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

Revising the Roles of Aldosterone in Vascular Physiology and Pathophysiology: From Electocortin to Baxdrostat

Aldosterone was initially identified as a hormone primarily related to regulation of fluid and electrolyte homeostasis. However, over the past 20 years there has been an increasing appreciation of its role in regulation of vascular function and pathophysiology in the setting of hypertension, atherosclerosis, and heart failure. This review highlights recent advances in our understanding the biology of aldosterone as it relates to the pathophysiology and the management of vascular disease-especially related to hypertension. The review focuses on 3 key areas: 1) advances in our understanding of the cellular mechanisms by which aldosterone mediates its cellular effects, 2) identification of the hidden epidemic of aldosteronism as a mediator of hypertension, and 3) appreciating new therapeutic advances in the clinical pharmacology of aldosterone inhibition in cardiovascular and renal disease.

Importance of Micromilieu for Pathophysiologic Mineralocorticoid Receptor Activity—When the Mineralocorticoid Receptor Resides in the Wrong Neighborhood

The mineralocorticoid receptor (MR) is a member of the steroid receptor family and acts as a ligand-dependent transcription factor. In addition to its classical effects on water and electrolyte balance, its involvement in the pathogenesis of cardiovascular and renal diseases has been the subject of research for several years. The molecular basis of the latter has not been fully elucidated, but an isolated increase in the concentration of the MR ligand aldosterone or MR expression does not suffice to explain long-term pathologic actions of the receptor. Several studies suggest that MR activity and signal transduction are modulated by the surrounding microenvironment, which therefore plays an important role in MR pathophysiological effects. Local changes in micromilieu, including hypoxia, ischemia/reperfusion, inflammation, radical stress, and aberrant salt or glucose concentrations affect MR activation and therefore may influence the probability of unphysiological MR actions. The surrounding micromilieu may modulate genomic MR activity either by causing changes in MR expression or MR activity; for example, by inducing posttranslational modifications of the MR or novel interaction with coregulators, DNA-binding sites, or non-classical pathways. This should be considered when developing treatment options and strategies for prevention of MR-associated diseases.

The Potential Tumor-Suppressor DHRS7 Inversely Correlates with EGFR Expression in Prostate Cancer Cells and Tumor Samples

Simple Summary

Prostate cancer is one of the most common malignancies in men. Current therapies are initially effective but resistance often develops, leading to tumor recurrence and death. Further research on new players, mechanisms involved in prostate cancer, and therapy resistance is needed. We studied the role of DHRS7, a potential tumor suppressor with currently unknown physiological function, in prostate cancer cells using proteome and gene expression analyses. Despite the fact that DHRS7 can inactivate 5α-dihydrotestosterone, its effect on prostate cancer cells seems to be unrelated to androgen metabolism. When comparing three widely studied prostate cancer cell lines, we observed a negative correlation between DHRS7 and EGFR expression. DHRS7 knockdown enhanced EGFR expression, while knockdown of EGFR tended to increase DHRS7 expression. Importantly, DHRS7 expression negatively correlates with EGFR expression and positively with survival rates in prostate cancer patients. This study suggests a tumor-suppressor role for DHRS7 by modulating EGFR expression in prostate cancer.

Abstract

Prostate cancer (PCa), one of the most common malignancies in men, typically responds to initial treatment, but resistance to therapy often leads to metastases and death. The dehydrogenase/reductase 7 (DHRS7, SDR34C1) is an “orphan” enzyme without known physiological function. DHRS7 was previously found to be decreased in higher-stage PCa, and siRNA-mediated knockdown increased the aggressiveness of LNCaP cells. To further explore the role of DHRS7 in PCa, we analyzed the proteome of LNCaP cells following DHRS7 knockdown to assess potentially altered pathways. Although DHRS7 is able to inactivate 5α-dihydrotestosterone, DHRS7 knockdown did not affect androgen receptor (AR) target gene expression, and its effect on PCa cells seems to be androgen-independent. Importantly, proteome analyses revealed increased expression of epidermal growth factor receptor (EGFR), which was confirmed by RT-qPCR and Western blotting. Comparison of AR-positive LNCaP with AR-negative PC-3 and DU145 PCa cell lines revealed a negative correlation between DHRS7 and EGFR expression. Conversely, EGFR knockdown enhanced DHRS7 expression in these cells. Importantly, analysis of patient samples revealed a negative correlation between DHRS7 and EGFR expression, both at the mRNA and protein levels, and DHRS7 expression correlated positively with patient survival rates. These results suggest a protective role for DHRS7 in PCa.

Neurohormones, inflammatory mediators, and cardiovascular injury in the setting of heart failure

Neurohormones and inflammatory mediators have effects in both the heart and the peripheral vasculature. In patients with heart failure (HF), neurohormonal activation and increased levels of inflammatory mediators promote ventricular remodeling and development of HF, as well as vascular dysfunction and arterial stiffness. These processes may lead to a vicious cycle, whereby arterial stiffness perpetuates further ventricular remodeling leading to exacerbation of symptoms. Although significant advances have been made in the treatment of HF, currently available treatment strategies slow, but do not halt, this cycle. The current treatment for HF patients involves the inhibition of neurohormonal activation, which can reduce morbidity and mortality related to this condition. Beyond benefits associated with neurohormonal blockade, other strategies have focused on inhibition of inflammatory pathways implicated in the pathogenesis of HF. Unfortunately, attempts to target inflammation have not yet been successful to improve prognosis of HF. Further work is required to interrupt key maladaptive mechanisms involved in disease progression.

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.

Impact of Aldosterone on the Failing Myocardium: Insights from Mitochondria and Adrenergic Receptors Signaling and Function

The mineralocorticoid aldosterone regulates electrolyte and blood volume homeostasis, but it also adversely modulates the structure and function of the chronically failing heart, through its elevated production in chronic human post-myocardial infarction (MI) heart failure (HF). By activating the mineralocorticoid receptor (MR), a ligand-regulated transcription factor, aldosterone promotes inflammation and fibrosis of the heart, while increasing oxidative stress, ultimately induding mitochondrial dysfunction in the failing myocardium. To reduce morbidity and mortality in advanced stage HF, MR antagonist drugs, such as spironolactone and eplerenone, are used. In addition to the MR, aldosterone can bind and stimulate other receptors, such as the plasma membrane-residing G protein-coupled estrogen receptor (GPER), further complicating it signaling properties in the myocardium. Given the salient role that adrenergic receptor (ARs)—particularly βARs—play in cardiac physiology and pathology, unsurprisingly, that part of the impact of aldosterone on the failing heart is mediated by its effects on the signaling and function of these receptors. Aldosterone can significantly precipitate the well-documented derangement of cardiac AR signaling and impairment of AR function, critically underlying chronic human HF. One of the main consequences of HF in mammalian models at the cellular level is the presence of mitochondrial dysfunction. As such, preventing mitochondrial dysfunction could be a valid pharmacological target in this condition. This review summarizes the current experimental evidence for this aldosterone/AR crosstalk in both the healthy and failing heart, and the impact of mitochondrial dysfunction in HF. Recent findings from signaling studies focusing on MR and AR crosstalk via non-conventional signaling of molecules that normally terminate the signaling of ARs in the heart, i.e., the G protein-coupled receptor-kinases (GRKs), are also highlighted.

