Diastolic Stiffness Research Articles

Myocardial Titin and Collagen in Cardiac Diastolic Dysfunction

High myocardial diastolic stiffness has usually been attributed to excessive myocardial collagen deposition. Over the last decennium, stiff cardiomyocytes were also identified as important contributors to high myocardial diastolic stiffness, especially in heart failure (HF) with preserved ejection fraction (HFPEF).1–3 Cardiomyocyte stiffness relates to elasticity of the giant cytoskeletal protein titin, which spans the sarcomere from the Z disk to the M line and functions as a bidirectional spring responsible for early diastolic recoil and late diastolic distensibility of cardiomyocytes.4 In HFPEF patients and in HFPEF animal models,5 the observed increase in cardiomyocyte stiffness was always accompanied by increased deposition of collagen; therefore, it remained unclear whether impaired elasticity of titin could be solely responsible for high myocardial diastolic stiffness and HFPEF. In this issue of Circulation , however, Chung et al6 provide compelling evidence for titin being the sole perpetrator in the diastolic left ventricular (LV) dysfunction of an HFPEF mouse model. They generated mice with a deletion of nine immunoglobulin (Ig)-like domains from the proximal tandem Ig segment of the titin spring region (IG KO). This deletion extended the remaining titin spring segments and increased overall titin stiffness. Despite unaltered myocardial collagen content or composition, the IG KO mice developed HFPEF, evident from a reduced exercise tolerance, an enlarged left atrium, and a steeper LV end-diastolic pressure-volume relationship. The elegant study by Chung et al therefore clearly establishes myocardial titin to be able to sufficiently compromise diastolic LV function to induce HFPEF. Article see p 19 Titin, with a molecular mass of up to 3800 kDa, spans half-sarcomeres from the Z disk to the M band and contains a molecular spring segment, the I-band region, that supports early diastolic recoil and late diastolic resistance to stretch (Figure 1A). The I-band region has …

Effect of lifestyle modifications on diastolic functions and aortic stiffness in prehypertensive subjects: a prospective cohort study

Prehypertension is one of the primary causes of major cardiovascular events independent from other cardiovascular risk factors. The aim of the study was to evaluate the effect of therapeutic lifestyle modifications (LSMs) on cardiac diastolic function and aortic stiffness in prehypertensive subjects. This study designed as a prospective cohort study. Sixty-one prehypertensive adults were included in this study. The goals of LMS were weight loss of at least 5 kg in subjects with a BMI ≥25 kg/m² and moderate-intensity physical activity at least 180 minutes per week. We evaluated left ventricular (LV) diastolic function and aortic stiffness parameters at baseline and after 6 months by conventional and tissue Doppler imaging (TDI) echocardiography. Statistical analyses were performed using Wilcoxon-signed rank test and the paired sample t test. Transmitral early velocity (E), the ratio of E to transmitral late velocity (E/A), TDI diastolic early septal velocity (septal E), TDI systolic septal velocity (septal S), TDI early lateral velocity (lateral E), the ratio of septal E to TDI late septal (septal A) velocity (septal E/A) and the ratio of lateral E to late lateral (lateral A) velocity (lateral E/A) were found to be significantly increased after the LSMs (p<0.05 for all). The beta stiffness index was decreased (12.07 vs. 6.33; p<0.001) and the aortic compliance (0.02 cm/mmHg vs. 0.05 cm/mmHg; p<0.001) and the aortic strain (3.28% vs. 7.02%; p<0.001) were increased significantly after the LSMs. LSMs improve conventional and TDI echocardiographic parameters and aortic stiffness measurements in subjects with prehypertension.

Diastolic dysfunction and arterial stiffness: the chicken or the egg

Diastolic dysfunction and arterial stiffness: the chicken or the egg

Effect of circadian rhythm of blood pressure on arterial wall stiffness and on left ventricular diastolic dysfunction

