Control of aldosterone secretion: a model for convergence in cellular signaling pathways

Modulation of Calcium Signaling on Demand to Decipher the Molecular Mechanisms of Primary Aldosteronism

BACKGROUND

Primary aldosteronism is the most common form of secondary hypertension. The most frequent genetic cause of aldosterone-producing adenomas is somatic mutations in the potassium channel KCNJ5. They affect the ion selectivity of the channel, with sodium influx leading to cell membrane depolarization and activation of calcium signaling, the major trigger for aldosterone biosynthesis.

METHODS

To investigate how KCNJ5 mutations lead to the development of aldosterone-producing adenomas, we established an adrenocortical cell model in which sodium entry into the cells can be modulated on demand using chemogenetic tools [H295R-S2 α7-5HT3-R (α7-5HT3 receptor) cells]. We investigated their functional and molecular characteristics with regard to aldosterone biosynthesis and cell proliferation.

RESULTS

A clonal cell line with stable expression of the chimeric α7-5HT3-R in H295R-S2 (human adrenocortical carcinoma cell line, Strain 2) cells was obtained. Increased sodium entry through α7-5HT3-R upon stimulation with uPSEM-817 (uPharmacologically Selective Effector Molecule-817) led to cell membrane depolarization, opening of voltage-gated Ca2+ channels, and increased intracellular Ca2+ concentrations, resulting in the stimulation of CYP11B2 expression and increased aldosterone biosynthesis. Increased intracellular sodium influx did not increase proliferation but rather induced apoptosis. RNA sequencing and steroidome analyses revealed unique profiles associated with Na+ entry, with only partial overlap with Ang II (angiotensin II) or potassium-induced changes.

CONCLUSIONS

H295R-S2 α7-5HT3-R cells are a new model reproducing the major features of cells harboring KCNJ5 mutations. Increased expression of CYP11B2 and stimulation of the mineralocorticoid biosynthesis pathway are associated with a decrease of cell proliferation and an increase of apoptosis, indicating that additional events may be required for the development of aldosterone-producing adenomas.

Identification of angiotensin II-responsive circadian clock gene expression in adrenal zona glomerulosa cells and human adrenocortical H295R cells

The mammalian circadian timing system is organized in a hierarchy, with the master clock residing in the suprachiasmatic nucleus (SCN) of the hypothalamus and subsidiary peripheral clocks in peripheral tissues. Because of the diversity of peripheral tissues and cell-types in the body, the existence of autonomous clock and identification of its potential entrainment signals need to be empirically defined on a cell type-by-cell type basis. In this study, we characterized the basic circadian clock properties of the adrenal zona glomerulosa cells, or ZG cells. Using isolated adrenal explants from Per2Luc mice, dissociated ZG cells from Per2-dluc rats, and a related human adrenocortical cell line H295R, we showed that ZG cells possess genetically-encoded, self-sustained and cell-autonomous circadian clock. As to the potential entrainment signals, angiotensin II (Ang II) caused phase-dependent phase-shifts of adrenal ZG cells in cultured slices. Ang II treatment also drove initiation (or reset) of circadian clock gene expression in H295R cells with associated immediate up-regulation of PER1 and E4BP4 mRNA expression. We found that the type I Ang II receptor blocker CV11974, one of the most widely used clinical drugs for hypertensive diseases, caused attenuation of the phase resetting of H295R cells. Our in vitro data provide a basis to understand and argue for the adrenal gland ZG cells as a component of autonomous and entrainable peripheral clocks.

The effect of consuming a sucrose-containing sports drink on acute kidney injury risk during a 4 h simulated occupational heat stress

Occupational heat stress increases acute kidney injury risk. Drinking a soft drink sweetened with high fructose corn syrup further elevates this acute kidney injury risk. However, the impact of sucrose, another fructose-containing sweetener, on acute kidney injury risk remains unexplored. We tested the hypothesis that drinking a sucrose-containing sports drink increases acute kidney injury risk when compared to drinking a sugar-free sports drink during 4 h of simulated occupational heat stress. Ten healthy adults consumed a sucrose-containing or sugar-free sport drink ad libitum during 4 h exposures to wet bulb globe temperatures of ∼28 °C. Thirty min of work and 30 min of rest were completed each hour. Work involved treadmill walking at a fixed rate of metabolic heat production (sucrose-containing: 6.0 ± 1.2 W/kg, sugar-free: 5.5 ± 0.9 W/kg, p = 0.267). The product of urinary insulin-like growth factor-binding protein 7 and tissue inhibitor of metalloproteinase-2, normalized to urine specific gravity ([IGFBP7·TIMP-2]USG), provided an acute kidney injury risk index. Mean core (intestinal: n = 13, rectal: n = 7) temperature (sucrose-containing: 37.5 ± 0.1 °C, sugar-free: 37.5 ± 0.3 °C; p = 0.914), peak core temperature (sucrose-containing: 37.8 ± 0.2 °C, sugar-free: 37.9 ± 0.3 °C; p = 0.398), and percent changes in body mass (sucrose-containing: -0.5 ± 0.4%, sugar-free: -0.3 ± 0.6%; p = 0.386) did not differ between groups. [IGFBP7∙TIMP-2]USG increased in both groups (time effect: p = 0.025) with no drink (p = 0.675) or interaction (p = 0.715) effects. Peak change [IGFBP7∙TIMP-2]USG did not differ between sucrose-containing (median 0.0116 [-0.0012, 0.1760] (ng/mL)2/1000) and sugar-free (median 0.0021 [0.0003, 0.2077] (ng/mL)2/1000; p = 0.796). Sucrose-containing sports drink consumption during simulated occupational heat stress does not modify acute kidney injury risk when compared to sugar free-sport drink consumption.

An In Silico Investigation of the Pathogenic G151R G Protein-Gated Inwardly Rectifying K+ Channel 4 Variant to Identify Small Molecule Modulators

Primary aldosteronism is characterised by the excessive production of aldosterone, which is a key regulator of salt metabolism, and is the most common cause of secondary hypertension. Studies have investigated the association between primary aldosteronism and genetic alterations, with pathogenic mutations being identified. This includes a glycine-to-arginine substitution at position 151 (G151R) of the G protein-activated inward rectifier potassium (K+) channel 4 (GIRK4), which is encoded by the KCNJ5 gene. Mutations in GIRK4 have been found to reduce the selectivity for K+ ions, resulting in membrane depolarisation, the activation of voltage-gated Ca2+ channels, and an increase in aldosterone secretion. As a result, there is an interest in identifying and exploring the mechanisms of action of small molecule modulators of wildtype (WT) and mutant channels. In order to investigate the potential modulation of homotetrameric GIRK4WT and GIRK4G151R channels, homology models were generated. Molecular dynamics (MD) simulations were performed, followed by a cluster analysis to extract starting structures for molecular docking. The central cavity has been previously identified as a binding site for small molecules, including natural compounds. The OliveNetTM database, which consists of over 600 compounds from Olea europaea, was subsequently screened against the central cavity. The binding affinities and interactions of the docked ligands against the GIRK4WT and GIRK4G151R channels were then examined. Based on the results, luteolin-7-O-rutinoside, pheophorbide a, and corosolic acid were identified as potential lead compounds. The modulatory activity of olive-derived compounds against the WT and mutated forms of the GIRK4 channel can be evaluated further in vitro.

Suppression of neurons in circumventricular organs enables months-long survival without water in thirteen-lined ground squirrels

Water deprivation is a life-threatening condition that engages a protective physiological response to couple osmolyte retention with potentiation of thirst. This response, typical for most mammals, safeguards against short-term water deprivation but fails in the long term. Thirteen-lined ground squirrels (Ictidomys tridecemlineatus) use the short-term response during summer, whereas during winter, they lack thirst and survive without water for months. In this work, we show that long-term thirst suppression occurs despite hormonal and behavioral signs of a substantial fluid deficit and originates from hypoactivity of neurons in the circumventricular organs, which exhibit marked functional suppression during winter that blunts their sensitivity to thirst cues. Our work reveals a notable capacity of the evolutionarily conserved brain regions that control fluid homeostasis in mammals to enable long-term survival without water.

Associating plasma aldosterone concentration with the prevalence of MAFLD in hypertensive patients: insights from a large-scale cross-sectional study

Objective

To explore the link between plasma aldosterone concentration (PAC) and the prevalence of metabolic dysfunction-related fatty liver disease (MAFLD) in hypertensive patients.

Methods

We analyzed data from 41,131 hospitalized patients from January 1, 2014, to December 31, 2023. Multivariate logistic regression models tested associations, with threshold, subgroup, and sensitivity analyses conducted to validate findings.

