Aldosterone Mineralocorticoid Receptor Research Articles

FRI135 Differential Expression Of Circulating MicroRNAs In Primary Aldosteronism: Potential Biomarkers For Improved Diagnosis

Abstract Disclosure: S. Lamprou: None. S.M. MacKenzie: None. J.D. McClure: None. S. Robertson: None. A. Riddell: None. J.C. van Kralingen: None. A. Gimenez-Roqueplo: None. P. Reel: None. S. Reel: None. G. Assié: None. A. Laurence: None. F. Beuschlein: None. G. Rossi: None. J. Deinum: None. M. Reincke: None. G. Eisenhofer: None. E. Jefferson: None. M. Zennaro: None. E. Davies: None. Primary Aldosteronism (PA) is the most common endocrine hypertension subtype, caused by autonomous aldosterone secretion. While readily treatable, accurate diagnosis of PA – particularly its differentiation from primary hypertension (PHT) – is a complex and protracted process that can entail delays in effective treatment and lead to more severe comorbidities. Given the established role of microRNAs (miRNA) in regulating aldosterone biosynthesis, we hypothesize that circulating miRNAs are potentially viable biomarkers for PA that could inform more accurate and rapid diagnosis. To detect changes in circulating miRNA profiles specific to PA, we analyzed plasma levels of 172 selected microRNAs in a retrospectively-generated cohort of PHT (n=111) and PA patients (n=109). The dataset consisted of ΔCt values for each miRNA (normalized to multiple endogenous miRNAs), as determined by real time RT-qPCR assay. Two-sample t-tests were used to assess whether the means of the two disease groups are equal, corrected using False Discovery Rate (FDR; significance level q < 0.05). Ingenuity Pathway Analysis software (QIAGEN) was employed to analyze the miRNAs bioinformatically and identify mRNA targets involved in blood pressure regulation. Pathway analysis was performed to discover associations between PA and differentially-expressed miRNAs. We identified 83 circulating microRNAs that showed significant differential expression: 27 were upregulated and 56 downregulated in PA relative to PHT. The upregulated miRNA demonstrating the greatest fold change was hsa-miR-451a (FC:1.8, q=0.001), while the most downregulated was hsa-miR-409-3p (FC:0.5, q=0.001). Bioinformatics analysis predicted several dysregulated miRNAs to target mRNAs in PA-related pathways. For example, the most upregulated miRNA, hsa-miR-451a, is predicted to target mRNAs in biochemical pathways relevant to PA pathophysiology, including SGK1 and MAP3K1. SGK1 contributes to the signaling cascade induced by the mineralocorticoid receptor-aldosterone complex that stimulates Na+ reabsorption in the kidney, while MAP3K1 participates in the Renin-Angiotensin system, a key regulator of aldosterone secretion, as part of a signaling cascade that leads to the activation of the AP1 complex in the nucleus. In addition to hsa-miR-451a, other differentially-expressed miRNAs were also revealed to target multiple mRNAs with direct and indirect connections to PA. In summary, analysis has identified miRNAs that are significantly differentially expressed in the plasma of PA patients compared to PHT patients, indicating promise for a biomarker-based approach to PA diagnosis utilizing distinctive circulating microRNA signatures. Further analysis is now being conducted to validate our findings in an independent population of hypertensive patients. Presentation: Friday, June 16, 2023

Brain mineralocorticoid receptor in health and disease: From molecular signalling to cognitive and emotional function.

Brain mineralocorticoid receptors (MR) mediate effects of glucocorticoid hormones in stress adaptation, as well as the effects of aldosterone itself in relation to salt homeostasis. Brain stem MRs respond to aldosterone, whereas forebrain MRs mediate rapid and delayed glucocorticoid effects in conjunction with the glucocorticoid receptor (GR). MR‐mediated effects depend on age, gender, genetic variations, and environmental influences. Disturbed MR activity through chronic stress, certain (endocrine) diseases or during glucocorticoid therapy can cause deleterious effects on affective state, cognitive and behavioural function in susceptible individuals. Considering the important role MR plays in cognition and emotional function in health and disease, MR modulation by pharmacological intervention could relieve stress‐ and endocrine‐related symptoms. Here, we discuss recent pharmacological interventions in the clinic and genetic developments in the molecular underpinnings of MR signalling. Further understanding of MR‐dependent pathways may help to improve psychiatric symptoms in a diversity of settings.LINKED ARTICLESThis article is part of a themed issue on Emerging Fields for Therapeutic Targeting of the Aldosterone‐Mineralocorticoid Receptor Signaling Pathway. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.13/issuetoc

The role of the mineralocorticoid receptor in immune cells in cardiovascular disease.

