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Synthetic agonists of liver X-receptors (LXRα, NR1H3 and LXRβ, NR1H2) or cholesterol-loading signiﬁcantly induced the expression of ABCA1 protein in mouse RAW 264.7 and human THP-1 macrophage cell lines (Beyea MM et al. 2007; Ku CS et al. 2012). Similar regulation of ABCA1 protein expression by NR1H2, 3 agonists was observed in human peripheral blood-derived monocytes (Mauerer R et al. 2009). Treatment of THP-1 macrophages with endogenous (25-hydroxycholesterol) or synthetic (T0901317) ligands of NR1H2,3 stimulated both transcriptional and posttranscriptional pathways to enhance ABCA1 expression (Ignatova ID et al. 2013). Further, partial inhibition of oxidosqualene:lanosterol cyclase (OSC) stimulated synthesis of the NR1H2,3 agonist 24(S),25-epoxycholesterol (24(S),25-epoxy) and enhanced ABCA1-mediated cholesterol efflux in THP-1 cells (Beyea MM et al. 2007). NR1H3 and NR1H2-induced expression of ABCA1 is thought to promote cellular cholesterol transfer to lipid-poor apolipoproteins such as ApoA1 and ApoE in the formation of nascent HDL particles (Ignatova ID et al. 2013; Vedhachalam C et al. 2007). Loss of ABCA1 in humans results in Tangier disease, a condition in which patients have extremely low levels of circulating HDL, massive accumulation of cholesterol in macrophages, and an increased risk for developing atherosclerosis (Rust S et al. 1999).
MicroRNAs miR-26 and miR-33 negatively regulate the translation of ABCA1 mRNA and thus repress the NR1H2, NR1H3-dependent cholesterol efflux from macrophages (Sun D et al. 2012; Rayner KJ et al. 2010). MicroRNA miR-144 also binds the ABCA1 3’UTR to prohibit translation and reduce ABCA1-mediated cholesterol efflux from hepatocytes (de Aguiar Vallim TQ et al. 2013)