Low level of glucocorticoid receptor messenger ribonucleic acid in pituitary adenomas manifesting Cushing's disease with resistance to a high dose-dexamethasone suppression test

Context is key: glucocorticoid receptor and corticosteroid therapeutics in outcomes after traumatic brain injury

Traumatic brain injury (TBI) is a global health burden, and survivors suffer functional and psychiatric consequences that can persist long after injury. TBI induces a physiological stress response by activating the hypothalamic-pituitary-adrenal (HPA) axis, but the effects of injury on the stress response become more complex in the long term. Clinical and experimental evidence suggests long lasting dysfunction of the stress response after TBI. Additionally, pre- and post-injury stress both have negative impacts on outcome following TBI. This bidirectional relationship between stress and injury impedes recovery and exacerbates TBI-induced psychiatric and cognitive dysfunction. Previous clinical and experimental studies have explored the use of synthetic glucocorticoids as a therapeutic for stress-related TBI outcomes, but these have yielded mixed results. Furthermore, long-term steroid treatment is associated with multiple negative side effects. There is a pressing need for alternative approaches that improve stress functionality after TBI. Glucocorticoid receptor (GR) has been identified as a fundamental link between stress and immune responses, and preclinical evidence suggests GR plays an important role in microglia-mediated outcomes after TBI and other neuroinflammatory conditions. In this review, we will summarize GR-mediated stress dysfunction after TBI, highlighting the role of microglia. We will discuss recent studies which target microglial GR in the context of stress and injury, and we suggest that cell-specific GR interventions may be a promising strategy for long-term TBI pathophysiology.

The expression of glucocorticoid and mineralocorticoid receptors in pituitary tumors causing Cushing's disease and silent corticotroph tumors

OBJECTIVE

Pituitary neuroendocrine corticotroph tumors commonly cause Cushing's disease (CD) that results from increased adrenocorticotropic hormone (ACTH) secretion by the pituitary tumor and consequent increase of cortisol levels in blood. However, in some patients, corticotroph tumors remain clinically non-functioning. Cortisol secretion is regulated by the hypothalamic-pituitary-adrenal axis and includes a negative feedback between cortisol and ACTH secretion. Glucocorticoids reduce ACTH level both by hypothalamic regulation and acting on corticotrophs via glucocorticoid (GR) and mineralocorticoid (MR) receptors. The aim of the study was to determine the role of GR and MR expression at mRNA and protein levels in both functioning and silent corticotroph tumors.

METHODS

Ninety-five patients were enrolled, including 70 with CD and 25 with silent corticotroph tumors. Gene expression levels of NR3C1 and NR3C2 coding for GR and MR, respectively, were determined with qRT-PCR in the two tumor types. GR and MR protein abundance was assessed with immunohistochemistry.

RESULTS

Both GR and MR were expressed in corticotroph tumors. Correlation between NR3C1 and NR3C2 expression levels was observed. NR3C1 expression was higher in silent than in functioning tumors. In CD patients NR3C1 and NR3C2 levels were negatively correlated with morning plasma ACTH levels and tumor size. Higher NR3C2 was confirmed in patients with remission after surgery and in densely granulated tumors. Expression of both genes and GR protein was higher in USP8-mutated tumors. Similar relationship between USP8 mutations and expression levels were observed in analysis of silent tumors that also revealed a negative correlation between GR and tumor size and higher NR3C1 expression in densely granulated tumors.

CONCLUSIONS

Although the associations between gene/protein expression and patients clinical features are not strong, they consistently show an evident trend in which higher receptor expression corresponds to more favorable clinical characteristics.

The Role of Glucocorticoid Receptor in the Pathophysiology of Pituitary Corticotroph Adenomas

Adrenocorticotropic Hormone (ACTH)-secreting pituitary adenomas are rare tumors characterized by autonomous ACTH secretion with a consequent increase in circulating cortisol levels. The resulting clinical picture is called Cushing’s disease (CD), a severe condition burdened with high morbidity and mortality. Apart from increased cortisol levels, CD patients exhibit a partial resistance to the negative glucocorticoid (GC) feedback, which is of paramount clinical utility, as the lack of suppression after dexamethasone administration is one of the mainstays for the differential diagnosis of CD. Since the glucocorticoid receptor (GR) is the main regulator of negative feedback of the hypothalamic–pituitary–adrenal axis in normal conditions, its implication in the pathophysiology of ACTH-secreting pituitary tumors is highly plausible. In this paper, we review GR function and structure and the mechanisms of GC resistance in ACTH-secreting pituitary tumors and assess the effects of the available medical therapies targeting GR on tumor growth.