Results

For each 5-unit increase in PAC, the risk of MAFLD rose by 1.57 times, consistent even in the fully adjusted model. The odds ratios for the Q2, Q3, and Q4 groups compared to Q1 were 1.21, 2.12, and 3.14, respectively. A threshold effect was observed at 14 ng/dL, with subgroup and sensitivity analyses supporting these results.

Conclusions

This study reveals a significant positive association between elevated PAC levels and the prevalence of MAFLD in hypertensive patients. These findings underscore the imperative for further large-scale, prospective studies to validate and expand upon this correlation.

Clinical Properties and Non-Clinical Testing of Mineralocorticoid Receptor Antagonists in In Vitro Cell Models

Mineralocorticoid receptor antagonists (MRAs) are one of the renin-angiotensin-aldosterone system inhibitors widely used in clinical practice. While spironolactone and eplerenone have a long-standing profile in clinical medicine, finerenone is a novel agent within the MRA class. It has a higher specificity for mineralocorticoid receptors, eliciting less pronounced adverse effects. Although approved for clinical use in patients with chronic kidney disease and heart failure, intensive non-clinical research aims to further elucidate its mechanism of action, including dose-related selectivity. Within the field, animal models remain the gold standard for non-clinical testing of drug pharmacological and toxicological properties. Their role, however, has been challenged by recent advances in in vitro models, mainly through sophisticated analytical tools and developments in data analysis. Currently, in vitro models are gaining momentum as possible platforms for advanced pharmacological and pathophysiological studies. This article focuses on past, current, and possibly future in vitro cell models research with clinically relevant MRAs.

Nephrectomy and high-salt diet inducing pulmonary hypertension and kidney damage by increasing Ang II concentration in rats

BACKGROUND

Chronic kidney disease (CKD) is a significant risk factor for pulmonary hypertension (PH), a complication that adversely affects patient prognosis. However, the mechanisms underlying this association remain poorly understood. A major obstacle to progress in this field is the lack of a reliable animal model replicating CKD-PH.

METHODS

This study aimed to establish a stable rat model of CKD-PH. We employed a combined approach, inducing CKD through a 5/6 nephrectomy and concurrently exposing the rats to a high-salt diet. The model's hemodynamics were evaluated dynamically, alongside a comprehensive assessment of pathological changes in multiple organs. Lung tissues and serum samples were collected from the CKD-PH rats to analyze the expression of angiotensin-converting enzyme 2 (ACE2), evaluate the activity of key vascular components within the renin-angiotensin-aldosterone system (RAAS), and characterize alterations in the serum metabolic profile.

RESULTS

At 14 weeks post-surgery, the CKD-PH rats displayed significant changes in hemodynamic parameters indicative of pulmonary arterial hypertension. Additionally, right ventricular hypertrophy was observed. Notably, no evidence of pulmonary vascular remodeling was found. Further analysis revealed RAAS dysregulation and downregulated ACE2 expression within the pulmonary vascular endothelium of CKD-PH rats. Moreover, the serum metabolic profile of these animals differed markedly from the sham surgery group.

CONCLUSIONS

Our findings suggest that the development of pulmonary arterial hypertension in CKD-PH rats is likely a consequence of a combined effect: RAAS dysregulation, decreased ACE2 expression in pulmonary vascular endothelial cells, and metabolic disturbances.

The ex vivo perfused mouse adrenal gland-a new model to study aldosterone secretion

Aldosterone is a steroid hormone that is important for maintaining the volume and ionic composition of extracellular fluids and is produced in the zona glomerulosa of the adrenal cortex. The basic mechanisms controlling aldosterone secretion are known. However, more detailed studies on the regulation of aldosterone secretion often fail due to the lack of suitable models: although secretion can be studied in cultured adrenocortical cells under defined conditions, the differentiation status of the cells is difficult to control and the complex anatomy of the adrenal cortex is lost. In living animals, the physiological context is intact, but the influences are manifold and the examination conditions cannot be sufficiently controlled. One method that closes the gap between cell models and studies in living animals is the isolated perfused adrenal gland. In the past, this method has provided important data on the pathophysiology of adrenal glands from larger animals, but the technique was not used in mice. Here, we developed a method for isolation and perfusion of the mouse adrenal gland to study aldosterone secretion. This technique preserves the complex anatomical and functional context of the mouse adrenal cortex, to ensure defined experimental conditions and to minimize extra-adrenal influences. Initial series of experiments with the ex vivo perfused mouse adrenal gland show that this model offers the possibility for unique insights into pathophysiological regulatory principles and is suitable for the use of genetically modified mouse models.

Characterization of a Biochemical Mouse Model of Primary Aldosteronism for Thermal Therapies

Introduction

Aldosterone-producing adenoma (APA) is the most common cause of endocrine-related hypertension but surgery is not always feasible. Current medical interventions are associated with significant side effects and poor patient compliance. New APA animal models that replicate basic characteristics of APA and give physical and biochemical feedback are needed to test new non-surgical treatment methods, such as image-guided thermal ablation.

Methods

A model of APA was developed in nude mice using HAC15 cells, a human adrenal carcinoma cell line. Tumor growth, aldosterone production, and sensitivity to angiotensin II were characterized in the model. The utility of the model was validated via treatment with microwave ablation and characterization of the resulting physical and biochemical changes in the tumor.

Results

The APA model showed rapid and relatively homogeneous growth. The tumors produced aldosterone and steroid precursors in response to angiotensin II challenge, and plasma aldosterone levels were significantly higher in tumor bearing mice two hours after challenge verses non-tumor bearing mice. The model was useful for testing microwave ablation therapy, reducing aldosterone production by 80% in treated mice.

Conclusion

The HAC15 model is a useful tumor model to study and develop localized treatment methods for APA.

Targeting androgen biosynthesis in prostate cancer: implications on endocrine physiology

PURPOSE OF REVIEW

Targeting specific steroidogenic enzymes is effective in decreasing testosterone synthesis, resulting in significant antitumor effects in prostate cancer. Such treatments result in disruptions of complicated and intertwining pathways with systemic physiologic consequences via effects on the adrenal gland and renin-angiotensin-aldosterone axis. This review highlights some of these aspects that need to be taken into consideration when treating patients with androgen biosynthesis inhibitors.

RECENT FINDINGS

Targeting CYP17A1, a key enzyme involved in androgen biosynthesis, is a well established treatment in prostate cancer. More recently, efforts are underway to target a gatekeeper enzyme of steroidogenesis, CYP11A1. This enzyme mediates conversion of cholesterol to pregnenolone, the first step in steroid hormone biogenesis. Studies are beginning to demonstrate antitumor effects of ODM-208, a CYP11A1 inhibitor in prostate cancer. Although anticipated to have a therapeutic role in prostate cancer, there are potential downstream effects of CYP11A1 targeting arising from suppression of the entire adrenal cortex, including long-term adrenal insufficiency and possibly cardiovascular dysregulation.

SUMMARY

Agents targeting androgen biosynthesis can have systemic implications. Balancing management of prostate cancer with better understanding of the mechanisms associated with potential side effects will allow for patients to obtain improved antitumor benefit while mitigating against treatment-associated adverse effects.

Juxtaglomerular apparatus-mediated homeostatic mechanisms: therapeutic implication for chronic kidney disease

INTRODUCTION

Juxtaglomerular apparatus (JGA)-mediated homeostatic mechanism links to how sodium-glucose cotransporter 2 inhibitors (SGLT2is) slow progression of chronic kidney disease (CKD) and may link to how tolvaptan slows renal function decline in autosomal dominant polycystic kidney disease (ADPKD).

AREA COVERED

JGA-mediated homeostatic mechanism has been hypothesized based on investigations of tubuloglomerular feedback and renin-angiotensin system. We reviewed clinical trials of SGLT2is and tolvaptan to assess the relationship between this mechanism and these drugs.

EXPERT OPINION

When sodium load to macula densa (MD) increases, MD increases adenosine production, constricting afferent arteriole (Af-art) and protecting glomeruli. Concurrently, MD signaling suppresses renin secretion, increases urinary sodium excretion, and counterbalances reduced sodium filtration. However, when there is marked increase in sodium load per-nephron, as in advanced CKD, MD adenosine production increases, relaxing Af-art and maintaining sodium homeostasis at the expense of glomeruli. The beneficial effects of tolvaptan on renal function in ADPKD may also depend on the JGA-mediated homeostatic mechanisms since tolvaptan inhibits sodium reabsorption in the thick ascending limb.The JGA-mediated homeostatic mechanism regulates Af-arts, constricting to relaxing according to homeostatic needs. Understanding this mechanism may contribute to the development of pharmacotherapeutic compounds and better care for patients with CKD.

