Deletion Of Mineralocorticoid Receptor Research Articles

OR28-1 Role of Mineralocorticoid Receptor in Metabolic Syndrome

Rates of obesity and metabolic syndrome (MetS) are at epidemic levels, leading to a rise of individuals at higher risk of developing diabetes and heart disease. Increased visceral adiposity and hyperglycemia are two shared features of MetS and excess glucocorticoids (GCs). GCs are hormones—acting primarily via the glucocorticoid receptor (GR)—commonly prescribed for inflammatory disorders, yet their use is limited due to many detrimental metabolic side effects. Additionally, GCs are used to facilitate adipogenesis in vitro, though our lab has recently shown that GR is not absolutely required for adipogenesis in vitro or in vivo. In addition to GR, GCs also bind the mineralocorticoid receptor (MR), but there are many conflicting studies as to the exact role of MR in adipogenesis. Though metabolic studies using full body MR-/- mice are impractical since these mice die within 10 days of birth due to salt wasting, we do show that MR-/- mice have white and brown adipose depots that are similar to wild-type littermates at 5 postnatal. To define the role of MR in metabolic syndrome in vivo, we created mice with an adipose-specific deletion of MR (FMRKO) by crossing MRflox/flox mice to adiponectin-cre mice. We first induced MetS by treating FMRKO and MRflox/flox control mice with corticosterone (100µg/mL) via drinking water for 4 weeks. After treatment, fat mass was increased in both FMRKO (from 3.4±0.3 to 9.3±0.7g, p<0.0001) and control mice (from 3.5±0.4 to 9.6±1.6g, p<0.0001). Additionally, fasting glucose was elevated in FMRKO (from 128±18 to 235±89mg/dL, p=0.003) and control mice (from 112±13 to 219±39mg/dL, p=0.023); however, there was no difference between groups for fat mass or blood glucose. Separately, we fed mice a high-fat diet (HFD) for 16 weeks. We saw that FMRKO mice had reduced body weight (39.3±4.2 vs 45.2±3.3g, p=0.002), primarily due to a decrease in fat mass (14.8±2.4 vs 19.2±2.3g, p<0.001) relative to control mice. While there was no difference in glucose tolerance between groups, FMRKO mice had significantly decreased plasma insulin (14.5±5.9 vs 6.4±3.3ng/mL, p=0.001). Impressively, FMRKO mice had increased oxygen consumption and energy expenditure compared to control mice. Furthermore, FMRKO had reduced expression of genes involved in adipogenesis and lipogenesis in adipose tissue, relative to control mice. Collectively, these studies provide new insight to the potential value of MR as a therapeutic target in treating conditions associated with MetS. Unless otherwise noted, all abstracts presented at ENDO are embargoed until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. s presented at a news conference are embargoed until the date and time of the news conference. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.

Prevention of Obesity‐Associated Coronary and Cardiac Diastolic Dysfunction by Deletion of Smooth Muscle Cell Mineralocorticoid Receptor in Females

Coronary microvascular dysfunction is independently predictive of cardiac diastolic dysfunction and both conditions are common in obesity and associated metabolic syndrome. Recent work by us and others indicates that mineralocorticoid receptor (MR) antagonism treats obesity‐associated coronary and cardiac diastolic dysfunction. Vascular cell‐specific MR involvement in these obesity‐related defects remains unclear. Thus, we evaluated the hypothesis that deletion of smooth muscle cell (SMC) MR would prevent obesity‐associated coronary and cardiac diastolic dysfunction in females. Female wild‐type (WT) and SMC MR knockout (KO) mice were fed a standard chow or western diet (WD) to induce obesity for 16 weeks. WD feeding induced obesity, hyperinsulinemia, hypercholesterolemia, and visceral adipose inflammation in both WT and SMC MR KO mice. Assessment of coronary vascular function via wire myography revealed WD‐induced impairment of endothelium‐dependent vasodilation and enhanced vasoconstriction to the thromboxane A2 analog U46619 in WT but not SMC MR KO mice. Vasodilation to the nitric‐oxide donor sodium nitroprusside was unchanged by WD feeding. Global quantitative proteomics of aortas from each group revealed a number of differentially expressed proteins following WD feeding including upregulation of the oxidative stress‐related small GTPase Rac‐1 in WT but not SMC MR KO aortas. Accordingly, pretreatment of coronary arteries with the superoxide dismutase mimetic Tempol restored endothelium‐dependent vasodilation in WD‐fed WT mice with no effect in SMC MR KO vessels. Furthermore, WD feeding induced cardiac diastolic dysfunction assessed by echocardiography (i.e., increased E/E′, reduced E′/A′, increased diastolic stiffness). Coincident with prevention of WD‐induced coronary dysfunction, SMC MR deletion prevented WD‐induced cardiac diastolic dysfunction. Importantly, this cardioprotective effect of SMC MR deletion occurred independent of changes in left ventricular hypertrophy, blood pressure, aortic stiffening, and proteinuria. Taken together, our data demonstrate a central role of SMC MR signaling underlying WD‐induced coronary and cardiac diastolic dysfunction in females. Importantly, this study adds to an emerging body of evidence suggesting a vascular origin of cardiac dysfunction in obesity.Support or Funding InformationSupported by NIH (HL136386 to SBB, HL119290 to IZJ) and the Department of Veterans Affairs BLR&amp;D (CDA‐2 IK2 BX002030). BC is supported by Department of Veterans Affairs (IK6 BX004016 and I01 BX002255).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Mineralocorticoid receptor antagonism limits experimental choroidal neovascularization and structural changes associated with neovascular age-related macular degeneration

