鳥類腦乙型類澱粉沉著症回溯性研究

A Retrospective Survey of Cerebral Beta-Amyloid Accumulation in Avian Species

陳彥涵(Yen-Han Chen)

指導教授 ： 鄭謙仁

共同指導教授 ： 張惠雯 ； 張晏禎(Yen-Chen Chang)

國立臺灣大學/獸醫專業學院/分子暨比較病理生物學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202101098

摘要

阿茲海默症（Alzheimer’s Disease, AD）是人類老年醫學造成「失智症」最重要的疾病，約佔失智症人口60-70%。本病是進行性的神經性病變，可引起程度不一的認知功能障礙，最重要的組織病變包含：(1) 細胞外可見乙型類澱粉蛋白（Beta-amyloid）沉著，形成類澱粉斑塊（Aß plaques, senile plaques）或出現腦部類澱粉血管病變（Cerebral amyloid angiopathy, CAA）；(2) 細胞內過磷化tau蛋白（hp-tau）堆積，嚴重者可造成神經元壞死，形成神經元纖維纏結（Neurofibrillary tangles, NFTs）。至今，本病仍有部分致病機轉尚未全然解開。根據文獻，許多老年動物被發現有類似人類阿茲海默症的腦部病變，包含不同程度的乙型類澱粉蛋白（Beta-amyloid）沉積與神經元纖維纏結（NFTs）的神經元內堆積，包括靈長目、食肉目、鯨偶蹄目、囓齒目、兔型目、馬（奇蹄目）與其他海洋哺乳類，且於不同物種有不同的病變發展。不過，相關的研究在鳥類中仍非常少。本論文為老年鳥類乙型類澱粉蛋白（Beta-amyloid）沉著提供一個回溯性研究，並發現於鳥類可有三種不同型態的乙型類澱粉蛋白沉積，以及證實了腦血管乙型類澱粉沉著可於鳥類中被發現。本研究樣本共包含13個目，29個物種，共50隻個體，並以免疫組織化學染色進行四種（6E10、4G8、x-40、x-42）抗乙型類澱粉蛋白（Beta-amyloid）及一種（AT100）抗過磷酸化tau蛋白染色，偵測是否有AD相關之異常蛋白存在於鳥類腦組織中。研究結果發現，除一34歲白腹海鵰可在H E染色下看到明顯微小膠細胞增多以及聚集在神經纖維周圍之外，其他病例的腦組織皆未出現明顯組織病變。在IHC染色結果，本實驗首次發現了白腹海鵰腦組織病例可顯示出3+強陽性，且可見明顯類澱粉斑塊（Aß plaques）及多發局部的類澱粉血管病變（CAA），呈現diffuse to compact斑塊（Diffuse/compact plaque）。此外，另一熊鷹（赫氏角鷹，Nisaetus nipalensis）病例亦為首次發現，可見大腦及小腦腦膜血管出現明顯多發Aß陽性訊號。挑選幾個乙型類澱粉蛋白（Beta-amyloid）陽性樣本進一步以甲烯胺嗜銀染色（Methenamine silver，MS）染色及類澱粉樣染色（Congo Red stain），以確定類澱粉斑塊（Aß plaques）的結構存在。所有老年鳥類樣本經AT100染色後皆為陰性，未見明顯細胞內tau蛋白堆積的證據。而兩例IHC陽性病例，皆呈現類澱粉樣染色（Congo Red stain）陰性結果。此外，Aß (x)-40與42兩種抗體的染色，在本實驗結果討論中，被認為是於鳥類研究中較有意義的抗體。本研究提供關於老年鳥類腦部乙型類澱粉蛋白（Beta-amyloid）沉著的初步視野，並發現乙型類澱粉蛋白（Beta-amyloid）的異常堆積可能具有好發於鷹科海鵰屬（Haliaeetus spp.）或其他老年猛禽類的傾向，但相關疾病機轉仍需要更進一步的探究。據此，老年鳥類可能是自然發生類阿茲海默症腦部病變的動物，可出現與人類或其他哺乳動物類似乙型類澱粉蛋白（Beta-amyloid）的堆積，但沒有神經原內的異常tau蛋白形成。

關鍵字

鳥類腦神經病變 ； 乙型類澱粉蛋白 ； 腦部類澱粉血管病變 ； 海鵰屬 ； 熊鷹

並列摘要

In human medicine, Alzheimer’s disease (AD) is the most common and important form of dementia (60–70% of cases), characterized as degenerative and progressive disorders in neurocognitive symptoms. The histopathological features of AD include two major patterns: (1) extraneural lesions: accumulation of the protein fragment beta-amyloid (Aß plaques); (2) intraneural lesion: twisted strands of the hyperphosphorylated-tau (hp-tau) tangles (neurofibrillary tangles, NFTs). Several laboratory transgenic mice have been established for study of pathogenesis of human AD, but the whole picture of the pathogenesis of AD-like lesions are not totally understood. Till now, various species of wildlife, including Primates, Carnivora, Cetartiodactyla, rodents, rabbits, horses, marine mammals and avian, have been investigated for the AD-liked neurodegenerative lesions and varying histopathological characteristics were revealed in the brain tissue of different terrestrial/marine mammals. However, studies of AD-like lesions are extremely rare in avian species. Herein, the current study provided a preliminary knowledge of age-associated cerebral beta-amyloid deposition with three types of amyloid plaques and cerebral amyloid angiopathy (CAA) in aged avian species. There were 13 orders, 29 species and total 50 aged/adult birds involved in this study. Four anti-Aβ antibodies (6E10, 4G8, x-40, x-42) and one anti-hyperphospharylated tau antibody (AT100) were used for immunohistochemical (IHC) staining examination. For the first time, the results of IHC staining revealed multifocal 3+ strong Aβ deposition argyrophilic plaques which were also diffuse to compact plaques in the cerebral cortex in a 34 years old white-bellied sea eagle (Haliaeetus leucogaster); besides, multifocally prominent cerebral and cerebellar meningeal vascular Aβ deposition was also observed in one Hodgson's hawk-eagle (Nisaetus nipalensis) in the first time. Neither of the two aged individuals were positive for the intraneural tau protein. Most of other cases showed non-specific histopathological abnormality H E staining, except the white-bellied sea eagle (Haliaeetus leucogaster). Under the histochemical staining, including the methenamine silver (MS) and Congo red staining, only the case of white-bellied sea eagle displayed MS-positivity and all of the cases were negative for Congo red staining. The results of x-40 and x-42 were more meaningful for the detecting aging changes in avian brain. The current study suggested that some avian species may develop natural accumulation of Aβ in the brain with age, similar to that of human AD or these animal species with the AD-related pathologic changes. No hp-related tau protein revealed in all aged cases. Furthermore, Haliaeetus spp. and other raptor-birds may show more tendency with beta-amyloid accumulation but the mechanism and pathogenesis are still need more investigation.

並列關鍵字

Avian neuroscience ； Beta-amyloid (Aβ) ； Cerebral amyloid angiopathy (CAA) ； Sea eagle (Haliaeetus spp.) ； Hodgson's hawk-eagle (Nisaetus nipalensis)

參考文獻

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