Inducible Knock-Down of the Mineralocorticoid Receptor in Mice Disturbs Regulation of the Renin-Angiotensin-Aldosterone System and Attenuates Heart Failure Induced by Pressure Overload

Extracellular matrix induced by steroids and aging through a G-protein-coupled receptor in a Drosophila model of renal fibrosis

Aldosterone is produced by the mammalian adrenal cortex to modulate blood pressure and fluid balance; however, excessive, prolonged aldosterone promotes fibrosis and kidney failure. How aldosterone triggers disease may involve actions independent of its canonical mineralocorticoid receptor. Here, we present a Drosophila model of renal pathology caused by excess extracellular matrix formation, stimulated by exogenous aldosterone and by insect ecdysone. Chronic administration of aldosterone or ecdysone induces expression and accumulation of collagen-like Pericardin in adult nephrocytes - podocyte-like cells that filter circulating hemolymph. Excess Pericardin deposition disrupts nephrocyte (glomerular) filtration and causes proteinuria in Drosophila, hallmarks of mammalian kidney failure. Steroid-induced Pericardin production arises from cardiomyocytes associated with nephrocytes, potentially reflecting an analogous role of mammalian myofibroblasts in fibrotic disease. Remarkably, the canonical ecdysteroid nuclear hormone receptor, Ecdysone receptor (EcR), is not required for aldosterone or ecdysone to stimulate Pericardin production or associated renal pathology. Instead, these hormones require a cardiomyocyte-associated G-protein-coupled receptor, Dopamine-EcR (DopEcR), a membrane-associated receptor previously characterized in the fly brain to affect behavior. DopEcR in the brain is known to affect behavior through interactions with the Drosophila Epidermal growth factor receptor (Egfr), referred to as dEGFR. Here, we find that the steroids ecdysone and aldosterone require dEGFR in cardiomyocytes to induce fibrosis of the cardiac-renal system. In addition, endogenous ecdysone that becomes elevated with age is found to foster age-associated fibrosis, and to require both cardiomyocyte DopEcR and dEGFR. This Drosophila renal disease model reveals a novel signaling pathway through which steroids may modulate mammalian fibrosis through potential orthologs of DopEcR.

The endothelial mineralocorticoid receptor: Contributions to sex differences in cardiovascular disease

Cardiovascular disease remains the leading cause of death for both men and women. The observation that premenopausal women are protected from cardiovascular disease relative to age-matched men, and that this protection is lost with menopause, has led to extensive study of the role of sex steroid hormones in the pathogenesis of cardiovascular disease. However, the molecular basis for sex differences in cardiovascular disease is still not fully understood, limiting the ability to tailor therapies to male and female patients. Therefore, there is a growing need to investigate molecular pathways outside of traditional sex hormone signaling to fully understand sex differences in cardiovascular disease. Emerging evidence points to the mineralocorticoid receptor (MR), a steroid hormone receptor activated by the adrenal hormone aldosterone, as one such mediator of cardiovascular disease risk, potentially serving as a sex-dependent link between cardiovascular risk factors and disease. Enhanced activation of the MR by aldosterone is associated with increased risk of cardiovascular disease. Emerging evidence implicates the MR specifically within the endothelial cells lining the blood vessels in mediating some of the sex differences observed in cardiovascular pathology. This review summarizes the available clinical and preclinical literature concerning the role of the MR in the pathophysiology of endothelial dysfunction, hypertension, atherosclerosis, and heart failure, with a special emphasis on sex differences in the role of endothelial-specific MR in these pathologies. The available data regarding the molecular mechanisms by which endothelial-specific MR may contribute to sex differences in cardiovascular disease is also summarized. A paradigm emerges from synthesis of the literature in which endothelial-specific MR regulates vascular function in a sex-dependent manner in response to cardiovascular risk factors to contribute to disease. Limitations in this field include the relative paucity of women in clinical trials and, until recently, the nearly exclusive use of male animals in preclinical investigations. Enhanced understanding of the sex-specific roles of endothelial MR could lead to novel mechanistic insights underlying sex differences in cardiovascular disease incidence and outcomes and could identify additional therapeutic targets to effectively treat cardiovascular disease in men and women.

