Peroxisomal integrity in myeloid cells is required for myelin debris clearance and remyelination
During demyelination myeloid cells remove myelin debris and promote remyelination. Dysfunctional myeloid cells are associated with peroxisomal leukodystrophies, yet the role of peroxisomes in myeloid cells responding to demyelination remains unknown. The impact of dysfunctional peroxisomes in demyelination-responding myeloid cells was interrogated in Abcd1 and Pex5 knockout mice using the cuprizone model for myelin damage. Abcd1 loss did not affect the demyelination response in myeloid cells, however, Pex5 deficiency impaired remyelination and significantly undermined myelin debris clearance. Molecular analysis in Pex5 depleted macrophages revealed repressed APOE activity and attenuated expression of the sterol exporter pathway integral to myelin debris metabolism, which was associated with an aggravated foamy macrophage phenotype in myelin engulfing myeloid cells. In summary, we report a critical contribution of peroxisomes to myelin debris clearance, myelin lipid processing, and pro-remyelinating properties in myeloid cells. Overall design: Adult mice (8 to 12-weeks, all males) received 100 uL of tamoxifen (20 mg/mL dissolved in corn oil) via intraperitoneal injection daily for five consecutive days. 1 week post injection, mice were fed 0.2% cuprizone diet  (CPZ) or standard chow (baseline) for 6 weeks. After 6 weeks, the mice were perfused with PBS transcardially and the brain was excised and flash frozen in liquid nitrogen. Frozen brain, including corpus callosum, was homogenized to release nuclei, which were stained with DAPI and PI to enable fluorescence-activated nuclei sorting. Purified nuclei were used to generate 10X v3.1 dual index libraries for single nuclei RNA sequencing.