Angiotensin II-induced transactivation of epidermal growth factor receptor regulates fibronectin and transforming growth factor-beta synthesis via transcriptional and posttranscriptional mechanisms

Angiotensin II Receptor Blockers Are Associated With Reduced Valvular Fibrosis in Women With Aortic Stenosis

BACKGROUND

Angiotensin receptor blockers (ARBs) may slow down the progression of aortic stenosis (AS) through their antifibrotic effect. Women present more valvular fibrosis than men, so ARBs may have more effect in females. Our aim was to assess the impact of ARBs on the remodelling of the aortic valve in men and women.

METHODS

We included patients who had an aortic valve replacement with or without coronary bypass grafting from 2006 to 2013. Patients with missing echocardiographic or histologic data were excluded. Warren-Yong and fibrosis scores of the explanted valves were performed. Patients were divided into 4 phenotypes according to their Warren-Yong and fibrosis scores: mild calcification/fibrosis, severe calcification/fibrosis group, predominant fibrosis group, predominant calcification group.

RESULTS

Among the 1321 included patients, the vast majority (89%) has severe AS. Patients in the predominant fibrosis group, compared with the predominant calcium group, were more often female (39% vs 31%; P = 0.008) with bicuspid valves (44% vs 34%; P = 0.002), and less often used ARBs (25% vs 30%; P = 0.046). Female sex was independently associated with being in the predominant fibrosis group (odds ratio 1.45, 95% confidence interval 1.08-1.95; P = 0.01), with a significant interaction between female sex and ARBs. Women taking ARBs compared with women not taking ARBs had significantly lower fibrosis scores (P < 0.001). This difference was not seen in men.

CONCLUSIONS

In this large series of patients with moderate-severe AS, among the women there was a negative association between intake of ARBs and valvular fibrosis. Thus, the possible effects of ARBs may be sex specific, with a larger therapeutic role in women.

Tissue kallikrein-related peptidase8 accentuates cardiac fibrosis after myocardial ischemia-reperfusion injury via regulation of cardiac fibroblasts

AIMS

Tissue kallikrein-related peptidase8 (KLK8) has been found to mitigate acute myocardial ischemia-reperfusion (IR) injury. However, the effect of KLK8 on cardiac remodeling in response to IR injury has not been determined.

MATERIALS AND METHODS

KLK8 overexpressing transgenic rat (KLK8-TG) was used as the animal model. IR injury was induced by ligating the left anterior descending coronary artery for 1 h and subsequent reperfusion. The functional and morphological changes of the heart were examined 14 days after the injury. Neonatal rat cardiac fibroblasts (CFs) were used to investigate the molecular mechanisms in vitro.

KEY FINDINGS

KLK8 overexpression enhanced cardiac diastolic dysfunction, fibrosis, and hypertrophy after IR injury, indicating that KLK8 accentuated cardiac remodeling in response to IR injury. Moreover, KLK8 overexpression increased epidermal growth factor (EGF) release and promoted the phosphorylation of EGF receptor (EGFR) and ERK1/2 in the heart after IR injury. It was interesting to find that both EGFR antagonist (AG 1478) and MEK inhibitor (PD98059) attenuated the KLK8-induced proliferation and activation of CFs in vitro, indicating that EGFR signaling might mediate the pro-fibrotic action of KLK8.

SIGNIFICANCE

KLK8 plays a crucial role in cardiac remodeling after myocardial infarction. KLK8 accentuates cardiac fibrosis after IR injury, possibly mediated by EGFR signaling in CFs.

Fibrotic Signaling in Cardiac Fibroblasts and Vascular Smooth Muscle Cells: The Dual Roles of Fibrosis in HFpEF and CAD

Patients with heart failure with preserved ejection fraction (HFpEF) and atherosclerosis-driven coronary artery disease (CAD) will have ongoing fibrotic remodeling both in the myocardium and in atherosclerotic plaques. However, the functional consequences of fibrosis differ for each location. Thus, cardiac fibrosis leads to myocardial stiffening, thereby compromising cardiac function, while fibrotic remodeling stabilizes the atherosclerotic plaque, thereby reducing the risk of plaque rupture. Although there are currently no drugs targeting cardiac fibrosis, it is a field under intense investigation, and future drugs must take these considerations into account. To explore similarities and differences of fibrotic remodeling at these two locations of the heart, we review the signaling pathways that are activated in the main extracellular matrix (ECM)-producing cells, namely human cardiac fibroblasts (CFs) and vascular smooth muscle cells (VSMCs). Although these signaling pathways are highly overlapping and context-dependent, effects on ECM remodeling mainly act through two core signaling cascades: TGF-β and Angiotensin II. We complete this by summarizing the knowledge gained from clinical trials targeting these two central fibrotic pathways.

Mitogen-activated protein kinases contribute to temperature-induced cardiac remodelling in rainbow trout (Oncorhynchus mykiss)

Rainbow trout (Oncorhynchus mykiss) live in environments where water temperatures range between 4 °C and 20 °C. Laboratory studies demonstrate that cold and warm acclimations of male trout can have oppositional effects on cardiac hypertrophy and the collagen content of the heart. The cellular mechanisms behind temperature-induced cardiac remodelling are unclear, as is why this response differs between male and female fish. Studies with cultured trout cardiac fibroblasts suggests that collagen deposition is regulated, at least in part, by mitogen-activated protein kinase (MAPK) cell signalling pathways. We, therefore, hypothesized that temperature-dependent cardiac remodelling is regulated by these signalling pathways. To test this, male and female trout were acclimated to 18 °C (warm) in the summer and to 4 °C (cold) in the winter and the activation of MAPK pathways in the hearts were characterized and compared to that of control fish maintained at 12 °C. In addition, cardiac collagen content, cardiac morphology and the expression of gene transcripts for matrix metalloproteinases (MMP) -9, MMP-2, tissue inhibitor of matrix metalloproteinases and collagen 1α were characterized. p38 MAPK phosphorylation increased in the hearts of female fish with cold acclimation and the phosphorylation of extracellular signal-regulated kinase increased in the hearts of male fish with warm acclimation. However, there was no effect of thermal acclimation on cardiac morphology or collagen content in either male or female fish. These results indicate that thermal acclimation has transient and sex-specific effects on the phosphorylation of MAPKs but also how variable the response of the trout heart is to thermal acclimation.

The Impact of microRNAs in Renin-Angiotensin-System-Induced Cardiac Remodelling

Current knowledge on the renin-angiotensin system (RAS) indicates its central role in the pathogenesis of cardiovascular remodelling via both hemodynamic alterations and direct growth and the proliferation effects of angiotensin II or aldosterone resulting in the hypertrophy of cardiomyocytes, the proliferation of fibroblasts, and inflammatory immune cell activation. The noncoding regulatory microRNAs has recently emerged as a completely novel approach to the study of the RAS. A growing number of microRNAs serve as mediators and/or regulators of RAS-induced cardiac remodelling by directly targeting RAS enzymes, receptors, signalling molecules, or inhibitors of signalling pathways. Specifically, microRNAs that directly modulate pro-hypertrophic, pro-fibrotic and pro-inflammatory signalling initiated by angiotensin II receptor type 1 (AT1R) stimulation are of particular relevance in mediating the cardiovascular effects of the RAS. The aim of this review is to summarize the current knowledge in the field that is still in the early stage of preclinical investigation with occasionally conflicting reports. Understanding the big picture of microRNAs not only aids in the improved understanding of cardiac response to injury but also leads to better therapeutic strategies utilizing microRNAs as biomarkers, therapeutic agents and pharmacological targets.

Reversion inducing cysteine rich protein with Kazal motifs and cardiovascular diseases: The RECKlessness of adverse remodeling

The Reversion Inducing Cysteine Rich Protein With Kazal Motifs (RECK) is a glycosylphosphatidylinositol (GPI) anchored membrane-bound regulator of matrix metalloproteinases (MMPs). It is expressed throughout the body and plays a role in extracellular matrix (ECM) homeostasis and inflammation. In initial studies, RECK expression was found to be downregulated in various invasive cancers and associated with poor prognostic outcome. Restoring RECK, however, has been shown to reverse the metastatic phenotype. Downregulation of RECK expression is also reported in non-malignant diseases, such as periodontal disease, renal fibrosis, and myocardial fibrosis. As such, RECK induction has therapeutic potential in several chronic diseases. Mechanistically, RECK negatively regulates various matrixins involved in cell migration, proliferation, and adverse remodeling by targeting the expression and/or activation of multiple MMPs, A Disintegrin And Metalloproteinase Domain-Containing Proteins (ADAMs), and A Disintegrin And Metalloproteinase With Thrombospondin Motifs (ADAMTS). Outside of its role in remodeling, RECK has also been reported to exert anti-inflammatory effects. In cardiac diseases, for example, it has been shown to counteract several downstream effectors of Angiotensin II (Ang-II) that play a role in adverse cardiac and vascular remodeling, such as Interleukin-6 (IL-6)/IL-6 receptor (IL-6R)/glycoprotein 130 (IL-6 signal transducer) signaling and Epidermal Growth Factor Receptor (EGFR) transactivation. This review article focuses on the current understanding of the multifunctional effects of RECK and how its downregulation may contribute to adverse cardiovascular remodeling.

