Protein kinase C increases 11beta-hydroxysteroid dehydrogenase oxidation and inhibits reduction in rat Leydig cells

Hormonal Regulation of Glucocorticoid Inactivation and Reactivation in αT3-1 and LβT2 Gonadotroph Cells

The regulation of reproductive function by glucocorticoids occurs at all levels of the hypothalamo-pituitary-gonadal axis. Within the pituitary, glucocorticoids have been shown to directly alter gene expression in gonadotrophs, indicating that these cell types are sensitive to regulation by the glucocorticoid receptor. Whilst the major glucocorticoid metabolising enzymes, 11β-hydroxysteroid dehydrogenase (11βHSD; HSD11B1 and HSD11B2), have been described in human pituitary adenomas, the activity of these enzymes within different pituitary cell types has not been reported. Radiometric conversion assays were performed in αT3-1, LβT2 (gonadotrophs), AtT-20 (corticotrophs) and GH3 (somatolactotrophs) anterior pituitary cell lines, using tritiated cortisol, corticosterone, cortisone or 11-dehydrocorticosterone as substrates. The net oxidation of cortisol/corticosterone and net reduction of cortisone/11-dehydrocorticosterone were significantly higher in the two gonadotroph cells lines compared with the AtT-20 and GH3 cells after 4 h. Whilst these enzyme activities remained the same in αT3-1 and LβT2 cells over a 24 h period, there was a significant increase in glucocorticoid metabolism in both AtT-20 and GH3 cells over this same period, suggesting cell-type specific activity of the 11βHSD enzyme(s). Stimulation of both gonadotroph cell lines with either 100 nM GnRH or PACAP (known physiological regulators of gonadotrophs) resulted in significantly increased 11β-dehydrogenase (11βDH) and 11-ketosteroid reductase (11KSR) activities, over both 4 and 24 h. These data reveal that gonadotroph 11βHSD enzyme activity can act to regulate local glucocorticoid availability to mediate the influence of the HPA axis on gonadotroph function.

The cross talk of adrenal and Leydig cell steroids in Leydig cells

Glucocorticoid is secreted by adrenal cortex, which binds to intracellular glucocorticoid and mineralocorticoid receptors to regulate steroidogenesis-related gene expression and testosterone production in Leydig cells. Glucocorticoid receptor activity shows inhibitory action on Leydig cell steroidogenesis, while mineralocorticoid receptor activity shows the stimulatory action. Leydig cells contain two important glucocorticoid-metabolizing enzymes, 11β-hydroxysteroid dehydrogenase type 1 and type 2, regulating the intracellular levels of glucocorticoids by a pre-receptor mechanism. 11β-Hydroxysteroid dehydrogenase type 1 is a bidirectional enzyme, and its direction is regulated by intracellular NADP⁺/NADPH redox potential. Leydig cells contain many steroidogenic enzymes, possibly regulating NADP⁺/NADPH redox potential by coupling with 11β-hydroxysteroid dehydrogenase type 1. Here, we review the 11β-hydroxysteroid dehydrogenase regulation and possible consequences in Leydig cell biology and pathology.

Regulation of glucocorticoid metabolism in the boar testis and caput epididymidis by the gonadotrophin-cAMP signalling pathway

In target tissues, cortisol is metabolised by two 11β-hydroxysteroid dehydrogenase (11βHSD) isoenzymes, namely 11βHSD1 and 11βHSD2, both of which are co-expressed in the boar testis and reproductive tract. The present study has assessed whether cortisol-cortisone metabolism in boar testis and caput epididymidis can be regulated via the gonadotrophin-cAMP signalling pathway. 11βHSD activities were measured by using a radiometric conversion assay in static tissue culture. In both testis and caput epididymidis, the net reduction of cortisone but not the net oxidation of cortisol, was significantly decreased by luteinising hormone (by 53 ± 20% and 45 ± 9%, respectively, P < 0.05), forskolin (by 60 ± 7% and 57 ± 9%, respectively, P < 0.01) and 8-bromo-cAMP (by 54 ± 4% and 64 ± 1%, respectively, P < 0.01). This suppression of 11-ketosteroid reductase activity in the boar testis by forskolin could be attenuated by the protein kinase A (PKA) inhibitor, H89. Hence, within the boar testis and the caput epididymidis, the local actions of glucocorticoids are modulated by gonadotrophin-cAMP-PKA signalling via their selective effects on the reductase activity of 11βHSD.

