Functional mineralocorticoid receptors in human vascular endothelial cells regulate intercellular adhesion molecule-1 expression and promote leukocyte adhesion

Impact of Adrenal Steroids on Regulation of Adipose Tissue

Corticosteroids are secreted by the adrenal glands and control the functions of adipose tissue via the activation of mineralocorticoid receptor (MR) and glucocorticoid receptor (GR). In turn, adipocytes release a large variety of adipokines into the bloodstream, regulating the function of several organs and tissues, including the adrenal glands, hereby controlling corticosteroid production. In adipose tissue, the activation of the MR by glucocorticoids (GC) and aldosterone affects important processes such as adipocyte differentiation, oxidative stress, autophagic flux, adipokine expression as well as local production of GC through upregulation of the enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). Notably, the proinflammatory responses induced by the MR are counteracted by activation of the GR, whose activity inhibits the expression of inflammatory adipokines. Both GR and MR are deeply involved in adipogenesis and adipose expansion; hence pharmacological blockade of these two receptors has proven effective against adipose tissue dysfunction in experimental models of obesity and metabolic syndrome (MetS), suggesting a potential use for MR and GR antagonists in these clinical settings. Importantly, obesity and Cushing's syndrome (CS) share metabolic similarities and are characterized by high levels of circulating corticosteroids, which in turn are able to deeply affect adipose tissue. In addition, pharmacological approaches aimed at reducing aldosterone and GC levels, by means of the inhibition of CYP11B2 (aldosterone synthase) or 11β-HSD1, represent alternative strategies to counter the detrimental effects of excessive levels of corticosteroids, which are often observed in obesity and, more general, in MetS. © 2017 American Physiological Society. Compr Physiol 7:1425-1447, 2017.

Glucocorticoids and gut bacteria: "The GALF Hypothesis" in the metagenomic era

A new concept is emerging in biomedical sciences: the gut microbiota is a virtual 'organ' with endocrine function. Here, we explore the literature pertaining to the role of gut microbial metabolism of endogenous adrenocorticosteroids as a contributing factor in the etiology of essential hypertension. A body of literature demonstrates that bacterial products of glucocorticoid metabolism are absorbed into the portal circulation, and pass through the kidney before excretion into urine. Apparent mineralocorticoid excess (AME) syndrome patients were found to have congenital mutations resulting in non-functional renal 11β-hydroxysteroid dehydrogenase-2 (11β-HSD2) and severe hypertension often lethal in childhood. 11β-HSD2 acts as a "guardian" enzyme protecting the mineralocorticoid receptor from excess cortisol, preventing sodium and water retention in the normotensive state. Licorice root, whose active ingredient, glycerrhetinic acid (GA), inhibits renal 11β-HSD2, and thereby causes hypertension in some individuals. Bacterially derived glucocorticoid metabolites may cause hypertension in some patients by a similar mechanism. Parallel observations in gut microbiology coupled with screening of endogenous steroids as inhibitors of 11β-HSD2 have implicated particular gut bacteria in essential hypertension through the production of glycerrhetinic acid-like factors (GALFs). A protective role of GALFs produced by gut bacteria in the etiology of colorectal cancer is also explored.

Long-term spironolactone treatment reduces coronary TRPC expression, vasoconstriction, and atherosclerosis in metabolic syndrome pigs

Coronary transient receptor potential canonical (TRPC) channel expression is elevated in metabolic syndrome (MetS). However, differential contribution of TRPCs to coronary pathology in MetS is not fully elucidated. We investigated the roles of TRPC1 and TRPC6 isoforms in coronary arteries of MetS pigs and determined whether long-term treatment with a mineralocorticoid receptor inhibitor, spironolactone, attenuates coronary TRPC expression and associated dysfunctions. MetS coronary arteries exhibited significant atherosclerosis, endothelial dysfunction, and increased histamine-induced contractions. Immunohistochemical studies revealed that TRPC6 immunostaining was significantly greater in the medial layer of MetS pig coronary arteries compared to that in Lean pigs, whereas little TRPC6 immunostaining was found in atheromas. Conversely, TRPC1 immunostaining was weak in the medial layer but strong in MetS atheromas, where it was predominantly localized to macrophages. Spironolactone treatment significantly decreased coronary TRPC expression and dysfunctions in MetS pigs. In vivo targeted delivery of the dominant-negative (DN)-TRPC6 cDNA to the coronary wall reduced histamine-induced calcium transients in the MetS coronary artery medial layer, implying a role for TRPC6 in mediating calcium influx in MetS coronary smooth muscles. Monocyte adhesion was increased in Lean pig coronary arteries cultured in the presence of aldosterone; and spironolactone antagonized this effect, suggesting that coronary mineralocorticoid receptor activation may regulate macrophage infiltration. TRPC1 expression in atheroma macrophages was associated with advanced atherosclerosis, whereas medial TRPC6 upregulation correlated with increased histamine-induced calcium transients and coronary contractility. We propose that long-term spironolactone treatment may be a therapeutic strategy to decrease TRPC expression and coronary pathology associated with MetS.

30 YEARS OF THE MINERALOCORTICOID RECEPTOR: The role of the mineralocorticoid receptor in the vasculature

Since the mineralocorticoid receptor (MR) was cloned 30 years ago, it has become clear that MR is expressed in extra-renal tissues, including the cardiovascular system, where it is expressed in all cells of the vasculature. Understanding the role of MR in the vasculature has been of particular interest as clinical trials show that MR antagonism improves cardiovascular outcomes out of proportion to changes in blood pressure. The last 30 years of research have demonstrated that MR is a functional hormone-activated transcription factor in vascular smooth muscle cells and endothelial cells. This review summarizes advances in our understanding of the role of vascular MR in regulating blood pressure and vascular function, and its contribution to vascular disease. Specifically, vascular MR contributes directly to blood pressure control and to vascular dysfunction and remodeling in response to hypertension, obesity and vascular injury. The literature is summarized with respect to the role of vascular MR in conditions including: pulmonary hypertension; cerebral vascular remodeling and stroke; vascular inflammation, atherosclerosis and myocardial infarction; acute kidney injury; and vascular pathology in the eye. Considerations regarding the impact of age and sex on the function of vascular MR are also described. Further investigation of the precise molecular mechanisms by which MR contributes to these processes will aid in the identification of novel therapeutic targets to reduce cardiovascular disease (CVD)-related morbidity and mortality.

