Apolipoprotein M and sphingosine-1-phosphate complex alleviates TNF-α-induced endothelial cell injury and inflammation through PI3K/AKT signaling pathway

BACKGROUND: In spite of the important role of Apolipoprotein-M (ApoM) and Sphingosine-1-Phosphate (S1P) played in atherosclerosis (AS), there was few related research reporting ApoM and S1P complex (ApoM-S1P) on biological activities of human umbilical vein endothelial cells (HUVECs). In this study, we explored the effect and mechanism of ApoM-S1P on TNF-α-induced inflammation in HUVECs. METHODS: TNF-α was utilized to induce HUVEC injury and inflammation. After HUVECs were treated with antagonists of ApoM, S1P, ApoM + S1P, and ApoM + S1P + S1PR, calcein-acetoxymethyl ester was employed for the assessment of the adhesion of HUVECs to THP-1, immunofluorescence for the observation of caspase-1expression in HUVECs, reactive oxygen species (ROS) kit for the detection of ROS level in HUVECs. The impact of TNF-α, ApoM, S1P and S1PR antagonists on inflammatory response, pyroptosis and adhesion of THP-1 monocytes to HUVECs were determined by detecting expressions of pyroptosis related proteins (IL-1β, IL-18, ASC, NLRP3 and caspase-1), inflammatory cytokines (IL-6 and IL-10), adhesion molecules (E-selectin, ICAM-1, and VCAM-1) and p-PI3K/p-AKT by qRT-PCR and Western blot, as well as by ELISA. RESULTS: TNF-α could increase adhesion of THP-1 monocytes to HUVECs and induce inflammatory response and pyroptosis in HUVECs, indicated by up-regulated expressions of E-selectin, ICAM-1, VCAM-1, IL-1β, IL-18, caspase-1, ASC, NLRP3, and IL-6, and down-regulated expression of IL-10. Co-treatment of ApoM-S1P on TNF-α treated HUVECs could protect HUVECs from injury and inflammation, evidenced by the attenuation of expressions of pyroptosis related proteins, inflammatory cytokines, and adhesion molecules, as well as the augment of PI3K and AKT phosphorylation. JTE-013, an antagonist of S1PR2, could reverse the amelioration of ApoM-S1P on pyroptosis and inflammation of HUVECs, indicating that ApoM-S1P could bind to S1PR2 to protect HUVECs from injury and inflammation through activating PI3K/AKT pathway. CONCLUSION: ApoM-S1P could attenuate TNF-α induced injury and inflammatory response in HUVECs by binding to S1PR2 to activate PI3K/AKT pathway.