The Molecular Mechanisms Underlying the Systemic Effects Mediated by Parathormone in the Context of Chronic Kidney Disease

Chronic kidney disease (CKD) stands as a prominent non-communicable ailment, significantly impacting life expectancy. Physiopathology stands mainly upon the triangle represented by parathormone-Vitamin D-Fibroblast Growth Factor-23. Parathormone (PTH), the key hormone in mineral homeostasis, is one of the less easily modifiable parameters in CKD; however, it stands as a significant marker for assessing the risk of complications. The updated "trade-off hypothesis" reveals that levels of PTH spike out of the normal range as early as stage G2 CKD, advancing it as a possible determinant of systemic damage. The present review aims to review the effects exhibited by PTH on several organs while linking the molecular mechanisms to the observed actions in the context of CKD. From a diagnostic perspective, PTH is the most reliable and accessible biochemical marker in CKD, but its trend bears a higher significance on a patient's prognosis rather than the absolute value. Classically, PTH acts in a dichotomous manner on bone tissue, maintaining a balance between formation and resorption. Under the uremic conditions of advanced CKD, the altered intestinal microbiota majorly tips the balance towards bone lysis. Probiotic treatment has proven reliable in animal models, but in humans, data are limited. Regarding bone status, persistently high levels of PTH determine a reduction in mineral density and a concurrent increase in fracture risk. Pharmacological manipulation of serum PTH requires appropriate patient selection and monitoring since dangerously low levels of PTH may completely inhibit bone turnover. Moreover, the altered mineral balance extends to the cardiovascular system, promoting vascular calcifications. Lastly, the involvement of PTH in the Renin-Angiotensin-Aldosterone axis highlights the importance of opting for the appropriate pharmacological agent should hypertension develop.

T- and L-Type Calcium Channels Maintain Calcium Oscillations in the Murine Zona Glomerulosa

BACKGROUND

The zona glomerulosa of the adrenal gland is responsible for the synthesis and release of the mineralocorticoid aldosterone. This steroid hormone regulates salt reabsorption in the kidney and blood pressure. The most important stimuli of aldosterone synthesis are the serum concentrations of angiotensin II and potassium. In response to these stimuli, voltage and intracellular calcium levels in the zona glomerulosa oscillate, providing the signal for aldosterone synthesis. It was proposed that the voltage-gated T-type calcium channel CaV3.2 is necessary for the generation of these oscillations. However, Cacna1h knock-out mice have normal plasma aldosterone levels, suggesting additional calcium entry pathways.

METHODS

We used a combination of calcium imaging, patch clamp, and RNA sequencing to investigate calcium influx pathways in the murine zona glomerulosa.

RESULTS

Cacna1h-/- glomerulosa cells still showed calcium oscillations with similar concentrations as wild-type mice. No calcium channels or transporters were upregulated to compensate for the loss of CaV3.2. The calcium oscillations observed were instead dependent on L-type voltage-gated calcium channels. Furthermore, we found that L-type channels can also partially compensate for an acute inhibition of CaV3.2 in wild-type mice. Only inhibition of both T- and L-type calcium channels abolished the increase of intracellular calcium caused by angiotensin II in wild-type.

CONCLUSIONS

Our study demonstrates that T-type calcium channels are not strictly required to maintain glomerulosa calcium oscillations and aldosterone production. Pharmacological inhibition of T-type channels alone will likely not significantly impact aldosterone production in the long term.

Adrenal Anion Channels: New Roles in Zona Glomerulosa Physiology and in the Pathophysiology of Primary Aldosteronism

The mineralocorticoid aldosterone is produced in the zona glomerulosa of the adrenal cortex. Its synthesis is regulated by the serum concentrations of the peptide hormone angiotensin II and potassium. The primary role of aldosterone is to control blood volume and electrolytes. The autonomous production of aldosterone (primary aldosteronism, PA) is considered the most frequent cause of secondary hypertension. Aldosterone-producing adenomas and (micro-)nodules are frequent causes of PA and often carry somatic mutations in ion channels and transporters. Rare familial forms of PA are due to germline mutations. Both somatic and germline mutations in the chloride channel gene CLCN2, encoding ClC-2, have been identified in PA. Clinical findings and results from cell culture and animal models have advanced our knowledge about the role of anions in PA. The zona glomerulosa of the adrenal gland has now been firmly established as a tissue in which anions play a significant role for signaling. In this overview, we aim to summarize the current knowledge and highlight novel concepts as well as open questions.

Role of aldosterone and mineralocorticoid receptor (MR) in addiction: A scoping review

Preclinical and human studies suggest a role of aldosterone and mineralocorticoid receptor (MR) in addiction. This scoping review aimed to summarize (1) the relationship between alcohol and other substance use disorders (ASUDs) and dysfunctions of the aldosterone and MR, and (2) how pharmacological manipulations of MR may affect ASUD-related outcomes. Our search in four databases (MEDLINE, Embase, Web of Science, and Cochrane Library) indicated that most studies focused on the relationship between aldosterone, MR, and alcohol (n = 30), with the rest focused on opioids (n = 5), nicotine (n = 9), and other addictive substances (n = 9). Despite some inconsistencies, the overall results suggest peripheral and central dysregulations of aldosterone and MR in several species and that these dysregulations depended on the pattern of drug exposure and genetic factors. We conclude that MR antagonism may be a promising target in ASUD, yet future studies are warranted.

Englerin A Inhibits T-Type Voltage-Gated Calcium Channels at Low Micromolar Concentrations

Englerin A (EA) is a potent agonist of tetrameric transient receptor potential canonical (TRPC) ion channels containing TRPC4 and TRPC5 subunits. TRPC proteins form cation channels that are activated by plasma membrane receptors. They convert extracellular signals such as angiotensin II into cellular responses, whereupon Na+ and Ca2+ influx and depolarization of the plasma membrane occur. Via depolarization, voltage-gated Ca2+ (CaV) channels can be activated, further increasing Ca2+ influx. We investigated the extent to which EA also affects the functions of CaV channels using the high-voltage-activated L-type Ca2+ channel CaV1.2 and the low-voltage-activated T-type Ca2+ channels CaV3.1, CaV3.2, and CaV3.3. After expression of cDNAs in human embryonic kidney (HEK293) cells, EA inhibited currents through all T-type channels at half-maximal inhibitory concentrations (IC50) of 7.5 to 10.3 μM. In zona glomerulosa cells of the adrenal gland, angiotensin II-induced elevation of cytoplasmic Ca2+ concentration leads to aldosterone release. We identified transcripts of low- and high-voltage-activated CaV channels and of TRPC1 and TRPC5 in the human adrenocortical (HAC15) zona glomerulosa cell line. Although no EA-induced TRPC activity was measurable, Ca2+ channel blockers distinguished T- and L-type Ca2+ currents. EA blocked 60% of the CaV current in HAC15 cells and T- and L-type channels analyzed at -30 mV and 10 mV were inhibited with IC50 values of 2.3 and 2.6 μM, respectively. Although the T-type blocker Z944 reduced basal and angiotensin II-induced 24-hour aldosterone release, EA was not effective. In summary, we show here that EA blocks CaV1.2 and T-type CaV channels at low-micromolar concentrations. SIGNIFICANCE STATEMENT: In this study we showed that englerin A (EA), a potent agonist of tetrameric transient receptor potential canonical (TRPC)4- or TRPC5-containing channels and currently under investigation to treat certain types of cancer, also inhibits the L-type voltage-gated Ca2+ (CaV) channel CaV1.2 and the T-type CaV channels CaV3.1, CaV3.2, and CaV3.3 channels at low micromolar concentrations.

Regulation of the renin-angiotensin-aldosterone system by cyclic nucleotides and phosphodiesterases

The renin-angiotensin-aldosterone system (RAAS) is one of the key players in the regulation of blood volume and blood pressure. Dysfunction of this system is connected with cardiovascular and renal diseases. Regulation of RAAS is under the control of multiple intracellular mechanisms. Cyclic nucleotides and phosphodiesterases are the major regulators of this system since they control expression and activity of renin and aldosterone. In this review, we summarize known mechanisms by which cyclic nucleotides and phosphodiesterases regulate renin gene expression, secretion of renin granules from juxtaglomerular cells and aldosterone production from zona glomerulosa cells of adrenal gland. We also discuss several open questions which deserve future attention.

