Connective tissue and repair in the heart. Potential regulatory mechanisms

Therapeutic effects of equine amniotic membrane suspension on corneal re-epithelialization and haze in a modified lagomorph ex vivo wound healing model

OBJECTIVE

To investigate the therapeutic effects of topical equine amniotic membrane (eAM) suspension following corneal wounding in a controlled experimental setting.

PROCEDURES

Equine amniotic membrane was collected, gamma irradiated, homogenized for topical suspension preparation, and cryopreserved. Corneoscleral rims harvested from fresh rabbit globes were wounded via keratectomy and were maintained in an air-liquid interface ex vivo corneal culture model. Treatment groups included topical gamma irradiated eAM suspension (n = 20) and a control group (n = 20). Re-epithelialization of the wound was assessed with daily photographic evaluation of area of fluorescein uptake (mm² ). Corneal wound haze after a 21-day period was assessed by photographic analysis of haze area (mm² ) and pixel intensity (0-255). Histologic processing of corneal tissue was performed, and protein identification of eAM suspension using Liquid chromatography-mass spectrometry (LC-MS).

RESULTS

The average day of complete corneal re-epithelialization in controls (5.5 ± 1.1) and topically treated (5.5 ± 0.6) corneas, and rates of reduction in area of fluorescein uptake over time did not significantly differ (p = .44). The corneal wound haze was significantly reduced in mean area by approximately 52% and intensity by 57% in corneas treated with topical eAM suspension (p < .05), compared to controls 21 days following wounding. Protein analysis identified numerous proteins, specifically decorin, dermatopontin, and lumican, which have previously been documented in eAM.

CONCLUSIONS

Area and intensity of corneal wound haze were significantly reduced in corneas treated with gamma irradiated eAM suspension, which may be due to previously identified therapeutic proteins which promote corneal clarity.

Loss of Function in Dopamine D3 Receptor Attenuates Left Ventricular Cardiac Fibroblast Migration and Proliferation in vitro

Evidence suggests the existence of an intracardiac dopaminergic system that plays a pivotal role in regulating cardiac function and fibrosis through G-protein coupled receptors, particularly mediated by dopamine receptor 3 (D3R). However, the expression of dopamine receptors in cardiac tissue and their role in cardiac fibroblast function is unclear. In this brief report, first we determined expression of D1R and D3R both in left ventricle (LV) tissue and fibroblasts. Then, we explored the role of D3R in the proliferation and migration of fibroblast cell cultures using both genetic and pharmaceutical approaches; specifically, we compared cardiac fibroblasts isolated from LV of wild type (WT) and D3R knockout (D3KO) mice in response to D3R-specific pharmacological agents. Finally, we determined if loss of D3R function could significantly alter LV fibroblast expression of collagen types I (Col1a1) and III (Col3a1). Cardiac fibroblast proliferation was attenuated in D3KO cells, mimicking the behavior of WT cardiac fibroblasts treated with D3R antagonist. In response to scratch injury, WT cardiac fibroblasts treated with the D3R agonist, pramipexole, displayed enhanced migration compared to control WT and D3KO cells. Loss of function in D3R resulted in attenuation of both proliferation and migration in response to scratch injury, and significantly increased the expression of Col3a1 in LV fibroblasts. These findings suggest that D3R may mediate cardiac fibroblast function during the wound healing response. To our knowledge this is the first report of D3R's expression and functional significance directly in mouse cardiac fibroblasts.

Characterization of fibrillar collagen isoforms in infarcted mouse hearts using second harmonic generation imaging

We utilized collagen specific second harmonic generation (SHG) signatures coupled with correlative immunofluorescence imaging techniques to characterize collagen structural isoforms (type I and type III) in a murine model of myocardial infarction (MI). Tissue samples were imaged over a four week period using SHG, transmitted light microscopy and immunofluorescence imaging using fluorescently-labeled collagen antibodies. The post-mortem cardiac tissue imaging using SHG demonstrated a progressive increase in collagen deposition in the left ventricle (LV) post-MI. We were able to monitor structural morphology and LV remodeling parameters in terms of extent of LV dilation, stiffness and fiber dimensions in the infarcted myocardium.

Oscillatory fluid-induced mechanobiology in heart valves with parallels to the vasculature

Forces generated by blood flow are known to contribute to cardiovascular development and remodeling. These hemodynamic forces induce molecular signals that are communicated from the endothelium to various cell types. The cardiovascular system consists of the heart and the vasculature, and together they deliver nutrients throughout the body. While heart valves and blood vessels experience different environmental forces and differ in morphology as well as cell types, they both can undergo pathological remodeling and become susceptible to calcification. In addition, while the plaque morphology is similar in valvular and vascular diseases, therapeutic targets available for the latter condition are not effective in the management of heart valve calcification. Therefore, research in valvular and vascular pathologies and treatments have largely remained independent. Nonetheless, understanding the similarities and differences in development, calcific/fibrous pathologies and healthy remodeling events between the valvular and vascular systems can help us better identify future treatments for both types of tissues, particularly for heart valve pathologies which have been understudied in comparison to arterial diseases.

Deletion of protein kinase B2 preserves cardiac function by blocking interleukin-6-mediated injury and restores blood pressure during angiotensin II/high-salt-diet-induced hypertension

OBJECTIVE

Protein kinase B2 (AKT2) is implicated in cardiomyocyte survival during various stress conditions. However, the role of AKT2 in heart function, cardiac hypertrophy and blood pressure (BP) control during hypertension is not fully understood. Therefore, we sought to determine whether the deletion of AKT2 protects cardiac function during angiotensin II/high-salt-diet (AngII/HSD) treatment and find out the signaling pathway.

METHODS

Male C57BL/6J (wild type), AKT2 knockout and interleukin (IL)-6 knockout mice were fed a 4% NaCl diet for 5 weeks. In the last week, mice were split in two groups and infused subcutaneously with either vehicle or AngII (1.5 μg/h per mouse) for 1 week. Then, BP and cardiac function were assessed. Immunohistology of IL-6 and monocyte chemoattractant protein 1 was performed to detect inflammation in the heart. Masson's trichrome staining was performed to evaluate cardiac fibrosis. Heart tissue homogenates and neonatal mice cardiomyocytes were collected to analyze oxidative stress.

RESULTS

Compared with wild-type mice, AKT2 knockout mice maintained BP and showed better left ventricle ejection fraction, lower level of fibrosis, reduced oxidative stress, reduced IL-6 expression and less macrophage infiltration, when treated with AngII/HSD. IL-6 knockout mice treated with AngII/HSD also showed alleviated left ventricular function, fibrosis, oxidative stress and macrophage infiltration compared with wild type.

