Alterations of beta-adrenergic signaling and cardiac hypertrophy in transgenic mice overexpressing TGF-beta(1)

Single-molecule imaging revealed enhanced dimerization of transforming growth factor β type II receptors in hypertrophic cardiomyocytes

Transforming growth factor β (TGF-β) signaling plays an important role in the pathogenesis of cardiac hypertrophy. However, the molecular mechanism of TGF-β signaling during the process of cardiac remodeling remains poorly understood. In the present study, by employing single-molecule fluorescence imaging approach, we demonstrated that in neonatal rat cardiomyocytes, TGF-β type II receptors (TβRII) existed as monomers at the low expression level, and dimerized upon TGF-β1 stimulation. Importantly, for the first time, we found the increased dimerization of TβRII in hypertrophic cardiomyocytes comparing to the normal cardiomyocytes. The enhanced TβRII dimerization was correlated with the enhanced Smad3 phosphorylation levels. These results provide new information on the mechanism of TGF-β signaling in cardiac remodeling.

Remodeling and homeostasis of the extracellular matrix: implications for fibrotic diseases and cancer

Dynamic remodeling of the extracellular matrix (ECM) is essential for development, wound healing and normal organ homeostasis. Life-threatening pathological conditions arise when ECM remodeling becomes excessive or uncontrolled. In this Perspective, we focus on how ECM remodeling contributes to fibrotic diseases and cancer, which both present challenging obstacles with respect to clinical treatment, to illustrate the importance and complexity of cell-ECM interactions in the pathogenesis of these conditions. Fibrotic diseases, which include pulmonary fibrosis, systemic sclerosis, liver cirrhosis and cardiovascular disease, account for over 45% of deaths in the developed world. ECM remodeling is also crucial for tumor malignancy and metastatic progression, which ultimately cause over 90% of deaths from cancer. Here, we discuss current methodologies and models for understanding and quantifying the impact of environmental cues provided by the ECM on disease progression, and how improving our understanding of ECM remodeling in these pathological conditions is crucial for uncovering novel therapeutic targets and treatment strategies. This can only be achieved through the use of appropriate in vitro and in vivo models to mimic disease, and with technologies that enable accurate monitoring, imaging and quantification of the ECM.

Transforming Growth Factor-β1 as a Common Target Molecule for Development of Cardiovascular Diseases, Renal Insufficiency and Metabolic Syndrome

Transforming growth factor-β1 (TGF-β1) is a polypeptide member of the transforming growth factor β superfamily of cytokines. It is a secreted protein that performs many cellular functions including control of cell growth, cell proliferation, cell differentiation and apoptosis. In the cardiovascular system, TGF-β1 plays pivotal roles in the pathogenesis of hypertension, restenosis after percutaneous coronary intervention, atherosclerosis, cardiac hypertrophy and heart failure. In addition, TGF-β1 has been shown to be increased in adipose tissue of obese subjects with insulin resistance. Furthermore, TGF-β1 is a potent initiator of proliferation of renal mesangial cells leading to chronic kidney disease. Some currently available agents can manipulate TGF-β1 expression leading to amelioration of cardiovascular diseases. Thus, an understanding of interactions between chronic kidney disease and metabolic syndrome and the development of cardiovascular diseases is an important issue, and attention should be given to TGF-β1 as a crucial factor for regulation and modulation of those pathological conditions.

Cardiac myosin light chain kinase is necessary for myosin regulatory light chain phosphorylation and cardiac performance in vivo

In contrast to studies on skeletal and smooth muscles, the identity of kinases in the heart that are important physiologically for direct phosphorylation of myosin regulatory light chain (RLC) is not known. A Ca(2+)/calmodulin-activated myosin light chain kinase is expressed only in cardiac muscle (cMLCK), similar to the tissue-specific expression of skeletal muscle MLCK and in contrast to the ubiquitous expression of smooth muscle MLCK. We have ablated cMLCK expression in male mice to provide insights into its role in RLC phosphorylation in normally contracting myocardium. The extent of RLC phosphorylation was dependent on the extent of cMLCK expression in both ventricular and atrial muscles. Attenuation of RLC phosphorylation led to ventricular myocyte hypertrophy with histological evidence of necrosis and fibrosis. Echocardiography showed increases in left ventricular mass as well as end-diastolic and end-systolic dimensions. Cardiac performance measured as fractional shortening decreased proportionally with decreased cMLCK expression culminating in heart failure in the setting of no RLC phosphorylation. Hearts from female mice showed similar responses with loss of cMLCK associated with diminished RLC phosphorylation and cardiac hypertrophy. Isoproterenol infusion elicited hypertrophic cardiac responses in wild type mice. In mice lacking cMLCK, the hypertrophic hearts showed no additional increases in size with the isoproterenol treatment, suggesting a lack of RLC phosphorylation blunted the stress response. Thus, cMLCK appears to be the predominant protein kinase that maintains basal RLC phosphorylation that is required for normal physiological cardiac performance in vivo.

Transforming growth factor (TGF)-β signaling in cardiac remodeling

Myocardial TGF-β expression is upregulated in experimental models of myocardial infarction and cardiac hypertrophy, and in patients with dilated or hypertrophic cardiomyopathy. Through its effects on cardiomyocytes, mesenchymal and immune cells, TGF-β plays an important role in the pathogenesis of cardiac remodeling and fibrosis. TGF-β overexpression in the mouse heart is associated with fibrosis and hypertrophy. Endogenous TGF-β plays an important role in the pathogenesis of cardiac fibrotic and hypertrophic remodeling, and modulates matrix metabolism in the pressure-overloaded heart. In the infarcted heart, TGF-β deactivates inflammatory macrophages, while promoting myofibroblast transdifferentiation and matrix synthesis through Smad3-dependent pathways. Thus, TGF-β may serve as the "master switchThis article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure". for the transition of the infarct from the inflammatory phase to formation of the scar. Because of its crucial role in cardiac remodeling, the TGF-β system may be a promising therapeutic target for patients with heart failure. However, efforts to translate these concepts into therapeutic strategies, in order to prevent cardiac hypertrophy and fibrosis, are hampered by the complex, pleiotropic and diverse effects of TGF-β signaling, by concerns regarding deleterious actions of TGF-β inhibition and by the possibility of limited benefit in patients receiving optimal treatment with ACE inhibitors and β-adrenergic blockers. Dissection of the pathways responsible for specific TGF-β-mediated actions and understanding of cell-specific actions of TGF-β are needed to design optimal therapeutic strategies. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure".

Effect of celiprolol on prevention of cardiovascular events in vascular Ehlers-Danlos syndrome: a prospective randomised, open, blinded-endpoints trial

BACKGROUND

Vascular Ehlers-Danlos syndrome is a rare severe disease that causes arterial dissections and ruptures that can lead to early death. No preventive treatment has yet been validated. Our aim was to assess the ability of celiprolol, a β(1)-adrenoceptor antagonist with a β(2)-adrenoceptor agonist action, to prevent arterial dissections and ruptures in vascular Ehlers-Danlos syndrome.

METHODS

Our study was a multicentre, randomised, open trial with blinded assessment of clinical events in eight centres in France and one in Belgium. Patients with clinical vascular Ehlers-Danlos syndrome were randomly assigned to 5 years of treatment with celiprolol or to no treatment. Randomisation was done from a centralised, previously established list of sealed envelopes with stratification by patients' age (≤32 years or >32 years). 33 patients were positive for mutation of collagen 3A1 (COL3A1). Celiprolol was administered twice daily and uptritrated by 100 mg steps every 6 months to a maximum of 400 mg per day. [DOSAGE ERROR CORRECTED]. The primary endpoints were arterial events (rupture or dissection, fatal or not). This study is registered with ClinicalTrials.gov, number NCT00190411.

