Transcriptome analysis reveals differentially expressed transcripts in rat adrenal zona glomerulosa and zona fasciculata

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.

Transcriptome Profile of the Rat Adrenal Gland: Parenchymal and Interstitial Cells

The homeostasis of the adrenal gland plays a decisive role in its proper functioning, both in non-stressful conditions and under the influence of various types of stress. This consists of interactions between all types of cells that make up the organ, including parenchymal and interstitial cells. The amount of available information on this subject in the rat adrenal glands under non-stressful conditions is insufficient; the aim of the research was to determine the expression of marker genes for rat adrenal cells depending on their location. The material for the study consisted of adrenal glands taken from intact adult male rats that were separated into appropriate zones. Transcriptome analysis by means of Affymetrix^® Rat Gene 2.1 ST Array was used in the study, followed by real-time PCR validation. Expression analysis of interstitial cell marker genes revealed both the amount of expression of these genes and the zone in which they were expressed. The expression of marker genes for fibroblasts was particularly high in the cells of the ZG zone, while the highest expression of specific macrophage genes was observed in the adrenal medulla. The results of this study, especially with regard to interstitial cells, provide a so far undescribed model of marker gene expression of various cells, both in the cortex and medulla of the sexually mature rat adrenal gland. The interdependence between parenchymal and interstitial cells creates a specific microenvironment that is highly heterogeneous within the gland with respect to some of the interstitial cells. This phenomenon most likely depends on the interaction with the differentiated parenchymal cells of the cortex, as well as the medulla of the gland.

Update on Biology and Genomics of Adrenocortical Carcinomas: Rationale for Emerging Therapies

The adrenal glands are paired endocrine organs that produce steroid hormones and catecholamines required for life. Adrenocortical carcinoma (ACC) is a rare and often fatal cancer of the peripheral domain of the gland, the adrenal cortex. Recent research in adrenal development, homeostasis, and disease have refined our understanding of the cellular and molecular programs controlling cortical growth and renewal, uncovering crucial clues into how physiologic programs are hijacked in early and late stages of malignant neoplasia. Alongside these studies, genome-wide approaches to examine adrenocortical tumors have transformed our understanding of ACC biology, and revealed that ACC is composed of distinct molecular subtypes associated with favorable, intermediate, and dismal clinical outcomes. The homogeneous transcriptional and epigenetic programs prevailing in each ACC subtype suggest likely susceptibility to any of a plethora of existing and novel targeted agents, with the caveat that therapeutic response may ultimately be limited by cancer cell plasticity. Despite enormous biomedical research advances in the last decade, the only potentially curative therapy for ACC to date is primary surgical resection, and up to 75% of patients will develop metastatic disease refractory to standard-of-care adjuvant mitotane and cytotoxic chemotherapy. A comprehensive, integrated, and current bench-to-bedside understanding of our field's investigations into adrenocortical physiology and neoplasia is crucial to developing novel clinical tools and approaches to equip the one-in-a-million patient fighting this devastating disease.

Rare forms of genetic steroidogenic defects affecting the gonads and adrenals

Pathogenic variants have been found in all genes involved in the classic pathways of human adrenal and gonadal steroidogenesis. Depending on their function and severity, they cause characteristic disorders of corticosteroid and/or sex hormone deficiency, may result in atypical sex development at birth and/or puberty, and mostly lead to sexual dysfunction and infertility. Genetic disorders of steroidogenesis are all inherited in an autosomal recessive fashion. Loss of function mutations lead to typical phenotypes, while variants with partial activity may manifest with milder, non-classic, late-onset disorders that share similar phenotypes. Thus, these disorders of steroidogenesis are diagnosed by comprehensive phenotyping, steroid profiling and genetic testing using next generation sequencing techniques. Treatment comprises of steroid replacement therapies, but these are insufficient in many aspects. Therefore, studies are currently ongoing towards newer approaches such as lentiviral transmitted enzyme replacement therapy and reprogrammed stem cell-based gene therapy.

Non-Canonical Effects of ACTH: Insights Into Adrenal Insufficiency

Introduction

Adrenocorticotropic hormone (ACTH) is produced from proopiomelanocortin, which is predominantly synthetized in the corticotroph and melanotroph cells of the anterior and intermediate lobes of the pituitary gland and the arcuate nucleus of the hypothalamus. Although ACTH clearly has an effect on adrenal homeostasis and maintenance of steroid hormone production, it also has extra-adrenal effects that require further elucidation.

Methods

We comprehensively reviewed English language articles, regardless of whether they reported the presence or absence of adrenal and extra-adrenal ACTH effects.

Results

In the present review, we provide an overview on the current knowledge on adrenal and extra-adrenal effects of ACTH. In the section on adrenal ACTH effects, we focused on corticosteroid rhythmicity and effects on steroidogenesis, mineralocorticoids and adrenal growth. In the section on extra-adrenal effects, we have analyzed the effects of ACTH on the osteoarticular and reproductive systems, adipocytes, immune system, brain and skin. Finally, we focused on adrenal insufficiency.

Conclusions

The role of ACTH in maintaining the function of the hypothalamic-pituitary-adrenal axis is well known. Conversely, if we broaden our vision and analyze its role as a potential treatment strategy in other conditions, it will be evident in the literature that researchers seem to have abandoned this aspect in studies conducted several years ago. We believe it is worth re-evaluating the role of ACTH considering its noncanonical effects on the adrenal gland itself and on extra-adrenal organs and tissues; however, this would not have been possible without the recent advances in the pertinent technologies.