Pathophysiological mechanisms of mineralocorticoid receptor-dependent cardiovascular and chronic kidney disease

Accumulating evidence has indicated the potential contributions of aldosterone and mineralocorticoid receptor (MR) to the pathophysiology of cardiovascular disease (CVD) and chronic kidney disease (CKD). Patients with primary aldosteronism have a higher risk of CVD and CKD than those with essential hypertension. MR is strongly expressed in endothelial cells, vascular smooth muscle cells, cardiomyocytes, fibroblasts, macrophages, glomerular mesangial cells, podocytes, and proximal tubular cells. In these cardiovascular and renal cells, aldosterone-induced cell injury is prevented by MR blockade. Interestingly, MR antagonists elicit beneficial effects on CVD and CKD in subjects with low or normal plasma aldosterone levels. Recent studies have shown that during development of CVD and CKD, cardiovascular and renal MR is activated by glucocorticoid and ligand-independent mechanisms, such as Rac1 signaling pathways. These data indicate that inappropriate activation of local MR contributes to cardiovascular and renal tissue injury through aldosterone-dependent and -independent mechanisms. In this review, recent findings on the specific role of cardiovascular and renal MR in the pathogenesis of CVD and CKD are summarized.

CD8+-T Cells With Specificity for a Model Antigen in Cardiomyocytes Can Become Activated After Transverse Aortic Constriction but Do Not Accelerate Progression to Heart Failure

Heart failure due to pressure overload is frequently associated with inflammation. In addition to inflammatory responses of the innate immune system, autoimmune reactions of the adaptive immune system appear to be triggered in subgroups of patients with heart failure as demonstrated by the presence of autoantibodies against myocardial antigens. Moreover, T cell-deficient and T cell-depleted mice have been reported to be protected from heart failure induced by transverse aortic constriction (TAC) and we have shown recently that CD4⁺-helper T cells with specificity for an antigen in cardiomyocytes accelerate TAC-induced heart failure. In this study, we set out to investigate the potential contribution of CD8⁺-cytotoxic T cells with specificity to a model antigen (ovalbumin, OVA) in cardiomyocytes to pressure overload-induced heart failure. In 78% of cMy-mOVA mice with cardiomyocyte-specific OVA expression, a low-grade OVA-specific cellular cytotoxicity was detected after TAC. Adoptive transfer of OVA-specific CD8⁺-T cells from T cell receptor transgenic OT-I mice before TAC did not increase the risk of OVA-specific autoimmunity in cMy-mOVA mice. After TAC, again 78% of the mice displayed an OVA-specific cytotoxicity with on average only a three-fold higher killing of OVA-expressing target cells. More CD8⁺ cells were present after TAC in the myocardium of cMy-mOVA mice with OT-I T cells (on average 17.5/mm²) than in mice that did not receive OVA-specific CD8⁺-T cells (3.6/mm²). However, the extent of fibrosis was similar in both groups. Functionally, as determined by echocardiography, the adoptive transfer of OVA-specific CD8⁺-T cells did not significantly accelerate the progression from hypertrophy to heart failure in cMy-mOVA mice. These findings argue therefore against a major impact of cytotoxic T cells with specificity for autoantigens of cardiomyocytes in pressure overload-induced heart failure.

Eplerenone attenuates pathological pulmonary vascular rather than right ventricular remodeling in pulmonary arterial hypertension

Background

Aldosterone is a mineralocorticoid hormone critically involved in arterial blood pressure regulation. Although pharmacological aldosterone antagonism reduces mortality and morbidity among patients with severe left-sided heart failure, the contribution of aldosterone to the pathobiology of pulmonary arterial hypertension (PAH) and right ventricular (RV) heart failure is not fully understood.

