Endothelial cell-derived oxysterol ablation attenuates experimental autoimmune encephalomyelitis

The vasculature is a key regulator of leukocyte trafficking into the central nervous system (CNS) during inflammatory diseases including multiple sclerosis. However, the impact of endothelial-derived factors on other aspects of CNS immune responses remains unknown. Bioactive lipids, in particular oxysterols downstream Cholesterol-25-hydroxylase (Ch25h) promote neuroinflammation but their functions in the CNS remain unclear. Using a floxed-reporter Ch25h knock-in mice, we traced Ch25h expression to CNS endothelial cells (ECs) and myeloid cells and demonstrated that Ch25h-specific ablation in ECs attenuates experimental autoimmune encephalomyelitis. Mechanistically, inflamed Ch25h-deficient CNS ECs displayed altered lipid metabolism favoring polymorphonuclear myeloid-derived suppressor cells (PMN-MDSC) expansion relative to other leukocyte subsets that suppress encephalitogenic T lymphocytes proliferation. Finally, endothelial Ch25h-deficiency combined with mobilization of immature neutrophils into circulation resulted in nearly complete EAE protection. Our findings reveal a central role for CNS endothelial-derived Ch25h in promoting neuroinflammation by regulating expansion of immunosuppressive myeloid cell populations. Comparative gene expression profiling analysis of RNA-seq data for primary brain microvascular endothelial cells isolated from Ch25h-sufficient (Ch25hfl/fl x VE-Cadherin-Cre-) or mice with endothelial-specific Ch25h deletion (Ch25hfl/fl x VE-Cadherin-Cre+), treated or not with IL-1beta