An Abbreviated History of Aldosterone Metabolism, Current and Future Challenges

The initial isolation of adrenal steroids from large quantities of animal adrenals resulted in an amorphous fraction resistant to crystallization and identification and had potent effects on electrolyte transport. Aldosterone was eventually isolated and identified in the fraction and was soon shown to cause hypertension when in excess. The autonomous and excessive production of aldosterone, primary aldosteronism, is the most common cause of secondary hypertension. Aldosterone is metabolized in the liver and kidney, and its metabolites are conjugated with glucuronic acid for excretion. The most common liver metabolite is 3α,5β-tetrahydroaldosterone-3-glucuronide, while that of the kidney is aldosterone-18-oxo-glucuronide. In terms of their value, especially the aldosterone-18-oxo-glucuronide, is commonly used for the diagnosis of primary aldosteronism because they provide an integrated value of the total daily production of aldosterone. Conversion of aldosterone to 18-oxo-glucuronide is impeded by drugs, like some common non-steroidal anti-inflammatory drugs that compete for UDP-glucuronosyltransferase-2B7, the most important glucuronosyltransferase for aldosterone metabolism. Tetrahydroaldosterone is the most abundant metabolite and the most reliable for the diagnosis of primary aldosteronism, but it is not commonly measured.

Calcineurin regulates aldosterone production via dephosphorylation of NFATC4

The mineralocorticoid aldosterone, secreted by the adrenal zona glomerulosa (ZG), is critical for life, maintaining ion homeostasis and blood pressure. Therapeutic inhibition of protein phosphatase 3 (calcineurin, Cn) results in inappropriately low plasma aldosterone levels despite concomitant hyperkalemia and hyperreninemia. We tested the hypothesis that Cn participates in the signal transduction pathway regulating aldosterone synthesis. Inhibition of Cn with tacrolimus abolished the potassium-stimulated (K+-stimulated) expression of aldosterone synthase, encoded by CYP11B2, in the NCI-H295R human adrenocortical cell line as well as ex vivo in mouse and human adrenal tissue. ZG-specific deletion of the regulatory Cn subunit CnB1 diminished Cyp11b2 expression in vivo and disrupted K+-mediated aldosterone synthesis. Phosphoproteomics analysis identified nuclear factor of activated T cells, cytoplasmic 4 (NFATC4), as a target for Cn-mediated dephosphorylation. Deletion of NFATC4 impaired K+-dependent stimulation of CYP11B2 expression and aldosterone production while expression of a constitutively active form of NFATC4 increased expression of CYP11B2 in NCI-H295R cells. Chromatin immunoprecipitation revealed NFATC4 directly regulated CYP11B2 expression. Thus, Cn controls aldosterone production via the Cn/NFATC4 pathway. Inhibition of Cn/NFATC4 signaling may explain low plasma aldosterone levels and hyperkalemia in patients treated with tacrolimus, and the Cn/NFATC4 pathway may provide novel molecular targets to treat primary aldosteronism.

The Role of Renin-Angiotensin System in Diabetic Cardiomyopathy: A Narrative Review

Diabetic cardiomyopathy refers to myocardial dysfunction in type 2 diabetes, but without the traditional cardiovascular risk factors or overt clinical atherosclerosis and valvular disease. The activation of the renin-angiotensin system (RAS), oxidative stress, lipotoxicity, maladaptive immune responses, imbalanced mitochondrial dynamics, impaired myocyte autophagy, increased myocyte apoptosis, and fibrosis contribute to diabetic cardiomyopathy. This review summarizes the studies that address the link between cardiomyopathy and the RAS in humans and presents proposed pathophysiological mechanisms underlying this association. The RAS plays an important role in the development and progression of diabetic cardiomyopathy. The over-activation of the classical RAS axis in diabetes leads to the increased production of angiotensin (Ang) II, angiotensin type 1 receptor activation, and aldosterone release, contributing to increased oxidative stress, fibrosis, and cardiac remodeling. In contrast, Ang-(1-7) suppresses oxidative stress, inhibits tissue fibrosis, and prevents extensive cardiac remodeling. Angiotensin-converting-enzyme (ACE) inhibitors and angiotensin receptor blockers improve heart functioning and reduce the occurrence of diabetic cardiomyopathy. Experimental studies also show beneficial effects for Ang-(1-7) and angiotensin-converting enzyme 2 infusion in improving heart functioning and tissue injury. Further research is necessary to fully understand the pathophysiology of diabetic cardiomyopathy and to translate experimental findings into clinical practice.

Serotonin and the serotonin transporter in the adrenal gland

The adrenal glands are key components of the mammalian endocrine system, helping maintain physiological homeostasis and the coordinated response to stress. Each adrenal gland has two morphologically and functionally distinct regions, the outer cortex and inner medulla. The cortex is organized into three concentric zones which secrete steroid hormones, including aldosterone and cortisol. Neural crest-derived chromaffin cells in the medulla are innervated by preganglionic sympathetic neurons and secrete catecholamines (epinephrine, norepinephrine) and neuropeptides into the bloodstream, thereby functioning as the neuroendocrine arm of the sympathetic nervous system. In this article we review serotonin (5-HT) and the serotonin transporter (SERT; SLC6A4) in the adrenal gland. In the adrenal cortex, 5-HT, primarily sourced from resident mast cells, acts as a paracrine signal to stimulate aldosterone and cortisol secretion through 5-HT4/5-HT7 receptors. Medullary chromaffin cells contain a small amount of 5-HT due to SERT-mediated uptake and express 5-HT1A receptors which inhibit secretion. The atypical mechanism of the 5-HT1A receptors and interaction with SERT fine tune this autocrine pathway to control stress-evoked catecholamine secretion. Receptor-independent signaling by SERT/intracellular 5-HT modulates the amount and kinetics of transmitter release from single vesicle fusion events. SERT might also influence stress-evoked upregulation of tyrosine hydroxylase transcription. Transient signaling via 5-HT3 receptors during embryonic development can limit the number of chromaffin cells found in the mature adrenal gland. Together, this emerging evidence suggests that the adrenal medulla is a peripheral hub for serotonergic control of the sympathoadrenal stress response.

CaV3.2 (CACNA1H) in Primary Aldosteronism

Aldosterone is a steroid hormone produced in the zona glomerulosa (ZG) of the adrenal cortex. The most prominent function of aldosterone is the control of electrolyte homeostasis and blood pressure via the kidneys. The primary factors regulating aldosterone synthesis are the serum concentrations of angiotensin II and potassium. The T-type voltage-gated calcium channel Ca_V3.2 (encoded by CACNA1H) is an important component of electrical as well as intracellular calcium oscillations, which govern aldosterone production in the ZG. Excessive aldosterone production that is (partially) uncoupled from physiological stimuli leads to primary aldosteronism, the most common cause of secondary hypertension. Germline gain-of-function mutations in CACNA1H were identified in familial hyperaldosteronism, whereas somatic mutations are a rare cause of aldosterone-producing adenomas. In this review, we summarize these findings, put them in perspective, and highlight missing knowledge.

Angiotensin II-dependent aldosterone production in the adrenal cortex

The adrenal cortex is responsible for production of adrenal steroid hormones and is anatomically divided into three distinct zones: zona glomerulosa secreting mineralocorticoids (mainly aldosterone), zona fasciculata secreting glucocorticoids (cortisol), and zona reticularis producing androgens. Importantly, due to their high lipophilicity, no adrenal steroid hormone (including aldosterone) is stored in vesicles but rather gets synthesized and secreted instantly upon cell stimulation with specific stimuli. Aldosterone is the most potent mineralocorticoid hormone produced from the adrenal cortex in response to either angiotensin II (AngII) or elevated K+ levels in the blood (hyperkalemia). AngII, being a peptide, cannot cross cell membranes and thus, uses two distinct G protein-coupled receptor (GPCR) types, AngII type 1 receptor (AT1R) and AT2R to exert its effects inside cells. In zona glomerulosa cells, AT1R activation by AngII results in aldosterone synthesis and secretion via two main pathways: (a) Gq/11 proteins that activate phospholipase C ultimately raising intracellular free calcium concentration; and (b) βarrestin1 and -2 (also known as Arrestin-2 and -3, respectively) that elicit sustained extracellular signal-regulated kinase (ERK) activation. Both pathways induce upregulation and acute activation of StAR (steroidogenic acute regulatory) protein, the enzyme that catalyzes the rate-limiting step in aldosterone biosynthesis. This chapter describes these two salient pathways underlying AT1R-induced aldosterone production in zona glomerulosa cells. We also highlight some pharmacologically important notions pertaining to the efficacy of the currently available AT1R antagonists, also known as angiotensin receptor blockers (ARBs) or sartans at suppressing both pathways, i.e., their inverse agonism efficacy at G proteins and βarrestins.

