Cerebral microvascular endothelial cell-derived extracellular vesicles regulate blood−brain barrier function

Abstract

Abstract Autoreactive T lymphocytes crossing the blood-brain barrier (BBB) into the central nervous system (CNS) play a crucial role in the initiation of demyelination and neurodegeneration in multiple sclerosis (MS). Recently, extracellular vesicles (EV) secreted by BBB endothelial cells (BBB-EC) have emerged as a unique form of cell-to-cell communication that contributes to cerebrovascular dysfunction. However, the precise impact of different size-based subpopulations of BBB-EC-derived EV (BBB-EV) on the early stages of MS remains unclear. Therefore, our objective was to investigate the content and function of distinct BBB-EV subpopulations in regulating BBB integrity and their role in T cell transendothelial migration, both in vitro and in vivo. Our study reveals that BBB-ECs release two distinct size based EV populations, namely small EVs (sEVs; 30-150nm) and large EVs (lEVs; 150-300nm), with a significantly higher secretion of sEVs during inflammation. Notably, the expression patterns of cytokines and adhesion markers differ significantly between these BBB-EV subsets, indicating specific functional differences in the regulation of T cell migration. Through in vitro experiments, we demonstrate that lEVs, which predominantly reflect their cellular source, play a major role in BBB integrity loss and the enhanced migration of proinflammatory Th1 and Th17.1 cells. Conversely, sEVs appear to protect BBB function by inducing an anti-inflammatory phenotype in BBB-ECs. These findings align with our in vivo data, where the administration of sEVs to mice with experimental autoimmune encephalomyelitis (EAE) results in lower disease severity compared to the administration of lEVs, which exacerbates disease symptoms. In conclusion, our study highlights the distinct and opposing effects of BBB-EV subpopulations on the BBB, both in vitro and in vivo. These findings underscore the need for further investigation into the diagnostic and therapeutic potential of BBB-EVs in the context of MS.