A Comprehensive Approach to Predicting the Outcomes of Transsphenoidal Endoscopic Adenomectomy in Patients with Cushing’s Disease

Persistent and recurrent hypercortisolism after transsphenoidal endoscopic surgery (TSS) is considered to be an urgent issue prompting the search for Cushing’s disease (CD) remission predictors. The goal was to find a combination of predictors that can forecast the remission of CD after TSS. A total of 101 patients with CD who had undergone TSS were included. One year after surgery, CD remission status was evaluated. Preoperative pituitary magnetic resonance imaging (MRI) data, preoperative results of a high-dose dexamethasone suppression test (HDDST) and morning serum cortisol level collected 24 h after TSS (24 h MSeC) were compared in patients with and without remission of hypercortisolism. Remission one year after TSS was confirmed in 63 patients. CD remission predictors one year after TSS were: adenoma size ≥ 3 mm in the absence of invasive growth and the suppression of serum cortisol ≥ 74% in the HDDST, 24 h MSeC ≤ 388 nmol/L. A total of 38 patients had three favorable values of detected predictors; all of them had CD remission one year after TSS. With long-term follow-up, 36 of them remained in remission. Patients who had no one favorable predictor had no remission of hypercortisolism one year after TSS. Our data confirmed the prospects of using a combination of selected predictors to forecast CD remission after TSS.

Difference in miRNA Expression in Functioning and Silent Corticotroph Pituitary Adenomas Indicates the Role of miRNA in the Regulation of Corticosteroid Receptors

Corticotroph pituitary adenomas commonly cause Cushing’s disease (CD), but some of them are clinically silent. The reason why they do not cause endocrinological symptoms remains unclear. We used data from small RNA sequencing in adenomas causing CD (n = 28) and silent ones (n = 20) to explore the role of miRNA in hormone secretion and clinical status of the tumors. By comparing miRNA profiles, we identified 19 miRNAs differentially expressed in clinically functioning and silent corticotroph adenomas. The analysis of their putative target genes indicates a role of miRNAs in regulation of the corticosteroid receptors expression. Adenomas causing CD have higher expression of hsa-miR-124-3p and hsa-miR-135-5p and lower expression of their target genes NR3C1 and NR3C2. The role of hsa-miR-124-3p in the regulation of NR3C1 was further validated in vitro using AtT-20/D16v-F2 cells. The cells transfected with miR-124-3p mimics showed lower levels of glucocorticoid receptor expression than control cells while the interaction between miR-124-3p and NR3C1 3′ UTR was confirmed using luciferase reporter assay. The results indicate a relatively small difference in miRNA expression between clinically functioning and silent corticotroph pituitary adenomas. High expression of hsa-miR-124-3p in adenomas causing CD plays a role in the regulation of glucocorticoid receptor level and probably in reducing the effect of negative feedback mediated by corticosteroids.

Effect of 3 NR3C1 Mutations in the Pathogenesis of Pituitary ACTH Adenoma

CONTEXT

Glucocorticoids act through the glucocorticoid receptor (GR) encoded by the nuclear receptor subfamily 3 group C member 1 (NR3C1) gene.

OBJECTIVE

This study aimed to examine the function of NR3C1 variants and their possible pathogenic role in Cushing disease (CD).

METHODS

Next-generation sequencing was conducted in 49 CD patients. Corticotroph tumor GR protein expression was examined by immunohistochemistry (IHC). Constructs harboring the 3 NR3C1-mutant and wild-type (WT) GR were transfected into the murine corticotropic adenoma cell line (AtT-20), and GR protein expression was quantified by Western blot. Translocation activity was assessed by immunofluorescence and effects of the GR mutants on corticotroph tumor proliferation, pro-opiomelanocortin (POMC) transcription, and ACTH secretion were tested.