CONCLUSION

AKT2 deficiency prevents the development of AngII/HSD-induced hypertension, cardiac dysfunction and myocardial injury including oxidative stress, fibrosis and inflammation by suppressing IL-6 expression. These data reveal an important role of the AKT2-IL-6 pathway in mediating AngII/HSD-induced hypertension and cardiomyopathy.

Mitochondrial oxidative stress and cardiac ageing

According with different international organizations, cardiovascular diseases are becoming the first cause of death in western countries. Although exposure to different risk factors, particularly those related to lifestyle, contribute to the etiopathogenesis of cardiac disorders, the increase in average lifespan and aging are considered major determinants of cardiac diseases events. Mitochondria and oxidative stress have been pointed out as relevant factors both in heart aging and in the development of cardiac diseases such as heart failure, cardiac hypertrophy and diabetic cardiomyopathy. During aging, cellular processes related with mitochondrial function, such as bioenergetics, apoptosis and inflammation are altered leading to cardiac dysfunction. Increasing our knowledge about the mitochondrial mechanisms related with the aging process, will provide new strategies in order to improve this process, particularly the cardiovascular ones.

MicroRNA-214 exerts a Cardio-protective effect by inhibition of fibrosis

The miRNAs play important roles in regulating myocardial fibrosis. The purpose of this study was to determine the potential roles of microRNA-214 (miR-214) in cardiac fibrosis in vitro and in vivo. In vitro experiment, Ang II-induced cardiac fibroblasts (CFBs) are transfected with pre-miR-214, anti-miR-214 and their oligo controls. Gene expression was checked by Quantitative realtime-PCR (qRT-PCR) and western blotting. In the present experiment, compared with controls, expressions of collagen type I (COL I), collagen type III (COL III), transforming growth factor (TGF)-β1, and tissue inhibitors of metalloproteinase (TIMP)-1 were all increased, but matrix metalloproteinase (MMP)-1 was reduced in CFB by Ang II treatment at both mRNA and protein levels, and these alterations were found reversed by miR-214 transfection. In vivo, an anterior transmural acute myocardial infarction (AMI) was created by occlusion of the left anterior descending coronary artery after Ad-pre-miR-214, Ad-anti-miR-214 or Ad-GFP was delivered separately. Four weeks after AMI, protein contents of COL I, COL III and TGF-β1 in tissue from border area were found increased after AMI, but impaired by overexpression of miR-214. While the expression of MMP-1 was increased by miR-214 stimulation but decreased by miR-214 inhibition. These results suggested that miR-214 exerts cardio-protective effects by inhibition of fibrosis and the inhibitory effect involves TGF-β1 suppression and MMP-1/TIMP-1 regulation. Anat Rec, 299:1348-1357, 2016. © 2016 Wiley Periodicals, Inc.

Mitochondria and oxidative stress in heart aging

As average lifespan of humans increases in western countries, cardiac diseases become the first cause of death. Aging is among the most important risk factors that increase susceptibility for developing cardiovascular diseases. The heart has very aerobic metabolism, and is highly dependent on mitochondrial function, since mitochondria generate more than 90 % of the intracellular ATP consumed by cardiomyocytes. In the last few decades, several investigations have supported the relevance of mitochondria and oxidative stress both in heart aging and in the development of cardiac diseases such as heart failure, cardiac hypertrophy, and diabetic cardiomyopathy. In the current review, we compile different studies corroborating this role. Increased mitochondria DNA instability, impaired bioenergetic efficiency, enhanced apoptosis, and inflammation processes are some of the events related to mitochondria that occur in aging heart, leading to reduced cellular survival and cardiac dysfunction. Knowing the mitochondrial mechanisms involved in the aging process will provide a better understanding of them and allow finding approaches to more efficiently improve this process.

Cellular recruitment in myocardial ischaemia/reperfusion injury

BACKGROUND

Myocardial infarction (MI) is strictly linked to atherosclerosis. Beyond the mechanical narrowing of coronary vessels lumen, during MI a great burden of inflammation is carried out. One of the crucial events is represented by the ischaemia/reperfusion injury, a complex event involving inflammatory cells (such as neutrophils, platelets, monocytes/macrophages, lymphocytes and mast cells) and key activating signals (such as cytokines, chemokines and growth factors). Cardiac repair following myocardial infarction is dependent on a finely regulated response involving a sequential recruitment and the clearance of different subsets of inflammatory cells.

MATERIALS AND METHODS

This narrative review was based on the works detected on PubMed and MEDLINE up to November 2015.

RESULTS

Infarct healing classically follows three overlapping phases: the inflammatory phase, in which the innate immune pathways are activated and inflammatory leucocytes are recruited in order to clear the wound from dead cells; the proliferative phase, characterized by the suppression of pro-inflammatory signalling and infiltration of 'repairing' cells secreting matrix proteins in the injured area; and the maturation phase, which is associated with the quiescence and the elimination of the reparative cells together with cross-linking of the matrix. All these phases are timely regulated by the production of soluble mediators, such as cytokines, chemokines and growth factors.

CONCLUSION

Targeting inflammatory cell recruitment early during reperfusion and healing might be promising to selectively inhibit injury and favour repair. This approach might substantially improve adverse postischaemic left ventricle remodelling, characterized by dilation, hypertrophy of viable segments and progressive dysfunction.

Histopathological evaluation of melatonin as a protective agent in heart injury induced by radiation in a rat model

INTRODUCTION

Melatonin is a hormone which is known to be a powerful cardioprotective agent due to its free radical-scavenging properties. This study was carried out to evaluate whether melatonin administration prior to irradiation would have a protective effect on cardiac histopathological changes in an experimental rat model.

METHODS

Rats were divided into four groups. Single dose of 18 Gy radiation and sham radiation exposure were used in related groups. 50mg/kg dose of melatonin were injected intraperitonally 15 min prior to radiation exposure. Analyses and assessments were performed 6 months after radiation exposure.

RESULTS

Severe myocardial fibrosis was observed prominently in three regions: the apex, tips of papillary muscles and adjacent to the atrioventricular valves. Inflammation was found to be more in irradiated groups. Increased inflammation and fibrosis were in concordance. The number of mast cells was found to be decreased in irradiated groups. Myocyte necrosis and fibrosis were diminished with melatonin while vasculitis was prevented.

CONCLUSIONS

Elementary pathological lesions of radiation-induced heart disease (RIHD) are fibrosis, vascular damage, vasculitis and myocyte necrosis. Development of vasculitis was prevented by the use of melatonin. Fibrosis and necrosis were prominently decreased. Prevention of RIHD with the use of melatonin at the long term is encouraging according to the histopathological results.

