Peroxisomal integrity in demyelination-associated microglia enables cellular debris clearance and myelin renewal in mice.

Demyelination associated microglia (DMAM) orchestrate the regenerative response to demyelination by clearing myelin debris and promoting oligodendrocyte maturation. Peroxisomal metabolism has emerged as a candidate regulator of DMAMs, though the cell-intrinsic contribution in microglia remains undefined. Here we elucidate the role of peroxisome integrity in DMAMs, using cuprizone-mediated demyelination coupled with conditional KO of peroxisome biogenesis factor 5 (PEX5) in microglia. Absent demyelination, PEX5 conditional KO (PEX5cKO) had minimal impact on homeostatic microglia. However, during cuprizone-induced demyelination, the emergence of DMAMs unmasked a critical requirement for peroxisome integrity. At peak demyelination, PEX5cKO DMAMs exhibited increased lipid droplet burden and reduced lipophagy suggestive of impaired lipid catabolism. Although lipid droplet burden declined during the remyelination phase, PEX5cKO DMAMs accumulated intralysosomal crystals and curvilinear profiles, features that were largely absent in controls. Aberrant lipid processing was accompanied by elevated numbers of lysosomal damage markers and downregulation of the lipid exporter gene Apoe, consistent with defective lipid clearance. Furthermore, the disruptions in PEX5cKO DMAMs were associated with defective myelin debris clearance and impaired remyelination. Together, these findings delineate a stage-specific role for peroxisomes in coordinating lipid processing pathways essential to DMAM function and for enabling a pro-remyelinating environment.