Mutations in the human CSF1R gene impact microglia's maintenance of brain white matter integrity.

Microglia, the brain's resident macrophages, depend on interleukin-34 and colony-stimulating factor 1 (CSF1) for their development and maintenance, engaging the CSF1 receptor (CSF1R). Adult-onset leukoencephalopathy with axonal spheroids and pigmented glia (ALSP), a neurodegenerative disorder affecting the brain's white matter, is caused by heterozygous pathogenic mutations in the CSF1R gene. This study investigated molecular mechanisms underlying ALSP using single-nucleus RNA sequencing on postmortem brain specimens. Results showed a significant reduction in microglia in ALSP brains, with remaining cells exhibiting a unique activation signature. This reduction correlated with decreased myelinating oligodendrocytes (OLs) and increased neuropilin-2(+) OLs with a stress-response and anti-apoptotic signature, driven by STAT3 and fibroblast growth factor receptor pathways. Additionally, astrocytes displayed maladaptive activation and stress responses. These findings underscore microglia's crucial role in supporting OL myelination and limiting astrocyte repair responses, suggesting therapeutic strategies balancing CSF1R, fibroblast growth factor receptor and STAT3 pathways for ALSP and other genetically caused microgliopathies.