Intervention mechanism of epigenetics of lncRNA MEG3 gene on macrophage lipid metabolism

Objective To observe the effects of long non-coding RNA maternally expressed gene 3 (lncRNA MEG3) and microRNA (miR)-642a-5p on lipoprotein lipase (LPL) as a rate-limiting enzyme for triglyceride (TG) synthesis in a macrophage model, and to explore the refined mechanisms underlying TG reduction and anti-atherosclerosis (AS) at the epigenetic level.

Methods A human monocytic leukemia cell (THP-1) model was established by 50 mg/L oxidized low-density lipoprotein (ox-LDL) and subjected to various transfection interventions. Gene expression levels of lncRNA MEG3, miR-642a-5p, angiopoietin-like protein 4 (ANGPTL₄), and LPL were detected by real-time quantitative polymerase chain reaction (qPCR). Protein expression levels of ANGPTL₄ and LPL were assessed by Western blotting (WB). Oil red O staining wasused to quantify the number of cells containing red lipid droplets (representing cellular lipid deposition).

Results ① In the ox-LDL-exposed THP-1 cell model, lncRNA MEG3 and ANGPTL₄ were highly expressed, while miR-642a-5p and LPL were under-expressed. The number of cells with red lipid droplets was significantly elevated (P < 0.01). ② A negative correlation was observed between the relative expression levels of lncRNA MEG3 and miR-642a-5p (r=-0.764 9, P=0.045), miR-642a-5p and ANGPTL₄ (r=-0.976 5, P=0.001 2), and ANGPTL₄ and LPL protein expression (r=-0.929 3, P=0.002 5). A positive correlation was found between ANGPTL₄ and the number of cells with red lipid droplets (r=0.897 1, P=0.025). ③ Upregulation of miR-642a-5p significantly reduced the relative expression levels of ANGPTL₄ protein and gene while increasing those of LPL protein and gene (P < 0.01). Conversely, downregulation of miR-642a-5p increased ANGPTL₄ protein and gene expression, while LPL protein and gene expression deereased (P < 0.01). ④ Knockout of lncRNA MEG3 decreased ANGPTL₄ protein and gene expression while miR-642a-5p gene expression and LPL protein and gene expression increased (P < 0.01). ⑤ Combined knockout of lncRNA MEG3 and upregulation of miR-642a-5p increased the relative expression levels of miR-642a-5p gene, LPL gene, and protein while those of ANGPTL₄ gene and protein deereased (P < 0.01).Conversely, combined knockout of lncRNA MEG3 and downregulation of miR-642a-5p decreased miR-642a-5p gene, LPL gene, and protein expression while ANGPTL₄ gene and protein expression increased (P < 0.01).

Conclusion ANGPTL₄ inhibits LPL, acting as a novel pro-inflammatory factor promoting lipid deposition. MiR-642a-5p reduces macrophage lipid deposition by targeting and inhibiting ANGPTL₄ gene expression. LncRNA MEG3 may function as a competing endogenous RNA, suppressing miR-642a-5p via a "sponge effect", thereby increasing downstream ANGPTL₄ gene transcription and inhibiting LPL to promote TG synthesis.