Gerhild Taimor

Redox-sensitive intermediates mediate angiotensin II-induced p38 MAP kinase activation, AP-1 binding activity, and TGF-β expression in adult ventricular cardiomyocytes

Cardiac hypertrophy as an adaptation to increased blood pressure leads to an increase in ventricular expression of transforming growth factor β (TGF‐β), probably via the renin‐angiotensin system. We studied in vivo to determine whether angiotensin II affects TGF‐β expression independent from mechanical effects caused by the concomitant increase in blood pressure and in vitro intracellular signaling involved in angiotensin II‐dependent TGF‐β1 induction. In vivo, the AT1 receptor antagonist losartan, but not reduction of blood pressure by hydralazine, inhibited the increase in TGF‐β1 expression caused by angiotensin II. In vitro, angiotensin II caused an induction of TGF‐β1 expression in adult ventricular cardiomyocytes and induced AP‐1 binding activity. Transfection with “decoys” directed against the binding site of AP‐1 binding proteins inhibited the angiotensin II‐dependent TGF‐β induction. Angiotensin II induced TGF‐β expression in a p38‐MAP kinase‐dependent way. p38‐MAP kinase activation was diminished in presence of the antioxidants or diphenyleneiodium chloride, or by pretreatment with antisense nucleotides directed against phox22 and nox, components of smooth muscle type NAD(P)H oxidase. Thus, our study identifies a previously unrecognized coupling of cardiac AT receptors to a NAD(P)H oxidase complex similar to that expressed in smooth muscle cells and identifies p38‐MAP kinase activation as an important downstream target.

Apoptosis induction by nitric oxide in adult cardiomyocytes via cGMP-signaling and its impairment after simulated ischemia

OBJECTIVE Nitric oxide (NO) has been shown to induce apoptosis in cardiomyocytes under normoxic conditions. The ability of NO to induce apoptosis after ischemia-reperfusion, a situation of increased NO release in vivo, has not been investigated. The present study was undertaken to characterize the pathway of induction of apoptosis by NO and the influence of ischemia on this pathway in cardiomyocytes. METHODS The study was performed on isolated adult cardiomyocytes of the rat. Ischemia was simulated by anoxia in a glucose free medium, pH 6.4. Induction of apoptosis was detected (1) by annexinV-fluorescein isothiocyanate (annexinV-FITC) binding to cells under exclusion of propidium iodide and (2) by laddering of genomic DNA. RESULTS Incubation of cardiomyocytes with the NO-donor (+/-)-S-nitroso-N-acetylpenicillamine (SNAP, 100 microM) induced apoptosis in 14.1 +/- 1.9% of the cells and necrosis in 24.4 +/- 4.6%. The induction of apoptosis but not necrosis could be blocked by inhibition of soluble guanylyl cyclase or of protein kinase G. Apoptosis induction was mimicked by incubation of cardiomyocytes with 8-pCPT-cGMP (100 microM, 9.6 +/- 0.6% apoptotic cells) or YC-1 (75 microM, 14.6 +/- 2.8% apoptotic cells), a direct activator of soluble guanylyl cyclase. After 3 h of anoxia, cardiomyocytes were transiently protected against apoptosis induced by NO, but not by 8-pCPT-cGMP or YC-1 (8.9 +/- 0.7% or 13.4 +/- 2.4% apoptotic cells). A correlation of the apoptotic response to SNAP or YC-1 with an increased activity of soluble guanylyl cyclase, determined by measurements of intracellular cGMP contents, was found. CONCLUSIONS NO induces apoptosis in a cGMP dependent manner in isolated adult cardiomyocytes whereas induction of necrosis seems cGMP-independent. After simulated in vitro ischemia the activation of soluble guanylyl cyclase by NO is transiently inhibited resulting in a transient anti-apoptotic protection.

Transcription activator protein 1 (AP-1) mediates NO-induced apoptosis of adult cardiomyocytes

