OBJECTIVE: To explore the effect and correlation of long non-coding RNA (lncRNA) IDI2-AS1/microRNA-33b-5p (miR-33b-5p)/nuclear receptor-associated protein NR4A2 competitive endogenous RNA (ceRNA) regulatory network on acute myocardial infarction (AMI), and to verify whether IDI2-AS1 regulates NR4A2 through miR-33b-5p to affect the occurrence and development of myocardial infarction.
METHODS: The miRNA and mRNA expression chips related to myocardial infarction were obtained from gene expression omnibus (GEO), and the differential expression was analyzed. The upstream regulatory mechanism of NR4A2 was predicted using TargetScan database. Thirty-two male C57/BL6 mice were divided into Sham group, AMI model group, miR-33b-5p mimic group [miR-33b-5p mimic lentivirus (5×107 TU) was injected locally into the heart tissue during ligation] and miR-33b-5p inhibitor group [miR-33b-5p inhibitor lentivirus (5×107 TU) was injected locally into the heart tissue during ligation] according to random number table method, with 8 mice per group. Left ventricular end-diastolic diameter (LVEDD) and left ventricular end-systolic diameter (LVESD) were asseessed by echocardiography, left ventricular fractional shortening (LVFS) and left ventricular ejection fraction (LVEF) were calculated. After the last weighing, the anesthetized mice were sacrificed and the heart tissues were taken. Masson staining of the heart tissues was observed under light microscope, myocardial collagen volume fraction (CVF) and infarct size were calculated. Cardiomyocytes of SPF grade SD rats were collected. They were divided into normal control group (control group), ischemia-hypoxia model group, miR-33b-5p mimic transfection group (miR-33b-5p mimic transfection group before ischemia and hypoxia treatment) and miR-33b-5p inhibitor transfection group (miR-33b-5p inhibitor transfection group before ischemia and hypoxia treatment). The activity of caspase-3/7 in cardiomyocytes was measured. The levels of interleukins (IL-1β, IL-6) and tumor necrosis factor-α (TNF-α) were detected by enzyme-linked immunosorbent assay (ELISA). The levels of malondialdehyde (MDA), superoxide dismutase (SOD), creatine kinase (CK), MB isoenzyme of creatine kinase (CK-MB) and lactate dehydrogenase (LDH) were detected by colorimetry. Real-time quantitative polymerase chain reaction (RT-qPCR) was used to detect the expression of apoptosis-related proteins Bax and Bcl-2, cytochrome C (Cyt C) and IDI2-AS1/miR-33b-5p/NR4A2 regulatory axis genes.
RESULTS: The myocardial infarction microarray analysis showed that NR4A2 expression was significantly up-regulated in myocardial infarction, with predicted upstream regulatory mechanisms indicating its possible influence through the IDI2-AS1/miR-33b-5p/NR4A2 regulatory axis. Echocardiographic detection showed that compared with AMI model group and miR-33b-5p inhibitor group, LVEF and LVFS in the heart tissue of mice in miR-33b-5p mimic group were significantly increased, while the levels of LVEDD, LVESD, CK, CK-MB and LDH were significantly decreased, with statistical significance. Light microscope showed myocardial fibrosis and myocardial infarction in AMI model group and miR-33b-5p inhibitor group. In the miR-33b-5p mimic group, the degree of myocardial fibrosis was decreased and the myocardial infarction size was significantly reduced. Compared with AMI model group and miR-33b-5p inhibitor group, the levels of MDA, IL-1β, IL-6, TNF-α and the expressions of Bax and Cyt C in the heart tissue of mice in miR-33b-5p mimic group were significantly decreased, while the levels of SOD and Bcl-2 expression were significantly increased, and the differences were statistically significant. The expressions of IDI2-AS1 and NR4A2 in the heart tissue of mice in miR-33b-5p mimic group were significantly lower than those in AMI model group and miR-33b-5p inhibitor group [IDI2-AS1 (2-ΔΔCt): 1.96±0.08 vs. 2.73±0.08, 3.10±0.05, NR4A2 (2-ΔΔCt): 2.36±0.07 vs. 3.16±0.08, 3.80±0.08, all P < 0.01]. The expression of miR-33b-5p was significantly higher than that of AMI model group and miR-33b-5p inhibitor group (2-ΔΔCt: 0.88±0.07 vs. 0.57±0.07, 0.23±0.01, both P < 0.01). The cell experiment results showed that the caspase-3/7 activity of rat neonatal cardiomyocytes in the miR-33b-5p mimic transfection group was significantly lower than that in the ischemia-hypoxia model group and the miR-33b-5p inhibitor transfection group, suggesting that miR-33b-5p can significantly reduce the apoptosis level of the ischemia-hypoxia model. The levels of peroxidation and inflammation indexes, important genes of apoptosis pathway and the expression of IDI2-AS1/miR-33b-5p/NR4A2 regulatory axis of rat neonatal cardiomyocytes in all groups were consistent with the above.
CONCLUSIONS: IDI2-AS1 can regulate NR4A2 through miR-33b-5p, thus affecting the occurrence and development of AMI.