RESULTS

Clinical features were similar in patients harboring the NR3C1 mutations and WT GR. Recurrent adenomas showed higher GR IHC scores than nonrecurrent tumors. In vitro studies demonstrated that the p.R469X mutant generated a truncated GR protein, and the p.D590G and p.Y693D GR mutants resulted in lower GR expression. Dexamethasone (DEX) treatment of AtT-20 cells demonstrated decreased DEX-induced nuclear translocation, increased cell proliferation, and attenuated suppression of POMC transcription of 3 GR mutants. Interestingly, the p.R469X GR mutant resulted in increased murine corticotroph tumor ACTH secretion compared to WT GR.

CONCLUSION

Our findings identify 3/49 (6.1%) consecutive human corticotroph tumors harboring GR mutations. Further findings demonstrate the role NR3C1 plays in CD pathogenesis and offer insights into a novel treatment approach in this patient subset.

Proopiomelanocortin, glucocorticoid, and CRH receptor expression in human ACTH-secreting pituitary adenomas

ACTH-secreting pituitary tumors are by definition partially autonomous, i.e., secrete ACTH independent of physiological control. However, only few, small-sized studies on proopiomelanocortin (POMC) and its regulation by corticotropin-releasing hormone (CRH) or glucocorticoids are available. Objective of the present study was to report on constitutive and CRH- and dexamethasone-regulated POMC, CRH (CRH-R1), and glucocorticoid receptor (NR3C1) gene expression in a large series of human corticotrope adenomas. Fifty-three ACTH-secreting adenomas were incubated with 10 nM CRH or 10 nM dexamethasone for 24 h. POMC, CRH-R1, NR3C1, and its alpha and beta isoforms were quantified and medium ACTH measured. Constitutive POMC expression proved extremely variable, with macroadenomas exhibiting higher levels than microadenomas. POMC increased during CRH in most specimens; conversely, changes induced by dexamethasone were varied, ranging from decrease to paradoxical increase. No correlation between POMC and ACTH was detected in any experimental condition. CRH-R1 expression was not linked to the response to CRH while NR3C1 was expressed at greater levels in specimens who failed to inhibit during dexamethasone; glucocorticoid receptor α was the more abundant isoform and subject to down-regulation by dexamethasone. Our results demonstrate a considerable variability in POMC expression among tumors and no correlation between POMC and ACTH, suggesting that POMC peptide processing/transport plays a major role in modulating ACTH secretion. Further, CRH-R1 and NR3C1 expression were not linked to the expected ligand-induced outcome, indicating that receptor signaling rather than abundance determines corticotrope responses. Our findings pave the way to new avenues of research into Cushing's disease pathophysiology.

The New Molecular Landscape of Cushing's Disease

Cushing's disease (CD) is caused by corticotropin-secreting pituitary adenomas and results in substantial morbidity and mortality. Its molecular basis has remained poorly understood until the past few years, when several proteins and genes [such as testicular orphan nuclear receptor 4 (TR4) and heat shock protein 90 (HSP90)] were found to play key roles in the disease. Most recently, mutations in the gene of ubiquitin-specific peptidase 8 (USP8) increasing its deubiquination activity were discovered in a high percentage of corticotroph adenomas. Here, we will discuss emerging insights in the molecular alterations that finally result in CD. The therapeutic potential of these findings needs to be carefully evaluated in the near future, hopefully resulting in new treatment options for this devastating disorder.

The glucocorticoid receptor and its expression in the anterior pituitary and the adrenal cortex: a source of variation in hypothalamic-pituitary-adrenal axis function; implications for pituitary and adrenal tumors

OBJECTIVE

To review the expression of the glucocorticoid receptor (GR) in anterior pituitary and adrenocortical cells and tumors derived from these tissues as well as factors that may influence its expression.

METHODS

We present an overview of the relevant literature, with a focus on data generated from our studies.

