Study of regeneration of peripheral nervous system with adenoviral vectors

对于周围神经的再生，轴突的伸长及其髓鞘形成是必不可少的。雪旺细胞是周围神经系统的髓鞘胶质细胞，其发育受多种生长因子的调控。然而，这些配体刺激在雪旺细胞分化过程中的细胞内信号通路机制仍不清楚。在这里，我们证明，在培养的雪旺细胞中，神经调节蛋白和PDGF抑制髓鞘相关蛋白标志物的表达，而IGF-I则促进髓鞘相关蛋白标志物的表达。虽然这些配体激活了常见的下游信号通路，即细胞外信号调节激酶（Erk）和磷脂酰肌醇-3-激酶(PI3K)/Akt通路，但不同配体的激活谱各不相同。为了阐明这些途径的功能和雪旺细胞分化的机制，我们使用腺病毒载体选择性地激活或灭活这些途径。在大鼠嗜铬细胞瘤细胞系PC12细胞中，CA-MEK病毒感染诱导ERKs持续激活并刺激神经营养因子缺失的神经突生长。我们发现Erk通路的选择性激活抑制了雪旺细胞的分化，而PI3K通路的选择性激活则促进了雪旺细胞的分化。在体外雪旺细胞- drg神经元共培养和体内同种异体神经移植实验中，基因转移选择性激活雪旺细胞PI3K通路进一步证实了髓鞘形成增加。我们得出结论，PI3K/Akt介导的信号对于髓鞘形成的起始至关重要，生长因子的作用在很大程度上取决于Erk和PI3K/Akt激活之间的平衡。我们的研究结果还提出了在未来的细胞治疗中通过调节细胞内信号来增强雪旺细胞功能的可能性。

For regeneration of peripheral nerves, the elongation of axons and their myelination are essential. Schwann cells are the myelinating glia of the peripheral nervous system and their development is regulated by various growth factors. However, the mechanisms of intracellular signaling pathways following these ligands stimuli in Schwann cells differentiation remain elusive. Here, we demonstrated that, in cultured Schwann cells, neuregulin and PDGF suppressed the expression of myelin associated protein markers, while IGF-I promoted it. Although these ligands activated common downstream signaling pathways, i.e., extracellular signal-regulated kinase (Erk) and phosphatidylinositol-3-kinase (PI3K)/Akt pathways, the profiles of activation varied among ligands. To elucidate the function of these pathways and the mechanisms underlying Schwann cell differentiation, we used adenoviral vectors to selectively activate or inactivate these pathways. In rat pheocromocytoma cell line PC12 cells, CA-MEK virus infection induced sustained activation of ERKs and stimulated neurite outgrowth in the absence of neurotrophic factors. We found that the selective activation of Erk pathways suppressed Schwann cell differentiation, while that of PI3K pathways promoted it. Selective activation of PI3K pathways in Schwann cells by gene transfer further demonstrated increased myelination in in vitro Schwann cell-DRG neuron cocultures and in vivo allogenic nerve graft experiment. We conclude that signals mediated by PI3K/Akt are crucial for initiation of myelination and the effects of growth factors are largely dependent on the balance between Erk and PI3K/Akt activation. Our results also propose the possibilities to augment Schwann cell functions by modulating intracellular signals in the light of future cell therapies.