Mineralocorticoid Receptor Signaling as a Therapeutic Target for Renal and Cardiac Fibrosis

Activation of the mineralocorticoid receptor (MR) plays important roles in both physiological and pathological events. Blockade of MR signaling with MR antagonists (MRAs) has been used clinically to treat kidney and cardiac disease associated with hypertension and other chronic diseases, resulting in suppression of fibrosis in these organs. However, the current use of steroidal MRAs has been limited by off target effects on other hormone receptors or adverse effects on kidney tubular function. In this review, we summarize recent insights into the profibrotic roles of MR signaling in kidney and cardiovascular disease. We review experimental in vitro data identifying the pathological mechanisms associated with MR signaling in cell types found in the kidney (mesangial cells, podocytes, tubular cells, macrophages, interstitial fibroblasts) and heart (cardiomyocytes, endothelial cells, vascular smooth muscle cells, macrophages). In addition, we demonstrate the in vivo importance of MR signaling in specific kidney and cardiac cell types by reporting the outcomes of cell type selective MR gene deletion in animal models of kidney and cardiac disease and comparing these findings to those obtained with MRAs treatment. This review also includes a discussion of the potential benefits of novel non-steroidal MRAs for targeting kidney and cardiac fibrosis compared to existing steroidal MRAs, as well as the possibility of novel combination therapies and cell selective delivery of MRAs.

Possible increase in insulin resistance and concealed glucose-coupled potassium-lowering mechanisms during acute coronary syndrome documented by covariance structure analysis

Objective

Although glucose-insulin-potassium (GIK) therapy ought to be beneficial for ischemic heart disease in general, variable outcomes in many clinical trials of GIK in acute coronary syndrome (ACS) had a controversial impact. This study was designed to examine whether “insulin resistance” is involved in ACS and to clarify other potential intrinsic compensatory mechanisms for GIK tolerance through highly statistical procedure.

Methods and results

We compared the degree of insulin resistance during ACS attack and remission phase after treatment in individual patients (n = 104). During ACS, homeostasis model assessment of insulin resistance (HOMA-IR) values were significantly increased (P<0.001), while serum potassium levels were transiently decreased (degree of which was indicated by ΔK) (P<0.001). This finding provides a renewed paradox, as ΔK, a surrogate marker of intrinsic GIK cascade activation, probably reflects the validated glucose metabolism during ischemic attack. Indeed, multiple regression analysis revealed that plasma glucose level during ACS was positively correlated with ΔK (P = 0.026), whereas HOMA-IR had no impact on ΔK. This positive correlation between ΔK and glucose was confirmed by covariance structure analysis with a strong impact (β: 0.398, P = 0.015). Intriguingly, a higher incidence of myocardial infarction relative to unstable angina pectoris, as well as a longer hospitalization period were observed in patients with larger ΔK, indicating that ΔK also reflects disease severity of ACS.

Conclusions

Insulin resistance most likely increases during ACS; however, ΔK was positively correlated with plasma glucose level, which overwhelmed insulin resistance condition. The present study with covariance structure analysis suggests that there are potential endogenous glucose-coupled potassium lowering mechanisms, other than insulin, regulating glucose metabolism during ACS.

Unliganded estrogen receptor alpha regulates vascular cell function and gene expression

The unliganded form of the estrogen receptor is generally thought to be inactive. Our prior studies, however, suggested that unliganded estrogen receptor alpha (ERα) exacerbates adverse vascular injury responses in mice. Here, we show that the presence of unliganded ERα decreases vascular endothelial cell (EC) migration and proliferation, increases smooth muscle cell (SMC) proliferation, and increases inflammatory responses in cultured ECs and SMCs. Unliganded ERα also regulates many genes in vascular ECs and mouse aorta. Activation of ERα by E2 reverses the cell physiological effects of unliganded ERα, and promotes gene regulatory effects that are predicted to counter the effects of unliganded ERα. These results reveal that the unliganded form of ERα is not inert, but significantly impacts gene expression and physiology of vascular cells. Furthermore, they indicate that the cardiovascular protective effects of estrogen may be connected to its ability to counteract these effects of unliganded ERα.

Essential role of ICAM-1 in aldosterone-induced atherosclerosis

OBJECTIVE

Elevated aldosterone is associated with increased risk of atherosclerosis complications, whereas treatment with mineralocorticoid receptor (MR) antagonists decreases the rate of cardiovascular events. Here we test the hypothesis that aldosterone promotes early atherosclerosis by modulating intercellular adhesion molecule-1 (ICAM-1) expression and investigate the molecular mechanisms by which aldosterone regulates ICAM-1 expression.

METHODS AND RESULTS

Apolipoprotein-E (ApoE)^-/- mice fed an atherogenic diet and treated with aldosterone for 4weeks showed increased vascular expression of ICAM-1, paralleled by enhanced atherosclerotic plaque size in the aortic root. Moreover, aldosterone treatment resulted in increased plaque lipid and inflammatory cell content, consistent with an unstable plaque phenotype. ApoE/ICAM-1 double knockout (ApoE^-/-/ICAM-1^-/-) littermates were protected from the aldosterone-induced increase in plaque size, lipid content and macrophage infiltration. Since aldosterone is known to regulate ICAM-1 transcription via MR in human endothelial cells, we explored MR regulation of the ICAM-1 promoter. Luciferase reporter assays performed in HUVECs using deletion constructs of the human ICAM-1 gene promoter showed that a region containing a predicted MR-responsive element (MRE) is required for MR-dependent transcriptional regulation of ICAM-1.

CONCLUSIONS

Pro-atherogenic effects of aldosterone are mediated by increased ICAM-1 expression, through transcriptional regulation by endothelial MR. These data enhance our understanding of the molecular mechanism by which MR activation promotes atherosclerosis complications.

Mineralocorticoid regulation of cell function: the role of rapid signalling and gene transcription pathways

The mineralocorticoid receptor (MR) and mineralocorticoids regulate epithelial handling of electrolytes, and induces diverse effects on other tissues. Traditionally, the effects of MR were ascribed to ligand-receptor binding and activation of gene transcription. However, the MR also utilises a number of intracellular signalling cascades, often by transactivating unrelated receptors, to change cell function more rapidly. Although aldosterone is the physiological mineralocorticoid, it is not the sole ligand for MR. Tissue-selective and mineralocorticoid-specific effects are conferred through the enzyme 11β-hydroxysteroid dehydrogenase 2, cellular redox status and properties of the MR itself. Furthermore, not all aldosterone effects are mediated via MR, with implication of the involvement of other membrane-bound receptors such as GPER. This review will describe the ligands, receptors and intracellular mechanisms available for mineralocorticoid hormone and receptor signalling and illustrate their complex interactions in physiology and disease.

Emerging Roles of the Mineralocorticoid Receptor in Pathology: Toward New Paradigms in Clinical Pharmacology

The mineralocorticoid receptor (MR) and its ligand aldosterone are the principal modulators of hormone-regulated renal sodium reabsorption. In addition to the kidney, there are several other cells and organs expressing MR, in which its activation mediates pathologic changes, indicating potential therapeutic applications of pharmacological MR antagonism. Steroidal MR antagonists have been used for decades to fight hypertension and more recently heart failure. New therapeutic indications are now arising, and nonsteroidal MR antagonists are currently under development. This review is focused on nonclassic MR targets in cardiac, vascular, renal, metabolic, ocular, and cutaneous diseases. The MR, associated with other risk factors, is involved in organ fibrosis, inflammation, oxidative stress, and aging; for example, in the kidney and heart MR mediates hormonal tissue-specific ion channel regulation. Genetic and epigenetic modifications of MR expression/activity that have been documented in hypertension may also present significant risk factors in other diseases and be susceptible to MR antagonism. Excess mineralocorticoid signaling, mediated by aldosterone or glucocorticoids binding, now appears deleterious in the progression of pathologies that may lead to end-stage organ failure and could therefore benefit from the repositioning of pharmacological MR antagonists.

