Induction Of Left Ventricular Hypertrophy Research Articles

SCD4 deficiency decreases cardiac steatosis and prevents cardiac remodeling in mice fed a high-fat diet

Stearoyl-CoA desaturase (SCD) is a lipogenic enzyme that catalyzes formation of the first double bond in the carbon chain of saturated fatty acids. Four isoforms of SCD have been identified in mice, the most poorly characterized of which is SCD4, which is cardiac-specific. In the present study, we investigated the role of SCD4 in systemic and cardiac metabolism. We used WT and global SCD4 KO mice that were fed standard laboratory chow or a high-fat diet (HFD). SCD4 deficiency reduced body adiposity and decreased hyperinsulinemia and hypercholesterolemia in HFD-fed mice. The loss of SCD4 preserved heart morphology in the HFD condition. Lipid accumulation decreased in the myocardium in SCD4-deficient mice and in HL-1 cardiomyocytes with knocked out Scd4 expression. This was associated with an increase in the rate of lipolysis and, more specifically, adipose triglyceride lipase (ATGL) activity. Possible mechanisms of ATGL activation by SCD4 deficiency include lower protein levels of the ATGL inhibitor G0/G1 switch protein 2 and greater activation by protein kinase A under lipid overload conditions. Moreover, we observed higher intracellular Ca2+ levels in HL-1 cells with silenced Scd4 expression. This may explain the activation of protein kinase A in response to higher Ca2+ levels. Additionally, the loss of SCD4 inhibited mitochondrial enlargement, NADH overactivation, and reactive oxygen species overproduction in the heart in HFD-fed mice. In conclusion, SCD4 deficiency activated lipolysis, resulting in a reduction of cardiac steatosis, prevented the induction of left ventricular hypertrophy, and reduced reactive oxygen species levels in the heart in HFD-fed mice.

Ablation of Vitamin D Signaling in Cardiomyocytes Leads to Functional Impairment and Stimulation of Pro-Inflammatory and Pro-Fibrotic Gene Regulatory Networks in a Left Ventricular Hypertrophy Model in Mice.

The association between vitamin D deficiency and cardiovascular disease remains a controversial issue. This study aimed to further elucidate the role of vitamin D signaling in the development of left ventricular (LV) hypertrophy and dysfunction. To ablate the vitamin D receptor (VDR) specifically in cardiomyocytes, VDRfl/fl mice were crossed with Mlcv2-Cre mice. To induce LV hypertrophy experimentally by increasing cardiac afterload, transverse aortic constriction (TAC) was employed. Sham or TAC surgery was performed in 4-month-old, male, wild-type, VDRfl/fl, Mlcv2-Cre, and cardiomyocyte-specific VDR knockout (VDRCM-KO) mice. As expected, TAC induced profound LV hypertrophy and dysfunction, evidenced by echocardiography, aortic and cardiac catheterization, cardiac histology, and LV expression profiling 4 weeks post-surgery. Sham-operated mice showed no differences between genotypes. However, TAC VDRCM-KO mice, while having comparable cardiomyocyte size and LV fibrosis to TAC VDRfl/fl controls, exhibited reduced fractional shortening and ejection fraction as measured by echocardiography. Spatial transcriptomics of heart cryosections revealed more pronounced pro-inflammatory and pro-fibrotic gene regulatory networks in the stressed cardiac tissue niches of TAC VDRCM-KO compared to VDRfl/fl mice. Hence, our study supports the notion that vitamin D signaling in cardiomyocytes plays a protective role in the stressed heart.

Abstract 16898: Myocardial Recovery Associated Gene Cdcp1 Expression Attenuates Cardiac Fibrosis in a Pressure Over-Load Mouse Model

