects of the metabolic syndrome and accelerates atherosclerosis in female mice.

Background: The Angiotensin Converting Enzyme (ACE) gene may influence the risk of heart disease and the response to various forms of exercise training may be at least partly dependent on the ACE genotype. We aimed to determine the effect of ACE genotype on the response to moderate intensity circuit resistance training in chronic heart failure (CHF) patients., Methods: The relationship between ACE genotype and the response to 11weeks of resistance exercise training was determined in 37 CHF patients (New York Heart Association Functional Class=2.3±0.5; left ventricular ejection fraction 28±7%; age 64±12years; 32:5 male:female) who were randomised to either resistance exercise (n=19) or inactive control group (n=18). Outcome measures included V˙O(2peak), peak power output and muscle strength and endurance. ACE genotype was determined using standard methods., Results: At baseline, patients who were homozygous for the I allele had higher V˙O(2peak) (p=0.02) and peak power (p=0.003) compared to patients who were homozygous for the D allele. Patients with the D allele, who were randomised to resistance training, compared to non-exercising controls, had greater peak power increases (ID p<0.001; DD p<0.001) when compared with patients homozygous for the I allele, who did not improve. No significant genotype-dependent changes were observed in V˙O(2peak), muscle strength, muscle endurance or lactate threshold., Conclusion: ACE genotype may have a role in exercise tolerance in CHF and could also influence the effectiveness of resistance training in this condition., (Copyright © 2010 Elsevier Ireland Ltd. All rights reserved.)

Inflammation plays an important role in mediating and exacerbating myocardial ischemia-reperfusion (I/R) injury. Macrophage migration inhibitory factor (MIF), a pleiotropic cytokine, facilitates inflammation and modulates metabolism. However, the role of MIF in mediating local inflammation subsequent to ischemic myocardial injury has not been established. We hypothesized that genetic deletion of MIF protects the heart against severe I/R injury by suppressing inflammation and/or modulating energy metabolism. We showed in the mouse I/R model that duration of both ischemia and reperfusion is a determinant for the degree of regional inflammation and tissue damage. Following a prolonged cardiac I/R (60 min/24h) MIF KO mice had a significant reduction in both infarct size (26±3% vs. 45±4%, P<0.05) and cardiomyocyte apoptosis (1.4±0.2% vs. 5.4±0.4%, P<0.05) and preserved contractile function compared with WT. MIF KO mice with I/R had reduced expression of various inflammatory cytokines and mediators (P<0.05), suppressed infiltration of neutrophils (-40%) and macrophages (-33%, both P<0.05), and increased macrophage apoptosis (14.4±1.4% vs. 5.2±0.6%, P<0.05). Expression of toll-like receptor-4 (TLR-4), phosphorylation of c-Jun N-terminal kinase (JNK), and nuclear fraction of NF-κB p65 were also significantly lower in MIF KO hearts with I/R. Further, MIF KO mice exhibited a lower glucose uptake but higher fatty acid oxidation rate than that in WT (both P<0.05). In conclusion, MIF deficiency protected the heart from prolonged/severe I/R injury by suppressing inflammatory responses. We have identified a critical role of MIF in mediating severe I/R injury. Thus, MIF inhibitory therapy may be a novel strategy to protect the heart against severe I/R injury., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Aims/hypothesis: Recent work has identified the important roles of M1 pro-inflammatory and M2 anti-inflammatory macrophages in the regulation of insulin sensitivity. Specifically, increased numbers of M2 macrophages and a decrease in M1 macrophages within the adipose tissue are associated with a state of enhanced insulin sensitivity. IL-10 is an anti-inflammatory cytokine and is a critical effector molecule of M2 macrophages., Methods: In the present study, we examined the contribution of haematopoietic-cell-derived IL-10 to the development of obesity-induced inflammation and insulin resistance. We hypothesised that haematopoietic-cell-restricted deletion of IL-10 would exacerbate obesity-induced inflammation and insulin resistance. Lethally irradiated wild-type recipient mice receiving bone marrow from either wild-type or Il10-knockout mice were placed on either a chow or a high-fat diet for a period of 12 weeks and assessed for alterations in body composition, tissue inflammation and glucose and insulin tolerance., Results: Contrary to our hypothesis, neither inflammation, as measured by the activation of pro-inflammatory stress kinases and gene expression of several pro-inflammatory cytokines in the adipose tissue and liver, nor diet-induced obesity and insulin resistance were exacerbated by the deletion of haematopoietic-cell-derived IL-10. Interestingly, however, Il10 mRNA expression and IL-10 protein production in liver and/or adipose tissue were markedly elevated in Il10-knockout bone-marrow-transplanted mice relative to wild-type bone marrow-transplanted mice., Conclusions/interpretation: These data show that deletion of IL-10 from the haematopoietic system does not potentiate high-fat diet-induced inflammation or insulin resistance.