FINDINGS

53 patients were randomly assigned to celiprolol (25 patients) or control groups (28). Mean duration of follow-up was 47 (SD 5) months, with the trial stopped early for treatment benefit. The primary endpoints were reached by five (20%) in the celiprolol group and by 14 (50%) controls (hazard ratio [HR] 0·36; 95% CI 0·15-0·88; p=0·040). Adverse events were severe fatigue in one patient after starting 100 mg celiprolol and mild fatigue in two patients related to dose uptitration.

INTERPRETATION

We suggest that celiprolol might be the treatment of choice for physicians aiming to prevent major complications in patients with vascular Ehlers-Danlos syndrome. Whether patients with similar clinical presentations and no mutation are also protected remains to be established.

FUNDING

French Ministry of Health, Programme Hospitalier de Recherche Clinique 2001.

Pathogenetic mechanisms in radiation fibrosis

Deregulation of normal regenerative responses to physical, chemical and biological toxins in susceptible individuals leads to abnormal remodelling of extracellular matrix with pathological fibrosis. Processes deregulated after radiotherapy have much in common with processes associated with fibrotic diseases affecting the heart, skin, lungs, kidneys, gastro-intestinal tract and liver. Among the secreted factors driving fibrosis, transforming growth factor beta 1 (TGFβ1) produced by a wide range of inflammatory, mesenchymal and epithelial cells converts fibroblasts and other cell types into matrix-producing myofibroblasts. Even if required for the initiation of fibrosis, inflammation and the continued stimulus of TGFβ1 may not be needed to maintain it. After myofibroblast activation, collagen production can be perpetuated independently of TGFβ1 by autocrine induction of a cytokine called connective tissue growth factor. The role of inflammation, the origins and activation of myofibroblasts as biosynthetic cells and the downstream pathways of extracellular matrix synthesis in common fibrotic states are reviewed. Oxidative stress, hypoxia and microvascular damage are also considered, before examining the same processes in the context of radiotherapy. One of the main uncertainties is the relevance of very early events, including inflammatory responses in blood vessels, to fibrosis. Despite the power of animal models, including genetic systems, the potential contribution of research based on human tissue samples has never been greater. A closer interaction between scientists researching fibrosis and radiation oncologists holds enormous promise for therapeutic advances.

Stretch-induced hypertrophy of isolated adult rabbit cardiomyocytes

Both mechanical and humoral triggers have been put forward to explain the hypertrophic response of the challenged cardiomyocyte. The aim of the present study was to investigate whether cyclic equibiaxial stretch is a direct stimulus for isolated adult rabbit cardiomyocytes to develop hypertrophy and to explore the potential involvement of the autocrine/paracrine factors ANG II, transforming growth factor (TGF)-beta(1), and IGF-I in this process. Isolated cardiomyocytes were exposed to 10% cyclic equibiaxial stretch (1 Hz) for up to 48 h or treated with ANG II (100 nM), TGF-beta(1) (5 ng/ml), IGF-I (100 ng/ml), ANG II type 1 (AT(1)) receptor blockers, or conditioned medium of stretched fibroblasts. Cyclic stretch significantly increased cell surface area (+3.1%), protein synthesis (+21%), and brain natriuretic peptide (BNP) mRNA expression (6-fold) in cardiomyocytes. TGF-beta(1) expression increased (+42%) transiently at 4 h, whereas cardiomyocyte IGF-I expression was not detectable under all experimental conditions. The AT(1) receptor blockers candesartan and irbesartan (100 nM) did not prevent the stretch-induced hypertrophic response. Direct exposure to ANG II, TGF-beta(1), or IGF-I did not enhance cardiomyocyte BNP expression. In cardiac fibroblasts, stretch elicited a significant approximately twofold increase in TGF-beta(1) and IGF-I expression. Conditioned medium of stretched fibroblasts increased BNP expression in cardiomyocytes ( approximately 2-fold, P = 0.07). This study clearly indicates that cyclic stretch is a strong, direct trigger to induce hypertrophy in fully differentiated rabbit cardiomyocytes. The present findings do not support the notion that stretch-mediated hypertrophy of adult rabbit cardiomyocytes involves autocrine/paracrine actions of ANG II, TGF-beta(1), or IGF-I.

Elevated systemic TGF-beta impairs aortic vasomotor function through activation of NADPH oxidase-driven superoxide production and leads to hypertension, myocardial remodeling, and increased plaque formation in apoE(-/-) mice

The role of circulating, systemic TGF-beta levels in endothelial function is not clear. TGF-beta(1) may cause endothelial dysfunction in apolipoprotein E-deficient (apoE(-/-)) mice via stimulation of reactive oxygen species (ROS) production by the NADPH oxidase (NOX) system and aggravate aortic and heart remodeling and hypertension. Thoracic aorta (TA) were isolated from 4-mo-old control (C57Bl/6), apoE(-/-), TGF-beta(1)-overexpressing (TGFbeta(1)), and crossbred apoE(-/-) x TGFbeta(1) mice. Endothelium-dependent relaxation was measured before and after incubation with apocynin (NOX inhibitor) or superoxide dismutase (SOD; ROS scavenger). Superoxide production within the vessel wall was determined by dihydroethidine staining under confocal microscope. In 8-mo-old mice, aortic and myocardial morphometric changes, plaque formation by en face fat staining, and blood pressure were determined. Serum TGF-beta(1) levels (ELISA) were elevated in TGFbeta(1) mice without downregulation of TGF-beta-I receptor (immunohistochemistry). In the aortic wall, superoxide production was enhanced and NO-dependent relaxation diminished in apoE(-/-) x TGFbeta(1) mice but improved significantly after apocynin or SOD. Myocardial capillary density was reduced, fibrocyte density increased, aortic wall was thicker, combined lesion area was greater, and blood pressure was higher in the apoE(-/-) x TGFbeta vs. C57Bl/6 mice. Our results demonstrate that elevated circulating TGF-beta(1) causes endothelial dysfunction through NOX activation-induced oxidative stress, accelerating atherosclerosis and hypertension in apoE(-/-) mice. These findings may provide a mechanism explaining accelerated atherosclerosis in patients with elevated plasma TGFbeta(1).

Molecular distinction between physiological and pathological cardiac hypertrophy: experimental findings and therapeutic strategies

Cardiac hypertrophy can be defined as an increase in heart mass. Pathological cardiac hypertrophy (heart growth that occurs in settings of disease, e.g. hypertension) is a key risk factor for heart failure. Pathological hypertrophy is associated with increased interstitial fibrosis, cell death and cardiac dysfunction. In contrast, physiological cardiac hypertrophy (heart growth that occurs in response to chronic exercise training, i.e. the 'athlete's heart') is reversible and is characterized by normal cardiac morphology (i.e. no fibrosis or apoptosis) and normal or enhanced cardiac function. Given that there are clear functional, structural, metabolic and molecular differences between pathological and physiological hypertrophy, a key question in cardiovascular medicine is whether mechanisms responsible for enhancing function of the athlete's heart can be exploited to benefit patients with pathological hypertrophy and heart failure. This review summarizes key experimental findings that have contributed to our understanding of pathological and physiological heart growth. In particular, we focus on signaling pathways that play a causal role in the development of pathological and physiological hypertrophy. We discuss molecular mechanisms associated with features of cardiac hypertrophy, including protein synthesis, sarcomeric organization, fibrosis, cell death and energy metabolism and provide a summary of profiling studies that have examined genes, microRNAs and proteins that are differentially expressed in models of pathological and physiological hypertrophy. How gender and sex hormones affect cardiac hypertrophy is also discussed. Finally, we explore how knowledge of molecular mechanisms underlying pathological and physiological hypertrophy may influence therapeutic strategies for the treatment of cardiovascular disease and heart failure.

