Antisense to epidermal growth factor receptor prevents the development of left ventricular hypertrophy

Exploring the mechanism of curcumin in the treatment of doxorubicin-induced cardiotoxicity based on network pharmacology and molecular docking technology

Doxorubicin (DOX) is one of the most effective chemotherapeutic agents. However, the nonselective effect leads to serious cardiotoxicity risk in clinical use. Curcumin is a well-known dietary polyphenol that showed a protective effect against the cardiotoxic effect of DOX. This study aimed to assess the role of curcumin in protection against DOX-induced cardiotoxicity. Potential compound and disease targets were obtained from relevant databases, and common targets were screened. Protein-protein interaction (PPI) was used to predict the core targets. Gene ontology (GO) bioprocess analysis and Kyoto encyclopedia of genes and genome enrichment analysis enriched the possible biological processes (BP), cellular components, molecular function, and signaling pathways involved. Finally, the binding of curcumin to target proteins was evaluated through molecular docking. The docking score verified the reliability of the prediction results. In total, 205 curcumin and 700 disease targets were identified. A topological analysis of the PPI network revealed 10 core targets including TP53, tumor necrosis factor-alpha (TNF), AKT1, vascular endothelial growth factor A (VEGFA), prostaglandin-endoperoxide synthase 2 (PTGS2), signal transducer and activator of the transcription 3 (STAT3), HIF1A, MYC, epidermal growth factor receptor (EGFR), and CASP3 (Caspase-3). Furthermore, the enrichment analyses indicated that the effects of curcumin were mediated by genes related to oxidation, inflammation, toxification, cell proliferation, migration, apoptosis, wounding, metabolism, proteolysis, and the signaling pathway of calcium (Ca2+). Molecular docking showed that curcumin could bind with the target proteins with strong molecular force, exhibiting good docking activity. Curcumin has a multi-cardioprotective effect by modulating the core targets' expression in DOX-induced cardiotoxicity. This study elucidated the key target proteins and provided a theoretical basis for further exploring curcumin in the prevention and treatment of DOX-induced cardiotoxicity.

The role of EGFR in vascular AT1R signaling: From cellular mechanisms to systemic relevance

The epidermal growth factor receptor (EGFR) belongs to the ErbB-family of receptor tyrosine kinases that are of importance in oncology. During the last years, substantial evidence accumulated for a crucial role of EGFR concerning the action of the angiotensin II type 1 receptor (AT1R) in blood vessels, resulting form AT1R-induced EGFR transactivation. This transactivation occurs through the release of membrane-anchored EGFR-ligands, cytosolic tyrosine kinases, heterocomplex formation or enhanced ligand expression. AT1R-EGFR crosstalk amplifies the signaling response and enhances the biological effects of angiotensin II. Downstream signaling cascades include ERK1/2 and p38 MAPK, PLCγ and STAT. AT1R-induced EGFR activation contributes to vascular remodeling and hypertrophy via e.g. smooth muscle cell proliferation, migration and extracellular matrix production. EGFR transactivation results in increased vessel wall thickness and reduced vascular compliance. AT1R and EGFR signaling pathways are also implicated the induction of vascular inflammation. Again, EGFR transactivation exacerbates the effects, leading to endothelial dysfunction that contributes to vascular inflammation, dysfunction and remodeling. Dysregulation of the AT1R-EGFR axis has been implicated in the pathogenesis of various cardiovascular diseases and inhibition or prevention of EGFR signaling can attenuate part of the detrimental impact of enhanced renin-angiotensin-system (RAAS) activity, highlighting the importance of EGFR for the adverse consequences of AT1R activation. In summary, EGFR plays a critical role in vascular AT1R action, enhancing signaling, promoting remodeling, contributing to inflammation, and participating in the pathogenesis of cardiovascular diseases. Understanding the interplay between AT1R and EGFR will foster the development of effective therapeutic strategies of RAAS-induced disorders.

The epidermal growth factor receptor in healthy pregnancy and preeclampsia

The epidermal growth factor receptor (EGFR) is expressed robustly in the placenta, and critical processes of pregnancy such as placental growth and trophoblast fusion are dependent on EGFR function. However, the role that aberrant EGFR signaling might play in the etiology and/or maintenance of preeclampsia (PE) remains largely unexplored. Recently, we have shown that overexpression of EGFR in cultured uterine artery endothelial cells (UAEC), which express little endogenous EGFR, remaps responsiveness away from vascular endothelial growth factor receptor (VEGFR) signaling and toward EGFR, suggesting that endothelial EGFR expression may be kept low to preserve VEGFR control of angiogenesis. Here we will consider the evidence for the possibility that the endothelial dysfunction observed in PE might in some cases result from elevation of endothelial EGFR. During pregnancy, trophoblasts are known to synthesize large amounts of EGFR protein, and the placenta regularly releases syncytiotrophoblast-derived exosomes and microparticles into the maternal circulation. Although there are no reports of elevated EGFR gene expression in preeclamptic endothelial cells, the ongoing shedding of placental vesicles into the vascular system raises the possibility that EGFR-rich vesicles might fuse with endothelium, thereby contributing to the symptoms of PE by interrupting angiogenesis and blocking pregnancy-adapted vasodilatory function.

Hub Genes Identification, Small Molecule Compounds Prediction for Atrial Fibrillation and Diagnostic Model Construction Based on XGBoost Algorithm

Background

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia and engenders significant global health care burden. The underlying mechanisms of AF is remained to be revealed and current treatment options for AF have limitations. Besides, a detection system can help identify those at risk of developing AF and will enable personalized management.

Materials and Methods

In this study, we utilized the robust rank aggregation method to integrate six AF microarray datasets from the Gene Expression Omnibus database, and identified a set of differentially expressed genes between patients with AF and controls. Potential compounds were identified by mining the Connectivity Map database. Functional modules and closely-interacted clusters were identified using weighted gene co-expression network analysis and protein–protein interaction network, respectively. The overlapped hub genes were further filtered. Subsequent analyses were performed to analyze the function, biological features, and regulatory networks. Moreover, a reliable Machine Learning-based diagnostic model was constructed and visualized to clarify the diagnostic features of these genes.

Results

A total of 156 upregulated and 34 downregulated genes were identified, some of which had not been previously investigated. We showed that mitogen-activated protein kinase and epidermal growth factor receptor inhibitors were likely to mitigate AF based on Connectivity Map analysis. Four genes, including CXCL12, LTBP1, LOXL1, and IGFBP3, were identified as hub genes. CXCL12 was shown to play an important role in regulation of local inflammatory response and immune cell infiltration. Regulation of CXCL12 expression in AF was analyzed by constructing a transcription factor-miRNA-mRNA network. The Machine Learning-based diagnostic model generated in this study showed good efficacy and reliability.

Conclusion

Key genes involving in the pathogenesis of AF and potential therapeutic compounds for AF were identified. The biological features of CXCL12 in AF were investigated using integrative bioinformatics tools. The results suggested that CXCL12 might be a biomarker that could be used for distinguishing subsets of AF, and indicated that CXCL12 might be an important intermediate in the development of AF. A reliable Machine Learning-based diagnostic model was constructed. Our work improved understanding of the mechanisms of AF predisposition and progression, and identified potential therapeutic avenues for treatment of AF.