Background Arterial stiffness is a risk factor for cardiovascular morbidity and mortality. Variability of blood pressure has been reported to be related to worse cardiovascular outcome. The relationship between the arterial stiffness and the circadian rhythm of blood pressure (BP) has been controversial. The objective was to the examine impacts of BP variability on left ventricular diastolic function and arterial stiffness in the hypertensive patients. Methods Ambulatory BP monitoring, pulse wave velocity, and echocardiography were performed in 268 patients (153 males, 47 ± 11 years) with HTN and pre-HTN. BP was measured at the outpatient clinic and 24-h ABPM was performed. Using carotid femoral applanation tonometry, PWA was performed for evaluation of systemic arterial stiffness expressed as augmentation index. Echocardiograms were performed and an average of 3–6 cardiac cycles was done for all measurements including the left ventricular mass index (LVMI), relative wall thickness (RWT), trans mitral flow propagation velocity (Vp), TDI, and midwall shortening fraction (MWSF). Nocturnal dipping was defined as a reduction of diastolic BP (DBP) by >10% of systolic BP (SBP) when compared with the daytime values. Isolated systolic nondipping, is reduction of Results Among groups, the clinic SBP and DBP, daytime mean BP of 24-h ABPM, gender and body mass index were not statistically different. Augmentation pressure (AP), augmentation index (AI) showed statistically significant difference ( p = 0.008 and 0.021, respectively). Multivariate analysis showed that isolated diastolic non-dipping was correlated with arterial stiffness expressed as AI only in young group.

Diagnosis of heart failure with preserved ejection fraction: role of clinical Doppler echocardiography

In developed countries, at least 38–54% of patients with heart failure show preserved left ventricular (LV) ejection fraction.1–3 The prevalence of heart failure with preserved ejection fraction (HFPEF) is steadily...

Beneficial Cardiac Effects of Caloric Restriction Are Lost with Age in a Murine Model of Obesity

Obesity is associated with increased diastolic stiffness and myocardial steatosis and dysfunction. The impact of aging on the protective effects of caloric restriction (CR) is not clear. We studied 2-month (younger) and 6-7-month (older)-old ob/ob mice and age-matched C57BL/6J controls (WT). Ob/ob mice were assigned to diet ad libitum or CR for 4weeks. We performed echocardiograms, myocardial triglyceride assays, Oil Red O staining, and measured free fatty acids, superoxide, NOS activity, ceramide levels, and Western blots. In younger mice, CR restored diastolic function, reversed myocardial steatosis, and upregulated Akt phosphorylation. None of these changes was observed in the older mice; however, CR decreased oxidative stress and normalized NOS activity in these animals. Interestingly, myocardial steatosis was not associated with increased ceramide, but CR altered the composition of ceramides. In this model of obesity, aging attenuates the benefits of CR on myocardial structure and function.

Azelnidipine plus olmesartan versus amlodipine plus olmesartan on arterial stiffness and cardiac function in hypertensive patients: a randomized trial

PurposeTo compare the long-term effects of olmesartan combined with either azelnidipine or amlodipine on central blood pressure (CBP), left ventricular (LV) mass index (LVMI), LV diastolic function (e′ velocity, E/e′ ratio, E/A ratio) and arterial stiffness (brachial-ankle pulse wave velocity [baPWV] and augmentation index normalized for a heart rate of 75 bpm [AIx]).Patients and methodsPatients with systolic BP ≥ 140 mmHg and/or diastolic BP ≥ 90 mmHg received olmesartan monotherapy (20 mg/day) for 12 weeks. They were then randomly assigned to fixed-dose add-on therapy with azelnidipine (16 mg/day; n = 26) or amlodipine (5 mg/day; n = 26) for a further 2 years. CBP, LVMI, e′ velocity, E/e′ ratio, E/A ratio, baPWV, and AIx were measured at baseline, 6 months, and 2 years.ResultsBaseline characteristics of both groups were similar. The decrease in brachial BP over 2 years was similar in both groups. CBP, LVMI, E/e′ ratio, baPWV, and AIx decreased significantly, and the E/A ratio and e′ velocity increased significantly in both groups. The decreases in CBP (P < 0.001), AIx (P < 0.001), baPWV (P < 0.001), LVMI (P < 0.001), and E/e′ (P = 0.002) as well as the increase in E/A ratio (P = 0.03) over 2 years were significantly greater in the olmesartan/azelnidipine group than in the olmesartan/amlodipine group. Multivariate linear regression analyses showed that the changes in baPWV (β = 0.41, P < 0.001) and CBP (β = 0.47, P = 0.01) were independently associated with the change in LVMI, the change in baPWV (β = 0.25, P < 0.001) was independently associated with the change in E/e′ ratio, and the changes in baPWV (β = 0.21, P = 0.001) and AIx (β = 0.25, P = 0.03) were independently associated with the change in E/A ratio.ConclusionTreatment with olmesartan/azelnidipine for 2 years resulted in greater improvements in CBP, LVMI, and LV diastolic function, and arterial stiffness compared with olmesartan/amlodipine. Improvements in LV diastolic function were associated with improvements in arterial stiffness.

