Regulation of aldosterone synthesis and secretion

Long-term triphenyltin exposure disrupts adrenal function in adult male rats

Triphenyltin is an organotin, which is widely used as a fungicide in agriculture. Here, we reported the effects of triphenyltin on adrenal function in adult male rats. Adult male Sprague Dawley rats were daily gavaged with triphenyltin (0, 0.5, 1, and 2 mg/kg body weight) from postnatal day 56-86. Triphenyltin significantly decreased serum corticosterone levels at 1 and 2 mg/kg without affecting serum levels of aldosterone and adrenocorticotropic hormone. Triphenyltin increased thickness of zona glomerulosa without affecting that of zona fasciculata. Triphenyltin did not affect cell number in zona fasciculata and zona glomerulosa. Triphenyltin down-regulated the expression of Scarb1, Star, Cyp11a1, Hsd3b1, Cyp21, Cyp11b1, and Hsd11b1 at 1 and/or 2 mg/kg while it up-regulated the expression of At1, Nr4a2, and Hsd11b2 at 2 mg/kg. Triphenyltin activated the phosphorylation of AMPKα while suppressed the phosphorylation of AKT1 and SIRT1/PGC-1α in rat adrenals in vivo and H295R cells in vitro. In vitro, triphenyltin also induced ROS production in H295R cells at 100 nM, a concentration at which no apoptosis was induced. In conclusion, triphenyltin disrupts glucocorticoid synthesis in rat adrenal cortex via several mechanisms: 1) lowering AKT1 phosphorylation and SIRT1/PGC-1α levels; 2) activating AMPKα; and 3) possibly inducing ROS production.

Effects of eplerenone on cerebral aldosterone levels and brain lesions in spontaneously hypertensive rats

Evidence indicates that renin-angiotensin-aldosterone system (RAS) inhibitors can protect the brain in Alzheimer's disease and Parkinson's disease. The current study evaluated the relationship between aldosterone and tissue damage in the brains of spontaneously hypertensive rats (SHRs) and whether the RAS inhibitor eplerenone can mitigate the damage seen in these rats. SHRs were randomly divided into eplerenone (n = 10) and SHR (n = 10) groups, and Wistar-Kyoto (WKY) rats (n = 10) were used as controls. Eplerenone 50 mg/kg/day was administered orally to the eplerenone group. Pathological changes to the hippocampal formation, plasma and encephalic aldosterone, and plasma potassium levels were compared among the groups. After 10 weeks, rats in the eplerenone and SHR groups showed higher systolic BP (p = .01) than the control group. Aldosterone levels in the brain were higher in the SHR group (0.20 ± 0.06 pg/ml) than in the eplerenone (0.14 ± 0.05 pg/ml, p = .044) or control (0.12 ± 0.07 pg/ml, p = .007) groups. Plasma aldosterone levels in the SHR group were 1.7 times higher than those in the control group (p = .006). Cerebral cortex was thinner in the SHR group (225.18 ± 15.43 μm) than in the eplerenone (240.38 ± 12.85 μm, p < .01) or control (244.72 ± 18.92 μm, p < .01) groups. Thickness did not differ between the latter two groups. The SHR group exhibited apoptotic cells in the hippocampal formation, which were rare in the eplerenone and control groups. Plasma potassium levels were higher in the eplerenone group than those in the other two groups (p < .05). Our results showed that eplerenone can alleviate brain damage (thinning of cortex and increased apoptosis) caused by aldosterone in a rat model of hypertension.

Dry Fasting Physiology: Responses to Hypovolemia and Hypertonicity

OBJECTIVE

The aim of this study was to provide a deeper insight into dry fasting (DF) physiology.

DESIGN

Ten participants performed DF for 5 consecutive days.

METHODS

The following parameters were monitored daily: cortisol, aldosterone, high-sensitivity C-reactive protein (CRP), erythropoietin, albumin, uric acid, and vitamin C in serum; vasopressin (ADH), adrenocorticotropic hormone (ACTH), renin, angiotensin II, and total antioxidant capacity (TAC) in plasma; hematocrit and erythrocytes in whole blood; osmolality, noradrenaline, dopamine, adrenaline, Na+, and K+ in 24-h urine; waist circumference and body, urine, and stool weight.

RESULTS

The following parameters increased: ADH (60 ± 11%), ACTH (176 ± 34%), cortisol (495 ± 75%), urine osmolality (20 ± 4%), CRP (167 ± 77%), renin (315 ± 63%), angiotensin II (74 ± 21%), aldosterone (61 ± 21%), TAC (80.4 ± 17%), uric acid (103 ± 19%), albumin (18.4 ± 2.4%), erythrocytes (13.4 ± 2.2%), hematocrit (11 ± 1.8%), and the excretion of noradrenaline (40.3 ± 10%) and dopamine (17 ± 5%). The following parameters decreased: waist circumference (8.20 ± 0.61 cm), body weight (7.010 ± 0.3 kg), erythropoietin (65 ± 18%), and the excretion of adrenaline (38 ± 4%) and Na+ (60 ± 16%). The excretion of K+ remained unchanged. Vitamin C decreased, showing a half-life of 4.8 ± 0.7 days. The percent ratios of lost weight components were: urine (52.2 ± 3.7%), insensible water loss (32.2 ± 1.4%), stool (5 ± 0.3%), and respiratory gases, i.e., expired CO2 - incorporated O2 (10.6 ± 5.4%).

CONCLUSION

The mechanisms underlying the hypertonicity and hypovolemia compensation and the ratio analysis of lost weight components were presented. DF demonstrated short-term antioxidant, anti-ischemic, immune-stimulating, anti-edematous, and anti-inflammatory effects. The results may have an impact on developing new concepts for the treatment of edema, obesity, and inflammatory and ischemic diseases.

The role of miRNAs in regulating adrenal and gonadal steroidogenesis

miRNAs are endogenous noncoding single-stranded small RNAs of ~22 nucleotides in length that post-transcriptionally repress the expression of their various target genes. They contribute to the regulation of a variety of physiologic processes including embryonic development, differentiation and proliferation, apoptosis, metabolism, hemostasis and inflammation. In addition, aberrant miRNA expression is implicated in the pathogenesis of numerous diseases including cancer, hepatitis, cardiovascular diseases and metabolic diseases. Steroid hormones regulate virtually every aspect of metabolism, and acute and chronic steroid hormone biosynthesis is primarily regulated by tissue-specific trophic hormones involving transcriptional and translational events. In addition, it is becoming increasingly clear that steroidogenic pathways are also subject to post-transcriptional and post-translational regulations including processes such as phosphorylation/dephosphorylation, protein‒protein interactions and regulation by specific miRNAs, although the latter is in its infancy state. Here, we summarize the recent advances in miRNA-mediated regulation of steroidogenesis with emphasis on adrenal and gonadal steroidogenesis.

The Effects of Different Calcium Channel Blockers on Aldosterone-Producing Adenoma Cells

Purpose: The aim of this study is to examine the effects of different kinds of calcium channel blockers (CCBs) on primary aldosterone-producing adenoma (APA) mainly with KCNJ5 mutations. Primary cultured APA cells were treated with different calcium channel blockers (L/T type CCB benidipine, T-type CCB mibefradil and L-type CCB nifedipine), and aldosterone secretagogues with or without nifedipine. Aldosterone level, aldosterone synthase (CYP11B2) mRNA expression and cell proliferation were detected. The results showed that all three CCBs significantly inhibit aldosterone secretion and CYP11B2 mRNA expression. Benidipine was relatively more effective than mibefradil or nifedipine. In addition, only mibefradil marginally inhibited cell proliferation. Adrenocorticotropin (ACTH) had a much stronger effect in stimulating aldosterone secretion and promoting cell proliferation from APA's than angiotensin II (ATII). Different from ACTH and ATII, potassium had no effect. Nifedipine inhibited the basal and ACTH-, ATII-elicited aldosterone secretion. Twenty three of 24 APAs had somatic KCNJ5 mutation. In conclusion, benidipine, mibefradil and nifedipine significantly inhibit aldosterone secretion in primary cultured APA cells.

