Mineralocorticoid Receptor Signaling Research Articles

Cell-type specific effects of mineralocorticoid receptor gene expression suggest intercellular communication regulating fibrosis in skeletal muscle disease.

Introduction: Duchenne muscular dystrophy (DMD) is a fatal striated muscle degenerative disease. DMD is caused by loss of dystrophin protein, which results in sarcolemmal instability and cycles of myofiber degeneration and regeneration. Pathology is exacerbated by overactivation of infiltrating immune cells and fibroblasts, which leads to chronic inflammation and fibrosis. Mineralocorticoid receptors (MR), a type of nuclear steroid hormone receptors, are potential therapeutic targets for DMD. MR antagonists show clinical efficacy on DMD cardiomyopathy and preclinical efficacy on skeletal muscle in DMD models. Methods: We have previously generated myofiber and myeloid MR knockout mouse models to dissect cell-specific functions of MR within dystrophic muscles. Here, we compared skeletal muscle gene expression from both knockouts to further define cell-type specific signaling downstream from MR. Results: Myeloid MR knockout increased proinflammatory and profibrotic signaling, including numerous myofibroblast signature genes. Tenascin C was the most highly upregulated fibrotic gene in myeloid MR-knockout skeletal muscle and is a component of fibrosis in dystrophic skeletal muscle. Surprisingly, lysyl oxidase (Lox), canonically a collagen crosslinker, was increased in both MR knockouts, but did not localize to fibrotic regions of skeletal muscle. Lox localized within myofibers, including only a region of quadriceps muscles. Lysyl oxidase like 1 (Loxl1), another Lox family member, was increased only in myeloid MR knockout muscle and localized specifically to fibrotic regions. Discussion: This study suggests that MR signaling in the dystrophic muscle microenvironment involves communication between contributing cell types and modulates inflammatory and fibrotic pathways in muscle disease.

Independent Link Between Use of Mineralocorticoid Receptor Antagonists and Muscle Wasting in Heart Failure Patients Not Receiving Renin-Angiotensin System Inhibitors.

The renin-angiotensin system (RAS) activation is a proposed mechanism of muscle wasting (MW i.e., reduction in muscle mass). Although we reported that RAS inhibitors (RASIs) were associated with lower prevalence of MW in heart failure (HF) patients, the relationship between mineralocorticoid receptor (MR) signaling and MW has not been analyzed.Methods and Results: We analyzed data from 320 consecutive Japanese HF patients who underwent dual-energy X-ray absorptiometry scanning for assessment of appendicular skeletal muscle mass index (ASMI). In multiple linear regression analyses, plasma renin activity (PRA) was negatively correlated with ASMI in patients not receiving RASIs, indicating an untoward role of the RAS in MW. Results of analysis of covariance in which risk factors of MW served as covariates showed that use of MR antagonists (MRAs) was associated with lower ASMI and higher PRA in the non-RASIs group. The close relationship between use of MRAs and lower ASMI or higher PRA in the non-RASIs group was confirmed in analyses in which the differences in baseline characteristics between users and non-users of MRAs were minimized by using an inverse probability of treatment weighting. Increased PRA by MR inhibition without concurrent RAS inhibition, possibly contributing to upregulation of angiotensin II signaling, may be associated with reduction in muscle mass.

OR22-03 Enhanced Endothelial Mineralocorticoid Receptor Signaling Mediates Diet - Induced Soleus Fat Infiltration And Insulin Resistance

