Inflammatory microglia with lysosomal and lipid dysfunction drive chronic progressive demyelination

Dysfunctional immune responses impair tissue repair and contribute to neurodegeneration. We examined whether chronic demyelination could drive inflammation towards a pathological, tissue-destructive state. Comparative analysis of genetic and toxic models of acute and chronic demyelination identified a disease-promoting microglial state, characterized by sustained pro-inflammatory activation and enhanced myelin-destructive activity in chronic demyelination. Mechanistically, they exhibited lysosomal cholesterol sequestration with reduced lipid droplet formation. Lipidomic profiling showed defective cholesterol esterification, while transcriptomics uncovered a dysregulated metabolic program marked by upregulated cholesterol synthesis and diminished sterol efflux. Restoring cholesterol homeostasis with a brain-penetrant desmosterol mimetic normalized microglial function, reduced pro-inflammatory activation (e.g. C-C Motif Chemokine Ligand 4 expression), mitigated myelin damage, and improved motor performance in a mouse model of leukodystrophy. Our findings uncover a previously unrecognized pro-inflammatory microglial state characterized by lysosomal dysfunction and increased myelin reactivity, highlighting a novel therapeutic target for demyelinating disorders.