Role of Angiotensin II in Cardiovascular Diseases: Introducing Bisartans as a Novel Therapy for Coronavirus 2019

Cardiovascular diseases (CVDs) are the main contributors to global morbidity and mortality. Major pathogenic phenotypes of CVDs include the development of endothelial dysfunction, oxidative stress, and hyper-inflammatory responses. These phenotypes have been found to overlap with the pathophysiological complications of coronavirus disease 2019 (COVID-19). CVDs have been identified as major risk factors for severe and fatal COVID-19 states. The renin-angiotensin system (RAS) is an important regulatory system in cardiovascular homeostasis. However, its dysregulation is observed in CVDs, where upregulation of angiotensin type 1 receptor (AT1R) signaling via angiotensin II (AngII) leads to the AngII-dependent pathogenic development of CVDs. Additionally, the interaction between the spike protein of severe acute respiratory syndrome coronavirus 2 with angiotensin-converting enzyme 2 leads to the downregulation of the latter, resulting in the dysregulation of the RAS. This dysregulation favors AngII/AT1R toxic signaling pathways, providing a mechanical link between cardiovascular pathology and COVID-19. Therefore, inhibiting AngII/AT1R signaling through angiotensin receptor blockers (ARBs) has been indicated as a promising therapeutic approach to the treatment of COVID-19. Herein, we review the role of AngII in CVDs and its upregulation in COVID-19. We also provide a future direction for the potential implication of a novel class of ARBs called bisartans, which are speculated to contain multifunctional targeting towards COVID-19.

Aldosterone: Renal Action and Physiological Effects

Aldosterone exerts profound effects on renal and cardiovascular physiology. In the kidney, aldosterone acts to preserve electrolyte and acid-base balance in response to changes in dietary sodium (Na+ ) or potassium (K+ ) intake. These physiological actions, principally through activation of mineralocorticoid receptors (MRs), have important effects particularly in patients with renal and cardiovascular disease as demonstrated by multiple clinical trials. Multiple factors, be they genetic, humoral, dietary, or otherwise, can play a role in influencing the rate of aldosterone synthesis and secretion from the adrenal cortex. Normally, aldosterone secretion and action respond to dietary Na+ intake. In the kidney, the distal nephron and collecting duct are the main targets of aldosterone and MR action, which stimulates Na+ absorption in part via the epithelial Na+ channel (ENaC), the principal channel responsible for the fine-tuning of Na+ balance. Our understanding of the regulatory factors that allow aldosterone, via multiple signaling pathways, to function properly clearly implicates this hormone as central to many pathophysiological effects that become dysfunctional in disease states. Numerous pathologies that affect blood pressure (BP), electrolyte balance, and overall cardiovascular health are due to abnormal secretion of aldosterone, mutations in MR, ENaC, or effectors and modulators of their action. Study of the mechanisms of these pathologies has allowed researchers and clinicians to create novel dietary and pharmacological targets to improve human health. This article covers the regulation of aldosterone synthesis and secretion, receptors, effector molecules, and signaling pathways that modulate its action in the kidney. We also consider the role of aldosterone in disease and the benefit of mineralocorticoid antagonists. © 2023 American Physiological Society. Compr Physiol 13:4409-4491, 2023.

New advances in endocrine hypertension: from genes to biomarkers

Hypertension (HT) is a major cardiovascular risk factor that affects 10% to 40% of the general population in an age-dependent manner. Detection of secondary forms of HT is particularly important because it allows the targeted management of the underlying disease. Among hypertensive patients, the prevalence of endocrine HT reaches up to 10%. Adrenal diseases are the most frequent cause of endocrine HT and are associated with excess production of mineralocorticoids (mainly primary aldosteronism), glucocorticoids (Cushing syndrome), and catecholamines (pheochromocytoma). In addition, a few rare diseases directly affecting the action of mineralocorticoids and glucocorticoids in the kidney also lead to endocrine HT. Over the past years, genomic and genetic studies have allowed improving our knowledge on the molecular mechanisms of endocrine HT. Those discoveries have opened new opportunities to transfer knowledge to clinical practice for better diagnosis and specific treatment of affected subjects. In this review, we describe the physiology of adrenal hormone biosynthesis and action, the clinical and biochemical characteristics of different forms of endocrine HT, and their underlying genetic defects. We discuss the impact of these discoveries on diagnosis and management of patients, as well as new perspectives related to the use of new biomarkers for improved patient care.

Mammalian Target of Rapamycin Inhibition Decreases Angiotensin II-Induced Steroidogenesis in HAC15 Human Adrenocortical Carcinoma Cells

BACKGROUND

Mammalian target of rapamycin (mTOR) inhibitors suppress adrenal cortical carcinoma cell proliferation and cortisol production; the relationship between mTOR and aldosterone production has not been examined.

METHODS

HAC15 cells were incubated with an mTOR activator and several inhibitors including AZD8055 (AZD) in the presence and absence of angiotensin II (AngII). The expression of rapamycin-sensitive adapter protein of mTOR (Raptor) and rapamycin-insensitive companion of mTOR (Rictor), adaptor proteins of mTOR complex 1 and 2, respectively, were studied in the HAC15 cells and deleted by CRISPR/gRNA.

RESULTS

The mTOR inhibitors decreased aldosterone induced by AngII. Inhibition of mTOR by AZD significantly suppressed AngII-induced aldosterone and cortisol formation in a dose-dependent manner, whereas the mTOR activator MHY had no effect. AZD did not alter forskolin-induced aldosterone production showing that it is specific to the AngII signaling pathway. AngII-mediated ERK and mTOR activation were suppressed by AZD, along with a concomitant dose-dependent reduction of AngII-induced steroidogenic enzymes including steroidogenic acute regulatory protein, 3β-hydroxysteroid dehydrogenase-type 2, CYP17A1, and aldosterone synthase protein. Furthermore, mTOR components ribosomal protein S6 kinase (P70S6K) and protein kinase B phosphorylation levels were decreased by AZD. As mTOR exerts its main effects by forming complexes with adaptor proteins Raptor and Rictor, the roles of these individual complexes were studied. We found an increase in the phosphorylation of Raptor and Rictor by AngII and that their CRISPR/gRNA-mediated knockdown significantly attenuated AngII-induced aldosterone and cortisol production.

CONCLUSION

mTOR signaling has a critical role in transducing the AngII signal initiating aldosterone and cortisol synthesis in HAC15 cells and that inhibition of mTOR could be a therapeutic option for conditions associated with excessive renin-angiotensin system-mediated steroid synthesis.

Routinely accessible parameters of mineralocorticoid receptor function, depression subtypes and response prediction: a post-hoc analysis from the early medication change trial in major depressive disorder

OBJECTIVES

Previous studies indicated a relationship between aldosterone, the mineralocorticoid receptor (MR), and antidepressant treatment outcome. Physiological indicators of MR function (blood pressure and electrolytes) are easily accessible and may therefore serve as useful predictors. Thus, our aim was to investigate the predictive value of peripheral MR-related markers for antidepressant treatment outcomes.

METHODS

826 MDD patients who had participated in the randomised-controlled Early Medication Change (EMC) trial were analysed. Depression severity and MR-related markers were assessed weekly. In 562 patients, genetic variation of five MR-related genes was determined.

RESULTS

Patients with blood pressure <120mmHg showed higher depression severity (p = 0.005) than patients with blood pressure ≥120mmHg. Patients with a melancholic subtype had significantly lower blood pressures (p = 0.004). Na⁺/K⁺ ratio was positively and K⁺-concentration was negatively correlated to depression severity and to relative changes in HAMD from baseline to day 14, and 56 respectively (p < 0.001). For none of the MR-related genes, genetic variation was associated with treatment outcomes.

CONCLUSIONS

We confirmed early observations of an altered peripheral MR sensitivity, reflected by lower blood pressure, low K⁺ or high Na⁺/K⁺ ratio in patients with more severe depression. These routinely collected biomarkers may potentially be useful for risk stratification in an early stage of treatment. Trial Registration: clinicaltrials.gov Identifier: NCT00974155; https://www.clinicaltrials.gov/ct2/results?term=NCT00974155.

Identification of risk loci for primary aldosteronism in genome-wide association studies

Primary aldosteronism affects up to 10% of hypertensive patients and is responsible for treatment resistance and increased cardiovascular risk. Here we perform a genome-wide association study in a discovery cohort of 562 cases and 950 controls and identify three main loci on chromosomes 1, 13 and X; associations on chromosome 1 and 13 are replicated in a second cohort and confirmed by a meta-analysis involving 1162 cases and 3296 controls. The association on chromosome 13 is specific to men and stronger in bilateral adrenal hyperplasia than aldosterone producing adenoma. Candidate genes located within the two loci, CASZ1 and RXFP2, are expressed in human and mouse adrenals in different cell clusters. Their overexpression in adrenocortical cells suppresses mineralocorticoid output under basal and stimulated conditions, without affecting cortisol biosynthesis. Our study identifies the first risk loci for primary aldosteronism and highlights new mechanisms for the development of aldosterone excess.

