Kee Anthony J, Taylor Alan J, Carlsson Anthony R, Sevette Andre, Smith Ross C, Thompson Martin W
Department of Surgery, Royal North Shore Hospital, University of Sydney, St. Leonards, New South Wales 2065, Australia.
J Appl Physiol (1985). 2002 Jun;92(6):2277-84. doi: 10.1152/japplphysiol.01030.2001.
Both exercise and insulin-like growth factor I (IGF-I) are known to have major hypertrophic effects in skeletal muscle; however, the interactive effect of exogenous IGF-I and exercise on muscle protein turnover or the ubiquitin-proteasome pathway has not been reported. In the present study, we have examined the interaction between endurance exercise training and IGF-I treatment on muscle protein turnover and the ubiquitin-proteasome pathway in the postexercise period. Adult male rats (270-280 g) were randomized to receive 5 consecutive days of progressive treadmill exercise and/or IGF-I treatment (1 mg. kg body wt(-1). day(-1)). Twenty-four hours after the last bout of exercise, the rate of protein breakdown in incubated muscles was significantly reduced compared with that in unexercised rats. This was associated with a significant reduction in the chymotrypsin-like activity of the proteasome and the rate of ubiquitin-proteasome-dependent casein hydrolysis in muscle extracts from exercised compared with unexercised rats. In contrast, the muscle expression of the 20S proteasome subunit beta-1, ubiquitin, and the 14-kDa E2 ubiquitin-conjugating enzyme was not altered by exercise or IGF-I treatment 24 h postexercise. Exercise had no effect on the rates of total mixed muscle protein synthesis in incubated muscles 24 h postexercise. IGF-I treatment had no effect on muscle weights or the rates of protein turnover 24 h after endurance exercise. These results suggest that a suppression of the ubiquitin-proteasome proteolytic pathway after endurance exercise may contribute to the acute postexercise net protein gain.
运动和胰岛素样生长因子I（IGF-I）均已知对骨骼肌具有主要的肥大作用；然而，外源性IGF-I与运动对肌肉蛋白质周转或泛素-蛋白酶体途径的交互作用尚未见报道。在本研究中，我们检测了耐力运动训练与IGF-I治疗在运动后时期对肌肉蛋白质周转及泛素-蛋白酶体途径的交互作用。成年雄性大鼠（270 - 280 g）被随机分组，连续5天接受递增式跑步机运动和/或IGF-I治疗（1 mg·kg体重⁻¹·天⁻¹）。在最后一次运动 bout 后24小时，与未运动的大鼠相比，孵育肌肉中的蛋白质分解速率显著降低。这与运动大鼠肌肉提取物中蛋白酶体的胰凝乳蛋白酶样活性以及泛素-蛋白酶体依赖性酪蛋白水解速率的显著降低相关。相比之下，运动或IGF-I治疗在运动后24小时并未改变20S蛋白酶体亚基β-1、泛素以及14-kDa E2泛素结合酶的肌肉表达。运动对运动后24小时孵育肌肉中的总混合肌肉蛋白质合成速率没有影响。IGF-I治疗对耐力运动后24小时的肌肉重量或蛋白质周转速率没有影响。这些结果表明，耐力运动后泛素-蛋白酶体蛋白水解途径的抑制可能有助于运动后急性净蛋白质增加。