The mineralocorticoid receptor leads to increased expression of EGFR and T-type calcium channels that support HL-1 cell hypertrophy

The EGF receptor (EGFR) has been extensively studied in tumor biology and recently a role in cardiovascular pathophysiology was suggested. The mineralocorticoid receptor (MR) is an important effector of the renin-angiotensin-aldosterone-system and elicits pathophysiological effects in the cardiovascular system; however, the underlying molecular mechanisms are unclear. Our aim was to investigate the importance of EGFR for MR-mediated cardiovascular pathophysiology because MR is known to induce EGFR expression. We identified a SNP within the EGFR promoter that modulates MR-induced EGFR expression. In RNA-sequencing and qPCR experiments in heart tissue of EGFR KO and WT mice, changes in EGFR abundance led to differential expression of cardiac ion channels, especially of the T-type calcium channel CACNA1H. Accordingly, CACNA1H expression was increased in WT mice after in vivo MR activation by aldosterone but not in respective EGFR KO mice. Aldosterone- and EGF-responsiveness of CACNA1H expression was confirmed in HL-1 cells by Western blot and by measuring peak current density of T-type calcium channels. Aldosterone-induced CACNA1H protein expression could be abrogated by the EGFR inhibitor AG1478. Furthermore, inhibition of T-type calcium channels with mibefradil or ML218 reduced diameter, volume and BNP levels in HL-1 cells. In conclusion the MR regulates EGFR and CACNA1H expression, which has an effect on HL-1 cell diameter, and the extent of this regulation seems to depend on the SNP-216 (G/T) genotype. This suggests that the EGFR may be an intermediate for MR-mediated cardiovascular changes and that SNP analysis can help identify subgroups of patients that will benefit most from MR antagonists.

Vitamin A deficiency indicating as low expression of LRAT may be a novel biomarker of primary hypertension

AIMS

Vitamin A (VA) deficiency triggers many diseases and is a worldwide nutrition problem. The Retinol acyltransferase (LRAT) is an indicator of VA storage function, and the relationship between LRAT and blood pressure level and the regulation mechanism will be elucidated.

METHODS

160 children aged 6-12 years were included, and the serum VA and, the transcription levels of LRAT and RARs, were measured. Spontaneously hypertensive rats (SHRs) and WKY rats were treated with VA deficiency (VAD) or normal (VAN) fodder for 20 weeks. LRAT, retinoic acid, renin angiotensin system (RAS) biomarkers, and the structure and function of the heart for SHRs were measured.

RESULTS

The serum retinol and serum retinol/BMI levels were lower in children in the low LRAT group (LRAT<P₅₀) compared with the high LRAT group (LRAT≥P₅₀)(0.82 μmol/L vs. 0.94 μmol/L, 0.04 vs. 0.05, all P < .01). Moreover, SBP, DBP, and Ang Ⅱ were lower in the low LRAT group (all P < .01). Compared with VAN-treated SHRs, LRAT, retinoic acid receptor alpha (RARα), ACE2, and Ang (1-7) protein expression levels were decreased, while ACE and AT1R expression levels were increased in VAD SHRs. Notably, heart weight (HW), left ventricle weight, the HW-to-body weight ratio and the left ventricle weight-to-body weight ratio were significantly increased in VAD SHRs compared with those in VAN SHRs (P < .01). Cardiomyocyte hypertrophy and ventricular fibrosis were significantly increased in VAD SHRs compared with those in VAN SHRs (both P < .01).

CONCLUSIONS

LRAT may be an important biomarker of vitamin A deficiency in target organs and may regulate BP by affecting RAS biomarkers.

Adenoviral transduction of EGFR into pregnancy-adapted uterine artery endothelial cells remaps growth factor induction of endothelial dysfunction

During pregnancy, uterine vascular vasodilation is enhanced through adapted Ca2+ signaling, facilitated through increased endothelial connexin 43 (Cx43) gap junctional communication (GJC). In preeclampsia (PE), this adaptive response is missing. Of note, the angiogenic factor VEGF can also act via Src and ERK to close Cx43 gap junctions. While VEGFR2 is necessary for such closure, a role VEGFR1 is less clear. We reasoned if VEGFR2 is acting alone, then substituting another growth factor receptor with VEGFR2-like signaling should have the same effect. In uterine artery endothelial cells derived from pregnant sheep (P-UAEC), endogenous EGFR expression is very low. When we used adenovirus to raise EGFR, we also dose-dependently induced EGF-sensitive Cx43 phosphorylation mainly via ERK, and corresponding loss of Ca2+ bursts, but eliminated VEGF effects on phosphorylation of Cx43 or loss of Ca2+ bursting. This surprising observation suggests that while activated EGFR may indeed substitute for VEGFR2, it also sequesters a limited pool of effector molecules needed for VEGFR2 to phosphorylate Cx43. Thus, low endogenous EGFR expression in P-UAEC may be a necessary strategy to allow VEGFR-2 control of GJC, a first step in initiating angiogenesis in healthy pregnancy. Of further note, trophoblasts are rich in EGFR, and we have demonstrated shed PLAP+/EGFR + extracellular vesicles in maternal circulation in first trimester plasma samples using nanoscale high resolution flow cytometry. Collectively our data suggest that placenta derived exosomes positive for EGFR should be further considered as a possible cause of endothelial dysfunction in women with PE.

Epidermal growth factor receptor/extracellular signal-regulated kinase pathway enhances mineralocorticoid receptor transcriptional activity through protein stabilization

Activation of mineralocorticoid receptor (MR) is evoked by aldosterone, and it induces hypertension and cardiovascular disease when it's concomitant with excessive salt loading. We have proposed the notion of "MR-associated hypertension", in which add-on therapy of MR blockers is effective even though serum aldosterone level is within normal range. To elucidate its underlying molecular mechanism, we focused on the effect of epidermal growth factor receptor (EGFR)/extracellular signal-regulated kinase (ERK) activation on MR activity. Epidermal growth factor (EGF) administration increased MR transcriptional activity through EGFR/ERK pathway and increased protein level by counteracting MR ubiquitylation in vitro. EGF administration in vivo also increased MR protein level and target gene expression in kidney, which were decreased by EGFR inhibitor. In addition, the administration of EGFR inhibitor lowered systolic blood pressure and MR activity in DOCA/salt-treated mice. In conclusion, EGFR/ERK pathway activation is considered as one of the underlying mechanisms of aberrant MR activation and EGFR/ERK pathway blockade could be an alternative approach for the prevention of MR-related cardiovascular events.

Crucial Role of ROCK2-Mediated Phosphorylation and Upregulation of FHOD3 in the Pathogenesis of Angiotensin II-Induced Cardiac Hypertrophy

Cardiac hypertrophy is characterized by increased myofibrillogenesis. Angiotensin II (Ang-II) is an essential mediator of the pressure overload-induced cardiac hypertrophy in part through RhoA/ROCK (small GTPase/Rho-associated coiled-coil containing protein kinase) pathway. FHOD3 (formin homology 2 domain containing 3), a cardiac-restricted member of diaphanous-related formins, is crucial in regulating myofibrillogenesis in cardiomyocytes. FHOD3 maintains inactive through autoinhibition by an intramolecular interaction between its C- and N-terminal domains. Phosphorylation of the 3 highly conserved residues (1406S, 1412S, and 1416T) within the C terminus (CT) of FHOD3 by ROCK1 is sufficient for its activation. However, it is unclear whether ROCK-mediated FHOD3 activation plays a role in the pathogenesis of Ang-II-induced cardiac hypertrophy. In this study, we detected increases in FHOD3 expression and phosphorylation in cardiomyocytes from Ang-II-induced rat cardiac hypertrophy models. Valsartan attenuated such increases. In cultured neonate rat cardiomyocytes, overexpression of phosphor-mimetic mutant FHOD3-DDD, but not wild-type FHOD3, resulted in myofibrillogenesis and cardiomyocyte hypertrophy. Expression of a phosphor-resistant mutant FHOD3-AAA completely abolished myofibrillogenesis and attenuated Ang-II-induced cardiomyocyte hypertrophy. Pretreatment of neonate rat cardiomyocytes with ROCK inhibitor Y27632 reduced Ang-II-induced FHOD3 activation and upregulation, suggesting the involvement of ROCK activities. Silencing of ROCK2, but not ROCK1, in neonate rat cardiomyocytes, significantly lessened Ang-II-induced cardiomyocyte hypertrophy. ROCK2 can directly phosphorylate FHOD3 at both 1412S and 1416T in vitro and is more potent than ROCK1. Both kinases failed to phosphorylate 1406S. Coexpression of FHOD3 with constitutively active ROCK2 induced more stress fiber formation than that with constitutively active ROCK1. Collectively, our results demonstrated the importance of ROCK2 regulated FHOD3 expression and activation in Ang-II-induced myofibrillogenesis, thus provided a novel mechanism for the pathogenesis of Ang-II-induced cardiac hypertrophy.