Background: We have previously demonstrated by performing a genome-wide association study that a genetic locus resulting in ↓CDCP1 expression was associated with myocardial recovery in patients with dilated cardiomyopathy (DCM). We have subsequently shown that ↓CDCP1 decreases human cardiac fibroblast proliferation in vitro , however, its potential role in modulating cardiac fibrosis and function in vivo is unknown. Methods: A Cdcp1 knock-out (KO) mouse was generated on FVB/NJ background. Angiotensin II/Phenylephrine (AngII/PE) or saline was infused by an osmotic pump into mice ( Cdcp1 KO n=20; wild type/wt n=18) for 4 weeks. Echocardiography was performed at 0 and 4 weeks. Picrosirius red (PSR) staining was performed on cross-sectional heart tissue to identify cardiac fibrosis, which was quantified, using ImageJ software, as a percentage of left ventricular (LV) area stained by PSR. Results: LV mass index (LVMI) significantly increased in AngII/PE wt mice as compared to saline wt (figure a. 3.65±0.15 mg/g vs 3.05±0.17mg/g, p=0.01), however, AngII/PE Cdcp1 KO mice had significantly decreased LVMI as compared to AngII/PE wt mice (figure a. 3.17±0.09 mg/g vs 3.65±0.15 mg/g, p=0.01). In addition, fractional shortening trended higher in AngII/PE Cdcp1 KO mice as compared to AngII/PE wt mice (figure b. 50.36±2.06% vs 45.48±1.43%, p=0.07). Extent of cardiac fibrosis was significantly higher in AngII/PE wt mice as compared to saline wt (figure c. 15.79±0.49% vs 7.93±0.39%, p<0.0001), however AngII/PE Cdcp1 KO mice had significantly reduced cardiac fibrosis as compared to AngII/PE wt mice (figure c. 9.41±0.43%, p<0.0001). Conclusions: CDCP1 KO significantly reduces pressure over-load induced LV hypertrophy and cardiac fibrosis. Its role as a novel therapeutic target in attenuating fibrosis and improving cardiac function in DCM needs to be further explored.

The Ca2+-activated cation channel TRPM4 is a positive regulator of pressure overload-induced cardiac hypertrophy.

Pathological left ventricular hypertrophy (LVH) occurs in response to pressure overload and remains the single most important clinical predictor of cardiac mortality. The molecular pathways in the induction of pressure overload LVH are potential targets for therapeutic intervention. Current treatments aim to remove the pressure overload stimulus for LVH, but do not completely reverse adverse cardiac remodelling. Although numerous molecular signalling steps in the induction of LVH have been identified, the initial step by which mechanical stretch associated with cardiac pressure overload is converted into a chemical signal that initiates hypertrophic signalling remains unresolved. In this study, we show that selective deletion of transient receptor potential melastatin 4 (TRPM4) channels in mouse cardiomyocytes results in an approximately 50% reduction in the LVH induced by transverse aortic constriction. Our results suggest that TRPM4 channel is an important component of the mechanosensory signalling pathway that induces LVH in response to pressure overload and represents a potential novel therapeutic target for the prevention of pathological LVH.

Voluntary activity reverses spermidine-induced myocardial fibrosis and lipid accumulation in the obese male mouse

Obesity due to high calorie intake induces cardiac hypertrophy and dysfunction, thus contributing to cardiovascular morbidity and mortality. Recent studies in aging suggest that oral supplementation with the natural polyamine spermidine has a cardioprotective effect. Here, the hypothesis was tested that spermidine or voluntary activity alone or in combination protect the heart from adverse effects induced by obesity. Therefore, C57Bl/6 mice (n = 8–10 per group) were subjected to control or high fat diet (HFD) and were left untreated, or either received spermidine via drinking water or were voluntarily active or both. After 30 weeks, the mice were killed and the left ventricle of the hearts was processed for light and electron microscopy. Design-based stereology was used to estimate parameters of hypertrophy, fibrosis, and lipid accumulation. HFD induced cardiac hypertrophy as demonstrated by higher volumes of the left ventricle, cardiomyocytes, interstitium, myofibrils and cardiomyocyte mitochondria. These changes were not influenced by spermidine or voluntary activity. HFD also induced myocardial fibrosis and accumulation of lipid droplets within cardiomyocytes. These HFD effects were enhanced in spermidine treated animals but not in voluntarily active mice. This was even the case in voluntarily active mice that received spermidine. In conclusion, the data confirm the induction of left ventricular hypertrophy by high-fat diet and suggest that—under high fat diet—spermidine enhances cardiomyocyte lipid accumulation and interstitial fibrosis which is counteracted by voluntary activity.

