Angiotensin II regulation of adrenocortical gene transcription

Changes in nonfunctional adrenal incidentaloma after COVID-19 infection and a model for predicting benign and malignant adrenal incidentaloma

Aims

To compare nonfunctional adrenal incidentalomas (NFAI) in individuals with and without a history of COVID-19 infection, while also establishing predictive models for distinguishing between benign and malignant adrenal incidentalomas (AI).

Methods

A retrospective collection of data from patients with AI who underwent surgery and were verified in our hospital between April 2022 and June 2023 was conducted. A total of 121 patients were included in the study. Demographic information, tumor characteristics, functional indicators, and complications were compared among the patients. Statistical analyses utilized the t-test for continuous variables and Pearson chi-square test or Fisher's exact test for categorical variables.

Results

Patients with COVID-19 exhibited a higher prevalence of obesity (84.2% vs. 63.3%, P=0.048) and elevated direct bilirubin (DBIL) levels (44.1% vs. 19.2%, P=0.043) compared to those without COVID-19. Moreover, patients with Malignant AI, in contrast to Benign AI, showed higher normal total protein (TP) levels (28.8% vs. 57.1%, P=0.016) and larger tumor sizes (20 vs. 32.5mm, P=0.009). Univariate analysis identified low TP (OR=0.303, 95% CI=0.111-0.825, P=0.020) and tumor size (OR=1.045, 95% CI=1.011-1.080, P=0.009) as potential risk factors for multivariate analysis. A predictive model comprising clinical risk factors (tumor size and low TP) demonstrated an AUC of 0.754 (95% CI, 0.603-0.904) with a sensitivity of 0.75 and specificity of 0.775. The calibration curve revealed a bias-corrected AUC of 0.77.

Conclusion

No discernible differences in the clinical manifestations of adrenal incidentalomas were observed between cases with and without a history of COVID-19 infection. However, AI with larger tumor diameters and lower than normal levels of total protein exhibited a more pronounced malignant potential.

Perfluorotetradecanoic acid exposure to adult male rats stimulates corticosterone biosynthesis but inhibits aldosterone production

Perfluorotetradecanoic acid (PFTeDA) is a novel perfluoroalkyl substance that ubiquitously exists in the environment. However, whether PFTeDA affects adrenal cortex function remains unclear. Male Sprague-Dawley rats (age of 60 days) were daily administered with PFTeDA (0, 1, 5, and 10 mg/kg body weight) through gavage for 28 days. PFTeDA did not change body and adrenal gland weights. PFTeDA markedly elevated serum corticosterone level at 10 mg/kg but lowering serum aldosterone level at this dosage without influencing serum adrenocorticotropic hormone level. PFTeDA thickened zona fasciculata without affecting zona glomerulosa. PFTeDA remarkably upregulated the expression of corticosterone biosynthetic genes (Mc2r, Scarb1, Star, Cyp21, Cyp11b1, and Hsd11b1) and their proteins, whereas downregulating aldosterone biosynthetic enzyme Cyp11b2 and its protein, thereby distinctly altering their serum levels. PFTeDA markedly downregulated the expression of antioxidant genes (Sod1 and Sod2) and their proteins at 10 mg/kg. PFTeDA significantly decreased SIRT1/PGC1α and AMPK signaling while stimulating AKT1/mTOR signaling. Corticosterone significantly inhibited testosterone production by adult Leydig cells at >0.1 μM in vitro; however aldosterone significantly stimulated testosterone production at 0.1 nM. In conclusion, exposure to PFTeDA at male rat adulthood causes corticosterone excess and aldosterone deficiency via SIRT1/PGC1α, AMPK, and AKT1/mTOR signals, which in turn additively leads to testosterone deficiency.

Double somatic mutations in CTNNB1 and GNA11 in an aldosterone-producing adenoma

Double somatic mutations in CTNNB1 and GNA11/Q have recently been identified in a small subset of aldosterone-producing adenomas (APAs). As a possible pathogenesis of APA due to these mutations, an association with pregnancy, menopause, or puberty has been proposed. However, because of its rarity, characteristics of APA with these mutations have not been well characterized. A 46-year-old Japanese woman presented with hypertension and hypokalemia. She had two pregnancies in the past but had no history of pregnancy-induced hypertension. She had regular menstrual cycle at presentation and was diagnosed as having primary aldosteronism after endocrinologic examinations. Computed tomography revealed a 2 cm right adrenal mass. Adrenal venous sampling demonstrated excess aldosterone production from the right adrenal gland. She underwent right laparoscopic adrenalectomy. The resected right adrenal tumor was histologically diagnosed as adrenocortical adenoma and subsequent immunohistochemistry (IHC) revealed diffuse immunoreactivity of aldosterone synthase (CYP11B2) and visinin like 1, a marker of the zona glomerulosa (ZG), whereas 11β-hydroxylase, a steroidogenic enzyme for cortisol biosynthesis, was mostly negative. CYP11B2 IHC-guided targeted next-generation sequencing identified somatic CTNNB1 (p.D32Y) and GNA11 (p.Q209H) mutations. Immunofluorescence staining of the tumor also revealed the presence of activated β-catenin, consistent with features of the normal ZG. The expression patterns of steroidogenic enzymes and related proteins indicated ZG features of the tumor cells. PA was clinically and biochemically cured after surgery. In conclusion, our study indicated that CTNNB1 and GNA11-mutated APA has characteristics of the ZG. The disease could occur in adults with no clear association with pregnancy or menopause.

MicroRNA-19 is regulated by aldosterone in a sex-specific manner to alter kidney sodium transport

A key regulator of blood pressure homeostasis is the steroid hormone aldosterone, which is released as the final signaling hormone of the renin-angiotensin-aldosterone-signaling (RAAS) system. Aldosterone increases sodium (Na+) reabsorption in the kidney distal nephron to regulate blood volume. Unregulated RAAS signaling can lead to hypertension and cardiovascular disease. The serum and glucocorticoid kinase (SGK1) coordinates much of the Na+ reabsorption in the cortical collecting duct (CCD) tubular epithelial cells. We previously demonstrated that aldosterone alters the expression of microRNAs (miRs) in CCD principal cells. The aldosterone-regulated miRs can modulate Na+ transport and the cellular response to aldosterone signaling. However, the sex-specific regulation of miRs by aldosterone in the kidney distal nephron has not been explored. In this study, we report that miR-19, part of the miR-17-92 cluster, is upregulated in female mouse CCD cells in response to aldosterone activation. Mir-19 binding to the 3'-untranslated region of SGK1 was confirmed using a dual-luciferase reporter assay. Increasing miR-19 expression in CCD cells decreased SGK1 message and protein expression. Removal of this cluster using a nephron-specific, inducible knockout mouse model increased SGK1 expression in female mouse CCD cells. The miR-19-induced decrease in SGK1 protein expression reduced the response to aldosterone stimulation and may account for sex-specific differences in aldosterone signaling. By examining evolution of the miR-17-92 cluster, phylogenetic sequence analysis indicated that this cluster arose at the same time that other Na+-sparing and salt regulatory proteins, specifically SGK1, first emerged, indicating a conserved role for these miRs in kidney function of salt and water homeostasis.NEW & NOTEWORTHY Expression of the microRNA-17-92 cluster is upregulated by aldosterone in mouse cortical collecting duct principal cells, exclusively in female mice. MiR-19 in this cluster targets the serum and glucocorticoid kinase (SGK1) to downregulate both mRNA and protein expression, resulting in a decrease in sodium transport across epithelial cells of the collecting duct. The miR-17-92 cluster is evolutionarily conserved and may act as a novel feedback regulator for aldosterone signaling in females.

