Maternal depressive symptoms throughout pregnancy are associated with increased placental glucocorticoid sensitivity

BACKGROUND

Maternal prenatal depression predicts post-partum depression and increases risk of prematurity and low birth weight. These effects may be mediated by altered placental function. We hypothesized that placental function would be influenced by the gestational week of experiencing depressive symptoms and aimed to examine associations between maternal depressive symptoms during pregnancy and placental expression of genes involved in glucocorticoid and serotonin transfer between mother and fetus.

METHOD

We studied women participating in a prospective pregnancy cohort: the Prediction and Prevention of Preeclampsia (PREDO) Study, Helsinki, Finland. Maternal depressive symptoms were assessed at 2-week intervals throughout pregnancy in 56 healthy women with singleton, term pregnancies. Messenger ribonucleic acid (mRNA) levels of glucocorticoid (GR) and mineralocorticoid (MR) receptors and serotonin transporter (SLC6A4), 11β-hydroxysteroid dehydrogenase type 1 (HSD1) and 2 (HSD2) were quantified in placental biopsies.

RESULTS

In adjusted analyses women who reported higher depressive symptoms across the whole pregnancy had higher mRNA levels of GR [effect size 0.31 s.d. units, 95% confidence interval (CI) 0.01-0.60, p = 0.042] and MR (effect size 0.34 s.d. units, 95% CI 0.01-0.68, p = 0.047). These effects were significant for symptoms experienced in the third trimester of pregnancy for GR; findings for MR were also significant for symptoms experienced in the second trimester. GR and MR mRNA levels increased linearly by having the trimester-specific depressive symptoms scores 0, 1 or 2-3 times above the clinical cut-off for depression (p = 0.003, p = 0.049, respectively, and p = 0.004, p = 0.15 in adjusted analyses).

CONCLUSIONS

Our findings offer potential gestational-age-specific mechanisms linking maternal depressive symptoms during pregnancy via placental biology. Future studies will test whether these also link with adverse offspring outcomes.

Chronic corticosterone administration from adolescence through early adulthood attenuates depression-like behaviors in mice

There is evidence that depression may have a different neural basis at different ages. Although chronic stress and elevated glucocorticoid levels have been demonstrated to lead to the emergence of mood disorders, it remains unclear how moderate elevation of glucocorticoid levels in young animals influences depression-like behaviors and brain functions. To address this issue, the present study examines how chronic corticosterone (CORT) administration during adolescence and early adulthood influences depression-like behaviors, hypothalamic-pituitary-adrenal (HPA) axis response and hippocampal cell proliferation. Male mice were chronically administrated with CORT drinking water (20mg/L) during adolescence. After two months of treatment, serum CORT levels were measured using enzyme immunoassay. Hippocampal glucocorticoid and mineralocorticoid receptors were characterized using Western blot. Tail suspension and forced swim tests were used to assess depression-related behaviors in mice. Immunohistochemistry was performed to measure bromodeoxyuridine (BrdU) incorporation in order to assess cell proliferation in the hippocampus. Our results suggest that chronic CORT administration induced a mild but not significant elevation in basal CORT levels and attenuated the physiological responses to stress. Chronic CORT administration also reduced expression of the hippocampal mineralocorticoid receptor and decreased immobility time in both the tail suspension test and the forced swim test. Moreover, chronic CORT administration increased the BrdU immunoreactivities in the hippocampus. Taken together, these findings suggest that chronic mild elevation by CORT administration during the adolescence and early adulthood attenuates depression-like behaviors.

Rapid effects of corticosterone in the mouse dentate gyrus via a nongenomic pathway

Corticosterone activates two types of intracellular receptors in the rodent brain: the high affinity mineralocorticoid receptor (MR) and lower affinity glucocorticoid receptor (GR). These receptors act as transcriptional regulators and mediate slow changes in neuronal activity in a region-dependent manner. For example, in CA1 pyramidal cells, corticosterone slowly changes Ca(2+) currents and glutamate transmission but dentate granule cells appear to be resistant. Recent studies have shown that corticosteroids also exert rapid MR-dependent, nongenomic effects on hippocampal CA1 cells [e.g. increasing the frequency of miniature excitatory postsynaptic currents (mEPSCs)]. In the present study, we investigated whether dentate granule cells are also resistant to the rapid effects of corticosterone. We found that, comparable to the CA1 area, corticosterone quickly and reversibly increases mEPSC frequency but not amplitude of dentate cells. This effect did not require protein synthesis and displayed the pharmacological profile of an MR- rather than GR-dependent event. These data support the hypothesis that, unlike the slow gene-mediated effects of corticosterone, rapid hormonal actions are quite similar for CA1 and dentate cells.

Effect of neonatal handling on adult rat spatial learning and memory following acute stress

Brief neonatal handling permanently alters hypothalamic-pituitary-adrenal axis function resulting in increased ability to cope with stress. Since stress is known to affect cognitive abilities, in the present study we investigated the effect of brief (15 min) handling on learning and memory in the Morris water maze, following exposure to an acute restraint stress either before training or recall. Exposure of non-handled rats to the acute stress prior to training resulted in quicker learning of the task, than in the absence of the stressor. When acute stress preceded acquisition, male handled rats showed an overall better learning performance, and both sexes of handled animals were less impaired in the subsequent memory trial, compared to the respective non-handled. In addition, the number of neurons immunoreactive for GR was higher in all areas of Ammon's horn of the handled rats during the recall. In contrast, the number of neurons immunoreactive for MR was higher in the CA1 and CA2 areas of the non-handled males. When the acute restraint stress was applied prior to the memory test, neonatal handling was not effective in preventing mnemonic impairment, as all animal groups showed a similar deficit in recall. In this case, no difference between handled and non-handled rats was observed in the number of GR positive neurons in the CA2 and CA3 hippocampal areas during the memory test. These results indicate that early experience interacts with sex and acute stress exposure in adulthood to affect performance in the water maze. Hippocampal corticosterone receptors may play a role in determining the final outcome.

Identification of the mineralocorticoid receptor in human spermatozoa

Aldosterone seems to play a role in the regulation of the electrolyte content of sperm and in the motility of spermatozoa. The aim of the study was to evaluate the presence of the mineralocorticoid receptor (MR) in human ejaculated spermatozoa. We have assayed MR on spermatozoa of freshly ejaculated sperm from healthy donors. The identification of MR was made by using immunohistochemistry and immunofluorescence analyses, while MR mRNA expression was evaluated by real-time PCR assay. The immunohistochemical and immunofluorescence analyses showed positive staining both in the midpiece and in the tail of the spermatozoa. Relative quantification of MR by using real-time PCR shows that the mRNA expression of MR in spermatozoa is lower than in mononuclear leukocytes (positive controls). Sequencing showed complete identity between the sequence obtained from spermatozoa and the human MR cDNA sequence. Further studies should be performed in order to elucidate a possible physiological role of aldosterone in regulating electrolyte concentration, and the pro-oxidant effect of excess aldosterone in this new target tissue.

AAV delivery of mineralocorticoid receptor shRNA prevents progression of cold-induced hypertension and attenuates renal damage

The aim of this study was to determine the effect of RNA interference inhibition of mineralocorticoid receptor (MR) on cold-induced hypertension (CIH) and renal damage. Recombinant adeno-associated virus (AAV) carrying short hairpin small interference (si)RNA for MR (AAV.MR-shRNA) was constructed and tested for the ability to inhibit renal MR and to control CIH. Three groups of rats with CIH received AAV.MR-shRNA (1.25 x 10(9) particles/rat, intravenous), AAV carrying scrambled shRNA (AAV.Control-shRNA) (1.25 x 10(9) particles/rat, intravenous) and phosphate buffer solution (PBS), respectively. All rats were kept in a cold chamber (6.7 degrees C) throughout the experiment. Adeno-associated virus delivery of MR-shRNA prevented progression of CIH. Blood pressure (BP) of the AAV.MR-shRNA-treated group did not increase and remained at 145+/-3 mm Hg, whereas BP of the AAV.Control-shRNA-treated and PBS-treated group increased to 167+/-4 and 161+/-3 mm Hg, respectively, at 3 weeks after gene delivery. Thus, the antihypertensive effect of a single injection of AAV.MR-shRNA lasted for at least 3 weeks (length of the study). Adeno-associated virus carrying short hairpin siRNA for MR significantly increased urinary sodium excretion and decreased proteinuria. It also decreased serum creatinine and blood urea nitrogen, suggesting enhanced renal function. Both Western blot and immunohistochemical analysis showed that MR expression was decreased significantly in the kidney in the AAV.MR-shRNA-treated rats, confirming that renal MR is effectively inhibited by AAV.MR-shRNA. Adeno-associated virus carrying short hairpin siRNA for MR also significantly attenuated renal hypertrophy. In addition, AAV delivery of MR-shRNA prevented atrophy and dilation of renal tubules and abolished tubular deposition of proteinaceous material seen in CIH rats.

