Targeting Complement Component 3 in a Model of Synucleinopathy

项目总结 帕金森病(PD)是一种复杂的进行性神经退行性疾病，最终导致 含有α-突触核蛋白(a-syn)的蛋白质聚集体的沉积，称为路易小体，以及 黑质纹状体多巴胺神经元变性。有证据表明，神经炎症是一种致病因素 在帕金森病发病中的作用。帕金森病大脑的尸检和纵向PET成像研究显示 活化的小胶质细胞的数量增加，这些细胞出现在疾病过程的早期，并保持高水平 在疾病的整个过程中。激活的小胶质细胞可以将星形胶质细胞转化为毒性的A1-亚型 “星形胶质细胞”，这些反应性星形胶质细胞在帕金森病患者的大脑中被观察到。A1星形胶质细胞配位选择性 通过释放补体系统的成分而导致的神经退化。补语系统是一个分部 协调清除病原体和细胞碎片的先天免疫系统。然而， 补体系统，特别是补体成分3(C3)，也被中枢神经使用 标记易受攻击的突触和神经元进行吞噬清除的系统。在帕金森病的大脑中，有毒的A1- 星形胶质细胞显著增加C3的表达。综上所述，我们假设以下是 来自A1星形胶质细胞的初始免疫原性信号(病理性a-syn错误折叠)C3用于标记 小胶质细胞破坏的含包涵体神经元。支持这一观点的是，中脑多巴胺 帕金森病患者大脑中的神经元和路易小体被激活的C3标记。 几乎每一种帕金森病模型都有神经炎症的报道。然而，大多数PD模型都失败了 准确概括帕金森病病理的定义特征：内源性进行性聚集 A-SYN和随后黑质纹状体神经元的变性。相比之下，纹状体内注射重组α- SYN预成型纤维(PFF)能够准确地模拟PD病理的这些特征，并且 模仿人类疾病的神经炎性反应。我们已经广泛地描述了这种模式的特点 并发现将a-syn pff注射到大鼠纹状体可导致a-syn聚集体在 注射后2个月黑质致密部(SNC)，随后黑质显著变性 六个月。在a-syn聚集的高峰期，我们观察到小胶质细胞活化的高峰期以及 星形胶质细胞增多症。反应性星形胶质细胞的遗传表达和形态特征与 存在有毒的A1-星形胶质细胞。因此，我们假设使用来自A1反应性星形胶质细胞的C3 标记含有包涵体的黑质神经元以供破坏。支持这一想法，我们观察到 C3在这一时间点的表达，并将C3定位于反应性星形胶质细胞。重要的是， 毒性A1-星形胶质细胞的存在和C3表达的增加发生在显性黑质之前的几个月 退变，提示星形细胞C3可能在退变过程中起作用。因此，防止 C3的释放或激活可以防止α-syn聚集引起的退行性变。 在目前的探索性R21应用程序中，我们建议表征并直接测试 突触核病所致神经变性中的补体系统。最重要的是 这一应用的假设是，来自A1-星形胶质细胞的C3，在a-syn聚集之后，起作用 以协调黑质神经元的选择性变性。

PROJECT SUMMARY Parkinson's Disease (PD) is a complex and progressive neurodegenerative disorder that culminates in the deposition of alpha synuclein (a-syn) containing protein aggregates, named Lewy bodies, and the degeneration of nigrostriatal dopamine neurons. Evidence suggests that neuroinflammation plays a causative role in the pathogenesis of PD. Post-mortem- and longitudinal PET imaging studies of the PD brain reveal an increase in the number of activated microglia that occur early in the disease process and remain elevated throughout the course of the disease. Activated microglia can convert astrocytes to a subtype of toxic “A1- astrocyte” and these reactive astrocytes are observed in the PD brain. A1 astrocytes coordinate selective neurodegeneration by releasing components of the complement system. The complement system is a division of the innate immune system that coordinates the removal of pathogens and cell debris. However, the complement system, and specifically complement component 3 (C3), is also used by the central nervous system to tag vulnerable synapses and neurons for phagocytic clearance. Within the PD brain, toxic A1- astrocytes dramatically increase the expression of C3. Taken together, we hypothesize that following an initial immunogenic signal (pathological a-syn misfolding) C3 derived from A1 astrocytes is used to tag inclusion-containing neurons for destruction by microglia. Supporting this idea, both midbrain dopamine neurons and Lewy bodies label with activated C3 in the PD brain. Neuroinflammation has been reported with virtually every model of PD. However the majority of PD models fail to accurately recapitulate the defining features of PD pathology: The progressive aggregation of endogenous a-syn and subsequent degeneration of nigrostriatal neurons. In contrast, intrastriatal injection of recombinant a- syn pre-formed fibrils (PFFs) is able to accurately model these hallmarks of PD pathology, and a neuroinflammatory response that mimics the human disease. We have extensively characterized this model and found that injection of a-syn PFFs into the rat striatum results in peak a-syn aggregate formation within the substantia nigra pars compacta (SNc) at 2 months post-injection, followed by significant nigral degeneration by 6 months. During the peak of a-syn aggregation we observe peak microglial activation as well as robust astrogliosis. Genetic expression and morphological profiling of reactive astrocytes is consistent with the presence of toxic A1-astrocytes. As such we hypothesize that C3 derived from A1 reactive astrocytes is used to tag inclusion-containing nigral neurons for destruction. Supporting this idea, we observe a large increase in the expression of C3 during this time point, and have localized C3 to reactive astrocytes. Importantly, the presence of toxic A1-astrocytes and the increase in C3 expression occurs months prior to overt nigral degeneration, suggesting astrocytic C3 may play a role in the degenerative process. Thus, preventing release or activation of C3 may prevent the degeneration induced by a-syn aggregation. In the present exploratory R21 application we propose to both characterize and directly test the role of the complement system in the neurodegeneration induced following synucleinopathy. The overarching hypothesis of this application is that C3 derived from A1-astrocytes, following a-syn aggregation, acts to coordinate the selective degeneration of nigral neurons.