Expression and Function of the Epidermal Growth Factor Receptor in Physiology and Disease

The epidermal growth factor receptor (EGFR) is the prototypical member of a family of membrane-associated intrinsic tyrosine kinase receptors, the ErbB family. EGFR is activated by multiple ligands, including EGF, transforming growth factor (TGF)-α, HB-EGF, betacellulin, amphiregulin, epiregulin, and epigen. EGFR is expressed in multiple organs and plays important roles in proliferation, survival, and differentiation in both development and normal physiology, as well as in pathophysiological conditions. In addition, EGFR transactivation underlies some important biologic consequences in response to many G protein-coupled receptor (GPCR) agonists. Aberrant EGFR activation is a significant factor in development and progression of multiple cancers, which has led to development of mechanism-based therapies with specific receptor antibodies and tyrosine kinase inhibitors. This review highlights the current knowledge about mechanisms and roles of EGFR in physiology and disease.

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.

Oxidative stress contributes to the enhanced expression of Gqα/PLCβ1 proteins and hypertrophy of VSMC from SHR: role of growth factor receptor transactivation

We showed previously that vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHRs) exhibit overexpression of Gqα/PLCβ1 proteins, which contribute to increased protein synthesis through the activation of MAP kinase signaling. Because oxidative stress has been shown to be increased in hypertension, the present study was undertaken to examine the role of oxidative stress and underlying mechanisms in enhanced expression of Gqα/PLCβ1 proteins and VSMC hypertrophy. Protein expression was determined by Western blotting, whereas protein synthesis and cell volume, markers for VSMC hypertrophy, were determined by [3H]-leucine incorporation and three-dimensional confocal imaging, respectively. The increased expression of Gqα/PLCβ1 proteins, increased protein synthesis, and augmented cell volume exhibited by VSMCs from SHRs were significantly attenuated by antioxidants N-acetyl-cysteine (NAC), a scavenger of superoxide anion, DPI, an inhibitor of NAD(P)H oxidase. In addition, PP2, AG1024, AG1478, and AG1295, inhibitors of c-Src, insulin-like growth factor receptor (IGFR), epidermal growth factor receptor (EGFR), and platelet-derived growth factor receptor (PDGFR), respectively, also attenuated the enhanced expression of Gqα/PLCβ1 proteins and enhanced protein synthesis in VSMCs from SHRs toward control levels. Furthermore, the levels of IGF-1R and EGFR proteins and not of PDGFR were also enhanced in VSMCs from SHRs, which were attenuated significantly by NAC, DPI, and PP2. In addition, NAC, DPI, and PP2 also attenuated the enhanced phosphorylation of IGF-1R, PDGFR, EGFR, c-Src, and EKR1/2 in VSMCs from SHRs. These data suggest that enhanced oxidative stress in VSMCs from SHRs activates c-Src, which through the transactivation of growth factor receptors and MAPK signaling contributes to enhanced expression of Gqα/PLCβ1 proteins and resultant VSMC hypertrophy.

Epidermal Growth Factor Receptor Transactivation: Mechanisms, Pathophysiology, and Potential Therapies in the Cardiovascular System

Epidermal growth factor receptor (EGFR) activation impacts the physiology and pathophysiology of the cardiovascular system, and inhibition of EGFR activity is emerging as a potential therapeutic strategy to treat diseases including hypertension, cardiac hypertrophy, renal fibrosis, and abdominal aortic aneurysm. The capacity of G protein-coupled receptor (GPCR) agonists, such as angiotensin II (AngII), to promote EGFR signaling is called transactivation and is well described, yet delineating the molecular processes and functional relevance of this crosstalk has been challenging. Moreover, these critical findings are dispersed among many different fields. The aim of our review is to highlight recent advancements in defining the signaling cascades and downstream consequences of EGFR transactivation in the cardiovascular renal system. We also focus on studies that link EGFR transactivation to animal models of the disease, and we discuss potential therapeutic applications.

Epidermal growth factor induces Ca(2+) sensitization through Rho-kinase-dependent phosphorylation of myosin phosphatase target subunit 1 in vascular smooth muscle

We previously found that the protein tyrosine phosphatase inhibitor orthovanadate evoked a vasoconstrictor effect in rat aortas via Rho-kinase-dependent inactivation of myosin light chain phosphatase (MLCP) downstream of epidermal growth factor (EGF) receptor signaling. To determine whether the direct activation of EGF receptor by EGF also induces Rho-kinase-dependent vasoconstriction, isometric tension changes were measured in rat aortic rings without endothelium. Although EGF did not produce a contractile effect, the Ca(2+)-induced force in Ca(2+)-depleted rings significantly increased after treatment with 100nM EGF, suggesting that EGF induces Ca(2+) sensitization by MLCP inactivation. In addition, EGF induced the activation of Rho-kinase and phosphorylation of myosin phosphatase target subunit 1 (MYPT1) in rat aortic smooth muscle cells (VSMCs). The effects of EGF on Ca(2+) sensitivity in aortas and MYPT1 phosphorylation in VSMCs were blocked by inhibitors of EGF receptor (AG1478), Rho-kinase (Y27632), extracellular signal-regulated kinase 1/2 (Erk1/2; FR180204), and mitogen/extracellular signal-regulated kinase (MEK; PD98059), but not by inhibitors of p38 kinase (SB203580) and c-Jun amino-terminal kinase (AS601245). EGF-induced Erk1/2 phosphorylation was not abrogated by the Rho-kinase inhibitor, suggesting that Rho-kinase-dependent phosphorylation of MYPT1 is downstream of EGF receptor/MEK/Erk1/2 signaling. These results suggest that EGF induces Ca(2+) sensitization in vascular smooth muscle by Rho-kinase-dependent inactivation of MLCP mediated by the EGF receptor/MEK/Erk1/2 pathway.

Mineralocorticoid receptor signaling: crosstalk with membrane receptors and other modulators

The mineralocorticoid receptor (MR) belongs to the steroid receptor superfamily. Classically, it acts as a ligand-bound transcription factor in epithelial tissues, where it regulates water and electrolyte homeostasis and controls blood pressure. Additionally, the MR has been shown to elicit pathophysiological effects including inflammation, fibrosis and remodeling processes in the cardiovascular system and the kidneys and MR antagonists have proven beneficial for patients with certain cardiovascular and renal disease. The underlying molecular mechanisms that mediate MR effects have not been fully elucidated but very likely rely on interactions with other signaling pathways in addition to genomic actions at hormone response elements. In this review we will focus on interactions of MR signaling with different membrane receptors, namely receptor tyrosine kinases and the angiotensin II receptor because of their potential relevance for disease. In addition, GPR30 is discussed as a new aldosterone receptor. To gain insights into the problem why the MR only seems to mediate pathophysiological effects in the presence of additional permissive factors we will also briefly discuss factors that lead to modulation of MR activity as well. Overall, MR signaling is part of an intricate network that still needs to be investigated further.

