Aldosterone increases osteopontin gene expression in rat endothelial cells

Osteopontin in Pulmonary Hypertension

Pulmonary hypertension (PH) is a pathological condition with multifactorial etiology, which is characterized by elevated pulmonary arterial pressure and pulmonary vascular remodeling. The underlying pathogenetic mechanisms remain poorly understood. Accumulating clinical evidence suggests that circulating osteopontin may serve as a biomarker of PH progression, severity, and prognosis, as well as an indicator of maladaptive right ventricular remodeling and dysfunction. Moreover, preclinical studies in rodent models have implicated osteopontin in PH pathogenesis. Osteopontin modulates a plethora of cellular processes within the pulmonary vasculature, including cell proliferation, migration, apoptosis, extracellular matrix synthesis, and inflammation via binding to various receptors such as integrins and CD44. In this article, we provide a comprehensive overview of the current understanding of osteopontin regulation and its impact on pulmonary vascular remodeling, as well as consider research issues required for the development of therapeutics targeting osteopontin as a potential strategy for the management of PH.

Sex-Related Signaling of Aldosterone/Mineralocorticoid Receptor Pathway in Calcific Aortic Stenosis

BACKGROUND

There are sex differences in the pathophysiology of aortic valve (AV) calcification in patients with aortic stenosis, although the molecular and cellular mechanisms have not been elucidated. Aldosterone (Aldo) promotes proteoglycan synthesis in valve interstitial cells (VICs) from mitral valves via the mineralocorticoid receptor (MR). We investigated the influence of sex in the role of Aldo/MR pathway in AV alterations in patients with aortic stenosis.

METHODS AND RESULTS

MR was expressed by primary aortic VICs and in AVs from patients with aortic stenosis. MR expression positively correlated with VIC activation markers in AVs from both sexes. However, MR expression was positively associated with molecules involved in AV calcification only in AV from men. Aldo enhanced VIC activation markers in cells from men and women. Interestingly, Aldo increased the expression of calcification markers only in VICs isolated from men. In female VICs, Aldo enhanced fibrotic molecules. MR antagonism (spironolactone) blocked all the above effects. Cytokine arrays showed ICAM (intercellular adhesion molecule)-1 and osteopontin to be specifically increased by Aldo in male VICs. In AVs from men, MR expression positively associated with both ICAM-1 (intercellular adhesion molecule-1) and osteopontin. Only in female VICs, estradiol treatment blocked Aldo-induced VICs activation, inflammation, and fibrosis.

CONCLUSIONS

These findings demonstrate that the Aldo/MR pathway could play a role in early stages of aortic stenosis by promoting VICs activation, fibrosis, and ulterior calcification. Importantly, Aldo/MR pathway is involved in fibrosis in women and in early AV calcification only in men. Accordingly, MR antagonism emerges as a new sex-specific pharmacological treatment to prevent AV alterations.

Direct Blood Pressure-Independent Anti-Fibrotic Effects by the Selective Nonsteroidal Mineralocorticoid Receptor Antagonist Finerenone in Progressive Models of Kidney Fibrosis

INTRODUCTION

The nonsteroidal mineralocorticoid receptor (MR) antagonist finerenone and sodium-glucose cotransporter-2 (SGLT2) inhibitors have demonstrated clinical benefits in chronic kidney disease patients with type 2 diabetes. Precise molecular mechanisms responsible for these benefits are incompletely understood. Here, we investigated potential direct anti-fibrotic effects and mechanisms of nonsteroidal MR antagonism by finerenone or SGLT2 inhibition by empagliflozin in 2 relevant mouse kidney fibrosis models: unilateral ureter obstruction and sub-chronic ischemia reperfusion injury.

METHODS

Kidney fibrosis was induced in mice via unilateral ureteral obstruction or ischemia. In a series of experiments, mice were treated orally with the MR antagonist finerenone (3 or 10 mg/kg), the SGLT2 inhibitor empagliflozin (10 or 30 mg/kg), or in a direct comparison of both drugs. Interstitial myofibroblast accumulation was quantified via alpha-smooth muscle actin and interstitial collagen deposition via Sirius Red/Fast Green staining in both models. Secondary analyses included the assessment of inflammatory cells, kidney mRNA expression of fibrotic markers as well as functional parameters (serum creatinine and albuminuria) in the ischemic model. Blood pressure was measured via telemetry in healthy conscious compound-treated animals.

