A novel KCNJ5-insT149 somatic mutation close to, but outside, the selectivity filter causes resistant hypertension by loss of selectivity for potassium

Double CYP11B1/CYP11B2 Immunohistochemistry and Detection of KCNJ5 Mutations in Primary Aldosteronism

CONTEXT

The search for somatic mutations in adrenals resected from primary aldosteronism (PA) patients is being performed by Sanger sequencing, often implemented with immunohistochemistry (IHC)-guidance focused on aldosterone-producing (CYP11B2-positive) areas.

OBJECTIVE

To investigate the impact of double IHC for CYP11B1 and CYP11B2 on Sanger and next generation sequencing (NGS).

METHODS

We investigated 127 consecutive adrenal aldosterone producing adenoma from consenting surgically cured PA patients using double IHC for CYP11B1 and CYP11B2, Sanger sequencing and NGS.

RESULTS

Double IHC for CYP11B2 and CYP11B1 revealed 3 distinct patterns: CYP11B2-positive adenoma (pattern 1), mixed CYP11B1/CYP11B2-positive adenoma (pattern 2), and adrenals with multiple small CYP11B2-positive nodules (pattern 3). Sanger sequencing allowed detection of KCNJ5 mutations in 44% of the adrenals; NGS revealed such mutations in 10% of those negative at Sanger and additional mutations in 61% of the cases. Importantly the rate of KCNJ5 mutations differed across patterns: 17.8% in pattern 1, 71.4% in pattern 2, and 10.7% in pattern 3 (χ2=22.492, p<0.001).

CONCLUSIONS

NGS allowed detection of mutations in many adrenals that tested negative at Sanger sequencing. Moreover, the different distribution of KCNJ5 mutations across IHC patterns indicates that IHC-guided sequencing protocols selecting CYP11B2-positive areas could furnish results that might not be representative of the entire mutational status of the excised adrenal, which is important at a time when KCNJ5 mutations are suggested to drive management of APA patient.

Primary aldosteronism: molecular medicine meets public health

Primary aldosteronism is the most common single cause of hypertension and is potentially curable when only one adrenal gland is the culprit. The importance of primary aldosteronism to public health derives from its high prevalence but huge under-diagnosis (estimated to be <1% of all affected individuals), despite the consequences of poor blood pressure control by conventional therapy and enhanced cardiovascular risk. This state of affairs is attributable to the fact that the tools used for diagnosis or treatment are still those that originated in the 1970-1990s. Conversely, molecular discoveries have transformed our understanding of adrenal physiology and pathology. Many molecules and processes associated with constant adrenocortical renewal and interzonal metamorphosis also feature in aldosterone-producing adenomas and aldosterone-producing micronodules. The adrenal gland has one of the most significant rates of non-silent somatic mutations, with frequent selection of those driving autonomous aldosterone production, and distinct clinical presentations and outcomes for most genotypes. The disappearance of aldosterone synthesis and cells from most of the adult human zona glomerulosa is the likely driver of the mutational success that causes aldosterone-producing adenomas, but insights into the pathways that lead to constitutive aldosterone production and cell survival may open up opportunities for novel therapies.

Cardiovascular and metabolic characters of KCNJ5 somatic mutations in primary aldosteronism

BACKGROUND

Primary aldosteronism (PA) is the leading cause of curable endocrine hypertension, which is associated with a higher risk of cardiovascular and metabolic insults compared to essential hypertension. Aldosterone-producing adenoma (APA) is a major cause of PA, which can be treated with adrenalectomy. Somatic mutations are the main pathogenesis of aldosterone overproduction in APA, of which KCNJ5 somatic mutations are most common, especially in Asian countries. This article aimed to review the literature on the impacts of KCNJ5 somatic mutations on systemic organ damage.

EVIDENCE ACQUISITION

PubMed literature research using keywords combination, including "aldosterone-producing adenoma," "somatic mutations," "KCNJ5," "organ damage," "cardiovascular," "diastolic function," "metabolic syndrome," "autonomous cortisol secretion," etc.

RESULTS

APA patients with KCNJ5 somatic mutations are generally younger, female, have higher aldosterone levels, lower potassium levels, larger tumor size, and higher hypertension cure rate after adrenalectomy. This review focuses on the cardiovascular and metabolic aspects of KCNJ5 somatic mutations in APA patients, including left ventricular remodeling and diastolic function, abdominal aortic thickness and calcification, arterial stiffness, metabolic syndrome, abdominal adipose tissue, and correlation with autonomous cortisol secretion. Furthermore, we discuss modalities to differentiate the types of mutations before surgery.

CONCLUSION

KCNJ5 somatic mutations in patients with APA had higher left ventricular mass (LVM), more impaired diastolic function, thicker aortic wall, lower incidence of metabolic syndrome, and possibly a lower incidence of concurrent autonomous cortisol secretion, but better improvement in LVM, diastolic function, arterial stiffness, and aortic wall thickness after adrenalectomy compared to patients without KCNJ5 mutations.

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.

Pathogenesis of Primary Aldosteronism: Impact on Clinical Outcome

Primary aldosteronism (PA) is the most common form of secondary arterial hypertension, with a prevalence of approximately 20% in patients with resistant hypertension. In the last decade, somatic pathogenic variants in KCNJ5, CACNA1D, ATP1A1 and ATP2B3 genes, which are involved in maintaining intracellular ionic homeostasis and cell membrane potential, were described in aldosterone-producing adenomas (aldosteronomas). All variants in these genes lead to the activation of calcium signaling, the major trigger for aldosterone production. Genetic causes of familial hyperaldosteronism have been expanded through the report of germline pathogenic variants in KCNJ5, CACNA1H and CLCN2 genes. Moreover, PDE2A and PDE3B variants were associated with bilateral PA and increased the spectrum of genetic etiologies of PA. Of great importance, the genetic investigation of adrenal lesions guided by the CYP11B2 staining strongly changed the landscape of somatic genetic findings of PA. Furthermore, CYP11B2 staining allowed the better characterization of the aldosterone-producing adrenal lesions in unilateral PA. Aldosterone production may occur from multiple sources, such as solitary aldosteronoma or aldosterone-producing nodule (classical histopathology) or clusters of autonomous aldosterone-producing cells without apparent neoplasia denominated aldosterone-producing micronodules (non-classical histopathology). Interestingly, KCNJ5 mutational status and classical histopathology of unilateral PA (aldosteronoma) have emerged as relevant predictors of clinical and biochemical outcome, respectively. In this review, we summarize the most recent advances in the pathogenesis of PA and discuss their impact on clinical outcome.

A revised mechanism of action of hyperaldosteronism-linked mutations in cytosolic domains of GIRK4 (KCNJ5)

KEY POINTS

Mutations in GIRK4 (KCNJ5) G-protein gated channels cause primary aldosteronism, a major cause of secondary hypertension. The primary mechanism is believed to be loss of K⁺ selectivity. R52H and E246K, aldosteronism-causing mutations in cytosolic N- and C- termini of GIRK4, were reported to cause loss of K⁺ selectivity. We show that R52H, E246K and G247R mutations render homotetrameric GIRK channels non-functional. In heterotetrameric context with GIRK1, these mutations impair membrane expression, interaction with Gβγ and open probability, but do not alter K⁺ selectivity or inward rectification. In human aldosterone-secreting cell line, a GIRK4 opener and overexpression of heterotetrameric GIRK1/4_WT , but not over-expression of GIRK1/4 mutants, reduced aldosterone secretion. Aldosteronism-causing mutations in cytosolic domain of GIRK4 are loss-of-function mutations rather than gain-of-function, selectivity-loss mutations. Deciphering of exact biophysical mechanism that impairs the channel is crucial for setting the course of treatment.

