Soraphen A enhances macrophage cholesterol efflux via indirect LXR activation and ABCA1 upregulation

Abstract

Increased cholesterol efflux from macrophage foam cells in the subendothelial space confers protection against atherosclerosis. Soraphen A, a myxobacterial macrolactone, is an inhibitor of acetyl coenzyme A carboxylases (ACC), which control fatty acid synthesis and oxidation. To assess a potential direct link between macrophage cholesterol efflux and ACC inhibition, we examined [³H]-cholesterol efflux from human THP-1-derived foam cells in the presence of soraphen A. We dissected underlying molecular events by western blot analyses, RT-qPCR, reporter gene and coactivator recruitment assays as well as relative quantification of free and total cholesterol. Soraphen A increased cholesterol efflux from macrophage foam cells via upregulation of the cholesterol transporter ATP-binding cassette transporter A1 (ABCA1). Soraphen A enhanced transcription of ABCA1 in an LXR-dependent manner, however, without direct binding to the ligand-binding domain of this nuclear receptor. Soraphen A elevated the cellular level of free cholesterol, and failed to activate LXR upon exogenous supplementation with fatty acids or inhibition of cholesterol synthesis. Thus, impeded conversion from acetyl- to malonyl-CoA by soraphen A may lead to more unesterified cholesterol and thus potential LXR agonists. The present study reveals ACC inhibition as a previously unrecognized mechanism to regulate macrophage cholesterol efflux via indirect LXR activation and ABCA1 upregulation.

Keywords: ATP-binding cassette transporter A1; Acetyl coenzyme A carboxylases; Atherosclerosis; Cardiovascular diseases; Fatty acids; Soraphen A.