Release of nitric oxide (NO) during inflammation can induce apoptosis in the heart. Here we analyzed the involvement of members of the mitogen‐activated protein kinase (MAPK) family and their downstream target, the transcription factor AP‐1, in induction of apoptosis by NO in isolated adult cardiomyocytes of rat. The NO‐donor (±)‐S‐nitroso‐N‐acetylpenicillamine (100 μM SNAP)‐induced apoptosis in 10.5 ± 0.7% of cardiomyocytes and activated the transcription activator protein AP‐1 by 333.6 ± 122.3%. Intracellular scavenging of AP‐1 with decoy‐oligonucleotides blocked NO‐induced apoptosis to control levels (3.8 ± 0.5% apoptotic cells). Activation of AP‐1 with a c‐Jun amino‐terminal kinase (JNK) activator (Ro318220, 10 μM) provoked apoptosis in 18.7 ± 1.2% cardiomyocytes, which was again blocked by intracellular scavenging of AP‐1. NO activated JNK by 87.0 ± 27.3% and extracellular signal‐regulated kinase (ERK) by 35 ± 3%. Inhibition of ERK by the mitogen‐activated protein kinase kinase (MEK1) inhibitor PD98059 (10 μM) abolished AP‐1 activation and apoptosis induction with SNAP. Evidence that p38 MAPK plays a role in NO‐induced apoptosis was not found. These results clearly demonstrate the involvement of the transcription factor AP‐1 in NO‐induced apoptosis in cardiomyocytes. The activation of AP‐1 is mediated by the two MAP kinases JNK and ERK.

Role of phosphatidylinositol 3-kinase activation in the hypertrophic growth of adult ventricular cardiomyocytes

OBJECTIVE The present study investigated whether activation of phosphatidylinositol 3-kinase (PI3-kinase) is involved in the stimulation of hypertrophic growth of adult ventricular cardiomyocytes under alpha- or beta-adrenoceptor stimulation. METHODS Adult ventricular rat cardiomyocytes were used either directly after isolation (day 1 culture) or after cultivation for 6 days in presence of 20% fetal calf serum (day 7 culture). PI3-kinase activity was determined in extracts of cardiomyocytes after immunoprecipitation with an antibody against the p85 subunit of PI3-kinase. The influence of PI3-kinase inhibition on myocardial growth was determined using the specific PI3-kinase inhibitors wortmannin and LY294002. RESULTS In day 1 cultures alpha-adrenoceptor stimulation, but not beta-adrenoceptor stimulation caused activation of PI3-kinase. In response to alpha-adrenoceptor stimulation but not beta-adrenoceptor stimulation an acceleration of protein synthesis (incorporation of 14C-phenylalanine) and an increase in the total masses of cellular protein and RNA was observed. In these cultures inhibition of PI3-kinase attenuated the acceleration of protein synthesis and the increase in cellular masses of protein or RNA in response to alpha-adrenoceptor stimulation. In day 7 cultures alpha- and beta-adrenoceptor stimulation caused activation of PI3-kinase and increased protein synthesis. In these cultures inhibition of PI3-kinase attenuated the growth response to alpha- and beta-adrenoceptor stimulation. CONCLUSIONS PI3-kinase activation via protein kinase C-dependent or cAMP-dependent pathways is required for hypertrophic growth of adult cardiomyocytes.

Early response kinase and PI 3-kinase activation in adult cardiomyocytes and their role in hypertrophy

The present study investigated the role of early response kinase (ERK) and phosphatidylinositol 3 (PI 3)-kinase in ventricular cardiomyocytes from adult rat for the hypertrophic response to α-adrenoceptor stimulation. Parameters of the hypertrophic response were stimulation of protein synthesis and induction of creatine kinase BB. The α-adrenoceptor agonist phenylephrine (10 μmol/l) activated ERK2 and PI 3-kinase. The protein kinase C inhibitor bisindolylmaleimide (5 μmol/l) and the mitogen-activated protein kinase kinase inhibitor PD-98059 (10 μmol/l) but not the tyrosine kinase inhibitor genistein (100 μmol/l) blocked ERK2 activation. Inhibition of ERK2 activation abolished induction of creatine kinase BB by phenylephrine but not the increase in protein synthesis. The PI 3-kinase inhibitor wortmannin (100 nmol/l) blocked protein synthesis under α-adrenoceptor stimulation but did not interfere with ERK2 activation. Inhibition of the ERK2 pathway with PD-98059 did not affect PI 3-kinase activation. We conclude that ERK2- and PI 3-kinase-dependent pathways represent two mutually exclusive ways of signaling that lead to different aspects of the hypertrophic response to α-adrenoceptor stimulation.The present study investigated the role of early response kinase (ERK) and phosphatidylinositol 3 (PI 3)-kinase in ventricular cardiomyocytes from adult rat for the hypertrophic response to alpha-adrenoceptor stimulation. Parameters of the hypertrophic response were stimulation of protein synthesis and induction of creatine kinase BB. The alpha-adrenoceptor agonist phenylephrine (10 micromol/l) activated ERK2 and PI 3-kinase. The protein kinase C inhibitor bisindolylmaleimide (5 micromol/l) and the mitogen-activated protein kinase kinase inhibitor PD-98059 (10 micromol/l) but not the tyrosine kinase inhibitor genistein (100 micromol/l) blocked ERK2 activation. Inhibition of ERK2 activation abolished induction of creatine kinase BB by phenylephrine but not the increase in protein synthesis. The PI 3-kinase inhibitor wortmannin (100 nmol/l) blocked protein synthesis under alpha-adrenoceptor stimulation but did not interfere with ERK2 activation. Inhibition of the ERK2 pathway with PD-98059 did not affect PI 3-kinase activation. We conclude that ERK2- and PI 3-kinase-dependent pathways represent two mutually exclusive ways of signaling that lead to different aspects of the hypertrophic response to alpha-adrenoceptor stimulation.

