Extracellular matrix regulation in the development of Syrian cardiomyopathic Bio 14.6 and Bio 53.58 hamsters

Framing Heartaches: The Cardiac ECM and the Effects of Age

The cardiac extracellular matrix (ECM) is involved in several pathological conditions, and age itself is also associated with certain changes in the heart: it gets larger and stiffer, and it develops an increased risk of abnormal intrinsic rhythm. This, therefore, makes conditions such as atrial arrythmia more common. Many of these changes are directly related to the ECM, yet the proteomic composition of the ECM and how it changes with age is not fully resolved. The limited research progress in this field is mainly due to the intrinsic challenges in unravelling tightly bound cardiac proteomic components and also the time-consuming and costly dependency on animal models. This review aims to give an overview of the composition of the cardiac ECM, how different components aid the function of the healthy heart, how the ECM is remodelled and how it is affected by ageing.

Effects of a novel bradykinin B1 receptor antagonist and angiotensin II receptor blockade on experimental myocardial infarction in rats

Background

The aim of the present study was to evaluate the cardiovascular effects of the novel bradykinin B1 receptor antagonist BI-113823 following myocardial infarction (MI) and to determine whether B1 receptor blockade alters the cardiovascular effects of an angiotensin II type 1 (AT1) receptor antagonist after MI in rats.

Methodology/Principal Findings

Sprague Dawley rats were subjected to permanent occlusion of the left descending coronary artery. Cardiovascular function was determined at 7 days post MI. Treatment with either B1 receptor antagonist (BI-113823) or AT1 receptor antagonist (irbesartan) alone or in combination improved post-MI cardiac function as evidenced by attenuation of elevated left ventricular end diastolic pressure (LVEDP); greater first derivative of left ventricular pressure (± dp/dt max), left ventricle ejection fraction, fractional shorting, and better wall motion; as we as reductions in post-MI up-regulation of matrix metalloproteinases 2 (MMP-2) and collagen III. In addition, the cardiac up-regulation of B1 receptor and AT1 receptor mRNA were markedly reduced in animals treated with BI 113823, although bradykinin B2 receptor and angiotensin 1 converting enzyme (ACE1) mRNA expression were not significantly affected by B1 receptor blockade.

Conclusions/Significance

The present study demonstrates that treatment with the novel B1 receptor antagonist, BI-113823 improves post-MI cardiac function and does not influence the cardiovascular effects of AT1 receptor antagonist following MI.

Implications of protease activation in cardiac dysfunction and development of genetic cardiomyopathy in hamsters

It has become evident that protein degradation by proteolytic enzymes, known as proteases, is partly responsible for cardiovascular dysfunction in various types of heart disease. Both extracellular and intracellular alterations in proteolytic activities are invariably seen in heart failure associated with hypertrophic cardiomyopathy, dilated cardiomyopathy, hypertensive cardiomyopathy, diabetic cardiomyopathy, and ischemic cardiomyopathy. Genetic cardiomyopathy displayed in different strains of hamsters provides a useful model for studying heart failure due to either cardiac hypertrophy or cardiac dilation. Alterations in the function of several myocardial organelles such as sarcolemma, sarcoplasmic reticulum, myofibrils, mitochondria, as well as extracellular matrix have been shown to be due to subcellular remodeling as a consequence of changes in gene expression and protein content in failing hearts from cardiomyopathic hamsters. In view of the increased activities of various proteases, including calpains and matrix metalloproteinases in the hearts of genetically determined hamsters, it is proposed that the activation of different proteases may also represent an important determinant of subcellular remodeling and cardiac dysfunction associated with genetic cardiomyopathy.

