The Sydney Heart Bank: improving translational research while eliminating or reducing the use of animal models of human heart disease

The Sydney Heart Bank (SHB) is one of the largest human heart tissue banks in existence. Its mission is to provide high-quality human heart tissue for research into the molecular basis of human heart failure by working collaboratively with experts in this field. We argue that, by comparing tissues from failing human hearts with age-matched non-failing healthy donor hearts, the results will be more relevant than research using animal models, particularly if their physiology is very different from humans. Tissue from heart surgery must generally be used soon after collection or it significantly deteriorates. Freezing is an option but it raises concerns that freezing causes substantial damage at the cellular and molecular level. The SHB contains failing samples from heart transplant patients and others who provided informed consent for the use of their tissue for research. All samples are cryopreserved in liquid nitrogen within 40 min of their removal from the patient, and in less than 5-10 min in the case of coronary arteries and left ventricle samples. To date, the SHB has collected tissue from about 450 failing hearts (>15,000 samples) from patients with a wide range of etiologies as well as increasing numbers of cardiomyectomy samples from patients with hypertrophic cardiomyopathy. The Bank also has hearts from over 120 healthy organ donors whose hearts, for a variety of reasons (mainly tissue-type incompatibility with waiting heart transplant recipients), could not be used for transplantation. Donor hearts were collected by the St Vincent's Hospital Heart and Lung transplantation team from local hospitals or within a 4-h jet flight from Sydney. They were flushed with chilled cardioplegic solution and transported to Sydney where they were quickly cryopreserved in small samples. Failing and/or donor samples have been used by more than 60 research teams around the world, and have resulted in more than 100 research papers. The tissues most commonly requested are from donor left ventricles, but right ventricles, atria, interventricular system, and coronary arteries vessels have also been reported. All tissues are stored for long-term use in liquid N or vapor (170-180 °C), and are shipped under nitrogen vapor to avoid degradation of sensitive molecules such as RNAs and giant proteins. We present evidence that the availability of these human heart samples has contributed to a reduction in the use of animal models of human heart failure.

CX3CR1 knockout aggravates Coxsackievirus B3-induced myocarditis

Studies on inflammatory disorders elucidated the pivotal role of the CX3CL1/CX3CR1 axis with respect to the pathophysiology and diseases progression. Coxsackievirus B3 (CVB3)-induced myocarditis is associated with severe cardiac inflammation, which may progress to heart failure. We therefore investigated the influence of CX3CR1 ablation in the model of acute myocarditis, which was induced by inoculation with 5x105 plaque forming units of CVB3 (Nancy strain) in either CX3CR1-/- or C57BL6/j (WT) mice. Seven days after infection, myocardial inflammation, remodeling, and titin expression and phosphorylation were examined by immunohistochemistry, real-time PCR and Pro-Q diamond stain. Cardiac function was assessed by tip catheter. Compared to WT CVB3 mice, CX3CR1-/- CVB3 mice exhibited enhanced left ventricular expression of inflammatory cytokines and chemokines, which was associated with an increase of immune cell infiltration/presence. This shift towards a pro-inflammatory immune response further resulted in increased cardiac fibrosis and cardiomyocyte apoptosis, which was reflected by an impaired cardiac function in CX3CR1-/- CVB3 compared to WT CVB3 mice. These findings demonstrate a cardioprotective role of CX3CR1 in CVB3-infected mice and indicate the relevance of the CX3CL1/CX3CR1 system in CVB3-induced myocarditis.

Defined Engineered Human Myocardium With Advanced Maturation for Applications in Heart Failure Modeling and Repair

BACKGROUND

Advancing structural and functional maturation of stem cell-derived cardiomyocytes remains a key challenge for applications in disease modeling, drug screening, and heart repair. Here, we sought to advance cardiomyocyte maturation in engineered human myocardium (EHM) toward an adult phenotype under defined conditions.

METHODS

We systematically investigated cell composition, matrix, and media conditions to generate EHM from embryonic and induced pluripotent stem cell-derived cardiomyocytes and fibroblasts with organotypic functionality under serum-free conditions. We used morphological, functional, and transcriptome analyses to benchmark maturation of EHM.

