Transforming growth factor-beta(1) induces angiotensin-converting enzyme synthesis in rat cardiac fibroblasts during their differentiation to myofibroblasts

Relationship between ω3 and ω6 polyunsaturated fatty acids and atrial fibrillation in acute ischemic stroke

BACKGROUND & AIMS

Some ω3 polyunsaturated fatty acids (PUFAs) are said to demonstrate a dose-related risk of atrial fibrillation (AF), conversely, some ω6 PUFAs might have AF protective potential. However, few investigated the relation among ischemic strokes. Primarily, we aimed to examine a relation between ω3 and ω6 PUFAs and the presence of AF in ischemic strokes. Further, since, some PUFAs are said to affect the cardiac load, we secondarily aimed to investigate the association between ω3 and ω6 PUFAs and brain natriuretic peptide (BNP) and the occurrence of cerebral large vessel occlusion (LVO) in ischemic strokes with AF.

METHODS

Consecutive patients with ischemic stroke admitted between 2012 and 2022 were retrospectively screened. Plasma levels of PUFAs, including eicosapentaenoic acid (EPA), docosahexaenoic acid, dihomo-γ-linolenic acid (DGLA) and arachidonic acid (AA), were assayed. Data were analyzed using a Poisson regression analysis with a robust variance estimator and a multiple linear regression analysis.

RESULTS

We screened 2112 consecutive ischemic strokes, including 1574 (1119 [71%] males, median age 69 years). Lower DGLA (prevalence ratio (PR) 0.885, 95% CI 0.811-0.966, p = 0.006), lower AA (PR 0.797, 95% CI 0.649-0.978, p = 0.030), and higher EPA/AA ratio (PR 1.353, 95% CI 1.036-1.767, p = 0.026) were associated with AF. Checking the linearity between AF and PUFAs, negative linear trends were observed between DGLA quartiles (Q1: PR 1.901, Q2: PR 1.550, Q3: PR 1.423, Q4: 1.000, p < 0.001 for trend) and AA quartiles (Q1: PR 1.499, Q2: PR 1.204, Q3: PR 1.125, Q4: 1.000, p = 0.004 for trend), with positive linear trends between EPA/AA ratio quartiles (Q1: 1.000, Q2: PR 1.555, Q3: PR 1.612, Q4: PR 1.797, p = 0.001 for trend). Among patients with AF, a negative association between AA and BNP (unstandardized coefficient -1.316, 95% CI -2.290∼-0.342, p = 0.008) was observed, and lower AA was associated with LVO (PR 0.707, 95% CI 0.527-0.950, p = 0.021).

CONCLUSION

Lower DGLA and AA and a higher EPA/AA ratio might be related to the development of AF in ischemic strokes. Further, AA might have a cardio-cerebrovascular protective role in ischemic strokes with AF.

Using different geometries to modulate the cardiac fibroblast phenotype and the biomechanical properties of engineered connective tissues

Tissue engineering with human cardiac fibroblasts (CF) allows identifying novel mechanisms and anti-fibrotic drugs in the context of cardiac fibrosis. However, substantial knowledge on the influences of the used materials and tissue geometries on tissue properties and cell phenotypes is necessary to be able to choose an appropriate model for a specific research question. As there is a clear lack of information on how CF react to the mold architecture in engineered connective tissues (ECT), we first compared the effect of two mold geometries and materials with different hardnesses on the biomechanical properties of ECT. We could show that ECT, which formed around two distant poles (non-uniform model) were less stiff and more strain-resistant than ECT, which formed around a central rod (uniform model), independent of the materials used for poles and rods. Next, we investigated the cell state and could demonstrate that in the uniform versus non-uniform model, the embedded cells have a higher cell cycle activity and display a more pronounced myofibroblast phenotype. Differential gene expression analysis revealed that uniform ECT displayed a fibrosis-associated gene signature similar to the diseased heart. Furthermore, we were able to identify important relationships between cell and tissue characteristics, as well as between biomechanical tissue parameters by implementing cells from normal heart and end-stage heart failure explants from patients with ischemic or dilated cardiomyopathy. Finally, we show that the application of pro- and anti-fibrotic factors in the non-uniform and uniform model, respectively, is not sufficient to mimic the effect of the other geometry. Taken together, we demonstrate that modifying the mold geometry in tissue engineering with CF offers the possibility to compare different cellular phenotypes and biomechanical tissue properties.

Local Renin-Angiotensin System Signaling Mediates Cellular Function of Aortic Valves

The renin-angiotensin system (RAS) is activated in aortic valve disease, yet little is understood about how it affects the acute functional response of valve interstitial cells (VICs). Herein, we developed a gelatin-based valve thin film (vTF) platform to investigate whether the contractile response of VICs can be regulated via RAS mediators and inhibitors. First, the impact of culture medium (quiescent, activated, and osteogenic medium) on VIC phenotype and function was assessed. Contractility of VICs was measured upon treatment with angiotensin I (Ang I), angiotensin II (Ang II), angiotensin-converting enzyme (ACE) inhibitor, and Angiotensin II type 1 receptor (AT1R) inhibitor. Anisotropic cell alignment on gelatin vTF was achieved independent of culture conditions. Cells cultured in activated and osteogenic conditions were found to be more elongated than in quiescent medium. Increased α-SMA expression was observed in activated medium and no RUNX2 expression were observed in cells. VIC contractile stress increased with increasing concentrations (from 10-10 to 10-6 M) of Ang I and Ang II. Moreover, cell contraction was significantly reduced in all ACE and AT1R inhibitor-treated groups. Together, these findings suggest that local RAS is active in VICs, and our vTF may provide a powerful platform for valve drug screening and development.

Isolation and culture of adult murine cardiac atrial and ventricular fibroblasts and myofibroblasts

Cardiac fibroblasts play a critical role in extracellular matrix homeostasis, wound healing, and cardiac interstitial fibrosis: the latter being a pathophysiological response to a chronic increase in afterload. Using a standard protocol to isolate cardiac fibroblasts and maintain them in their quiescent phenotype in vitro will enable a better understanding of cardiac fibroblast biology and their role in the response to profibrotic stimuli. Here, we describe an enzymatic method for isolating cardiac fibroblasts. The resulting cells are maintained on either a collagen-coated hydrogel-bound polystyrene (compliant) substrate or standard polystyrene culture dishes (non-compliant) to obtain quiescent fibroblasts and activated fibroblasts (myofibroblasts), respectively. Fibroblasts maintained on a non-compliant substrate developed a myofibroblast phenotype, in which the αSMA immunoreactivity was markedly elevated and incorporated into the stress fibers. In contrast, ventricular and atrial fibroblasts retain their quiescent phenotype for up to 3 passages when maintained on a compliant substrate. Hence, the methodology described herein provides a simple and reproducible way to isolate adult murine atrial and ventricular cardiac fibroblasts from a single animal and, by selecting a substrate with the appropriate compliance, examine the mediators of fibroblast activation or inactivation.

