A novel ex vivo model of muscle contraction to measure muscle endocrine and paracrine signalling

Skeletal muscle is a highly organized tissue that possesses the ability to contract and that exerts metabolic, endocrine and paracrine functions. Previous studies explored these functions through in vitro models, computational analyses, and endpoint measurements. To include the cellular complexity that modulates muscle endocrine and paracrine functions, and to allow us to study the kinetics of released and/or depleted factors, we developed a novel setup for ex vivo contraction of whole skeletal muscle. Ex vivo contraction of the Extensor Digitorum Longus (EDL) induced by either electrical field stimulation or direct nerve stimulation resulted in a reduction of relative maximal force and a depletion of muscle glycogen content. Differential proteomics confirmed that proteins upregulated upon electrical pulse stimulation (EPS) were enriched for biological processes and molecular functions associated to cytoskeletal organization and muscle contraction. Finally, EPS induced the release of lactate, and IL6 secretion was induced after cessation of EPS. Taken together, we have developed and validated a new model of ex vivo contraction that includes the full cellular complexity of the muscle and mimics the in vivo physiological response to contraction. Importantly, this model supports for the first time to study the kinetics of the endocrine and paracrine response of the muscle to contraction, and to investigate its effects on various cell-types in vitro .