The Orphan Nuclear Receptors NURR1 and NGFIB Regulate Adrenal Aldosterone Production

Somatic Mutations in MCOLN3 in Aldosterone-Producing Adenomas cause Primary Aldosteronism

Primary aldosteronism is characterized by renin-independent hyperaldosteronism that originates from aldosterone-producing lesions in the adrenal glands. Under physiological conditions, aldosterone synthase ( CYP11B2 ) expression is confined to the adrenal zona glomerulosa where it catalyzes the final reaction yielding aldosterone. The regulation of CYP11B2 transcription depends on the control of cellular membrane potential and cytosolic calcium activity. In primary aldosteronism, aldosterone-producing adenomas (APAs) are characterized by disrupted regulation of CYP11B2 expression resulting in autonomous biosynthesis of aldosterone. These lesions often harbor aldosterone-driver somatic mutations in genes encoding ion transporters/channels/pumps that increase cytosolic calcium activity causing increased CYP11B2 expression and aldosterone biosynthesis. We investigated APAs devoid of known somatic mutations and detected a missense mutation and a deletion-insertion variant in MCOLN3 which encodes for mucolipin-3 (TRPML3) - a highly conserved inwardly-rectifying, cation-permeable channel. These MCOLN3 mutations were identified in three APAs derived from male patients with primary aldosteronism: p. Y391D and p.N411_V412delinsI. Both mutations are located near the ion pore and selectivity filter of TRPML3. This is the first report of disease-causing MCOLN3 mutations in humans. Functional studies suggest MCOLN3 Y391D might directly or indirectly via membrane depolarization alter calcium influx of transfected adrenocortical cells, resulting in increased CYP11B2 transcription and aldosterone production. This study implicates mutated MCOLN3 as a driver of aldosterone excess in primary aldosteronism.

Significance Statement

Primary aldosteronism is a common but under-diagnosed endocrine disease that contributes to global hypertension burden and cardiovascular mortality and morbidity. Hyperaldosteronism in primary aldosteronism is mainly caused by adrenal lesions harboring somatic mutations that disrupt intracellular calcium levels and consequently aldosterone synthase expression and aldosterone production. Majority of these mutations have been identified in genes encoding ion transporters/channels/pumps. Herein, we report the first disease-causing somatic mutations in human MCOLN3 in aldosterone-producing adenomas (APAs) devoid of known mutations. In vitro investigations showed the MCOLN3 variant (p.Y391D) caused an influx of cytosolic calcium in adrenocortical cells and the subsequent increase in aldosterone synthase and aldosterone biosynthesis.

Chronic activation of adrenal Gq signaling induces Cyp11b2 expression in the zona fasciculata and hyperaldosteronism

Hyperaldosteronism is often associated with inappropriate aldosterone production and aldosterone synthase (Cyp11b2) expression. Normally, Cyp11b2 expression is limited to the adrenal zona glomerulosa (ZG) and regulated by angiotensin II which signals through Gq protein-coupled receptors. As cells migrate inwards, they differentiate into 11β-hydroxylase-expressing zona fasciculata (ZF) cells lacking Cyp11b2. The mechanism causing ZG-specific aldosterone biosynthesis is still unclear. We investigated the effect of chronic Gq signaling using transgenic mice with a clozapine N-oxide (CNO)-activated human M3 muscarinic receptor (DREADD) coupled to Gq (hM3Dq) that was expressed throughout the adrenal cortex. CNO raised circulating aldosterone in the presence of a high sodium diet with greater response seen in females compared to males. Immunohistochemistry and transcriptomics indicated disrupted zonal Cyp11b2 expression while Wnt signaling remained unchanged. Chronic Gq-DREADD signaling also induced an intra-adrenal RAAS in CNO-treated mice. Chronic Gq signaling disrupted adrenal cortex zonal aldosterone production associated with ZF expression of Cyp11b2.

Zona Glomerulosa-Derived Klotho Modulates Aldosterone Synthase Expression in Young Female Mice

Klotho plays a critical role in the regulation of ion and fluid homeostasis. A previous study reported that haplo-insufficiency of Klotho in mice results in increased aldosterone synthase (CYP11B2) expression, elevated plasma aldosterone, and high blood pressure. This phenotype was presumed to be the result of diminished Klotho expression in zona glomerulosa (zG) cells of the adrenal cortex; however, systemic effects on adrenal aldosterone production could not be ruled out. To examine whether Klotho expressed in the zG is indeed a critical regulator of aldosterone synthesis, we generated a tamoxifen-inducible, zG-specific mouse model of Klotho deficiency by crossing Klotho-flox mice with Cyp11b2-CreERT mice (zG-Kl-KO). Tamoxifen-treated Cyp11b2-CreERT animals (zG-Cre) served as controls. Rosa26-mTmG reporter mice were used for Cre-dependent lineage-marking. Two weeks after tamoxifen induction, the specificity of the zG-Cre line was verified using immunofluorescence analysis to show that GFP expression was restricted to the zG. RNA in situ hybridization revealed a 65% downregulation of Klotho messenger RNA expression in the zG of zG-Kl-KO female mice at age 12 weeks compared to control mice. Despite this significant decrease, zG-Kl-KO mice exhibited no difference in plasma aldosterone levels. However, adrenal CYP11B2 expression and the CYP11B2 promotor regulatory transcription factors, NGFIB and Nurr1, were enhanced. Together with in vitro experiments, these results suggest that zG-derived Klotho modulates Cyp11b2 but does not evoke a systemic phenotype in young adult mice on a normal diet. Further studies are required to investigate the role of adrenal Klotho on aldosterone synthesis in aged animals.

Calcineurin regulates aldosterone production via dephosphorylation of NFATC4

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

TSPAN12 (Tetraspanin 12) Is a Novel Negative Regulator of Aldosterone Production in Adrenal Physiology and Aldosterone-Producing Adenomas

BACKGROUND

Aldosterone-producing adenomas (APAs) are a major cause of primary aldosteronism, a condition of low-renin hypertension, in which aldosterone overproduction is usually driven by a somatic activating mutation in an ion pump or channel. TSPAN12 is differentially expressed in different subgroups of APAs suggesting a role in APA pathophysiology. Our objective was to determine the function of TSPAN12 (tetraspanin 12) in adrenal physiology and pathophysiology.

METHODS

APA specimens, pig adrenals under dietary sodium modulation, and a human adrenocortical cell line HAC15 were used for functional characterization of TSPAN12 in vivo and in vitro.

RESULTS

Gene ontology analysis of 21 APA transcriptomes dichotomized according to high versus low TSPAN12 transcript levels highlighted a function for TSPAN12 related to the renin-angiotensin system. TSPAN12 expression levels in a cohort of 30 APAs were inversely correlated with baseline plasma aldosterone concentrations (R=-0.47; P=0.009). In a pig model of renin-angiotensin system activation by dietary salt restriction, TSPAN12 mRNA levels and TSPAN12 immunostaining were markedly increased in the zona glomerulosa layer of the adrenal cortex. In vitro stimulation of human adrenocortical human adrenocortical cells with 10 nM angiotensin II for 6 hours caused a 1.6-fold±0.13 increase in TSPAN12 expression, which was ablated by 10 μM nifedipine (P=0.0097) or 30 μM W-7 (P=0.0022). Gene silencing of TSPAN12 in human adrenocortical cells demonstrated its inverse effect on aldosterone secretion under basal and angiotensin II stimulated conditions.

CONCLUSIONS

Our findings show that TSPAN12 is a negative regulator of aldosterone production and could contribute to aldosterone overproduction in primary aldosteronism.

