High density lipoprotein prevents oxidized low density lipoprotein-inducedinhibition of endothelial nitric-oxide synthase localization and activation in caveolae

Oxidized LDL (oxLDL) depletes caveolae of cholesterol, resulting in the dis placement of endothelial nitric-oxide synthase (eNOS) from caveolae and imp aired eNOS activation. In the present study, we determined if the class B s cavenger receptors, CD36 and SR-BI, are involved in regulating nitric-oxide synthase localization and function, We demonstrate that CD36 and SRBI are expressed in endothelial cells, co-fractionate with caveolae, and co-immuno precipitate with caveolin-1, Go-incubation of cells with 10 mu g/ml high de nsity lipoprotein (HDL) prevented oxLDL-induced translocation of eNOS from caveolae and restored acetylcholine-induced nitric-oxide synthase stimulati on. Acetylcholine caused eNOS activation in cells incubated with 10 mu g/ml oxLDL (10-15 thiobarbituric acid-reactive substances) and blocking antibod ies to CD36, whereas cells treated with only oxLDL were unresponsive. Furth ermore, CD36-blocking antibodies prevented oxLDL-induced redistribution of eNOS, SR-BI-blocking antibodies were used to demonstrate that the effects o f HDL are mediate by SR-BI. HDL binding to SR-BI maintained the concentrati on of caveola-associated cholesterol by promoting the uptake of cholesterol esters, thereby preventing oxLDL-induced depletion of caveola cholesterol, we conclude that CD36 mediates the effects of oxLDL on caveola composition and eNOS activation. Furthermore, HDL prevents oxLDL from decreasing the c apacity for eNOS activation by preserving the cholesterol concentration in caveolae and, thereby maintaining the subcellular location of eNOS.