Development of novel nutritional methods to inhibit muscle atrophy caused by microgravity.

我们之前报道过，航天飞行和尾部悬吊增强了大鼠肌球蛋白重链（MHC）的降解，并激活了泛素依赖的蛋白水解途径。在连续研究中，通过DNA微阵列分析获得了航天或悬尾大鼠约26000条腓肠肌基因表达，我们发现这些大鼠中泛素依赖蛋白水解的基因表达上调。在本研究中，为了阐明基因表达改变是否伴随着氧化应激，我们测量了氧化应激标志物，如硫代巴比妥酸？尾悬大鼠腓肠肌反应性物质（TBARS）、谷胱甘肽二硫（GSSG）和谷胱甘肽（GSH）。尾悬液在增加蛋白质泛素化的同时，也增加了TBARS和GSSG的浓度，提示氧化应激可能在尾悬液引起的蛋白质泛素化中起重要作用。为了防止与氧化应激相关的泛素化，我们还给尾悬大鼠注射了抗氧化营养素，半胱氨酸和维生素E。与补充等量的丙氨酸相比，胃内补充140 mg/大鼠半胱氨酸2周或更长时间使肌肉中GSH与GSSG的比例正常化，并抑制蛋白质泛素化和MHC碎片化。补充半胱氨酸可显著抑制后肢肌肉质量的损失。15 mg/大鼠α-生育酚不仅没有抑制蛋白质泛素化和MHC碎片化，而且还会导致后肢肌肉量的减少。我们的研究结果表明，抗氧化营养素的作用取决于补充量，可能有助于防止肌肉蛋白因体重减轻而泛素化。

We have previously reported that spaceflight and tail suspension enhanced degradation of rat myosin heavy chain (MHC) in association with activation of a ubiquitin-dependent proteolytic pathway. In the serial study, about 26,000 gastrocnemius muscle gene expression in rats exposed to the spaceflight or tail-suspension was accessed by DNA microarray analysis, and we found that gene expression in the ubiquitin-dependent proteolysis in these rats was up-regulated. In the present study, to elucidate whether the altered gene expression is accompanied by oxidative stress, we measured markers for oxidative stress, such as thiobarbituric acid ?reactive substance (TBARS), glutathione disulfide (GSSG), and glutathione (GSH), in gastrocnemius muscle of tail-suspended rat. Tail-suspension reciprocally increased concentration of TBARS and GSSG in parallel with enhancement of protein ubiquitination, suggesting that oxidative stress may play an important role in protein ubiquitination caused by tail-suspension. To prevent ubiquitination associated with oxidative stress, we also administered an antioxidative nutrient, cysteine and vitamin E, to tail-suspension rats. Intragastric supplementation of 140 mg/rat of cysteine for 2 weeks or longer normalized the ratio of GSH to GSSG in the muscle and suppressed protein ubiquitination and MHC fragmentation, compared with supplementation of the equimolar amount of alanine. The cysteine supplementation significantly suppressed the loss of hindlimb muscle mass. Not only supplementation of 15 mg/rat of α-tocopherol did not suppressed protein ubiquitination and MHC fragmentation, but also loss of hindlimb muscle mass. Our results suggest that effect of antioxidative nutrients depend on supplement amount and may be beneficial for preventing ubiquitination of muscle proteins caused by unweighting.