MicroRNA regulation of adrenal glucocorticoid and androgen biosynthesis

Steroid hormones are derived from a common precursor molecule, cholesterol, and regulate a wide range of physiologic function including reproduction, salt balance, maintenance of secondary sexual characteristics, response to stress, neuronal function, and various metabolic processes. Among the steroids synthesized by the adrenal and gonadal tissues, adrenal mineralocorticoids, and glucocorticoids are essential for life. The process of steroidogenesis is regulated at multiple levels largely by transcriptional, posttranscriptional, translational, and posttranslational regulation of the steroidogenic enzymes (i.e., cytochrome P450s and hydroxysteroid dehydrogenases), cellular compartmentalization of the steroidogenic enzymes, and cholesterol processing and transport proteins. In recent years, small noncoding RNAs, termed microRNAs (miRNAs) have been recognized as major post-transcriptional regulators of gene expression with essential roles in numerous biological processes and disease pathologies. Although their role in the regulation of steroidogenesis is still emerging, several recent studies have contributed significantly to our understanding of the role miRNAs play in the regulation of the steroidogenic process. This chapter focuses on the recent developments in miRNA regulation of adrenal glucocorticoid and androgen production in humans and rodents.

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.

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.

Mineralocorticoid Receptor Antagonists Eplerenone and Spironolactone Modify Adrenal Cortex Morphology and Physiology

Mineralocorticoid receptor antagonists (MRAs) are a class of anti-hypertensive drugs that act by blocking aldosterone action. The aim of this study was to evaluate whether the MRAs spironolactone and eplerenone influence adrenal cortical physiology and morphology. Spontaneous hypertensive rats (SHR, n = 18) and normotensive rats (WKY, n = 18) were randomly exposed to a daily dose of spironolactone (n = 6), eplerenone (n = 6), or no drug (n = 6) over 28 days. After that, aldosterone, corticosterone, and 11-deoxycorticosterone plasma concentrations were quantified. Adrenal glands were subjected to morphological analysis to assess lipid droplets content, capsular width, cell proliferation, and steroidogenic proteins expression. The adrenal cortex in untreated SHR showed higher lipid droplet content as than in WKY. In SHR, MRA treatment was associated with higher circulating aldosterone levels and Ki-67 expression in aldosterone-secreting cells. In WKY, the only difference observed after MRA spironolactone treatment was a narrower capsule. There was no difference in abundance of steroidogenic enzyme between groups. In conclusion, MRAs modify adrenal gland function and morphology in SHR. The effects observed within the adrenal glomerulosa with aldosterone-secreting cell proliferation and higher circulating aldosterone levels suggests that MRA treatment provokes activation of the renin angiotensin system. The prognostic value of hyperaldosteronism secondary to MRAs blockade requires further investigation.

Non-coding RNAs and the mineralocorticoid receptor in the kidney

The final steps in the Renin-Angiotensin-Aldosterone signaling System (RAAS) involve binding of the corticosteroid hormone, aldosterone to its mineralocorticoid receptor (MR). The bound MR interacts with response elements to induce or repress the transcription of aldosterone-regulated genes. Along with the classic genomic targets of aldosterone that alter mRNA and protein expression, aldosterone also regulates the expression of non-coding RNAs (ncRNAs). Short ncRNAs termed microRNAs (miRs) have been shown to play a role in transducing aldosterone's actions via MR signaling. The role of miRs in homeostatic regulation of aldosterone signaling, and the potential for aldosterone-regulated miRs to act as feedback regulators of MR have been recently reported. In this review, the role of miRs in RAAS signaling and feedback regulation of MR in kidney epithelial cells will be discussed.

Aldosterone-induced microRNAs act as feedback regulators of mineralocorticoid receptor signaling in kidney epithelia

The final steps in the Renin-Angiotensin-Aldosterone signaling System (RAAS) involve binding of the corticosteroid hormone, aldosterone to its mineralocorticoid receptor (MR). The bound MR interacts with response elements to induce or repress the transcription of aldosterone-regulated genes. A well characterized aldosterone-induced gene is the serum and glucocorticoid-induced kinase (SGK1), which acts downstream to increase sodium transport in distal kidney nephron epithelial cells. The role of microRNAs (miRs) induced by extended aldosterone stimulation in regulating MR and SGK1 has not been reported. In these studies, miRs predicted to bind to the 3'-UTR of mouse MR were profiled by qRT-PCR after aldosterone stimulation. The miR-466a/b/c/e family was upregulated in mouse kidney cortical collecting duct epithelial cells. A luciferase reporter assay confirmed miR-466 binding to both MR and SGK1 3'-UTRs. Inhibition of miR-466 increased MR and SGK1 mRNA and protein levels. Inhibiting miR-466b and preventing its upregulation after aldosterone stimulation increased amiloride-sensitive sodium transport and sensitivity to aldosterone stimulation. In vivo upregulation of miR-466 was confirmed in distal nephrons of mice on low Na+ diets. Repression of MR and SGK1 by aldosterone-induced miRs may represent a negative feedback loop that contributes to a form of aldosterone escape in vivo.

Steroid biomarkers in human adrenal disease

Adrenal steroidogenesis is a robust process, involving a series of enzymatic reactions that facilitate conversion of cholesterol into biologically active steroid hormones under the stimulation of angiotensin II, adrenocorticotropic hormone and other regulators. The biosynthesis of mineralocorticoids, glucocorticoids, and adrenal-derived androgens occur in separate adrenocortical zones as a result of the segregated expression of steroidogenic enzymes and cofactors. This mini review provides the principles of adrenal steroidogenesis, including the classic and under-appreciated 11-oxygenated androgen pathways. Several adrenal diseases result from dysregulated adrenal steroid synthesis. Herein, we review growing evidence that adrenal diseases exhibit characteristic modifications from normal adrenal steroid pathways that provide opportunities for the discovery of biomarker steroids that would improve diagnosis and monitoring of adrenal disorders.

Angiotensin II Signal Transduction: An Update on Mechanisms of Physiology and Pathophysiology

The renin-angiotensin-aldosterone system plays crucial roles in cardiovascular physiology and pathophysiology. However, many of the signaling mechanisms have been unclear. The angiotensin II (ANG II) type 1 receptor (AT₁R) is believed to mediate most functions of ANG II in the system. AT₁R utilizes various signal transduction cascades causing hypertension, cardiovascular remodeling, and end organ damage. Moreover, functional cross-talk between AT₁R signaling pathways and other signaling pathways have been recognized. Accumulating evidence reveals the complexity of ANG II signal transduction in pathophysiology of the vasculature, heart, kidney, and brain, as well as several pathophysiological features, including inflammation, metabolic dysfunction, and aging. In this review, we provide a comprehensive update of the ANG II receptor signaling events and their functional significances for potential translation into therapeutic strategies. AT₁R remains central to the system in mediating physiological and pathophysiological functions of ANG II, and participation of specific signaling pathways becomes much clearer. There are still certain limitations and many controversies, and several noteworthy new concepts require further support. However, it is expected that rigorous translational research of the ANG II signaling pathways including those in large animals and humans will contribute to establishing effective new therapies against various diseases.

