Size-selective opening of the blood–brain barrier by targeting endothelial sphingosine 1–phosphate receptor 1

The vasculature of the central nervous system (CNS) forms a selective barrier termed the blood–brain barrier (BBB). Disruption of the BBB may contribute to various CNS diseases. Conversely, the intact BBB restricts efficient penetration of CNS-targeted drugs. Here, we report the BBB-regulatory role of endothelial sphingosine 1–phosphate (S1P) receptor-1, a G protein-coupled receptor known to promote the barrier function in peripheral vessels. Endothelial-specific S1pr1 knockout mice ( S1pr1 iECKO ) showed BBB breach for small-molecular-mass fluorescence tracers ( 10 kDa). Chronic BBB leakiness was associated with cognitive impairment, as assessed by the novel object recognition test, but not signs of brain inflammation. Brain microvessels of S1pr1 iECKO mice showed altered subcellular distribution of tight junctional proteins. Pharmacological inhibition of S1P 1 function led to transient BBB breach. These data suggest that brain endothelial S1P 1 maintain the BBB by regulating the proper localization of tight junction proteins and raise the possibility that endothelial S1P 1 inhibition may be a strategy for transient BBB opening and delivery of small molecules into the CNS.