SR-BI as target in atherosclerosis and cardiovascular disease - A comprehensive appraisal of the cellular functions of SR-BI in physiology and disease

High-density lipoprotein (HDL) is considered an anti-atherogenic lipoprotein species due to its role in reverse cholesterol transport. HDL delivers cholesterol esters to the liver through selective uptake by scavenger receptor class B type I (SR-BI). In line with the protective role for HDL in the context of cardiovascular disease, studies in mice and recently also in humans have shown that a disruption of normal SR-BI function predisposes subjects to the development of atherosclerotic lesions and cardiovascular disease. Although SR-BI function has been studied primarily in the liver, it should be acknowledged that the SR-BI protein is expressed in multiple tissues and cell types across the body, albeit at varying levels between the different tissues. Given that SR-BI is widely expressed throughout the body, multiple cell types and tissues can theoretically contribute to the atheroprotective effect of SR-BI. In this review the different functions of SR-BI in normal physiology are highlighted and the (potential) consequences of cell type-specific disruption of SR-BI function for atherosclerosis and cardiovascular disease susceptibility discussed. It appears that hepatocyte and platelet SR-BI inhibit respectively the development of atherosclerotic lesions and thrombosis, suggesting that SR-BI located on these cell compartments should be regarded as being a protective factor in the context of cardiovascular disease. The relative contribution of SR-BI present on endothelial cells, steroidogenic cells, adipocytes and macrophages to the pathogenesis of atherosclerosis and cardiovascular disease remains less clear, although proper SR-BI function in these cells does appear to influence multiple processes that impact on cardiovascular disease susceptibility.