Isolation and characterization of adrenocortical progenitors involved in the adaptation to stress

Humans are constantly confronted with multiple stressors, to which the bodily response and adaptation are essential. The adrenal gland plays a major role in the response to physiological challenges. Maintenance of the adrenal is partly accomplished by proliferation and differentiation of adult progenitors and stem cells in the cortex and medulla. In this study, we have isolated and characterized a subpopulation of adrenocortical progenitors, which are interconnected with adrenomedullary stress-dependent progenitors. Under stress, the adrenocortical progenitors are also activated and they mobilize, giving rise to steroidogenic cells. Our findings demonstrate the coordinated action of stress-inducible stem cells to ensure tissue remodeling and cellular and functional adaptation to stress.

The adrenal gland is a master regulator of the human body during response to stress. This organ shows constant replacement of senescent cells by newly differentiated cells. A high degree of plasticity is critical to sustain homeostasis under different physiological demands. This is achieved in part through proliferation and differentiation of adult adrenal progenitors. Here, we report the isolation and characterization of a Nestin⁺ population of adrenocortical progenitors located under the adrenal capsule and scattered throughout the cortex. These cells are interconnected with progenitors in the medulla. In vivo lineage tracing revealed that, under basal conditions, this population is noncommitted and slowly migrates centripetally. Under stress, this migration is greatly enhanced, and the cells differentiate into steroidogenic cells. Nestin⁺ cells cultured in vitro also show multipotency, as they differentiate into mineralocorticoid and glucocorticoid-producing cells, which can be further influenced by the exposure to Angiotensin II, adrenocorticotropic hormone, and the agonist of luteinizing hormone-releasing hormone, triptorelin. Taken together, Nestin⁺ cells in the adult adrenal cortex exhibit the features of adrenocortical progenitor cells. Our study provides evidence for a role of Nestin⁺ cells in organ homeostasis and emphasizes their role under stress. This cell population might be a potential source of cell replacement for the treatment of adrenal insufficiency.

Current knowledge on the acute regulation of steroidogenesis

How rapid induction of steroid hormone biosynthesis occurs in response to trophic hormone stimulation of steroidogenic cells has been a subject of intensive investigation for approximately six decades. A key observation made very early was that acute regulation of steroid biosynthesis required swift and timely synthesis of a new protein whose role appeared to be involved in the delivery of the substrate for all steroid hormones, cholesterol, from the outer to the inner mitochondrial membrane where the process of steroidogenesis begins. It was quickly learned that this transfer of cholesterol to the inner mitochondrial membrane was the regulated and rate-limiting step in steroidogenesis. Following this observation, the quest for this putative regulator protein(s) began in earnest in the late 1950s. This review provides a history of this quest, the candidate proteins that arose over the years and facts surrounding their rise or decline. Only two have persisted-translocator protein (TSPO) and the steroidogenic acute regulatory protein (StAR). We present a detailed summary of the work that has been published for each of these two proteins, the specific data that has appeared in support of their role in cholesterol transport and steroidogenesis, and the ensuing observations that have arisen in recent years that have refuted the role of TSPO in this process. We believe that the only viable candidate that has been shown to be indispensable is the StAR protein. Lastly, we provide our view on what may be the most important questions concerning the acute regulation of steroidogenesis that need to be asked in future.

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.

Age-Related Autonomous Aldosteronism

BACKGROUND

Both aging and inappropriate secretion of aldosterone increase the risk for developing cardiovascular disease; however, the influence of aging on aldosterone secretion and physiology is not well understood.

METHODS

The relationship between age and adrenal aldosterone synthase (CYP11B2) expression was evaluated in 127 normal adrenal glands from deceased kidney donors (age, 9 months to 68 years). Following immunohistochemistry, CYP11B2-expressing area and areas of abnormal foci of CYP11B2-expressing cells, called aldosterone-producing cell clusters, were analyzed. In a separate ancillary clinical study of 677 participants without primary aldosteronism, who were studied on both high and restricted sodium diets (age, 18-71 years), we used multivariable linear regression to assess the independent associations between age and renin-angiotensin-aldosterone system physiology.

RESULTS

In adrenal tissue, the total CYP11B2-expressing area was negatively correlated with age (r=-0.431, P<0.0001), whereas the total aldosterone-producing cell cluster area was positively correlated with age (r=0.390, P<0.0001). The integrated ratio of aldosterone-producing cell cluster to CYP11B2-expressing area was most strongly and positively correlated with age (r=0.587, P<0.0001). When participants in the clinical study were maintained on a high sodium balance, renin activity progressively declined with older age, whereas serum and urinary aldosterone did not significantly decline. Correspondingly, the aldosterone-to-renin ratio was positively and independently associated with older age (adjusted β=+5.54 ng/dL per ng/mL per hour per 10 years, P<0.001). In contrast, when participants were assessed under sodium-restricted conditions, physiological stimulation of aldosterone was blunted with older age (β=-4.6 ng/dL per 10 years, P<0.0001).

CONCLUSIONS

Aging is associated with a pattern of decreased normal zona glomerulosa CYP11B2 expression and increased aldosterone-producing cell cluster expression. This histopathologic finding parallels an age-related autonomous aldosteronism and abnormal aldosterone physiology that provides 1 potential explanation for age-related cardiovascular risk.

Secretin is involved in sodium conservation through the renin-angiotensin-aldosterone system

Secretin (SCT) and its receptor (SCTR) are important in fluid regulation at multiple levels via the modulation of expression and translocation of renal aquaporin 2 and functions of central angiotensin II (ANGII). The functional interaction of SCT with peripheral ANGII, however, remains unknown. As the ANGII-aldosterone axis dominates the regulation of renal epithelial sodium channel (ENaC) function, we therefore tested whether SCT/SCTR can regulate sodium homeostasis via the renin-angiotensin-aldosterone system. SCTR-knockout (SCTR^-/-) mice showed impaired aldosterone synthase (CYP11B2) expression and, consequently, aldosterone release upon intraperitoneal injection of ANGII. Endogenous ANGII production induced by dietary sodium restriction was higher in SCTR^-/- than in C57BL/6N [wild-type (WT)] mice, but CYP11B2 and aldosterone synthesis were not elevated. Reduced accumulation of cholesteryl ester-the precursor of aldosterone-was observed in adrenal glands of SCTR^-/- mice that were fed a low-sodium diet. Absence of SCTR resulted in elevated basal transcript levels of adrenal CYP11B2 and renal ENaCs. Although transcript and protein levels of ENaCs were similar in WT and SCTR^-/- mice under sodium restriction, ENaCs in SCTR^-/- mice were less sensitive to amiloride hydrochloride. In summary, the SCT/SCTR axis is involved in aldosterone precursor uptake, and the knockout of SCTR results in defective aldosterone biosynthesis/release and altered sensitivity of ENaCs to amiloride.-Bai, J., Chow, B. K. C. Secretin is involved in sodium conservation through the renin-angiotensin-aldosterone system.