RESULTS

The expression of the GR is an essential element of the negative feedback that closes the loop formed by corticotropin-releasing hormone, adrenocorticotropic hormone, and cortisol in the context of the hypothalamic-pituitary-adrenal (HPA) axis. Although the GR expression in anterior pituitary cells-and in particular the corticotrophs-was first demonstrated several years ago, it was not known until relatively recently where, by what cells, and in what form the GR is expressed in the adrenal cortex. The variability in the expression of the GR in pituitary and adrenocortical cells may underlie the substantial differences in HPA axis function across individuals, especially when testing for tumors associated with hypercortisolemia. This expression is influenced by a multitude of tissue-specific factors, which may explain why it is so difficult to interpret (or reproduce) studies that are based on GR functional polymorphisms on different cohorts of patients or even different sets of laboratory animals.

CONCLUSION

This review highlights the variability in expression and function of the GR in pituitary and adrenocortical cells as one of the reasons for the appreciable differences in HPA axis function across individuals. Particular attention was paid to interactions that may affect the interpretation of diagnostic testing of the HPA axis in patients with pituitary adenomas (Cushing disease) or adrenocortical tumors (Cushing syndrome).

Responses to corticotrophin-releasing hormone and dexamethasone in a large series of human adrenocorticotrophic hormone-secreting pituitary adenomas in vitro reveal manifold corticotroph tumoural phenotypes

Patients with Cushing's disease are known to present a variable secretory response to stimulatory and inhibitory challenges. Evaluation of the secretory behaviour of pituitary adrenocorticotrophic hormone (ACTH)-secreting adenomas in vitro aids in the comprehension of its behaviour in vivo; however, given the small size of these tumours and the consequent paucity of material available to in vitro studies, a comprehensive study on the secretory behaviour of human corticotroph tumours has not yet been performed. The present study aimed to assess the spectrum of responses to the two main corticotroph modulators, corticotrophin-releasing hormone (CRH) and dexamethasone, in a large series of human ACTH-secreting pituitary tumours. Seventy-two ACTH-secreting pituitary tumours were collected during surgery and established in culture. Specimens were incubated with 10 nm CRH and/or 10 nm dexamethasone for 4 h and 24 h. Secretion in unstimulated, control wells was set at 100% and changes in ACTH concentrations by at least 20% were considered as responses. Parallel experiments in 12 rat anterior pituitary primary cultures were evaluated. A marked ACTH increase was observed during incubation with CRH in 70% of tumoural specimens at 4 h (range 124-3500% of control wells) and in 57% at 24 h (range 122-3323%). Dexamethasone reduced ACTH secretion in almost 50% of tumours (range 78-2% of control at 4 h; 76-3% at 24 h), whereas it did not affect ACTH medium levels in 30% of specimens and induced a paradoxical ACTH increase in 20% of tumours (range 130-327% of control at 4 h; 156-348% at 24 h). By comparison, CRH uniformly increased ACTH levels in rat anterior pituitary primary cultures (mean 745 ± 84% at 4 h; 347 ± 25% at 24 h), whereas dexamethasone decreased ACTH levels by 40-50% in all experiments. In conclusion, the present study of a large series of human ACTH-secreting pituitary tumours in vitro revealed a considerable variability in the responses to CRH and dexamethasone. This finding indicates the existence of multiple corticotroph tumoural phenotypes and may account for the different responses to physiological and pharmacological modulators in vivo.

A comparative study by age and gender of the pituitary adenoma and ACTH and alpha-MSH secretion in dogs with pituitary-dependent hyperadrenocorticism

Pituitary-dependent hyperadrenocorticism (PDH) is frequent in dogs. Little is known about its presentation in different age groups and its characteristics. Dividing the population under study (n=107) into three age groups we observed that 11.2% were young, 51.4% adults and 37.4% aged. Using magnetic resonance, pituitary tumours were intra-sellar (IS) in 30.8% and extra-sellar (ES) in 62.6% and the pars intermedia (PI) was affected in 6.5%. ES are predominant in females and IS in males (p<0.0001). In the adult-aged population, the ES and PI are predominant, while in the young, the IS predominate (p<0.0001). ACTH concentration was greater in the ES vs. IS (p<0.05). alpha-MSH did not present significant differences according to tumour size, showing a negative correlation (r=-0.47; p<0.01) vs. ACTH. Differences in adenoma size according to gender and their age-related frequency of apparition could be because of different origins of the corticotrophinoma.