Update on the Genetics of Primary Aldosteronism and Aldosterone-Producing Adenomas

PURPOSE OF THE REVIEW

Primary aldosteronism (PA) is the leading cause of secondary hypertension, accounting for over 10% of patients with high blood pressure. It is characterized by autonomous production of aldosterone from the adrenal glands leading to low-renin levels. The two most common forms arise from bilateral adrenocortical hyperplasia (BAH) and aldosterone-producing adenoma (APA). We discuss recent discoveries in the genetics of PA.

RECENT FINDINGS

Most APAs harbor variants in the KCNJ5, CACNA1D, ATP1A1, ATP2B3, and CTNNB1 genes. With the exception of β-catenin (CTNNB1), all other causative genes encode ion channels; pathogenic variants found in PA lead to altered ion transportation, cell membrane depolarization, and consequently aldosterone overproduction. Some of these genes are found mutated in the germline state (CYP11B2, CLCN2, KCNJ5, CACNA1H, and CACNA1D), leading then to familial hyperaldosteronism, and often BAH rather than single APAs. Several genetic defects in the germline or somatic state have been identified in PA. Understanding how these molecular abnormalities lead to excess aldosterone contributes significantly to the elucidation of the pathophysiology of low-renin hypertension. It may also lead to new and more effective therapies for this disease acting at the molecular level.

Directing two-way traffic in the kidney: A tale of two ions

The kidneys regulate levels of Na+ and K+ in the body by varying urinary excretion of the electrolytes. Since transport of each of the two ions can affect the other, controlling both at the same time is a complex task. The kidneys meet this challenge in two ways. Some tubular segments change the coupling between Na+ and K+ transport. In addition, transport of Na+ can shift between segments where it is coupled to K+ reabsorption and segments where it is coupled to K+ secretion. This permits the kidney to maintain electrolyte balance with large variations in dietary intake.

Clinical Translationality of KCNJ5 Mutation in Aldosterone Producing Adenoma

Hypertension due to primary aldosteronism poses a risk of severe cardiovascular complications compared to essential hypertension. The discovery of the KCNJ5 somatic mutation in aldosteroene producing adenoma (APA) in 2011 and the development of specific CYP11B2 antibodies in 2012 have greatly advanced our understanding of the pathophysiology of primary aldosteronism. In particular, the presence of CYP11B2-positive aldosterone-producing micronodules (APMs) in the adrenal glands of normotensive individuals and the presence of renin-independent aldosterone excess in normotensive subjects demonstrated the continuum of the pathogenesis of PA. Furthermore, among the aldosterone driver mutations which incur excessive aldosterone secretion, KCNJ5 was a major somatic mutation in APA, while CACNA1D is a leading somatic mutation in APMs and idiopathic hyperaldosteronism (IHA), suggesting a distinctive pathogenesis between APA and IHA. Although the functional detail of APMs has not been still uncovered, its impact on the pathogenesis of PA is gradually being revealed. In this review, we summarize the integrated findings regarding APA, APM or diffuse hyperplasia defined by novel CYP11B2, and aldosterone driver mutations. Following this, we discuss the clinical implications of KCNJ5 mutations to support better cardiovascular outcomes of primary aldosteronism.

Expression of p11 and heteromeric TASK channels in mouse adrenal cortical cells and H295R cells

TWIK-related acid-sensitive K⁺ (TASK) channels are thought to contribute to the resting membrane potential in adrenal cortical (AC) cells. However, the molecular identity of TASK channels in AC cells have not yet been elucidated. Thus, immunocytochemical and molecular biological approaches were employed to investigate the expression and intracellular distribution of TASK1 and TASK3 in mouse AC cells and H295R cells derived from human adrenocortical carcinoma. Immunocytochemical study revealed that immunoreactive materials were mainly located in the cytoplasm for TASK1 and at the cell periphery for TASK3 in mouse AC cells. A similar pattern of localization was observed when GFP-TASK1 and GFP-TASK3 were exogenously expressed in H295R cells. In addition, p11 that is known to suppress the endoplasmic reticulum exit of TASK1 was localized in the cytoplasm in mouse AC and H295R cells, but not in adrenal medullary cells. Proximity ligation assay (PLA) suggested formation of heteromeric TASK1-3 channels that were found predominantly in the cytoplasm and weakly at the cell periphery. A similar distribution was observed following exogenous expression of tandem TASK1-3 channels in H295R cells. When stimulated by angiotensin II, however, tandem TASK1-3 channels were present mainly in the cytoplasm in all H295R cells. In contrast to that in H295R cells, tandem channels were exclusively located at the cell periphery in all non-stimulated and exclusively in the cytoplasm in stimulated PC12 cells, respectively. From these results, we conclude that TASK1 proteins are present mainly in the cytoplasm and minimally at the cell periphery as a heteromeric channel with TASK3, whereas the majority of TASK3 is at the cell periphery as homomeric and heteromeric channels.

Aldosterone breakthrough from a pharmacological perspective

Aldosterone (Aldo) breakthrough is a well-known phenomenon that occurs in patients with long-term renin-angiotensin aldosterone system (RAAS) blockade using inhibitors of renin or angiotensin converting enzyme or angiotensin II type 1 receptor blockers. The blockade of the mineralocorticoid receptor (MR), an Aldo binding receptor, is effective in managing patients with resistant hypertension, defined as uncontrollable blood pressure despite the concurrent use of three antihypertensive drugs. In other words, MR inhibitors are not used as first-line antihypertensive drugs in most guidelines for hypertension management. Aldo breakthrough puts hypertensive patients at higher risk of cardiovascular disease and worsens future outcomes. This review discusses Aldo secretion and the mechanism of Aldo breakthrough, dependent or independent of the RAAS, with consideration of the pharmacological aspects of this phenomenon, as well as hypothetical views.

Genetic Alterations in Benign Adrenal Tumors

The genetic basis of most types of adrenal adenomas has been elucidated over the past decade, leading to the association of adrenal gland pathologies with specific molecular defects. Various genetic studies have established links between variants affecting the protein kinase A (PKA) signaling pathway and benign cortisol-producing adrenal lesions. Specifically, genetic alterations in GNAS, PRKAR1A, PRKACA, PRKACB, PDE11A, and PDE8B have been identified. The PKA signaling pathway was initially implicated in the pathogenesis of Cushing syndrome in studies aiming to understand the underlying genetic defects of the rare tumor predisposition syndromes, Carney complex, and McCune-Albright syndrome, both affected by the same pathway. In addition, germline variants in ARMC5 have been identified as a cause of primary bilateral macronodular adrenal hyperplasia. On the other hand, primary aldosteronism can be subclassified into aldosterone-producing adenomas and bilateral idiopathic hyperaldosteronism. Various genes have been reported as causative for benign aldosterone-producing adrenal lesions, including KCNJ5, CACNA1D, CACNA1H, CLCN2, ATP1A1, and ATP2B3. The majority of them encode ion channels or pumps, and genetic alterations lead to ion transport impairment and cell membrane depolarization which further increase aldosterone synthase transcription and aldosterone overproduction though activation of voltage-gated calcium channels and intracellular calcium signaling. In this work, we provide an overview of the genetic causes of benign adrenal tumors.

Genetics of Primary Aldosteronism

Primary aldosteronism is considered the commonest cause of secondary hypertension. In affected individuals, aldosterone is produced in an at least partially autonomous fashion in adrenal lesions (adenomas, [micro]nodules or diffuse hyperplasia). Over the past decade, next-generation sequencing studies have led to the insight that primary aldosteronism is largely a genetic disorder. Sporadic cases are due to somatic mutations, mostly in ion channels and pumps, and rare cases of familial hyperaldosteronism are caused by germline mutations in an overlapping set of genes. More than 90% of aldosterone-producing adenomas carry somatic mutations in K⁺ channel Kir3.4 (KCNJ5), Ca²⁺ channel Ca_V1.3 (CACNA1D), alpha-1 subunit of the Na⁺/K⁺ ATPase (ATP1A1), plasma membrane Ca²⁺ transporting ATPase 3 (ATP2B3), Ca²⁺ channel Ca_V3.2 (CACNA1H), Cl⁻ channel ClC-2 (CLCN2), β-catenin (CTNNB1), and/or G-protein subunits alpha q/11 (GNAQ/11). Mutations in some of these genes have also been identified in aldosterone-producing (micro)nodules, suggesting a disease continuum from a single cell, acquiring a somatic mutation, via a nodule to adenoma formation, and from a healthy state to subclinical to overt primary aldosteronism. Individual glands can have multiple such lesions, and they can occur on both glands in bilateral disease. Familial hyperaldosteronism, typically with early onset, is caused by germline mutations in steroid 11-beta hydroxylase/ aldosterone synthase (CYP11B1/2), CLCN2, KCNJ5, CACNA1H, and CACNA1D.