Choroidal neovascularization (CNV) is a major cause of visual impairment in patients suffering from wet age-related macular degeneration (AMD), particularly when refractory to intraocular anti-VEGF injections. Here we report that treatment with the oral mineralocorticoid receptor (MR) antagonist spironolactone reduces signs of CNV in patients refractory to anti-VEGF treatment. In animal models of wet AMD, pharmacological inhibition of the MR pathway or endothelial-specific deletion of MR inhibits CNV through VEGF-independent mechanisms, in part through upregulation of the extracellular matrix protein decorin. Intravitreal injections of spironolactone-loaded microspheres and systemic delivery lead to similar reductions in CNV. Together, our work suggests MR inhibition as a novel therapeutic option for wet AMD patients unresponsive to anti-VEGF drugs.

Endothelial cell mineralocorticoid receptors oppose VEGF-induced gene expression and angiogenesis.

Aldosterone is a key factor in adverse cardiovascular remodeling by acting on the mineralocorticoid receptor (MR) in different cell types. Endothelial MR activation mediates hypertrophy, inflammation and fibrosis. Cardiovascular remodeling is often accompanied by impaired angiogenesis, which is a risk factor for the development of heart failure. In this study, we evaluated the impact of MR in endothelial cells on angiogenesis. Deoxycorticosterone acetate (DOCA)-induced hypertension was associated with capillary rarefaction in the heart of WT mice but not of mice with cell type-specific MR deletion in endothelial cells. Consistently, endothelial MR deletion prevented the inhibitory effect of aldosterone on the capillarization of subcutaneously implanted silicon tubes and on capillary sprouting from aortic ring segments. We examined MR-dependent gene expression in cultured endothelial cells by RNA-seq and identified a cluster of differentially regulated genes related to angiogenesis. We found opposing effects on gene expression when comparing activation of the mineralocorticoid receptor in ECs to treatment with vascular endothelial growth factor (VEGF), a potent activator of angiogenesis. In conclusion, we demonstrate here that activation of endothelial cell MR impaired angiogenic capacity and lead to capillary rarefaction in a mouse model of MR-driven hypertension. MR activation opposed VEGF-induced gene expression leading to the dysregulation of angiogenesis-related gene networks in endothelial cells. Our findings underscore the pivotal role of endothelial cell MR in the pathophysiology of hypertension and related heart disease.

Macrophage Mineralocorticoid Receptor Is a Pleiotropic Modulator of Myocardial Infarct Healing.

Myocardial infarction (MI) is a major cause of death worldwide. Here, we identify the macrophage MR (mineralocorticoid receptor) as a crucial pathogenic player in cardiac wound repair after MI. Seven days after left coronary artery ligation, mice with myeloid cell-restricted MR deficiency compared with WT (wild type) controls displayed improved cardiac function and remodeling associated with enhanced infarct neovascularization and scar maturation. Gene expression profiling of heart-resident and infarct macrophages revealed that MR deletion drives macrophage differentiation in the ischemic microenvironment toward a phenotype outside the M1/M2 paradigm, with regulation of multiple interrelated factors controlling wound healing and tissue repair. Mechanistic and functional data suggest that inactivation of the macrophage MR promotes myocardial infarct healing through enhanced efferocytosis of neutrophils, the suppression of free radical formation, and the modulation of fibroblast activation state. Crucially, targeted delivery of MR antagonists to macrophages, with a single administration of RU28318 or eplerenone-containing liposomes at the onset of MI, improved the healing response and protected against cardiac remodeling and functional deterioration, offering an effective and unique therapeutic strategy for cardiac repair.

