α突觸核蛋白聚集體在中樞神經系統和其他器官中的傳播機制

Abstract

帕金森氏症 (PD) 是第二常見的神經退化性疾病，並且具有全身症性狀包含運動、嗅覺、腸道和視覺問題， PD 病因是由於中腦黑質緻密部 (SNc) 中多巴胺能神經元的喪失，在死亡的多巴胺能神經元中發現了大量的 α-突觸核蛋白 (α-Syn) 聚集體，稱為路易體，聚集的 α-Syn 標誌是在於其絲氨酸 129 位點 (pS129) 磷酸化的程度增加。近期研究表明，使用人類α-Syn (hα-Syn) 預形成的原纖維 (PFF) 注入十二指腸可以使其傳播到大腦並引起 PD 病理特徵，以此為動物模型中的 hα-Syn 傳播提供了證據；然而隨著 PD 研究的進展，hα-Syn 傳播的機制仍理解不多。在這項研究中，我們使用已建立的 PD 大鼠模型，經由活體內電穿孔技術表達對照質體（偽手術組）、人類野生型 α-Syn (hWT) 或其突變體 [α-Syn-A53T (hA53T ); α-Syn-A30P、E46K、H50Q、G51D、A53T (hPenta)]，發現轉染後 1-3 個月後所有 hα-Syn 質體均誘導PD 症狀以及 hα-Syn 聚集體，我們更進一步探討了 hα-Syn 從大腦傳播到其他器官的潛在機制和時間進程，在轉染後 1 個月，hα-Syn 從右側 SNc 傳播到左側大腦、小腦、十二指腸、盲腸和乙狀結腸等腸道消化器官，但在這些器官中未檢測到 hα-Syn 聚集體的形成，這些數據表明 hα-Syn 可能在轉染後 1 個月從腦傳播到胃腸 (GI) 系統；相比之下，在轉染 3 個月後，我們除了在上述器官中發現 hα-Syn 聚集體，亦在其他器官中也發現了新形成的 hα-Syn 聚集體，包括嗅球、視神經和視網膜，有趣的是，特別在左側視神經（尤其是 hPenta）中發現了豐富的 hα-Syn 聚集體，鑑於視網膜主要投射到大腦的對側，hα-Syn 聚集體可能從右腦逆行傳播，通過左側視神經最後到達左側視網膜，表明 hα-Syn 聚集體可能通過視覺迴路傳播，最後我們也發現血漿中之細胞外囊泡（EV）在轉染後 3 個月後含有 hα-Syn 聚集體。綜上所述，從大腦到腸道的傳播要早於眼睛，並且來自血漿 EV 中的 hα-Syn 也可以作為早期檢測 PD 的診斷方法。

Parkinson’s disease (PD) is a second common neurodegenerative disease with systemic symptoms, including motor, olfactory, defecation, and visual defects. PD results from the loss of dopaminergic (DA) neurons in substantial nigra par compacta (SNc) of the midbrain. The enormous aggregates of alpha-synuclein (α-Syn), called Lewy bodies, are found in the dead DA neurons. The hallmark of the aggregated α-Syn is the increase in phosphorylation at serine 129 (pS129). Emerging studies indicated the human α-Syn (hα-Syn)-preformed fibrils (PFF) can propagate from mouse duodenum to brain and cause the PD pathological features, providing the evidence for hα-Syn propagation in animal models. However, how hα-Syn may propagate as PD progression remains unclear. In this study, we established the PD rat model using in vivo electroporation to transfect the right SNc with the control plasmid (sham control), human wild-type α-Syn (hWT), or its mutants [α-Syn-A53T (hA53T); α-Syn-A30P,E46K,H50Q,G51D,A53T (hPenta)]. After 1-3 months post transfection, all hα-Syn plasmids induced the progressive PD symptoms as well as α-Syn aggregates. Further, we explored the time course of hα-Syn propagation from brain to other organs. At 1 month post transfection, hα-Syn propagates from the right SNc to the left cerebrum, cerebellum, and guts such as duodenum, cecum, and sigmoid colon, with no-detectable hα-Syn aggregates in these organs. These suggest that hα-Syn may propagate from brain to the gastrointestinal (GI) system at 1 month post transfection. By contrast, after 3 months post transfection, we found α-Syn aggregates in the organs mentioned above. Moreover, α-Syn aggregates were found in some other organs, including olfactory bulbs, optic nerves, and retinas. Particularly, abundant hα-Syn aggregates were found in the left optic nerves (especially for hPenta). Given that retinas mainly project to the contralateral side of brain, hα-Syn aggregates may retrogradely propagate from the right brain, through the left optic nerves, and finally to the left retinas, indicating that hα-Syn aggregates may propagate through visual circuits. Furthermore, we found that plasma may contain extracellular vesicles (EVs) harboring hα-Syn and hα-Syn aggregates after 3 months post transfection. Taken together, the propagation from brain to gut is earlier than to eyes. The hα-Syn in the EVs from plasma may also serve as a diagnosis way to detect PD at the early stage.