Myofibroblasts and Fibrosis: Mitochondrial and Metabolic Control of Cellular Differentiation

Cardiac fibrosis is mediated by the activation of resident cardiac fibroblasts, which differentiate into myofibroblasts in response to injury or stress. Although myofibroblast formation is a physiological response to acute injury, such as myocardial infarction, myofibroblast persistence, as occurs in heart failure, contributes to maladaptive remodeling and progressive functional decline. Although traditional pathways of activation, such as TGFβ (transforming growth factor β) and AngII (angiotensin II), have been well characterized, less understood are the alterations in mitochondrial function and cellular metabolism that are necessary to initiate and sustain myofibroblast formation and function. In this review, we highlight recent reports detailing the mitochondrial and metabolic mechanisms that contribute to myofibroblast differentiation, persistence, and function with the hope of identifying novel therapeutic targets to treat, and potentially reverse, tissue organ fibrosis.

Exosomes: From Potential Culprits to New Therapeutic Promise in the Setting of Cardiac Fibrosis

Fibrosis is a significant global health problem associated with many inflammatory and degenerative diseases affecting multiple organs, individually or simultaneously. Fibrosis develops when extracellular matrix (ECM) remodeling becomes excessive or uncontrolled and is associated with nearly all forms of heart disease. Cardiac fibroblasts and myofibroblasts are the main effectors of ECM deposition and scar formation. The heart is a complex multicellular organ, where the various resident cell types communicate between themselves and with cells of the blood and immune systems. Exosomes, which are small extracellular vesicles, (EVs), contribute to cell-to-cell communication and their pathophysiological relevance and therapeutic potential is emerging. Here, we will critically review the role of endogenous exosomes as possible fibrosis mediators and discuss the possibility of using stem cell-derived and/or engineered exosomes as anti-fibrotic agents.

The cofilin phosphatase slingshot homolog 1 restrains angiotensin II-induced vascular hypertrophy and fibrosis in vivo

The dual specificity phosphatase slingshot homolog 1 (SSH1) contributes to actin remodeling by dephosphorylating and activating the actin-severing protein cofilin. The reorganization of the actin cytoskeleton has been implicated in chronic hypertension and the subsequent mechano-adaptive rearrangement of vessel wall components. Therefore, using a novel Ssh1^-/- mouse model, we investigated the potential role of SSH1 in angiotensin II (Ang II)-induced hypertension, and vascular remodeling. We found that loss of SSH1 did not produce overt phenotypic changes and that baseline blood pressures as well as heart rates were comparable between Ssh1^+/+ and Ssh1^-/- mice. Although 14 days of Ang II treatment equally increased systolic blood pressure in both genotypes, histological assessment of aortic samples indicated that medial thickening was exacerbated by the loss of SSH1. Consequently, reverse-transcription quantitative PCR analysis of the transcripts from Ang II-infused animals confirmed increased aortic expression levels of fibronectin, and osteopontin in Ssh1^-/- when compared to wild-type mice. Mechanistically, our data suggest that fibrosis in SSH1-deficient mice occurs by a process that involves aberrant responses to Ang II-induced TGFβ1. Taken together, our work indicates that Ang II-dependent fibrotic gene expression and vascular remodeling, but not the Ang II-induced pressor response, are modulated by SSH1-mediated signaling pathways and SSH1 activity is protective against Ang II-induced remodeling in the vasculature.

Cardiac fibrosis: new insights into the pathogenesis

Cardiac fibrosis is defined as the imbalance of extracellular matrix (ECM) production and degradation, thus contributing to cardiac dysfunction in many cardiac pathophysiologic conditions. This review discusses specific markers and origin of cardiac fibroblasts (CFs), and the underlying mechanism involved in the development of cardiac fibrosis. Currently, there are no CFs-specific molecular markers. Most studies use co-labelling with panels of antibodies that can recognize CFs. Origin of fibroblasts is heterogeneous. After fibrotic stimuli, the levels of myocardial pro-fibrotic growth factors and cytokines are increased. These pro-fibrotic growth factors and cytokines bind to its receptors and then trigger the activation of signaling pathway and transcriptional factors via Smad-dependent or Smad independent-manners. These fibrosis-related transcriptional factors regulate gene expression that are involved in the fibrosis to amplify the fibrotic response. Understanding the mechanisms responsible for initiation, progression, and amplification of cardiac fibrosis are of great clinical significance to find drugs that can prevent the progression of cardiac fibrosis.

EGFR mediates hyperlipidemia-induced renal injury via regulating inflammation and oxidative stress: the detrimental role and mechanism of EGFR activation

Previous studies have implicated inflammation, oxidative stress, and fibrosis as key factors in the development of obesity-induced kidney diseases. Epidermal growth factor receptor (EGFR) plays an important role in cancer development. Recently, the EGFR pathway has been increasingly implicated in chronic cardiovascular diseases via regulating inflammation and oxidative stress. However, it is unclear if EGFR is involved in obesity-related kidney injury. Using ApoE-/- and C57BL/6 mice models and two specific EGFR inhibitors, we investigated the potential effects of EGFR inhibition in the treatment of obesity-related nephropathy and found that EGFR inhibition alleviates renal inflammation, oxidative stress and fibrosis. In NRK-52E cells, we also elucidated the mechanism behind hyperlipidemia-induced EGFR activation. We observed that c-Src and EGFR forms a complex, and following PA stimulation, it is the successive phosphorylation, not formation, of the c-Src/EGFR complex that results in the subsequent cascade activation. Second, we found that TLR4 regulates the activation EGFR pathway mainly through the phosphorylation of the c-Src/EGFR complex. These results demonstrate the detrimental role of EGFR in the pathogenesis of obesity-related nephropathy, provide a new understanding of the mechanism behind hyperlipidemia/FFA-induced EGFR activation, and support the use of EGFR inhibitors in the treatment of obesity-induced kidney diseases.

A Disintegrin and Metalloprotease 17 in the Cardiovascular and Central Nervous Systems

ADAM17 is a metalloprotease and disintegrin that lodges in the plasmatic membrane of several cell types and is able to cleave a wide variety of cell surface proteins. It is somatically expressed in mammalian organisms and its proteolytic action influences several physiological and pathological processes. This review focuses on the structure of ADAM17, its signaling in the cardiovascular system and its participation in certain disorders involving the heart, blood vessels, and neural regulation of autonomic and cardiovascular modulation.

EGFR Inhibition Blocks Palmitic Acid-induced inflammation in cardiomyocytes and Prevents Hyperlipidemia-induced Cardiac Injury in Mice

Obesity is often associated with increased risk of cardiovascular diseases. Previous studies suggest that epidermal growth factor receptor (EGFR) antagonism may be effective for the treatment of angiotensin II-induced cardiac hypertrophy and diabetic cardiomyopathy. This study was performed to demonstrate if EGFR plays a role in the pathogenesis of hyperlipidemia/obesity-related cardiac injuries. The in vivo studies using both wild type (WT) and apolipoprotein E (ApoE) knockout mice fed with high fat diet (HFD) showed the beneficial effects of small-molecule EGFR inhibitors, AG1478 and 542, against obesity-induced myocardial injury. Administration of AG1478 and 542 significantly reduced myocardial inflammation, fibrosis, apoptosis, and dysfunction in both two obese mouse models. In vitro, EGFR signaling was blocked by either siRNA silencing or small-molecule EGFR inhibitors in palmitic acid (PA)-stimulated cardiomyocytes. EGFR inhibition attenuated PA-induced inflammatory response and apoptosis in H9C2 cells. Furthermore, we found that PA-induced EGFR activation was mediated by the upstream TLR4 and c-Src. This study has confirmed the detrimental effect of EGFR activation in the pathogenesis of obesity-induced cardiac inflammatory injuries in experimental mice, and has demonstrated the TLR4/c-Src-mediated mechanisms for PA-induced EGFR activation. Our data suggest that EGFR may be a therapeutic target for obesity-related cardiovascular diseases.

