P450c11B3 mRNA, transcribed from a third P450c11 gene, is expressed in a tissue-specific, developmentally, and hormonally regulated fashion in the rodent adrenal and encodes a protein with both 11-hydroxylase and 18-hydroxylase activities

DHEA in Prenatal and Postnatal Life: Implications for Brain and Behavior

Dehydroepiandrosterone (DHEA) and its sulfated congener (DHEAS) are the principal C₁₉ steroid produced by the adrenal gland in many mammals, including humans. It is secreted in high concentrations during fetal life, but synthesis decreases after birth until, in humans and some other primates, there is a prepubertal surge of DHEA production by the adrenal gland-a phenomenon known as adrenarche. There remains considerable uncertainty about the physiological role of DHEA and DHEAS. Moreover, the origin of the trophic drives that determine the waxing and waning of DHEA synthesis are poorly understood. These gaps in knowledge arise in some measure from the difficulty of understanding mechanistic determinants from observations made opportunistically in humans and primates, and have stimulated a search for other suitable species that exhibit adrenarche- and adrenopause-like changes of adrenal function. DHEA and DHEAS are clearly neuroactive steroids with actions at several neurotransmitter receptors; indeed, DHEA is now known to be also synthesized by many parts of the brain, and this capacity undergoes ontogenic changes, but whether this is dependent or independent of the changes in adrenal synthesis is unknown. In this chapter we review key contributions to this field over the last 50+ years, and speculate on the importance of DHEA for the brain, both during development and for maturation and aging of cerebral function and behavior.

Adrenal Mitochondria and Steroidogenesis: From Individual Proteins to Functional Protein Assemblies

The adrenal cortex is critical for physiological function as the central site of glucocorticoid and mineralocorticoid synthesis. It possesses a great degree of specialized compartmentalization at multiple hierarchical levels, ranging from the tissue down to the molecular levels. In this paper, we discuss this functionalization, beginning with the tissue zonation of the adrenal cortex and how this impacts steroidogenic output. We then discuss the cellular biology of steroidogenesis, placing special emphasis on the mitochondria. Mitochondria are classically known as the "powerhouses of the cell" for their central role in respiratory adenosine triphosphate synthesis, and attention is given to mitochondrial electron transport, in both the context of mitochondrial respiration and mitochondrial steroid metabolism. Building on work demonstrating functional assembly of large protein complexes in respiration, we further review research demonstrating a role for multimeric protein complexes in mitochondrial cholesterol transport, steroidogenesis, and mitochondria-endoplasmic reticulum contact. We aim to highlight with this review the shift in steroidogenic cell biology from a focus on the actions of individual proteins in isolation to the actions of protein assemblies working together to execute cellular functions.

Identification of functional consequence of a novel selection signature in CYP11b1 gene for milk fat content in Bubalus bubalis

Genomic selection for traits of economic importance is an emerging approach carrying tremendous potentials. Many of polygenic traits as milk fat, protein and yield have been characterize at genomic level and important selection signatures have been identified. Cytochrome P450 enzymes are potential loci for affecting many of dairy capabilities. Present study was conducted for genomic dissection of CYP11b1 gene in riverine buffaloes and seven genetic variations were identified. Out of these, one novel polymorphism (p.A313T) was found well associated with milk fat %age. AB genotyped buffaloes were found to have higher milk fat %age (8.9%) for this loci. p.A313T was further validated at larger data set by restriction digestion using CviAII enzyme. Functional consequences of this locus were also predicted by studying three dimensional structure of CYP11b1 protein. For this purpose, 3D protein model was predicted by homology modeling, secondary structural attributes were determined, signal peptide was predicted and a transmembrane helix was also identified. One of polymorphism (p.Y205L) was found in the vicinity of functionally significant F-G loop region, which is the part of protein gets attached to the inner mitochondrial membrane. But this variation could not be associated and needs further investigation. p.A30V, a popular selection marker in cattle, was found in buffaloes as well but could not be associated and might need further confirmation on larger data set. Results of this study illustrate the impending potential of this gene in determining dairy capabilities of buffaloes and might have a role in selection of superior dairy buffaloes.

Hedgehog signaling and steroidogenesis

Since its discovery nearly 30 years ago, the Hedgehog (Hh) signaling pathway has been shown to be pivotal in many developmental and pathophysiological processes in several steroidogenic tissues, including the testis, ovary, adrenal cortex, and placenta. New evidence links the evolutionarily conserved Hh pathway to the steroidogenic organs, demonstrating how Hh signaling can influence their development and homeostasis and can act in concert with steroids to mediate physiological functions. In this review, we highlight the role of the components of the Hh signaling pathway in steroidogenesis of endocrine tissues.

The CYP11B subfamily

The biosynthesis of steroid hormones is dependent on P450-catalyzed reactions. In mammals, cholesterol is the common precursor of all steroid hormones, and its conversion to pregnenolone is the initial and rate-limiting step in hormone biosynthesis in steroidogenic tissues such as gonads and adrenal glands. The production of glucocorticoids and mineralocorticoids takes place in the adrenal gland and the final steps are catalyzed by 2 mitochondrial cytochromes P450, CYP11B1 (11β-hydroxylase or P45011β) and CYP11B2 (aldosterone synthase or P450aldo). The occurrence and development of these 2 enzymes in different species, their contribution to the biosynthesis of steroid hormones as well as their regulation at different levels (gene expression, cellular regulation, regulation on the level of proteins) is the topic of this chapter.

Human cytochromes P450 in health and disease

There are 18 mammalian cytochrome P450 (CYP) families, which encode 57 genes in the human genome. CYP2, CYP3 and CYP4 families contain far more genes than the other 15 families; these three families are also the ones that are dramatically larger in rodent genomes. Most (if not all) genes in the CYP1, CYP2, CYP3 and CYP4 families encode enzymes involved in eicosanoid metabolism and are inducible by various environmental stimuli (i.e. diet, chemical inducers, drugs, pheromones, etc.), whereas the other 14 gene families often have only a single member, and are rarely if ever inducible or redundant. Although the CYP2 and CYP3 families can be regarded as largely redundant and promiscuous, mutations or other defects in one or more genes of the remaining 16 gene families are primarily the ones responsible for P450-specific diseases-confirming these genes are not superfluous or promiscuous but rather are more directly involved in critical life functions. P450-mediated diseases comprise those caused by: aberrant steroidogenesis; defects in fatty acid, cholesterol and bile acid pathways; vitamin D dysregulation and retinoid (as well as putative eicosanoid) dysregulation during fertilization, implantation, embryogenesis, foetogenesis and neonatal development.