Steroidogenic acute regulatory protein/aldosterone synthase mediates angiotensin II-induced cardiac fibrosis and hypertrophy

Aldosterone produced in adrenal glands by angiotensin II (Ang II) is known to elicit myocardial fibrosis and hypertrophy. This study was designed to test the hypothesis that Ang II causes cardiac morphological changes through the steroidogenic acute regulatory protein (StAR)/aldosterone synthase (AS)-dependent aldosterone synthesis primarily initiated in the heart. Sprague-Dawley rats were randomized to following groups: Ang II infusion for a 4-week period, treatment with telmisartan, spironolactone or adrenalectomy during Ang II infusion. Sham-operated rats served as control. Relative to Sham rats, Ang II infusion significantly increased the protein levels of AT1 receptor, StAR, AS and their tissue expression in the adrenal glands and heart. In coincidence with reduced aldosterone level in the heart, telmisartan, an AT1 receptor blocker, significantly down-regulated the protein level and expression of StAR and AS. Ang II induced changes in the expression of AT1/StAR/AS were not altered by an aldosterone receptor antagonist spironolactone. Furthermore, Ang II augmented migration of macrophages, protein level of TGFβ1, phosphorylation of Smad2/3 and proliferation of myofibroblasts, accompanied by enhanced perivascular/interstitial collagen deposition and cardiomyocyte hypertrophy, which all were significantly abrogated by telmisartan or spironolactone. However, adrenalectomy did not fully suppress Ang II-induced cell migration/proliferation and fibrosis/hypertrophy, indicating a role of aldosterone synthesized within the heart in pathogenesis of Ang II induced injury. These results indicate that myocardial fibrosis and hypertrophy stimulated by Ang II is associated with tissue-specific activation of aldosterone synthesis, primarily mediated by AT1/StAR/AS signaling pathways.

Impaired 11β-Hydroxysteroid Dehydrogenase Type 2 in Glucocorticoid-Resistant Patients

CONTEXT

Six patients carrying heterozygous loss-of-function mutations of glucocorticoid (GC) receptor (GR) presented with hypercortisolism, associated with low kalemia, low plasma renin, and aldosterone levels, with or without hypertension, suggesting a pseudohypermineralocorticism whose mechanisms remain unclear. We hypothesize that an impaired activity of the 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2; encoded by the HSD11B2 gene), catalyzing cortisol (F) inactivation, may account for an inappropriate activation of a renal mineralocorticoid signaling pathway in these GC-resistant patients.

OBJECTIVE

We aim at studying the GR-mediated regulation of HSD11B2.

DESIGN

The HSD11B2 promoter was subcloned and luciferase reporter assays evaluated GR-dependent HSD11B2 regulation, and 11β-HSD2 expression/activity was studied in human breast cancer MCF7 cells, endogenously expressing this enzyme.

RESULTS

Transfection assays revealed that GR transactivated the long (2.1-kbp) HSD11B2 promoter construct, whereas a defective 501H GR mutant was unable to stimulate luciferase activity. GR-mediated transactivation of the HSD11B2 gene was inhibited by the GR antagonist RU486. A threefold increase in HSD11B2 mRNA levels was observed after dexamethasone (DXM) treatment of MCF7 cells, inhibited by RU486 or by actinomycin, supporting a GR-dependent transcription. Chromatin immunoprecipitation further demonstrated a DXM-dependent GR recruitment onto the HSD11B2 promoter. 11β-HSD2 activity, evaluated by the cortisone/F ratio, quantified by liquid chromatography/tandem mass spectrometry, was 10-fold higher in the supernatant of DXM-treated cells than controls, consistent with a GR-dependent stimulation of 11β-HSD2 catalytic activity.

CONCLUSION

Collectively, we demonstrate that 11β-HSD2 expression and activity are transcriptionally regulated by GR. In the context of GR haploinsufficiency, these findings provide evidence that defective GR signaling may account for apparent mineralocorticoid excess in GC-resistant patients.

Aldosterone Rapidly Enhances Levels of the Striatin and Caveolin-1 Proteins in Rat Kidney: The Role of the Mineralocorticoid Receptor

BACKGROUND

Striatin and caveolin-1 (cav-1) are scaffolding/regulating proteins that are associated with salt-sensitive high blood pressure and promote renal sodium and water reabsorption, respectively. The mineralocorticoid receptor (MR) interacts with striatin and cav-1, while aldosterone increases striatin and cav-1 levels. However, no in vivo data have been reported for the levels of these proteins in the kidney.

METHODS

Male Wistar rats were intraperitoneally injected with normal saline solution, aldosterone alone (Aldo: 150 μg/kg body weight), or aldosterone after pretreatment with eplerenone, an MR blocker, 30 minutes before the aldosterone injection (eplerenone [Ep.]+Aldo). Thirty minutes after the aldosterone injection, the amount and localization of striatin and cav-1 were determined by Western blot analysis and immunohistochemistry, respectively.

RESULTS

Aldosterone increased striatin levels by 150% (P<0.05), and cav-1 levels by 200% (P<0.001). Eplerenone had no significant effect on striatin levels, but partially blocked the aldosterone-induced increase in cav-1 levels. Aldosterone stimulated striatin and cav-1 immunoreactivity in both the cortex and medulla. Eplerenone reduced cav-1 immunostaining in both areas; however, striatin intensity was reduced in the cortex, but increased in the medulla.

CONCLUSION

This is the first in vivo study demonstrating that aldosterone rapidly enhances renal levels of striatin and cav-1. Aldosterone increases striatin levels via an MR-independent pathway, whereas cav-1 is partially regulated through MR.

Short-term exposure to 12‰ brackish water has significant effects on the endocrine physiology of juvenile American alligator (Alligator mississippiensis)

American alligators (Alligator mississippiensis) mainly inhabit freshwater habitats but can be exposed to a wide range of salinities during storm surges, droughts or from alterations in freshwater flows. Although some salinization events last weeks, others only last a few days. This study assessed changes in the endocrine function of the renin-angiotensin-aldosterone system (RAAS) and steroid hormone production (steroidogenesis) in juvenile alligators exposed to brackish water (12‰) for 7 days. We quantified plasma levels of angiotensin II and the corticosteroids (aldosterone, corticosterone and 11-deoxycortisol). Various progestogens, androgens, and estrogens were further assessed. The protein expression for the RAAS enzymes, renin and angiotensin converting enzyme (ACE), was quantified immunohistochemically in kidney and lung tissue, respectively, and histology was performed on kidney, lung and gonad tissues. Finally, blood biochemistry parameters such as electrolyte levels and diagnostic indicators for dehydration, renal, and hepatic function were measured. Corticosterone, 11-deoxycortisol, Na⁺, Cl^-, total protein, albumin, uric acid, and cholesterol levels were all significantly elevated in alligators exposed to brackish water compared with alligators in freshwater. The levels of 17β-estradiol and estrone were significantly lowered while histology showed alterations in gonad tissue in the brackish water exposed group. In contrast, while there were no effects of exposure on aldosterone levels, angiotensin II was significantly reduced in brackish water exposed alligators. These results correlated with significantly decreased expressions for both renin and ACE in kidney and lung tissue. Overall, this study showed that short-term exposure of alligators to 12‰ brackish water has significant endocrine effects on juvenile alligators.

Steroidogenic Acute Regulatory Protein: Structure, Functioning, and Regulation

Steroidogenesis takes place mainly in adrenal and gonadal cells that produce a variety of structurally similar hormones regulating numerous body functions. The rate-limiting stage of steroidogenesis is cholesterol delivery to the inner mitochondrial membrane, where it is converted by cytochrome P450scc into pregnenolone, a common precursor of all steroid hormones. The major role of supplying mitochondria with cholesterol belongs to steroidogenic acute regulatory protein (STARD1). STARD1, which is synthesized de novo as a precursor containing mitochondrial localization sequence and sterol-binding domain, significantly accelerates cholesterol transport and production of pregnenolone. Despite a tremendous interest in STARD1 fueled by its involvement in hereditary diseases and extensive efforts of numerous laboratories worldwide, many aspects of STARD1 structure, functioning, and regulation remain obscure and debatable. This review presents current concepts on the structure of STARD1 and other lipid transfer proteins, the role of STARD1 in steroidogenesis, and the mechanism of its functioning, as well as identifies the most controversial and least studied questions related to the activity of this protein.

The Mechanisms of Actions of Aldosterone and its Antagonists in Cardiovascular Disease

Background:

Aldosterone, through its actions on Mineralcorticosteroid Receptors (MR), controls fluid and electrolyte balance, but also exerts various direct deleterious actions on the vasculature. A number of aldosterone antagonists have been manufactured to reverse these effects.

Objective:

A comprehensive review of the underlying mechanisms of the actions of aldosterone and its antagonists in cardiovascular disease.

Method:

The relevant studies indexed in PubMed, Scopus and Google Scholar databases, published from 2003 to May 2018 were identified and reported.

