Purpose of review: This review briefly discusses the ATP-binding cassette transporter G (ABCG) family members and emphasizes recent studies that identify ABCG1 as a key regulator of cellular lipid homeostasis.
Recent findings: The in-vivo importance of ABCG1 has recently been demonstrated with both loss-of-function and gain-of-function studies in mice. Administration of a diet high in both fat and cholesterol to ABCG1 mice results in massive cholesterol accumulation in both the liver and lungs. In contrast, lipid accumulation is greatly attenuated in transgenic mice that express both the murine and human ABCG1 genes. Despite the observed tissue lipid accumulation, plasma lipid levels and lipoprotein cholesterol distribution are not significantly different between wild-type, ABCG1, and hABCG1 transgenic mice. Other studies show that ABCG1 expression is induced following activation of the nuclear receptor LXR and that over expression of ABCG1 results in increased efflux of cellular cholesterol to HDL or phospholipid vesicles.
Summary: The ABCG1 transporter plays a key role in regulating cellular cholesterol and lipid homeostasis. Elucidation of the molecular mechanism by which ABCG1 controls sterol flux should provide critical information that may link ABCG1 to the reverse cholesterol transport pathway or diseases such as atherosclerosis.