Loss of Sox9 in cardiomyocytes delays the onset of cardiac hypertrophy and fibrosis

BackgroundThe transcription factor Sox9 has been associated with cardiac injury and remodeling. Studies of mammalian hearts confirm Sox9 upregulation in fibroblasts following ischemic insults associated with enhanced fibrosis. The role of cardiomyocyte-specific Sox9 remains unclear. This study aimed to evaluate the role of cardiomyocyte-specific Sox9 in development and progression of left ventricular (LV) hypertrophy and fibrosis. MethodsIn male conditional Sox9 knockout mice (Sox9-KO) or floxed littermates (control group) transverse aortic constriction (TAC) was performed to induce LV hypertrophy. LV function and wall thickness were assessed weekly using echocardiography. LV mRNA- and protein expression levels of hypertrophy-, fibrosis-, and remodeling-associated genes were analyzed for each time point. Histological sections were stained for fibrosis and Sox9 expression. ResultsOnly one week after TAC, the control group showed significantly enhanced heart weights and thickened LV posterior walls accompanied by elevated Anp- and Lox-mRNA levels. Simultaneously, Col1a1- and Col3a1-levels as well as Sox9 expression were strongly upregulated, Contrary, Sox9-KO mice did not develop cardiac hypertrophy until 4 weeks after TAC. Collagen and Sox9 expression also peaked at that later time point. Ejection fraction declined similarly in both groups after TAC. However, the control group showed a slightly better cardiac performance at 2 weeks after TAC. ConclusionsCardiomyocyte-specific Sox9 mediates hypertrophy and early fibrosis, following cardiac pressure-overload. Loss of Sox9 delays cardiac growth and remodeling processes, however, does not preserve the cardiac function. We suggest that cardiomyocyte-driven Sox9 initiates a pro-hypertrophic cascade, possibly involving a cross-talk between myocytes and fibroblasts.

Technique of Minimally Invasive Transverse Aortic Constriction in Mice for Induction of Left Ventricular Hypertrophy.

Transverse aortic constriction (TAC) in mice is one of the most commonly used surgical techniques for experimental investigation of pressure overload-induced left ventricular hypertrophy (LVH) and its progression to heart failure. In the majority of the reported investigations, this procedure is performed with intubation and ventilation of the animal which renders it demanding and time-consuming and adds to the surgical burden to the animal. The aim of this protocol is to describe a simplified technique of minimally invasive TAC without intubation and ventilation of mice. Critical steps of the technique are emphasized in order to achieve low mortality and high efficiency in inducing LVH. Male C57BL/6 mice (10-week-old, 25-30 g, n=60) were anesthetized with a single intraperitoneal injection of a mixture of ketamine and xylazine. In a spontaneously breathing animal following a 3-4 mm upper partial sternotomy, a segment of 6/0 silk suture threaded through the eye of a ligation aid was passed under the aortic arch and tied over a blunted 27-gauge needle. Sham-operated animals underwent the same surgical preparation but without aortic constriction. The efficacy of the procedure in inducing LVH is attested by a significant increase in the heart/body weight ratio. This ratio is obtained at days 3, 7, 14 and 28 after surgery (n = 6 - 10 in each group and each time point). Using our technique, LVH is observed in TAC compared to sham animals from day 7 through day 28. Operative and late (over 28 days) mortalities are both very low at 1.7%. In conclusion, our cost-effective technique of minimally invasive TAC in mice carries very low operative and post-operative mortalities and is highly efficient in inducing LVH. It simplifies the operative procedure and reduces the strain put on the animal. It can be easily performed by following the critical steps described in this protocol.