OPALS: A New Osimertinib Adjunctive Treatment of Lung Adenocarcinoma or Glioblastoma Using Five Repurposed Drugs

Background: Pharmacological targeting aberrant activation of epidermal growth factor receptor tyrosine kinase signaling is an established approach to treating lung adenocarcinoma. Osimertinib is a tyrosine kinase approved and effective in treating lung adenocarcinomas that have one of several common activating mutations in epidermal growth factor receptor. The emergence of resistance to osimertinib after a year or two is the rule. We developed a five-drug adjuvant regimen designed to increase osimertinib’s growth inhibition and thereby delay the development of resistance. Areas of Uncertainty: Although the assembled preclinical data is strong, preclinical data and the following clinical trial results can be discrepant. The safety of OPALS drugs when used individually is excellent. We have no data from humans on their tolerability when used as an ensemble. That there is no data from the individual drugs to suspect problematic interaction does not exclude the possibility. Data Sources: All relevant PubMed.org articles on the OPALS drugs and corresponding pathophysiology of lung adenocarcinoma and glioblastoma were reviewed. Therapeutic Opinion: The five drugs of OPALS are in wide use in general medicine for non-oncology indications. OPALS uses the anti-protozoal drug pyrimethamine, the antihistamine cyproheptadine, the antibiotic azithromycin, the antihistamine loratadine, and the potassium sparing diuretic spironolactone. We show how these inexpensive and generically available drugs intersect with and inhibit lung adenocarcinoma growth drive. We also review data showing that both OPALS adjuvant drugs and osimertinib have data showing they may be active in suppressing glioblastoma growth.

Secreted Phospholipase A2-IIA Modulates Transdifferentiation of Cardiac Fibroblast through EGFR Transactivation: An Inflammation-Fibrosis Link

Secreted phospholipase A₂-IIA (sPLA₂-IIA) is a pro-inflammatory protein associated with cardiovascular disorders, whose functions and underlying mechanisms in cardiac remodelling are still under investigation. We herein study the role of sPLA₂-IIA in cardiac fibroblast (CFs)-to-myofibroblast differentiation and fibrosis, two major features involved in cardiac remodelling, and also explore potential mechanisms involved. In a mice model of dilated cardiomyopathy (DCM) after autoimmune myocarditis, serum and cardiac sPLA₂-IIA protein expression were found to be increased, together with elevated cardiac levels of the cross-linking enzyme lysyl oxidase (LOX) and reactive oxygen species (ROS) accumulation. Exogenous sPLA₂-IIA treatment induced proliferation and differentiation of adult rat CFs. Molecular studies demonstrated that sPLA₂-IIA promoted Src phosphorylation, shedding of the membrane-anchored heparin-binding EGF-like growth factor (HB-EGF) ectodomain and EGFR phosphorylation, which triggered phosphorylation of ERK, P70S6K and rS6. This was also accompanied by an up-regulated expression of the bone morphogenic protein (BMP)-1, LOX and collagen I. ROS accumulation were also found to be increased in sPLA₂-IIA-treated CFs. The presence of inhibitors of the Src/ADAMs-dependent HB-EGF shedding/EGFR pathway abolished the CF phenotype induced by sPLA₂-IIA. In conclusion, sPLA₂-IIA may promote myofibroblast differentiation through its ability to modulate EGFR transactivation and signalling as key mechanisms that underlie its biological and pro-fibrotic effects.

Role of Aldosterone in Renal Fibrosis

Aldosterone is a mineralocorticoid hormone, as its main renal effect has been considered as electrolyte and water homeostasis in the distal tubule, thus maintaining blood pressure and extracellular fluid homeostasis through the activation of mineralocorticoid receptor (MR) in epithelial cells. However, over the past decade, numerous studies have documented the significant role of aldosterone in the progression of chronic kidney disease (CKD) which has become a subject of interest. It is being studied that aldosterone can affect cardiovascular and renal system, thereby contributing to tissue inflammation, injury, glomerulosclerosis, and interstitial fibrosis. Aldosterone acts on renal vessels, renal cells (glomerular mesangial cells, podocytes, vascular smooth muscle cells, tubular epithelial cells, and interstitial fibroblasts), and infiltrating inflammatory cells, inducing reactive oxygen species (ROS) production, upregulated epithelial growth factor receptor (EGFR), and type 1 angiotensin (AT1) receptor expressions, and activating nuclear factor kappa B (NF-κB), activator protein-1 (AP-1), and EGFR to further promote cell proliferation, apoptosis, and proliferation. Phenotypic transformation of epithelial cells stimulates the expression of transforming growth factor-β (TGF-β), connective tissue growth factor (CTGF), osteopontin (OPN), and plasminogen activator inhibitor-1 (PAI-1), eventually leading to renal fibrosis. MR antagonisms are related to inhibition of aldosterone-mediated pro-inflammatory and pro-fibrotic effect. In this review, we will summarize the important role of aldosterone in the pathogenesis of renal injury and fibrosis, emphasizing on its multiple underlying mechanisms and advances in aldosterone research along with the potential therapeutics for targeting MR in a renal fibrosis.

Novel Insights into the Crosstalk between Mineralocorticoid Receptor and G Protein-Coupled Receptors in Heart Adverse Remodeling and Disease

The mineralocorticoid hormone aldosterone regulates sodium and potassium homeostasis but also adversely modulates the maladaptive process of cardiac adverse remodeling post-myocardial infarction. Through activation of its mineralocorticoid receptor (MR), a classic steroid hormone receptor/transcription factor, aldosterone promotes inflammation and fibrosis of the heart, the vasculature, and the kidneys. This is why MR antagonists reduce morbidity and mortality of heart disease patients and are part of the mainstay pharmacotherapy of advanced human heart failure. A plethora of animal studies using cell type⁻specific targeting of the MR gene have established the importance of MR signaling and function in cardiac myocytes, vascular endothelial and smooth muscle cells, renal cells, and macrophages. In terms of its signaling properties, the MR is distinct from nuclear receptors in that it has, in reality, two physiological hormonal agonists: not only aldosterone but also cortisol. In fact, in several tissues, including in the myocardium, cortisol is the primary hormone activating the MR. There is a considerable amount of evidence indicating that the effects of the MR in each tissue expressing it depend on tissue- and ligand-specific engagement of molecular co-regulators that either activate or suppress its transcriptional activity. Identification of these co-regulators for every ligand that interacts with the MR in the heart (and in other tissues) is of utmost importance therapeutically, since it can not only help elucidate fully the pathophysiological ramifications of the cardiac MR's actions, but also help design and develop novel better MR antagonist drugs for heart disease therapy. Among the various proteins the MR interacts with are molecules involved in cardiac G protein-coupled receptor (GPCR) signaling. This results in a significant amount of crosstalk between GPCRs and the MR, which can affect the latter's activity dramatically in the heart and in other cardiovascular tissues. This review summarizes the current experimental evidence for this GPCR-MR crosstalk in the heart and discusses its pathophysiological implications for cardiac adverse remodeling as well as for heart disease therapy. Novel findings revealing non-conventional roles of GPCR signaling molecules, specifically of GPCR-kinase (GRK)-5, in cardiac MR regulation are also highlighted.