RESULTS

EHM demonstrated important structural and functional properties of postnatal myocardium, including: (1) rod-shaped cardiomyocytes with M bands assembled as a functional syncytium; (2) systolic twitch forces at a similar level as observed in bona fide postnatal myocardium; (3) a positive force-frequency response; (4) inotropic responses to β-adrenergic stimulation mediated via canonical β₁- and β₂-adrenoceptor signaling pathways; and (5) evidence for advanced molecular maturation by transcriptome profiling. EHM responded to chronic catecholamine toxicity with contractile dysfunction, cardiomyocyte hypertrophy, cardiomyocyte death, and N-terminal pro B-type natriuretic peptide release; all are classical hallmarks of heart failure. In addition, we demonstrate the scalability of EHM according to anticipated clinical demands for cardiac repair.

CONCLUSIONS

We provide proof-of-concept for a universally applicable technology for the engineering of macroscale human myocardium for disease modeling and heart repair from embryonic and induced pluripotent stem cell-derived cardiomyocytes under defined, serum-free conditions.

Dietary spermidine for lowering high blood pressure

Loss of cardiac macroautophagy/autophagy impairs heart function, and evidence accumulates that an increased autophagic flux may protect against cardiovascular disease. We therefore tested the protective capacity of the natural autophagy inducer spermidine in animal models of aging and hypertension, which both represent major risk factors for the development of cardiovascular disease. Dietary spermidine elicits cardioprotective effects in aged mice through enhancing cardiac autophagy and mitophagy. In salt-sensitive rats, spermidine supplementation also delays the development of hypertensive heart disease, coinciding with reduced arterial blood pressure. The high blood pressure-lowering effect likely results from improved global arginine bioavailability and protection from hypertension-associated renal damage. The polyamine spermidine is naturally present in human diets, though to a varying amount depending on food type and preparation. In humans, high dietary spermidine intake correlates with reduced blood pressure and decreased risk of cardiovascular disease and related death. Altogether, spermidine represents a cardio- and vascular-protective autophagy inducer that can be readily integrated in common diets.

Left Atrial Remodeling and Atrioventricular Coupling in a Canine Model of Early Heart Failure With Preserved Ejection Fraction

BACKGROUND

Left atrial (LA) compliance and contractility influence left ventricular stroke volume. We hypothesized that diminished LA compliance and contractile function occur early during the development of heart failure with preserved ejection fraction (HFpEF) and impair overall cardiac performance.

METHODS AND RESULTS

Cardiac magnetic resonance imaging, echocardiography, left ventricular and LA pressure-volume studies, and tissue analyses were performed in a model of early HFpEF (elderly dogs, renal wrap-induced hypertension, exogenous aldosterone; n=9) and young control dogs (sham surgery; n=13). Early HFpEF was associated with LA enlargement, cardiomyocyte hypertrophy, and enhanced LA contractile function (median active emptying fraction 16% [95% confidence interval, 13-24]% versus 12 [10-14]%, P=0.008; end-systolic pressure-volume relationship slope 2.4 [1.9-3.2]mm Hg/mL HFpEF versus 1.5 [1.2-2.2]mm Hg/mL controls, P=0.01). However, atrioventricular coupling was impaired and the curvilinear LA end-reservoir pressure-volume relationship was shifted upward/leftward in HFpEF (LA stiffness constant [β_LA] 0.16 [0.11-0.18]mm Hg/mL versus 0.06 [0.04-0.10]mm Hg/mL controls; P=0.002), indicating reduced LA compliance. Impaired atrioventricular coupling and lower LA compliance correlated with lower left ventricular stroke volume. Total fibrosis and titin isoform composition were similar between groups; however, titin was hyperphosphorylated in HFpEF and correlated with β_LA. LA microvascular reactivity was diminished in HFpEF versus controls. LA microvascular density tended to be lower in HFpEF and inversely correlated with β_LA.