Abstract Disclosure: C. Homan: None. J. Habibi: None. D. Chen: None. A. Whaley-Connell: None. J.R. Sowers: None. G. Jia: None. Skeletal muscle is an important organ in the storage and release of lipids in response to physiological changes in free fatty acid (FFA) supply and demand. Once fat tissue mass expansion exceeds its blood supply excess lipids are stored ectopically as small lipid droplets in non-adipose tissues such as skeletal muscle. Recently, our data found that mineralocorticoid receptors (MRs) mediate Western diet (WD)-induced lipid infiltration of skeletal muscle and insulin resistance. Related to this, MRs, the principal receptors for the hormone aldosterone in the kidney, also exist in vascular cells, including endothelial cells (ECs). Moreover, enhanced MR signaling in ECs (ECMR) induces arterial stiffening and impairs microcirculation. However, our understanding of the precise mechanisms by which enhanced ECMR activation promotes skeletal muscle insulin resistance remains unclear. In this study we investigated the roles of ECMR in soleus lipid accumulation and corresponding insulin resistance in diet-induced obesity. Six-week-old ECMR wild type (ECMR+/+) and knockout (ECMR-/-) mice were fed either a mouse chow diet or WD for 16 weeks. 16 weeks of WD induced increases in glucose intolerance, fasting plasma insulin levels, HOMA-IR and insulin resistance index were found to be blunted in ECMR-/- mice. ECMR-/- prevented WD-induced increase in soleus FFA levels without changing serum FFA levels. Meanwhile, WD also increased soleus intramyocellular lipid content, plasma EC derived exosomal CD36 and soleus CD36 protein levels. These abnormalities were related to reduced soleus insulin metabolic signaling in PI3K/Akt pathways, as these pathways were blunted in ECMR-/- mice. These findings indicate that EC specific MR activation contributes to diet-induced increases in CD36 expression, soleus fat infiltration, as well as systemic and skeletal muscle insulin resistance. Presentation: Saturday, June 17, 2023

Aldosterone Antagonism Is More Effective at Reducing Blood Pressure and Excessive Renal ENaC Activity in AngII-Infused Female Rats Than in Males.

AngII (angiotensin II)-dependent hypertension causes comparable elevations of blood pressure (BP), aldosterone levels, and renal ENaC (epithelial Na+ channel) activity in male and female rodents. Mineralocorticoid receptor (MR) antagonism has a limited antihypertensive effect associated with insufficient suppression of renal ENaC in male rodents with AngII-hypertension. While MR blockade effectively reduces BP in female mice with salt-sensitive and leptin-induced hypertension, MR antagonism has not been studied in female rodents with AngII-hypertension. We hypothesize that overstimulation of renal MR signaling drives redundant ENaC-mediated Na+ reabsorption and BP increase in female rats with AngII-hypertension. We employ a combination of physiological, pharmacological, biochemical, and biophysical approaches to compare the effect of MR inhibitors on BP and ENaC activity in AngII-infused male and female Sprague Dawley rats. MR blockade markedly attenuates AngII-hypertension in female rats but has only a marginal effect in males. Spironolactone increases urinary sodium excretion and urinary sodium-to-potassium ratio in AngII-infused female, but not male, rats. The expression of renal MR and HSD11β2 (11β-hydroxysteroid dehydrogenase type 2) that determines the availability of MR to aldosterone is significantly higher in AngII-infused female rats than in males. ENaC activity is ≈2× lower in spironolactone-treated AngII-infused female rats than in males. Reduced ENaC activity in AngII-infused female rats on spironolactone correlates with increased interaction with ubiquitin ligase Nedd4-2, targeting ENaC for degradation. MR-ENaC axis is the primary determinant of excessive renal sodium reabsorption and an attractive antihypertensive target in female rats with AngII-hypertension, but not in males.

Mineralocorticoid receptor signalling in primary aldosteronism.

Primary Aldosteronism, or Conn Syndrome, is the most common endocrine cause of hypertension. It is associated with a higher risk of cardiovascular, metabolic and renal diseases, as well as a lower quality of life than for hypertension due to other causes. The multi-systemic effects of primary aldosteronism can be attributed to aldosterone-mediated activation of the mineralocorticoid receptor in a range of tissues. In this review, we explore the signalling pathways of the mineralocorticoid receptor, with a shift from the traditional focus on the regulation of renal sodium-potassium exchange to a broader understanding of its role in the modulation of tissue inflammation, fibrosis and remodelling. The appreciation of primary aldosteronism as a multi-system disease with tissue-specific pathophysiology may lead to more vigilant testing and earlier institution of targeted interventions.