Relaxin suppresses atrial fibrillation by reversing fibrosis and myocyte hypertrophy and increasing conduction velocity and sodium current in spontaneously hypertensive rat hearts

RATIONALE

Atrial fibrillation (AF) contributes significantly to morbidity and mortality in elderly and hypertensive patients and has been correlated to enhanced atrial fibrosis. Despite a lack of direct evidence that fibrosis causes AF, reversal of fibrosis is considered a plausible therapy.

OBJECTIVE

To evaluate the efficacy of the antifibrotic hormone relaxin (RLX) in suppressing AF in spontaneously hypertensive rats (SHR).

METHODS AND RESULTS

Normotensive Wistar-Kyoto (WKY) and SHR were treated for 2 weeks with vehicle (WKY+V and SHR+V) or RLX (0.4 mg/kg per day, SHR+RLX) using implantable mini-pumps. Hearts were perfused, mapped optically to analyze action potential durations, intracellular Ca²⁺ transients, and restitution kinetics, and tested for AF vulnerability. SHR hearts had slower conduction velocity (CV; P<0.01 versus WKY), steeper CV restitution kinetics, greater collagen deposition, higher levels of transcripts for transforming growth factor-β, metalloproteinase-2, metalloproteinase-9, collagen I/III, and reduced connexin 43 phosphorylation (P<0.05 versus WKY). Programmed stimulation triggered sustained AF in SHR (n=5/5) and SHR+V (n=4/4), but not in WKY (n=0/5) and SHR+RLX (n=1/8; P<0.01). RLX treatment reversed the transcripts for fibrosis, flattened CV restitution kinetics, reduced action potential duration at 90% recovery to baseline, increased CV (P<0.01), and reversed atrial hypertrophy (P<0.05). Independent of antifibrotic actions, RLX (0.1 µmol/L) increased Na⁺ current density, INa (≈2-fold in 48 hours) in human cardiomyocytes derived from inducible pluripotent stem cells (n=18/18; P<0.01).

CONCLUSIONS

RLX treatment suppressed AF in SHR hearts by increasing CV from a combination of reversal of fibrosis and hypertrophy and by increasing INa. The study provides compelling evidence that RLX may provide a novel therapy to manage AF in humans by reversing fibrosis and hypertrophy and by modulating cardiac ionic currents.

Monitoring cardiac fibrosis: a technical challenge

The heart contains a collagen network that contributes to the contractility of the heart and provides cardiac strength. In cardiac diseases, an increase in collagen deposition is often observed. This fibrosis formation causes systolic and diastolic dysfunction, and plays a major role in the arrythmogenic substrate. Therefore, accurate detection of cardiac fibrosis and its progression is of clinical importance with regard to diagnostics and therapy for patients with cardiac disease. To evaluate cardiac collagen deposition, both invasive and non-invasive techniques are used. In this review the different techniques that are currently used in clinical and experimental setting are summarised, and the advantages and disadvantages of these techniques are discussed.

Fibroblasts in post-infarction inflammation and cardiac repair

Fibroblasts are the predominant cell type in the cardiac interstitium. As the main matrix-producing cells in the adult mammalian heart, fibroblasts maintain the integrity of the extracellular matrix network, thus preserving geometry and function. Following myocardial infarction fibroblasts undergo dynamic phenotypic alterations and direct the reparative response. Due to their strategic location, cardiac fibroblasts serve as sentinel cells that sense injury and activate the inflammasome secreting cytokines and chemokines. During the proliferative phase of healing, infarct fibroblasts undergo myofibroblast transdifferentiation forming stress fibers and expressing contractile proteins (such as α-smooth muscle actin). Mechanical stress, transforming growth factor (TGF)-β/Smad3 signaling and alterations in the composition of the extracellular matrix induce acquisition of the myofibroblast phenotype. In the highly cellular and growth factor-rich environment of the infarct, activated myofibroblasts produce matrix proteins, proteases and their inhibitors regulating matrix metabolism. As the infarct matures, "stress-shielding" of myofibroblasts by the cross-linked matrix and growth factor withdrawal may induce quiescence and ultimately cause apoptotic death. Because of their critical role in post-infarction cardiac remodeling, fibroblasts are promising therapeutic targets following myocardial infarction. However, the complexity of fibroblast functions and the pathophysiologic heterogeneity of post-infarction remodeling in the clinical context discourage oversimplified approaches in clinical translation. This article is part of a Special Issue entitled: Cardiomyocyte Biology: Cardiac Pathways of Differentiation, Metabolism and Contraction.

Angiotensin-(1-7) receptor Mas is an essential modulator of extracellular matrix protein expression in the heart

In this study we investigated the effects of genetic deletion of the Angiotensin-(1-7) receptor Mas or the Angiotensin II receptor AT(2) on the expression of specific extracellular matrix (ECM) proteins in atria, right ventricles and atrioventricular (AV) valves of neonatal and adult mice. Quantification of collagen types I, III and VI and fibronectin was performed using immunofluorescence-labeling and confocal microscopy. Picrosirius red staining was used for the histological assessment of the overall collagen distribution pattern. ECM proteins, metalloproteinases (MMP), ERK1/2 and p38 levels were quantified by western blot analysis. Gelatin zymography was used to evaluate the activity of MMP-2 and MMP-9. We observed that the relative levels of collagen types I and III and fibronectin are significantly higher in both the right ventricle and AV valves of neonatal Mas(-/-) mouse hearts (e.g., collagen type I: 85.28±6.66 vs 43.50±4.41 arbitrary units in the right ventricles of Mas(+/+) mice). Conversely, the level of collagen type VI was lower in the right ventricle and AV valves of Mas(-/-) mice. Adult Mas(-/-) mouse hearts presented similar patterns as observed in neonates. No significant differences in ECM protein level were detected in atria. Likewise, no changes in ECM levels were observed in AT(2) knockout mouse hearts. Although deletion of Mas induced a significant reduction in the level of the active form of MMP-2 in neonate hearts and a reduction of both MMP-2 and MMP-9 in adult Mas(-/-) mice, no significant differences were observed in MMP enzymatic activities when compared to controls. The levels of the active, phosphorylated forms of ERK1/2 and p38 were higher in hearts of both neonatal and adult Mas(-/-) mice. These observations suggest that Mas is involved in the selective expression of specific ECM proteins within both the ventricular myocardium and AV valves. The changes in the ECM profile may alter the connective tissue framework and contribute to the decreased cardiac performance observed in Mas(-/-) mice.