International Union of Basic and Clinical Pharmacology. XCIX. Angiotensin Receptors: Interpreters of Pathophysiological Angiotensinergic Stimuli [corrected]

The renin angiotensin system (RAS) produced hormone peptides regulate many vital body functions. Dysfunctional signaling by receptors for RAS peptides leads to pathologic states. Nearly half of humanity today would likely benefit from modern drugs targeting these receptors. The receptors for RAS peptides consist of three G-protein-coupled receptors—the angiotensin II type 1 receptor (AT1 receptor), the angiotensin II type 2 receptor (AT2 receptor), the MAS receptor—and a type II trans-membrane zinc protein—the candidate angiotensin IV receptor (AngIV binding site). The prorenin receptor is a relatively new contender for consideration, but is not included here because the role of prorenin receptor as an independent endocrine mediator is presently unclear. The full spectrum of biologic characteristics of these receptors is still evolving, but there is evidence establishing unique roles of each receptor in cardiovascular, hemodynamic, neurologic, renal, and endothelial functions, as well as in cell proliferation, survival, matrix-cell interaction, and inflammation. Therapeutic agents targeted to these receptors are either in active use in clinical intervention of major common diseases or under evaluation for repurposing in many other disorders. Broad-spectrum influence these receptors produce in complex pathophysiological context in our body highlights their role as precise interpreters of distinctive angiotensinergic peptide cues. This review article summarizes findings published in the last 15 years on the structure, pharmacology, signaling, physiology, and disease states related to angiotensin receptors. We also discuss the challenges the pharmacologist presently faces in formally accepting newer members as established angiotensin receptors and emphasize necessary future developments.

Epicardium is required for sarcomeric maturation and cardiomyocyte growth in the ventricular compact layer mediated by transforming growth factor β and fibroblast growth factor before the onset of coronary circulation

The epicardium, which is derived from the proepicardial organ (PE) as the third epithelial layer of the developing heart, is crucial for ventricular morphogenesis. An epicardial deficiency leads to a thin compact layer for the developing ventricle; however, the mechanisms leading to the impaired development of the compact layer are not well understood. Using chick embryonic hearts, we produced epicardium-deficient hearts by surgical ablation or blockade of the migration of PE and examined the mechanisms underlying a thin compact myocardium. Sarcomeric maturation (distance between Z-lines) and cardiomyocyte growth (size) were affected in the thin compact myocardium of epicardium-deficient ventricles, in which the amounts of phospho-smad2 and phospho-ERK as well as expression of transforming growth factor (TGF)β2 and fibroblast growth factor (FGF)2 were reduced. TGFβ and FGF were required for the maturation of sarcomeres and growth of cardiomyocytes in cultured ventricles. In ovo co-transfection of dominant negative (dN)-Alk5 (dN-TGFβ receptor I) and dN-FGF receptor 1 to ventricles caused a thin compact myocardium. Our results suggest that immature sarcomeres and small cardiomyocytes are the causative architectures of an epicardium-deficient thin compact layer and also that epicardium-dependent signaling mediated by TGFβ and FGF plays a role in the development of the ventricular compact layer before the onset of coronary circulation.

A century old renin-angiotensin system still grows with endless possibilities: AT1 receptor signaling cascades in cardiovascular physiopathology

Ang II, the primary effector pleiotropic hormone of the renin-angiotensin system (RAS) cascade, mediates physiological control of blood pressure and electrolyte balance through its action on vascular tone, aldosterone secretion, renal sodium absorption, water intake, sympathetic activity and vasopressin release. It affects the function of most of the organs far beyond blood pressure control including heart, blood vessels, kidney and brain, thus, causing both beneficial and deleterious effects. However, the protective axis of the RAS composed of ACE2, Ang (1-7), alamandine, and Mas and MargD receptors might oppose some harmful effects of Ang II and might promote beneficial cardiovascular effects. Newly identified RAS family peptides, Ang A and angioprotectin, further extend the complexities in understanding the cardiovascular physiopathology of RAS. Most of the diverse actions of Ang II are mediated by AT1 receptors, which couple to classical Gq/11 protein and activate multiple downstream signals, including PKC, ERK1/2, Raf, tyrosine kinases, receptor tyrosine kinases (EGFR, PDGF, insulin receptor), nuclear factor κB and reactive oxygen species (ROS). Receptor activation via G12/13 stimulates Rho-kinase, which causes vascular contraction and hypertrophy. The AT1 receptor activation also stimulates G protein-independent signaling pathways such as β-arrestin-mediated MAPK activation and Src-JAK/STAT. AT1 receptor-mediated activation of NADPH oxidase releases ROS, resulting in the activation of pro-inflammatory transcription factors and stimulation of small G proteins such as Ras, Rac and RhoA. The components of the RAS and the major Ang II-induced signaling cascades of AT1 receptors are reviewed.

The epidermal growth factor receptor and its ligands in cardiovascular disease

The epidermal growth factor receptor (EGFR) family and its ligands serve as a switchboard for the regulation of multiple cellular processes. While it is clear that EGFR activity is essential for normal cardiac development, its function in the vasculature and its role in cardiovascular disease are only beginning to be elucidated. In the blood vessel, endothelial cells and smooth muscle cells are both a source and a target of EGF-like ligands. Activation of EGFR has been implicated in blood pressure regulation, endothelial dysfunction, neointimal hyperplasia, atherogenesis, and cardiac remodeling. Furthermore, increased circulating EGF-like ligands may mediate accelerated vascular disease associated with chronic inflammation. Although EGFR inhibitors are currently being used clinically for the treatment of cancer, additional studies are necessary to determine whether abrogation of EGFR signaling is a potential strategy for the treatment of cardiovascular disease.

Inhibition of farnesyl pyrophosphate synthase attenuates angiotensin II-induced cardiac hypertrophy and fibrosis in vivo

Farnesyl pyrophosphate synthase (FPPS), as a key branchpoint of the mevalonate pathway, catalyzes the synthesis of isoprenoid intermediates. The isoprenoid intermediates are needed for protein isoprenylation to participate in cardiac remodeling. We have previously demonstrated that both knockdown of FPPS with small interfering RNA and inhibition of FPPS by alendronate could prevent Ang II-induced hypertrophy in cultured cardiomyocytes. In this study, we evaluated the effects of FPPS inhibition in Ang II-mediated cardiac hypertrophy and fibrosis in vivo. Wild type mice were separately treated with saline, Ang II (2.88 mg/kg per day), FPPS inhibitor alendronate (0.1 mg/kg per day), or the combination of Ang II (2.88 mg/kg per day) and alendronate (0.1 mg/kg per day) for 4 weeks. The results showed that Ang II increased FPPS expression, and the increases of Ang II-induced synthesis of the isoprenoid intermediates, FPP and GGPP, were significantly inhibited by FPPS inhibitor. In the meantime, FPPS inhibition attenuated Ang II-mediated cardiac hypertrophy and fibrosis as indexed by the heart weight to body weight ratio, echocardiographic parameters, histological examinations and expression of ANP and BNP mRNA. Furthermore, it was also found that FPPS inhibitor attenuated Ang II-induced increases of RhoA activity and p-38 MAPK phosphorylation and TGF-β1 mRNA expression. In conclusion, FPPS might play an important role in Ang II-induced cardiac hypertrophy and fibrosis in vivo, at least in part through RhoA, p-38 MAPK and TGF-β1.

Aldosterone and angiotensin: Role in diabetes and cardiovascular diseases

The present review shall familiarize the readers with the role of renin-angiotensin aldosterone system (RAAS), which regulates blood pressure, electrolyte and fluid homeostasis. The local RAAS operates in an autocrine, paracrine and/or intracrine manner and exhibits multiple physiological effects at the cellular level. In addition to local RAAS, there exists a complete pancreatic RAAS which has multi-facet role in diabetes and cardiovascular diseases. Aldosterone is known to mediate hyperinsulinemia, hypertension, cardiac failure and myocardial fibrosis while angiotensin II mediates diabetes, endothelial dysfunction, vascular inflammation, hypertrophy and remodeling. As the understanding of this biology of RAAS increases, it serves to exploit this for the pharmacotherapy of diabetes and cardiovascular diseases.

β-adrenergic receptor stimulation transactivates protease-activated receptor 1 via matrix metalloproteinase 13 in cardiac cells

BACKGROUND

Chronic β-adrenergic receptor (β-AR) overstimulation, a hallmark of heart failure, is associated with increased cardiac expression of matrix metalloproteinases (MMPs). MMP-1 has been shown to cleave and activate the protease-activated receptor 1 (PAR1) in noncardiac cells. In the present study, we hypothesized that β-AR stimulation would result in MMP-dependent PAR1 transactivation in cardiac cells.

METHODS AND RESULTS

β-AR stimulation of neonatal rat ventricular myocytes (NRVMs) or cardiac fibroblasts with isoproterenol transduced with an alkaline phosphatase-tagged PAR1 elicited a significant increase in alkaline phosphatase-PAR1 cleavage. This isoproterenol-dependent cleavage was significantly reduced by the broad-spectrum MMP inhibitor GM6001. Importantly, specific MMP-13 inhibitors also decreased alkaline phosphatase-PAR1 cleavage in isoproterenol-stimulated NRVMs, as well as in NRVMs stimulated with conditioned medium from isoproterenol-stimulated cardiac fibroblasts. Moreover, we found that recombinant MMP-13 stimulation cleaved alkaline phosphatase-PAR1 in NRVMs at DPRS(42)↓(43)FLLRN. This also led to the activation of the ERK1/2 pathway through Gαq in NRVMs and via the Gαq/ErbB receptor pathways in cardiac fibroblasts. MMP-13 elicited similar levels of ERK1/2 activation but lower levels of generation of inositol phosphates in comparison to thrombin. Finally, we demonstrated that either PAR1 genetic ablation or pharmacological inhibition of MMP-13 prevented isoproterenol-dependent cardiac dysfunction in mice.

