Systemic inflammation differentially modulates the levels of EBI2 and CH25H/CYP7B1 enzymes in the brain microvascular cells.

The endogenous ligand for the EBI2 receptor, oxysterol 7,25OHC, crucial for immune responses, is finely regulated by CH25H, CYP7B1 and HSD3B7 enzymes. Lymphoid stromal cells and follicular dendritic cells within T cell follicles maintain a gradient of 7,25OHC, with stromal cells increasing and dendritic cells decreasing its concentration. This gradient is pivotal for proper B cell positioning in lymphoid tissue. In the animal model of multiple sclerosis, the experimental autoimmune encephalomyelitis, the levels of 7,25OHC rapidly increase in the central nervous system driving the migration of EBI2 expressing immune cells through the blood-brain barrier (BBB). To explore if blood vessel cells in the brain express these enzymes, we examined normal mouse brain microvessels and studied their expression changes during inflammation. EBI2 was abundantly expressed in endothelial cells, pericytes/smooth muscle cells, and astrocytic endfeet. CH25H, CYP7B1, and HSD3B7 were variably detected in each cell type, suggesting their active involvement in oxysterol 7,25OHC synthesis and gradient maintenance under normal conditions. Under acute inflammatory conditions, EBI2 and synthesizing enzyme modulation occurred in brain vasculature, with variations based on the enzyme and cell type. Significant species-specific differences emerged in EBI2 and enzyme levels between mouse and human BBB-forming cells. Overall, our investigation suggest a direct role of the brain microvascular cells in regulating 7,25OHC levels, shedding light on potential therapeutic targets for neuroinflammatory disorders.