Results:

Aldosterone binds to MR, activating them as intracellular transcription factors. Moreover, aldosterone, through its actions on MR, as well as on another not fully explored class of receptors, triggers several signaling pathways that produce rapid, non-genomic actions. In the vasculature, all these changes favor the establishment of inflammation and cardiovascular dysfunction, which, in turn, lead to or exacerbate various cardiovascular diseases. Mineralcorticosteroid Antagonists (MRA) are compounds that antagonize the action of aldosterone on MR. Spironolactone was the first steroidal MRA to be commercially used. It showed beneficial clinical results, but also a number of adverse effects. The next generation of steroidal MRA, exhibited lower potency but did not induce many of these adverse reactions, due to their high selectivity for MR. The third generation of MRA compromises the newly introduced non-steroidal MRA, which have a completely different chemical structure, they induce different and more drastic changes to MR, they are much more specific and currently under clinical trials.

Conclusion:

New MRA, which block the aldosterone induced pathways in the vasculature, hold promising results for the treatment of cardiovascular disease.

Influence of Sodium Citrate Supplementation after Dehydrating Exercise on Responses of Stress Hormones to Subsequent Endurance Cycling Time-Trial in the Heat

Background and objectives: In temperate environments, acute orally induced metabolic alkalosis alleviates exercise stress, as reflected in attenuated stress hormone responses to relatively short-duration exercise bouts. However, it is unknown whether the same phenomenon occurs during prolonged exercise in the heat. This study was undertaken with aim to test the hypothesis that ingestion of an alkalizing substance (sodium citrate; CIT) after dehydrating exercise would decrease blood levels of stress hormones during subsequent 40 km cycling time-trial (TT) in the heat. Materials and Methods: Male non-heat-acclimated athletes (n = 20) lost 4% of body mass by exercising in the heat. Then, during a 16 h recovery period prior to TT in a warm environment (32 °C), participants ate the prescribed food and ingested CIT (600 mg·kg-1) or placebo (PLC) in a double-blind, randomized, crossover manner with 7 days between the two trials. Blood aldosterone, cortisol, prolactin and growth hormone concentrations were measured before and after TT. Results: Total work performed during TT was similar in the two trials (p = 0.716). In CIT compared to PLC trial, lower levels of aldosterone occurred before (72%) and after (39%) TT (p ˂ 0.001), and acute response of aldosterone to TT was blunted (29%, p ˂ 0.001). Lower cortisol levels in CIT than in PLC trial occurred before (13%, p = 0.039) and after TT (14%, p = 0.001), but there were no between-trial differences in the acute responses of cortisol, prolactin or growth hormone to TT, or in concentrations of prolactin and growth hormone before or after TT (in all cases p > 0.05). Conclusions: Reduced aldosterone and cortisol levels after TT and blunted acute response of aldosterone to TT indicate that CIT ingestion during recovery after dehydrating exercise may alleviate stress during the next hard endurance cycling bout in the heat.

A steady state system for in vitro evaluation of steroidogenic pathway dynamics: Application for CYP11B1, CYP11B2 and CYP17 inhibitors

Disorders featuring dysregulated adrenal steroidogenesis, such as primary aldosteronism, can benefit from targeted therapies. The aldosterone and cortisol producing enzymes, aldosterone synthase (CYP11B2) and 11-beta-hydroxylase (CYP11B1), share 93% homology requiring selective drugs for pharmacological treatment. Herein, we introduce an effective in vitro assay for evaluation of steroidogenic enzyme kinetics based on intracellular flux calculations. H295RA cells were cultured in chambers under constant medium flow. Four hourly samples were collected (control samples), followed by collections over an additional four hours after treatment with fadrozole (10 nM), metyrapone (10 μM), SI_191 (5 nM), a novel CYP11B2 inhibitor or SI_254 (100 nM), a newly synthesized 17-alpha-hydroxylase/17,20-lyase inhibitor. Mass spectrometric measurements of multiple steroids combined with linear system computational modeling facilitated calculation of intracellular fluxes and changes in rate constants at different steroidogenic pathway steps, enabling selectivity of drugs for those steps to be evaluated. While treatment with fadrozole, metyrapone and SI_191 all reduced fluxes of aldosterone, corticosterone and cortisol production, treatment with SI_254 led to increased flux through the mineralocorticoid pathway and reduced production of steroids downstream of 17-alpha-hydroxylase/17,20-lyase. Drug-induced decreases in rate constants revealed higher selectivity of SI_191 compared to other drugs for CYP11B2 over CYP11B1, this reflecting additional inhibitory actions of SI_191 on catalytic steps of CYP11B2 downstream from the initial 11-beta-hydroxlase step. By culturing cells under perfusion the described system provides a realistic model for simple and rapid calculations of intracellular fluxes and changes in rate constants, thereby offering a robust procedure for investigating drug or other effects at specific steps of steroidogenesis.

Atorvastatin inhibits pro-inflammatory actions of aldosterone in vascular smooth muscle cells by reducing oxidative stress

Vascular inflammatory responses play an important role in several cardiovascular diseases. Of the many pro-inflammatory vasoactive factors implicated in this process, is aldosterone, an important mediator of vascular oxidative stress. Statins, such as atorvastatin, are cholesterol-lowering drugs that have pleiotropic actions, including anti-oxidant properties independently of their cholesterol-lowering effect. This study investigated whether atorvastatin prevents aldosterone-induced VSMC inflammation by reducing reactive oxygen species (ROS) production. Vascular smooth muscle cells (VSMC) from WKY rats were treated with 1 μM atorvastatin for 60 min or for 72 h prior to aldosterone (10-7 mol/L) stimulation. Atorvastatin inhibited Rac1/2 and p47phox translocation from the cytosol to the membrane, as well as reduced aldosterone-induced ROS production. Atorvastatin also attenuated aldosterone-induced vascular inflammation and macrophage adhesion to VSMC. Similarly EHT1864, a Rac1/2 inhibitor, and tiron, ROS scavenger, reduced macrophage adhesion. Through its inhibitory effects on Rac1/2 activation and ROS production, atorvastatin reduces vascular ROS generation and inhibits VSMC inflammation. Our data suggest that in conditions associated with aldosterone-induced vascular damage, statins may have vasoprotective effects by inhibiting oxidative stress and inflammation.

Glycemia Lowering Effect of an Aqueous Extract of Hedychium coronarium Leaves in Diabetic Rodent Models

Hedychium coronarium has a long history of use worldwide as a food and in folk medicine. In this study, we aimed to investigate the effect of an aqueous extract of H. coronarium leaves (HC) on type 2 diabetes mellitus (T2DM). Two types of animal models were used in this study: Streptozotocin (STZ)-induced T2DM (Wistar rats; N = 8) and C57BKSdb/db mice (N = 5). After treatment with HC for 28 days, glucose tolerance improved in both of the diabetic animal models. As significant effects were shown after 14 days of treatment in the STZ-induced T2DM model, we carried out the experiments with it. After 28 days of treatment with HC, the levels of cholesterol, triglyceride, high-density lipoprotein, and low-density lipoprotein were significantly improved in the STZ-induced T2DM model. The lesions degree of islet β-cells was decreased after the HC treatment. Although the insulin level increased moderately, the aldosterone level was significantly decreased in the HC-treated groups, suggesting that aldosterone might play an important role in this effect. In summary, HC is a natural product and it is worth exploring its effect on T2DM.

Hypertension linked to allostatic load: from psychosocial stress to inflammation and mitochondrial dysfunction

Although a large number of available treatments and strategies, the prevalence of cardiovascular diseases continues to grow worldwide. Emerging evidence supports the notion of counteracting stress as a critical component of a comprehensive therapeutic strategy for cardiovascular disease. Indeed, an unhealthy lifestyle is a burden to biological variables such as plasma glucose, lipid profile, and blood pressure control. Recent findings identify allostatic load as a new paradigm for an integrated understanding of the importance of psychosocial stress and its impact on the development and maintenance of cardiovascular disease. Allostasis complement homeostasis and integrates behavioral and physiological mechanisms by which genes, early experiences, environment, lifestyle, diet, sleep, and physical exercise can modulate and adapt biological responses at the cellular level. For example, variability is a physiological characteristic of blood pressure necessary for survival and the allostatic load in hypertension can contribute to its related cardiovascular morbidity and mortality. Therefore, the current review will focus on the mechanisms that link hypertension to allostatic load, which includes psychosocial stress, inflammation, and mitochondrial dysfunction. We will describe and discuss new insights on neuroendocrine-immune effects linked to allostatic load and its impact on the cellular and molecular responses; the links between allostatic load, inflammation, and endothelial dysfunction; the epidemiological evidence supporting the pathophysiological origins of hypertension; and the biological embedding of allostatic load and hypertension with an emphasis on mitochondrial dysfunction.

