Single-cell microglial transcriptomics during demyelination defines a microglial state required for lytic carcass clearance

How microglia respond and regulate demyelination is not fully understood. To understand how microglia respond during demyelination, we fed mice cuprizone and assessed the response of genetically fate-mapped microglia. Cuprizone-induced demyelination generated a robust microglial response. We conducted single-cell RNA sequencing and identified several cuprizone-associated microglia (CAM) clusters during demyelination. These clusters expressed a transcriptomic signature indicative of cytokine regulation and reactive oxygen species production with altered lysosomal and metabolic changes consistent with ongoing phagocytosis. To understand how microglia contribute to the clearance of dead oligodendrocytes, we ablated microglia starting at the peak of cell death. We used the viability dye acridine orange and monitored apoptotic and lytic cell morphologies after microglial ablation and found that microglia preferentially phagocytose lytic carcasses. In culture, microglia exposed to lytic carcasses partially recapitulated the CAM state, suggesting that phagocytosis contributes to this distinct microglial state during cuprizone demyelination. Microglia and Macrophages of the cuprizone-treated and control C57BL/6 mice were isolated by Fluorescence-activated cell sorting (FACS) according to the presence of Cd11b-FITC signal and analyzed using scRNAseq.