11Beta-hydroxysteroid dehydrogenase type 2 and mineralocorticoid receptor in human fetal development

11βHSD2 Efficacy in Preventing Transcriptional Activation of the Mineralocorticoid Receptor by Corticosterone

Affinity of the mineralocorticoid receptor (MR) is similar for aldosterone and the glucocorticoids (GC) cortisol and corticosterone, which circulate at concentrations far exceeding those of aldosterone. 11β-hydroxysteroid dehydrogenase type 2 (11βHSD2) inactivation of GC within the immediate vicinity of the MR is credited with prereceptor specificity for aldosterone in cells coexpressing MR and 11βHSD2. 11βHSD2 efficacy is also critical to other recently described 11βHSD2 substrates. The aim of this work was to address doubts that low levels of expression of 11βHSD2 in aldosterone target tissues suffice to prevent the initiation of gene transcription by the MR activated by physiological concentrations of corticosterone. Cell models stably expressing an MR/Gaussia luciferase reporter and various levels of constitutive or induced 11βHSD2 at concentrations lower than those in rat kidney homogenates and microsomes were produced. Aldosterone and corticosterone were equipotent transactivators of the MR reporter gene in cells without 11βHSD2. Rate of conversion of tritiated corticosterone to 11-dehydrocorticosterone increased and corticosterone-induced nuclear translocation of MR decreased, as 11βHSD2 expression increased. The 50% maximal MR activation for the reporter gene stimulation by corticosterone rose with increasing 11βHSD2 expression, shifting the steroid dose-response curve for corticosterone-induced MR transactivation to the right. Several stable cell lines expressing an easily and reproducibly measured MR reporter system and consistent incremental amounts of 11βHSD2 protein were produced and used to document that 11βHSD2 within low physiological levels inactivates relevant concentrations of GC and decreases MR transactivation by GC in a dose-dependent fashion, laying to rest doubts of the efficacy of this enzyme.

11β-hydroxysteroid dehydrogenases: A growing multi-tasking family

This review briefly addresses the history of the discovery and elucidation of the three cloned 11β-hydroxysteroid dehydrogenase (11βHSD) enzymes in the human, 11βHSD1, 11βHSD2 and 11βHSD3, an NADP⁺-dependent dehydrogenase also called the 11βHSD1-like dehydrogenase (11βHSD1L), as well as evidence for yet identified 11βHSDs. Attention is devoted to more recently described aspects of this multi-functional family. The importance of 11βHSD substrates other than glucocorticoids including bile acids, 7-keto sterols, neurosteroids, and xenobiotics is discussed, along with examples of pathology when functions of these multi-tasking enzymes are disrupted. 11βHSDs modulate the intracellular concentration of glucocorticoids, thereby regulating the activation of the glucocorticoid and mineralocorticoid receptors, and 7β-27-hydroxycholesterol, an agonist of the retinoid-related orphan receptor gamma (RORγ). Key functions of this nuclear transcription factor include regulation of immune cell differentiation, cytokine production and inflammation at the cell level. 11βHSD1 expression and/or glucocorticoid reductase activity are inappropriately increased with age and in obesity and metabolic syndrome (MetS). Potential causes for disappointing results of the clinical trials of selective inhibitors of 11βHSD1 in the treatment of these disorders are discussed, as well as the potential for more targeted use of inhibitors of 11βHSD1 and 11βHSD2.

Pathology of Aldosterone Biosynthesis and its Action

Aldosterone plays pivotal roles in renin-angiotensin-aldosterone system in order to maintain the equilibrium of liquid volume and electrolyte metabolism. Aldosterone action is mediated by both mineralocorticoid receptor and 11β-hydroxysteroid dehydrogenase type 2 (11β-HSD2). Its excessive actions directly induced tissue injuries in its target organs such as myocardial and vascular fibrosis in addition to chronic kidney diseases. Excessive aldosterone actions were also reported to be involved in unbalanced electrolyte metabolism in inflammatory bowel disease and development of pulmonary diseases. Hyperaldosteronism is tentatively classified into primary and secondary types. Primary aldosteronism is more frequent and has been well known to result in secondary hypertension with subsequent cardiovascular damages. Primary aldosteronism is also further classified into distinctive subtypes and among those, aldosterone-producing adenoma is the most frequent one accounting for the great majority of unilateral primary aldosteronism cases. In bilateral hyperaldosteronism, aldosterone-producing diffuse hyperplasia and aldosterone-producing micronodules or nodules are the major subtypes. All these aldosterone-producing lesions were reported to harbor somatic mutations including KCNJ5, CACNA1D, ATP1A1 and ATP2B3, which were all related to excessive aldosterone production. Among those mutations above, somatic mutation of KCNJ5 is the most frequent in aldosterone-producing adenoma and mostly composed of clear cells harboring abundant aldosterone synthase expression. In contrast, CACNA1D-mutated aldosterone-producing micronodules or aldosterone-producing nodules were frequently detected not only in primary aldosteronism patients but also in the zona glomerulosa of normal adrenal glands, which could eventually lead to an autonomous aldosterone production resulting in normotensive or overt primary aldosteronism, but their details have remained unknown.

