結締組織生長因子於阿茲海默症果蠅之功能驗證

Abstract

阿茲海默症(Alzheimer’s disease, AD)是最常見的神經退化性疾病且導致失智的主要原因，症狀有認知上的障礙和記憶力的喪失；然而導致神經退化的機制仍是有爭論的。結締組織生長因子(CTGF)分泌型蛋白，可調控細胞內之行為如貼附、遷移、浸襲、增殖、凋亡和分化等；然而CTGF於AD所扮演的角色仍不清楚。為了在in vivo中釐清CTGF與AD進程之效應，我們建立AD果蠅(Drosophila)作為動物模式。果蠅異位表現表現人類Aβ42在眼睛和神經中樞系統中會誘發神經毒性，可以用眼睛外觀、螢光染色、果蠅爬行和壽命等來做測定。使用GMR-Gal4 異位表現Aβ42在果蠅眼睛的感光體中(photoreceptors)，發現Aβ42會累積毒性而造成粗糙的眼睛表面和不正常的感光體排列。相同地，全身性表現Aβ42會導致腦部結構的退化和縮短壽命。我們把全長CTGF的 cDNA轉殖基因果蠅在upstream activating sequence (UAS)的啟動子上，與Aβ42共同表現則可有效改善不規則的眼睛表面、延長果蠅壽命和減少Aβ42毒性造成的腦部空洞。在本篇論文中證明，CTGF可藉由增加MMP1的mRNA表現量而促進Aβ之清除。因此，過度表現CTGF可以保護果蠅之神經對抗Aβ42的毒性，總概括CTGF之蛋白質可以是未來一個新穎治療AD的方法。

Alzheimer’s disease (AD) is the most common neurodegenerative disease and the leading cause of dementia, with symptoms manifested as cognitive impairment and memory loss. However, the causal mechanism underlying the neurodegeneration remains controversial. Connective tissue growth factor (CTGF) is a known secretory protein that modulates multiple cellular events including cell adhesion, migration, invasion, proliferation, apoptosis and differentiation in a variety of cancer; however, its role in AD is largely unclear. To investigate the functional relevance of CTGF in AD in vivo, we utilized the fruit fly Drosophila as an animal model. In the fly model of Alzheimer’s disease, the human Aβ42 can be expressed in the eyes and central nervous system (CNS) to induce the neurotoxicity, and the neurodegeneration can be quantified by functional assays including morphology of photoreceptors, immunostaining, climbing and longevity. Using GMR-Gal4 driver to ectopically express Aβ42 in the photoreceptors, we demonstrated that Aβ42 accumulation caused neurotoxicity including rough eyes and disorganized photoreceptors. Consistently, pan-neuronal Aβ42 expression led to the degenerated structure in the brain and shortened the lifespan. To examine the neuron protective role of CTGF, we generated the inducible CTGF-expressing transgenic fly by incorporating the human full-length CTGF cDNA into fly genome under the control of the upstream activating sequence (UAS) promotor. Interestingly, co-expressing CTGF ameliorated the disorganized eyes, extended the lifespan and shrank the brain hole caused by the neurotoxic Aβ42. In this study, we found out CTGF expression increased MMP1 mRNA level. Therefore, overexpression of CTGF can protect neurons from Aβ42 challenges thought MMP pathway, suggesting that CTGF could be a novel therapeutic target for AD.