The transformation of hormonal stress responses throughout puberty and adolescence

Prepubertal rats display heightened hormonal stress reactivity compared with adults in that levels of ACTH and corticosterone take twice as long (i.e. 40-60 min) to return to baseline following an acute stressor. Despite this substantial change in stress responsiveness, and the critical nature of the adolescence period of development, the maturation of the hormonal stress response from the time of pubertal onset to adulthood has not been thoroughly investigated. To examine this, we measured ACTH, corticosterone, and testosterone in 30-, 40-, 50-, 60-, and 70-day-old (i.e. spanning pubertal and adolescent development) male rats before and after a 30 min session of restraint stress. We found that the adult-like ACTH stress response develops between 50 and 60 days of age, while the corticosterone response changes between 30 and 40 days of age. We also found that adrenal corticosterone concentrations paralleled the plasma corticosterone response following restraint, suggesting that stress-induced adrenal corticosterone synthesis decreases during adolescent development and may, at least in part, contribute to the differential stress response observed before and after puberty. Finally, stress leads to increases in testosterone secretion, but only after 50 days of age. Collectively, these results indicate that shifts in hormonal stress responses occur throughout adolescent maturation and that these responses show distinct developmental profiles.

The molecular biology, biochemistry, and physiology of human steroidogenesis and its disorders

Steroidogenesis entails processes by which cholesterol is converted to biologically active steroid hormones. Whereas most endocrine texts discuss adrenal, ovarian, testicular, placental, and other steroidogenic processes in a gland-specific fashion, steroidogenesis is better understood as a single process that is repeated in each gland with cell-type-specific variations on a single theme. Thus, understanding steroidogenesis is rooted in an understanding of the biochemistry of the various steroidogenic enzymes and cofactors and the genes that encode them. The first and rate-limiting step in steroidogenesis is the conversion of cholesterol to pregnenolone by a single enzyme, P450scc (CYP11A1), but this enzymatically complex step is subject to multiple regulatory mechanisms, yielding finely tuned quantitative regulation. Qualitative regulation determining the type of steroid to be produced is mediated by many enzymes and cofactors. Steroidogenic enzymes fall into two groups: cytochrome P450 enzymes and hydroxysteroid dehydrogenases. A cytochrome P450 may be either type 1 (in mitochondria) or type 2 (in endoplasmic reticulum), and a hydroxysteroid dehydrogenase may belong to either the aldo-keto reductase or short-chain dehydrogenase/reductase families. The activities of these enzymes are modulated by posttranslational modifications and by cofactors, especially electron-donating redox partners. The elucidation of the precise roles of these various enzymes and cofactors has been greatly facilitated by identifying the genetic bases of rare disorders of steroidogenesis. Some enzymes not principally involved in steroidogenesis may also catalyze extraglandular steroidogenesis, modulating the phenotype expected to result from some mutations. Understanding steroidogenesis is of fundamental importance to understanding disorders of sexual differentiation, reproduction, fertility, hypertension, obesity, and physiological homeostasis.

The prolactin regulatory element-binding regulates of the 11beta-hydroxylase gene

Prolactin regulatory element-binding (PREB) protein is a transcription factor not only in pituitary but also adrenal gland. Steroid 11beta-hydroxylase (CYP11B1), a member of the cytochrome p-450 superfamily, is responsible for the last step of glucocorticoid biosynthesis in the adrenal cortices of many kinds of animals. In the present study, we have examined the role of PREB in regulating CYP11B1. CYP11B1 expression was found to be regulated by cAMP, which stimulated the expression of PREB. In addition, PREB induced the expression of the luciferase reporter protein that was under the control of the CYP11B1 promoter. Electrophoretic mobility shift analysis (EMSA) showed that PREB mediates its transcriptional effect by binding to the PREB-responsive cis-element (PRCE) of the CYP11B1 promoter. The knockdown of PREB expression attenuated the effects of cAMP on CYP11B1 expression. In summary, our data showed that in the adrenal gland, PREB regulates the transcription of the CYP11B1 gene via cAMP.

A lifetime of aldosterone excess: long-term consequences of altered regulation of aldosterone production for cardiovascular function

Up to 15% of patients with essential hypertension have inappropriate regulation of aldosterone; although only a minority have distinct adrenal tumors, recent evidence shows that mineralocorticoid receptor activation contributes to the age-related blood pressure rise and illustrates the importance of aldosterone in determining cardiovascular risk. Aldosterone also has a major role in progression and outcome of ischemic heart disease. These data highlight the need to understand better the regulation of aldosterone synthesis and its action. Aldosterone effects are mediated mainly through classical nuclear receptors that alter gene transcription. In classic epithelial target tissues, signaling mechanisms are relatively well defined. However, aldosterone has major effects in nonepithelial tissues that include increased synthesis of proinflammatory molecules and reactive oxygen species; it remains unclear how these effects are controlled and how receptor specificity is maintained. Variation in aldosterone production reflects interaction of genetic and environmental factors. Although the environmental factors are well understood, the genetic control of aldosterone synthesis is still the subject of debate. Aldosterone synthase (encoded by the CYP11B2 gene) controls conversion of deoxycorticosterone to aldosterone. Polymorphic variation in CYP11B2 is associated with increased risk of hypertension, but the molecular mechanism that accounts for this is not known. Altered 11beta-hydroxylase efficiency (conversion of deoxycortisol to cortisol) as a consequence of variation in the neighboring gene (CYP11B1) may be important in contributing to altered control of aldosterone synthesis, so that the risk of hypertension may reflect a digenic effect, a concept that is discussed further. There is evidence that a long-term increase in aldosterone production from early life is determined by an interaction of genetic and environmental factors, leading to the eventual phenotypes of aldosterone-associated hypertension and cardiovascular damage in middle age and beyond. The importance of aldosterone has generated interest in its therapeutic modulation. Disadvantages associated with spironolactone (altered libido, gynecomastia) have led to a search for alternative mineralocorticoid receptor antagonists. Of these, eplerenone has been shown to reduce cardiovascular risk after myocardial infarction. The benefits and disadvantages of this therapeutic approach are discussed.