RESULTS

Finerenone dose-dependently decreased pathological myofibroblast accumulation and collagen deposition with no effects on systemic blood pressure and inflammatory markers in the tested dose range. Reduced kidney fibrosis was paralleled by reduced kidney plasminogen activator inhibitor-1 (PAI-1) and naked cuticle 2 (NKD2) expression in finerenone-treated mice. In contrast, treatment with empagliflozin strongly increased urinary glucose excretion in both models and reduced ischemia-induced albuminuria but had no effects on kidney myofibroblasts or collagen deposition.

DISCUSSION/CONCLUSION

Finerenone has direct anti-fibrotic properties resulting in reduced myofibroblast and collagen deposition accompanied by a reduction in renal PAI-1 and NKD2 expression in mouse models of progressive kidney fibrosis at blood pressure-independent dosages.

Deletion of Osteopontin Enhances β₂-Adrenergic Receptor-Dependent Anti-Fibrotic Signaling in Cardiomyocytes

Cardiac β₂-adrenergic receptors (ARs) are known to inhibit collagen production and fibrosis in cardiac fibroblasts and myocytes. The β₂AR is a Gs protein-coupled receptor (GPCR) and, upon its activation, stimulates the generation of cyclic 3′,5′-adenosine monophosphate (cAMP). cAMP has two effectors: protein kinase A (PKA) and the exchange protein directly activated by cAMP (Epac). Epac1 has been shown to inhibit cardiac fibroblast activation and fibrosis. Osteopontin (OPN) is a ubiquitous pro-inflammatory cytokine, which also mediates fibrosis in several tissues, including the heart. OPN underlies several cardiovascular pathologies, including atherosclerosis and cardiac adverse remodeling. We found that the cardiotoxic hormone aldosterone transcriptionally upregulates OPN in H9c2 rat cardiac myoblasts—an effect prevented by endogenous β₂AR activation. Additionally, CRISPR-mediated OPN deletion enhanced cAMP generation in response to both β₁AR and β₂AR activation in H9c2 cardiomyocytes, leading to the upregulation of Epac1 protein levels. These effects rendered β₂AR stimulation capable of completely abrogating transforming growth factor (TGF)-β-dependent fibrosis in OPN-lacking H9c2 cardiomyocytes. Finally, OPN interacted constitutively with G_αs subunits in H9c2 cardiac cells. Thus, we uncovered a direct inhibitory role of OPN in cardiac β₂AR anti-fibrotic signaling via cAMP/Epac1. OPN blockade could be of value in the treatment and/or prevention of cardiac fibrosis.

Spironolactone (an adjuvant therapy) in rheumatoid arthritis: a case control study

OBJECTIVES

Disease-modifying anti-rheumatic drugs (DMARDs) are conventionally used in rheumatoid arthritis (RA). The role of spironolactone as add on therapy to DMARDs in RA patients was evaluated.

MATERIAL AND METHODS

A total of 100 patients with rheumatoid arthritis diagnosed as per 1987 criteria having evidence of active disease despite ongoing DMARD therapy were enrolled in this study. Patients were assigned randomly to two groups. Group I (n = 50) patients were treated with 50 mg/day of spironolactone along with their maintenance DMARD and NSAID therapy. Group II (n = 50) patients continued their maintenance DMARD therapy without spironolactone. Disease activity was assessed using the Disease Activity Score-28 (DAS28) and the Clinical Disease Activity Index (CDAI) in each patient of each group was evaluated monthly for the next three months.

RESULTS

All patients completed the study. Mean age of group I was 46.44 ±11.67 and of group II 44.52 ±11.82. DAS28 assessed in time according to the schedule was for group I 6.78 ±0.74, 5.34 ±0.74, 3.98 ±0.7, 3.00 ±0.75, while in group II it was 6.61 ±0.82, 5.49 ±0.90, 4.58 ±0.81, 3.55 ±0.93 at baseline, 4, 8, and 12 weeks respectively. CDAI in group I was 41.68 ±11.14, 24.36 ±8.13, 12.34 ±5.73, 6.42 ±4.4 and in group II 37.84 ±11.12, 24.54 ±9.4, 16.38 ±6.81, 9.62 ±6.1 at baseline, 4, 8, and 12 weeks respectively. Group I showed significant improvement in disease activity in the form of tender joint count (p = 0.001), swollen joint count (p = 0.023), patient global assessment (p = 0.001), physician global health (p = 0.001), DAS28 (p < 0.001) and CDAI (p = 0.001) but other parameters showed non-significant improvement compared to group II. No serious adverse events were observed in either group during the course of the study.