Phosphorylation of CaMK and CREB-Mediated Cardiac Aldosterone Synthesis Induced by Arginine Vasopressin in Rats with Myocardial Infarction

Both aldosterone and arginine vasopressin (AVP) are produced in the heart and may participate in cardiac fibrosis. However, their relationship remains unknown. This study aims to demonstrate the regulation and role of AVP in aldosterone synthesis in the heart. Rats were subjected to a sham operation or myocardial infarction (MI) by ligating the coronary artery. Cardiac function and fibrosis were assessed using echocardiography and immunohistochemical staining, respectively. In addition, the effects of AVP stimulation on cardiac microvascular endothelial cells (CMECs) were studied using ELISA, real-time PCR, and Western blotting. Compared with the rats having undergone a sham operation, the MI rats had an increased LVMI, type I collagen composition, and concentrations of aldosterone and AVP in the heart but decreased cardiac function. As the MI rats aged, the LVMI, type I collagen, aldosterone, and AVP increased, while the LVMI decreased. Furthermore, AVP time-dependently induced aldosterone secretion and CYP11B2 mRNA expression in CMECs. The p-CREB levels were significantly increased by AVP. Nevertheless, these effects were completely blocked by SR49059 or partially inhibited by KN93. This study demonstrated that AVP could induce the secretion of local cardiac aldosterone, which may involve CaMK and CREB phosphorylation and CYP11B2 upregulation through V1 receptor activation.

YM750, an ACAT Inhibitor, Acts on Adrenocortical Cells to Inhibit Aldosterone Secretion Due to Depolarization

Primary aldosteronism (PA) is considered the most common form of secondary hypertension, which is associated with excessive aldosterone secretion in the adrenal cortex. The cause of excessive aldosterone secretion is the induction of aldosterone synthase gene (CYP11B2) expression by depolarization of adrenocortical cells. In this study, we found that YM750, an Acyl-coenzyme A: cholesterol acyltransferase (ACAT) inhibitor, acts on adrenocortical cells to suppress CYP11B2 gene expression and aldosterone secretion. YM750 inhibited the induction of CYP11B2 gene expression by KCl stimulation, but not by angiotensin II and forskolin stimulation. Interestingly, YM750 did not inhibit KCl-stimulated depolarization via an increase in intracellular calcium ion concentration. Moreover, ACAT1 expression was relatively abundant in the zona glomerulosa (ZG) including these CYP11B2-positive cells. Thus, YM750 suppresses CYP11B2 gene expression by suppressing intracellular signaling activated by depolarization. In addition, ACAT1 was suggested to play an important role in steroidogenesis in the ZG. YM750 suppresses CYP11B2 gene expression and aldosterone secretion in the adrenal cortex, suggesting that it may be a potential therapeutic agent for PA.

Effects of bis (2-butoxyethyl) phthalate on adrenocortical function in male rats in puberty partially via down-regulating NR5A1/NR4A1/NR4A2 pathways

Phthalates may interfere with the biosynthesis of steroid hormones in the adrenal cortex. Bis (2-butoxyethyl) phthalate (BBOP) is a phthalate containing oxygen atoms in the alcohol moiety. In this study, 35-day-old male Sprague-Dawley rats were daily gavaged with BBOP (0, 10, 100, 250, and 500 mg/kg body weight) for 21 days. BBOP did not affect the weight of body and adrenal glands. BBOP significantly reduced serum corticosterone levels at 250 and 500 mg/kg, and lowered aldosterone level at 500 mg/kg without affecting adrenocorticotropic hormone. BBOP did not alter the thickness of the adrenal cortex. BBOP significantly down-regulated the expression of steroidogenesis-related genes (Scarb1, Star, Cyp11a1, Cyp21, Cyp11b1, Cyp11b2, Nr5a1, Nr4a1, and Nr4a2) and proteins, and antioxidant enzymes (Sod1, Sod2, Gpx1, and Cat) and their proteins, while up-regulating the expression of Mc2r and Agtr1a at various doses. BBOP reduced the phosphorylation of AKT1, AKT2, and ERK1/2, as well as the levels of SIRT1 and PGC1α without affecting the phosphorylation of AMPK. BBOP significantly induced the production of reactive oxygen species and apoptosis rate in H295R cells at 100 μM and higher after 24 h of treatment. In conclusion, male rats exposed to BBOP in puberty have significant reduction of steroid biosynthesis with a potential mechanism that is involved in the decrease in the phosphorylation of AKT1, AKT2, ERK1/2, as well as SIRT1 and PGC1α and increase in ROS.

Congenital Adrenal Hyperplasia-Current Insights in Pathophysiology, Diagnostics, and Management

Congenital adrenal hyperplasia (CAH) is a group of autosomal recessive disorders affecting cortisol biosynthesis. Reduced activity of an enzyme required for cortisol production leads to chronic overstimulation of the adrenal cortex and accumulation of precursors proximal to the blocked enzymatic step. The most common form of CAH is caused by steroid 21-hydroxylase deficiency due to mutations in CYP21A2. Since the last publication summarizing CAH in Endocrine Reviews in 2000, there have been numerous new developments. These include more detailed understanding of steroidogenic pathways, refinements in neonatal screening, improved diagnostic measurements utilizing chromatography and mass spectrometry coupled with steroid profiling, and improved genotyping methods. Clinical trials of alternative medications and modes of delivery have been recently completed or are under way. Genetic and cell-based treatments are being explored. A large body of data concerning long-term outcomes in patients affected by CAH, including psychosexual well-being, has been enhanced by the establishment of disease registries. This review provides the reader with current insights in CAH with special attention to these new developments.

Molecular Mechanisms of Functional Adrenocortical Adenoma and Carcinoma: Genetic Characterization and Intracellular Signaling Pathway

The adrenal cortex produces steroid hormones as adrenocortical hormones in the body, secreting mineralocorticoids, glucocorticoids, and adrenal androgens, which are all considered essential for life. Adrenocortical tumors harbor divergent hormonal activity, frequently with steroid excess, and disrupt homeostasis of the body. Aldosterone-producing adenomas (APAs) cause primary aldosteronism (PA), and cortisol-producing adenomas (CPAs) are the primary cause of Cushing’s syndrome. In addition, adrenocortical carcinoma (ACC) is a highly malignant cancer harboring poor prognosis. Various genetic abnormalities have been reported, which are associated with possible pathogenesis by the alteration of intracellular signaling and activation of transcription factors. In particular, somatic mutations in APAs have been detected in genes encoding membrane proteins, especially ion channels, resulting in hypersecretion of aldosterone due to activation of intracellular calcium signaling. In addition, somatic mutations have been detected in those encoding cAMP-PKA signaling-related factors, resulting in hypersecretion of cortisol due to its driven status in CPAs. In ACC, mutations in tumor suppressor genes and Wnt-β-catenin signaling-related factors have been implicated in its pathogenesis. In this article, we review recent findings on the genetic characteristics and regulation of intracellular signaling and transcription factors in individual tumors.

RNA-binding proteins regulate aldosterone homeostasis in human steroidogenic cells

Angiotensin II (AngII) stimulates adrenocortical cells to produce aldosterone, a master regulator of blood pressure. Despite extensive characterization of the transcriptional and enzymatic control of adrenocortical steroidogenesis, there are still major gaps in the precise regulation of AII-induced gene expression kinetics. Specifically, we do not know the regulatory contribution of RNA-binding proteins (RBPs) and RNA decay, which can control the timing of stimulus-induced gene expression. To investigate this question, we performed a high-resolution RNA-seq time course of the AngII stimulation response and 4-thiouridine pulse labeling in a steroidogenic human cell line (H295R). We identified twelve temporally distinct gene expression responses that contained mRNA encoding proteins known to be important for various steps of aldosterone production, such as cAMP signaling components and steroidogenic enzymes. AngII response kinetics for many of these mRNAs revealed a coordinated increase in both synthesis and decay. These findings were validated in primary human adrenocortical cells stimulated ex vivo with AngII. Using a candidate screen, we identified a subset of RNA-binding protein and RNA decay factors that activate or repress AngII-stimulated aldosterone production. Among the repressors of aldosterone were BTG2, which promotes deadenylation and global RNA decay. BTG2 was induced in response to AngII stimulation and promoted the repression of mRNAs encoding pro-steroidogenic factors indicating the existence of an incoherent feedforward loop controlling aldosterone homeostasis. These data support a model in which coordinated increases in transcription and decay facilitate the major transcriptomic changes required to implement a pro-steroidogenic expression program that actively resolved to prevent aldosterone overproduction.