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.

Rapid actions of aldosterone revisited: Receptors in the limelight

Steroid hormones like aldosterone have been conclusively shown to elicit both late genomic and rapid, nongenomically initiated responses. Aldosterone was among the first for which rapid, clinically relevant effects were even shown in humans. Yet, after over 30 years of research, the nature of receptors involved in rapid actions of aldosterone is still unclear. Such effects may be assigned to the classical, intracellular steroid receptors, in this case mineralocorticoid receptors (MR, class IIa action Mannheim classification). They typically disappear in knockout models and are blocked by MR-antagonists such as spironolactone, as shown for several cellular and physiological, e.g. renal or cardiovascular effects. In contrast, there is also consistent evidence suggesting type IIb effects involving structurally different receptors ("membrane receptors") being insensitive to classic antagonists and persistent in knockout models; IIb effects have lately even been confirmed by atomic force detection of surface receptors which bind aldosterone but not spironolactone. Type IIa and b may coexist in the same cell with IIa often augmenting early IIb effects. So far cloning of IIb receptors was unsuccessful; therefore results on G-protein coupled estrogen receptor 1 (GPER1) being potentially involved in rapid aldosterone action raised considerable interest. Surprisingly, GPER1 does not bind aldosterone. Though under these circumstances GPER1 should not yet be considered as IIb-receptor, it might be an intermediary signaling enhancer of mineralocorticoid action as shown for epithelial growth factor receptors reconciling those results. We still seem to be left without IIb-receptors whose identification would however be highly desirable and essential for clinical translation.

The role of oxidative stress in the crosstalk between leptin and mineralocorticoid receptor in the cardiac fibrosis associated with obesity

We have investigated whether mineralocorticoid receptor activation can participate in the profibrotic effects of leptin in cardiac myofibroblasts, as well as the potential mechanisms involved. The presence of eplerenone reduced the leptin-induced increase in protein levels of collagen I, transforming growth factor β, connective tissue growth factor and galectin-3 and the levels of both total and mitochondrial of superoxide anion (O₂^.−) in cardiac myofibroblasts. Likewise, the MEK/ERK inhibitor, PD98059, and the PI3/Akt inhibitor, LY294002, showed a similar pattern. Mitochondrial reactive oxygen species (ROS) scavenger (MitoTempo) attenuated the increase in body weight observed in rats fed a high fat diet (HFD). No differences were found in cardiac function or blood pressure among any group. However, the cardiac fibrosis and enhanced O₂^.-levels observed in HFD rats were attenuated by MitoTempo, which also prevented the increased circulating leptin and aldosterone levels in HFD fed animals. This study supports a role of mineralocorticoid receptor in the cardiac fibrosis induced by leptin in the context of obesity and highlights the role of the mitochondrial ROS in this process.

Roles of aldosterone in vascular calcification: An update

Both clinical and experimental studies have demonstrated that vascular calcification (VC) is a common pathology shared in many chronic diseases such as chronic kidney disease (CKD) and diabetes. It's an independent risk factor for cardiovascular events. Since the pathogenesis of VC is complicated, current therapies have limited effects on the regression of VC. Therefore, it is urgent to investigate the potential mechanisms and find new targets for the treatment of VC. Aldosterone (Aldo), a mineralocorticoid hormone, is the metabolite of renin-angiotensin-aldosterone system (RAAS) activation, which can exert genomic and non-genomic effects on the cardiovascular system. Recent data suggests that Aldo can promote VC. Here, we summarized the roles of Aldo in the process of VC and a series of findings indicated that Aldo could act as a potentially therapeutic target for treating VC.

Update on RAAS Modulation for the Treatment of Diabetic Cardiovascular Disease

Since the advent of insulin, the improvements in diabetes detection and the therapies to treat hyperglycemia have reduced the mortality of acute metabolic emergencies, such that today chronic complications are the major cause of morbidity and mortality among diabetic patients. More than half of the mortality that is seen in the diabetic population can be ascribed to cardiovascular disease (CVD), which includes not only myocardial infarction due to premature atherosclerosis but also diabetic cardiomyopathy. The importance of renin-angiotensin-aldosterone system (RAAS) antagonism in the prevention of diabetic CVD has demonstrated the key role that the RAAS plays in diabetic CVD onset and development. Today, ACE inhibitors and angiotensin II receptor blockers represent the first line therapy for primary and secondary CVD prevention in patients with diabetes. Recent research has uncovered new dimensions of the RAAS and, therefore, new potential therapeutic targets against diabetic CVD. Here we describe the timeline of paradigm shifts in RAAS understanding, how diabetes modifies the RAAS, and what new parts of the RAAS pathway could be targeted in order to achieve RAAS modulation against diabetic CVD.

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.

Treatment for pulmonary arterial hypertension-associated right ventricular dysfunction

Pulmonary arterial hypertension (PAH) includes a heterogeneous group of diseases characterized by pulmonary vasoconstriction and remodeling of the lung circulation. Although PAH is a disease of the lungs, patients with PAH frequently die of right heart failure. Indeed, survival of patients with PAH depends on the adaptive response of the right ventricle (RV) to the changes in the lung circulation. PAH-specific drugs affect the function of the RV through afterload reduction and perhaps also through direct effects on the myocardium. Prostacyclins, type 5 phosphodiesterase inhibitors, and guanylyl cyclase stimulators may directly enhance myocardial contractility through increased cyclic adenosine and guanosine monophosphate availability. Although this may initially improve cardiac performance, the long-term effects on myocardial oxygen consumption and function are unclear. Cardiac effects of endothelin receptor antagonists may be opposite, as endothelin-1 is known to suppress cardiac contractility. Because PAH is increasingly considered as a disease with quasimalignant growth of cells in the pulmonary vascular wall, therapies are being developed that inhibit hypertrophy and angiogenesis, and promote apoptosis. The inherent danger of these therapies is a further compromise to the already ischemic, fibrotic, and dysfunctional RV. More recently, the right heart has been identified as a direct treatment target in PAH. The effects of well established therapies for left heart failure, such as β-adrenergic receptor blockers, inhibitors of the renin-angiotensin system, exercise training, and assist devices, are currently being investigated in PAH. Future treatment of patients with PAH will likely consist of a multifaceted approaches aiming to reduce the pressure in the lung circulation and improving right heart adaptation simultaneously.

