Diastolic Dysfunction In Mice Research Articles

Calcium desensitizer catechin reverses diastolic dysfunction in mice with restrictive cardiomyopathy

Diastolic dysfunction refers to an impaired relaxation and an abnormality in ventricular blood filling during diastole while systolic function is preserved. Cardiac myofibril hypersensitivity to Ca2+ is a major factor that causes impaired relaxation of myocardial cells. The present study investigates the effect of the green tea extract catechins on myofibril calcium desensitization and restoration of diastolic function in a restrictive cardiomyopathy (RCM) mouse model with cardiac troponin mutations. Wild type (WT) and RCM mice were treated daily with catechin (epigallocatechin-3-gallate, EGCg, 50mg/kg body weight) for 3months. Echocardiography and cell based assays were performed to measure cardiac structure and flow-related variables including chamber dimensions, fraction shortening, trans-mitral flow patterns in the experimental mice. In addition, myocyte contractility and calcium dynamics were measured in WT and RCM cardiomyocytes treated in vitro with 5μM EGCg. Our data indicated that RCM mice treated with EGCg showed an improved diastolic function while systolic function remained unchanged. At the cellular level, sarcomere relaxation and calcium decay were accelerated in RCM myocardial cells treated with EGCg. These results suggest that catechin is effective in reversing the impaired relaxation in RCM myocardial cells and rescuing the RCM mice with diastolic dysfunction.

Apocynin attenuates oxidative stress and cardiac fibrosis in angiotensin II-induced cardiac diastolic dysfunction in mice

To investigate whether apocynin, a NADPH oxidase inhibitor, produced cardioproteictive effects in Ang II-induced hypertensive mice, and to elucidate the underlying mechanisms. C57BL/6 mice were subcutaneously infused Ang II for 4 weeks to mimic cardiac remodeling and fibrosis. Concomitantly the mice were administered apocynin (100 mg·kg(-1)·d(-1)) or/and the aldosterone receptor blocker eplerenone (200 mg·kg(-1)·d(-1)) via gavage for 4 weeks. Systolic blood pressure (SBP) and heart rate were measured, and transthoracic echocardiography was performed. For in vitro study, cardiac fibroblasts were treated with Ang II (10(-7) mol/L) in the presence of apocynin (10(-5) mol/L) or/and eplerenone (10(-5) mol/L). Immunohistochemistry and Western blotting were used to quantify the expression levels of NADPH oxidase and osteopontin (OPN) proteins in the cells. Both apocynin and eplerenone significantly decreased SBP, and markedly improved diastolic dysfunction in Ang II-induced hypertensive mice, accompanied with ameliorated oxidative stress and cardiac fibrosis. In the Ang II-treated cardiac fibroblasts, the expression levels of NOX4 and OPN proteins were markedly upregulated. Both Apocynin and eplerenone significantly suppressed the increased expression levels of NOX4 and OPN proteins in the Ang II-treated cells. In all the experiments, apocynin and eplerenone produced comparable effects. Co-administration of the two agents did not produce synergic effects. Apocynin produces cardioproteictive effects comparable to those of eplerenone. The beneficial effects of apocynin on myocardial oxidative stress and cardiac fibrosis might be mediated partly through a pathway involving NADPH oxidase and OPN.

Identification of Key Residues Essential for the Structural Fold and Receptor Selectivity within the A-chain of Human Gene-2 (H2) Relaxin

Human gene-2 (H2) relaxin is currently in Phase III clinical trials for the treatment of acute heart failure. It is a 53-amino acid insulin-like peptide comprising two chains and three disulfide bonds. It interacts with two of the relaxin family peptide (RXFP) receptors. Although its cognate receptor is RXFP1, it is also able to cross-react with RXFP2, the native receptor for a related peptide, insulin-like peptide 3. In order to understand the basis of this cross-reactivity, it is important to elucidate both binding and activation mechanisms of this peptide. The primary binding mechanism of this hormone has been extensively studied and well defined. H2 relaxin binds to the leucine-rich repeats of RXFP1 and RXFP2 using B-chain-specific residues. However, little is known about the secondary interaction that involves the A-chain of H2 relaxin and transmembrane exoloops of the receptors. We demonstrate here through extensive mutation of the A-chain that the secondary interaction between H2 relaxin and RXFP1 is not driven by any single amino acid, although residues Tyr-3, Leu-20, and Phe-23 appear to contribute. Interestingly, these same three residues are important drivers of the affinity and activity of H2 relaxin for RXFP2 with additional minor contributions from Lys-9, His-12, Lys-17, Arg-18, and Arg-22. Our results provide new insights into the mechanism of secondary activation interaction of RXFP1 and RXFP2 by H2 relaxin, leading to a potent and RXFP1-selective analog, H2:A(4-24)(F23A), which was tested in vitro and in vivo and found to significantly inhibit collagen deposition similar to native H2 relaxin.

