Abstract: Objective To observe the effect of long non-coding ribonucleic acid human maternal expressed gene 3 (LncRNA MEG3) targeting microribonuclease-21 (miR-21) mediating Toll like receptor 4 (TLR4) and nuclear factor-κB (NF-κB) pathway on myocardial ischemia-reperfusion injury (MIRI) in mice. Methods A total of 54 BAB/c mice were randomly divided into LncRNA MEG3 upregulation group, LncRNA MEG3 downregulation group, miR-21 upregulation group, miR-21 downregulation group, both upregulation group, both downregulation group, empty load group, model group, and sham surgery group, with 6 mice in each group. Except for the sham group, MIRI models were established for all mice. After 24 hours of modeling, mice in each group were euthanized. Abdominal aortic blood was collected and enzyme-linked immunosorbent assay was used to detect the levels of myocardial injury markers [cardiac troponin I (cTnI), creatine kinase isoenzyme (CK-MB), brain natriuretic peptide (BNP), and myoglobin (Mb)] and inflammatory factors [tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), IL-8]. Morphological changes in myocardial tissue were observed using hematoxylin eosin (HE) staining. The expressions of TLR4 and NF-κB p65 genes and the expressions of TLR4, NF-κB p65 protein in cytoplasm and nucleus in myocardial tissues were detected. The dual luciferase gene reporter experiment and RNA pull-down experiment were used to validate the targeted regulation of miR-21 by LncRNA MEG3. Results Myocardial injury markers, inflammatory factor levels among different groups showed LncRNA MEG3 downregulation group>miR-21 upregulation group>both downregulation group>model group/empty vector group>both upregulation group>miR-21 downregulation group>LncRNA MEG3 upregulation group>sham group (P<0.05). TLR4 gene and protein in myocardial tissues, NF-κB p65 gene and nuclear NF-κB p65 protein expression showed LncRNA MEG3 downregulation group>miR-21 upregulation group>both downregulation group>model group>both upregulation group>miR-21 downregulation group>LncRNA MEG3 upregulation group>sham surgery group/empty load group (P<0.05), and the trend of cytoplasmic NF-κB p65 protein expression was positively opposite (P<0.05). There were no changes in the morphology of myocardial tissue in the sham surgery group, and the changes in the model group/empty load group, both downregulation group, miR-21 upregulation group, and LncRNA MEG3 downregulation group gradually became increasingly severe, while the changes in the both upregulation group, miR-21 downregulation group, and LncRNA MEG3 upregulation group gradually decreased. The dual luciferase gene reporter experiment and RNA pull-down experiment revealed that LncRNA MEG3 could negatively feedback and target miR-21 regulation. Conclusions Upregulation of LncRNA MEG3 expression can inhibit miR-21, downregulate TLR4/NF-κB pathway, alleviate MIRI and inflammatory response in mice, and also antagonize myocardial injury caused by miR-21 upregulation.

Key words: long non-coding ribonucleic acid human maternal expression gene 3, microribonuclease-21, Toll like receptor 4, nuclear factor-κB, myocardial ischemia-reperfusion injury, inflammatory reaction