STUDIES ON PROTEOLYTIC SYSTEM-RELATED GENES IN THE PORCINE MUSCLE ATROPHY

猪应激综合征（PSS）是由遗传和环境因素共同引起的。一般来说，PSS猪表现出苍白，柔软和渗出的肉，其中细胞蛋白水解系统被诱导和激活，导致加速蛋白水解。本研究旨在阐明应激激素糖皮质激素引起肌肉异常的细胞和分子机制。[EXP 1]在用分解代谢剂量的皮质醇（10或30 mg/kg/BW）处理的猪的萎缩肌肉中，研究了肌萎缩特异性泛素连接酶atrogin-1的mRNA表达。采用实时定量PCR方法检测atrogin-1和GAPDH的mRNA表达。出乎意料的是，atrogin-1 mRNA的表达下降，响应皮质醇给药的剂量依赖性方式。[EXP 2]观察地塞米松（Dex）、胰岛素样生长因子1（IGF-1）和睾酮对C2 C12肌管atrogin-1 mRNA表达的影响。地塞米松显著增加atrogin-1的表达（对照的7-8倍），另一方面，IGF-1和睾酮轻微降低增加的表达。通过释放3-甲基组氨酸作为肌原纤维降解的指标来评估的蛋白质分解速率在Dex的存在下显著增加，但在Dex和IGF-1两者的存在下没有改变。[EXP[3]应用透射电镜和免疫电镜观察Dex（1 mg/kgBW/day）和禁食48 h所致小鼠肌肉萎缩的细胞超微结构变化。肌原纤维结构是脆的，肌原纤维的M-丝中的结构蛋白结蛋白的量在萎缩的肌肉中减少。这些结果表明argoin-1在肌肉萎缩的发生和发展中起重要作用，IGF-1可用于治疗肌肉萎缩。

Porcine Stress Syndrome (PSS) is caused by a combined genetic and environmental factor. In generally PSS pig exhibits the pale, soft and exudative meat in which cellular proteolytic systems are induced and activated resulting in accelerated proteolysis. The purpose of this study was to clarify the cellular and molecular mechanism of the muscle abnormality caused by stress hormone, glucocorticoid. [EXP 1] mRNA expression of atrogin-1, a muscle atrophy specific ubiquitin ligase, was investigated in the atrophying muscles from pigs treated with catabolic dose of cortisol (10 or 30 mg/kg/BW). The mRNA expressions of atrogin-1 and GAPDH as an internal marker gene were determined by the real-time quantitative PCR method. Unexpectedly, atrogin-1 mRNA expression was decreased in response to cortisol administration in a dose dependent manner. [EXP 2] Effects of dexamethasone (Dex), insulin-like growth factor 1 (IGF-1), and testosterone on mRNA expression of atrogin-1 in C2C12 myotubes were examined. Dex markedly increased the atrogin-1 expression (7-8-fold of control), on the other hand, IGF-1 and testosterone slightly reduced the increased expression. The rate of protein breakdown evaluated by the release of 3-methlyhisitidine as an index of myofibrillar degradation was significantly increased in the presence of Dex, but not changed in the presence of both of Dex and IGF-1. [EXP 3] Changes in cellular ultrastructure of the mouse muscle atrophies induced by Dex administration (1mg/kgBW/day) or 48h-fasting were investigated by using transmission electron microscope (TEM) and immune TEM with gold-conjugate secondary antibody. The myofibrillar structure was brittle, and the amount of desmin, a structural protein in the M-filament of myofibril, was reduced in the atrophying muscles. These results suggest that argoin-1 plays an important role in the initiation and progression of the muscle atrophies, and IGF-1 is could be used for the treatment of muscle atrophies.