Aldosterone stimulates elastogenesis in cardiac fibroblasts via mineralocorticoid receptor-independent action involving the consecutive activation of Galpha13, c-Src, the insulin-like growth factor-I receptor, and phosphatidylinositol 3-kinase/Akt

Biomarkers to Guide Medical Therapy in Primary Aldosteronism

Primary aldosteronism (PA) is an endocrinopathy characterized by dysregulated aldosterone production that occurs despite suppression of renin and angiotensin II, and that is non-suppressible by volume and sodium loading. The effectiveness of surgical adrenalectomy for patients with lateralizing PA is characterized by the attenuation of excess aldosterone production leading to blood pressure reduction, correction of hypokalemia, and increases in renin-biomarkers that collectively indicate a reversal of PA pathophysiology and restoration of normal physiology. Even though the vast majority of patients with PA will ultimately be treated medically rather than surgically, there is a lack of guidance on how to optimize medical therapy and on key metrics of success. Herein, we review the evidence justifying approaches to medical management of PA and biomarkers that reflect endocrine principles of restoring normal physiology. We review the current arsenal of medical therapies, including dietary sodium restriction, steroidal and nonsteroidal mineralocorticoid receptor antagonists, epithelial sodium channel inhibitors, and aldosterone synthase inhibitors. It is crucial that clinicians recognize that multimodal medical treatment for PA can be highly effective at reducing the risk for adverse cardiovascular and kidney outcomes when titrated with intention. The key biomarkers reflective of optimized medical therapy are unsurprisingly similar to the physiologic expectations following surgical adrenalectomy: control of blood pressure with the fewest number of antihypertensive agents, normalization of serum potassium without supplementation, and a rise in renin. Pragmatic approaches to achieve these objectives while mitigating adverse effects are reviewed.

The Effect of Aldosterone on Cardiorenal and Metabolic Systems

Aldosterone, a vital hormone of the human body, has various pathophysiological roles. The excess of aldosterone, also known as primary aldosteronism, is the most common secondary cause of hypertension. Primary aldosteronism is associated with an increased risk of cardiovascular disease and kidney dysfunction compared to essential hypertension. Excess aldosterone can lead to harmful metabolic and other pathophysiological alterations, as well as cause inflammatory, oxidative, and fibrotic effects in the heart, kidney, and blood vessels. These alterations can result in coronary artery disease, including ischemia and myocardial infarction, left ventricular hypertrophy, heart failure, arterial fibrillation, intracarotid intima thickening, cerebrovascular disease, and chronic kidney disease. Thus, aldosterone affects several tissues, especially in the cardiovascular system, and the metabolic and pathophysiological alterations are related to severe diseases. Therefore, understanding the effects of aldosterone on the body is important for health maintenance in hypertensive patients. In this review, we focus on currently available evidence regarding the role of aldosterone in alterations of the cardiovascular and renal systems. We also describe the risk of cardiovascular events and renal dysfunction in hyperaldosteronism.

A Novel Approach to Medical Management of Heart Failure With Reduced Ejection Fraction

The advent of newly available medical therapies for heart failure with reduced ejection fraction (HFrEF) has resulted in many potential therapeutic combinations, increasing treatment complexity. Publication of expert consensus guidelines and initiatives aimed to improve implementation of treatment has emphasized sequential stepwise initiation and titration of medical therapy, which is labour intensive. Data taken from heart failure registries show suboptimal use of medications, prolonged titration times, and consequently little change in dose intensity, all of which indicate therapeutic inertia. Recently published evidence indicates that 4 medication classes-renin-angiotensin-neprilysin inhibitors, β-blockers, mineralocorticoid antagonists, and sodium-glucose cotransporter inhibitors-which we refer to as Foundational Therapy, confer rapid and robust reduction in both morbidity and mortality in most patients with HFrEF and that they work in additive fashion. Additional morbidity and mortality may be observed following addition of several personalized therapies in specific subgroups of patients. In this review, we discuss mechanisms of action of these therapies and propose a framework for their implementation, based on several principles. These include the critical importance of rapid initiation of all 4 Foundational Therapies followed by their titration to target doses, emphasis on multiple simultaneous drug changes with each patient encounter, attention to patient-specific factors in choice of medication class, leveraging inpatient care, use of the entire health care team, and alternative (ie, virtual visits) modes of care. We have incorporated these principles into a Cluster Scheme designed to facilitate timely and optimal medical treatment for patients with HFrEF.

CMR-Verified Myocardial Fibrosis Is Associated With Subclinical Diastolic Dysfunction in Primary Aldosteronism Patients

OBJECTIVES

The main cardiac features of primary aldosteronism (PA) are impaired left ventricular (LV) diastolic function, and some articles also reported more cardiac fibrosis in PA patients. However, the correlation between LV dysfunction and diffuse myocardial fibrosis in PA remains unknown.

METHODS

We enrolled 84 PA patients and 28 essential hypertension (EH) patients in West China Hospital. Cardiac magnetic resonance imaging (CMR) contrast enhancement was arranged for all subjects. Postcontrast T1 time and left ventricular myocardial strains and strain rates were measured.

RESULTS

76 PA patients and 27 essential hypertension (EH) patients were included in the final analysis. Blood pressure, LV mass indexes, and LV ejection fractions were comparable in both groups, while the global circumferential peak diastolic strain rate (PDSR) was lower (0.9 ± 0.3 vs. 1.1 ± 0.4, p <0.01) and the postcontrast T1 time was shorter (520 ± 38 vs. 538 ± 27, p = 0.01) in PA patients than those in EH patients. Postcontrast T1 time (p = 0.01) was independently related to global circumferential PDSR after adjusting for age and duration of hypertension in PA patients. Furthermore, plasma aldosterone concentration was negatively associated with postcontrast T1 time (R = -0.253, p = 0.028) in PA patients.

CONCLUSIONS

The global circumferential PDSR derived by CMR is decreased, and the diffuse myocardial fibrosis is increased in PA patients compared to those in blood pressure matched EH patients. The severity of cardiac diastolic dysfunction independently relates to the degree of diffuse myocardial fibrosis in PA patients, and the diffuse myocardial fibrosis may be caused by high PAC level.

CLINICAL TRIAL REGISTRATION

http://www.chictr.org.cn/listbycreater.asp, identifier ChiCTR2000031792.