CONCLUSIONS

(1) AAV delivery of MR-shRNA effectively silenced MR in vivo. (2) RNA interference inhibition of MR may open a new avenue for the long-term control of hypertension and renal damage.

Aldosterone target neurons in the nucleus tractus solitarius drive sodium appetite

Sodium appetite can be enhanced by the adrenal steroid aldosterone via an unknown brain mechanism. A novel group of neurons in the nucleus tractus solitarius expresses the enzyme 11-beta-hydroxysteroid dehydrogenase type 2, which makes them selectively responsive to aldosterone. Their activation parallels sodium appetite in different paradigms of salt loss even in the absence of aldosterone. These unique aldosterone target neurons may represent a previously unrecognized central convergence point at which hormonal and neural signals can be integrated to drive sodium appetite.

Changes in basal hypothalamo-pituitary-adrenal activity during exercise training are centrally mediated

The effects of exercise training on hypothalamo-pituitary-adrenal (HPA) function are unclear. We investigated whether pituitary-adrenal adaptation during exercise training is mediated by changes in neuropeptide and corticosteroid receptor gene expression in the brain and pituitary. Sprague-Dawley rats were subject to either daily swimming (DS) or sham exercise (SE) for 45 min/day, 5 days/week, for 2 (2W), 4 (4W), or 6 wk (6W) ( n = 7–10/group). Corticosterone (Cort) and catecholamine responses during swimming were robust at 6W compared with 2W and 4W, indicating that HPA response to exercise during training is not attenuated when absolute intensity is progressively increased. In DS, basal (morning) plasma ACTH and Cort levels increased from 2W to 4W but plateaued at 6W, whereas in SE, they increased from 4W to 6W, with 6W values higher than in DS. In DS, there was a transient decrease in glucocorticoid receptor (GR) mRNA in the paraventricular nucleus (PVN) and pituitary and a transient increase in corticotrophin-releasing hormone (CRH) mRNA. In contrast, hippocampal mineralocorticoid receptor mRNA and PVN GR mRNA decreased from 4W to 6W in SE, with 6W values lower than in DS. These findings suggest that exercise training prevents an elevation in basal pituitary-adrenal activity potentially via transient alterations in the gene transcription of PVN and pituitary GR as well as CRH to suppress central drive to the HPA axis. In contrast, the increase in basal pituitary-adrenal activity with repeated sham exercise appears to be associated with decreases in hippocampal MR and PVN GR mRNA expression.

Aldosterone directly induces myocyte apoptosis through calcineurin-dependent pathways

BACKGROUND

Aldosterone has recently attracted considerable attention for its involvement in the pathophysiology of heart failure, in which apoptotic cell loss plays a critical role. This study examined whether aldosterone directly induces myocyte apoptosis via its specific receptors.

METHODS AND RESULTS

Neonatal rat cardiac myocytes were exposed to aldosterone (10(-8) to 10(-5) mol/L). Nuclear staining with Hoechst 33258 showed that aldosterone induced myocyte apoptosis in a dose- and time-dependent fashion. Treatment of myocytes with 10(-5) mol/L aldosterone significantly increased the percentage of apoptosis (15.5+/-1.4%) compared with serum-deprived control (7.3+/-0.6%). Radio ligand binding assay revealed the existence of plasma membrane receptor with high affinity (K(d), 0.2 nmol/L) for aldosterone in cardiac myocytes but not in fibroblasts. Aldosterone rapidly (approximately 30 seconds) mobilized [Ca2+]i that was blocked by neomycin. Aldosterone induced dephosphorylation of the proapoptotic protein Bad, enhancement of mitochondrial permeability transition, decrease in mitochondrial membrane potential, and release of cytochrome c from the mitochondria into the cytosol with concomitant activation of caspase-3. These effects of aldosterone were inhibited by concurrent treatment with either an L-type Ca2+ channel antagonist, nifedipine, or inhibitors for the Ca2+-dependent phosphatase calcineurin, cyclosporin A and FK506.

CONCLUSIONS

The present study demonstrates for the first time that the specific plasma membrane receptor (coupled with phospholipase C) for aldosterone is present on cardiac myocytes and that aldosterone accelerates the mitochondrial apoptotic pathway through activation of calcineurin and dephosphorylation of Bad, suggesting that the proapoptotic action of aldosterone may directly contribute to the progression of heart failure.

Enhancement of Glucocorticoid and Mineralocorticoid Receptor Density in the Microcirculation of the Spontaneously Hypertensive Rat

OBJECTIVE

Elevated blood pressure and abnormal physiological parameters in the microcirculation of the spontaneously hypertensive rat (SHR) can be normalized by adrenalectomy. Thus glucocorticoids and mineralocorticoids may have major control over blood pressure status and organ injury mechanisms in SHRs. As background, this study was designed to examine the distribution of the glucocorticoid and mineralocorticoid receptors in a microvascular network.

METHODS

Mature SHR and their normotensive controls, the Wistar-Kyoto (WKY) rat, were studied. An immunohistochemical method was developed that provides a comprehensive display of the receptors in all segments of the mesentery microcirculation and the surrounding tissue parenchyma.

RESULTS

All cells in the mesentery exhibit immunolabeling of the glucocorticoid receptor with predominant expression in the nuclei of parenchymal and endothelial cells. The mineralocorticoid receptor is expressed also in most cells of the microcirculation and adjacent parenchymal tissue. Both receptors exhibit the highest levels of immunolabel in the wall of the arterioles and venules, with lower levels in capillaries. Compared with WKY rats, the SHRs exhibit significantly enhanced density of glucocorticoid and mineralocorticoid receptors in endothelial cells of arterioles and venules as well as in parenchymal cells.

CONCLUSIONS

These results suggest that the enhanced sensitivity of the SHR to glucocorticoids and aldosterone may be in part associated with enhanced glucocorticoid and mineralocorticoid receptor densities in the microcirculation.

Pharmacology and physiology of ovine corticosteroid receptors

The aim of these studies was to characterize the ovine corticosteroid receptors (MR, mineralocorticoid receptors and GR, glucocorticoid receptors) in ovine hippocampus and brainstem. Adrenal-intact and adrenalectomized ewes were studied; adrenalectomized ewes were killed 47 +/- 9 h after steroid withdrawal, when symptoms of hypotension and/or hyperkalemia became evident. RT-PCR, immunoblotting and pharmacologic studies indicated the presence of both MR and GR in hippocampus and brainstem. Competitive binding studies using 3H-cortisol in brain tissue showed that the ovine MR binds cortisol, aldosterone and progesterone with equal affinity. Differences in receptor availability in intact and adrenalectomized ewes, along with determination of the binding affinity (K(d)) of MR and GR, suggested that MR occupancy is about 90%, whereas GR occupancy is about 30%, in normal animals. There was a significant increase in protein level of MR in brainstem, and the appearance of a higher molecular weight band for MR in hippocampus following steroid withdrawal, however no significant change in mRNA was detected by semiquantitative RT-PCR for either MR or GR in hippocampus or brainstem following steroid withdrawal. These studies suggest that physiological ligands of MR in the sheep brain include progesterone and cortisol, and that, as in other species, affinity of MR for cortisol is greater than that of GR.

Rapid corticosteroid-dependent regulation of mineralocorticoid receptor protein expression in rat brain

Corticosteroid hormones regulate many aspects of neural function via mineralocorticoid receptors (MR) and glucocorticoid receptors (GR). Although GR expression is negatively regulated by endogenous corticosteroids, the autologous regulation of MR expression has been less well studied, partly due to limitations of receptor binding assays that cannot measure the ligand-activated form of MR. Using MR-reactive antibodies and Western blot, we examined relative MR protein expression in rat brain and its potential autoregulation by corticosteroids. We found that MR protein expression is autoregulated in a negative fashion by adrenal steroids. Compared with GR, we see a more rapid regulation of MR, such that there is a substantial increase in MR protein within 12 h after adrenalectomy, whereas GR levels show very little increase until more than 24 h after adrenalectomy. Also, in contrast to GR, which has been found to be regulated by both MR and GR, adrenalectomy-induced increase in MR was prevented by treatment with the MR selective agonist, aldosterone, but not the GR selective agonist, RU28362. Interestingly, acute treatment of adrenalectomized rats with corticosterone produced a significant decrease in whole-cell MR protein within 45 min, suggesting ligand-induced rapid degradation of MR. Chronic high levels of corticosterone also produced a significant decrease in MR protein levels below adrenal-intact rat levels. These results have important implications for previous studies that estimated the proportion of MR that are occupied in vivo by various circulating levels of corticosterone. Those studies compared available MR binding levels in adrenal-intact rats with 24-h adrenalectomized rats, with the assumption that there were no differences between the various conditions in total receptor expression. Those studies concluded that MR is nearly fully occupied by even the lowest circulating corticosterone levels. Given the 2- to 3-fold increase in MR protein that we have observed within 24 h after adrenalectomy, it is likely that those studies significantly overestimated the proportion of MR that were occupied by low basal corticosterone levels. These results support the prospect that MR as well as GR can participate in the transduction of phasic corticosteroid signals.

