Department of Neuroscience and Neurology, Cellular Neuroscience, Neurodegeneration & Repair Program, Yale School of Medicine, New Haven, Connecticut, USA; Department of Cell Biology, Kyoto Pharmaceutical University, Kyoto, Japan.
Department of Neuroscience and Neurology, Cellular Neuroscience, Neurodegeneration & Repair Program, Yale School of Medicine, New Haven, Connecticut, USA.
J Biol Chem. 2023 Oct;299(10):105232. doi: 10.1016/j.jbc.2023.105232. Epub 2023 Sep 9.
After adult mammalian central nervous system injury, axon regeneration is extremely limited or absent, resulting in persistent neurological deficits. Axon regeneration failure is due in part to the presence of inhibitory proteins, including NogoA (Rtn4A), from which two inhibitory domains have been defined. When these inhibitory domains are deleted, but an amino-terminal domain is still expressed in a gene trap line, mice show axon regeneration and enhanced recovery from injury. In contrast, when there is no amino-terminal Nogo-A fragment in the setting of inhibitory domain deletion, then axon regeneration and recovery are indistinguishable from WT. These data indicated that an amino-terminal Nogo-A fragment derived from the gene trap might promote axon regeneration, but this had not been tested directly and production of this fragment without gene targeting was unclear. Here, we describe posttranslation production of an amino-terminal fragment of Nogo-A from the intact gene product. This fragment is created by proteolysis near amino acid G214-N215 and levels are enhanced by axotomy. Furthermore, this fragment promotes axon regeneration in vitro and acts cell autonomously in neurons, in contrast to the inhibitory extracellular action of other Nogo-A domains.Proteins interacting with the amino-terminal Nogo-A fragment by immunoprecipitation include HSPA8 (HSC70, HSP7C). Suppression of HSPA8 expression by shRNA decreases axon regeneration from cerebral cortical neurons and overexpression increases axon regeneration. Moreover, the amino-terminal Nogo-A fragment increases HSPA8 chaperone activity. These data provide an explanation for varied results in different gene-targeted Nogo-A mice, as well as revealing an axon regeneration promoting domain of Nogo-A.
成年哺乳动物中枢神经系统损伤后，轴突再生极为有限或不存在，导致持续的神经功能缺损。轴突再生失败部分归因于抑制蛋白的存在，包括 NogoA（Rtn4A），其中已经定义了两个抑制结构域。当这些抑制结构域被删除，但一个氨基末端结构域仍在基因陷阱线中表达时，小鼠表现出轴突再生和损伤后恢复增强。相比之下，当抑制结构域缺失时没有氨基末端 Nogo-A 片段，则轴突再生和恢复与 WT 没有区别。这些数据表明，基因陷阱中氨基末端 Nogo-A 片段可能促进轴突再生，但这尚未得到直接测试，并且在没有基因靶向的情况下产生该片段尚不清楚。在这里，我们描述了完整基因产物中 Nogo-A 的氨基末端片段的翻译后产生。该片段是由氨基酸 G214-N215 附近的蛋白水解产生的，并且轴突切断后水平增强。此外，该片段在体外促进轴突再生，并在神经元中自主发挥作用，与其他 Nogo-A 结构域的抑制细胞外作用相反。通过免疫沉淀与氨基末端 Nogo-A 片段相互作用的蛋白质包括 HSPA8（HSC70、HSP7C）。通过 shRNA 抑制 HSPA8 表达可减少皮质神经元的轴突再生，而过表达则增加轴突再生。此外，氨基末端 Nogo-A 片段增加了 HSPA8 伴侣活性。这些数据为不同基因靶向 Nogo-A 小鼠中的不同结果提供了解释，同时也揭示了 Nogo-A 的一个促进轴突再生的结构域。