CONCLUSIONS

Spironolactone as an adjuvant therapy can improve the effect of conventional DMARD treatment of patients with RA.

Steroidal and Novel Non-steroidal Mineralocorticoid Receptor Antagonists in Heart Failure and Cardiorenal Diseases: Comparison at Bench and Bedside

Characterization of mice with cell-specific deletion or overexpression of the mineralocorticoid receptor (MR) shed a new light on its role in health and disease. Pathophysiological MR activation contributes to a plethora of deleterious molecular mechanisms in the development of cardiorenal diseases like chronic kidney disease (CKD) and heart failure (HF). Accordingly, the available steroidal MR antagonists (MRAs) spironolactone (first generation MRA) and eplerenone (second generation MRA) have been shown to be effective in reducing cardiovascular (CV) mortality and morbidity in patients with chronic HF and a reduced left ventricular ejection fraction (HFrEF). However, they remain underutilized, in large part owing to the risk inducing severe adverse events including hyperkalemia and worsening of kidney function, particularly when given on top of inhibitors of the renin angiotensin system (RAS) to patients with concomitant kidney dysfunction. Novel, potent, and selective non-steroidal MRAs (third generation) were identified in drug discovery campaigns and a few entered clinical development recently. One of these is finerenone with different physicochemical, pharmacokinetics, and pharmacological properties in comparison with the steroidal MRAs. Available data from five clinical phase II trials with finerenone in more than 2,000 patients with HF and additional CKD and/or diabetes as well as in patients with diabetic kidney disease demonstrated that neither hyperkalemia nor reductions in kidney function were limiting factors to its use. Moreover, finerenone demonstrated a nominally improved outcome compared to eplerenone in a phase IIb trial with 1,066 patients with HFrEF and concomitant type 2 diabetes mellitus (T2DM) and/or CKD.

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.

Aldosterone-induced osteopontin gene transcription in vascular smooth muscle cells involves glucocorticoid response element

Osteopontin (OPN) is known to be one of the cytokines that is involved in the vascular inflammation caused by aldosterone (Aldo). Previous reports have shown that Aldo increases OPN transcripts, and the mechanisms for this remain to be clarified. In this study, we investigated how Aldo increases OPN transcripts in the vascular smooth muscle cells of rats. Aldosterone increased OPN transcripts time-dependently as well as dose-dependently. This increase was diminished by eplerenone, a mineralocorticoid receptor (MR) antagonist. Luciferase promoter assays showed that the OPN promoter deleted to the -1599 site retained the same promoting ability as the full-length OPN promoter when stimulated by 10(-7) M Aldo, but the promoter deleted to the -1300 site lost the promoting ability. A glucocorticoid response element (GRE) is located in that deleted region. Luciferase assays of a mutated promoter without the GRE lost the luciferase upregulation, although mutated promoters with the deletion of other consensus sites maintained the promoter activity. The binding of the Aldo-MR complex to the GRE fragment was confirmed by an electrophoretic-mobility shift assay. This is the first report showing that Aldo regulates the transcriptional levels of OPN and inflammatory responses in the vasculature through a specific GRE site in the OPN promoter region.

Transcriptome analysis of aldosterone-regulated genes in human vascular endothelial cell lines stably expressing mineralocorticoid receptor

A series of studies have demonstrated that endothelial cell is one of the target tissues of aldosterone. Here, we have conducted a transcriptome analysis of aldosterone-inducible genes in human endothelial cell lines stably expressing human mineralocorticoid receptor (MR) by retroviral system (MR-EAhy). We found that aldosterone in physiologic concentrations robustly induced MR-dependent transcriptional response in MR-EAhy. By DNA microarray analysis, we validated 12 aldosterone-up-regulated genes among which at least seven were concomitantly associated with increased protein expression. We also found five aldosterone-down-regulated genes. Among 11 aldosterone-up-regulated genes tested, mRNA expressions of three (ESM1, SNF1LK, ANGPTL4) were significantly up-regulated in aortic tissue from aldosterone-induced hypertensive rats compared to those from control rats, suggesting their potential pathophysiologic significance in vivo. In conclusion, using MR stably expressed human endothelial cell lines, we identified a variety of aldosterone-inducible genes, suggesting their possible roles in the development and/or the protection for aldosterone-induced vascular injury.