Aging and susceptibility to toluene in rats: a pharmacokinetic, biomarker, and physiological approach

Aging adults are a growing segment of the U.S. population and are likely to exhibit increased susceptibility to many environmental toxicants. However, there is little information on the susceptibility of the aged to toxicants. The toxicity of toluene has been well characterized in young adult rodents but there is little information in the aged. Three approaches were used: (1) pharmacokinetic (PK), (2) cardiac biomarkers, and (3) whole-animal physiology to assess whether aging increases susceptibility to toluene in the Brown Norway (BN) rat. Three life stages, young adult, middle aged, and aged (4, 12, and 24 mo, respectively), were administered toluene orally at doses of 0, 0.3, 0.65, or 1 g/kg and subjected to the following: terminated at 45 min or 4 h post dosing, and blood and brain toluene concentration were measured; terminated at 4 h post dosing, and biomarkers of cardiac function were measured; or monitor heart rate (HR), core temperature (Tc), and motor activity (MA) by radiotelemetry before and after dosing. Brain toluene concentration was significantly elevated in aged rats at 4 h after dosing with either 0.3 or 1 g/kg. Blood toluene concentrations were unaffected by age. There were various interactions between aging and toluene-induced effects on cardiac biomarkers. Most notably, toluene exposure led to reductions in mRNA markers for oxidative stress in aged but not younger animals. Toluene also produced a reduction in cardiac endothelin-1 in aged rats. Higher doses of toluene led to tachycardia, hypothermia, and a transient elevation in MA. Aged rats were less sensitive to the tachycardic effects of toluene but showed a prolonged hypothermic response. Elevated brain levels of toluene in aged rats may be attributed to their suppressed cardiovascular and respiratory responses. The expression of several cardiac biochemical markers of toluene exposure in the aged may also reflect differential susceptibility to this toxicant.

Improving insulin sensitivity via activation of PPAR-gamma increases telomerase activity in the heart of OLETF rats

This study was conducted to examine telomere biology in terms of improving insulin sensitivity in a type 2 diabetic animal model: Otsuka Long-Evans Tokushima fatty (OLETF) rats. To improve insulin sensitivity, pioglitazone (PG; 10 mg.kg(-1).day(-1)) was administrated to OLETF rats from 20 to 40 wk of age, and the effects of treatment were compared with those in untreated OLETF or control Long-Evans Tokushima Otsuka fatty rats. At the end of the study, the homeostasis model assessment of insulin resistance significantly increased in OLETF rats but decreased in OLETF rats treated with PG. No shortening of telomere length was observed in the heart tissue of OLETF rats, whereas telomerase activity was decreased in OLETF heart tissue. The mRNA expression of both telomerase reverse transcriptase and telomere repeat binding factor 2 was downregulated in the hearts of OLETF rats. The protein expression of phospho-Akt, insulin-like growth factor, and endothelial nitric oxide synthase was reduced in OLETF rats. On the other hand, myocardial matrix metalloproteinase-9 expression was elevated in OLETF rats. The changes observed in OLETF rats were inhibited by PG treatment. However, protein and mRNA expression of Sirt1, a lifespan modulator, were attenuated in OLETF rat hearts, although they were enhanced in OLETF rats with PG treatment. Myocardial fibrosis was less extensive and diastolic dysfunction more greatly ameliorated in PG-treated OLETF rats than in OLETF rats. These findings suggest that improving insulin sensitivity via the activation of peroxisom proliferator-activated receptor-gamma may exert regulatory effects on cardiac telomere biology and may have desirable morphological and functional effects on the diabetic heart.

The Possible Role of Caspase-3 in Pathological and Physiological Cardiac Hypertrophy in Rats

The present study has been designed to investigate the effect of Ac-DEVD-CHO, a specific caspase-3 inhibitor in partial abdominal aortic constriction for 4 week-induced pathological and chronic swimming training for 8 week-induced physiological cardiac hypertrophy. Ac-DEVD-CHO (2 mg/kg intraperitoneally, day(-1)) treatment was started three days before partial abdominal aortic constriction and chronic swimming test and it was continued for 4 weeks in partial abdominal aortic constriction and 8 weeks in chronic swimming test experimental model. The left ventricular (LV) function and LV hypertrophy were assessed by measuring LV developed pressure, dp/dt(max), dp/dt(min), ratio of LV weight to body weight, LV wall thickness, LV collagen content, protein content and RNA concentration. Further, venous pressure and mean arterial blood pressure were recorded. The partial abdominal aortic constriction but not chronic swimming test produced LV dysfunction by decreasing LV developed pressure, dp/dt(max), dp/dt(min.)and increasing LV collagen content. Further, partial abdominal aortic constriction and chronic swimming test were noted to produce LV hypertrophy by increasing ratio of LV weight to body weight, LV wall thickness, LV protein content and LV RNA concentration. Moreover, in contrast to chronic swimming test, partial abdominal aortic constriction has significantly increased venous pressure and mean arterial blood pressure. The Ac-DEVD-CHO has markedly attenuated partial abdominal aortic constriction-induced LV dysfunction, LV hypertrophy, increase in venous pressure and mean arterial blood pressure. However it did not modulate chronic swimming test-induced LV hypertrophy. These results have implicated caspase-3 in partial abdominal aortic constriction-induced LV dysfunction and pathological cardiac hypertrophy. However, caspase-3 may not be involved in chronic swimming test-induced physiological cardiac hypertrophy.

