Adult skeletal muscle has the remarkable property of regenerating after damage, owing to satellite cells and myogenic precursor cells becoming committed to adult myogenesis to rebuild the muscle. This process is accompanied by the continuing presence of macrophages, from the phagocytosis of damaged myofibres to the full re-formation of new myofibres. In recent years, there has been huge progress in our understanding of the roles of macrophages during skeletal muscle regeneration, notably concerning their effects on myogenic precursor cells. Here, we review the most recent knowledge acquired on monocyte entry into damaged muscle, the various macrophage subpopulations, and their respective roles during the sequential phases of muscle repair. We also discuss the role of macrophages after exercise-induced muscle damage, notably in humans.
Skeletal muscle regenerates after injury thanks to myogenic precursor cells. Macrophages are continuously present during muscle regeneration. While in resting muscle, macrophages are located in the epimysium, they infiltrate the parenchyma after muscle injury. A sequence of pro-inflammatory then anti-inflammatory macrophages accompanies muscle regeneration, each subset of macrophages providing specific cues to myogenic cells for proliferation then differentiation.