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We characterized the molecular mechanisms by which high density lipoprotein (HDL) inhibits the expression of adhesion molecules, including vascular cell adhesion molecule-1 and intercellular adhesion molecule-1, induced by sphingosine 1-phosphate (S1P) and tumor necrosis factor (TNF) ␣ in endothelial cells. HDL inhibited S1P-induced nuclear factor B activation and adhesion molecule expression in human umbilical vein endothelial cells. The inhibitory HDL actions were associated with nitric-oxide synthase (NOS) activation and were reversed by inhibitors for phosphatidylinositol 3-kinase and NOS. The HDL-induced inhibitory actions were also attenuated by the down-regulation of scavenger receptor class B type I (SR-BI) and its associated protein PDZK1. When TNF␣ was used as a stimulant, the HDL-induced NOS activation and the inhibitory action on adhesion molecule expression were, in part, attenuated by the down-regulation of the expression of S1P receptors, especially S1P 1 , in addition to SR-BI. Reconstituted HDL composed mainly of apolipoprotein A-I and phosphatidylcholine mimicked the SR-BI-sensitive part of HDL-induced actions. Down-regulation of S1P 3 receptors severely suppressed the stimulatory actions of S1P. Although G i/o proteins may play roles in either stimulatory or inhibitory S1P actions, as judged from pertussis toxin sensitivity, the coupling of S1P 3 receptors to G 12/13 proteins may be critical to distinguish the stimulatory pathways from the inhibitory ones. In conclusion, even though S1P alone stimulates adhesion molecule expression, HDL overcomes S1P 3 receptor-mediated stimulatory actions through SR-BI/PDZK1-mediated signaling pathways involving phosphatidylinositol 3-kinase and NOS. In addition, the S1P component of HDL plays a role in the inhibition of TNF␣-induced actions through S1P receptors, especially S1P 1 .The plasma level of HDL 2 has been shown to be inversely correlated with the risk of atherosclerosis and associated cardiovascular disease (1, 2). HDL can remove excess cholesterol from arterial and nonliver cells, transport it to the liver, and excrete it as bile acids. The so-called reverse cholesterol transport is thought to be an important anti-atherogenic action of HDL (1, 2). In recent studies, however, HDL has been shown to exert a variety of actions that are independent of cholesterol metabolism. For example, HDL inhibits LDL oxidation, smooth muscle cell migration, platelet aggregation, and endothelial dysfunction (3, 4). The inhibition of endothelial dysfunction may be achieved by several responses to HDL, including the stimulation of proliferation, cell survival, migration, and NO synthesis, or the inhibition of apoptosis and of the expression of adhesion molecules, such as vascular cell adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) (3-5). An increase in the expression of the adhesion molecules stimulates monocyte interaction with endothelial cells and cell penetration into subendothelial space or the intima of arterial walls. Thus, the expr...