Modulation of Mineralocorticoid Receptor Signalling With AZD9977 for the Treatment of Diabetic Cardiac Myopathies

Modulation of Mineralocorticoid Receptor Signalling With AZD9977 for the Treatment of Diabetic Cardiac Myopathies

Mineralocorticoid receptor knockout in Schwann cells alters myelin sheath thickness.

Myelination allows fast and synchronized nerve influxes and is provided by Schwann cells (SCs) in the peripheral nervous system. Glucocorticoid hormones are major regulators of stress, metabolism and immunity affecting all tissues. They act by binding to two receptors, the low-affinity glucocorticoid receptor (GR) and the high-affinity mineralocorticoid receptor (MR). Little is known about the effect of glucocorticoid hormones on the PNS, and this study focuses on deciphering the role of MR in peripheral myelination. In this work, the presence of a functional MR in SCs is demonstrated and the expression of MR protein in mouse sciatic nerve SC is evidenced. Besides, knockout of MR in SC (SCMRKO using Cre-lox system with DesertHedgeHog (Dhh) Cre promoter) was undertaken in mice. SCMRKO was not associated with alterations of performance in motor behavioral tests on 2- to 6-month-old male mice compared to their controls. No obvious modifications of myelin gene expression or MR signaling gene expression were observed in the SCMRKO sciatic nerves. Nevertheless, Gr transcript and GR protein amounts were significantly increased in SCMRKO nerves compared to controls, suggesting a possible compensatory effect. Besides, an increase in myelin sheath thickness was noted for axons with perimeters larger than 15 µm in SCMRKO illustrated by a significant 4.5% reduction in g-ratio (axon perimeter/myelin sheath perimeter). Thus, we defined MR as a new player in peripheral system myelination and in SC homeostasis.

Mineralocorticoid Receptor Antagonists for Preventing Chronic Kidney Disease Progression: Current Evidence and Future Challenges.

Regulation and action of the mineralocorticoid receptor (MR) have been the focus of intensive research over the past 80 years. Genetic and physiological/biochemical analysis revealed how MR and the steroid hormone aldosterone integrate the responses of distinct tubular cells in the face of environmental perturbations and how their dysregulation compromises fluid homeostasis. In addition to these roles, the accumulation of data also provided unequivocal evidence that MR is involved in the pathophysiology of kidney diseases. Experimental studies delineated the diverse pathological consequences of MR overactivity and uncovered the multiple mechanisms that result in enhanced MR signaling. In parallel, clinical studies consistently demonstrated that MR blockade reduces albuminuria in patients with chronic kidney disease. Moreover, recent large-scale clinical studies using finerenone have provided evidence that the non-steroidal MR antagonist can retard the kidney disease progression in diabetic patients. In this article, we review experimental data demonstrating the critical importance of MR in mediating renal injury as well as clinical studies providing evidence on the renoprotective effects of MR blockade. We also discuss areas of future investigation, which include the benefit of non-steroidal MR antagonists in non-diabetic kidney disease patients, the identification of surrogate markers for MR signaling in the kidney, and the search for key downstream mediators whereby MR blockade confers renoprotection. Insights into these questions would help maximize the benefit of MR blockade in subjects with kidney diseases.

Therapeutic targeting of mineralocorticoid receptors in pulmonary hypertension: Insights from basic research.

Pulmonary hypertension (PH) is characterized by pulmonary vascular remodeling and associated with adverse outcomes. In patients with PH, plasma aldosterone levels are elevated, suggesting that aldosterone and its receptor, the mineralocorticoid receptor (MR), play an important role in the pathophysiology of PH. The MR plays a crucial role in adverse cardiac remodeling in left heart failure. A series of experimental studies from the past few years indicate that MR activation promotes adverse cellular processes that lead to pulmonary vascular remodeling, including endothelial cell apoptosis, smooth muscle cell (SMC) proliferation, pulmonary vascular fibrosis, and inflammation. Accordingly, in vivo studies have demonstrated that pharmacological inhibition or cell-specific deletion of the MR can prevent disease progression and partially reverse established PH phenotypes. In this review, we summarize recent advances in MR signaling in pulmonary vascular remodeling based on preclinical research and discuss the potential, but also the challenges, in bringing MR antagonists (MRAs) into clinical application.

