Effects of denervation on cell cycle control in laryngeal muscle

Denervation of skeletal muscle is thought to lead to an accelerated proliferation of myogenic stem cells known as satellite cells. The transition of these cells from a quiescent to a proliferative state is thought to require satellite cells to enter the cell cycle and replicate. Little is known about the expression of genes associated with cell cycle control, and so the objective of this study was to examine the effects of denervation and reinnervation of the posterior cricoarytenoid (PCA) muscle on key cell cycle genes. Female Sprague-Dawley rats were assigned to control, denervated, or reinnervated groups. Animals were killed at 7, 14, and 30 days after ligation of the recurrent laryngeal nerve. The PCA muscle was then analyzed for changes in the messenger RNA levels of key genes associated with cell cycle control, differentiation, and proliferation. Cyclin D1 is a key gene responsible for initiating progression of the cell cycle from G1 to S phase. Interestingly, neither denervation nor reinnervation affected the expression of this gene. In contrast, we found large increases in key cell cycle inhibitors (p21 and the growth arrest and DNA destruction 45 [GADD45] gene) in both the denervated and reinnervated groups. We interpret the increases in these cell cycle inhibitors to reflect (1) an inhibition of satellite cell proliferation and/or (2) a special form of apoptosis that results in the loss of myonuclei known to occur under atrophic conditions. To our knowledge, this is the first study to examine the effects of denervation on cell cycle regulation.