CONCLUSIONS

In this study, we demonstrate that β-AR stimulation leads to MMP-13 transactivation of PAR1 in both cardiac fibroblasts and cardiomyocytes and that this likely contributes to pathological activation of Gαq and ErbB receptor-dependent pathways in the heart. We propose that this mechanism may underlie the development of β-AR overstimulation-dependent cardiac dysfunction.

Renin-Angiotensin system hyperactivation can induce inflammation and retinal neural dysfunction

The renin-angiotensin system (RAS) is a hormone system that has been classically known as a blood pressure regulator but is becoming well recognized as a proinflammatory mediator. In many diverse tissues, RAS pathway elements are also produced intrinsically, making it possible for tissues to respond more dynamically to systemic or local cues. While RAS is important for controlling normal inflammatory responses, hyperactivation of the pathway can cause neural dysfunction by inducing accelerated degradation of some neuronal proteins such as synaptophysin and by activating pathological glial responses. Chronic inflammation and oxidative stress are risk factors for high incidence vision-threatening diseases such as diabetic retinopathy (DR), age-related macular degeneration (AMD), and glaucoma. In fact, increasing evidence suggests that RAS inhibition may actually prevent progression of various ocular diseases including uveitis, DR, AMD, and glaucoma. Therefore, RAS inhibition may be a promising therapeutic approach to fine-tune inflammatory responses and to prevent or treat certain ocular and neurodegenerative diseases.

Renin and cardiovascular disease: Worn-out path, or new direction

Inhibition of the renin angiotensin system has beneficial effects in cardiovascular prevention and treatment. The advent of orally active direct renin inhibitors adds a novel approach to antagonism of the renin-angiotensin system. Inhibition of the first and rate-limiting step of the renin angiotensin cascade offers theoretical advantages over downstream blockade. However, the recent discovery of the (pro)renin receptor which binds both renin and prorenin, and which can not only augment catalytic activity of both renin and prorenin in converting angiotensinogen to angiotensin I, but also signal intracellularly via various pathways to modulate gene expression, adds a significant level of complexity to the field. In this review, we will examine the basic and clinical data on renin and its inhibition in the context of cardiovascular pathophysiology.

Intramyocardial fibroblast myocyte communication

Cardiac fibroblasts are emerging as key components of normal cardiac function, as well as the response to stressors and injury. These most numerous cells of the heart interact with myocytes via paracrine mechanisms, alterations in extracellular matrix homeostasis, and direct cell-cell interactions. It is possible that they are a contributor to the inability of adult myocytes to proliferate and may influence cardiac progenitor biology. Furthering our understanding of how cardiac fibroblasts and myocytes interact may provide an avenue to novel treatments for heart failure prevention. This review discusses the most recent concepts in cardiac fibroblast-myocyte communication and areas of potential future research.

Transforming growth factorbeta(1) transactivates EGFR via an H(2)O(2)-dependent mechanism in squamous carcinoma cell line

TGFbeta is known to transactivate EGFR. However, the signaling component involved in this crosstalk has yet to be revealed. Here, we found that TGFbeta(1) phosphorylated EGFR in a dose-dependent manner in SCC13 and A431 cells, and it was not blocked by EGF-neutralizing antibody. H(2)O(2) was increased by TGFbeta(1) treatment in the same time-kinetics as EGFR activation. Pretreatment of N-acetyl cysteine abolished TGFbeta(1)-induced H(2)O(2) induction and EGFR activation. Direct treatment of H(2)O(2) phosphorylated EGFR and catalase inhibitor prolonged TGFbeta(1)-induced EGFR activation. These results show that TGFbeta(1) activates EGFR via an H(2)O(2)-dependent mechanism, which subsequently leads to the activation of Erk(1/2).

Single nucleotide variants of the TGACTCA motif modulate energetics and orientation of binding of the Jun-Fos heterodimeric transcription factor

The Jun-Fos heterodimeric transcription factor is the terminal link between the transfer of extracellular information in the form of growth factors and cytokines to the site of DNA transcription within the nucleus in a wide variety of cellular processes central to health and disease. Here, using isothermal titration calorimetry, we report detailed thermodynamics of the binding of bZIP domains of Jun-Fos heterodimer to synthetic dsDNA oligos containing the TGACTCA cis element and all possible single nucleotide variants thereof encountered widely within the promoters of a diverse array of genes. Our data show that Jun-Fos heterodimer tolerates single nucleotide substitutions and binds to TGACTCA variants with affinities in the physiologically relevant micromolar to submicromolar range. The energetics of binding are richly favored by enthalpic forces and opposed by entropic changes across the entire spectrum of TGACTCA variants in agreement with the notion that protein-DNA interactions are largely driven by electrostatic interactions and intermolecular hydrogen bonding. Of particular interest is the observation that the Jun-Fos heterodimer binds to specific TGACTCA variants in a preferred orientation. Our 3D atomic models reveal that such orientational preference results from asymmetric binding and may in part be attributable to chemically distinct but structurally equivalent residues R263 and K148 located within the basic regions of Jun and Fos, respectively. Taken together, our data suggest that the single nucleotide variants of the TGACTCA motif modulate energetics and orientation of binding of the Jun-Fos heterodimer and that such behavior may be a critical determinant of differential regulation of specific genes under the control of this transcription factor. Our study also bears important consequences for the occurrence of single nucleotide polymorphisms within the TGACTCA cis element at specific gene promoters between different individuals.

NADPH oxidases and angiotensin II receptor signaling

Over the last decade many studies have demonstrated the importance of reactive oxygen species (ROS) production by NADPH oxidases in angiotensin II (Ang II) signaling, as well as a role for ROS in the development of different diseases in which Ang II is a central component. In this review, we summarize the mechanism of activation of NADPH oxidases by Ang II and describe the molecular targets of ROS in Ang II signaling in the vasculature, kidney and brain. We also discuss the effects of genetic manipulation of NADPH oxidase function on the physiology and pathophysiology of the renin-angiotensin system.

Role of TGF-beta on cardiac structural and electrical remodeling

The type β transforming growth factors (TGF-βs) are involved in a number of human diseases, including heart failure and myocardial arrhythmias. In fact, during the last 20 years numerous studies have demonstrated that TGF-β affects the architecture of the heart under both normal and pathological conditions. Moreover, TGF-β signaling is currently under investigation, with the aim of discovering potential therapeutic roles in human disease. In contrast, only few studies have investigated whether TGF-β affects electrophysiological properties of the heart. This fact is surprising since electrical remodeling represents an important substrate for cardiac disease. This review discusses the potential role of TGF-β on cardiac excitation-contraction (EC) coupling, action potentials, and ion channels. We also discuss the effects of TGF-β on cardiac development and disease from structural and electrophysiological points of view.

Angiotensin II, mitochondria, cytoskeletal, and extracellular matrix connections: an integrating viewpoint

Malfunctioning mitochondria strongly participate in the pathogenesis of cardiovascular damage associated with hypertension and other disease conditions. Eukaryotic cells move, assume their shape, resist mechanical stress, accommodate their internal constituents, and transmit signals by relying on the constant remodeling of cytoskeleton filaments. Mitochondrial ATP is needed to support cytoskeletal dynamics. Conversely, mitochondria need to interact with cytoskeletal elements to achieve normal motility, morphology, localization, and function. Extracellular matrix (ECM) quantity and quality influence cellular growth, differentiation, morphology, survival, and mobility. Mitochondria can sense ECM composition changes, and changes in mitochondrial functioning modify the ECM. Maladaptive ECM and cytoskeletal alterations occur in a number of cardiac conditions and in most types of glomerulosclerosis, leading to cardiovascular and renal fibrosis, respectively. Angiotensin II (ANG II), a vasoactive peptide and growth factor, stimulates cytosolic and mitochondrial oxidant production, eventually leading to mitochondrial dysfunction. Also, by inducing integrin/focal adhesion changes, ANG II regulates ECM and cytoskeletal composition and organization and, accordingly, contributes to the pathogenesis of cardiovascular remodeling. ANG II-initiated integrin signaling results in the release of transforming growth factor-β1 (TGF-β1), a cytokine that modifies ECM composition and structure, induces reorganization of the cytoskeleton, and modifies mitochondrial function. Therefore, it is possible to hypothesize that the depression of mitochondrial energy metabolism brought about by ANG II is preceded by ANG II-induced integrin signaling and the consequent derangement of the cytoskeletal filament network and/or ECM organization. ANG II-dependent TGF-β1 release is a potential link between ANG II, ECM, and cytoskeleton derangements and mitochondrial dysfunction. It is necessary to emphasize that the present hypothesis is among many other plausible explanations for ANG II-mediated mitochondrial dysfunction. A potential limitation of this proposal is that the results compiled here were obtained in different cells, tissues, and/or experimental models.