Impact of MR on mature adipocytes in high-fat/high-sucrose diet-induced obesity

Active glucocorticoid levels are elevated in the adipose tissue of obesity due to the enzyme 11 beta-hydroxysteroid dehydrogenase type 1. Glucocorticoids can bind and activate both glucocorticoid receptor (GR) and mineralocorticoid receptor (MR), and pharmacological blockades of MR prevent high-fat diet-induced obesity and glucose intolerance. To determine the significance of MR in adipocytes, we generated adipocyte-specific MR-knockout mice (AdipoMR-KO) and fed them high-fat/high-sucrose diet. We found that adipocyte-specific deletion of MR did not affect the body weight, fat weight, glucose tolerance or insulin sensitivity. While liver weight was slightly reduced in AdipoMR-KO, there were no significant differences in the mRNA expression levels of genes associated with lipogenesis, lipolysis, adipocytokines and oxidative stress in adipose tissues between the control and AdipoMR-KO mice. The results indicated that MR in mature adipocytes plays a minor role in the regulation of insulin resistance and inflammation in high-fat/high-sucrose diet-induced obese mice.

Abstract 096: Progesterone Upregulates Endothelial Mineralocorticoid Receptor Expression Which Predisposes Female Mice to Obesity-Induced Endothelial Dysfunction

Compelling evidence indicates a higher efficacy of mineralocorticoid receptor (MR) blockade for the treatment of cardiovascular disease in females with obesity and diabetes than in males, however, the origin of this sex-specific effect is unknown. We have shown that leptin induces endothelial dysfunction in obese female mice via aldosterone-dependent activation of MR and that only female mice develop endothelial dysfunction (vasorelaxation to acetylcholine) in response to aldosterone ex vivo . Therefore, we hypothesized that females express higher endothelial MR (ECMR) expression than males which predisposes females to obesity-associated endothelial dysfunction. RT-PCR analysis in isolated aortic endothelial cells of Balb/C mice revealed a higher NR3C2 (MR gene) expression in females compared to males (2.9±0.5-fold from male, P&lt;0.05), however, no such difference was observed in non-endothelial cells. Similarly, human adipose tissue endothelial cells exhibited higher ECMR mRNA expression than males (2.1±0.1 fold from male). Female sex-hormone suppression (ovariectomy) decreased ECMR expression in female mice (-0.8±0.2-fold from sham), which was restored by progesterone supplementation (-0.1±0.1-fold from sham). NR3C2 mRNA gradually increased with progesterone in diestrous (1.6±0.1-fold from estrous) phase and increased further in pregnancy day 16 (9.2±0.2-fold from estrous). Furthermore, progesterone dose-dependently increased ECMR protein expression in human endothelial cells in vitro (P&lt;0.05). Increases in ECMR associated with higher progesterone levels in diestrus and pregnant females were associated with an increased sensitivity to leptin-induced endothelial dysfunction in mice. In parallel, while leptin induced endothelial dysfunction in intact ECMR female mice (P&lt;0.05), specific deletion of MR in endothelial cells protected female mice from leptin-induced endothelial dysfunction. These data indicate that progesterone drives the sex-difference in the levels of ECMR expression and predisposes female mice to leptin-induced endothelial dysfunction. In addition, these data provide a rational for the higher efficacy of MR blockade in obese and diabetic women suffering from cardiovascular disease.

Abstract 699: Endothelial Mineralocorticoid Receptor and Neutrophils Mediate Aldo plus Salt-Induced Abdominal Aortic Aneurysm

Background: We recently reported that administration of mice with Aldo or deoxycorticosterone acetate (DOCA) plus salt induces abdominal aortic aneurysm (AAA) and treatment of mice with mineralocorticoid receptor (MR) blockers abolished Aldo plus salt-induced AAA. However, the mechanism by which Aldo plus salt induces AAA is largely unknown. Methods: A tamoxifen inducible EC (EC)-specific MR knockout mouse model (iECMRKO) was developed. ECMRKO mice, and control mice were administered with Aldo or DOCA plus sat salt to induce AAA. C57BL/6 mice were injected with anti-mouse polymorphonuclear (PMN) leukocytes antibody to deplete neutrophils. The aortic internal and external diameter, the aortic dilation rate, and the incidence of AAA were determined. Results: Selective genetic deletion of MR from ECs, protects mice from Aldo or DOCA plus salt-induced AAA. EC-specific MR deletion had little effect on Aldo plus salt-induced sodium retention, hypertension, and renal fibrosis, but largely suppressed aortic elastin degradation, matrix metallopeptidase (MMP) 2 and MMP9 upregulation, macrophage and neutrophil infiltration. Surprisingly, neutrophil, but not macrophage, was observed in aorta from control mice, but not iECMRKO mice, indicating that neutrophils but not macrophages is involved in the early processes of Aldo plus salt-induced and endothelia MR-mediated AAA development. Treatment of C57BL/6 mice with of anti- PMN antibody selectively suppressed DOCA plus salt-induced circulating Ly6G-postive neutrophils, but not CD4-postive leukocytes, protected mice from DOCA plus salt-induced AAA. Aldo-induced endothelial adhesion molecule (E-selectin, P-selectin, ICAMP1, and VCAM-1) and proinflammatory cytokine (IL-6 and MCP-1) mRNA expressions were abolished in cultured MR-deficient ECs. Aldo plus salt-induced ICAM-1 but not VCAM-1 protein upregulation was abolished in aorta from ECMRKO mice. Conclusions: Our results demonstrate a significant role of endothelial MR, in Aldo plus salt-induced AAA. Moreover, our results also reveal a provocative mechanism by which ICAM-1, but not VCAM-1, and neutrophils, but not macrophages, mediates the early processes of Aldo plus salt-induced and endothelia MR-mediated AAA development.