Comparison of central corticosteroid receptor expression in male Lewis and Fischer rats

The histocompatible inbred Lewis (LEW) and Fischer (F344) rat strains exhibit marked phenotypic differences in the hormonal activity of the hypothalamic-pituitary-adrenal (HPA) axis. As such they provide an important comparative model for the study of HPA regulation including the central feedback regulation by the glucocorticoid transcription factors, the mineralocorticoid receptor (MR) and the glucocortiocoid receptor (GR). In adult male rats, basal nadir plasma corticosterone values were similar in the two strains whereas the amplitude and duration of the corticosterone response to restraint were significantly reduced in LEW. MR and GR mRNA expression were compared in LEW and F344 throughout the rostrocaudal extent of the hippocampus. Hippocampal MR expression was consistent throughout the rostrocaudal extent and similar in F344 and LEW males. Hippocampal GR expression was consistent throughout the rostrocaudal extent, but significantly greater in the rostral dentate gyrus and Cornu ammonis subfields in LEW males compared with F344 males. The LEW phenotype of relatively high hippocampal GR expression and HPA hypoactivity is shared by outbred rats exposed to neonatal handling and GR-overexpressing transgenic mice. Whether or not this relationship is causal, as well as the functional significance of the rostral-extent specific GR difference, remains to be elucidated.

19-Noraldosterone in pregnancy-induced hypertension

Pregnancy-induced hypertension (PIH) is a frequent cause of maternal and neonatal morbidity and mortality. 19-Noraldosterone, which was shown to be synthesized in the human adrenal gland, exhibits potent mineralocorticoid and hypertensive activity. To examine the role of mineralocorticoids in the pathophysiology of PIH, we studied urinary 19-noraldosterone, tetrahydroaldosterone, free cortisol, and cortisone concentrations and mineralocorticoid receptor levels in peripheral blood mononuclear leukocytes, from 17 women with PIH and 16 normal pregnant women as controls. Sequence analysis of the mineralocorticoid receptor gene in PIH patients was also done. The 24-h urinary excretion of 19-noraldosterone was significantly lower in PIH (120 +/- 38 pmol/day) than in controls (358 +/- 55 pmol/day) (P < 0.05). Urinary tetrahydroaldosterone was also decreased in PIH compared with controls. Ratios of urinary free cortisol to cortisone (a measure of 11beta-hydroxysteroid dehydrogenase 2 activity) did not differ significantly between groups. Mineralocorticoid receptor density was significantly (P < 0.05) decreased in the PIH group (133 +/- 15 binding sites/cell) compared with controls (255 +/- 21 binding sites/cell). No mutations were found in the coding region of the mineralocorticoid receptor gene in PIH. These results suggest that circulating aldosterone, 19-noraldosterone, and renal 11beta-hydroxysteroid dehydrogenase2 do not contribute to the pathogenesis of PIH. Regulatory factors that cause the down-regulation of the mineralocorticoid receptor in PIH should be clarified.

Colocalization of glucocorticoid and mineralocorticoid receptors in human bone

Osteoporosis is a poorly understood but common complication of glucocorticoid therapy. The actions of glucocorticoids are mediated via glucocorticoid receptors (GRs), but in vitro, glucocorticoids also can bind to mineralocorticoid receptors (MRs). It is not known if MR protein is present in human bone and little is known of GR isoform expression (GRalpha and GRbeta). GR and MR protein expression and possible sites of action were investigated in neonatal rib and adult iliac crest biopsy specimens using antibodies specific for MR, GRalpha, and GRalphabeta. Colocalization [MR GRalpha] [MR GRalphabeta] was performed using fluorescent-conjugated secondary antibodies. GRalpha, GRbeta, and MR show distinct but overlapping patterns of expression, suggesting important functions for each receptor type. Osteoclasts showed no staining for GRalpha but strong staining for GRalphabeta, indicating expression of GRbeta and a specific role in addition to antagonizing the transcriptional activity of GRalpha. MR also was observed in osteoclasts and colocalized with GRalphabeta. Coexpression of MR, GRalpha, and GRalphabeta was seen in osteoblasts. Reverse-transcription-polymerase chain reaction (RT-PCR) of cultured osteoblast RNA confirmed expression of both GRalpha and GRbeta. Osteocytes stained with MR, GRalpha, and GRalphabeta antibodies but to a lesser degree than osteoblasts. In the neonatal rib cartilage, staining for GRalpha, GRalphabeta, and MR was present in approximately one-half of the resting and hypertrophic chondrocytes and in most of proliferating chondrocytes and chondrocytes within the mineralizing matrix. Identification of MR raises the possibility that the physiological and pharmacologic effects of glucocorticoids on bone may be mediated via MR as well as GR and that GRalpha, GRbeta, and MR synergize to influence corticosteroid metabolism in human bone.

Dynamic changes in subcellular localization of mineralocorticoid receptor in living cells: in comparison with glucocorticoid receptor using dual-color labeling with green fluorescent protein spectral variants

Mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) are ligand-dependent transcription factors. Although it is generally accepted that GR is translocated into the nucleus from the cytoplasm only after ligand binding, the subcellular localization of MR is still quite controversial. We examined the intracellular trafficking of MR in living neurons and nonneural cells using a fusion protein of green fluorescent protein (GFP) and rat MR (GFP-MR). Corticosterone (CORT) induced a rapid nuclear accumulation of GFP-MR, whereas in the absence of ligand, GFP-MR was distributed in both cytoplasm and nucleus in the majority of transfected cells. Given the differential action of MR and GR in the central nervous system, it is important to elucidate how the trafficking of these receptors between cytoplasm and nucleus is regulated by ligand. To examine the simultaneous trafficking of MR and GR within single living cells, we use different spectral variants of GFP, yellow fluorescent protein (YFP) and cyan fluorescent protein (CFP), linked to MR and GR, respectively. In COS-1 cells, expressing no endogenous corticosteroid receptors, the YFP-MR chimera was accumulated in the nucleus faster than the CFP-GR chimera in the presence of 10(-9) M CORT, while there was no significant difference in the nuclear accumulation rates in the presence of 10(-6) M CORT. On the other hand, in primary cultured hippocampal neurons expressing endogenous receptors, the nuclear accumulation rates of the YFP-MR chimera and CFP-GR chimera were nearly the same in the presence of both concentrations of CORT. These results suggest that CORT-induced nuclear translocation of MR and GR exhibits differential patterns depending on ligand concentrations or cell types.

Immunohistochemical distribution of 11beta-hydroxysteroid dehydrogenase in human eye

11beta-hydroxysteroid dehydrogenase (11beta-HSD) regulates local actions of corticosteroids at glucocorticoid and mineralocorticoid receptors. Corticosteroids are thought to play important roles in ocular function. However, mechanisms of intraocular corticosteroid action are still unclear. Therefore, in this study, we examined the immunohistochemical localization of 11beta-HSD type 1 (11beta-HSD1), 11beta-HSD type 2 (11beta-HSD2), mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) in human ocular tissues from patients (6 months to 78 years of age; n = 10) retrieved from surgical pathology files. Both 11beta-HSD2 and MR immunoreactivity was detected only in non-pigmented epithelium of the ciliary body, but was undetectable in cornea, lens, iris, retina, choroid and sclera, in all the cases examined. GR was detected in all cell types in the human eye. 11beta-HSD1 immunoreactivity was not detected in the human eye in this study. These results suggest that 11beta-HSD2 play an important role in human ocular mineralocorticoid action, such as the production of aqueous humor, in the ciliary body. The widespread expression of GR suggests that glucocorticoids may play an important role in the function and homeostasis of the human eye.

