Mouse Model Of Dilated Cardiomyopathy Research Articles

Effects of candesartan on electrical remodeling in the hearts of inherited dilated cardiomyopathy model mice.

Inherited dilated cardiomyopathy (DCM) is characterized by dilatation and dysfunction of the ventricles, and often results in sudden death or heart failure (HF). Although angiotensin receptor blockers (ARBs) have been used for the treatment of HF, little is known about the effects on postulated electrical remodeling that occurs in inherited DCM. The aim of this study was to examine the effects of candesartan, one of the ARBs, on cardiac function and electrical remodeling in the hearts of inherited DCM model mice (TNNT2 ΔK210). DCM mice were treated with candesartan in drinking water for 2 months from 1 month of age. Control, non-treated DCM mice showed an enlargement of the heart with prolongation of QRS and QT intervals, and died at t1/2 of 70 days. Candesartan dramatically extended the lifespan of DCM mice, suppressed cardiac dilatation, and improved the functional parameters of the myocardium. It also greatly suppressed prolongation of QRS and QT intervals and action potential duration (APD) in the left ventricular myocardium and occurrence of ventricular arrhythmia. Expression analysis revealed that down-regulation of Kv4.2 (Ito channel protein), KChIP2 (auxiliary subunit of Kv4.2), and Kv1.5 (IKur channel protein) in DCM was partially reversed by candesartan administration. Interestingly, non-treated DCM heart had both normal-sized myocytes with moderately decreased Ito and IKur and enlarged cells with greatly reduced K+ currents (Ito, IKur IK1 and Iss). Treatment with candesartan completely abrogated the emergence of the enlarged cells but did not reverse the Ito, and IKur in normal-sized cells in DCM hearts. Our results indicate that candesartan treatment suppresses structural remodeling to prevent severe electrical remodeling in inherited DCM.

In vivo effects of propyl gallate, a novel Ca2 + sensitizer, in a mouse model of dilated cardiomyopathy caused by cardiac troponin T mutation

AimsWe have previously demonstrated that propyl gallate has a Ca2+ sensitizing effect on the force generation in membrane-permeabilized (skinned) cardiac muscle fibers. However, in vivo beneficial effects of propyl gallate as a novel Ca2+ sensitizer remain uncertain. In the present study, we aim to explore in vivo effects of propyl gallate. Main methodsWe compared effects of propyl gallate on ex vivo intact cardiac muscle fibers and in vivo hearts in healthy mice with those of pimobendan, a clinically used Ca2+ sensitizer. The therapeutic effect of propyl gallate was investigated using a mouse model of dilated cardiomyopathy (DCM) with reduced myofilament Ca2+ sensitivity due to a deletion mutation ΔK210 in cardiac troponin T. Key findingsPropyl gallate, as well as pimobendan, showed a positive inotropic effect. Propyl gallate slightly increased the blood pressure without changing the heart rate in healthy mice, whereas pimobendan decreased the blood pressure probably through vasodilation via inhibition of phosphodiesterase and increased the heart rate. Propyl gallate prevented cardiac remodeling and systolic dysfunction and significantly improved the life-expectancy of knock-in mouse model of DCM with reduced myofilament Ca2+ sensitivity due to a mutation in cardiac troponin T. On the other hand, gallate, a similarly strong antioxidant polyphenol lacking Ca2+ sensitizing action, had no beneficial effects on the DCM mice. SignificanceThese results suggest that propyl gallate might be useful for the treatment of inherited DCM caused by a reduction in the myofilament Ca2+ sensitivity.

Therapeutic efficacy of cardiosphere-derived cells in a transgenic mouse model of non-ischaemic dilated cardiomyopathy.

Cardiosphere-derived cells (CDCs) produce regenerative effects in the post-infarct setting. However, it is unclear whether CDCs are beneficial in non-ischaemic dilated cardiomyopathy (DCM). We tested the effects of CDC transplantation in mice with cardiac-specific Gαq overexpression, which predictably develop progressive cardiac dilation and failure, with accelerated mortality. Wild-type mouse CDCs (10(5) cells) or vehicle only were injected intramyocardially in 6-, 8-, and 11-week-old Gαq mice. Cardiac function deteriorated in vehicle-treated mice over 3 months of follow-up, accompanied by oxidative stress, inflammation and adverse ventricular remodelling. In contrast, CDCs preserved cardiac function and volumes, improved survival, and promoted cardiomyogenesis while blunting Gαq-induced oxidative stress and inflammation in the heart. The mechanism of benefit is indirect, as long-term engraftment of transplanted cells is vanishingly low. Cardiosphere-derived cells reverse fundamental abnormalities in cell signalling, prevent adverse remodelling, and improve survival in a mouse model of DCM. The ability to impact favourably on disease progression in non-ischaemic heart failure heralds new potential therapeutic applications of CDCs.

