Regulation of myogenic stem cell behavior by vessel cells: the "ménage à trois" of satellite cells, periendothelial cells and endothelial cells.

In skeletal muscle, satellite cells, that are responsible of muscle repair, are localized close to capillaries. Although angiogenesis is known for a long time to be crucial for muscle repair and satellite cell survival, cellular interplays between vessel cells and satellite/myogenic cells have been poorly explored. We analyzed the interrelationships between myogenic cells, endothelial cells, and periendothelial cells that includes smooth muscle cells and endomysial fibroblasts. We found that endothelial cells strongly stimulate myogenic cell growth and, inversely, myogenic cells increase angiogenesis. VEGF plays an essential role in this bidirectional interaction. On the contrary, periendothelial cells promote the return to quiescence of a subset of muscle precursor cells that ensures self-renewal of adult muscle stem cells. We have shown that Angiopoietin-1/Tie-2 signaling controls the entry into quiescence. We propose that during muscle regeneration, i.e., while vessels are not stabilized, endothelial cells and myogenic cells interact with each other to promote both myogenesis and angiogenesis, that have been shown to be concomitant processes in several models. On the other hand, once homeostasis of muscle is reached, the proximity of satellite cells and periendothelial cells allows the responsiveness of satellite cells, that bear Tie-2 receptor, to the secretion of Angiopoietin-1 by periendothelial cells, that, in the same time, stabilize vessels by promoting quiescence of endothelial cells.