Matrix metalloproteinase‐9 deletion attenuates age‐related periostin induction and diastolic dysfunction in mice

Diastolic dysfunction is a characteristic of cardiac aging, and altered extracellular matrix structure has been shown to regulate diastolic function. Matrix metalloproteinase-9 (MMP-9) levels increase with age in the left ventricle (LV), but a causal link between MMP-9 and age-related diastolic dysfunction has not been established. To investigate the role of MMP-9 on diastolic function, Doppler echocardiography was performed on young and senescent WT and MMP-9 null mice (n=5–7 per group). The peak early to late diastolic filling velocity ratio (E/A ratio) decreased from 1.5±0.2 in young WT to 1.1±0.1 in senescent WT mice (p<0.05). Strikingly, the E/A ratio of senescent MMP-9 null mice was similar to the young null value (1.3±0.1 vs 1.4±0.2, p=ns), indicating that the decline in diastolic function in senescent WT was attenuated by MMP-9 deletion. By real-time PCR, periostin mRNA levels increased in senescent WT but not MMP-9 null LV compared to young controls, and senescent WT LV expressed higher levels of periostin than senescent MMP-9 null LV (all p<0.05). Periostin regulates collagen fibrillogenesis and fibroblast-myocyte interactions, two processes that can modulate myocardial stiffness. In conclusion, MMP-9 deletion attenuates the age-related decline in diastolic function in mice, potentially by suppressing periostin induction. UTHSCSA TST (YAC), NIH 1SC2 HL101430 (YJ), and VA Merit Award (MLL).

Early activation of matrix metalloproteinases underlies the exacerbated systolic and diastolic dysfunction in mice lacking TIMP3 following myocardial infarction

Extracellular matrix (ECM) remodeling is a critical aspect of cardiac remodeling following myocardial infarction. Tissue inhibitors of metalloproteinases (TIMPs) are physiological inhibitors of matrix metalloproteinases (MMPs) that degrade the ECM proteins. TIMP3 is highly expressed in the heart, and is markedly downregulated in patients with ischemic cardiomyopathy. We therefore examined the time- and region-dependent role of TIMP3 in the cardiac response to myocardial infarction (MI). TIMP3(-/-) and wild-type (WT) mice were subjected to MI by ligation of the left anterior descending artery. TIMP3(-/-)-MI mice exhibited a significantly compromised rate of survival compared with WT-MI mice, primarily due to increased left ventricular (LV) rupture, greater infarct expansion, exacerbated LV dilation, and greater systolic and diastolic dysfunction. Second harmonic generation imaging of unfixed and unstained hearts revealed greater collagen disarray and reduced density in the TIMP3(-/-) infarct myocardium compared with the WT group. Gelatinolytic and collagenolytic activities increased in TIMP3(-/-) compared with WT hearts at 1 day post-MI but not at 3 days or 1 wk post-MI. Neutrophil infiltration and inflammatory MMPs were significantly increased in the infarct and peri-infarct regions of TIMP3(-/-)-MI hearts. Treatment of TIMP3(-/-) mice with a broad-spectrum MMP inhibitor (PD-166793) for 2 days before and 2 days after MI markedly improved post-MI infarct expansion, LV rupture incident, LV dilation, and systolic dysfunction in these mice up to 1 wk post-MI. Our data demonstrate that the initial rise in proteolytic activities early post-MI is a triggering factor for subsequent LV adverse remodeling, LV rupture, and dilated cardiomyopathy. Hence, timing of treatments to improve cardiac response to MI may be critical in producing favorable outcome.

T-lymphocytes mediate left ventricular fibrillar collagen cross-linking and diastolic dysfunction in mice

Aberrant concentrations of cardiac extracellular matrix (ECM) fibrillar collagen cross-linking have been proposed to be an underlying cause of cardiac diastolic dysfunction however the role of the adaptive immune system in this process has yet to be investigated. Fibrillar collagen cross-linking is a product of the enzymatic activities of lysyl oxidase (LOX and LOXL-3) released by the cardiac fibroblast and possibly cardiac myocytes. Our hypothesis is that stimulation of the TH1 lymphocytes activates lysyl oxidase mediated ECM cross-linking and thereby alters left ventricular function. Three-month old C57BL/J female mice were treated with selective TH1 lymphocyte inducers — T-cell receptor Vβ peptides (TCR). After 6weeks, candidate gene expression, tissue enzymatic activity, ECM composition, and left ventricular mechanics were quantified. Lymphocyte gene expression and cytokine assay revealed TH1 immune polarization with TCR administration which was associated with a 2.6-fold and 3.1-fold increase of LOX and LOXL3 gene expression, respectively, and a 55% increase in cardiac LOX enzymatic activity. The ECM cross-linked fibrillar collagen increased by 95% when compared with the control. Concurrently, there was a 33% increased ventricular stiffness, decreased cardiac output, and normal ejection fraction. These data implicate the TH1 lymphocyte in the pathogenesis of diastolic dysfunction which has potential clinical application in the pathogenesis of diastolic heart failure.