Moderate inappropriately high aldosterone/NaCl constellation in mice: cardiovascular effects and the role of cardiovascular epidermal growth factor receptor

Non-physiological activation of the mineralocorticoid receptor (MR), e.g. by aldosterone under conditions of high salt intake, contributes to the pathogenesis of cardiovascular diseases, although beneficial effects of aldosterone also have been described. The epidermal growth factor receptor (EGFR) contributes to cardiovascular alterations and mediates part of the MR effects. Recently, we showed that EGFR is required for physiological homeostasis and function of heart and arteries in adult animals. We hypothesize that moderate high aldosterone/NaCl, at normal blood pressure, affects the cardiovascular system depending on cardiovascular EGFR. Therefore we performed an experimental series in male and female animals each, using a recently established mouse model with EGFR knockout in vascular smooth muscle cells and cardiomyocytes and determined the effects of a mild-high aldosterone-to-NaCl constellation on a.o. marker gene expression, heart size, systolic blood pressure, impulse conduction and heart rate. Our data show that (i) cardiac tissue of male but not of female mice is sensitive to mild aldosterone/NaCl treatment, (ii) EGFR knockout induces stronger cardiac disturbances in male as compared to female animals and (iii) mild aldosterone/NaCl treatment requires the EGFR in order to disturb cardiac tissue homeostasis whereas beneficial effects of aldosterone seem to be independent of EGFR.

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.

Aldosterone synthase inhibitors in cardiovascular and renal diseases

Aldosterone is involved in various cardiovascular pathologies, including hypertension, heart failure, atherosclerosis and fibrosis. Mineralocorticoid receptor (MR)-dependent and -independent, genomic and non-genomic processes mediate its complex effects. Spironolactone and eplerenone, both MR antagonists, are the only commercially available compounds targeting directly the actions of aldosterone. However, due to the poor selectivity (spironolactone), low potency (eplerenone) and the fact that only MR-dependent effects of aldosterone can be inhibited, these drugs have limited clinical use. An attractive approach to abolish potentially all of aldosterone-mediated pathologies is the inhibition of aldosterone synthase. This review summarizes current knowledge on the complex effects mediated by aldosterone, potential advantages and disadvantages of aldosterone inhibition and novel directions in the development of aldosterone synthase inhibitors.

Role of epidermal growth factor receptor in vascular structure and function

PURPOSE OF THE REVIEW

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase with a wide implication in tumor biology, wound healing and development. Besides acting as a growth factor receptor activated by ligands such as EGF, the EGFR can also be transactivated and thereby mediate cross-talk with different signaling pathways. The aim of this review is to illustrate the Janus-faced function of the EGFR in the vasculature with its relevance for vascular biology and disease.

RECENT FINDINGS

Over recent years, the number of identified signaling partners of the EGFR has steadily increased, as have the biological processes in which the EGFR is thought to be involved. Recently, new models have allowed investigation of EGFR effects in vivo, shedding some light on the overall function of the EGFR in the vasculature. At the same time, EGFR inhibitors and antibodies have become increasingly established in cancer therapy, providing potential therapeutic tools for decreasing EGFR signaling.

SUMMARY

The EGFR is a versatile signaling pathway integrator associated with vascular homeostasis and disease. In addition to modulating basal vascular tone and tissue homeostasis, the EGFR also seems to be involved in proinflammatory, proliferative, migratory and remodeling processes, with enhanced deposition of extracellular matrix components, thereby promoting vascular diseases such as hypertension or atherosclerosis.

Adipokines: novel players in resistant hypertension

Resistant hypertension (RH) is a multifactorial disease, frequently associated with obesity and characterized by blood pressure above goal (140/90 mm Hg) despite the concurrent use of ≥3 antihypertensive drugs of different classes. The mechanisms of obesity-related hypertension include, among others, aldosterone excess and inflammatory adipokines, which have demonstrated a significant role in the pathogenesis of metabolic syndrome and RH. This review aims to summarize recent studies on the role of the adipokines leptin, resistin, and adiponectin in the pathophysiology of RH and target-organ damage associated with this condition. The deregulation of adipokine levels has been associated with clinical characteristics frequently recognized in RH such as diabetes, hyperactivity of sympathetic and renin-angiotensin-aldosterone systems, and vascular and renal damage. Strategies to regulate adipokines may be promising for the management of RH and some clinical implications must be considered when managing controlled and uncontrolled patients with RH.

The autocrine/paracrine loop after myocardial stretch: mineralocorticoid receptor activation

The stretch of cardiac muscle increases developed force in two phases. The first phase, which occurs rapidly, constitutes the well-known Frank-Starling mechanism and it is generally attributed to enhanced myofilament responsiveness to Ca(2+). The second phase or slow force response (SFR) occurs gradually and is due to an increase in the calcium transient amplitude as a result of a stretch-triggered autocrine/paracrine mechanism. We previously showed that Ca(2+) entry through reverse Na(+)/Ca(2+) exchange underlies the SFR, as the final step of an autocrine/paracrine cascade involving release of angiotensin II/endothelin, and a Na(+)/H(+) exchanger (NHE-1) activation-mediated rise in Na+. In the present review we mainly focus on our three latest contributions to the understanding of this signalling pathway triggered by myocardial stretch: 1) The finding that an increased production of reactive oxygen species (ROS) from mitochondrial origin is critical in the activation of the NHE-1 and therefore in the genesis of the SFR; 2) the demonstration of a key role played by the transactivation of the epidermal growth factor receptor; and 3) the involvement of mineralocorticoid receptors (MR) activation in the stretch-triggered cascade leading to the SFR. Among these novel contributions, the critical role played by the MR is perhaps the most important one. This finding may conceivably provide a mechanistic explanation to the recently discovered strikingly beneficial effects of MR antagonism in humans with cardiac hypertrophy and failure.

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.

Aldosterone stimulates fibronectin synthesis in renal fibroblasts through mineralocorticoid receptor-dependent and independent mechanisms

In addition to its role in regulation of salt transport in the kidney, the mineralocorticoid hormone aldosterone plays an independent role as a mediator of kidney injury and progression of chronic kidney disease. Studies in both animal models and patients have shown that aldosterone enhances the accumulation of extracellular matrix and progression of fibrosis in the kidney. However, the cellular mechanisms that lead to aldosterone-dependent fibrogenesis are poorly understood. In this study we find that aldosterone stimulates fibronectin synthesis through mineralocorticoid receptor (MCR) dependent activation of the c-Jun NH2-terminal protein kinase (JNK) and subsequent phosphorylation of the AP1 transcription factor c-jun, which forms a nuclear complex with the mineralocorticoid receptor in a kidney fibroblast cell line (NRK 49f). Furthermore, MCR-independent phosphorylation of Src family kinase induces IgF1 receptor phosphorylation, which leads to stimulation of the extracellular signal-regulated kinase (ERK1/2) to enhanced fibronectin synthesis. We further find that the IgF1-R-dependent signaling pathway activates fibronectin expression faster than the MCR-dependent pathway. We propose that the mechanisms described in this study are important to aldosterone-dependent progression of interstitial fibrosis in the kidney. Due to the duality of aldosterone-dependent activation of fibronectin synthesis in kidney fibroblasts, MCR-specific inhibitors may not entirely prevent the progression of fibrosis by aldosterone in the kidney.

