The proton-sensing GPR4 receptor regulates paracellular gap formation and permeability of vascular endothelial cells
Tissue acidosis can be a consequence of numerous disease states including stroke, myocardial infarction, limb ischemia, and inflammation. Blood vessels existing in the affected tissues are associated with the progression of acidosis-related diseases. However, the mechanisms by which endothelial cells (ECs) lining the affected blood vessels sense and respond to an acidic microenvironment remain largely unclear. We investigated the functional effects of the proton-sensing G protein-coupled receptor GPR4 in acidosis-induced endothelial inflammation. GPR4 is highly expressed in ECs and known to regulate EC inflammation and endoplasmic reticulum stress responses within acidic microenvironments. Using genetic and pharmacological approaches, we demonstrate that GPR4 activation by acidosis increases EC paracellular gap formation and permeability. We further demonstrate that GPR4-mediated paracellular gap formation is dependent on the G12/13 signaling pathway. To assess the functional role of GPR4 in the inflammatory response in vivo, we utilized an acute hindlimb ischemia-reperfusion mouse model. We demonstrate that both genetic deletion and pharmacological inhibition of GPR4 reduce tissue edema, exudate formation, endothelial adhesion molecule expression, and leukocyte infiltration in the inflamed tissue. Collectively, these data suggest GPR4/G12/13 signaling mediates acidosis-induced endothelial paracellular gap formation and permeability. This study implicates GPR4 as a candidate therapeutic target for the remediation of inflammation and tissue edema.