Katrin Wittköpper

Inhibition of Elevated Ca2+/Calmodulin-Dependent Protein Kinase II Improves Contractility in Human Failing Myocardium

Rationale: Heart failure (HF) is known to be associated with increased Ca2+/calmodulin-dependent protein kinase (CaMK)II expression and activity. There is still controversial discussion about the functional role of CaMKII in HF. Moreover, CaMKII inhibition has never been investigated in human myocardium. Objective: We sought to investigate detailed CaMKII&dgr; expression in end-stage failing human hearts (dilated and ischemic cardiomyopathy) and the functional effects of CaMKII inhibition on contractility. Methods and Results: Expression analysis revealed that CaMKII&dgr;, both cytosolic &dgr;C and nuclear &dgr;B splice variants, were significantly increased in both right and left ventricles from patients with dilated or ischemic cardiomyopathy versus nonfailing. Experiments with isometrically twitching trabeculae revealed significantly improved force frequency relationships in the presence of CaMKII inhibitors (KN-93 and AIP). Increased postrest twitches after CaMKII inhibition indicated an improved sarcoplasmic reticulum (SR) Ca2+ loading. This was confirmed in isolated myocytes by a reduced SR Ca2+ spark frequency and hence SR Ca2+ leak, resulting in increased SR Ca2+ load when inhibiting CaMKII. Ryanodine receptor type 2 phosphorylation at Ser2815, which is known to be phosphorylated by CaMKII thereby contributing to SR Ca2+ leak, was found to be markedly reduced in KN-93–treated trabeculae. Interestingly, CaMKII inhibition did not influence contractility in nonfailing sheep trabeculae. Conclusions: The present study shows for the first time that CaMKII inhibition acutely improves contractility in human HF where CaMKII&dgr; expression is increased. The mechanism proposed consists of a reduced SR Ca2+ leak and consequently increased SR Ca2+ load. Thus, CaMKII inhibition appears to be a possible therapeutic option for patients with HF and merits further investigation.

Constitutively active phosphatase inhibitor-1 improves cardiac contractility in young mice but is deleterious after catecholaminergic stress and with aging

Phosphatase inhibitor-1 (I-1) is a distal amplifier element of beta-adrenergic signaling that functions by preventing dephosphorylation of downstream targets. I-1 is downregulated in human failing hearts, while overexpression of a constitutively active mutant form (I-1c) reverses contractile dysfunction in mouse failing hearts, suggesting that I-1c may be a candidate for gene therapy. We generated mice with conditional cardiomyocyte-restricted expression of I-1c (referred to herein as dTGI-1c mice) on an I-1-deficient background. Young adult dTGI-1c mice exhibited enhanced cardiac contractility but exaggerated contractile dysfunction and ventricular dilation upon catecholamine infusion. Telemetric ECG recordings revealed typical catecholamine-induced ventricular tachycardia and sudden death. Doxycycline feeding switched off expression of cardiomyocyte-restricted I-1c and reversed all abnormalities. Hearts from dTGI-1c mice showed hyperphosphorylation of phospholamban and the ryanodine receptor, and this was associated with an increased number of catecholamine-induced Ca2+ sparks in isolated myocytes. Aged dTGI-1c mice spontaneously developed a cardiomyopathic phenotype. These data were confirmed in a second independent transgenic mouse line, expressing a full-length I-1 mutant that could not be phosphorylated and thereby inactivated by PKC-alpha (I-1S67A). In conclusion, conditional expression of I-1c or I-1S67A enhanced steady-state phosphorylation of 2 key Ca2+-regulating sarcoplasmic reticulum enzymes. This was associated with increased contractile function in young animals but also with arrhythmias and cardiomyopathy after adrenergic stress and with aging. These data should be considered in the development of novel therapies for heart failure.

