Macrophages enhance muscle satellite cell proliferation and delay their differentiation

This study investigated the effect of macrophages on in vitro satellite cell myogenesis in the turkey and mouse. Macrophages are considered to act as scavengers of tissue debris during the muscle degeneration-regeneration process. The number of dividing cells and of myoblasts expressing the myogenic regulatory factor MyoD indicated that macrophages enhanced satellite cell proliferation in both species. This was confirmed by observations with cultures treated for bromodeoxyuridine (BrdU) incorporation. In mouse and turkey macrophage–satellite cell cocultures, the number of differentiated myoblasts, the frequency of myogenin-positive cells, and the expression of developmental myosin isoforms were reduced as compared with control cultures, indicating that macrophages delayed satellite cell differentiation. The possibility that macrophages facilitate muscle fiber reconstitution by enhancing satellite cell proliferation should be taken into consideration in designing future strategies of satellite cell transplantation as a treatment for muscular dystrophies. © 1999 John Wiley & Sons, Inc. Muscle Nerve 22: 724–732, 1999.