Single nucleus analysis of brain tissues from DAP12 loss-of-function (Kdelta75) mice

The TREM2-DAP12 receptor complex sustains microglia functions. Heterozygous TREM2 variants subtly impair microglia, facilitating manifestation of Alzheimer's Disease in the elderly. Homozygous inactivating mutations of TREM2 or DAP12 cause Nasu-Hakola disease (NHD), an early-onset dementia with leukoencephalopathy, myelin loss and gliosis. Here we investigated the impact of DAP12 deficiency in microglia and collateral damage to other brain cells by single-nucleus RNA-seq in NHD patients and DAP12 loss-of-function (Kdelta75) mice. Kdelta75 mice showed signatures of impaired microglia activation that reverberated in mild dysfunction of other brain cells. Paradoxically, NHD microglia were activated and associated with astrocytosis, hypoxia, and neuronal loss signatures. We envision that Kdelta75 signatures recapitulate an early NHD stage in which DAP12-deficient microglia fail to clear toxic products generated during brain development and homeostasis. Conversely, NHD signatures reflect a late disease stage in which accumulated toxic products cause a widespread tissue damage that elicits TREM2-DAP12-independent microgliosis, astrogliosis, hypoxia, and neuronal death. This TREM2-DAP12-independent microglia activation in NHD has bearing on potential microglia-based therapies. Compare the transcriptomics of Kdelta75 with WT controlsTREM2-DAP12受体复合物（TREM2-DAP12 receptor complex）可维持小胶质细胞（microglia）的功能。杂合型TREM2变异会轻度损伤小胶质细胞，促使老年群体出现阿尔茨海默病（Alzheimer's Disease）表型。TREM2或DAP12的纯合失活突变会引发纳苏-哈科拉病（Nasu-Hakola disease, NHD），这是一种早发性痴呆，伴随脑白质病、髓鞘脱失及胶质增生。本研究通过对纳苏-哈科拉病患者及DAP12功能丧失型（loss-of-function）Kdelta75小鼠开展单细胞核RNA测序（single-nucleus RNA-seq），探究了DAP12缺失对小胶质细胞的影响，及其对其他脑细胞的间接损伤效应。Kdelta75小鼠呈现出小胶质细胞活化受损的特征，该特征可波及其他脑细胞，引发轻度功能异常。令人意外的是，纳苏-哈科拉病患者的小胶质细胞却处于活化状态，且与星形胶质细胞增生、缺氧及神经元丢失的特征相关。我们推测，Kdelta75小鼠的转录组特征可复现纳苏-哈科拉病的早期阶段：此时DAP12缺失的小胶质细胞无法清除脑发育及内稳态过程中产生的毒性产物。反之，纳苏-哈科拉病的转录组特征则反映了疾病晚期阶段：此时累积的毒性产物引发广泛的组织损伤，进而诱导不依赖TREM2-DAP12的小胶质细胞活化、星形胶质细胞增生、缺氧及神经元死亡。纳苏-哈科拉病中这种不依赖TREM2-DAP12的小胶质细胞活化，为基于小胶质细胞的潜在治疗策略提供了研究依据。本研究对比了Kdelta75小鼠与野生型（WT）对照组的转录组学特征。