Leptin‐Induced Endothelial Dysfunction is Mediated by Endothelial Mineralocorticoid Receptor Epithelial Sodium Channel Activation in Female Mice

Rising rates of hypertension are significantly associated with rising rates of obesity. While the mechanisms of obesity‐associated hypertension have been heavily investigated, these studies have overwhelmingly favored men and male rodents as research subjects. Therefore, the sex‐specific mechanisms of obesity‐associated hypertension require investigation. Our lab has previously shown that the adipocyte‐derived hormone leptin, whose levels are drastically increased in obesity, is required for hypertension and endothelial dysfunction in obese female mouse models, the development of which is dependent on leptin‐induced aldosterone secretion and subsequent mineralocorticoid receptor (MR) activation. The epithelial sodium channel alpha (ENaC), whose transcription is directly upregulated by MR activation, has also been implicated in endothelial dysfunction in female mice. We therefore sought to test the hypothesis that endothelial MR activation mediates leptin‐induced endothelial dysfunction via increased activation of ENaC. To test that endothelial MR activation, specifically, is required for leptin‐induced endothelial dysfunction we infused female endothelial cell‐specific MR knockout mice (ECMR KO) with leptin (0.9 mg/kg/day) via subcutaneous osmotic minipump. Wild‐type mice (WT) developed endothelial dysfunction, as assessed by vascular (aortic rings) relaxation to acetylcholine (10−9 M–10−5 M, nonlinear fit curve), in response to leptin infusion (P&lt;0.05, two‐way ANOVA, n=4–6). However, ECMR KO female mice infused with leptin were protected from endothelial dysfunction (n=6–7), indicating that endothelial MR activation mediates leptin‐induced endothelial dysfunction in female mice. In contrast, no effect of leptin nor endothelial MR deletion was observed on endothelial function in male WT and ECMR KO mice (n=2–5). To assess if MR‐mediated ENaC activation plays a role in leptin‐induced endothelial dysfunction, leptin‐infused female mice were treated with amiloride (ENaC antagonist, 100 ug/day in drinking water) which ablated endothelial dysfunction in female leptin‐infused mice (P&lt;0.05, two‐way ANOVA, n=4), indicating that leptin‐induced endothelial dysfunction requires ENaC activation. In addition, we sought to assess the potential for leptin to upregulate endothelial cell ENaC expression in female mice. Isolated endothelial cells, which were obtained from the aorta via CD31‐specific magnetic bead sorting, were extracted from female Agouti hyperleptinemic obese mice and RT‐PCR analysis for mRNA expression of ENaC demonstrated elevated ENaC expression in hyperleptinemic mice (10.8±0.5‐fold change from lean control female mice, n=2–3). These elevations in endothelial ENaC mRNA expression are associated with elevated plasma aldosterone in hyperleptinemic female mice, indicating that leptin‐induced aldosterone induces endothelial dysfunction via increased MR activation, which ultimately leads to elevated ENaC expression and activation. Therefore, MR‐stimulated ENaC upregulation may play a crucial role in the development of leptin‐mediated cardiovascular diseases in obese females.Support or Funding InformationThis work was supported by the following: NIH 1R01HL130301‐01, AHA 16IRG27770047, NIH 5F32HL136191‐0This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Smooth Muscle Cell-Mineralocorticoid Receptor as a Mediator of Cardiovascular Stiffness With Aging.

