Non-ionotropic action of endothelial NMDA receptors on blood-brain barrier permeability via Rho/ROCK mediated phosphorylation of myosin

Increase in blood-brain barrier (BBB) permeability is a crucial step in neuroinflammatory processes. We previously showed that N methyl-D-aspartate (NMDA) receptors, expressed on cerebral endothelial cells forming the BBB, regulate immune cell infiltration across this barrier in the mouse. Here, we describe the mechanism responsible for the action of NMDA receptors on BBB permeabilization. We report that mouse CNS endothelial NMDA receptors display the regulatory GluN3A subunit. This composition confers to NMDA receptors unconventional properties: these receptors do not induce Ca2+ influx, but rather show non-ionotropic properties. In inflammatory conditions, co-stimulation of human brain endothelial cells by NMDA agonists (NMDA or glycine) and the serine protease tissue plasminogen activator (tPA) -previously shown to potentiate NMDA receptor activity- induces metabotropic signalling via Rho/ROCK pathway. This pathway leads to an increase in permeability via phosphorylation of myosin light chain and subsequent shrinkage of human brain endothelial cells. Together, these data draw a link between NMDA receptors and the cytoskeleton in brain endothelial cells that regulates BBB permeability in inflammatory conditions. SIGNIFICANCE STATEMENT The authors describe how NMDA receptors expressed on endothelial cells regulate blood-brain barrier function via myosin light chain phosphorylation and increase in permeability. They report that these non-neuronal NMDA receptors display distinct structural, functional and pharmacological features than their neuronal counterparts.