Involvement of two distinct signalling pathways in IGF-1-mediated central control of hypotensive effects in normotensive and hypertensive rats

AIMS

Insulin-like growth factor-1 (IGF-1) is abundantly expressed in the nucleus tractus solitarii (NTS). In a previous study, we revealed that the induction of nitric oxide (NO) production in the NTS reduces blood pressure (BP). It is well known that both acute administration and chronic administration of IGF-I reduce BP. The aim of this study was to evaluate the short-term hypotensive effect of IGF-1 in the NTS and to delineate the underlying molecular mechanisms of IGF-1 in the NTS of normotensive WKY rats and spontaneously hypertensive rats (SHRs).

METHOD

Microinjections of the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 and the MAP kinase-ERK kinase (MEK) inhibitor PD98059 into the NTS in WKY rats and SHRs were used to study the involvement of IGF-1-induced depressor effects.

RESULT

An IGF-1 (7.7 pmol) injection into the NTS resulted in a significant decrease in BP and HR in WKY rats and SHRs. Immunoblotting and immunohistochemical analysis showed that the microinjection of LY294002 (0.6 pmol) or PD98059 (3.0 pmol) into the NTS attenuated the IGF-1-induced depressor effects and Akt or ERK phosphorylation in WKY rats. An attenuation effect of LY294002, but not PD98059, was found in the SHRs. However, the mRNA and protein expression levels of the IGF-1R showed no significant differences in the NTS of the WKY rats and the SHRs.

CONCLUSION

These results suggest that distinct Akt and ERK signalling pathways mediated the IGF-1 control of the central depressor effects in WKY rats and SHRs. ERK signalling defects may be associated with the development of hypertension.

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.

Upregulation of Nox4 promotes angiotensin II-induced epidermal growth factor receptor activation and subsequent cardiac hypertrophy by increasing ADAM17 expression

BACKGROUND

Activation of epidermal growth factor receptor (EGFR) plays an important role in angiotensin II (Ang II)-induced cardiac hypertrophy, but little is known about the underlying mechanism that results in EGFR activation. In this study, we aimed to confirm the important role of nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4) in Ang II-induced EGFR activation and subsequent cardiac hypertrophy by upregulating expression of a disintegrin and metalloproteinase (MMP)-17 (ADAM17).

METHODS

Small interference RNA (siRNA) was adopted to knock down ADAM17 or Nox4 expression. Nox4 plasmid was used to construct cardiomyocytes with Nox4 overexpression.

RESULTS

Nox4 and ADAM17 increased in an abdominal artery coarctation-induced model of myocardial hypertrophy. In vitro studies showed that Nox4 was required in Ang II-induced EGFR activation and subsequent myocardial hypertrophy. Nox4 siRNA and Nox4 overexpression demonstrated that Nox4 controlled the transcription and translation of ADAM17. Furthermore, we observed that the ratio of phosphor-EGFR (p-EGFR) to EGFR was significantly reduced by ADAM17 siRNA in hypertrophic cardiomyocytes. Enzyme-linked immunosorbent assay studies revealed that Nox4 and ADAM17 mediated the release of mature heparin-binding EGF-like growth factor (HB-EGF), which played a critical role in the Ang II-induced EGFR activation. Moreover, the results of reactive oxygen species (ROS) scavenging by N-acetyl cysteine (NAC) indicated that ROS were required in the Nox4-mediated upregulation of ADAM17 expression.

CONCLUSIONS

In summary, Nox4 is required in Ang II-induced EGFR activation and subsequent cardiac hypertrophy; it increased the expression of ADAM17, which induced the release of mature HB-EGF. ROS were also required in the Nox4-mediated upregulation of ADAM17 expression.

α1-Adrenoceptor-mediated contraction of rat aorta is partly mediated via transactivation of the epidermal growth factor receptor

BACKGROUND AND PURPOSE

High level of plasma catecholamines is a risk factor for vascular diseases such as hypertension and atherosclerosis. Catecholamines induce hypertrophy of vascular smooth muscle through α(1) -adrenoceptors, which in cell culture involves the transactivation of epidermal growth factor receptor (EGFR). We hypothesized that EGFR transactivation was also involved in contractions of rat aorta mediated by α(1) -adrenoceptors.

EXPERIMENTAL APPROACH

Thoracic aorta was isolated from 12-14 week old male Wistar rats. In vitro aortic contractile responses to cumulative doses of phenylephrine were characterized in the absence and presence of the EGFR kinase inhibitors, AG1478 and DAPH, in intact and endothelium-denuded rings. Involvement of signal transduction pathways was investigated by using heparin and inhibitors of Src, matrix metalloproteinase (MMP), extracellular signal-regulated kinase (ERK)1/2 and phosphatidyl inositol 3-kinase (PI3K). Phosphorylation of EGFR and ERK1/2 was measured after short-term phenylephrine or EGF stimulation in aorta segments in the presence of AG1478 and the PI3K inhibitor, wortmannin.

KEY RESULTS

AG1478 and DAPH concentration dependently attenuated phenylephrine-induced contractile responses in intact or endothelium-denuded aortic rings. Inhibition of PI3K (wortmannin and LY294002) but not heparin or inhibitors of Src or MMP, prevented the effect of AG1478 on the responses to phenylephrine. Phenylephrine induced phosphorylation of EGFR, which was partially blocked by AG1478. Phenylephrine also increased phosphorylation of ERK1/2, time-dependently and was blocked by AG1478 and wortmannin.

CONCLUSIONS AND IMPLICATIONS

Contractions of rat thoracic aorta mediated by α(1) -adrenoceptors involved transactivation of EGFR, mediated via a PI3K and ERK1/2 dependent pathway.

Aerobic exercise training-induced left ventricular hypertrophy involves regulatory MicroRNAs, decreased angiotensin-converting enzyme-angiotensin ii, and synergistic regulation of angiotensin-converting enzyme 2-angiotensin (1-7)

Aerobic exercise training leads to a physiological, nonpathological left ventricular hypertrophy; however, the underlying biochemical and molecular mechanisms of physiological left ventricular hypertrophy are unknown. The role of microRNAs regulating the classic and the novel cardiac renin-angiotensin (Ang) system was studied in trained rats assigned to 3 groups: (1) sedentary; (2) swimming trained with protocol 1 (T1, moderate-volume training); and (3) protocol 2 (T2, high-volume training). Cardiac Ang I levels, Ang-converting enzyme (ACE) activity, and protein expression, as well as Ang II levels, were lower in T1 and T2; however, Ang II type 1 receptor mRNA levels (69% in T1 and 99% in T2) and protein expression (240% in T1 and 300% in T2) increased after training. Ang II type 2 receptor mRNA levels (220%) and protein expression (332%) were shown to be increased in T2. In addition, T1 and T2 were shown to increase ACE2 activity and protein expression and Ang (1-7) levels in the heart. Exercise increased microRNA-27a and 27b, targeting ACE and decreasing microRNA-143 targeting ACE2 in the heart. Left ventricular hypertrophy induced by aerobic training involves microRNA regulation and an increase in cardiac Ang II type 1 receptor without the participation of Ang II. Parallel to this, an increase in ACE2, Ang (1-7), and Ang II type 2 receptor in the heart by exercise suggests that this nonclassic cardiac renin-angiotensin system counteracts the classic cardiac renin-angiotensin system. These findings are consistent with a model in which exercise may induce left ventricular hypertrophy, at least in part, altering the expression of specific microRNAs targeting renin-angiotensin system genes. Together these effects might provide the additional aerobic capacity required by the exercised heart.