Hemodynamics and mechanobiology of aortic valve inflammation and calcification

Cardiac valves function in a mechanically complex environment, opening and closing close to a billion times during the average human lifetime, experiencing transvalvular pressures and pulsatile and oscillatory shear stresses, as well as bending and axial stress. Although valves were originally thought to be passive pieces of tissue, recent evidence points to an intimate interplay between the hemodynamic environment and biological response of the valve. Several decades of study have been devoted to understanding these varied mechanical stimuli and how they might induce valve pathology. Here, we review efforts taken in understanding the valvular response to its mechanical milieu and key insights gained from in vitro and ex vivo whole-tissue studies in the mechanobiology of aortic valve remodeling, inflammation, and calcification.

Design and physical characterization of a synchronous multivalve aortic valve culture system

For many tissues, cyclic mechanical stimulation is considered necessary to maintain the normal morphology in vitro. The aim of this study was to design and evaluate a simple bioreactor system capable of medium-term (more than 2 weeks) culture of native and engineered aortic valves. The system consists of three pistons in separate cylindrical chambers that are simultaneously driven through the culture medium by a crank and cam assembly. The faces of these pistons have unidirectional valves mounted in opposing orientations that permit flow from one side of the face to the other. A custom designed stent was employed to secure either native or engineered tri-leaflet valves to the pistons. Computational fluid dynamics and finite element modeling was used to assist selection of materials and components in the system. Finally, sterility testing using base culture medium was performed to verify the ability of the system to retain sterile conditions. The current design permits the cyclic opening and closing of three aortic valves, however this device can be modified to accommodate up to 12 valves simultaneously. This new bioreactor system has applications not only for development of tissue-engineered valves, but for also studying disease models in the aortic valve.

Chemokines and cardiac fibrosis

Several members of the chemokine family play an important role in reparative fibrosis and are involved in the pathogenesis of remodeling following myocardial infarction. Chemokines may regulate the fibrotic process through recruitment and activation of mononuclear cell subsets and fibroblast progenitors (fibrocytes), by exerting direct effects on resident fibroblasts, and by modulating angiogenesis. Monocyte Chemoattractant Protein (MCP)-1/CCL2 is the best studied chemokine in cardiac fibrosis. Disruption of the MCP-1 axis reduces fibrosis attenuating dilation of the infarcted ventricle. In addition, MCP-1 signaling is activated in response to insults that do not cause cardiomyocyte death, such as brief ischemia or pressure overload and regulates fibrous tissue deposition in experimental models of fibrotic non-infarctive cardiomyopathy. Understanding the role of chemokine-mediated interactions in the development of cardiac fibrosis may identify novel therapeutic targets for treatment of patients with heart failure.

Altered shear stress stimulates upregulation of endothelial VCAM-1 and ICAM-1 in a BMP-4- and TGF-beta1-dependent pathway

OBJECTIVE

Hemodynamics has been associated with aortic valve (AV) inflammation, but the underlying mechanisms are not well understood. Here we tested the hypothesis that altered shear stress conditions stimulate the expression of cytokines and adhesion molecules in AV leaflets via a bone morphogenic protein (BMP)- and transforming growth fact (TGF)-beta1-dependent pathway.

METHODS AND RESULTS

The ventricularis or aortic surface of porcine AV leaflets were exposed for 48 hours to unidirectional pulsatile and bidirectional oscillatory shear stresses ex vivo. Immunohistochemistry was performed to detect expressions of the 4 inflammatory markers VCAM-1, ICAM-1, BMP-4, and TGF-beta1. Exposure of the aortic surface to pulsatile shear stress (altered hemodynamics), but not oscillatory shear stress, increased expression of the inflammatory markers. In contrast, neither pulsatile nor oscillatory shear stress affected expression of the inflammatory markers on the ventricularis surface. The shear stress-dependent expression of VCAM-1, ICAM-1, and BMP-4, but not TGF-beta1, was significantly reduced by the BMP inhibitor noggin, whereas the TGF-beta1 inhibitor SB431542 blocked BMP-4 expression on the aortic surface exposed to pulsatile shear stress.

CONCLUSIONS

The results demonstrate that altered hemodynamics stimulates the expression of AV leaflet endothelial adhesion molecules in a TGF-beta1- and BMP-4-dependent manner, providing some potential directions for future drug-based therapies for AV diseases.

The immune system and cardiac repair

Myocardial infarction is the most common cause of cardiac injury and results in acute loss of a large number of myocardial cells. Because the heart has negligible regenerative capacity, cardiomyocyte death triggers a reparative response that ultimately results in formation of a scar and is associated with dilative remodeling of the ventricle. Cardiac injury activates innate immune mechanisms initiating an inflammatory reaction. Toll-like receptor-mediated pathways, the complement cascade and reactive oxygen generation induce nuclear factor (NF)-kappaB activation and upregulate chemokine and cytokine synthesis in the infarcted heart. Chemokines stimulate the chemotactic recruitment of inflammatory leukocytes into the infarct, while cytokines promote adhesive interactions between leukocytes and endothelial cells, resulting in transmigration of inflammatory cells into the site of injury. Monocyte subsets play distinct roles in phagocytosis of dead cardiomyocytes and in granulation tissue formation through the release of growth factors. Clearance of dead cells and matrix debris may be essential for resolution of inflammation and transition into the reparative phase. Transforming growth factor (TGF)-beta plays a crucial role in cardiac repair by suppressing inflammation while promoting myofibroblast phenotypic modulation and extracellular matrix deposition. Myofibroblast proliferation and angiogenesis result in formation of highly vascularized granulation tissue. As the healing infarct matures, fibroblasts become apoptotic and a collagen-based matrix is formed, while many infarct neovessels acquire a muscular coat and uncoated vessels regress. Timely resolution of the inflammatory infiltrate and spatial containment of the inflammatory and reparative response into the infarcted area are essential for optimal infarct healing. Targeting inflammatory pathways following infarction may reduce cardiomyocyte injury and attenuate adverse remodeling. In addition, understanding the role of the immune system in cardiac repair is necessary in order to design optimal strategies for cardiac regeneration.