Substrates and Clearance Products of Fetal Adrenal Glucocorticoid Synthesis in Full-Term Human Umbilical Circulation

In full-term elective caesarian sections, fetal flow of adrenal substrate steroids to products differs by sex, with males (M) in molar equilibrium whereas females (F) add net molarity and synthesize more cortisol. Using the same sampling design, paired, full-term, arterial, and venous umbilical cord samples and intrapartum chart records were obtained at the time of vaginal delivery (N = 167, 85 male) or emergency C-section (N = 38, 22 male). Eight steroids were quantified by liquid chromatography coupled to tandem mass spectrometry (adrenal glucocorticoids [cortisol, corticosterone], sequential cortisol precursor steroids [17-hydroxyprogesterone, 11-deoxycortisol], cortisol and corticosterone metabolites [cortisone and 11-dehydrocorticosterone], and gonadal steroids [androstenedione, testosterone]). Fetal sex was not significant in any analytic models. Going through both phase 1 and phase 2 labor increased fetal adrenal steroidogenesis and decreased male testosterone relative to emergency C-sections that do not reach stage 2 of labor (ie, head compressions) and elective C-sections with no labor. Sum adrenal steroid molarity arriving in venous serum was almost double the equivalent metric for deliveries without labor. No effects of operative vaginal delivery were noted. Maternal regional anesthetic suppressed venous concentrations, and fetal synthesis replaced that steroid. Approximate molar equivalence between substrate pool depletion and net glucocorticoid synthesis was seen. Paired venous and arterial umbilical cord serum has the potential to identify sex differences that underlie antenatal programming of hypothalamic-pituitary-adrenal axis function in later life. However, stage 2 labor before the collection of serum, and regional anesthetic for the mother, mask those sex differences.

Brain mineralocorticoid receptors in cognition and cardiovascular homeostasis

Mineralocorticoid receptors (MR) mediate diverse functions supporting osmotic and hemodynamic homeostasis, response to injury and inflammation, and neuronal changes required for learning and memory. Inappropriate MR activation in kidneys, heart, vessels, and brain hemodynamic control centers results in cardiovascular and renal pathology and hypertension. MR binds aldosterone, cortisol and corticosterone with similar affinity, while the glucocorticoid receptor (GR) has less affinity for cortisol and corticosterone. As glucocorticoids are more abundant than aldosterone, aldosterone activates MR in cells co-expressing enzymes with 11β-hydroxydehydrogenase activity to inactivate them. MR and GR co-expressed in the same cell interact at the molecular and functional level and these functions may be complementary or opposing depending on the cell type. Thus the balance between MR and GR expression and activation is crucial for normal function. Where 11β-hydroxydehydrogenase 2 (11β-HSD2) that inactivates cortisol and corticosterone in aldosterone target cells of the kidney and nucleus tractus solitarius (NTS) is not expressed, as in most neurons, MR are activated at basal glucocorticoid concentrations, GR at stress concentrations. An exception may be pre-autonomic neurons of the PVN which express MR and 11β-HSD1 in the absence of hexose-6-phosphate dehydrogenase required to generate the requisite cofactor for reductase activity, thus it acts as a dehydrogenase. MR antagonists, valuable adjuncts to the treatment of cardiovascular disease, also inhibit MR in the brain that are crucial for memory formation and exacerbate detrimental effects of excessive GR activation on cognition and mood. 11β-HSD1 inhibitors combat metabolic and cognitive diseases related to glucocorticoid excess, but may exacerbate MR action where 11β-HSD1 acts as a dehydrogenase, while non-selective 11β-HSD1&2 inhibitors cause injurious disruption of MR hemodynamic control. MR functions in the brain are multifaceted and optimal MR:GR activity is crucial. Therefore selectively targeting down-stream effectors of MR specific actions may be a better therapeutic goal.