Exercise training inhibits inflammatory cytokines and more than prevents myocardial dysfunction in rats with sustained beta-adrenergic hyperactivity

Myocardial hypertrophy and dysfunction occur in response to excessive catecholaminergic drive. Adverse cardiac remodelling is associated with activation of proinflammatory cytokines in the myocardium. To test the hypothesis that exercise training can prevent myocardial dysfunction and production of proinflammatory cytokines induced by beta-adrenergic hyperactivity, male Wistar rats were assigned to one of the following four groups: sedentary non-treated (Con); sedentary isoprenaline treated (Iso); exercised non-treated (Ex); and exercised plus isoprenaline (Iso+Ex). Echocardiography, haemodynamic measurements and isolated papillary muscle were used for functional evaluations. Real-time RT-PCR and Western blot were used to quantify tumour necrosis factor alpha, interleukin-6, interleukin-10 and transforming growth factor beta(1) (TGF-beta(1)) in the tissue. NF-B expression in the nucleus was evaluated by immunohistochemical staining. The Iso rats showed a concentric hypertrophy of the left ventricle (LV). These animals exhibited marked increases in LV end-diastolic pressure and impaired myocardial performance in vitro, with a reduction in the developed tension and maximal rate of tension increase and decrease, as well as worsened recruitment of the Frank-Starling mechanism. Both gene and protein levels of tumour necrosis factor alpha and interleukin-6, as well as TGF-beta(1) mRNA, were increased. In addition, the NF-B expression in the Iso group was significantly raised. In the Iso+Ex group, the exercise training had the following effects: (1) it prevented LV hypertrophy; (ii) it improved myocardial contractility; (3) it avoided the increase of proinflammatory cytokines and improved interleukin-10 levels; and (4) it attenuated the increase of TGF-beta(1) mRNA. Thus, exercise training in a model of beta-adrenergic hyperactivity can avoid the adverse remodelling of the LV and inhibit inflammatory cytokines. Moreover, the cardioprotection is related to beneficial effects on myocardial performance.

The opposing effects of CCN2 and CCN5 on the development of cardiac hypertrophy and fibrosis

CCN family members are matricellular proteins with diverse roles in cell function. The differential expression of CCN2 and CCN5 during cardiac remodeling suggests that these two members of the CCN family play opposing roles during the development of cardiac hypertrophy and fibrosis. We aimed to evaluate the role of CCN2 and CCN5 in the development of cardiac hypertrophy and fibrosis. In isolated cardiomyocytes, overexpression of CCN2 induced hypertrophic growth, whereas the overexpression of CCN5 inhibited both phenylephrine (PE)- and CCN2-induced hypertrophic responses. Deletion of the C-terminal (CT) domain of CCN2 transformed CCN2 into a CCN5-like dominant negative molecule. Fusion of the CT domain to the Carboxy-terminus of CCN5 transformed CCN5 into a CCN2-like pro-hypertrophic molecule. CCN2 transgenic (TG) mice did not develop cardiac hypertrophy at baseline but showed significantly increased fibrosis in response to pressure overload. In contrast, hypertrophy and fibrosis were both significantly inhibited in CCN5 TG mice. CCN2 TG mice showed an accelerated deterioration of cardiac function in response to pressure overload, whereas CCN5 TG mice showed conserved cardiac function. TGF-beta-SMAD signaling was elevated in CCN2 TG mice, but was inhibited in CCN5 TG mice. CCN2 is pro-hypertrophic and -fibrotic, whereas CCN5 is anti-hypertrophic and -fibrotic. CCN5 lacking the CT domain acts as a dominant negative molecule. CCN5 may provide a novel therapeutic target for the treatment of cardiac hypertrophy and heart failure.

Alternate-day fasting protects the rat heart against age-induced inflammation and fibrosis by inhibiting oxidative damage and NF-kB activation

The free radical theory of aging is currently one of the most popular. In parallel, many studies have demonstrated the association of fibrosis and increased oxidative stress in the pathogenesis of some chronic human diseases, and fibrosis is often characteristic of aging tissues. One of the few interventions that effectively slow aging is calorie restriction and the protection against the age-associated increase of oxidative stress remains one of the foremost hypotheses to explain this action. As an alternative to traditional calorie restriction, another dietary regimen, termed alternate-day fasting, has also been tested, whose antiaging mechanisms have not been explored so much extensively. We thus studied the effects of alternate-day fasting, started at 2 months of age, on oxidative stress and fibrosis in the heart during aging. In the left ventricle of the heart of elderly (aged 24 months) versus young (aged 6 months) male rats we found a significant increase in oxidative stress paralleled by increased fibrosis. In parallel there was a significant increase in inflammatory cytokine levels and in NF-kB DNA binding activity with advancing age. Alternate-day fasting protected against all these age-related phenomena. These data support the hypothesis that this kind of dietary restriction protects against age-related fibrosis, at least in part by reducing inflammation and oxidative damage, and this protection can thus be considered a factor in the prevention of age-related diseases with sclerotic evolution.

Inhibition of transforming growth factor-beta signaling induces left ventricular dilation and dysfunction in the pressure-overloaded heart

This study utilized a transgenic mouse model that expresses an inducible dominant-negative mutation of the transforming growth factor (TGF)-beta type II receptor (DnTGFbetaRII) to define the structural and functional responses of the left ventricle (LV) to pressure-overload stress in the absence of an intact TGF-beta signaling cascade. DnTGFbetaRII and nontransgenic (NTG) control mice (male, 8-10 wk) were randomized to receive Zn(2+) (25 mM ZnSO(4) in drinking H(2)O to induce DnTGFbetaRII gene expression) or control tap H(2)O and then further randomized to undergo transverse aortic constriction (TAC) or sham surgery. At 7 days post-TAC, interstitial nonmyocyte proliferation (Ki67 staining) was greatly reduced in LV of DnTGFbetaRII+Zn(2+) mice compared with the other TAC groups. At 28 and 120 days post-TAC, collagen deposition (picrosirius-red staining) in LV was attenuated in DnTGFbetaRII+Zn(2+) mice compared with the other TAC groups. LV end systolic diameter and end systolic and end diastolic volumes were markedly increased, while ejection fraction and fractional shortening were significantly decreased in TAC-DnTGFbetaRII+Zn(2+) mice compared with the other groups at 120 days post-TAC. These data indicate that interruption of TGF-beta signaling attenuates pressure-overload-induced interstitial nonmyocyte proliferation and collagen deposition and promotes LV dilation and dysfunction in the pressure-overloaded heart, thus creating a novel model of dilated cardiomyopathy.

Cardiac insulin-like growth factor-1 and cyclins gene expression in canine models of ischemic or overpacing cardiomyopathy

Background

Insulin-like growth factor-1 (IGF-1), transforming growth factor β (TGFβ) and cyclins are thought to play a role in myocardial hypertrophic response to insults. We investigated these signaling pathways in canine models of ischemic or overpacing-induced cardiomyopathy.

Methods

Echocardiographic recordings and myocardial sampling for measurements of gene expressions of IGF-1, its receptor (IGF-1R), TGFβ and of cyclins A, B, D1, D2, D3 and E, were obtained in 8 dogs with a healed myocardial infarction, 8 dogs after 7 weeks of overpacing and in 7 healthy control dogs.

Results

Ischemic cardiomyopathy was characterized by moderate left ventricular systolic dysfunction and eccentric hypertrophy, with increased expressions of IGF-1, IGF-1R and cyclins B, D1, D3 and E. Tachycardiomyopathy was characterized by severe left ventricular systolic dysfunction and dilation with no identifiable hypertrophic response. In the latter model, only IGF-1 was overexpressed while IGF-1R, cyclins B, D1, D3 and E stayed unchanged as compared to controls. The expressions of TGFβ, cyclins A and D2 were comparable in the 3 groups. The expression of IGF-1R was correlated with the thickness of the interventricular septum, in systole and diastole, and to cyclins B, D1, D3 and E expression.

Conclusion

These results agree with the notion that IGF-1/IGF-1R and cyclins are involved in the hypertrophic response observed in cardiomyopathies.