Ferulic Acid Improves Cardiovascular and Kidney Structure and Function in Hypertensive Rats

Ferulic acid is a simple phenolic acid commonly present in cereals. In this study, changes in heart and kidney structure and function were measured in young N(ω)-nitro-L-arginine methyl ester (L-NAME)-treated Wistar rats and 10-month-old spontaneously hypertensive rats (SHR) alone and after chronic treatment with ferulic acid (FA; 50 mg·kg⁻¹·d⁻¹; n = 6-10; *P < 0.05). Systolic blood pressures were increased after L-NAME treatment (control 125 ± 2 mm Hg, L-NAME 205 ± 6* mm Hg after 8 weeks) and in SHR (250 ± 2 mm Hg; WKY 149 ± 4 mm Hg). Hypertensive rats developed left ventricular hypertrophy, increased ventricular diastolic stiffness (κ; Wistar, 21.4 ± 1.6; L-NAME, 30.1 ± 0.9*; WKYs, 24.1 ± 0.9; SHR 29.5 ± 0.7) and fibrosis of heart and kidneys. Treatment with ferulic acid reduced systolic blood pressure (L-NAME + FA, 157 ± 4*; SHR + FA 214 ± 8* mm Hg), reduced left ventricular diastolic stiffness (L-NAME + FA, 25.2 ± 0.5*; SHR + FA 26.3 ± 0.5*) and attenuated inflammatory cell infiltration, ferric iron accumulation, and collagen deposition in left ventricles and kidneys. Ferulic acid improved both endothelium-dependent relaxation in isolated thoracic aortic rings and antioxidant status by increasing superoxide dismutase and catalase activity in the heart and kidneys. FA decreased plasma liver enzyme activities and plasma creatinine concentrations. Thus, FA improved the structure and function of the heart, blood vessels, liver, and kidneys in hypertensive rats.

Effect of an Increase in Left Ventricular Pressure Overload on Left Atrial‐Left Ventricular Coupling in Patients with Hypertension: A Two‐Dimensional Speckle Tracking Echocardiographic Study

Two-dimensional speckle tracking echocardiography (2DSTE) has recently been applied to evaluate left atrial (LA) function in addition to left ventricular (LV) function. However, whether 2DSTE can provide insight into LA-LV interaction related to an increase in LV pressure overload remains unknown. One hundred five asymptomatic patients with hypertension were studied by conventional, pulsed and tissue Doppler, and 2DSTE. Hypertensive patients were classified into 2 groups according to the ratio of early diastolic to atrial systolic velocity (E/A) of transmitral flow: E/A≥1 (n=37) and E/A<1 (n=68). We used (E/peak early diastolic mitral annular motion velocity [e'])/peak systolic LA strain (S-LAs) and E/e', as parameters of LA stiffness during ventricular systole and LV diastolic stiffness, respectively. The peak early diastolic LV longitudinal strain rate, and peak early diastolic LA strain and strain rate were lower in the E/A<1 group than in the E/A≥1 group. The E/e'/S-LAs and E/e' were greater in the E/A<1 group. In the E/A<1 group, systolic blood pressure (SBP) correlated with LV wall thickness parameters, A, e', E/e', peak early diastolic LV longitudinal strain rate, and E/e'/S-LAs. Multivariate regression analysis indicated that A, E/e', and E/e'/S-LAs were defined as strong predictors related to SBP. In patients with hypertension, an elevation in SBP leads to increased LA stiffness during ventricular systole and LV diastolic stiffness, in association with continued and further advanced LV diastolic dysfunction. 2DSTE is considered a sensitive tool for detecting abnormal LA-LV coupling related to an increased LV pressure overload.