Effect of potassium on DNA methylation of aldosterone synthase gene

BACKGROUND

Aldosterone synthase gene, CYP11B2 is regulated by potassium and angiotensin II (Ang II). We have reported that Ang II could change the DNA methylation status around transcription factor-binding sites and a transcription start site (TSS) and activate expression of CYP11B2. Similar to Ang II, small increases in extracellular potassium levels also increase CYP11B2 mRNA levels.

METHODS AND RESULTS

Adrenocortical H295R cells were treated with different doses of potassium. Methylation analysis of CYP11B2 promoter region was done by bisulfite sequencing. CYP11B2 mRNA and protein levels, chromatin accessibility, methylation and demethylation activity were estimated. The transcriptional ability of CYP11B2 promoter with or without methylation was assessed. Potassium stimulation caused DNA demethylation around cyclic AMP responsive element binding protein 1 (CREB1) and nuclear receptor subfamily 4 group A (NR4A) family-binding sites and a TSS; demethylation was accompanied by recruitment of CREB1 and NR4A1 and increased chromatin accessibility of the CYP11B2 promoter. DNA methylation activity decreased in the nucleus. DNA demethylation at CpG1 (Ad1), CpG2 (Ad5) and CpG3 were detected within 2 to 4 days after potassium (16 mmol/l) stimulation. The changes reached a maximum level by day 7. DNA at CpG2 (Ad5) and CpG3 was re-methylated to levels that were similar to those of nontreated cells at day 9. Potassium treatment significantly reduced DNA methylation activity at days 7 and 9. DNA demethylation activity was not changed by potassium.

CONCLUSION

: Potassium induced reversibly DNA demethylation, which switches the phenotype of CYP11B2 expression from an inactive to an active state.

Aldosterone-Regulating Receptors and Aldosterone-Driver Somatic Mutations

BACKGROUND

Somatic gene mutations that facilitate inappropriate intracellular calcium entrance have been identified in most aldosterone-producing adenomas (APAs). Studies suggest that angiotensin II and adrenocorticotropic hormone (ACTH) augment aldosterone production from APAs. Little is known, however, regarding possible variations in response to hormonal stimuli between APAs with different aldosterone-driver mutations.

OBJECTIVE

To analyze the transcript expression of type 1 angiotensin II receptors (AGTR1), ACTH receptors (MC2R), and melanocortin 2 receptor accessory protein (MRAP) in APAs with known aldosterone-driver somatic mutations.

METHODS

RNA was isolated from APAs with mutations in: KCNJ5 (n = 14), ATP1A1 (n = 14), CACNA1D (n = 14), and ATP2B3 (n = 5), and from normal adjacent adrenal tissue (n = 45). Transcript expression of MC2R, MRAP, AGTR1, aldosterone synthase (CYP11B2), 17α-hydroxylase/17,20-lyase (CYP17A1), and 11β-hydroxylase (CYP11B1) were quantified using quantitative RT-PCR and normalized to β-actin.

RESULTS

Compared to adjacent normal adrenal tissue, APAs had higher transcript levels of CYP11B2 (2,216.4 [1,112.0, 2,813.5]-fold, p < 0.001), MC2R (2.88 [2.00, 4.52]-fold, p < 0.001), and AGTR1 (1.80 [1.02, 2.80]-fold, p < 0.001]), and lower transcript levels of MRAP, CYP17A1, and CYP11B1 (0.28-0.36, p < 0.001 for all). MC2R and CYP11B2 transcripts were lower in APAs with KCNJ5 vs. other mutations (p < 0.01 for both). MC2R expression correlated positively with that of AGTR1 in APAs harboring KCNJ5 and CACNA1D mutations, and with MRAP expression in APAs harboring ATPase mutations.

CONCLUSIONS

While MC2R and AGTR1 are expressed in all APAs, differences were observed based on the underlying aldosterone-driver somatic mutations. In tandem, our findings suggest that APAs with ATPase-mutations are more responsive to ACTH than KCNJ5-mutated APAs.

Reactive oxygen species in renal vascular function

Reactive oxygen species (ROS) are produced by the aerobic metabolism. The imbalance between production of ROS and antioxidant defence in any cell compartment is associated with cell damage and may play an important role in the pathogenesis of renal disease. NADPH oxidase (NOX) family is the major ROS source in the vasculature and modulates renal perfusion. Upregulation of Ang II and adenosine activates NOX via AT1R and A1R in renal microvessels, leading to superoxide production. Oxidative stress in the kidney prompts renal vascular remodelling and increases preglomerular resistance. These are key elements in hypertension, acute and chronic kidney injury, as well as diabetic nephropathy. Renal afferent arterioles (Af), the primary resistance vessel in the kidney, fine tune renal hemodynamics and impact on blood pressure. Vice versa, ROS increase hypertension and diabetes, resulting in upregulation of Af vasoconstriction, enhancement of myogenic responses and change of tubuloglomerular feedback (TGF), which further promotes hypertension and diabetic nephropathy. In the following, we highlight oxidative stress in the function and dysfunction of renal hemodynamics. The renal microcirculatory alterations brought about by ROS importantly contribute to the pathophysiology of kidney injury, hypertension and diabetes.

Chemogenetic activation of adrenocortical Gq signaling causes hyperaldosteronism and disrupts functional zonation

The mineralocorticoid aldosterone is produced in the adrenal zona glomerulosa (ZG) under the control of the renin-angiotensin II (AngII) system. Primary aldosteronism (PA) results from renin-independent production of aldosterone and is a common cause of hypertension. PA is caused by dysregulated localization of the enzyme aldosterone synthase (Cyp11b2), which is normally restricted to the ZG. Cyp11b2 transcription and aldosterone production are predominantly regulated by AngII activation of the Gq signaling pathway. Here, we report the generation of transgenic mice with Gq-coupled designer receptors exclusively activated by designer drugs (DREADDs) specifically in the adrenal cortex. We show that adrenal-wide ligand activation of Gq DREADD receptors triggered disorganization of adrenal functional zonation, with induction of Cyp11b2 in glucocorticoid-producing zona fasciculata cells. This result was consistent with increased renin-independent aldosterone production and hypertension. All parameters were reversible following termination of DREADD-mediated Gq signaling. These findings demonstrate that Gq signaling is sufficient for adrenocortical aldosterone production and implicate this pathway in the determination of zone-specific steroid production within the adrenal cortex. This transgenic mouse also provides an inducible and reversible model of hyperaldosteronism to investigate PA therapeutics and the mechanisms leading to the damaging effects of aldosterone on the cardiovascular system.

Molecular Basis of Primary Aldosteronism and Adrenal Cushing Syndrome

This review reports the main molecular alterations leading to development of benign cortisol- and/or aldosterone-secreting adrenal tumors. Causes of adrenal Cushing syndrome can be divided in 2 groups: multiple bilateral tumors or adenomas secreting cortisol. Bilateral causes are mainly primary pigmented nodular adrenocortical disease, most of the time due to PRKAR1A germline-inactivating mutations, and primary bilateral macronodular adrenal hyperplasia that can be caused in some rare syndromic cases by germline-inactivating mutations of MEN1, APC, and FH and of ARMC5 in isolated forms. PRKACA somatic-activating mutations are the main alterations in unilateral cortisol-producing adenomas. In primary hyperaldosteronism (PA), familial forms were identified in 1% to 5% of cases: familial hyperaldosteronism type I (FH-I) due to a chimeric CYP11B1/CYP11B2 hybrid gene, FH-II due to CLCN-2 germline mutations, FH-III due to KCNJ5 germline mutations, FH-IV due to CACNA1H germline mutations and PA, and seizures and neurological abnormalities syndrome due to CACNA1D germline mutations. Several somatic mutations have been found in aldosterone-producing adenomas in KCNJ5, ATP1A1, ATP2B3, CACNA1D, and CTNNB1 genes.

