Abstract: Objective To investigate whether knockout of S1PR3 improves lipopolysaccharide (LPS)-induced acute lung injury in mice by inhibiting mitogen activated protein kinases (MAPKs). Methods Male C57BL/6J and S1PR3 knockout (S1PR3-/-) mice were both randomized into two groups (n=8) for intratracheal instillation of normal saline or LPS to induce acute lung injury. The expressions of S1PR3, IL-1β and IL-18 in the lung tissues were detected using RT-qPCR, lung tissue injury was observed with HE staining, and cell apoptosis was detected using flow cytometry. Western blotting was performed to detect the expression levels of caspase-1, GSDMD, p- JNK, p-ERK and p-p38 proteins. In the cell experiment, type II alveolar epithelial cells (MLE-12 cells) were treated with PBS, LPS, CYM5541 (a S1PR3 agonist), or CYM5541 + LPS, and the cell apoptosis and expression levels of MAPK signal pathway molecules were detected. Results The expression of S1PR3 was up-regulated and serum IL-1β and IL-18 levels were elevated significantly in the nontransgenic mice with acute lung injury (P<0.001). By comparison, the elevation of IL-1β and IL-18 levels was obviously reduced in S1PR3 knockout mice with acute lung injury, which also showed significant improvement of pulmonary hemorrhage, inflammation and exudation, lowered wet-to-dry ratio of the lungs, and decreased cell apoptosis and expressions of cleaved caspase-1 and GSDMD (P<0.05). In MLE-12 cells, treatment with the S1PR3 agonist significantly increased the expression of pyroptosis-associated proteins (P<0.05). S1PR3 knockout strongly inhibited the activation of MAPKs family (JNK and ERK p38; P<0.05), but their expressions were significantly increased following treatment with the S1PR3 agonist (P<0.05). Conclusion Inhibition of S1PR3 can improve LPS-induced acute lung injury in mice by inhibiting the activation of MAPK signaling.

Key words: S1PR3; acute lung injury; MAPK pathway; cell pyroptosis; CYM5541