Mineralocorticoid receptor-mediated signaling regulates the ion gated sodium channel in vascular endothelial cells and requires an intact cytoskeleton

The PCR analysis followed by sequence alignment showed that both the mineralocorticoid receptor (MCR) and the epithelial sodium channel (ENaC) genes were expressed in the human vascular endothelial cell line (ECV). The growth and multiplication of the ECV in culture were influenced by both aldosterone and the MCR-specific antagonist ZK 91587. Following double labelled immunofluorescence recorded by confocal microscopy, both the MCR and the ENaC were found to colocalize with the tubulin filaments in ECV cells in situ; no association was observed with cellular actin. ZK 91587 not only eliminated the basal expression, but it also impaired the transactivation of the ENaC gene by aldosterone. The disruption of actin and tubulin by cytochalasin D and colchicine, respectively, resulted in the total elimination of ENaC induction by aldosterone. These studies suggest that (i) the transcriptional regulation of the ENaC gene by the MCR-mediated signalling is not restricted to epithelial cells and requires cytoskeleton integrity in ECV cells in situ, (ii) tubulin may form a new and novel mediator in cell regulation, and (iii) the vascular tone may actually be regulated via transactivation of the ion gated sodium channel in the endothelial cell of the blood vessels under direct, receptor-mediated action of aldosterone.

Epithelial sodium channel and the mineralocorticoid receptor in cultured rat Müller glial cells

Müller glial cells are the major non-neuronal cells of the retina. They are involved in retinal function and exert a profound influence on the function of retinal neurons. We present an in vitro study of the localization of the mineralocorticoid receptor (MCR) and of the epithelial sodium channel (ENaC) in rat Müller glial cells isolated from rat retina, using respectively, a polyclonal antiserum raised against the rat purified MCR, and a rabbit polyclonal antibody against the 14-amino acid (aa) peptide QGLGKGDKREEQGL, which corresponds to the N-terminal region (44-58aa) of the alpha-subunit of the ENaC. In an immunocytochemical study using anti-MCR and anti-ENaC antibodies, the MCR was detected as a protein present in the cytoplasm and in the nucleus, whereas ENaC was detected as a membrane-bound protein. Reverse transcription-polymerase chain reaction (RT-PCR) analysis using specific primers, 5'-CTGCCTTTATGGATGATGGT-3' (sense), 5'-GTTCAGCTCGAAGAAGA-3' (antisense) for ENaC and 5'-AGGCTACCACAGTCTCCCTG-3' (sense) and 5'-GCAGTGTAAAATCTCCAGTC-3' (antisense) for MCR, showed expression of the ENaC and MCR genes in Müller cells. The presence of ENaC and MCR was detected as the predicted bands of 520 bp and 843 bp, respectively. In both cases, 100% identity was observed between the sequences of rat Müller cell (RMC) PCR products and rat kidney. Interestingly, the basal levels of ENaC were increased in vitro by the MCR-specific hormone, aldosterone. Thus, our results strongly suggest that the Müller glial cells may play a role in the regulation of extracellular Na+ concentration, which could be regulated by steroid-mediated sodium uptake.

Dietary restriction selectively decreases glucocorticoid receptor expression in the hippocampus and cerebral cortex of rats

Dietary restriction (DR) can extend life span and reduce the incidence of age-related disease in rodents and primates. DR can be considered as a metabolic stress and might therefore be expected to modify neuroendocrine systems that regulate stress responses. We now report that maintenance of adult rats on a DR regimen results in a significant decrease in the levels of glucocorticoid receptor mRNA and protein in the hippocampus and cerebral cortex, without a change in levels of mineralocorticoid receptors. These findings suggest that DR can alter the responsiveness of brain cells to glucocorticoids, an adaptation that may contribute to beneficial effects of DR on neuronal plasticity and survival demonstrated in recent studies.

[Corticosteroid receptor and stress]

Adrenal corticosteroids readily enter the brain and exert markedly diverse effects, such as stress response of the target neural cells. These effects are regulated via two receptor systems, the mineralocorticoid receptor (MR; type I corticosteroid receptor) and the glucocorticoid receptor (GR; type II corticosteroid receptor), both of which are ligand-dependent transcription factors. MR is localized mainly in the hippocampus, and GR is distributed throughout the brain. MR and GR, however, are highly colocalized in the hippocampus, which is a target of the stress hormone and an especially plastic and vulnerable region of the brain. MR has a high affinity for corticosterone/cortisol, a common endogenous ligand for MR and GR, and is extensively bound at low levels of circulating corticosterone/cortisol. GR has a lower affinity and is extensively bound at high levels of circulating corticosterone/cortisol. These findings suggest that MR plays major roles under physiological conditions, whereas GR is mainly effective at high concentrations of corticosterone/cortisol, such as stressful conditions. The interactions of MR and GR in the hippocampal regions could be important for regulating stress response in the brain.

Identification and role of aldosterone receptors in the cardiovascular system

The cardiovascular system is now recognized as an important mineralocorticoid target. All -components required for specific and selective aldosterone effects are present in the cardiovascular system. Mineralocorticoid receptors (MR) are expressed in the heart and large blood vessels together with the 11 B-hydroxysteroid dehydrogenase type II, which ensures the enzymatic protection of MR against glucocorticoids. The recent description of local vascular and cardiac aldosterone biosynthesis strongly supports an autocrine/paracrine hormonal action. Establishment of transgenic mice models of targeted overexpression of the mineralocorticoid receptor should facilitate new insights into the molecular and cellular mechanisms of aldo-sterone actions in the cardiovascular system.

Transcriptional regulation of the human Na/K ATPase via the human mineralocorticoid receptor

The mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR) are members of the steroid/thyroid hormone receptor superfamily of ligand inducible transcription factors and have been shown to bind the glucocorticoid response element (GRE). Sodium-potassium ATPase (Na/KATPase) is a major target of mineralocorticoids. Both aldosterone and glucocorticoids activate the human Na/K ATPase alpha1 subunit and beta1 subunit genes transcriptionally. However, the mechanisms of corticosteroid regulation of mammalian Na/K ATPase subunit gene expression are not known. In this investigation, we report for the first time that cell lines (T-84 and 293) express endogenous MR by RT-PCR message expression. However, the protein product was not expressed as determined by western blot analyses. In transactivation studies of MR with GRE31, we detected MR expression at low concentrations of aldosterone. We also performed Northern blot and nuclear run-off transcription assays to further confirm that the regulation is transcriptional. We conclude that the transcriptional regulation of the human Na/K ATPase alpha1 and beta1 subunits by aldosterone occurs via the involvement of the MR.

General overview of mineralocorticoid hormone action

The adrenal cortex elaborates two major groups of steroids that have been arbitrarily classified as glucocorticoids and mineralocorticoids, despite the fact that carbohydrate metabolism is intimately linked to mineral balance in mammals. In fact, glucocorticoids assured both of these functions in all living cells, animal and photosynthetic, prior to the appearance of aldosterone in teleosts at the dawn of terrestrial colonization. The evolutionary drive for a hormone specifically designed for hydromineral regulation led to zonation for the conversion of 18-hydroxycorticosterone into aldosterone through the catalytic action of a synthase in the secluded compartment of the adrenal zona glomerulosa. Corticoid hormones exert their physiological action by binding to receptors that belong to a transcription factor superfamily, which also includes some of the proteins regulating steroid synthesis. Steroids stimulate sodium absorption by the activation and/or de novo synthesis of the ion-gated, amiloride-sensitive sodium channel in the apical membrane and that of the Na+/K+-ATPase in the basolateral membrane. Receptors, channels, and pumps apparently are linked to the cytoskeleton and are further regulated variously by methylation, phosphorylation, ubiquination, and glycosylation, suggesting a complex system of control at multiple checkpoints. Mutations in genes for many of these different proteins have been described and are known to cause clinical disease.

Coexpression of mineralocorticoid receptors and 11beta-hydroxysteroid dehydrogenase 2 in human gastric mucosa

The role of mineralocorticoids in human gastrointestinal tract is well established. In the stomach, aldosterone is thought to regulate electrolyte transport associated with gastric acid secretion. In mineralocorticoid target organs, the action of the glucocorticoid inactivating enzyme 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) facilitates aldosterone binding to a nonselective mineralocorticoid receptor (MR) in the face of high levels of circulating glucocorticoids. In the present study, we examined 25 specimens of human stomach for the presence of MR and 11beta-HSD2 using a [3H]aldosterone binding assay, Northern blot analysis, RT-PCR, and immunohistochemistry. Specific [3H]aldosterone binding sites were detected in gastric fundic mucosa, but not in the antrum. In fundic mucosa the Kd was 0.72+/-0.05 nmol/L (mean +/- SE), and Bmax was 6.0+/-1.4 fmol per milligram of protein. Northern blot analysis demonstrated a faint band for MR mRNA at 6.0 kb, although message for 11beta-HSD2 was undetectable. However, RT-PCR demonstrated specific PCR products for both MR and 11beta-HSD2. Immunohistochemistry demonstrated the colocalization of MR and 11beta-HSD2 only in parietal cells. MR-positive cells were further characterized by electron microscopy, confirming the identity of parietal cells. This study shows that parietal cells contain both MR and 11beta-HSD2, suggesting that the human stomach is a novel target organ for mineralocorticoids. Aldosterone may, therefore, regulate biological functions of parietal cells including gastric acid secretion.