Inhibitory actions of mibefradil on steroidogenesis in mouse Leydig cells: involvement of Ca(2+) entry via the T-type Ca(2+) channel

Intracellular cAMP and Ca(2+) are involved in the regulation of steroidogenic activity in Leydig cells, which coordinate responses to luteinizing hormone (LH) and human chorionic gonadotropin (hCG). However, the identification of Ca(2+) entry implicated in Leydig cell steroidogenesis is not well defined. The objective of this study was to identify the type of Ca(2+) channel that affects Leydig cell steroidogenesis. In vitro steroidogenesis in the freshly dissociated Leydig cells of mice was induced by hCG incubation. The effects of mibefradil (a putative T-type Ca(2+) channel blocker) on steroidogenesis were assessed using reverse transcription (RT)-polymerase chain reaction analysis for the steroidogenic acute regulatory protein (StAR) mRNA expression and testosterone production using radioimmunoassay. In the presence of 1.0 mmol L(-1) extracellular Ca(2+), hCG at 1 to 100 IU noticeably elevated both StAR mRNA level and testosterone secretion (P < 0.05), and the stimulatory effects of hCG were markedly diminished by mibefradil in a dose-dependent manner (P < 0.05). Moreover, the hCG-induced increase in testosterone production was completely removed when external Ca(2+) was omitted, implying that Ca(2+) entry is needed for hCG-induced steroidogenesis. Furthermore, a patch-clamp study revealed the presence of mibefradil-sensitive Ca(2+) currents seen at a concentration range that nearly paralleled those inhibiting steroidogenesis. Collectively, our data provide evidence that hCG-stimulated steroidogenesis is mediated at least in part by Ca(2+) entry carried out by the T-type Ca(2+) channel in the Leydig cells of mice.

11beta-Hydroxysteroid dehydrogenase type 1 is an important regulator at the interface of obesity and inflammation

Systemic glucocorticoid excess, as exemplified by the Cushing syndrome, leads to obesity and all further symptoms of the metabolic syndrome. The current obesity epidemic, however, is not characterized by increased plasma cortisol concentrations, but instead comes along with chronic low-grade inflammation in adipose tissue and concomitant increased levels of 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1, gene HSD11B1), a parameter known to cause obesity in a mouse model. 11beta-HSD1 represents an intracellular amplifier of active glucocorticoid, thus enhances the associated effects on the inflammatory response as well as on nutrient and energy metabolism, and may therefore cause and exacerbate obesity by local increase of glucocorticoid concentrations. Obtained by extensive literature and database searching, the present review includes comprehensive lists of primary glucocorticoid-sensitive genes and gene products as well as of the thus far known regulators of HSD11B1 expression with implication in inflammation and metabolic disease. Collectively, the data clearly show that, in addition to amplifying active glucocorticoid and thus profoundly modulating inflammation and nutrient metabolism, 11beta-HSD1 is subject to tight control of multiple additional immunomodulatory and metabolic regulators. Hence, 11beta-HSD1 acts at the interface of inflammation and obesity and represents an efficient integrator and effector of local inflammatory and metabolic state.

Ca(2+)-Calmodulin regulation of testicular androgen production in Mozambique tilapia (Oreochromis mossambicus)

