Proteasomal Inhibition Promotes ATP-Binding Cassette Transporter A1 (ABCA1) and ABCG1 Expression and Cholesterol Efflux From Macrophages In Vitro and In Vivo

Abstract

Objective-ATP-binding cassette transporter A1 (ABCA1) and ABCG1 are key molecules in an initial step of reverse cholesterol transport (RCT), a major antiatherogenic property of high-density lipoprotein (HDL). The ubiquitinproteasome system (UPS) mediates nonlysosomal pathways for protein degradation and is known to be involved in atherosclerosis. However, little is known about the effects of the UPS on these molecules and overall RCT. We therefore investigated whether UPS inhibition affects ABCA1/G1 expression in macrophages and RCT in vitro and in vivo. Methods and Results-Various proteasome inhibitors increased ABCA1/G1 expression in macrophages, translating into enhanced apolipoprotein A-I-and HDL-mediated cholesterol efflux from macrophages. ABCA1 and ABCG1 were found to undergo polyubiquitination in the macrophages and HEK293 cells overexpressing these proteins, and pulse-chase analysis revealed that proteasome inhibitors inhibited ABCA1/G1 protein degradation. In in vivo experiments, the proteasome inhibitor bortezomib increased ABCA1/G1 protein levels in mouse peritoneal macrophages, and RCT assays showed that it significantly increased the fecal (54% increase compared with saline) and plasma (23%) appearances of the tracer derived from intraperitoneally injected 3 H-cholesterol-labeled macrophages. Conclusion-The present study provided evidence that the UPS is involved in ABCA1/G1 degradation, thereby affecting RCT in vivo. Therefore, specific inhibition of the UPS pathway might lead to a novel HDL therapy that enhances RCT. Key Words: ABC Transporter Ⅲ Macrophages Ⅲ HDL Ⅲ reverse cholesterol transport Ⅲ ubiquitin-proteasome system H igh-density lipoprotein (HDL) removes cholesterol pathologically accumulated in atherosclerotic lesion macrophages and transports it back to the liver for subsequent conversion to bile in a process called reverse cholesterol transport (RCT). 1,2 ATP-binding cassette transporter A1 (ABCA1) and ABCG1 play essential roles in cholesterol efflux from macrophages and HDL formation by acting in a sequential manner: ABCA1 generates nascent HDL particles from lipid-poor apolipoprotein A-I (apoA-I), 3 which then facilitate cholesterol efflux via ABCG1, followed by formation of mature HDL particles. 4 Deletion of both ABCA1 and ABCG1 in macrophages reportedly accelerated atherosclerotic legion development as compared with deletion of either ABCA1 or ABCG1, 5 indicating that ABCA1 and ABCG1 have a synergetic role in antiatherogenesis. See accompanying article on page 1939Evidence regarding the regulation of ABCA1/G1 expression, such as via transactivation by ligand-activated liver X receptor/retinoid X receptor heterodimer, 6 has been accumulating. ABCA1 and ABCG1 have been emerging as therapeutic targets for the treatment of atherosclerotic diseases because enhancement of their expression can promote RCT by increasing cholesterol efflux from macrophages and raising HDL levels. However, strategies using liver X receptor ligands suffer from major drawbacks, including development of fat...

Probucol-Oxidized Products, Spiroquinone and Diphenoquinone, Promote Reverse Cholesterol Transport in Mice

“…10,11 Spiroquinone and diphenoquinone increased HDL-cholesterol (HDL-C) levels and reduced development of atherosclerosis in rabbits. 10 We have also demonstrated that ABCA1 and ABCG1 undergo proteasomal degradation, and proteasome inhibitors enhanced cholesterol efflux by increasing ABCA1 and ABCG1, translating into promotion of macrophage-to-feces RCT in vivo, 12 using a validated murine assay. 13 We therefore decided to investigate how spiroquinone and diphenoquinone exert beneficial effects with respect to promotion of RCT in vivo and in this study demonstrated that spiroquinone and diphenoquinone enhance overall RCT in mice.…”

The E3 Ubiquitin Ligases, HUWE1 and NEDD4-1, Are Involved in the Post-translational Regulation of the ABCG1 and ABCG4 Lipid Transporters

“…The post-translational regulation of the transporter is less well established, but thought to be equally important in the fine-tuning of transporter activity. Previously, it has been demonstrated that ABCG1 is ubiquitinated and degraded via ubiquitin-mediated proteasomal degradation (17). In addition, Hsieh et al showed that the cellular cholesterol status is important in the control of the proteasomal degradation of ABCG1 (18).…”

Sage weed (Salvia plebeia) extract antagonizes foam cell formation and promotes cholesterol efflux in murine macrophages

“…These proteins mediate the movement of cholesterol between cells and extracellular acceptors (23). ABCA1 is responsible for the export of cholesterol and phospholipids to generate precursors for HDL particles (6,8).…”