Cerebro-Cardiovascular Risk, Target Organ Damage, and Treatment Outcomes in Primary Aldosteronism

Primary aldosteronism (PA) is the most common type of endocrine hypertension, and numerous experimental and clinical evidence have verified that prolonged exposure to excess aldosterone is responsible for an increased risk of cerebro-cardiovascular events and target organ damage (TOD) in patients with PA. Therefore, focusing on restoring the toxic effects of excess aldosterone on the target organs is very important to reduce cerebro-cardiovascular events. Current evidence convincingly demonstrates that both surgical and medical treatment strategies would benefit cerebro-cardiovascular outcomes and mortality in the long term. Understanding cerebro-cardiovascular risk in PA would help clinical doctors to achieve both early diagnosis and treatment. Therefore, in this review, we will summarize the cerebro-cardiovascular risk in PA, focusing on the TOD of aldosterone, including brain, heart, vascular system, renal, adipose tissues, diabetes, and obstructive sleep apnea (OSA). Furthermore, the various treatment outcomes of adrenalectomy and medical treatment for patients with PA will also be discussed. We hope this knowledge will help improve cerebro-cardiovascular prognosis and reduce the incidence and mortality of cerebro-cardiovascular events in patients with PA.

A Novel Somatic Mutation of CACNA1H p.V1937M in Unilateral Primary Hyperaldosteronism

BACKGROUND

Somatic mutations for excess aldosterone production have been frequently identified as important roles in the pathogenesis of unilateral primary hyperaldosteronism (uPA). Although CACNA1H mutation represents a minor etiology in primary aldosteronism, it plays a significant role in causing uPAs in sporadic cases.

OBJECTIVE

To identify novel somatic CACNA1H mutation in patients with uPA and investigate the pathophysiological, immunohistological, and clinical characteristics of the variant.

METHODS

We applied a customized and targeted gene panel next-generation sequencing approach to detect mutations from the uPA cohort in Taiwan Primary Aldosteronism Investigation study group. Information from pre-diagnostic to postoperative data was collected, including past history, medications, blood pressure readings, biochemical data, and image studies. The functional role of the variant was confirmed by in vitro studies, demonstrating aldosterone production in variant-transfected human adrenal cell lines.

RESULTS

We identified a novel somatic CACNA1H mutation c.5809G>A (p.Val1937Met) in a uPA case. The CACNA1H gene encodes the pore-forming alpha-1H subunit of the voltage-dependent T-type calcium channel Cav3.2. This somatic CACNA1H p.V1937M variant showed excellent clinical and biochemical outcomes after ipsilateral adrenalectomy. The functional effect of somatic CACNA1H p.V1937M variant results in increased CYP11B2 expression and aldosterone biosynthesis in HAC15 cells. A distinct heterogeneous foamy pattern of CYP11B2 and CYP17A1 expression was identified in immunohistological staining, supporting the pathological evidence of aldosterone synthesis.

CONCLUSIONS

The somatic mutation of CACNA1H p.V1937M might be a pathogenic driver in aldosterone overproduction. This study provides new insight into the molecular mechanism and disease outcomes of uPA.

Inflammation: A Mediator Between Hypertension and Neurodegenerative Diseases

Hypertension is the most prevalent and modifiable risk factor for stroke, vascular cognitive impairment, and Alzheimer's disease. However, the mechanistic link between hypertension and neurodegenerative diseases remains to be understood. Recent evidence indicates that inflammation is a common pathophysiological trait for both hypertension and neurodegenerative diseases. Low-grade chronic inflammation at the systemic and central nervous system levels is now recognized to contribute to the physiopathology of hypertension. This review speculates that inflammation represents a mediator between hypertension and neurodegenerative diseases, either by a decrease in cerebral blood flow or a disruption of the blood-brain barrier which will, in turn, let inflammatory cells and neurotoxic molecules enter the brain parenchyma. This may impact brain functions including cognition and contribute to neurodegenerative diseases. This review will thus discuss the relationship between hypertension, systemic inflammation, cerebrovascular functions, neuroinflammation, and brain dysfunctions. The potential clinical future of immunotherapies against hypertension and associated cerebrovascular risks will also be presented.

Diet-dependent acid load associates with mean arterial pressure in a cohort of non-obese, non-black, post-menopausal women

Higher sodium (Na+) intakes are associated with higher blood pressure (BP). Whether this relationship is stronger with diet-dependent acid load (DAL) and in patients with diagnosed hypertension or normal BP is not well determined. We studied 170 postmenopausal women randomized to potassium bicarbonate or placebo till 36 months where 24-hour urine and arterialized blood were collected. We investigated the association of DAL estimated as urinary potential renal acid load (UPRAL) and mean arterial pressure (MAP) using mixed-effects model, adjusting for age, anthropometrics, creatinine clearance, and treatment. Adjusted regression estimates for change in Na+ and UPRAL on MAP after 12 months follow-up were calculated, and further adjustments were made for change in potassium (K+) and body mass index (BMI). MAP was inversely associated with UPRAL (β [95% CI]:-0.11[-0.25,-0.001]). There was effect modification by hypertension (p-interaction=0.04); MAP decreased significantly in normotensives but the association was not significant in hypertensives. A decrease of 0.70 mmHg in MAP (0.13,1.69) per 50 mmol/24 hr reduction in Na+ was noted when the model was adjusted for change in K+. Our results with UPRAL exhibited stronger dose-response for MAP, which remained significant after adjustment for BMI. UPRAL was independently associated with MAP even after adjustment for potential confounders, and the data showed this association to be more pronounced in normotensives. Novelty: • First longitudinal study on the association of UPRAL and MAP • Association was a more robust relationship than between U[Na/K] ratio and MAP • UPRAL may play a significant role in the pathogenesis of primary hypertension.

Non-coding Single Nucleotide Variants of Renin and the (Pro)renin Receptor are Associated with Polygenic Diseases in a Bangladeshi Population

Non-coding variants or single-nucleotide polymorphisms (SNPs) play pivotal roles in orchestrating pathogeneses of polygenic diseases, including hypertension (HTN) and diabetes. Renin-angiotensin system (RAS) components-renin and (pro)renin receptor [(P)RR]-maintain homeostasis of body fluids. Genetic variants of RAS components are associated with risk of HTN and type 2 diabetes (T2D) in different ethnic groups. We identified associations of SNPs within the renin and (P)RR genes with HTN, T2D, and T2D-associated hypertension in 911 unrelated Bangladeshi individuals. Five non-coding SNPs were involved in modulating regulatory elements in diverse cell types when tagged with other SNPs. rs61827960 was not associated with any disease; rs3730102 was associated with increased risk of HTN and T2D while under dominant model, it showed protective role against T2D-associated HTN. SNP rs11571079 was associated with increased risk of HTN and T2D-associated HTN and decreased risk of T2D, exerting a protective effect. Renin haplotypes GCA and GTG were related to increased risk of T2D and T2D-associated HTN, respectively. Heterogeneous linkage of genotypic and allelic frequencies of rs2968915 and rs3112298 of (P)RR was observed. The (P)RR haplotype GA was associated with increased risk of HTN and significantly decreased risk of T2D. These findings highlight important roles of non-coding variants of renin and (P)RR genes in the etiology of several polygenic diseases.

A Review of the Molecular Mechanisms Underlying Cardiac Fibrosis and Atrial Fibrillation

The cellular and molecular mechanism involved in the pathogenesis of atrial fibrosis are highly complex. We have reviewed the literature that covers the effectors, signal transduction and physiopathogenesis concerning extracellular matrix (ECM) dysregulation and atrial fibrosis in atrial fibrillation (AF). At the molecular level: angiotensin II, transforming growth factor-β1, inflammation, and oxidative stress are particularly important for ECM dysregulation and atrial fibrotic remodelling in AF. We conclude that the Ang-II-MAPK and TGF-β1-Smad signalling pathways play a major, central role in regulating atrial fibrotic remodelling in AF. The above signalling pathways induce the expression of genes encoding profibrotic molecules (MMP, CTGF, TGF-β1). An important mechanism is also the generation of reactive oxygen species. This pathway induced by the interaction of Ang II with the AT₂R receptor and the activation of NADPH oxidase. Additionally, the interplay between cardiac MMPs and their endogenous tissue inhibitors of MMPs, is thought to be critical in atrial ECM metabolism and fibrosis. We also review recent evidence about the role of changes in the miRNAs expression in AF pathophysiology and their potential as therapeutic targets. Furthermore, keeping the balance between miRNA molecules exerting anti-/profibrotic effects is of key importance for the control of atrial fibrosis in AF.