Mineralocorticoid receptor interaction with SP1 generates a new response element for pathophysiologically relevant gene expression

The mineralocorticoid receptor (MR) is a ligand-induced transcription factor belonging to the steroid receptor family and involved in water-electrolyte homeostasis, blood pressure regulation, inflammation and fibrosis in the renocardiovascular system. The MR shares a common hormone-response-element with the glucocorticoid receptor but nevertheless elicits MR-specific effects including enhanced epidermal growth factor receptor (EGFR) expression via unknown mechanisms. The EGFR is a receptor tyrosine kinase that leads to activation of MAP kinases, but that can also function as a signal transducer for other signaling pathways. In the present study, we mechanistically investigate the interaction between a newly discovered MR- but not glucocorticoid receptor- responsive-element (=MRE1) of the EGFR promoter, specificity protein 1 (SP1) and MR to gain general insights into MR-specificity. Biological relevance of the interaction for EGFR expression and consequently for different signaling pathways in general is demonstrated in human, rat and murine vascular smooth muscle cells and cells of EGFR knockout mice. A genome-wide promoter search for identical binding regions followed by quantitative PCR validation suggests that the identified MR-SP1-MRE1 interaction might be applicable to other genes. Overall, a novel principle of MR-specific gene expression is explored that applies to the pathophysiologically relevant expression of the EGFR and potentially also to other genes.

Contribution of aldosterone to cardiovascular and renal inflammation and fibrosis

The steroid hormone aldosterone regulates sodium and potassium homeostasis. Aldosterone and activation of the mineralocorticoid receptor also causes inflammation and fibrosis of the heart, fibrosis and remodelling of blood vessels and tubulointerstitial fibrosis and glomerular injury in the kidney. Aldosterone and mineralocorticoid-receptor activation initiate an inflammatory response by increasing the generation of reactive oxygen species by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and mitochondria. High salt intake potentiates these effects, in part by activating the Rho family member Rac1, a regulatory subunit of reduced NADPH oxidase that activates the mineralocorticoid receptor. Studies in mice in which the mineralocorticoid receptor has been deleted from specific cell types suggest a key role for macrophages in promoting inflammation and fibrosis. Aldosterone can exert mineralocorticoid-receptor-independent effects via the angiotensin II receptor and via G-protein-coupled receptor 30. Mineralocorticoid-receptor antagonists are associated with decreased mortality in patients with heart disease and show promise in patients with kidney injury, but can elevate serum potassium concentration. Studies in rodents genetically deficient in aldosterone synthase or treated with a pharmacological aldosterone-synthase inhibitor are providing insight into the relative contribution of aldosterone compared with the contribution of mineralocorticoid-receptor activation in inflammation, fibrosis, and injury. Aldosterone-synthase inhibitors are under development in humans.

Evolving research in nongenomic actions of aldosterone

PURPOSE OF REVIEW

Aldosterone is now recognized as an increasingly important contributor to cardiometabolic pathology via inflammatory and fibrosis-related pathways in addition to its classically described role in sodium and volume regulation. Consequently, much effort has been directed towards characterizing the molecular pathways involved in aldosterone-mediated fibrosis and inflammation. What was once viewed as straightforward steroid hormone biology is now appreciated as a highly complex and tightly regulated series of pathways and interactions. These recognitions have fuelled a multidisciplinary effort to identify precisely how aldosterone mediates intracellular activation of both genomic (latent) and nongenomic (rapid) mechanisms of influence. This review will explore recent novel pathways regulating aldosterone action, focusing on the nongenomic pathways.

RECENT FINDINGS

Several recent discoveries have redefined our understanding of aldosterone interactions at the cellular level. This includes activation of the mineralocorticoid receptor at the plasma membrane instead of via classical nuclear hormone receptor interaction, and identification of novel cofactor scaffolding proteins that modify aldosterone influence at the cellular level. In addition, aldosterone activation of secondary messenger system cascades can occur directly and independent of mineralocorticoid receptor interaction.

SUMMARY

Substantial progress in detailing the molecular biology of aldosterone regulation and action should facilitate study of how it exerts detrimental effects in cardiometabolic diseases. However, to date, the clinical impact of these discoveries has not been validated. Translational efforts are now required to determine if novel therapeutic targets can be developed.

Mitochondrial reactive oxygen species (ROS) as signaling molecules of intracellular pathways triggered by the cardiac renin-angiotensin II-aldosterone system (RAAS)

Mitochondria represent major sources of basal reactive oxygen species (ROS) production of the cardiomyocyte. The role of ROS as signaling molecules that mediate different intracellular pathways has gained increasing interest among physiologists in the last years. In our lab, we have been studying the participation of mitochondrial ROS in the intracellular pathways triggered by the renin-angiotensin II-aldosterone system (RAAS) in the myocardium during the past few years. We have demonstrated that acute activation of cardiac RAAS induces mitochondrial ATP-dependent potassium channel (mitoK_ATP) opening with the consequent enhanced production of mitochondrial ROS. These oxidant molecules, in turn, activate membrane transporters, as sodium/hydrogen exchanger (NHE-1) and sodium/bicarbonate cotransporter (NBC) via the stimulation of the ROS-sensitive MAPK cascade. The stimulation of such effectors leads to an increase in cardiac contractility. In addition, it is feasible to suggest that a sustained enhanced production of mitochondrial ROS induced by chronic cardiac RAAS, and hence, chronic NHE-1 and NBC stimulation, would also result in the development of cardiac hypertrophy.

Smooth muscle cell mineralocorticoid receptors: role in vascular function and contribution to cardiovascular disease

The mineralocorticoid receptor (MR), a member of the steroid receptor family, regulates blood pressure by mediating the effects of the hormone aldosterone on renal sodium handling. In recent years, it has become clear that MR is expressed in vascular smooth muscle cells (SMCs), and interest has grown in understanding the direct role of SMC MR in regulating vascular function. This interest stems from multiple clinical studies where MR inhibitor treatment reduced the incidence of cardiovascular events and mortality. This review summarizes the most recent advances in our understanding of SMC MR in regulating normal vascular function and in promoting vascular disease. Many new studies suggest a role for SMC MR activation in stimulating vascular contraction and contributing to vessel inflammation, fibrosis, and remodeling. These detrimental vascular effects of MR activation appear to be independent of changes in blood pressure and are synergistic with the presence of endothelial dysfunction or damage. Thus, in humans with underlying cardiovascular disease or cardiovascular risk factors, SMC MR activation may promote hypertension, atherosclerosis, and vascular aging. Further exploration of the molecular mechanisms for the effects of SMC MR activation has the potential to identify novel therapeutic targets to prevent or treat common cardiovascular disorders.

