Direct microglia replacement reveals pathologic and therapeutic contributions of brain macrophages to a monogenic neurological disease [RNA-seq]

Krabbe disease, also named Globoid Cell Leukodystrophy (GLD) for its distinct lipid- laden macrophages, is a severe leukodystrophy caused by galactosylceramidase (GALC) mutations. Hematopoietic stem cell transplant (HSCT) ameliorates disease and is associated with central nervous system (CNS) engraftment of GALC+ donor macrophages. Yet, the role of macrophages in GLD pathophysiology and HSCT remains unclear. Using single-cell sequencing we revealed early interferon response signatures which precede progressively severe macrophage dyshomeostasis, and identified a molecular signature of globoid cells, which we validated in human brain specimens. Genetic depletion and direct microglia replacement by CNS monocyte injection rapidly replaced >80% of endogenous microglia with healthy monocytes in the twitcher (GalcW355*) mouse, a faithful model of GLD. Perinatal microglia replacement completely normalized transcriptional signatures, rescued histopathology, and doubled average survival. Overall, we uncovered distinct forms of microglia dysfunction, and evidence that direct, CNS-limited microglia replacement improves a monogenic neurodegenerative disease, a promising therapeutic target.