Consequences of epidermal growth factor receptor (ErbB1) loss for vascular smooth muscle cells from mice with targeted deletion of ErbB1

OBJECTIVE

Pathophysiological effects of the epidermal growth factor receptor (EGFR or ErbB1) include vascular remodeling. EGFR transactivation is proposed to contribute significantly to heterologous signaling and remodeling in vascular smooth muscle cells (VSMC).

METHODS AND RESULTS

We investigated the importance of EGFR in primary VSMC from aorta of mice with targeted deletion of the EGFR (EGFR(Δ/Δ VSMC)→VSMC(EGFR-/-) and EGFR(Δ/+ VSMC)→VSMC(EGFR+/-)) and the respective littermate controls (EGFR(+/+ VSMC)→VSMC(EGFR+/+)) with respect to survival, pentose phosphate pathway activity, matrix homeostasis, extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation, and Ca(2+) homeostasis. In VSMC(EGFR-/-), epidermal growth factor-induced signaling was abolished; VSMC(EGFR+/-) showed an intermediate phenotype. EGFR deletion enhanced spontaneous cell death, reduced pentose phosphate pathway activity, disturbed cellular matrix homeostasis (collagen III and fibronectin), and abolished epidermal growth factor sensitivity. In VSMC(EGFR-/-) endothelin-1- or α(1)-adrenoceptor-induced ERK1/2 phosphorylation and the fraction of Ca(2+) responders were significantly reduced, whereas responsive cells showed a significantly stronger Ca(2+) signal. Oxidative stress (H(2)O(2)) induced ERK1/2 activation in VSMC(EGFR+/+) and VSMC(EGFR+/-) but not in VSMC(EGFR-/-). The Ca(2+) signal was enhanced in VSMC(EGFR-/-), similar to purinergic stimulation by ATP.

CONCLUSIONS

In conclusion, EGFR was found to be important for basal VSMC homeostasis and ERK1/2 activation by the tested G-protein-coupled receptors or radical stress. Ca(2+) signaling was modulated by EGFR differentially with respect to the fraction of responders and magnitude of the signal. Thus, EGFR seems to be Janus-faced for VSMC biology.

Targeting non-malignant disorders with tyrosine kinase inhibitors

Receptor and non-receptor tyrosine kinases are involved in multiple proliferative signalling pathways. Imatinib, one of the first tyrosine kinase inhibitors (TKIs) to be approved, revolutionized the treatment of chronic myelogenous leukaemia, and other TKIs with different spectra of kinase inhibition are used to treat renal cell carcinoma, non-small-cell lung cancer and colon cancer. Studies also support the potential use of TKIs as anti-proliferative agents in non-malignant disorders such as cardiac hypertrophy, and in benign-proliferative disorders including pulmonary hypertension, lung fibrosis, rheumatoid disorders, atherosclerosis, in-stent restenosis and glomerulonephritis. In this Review, we provide an overview of the most recent developments--both experimental as well as clinical--regarding the therapeutic potential of TKIs in non-malignant disorders.

Silibinin attenuates cardiac hypertrophy and fibrosis through blocking EGFR-dependent signaling

Cardiac hypertrophy is a major determinant of heart failure. The epidermal growth factor receptor (EGFR) plays an important role in cardiac hypertrophy. Since silibinin suppresses EGFR in vitro and in vivo, we hypothesized that silibinin would attenuate cardiac hypertrophy through disrupting EGFR signaling. In this study, we examined this hypothesis using neonatal cardiac myocytes and fibroblasts induced by angiotensin II (Ang II) and animal model by aortic banding (AB) mice. Our data revealed that silibinin obviously blocked cardiac hypertrophic responses induced by pressure overload. Meanwhile, silibinin markedly reduced the increased generation of EGFR. Moreover, these beneficial effects were associated with attenuation of the EGFR-dependent ERK1/2, PI3K/Akt signaling cascade. We further demonstrated silibinin decreased inflammation and fibrosis by blocking the activation of NF-kappaB and TGF-beta1/Smad signaling pathways in vitro and in vivo. Our results indicate that silibinin has the potential to protect against cardiac hypertrophy, inflammation, and fibrosis through blocking EGFR activity and EGFR-dependent different intracellular signaling pathways.

Modulation of Gi Proteins in Hypertension: Role of Angiotensin II and Oxidative Stress

Guanine nucleotide regulatory proteins (G-proteins) play a key role in the regulation of various signal transduction systems including adenylyl cyclase/cAMP and phospholipase C (PLC)/phosphatidyl inositol turnover (PI). These are implicated in the modulation of a variety of physiological functions such as platelet functions, cardiovascular functions, including arterial tone and reactivity. Several abnormalities in adenylyl cyclase activity, cAMP levels and G proteins have shown to be responsible for the altered cardiac performance and vascular functions observed in cardiovascular disease states. The enhanced or unaltered levels of inhibitory G-proteins (Giα-2 and Giα-3) and mRNA have been reported in different models of hypertension, whereas Gsα levels were shown to be unaltered. These changes in G-protein expression were associated with Gi functions. The enhanced levels of Giα proteins precede the development of blood pressure and suggest that overexpression of Gi proteins may be one of the contributing factors for the pathogenesis of hypertension. The augmented levels of vasoactive peptides, including angiotensin II (AngII), were shown to contribute to enhanced expression of Giα proteins and associated adenylyl cyclase signaling and thereby increased blood pressure. In addition, enhanced oxidative stress in hypertension due to Ang II may also be responsible for the enhanced expression of Giα proteins observed in hypertension. The mechanism by which oxidative stress enhances the expression of Gi proteins appears to be through the activation of mitogen activated protein (MAP) kinase activity.

Acute and chronic adrenergic stimulation of submandibular salivary glands. Effects on the endocrine function of epidermal growth factor in mice

Submandibular salivary glands are the major source of epidermal growth factor (EGF) in mice. Acute secretion of EGF from these glands protects the heart against catecholamine-induced injury. Little is known about chronic adrenergic stimulation of salivary glands and the contribution of accumulated EGF to the adaptive hypertrophic response of the heart to such chronic adrenergic stimulation. Here we show that the EGF content of submandibular glands did not recover to normal values 24 h after a single phenylephrine injection or an aggressive encounter. Repeated (twice a day for 2 days) adrenergic stimulation resulted in an almost 90% decrease in EGF content in the submandibular glands. In these conditions, new adrenergic stimulation did not result in an increase in plasma EGF concentration, or in the activation of liver ErbB1 (the EGF receptor). Chronic isoproterenol or phenylephrine administration (7 days) induced atrial natriuretic factor expression in the heart and an increase in both ventricular weight and protein. The surgical removal of submandibular glands (sialoadenectomy) did not affect these adaptive responses of the heart. We conclude that EGF from submandibular glands does not contribute to heart hypertrophy, one of the adaptive responses induced by chronic adrenergic stimulation.