The impact of maternal obesity in pregnancy on placental glucocorticoid and macronutrient transport and metabolism

Maternal obesity is the most common metabolic disturbance in pregnancy affecting >1 in 5 women in some countries. Babies born to obese women are heavier with more adiposity at birth, and are vulnerable to obesity and metabolic disease across the lifespan suggesting offspring health is 'programmed' by fetal exposure to an obese intra-uterine environment. The placenta plays a major role in dictating the impact of maternal health on prenatal development. Maternal obesity impacts the function of integral placental receptors and transporters for glucocorticoids and nutrients, key drivers of fetal growth, though mechanisms remain poorly understood. This review aims to summarise current knowledge in this area, and considers the impact of obesity on the epigenetic machinery of the placenta at this vital juncture in offspring development. Further research is required to advance understanding of these areas in the hope that the trans-generational cycle of obesity can be alleviated.

The Role of Mineralocorticoid Receptor Antagonists in the Management of Heart Failure with Preserved Ejection Fraction

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF) is associated with increased risk for hospitalization and all-cause mortality. Currently, there is no established treatment to improve the survival of these patients. Aldosterone appears to play a role in the pathogenesis of HFpEF.

OBJECTIVE

To discuss the findings of studies that evaluated the effects of mineralocorticoid receptor (MR) antagonists on the outcome of patients with HFpEF.

METHODS

PubMed was searched for relevant papers. References of retrieved articles were also evaluated for pertinent material.

RESULTS

Accumulating data suggest that MR antagonists might be useful in the management of patients with HFpEF. However, existing evidence is limited and conflicting.

CONCLUSIONS

More studies are needed to clearly define the therapeutic potential of MR antagonists in HFpEF. Given the heterogeneity of this disease and the low specificity of the criteria used for its diagnosis, it is also important to improve the definition of HFpEF and include appropriately selected patients in these studies.

Aldosterone and Mineralocorticoid Receptor System in Cardiovascular Physiology and Pathophysiology

The mineralocorticoid hormone aldosterone (Aldo) has been intensively studied for its ability to influence both the physiology and pathophysiology of the cardiovascular system. Indeed, although research on Aldo actions for decades has mainly focused on its effects in the kidney, several lines of evidence have now demonstrated that this hormone exerts disparate extrarenal adverse effects, especially in the circulatory system. Accordingly, in the last lusters, a number of studies in preclinical models (in vitro and in vivo) and in humans have established that Aldo, following the interaction with its receptor-the mineralocorticoid receptor (MR)-is able to activate specific intracellular genomic and nongenomic pathways, thus regulating the homeostasis of the cardiovascular system. Importantly, through this mechanism of action, this hormone becomes a crucial regulator of the function and growth of different types of cells, including fibroblasts, cardiomyocytes, and vascular cells. For this main reason, it is plausible that when Aldo is present at high levels in the blood, it profoundly modifies the physiology of these cells, therefore being at the foundation of several cardiovascular disorders, such as heart failure (HF). On these grounds, in this review, we will provide an updated account on the current knowledge concerning Aldo activity in the cardiovascular system and the most recent preclinical studies and clinical trials designed to test better approaches able to counter the hyperactivity of the Aldo/MR signaling pathway in the setting of cardiovascular diseases.

Endothelial mineralocorticoid receptor contributes to systolic dysfunction induced by pressure overload without modulating cardiac hypertrophy or inflammation

Heart Failure (HF) is associated with increased circulating levels of aldosterone and systemic inflammation. Mineralocorticoid receptor (MR) antagonists block aldosterone action and decrease mortality in patients with congestive HF. However, the molecular mechanisms underlying the therapeutic benefits of MR antagonists remain unclear. MR is expressed in all cell types in the heart, including the endothelial cells (EC), in which aldosterone induces the expression of intercellular adhesion molecule 1 (ICAM‐1). Recently, we reported that ICAM‐1 regulates cardiac inflammation and cardiac function in mice subjected to transverse aortic constriction (TAC). Whether MR specifically in endothelial cells (EC) contributes to the several mechanisms of pathological cardiac remodeling and cardiac dysfunction remains unclear. Basal cardiac function and LV dimensions were comparable in mice with MR selectively deleted from ECs (EC‐MR^−/−) and wild‐type littermate controls (EC‐MR^+/+). MR was specifically deleted in heart EC, and in EC‐containing tissues, but not in leukocytes of TAC EC‐MR^−/− mice. While EC‐MR^−/−TAC mice showed preserved systolic function and some alterations in the expression of fetal genes, the proinflammatory cytokine TNFα and the endothelin receptors in the LV as compared to EC‐MR^+/+TAC mice, no difference was observed between both TAC groups in overall cardiac hypertrophy, ICAM‐1 LV expression and leukocyte infiltration, cardiac fibrosis or capillary rarefaction, all hallmarks of pathological cardiac remodeling. Our data indicate that EC‐MR contributes to the transition of cardiac hypertrophy to systolic dysfunction independently of other maladaptive changes induced by LV pressure overload.

30 YEARS OF THE MINERALOCORTICOID RECEPTOR: Nongenomic effects via the mineralocorticoid receptor

The mineralocorticoid receptor (MR) belongs to the steroid hormone receptor family and classically functions as a ligand-dependent transcription factor. It is involved in water-electrolyte homeostasis and blood pressure regulation but independent from these effects also furthers inflammation, fibrosis, hypertrophy and remodeling in cardiovascular tissues. Next to genomic effects, aldosterone elicits very rapid actions within minutes that do not require transcription or translation and that occur not only in classical MR epithelial target organs like kidney and colon but also in nonepithelial tissues like heart, vasculature and adipose tissue. Most of these effects can be mediated by classical MR and its crosstalk with different signaling cascades. Near the plasma membrane, the MR seems to be associated with caveolin and striatin as well as with receptor tyrosine kinases like EGFR, PDGFR and IGF1R and G protein-coupled receptors like AT1 and GPER1, which then mediate nongenomic aldosterone effects. GPER1 has also been named a putative novel MR. There is a close interaction and functional synergism between the genomic and the nongenomic signaling so that nongenomic signaling can lead to long-term effects and support genomic actions. Therefore, understanding nongenomic aldosterone/MR effects is of potential relevance for modulating genomic aldosterone effects and may provide additional targets for intervention.