In addition to these genetic alterations, genome-wide approaches identified several new alterations in transcriptome, methylome, and miRnome studies, highlighting new pathways involved in steroid dysregulation.

Dog Steroidogenic Factor-1: Molecular cloning and analysis of epigenetic regulation

Steroidogenic factor 1 (SF-1) is a nuclear receptor that is important in steroid hormone production, and adrenal and gonad development. The SF-1 gene is highly conserved among most vertebrates. However, dog SF-1 registered in public databases, such as CanFam3.1, lacks the 5' end compared to other mammals including mouse, human, bovine, and cat. Whether this defect is due to species differences or database error is unclear. Here, we determined the full-length dog SF-1 cDNA sequence and identified the missing 5' end sequence in the databases. The coding region of the dog SF-1 gene has 1,386 base pairs, and the protein has 461 amino acid residues. Sequence alignment analysis among vertebrates revealed that the 5' end sequence of dog SF-1 cDNA is highly conserved compared to other vertebrates. The genomic position of the first exon was determined, and its promoter region sequence was analyzed. The DNA methylation state at the basal promoter and the expression of dog SF-1 in steroidogenic tissues and non-steroidogenic cells were examined. CpG sites at the basal promoter displayed methylation kinetics inversely correlated with gene expression. The promoter was hypomethylated and hypermethylated in SF-1 expressing and non-SF-1 expressing tissues, respectively. In conclusion, we identified the true full sequence of dog SF-1 cDNA and determined the genome sequence around the first exon. The gene is under the control of epigenetic regulation, such as DNA methylation, at the promoter.

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

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

Amhr2-Cre-Mediated Global Tspo Knockout

Although the role of translocator protein (TSPO) in cholesterol transport in steroid-synthesizing cells has been studied extensively, recent studies of TSPO genetic depletion have questioned its role. Amhr2-Cre mice have been used to generate Leydig cell-specific Tspo conditional knockout (cKO) mice. Using the same Cre line, we were unable to generate Tspo cKO mice possibly because of genetic linkage between Tspo and Amhr2 and coexpression of Amhr2-Cre and Tspo in early embryonic development. We found that Amhr2-Cre is expressed during preimplantation stages, resulting in global heterozygous mice (gHE; Amhr2-Cre+/-,Tspo -/+). Two gHE mice were crossed, generating Amhr2-Cre-mediated Tspo global knockout (gKO; Tspo -/-) mice. We found that 33.3% of blastocysts at E3.5 to E4.5 showed normal morphology, whereas 66.7% showed delayed development, which correlates with the expected Mendelian proportions of Tspo +/+ (25%), Tspo -/- (25%), and Tspo +/- (50%) genotypes from crossing 2 Tspo -/+ mice. Adult Tspo gKO mice exhibited disturbances in neutral lipid homeostasis and reduced intratesticular and circulating testosterone levels, but no change in circulating basal corticosterone levels. RNA-sequencing data from mouse adrenal glands and lungs revealed transcriptome changes in response to the loss of TSPO, including changes in several cholesterol-binding and transfer proteins. This study demonstrates that Amhr2-Cre can be used to produce Tspo gKO mice instead of cKO, and can serve as a new global "Cre deleter." Moreover, our results show that Tspo deletion causes delayed preimplantation embryonic development, alters neutral lipid storage and steroidogenesis, and leads to transcriptome changes that may reflect compensatory mechanisms in response to the loss of function of TSPO.

Role of SCTR/AT1aR heteromer in mediating ANGII-induced aldosterone secretion

The involvement of secretin (SCT) and its receptor (SCTR) in angiotensin II (ANGII)-mediated osmoregulation by forming SCTR/ angiotensin II type 1 receptor (AT1R) heteromer is well established. In this study, we demonstrated that SCTR/AT1R complex can mediate ANGII-induced aldosterone secretion/release through potentiating calcium mobilization. Through IHC and cAMP studies, we showed the presence of functional SCTR and AT1R in the primary zona glomerulosa (ZG) cells of C57BL/6N (C57), and functional AT1R and non-functional SCTR in SCTR knockout (SCTR-/-) mice. Calcium mobilization studies revealed the important role of SCTR on ANGII-mediated calcium mobilization in adrenal gland. The fluo4-AM loaded primary adrenal ZG cells from the C57 mice displayed a dose-dependent increase in intracellular calcium influx ([Ca2+]i) when exposed to ANGII but not from the SCTR-/- ZG cells. Synthetic SCTR transmembrane (TM) peptides STM-II/-IV were able to alter [Ca2+]i in C57 mice, but not the mice with mutated STM-II/-IV (STM-IIm/IVm) peptides. Through enzyme immunoassay (EIA), we measured the aldosterone release from primary ZG cells of both C57 and SCTR-/- mice by exposing them to ANGII (10nM). SCTR-/- ZG cells showed impaired ANGII-induced aldosterone secretion compared to the C57 mice. TM peptide, STM-II hindered the aldosterone secretion in ZG cells of C57 mice. These findings support the involvement of SCTR/AT1R heterodimer complex in aldosterone secretion/release through [Ca2+]i.

NURR1 activation in skeletal muscle controls systemic energy homeostasis

Skeletal muscle plays a central role in the control of metabolism and exercise tolerance. Analysis of muscle enhancers activated after exercise in mice revealed the orphan nuclear receptor NURR1/NR4A2 as a prominent component of exercise-responsive enhancers. We show that exercise enhances the expression of NURR1, and transgenic overexpression of NURR1 in skeletal muscle enhances physical performance in mice. NURR1 expression in skeletal muscle is also sufficient to prevent hyperglycemia and hepatic steatosis, by enhancing muscle glucose uptake and storage as glycogen. Furthermore, treatment of obese mice with putative NURR1 agonists increases energy expenditure, improves glucose tolerance, and confers a lean phenotype, mimicking the effects of exercise. These findings identify a key role for NURR1 in governance of skeletal muscle glucose metabolism, and reveal a transcriptional link between exercise and metabolism. Our findings also identify NURR1 agonists as possible exercise mimetics with the potential to ameliorate obesity and other metabolic abnormalities.

Introduction to the 2018 Keith L. Parker Award Lecture, William E. Rainey, PhD

The Adrenal Cortex Meeting celebrated the awarding of the Keith L. Parker Award Lecture to William E. (Bill) Rainey, and this article reviews his training, career, and contributions to the field of adrenal biology.

NR4A nuclear receptors in cardiac remodeling and neurohormonal regulation

Heart failure is characterized by the constant interplay between the underlying cardiac insult, degree of myocardial dysfunction and the activity of compensatory neurohormonal mechanisms. The sympathetic nervous system (SNS) and renin-angiotensin-aldosterone system (RAAS) become activated to maintain cardiac output; however, their chronic hyperactivity will eventually become deleterious. Several nuclear hormone receptors, including the mineralocorticoid receptor and estrogen receptor, are well-known to modulate cardiac disease. Recently, the subfamily of NR4A nuclear receptors i.e. Nur77, Nurr1 and NOR-1, are emerging as key players in cardiac stress responses, as well as pivotal regulators of neurohormonal mechanisms. In this review, we summarize current literature on NR4A nuclear receptors in the heart and in various components of the SNS, RAAS and immune system and discuss the functional implications for NR4As in cardiac function and disease.