Phosphodiesterase-2 Is Up-Regulated in Human Failing Hearts and Blunts β-Adrenergic Responses in Cardiomyocytes

OBJECTIVES This study investigated whether myocardial phosphodiesterase-2 (PDE2) is altered in heart failure (HF) and determined PDE2-mediated effects on beta-adrenergic receptor (β-AR) signaling in healthy and diseased cardiomyocytes. BACKGROUND Diminished cyclic adenosine monophosphate (cAMP) and augmented cyclic guanosine monophosphate (cGMP) signaling is characteristic for failing hearts. Among the PDE superfamily, PDE2 has the unique property of being able to be stimulated by cGMP, thus leading to a remarkable increase in cAMP hydrolysis mediating a negative cross talk between cGMP and cAMP signaling. However, the role of PDE2 in HF is poorly understood. METHODS Immunoblotting, radioenzymatic- and fluorescence resonance energy transfer-based assays, video edge detection, epifluorescence microscopy, and L-type Ca2(+) current measurements were performed in myocardial tissues and/or isolated cardiomyocytes from human and/or experimental HF, respectively. RESULTS Myocardial PDE2 expression and activity were ~2-fold higher in advanced human HF. Chronic β-AR stimulation via catecholamine infusions in rats enhanced PDE2 expression ~2-fold and cAMP hydrolytic activity ~4-fold, which correlated with blunted cardiac β-AR responsiveness. In diseased cardiomyocytes, higher PDE2 activity could be further enhanced by stimulation of cGMP synthesis via nitric oxide donors, whereas specific PDE2 inhibition partially restored β-AR responsiveness. Accordingly, PDE2 overexpression in healthy cardiomyocytes reduced the rise in cAMP levels and L-type Ca2(+) current amplitude, and abolished the inotropic effect following acute β-AR stimulation, without affecting basal contractility. Importantly, PDE2-overexpressing cardiomyocytes showed marked protection from norepinephrine-induced hypertrophic responses. CONCLUSIONS PDE2 is markedly up-regulated in failing hearts and desensitizes against acute β-AR stimulation. This may constitute an important defense mechanism during cardiac stress, for example, by antagonizing excessive β-AR drive. Thus, activating myocardial PDE2 may represent a novel intracellular antiadrenergic therapeutic strategy in HF.

Phosphatase-1 inhibitor-1 in physiological and pathological β-adrenoceptor signalling

Control of protein phosphorylation-dephosphorylation events occurs through regulation of protein kinases and phosphatases. Phosphatase type 1 (PP-1) provides the main activity of serine/threonine protein phosphatases in the heart. Inhibitor-1 (I-1) was the first endogenous molecule found to inhibit PP-1 specifically. Notably, I-1 is activated by cAMP-dependent protein kinase A (PKA), and the subsequent prevention of target dephosphorylation by PP-1 provides distal amplification of β-adrenoceptor (β-AR) signalling. I-1 was found to be down-regulated and hypo-phosphorylated in human and experimental heart failure but hyperactive in human atrial fibrillation, implicating I-1 in the pathogenesis of heart failure and arrhythmias. Consequently, the therapeutic potential of I-1 in heart failure and arrhythmias has recently been addressed by the generation and analysis of several I-1 genetic mouse models. This review summarizes and discusses these data, highlights partially controversial issues on whether I-1 should be therapeutically reinforced or inhibited and suggests future directions to better understand the functional role of I-1 in physiological and pathological β-AR signalling.

Follistatin-Like 1 in Chronic Systolic Heart Failure A Marker of Left Ventricular Remodeling

