Resolving the function of progranulin in lysosomal lipid metabolism and the etiology of Alzheimer's disease and frontotemporal dementia

额颞叶变性（FTD）和阿尔茨海默病（AD）是两个最常见的原因 老年痴呆症的发病机制重叠，是巨大的健康负担，但无法治愈。该提案重点 阐明颗粒蛋白前体（PGRN）的丢失如何导致溶酶体功能障碍和脂质失调 与FTD和AD相关。PGRN是一种由7.5个串联结构域组成的分泌蛋白，称为颗粒蛋白。 颗粒蛋白前体基因（GRN）中的遗传变异和功能丧失突变，减少了PGRN，增加了 AD的风险和导致FTD。尽管它在大脑健康中的重要性，PGRN的确切功能和 颗粒蛋白是未知的。我们已经发现PGRN被切割成6 kDa的颗粒蛋白， 溶酶体我们实验室和其他人的工作支持PGRN作为溶酶体前体的观点， 颗粒蛋白介导溶酶体稳态，颗粒蛋白的损失导致溶酶体功能受损。 然而，颗粒蛋白在溶酶体中的功能仍然难以捉摸。基于我们已发表的工作和新的 根据这些数据，我们认为颗粒蛋白的丢失损害了溶酶体的脂质代谢，这是主要的缺陷 最终导致神经退化Grn−/−小鼠代谢组和脂质组的综合分析 揭示了鞘糖脂、磷脂和甘油单酯的早期积累。系统生物学 对这些数据的分析表明，溶酶体脂质通量失调是Grn−/−组织中的主要缺陷。我们还 指出一种新的溶酶体水解酶的活性降低是关键因素。根据这些数据，我们 假设颗粒蛋白结合并调节溶酶体脂质水解酶活性以防止脂质 积累和神经变性。在这个项目中，我们将1）确定全球和溶酶体特异性 人诱导多能干细胞（iPSC）衍生的神经元中PGRN缺陷引起的分子缺陷 和小胶质细胞，2）检验颗粒蛋白调节溶酶体腔中脂质水解酶活性的假设， 和3）确定PGRN缺乏如何改变小鼠和人的代谢组和脂质组。完成 这些研究将为溶酶体中颗粒蛋白的功能提供新的系统水平的见解。的 我们产生的试剂和数据将被广泛分享，以促进我们对PGRN功能的理解。 我们的团队非常适合完成拟议的研究，这些研究批判性地评估了新的假设， 颗粒蛋白通过激活新的脂质水解酶促进溶酶体中不同脂质的代谢， 防止脂质积聚和神经退化。通过这样做，我们将揭示为什么PGRN水平下降， 和颗粒蛋白引起FTD、AD，并揭示了治疗由PGRN缺乏引起的疾病的新靶点。

Frontotemporal degeneration (FTD) and Alzheimer's disease (AD) are two of the most common causes of dementia, share overlapping pathologies, are huge health burdens, yet are incurable. This proposal focuses on elucidating how loss of progranulin (PGRN) causes lysosome dysfunction and lipid dysregulation associated with FTD and AD. PGRN is a secreted protein composed of 7.5 tandem domains called granulins. Genetic variants and loss-of-function mutations in the progranulin gene (GRN), reduce PGRN and increase the risk of AD and cause FTD, respectively. Despite its importance in brain health, the exact function of PGRN and granulins are unknown. We have discovered that PGRN is cleaved into 6 kDa granulin proteins in the lysosome. Work from our lab and others support the idea that PGRN serves as a precursor to lysosomal granulins, which mediate lysosome homeostasis and loss of granulins causes impaired lysosome function. However, the function of granulins in the lysosome remains elusive. Based on our published work and new data, we propose that loss of granulins impair lysosomal lipid metabolism, which is the primary defect that ultimately leads to neurodegeneration. Integrated analysis of the Grn−/− mouse metabolome and lipidome revealed early accumulation of glycosphingolipids, phospholipids, and monoglycerides. Systems biology analysis of these data identify dysregulated lysosomal lipid flux as a primary defect in Grn−/− tissue. Further, we pinpoint decreased activity of a novel lysosomal hydrolase as a key factor. Based on these data, we hypothesize that granulins bind and modulate the activity of lysosomal lipid hydrolases to prevent lipid accumulation and neurodegeneration. In this project we will 1) determine the global and lysosome-specific molecular defects caused by PGRN deficiency in human induced pluripotent stem cell (iPSC)-derived neurons and microglia, 2) test the hypothesis that granulins modulate activity of lipid hydrolases in the lysosomal lumen, and 3) define how PGRN deficiency alters the metabolome and lipidome in mice and humans. Completion of these studies will provide novel systems-level insight into the function of granulins in the lysosome. The reagents and data we generate will be widely shared to advance our field's understanding of PGRN function. Our team is ideally suited to complete the proposed studies, which critically evaluate the novel hypothesis that granulins facilitate metabolism of distinct lipids in the lysosome through activation of novel lipid hydrolases to prevent lipid accumulation and neurodegeneration. In doing so, we will uncover why decreased levels of PGRN and granulins cause FTD, AD, and reveal new targets to treat diseases caused by PGRN deficiency.