Plasma components to protect the endothelial barrier after shock: A role for sphingosine 1-phosphate.

BACKGROUND: Hemorrhagic shock leads to endothelial glycocalyx shedding, endothelial cellular inflammation, and increased vascular permeability. Early plasma administration improves survival in severely injured patients; this may be due in part to its ability to ameliorate this trauma-induced endotheliopathy. The protective effect of early plasma administration may be due to its sphingosine 1-phosphate content. Principle carriers of plasma sphingosine 1-phosphate include apolipoprotein M and albumin. The relative roles of these carriers on sphingosine 1-phosphate protective effects are unknown and were studied in an in vitro model of microcirculation. METHODS: Endothelial cell monolayers were established in microfluidic perfusion devices and exposed to control or biomimetic shock conditions. Sphingosine 1-phosphate, albumin + sphingosine 1-phosphate, or apolipoprotein M + sphingosine 1-phosphate were added later to the perfusate. Biomarkers of endothelial and glycocalyx activation and damage were then determined. RESULTS: Sphingosine 1-phosphate preserved endothelial and glycocalyx barrier function after exposure to conditions of shock in the microcirculation. The protective effect was related to sphingosine 1-phosphate chaperones; the apolipoprotein M loaded with sphingosine 1-phosphate had the most profound effect. CONCLUSION: Carrier-based sphingosine 1-phosphate may be a useful adjunct in early hemorrhagic shock resuscitation.

Propofol promotes migration, alleviates inflammation, and apoptosis of lipopolysaccharide-induced human pulmonary microvascular endothelial cells by activating PI3K/AKT signaling pathway via upregulating APOM expression.

Propofol (PRO), a clinical potent intravenous anesthetic, plays a significant role in relieving inflammatory diseases by repressing the release of inflammatory cytokines. The present study was aimed to reveal a novel mechanism by which PRO alleviates acute lung injury (ALI). Lipopolysaccharide (LPS) was utilized to induce human pulmonary microvascular endothelial cells (HPMECs) so as to simulate the microenvironment of ALI, and the expression of apolipoprotein M (APOM) was examined with western blotting. Then, APOM was silenced and profopol was used to treat the LPS-injured HPMECs. The cell viability, migration, and apoptosis were respectively observed after the processes of cell counting kit-8, wound healing, transwell, and TUNEL assay. Meanwhile, the inflammatory response was detected by determining the contents of inflammatory cytokines. Subsequently, the relationship between phosphoinositide-3 kinase (PI3K)/protein kinase B (AKT) signaling pathway and PRO was analyzed by western blotting. PI3K/AKT inhibitor LY294002 was employed to evaluate whether the effects of PRO on LPS-challenged HPMECs injury were mediated by this pathway. Results revealed that APOM was notably downregulated in HPMECs after LPS exposure. PRO treatment promoted cell proliferation and migration while alleviated inflammation and apoptosis of LPS-treated HPMECs, which was reversed by APOM-downregulation. PRO brought about the upregulation of proteins in PI3K/AKT signaling pathway, and LY294002 intervention further accentuated the impacts of APOM-knockdown on LPS-challenged HPMECs injury. To conclude, PRO promotes migration and alleviates inflammation and apoptosis of LPS-treated HPMECs by PI3K/AKT signaling pathway via upregulating APOM, which laid an experimental foundation for the future study and clinical application of PRO.

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-1ß, 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-1ß, 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.

ApoM-S1P Modulates Ox-LDL-Induced Inflammation Through the PI3K/Akt Signaling Pathway in HUVECs.

Studies have shown that apolipoprotein M (apoM), the main carrier of sphingosine-1-phosphate (S1P), is closely related to lipid metabolism and inflammation. While there are many studies on apoM and lipid metabolism, little is known about the role of apoM in inflammation. Atherosclerosis is a chronic inflammatory process. To clarify what role apoM plays in atherosclerosis, we used oxidized low-density lipoprotein (ox-LDL) to induce an inflammatory model of atherosclerosis. Our preliminary results indicate that ox-LDL upregulates the expression of S1P receptor 2 (S1PR2) in human umbilical vein endothelial cells (HUVECs). Ox-LDL-induced HUVECs were treated with apoM-bound S1P (apoM-S1P), free S1P or apoM, and apoM-S1P was found to significantly inhibit the expression of inflammatory factors and adhesion molecules. In addition, apoM-S1P inhibits ox-LDL-induced cellular inflammation via S1PR2. Moreover, apoM-S1P induces phosphorylation of phosphatidylinositol 3-kinase (PI3K)/Akt, preventing nuclear translocation of nuclear factor-κB (NF-κB). PI3K-specific inhibitors and Akt inhibitors suppress apoM-S1P/S1PR2-induced interleukin-1ß (IL-1ß) and tumor necrosis factor-α (TNF-α) release and affect nuclear translocation of NF-κB. In conclusion, the results demonstrate for the first time that apoM-S1P inhibits ox-LDL-induced inflammation in HUVECs via the S1PR2-mediated PI3K/Akt signaling pathway. This finding may aid in the development of new treatments for atherosclerosis.