Background— Follistatin-like 1 (FSTL1) is an extracellular glycoprotein found in human serum. Recent work suggests that FSTL1 is secreted in response to ischemic injuries and that its overexpression is protective in the heart and vasculature. Methods and Results— We examined serum FSTL1 levels in patients with chronic heart failure with left ventricular (LV) ejection fraction <40% (n=86). The sample was separated into three tertiles of patients with low, medium, and high FSTL1 levels. Serum FSTL1 was increased 56% above age- and sex-matched healthy controls. Diabetes mellitus, brain natriuretic peptide level, left atrial size, LV posterior wall thickness, LV end-diastolic diameter, and LV mass were significant determinants of FSTL1 serum levels by bivariate analysis. After controlling for significant covariates, FSTL1 levels predicted LV hypertrophy (as measured by LV mass index) by multivariate linear regression analysis ( P <0.001). Unadjusted survival analysis demonstrated increased mortality in patients with increasing FSTL1 levels ( P =0.09). After adjusting for significant parameters, patients with increased FSTL1 remained at the highest risk of death (hazard ratio, 1.028; 95% CI, 0.98 to 1.78; P =0.26). To determine whether elevated FSTL1 levels may be derived from the myocardium, FSTL1 protein expression was measured in explanted failing (n=18) and nonfailing (n=7) human hearts. LV failing hearts showed 2.5-fold higher FSTL1 protein levels over nonfailing control hearts ( P <0.05). Conclusions— Elevated serum FSTL1 in patients with heart failure was associated with LV hypertrophy. Further studies on the role of FSTL1 as a biomarker in chronic systolic heart failure are warranted.Background— Follistatin-like 1 (FSTL1) is an extracellular glycoprotein found in human serum. Recent work suggests that FSTL1 is secreted in response to ischemic injuries and that its overexpression is protective in the heart and vasculature. Methods and Results— We examined serum FSTL1 levels in patients with chronic heart failure with left ventricular (LV) ejection fraction <40% (n=86). The sample was separated into three tertiles of patients with low, medium, and high FSTL1 levels. Serum FSTL1 was increased 56% above age- and sex-matched healthy controls. Diabetes mellitus, brain natriuretic peptide level, left atrial size, LV posterior wall thickness, LV end-diastolic diameter, and LV mass were significant determinants of FSTL1 serum levels by bivariate analysis. After controlling for significant covariates, FSTL1 levels predicted LV hypertrophy (as measured by LV mass index) by multivariate linear regression analysis (P<0.001). Unadjusted survival analysis demonstrated increased mortality in patients with increasing FSTL1 levels (P=0.09). After adjusting for significant parameters, patients with increased FSTL1 remained at the highest risk of death (hazard ratio, 1.028; 95% CI, 0.98 to 1.78; P=0.26). To determine whether elevated FSTL1 levels may be derived from the myocardium, FSTL1 protein expression was measured in explanted failing (n=18) and nonfailing (n=7) human hearts. LV failing hearts showed 2.5-fold higher FSTL1 protein levels over nonfailing control hearts (P<0.05). Conclusions— Elevated serum FSTL1 in patients with heart failure was associated with LV hypertrophy. Further studies on the role of FSTL1 as a biomarker in chronic systolic heart failure are warranted.

The new HNO donor, 1-nitrosocyclohexyl acetate, increases contractile force in normal and β-adrenergically desensitized ventricular myocytes

Contractile dysfunction and diminished response to β-adrenergic agonists are characteristics for failing hearts. Chemically donated nitroxyl (HNO) improves contractility in failing hearts and thus may have therapeutic potential. Yet, there is a need for pharmacologically suitable donors. In this study we tested whether the pure and long acting HNO donor, 1-nitrosocyclohexyl acetate (NCA), affects contractile force in normal and pathological ventricular myocytes (VMs) as well as in isolated hearts. VMs were isolated from mice either subjected to isoprenaline-infusion (ISO; 30 μg/g per day) or to vehicle (0.9% NaCl) for 5 days. Sarcomere shortening and Ca2+ transients were simultaneously measured using the IonOptix system. Force of contraction of isolated hearts was measured by a Langendorff-perfusion system. NCA increased peak sarcomere shortening by+40-200% in a concentration-dependent manner (EC50 ∼55 μM). Efficacy and potency did not differ between normal and chronic ISO VMs, despite the fact that the latter displayed a markedly diminished inotropic response to acute β-adrenergic stimulation with ISO (1 μM). NCA (60 μM) increased peak sarcomere shortening and Ca2+ transient amplitude by ∼200% and ∼120%, respectively, suggesting effects on both myofilament Ca2+ sensitivity and sarcoplasmic reticulum (SR) Ca2+ cycling. Importantly, NCA did not affect diastolic Ca2+ or SR Ca2+ content, as assessed by rapid caffeine application. NCA (45 μM) increased force of contraction by 30% in isolated hearts. In conclusion, NCA increased contractile force in normal and β-adrenergically desensitized VMs as well as in isolated mouse hearts. This profile warrants further investigations of this HNO donor in the context of heart failure.