Obesity-induced Vitamin D Deficiency Contributes to Lung Fibrosis and Airway Hyperresponsiveness

Vitamin D (VitD) has pleiotropic effects. VitD deficiency is closely involved with obesity and may contribute to the development of lung fibrosis and aggravation of airway hyperresponsiveness (AHR). We evaluated the causal relationship between VitD deficiency and the lung pathologies associated with obesity. In vivo effects of VitD supplementation were analyzed using high-fat diet (HFD)-induced obese mice and TGF-β1 (transforming growth factor-β1) triple transgenic mice. Effects of VitD supplementation were also evaluated in both BEAS-2B and primary lung cells from the transgenic mice. Obese mice had decreased 25-OH VitD and VitD receptor expressions with increases of insulin resistance, renin and angiotensin-2 system (RAS) activity, and leptin. In addition, lung pathologies such as a modest increase in macrophages, enhanced TGF-β1, IL-1β, and IL-6 expression, lung fibrosis, and AHR were found. VitD supplementation to HFD-induced obese mice recovered these findings. TGF-β1-overexpressing transgenic mice enhanced macrophages in BAL fluid, lung expression of RAS, epithelial-mesenchymal transition markers, AHR, and lung fibrosis. VitD supplementation also attenuated these findings in addition to the attenuation of the expressions of TGF-β1, and phosphorylated Smad-2/3 in lung. Supplementing in vitro-stimulated BEAS-2B and primary lung cells with VitD inhibited TGF-β1 expression, supporting the suppressive effect of VitD for TGF-β1 expression. These results suggest that obesity leads to VitD deficiency and worsens insulin resistance while enhancing the expression of leptin, RAS, TGF-β1, and proinflammatory cytokines. These changes may contribute to the development of lung fibrosis and AHR. VitD supplementation rescues these changes and may have therapeutic potential for asthma with obesity.

Cardiac fibrosis

Myocardial fibrosis, the expansion of the cardiac interstitium through deposition of extracellular matrix proteins, is a common pathophysiologic companion of many different myocardial conditions. Fibrosis may reflect activation of reparative or maladaptive processes. Activated fibroblasts and myofibroblasts are the central cellular effectors in cardiac fibrosis, serving as the main source of matrix proteins. Immune cells, vascular cells and cardiomyocytes may also acquire a fibrogenic phenotype under conditions of stress, activating fibroblast populations. Fibrogenic growth factors (such as transforming growth factor-β and platelet-derived growth factors), cytokines [including tumour necrosis factor-α, interleukin (IL)-1, IL-6, IL-10, and IL-4], and neurohumoral pathways trigger fibrogenic signalling cascades through binding to surface receptors, and activation of downstream signalling cascades. In addition, matricellular macromolecules are deposited in the remodelling myocardium and regulate matrix assembly, while modulating signal transduction cascades and protease or growth factor activity. Cardiac fibroblasts can also sense mechanical stress through mechanosensitive receptors, ion channels and integrins, activating intracellular fibrogenic cascades that contribute to fibrosis in response to pressure overload. Although subpopulations of fibroblast-like cells may exert important protective actions in both reparative and interstitial/perivascular fibrosis, ultimately fibrotic changes perturb systolic and diastolic function, and may play an important role in the pathogenesis of arrhythmias. This review article discusses the molecular mechanisms involved in the pathogenesis of cardiac fibrosis in various myocardial diseases, including myocardial infarction, heart failure with reduced or preserved ejection fraction, genetic cardiomyopathies, and diabetic heart disease. Development of fibrosis-targeting therapies for patients with myocardial diseases will require not only understanding of the functional pluralism of cardiac fibroblasts and dissection of the molecular basis for fibrotic remodelling, but also appreciation of the pathophysiologic heterogeneity of fibrosis-associated myocardial disease.

Epigenetic Control of circHNRNPH1 in Postischemic Myocardial Fibrosis through Targeting of TGF-β Receptor Type I

Postischemic myocardial fibrosis is a factor for the development of cardiac dysfunction and malignant cardiac arrhythmias, and no effective therapy is currently available. Circular RNAs are emerging as important epigenetic players in various biological functions; however, their roles in cardiac fibrosis are unknown. With the use of a rat model of postischemic myocardial fibrosis, we identified an increase in circHNRNPH1 in the ischemic myocardium after myocardial infarction, particularly in cardiac fibroblasts. In cardiac fibroblasts, circHNRNPH1 was responsive to transforming growth factor β1 (TGF-β1), the principal profibrotic factor. The downregulation of circHNRNPH1, in contrast to its overexpression, promoted myofibroblast migration and α-smooth muscle actin and collagen I expression and inhibited myofibroblast apoptosis. The recombinant adeno-associated virus 9 (rAAV9)-mediated, cardiac-specific knockdown of circHNNRPH1 accordingly facilitated cardiac fibrosis and aggravated cardiac dysfunction. Mechanistically, circHNRNPH1 colocalized with and sponged microRNA (miR)-216-5p in the cytoplasm of cardiac fibroblasts to induce SMAD7 (protein family of signal transduction component of the canonical transforming growth factor-β signaling pathway) expression, accelerating the degradation of TGF-β receptor I. Thus, our results indicated that circHNRNPH1 negatively regulates the fibrogenesis of cardiac fibroblasts and may provide a new therapeutic strategy for postischemic myocardial fibrosis.

Localized Antileptin Therapy Prevents Aortic Root Dilatation and Preserves Left Ventricular Systolic Function in a Murine Model of Marfan Syndrome

Background Marfan syndrome (MFS) is a genetically transmitted connective tissue disorder characterized by aortic root dilatation, dissection, and rupture. Molecularly, MFS pathological features have been shown to be driven by increased angiotensin II in the aortic wall. Using an angiotensin II-driven aneurysm mouse model, we have recently demonstrated that local inhibition of leptin activity restricts aneurysm formation in the ascending and abdominal aorta. As we observed de novo leptin synthesis in the ascending aortic aneurysm wall of patients with MFS, we hypothesized that local counteracting of leptin activity in MFS may also prevent aortic cardiovascular complications in this context. Methods and Results Fbn1^C1039G/+ mice underwent periaortic application of low-dose leptin antagonist at the aortic root. Treatment abolished medial degeneration and prevented increase in aortic root diameter (P<0.001). High levels of leptin, transforming growth factor β1, Phosphorylated Small mothers against decapentaplegic 2, and angiotensin-converting enzyme 1 observed in saline-treated MFS mice were downregulated in leptin antagonist-treated animals (P<0.01, P<0.05, P<0.001, and P<0.001, respectively). Leptin and angiotensin-converting enzyme 1 expression levels in left ventricular cardiomyocytes were also decreased (P<0.001) and coincided with prevention of left ventricular hypertrophy and aortic and mitral valve leaflet thickening (P<0.01 and P<0.05, respectively) and systolic function preservation. Conclusions Local, periaortic application of leptin antagonist prevented aortic root dilatation and left ventricular valve remodeling, preserving left ventricular systolic function in an MFS mouse model. Our results suggest that local inhibition of leptin may constitute a novel, stand-alone approach to prevent MFS aortic root aneurysms and potentially other similar angiotensin II-driven aortic pathological features.

Investigation of cardiac fibroblasts using myocardial slices

Aims

Cardiac fibroblasts (CFs) are considered the principal regulators of cardiac fibrosis. Factors that influence CF activity are difficult to determine. When isolated and cultured in vitro, CFs undergo rapid phenotypic changes including increased expression of α-SMA. Here we describe a new model to study CFs and their response to pharmacological and mechanical stimuli using in vitro cultured mouse, dog and human myocardial slices.

