Nazha Hamdani - Academia.edu (original) (raw)

Papers by Nazha Hamdani

European journal of heart failure, Jan 23, 2015

Cell-cell or inter-organ communication allows the exchange of information and messages, which is ... more Cell-cell or inter-organ communication allows the exchange of information and messages, which is essential for the coordination of cell/organ functions and the maintenance of homeostasis. It has become evident that dynamic interactions of different cell types play a major role in the heart, in particular during the progression of heart failure, a leading cause of mortality worldwide. Heart failure is associated with compensatory structural and functional changes mostly in cardiomyocytes and cardiac fibroblasts, which finally lead to cardiomyocyte hypertrophy and fibrosis. Intercellular communication within the heart is mediated mostly via direct cell-cell interaction or the release of paracrine signalling mediators such as cytokines and chemokines. However, recent studies have focused on the exchange of genetic information via the packaging into vesicles as well as the crosstalk of lipids and other paracrine molecules within the heart and distant organs, such as kidney and adipose t...

American Journal of Physiology - Heart and Circulatory Physiology, 2015

Heart failure with preserved ejection fraction (HFPEF) evolves with the accumulation of risk fact... more Heart failure with preserved ejection fraction (HFPEF) evolves with the accumulation of risk factors. Relevant animal models to identify potential therapeutic targets and to test novel therapies for HFPEF are missing. We induced hypertension and hyperlipidemia in landrace pigs (n=8) by deoxycorticosteroneacetate (DOCA, 100 mg/kg, 90d-release subcutaneous depot) and a western diet (WD) containing high amounts of salt, fat, cholesterol and sugar for 12 wks. Compared to weight-matched controls (n=8), DOCA/WD treated pigs showed left ventricular (LV) concentric hypertrophy and left atrial (LA) dilatation in the absence of significant changes in LV ejection fraction or symptoms of heart failure at rest. The LV end-diastolic pressure-volume relationship (EDPVR) was markedly shifted leftwards. During simultaneous right atrial pacing and dobutamine infusion, cardiac output reserve and LV peak inflow velocities were lower in DOCA/WD treated pigs at higher LV end-diastolic pressures. In LV biopsies, we observed myocyte hypertrophy, a shift towards the stiffer titin isoform N2B and reduced total-titin phosphorylation. LV superoxide production was increased, in part due to nitric oxide synthase (NOS) uncoupling, while AKT and NOS isoform expression and phosphorylation were unchanged. In conclusion, we developed a large animal model where loss of LV capacitance was associated with a titin isoform shift and dysfunctional NOS, in the presence of preserved LV ejection fraction. Our findings identify potential targets for the treatment of HFPEF in a relevant large animal model.

European Journal of Heart Failure Supplements

Biophysical Journal, 2014

Biophysical Journal, 2014

Biophysical Journal, 2014

European Journal of Heart Failure Supplements, 2006

Basic research in cardiology, 2014

Increased levels of interleukin-6 (IL-6) have been observed in patients with acute myocarditis an... more Increased levels of interleukin-6 (IL-6) have been observed in patients with acute myocarditis and are associated with poor prognosis. This study was designed to examine whether treatment with anti-IL-6 receptor antibody improves cardiac dysfunction and left ventricular (LV) remodeling in experimental Coxsackie virus B3 (CVB3)-induced myocarditis. C57BL6/J mice were subjected to acute CVB3 infection. One day after viral infection mice were treated with a single injection of an anti-IL-6 receptor antibody (MR16-1, tocilizumab) or control IgG. Seven days after viral infection, LV function was examined by conductance catheter technique, cardiac remodeling assessed by estimation of titin phosphorylation, cardiac fibrosis, and inflammatory and antiviral response by immunohistochemistry, RT-PCR and cell culture experiments. Compared to controls, infected mice displayed an impaired systolic and diastolic LV function associated with an increase in cardiac inflammation, fibrosis and impaired...