Cardiovascular Disease in Obstructive Sleep Apnea: Putative Contributions of Mineralocorticoid Receptors.

Obstructive sleep apnea (OSA) is a chronic and highly prevalent condition that is associated with oxidative stress, inflammation, and fibrosis, leading to endothelial dysfunction, arterial stiffness, and vascular insulin resistance, resulting in increased cardiovascular disease and overall mortality rates. To date, OSA remains vastly underdiagnosed and undertreated, with conventional treatments yielding relatively discouraging results for improving cardiovascular outcomes in OSA patients. As such, a better mechanistic understanding of OSA-associated cardiovascular disease (CVD) and the development of novel adjuvant therapeutic targets are critically needed. It is well-established that inappropriate mineralocorticoid receptor (MR) activation in cardiovascular tissues plays a causal role in a multitude of CVD states. Clinical studies and experimental models of OSA lead to increased secretion of the MR ligand aldosterone and excessive MR activation. Furthermore, MR activation has been associated with worsened OSA prognosis. Despite these documented relationships, there have been no studies exploring the causal involvement of MR signaling in OSA-associated CVD. Further, scarce clinical studies have exclusively assessed the beneficial role of MR antagonists for the treatment of systemic hypertension commonly associated with OSA. Here, we provide a comprehensive overview of overlapping mechanistic pathways recruited in the context of MR activation- and OSA-induced CVD and propose MR-targeted therapy as a potential avenue to abrogate the deleterious cardiovascular consequences of OSA.

S-07-7: ANGIOTENSIN, VASCULAR AGING AND HYPERTENSION

Aging is a major non-modifiable risk factor underlying hypertension and associated cardiovascular disease. With aging, the vasculature undergoes structural, functional and mechanical alterations characterized by endothelial dysfunction, media thickening, reduced distensibility, and arterial stiffening. Many of these processes are associated with activation of the renin angiotensin aldosterone system (RAAS), which is characteristically associated with the pathophysiology of hypertension. In particular Ang II, through the AT1 receptor, and aldosterone through the mineralocorticoid receptor, activate pro-inflammatory and pro-fibrotic signaling pathways that lead to vascular fibrosis, extracellular matrix (ECM) deposition, arterial remodelling, perivascular inflammation and hyperreactivity. These processes are also associated with aging and are amplified by hypertension. Molecular mechanisms underlying these events include increased expression and activation of matrix metalloproteinases, activation of transforming growth factor1/SMAD signalling, upregulation of galectin-3, activation of aging signaling pathways, eg p66Shc, c-Src, and oxidative stress. Fundamental to these processes is phenotypic switching of vascular smooth muscle cells from a contractile to de-differentiated state. This involves epigenetic changes and alterations in the vascular proteome. Complex interplay between the “aging process” and prohypertensive factors, including Ang II and aldosterone, result in accelerated vascular remodelling and fibrosis and increased arterial stiffness, which is typically observed in hypertension. Because the vascular phenotype in a young hypertensive individual resembles that of an elderly otherwise healthy individual, the notion of “early” or “premature” vascular aging is frequently used to describe hypertension-associated vascular disease. This presentation discusses the vascular phenotype in aging and hypertension and the role of the RAAS. In addition novel molecular mechanisms, focusing on oxidative stress and the vascular proteome will be highlighted.