A genome-wide scan for diversifying selection signatures in selected horse breeds

The genetic differentiation of the current horse population was evolutionarily created by natural or artificial selection which shaped the genomes of individual breeds in several unique ways. The availability of high throughput genotyping methods created the opportunity to study this genetic variation on a genome-wide level allowing detection of genome regions divergently selected between separate breeds as well as among different horse types sharing similar phenotypic features. In this study, we used the population differentiation index (FST) that is generally used for measuring locus-specific allele frequencies variation between populations, to detect selection signatures among six horse breeds maintained in Poland. These breeds can be classified into three major categories, including light, draft and primitive horses, selected mainly in terms of type (utility), exterior, performance, size, coat color and appearance. The analysis of the most pronounced selection signals found in this study allowed us to detect several genomic regions and genes connected with processes potentially important for breed phenotypic differentiation and associated with energy homeostasis during physical effort, heart functioning, fertility, disease resistance and motor coordination. Our results also confirmed previously described association of loci on ECA3 (spanning LCORL and NCAPG genes) and ECA11 (spanning LASP1 gene) with the regulation of body size in our draft and primitive (small size) horses. The efficiency of the applied FST-based approach was also confirmed by the identification of a robust selection signal in the blue dun colored Polish Konik horses at the locus of TBX3 gene, which was previously shown to be responsible for dun coat color dilution in other horse breeds. FST-based method showed to be efficient in detection of diversifying selection signatures in the analyzed horse breeds. Especially pronounced signals were observed at the loci responsible for fixed breed-specific features. Several candidate genes under selection were proposed in this study for traits selected in separate breeds and horse types, however, further functional and comparative studies are needed to confirm and explain their effect on the observed genetic diversity of the horse breeds.

M3-subtype muscarinic receptor activation stimulates intracellular calcium oscillations and aldosterone production in human adrenocortical HAC15 cells

A previous body of work in bovine and rodent models shows that cholinergic agonists modulate the secretion of steroid hormones from the adrenal cortex. In this study we used live-cell Ca²⁺ imaging to investigate cholinergic activity in the HAC15 human adrenocortical carcinoma cell line. The cholinergic agonists carbachol and acetylcholine triggered heterogeneous Ca²⁺ oscillations that were strongly inhibited by antagonists with high affinity for the M₃ muscarinic receptor subtype, while preferential block of M₁ or M₂ receptors was less effective. Acute exposure to carbachol and acetylcholine modestly elevated aldosterone secretion in HAC15 cells, and this effect was also diminished by M₃ inhibition. HAC15 cells expressed relatively high levels of mRNA for M₃ and M₂ receptors, while M₁ and M₅ mRNA were much lower. In conclusion, our data extend previous findings in non-human systems to implicate the M₃ receptor as the dominant muscarinic receptor in the human adrenal cortex.

Paracrine Regulation of Aldosterone Secretion in Physiological and Pathophysiological Conditions

Aldosterone secretion by the zona glomerulosa of the adrenal cortex is controlled by circulating factors including the renin angiotensin system (RAS) and potassium. Mineralocorticoid production is also regulated through an autocrine/paracrine mechanism by a wide variety of bioactive signals released in the vicinity of adrenocortical cells by chromaffin cells, nerve endings, cells of the immune system, endothelial cells and adipocytes. These regulatory factors include conventional neurotransmitters and neuropeptides. Their physiological role in the control of aldosterone secretion is not fully understood, but it is likely that they participate in the RAS-independent regulation of zona glomerulosa cells. Interestingly, recent observations indicate that autocrine/paracrine processes are involved in the pathophysiology of primary aldosteronism. The intraadrenal regulatory systems observed in aldosterone-producing adenomas (APA), although globally similar to those occurring in the normal adrenal gland, harbor alterations at different levels, which tend to strengthen the potency of paracrine signals to activate aldosterone secretion. Enhancement of paracrine stimulatory tone may participate to APA expansion and aldosterone hypersecretion together with somatic mutations of driver genes which activate the calcium signaling pathway and subsequently aldosterone synthase expression. Intraadrenal regulatory mechanisms represent thus promising pharmacological targets for the treatment of primary aldosteronism.

The regulation of aldosterone secretion by leptin: implications in obesity-related cardiovascular disease

PURPOSE OF REVIEW

Although it has been known for some time that increases in body mass enhance aldosterone secretion, particularly in women, the origin of this elevation in aldosterone production is not well defined. Adipocyte-derived factors have emerged as potential candidates to increase aldosterone production in obesity.

RECENT FINDINGS

Emerging evidence suggests the presence of a mechanistic link in which the adipocyte-derived hormone leptin stimulates aldosterone production in obesity, thereby creating a positive feedback loop for obesity-associated cardiovascular disease. In addition, recent reports give credence to the concept that this leptin-aldosterone stimulation pathway in obesity is an underlying mechanism for sex-discrepancies in obesity-associated cardiovascular disease.

SUMMARY

Leptin appears as a new direct regulator of adrenal aldosterone production and leptin-mediated aldosterone production is a novel candidate mechanism underlying obesity-associated hypertension, particularly in females.

Regulation of Aldosterone Secretion

Secretion of the major mineralocorticoid aldosterone from the adrenal cortex is a tightly-regulated process enabling this hormone to regulate sodium homeostasis and thereby contribute to blood pressure control. The circulating level of aldosterone is the result of various regulatory mechanisms, the most significant being those controlled by the renin-angiotensin system and plasma potassium levels. The importance of maintaining tight control over aldosterone secretion is demonstrated by cases of dysregulation, which can result in severe hypertension and significantly increased cardiovascular risk. In this article we summarize current knowledge of the major regulatory mechanisms, focusing particularly on the systems operating within the adrenocortical zona glomerulosa cells; we also describe some of the other factors that influence aldosterone production to a lesser but still significant extent. Finally, we discuss the influence of common genetic polymorphisms on aldosterone secretion in large sections of the population and also the emerging role of microRNA as significant regulators of this system.

Effects of chronic exposure to 12‰ saltwater on the endocrine physiology of juvenile American alligator (Alligator mississippiensis)

American alligator (Alligator mississippiensis) habitats are prone to saltwater intrusion following major storms, hurricanes or droughts. Anthropogenic impacts affecting hydrology of freshwater systems may exacerbate saltwater intrusion into freshwater habitats. The endocrine system of alligators is susceptible to changes in the environment but it is currently not known how the crocodilian physiological system responds to environmental stressors such as salinity. Juvenile alligators were exposed to 12‰ saltwater for 5 weeks to determine the effects of chronic exposure to saline environments. Following 5 weeks, plasma levels of hormones [e.g. progesterone, testosterone, estradiol, corticosterone, aldosterone (ALDO), angiotensin II (ANG II)] were quantified using liquid chromatography and tandem mass spectrometry. Compared with freshwater-kept subjects, saltwater-exposed alligators had significantly elevated plasma levels of corticosterone, 11-deoxycortisol, 17α-hydroxyprogesterone, testosterone, 17β-estradiol, estrone and estriol whereas pregnenolone and ANG II were significantly depressed and ALDO levels were unchanged (slightly depressed). On the one hand, saltwater exposure did not affect gene expression of renal mineralocorticoid and glucorticoid and angiotensin type 1 (AT-1) receptors or morphology of lingual glands. On the other hand, saltwater exposure significantly reduced plasma glucose concentrations whereas parameters diagnostic of perturbed liver function (aspartate aminotransferase and alanine aminotransferase) and kidney function (creatinine and creatine kinase) were significantly elevated. Except for plasma potassium levels (K⁺), plasma ions Na⁺ and Cl^- were significantly elevated in saltwater alligators. Overall, this study demonstrated significant endocrine and physiological effects in juvenile alligators chronically exposed to a saline environment. Results provide novel insights into the effects of a natural environmental stressor (salinity) on the renin-angiotensin-aldosterone system and steroidogenesis of alligators.

