CCAAT/enhancer binding protein β is required for satellite cell self-renewal.

Postnatal growth and repair of skeletal muscle relies upon a population of quiescent muscle precursor cells, called satellite cells that can be activated to proliferate and differentiate into new myofibers, as well as self-renew to replenish the satellite cell population. The balance between differentiation and self-renewal is critical to maintain muscle tissue homeostasis, and alterations in this equilibrium can lead to chronic muscle degeneration. The transcription factor CCAAT/enhancer binding protein beta (C/EBPβ) is expressed in Pax7+ satellite cells of healthy muscle and is downregulated during myoblast differentiation. Persistent expression of C/EBPβ upregulates Pax7, inhibits MyoD, and blocks myogenic differentiation. Using genetic tools to conditionally abrogate C/EBPβ expression in Pax7+ cells, we examined the role of C/EBPβ in self-renewal of satellite cells during muscle regeneration. We find that loss of C/EBPβ leads to precocious differentiation at the expense of self-renewal in primary myoblast and myofiber cultures. After a single muscle injury, C/EBPβ-deficient satellite cells fail to self-renew resulting in a reduction of satellite cells available for future rounds of regeneration. After a second round of injury, muscle regeneration is impaired in C/EBPβ conditional knockout mice compared to wild-type control mice. We find that C/EBPβ can regulate Notch2 expression and that restoration of Notch activity in myoblasts lacking C/EBPβ prevents precocious differentiation. These findings demonstrate that C/EBPβ is a novel regulator of satellite cell self-renewal during muscle regeneration acting at least in part through Notch2.