Naturally occurring C-terminal splice variants of nuclear receptors

Alternative mRNA splicing in the region encoding the C-terminus of nuclear receptors results in receptor variants lacking the entire ligand-binding domain (LBD), or a part of it, and instead contain a sequence of splice variant-specific C-terminal amino acids. A total of thirteen such splice variants have been shown to occur in vertebrates, and at least nine occur in humans. None of these receptor variants appear to be able to bind endogenous ligands and to induce transcription on promoters containing the response element for the respective canonical receptor variant. Interestingly, ten of these C-terminal splice variants have been shown to display dominant-negative activity on the transactivational properties of their canonical equivalent. Research on most of these splice variants has been limited, and the dominant-negative effect of these receptor variants has only been demonstrated in reporter assays in vitro, using transiently transfected receptors and reporter constructs. Therefore, the in vivo function and relevance of most C-terminal splice variants remains unclear. By reviewing the literature on the human glucocorticoid receptor beta-isoform (hGRbeta), we show that the dominant-negative effect of hGRbeta is well established using more physiologically relevant readouts. The hGR beta-isoform may alter gene transcription independent from the canonical receptor and increased hGRbeta levels correlate with glucocorticoid resistance and the occurrence of several immune-related diseases. Thus, available data suggests that C-terminal splice variants of nuclear receptors act as dominant-negative inhibitors of receptor-mediated signaling in vivo, and that aberrant expression of these isoforms may be involved in the pathogenesis of a variety of diseases.

The zebrafish as a model system for glucocorticoid receptor research

Glucocorticoids regulate a plethora of physiological processes, and are widely used clinically as anti-inflammatory drugs. Their effects are mediated by the glucocorticoid receptor (GR), a ligand-activated transcription factor. Currently, zebrafish embryos are being developed into a model system for GR research, since they are easy to manipulate genetically and their phenotype can easily be visualized because of their transparent bodies. In addition, the zebrafish GR gene shows a relatively high level of similarity with its human equivalent. First, both the zebrafish and the human genome contain only a single gene encoding the GR. In all other fish species studied thus far, two GR genes have been found. Second, the zebrafish contains a C-terminal GR splice variant with high similarity to the human GRbeta, which has been shown to be a dominant-negative inhibitor of the canonical GRalpha and may be involved in glucocorticoid resistance. Thus, zebrafish embryos are potentially a useful model system for glucocorticoid receptor research, but currently only a limited number of tools is available. In this review, we discuss which tools are available and which need to be developed, in order to exploit the full potential of the zebrafish as a model system for GR research.

Discovery of a functional glucocorticoid receptor beta-isoform in zebrafish

In humans, two glucocorticoid receptor (GR) splice variants exist: GRalpha and GRbeta, which are identical between amino acids 1-727 and then diverge. Whereas GRalpha (the canonical GR) acts as a ligand-activated transcription factor, GRbeta does not bind traditional glucocorticoid agonists, lacks GRalpha's transactivational activity, and acts as a dominant-negative inhibitor of GRalpha. It has been suggested that this receptor isoform is involved in the induction of glucocorticoid resistance in asthma patients. Unfortunately, a GR beta-isoform has been detected in only humans, and therefore, an animal model for studies on this isoform is lacking. In the present study, we demonstrate that in zebrafish a GR isoform exists that diverges from the canonical zebrafish GR at the same position as human GRbeta from human GRalpha. The zebrafish GR beta-isoform acts as a dominant-negative inhibitor in reporter assays, and the extent of inhibition and the effective GRalpha/GRbeta ratio is similar to studies performed with the human GR isoforms. In addition, the subcellular localization of zebrafish GRbeta is similar to its human equivalent. Finally, expression levels of GRalpha and GRbeta were determined in adult zebrafish tissues and at several developmental stages. Both receptor isoforms were detected throughout the body, and GRbeta mRNA levels were relatively low compared with GRalpha mRNA levels, as in humans. Thus, for the first time, a GR beta-isoform has been identified in a nonhuman animal species, shedding new light on the relevance of this GR splice variant and providing a versatile animal model for studies on the GR system.