Endogenous Purification of NR4A2 (Nurr1) Identified Poly(ADP-Ribose) Polymerase 1 as a Prime Coregulator in Human Adrenocortical H295R Cells

Aldosterone is synthesized in zona glomerulosa of adrenal cortex in response to angiotensin II. This stimulation transcriptionally induces expression of a series of steroidogenic genes such as HSD3B and CYP11B2 via NR4A (nuclear receptor subfamily 4 group A) nuclear receptors and ATF (activating transcription factor) family transcription factors. Nurr1 belongs to the NR4A family and is regarded as an orphan nuclear receptor. The physiological significance of Nurr1 in aldosterone production in adrenal cortex has been well studied. However, coregulators supporting the Nurr1 function still remain elusive. In this study, we performed RIME (rapid immunoprecipitation mass spectrometry of endogenous proteins), a recently developed endogenous coregulator purification method, in human adrenocortical H295R cells and identified PARP1 as one of the top Nurr1-interacting proteins. Nurr1-PARP1 interaction was verified by co-immunoprecipitation. In addition, both siRNA knockdown of PARP1 and treatment of AG14361, a specific PARP1 inhibitor suppressed the angiotensin II-mediated target gene induction in H295R cells. Furthermore, PARP1 inhibitor also suppressed the aldosterone secretion in response to the angiotensin II. Together, these results suggest PARP1 is a prime coregulator for Nurr1.

Epigenetic Regulation of Aldosterone Synthase Gene by Sodium and Angiotensin II

Background

DNA methylation is believed to be maintained in adult somatic cells. Recent findings, however, suggest that all methylation patterns are not stable. We demonstrate that stimulatory signals can change the DNA methylation status around transcription factor binding sites and a transcription start site and activate expression of the aldosterone synthase gene (CYP11B2).

Methods and Results

DNA methylation of CYP11B2 was analyzed in aldosterone‐producing adenomas, nonfunctioning adrenal adenomas, and adrenal glands and compared with the gene expression levels. CpG dinucleotides in the CYP11B2 promoter were found to be hypormethylated in tissues with high expression, but not in those with low expression, of CYP11B2. Methylation of the CYP11B2 promoter fused to a reporter gene decreased transcriptional activity. Methylation of recognition sequences of transcription factors, including CREB1, NGFIB (NR4A1), and NURR1 (NR4A2) diminished their DNA‐binding activity. A methylated‐CpG‐binding protein MECP2 interacted directly with the methylated CYP11B2 promoter. In rats, low salt intake led to upregulation of CYP11B2 expression and DNA hypomethylation in the adrenal gland. Treatment with angiotensin II type 1 receptor antagonist decreased CYP11B2 expression and led to DNA hypermethylation.

Conclusions

DNA demethylation may switch the phenotype of CYP11B2 expression from an inactive to an active state and regulate aldosterone biosynthesis.

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

CONTEXT

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

CLCN2 chloride channel mutations in familial hyperaldosteronism type II

Primary aldosteronism, a common cause of severe hypertension¹, features constitutive production of the adrenal steroid aldosterone. We analyzed a multiplex family with familial hyperaldosteronism type II (FH-II)² and 80 additional probands with unsolved early-onset primary aldosteronism. Eight probands had novel heterozygous variants in CLCN2, including two de novo mutations and four independent occurrences of the identical p.Arg172Gln mutation; all relatives with early-onset primary aldosteronism carried the CLCN2 variant found in probands. CLCN2 encodes a voltage-gated chloride channel expressed in adrenal glomerulosa that opens at hyperpolarized membrane potentials. Channel opening depolarizes glomerulosa cells and induces expression of aldosterone synthase, the rate-limiting enzyme for aldosterone biosynthesis. Mutant channels cause gain of function, with higher open probabilities at the glomerulosa resting potential. These findings for the first time demonstrate a role of anion channels in glomerulosa membrane potential determination, aldosterone production and hypertension. They establish the cause of a substantial fraction of early-onset primary aldosteronism.

Csk Regulates Blood Pressure by Controlling the Synthetic Pathways of Aldosterone

BACKGROUND

Blood pressure is regulated by a network of diverse physiological pathways. The C-terminal Src kinase (CSK) locus (15q24) is associated with blood pressure in various ethnic groups. It was recently reported thatCskinsufficiency increases blood pressure through Src. The mechanisms of hypertension inCsk+/-mice are examined further in this study.

METHODS AND RESULTS

To identify a causal component responsible for hypertension inCsk+/-, the heart rate was measured by electrocardiogram and plasma volume by Evans blue dilution. Plasma volume increased inCsk+/-compared with wild-types, while the heart rate did not change. Plasma sodium and aldosterone levels rose consistently inCsk+/-vs. wild-types, and spironolactone, a mineralocorticoid receptor antagonist, reduced blood pressure. The amounts of Sgk1 and Na+/K+-ATPase (NKA) increased in the kidney ofCsk+/-compared with wild-types. It was also found that Cyp11b2 (aldosterone synthase) was upregulated in the adrenal glands ofCsk+/-, and that Csk was enriched in the zona glomerulosa of adrenals, the major site of aldosterone production in the normal mouse.

CONCLUSIONS

The results of the present study identify a physiological pathway by which blood pressure is regulated, in which the insufficiency ofCskinduces aldosterone production with zonal specificity in the adrenal glands, increasing sodium reabsorption and plasma volume and thus resulting in hypertension.

High glucose stimulates expression of aldosterone synthase (CYP11B2) and secretion of aldosterone in human adrenal cells

Aldosterone synthase is the key rate‐limiting enzyme in adrenal aldosterone production, and induction of its gene (CYP11B2) results in the progression of hypertension. As hypertension is a frequent complication among patients with diabetes, we set out to elucidate the link between diabetes mellitus and hypertension. We examined the effects of high glucose on CYP11B2 expression and aldosterone production using human adrenal H295R cells and a stable H295R cell line expressing a CYP11B2 5′‐flanking region/luciferase cDNA chimeric construct. d‐glucose (d‐glu), but not its enantiomer l‐glucose, dose dependently induced CYP11B2 transcription and mRNA expression. A high concentration (450 mg·dL⁻¹) of d‐glu time dependently induced CYP11B2 transcription and mRNA expression. Moreover, high glucose stimulated secretion of aldosterone into the media. Transient transfection studies using deletion mutants/nerve growth factor‐induced clone B (NGFIB) response element 1 (NBRE‐1) point mutant of CYP11B2 5′‐flanking region revealed that the NBRE‐1 element, known to be activated by transcription factors NGFIB and NURR1, was responsible for the high glucose‐mediated effect. High glucose also induced the mRNA expression of these transcription factors, especially that of NURR1, but NURR1 knockdown using its siRNA did not affect high glucose‐induced CYP11B2 mRNA expression. Taken together, it is speculated that high glucose may induce CYP11B2 transcription via the NBRE‐1 element in its 5′‐flanking region, resulting in the increase in aldosterone production although high glucose‐induced NURR1 is not directly involved in the effect. Additionally, glucose metabolism and calcium channels were found to be involved in the high glucose effect. Our observations suggest one possible explanation for the high incidence of hypertension in patients with diabetes.