Stiffening of the vasculature with aging is a strong predictor of adverse cardiovascular events, independent of all other risk factors including blood pressure, yet no therapies target this process. MRs (mineralocorticoid receptors) in smooth muscle cells (SMCs) have been implicated in the regulation of vascular fibrosis but have not been explored in vascular aging. Comparing SMC-MR-deleted male mice to MR-intact littermates at 3, 12, and 18 months of age, we demonstrated that aging-associated vascular stiffening and fibrosis are mitigated by MR deletion in SMCs. Progression of cardiac stiffness and fibrosis and the decline in exercise capacity with aging were also mitigated by MR deletion in SMC. Vascular gene expression profiling analysis revealed that MR deletion in SMC is associated with recruitment of a distinct antifibrotic vascular gene expression program with aging. Moreover, long-term pharmacological inhibition of MR in aged mice prevented the progression of vascular fibrosis and stiffness and induced a similar antifibrotic vascular gene program. Finally, in a small trial in elderly male humans, short-term MR antagonism produced an antifibrotic signature of circulating biomarkers similar to that observed in the vasculature of SMC-MR-deleted mice. These findings suggest that SMC-MR contributes to vascular stiffening with aging and is a potential therapeutic target to prevent the progression of aging-associated vascular fibrosis and stiffness.

Endothelial Mineralocorticoid Receptor Mediates Parenchymal Arteriole and Posterior Cerebral Artery Remodeling During Angiotensin II-Induced Hypertension.

The brain is highly susceptible to injury caused by hypertension because the increased blood pressure causes artery remodeling that can limit cerebral perfusion. Mineralocorticoid receptor (MR) antagonism prevents hypertensive cerebral artery remodeling, but the vascular cell types involved have not been defined. In the periphery, the endothelial MR mediates hypertension-induced vascular injury, but cerebral and peripheral arteries are anatomically distinct; thus, these findings cannot be extrapolated to the brain. The parenchymal arterioles determine cerebrovascular resistance. Determining the effects of hypertension and MR signaling on these arterioles could lead to a better understanding of cerebral small vessel disease. We hypothesized that endothelial MR signaling mediates inward cerebral artery remodeling and reduced cerebral perfusion during angiotensin II (AngII) hypertension. The biomechanics of the parenchymal arterioles and posterior cerebral arteries were studied in male C57Bl/6 and endothelial cell-specific MR knockout mice and their appropriate controls using pressure myography. AngII increased plasma aldosterone and decreased cerebral perfusion in C57Bl/6 and MR-intact littermates. Endothelial cell MR deletion improved cerebral perfusion in AngII-treated mice. AngII hypertension resulted in inward hypotrophic remodeling; this was prevented by MR antagonism and endothelial MR deletion. Our studies suggest that endothelial cell MR mediates hypertensive remodeling in the cerebral microcirculation and large pial arteries. AngII-induced inward remodeling of cerebral arteries and arterioles was associated with a reduction in cerebral perfusion that could worsen the outcome of stroke or contribute to vascular dementia.

Chronic in vivo nitric oxide deficiency impairs cardiac functional recovery after ischemia in female (but not male) mice

Nitric oxide (NO) is an important regulator of cardiac function and plays a key role in ischemic cardioprotection. The role of chronic NO deficiency in coordinating ischemic vulnerability in female myocardium has not been established. The aim of this study was to determine the influence of chronic in vivo NO synthase inhibition in modulating ex vivo ischemia-reperfusion responses in female hearts (relative to males). Mice were subjected to l-NAME (l-NG-Nitroarginine-methyl-ester) treatment in vivo for 8weeks. Cardiac fibrotic, inflammatory and cardiomyocyte Ca2+ handling related gene expression changes were assessed. Hearts were Langendorff-perfused, subjected to 20min global ischemia with 45min reperfusion. In response to this moderate ex vivo ischemic insult, hearts derived from l-NAME treated female animals exhibited increased incidence of reperfusion arrhythmias, diastolic abnormality and reduced contractile recovery in reperfusion. This differential response was observed even though baseline performance of hearts from l-NAME treated animals was not different to vehicle controls, myocardial inflammatory and fibrotic indices were similar in males and females and the systolic blood pressure effect of l-NAME administration was equivalent in both sexes. Evaluation of a subgroup of mice with cardiomyocyte specific mineralocorticoid receptor deletion suggests involvement of this receptor in NO-deficiency mediated responses. To examine underlying pre-disposing mechanisms, expression of a panel of candidate genes encoding proteins involved in electromechanical homeostasis (particularly relevant to ischemic challenge) was evaluated in normoxic myocardial tissues from the l-NAME- and vehicle-treated animals. Analysis revealed that l-NAME treatment in females selectively regulated expression of genes related directly and indirectly to cardiomyocyte Ca2+ handling in a manner consistent with destabilization of Ca2+ homeostasis and arrhythmogenesis. Our investigation provides new insight into the role of sustained decrease in NO bioavailability in determining distinctive female cardiac vulnerability to ischemic challenge.

Benefit of Mineralocorticoid Receptor Antagonism in AKI: Role of Vascular Smooth Muscle Rac1.