Cardiomyocyte-specific expression of CRNK, the C-terminal domain of PYK2, maintains ventricular function and slows ventricular remodeling in a mouse model of dilated cardiomyopathy

Up-regulation and activation of PYK2, a member of the FAK family of protein tyrosine kinases, is involved in the pathogenesis of left ventricular (LV) remodeling and heart failure (HF). PYK2 activation can be prevented by CRNK, the C-terminal domain of PYK2. We previously demonstrated that adenoviral-mediated CRNK gene transfer improved survival and LV function, and slowed LV remodeling in a rat model of coronary artery ligation-induced HF. We now interrogate whether cardiomyocyte-specific, transgenic CRNK expression prevents LV remodeling and HF in a mouse model of dilated cardiomyopathy (DCM) caused by constitutively active Protein Kinase Cε (caPKCε). Transgenic (TG; FVB/N background) mice were engineered to express rat CRNK under control of the α-myosin heavy chain promoter, and crossed with FVB/N mice with cardiomyocyte-specific expression of caPKCε to create double TG mice. LV structure, function, and gene expression were evaluated in all 4 groups (nonTG FVB/N; caPKCε(+/−); CRNK(+/−); and caPKCε×CRNK (PXC) double TG mice) at 1, 3, 6, 9 and 12mo of age. CRNK expression followed a Mendelian distribution, and CRNK mice developed and survived normally through 12mo. Cardiac structure, function and selected gene expression of CRNK mice were similar to nonTG littermates. CRNK had no effect on caPKCε expression and vice versa. PYK2 was up-regulated ~6-fold in caPKCε mice, who developed a non-hypertrophic, progressive DCM with reduced systolic (Contractility Index=151±5 vs. 90±4s−1) and diastolic (Tau=7.5±0.5 vs. 14.7±1.3ms) function, and LV dilatation (LV Remodeling Index (LVRI)=4.2±0.1 vs. 6.0±0.3 for FVB/N vs. caPKCε mice, respectively; P<0.05 for each at 12mo). In double TG PXC mice, CRNK expression significantly prolonged survival, improved contractile function (Contractile Index=115±8s−1; Tau=9.5±1.0ms), and reduced LV remodeling (LVRI=4.9±0.1). Cardiomyocyte-specific expression of CRNK improves contractile function and slows LV remodeling in a mouse model of DCM.

Calponin1 inhibits dilated cardiomyopathy development in mice through the εPKC pathway

BackgroundCalponin1 (CNN1) is involved in the regulation of smooth muscle contraction in physiological situation and it also expresses abnormally in a variety of pathological situations. We found that the expression of CNN1 decreased significantly in the heart tissue of a cTnTR141W transgenic dilated cardiomyopathy (DCM) mouse model and an adriamycin (ADR)-induced DCM mouse model, suggesting that CNN1 is involved in the pathogenesis of DCM. However, the role of CNN1 on cardiac function, especially on pathogenesis of DCM, has not been clarified. In this study, we tested whether rescued expression of CNN1 could prevent the development of DCM and investigated its possible mechanisms. Methods and resultsThe DCM phenotypes were significantly improved with the transgenic expression of CNN1 in the cTnTR141W×CNN1 double transgenic (DTG) mice, which was demonstrated by the survival, cardiac geometry and function analyses, as well as microstructural and ultrastructural observations based on echocardiography and histology examination. The expression of CNN1 could also resist the cardiac geometry breakage and dysfunction in the ADR-induced DCM mice model. Meanwhile, the epsilon isoform of protein kinase C (εPKC) activator and inhibitor could reverse the activation of εPKC/ERK/mTOR pathway and DCM phenotypes in the cTnTR141W and cTnTR141W×CNN1 double transgenic (DTG) mice. ConclusionsεPKC/ERK/mTOR pathway activation induced by the rescued expression of CNN1 contributed to the improvement of cardiac dysfunction and pathological changes observed in the DTG mice. CNN1 could be a therapeutic target to prevent the development of DCM and heart failure (HF).

