KCNJ5 Mutations: Sex, Salt and Selection

Exploring heterogeneity of tumor immune cells and adrenal cells in aldosterone-producing adenomas using single-cell RNA-seq and investigating differences by sex

The mechanism behind the higher incidence of aldosterone-producing adenoma (APA) in women compared to men is not yet understood. In this study, we utilized single-cell RNA sequencing (scRNA-seq) to investigate the immune cell infiltration and adrenal cell characteristics in APA. Our findings revealed a high presence of immune cells in the tumor microenvironment, with macrophages and T lymphocytes being the most prevalent. Comparison of infiltrating cells between males and females showed that female CD8+T cells had stronger cytotoxic and inflammation-related functions, while female myeloid cells had more enrichment in inflammatory pathways. Additionally, we found that female adrenal cells had greater upregulation of immune-related and antigen presentation pathways. Furthermore, our analysis revealed that zona glomerulosa (ZG) cells had a higher capability for aldosterone synthesis. These results provide a deeper understanding of the APA microenvironment in patients of different sexes and offer new insights into the onset of APA.

Histopathology and Genetic Causes of Primary Aldosteronism in Young Adults

CONTEXT

Due to its rare incidence, molecular features of primary aldosteronism (PA) in young adults are largely unknown. Recently developed targeted mutational analysis identified aldosterone-driver somatic mutations in aldosterone-producing lesions, including aldosterone-producing adenomas (APAs), aldosterone-producing nodules (APNs), and aldosterone-producing micronodules, formerly known as aldosterone-producing cell clusters.

OBJECTIVE

To investigate histologic and genetic characteristics of lateralized PA in young adults.

METHODS

Formalin-fixed, paraffin-embedded adrenal tissue sections from 74 young patients with lateralized PA (<35 years old) were used for this study. Immunohistochemistry (IHC) for aldosterone synthase (CYP11B2) was performed to define the histopathologic diagnosis. Somatic mutations in aldosterone-producing lesions were further determined by CYP11B2 IHC-guided DNA sequencing.

RESULTS

Based on the CYP11B2 IHC results, histopathologic classification was made as follows: 48 APAs, 20 APNs, 2 multiple aldosterone-producing nodules (MAPN), 1 double APN, 1 APA with MAPN, and 2 nonfunctioning adenomas (NFAs). Of 45 APAs with successful sequencing, 43 (96%) had somatic mutations, with KCNJ5 mutations being the most common genetic cause of young-onset APA (35/45, 78%). Of 18 APNs with successful sequencing, all of them harbored somatic mutations, with CACNA1D mutations being the most frequent genetic alteration in young-onset APN (8/18, 44%). Multiple CYP11B2-expressing lesions in patients with MAPN showed several aldosterone-driver mutations. No somatic mutations were identified in NFAs.

CONCLUSION

APA is the most common histologic feature of lateralized PA in young adults. Somatic KCNJ5 mutations are common in APAs, whereas CACNA1D mutations are often seen in APNs in this young PA population.

Adrenal Venous Sampling Could Be Omitted before Surgery in Patients with Conn’s Adenoma Confirmed by Computed Tomography and Higher Normal Aldosterone Concentration after Saline Infusion Test

Purpose: Adrenal venous sampling (AVS) performed to distinguish unilateral and bilateral primary aldosteronism (PA) is invasive and poorly standardized. This study aimed to identify non-invasive characteristics that can select the patients with unilateral PA who could bypass AVS before surgery. Methods: A single-center study collected a total of 450 patients with PA. Development and validation cohorts included 242 and 208 patients. The AVS was successful in 150 and 138 patients from the cohorts, and the unilateral PA was found in 96 and 94 patients, respectively. Clinical factors independently associated with lateralized AVS in multivariable logistic regression were used to construct a unilateral PA prediction score (SCORE). Results: The proposed SCORE was calculated as a sum of the prevalence of adrenal nodule on computed tomography (2 points) and plasma/serum aldosterone concentration ≥ 165 ng/L after the saline infusion test (SIT) (1 point). Importantly, the SCORE = 3 points identified 48% of unilateral PA patients with a specificity of 100% in the development cohort. The zero rate of false-positive classifications was preserved with the same cut-off value in the validation cohort. Conclusions: AVS could be omitted before surgery in patients with typical Conn´s adenoma provided the aldosterone concentration ≥ 165 ng/L after the SIT.

Biochemical, Histopathological, and Genetic Characterization of Posture-Responsive and Unresponsive APAs

CONTEXT AND OBJECTIVE

Posture-responsive and posture-unresponsive aldosterone-producing adenomas (APAs) account for approximately 40% and 60% of APAs, respectively. Somatic gene mutations have been recently reported to exist in approximately 90% of APAs. This study was designed to characterize the biochemical, histopathologic, and genetic properties of these 2 types of APA.