AKI is a frequent complication in hospitalized patients. Unfortunately, there is no effective pharmacologic approach for treating or preventing AKI. In rodents, mineralocorticoid receptor (MR) antagonism prevents AKI induced by ischemia-reperfusion (IR). We investigated the specific role of vascular MR in mediating AKI induced by IR. We also assessed the protective effect of MR antagonism in IR-induced AKI in the Large White pig, a model of human AKI. In mice, MR deficiency in smooth muscle cells (SMCs) protected against kidney IR injury. MR blockade by the novel nonsteroidal MR antagonist, finerenone, or genetic deletion of MR in SMCs associated with weaker oxidative stress production. Moreover, ischemic kidneys had higher levels of Rac1-GTP, required for NADPH oxidase activation, than sham control kidneys, and genetic deletion of Rac1 in SMCs protected against AKI. Furthermore, genetic deletion of MR in SMCs blunted the production of Rac1-GTP after IR. Pharmacologic inhibition of MR also prevented AKI induced by IR in the Large White pig. Altogether, we show that MR antagonism, or deletion of the MR gene in SMCs, limited the renal injury induced by IR through effects on Rac1-mediated MR signaling. The benefits of MR antagonism in the pig provide a rational basis for future clinical trials assessing the benefits of this approach in patients with IR-mediated AKI.

0542 : Vascular smooth muscle mineralocorticoid receptor contributes to coronary and left ventricular dysfunction after myocardial infarction

Mineralocorticoid receptor (MR) antagonists slow down the progression of heart failure after myocardial infarction (MI), but the cell-specific role of MR in these benefits is unclear. In the present study, the role of MR expressed in vascular smooth muscle cells (VSMC) was investigated. Two months after coronary artery ligation causing MI, mice with VSMC-specific MR deletion (MI-MRSMKO) and mice treated with the MR antagonist finerenone (MIfine) had improved left ventricular (LV) compliance and elastance when compared to infarcted control mice (MI-CTL), as well as reduced interstitial fibrosis. Importantly, the coronary reserve assessed by magnetic resonance imaging was preserved (difference in myocardial perfusion before and after induction of vasodilatation, ml/mg/min: MI-CTL: 1.1±0.5, NS; MIMRSMKO: 4.6±1.6, P<0.05; MI-fine: 3.6±0.7, P<0.01). The endothelial function, tested on isolated septal coronary arteries by analyzing the acetylcholineinduced NO-dependent relaxation, was also improved by MR deletion in VSMC or by finerenone treatment (relaxation %: MI-CTL: 36±5, MIMRSMKO: 54±3 and MI-fine: 76±4; P<0.05). Such impairment of the coronary endothelial function upon MI involved an oxidative-stress that was reduced when MR was deleted in VSMC or by finerenone treatment. Moreover, short-term incubation of coronary arteries isolated from non-infarcted animals with low dose angiotensin-II (10-9mol/L) induced oxidative-stress and impaired acetylcholine-induced relaxation in CTL but neither in MRSMKO nor in mice pre-treated with finerenone. In conclusion, deletion of MR in VSMC improved LV dysfunction after MI, likely through maintenance of the coronary reserve and improvement of coronary endothelial function. MR blockage by finerenone had similar effects. The author hereby declares no conflict of interest

The mineralocorticoid receptor (MR) regulates ENaC but not NCC in mice with random MR deletion

The mineralocorticoid receptor (MR) and its ligand aldosterone increase renal sodium reabsorption via regulation of the epithelial Na+ channel (ENaC) and the Na‐K‐ATPase in the renal collecting system. Previous studies suggested that aldosterone also regulates the thiazide‐sensitive cotransporter in the renal distal convoluted tubule (DCT). However, whether aldosterone directly regulates NCC via MR, or indirectly through systemic alterations such as changed plasma potassium, remained controversial. We have now generated a mouse model carrying a targeted deletion of MR in ~16% of cells randomly scattered along the renal tubule (MRko mice). In this model, MR‐positive and MR‐negative cells can be studied next to each other in the same physiological context via immunofluorescence. To evaluate microscope images objectively, we further developed an ImageJ script allowing radial quantification of optical density, thus allowing comparison of apical staining intensities. Although newborn MRko mice need NaCl supplementation to thrive, adult MRko do not show any differences to wildtype littermates in terms of general physiology, mRNA and protein expression of renal ion transport proteins and urine concentrating capacity, under both normal and low salt diet. MR‐negative cells in the renal collecting system of MRko mice do not show any detectable alphaENaC expression, while gammaENaC is diffusely distributed over the cytoplasm. In MR‐positive cells, these ENaC subunits are targeted to the apical cell surface. Although dietary Na+ restriction increases NCC abundance and phosphorylation to a similar extent in control and MRko mice, no differences in NCC regulation were observed between MR‐negative and MR‐positive DCT cells. In conclusion, MR is crucial for ENaC regulation but dispensable for the maintenance of NCC expression and phosphorylation under control conditions and for NCC upregulation in response to dietary Na+ restriction.Support or Funding InformationThis work was supported by a collaborative project grant from the Zurich Center for Integrative Human Physiology (ZIHP), research funds from the Swiss National Center for Competence in Research “Kidney.CH” and by a project grant (310030_143929/1) from the Swiss National Science Foundation.