ABSTRACT

G-protein gated, inwardly rectifying potassium channels (GIRK) mediate inhibitory transmission in brain and heart, and are present in adrenal cortex. GIRK4 (KCNJ5) subunits are abundant in the heart and adrenal cortex. Multiple mutations of KCNJ5 cause primary aldosteronism (PA). Mutations in the pore region of GIRK4 cause loss of K⁺ selectivity, Na⁺ influx, and depolarization of zona glomerulosa cells followed by hypersecretion of aldosterone. The concept of selectivity loss has been extended to mutations in cytosolic domains of GIRK4 channels, remote from the pore. We expressed aldosteronism-linked GIRK4_R52H , GIRK4_E246K , and GIRK4_G247R mutants in Xenopus oocytes. Whole-cell currents of heterotetrameric GIRK1/4_R52H and GIRK1/4_E246K channels were greatly reduced compared to GIRK1/4_WT . Nevertheless, all heterotetrameric mutants retained full K⁺ selectivity and inward rectification. When expressed as homotetramers, only GIRK4_WT , but none of the mutants, produced whole-cell currents. Confocal imaging, single channel and Förster Resonance Energy Transfer (FRET) analyses showed: 1) reduction of membrane abundance of all mutated channels, especially as homotetramers, 2) impaired interaction with Gβγ subunits, and 3) reduced open probability of GIRK1/4_R52H . VU0529331, a GIRK4 opener, activated homotetrameric GIRK4_G247R channels, but not GIRK4_R52H and GIRK4_E246K . In human adrenocortical carcinoma cell line (HAC15), VU0529331 and over-expression of heterotetrameric GIRK1/4_WT , but not over-expression of GIRK1/4 mutants, reduced aldosterone secretion. Our results suggest that, contrary to pore mutants of GIRK4, non-pore mutants R52H and E246K mutants are loss-of-function rather than gain-of-function/selectivity-loss mutants. Hence, GIRK4 openers may be a potential course of treatment for patients with cytosolic N- and C-terminal mutations. Abstract Figure: There are two mutations types in KCNJ5 (GIRK4) that can cause excessive secretion of aldosterone, leading to primary aldosteronism. Mutations of the first type render the channel non-selective to monovalent cations and often constitutively active, thus depolarizing the zona granulosa cells. This previously described mechanism underlies the disease-causing effects of mutations of amino acid residues located in the pore region (red color). Blockers of the channel may be useful as potential treatment to reduce aldosterone secretion. Here we show that mutations of the second type, located in the cytosolic domain remote from the pore, act by a different mechanism. They do not alter channel's ion selectivity or rectification but cause poor expression or poor activation by Gβγ, resulting in a reduction in cell's K⁺ conductance and depolarization. In this case, GIRK4 openers can potentially be useful to prevent the excessive aldosterone secretion. This article is protected by copyright. All rights reserved.

Update on Genetics of Primary Aldosteronism

Primary aldosteronism (PA) is the most common form of secondary hypertension, with a prevalence of 5–10% among patients with hypertension. PA is mainly classified into two subtypes: aldosterone-producing adenoma (APA) and bilateral idiopathic hyperaldosteronism. Recent developments in genetic analysis have facilitated the discovery of mutations in KCNJ5, ATP1A1, ATP2B3, CACNA1D, CACNA1H, CLCN2, and CTNNB1 in sporadic or familial forms of PA in the last decade. These findings have greatly advanced our understanding of the mechanism of excess aldosterone synthesis, particularly in APA. Most of the causative genes encode ion channels or pumps, and their mutations lead to depolarization of the cell membrane due to impairment of ion transport. Depolarization activates voltage-gated Ca²⁺ channels and intracellular calcium signaling and promotes the transcription of aldosterone synthase, resulting in overproduction of aldosterone. In this article, we review recent findings on the genetic and molecular mechanisms of PA.

Approaches to Gene Mutation Analysis Using Formalin-Fixed Paraffin-Embedded Adrenal Tumor Tissue From Patients With Primary Aldosteronism

Aldosterone production is physiologically under the control of circulating potassium and angiotensin II as well as adrenocorticotropic hormone and other secretagogues such as serotonin. The adrenal's capacity to produce aldosterone relies heavily on the expression of a single enzyme, aldosterone synthase (CYP11B2). This enzyme carries out the final reactions in the synthesis of aldosterone and is expressed almost solely in the adrenal zona glomerulosa. From a disease standpoint, primary aldosteronism (PA) is the most common of all adrenal disorders. PA results from renin-independent adrenal expression of CYP11B2 and production of aldosterone. The major causes of PA are adrenal aldosterone-producing adenomas (APA) and adrenal idiopathic hyperaldosteronism. Our understanding of the genetic causes of APA has significantly improved through comprehensive genetic profiling with next-generation sequencing. Whole-exome sequencing has led to the discovery of mutations in six genes that cause renin-independent aldosterone production and thus PA. To facilitate broad-based prospective and retrospective studies of APA, recent technologic advancements have allowed the determination of tumor mutation status using formalin-fixed paraffin-embedded (FFPE) tissue sections. This approach has the advantages of providing ready access to archival samples and allowing CYP11B2 immunohistochemistry-guided capture of the exact tissue responsible for inappropriate aldosterone synthesis. Herein we review the methods and approaches that facilitate the use of adrenal FFPE material for DNA capture, sequencing, and mutation determination.

Primary aldosteronism diagnostics: KCNJ5 mutations and hybrid steroid synthesis in aldosterone-producing adenomas

Primary aldosteronism (PA) is characterized by autonomous aldosterone production by renin-independent mechanisms and is most commonly sporadic. While 60-70% of sporadic PA can be attributed to bilateral hyperaldosteronism, the remaining 30-40% is caused by a unilateral aldosterone-producing adenoma (APA). Somatic mutations in or near the selectivity filter the KCNJ5 gene (encoding the potassium channel GIRK4) have been implicated in the pathogenesis of both sporadic and familial PA. Several studies using tumor tissue, peripheral and adrenal vein samples from PA patients have demonstrated that along with aldosterone, the hybrid steroids 18-hydroxycortisol (18OHF) and 18-oxocortisol (18oxoF) are a hallmark of APA harboring KCNJ5 mutations. Herein, we review the recent advances with respect to the molecular mechanisms underlying the pathogenesis of PA and the steroidogenic fingerprints of KCNJ5 mutations. In addition, we present an outlook toward the future of PA subtyping and diagnostic work-up utilizing steroid profiling.

