Adult skeletal muscle is a plastic tissue that can adapt its size to workload. Here, we show that RhoA within myofibers is needed for overload-induced hypertrophy by controlling satellite cell (SC) fusion to the growing myofibers without affecting protein synthesis. At the molecular level, we demonstrate that RhoA controls in a cell autonomous manner Erk1/2 activation and the expressions of extracellular matrix (ECM) regulators such as Mmp9/Mmp13/Adam8 and macrophage chemo-attractants such as Ccl3/Cx3cl1. Their decreased expression in RhoA mutants is associated with ECM and fibrillar collagen disorganization and lower macrophage infiltration. Moreover, matrix metalloproteinases inhibition and macrophage depletion in controls phenocopied the altered growth of RhoA mutants while having no effect in mutants showing that their action is RhoA-dependent. These findings unravel the implication of RhoA within myofibers, in the building of a permissive microenvironment for muscle hypertrophic growth and for SC accretion through ECM remodeling and inflammatory cell recruitment.

SummaryAdult skeletal muscle is a plastic tissue that can adapt its size to workload. Here, we show that RhoA within myofibers is needed for overload-induced hypertrophy by controlling satellite cell fusion to the growing myofibers without affecting protein synthesis. At the molecular level, we demonstrate that, in response to increased workload, RhoA controls in a cell autonomous manner Erk1/2 activation and the expressions of extracellular matrix (ECM) regulators such as Mmp9/Mmp13/Adam8 and of macrophage chemo-attractants such as Ccl3/Cx3cl1. Their decreased expression in RhoA mutant is associated with ECM and fibrillar collagen disorganization and lower macrophage infiltration. Moreover, Mmps inhibition and macrophage depletion in controls phenocopied the lack of growth of RhoA mutants. These findings unravel the implication of RhoA within myofibers, in response to increase load, in the building of a permissive microenvironment for muscle growth and for satellite cell accretion through ECM remodeling and inflammatory cell recruitment.