Evidence for activation of inflammatory lipoxygenase pathways in visceral adipose tissue of obese Zucker rats

Central obesity is associated with low-grade inflammation that promotes type 2 diabetes and cardiovascular disease in obese individuals. The 12- and 5-lipoxygenase (12-LO and 5-LO) enzymes have been linked to inflammatory changes, leading to the development of atherosclerosis. 12-LO has also been linked recently to inflammation and insulin resistance in adipocytes. We analyzed the expression of LO and proinflammatory cytokines in adipose tissue and adipocytes in obese Zucker rats, a widely studied genetic model of obesity, insulin resistance, and the metabolic syndrome. mRNA expression of 12-LO, 5-LO, and 5-LO-activating protein (FLAP) was upregulated in adipocytes and adipose tissue from obese Zucker rats compared with those from lean rats. Concomitant with increased LO gene expression, the 12-LO product 12-HETE and the 5-LO products 5-HETE and leukotriene B4 (LTB4) were also increased in adipocytes. Furthermore, upregulation of key proinflammatory markers interleukin (IL)-6, TNFα, and monocyte chemoattractant protein-1 were observed in adipocytes isolated from obese Zucker rats. Immunohistochemistry indicated that the positive 12-LO staining in adipose tissue represents cells in addition to adipocytes. This was confirmed by Western blotting in stromal vascular fractions. These changes were in part reversed by the novel anti-inflammatory drug lisofylline (LSF). LSF also reduced p-STAT4 in visceral adipose tissue from obese Zucker rats and improved the metabolic profile, reducing fasting plasma glucose and increasing insulin sensitivity in obese Zucker rats. In 3T3-L1 adipocytes, LSF abrogated the inflammatory response induced by LO products. Thus, therapeutic agents reducing LO or STAT4 activation may provide novel tools to reduce obesity-induced inflammation.

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.

Mineralocorticoid accelerates transition to heart failure with preserved ejection fraction via "nongenomic effects"

BACKGROUND

Mechanisms promoting the transition from hypertensive heart disease to heart failure with preserved ejection fraction are poorly understood. When inappropriate for salt status, mineralocorticoid (deoxycorticosterone acetate) excess causes hypertrophy, fibrosis, and diastolic dysfunction. Because cardiac mineralocorticoid receptors are protected from mineralocorticoid binding by the absence of 11-beta hydroxysteroid dehydrogenase, salt-mineralocorticoid-induced inflammation is postulated to cause oxidative stress and to mediate cardiac effects. Although previous studies have focused on salt/nephrectomy in accelerating mineralocorticoid-induced cardiac effects, we hypothesized that hypertensive heart disease is associated with oxidative stress and sensitizes the heart to mineralocorticoid, accelerating hypertrophy, fibrosis, and diastolic dysfunction.

METHODS AND RESULTS

Cardiac structure and function, oxidative stress, and mineralocorticoid receptor-dependent gene transcription were measured in sham-operated and transverse aortic constriction (studied 2 weeks later) mice without and with deoxycorticosterone acetate administration, all in the setting of normal-salt diet. Compared with sham mice, sham plus deoxycorticosterone acetate mice had mild hypertrophy without fibrosis or diastolic dysfunction. Transverse aortic constriction mice displayed compensated hypertensive heart disease with hypertrophy, increased oxidative stress (osteopontin and NOX4 gene expression), and normal systolic function, filling pressures, and diastolic stiffness. Compared with transverse aortic constriction mice, transverse aortic constriction plus deoxycorticosterone acetate mice had similar left ventricular systolic pressure and fractional shortening but more hypertrophy, fibrosis, and diastolic dysfunction with increased lung weights, consistent with heart failure with preserved ejection fraction. There was progressive activation of markers of oxidative stress across the groups but no evidence of classic mineralocorticoid receptor-dependent gene transcription.

CONCLUSIONS

Pressure-overload hypertrophy sensitizes the heart to mineralocorticoid excess, which promotes the transition to heart failure with preserved ejection fraction independently of classic mineralocorticoid receptor-dependent gene transcription.