Old and new genes in primary aldosteronism

Primary aldosteronism (PA) is the most common form of secondary hypertension affecting 5%-10% of patients with arterial hypertension. In PA, high blood pressure is associated with high aldosterone and low renin levels, and often hypokalemia. In a majority of cases, autonomous aldosterone production by the adrenal gland is caused by an aldosterone producing adenoma (APA) or bilateral adrenal hyperplasia (BAH). During the last ten years, a better knowledge of the pathophysiology of PA came from the discovery of somatic and germline mutations in different genes in both sporadic and familial forms of the disease. Those genes code for ion channels and pumps, as well as proteins involved in adrenal cortex development and function. Targeted next generation sequencing following immunohistochemistry guided detection of aldosterone synthase expression allows detection of somatic mutations in up to 90% of APA, while whole exome sequencing has discovered the genetic causes of four different familial forms of PA. The identification, in BAH, of somatic mutations in aldosterone producing cell clusters open new perspectives in our understanding of the bilateral form of the disease and the development of new therapeutic approaches.

Molecular and Electrophysiological Analyses of ATP2B4 Gene Variants in Bilateral Adrenal Hyperaldosteronism

Primary aldosteronism (PA) is the most common cause of secondary hypertension with a high prevalence among patients with resistant hypertension. Despite the recent discovery of somatic variants in aldosterone-producing adenoma (APA)-associated PA, causes for PA due to bilateral aldosterone production (bilateral hyperaldosteronism; BHA) remain unknown. Herein, we identified rare gene variants in ATP2B4, in a cohort of patients with BHA. ATP2B4 belongs to the same family of Ca-ATPases as ATP2B3, which is involved in the pathogenesis of APA. Endogenous ATP2B4 expression was characterized in adrenal tissue, and the gene variants were functionally analyzed for effects on aldosterone synthase (CYP11B2) expression, steroid production in basal and agonist-stimulated conditions, and for changes in biophysical properties of channel properties. Knockdown of ATP2B4 in HAC15 exhibited reduced angiotensin II stimulation in one of four shRNA clones. Stable HAC15 cell lines with doxycycline (dox) - inducible wild-type and variant forms of ATP2B4 - were generated, and dox-induced upregulation of ATP2B4 mRNA and protein was confirmed. However, ATP2B4 variants did not alter basal or agonist-stimulated CYP11B2 expression. Whole-cell recordings in HAC15 cells indicated robust endogenous ATP2B4 conductance in native cells but reduced conductance with overexpressed WT and variant ATP2B4. The previously defined PA-causing ATP2B3 variant served as a positive control and exhibited elevated CYP11B2 mRNA. In conclusion, while this study did not confirm a pathogenic role for ATP2B4 variants in BHA, we describe the sequencing analysis for familial and sporadic BHA and outline a template for the thorough in vitro characterization of gene variants.

Genetic Characteristics of Aldosterone-Producing Adenomas in Blacks

Somatic mutations have been identified in aldosterone-producing adenomas (APAs) in genes that include KCNJ5, ATP1A1, ATP2B3, and CACNA1D. Based on independent studies, there appears to be racial differences in the prevalence of somatic KCNJ5 mutations, particularly between East Asians and Europeans. Despite the high cardiovascular disease mortality of blacks, there have been no studies focusing on somatic mutations in APAs in this population. In the present study, we investigated genetic characteristics of APAs in blacks using a CYP11B2 (aldosterone synthase) immunohistochemistry-guided next-generation sequencing approach. The adrenal glands with adrenocortical adenomas from 79 black patients with primary aldosteronism were studied. Seventy-three tumors from 69 adrenal glands were confirmed to be APAs by CYP11B2 immunohistochemistry. Sixty-five of 73 APAs (89%) had somatic mutations in aldosterone-driver genes. Somatic CACNA1D mutations were the most prevalent genetic alteration (42%), followed by KCNJ5 (34%), ATP1A1 (8%), and ATP2B3 mutations (4%). CACNA1D mutations were more often observed in APAs from males than those from females (55% versus 29%, P=0.033), whereas KCNJ5 mutations were more prevalent in APAs from females compared with those from males (57% versus 13%, P<0.001). No somatic mutations in aldosterone-driver genes were identified in tumors without CYP11B2 expression. In conclusion, 89% of APAs in blacks harbor aldosterone-driving mutations, and unlike Europeans and East Asians, the most frequently mutated aldosterone-driver gene was CACNA1D. Determination of racial differences in the prevalence of aldosterone-driver gene mutations may facilitate the development of personalized medicines for patients with primary aldosteronism.

Familial hyperaldosteronism type III a novel case and review of literature

Less than 15% of hypertension cases in children are secondary to a primary hyperaldosteronism. This is idiopathic in 60% of the cases, secondary to a unilateral adenoma in 30% and 10% remaining by primary adrenal hyperplasia, familial hyperaldosteronism, ectopic aldosterone production or adrenocortical carcinoma.To date, four types of familial hyperaldosteronism (FH I to FH IV) have been reported. FH III is caused by germline mutations in KCNJ5, encoding the potassium channel Kir3.4. The mutations cause the channel to lose its selectivity for potassium, allowing large quantities of sodium to enter the cell. As a consequence, the membrane depolarizes, voltage-gated calcium channels open, calcium enters the cell, initiating the cascade that leads to aldosterone synthesis. Somatic mutations in KCNJ5 has also been described in aldosterone-producing adenomas. The most frequent presentation of FH III is with severe hyperaldosteronism symptoms and resistance to pharmacological therapy which leads to bilateral adrenalectomy. We will review current literature and describe a child with FH III due to a novel de novo deletion in KCNJ5 with wild phenotype as a sign of clinical variability of this disease.

Urinary Metabolic Signature of Primary Aldosteronism: Gender and Subtype-Specific Alterations

PURPOSE

The current clinical investigation for primary aldosteronism (PA) diagnosis requires complex expensive tests from the initial suspicion to the final subtype classification, including invasive approaches; therefore, appropriate markers for subtype definition are greatly desirable. The present study performs a metabolomics analysis to further examine specific molecular signatures of PA urines EXPERIMENTAL DESIGN: The study considered PA subtype and gender-related differences using two orthogonal advanced UHPLC-MS metabolomics approaches. Patients with essential hypertension (n = 36) and PA (n = 50) who were referred to the outpatient hypertension clinic and matched healthy subjects (n = 10) are investigated.

RESULTS

Statistically significant changes (p < 0.05 ANOVA, Fc > 1.5) of metabolites involved in central carbon, energy, and nitrogen metabolism are identified, especially purine and pyrimidine nucleosides and precursors, and free amino acids. PLS-DA interpretation provides strong evidence of a disease-specific metabolic pattern with dAMP, diiodothyronine, and 5-methoxytryptophan as leading factors, and a sex-specific metabolic pattern associated with orotidine 5-phosphate, N-acetylalanine, hydroxyproline, and cysteine. The results are verified using an independent sample set, which confirms the identification of specific signatures.

CONCLUSIONS AND CLINICAL RELEVANCE

Metabolomics is used to identify low molecular weight molecular markers of PA, which paves the way for follow-up validation studies in larger cohorts.