Role of the Renin Angiotensin System in Blood Pressure Allostasis-induced by Severe Food Restriction in Female Fischer rats

Severe food restriction (FR) is associated with blood pressure (BP) and cardiovascular dysfunction. The renin-angiotensin system (RAS) regulates BP and its dysregulation contributes to impaired cardiovascular function. Female Fischer rats were maintained on a control (CT) or severe FR (40% of CT) diet for 14 days. In response to severe FR, BP allostasis was achieved by up-regulating circulating Ang-[1–8] by 1.3-fold through increased angiotensin converting enzyme (ACE) activity and by increasing the expression of AT₁Rs 1.7-fold in mesenteric vessels. Activation of the RAS countered the depressor effect of the severe plasma volume reduction (≥30%). The RAS, however, still underperformed as evidenced by reduced pressor responses to Ang-[1–8] even though AT₁Rs were still responsive to the depressor effects of an AT₁R antagonist. The aldosterone (ALDO) response was also inadequate as no changes in plasma ALDO were observed after the large fall in plasma volume. These findings have implications for individuals who have experienced a period(s) of severe FR (e.g., anorexia nervosa, dieters, natural disasters) and suggests increased activity of the RAS in order to achieve allostasis contributes to the cardiovascular dysfunction associated with inadequate food intake.

Mitochondrial cAMP and Ca2+ metabolism in adrenocortical cells

The biological effects of physiological stimuli of adrenocortical glomerulosa cells are predominantly mediated by the Ca²⁺ and the cAMP signal transduction pathways. The complex interplay between these signalling systems fine-tunes aldosterone secretion. In addition to the well-known cytosolic interactions, a novel intramitochondrial Ca²⁺-cAMP interplay has been recently recognised. The cytosolic Ca²⁺ signal is rapidly transferred into the mitochondrial matrix where it activates Ca²⁺-sensitive dehydrogenases, thus enhancing the formation of NADPH, a cofactor of steroid synthesis. Quite a few cell types, including H295R adrenocortical cells, express the soluble adenylyl cyclase within the mitochondria and the elevation of mitochondrial [Ca²⁺] activates the enzyme, thus resulting in the Ca²⁺-dependent formation of cAMP within the mitochondrial matrix. On the other hand, mitochondrial cAMP (mt-cAMP) potentiates the transfer of cytosolic Ca²⁺ into the mitochondrial matrix. This cAMP-mediated positive feedback control of mitochondrial Ca²⁺ uptake may facilitate the rapid hormonal response to emergency situations since knockdown of soluble adenylyl cyclase attenuates aldosterone production whereas overexpression of the enzyme facilitates steroidogenesis in vitro. Moreover, the mitochondrial Ca²⁺-mt-cAMP-Ca²⁺ uptake feedback loop is not a unique feature of adrenocortical cells; a similar signalling system has been described in HeLa cells as well.

Molecular remodeling of the renin-angiotensin system after kidney transplantation

Objective:

We aimed at assessing the molecular adaptation of the renin-angiotensin system (RAS) after successful kidney transplantation (KTX).

Materials and methods:

In this prospective, exploratory study we analyzed 12 hemodialysis (HD) patients, who received a KTX and had excellent graft function six to 12 months thereafter. The concentrations of plasma Angiotensin (Ang) peptides (Ang I, Ang II, Ang-(1–7), Ang-(1–5), Ang-(2–8), Ang-(3–8)) were simultaneously quantified with a novel mass spectrometry-based method. Further, renin and aldosterone concentrations were determined by standard immunoassays.

Results:

Ang values showed a strong inter-individual variability among HD patients. Yet, despite a continued broad dispersion of Ang values after KTX, a substantial improvement of the renin/Ang II correlation was observed in patients without RAS blockade or on angiotensin receptor blocker (HD: renin/Ang II R² = 0.660, KTX: renin/Ang II R² = 0.918). Ang-(1–7) representing the alternative RAS axis was only marginally detectable both on HD and after KTX.

Conclusions:

Following KTX, renin-dependent Ang II formation adapts in non-ACE inhibitor-treated patients. Thus, a largely normal RAS regulation is reconstituted after successful KTX. However, individual Ang concentration variations and a lack of potentially beneficial alternative peptides after KTX call for individualized treatment. The long-term post-transplant RAS regulation remains to be determined.

Purkinje Cell Protein 4 Expression Is Associated With DNA Methylation Status in Aldosterone-Producing Adenoma

CONTEXT

Aldosterone production is stimulated by activation of calcium signaling in aldosterone-producing adenomas (APAs), and epigenetic factors such as DNA methylation may be associated with the expression of genes involved in aldosterone regulation.

OBJECTIVE

Our aim was to investigate the DNA methylation of genes related to calcium signaling cascades in APAs and the association of mutations in genes linked to APAs with DNA methylation levels.

METHODS

Nonfunctioning adrenocortical adenoma (n = 12) and APA (n = 35) samples were analyzed. The KCNJ5 T158A mutation was introduced into human adrenocortical cell lines (HAC15 cells) using lentiviral delivery. DNA methylation array analysis was conducted using adrenal tumor samples and HAC15 cells.

RESULTS

The Purkinje cell protein 4 (PCP4) gene was one of the most hypomethylated in APAs. DNA methylation levels in two sites of PCP4 showed a significant inverse correlation with messenger RNA expression in adrenal tumors. Bioinformatics and multiple regression analysis revealed that CCAAT/enhancer binding protein alpha (CEBPA) may bind to the methylation site of the PCP4 promoter. According to chromatin immunoprecipitation assay, CEBPA was bound to the PCP4 hypomethylated region by chromatin immunoprecipitation assay. There were no significant differences in PCP4 methylation levels among APA genotypes. Moreover, KCNJ5 T158A did not influence PCP4 methylation levels in HAC15 cells.

CONCLUSIONS

We showed that the PCP4 promoter was one of the most hypomethylated in APAs and that PCP4 transcription may be associated with demethylation as well as with CEBPA in APAs. KCNJ5 mutations known to result in aldosterone overproduction were not related to PCP4 methylation in either clinical or in vitro studies.

Angiotensin II AT2 Receptors Contribute to Regulate the Sympathoadrenal and Hormonal Reaction to Stress Stimuli

Angiotensin II, through AT1 receptor stimulation, mediates multiple cardiovascular, metabolic, and behavioral functions including the response to stressors. Conversely, the function of Angiotensin II AT2 receptors has not been totally clarified. In adult rodents, AT2 receptor distribution is very limited but it is particularly high in the adrenal medulla. Recent results strongly indicate that AT2 receptors contribute to the regulation of the response to stress stimuli. This occurs in association with AT1 receptors, both receptor types reciprocally influencing their expression and therefore their function. AT2 receptors appear to influence the response to many types of stressors and in all components of the hypothalamic-pituitary-adrenal axis. The molecular mechanisms involved in AT2 receptor activation, the complex interactions with AT1 receptors, and additional factors participating in the control of AT2 receptor regulation and activity in response to stressors are only partially understood. Further research is necessary to close this knowledge gap and to clarify whether AT2 receptor activation may carry the potential of a major translational advance.

Calneuron 1 Increased Ca2+ in the Endoplasmic Reticulum and Aldosterone Production in Aldosterone-Producing Adenoma

Aldosterone production is initiated by angiotensin II stimulation and activation of intracellular Ca²⁺ signaling. In aldosterone-producing adenoma (APA) cells, the activation of intracellular Ca²⁺ signaling is independent of the renin-angiotensin-aldosterone systems. The purpose of our study was to clarify molecular mechanisms of aldosterone production related to Ca²⁺ signaling. Transcriptome analysis revealed that the CALN1 gene encoding calneuron 1 had the strongest correlation with CYP11B2 (aldosterone synthase) among genes encoding Ca²⁺-binding proteins in APA. CALN1 modulation and synthetic or fluorescent compounds were used for functional studies in human adrenocortical carcinoma (HAC15) cells. CALN1 expression was 4.4-fold higher in APAs than nonfunctioning adrenocortical adenomas. CALN1 expression colocalized with CYP11B2 expression as investigated using immunohistochemistry in APA and zona glomerulosa of male rats fed by a low-salt diet. CALN1 expression was detected in the endoplasmic reticulum (ER) by using GFP-fused CALN1, CellLight ER-RFP, and the corresponding antibodies. CALN1-overexpressing HAC15 cells showed increased Ca²⁺ in the ER and cytosol fluorescence-based studies. Aldosterone production was potentiated in HAC15 cells by CALN1 expression, and dose-responsive inhibition with TMB-8 showed that CALN1-mediated Ca²⁺ storage in ER involved sarcoendoplasmic reticulum calcium transport ATPase. The silencing of CALN1 decreased Ca²⁺ in ER, and abrogated angiotensin II- or KCNJ5 T158A-mediated aldosterone production in HAC15 cells. Increased CALN1 expression in APA was associated with elevated Ca²⁺ storage in ER and aldosterone overproduction. Suppression of CALN1 expression prevented angiotensin II- or KCNJ5 T158A-mediated aldosterone production in HAC15 cells, suggesting that CALN1 is a potential therapeutic target for excess aldosterone production.