Induction of necrosis but not apoptosis after anoxia and reoxygenation in isolated adult cardiomyocytes of rat

OBJECTIVES Apoptosis is one feature of myocardial damage after ischemia-reperfusion, but the causes for its induction are unclear. The present study was undertaken to investigate whether apoptosis in cardiomyocytes is directly initiated by their sub-lethal injury that results from ischemia-reperfusion. METHODS Ischemia was simulated on isolated ventricular cardiomyocytes of adult rats by anoxia in a glucose free medium, pH 6.4. Induction of apoptosis was detected by (1) DNA laddering of genomic DNA, (2) TUNEL positive cells (terminal deoxynucleotidyl transferase-mediated-UTP nick end labelling) and (3) annexinV-fluorescein isothiocyanate (annexinV-FITC) binding to cells under exclusion of propidium iodide. Necrotic cells were identified by (1) staining with both annexinV-FITC and propidium iodide, (2) unspecific DNA degradation and (3) enzyme release. RESULTS Simulated ischemia caused a > 75% loss of high-energy phosphates within 2 h, which was reversible upon reoxygenation at pH 7.4. Even after 18 h of simulated ischemia, creatine phosphate contents recovered to 55.2 +/- 7.3% of control within 1 h. Apoptosis could be induced by UV irradiation (80 J/m2), H2O2 and the NO-donor N2-acetyl-S-nitroso-D,L-penicillinaminamide. In contrast to this, simulated ischemia and reoxygenation could not induce apoptosis in the cells, but with prolonged ischemia more cells became necrotic. After 18 hours of simulated ischemia and 4 h of reoxygenation 41.2 +/- 10.2% myocytes were necrotic (vs. 6.3 +/- 4.4% of control) and only 1.7 +/- 0.5% (vs. 8.7 +/- 4.6% of control) were apoptotic. The percentage of necrotic cells correlated with an increase in lactate dehydrogenase release from 9.9 +/- 0.6% (of total activity) of normoxic controls to 37.9 +/- 5.1% after 18 h of simulated ischemia and 12 h of reoxygenation. CONCLUSIONS Simulated ischemia-reoxygenation causes necrosis of isolated cardiomyocytes but is not sufficient for induction of apoptosis.

Expression, Release, and Biological Activity of Parathyroid Hormone–Related Peptide From Coronary Endothelial Cells

Ventricular cardiomyocytes have previously been identified as potential target cells for parathyroid hormone-related peptide (PTHrP). Synthetic PTHrP peptides exert a positive contractile effect. Because systemic PTHrP levels are normally negligible, this suggests that PTHrP is expressed in the ventricle and acts as a paracrine mediator. We investigated the ventricular expression of PTHrP and its expression in cultured cells isolated from the ventricle, studied the release of PTHrP from hearts and cultures, and investigated whether this authentic PTHrP mimics the biological effects previously described for synthetic PTHrP on ventricular cardiomyocytes. We found PTHrP expressed in ventricles of neonatal and adult rat hearts. In cells isolated from adult hearts, we found PTHrP expression exclusively in coronary endothelial cells but not in cardiomyocytes. The latter, however, are target cells for PTHrP. PTHrP was released from isolated perfused hearts during hypoxic perfusion and from cultured coronary endothelial cells under energy-depleting conditions. This PTHrP was biologically active; ie, it exerted a positive contractile and lusitropic effect on cardiomyocytes. Authentic PTHrP was glycosylated and showed a slightly higher potency than synthetic PTHrP. These results suggest that PTHrP is an endothelium-derived modulator of ventricular function.

