Parkin and MGRN1: common roles in mitochondria and neurodegeneration?

描述(由申请人提供)：常见神经退行性疾病的分子机制尚不清楚，尽管研究已涉及线粒体功能障碍和泛素-蛋白酶体缺陷。冈恩实验室研究环型E3泛素连接酶Mahogunin Ring Finger-1(MGRN1)，它的缺失会导致1岁大的小鼠进行性、广泛性海绵状神经变性。在1个月龄时，Mgrn1缺失突变体的大脑中检测到线粒体功能障碍和氧化应激增加。另一种环型E3基因Parkin(PARK2)的突变导致了约50%的遗传性早发性帕金森病和10%-15%的散发性早发性帕金森病，并导致小鼠线粒体功能障碍。最近的研究表明，Parkin参与了受损的去极化线粒体的自噬清除。我们的初步研究表明，1)许多与MGRN1相互作用的蛋白也与parkin相关或在parkin缺失突变小鼠的大脑中表现出变化的表达；2)MGRN1与几种线粒体蛋白相互作用并与线粒体共存。我们假设MGRN1是线粒体伴侣系统的一个组成部分，MGRN1功能的丧失会导致线粒体功能障碍，从而触发parkin介导的有丝分裂。这一假说暗示了泛素化和线粒体功能之间的直接联系，并代表了一种新的方法来考虑它们与神经退行性变的关系。如果MGRN1对线粒体有直接作用，未来的研究可能会测试不同的线粒体靶向治疗对Mgrn1缺失突变的海绵状神经变性的发生和进展的影响，以及MGRN1功能的丧失是否是其他神经退行性疾病的易感因素。目的1：检测Mgrn1和Parkin之间是否存在遗传交互作用。我们将通过产生Mgrn1；parkin复合缺失突变小鼠并进行组织学和线粒体分析来测试MGRN1和parkin具有重叠功能的假设，以确定是否丢失1或2个功能性Mgrn1等位基因改变了parkin缺失突变小鼠的中枢神经系统表型，反之亦然。目的2：研究Parkin和MGRN1是否具有相关的线粒体功能。我们将通过检测干扰MGRN1对线粒体呼吸和形态的影响，并确定MGRN1功能的丧失是否触发Parkin介导的有丝分裂，来检验MGRN1是线粒体伴侣系统的一个组成部分的假设。我们还将研究MGRN1是否与特定线粒体蛋白相互作用、泛素化和/或调节特定线粒体蛋白的水平。 公共卫生相关性：神经退行性疾病对受影响的个人、他们的家庭、卫生保健系统和整个社会都有重大影响。它们有许多潜在的原因，但即使当一种特定的蛋白质被证明会导致神经退化，它到底是如何扰乱神经元功能和存活的还不是很清楚。这项提案中概述的工作将帮助我们更多地了解一种名为Mahogunin Ring Finger-1的蛋白质的功能，以及它在细胞中是否具有与Parkin相似的功能(S)，Parkin在一些遗传型帕金森病患者中受到干扰。我们希望我们的工作将帮助我们了解这些疾病是如何产生的，并最终了解我们如何预防或更好地治疗它们。

DESCRIPTION (provided by applicant): The molecular mechanisms that underlie common neurodegenerative diseases remain unclear, although studies have implicated mitochondrial dysfunction and ubiquitin-proteasome defects. The Gunn laboratory studies the RING-type E3 ubiquitin ligase Mahogunin Ring Finger-1 (MGRN1), loss of which causes progressive, widespread spongiform neurodegeneration in mice by 1 year of age. Mitochondrial dysfunction and elevated oxidative stress were detected in the brains of Mgrn1 null mutants by 1 month of age. Mutations in another RING-type E3, Parkin (PARK2), underlie ~50% of inherited and 10-15% of sporadic early-onset Parkinson's disease and cause mitochondrial dysfunction in mice. Recent studies implicate parkin in the autophagic clearance of damaged, depolarized mitochondria. Our preliminary studies indicate that 1) many MGRN1-interacting proteins also associate with parkin or show altered expression in the brains of parkin null mutant mice; 2) MGRN1 interacts with several mitochondrial proteins and colocalizes with mitochondria. We hypothesize that MGRN1 is a component of the mitochondrial chaperone system and that loss of MGRN1 function causes mitochondrial dysfunction that triggers parkin-mediated mitophagy. This hypothesis implies a direct connection between ubiquitination and mitochondrial function and represents a novel approach to considering their relationship to neurodegeneration. If MGRN1 has a direct role in mitochondria, future studies could test the effect of different mitochondrial-targeted therapies on the onset and progression of spongiform neurodegeneration in Mgrn1 null mutants and whether loss of MGRN1 function is a susceptibility factor for other neurodegenerative disorders. Aim 1: To test whether there is a genetic interaction between Mgrn1 and parkin. We will test the hypothesis that MGRN1 and parkin have overlapping functions by generating Mgrn1; parkin compound null mutant mice and performing histological and mitochondrial assays to determine whether loss of 1 or 2 functional Mgrn1 alleles alters the CNS phenotype of parkin null mutant mice, and vice versa. Aim 2: To examine whether parkin and MGRN1 have related mitochondrial functions. We will test the hypothesis that MGRN1 is a component of the mitochondrial chaperone system by examining the effect of disrupting MGRN1 on mitochondrial respiration and morphology and determining whether loss of MGRN1 function triggers parkin-mediated mitophagy. We will also examine whether MGRN1 interacts with, ubiquitinates and/or regulates the levels of specific mitochondrial proteins. PUBLIC HEALTH RELEVANCE: Neurodegenerative disorders have a significant impact on affected individuals, their families, the health care system, and society as a whole. They have many potential causes but even when a particular protein has been shown to cause neurodegeneration, exactly how it disrupts neuron function and survival is not well understood. The work outlined in this proposal will help us understand more about the function of a protein called Mahogunin Ring Finger-1 and whether it has similar function(s) in cells as parkin, which is disrupted in some people with inherited forms of Parkinson's disease. We hope that our work will help us understand how these diseases arise and, ultimately, how we can prevent or better treat them.