Technique of Minimally Invasive Transverse Aortic Constriction in Mice for Induction of Left Ventricular Hypertrophy

Technique of Minimally Invasive Transverse Aortic Constriction in Mice for Induction of Left Ventricular Hypertrophy

Assessing structural and functional responses of murine hearts to acute and sustained β-adrenergic stimulation in vivo

IntroductionGiven the importance of β-adrenoceptor signalling in regulating cardiac structure and function, robust protocols are required to assess potential alterations in such regulation in murine models in vivo. MethodsEchocardiography was performed in naïve and stressed (isoprenaline; 30μg/g/day s.c. for up to 14days) mice, in the absence or presence of acute β-adrenergic stimulation (dobutamine 0.75μg/g, i.p.). Controls received saline infusion and/or injection. Hearts were additionally analysed gravimetrically, histologically and biochemically. ResultsIn naïve mice, acute β-adrenoceptor stimulation with dobutamine increased heart rate, left ventricular (LV) fractional shortening (LVFS), ejection fraction (LVEF) and wall thickness and decreased LV diameter (p<0.05). In stressed mice, dobutamine failed to induce further inotropic and chronotropic responses. Furthermore, following dobutamine injection, these mice exhibited lower LVEF and LVFS at identical heart rates, relative to corresponding controls. Sustained isoprenaline infusion induced LV hypertrophy (increased heart weight, heart weight/body weight ratio, heart weight/tibia length ratio and LV wall thickness (p<0.05)) by 3days, with little further change at 14days. In contrast, increases in LVEF and LVFS were seen only at 14days (p<0.05). DiscussionWe describe protocols for and illustrative data from the assessment of murine cardiac responses to acute and sustained β-adrenergic stimulation in vivo, which would be of value in determining the impact of genetic or pharmacological interventions on such responses. Additionally, our data indicate that acute dobutamine stimulation unmasks early signs of LV dysfunction in the remodelled heart, even at a stage when basal function is enhanced.

Impact of chronic use of cibenzoline on left ventricular pressure gradient and left ventricular remodeling in patients with hypertrophic obstructive cardiomyopathy

BackgroundCibenzoline, a class Ia antiarrhythmic drug, is useful for reducing the left ventricular pressure gradient (LVPG) in patients with hypertrophic obstructive cardiomyopathy (HOCM). However, chronic effects of cibenzoline on LVPG and left ventricular (LV) remodeling are unknown. MethodsForty-one patients with HOCM participated in this study. Echocardiographic, electrocardiographic, and brain natriuretic peptide (BNP) data collected before and after cibenzoline treatment were compared. From the relation between LVPG and plasma concentration of cibenzoline, an efficacious plasma concentration of cibenzoline was estimated. ResultsThe mean follow-up period was 74.2±47.1 months. The LVPG decreased from 104.8±62.6mmHg to 27.6±30.5mmHg (p<0.0001). The LV end-diastolic dimension increased from 42.8±5.8mm to 46.2±5.4mm (p<0.0001), but neither LV end-systolic dimension nor LV fractional shortening changed significantly. The left atrial dimension decreased from 40.0±4.7mm to 36.2±5.1mm (p<0.0001). The E-wave velocity/A-wave velocity ratio increased, early diastolic annular velocity (Ea) increased, and E/Ea ratio decreased. The interventricular septal wall thickness, LV posterior wall thickness, the Sokolow-Lyon index, and the depth of negative T wave decreased. The heart rate-corrected QT interval was shortened. Plasma BNP level decreased from 418.8±423.7pg/ml to 213.7±154.1pg/ml (p<0.02). The safe and efficacious plasma concentration of cibenzoline was between 300ng/mL and 1500ng/mL. ConclusionsLong-term treatment with cibenzoline attenuated LVPG, improved LV diastolic dysfunction, and induced LV hypertrophy regression in patients with HOCM without causing serious complications.

Abstract 13407: A Mouse Model of Heart Failure with Preserved Ejection Fraction (HFpEF) due to Chronic Infusion of a Low Subpressor Dose of Angiotensin II