Suppressive effects of RXR agonist PA024 on adrenal CYP11B2 expression, aldosterone secretion and blood pressure

The effects of retinoids on adrenal aldosterone synthase gene (CYP11B2) expression and aldosterone secretion are still unknown. We therefore examined the effects of nuclear retinoid X receptor (RXR) pan-agonist PA024 on CYP11B2 expression, aldosterone secretion and blood pressure, to elucidate its potential as a novel anti-hypertensive drug. We demonstrated that PA024 significantly suppressed angiotensin II (Ang II)-induced CYP11B2 mRNA expression, promoter activity and aldosterone secretion in human adrenocortical H295R cells. Human CYP11B2 promoter functional analyses using its deletion and point mutants indicated that the suppression of CYP11B2 promoter activity by PA024 was in the region from -1521 (full length) to -106 including the NBRE-1 and the Ad5 elements, and the Ad5 element may be mainly involved in the PA024-mediated suppression. PA024 also significantly suppressed the Ang II-induced mRNA expression of transcription factors NURR1 and NGFIB that bind to and activate the Ad5 element. NURR1 overexpression demonstrated that the decrease of NURR1 expression may contribute to the PA024-mediated suppression of CYP11B2 transcription. PA024 also suppressed the Ang II-induced mRNA expression of StAR, HSD3β2 and CYP21A2, a steroidogenic enzyme group involved in aldosterone biosynthesis. Additionally, the PA024-mediated CYP11B2 transcription suppression was shown to be exerted via RXRα. Moreover, the combination of PPARγ agonist pioglitazone and PA024 caused synergistic suppressive effects on CYP11B2 mRNA expression. Finally, PA024 treatment significantly lowered both the systolic and diastolic blood pressure in Tsukuba hypertensive mice (hRN8-12 x hAG2-5). Thus, RXR pan-agonist PA024 may be a candidate anti-hypertensive drugs that acts via the suppression of aldosterone synthesis and secretion.

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.

Fundamental studies of adrenal retinoid-X-receptor: Protein isoform, tissue expression, subcellular distribution, and ligand availability

Adrenal gland reportedly expresses many nuclear receptors that are known to heterodimerize with retinoid-X-receptor (RXR) for functions, but the information regarding the glandular RXR is not adequate. Studies of rat adrenal homogenate by Western blotting revealed three RXR proteins: RXRα (55kDa), RXRβ (47kDa) and RXR (56kDa). RXRγ was not detectable. After fractionation, RXRα was almost exclusively localized in the nuclear fraction. In comparison, substantial portions of RXRβ and RXR were found in both nuclear and post-nuclear particle fractions, suggesting genomic and non-genomic functions. Cells immunostained for RXRα were primarily localized in zona fasciculata (ZF) and medulla, although some stained cells were found in zona glomerulosa (ZG) and zona reticularis (ZR). In contrast, cells immunostained for RXRβ were concentrated principally in ZG, although some stained cells were seen in ZR, ZF, and medulla (in descending order, qualitatively). Analysis of adrenal lipid extracts by LC/MS did not detect 9-cis-retinoic acid (a potent RXR-ligand) but identified all-trans retinoic acid. Since C20 and C22 polyunsaturated fatty acids (PUFAs) can also activate RXR, subcellular availabilities of unesterified fatty acids were investigated by GC/MS. As results, arachidonic acid (C20:4), adrenic acid (C22:4), docosapentaenoic acid (C22:5), and cervonic acid (C22:6) were detected in the lipids extracted from each subcellular fraction. Thus, the RXR-agonizing PUFAs are available in all the main subcellular compartments considerably. The present findings not only shed light on the adrenal network of RXRs but also provide baseline information for further investigations of RXR heterodimers in the regulation of adrenal steroidogenesis.

Expression of CYP11B2 in Aldosterone-Producing Adrenocortical Adenoma: Regulatory Mechanisms and Clinical Significance

Aldosterone-producing adrenocortical adenoma (APA) is responsible for the majority of cases clinically diagnosed as primary aldosteronism. Aldosterone synthase (CYP11B2) is one of the enzymes that play essential roles in aldosterone synthesis and is involved in the pathogenesis of APA. Recent studies have demonstrated that various factors and regulators influence the expression and function of CYP11B2 in APA. In particular, somatic mutations, such as gain-of-function and loss-of-function mutations, have been identified in several genes, each of which encodes a pivotal protein that affects the calcium signaling pathway, the expression of CYP11B2, and aldosterone production. The gain-of-function mutations were reported in KCNJ5 that encodes G-protein activated inward rectifier K⁺ channel 4 (Kir3.4) and in CACNA1D, encoding calcium channel, voltage-dependent, L type, alpha subunit Cav1.3. The loss-of-function mutations were found in ATP1A1 that encodes Na⁺/K⁺ ATPase α subunit and in ATP2B3, encoding Ca²⁺ ATPase. Furthermore, the aberrant expression of gonadotropin-releasing hormone receptor is associated with the overexpression of CYP11B2 and overproduction of aldosterone in APA with activating mutations in CTNNB1 encoding β-catenin. On the other hand, CYP11B2 also catalyzes the conversion of cortisol to 18-hydroxycortisol and subsequently converts 18-hydroxycortisol to 18-oxocortisol. The recent studies have identified 18-oxocortisol as an important and distinct biomarker to diagnose primary aldosteronism. In this review, we summarize the recent findings on CYP11B2 and discuss the molecular pathogenesis of APA and the clinical significance of CYP11B2.

Salt-dependent Blood Pressure in Human Aldosterone Synthase-Transgenic Mice

Hypertension is one of the most important, preventable causes of premature morbidity and mortality in the developed world. Aldosterone is a major mineralocorticoid hormone that plays a key role in the regulation of blood pressure and is implicated in the pathogenesis of hypertension and heart failure. Aldosterone synthase (AS, cytochrome P450 11B2, cyp11B2) is the sole enzyme responsible for the production of aldosterone in humans. To determine the effects of increased expression of human aldosterone synthase (hAS) on blood pressure (BP), we established transgenic mice carrying the hAS gene (cyp11B2). We showed that hAS overexpression increased levels of aldosterone in hAS^+/- mice. On high salt diet (HS), BPs of hAS^+/- mice were significantly increased compared with WT mice. Fadrozole (an inhibitor of aldosterone synthase) treatment significantly reduced BPs of hAS^+/- mice on HS. This is the first time overexpression of AS in a transgenic mouse line has shown an ability to induce HP. Specifically inhibiting AS activity in these mice is a promising therapy for reducing hypertension. This hAS transgenic mouse model is therefore an ideal animal model for hypertension therapy studies.

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.

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.

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.

Stimulation of orphan nuclear receptor HR38 gene expression by PTTH in prothoracic glands of the silkworm, Bombyx mori

A complex signaling network appears to be involved in prothoracicotropic hormone (PTTH)-stimulated ecdysteroidogenesis in insect prothoracic glands (PGs). Less is known about the genomic action of PTTH signaling. In the present study, we investigated the effect of PTTH on the expression of Bombyx mori HR38, an immediate early gene (IEG) identified in insect systems. Our results showed that treatment of B. mori PGs with PTTH in vitro resulted in a rapid increase in HR38 expression. Injection of PTTH into day-5 last instar larvae also greatly increased HR38 expression, verifying the in vitro effect. Cycloheximide did not affect induction of HR38 expression, suggesting that protein synthesis is not required for PTTH's effect. A mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitor (U0126), and a phosphoinositide 3-kinase (PI3K) inhibitor (LY294002), partially inhibited PTTH-stimulated HR38 expression, implying the involvement of both the ERK and PI3K signaling pathways. When PGs were treated with agents that directly elevate the intracellular Ca(2+) concentration (either A23187 or thapsigargin), an increase in HR38 expression was also detected, indicating that Ca(2+) is involved in PTTH-stimulated HR38 gene expression. A Western blot analysis showed that PTTH treatment increased the HR38 protein level, and protein levels showed a dramatic increase during the later stages of the last larval instar. Expression of HR38 transcription in response to PTTH appeared to undergo development-specific changes. Treatment with ecdysone in vitro did not affect HR38 expression. However, 20-hydroxyecdysone treatment decreased HR38 expression. Taken together, these results demonstrate that HR38 is a PTTH-stimulated IEG that is, at least in part, induced through Ca(2+)/ERK and PI3K signaling. The present study proposes a potential cross talk mechanism between PTTH and ecdysone signaling to regulate insect development and lays a foundation for a better understanding of the mechanisms of PTTH's actions.

