Evidence of Notch-Hesr-Nrf2 Axis in Muscle Stem Cells, but Absence of Nrf2 Has No Effect on Their Quiescent and Undifferentiated State.

Nrf2 is a master regulator of oxidative stresses through the induction of anti-oxidative genes. Nrf2 plays roles in maintaining murine hematopoietic stem cells and fly intestinal stem cells. The canonical Notch signaling pathway is also crucial for maintaining several types of adult stem cells including muscle stem cells (satellite cells). Here, we show that Dll1 induced Nrf2 expression in myogenic cells. In addition, primary targets of Notch signaling, Hesr1 and Hesr3, were involved in the up-regulation of Nrf2 mRNA and expression of its target genes. In vitro, Nrf2 had anti-myogenic and anti-proliferative effects on primary myoblasts. In vivo, although Nrf2-knockout mice showed decreased expression of its target genes in muscle stem cells, adult muscle stem cells of Nrf2-knockout mice did not exhibit the phenotype. Taken together, in muscle stem cells, the Notch-Hesr-Nrf2 axis is a pathway potentially inducing anti-oxidative genes, but muscle stem cells either do not require Nrf2-mediated anti-oxidative gene expression or they have a complementary system compensating for the loss of Nrf2.