The Biology of Normal Zona Glomerulosa and Aldosterone-Producing Adenoma: Pathological Implications

The identification of several germline and somatic ion channel mutations in aldosterone-producing adenomas (APAs) and detection of cell clusters that can be responsible for excess aldosterone production, as well as the isolation of autoantibodies activating the angiotensin II type 1 receptor, have rapidly advanced the understanding of the biology of primary aldosteronism (PA), particularly that of APA. Hence, the main purpose of this review is to discuss how discoveries of the last decade could affect histopathology analysis and clinical practice. The structural remodeling through development and aging of the human adrenal cortex, particularly of the zona glomerulosa, and the complex regulation of aldosterone, with emphasis on the concepts of zonation and channelopathies, will be addressed. Finally, the diagnostic workup for PA and its subtyping to optimize treatment are reviewed.

Targeted Molecular Characterization of Aldosterone-Producing Adenomas in White Americans

CONTEXT

Somatic mutations have been identified in more than half of aldosterone-producing adenomas (APAs) through mutation hotspot sequencing. The underlying pathogenesis of inappropriate aldosterone synthesis in the remaining population is still unknown.

OBJECTIVE

To investigate the prevalence and spectrum of somatic mutations in APAs using an aldosterone synthase (CYP11B2) immunohistochemistry (IHC)‒guided next-generation sequencing (NGS) approach.

METHODS

Formalin-fixed paraffin-embedded adrenal tissue from white American patients with primary aldosteronism who underwent adrenalectomy at the University of Michigan was used. Genomic DNA was isolated from 75 APAs (identified by CYP11B2 IHC). NGS was performed to identify somatic mutations by sequencing the entire coding region of a panel of genes mutated in APAs.

RESULTS

Somatic mutations were identified in 66 of 75 APAs (88%). Of the APAs with somatic mutations, six were smaller than coexisting CYP11B2-negative adrenocortical adenomas. The most frequently mutated gene was KCNJ5 (43%), followed by CACNA1D (21%), ATP1A1 (17%), ATP2B3 (4%), and CTNNB1 (3%). In addition to identification of previously reported mutations, we identified five previously unreported mutations (two in KCNJ5, one in ATP1A1, one in ATP2B3, and one in CACNA1D genes). KCNJ5 mutations were more frequent in women (70% vs 24% in men).

CONCLUSION

Comprehensive NGS of CYP11B2-expressing adrenal tumors identified somatic mutations in aldosterone-driving genes in 88% of APAs, a higher rate than in previous studies using conventional approaches.

Mutations of the Twik-Related Acid-Sensitive K+ Channel 2 Promoter in Human Primary Aldosteronism

Because blunted expression of the twik-related acid-sensitive K+ channel 2 (TASK-2) is a common feature of aldosterone-producing adenoma (APA) causing primary aldosteronism (PA), we sequenced the promoter region of the TASK-2 gene (KCNK5) in APAs (n = 76), primary hypertensive patients (n = 98), and 20-year-old healthy volunteers (n = 71), searching for variants that could affect expression of this channel. We found TASK-2 promoter mutations in 25% of the APAs: C999T in 6.6%, G595A in 5.3%, G36A in 5.3%, and C562T, Gins468, G265C, C1247T, G1140T, and C1399T in 1.3% each. The C999T mutation was found in only one of the 98 primary hypertensive patients, but mutations were detected also in 12% of volunteers: 4 carried the C999T, 3 G1288C, 1 the G1140T mutation, and 1 the 468ins mutation. After a 16-year follow-up, none of these patients developed hypertension or PA. The effect of C999T mutation was investigated in H295R cells using reporter vectors with the mutated or the wild-type (WT) TASK-2 promoters. TASK-2 gene expression was decreased by 31% ± 18% (P = 0.01) in mutated compared with WT APA. Likewise, in transfected H295R cells, the C999T mutation decreased TASK-2 transcriptional activity by 35% (normalized luciferase signal fold change: 0.65 ± 0.25, P < 0.001). Thus, mutations in the promoter region of the TASK-2 gene can account for the low expression in ∼25% of APAs. As they did not result in hypertension or PA during long-term follow-up in healthy participants, these mutations do not seem to be a factor in causing PA by themselves.

Macrolides for KCNJ5-mutated aldosterone-producing adenoma (MAPA): design of a study for personalized diagnosis of primary aldosteronism

PURPOSE

Aldosterone-producing adenoma (APA) is the main curable cause of endocrine hypertension cause of primary aldosteronism (PA) and it is in up to 66% of all cases investigated with adrenal vein sampling (AVS). Mutations in the KCNJ5 potassium channel involve up to 70% of APA and cause the most florid PA phenotypes. The recent finding that macrolide antibiotics specifically inhibit in vitro the altered function of mutated KCNJ5 channels has opened new horizons for the diagnosis and treatment of APA with KCNJ5 mutations in that it can allow identification and target treatment of PA patients harbouring a mutated APA. Thus, we aimed at investigating if clarithromycin and roxithromycin, two macrolides that potently blunt mutated Kir3.4 channel function in vitro, affect plasma aldosterone concentration in adrenal vein blood during AVS and in peripheral blood, respectively, in PA patients with a mutated APA.

METHODS AND DESIGN

We designed two proof of concept studies. In study A: consecutive patients with an unambiguous biochemical evidence of PA will be exposed to a single dose of 250 mg clarithromycin during AVS, to assess its effect on the relative aldosterone secretion index in adrenal vein blood from the gland with and without APA. In study B: consecutive hypertensive patients submitted to the work-up for hypertension will receive a single oral dose of 150 mg roxithromycin. The experimental endpoints will be the change induced by roxithromycin of plasma aldosterone concentration and other steroids, direct active renin concentration, serum K⁺, systolic and diastolic blood pressure.

DISCUSSION

We expect to prove that: (i) clarithromycin allows identification of mutated APA before adrenalectomy and sequencing of tumour DNA; (ii) the acute changes of plasma aldosterone concentration, direct active renin concentration, and blood pressure in peripheral venous blood after roxithromycin can be a proxy for the presence of an APA with somatic mutations.

Genetic Causes of Functional Adrenocortical Adenomas

Aldosterone and cortisol, the main mineralocorticoid and glucocorticoid hormones in humans, are produced in the adrenal cortex, which is composed of three concentric zones with specific functional characteristics. Adrenocortical adenomas (ACAs) can lead to the autonomous secretion of aldosterone responsible for primary aldosteronism, the most frequent form of secondary arterial hypertension. In the case of cortisol production, ACAs lead to overt or subclinical Cushing syndrome. Genetic analysis driven by next-generation sequencing technology has enabled the discovery, during the past 7 years, of the genetic causes of a large subset of ACAs. In particular, somatic mutations in genes regulating intracellular ionic homeostasis and membrane potential have been identified in aldosterone-producing adenomas. These mutations all promote increased intracellular calcium concentrations, with activation of calcium signaling, the main trigger for aldosterone production. In cortisol-producing adenomas, recurrent somatic mutations in PRKACA (coding for the cyclic adenosine monophosphate-dependent protein kinase catalytic subunit α) affect cyclic adenosine monophosphate-dependent protein kinase A signaling, leading to activation of cortisol biosynthesis. In addition to these specific pathways, the Wnt/β-catenin pathway appears to play an important role in adrenal tumorigenesis, because β-catenin mutations have been identified in both aldosterone- and cortisol-producing adenomas. This, together with different intermediate states of aldosterone and cortisol cosecretion, raises the possibility that the two conditions share a certain degree of genetic susceptibility. Alternatively, different hits might be responsible for the diseases, with one hit leading to adrenocortical cell proliferation and nodule formation and the second specifying the hormonal secretory pattern.