Introduction: Heart failure with preserved ejection fracture (HFpEF) is a clinical syndrome of HF symptoms associated with impaired diastolic function. Although it represents approximately 50% of all patients with HF, the mechanisms of disease are poorly understood, animal models of HFpEF not due pressure overload are lacking, and therapies for HFpEF are generally ineffective. Hypothesis: A continuous infusion of low dose of angiotensin II (ATII) may be sufficient to induce changes in left ventricular (LV) diastolic function without increasing blood pressure nor induce LV hypertrophy. Methods: Osmotic pumps were implanted subcutaneously in 8 week-old CD1 male mice randomly assigned to the ATII (200 ng/kg/day) or vehicle (N=8/group). Transthoracic echocardiography was performed at baseline and 4 weeks to measure LV dimensions, systolic and diastolic function. Aortic systolic and diastolic pressures (AoP), LV peak systolic and end-diastolic pressures (LVPSP, LVEDP) were measured at LV catheterization. Fibrosis was measured using Masson’s trichrome stain. The expression of Interleukin (IL)-18 mRNA levels, a cytokine associated with impaired cardiomyocyte relaxation, was measured at 4 weeks. Results: When compared to the baseline values or vehicle group, ATII infusion had no effects on AoP, LVPSP and HR, and had no effects on LV dimensions or mass, nor on LVEF (all P&gt;0.2). ATII induced a significant impairment in LV diastolic function as measured by an increase (worsening) of the myocardial performance index (MPI), the LV isovolumetric relaxation time (IVRT) and of LVEDP (Figure). Cardiac expression of IL-18 mRNA was significantly increased 7-fold after ATII infusion (P&lt;0.001), suggesting a potential mechanistic role of IL-18. Conclusion: Chronic infusion of low dose ATII recapitulates the HFpEF phenotype in the mouse, without increasing blood pressure. The use of this mouse model may help understanding the mechanisms leading to HFpEF syndrome in patients.

Metformin Protects Against Systolic Overload–Induced Heart Failure Independent of AMP-Activated Protein Kinase α2

Activation of AMP-activated protein kinase (AMPK)-α2 protects the heart against pressure overload-induced heart failure in mice. Although metformin is a known activator of AMPK, it is unclear whether its cardioprotection acts independently of an AMPKα2-dependent pathway. Because the role of AMPKα1 stimulation on remodeling of failing hearts is poorly defined, we first studied the effects of disruption of both the AMPKα1 and AMPKα2 genes on the response to transverse aortic constriction-induced left ventricular (LV) hypertrophy and dysfunction in mice. AMPKα2 gene knockout significantly exacerbated the degree of transverse aortic constriction-induced LV hypertrophy and dysfunction, whereas AMPKα1 gene knockout had no effect on the degree of transverse aortic constriction-induced LV hypertrophy and dysfunction. Administration of metformin was equally effective in attenuating transverse aortic constriction-induced LV remodeling in both wild-type and AMPKα2 knockout mice, as evidenced by reduced LV and lung weights, a preserved LV ejection fraction, and reduced phosphorylation of mammalian target of rapamycin (p-mTOR(Ser2448)) and its downstream target p-p70S6K(Thr389). These data support the notion that activation of AMPKα1 plays a negligible role in protecting the heart against the adverse effects of chronic pressure overload, and that metformin protects against adverse remodeling through a pathway that seems independent of AMPKα2.

Microtubule Actin Cross-Linking Factor 1 Regulates Cardiomyocyte Microtubule Distribution and Adaptation to Hemodynamic Overload

Aberrant cardiomyocyte microtubule growth is a feature of pressure overload induced cardiac hypertrophy believed to contribute to left ventricular (LV) dysfunction. Microtubule Actin Cross-linking Factor 1 (MACF1/Acf7) is a 600 kd spectraplakin that stabilizes and guides microtubule growth along actin filaments. MACF1 is expressed in the heart, but its impact on cardiac microtubules, and how this influences cardiac structure, function, and adaptation to hemodynamic overload is unknown. Here we used inducible cardiac-specific MACF1 knockout mice (MACF1 KO) to determine the impact of MACF1 on cardiac microtubules and adaptation to pressure overload (transverse aortic constriction (TAC).In adult mouse hearts, MACF1 expression was low under basal conditions, but increased significantly in response to TAC. While MACF1 KO had no observable effect on heart size or function under basal conditions, MACF1 KO exacerbated TAC induced LV hypertrophy, LV dilation and contractile dysfunction. Interestingly, subcellular fractionation of ventricular lysates revealed that MACF1 KO altered microtubule distribution in response to TAC, so that more tubulin was associated with the cell membrane fraction. Moreover, TAC induced microtubule redistribution into this cell membrane fraction in both WT and MACF1 KO mice correlated strikingly with the level of contractile dysfunction (r2 = 0.786, p<.001). MACF1 disruption also resulted in reduction of membrane caveolin 3 levels, and increased levels of membrane PKCα and β1 integrin after TAC, suggesting MACF1 function is important for spatial regulation of several physiologically relevant signaling proteins during hypertrophy. Together, these data identify for the first time, a role for MACF1 in cardiomyocyte microtubule distribution and in adaptation to hemodynamic overload.

