Autocrine positive regulatory feedback of glucocorticoid secretion: glucocorticoid receptor directly impacts H295R human adrenocortical cell function

Dexamethasone affects human fetal adrenal steroidogenesis and subsequent ACTH response in an ex vivo culture model

Introduction

Administration of dexamethasone (DEX) has been used experimentally to suppress androgenization of external genitalia in 46,XX fetuses with congenital adrenal hyperplasia. Despite this, the prenatal biological mechanism-of-action of DEX on fetal development is not known. This study aimed to examine direct effects of DEX on human fetal adrenal (HFA) steroidogenic activity including possible effects on the subsequent response to ACTH-stimulation.

Methods

Human fetal adrenal (HFA) tissue from 30 fetuses (1^st trimester) were cultured ex vivo with A) DEX (10 µm) for 14 days, or B) DEX (10 µm) for 10 days followed by ACTH (1 nM) for 4 days. DEX-mediated effects on HFA morphology, viability, and apoptosis (immunohistochemistry), gene expression (quantitative PCR), and steroid hormone secretion (LC-MS/MS) were investigated.

Results

DEX-treatment caused decreased androstenedione (p<0.05) and increased cortisol (p<0.01) secretion suggesting that direct effects on the adrenal gland may contribute to the negative feedback on the hypothalamic-pituitary-adrenal axis in vivo. An altered response to ACTH stimulation in HFA pre-treated with DEX included increased androgen (p<0.05) and reduced cortisol production (p<0.05), supporting clinical observations of a temporary decreased ACTH-response following prenatal DEX-treatment. Additionally, the secretion of corticosterone was decreased (p<0.0001) following ACTH-stimulation in the initially DEX-treated HFAs.

Discussion

The observed effects suggest that prenatal DEX-treatment can cause direct effects on HFA steroidogenesis and in the subsequent response to ACTH-stimulation. This may indicate a requirement for careful monitoring of adrenal function in prenatally DEX-treated neonates, with particular focus on their mineralocorticoid levels.

Corticosteroid-binding Globulin (SERPINA6) Establishes Postpubertal Sex Differences in Rat Adrenal Development

Encoded by SerpinA6, plasma corticosteroid-binding globulin (CBG) transports glucocorticoids and regulates their access to cells. We determined how CBG influences plasma corticosterone and adrenal development in rats during the pubertal to adult transition using CRISPR/cas9 to disrupt SerpinA6 gene expression. In the absence of CBG, total plasma corticosterone levels were ∼80% lower in adult rats of both sexes, with a greater absolute reduction in females than in males. Notably, free corticosterone and adrenocorticotropic hormone were comparable between all groups. Between 30 and 90 days of age, wild-type female rats showed increases in adrenal weight and the size of the corticosterone-producing region, the zona fasciculata (zf), in tandem with increases in plasma CBG and corticosterone concentrations, whereas no such changes were observed in males. This sex difference was lost in rats without CBG, such that adrenal growth and zf expansion were similar between sexes. The sex-specific effects of CBG on adrenal morphology were accompanied by remarkable changes in gene expression: ∼40% of the adrenal transcriptome was altered in females lacking CBG, whereas almost no effect was seen in males. Over half of the adrenal genes that normally exhibit sexually dimorphic expression after puberty were similarly expressed in males and females without CBG, including those responsible for cholesterol biosynthesis and mobilization, steroidogenesis, and growth. Rat adrenal SerpinA6 transcript levels were very low or undetectable. Thus, sex differences in adrenal growth, morphology and gene expression profiles that emerge during puberty in rats are dependent on concomitant increases in plasma CBG produced by the liver.

Role of glucocorticoid receptor mutations in hypertension and adrenal gland hyperplasia

Hypertension is one of the leading causes of premature death in humans and exhibits a complex aetiology including environmental and genetic factors. Mutations within the glucocorticoid receptor (GR) can cause glucocorticoid resistance, which is characterized by several clinical features like hypercortisolism, hypokalaemia, adrenal hyperplasia and hypertension. Altered glucocorticoid receptor signalling further affects sodium and potassium homeostasis as well as blood pressure regulation and cell proliferation and differentiation that influence organ development and function. In salt-sensitive hypertension, excessive renal salt transport and sympathetic nervous system stimulation may occur simultaneously, and, thus, both the mineralocorticoid receptor (MR) and the GR-signalling may be implicated or even act interdependently. This review focuses on identified GR mutations in human primary generalized glucocorticoid resistance (PGGR) patients and their related clinical phenotype with specific emphasis on adrenal gland hyperplasia and hypertension. We compare these findings to mouse and rat mutants harbouring genetically engineered mutations to further dissect the cause and/or the consequence of clinical features which are common or different.

