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

Changes in plasma lipoprotein profiles, especially low levels of high-density lipoprotein (HDL), are a common biomarker for several inflammatory and immune diseases, including atherosclerosis and rheumatoid arthritis. We examined the effect of simvastatin on RDL-induced anti-inflammatory actions. RDL and sphingosine I-phosphate (SIP), a bioactive lipid component of the lipoprotein, inhibited TNF alpha-induced expression of VCAM-1, which was associated with NO synthase (NOS) activation, in human umbilical venous endothelial cells. The RDL- but not S1P-induced anti-inflammatory actions were enhanced by a prior treatment of the cells with simvastatin in a manner sensitive to mevalonic acid. Simvastatin stimulated the expression of scavenger receptor class B type I (SR-BI) and endothelial NOS. As for SIP receptors, however, the statin inhibited the expression of SIP, receptor mRNA but caused no detectable change in S1P(1) receptor expression. The reconstituted HDL, a stimulator of SR-BI, mimicked HDL actions in a sirnvastatin-sensitive manner. The HDL- and reconstituted HDL-induced actions were blocked by small interfering RNA specific to SR-BI regardless of simvastatin treatment. The statin-induced expression of SR-BI was attenuated by constitutively active RhoA and small interfering RNA specific to peroxisome proliferator-activated receptor-alpha. Administration of simvastatin in vivo stimulated endothelial SR-BI expression, which was accompanied by the inhibition of the ex vivo monocyte adhesion in aortas from TNF alpha-injected mice. In conclusion, simvastatin induces endothelial SR-BI expression through a RhoA- and peroxisome proliferator-activated receptor-alpha-dependent mechanism, thereby enhancing the RDL-induced activation of NOS and the inhibition of adhesion molecule expression. The Journal of Immunology, 2008, 181: 7332-7340.