52 EFFECTS ON CARDIAC STRUCTURE IN ADULT RATS WHEN INTRAUTERINE GROWTH RESTRICTION IS COUPLED WITH HYPERGLYCEMIA

Objective: Aim of this study was to examine the effect of type 1 diabetes on myocardial collagen deposition and cardiac function in IUGR rat offspring when blood glucose levels were maintained at either mild or moderate levels. Methods: IUGR was induced in Wistar-Kyoto rats by maternal protein restriction. At 24 weeks of age, diabetes was induced in male IUGR and non-IUGR offspring by streptozotocin injection; insulin was injected daily to maintain blood glucose levels at either a mild level (7-10mmol/L; n = 8 per group) or a moderate level (10-15mmol/L; n = 8 per group). Results: Morphological and echocardiographical analyses of the heart were performed at 32 weeks of age. There was induction of left ventricular hypertrophy in IUGR offspring of 32 weeks of age; this was accompanied by a thicker posterior wall and increased interstitial fibrosis. Induction of hyperglycemia also led to an increase in heart size and myocardial fibrosis. The response to hyperglycemia was not different between IUGR and non-IUGR adult rats however, cardiac fibrosis was greatest when diabetes was combined with IUGR. Conclusion: Tight glycemic control attenuated the adverse effects of hyperglycemia but did not reverse the increased collagen deposition. Exacerbated fibrosis in diabetic IUGR hearts even when glycemia is tightly controlled may lead to long-term cardiac dysfunction.

Cardiac Lineage Protein-1 (CLP-1) Regulates Cardiac Remodeling via Transcriptional Modulation of Diverse Hypertrophic and Fibrotic Responses and Angiotensin II-transforming Growth Factor β (TGF-β1) Signaling Axis

It is well known that the renin-angiotensin system contributes to left ventricular hypertrophy and fibrosis, a major determinant of myocardial stiffness. TGF-β1 and renin-angiotensin system signaling alters the fibroblast phenotype by promoting its differentiation into morphologically distinct pathological myofibroblasts, which potentiates collagen synthesis and fibrosis and causes enhanced extracellular matrix deposition. However, the atrial natriuretic peptide, which is induced during left ventricular hypertrophy, plays an anti-fibrogenic and anti-hypertrophic role by blocking, among others, the TGF-β-induced nuclear localization of Smads. It is not clear how the hypertrophic and fibrotic responses are transcriptionally regulated. CLP-1, the mouse homolog of human hexamethylene bis-acetamide inducible-1 (HEXIM-1), regulates the pTEFb activity via direct association with pTEFb causing inhibition of the Cdk9-mediated serine 2 phosphorylation in the carboxyl-terminal domain of RNA polymerase II. It was recently reported that the serine kinase activity of Cdk9 not only targets RNA polymerase II but also the conserved serine residues of the polylinker region in Smad3, suggesting that CLP-1-mediated changes in pTEFb activity may trigger Cdk9-dependent Smad3 signaling that can modulate collagen expression and fibrosis. In this study, we evaluated the role of CLP-1 in vivo in induction of left ventricular hypertrophy in angiotensinogen-overexpressing transgenic mice harboring CLP-1 heterozygosity. We observed that introduction of CLP-1 haplodeficiency in the transgenic α-myosin heavy chain-angiotensinogen mice causes prominent changes in hypertrophic and fibrotic responses accompanied by augmentation of Smad3/Stat3 signaling. Together, our findings underscore the critical role of CLP-1 in remodeling of the genetic response during hypertrophy and fibrosis.