Chronic low-grade inflammation and immune cell activation are important mechanisms in the pathophysiology of cardiovascular disease (CVD). Therefore, targeted immunosuppression is a promising novel therapy to reduce cardiovascular risk. In this review, we identify the mineralocorticoid receptor (MR) on immune cells as a potential target to modulate inflammation. The MR is present in almost all cells of the cardiovascular system, including immune cells. Activation of the MRs in innate and adaptive immune cells induces inflammation which can contribute to CVD, by inducing endothelial dysfunction and hypertension. Moreover, it accelerates atherosclerotic plaque formation and destabilization and impairs tissue regeneration after ischaemic events. Identifying the molecular targets for these non-renal actions of the MR provides promising novel cardiovascular drug targets for mineralocorticoid receptor antagonists (MRAs), which are currently mainly applied in hypertension and heart failure. LINKED ARTICLES: This article is part of a themed issue on Emerging Fields for Therapeutic Targeting of the Aldosterone-Mineralocorticoid Receptor Signaling Pathway. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.13/issuetoc.

Mineralocorticoid receptors in non-alcoholic fatty liver disease.

Liver diseases are the fourth common death in Europe responsible for about 2 million death per year worldwide. Among the known detrimental causes for liver dysfunction are virus infections, intoxications and obesity. The mineralocorticoid receptor (MR) is a ligand-dependent transcription factor activated by aldosterone or glucocorticoids but also by pathological milieu factors. Canonical actions of the MR take place in epithelial cells of kidney, colon and sweat glands and contribute to sodium reabsorption, potassium secretion and extracellular volume homeostasis. The non-canonical functions can be initiated by inflammation or an altered micro-milieu leading to fibrosis, hypertrophy and remodelling in various tissues. This narrative review summarizes the evidence regarding the role of MR in portal hypertension, non-alcoholic fatty liver disease, liver fibrosis and cirrhosis, demonstrating that inhibition of the MR in vivo seems to be beneficial for liver function and not just for volume regulation. Unfortunately, the underlying molecular mechanisms are still not completely understood. LINKED ARTICLES: This article is part of a themed issue on Emerging Fields for Therapeutic Targeting of the Aldosterone-Mineralocorticoid Receptor Signaling Pathway. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.13/issuetoc.

Mineralocorticoid pathway in retinal health and diseases.

In the retina, the mineralocorticoid receptor is expressed in retinal and choroidal vessels and in cells from neural and glial origins. Like in the brain, the major ligand of the mineralocorticoid receptor is cortisol, and the mineralocorticoid/glucocorticoid receptor balance regulates the activation of the MR pathway. Experimental mineralocorticoid receptor pathway activation using either pharmacological agents or transgenic manipulation favours retinal and choroidal pathology. In various models of retinal diseases, such as glaucomatous neuropathy, retinopathy of prematurity, ischaemic retinopathies, diabetic retinopathy and choroidal neovascularization, mineralocorticoid receptor antagonism exerts beneficial effects, demonstrating its potential in the treatment of major blinding retinal diseases. But specific formulations are required to optimize the bioavailability of mineralocorticoid receptor antagonists in various compartments of the eye, and molecular biomarkers of mineralocorticoid receptor pathway activation remain to be identified in humans to select patients amenable to clinical trials. LINKED ARTICLES: This article is part of a themed issue on Emerging Fields for Therapeutic Targeting of the Aldosterone-Mineralocorticoid Receptor Signaling Pathway. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.13/issuetoc.

The Sweet and Salty Dietary Face of Hypertension and Cardiovascular Disease in Lebanon.

