Functional analyses of glial cell line-derived neurotrophic factor family

为了探讨胶质细胞源性神经营养因子(GDNF)在人体肌肉中的生理作用，我们采用RNA印迹和免疫组织化学方法对GDNF在成人肌肉中的表达进行了分析。GDNF在人骨骼肌中的表达高于在小鼠骨骼肌中的表达。GDNF在骨骼肌质膜附近有密集的免疫反应，尤其集中在神经肌肉连接处。周围神经束的轴突和周围的雪旺细胞也被GDNF抗体染色。逆转录聚合酶链式反应(RT-PCR)分析表明，GDNF mRNA在人肌肉中扩增，但在人脊髓前角细胞中不扩增。这些结果表明，GDNF在骨骼肌中产生，被神经末梢摄取，并通过轴突运输，可能作为靶源性神经营养因子促进运动神经元存活。然后，我们检测了神经肌肉疾病肌肉中GDNF的表达。免疫组织化学分析显示，GDNF在多发性肌炎(PM)和Duchenne型肌营养不良症(DMD)再生纤维中表达上调。RT-PCR分析表明，PM和DM0肌肉上调了全长GDNF的表达，而正常肌肉表现出大部分截短的GDNF。这一结果表明GDNF在人骨骼肌再生过程中受到调控。

We performed the expression analysis of glial cell line-derived neurotrophic factor (GDNF) in adult human muscle by RNA blot and immunohistochemical analysis to address the physiological role of GDNF in humans. GDNF mRNA was highly expressed in the human skeletal muscle compared to that in the mouse skeletal muscle. Condensed immunoreactivity of GDNF was observed in the vicinity of plasma membranes of skeletal muscle and especially concentrated at neuromuscular junctions. The axons and surrounding Schwann cells of peripheral nerve bundles were also stained with the GDNF antibody. Reverse transcriptase polymerase chain reaction (RT-PCR) analyses revealed hat GDNF mRNA was amplified in the human muscle, but not in the anterior horn cells of the human spinal cord. These results suggest that GDNF is produced in the skeletal muscle, taken up by nerve terminals, and transported through the axons and might promote motor neuron survival as a target-derived neurotrophic factor.We, then, examined expression of GDNF in muscles from neuromuscular diseases. Immunohistochemical analyses revealed that GDNF was up-regulated in regenerating fibers of polymyositis (PM) and Duchenne type muscular dystrophy (DMD). RT-PCR analyses showed that PM and DM0 muscles up-regulated the full length GDNF, meanwhile normal muscle exhibits mostly truncated GDNF.These results indicate that the GDNF expression is regulated in the regeneration of human skeletal muscle.