Abstract 18790: Therapeutic Efficacy of Cardiosphere-Derived Cells in a Transgenic Mouse Model of Nonischemic Dilated Cardiomyopathy

Introduction: Cardiosphere-derived cells (CDCs) produce regenerative effects and improve function in the post-infarct setting. However, it is unclear whether CDCs are beneficial in non-ischemic dilated cardiomyopathy (DCM). We tested the effects of CDC transplantation in mice with cardiac-specific Gαq overexpression, which leads to intense myocardial oxidative/nitrosative stress and inflammation. These mice predictably develop progressive cardiac dilation and failure, with accelerated mortality. Methods and Results: A total of 71 mice were investigated in this study. Wild-type syngeneic mouse CDCs (10 5 cells total) or vehicle only were injected intramyocardially at five left ventricular sites in 6-, 8- and 11-week old Gαq mice. Cardiac function deteriorated in vehicle-treated mice over 3 months of follow-up, accompanied by oxidative stress, inflammation and adverse ventricular remodeling. Left ventricular (LV) ejection fraction and LV end-diastolic and end-systolic volumes were progressively worsened over 3 months observational period in vehicle-treated mice compared to CDC-treated group (p&lt;0.05). This was associated with upregulation of reactive oxygen species- and nitric oxide-producing enzymes [NAD(P)H oxidase and inducible nitric oxide synthase], accumulation of proinflammatory oxidant product, 3-Nitrotyrosine, intense infiltration of inflammatory cells [CD68 + macrophages and CD3 + T cells], increased apoptosis and activation of pathologic remodeling pathway, PKC-PKD-CREB. Concomitantly, marked collagen I and III deposition and fibrosis were observed in the vehicle-treated Gαq mouse heart. In contrast, CDCs preserved cardiac function and volumes (p&lt;0.05), and promoted cardiomyocyte cycling (p&lt;0.01) while blunting Gαq-induced oxidative stress, inflammation and fibrosis in the heart. Survival was enhanced by CDCs (p&lt;0.005) in Gαq mice that had been subjected to doxoribicin stress. Conclusions: CDCs reverse fundamental abnormalities in cell signaling, prevent adverse remodeling and improve survival in a mouse model of DCM. These findings motivate testing of CDCs as a potential therapeutic to prevent disease progression in patients with early-stage DCM.

Decreasing Tropomyosin Phosphorylation Rescues Tropomyosin-induced Familial Hypertrophic Cardiomyopathy

Studies indicate that tropomyosin (Tm) phosphorylation status varies in different mouse models of cardiac disease. Investigation of basal and acute cardiac function utilizing a mouse model expressing an α-Tm protein that cannot be phosphorylated (S283A) shows a compensated hypertrophic phenotype with significant increases in SERCA2a expression and phosphorylation of phospholamban Ser-16 (Schulz, E. M., Correll, R. N., Sheikh, H. N., Lofrano-Alves, M. S., Engel, P. L., Newman, G., Schultz Jel, J., Molkentin, J. D., Wolska, B. M., Solaro, R. J., and Wieczorek, D. F. (2012) J. Biol. Chem. 287, 44478-44489). With these results, we hypothesized that decreasing α-Tm phosphorylation may be beneficial in the context of a chronic, intrinsic stressor. To test this hypothesis, we utilized the familial hypertrophic cardiomyopathy (FHC) α-Tm E180G model (Prabhakar, R., Boivin, G. P., Grupp, I. L., Hoit, B., Arteaga, G., Solaro, R. J., and Wieczorek, D. F. (2001) J. Mol. Cell. Cardiol. 33, 1815-1828). These FHC hearts are characterized by increased heart:body weight ratios, fibrosis, increased myofilament Ca(2+) sensitivity, and contractile defects. The FHC mice die by 6-8 months of age. We generated mice expressing both the E180G and S283A mutations and found that the hypertrophic phenotype was rescued in the α-Tm E180G/S283A double mutant transgenic animals; these mice exhibited no signs of cardiac hypertrophy and displayed improved cardiac function. These double mutant transgenic hearts showed increased phosphorylation of phospholamban Ser-16 and Thr-17 compared with the α-Tm E180G mice. This is the first study to demonstrate that decreasing phosphorylation of tropomyosin can rescue a hypertrophic cardiomyopathic phenotype.

