The regulation of skeletal muscle fatigability and mitochondrial function by chronically elevated interleukin-6.

NEW FINDINGS: What is the central question of this study? Interleukin-6 has been associated with muscle mass and metabolism in both physiological and pathological conditions. A causal role for interleukin-6 in the induction of fatigue and disruption of mitochondrial function has not been determined. What is the main finding and its importance? We demonstrate that chronically elevated interleukin-6 increased skeletal muscle fatigability and disrupted mitochondrial content and function independent of changes in fibre type and mass. ABSTRACT: Interleukin-6 (IL-6) can initiate intracellular signalling in skeletal muscle by binding to the IL-6-receptor and interacting with the transmembrane gp130 protein. Circulating IL-6 has established effects on skeletal muscle mass and metabolism in both physiological and pathological conditions. However, the effects of circulating IL-6 on skeletal muscle function are not well understood. The purpose of this study was to determine whether chronically elevated systemic IL-6 was sufficient to disrupt skeletal muscle force, fatigue and mitochondrial function. Additionally, we examined the role of muscle gp130 signalling during overexpression of IL-6. Systemic IL-6 overexpression for 2 weeks was achieved by electroporation of an IL-6 overexpression plasmid or empty vector into the quadriceps of either C57BL/6 (WT) or skeletal muscle gp130 knockout (KO) male mice. Tibialis anterior muscle in situ functional properties and mitochondrial respiration were determined. Interleukin-6 accelerated in situ skeletal muscle fatigue in the WT, with a 18.5% reduction in force within 90 s of repeated submaximal contractions and a 7% reduction in maximal tetanic force after 5 min. There was no difference between fatigue in the KO and KO+IL-6. Interleukin-6 reduced WT muscle mitochondrial respiratory control ratio by 36% and cytochrome c oxidase activity by 42%. Interleukin-6 had no effect on either KO respiratory control ratio or cytochrome c oxidase activity. Interleukin-6 also had no effect on body weight, muscle mass or tetanic force in either genotype. These results provide evidence that 2 weeks of elevated systemic IL-6 is sufficient to increase skeletal muscle fatigability and decrease muscle mitochondrial content and function, and these effects require muscle gp130 signalling.