According to the World Health Organization (WHO), an estimated 1.28 billion adults aged 30–79 years worldwide have hypertension; and every year, hypertension takes 7.6 million lives. High intakes of salt and sugar (mainly fructose from added sugars) have been linked to the etiology of hypertension, and this may be particularly true for countries undergoing the nutrition transition, such as Lebanon. Salt-induced hypertension and fructose-induced hypertension are manifested in different mechanisms, including Inflammation, aldosterone-mineralocorticoid receptor pathway, aldosterone independent mineralocorticoid receptor pathway, renin-angiotensin system (RAS), sympathetic nervous system (SNS) activity, and genetic mechanisms. This review describes the evolution of hypertension and cardiovascular diseases (CVDs) in Lebanon and aims to elucidate potential mechanisms where salt and fructose work together to induce hypertension. These mechanisms increase salt absorption, decrease salt excretion, induce endogenous fructose production, activate fructose-insulin-salt interaction, and trigger oxidative stress, thus leading to hypertension. The review also provides an up-to-date appraisal of current intake levels of salt and fructose in Lebanon and their main food contributors. It identifies ongoing salt and sugar intake reduction strategies in Lebanon while acknowledging the country’s limited scope of regulation and legislation. Finally, the review concludes with proposed public health strategies and suggestions for future research, which can reduce the intake levels of salt and fructose levels and contribute to curbing the CVD epidemic in the country.

Novel non‐steroidal mineralocorticoid receptor antagonists in cardiorenal disease

Mineralocorticoid receptor antagonists (MRAs) are key agents in guideline-oriented drug therapy for cardiovascular diseases such as chronic heart failure with reduced ejection fraction and resistant hypertension. Currently available steroidal MRAs are efficacious in reducing morbidity and mortality; however, they can be associated with intolerable side effects including hyperkalaemia in everyday clinical practice. Recently, a new class of non-steroidal MRAs (including esaxerenone, AZD9977, apararenone, KBP-5074 and finerenone) have been developed with an improved benefit-risk profile and a novel indication for finerenone for diabetic kidney disease. To better understand the non-steroidal MRAs, this review provides information on the molecular pharmacology as well as relevant current preclinical and clinical data on cardiorenal outcomes. A comparative review of all compounds in the class is discussed with regard to clinical efficacy and safety as well as a perspective outlining their future use in clinical practice. LINKED ARTICLES: This article is part of a themed issue on Emerging Fields for Therapeutic Targeting of the Aldosterone-Mineralocorticoid Receptor Signaling Pathway. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.13/issuetoc.

The mineralocorticoid receptor in chronic kidney disease.

Chronic kidney disease (CKD) is a major public health concern, affecting approximately 10% of the population worldwide. CKD of glomerular or tubular origin leads to the activation of stress mechanisms, including the renin-angiotensin-aldosterone system and mineralocorticoid receptor (MR) activation. Over the last two decades, blockade of the MR has arisen as a potential therapeutic approach against various forms of kidney disease. In this review, we summarize the experimental studies that have shown a protective effect of MR antagonists (MRAs) in nondiabetic and diabetic CKD animal models. Moreover, we review the main clinical trials that have shown the clinical application of MRAs to reduce albuminuria and, importantly, to slow CKD progression. Recent evidence from the FIDELIO trial showed that the MRA finerenone can reduce hard kidney outcomes when added to the standard of care in CKD associated with type 2 diabetes. Finally, we discuss the effects of MRAs relative to those of SGLT2 inhibitors, as well as the potential benefit of combination therapy to maximize organ protection. LINKED ARTICLES: This article is part of a themed issue on Emerging Fields for Therapeutic Targeting of the Aldosterone-Mineralocorticoid Receptor Signaling Pathway. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.13/issuetoc.

The mineralocorticoid receptor in skin disease.

The mineralocorticoid receptor (MR or NR3C2) is expressed in all types of cells from the different skin compartments. The binding and activation by glucocorticoids has a higher affinity than that on the closely related glucocorticoid receptor (GR or NR3C1). As both corticosteroid receptors are co-express in the skin and considering the therapeutic relevance of glucocorticoids to combat skin inflammatory diseases, it was proposed that several of the major side effects of topical glucocorticoids, such as skin atrophy and delayed wound healing, were due to unintended activation of the MR. Indeed, cutaneous MR blockade using genetic and pharmacological approaches in mice and human reduced corticosteroid-associated skin atrophy in conditions of endogenous and pharmacological glucocorticoid excess. Although data support the safety of topical MR antagonists combined with glucocorticoid, it is crucial to address the efficacy of treatment in skin inflammatory conditions and its impact on the overall metabolism. LINKED ARTICLES: This article is part of a themed issue on Emerging Fields for Therapeutic Targeting of the Aldosterone-Mineralocorticoid Receptor Signaling Pathway. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.13/issuetoc.