Depressed Frank–Starling mechanism in the left ventricular muscle of the knock-in mouse model of dilated cardiomyopathy with troponin T deletion mutation ΔK210

It has been reported that the Frank–Starling mechanism is coordinately regulated in cardiac muscle via thin filament “on–off” equilibrium and titin-based lattice spacing changes. In the present study, we tested the hypothesis that the deletion mutation ΔK210 in the cardiac troponin T gene shifts the equilibrium toward the “off” state and accordingly attenuate the sarcomere length (SL) dependence of active force production, via reduced cross-bridge formation. Confocal imaging in isolated hearts revealed that the cardiomyocytes were enlarged, especially in the longitudinal direction, in ΔK210 hearts, with striation patterns similar to those in wild type (WT) hearts, suggesting that the number of sarcomeres is increased in cardiomyocytes but the sarcomere length remains unaltered. For analysis of the SL dependence of active force, skinned muscle preparations were obtained from the left ventricle of WT and knock-in (ΔK210) mice. An increase in SL from 1.90 to 2.20μm shifted the mid-point (pCa50) of the force-pCa curve leftward by ~0.21pCa units in WT preparations. In ΔK210 muscles, Ca2+ sensitivity was lower by ~0.37pCa units, and the SL-dependent shift of pCa50, i.e., ΔpCa50, was less pronounced (~0.11pCa units), with and without protein kinase A treatment. The rate of active force redevelopment was lower in ΔK210 preparations than in WT preparations, showing blunted thin filament cooperative activation. An increase in thin filament cooperative activation upon an increase in the fraction of strongly bound cross-bridges by MgADP increased ΔpCa50 to ~0.21pCa units. The depressed Frank–Starling mechanism in ΔK210 hearts is the result of a reduction in thin filament cooperative activation.

Efficacy of epicardially delivered adipose stroma cell sheets in dilated cardiomyopathy

Few studies have assessed the effects of cell therapy in non-ischaemic cardiomyopathies which, however, contribute to a large number of cardiac failures. Assuming that such conditions are best suited for a global delivery of cells, we assessed the effects of epicardially delivered adipose tissue-derived stroma cell (ADSC) sheets in a mouse model of dilated cardiomyopathy based on cardiac-specific and tamoxifen-inducible invalidation of serum response factor. Three weeks after tamoxifen administration, the function of the left ventricle (LV) was assessed by echocardiography. Twenty-nine mice were then allocated to control (n = 9, non-transgenic), sham (n = 10, transgenic non-treated), and treated (n = 10, transgenic) groups. In the treated group, 3 × 10(6) allogeneic ADSCs were cultured for 2 days onto temperature-responsive polymers and the generated sheets were then transplanted over the surface of the heart. In 10 additional mice, the sheet was made of green fluorescent protein (GFP)-labelled ADSCs to track cell fate. Function, engraftment, and fibrosis were blindly assessed after 3 weeks. In the non-treated group, fractional shortening declined compared with baseline, whereas the sheet application resulted in its stabilization. This correlated with a lesser degree of LV remodelling, as LV end-diastolic and end-systolic diameters did not differ from baseline values. Many GFP(+) cells were identified in the epicardial graft and in the myocardium. Treated animals also displayed a reduced expression of the stress-induced atrial natriuretic factor and beta-myosin heavy chain genes. These protective effects were also accompanied by a reduction of myocardial fibrosis. These results strongly suggest the functional relevance of epicardially delivered cell-seeded biomaterials to non-ischaemic heart failure.

Increased Expression of HCN Channels in the Ventricular Myocardium Contributes to Enhanced Arrhythmicity in Mouse Failing Hearts

