The Nogo-A protein, originally discovered as a potent myelin-associated inhibitor of neurite outgrowth, is also expressed by certain neurons, especially during development and after injury, but its role in neuronal function is not completely known. In this report, we overexpressed Nogo-A in PC12 cells to use as a model to identify potential neuronal signaling pathways affected by endogenously expressed Nogo-A. Unexpectedly, our results show that viability of Nogo-A-overexpressing cells was reduced progressively due to apoptotic cell death following NGF treatment, but only after 24 h. Inhibitors of neutral sphingomyelinase prevented this loss of viability, suggesting that NGF induced the activation of a ceramide-dependent cell death pathway. Nogo-A over-expression also changed NGF-induced phosphorylation of TrkA at tyrosines 490 and 674/675 from sustained to transient, and prevented the regulated intramembrane proteolysis of p75^NTR, indicating that Nogo-A was altering the function of the two neurotrophin receptors. Co-immunoprecipitation studies revealed that there was a physical association between TrkA and Nogo-A which appeared to be dependent on interactions in the Nogo-A-specific region of the protein. Taken together, our results indicate that Nogo-A influences NGF-mediated mechanisms involving the activation of TrkA and its interaction with p75^NTR.

Nogo-A蛋白最初是作为有效的髓鞘相关的神经突增生抑制剂而发现的，它也由某些神经元表达，特别是在发育过程中和损伤后，但其在神经元功能中的作用尚不完全清楚。在此报告中，我们在PC12细胞中过表达Nogo-A，用作鉴定受内源表达Nogo-A影响的潜在神经元信号通路的模型。出乎意料的是，我们的结果表明，NGF处理后，凋亡细胞死亡导致Nogo-A过表达细胞的活力逐渐降低，但仅在24小时后。中性鞘磷脂酶的抑制剂阻止了这种活力的丧失，表明NGF诱导了神经酰胺依赖性细胞死亡途径的激活。^NTR，表明Nogo-A正在改变两种神经营养蛋白受体的功能。免疫共沉淀研究表明，TrkA和Nogo-A之间存在物理联系，这似乎取决于蛋白质Nogo-A特异性区域中的相互作用。两者合计，我们的结果表明Nogo-A影响NGF介导的机制，涉及TrkA的激活及其与p75 ^NTR的相互作用。