New aspects of rapid aldosterone signaling

Aldosterone, the endogenous ligand of the mineralocorticoid receptor (MR) in humans, is a steroid hormone that regulates salt and water homeostasis. Recently, additional pathophysiological effects in the renocardiovascular system have been identified. Besides genomic effects mediated by activated MR, rapid aldosterone actions that are independent of translation and transcription have been documented. While these nongenomic actions influence electrolyte homeostasis, pH and cell volume in classical MR target organs, they also participate in pathophysiological effects in the renocardiovascular system causing endothelial dysfunction, inflammation and remodeling. The mechanisms conveying these rapid effects consist of a multitude of signaling molecules and include a cross-talk with genomic aldosterone effects as well as with angiotensin II and epidermal growth factor receptor signaling. Rapid corticosteroid signaling via the MR has also been demonstrated in the brain. Altogether, the function of nongenomic aldosterone effects seems to be to modulate other signaling cascades, depending on the surrounding milieu.

Global upregulation of gene expression associated with renal dysfunction in DOCA-salt-induced hypertensive rats occurs via signaling cascades involving epidermal growth factor receptor: a microarray analysis

Renal dysfunction is a major cause of morbidity and mortality in patients with hypertension. In an attempt to understand the molecular mechanisms leading to renal dysfunction and in particular that of epidermal growth factor receptor (EGFR) and RasGTPase signaling, we analyzed global gene expression changes in the kidneys of deoxycorticosterone acetate (DOCA)-salt-induced hypertensive rats with and without treatment with AG1478, a selective inhibitor of EGFR tyrosine kinase, or FPTIII, a farnesyl transferase inhibitor known to inhibit RasGTPase. Microarray-based global gene expression analysis was performed in triplicate for each rat kidney taken from normotensive Wistar rats, DOCA-salt hypertensive (DH) rats, DH rats treated with AG1478, or DH rats treated with FPTIII. From the initial data set of 10,163 gene spots per group, upregulation of 2398 genes and downregulation of only 50 genes by more than 2-fold was observed in hypertensive rat kidneys compared to non-diseased controls. Interestingly, treatment of animals with AG1478 or FPTIII prevented upregulation of more than 97% of genes associated with hypertension in the rat kidney. Analysis of proteinuria, renal artery responsiveness and histopathology studies confirmed that DOCA-salt hypertensive rats had developed kidney damage over the study period and that this kidney dysfunction could be significantly prevented upon AG1478 or FPTIII treatment without normalising blood pressure. Taken together, our data imply that signaling cascades involving EGFR and/or RasGTPase pathways are key contributors to the induction of renal damage in hypertension and these and potentially other downstream effector molecules may serve as novel targets for therapeutic intervention.

Overcoming biological barriers to in vivo efficacy of antisense oligonucleotides

Antisense oligonucleotides as a therapeutic platform have been slow to progress since the approval of the first antisense drug in 1998. Recently, there have been several examples of convincing antisense interventions in animal models and promising clinical trial data. This review considers the factors determining the success of antisense oligonucleotides as therapeutic agents. In order to produce target knockdown after systemic delivery, antisense oligonucleotides must avoid nuclease degradation, reticuloendothelial-system uptake and rapid renal excretion, and extravasate to the target cell type outside the vasculature. They then must enter the target cell, and escape the endosome-lysosome pathway so as to be free to interact with the target mRNA. We consider the significance of these limiting factors based on the literature and our own experience using systemic administration of antisense oligonucleotides.

Targeted expression of receptor-associated late transducer inhibits maladaptive hypertrophy via blocking epidermal growth factor receptor signaling

Receptor-associated late transducer (RALT) is a feedback inhibitor of epidermal growth factor receptor signaling. RALT has been shown previously to be induced in the ischemic heart and to promote cardiomyocyte apoptosis in vitro. However, the role of RALT in cardiac hypertrophy remains unclear. We hypothesized that forced expression of RALT in the murine heart would protect the heart against cardiac hypertrophy in vivo. We investigated the effect of cardiac overexpression of rat RALT on cardiac hypertrophy induced by angiotensin II and isoproterenol in RALT transgenic mice and wild-type littermates. The extent of cardiac hypertrophy was assessed by 2D and M-mode echocardiography as well as by molecular and pathological analyses of cardiac samples. Constitutive expression of rat RALT in cardiac myocytes of murine heart attenuated both hypertrophic and inflammatory responses and preserved cardiac function. These beneficial effects were associated with the attenuation of the epidermal growth factor receptor-dependent cascade that was triggered by angiotensin II and isoproterenol stimulation. Additional evidence demonstrated that RALT expression blocked fibrosis in vivo and collagen synthesis in vitro. Therefore, cardiac overexpression of RALT improves cardiac function and inhibits maladaptive hypertrophy, inflammation, and fibrosis through attenuating epidermal growth factor receptor-dependent signaling.

Aldosterone-and-salt-induced cardiac fibrosis is independent from angiotensin II type 1a receptor signaling in mice

Aldosterone infusion with high salt treatment induces cardiac fibrosis in rats. Aldosterone enhanced angiotensin II (Ang II) has been shown to induce proliferation and increase the expression of Ang II receptor mRNA and Ang II binding in vitro. To investigate the role of Ang II type 1a receptor (AT1aR) in aldosterone-and-salt (Ald-NaCl)-induced cardiac fibrosis, we subcutaneously infused aldosterone (0.15 microg/h) and 1% NaCl (Ald-NaCl) into AT1aR knockout mice (AT1aR-KO) or wild type mice (Wt). To examine the role of NaCl on cardiac fibrosis, we gave some of the aldosterone-treated AT1aR-KO tap water (Ald-H2O). Ald-NaCl treatment increased systolic blood pressure and induced cardiac hypertrophy in both strains, whereas there were no such changes in the mice without aldosterone. Severe cardiac fibrosis was seen in Ald-NaCl-treated AT1aR-KO and not in Ald-NaCl-treated Wt. In contrast, Ald-NaCl-treated Wt with co-administration of an active metabolite of olmesartan, the AT1aR antagonist (10 mg/kg/day) did not show cardiac fibrosis. Na+/H+ exchanger, and Na+-K+ ATPase alpha2 subunit mRNA were decreased in AT1aR-KO. Na+/Ca2) exchanger mRNA was lower in AT1aR-KO than Wt and was decreased by Ald-NaCl in both strains. Phosphorylation of epidermal growth factor receptor and extracellular signal-regulated kinase was increased by Ald-NaCl treatment in AT1aR-KO. Connective tissue growth factor (CTGF) and osteopontin mRNA were increased and accumulation of CTGF proteins was seen in the hearts of Ald-NaCl-treated AT1aR-KO. Ald-H2O-treated AT1aR-KO did not show any cardiac fibrosis. These results suggest that Ald-NaCl-induced cardiac fibrosis required both aldosterone and salt. Because cardiac fibrosis was exaggerated in Ald-NaCl-treated AT1aR-KO but was not seen in Wt treated with Ald-NaCl and olmesartan, AT1aR may not play a primary role in progression of cardiac fibrosis by Ald-NaCl, and gene disruption of AT1aR may have some implications in this model.

Non-classical actions of the mineralocorticoid receptor: misuse of EGF receptors?

The mineralocorticoid receptor (MR) plays a key role in cardiovascular and renal injury. The underlying mechanisms seem to involve the epidermal growth factor receptor (EGFR) for the development of fibrosis and vascular dysfunction. Both enhanced EGFR transactivation by activated MR as well as upregulation of EGFR expression by aldosterone-bound MR have been described. While the former seems to be mediated by the tyrosine kinase cSrc, reporter gene assays and chromatin immunoprecipitation data indicate that the latter is caused by an interaction between MR and the EGFR promoter. Pharmacological inhibition of EGFR function prevents some of MR's pathological actions in cell culture systems, like vascular smooth muscle cells. Thus, transactivation as well as enhanced expression of EGFR may be an important switch for the pathophysiological actions in the reno-cardiovascular continuum. Furthermore, EGFR signaling may serve as a negative feedback loop to limit sodium retention. Overall, MR's "misuse" of the EGFR is one possible explanation for the pathophysiological effects of aldosterone, making the EGFR a potential target for therapeutical interventions against reno-cardiovascular remodelling.