Methods and results

Unloading of myocardial slices induced CF proliferation without α-SMA expression up to 7 days in culture. CFs migrating onto the culture plastic support or cultured on glass expressed αSMA within 3 days. The cells on the slice remained αSMA(−) despite transforming growth factor-β (20 ng/ml) or angiotensin II (200 µM) stimulation. When diastolic load was applied to myocardial slices using A-shaped stretchers, CF proliferation was significantly prevented at Days 3 and 7 (P < 0.001).

Conclusions

Myocardial slices allow the study of CFs in a multicellular environment and may be used to effectively study mechanisms of cardiac fibrosis and potential targets.

Angiotensin, transforming growth factor β and aortic dilatation in Marfan syndrome: Of mice and humans

Marfan syndrome is consequent upon mutations in FBN1, which encodes the extracellular matrix microfibrillar protein fibrillin-1. The phenotype is characterised by development of thoracic aortic aneurysm. Current understanding of the pathogenesis of aneurysms in Marfan syndrome focuses upon abnormal vascular smooth muscle cell signalling through the transforming growth factor beta (TGFβ) pathway. Angiotensin II (Ang II) can directly induce aortic dilatation and also influence TGFβ synthesis and signalling. It has been hypothesised that antagonism of Ang II signalling may protect against aortic dilatation in Marfan syndrome. Experimental studies have been supportive of this hypothesis, however results from multiple clinical trials are conflicting. This paper examines current knowledge about the interactions of Ang II and TGFβ signalling in the vasculature, and critically interprets the experimental and clinical findings against these signalling interactions.

(Pro)renin Receptor Blockade Ameliorates Cardiac Injury and Remodeling and Improves Function After Myocardial Infarction

BACKGROUND

The (pro)renin receptor [(P)RR] is implicated in the pathogenesis of cardiovascular disease. We investigated the effects of (P)RR blockade after myocardial infarction (MI) in a mouse coronary-ligation model.

METHODS AND RESULTS

Mice underwent sham control surgeries (n = 8) or induction of MI followed by 28 days' treatment with a vehicle control (n = 8) or (P)RR antagonist (n = 8). Compared with sham control subjects, MI + vehicle mice demonstrated reduced left ventricular (LV) ejection fraction (LVEF: P < .001) and fractional shortening (P < .001), and increased LV end-systolic and -diastolic volumes (LVESV: P < .001; LVEDV: P < .001) 28 days after MI. In addition, MI decreased LV posterior wall and septal diameters (both P < .001), increased heart weight-body weight ratios (P < .05), LV collagen deposition, and cardiomyocyte diameter (both P < .001), and up-regulated collagen 1 (P < .01) and β-myosin heavy chain (β-MHC: P < .05) mRNA. Compared with MI + vehicle mice, (P)RR antagonism after MI reduced infarct size (P < .01), improved LVEF (P < .001), fractional shortening (P < .001), and stroke volume (P < .05), and decreased LVESV (P < .001) and LVEDV (P < .001). (P)RR antagonism also reversed MI-induced transmural thinning (P < .001) and reduced LV fibrosis (P < .01), cardiomyocyte size (P < .001), and ventricular collagen 1 (P < .01), β-MHC (P = .06), transforming growth factor β1 (P < .01), and angiotensin-converting enzyme (P < .05) expression.

CONCLUSIONS

The present study found that (P)RR blockade after MI in mice ameliorates infarct size, cardiac fibrosis/hypertrophy, and cardiac dysfunction and identifies the receptor as a potential therapeutic target in this setting.

Inhibitory effects of C-type natriuretic peptide on the differentiation of cardiac fibroblasts, and secretion of monocyte chemoattractant protein-1 and plasminogen activator inhibitor-1

The present study aimed to investigate the effect of C-type natriuretic peptide (CNP) on the function of cardiac fibroblasts (CFs). Western blotting was used to investigate the expression of myofibroblast marker proteins: α-smooth muscle actin (α-SMA), extra domain-A fibronectin, collagen I and collagen III, and the activity of extracellular signal-regulated kinase 1/2 (ERK1/2). Immunofluorescence was used to examine the morphological changes; a transwell assay was used to analyze migration, and reverse transcription-quantitative polymerase chain reaction and ELISA were employed to determine the mRNA expression and protein secretion of monocyte chemoattractant protein-1 (MCP-1) and plasminogen activator inhibitor-1 (PAI-1). The results demonstrated that CNP significantly reduced the protein expression of α-SMA, fibronectin, collagen I and collagen III, and suppressed the migratory ability of CFs. Additionally, the mRNA and protein expression of MCP-1 and PAI-1 was inhibited under the CNP treatment; and this effect was mediated by the inhibition of the ERK1/2 activity. In conclusion, CNP inhibited cardiac fibroblast differentiation and migration, and reduced the secretion of MCP-1 and PAI-1, which demonstrates novel mechanisms to explain the antifibrotic effect of CNP.

The role of transforming growth factor β1 in the regulation of blood pressure

Although human association studies suggest a link between polymorphisms in the gene encoding transforming growth factor (TGF) β1 and differing blood pressure levels, a causative mechanism for this correlation remains elusive. Recently we have generated a series of mice with graded expression of TGFβ1, ranging from approximately 10% to 300% compared to normal. We have found that blood pressure and plasma volume are negatively regulated by TGFβ1. Of note, the 10% hypomorph exhibits primary aldosteronism and markedly impaired urinary excretion of water and electrolytes. We here review previous literature highlighting the importance of TGFβ signaling as a natriuretic system, which we postulate is a causative mechanism explaining how polymorphisms in TGFβ1 could influence blood pressure levels.

Reversible and irreversible differentiation of cardiac fibroblasts

AIMS

Differentiation of cardiac fibroblasts (Fbs) into myofibroblasts (MyoFbs) is responsible for connective tissue build-up in myocardial remodelling. We examined MyoFb differentiation and reversibility.

METHODS AND RESULTS

Adult rat cardiac Fbs were cultured on a plastic substratum providing mechanical stress, with conditions to obtain different levels of Fb differentiation. Fb spontaneously differentiated to proliferating MyoFb (p-MyoFb) with stress fibre formation decorated with alpha-smooth muscle actin (α-SMA). Transforming growth factor-β1 (TGF-β1) promoted differentiation into α-SMA-positive MyoFb showing near the absence of proliferation, i.e. non-p-MyoFb. SD-208, a TGF-β-receptor-I (TGF-β-RI) kinase blocker, inhibited p-MyoFb differentiation as shown by stress fibre absence, low α-SMA expression, and high proliferation levels. Fb seeded in collagen matrices induced no contraction, whereas p-MyoFb and non-p-MyoFb induced 2.5- and four-fold contraction. Fb produced little collagen but high levels of interleukin-10. Non-p-MyoFb had high collagen production and high monocyte chemoattractant protein-1 and tissue inhibitor of metalloproteinases-1 levels. Transcriptome analysis indicated differential activation of gene networks related to differentiation of MyoFb (e.g. paxilin and PAK) and reduced proliferation of non-p-MyoFb (e.g. cyclins and cell cycle regulation). Dedifferentiation of p-MyoFb with stress fibre de-polymerization, but not of non-p-MyoFb, was induced by SD-208 despite maintained stress. Stress fibre de-polymerization could also be induced by mechanical strain release in p-MyoFb and non-p-MyoFb (2-day cultures in unrestrained 3-D collagen matrices). Only p-MyoFb showed true dedifferentiation after long-term 3-D cultures.

