Characterization of powerful myogenic factors present in media conditioned by murine or human macrophages

Introduction : The inflammatory processes associated with traumatic damage, diseases or strenuous exercise play a key role during muscle regeneration. Many of the signals associated to muscle injury are actually exchanged between macrophages and muscle precursors, but the precise role of macrophage-secreted myogenic factors is still poorly characterized. Objectives : The outcome of the project presented here will help to understand the identity and the role of the myogenic factors released in medium by macrophages (mMCM: Medium Conditioned by murine Macrophage ). Methods : Cellular and molecular analyses on proliferation, differentiation and chemotaxis were carried out on rat and human satellite cells, rat muscle cultures and DMD myoblasts. The presence of known myogenic factors in mMCM was assessed by western blot analyses. Results : We set-up a pseudo-organotipic rat cell culture that is strongly myogenic when treated with mMCM. In vitro mMCM enhances the proliferation rate of slow-growing myogenic cells, favouring division over cytoplasmic growth and allowing satellite cells to keep their ability to form myotubes even in sub-optimal conditions. A positive chemotactic effect is exterted by mMCM on C2C12 cells and primary rat myoblasts. Murine or human-derived MCM (hMCM) stimulates the in vitro proliferation of myoblasts from healthy or dystrophic (DMD) patients. Conclusions : A full characterization of cytokines released in vivo as signals during necrotic and inflammatory processes would be of paramount importance for the muscle regeneration. A better understanding of the macrophageproduced myogenic factors would be beneficial in almost any muscle diseases, genetic (i.e. muscular dystrophies) or acquired.