Mineralocorticoid Receptor Deficiency in Macrophages Inhibits Neointimal Hyperplasia and Suppresses Macrophage Inflammation Through SGK1-AP1/NF-κB Pathways.

Restenosis after percutaneous coronary intervention remains to be a serious medical problem. Although mineralocorticoid receptor (MR) has been implicated as a potential target for treating restenosis, the cellular and molecular mechanisms are largely unknown. This study aims to explore the functions of macrophage MR in neointimal hyperplasia and to delineate the molecular mechanisms. Myeloid MR knockout (MMRKO) mice and controls were subjected to femoral artery injury. MMRKO reduced intima area and intima/media ratio, Ki67- and BrdU-positive vascular smooth muscle cells, expression of proinflammatory molecules, and macrophage accumulation in injured arteries. MMRKO macrophages migrated less in culture. MMRKO decreased Ki67- and BrdU-positive macrophages in injured arteries. MMRKO macrophages were less Ki67-positive in culture. Conditioned media from MMRKO macrophages induced less migration, Ki67 positivity, and proinflammatory gene expression of vascular smooth muscle cells. After lipopolysaccharide treatment, MMRKO macrophages had decreased p-cFos and p-cJun compared with control macrophages, suggesting suppressed activation of activator protein-1 (AP1). Nuclear factor-κB (NF-κB) pathway was also inhibited by MMRKO, manifested by decreased p-IκB kinase-β and p-IκBα, increased IκBα expression, decreased nuclear translocation of p65 and p50, as welll as decreased phosphorylation and expression of p65. Finally, overexpression of serum-and-glucocorticoid-inducible-kinase-1 (SGK1) attenuated the effects of MR deficiency in macrophages. Selective deletion of MR in myeloid cells limits macrophage accumulation and vascular inflammation and, therefore, inhibits neointimal hyperplasia and vascular remodeling. Mechanistically, MR deficiency suppresses migration and proliferation of macrophages and leads to less vascular smooth muscle cell activation. At the molecular level, MR deficiency suppresses macrophage inflammatory response via SGK1-AP1/NF-κB pathways.

Vascular Smooth Muscle Mineralocorticoid Receptor Contributes to Coronary and Left Ventricular Dysfunction After Myocardial Infarction

Mineralocorticoid receptor (MR) antagonists slow down the progression of heart failure after myocardial infarction (MI), but the cell-specific role of MR in these benefits is unclear. In this study, the role of MR expressed in vascular smooth muscle cells (VSMCs) was investigated. Two months after coronary artery ligation causing MI, mice with VSMC-specific MR deletion (MI-MR(SMKO)) and mice treated with the MR antagonist finerenone (MI-fine) had improved left ventricular compliance and elastance when compared with infarcted control mice (MI-CTL), as well as reduced interstitial fibrosis. Importantly, the coronary reserve assessed by magnetic resonance imaging was preserved (difference in myocardial perfusion before and after induction of vasodilatation, mL mg(-1) min(-1): MI-CTL: 1.1 ± 0.5, nonsignificant; MI-MR(SMKO): 4.6 ± 1.6 [P<0.05]; MI-fine: 3.6 ± 0.7 [P<0.01]). The endothelial function, tested on isolated septal coronary arteries by analyzing the acetylcholine-induced nitric oxide-dependent relaxation, was also improved by MR deletion in VSMCs or by finerenone treatment (relaxation %: MI-CTL: 36 ± 5, MI-MR(SMKO): 54 ± 3, and MI-fine: 76 ± 4; P<0.05). Such impairment of the coronary endothelial function on MI involved an oxidative stress that was reduced when MR was deleted in VSMCs or by finerenone treatment. Moreover, short-term incubation of coronary arteries isolated from noninfarcted animals with low-dose angiotensin-II (10(-9) mol/L) induced oxidative stress and impaired acetylcholine-induced relaxation in CTL but neither in MR(SMKO) nor in mice pretreated with finerenone. In conclusion, deletion of MR in VSMCs improved left ventricular dysfunction after MI, likely through maintenance of the coronary reserve and improvement of coronary endothelial function. MR blockage by finerenone had similar effects.

The mineralocorticoid receptor (MR) regulates ENaC but not NCC in mice with random MR deletion.