Approaches towards tissue-selective pharmacology of the mineralocorticoid receptor.

Mineralocorticoid receptor antagonists (MRAs) are highly effective therapies for cardiovascular and renal disease. However, the widespread clinical use of currently available MRAs in cardiorenal medicine is hampered by an increased risk of hyperkalaemia. The mineralocorticoid receptor (MR) is a nuclear receptor responsible for fluid and electrolyte homeostasis in epithelial tissues, whereas pathophysiological MR activation in nonepithelial tissues leads to undesirable pro-inflammatory and profibrotic effects. Therefore, new strategies that selectively target the deleterious effects of the MR but spare its physiological function are needed. In this review, we discuss recent pharmacological developments starting from novel non-steroidal MRAs, such as finerenone or esaxerenone, that are now entering clinical use, to concepts arising from the current knowledge of the MR signalling pathway, aiming at receptor-coregulator interaction, epigenetics or downstream effectors of the MR. LINKED ARTICLES: This article is part of a themed issue on Emerging Fields for Therapeutic Targeting of the Aldosterone-Mineralocorticoid Receptor Signaling Pathway. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.13/issuetoc.

Structural and molecular determinants of mineralocorticoid receptor signalling

During the past decades, the mineralocorticoid receptor (MR) has evolved from a much-overlooked member of the steroid hormone receptor family to an important player, not only in volume and electrolyte homeostasis but also in pathological changes occurring in an increasing number of tissues, especially the renal and cardiovascular systems. Simultaneously, a wealth of information about the structure, interaction partners and chromatin requirements for genomic signalling of steroid hormone receptors became available. However, much of the information for the MR has been deduced from studies of other family members and there is still a lack of knowledge about MR-specific features in ligand binding, chromatin remodelling, co-factor interactions and general MR specificity-conferring mechanisms that can completely explain the differences in pathophysiological function between MR and its closest relative, the glucocorticoid receptor. This review aims to give an overview of the current knowledge of MR structure, signalling and co-factors modulating its activity. LINKED ARTICLES: This article is part of a themed issue on Emerging Fields for Therapeutic Targeting of the Aldosterone-Mineralocorticoid Receptor Signaling Pathway. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.13/issuetoc.

Mineralocorticoid receptor in cardiovascular diseases-Clinical trials and mechanistic insights.

Aldosterone binds to the mineralocorticoid receptor (NR3C2), a transcription factor of the nuclear receptor family, present in the kidney and in various other non-epithelial cells including the heart and the vasculature. Indeed, extra-renal pathophysiological effects of this hormone have been characterized, extending its actions to the cardiovascular system. A growing body of clinical and pre-clinical evidence suggests that mineralocorticoid receptor overactivation plays an important pathophysiological role in cardiovascular remodelling by promoting cardiac hypertrophy, fibrosis, arterial stiffness and in inflammation and oxidative stress. The following review article outlines the role of mineralocorticoid receptor in cardiovascular disease with a focus on myocardial remodelling and heart failure (HF) including clinical trials as well as cellular and animal studies. LINKED ARTICLES: This article is part of a themed issue on Emerging Fields for Therapeutic Targeting of the Aldosterone-Mineralocorticoid Receptor Signaling Pathway. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.13/issuetoc.

Mineralocorticoid Dysfunction during Critical Illness: A Review of the Evidence.

The recent demonstration of the significant reduction in mortality in patients with septic shock treated with adjunctive glucocorticoids combined with fludrocortisone and the effectiveness of angiotensin II in treating vasodilatory shock have renewed interest in the role of the mineralocorticoid axis in critical illness. Glucocorticoids have variable interactions at the mineralocorticoid receptor. Similarly, mineralocorticoid receptor-aldosterone interactions differ from mineralocorticoid receptor-glucocorticoid interactions and predicate receptor-ligand interactions that differ with respect to cellular effects. Hyperreninemic hypoaldosteronism or selective hypoaldosteronism, an impaired adrenal response to increasing renin levels, occurs in a subgroup of hemodynamically unstable critically ill patients. The suggestion is that there is a defect at the level of the adrenal zona glomerulosa associated with a high mortality rate that may represent an adaptive response aimed at increasing cortisol levels. Furthermore, cross-talk exists between angiotensin II and aldosterone, which needs to be considered when employing therapeutic strategies.