Mineralocorticoid regulation of cell function: the role of rapid signalling and gene transcription pathways

The mineralocorticoid receptor (MR) and mineralocorticoids regulate epithelial handling of electrolytes, and induces diverse effects on other tissues. Traditionally, the effects of MR were ascribed to ligand-receptor binding and activation of gene transcription. However, the MR also utilises a number of intracellular signalling cascades, often by transactivating unrelated receptors, to change cell function more rapidly. Although aldosterone is the physiological mineralocorticoid, it is not the sole ligand for MR. Tissue-selective and mineralocorticoid-specific effects are conferred through the enzyme 11β-hydroxysteroid dehydrogenase 2, cellular redox status and properties of the MR itself. Furthermore, not all aldosterone effects are mediated via MR, with implication of the involvement of other membrane-bound receptors such as GPER. This review will describe the ligands, receptors and intracellular mechanisms available for mineralocorticoid hormone and receptor signalling and illustrate their complex interactions in physiology and disease.

Oxymatrine inhibits aldosterone-induced rat cardiac fibroblast proliferation and differentiation by attenuating smad-2,-3 and-4 expression: an in vitro study

BACKGROUND

We previously demonstrated oxymatrine, an alkaloid from the Chinese medicine radix Sophorae flavescentis, ameliorates hemodynamic disturbances and cardiac fibrosis; however, the underlying mechanisms are unclear. Here, we investigated the effect and mechanism of action of oxymatrine on aldosterone-induced cardiac fibroblast to myofibroblast differentiation in vitro.

METHODS

Cardiac fibroblasts were isolated purified from neonatal Sprague Dawley rats. The optimal concentration of aldosterone to stimulate cardiac fibroblast proliferation was determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Cardiac fibroblasts were pretreated with 7.57 × 10(-4) mol/L or 3.78 × 10(-4) mol/L oxymatrine or without oxymatrine for 2 h, and then coincubated with 1 × 10(-8) mol/L aldosterone for 48 h. The MTT assay and Masson staining were used to detect the cardiac fibroblast proliferation and myofibroblast differentiation. The secretion of type I and III collagen was measured by commercial ELISA kits, and the hydroxyproline content was determined by the colorimetric assay. Western blotting assayed the Smad-2, Smad-3, and Smad-4 protein expression in cardiac fibroblasts.

RESULTS

The present results confirmed that aldosterone induced cardiac fibroblast to myofibroblast proliferation and differentiation. The MTT assay and Masson staining indicated oxymatrine significantly inhibited aldosterone-induced cardiac fibroblast proliferation and myofibroblast differentiation. Oxymatrine significantly inhibited aldosterone-induced secretion of type I and III collagen, as indicated by commercial ELISA kits, and aldosterone-induced increase in hydroxyproline content, as indicated by a colorimetric assay. Western blotting revealed oxymatrine attenuated aldosterone-induced Smad-2, Smad-3, and Smad-4 expression in cardiac fibroblasts.

CONCLUSION

Oxymatrine can inhibit cardiac fibroblast proliferation and differentiation into myofibroblasts via a mechanism linked to attenuation of the Smad signaling pathway.

Update on RAAS Modulation for the Treatment of Diabetic Cardiovascular Disease

Since the advent of insulin, the improvements in diabetes detection and the therapies to treat hyperglycemia have reduced the mortality of acute metabolic emergencies, such that today chronic complications are the major cause of morbidity and mortality among diabetic patients. More than half of the mortality that is seen in the diabetic population can be ascribed to cardiovascular disease (CVD), which includes not only myocardial infarction due to premature atherosclerosis but also diabetic cardiomyopathy. The importance of renin-angiotensin-aldosterone system (RAAS) antagonism in the prevention of diabetic CVD has demonstrated the key role that the RAAS plays in diabetic CVD onset and development. Today, ACE inhibitors and angiotensin II receptor blockers represent the first line therapy for primary and secondary CVD prevention in patients with diabetes. Recent research has uncovered new dimensions of the RAAS and, therefore, new potential therapeutic targets against diabetic CVD. Here we describe the timeline of paradigm shifts in RAAS understanding, how diabetes modifies the RAAS, and what new parts of the RAAS pathway could be targeted in order to achieve RAAS modulation against diabetic CVD.

Aldosterone stimulates the cardiac sodium/bicarbonate cotransporter via activation of the g protein-coupled receptor gpr30

Some cardiac non-genomic effects of aldosterone (Ald) are reported to be mediated through activation of the classic mineralocorticoid receptor (MR). However, in the last years, it was proposed that activation of the novel G protein-coupled receptor GPR30 mediates certain non-genomic effects of Ald. The aim of this study was to elucidate if the sodium/bicarbonate cotransporter (NBC) is stimulated by Ald and if the activation of GPR30 mediates this effect. NBC activity was evaluated in rat cardiomyocytes perfused with HCO3(-)/CO2 solution in the continuous presence of HOE642 (sodium/hydrogen exchanger blocker) during recovery from acidosis using intracellular fluorescence measurements. Ald enhanced NBC activity (% of ΔJHCO3(-); control: 100±5.82%, n=7 vs Ald: 151.88±11.02%, n=5; P<0.05), which was prevented by G15 (GPR30 blocker, 90.53±7.81%, n=7). Further evidence for the involvement of GPR30 was provided by G1 (GPR30 agonist), which stimulated NBC (185.13±18.28%, n=6; P<0.05) and this effect was abrogated by G15 (124.19±10.96%, n=5). Ald- and G1-induced NBC stimulation was abolished by the reactive oxygen species (ROS) scavenger MPG and by the NADPH oxidase inhibitor apocynin. In addition, G15 prevented Ald- and G1-induced ROS production. Pre-incubation of myocytes with wortmannin (PI3K-AKT pathway blocker) prevented Ald- or G1-induced NBC stimulation. In summary, Ald stimulates NBC by GPR30 activation, ROS production and AKT stimulation.

Synthetic ligands of the elastin receptor induce elastogenesis in human dermal fibroblasts via activation of their IGF-1 receptors

BACKGROUND

We have previously reported that a mixture of peptides obtained after chemical or enzymatic degradation of bovine elastin, induced new elastogenesis in human skin.

OBJECTIVE

Now, we investigated the elastogenic potential of synthetic peptides mimicking the elastin-derived, VGVAPG sequence, IGVAPG sequence that we found in the rice bran, and a similar peptide, VGVTAG that we identified in the IGF-1-binding protein-1 (IGFBP-1).