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.

Therapeutic potential of the epidermal growth factor receptor transactivation in hypertension: a convergent signaling pathway of vascular tone, oxidative stress, and hypertrophic growth downstream of vasoactive G-protein-coupled receptors?

The concurrence of enhanced vascular tone, oxidative stress, and hypertrophic growth is a hallmark of hypertension, the condition characterized by sustained elevated blood pressure. However, it is unclear how and why such apparently distinct processes coincide in hypertension. Elevated levels of certain vasoactive G-protein-coupled receptor agonists (such as catecholamines, endothelin-1, and angiotensin II) can explain, at least in part, the development and progression of many hypertensive disorders. Here, we review findings made by other investigators and ourselves suggesting that enhanced vascular tone, oxidative stress, and hypertrophic growth characteristically induced by these agonists involve the transactivation of growth factor receptors. The first step in this transactivation mechanism is agonist-induced activation of metalloproteinase-dependent shedding of growth factors. Shed growth factors then trigger intracellular signaling cascades necessary for growth, production of reactive oxygen species, and maintenance of vascular tone. If this hypothesis is proven generally correct, then transactivation blockers have general therapeutic potential in hypertension regardless of the causative agonist.

The Popdc gene family in the rat: molecular cloning, characterization and expression analysis in the heart and cultured cardiomyocytes

Three Popeye domain-containing (Popdc 1-3) family-members are known in vertebrates. Their exact function is as yet unknown although involvement in cell adhesion has been suggested. We report herein sequencing of the rat Popdc 1-3 cDNAs that show high homology to other vertebrate orthologs and are expressed primarily in the heart and skeletal muscles. Popdc2 splice variants were identified, with Popdc2C showing a distinctive age-dependent decline. In isolated cardiomyocytes, Popdc genes were negatively regulated by serum, an effect that was reversed by EGFR-kinase inhibition, suggesting an EGFR-dependent modulation of Popdc gene expression.

Aldosterone-induced EGFR expression: interaction between the human mineralocorticoid receptor and the human EGFR promoter

Aldosterone plays a key role in cardiovascular and renal injury. The underlying mechanisms are not completely understood. Because the epidermal growth factor receptor (EGFR) is involved in the development of fibrosis and vascular dysfunction, upregulation of EGFR expression by aldosterone-bound mineralocorticoid receptor (MR) is an attractive hypothesis. We investigated the effect of aldosterone on EGFR expression in the aorta of adrenalectomized rats and in human aorta smooth muscle cells (HAoSMC) in primary culture. Aldosterone, but not dexamethasone, stimulated EGFR expression in vivo in the aorta as well as in HAoSMC. EGFR degradation was not affected. Aldosterone-induced EGFR expression in HAoSMC was dose dependent and prevented by spironolactone. Furthermore, incubation of HAoSMC with aldosterone led to enhanced EGF-induced ERK1/2 phosphorylation and an EGFR-dependent increase in media fibronectin. EGFR promoter reporter gene assay as well as chromatin immunoprecipitation data indicate that MR interacts with the EGFR promoter. With deletion constructs we gained evidence that this interaction takes place between the hMR and the EGFR promoter regions 316-163 (stronger activation site, EC50 approximately 1.0 nM) and 163-1 (weaker activation site, EC50 approximately 0.7 nM), which do not comprise canonical glucocorticoid response elements and are not activated by the human glucocorticoid receptor. The interactions require in part the NH2-terminal domains of MR. ELISA-based transcription factor DNA binding assay with in vitro synthesized hMR suggest direct binding to region 163-1. Our results indicate that aldosterone leads to enhanced EGFR expression via an interaction with the EGFR promoter, which is MR specific and could contribute to the aldosterone-induced increase in fibronectin abundance.

Altered collagen homeostasis in human aortic smooth muscle cells (HAoSMCs) induced by aldosterone

The importance of aldosterone for cardiovascular diseases is well established. Most of the adverse effects seem to originate from its ability to produce vascular injury, including fibrosis. It is currently under debate whether aldosterone per se is able to induce fibrosis or whether it acts as a cofactor under pathological conditions. We tested whether aldosterone per se and in the presence of reactive oxygen stress (H(2)O(2)) enhances collagen abundance in human aortic smooth muscle cell (HAoSMC) media in primary culture and, if so, by which means. Collagen abundance, as well as epidermal growth factor receptor (EGFR) expression and ERK1/2 phosphorylation, was investigated by ELISA and Western blot. Collagenase activity and H(2)O(2) formation were determined by fluorometry and luminometry. Aldosterone alone did not affect collagen abundance but potentiated the stimulatory effect of low concentrations of H(2)O(2) (1-10 micromol/l). This effect disappeared when shedding of membrane-bound EGFR ligands was prevented by GM6001. EGFR expression and cellular EGF responsiveness were enhanced by aldosterone. Inhibition of the EGFR kinase (tyrphostin AG1478) prevented the increase of collagen. The increase in collagen abundance was prevented by blockade of the mineralocorticoid receptor (MR) and could be reproduced by MR transfection into Chinese hamster ovary cells. We conclude that aldosterone sensitizes HAoSMC for H(2)O(2)-induced increase of collagen abundance at least in part by enhanced EGFR expression.

Impaired IGF-I signalling of hypertrophic hearts in the developmental phase of hypertension in genetically hypertensive rats

Insulin-like growth factor-I (IGF-I) signalling is reported to contribute to the modulation of blood pressure and set survival and hypertrophic responses in cardiac tissue. However, whether IGF-I signalling normally acts in cardiac tissues of hypertensive rats is unknown. In this study, using spontaneously hypertensive rats (SHR) and stroke-prone spontaneously hypertensive rats (SPSHR), both with early blood pressure increases, and Wistar-Kyoto (WKY) rats as controls, we measured the hypertrophic and IGF-I signalling activity changes in rat hearts at 4, 6 and 12 weeks of age. Both SHR and SPSHR were found to have significantly increased blood pressures and ratios of heart- and left ventricle- to body weight at 12 weeks of age. However, IGF-IR and its downstream signalling, including the protein levels of PI3K and phosphorylated Akt, known to maintain physiological cardiac hypertrophy and cardiomyocyte survival, were downregulated. The results of dot blotting showed that cardiac mRNA levels of IGF-I in hypertensive rats were higher than those in controls starting from the age of 4 weeks. This difference suggests the increased ligand IGF-I mRNA levels may be a compensatory response caused by the impaired IGF-I signalling. Moreover, enhanced cardiac cytosolic cytochrome-c, a mitochondria-dependent apoptotic pathway component, tended to occur in both hypertensive rats, although it did not reach a significant level. These findings indicate that impaired IGF-IR signalling occurs at early stages, and it may contribute, at least partially, to the development of hypertension and pathological cardiac hypertrophy and to cardiomyocyte apoptosis at later stages in SHR and SPSHR.

