Author(s): KANO, R., TAKEDA, R., POOLE, D., KANO, Y., HOSHINO, D. , Institution: UNIVERSITY OF ELECTRO-COMMUNICATIONS, Country: JAPAN, Abstract-ID: 792

INTRODUCTION:
Cooling interventions after exercise have been used to enhance skeletal muscle mitochondrial adaptations to endurance exercise (1). Recently, we found that intermittent cooling of skeletal muscle for 1 hour modulates intramyocyte [hydrogen peroxide], which plays an important role in intramuscular signaling. This cooling pattern increases gene expression of Nrf2, a transcription factor that responds to altered [hydrogen peroxide]. Increased Nrf2 expression prior to endurance exercise enhances exercise-induced mitochondrial adaptations (2). Therefore, this investigation was designed to test the hypothesis that local cooling of skeletal muscle prior to running exercise would enhance mitochondrial adaptations in mouse skeletal muscles.
METHODS:
Acute experiment: Male C57Bl/6J mice (9 and 10 weeks old) were divided into sedentary (n=7) and exercise (n=7) groups. Both groups were subjected to cooling stimulation (muscle temperature: 35~13~35°C x 6 sets, total 60 min) on the left leg. The sub-groups were Room temperature + sedentary (RT + Sed), ICE + sedentary (ICE + Sed), Room temperature + exercise (RT + Ex), and ICE + exercise (ICE + Ex). The exercise group performed a 60-minute treadmill running (15 m/min, slope 10 degree incline) immediately after the temperature intervention whereas Sed animals rested. Three hours after the the exercise or rest, tibialis anterior (TA) muscles of all groups were excised, and mRNA levels of PGC1α, Ucp3, and pdk4 were measured. Training experiment: In 14 mice, the same cooling and exercise protocol as in the acute model was performed 4 times / week for 4 weeks, and 24 hours after the last training bout, TA and EDL muscles were harvested. Mitochondrial enzyme activity, mitochondrial and antioxidant-related proteins were measured. Statistical analyses using a paired two-way ANOVA, and multiple comparison tests were performed for interaction effects. A statistical level of p<0.05 was accepted.
RESULTS:
Acute Responses: ICE + Ex showed significantly higher levels of PGC1α mRNA than RT + Ex (+14%, p=0.012). Ucp3 and Pdk4 increased with exercise (p<0.001), but decreased with cooling stimulation (p<0.05). Training Responses: CS activity increased additively (+18%) with the combination of training and cooling as did β-HAD activity compared with training alone (+24%, p=0.017). There were no differences in the levels of mitochondrial-related proteins OXPHOS, PGC1α, or antioxidant enzymes Sod1,2 among groups.
CONCLUSION:
Local cooling stimulation of skeletal muscle prior to acute running exercise promoted an increase in PGC1α mRNA levels. Running training under pre-cooling conditions increased the activity of the mitochondrial enzymes CS and β-HAD compared to training under normal conditions. This study demonstrates that pre-conditioning with local cooling has a synergistic effect on the mitochondrial adaptations induced by running exercise.