Adrenal cortex development and related disorders leading to adrenal insufficiency

The adult human adrenal cortex produces steroid hormones that are crucial for life, supporting immune response, glucose homeostasis, salt balance and sexual maturation. It consists of three histologically distinct and functionally specialized zones. The fetal adrenal forms from mesodermal material and produces predominantly adrenal C₁₉ steroids from its fetal zone, which involutes after birth. Transition to the adult cortex occurs immediately after birth for the formation of the zona glomerulosa and fasciculata for aldosterone and cortisol production and continues through infancy until the zona reticularis for adrenal androgen production is formed with adrenarche. The development of this indispensable organ is complex and not fully understood. This article gives an overview of recent knowledge gained of adrenal biology from two perspectives: one, from basic science studying adrenal development, zonation and homeostasis; and two, from adrenal disorders identified in persons manifesting with various isolated or syndromic forms of primary adrenal insufficiency.

Ion Channel Function and Electrical Excitability in the Zona Glomerulosa: A Network Perspective on Aldosterone Regulation

Aldosterone excess is a pathogenic factor in many hypertensive disorders. The discovery of numerous somatic and germline mutations in ion channels in primary hyperaldosteronism underscores the importance of plasma membrane conductances in determining the activation state of zona glomerulosa (zG) cells. Electrophysiological recordings describe an electrically quiescent behavior for dispersed zG cells. Yet, emerging data indicate that in native rosette structures in situ, zG cells are electrically excitable, generating slow periodic voltage spikes and coordinated bursts of Ca²⁺ oscillations. We revisit data to understand how a multitude of conductances may underlie voltage/Ca²⁺ oscillations, recognizing that zG layer self-renewal and cell heterogeneity may complicate this task. We review recent data to understand rosette architecture and apply maxims derived from computational network modeling to understand rosette function. The challenge going forward is to uncover how the rosette orchestrates the behavior of a functional network of conditional oscillators to control zG layer performance and aldosterone secretion.

Effect of Dietary Sodium Modulation on Pig Adrenal Steroidogenesis and Transcriptome Profiles

Primary aldosteronism is a frequent form of endocrine hypertension caused by aldosterone overproduction from the adrenal cortex. Regulation of aldosterone biosynthesis has been studied in rodents despite differences in adrenal physiology with humans. We, therefore, investigated pig adrenal steroidogenesis, morphology, and transcriptome profiles of the zona glomerulosa (zG) and zona fasciculata in response to activation of the renin-angiotensin-aldosterone system by dietary sodium restriction. Six-week-old pigs were fed a low- or high-sodium diet for 14 days (3 pigs per group, 0.4 g sodium/kg feed versus 6.8 g sodium/kg). Plasma aldosterone concentrations displayed a 43-fold increase (P=0.011) after 14 days of sodium restriction (day 14 versus day 0). Low dietary sodium caused a 2-fold increase in thickness of the zG (P<0.001) and an almost 3-fold upregulation of CYP11B (P<0.05) compared with high dietary sodium. Strong immunostaining of the KCNJ5 (G protein-activated inward rectifier potassium channel 4), which is frequently mutated in primary aldosteronism, was demonstrated in the zG. mRNA sequencing transcriptome analysis identified significantly altered expression of genes modulated by the renin-angiotensin-aldosterone system in the zG (n=1172) and zona fasciculata (n=280). These genes included many with a known role in the regulation of aldosterone synthesis and adrenal function. The most highly enriched biological pathways in the zG were related to cholesterol biosynthesis, steroid metabolism, cell cycle, and potassium channels. This study provides mechanistic insights into the physiology and pathophysiology of aldosterone production in a species closely related to humans and shows the suitability of pigs as a translational animal model for human adrenal steroidogenesis.

Aldosterone and 18-Oxocortisol Coaccumulation in Aldosterone-Producing Lesions

Primary aldosteronism is a secondary hypertensive disease caused by autonomous aldosterone production that often caused by an aldosterone-producing adenoma (APA). Immunohistochemistry of aldosterone synthase (CYP11B2) shows the presence of aldosterone-producing cell clusters (APCCs) even in non-primary aldosteronism adult adrenal cortex. An APCC-like structure also exists as possible APCC-to-APA transitional lesions (a speculative designation) in primary aldosteronism adrenals. However, whether APCCs produce aldosterone or 18-oxocortisol, a potential serum marker of APA, remains unknown because of lack of technology to visualize adrenocorticosteroids on tissue sections. To address this obstacle, in this study, we used highly sensitive Fourier transform ion cyclotron resonance mass spectrometry to image various adrenocorticosteroids, including 18-oxocortisol, in adrenal tissue sections from 8 primary aldosteronism patients with APCC (cases 1-4), possible APCC-to-APA transitional lesions (case 5), and APA (cases 6-8). Further analyses by tandem mass spectrometry imaging allowed us to differentially visualize aldosterone from cortisone, which share identical mass-to-charge ratio value ( m/z). In conclusion, these advanced imaging techniques revealed that aldosterone and 18-oxocortisol coaccumulated within CYP11B2-expressing lesions. These imaging outcomes along with a growing body of aldosterone research led us to build a progressive development hypothesis of an aldosterone-producing pathology in the adrenal glands.

Steroidogenic differentiation and PKA signaling are programmed by histone methyltransferase EZH2 in the adrenal cortex

Adrenal cortex steroids are essential for body homeostasis, and adrenal insufficiency is a life-threatening condition. Adrenal endocrine activity is maintained through recruitment of subcapsular progenitor cells that follow a unidirectional differentiation path from zona glomerulosa to zona fasciculata (zF). Here, we show that this unidirectionality is ensured by the histone methyltransferase EZH2. Indeed, we demonstrate that EZH2 maintains adrenal steroidogenic cell differentiation by preventing expression of GATA4 and WT1 that cause abnormal dedifferentiation to a progenitor-like state in Ezh2 KO adrenals. EZH2 further ensures normal cortical differentiation by programming cells for optimal response to adrenocorticotrophic hormone (ACTH)/PKA signaling. This is achieved by repression of phosphodiesterases PDE1B, 3A, and 7A and of PRKAR1B. Consequently, EZH2 ablation results in blunted zF differentiation and primary glucocorticoid insufficiency. These data demonstrate an all-encompassing role for EZH2 in programming steroidogenic cells for optimal response to differentiation signals and in maintaining their differentiated state.