RF04 | PSUN334 Mineralocorticoid receptors mediate diet - induced lipid infiltration of skeletal muscle and insulin resistance

Abstract Excess blood lipids increase the total intramyocellular (IMC) lipid content and ectopic fat storage resulting in lipotoxicity and insulin resistance in skeletal muscle, which is one of the main targets of insulin whose action is central for the maintenance of glucose homeostasis. Consumption of a diet high in fat and refined sugars, a Western Diet (WD), has been shown to activate mineralocorticoid receptors (MRs) to promote insulin resistance. However, our understanding of the precise mechanisms by which enhanced MR activation promotes skeletal muscle insulin resistance remains unclear. In this study we investigated the roles and mechanisms by which enhanced MR signaling in soleus muscle promotes ectopic lipid accumulation and related insulin resistance in diet-induced obesity. Six week-old C57BL6J mice were fed either a mouse chow diet or WD with or without spironolactone (1 mg/kg/day) for 16 weeks. Spironolactone attenuated 16 weeks of WD - induced in vivo glucose intolerance and improved soleus insulin metabolic signaling (protein kinase B and AMP kinase α pathways). Improved insulin sensitivity was accompanied by increased Glut-4 expression in conjunction with decreased IMC lipid content and reduced free fatty acid (FFA) levels and CD36 expression in soleus skeletal muscle tissue. Related to this, miR-99a was identified to negatively target CD36(www.targetscan.org/vert_72/) and elevated CD36 induced excessive FFA uptake, ectopic lipid accumulation, as well as systemic and tissue insulin resistance. Furthermore, in skeletal muscle cells spironolactone prevented enhanced MR signaling mediated reduction of miR-99a and related increased CD36. These data indicate that inhibition of MR activation with spironolactone reversed diet - induced reduction of miR-99a, thereby reducing CD36 expression, leading to reduced IMC lipid content and improved soleus insulin sensitivity. Presentation: Saturday, June 11, 2022 1:48 p.m. - 1:53 p.m., Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.

Mineralocorticoid receptor antagonists and glucocorticoids differentially affect skeletal muscle inflammation and pathology in muscular dystrophy.

Mineralocorticoid receptor antagonists (MRAs) slow cardiomyopathy in patients with Duchenne muscular dystrophy (DMD) and improve skeletal muscle pathology and function in dystrophic mice. However, glucocorticoids, known antiinflammatory drugs, remain a standard of care for DMD, despite substantial side effects. Exact mechanisms underlying mineralocorticoid receptor (MR) signaling contribution to dystrophy are unknown. Whether MRAs affect inflammation in dystrophic muscles and how they compare with glucocorticoids is unclear. The MRA spironolactone and glucocorticoid prednisolone were each administered for 1 week to dystrophic mdx mice during peak skeletal muscle necrosis to compare effects on inflammation. Both drugs reduced cytokine levels in mdx quadriceps, but prednisolone elevated diaphragm cytokines. Spironolactone did not alter myeloid populations in mdx quadriceps or diaphragms, but prednisolone increased F4/80hi macrophages. Both spironolactone and prednisolone reduced inflammatory gene expression in myeloid cells sorted from mdx quadriceps, while prednisolone additionally perturbed cell cycle genes. Spironolactone also repressed myeloid expression of the gene encoding fibronectin, while prednisolone increased its expression. Overall, spironolactone exhibits antiinflammatory properties without altering leukocyte distribution within skeletal muscles, while prednisolone suppresses quadriceps cytokines but increases diaphragm cytokines and pathology. Antiinflammatory properties of MRAs and different limb and respiratory muscle responses to glucocorticoids should be considered when optimizing treatments for patients with DMD.

Esaxerenone Blocks Vascular Endothelial Inflammation Through SGK1.

