·The lncRNA-B230352I09 overexpression vector (pcDNA-B230352I09) and the negative control vector pcDNA-negative control group (NC) were constructed and transfected into H9C2 cardiomyocytes with the Lipofectamine 3000 (Lipo3000) transfection solution. The expression of lncRNA-B230352I09 was measured by real-time fluorescence quantitative polymerase chain reaction (RT-PCR) to verify its transfection efficiency. The H9C2 cardiomyocytes were divided into blank control group, pcDNA-NC group, and lncRNA-B230352I09 overexpression group. Cell counting kit-8 (CCK8) was used to measure the absorbance (optical density, OD) of H9C2 cardiomyocytes at a wavelength of 450 nm and draw a growth curve; 5-ethynyl-2'-deoxyuridine (EdU) was used to label proliferating H9C2 cardiomyocytes, the numbers of which were observed by fluorescence microscopy. Cardiomyocyte cycle was assessed by flow cytometry and cycle-related genes expression was measured by RT-PCR.

·Compared with the pcDNA-NC group, the expression level of lncRNA-B230352I09 was significantly higher in the lncRNA-B230352I09 overexpression group (P＝0.000), suggesting that the lncRNA-B230352I09-transfected H9C2 cardiomyocyte model was successfully constructed. Compared with the pcDNA-NC group, the CCK8 assay showed that lncRNA-B230352I09 overexpression significantly increased the OD of H9C2 cardiomyocytes and promoted the proliferation of H9C2 cardiomyocytes with a significant time-dependent enhancement of cell proliferation (24 h: P=0.000; 48 h: P=0.000; 72 h: P=0.001). Fluorescence microscopy revealed that the proportion of EdU-labeled positive H9C2 cardiomyocytes was significantly increased in the lncRNA-B230352I09 overexpression group compared to the pcDNA-NC group. Flow cytometric analysis showed a significant increase in the proportion of H9C2 cardiomyocytes in S phase and a decrease in G₁ phase in the lncRNA-B230352I09 overexpression group compared to the pcDNA-NC group (P＝0.000). RT-PCR showed that the mRNA expression levels of cyclin D1 and cyclin dependent protein kinase 1 (CDK1) in the lncRNA-B230352I09 overexpression group were significantly higher compared with the pcDNA-NC group (P＝0.000).

·lncRNA-B230352I09 can enhance myocardial proliferative capacity by regulating cyclin D1 and CDK1 to promote the entry of cardiomyocytes to into S phase.