NNT is a key regulator of adrenal redox homeostasis and steroidogenesis in male mice

Nicotinamide nucleotide transhydrogenase, NNT, is a ubiquitous protein of the inner mitochondrial membrane with a key role in mitochondrial redox balance. NNT produces high concentrations of NADPH for detoxification of reactive oxygen species by glutathione and thioredoxin pathways. In humans, NNT dysfunction leads to an adrenal-specific disorder, glucocorticoid deficiency. Certain substrains of C57BL/6 mice contain a spontaneously occurring inactivating Nnt mutation and display glucocorticoid deficiency along with glucose intolerance and reduced insulin secretion. To understand the underlying mechanism(s) behind the glucocorticoid deficiency, we performed comprehensive RNA-seq on adrenals from wild-type (C57BL/6N), mutant (C57BL/6J) and BAC transgenic mice overexpressing Nnt (C57BL/6J^BAC). The following results were obtained. Our data suggest that Nnt deletion (or overexpression) reduces adrenal steroidogenic output by decreasing the expression of crucial, mitochondrial antioxidant (Prdx3 and Txnrd2) and steroidogenic (Cyp11a1) enzymes. Pathway analysis also revealed upregulation of heat shock protein machinery and haemoglobins possibly in response to the oxidative stress initiated by NNT ablation. In conclusion, using transcriptomic profiling in adrenals from three mouse models, we showed that disturbances in adrenal redox homeostasis are mediated not only by under expression of NNT but also by its overexpression. Further, we demonstrated that both under expression or overexpression of NNT reduced corticosterone output implying a central role for it in the control of steroidogenesis. This is likely due to a reduction in the expression of a key steroidogenic enzyme, Cyp11a1, which mirrored the reduction in corticosterone output.

Immunohistochemistry of aldosterone synthase leads the way to the pathogenesis of primary aldosteronism

Our group previously purified human and rat aldosterone synthase (CYP11B2 and Cyp11b2, respectively) from their adrenals and verified that it is distinct from steroid 11β-hydroxylase (CYP11B1 or Cyp11b1), the cortisol- or corticosterone-synthesizing enzyme. We now describe their distributions immunohistochemically with specific antibodies. In rats, there is layered functional zonation with the Cyp11b2-positive zona glomerulosa (ZG), Cyp11b1-positive zona fasciculata (ZF), and Cyp11b2/Cyp11b1-negative undifferentiated zone between the ZG and ZF. In human infants and children (<12 years old), the functional zonation is similar to that in rats. In adults, the adrenal cortex remodels and subcapsular aldosterone-producing cell clusters (APCCs) replace the continuous ZG layer. We recently reported possible APCC-to-APA transitional lesions (pAATLs) in 2 cases of unilateral multiple adrenocortical micro-nodules. In this review, we present 4 additional cases of primary aldosteronism, from which the extracted adrenals contain pAATLs, with results of next generation sequencing for these lesions. Immunohistochemistry for CYP11B2 and CYP11B1 has become an important tool for the diagnosis of and research on adrenocortical pathological conditions and suggests that APCCs may be the origin of aldosterone-producing adenoma.

Transcriptome Pathway Analysis of Pathological and Physiological Aldosterone-Producing Human Tissues

Supplemental Digital Content is available in the text.

Primary aldosteronism is present in ≈10% of hypertensives. We previously performed a microarray assay on aldosterone-producing adenomas and their paired zona glomerulosa and fasciculata. Confirmation of top genes validated the study design and functional experiments of zona glomerulosa selective genes established the role of the encoded proteins in aldosterone regulation. In this study, we further analyzed our microarray data using AmiGO 2 for gene ontology enrichment and Ingenuity Pathway Analysis to identify potential biological processes and canonical pathways involved in pathological and physiological aldosterone regulation. Genes differentially regulated in aldosterone-producing adenoma and zona glomerulosa were associated with steroid metabolic processes gene ontology terms. Terms related to the Wnt signaling pathway were enriched in zona glomerulosa only. Ingenuity Pathway Analysis showed "NRF2-mediated oxidative stress response pathway" and "LPS (lipopolysaccharide)/IL-1 (interleukin-1)–mediated inhibition of RXR (retinoid X receptor) function" were affected in both aldosterone-producing adenoma and zona glomerulosa with associated genes having up to 21- and 8-fold differences, respectively. Comparing KCNJ5-mutant aldosterone-producing adenoma, zona glomerulosa, and zona fasciculata samples with wild-type samples, 138, 56, and 59 genes were differentially expressed, respectively (fold-change >2; P<0.05). ACSS3, encoding the enzyme that synthesizes acetyl-CoA, was the top gene upregulated in KCNJ5-mutant aldosterone-producing adenoma compared with wild-type. NEFM, a gene highly upregulated in zona glomerulosa, was upregulated in KCNJ5 wild-type aldosterone-producing adenomas. NR4A2, the transcription factor for aldosterone synthase, was highly expressed in zona fasciculata adjacent to a KCNJ5-mutant aldosterone-producing adenoma. Further interrogation of these genes and pathways could potentially provide further insights into the pathology of primary aldosteronism.

11-Ketotestosterone Is a Major Androgen Produced in Human Gonads

CONTEXT

11-ketotestosterone (11-KT) is a novel class of active androgen. However, the detail of its synthesis remains unknown for humans.

