The role of Parkin in selective dopamine neuronal degeneration

描述（由申请人提供）：黑质纹状体（NS）多巴胺（DA）神经元的进行性变性是帕金森病（PD）运动症状的基础，缺乏缓慢进展的治疗方法。异常DA代谢被认为是NSDA神经元选择性变性的机制之一。然而，PD对所有DA神经元的影响程度不同。当中脑NSDA神经元严重丢失时，下丘脑基底结节（TI） DA神经元保持完整。当这些DA神经元群体暴露于线粒体复合体I抑制剂时，在体外和体内可以看到类似的易感性模式。尽管NSDA和TIDA神经元对复合物I抑制具有相似的初始反应，但只有TIDA神经元能够通过依赖于新蛋白合成的机制恢复。我们的初步数据还表明，parkin参与了这种差异易感性，因为在急性毒性损伤后，它在TIDA中显著上调，而在NSDA神经元中则没有上调。Parkin是一种支持正常线粒体功能的多功能蛋白，具有E3连接酶，可标记错误折叠的蛋白以进行蛋白体降解，并似乎可保护DA神经元免受各种毒性损伤。Parkin还具有重要的蛋白体独立功能，可以促进DA神经元的存活。该项目的总体目标是阐明帕金森介导的NSDA神经元对外源性神经毒素暴露敏感和TIDA神经元抵抗的分子机制。我们假设parkin主要通过不依赖于蛋白体的机制来保护TIDA神经元，并可以拯救由PD相关病理应激、线粒体复合体I抑制引起的NSDA神经元损伤。为了解决中心假设，raav介导的，空间限制的帕金表达操作将在野生型小鼠和具有帕金零背景的小鼠中进行。外源性调节parkin表达对TIDA和NSDA神经元对急性和慢性神经毒性应激反应的影响将被评估，以确认parkin在允许DA神经元在初始损伤后恢复中的核心作用。分子和药理学方法将用于阐明帕金神经保护作用的初始下游介质。尽管观察到在临床上可观察到的PD症状开始时，很大一部分DA神经元已经丢失，但似乎有一些神经元处于危险和功能失调中，但如果提供必要的恢复机制，它们可以恢复。由于TIDA神经元在PD相关病理应激源诱导的损伤中具有独特的恢复能力，因此它们为解剖帕金森介导的DA神经元恢复机制提供了强大的平台，并可能为神经保护治疗的发展提供新的靶点。

DESCRIPTION (provided by applicant): Progressive degeneration of nigrostriatal (NS) dopamine (DA) neurons underlies the motor symptoms of Parkinson's disease (PD) and therapies that slow progression are lacking. Abnormal DA metabolism has been proposed as a mechanism for the selective degeneration of NSDA neurons. All DA neurons, however, are not affected to the same extent in PD. While there is severe loss of midbrain NSDA neurons, the hypothalamic tuberoinfundibular (TI) DA neurons remain intact. A similar pattern of susceptibility can be seen in these DA neuronal populations when they are exposed to mitochondrial complex I inhibitors in vitro and in vivo. Although NSDA and TIDA neurons have a similar initial response to complex I inhibition, only TIDA neurons are able to recover using a mechanism that is dependent on new protein synthesis. Our preliminary data also implicate that parkin is involved in this differential susceptibility since it is markedly upregulated in TIDA, but not NSDA neurons following an acute toxic injury. Parkin is a multifunctional protein that supports normal mitochondrial function, has an E3 ligase that tags misfolded proteins for proteosomal degradation and appears to protect DA neurons from a variety of toxic insults. Parkin also has important proteosome independent functions that could promote DA neuronal survival. The overall goal of this project is to elucidate the parkin-mediated molecular mechanisms that render NSDA neurons sensitive and TIDA neurons resistant to exogenous neurotoxin exposure. We hypothesize that parkin, acting primarily via proteosome-independent mechanisms, protects TIDA neurons and can rescue NSDA neurons from injury induced by a PD relevant pathological stress, mitochondrial complex I inhibition. To address the central hypothesis, rAAV-mediated, spatially restricted manipulation of parkin expression will be performed in wild-type mice and on mice with a parkin null background. The impact of exogenously modulating parkin expression on the TIDA and NSDA neuronal responses to both acute and chronic neurotoxic stress will be assessed to confirm the central role of parkin in allowing DA neurons to recover following an initial insult. Molecular and pharmacological methods will be used to elucidate the initial downstream mediators of the neuroprotective effects of parkin. Despite the observation that a significant portion of DA neurons have been lost at the onset of clinically observable symptoms of PD, it is plausible that there are neurons that are at risk and dysfunctional, but that could recover if provided the necessary machinery for recovery. Since TIDA neurons are unique amongst DA neurons in their ability to recover from an injury induced by a PD relevant pathological stressor, they provide a powerful platform to dissect the parkin-mediated mechanisms of DA neuronal recovery and could yield novel targets for neuroprotective therapy development. PUBLIC HEALTH RELEVANCE: Parkin protein appears to facilitate the recovery of neurons following exposure to pathological stressors seen in Parkinson's disease. The protective mechanisms of parkin will be determined as a strategy to develop new therapies for Parkinson's disease.