Responses to oleic, linoleic and α-linolenic acids in high-carbohydrate, high-fat diet-induced metabolic syndrome in rats

We investigated the changes in adiposity, cardiovascular and liver structure and function, and tissue fatty acid compositions in response to oleic acid-rich macadamia oil, linoleic acid-rich safflower oil and α-linolenic acid-rich flaxseed oil (C18 unsaturated fatty acids) in rats fed either a diet high in simple sugars and mainly saturated fats or a diet high in polysaccharides (cornstarch) and low in fat. The fatty acids induced lipid redistribution away from the abdomen, more pronounced with increasing unsaturation; only oleic acid increased whole-body adiposity. Oleic acid decreased plasma total cholesterol without changing triglycerides and nonesterified fatty acids, whereas linoleic and α-linolenic acids decreased plasma triglycerides and nonesterified fatty acids but not cholesterol. α-Linolenic acid improved left ventricular structure and function, diastolic stiffness and systolic blood pressure. Neither oleic nor linoleic acid changed the left ventricular remodeling induced by high-carbohydrate, high-fat diet, but both induced dilation of the left ventricle and functional deterioration in low fat-diet-fed rats. α-Linolenic acid improved glucose tolerance, while oleic and linoleic acids increased basal plasma glucose concentrations. Oleic and α-linolenic acids, but not linoleic acid, normalized systolic blood pressure. Only oleic acid reduced plasma markers of liver damage. The C18 unsaturated fatty acids reduced trans fatty acids in the heart, liver and skeletal muscle with lowered stearoyl-CoA desaturase-1 activity index; linoleic and α-linolenic acids increased accumulation of their C22 elongated products. These results demonstrate different physiological and biochemical responses to primary C18 unsaturated fatty acids in a rat model of human metabolic syndrome.

Crucial Role for Ca 2+ /Calmodulin-Dependent Protein Kinase-II in Regulating Diastolic Stress of Normal and Failing Hearts via Titin Phosphorylation

Myocardial diastolic stiffness and cardiomyocyte passive force (F(passive)) depend in part on titin isoform composition and phosphorylation. Ca(2+)/calmodulin-dependent protein kinase-II (CaMKII) phosphorylates ion channels, Ca(2+)-handling proteins, and chromatin-modifying enzymes in the heart, but has not been known to target titin. To elucidate whether CaMKII phosphorylates titin and modulates F(passive) in normal and failing myocardium. Titin phosphorylation was assessed in CaMKIIδ/γ double-knockout (DKO) mouse, transgenic CaMKIIδC-overexpressing mouse, and human hearts, by Pro-Q-Diamond/Sypro-Ruby staining, autoradiography, and immunoblotting using phosphoserine-specific titin-antibodies. CaMKII-dependent site-specific titin phosphorylation was quantified in vivo by mass spectrometry using stable isotope labeling by amino acids in cell culture mouse heart mixed with wild-type (WT) or DKO heart. F(passive) of single permeabilized cardiomyocytes was recorded before and after CaMKII-administration. All-titin phosphorylation was reduced by >50% in DKO but increased by up to ≈100% in transgenic versus WT hearts. Conserved CaMKII-dependent phosphosites were identified within the PEVK-domain of titin by quantitative mass spectrometry and confirmed in recombinant human PEVK-fragments. CaMKII also phosphorylated the cardiac titin N2B-unique sequence. Phosphorylation at specific PEVK/titin N2B-unique sequence sites was decreased in DKO and amplified in transgenic versus WT hearts. F(passive) was elevated in DKO and reduced in transgenic compared with WT cardiomyocytes. CaMKII-administration lowered F(passive) of WT and DKO cardiomyocytes, an effect blunted by titin antibody pretreatment. Human end-stage failing hearts revealed higher CaMKII expression/activity and phosphorylation at PEVK/titin N2B-unique sequence sites than nonfailing donor hearts. CaMKII phosphorylates the titin springs at conserved serines/threonines, thereby lowering F(passive). Deranged CaMKII-dependent titin phosphorylation occurs in heart failure and contributes to altered diastolic stress.

Passive Viscosity Decreases with Deletion of PEVK Region of Cardiac Titin

Diastolic dysfunction is a poorly understood but clinically pervasive syndrome that is characterized by increased diastolic stiffness. Diastolic stiffness needs to be better understood, especially the mechanisms that give rise to viscous stiffness. Viscous stiffness is strain-rate sensitive stiffness giving rise to hysteresis and stress relaxation. Here we focused on passive viscosity by measuring hysteresis from the area between the stretch and release passive force-sarcomere length curves and used both wild-type (WT) mice and PEVK knockout (KO) mice in which the PEVK element has been deleted. The PEVK element is a proline-glutamate-valine-lysine (PEVK) rich segment that is part of titin's spring region and that has previously been shown to be an important source of viscosity in the cardiac sarcomere. A physiological stretch protocol which mimics the cardiac cycle was performed on both KO and WT skinned fiber bundles. This protocol consists of a series of triangles stretches which take the prep from slack sarcomere length to a sarcomere length of 2.2 μm at 300%/s (i.e. ∼600 beats/min). In both KO and WT, hysteresis during the first stretch and release cycle was highest and quickly decreased to about ∼45% of the initial value during steady state. Hysteresis was significantly lower in the KO during both the initial stretch and steady state but did not completely disappear. After 100 cycles, hysteresis was 225±53 pJ/mm2/sarcomere in the WT and 120±32 pJ/mm2/sarcomere in the KO. Because hysteresis was not completely absent in the PEVK KO tissues, we are currently studying the possibility that cMyBP-C contributes to viscosity as well, using both cMyBP-C extraction and post-translational modifications of cMyBP-C.