Direct effects of IL-15 on corticosterone secretion by rat adrenocortical cells

Cytokines might regulate the function of the hypothalamic-pituitary-adrenal axis. IL-15 is a potent non-T-cell-derived cytokine with IL-2-like activities. It has been shown that IL-15 can reverse the inhibition of glucocorticoids on PBMC. In vitro experiments were designed to assess the direct effect of IL-15 on corticosterone (CORT) secretion in the adrenal zona fasciculata-reticularis (ZFR) cells of male rats. Administration of IL-15 dose dependently decreased the basal and adrenocorticotropin-stimulated release of CORT and production of cAMP in ZFR cells. The stimulatory effect of forskolin (an adenylate cyclase activator) on CORT secretion and accumulation of cAMP in ZFR cells was attenuated by the administration of IL-15. However, 8-Br-cAMP (a cAMP analogue)-stimulated release of CORT was not affected by IL-15. Exogenous administration of IL-15 (10(-7) mol/L) significantly attenuated the pregnenolone (the substrate of 3beta-hydroxysteroid dehydrogenase)- or deoxycorticosterone (the substrate of 11beta-hydroxylase)-induced release of CORT. The results indicate that decrease of CORT secretion by IL-15 is in part because of (i) the decrease of adenylate cyclase activity and cAMP production and (ii) the inhibition of 3beta-hydroxysteroid dehydrogenase and 11beta-hydroxylase activities in rat ZFR cells.

Overview of steroidogenic enzymes in the pathway from cholesterol to active steroid hormones

Significant advances have taken place in our knowledge of the enzymes involved in steroid hormone biosynthesis since the last comprehensive review in 1988. Major developments include the cloning, identification, and characterization of multiple isoforms of 3beta-hydroxysteroid dehydrogenase, which play a critical role in the biosynthesis of all steroid hormones and 17beta-hydroxysteroid dehydrogenase where specific isoforms are essential for the final step in active steroid hormone biosynthesis. Advances have taken place in our understanding of the unique manner that determines tissue-specific expression of P450aromatase through the utilization of alternative promoters. In recent years, evidence has been obtained for the expression of steroidogenic enzymes in the nervous system and in cardiac tissue, indicating that these tissues may be involved in the biosynthesis of steroid hormones acting in an autocrine or paracrine manner. This review presents a detailed description of the enzymes involved in the biosynthesis of active steroid hormones, with emphasis on the human and mouse enzymes and their expression in gonads, adrenal glands, and placenta.

Estrogen-producing steroidogenic pathways in parietal cells of the rat gastric mucosa

Recently we demonstrated the presence of aromatase (P450(arom)), estrogen synthetase, and the active production of estrogen in parietal cells of the rat stomach. We therefore investigated the steroidogenic pathways of estrogen and also other steroid metabolites in the gastric mucosa of male rats, by showing the mRNA expression of steroidogenic enzymes using RT-PCR and in situ hybridization histochemistry, and by measuring the blood concentration of steroids in the artery and the portal vein. RT-PCR analysis showed the strong mRNA expression of 17alpha-hydroxylase/17,20-lyase (P450(17alpha)), 17beta-hydroxysteroid dehydrogenase (HSD) type III and P450(arom), and the weak mRNA expression of 17beta-HSD type II, 5alpha-reductase type I and 3alpha-HSD. The other mRNAs of steroidogenic enzymes examined were not detected. In situ hybridization histochemistry demonstrated the localization of mRNAs for P450(17alpha), 17beta-HSD type III and P450(arom) in the parietal cells. Higher levels of progesterone and testosterone were found in the artery compared with the portal vein. Higher amounts of estrone and 17beta-estradiol, by contrast, were present in the portal vein compared with the artery. These results indicate that parietal cells of rat stomach convert circulating progesterone and/through androstenedione and testosterone to synthesize both estrone and 17beta-estradiol, which then enter the liver via the portal vein.

Modulation of aldosterone and cortisol synthesis on the molecular level

CYP11B1 and the closely related CYP11B2 are involved in the production of adrenal steroid hormones. Although in human their primary structure is 93% identical they are involved in the biosynthesis of functionally diverse products, such as glucocorticoids and mineralocorticoids, respectively. In contrast, bovine CYP11B1 combines both activities in one single enzyme. The CYP11B family belongs to class I cytochromes P450 that have been described in bacteria and mitochondria and receive their electrons from a low molecular weight iron sulphur protein which is reduced by a NADPH-dependent FAD-containing reductase. In this review, we summarise the current knowledge on the modulation of aldosterone and cortisol synthesis by transcriptional regulation, on the molecular level as consequence of mutations found in patients suffering from steroid hormone-related diseases as well as introduced by site-directed mutagenesis and as consequence of protein-protein interaction with both CYP11A1 and the natural redox partner adrenodoxin.

Extra-adrenal production of corticosteroids

1. The major corticosteroids aldosterone and cortisol (corticosterone in rodents) are secreted from the adrenal cortex under the regulation of the renin-angiotensin system and the hypothalamic-pituitary-adrenal axis. 2. In addition to their accepted roles in such processes as blood pressure regulation, glycogenesis, hepatic glyconeogenesis and immunosuppression, the corticosteroids have been implicated in the development of cardiac fibrosis, modulation of hippocampal neuron excitability, memory formation and neurodegeneration. 3. The advent of sensitive molecular biological techniques has produced a wealth of evidence to support the existence of extra-adrenal corticosteroidogenic systems. Most attention has been paid to the cardiovascular system and the central nervous system, where the full array of enzymes required for the de novo synthesis of corticosteroids from cholesterol has been identified. 4. Although the evidence for local corticosteroid production is strong, the quantities of steroid would be small compared with adrenal production. Therefore, it is still a matter of debate as to whether extra-adrenal corticosteroids are of any physiological significance. This will depend on factors such as local concentration, proximity to target cells and, possibly, to tissue-specific control mechanisms.