RESULTS

We now demonstrate that treatment with each of these xGVxxG peptides (recognizable by the anti-elastin antibody), up-regulated the levels of elastin-encoding mRNA, tropoelastin protein, and the deposition of new elastic fibers in cultures of human dermal fibroblasts and in cultured explants of human skin. Importantly, we found that such induction of new elastogenesis may involve two parallel signaling pathways triggered after activation of IGF-1 receptor. In the first one, the xGVxxG peptides interact with the cell surface elastin receptor, thereby causing the downstream activation of the c-Src kinase and a consequent cross-activation of the adjacent IGF-1R, even in the absence of its principal ligand. In the second pathway their hydrophobic association with the N-terminal domain (VGVTAG) of the serum-derived IGFBP-1 induces conformational changes of this IGF-1 chaperone allowing for the release of its cargo and a consequent ligand-specific phosphorylation of IGF-1R.

CONCLUSION

We present a novel, clinically relevant mechanism in which products of partial degradation of dermal elastin may stimulate production of new elastic fibers by dermal fibroblasts. Our findings particularly encourage the use of biologically safe synthetic xGVxxG peptides for regeneration of the injured or aged human skin.

Aldosterone effects on glomerular structure and function

OBJECTIVE

Experimental evidence suggests that aldosterone directly contributes to organ damage by promoting cell growth, fibrosis, and inflammation. Based on these premises, this work aimed to assess the glomerular effects of aldosterone, alone and in combination with salt.

METHODS

After undergoing uninephrectomy, 75 rats were allocated to five groups: control, salt diet, aldosterone, aldosterone + salt diet, aldosterone + salt diet and eplerenone, and they were all studied for four weeks. We focused on glomerular structural, functional, and molecular changes, including slit diaphragm components, local renin-angiotensin system activation, as well as pro-oxidative and profibrotic changes.

RESULTS

Aldosterone significantly increased systolic blood pressure, led to glomerular hypertrophy, mesangial expansion, and it significantly increased the glomerular permeability to albumin and the albumin excretion rate, indicating the presence of glomerular damage. These effects were worsened by adding salt to aldosterone, while they were reduced by eplerenone. Aldosterone-induced glomerular damage was associated with glomerular angiotensin-converting enzyme (ACE) 2 downregulation, with ACE/ACE2 ratio increase, ANP decrease, as well as with glomerular pro-oxidative and profibrotic changes.

CONCLUSIONS

Aldosterone damages not only the structure but also the function of the glomerulus. ACE/ACE2 upregulation, ACE2 and ANP downregulation, and pro-oxidative and profibrotic changes are possible mechanisms accounting for aldosterone-induced glomerular injury.

Galectin-3 blockade inhibits cardiac inflammation and fibrosis in experimental hyperaldosteronism and hypertension

Hypertensive cardiac remodeling is accompanied by molecular inflammation and fibrosis, 2 mechanisms that finally affect cardiac function. At cardiac level, aldosterone promotes inflammation and fibrosis, although the precise mechanisms are still unclear. Galectin-3 (Gal-3), a β-galactoside-binding lectin, is associated with inflammation and fibrosis in the cardiovascular system. We herein investigated whether Gal-3 inhibition could block aldosterone-induced cardiac inflammation and fibrosis and its potential role in cardiac damage associated with hypertension. Aldosterone-salt-treated rats presented hypertension, cardiac inflammation, and fibrosis that were prevented by the pharmacological inhibition of Gal-3 with modified citrus pectin. Cardiac inflammation and fibrosis presented in spontaneously hypertensive rats were prevented by modified citrus pectin treatment, whereas Gal-3 blockade did not modify blood pressure levels. In the absence of blood pressure modifications, Gal-3 knockout mice were resistant to aldosterone-induced cardiac inflammation. In human cardiac fibroblasts, aldosterone increased Gal-3 expression via its mineralocorticoid receptor. Gal-3 and aldosterone enhanced proinflammatory and profibrotic markers, as well as metalloproteinase activities in human cardiac fibroblasts, effects that were not observed in Gal-3-silenced cells treated with aldosterone. In experimental hyperaldosteronism, the increase in Gal-3 expression was associated with cardiac inflammation and fibrosis, alterations that were prevented by Gal-3 blockade independently of blood pressure levels. These data suggest that Gal-3 could be a new molecular mechanism linking cardiac inflammation and fibrosis in situations with high-aldosterone levels, such as hypertension.

Gα13 Stimulates the Tyrosine Phosphorylation of Ric-8A

The G12 family of heterotrimeric G proteins is defined by their α-subunits, Gα₁₂ and Gα₁₃. These α-subunits regulate cellular homeostasis, cell migration, and oncogenesis in a context-specific manner primarily through their interactions with distinct proteins partners that include diverse effector molecules and scaffold proteins. With a focus on identifying any other novel regulatory protein(s) that can directly interact with Gα₁₃, we subjected Gα₁₃ to tandem affinity purification-coupled mass spectrometric analysis. Our results from such analysis indicate that Gα₁₃ potently interacts with mammalian Ric-8A. Our mass spectrometric analysis data also indicates that Ric-8A, which was tandem affinity purified along with Gα₁₃, is phosphorylated at Ser-436, Thr-441, Thr-443 and Tyr-435. Using a serial deletion approach, we have defined that the C-terminus of Gα₁₃ containing the guanine-ring interaction site is essential and sufficient for its interaction with Ric-8A. Evaluation of Gα₁₃-specific signaling pathways in SKOV3 or HeyA8 ovarian cancer cell lines indicate that Ric-8A potentiates Gα₁₃-mediated activation of RhoA, Cdc42, and the downstream p38MAPK. We also establish that the tyrosine phosphorylation of Ric-8A, thus far unidentified, is potently stimulated by Gα₁₃. Our results also indicate that the stimulation of tyrosine-phosphorylation of Ric-8A by Gα₁₃ is partially sensitive to inhibitors of Src-family of kinases, namely PP2 and SI. Furthermore, we demonstrate that Gα₁₃ promotes the translocation of Ric-8A to plasma membrane and this translocation is attenuated by the Src-inhibitors, SI1 and PP2. Thus, our results demonstrate for the first time that Gα₁₃ stimulates the tyrosine phosphorylation of Ric-8A and Gα₁₃-mediated tyrosine-phosphorylation plays a critical role in the translocation of Ric-8A to plasma membrane.