Aldosterone induces myofibroblast EGF secretion to regulate epithelial colonic permeability

In vivo studies show that raised aldosterone (Aldo) during low-Na adaptation regulates the growth of pericryptal myofibroblasts and reduces the permeability of the colonic epithelium. The aim of this study was to reproduce in vitro the in vivo condition of increased Aldo using human CCD-18Co myofibroblasts and T84 colonic epithelial cells to measure myofibroblast and epithelial proliferation and the expression of intercellular junction proteins. Proliferation was quantified by measuring 5-bromo-2′-deoxyuridine incorporation. The myofibroblast expression of EGF, VEGFa, and transforming growth factor-β1 (TGF-β1) was measured by real-time PCR and the expression of junctional complex proteins by Western blot. Aldo stimulated the proliferation of myofibroblasts by 70% ( P < 0.05) and increased EGF mRNA expression by 30% ( P < 0.05) without affecting VEGFa and TGF-β1. EGF concentration in the incubation medium increased by 30% ( P < 0.05) 24 h after Aldo addition, and these effects were prevented by the addition of spironolactone. Myofibroblast proliferation in response to Aldo was mediated by EGF receptor (EGFR) and involved both MAPKK and phosphatidylinositol 3-kinase pathways. When T84 cells were incubated with medium from myofibroblasts stimulated with Aldo (conditioned medium), the expression of β-catenin and claudin IV was increased by 30% ( P < 0.05) and proliferation by 40% ( P < 0.05). T84 proliferation decreased when α-EGF, or the EGFR antagonist AG1478, was present. Results in vivo indicate that rats fed a low-salt diet showed an increased expression of EGF and EGFR in the colonic mucosa. These results support the view that changes in colonic permeability during low-Na adaptation are mediated by the EGF secreted by myofibroblasts in response to raised Aldo.

Aldosterone and cardiovascular disease: the heart of the matter

Aldosterone contributes to the endocrine basis of heart failure, and studies on cardiac aldosterone signaling have reinforced its value as a therapeutic target. Recent focus has shifted to new roles of aldosterone that appear to depend on coexisting pathologic stimuli, cell type, and disease etiology. This review evaluates recent advances in mechanisms underlying aldosterone-induced cardiac disease and highlights the interplay between aldosterone and Ca(2+)/calmodulin dependent protein kinase II, whose hyperactivity during heart failure contributes to disease progression. Increasing evidence implicates aldosterone in diastolic dysfunction, and there is a need to develop more targeted therapeutics such as aldosterone synthase inhibitors and molecularly specific antioxidants. Despite accumulating knowledge, many questions still persist and will likely dictate areas of future research.

Aldosterone-induced osteopontin expression in vascular smooth muscle cells involves MR, ERK, and p38 MAPK

Osteopontin (OPN) is known to be one of the cytokines that is involved in the vascular inflammation caused by aldosterone (Ald). Previous reports have shown that Ald increases OPN expression, and the mechanisms for this remain to be clarified. In this study, we investigated how Ald increases OPN expression in the vascular smooth muscle cells (VSMCs) of rats. Ald increased OPN expression time dependently as well as dose dependently. This increase was diminished by spironolactone, a mineralocorticoid receptor (MR) antagonist. PD98059, an inhibitor of p42/44 MAPK pathway, and SB203580, an inhibitor of p38 MAPK pathway, suppressed Ald-induced OPN expression and secretion in VSMCs. VSMCs migration stimulated by aldosterone required OPN expression. In conclusion, these data suggest that Ald-induced OPN expression in VSMC is mediated by MR and signaling cascades involving ERK and p38 MAPK. These molecules may represent therapeutic targets for the prevention of pathological vascular remodeling.

The mineralocorticoid receptor-p38MAPK-NFκB or ERK-Sp1 signal pathways mediate aldosterone-stimulated inflammatory and profibrotic responses in rat vascular smooth muscle cells

AIM

To explore the signalling pathways involved in aldosterone-induced inflammation and fibrosis in rat vascular smooth muscle cells (VSMCs).

METHODS

Using Western blotting and real-time RT-PCR, we investigated the effects of aldosterone on the expression of cyclooxygenase-2 (Cox-2) and IL-6, two important proinflammatory factors, and TGFβ1, a critical profibrotic factor, in VSMCs.

RESULTS

Aldosterone treatment significantly increased the expression of Cox-2 and IL-6 and activation of p38MAPK and NF-κB. The expression of both Cox-2 and IL-6 could be blocked by the mineralocorticoid receptor (MR) antagonist spironolactone and the p38MAPK inhibitor SB203580. Also, the rapid phosphorylation of p38MAPK could be suppressed by SB203580 but not by spironolactone, implicating in nongenomic effects of aldosterone. Similar to SB203580 and spironolactone, the NF-κB inhibitor α-p-tosyl-L-lysine chloromethyl ketone (TLCK) markedly attenuated expression of Cox-2, indicating that MR, p38MAPK and NF-κB are associated with aldosterone-induced inflammatory responses. Furthermore, aldosterone enhanced expression of TGFβ1 in rat VSMCs. This result may be related to activation of the MR/ERK-Sp1 signalling pathway because PD98059, an ERK1/2 inhibitor, significantly blocked the rapid phosphorylation of ERK1/2 and function of Sp1 and led to reduced expression of TGFβ1. Spironolactone was also shown to significantly inhibit TGFβ1 and Sp1 expression but not ERK1/2 phosphorylation.

CONCLUSION

These results suggest that aldosterone-induced inflammatory responses and fibrotic responses may be mediated by the MR/p38MAPK-NF-κB pathways and the MR/ERK-Sp1 pathways in VSMCs, respectively.

Mineralocorticoid receptor-associated hypertension and its organ damage: clinical relevance for resistant hypertension

The role of aldosterone in the pathogenesis of hypertension and cardiovascular diseases has been clearly shown in congestive heart failure and endocrine hypertension due to primary aldosteronism. In resistant hypertension, defined as a failure of concomitant use of three or more different classes of antihypertensive agents to control blood pressure (BP), add-on therapy with mineralocorticoid receptor (MR) antagonists is frequently effective, which we designate as "MR-associated hypertension". The MR-associated hypertension is classified into two subtypes, that with elevated plasma aldosterone levels and that with normal plasma aldosterone levels. The former subtype includes primary aldosteronism (PA), aldosterone-associated hypertension which exhibited elevated aldosterone-to-renin ratio and plasma aldosterone levels, but no PA, aldosterone breakthrough phenomenon elicited when angiotensin-converting enzyme inhibitor (ACE-I) or angiotensin II receptor blocker (ARB) is continued to be given, and obstructive sleep apnea. In contrast, the latter subtype includes obesity, diabetes mellitus, chronic kidney disease (CKD), and polycystic ovary syndrome (PCOS). The pathogenesis of MR-associated hypertension with normal plasma aldosterone levels is considered to be mediated by MR activation by pathways other than high aldosterone levels, such as increased MR levels, increased MR sensitivity, and MR overstimulation by other factors such as Rac1. For resistant hypertension with high plasma aldosterone levels, MR antagonist should be given as a first-line therapy, whereas for resistant hypertension with normal aldosterone levels, ARB or ACE-I should be given as a first-line therapy and MR antagonist would be given as an add-on agent.