Transcriptomic Response Dynamics of Human Primary and Immortalized Adrenocortical Cells to Steroidogenic Stimuli

Adrenal steroid hormone production is a dynamic process stimulated by adrenocorticotropic hormone (ACTH) and angiotensin II (AngII). These ligands initialize a rapid and robust gene expression response required for steroidogenesis. Here, we compare the predominant human immortalized cell line model, H295R cell, with primary cultures of adult adrenocortical cells derived from human kidney donors. We performed temporally resolved RNA-seq on primary cells stimulated with either ACTH or AngII at multiple time points. The magnitude of the expression dynamics elicited by ACTH was greater than AngII in primary cells. This is likely due to the larger population of adrenocortical cells that are responsive to ACTH. The dynamics of stimulus-induced expression in H295R cells are mostly recapitulated in primary cells. However, there are some expression responses in primary cells absent in H295R cells. These data are a resource for the endocrine community and will help researchers determine whether H295R is an appropriate model for the specific aspect of steroidogenesis that they are studying.

Diseases caused by mutations in the Na+/K+ pump α1 gene ATP1A1

Human cell survival requires function of the Na⁺/K⁺ pump; the heteromeric protein that hydrolyzes ATP to extrude Na⁺ and import K⁺ across the plasmalemma, thereby building and maintaining these ions' electrochemical gradients. Numerous dominant diseases caused by mutations in genes encoding for Na⁺/K⁺ pump catalytic (α) subunit isoforms highlight the importance of this protein. Here, we review literature describing disorders caused by missense mutations in ATP1A1, the gene encoding the ubiquitously expressed α1 isoform of the Na⁺/K⁺ pump. These various maladies include primary aldosteronism with secondary hypertension, an endocrine syndrome, Charcot-Marie-Tooth disease, a peripheral neuropathy, complex spastic paraplegia, another neuromuscular disorder, as well as hypomagnesemia accompanied by seizures and cognitive delay, a condition affecting the renal and central nervous systems. This article focuses on observed commonalities among these mutations' functional effects, as well as on the special characteristics that enable each particular mutation to exclusively affect a certain system, without affecting others. In this respect, it is clear how somatic mutations localized to adrenal adenomas increase aldosterone production without compromising other systems. However, it remains largely unknown how and why some but not all de novo germline or familial mutations (where the mutant must be expressed in numerous tissues) produce a specific disease and not the other diseases. We propose hypotheses to explain this observation and the approaches that we think will drive future research on these debilitating disorders to develop novel patient-specific treatments by combining the use of heterologous protein-expression systems, patient-derived pluripotent cells, and gene-edited cell and mouse models.

Angiotensin peptides in the regulation of adrenal cortical function

The adrenal cortex plays a key role in the regulation of metabolism, salt and water homeostasis and sex differentiation by synthesizing glucocorticoid, mineralocorticoid and androgen hormones. Evidence exists that angiotensin II regulates adrenocortical function and it has been contended that angiotensin peptides of the non-canonical branch of the renin angiotensin system (RAS) might also modulate steroidogenesis in adrenals. Thus, the aim of this review is to examine the role of the RAS, and particularly of the angiotensin peptides and their receptors, in the regulation of adrenocortical hormones with particular focus on aldosterone production.

Comparative proteomic analysis to identify the novel target gene of angiotensin II in adrenocortical H295R cells

Angiotensin II (Ang II) is a well-known peptide that maintains the balance of electrolytes in the higher vertebrates. Ang II stimulation in the adrenal gland induces the synthesis of mineralocorticoids, mainly aldosterone, through the up-regulation of aldosterone synthase (CYP11B2) gene expression. Additionally, it has been reported that Ang II activates multiple signaling pathways such as mitogen-activated protein kinase (MAPK) and Ca²⁺ signaling. Although Ang II has various effects on the cellular signaling in the adrenal cells, its biological significance, except for the aldosterone synthesis, is still unclear. In this study, we attempted to search the novel target gene(s) of Ang II in the human adrenal H295R cells using a proteomic approach combined with stable isotopic labeling using amino acid in cell culture (SILAC). Interestingly, we found that Ang II stimulation elevated the expression of phosphofructokinase type platelet (PFKP) in both protein and mRNA levels. Moreover, transactivation of PFKP by Ang II was dependent on extracellular-signal-regulated kinase (ERK) 1/2 activation. Finally, we observed that Ang II treatment facilitated glucose uptake in the H295R cells. Taken together, we here identified PFKP as a novel target gene of Ang II, indicating that Ang II not only stimulates steroidogenesis but also affects glucose metabolism.

Enhanced Ca2+ signaling, mild primary aldosteronism, and hypertension in a familial hyperaldosteronism mouse model (Cacna1h M1560V/+ )

Primary aldosteronism (increased production of the adrenal steroid hormone aldosterone) is the most common cause of secondary hypertension. We here generated a mouse model of familial hyperaldosteronism type IV with a heterozygous gain-of-function mutation in a calcium channel gene (Cacna1h^M1560V/+). Cacna1h^M1560V/+ mice have about twofold elevated aldosterone:renin ratios (a screening parameter for primary aldosteronism) and elevated blood pressure, with an overall mild phenotype. Elevated adrenal aldosterone synthase expression in Cacna1h^M1560V/+ mice is associated with increased intracellular calcium concentrations in glomerulosa cells. This model allows for the ex vivo analysis of calcium signaling in aldosterone-producing glomerulosa cells of the adrenal gland. Cacna1h^−/− mice have normal aldosterone synthase expression, with implications for the evaluation of CACNA1H as a therapeutic target.

Gain-of-function mutations in the CACNA1H gene (encoding the T-type calcium channel Ca_V3.2) cause autosomal-dominant familial hyperaldosteronism type IV (FH-IV) and early-onset hypertension in humans. We used CRISPR/Cas9 to generate Cacna1h^M1560V/+ knockin mice as a model of the most common FH-IV mutation, along with corresponding knockout mice (Cacna1h^−/−). Adrenal morphology of both Cacna1h^M1560V/+ and Cacna1h^−/− mice was normal. Cacna1h^M1560V/+ mice had elevated aldosterone:renin ratios (a screening parameter for primary aldosteronism). Their adrenal Cyp11b2 (aldosterone synthase) expression was increased and remained elevated on a high-salt diet (relative autonomy, characteristic of primary aldosteronism), but plasma aldosterone was only elevated in male animals. The systolic blood pressure of Cacna1h^M1560V/+ mice was 8 mmHg higher than in wild-type littermates and remained elevated on a high-salt diet. Cacna1h^−/− mice had elevated renal Ren1 (renin-1) expression but normal adrenal Cyp11b2 levels, suggesting that in the absence of Ca_V3.2, stimulation of the renin-angiotensin system activates alternative calcium entry pathways to maintain normal aldosterone production. On a cellular level, Cacna1h^M1560V/+ adrenal slices showed increased baseline and peak intracellular calcium concentrations in the zona glomerulosa compared to controls, but the frequency of calcium spikes did not rise. We conclude that FH-IV, on a molecular level, is caused by elevated intracellular Ca²⁺ concentrations as a signal for aldosterone production in adrenal glomerulosa cells. We demonstrate that a germline Cacna1h gain-of-function mutation is sufficient to cause mild primary aldosteronism, whereas loss of Ca_V3.2 channel function can be compensated for in a chronic setting.

Cellular and mitochondrial calcium communication in obstructive lung disorders

Calcium (Ca²⁺) signalling is well known to dictate cellular functioning and fate. In recent years, the accumulation of Ca²⁺ in the mitochondria has emerged as an important factor in Chronic Respiratory Diseases (CRD) such as Asthma and Chronic Obstructive Pulmonary Disease (COPD). Various reports underline an aberrant increase in the intracellular Ca²⁺, leading to mitochondrial ROS generation, and further activation of the apoptotic pathway in these diseases. Mitochondria contribute to Ca²⁺ buffering which in turn regulates mitochondrial metabolism and ATP production. Disruption of this Ca²⁺ balance leads to impaired cellular processes like apoptosis or necrosis and thus contributes to the pathophysiology of airway diseases. This review highlights the key role of cytoplasmic and mitochondrial Ca²⁺ signalling in regulating CRD, such as asthma and COPD. A better understanding of the dysregulation of mitochondrial Ca²⁺ homeostasis in these diseases could provide cues for the development of advanced therapeutic interventions in these diseases.