Differential Role of Rho-Kinase in Pathological and Physiological Cardiac Hypertrophy in Rats

The present study was undertaken to investigate the effect of fasudil, a specific Rho-kinase inhibitor, in pathological cardiac hypertrophy induced by partial abdominal aortic constriction (PAAC) for 4 weeks in comparison with physiological cardiac hypertrophy caused by chronic swimming training (CST) for 8 weeks in rats. Fasudil (15 and 30 mg/kg day(-1) p.o.) treatment was started 3 days before PAAC and CST, and was continued for 4 weeks in PAAC and 8 weeks in the CST experimental model. Left ventricular (LV) function and LV hypertrophy were assessed by measuring LVDP, +dp/dt(max), -dp/dt(max), ratio of LV weight to body weight (LVW/BW), LV wall thickness (LVWT), LV collagen content, protein content and RNA concentration. Further, venous pressure (VP) and mean arterial blood pressure (MABP) were recorded. Moreover, DNA gel electrophoresis was employed to assess myocardial cell death. PAAC but not CST produced LV dysfunction by decreasing LVDP, +dp/dt(max), -dp/dt(max) and increasing LV collagen content. Further, PAAC and CST were noted to produce LV hypertrophy by increasing LVW/BW, LVWT, LV protein content and LV RNA concentration. Moreover, in contrast to CST, PAAC has significantly increased VP, MABP and LV necrotic cell death. Fasudil, a Rho-kinase inhibitor, markedly attenuated PAAC-induced LV dysfunction, LV hypertrophy, increase in VP, MABP and LV necrotic cell death. However, it did not modulate the CST-induced LV hypertrophy. These results have implicated Rho-kinase in PAAC-induced LV dysfunction and pathological cardiac hypertrophy. However, Rho-kinase may not be involved in CST-induced physiological cardiac hypertrophy.

Cardiac remodeling and failure From molecules to man (Part II)

Once considered an inert physical scaffolding, the extracellular matrix (ECM) is increasingly being appreciated as a central structural support and dynamic signaling system for cells to assemble into functional tissues. The ECM can respond to environmental stimuli and tissue injury by altering its abundance, composition, and spatial organization, with profound consequences on the structure and function of the tissues that it inhabits. ECM remodeling is now recognized as a central process underlying the maladaptive reorganization of cardiac size, shape, and function during the progression of CHF. ECM remodeling is largely determined by the balance of degradative enzymes, the MMPs, with respect to a highly regulated and complex assortment of multifunctional endogenous inhibitors, the TIMPs. Clinical studies over the past decade document increased MMP activities associated with diseased hearts. Animal models of cardiovascular disease, as well as transgenic mouse models, further support a role for MMPs in cardiac remodeling. Similarly, clinical, experimental, and genetic approaches implicate the involvement of TIMPs in heart disease, and TIMP expression is selectively reduced in the failing heart. The four known TIMP species are differentially regulated in the heart, and their specific role during the progression of CHF is not clear. Unique among TIMPs, TIMP-3 is ECM bound, highly expressed in the heart, uniformly reduced in failing hearts, and a potent endogenous inhibitor of MMPs and A Disintegrin and metalloproteinase (ADAMs) implicated in cardiac disease. The control of ECM remodeling in the failing heart may provide a missing link in our currently inadequate armamentarium of treatments for patients with CHF, and a better understanding of the complex role of TIMP proteins in the normal and failing myocardium, particularly the unique role of TIMP-3, may facilitate the development of targeted anti-remodeling strategies.