Secretin, at the hub of water-salt homeostasis

Water and salt metabolism are tightly regulated processes. Maintaining this milieu intérieur within narrow limits is critical for normal physiological processes to take place. Disturbances to this balance can result in disease and even death. Some of the better-characterized regulators of water and salt homeostasis include angiotensin II, aldosterone, arginine vasopressin, and oxytocin. Although secretin (SCT) was first described >100 years ago, little is known about the role of this classic gastrointestinal hormone in the maintenance of water-salt homeostasis. In recent years, increasing body of evidence suggested that SCT and its receptor play important roles in the central nervous system and kidney to ensure that the mammalian extracellular fluid osmolarity is kept within a healthy range. In this review, we focus on recent advances in our understanding of the molecular, cellular, and network mechanisms by which SCT and its receptor mediate the control of osmotic homeostasis. Implications of hormonal cross talk and receptor-receptor interaction are highlighted.

Gonadotropin-Releasing Hormone Stimulate Aldosterone Production in a Subset of Aldosterone-Producing Adenoma

We aimed to detect novel genes associated with G protein-coupled receptors (GPCRs) in aldosterone-producing adenoma (APA) and elucidate the mechanisms underlying aldosterone production.Microarray analysis targeting GPCR-associated genes was conducted using APA without known mutations (APA-WT) samples (n = 3) and APA with the KCNJ5 mutation (APA-KCNJ5; n = 3). Since gonadotropin-releasing hormone receptor (GNRHR) was the highest expression in APA-WT by microarray analysis, we investigated the effect of gonadotropin-releasing hormone (GnRH) stimulation on aldosterone production.The quantitative polymerase chain reaction assay results revealed higher GNRHR expression levels in APA-WT samples those in APA-KCNJ5 samples (P < 0.05). LHCGR levels were also significantly elevated in APA-WT samples, and there was a significant and positive correlation between GNRHR and LHCGR expression in all APA samples (r = 0.476, P < 0.05). Patients with APA-WT (n = 9), which showed higher GNRHR and LHCGR levels, had significantly higher GnRH-stimulated aldosterone response than those with APA-KCNJ5 (n = 13) (P < 0.05). Multiple regression analysis revealed that the presence of the KCNJ5 mutation was linked to GNRHR mRNA expression (β = 0.94 and P < 0.01). HAC15 cells with KCNJ5 gene carrying T158A mutation exhibited a significantly lower GNRHR expression than that in control cells (P < 0.05).We clarified increased expression of GNRHR and LHCGR in APA-WT, and the molecular analysis including the receptor expression associated with clinical findings of GnRH stimulation.

Disruption of steroidogenesis: Cell models for mechanistic investigations and as screening tools

In the modern world, humans are exposed during their whole life to a large number of synthetic chemicals. Some of these chemicals have the potential to disrupt endocrine functions and contribute to the development and/or progression of major diseases. Every year approximately 1000 novel chemicals, used in industrial production, agriculture, consumer products or as pharmaceuticals, are reaching the market, often with limited safety assessment regarding potential endocrine activities. Steroids are essential endocrine hormones, and the importance of the steroidogenesis pathway as a target for endocrine disrupting chemicals (EDCs) has been recognized by leading scientists and authorities. Cell lines have a prominent role in the initial stages of toxicity assessment, i.e. for mechanistic investigations and for the medium to high throughput analysis of chemicals for potential steroidogenesis disrupting activities. Nevertheless, the users have to be aware of the limitations of the existing cell models in order to apply them properly, and there is a great demand for improved cell-based testing systems and protocols. This review intends to provide an overview of the available cell lines for studying effects of chemicals on gonadal and adrenal steroidogenesis, their use and limitations, as well as the need for future improvements of cell-based testing systems and protocols.

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.

Gene and microRNA transcriptional signatures of angiotensin II in endothelial cells

Growth of atherosclerotic plaque requires neovascularization (angiogenesis). To elucidate the involvement of angiotensin II (Ang II) in angiogenesis, we performed gene microarray and microRNA (miRNA) polymerase chain reaction array analyses on human coronary artery endothelial cells exposed to moderate concentration of Ang II for 2 and 12 hours. At 12, but not 2, hours, cultures treated with Ang II exhibited shifts in transcriptional activity involving 267 genes (>1.5-fold difference; P < 0.05). Resulting transcriptome was most significantly enriched for genes associated with blood vessel development, angiogenesis, and regulation of proliferation. Majority of upregulated genes implicated in angiogenesis shared a commonality of being either regulators (HES1, IL-18, and CXCR4) or targets (ADM, ANPEP, HES1, KIT, NOTCH4, PGF, and SOX18) of STAT3. In line with these findings, STAT3 inhibition attenuated Ang II-dependent stimulation of tube formation in Matrigel assay. Expression analysis of miRNAs transcripts revealed that the pattern of differential expression for miRNAs was largely consistent with proangiogenic response with a prominent theme of upregulation of miRs targeting PTEN (miR-19b-3p, miR-21-5p, 23b-3p, and 24-3p), many of which are directly or indirectly STAT3 dependent. We conclude that STAT3 signaling may be an intrinsic part of Ang II-mediated proangiogenic response in human endothelial cells.

Interaction between Angiotensin II and Insulin/IGF-1 Exerted a Synergistic Stimulatory Effect on ERK1/2 Activation in Adrenocortical Carcinoma H295R Cells

The cross talk between angiotensin II (Ang II) and insulin has been described mainly in cardiovascular cells, hepatocytes, adipocytes, and so forth, and to date no such cross talk was reported in adrenal. In this study, we examined the interaction between Ang II and insulin/IGF-1 in ERK and AKT signaling pathways and expression of steroidogenic enzymes in H295R cells. Compared to the control, 100 nM Ang II increased phospho-ERK1/2 approximately 3-fold. Insulin (100 nM) or IGF-1 (10 nM) alone raised phospho-ERK1/2 1.8- and 1.5-fold, respectively, while, after pretreatment with 100 nM Ang II for 30 min, insulin (100 nM) or IGF-1 (10 nM) elevated phospho-ERK1/2 level 8- and 7-fold, respectively. The synergistic effect of Ang II and insulin/IGF-1 on ERK1/2 activation was inhibited by selective AT1 receptor blocker, PKC inhibitor, and MEK1/2 inhibitor. Ang II marginally suppressed AKT activation under the basal condition, while it had no effect on phospho-AKT induced by insulin/IGF-1. Ang II significantly stimulated mRNA expression of CYP11B1 and CYP11B2, and such stimulatory effects were enhanced when cells were cotreated with insulin/IGF-1. We are led to conclude that Ang II in combination with insulin/IGF-1 had an evident synergistic stimulatory effect on ERK1/2 activation in H295R cells and the effect may be responsible for the enhanced steroid hormone production induced by Ang II plus insulin/IGF-1.

Combined Use of Etomidate and Dexmedetomidine Produces an Additive Effect in Inhibiting the Secretion of Human Adrenocortical Hormones

Background

The direct effects of etomidate were investigated on the secretion of cortisol and its precursors by dispersed cells from the adrenal cortex of human of animals. Dexmedetomidine (DEX) is an anesthetic agent that may interfere with cortisol secretion via an unknown mechanism, such as involving inhibition of 11β-hydroxylase and the cholesterol side-chain cleavage enzyme system. The aim of this study was to determine whether dexmedetomidine (DEX) has a similar inhibitory effect on adrenocortical function, and whether combined use of etomidate (ETO) and DEX could produce a synergistic action in inhibiting the secretion of human adrenocortical hormones.