Spironolactone Prevents Endothelial Nitric Oxide Synthase Uncoupling and Vascular Dysfunction Induced by β-Adrenergic Overstimulation: Role of Perivascular Adipose Tissue

Supplemental Digital Content is available in the text.

Sustained stimulation of β-adrenoceptors (β-ARs) and activation of renin–angiotensin–aldosterone system are common features of cardiovascular diseases with rising sympathetic activation, including essential hypertension, myocardial infarction, and heart failure. In this study, we investigated the role of AT1 receptor and mineralocorticoid receptor (MR) in the vascular alterations caused by β-AR overstimulation. β-AR overstimulation with associated cardiac hypertrophy and increased vasoconstrictor response to phenylephrine in aorta were modeled in rats by 7-day isoproterenol treatment. The increased vasoconstrictor response to phenylephrine in this model was blunted by the MR antagonist spironolactone, but not by the AT1 receptor antagonist losartan, despite the blunting of cardiac hypertrophy with both drugs. Spironolactone, but not losartan, restored NO bioavailability in association with lower endothelial nitric oxide synthase–derived superoxide production, increased endothelial nitric oxide synthase dimerization, and aortic HSP90 upregulation. MR genomic and nongenomic functions were activated in aortas from isoproterenol-treated rats. Isoproterenol did not modify plasma levels of MR ligands aldosterone and corticosterone but rather increased perivascular adipose tissue–derived corticosterone in association with increased expression of 11β-hydroxysteroid dehydrogenase type 1. The anticontractile effect of aortic perivascular adipose tissue was impaired by β-AR overstimulation and restored by MR blockade. These results suggest that activation of vascular MR signaling contributes to the vascular dysfunction induced by β-AR overstimulation associated with endothelial nitric oxide synthase uncoupling. These findings reveal an additional explanation for the protective effects of MR antagonists in cardiovascular disorders with sympathetic activation.

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.

New therapy, new challenges: The effects of long-term continuous flow left ventricular assist device on inflammation

Surgically implanted continuous flow left ventricular assist devices (CF-LVADs) are currently used in patients with end-stage heart failure (HF). However, CF-LVAD therapy introduces a new set of complications and adverse events in these patients. Major adverse events with the CF-LVAD include right heart failure, vascular dysfunction, stroke, hepatic failure, and multi-organ failure, complications that may have inflammation as a common etiology. Our aim was to review the current evidence showing a relationship between these adverse events and elevated levels of inflammatory biomarkers in CF-LVAD recipients.

ER Alpha Rapid Signaling Is Required for Estrogen Induced Proliferation and Migration of Vascular Endothelial Cells

Estrogen promotes the proliferation and migration of vascular endothelial cells (ECs), which likely underlies its ability to accelerate re-endothelialization and reduce adverse remodeling after vascular injury. In previous studies, we have shown that the protective effects of E2 (the active endogenous form of estrogen) in vascular injury require the estrogen receptor alpha (ERα). ERα transduces the effects of estrogen via a classical DNA binding, "genomic" signaling pathway and via a more recently-described "rapid" signaling pathway that is mediated by a subset of ERα localized to the cell membrane. However, which of these pathways mediates the effects of estrogen on endothelial cells is poorly understood. Here we identify a triple point mutant version of ERα (KRR ERα) that is specifically defective in rapid signaling, but is competent to regulate transcription through the "genomic" pathway. We find that in ECs expressing wild type ERα, E2 regulates many genes involved in cell migration and proliferation, promotes EC migration and proliferation, and also blocks the adhesion of monocytes to ECs. ECs expressing KRR mutant ERα, however, lack all of these responses. These observations establish KRR ERα as a novel tool that could greatly facilitate future studies into the vascular and non-vascular functions of ERα rapid signaling. Further, they support that rapid signaling through ERα is essential for many of the transcriptional and physiological responses of ECs to E2, and that ERα rapid signaling in ECs, in vivo, may be critical for the vasculoprotective and anti-inflammatory effects of estrogen.

Intercellular Adhesion Molecule 1 Regulates Left Ventricular Leukocyte Infiltration, Cardiac Remodeling, and Function in Pressure Overload-Induced Heart Failure

Background

Left ventricular dysfunction and heart failure are strongly associated in humans with increased circulating levels of proinflammatory cytokines, T cells, and soluble intercellular cell adhesion molecule 1 (ICAM1). In mice, infiltration of T cells into the left ventricle contributes to pathological cardiac remodeling, but the mechanisms regulating their recruitment to the heart are unclear. We hypothesized that ICAM1 regulates cardiac inflammation and pathological cardiac remodeling by mediating left ventricular T‐cell recruitment and thus contributing to cardiac dysfunction and heart failure.

Methods and Results

In a mouse model of pressure overload–induced heart failure, intramyocardial endothelial ICAM1 increased within 48 hours in response to thoracic aortic constriction and remained upregulated as heart failure progressed. ICAM1‐deficient mice had decreased T‐cell and proinflammatory monocyte infiltration in the left ventricle in response to thoracic aortic constriction, despite having numbers of circulating T cells and activated T cells in the heart‐draining lymph nodes that were similar to those of wild‐type mice. ICAM1‐deficient mice did not develop cardiac fibrosis or systolic and diastolic dysfunction in response to thoracic aortic constriction. Exploration of the mechanisms regulating ICAM1 expression revealed that endothelial ICAM1 upregulation and T‐cell infiltration were not mediated by endothelial mineralocorticoid receptor signaling, as demonstrated in thoracic aortic constriction studies in mice with endothelial mineralocorticoid receptor deficiency, but rather were induced by the cardiac cytokines interleukin 1β and 6.

Conclusions

ICAM1 regulates pathological cardiac remodeling by mediating proinflammatory leukocyte infiltration in the left ventricle and cardiac fibrosis and dysfunction and thus represents a novel target for treatment of heart failure.