The protein deacetylase SIRT1, and its activator resveratrol, exert beneficial effects on glucose metabolism. Different SIRT1 targets have been identified, including PTP1B, AMPK, FOXO, PGC-1α and IRS2. The latter may underscore a tight link between SIRT1 and insulin signaling components. However, whether SIRT1 has a direct effect on insulin resistance and whether resveratrol acts directly or indirectly in this context is still a matter of controversy and this question has not been addressed in muscle cells. Here, we show that SIRT1 protein expression is decreased in muscle biopsies and primary myotubes derived from type 2 diabetic patients, suggesting a contribution of diminished SIRT1 in the determination of muscle insulin resistance. To investigate the functional impact of SIRT1 on the insulin pathway, the activation of insulin downstream effector PKB was evaluated after SIRT1 inactivation by RNAi, SIRT1 overexpression, or resveratrol treatments. In muscle cells and HEK293 cells, downregulation of SIRT1 reduced, while overexpression increased, insulin-induced PKB activatory phosphorylation. Further molecular characterisation revealed that SIRT1 interacts in an insulin-independent manner with the PI3K adapter subunit p85. We then investigated whether resveratrol may improve insulin signaling in muscle cells via SIRT1, or alternative targets. Incubation of muscle cells with resveratrol reverted the insulin-resistant state induced by prolonged TNFα or insulin treatment. Resveratrol-dependent improvement of insulin-resistance occurred through inhibition of serine phosphorylation of IRS1/2, implicating resveratrol as a serine kinase inhibitor. Finally, a functional interaction between PI3K and SIRT1 was demonstrated in C. elegans, where constitutively active PI3K - mimicking increased IIS signaling - lead to shortened lifespan, while removal of sir-2.1 abolished PI3K-induced lifespan shortening. Our data identify SIRT1 as a positive modulator of insulin signaling in muscle cells through PI3K, and this mechanism appears to be conserved from C. elegans through humans., (Copyright © 2011 Elsevier Ireland Ltd. All rights reserved.)

Cystatin C (CstC) is a cysteine protease inhibitor of major clinical importance. Low concentration of serum CstC is linked to atherosclerosis. CstC can prevent formation of amyloid β associated with Alzheimer's disease and can itself form toxic aggregates. CstC regulates NO secretion by macrophages and is a TGF-β antagonist. Finally, the serum concentration of CstC is an indicator of kidney function. Yet, little is known about the regulation of CstC expression in vivo. In this study, we demonstrate that the transcription factor IFN regulatory factor 8 (IRF-8) is critical for CstC expression in primary dendritic cells. Only those cells with IRF-8 bound to the CstC gene promoter expressed high levels of the inhibitor. Secretion of IL-10 in response to inflammatory stimuli downregulated IRF-8 expression and consequently CstC synthesis in vivo. Furthermore, the serum concentration of CstC decreased in an IL-10-dependent manner in mice treated with the TLR9 agonist CpG. CstC synthesis is therefore more tightly regulated than hitherto recognized. The mechanisms involved in this regulation might be targeted to alter CstC production, with potential therapeutic value. Our results also indicate that caution should be exerted when using the concentration of serum CstC as an indicator of kidney function in conditions in which inflammation may alter CstC production.

The incidence of obesity and related co-morbidities such as insulin resistance, dyslipidemia and hypertension are increasing at an alarming rate worldwide. Current interventions seem ineffective to halt this progression. With the failure of leptin as an anti-obesity therapeutic, ciliary neurotrophic factor (CNTF) has proven efficacious in models of obesity and leptin resistance, where leptin proved ineffective. CNTF is a gp130 ligand that has been found to act centrally and peripherally to promote weight loss and insulin sensitivity in both human and rodent models. Future research into novel gp130 ligands may offer new candidates for obesity-related drug therapy.

