Inhibition of miR-33a-5p in Macrophage-like Cells In Vitro Promotes apoAI-Mediated Cholesterol Efflux

Atherosclerosis is caused by cholesterol accumulation within arteries. The intima is where atherosclerotic plaque accumulates and where lipid-laden foam cells reside. Intimal foam cells comprise of both monocyte-derived macrophages and macrophage-like cells (MLC) of vascular smooth muscle cell (VSMC) origin. Foam cells can remove cholesterol via apoAI-mediated cholesterol efflux and this process is regulated by the transporter ABCA1. The microRNA miR-33a-5p is thought to be atherogenic via silencing ABCA1 which promotes cholesterol retention and data has shown inhibiting miR-33a-5p in macrophages may be atheroprotective via enhancing apoAI-mediated cholesterol efflux. However, it is not entirely elucidated whether precisely inhibiting miR-33a-5p in MLC also increases ABCA1-dependent cholesterol efflux. Therefore, the purpose of this work is to test the hypothesis that inhibition of miR-33a-5p in cultured MLC enhances apoAI-mediated cholesterol efflux. In our study, we utilized the VSMC line MOVAS cells in our experiments, and cholesterol-loaded MOVAS cells to convert this cell line into MLC. Inhibition of miR-33a-5p was accomplished by transducing cells with a lentivirus that expresses an antagomiR directed at miR-33a-5p. Expression of miR-33a-5p was analyzed by qRT-PCR, ABCA1 protein expression was assessed via immunoblotting, and apoAI-mediated cholesterol efflux was measured using cholesterol efflux assays. In our results, we demonstrated that lentiviral vector-mediated knockdown of miR-33a-5p resulted in decreasing expression of this microRNA in cultured MLC. Moreover, reduction of miR-33a-5p in cultured MLC resulted in de-repression of ABCA1 expression, which caused ABCA1 protein upregulation in cultured MLC. Additionally, this increase in ABCA1 protein expression resulted in enhancing ABCA1-dependent cholesterol efflux through increasing apoAI-mediated cholesterol efflux in cultured MLC. From these findings, we conclude that inhibiting miR-33a-5p in MLC may protect against atherosclerosis by promoting ABCA1-dependent cholesterol efflux.