Antenatal dexamethasone: effect on ovine placental 11beta-hydroxysteroid dehydrogenase type 2 expression and fetal growth

Antenatal glucocorticoids are routinely given to women at risk for preterm delivery. The fetus is protected from excessive glucocorticoids by the placental enzyme 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD-2), which catalyzes the conversion of cortisol to its biologically inactive metabolite, cortisone. We examined the effects of antenatal dexamethasone on the expression of placental 11beta-HSD-2 in fetal sheep. Ewes were randomized to receive repeated or single courses of dexamethasone or placebo beginning at 76-78 or 104-106 d of gestation, respectively. In the single course group, the ewes received dexamethasone (6 mg, n = 7) or placebo (n = 6) as four intramuscular injections over 48 h up to 18 h before placental harvest. In the repeated course group, the ewes received the same treatment (dexamethasone, n = 10, or placebo, n = 9) once a week for 5 consecutive weeks starting at 76-78 d of gestation. Placental harvest occurred at 106-108 d of gestation in the four groups. By semi-quantitative RT-PCR, we found that placental 11beta-HSD-2 expression was lower in the fetuses of ewes exposed to a single course of dexamethasone than placebo (p < 0.05). Placental 11beta-HSD-2 expression did not differ significantly between fetuses of ewes treated with repeated courses of dexamethasone compared with placebo, or a single course of dexamethasone. Fetuses of dexamethasone treated ewes weighed less than those of placebo treated ewes (ANOVA, main effects for dexamethasone versus placebo treatment: F = 14.5, p = 0.007). Fetuses of ewes exposed to repeated courses of dexamethasone weighed less than those of ewes exposed to placebo or a single course of dexamethasone (p < 0.05). We conclude that maternal antenatal dexamethasone treatment reduces placental 11beta-HSD-2 expression and fetal weight at mid-gestation in the ovine pregnancy.

Analyses of the CYP11B gene family in the guinea pig suggest the existence of a primordial CYP11B gene with aldosterone synthase activity

In this study we describe the isolation of three genes of the CYP11B family of the guinea pig. CYP11B1 codes for the previously described 11beta-hydroxylase [Bülow, H.E.,Möbius, K., Bähr, V. & Bernhardt, R. (1996) Biochem. Biophys. Res. Commun. 221, 304-312] while CYP11B2 represents the aldosterone synthase gene. As no expression for CYP11B3 was detected this gene might represent a pseudogene. Transient transfection assays show higher substrate specificity for its proper substrate for CYP11B1 as compared to CYP11B2, which could account for the zone-specific synthesis of mineralocorticoids and glucocorticoids, respectively. Thus, CYP11B2 displayed a fourfold higher ability to perform 11beta-hydroxylation of androstenedione than CYP11B1, while this difference is diminished with the size of the C17 substituent of the substrate. Furthermore, analyses with the electron transfer protein adrenodoxin indicate differential sensitivity of CYP11B1 and CYP11B2 as well as the three hydroxylation steps catalysed by CYP11B2 to the availability of reducing equivalents. Together, both mechanisms point to novel protein intrinsic modalities to achieve tissue-specific production of mineralocorticoids and glucocorticoids in the guinea pig. In addition, we conducted phylogenetic analyses. These experiments suggest that a common CYP11B ancestor gene that possessed both 11beta-hydroxylase and aldosterone synthase activity underwent a gene duplication event before or shortly after the mammalian radiation with subsequent independent evolution of the system in different lines. Thus, a differential mineralocorticoid and glucocorticoid synthesis might be an exclusive achievement of mammals.

Genetic analysis of the cytochrome P-450c17alpha (CYP17) and aldosterone synthase (CYP11B2) in Japanese patients with 17alpha-hydroxylase deficiency

OBJECTIVE

To determine the clinical and molecular genetic characterization of two Japanese patients with 17alpha-hydroxylase deficiency, we analysed the 17alpha-hydroxylase/17,20-lyase gene (CYP17). Next, to clarify the mechanism of hypoaldosteronism in 17alpha-hydroxylase deficiency, we analysed the expression of aldosterone synthase (CYP11B2) messenger RNA and sequenced CYP11B2 in these patients.

PATIENTS

Patient 1 (46 XY), phenotypically female, sought medical attention for hypertension, amenorrhea and infantile genitalia. Patient 2 (46 XX), phenotypically female, presented for hypertension and amenorrhea. Hormonal data in both patients showed decreased levels of sex steroids, cortisol, aldosterone and plasma renin activity and extreme elevation of deoxycortisol.

DESIGN

Direct sequencing of CYP17 and CYP11B2 was performed using genomic DNA from the patients. An expression studies of mutated forms of CYP17 was performed using COS-1 cells. The expression of CYP11B2 messenger RNA in mononuclear leucocytes (MNLs) of these patients and normal subjects was measured using the competitive polymerase chain reaction

METHOD

The effect of renin secretion stimulation on the levels of CYP11B2 messenger RNA in MNLs of normal subjects was also studied.

RESULTS

We detected two novel genetic defects in 17alpha-hydroxylase. Sequence analysis revealed one base pair deletion (T) at codon 243 in exon 4 in patient 1. CYP17 in patient 2 contained a point mutation (C to T) at position 415 in exon 8. Transfected cells of mutant from patient 1 had no 17alpha-hydroxylase or 17,20-lyase activity. The R415C mutant protein showed very weak activity of 17alpha-hydroxylase or 17,20-lyase activity. In the renin secretion stimulating test, the increase in CYP11B2 messenger RNA levels in MNLs was parallel with that of plasma aldosterone concentration. The expression of CYP11B2 mRNA in NMLs of these patients was lower compared to controls. No mutations in CYP11B2, including the 5' flanking region, were found.

CONCLUSIONS

These results indicate that the novel mutations of the CYP17 gene found in these patients inactivate cytochrome P450c17 function, and that hypoaldosteronism in these patients may be partly explained by a decreased activity of aldosterone synthase, which is regulated at the transcriptional level.

Modulation of steroidogenesis by selenium in a novel adrenal cell line developed using targeted tumorigenesis

Glutathione peroxidase (GPx-1) is a selenoenzyme that metabolizes H(2)O(2), a source of potentially toxic free radicals. Steroidogenesis is markedly inhibited by H(2)O(2) in vitro.

OBJECTIVE

to study the effects of selenium deficiency on GPx activity and adrenal steroidogenesis in a novel adrenal cell line developed using targeted tumorigenesis.

METHODS

AN4Rppc7 cells were grown for 7 days in serum-free medium. 8-Br-cAMP-stimulated concentrations of steroid hormones were measured by RIA. StAR (Steroid Acute Reactive Protein) mRNA was measured by Northern blot.