BMC Pharmacology and Toxicology, 2013

Cardiovascular Research, 2014

Obesity and Type 2 diabetes mellitus (DM) induce left ventricular (LV) diastolic dysfunction, whi... more Obesity and Type 2 diabetes mellitus (DM) induce left ventricular (LV) diastolic dysfunction, which contributes to an increasing prevalence of heart failure with a preserved LV ejection fraction. We investigated the effects of sitagliptin (SITA), an inhibitor of dipeptidylpeptidase-4 (DPP-4) and anti-diabetic drug, on LV structure and function of obese mice with Type 2 DM. Obese Type 2 diabetic mice (Lepr(db/db), BKS.Cg-Dock7(m)+/+ Lepr(db)/J), displaying increased cardiomyocyte and LV stiffness at the age of 16 weeks, were treated with SITA (300 mg/kg/day) or vehicle for 8 weeks. SITA severely impaired serum DPP-4 activity, but had no effect on glycaemia. Invasive haemodynamic recordings showed that SITA reduced LV passive stiffness and increased LV stroke volume; LV end-systolic elastance remained unchanged. In addition, SITA reduced resting tension of isolated single cardiomyocytes and intensified phosphorylation of the sarcomeric protein titin. SITA also increased LV concentrations of cGMP and increased activity of protein kinase G (PKG). In vitro activation of PKG decreased resting tension of cardiomyocytes from vehicle-treated mice, but had no effect on resting tension of cardiomyocytes from SITA-treated mice. In obese Type 2 diabetic mice, in the absence of hypoglycaemic effects, inhibition of DPP-4 decreases LV passive stiffness and improves global LV performance. These effects seem at least partially mediated by stimulatory effects on the myocardial cGMP-PKG pathway and, hence, on the phosphorylation status of titin and the hereto coupled cardiomyocyte stiffness modulus.

Frontiers in Physiology, 2011

Aim: Transmural differences in sarcomeric protein composition and function across the left ventri... more Aim: Transmural differences in sarcomeric protein composition and function across the left ventricular (LV) wall have been reported. We studied in pigs sarcomeric function and protein phosphorylation in subepicardial (EPI) and subendocardial (ENDO) layers of remote LV myocardium after myocardial infarction (MI), induced by left circumflex coronary artery ligation. Methods: EPI and ENDO samples were taken 3 weeks after sham surgery (n = 12) or induction of MI (n = 12) at baseline (BL) and during β-adrenergic receptor (βAR) stimulation with dobutamine. Isometric force was measured in single cardiomyocytes at various [Ca 2+ ] and 2.2 μm sarcomere length. Results: In sham hearts, no significant transmural differences were observed in myofilament function or protein phosphorylation. Myofilament Ca 2+ -sensitivity was significantly higher in both EPI and ENDO of MI compared to sham hearts. Maximal force was significantly reduced in MI compared to sham, but solely in ENDO cells. A higher passive force was observed in MI hearts, but only in EPI cells. The proportion of stiff N2B isoform was higher in EPI than in ENDO in both sham and MI hearts, and a trend toward increased N2B-proportion appeared in MI EPI, but not MI Endo. Analysis of myofilament protein phosphorylation did not reveal significant transmural differences in phosphorylation of myosin binding protein C, desmin, troponin T, troponin I (cTnI), and myosin light chain 2 (MLC-2) both at BL and during βAR stimulation with dobutamine infusion. A significant increase in MLC-2 phosphorylation was observed during dobutamine only in sham. In addition, the increase in cTnI phosphorylation upon dobutamine was twofold lower in MI than in sham. Conclusion: Myofilament dysfunction is present in both EPI and ENDO in post-MI remodeled myocardium, but shows a high degree of qualitative heterogeneity across the LV wall. These heterogeneous transmural changes in sarcomeric properties likely contribute differently to systolic vs. diastolic global LV dysfunction after MI.

