The PGE2-Stat3 interaction in doxorubicin-induced myocardial apoptosis

Abstract

Both cyclooxygenase-2 (COX-2) and the transcription factor signal transducer and activator of transcription 3 (Stat3) are involved in adaptive growth and survival of cardiomyocytes. In ventricular cardiomyocytes, prostaglandin E₂ (PGE₂), a major COX-2 product, leads to adaptive growth via Stat3 activation, but whether this transcription factor acts as a signalling molecule in PGE₂-induced cell survival is unknown. Therefore, the purpose of this study was to determine whether PGE₂ counteracts cardiac apoptosis induced by doxorubicin (DOX), and if so, whether Stat3 plays a critical role in this cardioprotective effect. Neonatal rat ventricular cardiomyocytes were incubated with DOX (0.5 µM) and/or PGE₂ (1 µM). Apoptosis was assessed by determining caspase3 activation and apoptotic DNA fragmentation. The role of Stat3 was evaluated in vitro and in vivo by transfecting cardiomyocytes with siRNA targeting rat Stat3 and by using cardiomyocyte-restricted Stat3 knockout (Stat3 KO) mice, respectively. Incubation of ventricular cardiomyocytes with PGE₂ led to a time-dependent decrease in the DOX-induced caspase3 activation, reaching a maximal inhibition of 70 ± 5% after 4 h. Similarly, PGE₂ inhibited DOX-induced DNA fragmentation by 58 ± 5% after 24 h. This antiapoptotic action of PGE₂ was strongly reduced by the ERK1/2 inhibitor, U0126, whereas the p38 MAP kinase inhibitor, SB203580, had no effect. Depleting Stat3 expression by 50–60% in isolated ventricular cardiomyocytes markedly reduced the protective effect of PGE₂ on DOX-induced caspase3 activation and DNA fragmentation. Likewise, the stable PGE₂ analogue, 16,16-dimethyl-PGE₂, was unable to counteract cardiac apoptosis induced by DOX in Stat3 KO mice. Our results demonstrate that PGE₂ prevents myocardial apoptosis induced by DOX. This protection requires the activation of the prosurvival pathways of Stat3 and ERK1/2.