Angiotensin II promotes poly(ADP-ribosyl)ation of c-Jun/c-Fos in cardiac fibroblasts

Although c-Jun/c-Fos (activator protein 1, AP1) contributes importantly to Ang II-induced cardiac fibrosis through induction of extracellular matrix protein over-expression in cardiac fibroblasts, the mechanism by which Ang II promotes c-Jun/c-Fos transactivation remains unclear. In this study, we demonstrated that c-Fos and c-Jun were poly(ADP-ribosyl)ated in cultured cardiac fibroblasts. Southwestern blot and EMSA assays showed that incubation of nuclear extracts with NAD(+) and active DNA increased the basal DNA binding activities of c-Jun (31.0+/-1.0%, P<0.01) and AP1 (14.2+/-3.1%, P<0.01); incubation of recombinant c-Fos or/and c-Jun with PARP-1, NAD(+) and active DNA increased the basal DNA binding activities of c-Jun (48.3+/-4.2%, P<0.01) and AP1 (21.2+/-1.5%, P<0.01). Treatment with Ang II promoted PARP-1 activation and enhanced poly(ADP-ribosyl)ation of c-Fos (14.1+1.1%, P<0.01) and c-Jun (15.5+/-5.6%, P<0.01). Ang II also increased the basal DNA binding activities of c-Jun (13.5+/-2.4%, P<0.01) and AP1 (18.7+/-3.5%, P<0.01) in cultured cells. Inhibition of PARP-1 by PJ34 or siRNA effectively prevented Ang II-induced increases in the DNA binding of c-Jun and AP1, and decreased AP1-driven transcription (including collagen Ialpha1 and IIIalpha1, MMP-9 and TIMP-1). This study illustrated that c-Jun and c-Fos were poly(ADP-ribosyl)ated by PARP-1, and poly(ADP-ribosyl)ation enhanced the DNA binding of AP1. Ang II promoted poly(ADP-ribosyl)ation of c-Jun and c-Fos through activation of PARP-1 and, subsequently, enhanced AP1-driven transcription in cardiac fibroblasts.

ACE2 overexpression inhibits hypoxia-induced collagen production by cardiac fibroblasts

Cardiac remodelling is a key risk factor for the development of heart failure in the chronic phase following myocardial infarction. Our previous studies have shown an anti-remodelling role of ACE2 (angiotensin-converting enzyme 2) in vivo during hypertension and that these protective effects are mediated through increased circulating levels of Ang-(1–7) [angiotensin-(1–7)]. In the present study, we have demonstrated that cardiac myocytes have modest ACE2 activity, whereas cardiac fibroblasts do not exhibit any endogenous activity. As fibroblasts are the major cell type found in an infarct zone following a myocardial infarction, we examined the effects of ACE2 gene delivery to cultured cardiac fibroblasts after acute hypoxic exposure. Cardiac fibroblasts from 5-day-old Sprague–Dawley rat hearts were grown to confluence and transduced with a lentiviral vector containing murine ACE2 cDNA under transcriptional control by the EF1α (elongation factor 1α) promoter (lenti-ACE2). Transduction of fibroblasts with lenti-ACE2 resulted in a viral dose-dependent increase in ACE2 activity. This was associated with a significant attenuation of both basal and hypoxia/re-oxygenation-induced collagen production by the fibroblasts. Cytokine production, specifically TGFβ (transforming growth factor β), by these cells was also significantly attenuated by ACE2 expression. Collectively, these results indicate that: (i) endogenous ACE2 activity is observed in cardiac myocytes, but not in cardiac fibroblasts; (ii) ACE2 overexpression in the cardiac fibroblast attenuates collagen production; and (iii) this prevention is probably mediated by decreased expression of cytokines. We conclude that ACE2 expression, limited to cardiac fibroblasts, may represent a novel paradigm for in vivo therapy following acute ischaemia.

Collagen I induction by high glucose levels is mediated by epidermal growth factor receptor and phosphoinositide 3-kinase/Akt signalling in mesangial cells

AIMS/HYPOTHESIS

Glomerular matrix accumulation is a hallmark of diabetic nephropathy. Recent data have linked the serine/threonine kinase protein kinase B (Akt) to matrix modulation. Here, we studied its role in high glucose-induced collagen elaboration by mesangial cells.

METHODS

Primary rat mesangial cells were treated with high glucose levels (30 mmol/l) or mannitol as osmotic control. Western blots, northern blots, ELISA and immunohistochemistry were used for assessment. Diabetes was induced in rats by streptozotocin.

RESULTS

Phosphorylated Akt at S473 (pAktS473), corresponding to Akt activation, was seen in diabetic glomeruli. In mesangial cells, high glucose levels induced pAktS473 by 20 min. This was sustained to 72 h, while mannitol had no effect. Akt activation by kinase assay and phosphorylation on threonine 308 was also observed. Phosphoinositide 3-kinase (PI3K) inhibitors LY294002 (20 micromol/l) and wortmannin (100 nmol/l) prevented pAktS473. Collagen IA1 transcript and collagen I protein upregulation by high glucose levels were inhibited by PI3K blockade, as was collagen I secretion into the medium (ELISA). Dominant-negative Akt overexpression also inhibited high glucose-induced collagen IA1 transcript and collagen I protein production. Since signalling through the epidermal growth factor receptor (EGFR) can activate PI3K-Akt, we studied its activation by high glucose levels. EGFR was correspondingly activated by 10 min; mannitol had no effect. EGFR activation was also seen in glomeruli from diabetic rats and co-localised with collagen IA1 in diabetic glomeruli. Specific EGFR inhibition (AG1478, 5 micromol/l or dominant-negative EGFR) blocked high glucose-induced pAktS473, phosphorylation on threonine 308 and activation of the EGFR downstream target p44 extracellular signal-regulated kinase (Erk) mitogen-activated protein kinase. Finally, EGFR inhibition also blocked high glucose-induced collagen I upregulation at transcriptional and protein levels.

CONCLUSIONS/INTERPRETATION

We conclude that EGFR-PI3K-Akt signalling mediates high glucose-induced collagen I upregulation in mesangial cells and that this pathway is activated in diabetic glomeruli. Targeting its components may provide a new therapeutic approach to diabetic kidney disease.

Differential regulation of hypoxia-inducible factor-1 through receptor tyrosine kinase transactivation in vascular smooth muscle cells

Hypoxia-inducible factor-1 (HIF-1) is a decisive element for the transcriptional regulation of many genes expressed in hypoxic conditions. In vascular smooth muscle cells, the vasoactive hormone angiotensin II (Ang II) is a very potent inducer and activator of HIF-1. As opposed to hypoxia, which induces HIF-1alpha by protein stabilization, Ang II induced HIF-1alpha through transcriptional and translational mechanisms. Interestingly, a number of intracellular signaling events triggered by Ang II are mediated by the transactivation of receptor tyrosine kinases. The major receptor tyrosine kinases shown to be transactivated by Ang II in vascular smooth muscle cells are the epidermal growth factor receptor and the IGF-I receptor. In this study, we demonstrate that the transactivation of both these receptor tyrosine kinases is involved in HIF-1 complex activation by Ang II. More interestingly, this modulation of HIF-1 is at different degrees and through different pathways. Our results show that transactivation of IGF-I receptor is essential for HIF-1alpha protein translation through phosphatidylinositol 3-kinase/p70S6 kinase pathway activation, and epidermal growth factor receptor transactivation is implicated in HIF-1 complex activation through the stimulation of the p42/p44 MAPK pathway. Our results therefore show that Ang II-induced receptor tyrosine kinase transactivation is essential in both the induction and activation of HIF-1. These findings identify novel and intricate signaling mechanisms involved in HIF-1 complex activation.

Transactivation of the epidermal growth factor receptor by formylpeptide receptor exacerbates the malignant behavior of human glioblastoma cells

The G protein-coupled formylpeptide receptor (FPR), which mediates leukocyte migration in response to bacterial and host-derived chemotactic peptides, promotes the chemotaxis, survival, and tumorigenesis of highly malignant human glioblastoma cells. Because glioblastoma cells may also express other receptors for growth signals, such as the epidermal growth factor (EGF) receptor (EGFR), we investigated the role of EGFR in the signaling cascade of FPR and how two receptors cross-talk to exacerbate tumor growth. We found that N-formyl-methionyl-leucyl-phenylalanine, an FPR agonist peptide, rapidly induced EGFR phosphorylation at tyrosine residue (Tyr) 992, but not residues 846, 1068, or 1173, in glioblastoma cells, whereas all these residues were phosphorylated after only EGF treatment. The FPR agonist-induced EGFR phosphorylation in tumor cells was dependent on the presence of FPR as well as Galphai proteins, and was controlled by Src tyrosine kinase. The transactivation of EGFR contributes to the biological function of FPR in glioblastoma cells because inhibition of EGFR phosphorylation significantly reduced FPR agonist-induced tumor cell chemotaxis and proliferation. Furthermore, depletion of both FPR and EGFR by short interference RNA abolished the tumorigenesis of the glioblastoma cells. Our study indicates that the glioblastoma-promoting activity of FPR is mediated in part by transactivation of EGFR and the cross-talk between two receptors exacerbates the malignant phenotype of tumor cells. Thus, targeting both receptors may yield antiglioblastoma agents superior to those targeting one of them.