Material/Methods

Human adrenocortical cells were exposed to different concentrations of ETO and DEX. The dose-effect model between the ETO concentration and the mean secretion of cortisone (CORT) and aldosterone (ALDO) per hour was estimated.

Results

Hill’s equation well-described the dose-effect correlation between the ETO concentration and the amount of ALDO and CORT secretion. When the DEX concentration was introduced into the model by using E₀ (basal secretion) as the covariate, the goodness of fit of the ETO-CORT dose-effect model was improved significantly and the objective function value was reduced by 4.55 points (P<0.05). The parameters of the final ETO-ALDO pharmacodynamics model were EC₅₀=9.74, E_max=1.20, E₀=1.33, and γ=18.5; the parameters of the final ETO-CORT pharmacodynamics model were EC₅₀=9.49, E_max=8.16, E₀=8.57, and γ=37.0. In the presence of DEX, E₀ was 8.57–0.0247×(CDEX–4.6), and the other parameters remained unchanged. All parameters but γ were natural logarithm conversion values.

Conclusions

Combined use of DEX and ETO reduced ETO’s inhibitory E₀ (basal secretion) of CORT from human adrenocortical cells in a dose-dependent manner, suggesting that combined use of ETO and DEX produced an additive effect in inhibiting the secretion of human adrenocortical hormones.

Transcriptional network analysis reveals that AT1 and AT2 angiotensin II receptors are both involved in the regulation of genes essential for glioma progression

Gliomas are aggressive primary brain tumors with high infiltrative potential. The expression of Angiotensin II (Ang II) receptors has been associated with poor prognosis in human astrocytomas, the most common type of glioma. In this study, we investigated the role of Angiotensin II in glioma malignancy through transcriptional profiling and network analysis of cultured C6 rat glioma cells exposed to Ang II and to inhibitors of its membrane receptor subtypes. C6 cells were treated with Ang II and specific antagonists of AT1 and AT2 receptors. Total RNA was isolated after three and six hours of Ang II treatment and analyzed by oligonucleotide microarray technology. Gene expression data was evaluated through transcriptional network modeling to identify how differentially expressed (DE) genes are connected to each other. Moreover, other genes co-expressing with the DE genes were considered in these analyses in order to support the identification of enriched functions and pathways. A hub-based network analysis showed that the most connected nodes in Ang II-related networks exert functions associated with cell proliferation, migration and invasion, key aspects for glioma progression. The subsequent functional enrichment analysis of these central genes highlighted their participation in signaling pathways that are frequently deregulated in gliomas such as ErbB, MAPK and p53. Noteworthy, either AT1 or AT2 inhibitions were able to down-regulate different sets of hub genes involved in protumoral functions, suggesting that both Ang II receptors could be therapeutic targets for intervention in glioma. Taken together, our results point out multiple actions of Ang II in glioma pathogenesis and reveal the participation of both Ang II receptors in the regulation of genes relevant for glioma progression. This study is the first one to provide systems-level molecular data for better understanding the protumoral effects of Ang II in the proliferative and infiltrative behavior of gliomas.

Metallothionein-3 (MT-3) in the human adrenal cortex and its disorders

Metallothionein-3 (MT-3) is an intracellular, low molecular weight protein mainly distributed in the central nervous system but also in various peripheral organs and several types of human neoplasms. However, details of MT-3 expression have not been examined in human adrenal cortex and its disorders. The mRNA levels of MT-3 were first evaluated by quantitative RT-PCR (qPCR) in adrenocortical aldosterone-producing adenoma (APA: 11) and cortisol-producing adenoma (CPA: 14). In addition, MT-3 immunohistochemistry was performed in non-pathological adrenal glands (NA: 19), idiopathic hyperaldosteronism (IHA: 10), APA (20), CPA (24), adjacent non-neoplastic adrenal glands of adenoma (AAG: 20), and adrenocortical carcinoma (ACC: 8). H295R cells were also treated with angiotensin-II or forskolin in a time-dependent manner, and the changes of MT-3 mRNA levels were evaluated by qPCR. Results of qPCR analysis demonstrated that MT-3 mRNA levels were significantly higher in APA than CPA (P = 0.0004). MT-3 immunoreactivity was detected in the zona glomerulosa of NA, IHA, and AAG, as well as in APA, CPA, and ACC. When treated with angiotensin-II and forskolin, MT-3 mRNA levels reached a peak by 12 h in H295R cells, with significantly higher levels compared to control non-treated cells (P < 0.01). The presence of MT-3 in the ZG of NA, IHA, and AAG, as well as APA may imply a role in the pathophysiology of aldosterone-producing tissues.

Angiotensin II triggers expression of the adrenal gland zona glomerulosa-specific 3β-hydroxysteroid dehydrogenase isoenzyme through de novo protein synthesis of the orphan nuclear receptors NGFIB and NURR1

The 3β-hydroxysteroid dehydrogenase (3β-HSD) is an enzyme crucial for steroid synthesis. Two different 3β-HSD isoforms exist in humans. Classically, HSD3B2 was considered the principal isoform present in the adrenal. However, we recently showed that the alternative isoform, HSD3B1, is expressed specifically within the adrenal zona glomerulosa (ZG), where aldosterone is produced, raising the question of why this isozyme needs to be expressed in this cell type. Here we show that in both human and mouse, expression of the ZG isoform 3β-HSD is rapidly induced upon angiotensin II (AngII) stimulation. AngII is the key peptide hormone regulating the capacity of aldosterone synthesis. Using the human adrenocortical H295R cells as a model system, we show that the ZG isoform HSD3B1 differs from HSD3B2 in the ability to respond to AngII. Mechanistically, the induction of HSD3B1 involves de novo protein synthesis of the nuclear orphan receptors NGFIB and NURR1. The HSD3B1 promoter contains a functional NGFIB/NURR1-responsive element to which these proteins bind in response to AngII. Knockdown of these proteins and overexpression of a dominant negative NGFIB both reduce the AngII responsiveness of HSD3B1. Thus, the AngII-NGFIB/NURR1 pathway controls HSD3B1. Our work reveals HSD3B1 as a new regulatory target of AngII.

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.

Glucocorticoid-dependent hippocampal transcriptome in male rats: pathway-specific alterations with aging

Although glucocorticoids (GCs) are known to exert numerous effects in the hippocampus, their chronic regulatory functions remain poorly understood. Moreover, evidence is inconsistent regarding the long-standing hypothesis that chronic GC exposure promotes brain aging/Alzheimer disease. Here, we adrenalectomized male F344 rats at 15 months of age, maintained them for 3 months with implanted corticosterone (CORT) pellets producing low or intermediate (glucocorticoid receptor-activating) blood levels of CORT, and performed microarray/pathway analyses in hippocampal CA1. We defined the chronic GC-dependent transcriptome as 393 genes that exhibited differential expression between intermediate and low CORT groups. Short-term CORT (4 days) did not recapitulate this transcriptome. Functional processes/pathways overrepresented by chronic CORT-up-regulated genes included learning/plasticity, differentiation, glucose metabolism, and cholesterol biosynthesis, whereas processes overrepresented by CORT-down-regulated genes included inflammatory/immune/glial responses and extracellular structure. These profiles indicate that GCs chronically activate neuronal/metabolic processes while coordinately repressing a glial axis of reactivity/inflammation. We then compared the GC transcriptome with a previously defined hippocampal aging transcriptome, revealing a high proportion of common genes. Although CORT and aging moved expression of some common genes in the same direction, the majority were shifted in opposite directions by CORT and aging (eg, glial inflammatory genes down-regulated by CORT are up-regulated with aging). These results contradict the hypothesis that GCs simply promote brain aging and also suggest that the opposite direction shifts during aging reflect resistance to CORT regulation. Therefore, we propose a new model in which aging-related GC resistance develops in some target pathways, whereas GC overstimulation develops in others, together generating much of the brain aging phenotype.