The impact of galectin-3 inhibition on aldosterone-induced cardiac and renal injuries

OBJECTIVES

This study investigated whether galectin (Gal)-3 inhibition could block aldosterone-induced cardiac and renal fibrosis and improve cardiorenal dysfunction.

BACKGROUND

Aldosterone is involved in cardiac and renal fibrosis that is associated with the development of cardiorenal injury. However, the mechanisms of these interactions remain unclear. Gal-3, a β-galactoside-binding lectin, is increased in heart failure and kidney injury.

METHODS

Rats were treated with aldosterone-salt combined with spironolactone (a mineralocorticoid receptor antagonist) or modified citrus pectin (a Gal-3 inhibitor), for 3 weeks. Wild-type and Gal-3 knockout mice were treated with aldosterone for 3 weeks. Hemodynamic, cardiac, and renal parameters were analyzed.

RESULTS

Hypertensive aldosterone-salt-treated rats presented cardiac and renal hypertrophy (at morphometric, cellular, and molecular levels) and dysfunction. Cardiac and renal expressions of Gal-3 as well as levels of molecular markers attesting fibrosis were also augmented by aldosterone-salt treatment. Spironolactone or modified citrus pectin treatment reversed all of these effects. In wild-type mice, aldosterone did not alter blood pressure levels but increased cardiac and renal Gal-3 expression, fibrosis, and renal epithelial-mesenchymal transition. Gal-3 knockout mice were resistant to aldosterone effects.

CONCLUSIONS

In experimental hyperaldosteronism, the increase in Gal-3 expression was associated with cardiac and renal fibrosis and dysfunction but was prevented by pharmacological inhibition (modified citrus pectin) or genetic disruption of Gal-3. These data suggest a key role for Gal-3 in cardiorenal remodeling and dysfunction induced by aldosterone. Gal-3 could be used as a new biotarget for specific pharmacological interventions.

Aldosterone synthase inhibitors in cardiovascular and renal diseases

Aldosterone is involved in various cardiovascular pathologies, including hypertension, heart failure, atherosclerosis and fibrosis. Mineralocorticoid receptor (MR)-dependent and -independent, genomic and non-genomic processes mediate its complex effects. Spironolactone and eplerenone, both MR antagonists, are the only commercially available compounds targeting directly the actions of aldosterone. However, due to the poor selectivity (spironolactone), low potency (eplerenone) and the fact that only MR-dependent effects of aldosterone can be inhibited, these drugs have limited clinical use. An attractive approach to abolish potentially all of aldosterone-mediated pathologies is the inhibition of aldosterone synthase. This review summarizes current knowledge on the complex effects mediated by aldosterone, potential advantages and disadvantages of aldosterone inhibition and novel directions in the development of aldosterone synthase inhibitors.

Preconditioning actions of aldosterone through p38 signaling modulation in isolated rat hearts

Although persistent excessive actions of aldosterone have unfavorable effects on the cardiovascular system, primarily via mineralocorticoid receptor (MR)-dependent pathways, the pathophysiological significance of aldosterone cascade activation in heart diseases has not yet been fully clarified. We herein examined the effects of short-term aldosterone stimulation at a physiological dose on cardiac function during ischemia-reperfusion injury (IRI). In order to study the effects of aldosterone preconditioning, male Wistar rat Langendorff hearts were perfused with 10(-9) mol/l of aldosterone for 10 min before ischemia, and the response to IRI was assessed. Although aldosterone did not affect the baseline hemodynamic parameters, preconditioning actions of aldosterone significantly improved the recovery in left ventricular contractility and left ventricular end-diastolic pressure associated with a reduced activity of creatine phosphokinase released into the perfusate after ischemia-reperfusion. Notably, the MR inhibitor eplerenone did not abrogate these beneficial effects. Biochemical analyses revealed that p38MAPK phosphorylation was significantly increased during aldosterone preconditioning before ischemia, whereas its phosphorylation was substantially attenuated during sustained ischemia-reperfusion, compared with the results for in the non-preconditioned control hearts. This dual regulation of p38MAPK was not affected by eplerenone. The phosphorylation levels of other MAPKs were not altered by aldosterone preconditioning. In conclusion, the temporal induction of the aldosterone cascade, at a physiological dose, has favorable effects on cardiac functional recovery and injury following ischemia-reperfusion in a MR-independent manner. Phasic dynamism of p38MAPK activation may play a key role in the physiological compensatory pathway of aldosterone under severe cardiac pathological conditions.

A Blk-p190RhoGAP signaling module downstream of activated Gα13 functionally opposes CXCL12-stimulated RhoA activation and cell invasion

Activation of the GTPase RhoA linked to cell invasion can be tightly regulated following Gα13 stimulation. We have used a cellular model displaying Gα13-dependent inhibition of RhoA activation associated with defective cell invasion to the chemokine CXCL12 to characterize the molecular players regulating these processes. Using both RNAi transfection approaches and protein overexpression experiments here we show that the Src kinase Blk is involved in Gα13-activated tyrosine phosphorylation of p190RhoGAP, which causes RhoA inactivation and ultimately leads to deficient cell invasion. Characterization of molecular interplays between Gα13, Blk and p190RhoGAP revealed that Blk binds Gα13, and that Blk-mediated p190RhoGAP phosphorylation upon Gα13 activation correlates with weakening of Gα13-Blk association connected to increased Blk-p190RhoGAP assembly. These results place Blk upstream of the p190RhoGAP-RhoA pathway in Gα13-activated cells, overall representing an opposing signaling module during CXCL12-triggered invasion. In addition, analyses with Blk- or Gα13-knockdown cells indicated that Blk can also mediate CXCL12-triggered phosphorylation of p190RhoGAP independently of Gα13. However, even if CXCL12 induces the Blk-mediated GAP phosphorylation, the simultaneous stimulation of the guanine-nucleotide exchange factor Vav1 by the chemokine, as earlier reported, leads to a net increase in RhoA activation. Therefore, when Gα13 is concurrently stimulated with CXCL12 there appears to be sufficient Blk activity to promote adequate levels of p190RhoGAP tyrosine phosphorylation to inactivate RhoA and to impair cell invasiveness.