Cardiac hypertrophy: mechanisms and therapeutic opportunities

Cardiac hypertrophy and heart failure are major causes of morbidity and mortality in Western societies. Many factors have been implicated in cardiac remodeling, including alterations in gene expression in myocytes, cardiomyocytes apoptosis, cytokines and growth factors that influence cardiac dynamics, and deficits in energy metabolism as well as alterations in cardiac extracellular matrix composition. Many therapeutic means have been shown to prevent or reverse cardiac hypertrophy. New concepts for characterizing the pathophysiology of cardiac hypertrophy have been drawn from various aspects, including medical therapy and gene therapy, or use of stem cells for tissue regeneration. In this review, we focus on various types of cardiac hypertrophy, defining the causes of hypertrophy, describing available animal models of hypertrophy, discussing the mechanisms for development of hypertrophy and its transition to heart failure, and presenting the potential use of novel promising therapeutic strategies derived from new advances in basic scientific research.

Vascular signaling through cholesterol-rich domains: implications in hypertension

PURPOSE OF REVIEW

Lipid rafts are emerging as key players in the integration of cellular responses. Alterations in these highly regulated signaling cascades are important in structural, mechanical and functional abnormalities that underlie vascular pathological processes. The present review focuses on recent advances in signal transduction through caveolae/lipid rafts, implicated in hypertensive processes.

RECENT FINDINGS

Caveolae/lipid rafts function as sites of dynamic regulatory events in receptor-induced signal transduction. Mediators of vascular function, including G-protein coupled receptors, Src family tyrosine kinases, receptor tyrosine kinases, protein phosphatases and nitric oxide synthase, are concentrated within these microdomains. The assembly of functionally active nicotinamide adenine dinucleotide phosphate oxidase and subsequent reactive oxygen species production are also dependent on interactions within the caveolae/lipid rafts. Recent findings have also demonstrated the importance of actin-cytoskeleton and focal adhesion sites for protein interactions with caveolae/lipid raft.

SUMMARY

Many vascular signaling processes are altered in hypertension. Whether these events involve lipid rafts/caveolae remains unclear. A better understanding of how signaling molecules compartmentalize in lipid rafts/caveolae will provide further insights into molecular mechanisms underlying vascular damage in cardiovascular disease.

Characterization and localization of Ac-SDKP receptor binding sites using 125I-labeled Hpp-Aca-SDKP in rat cardiac fibroblasts

We have shown that the tetrapeptide N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) inhibited endothelin-1 (ET-1)-induced cell proliferation and collagen synthesis in cultured rat cardiac fibroblasts (CFs) and reduced left ventricle collagen deposition in rats with aldosterone (salt)- and ANG II-induced hypertension. However, it is not known whether these effects are mediated by receptor binding sites specific for Ac-SDKP. We hypothesized that Ac-SDKP exerts antifibrotic effects by binding to specific receptor sites in cultured rat CFs, which mediate the inhibitory effects of Ac-SDKP on ET-1-stimulated collagen synthesis. Ac-SDKP binding sites in rat CFs and hearts were characterized by a specific radioligand, (125)I-labeled 3-(p-hydroxyphenyl)-propionic acid (or desaminotyrosine) (Hpp)-Aca-SDKP, a biologically active analog of Ac-SDKP. (125)I-labeled Hpp-Aca-SDKP bound to rat CFs and fractionated membranes with similar affinities and specificity in a concentration- and time-dependent fashion. Scatchard plot analyses revealed a single class of high-affinity Hpp-Aca-SDKP binding sites (maximal binding: 1,704 +/- 198 fmol/mg protein; dissociation constant: 3.3 +/- 0.6 nM). (125)I-labeled Hpp-Aca-SDKP binding in CFs was displaced by unlabeled native peptide Ac-SDKP (inhibition constant: 0.69 +/- 0.15 nM) and the analog Hpp-Aca-SDKP (inhibition constant: 10.4 +/- 0.2 nM) but not the unrelated peptide ANG II or ET-1 (10 microM). In vitro, both Ac-SDKP and Hpp-Aca-SDKP inhibited ET-1-stimulated collagen synthesis in CFs in a dose-dependent fashion, reaching a maximal effect at 1 nM (control: 7.5 +/- 0.4, ET-1: 19.9 +/- 1.2, ET-1+SDKP: 7.7 +/- 0.4, ET-1+Hpp-Aca-SDKP: 9.7 +/- 0.1 microg/mg protein; P < 0.001). Ac-SDKP also significantly attenuated ET-1-induced increases in intracellular calcium and MAPK ERK1/2 phosphorylation in CFs. In the rat heart, in vitro autoradiography revealed specific (125)I-labeled Hpp-Aca-SDKP binding throughout the myocardium, primarily interstitially. We believe that these results demonstrate for the first time that Hpp-Aca-SDKP is a functional ligand specific for Ac-SDKP receptor binding sites and that both Ac-SDKP and Hpp-Aca-SDKP exert antifibrotic effects by binding to Ac-SDKP receptors in rat CFs.

Mitigation of radiation-induced optic neuropathy in rats by ACE inhibitor ramipril: importance of ramipril dose and treatment time

PURPOSE

Radiation-induced optic nerve damage was reduced by ramipril, a prodrug angiotensin-converting enzyme inhibitor (ACEI). This study was to determine the optimum dose and administration time of ramipril for mitigating radiation-induced optic neuropathy.

MATERIALS AND METHOD

Adult Fischer 344 male rats were treated with a single dose radiation 30 Gy by using radiosurgical technique. After irradiation, the animals were randomly assigned into groups of different ramipril doses and administration time; control (no treatment), radiation alone, radiation+ramipril in different doses and starting times of drug. Ramipril was given 0.5-1.5 mg/kg/day and AT1R blocker Losartan 20 mg/kg/day in drinking water for 180 days. Functional endpoint with visual evoked potential (VEP) and anatomical endpoint with gross and histological analysis with immunohistochemical (IHC) stain were used.

RESULTS

Normal VEP measurements in un-irradiated rats were 46.2+/-7.9 ms. There was no change of VEP value until 4 months, but was lengthened to 188.1+/-58.7 ms at 6 months after radiation. By ramipril treatment with the dose of 1.5 mg starting at 2 weeks after radiation, VEP was significantly shortened to 105.7+/-88.5 ms at 6 months. Gross and microscopic structure of the irradiated optic nerve was well preserved in the ramipril-treated group.

CONCLUSION

Ramipril can mitigate the radiation-induced optic nerve damage and preserve the functional integrity of the nerve. The results support early treatment with a high dose of ramipril after radiation.

Angiotensin II stimulates apoptosis via TGF-beta1 signaling in ventricular cardiomyocytes of rat

Elevations in angiotensin II (AngII) and transforming growth factor (TGF-beta1) levels are often found under conditions leading to progression of heart failure. From several studies, it is evident that AngII enhances TGF-beta1 expression via activator protein 1 (AP-1) activation, and that this pathway is involved in hypertrophic growth of the heart muscle and in the development of cardiac fibrosis. We now continued characterization of the signaling pathway stimulated by AngII in ventricular cardiomyocytes of rat and analyzed if the enhancement of TGF-beta1 expression by AngII may also contribute to apoptosis induction, which is another predictor of heart failure progression. Stimulation of cardiomyocytes with 100 nM AngII for 2 h activated the transcription factors AP-1 and GATA by 68.6+/-23.9 or 70.7+/-9.8%. Induction of both factors was mediated by p38 mitogen-activated protein kinase (MAPK) because it was totally blocked using a specific inhibitor of the kinase (SB202190). When GATA was inhibited by transformation of cardiomyocytes with decoy oligonucleotides, AngII could not enhance TGF-beta1 expression. This inhibition was observed on the mRNA level in real-time polymerase chain reaction and on the protein level in Western blots. As a consequence, upon AngII stimulation for 24 h, release of TGF-beta1 from cardiomyocytes was also reduced from 240.5+/-50.4 to 130.5+/-22.1% (p<0.05). In contrast to the early induction of GATA and AP-1, the transcription factor similar to mothers against decapentaplegic homolog (SMAD) was induced by AngII after 24 h. This stimulation was dependent on TGF-beta1 because it was blocked by antibodies specific for TGF-beta1. Twenty-four hours after AngII addition, the number of apoptotic cardiomyocytes increased by 6.5+/-1.2%, and this apoptosis induction was blocked when SMAD activity was inhibited by transformation of cardiomyocytes with SMAD decoy oligonucleotides. In conclusion, the transcription factors AP-1 and GATA are activated by p38 MAPK upon AngII stimulation, and both are needed to enhance TGF-beta1 expression in ventricular cardiomyocytes. TGF-beta1 acts in an autocrine loop on the cells to induce apoptosis via SMAD signaling. Thus, the often-found correlation between AngII, TGF-beta1, AP-1, and SMAD in pathogenesis of heart disease reflects the proapoptotic signaling pathway induced by AngII in cardiomyocytes.