Macrolides Blunt Aldosterone Biosynthesis: A Proof-of-Concept Study in KCNJ5 Mutated Adenoma Cells Ex Vivo

Aldosterone-producing adenoma (APA), a major subtype of primary hyperaldosteronism, the main curable cause of human endocrine hypertension, involves somatic mutations in the potassium channel Kir3.4 (KCNJ5) in 30% to 70% of cases, typically the more florid phenotypes. Because KCNJ5 mutated channels were reported to be specifically sensitive to inhibition by macrolide antibiotics, which concentration dependently blunts aldosterone production in HAC15 transfected with the G151R and L168R mutated channel, we herein tested the effect of clarithromycin on aldosterone synthesis and secretion in a pure population of aldosterone-secreting cells obtained by immunoseparation (CD56⁺ cells) from APA tissues with/without the 2 most common KCNJ5 mutations. From a large cohort of patients with an unambiguous APA diagnosis, we recruited those who were wild type (n=3) or had G151R (n=2) and L168R (n=2) mutations. We found that clarithromycin concentration dependently lowered CYP11B2 gene expression (by 60%) and aldosterone secretion (by 70%; P<0.001 for both) in CD56⁺ cells isolated ex vivo from KCNJ5 mutated APAs, although it was ineffective in CD56⁺ cells from wild-type APAs. By proving the principle that the oversecretion of aldosterone can be specifically blunted in APA cells ex vivo with G151R and L168R mutations, these results provide compelling evidence of the possibility of specifically correcting aldosterone excess in patients with APA carrying the 2 most common KCNJ5 somatic mutations.

Sodium permeable and "hypersensitive" TREK-1 channels cause ventricular tachycardia

In a patient with right ventricular outflow tract (RVOT) tachycardia, we identified a heterozygous point mutation in the selectivity filter of the stretch-activated K_2P potassium channel TREK-1 (KCNK2 or K_2P2.1). This mutation introduces abnormal sodium permeability to TREK-1. In addition, mutant channels exhibit a hypersensitivity to stretch-activation, suggesting that the selectivity filter is directly involved in stretch-induced activation and desensitization. Increased sodium permeability and stretch-sensitivity of mutant TREK-1 channels may trigger arrhythmias in areas of the heart with high physical strain such as the RVOT We present a pharmacological strategy to rescue the selectivity defect of the TREK-1 pore. Our findings provide important insights for future studies of K_2P channel stretch-activation and the role of TREK-1 in mechano-electrical feedback in the heart.

CTNNB1 Mutation in Aldosterone Producing Adenoma

Discoveries of somatic mutations permit the recognition of subtypes of aldosterone-producing adenomas (APAs) with distinct clinical presentations and pathological features. Catenin β1 (CTNNB1) mutation in APAs has been recently described and discussed in the literature. However, significant knowledge gaps still remain regarding the prevalence, clinical characteristics, pathophysiology, and outcomes in APA patients harboring CTNNB1 mutations. Aberrant activation of the Wnt/β-catenin signaling pathway will further modulate tumorigenesis. We also discuss the recent knowledge of CTNNB1 mutation in adrenal adenomas.

Of channels and pumps: different ways to boost the aldosterone?

The mineralocorticoid aldosterone is a major factor controlling the salt and water balance and thereby also the arterial blood pressure. Accordingly, primary aldosteronism (PA) characterized by an inappropriately high aldosterone secretion is the most common form of secondary hypertension. The physiological stimulation of aldosterone synthesis in adrenocortical glomerulosa cells by angiotensin II and an increased plasma K⁺ concentration depends on a membrane depolarization and an increase in the cytosolic Ca²⁺ activity. Recurrent gain-of-function mutations of ion channels and transporters have been identified in a majority of cases of aldosterone-producing adenomas and in familial forms of PA. In this review, the physiological role of these genes in the regulation of aldosterone synthesis and the altered function of the mutant proteins as well are described. The specific changes of the membrane potential and the cellular ion homoeostasis in adrenal cells expressing the different mutants are compared, and their impact on autonomous aldosterone production and proliferation is discussed.

Genetics of adrenocortical tumours

The recently available genomic sequencing techniques have led to breakthroughs in understanding of the underlying genetic mechanisms in adrenocortical tumours. Disease-causing mutations have been described for aldosterone-producing adenomas, cortisol-producing adenomas and adrenocortical carcinomas. Further, knowledge gained from transcriptome analyses and methylation arrays has provided new insights into the development of these tumours. Elucidation of the genomic landscape of adrenocortical tumours and improved techniques may in the future be useful for early diagnosis through the detection of mutated DNA in the circulation. Moreover, compounds that bind specifically to altered proteins may be used as screening targets or therapeutic agents. Regulation of cortisol release by interaction with an altered subunit in adenylate cyclase may be more complex, but may provide a new option for regulating steroid release. Information about derangements in adrenocortical carcinoma is already helpful for determining patient prognosis. With further knowledge, we may be able to identify novel biomarkers that effectively and noninvasively help in differentiating between benign and malignant disease. It is clear that the next few years will provide much novel information that hopefully will aid in the treatment of patients with adrenocortical tumours.

Primary Aldosteronism: Changing Definitions and New Concepts of Physiology and Pathophysiology Both Inside and Outside the Kidney

In the 60 years that have passed since the discovery of the mineralocorticoid hormone aldosterone, much has been learned about its synthesis (both adrenal and extra-adrenal), regulation (by renin-angiotensin II, potassium, adrenocorticotrophin, and other factors), and effects (on both epithelial and nonepithelial tissues). Once thought to be rare, primary aldosteronism (PA, in which aldosterone secretion by the adrenal is excessive and autonomous of its principal regulator, angiotensin II) is now known to be the most common specifically treatable and potentially curable form of hypertension, with most patients lacking the clinical feature of hypokalemia, the presence of which was previously considered to be necessary to warrant further efforts towards confirming a diagnosis of PA. This, and the appreciation that aldosterone excess leads to adverse cardiovascular, renal, central nervous, and psychological effects, that are at least partly independent of its effects on blood pressure, have had a profound influence on raising clinical and research interest in PA. Such research on patients with PA has, in turn, furthered knowledge regarding aldosterone synthesis, regulation, and effects. This review summarizes current progress in our understanding of the physiology of aldosterone, and towards defining the causes (including genetic bases), epidemiology, outcomes, and clinical approaches to diagnostic workup (including screening, diagnostic confirmation, and subtype differentiation) and treatment of PA.

Double adrenocortical adenomas harboring independent KCNJ5 and PRKACA somatic mutations

OBJECTIVE

Co-secretion of cortisol and aldosterone can be observed in adrenal adenomas. The aim of this study was to investigate the molecular characteristics of a co-existing aldosterone- and a cortisol-producing adenoma (CPA) in the same patient.