Low coronary driving pressure early in the course of myocardial infarction is associated with subendocardial remodelling and left ventricular dysfunction

Subendocardial remodelling of the left ventricular (LV) non-infarcted myocardium has been poorly investigated. Previously, we have demonstrated that low coronary driving pressure (CDP) early postinfarction was associated with the subsequent development of remote subendocardial fibrosis. The present study aimed at examining the role of CDP in LV remodelling and function following infarction. Haemodynamics were performed in Wistar rats immediately after myocardial infarction (MI group) or sham surgery (SH group) and at days 1, 3, 7 and 28. Heart tissue sections were stained with HE, Sirius red and immunostained for alpha-actin. Two distinct LV regions remote to infarction were examined: subendocardium (SE) and interstitium (INT). Myocyte necrosis, leucocyte infiltration, myofibroblasts and collagen volume fraction were determined. Compared with SH, MI showed lower CDP and LV systolic and diastolic dysfunction. Necrosis was evident in SE at day 1. Inflammation and fibroplasia predominated in SE as far as day 7. Fibrosis was restricted to SE from day 3 on. Inflammation occurred in INT at days 1 and 3, but at a lower grade than in SE. CDP correlated inversely with SE necrosis (r = -0.65, P = 0.003, at day 1), inflammation (r = -0.76, P < 0.001, at day 1), fibroplasia (r = -0.47, P = 0.04, at day 7) and fibrosis (r = -0.83, P < 0.001, at day 28). Low CDP produced progressive LV expansion. Necrosis at day 1, inflammation at days 3 and 7, and fibroplasia at day 7 correlated inversely with LV function. CDP is a key factor to SE integrity and affects LV remodelling and function following infarction.

17β-Estradiol inhibits angiotensin II-induced collagen synthesis of cultured rat cardiac fibroblasts via modulating angiotensin II receptors

Circulating endogenous estrogen is considered to be cardiovascular protective, but the underlying mechanisms remain obscure. The cardiac fibroblasts, the most abundant cell type present in the heart, are responsible for the deposition of extracellular matrix. Angiotensin II has been known to stimulate cardiac collagen gene expression. The present study was designed to investigate the effect of 17beta-estradiol on the angiotensin II-induced proliferation and collagen synthesis in cultured cardiac fibroblasts by using real-time polymerase chain reaction (PCR), Western blot and 3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyl-tetrazolium bromide proliferation assay. Angiotensin II increased the cell proliferation and synthesis of collagen types I and III. Angiotensin II up-regulated the gene expression of the angiotensin AT(1) receptor and down-regulated the gene expression of the angiotensin AT(2) receptor in cardiac fibroblasts. The effects of angiotensin II was abolished by the angiotensin AT(1) receptor antagonist, losartan, but not by the angiotensin AT(2) receptor antagonist, PD 123319. 17beta-estradiol prevented increases in proliferation and attenuated the collagen synthesis in response to angiotensin II. The increased AT(1) receptor mRNA levels and decreased AT(2) receptor mRNA levels were partially reversed by 17beta-estradiol treatment. In conclusion, the down-regulation of angiotensin AT(1) receptor expression and function is likely to be an important mechanism accounting for the inhibitory effect of 17beta-estradiol on angiotensin II-stimulated proliferation and collagen synthesis in cardiac fibroblasts. This effect may confer at least in part the cardiac protective action of 17beta-estradiol under pathological conditions with increased activity of the rennin-angiotensin system.

Selective spatiotemporal induction of matrix metalloproteinase-2 and matrix metalloproteinase-9 transcription after myocardial infarction

Myocardial remodeling after myocardial infarction (MI) is associated with increased levels of the matrix metalloproteinases (MMPs). Levels of two MMP species, MMP-2 and MMP-9, are increased after MI, and transgenic deletion of these MMPs attenuates post-MI left ventricular (LV) remodeling. This study characterized the spatiotemporal patterns of gene promoter induction for MMP-2 and MMP-9 after MI. MI was induced in transgenic mice in which the MMP-2 or MMP-9 promoter sequence was fused to the β-galactosidase reporter, and reporter level was assayed up to 28 days after MI. Myocardial localization with respect to cellular sources of MMP-2 and MMP-9 promoter induction was examined. After MI, LV diameter increased by 70% ( P < 0.05), consistent with LV remodeling. β-Galactosidase staining in MMP-2 reporter mice was increased by 1 day after MI and increased further to 64 ± 6% of LV epicardial area by 7 days after MI ( P < 0.05). MMP-2 promoter activation occurred in fibroblasts and myofibroblasts in the MI region. In MMP-9 reporter mice, promoter induction was detected after 3 days and peaked at 7 days after MI (53 ± 6%, P < 0.05) and was colocalized with inflammatory cells at the peri-infarct region. Although MMP-2 promoter activation was similarly distributed in the MI and border regions, activation of the MMP-9 promoter was highest at the border between the MI and remote regions. These unique findings visually demonstrated that activation of the MMP-2 and MMP-9 gene promoters occurs in a distinct spatial relation with reference to the MI region and changes in a characteristic time-dependent manner after MI.

The mechanistic basis of infarct healing

Myocardial infarction triggers an inflammatory cascade that results in healing and replacement of the damaged tissue with scar. Cardiomyocyte necrosis triggers innate immune mechanisms eliciting Toll-like receptor- mediated responses, activating the complement cascade and generating reactive oxygen species. Subsequent activation of NF-kappaB is a critical element in the regulation of cytokine, chemokine, and adhesion molecule expression in the ischemic myocardium. Chemokine induction mediates leukocyte recruitment in the myocardium. Pleiotropic proinflammatory cytokines, such as TNF-alpha, IL-1, and IL-6, are also upregulated in the infarct and exert a wide range of effects on a variety of cell types. Timely repression of proinflammatory gene synthesis is crucial for optimal healing; IL-10 and TGF-beta-mediated pathways may be important for suppression of chemokine and cytokine expression and for resolution of the leukocytic infiltrate. In addition, TGF-beta may be critically involved in inducing myofibroblast differentiation and activation, promoting extracellular matrix protein deposition in the infarcted area. The composition of the extracellular matrix plays an important role in regulating cell behavior. Both structural and matricellular proteins modulate cell signaling through interactions with specific surface receptors. The molecular and cellular changes associated with infarct healing directly influence ventricular remodeling and affect prognosis in patients with myocardial infarction.

Cardiac function and remodeling is attenuated in transgenic rats expressing the human kallikrein-1 gene after myocardial infarction

Bradykinin coronary outflow, left ventricular performance and left ventricular dimensions of transgenic rats harboring the human tissue kallikrein-1 gene TGR(hKLK1) were investigated under basal and ischemic conditions. Bradykinin content in the coronary outflow of buffer-perfused, isolated hearts of controls and TGR(hKLK1) was measured by specific radioimmunoassay before and after global ischemia. Left ventricular function and left ventricular dimensions were determined in vivo using a tip catheter and echocardiography 6 days and 3 weeks after induction of myocardial infarction. Left ventricular type I collagen mRNA expression was analyzed by RNase protection assay. Compared to controls, basal bradykinin outflow was 3.5 fold increased in TGR(hKLK1). Ischemia induced an increase of bradykinin coronary outflow in controls but did not induce a further increase in TGR(hKLK1). However, despite similar unchanged infarction sizes, left ventricular function and remodeling improved in TGR(hKLK1) after myocardial infarction, indicated by an increase in left ventricular pressure (+34%; P<0.05), contractility (dp/dt max. +25%; P<0.05), and in ejection fraction (+20%; P<0.05) as well as by a reduction in left ventricular enddiastolic pressure (-49%, P<0.05), left ventricular enddiastolic diameter (-20%, P<0.05), and collagen mRNA expression (-15%, P<0.05) compared to controls. A chronically activated transgenic kallikrein kinin system with expression of human kallikrein-1 gene counteracts the progression of left ventricular contractile dysfunction after experimental myocardial infarction. Further studies have to show whether these results can be caused by other therapeutically options. Long acting bradykinin receptor agonists might be an alternative option to improve ischemic heart disease.