OBJECTIVE

The objective of this study was to clarify the production and properties of 11-KT in human. Design, Participants, and Methods: Expression of cytochrome P450 and 11β-hydroxysteroid dehydrogenase types 1 and 2 (key enzymes involved in the synthesis of 11-KT) were investigated in human gonads. The production of 11-KT was investigated in Leydig cells. Plasma concentrations of testosterone and 11-KT were measured in 10 women and 10 men of reproductive age. Investigation of its properties was performed using breast cancer-derived MCF-7 cells.

RESULTS

Cytochrome P450 and 11β-hydroxysteroid dehydrogenase types 1 and 2 were detected in Leydig cells and theca cells. Leydig cells produced 11-KT, and relatively high levels of plasma 11-KT were measured in both men and women. There was no sexual dimorphism in the plasma levels of 11-KT, even though testosterone levels were more than 20 times higher in men than in women. It is noteworthy that the levels of testosterone and 11-KT were similar in women. In a luciferase reporter system, 11-KT activated human androgen receptor-mediated transactivation. Conversely, 11-KT did not activate estrogen receptor-mediated transactivation in aromatase-expressed MCF-7 cells, whereas testosterone did following conversion to estrogen. 11-KT did not affect the estrogen/estrogen receptor -mediated cell proliferation of MCF-7 cells. Furthermore, it significantly inhibited cell proliferation when androgen receptor was transfected into MCF-7 cells.

CONCLUSIONS

The current study indicates that 11-KT is produced in the gonads and represents a major androgen in human. It can potentially serve as a nonaromatizable androgen.

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.

60 YEARS OF POMC: Adrenal and extra-adrenal functions of ACTH

The pituitary adrenocorticotropic hormone (ACTH) plays a pivotal role in homeostasis and stress response and is thus the major component of the hypothalamo-pituitary-adrenal axis. After a brief summary of ACTH production from proopiomelanocortin (POMC) and on ACTH receptor properties, the first part of the review covers the role of ACTH in steroidogenesis and steroid secretion. We highlight the mechanisms explaining the differential acute vs chronic effects of ACTH on aldosterone and glucocorticoid secretion. The second part summarizes the effects of ACTH on adrenal growth, addressing its role as either a mitogenic or a differentiating factor. We then review the mechanisms involved in steroid secretion, from the classical Cyclic adenosine monophosphate second messenger system to various signaling cascades. We also consider how the interaction between the extracellular matrix and the cytoskeleton may trigger activation of signaling platforms potentially stimulating or repressing the steroidogenic potency of ACTH. Finally, we consider the extra-adrenal actions of ACTH, in particular its role in differentiation in a variety of cell types, in addition to its known lipolytic effects on adipocytes. In each section, we endeavor to correlate basic mechanisms of ACTH function with the pathological consequences of ACTH signaling deficiency and of overproduction of ACTH.

Human Adrenocortical Remodeling Leading to Aldosterone-Producing Cell Cluster Generation

Background. The immunohistochemical detection of aldosterone synthase (CYP11B2) and steroid 11β-hydroxylase (CYP11B1) has enabled the identification of aldosterone-producing cell clusters (APCCs) in the subcapsular portion of the human adult adrenal cortex. We hypothesized that adrenals have layered zonation in early postnatal stages and are remodeled to possess APCCs over time. Purposes. To investigate changes in human adrenocortical zonation with age. Methods. We retrospectively analyzed adrenal tissues prepared from 33 autopsied patients aged between 0 and 50 years. They were immunostained for CYP11B2 and CYP11B1. The percentage of APCC areas over the whole adrenal area (AA/WAA, %) and the number of APCCs (NOA, APCCs/mm²) were calculated by four examiners. Average values were used in statistical analyses. Results. Adrenals under 11 years old had layered zona glomerulosa (ZG) and zona fasciculata (ZF) without apparent APCCs. Some adrenals had an unstained (CYP11B2/CYP11B1-negative) layer between ZG and ZF, resembling the rat undifferentiated cell zone. Average AA/WAA and NOA correlated with age, suggesting that APCC development is associated with aging. Possible APCC-to-APA transitional lesions were incidentally identified in two adult adrenals. Conclusions. The adrenal cortex with layered zonation remodels to possess APCCs over time. APCC generation may be associated with hypertension in adults.

Potassium channels related to primary aldosteronism: Expression similarities and differences between human and rat adrenals

Three potassium channels have been associated with primary aldosteronism (PA) in rodents and humans: KCNK3 (TASK-1), KCNK9 (TASK-3), and KCNJ5 (Kir3.4). Mice with deficiency in Kcnk3 and Kcnk9 have elevated aldosterone production and blood pressure. In humans, adrenal tumors with somatic mutations in KCNJ5 cause PA. However, there are very few reports on the expression patterns of these genes in humans versus rodents. Herein, we compared human and rat mRNA expression (by quantitative real-time polymerase chain reaction (qPCR) and protein levels (by immunohistochemistry) across three tissues (adrenal, brain, heart) and two laser-captured adrenal zones (zona glomerulosa, zona fasciculata). Our findings show that expression patterns of KCNK3, KCNK9, and KCNJ5 are inconsistent between rats and humans across both tissues and adrenal zones. Thus, species variation in the expression of PA-related potassium channels indicates an evolutionary divergence in their role in regulating adrenal aldosterone production.