Effects of AT1- and beta-adrenergic receptor antagonists on TGF-beta1-induced fibrosis in transgenic mice

BACKGROUND

Transforming growth factor-beta1 (TGF-beta1) is involved in interstitial remodelling promoting collagen synthesis and suppressing collagen degradation by inhibition of collagenases. TGF-beta1 mediates angiotensin II-dependent effects and modulates beta1-adrenergic signalling. To study the effect of neuroendocrine antagonism on TGF-beta-induced hypertrophic and fibrotic phenotype, we treated TGF-beta1 (Cys223,225Ser) transgenic mice (TGF-beta1-TG) with either the beta1-receptor blocker metoprolol (MET), the angiotensin II type I (AT1)-receptor antagonist telmisartan (TEL) or an antibody blocking TGF-beta1 signalling (TGFbeta1-sR-Ab).

MATERIAL AND METHODS

Transforming growth factor-beta1-TG mice (8 weeks) overexpressing TGF-beta1 were treated with either TEL (10 mg kg(-1)), MET (350 mg kg(-1)) or a soluble TGF-beta1 receptor antibody (1 mg kg(-1)) for 6 weeks. Morphological analyses of interstitium and cardiomyocytes were related to expression of matrix metalloproteinases (MMPs) and their inhibitors (TIMPs) by immunoblotting and zymography.

RESULTS

In TGF-beta1-TG mice, myocardial interstitial total collagen content was fourfold elevated compared to that of controls (P < 0.05) and was lowered under the treatment with TEL (P < 0.05). Protein expression of TIMP-1 and -4 was increased in TGF-beta1-TG but inhibited by TEL (TIMP-1 and TIMP-4) and MET (TIMP-1), while collagenase activity was decreased in TGF-beta1-TG and normalized by treatment with TEL (MMP-1 and MMP-13) and MET (MMP-1) (P < 0.05). Morphometric measurements of cardiomyocyte diameter and area demonstrated similar antihypertrophic effects for all treatment groups.

CONCLUSION

The AT1-antagonist TEL reduced myocardial hypertrophy and interstitial fibrosis in TGF-beta1-TG mice by normalizing MMP/TIMP ratio. beta1-Adrenergic inhibition by MET as well as TGF-beta1 antagonism induced antihypertrophic rather than antifibrotic effects. Inhibition of both renin-angiotensin system and beta1-adrenergic system may exert different but synergistic effects to reduce myocardial remodelling.

Adaptive and maladptive effects of SMAD3 signaling in the adult heart after hemodynamic pressure overloading

BACKGROUND

Previous studies suggest that transforming growth factor-beta provokes cardiac hypertrophy and myocardial fibrosis; however, it is unclear whether the deleterious effects of transforming growth factor-beta signaling are conveyed through SMAD-dependent or SMAD-independent signaling pathways.

METHODS AND RESULTS

To determine the contribution of SMAD-dependent signaling to cardiac remodeling, we performed transaortic constriction in SMAD3 null (SMAD3(-/-)) and littermate control mice (age, 10 to 12 weeks). Cumulative survival 20 days after transaortic constriction was significantly less in the SMAD3(-/-) mice when compared with littermate controls (43.6% versus 90.9%, P<0.01). Transaortic constriction resulted in a significant increase in cardiac hypertrophy in the SMAD3(-/-) mice, denoted by an increase in the heart weight to tibial length ratio and increased myocyte cross-sectional area. Loss of SMAD3 signaling also resulted in a significant 60% decrease in myocardial fibrosis (P<0.05). A microRNA microarray showed that 55 microRNAs were differentially expressed in littermate and SMAD3(-/-) mice and that 10 of these microRNAs were predicted to bind to genes that regulate the extracellular matrix. Of these 10 candidate microRNAs, both miR-25 and miR-29a were sufficient to decrease collagen gene expression when transfected into isolated cardiac fibroblasts in vitro.

CONCLUSIONS

The results suggest that SMAD3 signaling plays dual roles in the heart: one beneficial role by delimiting hypertrophic growth and the other deleterious by modulating myocardial fibrosis, possibly through a pathway that entails accumulation of microRNAs that decrease collagen gene expression.

B-type natriuretic peptide attenuates cardiac hypertrophy via the transforming growth factor-ß1/smad7 pathway in vivo and in vitro

1. Previously, we showed that long-term treatment of rats after myocardial infarction (MI) with B-type natriuretic peptide (BNP) prevented ventricular remodelling. However, it is unclear whether long-term BNP treatment affects cardiac hypertrophy and, if so, its mechanism of action. In the present study, we investigated the effects of long-term BNP treatment on cardiac hypertrophy and the molecular mechanisms involved. 2. Cardiac hypertrophy was established in rats by ligation of the left anterior descending coronary artery. After treatment with BNP (5 or 15 microg/kg per day) for 8 weeks, indices of cardiac hypertrophy were determined. In separate in vitro experiments, cardiomyocyte hypertrophy was induced by treatment of cardiomyocytes with 10(-6) mol/L angiotensin (Ang) II for 48 h and cell surface area and [(3)H] incorporation were measured. Transforming growth factor (TGF)-beta1 and smad7 mRNA and protein expression in vivo and in vitro were detected using reverse transcription-polymerase chain reaction and western blotting. 3. Long-term BNP treatment dose-dependently attenuated cardiac hypertrophy and improved cardiac function in rats after MI. Furthermore, BNP attenuated the upregulation of TGF-beta1 and downregulation of smad7 mRNA and protein expression. The in vitro experiments further proved that BNP inhibited cardiac hypertrophy and changes in the TGF-beta1/smad7 pathway, which were completely blocked by the cyclic GMP-dependent protein kinase (PKG) inhibitor, KT5823 (cells were treated with 10(-6) mol/L KT5823 for 48 h). 4. The results of the present study demonstrate that long-term treatment of rats with BNP dose-dependently attenuates cardiac hypertrophy and that this is associated with downregulation of TGF-beta1 and upregulation of smad7 via PKG signalling. Long-term BNP treatment may be a new therapeutic strategy to prevent cardiac hypertrophy and progression to heart failure.

The effect of tanshinone IIA upon the TGF-beta1/Smads signaling pathway in hypertrophic myocardium of hypertensive rats

To investigate the molecular mechanism by which Tanshinone IIA (TSN IIA) prevents left ventricular hypertrophy (LVH), we examined the expression of AT1R, TGF-beta1 and Smads gene in the hypertrophic myocardium of hypertensive rats with abdominal aorta constriction. LVH model was established by creating abdominal aorta constriction. Four weeks later, animals were randomly divided into 4 groups with 8 animals in each. One group was used as model control, the other three groups were treated with TSN IIA (20 mg/kg), TSN IIA (10 mg/kg) and valsartan (10 mg/kg), respectively. Another 8 SD rats were subjected to sham surgery and served as blank control. After 8-week treatment, the caudal artery pressure of the animals was measured. The tissues of left ventricle were taken for the measurement of the left ventricular mass index (LVMI) and pathological sectioning and HE-staining were used for determining the myocardial fiber dimension (MFD). The mRNA expression of AT1R, protein expression of TGF-beta1 and activity of Smad-2, 4, 7 were detected by RT-PCR and Western blotting, respectively. Our results showed that (1) the blood pressure of rats treated with TSN IIA, either at high or low dose, was significantly higher than those in the control and valsartan-treated group (P<0.01, P<0.05); (2) LVMI and MFD in TSN IIA and valsartan-treated rats were higher than those in the control group (P<0.05) but significantly lower than those in the model control (P<0.01); (3) the high doses of TSN IIA and valsartan significantly down-regulated the mRNA expression of AT1R and protein expression of TGF-beta1 and Smad-3 in the hypertrophic myocardium (P<0.01), and TGF-beta1 in valsartan-treated animals was more significantly lower than that in rats treated with TSN IIA; (4) the two doses of TSN IIA and valsartan significantly up-regulated the protein expression of Smad-7 in the hypertrophic myocardium (P<0.01), and Smad-7 in the animals treated with high-dose TSN IIA was significantly higher than that in rats treated with valsartan. It is concluded that inhibition of myocardial hypertrophy induced by TSN IIA independent of blood pressure. The underlying mechanism might be the down-regulated expression of AT1R mRNA and Smad-3, increased production of Smad-7, and blocking effect of TSN IIA on TGF beta1/Smads signal pathway in local myocardium.