Normal Physiological Conditions Maintain the Biological Characteristics of Porcine Aortic Heart Valves: An Ex Vivo Organ Culture Study

The aortic valve functions in a complex mechanical environment which leads to force-dependent cellular and tissue responses. Characterization of these responses provides a fundamental understanding of valve pathogenesis. The aim of this work was to study the biological characteristics of native porcine aortic valves cultured in an ex vivo pulsatile organ culture system capable of maintaining physiological pressures (120/80 mmHg) and cardiac output (4.2 l/min). Collagen, sGAG and elastin contents of the valve leaflets were measured and cusp morphology, cell phenotype, cell proliferation and apoptosis were examined. Presence of endothelial cells (ECs) on the leaflet surface was also evaluated. The differences in collagen, sGAG and elastin contents were not significant (p > 0.05) between the cultured and fresh valve leaflets. The cultured valves maintained the native ECM composition of the leaflets while preserving the morphology and cell phenotype. Cell phenotype in leaflets incubated statically under atmospheric conditions decreased compared to fresh and cultured valve leaflets, indicating the importance of mechanical forces in maintaining the natural biology of the valve leaflets. ECs were retained on the surfaces of cultured leaflets with no remodeling of the leaflets. The number of apoptotic cells in the cultured leaflets was significantly (p < 0.05) less than in the statically incubated leaflets and comparable to fresh leaflets. The sterile ex vivo organ culture system thus maintained the viability and native biological characteristics of the aortic valves that were cultured under dynamic conditions for a period of 48 h.

Anoxia-Reoxygenation Stimulates Collagen Type-I and MMP-1 Expression in Cardiac Fibroblasts

BACKGROUND

Cardiac remodeling after ischemic injury is a major cause of heart failure. In this process, fibroblast growth and collagen synthesis and degradation play a critical role. Recent studies indicate that ligands of the peroxisome proliferator-activated receptors-gamma (PPAR-gamma) alter cardiac remodeling during chronic ischemia. This study was designed to investigate if the PPAR-gamma ligand pioglitazone would modulate fibroblast growth and collagen type-I synthesis (and expression) in cardiac fibroblasts exposed to anoxia-reoxygenation (A-R).

METHODS AND RESULTS

Cardiac fibroblasts were exposed to anoxia (95% N2/5% CO2) and then reoxygenation (95% air/5% CO2). A-R increased fibroblast growth (MTT assay) as well as collagen type-I synthesis (H-proline incorporation) and protein expression (Western analysis). Concurrently, there was a parallel increase in the expression of matrix metalloproteinase-1 (MMP-1) in fibroblasts. Pretreatment of cardiac fibroblasts with pioglitazone (10 M) reduced all these effects of A-R. Further, A-R stimulated intracellular reactive oxygen species (ROS) generation and activated the redox-sensitive transcription factor NF-kappaB (both P < 0.05). Both these phenomena were inhibited by pretreatment of cells with pioglitazone.

CONCLUSION

Thus, it appears that A-R stimulates fibroblast cell growth, collagen type-I synthesis, and MMP-1 expression in cardiac fibroblasts, most likely a result of ROS generation. Inhibition of ROS generation and induction of NF-kappaB in cardiac fibroblasts during A-R may be a mechanism of action of pioglitazone.

Angiotensin II Regulation of Collagen Type I Expression in Cardiac Fibroblasts

Angiotensin II (Ang II)-mediated stimulation of fibroblast growth and collagen type I synthesis is believed to be an important component of the cardiac remodeling process in hypertension and chronic ischemia. Ang II-mediated oxidative stress could be important in enhanced fibroblast growth and collagen formation. Accordingly, we postulated that the PPAR-gamma ligand, pioglitazone, which is known to modulate oxidative stress, would alter Ang II-induced formation of collagen type I in cardiac fibroblasts. Cardiac fibroblasts were treated with different concentrations (10(-8) to 10(-6) M) of Ang II for different times (6 hours, 12 hours, and 24 hours). Ang II increased the expression of collagen type I in a concentration- and time-dependent fashion (P<0.01 versus control). Ang II also decreased the expression and activity of matrix metalloproteinase (MMP)-1 (MMP-1, P<0.05 versus control). These effects of Ang II were attenuated by pretreatment of cells with pioglitazone (10 micromol/L). Ang II stimulated the intracellular generation of reactive oxygen species (ROS), and this effect was also attenuated by pioglitazone. Ang II treatment activated the redox-sensitive transcription factor NF-kappaB, and pioglitazone pretreatment blocked this effect of Ang II. Ang II also activated another transcription factor, AP-1, but this effect of Ang II was not modulated by pioglitazone. In other experiments, we observed that trolox, the water soluble analog of vitamin E, attenuated the effects of Ang II on the expression of collagen type I and MMP-1, in a manner similar to pioglitazone. Thus, pioglitazone attenuates Ang II-mediated collagen type I synthesis in cardiac fibroblasts. The effects of pioglitazone are mediated by the modulation of ROS release and redox-sensitive transcription factor NF-kappaB.

