ATP-binding cassette transporters G1 and G4 mediate cellular cholesterol efflux to high-density lipoproteins

Area of Science:

• Biochemistry
• Molecular Biology
• Cardiovascular Science

Background:

• The link between high-density lipoprotein (HDL) levels and atherosclerotic cardiovascular disease (ASCVD) is inverse but mechanistically unclear.
• ATP-binding cassette transporter A1 (ABCA1) facilitates cholesterol efflux to lipid-poor apolipoproteins, not to mature HDL particles.

Purpose of the Study:

• To investigate the function of ABCG1 and ABCG4 in cellular cholesterol efflux to HDL.
• To elucidate the role of these transporters in the context of ASCVD risk.

Main Methods:

• Utilized transfected 293 cells to assess cholesterol efflux mediated by ABCG1 and ABCG4.
• Investigated the effect of liver X receptor (LXR) activation and RNA interference on ABCG1 expression and cholesterol efflux in macrophages.

Main Results:

• ABCG1 and ABCG4 were shown to mediate cholesterol efflux to both HDL-3 and HDL-2 subclasses.
• LXR activator treatment upregulated ABCG1 expression and increased cholesterol efflux to HDL in macrophages.
• RNA interference knockdown of ABCG1 reduced cholesterol efflux to HDL in activated macrophages.

Conclusions:

• ABCG1 and ABCG4 actively promote cellular cholesterol efflux to HDL particles.
• ABCG1, highly expressed in macrophages, likely mediates cholesterol removal from foam cells to HDL, potentially explaining the inverse relationship between HDL and ASCVD risk.