Microglia protect against age-associated brain pathologies

Microglia are brain-resident macrophages that contribute to central nervous system development, maturation, and preservation. Here, we examine the consequences of lifelong absence of microglia on ageing using the Csf1rΔFIRE/ΔFIRE mouse model. In juvenile Csf1rΔFIRE/ΔFIRE mice, we show that microglia are largely dispensable for the transcriptomic maturation of other brain cell types. In contrast, with advancing age, multiple pathologies accumulate in Csf1rΔFIRE/ΔFIRE brains, astrocytes and oligodendrocyte-lineage cells become increasingly dysregulated, and white matter integrity declines, mimicking many of the pathological features of human CSF1R-related leukoencephalopathy. The thalamus is particularly sensitive to neuropathological changes in the absence of microglia, with atrophy, neuron loss, vascular disturbances, macroglial dysregulation, and severe calcifications all detected in this region. Thalamic calcification formation, which often occurs with normal ageing, is dramatically accelerated in Csf1rΔFIRE/ΔFIRE brains but can be prevented via transplantation of wild-type microglia. Our results indicate that lifelong absence of microglia results in an age-related neurodegenerative condition that can be prevented by the transplantation of healthy microglia.