ABSTRACT
Endothelial dysfunction plays a vital role during the initial stage of atherosclerosis. Oxidized low-density lipoprotein (ox-LDL) induces vascular endothelial injury and vessel wall inflammation. Sphingosine-1-phosphate (S1P) exerts numerous vasoprotective effects by binding to diverse S1P receptors (S1PRs; S1PR1-5). A number of studies have shown that in endothelial cells (ECs), S1PR2 acts as a pro-atherosclerotic mediator by stimulating vessel wall inflammation through the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway. Scavenger receptor class B member I (SR-BI), a high-affinity receptor for apolipoprotein A-I (apoA-I)/high-density lipoprotein (HDL), inhibits nuclear factor-κB (NF-κB) translocation and decreases the plasma levels of inflammatory mediators via the PI3K/Akt pathway. We hypothesized that the inflammatory effects of S1P/S1PR2 on ECs may be regulated by apoA-I/SR-BI. The results showed that ox-LDL, a pro-inflammatory factor, augmented the S1PR2 level in human umbilical vein endothelial cells (HUVECs) in a dose- and time-dependent manner. In addition, S1P/S1PR2 signaling influenced the levels of inflammatory factors, including tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and IL-10, aggravating inflammation in HUVECs. Moreover, the pro-inflammatory effects induced by S1P/S1PR2 were attenuated by SR-BI overexpression and enhanced by an SR-BI inhibitor, BLT-1. Further experiments showed that the PI3K/Akt signaling pathway was involved in this process. Taken together, these results demonstrate that apoA-I/SR-BI negatively regulates S1P/S1PR2-mediated inflammation in HUVECs by activating the PI3K/Akt signaling pathway (AU)
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Subject(s)
Humans , Endothelium, Vascular/metabolism , Lysophospholipids/metabolism , Scavenger Receptors, Class B/agonists , Receptors, Lysosphingolipid/agonists , Sphingosine/analogs & derivatives , Signal Transduction , Phosphatidylinositol 3-Kinases/metabolism , Gene Expression Regulation , Active Transport, Cell Nucleus , Cyclopentanes/pharmacology , Thiosemicarbazones/pharmacology , Tumor Necrosis Factor-alpha , Human Umbilical Vein Endothelial Cells , Lipoproteins, LDL , Proto-Oncogene Proteins c-aktABSTRACT
Endothelial dysfunction plays a vital role during the initial stage of atherosclerosis. Oxidized low-density lipoprotein (ox-LDL) induces vascular endothelial injury and vessel wall inflammation. Sphingosine-1-phosphate (S1P) exerts numerous vasoprotective effects by binding to diverse S1P receptors (S1PRs; S1PR1-5). A number of studies have shown that in endothelial cells (ECs), S1PR2 acts as a pro-atherosclerotic mediator by stimulating vessel wall inflammation through the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway. Scavenger receptor class B member I (SR-BI), a high-affinity receptor for apolipoprotein A-I (apoA-I)/high-density lipoprotein (HDL), inhibits nuclear factor-κB (NF-κB) translocation and decreases the plasma levels of inflammatory mediators via the PI3K/Akt pathway. We hypothesized that the inflammatory effects of S1P/S1PR2 on ECs may be regulated by apoA-I/SR-BI. The results showed that ox-LDL, a pro-inflammatory factor, augmented the S1PR2 level in human umbilical vein endothelial cells (HUVECs) in a dose- and time-dependent manner. In addition, S1P/S1PR2 signaling influenced the levels of inflammatory factors, including tumor necrosis factor-α (TNF-α), interleukin-1ß (IL-1ß), and IL-10, aggravating inflammation in HUVECs. Moreover, the pro-inflammatory effects induced by S1P/S1PR2 were attenuated by SR-BI overexpression and enhanced by an SR-BI inhibitor, BLT-1. Further experiments showed that the PI3K/Akt signaling pathway was involved in this process. Taken together, these results demonstrate that apoA-I/SR-BI negatively regulates S1P/S1PR2-mediated inflammation in HUVECs by activating the PI3K/Akt signaling pathway.