Objective-Plasma high-density lipoprotein (HDL) level is inversely correlated with the risk of atherosclerosis. However, the cellular mechanism by which HDL exerts antiatherogenic actions is not well understood. In this study, we focus on the lipid components of HDL as mediators of the lipoprotein-induced antiatherogenic actions. Methods and Results-HDL and sphingosine 1-phosphate (S1P) stimulated the migration and survival of human umbilical vein endothelial cells. These responses to HDL and S1P were almost completely inhibited by pertussis toxin and other specific inhibitors for intracellular signaling pathways, although the inhibition profiles of migration and survival were different. The HDL-stimulated migration and survival of the cells were markedly inhibited by antisense oligonucleotides against the S1P receptors EDG-1/S1P 1 and EDG-3/S1P 3 . Cell migration was sensitive to both receptors, but cell survival was exclusively sensitive to S1P 1 . The S1P-rich fraction and chromatographically purified S1P from HDL stimulated cell migration, but the rest of the fraction did not, as was the case of the cell survival. Key Words: high-density lipoprotein Ⅲ sphingosine 1-phosphate Ⅲ migration Ⅲ EDG Ⅲ endothelial cell P lasma lipoproteins are responsible for the transport of cholesterol to cells and the control of cholesterol synthesis. 1-3 Low-density lipoprotein (LDL) provides cholesterol to cells through LDL receptors, whereas high-density lipoprotein (HDL) has been shown to remove excess cholesterol from the cells. The so-called reverse transport of cholesterol is thought to be an important mechanism for the antiatherogenic actions of HDL. 1,2 Recent studies have shown that HDL induces cytoprotective actions, 3,4 proliferation, 5 and migration in endothelial cells, 2,6 activities presumably independent of cholesterol metabolism, 2,3 although the mechanism by which HDL induces these antiatherogenic actions has not been well characterized. It has been reported recently that HDL activates endothelial nitric oxide (NO) production through the scavenger receptor-BI (SR-BI). 7 NO production has been shown to be involved in the cytoprotective action of endothelial cells. 8 In endothelial cells, sphingosine 1-phosphate (S1P) has been shown to regulate a wide range of cellular activities associated with angiogenesis, wound healing, apoptosis, and atherosclerosis. 3,4,8 -18 S1P promotes cell migration, 10 -13,16 -18 DNA synthesis, 10 cell survival, 4,9 cell barrier integrity, 15 NO production, 8,14,16,17 and the expression of several cell adhesion molecules. 3 We recently reported that S1P accumulates in the lipoprotein fraction, especially the HDL fraction, and that HDL-associated S1P mediates the cytoprotective actions of HDL in human umbilical vein endothelial cells (HUVECs). 4,19 Nofer et al 20 reported that sphingosylphosphorylcholine (SPC) and lysosulfatide (LSF) were major components of HDL responsible for these cytoprotective actions. Thus, lipoproteinassociated lipids may also be involved in some HDL-induced...

BACKGROUND A protein that is expressed on capillary endothelial cells, called GPIHBP1 (glycosylphosphatidylinositol-anchored high-density lipoprotein binding protein 1), binds lipoprotein lipase and shuttles it to its site of action in the capillary lumen. A deficiency in GPIHBP1 prevents lipoprotein lipase from reaching the capillary lumen. Patients with GPIHBP1 deficiency have low plasma levels of lipoprotein lipase, impaired intravascular hydrolysis of triglycerides, and severe hypertriglyceridemia (chylomicronemia). During the characterization of a monoclonal antibody–based immunoassay for GPIHBP1, we encountered two plasma samples (both from patients with chylomicronemia) that contained an interfering substance that made it impossible to measure GPIHBP1. That finding raised the possibility that those samples might contain GPIHBP1 autoantibodies. METHODS Using a combination of immunoassays, Western blot analyses, and immunocytochemical studies, we tested the two plasma samples (as well as samples from other patients with chylomicronemia) for the presence of GPIHBP1 autoantibodies. We also tested the ability of GPIHBP1 autoantibodies to block the binding of lipoprotein lipase to GPIHBP1. RESULTS We identified GPIHBP1 autoantibodies in six patients with chylomicronemia and found that these autoantibodies blocked the binding of lipoprotein lipase to GPIHBP1. As in patients with GPIHBP1 deficiency, those with GPIHBP1 autoantibodies had low plasma levels of lipoprotein lipase. Three of the six patients had systemic lupus erythematosus. One of these patients who had GPIHBP1 autoantibodies delivered a baby with plasma containing maternal GPIHBP1 autoantibodies; the infant had severe but transient chylomicronemia. Two of the patients with chylomicronemia and GPIHBP1 autoantibodies had a response to treatment with immunosuppressive agents. CONCLUSIONS In six patients with chylomicronemia, GPIHBP1 autoantibodies blocked the ability of GPIHBP1 to bind and transport lipoprotein lipase, thereby interfering with lipoprotein lipase–mediated processing of triglyceride-rich lipoproteins and causing severe hypertriglyceridemia.