Nuclear receptor signaling in BACE1 gene repression under neuroinflammation

描述（由申请人提供）：年龄相关的代谢危险因素或营养失衡，如过量的脂肪和胆固醇摄入或维生素缺乏症，通常与淀粉样蛋白生成增加有关，如迟发性散发性阿尔茨海默病（SAD）。在SAD大脑中观察到β -分泌酶BACE1的表达升高。在培养的神经元模型中，我们发现BACE1转录通过代谢危险因素上调。过表达关键代谢调节因子PGC-1或全反式维甲酸（atRA）可以降低高脂高胆固醇饮食（HFD）引起的炎症引起的BACE1表达升高。饲喂HFD 2个月小鼠前脑中BACE1的RNA和蛋白水平也显著升高；atRA治疗2个月后，HFD喂养后BACE1 mRNA和表达恢复。鉴于类视黄醛信号在AD中的重要性日益得到认可，以及基于类视黄醛的治疗前景，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形成方面的有益作用和潜在的分子机制。在本应用中，我们将首先验证以下假设：atRA通过将配体RARs募集到启动子上抑制BACE1表达；其次，包括PGC-1和核共抑制因子在内的共调节因子参与转录抑制；最后，atRA和RARs干扰NF-gammaB介导的BACE1诱导。本文提出了两个研究目的：1)atRA负调控BACE1转录的分子机制；2)atRA在炎症作用下调节nf - γ - b活性的机制。我们将采用体外细胞（TNFalpha +LPS）和动物模型来代表急性和慢性神经炎症（全身性LPS， HFD等）。鉴于异常活化的nf - γ - b在AD发病机制中的新作用，研究atRA对该分子的调控不仅对BACE1基因调控具有潜在的广泛影响，而且对AD大脑中nf - γ - b敏感基因的大队列具有潜在的广泛影响。尽管BACE1在缺氧和代谢应激条件下（包括ROS）的调控已被广泛研究，但其在神经炎症条件下的上调在很大程度上尚未得到充分研究。因此，我们研究核受体对炎症的负调控具有很高的新颖性。该项目的成功完成将有助于未来寻求促进类维生素a信号和胰岛素致敏的药物（PPARgamma激动剂等）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).