Activated mineralocorticoid receptor regulates micro-RNA-29b in vascular smooth muscle cells

Inappropriately activated mineralocorticoid receptor (MR) is a risk factor for vascular remodeling with unclear molecular mechanism. Recent findings suggest that post-transcriptional regulation by micro-RNAs (miRs) may be involved. Our aim was to search for MR-dependent miRs in vascular smooth muscle cells (VSMCs) and to explore the underlying molecular mechanism and the pathologic relevance. We detected that aldosteroneviathe MR reduces miR-29bin vivoin murine aorta and in human primary and cultured VSMCs (ED50= 0.07 nM) but not in endothelial cells [quantitative PCR (qPCR), luciferase assays]. This effect was mediated by an increased decay of miR-29b in the cytoplasm with unchanged miR-29 family member or primary-miR levels. Decreased miR-29b led to an increase in extracellular matrix measured by ELISA and qPCR and enhanced VSMC migration in single cell-tracking experiments. Additionally, cell proliferation and the apoptosis/necrosis ratio (caspase/lactate dehydrogenase assay) was modulated by miR-29b. Enhanced VSMC migration by aldosterone required miR-29b regulation. Control experiments were performed with scrambled RNA and empty plasmids, by comparing aldosterone-stimulated with vehicle-incubated cells. Overall, our findings provide novel insights into the molecular mechanism of aldosterone-mediated vascular pathogenesis by identifying miR-29b as a pathophysiologic relevant target of activated MR in VSMCs and by highlighting the importance of miR processing for miR regulation.-Bretschneider, M., Busch, B., Mueller, D., Nolze, A., Schreier, B., Gekle, M., Grossmann, C. Activated mineralocorticoid receptor regulates micro-RNA-29b in vascular smooth muscle cells.

Targeting inflammation in metabolic syndrome

The metabolic syndrome (MetS) is comprised of a cluster of closely related risk factors, including visceral adiposity, insulin resistance, hypertension, high triglyceride, and low high-density lipoprotein cholesterol; all of which increase the risk for the development of type 2 diabetes and cardiovascular disease. A chronic state of inflammation appears to be a central mechanism underlying the pathophysiology of insulin resistance and MetS. In this review, we summarize recent research which has provided insight into the mechanisms by which inflammation underlies the pathophysiology of the individual components of MetS including visceral adiposity, hyperglycemia and insulin resistance, dyslipidemia, and hypertension. On the basis of these mechanisms, we summarize therapeutic modalities to target inflammation in the MetS and its individual components. Current therapeutic modalities can modulate the individual components of MetS and have a direct anti-inflammatory effect. Lifestyle modifications including exercise, weight loss, and diets high in fruits, vegetables, fiber, whole grains, and low-fat dairy and low in saturated fat and glucose are recommended as a first line therapy. The Mediterranean and dietary approaches to stop hypertension diets are especially beneficial and have been shown to prevent development of MetS. Moreover, the Mediterranean diet has been associated with reductions in total and cardiovascular mortality. Omega-3 fatty acids and peroxisome proliferator-activated receptor α agonists lower high levels of triglyceride; their role in targeting inflammation is reviewed. Angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and aldosterone blockers comprise pharmacologic therapies for hypertension but also target other aspects of MetS including inflammation. Statin drugs target many of the underlying inflammatory pathways involved in MetS.

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.

Acute effect of mineralocorticoid receptor antagonism on vascular function in healthy older adults

Mineralocorticoid receptor (MR) activation by aldosterone may regulate vascular function in health or contribute to vascular dysfunction in cardiovascular disease. Whether the effects are beneficial or detrimental to vascular function appear to be dependent on the integrity of the vascular endothelium and whether the responses are short-term or chronic. Acute modulation of MR activation has resulted in conflicting outcomes on vascular function in young healthy adults. Little is known about the vascular role of aldosterone and MR activation in healthy human aging. The primary objective of this study was to examine whether acute inhibition of MR by the selective antagonist eplerenone, influences vascular function in healthy older adults. We performed a randomized, double-blind, placebo-controlled crossover study in 22 adults (61±1 years; mean±SE, 53-79 years) who were free from overt clinical cardiovascular disease. We measured brachial artery flow-mediated endothelium-dependent dilation and endothelium-independent dilation to sublingual nitroglycerin (0.4 mg) following eplerenone (100 mg/dose, 2 doses, 24h between doses) or placebo. In response to acute MR antagonism, flow-mediated dilation decreased by 19% (from 6.9±0.5 to 5.6±0.6%, P=0.02; placebo vs. eplerenone). Endothelial nitric oxide synthase (eNOS) activity also decreased following MR antagonism based on the ratio of phosphorylated eNOS(Ser1177) to total eNOS (1.53±0.08 vs. 1.29±0.06, P=0.02). Nitroglycerin-induced dilation and blood pressure were unaffected (nitroglycerin-induced dilation: 21.9±1.9 vs. 21.0±1.5%, P=0.5 and systolic/diastolic blood pressure: 135/77±4/2 vs. 134/77±4/2 mmHg, P≥0.6). In conclusion, acute MR antagonism impairs vascular endothelial function in healthy older adults without influencing vascular smooth muscle responsiveness to exogenous nitric oxide or blood pressure.

Endothelial Mineralocorticoid Receptors Differentially Contribute to Coronary and Mesenteric Vascular Function Without Modulating Blood Pressure

Arteriolar vasoreactivity tightly regulates tissue-specific blood flow and contributes to systemic blood pressure (BP) but becomes dysfunctional in the setting of cardiovascular disease. The mineralocorticoid receptor (MR) is known to regulate BP via the kidney and by vasoconstriction in smooth muscle cells. Although endothelial cells (EC) express MR, the contribution of EC-MR to BP and resistance vessel function remains unclear. To address this, we created a mouse with MR specifically deleted from EC (EC-MR knockout [EC-MR-KO]) but with intact leukocyte MR expression and normal renal MR function. Telemetric BP studies reveal no difference between male EC-MR-KO mice and MR-intact littermates in systolic, diastolic, circadian, or salt-sensitive BP or in the hypertensive responses to aldosterone±salt or angiotensin II±l-nitroarginine methyl ester. Vessel myography demonstrated normal vasorelaxation in mesenteric and coronary arterioles from EC-MR-KO mice. After exposure to angiotensin II-induced hypertension, impaired endothelial-dependent relaxation was prevented in EC-MR-KO mice in mesenteric vessels but not in coronary vessels. Mesenteric vessels from angiotensin II-exposed EC-MR-KO mice showed increased maximum responsiveness to acetylcholine when compared with MR-intact vessels, a difference that is lost with indomethacin+l-nitroarginine methyl ester pretreatment. These data support that EC-MR plays a role in regulating endothelial function in hypertension. Although there was no effect of EC-MR deletion on mesenteric vasoconstriction, coronary arterioles from EC-MR-KO mice showed decreased constriction to endothelin-1 and thromboxane agonist at baseline and also after exposure to hypertension. These data support that EC-MR participates in regulation of vasomotor function in a vascular bed-specific manner that is also modulated by risk factors, such as hypertension.