CONCLUSIONS

Fb, p-MyoFb, and non-p-MyoFb have a distinct gene expression, ultrastructural, and functional profile. Both reduction in mechanical strain and TGF-β-RI kinase inhibition can reverse p-MyoFb differentiation but not non-p-MyoFb.

Phenanthrene exposure produces cardiac defects during embryo development of zebrafish (Danio rerio) through activation of MMP-9

Phenanthrene (Phe) is one of the most abundant polycyclic aromatic hydrocarbons in the aquatic environment as a result of human activities. It is widely accepted that Phe has cardiotoxic effects. Even so, knowledge concerning the mechanism(s) of cardiac development toxicity is still limited. In this study, we exposed zebrafish embryos to environmentally relevant concentrations of Phe and then investigated its cardiotoxic effects and the mechanism(s) involved. Some cardiac morphogenetic defects, which was characterized by an abnormally looped and enlarged heart, dilated and thinner ventricular wall, and increased interstitial fibrosis, were observed in the Phe treated groups. The mRNA and protein expression levels of matrix metalloproteinase-9 (MMP-9), as well as the MMP-9 activity, were induced. Moreover, during co-treatment of the zebrafish embryos with MMP-9 inhibitor, the cardiac defects caused by Phe were attenuated. In addition, Phe exposure led to an up-regulation of transforming growth factor β (TGF-β), which plays a crucial role in mediating cardiac fibrosis. Taken together, our data indicated that the exposure to Phe of zebrafish embryos disrupted normal cardiac development, and that the cardiac defects induced by Phe were mediated by the MMP-9, while TGF-β was also involved in these cardiac defects.

Qindan capsule changes adventitial collagen synthesis in spontaneously hypertensive rats

OBJECTIVE

To investigate the effect of Qindan capsule (QC) on collagen synthesis and the mechanism underlying the process in spontaneously hypertensive rats (SHRs).

METHODS

Twentyfour SHRs were divided into three groups: the hypertension model group, the QC treatment group, and the losartan treatment group. Eight Wistar Kyoto (WKY) rats were used as the normal control group. The systolic blood pressure (SBP) of the rats was monitored, and the thoracic aorta adventitia of the rats was segregated. The expressions of transforming growth factor 1 (TGF-β1), Smad3, and collagens I and were measured by histological staining and reverse transcription polymerase chain reaction.

RESULTS

The SBP was significantly higher in the model group than in the normal control group (P<0.01). However, a significant SBP-lowering effect was observed in QC or losartan treatment groups (P<0.05 or P<0.01) after 3 weeks of treatment. QC-treated rats showed a decrease of approximately 40 mm Hg, and the losartan-treated rats showed a decrease of approximately 50 mm Hg at the end of treatment compared with the beginning of treatment. The protein and gene levels of TGF-β1, Smad3, and collagens I and in the model group were significantly increased compared with those in the normal control group (P<0.01). However, the levels were significantly decreased in the QC or losartan treatment group compared with the model group (P<0.05 or P<0.01). However, there was no significant difference between the QC and losartan treatment groups (P<0.05).

CONCLUSIONS

QC could exert its antihypertensive effect through down-regulating TGF-β1-stimulated collagen expressions. The TGF-β1/Smad3 signaling pathway may be involved in this process.

TGF-β signalling and reactive oxygen species drive fibrosis and matrix remodelling in myxomatous mitral valves

AIMS

Myxomatous mitral valve disease (MMVD) is associated with leaflet thickening, fibrosis, matrix remodelling, and leaflet prolapse. Molecular mechanisms contributing to MMVD, however, remain poorly understood. We tested the hypothesis that increased transforming growth factor-β (TGF-β) signalling and reactive oxygen species (ROS) are major contributors to pro-fibrotic gene expression in human and mouse mitral valves.

METHODS AND RESULTS

Using qRT-PCR, we found that increased expression of TGF-β1 in mitral valves from humans with MMVD (n = 24) was associated with increased expression of connective tissue growth factor (CTGF) and matrix metalloproteinase 2 (MMP2). Increased levels of phospho-SMAD2/3 (western blotting) and expression of SMAD-specific E3 ubiquitin-protein ligases (SMURF) 1 and 2 (qRT-PCR) suggested that TGF-β1 signalling occurred through canonical signalling cascades. Oxidative stress (dihydroethidium staining) was increased in human MMVD tissue and associated with increases in NAD(P)H oxidase catalytic subunits (Nox) 2 and 4, occurring despite increases in superoxide dismutase 1 (SOD1). In mitral valves from SOD1-deficient mice, expression of CTGF, MMP2, Nox2, and Nox4 was significantly increased, suggesting that ROS can independently activate pro-fibrotic and matrix remodelling gene expression patterns. Furthermore, treatment of mouse mitral valve interstitial cells with cell permeable antioxidants attenuated TGF-β1-induced pro-fibrotic and matrix remodelling gene expression in vitro.

CONCLUSION

Activation of canonical TGF-β signalling is a major contributor to fibrosis and matrix remodelling in MMVD, and is amplified by increases in oxidative stress. Treatments aimed at reducing TGF-β activation and oxidative stress in early MMVD may slow progression of MMVD.

Conundrum of angiotensin II and TGF-β interactions in aortic aneurysms

Angiotensin II (AngII) has been invoked as a principal mediator for the development and progression of both thoracic and abdominal aortic aneurysms. While there is consistency in experimental and clinical studies that overactivation of the renin angiotensin system promotes aortic aneurysm development, there are many unknowns regarding the mechanistic basis underlying AngII-induced aneurysms. Interactions of AngII with TGF-β in both thoracic and abdominal aortic aneurysms have been the focus of recent studies. While these studies have demonstrated profound effects of manipulating TGF-β activity on AngII-induced aortic aneurysms, they have also led to more questions regarding the interactions between AngII and this multifunctional cytokine. This review compiled the recent literature to provide insights into understanding the potentially complex interactions between AngII and TGF-β in the development of aortic aneurysms.

In vitro effects of pirfenidone on cardiac fibroblasts: proliferation, myofibroblast differentiation, migration and cytokine secretion

Cardiac fibroblasts (CFs) are the primary cell type responsible for cardiac fibrosis during pathological myocardial remodeling. Several studies have illustrated that pirfenidone (5-methyl-1-phenyl-2-[1H]-pyridone) attenuates cardiac fibrosis in different animal models. However, the effects of pirfenidone on cardiac fibroblast behavior have not been examined. In this study, we investigated whether pirfenidone directly modulates cardiac fibroblast behavior that is important in myocardial remodeling such as proliferation, myofibroblast differentiation, migration and cytokine secretion. Fibroblasts were isolated from neonatal rat hearts and bioassays were performed to determine the effects of pirfenidone on fibroblast function. We demonstrated that treatment of CFs with pirfenidone resulted in decreased proliferation, and attenuated fibroblast α-smooth muscle actin expression and collagen contractility. Boyden chamber assay illustrated that pirfenidone inhibited fibroblast migration ability, probably by decreasing the ratio of matrix metalloproteinase-9 to tissue inhibitor of metalloproteinase-1. Furthermore, pirfenidone attenuated the synthesis and secretion of transforming growth factor-β1 but elevated that of interleukin-10. These direct and pleiotropic effects of pirfenidone on cardiac fibroblasts point to its potential use in the treatment of adverse myocardial remodeling.