BackgroundThe efficacy of pharmacological interventions to prevent sudden arrhythmic death in patients with chronic heart failure remains limited. Evidence now suggests increased ventricular expression of hyperpolarization‐activated cation (HCN) channels in hypertrophied and failing hearts contributes to their arrythmicity. Still, the role of induced HCN channel expression in the enhanced arrhythmicity associated with heart failure and the capacity of HCN channel blockade to prevent lethal arrhythmias remains undetermined.Methods and ResultsWe examined the effects of ivabradine, a specific HCN channel blocker, on survival and arrhythmicity in transgenic mice (dnNRSF‐Tg) expressing a cardiac‐specific dominant‐negative form of neuron‐restrictive silencer factor, a useful mouse model of dilated cardiomyopathy leading to sudden death. Ivabradine (7 mg/kg per day orally) significantly reduced ventricular tachyarrhythmias and improved survival among dnNRSF‐Tg mice while having no significant effect on heart rate or cardiac structure or function. Ivabradine most likely prevented the increase in automaticity otherwise seen in dnNRSF‐Tg ventricular myocytes. Moreover, cardiac‐specific overexpression of HCN2 in mice (HCN2‐Tg) made hearts highly susceptible to arrhythmias induced by chronic β‐adrenergic stimulation. Indeed, ventricular myocytes isolated from HCN2‐Tg mice were highly susceptible to β‐adrenergic stimulation‐induced abnormal automaticity, which was inhibited by ivabradine.ConclusionsHCN channel blockade by ivabradine reduces lethal arrhythmias associated with dilated cardiomyopathy in mice. Conversely, cardiac‐specific overexpression of HCN2 channels increases arrhythmogenicity of β‐adrenergic stimulation. Our findings demonstrate the contribution of HCN channels to the increased arrhythmicity seen in failing hearts and suggest HCN channel blockade is a potentially useful approach to preventing sudden death in patients with heart failure.

Usefulness of Running Wheel for Detection of Congestive Heart Failure in Dilated Cardiomyopathy Mouse Model

BackgroundInherited dilated cardiomyopathy (DCM) is a progressive disease that often results in death from congestive heart failure (CHF) or sudden cardiac death (SCD). Mouse models with human DCM mutation are useful to investigate the developmental mechanisms of CHF and SCD, but knowledge of the severity of CHF in live mice is necessary. We aimed to diagnose CHF in live DCM model mice by measuring voluntary exercise using a running wheel and to determine causes of death in these mice.Methodology/Principal FindingsA knock-in mouse with a mutation in cardiac troponin T (ΔK210) (DCM mouse), which results in frequent death with a t1/2 of 70 to 90 days, was used as a DCM model. Until 2 months of age, average wheel-running activity was similar between wild-type and DCM mice (approximately 7 km/day). At approximately 3 months, some DCM mice demonstrated low running activity (LO: <1 km/day) while others maintained high running activity (HI: >5 km/day). In the LO group, the lung weight/body weight ratio was much higher than that in the other groups, and the lungs were infiltrated with hemosiderin-loaded alveolar macrophages. Furthermore, echocardiography showed more severe ventricular dilation and a lower ejection fraction, whereas Electrocardiography (ECG) revealed QRS widening. There were two patterns in the time courses of running activity before death in DCM mice: deaths with maintained activity and deaths with decreased activity.Conclusions/SignificanceOur results indicate that DCM mice with low running activity developed severe CHF and that running wheels are useful for detection of CHF in mouse models. We found that approximately half of ΔK210 DCM mice die suddenly before onset of CHF, whereas others develop CHF, deteriorate within 10 to 20 days, and die.

Dynamic Obstruction is Associated With Abnormal Myocardial Mechanics in Hypertrophic Cardiomyopathy

Introduction: Dilated cardiomyopathy (DCM) is a progressive disease characterised by ventricular dilatation, impaired systolic function and diffuse interstitial fibrosis. Recently in the setting of mineralocorticoid-induced cardiac fibrosis, we demonstrated that activation of the SDF-1:CXCR4 axis was central to the development of cardiac fibrosis. In this study we tested the hypothesis that the SDF-1:CXCR4 axis is implicated in the pathogenesis of fibrosis in DCM. Methods and results: A transgenic mouse model (Mst1) of DCM and fibrosis was used. The effect of the CXCR4 antagonist (AMD3100, 6mg/kg/d) on cardiac fibrosis (quantitative Masson’s stain) was examined. After 12wks, blood pressure and left ventricular morphology was analysed. As indicated in the Table, Mst1 mice demonstrated ventricular dilatation and significant cardiac fibrosis. AMD3100 significantly attenuated the development of left ventricular fibrosis (p< 0.01). Conclusion: CXCR4/SDF-1 signalling pathway plays a central role in thepathogenesis of cardiac fibrosis inDCM.

