ABSTRACT
Cardiomyocyte apoptosis leads to the functional incapacitation of myocardial plasmodium and plays an important role in the pathogenesis of heart failure transformed from compensable cardiac hypertrophy. Mitochondria are the main source of apoptosis-inducing molecule of various cells, and the role of caspartate-specific cysteinyl proteinase (caspase)-dependent mechanism has generally been accepted in the cardiomyocyte apoptosis. However, the significance of caspase-independent apoptosis-inducing factor (AIF) mechanism is not yet understood. The purpose of this study was to evaluate hypoxia-reperfusion-induced alterations of AIF mRNA and protein expressions in hypertrophic cardiomyocytes. Cardiomyocyte hypertrophy was produced by angiotensin II (0.1 mumol/L). The cells were cultured under the condition of hypoxia (95% N2 and 5% CO2; the O2 partial pressure was lower than 5 mmHg) for 8 h or 12 h (named as H8h and H12h groups, respectively), and then exposed to normal culture environment (named as H8h/R and H12h/R groups, respectively). Apoptosis was detected with Hoechst 33258 staining. The AIF mRNA and protein expressions were detected by RT-PCR and Western blot and quantified by gel scanning. The results were as follows: (1) The level of AIF mRNA expression was 0.29+/-0.08 (optical density, relative value) in the control group (hypertrophic cardiomyocytes cultured in normal environment). Compared with that in the control group, the levels of AIF mRNA expression were significantly higher in the groups of H8h and H12h (0.52+/-0.04 and 0.85+/-0.10), indicating that this effect was time-dependent. A further increase of AIF mRNA expression was observed in the groups of H8h/R (1.09+/-0.12) and H12h/R (1.41+/-0.23). (2) The level of AIF protein expression was 0.29+/-0.04 in the control group. Compared with that in the control group, the levels of AIF protein expression were significantly higher in the groups of H8h and H12h (2.07+/-0.15 and 3.12+/-0.19). The AIF protein expression was increased further in the groups of H8h/R (4.57+/-0.25) and H12h/R (5.71+/-0.27). The nuclear translocation of AIF protein was obvious only in the groups of H8h/R and H12h/R. (3) The expressions of AIF mRNA and protein were almost completely inhibited by AIF siRNA transfection. The siRNA transfection also reduced the apoptosis of hypertrophic cardiomyocytes in the groups of H8h/R and H12h/R but not in the groups of H8h and H12h. The apoptosis rate was significantly reduced by both AIF siRNA transfection and Ac-DEVD-cmk, an inhibitor of caspase-3. This reduction induced by two factors was more evident than that by one factor. (4) AIF nuclear translocation induced by hypoxia-reperfusion was not affected by inhibition of the activity of caspase-3. These data suggest that AIF plays a pivotal role in the apoptosis of hypertrophic cardiomyocytes induced by hypoxia-reperfusion.