Antifibrotic properties of c-Ski and its regulation of cardiac myofibroblast phenotype and contractility

Cardiac myofibroblasts are key players in chronic remodeling of the cardiac extracellular matrix, which is mediated in part by elevated transforming growth factor-β₁ (TGF-β₁). The c-Ski proto-oncoprotein has been shown to modify TGF-β₁ post-receptor signaling through receptor-activated Smads (R-Smads); however, little is known about how c-Ski regulates fibroblast phenotype and function. We sought to elucidate the function of c-Ski in primary cardiac myofibroblasts using a c-Ski overexpression system. Cardiac myofibroblasts expressed three forms of c-Ski with the predominant band at 105 kDa, and adenoviral c-Ski treatment resulted in overexpression of 95-kDa c-Ski in cellular nuclei. Exogenous c-Ski led to significant inhibition of type I collagen secretion and myofibroblast contractility using two-dimensional semifloating gel contraction assay in both basal and with TGF-β₁ (10 ng/ml for 24 h) stimulation. Overexpressed c-Ski did not inhibit nuclear translocation of phosphorylated R-Smad2, despite their binding, as demonstrated by immunoprecipitation. Acute treatment of primary myofibroblasts with TGF-β₁ in vitro revealed a marked nuclear shuttling of c-Ski at 24 and 48 h following stimulation. Remarkably, overexpression of c-Ski led to a stepwise reduction of the myofibroblast marker α-smooth muscle actin with increasing multiplicity of infection, and these results indicate that 95-kDa c-Ski overexpression may effect a loss of the myofibroblastic phenotype. Furthermore, adenovirus (Ad) for hemagglutinin-tagged c-Ski infection led to a reduction in the number of myofibroblasts versus Ad-LacZ-infected and uninfected controls, due to induction of apoptosis. Finally, we observed a significant increase in 105-kDa c-Ski in the cytosolic fraction of cells of the infarct scar and adjacent remnant myocardium vs. noninfarcted controls.

Effects of arginine vasopressin on differentiation of cardiac fibroblasts into myofibroblasts

BACKGROUND

Differentiation of cardiac fibroblasts (CFs) into myofibroblasts is a critical event in the initiation of myocardial fibrosis (MF). Previous studies have shown that arginine vasopressin (AVP) facilitates MF. However, the effects of AVP on CFs-myofibroblasts transformation, and its possible mechanisms are still unknown.

METHODS

CFs obtained from neonatal Sprague-Dawley rats were stimulated with AVP in the absence or presence of AVP V1a receptor specific antagonist [d(CH2)5Tyr(Me)]AVP. CFs-myofibroblast transformation was detected by expression of alpha-smooth muscle actin (alpha-SMA) and collagen synthesis. Western bolt and immunofluorescent staining were used to detect expression of alpha-SMA, [H]Proline incorporation was used to detect collagen synthesis. AVP-induced transforming growth factor-beta1 (TGF-beta1) secretion was detected by enzyme-linked immunosorbent assay. CFs was also stimulated with exogenous TGF-beta1 to find out the required dose to induce CFs-myofibroblast transformation.

RESULTS

10 mol/L AVP increased alpha-SMA expression and collagen synthesis significantly, and this effect was blocked by [d(CH2)5Tyr(Me)]AVP at the concentration of 10 mol/L. Meanwhile, AVP significantly increased TGF-beta1 secretion of CFs in a dose-dependent manner, and this effect was also blocked by 10 mol/L [d(CH2)5Tyr(Me)]AVP. However, the maximum production of biologic active TGF-beta1 induced by AVP is far less than the dose of exogenous TGF-beta1 needed to induce CFs-myofibroblast transformation.

CONCLUSIONS

AVP can induce CFs-myofibroblast transformation via its V1a receptor, AVP-induced increase of TGF-beta1 synthesis, which also is mediated by V1a receptor, may play a minor role in the transformation. Inducing differentiation of CFs into myofibroblasts may be a mechanism of AVP contributing to MF.

Stromal cell biology--a way to understand the evolution of cardiovascular diseases

Stromal cells, composed of fibroblasts, microvascular endothelial cells, immune cells and inflammatory cells, are critical determinants of the mechanical properties and function of the heart and vasculature, and the mechanisms whereby these types of cells are activated are important to understand the progression of cardiovascular diseases. Emerging studies have suggested that the activation of autocrine and paracrine signaling pathways by stromal cell-derived growth factors, cytokines and bioactive molecules contributes to disease progression. Disruption of the stromal network will result in alterations in the geometry and function in these organs. Interventions targeting the stromal cells (eg, myofibroblasts, microvascular endothelial cells, inflammatory cells) by pharmacological agents or direct gene delivery/small interfering RNA would be potential novel therapeutic strategies to prevent/attenuate the progression of cardiovascular disorders.

Early expression of monocyte chemoattractant protein-1 correlates with the onset of isoproterenol-induced cardiac fibrosis in rats with distinct angiotensin-converting enzyme polymorphism

INTRODUCTION

Isoproterenol treatment of Brown Norway and Lewis rats (high and low plasma angiotensin-I-converting enzyme activity, respectively) results in similar cardiac hypertrophy but higher cardiac fibrosis in Brown Norway rats.

MATERIALS AND METHODS

Rats were infused in vivo with isoproterenol for two or 10 days. Cardiac fibrosis and inflammation were evaluated histochemically. We measured the mRNAs of pro-fibrotic factors (transforming growth factor beta(1), endothelin-1) and pro-inflammatory factors (monocyte chemoattractant protein-1). In studies with cardiac fibroblasts incubated with isoproterenol in vitro , we measured cell proliferation, angiotensin-I-converting enzyme and matrix metalloprotease 2 activities and deposition of collagen type I and fibronectin.

RESULTS

After treatment with isoproterenol for two days, there were large areas of myocardial injury and numerous inflammatory foci in the left ventricle, these being greater in Brown-Norway than in Lewis rats. After treatment with isoproterenol for 10 days, there were large areas of damage with extensive collagen deposition only in the left ventricle; both strains exhibited this damage which was, however, more severe in Brown-Norway than in Lewis rats. After treatment with isoproterenol for two, but not 10, days, greater amounts of monocyte chemoattractant protein-1 mRNA were found in Brown Norway than in Lewis rats. Cell proliferation, activities of angiotensin-I-converting enzyme and matrix metalloprotease 2, amounts of collagen type I and fibronectin were similar in cardiac fibroblasts from both strains; changes after isoproterenol (10 microM) were also similar in both strains.

CONCLUSION

We conclude that the greater cardiac fibrosis in Brown Norway rats treated with isoproterenol correlates with the early and higher expression of proinflammatory factors.

