A muscle secreting protein attractin regulates expression of UCP-2 in adipocytes.

长时间的太空飞行和卧床休息会导致明显的食欲减退。许多研究人员认为，这种食欲下降可能是由于心理压力。在目前的研究中，我们推断骨骼肌萎缩是通过一种新的肌肉分泌酶，吸引力来卸载受调节的能量消耗。我们的DNA微阵列分析显示，骨骼肌萎缩的卸载显著表达分泌型吸引。此外，饥饿刺激骨骼肌中吸引因子的表达，表明能量摄入可能调节肌肉中吸引因子的表达。我们将3T3-L1脂肪细胞与过表达吸引素的Cos7细胞共培养，结果表明Cos7细胞分泌的吸引力刺激了脂肪细胞中解偶联蛋白2 （uncoupled protein-2, UCP-2）的表达。这一发现提示，吸引可能刺激脂肪细胞的热转化，从而预防肥胖。到目前为止，还没有关于吸引表达的调节因素的报道。我们发现只有胰岛素降低了骨骼肌中吸引蛋白的表达，这表明血糖水平可能参与了吸引蛋白的表达。基于这些发现，我们提出骨骼肌可能分泌几种细胞因子（所谓的肌因子），这些肌因子可能调节脂肪组织的生长和功能。

Prolonged spaceflight and bed-resting cause remark appetite loss. A lot of investigators suggest that this appetite loss is probably due to psychological stress. In the present study, we reasoned that skeletal muscle atrophied by unloading regulated energy consumption via a novel muscle-secreting enzyme, attractin. Our DNA microarray analysis revealed that skeletal muscle atrophied by unloading remarkably expressed the secreted-type attractin. In addition, starvation stimulated expression of attractin in skeletal muscle, indicating that energy intake may regulate attractin expression in the muscle. Our co-culturing system with 3T3-L1 adipocytes and attractin-overexpressing Cos7 cells showed that the secreted attractin from Cos7 cells stimulated expression of uncoupled protein-2 (UCP-2) in the adipocytes. This finding suggests that attractin may stimulate heat conversion in adipocytes and prevent the obesity. Up to now, there is no report about the factors regulating attractin expression. We found that only insulin decreased expression of attractin in skeletal muscle, indicating that blood glucose levels may be involved in attractin expression. Based on these findings, we propose that skeletal muscle may secrete several cytokines (so called myokines), and these myokines may regulate the growth and function of adipose tissues.