Circulating transforming growth factor-beta in Marfan syndrome

BACKGROUND

Marfan syndrome (MFS) is caused by mutations in the fibrillin-1 gene and dysregulation of transforming growth factor-beta (TGF-beta). Recent evidence suggests that losartan, an angiotensin II type 1 blocker that blunts TGF-beta activation, may be an effective treatment for MFS. We hypothesized that dysregulation of TGF-beta might be mirrored in circulating TGF-beta concentrations.

METHODS AND RESULTS

Serum obtained from MFS mutant mice (Fbn1(C1039G/+)) treated with losartan was analyzed for circulating TGF-beta1 concentrations and compared with those from placebo-treated and wild-type mice. Aortic root size was measured by echocardiography. Data were validated in patients with MFS and healthy individuals. In mice, circulating total TGF-beta1 concentrations increased with age and were elevated in older untreated Fbn1(C1039G/+) mice compared with wild-type mice (P=0.01; n=16; mean+/-SEM, 115+/-8 ng/mL versus n=17; mean+/-SEM, 92+/-4 ng/mL). Losartan-treated Fbn1(C1039G/+) mice had lower total TGF-beta1 concentrations compared with age-matched Fbn1(C1039G/+) mice treated with placebo (P=0.01; n=18; 90+/-5 ng/mL), and circulating total TGF-beta1 levels were indistinguishable from those of age-matched wild-type mice (P=0.8). Correlation was observed between circulating TGF-beta1 levels and aortic root diameters in Fbn1(C1039G/+) and wild-type mice (P=0.002). In humans, circulating total TGF-beta1 concentrations were elevated in patients with MFS compared with control individuals (P<0.0001; n=53; 15+/-1.7 ng/mL versus n=74; 2.5+/-0.4 ng/mL). MFS patients treated with losartan (n=55) or beta-blocker (n=80) showed significantly lower total TGF-beta1 concentrations compared with untreated MFS patients (P< or =0.05).

CONCLUSIONS

Circulating TGF-beta1 concentrations are elevated in MFS and decrease after administration of losartan, beta-blocker therapy, or both and therefore might serve as a prognostic and therapeutic marker in MFS.

TGF-beta and fibrosis in different organs - molecular pathway imprints

The action of transforming-growth-factor (TGF)-beta following inflammatory responses is characterized by increased production of extracellular matrix (ECM) components, as well as mesenchymal cell proliferation, migration, and accumulation. Thus, TGF-beta is important for the induction of fibrosis often associated with chronic phases of inflammatory diseases. This common feature of TGF-related pathologies is observed in many different organs. Therefore, in addition to the description of the common TGF-beta-pathway, this review focuses on TGF-beta-related pathogenetic effects in different pathologies/organs, i. e., arthritis, diabetic nephropathy, colitis/Crohn's disease, radiation-induced fibrosis, and myocarditis (including their similarities and dissimilarities). However, TGF-beta exhibits both exacerbating and ameliorating features, depending on the phase of disease and the site of action. Due to its central role in severe fibrotic diseases, TGF-beta nevertheless remains an attractive therapeutic target, if targeted locally and during the fibrotic phase of disease.

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.

Chymase plays an important role in left ventricular remodeling induced by intermittent hypoxia in mice

Intermittent hypoxia caused by sleep apnea is associated with cardiovascular disease. Chymase has been reported to play an important role in the development of cardiovascular disease, but it is unclear whether chymase is involved in the pathogenesis of left ventricular remodeling induced by intermittent hypoxia. The aim of this study was to evaluate the effect of a novel chymase inhibitor (NK3201) on hypoxia-induced left ventricular remodeling in mice. Male C57BL/6J mice (9 weeks old) were exposed to intermittent hypoxia or normoxia and were treated with NK3201 (10 mg/kg per day) or the vehicle for 10 days. Left ventricular systolic pressure showed no significant differences among all of the experimental groups. Exposure to intermittent hypoxia increased left ventricular chymase activity and angiotensin II expression, which were both suppressed by treatment with NK3201. Intermittent hypoxia also increased the mean cardiomyocyte diameter, perivascular fibrosis, expression of inflammatory cytokines, oxidative stress, and NADPH-dependent superoxide production in the left ventricular myocardium. These changes were all suppressed by NK3201 treatment. Therefore, chymase might play an important role in intermittent hypoxia-induced left ventricular remodeling, which is independent of the systemic blood pressure.

Cardiac fibroblasts: at the heart of myocardial remodeling

Cardiac fibroblasts are the most prevalent cell type in the heart and play a key role in regulating normal myocardial function and in the adverse myocardial remodeling that occurs with hypertension, myocardial infarction and heart failure. Many of the functional effects of cardiac fibroblasts are mediated through differentiation to a myofibroblast phenotype that expresses contractile proteins and exhibits increased migratory, proliferative and secretory properties. Cardiac myofibroblasts respond to proinflammatory cytokines (e.g. TNFalpha, IL-1, IL-6, TGF-beta), vasoactive peptides (e.g. angiotensin II, endothelin-1, natriuretic peptides) and hormones (e.g. noradrenaline), the levels of which are increased in the remodeling heart. Their function is also modulated by mechanical stretch and changes in oxygen availability (e.g. ischaemia-reperfusion). Myofibroblast responses to such stimuli include changes in cell proliferation, cell migration, extracellular matrix metabolism and secretion of various bioactive molecules including cytokines, vasoactive peptides and growth factors. Several classes of commonly prescribed therapeutic agents for cardiovascular disease also exert pleiotropic effects on cardiac fibroblasts that may explain some of their beneficial outcomes on the remodeling heart. These include drugs for reducing hypertension (ACE inhibitors, angiotensin receptor blockers, beta-blockers), cholesterol levels (statins, fibrates) and insulin resistance (thiazolidinediones). In this review, we provide insight into the properties of cardiac fibroblasts that underscores their importance in the remodeling heart, including their origin, electrophysiological properties, role in matrix metabolism, functional responses to environmental stimuli and ability to secrete bioactive molecules. We also review the evidence suggesting that certain cardiovascular drugs can reduce myocardial remodeling specifically via modulatory effects on cardiac fibroblasts.

TGF-beta signaling in vascular biology and dysfunction

Transforming growth factor (TGF)-beta family members are multifunctional cytokines that elicit their effects on cells, including endothelial and mural cells, via specific type I and type II serine/threonine kinase receptors and intracellular Smad transcription factors. Knock-out mouse models for TGF-beta family signaling pathway components have revealed their critical importance in proper yolk sac angiogenesis. Genetic studies in humans have linked mutations in these signaling components to specific cardiovascular syndromes such as hereditary hemorrhagic telangiectasia, primary pulmonary hypertension and Marfan syndrome. In this review, we present recent advances in our understanding of the role of TGF-beta receptor signaling in vascular biology and disease, and discuss how this may be applied for therapy.

A synthetic peptide from transforming growth factor-beta1 type III receptor prevents myocardial fibrosis in spontaneously hypertensive rats

AIM

We investigated whether P144, a synthetic peptide from transforming growth factor-beta(1) (TGF-beta(1)) type III receptor betaglycan, exhibits cardiac antifibrotic properties.