Angiotensin II cell signaling: physiological and pathological effects in the cardiovascular system

The renin-angiotensin system is a central component of the physiological and pathological responses of cardiovascular system. Its primary effector hormone, angiotensin II (ANG II), not only mediates immediate physiological effects of vasoconstriction and blood pressure regulation, but is also implicated in inflammation, endothelial dysfunction, atherosclerosis, hypertension, and congestive heart failure. The myriad effects of ANG II depend on time (acute vs. chronic) and on the cells/tissues upon which it acts. In addition to inducing G protein- and non-G protein-related signaling pathways, ANG II, via AT(1) receptors, carries out its functions via MAP kinases (ERK 1/2, JNK, p38MAPK), receptor tyrosine kinases [PDGF, EGFR, insulin receptor], and nonreceptor tyrosine kinases [Src, JAK/STAT, focal adhesion kinase (FAK)]. AT(1)R-mediated NAD(P)H oxidase activation leads to generation of reactive oxygen species, widely implicated in vascular inflammation and fibrosis. ANG II also promotes the association of scaffolding proteins, such as paxillin, talin, and p130Cas, leading to focal adhesion and extracellular matrix formation. These signaling cascades lead to contraction, smooth muscle cell growth, hypertrophy, and cell migration, events that contribute to normal vascular function, and to disease progression. This review focuses on the structure and function of AT(1) receptors and the major signaling mechanisms by which angiotensin influences cardiovascular physiology and pathology.

Influence of ACE-inhibition and mechanical unloading on the regulation of extracellular matrix proteins in the myocardium of heart transplantation candidates bridged by ventricular assist devices

BACKGROUND

Whether adverse structural changes in the myocardium due to remodelling can be reversed by ventricular assist device (VAD) support in patients with end-stage heart failure is controversial.

AIMS

To investigate the effect of VAD support on the extra-cellular matrix.

METHODS

We analysed the collagen content in terminal failing ventricles of VAD-patients and donor hearts using 4-hydroxyproline for total collagen and real time RT-PCR for fibronectin (FN), collagen I alpha 1 (Col1A1), III alpha 1 (Col3A1) and TGF beta 1 analysis.

RESULTS

Compared to donor hearts we found similar increases in Col1A1 and TGF beta1 but not Col3A1 and FN mRNAs, which were similar in the myocardium from patients receiving a VAD or heart transplant. However, patients receiving ACE-I during VAD-support had lower Col1A1 mRNA content at transplantation. The total collagen content was not influenced by mechanical unloading or by ACE-I medication.

CONCLUSION

Mechanical unloading by VAD does not reduce the collagen content of the terminal failing ventricle possibly due to increased TGF beta1 levels. However, Col1A1 production may be reduced by ACE-I medication during VAD support.

Differential expression of angiotensin receptors in human cutaneous wound healing

BACKGROUND

Angiotensin AT1 and AT2 receptors are expressed in human skin. Furthermore, AT2 receptors have been reported to be upregulated during tissue repair and remodelling in various noncutaneous human tissues.

OBJECTIVES

Detection of alterations in angiotensin II receptor expression during wound healing in human skin.

METHODS

Three models were employed. (i) Primary human keratinocytes were razor scraped in culture flasks and alterations in the expression of angiotensin receptor mRNA determined by semiquantitative reverse transcription-polymerase chain reaction for 1-12 h thereafter. (ii) Early wound healing (48 h after cutting) was studied in punch biopsies from human skin ex vivo by means of immunohistochemical staining using polyclonal antibodies against the AT1 or AT2 receptor. (iii) In vivo wound healing was studied in sections of human cutaneous scars by immunohistochemistry to determine receptor expression early (2 days) and late (2 weeks-3 months) after surgery.

RESULTS

In all experimental settings, an upregulation of both receptor subtypes was noticed after wounding. Immunohistochemically stained skin sections showed a stronger expression of AT2 than of AT1 receptors within the area of scarring. Enhanced receptor expression was detectable as early as 24 h after injury and lasted for up to 3 months.

CONCLUSIONS

From these data, we conclude that angiotensin AT1 and AT2 receptors are upregulated in human cutaneous wounds, giving further support to the concept that angiotensin II plays a role even at an early stage during cutaneous wound healing.

TGF-beta1-induced EMT can occur independently of its proapoptotic effects and is aided by EGF receptor activation

Apoptosis and epithelial-mesenchymal transdifferentiation (EMT) occur in stressed tubular epithelial cells and contribute to renal fibrosis. Transforming growth factor (TGF)-beta(1) promotes these responses and we examined whether the processes were interdependent in vitro. Direct (caspase inhibition) and indirect [epidermal growth factor (EGF) receptor stimulation] strategies were used to block apoptosis during TGF-beta(1) stimulation, and the subsequent effect on EMT was assessed. HK-2 cells were exposed to TGF-beta(1) with or without preincubation with ZVAD-FMK (pan-caspase inhibitor) or concomitant treatment with EGF plus or minus preincubation with LY-294002 (PI3-kinase inhibitor). Cells were then assessed for apoptosis and proliferation by flow cytometry, crystal violet assay, and Western blotting. Markers of EMT were assessed by microscopy, immunofluorescence, real-time RT-PCR, Western blotting, PAI-1 reporter assay, and collagen gel contraction assay. TGF-beta(1) caused apoptosis and priming for staurosporine-induced apoptosis. This was blocked by ZVAD-FMK. However, ZVAD-FMK did not prevent EMT following TGF-beta(1) treatment. EGF inhibited apoptosis and facilitated TGF-beta(1) induction of EMT by increasing proliferation and accentuating E-cadherin loss. Additionally, EGF significantly enhanced TGF-beta(1)-induced collagen I gel contraction. EGF increased Akt phosphorylation during EMT, and the prosurvival effect of this was confirmed using LY-294002, which reduced EGF-induced Akt phosphorylation and reversed its antiapoptotic and proproliferatory effects. TGF-beta(1) induces EMT independently of its proapoptotic effects. TGF-beta(1) and EGF together lead to EMT. EGF increases proliferation and resistance to apoptosis during EMT in a PI3-K Akt-dependent manner. In vivo, EGF receptor activation may assist in the selective survival of a transdifferentiated, profibrotic cell type.

Tackling the EGFR in pathological tissue remodelling

Tissue remodelling is an adaptive physiological event initiated by physical and/or hormonal stimuli and characterised by extracellular matrix modifications, inflammation, cellular hypertrophy, proliferation and/or apoptosis. Although its initial effects may be beneficial for the maintenance of organ function, it is evident that sustained remodelling processes can lead to pathological outcomes, such as fibrosis in asthma, and cardiac hypertrophy in heart failure. Our research is focussed upon cardiac hypertrophy and the significant contribution of the molecular pathway, termed 'the triple membrane-passing signalling' paradigm (TMPS), to this phenomenon. Cardiac hypertrophy describes the enlargement, but not proliferation, of cardiomyocytes in response to mechanical or hormonal factors to normalise cardiac output and accompanies other features of cardiac remodelling. As a major independent risk factor for heart failure, it is imperative that the molecular mechanisms that govern this phenotype are determined to identify possible therapeutic targets. This review will focus on the importance of matrix metalloproteases and epidermal growth factor receptors in the TMPS pathway and their potential as pharmacological targets for heart failure therapy. The evidence provided may have implications for pathological tissue remodelling in other organs.

Angiotensin II stimulates arachidonic acid release from bone marrow stromal cells

INTRODUCTION

Angiotensin II (Ang II) is recognised as a regulator of haematopoiesis, but its actions within the bone marrow are not fully understood. Support of haematopoiesis by bone marrow stromal cells (MSC) is dependent on factors that include arachidonic acid and macrophage colony stimulating factor (MCSF), both of which are increased by Ang II stimulation in other tissues. To further elucidate the mechanisms of Ang II-regulated haematopoiesis, we determined whether Ang II-stimulation alters arachidonic acid release and MCSF secretion from MSC.