Effects of Angiotensin II Receptor Blocker on the Progression of Electrical Remodeling in Hearts of Inherited DCM Model Mice

Inherited dilated cardiomyopathy (DCM), characterized by dilation and impaired systolic function of ventricle, is a progressive disease often resulting in death with congestive heart failure (CHF) or sudden death (SD). It remains unclear how electrical remodeling proceed in inherited DCM. Furthermore, although angiotensin II receptor blockers (ARBs) is known to have beneficial effects on HF in general, little is known about the effects of ARB on the electrical remodeling in inherited DCM. The aim of our study was to investigate effects of ARB on the remodeling in inherited DCM hearts using a knock-in mouse model of DCM (TNNT2 ΔK210). In DCM mice at 2 months of age when mortality rate abruptly increased, myocardium showed a significant reduction in K+ current density with substantial decreases in expression of Kv4.2, Kv1.5 and KChIP2. In contrast, at 1 month, down-regulation of Kv1.5 or KChIP2 was not observed, but up-regulation of Cav3.1 was detected. At 3 months, some of DCM mice showed a lung edema, a sign of CHF. CHF myocardium showed further decrease in expression of the various K+ channels. Treatment with ARB, candesartan, started at 1 months, considerably extended lifespan of DCM mice. Interestingly, expression changes that occurred in later phase were inhibited by ARB whereas changes occurred at early stage were not affected. Our results indicate that the electrical remodeling at later stage of DCM is critical for survival of this mouse model and the remodeling is controllable by ARB.

No Contribution of IP 3 -R(2) to Disease Phenotype in Models of Dilated Cardiomyopathy or Pressure Overload Hypertrophy

We investigated the contribution of inositol(1,4,5)-trisphosphate (Ins(1,4,5)P3 [IP3]) receptors (IP3-R) to disease progression in mouse models of dilated cardiomyopathy (DCM) and pressure overload hypertrophy. Mice expressing mammalian sterile 20-like kinase and dominant-negative phosphatidylinositol-3-kinase in heart (Mst1×dn-PI3K-2Tg; DCM-2Tg) develop severe DCM and conduction block, associated with increased expression of type 2 IP3-R (IP3-R(2)) and heightened generation of Ins(1,4,5)P3. Similar increases in Ins(1,4,5)P3 and IP3-R(2) are caused by transverse aortic constriction. To evaluate the contribution of IP3-R(2) to disease progression, the DCM-2Tg mice were further crossed with mice in which the type 2 IP3-R (IP3-R(2)-/-) had been deleted (DCM-2Tg×IP3-R(2)-/-) and transverse aortic constriction was performed on IP3-R(2)-/- mice. Hearts from DCM-2Tg mice and DCM-2Tg×IP3-R(2)-/- were similar in terms of chamber dilatation, atrial enlargement, and ventricular wall thinning. Electrophysiological changes were also similar in the DCM-2Tg mice, with and without IP3-R(2). Deletion of IP3-R(2) did not alter the progression of heart failure, because DCM-2Tg mice with and without IP3-R(2) had similarly reduced contractility, increased lung congestion, and atrial thrombus, and both strains died between 10 and 12 weeks of age. Loss of IP3-R(2) did not alter the progression of hypertrophy after transverse aortic constriction. We conclude that IP3-R(2) do not contribute to the progression of DCM or pressure overload hypertrophy, despite increased expression and heightened generation of the ligand, Ins(1,4,5)P3.

Characterization of the cardiac response to a low and high dose of dobutamine in the mouse model of dilated cardiomyopathy by MRI in vivo

To assess the cardiac response to low (0.15-0.5 mg/kg i.p.) and high (1.5-20 mg/kg i.p.) doses of dobutamine in Tgαq*44 mice with dilated cardiomyopathy at the stage of advanced heart failure. Inotropic, lusitropic, and chronotropic response to β(1) -adrenergic stimulation was assessed by the cine magnetic resonance imaging (MRI) protocol based on the electrocardiogram (ECG)-triggered bright-blood images of one midventricular short-axis slice. In wildtype mice increasing doses of dobutamine resulted in subsequent increase in the left ventricular function and heart rate acceleration, but significant inotropic, lusitropic, and chronotropic cardiac response was observed only after high doses of dobutamine, what is typical. In the Tgαq*44 mice low doses of dobutamine significantly increased inotropic and lusitropic cardiac performance without chronotropic changes. An increased heart rate was observed only after high doses of dobutamine, but then inotropic and lusitropic cardiac functional reserve was lost. We described MRI stress test protocol based on a low and high dose of dobutamine induced response that proves useful in revealing alternation in cardiac function in mice with heart failure.