METHODS AND RESULTS

The study was carried out in one group of 10-week-old normotensive Wistar-Kyoto rats treated with vehicle (V-WKY), one group of 10-week-old spontaneously hypertensive rats treated with vehicle (V-SHR), and one group of 10-week-old SHR treated with P144 (P144-SHR) for 12 weeks. Two more groups of 10-week-old untreated WKY and SHR were used to assess baseline values of the parameters tested. In addition, the effects of P144 on rat cardiac fibroblasts stimulated with TGF-beta(1) were also studied. Compared with V-WKY, V-SHR exhibited significant increases in the myocardial expression of phosphorylated Smad2, 38 and 42 kDa connective tissue growth factor (CTGF) isoforms, procollagen alpha1 (I) mRNA, and collagen type I protein, as well as in the expression of lysyl oxidase (LOX) mRNA and protein, collagen cross-linking and deposition. P144 administration was associated with significant reduction in all these parameters in P144-SHR. TGF-beta(1)-stimulated fibroblasts exhibited significant increases in phosphorylated Smad2, 38 and 42 kDa CTGF proteins, and procollagen alpha(1) (I) mRNA compared with control fibroblasts. No significant differences were found in these parameters between fibroblasts incubated with TGF-beta(1) and P144 and control fibroblasts.

CONCLUSION

These results show that P144 inhibits TGF-beta(1)-dependent signalling pathway and collagen type I synthesis in cardiac fibroblasts. These effects may be involved in the ability of this peptide to prevent myocardial fibrosis in SHR.

Inhibition of ADP-ribosyl cyclase attenuates angiotensin II-induced cardiac hypertrophy

AIMS

Here, we report the discovery of a small molecule inhibitor, 2,2'-dihydroxyazobenzene (DAB), of ADP ribosyl cyclase (ADPR-cyclase) and showed that this inhibitor attenuated angiotensin (Ang) II-induced hypertrophic responses.

METHODS

and results The intracellular concentration of free Ca(2+) [Ca(2+)](i) in adult rat cardiomyocytes was measured by using a confocal microscope. Cardiac hypertrophy was induced by the two-kidney one-clip (2K1C) method. Hypertrophy was determined by de novo protein synthesis, cell volume, echocardiography, nuclear translocation of nuclear factor of activated T-cells, and transforming growth factor-beta1 protein expression. Treatment of cardiomyocytes with Ang II generated a biphasic [Ca(2+)](i) increase that included an initial Ca(2+)peak and sustained Ca(2+) rise via inositol trisphosphate and cyclic ADP-ribose (cADPR) formation, respectively. A cADPR antagonistic analogue, 8-Br-cADPR, and an ADPR-cyclase inhibitor, DAB, blocked the sustained Ca(2+) signal, but not the initial Ca(2+) rise. Furthermore, DAB significantly inhibited Ang II-mediated cADPR formation and hypertrophic responses in vitro. Echocardiography and histological examination revealed significant cardiac hypertrophy in 2K1C rats that was potently inhibited by treatment with DAB. In addition, the hypertrophic responses induced by Ang II in vitro were significantly increased by 2K1C, and DAB treatment reversed these hypertrophic responses to the levels of sham Control.

CONCLUSION

ADPR-cyclase is an important mediator of cardiac hypertrophy, and inhibition of ADPR-cyclase by DAB may provide a new therapeutic strategy for cardiac diseases.

Cellular and molecular mechanisms of fibrosis

Fibrosis is defined by the overgrowth, hardening, and/or scarring of various tissues and is attributed to excess deposition of extracellular matrix components including collagen. Fibrosis is the end result of chronic inflammatory reactions induced by a variety of stimuli including persistent infections, autoimmune reactions, allergic responses, chemical insults, radiation, and tissue injury. Although current treatments for fibrotic diseases such as idiopathic pulmonary fibrosis, liver cirrhosis, systemic sclerosis, progressive kidney disease, and cardiovascular fibrosis typically target the inflammatory response, there is accumulating evidence that the mechanisms driving fibrogenesis are distinct from those regulating inflammation. In fact, some studies have suggested that ongoing inflammation is needed to reverse established and progressive fibrosis. The key cellular mediator of fibrosis is the myofibroblast, which when activated serves as the primary collagen-producing cell. Myofibroblasts are generated from a variety of sources including resident mesenchymal cells, epithelial and endothelial cells in processes termed epithelial/endothelial-mesenchymal (EMT/EndMT) transition, as well as from circulating fibroblast-like cells called fibrocytes that are derived from bone-marrow stem cells. Myofibroblasts are activated by a variety of mechanisms, including paracrine signals derived from lymphocytes and macrophages, autocrine factors secreted by myofibroblasts, and pathogen-associated molecular patterns (PAMPS) produced by pathogenic organisms that interact with pattern recognition receptors (i.e. TLRs) on fibroblasts. Cytokines (IL-13, IL-21, TGF-beta1), chemokines (MCP-1, MIP-1beta), angiogenic factors (VEGF), growth factors (PDGF), peroxisome proliferator-activated receptors (PPARs), acute phase proteins (SAP), caspases, and components of the renin-angiotensin-aldosterone system (ANG II) have been identified as important regulators of fibrosis and are being investigated as potential targets of antifibrotic drugs. This review explores our current understanding of the cellular and molecular mechanisms of fibrogenesis.

Fluvastatin decreases cardiac fibrosis possibly through regulation of TGF-beta(1)/Smad 7 expression in the spontaneously hypertensive rats

Statins ameliorate myocardial fibrosis after myocardial infarction. We designed this study to determine whether fluvastatin reduced hypertension-induced myocardial hypertrophy and fibrosis and whether these fluvastatin effects involved transforming growth factor beta1 (TGF-beta1) and Smad 7, factors known to play a role in the myocardial hypertrophy and fibrosis. We randomized 14 week old spontaneously hypertensive rats (SHRs) to receiving vehicle or 5-20 mg/kg/day fluvastatin for 8 weeks. Wistar Kyoto (WKY) rats receiving vehicle or 10 mg/kg/day fluvastatin were also studied. SHRs had an increased blood pressure, left ventricular hypertrophy and fibrosis compared with WKY rats. SHRs also had an elevated TGF-beta1 expression and a decreased Smad 7 expression. These changes in SHRs were dose-dependently attenuated by fluvastatin. For example, the hydroxyproline content was 3.2+/-0.1, 4.0+/-0.1 and 3.5+/-0.1 microg/mg heart and the Smad 7 protein expression was 5.1+/-0.6, 1.0+/-0.1 and 4.1+/-0.7 arbitrary units for WKY rats, SHRs and SHRs receiving 20 mg/kg/day fluvastatin, respectively. The hydroxyproline content in the SHRs treated with or without fluvastatin was positively correlated with the left ventricular mass index, systolic blood pressure and the amount of TGF-beta1 proteins and negatively correlated with the Smad 7 expression level. The left ventricular mass index was positively correlated with the systolic blood pressure. Fluvastatin did not alter the blood pressure, left ventricular mass index and collagen content of WKY rats. These results suggest that fluvastatin reduces hypertension-induced myocardial hypertrophy and fibrosis. These effects may involve an increased expression of Smad 7 and a decreased expression of TFG-beta1. Our results call for clinical studies to evaluate these fluvastatin effects in hypertensive patients.

Role of gp91phox-containing NADPH oxidase in left ventricular remodeling induced by intermittent hypoxic stress

Intermittent hypoxia due to sleep apnea syndrome is associated with cardiovascular diseases. However, the precise mechanisms by which intermittent hypoxic stress accelerates cardiovascular diseases are largely unclear. The aim of this study was to investigate the role of gp91(phox)-containing NADPH oxidase in the development of left ventricular (LV) remodeling induced by intermittent hypoxic stress in mice. Male gp91(phox)-deficient (gp91(-/-)) mice (n = 26) and wild-type (n = 39) mice at 7-12 wk of age were exposed to intermittent hypoxia (30 s of 4.5-5.5% O(2) followed by 30 s of 21% O(2) for 8 h/day during daytime) or normoxia for 10 days. Mean blood pressure and LV systolic and diastolic function were not changed by intermittent hypoxia in wild-type or gp91(-/-) mice, although right ventricular systolic pressure tended to be increased. In wild-type mice, intermittent hypoxic stress significantly increased the diameter of cardiomyocytes and interstitial fibrosis in LV myocardium. Furthermore, intermittent hypoxic stress increased superoxide production, 4-hydroxy-2-nonenal protein, TNF-alpha and transforming growth factor-beta mRNA, and NF-kappaB binding activity in wild-type, but not gp91(-/-), mice. These results suggest that gp91(phox)-containing NADPH oxidase plays a crucial role in the pathophysiology of intermittent hypoxia-induced LV remodeling through an increase of oxidative stress.