Cardiac overexpression of myotrophin triggers myocardial hypertrophy and heart failure in transgenic mice

Cardiac hypertrophy and heart failure remain leading causes of death in the United States. Many studies have suggested that, under stress, myocardium releases factors triggering protein synthesis and stimulating myocyte growth. We identified and cloned myotrophin, a 12-kDa protein from hypertrophied human and rat hearts. Myotrophin (whose gene is localized on human chromosome 7q33) stimulates myocyte growth and participates in cellular interaction that initiates cardiac hypertrophy in vitro. In this report, we present data on the pathophysiological significance of myotrophin in vivo, showing the effects of overexpression of cardio-specific myotrophin in transgenic mice in which cardiac hypertrophy occurred by 4 weeks of age and progressed to heart failure by 9-12 months. This hypertrophy was associated with increased expression of proto-oncogenes, hypertrophy marker genes, growth factors, and cytokines, with symptoms that mimicked those of human cardiomyopathy, functionally and morphologically. This model provided a unique opportunity to analyze gene clusters that are differentially up-regulated during initiation of hypertrophy versus transition of hypertrophy to heart failure. Importantly, changes in gene expression observed during initiation of hypertrophy were significantly different from those seen during its transition to heart failure. Our data show that overexpression of myotrophin results in initiation of cardiac hypertrophy that progresses to heart failure, similar to changes in human heart failure. Knowledge of the changes that take place as a result of overexpression of myotrophin at both the cellular and molecular levels will suggest novel strategies for treatment to prevent hypertrophy and its progression to heart failure.

Beneficial effects of angiotensin-converting enzyme inhibition on sarcoplasmic reticulum function in the failing heart of the Dahl rat

Inhibition of angiotensin-converting enzyme (ACE) retards the process of myocardial remodeling and contractile dysfunction that leads to heart failure. However, the intracellular mechanisms by which ACE inhibition preserves myocardial contractility are largely unclear. Using a model of heart failure induced by hypertension in Dahl salt-sensitive (DS) rats, the mechanisms by which ACE inhibitors (ACEI) exert a beneficial effect on myocardial contractility were studied. Dahl salt-resistant (DR) rats, DS rats not given temocapril (DS/T-), and DS rats treated with temocapril (10 mg/kg per day from 10 to 17 weeks of age, DS/T+) were fed an 8% NaCl diet from 8 to 17 weeks of age (n=8, each group). Echocardiography, hemodynamic measurement, histology, contraction of isolated skinned papillary muscle, and Western blot analysis were carried out. At an elevated final blood pressure similar to that of the DS/T- rats, DS/T+ rats exhibited (1) a decrease in left ventricular (LV) mass associated with decreases in both cardiomyocyte size and interstitial fibrosis; (2) improvement of both systolic and diastolic LV function; and (3) an increase in caffeine contraction after constant Ca(2+)-loading with 8-bromo-cAMP into the sarcoplasmic reticulum (SR) associated with an increase in Ser16-phosphorylated phospholamban, as compared with the DS/T- rats. In addition to inhibition of myocardial remodeling, a restoration of the Ca(2+)-handling ability of the SR by normalized phosphorylated phospholamban may contribute to the improved LV contractile function achieved by chronic treatment with an ACEI.

Matrix remodeling in experimental and human heart failure: a possible regulatory role for TIMP-3