Regulation of human (adrenal) androgen biosynthesis-New insights from novel throughput technology studies

Androgens are precursors for sex steroids and are predominantly produced in the human gonads and the adrenal cortex. They are important for intrauterine and postnatal sexual development and human reproduction. Although human androgen biosynthesis has been extensively studied in the past, exact mechanisms underlying the regulation of androgen production in health and disease remain vague. Here, the knowledge on human androgen biosynthesis and regulation is reviewed with a special focus on human adrenal androgen production and the hyperandrogenic disorder of polycystic ovary syndrome (PCOS). Since human androgen regulation is highly specific without a good animal model, most studies are performed on patients harboring inborn errors of androgen biosynthesis, on human biomaterials and human (tumor) cell models. In the past, most studies used a candidate gene approach while newer studies use high throughput technologies to identify novel regulators of androgen biosynthesis. Using genome wide association studies on cohorts of patients, novel PCOS candidate genes have been recently described. Variant 2 of the DENND1A gene was found overexpressed in PCOS theca cells and confirmed to enhance androgen production. Transcriptome profiling of dissected adrenal zones established a role for BMP4 in androgen synthesis. Similarly, transcriptome analysis of human adrenal NCI-H295 cells identified novel regulators of androgen production. Kinase p38α (MAPK14) was found to phosphorylate CYP17 for enhanced 17,20 lyase activity and RARB and ANGPTL1 were detected in novel networks regulating androgens. The discovery of novel players for androgen biosynthesis is of clinical significance as it provides targets for diagnostic and therapeutic use.

POD-1/Tcf21 overexpression reduces endogenous SF-1 and StAR expression in rat adrenal cells

During gonad and adrenal development, the POD-1/capsulin/TCF21transcription factor negatively regulates SF-1/NR5A1expression, with higher SF-1 levels being associated with increased adrenal cell proliferation and tumorigenesis. In adrenocortical tumor cells, POD-1 binds to the SF-1 E-box promoter region, decreasing SF-1 expression. However, the modulation of SF-1 expression by POD-1 has not previously been described in normal adrenal cells. Here, we analyzed the basal expression of Pod-1 and Sf-1 in primary cultures of glomerulosa (G) and fasciculata/reticularis (F/R) cells isolated from male Sprague-Dawley rats, and investigated whether POD-1 overexpression modulates the expression of endogenous Sf-1 and its target genes in these cells. POD-1 overexpression, following the transfection of pCMVMycPod-1, significantly decreased the endogenous levels of Sf-1 mRNA and protein in F/R cells, but not in G cells, and also decreased the expression of the SF-1 target StAR in F/R cells. In G cells overexpressing POD-1, no modulation of the expression of SF-1 targets, StAR and CYP11B2, was observed. Our data showing that G and F/R cells respond differently to ectopic POD-1 expression emphasize the functional differences between the outer and inner zones of the adrenal cortex, and support the hypothesis that SF-1 is regulated by POD-1/Tcf21 in normal adrenocortical cells lacking the alterations in cellular physiology found in tumor cells.

Aldosterone-stimulating somatic gene mutations are common in normal adrenal glands

Primary aldosteronism (PA) represents the most common cause of secondary hypertension, but little is known regarding its adrenal cellular origins. Recently, aldosterone-producing cell clusters (APCCs) with high expression of aldosterone synthase (CYP11B2) were found in both normal and PA adrenal tissue. PA-causing aldosterone-producing adenomas (APAs) harbor mutations in genes encoding ion channels/pumps that alter intracellular calcium homeostasis and cause renin-independent aldosterone production through increased CYP11B2 expression. Herein, we hypothesized that APCCs have APA-related aldosterone-stimulating somatic gene mutations. APCCs were studied in 42 normal adrenals from kidney donors. To clarify APCC molecular characteristics, we used microarrays to compare the APCC transcriptome with conventional adrenocortical zones [zona glomerulosa (ZG), zona fasciculata, and zona reticularis]. The APCC transcriptome was most similar to ZG but with an enhanced capacity to produce aldosterone. To determine if APCCs harbored APA-related mutations, we performed targeted next generation sequencing of DNA from 23 APCCs and adjacent normal adrenal tissue isolated from both formalin-fixed, paraffin-embedded, and frozen tissues. Known aldosterone driver mutations were identified in 8 of 23 (35%) APCCs, including mutations in calcium channel, voltage-dependent, L-type, α1D-subunit (CACNA1D; 6 of 23 APCCs) and ATPase, Na(+)/(K+) transporting, α1-polypeptide (ATP1A1; 2 of 23 APCCs), which were not observed in the adjacent normal adrenal tissue. Overall, we show three major findings: (i) APCCs are common in normal adrenals, (ii) APCCs harbor somatic mutations known to cause excess aldosterone production, and (iii) the mutation spectrum of aldosterone-driving mutations is different in APCCs from that seen in APA. These results provide molecular support for APCC as a precursor of PA.

Bone Morphogenetic Protein-4 (BMP4): A Paracrine Regulator of Human Adrenal C19 Steroid Synthesis

Bone morphogenetic proteins (BMPs) comprise one of the largest subgroups in the TGF-β ligand superfamily. We have identified a functional BMP system equipped with the ligand (BMP4), receptors (BMP type II receptor, BMP type IA receptor, also called ALK3) and the signaling proteins, namely the mothers against decapentaplegic homologs 1, 4, and 5 in the human adrenal gland and the human adrenocortical cell line H295R. Microarray, quantitative RT-PCR, and immunohistochemistry confirmed that BMP4 expression was highest in the adrenal zona glomerulosa followed by the zona fasciculata and zona reticularis. Treatment of H295R cells with BMP4 caused phosphorylation of the mothers against decapentaplegic and a profound decrease in synthesis of the C19 steroids dehydroepiandrosterone (DHEA), DHEA sulfate, and androstenedione. Administration of BMP4 to cultures of H295R cells also caused a profound decrease in the mRNA and protein levels of 17α-hydroxylase/17,20-lyase (CYP17A1 and P450c17, respectively) but no significant effect on the mRNA levels of cholesterol side-chain cleavage cytochrome P450 (CYP11A1) or type 2 3β-hydroxysteroid dehydrogenase (HSD3B2). Furthermore, Noggin (a BMP inhibitor) was able to reverse the negative effects of BMP4 with respect to both CYP17A1 transcription and DHEA secretion in the H295R cell line. Collectively the present data suggest that BMP4 is an autocrine/paracrine negative regulator of C19 steroid synthesis in the human adrenal and works by suppressing P450c17.

