Martin Whitham

From cytokine to myokine: the emerging role of interleukin-6 in metabolic regulation

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.

Effect of a carbohydrate mouthwash on running time-trial performance

Abstract The aim of the present study was to determine the effect of a carbohydrate mouthwash on running time-trial performance. On two separate occasions, seven recreationally active males ([Vdot]O2max 57.8 ml · kg−1 · min−1, s = 3.7) completed a preloaded (15 min at 65%[Vdot]O2max) time-trial of 45 min in duration on a motorized treadmill. At 6-min intervals during the preload and time-trial, participants were given either a 6% maltodextrin, 3% lemon juice solution (carbohydrate trial) or a 3% lemon juice placebo mouthwash (placebo trial) in a double-blind, randomized crossover design. Heart rate, oxygen consumption ([Vdot]O2), respiratory exchange ratio (RER), and ratings of perceived exertion (RPE) were measured during the preload, and blood glucose and lactate were measured before and after the preload and time-trial. There were no significant differences in distance covered between trials (carbohydrate: 9333 m, s = 988; placebo: 9309 m, s = 993). Furthermore, there were no significant between-trial differences in heart rate and running speed during the time-trial, or [Vdot]O2, RER or RPE during the preload. Blood lactate and glucose increased as a result of the exercise protocol, with no between-trial differences. In conclusion, there was no positive effect of a carbohydrate mouthwash on running performance of ∼1 h duration.

Exercise Induces a Marked Increase in Plasma Follistatin: Evidence That Follistatin Is a Contraction-Induced Hepatokine

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.

Life events, perceived stress and antibody response to influenza vaccination in young, healthy adults.

OBJECTIVES Chronic stress has been associated with impaired response to influenza vaccination in the elderly. This study investigated whether mild, intermittent stress experienced by young, healthy adults has a similar effect. METHODS Antibody and psychological status were determined prevaccination and 5 weeks and 5 months later; a fourfold increase in antibody to at least one viral strain was considered protective. RESULTS At 5 months, unprotected participants reported significantly more life events and tended to report more perceived stress than those who were protected. CONCLUSIONS Psychological stress is detrimental to long-term maintenance of antibody levels following vaccination in young, healthy adults.

Contraction-induced interleukin-6 gene transcription in skeletal muscle is regulated by c-Jun terminal kinase/activator protein-1

Background: IL-6 is up-regulated by contraction in skeletal muscle. Results: Contraction-induced IL-6 expression is blunted by JNK inhibition. Conclusion: The JNK/AP-1 pathway regulates IL-6 expression in contracting muscle. Significance: This highlights a novel contraction-mediated transcriptional pathway for IL-6 in skeletal muscle. 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 Ca2+ carrier calcimycin (A23187) because contraction induces marked increases in cytosolic Ca2+ levels or the classical IκB kinase/NFκB inflammatory response elicited by H2O2. We demonstrate that, unlike H2O2-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.

Chaperoning to the metabolic party: The emerging therapeutic role of heat-shock proteins in obesity and type 2 diabetes.

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.

Targeting gp130 to prevent inflammation and promote insulin action.

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), Crohns 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.

The effect of exercise training on the kinetics of the antibody response to influenza vaccination

The significance of in vitro changes in immune function accompanying exercise training is unclear. To determine the effect of exercise on the response of the intact immune system to a challenge in vivo, we measured the speed and overall immunoglobulin G (IgG) response to influenza vaccination in humans engaged in different intensities of activity. Male participants (n = 21) were split into heavy and light training groups. Venous blood samples were collected 0, 2, 4, 7, 10 and 14 days after vaccination with trivalent influenza vaccine, and also 12 months after initial vaccination. Serum IgG was determined by enzyme-linked immunosorbant assay. There was a significant difference in baseline IgG between groups, but no difference in IgG concentration 14 days after vaccination. The IgG concentration remained elevated 12 months post-vaccination in the heavy training group. The results suggest a positive relationship between habitual physical activity and baseline antibody concentrations, which, in turn, affects the relative magnitude (fold or percentage increase) of the antibody response to vaccination. The training loads of the participants in this study had no effect on overall IgG measured 14 days after vaccination.

HSP and Diabetes

As the prevalence of diabetes continues to rise, strategies that aim to prevent and treat the condition continue to gain importance. Obesity is thought to induce a state of low-grade inflammation, which ultimately disrupts insulin signalling and predisposes individuals to type II diabetes. In particular, 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). These kinases in turn inhibit insulin signalling, predominantly through inhibitory phosphorylation of the insulin receptor substrate (IRS). The current chapter reviews the literature that describes this process and the potential that heat shock proteins have in preventing inflammatory disruption of insulin signalling. In particular, data are presented that demonstrate the role of Hsp72 in the prevention of insulin resistance in diet and genetic models of murine obesity. The role of HSP in the autoimmunity of type I diabetes is also discussed