Cytokine-induced skeletal muscle atrophy : protective effect of resveratrol

Sarcopenia, the loss of muscle mass and function as we age, affects all individuals from approximately the 4th decade of life and results in a poor quality of life. The mechanisms responsible for sarcopenia are unclear and it is likely that it is a multifactorial disease. However, it is hypothesised that an increase in systemic and/or muscle pro-inflammatory cytokine levels play a major role. Interferon induced protein 10 (IP10) is a chemokine that has been shown to be increased in serum as we age. Polyphenols are extracts from plants and have been shown to have anti-inflammatory effects with benefits in multiple diseases. Therefore, the main aim of this thesis was to establish an in vitro model to study the effect of increased levels of IP10 on muscle atrophy and inflammation and to examine whether resveratrol treatment was able to protect against IP10 induced effects on skeletal muscle atrophy or inflammation. Primary myoblasts were isolated from rat muscles and treated with 0. 1µM, 1µM and 10µM of resveratrol to identify a functional concentration. Treatment of cells with 1µM of resveratrol increased myoblast growth, increased myotube diameter and decreased production of hydrogen peroxide of the cell media. Furthermore, treatment of myoblasts with 1µM resveratrol led to increases in the protein content of known resveratrol targets; MnSOD and catalase and caused transient increases in Sirt1 protein content. Treatment of cells with 1µM resveratrol also increased MnSOD and catalase content of myotubes and resulted in a decrease in the content of Sirt1, coupled with an increase in the acetylation status of proteins compared with untreated myotubes. As these data suggested that 1µM of resveratrol was functional in myotubes, this concentration was used to pre-treat myotubes before IP10 treatment. Treatment of myotubes with IP10 at levels found in older people (200pg/ml) led to decreases in myotube diameter and increases in the atrophy marker, Atrogin1. Pre-treatment of myotubes with resveratrol provided protection against both of these effects. Treatment of myotubes with a concentration of IP10 found in the young (150pg/ml) had no effect on markers of atrophy. Both concentrations of IP10 were found to have similar effects on cytokine release by myotubes and resveratrol treatment had only marginal effects on this. The second aim of this study was to identify an effective concentration of resveratrol in vivo and examine the effect of this on skeletal muscle force generation in adult and old mice. Treatment of mice with 125mg resveratrol/kg/day resulted in an increase in MnSOD and Sirt1 contents of skeletal muscle from young mice but had no effect on skeletal muscle force generation by EDL muscles of either adult or old mice. Overall data suggest that the increase in IP10 levels seen in ageing contributes to sarcopenia; however it is unlikely this acts through changes to the cytokine profile of muscle. Resveratrol prevented some atrophic effects induced by IP10, suggesting that, the mechanism through which resveratrol may protect against sarcopenia may be through the prevention of increases in atrophic pathways.