Methods

The effects of Eplerenone (0.1% Inspra® mixed in chow) on pulmonary vascular and RV remodeling were evaluated in mice with pulmonary hypertension (PH) caused by Sugen5416 injection with concomitant chronic hypoxia (SuHx) and in a second animal model with established RV dysfunction independent from lung remodeling through surgical pulmonary artery banding.

Results

Preventive Eplerenone administration attenuated the development of PH and pathological remodeling of pulmonary arterioles. Therapeutic aldosterone antagonism – starting when RV dysfunction was established - normalized mineralocorticoid receptor gene expression in the right ventricle without direct effects on either RV structure (Cardiomyocyte hypertrophy, Fibrosis) or function (assessed by non-invasive echocardiography along with intra-cardiac pressure volume measurements), but significantly lowered systemic blood pressure.

Conclusions

Our data indicate that aldosterone antagonism with Eplerenone attenuates pulmonary vascular rather than RV remodeling in PAH.

T helper cells with specificity for an antigen in cardiomyocytes promote pressure overload-induced progression from hypertrophy to heart failure

We investigated whether CD4⁺-T cells with specificity for an antigen in cardiomyocytes promote the progression from hypertrophy to heart failure in mice with increased pressure load due to transverse aortic constriction (TAC). OT-II mice expressing a transgenic T cell receptor (TCR) with specificity for ovalbumin (OVA) on CD4⁺-T cells and cMy-mOVA mice expressing OVA on cardiomyocytes were crossed. The resulting cMy-mOVA-OT-II mice did not display signs of spontaneous autoimmunity despite the fact that their OVA-specific CD4⁺-T cells were not anergic. After TAC, progression to heart failure was significantly accelerated in cMy-mOVA-OT-II compared to cMy-mOVA mice. No OVA-specific antibodies were induced in response to TAC in cMy-mOVA-OT-II mice, yet more CD3⁺ T cells infiltrated their myocardium when compared with TAC-operated cMy-mOVA mice. Systemically, the proportion of activated CD4⁺-T cells with a Th₁ and Th₁₇ cytokine profile was increased in cMy-mOVA-OT-II mice after TAC. Thus, T helper cells with specificity for an antigen in cardiomyocytes can directly promote the progression of heart failure in response to pressure overload independently of autoantibodies.

Deletion of the Mineralocorticoid Receptor in Myeloid Cells Attenuates Central Nervous System Autoimmunity

Myeloid cells play an important role in the pathogenesis of multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE). Monocytes, macrophages, and microglia can adopt two distinct phenotypes, with M1-polarized cells being more related to inflammation and autoimmunity while M2-polarized cells contribute to tissue repair and anti-inflammatory processes. Here, we show that deletion of the mineralocorticoid receptor (MR) in bone marrow-derived macrophages and peritoneal macrophages caused their polarization toward the M2 phenotype with its distinct gene expression, altered phagocytic and migratory properties, and dampened NO production. After induction of EAE, mice that are selectively devoid of the MR in their myeloid cells (MR^lysM mice) showed diminished clinical symptoms and ameliorated histological hallmarks of neuroinflammation. T cells in peripheral lymphoid organs of these mice produced less pro-inflammatory cytokines while their proliferation and the abundance of regulatory T cells were unaltered. The numbers of inflammatory monocytes and reactive microglia in the central nervous system (CNS) in MR^lysM mice were significantly lower and they adopted an M2-polarized phenotype based on their gene expression profile, presumably explaining the ameliorated neuroinflammation. Our results indicate that the MR in myeloid cells plays a critical role for CNS autoimmunity, providing a rational to interfere with diseases such as MS by pharmacologically targeting this receptor.