Cardiovascular Research, 2014

ABSTRACT Neuregulin (NRG)-1 is involved in the preservation of left ventricular performance. Neve... more ABSTRACT Neuregulin (NRG)-1 is involved in the preservation of left ventricular performance. Nevertheless, the role of NRG-1 in pulmonary arterial hypertension(PAH) and right ventricular(RV) diastolic stiffness is unknown. We analysed the presence and possible underlying mechanisms of RV diastolic dysfunction in an animal model of PAH and the role of NRG-1 in this context. Wistar rats randomly received monocrotaline (MCT,60mg/Kg,sc) or vehicle. After 14 days, rats received NRG-1 (40ug/Kg/day,ip) or vehicle. The study resulted in 4 groups: control(CTRL,n=16); CTRL+NRG(n=15); MCT(n=13); MCT+NRG(n=18). RV invasive hemodynamic studies and sample collection were performed 25-28 days after MCT administration. Isolated cardiomyocytes were stretched to measure resting tension and phosphorylation of titin isoforms was analyzed (ProQ Diamond and SYPRO Ruby protein gel stains). Only significant results (p<0.05) are given. RV diastolic stiffness (β) was increased in MCT rats (MCT vs CTRL:0.016±0.002 vs 0.008±0.001). However, NRG-1 treatment attenuated this change (MCT+NRG:0.007±0.001). Histological analyses revealed increased cardiomyocyte cross-sectional areas (MCT vs CTRL:536.67±59.46 vs 375.39±47.43μm2), indicating RV hypertrophy. In addition, the amount of RV fibrosis was enhanced in PAH tissue (MCT vs CTRL:2.04±0.17 vs 0.98±0.07%). NRG-1 also attenuated both changes (MCT+NRG:409.01±19.72μm2 and 1.00±0.17%, respectively). MCT-group isolated cardiomyocytes developed higher passive force when compared to CTRL-group cells at the sarcomere lengths of 2.0 (MCT vs CTRL:1.90±0.43 vs 1.43±0.29N/m2), 2.2 (MCT vs CTRL:3.66±0.69 vs 2.68±0.24N/m2), and 2.3μm (MCT vs CTRL: 5.76±1.15 vs 3.86±0.87N/m2). NRG-1 restored passive force development to levels similar to the CTRL-group, at 2.0, 2.2, and 2.3μm (MCT+NRG:1.28±0.25, 3.04±0.55, and 3.63±0.89N/m2, respectively). CTRL+NRG-group cells developed less passive force compared to CTRL-group (CTRL+NRG:1.16±0.31, 2.27±0.38, and 3.05±0.54N/m2, at 2.0, 2.2, and 2.3μm respectively). Titin phosphorylation was reduced in RV tissue of MCT rats (MCT vs CTRL:1.06±0.38 vs 1.62±0.85,arbitrary units) and increased in MCT+NRG group (2.28±0.61). RV diastolic stiffness is increased in MCT rats, with important contributions from increased fibrosis and intrinsic stiffening of the RV cardiomyocyte sarcomeres. NRG-1 treatment decreases the passive force and thus myocardial stiffness, either in rats with RV hypertrophy or in healthy animals. These findings show that NRG-1 pathway regulates systolic and diastolic function at the cellular level, suggesting a potential therapeutic role of this pathway in PAH.

Biophysical Journal, 2015

Current Heart Failure Reports, 2012

Heart failure with preserved ejection fraction (HFpEF) is highly prevalent and is frequently asso... more Heart failure with preserved ejection fraction (HFpEF) is highly prevalent and is frequently associated with metabolic risk factors. Patients with HFpEF have only a slightly lower mortality than patients with HF and reduced EF. The pathophysiology of HFpEF is currently incompletely understood, which precludes specific therapy. Both HF phenotypes demonstrate distinct cardiac remodeling processes at the macroscopic, microscopic, and ultrastructural levels. Increased diastolic left-ventricular (LV) stiffness and impaired LV relaxation are important features of HFpEF, which can be explained by changes in the extracellular matrix and the cardiomyocytes. In HFpEF, elevated intrinsic cardiomyocyte stiffness contributes to high diastolic LV stiffness. Posttranslational changes in the sarcomeric protein titin, affecting titin isoform expression and phosphorylation, contribute to elevated cardiomyocyte stiffness. Increased nitrosative/oxidative stress, impaired nitric oxide bioavailability, and down-regulation of myocardial cyclic guanosine monophosphate and protein kinase G signaling could trigger posttranslational modifications of titin, thereby augmenting cardiomyocyte and LV diastolic stiffness.