Shortening of Titin's Elastic Tandem Ig Segment Leads to Cardiac Hypertrophy and Diastolic Dysfunction

Diastolic dysfunction is a poorly understood but clinically pervasive syndrome. Titin is the main determinant of cellular passive stiffness. However, the physiological role that titin's tandem Ig segment plays in stiffness generation and whether shortening this segment is sufficient to cause diastolic dysfunction needs to be established by performing studies at a wide range of organizational levels (skinned cells to the in vivo LV chamber). We produced a novel KO model by deleting nine immunoglobulin(Ig)-like domains from the proximal tandem Ig segment (Ig 3-11) of titin's spring region (IG KO). Exon microarray analysis revealed no adaptations in titin splicing, while novel phospho-specific antibodies did not detect changes in titin phosphorylation. Passive myocyte stiffness was increased in the KO and immunoelectron microscopy revealed increased extension of the remaining titin spring segments as the likely underlying mechanism. Diastolic stiffness was increased at the tissue and organ levels; myocardial stiffness studies did not detect changes in extracellular matrix based passive stiffness, supporting a titin-based mechanism. IG KO mice have a reduced exercise tolerance and develop LV hypertrophy that is associated with a marked increase in expression of hypertrophy-associated four and a half LIM proteins (FHL). These findings suggest that titin-based stiffness plays a role in diastolic dysfunction and hypertrophic signaling and that increased titin-based passive stiffness is sufficient to cause diastolic dysfunction with exercise intolerance and LV hypertrophy.

Volume Overload Heart Failure Increases Myocardiac Passive Stiffness in a Mouse Model

Volume overload (VO) heart failure occurs due to pathologies such as mitral valve regurgitation, infarcts and ventricular septal defects, and leads to characteristic eccentric dilation. Changes in passive myocardial stiffness are not well understood and here we dissected the contribution of extracellular matrix (ECM)-based and titin-based stiffness to overall passive stiffness. Titin is a giant protein that regulates passive tension and hence diastolic function in the myocardium. In heart failure, differential splicing and phosphorylation events can occur that alter the stiffness of this protein and influence hemodynamics. Increased diastolic stiffness due to differential splicing and phosphorylation of titin has been observed in pressure overload hypertrophy; however, there are no published studies investigating whether pure LV VO during compensated heart failure leads to changes in titin based passive stiffness. We studied the role of titin in modulating diastolic function in VO induced by aortocaval fistula (ACF) in the mouse. ACF was induced in three-month-old male C57BL/6 animals and allowed to progress for 4 weeks. At 4 weeks, echocardiography confirmed the presence of eccentric dilation and decreased systolic function as expected. Tissues mechanics indicated an increase in titin, which correlated with a significant decrease in N2BA/N2B ratio. ECM based passive stiffness was unchanged in VO. In summary, VO causes an increase in titin based passive stiffness.

Crucial Role for Ca2+/Calmodulin-Dependent Protein Kinase-II Delta in Regulating Diastolic Stress of Normal and Failing Hearts via Titin Phosphorylation