Aldosterone binds to the mineralocorticoid receptor (MR) and increases renal Na(+) reabsorption via up-regulation of the epithelial Na(+) channel (ENaC) and the Na(+)-K(+)-ATPase in the collecting system (CS) and possibly also via the NaCl cotransporter (NCC) in the distal convoluted tubule (DCT). However, whether aldosterone directly regulates NCC via MR or indirectly through systemic alterations remains controversial. We used mice with deletion of MR in ∼20% of renal tubule cells (MR/X mice), in which MR-positive (MR(wt)) and -negative (MR(ko)) cells can be studied side-by-side in the same physiological context. Adult MR/X mice showed similar mRNA and protein levels of renal ion transport proteins to control mice. In MR/X mice, no differences in NCC abundance and phosphorylation was seen between MR(wt) and MR(ko) cells and dietary Na(+) restriction up-regulated NCC to similar extent in both groups of cells. In contrast, MR(ko) cells in the CS did not show any detectable alpha-ENaC abundance or apical targeting of ENaC neither on control diet nor in response to dietary Na(+) restriction. Furthermore, Na(+)-K(+)-ATPase expression was unaffected in MR(ko) cells of the DCT, while it was lost in MR(ko) cells of the CS. In conclusion, MR is crucial for ENaC and Na(+)-K(+)-ATPase regulation in the CS, but is dispensable for NCC and Na(+)-K(+)-ATPase regulation in the DCT.

Adult nephron-specific MR-deficient mice develop a severe renal PHA-1 phenotype.

Aldosterone is the main mineralocorticoid hormone controlling sodium balance, fluid homeostasis, and blood pressure by regulating sodium reabsorption in the aldosterone-sensitive distal nephron (ASDN). Germline loss-of-function mutations of the mineralocorticoid receptor (MR) in humans and in mice lead to the "renal" form of type 1 pseudohypoaldosteronism (PHA-1), a case of aldosterone resistance characterized by salt wasting, dehydration, failure to thrive, hyperkalemia, and metabolic acidosis. To investigate the importance of MR in adult epithelial cells, we generated nephron-specific MR knockout mice (MR(Pax8/LC1)) using a doxycycline-inducible system. Under standard diet, MR(Pax8/LC1) mice exhibit inability to gain weight and significant weight loss compared to control mice. Interestingly, despite failure to thrive, MR(Pax8/LC1) mice survive but develop a severe PHA-1 phenotype with higher urinary Na(+) levels, decreased plasma Na(+), hyperkalemia, and higher levels of plasma aldosterone. This phenotype further worsens and becomes lethal under a sodium-deficient diet. Na(+)/Cl(-) co-transporter (NCC) protein expression and its phosphorylated form are downregulated in the MR(Pax8/LC1) knockouts, as well as the αENaC protein expression level, whereas the expression of glucocorticoid receptor (GR) is increased. A diet rich in Na(+) and low in K(+) does not restore plasma aldosterone to control levels but is sufficient to restore body weight, plasma, and urinary electrolytes. In conclusion, MR deletion along the nephron fully recapitulates the features of severe human PHA-1. ENaC protein expression is dependent on MR activity. Suppression of NCC under hyperkalemia predominates in a hypovolemic state.

Deletion of mineralocorticoid receptors in smooth muscle cells blunts renal vascular resistance following acute cyclosporine administration

Calcineurin inhibitors such as cyclosporine A (CsA) are still commonly used after renal transplantation, despite CsA--induced nephrotoxicity (CIN), which is partly related to vasoactive mechanisms. The mineralocorticoid receptor (MR) is now recognized as a key player in the control of vascular tone, and both endothelial cell- and vascular smooth muscle cell (SMC)-MR modulate the vasoactive responses to vasodilators and vasoconstrictors. Here we tested whether vascular MR is involved in renal hemodynamic changes induced by CsA. The relative contribution of vascular MR in acute CsA treatment was evaluated using mouse models with targeted deletion of MR in endothelial cell or SMC. Results indicate that MR expressed in SMC, but not in endothelium, contributes to the increase of plasma urea and creatinine, the appearance of isometric tubular vacuolization, and overexpression of a kidney injury biomarker (neutrophil gelatinase--associated lipocalin) after CsA treatment. Inactivation of MR in SMC blunted CsA--induced phosphorylation of contractile proteins. Finally, the in vivo increase of renal vascular resistance induced by CsA was blunted when MR was deleted from SMC cells, and this was associated with decreased L-type Ca2D channel activity. Thus, our study provides new insights into the role of vascular MR in renal hemodynamics during acute CIN, and provides rationale for clinical studies of MR antagonism to manage the side effects of calcineurin inhibitors.