CONCLUSIONS

In early-stage hypertensive HFpEF, LA cardiomyocyte hypertrophy, titin hyperphosphorylation, and microvascular dysfunction occur in association with increased systolic and diastolic LA chamber stiffness, impaired atrioventricular coupling, and decreased left ventricular stroke volume. These data indicate that maladaptive LA remodeling occurs early during HFpEF development, supporting a concept of global myocardial remodeling.

Sphingosine-1-Phosphate Receptor 1 Regulates Cardiac Function by Modulating Ca2+ Sensitivity and Na+/H+ Exchange and Mediates Protection by Ischemic Preconditioning

Background

Sphingosine‐1‐phosphate plays vital roles in cardiomyocyte physiology, myocardial ischemia–reperfusion injury, and ischemic preconditioning. The function of the cardiomyocyte sphingosine‐1‐phosphate receptor 1 (S1P₁) in vivo is unknown.

Methods and Results

Cardiomyocyte‐restricted deletion of S1P₁ in mice (S1P₁^αMHCCre) resulted in progressive cardiomyopathy, compromised response to dobutamine, and premature death. Isolated cardiomyocytes from S1P₁^αMHCCre mice revealed reduced diastolic and systolic Ca²⁺ concentrations that were secondary to reduced intracellular Na⁺ and caused by suppressed activity of the sarcolemmal Na⁺/H⁺ exchanger NHE‐1 in the absence of S1P₁. This scenario was successfully reproduced in wild‐type cardiomyocytes by pharmacological inhibition of S1P₁ or sphingosine kinases. Furthermore, Sarcomere shortening of S1P₁^αMHCCre cardiomyocytes was intact, but sarcomere relaxation was attenuated and Ca²⁺ sensitivity increased, respectively. This went along with reduced phosphorylation of regulatory myofilament proteins such as myosin light chain 2, myosin‐binding protein C, and troponin I. In addition, S1P₁ mediated the inhibitory effect of exogenous sphingosine‐1‐phosphate on β‐adrenergic–induced cardiomyocyte contractility by inhibiting the adenylate cyclase. Furthermore, ischemic precondtioning was abolished in S1P₁^αMHCCre mice and was accompanied by defective Akt activation during preconditioning.

Conclusions

Tonic S1P₁ signaling by endogenous sphingosine‐1‐phosphate contributes to intracellular Ca²⁺ homeostasis by maintaining basal NHE‐1 activity and controls simultaneously myofibril Ca²⁺ sensitivity through its inhibitory effect on adenylate cyclase. Cardioprotection by ischemic precondtioning depends on intact S1P₁ signaling. These key findings on S1P₁ functions in cardiac physiology may offer novel therapeutic approaches to cardiac diseases.

Titin stiffness modifies the force-generating region of muscle sarcomeres

The contractile units of striated muscle, the sarcomeres, comprise the thick (myosin) and thin (actin) filaments mediating active contraction and the titin filaments determining "passive" elasticity. We hypothesized that titin may be more active in muscle contraction by directly modulating thick-filament properties. We used single-myofibril mechanical measurements and atomic force microscopy of individual sarcomeres to quantify the effects of sarcomere strain and titin spring length on both the inter-filament lattice spacing and the lateral stiffness of the actin-myosin overlap zone (A-band). We found that strain reduced the lattice spacing similarly in sarcomeres with stiff (rabbit psoas) or compliant titin (rabbit diaphragm), but increased A-band lateral stiffness much more in psoas than in diaphragm. The strain-induced alterations in A-band stiffness that occur independently of lattice spacing effects may be due to titin stiffness-sensing by A-band proteins. This mechanosensitivity could play a role in the physiologically important phenomenon of length-dependent activation of striated muscle.