Regulation of the Intestinal Extra-Adrenal Steroidogenic Pathway Component LRH-1 by Glucocorticoids in Ulcerative Colitis

Ulcerative colitis (UC) is an inflammatory bowel disease (IBD) and can be treated with glucocorticoids (GC), although some patients are unresponsive to this therapy. The transcription factor LRH-1/NR5A2 is critical to intestinal cortisol production (intestinal steroidogenesis), being reduced in UC patients. However, the relationship between LRH-1 expression and distribution with altered corticosteroid responses is unknown. To address this, we categorized UC patients by their steroid response. Here, we found that steroid-dependent and refractory patients presented reduced glucocorticoid receptor (GR)-mediated intestinal steroidogenesis compared to healthy individuals and responder patients, possibly related to increased colonic mucosa GR isoform beta (GRβ) content and cytoplasmic LRH-1 levels in epithelial and lamina propria cells. Interestingly, an intestinal epithelium-specific GR-induced knockout (GR^iKO) dextran sodium sulfate (DSS)-colitis mice model presented decreased epithelial LRH-1 expression, whilst it increased in the lamina propria compared to DSS-treated control mice. Mechanistically, GR directly induced NR5A2 gene expression in CCD841CoN cells and human colonic organoids. Furthermore, GR bound to two glucocorticoid-response elements within the NR5A2 promoter in dexamethasone-stimulated CCD841CoN cells. We conclude that GR contributes to intestinal steroidogenesis by inducing LRH-1 in epithelial cells, suggesting LRH-1 as a potential marker for glucocorticoid-impaired response in UC. However, further studies with a larger patient cohort will be necessary to confirm role of LRH-1 as a therapeutic biomarker.

Alterations of estrous cycle, 3β hydroxysteroid dehydrogenase activity and progesterone synthesis in female rats after exposure to hypobaric hypoxia

The underlying mechanism regulating hypoxia induced alteration in female steroid hormones is first time explored in this study. To understand the mechanistic approach, female Sprague- Dawley rats were exposed to acute and chronic hypobaric hypoxia (282 mm-Hg, ~7620 m, 6 hours, 3 and 7 days). Estrous cycle, body weight, plasma progesterone and estradiol levels, morphology, histology and two key steroidogenic enzymes: 3ß hydroxysteroid dehydrogenase (HSD) and 17ß HSD activity of ovary and adrenal gland were studied. A persistent diestrous phase and a significant decrease in body weight were found in chronic hypoxia groups. Histological study suggested degenerative changes in ovarian corpus luteum of 7 days chronic hypobaric hypoxia (7CHH) group and a declined percentage of adrenocortical cells in 3 days chronic hypobaric hypoxia (3CHH) and 7CHH groups. Plasma estradiol level was unaltered, but progesterone level was decreased significantly in all hypoxic groups. Ovarian 3ß HSD activity was decreased significantly with increasing days of hypoxic treatment along with a significantly low adrenal 3ß HSD activity in 7CHH. In conclusion, hypobaric hypoxia causes a state of low circulatory progesterone level in females likely due to the degenerative changes in the female ovarian and adrenal tissues together with low steroidogenic 3ß HSD enzyme activity.