Mineralocorticoid receptors in vascular function and disease

The mineralocorticoid receptor (MR), a member of the steroid receptor family, regulates blood pressure by mediating the effects of the hormone aldosterone (Aldo) on renal sodium handling. Over the past decade, it has become clear that MR is expressed in the cardiovascular system and interest has grown in understanding the direct role of the MR in regulating vascular function and contributing to cardiovascular disease. This interest stems from multiple clinical studies in which drugs that decrease MR activation also reduce the incidence of heart attacks, strokes, and mortality out of proportion to modest changes in systemic blood pressure. The presence of functional mineralocorticoid receptors in vascular smooth muscle and endothelial cells is now well established and, while still controversial, data supports the vasculature as an Aldo-responsive tissue. This review summarizes recent advances in our understanding of the role of vascular MR in regulating normal vascular function and in promoting vascular disease. In vitro data, in vivo animal studies, and human data are reviewed suggesting a role for MR-activation in promoting vascular oxidative stress, inhibiting vascular relaxation, and contributing to vessel inflammation, fibrosis, and remodeling. These detrimental vascular effects of MR activation appear to be independent of changes in blood pressure and are synergistic with the presence of endothelial dysfunction or damage. Thus, in humans with underlying cardiovascular disease or cardiovascular risk factors, vascular MR activation may promote vascular aging and atherosclerosis thereby contributing to the pathophysiology of heart attack, stroke, and possibly even hypertension. Further exploration of the molecular mechanisms for the detrimental vascular effects of MR activation has the potential to identify novel therapeutic targets to prevent or treat common cardiovascular disorders.

Interaction between mineralocorticoid receptor and epidermal growth factor receptor signaling

The mineralocorticoid receptor (MR) is a steroid receptor that physiologically regulates water and electrolyte homeostasis but that can also induce pathophysiological effects in the renocardiovascular system. Classically, the MR acts as a transcription factor at glucocorticoid response elements but additional protein-protein interactions with other signaling cascades have been described. Of these, the crosstalk with EGFR signaling is especially interesting because various vasoactive substances like angiotensin II and endothelin-1 also mediate their pathophysiological effects via the EGFR. Recently, the MR has been shown to interact nongenomically (via transactivation) and genomically with the epidermal growth factor receptor (via altered expression). These interactions seem to contribute to physiological (e.g. salt homeostasis) as well as pathophysiological (e.g. vascular function) MR effects. The current knowledge on the mechanisms of interaction and on the possible cellular and systemic physiological as well as pathophysiological relevance is reviewed in this article.

Non-genomic actions of aldosterone: from receptors and signals to membrane targets

In tissues which express the mineralocorticoid receptor (MR), aldosterone modulates the expression of membrane targets such as the subunits of the epithelial Na(+) channel, in combination with important signalling intermediates such as serum and glucocorticoid-regulated kinase-1. In addition, the rapid 'non-genomic' activation of protein kinases and secondary messenger signalling cascades has also been detected in aldosterone-sensitive tissues of the nephron, distal colon and cardiovascular system. These rapid actions are variously described as being coupled to MR or to an as yet unidentified, membrane-associated aldosterone receptor. The rapidly activated signalling cascades add a level of fine-tuning to the activity of aldosterone-responsive membrane transporters and also modulate the aldosterone-induced changes in gene expression through receptor and transcription factor phosphorylation.

Interactions of the mineralocorticoid receptor--within and without

The mineralocortoid receptor (MR) regulates salt homeostasis in the kidneys and plays a range of other roles in the heart, vasculature, brain and adipose tissue. It interacts with both mineralocorticoids and glucocorticoids to mediate transcription of target genes. The ability of the MR to exert tissue- and ligand-specific effects relies on its interactions with a range of binding partners, including the chaperone proteins, coregulators, other transcription factors, DNA and modifying proteins. Interactions within the domains of the MR also modulate the overall transcriptional complex. This review will discuss the current understanding of interactions involving the MR and highlight their relevance to ligand- or tissue-specificity as well as their suitability as therapeutic targets.

The epidermal growth factor receptor is involved in angiotensin II but not aldosterone/salt-induced cardiac remodelling

Experimental and clinical studies have shown that aldosterone/mineralocorticoid receptor (MR) activation has deleterious effects in the cardiovascular system; however, the signalling pathways involved in the pathophysiological effects of aldosterone/MR in vivo are not fully understood. Several in vitro studies suggest that Epidermal Growth Factor Receptor (EGFR) plays a role in the cardiovascular effects of aldosterone. This hypothesis remains to be demonstrated in vivo. To investigate this question, we analyzed the molecular and functional consequences of aldosterone exposure in a transgenic mouse model with constitutive cardiomyocyte-specific overexpression of a mutant EGFR acting as a dominant negative protein (DN-EGFR). As previously reported, Angiotensin II-mediated cardiac remodelling was prevented in DN-EGFR mice. However, when chronic MR activation was induced by aldosterone-salt-uninephrectomy, cardiac hypertrophy was similar between control littermates and DN-EGFR. In the same way, mRNA expression of markers of cardiac remodelling such as ANF, BNF or β-Myosin Heavy Chain as well as Collagen 1a and 3a was similarly induced in DN-EGFR mice and their CT littermates. Our findings confirm the role of EGFR in AngII mediated cardiac hypertrophy, and highlight that EGFR is not involved in vivo in the damaging effects of aldosterone on cardiac function and remodelling.

Aldosterone Stimulates the Cardiac Na + /H + Exchanger via Transactivation of the Epidermal Growth Factor Receptor

The use of antagonists of the mineralocorticoid receptor in the treatment of myocardial hypertrophy and heart failure has gained increasing importance in the last years. The cardiac Na + /H + exchanger (NHE-1) upregulation induced by aldosterone could account for the genesis of these pathologies. We tested whether aldosterone-induced NHE-1 stimulation involves the transactivation of the epidermal growth factor receptor (EGFR). Rat ventricular myocytes were used to measure intracellular pH with epifluorescence. Aldosterone enhanced the NHE-1 activity. This effect was canceled by spironolactone or eplerenone (mineralocorticoid receptor antagonists), but not by mifepristone (glucocorticoid receptor antagonist) or cycloheximide (protein synthesis inhibitor), indicating that the mechanism is mediated by the mineralocorticoid receptor triggering nongenomic pathways. Aldosterone-induced NHE-1 stimulation was abolished by the EGFR kinase inhibitor AG1478, suggesting that is mediated by transactivation of EGFR. The increase in the phosphorylation level of the kinase p90 RSK and NHE-1 serine703 induced by aldosterone was also blocked by AG1478. Exogenous epidermal growth factor mimicked the effects of aldosterone on NHE-1 activity. Epidermal growth factor was also able to increase reactive oxygen species production, and the epidermal growth factor–induced activation of the NHE-1 was abrogated by the reactive oxygen species scavenger N -2-mercaptopropionyl glycine, indicating that reactive oxygen species are participating as signaling molecules in this mechanism. Aldosterone enhances the NHE-1 activity via transactivation of the EGFR, formation of reactive oxygen species, and phosphorylation of the exchanger. These results call attention to the consideration of the EGFR as a new potential therapeutic target of the cardiovascular pathologies involving the participation of aldosterone.