The Ca(2+)-Calmodulin (CaM) signaling pathway has previously been shown to be involved in the regulation of teleost fish ovarian steroidogenesis. However, a putative role of CaM in testicular steroidogenesis and potential targets has not been examined. To examine whether basal steroidogenesis is modulated by Ca(2+) and CaM levels in the testis of Mozambique tilapia (Oreochromis mossambicus) we have incubated testicular fragments in vitro under different conditions and analyzed steroid output. Calcium-free medium with or without EGTA did not affect testicular basal 11-ketotestosterone (11-KT) and testosterone (T) secretion. However, addition of 80microM the CaM inhibitor W7 significantly reduced basal 11-KT, T and androstenedione secretion. Interestingly, the decreased androgen production by 80microM of W7 was accompanied by increased 11-desoxicortisol output and by the activation of cortisol synthesis in the testis, the latter undetected in untreated tissues. However, production of 17,20alpha-dihydroxy-4-pregnen-3-one was unaltered by W7. This suggests that C17,20 desmolase, 21-hydroxylase and possibly 11beta-hydroxysteroid dehydrogenase are targets for CaM. In addition, androgen production was also found to be regulated by the level of cAMP since incubations with forskolin (FK) significantly increased 11-KT and T output. A cross-talk between the cAMP and Ca(2+)-CaM signaling pathways was detected since W7 administration also decreased FK stimulated androgen production. Altogether, these data show that both basal and cAMP stimulated androgen levels were modulated by intracellular Ca(2+)-dependent CaM and that possibly Ca(2+)-CaM determines the shift in steroidogenesis from C21 steroids to androgens.

Rapid mechanisms of glucocorticoid signaling in the Leydig cell

Stress-mediated elevations in circulating glucocorticoid levels lead to corresponding rapid declines in testosterone production by Leydig cells in the testis. In previous studies we have established that glucocorticoids act on Leydig cells directly, through the classic glucocorticoid receptor (GR), and that access to the GR is controlled prior to the GR by a metabolizing pathway mediated by the type 1 isoform of 11beta-hydroxysteroid dehydrogenase (11betaHSD1). This enzyme is bidirectional (with both oxidase and reductase activities) and in the rat testis is exclusively localized in Leydig cells where it is abundantly expressed and may catalyze the oxidative inactivation of glucocorticoids. The predominant reductase direction of 11betaHSD1 activity in liver cells is determined by an enzyme, hexose-6-phosphate dehydrogenase (H6PDH), on the luminal side of the smooth endoplasmic reticulum (SER). Generation of the pyridine nucleotide cofactor NADPH by H6PDH stimulates the reductase direction of 11betaHSD1 resulting in increased levels of active glucocorticoids in liver cells. Unlike liver cells, steroidogenic enzymes including 17beta-hydroxysteroid dehydrogenase 3 (17betaHSD3) forms the coupling with 11betaHSD1. Thus the physiological concentrations of androstenedione serve as a substrate for 17betaHSD3 utilizing NADPH to generate NADP+, which drives 11betaHSD1 in Leydig cells primarily as an oxidase; thus eliminating the adverse effects of glucocorticoids on testosterone production. At the same time 11betaHSD1 generates NADPH which promotes testosterone biosynthesis by stimulating 17betaHSD3 in a cooperative cycle. This enzymatic coupling constitutes a rapid mechanism for modulating glucocorticoid control of testosterone biosynthesis. Under stress conditions, glucocorticoids also have rapid actions to suppress cAMP formation thus to lower testosterone production.

Stress hormone and male reproductive function

The Leydig cell is the primary source of testosterone in males. Levels of testosterone in circulation are determined by the steroidogenic capacities of individual Leydig cells and the total numbers of Leydig cells per testis. Stress-induced increases in serum glucocorticoid concentrations inhibit testosterone-biosynthetic enzyme activity, leading to decreased rates of testosterone secretion. It is unclear, however, whether the excessive glucocorticoid stimulation also affects total Leydig cell numbers through induction of apoptosis and thereby contributes to the stress-induced suppression of androgen levels. Exposure of Leydig cells to high concentrations of corticosterone (CORT, the endogenously secreted glucocorticoid in rodents) increases their frequency of apoptosis. Studies of immobilization stress indicate that stress-induced increases in CORT are directly responsible for Leydig cell apoptosis. Access to glucocorticoid receptors in Leydig cells is modulated by oxidative inactivation of glucocorticoid by 11 beta-hydroxysteroid dehydrogenase (11 betaHSD). Under basal levels of glucocorticoid, sufficient levels of glucocorticoid metabolism occur and there is likely to be minimal binding of the glucocorticoid receptor. We have established that Leydig cells express type 1 11 betaHSD, an oxidoreductase, and type 2, a unidirectional oxidase. Generation of redox potential through synthesis of the enzyme cofactor NADPH, a byproduct of glucocorticoid metabolism by 11 betaHSD-1, may potentiate testosterone biosynthesis, as NADPH is the cofactor used by steroidogenic enzymes such as type 3 17beta-hydroxysteroid dehydrogenase. In this scenario, inhibition of steroidogenesis will only occur under stressful conditions when high input amounts of CORT exceed the capacity of oxidative inaction by 11 betaHSD. Changes in autonomic catecholaminergic activity may contribute to suppressed Leydig cell function during stress, and may explain the rapid onset of inhibition. However, recent analysis of glucocorticoid action in Leydig cells indicates the presence of a fast, non-genomic pathway that will merit further investigation.