Characterization of mineralocorticoid and glucocorticoid receptors in pigs: comparison of Meishan and Large White breeds

Corticosteroids receptors were characterized and compared in central and peripheral tissues of two pig breeds, the Meishan (MS) and the Large White (LW) pigs, that display differences in the basal activity and stress-induced reactivity of the hypothalamic-pituitary-adrenal (HPA) axis. In vitro kinetic experiments on kidney and liver cytosols from adrenalectomized pigs allowed to identify two distinct corticosteroid receptors referred to as mineralocorticoid (MR) and glucocorticoid (GR) receptors. The binding specificities were determined for kidney and hippocampal MR and for liver and hippocampal GR. In hippocampus and peripheral tissues, cortisol showed a greater affinity for MR than for GR. As already described in the dog, mouse and human, dexamethasone and progesterone display a moderate affinity for MR. Putative differences in corticosteroid receptors binding capacities and affinities were investigated by saturation binding studies in specific regions implicated in the regulation of HPA axis (hippocampus and pituitary). The MS pigs evidenced higher densities of hippocampal MR, while LW pigs had higher densities of pituitary GR. Thus, this study suggests that a difference in the MR/GR balance in hippocampus and pituitary could be implicated in the different HPA activity between MS and LW pigs.

Glucocorticoid resistance caused by reduced expression of the glucocorticoid receptor in cells from human vascular lesions

Mechanisms that control the balance between cell proliferation and death are important in the development of vascular lesions. Rat primary smooth muscle cells were 80% inhibited by low microgram doses of hydrocortisone (HC) and 50% inhibited by nanogram concentrations of transforming growth factor-beta1 (TGF-beta1), although some lines acquired resistance in late passage. However, comparable doses of HC, or TGF-beta1, failed to inhibit most human lesion-derived cell (LDC) lines. In sensitive LDC, HC (10 microg/mL) inhibited proliferation by up to 50%, with obvious apoptosis in some lines, and TGF-beta1 inhibited proliferation by more than 90%. Collagen production, as measured by [3H]proline incorporation or RIA for type III pro-collagen, was either unaffected or increased in the LDCs by HC. These divergent responses between LDC lines were partially explained by the absence of the glucocorticoid receptor (GR) and heat shock protein 90 mRNA in 10 of 12 LDC lines, but the presence of the mineralocorticoid receptor and 11beta-hydroxysteroid dehydrogenase type II. Western blot analysis confirmed the absence of the GR protein in cells lacking GR mRNA. Immunohistochemistry of human carotid lesions showed high levels of GR in the tunica media, but large areas lacking GR in the fibrous lesion. Considering the absence of the GR in most lines, the effects of HC may be elicited through the mineralocorticoid receptor. Functional resistance to the antiproliferative and antifibrotic effects of HC may contribute to excessive wound repair in atherosclerosis and restenosis.

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

11Beta-Hydroxysteroid dehydrogenase type II (11betaHSD2) confers specificity on the mineralocorticoid receptor (MR) by converting biologically active glucocorticoids to inactive 11-keto metabolites. The biological significance of 11betaHSD2 activity during fetal development is currently being explored, but the temporal and spatial distributions of the enzyme and receptor have not been examined. We therefore examined their distributions during various stages of human fetal development using immunohistochemistry. Both 11betaHSD2 and MR immunoreactivity were detected in the distal convoluted and collecting tubules of the kidney from early in gestation. Fetal skin, intermediate layer of the epidermis, peridermal cells, and hair follicles were positive for both 11betaHSD2 and MR. Weak 11betaHSD2 and MR immunoreactivity was detected in the superficial ciliated epithelium of the esophagus, the deep layer of gastric epithelial cells, and the superficial epithelium of the small intestine. Columnar epithelium in the terminal bronchiolar budding component of fetal lung and tracheal and bronchial ciliated epithelium were also positive for MR and 11betaHSD2 from early gestation. Colonic epithelium and pancreatic exocrine duct cells, which demonstrated marked immunoreactivity of both MR and 11betaHSD2 in the adult, did not express MR and 11betaHSD2 until very late in gestation. These results imply that mineralocorticoid action in the upper fetal gastrointestinal tract, kidney, skin, and lung is facilitated by 11betaHSD2 and is involved in water and electrolyte transport between fetus and amniotic fluid as well as fetal urine production.

Expression of mRNAs encoding hormone receptors in the endolymphatic sac of the rat

The endolymphatic sac (ES) is believed to absorb the endolymphatic fluid produced by the stria vascularis and vestibular dark cells. Recent studies have implied that the function of the ES may be controlled by circulating hormones, suggesting that hormone receptors should exist there. In the present study, the expression of genes encoding receptors for aldosterone, atrial natriuretic peptide (ANP) and vasopressin in the ES was examined by reverse transcription-polymerase chain reaction (RT-PCR). Next, the cellular localization of the expression of these genes was investigated by in situ hybridization. RT-PCR indicated that aldosterone. ANP-A and vasopressin V1a receptor genes were expressed in the ES. In contrast, neither ANP-B nor vasopressin V2 receptor gene expression was detected. In situ hybridization experiments demonstrated aldosterone receptor gene expression in epithelial cells of the intermediate potion of the ES, while expression of ANP-A or V1a receptor genes was not detected. The present results suggested that aldosterone may play a specific role in the function of the ES. However, we could not conclude that ANP and vasopressin play physiological roles in the ES because receptors for these hormones were detected only by highly sensitive PCR.

Regulation of hippocampal glucocorticoid receptor gene transcription and protein expression in vivo

Glucocorticoid receptors (GRs) are glucocorticoid-activated transcription factors that modulate expression of a variety of neuronal genes. Appropriate control of GR expression is therefore critical for maintenance of cellular and organismic homeostasis. The present study assessed glucocorticoid regulation of the GR at the gene, mRNA, and protein level. Removal of circulating glucocorticoids (adrenalectomy) increased GR mRNA expression in CA1 and dentate gyrus (DG). Corticosterone (CORT) replacement normalized GR mRNA expression, whereas high doses slightly decreased GR mRNA in CA1. Parallel increases were observed using a probe complementary to the distal 3' untranslated region, indicating that mRNA changes were not attributable to selection of alternative polyadenylation site. Expression of a GR intronic sequence was also increased by adrenalectomy, consistent with increased gene transcription. Analysis of regional GR protein expression by immunoautoradiography did not reveal changes in GR protein in pyramidal cell layers; however, increased GR signal was seen in the stratum radiatum, indicating redistribution of GR to the cytosol. Western blot analysis confirmed adrenalectomy-induced increases in hippocampal GR levels. Administration of the mineralocorticoid receptor (MR) antagonist spironolactone increased both GR mRNA and protein in CA1 and DG, consistent with MR-mediated inhibition of GR transcription. However, high-dose CORT treatment did not decrease GR mRNA or protein levels. Chronic stress exposure did not downregulate GR mRNA or protein in hippocampus. The results suggest that the hippocampal GR is subject to heterologous regulation by the MR. In contrast, GR autoregulation is only evident during prolonged exposure to high-circulating glucocorticoid levels.