Rac-induced left ventricular dilation in thyroxin-treated ZmRacD transgenic mice: role of cardiomyocyte apoptosis and myocardial fibrosis.

The pathways inducing the critical transition from compensated hypertrophy to cardiac dilation and failure remain poorly understood. The goal of our study is to determine the role of Rac-induced signaling in this transition process. Our previous results showed that Thyroxin (T4) treatment resulted in increased myocardial Rac expression in wild-type mice and a higher level of expression in Zea maize RacD (ZmRacD) transgenic mice. Our current results showed that T4 treatment induced physiologic cardiac hypertrophy in wild-type mice, as demonstrated by echocardiography and histopathology analyses. This was associated with significant increases in myocardial Rac-GTP, superoxide and ERK1/2 activities. Conversely, echocardiography and histopathology analyses showed that T4 treatment induced dilated cardiomyopathy along with compensatory cardiac hypertrophy in ZmRacD mice. These were linked with further increases in myocardial Rac-GTP, superoxide and ERK1/2 activities. Additionally, there were significant increases in caspase-8 expression and caspase-3 activity. However, there was a significant decrease in p38-MAPK activity. Interestingly, inhibition of myocardial Rac-GTP activity and superoxide generation with pravastatin and carvedilol, respectively, attenuated all functional, structural, and molecular changes associated with the T4-induced cardiomyopathy in ZmRacD mice except the compensatory cardiac hypertrophy. Taken together, T4-induced ZmRacD is a novel mouse model of dilated cardiomyopathy that shares many characteristics with the human disease phenotype. To our knowledge, this is the first study to show graded Rac-mediated O2·− results in cardiac phenotype shift in-vivo. Moreover, Rac-mediated O2·− generation, cardiomyocyte apoptosis, and myocardial fibrosis seem to play a pivotal role in the transition from cardiac hypertrophy to cardiac dilation and failure. Targeting Rac signaling could represent valuable therapeutic strategy not only in saving the failing myocardium but also to prevent this transition process.

Abstract 323: Growth Differentiation Factor-15 Is Upregulated in Profibrotic States of Dilated Cardiomyopathy and Not Hypertrophic Cardiomyopathy

Introduction: Dilated cardiomyopathy (DCM) and hypertrophic cardiomyopathy (HCM) are leading causes of morbidity and mortality in the adult population. Both DCM and HCM arise from structural perturbations and remodeling of the heart, and many cases have been found to result from underlying familial mutations. The signaling pathways by which these mutations lead to pathological ventricular remodeling, fibrosis, and heart failure remain unknown. Methods: In this study we attempt to identify molecular pathways in a DCM mouse model and compare and contrast the results with those previously observed in HCM mouse models. We use a transgenic mouse expressing an arginine-to-cysteine (R9C) mutation in phospholamban (PLN), previously identified in DCM patients. To define molecules involved in disease progression, we generated expression profiles using high-throughput sequencing and assessed genes of interest by immunostaining. Results: PLN R9C/+ hearts exhibit increasing fibrosis, with proliferation of non-myocyte cells occurring throughout the disease spectrum. Losartan treatment, which effectively blocks the HCM phenotype, does not block the emergence of DCM and neither reduces fibrosis nor increases lifespan in PLN R9C/+ mice. Growth differentiation factor-15 (GDF15) RNA and protein levels are significantly upregulated in the left ventricles of PLN R9C/+ mice during DCM and heart failure. GDF15 is predominantly expressed in non-myocytes in WT mice, but in PLN R9C/+ mice, is upregulated almost 25-fold in myocytes and less than 1.5-fold in non-myocytes. Conclusion: Both fibrosis and the proliferation of non-myocytes in PLN R9C/+ mouse hearts increase as the DCM phenotype worsens, similar to that observed in HCM mouse models. However, losartan has no effect on the DCM phenotype suggesting that the molecular pathways of DCM and HCM may be different. This study identifies GDF15 as a signaling molecule that may play a unique role in DCM. GDF15 is upregulated in myocytes during DCM, but remains relatively unchanged in HCM. Understanding the genetic mechanisms underlying the progression of disease and fibrosis in both DCM and HCM will help us to characterize the distinct pathways of both diseases, as well as identify new, more specific targets for therapy.