LGR5 Activates Noncanonical Wnt Signaling and Inhibits Aldosterone Production in the Human Adrenal

CONTEXT

Aldosterone synthesis and cellularity in the human adrenal zona glomerulosa (ZG) is sparse and patchy, presumably due to salt excess. The frequency of somatic mutations causing aldosterone-producing adenomas (APAs) may be a consequence of protection from cell loss by constitutive aldosterone production.

OBJECTIVE

The objective of the study was to delineate a process in human ZG, which may regulate both aldosterone production and cell turnover.

DESIGN

This study included a comparison of 20 pairs of ZG and zona fasciculata transcriptomes from adrenals adjacent to an APA (n = 13) or a pheochromocytoma (n = 7).

INTERVENTIONS

Interventions included an overexpression of the top ZG gene (LGR5) or stimulation by its ligand (R-spondin-3).

MAIN OUTCOME MEASURES

A transcriptome profile of ZG and zona fasciculata and aldosterone production, cell kinetic measurements, and Wnt signaling activity of LGR5 transfected or R-spondin-3-stimulated cells were measured.

RESULTS

LGR5 was the top gene up-regulated in ZG (25-fold). The gene for its cognate ligand R-spondin-3, RSPO3, was 5-fold up-regulated. In total, 18 genes associated with the Wnt pathway were greater than 2-fold up-regulated. ZG selectivity of LGR5, and its absence in most APAs, were confirmed by quantitative PCR and immunohistochemistry. Both R-spondin-3 stimulation and LGR5 transfection of human adrenal cells suppressed aldosterone production. There was reduced proliferation and increased apoptosis of transfected cells, and the noncanonical activator protein-1/Jun pathway was stimulated more than the canonical Wnt pathway (3-fold vs 1.3-fold). ZG of adrenal sections stained positive for apoptosis markers.

CONCLUSION

LGR5 is the most selectively expressed gene in human ZG and reduces aldosterone production and cell number. Such conditions may favor cells whose somatic mutation reverses aldosterone inhibition and cell loss.

Role of Ca(2+)/calmodulin-dependent protein kinase kinase in adrenal aldosterone production

There is considerable evidence supporting the role of calcium signaling in adrenal regulation of both aldosterone synthase (CYP11B2) and aldosterone production. However, there have been no studies that investigated the role played by the Ca(2+)/calmodulin-dependent protein kinase kinase (CaMKK) in adrenal cells. In this study we investigated the role of CaMKK in adrenal cell aldosterone production. To determine the role of CaMKK, we used a selective CaMKK inhibitor (STO-609) in the HAC15 human adrenal cell line. Cells were treated with angiotensin II (Ang II) or K+ and evaluated for the expression of steroidogenic acute regulatory protein and CYP11B2 (mRNA/protein) as well as aldosterone production. We also transduced HAC15 cells with lentiviral short hairpin RNAs of CaMKK1 and CaMKK2 to determine which CaMKK plays a more important role in adrenal cell regulation of the calcium signaling cascade. The CaMKK inhibitor, STO-609, decreased aldosterone production in cells treated with Ang II or K+ in a dose-dependent manner. STO-609 (20 μM) also inhibited steroidogenic acute regulatory protein and CYP11B2 mRNA/protein induction. CaMKK2 knockdown cells showed significant reduction of CYP11B2 mRNA induction and aldosterone production in cells treated with Ang II, although there was no obvious effect in CaMKK1 knockdown cells. In immunohistochemical analysis, CaMKK2 protein was highly expressed in human adrenal zona glomerulosa with lower expression in the zona fasciculata. In conclusion, the present study suggests that CaMKK2 plays a pivotal role in the calcium signaling cascade regulating adrenal aldosterone production.

DACH1, a zona glomerulosa selective gene in the human adrenal, activates transforming growth factor-β signaling and suppresses aldosterone secretion

Common somatic mutations in CACNAID and ATP1A1 may define a subgroup of smaller, zona glomerulosa (ZG)-like aldosterone-producing adenomas. We have therefore sought signature ZG genes, which may provide insight into the frequency and pathogenesis of ZG-like aldosterone-producing adenomas. Twenty-one pairs of zona fasciculata and ZG and 14 paired aldosterone-producing adenomas from 14 patients with Conn's syndrome and 7 patients with pheochromocytoma were assayed by the Affymetrix Human Genome U133 Plus 2.0 Array. Validation by quantitative real-time polymerase chain reaction was performed on genes >10-fold upregulated in ZG (compared with zona fasciculata) and >10-fold upregulated in aldosterone-producing adenomas (compared with ZG). DACH1, a gene associated with tumor progression, was further analyzed. The role of DACH1 on steroidogenesis, transforming growth factor-β, and Wnt signaling activity was assessed in the human adrenocortical cell line, H295R. Immunohistochemistry confirmed selective expression of DACH1 in human ZG. Silencing of DACH1 in H295R cells increased CYP11B2 mRNA levels and aldosterone production, whereas overexpression of DACH1 decreased aldosterone production. Overexpression of DACH1 in H295R cells activated the transforming growth factor-β and canonical Wnt signaling pathways but inhibited the noncanonical Wnt signaling pathway. Stimulation of primary human adrenal cells with angiotensin II decreased DACH1 mRNA expression. Interestingly, there was little overlap between our top ZG genes and those in rodent ZG. In conclusion, (1) the transcriptome profile of human ZG differs from rodent ZG, (2) DACH1 inhibits aldosterone secretion in human adrenals, and (3) transforming growth factor-β signaling pathway is activated in DACH1 overexpressed cells and may mediate inhibition of aldosterone secretion in human adrenals.