Distinct ontogeny of glucocorticoid and mineralocorticoid receptor and 11beta-hydroxysteroid dehydrogenase types I and II mRNAs in the fetal rat brain suggest a complex control of glucocorticoid actions

Glucocorticoids (GCs) act via intracellular mineralocorticoid (MR) and glucocorticoid receptors (GR). However, it has recently been recognized that GC access to receptors is determined by the presence of tissue-specific 11beta-hydroxysteroid dehydrogenases (11beta-HSDs) that catalyze the interconversion of active corticosterone and inert 11-dehydrocorticosterone. 11beta-HSD type 1 (11beta-HSD1) is a bidirectional enzyme in vitro that acts predominantly as a reductase (regenerating corticosterone) in intact neurons. In contrast, 11beta-HSD type 2 (11beta-HSD2) is a higher affinity exclusive dehydrogenase that excludes GCs from MR in the kidney, producing aldosterone-selectivity in vivo. We have examined the ontogeny of 11beta-HSD mRNAs and enzyme activity during prenatal brain development and correlated this with GR and MR mRNA development. These data reveal that (1) 11beta-HSD2 mRNA is highly expressed in all CNS regions during midgestation, but expression is dramatically reduced during the third trimester except in the thalamus and cerebellum; (2) 11beta-HSD2-like activity parallels closely the pattern of mRNA expression; (3) 11beta-HSD1 mRNA is absent from the CNS until the the third trimester, and activity is low or undectectable; and (4) GR mRNA is highly expressed throughout the brain from midgestation, but MR gene expression is absent until the last few days of gestation. High 11beta-HSD2 at midgestation may protect the developing brain from activation of GR by GCs. Late in gestation, repression of 11beta-HSD2 gene expression may allow increasing GC activation of GR and MR, permitting key GC-dependent neuronal and glial maturational events.

Colocalization of 11 beta-hydroxysteroid dehydrogenase type II and mineralocorticoid receptor in human epithelia

The enzyme 11 beta-hydroxysteroid dehydrogenase type II (11 beta HSD2) has been shown to confer specificity on mineralocorticoid receptors (MR) by inactivating glucocorticoids. In the present study we examined the colocalization of 11 beta HSD2 and MR in various exocrine and secretory glands by immunostaining of serial mirror tissue sections with subsequent computerized image analysis. Both 11 beta HSD2 and MR proteins were expressed in the same cells in the distal convoluted tubules, Henle's loop, and collecting tubules of the kidney and the absorptive epithelia of duodenum, jejunum, ileum, colon, and excretory ducts of anal and esophageal glands. Significantly, 11 beta HSD2 and MR immunoreactivity also colocalized in the respiratory tract, in collecting ducts of the tracheal and bronchial glands, ciliated bronchial epithelial cells, and type II alveolar epithelial cells, suggesting important and unexpected roles for mineralocorticoids in the lung. In the skin, 11 beta HSD2 and MR were present only in excretory ducts of eccrine sweat glands, but not in sebaceous or apocrine glands. In eccrine glands, MR immunoreactivity was present in the basal cells of excretory ducts, while 11 beta HSD2 immunoreactivity was localized in the luminal cells. Neither 11 beta HSD2 nor MR proteins were expressed in the lacrimal gland, prostate, bile ducts, gall bladder, urinary bladder, urethra, or ureter. These results indicate that 11 beta HSD2 protein colocalizes with MR protein in the great majority of sodium-transporting epithelia involved in serous secretion and supports the proposal that 11 beta HSD2 is a pivotal determinant of mineralocorticoid receptor occupancy in man. Furthermore, our demonstration of colocalization in discrete areas of the lung suggests that mineralocorticoid agonists or antagonists, and/or inhibitors of 11 beta HSD2, may have unexpected applications in respiratory disease.

Localization of mineralocorticoid receptor and 11 beta-hydroxysteroid dehydrogenase type II in human breast and its disorders

Mineralocorticoid receptors have been detected in the normal human breast and breast cancers. The expression of mineralocorticoid receptor (MR) and 11 beta-hydroxysteroid dehydrogenase type II (11sHSD2), which confers specificity on MR for aldosterone, was examined by immunohistochemistry in 114 samples from normal human breast and benign and malignant breast lesions in order to study its possible biological significance. MR and 11sHSD2 were immunolocalized in the ductal epithelium in 39/40 (98%) and 36/40 cases (90%) of normal breast, 21/22 (95%) and 15/22 cases (68%) of fibrocystic changes, and 11/11 (100%) and 8/11 (73%) cases of fibroadenoma, respectively. Cases positive for 11 sHSD2 also expressed MR but the patterns of expression varied greatly among examples of normal breast and benign breast diseases. There was a significant correlation between labeling indices of MR and 11sHSD2 in normal breast (p < 0.01) and in benign breast disease (fibrocystic change (p < 0.05) and fibroadenoma (p < 0.05)). In invasive carcinomas, immunoreactivity for MR and 11sHSD2 was detected in malignant cells in 32/41(78%) and 16/41(39%) cases. Both MR and 11sHSD2 labeling indices were significantly higher in invasive ductal carcinoma (22 cases) than invasive lobular carcinoma (19 cases) (p < 0.01). There was a significant correlation between labeling indices of MR and 11sHSD2 when analyzing all infiltrating carcinomas (p < 0.01), but not when assessing invasive lobular or invasive ductal carcinomas separately. These results indicate that the 11 sHSD2 enzyme generally colocalizes with the MR in the ductal epithelial cells of human breast, which may allow aldosterone to occupy its physiological receptor, and the expression of MR and 11sHSD2 appears to be related to ductal differentiation of breast carcinomas.

Immunochemical demonstration of the mineralocorticoid receptor in ocular tissues

We studied the presence of the mineralocorticoid receptor (MCR) in the eye with the aid of a number of immunochemical techniques. Immunoblotting with a polyclonal antibody, directed against the rat renal MCR, revealed a single band of about 102 kD in extracts prepared from whole bovine or rat retina similar to that observed in cytosol from the kidney and myocardium from these species. Isolated cells of the bovine retinal pigment epithelium (RPE) similarly exhibited a 98- to 102-kD band in Western blots developed with the aid of anti-MCR antiserum. The 98- to 102-kD band was also obtained following autoradiography of RPE cytosol irradiated in the presence of 3H-R 5020. This fluorographic pattern was abolished when RU 26752, an antagonist specific to the MCR, was allowed to compete with radiolabelled promegestone. The MCR-3H-RU 26752 complex in RPE cytosol underwent heat activation, as judged by binding to DNA cellusose, and could also be precipitated by anti-MCR IgG. In primary cultures, the proliferation of the RPE cells was inhibited by the two MCR-specific antagonists RU 26752 and ZK 91587. The loss of the MCR-specific immunofluorescence in RPE cells after only 3 passages in culture was associated with refractoriness to the inhibitory effect of both of these spironolactones. Immunohistochemistry, using MCR-specific antiserum, revealed strong fluorescence in specific areas of the rat eye. In the retina, immunopositivity was observed in Müller cells, external and internal limiting membranes, the vitreous base lining and in the pigment epithelium. Epithelial cells of the ciliary body, iris and cornea also exhibited strong MCR-specific immunofluorescence. Thus, both the epithelial and the nonepithelial compartments of the ocular tissues form interesting new targets to delineate the mechanism of action of mineralotropic hormones.

Steroid receptors in the rat hippocampus: a note to the methodology of their binding assay

Mineralocorticoid (MR) and glucocorticoid (GR) receptors in the rat hippocampus are linked to several cognitive functions of the animal and seem to play an important role in the response to various stressors. Their assessment by binding experiments brings about problems associated with their intracellular compartmentalization, and in particular with the separation of the bound and free ligands. Adrenalectomy 24 h before sacrificing is commonly used to clear the circulating adrenal steroids, and to facilitate their dissociation from hippocampal MR and GR. We have successful attempted to use dialysis to these purposes and thus, to avoid a potential surgical stress. Without dialysis, only GR can be measured in the cytosol from intact rats, while the corresponding pellet contains MR as a component of the cell nuclei. The bound ligand fraction was separated by filtration on polyethyleneimine pretreated glass fiber filters as suggested earlier. The method has clear-cut preferences compared to any alternative used up to now. Discrimination between the two receptor types can be optimally achieved in a cross-displacement experiment in which two labeled ligands possessing various affinities to individual receptors (in our case: corticosterone and aldosterone, or their synthetic analogs) are displaced with the two corresponding nonlabelled ligands from their receptors. Computations can be carried out with LIGAND software which yield accurate values of binding parameters.

Expression of glucocorticoid and mineralocorticoid receptors in an immortalized hippocampal neuronal cell line

A clonal cell line of rat embryonic hippocampal origin (H19-7) has been examined for the expression of glucocorticoid receptors (GR) and mineralocorticoid receptors (MR). H19-7 cells grown at 33 degrees C continue to divide, however when grown at 39 degrees C in reduced levels of serum the cells undergo morphological differentiation and express neuronal properties. Immunocytochemistry demonstrated that H19-7 cells express both MR and GR when grown at either 33 degrees C or 39 degrees C. GR mRNA is readily detected in H19-7 cells by RNase protection assay. MR mRNA levels in H19-7 cells are too low to detect by RNase protection, but can be detected by RT-PCR. RT-PCR also demonstrated that H19-7 cells express more GR mRNA than primary hippocampal neurons. Since previous studies have shown that the level of MR mRNA is higher than that of GR mRNA in hippocampal neurons, these studies suggest that H19-7 cells represent hippocampal neurons immortalized at an early stage when the MR system is not yet fully differentiated.

