100 Section - Frequent tetanic exercise using electrical muscle stimulation may prevent immobilization-induced muscle fibrosis by reducing myonuclear apoptosis

Objectives : Immobilization-induced fibrosis is the primary cause of muscle contracture, and myonuclear apoptosis is the trigger. Tetanic exercise via electrical muscle stimulation may mitigate myonuclear apoptosis, which could provide an intervention strategy for immobilization-induced fibrosis. In the present study, this was tested using rat skeletal muscles.

Design: Eight-week-old male Wistar rats were divided into the control, immobilization (n = 9; immobilized treatment only), low-contraction frequency (LCF; n = 9; immobilized treatment and tetanic exercise with a 2-s (active)/6-s (rest) duty cycle for two weeks), and high-contraction frequency (HCF; n = 10; immobilized treatment and tetanic exercise with a 2-s (active)/2-s (rest) duty cycle for two weeks) groups. The soleus muscles were harvested after the experimental periods, and the soleus muscles were used for histological, immunohistological, biochemical, and molecular biological analyses.

Results: The number of TUNEL-positive myonuclei was 0.36 ± 0.11, 4.66 ± 0.90, 4.25 ± 0.99, and 1.90 ± 0.46 in the control, immobilization, LCF, and HCF groups, respectively. The HCF group was lower than the immobilization and LCF groups. The number of myonuclei and cross-sectional area (CSA) in the HCF group was higher than in the immobilization and LCF groups. The number of macrophages, mRNA expression of IL-1β, TGF-β1, and α-SMA, and hydroxyproline contents in the HCF group was lower than in the immobilization and LCF groups. There were moderate to strong negative correlations between the number of TUNEL-positive myonuclei and the number of myonuclei and between the CSA and the number of macrophages. Moderate to strong positive correlations were found between the number of myonuclei and the CSA, the number of macrophages and IL-1β, IL-1β and TGF-β1, TGF-β1 and α-SMA, and α-SMA and hydroxyproline contents.

Conclusion: Frequent tetanic exercise might mitigate macrophage accumulation caused by myonuclear apoptosis and suppress immobilization-induced muscle fibrosis due to the overexpression of fibrosis-associated molecules.