Sex-related gene expression profiles in the adrenal cortex in the mature rat: microarray analysis with emphasis on genes involved in steroidogenesis

Notable sex-related differences exist in mammalian adrenal cortex structure and function. In adult rats, the adrenal weight and the average volume of zona fasciculata cells of females are larger and secrete greater amounts of corticosterone than those of males. The molecular bases of these sex-related differences are poorly understood. In this study, to explore the molecular background of these differences, we defined zone- and sex-specific transcripts in adult male and female (estrous cycle phase) rats. Twelve-week-old rats of both genders were used and samples were taken from the zona glomerulosa (ZG) and zona fasciculata/reticularis (ZF/R) zones. Transcriptome identification was carried out using the Affymetrix^® Rat Gene 1.1 ST Array. The microarray data were compared by fold change with significance according to moderated t-statistics. Subsequently, we performed functional annotation clustering using the Gene Ontology (GO) and Database for Annotation, Visualization and Integrated Discovery (DAVID). In the first step, we explored differentially expressed transcripts in the adrenal ZG and ZF/R. The number of differentially expressed transcripts was notably higher in the female than in the male rats (702 vs. 571). The differentially expressed genes which were significantly enriched included genes involved in steroid hormone metabolism, and their expression levels in the ZF/R of adult female rats were significantly higher compared with those in the male rats. In the female ZF/R, when compared with that of the males, prevailing numbers of genes linked to cell fraction, oxidation/reduction processes, response to nutrients and to extracellular stimuli or steroid hormone stimuli were downregulated. The microarray data for key genes involved directly in steroidogenesis were confirmed by qPCR. Thus, when compared with that of the males, in the female ZF/R, higher expression levels of genes involved directly in steroid hormone synthesis were accompanied by lower expression levels of genes regulating basal cell functions.

Sodium deficiency regulates rat adrenal zona glomerulosa gene expression

Aldosterone is the primary adrenocortical hormone regulating sodium retention, and its production is under the control of the renin-angiotensin-aldosterone system (RAAS). In vitro, angiotensin II can induce aldosterone production in adrenocortical cells without causing cell proliferation. In vivo, a low-sodium diet activates the RAAS and aldosterone production, at least in part, through an expansion of the adrenal zona glomerulosa (zG) layer. Although these mechanisms have been investigated, RAAS effects on zG gene expression have not been fully elucidated. In this study, we took an unbiased approach to define the complete list of zG transcripts involved in RAAS activation. Adrenal glands were collected from 11-week old Sprague-Dawley rats fed either sodium-deficient (SDef), normal sodium (NS), or high-sodium (HS) diet for 72 hours, and laser-captured zG RNA was analyzed on microarrays containing 27 342 probe sets. When the SDef transcriptome was compared with NS transcriptome (SDef/NS comparison), only 79 and 10 probe sets were found to be up- and down-regulated more than two-fold in SDef, respectively. In SDef/HS comparison, 201 and 68 probe sets were up- and down-regulated in SDef, respectively. Upon gene ontology (GO) analysis of these gene sets, we identified three groups of functionally related GO terms: cell proliferation-associated (group 1), response to stimulus-associated (group 2), and cholesterol/steroid metabolism-associated (group 3) GO terms. Although genes in group 1 may play a critical role in zG layer expansion, those in groups 2 and 3 may have important functions in aldosterone production, and further investigations on these genes are warranted.

Vitamin D receptor, an important transcription factor associated with aldosterone-producing adenoma

OBJECTIVE

To explore the endocrine mechanisms of aldosterone-producing adenoma (APA) by using the microarray expression profiles of normal and APA samples.

METHODS

The gene expression profile GSE8514 was downloaded from Gene Expression Omnibus database, including samples from normal adrenals (n = 5) and APAs (n = 10). The differentially expressed genes (DEGs) were identified by samr package and endocrine DEGs were obtained according to Clinical Genome Database. Then, functional enrichment analysis of screened DEGs was performed by DAVID (Database for Annotation, Visualization and Integrated Discovery). Finally, a regulatory network was constructed to screen endocrine genes related with adrenal dysfunction and pathway enrichment analysis for the constructed network was performed.

RESULTS

A total of 2149 DEGs were identified including 379 up- and 1770 down-regulated genes. And 26 endocrine genes were filtered from the DEGs. Furthermore, the down-regulated DEGs are mainly related to protein kinase cascade, response to molecule of bacterial origin, response to lipopolysaccharide, cellular macromolecule catabolic process and macromolecule catabolic process, while the up-regulated DEGs are related with regulation of ion transport. The target genes of VDR (vitamin D receptor), one of the three endocrine genes differentially expressed in the regulatory network, were endocrine genes including CYP24A1 (25-hydroxyvitamin D-24-hydroxylase) and PTH (parathyroid hormone). Three pathways may be associated with APA pathogenesis including cytokine-cytokine receptor interaction, pathways in cancer and autoimmune thyroid disease.

CONCLUSION

The VDR is the most significant transcription factor and related endocrine genes might play important roles in the endocrine mechanisms of APA.

A novel sample preparation method that enables nucleic acid analysis from ultrathin sections

The ability to isolate and perform nucleic acid analyses of individual cells is critical to studying the development of various cell types and structures. We present a novel biological sample preparation method developed for laser capture microdissection-assisted nucleic acid analysis of ultrathin cell/tissue sections. We used cells of the mitotic bed of the tadpole teeth of Lithobates sphenocephalus (Southern Leopard Frog). Cells from the mitotic beds at the base of the developing teeth series were isolated and embedded in the methacrylate resin, Technovit® 9100®. Intact cells of the mitotic beds were thin sectioned and examined by bright-field and transmission electron microscopy. The cytological and ultrastructural anatomy of the immature and progressively more mature tooth primordia appeared well preserved and intact. A developmental series of tooth primordia were isolated by laser capture microdissection (LCM). Processing of these cells for RNA showed that intact RNA could be isolated. The study demonstrates that Technovit® 9100® can be used as an embedding medium for extremely small tissues and from individual cells, a prerequisite step to LCM and nucleic acid analyses. A relatively small amount of sample material was needed for the analysis, which makes this technique ideal for cell-specific analyses when the desired cells are limited in quantity.