30 YEARS OF THE MINERALOCORTICOID RECEPTOR: Mineralocorticoid receptor null mice: informing cell-type-specific roles

The mineralocorticoid receptor (MR) mediates the actions of two important adrenal corticosteroid hormones, aldosterone and cortisol. The cell signalling roles of the MR in vivo have expanded enormously since the cloning of human MR gene 30 years ago and the first MR gene knockout in mice nearly 20 years ago. Complete ablation of the MR revealed important roles postnatally for regulation of kidney epithelial functions, with MR-null mice dying 1-2 weeks postnatally from renal salt wasting and hyperkalaemia, with elevated plasma renin and aldosterone. Generation of tissue-selective MR-deficient mice using Cre recombinase-LoxP gene targeting has made it possible to analyse mice lacking MR only in specific cell types. Targeting renal-specific MR has differentiated roles in specific compartments of the kidney. Ablating MR in neurons of the forebrain reinforced important roles of the MR in response to stress, behaviour and anxiety, but suggested a minimal role in maintaining basal HPA axis tone. Deletion of the MR in macrophages and other cell types of the cardiovascular system clearly defined important roles for the regulation of cardiovascular physiology and pathophysiology. Knockdown of MR mRNA in vivo using antisense/siRNA approaches, and similarly MR overexpression, has provided useful rodent models to study physiological roles of MR signalling in vivo More recently, targeted mutation of specific domains of the MR such as the DBD has defined genomic vs non-genomic roles in vivo New tissue-selective MR-null models are required to define roles of MR signalling in other regions of the brain, the eye, gastrointestinal tract, lung, skin, breast and gonadal organs.

Mineralocorticoid Receptor Deficiency in T Cells Attenuates Pressure Overload-Induced Cardiac Hypertrophy and Dysfunction Through Modulating T-Cell Activation

Although antagonists of mineralocorticoid receptor (MR) have been widely used to treat heart failure, the underlying mechanisms are incompletely understood. Recent reports show that T cells play important roles in pathologic cardiac hypertrophy and heart failure. However, it is unclear whether and how MR functions in T cells under these pathologic conditions. We found that MR antagonist suppressed abdominal aortic constriction-induced cardiac hypertrophy and decreased the accumulation and activation of CD4⁺ and CD8⁺ T cells in mouse heart. T-cell MR knockout mice manifested suppressed cardiac hypertrophy, fibrosis, and dysfunction compared with littermate control mice after abdominal aortic constriction. T-cell MR knockout mice had less cardiac inflammatory response, which was illustrated by decreased accumulation of myeloid cells and reduced expression of inflammatory cytokines. Less amounts and activation of T cells were observed in the heart of T-cell MR knockout mice after abdominal aortic constriction. In vitro studies showed that both MR antagonism and deficiency repressed activation of T cells, whereas MR overexpression elevated activation of T cells. These results demonstrated that MR blockade in T cells protected against abdominal aortic constriction-induced cardiac hypertrophy and dysfunction. Mechanistically, MR directly regulated T-cell activation and modulated cardiac inflammation. Targeting MR in T cells specifically may be a feasible strategy for more effective treatment of pathologic cardiac hypertrophy and heart failure.

RNAi-mediated knockdown of mouse melanocortin-4 receptor in vitro and in vivo, using an siRNA expression construct based on the mir-187 precursor

RNA interference (RNAi) is a powerful tool for the study of gene function in mammalian systems, including transgenic mice. Here, we report a gene knockdown system based on the human mir-187 precursor. We introduced small interfering RNA (siRNA) sequences against the mouse melanocortin-4 receptor (mMc4r) to alter the targeting of miR-187. The siRNA-expressing cassette was placed under the control of the cytomegalovirus (CMV) early enhancer/chicken β-actin promoter. In vitro, the construct efficiently knocked down the gene expression of a co-transfected mMc4r-expression vector in cultured mammalian cells. Using this construct, we generated a transgenic mouse line which exhibited partial but significant knockdown of mMc4r mRNA in various brain regions. Northern blot analysis detected transgenic expression of mMc4r siRNA in these regions. Furthermore, the transgenic mice fed a normal diet ate 9% more and were 30% heavier than wild-type sibs. They also developed hyperinsulinemia and fatty liver as do mMc4r knockout mice. We determined that this siRNA expression construct based on mir-187 is a practical and useful tool for gene functional studies in vitro as well as in vivo.