Pressure-independent effects of pharmacological stimulation of soluble guanylate cyclase on fibrosis in pressure-overloaded rat heart

Cardiac fibrosis is a hallmark of cardiovascular remodeling associated with hypertension. The purpose of this study was to explore the effect and mechanism of soluble guanylate cyclase (sGC) stimulator BAY 41-2272, leading to intracellular cyclic guanosine monophosphate (cGMP) elevation, on the remodeling process induced by pressure overload. Seven-week-old male Wistar rats with hypertension induced by suprarenal aortic constriction (AC) were treated orally with 2 mg kg(-1) day(-1) of BAY 41-2272 for 14 days. BAY 41-2272 had no effects on blood pressure, but decreased AC-induced collagen accumulation in the left ventricle (LV), inhibiting the number of myofibroblasts and gene expressions of transforming growth factor-beta1 and type 1 collagen. In addition, the antifibrotic action of BAY 41-2272 was accompanied by reducing AC-induced angiotensin-converting enzyme (ACE) mRNA and its enzymatic activity, and angiotensin II concentration in LV. In cultured cardiac fibroblasts, BAY 41-2272 inhibited ACE synthesis and myofibroblast transformation, accompanied by elevating the intracellular cGMP concentration. These results suggest that sGC stimulator BAY 41-2272 might be effective to reduce fibrosis in hypertensive heart disease by attenuating angiotensin II generation through myofibroblast transformation.

Inhibition of superoxide dismutase induces collagen production in cardiac fibroblasts

BACKGROUND

The aim of this study was to determine whether inhibition of superoxide dismutase (SOD) with diethyldithiocarbamic acid (DETC) could affect the collagen production, the mRNA and protein expression of collagen types I and III, and fibronectin in control and angiotensin II (ANG II)-treated cardiac fibroblasts. Its effect was compared with the SOD mimetics tempol and EUK-8 and with polyethyleneglycol (PEG)-SOD.

METHODS

Cardiac fibroblasts were cultured to confluence, incubated in serum-free Dulbecco's modified Eagle's medium for 24 h, preincubated with(out) the tested inhibitors for 1 h and further incubated with(out) ANG II (1 micromol/l) for 24 h.

RESULTS

DETC dose-dependently inhibited the activity of CuZn-SOD in cardiac fibroblasts. Superoxide anion production was increased by DETC and decreased by tempol in control and ANG II-treated fibroblasts. DETC also reduced the intracellular generation of reactive oxygen species (ROS) (such as H2O2, hydroxyl radicals, hydroperoxides) in control and ANG II-treated fibroblasts, whereas tempol reduced the ROS production only in ANG II-treated fibroblasts. ANG II and DETC stimulated the collagen production and the collagen I and fibronectin content in fibroblasts. The SOD mimetics tempol and EUK-8 as well as PEG-SOD reduced the collagen production. ANG II and DETC stimulated the tissue inhibitor of metalloproteinase-1 (TIMP-1) and TIMP-2 levels, whereas tempol decreased the TIMP-2 content in control and ANG II-treated fibroblasts. Matrix metalloproteinase (MMP)-1 level was reduced by ANG II and DETC and increased by tempol.

CONCLUSION

These data suggest a vital role of SOD and the formed ROS in the accumulation of collagen in cardiac fibroblasts.

Atrial fibrosis: mechanisms and clinical relevance in atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia in the clinical setting, and traditional pharmacological approaches have proved to have important weaknesses. Structural remodeling has been observed in both clinical and experimental AF paradigms, and is an important feature of the AF substrate, producing fibrosis that alters atrial tissue composition and function. The precise mechanisms underlying atrial fibrosis are not fully elucidated, but recent experimental studies and clinical investigations have provided valuable insights. A variety of signaling systems, particularly involving angiotensin II and related mediators, seem to be centrally involved in the promotion of fibrosis. This paper reviews the current understanding of how atrial fibrosis creates a substrate for AF, summarizes what is known about the mechanisms underlying fibrosis and its progression, and highlights emerging therapeutic approaches aimed at attenuating structural remodeling to prevent AF.

TGF-beta1-induced cardiac myofibroblasts are nonproliferating functional cells carrying DNA damages

TGF-beta1 induces differentiation and total inhibition of cardiac MyoFb cell division and DNA synthesis. These effects of TGF-beta1 are irreversible. Inhibition of MyoFb proliferation is accompanied with the expression of Smad1, Mad1, p15Ink4B and total inhibition of telomerase activity. Surprisingly, TGF-beta1-activated MyoFbs are growth-arrested not only at G1-phase but also at S-phase of the cell cycle. Staining with TUNEL indicates that these cells carry DNA damages. However, the absolute majority of MyoFbs are non-apoptotic cells as established with two apoptosis-specific methods, flow cytometry and caspase-dependent cleavage of cytokeratin 18. Expression in MyoFbs of proliferative cell nuclear antigen even in the absence of serum confirms that these MyoFbs perform repair of DNA damages. These results suggest that TGF-beta1-activated MyoFbs can be growth-arrested by two checkpoints, the G1/S checkpoint, which prevents cells from entering S-phase and the intra-S checkpoint, which is activated by encountering DNA damage during the S phase or by unrepaired damage that escapes the G1/S checkpoint. Despite carrying of the DNA damages TGF-beta1-activated MyoFbs are highly functional cells producing lysyl oxidase and contracting the collagen matrix.

Genetic polymorphisms of the RAS-cytokine pathway and chronic kidney disease

Chronic kidney disease (CKD) in children is irreversible. It is associated with renal failure progression and atherosclerotic cardiovascular (CV) abnormalities. Nearly 60% of children with CKD are affected since birth with congenital or inherited kidney disorders. Preliminary evidence primarily from adult CKD studies indicates common genetic risk factors for CKD and atherosclerotic CV disease. Although multiple physiologic pathways share common genes for CKD and CV disease, substantial evidence supports our attention to the renin angiotensin system (RAS) and the interlinked inflammatory cascade because they modulate the progressions of renal and CV disease. Gene polymorphisms in the RAS-cytokine pathway, through altered gene expression of inflammatory cytokines, are potential factors that modulate the rate of CKD progression and CV abnormalities in patients with CKD. For studying such hypotheses, the cooperative efforts among scientific groups and the availability of robust and affordable technologies to genotype thousands of single nucleotide polymorphisms (SNPs) across the genome make genome-wide association studies an attractive paradigm for studying polygenic diseases such as CKD. Although attractive, such studies should be interpreted carefully, with a fundamental understanding of their potential weaknesses. Nevertheless, whole-genome association studies for diabetic nephropathy and future studies pertaining to other types of CKD will offer further insight for the development of targeted interventions to treat CKD and associated atherosclerotic CV abnormalities in the pediatric CKD population.