Multistep Ion Channel Remodeling and Lethal Arrhythmia Precede Heart Failure in a Mouse Model of Inherited Dilated Cardiomyopathy

BackgroundPatients with inherited dilated cardiomyopathy (DCM) frequently die with severe heart failure (HF) or die suddenly with arrhythmias, although these symptoms are not always observed at birth. It remains unclear how and when HF and arrhythmogenic changes develop in these DCM mutation carriers. In order to address this issue, properties of the myocardium and underlying gene expressions were studied using a knock-in mouse model of human inherited DCM caused by a deletion mutation ΔK210 in cardiac troponinT.Methodology/Principal FindingsBy 1 month, DCM mice had already enlarged hearts, but showed no symptoms of HF and a much lower mortality than at 2 months or later. At around 2 months, some would die suddenly with no clear symptoms of HF, whereas at 3 months, many of the survivors showed evident symptoms of HF. In isolated left ventricular myocardium (LV) from 2 month-mice, spontaneous activity frequently occurred and action potential duration (APD) was prolonged. Transient outward (Ito) and ultrarapid delayed rectifier K+ (IKur) currents were significantly reduced in DCM myocytes. Correspondingly, down-regulation of Kv4.2, Kv1.5 and KChIP2 was evident in mRNA and protein levels. In LVs at 3-months, more frequent spontaneous activity, greater prolongation of APD and further down-regulation in above K+ channels were observed. At 1 month, in contrast, infrequent spontaneous activity and down-regulation of Kv4.2, but not Kv1.5 or KChIP2, were observed.Conclusions/SignificanceOur results suggest that at least three steps of electrical remodeling occur in the hearts of DCM model mice, and that the combined down-regulation of Kv4.2, Kv1.5 and KChIP2 prior to the onset of HF may play an important role in the premature sudden death in this DCM model. DCM mice at 1 month or before, on the contrary, are associated with low risk of death in spite of inborn disorder and enlarged heart.

Preserved cardiomyocyte function and altered desmin pattern in transgenic mouse model of dilated cardiomyopathy

Taking advantage of the unique model of slowly developing dilated cardiomyopathy in mice with cardiomyocyte-specific transgenic overexpression of activated Gαq protein (Tgαq*44 mice) we analyzed the contribution of the cardiomyocyte malfunction, fibrosis and cytoskeleton remodeling to the development of heart failure in this model. Left ventricular (LV) in vivo function, myocardial fibrosis, cytoskeletal proteins expression and distribution, Ca(2+) handling and contractile function of isolated cardiomyocytes were evaluated at the stages of the early, compensated, and late, decompensated heart failure in 4-, 12- and 14-month-old Tgαq*44 mice, respectively, and compared to age-matched wild-type FVB mice. In the 4-month-old Tgαq*44 mice significant myocardial fibrosis, moderate myocyte hypertrophy and increased expression of regularly arranged and homogenously distributed desmin accompanied by increased phosphorylation of desmin chaperone protein, αB-crystallin, were found. Cardiomyocyte shortening, Ca(2+) handling and LV function were not altered. At 12 and 14 months of age, Tgαq*44 mice displayed progressive deterioration of the LV function. The contractile performance of isolated myocytes was still preserved, and the amplitude of Ca(2+) transients was even increased probably due to impairment of Na(+)/Ca(2+) exchanger function, while fibrosis was more extensive than in younger mice. Moreover, substantial disarrangement of desmin distribution accompanied by decreasing phosphorylation of αB-crystallin appeared. In Tgαq*44 mice disarrangement of desmin, at least partly related to inadequate phosphorylation of αB-crystallin seems to be importantly involved in the progressive deterioration of contractile heart function.

Rescue of a Dilated Cardiomyopathy Mouse Model Caused by a Mutation in Tropomyosin (E54K) by Expression of Slow Skeletal Troponin I

Dilated cardiomoypathy (DCM) is a disease characterized by decreased contractility and enlargement of cardiac chambers. We have previously shown that E54K mutation in α-tropomyosin (TM54) reduces myofilament Ca+2 sensitivity and causes DCM. Thus, we hypothesized that sensitization of the myofilament to Ca+2 in early phase of DCM would rescue the phenotype of the disease. Four groups were generated: non-transgenic (NTG), TM54,slow skeletal troponin I (ssTnI) and TM54/ssTnI. To sensitize TM54 myofilament we crossbred TM54 mice with ssTnI expressing mice, which increased Ca+2 sensitivity based on force pCa measurements.