RESULTS

selenium deficiency caused a 99% There was a 51%, progesterone, corticosterone and aldosterone production, respectively (p<0.05 by ANOVA). StAR mRNA was not affected by selenium.

CONCLUSIONS

selenium deficiency causes a marked decrease in GPx activity. Decreased steroid hormone production occurs for selenium concentrations equal or lower than 5 nM. The absence of changes in StAR mRNA content suggests that selenium deficiency does not affect cholesterol access to the mitochondria.

Differentiated corticosteroid production and regeneration after selective transplantation of cultured and noncultured adrenocortical cells in the adrenalectomized rat

Syngeneic transplantation of adrenocytes was investigated in Lewis rats in regard to differentiated hormone secretion and cortex regeneration after bilateral adrenalectomy as an alternative to steroid substitution.

METHODS

Purified cell suspensions of glomerulosa (density 1.061 +/- 0.001 g/ml) and fasciculata (density 1.034 +/- 0.003 g/ml) cells were obtained by density gradient separation and were transplanted under the kidney capsule either immediately or after a 29-day culture period. Animals were killed after transplantation of cultured glomerulosa (CG-Tx) or cultured fasciculata cells (CF-Tx), noncultured glomerulosa cells (G-Tx) or non-cultured fasciculata cells (F-Tx), or both cell types (GF-Tx) for morphological studies after 30, 120, and 360 days. Plasma samples were drawn for measurement of corticosterone and aldosterone as well as 24 hr-urine for sodium and potassium levels at day 3, 30, 120, and 360 after transplantation.

RESULTS

In primary culture fasciculata cell number remained stationary although glomerulosa cell number increased to almost 10-fold. Vital cortex cells were demonstrated in each explanted graft by histochemistry but only group G-Tx, CG-Tx, and GF-Tx (purified cell suspensions of zona glomerulosa and fasciculata) showed neocortex-like structures. We found plasma (urine) corticosterone to decrease from preoperatively 256-304 ng/ml (226-239 ng/day) in untreated animals to levels about half as high 3 days after transplantation, increasing to normal values in all study groups 30 days after treatment (data given as range). Plasma aldosterone concentrations, 150-180 pg/ml in untreated rats, decreased to nondetectable levels for 1 week after bilateral adrenalectomy. At day 30 group GF-Tx, G-Tx, and CG-Tx showed comparable aldosterone plasma concentrations (104-122 pg/ml); however, levels in F-Tx and CF-Tx were 19-49 pg/ml, and did not increase significantly within the observation period.

CONCLUSIONS

Cells derived from the zona glomerulosa maintain viability, produce both aldosterone and corticosterone, and regenerate a neocortex with cells that histologically resemble both zona glomerulosa and fasciculata cells. They are therefore suitable for adrenocortical transplantation. In contrast, cells derived from the zona fasciculata maintain viability, but do not regenerate zona glomerulosa and do not produce aldosterone. These results suggest that the cell migration model, in which zona glomerulosa cells can acquire the phenotype of zona fasciculata cells as they can migrate centripetally, is more likely the correct explanation of adrenocortical zonation.

Role of rat adrenal antioxidant defense systems in the aldosterone turn-off phenomenon

The mechanism(s) of the "aldosterone turn-off phenomenon", hypoaldosteronemia following chronic ACTH administration, remains unclear. Our previous observation that antioxidants prevented turn-off prompted us to evaluate the chronic effect of ACTH on the enzymatic antioxidant system as well as P450aldo activity and expression of CYP11B2 in adrenal zona glomerulosa. Male Wistar rats were administered ACTH-Z for 5 days with or without antioxidants, vitamin E or DMSO. Adrenal capsules were prepared for P450aldo activity measurement and mRNA content determination by competitive RT-PCR, and immunoreactivity of Mn-SOD in whole adrenals was evaluated. ACTH decreased the P450aldo activity and mRNA level of CYP11B2 in adrenal capsules, while co-administration of vitamin E or DMSO partially blocked this inhibition. ACTH increased Mn-SOD mRNA and immunoreactivity but decreased GPx mRNA. These results suggest that prolonged ACTH treatment increases oxidative stress in the zona glomerulosa and an imbalance in the ratio of Mn-SOD to GPx, possibly via corticosterone overproduction in the zona fasciculata, resulting in the downregulation of CYP11B2. Vitamin E and DMSO might thus protect CYP11B2 expression through their antioxidant actions.

Adrenocortical activity in fetal SHR and WKY rats

There is increasing evidence that the intrauterine milieu and corticosteroid exposure play a role in the etiology of hypertension. We examined adrenocortical gene expression and circulating corticosteroids in the d 21 fetal spontaneously hypertensive rat (SHR) and its normotensive genetic control, the Wistar-Kyoto (WKY) rat. By RNase protection assays, we found no differences in the relative abundances of mRNAs for P450scc and P450c11beta, and barely detectable P450c11AS mRNA in the adrenals of fetal SHR and WKY rats. P450c11B3 RNA was undetectable by reverse transcription polymerase chain reaction in both SHR and WKY fetuses. The zonal expression of P450c11 mRNA was comparable in SHR and WKY fetuses by in situ hybridization histochemistry. There were no significant differences in peripheral levels of aldosterone and corticosterone by radioimmunoassay in fetal SHR and WKY rats. Based upon the absence of distinct differences in the aspects of adrenocortical activity examined, it is unlikely that they are integral in the programming of hypertension in this model.

Adrenocortical imprint in the fetus of a diabetic gestation

Offspring of diabetics are at increased risk for diabetes as adults. As corticosteroids are intimately involved in glucose homeostasis, we investigated aspects of corticosteroid activity in the late gestation fetuses of control, moderately diabetic and insulin-controlled streptozotocin-induced diabetic rats. We found that moderate maternal diabetes had no effect upon litter size or fetal body weight. Uncontrolled maternal diabetes was accompanied by fetal hyperglycemia, hyperinsulinemia and elevated aldosterone. Maternal insulin treatment normalized fetal glucose and aldosterone; fetal insulin and corticosterone levels increased. Maternal diabetes had no effect upon fetal adrenal expression of P450scc mRNA; the abundance of P450c11beta mRNA increased, and returned to that of the control gestation upon insulin treatment. P450c11AS mRNA was barely detectable, and decreased in the fetuses of insulin-treated diabetics. P450c11B3 mRNA was undetectable in all fetal groups. Our results implicate aspects of maternal diabetes in the expression of a fetal adrenocortical imprint, manifested as a greater abundance of P450c11beta mRNA. Although not accompanied by elevated corticosterone in the fetus, this imprint could ultimately allow for greater potential corticosterone production in response to typical stimuli, and thus contribute to the tendency towards glucose dysregulation in these offspring of diabetic gestations.