Immunohistochemical analysis of 11-beta-hydroxysteroid dehydrogenase type 2 and glucocorticoid receptor in subclinical Cushing's disease due to pituitary macroadenoma

Subclinical Cushing's disease (SCD) is characterized by lack of clinically evident Cushingoid features, despite abnormal hypersecretion of ACTH. Nearly half the cases of SCD are due to macroadenomas, and in the majority of them, ACTH secretion is not inhibited even by high-dose dexamethasone. Impaired glucocorticoid (GC) action may be correlated with the proliferation and development of pituitary macroadenomas causing SCD. In this study, immunohistochemical analysis of the resected tumors were performed to evaluate the expression of 11beta-hydroxysteroid dehydrogenase type 2 (11betaHSD2) and glucocorticoid receptor (GR) in pituitary tissues obtained from two SCD (macroadenomas), eight Cushing's disease (CD) (microadenomas), nine acromegaly, and nine normal pituitary (NP). Scattered 11betaHSD2-immunopositive cells were detected in all NP tissues, but its immunoreactivity was totally absent in any tumorous tissues except two CD. Scattered GR-immunopositive cells were also detected and GR immunostaining was restricted to the cytosol in NP tissue. In contrast, GR-immunopositive cells were abundantly present and GR immunostaining was restricted to the nucleus in all the tumorous tissues. There were marked differences in both expression levels and localization between NP tissues and all the tumors. There may be a mechanism other than that via 11betaHSD2 for causes of impaired negative feedback action by GC in SCD and CD, but results of our present study suggest that impaired GC action may be involved, at least in part, in tumorigenesis of SCD and CD.

Very low levels of the glucocorticoid receptor beta isoform in the human hippocampus as shown by Taqman RT-PCR and immunocytochemistry

The hippocampus is an important target for glucocorticoid hormones. Glucocorticoid receptor (GR) mediated feedback in this area is important for control of behavioural adaptation. An alternative splice variant, the GRbeta (GRbeta) isoform, does not bind ligand and has been proposed to inhibit classic GRalpha-mediated transactivation of target genes. Hence, an increased ratio of GRbeta to GRalpha may induce relative corticosteroid-resistance, as e.g. presumed to occur in major depression. To investigate whether GRbeta is involved in the human hippocampus, we studied GRalpha and GRbeta expression levels in postmortem hippocampal tissue of control subjects by quantitative PCR (Taqman RT-PCR) and immunocytochemistry. Taqman RT-PCR demonstrated a very low relative abundance of GRbeta in the human hippocampus (GRalpha:GRbeta ratio approximately 14,500:1). Immunohistochemical analysis confirmed the occurrence of isolated profiles indeed displaying nuclear staining in the main hippocampal subregions. Subsequent double immunofluorescent analysis revealed that >98% of these GRbeta positive cells were double positive for leucocyte common antigen, that identifies exclusively blood-derived cells of haematopoietic origin, including microglia. We conclude that GRbeta is present in very low amounts in the control human hippocampus, and that of these low numbers of cells, notably, almost all are derived from blood which is inevitably present in postmortem tissue. A functionally relevant role for the GRbeta in control of the human hippocampus is therefore not very likely. Whether this is altered in disease conditions awaits further research.

Molecular mechanisms of glucocorticoid action and resistance

The actions of glucocorticoid hormones are mediated by an intracellular receptor, the glucocorticoid receptor (GR). The mechanism of action of this ligand-inducible transcription factor is discussed, focusing on mechanisms of glucocorticoid resistance. Three mechanisms are highlighted: ligand-induced down-regulation of the receptor, the dominant-negative inhibition by the beta-isoform of the receptor, and repression by the transcription factor NF-kappa B. It has been shown that these mechanisms can significantly inhibit glucocorticoid signaling, and could therefore seriously decrease the efficacy of glucocorticoids used clinically.