In the failing heart, an imbalance in matrix metalloproteinases (MMPs) and their biological regulators, the tissue inhibitors of MMPs (TIMPs), may result in cardiac dilatation from matrix degradation. We hypothesized that a reduction of myocardial TIMP-3 is associated with adverse matrix remodeling in both human and experimental heart failure. Cardiomyopathic hamsters at age 15 wk (normal), 25 wk (compensated stage), and 35 wk (overt failure) were compared with age-matched normal controls. MMP activity (gelatinase bioassay) was increased in cardiomyopathic hearts (P = 0.03) and peaked during the transition to overt heart failure. TIMP-3 content (immunoblot) was decreased compared with normal controls (74 +/- 5% at 25 wk, 69 +/- 10% at 35 wk; P = 0.001) and its reduction was associated with increased MMP activity (r = -0.6; P = 0.004). TIMP-1 increased progressively (P = 0.001), whereas TIMP-2, TIMP-4, and MMP protein levels were unchanged. Myocardial collagen (hydroxyproline content) increased with time during the progression to end-stage cardiac failure (P < 0.0001). Collagen synthesis ([(14)C]proline uptake) was elevated in cardiomyopathy at 15 and 25 wk (P < 0.05). The collagen cross-linking ratio (insoluble:soluble collagen) was reduced (P = 0.003) as the left ventricle dilated. By confocal microscopy restricted to viable myocardium, collagen content was reduced (P = 0.04) with fragmentation (P < 0.0001) and thinning (P = 0.003) of perimysial collagen fibers. Similarly, patients with end-stage congestive heart failure (n = 7) compared with nonfailing controls (n = 2) had elevated gelatinase MMP activity (P = 0.02) associated with isolated reductions in TIMP-3 (55 +/- 5% of normal; P = 0.003). Reductions of TIMP-3 parallel adverse matrix remodeling in the cardiomyopathic hamster and the failing human heart. TIMP-3 may contribute to the regulation of myocardial remodeling and its reduction may promote a transition from compensated to end-stage congestive heart failure.

Chronic inhibition of Rho kinase blunts the process of left ventricular hypertrophy leading to cardiac contractile dysfunction in hypertension-induced heart failure

The Gq-RhoA-Rho kinase pathway, activated by neurohormonal factors such as angiotensin II (Ang II), has been proposed to be one of the important signaling pathways involved in the progression of left ventricular (LV) hypertrophy to heart failure. We tested the hypothesis that chronic inhibition of Rho kinase prevents this process. Heart failure was induced in Dahl salt-sensitive (DS) rats fed an 8% NaCl diet from 8 until 17 weeks of age. Y-27632 (5 mg/kg per day), a selective Rho kinase inhibitor, was applied orally to DS rats starting at 10 weeks of age for 7 weeks (DS/Y+). DS rats without Y-27632 (DS/Y-) and Dahl salt-resistant (DR) rats fed the 8% NaCl diet were regarded as non-therapeutic and normotensive controls, respectively. At 17 weeks of age, there was no significant difference in the blood pressure of DS/Y- and DS/Y+ rats. DS/Y- rats exhibited: (1) increases in LV mass, cross-sectional area (CSA) of cardiomyocytes, and interstitial fibrosis; (2) contractile dysfunction, i.e. decreases in LV ejection fraction and % fractional shortening, and prolongation of time to peak tension as well as to 50% relaxation in the twitch contraction of isolated papillary muscle; and (3) increases in the protein expression of Galphaq and Rho kinase in the myocardial membrane fraction. In DS/Y+ rats, the degree of myocardial hypertrophy was significantly inhibited in association with improved contractile function, without a decrease in the degree of interstitial fibrosis. Our results suggest the possibility that the Gq-Rho kinase pathway plays an important role in the process of hypertension-induced LV hypertrophy leading to contractile dysfunction.

The gene expression fingerprint of human heart failure

Multiple pathways are responsible for transducing mechanical and hormonal stimuli into changes in gene expression during heart failure. In this study our goals were (i) to develop a sound statistical method to establish a comprehensive cutoff point for identification of differentially expressed genes, (ii) to identify a gene expression fingerprint for heart failure, (iii) to attempt to distinguish different etiologies of heart failure by their gene expression fingerprint, and (iv) to identify gene clusters that show coordinated up- or down-regulation in human heart failure. We used oligonucleotide microarrays to profile seven nonfailing (NF) and eight failing (F) human hearts with a diagnosis of end-stage dilated cardiomyopathy. Biological and experimental variability of the hybridization data were analyzed, and then a statistical analysis procedure was developed, including Student's t test after log-transformation and Wilcoxon Mann-Whitney test. A comprehensive cutoff point composed of fold change, average difference, and absolute call was then established and validated by TaqMan PCR. Of 6,606 genes on the GeneChip, 103 genes in 10 functional groups were differentially expressed between F and NF hearts. A dendrogram identified a gene expression fingerprint of F and NF hearts and also distinguished two F hearts with distinct etiologies (familial and alcoholic cardiomyopathy, respectively) with different expression patterns. K means clustering also revealed two potentially novel pathways associated with up-regulation of atrial natriuretic factor and brain natriuretic peptide and with increased expression of extracellular matrix proteins. Gene expression fingerprints may be useful indicators of heart failure etiologies.