Functional Zonation of the Adult Mammalian Adrenal Cortex

The standard model of adrenocortical zonation holds that the three main zones, glomerulosa, fasciculata, and reticularis each have a distinct function, producing mineralocorticoids (in fact just aldosterone), glucocorticoids, and androgens respectively. Moreover, each zone has its specific mechanism of regulation, though ACTH has actions throughout. Finally, the cells of the cortex originate from a stem cell population in the outer cortex or capsule, and migrate centripetally, changing their phenotype as they progress through the zones. Recent progress in understanding the development of the gland and the distribution of steroidogenic enzymes, trophic hormone receptors, and other factors suggests that this model needs refinement. Firstly, proliferation can take place throughout the gland, and although the stem cells are certainly located in the periphery, zonal replenishment can take place within zones. Perhaps more importantly, neither the distribution of enzymes nor receptors suggest that the individual zones are necessarily autonomous in their production of steroid. This is particularly true of the glomerulosa, which does not seem to have the full suite of enzymes required for aldosterone biosynthesis. Nor, in the rat anyway, does it express MC2R to account for the response of aldosterone to ACTH. It is known that in development, recruitment of stem cells is stimulated by signals from within the glomerulosa. Furthermore, throughout the cortex local regulatory factors, including cytokines, catecholamines and the tissue renin-angiotensin system, modify and refine the effects of the systemic trophic factors. In these and other ways it more and more appears that the functions of the gland should be viewed as an integrated whole, greater than the sum of its component parts.

Expression of steroidogenic enzymes and their transcription factors in cortisol-producing adrenocortical adenomas: immunohistochemical analysis and quantitative real-time polymerase chain reaction studies

Adrenal Cushing syndrome (CS) is caused by the overproduction of cortisol in adrenocortical tumors including adrenal cortisol-producing adenoma (CPA). In CS, steroidogenic enzymes such as 17α-hydroxylase/17, 20-lase (CYP17A1), 3β-hydroxysteroid dehydrogenase (HSD3B), and 11β-hydroxylase (CYP11B1) are abundantly expressed in tumor cells. In addition, several transcriptional factors have been reported to play pivotal roles in the regulation of these enzymes in CPA, but their correlations with those enzymes above have still remained largely unknown. Therefore, in this study, we examined the status of steroidogenic enzymes and their transcriptional factors in 78 and 15 CPA cases by using immunohistochemistry and quantitative real-time polymerase chain reaction (qPCR), respectively. Immunoreactivity of HSD3B2, CYP11B1, CYP17A1, steroidogenic factor-1 (SF1[NR5A1]), GATA6, and nerve growth factor induced-B (NGFIB[NR4A1]) was detected in tumor cells. Results of qPCR analysis revealed that expression of HSD3B2 mRNA was significantly higher than that of HSD3B1, and CYP11B1 mRNA was significantly higher than CYP11B2. In addition, the expression of CYP11B1 mRNA was positively correlated with those of NR5A1, GATA6, and NR4A1. These results all indicated that HSD3B2 but not HSD3B1 was mainly involved in cortisol overproduction in CPA. In addition, NR5A1, GATA6, and NR4A1 were all considered to play important roles in cortisol overproduction through regulating CYP11B1 gene transcription.

Genomic and proteomic analysis of the inhibition of synthesis and secretion of aldosterone hormone induced by quinocetone in NCI-H295R cells

Quinoxaline 1,4-dioxides (QdNOs) are widely used as a kind of antibacterial growth promoter in animal husbandry. The adrenal cortex was found to be one of the main toxic targets of QdNOs, accompanied by a decreased aldosterone level. However, the way in which QdNOs decrease production of the hormone aldosterone is far from clear. To illustrate the mechanism by which QdNOs damage the adrenal cortex and decrease aldosterone hormone levels, the QdNOs were screened to choose the drug with most toxic effects on aldosterone production, and then to reveal the mechanism between the gene and protein profiles in human adrenocortical cells (NCI-H295R cells). The results found that quinocetone (QCT) showed the highest adrenal toxic effect among QdNOs. After exposing H295R cells to 10 and 20μM QCT for 24h, compared with blank cells, the gene and protein expression profiles obtained were analyzed by microarray and MALDI TOF/TOF mass spectrometry, respectively. The results of microarray analysis suggested that ABCG1 and SREBF1, which were involved in the cholesterol biosynthetic and metabolic processes, and CYP17A1, NR4A2 and G6PD, which were related to aldosterone biosynthesis, were important molecular targets. It has been speculated that PKC and ERK pathways might be involved in the reduction of aldosterone production caused by QCT, through enhanced mRNA expression of CYP17A1. Additionally, JNK and p38MAPK signal transduction pathways might participate in apoptosis induced by QCT. Twenty-nine and 32 protein spots were successfully identified when cells were treated with 10 and 20μM QCT, respectively. These identified proteins mainly included material synthesis and energy metabolism-related proteins, transcription/translation processing-related proteins, signal transduction proteins, cytoskeletal proteins, molecular chaperones, proteins related to response to stress, and transport proteins. Further investigations suggested that oxidative stress caused by QCT was exacerbated through disruption of the Keap1/Nrf2/ARE anti-oxidative stress pathway. Taken together, the data demonstrated for the first time that the Keap1/Nrf2/ARE pathway plays a crucial role in adrenal toxicity, and that CYP17A1 was the key switch to reduce the aldosterone production induced by QCT. Furthermore, large numbers of genes and proteins and entry points for research in the inhibition of aldosterone synthesis induced by QCT were offered, which will provide new insight into the adrenal toxicity of QdNOs and help to provide a theoretical foundation for the formulation of safety controls for products obtained from animals and to design new QdNOs with less harmful effects.

Local Control of Aldosterone Production and Primary Aldosteronism

Primary aldosteronism (PA) is caused by excessive production of aldosterone by the adrenal cortex and is determined by a benign aldosterone-producing adenoma (APA) in a significant proportion of cases. Local mechanisms, as opposed to circulatory ones, that control aldosterone production in the adrenal cortex are particularly relevant in the physiopathological setting and in the pathogenesis of PA. A breakthrough in our understanding of the pathogenetic mechanisms in APA has been the identification of somatic mutations in genes controlling membrane potential and intracellular calcium concentrations. However, recent data show that the processes of nodule formation and aldosterone hypersecretion can be dissociated in pathological adrenals and suggest a model envisaging different molecular events for the pathogenesis of APA.

Signaling Interactions in the Adrenal Cortex

The major physiological stimuli of aldosterone secretion are angiotensin II (AII) and extracellular K(+), whereas cortisol production is primarily regulated by corticotropin (ACTH) in fasciculata cells. AII triggers Ca(2+) release from internal stores that is followed by store-operated and voltage-dependent Ca(2+) entry, whereas K(+)-evoked depolarization activates voltage-dependent Ca(2+) channels. ACTH acts primarily through the formation of cAMP and subsequent protein phosphorylation by protein kinase A. Both Ca(2+) and cAMP facilitate the transfer of cholesterol to mitochondrial inner membrane. The cytosolic Ca(2+) signal is transferred into the mitochondrial matrix and enhances pyridine nucleotide reduction. Increased formation of NADH results in increased ATP production, whereas that of NADPH supports steroid production. In reality, the control of adrenocortical function is a lot more sophisticated with second messengers crosstalking and mutually modifying each other's pathways. Cytosolic Ca(2+) and cGMP are both capable of modifying cAMP metabolism, while cAMP may enhance Ca(2+) release and voltage-activated Ca(2+) channel activity. Besides, mitochondrial Ca(2+) signal brings about cAMP formation within the organelle and this further enhances aldosterone production. Maintained aldosterone and cortisol secretion are optimized by the concurrent actions of Ca(2+) and cAMP, as exemplified by the apparent synergism of Ca(2+) influx (inducing cAMP formation) and Ca(2+) release during response to AII. Thus, cross-actions of parallel signal transducing pathways are not mere intracellular curiosities but rather substantial phenomena, which fine-tune the biological response. Our review focuses on these functionally relevant interactions between the Ca(2+) and the cyclic nucleotide signal transducing pathways hitherto described in the adrenal cortex.