The Journal of Physiology, 2007

The positive force-frequency relation, one of the key factors modulating performance of healthy m... more The positive force-frequency relation, one of the key factors modulating performance of healthy myocardium, has been attributed to an increased Ca 2+ influx per unit of time. In failing hearts, a blunted, flat or negative force-frequency relation has been found. In healthy and failing hearts frequency-dependent alterations in Ca 2+ sensitivity of the myofilaments, related to different phosphorylation levels of contractile proteins, could contribute to this process. Therefore, the frequency dependency of force, intracellular free Ca 2+ ([Ca 2+ ] i ), Ca 2+ sensitivity and contractile protein phosphorylation were determined in control and monocrotaline-treated, failing rat hearts. An increase in frequency from 0.5 to 6 Hz resulted in an increase in force in control (14.3 ± 3.0 mN mm −2 ) and a decrease in force in failing trabeculae (9.4 ± 3.2 mN mm −2 ), whereas in both groups the amplitude of [Ca 2+ ] i transient increased. In permeabilized cardiomyocytes, isolated from control hearts paced at 0 and 9 Hz, Ca 2+ sensitivity remained constant with frequency (pCa 50 : 5.55 ± 0.02 and 5.58 ± 0.01, respectively, P > 0.05), whereas in cardiomyocytes from failing hearts Ca 2+ sensitivity decreased with frequency (pCa 50 : 5.62 ± 0.01 and 5.57 ± 0.01, respectively, P < 0.05). After incubation of the cardiomyocytes with protein kinase A (PKA) this frequency dependency of Ca 2+ sensitivity was abolished. Troponin I (TnI) and myosin light chain 2 (MLC2) phosphorylation remained constant in control hearts but both increased with frequency in failing hearts. In conclusion, in heart failure frequency-dependent myofilament Ca 2+ desensitization, through increased TnI phosphorylation, contributes to the negative force-frequency relation and is counteracted by a frequency-dependent MLC2 phosphorylation. We propose a novel role for PKC-mediated TnI phosphorylation in modulating the force-frequency relation.

PROTEOMICS – CLINICAL APPLICATIONS, 2007

European journal of heart failure, Jan 23, 2015

Cell-cell or inter-organ communication allows the exchange of information and messages, which is ... more Cell-cell or inter-organ communication allows the exchange of information and messages, which is essential for the coordination of cell/organ functions and the maintenance of homeostasis. It has become evident that dynamic interactions of different cell types play a major role in the heart, in particular during the progression of heart failure, a leading cause of mortality worldwide. Heart failure is associated with compensatory structural and functional changes mostly in cardiomyocytes and cardiac fibroblasts, which finally lead to cardiomyocyte hypertrophy and fibrosis. Intercellular communication within the heart is mediated mostly via direct cell-cell interaction or the release of paracrine signalling mediators such as cytokines and chemokines. However, recent studies have focused on the exchange of genetic information via the packaging into vesicles as well as the crosstalk of lipids and other paracrine molecules within the heart and distant organs, such as kidney and adipose t...

American Journal of Physiology - Heart and Circulatory Physiology, 2015

Heart failure with preserved ejection fraction (HFPEF) evolves with the accumulation of risk fact... more Heart failure with preserved ejection fraction (HFPEF) evolves with the accumulation of risk factors. Relevant animal models to identify potential therapeutic targets and to test novel therapies for HFPEF are missing. We induced hypertension and hyperlipidemia in landrace pigs (n=8) by deoxycorticosteroneacetate (DOCA, 100 mg/kg, 90d-release subcutaneous depot) and a western diet (WD) containing high amounts of salt, fat, cholesterol and sugar for 12 wks. Compared to weight-matched controls (n=8), DOCA/WD treated pigs showed left ventricular (LV) concentric hypertrophy and left atrial (LA) dilatation in the absence of significant changes in LV ejection fraction or symptoms of heart failure at rest. The LV end-diastolic pressure-volume relationship (EDPVR) was markedly shifted leftwards. During simultaneous right atrial pacing and dobutamine infusion, cardiac output reserve and LV peak inflow velocities were lower in DOCA/WD treated pigs at higher LV end-diastolic pressures. In LV biopsies, we observed myocyte hypertrophy, a shift towards the stiffer titin isoform N2B and reduced total-titin phosphorylation. LV superoxide production was increased, in part due to nitric oxide synthase (NOS) uncoupling, while AKT and NOS isoform expression and phosphorylation were unchanged. In conclusion, we developed a large animal model where loss of LV capacitance was associated with a titin isoform shift and dysfunctional NOS, in the presence of preserved LV ejection fraction. Our findings identify potential targets for the treatment of HFPEF in a relevant large animal model.