Partial colocalization of glucocorticoid and mineralocorticoid receptors in discrete compartments in nuclei of rat hippocampus neurons

The glucocorticoid receptor and the mineralocorticoid receptor are hormone-dependent transcription factors. They regulate the excitability of rat hippocampus CA1 neurons in a coordinated fashion. We studied the spatial distribution of these transcription factors in nuclei of CA1 neurons by dual labeling immunocytochemistry and confocal microscopy, combined with novel image restoration and image analysis techniques. We found that both receptors are concentrated in about one thousand clusters within the nucleus. Some clusters contain either mineralocorticoid receptors or glucocorticoid receptors, but a significant number of clusters contains both receptors. These results indicate that the two receptor types are targeted to specific compartments in the nucleus. The coordinated action of the glucocorticoid and mineralocorticoid receptor on gene expression may be established in a specific set of nuclear domains that contain both receptors.

The mineralocorticoid hormone receptor and action in the eye

Immunoblotting with a polyclonal antibody, directed against the mineralocorticoid receptor protein purified from rat kidney in presence of the receptor-specific ligand RU 26752, labeled a single 98-102 kDa band in soluble extracts from bovine retina and from cultured bovine retinal pigment epithelial cells, identical to the receptor in several other tissues from the rat. The antibody also immunoprecipitated the receptor-3H-RU 26752 complex in bovine retinal extract. The growth of the isolated pigment epithelial cells was inhibited by RU 26752 and ZK91587, two ligands specific to the mineralocorticoid receptor. Successive passages in culture led to the disappearance of immunoreactivity in Western blots, concurrently with the refractoriness of the cells to growth inhibition by the two antagonists. On sections of the human eye, mineralocorticoid receptor-specific immunofluorescence was observed in retinal cone cells, pigment epithelium, epithelium of ciliary body, iris, cornea and lens. To our knowledge, this is the first ever demonstration of the mineralocorticoid receptor in ocular tissues.

Aldosterone: intracellular receptors in human heart

It has been suggested that aldosterone exerts direct effects on heart functioning, in particular by inducing cardiac fibrosis. We examined human heart tissue for the expression of aldosterone receptors (mineralocorticoid receptors, MRs) and of the MR-protecting enzyme, 11 beta hydroxysteroid dehydrogenase (11 beta HSD). In situ hybridization using cRNA probes specific for human MRs revealed the presence of mRNA encoding for MRs in cardiomyocytes. Immunohistochemistry with specific antibodies against the MR exhibited the expression of MR protein in cardiomyocytes. In contrast, intramyocardial small blood vessels showed no evidence of immunolabelling. A distinct 11 beta HSD activity, which was nicotinamide-adenine dinucleotide dependent, was also demonstrated in human cardiac tissue. These results illustrate that all the components required for a specific aldosterone effect are present in the human heart.

[3H]-aldosterone binding sites (type I receptors) in the lateral wall of the cochlea: distribution assessment by quantitative autoradiography

Mineralocorticoids, such as aldosterone, are steroids that enhance Na+ retention and K+ excretion in ion-transporting epithelial tissues through regulation of Na, K-ATPase. Previous studies suggest that aldosterone may regulate labyrinthine ion transport through up-regulation of Na, K-ATPase sites, a process mediated by high-affinity aldosterone (type I) receptors. In the present study, information concerning density and distribution of aldosterone binding sites in cochlear lateral wall tissues was determined by quantitative autoradiography using [3H]-aldosterone and RU-28362, a glucocorticoid agonist that blocks low affinity binding to glucocorticoid (type II) receptors. The results revealed that the distribution of aldosterone binding sites differs among the individual cochlear regions of the lateral wall. The highest level of binding was associated with the stria vascularis and epithelial cells of the spiral prominence. Elevated levels of binding were also observed in stromal cells of the spiral prominence, and to a lesser extent in the spiral ligament. The differential distribution of aldosterone binding sites in the lateral wall resembles the pattern of localization of Na, K-ATPase sites observed in previous studies and is compatible with the idea that mineralocorticoids play a role in the regulation of cochlear cation transport.

Prerequisite for cardiac aldosterone action. Mineralocorticoid receptor and 11 beta-hydroxysteroid dehydrogenase in the human heart

BACKGROUND

It has been proposed that aldosterone exerts direct effects on heart function, most notably on the development of myocardial fibrosis during ventricular hypertrophy in rat. Initial events in aldosterone action entail its binding to mineralocorticoid receptor (MR). Because MR displays similar affinities for aldosterone and glucocorticoids, the in vivo aldosterone selectivity of MR requires the presence of an enzyme, 11 beta-hydroxysteroid dehydrogenase (11-HSD), which metabolizes glucocorticoids into inactive derivatives. Although evidence exists for the presence of MR in rodent heart, no data are available for humans; moreover, the existence of cardiac 11-HSD is controversial.

METHODS AND RESULTS

The heart samples used originated from tissue removed during cardiac surgery in nontransplant patients or from endocavitary biopsies done for the follow-up of heart transplantation. The expression of MR was examined at the mRNA and protein level by in situ hybridization with cRNA probes specific for human MR mRNA and by immunodetection with two specific anti-MR antibodies. 11-HSD catalytic activity was determined by measurement of the metabolic rate of tritiated corticosteroids by cardiac samples. In nontransplanted hearts, an in situ hybridization signal equivalent to that found in the whole kidney was present on cardiomyocytes. Specific immunolabeling of cardiomyocytes with anti-MR antibodies demonstrated the presence of the MR protein. Cardiac 11-HSD activity was detected (243 +/- 26 fmol.30 min-1.mg protein-1) and was dependent on the cofactor NAD, not NADP, suggesting that it corresponds to the form of the enzyme specifically responsible for MR protection. In transplanted hearts that presented severe alterations, MR immunodetection was weaker and irregular, with no specific hybridization signal.

CONCLUSIONS

Our results demonstrate that MR is coexpressed with 11-HSD in human heart, which thus possesses the cellular machinery required for direct aldosterone action.

Pseudohypoaldosteronism: evaluation of type I receptors by radioreceptor assay and by antireceptor antibodies

We have previously demonstrated a deficiency of mineralocorticoid receptors in pseudohypoaldosteronism, by radioreceptorassay. We now report findings with an antireceptor antibody derived from the immunogenic region of the receptor. Lymphocytes from normal controls and from two cases of pseudohypoaldosteronism previously shown to lack receptor binding were tested. After the plasma membrane of lymphocytes was permeabilized with methanol the cells were incubated with a 1:200 dilution of antibody followed by fluorescent antirabbit immunoglobulin mouse serum. After washing fluorescence was detected by microscopy and cytofluorimetry in both controls and patients with pseudohypoaldosteronism. Recent studies on mineralocorticoid receptor cDNA in pseudohypoaldosteronism have not established a mutation in the sequence. We thus suggest that the pathogenesis of pseudohypoaldosteronism is not related to an abnormality of the receptor but rather due to intracellular factor(s) which can block the binding of aldosterone to its receptor.

Familial pseudohypoaldosteronism: a review on the heterogeneity of the syndrome

Pseudohypoaldosteronism is thought to be a rare salt-losing disorder, caused by resistance to the action of aldosterone. Defective aldosterone receptor binding is present in familial as well as sporadic cases and it has been suggested that the pathogenesis is due to a defect in the aldosterone receptor system. To date, however, molecular genetic analysis has been unable to identify a mutation in the aldosterone receptor gene itself. We have reviewed the findings in patients with pseudohypoaldosteronism, for clues which might enable us to identify the underlying pathogenesis. Although aldosterone receptor binding is regularly decreased or absent in monocytes of patients with pseudohypoaldosteronism, in some patients receptor protein can be detected with a fluorescence-labeled antibody. Receptor protein was detected in patients from familial autosomal dominant families and in sporadic cases, but was undetectable in two patients with the familial recessive form. To further elucidate the pattern of inheritance we studied the response of the renin-angiotensin-aldosterone system to the stimulation by sodium depletion in the familial autosomal dominant form and in two families with sporadic cases. In both "sporadic" families investigated, one parent and one sibling had an exaggerated response of renin and aldosterone to sodium depletion indicating a defect of sodium conservation apparent only during stress, leading to reclassification as familial cases. No additional family member in the "classical" autosomal dominant families responded abnormally to sodium depletion. These findings indicate that pseudohypoaldosteronism is unusually heterogeneous in its clinical, biochemical, and genetic presentations and findings and suggest that its pathogenesis is heterogeneous as well.