Preservation of left ventricular function and morphology in volume-loaded versus volume-unloaded heterotopic heart transplants

Total mechanical unloading of the heart in classical models of heterotopic heart transplantation leads to cardiac atrophy and functional deterioration. In contrast, partial unloading of failing human hearts with left ventricular (LV) assist devices (LVADs) can in some patients ameliorate heart failure symptoms. Here we tested in heterotopic rat heart transplant models whether partial volume-loading (VL; anastomoses: aorta of donor to aorta of recipient, pulmonary artery of donor to left atrium of donor, superior vena cava of donor to inferior vena cava of recipient; n = 27) is superior to the classical model of myocardial unloading (UL; anastomoses: aorta of donor to aorta of recipient, pulmonary artery of donor to inferior vena cava of recipient; n = 14) with respect to preservation of ventricular morphology and function. Echocardiography, magnetic resonance imaging, and LV-pressure-volume catheter revealed attenuated myocardial atrophy with ~30% higher LV weight and better systolic contractile function in VL compared with UL (fractional area shortening, 34% vs. 18%; maximal change in pressure over time, 2,986 ± 252 vs. 2,032 ± 193 mmHg/s). Interestingly, no differences in fibrosis (Picrosirus red staining) or glucose metabolism (2-[18F]-fluoro-2-deoxy-D-glucose-PET) between VL and UL were observed. We conclude that the rat model of partial VL attenuates atrophic remodelling and shows superior morphological as well as functional preservation, and thus should be considered more widely as a research model.

Follistatin-Like 1 in Chronic Systolic Heart FailureClinical Perspective

Background— Follistatin-like 1 (FSTL1) is an extracellular glycoprotein found in human serum. Recent work suggests that FSTL1 is secreted in response to ischemic injuries and that its overexpression is protective in the heart and vasculature. Methods and Results— We examined serum FSTL1 levels in patients with chronic heart failure with left ventricular (LV) ejection fraction <40% (n=86). The sample was separated into three tertiles of patients with low, medium, and high FSTL1 levels. Serum FSTL1 was increased 56% above age- and sex-matched healthy controls. Diabetes mellitus, brain natriuretic peptide level, left atrial size, LV posterior wall thickness, LV end-diastolic diameter, and LV mass were significant determinants of FSTL1 serum levels by bivariate analysis. After controlling for significant covariates, FSTL1 levels predicted LV hypertrophy (as measured by LV mass index) by multivariate linear regression analysis ( P <0.001). Unadjusted survival analysis demonstrated increased mortality in patients with increasing FSTL1 levels ( P =0.09). After adjusting for significant parameters, patients with increased FSTL1 remained at the highest risk of death (hazard ratio, 1.028; 95% CI, 0.98 to 1.78; P =0.26). To determine whether elevated FSTL1 levels may be derived from the myocardium, FSTL1 protein expression was measured in explanted failing (n=18) and nonfailing (n=7) human hearts. LV failing hearts showed 2.5-fold higher FSTL1 protein levels over nonfailing control hearts ( P <0.05). Conclusions— Elevated serum FSTL1 in patients with heart failure was associated with LV hypertrophy. Further studies on the role of FSTL1 as a biomarker in chronic systolic heart failure are warranted.Background— Follistatin-like 1 (FSTL1) is an extracellular glycoprotein found in human serum. Recent work suggests that FSTL1 is secreted in response to ischemic injuries and that its overexpression is protective in the heart and vasculature. Methods and Results— We examined serum FSTL1 levels in patients with chronic heart failure with left ventricular (LV) ejection fraction <40% (n=86). The sample was separated into three tertiles of patients with low, medium, and high FSTL1 levels. Serum FSTL1 was increased 56% above age- and sex-matched healthy controls. Diabetes mellitus, brain natriuretic peptide level, left atrial size, LV posterior wall thickness, LV end-diastolic diameter, and LV mass were significant determinants of FSTL1 serum levels by bivariate analysis. After controlling for significant covariates, FSTL1 levels predicted LV hypertrophy (as measured by LV mass index) by multivariate linear regression analysis (P<0.001). Unadjusted survival analysis demonstrated increased mortality in patients with increasing FSTL1 levels (P=0.09). After adjusting for significant parameters, patients with increased FSTL1 remained at the highest risk of death (hazard ratio, 1.028; 95% CI, 0.98 to 1.78; P=0.26). To determine whether elevated FSTL1 levels may be derived from the myocardium, FSTL1 protein expression was measured in explanted failing (n=18) and nonfailing (n=7) human hearts. LV failing hearts showed 2.5-fold higher FSTL1 protein levels over nonfailing control hearts (P<0.05). Conclusions— Elevated serum FSTL1 in patients with heart failure was associated with LV hypertrophy. Further studies on the role of FSTL1 as a biomarker in chronic systolic heart failure are warranted.