Differential and combined effects of cardiotrophin-1 and TGF-β1 on cardiac myofibroblast proliferation and contraction

Myofibroblasts respond to an array of signals from mitogens and cytokines during the course of wound healing following a myocardial infarction (MI), and these signals may coordinate ventricular myofibroblast proliferation. Furthermore, myofibroblasts are contractile and contribute to wound contraction by imparting mechanical tension on surrounding extracellular matrix. Although TGF-β1, CT-1, and PDGF-BB participate in various stages of post-MI wound healing, their combined net effect(s) on myofibroblast function is unknown. We investigated myofibroblast proliferation, expression of cell cycle proteins, and contractile function of cells treated with TGF-β1 and/or CT-1. We confirmed that TGF-β1 (10 ng/ml) suppresses proliferation of these cells, whereas CT-1 (10 ng/ml) and, for comparative purposes, PDGF-BB (1 ng/ml) treatments were associated with proliferation. Specific TGF-β1 treatment ablated CT-1-induced myofibroblast proliferation. TGF-β1 effects were specific, as they were suppressed by either TGF-β-neutralizing antibody or viral Smad7 overexpression. TGF-β1 treatment also increased expression of p27 and decreased expression of cyclin E and Cdk2 in primary cells. CT-1 (10 ng/ml) treatment of myofibroblasts had no effect on collagen gel deformation versus controls, whereas TGF-β1 (10 ng/ml) and PDGF (10 ng/ml) treatments were associated with significant cell contraction; again, TGF-β1-mediated contraction was unaffected by CT-1. Alone, CT-1 and TGF-β1 treatments exert opposing effects on myofibroblast function, whereas in combination TGF-β1-mediated effects supersede those of CT-1 (and PDGF-BB). Thus TGF-β1 and CT-1 exert differential effects on myofibroblast proliferation and contraction in vitro, and we suggest that a balance of these effects may be important for the execution of normal cardiac wound healing.

Regulation of collagen synthesis by inhibitory Smad7 in cardiac myofibroblasts

Transforming growth factor-beta(1) (TGF-beta(1)) signal and downstream Smads play an important role in tissue fibrosis and matrix remodeling in various etiologies of heart failure. Inhibitory Smad7 (I-Smad7) is an inducible regulatory Smad protein that antagonizes TGF-beta(1) signal mediated via direct abrogation of R-Smad phosphorylation. The effect of ectopic I-Smad7 on net collagen production was investigated using hydroxyproline assay. Adenovirus-mediated I-Smad7 gene (at 100 multiplicity of infection) transfer was associated with significant decrease of collagen synthesis in the presence and absence of TGF-beta(1) in primary rat cardiac myofibroblasts. In I-Smad7-infected cells, we also observed the ablation of TGF-beta(1)-induced R-Smad2 phosphorylation vs. LacZ controls. Overdriven I-Smad7 was associated with significantly increased expression of immunoreactive 65-kDa matrix metalloproteinase-2 (MMP-2) protein in culture medium of myofibroblast compared with LacZ-infected cells. Expression of the 72-kDa MMP-2 variant, e.g., the inactive form, was not altered by exogenous I-Smad7 transfection/overexpression. Furthermore, I-Smad7 overexpression was associated with a significant increase and decrease in expression of p27 and phospho-Rb protein, respectively, as well as reduced [(3)H]thymidine incorporation vs. Ad-LacZ-infected controls. We suggest that negative modulation of R-Smad phosphorylation by ectopic I-Smad7 may contribute to the downregulation of collagen in cardiac myofibroblasts and may suppress the proliferation of these cells. Thus treatments targeting the collagen deposition by overexpression of I-Smad7 may provide a new therapeutic strategy for cardiac fibrosis.

Angiotensin II-stimulated collagen production in cardiac fibroblasts is mediated by reactive oxygen species

OBJECTIVE

The aim of the present study was to determine whether inhibition of reduced nicotinamide adenine dinucleotide (phosphate) [NAD(P)H] oxidase and of various superoxide generating systems could affect the collagen production, the mRNA and protein expression of collagen types I and III in control and angiotensin II-treated cardiac fibroblasts.

METHODS

Cardiac fibroblasts from passage 2 from normal male adult rats were cultured to confluency and incubated in serum-free Dulbecco's modified Eagle's medium for 24 h. The cells were then preincubated with(out) the tested inhibitors for 1 h and then further incubated with(out) angiotensin II (1 micromol/l) for 24 h. Collagen production was measured spectrophotometrically with picrosirius red as dye and with [3H]proline incorporation; collagen type I and III content by enzyme-linked immunosorbent assay and collagen type I and III mRNA expression by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR). NAD(P)H-dependent superoxide anion production was assayed as superoxide dismutase-inhibitable cytochrome c reduction. Intracellular formation of reactive oxygen species was assessed with 2',7'-dichlorofluorescein diacetate as fluorescent probe.

RESULTS

Angiotensin II stimulated the collagen production, the collagen I and III content and mRNA expression in cardiac fibroblasts, and apocynin, a membrane NAD(P)H oxidase inhibitor, abolished this induction. Rotenone, allopurinol, indomethacin, nordihydroguiaretic acid, ketoconazole and nitro-L-arginine (inhibitors of mitochondrial NAD(P)H oxidase, xanthine oxidase, cyclooxygenase, lipoxygenase, cytochrome P450 oxygenase and nitric oxide synthase, respectively) did not affect the angiotensin II-induced collagen production. Angiotensin II increased the NAD(P)H-dependent superoxide anion production and the intracellular generation of reactive oxygen species in cardiac fibroblasts, and apocynin abrogated this rise.

CONCLUSIONS

Our data show that in adult rat cardiac fibroblasts the membrane-associated NAD(P)H oxidase complex is the predominant source of superoxide anion and reactive oxygen species generation in angiotensin II-stimulated adult cardiac fibroblasts. Inhibition of this NAD(P)H oxidase complex with apocynin completely blocked the angiotensin II-stimulated collagen production, and collagen I and III protein and mRNA expression.

Transforming growth factor-beta1 induces transdifferentiation of fibroblasts into myofibroblasts in hypoxic pulmonary vascular remodeling

The muscularization of non-muscular pulmonary arterioles is an important pathological feature of hypoxic pulmonary vascular remodeling. However, the origin of the cells involved in this process is still not well understood. The present study was undertaken to test the hypothesis that transforming growth factor-beta1 (TGF-beta1) can induce transdifferentiation of fibroblasts into myofibroblasts, which might play a key role in the muscularization of non-muscular pulmonary arterioles. It was found that mean pulmonary arterial pressure increased significantly after 7 d of hypoxia. Pulmonary artery remodeling index and right ventricular hypertrophy became evident after 14 d of hypoxia. The distribution of nonmuscular, partially muscular, and muscular vessels was significantly different after 7 d of hypoxia. Immunocytochemistry results demonstrated that the expression of a-smooth muscle actin was increased in intra-acinar pulmonary arteries with increasing hypoxic time. TGF-beta1 mRNA expression in pulmonary arterial walls was increased significantly after 14 d of hypoxia, but showed no obvious changes after 3 or 7 d of hypoxia. In pulmonary tunica adventitia and tunica media, TGF-beta1 protein staining was poorly positive in control rats, but was markedly enhanced after 3 d of hypoxia, reaching its peak after 7 d of hypoxia. The myofibroblast phenotype was confirmed by electron microscopy, which revealed microfilaments and a well-developed rough endoplasmic reticulum. Taken together, our results suggested that TGF-beta1 induces transdifferentiation of fibroblasts into myofibroblasts, which is important in hypoxic pulmonary vascular remodeling.

