CRMP2, mitochondria, and Huntington’s disease

线粒体动力学，表现为线粒体改变形态和运动的能力，起着至关重要的作用 神经元对波动的能量需求的反应。线粒体动力学的损害导致 不同的疾病，如阿尔茨海默氏症、帕金森氏症和亨廷顿病(HD)。在高清中， 突变的Huntingtin(MHTT)和Dynamin Related Protein 1(Drp1)导致Drp1活性增加，导致 线粒体分裂增强，伴随着线粒体流量的减少。尽管付出了巨大的努力，但 导致mHTT引起线粒体形态和运动性改变的分子机制尚未见报道 完全理解。在初步实验中，我们发现CRMP2，一种与轴突有关的蛋白质 引导和调节轴突生长，调节线粒体动力学。一种机械上的联系 CRMP2及其对线粒体动力学的调控从未被研究过。CRMP2与神经元结合 线粒体和其去磷酸化形式的mHTT。CRMP2与Drp1、Mitofusin 2和 Miro 2，分别参与线粒体分裂、融合和运动的调节。 用siRNA下调CRMP2会导致分裂增加和线粒体运输减少，这意味着 CRMP2在线粒体动力学调控中的作用蛋白抑制后CRMP2过度磷酸化 磷酸酶1和2 A与增加的分裂和减少的线粒体交通相关。相反， 减少CRMP2的磷酸化可以防止这些改变。最后，我们发现CRMP2基因下调 YAC128 HD模型小鼠纹状体组织和死后纹状体组织中的过度磷酸化 HD患者的比例。总体而言，文献和我们的初步数据强烈表明CRMP2参与了 线粒体形态和运动性的调节和CRMP2的过度磷酸化参与了 HD的发病机制导致过度分裂、线粒体运输减少和神经元丢失。 去磷酸化的CRMP2与mHTT和参与线粒体动力学的蛋白质结合，并减少它们的 活性，而CRMP2下调和过度磷酸化则破坏这些蛋白质-蛋白质 相互作用，释放CRMP2的结合伙伴，增加他们的活性。在目标1中，我们将确定 CRMP2在线粒体中的定位，建立蛋白质相互作用伙伴，并评估 CRMP2调节神经元中线粒体的动力学。在目标2中，CRMP2参与的调节机制 线粒体动力学的结果将会被确定。在目标3中，我们将建立CRMP2介导的机制 导致表达mHTT的人神经元线粒体动力学缺陷和细胞死亡。最后，在 目的4，我们将评估CRMP2去磷酸化在多大程度上改变蛋白质-蛋白质相互作用，保护 并纠正HD动物模型中的行为缺陷。拟议的研究将在很大程度上 提高对HD病理生理学的认识，为发现HD新的发病机制奠定坚实基础 HD的发病机制，开辟了HD研究的新途径。

Mitochondrial dynamics, manifest as ability of mitochondria to change morphology and motility, play a vital role in neuronal response to fluctuating energy demands. Impairment of mitochondrial dynamics contributes to different disorders such as Alzheimer’s, Parkinson’s, and Huntington’s diseases (HD). In HD, interaction of mutant huntingtin (mHtt) with dynamin related protein 1 (Drp1) results in an increased Drp1 activity, leading to augmented mitochondrial fission, accompanied by reduced mitochondrial traffic. Despite significant effort, the molecular mechanisms, leading to mHtt-induced changes in mitochondrial morphology and motility are not completely understood. In preliminary experiments, we found that CRMP2, a protein implicated in axon guidance and regulation of neurite outgrowth, regulates mitochondrial dynamics. A mechanistic link between CRMP2 and regulation of mitochondrial dynamics has never been investigated. CRMP2 binds to neuronal mitochondria and in its dephosphorylated form to mHtt. CRMP2 physically interacts with Drp1, Mitofusin 2, and Miro 2, proteins involved in regulation of mitochondrial fission, fusion, and motility, respectively. Downregulation of CRMP2 with siRNA leads to increased fission and reduced mitochondrial traffic, implicating CRMP2 in regulation of mitochondrial dynamics. CRMP2 hyperphosphorylation after inhibition of protein phosphatases 1 and 2A correlates with augmented fission and reduced mitochondrial traffic. Conversely, decreasing CRMP2 phosphorylation can prevent these alterations. Finally, we found CRMP2 downregulation and hyperphosphorylation in striatal tissues from YAC128 HD mouse model and in postmortem striatal tissues of HD patients. Overall, the literature and our preliminary data strongly suggest that CRMP2 is involved in regulation of mitochondrial morphology and motility and CRMP2 hyperphosphorylation contributes to HD pathogenesis leading to excessive fission, reduced mitochondrial traffic, and neuronal loss. Dephosphorylated CRMP2 binds to mHtt and to proteins involved in mitochondrial dynamics and reduces their activities, whereas CRMP2 downregulation and hyperphosphorylation disrupts these protein-protein interactions, liberates binding partners of CRMP2, and increases their activities. In Aim 1, we will determine CRMP2 localization in mitochondria, establish protein interaction partners, and assess the extent to which CRMP2 regulates mitochondrial dynamics in neurons. In Aim 2, the mechanisms of CRMP2-medited regulation of mitochondrial dynamics will be determined. In Aim 3, we will establish CRMP2-mediated mechanisms contributing to defects of mitochondrial dynamics and cell death in human neurons expressing mHtt. Finally, in Aim 4, we will assess to what extent CRMP2 dephosphorylation alters protein-protein interactions, protects neurons, and corrects behavioral deficits in animal models of HD. The proposed study will considerably improve our understanding of HD pathophysiology, lay a solid foundation for identifying new mechanisms of HD pathogenesis, and open novel avenues in HD research.