Rationale: Myocardial diastolic stiffness and cardiomyocyte passive force (Fpassive) depend in part on titin isoform composition and phosphorylation. Ca2+/calmodulin-dependent protein kinase-IIδ (CaMKIIδ) phosphorylates ion channels, Ca2+-handling and myofilament proteins in the heart, but has not been known to target titin.Objective: To elucidate whether CaMKIIδ phosphorylates titin and regulates Fpassive in normal and failing myocardium.Methods and Results: Titin phosphorylation was assessed in CaMKIIδ/γ double-knockout (DKO) and transgenic CaMKIIδC-overexpressing (TG) mouse hearts, as well as human hearts, by Pro-Q-Diamond/Sypro-Ruby staining, autoradiography, and immunoblotting using phosphospecific titin antibodies. CaMKII-dependent site-specific titin phosphorylation was quantified in vivo by mass spectrometry using SILAC mouse heart tissue mixed with wildtype (WT) or DKO heart. Fpassive of single permeabilized cardiomyocytes was recorded before and after CaMKII administration. We detected hypophosphorylation of all-titin in DKO and hyperphosphorylation in TG compared to WT hearts. Conserved CaMKII-dependent phosphosites were identified within titin's PEVK-domain by quantitative mass spectrometry and confirmed in recombinant human PEVK-fragments. CaMKII also phosphorylated the cardiac titin N2B-unique sequence (N2Bus). Phosphorylation at specific PEVK/N2Bus sites was decreased in DKO and amplified in TG versus WT hearts. Fpassive was elevated in DKO and reduced in TG compared to WT cardiomyocytes. CaMKII-administration lowered Fpassive of WT and DKO cardiomyocytes, an effect blunted by titin-phosphoantibody pretreatment. Human failing hypertrophic hearts revealed higher CaMKII expression/activity and phosphorylation at PEVK/N2Bus sites than nonfailing donor hearts.Conclusions: CaMKIIδ phosphorylates the titin springs at conserved serines/threonines, thereby lowering Fpassive. Deranged CaMKIIδ-dependent titin phosphorylation occurs in heart failure and contributes to altered diastolic stress.

Anti-Anginal and Anti-Ischemic Effects of Late Sodium Current Inhibition

The effective treatment of coronary artery disease targets two distinct goals, controlling symptomatic angina and decreasing the adverse events associated with ischemia. Traditional anti-anginal and anti-ischemic drugs function by altering the determinants of myocardial oxygen supply or demand, usually by altering loading conditions, changing the heart rate, or impacting contractility. Blockade of the late inward sodium current, late I(Na), offers another target for the treatment of ischemia. Blockade of late I(Na) reduces the sodium and calcium overload that follows ischemia. This improves myocardial relaxation and reduces left ventricular diastolic stiffness, in turn enhancing myocardial contractility and perfusion. Ranolazine, a late I(Na) inhibitor, has been shown to provide both anti-anginal and anti-ischemic benefits without significant alterations in the heart rate and blood pressure in patients with stable coronary artery disease. When evaluated in patients with acute coronary syndrome, ranolazine has been shown to decrease recurrent ischemia, but not significantly reduce the risk of death or myocardial infarction. This review will address the rationale that inhibition of the late sodium current is beneficial in reducing cardiac dysfunction during ischemia, and discuss the clinical studies supporting the use of ranolazine for its anti-anginal and anti-ischemic effects.

The multifunctional Ca2 +/calmodulin-dependent protein kinase II delta (CaMKIIδ) phosphorylates cardiac titin's spring elements

Titin-based passive stiffness is post-translationally regulated by several kinases that phosphorylate specific spring elements located within titin's elastic I-band region. Whether titin is phosphorylated by calcium/calmodulin dependent protein kinase II (CaMKII), an important regulator of cardiac function and disease, has not been addressed. The aim of this work was to determine whether CaMKIIδ, the predominant CaMKII isoform in the heart, phosphorylates titin, and to use phosphorylation assays and mass spectrometry to study which of titin's spring elements might be targeted by CaMKIIδ. It was found that CaMKIIδ phosphorylates titin in mouse LV skinned fibers, that the CaMKIIδ sites can be dephosphorylated by protein phosphatase 1 (PP1), and that under baseline conditions, in both intact isolated hearts and skinned myocardium, about half of the CaMKIIδ sites are phosphorylated. Mass spectrometry revealed that both the N2B and PEVK segments are targeted by CaMKIIδ at several conserved serine residues. Whether phosphorylation of titin by CaMKIIδ occurs in vivo, was tested in several conditions using back phosphorylation assays and phospho-specific antibodies to CaMKIIδ sites. Reperfusion following global ischemia increased the phosphorylation level of CaMKIIδ sites on titin and this effect was abolished by the CaMKII inhibitor KN-93. No changes in the phosphorylation level of the PEVK element were found suggesting that the increased phosphorylation level of titin in IR (ischemia reperfusion) might be due to phosphorylation of the N2B element. The findings of these studies show for the first time that titin can be phosphoryalated by CaMKIIδ, both in vitro and in vivo, and that titin's molecular spring region that determines diastolic stiffness is a target of CaMKIIδ.