How hematopoietic stem cells know and act in cardiac microenvironment for stem cell plasticity? Impact of local renin-angiotensin systems

Bone marrow-derived hematopoietic stem cells (HSC) can exhibit tremendous differentiation activity in numerous non-hematopoietic organs. This enigmatic process is called as 'stem cell plasticity' (SCP). HSC may promote structural and functional repair in several organs such as heart, liver, brain, and skeletal muscle via the SCP. The differentiation capacity of HSC is dependent on the specific signals present in the local tissue microenvironment. Those specific molecular signals required for the interactions of HSC and host tissues are currently unknown. The aim of this report is to propose a hypothesis on how HSC reach, recognize, and function in cardiac tissues in the context of SCP. Locally signaling cardiac microenvironment is essential for the seeding, expansion, and 'cardiomyocyte differentiation' of the HSC in the heart. Our hypothesis is that the receptors, ligands, and signaling pathways of the tissue renin-angiotensin system (RAS) serve as the link between HSC and local cardiac microenvironment in SCP. The RAS is considered as a 'tissue-based system' exhibiting paracrine functions within many organs. The presence of local hematopoietic bone marrow RAS and local cardiac RAS have been suggested. Both local tissue RASs share similar angiotensin peptide-signaling pathways such as JAK-STAT and mitogen-activated protein kinases. HSC have angiotensin type I (AT1a) receptors for the binding of angiotensin II, the active component of the RAS. Binding of angiotensin II to AT1a can increase hematopoietic progenitor cell proliferation. Local cardiac RAS has critical (patho)biological functions in the cardiomyocyte survival, renewal, and growth, as well as in cardiac remodeling. Therefore, the components of the local cardiac RAS and hematopoietic RAS could interact with each other during the SCP through myocardial tissue repair. Activation of the local myocardial RAS after injury may be related to homing and engraftment of the HSC to the cardiac tissue. Regenerating myocardial tissue may exert regulatory functions on circulating or resident HSC via the locally active RAS. Understanding the exact molecular basis of SCP in relation to local tissue RAS could offer new frontiers in the better management of ischemic cardiac diseases.

Reversal of Angiotensin II-Stimulated Collagen Gel Contraction in Cardiac Fibroblasts by Aminopeptidase Inhibition

The purpose of this investigation was to determine whether aminopeptidase inhibition could affect the angiotensin II-stimulated collagen gel contraction in basal (control) and TGF-beta1-treated cardiac fibroblasts (or myofibroblasts). The tested aminopeptidase inhibitors were the broad range aminopeptidase inhibitor bestatin, the specific inhibitor of alanine aminopeptidase leuhistin, and the specific inhibitor of arginine aminopeptidase arphamenine A. Cardiac fibroblasts (from normal male adult rats) from passage 2 were cultured to confluency and incubated with(out) 400 pmol/L TGF-beta1 in Dulbecco Modified Eagle Medium (DMEM) with 10% fetal bovine serum (FBS). These fibroblasts were then further incubated in a floating collagen gel lattice with the tested products (angiotensin II, bestatin, leuhistin, or arphamenine A) for 3 days in DMEM without FBS. The contraction of the collagen gel lattice by cardiac fibroblasts was determined by measuring the gel volume with tritiated water. Aminopeptidase activity was estimated by spectrophotometric determination of the liberation of p-nitroaniline from alanine- or arginine-p-nitroanilide. Angiotensin II (100 nmol/L) reduced the gel volume in control and TGF-beta1-treated cardiac fibroblasts. The angiotensin II-stimulated collagen gel contraction in control and TGF-beta1-treated fibroblasts was almost completely reversed by leuhistin and arphamenine A (100 micromol/L). Bestatin (100 micromol/L) only partially inhibited the angiotensin II-stimulated collagen gel contraction in control fibroblasts, although it did not affect the angiotensin II-induced contraction in TGF-beta1-treated fibroblasts. In control and TGF-beta1-treated cardiac fibroblasts, 100 micromol/L leuhistin or arphamenine A only partially inhibited alanine aminopeptidase activity, whereas bestatin (100 micromol/L) completely inhibited the alanine aminopeptidase activity. Arginine aminopeptidase activity was only partially inhibited by leuhistin and arphamenine A at 100 micromol/L in control and TGF-beta1-treated fibroblasts. Bestatin, however, completely blocked the arginine aminopeptidase activity in control fibroblasts and only partially in TGF-beta1-treated fibroblasts at 100 micromol/L. Our data suggest that both alanine and arginine aminopeptidases are involved in the reversal of the angiotensin II-stimulated collagen gel contraction in control and TGF-beta1-treated cardiac fibroblasts or myofibroblasts.

Collagen production in cardiac fibroblasts during inhibition of angiotensin-converting enzyme and aminopeptidases

OBJECTIVE

To determine whether lisinopril, an angiotensin-converting enzyme (ACE) inhibitor, and bestatin, an aminopeptidase inhibitor with broad specificity, could affect collagen production in control and transforming growth factor (TGF)-beta1-treated cardiac fibroblasts.

DESIGN AND METHODS

Cardiac fibroblasts from passage 2 from normal male adult rats were cultured to confluency, incubated with or without 600 pmol/l TGF-beta1 for 2 days in serum-free Dulbecco's modified Eagle's medium and then incubated with the test products (lisinopril or bestatin) for 1 day in this medium with added ascorbic acid, beta-aminoproprionitrile and tritiated proline. Soluble collagen was measured in the conditioned medium and non-soluble collagen in the cell layer. ACE activity was measured fluorimetrically with hippuryl-histidyl-leucine as substrate, and DNA with the bisbenzimide dye, Hoechst 33,258. Aminopeptidase activity was estimated by spectrophotometric determination of the liberation of p-nitroaniline from alanine-p-nitroanilide.

RESULTS

Lisinopril dose-dependently reduced ACE activity in control and TGF-beta1-treated cardiac fibroblasts. Bestatin inhibited the basal and TGF-beta1-stimulated aminopeptidase activity in a concentration-dependent manner. Lisinopril (10 micromol/l) decreased (P < 0.05) the production of soluble and non-soluble collagen in control cardiac fibroblasts. TGF-beta1 (600 pmol/l) increased (P < 0.05) the production of soluble and non-soluble collagen, and this effect was decreased (P < 0.05) by lisinopril. Bestatin (100 micromol/l) reduced (P < 0.01) the production of soluble collagen in control and TGF-beta1-treated cardiac fibroblasts, but did not affect the production of non-soluble collagen in these cells.

CONCLUSIONS

Our data suggest that ACE and aminopeptidases are involved in the basal and TGF-beta1-stimulated production of collagen in adult rat cardiac fibroblasts in culture.

[Interstitial lung disease]

Molecular investigation into the physiopathology of interstitial lung diseases has gained special interest through the trials carried out in the last decade. These trials seem to point at the role played by certain molecules, such as cytokines (transforming growth factor, platelet derived growth factor) and integrins, in the processes that lead to pulmonary fibrosis during the course of interstitial lung disease. They also demonstrate the important role that angiotensin II plays in increasing the secretion of transforming growth factor by several cells. The above-mentioned studies allow new therapeutic approaches to be considered which will possibly improve the serious prognosis of such diseases once they have reached the last stage of their course: pulmonary fibrosis.