Mineralocorticoid effects in the late gestation ovine fetal lung

This study was designed to determine the effects of corticosteroids at MR in the late‐gestation fetal lung. Since both the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR) are expressed at relatively high levels in the fetal lung, endogenous corticosteroids may act at MR as well as GR in the preterm fetal lung. The GR agonist, betamethasone, the MR agonist, aldosterone, or both were infused intravenously for 48 h in ovine fetuses of approximately 130 days gestation. Effects on airway pressures during stepwise inflation of the in situ lung, expression of ENaC alpha (SCNN1A), ENaC beta (SCNN1B), and Na,K ATPase (ATP1A1), and elastin and collagen content were determined after the infusions. We found that aldosterone significantly reduced the airway pressure measured during the initial step in inflation of the lung, although aldosterone had no overall effect on lung compliance, nor did aldosterone induce expression of ENaCα, ENaCβ or Na,K ATPaseα1. Betamethasone significantly increased expression of the epithelial sodium channel (ENaC) subunit mRNAs, and collagen and elastin content in the lungs, although this dose of betamethasone also had no effect on lung compliance. There was no synergy between effects of the MR and GR agonists. Transcriptomic analysis suggested that although aldosterone did not alter genes in pathways related to epithelial sodium transport, aldosterone did alter genes in pathways involved in cell proliferation in the lungs. The results are consistent with corticosteroid‐induced fluid reabsorption at birth through GR rather than MR, but suggest that MR facilitates lung maturation, and may contribute to inflation with the first breaths via mechanisms distinct from known aldosterone effects in other epithelia.

Infusion of the mineralocorticoid receptor agonist, aldosterone, to the ovine fetus resulted in reduced airway pressures with initial lung inflation. However, aldosterone did not alter lung surfactant or epithelial sodium transport genes which are classical MR gene targets. Transcriptomic analysis revealed an aldosterone effect on genes related to cell cycle, suggesting that MR have a role distinct form that of GR in the maturing lung.

Ontogeny of adrenal-like glucocorticoid synthesis pathway and of 20α-hydroxysteroid dehydrogenase in the mouse lung

BACKGROUND

Glucocorticoids exert recognized positive effects on lung development. The genes involved in the classical pathway of glucocorticoid synthesis normally occurring in adrenals were found to be expressed on gestation day (GD) 15.5 in the developing mouse lung. Recently, expression of two of these genes was also detected on GD 17.5 suggesting a more complex temporal regulation than previously expected. Here, we deepen the knowledge on expression of "adrenal" glucocorticoid synthesis genes in the mouse lung during the perinatal period and we also study expression of the gene encoding for the steroid inactivating enzyme 20α-hydroxysteroid dehydrogenase (20α-HSD).

RESULTS

We performed an ontogenic study of P450scc, 3β-hydroxysteroid dehydrogenase/Δ5-Δ4 isomerase 1 (3β-HSD1), 21-hydroxylase, 11β-hydroxylase, 11β-HSD1, and 11β-HSD2 expression up to post natal day (PN) 15. The substrate (progesterone) and the product (deoxycorticosterone) of 21-hydroxylase are substrates of 20α-HSD, thus 20α-HSD (Akr1c18) gene expression was investigated. In lung samples collected between GD 15.5 and PN 15, 11β-hydroxylase was only detected on GD 15.5. In contrast, all the other tested genes were expressed throughout the analyzed period with different temporal expression patterns. P450scc, 21-hydroxylase, 20α-HSD and 11β-HSD2 mRNA levels increased after birth with different patterns including an increase from PN 3 with a possible sex difference for 21-hydroxylase mRNA. Also, the 21-hydroxylase protein was observed by Western blot in perinatal lungs with higher levels after birth.

CONCLUSION

Progesterone is present at high levels during gestation and the product of 21-hydroxylase, deoxycorticosterone, can bind the glucocorticoid receptor with an affinity close to that of corticosterone. Detection of 21-hydroxylase at the protein level during antenatal lung development is the first evidence that the adrenal-like glucocorticoid synthesis pathway detected during lung development has the machinery to produce glucocorticoids in the fetal lung. Glucocorticoids from lung 21-hydroxylase appear to modulate lung ontogenesis through paracrine/intracrine actions.

