Endolysosomal trafficking and lipid metabolism defects in FTLD

项目总结 人类GRN基因显性突变导致原颗粒蛋白水平单倍性不足 是通过RNA结合蛋白TDP-43聚集的额颞叶退行性变的主要原因 (FTLD-TDP)。此外，GRN中的单核苷酸多态(SNP)已被确定为高血压的危险因素 以AD和边缘为主的年龄相关性TDP-43脑病(晚期)，记忆的主要原因 90岁以上患者的损害。尽管PGRN在大脑老化中起着关键作用，然而，确切的 PGRN单倍体不足促进神经退行性变的机制尚不清楚。通过 分析Grn基因敲除小鼠(Grn-/-)和人源化GrnR493X/R493X敲门小鼠的老化队列，我们发现 PGRN缺陷的小胶质细胞产生更多的补体蛋白和促炎细胞因子 脑老化过程中神经细胞死亡和TDP-43蛋白病变。有趣的是，我们正在进行的工作表明 阻断补体活化和促炎细胞因子TNFa和IL-1a并不能完全缓解 神经变性，而是发现了以深度堆积为特征的迟发性小胶质细胞病理 脂质在Grn-/-、Grn-/-、C1qa-/-、C3-/-和Grn-/-；C1qa-/-；肿瘤坏死因子-/-；IL1a-/-小胶质细胞中。利用脂质组学和亚细胞 分级，我们进一步表明，PGRN的丢失导致严重的阻断内溶酶体运输 Grn-/-小胶质细胞中的脂类干扰溶酶体介导的脂滴降解并增加 前炎性氧化磷脂的生产。总之，我们的结果提出了一种假设，即PGRN 缺乏导致小胶质细胞和星形胶质细胞脂类内体转运缺陷，促进 神经退行性变中的神经元脆弱性。为了验证这一假设，我们建议(1)描述机制 促进Grn-/-小胶质细胞脂质介导的毒性的内溶酶体转运和分泌性自噬，(2) 表征脂质依赖和非依赖机制在促进Grn-/-神经毒性中的作用 以及(3)用比较的SnRNA-RNA法研究脂质在FTLD-GRN胶质细胞毒性中的作用。 SEQ、IPSC衍生的有机物和死后组织。拟议中的人-鼠平行研究将揭示 GRN-/-小鼠和FTLD-GRN小鼠高度疾病易损区脂质介导毒性的贡献 揭示在脑老化过程中促进神经胶质病理和神经退行性变并导致 ADRD的新治疗靶点。

PROJECT SUMMARY Dominant mutations in the human GRN gene cause haploinsufficiency in Progranulin (PGRN) protein levels and are a leading cause of frontotemporal lobar degeneration with aggregation of RNA binding protein TDP-43 (FTLD-TDP). In addition, single nucleotide polymorphism (SNP) in GRN has been identified as a risk factor for AD and Limbic predominant, Age-related TDP-43 Encephalopathy (LATE), a major cause of memory impairments in patients over 90 years old. Despite the critical role of PGRN in brain aging, however, the exact mechanism by which PGRN haploinsufficiency promotes neurodegeneration remains poorly understood. By analyzing aging cohorts of Grn knockout (Grn-/-) and humanized GrnR493X/R493X knockin mice, we have shown that PGRN-deficient microglia produce more complement proteins and pro-inflammatory cytokines to promote neuronal cell death and TDP-43 proteinopathy during brain aging. Interestingly, our ongoing work shows that blocking complement activation and proinflammatory cytokines TNFa and IL-1a does not completely mitigate neurodegeneration, but rather uncover late-onset microglial pathology characterized by profound accumulation of lipids in Grn-/-, Grn-/-;C1qa-/-;C3-/-, and Grn-/-;C1qa-/-;Tnf-/-;Il1a-/- microglia. Using lipidomics and subcellular fractionation, we further show that loss of PGRN causes severe blockade in the endolysosomal trafficking of lipids in Grn-/- microglia, which interferes with lysosome-mediated degradation of lipid droplets and increased production of proinflammatory oxidized phospholipids. Together, our results broach the hypothesis that PGRN deficiency causes profound endolysosomal trafficking defects of lipids in microglia and astrocytes to promote neuronal vulnerability in neurodegeneration. To test this hypothesis, we propose to (1) delineate the mechanism of endolysosomal trafficking and secretory autophagy that promote lipid-mediated toxicity in Grn-/- microglia, (2) characterize the role of lipid-dependent and -independent mechanisms in promoting neurotoxicity in Grn-/- astrocytes, and (3) delineate the contributions of lipids to glial toxicity in FTLD-GRN using comparative snRNA- seq, IPSC-derived organoids and postmortem tissues. The proposed parallel human-mouse studies will uncover the contributions of lipid-mediated toxicity in highly disease vulnerable regions in Grn-/- mice and FTLD-GRN will uncover critical mechanisms that promote glial pathology and neurodegeneration during brain aging and lead to novel therapeutic targets for ADRD.