Aldosterone enhances 11beta-hydroxysteroid dehydrogenase type 2 expression in colonic epithelial cells in vivo

OBJECTIVE

[corrected] 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) metabolizes glucocorticoids, thus enabling aldosterone to bind to the mineralocorticoid receptor. However, little is known about the regulatory mechanism of epithelial 11beta-HSD2 expression in the gut.

MATERIALS AND METHODS

Sprague-Dawley rats were maintained on a sodium-depleted diet or subjected to continuous aldosterone infusion for 4 weeks. Plasma aldosterone and arginine-vasopressin (AVP) levels were measured by radioimmunoassay. Expression of 11beta-HSD2 in colonic epithelia was evaluated by Northern blotting and immunohistochemistry. T84 and Caco2 cells were stimulated with aldosterone, dexamethasone and AVP alone or in combination, and 11beta-HSD2 mRNA was measured by quantitative reverse transcription polymerase chain reaction (RT-PCR).

RESULTS

Sodium-depleted and aldosterone-infused rats showed an increase of plasma aldosterone and AVP. Both treatments resulted in induction of 11beta-HSD2 in the colonic epithelia at mRNA and protein levels. Positive immunoreactivity was detected in the cytoplasm of the surface epithelia in control rats. In contrast, epithelial cells in the crypt also showed immunoreactivity for 11beta-HSD2 in the proximal colon of dietary sodium-depleted and aldosterone-infused rats. Induction of 11beta-HSD2 mRNA was observed when T84 cells were stimulated with corticosteroids plus AVP.

CONCLUSIONS

Aldosterone has a pivotal role by increasing expression of 11beta-HSD2 in epithelial cells of the colon. AVP may act as a synergistic hormone in aldosterone-mediated 11beta-HSD2 induction.

11beta-hydroxysteroid dehydrogenase type 1: a tissue-specific regulator of glucocorticoid response

11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) interconverts inactive cortisone and active cortisol. Although bidirectional, in vivo it is believed to function as a reductase generating active glucocorticoid at a prereceptor level, enhancing glucocorticoid receptor activation. In this review, we discuss both the genetic and enzymatic characterization of 11beta-HSD1, as well as describing its role in physiology and pathology in a tissue-specific manner. The molecular basis of cortisone reductase deficiency, the putative "11beta-HSD1 knockout state" in humans, has been defined and is caused by intronic mutations in HSD11B1 that decrease gene transcription together with mutations in hexose-6-phosphate dehydrogenase, an endoluminal enzyme that provides reduced nicotinamide-adenine dinucleotide phosphate as cofactor to 11beta-HSD1 to permit reductase activity. We speculate that hexose-6-phosphate dehydrogenase activity and therefore reduced nicotinamide-adenine dinucleotide phosphate supply may be crucial in determining the directionality of 11beta-HSD1 activity. Therapeutic inhibition of 11beta-HSD1 reductase activity in patients with obesity and the metabolic syndrome, as well as in glaucoma and osteoporosis, remains an exciting prospect.