Dynamics of ACTH-Mediated Regulation of Gene Transcription in ATC1 and ATC7 Adrenal Zona Fasciculata Cell Lines

We tested the hypothesis that mouse ATC1 and ATC7 cells, the first adrenocortical cell lines to exhibit a complete zona fasciculata (ZF) cell phenotype, respond to dynamic ACTH stimulation in a similar manner as the adrenal gland in vivo. Exploiting our previous in vivo observations that gene transcription within the steroidogenic pathway is dynamically regulated in response to a pulse of ACTH, we exposed ATC1 and ATC7 cells to various patterns of ACTH, including pulsatile and constant, and measured the transcriptional activation of this pathway. We show that pulses of ACTH administered to ATC7 cells can reliably stimulate a pulsatile pattern of transcriptional activity that is comparable to that observed in adrenal ZF cells in vivo. Hourly pulses of ACTH stimulate dynamic increases in CREB phosphorylation (pCREB) and transcription of genes involved in critical steps of steroidogenesis including signal transduction (e.g., MRAP), cholesterol delivery (e.g., StAR), and steroid biosynthesis (e.g., CYP11A1), as well as those relating to transcriptional regulation of steroidogenic factors (e.g., SF-1 and Nur-77). In contrast, constant ACTH stimulation results in a prolonged and exaggerated pCREB and steroidogenic gene transcriptional response. We also show that when a large dose of ACTH (100 nM) is applied after these treatment regimens, a significant increase in steroidogenic transcriptional responsiveness is achieved only in cells that have been exposed to pulsatile, rather than constant, ACTH. Our data support our in vivo observations that pulsatile ACTH is important for the optimal transcriptional responsiveness of the adrenal. Importantly, our data suggest that ATC7 cells respond to dynamic ACTH stimulation.

High-Throughput H295R Steroidogenesis Assay: Utility as an Alternative and a Statistical Approach to Characterize Effects on Steroidogenesis

The U.S. Environmental Protection Agency Endocrine Disruptor Screening Program and the Organization for Economic Co-operation and Development (OECD) have used the human adrenocarcinoma (H295R) cell-based assay to predict chemical perturbation of androgen and estrogen production. Recently, a high-throughput H295R (HT-H295R) assay was developed as part of the ToxCast program that includes measurement of 11 hormones, including progestagens, corticosteroids, androgens, and estrogens. To date, 2012 chemicals have been screened at 1 concentration; of these, 656 chemicals have been screened in concentration-response. The objectives of this work were to: (1) develop an integrated analysis of chemical-mediated effects on steroidogenesis in the HT-H295R assay and (2) evaluate whether the HT-H295R assay predicts estrogen and androgen production specifically via comparison with the OECD-validated H295R assay. To support application of HT-H295R assay data to weight-of-evidence and prioritization tasks, a single numeric value based on Mahalanobis distances was computed for 654 chemicals to indicate the magnitude of effects on the synthesis of 11 hormones. The maximum mean Mahalanobis distance (maxmMd) values were high for strong modulators (prochloraz, mifepristone) and lower for moderate modulators (atrazine, molinate). Twenty-five of 28 reference chemicals used for OECD validation were screened in the HT-H295R assay, and produced qualitatively similar results, with accuracies of 0.90/0.75 and 0.81/0.91 for increased/decreased testosterone and estradiol production, respectively. The HT-H295R assay provides robust information regarding estrogen and androgen production, as well as additional hormones. The maxmMd from this integrated analysis may provide a data-driven approach to prioritizing lists of chemicals for putative effects on steroidogenesis.

Significant prevalence of NR3C1 mutations in incidentally discovered bilateral adrenal hyperplasia: results of the French MUTA-GR Study

BACKGROUND

Recently discovered mutations of NR3C1 gene, encoding for the GR, in patients with glucocorticoid resistance and bilateral adrenal incidentalomas prompted us to investigate whether GR mutations might be associated with adrenal hyperplasia.

OBJECTIVE

The multicenter French Clinical Research Program (Muta-GR) was set up to determine the prevalence of GR mutations and polymorphisms in patients harboring bilateral adrenal incidentalomas associated with hypertension and/or biological hypercortisolism without clinical Cushing's signs.