HEART DISEASE. Titin mutations in iPS cells define sarcomere insufficiency as a cause of dilated cardiomyopathy

Human mutations that truncate the massive sarcomere protein titin [TTN-truncating variants (TTNtvs)] are the most common genetic cause for dilated cardiomyopathy (DCM), a major cause of heart failure and premature death. Here we show that cardiac microtissues engineered from human induced pluripotent stem (iPS) cells are a powerful system for evaluating the pathogenicity of titin gene variants. We found that certain missense mutations, like TTNtvs, diminish contractile performance and are pathogenic. By combining functional analyses with RNA sequencing, we explain why truncations in the A-band domain of TTN cause DCM, whereas truncations in the I band are better tolerated. Finally, we demonstrate that mutant titin protein in iPS cell-derived cardiomyocytes results in sarcomere insufficiency, impaired responses to mechanical and β-adrenergic stress, and attenuated growth factor and cell signaling activation. Our findings indicate that titin mutations cause DCM by disrupting critical linkages between sarcomerogenesis and adaptive remodeling.

Molecular and structural transition mechanisms in long-term volume overload

Aim

We have previously reported that early phase (1 week) of experimental volume overload (VO) has an adaptive phenotype while wall stress‐matched pressure overload (PO) is maladaptive. Here we investigate the transition from adaptation to heart failure (HF) in long‐term VO.

Methods and results

FVB/N wild‐type mice were subjected to VO induced by aortocaval shunt, and were followed by serial echocardiography until in vivo left ventricular ejection fraction was below <50% (135 ± 35 days). Heart failure was evident from increased lung and liver weight and increased mortality compared with sham. Maladaptive remodelling resulted in significantly reduced sarcomeric titin phosphorylation (causing increased sarcomeric stiffness), whereas interstitial fibrosis was not increased. This was paralleled by re‐expression of the fetal gene program, activation of calcium/calmodulin‐dependent protein kinase II (CaMKII), decreased protein kinase B (Akt) phosphorylation, high oxidative stress, and increased apoptosis. Consistently, development of HF and mortality were significantly aggravated in Akt‐deficient mice.

Conclusion

Transition to HF in VO is associated with decreased Akt and increased CaMKII signalling pathways together with increased oxidative stress and apoptosis. Lack of interstitial fibrosis together with sarcomeric titin hypophosphorylation indicates an increased stiffness at the sarcomeric but not matrix level in VO‐induced HF (in contrast to PO). Transition to HF may result from myocyte loss and myocyte dysfunction owing to increased stiffness.

Myocardial Microvascular Inflammatory Endothelial Activation in Heart Failure With Preserved Ejection Fraction

OBJECTIVES

The present study investigated whether systemic, low-grade inflammation of metabolic risk contributed to diastolic left ventricular (LV) dysfunction and heart failure with preseved ejection fraction (HFpEF) through coronary microvascular endothelial activation, which alters paracrine signalling to cardiomyocytes and predisposes them to hypertrophy and high diastolic stiffness.

BACKGROUND

Metabolic risk is associated with diastolic LV dysfunction and HFpEF.

METHODS

We explored inflammatory endothelial activation and its effects on oxidative stress, nitric oxide (NO) bioavailability, and cyclic guanosine monophosphate (cGMP)-protein kinase G (PKG) signalling in myocardial biopsies of HFpEF patients and validated our findings by comparing obese Zucker diabetic fatty/Spontaneously hypertensive heart failure F1 hybrid (ZSF1)-HFpEF rats to ZSF1-Control (Ctrl) rats.

RESULTS

In myocardium of HFpEF patients and ZSF1-HFpEF rats, we observed the following: 1) E-selectin and intercellular adhesion molecule-1 expression levels were upregulated; 2) NADPH oxidase 2 expression was raised in macrophages and endothelial cells but not in cardiomyocytes; and 3) uncoupling of endothelial nitric oxide synthase, which was associated with reduced myocardial nitrite/nitrate concentration, cGMP content, and PKG activity.

CONCLUSIONS

HFpEF is associated with coronary microvascular endothelial activation and oxidative stress. These lead to a reduction of NO-dependent signalling from endothelial cells to cardiomyocytes, which can contribute to the high cardiomyocyte stiffness and hypertrophy observed in HFpEF.