Endothelial Mineralocorticoid Receptor Deletion Prevents Diet-Induced Cardiac Diastolic Dysfunction in Females

Overnutrition and insulin resistance are especially prominent risk factors for the development of cardiac diastolic dysfunction in females. We recently reported that consumption of a Western diet (WD) containing excess fat (46%), sucrose (17.5%), and high fructose corn syrup (17.5%) for 16 weeks resulted in cardiac diastolic dysfunction and aortic stiffening in young female mice and that these abnormalities were prevented by mineralocorticoid receptor blockade. Herein, we extend those studies by testing whether WD-induced diastolic dysfunction and factors contributing to diastolic impairment, such as cardiac fibrosis, hypertrophy, inflammation, and impaired insulin signaling, are modulated by excess endothelial cell mineralocorticoid receptor signaling. Four-week-old female endothelial cell mineralocorticoid receptor knockout and wild-type mice were fed mouse chow or WD for 4 months. WD feeding resulted in prolonged relaxation time, impaired diastolic septal wall motion, and increased left ventricular filling pressure indicative of diastolic dysfunction. This occurred in concert with myocardial interstitial fibrosis and cardiomyocyte hypertrophy that were associated with enhanced profibrotic (transforming growth factor β1/Smad) and progrowth (S6 kinase-1) signaling, as well as myocardial oxidative stress and a proinflammatory immune response. WD also induced cardiomyocyte stiffening, assessed ex vivo using atomic force microscopy. Conversely, endothelial cell mineralocorticoid receptor deficiency prevented WD-induced diastolic dysfunction, profibrotic, and progrowth signaling, in conjunction with reductions in macrophage proinflammatory polarization and improvements in insulin metabolic signaling. Therefore, our findings indicate that increased endothelial cell mineralocorticoid receptor signaling associated with consumption of a WD plays a key role in the activation of cardiac profibrotic, inflammatory, and growth pathways that lead to diastolic dysfunction in female mice.

Sulfenic Acid Modification of Endothelin B Receptor is Responsible for the Benefit of a Nonsteroidal Mineralocorticoid Receptor Antagonist in Renal Ischemia

AKI is associated with high mortality rates and the development of CKD. Ischemia/reperfusion (IR) is an important cause of AKI. Unfortunately, there is no available pharmacologic approach to prevent or limit renal IR injury in common clinical practice. Renal IR is characterized by diminished nitric oxide bioavailability and reduced renal blood flow; however, the mechanisms leading to these alterations are poorly understood. In a rat model of renal IR, we investigated whether the administration of the novel nonsteroidal mineralocorticoid receptor (MR) antagonist BR-4628 can prevent or treat the renal dysfunction and tubular injury induced by IR. Renal injury induced by ischemia was associated with increased oxidant damage, which led to a cysteine sulfenic acid modification in endothelin B receptor and consequently decreased endothelial nitric oxide synthase activation. These modifications were efficiently prevented by nonsteroidal MR antagonism. Furthermore, we demonstrated that the protective effect of BR-4628 against IR was lost when a selective endothelin B receptor antagonist was coadministered. These data describe a new mechanism for reduced endothelial nitric oxide synthase activation during renal IR that can be blocked by MR antagonism with BR-4628.

Modulation of Immunity and Inflammation by the Mineralocorticoid Receptor and Aldosterone

The mineralocorticoid receptor (MR) is a ligand dependent transcription factor. MR has been traditionally associated with the control of water and electrolyte homeostasis in order to keep blood pressure through aldosterone activation. However, there is growing evidence indicating that MR expression is not restricted to vascular and renal tissues, as it can be also expressed by cells of the immune system, where it responds to stimulation or antagonism, controlling immune cell function. On the other hand, aldosterone also has been associated with proinflammatory immune effects, such as the release of proinflammatory cytokines, generating oxidative stress and inducing fibrosis. The inflammatory participation of MR and aldosterone in the cardiovascular disease suggests an association with alterations in the immune system. Hypertensive patients show higher levels of proinflammatory mediators that can be modulated by MR antagonism. Although these proinflammatory properties have been observed in other autoimmune and chronic inflammatory diseases, the cellular and molecular mechanisms that mediate these effects remain unknown. Here we review and discuss the scientific work aimed at determining the immunological role of MR and aldosterone in humans, as well as animal models.

Aldosterone induces clonal β-cell failure through glucocorticoid receptor

Aldosterone excess causes insulin resistance in peripheral tissues and directly impairs the function of clonal β-cell. The aim of this study was to investigate the molecular mechanisms involved in the aldosterone-induced impairment of clonal β-cells. As expected, aldosterone induced apoptosis and β-cell dysfunction, including impairment of insulin synthesis and secretion, which were reversed by Glucocorticoid receptor (GR) antagonists or GR-specific siRNA. However, mineralocorticoid receptor (MR) antagonists or MR-specific siRNA had no effect on impairment of clonal β-cells induced by aldosterone. Besides, aldosterone significantly decreased expression and activity of MafA, while activated JNK and p38 MAPK in a GR-dependent manner. In addition, JNK inhibitors (SP600125) and/or p38 inhibitors (SB203580) could abolish the effect of aldosterone on MafA expression and activity. Importantly, overexpression of JNK1 or p38 reversed the protective effect of a GR antagonist on the decrease of MafA expression and activity. Furthermore, aldosterone inhibits MafA expression at the transcriptional and post-transcriptional level through activation of JNK and p38, respectively. Consequently, overexpression of MafA increased synthesis and secretion of insulin, and decreased apoptosis in clonal β-cells exposed to aldosterone. These findings identified aldosterone as an inducer of clonal β-cell failure that operates through the GR-MAPK-MafA signaling pathway.

Markers of inflammation in recipients of continuous-flow left ventricular assist devices

Although the newer continuous-flow left ventricular assist devices (CF-LVADs) provide clinical advantages over the pulsatile pumps, the effects of low pulsatility on inflammation are incompletely understood. The objective of our study was to examine the levels of inflammatory mediators in CF-LVAD recipients compared with both healthy control subjects and heart failure patients who were candidates for CF-LVAD support. Plasma levels of chemokines, cytokines, and inflammatory markers were measured in 18 CF-LVAD recipients and compared with those of 14 healthy control subjects and 14 heart failure patients who were candidates for CF-LVADs. The levels of granulocyte macrophage-colony stimulating factor, macrophage inflammatory proteins-1β, and macrophage-derived chemokine were significantly higher in the CF-LVAD group compared with both the heart failure and the healthy control groups, whereas no significant differences were observed between the healthy control subjects and the heart failure groups. Compared with the healthy controls, C-reactive protein, interferon gamma-induced protein-10, monocyte chemotactic protein-1, and interleukin-8 levels were significantly higher in both the CF-LVAD and heart failure groups, but no significant differences were observed between the CF-LVAD recipients and the heart failure patients. Inflammatory markers were elevated in CF-LVAD recipients compared with healthy control subjects and the heart failure patients. Further studies should investigate the clinical implications of elevated levels of inflammation in CF-LVAD recipients.