RESULTS

One hundred patients were included in whom NR3C1 sequencing revealed five original heterozygous GR mutations that impaired GR signaling in vitro. Mutated patients presented with mild glucocorticoid resistance defined as elevated urinary free cortisol (1.7 ± 0.7 vs 0.9 ± 0.8 upper limit of normal range, P = 0.006), incomplete 1 mg dexamethasone suppression test without suppressed 8-AM adrenocorticotrophin levels (30.9 ± 31.2 vs 16.2 ± 17.5 pg/mL) compared to the non-mutated patients. Potassium and aldosterone levels were lower in mutated patients (3.6 ± 0.2 vs 4.1 ± 0.5 mmol/L, P = 0.01, and 17.3 ± 9.9 vs 98.6 ± 115.4 pg/mL, P = 0.0011, respectively) without elevated renin levels, consistent with pseudohypermineralocorticism. Ex vivo characterization of mutated patients' fibroblasts demonstrated GR haploinsufficiency as revealed by below-normal glucocorticoid induction of FKBP5 gene expression. There was no association between GR polymorphisms and adrenal hyperplasia in this cohort, except an over-representation of BclI polymorphism.

CONCLUSION

The 5% prevalence of heterozygous NR3C1 mutations discovered in our series is higher than initially thought and encourages GR mutation screening in patients with adrenal incidentalomas to unambiguously differentiate from Cushing's states and to optimize personalized follow-up.

Detection and activity of 11 beta hydroxylase (CYP11B1) in the bovine ovary

Glucocorticoids (GCs) such as cortisol and corticosterone are important steroid hormones with different functions in intermediate metabolism, development, cell differentiation, immune response and reproduction. In response to physiological and immunological stress, adrenocorticotropic hormone (ACTH) acts on the adrenal gland by stimulating the synthesis and secretion of GCs. However, there is increasing evidence that GCs may also be synthesized by extra-adrenal tissues. Here, we examined the gene and protein expression of the enzyme 11β-hydroxylase P450c11 (CYP11B1), involved in the conversion of 11-deoxycortisol to cortisol, in the different components of the bovine ovary and determined the functionality of CYP11B1in vitro.CYP11B1mRNA was expressed in granulosa and theca cells in small, medium and large antral ovarian follicles, and CYP11B1 protein was expressed in medium and large antral follicles. After stimulation by ACTH, we observed an increased secretion of cortisol by the wall of large antral follicles. We also observed a concentration-dependent decrease in the concentration of cortisol in response to metyrapone, an inhibitor of CYP11B1. This decrease was significant at 10−5 µM metyrapone. In conclusion, this study demonstrated for the first time the presence of CYP11B1 in the bovine ovary. This confirms that there could be a local synthesis of GCs in the bovine ovary and therefore a potential endocrine responder to stress through these hormones.

Regulation of aldosterone secretion by mineralocorticoid receptor-mediated signaling

We posit the existence of a paracrine/autocrine negative feedback loop, mediated by the mineralocorticoid receptor (MR), regulating aldosterone secretion. To assess this hypothesis, we asked whether altering MR activity in zona glomerulosa (ZG) cells affects aldosterone production. To this end, we studied ex vivo ZG cells isolated from male Wistar rats fed chow containing either high (1.6% Na⁺ (HS)) or low (0.03% Na⁺ (LS)) amount of sodium. Western blot analyses demonstrated that MR was present in both the ZG and zona fasciculata/zona reticularis (ZF/ZR/ZR). In ZG cells isolated from rats on LS chow, MR activation by fludrocortisone produced a 20% and 60% reduction in aldosterone secretion basally and in response to angiotensin II (ANGII) stimulation, respectively. Corticosterone secretion was increased in these cells suggesting that aldosterone synthase activity was being reduced by fludrocortisone. In contrast, canrenoic acid, an MR antagonist, enhanced aldosterone production by up to 30% both basally and in response to ANGII. Similar responses were observed in ZG cells from rats fed HS. Modulating glucocorticoid receptor (GR) activity did not alter aldosterone production by ZG cells; however, altering GR activity did modify corticosterone production from ZF/ZR/ZR cells both basally and in response to adrenocorticotropic hormone (ACTH). Additionally, activating the MR in ZF/ZR/ZR cells strikingly reduced corticosterone secretion. In summary, these data support the hypothesis that negative ultra-short feedback loops regulate adrenal steroidogenesis. In the ZG, aldosterone secretion is regulated by the MR, but not the GR, an effect that appears to be secondary to a change in aldosterone synthase activity.

