Identification and Expression of Scavenger Receptor SR-BI in Endothelial Cells and Smooth Muscle Cells of Rat Aorta in Vitro and in Vivo

In this study, we used immunoelectron microscopy to investigate the subcellular localization of scavenger receptor class B type I (SR-BI) in the arterial walls of rats. The expression of SR-BI in cultured endothelial and smooth muscle cells of rat aorta after exposure to high-density lipoprotein (HDL) was also investigated by immunofluorescence microscopy and immunoblotting analysis. A peptide containing residues 495-509 from mouse SR-BI (mSR-BI) plus an NH2-terminal cysteine was coupled to hemocyanin to generate mSR-BI antiserum in rabbits. Reactivity of antiserum against the synthetic peptides was confirmed with an enzyme-linked immunosorbent assay (ELISA). The results showed that SR-BI was specifically localized on the surface of the endothelial cells and smooth muscle cells. SR-BI was also observed in the cytoplasm of smooth muscle cells. Immunoblotting analysis indicated that SR-BI was expressed in the cell membrane. The levels of SR-BI increased gradually from 1 to 3 h and decreased at 24 and 48 h after cholesterol-loaded cells were incubated in the culture medium containing HDL. We conclude that SR-BI, a functional receptor for HDL, is expressed in the aortic endothelial cells as well as in smooth muscle cells. This receptor also responds to the presence of HDL in the culture medium.