DESIGN AND METHODS

Two different adenomas within the same adrenal gland from a 49-year-old female patient with primary aldosteronism (PA) and Cushing's syndrome (CS) were studied. Multiple formalin-fixed paraffin-embedded tumor blocks were used for the analysis. Immunohistochemistry (IHC) was performed using a specific antibody against aldosterone synthase (CYP11B2). DNA and RNA were isolated separately from CYP11B2-positive and -negative tumor regions based on CYP11B2 IHC results.

RESULTS

CYP11B2 IHC clearly demonstrated that three pieces from one adenoma were positive for CYP11B2 and the remaining three from the other adenoma were negative for CYP11B2. In quantitative real-time RT-PCR, CYP11B2 mRNA was upregulated in CYP11B2-positive tumor specimens (219-fold vs CYP11B2-negative tumor specimens). Targeted next-generation sequencing (NGS) detected novel KCNJ5 gene mutations (p.T148I/T149S, present in the same reads) and a PRKACA gene hotspot mutation (p.L206R) in the CYP11B2-positive and -negative tumors, respectively. Sanger sequencing of DNA from each tumor specimen (CYP11B2-positive tumor, n=3; CYP11B2-negative tumor, n=3) showed concordant results with targeted NGS.

CONCLUSION

Our findings illustrate the co-existence of two different adrenocortical adenomas causing the concurrent diagnosis of PA and CS in the same patient. Molecular analysis was able to demonstrate that the two diseases resulted from independent somatic mutations seen in double adrenocortical adenomas.

Small-Conductance Ca2+-Activated Potassium Channels Negatively Regulate Aldosterone Secretion in Human Adrenocortical Cells

Aldosterone, which plays a key role in maintaining water and electrolyte balance, is produced by zona glomerulosa cells of the adrenal cortex. Autonomous overproduction of aldosterone from zona glomerulosa cells causes primary hyperaldosteronism. Recent clinical studies have highlighted the pathological role of the KCNJ5 potassium channel in primary hyperaldosteronism. Our objective was to determine whether small-conductance Ca(2+)-activated potassium (SK) channels may also regulate aldosterone secretion in human adrenocortical cells. We found that apamin, the prototypic inhibitor of SK channels, decreased membrane voltage, raised intracellular Ca(2+) and dose dependently increased aldosterone secretion from human adrenocortical H295R cells. By contrast, 1-Ethyl-2-benzimidazolinone, an agonist of SK channels, antagonized apamin's action and decreased aldosterone secretion. Commensurate with an increase in aldosterone production, apamin increased mRNA expression of steroidogenic acute regulatory protein and aldosterone synthase that control the early and late rate-limiting steps in aldosterone biosynthesis, respectively. In addition, apamin increased angiotensin II-stimulated aldosterone secretion, whereas 1-Ethyl-2-benzimidazolinone suppressed both angiotensin II- and high K(+)-stimulated production of aldosterone in H295R cells. These findings were supported by apamin-modulation of basal and angiotensin II-stimulated aldosterone secretion from acutely prepared slices of human adrenals. We conclude that SK channel activity negatively regulates aldosterone secretion in human adrenocortical cells. Genetic association studies are necessary to determine whether mutations in SK channel subtype 2 genes may also drive aldosterone excess in primary hyperaldosteronism.

Mutated KCNJ5 activates the acute and chronic regulatory steps in aldosterone production

Somatic and germline mutations in the inward-rectifying K(+) channel (KCNJ5) are a common cause of primary aldosteronism (PA) in aldosterone-producing adenoma and familial hyperaldosteronism type III, respectively. Dysregulation of adrenal cell calcium signaling represents one mechanism for mutated KCNJ5 stimulation of aldosterone synthase (CYP11B2) expression and aldosterone production. However, the mechanisms stimulating acute and chronic production of aldosterone by mutant KCNJ5 have not been fully characterized. Herein, we defined the effects of the T158A KCNJ5 mutation (KCNJ5(T158A)) on acute and chronic regulation of aldosterone production using an adrenal cell line with a doxycycline-inducible KCNJ5(T158A) gene (HAC15-TRE-KCNJ5(T158A)). Doxycycline incubation caused a time-dependent increase in KCNJ5(T158A) and CYP11B2 mRNA and protein levels. Electrophysiological analyses confirm the loss of inward rectification and increased Na(+) permeability in KCNJ5(T158A)-expressing cells. KCNJ5(T158A) expression also led to the activation of CYP11B2 transcriptional regulators, NURR1 and ATF2. Acutely, KCNJ5(T158A) stimulated the expression of total and phosphorylated steroidogenic acute regulatory protein (StAR). KCNJ5(T158A) expression increased the synthesis of aldosterone and the hybrid steroids 18-hydroxycortisol and 18-oxocortisol, measured with liquid chromatography-tandem mass spectrometry (LC-MS/MS). All of these stimulatory effects of KCNJ5(T158A) were inhibited by the L-type Ca(2+) channel blocker, verapamil. Overall, KCNJ5(T158A)increases CYP11B2 expression and production of aldosterone, corticosterone and hybrid steroids by upregulating both acute and chronic regulatory events in aldosterone production, and verapamil blocks KCNJ5(T158A)-mediated pathways leading to aldosterone production.

Normoaldosteronemic aldosterone-producing adenoma: immunochemical characterization and diagnostic implications

BACKGROUND

A high aldosterone-renin ratio (ARR) is commonly used to identify primary aldosteronism, but the ARR is high when renin is low, even if plasma aldosterone concentration values are normal, suggesting the existence of 'normoaldosteronemic' primary aldosteronism. However, most such cases did not undergo adrenalectomy; moreover, because of the lack of antibody for the human CYP11B2 (aldosterone synthase), conclusive demonstration of a normoaldosteronemic aldosterone-producing adenoma was not possible thus far.

METHOD

In 2003, a lady presented with severe hypertension a right adrenal nodule, low renin, high ARR, but normal plasma aldosterone concentration. As adrenal vein sampling showed lateralized aldosterone secretion, she underwent left adrenalectomy, which consistently normalized blood pressure (BP) and renin during 11-year follow-up.

RESULT AND CONCLUSION

The development of a novel monoclonal antibody for the human CYP11B2 in 2014 allowed immunochemically identification of a CYP11B2-positive adenoma in the resected adrenal. Moreover, this case unequivocally demonstrates for the first time the existence of normoaldosteronemic aldosterone-producing adenoma, which suggests that many cases of 'low renin-essential hypertension' might instead have a surgically curable form of primary aldosteronism.

Novel genetic determinants of adrenal aldosterone regulation

PURPOSE OF REVIEW

Aldosterone regulation in the adrenal plays an important role in blood pressure. The commonest curable cause of hypertension is primary aldosteronism. Recently, mutations in novel genes have been identified to cause primary aldosteronism. Elucidating the mechanism of action of these genetic abnormalities may help understand the cause of primary aldosteronism and the physiological regulation of aldosterone in the zona glomerulosa.