Development of functional zonation in the rat adrenal cortex

In an attempt to elucidate the mechanism(s) through which the functional adrenal cortex is established, we analyzed immunohistochemically the expression of various markers for the adrenocortical zones, i.e. the zona glomerulosa (zG), the zona fasciculata (zF), and the zona reticularis (zR), as well as markers for the medulla, and further examined the distribution and behavior of DNA-synthesizing cells in rat adrenal glands during development. The results showed that 1) separation of the cortex and medulla, and the development of functional zonation in the cortex began at around the time of birth, 2) at fetal stages when cortical zonation was not established, DNA-synthesizing cells were found scattered throughout the gland, where they proliferated without significant migration, and 3) after birth in the adrenal cortex with established cortical zonation, DNA-synthesizing cells were localized near the undifferentiated zone between zG and zF, and then they migrated centripetally. Cell death appeared to occur in the innermost portion of the cortex, where many resident macrophages are present. These findings illustrate basic processes underlying adrenal development and suggest that the undifferentiated region is apparently the stem cell zone of the adrenal cortex that maintains the cortical zonation.

Adrenal zonation: clues from 11beta-hydroxylase and aldosterone synthase

Aldosterone and cortisol are the major mineralocorticoid and glucocorticoid produced by the human adrenal. Circulating levels of angiotensin II and potassium control the adrenal production of aldosterone, while the production of cortisol is controlled mainly by adrenocorticotropin. The capacity of the adrenal cortex to differentially produce aldosterone and cortisol relies to a large degree on the expression of aldosterone synthase (CYP11B2) and 11beta-hydroxylase (CYP11B1). CYP11B2 catalyzes the final steps in the biosynthesis of aldosterone and is expressed solely in the glomerulosa of the adrenal cortex, while CYP11B1 catalyzes the final steps in the biosynthesis of cortisol and is expressed in the fasciculata/reticularis. The zonal expression of these two isozymes appears to result from transcriptional regulation of the two genes. Herein, the recent progress in defining the cellular mechanisms that regulate transcription of these two isozymes and thus the capacity of the adrenal gland to differentially produce aldosterone and cortisol is discussed.

Eel (Anguilla japonica) testis 11beta-hydroxylase gene is expressed in interrenal tissue and its product lacks aldosterone synthesizing activity

A recombinant expression vector containing Japanese eel (Anguilla japonica) testis cytochrome P450(11 beta) (11beta-hydroxylase) cDNA was introduced into COS-1 cells. Enzymatic activity of the expressed P450(11 beta) for corticosteroid synthesis was analysed by incubating transfected cells with 14C-labelled 11-deoxycorticosterone or 3H-labelled deoxycortisol as substrates. Thin layer chromatography of incubation medium revealed that a high percentage of 11-deoxycorticosterone was converted into corticosterone and 11-dehydrocorticosterone but no aldosterone was detected. Similarly, deoxycortisol was converted into cortisol and cortisone. These results show that eel P450(11beta) does not possess significant aldosterone synthesizing activity. Northern blot analysis detected a 1.8 kb transcript of P450(11beta) using RNA extracted from interrenals of untreated Japanese eel but no hybridization signal was apparent using RNA extracted from brain, spleen, heart, muscle or testis. Immunohistochemistry using an antiserum against P450(11beta) also revealed strong immunostaining in interrenal cells.

Development of adrenal zonation in fetal rats defined by expression of aldosterone synthase and 11beta-hydroxylase

The adult rat adrenal cortex is comprised of three concentric steroidogenic zones that are morphologically and functionally distinguishable: the zona glomerulosa, zona intermedia, and the zona fasciculata/reticularis. Expression of the zone-specific steroidogenic enzymes, cytochrome P450 aldosterone synthase (P450aldo), and P450 11beta hydroxylase (P45011beta), produced by the zona glomerulosa and zona fasciculata/reticularis, respectively, can be used to define the adrenal cortical cell phenotype of these two zones. In this study, immunohistochemistry and in situ hybridization were used to determine the ontogeny of expression of P450aldo and P45011beta to monitor the pattern of development of the rat adrenal cortex. RIA was used to measure adrenal content of aldosterone and corticosterone, the resulting products of the two enzymatic pathways. Double immunofluorescent staining for both enzymes at gestational day 16 (E16) showed P45011beta protein expressed in cells distributed throughout most of the adrenal intermixed with a separate, but smaller, population of cells expressing P450aldo protein. Whereas expression of P45011beta protein retained a similar pattern of distribution from E16 to adulthood (ignoring distribution of SA-1 positive, presumptive medullary cells), P450aldo protein changed its pattern of distribution by E19, becoming localized in a discontinuous ring of cells adjacent to the capsule. By postnatal day 1, P450aldo protein distribution was similar to that observed in adult glands; P450aldo-positive cells formed a continuous zone underlying the capsule. In situ hybridization showed that the pattern of P45011beta messenger RNA expression paralleled protein expression at all times, whereas P450aldo messenger RNA paralleled protein at E19 and after, but was undetectable before E19. However, adrenal aldosterone and corticosterone, as measured by RIA, were detected by E16, supporting the functional capacity of both phenotypes for all ages studied. These data suggest that the development of the adrenal zona glomerulosa occurs in two distinct phases; initial expression of the glomerulosa phenotype in scattered cells of the inner cortex before E17, followed by a change in distribution to the outer cortex between E17 and E19. It is hypothesized that this change in distribution occurs via cell differentiation, rather than cell migration, and that a possible regulator of these events is the fetal renin-angiotensin system.

