Molecular mechanisms of Progranulin in Neurodegeneration

项目摘要 额颞叶变性（FTD）和阿尔茨海默病（AD）是两个最常见的原因 痴呆症，共享重叠的病理，是巨大的健康负担，并且是不可治愈的。该提案重点 阐明颗粒蛋白前体（PGRN）及其成熟产物颗粒蛋白的丢失如何驱动神经退行性变 以及与FTD和AD相关的溶酶体功能障碍。PGRN是由7.5个串联的 这些结构域通过定义不明确的途径裂解成6 kDa颗粒蛋白（GRNs）。遗传 颗粒蛋白前体基因（Grn）的变异和功能丧失突变减少了颗粒蛋白前体的产生 （PGRN）蛋白和增加AD的风险和导致FTD。越来越多的证据表明 PGRN/颗粒蛋白水平的降低诱导溶酶体功能障碍，导致神经炎症， 通过未知的机制退化。根据我们已发表的工作和新的数据，我们提出， 颗粒蛋白是PGRN的功能单位，并在内-溶酶体途径中产生。我们发现 PGRN被运输到溶酶体并在多种组织和细胞中加工成稳定的颗粒蛋白。临床上， PGRN和颗粒蛋白在来自FTD-GRN携带者的iPSC衍生的神经元和脑组织中同样减少。 此外，FTD风险因子TMEM 106 B的表达减少颗粒蛋白。最后，细胞外颗粒蛋白可以 拯救Grn KO小鼠成纤维细胞中的溶酶体缺陷，为颗粒蛋白促进 溶酶体功能我们的发现符合更大的叙述，即溶酶体自噬功能障碍是一个关键的 FTD和AD的致病机制。我们的初步数据使我们提出假设，PGRN是 运输到溶酶体并加工成成熟的功能性颗粒蛋白，其介导溶酶体 稳态和神经保护。成功完成以下具体目标将推动 通过为测试颗粒蛋白作为神经退行性疾病的新疗法提供基于机制的理论基础， FTD和AD。我们将1）描绘运输PGRN到溶酶体的分子途径，2）确定PGRN的分子结构。 颗粒蛋白在溶酶体中产生和功能的分子机制，以及3）确定 PGRN和颗粒蛋白在溶酶体功能障碍和神经变性中的作用。完成拟议的研究将 使我们能够批判性地评估范式转变假说，即颗粒蛋白是溶酶体的，功能性的， 神经保护在这样做的过程中，我们将揭示为什么PGRN水平降低会导致FTD，AD或NCL， 治疗PGRN减少引起的疾病的新方法。

Project Summary Frontotemporal degeneration (FTD) and Alzheimer’s disease (AD) are two of the most common causes of dementia, share overlapping pathologies, are huge health burdens, and are incurable. This proposal focuses on elucidating how loss of progranulin (PGRN), and its mature products the granulins, drive neurodegeneration and lysosomal dysfunction associated with FTD and AD. PGRN is a secreted protein composed of 7.5 tandem domains that are cleaved into 6kDa granulin proteins (GRNs), through a poorly defined pathway. Genetic variants and loss-of-function mutations in the progranulin gene (Grn), reduce the production of the progranulin (PGRN) protein and increase the risk of AD and cause FTD, respectively. Converging evidence suggest that decreased levels of PGRN/granulins induce lysosomal dysfunction leading to neuroinflammation and degeneration through an unknown mechanism. Based on our published work and new data, we propose that granulins are the functional unit of PGRN and are produced in the endo-lysosomal pathway. We find PGRN is trafficked to the lysosome and processed into stable granulins in multiple tissues and cells. Clinically, PGRN and granulins are equally decreased in iPSC-derived neurons and brain tissue from FTD-GRN carriers. Further, expression of the FTD-risk-factor TMEM106B reduces granulins. Finally, extracellular granulin can rescue lysosomal defects in Grn KO mouse fibroblasts, providing strong evidence that granulins facilitate lysosome function. Our findings fit into the larger narrative that lysosome-autophagy dysfunction is a critical pathogenic mechanism in FTD and AD. Our preliminary data lead us to propose the hypothesis that PGRN is trafficked to the lysosome and processed into mature, functional granulins that mediate lysosomal homeostasis and neuroprotection. Successful completion of the following specific aims will advance the neurodegeneration field by providing mechanism-based rationale for testing granulins as a novel therapy for FTD and AD. We will 1) delineate the molecular pathways that traffic PGRN to the lysosome, 2) determine the molecular mechanisms of granulin production and function in the lysosome, and 3) determine the in vivo role of PGRN and granulins in lysosome dysfunction and neurodegeneration. Completion of the proposed studies will enable us to critically evaluate the paradigm-shifting hypothesis that granulins are lysosomal, functional, and neuroprotective. In doing so, we will uncover why decreased levels of PGRN lead to FTD, AD, or NCL and a new approach to treat diseases caused by decreased PGRN.