SUN-LB93 Mineralocorticoid Receptor Mediates Sex-Dependent Anticontractile Effect of Perivascular Adipose Tissue in Obese Mice

Obesity, a condition of excessive fat mass and subclinical inflammation, reached epidemic proportions with higher prevalence in women compared to men worldwide. Expansion of the perivascular adipose tissue (PVAT) is observed in obesity and clinical studies indicate a positive correlation between PVAT amount and body mass index. PVAT, a fat depot surrounding most of the vessels, modulates vascular function by releasing PVAT-derived factors such as adipokines that exert anticontractile effect in health individuals. Despite sexual dimorphism on PVAT morphology, it is still unknown whether or not there is sex differences in the PVAT modulating vascular function in the setting of obesity. Aldosterone-mineralocorticoid receptor (MR) signaling pathway has been demonstrated to be adipogenic and proinflammatory in classical fat depots and treatment with MR antagonists (A) might reverse vascular dysfunction and remodeling in obese models, especially in female sex. Therefore, we aimed to evaluate the anticontractile effect of PVAT in male and female obese mice and hypothesized that MR signaling would be involved in possible sex differences in PVAT dysfunction in obesity. Male and female C57Bl6/J mice were fed a chow or a high-fat diet (HFD, 60% energy from fat) for 20 weeks. At the last 4 weeks of HFD, female and male mice were treated with the MRA spironolactone (Spi, 100 mg/kg/day). HFD feeding significantly increased body weight and visceral adipose tissue, which was not modified by Spi treatment in both sexes. Resistance mesenteric arteries were isolated with or without PVAT and mounted in a wire myograph to evaluate vascular contractile responses. Lean male and female mice PVAT had an anticontractile effect in the response to phenylephrine that was greater in females than males. The anticontractile effect of PVAT was significantly impaired in obese females but not modified in males. HFD-induced dysfunctional PVAT was prevented by Spi treatment in females. Next, we evaluated the protein expression of aldosterone-synthase CYP11B2, serum and glucocorticoid-regulated kinase 1 (SGK1), and epithelial sodium channel subunits (ENaCs) in isolated mesenteric PVAT of lean and obese male and female mice. There was an increased expression of CYP11B2, SGK1 and ENaCs only in obese female PVAT. Protein expression of adiponectin, a major PVAT-released adipokine was also increased in female mesenteric PVAT. In conclusion, the findings suggest sexual dimorphism in PVAT function in health and in obesity. Although anticontractile role of PVAT was exacerbated in lean female mice, female sex was more susceptible to develop PVAT dysfunction in the setting of obesity which was prevented by MR blockade. HFD-induced PVAT dysfunction in females was associated with increased expression of SGK1 and ENaCs. Therefore, data suggest MR activation as a mechanism mediating sex differences in PVAT dysfunction.FAPESP, CAPES.

MiRNA-181a is a novel regulator of aldosterone-mineralocorticoid receptor-mediated cardiac remodelling.

The aldosterone-mineralocorticoid receptor (Aldo-MR) pathway is activated during cardiac stress, such as hypertension, myocardial infarction (MI), and heart failure. The importance of Aldo and MR in the pathogenesis of cardiac diseases is well established; however, the regulatory mechanisms behind Aldo/MR-induced cardiac remodelling remain uncertain. We here investigated potential miRNA-mediated regulation of the Aldo-MR pathway to improve mechanistic understanding. High-throughput screening of 2,555 miRNAs using an MR responsive stable cardiomyocyte cell line (MMTV-GFP-HL-1) identified miR-181a as a potential regulator of Aldo-MR pathway. MiR-181a was found to downregulate the expression of Ngal (lipocalin-2), a well-established downstream effector molecule of Aldo-MR. In addition, Aldo-induced cellular hypertrophy decreased significantly upon miR-181a overexpression. Genetic miR-181 knockout in murine MI model led to deteriorated cardiac function, cardiac remodelling, and activation of Aldo-MR pathway while AAV9-mediated miR-181a overexpression improved cardiac function and deactivated Aldo-MR pathway proving a cardio-protective role of miR-181a. Global RNA sequencing of cells under Aldo treatment with/without miR-181a overexpression identified potential miR-181a targets functionally contributing to Aldo-MR pathway. Adamts1, a direct target of miR-181a, was found to be downregulated with miR-181a overexpression and upregulated with inhibition. Similar to miR-181a overexpression, siRNA-mediated inhibition of Adamts1 inhibited Aldo-MR pathway. We here show that miR-181a is a novel regulator of the Aldo-MR pathway regulating the levels of Ngal via direct targeting of Adamts1. This new insight establishes miR-181a as a factor of immense value participating in downstream networks of Aldo-MR pathway. Our in vivo studies further confirmed miR-181a as cardio-protective under MI stress. Thus, miR-181a's involvement in Aldo-MR-mediated cardiac remodelling confers it with tremendous potential to be developed further as a new therapeutic target.

