Glycolysis drives vascular hyperpermeability in acute lung injury via lactate-GPR81 axis in endothelial cells

A growing body of evidence suggests that enhanced glycolysis profoundly reprograms inflammatory response in acute lung injury (ALI)/ acute respiratory distress syndrome (ARDS), but the underlying mechanisms largely remain unclear. Lactate is the end-product of glycolysis, which has been recently found to function as a bioactive metabolite via G-protein coupled receptor 81 (GPR81). In the present study, the potential roles of lactate-GPR81 axis were investigated in mice with lipopolysaccharide (LPS)-induced ALI. The results indicated that LPS challenge increased the level of lactate in bronchoalveolar lavage fluid (BALF). Pharmacological suppression of glycolysis or inhibition of lactate dehydrogenase decreased lactate level and alleviated lung injury, but supplementation with lactate or a GPR81 agonist exacerbated lung injury. Global deletion of GPR81 or endothelial-specific deletion of GPR81, but not myeloid-specific deletion of GPR81, resulted in alleviated lung injury. In endothelial cells, the differentially expressed genes (DEGs) in RNA-seq after lactate supplementation were enriched in cAMP signaling pathway. Consistently, supplementation with lactate resulted in decline of cAMP, reduction of VE-cadherin and enhanced phosphorylation of myosin light chain 2 (MLC2) in endothelial cells, whereas knockdown of GPR81 reversed these effects. In addition, the modulation of lactate/GPR81 on cAMP, VE-cadherin and MLC2 was validated in GPR81 knockout mice. Importantly, the elevation of lactate is positively correlated with the degree of protein leakage, the level of proinflammatory cytokines in BALF and APACHE II score from patients with ARDS. Taken together, the present study suggests that endothelial GPR81 molecularly bridges glycolysis and inflammation, which drives microvascular hyperpermeability and the development of ALI.