Age-associated changes in cardiac matrix and integrins

The progressive shift from young age to senescence is characterized by structural and functional changes in the cardiac extracellular matrix (ECM), which supports and aligns myocytes and blood vessels, and maintains myocardial mass, structure and function. As cardiac function declines with advancing age, ECM collagen and fibronectin influence diastolic stiffness. ECM binding to membrane-bound receptors, or integrins, directly links ECM to cardiac muscle and fibroblast cells, affording it the permissive role to modulate heart function. To better understand the ECM structure-function relationship in the old heart, we studied the relative protein content of these ECM proteins and integrins across three age groups. Old Balb-c mice (20 months) exhibit biventricular, cardiac hypertrophy, and greater left ventricular (LV) collagen, fibronectin, alpha 1 and alpha 5 integrin protein than middle-aged (12 months) or young (2 months) LV (P<0.05). beta1 integrin protein content is lower in old LV (P<0.05). These data show that advancing age is associated with greater collagen, fibronectin, alpha 1 and alpha 5 integrin content, suggesting that these matrix proteins undergo coordinated regulation in the aging heart. The differential integrin and ECM protein content suggests that there is regulatory signaling to the fibroblasts, which maintain the cardiac ECM.

Effects of losartan on the collagen degradative enzymes in hypertrophic and congestive types of cardiomyopathic hamsters

The present study was undertaken to determine the effects of AT1 receptor blockade which occurred in response to losartan, on the extracellular matrix (ECM) degradation process in the Bio 14.6 (n = 12) and Bio 53.58 (n = 12) strains which are referred as models of hypertrophic and dilated cardiomyopathy, respectively. The administration of losartan (30 mg/kg/day) in hamsters from 10-20 weeks of age reduced the accumulation of the left ventricular collagen matrix in both of the Bio 14.6 and the Bio 53.58 strains. According to the RT-PCR, the levels of mRNA for matrix metalloproteinase (MMP) and the tissue inhibitor of MMP (TIMP) were examined. MMP-1, -2, -3, and -9 were more enhanced in both myopathic strains than in the control F1beta, strains. With losartan, the levels of MMP-1, -2, -9, TIMP-1 and -2 decreased in the both strains but those for MMP-3 did not in Bio 14.6 strains. TIMP-3 and -4 mRNA levels did not change in any of the experimental hamsters, whether treated or untreated with losartan. The Western blots also showed similar observations in the both strains as seen in mRNA expressions although MMP-2 in the Bio 53.58 strains did not differ between treated and untreated with losartan. Although losartan has an inhibitory effect on collagen accumulation in the development of cardiomyopathy, MMPs (-1, -2, -9) and TIMPs (-1, -2) seem to be susceptible to responding to losartan in Bio cardiomyopathic hamsters.

Growth hormone reverses age-related cardiac myofilament dysfunction in rats

We tested the hypotheses that aging is associated with a reduction in overall cardiac contractility and myofilament force generation that could be reversed with growth hormone (GH) replacement. Three groups of male Brown-Norway rats were studied: young (Y(SAL): 8 mo old, n = 13), old (O(SAL): 28 mo old, n = 13), and old GH-treated (O(GH): 28 mo old, n = 12; 300 microg bovine GH, twice a day for 30 days). The left ventricular (LV) pressure-volume relation was derived in isolated hearts, after which isolated trabecular muscles from these hearts were permeabilized and maximal myofilament force generation (Fmax) was measured. LV developed pressures at a LV volume of 0.3 ml were significantly depressed with age: 84 +/- 6 vs. 71 +/- 6 mmHg (Y(SAL) vs. O(SAL), respectively, P = 0.001) and not restored by GH (69 +/- 4 mmHg). Fmax was reduced in the aged hearts: 47.5 +/- 3.12 vs. 35.9 +/- 3.03 mN/mm2 (Y(SAL) vs. O(SAL), respectively, P = 0.014) but was restored with GH replacement to 46.7 +/- 3.12 mN/mm2 (O(SAL) vs. O(GH), P = 0.021). Our results suggest that cellular myofilament contractility is reduced with aging and restored with GH replacement.