Myofibrillar instability exacerbated by acute exercise in filaminopathy

Filamin C (FLNC) mutations in humans cause myofibrillar myopathy (MFM) and cardiomyopathy, characterized by protein aggregation and myofibrillar degeneration. We generated the first patient-mimicking knock-in mouse harbouring the most common disease-causing filamin C mutation (p.W2710X). These heterozygous mice developed muscle weakness and myofibrillar instability, with formation of filamin C- and Xin-positive lesions streaming between Z-discs. These lesions, which are distinct from the classical MFM protein aggregates by their morphology and filamentous appearance, were greatly increased in number upon acute physical exercise in the mice. This pathology suggests that mutant filamin influences the mechanical stability of myofibrillar Z-discs, explaining the muscle weakness in mice and humans. Re-evaluation of biopsies from MFM-filaminopathy patients with different FLNC mutations revealed a similar, previously unreported lesion pathology, in addition to the classical protein aggregates, and suggested that structures previously interpreted as aggregates may be in part sarcomeric lesions. We postulate that these lesions define preclinical disease stages, preceding the formation of protein aggregates.

A porcine model of hypertensive cardiomyopathy: implications for heart failure with preserved ejection fraction

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, 90-day-release subcutaneous depot) and a Western diet (WD) containing high amounts of salt, fat, cholesterol, and sugar for 12 wk. Compared with weight-matched controls (n = 8), DOCA/WD-treated pigs showed left ventricular (LV) concentric hypertrophy and left atrial 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 was markedly shifted leftward. 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 toward the stiffer titin isoform N2B, and reduced total titin phosphorylation. LV superoxide production was increased, in part attributable to nitric oxide synthase (NOS) uncoupling, whereas AKT and NOS isoform expression and phosphorylation were unchanged. In conclusion, we developed a large-animal model in which 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.

Abstract 210: Titin Phosphorylation by Protein Kinase G as a Novel Mechanism of Diastolic Adaptation to Acute Hemodynamic Overload

Titin is the main determinant of myocardial passive tension and its distensibility is increased via phosphorylation by protein kinase G (PKG), activated by nitric oxide (NO) and natriuretic peptides (NP) upon acute overload. We hypothesized whether myocardial stretch led to decreased stiffness, optimizing diastolic filling along with the usual increase in contractility.

Intact rat Langendorff hearts, strips dissected from the LV or right atrium of cardiac surgery patients and rabbit papillary muscles were acutely stretched for 15min. Passive tension (PT) was measured in skinned cardiomyocytes extracted from the LV of control and stretched rat hearts for sarcomere lengths (SL) 1.8-2.3μm before and after incubation with PKG. Rabbit muscles were incubated with a PKG inhibitor or, simultaneously, a NO synthase inhibitor, a NO scavenger, a NP receptor A antagonist. All-total titin phosphorylation was stained with Pro-Q Diamond and indexed to total-protein signals using SYPRO Ruby. Values are given as mean±SEM and statistical significance was set to p<0.05.

After acute stretch there was a progressive decrease in passive tension/diastolic pressure over 15min: 27±8% and 27±6% in human atrium and ventricular muscles, respectively, and 43±2% in rabbit papillary muscles and isolated hearts. This decrease in myocardial stiffness was significantly blunted by PKG inhibition (40%) and NO/NP pathway inhibition (29%). PT of cardiomyocytes was significantly lower (≈60%) in the previously stretched group for all SL. A similar effect, only significant in the control group, was observed after incubation with PKG. Titin phosphorylation increased markedly 15 minutes after acute myocardial stretch in human (atrial: 11±1% vs 41±8%; LV: 27±8% vs 71±21%) and rabbit (13±2% vs 23±3%) myocardium.

The progressive decrease in myocardial stiffness after acute hemodynamic overload is preserved at the myofilamental level and seems to depend on PKG activity, representing a potential therapeutic target in patients with pathologically rigid myocardium. Moreover, blocking PKG activation seems to attenuate this adaptive diastolic response. Therefore, titin phosphorylation by this kinase is probably involved in this new myocardial response to stretch in both animals and humans.