Modulation of the renin-angiotensin-aldosterone system by steroid hormones during the oestrous cycle in mares.

In women and females of different species of laboratory animals, oestrogens stimulate the renin-angiotensin-aldosterone system (RAAS) by increasing tissue and circulating levels of angiotensinogen and renin during the preovulatory period. Progesterone and cortisol compete with aldosterone for mineralocorticoid receptors, which results in increased Na+ reabsorption during the postovulatory period. The purpose of the current research was to analyse the relationship of oestradiol-17β, progesterone and cortisol with RAAS in 23 mares during an oestrous cycle. During the preovulatory period, significant positive correlations of oestradiol-17β with renin and aldosterone concentrations and negative correlations of progesterone with renin and aldosterone concentrations were found. In contrast, during the postovulatory period, oestradiol-17β concentrations were positively correlated with angiotensin concentrations and progesterone was negatively correlated with this component of the RAAS. Cortisol concentrations were not correlated with the hormones of the RAAS, neither before nor after ovulation. This research demonstrates that, as occurs in other species, changes in the RAAS during the periovulatory period in mares may be modulated by variations in the concentrations of steroid hormones.

Compromised regulation of the collecting duct ENaC activity in mice lacking AT1a receptor.

ENaC-mediated sodium reabsorption in the collecting duct (CD) is a critical determinant of urinary sodium excretion. Existing evidence suggest direct stimulatory actions of Angiotensin II (Ang II) on ENaC in the CD, independently of the aldosterone-mineralocorticoid receptor (MR) signaling. Deletion of the major renal AT1 receptor isoform, AT1a R, decreases blood pressure and reduces ENaC abundance despite elevated aldosterone levels. The mechanism of this insufficient compensation is not known. Here, we used patch clamp electrophysiology in freshly isolated split-opened CDs to investigate how AT1a R dysfunction compromises functional ENaC activity and its regulation by dietary salt intake. Ang II had no effect on ENaC activity in CDs from AT1a R -/- mice suggesting no complementary contribution of AT2 receptors. We next found that AT1a R deficient mice had lower ENaC activity when fed with low (<0.01% Na+ ) and regular (0.32% Na+ ) but not with high (∼2% Na+ ) salt diet, when compared to the respective values obtained in Wild type (WT) animals. Inhibition of AT1 R with losartan in wild-type animals reproduces the effects of genetic ablation of AT1a R on ENaC activity arguing against contribution of developmental factors. Interestingly, manipulation with aldosterone-MR signaling via deoxycosterone acetate (DOCA) and spironolactone had much reduced influence on ENaC activity upon AT1a R deletion. Consistently, AT1a R -/- mice have a markedly diminished MR abundance in cytosol. Overall, we conclude that AT1a R deficiency elicits a complex inhibitory effect on ENaC activity by attenuating ENaC Po and precluding adequate compensation via aldosterone cascade due to decreased MR availability.

Albuminuria is associated with an increased prostasin in urine while aldosterone has no direct effect on urine and kidney tissue abundance of prostasin.