Characterization of the novel progestin gestodene by receptor binding studies and transactivation assays

Gestodene is a novel progestin used in oral contraceptives with an increased separation of progestogenic versus androgenic activity and a distinct antimineralocorticoid activity. This specific pharmacological profile of gestodene is defined by its pattern of binding affinities to a variety of steroid hormone receptors. In the present study the affinity of gestodene to the progesterone receptor (PR), the androgen receptor (AR), the glucocorticoid receptor (GR), the mineralocorticoid receptor (MR) and the estrogen receptor (ER) was re-evaluated by steroid binding assays and compared to those obtained for 3-keto-desogestrel and progesterone. The two synthetic progestins displayed identical high affinity to rabbit PR and similar marked binding to rat AR and GR, while progesterone showed high affinity to PR but only low binding to AR and GR. Furthermore, 3-keto-desogestrel exhibited almost no binding to MR, whereas gestodene, similar to progesterone, showed marked affinity to this receptor. In addition to receptor binding studies, transactivation assays were carried out to investigate the effects of gestodene on AR-, GR- and MR-mediated induction of transcription. In contrast to progesterone, which showed antiandrogenic activity, gestodene and 3-keto-desogestrel both exhibited androgenic activity. Furthermore, all three progestins exhibited weak GR-mediated antagonistic activity. In contrast to progesterone, which showed almost no glucocorticoid activity, gestodene and 3-keto-desogestrel showed weak glucocorticoid action. In addition, gestodene inhibited the aldosterone-induced reporter gene transcription, similar to progesterone, whereas unlike progesterone, gestodene did not induce reporter gene transcription. 3-Keto-desogestrel showed neither antimineralocorticoid nor mineralocorticoid action.

A conserved carboxy-terminal subdomain is important for ligand interpretation and transactivation by nuclear receptors

Nuclear receptors share a highly conserved region located at the very carboxy-terminal part of the ligand-binding domain. Site-directed mutagenesis of conserved hydrophobic residues in this region was reported to create mouse and human glucocorticoid receptors (GRs) and estrogen receptors that cannot transactivate but apparently maintain all the other functions. We constructed analogous mutations in the rat GR to compare the mechanism of deficiency to our recently generated trans-dominant-negative mutant. We found that in the rat GR these carboxy-terminal mutations do not generate trans-dominant-negative receptors. We show that these GR mutants fail to bind dexamethasone properly, and hence receptor transformation and subsequent functions are abolished. Furthermore, we report the identification of a GR mutant that is strongly responsive to the antagonist RU486 but is silent with the agonist dexamethasone. We demonstrate that the reversal of the responsiveness is restricted to GR, since analogous mutations in related receptors do not generate similar phenotypes. Contrary to the case of the progesterone receptor, we show that carboxyl-end truncated GR mutants are not activated by RU486. We conclude that sequence conservation of this subdomain does not necessarily imply functional conservation. Chimeric constructs with GAL4 revealed the importance of protein-protein interactions to exert ligand discrimination, which is mediated by the carboxy-terminal subdomain.

Human skin as target for aldosterone: coexpression of mineralocorticoid receptors and 11 beta-hydroxysteroid dehydrogenase

The expression of mineralocorticoid receptors (MR) and 11 beta-hydroxysteroid dehydrogenase (11HSD) activity has been investigated in the epidermis and appendages of the human skin. Aldosterone binds to MR and regulates sodium transport in tight epithelia. Mineralocorticoid selectivity is achieved through coexpression of MR and 11HSD, which prevents permanent MR occupancy by glucocorticoids. Some forms of hypertension may involve abnormalities of MR and/or 11HSD. However, their direct assessment in humans remains difficult in the kidney or colon. This led us to explore this system in human skin easily accessible to biopsy. In situ hybridization with specific MR complementary ribonucleic acid probes and immunohistochemistry using three different anti-MR antibodies showed that MR was expressed at both the messenger ribonucleic acid and protein levels in the keratinocytes of the epidermis, in the sweat and sebaceous glands, and in the hair follicles. A significant 11HSD activity was found in isolated sweat gland ducts (5 fmol/3-mm length.10-min incubation with 10 nmol/L corticosterone as substrate) and was very low in the epidermis. In both structures, reductase activity was 10 times lower than that of dehydrogenase. Studies on the cofactor specificity of the enzyme showed a nicotinamide-adenine-dinucleotide preference in sweat glands, contrasting with a nicotinamide-adenine-dinucleotide phosphate dependence in epidermis. Human skin appears as a new target for aldosterone because it coexpresses MR and 11HSD. Our findings present the possibility to explore the functionality of the MR system in human tissue and its implications in various physiopathological situations.

Increased expression of mineralocorticoid receptor in human ileum after total colectomy: immunohistochemical and immunoblotting studies

Aldosterone is known to regulate transmembrane ion transport and water absorption through its binding to mineralocorticoid receptor (MR) in the mammalian colon. A possible roles of aldosterone has been suggested in increased water absorption from remnant ileum in the patients with total colectomy. We, therefore, studied immunolocalization of MR in remnant ileal mucosa in the patients with total colectomy in order to study the role of aldosterone in water and sodium absorption in these patients. Immunohistochemical localization of MR was performed in ileal mucosa of 7 patients with total colectomy and 5 cases of normal ileum obtained from the resection of ascending colon due to carcinoma by using a polyclonal antibody raised against a mineralocorticoid receptor fusion protein as a primary antibody and a biotinstreptavidin system for immunostaining. Immunoblotting was also performed. Positive MR immunoreactivity was observed in both cytoplasm and nucleus of absorptive cells of ileum of total colectomy patients but not in control normal ileum. Immunoblotting revealed the presence of an approximately 100 kDa immunoreactive product corresponding to mineralocorticoid receptor. Aldosterone is considered to act on ileal mucosa following total colectomy and the aldosterone dependent sodium transport and water absorption may be accelerated in ileal mucosa after total colectomy, which is consistent with the postoperative decrease in the stool volume observed in these patients. In conclusion, increased expression of the mineralocorticoid receptor in remnant ileum may play an important role in intestinal adaptation in total colectomized patients.

Impaired renal 11 beta-oxidation of 9 alpha-fluorocortisol: an explanation for its mineralocorticoid potency

9 alpha-Fluorocortisol (9 alpha FF) is about 200 times more potent as a mineralocorticoid than cortisol (F) in man, although it binds with the same affinity as F and aldosterone to the human mineralocorticoid receptor. The low mineralocorticoid activity of F has been shown to be due to its rapid conversion by the kidney to cortisone (E), which does not bind to the receptor. Therefore, we compared the conversion of F to E with that of 9 alpha FF to 9 alpha-fluorocortisone (9 alpha FE) by 11-hydroxysteroid dehydrogenases in man in vivo and in vitro. Single oral doses of 9 alpha FF, 9 alpha FE, and F were given to normal males, and the excretion of free 9 alpha FF, 9 alpha FE, F, and E was measured in urine. Human kidney and liver slices were incubated with unlabeled steroids, and the free 11-hydroxy- and 11-oxosteroids were quantitated after high performance liquid chromatography separation by UV absorption. Oral F (5 mg) is excreted 70% as free E and 30% as free F (percentage of free steroids only). Oral 9 alpha FF (5 mg) is excreted 90% as free 9 alpha FF and 10% as free 9 alpha FE. Free 9 alpha FF excretion is 14 times greater than that of F after ingesting an identical dose. Oral 9 alpha FE (4 mg) is also excreted 90% as 9 alpha FF and 10% as 9 alpha FE. Kidney slices convert F much faster to E than 9 alpha FF to 9 alpha FE. The conversion of 9 alpha FE to 9 alpha FF is, on the contrary, much faster than that of E to F. Thus, the equilibrium of the reaction is on the 11-oxo side for F/E and on the 11-hydroxy side for 9 alpha FF/9 alpha FE. The interconversion of both pairs of steroids is inhibited by glycyrrhetinic acid in a dose-dependent manner. Liver slices do not measurably convert 9 alpha FF to 9 alpha FE, but do rapidly convert 9 alpha FE into 9 alpha FF. Reflecting this negligible conversion of 9 alpha FF to 9 alpha FE and the low plasma-protein binding of 9 alpha FF, free urinary 9 alpha FF excretion is much higher than that of F after the same oral dose.(ABSTRACT TRUNCATED AT 400 WORDS)