The Beneficial Effects of PGC-1 in Drosophila Models of Parkinson’sDisease

• Other Authors: Wu, Ka Chun (author.)
• Format: Others
• Language: English; Chinese
• Published: 2017
• Online Access: http://repository.lib.cuhk.edu.hk/en/item/cuhk-1292268

帕金森氏病（PD）是第二最常見的神經變性疾病。症狀包括靜止性震顫，強直，體位不穩和運動遲緩，相信是因多巴胺（DA）神經元在黑質的死亡造成的。最近的研究已經表明PD 很可能是多因素引起的。 α-突觸核蛋白聚集和線粒體功能障礙已被發現是PD 的中央標誌病變。目前，我們還缺乏可以根治PD 的治療方法。大量的研究一直致力於搜索有效根治或延遲PD 的治療策略。 === 最近大量的研究已發現轉錄調控因子PGC-1α 在線粒體合成，呼吸作用和葡萄糖穩態調節中發揮中心作用。增加PGC-1α 基因活性通常與健康相關，相反下調與各種神經變性疾病，如亨廷頓舞蹈病和PD 相關。最近的一項研究表明，PGC-1α 除了維持線粒體功能，甚至可以通過上調自噬清除有毒的蛋白聚集。因此，我們認為PGC-1α表達上調能抑制PD 中α-突觸核蛋白聚集和線粒體的缺陷。為了證明我們的假設，我們在兩個成熟的轉基因PD 果蠅中(A53T α-突觸核蛋白過表達和PINK1 缺乏果蠅模型) ，並研究果蠅PGC-1 過表達對疾病表型的影響。 === 在此研究的第一部分，我們在A53T α-突觸核蛋白過表達果蠅模型過表達PGC-1來研究PGC-1 如何調節α-突觸核蛋白毒性和潛在的機制。我們的結果顯示，過表達PGC-1 沒有影響A53T α-突觸核蛋白過表達果蠅存活率但在30 天顯著改善運動障礙。免疫組化結果顯示，過表達PGC-1 阻止了PPL1 和PPM3 DA 神經元數目的減少。在PGC-1 保護機制方面，我們首先研究過表達PGC-1 是否可以改變α-突觸核蛋白水平和溶解度。我們的結果顯示過表達PGC-1 對可溶α-突觸核蛋白和mRNA 水平沒有顯著影響，卻顯著增加不可溶的α-突觸核蛋白的水平。這些結果顯示，PGC-1 過表達可能通過改變α-突觸核蛋白的溶解度以緩解α-突觸核蛋白引起的疾病表型。 === 在此研究的第二部分，我們在PINK1 基因敲除果蠅模型過表達PGC-1 來研究PGC-1 過表達對PINK1 缺乏誘導的疾病表型的影響與保護機制。我們的數據顯示，PGC-1 過表達在PINK1 基因敲除果蠅沒有DA 神經元損失的時期已改善了運動障礙。進一步研究顯示，PGC-1 過表達在不廣泛影響大腦的線粒體形態和數量下維持了線粒體膜電位，ATP 水平和線粒體複合物I 活性。最後，PGC-1 過表達緩解了在30 天的運動障礙和DA 神經元丟失。但是，PGC-1 過表達導致的複合物I 活性恢復並不伴隨下垂翼姿勢的改善。這些結果顯示，在DA 神經元或腦中過表達PGC-1 或能通過線粒體功能恢復緩解PINK1 引起的疾病表型。 === 最後，我們的結果表明，PGC-1 過表達對PD 有益可能是通過改變α-突觸核蛋白的溶解性和維持線粒體功能。內源性的PGC-1α 現時可通過許多FDA 批准的藥物上調，上調PGC-1α 的治療策略可立刻在帕金森氏症患者測試治療效果。 === Parkinson’s disease (PD) is the second most common neurodegenerative disease manifested as resting tremor, rigidity, postural instability and brady kinesia, which are causedby the loss of dopaminergic (DA) neurons in the substantia nigra (SN). Recent research has shown that PD is likely to be multifactorial. α-synuclein accumulation and mitochondrial dysfunction have been found to be the central hallmarks of PD. Currently, we still lack effective treatment that can cure PD. In face of this, lots of research has been devoted to the search of disease-modifying therapeutic strategies. === Peroxisome proliferator-activating receptor γ coactivator 1α (PGC-1α) is a key transcriptional coactivator well-studied in muscle, and has been found to play a central role in the regulation of mitochondrial biogenesis, respiration and glucose homeostasis. Increased PGC-1α gene activity is generally associated with health benefits but found downregulated in a number of pathogenic conditions, including various neurodegenerative disorders such as Huntington’s disease and PD. A recent study has demonstrated that PGC-1α, besides maintaining mitochondrial functioning, can enhance clearance of toxic protein aggregates by upregulating autophagy. We hence propose that PGC-1α overexpression can suppress α-synuclein aggregation and rescue mitochondrial defects in PD. To prove our hypothesis, we overexpressed the PGC-1α fly homolog, PGC-1, in two well-established transgenic fly models of PD, with either A53T α-synuclein overexpression or PINK1 deficiency for modeling PDcausing synucleinopathies and mitochondrial dysfunction respectively, and investigate how disease phenotypes could be modified. === In first part of the study, we overexpressed