Subject(s)
Apolipoprotein A-I/metabolism , Endothelium, Vascular/metabolism , Lysophospholipids/metabolism , Phosphatidylinositol 3-Kinase/metabolism , Receptors, Lysosphingolipid/agonists , Scavenger Receptors, Class B/agonists , Signal Transduction , Sphingosine/analogs & derivatives , Active Transport, Cell Nucleus/drug effects , Apolipoprotein A-I/genetics , Cells, Cultured , Cyclopentanes/pharmacology , Endothelium, Vascular/cytology , Endothelium, Vascular/drug effects , Endothelium, Vascular/immunology , Gene Expression Regulation/drug effects , Human Umbilical Vein Endothelial Cells/cytology , Human Umbilical Vein Endothelial Cells/drug effects , Human Umbilical Vein Endothelial Cells/immunology , Human Umbilical Vein Endothelial Cells/metabolism , Humans , Interleukin-10/agonists , Interleukin-10/metabolism , Interleukin-1beta/agonists , Interleukin-1beta/metabolism , Kinetics , Lipoproteins, LDL/adverse effects , Lipoproteins, LDL/genetics , Lipoproteins, LDL/metabolism , Proto-Oncogene Proteins c-akt/agonists , Proto-Oncogene Proteins c-akt/metabolism , Receptors, Lysosphingolipid/genetics , Receptors, Lysosphingolipid/metabolism , Recombinant Proteins/chemistry , Recombinant Proteins/metabolism , Scavenger Receptors, Class B/antagonists & inhibitors , Scavenger Receptors, Class B/genetics , Scavenger Receptors, Class B/metabolism , Signal Transduction/drug effects , Sphingosine/metabolism , Sphingosine-1-Phosphate Receptors , Thiosemicarbazones/pharmacology , Tumor Necrosis Factor-alpha/agonists , Tumor Necrosis Factor-alpha/metabolismABSTRACT
OBJECTIVE: To develop a new high-throughput screening model for human high-density lipoprotein (HDL) receptor (CD36 and LIMPII analogous-1, CLA-1) agonists using CLA-1-expressing insect cells. METHODS: With the total RNA of human hepatoma cells BEL-7402 as template, the complementary DNA (cDNA) of CLA-1 was amplified by reverse transcription-polymerase chain reaction (RT-PCR). Bac-to-Bac baculovirus expression system was used to express CLA-1 in insect cells. CLA-1 cDNA was cloned downstream of polyhedrin promoter of Autographa californica nuclear polyhedrosis virus (AcNPV) into donor vector pFastBac1 and recombinant pFastBac1-CLA-1 was transformed into E. coli DH10Bac to transpose CLA-1 cDNA to bacmid DNA. Recombinant bacmid-CLA-1 was transfected into Spodoptera frugiperda Sf9 insect cells to produce recombinant baculovirus particles. Recombinant CLA-1 was expressed on the membrane of Sf9 cells infected with the recombinant baculoviruses. A series of parameters of DiI-lipoprotein binding assays of CLA-1-expressing Sf9 cells in 96-well plates were optimized. RESULTS: Western blot analysis and DiI-lipoprotein binding assays confirmed that CLA-1 expressed in insect cells had similar immunoreactivity and ligand binding activity as its native counterpart. A reliable and sensitive in vitro cell-based assay was established to assess the activity of CLA-1 and used to screen agonists from different sample libraries. CONCLUSION: Human HDL receptor CLA-1 was successfully expressed in Sf9 insect cells and a novel high-throughput screening model for CLA-1 agonists was developed. Utilization of this model allows us to identify potent and selective CLA-1 agonists which might possibly be used as therapeutics for atherosclerosis.