Evolutionarily Conserved Roles for Blood-Brain Barrier Xenobiotic Transporters in Endogenous Steroid Partitioning and Behavior

Central nervous system (CNS) chemical protection depends upon discrete control of small-molecule access by the blood-brain barrier (BBB). Curiously, some drugs cause CNS side-effects despite negligible transit past the BBB. To investigate this phenomenon, we asked whether the highly BBB-enriched drug efflux transporter MDR1 has dual functions in controlling drug and endogenous molecule CNS homeostasis. If this is true, then brain-impermeable drugs could induce behavioral changes by affecting brain levels of endogenous molecules. Using computational, genetic, and pharmacologic approaches across diverse organisms, we demonstrate that BBB-localized efflux transporters are critical for regulating brain levels of endogenous steroids and steroid-regulated behaviors (sleep in Drosophila and anxiety in mice). Furthermore, we show that MDR1-interacting drugs are associated with anxiety-related behaviors in humans. We propose a general mechanism for common behavioral side effects of prescription drugs: pharmacologically challenging BBB efflux transporters disrupts brain levels of endogenous substrates and implicates the BBB in behavioral regulation.

Dominance of the hypothalamus-pituitary-adrenal axis over the renin-angiotensin-aldosterone system is a risk factor for decreased insulin secretion

How the association between the hypothalamus-pituitary-adrenal (HPA) axis and the renin-angiotensin-aldosterone system (RAAS) affects glucose metabolism were not well examined in a general population. Participants of the population-based 2015 Iwaki study were enrolled (n: 1,016; age: 54.4 ± 15.1 years). Principal component (PC) analysis identified two PCs: PC1 represented levels of the HPA axis (serum cortisol) and the RAAS (plasma aldosterone) as a whole, and PC2 represented the HPA axis relative to the RAAS (HPA axis dominance). We examined the association between these PCs and glucose metabolism using homeostasis model assessment indices of reduced insulin sensitivity (HOMA-R) and secretion (HOMA-β). Univariate linear regression analyses showed a correlation between PC2 and HOMA-β (β = −0.248, p < 0.0001), but not between PC1 and HOMA-β (β = −0.004, p = 0.9048). The correration between PC2 and HOMA-β persisted after adjustment for multiple factors (β = −0.101, p = 0.0003). No correlations were found between the PCs and HOMA-R. When subjects were tertiled based on PC2, the highest tertile was at greater risk of decreased insulin secretion (defined as the lower one third of HOMA-β (≤68.9)) than the lowest tertile after adjustment for multiple factors (odds ratio, 2.00; 95% confidence interval, 1.35–2.97). The HPA axis dominance is associated with decreased insulin secretion in a Japanese population.

Dynamic Changes in the Renin-Angiotensin-Aldosterone System and the Beneficial Effects of Renin-Angiotensin-Aldosterone Inhibitors on Spatial Learning and Memory in a Rat Model of Chronic Cerebral Ischemia

Renin-angiotensin-aldosterone system (RAAS) plays an important role in the regulation of blood pressure and brain function. Therefore, we studied the dynamic changes in the RAAS in the blood, cerebral cortex, and hippocampus and the effects of RAAS inhibitors on spatial learning and memory and hippocampal apoptosis in a rat model of chronic cerebral ischemia (CCI) established by bilateral ligation of the common carotid arteries of rats. The levels of renin, angiotensin II (Ang II), and aldosterone (ALD) in the plasma, and the homogenates of the left side of cerebral cortex and whole hippocampus of rats were detected on day 1, 3, 7, 14, 21, and 30 by radioimmunoassay. Spatial learning and memory and hippocampal apoptosis were evaluated on day 30 by Morris water maze test (navigation and space exploration tests) and terminal dexynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) assay, respectively, after rats were orally administered with distilled water (DW), renin inhibitor aliskiren (30 mg/kg), Ang converting enzyme inhibitor enalapril (4 mg/kg), or Ang II receptor antagonist candesartan (2 mg/kg) daily for 30 days. The results showed that the levels of renin and Ang II were significantly higher but ALD fluctuated in the blood, cerebral cortex, and hippocampus in CCI rats compared to normal rats. However, aliskiren and enalapril could significantly decrease (p < 0.05) the levels of renin, Ang II and ALD in the blood, cerebral cortex, and hippocampus compared to DW treatment; while candesartan had similar effect on renin and ALD but no effect on Ang II in CCI rats. Furthermore, spatial learning and memory were significantly decreased but apoptosis in the hippocampus was obviously increased in CCI rats compared to normal rats (p < 0.05). However, aliskiren, enalapril, and candesartan were equally effective to improve spatial learning and memory and decrease apoptosis in the hippocampus. Therefore, RAAS plays an important role in the development of cerebral ischemia and RAAS inhibitors aliskiren, enalapril, and candesartan improve spatial learning and memory and protect brain injury by inhibiting hippocampal apoptosis in CCI rats.

Erythropoietin Regulation by Angiotensin II

The renin-angiotensin system (RAS) is a key regulator of blood pressure and blood volume homeostasis. The RAS is primarily comprised of the precursor protein angiotensinogen and the two proteases, renin and angiotensin-converting enzyme (ACE). Angiotensin I (Ang I) is derived from angiotensinogen by renin, but appears to have no biological activity. In contrast, angiotensin II (Ang II) that has a variety of biological functions in the cells is converted from Ang I through removal of two-C-terminal residues by ACE. The physiological effects of Ang II are due to Ang II signaling through specific receptor binding, resulting in muscle contraction leading to increased blood pressure and volume. To modulate RAS, three classes of drugs have been developed: (1) renin inhibitors to prevent angiotensinogen conversion to Ang I, (2) ACE inhibitors, to prevent Ang I processing to Ang II and (3) angiotensin receptor blockers, to inhibit Ang II signaling through its receptor. Studies using the RAS inhibitors and Ang II demonstrated that RAS signaling mediates actions of Ang II in the regulation of proliferation and differentiation of specific hematopoietic cell types, especially in the red blood cell lineage. Accumulating evidence indicates that RAS regulates EPO, an essential mediator of red cell production, for human anemia and erythropoiesis in vivo and in vitro. The regulation of EPO expression by Ang II may be responsible for maintaining red blood cell homeostasis. This review highlights the biological roles of RAS for blood cell and EPO homeostasis through Ang II signaling. The molecular mechanism for Ang II-induced EPO production of the cell or tissue type-specific expression is discussed.

Role of cAMP/PKA pathway and T-type calcium channels in the mechanism of action of serotonin in human adrenocortical cells

In human adrenal, serotonin (5-HT), produced by mast cells located in zona glomerulosa, stimulates production of corticosteroids through a paracrine mechanism involving the 5-HT receptor type 4 (5-HT₄). The aim of the present study was to investigate the transduction mechanisms associated with activation of 5-HT₄ receptors in human adrenocortical cells. Our results show that 5-HT₄ receptors are present in the outer adrenal cortex, both in glomerulosa and fasciculata zonae. In the zona glomerulosa. 5-HT₄ receptor was detected both in immunopositive and immunonegative cells for 11β-hydroxylase, an enzyme involved in cortisol synthesis. The data demonstrate that 5-HT₄ receptors are positively coupled to adenylyl cyclases and cAMP-dependent protein kinases (PKA). The activation of the cAMP-PKA pathway is associated with calcium influx through T-type calcium channels. Both the adenylyl cyclase/PKA pathway and the calcium influx are involved in 5-HT-induced cortisol secretion.

Regulation of zonation and homeostasis in the adrenal cortex

The adult adrenal cortex is organized into concentric zones, each specialized to produce distinct steroid hormones. Cellular composition of the cortex is highly dynamic and subject to diverse signaling controls. Cortical homeostasis and regeneration rely on centripetal migration of steroidogenic cells from the outer to the inner cortex, which is accompanied by direct conversion of zona glomerulosa (zG) into zona fasciculata (zF) cells. Given the important impact of tissue structure and growth on steroidogenic function, it is essential to understand the mechanisms governing adrenal zonation and homeostasis. Towards this end, we review the distinctions between each zone by highlighting their morphological and ultra-structural features, discuss key signaling pathways influencing zonal identity, and evaluate current evidence for long-term self-renewing stem cells in the adult cortex. Finally, we review data supporting zG-to-zF transdifferentiation/direct conversion as a major mechanism of adult cortical renewal.