Myocardial production of aldosterone and corticosterone in the rat. Physiological regulation

Increasing evidence suggests that mineralo- and glucocorticoids modulate cardiovascular homeostasis via the effects of circulating components generated within the adrenals but also through local synthesis. The aim of this study was to assess the existence of such a steroidogenic system in heart. Using the quantitative reverse transcriptase-polymerase chain reaction, the terminal enzymes of corticosterone and aldosterone synthesis (11beta-hydroxylase and aldosterone synthase, respectively) were detected in the rat heart. This pathway was shown to be physiologically active, since production of aldosterone, corticosterone, and their precursor, deoxycorticosterone, was detected in both the homogenate and perfusate of isolated rat hearts using radioimmunoassay after Celite column chromatography. Perfusion of angiotensin II or adrenocorticotropin for 3 h increased aldosterone and corticosterone production and decreased deoxycorticosterone, suggesting that aldosterone and corticosterone are formed within the isolated heart from a locally present substrate. Chronic regulation of this intracardiac system was then examined. As in adrenals cardiac 11beta-hydroxylase and aldosterone-synthase mRNAs were independently regulated by 1 week's treatment with either low sodium and high potassium diet (which increased aldosterone synthase mRNA level only), angiotensin II (which raised level of both mRNAs), or adrenocorticotropin (which stimulated the 11beta-hydroxylase gene exclusively). Changes in cardiac steroid levels during treatment were not directly related to their plasma levels suggesting independent regulating mechanisms. This study, therefore, provides the first evidence for the existence of an endocrine cardiac steroidogenic system in rat heart and emphasizes its potential physiological and pathological relevance.

Acute effects of thyroid hormones on the production of adrenal cAMP and corticosterone in male rats

The acute effects of thyroid hormones on glucocorticoid secretion were studied. Venous blood samples were collected from male rats after they received intravenous 3,5,3'-triiodothyronine (T3) or thyroxine (T4). Zona fasciculata-reticularis (ZFR) cells were treated with adrenocorticotropic hormone (ACTH), T3, T4, ACTH plus T3, or ACTH plus T4 at 37 degrees C for 2 h. Corticosterone concentrations in plasma and cell media, and also adenosine 3',5'-cyclic monophosphate (cAMP) production in ZFR cells in the presence of 3-isobutyl-1-methylxanthine, were determined. The effects of thyroid hormones on the activities of steroidogenic enzymes of ZFR cells were measured by the amounts of intermediate steroidal products separated by thin-layer chromatography. Administration of T3 and T4 suppressed the basal and the ACTH-stimulated levels of plasma corticosterone. In ZFR cells, both thyroid hormones inhibited ACTH-stimulated corticosterone secretion, but the basal corticosterone was inhibited only with T3 > 10(-10) M or T4 > 10(-8) M. Likewise, T3 or T4 at 10(-7) M inhibited the basal- and ACTH-stimulated levels of intracellular cAMP. Physiological doses of T3 and T4 decreased the activities of 3 beta-hydroxysteroid dehydrogenase, 21-hydroxylase, and 11 beta-hydroxylase. These results suggest that thyroid hormones counteract ACTH in adrenal steroidogenesis through their inhibition of cAMP production in ZFR cells.

Inhibition of steroidogenesis in rat adrenal cells by 18-ethynyldeoxycorticosterone: evidence for an alternative pathway of aldosterone biosynthesis

The effect of the mechanism-based inhibitor 18-ethynyldeoxycorticosterone (18-E-DOC) on the late steps of the aldosterone biosynthetic pathway was examined in freshly isolated cells of the zona glomerulosa (ZG) and fasciculata (ZF) from rat adrenal glands. ZG synthesis of aldosterone was inhibited by 18-E-DOC in a time- and concentration-dependent manner with a Ki of approximately 0.05 microM. The maximal degree of inhibition of ZG production of aldosterone and 18-hydroxycorticosterone (18-OH-B) was approximately 80%. ZF cells, perhaps surprisingly, were found to secrete 18-OH-B at levels approximately one-third to one-fourth those of ZG cells and the Ki of 18-E-DOC inhibition of 18-OH-B secretion was approximately 10 microM for ZF cells, 200-fold higher than for ZG cells. The inhibitor had no effect on the secretion of corticosterone by either ZG or ZF, and the secretion of 18-hydroxydeoxycorticosterone (18-OH-DOC) by both the ZG and ZF was inhibited only to a minor degree. 18-E-DOC inhibited the biosynthesis of aldosterone by ZG cells incubated with 10 microM added DOC or 18-OH-DOC by approximately 75%, similar to the degree of inhibition of aldosterone biosynthesis from endogenous substrate, whereas ZF biosynthesis of 18-OH-B from either substrate was inhibited by less than 40%. ZF cells do not express aldosterone synthase, the only enzyme known to convert 18-OH-DOC into 18-OH-B. Incubation of MA-10 cells stably transfected with the cDNA of the rat aldosterone synthase with 18-E-DOC resulted in a complete inhibition of the conversion of DOC to aldosterone with a Ki of approximately 0.02 microM. In addition, transfected cells expressing 11beta-hydroxylase convert DOC to 18-OH-B in very small quantities only and cannot convert 18-OH-DOC to 18-OH-B. These data suggest that neither 11beta-hydroxylase nor aldosterone synthase are responsible for the biosynthesis of 18-OH-B by ZF cells from DOC or 18-OH-DOC, that 20% of aldosterone synthesis appears not to be attributable to the actions of aldosterone synthase and that an unknown CYP11B enzyme is also involved in the biosynthesis of 18-OH-B.

Effects of gestation on enzymes controlling aldosterone synthesis in the rat adrenal

In the present study, the effects of gestation on various enzymes implicated in corticosteroid synthesis were evaluated in adrenal zona glomerulosa and zona fasciculata-reticularis of the Sprague-Dawley rat. The activity and expression of cholesterol side-chain cleavage cytochrome P450, 11beta-hydroxylase cytochrome P450, and aldosterone synthase cytochrome P450 (P450aldo) were analyzed. Plasma aldosterone levels were increased significantly at 22 days gestation (n = 10) and fell below the nonpregnant levels at 18-36 h postpartum (n = 11). The activity and expression of 11beta-hydroxylase cytochrome P450 and cholesterol side-chain cleavage cytochrome P450 were not modified by gestation. P450aldo activity increased at 14 days gestation (n = 4) and returned to the prepregnancy level at 2 weeks postpartum (n = 5). As shown by Northern blot analysis (n = 3), P450aldo messenger RNA increased significantly at 22 days gestation and decreased 18-36 h postpartum. We clearly demonstrated that elevated plasma aldosterone levels during pregnancy are associated with augmented activity and messenger RNA levels of P450aldo in the zona glomerulosa.