Association of plasma osteopontin levels with coronary calcification evaluated by tomographic coronary calcium scoring

Evidence indicates that proteins controlling bone mineralization are also involved in the regulation of coronary calcification. The aim of the present study is to evaluate the association between plasma osteopontin (OPN) levels and coronary calcification quantified by using tomographic coronary calcium scoring. Plasma OPN levels were measured from samples of 80 intermediate-risk asymptomatic patients (56 +/- 10 years) who underwent tomographic coronary calcium scoring via multislice computed tomography for incremental risk stratification. There was no significant difference regarding OPN levels between patients with and without coronary calcification in the whole study population. Of 49 patients not receiving renin-angiotensin system inhibitors and/or statins, plasma OPN levels of patients with coronary calcification (38.7%) were significantly higher than those without coronary calcification (61.3%) (8.88 +/- 2.85 vs. 6.79 +/- 2.41, P = 0.008, respectively). On a binary logistic regression model, only age and plasma OPN level were found to be significant independent associated variables for the presence of coronary calcification in patients not receiving these medications (odds ratio for age, 1.15, P = 0.017; for plasma OPN levels, 1.63, P = 0.014). Our results indicate that plasma OPN levels may be predictive of coronary calcification, suggesting an important role of OPN in the atherosclerotic calcification pathogenesis.

Aldosterone, but not angiotensin II, increases profibrotic factors in kidney of adrenalectomized stroke-prone spontaneously hypertensive rats

An increase in angiotensin II (ANG II) under conditions of high salt intake can result in renal damage. The extent to which ANG II does this directly or by way of stimulating aldosterone (Aldo) secretion is a subject of some debate. In the present study, we sought to determine the separate effects of Aldo and ANG II on the expression of plasminogen activator inhibitor-1 (PAI-1) and other factors related to renal fibrosis in the stroke-prone spontaneously hypertensive rat (SHRSP). Saline-drinking male SHRSPs underwent adrenalectomy (ADX) or sham operation (Sham). Treatment groups consisted of ADX + ANG II (25 ng/min sc) and ADX + Aldo (40 microg.kg(-1).day(-1) sc). After 2 wk of treatment, circulating Aldo levels were reduced to the limit of detection, renal PAI-1, transforming growth factor-beta1 (TGF-beta1), and osteopontin expression, and phospho-Smad2 (p-Smad2) level were decreased severalfold, and Smad7 (an inhibitory regulator of TGF-beta1 action) expression was increased in ADX compared with Sham rats. Infusion of Aldo into ADX SHRSPs restored the renal mRNA expression of PAI-1, TGF-beta1 (along with restored p-Smad2 level), and osteopontin and reduced that of Smad7, whereas ANG II had no or a lesser effect. The findings were confirmed by histological examination of renal tissue. In summary, in the saline-drinking SHRSP, Aldo increased renal profibrotic factors and produced renal injury whereas ANG II in the absence of the adrenals had no effect.

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

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

Aldosterone induces superoxide generation via Rac1 activation in endothelial cells

Currently, aldosterone is believed to be involved in the development of cardiovascular injury as a potential cardiovascular risk hormone. However, its exact cellular mechanisms remain obscure. This study was undertaken to examine the effect of aldosterone on superoxide production in cultured rat aortic endothelial cells with possible involvement of the small GTP-binding (G) protein Rac1. The aldosterone levels showed a time-dependent (6-24 h) and dose-dependent (10(-8) to 10(-6) m) increase in superoxide generation, whose effect was abolished by mineralocorticoid receptor antagonist (eplerenone), Src inhibitor (PP2), and reduced nicotinamide adenine dinucleotide phosphate [NAD(P)H] oxidase inhibitor (apocynin). Aldosterone activated NADP(H) oxidase and Rac1, whose effects were abolished by eplerenone. The aldosterone-induced superoxide generation was abolished either by nonselective small G protein inhibitor (Clostridium difficile toxin A) or dominant-negative Rac1. Dominant-negative Rac1 also inhibited aldosterone-induced ACE gene expression. Thus, the present study is the first to demonstrate that aldosterone induces superoxide generation via mineralocorticoid receptor-mediated activation of NAD(P)H-oxidase and Rac1 in endothelial cells, thereby contributing to the development of aldosterone-induced vascular injury.