Cardioprotective mechanisms of spironolactone associated with the angiotensin-converting enzyme/epidermal growth factor receptor/extracellular signal-regulated kinases, NAD(P)H oxidase/lectin-like oxidized low-density lipoprotein receptor-1, and Rho-kinase pathways in aldosterone/salt-induced hypertensive rats

Studies were performed to test the hypothesis that the angiotensin-converting enzyme (ACE)/epidermal growth factor receptor (EGFR)/extracellular signal-regulated kinases (ERK) pathway, nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase/lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) pathway, and Rho-kinase pathway contribute to the pathogenesis of aldosterone/salt-induced hypertensive rats. Wistar rats were given 1% NaCl to drink and treated with one of the following combinations for 6 weeks: vehicle; aldosterone (0.75 microg/h); aldosterone plus a mineralocorticoid receptor antagonist, spironolactone (20 mg/kg/day); aldosterone plus an ACE inhibitor, imidapril (1 mg/kg/day); aldosterone plus an NAD(P)H oxidase inhibitor, apocynin (0.5 mmol/l); and aldosterone plus an Rho-kinase inhibitor, Y-27632 (3 mg/kg/day). Upregulated expression of ACE and EGFR and p44/p42ERK phosphorylation were suppressed by spironolactone or imidapril. Upregulated NAD(P)H oxidase subunits and LOX-1 expression were inhibited by spironolactone or apocynin. Increased expression of RhoA and Rho-kinase and myosin light chain phosphorylation were decreased by spironolactone or Y-27632. Moreover, these drugs effectively inhibited the vascular lesion formation, as measured by the medial thickness and level of perivascular fibrosis, and suppressed the expression of transforming growth factor-beta1, type I and III collagen, and monocyte chemoattractant protein-1 mRNA. Spironolactone may be useful as a cardioprotective agent to prevent cardiovascular remodeling via the ACE/EGFR/ERK, NAD(P)H oxidase/LOX-1, and Rho-kinase pathways.

Human Mineralocorticoid Receptor Expression Renders Cells Responsive for Nongenotropic Aldosterone Actions

The steroid hormone aldosterone is important for salt and water homeostasis as well as for pathological tissue modifications in the cardiovascular system and the kidney. The mechanisms of action include a classical genomic pathway, but physiological relevant nongenotropic effects have also been described. Unlike for estrogens or progesterone, the mechanisms for these nongenotropic effects are not well understood, although pharmacological studies suggest a role for the mineralocorticoid receptor (MR). Here we investigated whether the MR contributes to nongenotropic effects. After transfection with human MR, aldosterone induced a rapid and dose-dependent phosphorylation of ERK1/2 and c-Jun NH2-terminal kinase (JNK) 1/2 kinases in Chinese hamster ovary or human embryonic kidney cells, which was reduced by the MR-antagonist spironolactone and involved cSrc kinase as well as the epidermal growth factor receptor. In primary human aortic endothelial cells, similar results were obtained for ERK1/2 and JNK1/2. Inhibition of MAPK kinase (MEK) kinase but not of protein kinase C prevented the rapid action of aldosterone and also reduced aldosterone-induced transactivation, most probably due to impaired nuclear-cytoplasmic shuttling of MR. Cytosolic Ca2+ was increased by aldosterone in mock- and in human MR-transfected cells to the same extend due to Ca2+ influx, whereas dexamethasone had virtually no effect. Spironolactone did not prevent the Ca2+ response. We conclude that some nongenotropic effects of aldosterone are MR dependent and others are MR independent (e.g. Ca2+), indicating a higher degree of complexity of rapid aldosterone signaling. According to this model, we have to distinguish three aldosterone signaling pathways: 1) genomic via MR, 2) nongenotropic via MR, and 3) nongenotropic MR independent.

PGE2-induced hypertrophy of cardiac myocytes involves EP4 receptor-dependent activation of p42/44 MAPK and EGFR transactivation

Upon induction of cyclooxygenase-2 (COX-2), neonatal ventricular myocytes (VMs) mainly synthesize prostaglandin E2 (PGE2). The biological effects of PGE2 are mediated through four different G protein-coupled receptor (GPCR) subtypes (EP1–4). We have previously shown that PGE2 stimulates cAMP production and induces hypertrophy of VMs. Because the EP4 receptor is coupled to adenylate cyclase and increases in cAMP, we hypothesized that PGE2 induces hypertrophic growth of cardiac myocytes through a signaling cascade that involves EP4-cAMP and activation of protein kinase A (PKA). To test this, we used primary cultures of VMs and measured [3H]leucine incorporation into total protein. An EP4 antagonist was able to partially block PGE2 induction of protein synthesis and prevent PGE2-dependent increases in cell surface area and activity of the atrial natriuretic factor promoter, which are two other indicators of hypertrophic growth. Surprisingly, a PKA inhibitor had no effect. In other cell types, G protein-coupled receptor activation has been shown to transactivate the epidermal growth factor receptor (EGFR) and result in p42/44 mitogen-activated protein kinase (MAPK) activation and cell growth. Immunoprecipitation of myocyte lysates demonstrated that the EGFR was rapidly phosphorylated by PGE2 in VMs, and the EP4 antagonist blocked this. In addition, the selective EGFR inhibitor AG-1478 completely blocked PGE2-induced protein synthesis. We also found that PGE2 rapidly phosphorylated p42/44 MAPK, which was inhibited by the EP4 antagonist and by AG-1478. Finally, the p42/44 MAPK inhibitor PD-98053 (25 μmol/l) blocked PGE2-induced protein synthesis. Altogether, we believe these are the first data to suggest that PGE2 induces protein synthesis in cardiac myocytes in part via activation of the EP4 receptor and subsequent activation of p42/44 MAPK. Activation of p42/44 MAPK is independent of the common cAMP-PKA pathway and involves EP4-dependent transactivation of EGFR.

Agonist-Induced Activation of Matrix Metalloproteinase-7 Promotes Vasoconstriction Through the Epidermal Growth Factor–Receptor Pathway

Matrix metalloproteinase (MMP)-dependent shedding of heparin-binding epidermal growth factor (HB-EGF) and subsequent activation of the EGF receptor (EGFR) in the cardiovasculature is emerging as a unique mechanism signaling growth effects of diverse G protein–coupled receptors (GPCRs). Among these GPCRs are adrenoceptors and angiotensin receptors that contribute to the pathogenesis of hypertension through their vasoconstrictive and growth effects. Focusing on α 1b -adrenoceptors, we suggest here that MMP-dependent activation of the EGFR promotes vasoconstriction as well as growth. We identified MMP-7 as a major HB-EGF sheddase in rat mesenteric arteries and α 1b -adrenoceptors, angiotensin receptors, and hypertension-stimulated MMP-7 activity. Adrenoceptors stimulated EGFR autophosphorylation in arteries, and this transactivation was opposed by the MMP-7 inhibitor GM6001 as well as MMP-7–specific antibodies. In isolated microperfused arteries, blockade of EGFR transactivation with inhibitors of the EGFR (AG1478 and PD153035), HB-EGF (CRM197 and neutralizing antibodies), or MMPs (doxycycline) inhibited adrenergic vasoconstriction. In spontaneously hypertensive rats but not in normotensive rats, the inhibition of MMPs with doxycycline (19.2 mg/d from week 7 until week 12) reduced systolic blood pressure and attenuated HB-EGF shedding in the mesenteric arteries. These findings suggest a previously unknown mechanism of vasoregulation whereby agonists of certain GPCRs (such as adrenoceptors and angiotensin receptors) activate MMPs (such as MMP-7) that shed EGFR ligands (such as HB-EGF), which then activate the EGFR, thereby promoting vasoconstriction as well as growth. Because this mechanism is triggered by agonists typically overexpressed in hypertension, its blockade may have therapeutic potential for simultaneously inhibiting pathological vasoconstriction and growth in hypertensive disorders.