NADPH oxidase-derived H(2)O(2) contributes to angiotensin II-induced aldosterone synthesis in human and rat adrenal cortical cells

BACKGROUND

The Renin-Angiotensin-Aldosterone-System plays a pivotal role in hypertension. Angiotensin II (Ang II) is a major regulator of aldosterone synthesis and secretion, and it is known to facilitate reactive oxygen species (ROS) generation in many cell types.

AIMS

Here, we assessed the role of ROS signaling in Ang II-induced aldosterone synthesis by focusing on the regulation of aldosterone synthase (CYP11B2), a cytochrome P450 oxidase that catalyzes the final step in aldosterone biosynthetic pathway.

RESULTS

Ang II increased CYP11B2 activity, mRNA and protein with a concomitant elevation of 6-Carboxy- 2',7'-dichlorodihydrofluorescein diacetate fluorescence, malondialdehyde and protein carbonyl levels (indices of ROS), NADPH oxidase (Nox) activity, and H(2)O(2) levels in human and rat adrenal cortical cells. The expression of nuclear receptor related 1 protein, a transcription factor known to regulate CYP11B2 expression, was also augmented by Ang II. These Ang II-evoked effects were either abolished or attenuated by pretreatment of cells with either Ang II type I receptor (AT(1)R) antagonist, or antioxidants or Nox inhibitor or siRNA silencing of Nox1, 2 and 4, or inhibitors of phospholipase C and protein kinase C. Exogenous H(2)O(2) mimicked the facilitatory effects of Ang II on CYP11B2 activity, mRNA, and protein expression, and these changes were significantly reduced by PEG-catalase.

INNOVATION

ROS, particularly H(2)O(2), is identified as a key regulator of aldosterone production.

CONCLUSION

Our results suggest that Ang II facilitates CYP11B2 activity and the ensuing aldosterone production via activation of AT(1)R-Nox-H(2)O(2) signaling pathway.

A new transgenic rat model overexpressing the angiotensin II type 2 receptor provides evidence for inhibition of cell proliferation in the outer adrenal cortex

This study aimed to elucidate the role of the AT(2) receptor (AT(2)R), which is expressed and upregulated in the adrenal zona glomerulosa (ZG) under conditions of increased aldosterone production. We developed a novel transgenic rat (TGR; TGRCXmAT(2)R) that overexpresses the AT(2)R in the adrenal gland, heart, kidney, brain, skeletal muscle, testes, lung, spleen, aorta, and vein. As a consequence the total angiotensin II (Ang II) binding sites increased 7.8-fold in the kidney, 25-fold in the heart, and twofold in the adrenals. The AT(2)R number amounted to 82-98% of total Ang II binding sites. In the ZG of TGRCXmAT(2)R, the AT(2)R density was elevated threefold relative to wild-type (WT) littermates, whereas AT(1)R density remained unchanged. TGRCXmAT(2)R rats were viable and exhibited normal reproduction, blood pressure, and kidney function. Notably, a slightly but significantly reduced body weight and a moderate increase in plasma urea were observed. With respect to adrenal function, 24-h urinary and plasma aldosterone concentrations were unaffected in TGRCXmAT(2)R at baseline. Three and 14 days of Ang II infusion (300 ng·min(-1)·kg(-1)) increased plasma aldosterone levels in WT and in TGR. These changes were completely abolished by the AT(1)R blocker losartan. Of note, glomerulosa cell proliferation, as indicated by the number of Ki-67-positive glomerulosa cells, was stimulated by Ang II in TGR and WT rats; however, this increase was significantly attenuated in TGR overexpressing the AT(2)R. In conclusion, AT(2)R in the adrenal ZG inhibits Ang II-induced cell proliferation but has no obvious lasting effect on the regulation of the aldosterone production at the investigated stages.

Local renin-angiotensin systems in the adrenal gland

In the adrenal gland all components of the renin-angiotensin system (RAS) are expressed in both the adrenal cortex and the adrenal medulla. In this review evidence shall be presented that a local secretory RAS exists in the adrenal cortex that stimulates aldosterone production and serves as an amplification system for circulating angiotensin (ANG) II. The regulation of the secretory adrenal RAS clearly differs from the regulation of the circulatory RAS in terms of renin expression as well as of renin secretion. For example under potassium load the activity of the renal and circulatory RAS is suppressed whereas the activity of the adrenal RAS is stimulated. Thus the activity of the adrenal RAS but not of the circulating RAS correlates well with the regulation of aldosterone production by potassium. The present review also summarizes the knowledge about the expression and functions of an additional renin transcript that has recently been discovered. This transcript encodes for a non-secretory cytosolic renin isoform. The cytosolic renin may be a basis for the existence of an intracellular renin system in the adrenal gland that has long been proposed. The present state of knowledge shall be discussed indicating that such an intracellular system modulates cell survival and cell death such as apoptosis and necrosis or cell functions such as aldosterone production.

Human adrenocortical carcinoma cell lines

The human adrenal cortex secretes mineralocorticoids, glucocorticoids and adrenal androgens. These steroids are produced from unique cell types located within the three distinct zones of the adrenal cortex. Disruption of adrenal steroid production results in a variety of diseases that can lead to hypertension, metabolic syndrome, infertility and androgen excess. The adrenal cortex is also a common site for the development of adenomas, and rarely the site for the development of carcinomas. The adenomas can lead to diseases associated with adrenal steroid excess, while the carcinomas are particularly aggressive and have a poor prognosis. In vitro cell culture models provide important tools to examine molecular and cellular mechanisms controlling both the normal and pathologic function of the adrenal cortex. Herein, we discuss currently available human adrenocortical carcinoma cell lines and their use as model systems for adrenal studies.

