Mechanical Loading-Induced Gene Expression Responses Of Young And Aged Myoblasts

Aging is characterized by cellular senescence and inflammation, while myogenesis also deteriorates in aged skeletal muscle cells. Mechanical loading can ameliorate the impaired myogenic potential and the inflammatory status of the aged muscle cells, however the loading conditions for optimum molecular responses remain unclear. PURPOSE: This study investigated and compared the effects of a specific mechanical loading protocol on the expression of myogenic regulatory factors and muscle-derived cytokines in aged and young myoblasts, in vitro. METHODS: Replicatively aged (80 population doublings) and young C2C12 myoblasts underwent a stretching protocol (15% elongation at a frequency of 1 Hz for 12 h) using the Flexcell Tension System and the expression of Myf5, MyoD, Myogenin, interleukin (IL)-6 and IL-4 was evaluated using Real Time-PCR. RESULTS: Increased expression of Myf5 was found in aged cells in response to stretching (p < 0.01), while mechanical loading resulted in downregulation of Myf5 in the young myoblasts (p < 0.001). A decreased expression of MyoD and Myogenin was induced by mechanical loading in both the aged and young cells compared to the unloaded myoblasts (p < 0.001). Moreover, the expression of the pleiotropic cytokine IL-6 was reduced in the aged (p < 0.01) and young (p < 0.001) myoblasts in response to stretching, while mechanical loading resulted in higher upregulation of the anti-inflammatory cytokine IL-4 in the aged compared to the young myoblasts (p < 0.01). CONCLUSIONS: Differential expression responses were caused in the aged compared to the young myoblasts by the stretching protocol used, suggesting that a loading-induced myogenic and anti-inflammatory potential of myoblasts may be senescence-stage dependent.