Soluble Adenylyl Cyclase in Vascular Endothelium

The Ca 2+ - and bicarbonate-activated soluble adenylyl cyclase (sAC) has been identified recently as an important mediator of aldosterone signaling in the kidney. Nuclear sAC has been reported to stimulate cAMP response element–binding protein 1 phosphorylation via protein kinase A, suggesting an alternative cAMP pathway in the nucleus. In this study, we analyzed the sAC as a potential modulator of endothelial stiffness in the vascular endothelium. We determined the contribution of sAC to cAMP response element–mediated transcriptional activation in vascular endothelial cells and kidney collecting duct cells. Inhibition of sAC by the specific inhibitor KH7 significantly reduced cAMP response element–mediated promoter activity and affected cAMP response element–binding protein 1 phosphorylation. Furthermore, KH7 and anti-sAC small interfering RNA significantly decreased mRNA and protein levels of epithelial sodium channel-α and Na + /K + -ATPase-α. Using atomic force microscopy, a nano-technique that measures stiffness and deformability of living cells, we detected significant endothelial cell softening after sAC inhibition. Our results suggest that the sAC is a regulator of gene expression involved in aldosterone signaling and an important regulator of endothelial stiffness. Additional studies are warranted to investigate the protective action of sAC inhibitors in humans for potential clinical use.

Phytoestrogen, tanshinone IIA diminishes collagen deposition and stimulates new elastogenesis in cultures of human cardiac fibroblasts

It has been previously reported that oral or intra-peritoneal administration of tanshinone IIA can alleviate the ventricular hypertrophy and fibrosis that develops in rats after experimental cardiac infarction. Our present studies, performed on cultures of human cardiac fibroblasts, investigated the mechanism by which tanshinone IIA produces these beneficial effects. We found that treatment of cardiac fibroblasts with 0.1-10µM tanshinone IIA significantly inhibited their deposition of collagen I, while enhancing production of new elastic fibers. Moreover, both anti-collagenogenic and pro-elastogenic effects of tanshinone IIA occurred only after selective activation of the G protein-coupled estrogen receptor (GPER). This subsequently leads to initiation of the PKA/CREB phosphorylation pathway that inversely modulated transcription of collagen I and elastin genes. Interestingly, treatment of human cardiac fibroblasts with tanshinone IIA additionally up-regulated the production of the 67-kDa elastin binding protein, which facilitates tropoelastin secretion, and increased synthesis of lysyl oxidase, catalyzing cross-linkings of tropoelastin. Moreover, tanshinone IIA also caused up-regulation in the synthesis of collagenolytic MMP-1, but down-regulated levels of elastolytic MMP-2 and MMP-9. In summary, our data validate a novel mechanism in which tanshinone IIA, interacting with a non-classic estrogen receptor, maintains the proper balance between the net deposition of collagen and elastin, allowing for optimal durability and resiliency of the newly deposited matrix.

Aldosterone stimulates fibronectin synthesis in renal fibroblasts through mineralocorticoid receptor-dependent and independent mechanisms

In addition to its role in regulation of salt transport in the kidney, the mineralocorticoid hormone aldosterone plays an independent role as a mediator of kidney injury and progression of chronic kidney disease. Studies in both animal models and patients have shown that aldosterone enhances the accumulation of extracellular matrix and progression of fibrosis in the kidney. However, the cellular mechanisms that lead to aldosterone-dependent fibrogenesis are poorly understood. In this study we find that aldosterone stimulates fibronectin synthesis through mineralocorticoid receptor (MCR) dependent activation of the c-Jun NH2-terminal protein kinase (JNK) and subsequent phosphorylation of the AP1 transcription factor c-jun, which forms a nuclear complex with the mineralocorticoid receptor in a kidney fibroblast cell line (NRK 49f). Furthermore, MCR-independent phosphorylation of Src family kinase induces IgF1 receptor phosphorylation, which leads to stimulation of the extracellular signal-regulated kinase (ERK1/2) to enhanced fibronectin synthesis. We further find that the IgF1-R-dependent signaling pathway activates fibronectin expression faster than the MCR-dependent pathway. We propose that the mechanisms described in this study are important to aldosterone-dependent progression of interstitial fibrosis in the kidney. Due to the duality of aldosterone-dependent activation of fibronectin synthesis in kidney fibroblasts, MCR-specific inhibitors may not entirely prevent the progression of fibrosis by aldosterone in the kidney.

Evolving research in nongenomic actions of aldosterone

PURPOSE OF REVIEW

Aldosterone is now recognized as an increasingly important contributor to cardiometabolic pathology via inflammatory and fibrosis-related pathways in addition to its classically described role in sodium and volume regulation. Consequently, much effort has been directed towards characterizing the molecular pathways involved in aldosterone-mediated fibrosis and inflammation. What was once viewed as straightforward steroid hormone biology is now appreciated as a highly complex and tightly regulated series of pathways and interactions. These recognitions have fuelled a multidisciplinary effort to identify precisely how aldosterone mediates intracellular activation of both genomic (latent) and nongenomic (rapid) mechanisms of influence. This review will explore recent novel pathways regulating aldosterone action, focusing on the nongenomic pathways.

RECENT FINDINGS

Several recent discoveries have redefined our understanding of aldosterone interactions at the cellular level. This includes activation of the mineralocorticoid receptor at the plasma membrane instead of via classical nuclear hormone receptor interaction, and identification of novel cofactor scaffolding proteins that modify aldosterone influence at the cellular level. In addition, aldosterone activation of secondary messenger system cascades can occur directly and independent of mineralocorticoid receptor interaction.

SUMMARY

Substantial progress in detailing the molecular biology of aldosterone regulation and action should facilitate study of how it exerts detrimental effects in cardiometabolic diseases. However, to date, the clinical impact of these discoveries has not been validated. Translational efforts are now required to determine if novel therapeutic targets can be developed.

