Objective: Several members of the ATP binding cassette (ABC)-transporter super family expressed in macrophages protect against atherosclerosis by promoting macrophage cholesterol and phospholipid efflux. Systemic disruption of ABCB4 in mice results in a virtual absence of phospholipids in bile and a strongly impaired biliary cholesterol secretion, indicating that ABCB4 plays an essential role in cellular lipid efflux. The aim of the current study was to determine the role of bone marrow-derived ABCB4 in atherosclerotic lesion development.
Methods: Chimeras were created that specifically lack ABCB4 in bone marrow-derived cells, including macrophages, by performing a bone marrow transplantation on LDL receptor knockout (LDLr-/-) mice. Atherosclerotic lesion development was induced by feeding a high-cholesterol diet (15% fat and 0.25% cholesterol).
Results: Serum cholesterol levels were significantly lower in mice reconstituted with ABCB4 knockout bone marrow as a result of reduced VLDL and LDL cholesterol levels. Despite the lower serum cholesterol levels, ABCB4 deficiency in bone marrow-derived cells resulted in a 1.8-fold (p=0.005) increase in lesion size. In vitro foam cell formation, induced with acetylated LDL (AcLDL) in peritoneal macrophages, was increased in the absence of ABCB4, possibly due to a 2-fold (p<0.05) increased association of AcLDL, while the efflux of cholesterol was unaffected.
Conclusion: Bone marrow-derived ABCB4 has an important anti-atherosclerotic function, probably by limiting macrophage foam cell formation.