Matrix-Metallo-Proteinases and their tissue inhibitors in radiation-induced lung injury

PURPOSE

Remodeling of extracellular matrix (ECM) after lung damage depends on collagen degrading Matrix-Metallo-Proteinases (MMP) and their endogenous inhibitors (Tissue-Inhibitors of Metallo-Proteinases, TIMP). Transforming growth factor (TGF)-beta1 has been implicated in the pathogenesis of radiation-induced lung fibrosis upon its effects on fibroblast proliferation and collagen synthesis. Lung cancer patients have often elevated TGF-beta1 plasma levels as a result of increased TGF-beta1 expression in their tumours. On this background, we investigated the effect of irradiation on the MMP/TIMP system in the lung tissue of normal and transgenic TGF-beta1 mice, in which TGF-beta1 is overexpressed in the liver resulting in high TGF-beta1 plasma levels.

MATERIAL AND METHODS

Transgenic (TG) and wild-type (WT) mice underwent thoracic irradiation with 12 Gy or sham-irradiation. For each study group (TG 12 Gy; TG 0 Gy; WT 12 Gy; WT 0 Gy) 8 mice were sacrificed at 4 and 8 weeks after (sham-) irradiation. The TGF-beta1, TIMP-1/-2/-3 expression in the lung tissue was quantified by Western blot; the MMP-2 and MMP-9 activity was analysed by zymography. The cellular origin of the MMP and TIMP was localised by immunohistochemistry.

RESULTS

Irradiation had no influence on the TIMP-1/-2/-3, but increased significantly the MMP-2 /-9 expression. In the lung tissue of TG mice the TIMP-1/-2/-3 expression was elevated, the MMP-9 activity was decreased. The immunhistochemical study showed that parenchymal and inflammatory cells express these MMP/TIMP.

CONCLUSION

Our results provide evidence that the overexpression of MMP-2 and MMP-9 is involved in the inflammatory response of radiation-induced lung injury. MMP-2 and MMP-9 are known to degrade collagen IV of basement membranes, therefore affecting the structural integrity of lung tissue. In contrast, in lung tissue of TG mice the TIMP-1/-2/-3 expression was up-regulated and the MMP-9 activity was diminished, thereby decreasing possibly the ECM degradation leading to lung fibrosis.

Mechanisms of cardiac fibrosis in hypertension

Changes in the composition of cardiac tissue develop in hypertensive patients with left ventricular hypertrophy (ie, hypertensive heart disease) and lead to structural remodeling of the myocardium. One of these changes is related to the disruption of the equilibrium between the synthesis and degradation of collagen types I and III molecules, which results in an excessive accumulation of collagen types I and III fibers within the myocardium. Myocardial fibrosis is the consequence of a number of pathologic processes mediated by mechanical, neurohormonal, and cytokine routes. The clinical relevance of fibrosis is that it may contribute to heart failure and other cardiac complications in patients with hypertensive heart disease. This brief review focuses on the mechanisms of hypertensive myocardial fibrosis.

Tissue kallikrein and kinin infusion rescues failing myocardium after myocardial infarction

BACKGROUND

Tissue kallikrein is a serine proteinase that generates the vasoactive kinin peptide, which produces vasodilatory, angiogenic, and antiapoptotic effects. In this study, we investigated the effect of a stable supply of kallikrein and kinin on ventricular remodeling and blood vessel growth in rats after myocardial infarction.

METHODS AND RESULTS

At 1 week after coronary artery ligation, tissue kallikrein or kinin was infused through a minipump for 4 weeks. At 5 weeks after myocardial infarction, kallikrein and kinin infusion significantly improved cardiac contractility and reduced diastolic dysfunction without affecting systolic blood pressure. Kallikrein and kinin infusion significantly increased capillary density in the noninfarcted region. Kallikrein and kinin infusion also reduced heart weight/body weight ratio, cardiomyocyte size, and atrial natriuretic peptide and brain natriuretic peptide expression in the noninfarcted area. Moreover, kallikrein and kinin infusion inhibited interstitial collagen deposition, collagen fraction volume, and collagen I and collagen III mRNA levels, transforming growth factor (TGF)-beta1 and plasminogen activator inhibitor-1 expression, and Smad2 phosphorylation. The effects of kallikrein and kinin on cardiac remodeling were associated with increased nitric oxide levels and reduced NADPH oxidase expression and activity, superoxide formation, and malondialdehyde levels. Furthermore, in cultured cardiac fibroblasts, kinin inhibited angiotensin II-stimulated TGF-beta1 production, and the effect was blocked by icatibant.

CONCLUSION

These results indicate that a subdepressor dose of kallikrein or kinin can restore impaired cardiac function in rats with postinfarction heart failure by inhibiting hypertrophy and fibrosis and promoting angiogenesis through increased nitric oxide formation and suppression of oxidative stress and TGF-beta1 expression.

The fibrosis and atrial fibrillation: is the transforming growth factor-beta 1 a candidate etiology of atrial fibrillation

Atrial fibrillation (AF) is the most commonly occurring arrhythmia in clinical practice, however, the mechanism of atrial fibrillation is not well explained. It has been considered that myocardial fibrosis plays a role in atrial fibrillation. Within the heart, this fibrosis is thought to be mediated by transforming growth factor-beta 1 (TGF-beta 1), a potent stimulator of collagen-producing cardiac fibroblasts. Recent studies indicate that atrial fibrillation is associated with elevated serum concentrations of TGF-beta 1 and C-terminal propeptide of procollagen type I (a marker of collagen type I synthesis). TGF-beta 1 was not only associated with the presence of atrial fibrillation but may also predict patients at increased risk for future development of atrial fibrillation. Why TGF-beta 1 in atrial fibrillation is high is a puzzling problem. We hypothesized that TGF-beta 1 is a possible cause of atrial fibrillation by initiating fibrosis response. Atrial interstitial fibrosis has been seen in patients with CHF and in animal models of pacing-induced heart failure. It was demonstrated that TGF-beta 1 levels were increased in the atria after the development of congestive heart failure in dogs. In a similar study, mice with increased expression of TGF-beta 1 were prone to atrial fibrillation development as a result of raised levels of atrial fibrosis. If the hypothesis is confirmed, administration of TGF-beta 1 monoclonal antibodies may be used to eliminate the etiology. It will be a new target point to treat atrial fibrillation.