Novel interactions of the mineralocorticoid receptor

The mineralocorticoid receptor (MR) differs from the other steroid receptors in that it responds to two physiological ligands, aldosterone and cortisol. In epithelial tissues, aldosterone selectivity is determined by 11β-hydroxysteroid dehydrogenase type II. In other tissues cortisol is the primary ligand; in some tissues cortisol may act as an antagonist. To better target MR, an understanding of the structural determinants of tissue and ligand-specific MR activation is required. Our focus is on interactions of the ligand-binding domain (LBD) with ligand, the N-terminal domain and putative co-regulatory molecules. Molecular modelling has identified a region in the LBD of the MR and indeed other steroid receptors that critically defines ligand-specificity for aldosterone and cortisol, yet is not part of the ligand-binding pocket. An interaction between the N-terminus and LBD observed in the MR is aldosterone-dependent but is unexpectedly antagonised by cortisol. The structural basis of this interaction has been defined. We have identified proteins which interact in the presence of either aldosterone or cortisol but not both. These have been confirmed as coactivators of the full-length hMR. The structural basis of this interaction has been determined for tesmin, a ligand-discriminant coactivator of the MR. The successful identification of the structural basis of antagonism and of ligand-specific interactions of the MR may provide the basis for the development of novel MR ligands with tissue specificity.

Aldosterone promotes cardiac endothelial cell proliferation in vivo

BACKGROUND

Experimentally, aldosterone in association with NaCl induces cardiac fibrosis, oxidative stress, and inflammation through mineralocorticoid receptor activation; however, the biological processes regulated by aldosterone alone in the heart remain to be identified.

METHODS AND RESULTS

Mice were treated for 7 days with aldosterone, and then cardiac transcriptome was analyzed. Aldosterone regulated 60 transcripts (51 upregulated and 9 downregulated) in the heart (fold change ≥1.5, false discovery rate <0.01). To identify the biological processes modulated by aldosterone, a gene ontology analysis was performed. The majority of aldosterone-regulated genes were involved in cell division. The cardiac Ki-67 index (an index of proliferation) of aldosterone-treated mice was higher than that of nontreated mice, confirming microarray predictions. Costaining of Ki-67 with vinculin, CD68, α-smooth muscle actin, CD31, or caveolin 1 revealed that the cycling cells were essentially endothelial cells. Aldosterone-induced mineralocorticoid receptor-dependent proliferation was confirmed ex vivo in human endothelial cells. Moreover, pharmacological-specific blockade of mineralocorticoid receptor by eplerenone inhibited endothelial cell proliferation in a preclinical model of heart failure (transverse aortic constriction).

CONCLUSIONS

Aldosterone modulates cardiac gene expression and induces the proliferation of cardiac endothelial cells in vivo.

Mineralocorticoid receptors in the heart: lessons from cell-selective transgenic animals

The clinical impact of cardiovascular disease cannot be underestimated. Equally, the importance of cost-effective management of cardiac failure is a pressing issue in the face of an ageing population and the increasing incidence of metabolic disorders worldwide. Targeting the mineralocorticoid receptor (MR) offers one approach for the treatment of heart failure with current strategies for novel MR therapeutics focusing on harnessing their cardio-protective benefits, but limiting the side effects of existing agents. It is now well accepted that activation of the MR in the cardiovascular system promotes tissue inflammation and fibrosis and has negative consequences for cardiac function and patient outcomes following cardiac events. Indeed, blockade of the MR using one of the two available antagonists (spironolactone and eplerenone) provides significant cardio-protective effects in the clinical and experimental setting. Although the pathways downstream of MR that translate receptor activation into tissue inflammation, fibrosis and dysfunction are still being elucidated, a series of recent studies using cell-selective MR (NR3C2)-null or MR-overexpressing mice have offered many new insights into the role of MR in cardiovascular disease and the control of blood pressure. Dissecting the cell-specific roles of MR signalling in the heart and vasculature to identify those pathways that are critical for MR-dependent responses is an important step towards achieving cardiac-selective therapeutics. The goal of this review is to discuss recent advances in this area that have emerged from the study of tissue-selective MR-null mice, and other targeted transgenic models and their relevance to clinical disease.

Mineralocorticoid receptor blockade improves coronary microvascular function in individuals with type 2 diabetes

Reduced coronary flow reserve (CFR), an indicator of coronary microvascular dysfunction, is seen in type 2 diabetes mellitus (T2DM) and predicts cardiac mortality. Since aldosterone plays a key role in vascular injury, the aim of this study was to determine whether mineralocorticoid receptor (MR) blockade improves CFR in individuals with T2DM. Sixty-four men and women with well-controlled diabetes on chronic ACE inhibition (enalapril 20 mg/day) were randomized to add-on therapy of spironolactone 25 mg, hydrochlorothiazide (HCTZ) 12.5 mg, or placebo for 6 months. CFR was assessed by cardiac positron emission tomography at baseline and at the end of treatment. There were significant and similar decreases in systolic blood pressure with spironolactone and HCTZ but not with placebo. CFR improved with treatment in the spironolactone group as compared with the HCTZ group and with the combined HCTZ and placebo groups. The increase in CFR with spironolactone remained significant after controlling for baseline CFR, change in BMI, race, and statin use. Treatment with spironolactone improved coronary microvascular function, raising the possibility that MR blockade could have beneficial effects in preventing cardiovascular disease in patients with T2DM.

Mineralocorticoid Receptors in the Pathophysiology of Vascular Inflammation and Atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the vasculature that causes significant morbidity and mortality from myocardial infarction, stroke, and peripheral vascular disease. Landmark clinical trials revealed that mineralocorticoid receptor (MR) antagonists improve outcomes in cardiovascular patients. Conversely, enhanced MR activation by the hormone aldosterone is associated with increased risk of MI, stroke, and cardiovascular death. This review summarizes recent advances in our understanding of the role of aldosterone and the MR in the pathogenesis of vascular inflammation and atherosclerosis as it proceeds from risk factor-induced endothelial dysfunction and inflammation to plaque formation, progression, and ultimately rupture with thrombosis, the cause of acute ischemia. The role of the MR in converting cardiac risk factors into endothelial dysfunction, in enhancing leukocyte adhesion and infiltration into the vasculature, in promoting systemic inflammation and vascular oxidative stress, and in plaque destabilization and thrombosis are discussed. A greater understanding of the mechanisms by which the MR promotes atherosclerosis has substantial potential to identify novel treatment targets to improve cardiovascular health and decrease mortality.

Longitudinal assessment of inflammation in recipients of continuous-flow left ventricular assist devices

BACKGROUND

The long-term effects of continuous-flow left ventricular assist device (CF-LVAD) support on trends of inflammatory markers over time are unknown. We examined the hypothesis that the levels of inflammatory markers in CF-LVAD recipients are higher than in healthy controls and that these levels increase over time with long-term CF-LVAD support.

METHODS

We examined the levels of inflammatory markers longitudinally at baseline before CF-LVAD implantation and at 3, 6, and 9 months after implantation. We then compared the levels of inflammatory markers to those in a healthy control group.

RESULTS

Compared with baseline values before CF-LVAD implantation, left ventricular end-diastolic diameter (LVEDd) and left ventricular end-systolic diameter (LVESd) decreased significantly at 3, 6, and 9 months after CF-LVAD implantation. Brain natriuretic peptide (BNP) levels dropped significantly after CF-LVAD implantation but did not normalize. Improvements in ejection fraction at 3, 6, and 9 months after CF-LVAD implantation did not reach significance. Monocyte chemoattractant protein-1, interferon γ-induced protein, and C-reactive protein levels were higher in the CF-LVAD recipients at each of the time points (baseline before CF-LVAD implantation and 3, 6, and 9 months after implantation) compared with levels in healthy controls. In CF-LVAD recipients, serum interleukin-8, tumour necrosis factor-α, and macrophage inflammatory protein-β increased significantly at 9 months, and macrophage-derived chemokine increased at 6 months after CF-LVAD implantation compared with baseline.