The Effects of Pressure Overload on Cardiac Geometry and Function are Aggravated by Aging

The aging heart undergoes structural and functional alterations, which are reminiscent of changes observed in the failing heart, and may thus increase the vulnerability of the aging heart to develop heart failure in response to mechanical overload. To investigate the effect of aging on left ventricular (LV) remodeling and dysfunction we subjected mice to pressure overload by transverse aortic constriction (TAC) at 3 and 24 months of age. Eight weeks after TAC, LV geometry, LV function and heart as well as lung weights were measured. Aging minimally affected cardiac geometry and function in sham operated animals. TAC not only induced LV hypertrophy, but also reduced fractional shortening in both age groups. However, only in 24 months old mice, TAC induced LV dilation from 3.5±0.2 mm in Sham mice to 4.4±0.2 mm in TAC mice and systolic dysfunction, demonstrated by a decrease in the rate of rise of LV pressure at 40 mmHg (dP/dtP40; Sham 7910±460 vs. TAC 4940±360 mmHg/s) as well as diastolic dysfunction evidenced by a decrease in dP/dtmin (Sham −6810±430 vs. TAC −5025±462 mmHg/s) and an increase in LV end diastolic pressure from 5±1 mmHg in Sham mice to 12±3 mmHg in TAC mice (all p&lt;0.05). In conclusion, the effects of pressure overload on cardiac geometry and function are aggravated by aging.

Diverse Effects of Exercise on Myofilament Function in Pathologic Left Ventricular Hypertrophy and Dysfunction

Effects of exercise (EX) on pathologic left ventricular (LV) remodelling and dysfunction remain incompletely understood. Here we studied the effects of 8 weeks voluntary EX on LV and myofilament function in mice with myocardial infarction (MI) or pressure‐overload by transverse aortic constriction (TAC). Eight weeks after TAC or MI, LV geometry and function were measured and isometric force determined in single permeabilized cardiomyocytes. MI and TAC induced LV hypertrophy, interstitial fibrosis and LV dilation as well as systolic (fractional shortening, dP/dtP40) and diastolic (dP/dtmin, end‐diastolic pressure [LVEDP]) dysfunction. Cardiomyocyte maximal force development (Fmax) was lower in MI, but unexpectedly elevated in TAC, coinciding with more pronounced LV systolic dysfunction in MI compared to TAC. Conversely, passive isometric myofilament force (Fpas) was elevated in TAC but unchanged in MI, coinciding with an elevated LVEDP in TAC. EX ameliorated LV dysfunction and fibrosis and increased Fmax after MI, without effecting Fpas. In contrast, EX had no effect on either LV dysfunction or Fmax in TAC mice. EX aggravated interstitial fibrosis, but did not further increase LVEDP, likely as a result of an EX‐induced decrease in Fpas. In conclusion, effects of EX on LV dysfunction depend critically on the underlying pathology which are in part explained by the diverse effects of EX on myofilament function.

Effects of Fixed-Dose Isosorbide Dinitrate/Hydralazine on Diastolic Function and Exercise Capacity in Hypertension-Induced Diastolic Heart Failure

Hypertension-induced diastolic heart failure accounts for a large proportion of all heart failure presentations. Hypertension also induces left ventricular (LV) hypertrophy. Fixed-dose isosorbide dinitrate/hydralazine (HISDN) decreased mortality in human systolic heart failure but it is unknown whether it improves maladaptive myocardial remodeling. We sought to test the hypothesis that chronic HISDN modulates LV hypertrophy and myocardial remodeling in hypertension-induced diastolic heart failure. FVB mice underwent either saline (n=18) or aldosterone (n=28) infusion. All underwent uninephrectomy and drank 1% salt water for 4 weeks. Mice were randomized after surgery to regular chow or chow containing HISDN (isosorbide dinitrate: 26 mg/kg per day; hydralazine: 50 mg/kg per day) for 4 weeks. Aldosterone infusion increased tail-cuff blood pressure (161+/-3 mm Hg) versus saline-infused mice (129+/-2 mm Hg). Aldosterone induced LV hypertrophy versus saline-infused mice (LV:body weight ratio: 4.2+/-0.1 versus 3.6+/-0.1 mg/g). HISDN attenuated the aldosterone-induced increased in systolic blood pressure (137+/-5 mm Hg) and also lowered blood pressure in saline-infused mice (114+/-2 mm Hg). However, HISDN did not cause LV hypertrophy regression in aldosterone-infused mice. Aldosterone increased LV end-diastolic dimensions that were not attenuated by HISDN. Similarly, neither aldosterone infusion nor HISDN affected LV end-systolic dimensions. LV ejection fraction and wet:dry lung ratio were not different between aldosterone-untreated and aldosterone-HISDN mice. However, mitral Doppler E/A ratio (a measure of diastolic function), exercise capacity, and plasma soluble vascular cell adhesion molecule 1 levels were improved in aldosterone-HISDN hearts. In conclusion, fixed-dose HISDN improved hypertension, diastolic function, and exercise capacity and reduced soluble vascular cell adhesion molecule 1 levels. There were no reductions in LV hypertrophy, cardiac fibrosis, or pulmonary congestion. These functional improvements are likely related to extracardiac effects, such as effects on the vasculature.

