The effects of melatonin on differentiated C2C12 myotubes in the absence of pathology: An oxygen-sparing action and enhancement of pro-survival signalling pathways

Previous research has demonstrated that melatonin protects against muscle damage while also improving the performance of injured muscle. However, its impact on healthy skeletal muscle remains largely unexplored. We exposed differentiated C2C12 myotubes to two melatonin concentrations (10 nM or 50 nM). The 10 nM concentration did not affect any of the mitochondrial respiration parameters. Whereas 50 nM concentration reduced mitochondrial complex II-linked oxidative phosphorylation (OXPHOS), electron transfer system (ETS) capacity, the contribution of complex II to ETS, and residual oxygen consumption (ROX). Neither concentration influenced the mitochondrial coupling control ratios, nor the coupling control efficiency ratios. Furthermore, neither concentration affected ATP production but reduced superoxide dismutase activity. The 50 nM increased catalase activity without affecting autophagy or citrate synthase activity. Moreover, 50 nM reduced activated JAK2 and STAT3 protein expression, while 10 nM reduced JAK2 without affecting STAT3. Th 50 nM increased activated AKT and ERK1/2 expression with no effect on p38 or PGC1-α expression. Our data suggests that melatonin (50 nM) triggers an oxygen-sparing effect on mitochondrial respiration, which is mediated via its antioxidant actions and its ability to enhance pro-survival pathways. Therefore, melatonin intake may have ergogenic effects on healthy muscles, in the absence of pathology, e.g., consumption before sporting events or physical exercise may aid in the reduction of oxidative stress often associated with such activities. However, this is an in vitro study, and therefore, the clinical relevance of the data should be considered with caution.