CONCLUSIONS

Despite improvements in LV dimensions and BNP levels, markers of inflammation remained higher in CF-LVAD recipients. High levels of inflammation in CF-LVAD recipients may result from heart failure preconditioning or the long-term device support, or both. Because inflammation may be detrimental to CF-LVAD recipients, future studies should determine whether inflammatory pathways are reversible.

Mineralocorticoid receptor in adipocytes and macrophages: a promising target to fight metabolic syndrome

Aldosterone is the primary ligand for the mineralocorticoid receptor (MR) and has been considered long time a "renal" hormone, acting at this site as a key regulator of plasma volume, electrolyte homeostasis and blood pressure. A new exciting era of MR biology began with the identification of MR in different non-epithelial tissues such as brain, heart, vessels, macrophages/monocytes, and adipose tissue. The distribution of MR in such a wide range of tissues has suggested novel and unexpected roles for MR, for example in energy metabolism and inflammation. An increasing body of evidence suggests a detrimental effect of aldosterone excess on the development of metabolic alterations. Disturbances in glucose metabolism due to inappropriate activation of MR are frequently observed in patients with primary aldosteronism as well as in obese subjects. MR antagonists have beneficial effects on glucose tolerance and metabolic parameters in experimental animals, whereas their role in humans remains unclear. The aim of this review is to discuss the pathophysiology of MR activation in experimental models, particularly at the level of adipocytes and macrophages, to discuss novel and sometimes contrasting insights from emerging studies, and to highlight deficiencies in the field.

Mineralocorticoid receptors in immune cells: emerging role in cardiovascular disease

Mineralocorticoid receptors (MRs) contribute to the pathophysiology of hypertension and cardiovascular disease in humans. As such, MR antagonists improve cardiovascular outcomes but the molecular mechanisms remain unclear. The actions of the MR in the kidney to increase blood pressure are well known, but the recent identification of MRs in immune cells has led to novel discoveries in the pathogenesis of cardiovascular disease that are reviewed here. MR regulates macrophage activation to the pro-inflammatory M1 phenotype and this process contributes to the pathogenesis of cardiovascular fibrosis in response to hypertension and to outcomes in mouse models of stroke. T lymphocytes have recently been implicated in the development of hypertension and cardiovascular fibrosis in mouse models. MR activation in vivo promotes T lymphocyte differentiation to the pro-inflammatory Th1 and Th17 subsets while decreasing the number of anti-inflammatory T regulatory lymphocytes. The mechanism likely involves activation of MR in antigen presenting dendritic cells that subsequently regulate Th1/Th17 polarization by production of cytokines. Alteration of the balance between T helper and T regulatory lymphocytes contributes to the pathogenesis of hypertension and atherosclerosis and the associated complications. B lymphocytes also express the MR and specific B lymphocyte-derived antibodies modulate the progression of atherosclerosis. However, the role of MR in B lymphocyte function remains to be explored. Overall, recent studies of MR in immune cells have identified new mechanisms by which MR activation may contribute to the pathogenesis of organ damage in patients with cardiovascular risk factors. Conversely, inhibition of leukocyte MR may contribute to the protective effects of MR antagonist drugs in cardiovascular patients. Further understanding of the role of MR in leukocyte function could yield novel drug targets for cardiovascular disease.

Aldosterone up-regulates MMP-9 and MMP-9/NGAL expression in human neutrophils through p38, ERK1/2 and PI3K pathways

Aldosterone and mineralocorticoid receptors are important regulators of inflammation. During this process, chemokines and extracellular matrix degradation by matrix metalloproteases, such as MMP-9, help leukocytes reaching swiftly and infiltrating the injured tissue, two processes essential for tissue repair. Leukocytes, such as neutrophils, are a rich source of MMP-9 and possess mineralocorticoid receptors (MR). The aim of our study was to investigate whether aldosterone was able to regulate proMMP-9, active MMP-9 and MMP-9/NGAL production in human neutrophils. Here we show that aldosterone increased MMP-9 mRNA in a dose- and time-dependent manner. This hormone up-regulated also dose-dependently proMMP-9 and active MMP-9 protein release as well as the MMP-9/NGAL protein complex. PI3K, p38 and ERK1/2 inhibition diminished these aldosterone-induced neutrophil productions. Furthermore, spironolactone, a MR antagonist, counteracted aldosterone-induced increases of proMMP-9, active MMP-9 and MMP-9/NGAL complex. These findings indicate that aldosterone could participate in tissue repair by modulating neutrophil activity and favoring extracellular matrix degradation.

Estrogen receptor inhibits mineralocorticoid receptor transcriptional regulatory function

The steroid hormone aldosterone (aldo) contributes to cardiovascular disease in animal models and in humans. Aldo activates the mineralocorticoid receptor (MR), a hormone-activated transcription factor, and indeed, pharmacological MR inhibition improves cardiovascular outcomes. Because the incidence of cardiovascular disease is lower in premenopausal women, we hypothesized that estrogen (E2) signaling through the estrogen receptor (ER) may protect the vasculature by inhibiting the detrimental effects of aldo signaling through the MR. We demonstrate that E2-activated ER inhibits MR-mediated gene transcription from the mouse mammary tumor virus reporter in human embryonic kidney-293 cells. In contrast, aldo-activated MR does not affect ER-mediated gene transcription. The ERα N terminus (amino acids 1-253) containing part of the DNA-binding domain is sufficient to inhibit MR genomic function, although point mutations reveal that DNA binding, ligand-independent activation, and rapid nongenomic ERα signaling are not required for this effect. Furthermore, ERα and MR are part of a complex in cell lysates, with amino acids 1-233 of the ERα N terminus being sufficient to complex with the MR. Overall, the ability of ERα to inhibit MR-mediated gene transcription correlates with the ability of ERα segments to both localize to the nucleus and complex with the MR. In cultured vascular endothelial cells expressing ERα, E2 inhibits aldo induction of the vascular MR target gene intercellular adhesion molecule-1 (ICAM-1). ICAM-1 induction by endothelial MR is known to promote vascular inflammation that could contribute to the mechanism of aldo-induced atherosclerosis. E2 also inhibits aldo induction of ICAM-1 protein and prevents aldo-enhanced leukocyte adhesion to endothelial cells. These studies support a new model in which E2-activated ER in endothelial cells forms a complex with MR in the nucleus to modulate MR regulation of the proinflammatory gene ICAM-1. Estrogen inhibition of MR regulation of genes that contribute to cardiovascular disease may be a new mechanism by which premenopausal women are protected from cardiovascular disease.