Adipose triglyceride lipase (ATGL) null (-/-) mice store vast amounts of triacylglycerol in key glucoregulatory tissues yet exhibit enhanced insulin sensitivity and glucose tolerance. The mechanisms underpinning these divergent observations are unknown but may relate to the reduced availability of circulating fatty acids. The aim of this study was to determine whether the enhancements in insulin stimulated glucose metabolism in ATGL-/- mice persist when challenged with a high-fat diet. ATGL-/- mice fed a low-fat diet exhibit improved whole-body insulin sensitivity and glucose tolerance compared with wild-type mice. Wild-type mice became hyperlipidemic and insulin-resistant when challenged with a high-fat diet (HFD, 60% fat) for 4 wk. ATGL-/- mice fed a HFD had elevated circulating fatty acids but had reduced fasting glycemia compared to pre-high-fat diet levels and were refractory to glucose intolerance and insulin resistance. This protection from high-fat diet-induced metabolic perturbations was associated with a preference for fatty acid utilization but reduced energy expenditure and no change in markers of mitochondrial capacity or density. The protection from high-fat diet-induced insulin resistance in ATGL-/- mice was due to increased cardiac and liver insulin-stimulated glucose clearance despite increased lipid content in these tissues. Additionally, there was no difference in skeletal muscle insulin-stimulated glucose disposal, but there was a reduction observed in brown adipose tissue. Overall, these results show that ATGL-/- mice are protected from HFD-induced insulin resistance and reveal a tissue specific disparity between lipid accumulation and insulin sensitivity.

Aging and pathophysiological conditions are linked to membrane changes which modulate membrane-controlled molecular switches, causing dysregulated heat shock protein (HSP) expression. HSP co-inducer hydroxylamines such as BGP-15 provide advanced therapeutic candidates for many diseases since they preferentially affect stressed cells and are unlikely have major side effects. In the present study in vitro molecular dynamic simulation, experiments with lipid monolayers and in vivo ultrasensitive fluorescence microscopy showed that BGP-15 alters the organization of cholesterol-rich membrane domains. Imaging of nanoscopic long-lived platforms using the raft marker glycosylphosphatidylinositol-anchored monomeric green fluorescent protein diffusing in the live Chinese hamster ovary (CHO) cell plasma membrane demonstrated that BGP-15 prevents the transient structural disintegration of rafts induced by fever-type heat stress. Moreover, BGP-15 was able to remodel cholesterol-enriched lipid platforms reminiscent of those observed earlier following non-lethal heat priming or membrane stress, and were shown to be obligate for the generation and transmission of stress signals. BGP-15 activation of HSP expression in B16-F10 mouse melanoma cells involves the Rac1 signaling cascade in accordance with the previous observation that cholesterol affects the targeting of Rac1 to membranes. Finally, in a human embryonic kidney cell line we demonstrate that BGP-15 is able to inhibit the rapid heat shock factor 1 (HSF1) acetylation monitored during the early phase of heat stress, thereby promoting a prolonged duration of HSF1 binding to heat shock elements. Taken together, our results indicate that BGP-15 has the potential to become a new class of pharmaceuticals for use in 'membrane-lipid therapy' to combat many various protein-misfolding diseases associated with aging.

Follistatin is a member of the TGF-β super family and inhibits the action of myostatin to regulate skeletal muscle growth. The regulation of follistatin during physical exercise is unclear but may be important because physical activity is a major intervention to prevent age-related sarcopenia. First, healthy subjects performed either bicycle or one-legged knee extensor exercise. Arterial-venous differences were assessed during the one-legged knee extensor experiment. Next, mice performed 1 h of swimming, and the expression of follistatin was examined in various tissues using quantitative PCR. Western blotting assessed follistatin protein content in the liver. IL-6 and epinephrine were investigated as drivers of follistatin secretion. After 3 h of bicycle exercise, plasma follistatin increased 3 h into recovery with a peak of 7-fold. No net release of follistatin could be detected from the exercising limb. In mice performing a bout of swimming exercise, increases in plasma follistatin as well as follistatin mRNA and protein expression in the liver were observed. IL-6 infusion to healthy young men did not affect the follistatin concentration in the circulation. When mice were stimulated with epinephrine, no increase in the hepatic mRNA of follistatin was observed. This is the first study to demonstrate that plasma follistatin is increased during exercise and most likely originates from the liver. These data introduce new perspectives regarding muscle-liver cross talk during exercise and during recovery from exercise.