The amino acid substitutions Ser288Gly and Val320Ala convert the cortisol producing enzyme, CYP11B1, into an aldosterone producing enzyme

Transfection studies with cDNAs encoding hybrids between the highly similar cytochrome P450 enzymes, CYP11B1 (steroid 11 beta-hydroxylase) and CYP11B2 (aldosterone synthase) have identified which amino acids determine the different activities of the enzymes.

Expression of cytochrome P45011B1 mRNA in the brain of normal and hypertensive transgenic rats

Cytochrome P45011B1 (11 beta-hydroxylase) was detected in the brain of male rats by in situ hybridization methods. Normal Sprague-Dawley rats were compared to the transgenic strain TGR(mRen2)27, characterized by the expression of the murine Ren-2d renin gene and the development of severe hypertension. Specific riboprobes were generated by in the vitro transcription of a 152 base-pair long cDNA template 35S-labeled riboprobes were hybridized to cryostat sections from adrenal glands and from two different levels of the brain using standard protocols and varying washing conditions. After exposure of the radiolabeled sections to X-ray film, the signals were quantified and compared. Following autoradiography and counterstaining, cytochrome P45011B1 mRNA was clearly localized in the zona fasciculata/reticularis of the adrenal cortex and in distinct layers of the cerebral cortex. High signal densities were obtained in the layers II-IV of the neocortex and in the layer II of the piriform cortex, although the concentrations of cytochrome P45011B1 mRNA were remarkably lower in the central nervous system as compared to adrenal glands. As revealed by the semi-quantitative analysis, there was a slight increase in adrenal 11 beta-hydroxylase mRNA in the transgenic rats, whereas the brain seems to express nearly the same amount of this enzyme in both strains. The cytochrome P45011B1 mRNA expression in distinct cells, probably nerve cells, and especially in regions with high densities of glucocorticoid receptors points to a possible function of brain derived corticosterone in receptor activation.

Mineralocorticoids, salt and high blood pressure

Essential hypertensive patients often respond to treatments mitigating mineralocorticoid action, even though circulating levels of these steroids are within normal ranges. In addition to the kidney, mineralocorticoid or Type I receptors are found in the brain and vascular smooth muscle where they mediate effects associated with several forms of experimental hypertension. Studies in which discrete anatomic or functional areas of the brain have been ablated demonstrate that the periventricular areas of the hypothalamus and the central sympathetic and baroreceptor systems are crucial for the development of hypertension in the renoprival, DOCA salt, and Dahl salt-sensitive rat. Intracerebroventricular (i.c.v.) infusion of aldosterone in both rats and dogs at doses that do not raise serum levels above normal produce hypertension. The hypertension produced by systemic mineralocorticoid excess, adrenal regeneration, and i.c.v. or oral administration of glycyrrhetinic acid or carbenoxolone in genetically normotensive rats and by dietary salt in the Dahl salt-sensitive rat is inhibited by the i.c.v. infusion of a mineralocorticoid receptor antagonist or a Na+ channel-selective amiloride analog. Recent data demonstrate the extraadrenal synthesis of steroids in aortic endothelial cells, smooth muscle cells and the brain. The role of the extraadrenal synthesis of steroids raises new avenues for research into the causes of hypertension.

Molecular mechanism of cytochrome P-450-dependent aldosterone biosynthesis in the adrenal cortex

In the adrenal cortex, the potent mineralocorticoid, aldosterone, is produced in the zoba glomerulosa but not in the zona fasciculata/reticularis. In rodents and humans, two distinct species of P-450(C18) (aldosterone synthase) and P-450(11beta) (11beta-hydroxylase) are expressed in the adrenal cortex. The selective expression of cytochrome P-450 species in different zones contributes to zone specificity of aldosterone synthesis. In the cow and pig, only one molecular species of P-450(11beta) having both 11beta-hydroxylase and aldosterone synthase activity is expressed throughout the adrenal cortex. P-450(11beta) in the zona fasciculata/reticularis catalyzes the formation of corticosterone but not that of aldosterone from 11-deoxycorticosterone; the same enzyme in the zona glomerulosa produces aldosterone from the same substrate, indicating that a local factor in mitochondria is likely to be involved in the selective suppression of the aldosterone synthetic activity of P-450(11beta) in the zona fasciculata/reticularis. The zone specificity of aldosterone synthesis catalyzed by P-450(11beta) in the bovine adrenal cortex appears to be due to differences in interactions between P-450(11beta) and P-450(SCC) in mitochondria in different cortical zones. Thus, two modes exist for aldosterone biosynthesis in mammals: rodent-human and bovine-porcine modes.

Molecular variants in the P450c11AS gene as determinants of aldosterone synthase activity in the Dahl rat model of hypertension

Dahl salt-sensitive (S) and salt-resistant (R) rats are widely used to study genetic determinants of salt-sensitive hypertension. Differences in blood pressure under a high sodium diet in these two strains may be due to differences in the synthesis of 18-OH-11-deoxycorticosterone (18-OH DOC). This difference in 18-OH-DOC synthesis is due to mutations in the Dahl R rat's gene for P450c11 beta (11 beta-hydroxylase), an adrenal enzyme involved in the synthesis of both corticosterone and 18-OH DOC from 11-deoxycorticosterone. Aldosterone/renin ratios in plasma and in the adrenals are greater in Dahl S than R rats, suggesting an altered physiologic relationship between the renin-angiotensin and aldosterone systems between these strains. We demonstrate that the mRNA for P450c11AS, (aldosterone synthase), an enzyme required for aldosterone synthesis, is identical in the Dahl S rat and in normotensive Sprague-Dawley rats, but that P450c11AS mRNA from the Dahl R rat contains 7 mutations that result in two amino acid substitutions. These two changes result in a form of P450c11AS that has a greater apparent Vmax and lower apparent Km, resulting in an enzyme that catalyzes the conversion of 11-deoxycorticosterone to aldosterone at a greater rate in Dahl R rats than the P450c11AS in Dahl S rats or Sprague-Dawley rats. Although plasma and adrenal renin are lower in Dahl S versus R rats, the regulation of P450c11AS mRNA expression in rats fed a low and high salt diet are identical in these strains. The current findings may explain both the reduced aldosterone concentrations and increased aldosterone/renin ratios previously reported in the Dahl S versus Dahl R rat.