Effect of constant compressive stress induced by imitating Tuina stimulation with various durations on the cell cycle, cellular secretion, apoptosis, and expression of myogenic differentiation and myogenic factor 5 of rat skeletal muscle cells in vitro.

OBJECTIVE: To investigate the effect of constant compressive stress induced by imitating Tuina stimulation with various durations on the cell cycle, cellular secretion, apoptosis, and expression of myogenic regulatory factors (MRFs), myogenic factor 5(Myf5) and myogenic differentiation (MyoD) of rat skeletal muscle cells (RSkMCs) in vitro. METHODS: Third passage RSkMCs were subjected to constant compressive stresses with various durations at 2000 strain for 15, 30, 60, 90, and 120 min via a four-point bending system. The control group (CG) was cultured in the absence of mechanical loading. Alterations of the cell cycle and apoptosis rate were detected by flow cytometry (FCM). The concentrations of interleukin 6 (IL-6) / prostaglandin E2 (PGE2) and nitric oxide (NO) in supernatants were determined by enzyme-linked immunosorbent assays and the nitrate reductase method, respectively. Expression of Myf5 and MyoD was detected by immunohistochemistry. RESULTS: Compared with the CG, a significant alteration was observed in the synthesis phase fraction (SPF) (P < 0.01). The SPF and proliferation index (PI) were reduced from 15 to 90 min, but reached levels similar to those at 120 min. Apoptosis was increased significantly at 30 min (P < 0.05) and especially at 90 and 120 min (P < 0.01). Expression of MyoD and Myf5 was increased significantly at 15, 30, and 90 min (P < 0.01). Compared with 15 and 30 min, MyoD and Myf5 expression at 60 and 120 min was decreased significantly (P < 0.01). Compared with 60 min, MyoD expression at 90 min was increased significantly (P < 0.05), whereas MyoD and Myf5 expression at 120 min was significantly lower (P < 0.05). The IL-6 concentration was increased at 60 min compared with the CG and 15 min (P < 0.05), whereas the concentrations of PGE2 and NO were the highest at 15 and 30 min, respectively, compared with the CG and other time points (P < 0.05). CONCLUSION: The cell cycle, secretion, apoptosis, and Myf5 and MyoD expression of RSkMCs were regulated by compressive stress in a time-dependent manner. SPF and PI were inhibited at short durations (< 90 min), but NO and PGE2 secretion was the highest at shorter durations (< 30 min). With the prolongation of stimulation time, SPF, PI, and apoptosis were increased, but Myf5 and MyoD expression was decreased gradually at 15-30 min.