PGC-1 in the well-established A53T α-synuclein fly model to examine how PGC-1 could modulate α-synuclein toxicity and the underlying mechanisms. Our data indicated that PGC-1 overexpression did not affect the reduced survival rate of A53T α-synuclein flies but significantly improved motor deficits 30 days post-eclosion, as revealed by negative geotaxis and open field. Whole-mount immunohistochemistry results indicated that DA neuronal loss in protocerebral posterior lateral 1 (PPL1) and paired posterior medial 3 (PPM3) cluster were rescued in 30 day-old A53T α-synuclein flies upon PGC-1 overexpression. To investigate the protective mechanism of PGC-1 against α-synuclein toxicity, we first checked whether PGC-1 overexpression could modify α-synuclein level and solubility. Our results showed that PGC-1 overexpression did not significantly affect α-synuclein mRNA level triton-soluble α-synuclein level when compared with age-matched A53T α-synuclein flies, but significantly increased tritoninsoluble fraction of α-synuclein, which may represent the more aggregated forms of α-synuclein. These findings indicated that PGC-1 overexpression could relieve α-synucleininduced disease phenotypes possibly via modifying solubility of α-synuclein. === In second part of the study, we overexpressed PGC-1 in the well-established PINK1- deficient fly model of PD to examine whether PGC-1 overexpression may modify PINK1 deficiency-induced disease phenotypes and the underlying mechanisms. Our data indicated that PGC-1 overexpression improved motor deficits, as revealed by negative geotaxis test, as early as 1 and 10d post-eclosion at which no significant loss of DA neurons was detected by whole-mount immunohistochemistry in PINK1-deficient flies. Further investigation revealed that PGC-1 overexpression preserved mitochondrial membrane potential, ATP level and mitochondrial complex I activity without significant effect on parkin mRNA level, and global mitochondrial morphology and number in fly brains of 10d PINK1-deficient flies. Finally, it was found that motor deficits and loss of DA neurons in PPL1 cluster in 30d PINK1-deficient flies were both alleviated upon PGC-1 overexpression. Interestingly, restoration of complex I activity by PGC-1 overexpression in muscle was not accompanied with improvement indrooped wing posture. These findings indicated that PGC-1 overexpression could relieve PINK1-induced disease phenotypes possibly via functional rescue of mitochondria. === To conclude, our results showed that PGC-1 overexpression is beneficial in PD potentially via modifying α-synuclein solubility and maintaining mitochondrial functionality. Manipulation of endogenous PGC-1α in DA neurons, which is possible via a number of FDAapproved drugs, can hence be a promising and readily translatable treatment strategy against α-synuclein and mitochondrial dysfunction-induced toxicity in PD. === Wu, Ka Chun. === Thesis M.Phil. Chinese University of Hong Kong 2017. === Includes bibliographical references (leaves ). === Abstracts also in Chinese. === Title from PDF title page (viewed on …). === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only. === Detailed summary in vernacular field only.