Inhibition of anti-apoptotic signals by Wortmannin induces apoptosis in the remote myocardium after LAD ligation: evidence for a protein kinase C-δ-dependent pathway.

It has been shown that, in the remote myocardium after infarction (MI), protein kinase C (PKC) inhibition reduces apoptosis both by blocking proapoptotic pathways and by activating antiapoptotic signals including the Akt pathway. However, it was open if vice versa, blockade of antiapoptotic pathways may influence proapoptotic signals. To clarify this, the present study tested the effects of the PI3-kinase blocker Wortmannin on proapoptotic signals and on apoptosis execution in the remote myocardium after infarction. Rats were subjected to MI by LAD ligation in situ. Some were pre-treated with Wortmannin alone or in combination with the PKC inhibitor Chelerythrine. After 24 h, pro- and anti-apoptotic signals (caspase-3, PKC isoforms, p38-MAPK, p42/44-MAPK, Akt, Bad), and marker of apoptosis execution (TUNEL) were quantified in the myocardium remote from the infarction. Wortmannin treatment increased apoptosis in the remote myocardium both at baseline and after MI, together with an activation of the PKC-δ/p38-MAPK-pathway. PKC-ε and p42/44-MAPK were unaffected. Combined treatment with Wortmannin and Chelerythrine fully reversed the pro-apoptotic effects of Wortmannin both at baseline and after MI. The PKC-δ-p38-MAPK-pathway as a strong signal for apoptosis in the non-infarcted myocardium can be influenced by targeting the anti-apoptotic PI3-kinase pathway. This gives evidence of a bi-directional crosstalk of pro- and anti-apoptotic signals after infarction.

Leucine Supplementation Improves Diastolic Function in HFpEF by HDAC4 Inhibition.

Heart failure with preserved ejection fraction (HFpEF) is a complex syndrome associated with a high morbidity and mortality rate. Leucine supplementation has been demonstrated to attenuate cardiac dysfunction in animal models of cachexia and heart failure with reduced ejection fraction (HFrEF). So far, no data exist on leucine supplementation on cardiac function in HFpEF. Thus, the current study aimed to investigate the effect of leucine supplementation on myocardial function and key signaling pathways in an established HFpEF rat model. Female ZSF1 rats were randomized into three groups: Control (untreated lean rats), HFpEF (untreated obese rats), and HFpEF_Leu (obese rats receiving standard chow enriched with 3% leucine). Leucine supplementation started at 20 weeks of age after an established HFpEF was confirmed in obese rats. In all animals, cardiac function was assessed by echocardiography at baseline and throughout the experiment. At the age of 32 weeks, hemodynamics were measured invasively, and myocardial tissue was collected for assessment of mitochondrial function and for histological and molecular analyses. Leucine had already improved diastolic function after 4 weeks of treatment. This was accompanied by improved hemodynamics and reduced stiffness, as well as by reduced left ventricular fibrosis and hypertrophy. Cardiac mitochondrial respiratory function was improved by leucine without alteration of the cardiac mitochondrial content. Lastly, leucine supplementation suppressed the expression and nuclear localization of HDAC4 and was associated with Protein kinase A activation. Our data show that leucine supplementation improves diastolic function and decreases remodeling processes in a rat model of HFpEF. Beneficial effects were associated with HDAC4/TGF-ß1/Collagenase downregulation and indicate a potential use in the treatment of HFpEF.

Stimulation of adenosine A2b receptors blocks apoptosis in the non-infarcted myocardium even when administered after the onset of infarction.

OBJECTIVE: Chronic adenosine A2b receptor stimulation has been shown to prevent ventricular remodelling after myocardial infarction (MI). We hypothesized that this effect is due to the inhibition of cardiac myocyte apoptosis in the myocardium remote from the infarction. METHODS: Rats were subjected to MI by LAD ligation in situ. Some animals were pre-treated with the stable adenosine analogue 2-chloro-adenosine (CADO). After 24 h, pro- and anti-apoptotic signals (protein kinase C isoforms, p38, g proteins, Bcl-2/Bax ratio, Akt, Bad), and marker of apoptosis execution (caspase-3, TUNEL) were quantified in the remote myocardium. RESULTS: CADO prevented the occurrence of apoptosis in the remote myocardium of an infarcted heart. This effect occured not only when CADO was started before the onset of ischemia but also when it started 3 h after the infarction. The anti-apoptotic effect of CADO was blocked by simultaneous administration of the selective adenosine A2b receptor antagonist MRS1754 (1 mg/kg). The anti-apoptotic effect of CADO seems to be mediated by g(alphaq) and by the activation of survival kinases (Bad) and by inhibition of the pro-apoptotic PKC-delta/p38-MAPK-pathway. CONCLUSION: Chronic adenosine A2b receptor stimulation blocks cardiac myocyte apoptosis in the remote myocardium even when started after the onset of infarction. This may explain the anti-remodelling-effect of the A2b receptor stimulation after infarction.

Loss of Sox9 in cardiomyocytes delays the onset of cardiac hypertrophy and fibrosis.

BACKGROUND: The transcription factor Sox9 has been associated with cardiac injury and remodeling. Studies of mammalian hearts confirm Sox9 upregulation in fibroblasts following ischemic insults associated with enhanced fibrosis. The role of cardiomyocyte-specific Sox9 remains unclear. This study aimed to evaluate the role of cardiomyocyte-specific Sox9 in development and progression of left ventricular (LV) hypertrophy and fibrosis. METHODS: In male conditional Sox9 knockout mice (Sox9-KO) or floxed littermates (control group) transverse aortic constriction (TAC) was performed to induce LV hypertrophy. LV function and wall thickness were assessed weekly using echocardiography. LV mRNA- and protein expression levels of hypertrophy-, fibrosis-, and remodeling-associated genes were analyzed for each time point. Histological sections were stained for fibrosis and Sox9 expression. RESULTS: Only one week after TAC, the control group showed significantly enhanced heart weights and thickened LV posterior walls accompanied by elevated Anp- and Lox-mRNA levels. Simultaneously, Col1a1- and Col3a1-levels as well as Sox9 expression were strongly upregulated, Contrary, Sox9-KO mice did not develop cardiac hypertrophy until 4 weeks after TAC. Collagen and Sox9 expression also peaked at that later time point. Ejection fraction declined similarly in both groups after TAC. However, the control group showed a slightly better cardiac performance at 2 weeks after TAC. CONCLUSIONS: Cardiomyocyte-specific Sox9 mediates hypertrophy and early fibrosis, following cardiac pressure-overload. Loss of Sox9 delays cardiac growth and remodeling processes, however, does not preserve the cardiac function. We suggest that cardiomyocyte-driven Sox9 initiates a pro-hypertrophic cascade, possibly involving a cross-talk between myocytes and fibroblasts.