Central role for ornithine decarboxylase in β-adrenoceptor mediated hypertrophy

Objective: TGF-β stimulation of cardiac myocytes induces a hypertrophic responsiveness to β-adrenoceptor stimulation. This study investigates whether this β-adrenoceptor mediated effect depends on induction of ornithine decarboxylase (ODC). Methods: Isolated adult ventricular cardiomyocytes from rats were used as an experimental model. Cells were either cultured in 20% (v/v) FCS to activate autocrine released TGF-β or used without pre-treatment. The hypertrophic response was characterized by an increased 14C-phenylalanine incorporation, RNA and protein mass or by an increased expression of atrionatriurectic factor and ODC. The results on cell cultures were compared to those achieved by isoprenaline perfused mice hearts from transgenic mice overexpressing TGF-β1. Results: ODC activity and expression increased within 2 h in TGF-β1 pre-treated cells under isoprenaline. In the presence of ODC inhibitors (α-methylornithine or difluoromethylornithine) this increase remained absent and the increases in 14C-phenylalanine incorporation, protein and RNA mass under isoprenaline were abolished. In cells not exposed to TGF-β no induction of ODC was observed. Isoprenaline also induced ODC in isolated perfused ventricles from transgenic mice overexpressing TGF-β1, but not in ventricles from their nontransgenic counterparts. Conclusions: This study shows first, a pivotal role for ODC induction in the hypertrophic response of cardiomyocytes to β-adrenoceptor stimulation and second, that ODC induction in vivo and in vitro requires pre-treatment of cardiomyocytes with TGF-β. It is concluded that TGF-β induces a hypertrophic responsiveness to β-adrenoceptor stimulation that is characterized by ODC induction.

Intracellular signaling leads to the hypertrophic effect of neuropeptide Y.

Signal transduction pathways involved in the hypertrophic effect of neuropeptide Y (NPY) were investigated in adult cardiomyocytes. Reduction of transforming growth factor-β activity in serum-supplemented media abolished the induction of hypertrophic responsiveness to NPY. In responsive cells, NPY (100 nM) increased protein synthesis, determined as incorporation of [14C]phenylalanine, by 35 ± 15% ( P < 0.05, n = 16 cultures). In these cells, NPY activated pertussis toxin (PTx)-sensitive G proteins and phosphatidylinositol (PI) 3-kinase. PTx and inhibition of PI 3-kinase abolished the hypertrophic effect of NPY. NPY also activated protein kinase C (PKC) and mitogen-activated protein (MAP) kinase. Inhibition of these two kinases attenuated the induction of creatine kinase (CK)-BB but not the growth response to NPY. In conclusion, NPY stimulates protein synthesis in adult cardiomyocytes via activation of PTx-sensitive G proteins and PI 3-kinase and it induces the fetal-type CK-BB via activation of PKC and MAP kinase.

Neuropeptide Y modifies the hypertrophic response of adult ventricular cardiomyocytes to norepinephrine

OBJECTIVE The hypertrophic response of adult rat cardiomyocytes to norepinephrine via alpha-adrenoceptor stimulation is limited by an inhibitory cross-talk of simultaneously beta-adrenoceptor stimulation. On the other hand, neuropeptide Y (NPY), known to be co-secreted with norepinephrine from intramural nerve endings of the heart, exerts an anti-beta-adrenergic effect. Therefore, it should be expected that NPY enhances the hypertrophic response to norepinephrine. This hypothesis was addressed in the present study. METHODS Isolated adult ventricular cardiomyocytes from rats were used. As parameters of hypertrophic growth we investigated cell volume, cross-sectional area, protein mass. Protein and RNA synthesis were determined by incorporation of [(14)C]phenylalanine or [(14)C]uridine, respectively. RESULTS Norepinephrine (1 micromol/l) did not significantly increase protein or RNA synthesis. In co-presence of NPY (100 nmol/l), however, norepinephrine increased protein synthesis by 44% and RNA synthesis by 18%. Under the same conditions, NPY enhanced the effect of norepinephrine on cell volume from +6.4 to +18.2%, its effect on cross-sectional area from +16 to +23%, and increased the protein/DNA ratio from 32.5 to 35.6 mg/mg. In parallel, norepinephrine caused a translocation of PKC-alpha and PKC-delta into the particular fractions and this effect of norepinephrine was also enhanced by co-presence of NPY. In contrast, NPY did not enhance ERK-activation caused by norepinephrine. CONCLUSION Our study indicates the anti-beta-adrenergic effect of NPY is sufficient to modulate the hypertrophic response of adult ventricular cardiomyocytes to norepinephrine. The results suggest that the hypertrophic effect of norepinephrine via alpha-adrenoceptor stimulation can be modulated by co-release of NPY from intramural nerve endings.