Foamy microglia link oxylipins to disease progression in multiple sclerosis

Multiple sclerosis (MS) is a chronic neuroinflammatory disease in which demyelinating white matter lesions accumulate and expand, driving irreversible disability. Here we identify a distinct population of foamy GPNMB+ microglia/macrophages associated with lesion expansion in secondary progressive MS. Using integrated lipidomic, transcriptomic, proteomic, chemical proteomic and histological analyses of human postmortem MS lesions, we show that lesions containing foamy microglia/macrophages exhibit disrupted lipid metabolism, lysosomal stress and markers associated with heightened phagocytosis and antigen presentation without classical pro-inflammatory signatures. These lesions are enriched for oxylipins, bismonoacylglycerolphosphates and cholesterol esters, and are associated with increased B cell infiltration and IgG1. Monoacylglycerol lipase (MAGL), a lipid-metabolizing enzyme enriched in lesions with foamy microglia/macrophages, emerged as a potential therapeutic target. Inhibition of MAGL promoted lesion recovery and reduced microgliosis in a mouse model of demyelination. Finally, oxylipins in cerebrospinal fluid correlate with the proportion of foamy lesions, suggesting potential biomarkers for progression. Our findings implicate disturbed lipid metabolism in chronic MS pathology and suggest that foamy microglia/macrophages are an interesting cell type to target for progressive disease.