C/EBPbeta is a Negative Regulator of Skeletal Muscle Differentiation

C/EBPβ is a bZIP transcription factor known to be involved in various physiological processes, including adipogenesis, osteogenesis and liver development. Previous studies in this laboratory revealed an inhibition of myogenesis and reduced myogenic protein expression in 5-azacytidine treated mesenchymal stem cells retrovirally transduced to overexpress C/EBPβ. The goal of this thesis was to evaluate the role of C/EBPβ in myogenic differentiation by overexpression in C2C12 myoblasts and primary myoblasts. We demonstrate reduced MyoD protein expression and subsequent downregulation of myogenic proteins during differentiation following C/EBPβ overexpression. We localized C/EBPβ to the quiescent Pax7+ satellite cells associated with the muscle fiber. Upon satellite cell activation, we observed the downregulation of C/EBPβ protein expression prior to MyoD protein expression. Furthermore, the re-expression of C/EBPβ correlated with the loss of MyoD expression later in differentiation. Histological analysis of C/EBPβ-/- mice revealed smaller fibers and a reduced Pax7+ satellite cell population as compared to control animals. In this thesis, we propose that C/EBPβ is a negative regulator of skeletal muscle differentiation by inhibiting the expression of MyoD, thus impairing proper progression through the myogenic program. In addition, we propose a role for C/EBPβ in the maintenance of undifferentiatied satellite cells