Single Cell Characterization of FTLD-GRN

阿尔茨海默病（AD）和相关的痴呆、额颞叶变性（FTLD）共享几个与阿尔茨海默病（AD）相关的疾病。 关键的临床和神经病理学特征，并被认为是疾病谱的两端。在 支持这一点的遗传学证据表明，颗粒蛋白前体（GRN）基因显性突变的患者 不可避免地发生FTLD伴TDP-43蛋白病，其特征在于RNA结合蛋白的积累 额叶皮层第2-3层的TDP-43。有趣的是，在3 'UTR的单核苷酸多态性（SNP）， GRN基因降低颗粒蛋白前体（PGRN）蛋白水平， 43 30-40%的AD患者存在边缘区蛋白质病变。尽管这些有趣的基因型-表型 然而，PGRN缺乏如何促进神经胶质和神经元病理学仍然知之甚少。到 为了研究PGRN缺乏时神经退行性变的机制，我们进行了单核RNA- 在衰老过程中，在Grn-/-小鼠的丘脑中进行snRNA-seq测序，结果显示，在PGRN中， 缺乏，小胶质细胞是第一种细胞类型，显示进行性丧失的稳态基因，并获得 促进神经元细胞死亡的促炎状态的转录组学和组织病理学特征， TDP-43蛋白质病。为了将这些结果与人类疾病联系起来，我们进行了一项试点研究， 比较来自snRNA-seq的结果，使用来自FTLD的额叶皮层和丘脑的死后组织， GRN病例与来自19个月大的Grn-/-小鼠相似脑区的病例。这种人鼠snRNA-seq 比较显示FTLD-GRN病例和Grn-/-小鼠中共有的转录组学变化，包括细胞 小胶质细胞（胞吐、免疫激活和趋化性）和星形胶质细胞（星形胶质细胞-血管 耦合、细胞粘附和突触组织）。此外，我们的研究发现， FTLD-GRN额叶皮层和丘脑兴奋性和抑制性神经元的转录组学变化 例，提示人类特有的神经元脆弱性。总之，这些结果提出了一个假设， PGRN缺陷破坏了小胶质细胞和星形胶质细胞的基因调控网络，并改变了复杂的胶质神经元 促进FLTD-GRN中神经变性的相互作用。为了验证这一点，我们建议1）绘制转录组 和基因调控网络，定义神经胶质病理学和额叶皮层神经元脆弱性， 2）表征视觉系统中神经元和胶质细胞的细胞弹性机制 FTLD-GRN的皮质通过映射其转录组和表观基因组;和3）描绘功能 使用基于IPSC的模型在FTLD-GRN中进行转录组学和表观遗传修饰的后果。这 该项目将提供关键数据，填补有关神经胶质细胞和神经元的轨迹的知识空白 病理学和FTLD-GRN中大脑区域特异性脆弱性和弹性。该项目的成果将 进一步提供了重要的见解，并能够发现预测疾病进展的生物标志物。

Alzheimer’s disease (AD) and the related dementia, frontotemporal lobar degeneration (FTLD), share several key clinical and neuropathological features and have been considered as two ends of a disease spectrum. In support of this, genetic evidence shows that patients with dominant mutations in the Progranulin (GRN) gene invariably develop FTLD with TDP-43 proteinopathy, characterized by the accumulation of RNA binding protein TDP-43 in layers 2-3 of the frontal cortex. Interestingly, single nucleotide polymorphisms (SNPs) in the 3’UTR of the GRN gene reduce Progranulin (PGRN) protein levels and have been associated with increased risk of TDP- 43 proteinopathy in the limbic regions in 30-40% of AD patients. Despite these intriguing genotype-phenotype correlations, how PGRN deficiency promotes glial and neuronal pathology remains poorly understood. To investigate the mechanism of neurodegeneration in PGRN deficiency, we performed single-nuclei RNA- sequencing (snRNA-seq) in the thalamus of Grn-/- mice during the aging process and showed that, in PGRN deficiency, microglia are the first cell type to show progressive loss of homeostatic genes and acquire transcriptomic and histopathological features of a pro-inflammatory state that promotes neuronal cell death and TDP-43 proteinopathy. To connect these results with human disease, we’ve conducted a pilot study by comparing the results from snRNA-seq using postmortem tissues from the frontal cortex and thalamus of FTLD- GRN cases with those from similar brain regions in 19-month-old Grn-/- mice. This human-mouse snRNA-seq comparison revealed shared transcriptomic changes in FTLD-GRN cases and Grn-/- mice, including cellular responses in microglia (exocytosis, immune activation, and chemotaxis) and astrocytes (astrocyte-vascular coupling, cell adhesion, and synaptic organization) in both brain regions. Furthermore, our results uncovered transcriptomic changes in excitatory and inhibitory neurons in the frontal cortex and thalamus of FTLD-GRN cases, suggesting human-specific neuronal vulnerability. Together, these results broach the hypothesis that PGRN deficiency disrupts the gene regulatory network in microglia and astrocytes and alters intricate glia-neuron interactions to promote neurodegeneration in FLTD-GRN. To test this, we propose to 1) Map the transcriptome and gene regulatory network that define glial pathology and neuronal vulnerability in the frontal cortex and thalamus of FTLD-GRN; 2) characterize the mechanism of cellular resilience in neurons and glia in the visual cortex of FTLD-GRN by mapping their transcriptomes and epigenomes; and 3) delineate the functional consequences of transcriptomic and epigenetic modifications in FTLD-GRN using IPSC-based models. This project will provide critical data that fill the knowledge gaps regarding the trajectories of glial and neuronal pathology, and brain region-specific vulnerability and resilience in FTLD-GRN. Results from this project will further provide important insights and enable the discovery of biomarkers that predict disease progression.