Nuclear receptor signaling in BACE1 gene repression under neuroinflammation

描述（由申请方提供）：阿尔茨海默病相关的代谢风险因素或营养失衡，如脂肪和胆固醇摄入过多或维生素缺乏症，通常与淀粉样蛋白生成增加有关，如在迟发性散发性阿尔茨海默病（SAD）中所见。在SAD脑中观察到β-分泌酶BACE 1的表达升高。在培养的神经元模型中，我们发现BACE 1转录通过代谢危险因素上调。PPARgamma辅激活因子（PGC-1）（一种关键的代谢调节因子）或全反式维甲酸（atRA）的过表达可以降低由高脂高胆固醇饮食（HFD）诱导的炎症引起的BACE 1表达升高。在喂食HFD 2个月的小鼠前脑中也发现BACE 1的RNA和蛋白水平显著增加;在喂食HFD后，用atRA治疗2个月恢复了BACE 1 mRNA和表达。鉴于类维生素A信号在AD中的重要性日益得到认可，以及基于类维生素A的治疗的前景，我们的长期目标是充分表征atRA在减轻神经炎症和淀粉样蛋白生成方面的有益作用和潜在的分子机制。在本申请中，我们将首先检验以下假设：atRA通过将配体RAR募集到启动子上来抑制BACE 1表达;其次，包括PGC-1和核辅阻遏物在内的辅调节因子参与转录抑制;最后，atRA和RAR干扰NF-γ B介导的BACE 1诱导。提出了两个目的来研究1）atRA负调节BACE 1转录的分子机制和2）atRA调节炎症后NF-γ B活性的机制。我们将采用体外细胞（TNF α +LPS）以及代表急性和慢性神经炎症（全身性LPS，HFD等）的动物模型。考虑到异常激活的NF-γ B在AD发病机制中的作用，研究atRA对该分子的调节不仅对BACE 1基因调节而且对AD脑中NF-γ B敏感基因的大群体具有潜在的广泛影响。虽然BACE 1调节已被广泛研究缺氧和代谢应激条件下，包括活性氧，其上调神经炎症条件下，在很大程度上是研究不足。因此，我们研究核受体对炎症反应的负调控具有很高的新奇。该项目的成功完成将有助于未来寻求促进类维生素A信号传导和胰岛素增敏的药物（PPARgamma激动剂等）之间的潜在联合治疗。

DESCRIPTION (provided by applicant): Age-associated metabolic risk factor(s) or nutritional imbalances, such as excessive fat and cholesterol intake or hypovitaminosis, are often linked to increased amyloidogenesis, as seen in late-onset sporadic Alzheimer's disease (SAD). Elevated expression of beta-secretase BACE1 is observed in SAD brains. In cultured neuronal models, we show that BACE1 transcription is upregulated through metabolic risk factors. Overexpression of the PPARgamma coactivator (PGC-1) a key metabolic regulator or all-trans retinoid acid (atRA) can reduce the elevated BACE1 expression resulting from inflammation induced by a high fat high cholesterol diet (HFD). Markedly increased RNA and protein levels of BACE1 were also found in the mouse forebrains fed HFD for 2 months; 2-months of treatment with atRA restored BACE1 mRNA and expression after HFD feeding. Given the increasingly recognized importance of retinoid signaling in AD and the promise of retinoid-based therapies, our long-term goal is to fully characterize the beneficial effects and the underlying molecular mechanisms of atRA in mitigating neuroinflammation and amyloidogenesis. In this application, we will test the hypotheses first that atRA suppresses BACE1 expression via recruitment of liganded RARs to the promoter, secondly that coregulators including PGC-1 and nuclear corepressors participate in the transcriptional repression and finally that atRA and RARs interfere with the NF-gammaB mediated induction of BACE1. Two aims are proposed to investigate 1) the molecular mechanism underlying the negative regulation of BACE1 transcription by atRA and 2) the mechanisms by which atRA modulates NF-gammaB activity upon inflammation. We will employ both in vitro cellular (TNFalpha +LPS) as well as animal models representing acute and chronic neuroinflammation (systemic LPS, HFD etc). Given the emerging role of aberrantly activated NF-gammaB in AD pathogenesis, studying atRA's regulation of this molecule is of potential broad impact not only for BACE1 gene regulation but also in large cohorts of NF-gammaB-sensitive genes in AD brains. Although BACE1 regulation has been extensively studied under hypoxic and metabolic stressed conditions including ROS, its upregulation under neuroinflammatory conditions is largely understudied. Hence, our focus of investigating its negative regulation by nuclear receptors upon inflammation is of high novelty. Successful completion of this project will be instrumental for future pursuing potential combination therapy between agents promoting retinoid signaling and insulin- sensitization (PPARgamma agonists etc).