Osthole, a coumadin analog from Cnidium monnieri (L.) Cusson, stimulates corticosterone secretion by increasing steroidogenic enzyme expression in mouse Y1 adrenocortical tumor cells

ETHNOPHARMACOLOGICAL RELEVANCE

Osthole is an O-methylated coumadin, which was isolated and purified from the seeds of Cnidium monnieri (L.) Cusson. Osthole is a commonly used traditional Chinese medicine to treat patients with Kidney-Yang deficiency patients, who exhibit clinical signs similar to those of glucocorticoid withdrawal. However, the mechanism of action of osthole is not fully understood.

OBJECTIVE

This study was designed to reveal the effects of osthole on corticosterone production in mouse Y1 cell.

MATERIALS AND METHODS

Mouse Y1 adrenocortical cells were used to evaluate corticosterone production, which was quantified by enzyme-linked immunosorbent assay (ELISA) kits. Cell viability was tested using the MTT assay, and the mRNA and protein expression of genes encoding steroidogenic enzymes and transcription factors was monitored by quantitative real-time reverse-transcription polymerase chain reaction (qRT-PCR) and western blotting, respectively.

RESULTS

Osthole stimulated corticosterone secretion from mouse Y1 cells in a dose- and time-dependent manner, and osthole enhanced the effect of dibutyryl-cAMP (Bu2cAMP) on corticosterone production. Further, osthole also increased StAR and CYP11B1 mRNA expression in a dose-dependent manner and enhanced the expression of transcription factors such as HSD3B1, FDX1, POR and RXRα as well as immediate early genes such as NR4A1. Moreover, osthole significantly increased SCARB1(SRB1) mRNA and StAR protein expression in the presence or absence of Bu2cAMP; these proteins are an important for the transport of the corticosteroid precursor cholesterol transport into mitochondria.

CONCLUSIONS

Our results show that the promotion of corticosterone biosynthesis and secretion is a novel effect of osthole, suggesting that this agent can be utilized for the prevention and treatment of Kidney-Yang deficiency syndrome.

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.

p54nrb/NONO regulates cyclic AMP-dependent glucocorticoid production by modulating phosphodiesterase mRNA splicing and degradation

Glucocorticoid production in the adrenal cortex is activated in response to an increase in cyclic AMP (cAMP) signaling. The nuclear protein p54(nrb)/NONO belongs to the Drosophila behavior/human splicing (DBHS) family and has been implicated in several nuclear processes, including transcription, splicing, and RNA export. We previously identified p54(nrb)/NONO as a component of a protein complex that regulates the transcription of CYP17A1, a gene required for glucocorticoid production. Based on the multiple mechanisms by which p54(nrb)/NONO has been shown to control gene expression and the ability of the protein to be recruited to the CYP17A1 promoter, we sought to further define the molecular mechanism by which p54(nrb)/NONO confers optimal cortisol production. We show here that silencing p54(nrb)/NONO expression in H295R human adrenocortical cells decreases the ability of the cells to increase intracellular cAMP production and subsequent cortisol biosynthesis in response to adrenocorticotropin hormone (ACTH) stimulation. Interestingly, the expression of multiple phosphodiesterase (PDE) isoforms, including PDE2A, PDE3A, PDE3B, PDE4A, PDE4D, and PDE11A, was induced in p54(nrb)/NONO knockdown cells. Investigation of the mechanism by which silencing of p54(nrb)/NONO led to increased expression of select PDE isoforms revealed that p54(nrb)/NONO regulates the splicing of a subset of PDE isoforms. Importantly, we also identify a role for p54(nrb)/NONO in regulating the stability of PDE transcripts by facilitating the interaction between the exoribonuclease XRN2 and select PDE transcripts. In summary, we report that p54(nrb)/NONO modulates cAMP-dependent signaling, and ultimately cAMP-stimulated glucocorticoid biosynthesis by regulating the splicing and degradation of PDE transcripts.

Stimulus-selective induction of the orphan nuclear receptor NGFIB underlies different influences of angiotensin II and potassium on the human adrenal gland zona glomerulosa-specific 3β-HSD isoform gene expression in adrenocortical H295R cells

In the adrenal, the type I 3β-hydroxysteroid dehydrogenase (HSD3B1) is expressed exclusively in the zona glomerulosa (ZG), where aldosterone is produced. Angiotensin II (AngII) and potassium (K(+)) are the major physiological regulators of aldosterone synthesis. However, their respective roles in regulation of aldosterone synthesis are not fully defined, particularly in terms of transcriptional regulation of steroidogenic enzyme genes. We previously showed that AngII can stimulate expression of HSD3B1. But, K(+) responsiveness of this gene has remained unexplored. Here, we report that K(+) stimulation lacks the ability to induce HSD3B1 expression in human adrenocortical H295R cells. Both AngII and K(+) were able to enhance transcription of the aldosterone synthase gene (CYP11B2). Promoter analysis revealed that although both AngII and K(+) activate transcription from the Ca(2+)/cAMP-responsive element (CRE) located in the CYP11B2 promoter, the orphan nuclear receptor NGFIB-responsive element (NBRE) located in the HSD3B1 promoter fails to respond to K(+), being only able to enhance transcription after AngII treatment. We found that induction of de novo protein synthesis of NGFIB occurs only after AngII treatment. This sharply contrasts with the phosphorylation that occurs in response to both AngII and K(+) on the CREB/ATF family transcription factor ATF2. Chromatin immunoprecipitation assay confirmed that the NGFIB protein occupies the HSD3B1 promoter only after AngII, while ATF2 binds to the CYP11B2 promoter in response to both AngII and K(+). These data provide evidence that downstream signals from AngII and K(+) can be uncoupled in the regulation of HSD3B1 in the human adrenocortical H295R cells.

Genome-wide identification of nuclear receptor (NR) superfamily genes in the copepod Tigriopus japonicus

Background

Nuclear receptors (NRs) are a large superfamily of proteins defined by a DNA-binding domain (DBD) and a ligand-binding domain (LBD). They function as transcriptional regulators to control expression of genes involved in development, homeostasis, and metabolism. The number of NRs differs from species to species, because of gene duplications and/or lineage-specific gene losses during metazoan evolution. Many NRs in arthropods interact with the ecdysteroid hormone and are involved in ecdysone-mediated signaling in arthropods. The nuclear receptor superfamily complement has been reported in several arthropods, including crustaceans, but not in copepods. We identified the entire NR repertoire of the copepod Tigriopus japonicus, which is an important marine model species for ecotoxicology and environmental genomics.

Results

Using whole genome and transcriptome sequences, we identified a total of 31 nuclear receptors in the genome of T. japonicus. Nomenclature of the nuclear receptors was determined based on the sequence similarities of the DNA-binding domain (DBD) and ligand-binding domain (LBD). The 7 subfamilies of NRs separate into five major clades (subfamilies NR1, NR2, NR3, NR4, and NR5/6). Although the repertoire of NR members in, T. japonicus was similar to that reported for other arthropods, there was an expansion of the NR1 subfamily in Tigriopus japonicus. The twelve unique nuclear receptors identified in T. japonicus are members of NR1L. This expansion may be a unique lineage-specific feature of crustaceans. Interestingly, E78 and HR83, which are present in other arthropods, were absent from the genomes of T. japonicus and two congeneric copepod species (T. japonicus and Tigriopus californicus), suggesting copepod lineage-specific gene loss.

Conclusions

We identified all NR receptors present in the copepod, T. japonicus. Knowledge of the copepod nuclear receptor repertoire will contribute to a better understanding of copepod- and crustacean-specific NR evolution.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-993) contains supplementary material, which is available to authorized users.