Comparison of aldosterone production among human adrenocortical cell lines

Several human adrenocortical cell lines have been used as model systems for aldosterone production. However, these cell lines have not been directly compared with each other. Human adrenal cell lines SW13, CAR47, the NCI-H295 and its sub-strains and sub-clones were compared with regard to aldosterone production and aldosterone synthase (CYP11B2) expression. Culture media was collected 48 h after incubation, aldosterone secretion was measured and the data were normalized to the amount of cell protein. RNA was isolated for microarray analysis and quantitative RT-PCR (qPCR). The cell lines with the highest aldosterone production were further tested with regard to angiotensin II (Ang II) stimulation. Neither aldosterone nor CYP11B2 transcript were detected in SW13 or CAR47 cells. The aldosterone production by the NCI-H295, H295A, H295R-S1, H295R-S2, H295R-S3, HAC13, HAC15 and HAC50 were 119, 1, 6, 826, 18, 139, 412, and 1 334 (pmol/mg protein/48 h), respectively. H295A and H295R-S1 expressed less CYP11B2 than the commonly used H295R-S3 cells; while NCI-H295, H295R-S2, HAC13, HAC15 and HAC50 expressed 24-, 14-, 3-, 10-, and 35-fold higher CYP11B2 compared with the H295R-S3 cells. When treated with Ang II, NCI-H295, H295R-S2, HAC13, HAC15 and HAC50 showed significantly higher aldosterone production than the basal level (p<0.05). A comparison of the available human adrenal cell lines indicates that the H295R-S2 and the clonal cell lines, HAC13, HAC15 and HAC50 produced the highest levels of aldosterone and responded well to Ang II.

Immediate-early transcriptional response to angiotensin II in human adrenocortical cells

Angiotensin II binds to the angiotensin II receptors type 1 (AT1 receptors) in adrenocortical cells and triggers an intracellular signaling cascade leading to changes in the gene expression pattern. Here, we show that stimulation with angiotensin II induces the expression of biologically active early growth response (Egr)-1, a zinc finger transcription factor, in human H295R adrenocortical cells. Expression of a dominant-negative mutant of the ternary complex factor Elk-1, a key transcriptional regulator of serum response element-driven gene transcription, prevented Egr-1 expression in angiotensin II-stimulated H295R cells, indicating that Ets-like protein-1 (Elk-1) or related ternary complex factors connect the intracellular signaling cascade elicited by activation of AT1 receptors with transcription of the Egr-1 gene. These data were corroborated by the fact that angiotensin II stimulation increased the transcription activation potential of Elk-1. In addition, activator protein-1 transcriptional activity was significantly elevated in angiotensin II-treated H295R cells. Expression of c-Jun and c-Fos was increased as well as the transcription activation potential of c-Fos. Expression of a dominant-negative mutant of Elk-1 reduced c-Fos expression in angiotensin II-stimulated adrenocortical cells, suggesting that the serum response element within the c-Fos promoter functions as an angiotensin II-response element. Expression of a dominant-negative mutant of c-Jun reduced activator protein-1 activity in angiotensin II-stimulated adrenocortical cells and reduced the up-regulation of c-Jun after angiotensin II stimulation. Thus, c-Jun regulates its own expression in adrenocortical cells. Together, the data show that angiotensin II stimulation activates the transcription factors Egr-1, Elk-1, c-Jun, and c-Fos in adrenocortical cells, leading to stimulus-dependent changes in the gene expression pattern.

Mechanistic profiling of the cAMP-dependent steroidogenic pathway in the H295R endocrine disrupter screening system: new endpoints for toxicity testing

The need for implementation of effects on steroid synthesis and hormone processing in screening batteries of endocrine disruptive compounds is widely acknowledged. In this perspective, hormone profiling in the H295R adrenocortical cell system is extensively examined and recently OECD validated (TG 456) as a replacement of the minced testis assay. To further elucidate the complete mechanisms and endocrine responsiveness of this cell system, microarray-based gene expression profiling of the cAMP response pathway, one of the major pathways in steroidogenesis regulation, was examined in H295R cells. Next to the steroid synthesis pathway, a broader lipid metabolic pathway, including cholesterol uptake/biosynthesis, hormone metabolization and many hormone and nuclear receptors, are sensitive towards cAMP stimulation in this cell system. Moreover, these pathways were clearly dose and time responsive, indicating early regulation (10 h) of cholesterol uptake and mobilization genes and later expression (24-48 h) of cholesterol biosynthesis and steroid synthesis. Transcription network analysis suggested several important transcription factors that could be involved in regulation of the steroid hormone pathway, of which HNF4α, a broader lipid metabolism related transcription factor, might indicate some new transcription regulation patterns in this cell line. Overall we can conclude that the time dependent gene expression patterns of the strongly coordinated cholesterol supply and steroidogenesis pathways in the H295R cell system seem to reflect well the in vivo ACTH/cAMP signalling cascade in adrenal cells. Moreover, the completeness of the steroidogenic related pathways in terms of gene expression sensitivity, indicates the H295R cell line as a promising cell line in omics-based endocrine disruption screening.

Development and function of the human fetal adrenal cortex: a key component in the feto-placental unit

Continuous efforts have been devoted to unraveling the biophysiology and development of the human fetal adrenal cortex, which is structurally and functionally unique from other species. It plays a pivotal role, mainly through steroidogenesis, in the regulation of intrauterine homeostasis and in fetal development and maturation. The steroidogenic activity is characterized by early transient cortisol biosynthesis, followed by its suppressed synthesis until late gestation, and extensive production of dehydroepiandrosterone and its sulfate, precursors of placental estrogen, during most of gestation. The gland rapidly grows through processes including cell proliferation and angiogenesis at the gland periphery, cellular migration, hypertrophy, and apoptosis. Recent studies employing modern technologies such as gene expression profiling and laser capture microdissection have revealed that development and/or function of the fetal adrenal cortex may be regulated by a panoply of molecules, including transcription factors, extracellular matrix components, locally produced growth factors, and placenta-derived CRH, in addition to the primary regulator, fetal pituitary ACTH. The role of the fetal adrenal cortex in human pregnancy and parturition appears highly complex, probably due to redundant and compensatory mechanisms regulating these events. Mounting evidence indicates that actions of hormones operating in the human feto-placental unit are likely mediated by mechanisms including target tissue responsiveness, local metabolism, and bioavailability, rather than changes only in circulating levels. Comprehensive study of such molecular mechanisms and the newly identified factors implicated in adrenal development should help crystallize our understanding of the development and physiology of the human fetal adrenal cortex.

In utero exposure to the antiandrogen di-(2-ethylhexyl) phthalate decreases adrenal aldosterone production in the adult rat

We previously reported that in utero exposure of the male fetus to the plasticizer di-(2-ethylhexyl) phthalate (DEHP) resulted in decreased circulating levels of testosterone in the adult without affecting Leydig cell numbers, luteinizing hormone levels, or steroidogenic enzyme expression. Fetal exposure to DEHP resulted in reduced mineralocorticoid receptor (MR; NR3C2) expression in adult Leydig cells. In the present studies, treatment of pregnant Sprague-Dawley dams from Gestational Day 14 until birth with 20, 50, 100, 300, or 750 mg kg(-1) day(-1) of DEHP resulted in significant sex-specific decreases in serum aldosterone but not corticosterone levels at Postnatal Day 60 (PND60) but not at PND21. There was no effect on circulating levels of potassium, angiotensin II or adrenocorticotropin hormone (ACTH). However, there was reduced expression of AT receptor Agtr1a, Agtr1b, and Agtr2 mRNAs. The mRNA levels of proteins and enzymes implicated in aldosterone biosynthesis were not affected by in utero DEHP treatment except for Cyp11b2, which was decreased at high (≥ 500 mg kg(-1) day(-1)) doses. The data presented herein, together with our previous observation that aldosterone stimulates testosterone production via an MR-mediated mechanism, suggest that in utero exposure to DEHP causes reduction in both adrenal aldosterone synthesis and MR expression in Leydig cells, leading to reduced testosterone production in the adult. Moreover, these results suggest the existence of a DEHP-sensitive adrenal-testis axis regulating androgen formation.

