細胞外Aβ-澱粉樣蛋白（Aβ）形成斑塊和胞內含磷酸化Tau蛋白質的神經纖維纏結（Neurofibrillary tangle, NFT）是阿玆海默氏症（AD）的兩個主要病理特徵。許多研究證明干擾斑塊和/或NFT的發生將會有助AD的治療。經研究顯示腦源性神經營養因子（BDNF）參與AD的發病機制，因其在AD患者腦中的表現會降低，研究發現BDNF對Aβ42和tau毒性具有神經保護作用。我的研究目標是利用果蠅阿茲海默氏症的疾病模式：（1）研究BDNF信息傳遞路徑對AD致病機轉中的作用;（2）以AD果蠅模式篩選有助益的小分子TrkB促效劑，並（3）研究這些促效劑的作用方式。我們發現以RNA干擾果蠅BDNF受體TrkB同源蛋白（Toll 6和Toll 7）的表現，加劇了Aβ42誘導複眼粗糙的表型，也增加細胞死亡的數目，以及類澱粉斑的沉積。顯示BDNF信息傳遞路徑確實伴演Aβ42誘導神經毒性中有一定的角色，此結果也合理化使用果蠅模式篩選TrkB促效劑收治療阿玆海默氏症的策略。以類黃酮及TrkB促效劑類似化合物為篩選目標藥物，在我們初步的篩選中，7,8-DHF, Wogonin, LMDS1及LMDS4可改善因Aβ42造成果蠅複眼退化的性狀，同樣的包括上述的四種小分子藥物及LM016也對因TauR406W突變蛋白造成果蠅背甲剛毛缺失的性狀有改善，進一步發現7,8-DHF，Wogonin，LMDS1及LMDS4降低Aβ42毒性的效果，可因Toll 6和Toll 7的表現下降而減緩，顯示上述藥物有部分是透過BDNF訊息傳遞路徑來改善阿滋海默氏症的病徵，未來我們將以類似方式檢查，藥物壓制TauR406W蛋白毒性是否也是經由強化BDNF息傳遞路徑而來，實驗也將以細胞死亡的數目，類澱粉斑的沉積，及磷酸化Tau蛋白質的表現量，強化上述論証，此外藥物處理是否改變BDNF息傳遞路徑下游基因(如CREB及GSK3β) 的表現量，將有助釐清我們篩選的藥物是否為TrkB促效劑。

The extracellular β-amyloid (Aβ) forming plaques and Tau containing intraneuronal neurofibrillary tangles (NFTs) are two defining features of Alzheimer disease (AD). Accumulated evidence has suggested that interfering the biogenesis of plaques and/or NFTs would be a therapeutic intervention for AD. The brain-derived neurotrophic factor (BDNF) has shown to be involved in the pathogenesis of AD, because its levels are reduced in the brains of AD patients, and BDNF was found to be neuroprotective against Aβ42 and tau toxicity. Noticeably, upregulation of BDNF signaling either by treating BDNF or TrkB agonists alleviates pathogenesis of AD in animal models. The objectives of my studies are: (1) To investigate the roles of BDNF signaling in AD; (2) To explode the beneficial effect of TrkB agonists in AD fly models; (3) To uncover how these TrkB agonists alleviating toxicity of amyloid and NFTs. In our preliminary studies, we found that down-regulation of Drosophila TrkB homologs, Toll 6 or Toll 7, by RNA interference driven by the eye-specific Gmr-gal4 driver exacerbates the Aβ42 induced rough eye phenotype, increasing apoptosis and Thioflavin S positive plaques, suggesting that the BDNF signaling plays a role in the disease progression of Aβ42 induced neurotoxicity. This results also justify our TrkB agonist screening strategy by using AD fly models. In our primary screening, we have identified four compounds, including 7,8-DHF, Wogonin, LMDS1and LMDS4, can alleviate amyloid induced retinal degeneration phenotype from derivatives of known TrkB agonists and flavonoids. The above-mentioned compounds can also suppress TauR406W induced bristle loss phenotype in Drosophila. Moreover, the beneficial effect of these compounds were attenuated by down-regulation Toll6 and/or Toll 7, indicating that the action of these compounds on suppressing amyloid toxicity was mediated partially through the BDNF signaling pathway. To further confirmed the selected compounds are TrkB agonists, we will quantify the numbers of death cells, the deposition of amyloid, and the expression levels of phospho-tau species. Additionally, the expression of several BDNF downstream targets, including phospho-CREB and phospho –GSK3β will be quantified.

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