Very low-density lipoprotein (VLDL)-induced signals mediating aldosterone production

Aldosterone, secreted by the adrenal zona glomerulosa, enhances sodium retention, thus increasing blood volume and pressure. Excessive production of aldosterone results in high blood pressure and contributes to cardiovascular and renal disease, stroke and visual loss. Hypertension is also associated with obesity, which is correlated with other serious health risks as well. Although weight gain is associated with increased blood pressure, the mechanism by which excess fat deposits increase blood pressure remains unclear. Several studies have suggested that aldosterone levels are elevated with obesity and may represent a link between obesity and hypertension. In addition to hypertension, obese patients typically have dyslipidemia, including elevated serum levels of very low-density lipoprotein (VLDL). VLDL, which functions to transport triglycerides from the liver to peripheral tissues, has been demonstrated to stimulate aldosterone production. Recent studies suggest that the signaling pathways activated by VLDL are similar to those utilized by AngII. Thus, VLDL increases cytosolic calcium levels and stimulates phospholipase D (PLD) activity to result in the induction of steroidogenic acute regulatory (StAR) protein and aldosterone synthase (CYP11B2) expression. These effects seem to be mediated by the ability of VLDL to increase the phosphorylation (activation) of their regulatory transcription factors, such as the cAMP response element-binding (CREB) protein family of transcription factors. Thus, research into the pathways by which VLDL stimulates aldosterone production may identify novel targets for the development of therapies for the treatment of hypertension, particularly those associated with obesity, and other aldosterone-modulated pathologies.

Actions of Quercetin, a Polyphenol, on Blood Pressure

Disorder of blood pressure control causes serious diseases in the cardiovascular system. This review focuses on the anti-hypertensive action of quercetin, a flavonoid, which is one of the polyphenols characterized as the compounds containing large multiples of phenol structural units, by varying the values of various blood pressure regulatory factors, such as vascular compliance, peripheral vascular resistance, and total blood volume via anti-inflammatory and anti-oxidant actions. In addition to the anti-inflammatory and anti-oxidant actions of quercetin, we especially describe a novel mechanism of quercetin’s action on the cytosolic Cl⁻ concentration ([Cl⁻]_c) and novel roles of the cytosolic Cl⁻ i.e., (1) quercetin elevates [Cl⁻]_c by activating Na⁺-K⁺-2Cl⁻ cotransporter 1 (NKCC1) in renal epithelial cells contributing to Na⁺ reabsorption via the epithelial Na⁺ channel (ENaC); (2) the quercetin-induced elevation of [Cl⁻]_c in renal epithelial cells diminishes expression of ENaC leading to a decrease in renal Na⁺ reabsorption; and (3) this reduction of ENaC-mediated Na⁺ reabsorption in renal epithelial cells drops volume-dependent elevated blood pressure. In this review, we introduce novel, unique mechanisms of quercetin’s anti-hypertensive action via activation of NKCC1 in detail.

Hypomethylation of CYP11B2 in Aldosterone-Producing Adenoma

The purpose of this study was to evaluate the DNA methylation levels of steroidogenic enzyme genes in aldosterone-producing adenoma (APA) and the effects of gene mutations in APA on the DNA methylation levels. DNA methylation array analysis was conducted using nonfunctioning adrenocortical adenoma (n=12) and APA (n=35) samples, including some with a KCNJ5 mutation (n=21), an ATP1A1 mutation (n=5), and without the known mutations (n=9). The quantitative polymerase chain reaction assay was performed for the detection of CYP11B2 and CYP11B1 expression levels in nonfunctioning adrenocortical adenoma and APA. We introduced the KCNJ5 T158A mutation using lentivirus delivery in the human adrenocortical 15 cell line, and analyzed the effects of the mutation on DNA methylation levels. We analyzed the 83 presumed DNA methylation sites of steroidogenic enzymes. In APA, we found 7 hypomethylated sites in CYP11B2 and 1 hypomethylated and 6 hypermethylated sites in CYP11B1 There were no differences in the steroidogenic enzymes gene DNA methylation of peripheral leukocytes between nonfunctioning adrenocortical adenoma and APA. No CYP11B2 methylation level was associated with CYP11B2 transcription levels in APA. All methylation sites, except for a CYP11B2 region, showed no difference among APAs with or without gene mutations. Human adrenocortical 15 cells with the KCNJ5 mutation showed no changes in CYP11B2 or CYP11B1 methylation levels compared with control cells. We demonstrated that CYP11B2 in APA was extensively hypomethylated, and CYP11B2 methylation in the region with hypomethylation was not induced by KCNJ5 or ATP1A1 mutations that cause aldosterone overproduction in APA and a KCNJ5 mutation human adrenocortical 15 cells.

Acetaminophen Increases Aldosterone Secretion While Suppressing Cortisol and Androgens: A Possible Link to Increased Risk of Hypertension

BACKGROUND

Acetaminophen (paracetamol) is a widely used analgesic and antipyretic drug. Potential side effects are of public health concern, and liver toxicity from acute overdose is well known. More recently, a regular use of acetaminophen has been associated with an increased risk of hypertension.

METHODS

We investigated effects of acetaminophen on steroidogenesis as a possible mechanism for the hypertensive action by using the human adrenocortical cell line, H295R. Cells were treated with 0.1, 0.5, and 1mM of acetaminophen for 24 hours, and secretion of steroids and gene expression of key steps in the steroidogenesis were investigated.

RESULTS

Progesterone and aldosterone secretion were increased dose dependently, while secretion of 17α-OH-progesterone and cortisol as well as dehydroepiandrosterone and androstenedione was decreased. CYP17α-hydroxylase activity, assessed by the ratio 17α-OH-progesterone/progesterone, and CYP17-lyase activity, assessed by the ratio androstenedione/17α-OH-progesterone, were both dose-dependently decreased by acetaminophen. No effects were revealed on cell viability. Treatment of cells with 0.5mM of acetaminophen did not cause any effects on the expression of 10 genes in the steroidogenic pathways.

CONCLUSIONS

The pattern of steroid secretion caused by acetaminophen can be explained by inhibition of CYP17A1 enzyme activity. A decreased secretion of glucocorticoids and androgens, as demonstrated by acetaminophen, would, in an in vivo situation, induce adrenocorticotropic hormone release via negative feedback in the hypothalamic-pituitary-adrenal axis and result in an upregulation of aldosterone secretion. Our results suggest a novel possible mechanism for acetaminophen-induced hypertension, which needs to be further elucidated in clinical investigations.

Cyp2c44 gene disruption exacerbated pulmonary hypertension and heart failure in female but not male mice

Epoxyeicosatrienoicacids (EETs), synthesized from arachidonic acid by epoxygenases of the CYP2C and CYP2J gene subfamilies, contribute to hypoxic pulmonary vasoconstriction (HPV) in mice. Despite their roles in HPV, it is controversial whether EETs mediate or ameliorate pulmonary hypertension (PH). A recent study showed that deficiency of Cyp2j did not protect male and female mice from hypoxia-induced PH. Since CYP2C44 is a functionally important epoxygenase, we hypothesized that knockout of the Cyp2c44 gene would protect both sexes of mice from hypoxia-induced PH. We tested this hypothesis in wild-type (WT) and Cyp2c44 knockout (Cyp2c44 (-/-)) mice exposed to normoxia (room air) and hypoxia (10% O2) for 5 weeks. Exposure of WT and Cyp2c44 (-/-) mice to hypoxia resulted in pulmonary vascular remodeling, increased pulmonary artery resistance, and decreased cardiac function in both sexes. However, in female Cyp2c44 (-/-) mice, compared with WT mice, (1) pulmonary artery resistance and right ventricular hypertrophy were greater, (2) cardiac index was lower, (3) left ventricular and arterial stiffness were higher, and (4) plasma aldosterone levels were higher, but (5) there was no difference in levels of EET in lungs and heart. Paradoxically and unexpectedly, we found that Cyp2c44 disruption exacerbated hypoxia-induced PH in female but not male mice. We attribute exacerbated PH in female Cyp2c44 (-/-) mice to elevated aldosterone and as-yet-unknown systemic factors. Therefore, we suggest a role for the human CYP2C genes in protecting women from severe PH and that this could be one of the underlying causes for a better 5-year survival rate in women than in men.