Lack of renal 11 beta-hydroxysteroid dehydrogenase type 2 at birth, a targeted temporal window for neonatal glucocorticoid action in human and mice

Background

Glucocorticoid hormones play a major role in fetal organ maturation. Yet, excessive glucocorticoid exposure in utero can result in a variety of detrimental effects, such as growth retardation and increased susceptibility to the development of hypertension. To protect the fetus, maternal glucocorticoids are metabolized into inactive compounds by placental 11beta-hydroxysteroid dehydrogenase type2 (11βHSD2). This enzyme is also expressed in the kidney, where it prevents illicit occupation of the mineralocorticoid receptor by glucocorticoids. We investigated the role of renal 11βHSD2 in the control of neonatal glucocorticoid metabolism in the human and mouse.

Methods

Cortisol (F) and cortisone (E) concentrations were measured in maternal plasma, umbilical cord blood and human newborn urine using HPLC. 11βHSD2 activity was indirectly assessed by comparing the F/E ratio between maternal and neonatal plasma (placental activity) and between plasma and urine in newborns (renal activity). Direct measurement of renal 11βHSD2 activity was subsequently evaluated in mice at various developmental stages. Renal 11βHSD2 mRNA and protein expression were analyzed by quantitative RT-PCR and immunohistochemistry during the perinatal period in both species.

Results

We demonstrate that, at variance with placental 11βHSD2 activity, renal 11βHSD2 activity is weak in newborn human and mouse and correlates with low renal mRNA levels and absence of detectable 11βHSD2 protein.

Conclusions

We provide evidence for a weak or absent expression of neonatal renal 11βHSD2 that is conserved among species. This temporal and tissue-specific 11βHSD2 expression could represent a physiological window for glucocorticoid action yet may constitute an important predictive factor for adverse outcomes of glucocorticoid excess through fetal programming.

Low renal mineralocorticoid receptor expression at birth contributes to partial aldosterone resistance in neonates

The human neonatal period is characterized by renal immaturity with impaired capacity to regulate water and sodium homeostasis, resembling partial aldosterone resistance. Because aldosterone effects are mediated by the mineralocorticoid receptor (MR), we postulated that this hormonal unresponsiveness could be related to low MR expression in the distal nephron. We measured aldosterone and renin levels in umbilical cord blood of healthy newborns. We used quantitative real-time PCR and immunohistochemistry to analyze the expression of MR and key players of the mineralocorticoid signaling pathway during human and mouse renal development. High aldosterone and renin levels were found at birth. MR mRNA was detected in mouse kidney at d 16 postcoitum, peaking at d 18 postcoitum, but its expression was surprisingly very low at birth, rising progressively afterward. Similar biphasic temporal expression was observed during human renal embryogenesis, with a transient expression between 15 and 24 wk of gestation but an undetectable immunoreactive MR in late gestational and neonatal kidneys. This cyclic MR expression was tightly correlated with the evolution of the 11beta-hydroxysteroid dehydrogenase type 2 and the epithelial sodium channel alpha-subunit. In contrast, glucocorticoid and vasopressin receptors and aquaporin 2 followed a progressive and sustained evolution during renal maturation. Our study provides the first evidence for a low renal MR expression level at birth, despite high aldosterone levels, which could account for compromised postnatal sodium handling. Elucidation of regulatory mechanisms governing MR expression should lead to new strategies for the management of sodium waste in preterms and neonates.

Novel mouse strain with Cre recombinase in 11beta-hydroxysteroid dehydrogenase-2-expressing cells

Here we describe the generation and characterization of a mouse strain that expresses an improved Cre (iCre) recombinase (48) under the control of the endogenous 11beta-hydroxysteroid dehydrogenase type 2 (11HSD2) promoter. Progeny of 11HSD2/iCre and ROSA26 reporter mice were used to determine the pattern of iCre expression by measuring the activity of the LacZ gene product beta-galactosidase in a panel of tissues. On Cre recombinase activity, intense beta-galactosidase activity (X-gal staining) was observed in the classic mineralocorticoid target segments of the kidney, as well as in the colon, and both female and male reproductive organs. Weaker iCre expression was detected in the lung and heart. In the brain, strong iCre activity was present in cardiovascular centers that are known to express 11HSD2 and mineralocorticoid receptors [nucleus tractus solitarius (NTS) and amygdala] as well as in the granular layer of the cerebellum. iCre expression was weaker in neonatal kidney and colon than in the adult but was present in the hair follicles and cartilage. These results indicate that in the 11HSD2/iCre strain iCre expression faithfully represents the expression pattern of endogenous 11HSD2. Thus this mouse model represents the first Cre deleter strain that can be used to eliminate desired genes in every mineralocorticoid target tissue. This mouse model should serve as a useful resource for investigators who want to study the function of genes involved in aldosterone action and genes in other pathways that are selectively expressed in these cells.