Sphingosine 1-Phosphate Receptor 1 Signaling Maintains Endothelial Cell Barrier Function and Protects Against Immune Complex-Induced Vascular Injury.

OBJECTIVE: Immune complex (IC) deposition activates polymorphonuclear neutrophils (PMNs), increases vascular permeability, and leads to organ damage in systemic lupus erythematosus and rheumatoid arthritis. The bioactive lipid sphingosine 1-phosphate (S1P), acting via S1P receptor 1 (S1P1 ), is a key regulator of endothelial cell (EC) barrier function. This study was undertaken to investigate whether augmenting EC integrity via S1P1 signaling attenuates inflammatory injury mediated by ICs. METHODS: In vitro barrier function was assessed in human umbilical vein endothelial cells (HUVECs) by electrical cell-substrate impedance sensing. Phosphorylation of myosin light chain 2 (p-MLC-2) and VE-cadherin staining in HUVECs were assessed by immunofluorescence. A reverse Arthus reaction (RAR) was induced in the skin and lungs of mice with S1P1 deleted from ECs (S1P1 EC-knockout [ECKO] mice) and mice treated with S1P1 agonists and antagonists. RESULTS: S1P1 agonists prevented loss of barrier function in HUVECs treated with IC-activated PMNs. S1P1 ECKO and wild-type (WT) mice treated with S1P1 antagonists had amplified RAR, whereas specific S1P1 agonists attenuated skin and lung RAR in WT mice. ApoM-Fc, a novel S1P chaperone, mitigated EC cell barrier dysfunction induced by activated PMNs in vitro and attenuated lung RAR. Expression levels of p-MLC-2 and disruption of VE-cadherin, each representing manifestations of cell contraction and destabilization of adherens junctions, respectively, that were induced by activated PMNs, were markedly reduced by treatment with S1P1 agonists and ApoM-Fc. CONCLUSION: Our findings indicate that S1P1 signaling in ECs modulates vascular responses to IC deposition. S1P1 agonists and ApoM-Fc enhance the EC barrier, limit leukocyte escape from capillaries, and provide protection against inflammatory injury. The S1P/S1P1 axis is a newly identified target to attenuate tissue responses to IC deposition and mitigate end-organ damage.

Apolipoprotein M Inhibits Angiogenic and Inflammatory Response by Sphingosine 1-Phosphate on Retinal Pigment Epithelium Cells.

Sphingosine 1-phosphate (S1P) is a potent lipid mediator that modulates inflammatory responses and proangiogenic factors. It has been suggested that S1P upregulates choroidal neovascularization (CNV) and may be deeply involved in the pathogenesis of exudative age-related macular degeneration (AMD). Recent studies have suggested that apolipoprotein M (ApoM), a carrier protein for S1P, modulates the biological properties of S1P in the pathogenesis of atherosclerosis. However, the role of ApoM/S1P in AMD has not been explored. We investigated the effect of S1P on proangiogenic factors in human retinal pigment epithelium (RPE) cell lines in vitro. S1P promoted the expression of vascular endothelial growth factor in RPE cells. Hypoxia inducible factor-1α expression was also upregulated. These S1P-induced enhancements in growth factors and chemotactic cytokines in RPE cells were significantly inhibited by ApoM treatment. Additionally, in vivo experiments using a laser-induced CNV murine model demonstrated that intravitreal ApoM injection significantly reduced the progression of CNV formation. Although the detailed mechanisms remain to be elucidated, the present results provide a novel potential therapeutic target for AMD, and demonstrate a suppressive role for ApoM and S1P in the pathology of CNV progression.