Angiotensin II stimulates apoptosis via TGF-β1 signaling in ventricular cardiomyocytes of rat

Elevations in angiotensin II (AngII) and transforming growth factor (TGF-beta 1) levels are often found under conditions leading to progression of heart failure. From several studies, it is evident that AngII enhances TGF-beta 1 expression via activator protein 1 (AP-1) activation, and that this pathway is involved in hypertrophic growth of the heart muscle and in the development of cardiac fibrosis. We now continued characterization of the signaling pathway stimulated by AngII in ventricular cardiomyocytes of rat and analyzed if the enhancement of TGF-beta 1 expression by AngII may also contribute to apoptosis induction, which is another predictor of heart failure progression. Stimulation of cardiomyocytes with 100 nM AngII for 2 h activated the transcription factors AP-1 and GATA by 68.6 +/- 23.9 or 70.7 +/- 9.8%. Induction of both factors was mediated by p38 mitogen-activated protein kinase (MAPK) because it was totally blocked using a specific inhibitor of the kinase (SB202190). When GATA was inhibited by transformation of cardiomyocytes with decoy oligonucleotides, AngII could not enhance TGF-beta 1 expression. This inhibition was observed on the mRNA level in real-time polymerase chain reaction and on the protein level in Western blots. As a consequence, upon AngII stimulation for 24 h, release of TGF-beta 1 from cardiomyocytes was also reduced from 240.5 +/- 50.4 to 130.5 +/- 22.1% (p < 0.05). In contrast to the early induction of GATA and AP-1, the transcription factor similar to mothers against decapentaplegic homolog (SMAD) was induced by AngII after 24 h. This stimulation was dependent on TGF-beta 1 because it was blocked by antibodies specific for TGF-beta 1. Twenty-four hours after AngII addition, the number of apoptotic cardiomyocytes increased by 6.5 +/- 1.2%, and this apoptosis induction was blocked when SMAD activity was inhibited by transformation of cardiomyocytes with SMAD decoy oligonucleotides. In conclusion, the transcription factors AP-1 and GATA are activated by p38 MAPK upon AngII stimulation, and both are needed to enhance TGF-beta 1 expression in ventricular cardiomyocytes. TGF-beta 1 acts in an autocrine loop on the cells to induce apoptosis via SMAD signaling. Thus, the often-found correlation between AngII, TGF-beta 1, AP-1, and SMAD in pathogenesis of heart disease reflects the proapoptotic signaling pathway induced by AngII in cardiomyocytes.