Therapeutic delivery of cyclin-A2 via recombinant adeno-associated virus serotype 9 restarts the myocardial cell cycle: an in vitro study.

Cyclin‑A2, which is downregulated following birth, has previously been established as a key regulator of the cell cycle. The present study aimed to detect the effects of cyclin‑A2 on myocardial cells by using recombinant adeno‑associated virus 9 (rAAV9). Sixty mice were selected and randomly divided into two groups (n=30). The control group were injected with saline and the experimental group were transfected with the rAAV9‑cyclinA2‑CMV vector by intravenous injection into the tail vein. Tissues were harvested at two and four weeks following injection. Cyclin‑A2 expression levels and localization were evaluated using western blot and immunohistochemical analyses. DNA synthesis and mitosis in the myocardium were confirmed by analyzing proliferating cell nuclear antigen (PCNA) and phospho‑histone H3 (H3P) expression levels. Expression of Cyclin‑A2 in the myocardium commenced two weeks following tail vein injection in the cyclin‑A2‑treated group, while no expression was observed in the control group. Four weeks following injection, expression levels of cyclin‑A2 were higher than those observed at two weeks following injection into the myocardium (two weeks: 0.146±0.013 vs. 27.1±3.33%, P<0.001; four weeks: 0.142±0.107 vs. 74.4±3.36%, P<0.001). PCNA displayed increased expression levels in the cyclin‑A2‑treated group (two weeks: 13.1±0.54 vs. 65.8±3.44%, P<0.001; four weeks: 13.2±0.55 vs. 71.2±1.58%, P<0.001); however, no change was observed in those of the control group. By contrast, no significant difference was observed in mitosis marker H3P expression levels between the two groups. Immunohistochemical analysis of cyclin‑A2 indicated cytoplasmic, but not nuclear, localization. cyclin‑A2 and PCNA expression levels in the liver, lung and kidney showed no significant difference between the two groups (P>0.05). It was therefore concluded that the delivery of cyclin‑A2 via rAAV9 to the mouse myocardium restarted the myocardial cell cycle, thereby establishing steady and specific expression in the myocardium. Furthermore, the effect of Cyclin‑A2 on the myocardium may provide a novel method for achieving cardiac regeneration following cardiac injury.