Inhibition of AP-1 signaling by JDP2 overexpression protects cardiomyocytes against hypertrophy and apoptosis induction.

AIMS: Expression and activity of the transcription factor AP-1 are enhanced during cardiac remodelling and heart failure progression. In order to test if AP-1 inhibition may limit processes contributing to cardiac remodelling, ventricular cardiomyocytes of mice with cardiac overexpression of the AP-1 inhibitor JDP2 were analysed under stimulation of hypertrophy, apoptosis, or contractile function. METHODS AND RESULTS: Three models of JDP2 overexpressing mice were analysed: JDP2 was overexpressed either life-long, for 7 weeks, or 1 week. Then cardiomyocytes were isolated and stimulated with ß-adrenoceptor agonist isoprenaline (ISO, 50 nM). This enhanced cross-sectional area and the rate of protein synthesis in WT but not in JDP2 overexpressing cardiomyocytes. To induce apoptosis, cardiomyocytes were stimulated with 3 ng/mL TGFß1. Again, JDP2 overexpression prevented apoptosis induction compared with WT cells. Determination of contractile function under electrical stimulation at 2 Hz revealed enhancement of cell shortening, and contraction and relaxation velocities under increasing ISO concentrations (0.3-30 nM) in WT cells. This inotropic effect was abrogated in JDP2 overexpression cells. Responsiveness to increased extracellular calcium concentrations was also impaired in JDP2 overexpressing cardiomyocytes. Simultaneously, a reduction of SERCA expression was found in JDP2 mice. CONCLUSION: A central role of AP-1 in the induction of hypertrophy and apoptosis in cardiomyocytes is demonstrated. Besides these protective effects of AP-1 inhibition on factors of cardiac remodelling, AP-1-inhibition impairs contractile function. Therefore, AP-1 acts as a double-edged sword that mediates mal-adaptive cardiac remodelling, but is required for maintaining a proper contractile function of cardiomyocytes.

TGFß receptor activation enhances cardiac apoptosis via SMAD activation and concomitant NO release.

UNLABELLED: Transforming growth factor ß (TGFß) expression is induced in the myocardium during transition from compensated hypertrophy to heart failure. In cardiomyocytes, stimulation with TGFß results in restricted contractile function and enhanced apoptosis. Nitric oxide (NO) also induces apoptosis and influences cardiac function. Therefore, we wanted to know whether NO is causally involved in TGFß-induced apoptosis. In isolated ventricular cardiomyocytes of adult rat incubation with TGFß(1) increased NO release which was inhibited by NOS inhibitor ETU but not with iNOS inhibitor (1400 W) or nNOS inhibitor (TFA). In addition, TGFß-induced apoptosis was blocked with ETU and ODQ, but not with 1400 W or TFA. The consequent assumption that endothelial NOS is involved in TGFß-induced NO formation and apoptosis was supported by increased phosphorylation of eNOS at serine 1177 and by the fact that TGFß did not increase NO release in eNOS KO mice. Furthermore, TGFß-induced apoptosis, NO formation, SMAD binding activity and SMAD2 phosphorylation were blocked by a TGFß receptor antagonist, but only apoptosis and NO formation could be blocked with ETU. Expression of SMAD7 was increased after TGFß stimulation and blocked with TGFß receptor antagonist but not after blocking NO synthase with ETU. CONCLUSION: In cardiomyocytes TGFß-induced apoptosis is mediated via TGFß receptor activation that concomitantly activates SMAD transcription factors and the eNOS/NO/sGC pathway. Both of these pathways are needed for apoptosis induction by TGFß. This reveals a new pathway of cardiac NO release and identifies NO as a possible contributor to heart failure progression mediated by TGFß.