Volume regulatory hormones and plasma volume in pregnant women with sickle cell disorder

Background:

Sickle cell disease (haemoglobin SS (HbSS)) mainly affects those of West African origin and is associated with hypervolaemia. Plasma volume rises by up to 50% in normal pregnancy but was previously found to be paradoxically contracted in late sickle cell pregnancy. The renin–angiotensin–aldosterone system is activated very early in human pregnancy to support the plasma volume expansion. We hypothesised that activation of the renin–angiotensin–aldosterone system would be blunted in pregnant women with sickle cell disease.

Materials and methods:

We measured plasma volume and concentrations of plasma renin, angiotensinogen, aldosterone and other volume-related hormones in a cross-sectional study of pregnant and non-pregnant Nigerian women with HbSS or HbAA.

Results:

Plasma volume was higher in non-pregnant HbSS than HbAA women, but had not risen by 16 weeks, unlike plasma volume in HbAA women. The concentration of plasma renin also rose significantly less by 16 weeks in HbSS; angiotensinogen and aldosterone concentrations increased.

Conclusions:

The lower plasma renin concentration at 16 weeks with HbSS could be either primary or secondary to vasoconstriction related to inadequate vasodilator activity. The contracted plasma volume might then stimulate aldosterone synthesis by non-angiotensin II dependent stimulation. Studies of vasodilators such as nitric oxide, vasodilator eicosanoids or the PlGF/VEGF/sFlT-1 axis in pregnant HbSS and HbAA women will test this hypothesis.

VLDL-activated cell signaling pathways that stimulate adrenal cell aldosterone production

Aldosterone plays an important role in regulating ion and fluid homeostasis and thus blood pressure, and hyperaldosteronism results in hypertension. Hypertension is also observed with obesity, which is associated with additional health risks, including cardiovascular disease. Obese individuals have high serum levels of very low-density lipoprotein (VLDL), which has been shown to stimulate aldosterone production; however, the mechanisms underlying VLDL-induced aldosterone production are still unclear. Here we demonstrate in human adrenocortical carcinoma (HAC15) cells that submaximal concentrations of angiotensin II and VLDL stimulate aldosterone production in an additive fashion, suggesting the possibility of common mechanisms of action. We show using inhibitors that VLDL-induced aldosterone production is mediated by the PLC/IP3/PKC signaling pathway. Our results suggest that PKC is upstream of the extracellular signal-regulated kinase (ERK) activation previously observed with VLDL. An understanding of the mechanisms mediating VLDL-induced aldosterone production may provide insights into therapies to treat obesity-associated hypertension.

The function and regulation of acid-sensing ion channels (ASICs) and the epithelial Na(+) channel (ENaC): IUPHAR Review 19

Acid-sensing ion channels (ASICs) and the epithelial Na(+) channel (ENaC) are both members of the ENaC/degenerin family of amiloride-sensitive Na(+) channels. ASICs act as proton sensors in the nervous system where they contribute, besides other roles, to fear behaviour, learning and pain sensation. ENaC mediates Na(+) reabsorption across epithelia of the distal kidney and colon and of the airways. ENaC is a clinically used drug target in the context of hypertension and cystic fibrosis, while ASIC is an interesting potential target. Following a brief introduction, here we will review selected aspects of ASIC and ENaC function. We discuss the origin and nature of pH changes in the brain and the involvement of ASICs in synaptic signalling. We expose how in the peripheral nervous system, ASICs cover together with other ion channels a wide pH range as proton sensors. We introduce the mechanisms of aldosterone-dependent ENaC regulation and the evidence for an aldosterone-independent control of ENaC activity, such as regulation by dietary K(+) . We then provide an overview of the regulation of ENaC by proteases, a topic of increasing interest over the past few years. In spite of the profound differences in the physiological and pathological roles of ASICs and ENaC, these channels share many basic functional and structural properties. It is likely that further research will identify physiological contexts in which ASICs and ENaC have similar or overlapping roles.

Clinical Practice Guideline for Management of Primary Aldosteronism: What is New in the 2016 Update?

Primary Aldosteronism is the single most common cause of secondary hypertension and is associated with increased target organ injury. The Endocrine Society has recently released the updated Clinical Practice Guideline for Primary Aldosteronism entitled “The Management of Primary Aldosteronism: Case Detection, Diagnosis, and Treatment: An Endocrine Society Clinical Practice Guideline”. We review the updated Clinical Practice Guideline, highlighting the new recommendations and the implications that they may have in clinical practice. The recognition by the Endocrine Society’s Task Force that Primary Aldosteronism is a public health issue and that the population at risk for screening should be significantly expanded will surely have an impact in the clinical practice which hopefully will translate in better detection, diagnosis and treatment of patients with Primary Aldosteronism.

Prenatal Testosterone Exposure Decreases Aldosterone Production but Maintains Normal Plasma Volume and Increases Blood Pressure in Adult Female Rats

Plasma testosterone levels are elevated in pregnant women with preeclampsia and polycystic ovaries; their offspring are at increased risk for hypertension during adult life. We tested the hypothesis that prenatal testosterone exposure induces dysregulation of the renin-angiotensin-aldosterone system, which is known to play an important role in water and electrolyte balance and blood pressure regulation. Female rats (6 mo old) prenatally exposed to testosterone were examined for adrenal expression of steroidogenic genes, telemetric blood pressure, blood volume and Na⁺ and K⁺ levels, plasma aldosterone, angiotensin II and vasopressin levels, and vascular responses to angiotensin II and arg⁸-vasopressin. The levels of Cyp11b2 (aldosterone synthase), but not the other adrenal steroidogenic genes, were decreased in testosterone females. Accordingly, plasma aldosterone levels were lower in testosterone females. Plasma volume and serum and urine Na⁺ and K⁺ levels were not significantly different between control and testosterone females; however, prenatal testosterone exposure significantly increased plasma vasopressin and angiotensin II levels and arterial pressure in adult females. In testosterone females, mesenteric artery contractile responses to angiotensin II were significantly greater, while contractile responses to vasopressin were unaffected. Angiotensin II type-1 receptor expression was increased, while angiotensin II type-2 receptor was decreased in testosterone arteries. These results suggest that prenatal testosterone exposure downregulates adrenal Cyp11b2 expression, leading to decreased plasma aldosterone levels. Elevated angiotensin II and vasopressin levels along with enhanced vascular responsiveness to angiotensin II may serve as an underlying mechanism to maintain plasma volume and Na⁺ and K⁺ levels and mediate hypertension in adult testosterone females.

Adipocytes, aldosterone and obesity-related hypertension

Understanding the mechanisms linking obesity with hypertension is important in the current obesity epidemic as it may improve therapeutic interventions. Plasma aldosterone levels are positively correlated with body mass index and weight loss in obese patients is reported to be accompanied by decreased aldosterone levels. This suggests a relationship between adipose tissue and the production/secretion of aldosterone. Aldosterone is synthesized principally by the adrenal glands, but its production may be regulated by many factors, including factors secreted by adipocytes. In addition, studies have reported local synthesis of aldosterone in extra-adrenal tissues, including adipose tissue. Experimental studies have highlighted a role for adipocyte-secreted aldosterone in the pathogenesis of obesity-related cardiovascular complications via the mineralocorticoid receptor. This review focuses on how aldosterone secretion may be influenced by adipose tissue and the importance of these mechanisms in the context of obesity-related hypertension.

Epigenomic changes associated with impaired norepinephrine transporter function in postural tachycardia syndrome

The postural tachycardia syndrome (POTS) is characterised clinically by symptoms of light-headedness, palpitations, fatigue and exercise intolerance occurring with standing and relieved by lying down. Symptoms occur in association with an inappropriate rise in heart rate in the absence of a fall in blood pressure with the assumption of standing. The pathophysiology of POTS is complicated and poorly understood. Plasma norepinephrine (NE) is often elevated in patients with POTS, resulting in consideration of dysfunction of the norepinephrine transporter (NET) encoded by SLC6A2 gene. Whilst some studies have implicated a defect in the SLC6A2 gene, the cause of reduced SLC6A2 expression and function remains unclear. The search to explain the molecular mechanism of NET dysfunction has focused on genetic variation in the SLC6A2 gene and remains inconclusive. More recent studies show epigenetic mechanisms implicated in the regulation of SLC6A2 expression. In this article, we discuss the epigenetic mechanisms involved in SLC6A2 repression and highlight the potential therapeutic application of targeting these mechanisms in POTS.