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目的研究不同持续时间后肢去负荷对小鼠运动耐力的影响并探讨其可能的机制。方法小鼠去负荷7、14、28 d,采用跑台记录小鼠运动至耗竭的距离以评价运动耐力,并利用免疫荧光染色、Western blot等方法检测快慢肌纤维蛋白的表达和肌纤维含量。结果在去负荷7、14、28 d肌萎缩形成过程中,小鼠运动耐力分别比对照组下降30.2%、65.5%、71.7%(P<0.001)。运动耐力进行性下降伴随小鼠后肢比目鱼肌肌肉重量的持续丢失,分别下降16.3%(P<0.05)、27.2%(P<0.001)、29.4%(P<0.001)。Western blot结果表明,比目鱼肌中慢肌纤维特异蛋白Troponin I-SS蛋白表达呈进行性下降,而快肌纤维特异蛋白Troponin I-FS的表达上升。免疫组化分析提示,去负荷7、14和28 d后比目鱼肌中慢肌纤维含量分别比对照组下降2.76%、7.75%(P<0.05)、14.97%(P<0.05)。可见伴随后肢去负荷时间的延长,运动耐力持续下降,且伴有显著慢肌萎缩及慢肌纤维含量减少。结论后肢去负荷可引起运动耐力的渐进性下降,且这种规律性变化与慢肌萎缩和慢肌纤维的选择性丢失有关。
Objective To study the effects of hindlimb deloading on exercise tolerance of mice with different durations and to explore its possible mechanism. Methods The mice were sacrificed for 7, 14, and 28 days. The treadmill movement distance to exhaustion was used to evaluate exercise endurance. The expression of muscle fiber and muscle fiber were detected by immunofluorescence staining and Western blot. Results During exercise 7, 14, and 28 days, the exercise tolerance of mice decreased by 30.2%, 65.5% and 71.7% (P <0.001) compared with the control group respectively. The progressive decline in exercise tolerance was accompanied by a sustained loss of muscle mass in the hindlimb soleus by 16.3% (P <0.05), 27.2% (P <0.001) and 29.4% (P <0.001), respectively. The results of Western blot showed that the expression of Troponin I-SS in the soleus muscle decreased progressively, while the expression of Troponin I-FS in the muscle fibers increased. Immunohistochemical analysis showed that the slow muscle fiber content in soleus decreased by 2.76%, 7.75% (P <0.05) and 14.97% (P <0.05) respectively after 7, 14 and 28 days. Visible with hindlimb load time extension, exercise tolerance continued to decline, accompanied by significant slow muscle atrophy and slow muscle fiber content decreased. Conclusions The hindlimb de-loading can cause gradual decline of exercise tolerance, and this regular change is related to the loss of slow muscle atrophy and selective loss of slow muscle fibers.