The proteinase prostasin is a candidate mediator for aldosterone-driven proteolytic activation of the epithelial sodium channel (ENaC). It was hypothesized that the aldosterone-mineralocorticoid receptor (MR) pathway stimulates prostasin abundance in kidney and urine. Prostasin was measured in plasma and urine from type 2 diabetic patients with resistant hypertension (n=112) randomized to spironolactone/placebo in a clinical trial. Prostasin protein level was assessed by immunoblotting in (1) human and rat urines with/without nephrotic syndrome, (2) human nephrectomy tissue, (3) urine and kidney from aldosterone synthase-deficient (AS-/-) mice and ANGII- and aldosterone-infused mice, and in (4) kidney from adrenalectomized rats. Serum aldosterone concentration related to prostasin concentration in urine but not in plasma. Plasma prostasin concentration increased significantly after spironolactone compared to control. Urinary prostasin and albumin related directly and were reduced by spironolactone. In patients with nephrotic syndrome, urinary prostasin protein was elevated compared to controls. In rat nephrosis, proteinuria coincided with increased urinary prostasin, unchanged kidney tissue prostasin, and decreased plasma prostasin while plasma aldosterone was suppressed. Prostasin protein abundance in human nephrectomy tissue was similar across gender and ANGII inhibition regimens. Prostasin urine abundance was not different in AS-/- and aldosterone-infused mice. Prostasin kidney level was not different from control in adrenalectomized rats and AS-/- mice. We found no evidence for a direct relationship between mineralocorticoid receptor signaling and kidney and urine prostasin abundance. The reduction of urinary prostasin in spironolactone-treated patients is most likely the result of an improved glomerular filtration barrier function and generally reduced proteinuria.

Abstract 096: Leptin and High Salt Diet Induce Greater Increases in Blood Pressure in Female than Male Mice

Recent studies by our group demonstrated that leptin is a direct regulator of aldosterone secretion and increases blood pressure via sex-specific mechanisms involving leptin-mediated activation of the aldosterone-mineralocorticoid receptor signaling pathway in females and sympatho-activation in males. Although it is well accepted that females secrete more leptin and aldosterone than males, it is unknown whether leptin infusion raises blood pressure similarly in male and female mice and whether higher aldosterone levels sensitize females to salt-induced hypertension. We hypothesized that female mice would be more sensitive to leptin than males and also have a potentiated blood pressure rise in response to high salt diet compared to males. Male and female Balb/C mice were implanted with radiotelemeters for continuous measurement of mean arterial pressure (MAP) at 10 weeks of age. MAP was measured for seven days prior to feeding with a high-salt diet (HS, 4%NaCl) for seven days. Following a recovery period, animals were then implanted with osmotic minipumps containing leptin (0.9mg/kg/day) recorded for seven days. Baseline MAP was similar between males and females (101.3±2.9 vs 99.3±3.7 mmHg, n=4 and 5, respectively), however, HS diet resulted in a greater MAP increase in females (15.0±2.6 mmHg) compared to males (3.1±4.5 mmHg, P&lt;0.05). MAP with leptin treatment was increased with leptin in females moreso than in males, however, this did not reach significance (6.8±5.8 vs 1.8±5.9 mmHg, respectively). This potential sex difference in blood pressure responses to leptin was not associated with changes in body weight (0.07±0.44 vs -0.22±0.2 g, respectively) nor changes in blood glucose (-19.67±15.06 vs -15.4±11.4 mg/dl, respectively) in males and females in response to leptin. In summary, female mice are more sensitive to HS diet-induced blood pressure increases than males. Females may be more sensitive to leptin-mediated blood pressure increases than males. Further investigation is needed to determine whether these sex differences in blood pressure responses to HS diet and leptin are mediated by aldosterone or other mechanisms.

Context-dependent mechanisms modulating aldosterone signaling in the kidney.

The aldosterone-mineralocorticoid receptor (MR) system serves as the major regulator of fluid homeostasis, and is an important drug target for the treatment of hypertension, heart failure, and chronic kidney disease. While the ligand aldosterone plays a central role in facilitating MR activity, recent studies have revealed that MR signaling is modulated through distinct mechanisms at the levels of the receptor and the downstream targets. Notably, phosphorylation of the ligand-binding domain in MR regulates the ability of the receptor to bind to ligand in renal intercalated cells, providing an additional layer of regulation that allows the cell-selective control of MR signaling. These mechanisms are involved in the context-dependent effects of aldosterone in the distal nephron. In this article, the recent progress in the understanding of mechanisms regulating the action of aldosterone is discussed, focusing on the connecting tubules and collecting duct in the kidney.