Lessons from the gene expression pattern of the rat zona glomerulosa

We recently identified hundreds of transcripts with differential expression in rat zona glomerulosa (zG) and zona fasciculata. Although the genes up-regulated in the zG may be playing important roles in aldosterone production, the relationship between most of these genes and aldosterone production has not been uncovered. Because aldosterone, in the presence of a high sodium diet, is now considered a significant cardiovascular risk factor, in this review we performed gene ontology and pathway analyses on the same microarray data to better define the genes that may influence zG function. Overall, we identified a number of genes that may be involved in aldosterone production through transforming growth factor β (TGF-β), WNT, calcium, potassium, and ACTH signaling pathways. The list of genes we present in the current report may become an important tool for researchers working on primary aldosteronism and aldosterone-related cardiovascular diseases.

Dicer deficiency reveals microRNAs predicted to control gene expression in the developing adrenal cortex

MicroRNAs (miRNAs) are small, endogenous, non-protein-coding RNAs that are an important means of posttranscriptional gene regulation. Deletion of Dicer, a key miRNA processing enzyme, is embryonic lethal in mice, and tissue-specific Dicer deletion results in developmental defects. Using a conditional knockout model, we generated mice lacking Dicer in the adrenal cortex. These Dicer-knockout (KO) mice exhibited perinatal mortality and failure of the adrenal cortex during late gestation between embryonic day 16.5 (E16.5) and E18.5. Further study of Dicer-KO adrenals demonstrated a significant loss of steroidogenic factor 1-expressing cortical cells that was histologically evident as early as E16.5 coincident with an increase in p21 and cleaved-caspase 3 staining in the cortex. However, peripheral cortical proliferation persisted in KO adrenals as assessed by staining of proliferating cell nuclear antigen. To further characterize the embryonic adrenals from Dicer-KO mice, we performed microarray analyses for both gene and miRNA expression on purified RNA isolated from control and KO adrenals of E15.5 and E16.5 embryos. Consistent with the absence of Dicer and the associated loss of miRNA-mediated mRNA degradation, we observed an up-regulation of a small subset of adrenal transcripts in Dicer-KO mice, most notably the transcripts coded by the genes Nr6a1 and Acvr1c. Indeed, several miRNAs, including let-7, miR-34c, and miR-21, that are predicted to target these genes for degradation, were also markedly down-regulated in Dicer-KO adrenals. Together these data suggest a role for miRNA-mediated regulation of a subset of genes that are essential for normal adrenal growth and homeostasis.

Angiotensin II and III metabolism and effects on steroid production in the HAC15 human adrenocortical cell line

Aldosterone is synthesized in the zona glomerulosa of the adrenal cortex under primary regulation by the renin-angiotensin system. Angiotensin II (A-II) acts through the angiotensin types 1 and 2 receptors (AT1R and AT2R). A-II is metabolized in different tissues by various enzymes to generate two heptapeptides A-III and angiotensin 1-7, which can then be catabolized into smaller peptides. A-II was more potent than A-III in stimulating aldosterone secretion in the adrenocortical cell line HAC15, and A-II, but not A-III, stimulated cortisol secretion. A-II stimulated mRNA expression of steroidogenic acute regulatory protein, 3β-hydroxysteroid dehydrogenase, CYP11B1, and CYP11B2, whereas A-III stimulated 3β-hydroxysteroid dehydrogenase, CYP11B1, and CYP11B2 but decreased the expression of CYP17A1 required for cortisol synthesis. The stimulation of aldosterone secretion by A-II and A-III was blocked by the AT1R receptor blocker, losartan, but not by an AT2R blocker. A-II was rapidly metabolized by the HAC15 cells to mainly to angiotensin 1-7, but not to A-III, and disappeared from the supernatant within 6 h. A-III was metabolized rapidly and disappeared within 1 h. In conclusion, A-II was not converted to A-III in the HAC15 cell and is the more potent stimulator of aldosterone secretion and cortisol of the two. A-III stimulated aldosterone secretion but not cortisol secretion.

Minireview: aldosterone biosynthesis: electrically gated for our protection

Aldosterone produced by adrenal zona glomerulosa (ZG) cells plays an important role in maintaining salt/water balance and, hence, blood pressure homeostasis. However, when dysregulated, aldosterone advances renal and cardiovascular disease states. Multiple steps in the steroidogenic pathway require Ca(2+), and the sustained production of aldosterone depends on maintained Ca(2+) entry into the ZG cell. Nevertheless, the recorded membrane potential of isolated ZG cells is extremely hyperpolarized, allowing the opening of only a small fraction of low-voltage-activated Ca(2+) channels of the Ca(v)3.x family, the major Ca(2+) conductance on the ZG cell membrane. As a consequence, to activate sufficient Ca(2+) channels to sustain the production of aldosterone, aldosterone secretagogs would be required to affect large decreases in membrane voltage, a requirement that is inconsistent with the exquisite sensitivity of aldosterone production in vivo to small changes (0.1 mm) in extracellular K(+). In this review, we evaluate the contribution of membrane voltage and voltage-dependent Ca(2+) channels to the control of aldosterone production and consider data highlighting the electrical excitability of the ZG cell. This intrinsic capacity of ZG cells to behave as electrical oscillators provides a platform from which to generate a recurring Ca(2+) signal that is compatible with the lengthy time course of steroidogenesis and provides an alternative model for the physiological regulation of aldosterone production that permits both amplitude and temporal modulation of the Ca(2+) signal.