Effects of fenofibrate on cardiac remodeling in aldosterone-induced hypertension

Hypertension and cardiac remodeling are associated with myocardial fibrosis, left ventricular (LV) hypertrophy, and diastolic heart failure. Fenofibrate suppresses aldosterone-mediated increases in myocyte matrix metalloproteinase activity and extracellular signal-regulated kinase phosphorylation. It is unknown whether the peroxisome proliferator-activated receptor-alpha agonist, fenofibrate, improves cardiac remodeling in a model of aldosterone-induced hypertension and LV hypertrophy. Twelve-week-old uninephrectomized FVB mice received 1% NaCl drinking water. Miniosmotic pumps delivered saline or aldosterone for 4 weeks. Mice were either untreated (n=14) or treated with fenofibrate 100 mg/kg per day (n=12) for 1 week before and 4 weeks after surgery. Aldosterone increased systolic blood pressure in untreated mice versus saline-untreated mice (134+/-3 versus 91+/-3 mm Hg; P<0.01). This was unaffected by fenofibrate (131+/-3 mm Hg). Aldosterone increased LV end-diastolic and end-systolic dimensions, which were significantly attenuated by fenofibrate (3.8+/-0.1 versus 3.5+/-0.1 mm, and 1.5+/-0.1 versus 1.15+/-0.1 mm, respectively). Fenofibrate also decreased aldosterone-induced LV hypertrophy (LV weight/body weight, 4.1+/-0.2 versus 4.6+/-0.1 mg/g) and improved percent LV fractional shortening (67+/-7% versus 60+/-2%). Additionally, fenofibrate ameliorated the increased matrix metalloproteinase-2/tissue inhibitors of metalloproteinase-2 ratio and fibrosis seen in aldosterone-untreated hearts (P<0.05 for both). Furthermore, in aldosterone-untreated hearts, fenofibrate decreased transforming growth factor-beta, collagen type III (P<0.05 for both), and collagen type I (P<0.01) protein expression. Conversely fenofibrate increased peroxisome proliferator-activated receptor-alpha, peroxisome proliferator-activated receptor-gamma coactivator-1alpha expression, and acetyl coenzyme A carboxylase phosphorylation (P<0.05 for all) in aldosterone-infused hearts; uncoupling protein-3 and medium-chain acyl coenzyme A dehydrogenase protein expression decreased with fenofibrate (P<0.05 and P<0.01, respectively, versus aldosterone-infused), suggesting that improved myocardial remodeling is independent of fatty acid oxidation. Thus, fenofibrate improved aldosterone-induced LV hypertrophy independently of an effect on blood pressure with decreased fibrosis and altered extracellular matrix.

ECM remodeling in hypertensive heart disease

Hypertensive heart disease (HHD) occurs in patients that clinically have both diastolic and systolic heart failure and will soon become the most common cause of heart failure. Two key aspects of heart failure secondary to HHD are the relatively highly prevalent LV hypertrophy and cardiac fibrosis, caused by changes in the local and systemic neurohormonal environment. The fibrotic state is marked by changes in the balance between MMPs and their inhibitors, which alter the composition of the ECM. Importantly, the fibrotic ECM impairs cardiomyocyte function. Recent research suggests that therapies targeting the expression, synthesis, or activation of the enzymes responsible for ECM homeostasis might represent novel opportunities to modify the natural progression of HHD.

Common and unique mechanisms regulate fibrosis in various fibroproliferative diseases

Fibroproliferative diseases, including the pulmonary fibroses, systemic sclerosis, liver cirrhosis, cardiovascular disease, progressive kidney disease, and macular degeneration, are a leading cause of morbidity and mortality and can affect all tissues and organ systems. Fibrotic tissue remodeling can also influence cancer metastasis and accelerate chronic graft rejection in transplant recipients. Nevertheless, despite its enormous impact on human health, there are currently no approved treatments that directly target the mechanism(s) of fibrosis. The primary goals of this Review series on fibrotic diseases are to discuss some of the major fibroproliferative diseases and to identify the common and unique mechanisms of fibrogenesis that might be exploited in the development of effective antifibrotic therapies.

Screening of the endothelin1 gene (EDN1) in a cohort of patients with essential left ventricular hypertrophy

Our objective was to analyse the role of endothelin1 gene (EDN1) variation in essential left ventricular hypertrophy (LVH). We searched for EDN1 variants in 145 Spanish patients with an essential form of LVH (not secondary to hypertension, aortic stenosis, or any other disease that could explain the hypertrophy). The five EDN1 coding exons and 1.5 kilobases of the promoter region were analysed through single strand conformation analysis and direct sequencing. We found four nucleotide changes: -1224 C/A (promoter), -131 ins/del A (exon 1, 5'-non-translated sequence), A/G in codon 106 (exon 3, silent), and G/T in codon 198 (exon 5, lys198asn). To determine the association between these polymorphisms and cardiac hypertrophy, we compared the genotype frequencies from these 145 patients with 250 healthy controls. We found a higher frequency of patients homozygous for 198 lys (198 KK) (65% vs. 52%; p = 0.01; OR = 1.76) and for -1224 AA (73% vs. 66%; p = 0.19). Homozygotes for -1224 A + 198 K (AA+KK) were significantly more frequent in patients (62% vs. 45%; p = 0.0007; OR = 2.10; 95% CI = 1.35-3.25). The expression of the -1224 C/A and exon 5 K198N variants was analysed with cells in culture. These in vitro studies showed that these variations did not differ in their expression levels. In conclusion, our work has shown that EDN1 variation, and in particular homozygosity for the -1224A/198K haplotype, is associated with the risk of developing cardiac hypertrophy. However, these EDN1 variants do not affect in vitro gene expression.

Molecular Signaling Mediated by Angiotensin II Type 1A Receptor Blockade Leading to Attenuation of Renal Dysfunction-Associated Heart Failure

BACKGROUND

In patients with end-stage renal disease, angiotensin II type 1A receptor (AT1) blockade attenuates the associated cardiac dysfunction. We investigated the molecular signaling mediating that effect.

METHODS AND RESULTS

We used 5/6 nephrectomy to induce significant renal dysfunction in AT1 knockout (AT1KO) and wild-type mice (WT). Twelve weeks after nephrectomy, WT showed significant left ventricular dilation and dysfunction that were accompanied by cardiomyocyte hypertrophy, fibrosis, and reduced capillary density. All of these effects were significantly mitigated in AT1KO. Nephrectomy led to upregulation of myocardial expression of AT1, transforming growth factor-beta1 (TGF-beta1), matrix metalloproteinase (MMP)-2, MMP-9, tissue inhibitor of metalloproteinase-1 (TIMP-1), and phosphorylated Akt (p-Akt), and also led to increased oxidative damage in cardiomyocytes. In AT1KO, TGF-beta1, TIMP-1, oxidative damage levels were lower, whereas MMPs and p-Akt levels were higher. Treating nephrectomized WT mice with valsartan (an AT1 blocker), but not hydralazine, improved cardiac function and altered molecular signaling in a manner similar to that seen in AT1KO mice. Notably, AT1 expression was downregulated in valsartan-treated but not hydralazine-treated hearts.

CONCLUSIONS

These findings provide novel insight into the mechanism underlying the beneficial effects of AT1 blockade on cardiac function in a model of renal dysfunction-associated heart failure.

Angiotensin type 1 (AT1) and type 2 (AT2) receptors mediate the increase in TGF-β1 in thyroid hormone-induced cardiac hypertrophy

Increased thyroid hormone (TH) levels are known to induce cardiac hypertrophy. Some studies have provided evidence for a functional link between angiotensin II (ANG II) and transforming growth factor beta1 (TGF-beta1) in the heart, both being able to also induce cardiac hypertrophy. However, the contribution of this growth factor activated directly by TH or indirectly by ANG II in cardiac hypertrophy development remains unknown. To analyze the possible role of TGF-beta1 in cardiac hypertrophy induced by TH and also to evaluate if the TGF-beta1 effect is mediated by ANG II receptors, we employed Wistar rats separated into control, hypothyroid (hypo) and hyperthyroid (T4 - 10) groups combined or not with ANG II receptor blockers (losartan or PD123319). Serum levels of T3 and T4, systolic pressure and heart rate confirmed the thyroid state of the groups. The T4 - 10 group presented a significant increase in cardiac TGF-beta1 levels; however, TGF-beta1 levels in the hypo group did not change in relation to the control. Inhibition of the increase in cardiac TGF-beta1 levels was observed in the groups treated with T4 in association with losartan or PD123319 when compared to the T4 - 10 group. These results demonstrate for the first time the TH-modulated induction of cardiac TGF-beta1 in cardiac hypertrophy, and that this effect is mediated by ANG II receptors.

Re-employment of developmental transcription factors in adult heart disease

A finite number of transcription factors constitute a combinatorial code that orchestrates cardiac development and the specification and differentiation of myocytes. Many, if not all of these same transcription factors are re-employed in the adult heart in response to disease stimuli that promote hypertrophic enlargement and/or dilated cardiomyopathy, as part of the so-called "fetal gene program". This review will discuss the transcription factors that regulate the hypertrophic growth response of the adult heart, with a special emphasis on those regulators that participate in cardiac development.