CRNK gene transfer improves function and reverses the myosin heavy chain isoenzyme switch during post-myocardial infarction left ventricular remodeling

PYK2 is a Ca 2+-dependent, nonreceptor protein tyrosine kinase that is involved in the induction of left ventricular hypertrophy (LVH) and its transition to heart failure. We and others have previously investigated PYK2's function in vitro using cultured neonatal and adult rat ventricular myocytes as model systems. However, the function of PYK2 in the in vivo adult heart remains unclear. Here we evaluate the effect of PYK2 inhibition following myocardial infarction (MI) using adenoviral (Adv) overexpression of the C-terminal domain of PYK2, known as CRNK. First we demonstrate that CRNK functions as a dominant-negative inhibitor of PYK2-dependent signaling, presumably by displacing PYK2 from focal adhesions and costameres. Then, male Sprague–Dawley rats (~ 300 g) underwent permanent left anterior descending coronary artery ligation. One wk post-MI, either Adv-GFP ( n = 34) or Adv-CRNK ( n = 28) was administered (10 10 pfu, 0.1 ml) via catheter-based, Optison ®-mediated gene transfer. LV structure and function were evaluated by echocardiography 1 and 3 wk after gene transfer, and LV tissue was analyzed by real-time RT-PCR and Western blotting. CRNK overexpression was readily detected by Western blotting 1 wk following gene transfer. Adv-CRNK improved overall survival ( P = 0.03; Logrank Test) and LV fractional shortening (23 ± 2% vs. 31 ± 2% for Adv-GFP vs. Adv-CRNK infected animals, respectively; P < 0.05). Whereas MI hearts exhibited increased β-, and decreased α-myosin heavy chain (MHC) mRNA expression characteristic of LVH, Adv-CRNK reversed the MHC isoenzyme switch (3.3 ± 1.4 fold increase in αMHC; 0.4 ± 0.1 fold decrease in βMHC; P < 0.05 for both). In summary, CRNK gene transfer improves survival, increases LV function, and alters MHC gene expression suggesting an attenuation of LV remodeling post-MI.

Fish Oil Prevents Left Ventricular Remodeling and Contractile Dysfunction in Pressure Overload Induced Hypertrophy

Clinical studies suggest that dietary ω-3 polyunsaturated fatty acids, like fish oils (FO), may decrease the risk of cardiovascular disease. Therefore, we studied the effects of dietary FO on left ventricular (LV) adaptations to pressure overload. Male Wistar rats were fed either a low fat/high carbohydrate chow (NC) or NC supplemented with FO (NC+FO, 4% of total energy from EPA/DHA). After 1 week rats underwent abdominal aortic banding (AB) or sham surgery (n=9–11/group) and at 8 weeks LV function was assessed by echocardiography. There were no differences in any parameters between the groups prior to surgery. AB led to a 26% increase in LV mass; however, this hypertrophic response was significantly reduced in the NC+FO group. FO also prevented AB induced LV remodeling and cardiac dysfunction (see table). Conclusion: Dietary FO prevented pressure overload induced LV hypertrophy, chamber dilation and contractile dysfunction.