Objective Downregulation of CyclinA2 till disappearance in mammalian heart after birth is associated with the withdrawal of cardiomyocytes from cell cycle. We hypothesis that exogenous CyclinA2 transferred into infracted myocardium might induce cardiac regeneration and reactivate cardiomyocytes cell cycle.
Methods Adeno-associated virus type 9 -CyclinA2-CMV recombinant was constructed and 2 × 1011vg constructs in 200ul of saline were deliveried into mice myocardium through tail vein one week before MI created (n = 20). The control group (n = 20) were injected with saline at a same volume and time. Post-MI observation were respectively 1 week and 3weeks. Echocardiography was performed to measure Left Ventricular End Diastole Diameter (LVEDD), Left Ventricular End Systolic Diameter (LVESD) and Ejection Fraction (EF). Western blot and immunohistochemical analysis were used to detect the expression and location of CyclinA2. DNA synthesis and mitosis were respectively analysed by PCNA and phosphohistone-H3. C-kit and connexin 43 were also measured. Masson’s trichrome stain was used to measue collagen volume in two groups.
Results CyclinA2 located in cytoplasm but not nuclear after transferred. Western blot showed that expression of CyclinA2 in two groups has a significant statistical difference (p group than control (0.75 + 0.03 VS 0.43 + 0.02, p = 0.036). However mitosis specific protein H3P had no statistical difference in two groups (p > 0.05). C-kit expression showed an increase in CyclinA2 treated group but no change in control (p < 0.05). Immunohistochemical analysis showed that PCNA positive cells in CyclinA2 treated group were 41.3 ± 2.1 VS control 25 ± 1.1 (p = 0.017). C-kit and connexin 43 positive cells and areas exhibit higher level in CyclinA2 treated group verus control. Masson’s trichrome stain showed a decrease level of collagen in CyclinA2 treated group than control (p = 0.029). Echocardiography showed that LVEDD, LVESD and EF in CyclinA2 treated groups and control were respectively 0.31 ± 0.02cm VS 0.44 ± 0.01cm (p < 0.05) and 0.21 ± 0.02cm VS 0.34 ± 0.01cm (p < 0.05) and 55 ± 2.3% VS 40 ± 1.7% (p < 0.05).
Conclusions Expression of Cyclin A2 via gene transfer induced cardiomyocyte DNA synthesis but no mitosis. Cyclin A2 might promote cardiac regeneration via the recruitment of c-kit+ cells which had been known as a cardiac stem cell marker. Continuous expression of CyclinA2 improved cardiac function after MI.