Prostaglandin E2 receptor EP2 is indispensable for maintenance of skeletal muscle stem cells

Muscle satellite cells are adult muscle stem cells indispensable for growth and regeneration of postnatal skeletal muscle. Notch plays a central role in maintenance of muscle satellite cells, but how Notch maintains the muscle stem cell pool is not fully understood. Previously, we reported that a prostaglandin E2 receptor, EP2, is upregulated by Notch signal and suppresses differentiation of human muscle progenitors. Here we examined the roles of EP2 in muscle satellite cells using a mouse Cre-LoxP conditional gene knockout system. Genetic inactivation of the EP2 gene (PTGER2) activated muscle satellite cells, caused their loss, and impaired muscle regeneration. These results indicate that EP2 is indispensable for maintenance of satellite cells. Ex vivo analysis using isolated myofibers showed that prostaglandin E2 (PGE2) delayed the activation of satellite cells via EP2. An extracellular signal-regulated kinase (ERK) 1/2 inhibitor blocked the activation of satellite cells on myofibers, and PGE2 attenuated the phosphorylation of ERK1/2 in muscle satellite cells. These results suggest that EP2 keeps the quiescence of satellite cells and maintains the satellite cell pool in part by inhibiting the ERK1/2 signaling pathway.