Osteopontin in Rat Renal Fibroblasts

Osteopontin (OPN), a proinflammatory cytokine, plays an important role in renal fibrosis. We reported that plasma OPN levels were higher in patients with primary aldosteronism than with essential hypertension. However, the regulatory mechanism of OPN by aldosterone remains unclear. Here, we report the transcriptional regulation of OPN expression by aldosterone and the functional effects of aldosterone-mediated OPN transcription in renal fibroblasts. Aldosterone induced OPN expression in a dose-dependent manner with significant responses at 10 nmol/L (1.6±0.2-fold of controls, P <0.05, n=5) and elicited maximal effects at 10 μmol/L (3.5±0.4-fold of controls, P <0.01, n=5). Aldosterone increased OPN expression in a time-dependent manner with a maximal effect after 48 hours (2.7±0.3-fold of controls, P <0.01, n=5). This effect was abolished by the mineralocorticoid receptor (MR) antagonist spironolactone. Luciferase promoter deletion assays identified a novel cis regulatory element (−2153 to −1758) in the OPN promoter that is responsive to aldosterone. This element contains an activator protein-1 (AP-1) and nuclear factor kappa B (NFκB) site. Electrophoretic mobility shift assays, supershift assays, and chromatin immunoprecipitation assays identified both AP-1 and NFκB as the DNA binding proteins induced by aldosterone with spironolactone inhibiting aldosterone-induced AP-1 or NFκB activity. OPN-siRNA inhibited completely the induction of cell proliferation, type I, III, and IV collagen synthesis by aldosterone. These results indicate that aldosterone induced MR-mediated OPN expression through AP-1 and NFκB activation and suggest that aldosterone plays an important role in renal fibrosis through the induction of OPN.

The mineralocorticoid receptor: insights into its molecular and (patho)physiological biology

The last decade has witnessed tremendous progress in the understanding of the mineralocorticoid receptor (MR), its molecular mechanism of action, and its implications for physiology and pathophysiology. After the initial cloning of MR, and identification of its gene structure and promoters, it now appears as a major actor in protein-protein interaction networks. The role of transcriptional coregulators and the determinants of mineralocorticoid selectivity have been elucidated. Targeted oncogenesis and transgenic mouse models have identified unexpected sites of MR expression and novel roles for MR in non-epithelial tissues. These experimental approaches have contributed to the generation of new cell lines for the characterization of aldosterone signaling pathways, and have also facilitated a better understanding of MR physiology in the heart, vasculature, brain and adipose tissues. This review describes the structure, molecular mechanism of action and transcriptional regulation mediated by MR, emphasizing the most recent developments at the cellular and molecular level. Finally, through insights obtained from mouse models and human disease, its role in physiology and pathophysiology will be reviewed. Future investigations of MR biology should lead to new therapeutic strategies, modulating cell-specific actions in the management of cardiovascular disease, neuroprotection, mineralocorticoid resistance, and metabolic disorders.

Aldosterone as a cardiovascular risk hormone

The pathophysiological role of aldosterone in the development of cardiovascular disease has long been considered to be due its potent volume expansion/hypertensive effect mainly via mineralocorticoid receptor (MR) expressed in renal tubular epithelial cells. However, recent accumulating lines of evidence from clinical and experimental studies have suggested that direct cardiovascular effect of aldosterone contributes to the development of cardiovascular injury via MRs in non-epithelial tissue. A series of recent clinical studies have revealed that patients with primary aldosteronism have higher incidence of cardiovascular and renal complications than those with essential hypertension, and that aldosterone antagonism has cardiovascular protective effect in patients with heart failure independent from blood pressure. Numerous experimental studies have shown that both inflammation and oxidative stress play an initial and key role in the development of aldosterone-induced cardiovascular injury via non-epithelial MR activation. In this review, we discuss recent research progress in aldosterone and MR effects, with special emphasis on the pathophysiological role of aldosterone in cardiovascular diseases and the possible molecular mechanism(s) of cardiovascular injury by non-epithelial MR activation.