METHODS

Plasma levels of aldosterone and hybrid steroids (18-oxocortisol and 18-hydroxycortisol) were measured by liquid chromatography-tandem mass spectrometry. Immunohistochemistry for CYP11B2 (aldosterone synthase) and CYP17A1 (17α-hydroxylase) and deoxyribonucleic acid sequencing (Sanger and next-generation sequencing) were performed on APA tissue collected from 23 posture-unresponsive and 17 posture-responsive APA patients.

RESULTS

Patients with posture-unresponsive APA displayed higher (P < 0.01) levels of hybrid steroids, recumbent aldosterone and cortisol, larger (P < 0.01) zona fasciculata (ZF)-like tumors with higher (P < 0.01) expression of CYP17A1 (but not of CYP11B2) than patients with posture-responsive APA (most of which were not ZF-like). Of 40 studied APAs, 37 (92.5%) were found to harbor aldosterone-driving somatic mutations (KCNJ5 = 14 [35.0%], CACNA1D = 13 [32.5%], ATP1A1 = 8 [20.0%], and ATP2B3 = 2 [5.0%]), including 5 previously unreported mutations (3 in CACNA1D and 2 in ATP1A1). Notably, 64.7% (11/17) of posture-responsive APAs carried CACNA1D mutations, whereas 56.5% (13/23) of posture-unresponsive APAs harbored KCNJ5 mutations.

CONCLUSIONS

The elevated production of hybrid steroids by posture-unresponsive APAs may relate to their ZF-like tumor cell composition, resulting in expression of CYP17A1 (in addition to somatic gene mutation-driven CYP11B2 expression), thereby allowing production of cortisol, which acts as the substrate for CYP11B2-generated hybrid steroids.

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.

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.

Autologous reference types can confound the detection of somatic mutation in solid cancers

Vast number of somatic mutations has been proved to be affected by the factors of sequencing methods, analysis pipelines and validation methods. We here showed the effect of autologous reference types on the detection of cancer-associated somatic mutations with the somatic single nucleotide variations (SNVs) and clinical data of solid tumors from the Cancer Genome Atlas (TCGA) and International Cancer Genome Consortium (ICGC). The distribution of somatic SNVs was significantly different among groups of autologous references in 6 cancers detected by whole genome sequencing (WGS) and 5 cancers detected by the random sequencing of exonic regions selected from the genome (WXS), especially in protein coding region of 5 cancers with age, gender and TNM adjusted. In addition, only 60.24% (95% CI: 49.65%-70.83%) of the somatic SNVs called from normal blood by WXS were found in those called from normal solid tissue tested by WXS / WGS, while 31.78% (95%CI: 4.14%-59.42%) of the somatic SNVs called from normal tissue adjacent to primary by WXS were found in those from normal blood tested by WXS / WGS. These findings suggested that more representative types of normal tissues should be included in detection of cancer-associated somatic mutations.

Comparative Genomics and Transcriptome Profiling in Primary Aldosteronism

Primary aldosteronism is the most common form of endocrine hypertension with a prevalence of 6% in the general population with hypertension. The genetic basis of the four familial forms of primary aldosteronism (familial hyperaldosteronism FH types I–IV) and the majority of sporadic unilateral aldosterone-producing adenomas has now been resolved. Familial forms of hyperaldosteronism are, however, rare. The sporadic forms of the disease prevail and these are usually caused by either a unilateral aldosterone-producing adenoma or bilateral adrenal hyperplasia. Aldosterone-producing adenomas frequently carry a causative somatic mutation in either of a number of genes with the KCNJ5 gene, encoding an inwardly rectifying potassium channel, a recurrent target harboring mutations at a prevalence of more than 40% worldwide. Other than genetic variations, gene expression profiling of aldosterone-producing adenomas has shed light on the genes and intracellular signalling pathways that may play a role in the pathogenesis and pathophysiology of these tumors.

Targeted disruption of the Kcnj5 gene in the female mouse lowers aldosterone levels