RECENT FINDINGS

KCNJ5, ATP1A1, ATP2B3, CACNA1D, CTNNB1, and CACNA1H mutations are causal of primary aldosteronism. ARMC5 may cause bilateral lesions resulting in primary aldosteronism.LGR5, DACH1, and neuron-specific proteins are highly expressed in the zona glomerulosa and regulate aldosterone production.

SUMMARY

Most mutations causing primary aldosteronism are in genes encoding cation channels or pumps, leading to increased calcium influx. Genotype-phenotype analyses identified two broad subtypes of aldosterone-producing adenomas (APAs), zona fasciculata-like and zona glomerulosa-like, and the likelihood of under-diagnosed zona glomerulosa-like APAs because of small size. Zona fasciculata-like APAs are only associated with KCNJ5 mutations, whereas zona glomerulosa-like APAs are associated with mutations in ATPase pumps, CACNA1D, and CTNNB1. The frequency of APAs, and the multiplicity of causal mutations, suggests a pre-existing drive for these mutations. We speculate that these mutations are selected for protecting against tonic inhibition of aldosterone in human zona glomerulosa, which express genes inhibiting aldosterone production.

Role of voltage-gated calcium channels in the regulation of aldosterone production from zona glomerulosa cells of the adrenal cortex

Zona glomerulosa cells (ZG) of the adrenal gland constantly integrate fluctuating ionic, hormonal and paracrine signals to control the synthesis and secretion of aldosterone. These signals modulate Ca²⁺ levels, which provide the critical second messenger to drive steroid hormone production. Angiotensin II is a hormone known to modulate the activity of voltage-dependent L- and T-type Ca²⁺ channels that are expressed on the plasma membrane of ZG cells in many species. Because the ZG cell maintains a resting membrane voltage of approximately -85 mV and has been considered electrically silent, low voltage-activated T-type Ca²⁺ channels are assumed to provide the primary Ca²⁺ signal that drives aldosterone production. However, this view has recently been challenged by human genetic studies identifying somatic gain-of-function mutations in L-type Ca_V 1.3 channels in aldosterone-producing adenomas of patients with primary hyperaldosteronism. We provide a review of these assumptions and challenges, and update our understanding of the state of the ZG cell in a layer in which native cellular associations are preserved. This updated view of Ca²⁺ signalling in ZG cells provides a unifying mechanism that explains how transiently activating Ca_V 3.2 channels can generate a significant and recurring Ca²⁺ signal, and how Ca_V 1.3 channels may contribute to the Ca²⁺ signal that drives aldosterone production.

Genetics of Aldosterone-Producing Adenoma in Korean Patients

Objectives

Recently, somatic mutations in KCNJ5, ATP1A1, ATP2B3, and CACNA1D genes were found to be associated with the pathogenesis of aldosterone-producing adenoma (APA). This study aimed to investigate the prevalence of somatic mutations in KCNJ5, ATP1A1, ATP2B3, and CACNA1D and examine the correlations between these mutations and the clinical and biochemical characteristics in Korean patients with APA.

Methods

We performed targeted gene sequencing in 66 patients with APA to detect somatic mutations in these genes.

Results

Somatic KCNJ5 mutations were found in 47 (71.2%) of the 66 patients with APA (31 cases of p.G151R and 16 cases of p.L168R); these two mutations were mutually exclusive. Somatic mutations in the ATP1A1, ATP2B3, and CACNA1D genes were not observed. Somatic KCNJ5 mutations were more prevalent in female patients (66% versus 36.8%, respectively; P = 0.030). Moreover, patients with KCNJ5 mutations comprised a significantly higher proportion of patients younger than 35 years of age (19.1% versus 0%, respectively; P = 0.040). There were no significant differences in pre-operative blood pressure, plasma aldosterone, serum potassium, lateralization index, and adenoma size according to mutational status. Patients with KCNJ5 mutations were less likely to need antihypertensive medications after adrenalectomy compared with those without mutation (36.2% versus 63.2%; P = 0.045).

Conclusions

The present study demonstrated the high prevalence of somatic KCNJ5 mutations in Korean patients with APA. Carriers of somatic KCNJ5 mutations were more likely to be female. Early diagnosis and better therapeutic outcomes were associated with somatic KCNJ5 mutations in APA.

Intracellular Molecular Differences in Aldosterone- Compared to Cortisol-Secreting Adrenal Cortical Adenomas

The adrenal cortex is a major site of steroid hormone production. Two hormones are of particular importance: aldosterone, which is produced in the zona glomerulosa in response to volume depletion and hyperkalemia, and cortisol, which is produced in the zona fasciculata in response to stress. In both cases, acute stimulation leads to increased hormone production, and chronic stimulation causes hyperplasia of the respective zone. Aldosterone- and cortisol-producing adenomas (APAs and CPAs) are benign tumors of the adrenal cortex that cause excess hormone production, leading to primary aldosteronism and Cushing's syndrome, respectively. About 40% of the APAs carry somatic heterozygous gain-of-function mutations in the K(+) channel KCNJ5. These mutations lead to sodium permeability, depolarization, activation of voltage-gated Ca(2+) channels, and Ca(2+) influx. Mutations in the Na(+)/K(+)-ATPase subunit ATP1A1 and the plasma membrane Ca(2+)-ATPase ATP2B3 similarly cause Na(+) or H(+) permeability and depolarization, whereas mutations in the Ca(2+) channel CACNA1D directly lead to increased calcium influx. One in three CPAs carries a recurrent gain-of-function mutation (L206R) in the PRKACA gene, encoding the catalytic subunit of PKA. This mutation causes constitutive PKA activity by abolishing the binding of the inhibitory regulatory subunit to the catalytic subunit. These mutations activate pathways that are relatively specific to the respective cell type (glomerulosa versus fasciculata), and there is little overlap in mutation spectrum between APAs and CPAs, but co-secretion of both hormones can occur. Mutations in CTNNB1 (beta-catenin) and GNAS (Gsα) are exceptions, as they can cause both APAs and CPAs through pathways that are incompletely understood.

KCNJ5 Mutations: Sex, Salt and Selection

Somatic mutations have been identified in the KCNJ5 gene (encoding the potassium channel GIRK4) in aldosterone-producing adenomas (APA). Most of these mutations are located in or near the selectivity filter of the GIRK4 channel pore and several have been shown to lead to the constitutive overproduction of aldosterone. KCNJ5 mutations in APA are more frequent in women; however, this gender dimorphism is a reported phenomenon of Western but not East Asian populations. In this review we discuss some of the issues that could potentially underlie this observation.

Primary Aldosteronism: New Answers, New Questions

There have been 2, and possibly 3, major questions for primary aldosteronism (PA) answered at least in principle over the past 5 years. The first is that of somatic mutations underlying the majority of aldosterone producing adenomas. The second is the extension of our knowledge of the genetics of familial hypertension, and the third the role of renal intercalated cells in sodium homeostasis. New questions for the next 5 years include a single accepted confirmatory/exclusion test; standardisation of assays and cut-offs; alternatives to universal adrenal venous sampling; reclassification of 'low renin hypertension'; recognition of the extent of 'occult' PA; inclusion of low-dose mineralocorticoid receptor antagonist in first-line therapy for hypertension; and finally, possible resolution of the aldosterone/inappropriate sodium status enigma at the heart of the cardiovascular damage in PA.

