Role of LXR and ABCA1 in Abeta Aggregation and Toxicity

描述(申请人提供)：ABCA1和载脂蛋白调节胆固醇和磷脂外流，以及高密度脂蛋白的形成。ABCA1Ko小鼠表现出胆固醇外流减少，载脂蛋白A-L和载脂蛋白E脂化不良。载脂蛋白的脂化不良会导致其分解代谢增加。最近，研究表明，ABCA1基因工程干扰的AD转基因小鼠的淀粉样蛋白沉积水平增加，认知障碍。LXR调节ABCA1和ApoE在人和啮齿动物中的表达。用LXR配体处理AD转基因小鼠可增加ABCA1和载脂蛋白的表达。这可能会增加载脂蛋白E和载脂蛋白A-L的脂化作用，导致Aβ与富含脂肪的载脂蛋白结合增加，最终减少其聚集性。研究表明，在对AD转基因小鼠进行短期LXR配体治疗后，不溶性A的水平降低，记忆力得到改善。该建议的目的是证明ABCA1在AP的毒性和病理性聚集中的作用，并强调ABCA1在疾病进展的相对早期阶段AD的分子发病机制中的重要性。我们假设LXR配体治疗将增加ABCA1调节的胆固醇外流和富含脂肪的载脂蛋白的产生，这是A？病理的关键介质。总之，这些数据将提供证据表明，LXR治疗可以减缓AD的进展，并建立长期的LXR治疗效果。为了验证这一假设，我们将建立LXR和ABCA1如何调节载脂蛋白E的脂化，以及载脂蛋白A-L如何影响A？聚集。我们将比较LXR配体处理的Abca1ko和WT小鼠星形胶质细胞条件培养液中分泌的脂质颗粒的胆固醇和磷脂含量。此外，我们还将确定载脂蛋白E和载脂蛋白A-L的脂化状态如何影响AP聚集。体外研究将比较LXR配体如何影响AD表型，并证明这种影响是通过ABCA1介导的。比较使用LXR配体治疗4个月的APP/Abca1wt和APP/Abca1ko小鼠，将证明ABCA1在介导LXR对淀粉样蛋白病理和认知的影响以及决定长期治疗效果方面是必不可少的。具体地说，在LXR配体治疗之后，将检查空间工作记忆、参考记忆和恐惧条件反射。认知功能减退将与大脑中淀粉样蛋白病理、胆碱能标志物以及载脂蛋白A-L和载脂蛋白E浓度相关。最后，基于基因阵列分析的结果，LXR处理的小鼠的脑表达谱将被组装并与先前子目标中确定的终点相关。更好地了解胆固醇代谢在AD病理中的作用将有助于开发新的治疗途径来减缓疾病的进展。

DESCRIPTION (provided by applicant): The Abca1 and apolipoproteins regulate cholesterol and phospholipids efflux, and HDL formation. Abca1 ko mice exhibit decreased cholesterol efflux and poorly-lipidated ApoA-l and ApoE. Poor lipidation of apolipoproteins result in their increased catabolism. Recently, studies demonstrated that AD transgenic mice with engineered disruption of Abca1 have an increased level of amyloid deposition and cognitive impairments. LXR regulates the expression of Abca1 and ApoE both in humans and rodents. Treatment of AD transgenic mice with LXR ligands increases the expression of Abca1 and apolipoprotein. This could increase the lipidation of ApoE and ApoA-l which would lead to increased binding of A¿ to lipid-rich apolipoproteins, eventually decreasing its aggregation. Studies have shown diminished levels of insoluble A¿ and improved memory after short-term LXR ligand treatment of AD transgenic mice. The goals of this proposal are to demonstrate the role of Abca1 in toxicity and pathological aggregation of Ap and to emphasize the importance of Abca1 in the molecular pathogenesis of AD at a relatively early stage of the disease progression. We hypothesize that LXR ligand treatment will increase Abca1-regulated cholesterol efflux and generation of lipid-rich apolipoproteins that are critical mediators of A¿ pathology. Altogether the data will provide evidence that LXR treatment can slow AD progression and establish long-term LXR treatment effects. To test the hypothesis we will establish how LXR and Abca1 regulated lipidation of ApoE and ApoA-l influences A¿ aggregation. We will compare cholesterol and phospholipid content of lipid particles secreted in conditioned media of astrocytes derived from Abca1ko and WT mice treated with LXR ligands. Furthermore, we will determine how the lipidation states of ApoE and ApoA-l affect AP aggregation. In vitro studies will compare how LXR ligands affect AD phenotype and prove that this effect is mediated through Abca1. Comparing APP/Abca1wt and APP/Abca1ko mice treated with LXR ligands for 4 months will demonstrate that Abca1 is essential in mediating LXR effects on amyloid pathology and cognition and determine long-term treatment effects. Specifically, following LXR ligand treatment spatial working memory, reference memory, and fear conditioning will be examined. Cognitive decline will be correlated with amyloid pathology in the brain, cholinergic markers, and concentrations of ApoA-l and ApoE. Finally, based on results from gene array assays brain expression profiles in LXR treated mice will be assembled and correlated to the endpoints determined in the previous subaims. Better understanding the role of cholesterol metabolism in AD pathology will help develop new routes of treatment to slow disease progression.