LPA(2) Alleviates Septic Acute Lung Injury via Protective Endothelial Barrier Function Through Activation of PLC-PKC-FAK

BACKGROUND: Increased endothelial permeability of pulmonary vessels is a primary pathological characteristic of septic acute lung injury (ALI). Previously, elevated lysophosphatidic acid (LPA) levels and LPA(2) (an LPA receptor) expression have been found in the peripheral blood and lungs of septic mice, respectively. However, the specific role of LPA(2) in septic ALI remains unclear. METHODS: A lipopolysaccharide (LPS)-induced model of sepsis was established in wild-type (WT) and global LPA(2) knockout (Lpar2(−/−)) mice. We examined mortality, lung injury, assessed endothelial permeability through Evans blue dye (EBD) assay in vivo, and transendothelial electrical resistance (TEER) of mouse lung microvascular endothelial cells (MLMECs) in vitro. Enzyme-linked immunosorbent assay (ELISA), histopathological, immunofluorescence, immunohistochemistry, and Western blot were employed to investigate the role of LPA(2) in septic ALI. RESULTS: Lpar2 deficiency increased vascular endothelial permeability, impaired lung injury, and increased mortality. Histological examination revealed aggravated inflammation, edema, hemorrhage and alveolar septal thickening in the lungs of septic Lpar2(−/−) mice. In vitro, loss of Lpar2 resulted in increased permeability of MLMECs. Pharmacological activation of LPA(2) by the agonist DBIBB led to significantly reduced inflammation, edema and hemorrhage, as well as increased expression of the vascular endothelial tight junction (TJ) protein zonula occludens-1 (ZO-1) and claudin-5, as well as the adheren junction (AJ) protein VE-cadherin. Moreover, DBIBB treatment was found to alleviate mortality by protecting against vascular endothelial permeability. Mechanistically, we demonstrated that vascular endothelial permeability was alleviated through LPA-LPA(2) signaling via the PLC-PKC-FAK pathway. CONCLUSION: These data provide a novel mechanism of endothelial barrier protection via PLC-PKC-FAK pathway and suggest that LPA(2) may contribute to the therapeutic effects of septic ALI.