Spontaneous Development of Left Ventricular Hypertrophy and Diastolic Dysfunction in Mice Lacking All Nitric Oxide Synthases

The role of the nitric oxide synthase (NOS) system in cardiac architecture and function remains unknown. This point was addressed in mice that lack all 3 NOS genes. Morphological, echocardiographic, and hemodynamic analyses were performed in wild-type (WT), singly nNOS(-/-), iNOS(-/-), eNOS(-/-), and triply n/i/eNOS(-/-) mice. At 5 months of age, but not at 2 months of age, significant left ventricular (LV) hypertrophy was noted in n/i/eNOS(-/-) mice and to a lesser extent in eNOS(-/-) mice, but not in nNOS(-/-) or iNOS(-/-) mice, compared with WT mice. Importantly, significant LV diastolic dysfunction (as evaluated by echocardiographic E/A wave ratio and hemodynamic -dP/dt and Tau), with preserved LV systolic function (as assessed by echocardiographic fractional shortening and hemodynamic +dP/dt), was noted only in n/i/eNOS(-/-) mice, and this was associated with enhanced LV end-diastolic pressure and increased lung wet weight, all of which are characteristics consistent with diastolic heart failure in humans. Finally, long-term oral treatment with an angiotensin II type 1 (AT(1)) receptor blocker, olmesartan, significantly prevented all these abnormalities of n/i/eNOS(-/-) mice. These results provide the first direct evidence that the complete disruption of all NOSs results in LV hypertrophy and diastolic dysfunction in mice in vivo through the AT(1) receptor pathway, demonstrating a pivotal role of the endogenous NOS system in maintaining cardiac homeostasis.

Diastolic Dysfunction in Mice with Diet-Induced Obesity is Ameliorated by the Polyphenol S17384

Diastolic Dysfunction in Mice with Diet-Induced Obesity is Ameliorated by the Polyphenol S17384

Genetic inhibition of calcineurin induces diastolic dysfunction in mice with chronic pressure overload

Calcineurin is a Ca(2+)/calmodulin-dependent protein phosphatase that induces myocardial growth in response to several physiological and pathological stimuli. Calcineurin inhibition, induced either via cyclosporine or genetically, can decrease myocardial hypertrophy secondary to pressure overload without affecting left ventricular (LV) systolic function. Since hypertrophy can also affect LV diastolic function, the goal of this study was to examine the effects of chronic pressure overload (2 wk aortic banding) in transgenic (Tg) mice overexpressing Zaki-4beta (TgZ), a specific endogenous inhibitor of calcineurin, on LV diastolic function. As expected, in the TgZ mice with calcineurin inhibitor overexpression, aortic banding reduced the degree of LV hypertrophy, as assessed by LV weight-to-body weight ratio (3.5 + or - 0.1) compared with that in non-Tg mice (4.6 + or - 0.2). LV systolic function remained compensated in both groups with pressure overload. However, the LV end-diastolic stress-to-LV end-diastolic dimension ratio, an index of diastolic stiffness and LV pressure half-time and isovolumic relaxation time, two indexes of isovolumic relaxation, increased significantly more in TgZ mice with aortic banding. Protein levels of phosphorylated phospholamban (PS16), sarco(endo)plasmic reticulum Ca(2+)-ATPase 2a, phosphorylated ryanodine receptor, and the Na(+)/Ca(2+) exchanger were also reduced significantly (P < 0.05) in the banded TgZ mice. As expected, genetic calcineurin inhibition inhibited the development of LV hypertrophy with chronic pressure overload but also induced LV diastolic dysfunction, as reflected by both impaired isovolumic relaxation and increased myocardial stiffness. Thus genetic calcineurin inhibition reveals a new mechanism regulating LV diastolic function.

IL-18 induction of osteopontin mediates cardiac fibrosis and diastolic dysfunction in mice

