Targeting Microglial Lipoprotein Lipase in Alzheimer's disease

摘要 阿尔茨海默病(AD)是一种毁灭性的、与年龄相关的、最终致命的神经退行性疾病。 尽管阿尔茨海默病的患病率正在增加，但目前还没有有效的疗法来预防或延缓阿尔茨海默病 开始了。 脑源性脂蛋白(BLP)，在大脑中运输脂质，是一个新兴的靶点 广告治疗学。例如，主要的BLP支架蛋白APOE的E4亚型可以稳定淀粉样蛋白- β(Aβ)，导致斑块形成和增加AD风险。然而，由于BLP的隔离不是最优的 在早期的研究中，以及未加脂的APOE4的使用中，重要的问题都没有得到回答。什么 调节BLP处理的因素，它们能否被靶向治疗AD？ 小胶质细胞在BLP的加工和AD的病理生理过程中起着重要作用。最近的研究表明， 吞噬性小胶质细胞的定义是其脂蛋白脂酶(LPL)的表达升高；限速 脂蛋白的水解酶和摄取酶。值得注意的是，表达Lp1的小胶质细胞吞噬了β以保护其免受 一种β斑块形成。LPL具有保护性的概念与流行病学研究显示的一致 具有功能获得性脂蛋白脂蛋白的个体减少Aβ斑块的形成和降低AD患病率 变种。尽管LPL是治疗AD的潜在靶点，但这还没有在体内得到验证。 我的实验室在脂代谢、LPL生物学和小胶质细胞方面拥有丰富的专业知识，是独一无二的 定位于研究LPL作为AD的治疗靶点。我们之前已经证明，LPL调节 小胶质细胞吞噬、脂蛋白摄取和免疫功能，因此确定LPL是一种 小胶质细胞中的免疫代谢守门人(Bruce等人，2018年；Loving等人，2021年)。此外，我们有说服力 初步数据表明，增加脂蛋白脂酶活性可以增强小胶质细胞对A、β和BLPS的摄取。 因此，我们推测，小胶质细胞-LPL有助于清除Aβ和过量的BLP，从而预防AD 发育和体内LPL活性增加可以改善AD的进展。为了测试这一点，在AIM中 I，我们将使用小胶质细胞特异性基因敲除小鼠(MiLPLKD)和阿尔茨海默病易感小鼠(5xFAD)进行实验 确定药物激活LPL是否可以阻止AD的进展。我们还将使用最先进的 代谢成像和组学方法确定LPL依赖的小胶质细胞控制机制 新陈代谢和功能。在AIM II中，我们将使用从人脑脊液中仔细分离的天然BLPs来定义LPL- 调节小胶质细胞处理脂蛋白的依赖机制以及确定是否增强 LPL活性是恢复APOE4携带者脂质代谢的合理策略。这项研究的结果将是 改变了我们对大脑中脂蛋白的处理和导致AD的机制的理解 神经发病机制。我们的研究不仅将确定LPL依赖的调节小胶质细胞的机制 代谢和功能，但也将确定新的LPL激活剂是否可以改善小胶质细胞功能 改善AD病理，这是一种具有重大临床影响的新策略。

ABSTRACT Alzheimer's disease (AD) is a devastating, age-associated, and ultimately fatal neurodegenerative disorder. Although the prevalence of AD is increasing, there are no effective therapies that can prevent or delay AD onset. Brain-derived Lipoproteins (BLps), transport lipids throughout the brain, and are an emerging target for AD therapeutics. For example, the E4 isoform of the major BLp scaffold protein APOE can stabilize amyloid- beta (Aβ), leading to plaque formation and increased AD risk. However, due to the suboptimal isolation of BLps in earlier studies, and the use of unlipidated APOE4, important questions have been left unanswered. What factors regulate BLp processing, and can they be targeted to treat AD? Microglia play a major role in BLp processing and AD pathophysiology. Recent studies have shown that phagocytic microglia are defined by their elevated expression of lipoprotein lipase (LPL); the rate-limiting enzyme in lipoprotein hydrolysis and uptake. Notably, LPL-expressing microglia engulf Aβ to protect against Aβ plaque formation. The notion that LPL is protective is consistent with epidemiological studies showing reduced Aβ plaque formation and decreased AD prevalence in individuals harboring gain-of-function LPL variants. Although LPL is a potential target for the treatment of AD, this has not been validated in vivo. My laboratory has substantial expertise in lipid metabolism, LPL biology, and microglia and is uniquely positioned to investigate LPL as a therapeutic target for AD. We have previously shown that LPL regulates microglial phagocytosis, lipoprotein uptake, and immune function, hence identifying LPL as an immunometabolic gatekeeper in microglia (Bruce et al., 2018; Loving et al., 2021). Furthermore, our compelling preliminary data has shown that increasing LPL activity can enhance microglial uptake of Aβ and BLps. Therefore, we hypothesize that microglial-LPL helps to clear Aβ and excess BLps to protect against AD development and that increasing LPL activity in vivo can ameliorate AD progression. To test this, in AIM I, we will use microglial-specific knockdown mice (MiLPLKD) and AD susceptible mice (5xFAD) to empirically determine whether pharmacological LPL activation can halt AD progression. We will also use state-of-the-art metabolic imaging and `omics approaches to identify LPL-dependent mechanisms controlling microglial metabolism and function. In AIM II, we will use native BLps carefully isolated from human CSF to define LPL- dependent mechanisms governing lipoprotein processing by microglia and to determine whether enhancing LPL activity is a rational strategy to restore lipid handling in APOE4 carriers. The findings from this study will be transformative to our understanding of lipoprotein handling in the brain and the mechanisms leading to AD neuropathogenesis. Our study will not only determine LPL-dependent mechanisms regulating microglial metabolism and function but will also ascertain whether novel LPL activators can improve microglial function to ameliorate AD pathology, a new strategy with major clinical impact.