FGF6-FGFR4-CaN通路调控骨骼肌肌纤维表型相互转化的作用及其机制研究

Skeletal muscle would gradually atrophy and the fast muscle fiber would converse into slow muscle fiber after denervation, while this conversion of muscle fiber phenotype could not be reversed by reinnervation, which obviously decreases the contractile power and speed of regenerated muscle eventually. Enhance the conversion of muscle fiber phenotype from slow type back to fast type could increase the functional recovery of regenerated skeletal muscle after reinnervation, but the mechanism is still unkonwn so far. Both FGF6 (Fibroblast growth factor 6) and Calcineurin activity were proved to have tight relationships with muscle fiber phenotype. We have previously successfully established denervated and reinnervated rat model and have built triple immunoenzyme staining for muscle fiber phenotyping; have successfully cultured C2C12 myoblast cells and found the optimal condition at which the FGF6 could promote C2C12 cells differentiation into mature muscle cells and multinucleated myotubes; have found that exogenous injection of FGF6 into soleus of rat could increase the proportionality of fast muscle fiber. We would explore that the function of FGF6 in the mutual conversion of muscle fiber phenotypes is regulated by calcineurin signial pathway, by usage of our established rat model and C2C12 cells, through injecting FGF6 factor or specifically knocking out FGF6 and calcineurin genes from skeletal muscle. This study has the possibility of clarifying the mechanism of mutual conversion of skelectal muscle fiber phenotype after denervation and reinnervation, and also offerring clues of developing new drugs for neuromuscular diseases.

周围神经损伤后其支配的骨骼肌逐渐萎缩，快肌纤维向慢肌纤维转化，即使萎缩的骨骼肌获得神经再支配后，也很难逆转上述转化过程，最终再生骨骼肌的收缩强度和速度明显受限。神经修复后，促进慢肌纤维回转为快肌纤维可增强再生骨骼肌功能恢复，但其机制不明。研究表明FGF6 （Fibroblast growth factor 6）和钙调神经磷酸酶（Calcineurin,CaN）活性均与肌纤维表型密切相关。我们已成功建立神经损伤与修复的大鼠模型及酶标三染免疫组化方法；发现FGF6促进C2C12细胞分化成肌细胞的条件，向大鼠比目鱼肌内注射FGF6后快肌纤维明显增多。我们将在已建立的大鼠模型及C2C12细胞上通过外源性给予FGF6或特异敲低骨骼肌的FGF6及CaN 基因表达，探讨FGF6在肌纤维表型相互转化中的作用是通过CaN信号通路调控的。该研究有望解释骨骼肌纤维表型相互转化的机理，为新药开发提供一定理论依据。

背景：严重的周围神经损伤导致骨骼肌萎缩和肢体功能受损，现有治疗方法未能充分改善。成纤维细胞生长因子6（FGF6）参与组织再生，在去神经大鼠肌肉中失调。然而，FGF6如何影响周围神经损伤后的骨骼肌修复尚未完全阐明。.方法：本研究采用成肌细胞和周围神经损伤模型，研究FGF6在去神经肌肉再生中的作用。.结果：FGF6通过FGFR1介导的cyclinD1上调，以剂量依赖的方式促进C2C12和原代成肌细胞的活力和迁移。低浓度的FGFG6通过FGFR4介导的ERK1 / 2激活促进成肌细胞分化，ERK1 / 2激活了MyHC，MyoD和myogenin的表达上调。在去神经大鼠肌肉中注射FGF6增强了MyHC-IIb肌肉纤维表型并防止了肌肉萎缩。.结论：FGF6促进骨骼肌萎缩，增强慢肌纤维向快速肌纤维的转化，促进再生后骨骼肌再生功能恢复。