Dual role of brain endothelial Gpr126 in blood-brain barrier development and ischemic stroke

The blood–brain barrier (BBB) acquires unique properties for regulation of the neuronal function during development. The genesis of the BBB coupled with angiogenesis is orchestrated by the Wnt/β-catenin signaling pathway. Aside from the importance of Wnt/β-catenin signaling, the molecular mechanisms that regulate these processes are poorly understood. Here, we identify the brain endothelial adhesion G-protein–coupled receptor Gpr126 as a novel target gene of Wnt/β-catenin signaling that is required for postnatal BBB development, and its expression is detrimental for ischemic stroke in adults. We show that Gpr126 expression is high in mouse brain endothelium during BBB formation, but decreases in the adult. Inactivation of Gpr126 in postnatal endothelial cells results in vessel enlargement and impairs acquisition of the BBB characteristics, such as increased neurovascular permeability, and reduced basement membrane protein deposition and pericyte coverage. Mechanistically, Gpr126 is required during developmental angiogenesis to promote endothelial cell migration, acting via an interaction between Lrp1 and α3β1-integrin, which couples vessel morphogenesis to BBB formation. Interestingly, in adult mice with an established BBB, the lack of Gpr126 expression in acute ischemic stroke is protective and coupled with reduced microglia activation, which contributes to an improved neurological outcome. These data identify Gpr126 as a promising therapeutic target to treat ischemic stroke. ### Competing Interest Statement The authors have declared no competing interest. * AU : arbitrary units BBB : blood-brain barrier BM : basement membrane cAMP : cyclic adenosine monophosphate (or 3’,5’-cyclic adenosine monophosphate) cBECs : cultured murine endothelial cells derived from the brain microvasculature cLEC : cultured lung-derived endothelial cells CNS : central nervous system CREB : cAMP response-element binding protein ECM : extracellular matrix ECs : endothelial cells eGFP : enhanced green fluorescent protein fBECs : freshly isolated brain endothelial cells fLECs : freshly isolated lung endothelial cells GAIN : GPCR autoproteolysis-inducing domain GO : gene ontology GPCRs : G-protein–coupled receptors JAM-A : junctional adhesion molecule-A MCAo : middle cerebral artery occlusion NS : not statistically significant NVU : neurovascular unit PECAM-1 : platelet/endothelial cell adhesion molecule-1 RT-qPCR : real time quantitative polymerase chain reaction TJs : tight junctions VEC : vascular endothelial cadherin WT : wild-type