Aldosterone production in human adrenocortical cells is stimulated by high-density lipoprotein 2 (HDL2) through increased expression of aldosterone synthase (CYP11B2)

Adrenal aldosterone production is regulated by physiological agonists at the level of early and late rate-limiting steps. Numerous studies have focused on the role of lipoproteins including high-density lipoprotein (HDL) as cholesterol providers in this process; however, recent research suggests that HDL can also act as a signaling molecule. Herein, we used the human H295R adrenocortical cell model to study the effects of HDL on adrenal aldosterone production and CYP11B2 expression. HDL, especially HDL2, stimulated aldosterone synthesis by increasing expression of CYP11B2. HDL treatment increased CYP11B2 mRNA in both a concentration- and time-dependent manner, with a maximal 19-fold increase (24 h, 250 μg/ml of HDL). Effects of HDL on CYP11B2 were not additive with natural agonists including angiotensin II or K(+). HDL effects were likely mediated by a calcium signaling cascade, because a calcium channel blocker and a calmodulin kinase inhibitor abolished the CYP11B2-stimulating effects. Of the two subfractions of HDL, HDL2 was more potent than HDL3 in stimulating aldosterone and CYP11B2. Further studies are needed to identify the active components of HDL, which regulate aldosterone production.

Angiotensin II-induced expression of brain-derived neurotrophic factor in human and rat adrenocortical cells

Angiotensin II (Ang II) is a major regulator of steroidogenesis in adrenocortical cells, and is also an effective inducer of cytokine and growth factor synthesis in several cell types. In microarray analysis of H295R human adrenocortical cells, the mRNA of brain-derived neurotrophic factor (BDNF), a neurotrophin widely expressed in the nervous system, was one of the most up-regulated genes by Ang II. The aim of the present study was the analysis of the Ang II-induced BDNF expression and BDNF-induced effects in adrenocortical cells. Real-time PCR studies have shown that BDNF is expressed in H295R and rat adrenal glomerulosa cells. In H295R cells, the kinetics of Ang II-induced BDNF expression was faster than that of aldosterone synthase (CYP11B2). Inhibition of calmodulin kinase by KN93 did not significantly affect the Ang II-induced stimulation of BDNF expression, suggesting that it occurs by a different mechanism from the CYP11B2-response. Ang II also caused candesartan-sensitive, type-1 Ang II receptor-mediated stimulation of BDNF gene expression in primary rat glomerulosa cells. In rat adrenal cortex, BDNF protein was localized to the subcapsular region. Ang II increased BDNF protein levels both in human and rat cells, and BDNF secretion of H295R cells. Ang II also increased type-1 Ang II receptor-mediated BDNF expression in vivo in furosemide-treated rats. In rat glomerulosa cells, BDNF induced tropomyosin-related kinase B receptor-mediated stimulation of EGR1 and TrkB expression. These data demonstrate that Ang II stimulates BDNF expression in human and rat adrenocortical cells, and BDNF may have a local regulatory function in adrenal glomerulosa cells.

Regulation of aldosterone synthase by activator transcription factor/cAMP response element-binding protein family members

Aldosterone synthesis is regulated by angiotensin II (Ang II) and K(+) acting in the adrenal zona glomerulosa, in part through the regulation of aldosterone synthase (CYP11B2). Here, we analyzed the role of cAMP response element (CRE)-binding proteins (CREBs) in the regulation of CYP11B2. Expression analysis of activator transcription factor (ATF)/CREB family members, namely the ATF1 and ATF2, the CREB, and the CRE modulator, in H295R cells and normal human adrenal tissue was performed using quantitative real-time PCR. Ang II-induced phosphorylation of ATF/CREB members was analyzed by Western blot analysis, and their subsequent binding to the CYP11B2 promoter using chromatin immunoprecipitation assay. Aldosterone production and CYP11B2 expression were measured in small interfering RNA-transfected cells to knockdown the expression of ATF/CREB members. CYP11B2 promoter activity was measured in H295R cells cotransfected with NURR1 (NR4A2) alone or with constitutively active vectors for ATF/CREB members. Ang II induced phosphorylation of ATF1, ATF2, and CRE modulator in a time-dependent manner. Based on chromatin immunoprecipitation analysis, there was an increased association of these proteins with the CYP11B2 promoter after Ang II and K(+) treatment. Phosphorylated ATF/CREB members also bound the CYP11B2 promoter. Knockdown of ATF/CREB members reduced Ang II and K(+) induction of adrenal cell CYP11B2 mRNA expression and aldosterone production. The constitutively active ATF/CREB vectors increased the promoter activity of CYP11B2 and had a synergistic effect with NURR1. In summary, these results suggest that ATF/CREB and NGFI-B family members play a crucial role in the transcriptional regulation of CYP11B2 and adrenal cell capacity to produce aldosterone.

SUMO and ubiquitin modifications during steroid hormone synthesis and function

Steroid hormones control many aspects of animal physiology and behaviour. They are highly regulated, among other mechanisms, by post-translational modifications of the transcription factors involved in their synthesis and response. In the present review, we will focus on the influence of SUMO (small ubiquitin-related modifier) and ubiquitin modifications on the function of transcription factors involved in adrenal cortex formation, steroidogenesis and the hormonal response.

Mechanisms of angiotensin II-mediated regulation of aldosterone synthase expression in H295R human adrenocortical and rat adrenal glomerulosa cells

In adrenal zona glomerulosa cells angiotensin II (Ang II) is a key regulator of steroidogenesis. Our purpose was to compare the mechanisms of Ang II-induced changes in the expression level of early transcription factors NR4A1 (NGFIB) and NR4A2 (Nurr1) genes, and the CYP11B2 gene encoding aldosterone synthase in H295R human adrenocortical tumor cells and in primary rat adrenal glomerulosa cells. Real-time PCR studies have demonstrated that Ang II increased the expression levels of NR4A1 and NR4A2 in H295R cells within 1 h after stimulation, which persisted up to 6 h; whereas in rat adrenal glomerulosa cells the kinetics of the expression of these genes were more rapid and transient. Ang II also induced prolonged nuclear translocation of Nurr1 and NGFIB proteins in both cell types. Studies using MEK inhibitor (PD98059, 20 microM), protein kinase C inhibitor (BIM1, 3 microM) and calmodulin kinase (CAMK) inhibitor (KN93, 10 microM) revealed that in rat adrenal glomerulosa cells CAMK-mediated mechanisms play a predominant role in the regulation of CYP11B2. In accordance with earlier findings, in H295R cells MEK inhibition increased the expression of NR4A1, NR4A2 and CYP11B2 genes, however, it decreased the Ang II-induced gene expression levels, suggesting that ERK activation has a role in control of expression of these genes. No such mechanism was detected in rat glomerulosa cells. Sar1-Ile4-Ile8-AngII, which can cause G protein-independent ERK activation, also stimulated the expression of CYP11B2 in H295R cells. These data suggest that the previously reported CAMK-mediated stimulation of early transcription factors NGFIB and Nurr1 has a predominant role in Ang II-induced CYP11B2 activation in rat adrenal glomerulosa cells, whereas in H295R cells ERK activation and G protein-independent mechanisms also contribute to this process.