European Journal of Heart Failure Supplements

Biophysical Journal, 2014

Biophysical Journal, 2014

Biophysical Journal, 2014

European Journal of Heart Failure Supplements, 2006

Basic research in cardiology, 2014

Increased levels of interleukin-6 (IL-6) have been observed in patients with acute myocarditis an... more Increased levels of interleukin-6 (IL-6) have been observed in patients with acute myocarditis and are associated with poor prognosis. This study was designed to examine whether treatment with anti-IL-6 receptor antibody improves cardiac dysfunction and left ventricular (LV) remodeling in experimental Coxsackie virus B3 (CVB3)-induced myocarditis. C57BL6/J mice were subjected to acute CVB3 infection. One day after viral infection mice were treated with a single injection of an anti-IL-6 receptor antibody (MR16-1, tocilizumab) or control IgG. Seven days after viral infection, LV function was examined by conductance catheter technique, cardiac remodeling assessed by estimation of titin phosphorylation, cardiac fibrosis, and inflammatory and antiviral response by immunohistochemistry, RT-PCR and cell culture experiments. Compared to controls, infected mice displayed an impaired systolic and diastolic LV function associated with an increase in cardiac inflammation, fibrosis and impaired...

BMC Pharmacology and Toxicology, 2013

Cardiovascular Research, 2014

Obesity and Type 2 diabetes mellitus (DM) induce left ventricular (LV) diastolic dysfunction, whi... more Obesity and Type 2 diabetes mellitus (DM) induce left ventricular (LV) diastolic dysfunction, which contributes to an increasing prevalence of heart failure with a preserved LV ejection fraction. We investigated the effects of sitagliptin (SITA), an inhibitor of dipeptidylpeptidase-4 (DPP-4) and anti-diabetic drug, on LV structure and function of obese mice with Type 2 DM. Obese Type 2 diabetic mice (Lepr(db/db), BKS.Cg-Dock7(m)+/+ Lepr(db)/J), displaying increased cardiomyocyte and LV stiffness at the age of 16 weeks, were treated with SITA (300 mg/kg/day) or vehicle for 8 weeks. SITA severely impaired serum DPP-4 activity, but had no effect on glycaemia. Invasive haemodynamic recordings showed that SITA reduced LV passive stiffness and increased LV stroke volume; LV end-systolic elastance remained unchanged. In addition, SITA reduced resting tension of isolated single cardiomyocytes and intensified phosphorylation of the sarcomeric protein titin. SITA also increased LV concentrations of cGMP and increased activity of protein kinase G (PKG). In vitro activation of PKG decreased resting tension of cardiomyocytes from vehicle-treated mice, but had no effect on resting tension of cardiomyocytes from SITA-treated mice. In obese Type 2 diabetic mice, in the absence of hypoglycaemic effects, inhibition of DPP-4 decreases LV passive stiffness and improves global LV performance. These effects seem at least partially mediated by stimulatory effects on the myocardial cGMP-PKG pathway and, hence, on the phosphorylation status of titin and the hereto coupled cardiomyocyte stiffness modulus.