TIEG1 inhibits breast cancer invasion and metastasis by inhibition of epidermal growth factor receptor (EGFR) transcription and the EGFR signaling pathway

TIEG1 can induce apoptosis of cancer cells, but its role in inhibiting invasion and metastasis has not been reported and is unclear. In this study, we find that decreased TIEG1 expression is associated with increased human epidermal growth factor receptor (EGFR) expression in breast cancer tissues and cell lines. TIEG1 plays an important role in suppressing transcription of EGFR by directly binding to the EGFR promoter. While overexpression of TIEG1 attenuates EGFR expression, knockdown of TIEG1 stimulates EGFR expression. Furthermore, TIEG1 and HDAC1 form a complex, which binds to Sp1 sites on the EGFR promoter and inhibits its transcription by suppressing histone acetylation. TIEG1 significantly inhibits breast cancer cell invasion, suppresses mammary tumorigenesis in xenografts in mice, and decreases lung metastasis by inhibition of EGFR gene transcription and the EGFR signaling pathway. Therefore, TIEG1 is an antimetastasis gene product; regulation of EGFR expression by TIEG1 may be part of an integral signaling pathway that determines and explains breast cancer invasion and metastasis.

Renal epidermal growth factor receptor: its role in sodium and water homeostasis in diabetic nephropathy

1. Volume expansion is observed in animal and human models of diabetic nephropathy, which is in a large part a result of disordered renal tubular cell sodium and water transport. 2. Sodium transport in the proximal tubule is increased in diabetes mellitus as a result of enhanced activity of the sodium-hydrogen exchanger-3 (NHE3), the key transporter for transcellular reabsorption of sodium. Transactivation of the epidermal growth factor receptor (EGFR) by factors inherent in the milieu of diabetes mellitus increases serum glucocorticoid regulated kinase-1 (Sgk1), a key regulator of NHE3. 3. Enhanced sodium and water reabsorption, occurring as a consequence of endogenous or pharmacological stimulation of the peroxisome proliferator-activated receptor gamma is Sgk1 mediated. 4. EGFR inhibitors, which are currently used clinically to treat malignancies, might have potential in attenuating the cellular mechanisms responsible for thiazolidinedione (TZD)-mediated sodium and water transport in diabetes. 5. In the present review, the authors focus on the importance of the EGFR in sodium and water uptake in the proximal tubule in the environment of pathophysiological and pharmacological influences.

Aldosterone induces arterial stiffness in absence of oxidative stress and endothelial dysfunction

AIMS

Monocyte/macrophages participate in inflammatory responses that may play an important role in mineralocorticoid-induced vascular damage. We hypothesized that monocyte/macrophages modulate aldosterone effects on oxidative stress, endothelial function, and ultimately vascular stiffness.

METHODS

Adult heterozygous osteopetrotic (Op/+) and wild-type mice were infused with aldosterone (600 microg/kg per day s.c. with Alzet osmotic minipumps) and received 1% NaCl in drinking water or were infused with vehicle for 14 days. Blood pressure was measured by the tail-cuff method. Endothelial function was determined in mesenteric arteries on a pressurized myograph by the response to acetylcholine following norepinephrine preconstriction. Extracellular matrix was quantified by immunohistochemistry, reactive oxygen species by image analysis of dihydroethidium staining, and reduced nicotinamide adenine dinucleotide phosphate oxidase activity by chemiluminescence.

RESULTS

Body weight and blood pressure did not change following aldosterone treatment. Aldosterone induced stiffening of resistance arteries among all treated animals, as reflected by decreased sum of squares of strain from 2.07 +/- 0.15 to 1.54 +/- 0.29 in wild type, and from 2.68 +/- 0.28 to 2.04 +/- 0.15 in Op/+, and increased fibronectin-to-elastin ratio from 1.12 +/- 0.40 to 4.52 +/- 0.47 and 0.92 +/- 0.47 to 5.26 +/- 0.88, respectively. Endothelial function was impaired and reactive oxygen species increased only in aldosterone-treated wild-type mice. Reduced nicotinamide adenine dinucleotide phosphate oxidase activity was unaffected.

CONCLUSION

Monocyte/macrophage deficiency in Op/+ mice results in absence of aldosterone-induced oxidative stress and endothelial dysfunction, but does not play a role in aldosterone-induced arterial stiffness. Thus, although monocyte/macrophage-mediated inflammatory responses play a role in oxidative stress and endothelial dysfunction, vascular stiffening in response to aldosterone may be independent of inflammation.

Aldosterone enhances IGF-I-mediated signaling and biological function in vascular smooth muscle cells

The IGF-I pathway and renin-angiotensin-aldosterone axis are both involved in the pathogenesis of hypertension and atherosclerosis, but no information is available about IGF-I and aldosterone interaction or their potential synergistic effects in vascular smooth muscle cells (VSMCs). The aims of this study were to investigate whether aldosterone influences IGF-I signaling and to determine the mechanism(s) by which aldosterone affects IGF-I function. Aldosterone resulted in significant increases in the Akt (1.87 ± 0.24, P < 0.001), MAPK (1.78 ± 0.13, P < 0.001), p70S6kinase (1.92 ± 0.15, P < 0.001), IGF-I receptor (1.69 ± 0.05, P < 0.01), and insulin receptor substrate-1 (1.7 ± 0.04, P < 0.01) (fold increase, mean ± SEM, n = 3) phosphorylation responses to IGF-I compared with IGF-I treatment alone. There were also significant increases in VSMC proliferation, migration, and protein synthesis (1.63 ± 0.03-, 1.56 ± 0.08-, and 1.51 ± 0.04-fold increases compared with IGF-I alone, respectively, n = 3, P < 0.001). Aldosterone induced osteopontin (OPN) mRNA expression and activation of αVβ3-integrin as well as an increase in the synthesis of IGF-I receptor. The enhancing effects of aldosterone were inhibited by eplerenone (10 μmol/liter), actinomycin-D (20 nmol/liter), and an anti-αVβ3-integrin antibody that blocks OPN binding. The antioxidant N-acetylcysteine (2 mmol/liter) completely inhibited the ability of aldosterone to induce any of these changes. In conclusion, our results show that aldosterone enhances IGF-I signaling and biological actions in VSMCs through induction of OPN followed by its subsequent activation of the αVβ3-integrin and by increasing IGF-I receptor. These changes are mediated in part through increased oxidative stress. The findings suggest a new mechanism by which aldosterone could accelerate the development of atherosclerosis.

Interaction between mineralocorticoid receptor and cAMP/CREB signaling

Besides regulating water and electrolyte homeostasis, the mineralocorticoid receptor (MR) elicits pathophysiological effects in the renocardiovascular system. Although the MR's closest relative, the glucocorticoid receptor (GR), acts as a transcription factor at the same hormone-response-element (HRE), activated glucocorticoid receptor mediates very different effects. One explanation for this discrepancy is that the MR interacts with additional signaling pathways in the cytosol. In the literature, there are several indications for an interaction between aldosterone/MR and the cAMP/CREB signaling. Here we summarize the current knowledge of the cross-talk between the two signaling pathways, including some unpublished observations of our own that indicate that MR/CREB signaling is mediated by calcineurin and has potentially pathophysiological consequences.