Aims/hypothesis: The role of IL-6 in the development of obesity and hepatic insulin resistance is unclear and still the subject of controversy. We aimed to determine whether global deletion of Il6 in mice (Il6 (-/-)) results in standard chow-induced and high-fat diet (HFD)-induced obesity, hepatosteatosis, inflammation and insulin resistance., Methods: Male, 8-week-old Il6 (-/-) and littermate control mice were fed a standard chow or HFD for 12 weeks and phenotyped accordingly., Results: Il6 (-/-) mice displayed obesity, hepatosteatosis, liver inflammation and insulin resistance when compared with control mice on a standard chow diet. When fed a HFD, the Il6 (-/-) and control mice had marked, equivalent gains in body weight, fat mass and ectopic lipid deposition in the liver relative to chow-fed animals. Despite this normalisation, the greater liver inflammation, damage and insulin resistance observed in chow-fed Il6 (-/-) mice relative to control persisted when both were fed the HFD. Microarray analysis from livers of mice fed a HFD revealed that genes associated with oxidative phosphorylation, the electron transport chain and tricarboxylic acid cycle were uniformly decreased in Il6 (-/-) relative to control mice. This coincided with reduced maximal activity of the mitochondrial enzyme β-hydroxyacyl-CoA-dehydrogenase and decreased levels of mitochondrial respiratory chain proteins., Conclusions/interpretation: Our data suggest that IL-6 deficiency exacerbates HFD-induced hepatic insulin resistance and inflammation, a process that appears to be related to defects in mitochondrial metabolism.

Obesity is linked with many deleterious health consequences and is associated with increased risk of chronic disease including type 2 diabetes, atherosclerosis and certain forms of cancer. Recent work has highlighted the impact of obesity to activate inflammatory gene networks and suggests a causal function of inflammation in the pathogenesis of the metabolic syndrome. Since 2005, when Dr Gokhan Hotamisligil chaired the fourth Stock Conference in Istanbul, Turkey, entitled 'Obesity and Inflammation', there has been an explosion of studies investigating the relationship between obesity, inflammation and substrate metabolism. The exuberance surrounding this field of research is exemplified by the body of work that has been published in these past 4 years, including over 1400 publications. During this time, several novel mechanisms relating to cellular inflammation have been uncovered including the role of the hematopoietic system, toll-like receptor activation, endoplasmic reticulum stress and very recently T-cell activation in obesity-induced insulin resistance. These discoveries have led us to rethink cellular nutrient sensing and its role in inflammation and metabolic disease. Despite burgeoning investigation in this field, there still remain a number of unanswered questions. This review that evolved from the 2009 Stock Conference summarizes current research and identifies the deficiencies in our understanding of this topic. The overall goal of this Stock Conference was to bring together leading investigators in the field of inflammation and obesity research in the hope of fostering new ideas, thus advancing the pursuit of novel therapeutic strategies to reduce disease risk and or better treat chronic disease including type 2 diabetes, cardiovascular disease and cancer., (© 2009 The Authors. obesity reviews © 2009 International Association for the Study of Obesity.)

Adiponectin and its receptors, AdipoR1 and AdipoR2, regulate glucose and fatty acid metabolism via activation of AMP-activated protein kinase. Recent work in Nature (Iwabu et al., 2010) demonstrates that adiponectin induces a marked Ca(2+) influx in skeletal muscle via AdipoR1 to control mitochondrial biogenesis, reduce oxidative stress, and enhance endurance capacity., (Copyright Copyright 2010 Elsevier Inc. All rights reserved.)

Objective: Myocardial infarction (MI) is a serious complication of atherosclerosis associated with increasing mortality attributable to heart failure. Activation of phosphoinositide 3-kinase [PI3K(p110 alpha)] is considered a new strategy for the treatment of heart failure. However, whether PI3K(p110 alpha) provides protection in a setting of MI is unknown, and PI3K(p110 alpha) is difficult to target because it has multiple actions in numerous cell types. The goal of this study was to assess whether PI3K(p110 alpha) is beneficial in a setting of MI and, if so, to identify cardiac-selective microRNA and mRNA that mediate the protective properties of PI3K(p110 alpha)., Methods and Results: Cardiomyocyte-specific transgenic mice with increased or decreased PI3K(p110 alpha) activity (caPI3K-Tg and dnPI3K-Tg, respectively) were subjected to MI for 8 weeks. The caPI3K-Tg subjected to MI had better cardiac function than nontransgenic mice, whereas dnPI3K-Tg had worse function. Using microarray analysis, we identified PI3K-regulated miRNA and mRNA that were correlated with cardiac function, including growth factor receptor-bound 14. Growth factor receptor-bound 14 is highly expressed in the heart and positively correlated with PI3K(p110 alpha) activity and cardiac function. Mice deficient in growth factor receptor-bound 14 have cardiac dysfunction., Conclusions: Activation of PI3K(p110 alpha) protects the heart against MI-induced heart failure. Cardiac-selective targets that mediate the protective effects of PI3K(p110 alpha) represent new drug targets for heart failure.