Frontiers in Physiology, 2011

Aim: Transmural differences in sarcomeric protein composition and function across the left ventri... more Aim: Transmural differences in sarcomeric protein composition and function across the left ventricular (LV) wall have been reported. We studied in pigs sarcomeric function and protein phosphorylation in subepicardial (EPI) and subendocardial (ENDO) layers of remote LV myocardium after myocardial infarction (MI), induced by left circumflex coronary artery ligation. Methods: EPI and ENDO samples were taken 3 weeks after sham surgery (n = 12) or induction of MI (n = 12) at baseline (BL) and during β-adrenergic receptor (βAR) stimulation with dobutamine. Isometric force was measured in single cardiomyocytes at various [Ca 2+ ] and 2.2 μm sarcomere length. Results: In sham hearts, no significant transmural differences were observed in myofilament function or protein phosphorylation. Myofilament Ca 2+ -sensitivity was significantly higher in both EPI and ENDO of MI compared to sham hearts. Maximal force was significantly reduced in MI compared to sham, but solely in ENDO cells. A higher passive force was observed in MI hearts, but only in EPI cells. The proportion of stiff N2B isoform was higher in EPI than in ENDO in both sham and MI hearts, and a trend toward increased N2B-proportion appeared in MI EPI, but not MI Endo. Analysis of myofilament protein phosphorylation did not reveal significant transmural differences in phosphorylation of myosin binding protein C, desmin, troponin T, troponin I (cTnI), and myosin light chain 2 (MLC-2) both at BL and during βAR stimulation with dobutamine infusion. A significant increase in MLC-2 phosphorylation was observed during dobutamine only in sham. In addition, the increase in cTnI phosphorylation upon dobutamine was twofold lower in MI than in sham. Conclusion: Myofilament dysfunction is present in both EPI and ENDO in post-MI remodeled myocardium, but shows a high degree of qualitative heterogeneity across the LV wall. These heterogeneous transmural changes in sarcomeric properties likely contribute differently to systolic vs. diastolic global LV dysfunction after MI.

Cardiovascular Research, 2014

ABSTRACT Neuregulin (NRG)-1 is involved in the preservation of left ventricular performance. Neve... more ABSTRACT Neuregulin (NRG)-1 is involved in the preservation of left ventricular performance. Nevertheless, the role of NRG-1 in pulmonary arterial hypertension(PAH) and right ventricular(RV) diastolic stiffness is unknown. We analysed the presence and possible underlying mechanisms of RV diastolic dysfunction in an animal model of PAH and the role of NRG-1 in this context. Wistar rats randomly received monocrotaline (MCT,60mg/Kg,sc) or vehicle. After 14 days, rats received NRG-1 (40ug/Kg/day,ip) or vehicle. The study resulted in 4 groups: control(CTRL,n=16); CTRL+NRG(n=15); MCT(n=13); MCT+NRG(n=18). RV invasive hemodynamic studies and sample collection were performed 25-28 days after MCT administration. Isolated cardiomyocytes were stretched to measure resting tension and phosphorylation of titin isoforms was analyzed (ProQ Diamond and SYPRO Ruby protein gel stains). Only significant results (p&lt;0.05) are given. RV diastolic stiffness (β) was increased in MCT rats (MCT vs CTRL:0.016±0.002 vs 0.008±0.001). However, NRG-1 treatment attenuated this change (MCT+NRG:0.007±0.001). Histological analyses revealed increased cardiomyocyte cross-sectional areas (MCT vs CTRL:536.67±59.46 vs 375.39±47.43μm2), indicating RV hypertrophy. In addition, the amount of RV fibrosis was enhanced in PAH tissue (MCT vs CTRL:2.04±0.17 vs 0.98±0.07%). NRG-1 also attenuated both changes (MCT+NRG:409.01±19.72μm2 and 1.00±0.17%, respectively). MCT-group isolated cardiomyocytes developed higher passive force when compared to CTRL-group cells at the sarcomere lengths of 2.0 (MCT vs CTRL:1.90±0.43 vs 1.43±0.29N/m2), 2.2 (MCT vs CTRL:3.66±0.69 vs 2.68±0.24N/m2), and 2.3μm (MCT vs CTRL: 5.76±1.15 vs 3.86±0.87N/m2). NRG-1 restored passive force development to levels similar to the CTRL-group, at 2.0, 2.2, and 2.3μm (MCT+NRG:1.28±0.25, 3.04±0.55, and 3.63±0.89N/m2, respectively). CTRL+NRG-group cells developed less passive force compared to CTRL-group (CTRL+NRG:1.16±0.31, 2.27±0.38, and 3.05±0.54N/m2, at 2.0, 2.2, and 2.3μm respectively). Titin phosphorylation was reduced in RV tissue of MCT rats (MCT vs CTRL:1.06±0.38 vs 1.62±0.85,arbitrary units) and increased in MCT+NRG group (2.28±0.61). RV diastolic stiffness is increased in MCT rats, with important contributions from increased fibrosis and intrinsic stiffening of the RV cardiomyocyte sarcomeres. NRG-1 treatment decreases the passive force and thus myocardial stiffness, either in rats with RV hypertrophy or in healthy animals. These findings show that NRG-1 pathway regulates systolic and diastolic function at the cellular level, suggesting a potential therapeutic role of this pathway in PAH.