Emerging importance of oxidative stress in regulating striated muscle elasticity

The contractile function of striated muscle cells is altered by oxidative/nitrosative stress, which can be observed under physiological conditions but also in diseases like heart failure or muscular dystrophy. Oxidative stress causes oxidative modifications of myofilament proteins and can impair myocyte contractility. Recent evidence also suggests an important effect of oxidative stress on muscle elasticity and passive stiffness via modifications of the giant protein titin. In this review we provide a short overview of known oxidative modifications in thin and thick filament proteins and then discuss in more detail those oxidative stress-related modifications altering titin stiffness directly or indirectly. Direct modifications of titin include reversible disulfide bonding within the cardiac-specific N2-Bus domain, which increases titin stiffness, and reversible S-glutathionylation of cryptic cysteines in immunoglobulin-like domains, which only takes place after the domains have unfolded and which reduces titin stiffness in cardiac and skeletal muscle. Indirect effects of oxidative stress on titin can occur via reversible modifications of protein kinase signalling pathways (especially the NO-cGMP-PKG axis), which alter the phosphorylation level of certain disordered titin domains and thereby modulate titin stiffness. Oxidative stress also activates proteases such as matrix-metalloproteinase-2 and (indirectly via increasing the intracellular calcium level) calpain-1, both of which cleave titin to irreversibly reduce titin-based stiffness. Although some of these mechanisms require confirmation in the in vivo setting, there is evidence that oxidative stress-related modifications of titin are relevant in the context of biomarker design and represent potential targets for therapeutic intervention in some forms of muscle and heart disease.

FHL2 expression and variants in hypertrophic cardiomyopathy

Based on evidence that FHL2 (four and a half LIM domains protein 2) negatively regulates cardiac hypertrophy we tested whether FHL2 altered expression or variants could be associated with hypertrophic cardiomyopathy (HCM). HCM is a myocardial disease characterized by left ventricular hypertrophy, diastolic dysfunction and increased interstitial fibrosis and is mainly caused by mutations in genes coding for sarcomeric proteins. FHL2 mRNA level, FHL2 protein level and I-band-binding density were lower in HCM patients than control individuals. Screening of 121 HCM patients without mutations in established disease genes identified 2 novel (T171M, V187L) and 4 known (R177Q, N226N, D268D, P273P) FHL2 variants in unrelated HCM families. We assessed the structural and functional consequences of the nonsynonymous substitutions after adeno-associated viral-mediated gene transfer in cardiac myocytes and in 3D-engineered heart tissue (EHT). Overexpression of FHL2 wild type or nonsynonymous substitutions in cardiac myocytes markedly down-regulated α-skeletal actin and partially blunted hypertrophy induced by phenylephrine or endothelin-1. After gene transfer in EHTs, force and velocity of both contraction and relaxation were higher with T171M and V187L FHL2 variants than wild type under basal conditions. Finally, chronic phenylephrine stimulation depressed EHT function in all groups, but to a lower extent in T171M-transduced EHTs. These data suggest that (1) FHL2 is down-regulated in HCM, (2) both FHL2 wild type and variants partially protected phenylephrine- or endothelin-1-induced hypertrophy in cardiac myocytes, and (3) FHL2 T171M and V187L nonsynonymous variants induced altered EHT contractility. These findings provide evidence that the 2 novel FHL2 variants could increase cardiac function in HCM.

Interleukin-6 receptor inhibition modulates the immune reaction and restores titin phosphorylation in experimental myocarditis

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 titin phosphorylation. IL-6 receptor blockade led to a shift of the immune response to a Th1 direction and significant reduction of viral load. In addition, cardiac immune response, extracellular matrix regulation and titin function improved, resulting in a preserved LV function. IL-6 receptor blockade exerts cardiac beneficial effects by antiviral and immunomodulatory actions after induction of an acute murine CVB3 virus myocarditis.

Left ventricular diastolic dysfunction and myocardial stiffness in diabetic mice is attenuated by inhibition of dipeptidyl peptidase 4

AIMS

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.

METHODS AND RESULTS

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.

CONCLUSIONS

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.