Aldosterone is released from adrenal zona glomerulosa (ZG) cells and plays an important role in Na and K homoeostasis. Mutations in the human inwardly rectifying K channel CNJ type (KCNJ) 5 (KCNJ5) gene encoding the G-coupled inwardly rectifying K channel 4 (GIRK4) cause abnormal aldosterone secretion and hypertension. To better understand the role of wild-type (WT) GIRK4 in regulating aldosterone release, we have looked at aldosterone secretion in a Kcnj5 knockout (KO) mouse. We found that female but not male KO mice have reduced aldosterone levels compared with WT female controls, but higher levels of aldosterone after angiotensin II (Ang-II) stimulation. These differences could not be explained by sex differences in aldosterone synthase (Cyp11B2) gene expression in the mouse adrenal. Using RNAseq analysis to compare WT and KO adrenals, we showed that females also have a much larger set of differentially expressed adrenal genes than males (395 compared with 7). Ingenuity Pathway Analysis (IPA) of this gene set suggested that peroxisome proliferator activated receptor (PPAR) nuclear receptors regulated aldosterone production and altered signalling in the female KO mouse, which could explain the reduced aldosterone secretion. We tested this hypothesis in H295R adrenal cells and showed that the selective PPARα agonist fenofibrate can stimulate aldosterone production and induce Cyp11b2. Dosing mice in vivo produced similar results. Together our data show that Kcnj5 is important for baseline aldosterone secretion, but its importance is sex-limited at least in the mouse. It also highlights a novel regulatory pathway for aldosterone secretion through PPARα that may have translational potential in human hyperaldosteronism.

Subtype Diagnosis of Primary Aldosteronism: Is Adrenal Vein Sampling Always Necessary?

Aldosterone producing adenoma and bilateral adrenal hyperplasia are the two most common subtypes of primary aldosteronism (PA) that require targeted and distinct therapeutic approaches: unilateral adrenalectomy or lifelong medical therapy with mineralocorticoid receptor antagonists. According to the 2016 Endocrine Society Guideline, adrenal venous sampling (AVS) is the gold standard test to distinguish between unilateral and bilateral aldosterone overproduction and therefore, to safely refer patients with PA to surgery. Despite significant advances in the optimization of the AVS procedure and the interpretation of hormonal data, a standardized protocol across centers is still lacking. Alternative methods are sought to either localize an aldosterone producing adenoma or to predict the presence of unilateral disease and thereby substantially reduce the number of patients with PA who proceed to AVS. In this review, we summarize the recent advances in subtyping PA for the diagnosis of unilateral and bilateral disease. We focus on the developments in the AVS procedure, the interpretation criteria, and comparisons of the performance of AVS with the alternative methods that are currently available.

Genetics of primary hyperaldosteronism

Hypertension is a common medical condition and affects approximately 20% of the population in developed countries. Primary aldosteronism is the most common form of secondary hypertension and affects 8-13% of patients with hypertension. The two most common causes of primary aldosteronism are aldosterone-producing adenoma and bilateral adrenal hyperplasia. Familial hyperaldosteronism types I, II and III are the known genetic syndromes, in which both adrenal glands produce excessive amounts of aldosterone. However, only a minority of patients with primary aldosteronism have one of these syndromes. Several novel susceptibility genes have been found to be mutated in aldosterone-producing adenomas: KCNJ5, ATP1A1, ATP2B3, CTNNB1, CACNA1D, CACNA1H and ARMC5 This review describes the genes currently known to be responsible for primary aldosteronism, discusses the origin of aldosterone-producing adenomas and considers the future clinical implications based on these novel insights.

Hyperaldosteronism: How to Discriminate Among Different Disease Forms?

Primary aldosteronism (PA), characterized by the inappropriate and abnormal adrenal secretion of aldosterone, is the most common cause of secondary hypertension. PA has been shown to increase cardiovasular and cerebrovascular risks in comparison with essential hypertension. PA is a multi-faceted disease, which comprises unilateral forms, benefitting from surgical treatment, and bilateral forms, which are the best managed medically. PA is more frequently sporadic, but in some cases, it displays a familial transmission pattern. For these reasons, it is important to diagnose PA early on and correctly distinguish and manage its different forms. In this review, we analyze the different forms of PA, with attention on the diagnostic pathway and the genetics of the disease.

Progress in Primary Aldosteronism: Translation on the Move

Hypertension is a major cardiovascular risk factor that affects between 10-40% of the general population in an age dependent manner. The renin-angiotensin-aldosterone system (RAAS) regulates blood pressure, fluid volume, and the vascular response to injury and inflammation 1. Chronic RAAS activation in the presence of sufficient sodium consumption leads to persistent hypertension, setting off a cascade of inflammatory, thrombotic, and atherogenic effects eventually leading to end-organ damage 2 3. Accordingly, numerous studies have demonstrated that elevated renin and/or aldosterone levels are predictors of adverse outcome in hypertension 4, heart failure 5 6, myocardial infarction 7, and renal insufficiency 8 and influence insulin resistance 9. Primary aldosteronism (PA) is the most common secondary form of hypertension with an estimated prevalence between 4 and 12% of hypertensives 10 11 12 and 11-20% in patients that are resistant to combined antihypertensive medication 13 14. Given the severe cardiovascular adverse effects of aldosterone excess that are independent of high blood pressure levels 15 16 17 18 detection and treatment of PA has important impact on clinical outcome and survival.