Effect of Mifepristone on Corticosteroid Production in Vitro by Adrenal Glands of Rats with Streptozotocin Diabetes

Changes in pregnenolone and corticosterone production by the adrenal glands of normoglycemic rats receiving the course of intraperitoneal mifepristone or NaCl administration were co-directed, but differed in magnitude. In rats with hyperglycemia, corticosteroid production increased after NaCl administration over 5 days and returned to the initial values after 15-day administration. On the contrary, pregnenolone and corticosterone production was suppressed after 5-day course of mifepristone, but significantly increased after mifepristone administration for 15 days. Intraperitoneal mifepristone administration almost completely abolished the response of rat adrenal glands with normo- and hyperglycemia to ACTH in vitro; this effect did not depend on the duration of administration.

Simultaneous profiling of 17 steroid hormones for the evaluation of endocrine-disrupting chemicals in H295R cells

Aim: There is urgent need to develop a new protocol for the evaluation of chemical substances to potentially interact with the endocrine system and induce numerous pathological issues. The recently validated in vitro screening assay is limited on monitoring two steroid hormones. Methodology & results: The H295R model cell was exposed to seven endocrine disrupting chemicals (EDCs). The levels of 17 steroid hormones in cell extracts were subsequently determined by a quantitative targeted GC/MS/MS method. Through wide coverage, this system managed to capture the effects of exposure to increasing EDCs concentrations in the entire steroidogenic pathways. Conclusion: The developed approach could be beneficial for the mechanistic investigation of EDCs.

Modulation of the circadian clock by glucocorticoid receptor isoforms in the H295R cell line

Peripheral clocks are set by different nervous, hormonal and metabolic stimuli, and regulate the circadian expression of several genes. We investigated whether a peripheral clock could be induced in the human adrenocortical cell line H295R and whether glucocorticoid receptor isoforms (GRα and GRß) are involved in this clock system. After synchronization of cells with serum shock, the rhythmic oscillation of clock genes PER1, PER2, REV-ERBα, and ARNTL was confirmed. In addition, H295R cells even without serum shock showed rhythmic expression of PER1, PER2, CRY1 and ARNTL. Glucocorticoid treatment induced a rapid response of PER1, PER2 and CRY1 in a GRα-dependent manner. Continuous glucocorticoid stimulation after 6h caused suppression of REV-ERBα. Administration of a GR antagonist, RU486, disrupted the circadian oscillation of clock genes and prevented the acute changes in PER1, PER2 and CRY1 levels. Overexpression of the GRß isoform alone did not alter the expression of the examined clock genes, but did prevent the GRα-related suppression of REV-ERBα. These alterations occurred independently from ACTH and CRH. Our data demonstrate that a peripheral clock system is present in a human adrenocortical cell line and that periodic oscillations of clock genes are influenced by glucocorticoids, mainly through GRα.

60 YEARS OF NEUROENDOCRINOLOGY: Glucocorticoid dynamics: insights from mathematical, experimental and clinical studies

A pulsatile pattern of secretion is a characteristic of many hormonal systems, including the glucocorticoid-producing hypothalamic-pituitary-adrenal (HPA) axis. Despite recent evidence supporting its importance for behavioral, neuroendocrine and transcriptional effects of glucocorticoids, there has been a paucity of information regarding the origin of glucocorticoid pulsatility. In this review we discuss the mechanisms regulating pulsatile dynamics of the HPA axis, and how these dynamics become disrupted in disease. Our recent mathematical, experimental and clinical studies show that glucocorticoid pulsatility can be generated and maintained by dynamic processes at the level of the pituitary-adrenal axis, and that an intra-adrenal negative feedback may contribute to these dynamics.

Dynamics of adrenal glucocorticoid steroidogenesis in health and disease

The activity of the hypothalamic-pituitary-adrenal (HPA) axis is characterized by an ultradian (pulsatile) pattern of hormone secretion. Pulsatility of glucocorticoids has been found critical for optimal transcriptional, neuroendocrine and behavioral responses. This review will focus on the mechanisms underlying the origin of the glucocorticoid ultradian rhythm. Our recent research shows that the ultradian rhythm of glucocorticoids depends on highly dynamic processes within adrenocortical steroidogenic cells. Furthermore, we have evidence that disruption of these dynamics leads to abnormal glucocorticoid secretion observed in disease and critical illness in both humans and rats.