METHODS

Cynomolgus monkey MSC isolated from bone marrow aspirates and the human HS-5 stromal cell line were studied for Ang II-mediated arachidonic acid (AA) release, while secretion of MCSF in response to Ang II was studied in HS-5 cells. Cells were labelled overnight with 3H-AA and the release of 3H-AA was measured in culture medium following 20 minutes stimulation with Ang II, alone or in combination with the AT1- or AT2-receptor antagonists, losartan and PD 123319, respectively. MCSF secretion into culture medium was measured using an enzyme immunoassay following 24 hours of treatment with Ang II alone or in combination with losartan or PD 123319. Phorbol-myristate-acetate, known to stimulate release of AA and MCSF, was used as a positive control in both experiments.

RESULTS

In response to Ang II, release of 3H-AA from monkey and human MSC was increased (p<0.05) to 147+/-4% and 124+/-3% of control, respectively. The AT1- and AT2-receptor antagonists, losartan and PD 123319, individually reduced Ang II-stimulated 3H-AA release. In contrast, Ang II had no effect on secretion of MCSF from HS-5 cells.

CONCLUSIONS

These results provide mechanistic evidence for Ang II-mediated haematopoiesis through AA release that may, in part, explain Ang II-facilitated recovery of haematopoiesis in experimental myelosuppression and the anaemias associated with Ang II receptor blockade.

Akt mediates mechanical strain-induced collagen production by mesangial cells

Increased glomerular hydrostatic pressure is an important determinant of glomerulosclerosis and can be modeled by in vitro exposure of mesangial cells to cyclic mechanical strain. Stretched mesangial cells increase extracellular matrix protein production, the hallmark of glomerulosclerosis. Recent data indicate that the serine/threonine kinase Akt may be involved in matrix modulation. Thus, Akt activation and matrix synthesis in stretched mesangial cells were studied. Exposure of mesangial cells to 1 Hz cyclic strain led to prompt Akt activation, which was biphasic to 24 h. Activation was dependent on signaling through phosphatidylinositol-3-kinase and required EGF receptor transactivation. Inhibition of signaling through the PDGF receptor, Src kinase, or cytoskeletal disruption failed to prevent strain-induced Akt activation. Collagen type 1A1 transcript expression, promoter activation, and protein secretion were increased by stretch at 24 h and were dependent on phosphatidylinositol-3 kinase. Overexpression of dominant-negative Akt inhibited strain-induced collagen 1A1 production. Conversely, overexpression of constitutively active Akt led to increased collagen 1A1 upregulation and secretion. Finally, Akt activation was observed in the glomeruli of remnant rat kidneys, a model marked by increased intraglomerular pressure. The authors conclude that mechanical strain induces Akt activation in mesangial cells through a mechanism requiring phosphatidylinositol-3-kinase and EGF receptor transactivation. Type 1 collagen production is dependent on Akt and can be induced by Akt overexpression. Akt activation is observed in remnant kidneys in vivo. Thus, the role of Akt in progression of chronic hemodynamic glomerular disease is worthy of further exploration.

Iron chelation and a free radical scavenger suppress angiotensin II-induced upregulation of TGF-β1 in the heart

Long-term administration of angiotensin II causes myocardial loss and cardiac fibrosis. We previously found iron deposition in the heart of the angiotensin II-infused rat, which may promote angiotensin II-induced cardiac damage. In the present study, we have investigated whether an iron chelator (deferoxamine) and a free radical scavenger (T-0970) affect the angiotensin II-induced upregulation of transforming growth factor-β1 (TGF-β1). Angiotensin II infusion for 7 days caused a robust increase in TGF-β1 mRNA expression in vascular smooth muscle cells, myofibroblast-like cells, and migrated monocytes/macrophages. T-0970 and deferoxamine suppressed the upregulation of TGF-β1 mRNA and reduced the extent of cardiac fibrosis in the heart of rats treated with angiotensin II. These agents blocked the angiotensin II-induced upregulation of heme oxygenase-1, a potent oxidative and cellular stress-responsive gene, but they did not significantly affect systolic blood pressure or plasma levels of aldosterone. In addition, T-0970 and deferoxamine suppressed the angiotensin II-induced upregulation of monocyte chemoattractant protein-1 in the heart. These results collectively suggest that iron and the iron-mediated generation of reactive oxygen species may contribute to angiotensin II-induced upregulation of profibrotic and proinflammatory genes, such as TGF-β1 and monocyte chemoattractant protein-1.

Translational regulation of vascular endothelial growth factor expression in renal epithelial cells by angiotensin II

ANG II regulates growth factor expression in the kidney. We investigated whether ANG II regulated vascular endothelial growth factor (VEGF) synthesis in proximal tubular epithelial (MCT) cells. ANG II (1 nM) increased VEGF protein expression within 5 min, the effect lasting for 30 min. There was no change in VEGF mRNA levels or mRNA stability, and transcription inhibitors did not affect ANG II-induced VEGF expression. Regulation of VEGF translation was investigated. Polyribosomal analysis revealed selective enrichment of heavy ribosomes (polysomes) with VEGF mRNA transcripts compared with light ribosomes in ANG II-treated cells, although distribution of GAPDH was unaltered. In vitro translation of total RNA from polysomal fractions showed selective increase in VEGF protein synthesis in ANG II-treated cells. Preincubation with LY-294002, a PI 3-kinase inhibitor, or expression of dominant-negative Akt prevented ANG II-stimulated increase in VEGF translation. ANG II increased phosphorylation of eukaryotic initiation factor 4E and its binding protein 4E-BP1, critical events that regulate the initiation phase of protein translation. ANG II failed to increase VEGF mRNA translation in cells stably expressing the phosphorylation mutant of 4E-BP1. Our data illustrate that a rapid increase in VEGF protein expression by ANG II is regulated at the initiation phase of translation of VEGF mRNA in renal epithelial cells. Regulation of VEGF translation by ANG II represents a novel pathway of renal response to injury.

Extracellular signal-regulated kinase (ERK) in glucose-induced and endothelin-mediated fibronectin synthesis

Increased extracellular matrix protein deposition and basement membrane thickening are important features of diabetic angiopathy. One key matrix protein that has been shown to be instrumental in basement membrane thickening is fibronectin (FN). We have previously demonstrated that glucose-induced increased expression of endothelin-1 (ET-1), may in part, be responsible for increased FN expression via nuclear factor-kappaB (NF-kappaB) and activating protein (AP-1) activation. The present study was aimed at elucidating the mechanism of ET-1 with respect to mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway activation and glucose-induced FN upregulation. Human endothelial cells were exposed to either low (5 mM) or high (25 mM) glucose levels. Cells in low glucose were also treated with ET-1 peptide (5 nM). In addition, we treated cells exposed to high glucose levels with specific MAPK/ERK inhibitor PD098059 (50 microM), dual ET-receptor antagonist, bosentan (10 microM), and PKC blocker, chelerythrine (1 microM). Following incubation period, RNA and total proteins were extracted for RT-PCR for FN and immunoblot analysis of MAPK/ERK activation. Confocal microscopy was performed for analysis of FN protein and nuclear localization of activated Elk. Electrophoretic mobility shift assay was carried out to detect NF-kappaB and AP-1 activation. Our data demonstrates that high glucose-induced upregulation of FN messenger RNA and protein levels occur via activation of MAPK/ERK pathway, which was prevented by treatment of cells with bosentan, PD098059 and PKC blocker chelerythrine. Confocal microscopy demonstrated nuclear localization of phospho-Elk protein. Glucose-induced FN expression was also associated with protein kinase C, NF-kappaB, and AP-1 activation. These results suggested that glucose-induced, ET- and PKC-dependent, upregulation of FN is, in part, mediated via MAPK/ERK activation.

Modification of radiation injury by ramipril, inhibitor of angiotensin-converting enzyme, on optic neuropathy in the rat

Inhibitors of angiotensin-converting enzyme (ACE) have been used to reduce radiation-induced normal tissue injury. The present study was carried out to determine whether ramipril, one of the inhibitors of ACE, would ameliorate radiation-induced brain damage, using a well-characterized optic neuropathy model in the rat, one of the most critical and radiosensitive structures in the brain. The brains of adult Fischer rats were irradiated stereotactically with 30 Gy using a single collimated beam. Six months after irradiation and 1.5 mg/kg day(-1) ramipril (started 2 weeks after irradiation), rats were assessed for optic nerve damage functionally, using visual evoked potential, and histologically. Results show that ramipril conferred significant modification of radiation injury, since rats receiving radiation alone showed a threefold lengthening in the mean peak latency in the visual evoked potential, whereas 75% of rats receiving radiation followed by ramipril had evoked potentials that resembled those of normal untreated control rats. The histology of irradiated and ramipril-treated optic nerves appeared nearly normal, while there was significant demyelination in both optic nerves of irradiated rats. The study represents the first demonstration of prophylaxis of radiation injury by a carboxyl-containing ACE inhibitor, providing a pharmacological strategy designed to reduce radiation-induced normal tissue damage.