Endurance training induces heat shock protein 72 expression in the diaphragm of young and old rats

Abstract

Objective: Heat shock proteins (HSPs) are now known as important physiological elements that promote adaptation to cellular stressors such as exercise in the skeletal muscle. Chronic exercise training is reported to induce HSP72 in both young and old rat skeletal muscle, and aging is associated with a blunted expression of HSP72. The diaphragm, which is primary respiratory muscle that constantly contracts and relaxes, is closely related to pulmonary function. However, the effects of chronic exercise training on HSP72 expression in the diaphragm have not been evaluated. Therefore, this study investigates the effects of chronic endurance training on HSP72 expression in the diaphragm of both young and old rats. Materials and methods: Young adult (12weeks) and old (100weeks) female Fisher 344 rats were assigned to four groups ; young untrained control, young training, old untrained control, and old training (n =6 for each group). The training groups performed treadmill exercise for 10 weeks (75-80% Vo₂max, 5 days/week). The costal diaphragm was removed and analyzed for HSP72 expression, myosin heavy chain (MHC) composition, and citrate synthase (CS) activity after completion of training. Results: Diaphragm type I MHC concentration was significantly increased (p<0.05) and type II d/x MHC concentration was significantly decreased (p<0.05) in old rats ; however, training did not alter the diaphragm MHC phenotype. Citrate synthase activity was significantly increased (p<0.05) in the young training group. Diaphragm HSP72 expression in the old control group (70.7±11.0) did not show any significant difference compared to that in the young control group (100±16.4). Diaphragm HSP72 expression was increased in both the young training group (197.8±59.7, p<0.05) and the old training group (113.0±40.4,p<0.05) compared to those in the young and old control groups, respectively. Thus, endurance training resulted in altered levels of HSP72 expression by +98% in the young training group and by +60% in the old training group, indicating a blunted response of HSP72 in the old training group. Conclusion: The present study demonstrated that chronic endurance training induced rat diaphragm HSP72 expression in both young and old rats and a blunted expression of HSP72 was associated with aging.