Prevention of cardiac fibrosis and left ventricular dysfunction in diabetic cardiomyopathy in rats by transgenic expression of the human tissue kallikrein gene

Diabetic cardiomyopathy includes fibrosis. Kallikrein (KLK) can inhibit collagen synthesis and promote collagen breakdown. We investigated cardiac fibrosis and left ventricular (LV) function in transgenic rats (TGR) expressing the human kallikrein 1 (hKLK1) gene in streptozotocin (STZ) -induced diabetic conditions. Six weeks after STZ injection, LV function was determined in male Sprague-Dawley (SD) rats and TGR(hKLK1) (n=10/group) by a Millar tip catheter. Total collagen content (Sirius Red staining) and expression of types I, III, and VI collagen were quantified by digital image analysis. SD-STZ hearts demonstrated significantly higher total collagen amounts than normoglycemic controls, reflected by the concomitant increment of collagen types I, III, and VI. This correlated with a significant reduction of LV function vs. normoglycemic controls. In contrast, surface-specific content of the extracellular matrix, including collagen types I, III, and VI expression, was significantly lower in TGR(hKLK1)-STZ, not exceeding the content of SD and TGR(hKLK1) controls. This was paralleled by a preserved LV function in TGR(hKLK1)-STZ animals. The kallikrein inhibitor aprotinin and the bradykinin (BK) B2 receptor antagonist icatibant reduced the beneficial effects on LV function and collagen content in TGR(hKLK1)-STZ animals. Transgenic expression of hKLK1 counteracts the progression of LV contractile dysfunction and extracellular matrix remodeling in STZ-induced diabetic cardiomyopathy via a BK B2 receptor-dependent pathway.

Effects of norepinephrine, HIV type 1 infection, and leukocyte interactions with endothelial cells on the expression of matrix metalloproteinases

The expression of matrix metalloproteinases (MMPs) associated with AIDS-related cardiomypathies and cocaine abuse was examined in an in vitro coculture model. Human peripheral blood mononuclear cells (PBMCs), HIV infected or uninfected, were placed in coculture with primary human cardiac microvascular endothelial cells (HMVEC-C) in the presence or absence of the cocaine-inducible catecholamine norepinephrine (NE). Culture supernatants were assayed for MMP-1, -2, -3, -7, -9, and -13, and for tissue inhibitor of metalloproteinase 1 (TIMP-1) and TIMP-2, by enzyme-linked immunosorbent assay. Low levels of constitutively expressed MMP-1 and -2 were detected in individual cultures of HMVEC-C and PBMCs. NE did not induce MMP or TIMP expression by HMVEC-C and caused modest increases (3- to 4-fold) in MMP-1 and -2 by uninfected PBMCs. Increased levels of NE-induced MMP-1 (5-fold) and MMP -2 (15-fold) were detected in cocultures of HMVEC-C and uninfected PBMCs. HIV infection enhanced MMP-1 (46-fold) and MMP-2 (48-fold) and active MMP-7 (33-fold) and MMP-9 (50-fold) by PBMCs. Coculture of HIV-infected PBMCs with HMVEC-C increased MMP-1 (110-fold) and MMP-2 (307-fold) but not active MMP-7 and -9. The combination of NE, HIV infection, and coculture increased MMP-1 (126-fold) and MMP-2 (467-fold), and active MMP-7 (65-fold) and MMP-9 (75-fold). MMP-3 or-13 was not detected in any of the treatment groups and TIMP-1 and -2 appeared inversely proportional to the observed levels of MMPs. These results suggest that HIV infection, NE, and leukocyte endothelial interactions demonstrate separate and overlapping cooperative effects on the regulation of expression of TIMPs and MMPs associated with AIDS-related cardiomyopathies.

Induction of cardiac fibrosis by transforming growth factor-beta(1)

The role of transforming growth factor-beta(1) (TGF-beta(1)) in the production and deposition of collagens and in the induction of gene expression in the myocardium in relation to the development of myocardial fibrosis will be discussed. Very low expression of TGF-beta(1) and collagen type I and III mRNA is seen in the normal rat heart. Both expressions are markedly increased in the infarcted heart and the levels of TGF-beta(1) mRNA precedes increases in mRNA levels for extracellular matrix (ECM) proteins, suggesting a possible role of TGF-beta(1) in remodeling processes in the myocardium. The TGF-beta(1) expression is normally only transient since continuous TGF-beta(1) overexpression seems to promote nonadaptive cardiac hypertrophy and myocardial fibrosis. In vitro, TGF-beta(1) induces an increase in collagen production and secretion and enhances the abundance of mRNA levels for collagen type I and III in rat cardiac fibroblasts in culture. TGF-beta(1) also stimulates in vivo the expression of ECM proteins and in vivo gene transfer of TGF-beta(1) can induce myocardial fibrosis. Increased myocardial TGF-beta(1) and ECM protein mRNA are found in myocardial fibrosis induced by angiotensin II infusion, by noradrenaline treatment, by isoprenaline infusion, and by long-term blockade of NO synthesis. In vivo antagonism of TGF-beta(1) by neutralizing anti-TGF-beta(1) antibodies or by proteoglycans prevents the increase in gene expression of ECM proteins and inhibits myocardial fibrosis, suggesting that the increases in matrix protein production and fibrosis are mediated by TGF-beta(1).

Induction of cardiac fibrosis by aldosterone

An intracardiac aldosterone system which responds to short- and long-term physiological stimuli has been described. This cardiac generated aldosterone has possibly autocrine or paracrine actions. Normal cardiac tissue contains mineralocorticoid receptors (MR) and cardiac high affinity MR are localized in cardiac myocytes and endothelial cells. Data concerning the presence of MR in cardiac fibroblasts are, however, controversial. MR are not specific for aldosterone but they also bind glucocorticoids. Cardiac fibroblasts however contain the enzyme 11beta-hydroxy-steroid dehydrogenase II which converts these glucocorticoids to inactive metabolites. Discordant findings on the in vitro effect of aldosterone on the collagen synthesis in cardiac fibroblasts are reported and can at least partly attributed to the presence of various fibroblasts phenotypes. During chronic aldosterone infusion in uninephrectomized rats on a high-salt diet, a marked accumulation of interstitial and to a lesser extent perivascular collagen occurs in the heart in both ventricles. This cardiac fibrosis in this aldosteronism model is prevented by spironolactone. This effect of aldosterone is crucially dependent on the salt status of the rat. Indeed, rats on a restricted salt intake infused with aldosterone had no cardiac fibrosis above control levels. During the continuous infusion of aldosterone in the rat the appearance of fibrosis was delayed and starts 4 weeks after the beginning of the infusion which argues against a direct effect of aldosterone. The mechanism of aldosterone-salt induced cardiac fibrosis possibly involves angiotensin II acting through upregulated AT1 receptors and the cardiac AT1 receptor is the target for aldosterone. An accumulation of collagen in the heart has also been found in patients with adrenal adenomas and during chronic activation of the renin-angiotensin-aldosterone system such as in surgically induced unilateral renal ischemia, unilateral renal artery banding or renovascular hypertension. Spironolactone prevents aortic collagen accumulation in spontaneously hypertensive rats. In patients with stable chronic heart failure spironolactone treatment in addition to diuretics and angiotensin-converting enzyme (ACE) inhibition reduced circulating levels of procollagen type III N-terminal aminopeptide. Also, in the Randomized Aldactone Evaluation Study spironolactone coadministered with conventional therapy of ACE inhibitors, loop diuretics and digitalis in patients with symptomatic heart failure defined as NYHA classes III-IV reduces total mortality by 30%.

