Gran Petra, Cameron-Smith David
Molecular Nutrition Unit, School of Exercise and Nutrition Sciences, Deakin University, Burwood, Victoria, Australia.
BMC Physiol. 2011 Jun 25;11:10. doi: 10.1186/1472-6793-11-10.
The branched-chain amino acid (BCAA) leucine has been identified to be a key regulator of skeletal muscle anabolism. Activation of anabolic signalling occurs via the mammalian target of rapamycin (mTOR) through an undefined mechanism. System A and L solute carriers transport essential amino acids across plasma membranes; however it remains unknown whether an exogenous supply of leucine regulates their gene expression. The aim of the present study was to investigate the effects of acute and chronic leucine stimulation of anabolic signalling and specific amino acid transporters, using cultured primary human skeletal muscle cells.
Human myotubes were treated with leucine, insulin or co-treated with leucine and insulin for 30 min, 3 h or 24 h. Activation of mTOR signalling kinases were examined, together with putative nutrient sensor human vacuolar protein sorting 34 (hVps34) and gene expression of selected amino acid transporters. Phosphorylation of mTOR and p70S6K was transiently increased following leucine exposure, independently to insulin. hVps34 protein expression was also significantly increased. However, genes encoding amino acid transporters were differentially regulated by insulin and not leucine.
mTOR signalling is transiently activated by leucine within human myotubes independently of insulin stimulation. While this occurred in the absence of changes in gene expression of amino acid transporters, protein expression of hVps34 increased.
支链氨基酸（BCAA）亮氨酸已被确定为骨骼肌合成代谢的关键调节因子。合成代谢信号通过哺乳动物雷帕霉素靶蛋白（mTOR）以一种未知机制激活。系统A和L溶质载体将必需氨基酸转运过质膜；然而，亮氨酸的外源性供应是否调节它们的基因表达仍不清楚。本研究的目的是使用培养的原代人骨骼肌细胞，研究急性和慢性亮氨酸刺激对合成代谢信号和特定氨基酸转运蛋白的影响。
将人肌管分别用亮氨酸、胰岛素处理或亮氨酸与胰岛素共同处理30分钟、3小时或24小时。检测mTOR信号激酶的激活情况，以及假定的营养传感器人类液泡蛋白分选34（hVps34）和所选氨基酸转运蛋白的基因表达。亮氨酸处理后，mTOR和p70S6K的磷酸化短暂增加，与胰岛素无关。hVps34蛋白表达也显著增加。然而，编码氨基酸转运蛋白的基因受胰岛素而非亮氨酸的差异调节。
在人肌管中，亮氨酸可独立于胰岛素刺激短暂激活mTOR信号。虽然此时氨基酸转运蛋白的基因表达没有变化，但hVps34的蛋白表达增加。