Emphysema in an adult with galactosialidosis linked to a defect in primary elastic fiber assembly

Galactosialidosis is a lysosomal storage disorder caused by loss of function of protective protein cathepsin A, which leads to secondary deficiencies of β-galactosidase and neuraminidase-1. Emphysema has not been previously reported as a possible complication of this disorder, but we now describe this condition in a 41-year-old, non-smoking male. Our patient did not display deficiency in α-1-antitrypsin, the most common cause of emphysema in non-smokers, which brings about disseminated elastolysis. We therefore hypothesized that loss of cathepsin A activity was responsible because of previously published evidence showing it is prerequisite for normal elastogenesis. We now present experimental evidence to support this theory by demonstrating impaired primary elastogenesis in cultures of dermal fibroblasts from our patient. The obtained data further endorse our previous finding that functional integrity of the cell surface-targeted molecular complex of cathepsin A, neuraminidase-1 and the elastin-binding protein (spliced variant of β-galactosidase) is prerequisite for the normal assembly of elastic fibers. Importantly, we also found that elastic fiber production was increased after exposure either to losartan, spironolactone, or dexamethasone. Of immediate clinical relevance, our data suggest that surviving patients with galactosialidosis should have periodic assessment of their pulmonary function. We also encourage further experimental exploration of therapeutic potential of the afore-mentioned elastogenesis-stimulating drugs for the alleviation of pathological processes in galactosialidosis that could be mechanistically linked to impaired deposition of elastic fibers.

Tissue-specific modulation of mineralocorticoid receptor function by 11β-hydroxysteroid dehydrogenases: an overview

In the last decade significant progress has been made in the understanding of mineralocorticoid receptor (MR) function and its implications for physiology and disease. The knowledge on the essential role of MR in the regulation of electrolyte concentrations and blood pressure has been significantly extended, and the relevance of excessive MR activation in promoting inflammation, fibrosis and heart disease as well as its role in modulating neuronal cell viability and brain function is now widely recognized. Despite considerable progress, the mechanisms of MR function in various cell-types are still poorly understood. Key modulators of MR function include the glucocorticoid receptor (GR), which may affect MR function by formation of heterodimers and by differential genomic and non-genomic responses on gene expression, and 11β-hydroxysteroid dehydrogenases (11β-HSDs), which determine the availability of intracellular concentrations of active glucocorticoids. In this review we attempted to provide an overview of the knowledge on MR expression with regard to the presence or absence of GR, 11β-HSD2 and 11β-HSD1/hexose-6-phosphate dehydrogenase (H6PDH) in various tissues and cell types. The consequences of cell-specific differences in the coexpression of MR with these proteins need to be further investigated in order to understand the role of this receptor in a given tissue as well as its systemic impact.

Insulin induces production of new elastin in cultures of human aortic smooth muscle cells

Diabetes mellitus accelerates atherosclerotic progression, peripheral angiopathy development, and arterial hypertension, all of which are associated with elastic fiber disease. However, the potential mechanistic links between insulin deficiency and impaired elastogenesis in diabetes have not been explored. Results of the present study reveal that insulin administered in therapeutically relevant concentrations (0.5 to 10 nmol/L) selectively stimulates formation of new elastic fibers in cultures of human aortic smooth muscle cells. These concentrations of insulin neither up-regulate collagen type I and fibronectin deposition nor stimulate cellular proliferation. Further, the elastogenic effect of insulin occurs after insulin receptor activation, which triggers the PI3K downstream signaling pathway and activates elastin gene transcription. In addition, the promoter region of the human elastin gene contains the CAAATAA sequence, consistent with the FoxO-recognized element, and the genomic effects of insulin occur after removal of the FoxO1 transcriptional inhibitor from the FoxO-recognized element in the elastin gene promoter. In addition, insulin signaling facilitates the association of tropoelastin with its specific 67-kDa elastin-binding protein/spliced form of β-galactosidase chaperone, enhancing secretion. These results are crucial to understanding of the molecular and cellular mechanisms of diabetes-associated vascular disease, and, in particular, endorse use of insulin therapy for treatment of atherosclerotic lesions in patients with type 1 diabetes, in which induction of new elastic fibers would mechanically stabilize the developing plaques and prevent arterial occlusions.

Aldosterone as a modulator of immunity: implications in the organ damage

High plasmatic levels of aldosterone cause hypertension and contribute to progressive organ damage to the heart, vasculature, and kidneys. Recent studies have demonstrated a role for the immune system in these pathological processes. Aldosterone promotes an inflammatory state characterized by vascular infiltration of immune cells, reactive oxidative stress, and proinflammatory cytokine production. Further, cells of the adaptive immune system, such as T cells, seem to participate in the genesis of mineralocorticoid hormone-induced hypertension. In addition, the observation that aldosterone can promote CD4⁺ T-cell activation and Th17 polarization suggests that this hormone could contribute to the onset of autoimmunity. Here we discuss recent evidence supporting a significant involvement of the immune system, especially adaptive immunity, in the genesis of hypertension and organ damage induced by primary aldosteronism. In addition, possible new therapeutic approaches consisting of immunomodulator drugs to control exacerbated immune responses triggered by elevated aldosterone concentrations will be described.

Unraveling the mechanisms underlying the rapid vascular effects of steroids: sorting out the receptors and the pathways

Aldosterone, oestrogens and other vasoactive steroids are important physiological and pathophysiological regulators of cardiovascular and metabolic function. The traditional view of the cardiovascular actions of these vasoactive steroids has focused on their roles as regulators of transcription via activation of their 'classical' receptors [mineralocorticoid receptors (MR) and oestrogen receptors (ER)]. However, based on a series of observations going back more than half a century, scientists have speculated that a range of steroids, including oestrogen and aldosterone, might have effects on regulation of smooth muscle contractility, cell growth and differentiation that are too rapid to be accounted for by transcriptional regulation. Recent studies performed in our laboratories (and those of others) have begun to elucidate the mechanism of rapid steroid-mediated cardiometabolic regulation. GPR30, now designated as GPER-1 (http://www.iuphar-db.org/DATABASE/FamilyIntroductionForward?familyId=22), a newly characterized 'orphan receptor', has been implicated in mediating the rapid effects of estradiol and most recently those of aldosterone. Studies to date have taught us that to understand the rapid vascular mechanisms of steroids, one must (i) know which vascular 'compartment' the steroid is acting; (ii) know which receptor the steroid hormone is activating; and (iii) not assume the receptor specificity of a steroid receptor ligand based solely on its selectivity for its traditional 'transcriptional' steroid receptor. Our newfound appreciation of the rapid effects of steroids such as aldosterone and oestrogens opens up a new vista for advancing our understanding of the biology and pathobiology of vascular regulation.