Follistatin-Like 1 in Chronic Systolic Heart FailureClinical Perspective: A Marker of Left Ventricular Remodeling

Background— Follistatin-like 1 (FSTL1) is an extracellular glycoprotein found in human serum. Recent work suggests that FSTL1 is secreted in response to ischemic injuries and that its overexpression is protective in the heart and vasculature. Methods and Results— We examined serum FSTL1 levels in patients with chronic heart failure with left ventricular (LV) ejection fraction <40% (n=86). The sample was separated into three tertiles of patients with low, medium, and high FSTL1 levels. Serum FSTL1 was increased 56% above age- and sex-matched healthy controls. Diabetes mellitus, brain natriuretic peptide level, left atrial size, LV posterior wall thickness, LV end-diastolic diameter, and LV mass were significant determinants of FSTL1 serum levels by bivariate analysis. After controlling for significant covariates, FSTL1 levels predicted LV hypertrophy (as measured by LV mass index) by multivariate linear regression analysis ( P <0.001). Unadjusted survival analysis demonstrated increased mortality in patients with increasing FSTL1 levels ( P =0.09). After adjusting for significant parameters, patients with increased FSTL1 remained at the highest risk of death (hazard ratio, 1.028; 95% CI, 0.98 to 1.78; P =0.26). To determine whether elevated FSTL1 levels may be derived from the myocardium, FSTL1 protein expression was measured in explanted failing (n=18) and nonfailing (n=7) human hearts. LV failing hearts showed 2.5-fold higher FSTL1 protein levels over nonfailing control hearts ( P <0.05). Conclusions— Elevated serum FSTL1 in patients with heart failure was associated with LV hypertrophy. Further studies on the role of FSTL1 as a biomarker in chronic systolic heart failure are warranted.Background— Follistatin-like 1 (FSTL1) is an extracellular glycoprotein found in human serum. Recent work suggests that FSTL1 is secreted in response to ischemic injuries and that its overexpression is protective in the heart and vasculature. Methods and Results— We examined serum FSTL1 levels in patients with chronic heart failure with left ventricular (LV) ejection fraction <40% (n=86). The sample was separated into three tertiles of patients with low, medium, and high FSTL1 levels. Serum FSTL1 was increased 56% above age- and sex-matched healthy controls. Diabetes mellitus, brain natriuretic peptide level, left atrial size, LV posterior wall thickness, LV end-diastolic diameter, and LV mass were significant determinants of FSTL1 serum levels by bivariate analysis. After controlling for significant covariates, FSTL1 levels predicted LV hypertrophy (as measured by LV mass index) by multivariate linear regression analysis (P<0.001). Unadjusted survival analysis demonstrated increased mortality in patients with increasing FSTL1 levels (P=0.09). After adjusting for significant parameters, patients with increased FSTL1 remained at the highest risk of death (hazard ratio, 1.028; 95% CI, 0.98 to 1.78; P=0.26). To determine whether elevated FSTL1 levels may be derived from the myocardium, FSTL1 protein expression was measured in explanted failing (n=18) and nonfailing (n=7) human hearts. LV failing hearts showed 2.5-fold higher FSTL1 protein levels over nonfailing control hearts (P<0.05). Conclusions— Elevated serum FSTL1 in patients with heart failure was associated with LV hypertrophy. Further studies on the role of FSTL1 as a biomarker in chronic systolic heart failure are warranted.