Oxybutynin chloride inhibits proliferation and suppresses gene expression in bladder smooth muscle cells

PURPOSE

We test the hypothesis that oxybutynin chloride inhibits bladder smooth muscle cell proliferation.

MATERIALS AND METHODS

Cultured rat bladder smooth muscle cells were grown in Medium 199 supplemented with 10% fetal bovine serum in the presence of 0, 1, 10 and 100 microM. oxybutynin. Cell proliferation was assessed by counting cell numbers 48 and 96 hours after plating. To investigate the role of oxybutynin in bladder smooth muscle cell proliferation after mechanical stretch, cells were grown on silicone elastomer bottomed culture plates and subjected to cyclical stretch-relaxation for 48 hours in the presence of 10 microM. oxybutynin. Deoxyribonucleic acid synthesis was assessed by tritiated thymidine incorporation assay. To examine the effect of oxybutynin on stretch activated gene expression, bladder smooth muscle cells were subjected to stretch-relaxation for 2 hours with and without 10 microM. oxybutynin, and relative c-jun messenger (m) ribonucleic acid (RNA) levels were assessed by semiquantitative reverse transcriptase-polymerase chain reaction with normalization to glyceraldehyde-3-phosphate dehydrogenase mRNA levels.

RESULTS

The serum stimulated increase in bladder smooth muscle cell growth was inhibited by oxybutynin in a dose dependent manner. In bladder smooth muscle cells there was a 4.7-fold increase in deoxyribonucleic acid synthesis after mechanical stretch, which decreased by 40% (p <0.01) when cells were stretched in the presence of oxybutynin. Stretch stimulated significant increase in c-jun mNRA levels, which was significantly decreased by oxybutynin.

CONCLUSIONS

Oxybutynin chloride inhibits bladder smooth muscle cell proliferation induced by serum and mechanical stretch. A potential mechanism by which oxybutynin inhibits proliferation may be the down regulation of growth promoting genes, such as c-jun. We speculate that oxybutynin may be useful for preventing permanent hypertrophic bladder changes in addition to decreasing intravesical pressure.

Adenosine inhibits collagen and protein synthesis in cardiac fibroblasts: role of A2B receptors

The objective of this study was to characterize the effects of exogenous and endogenous (cardiac fibroblast-derived) adenosine on [3H]proline and [3H]leucine incorporation, which are reliable markers of collagen and total protein synthesis, respectively, in rat left ventricular cardiac fibroblasts. Growth-arrested confluent cardiac fibroblast monolayers were stimulated with 2.5% fetal calf serum (FCS) in the presence and absence of adenosine, 2-chloroadenosine (stable adenosine analogue), or modulators of adenosine levels including (1) erythro-9-(2-hydroxy-3-nonyl) adenine (adenosine deaminase inhibitor), (2) dipyridamole (adenosine transport blocker), and (3) iodotubericidin (adenosine kinase inhibitor). All agents inhibited in a concentration-dependent fashion FCS-induced [3H]proline and [3H]leucine incorporation. These effects were blocked by KF17837 (selective A2 antagonist) and 1,3-dipropyl-8-(p-sulfophenyl)xanthine (A1/A2 receptor antagonist) but not by 8-cyclopentyl-1,3-dipropylxanthine (selective A1 antagonist), thus excluding the participation of A1 receptors. The lack of effect of CGS21680 (selective A2A agonist) excluded involvement of A2A receptors, thus suggesting a major role for A2B receptors. Comparisons of the inhibitory potencies of N6-cyclopentyladenosine (selective A1 agonist), 5'-N-ethylcarboxamidoadenosine (A1/A2 agonist), and 5'-N-methylcarboxamidoadenosine (A1/A2 agonist) were consistent with that of an A2B receptor subtype mediating the inhibitory effects. We conclude that adenosine inhibits FCS-induced collagen and total protein synthesis in cardiac fibroblasts via activation of A2B receptors. These studies suggest, but do not prove, that endogenous adenosine may protect against cardiac fibrosis.

Angiotensin converting enzyme inhibition modulates cardiac fibroblast growth

BACKGROUND

The progression of left ventricular hypertrophy and cardiac fibrosis in hypertensive heart disease is influenced by sex and age. Although angiotensin converting enzyme inhibition has been shown to prevent progression of the disease in postmenopausal women, the interaction of angiotensin II and estrogen in this process before and after the menopause is poorly understood.

OBJECTIVE

To investigate the influence of the angiotensin converting enzyme inhibitor moexiprilat on serum, estrogen and angiotensin II-induced cardiac fibroblast growth.

METHODS

Neonatal rat cardiac fibroblasts were incubated with 1 and 10% fetal calf serum, 10(-7) mol/l angiotensin II, 10(-9) mol/l estrone, 10(-9) mol/l 17beta-estradiol and 10(-8) mol/l moexiprilat. Proliferation was measured in terms of incorporation of bromodeoxyuridine. Western blot analysis was performed using antibodies directed against the growth-related immediate early genes c-fos and Sp-1. All experiments were performed at least three times.

RESULTS

Fetal calf serum stimulated cardiac fibroblast proliferation (1% fetal calf serum 2.0+/-0.028-fold; 10% fetal calf serum 2.7+/-0.028-fold). Angiotensin II and estrone stimulated proliferation of cardiac fibroblasts grown in the absence of fetal calf serum (angiotensin II 4.2+/-0.075-fold; estrone 2.9+/-0.034-fold) and further increased proliferation in the presence of 1% fetal calf serum (angiotensin 11 4.3+/-0.072-fold); estrone 3.8+/-0.045-fold) and 10% fetal calf serum (angiotensin II 4.8+/-0.112-fold; estrone 4.1+/-0.047-fold). Coincubation with moexiprilat specifically inhibited proliferation induced by angiotensin II and estrone but not by serum, and angiotensin II type 1 receptor blockade inhibited angiotensin II-induced but not estrone-induced cell growth. Western blot analysis showed that the expression of c-fos and Sp-1 was induced in a time-dependent fashion by angiotensin II (to maxima of 5.0-fold for c-fos and 3.0-fold for Sp-1) and estrone (15.2-fold for c-fos and 6.2-fold for Sp-1). This effect was completely inhibited by moexiprilat.

CONCLUSIONS

Angiotensin converting enzyme inhibition modulates cardiac fibroblast growth induced by angiotensin II and estrone. This mechanism might contribute to the beneficial effects of angiotensin converting enzyme inhibition in postmenopausal patients with hypertensive heart disease.