BAG-1M上调BACE1表达的分子机制及其在阿尔茨海默病发生中作用的研究

BACE1 hydrolyses APP to produce β-amyloid protein（Aβ）. It has been reported that overexpression of BACE1 is correlated with the pathogenesis of Alzheimer's disease (AD); the expression of BACE1 is repressed by PPARγ in neural cells; BAG-1M is overexpressed in the brain of the AD patients. Our data revealed that overexpressed BAG-1M promotes the expression of BACE1 in neural cells; while the expression of BACE1 is inhibited when BAG-1M is silenced by RNAi; BAG-1M interacts with PPARγ in vivo; the expression of BACE1 is repressed when the interaction of BAG-1M and PPARγ is blocked. We hypothesize that BAG-1M interacts with PPARγ and attenuates PPARγ-mediated transcriptional repression on BACE1 gene, leading to the overexpression of BACE1 and, subsequently, the increased generation of Aβ. We will further identify the interaction domains between BAG-1M and PPARγ; investigate whether BAG-1M forms a complex with PPARγ tethered to the PPRE in the promoter of BACE1 gene; compare the expression of BACE1 and the subsequent product Aβ in the cells containing null or endogenous BAG-1M; finally, with the use of AD mouse model, confirm that BAG-1M attenuates the trans-repressional activity of PPARγ on BACE1 gene transcription，resulting in overexpression of BACE1 and the subsequently increased Aβ. Therefore, the result of this project will provide evidence indicating BAG-1M is a novel target for the diagnosis and therapy of AD.

BACE1催化APP生成β淀粉样蛋白（Aβ）。文献报道BACE1表达增高与阿尔茨海默病（AD）发病相关；神经细胞中PPARγ抑制BACE1表达； BAG-1M在AD患者脑组织中过表达。我们前期发现，神经细胞中过表达的BAG-1M可促进BACE1表达；RNAi沉默BAG-1M则抑制BACE1表达；BAG-1M能够与PPARγ相互作用；阻断BAG-1M与PPARγ作用则抑制BACE1表达。因此提出BAG-1M通过抑制PPARγ活性上调BACE1表达并促进Aβ生成增加的研究假说。拟进一步探讨BAG-1M和PPARγ相互作用的结构域；BAG-1M是否和PPARγ形成复合物定位在BACE1启动子的PPRE上调控转录；含/不含内源性BAG-1M的细胞中BACE1表达及Aβ生成有无差异；利用AD动物模型验证BAG-1M通过抑制PPARγ活性促进BACE1表达及Aβ生成增加。为AD的诊断治疗提供靶标。

阿尔茨海默病（AD）严重危害健康，已成为我国今后重点防治疾病之一。本课题首先在细胞水平和分子水平上阐明了AD患者大脑中过表达的BAG-1M在AD发生中的作用及机制，即BAG-1M作为共激活因子与促进BACE1基因表达的转录因子NF-κB相互作用并定位在BACE1基因启动子NF-κB的反应原件上，共激活BACE1基因表达。同时BACE1轻度上调APP基因表达，BACE1蛋白量上升后进一步促进APP的水解产生过多的C99并最终导致Aβ生成增多。上述发现在AD模型鼠得到了进一步验证，即在AD模型鼠的海马中过表达BAG-1M后，脑组织中BACE1表达上调，C99和Aβ生成增多，淀粉样斑块增多，小鼠的记忆力和认知功能明显下降。本课题揭示了BAG-1M在AD发生中的作用机理及信号通路，表明BAG-1M过表达能够引起AD的发生，为AD的早期诊断和治疗提供了靶标。.本课题在研究过程中结合文献报道AD患者脑组织中ciRS-7下调，从而拓展研究了ciRS-7对APP和BACE1的作用，发现ciRS-7不调控APP和BACE1的基因转录，但是促进APP和BACE1的蛋白酶体和溶酶体途径的降解，而这个过程是通过抑制NF-κB 的翻译及诱导胞浆定位而释放对UCHL1的表达抑制而完成的，阐明了ciRS-7是一个具有神经保护作用的非编码RNA及AD发生及治疗的靶标。