The Difference of Apoptotic Responses in Denervated Muscle Atrophy of Aging Rat Skeletal Muscles

Abstract

Age-related change of skeletal muscles has become a significant burden to our society because it's strongly related to the decline of physical activity. Muscle cell apoptosis as one of intracellular mechanisms has been suggested in aging skeletal muscles, but its mechanism remained unclear and the findings are diverse. The purpose of this study is to investigate the characteristics of apoptosis-related responses in denervated muscle atrophy of rat aging skeletal muscles and to find the differences between young and old in completely denervated and partial denervated muscles. In research laboratory setting, 25 young (3 month old) and 25 aged (22 month old) male Sprague Dawley rats were used. The right sciatic nerve of rats were completely denervated (CD) by transection and partially denervated (PD) by crushing injury. At 2, 4 weeks after injury, their muscles were resected for the measurement of muscle weights(MW), TUNEL assay and the expression of BAX and Bcl-2. The MW ratio per body weight of aged rats was significantly lower than that of young rats 4 weeks after PD. (P=0.002). The MW ratio after CD decreased in both group similarly. TUNEL positive nuclei of CD group were more prevalent than those of PD group in both young and aged group (P<0.001; P=0.02, respectively). Old group showed higher BAX and Bcl-2 expressions than those of young group after PD but not after CD. In conclusion, apoptosis-related responses in partially denervated muscle atrophy were more prominent in aging skeletal muscles compared to young muscles but not in completely denervated muscles. This finding indicates increased apoptotic responses of in the aged muscles are related to low regenerative potential followed by denervation.