Down-regulation of adipose 11beta-hydroxysteroid dehydrogenase type 1 by high-fat feeding in mice: a potential adaptive mechanism counteracting metabolic disease

The enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD-1) amplifies intracellular glucocorticoid action in vivo. 11beta-HSD-1 activity is increased in adipose tissues of obese humans and genetically obese rodents, providing a mechanistic basis for the similarities between metabolic disease arising from high circulating glucocorticoids (Cushing's syndrome) and idiopathic obesity/metabolic syndrome where plasma glucocorticoids are typically unaltered. Fat-specific overexpression of 11beta-HSD-1 produces a metabolic syndrome in mice, whereas 11beta-HSD-1 null mice resist high-fat diet (HF)-induced visceral obesity and its metabolic consequences. Here we compared the effects of chronic (18 wk) HF feeding on adipose 11beta-HSD-1 activity in strains of mice that are either resistant (A/J) or prone (C57BL/6J) to metabolic disease. 11beta-HSD-1 activity was highest in sc fat, followed by epididymal fat, with lowest activity in the mesenteric visceral depot of both strains. 11beta-HSD-1 activity was lower in white adipose tissues of A/J compared with C57BL/6J mice. Chronic HF feeding unexpectedly caused a down-regulation of 11beta-HSD-1 in adipose tissues of both strains, despite comparable adiposity. However, A/J mice down-regulated adipose 11beta-HSD-1 to a significantly lower level than C57BL/6J mice in white and thermogenic brown adipose tissues. We propose that a lower adipose 11beta-HSD-1 set point affords a metabolic protection to A/J mice. Adaptive down-regulation of adipose 11beta-HSD-1 in response to chronic HF represents a novel mechanism that may counteract metabolic disease.

The functional roles of 11 beta-HSD1: vascular tissue, testis and brain

Glucocorticoid hormones bind both glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) exerting a broad spectrum of actions in various tissues. The concentrations of glucocorticoid hormones in the target cells are regulated by 11 beta-hydroxysteroid dehydrogenases, type 1 (11 beta-HSD1) and type 2 (11 beta-HSD2). 11 beta-HSD2 is a unidirectional dehydrogenase, which inactivates biologically active glucocorticoid into inert metabolite, while 11 beta-HSD1 is a bi-directional oxidoreductase, which either inactivates biologically active glucocorticoid or activates inert metabolite into active forms. GRs and MRs are present in various tissues and mediate a broad spectrum of physiological actions. The co-existence of 11 beta-HSD1 with these two types of receptors plays an important role in regulation of glucocorticoid actions. This review examines the roles of 11 beta-HSD1 in vascular tissues, testis, brain and other tissues such as placental, retinal and adipose tissues.

Enzymology and Molecular Biology of Glucocorticoid Metabolism in Humans

Glucocorticoids (GCs) are a vital class of steroid hormones that are secreted by the adrenal cortex and that are regulated by ACTH largely under the control of the hypothalamic-pituitary-adrenal axis. GCs mediate profound and diverse physiological effects in vertebrates, ranging from development, metabolism, neurobiology, anti-inflammation and programmed cell death to many other fuctions. Multiple factors "downstream" of GC secretion, such as glucocorticoid receptor (GR) number and the abundance of plasma binding proteins have originally been considered as modulators of GC action. However, in the last decade the role of tissue-specific GC activating and inactivating enzymes have been identified as additional determinants in GC signalling pathways. On the cellular level, they function as important pre-receptor regulators by acting as "molecular switches" for receptor-active and receptor-inactive GC hormones. According to their biologic activity to catalyze the interconversion of C11-hydroxyl and C11-oxo GCs these enzymes have been named 11beta-hydroxysteroid dehydrogenase (11beta-HSD; EC 1.1.1.146). Two isoforms of 11beta-HSD have been cloned and characterized so far. 11beta-HSD type 1 is found in a wide range of tissues, acts predominantly as a reductase in intact cells and tissues by regenerating active cortisol from cortisone, and has been described to regulate GC access to the GR. 11beta-HSD type 2 is found mainly in mineralocorticoid target tissues such as kidney and colon, acts only as a dehydrogenase by producing inactive cortisone, and has been found to protect the mineralocorticoid receptor from high levels of receptor-active cortisol. Recently, 11beta-HSD 1 has become highly topical due to the finding that 11beta-HSD 1 plays a pivotal role in the pathogenesis of central obesity and the appearance of the metabolic syndrome. This review provides an overview on the components involved in GC signalling of 11beta-HSD type 1 as an important pre-receptor control enzyme that modulates activation of the GR.