Osteopontin (OPN), a key component of the extracellular matrix, is associated with the fibrotic process during tissue remodeling. OPN and the cytokine interleukin (IL)-18 have been shown to be overexpressed in an array of human cardiac pathologies. In the present study, we determined the role of IL-18 in the regulation of cardiac OPN expression and the subsequent interstitial fibrosis and diastolic dysfunction. We demonstrated parallel increases in IL-18, OPN expression, and interstitial fibrosis in murine models of left ventricular pressure and volume overload. Exogenous recombinant (r)IL-18 administered for 2 wk increased cardiac OPN expression, interstitial fibrosis, and diastolic dysfunction. Stimulation of the T helper (Th)1 lymphocyte phenotype with a selective toll-like receptor (TLR)9 agonist induced cardiac IL-18 and OPN expression, which was associated with increased cardiac fibrillar collagen concentrations and interstitial fibrosis resulting in diastolic dysfunction. rIL-18 induced OPN expression and protein levels in primary of cardiac fibroblast cultures. Conditioned media from TLR9-stimulated T lymphocyte cultures induced IL-18 and OPN expression in cardiac fibroblasts, while blockade of the IL-18 receptor with a neutralizing antibody abolished the increase in OPN expression. Furthermore, a mutation in the transcriptional factor interferon regulatory factor (IRF)1 or IRF1 small interfering RNA (siRNA) resulted in the decreased expression of IL-18 and OPN in cardiac fibroblasts. With pressure overload, IRF1-mutant mice showed downregulation of IL-18 and OPN expression in cardiac tissue, reduced cardiac fibrotic development, and increased left ventricular function compared with wild type. These results provide direct evidence that the induction of IL-18 regulates OPN-mediated cardiac fibrosis and diastolic dysfunction.

Abstract 3430: Left Ventricular Hypertrophy and Diastolic Dysfunction in Mice Lacking All Nitric Oxide Synthase Isoforms

We have recently succeeded in developing mice in which all three nitric oxide synthase isoforms (nNOS, iNOS, and eNOS) are completely disrupted ( PNAS 2005). In this study, we examined cardiac morphology and function in those mice. Cardiac echocardiography and left ventricular (LV) hemodynamic measurement were performed in male wild-type (WT), singly nNOS −/− , iNOS −/− , eNOS −/− , and triply n/i/eNOS −/− mice at 2 and 5 months of age (n=5–8). At 2 months of age, no significant cardiac morphological or functional changes were detected in any strains studied. However, at 5 months of age, significant LV hypertrophy (wall thickness, mm) were noted in the triply n/i/eNOS −/− mice (1.3±0.1, P &lt;0.01) and to a lesser extent in the singly eNOS −/− mice (1.1±0.1, P &lt;0.05), but not in the singly nNOS −/− (0.8±0.1) or iNOS −/− mice (1.0±0.1), as compared with the WT mice (1.0±0.2). Furthermore, significant LV diastolic dysfunction (as evaluated by echocardiographic E/A ratio and by hemodynamic peak negative dP/dt), with preserved LV systolic function (as assessed by echocardiographic ejection fraction and by hemodynamic peak positive dP/dt), was noted only in the 5-month-old triply n/i/eNOS −/− mice (2.7±0.1 and 2505±60, both P &lt;0.05), but not in any singly nNOS −/− (2.1±0.2 and 3833±402), iNOS −/− (2.0±0.1 and 3773±747), or eNOS −/− mice (2.0±0.3 and 2934±122), as compared with the WT mice (1.9±0.1 and 4038±344). In addition, significant cardiac fibrosis (fibrosis area, %, Masson-trichrome staining) was also detected only in the 5-month-old triply n/i/eNOS −/− mice (1.4±0.2, P &lt;0.05) compared with the WT mice (0.3±0.1). Importantly, arterial blood pressure (mmHg, tail-cuff method) was significantly elevated in the triply n/i/eNOS −/− (143±3.1, P &lt;0.05) than in the WT mice (104±7.3), but the hypertensive level was comparable to that in the singly eNOS −/− mice (140±8.5). Thus, mechanism(s) other than hypertension appears to be involved in the cardiac abnormalities of the triply n/i/eNOS −/− mice. These results provide the first evidence that genetic disruption of all NOSs results in LV hypertrophy and diastolic dysfunction in mice in vivo, suggesting a pivotal role of the NOS system in maintaining cardiac homeostasis.

Understanding Diastolic Heart Failure With Preserved Ejection Fraction

Congestive heart failure (HF) is a frequent reason for hospital admission. Fifty percent of HF hospitalizations have normal ejection fraction (EF), 1 referred to as diastolic HF (DHF). In contrast, patients with systolic HF (SHF) have reduced EF. The DHF phenotype describes patients with signs and symptoms of HF, normal EF, normal left ventricular (LV) volume, hypertension with increased relative wall thickness, LV diastolic dysfunction, and predominantly elderly women. 1,2 Etiology of DHF Longstanding hypertension may result in significant myocardial hypertrophy, appearance of a smaller ventricular chamber, increased ventricular stiffness, and delayed relaxation. Increased ventricular stiffness requires increased pressure to maintain normal filling in the presence of normal or reduced chamber volume.3 Although DHF has not been studied as extensively as SHF, limited data obtained from patients hospitalized for DHF suggest that demographic characteristics, comorbidities, and pathology differ from those with SHF. Despite these differences, DHF is similar to SHF with regard to volume overload, reduced exercise capacity, impaired quality of life, and long-term mortality.1