Biophysical Journal, 2015

Current Heart Failure Reports, 2012

Heart failure with preserved ejection fraction (HFpEF) is highly prevalent and is frequently asso... more Heart failure with preserved ejection fraction (HFpEF) is highly prevalent and is frequently associated with metabolic risk factors. Patients with HFpEF have only a slightly lower mortality than patients with HF and reduced EF. The pathophysiology of HFpEF is currently incompletely understood, which precludes specific therapy. Both HF phenotypes demonstrate distinct cardiac remodeling processes at the macroscopic, microscopic, and ultrastructural levels. Increased diastolic left-ventricular (LV) stiffness and impaired LV relaxation are important features of HFpEF, which can be explained by changes in the extracellular matrix and the cardiomyocytes. In HFpEF, elevated intrinsic cardiomyocyte stiffness contributes to high diastolic LV stiffness. Posttranslational changes in the sarcomeric protein titin, affecting titin isoform expression and phosphorylation, contribute to elevated cardiomyocyte stiffness. Increased nitrosative/oxidative stress, impaired nitric oxide bioavailability, and down-regulation of myocardial cyclic guanosine monophosphate and protein kinase G signaling could trigger posttranslational modifications of titin, thereby augmenting cardiomyocyte and LV diastolic stiffness.

The Journal of Physiology, 2007

The positive force-frequency relation, one of the key factors modulating performance of healthy m... more The positive force-frequency relation, one of the key factors modulating performance of healthy myocardium, has been attributed to an increased Ca 2+ influx per unit of time. In failing hearts, a blunted, flat or negative force-frequency relation has been found. In healthy and failing hearts frequency-dependent alterations in Ca 2+ sensitivity of the myofilaments, related to different phosphorylation levels of contractile proteins, could contribute to this process. Therefore, the frequency dependency of force, intracellular free Ca 2+ ([Ca 2+ ] i ), Ca 2+ sensitivity and contractile protein phosphorylation were determined in control and monocrotaline-treated, failing rat hearts. An increase in frequency from 0.5 to 6 Hz resulted in an increase in force in control (14.3 ± 3.0 mN mm −2 ) and a decrease in force in failing trabeculae (9.4 ± 3.2 mN mm −2 ), whereas in both groups the amplitude of [Ca 2+ ] i transient increased. In permeabilized cardiomyocytes, isolated from control hearts paced at 0 and 9 Hz, Ca 2+ sensitivity remained constant with frequency (pCa 50 : 5.55 ± 0.02 and 5.58 ± 0.01, respectively, P > 0.05), whereas in cardiomyocytes from failing hearts Ca 2+ sensitivity decreased with frequency (pCa 50 : 5.62 ± 0.01 and 5.57 ± 0.01, respectively, P < 0.05). After incubation of the cardiomyocytes with protein kinase A (PKA) this frequency dependency of Ca 2+ sensitivity was abolished. Troponin I (TnI) and myosin light chain 2 (MLC2) phosphorylation remained constant in control hearts but both increased with frequency in failing hearts. In conclusion, in heart failure frequency-dependent myofilament Ca 2+ desensitization, through increased TnI phosphorylation, contributes to the negative force-frequency relation and is counteracted by a frequency-dependent MLC2 phosphorylation. We propose a novel role for PKC-mediated TnI phosphorylation in modulating the force-frequency relation.

PROTEOMICS – CLINICAL APPLICATIONS, 2007