Mineralocorticoids in the heart and vasculature: new insights for old hormones

The mineralocorticoid aldosterone is a key regulator of water and electrolyte homeostasis. Numerous recent developments have advanced the field of mineralocorticoid pharmacology—namely, clinical trials have shown the beneficial effects of aldosterone antagonists in chronic heart failure and post-myocardial infarction treatment. Experimental studies using cell type-specific gene targeting of the mineralocorticoid receptor (MR) gene in mice have revealed the importance of extrarenal aldosterone signaling in cardiac myocytes, endothelial cells, vascular smooth cells, and macrophages. In addition, several molecular pathways involving signal transduction via the classical MR as well as the G protein-coupled receptor GPER mediate the diverse spectrum of effects of aldosterone on cells. This knowledge has initiated the development of new pharmacological ligands to specifically interfere with targets on different levels of aldosterone signaling. For example, aldosterone synthase inhibitors such as LCI699 and the novel nonsteroidal MR antagonist BAY 94-8862 have been tested in clinical trials. Interference with the interaction between MR and its coregulators seems to be a promising strategy toward the development of selective MR modulators.

Crystal structure of the mineralocorticoid receptor DNA binding domain in complex with DNA

The steroid hormone receptors regulate important physiological functions such as reproduction, metabolism, immunity, and electrolyte balance. Mutations within steroid receptors result in endocrine disorders and can often drive cancer formation and progression. Despite the conserved three-dimensional structure shared among members of the steroid receptor family and their overlapping DNA binding preference, activation of individual steroid receptors drive unique effects on gene expression. Here, we present the first structure of the human mineralocorticoid receptor DNA binding domain, in complex with a canonical DNA response element. The overall structure is similar to the glucocorticoid receptor DNA binding domain, but small changes in the mode of DNA binding and lever arm conformation may begin to explain the differential effects on gene regulation by the mineralocorticoid and glucocorticoid receptors. In addition, we explore the structural effects of mineralocorticoid receptor DNA binding domain mutations found in type I pseudohypoaldosteronism and multiple types of cancer.

Mineralocorticoid receptor: a critical player in vascular remodeling

Vascular remodeling is a pathological condition with structural changes of blood vessels. Both inside-out and outside-in hypothesis have been put forward to describe mechanisms of vascular remodeling. An integrated model of these two hypotheses emphasizes the importance of immune cells such as monocytes/macrophages, T cells, and dendritic cells. These immune cells are at the center stage to orchestrate cellular proliferation, migration, and interactions of themselves and other vascular cells including endothelial cells (ECs), vascular smooth muscle cells (VSMCs), and fibroblasts. These changes on vascular wall lead to inflammation and oxidative stress that are largely responsible for vascular remodeling. Mineralocorticoid receptor (MR) is a classic nuclear receptor. MR agonist promotes inflammation and oxidative stress and therefore exacerbates vascular remodeling. Conversely, MR antagonists have the opposite effects. MR has direct roles on vascular cells through non-genomic or genomic actions to modulate inflammation and oxidative stress. Recent studies using genetic mouse models have revealed that MR in myeloid cells, VSMCs and ECs all contribute to vascular remodeling. In conclusion, data in the past years have demonstrated that MR is a critical control point in modulating vascular remodeling. Studies will continue to provide evidence with more detailed mechanisms to support this notion.

Interfering with mineralocorticoid receptor activation: the past, present, and future

Aldosterone is a potent mineralocorticoid produced by the adrenal gland. Aldosterone binds to and activates the mineralocorticoid receptor (MR) in a plethora of tissues, but the cardiovascular actions of aldosterone are of primary interest clinically. Although MR antagonists were developed as antihypertensive agents, they are now considered to be important therapeutic options for patients with heart failure. Specifically, blocking only the MR has proven to be a difficult task because of its similarity to other steroid receptors, including the androgen and progesterone receptors. This lack of specificity caused the use of the first-generation mineralocorticoid receptor antagonists to be fraught with difficulty because of the side effects produced by drug administration. However, in recent years, several advances have been made that could potentially increase the clinical use of agents that inhibit the actions of aldosterone. These will be discussed here along with some examples of the beneficial effects of these new therapeutic agents.

Preconditioning actions of aldosterone through p38 signaling modulation in isolated rat hearts

Although persistent excessive actions of aldosterone have unfavorable effects on the cardiovascular system, primarily via mineralocorticoid receptor (MR)-dependent pathways, the pathophysiological significance of aldosterone cascade activation in heart diseases has not yet been fully clarified. We herein examined the effects of short-term aldosterone stimulation at a physiological dose on cardiac function during ischemia-reperfusion injury (IRI). In order to study the effects of aldosterone preconditioning, male Wistar rat Langendorff hearts were perfused with 10(-9) mol/l of aldosterone for 10 min before ischemia, and the response to IRI was assessed. Although aldosterone did not affect the baseline hemodynamic parameters, preconditioning actions of aldosterone significantly improved the recovery in left ventricular contractility and left ventricular end-diastolic pressure associated with a reduced activity of creatine phosphokinase released into the perfusate after ischemia-reperfusion. Notably, the MR inhibitor eplerenone did not abrogate these beneficial effects. Biochemical analyses revealed that p38MAPK phosphorylation was significantly increased during aldosterone preconditioning before ischemia, whereas its phosphorylation was substantially attenuated during sustained ischemia-reperfusion, compared with the results for in the non-preconditioned control hearts. This dual regulation of p38MAPK was not affected by eplerenone. The phosphorylation levels of other MAPKs were not altered by aldosterone preconditioning. In conclusion, the temporal induction of the aldosterone cascade, at a physiological dose, has favorable effects on cardiac functional recovery and injury following ischemia-reperfusion in a MR-independent manner. Phasic dynamism of p38MAPK activation may play a key role in the physiological compensatory pathway of aldosterone under severe cardiac pathological conditions.

Vascular effects of aldosterone: sorting out the receptors and the ligands

Aldosterone has actions far beyond its role as a renal regulator of sodium reabsorption, and broader mechanisms of action than simply a transcriptional regulator. Aldosterone has a number of vascular effects, including regulation of vascular reactivity and vascular growth and/or development. Aldosterone-mediated effects on vascular reactivity reflect a balance between its endothelial-dependent vasodilator effects and its direct smooth muscle vasoconstrictor effects. The endothelial vasodilator effects of aldosterone are mediated by phosphatidylinositol 3-kinase-dependent activation of nitric oxide synthase. G-Protein oestrogen receptor (GPER) is a recently recognized G-protein coupled receptor (GPCR) that is activated by steroid hormones. It was first recognized as the GPCR mediating the rapid effects of oestrogens. Activation of GPER also mediates at least some of the vascular effects of aldosterone in smooth muscle and endothelial cells. In vascular endothelial cells, aldosterone activation of GPER mediates vasodilation. In contrast, activation of endothelial mineralocorticoid receptors has been linked to enhanced vasoconstrictor and/or impaired vasodilator responses.