GPR30 expression is required for the mineralocorticoid receptor-independent rapid vascular effects of aldosterone

It has been increasingly appreciated that steroids elicit acute vascular effects through rapid, so-called nongenomic signaling pathways. Though aldosterone, for example, has been demonstrated to mediate rapid vascular effects via both mineralocorticoid receptor-dependent and -independent pathways, the mechanism(s) of this mineralocorticoid receptor-independent effect of aldosterone is yet to be determined. For estrogen, its rapid effects have been reported to be, at least in part, mediated via the 7-transmembrane-spanning, G protein-coupled receptor GPR30. Previous studies have demonstrated common response outcomes in response to both aldosterone and estrogen on GPR30 expression, ie, activation of phosphatidylinositol 3-kinase-dependent contraction and extracellular signal-regulated kinase activation in vascular smooth muscle cells. The present studies were undertaken to test the hypothesis that the rapid response to aldosterone in smooth muscle is dependent on the availability of a GPR30-dependent signaling pathway. These findings not only reconcile differences in the literature for aldosterone response in freshly isolated versus cultured aortic smooth muscle cells but also suggest alternative therapeutic strategies for modulating aldosterone actions on the vasculature in vivo.

The hyperthermia-enhanced association between tropoelastin and its 67-kDa chaperone results in better deposition of elastic fibers

The results of our in vitro experiments indicate that exposing cultured human aortic smooth muscle cells and dermal fibroblasts to 39 to 41 °C induces a significant up-regulation in the net deposition of elastic fibers, but not of collagen I or fibronectin, and also decreases the deposition of chondroitin sulfate-containing moieties. We further demonstrate that mild hyperthermia also rectifies the insufficient elastogenesis notable in cultures of fibroblasts derived from the stretch-marked skin of adult patients and in cultures of dermal fibroblasts from children with Costello syndrome, which is characterized by the accumulation of chondroitin 6-sulfate glycosaminoglycans that induce shedding and inactivation of the 67-kDa elastin-binding protein. We have previously established that this protein serves as a reusable chaperone for tropoelastin and that its recycling is essential for the normal deposition of elastic fibers. We now report that hyperthermia not only inhibits deposition of chondroitin 6-sulfate moieties and the consequent preservation of elastin-binding protein molecules but also induces their faster recycling. This, in turn, triggers a more efficient preservation of tropoelastin, enhancement of its secretion and extracellular assembly into elastic fibers. The presented results encourage using mild hyperthermia to restore elastic fiber production in damaged adult skin and to enhance elastogenesis in children with genetic elastinopathies.

Aldosterone and mineralocorticoid receptor antagonists modulate elastin and collagen deposition in human skin

We have shown that the steroid hormone aldosterone, recognized for its action on the kidney and the cardiovascular system, also modulates deposition of extracellular matrix in human skin. We have shown that treatment of primary cultures of normal skin fibroblasts with aldosterone (10 n-1 μM), in addition to stimulation of collagen type I expression, induces elastin gene expression and elastic fiber deposition. We have further shown that the elastogenic effect of aldosterone, which can be enhanced in the presence of mineralocorticoid receptor (MR) antagonists spironolactone and eplerenone, is executed in a MR-independent manner via amplification of IGF-I receptor-mediated signaling. Because aldosterone applied alone stimulates both collagen and elastin deposition in cultures of fibroblasts and in cultures of skin explants derived from dermal stretch marks, we postulate that this steroid should be used in the treatment of damaged skin that loses its volume and elasticity. Moreover, aldosterone applied in conjunction with spironolactone or eplerenone induces matrix remodeling and exclusively enhances elastogenesis in cultures of fibroblasts and explants derived from dermal scars and keloids. We therefore propose that intra-lesional injection of these factors should be considered in therapy for disfiguring dermal lesions and especially in prevention of their recurrence after surgical excision.

Regulation of mineralocorticoid receptor expression during neuronal differentiation of murine embryonic stem cells

Mineralocorticoid receptor (MR) plays a critical role in brain function. However, the regulatory mechanisms controlling neuronal MR expression that constitutes a key element of the hormonal response are currently unknown. Two alternative P1 and P2 promoters drive human MR gene transcription. To examine promoter activities and their regulation during neuronal differentiation and in mature neurons, we generated stably transfected recombinant murine embryonic stem cell (ES) lines, namely P1-GFP and P2-GFP, in which each promoter drove the expression of the reporter gene green fluorescent protein (GFP). An optimized protocol, using embryoid bodies and retinoic acid, permitted us to obtain a reproducible neuronal differentiation as revealed by the decrease in phosphatase alkaline activity, the concomitant appearance of morphological changes (neurites), and the increase in the expression of neuronal markers (nestin, beta-tubulin III, and microtubule-associated protein-2) as demonstrated by immunocytochemistry and quantitative PCR. Using these cell-based models, we showed that MR expression increased by 5-fold during neuronal differentiation, MR being preferentially if not exclusively expressed in mature neurons. Although the P2 promoter was always weaker than the P1 promoter during neuronal differentiation, their activities increased by 7- and 5-fold, respectively, and correlated with MR expression. Finally, although progesterone and dexamethasone were ineffective, aldosterone stimulated both P1 and P2 activity and MR expression, an effect that was abrogated by knockdown of MR by small interfering RNA. In conclusion, we provide evidence for a tight transcriptional control of MR expression during neuronal differentiation. Given the neuroprotective and antiapoptotic role proposed for MR, the neuronal differentiation of ES cell lines opens potential therapeutic perspectives in neurological and psychiatric diseases.

Extracellular matrix remodeling in atrial fibrosis: mechanisms and implications in atrial fibrillation

Atrial fibrosis has been strongly associated with the presence of heart diseases/arrhythmias, including congestive heart failure (CHF) and atrial fibrillation (AF). Inducibility of AF as a result of atrial fibrosis has been the subject of intense recent investigation since it is the most commonly encountered arrhythmia in adults and can substantially increase the risk of premature death. Rhythm and rate control drugs as well as surgical interventions are used as therapies for AF; however, increased attention has been diverted to mineralocorticoid receptor (MR) antagonists including spironolactone as potential therapies for human AF because of their positive effects on reducing atrial fibrosis and associated AF in animal models. Spironolactone has been shown to exert positive effects in human patients with heart failure; however, the mechanisms and effects in human atrial fibrosis and AF remain undetermined. This review will discuss and highlight developments on (i) the relationship between atrial fibrosis and AF, (ii) spironolactone, as a drug targeted to atrial fibrosis and AF, as well as (iii) the distinct and common mechanisms important for regulating atrial and ventricular fibrosis, inclusive of the key extracellular matrix regulatory proteins involved.