細胞膜轉運蛋白在巴金森氏症致病機轉上扮演的角色探討 第一部分：老化及發炎對腦部微血管上有機陽離子轉運蛋白表現與神經毒素運送的影響 第二部分：Nramp1對α-synuclein降解及MPTP/MPP⁺引發神經毒性的影響

Roles of membrane transporters in the pathogenesis of Parkinson′s disease Part I: Effects of aging and inflammation on the expression of organic cation transporters and the mediated transport of neurotoxins in brain microvessels Part II: Nramp1 contributes to the degradation of α-synuclein and its implication to MPTP/MPP⁺-induced neurotoxicity

吳國禎(Kuo-Chen Wu)

指導教授 ： 林君榮

國立臺灣大學/醫學院/藥學研究所/博士(2017年)

https://doi.org/10.6342/NTU201703082

摘要

巴金森氏症（Parkinson′s disease）是一種與老化相關的神經退化性疾病，大腦黑質體的多巴胺神經元減少以及神經元內形成α-突觸核蛋白（α-synuclein）蛋白聚集體（Lewy bodies）為其主要病理特徵，目前廣泛認為環境或內生性神經毒素以及基因變異等多項危險因子可能是致病原因，然而詳細的病理機轉仍然不明。細胞膜轉運蛋白（membrane transporters）對於體內潛在神經毒性物質的分布與平衡扮演重要的角色，因此，本研究論文主要目的為探討細胞膜轉運蛋白與巴金森氏症病理機轉之間的關係。在第一部分的研究，我們發現老化及發炎以這兩個巴金森氏症重要的危險因子會調控有機陽離子轉運蛋白（organic cation transporters）包含Oct1、Oct2及Pmat於血腦屏障（blood-brain barrier）上的表現，進而影響有機陽離子神經毒性物質在腦內的濃度與其神經毒性。在第二部分的研究，我們發現人類大腦微膠細胞（microglia）內有表現自然抗性相關巨噬細胞蛋白-1（natural resistance-associated macrophage protein-1; Nramp1）蛋白，過去研究認為該蛋白能藉由調控溶酶體鐵質平衡來防禦外來病菌感染，而我們首次發現在高鐵質的病理狀態下，過度表現Nramp1蛋白能幫助微膠細胞降解細胞外α-synuclein oligomers；另外，我們發現人類多巴胺神經元內也有表現Nramp1蛋白，而在巴金森氏症病患的多巴胺神經元內該蛋白表現量低下，我們進一步的研究證實Nramp1蛋白表現可以正向調控細胞內α-synuclein的降解，並對於MPTP/MPP⁺誘發的巴金森氏症實驗模型有神經保護的作用。綜合以上結果，本研究論文以細胞膜轉運蛋白的角度探討神經毒性物質及鐵質平衡異常於巴金森氏症病理機轉之角色，並建立體內自然防禦機制與神經退化性疾病的相關性。

關鍵字

巴金森氏症 ； 神經毒素 ； α-突觸核蛋白 ； 有機陽離子轉運蛋白 ； 自然抗性相關巨噬細胞蛋白-1

並列摘要

Parkinson′s disease (PD) is an age-related neurodegenerative disease, characterized by a progressive loss of dopaminergic neurons and the presence of intracellular proteinaceous inclusions containing aggregated α-synuclein (known as Lewy bodies). Multiple etiological causes, including genetic factors, environmental insults, and endogenous neurotoxins, have been linked to the development of PD. However, the pathological mechanisms remain unclear. Membrane transporters play an important role for the distribution of their substrates including neurotoxic substances (either exogenous or endogenous origins). Therefore, the aim of this thesis is to gain insight into the involvement of membrane transporters in PD pathogenesis. In the first part, we show that normal aging and inflammation, two key risk factors for PD, can regulate the expression of organic cation transporters (including Oct1, Oct2, and Pmat) at the blood-brain barrier and subsequently affect brain distribution of toxic organic cations and their neurotoxicity. In the second part, we find that microglia express natural resistance-associated macrophage protein-1 (Nramp1) that is a lysosomal metal ion transporter responsible for natural resistance to infection with pathogens. We demonstrate that Nramp1 expression in microglia contributes to the degradation of extracellular α-synuclein oligomers under iron overload condition. Moreover, we show that Nramp1 is also expressed in dopaminergic neurons, of which the expression level is significantly reduced in PD patients. We further demonstrate that its expression has a protective role against MPTP/MPP⁺-induced up-regulation of α-synuclein and neurotoxicity. Taken together, the works described in this thesis support the pathological roles of neurotoxins and iron dyshomeostasis in PD by investigating membrane transporters and provide a connection between host defense mechanism and neurodegenerative diseases.

並列關鍵字

Parkinson′s disease ； neurotoxins ； α-synuclein ； organic cation transporters ； natural resistance-associated macrophage protein-1

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