Pathogenesis of Adrenal Aldosterone-Producing Adenomas Carrying Mutations of the Na(+)/K(+)-ATPase

Aldosterone-producing adenoma (APA) is a major cause of primary aldosteronism, leading to secondary hypertension. Somatic mutations in the gene for the α1 subunit of the Na(+)/K(+)-ATPase were found in about 6% of APAs. APA-related α1 subunit of the Na(+)/K(+)-ATPase mutations lead to a loss of the pump function of the Na(+)/K(+)-ATPase, which is believed to result in membrane depolarization and Ca(2+)-dependent stimulation of aldosterone synthesis in adrenal cells. In addition, H(+) and Na(+) leak currents via the mutant Na(+)/K(+)-ATPase were suggested to contribute to the phenotype. The aim of this study was to investigate the cellular pathophysiology of adenoma-associated Na(+)/K(+)-ATPase mutants (L104R, V332G, G99R) in adrenocortical NCI-H295R cells. The expression of these Na(+)/K(+)-ATPase mutants depolarized adrenal cells and stimulated aldosterone secretion. However, an increase of basal cytosolic Ca(2+) levels in Na(+)/K(+)-ATPase mutant cells was not detectable, and stimulation with high extracellular K(+) hardly increased Ca(2+) levels in cells expressing L104R and V332G mutant Na(+)/K(+)-ATPase. Cytosolic pH measurements revealed an acidification of L104R and V332G mutant cells, despite an increased activity of the Na(+)/H(+) exchanger. The possible contribution of cellular acidification to the hypersecretion of aldosterone was supported by the observation that aldosterone secretion of normal adrenocortical cells was stimulated by acetate-induced acidification. Taken together, mutations of the Na(+)/K(+)-ATPase depolarize adrenocortical cells, disturb the K(+) sensitivity, and lower intracellular pH but, surprisingly, do not induce an overt increase of intracellular Ca(2+). Probably, the autonomous aldosterone secretion is caused by the concerted action of several pathological signaling pathways and incomplete cellular compensation.

Somatic mutations of the ATP1A1 gene and aldosterone-producing adenomas

Primary aldosteronism is the most common form of secondary hypertension. It affects approximately 10% of patients with hypertension and causes greater cardiovascular morbidity and mortality compared to essential hypertension of similar severity and duration. The cause of primary aldosteronism in about half of these patients is an aldosterone-producing adenoma; over half of these adenomas have mutations in one of several ion channels and pumps, including the potassium channel KCNJ5, calcium channel Cav1.3, α1 subunit of the sodium potassium ATPase, and membrane calcium ATPase 3. This review concentrates on the molecular and physiological mechanisms by which mutations of the ATP1A1 gene increase aldosterone production.

Two-pore domain potassium channels in the adrenal cortex

The physiological control of steroid hormone secretion from the adrenal cortex depends on the function of potassium channels. The "two-pore domain K(+) channels" (K2P) TWIK-related acid sensitive K(+) channel 1 (TASK1), TASK3, and TWIK-related K(+) channel 1 (TREK1) are strongly expressed in adrenocortical cells. They confer a background K(+) conductance to these cells which is important for the K(+) sensitivity as well as for angiotensin II and adrenocorticotropic hormone-dependent stimulation of aldosterone and cortisol synthesis. Mice with single deletions of the Task1 or Task3 gene as well as Task1/Task3 double knockout mice display partially autonomous aldosterone synthesis. It appears that TASK1 and TASK3 serve different functions: TASK1 affects cell differentiation and prevents expression of aldosterone synthase in the zona fasciculata, while TASK3 controls aldosterone secretion in glomerulosa cells. TREK1 is involved in the regulation of cortisol secretion in fasciculata cells. These data suggest that a disturbed function of K2P channels could contribute to adrenocortical pathologies in humans.

Understanding primary aldosteronism: impact of next generation sequencing and expression profiling

Primary aldosteronism (PA) encompasses a broad, heterogeneous group of disorders including both sporadic and familial forms (familial hyperaldosteronism type I, II and III). PA is the most common form of secondary hypertension and associated with a higher rate of cardiovascular complications, compared with essential hypertension. Despite significant progress in the diagnosis and management of PA, until recently the molecular mechanisms leading to inappropriate aldosterone production were largely unknown. The introduction of next-generation sequencing has had a profound impact on the field of human genetics and has given new insight in the molecular determinants that lead to both sporadic and familial forms of PA. Here we review the recent progress toward understanding of the genetic and molecular mechanisms leading to autonomous aldosterone production in PA.

A case of severe hyperaldosteronism caused by a de novo mutation affecting a critical salt bridge Kir3.4 residue

CONTEXT

Familial hyperaldosteronism type III (FH-III) is a rare and clinically heterogeneous condition, that can display mild as well as severe phenotypes. Point mutations in the KCNJ5 gene, affecting the ion selectivity of the inward rectifier K(+) channel 4 (Kir3.4), underlie the molecular basis of FH-III.

OBJECTIVE

The objective of the study was to investigate the effects of a de novo germline KCNJ5 mutation.

PATIENTS AND METHODS

We describe the case of a girl who came to medical attention at the age of 2 years because of polydipsia, polyuria, and failure to thrive. The patient, affected by hypertension and hypokalemia, was diagnosed with primary aldosteronism on the basis of extremely high aldosterone levels and suppressed plasma renin activity. Genomic DNA was isolated and KCNJ5 sequenced. Human adrenocortical cells were used as an in vitro model for the functional characterization of the mutant channel.

RESULTS

KCNJ5 sequencing in the index case and her parents revealed a de novo p.Glu145Gln germline mutation. The substitution resulted in Na(+)-dependent depolarization of adrenal cells and increased intracellular calcium concentration, which activated the transcription of NR4A2 and, in turn, CYP11B2. Pharmacological studies revealed that the mutant channel was insensitive to tertiapin-Q and calcium-channel blocker verapamil.

CONCLUSIONS

Herein we report the identification of a novel KCNJ5 germline mutation responsible for severe hyperaldosteronism that presented in infancy with symptoms of diabetes insipidus. The findings of this study further elucidate the etiology of FH-III and expand our knowledge of this rare condition.

The molecular basis of primary aldosteronism: from chimeric gene to channelopathy

Primary aldosteronism (PA) is the most common endocrine cause of high blood pressure. Only a minority of the PA cases are familial and due to known (CYP11B2/CYP11B1 chimeric gene or mutations in the KCNJ5 gene) or unknown causes. In the most common sporadic cases the mechanisms by which the excess aldosterone production persists in spite of high blood pressure, sodium retention, suppression of the renin angiotensin system and low potassium levels, all factors that by themselves would be expected to shut off aldosterone production, were a puzzle for decades. Only recently the discovery of functional mutations and down-regulation of potassium channels provided some explanations. We herein reviewed these recent findings and their mechanistic implications. We also propose a clinical molecular classification of familial hyperaldosteronism, which can be important from the practical standpoint as it considers besides the molecular features also the responsiveness to treatment and the imaging features.