EFFECTS OF AGING & PGP ON AB EFFLUX FROM THE BRAIN

本申请是对PAR-03-056的响应，特别关注功能性衰老的主题。年龄是阿尔茨海默病（AD）的最强风险因素，阿尔茨海默病是美国痴呆症的最常见原因。证据表明可溶性淀粉样蛋白-β（A-β）肽在脑中积聚成不溶性淀粉样蛋白是AD发病机制的核心。虽然A-β的过度产生导致其在罕见的家族性AD中过早积累，但在散发性AD（>99%的AD病例）中没有过度产生的证据。因此，为什么A-β在最常见的AD形式中以年龄依赖性的方式积累？虽然对A-β的产生了解很多，但对其代谢知之甚少。A-β蓄积可能是从大脑到血液的A-β清除受损的结果。分子离开 通过血脑屏障（BBB）或经由通过间质液或脑脊液引流途径的大量流动来向脑内输送。报告已经证明A-β肽流出CNS，研究表明MDR 1 P-糖蛋白（Pgp）（一种由BBB细胞表达的转运蛋白）在此过程中可能发挥作用。最近的一项描述性研究表明，如果Pgp作为A-β外排泵发挥作用，它也可能影响A-β沉积和AD。我们假设，随着年龄的增长，A-β从CNS到血液的正常清除机制存在缺陷，这种损伤最终导致A-β在脑中蓄积并沉积为不溶性淀粉样蛋白。我们建议将小鼠中的Abeta流出作为年龄的函数，并研究Pgp在此过程中的作用，以及在AD小鼠模型中的A-β沉积。将具有已知转运机制的A-β和对照分子注射到不同年龄小鼠的大脑中，并在野生型和mdrla/B -/-小鼠以及用Pgp抑制剂治疗的野生型小鼠中评估外排动力学。我们还将评估与缺乏Pgp的mdrla，B -/-小鼠一起繁殖的APPsw（Tg 2576）转基因小鼠的脑A-β沉积和A β水平。支持这一假设将确立年龄依赖性缺陷在AD发病机制中的作用，重要的是，为治疗该疾病提供了一种新的治疗靶点。

The present application is in response to PAR-03-056, with particular focus on the topic of Functional Senescence. Age is the strongest risk factor for Alzheimer's disease (AD), the most common cause of dementia in the U.S. Evidence suggests brain accumulation of soluble amyloid-beta (A-beta) peptide into insoluble amyloid is central to the pathogenesis of AD. While overproduction of A-beta leads to its premature accumulation in rare familial AD, there is no evidence of overproduction in sporadic AD (>99% of AD cases). Thus, why does A-beta accumulate in an age-dependent manner in the most common form of AD? Although much is known about production of A-beta, very little is known about its metabolism. A-beta accumulation may be a result of impaired A-beta clearance from the brain to the blood. Molecules exit the brain through the blood-brain barrier (BBB) or via bulk flow through interstitial fluid or cerebrospinal fluid drainage pathways. Reports have demonstrated efflux of A-beta peptides out of the CNS, and studies suggest a possible role for MDR1 P-glycoprotein (Pgp), a transporter expressed by cells of the BBB, in this process. If Pgp plays a role as an A-beta efflux pump, it may also influence A-beta deposition and AD, as suggested by a recent descriptive study. We hypothesize that there is a defect in the normal clearance mechanism(s) of A-beta from the CNS to the blood with age, and that this impairment ultimately contributes to A-beta accumulation in the brain and its deposition as insoluble amyloid. We propose to characterize Abeta efflux in mice as a function of age and investigate the role of Pgp in this process, and in A-beta deposition in a mouse model of AD. A-beta and control molecules with known transport mechanisms will be injected into the brains of mice of different ages and efflux kinetics will be assessed in wild type and mdrla/b -/- mice and in wild type mice treated with Pgp inhibitors. We will also assess brain A-beta deposition and Abeta levels in APPsw (Tg2576) transgenic mice that have been bred with mdrla,b -/- mice lacking Pgp. Support for the hypothesis would establish a role for age-dependent defects in A-beta clearance from the brain in the pathogenesis of AD and, importantly, provide a novel therapeutic target for treatment of the disease.