Chronic low-grade inflammation and excess mineralocorticoid receptor (MR) activation are well-known pathological conditions of metabolic syndrome (MetS). To elucidate the crosstalk between inflammation and MR signaling, we focused on serum/glucocorticoid-regulated kinase 1 (SGK1) in vascular endothelial cells. We treated human aortic endothelial cells (HAECs) with esaxerenone (ESX), a novel nonsteroidal highly selective MR antagonist, or spironolactone (SPL), a classic competitive MR antagonist, followed by stimulation with tumor necrosis factor (TNF)-α. ESX at therapeutic concentrations attenuated the long-term induction of TNF-α-stimulated inflammatory molecules in HAEC, whereas SPL had only a minor effect at 10 μM. We found long-term TNF-α-stimulated induction of SGK1 mRNA and protein levels in HAEC and that ESX pretreatment significantly decreased SGK1 mRNA and protein levels at both the basal and the TNF-α-stimulated conditions, whereas SPL had no effect on SGK1 mRNA and protein levels. In addition, the TNF-α-induced nuclear factor kappa-light-chain-enhancer of activated B cell activity was suppressed by the treatment with ESX, and it was abrogated by SGK1 overexpression. These results indicated that ESX has direct anti-inflammatory effects in HAEC via the blocking of long-term TNF-α-induced SGK1 activation and that SGK1 could be a key molecule linking cytokine-induced vascular chronic inflammation and MR activation.

Mineralocorticoid Receptors Mediate Diet-Induced Lipid Infiltration of Skeletal Muscle and Insulin Resistance.

Excess circulating lipids increase total intramyocellular (IMC) lipid content and ectopic fat storage, resulting in lipotoxicity and insulin resistance in skeletal muscle. Consumption of a diet high in fat and refined sugars-a Western diet (WD)-has been shown to activate mineralocorticoid receptors (MRs) and promote insulin resistance. However, our understanding of the precise mechanisms by which enhanced MR activation promotes skeletal muscle insulin resistance remains unclear. In this study, we investigated the mechanisms by which enhanced MR signaling in soleus muscle promotes ectopic skeletal muscle lipid accumulation and related insulin resistance. Six-week-old C57BL/6J mice were fed either a mouse chow diet or a WD with or without spironolactone (1 mg/kg/day) for 16 weeks. Spironolactone attenuated 16 weeks of WD-induced in vivo glucose intolerance and insulin resistance, and improved soleus insulin metabolic signaling. Improved insulin sensitivity was accompanied by increased glucose transporter 4 (Glut4) expression in conjunction with decreased soleus free fatty acid and IMC lipid content, as well as CD36 expression. Additionally, spironolactone prevented WD-induced soleus mitochondria dysfunction. Furthermore, MR signaling also mediated WD/aldosterone-induced reductions in soleus microRNA (miR)-99a, which was identified to negatively target CD36 and prevented palmitic acid-induced increases in CD36 expression, lipid droplet formation, mitochondria dysfunction, and insulin resistance in C2C12 cells. These data indicate that inhibition of MR activation with spironolactone prevented diet-induced abnormal expression of miR-99a, which had the capacity to reduce CD36, leading to reduced IMC lipid content and improved soleus mitochondria function and insulin sensitivity.

Prenatal Lipopolysaccharides Exposure Induces Transgenerational Inheritance of Hypertension.

Adverse environmental exposure during the prenatal period can lead to diseases in the offspring, including hypertension. Whether or not the hypertensive phenotype can be transgenerationally transmitted is not known. Pregnant Sprague Dawley rats were intraperitoneally injected with lipopolysaccharide (LPS) on gestation days 6, 8, 10, and 12 to generate the prenatal LPS exposure model. Blood pressure was monitored by both telemetry and tail-cuff method. RNA sequencing was performed to analyze transcriptome alteration in the kidney of the third generation. Tempol and spironolactone were used to test the potential preventative and therapeutic effect of targeting reactive oxygen species and mineralocorticoid receptor signaling, respectively. Molecular biological experiments were performed to illustrate the mechanism of epigenetic and transcription regulation. Prenatal LPS exposure can impair the ability to excrete a salt load and induce hypertension from the first to the third generations, with the fourth and fifth generations, inducing salt-sensitive hypertension. Compared with control pups, the transcriptome in the kidney of the hypertensive third-generation prenatal LPS-exposed offspring have upregulation of the Ras-related C3 botulinum toxin substrate 1 (Rac1) gene and activation of mineralocorticoid receptor signaling. Furthermore, we found that LPS exposure during pregnancy triggered oxidative stress that upregulated KDM3B (histone lysine demethylase 3B) in the oocytes of first-generation female rats, leading to an inheritable low level of H3K9me2 (histone H3 lysine 9 dimethylation), resulting in the transgenerational upregulation of Rac1. Based on these findings, we treated the LPS-exposed pregnant rats with the reactive oxygen species scavenger, tempol, which successfully prevented hypertension in the first-generation offspring and the transgenerational inheritance of hypertension. These findings show that adverse prenatal exposure induces transgenerational hypertension through an epigenetic-regulated mechanism and identify potentially preventive and therapeutic strategies for hypertension.

