Lack of mechanical load leads to skeletal muscle atrophy, and one major underlying mechanism involves the myostatin pathway that negatively regulates protein synthesis and also activates Atrogin-1/MAFbx and MuRF1 genes. In hindlimb immobilization, leucine was observed to attenuate the upregulation of the referred atrogenes, thereby shortening the impact on fiber cross-sectional area, nonetheless, the possible connection with myostatin is still elusive. This study sought to verify the impact of leucine supplementation on myostatin expression. Male Wistar rats were supplemented with leucine and hindlimb immobilized for 3 and 7 days, after which soleus muscles were removed for morphometric measurements and analyzed for gene and protein expression by real-time PCR and Western blotting, respectively. Muscle wasting was prominent 7 days after immobilization, as expected, leucine feeding mitigated this effect. Atrogin-1/MAFbx gene expression was upregulated only after 3 days of immobilization, and this effect was attenuated by leucine supplementation. Atrogin-1/MAFbx protein levels were elevated after 7 days of immobilization, which leucine supplementation was not able to lessen. On the other hand, myostatin gene expression was upregulated in immobilization for 3 and 7 days, which returned to normal levels after leucine supplementation. Myostatin protein levels followed gene expression at a 3-day time point only. Follistatin gene expression was upregulated during immobilization and accentuated by leucine after 3 days of supplementation. Concerning protein expression, follistatin was not altered neither by immobilization nor in immobilized animals treated with leucine. In conclusion, leucine protects against skeletal muscle mass loss during disuse, and the underlying molecular mechanisms appear to involve myostatin inhibition and Atrogin-1 normalization independently of follistatin signaling.

中文翻译：

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亮氨酸的骨骼肌抗萎缩作用涉及肌肉生长抑制素抑制


缺乏机械负荷会导致骨骼肌萎缩，一种主要的潜在机制涉及肌肉生长抑制素途径，该途径会负向调节蛋白质合成并激活 Atrogin-1/MAFbx 和 MuRF1 基因。在后肢固定中，观察到亮氨酸减弱了所涉及的致萎缩基因的上调，从而缩短了对纤维横截面积的影响，尽管如此，与肌肉生长抑制素的可能联系仍然难以捉摸。本研究旨在验证亮氨酸补充对肌肉生长抑制素表达的影响。雄性 Wistar 大鼠补充亮氨酸，后肢固定 3 天和 7 天，然后取出比目鱼肌进行形态测量，并分别通过实时 PCR 和蛋白质印迹分析基因和蛋白质表达。固定后 7 天，肌肉萎缩很明显，正如预期的那样，亮氨酸喂养减轻了这种影响。 Atrogin-1/MAFbx 基因表达仅在固定 3 天后上调，并且这种效应通过补充亮氨酸而减弱。固定 7 天后，Atrogin-1/MAFbx 蛋白水平升高，亮氨酸补充无法降低这种水平。另一方面，肌肉生长抑制素基因表达在固定3天和7天时上调，补充亮氨酸后恢复到正常水平。肌生长抑制素蛋白水平仅在 3 天的时间点跟随基因表达。卵泡抑素基因表达在固定过程中上调，并在补充 3 天后被亮氨酸增强。关于蛋白质表达，卵泡抑素既不会因固定而改变，也不会在用亮氨酸处理的固定动物中改变。 总之，亮氨酸可防止废弃期间骨骼肌质量损失，其潜在的分子机制似乎涉及肌肉生长抑制素抑制和独立于卵泡抑素信号传导的 Atrogin-1 正常化。