Tissue-resident macrophages of the brain, including microglia, are implicated in the pathogenesis of various CNS disorders and are possible therapeutic targets by their chemical depletion or replenishment by hematopoietic stem cell therapy. Nevertheless, a comprehensive understanding of microglial function and the consequences of microglial depletion in the human brain is lacking. In human disease, heterozygous variants in CSF1R, encoding the Colony-stimulating factor 1 receptor, can lead to adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP) possibly caused by microglial depletion. Here, we investigate the effects of ALSP-causing CSF1R variants on microglia and explore the consequences of microglial depletion in the brain. In intermediate- and late-stage ALSP post-mortem brain, we establish that there is an overall loss of homeostatic microglia and that this is predominantly seen in the white matter. By introducing ALSP-causing missense variants into the zebrafish genomic csf1ra locus, we show that these variants act dominant negatively on the number of microglia in vertebrate brain development. Transcriptomics and proteomics on relatively spared ALSP brain tissue validated a downregulation of microglia-associated genes and revealed elevated astrocytic proteins, possibly suggesting involvement of astrocytes in early pathogenesis. Indeed, neuropathological analysis and in vivo imaging of csf1r zebrafish models showed an astrocytic phenotype associated with enhanced, possibly compensatory, endocytosis. Together, our findings indicate that microglial depletion in zebrafish and human disease, likely as a consequence of dominant-acting pathogenic CSF1R variants, correlates with altered astrocytes. These findings underscore the unique opportunity CSF1R variants provide to gain insight into the roles of microglia in the human brain, and the need to further investigate how microglia, astrocytes, and their interactions contribute to white matter homeostasis.

大脑的组织驻留巨噬细胞，包括小胶质细胞，与各种中枢神经系统疾病的发病机制有关，并且通过造血干细胞疗法通过化学耗竭或补充成为可能的治疗靶点。然而，缺乏对小胶质细胞功能和人脑中小胶质细胞耗竭后果的全面了解。在人类疾病中，编码集落刺激因子 1 受体的CSF1R杂合变异可导致成人发病的脑白质病，伴有轴突球体和色素神经胶质细胞 (ALSP)，可能由小胶质细胞耗竭引起。在这里，我们研究了引起 ALSP 的CSF1R的影响小胶质细胞的变异并探索大脑中小胶质细胞耗竭的后果。在中期和晚期 ALSP 死后大脑中，我们确定稳态小胶质细胞整体丧失，这主要见于白质。通过将引起 ALSP 的错义变异引入斑马鱼基因组csf1ra基因座，我们表明这些变异对脊椎动物大脑发育中的小胶质细胞数量起着显性的负面作用。相对保留的 ALSP 脑组织的转录组学和蛋白质组学证实了小胶质细胞相关基因的下调，并揭示了星形胶质细胞蛋白升高，这可能表明星形胶质细胞参与了早期发病机制。事实上， csf1r的神经病理学分析和体内成像斑马鱼模型显示星形胶质细胞表型与增强的、可能是代偿性的内吞作用相关。总之，我们的研究结果表明，斑马鱼和人类疾病中的小胶质细胞耗竭，可能是显性致病性CSF1R变异的结果，与改变的星形胶质细胞相关。这些发现强调了CSF1R变体为深入了解小胶质细胞在人脑中的作用提供的独特机会，以及进一步研究小胶质细胞、星形胶质细胞及其相互作用如何促进白质稳态的必要性。