Exercise-Induced Myostimulin Enhances Muscle Function in Health and Disease

Musculoskeletal diseases are a leading contributor to years lived with disability worldwide ^1,2 . While exercise offers significant benefits for people with these conditions, many individuals do not engage in adequate physical activity ³ . Consequently, there is growing interest in pharmacological interventions that can emulate essential health-promoting effects of exercise ^4,5 . By integrating transcriptomics data of exercised skeletal muscle, we identified C1orf54/ C1ORF54 as a novel exercise-responsive gene in mice and humans. We demonstrate that removal of the first sixteen N-terminal amino acids of C1ORF54 gives rise to a previously uncharacterized protein that stimulates the proliferation of muscle precursor cells and which we named myostimulin. Intriguingly, repeated intermittent treatment of mice with recombinant myostimulin boosts maximal isometric strength in mice within a week. Moreover, we have engineered a variant with improved biophysical properties, increased biological activity in vitro and enhanced efficacy in vivo . This variant even accelerates the recovery of muscle strength from axonotmesis, a condition associated with pronounced muscle weakness. Our data ascribe to myostimulin a role for enhancing the regenerative capacity of skeletal muscle and mediating functional adaptations characteristic of sustained resistance training. Therefore, myostimulin could be an innovative, fast acting therapeutic for certain human musculoskeletal diseases, injuries and other disorders that improve with exercise.