Personalised Modelling of In Vivo Myocardial Mechanics to Investigate Heart Failure Mechanisms

Introduction: The primary goal of this study, which forms part of the European FP-7-funded Ricordo project, was to develop methods for linking the finite element (FE) models of the heart with population-based atlases of segmented 3D cardiac image data. This study presents the automated fitting of a 3D FE model of left ventricle (LV) to the LV surface data extracted from a population database, defined at the unloaded, end-diastolic (ED) and end-systolic (ES) states. Mechanical properties are fitted to the kinematic data to extract measures of the diastolic stiffness and maximum activation tension of the patient-specific heart by running mechanics simulations through the cardiac cycle.

Abstract 18454: Calcium Calmodulin Dependent Protein Kinase II delta Modulates Cardiomyocytes Passive Stiffness by Phosphorylating Titin Spring Elements

Background: High diastolic stiffness of the failing heart can result from altered cardiomyocyte mechanical properties. Cardiomyocyte passive force (F passive ) is attributed mainly to the mechanical properties of titin, particularly isoform composition and phosphorylation. Titin can be phosphorylated by protein kinase(PK)A or PKG at the N2-Bus, which decreases F passive . However, PKCα phosphorylates titin's PEVK-region, which increases F passive . Whether other kinases relevant for cardiomyocyte function phosphorylate the titin springs has been unknown. Aim: To investigate whether Ca 2+ /calmodulin dependent protein kinase IIδ (CaMKIIδ) phosphorylates cardiac titin and affects cardiomyocyte F passive . Methods: Cardiac titin phosphorylation was assessed in CaMKIIδ/γ double knockout (DKO; n=8) and transgenic CaMKIIδC overexpressing mice (TG; n=6). A SILAC-DKO mouse was generated for quantitative proteomics in vivo . Cardiac titin separated by titin gel electrophoresis was also studied for phosphorylation sites using MudPIT mass spectrometry. Recombinant wildtype (WT) and mutant fragments of human cardiac titin were expressed and phosphorylated in vitro by CaMKIIδ. F passive of permeabilized isolated WT, DKO and TG mouse cardiomyocytes was recorded between 1.8 and 2.4 µm sarcomere length before and after CaMKIIδ administration. Results: Total titin phosphorylation was reduced in DKO and elevated in TG compared to WT hearts. CaMKIIδ treatment of cardiac tissue ex vivo increased titin phosphorylation. A CaMKII-dependent phosphosite was identified within the N2-Bus (S4062) by MudPIT and two phosphosites within the PEVK-region ( T12007 and S12022 ) by SILAC. Western blotting using phosphospecific antibodies against these sites in cardiac tissues or recombinant WT/mutant titin constructs confirmed that CaMKIIδ indeed phosphorylates these 3 sites. F passive was elevated in DKO and lowered in TG, compared to WT cardiomyocytes. Administering CaMKIIδ ex vivo lowered F passive in DKO but did not affect TG cardiomyocytes. Conclusion: CaMKIIδ phosphorylates the titin springs , thereby lowering F passive . Reducing titin-based stiffness through CaMKIIδ-dependent phosphorylation of titin N2-Bus and PEVK may benefit diastolic function.

Heart Failure with Preserved Ejection Fraction – A Review

Heart failure with preserved left ventricular ejection fraction (HF-PEF), sometimes named diastolic heart failure, is a common condition most frequently seen in the elderly and is associated with arterial hypertension and left ventricular (LV) hypertrophy. Symptoms are attributed to a stiff left ventricle with compensatory elevation of filling pressure and reduced ability to increase stroke volume by the Frank-Starling mechanism. LV interaction with stiff arteries aggravates these problems. Prognosis is almost as severe as for heart failure with reduced ejection fraction (HF-REF), in part reflecting co-morbidities. Before the diagnosis of HF-PEF is made, non-cardiac etiologies must be excluded. Due to the non-specific nature of heart failure symptoms, it is essential to search for objective evidence of diastolic dysfunction which, in the absence of invasive data, is done by echocardiography and demonstration of signs of elevated LV filling pressure, impaired LV relaxation, or increased LV diastolic stiffness. Antihypertensive treatment can effectively prevent HF-PEF. Treatment of HF-PEF is symptomatic, with similar drugs as in HF-REF.