Role of Scavenger Receptor Class B Type I and Sphingosine 1-Phosphate Receptors in High Density Lipoprotein-induced Inhibition of Adhesion Molecule Expression in Endothelial Cells

Abstract

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...

Induction of Scavenger Receptor Class B Type I Is Critical for Simvastatin Enhancement of High-Density Lipoprotein-Induced Anti-Inflammatory Actions in Endothelial Cells

“…Since the rHDL contains apoA-I, a ligand protein of SR-BI, but not bioactive lipid components, including S1P, the activity induced by rHDL is supposed to reflect the activity of SR-BI and its intracellular signaling pathway (22,24). As in the previous study (22), rHDL inhibited TNF-␣-induced VCAM-1 expression (Fig. 4A), which was associated with NOS activation (Fig.…”

“…To clarify whether these receptor systems are modulated by statin treatment, we first examined the effects of rHDL, which was prepared by reconstituting delipidated HDL with phosphatidylcholine. Since the rHDL contains apoA-I, a ligand protein of SR-BI, but not bioactive lipid components, including S1P, the activity induced by rHDL is supposed to reflect the activity of SR-BI and its intracellular signaling pathway (22,24). As in the previous study (22), rHDL inhibited TNF-␣-induced VCAM-1 expression (Fig.…”

“…HDL also inhibited TNF-␣-induced ICAM-1 expression, and simvastatin similarly enhanced HDL-induced actions (data not shown). We have shown that NO synthesis is involved in the inhibitory action of HDL on adhesion molecule expression (22). In fact, the HDL-induced action was almost completely reversed by L-NAME, an NOS inhibitor, regardless of the statin treatment (Fig.…”

“…The reconstituted discoidal lipoprotein particle (rHDL) was prepared as previously described (22). In brief, HDL was delipidated and then the lipid-free apolipoprotein mixture was dialyzed against 5 ϫ 1 liter Trisbuffered saline (0.01 M Tris buffer (pH 7.4) containing 0.15 M NaCl, 0.01% (w/v) EDTA, and 0.02% (w/v) NaN 3 ).…”

“…We have recently shown that HDL induced the stimulation of NOS and the inhibition of adhesion molecule expression through both apoA-I/SR-BI and the lipoprotein-associated S1P/S1P receptors (22). To clarify whether these receptor systems are modulated by statin treatment, we first examined the effects of rHDL, which was prepared by reconstituting delipidated HDL with phosphatidylcholine.…”