Scavenger receptor class B type I-mediated protection against atherosclerosis in LDL receptor-negative mice involves its expression in bone marrow-derived cells

Objective - Scavenger receptor class B type I (SR-BI) is a cell-surface HDL receptor that is implicated in reverse cholesterol transport and protection against atherosclerosis. We have previously demonstrated that SR-BI/apolipoprotein E double-knockout mice develop severe occlusive coronary artery disease and myocardial infarction and die at similar to 6 weeks of age. To determine if this is a general effect of a lack of SR-BI, we generated mice deficient in both SR-BI and the LDL receptor. Methods and Results - Complete ablation of SR-BI expression in LDL receptor knockout mice resulted in increased plasma cholesterol associated with HDL particles of abnormally large size and a 6-fold increase in diet-induced aortic atherosclerosis but no macroscopic evidence of early-onset coronary artery disease, cardiac pathology, or early death. Furthermore, selective elimination of SR-BI expression in bone marrow - derived cells resulted in increased diet-induced atherosclerosis in LDL receptor knockout mice without concomitant alterations in the distributions of plasma lipoprotein cholesterol. Conclusions - SR-BI expression protects against atherosclerosis in LDL receptor - deficient as well as apolipoprotein E - deficient mice, and its expression in bone marrow - derived cells contributes to this protection.