Background <p>Maternally expressed gene 3 (MEG3) is an abnormal methylation gene and low expression of lncRNA MEG3 have been observed in coronary heart disease (CHD). This study aims to investigate whether DNA methylation mediates the abnormal expression of lncRNA MEG3 and to explore the underlying mechanism by which lncRNA MEG3 regulates cholesterol efflux.</p> Methods <p>Real-time quantitative polymerase chain reaction (RT-qPCR) and western blot were used to assess molecular expressions. Oxidized low-density lipoprotein (Ox-LDL) treated human umbilical vein endothelial cells (HUVECs) were established as an in vitro model. Methylation-specific PCR was used to evaluate the methylation level of MEG3. BODIPY-cholesterol assay was performed to examine intracellular cholesterol efflux. Luciferase reporter gene assay was used to verify the interaction between miR-181a-5p and MEG3/ABCA1.</p> Results <p>LncRNA MEG3 was downregulated, while taurine upregulated gene 1 (TUG1) was upregulated in patients with CHD. Besides, ox-LDL treatment increased DNMT3B expression, decreased lncRNA MEG3 expression and elevated the level of MEG3 methylation in HUVECs. Further experiments showed that DNMT3B overexpression reduced lncRNA MEG3 expression and enhanced MEG3 methylation. Additionally, silencing MEG3 decreased ABCA1 expression to prevent cholesterol efflux in HUVECs. The interaction between miR-181a-5p and MEG3/ABCA1 were also confirmed. Rescue experiments suggested that MEG3 knockdown downregulated ABCA1 expression via miR-181a-5p, thereby preventing cholesterol efflux in HUVECs. Furthermore, the results showed that MEG3 collaborated with TUG1 in an independent manner to block ABCA1 mediated-cholesterol efflux in HUVECs.</p> Conclusion <p>Downregulation of lncRNA MEG3, mediated by DNMT3B, prevents cholesterol efflux through miR-181a-5p/ABCA1 axis in ox-LDL-induced HUVECs. Moreover, MEG3 collaborated with TUG1 in an independent manner to prevent ABCA1 mediated-cholesterol efflux in HUVECs.</p>