Effect of combining ACE inhibition with aldosterone blockade on proteinuria and renal damage in experimental nephrosis

Aldosterone has pro-fibrotic properties and is a potential target for additional intervention in patients with chronic renal disease showing resistance to therapy during treatment with angiotensin-converting enzyme inhibitors (ACEi). Combining ACEi and aldosterone receptor blockade (aldoRB) in proteinuric renal disease reduces proteinuria, but effects on proteinuria-induced renal damage are unknown. We studied the effect of ACEi/aldoRB in adriamycin nephrosis (AN). Six weeks after injection of adriamycin in Wistar rats, randomized treatment with vehicle (VEH, n=8), aldoRB (n=12), ACEi (n=10), or a combination of ACEi/aldoRB (n=14) was given for 12 weeks. Healthy rats served as controls (n=6). Renal damage was quantified by markers of tubular injury (osteopontin (OPN) and kidney injury molecule-1 (Kim-1)), pre-fibrotic lesions (alpha-smooth muscle actin (SMA)), interstitial fibrosis (IF), and focal glomerulosclerosis (FGS). In AN animals, proteinuria was increased compared with controls. ACEi and ACEi/aldoRB significantly reduced proteinuria compared with VEH, whereas aldoRB monotherapy was without effect. Blood pressure was reduced in ACEi and ACEi/aldoRB compared with VEH and aldoRB. OPN and Kim-1 were increased in AN animals, but significantly reduced by ACEi/aldoRB. Treatment with ACEi and ACEi/aldoRB prevented an increase of SMA, IF, and FGS. In conclusion, ACEi/aldoRB effectively reduced proteinuria and markers of tubular injury and prevented renal damage in this rat model of chronic proteinuria-induced renal damage.

Mineralocorticoid receptor antagonist reduces renal injury in rodent models of types 1 and 2 diabetes mellitus

To determine whether mineralocorticoid receptor (MR) activation plays a role in diabetic renal injury and whether this role differs in types 1 and 2 diabetes mellitus, we examined the effect of a MR antagonist on renal injury in rodent models of type 1 (streptozotocin-treated rat) and type 2 (db/db mouse) diabetes. We studied three groups of 8-wk-old, uninephrectomized Wistar rats for 4 wk: diabetic streptozotocin- (55 mg/kg) treated rats (n = 11), diabetic streptozotocin-treated rats receiving the MR antagonist eplerenone (n = 15), and nondiabetic rats (n = 9). In addition, we studied three groups of 8-wk-old mice for 16 wk: diabetic db/db mice (n = 10), diabetic db/db mice treated with eplerenone (n = 8), and nondiabetic, db/+ littermates (n = 11). Diabetic rats and mice developed albuminuria and histopathological evidence of renal injury, including glomerular hypertrophy, mesangial expansion, and tubulointerstitial injury as well as increased renal cortical levels of MR protein, MR mRNA, TGFbeta mRNA, and osteopontin mRNA. All of these changes were significantly reduced by treatment with eplerenone except for the elevated MR levels. The beneficial effects of eplerenone were not attributable to changes in blood pressure or glycemia. In summary, MR expression was increased in kidneys of diabetic rodents, and MR antagonists effectively reduced diabetic renal injury irrespective of the species or specific cause of the diabetes. Thus, these data suggest that MR activation is a critical factor in the early pathogenesis of renal disease in both type 1 and type 2 diabetes mellitus.

Osteopontin and carotid atherosclerosis in patients with essential hypertension

OPN (osteopontin), a pro-inflammatory cytokine, has recently emerged as a key factor in both vascular remodelling and the development of atherosclerosis. However, the relationship between OPN and atherosclerosis in patients without symptomatic cardiovascular disease is not clear. Therefore we measured plasma OPN levels and evaluated the correlation between plasma OPN levels and atherosclerosis as target organ damage in patients with EHT (essential hypertension). Plasma OPN levels were measured in 76 patients with EHT using a solid-phase sandwich ELISA. IMT (intima-media thickness), and Vd and Vs (mean diastolic and systolic flow velocities respectively) were evaluated by carotid ultrasound. The Vd/Vs ratio, an index of peripheral arterial resistance, was also calculated. The patients were divided on the basis of median OPN levels into a high-OPN group and a low-OPN group. The mean IMT and aldosterone levels were higher (P=0.024 and 0.031 respectively) and Vd/Vs was lower (P=0.007) in the high-OPN group than in the low-OPN group. Plasma OPN levels were positively correlated with mean IMT (r=0.308, P=0.0068) and negatively with Vd/Vs (r=−0.293, P=0.010). Stepwise regression analysis revealed that OPN was an independent determinant of mean IMT (P=0.007) and Vd/Vs (P=0.009), and aldosterone was an independent determinant of OPN. These results suggest that OPN plays a role in the development of atherosclerosis and may be a potential clinical marker for the prediction of atherosclerosis in patients with EHT.