T1R3 Anchors ACE2 at the Pulmonary Endothelial Cell Surface to Attenuate Vascular Injury Following SARS-CoV-2 Spike 1 Protein Exposure In Vitro.

The development of acute lung injury in COVID-19 patients is a major cause of lethality. Activation of the pulmonary vasculature, with inflammation, oxidative stress and barrier disruption, is initiated by the SARS-CoV-2 spike protein (Sp1) at the endothelial cell surface. We previously identified the presence of a novel G-Protein Coupled Receptor (GPCR) in the lung microvasculature, T1R3. The T1R3 agonist (T1R3-A) protects the endothelium from endotoxin-induced lung injury therefore we sought to investigate the effect of T1R3-A on Sp1-induced damage to the pulmonary endothelium. Sp1 induced significant disruption to the endothelium with elevated gap formation, monolayer leak and ROS accumulation. This damage was attenuated following exposure of the lung microvasculature to T1R3-A. We further demonstrated that this agonist promotes ACE2 expression at the endothelial cell surface. Using immunoprecipitation studies, we demonstrated that T1R3-A increases ACE2:T1R3 binding which may be a mechanism for protecting against Sp1-induced endothelial cell injury. Our findings highlight the protective effect of T1R3 activation in the pulmonary endothelium and that there is a close link between T1R3 and ACE2. We propose that T1R3 activation protects the endothelium by preventing Sp1-induced internalisation of ACE2, thereby blocking downstream ACE2 signalling leading to pulmonary vascular injury.