New Perspectives on Sex Steroid and Mineralocorticoid Receptor Signaling in Cardiac Ischemic Injury.

The global burden of ischemic heart disease is burgeoning for both men and women. Although advances have been made, the need for new sex-specific therapies targeting key differences in cardiovascular disease outcomes in men and women remains. Mineralocorticoid receptor directed treatments have been successfully used for blood pressure control and heart failure management and represent a potentially valuable therapeutic option for ischemic cardiac events. Clinical and experimental data indicate that mineralocorticoid excess or inappropriate mineralocorticoid receptor (MR) activation exacerbates ischemic damage, and many of the intracellular response pathways activated in ischemia and subsequent reperfusion are regulated by MR. In experimental contexts, where MR are abrogated genetically or mineralocorticoid signaling is suppressed pharmacologically, ischemic injury is alleviated, and reperfusion recovery is enhanced. In the chronic setting, mineralocorticoid signaling induces fibrosis, oxidative stress, and inflammation, which can predispose to ischemic events and exacerbate post-myocardial infarct pathologies. Whilst a range of cardiac cell types are involved in mineralocorticoid-mediated regulation of cardiac function, cardiomyocyte-specific MR signaling pathways are key. Selective inhibition of cardiomyocyte MR signaling improves electromechanical resilience during ischemia and enhances contractile recovery in reperfusion. Emerging evidence suggests that the MR also contribute to sex-specific aspects of ischemic vulnerability. Indeed, MR interactions with sex steroid receptors may differentially regulate myocardial nitric oxide bioavailability in males and females, potentially determining sex-specific post-ischemic outcomes. There is hence considerable impetus for exploration of MR directed, cell specific therapies for both women and men in order to improve ischemic heart disease outcomes.

Mineralocorticoid Receptor Signaling in the Inflammatory Skeletal Muscle Microenvironments of Muscular Dystrophy and Acute Injury

Duchenne muscular dystrophy (DMD) is a striated muscle degenerative disease due to loss of functional dystrophin protein. Loss of dystrophin results in susceptibility of muscle membranes to damage, leading to muscle degeneration and continuous inflammation and fibrosis that further exacerbate pathology. Long-term glucocorticoid receptor (GR) agonist treatment, the current standard-of-care for DMD, modestly improves prognosis but has serious side effects. The mineralocorticoid receptor (MR), a ligand-activated transcription factor present in many cell types, has been implicated as a therapeutic target for DMD. MR antagonists (MRAs) have fewer side effects than GR agonists and are used clinically for heart failure. MRA efficacy has recently been demonstrated for DMD cardiomyopathy and in preclinical studies, MRAs also alleviate dystrophic skeletal muscle pathology. MRAs lead to improvements in muscle force and membrane stability and reductions in degeneration, inflammation, and fibrosis in dystrophic muscles. Myofiber-specific MR knockout leads to most of these improvements, supporting an MR-dependent mechanism of action, but MRAs additionally stabilize myofiber membranes in an MR-independent manner. Immune cell MR signaling in dystrophic and acutely injured normal muscle contributes to wound healing, and myeloid-specific MR knockout is detrimental. More research is needed to fully elucidate MR signaling in striated muscle microenvironments. Direct comparisons of genomic and non-genomic effects of glucocorticoids and MRAs on skeletal muscles and heart will contribute to optimal temporal use of these drugs, since they compete for binding conserved receptors. Despite the advent of genetic medicines, therapies targeting inflammation and fibrosis will be necessary to achieve optimal patient outcomes.

