Objective  To observe the regulatory effect of lncRNA PAX8-AS1 on cardiomyocyte apoptosis after acute myocardial infarction (AMI) in mice.

  Methods  AMI model mice were established by ligation of the anterior descending branch of the left coronary artery. A total of 64 male mice successfully established by AMI model were selected, 48 mice were randomly selected, and every 8 mice were sacrificed at 0, 1, 2, 3, 4 and 5 d after operation, respectively(AMI group). The selection method of mice in Sham group was the same as that of AMI group, and the operations were the same as that of AMI mice, but they didn't perform ligation of the anterior descending branch of left coronary artery. Every 8 mice were sacrificed at 0, 1, 2, 3, 4 and 5 d after operation, respectively. The remaining mice in the Sham group were randomly divided into Sham+Ad-shCon group (8 mice) and Sham+Ad-shPAX8-AS1 group (8 mice); mice in the AMI group were randomly divided into AMI+Ad-shCon group (8 mice) and AMI+Ad-shPAX8-AS1 group (8 mice). Real-time fluorescence quantitative polymerase chain reaction (RT-qPCR) was used to detect the changes of PAX8-AS1 level in myocardial tissue of the AMI group and Sham group after operation. The infarct size (IS)/risk area (ARR) of mice in the Sham+Ad-shCon group, Sham+Ad-shPAX8-AS1 group, AMI+Ad-shCon group and AMI+Ad-shPAX8-AS1 group were detected by red tetrazolium (TTC) staining; the apoptosis level of mouse cardiomyocytes was detected by TUNEL staining, and the expression levels of PAX8-AS1, B lymphocyte tumor-2 associated x protein (Bax), B lymphocyte tumor-2 gene (Bcl-2) and lytic caspase-3 (cleaved-caspase3) in mouse myocardium were detected by reverse transcription-polymerase chain reaction (RT-PCR), immunohistochemistry and western blotting.

  Results  The expression level of PAX8-AS1 in the AMI group increased with the prolongation of time after AMI, and reached the highest level on the 3rd day after operation, which was higher than that in the Sham group, and the difference was statistically significant (P < 0.05). Compared with Sham+Ad-shCon group, the expression of PAX8-AS1 in Sham+Ad-shPAX8-AS1 group decreased significantly (P < 0.05), PAX8-AS1, IS/ARR, cardiomyocyte apoptosis index, Bax and cleaved-caspase3 were up-regulated and Bcl-2 was down-regulated in AMI+Ad-shCon group and AMI+Ad-shPAX8-AS1 group, the differences were statistically significant (P < 0.05). Compared with AMI+Ad-shCon group, PAX8-AS1, IS/ARR, cardiomyocyte apoptosis index, Bax and cleaved-caspase3 were down-regulated and Bcl-2 was up-regulated in the AMI+Ad-shPAX8-AS1 group, and the differences were statistically significant (P < 0.05).

  Conclusion  PAX8-AS1 is highly expressed in AMI myocardium, and low expression of PAX8-AS1 can reduce infarct size and inhibit myocardial apoptosis, which may be related to apoptotic protein regulation.