Long non-coding RNA MEG3 inhibits M2 macrophage polarization by activating TRAF6 via microRNA-223 down-regulation in viral myocarditis

Viral myocarditis (VMC) commonly triggers heart failure, for which no specific treatments are available. This study aims to explore the specific role of long non-coding RNA (lncRNA) maternally expressed 3 (MEG3) in VMC. A VMC mouse model was induced by Coxsackievirus B3 (CVB3). Then, MEG3 and TNF receptor-associated factor 6 (TRAF6) were silenced and microRNA-223 (miR-223) was over-expressed in the VMC mice, followed by determination of ventricular ejection fraction (LVEF) and left ventricular fractional shortening (LVFS). Dual-luciferase reporter assay was introduced to test the interaction among MEG3, TRAF6 and miR-223. Macrophages were isolated from cardiac tissues and bone marrow, and polarization of M1 or M2 macrophages was induced. Then, the expressions of components of NLRP3 inflammatory body (NLRP3, ASC, Caspase-1), M1 markers (CD86, iNOS and TNF-α) and M2 markers (CD206, Arginase-1 and Fizz-1) were measured following MEG3 silencing. In the VMC mouse model, MEG3 and TRAF6 levels were obviously increased, while miR-223 expression was significantly reduced. Down-regulation of MEG3 resulted in the inhibition of TRAF6 by promoting miR-223. TRAF6 was negatively correlated with miR-223, but positively correlated with MEG3 expression. Down-regulations of MEG3 or TRAF6 or up-regulation of miR-223 was observed to increase mouse weight, survival rate, LVEF and LVFS, while inhibiting myocarditis and inflammation via the NF-κB pathway inactivation in VMC mice. Down-regulation of MEG3 decreased M1 macrophage polarization and elevated M2 macrophage polarization by up-regulating miR-223. Collectively, down-regulation of MEG3 leads to the inhibition of inflammation and induces M2 macrophage polarization via miR-223/TRAF6/NF-κB axis, thus alleviating VMC.