The mineralocorticoid receptor signal could be a new molecular target for the treatment of diabetic retinal complication

ABSTRACT Background Activation of the mineralocorticoid receptor (MR) is involved in the pathophysiology of diabetic vascular complications. In recent years, it has been indicated that the MR expressed in retinal Müller cells plays an important role in regulating the potassium and water balance in the retina. Therefore, it has also been speculated that abnormal MR signaling contributes to edematous diseases of the retina. Research design and methods We examined the effect of high-glucose conditions on MR protein and mRNA levels in human retinal Müller cells and changes in cell size in vitro. We also investigated MR transcriptional activity and signaling in high-glucose conditions. Results The MR protein increased by 2.2-fold with high-glucose treatment. Additionally, high-glucose treatment induced Müller cell swelling. Aldosterone-induced MR transcriptional activity was enhanced in high-glucose conditions, resulting in the upregulation of αENaC, AQP4, and Kir4.1 mRNA. Treatment with an MR antagonist led to the suppression of aldosterone-induced cell swelling, MR transcriptional activity, and upregulation of the target genes in high-glucose conditions. Conclusions High glucose induces Müller cell swelling through activation of MR signaling, which could be associated with aggravation of macular edema. Thus, Müller cell swelling and diabetic macular edema may represent a target for treatment with MR antagonists.

Endothelial Mineralocorticoid Receptors Constrain Arteriogenesis and Perfusion Recovery Following Chronic Arterial Ligation in a Sex‐specific Manner

Vascular occlusive diseases are major contributors to cardiovascular morbidity and mortality. Prior work has implicated mineralocorticoid receptor (MR) signaling in perfusion recovery following arterial occlusion, however, cell‐specific MR signaling in the associated angiogenic and arteriogenic responses has not been elucidated. Further, accumulating evidence has revealed sex‐specific involvement of MR signaling in a number of cardiovascular disease states. Accordingly, we examined the hypothesis that MR signaling, specifically endothelial cell (EC) MR signaling, attenuates vascular compensation and perfusion recovery following femoral artery excision and that this effect would be more pronounced in females. Unilateral femoral artery ligation and excision was performed in male and female C57BL/6J mice treated with vehicle or the MR antagonist spironolactone (Spiro; 20 mg/kg/d, sc) as well as in male and female MR Intact and EC MR knockout (KO) mice. Serial assessment of hindlimb perfusion for 28 days following surgery revealed enhanced perfusion recovery following Spiro treatment in female, but not male, mice. Interestingly, Spiro increased gastrocnemius capillary density in both the ischemic and sham limb in males and females. Following perfusion fixation, collateral remodeling was assessed by micro‐computed tomography revealing enhanced collateral expansion following Spiro treatment in female, but not male, mice. Additional mechanistic experiments similarly revealed increased perfusion recovery and enhanced collateral expansion in female, not male, EC MR KO mice independent of capillary density. At 28 days post‐surgery, distribution analysis revealed larger overall arteriolar diameters only in the collateral zone of EC MR KO females. Further analysis revealed enhanced early (7 days post‐surgery) collateral expansion in male and female EC MR KO mice. In female, but not male, EC MR KO mice this was associated with increased CD68+ macrophages and CD206+ ‘M2’‐like macrophages in the collateral zone. Together, these data demonstrate that EC MR signaling constrains early arteriogenic collateralization following arterial excision in both sexes and constrains long‐term collateralization only in females involving limitation of pro‐arteriogenic CD206+ ‘M2’‐like macrophages in the collateral zone. To our knowledge, this is the first report of a role for EC MR signaling in arteriogenesis and highlights potential use of MR blockers in the treatment of vascular occlusive events.