Glucocorticoid receptor variants: clinical implications

Following exposure to stress, cortisol is secreted from the adrenal cortex under the control of the hypothalamic-pituitary-adrenal axis (HPA-axis). Central in the regulation of the HPA-axis is a two tied corticosteroid-receptor system, comprised of high and low affinity receptors, the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR), respectively. In addition, these corticosteroid receptors mediate the effects of cortisol during stress on both central and peripheral targets. Cortisol modulates gene-expression of corticosteroid-responsive genes, with the effect lasting from hours to days. Mutations in the GR-gene are being associated with corticosteroid resistance and haematological malignancies, although these mutations are relatively rare and probably not a common cause of these diseases. However, several GR-gene variants and single nucleotide polymorphisms (SNP) in the GR-gene have been identified which are relatively common in the human population. The GRbeta-variant, for example, has been proposed to influence corticosteroid-sensitivity and most evidence has been derived from the immune system and in particular asthma. With respect to polymorphisms, a BclI restriction fragment polymorphism and a Asp363Ser have been described, which not only influence the regulation of the HPA-axis, but are also associated with changes in metabolism and cardiovascular control. These associations of a GR-gene polymorphism with metabolism and cardivascular control, and also with the regulation of the HPA-axis, indicates an important underlying role of cortisol in the etiology of these complex disorders. Therefore, we propose that a common underlying defect in these complex disorders is a disregulation of the HPA-axis, especially during stress. The clinical implication is that the regulation of the HPA-axis should be envisioned as a primary target of new drugs for the treatment of stress-related disorders.

Pitavastatin enhanced BMP-2 and osteocalcin expression by inhibition of Rho-associated kinase in human osteoblasts

To clarify the mechanism of the stimulatory effect of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors (statins) on bone formation, we investigated the effect of pitavastatin, a newly developed statin, on expression of bone morphogenetic protein-2 (BMP-2) and osteocalcin in primary cultured human osteoblasts. Pitavastatin increased the expression level of mRNA for BMP-2, and much more effectively for osteocalcin. This stimulatory effect was abolished by the addition of geranylgeranyl pyrophosphate, an essential molecule for prenylation of small GTP-binding proteins such as Rho GTPase, but not by inhibitors of nitric oxide synthase and various protein kinases. Pitavastatin suppressed the Rho-associated kinase (Rho-kinase) activity. Hydroxyfasudil, a specific inhibitor of Rho-kinase, increased BMP-2 and osteocalcin expression. These mRNA levels were strongly suppressed by dexamethasone, but restored by co-treatment with hydroxyfasudil. These observations suggest that the Rho-kinase negatively regulates bone formation and the inhibition of Rho and Rho-kinase pathway is the major mechanism of the statin effect on bone. Moreover, a Rho-kinase inhibitor may be a new therapeutic reagent for the treatment of osteoporosis such as glucocorticoid-induced osteoporosis.

Determination of the proliferation and apoptotic index in adrenocorticotropin-secreting pituitary tumors : comparison between micro- and macroadenomas

We investigated the growth fraction and cell loss fraction in a large group of patients with Cushing's disease subdivided according to tumor size. Fifty-one patients, 8 males and 43 females, aged 12 through 61 years (mean age 34.6 +/- 1.5 years), were studied. Thirty-six patients had a microadenoma and the remaining 15 a macroadenoma. Immunohistochemical analysis was performed on paraffin-embedded material using a monoclonal antibody (MIB-1) directed against a proliferation-associated nuclear antigen, Ki-67, to measure the growth fraction. Apoptosis was assessed by the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling method, using a monoclonal antibody recognizing areas of DNA fragmentation. Ki-67 labeling index and apoptosis were counted on separate slides in at least 1000 evaluable cells. Patients with a macroadenoma had a significantly higher value of Ki-67 index (9.3 +/- 2.7%) than patients with microadenoma (2.8 +/- 0.5%; P < 0.002), whereas the apoptotic index was not significantly different in the two groups (1.7 +/- 0.8% in macroadenomas versus 0.8 +/- 0.3% in microadenomas). Our study shows that ACTH-secreting macroadenomas are characterized by a higher cell growth fraction than microadenomas, whereas the cell loss fraction is not different. A high proliferation rate seems to play a major role in determining the progression from small to large pituitary tumors in Cushing's disease.

Glucocorticoid Receptor beta: View I

Since the human glucocorticoid receptor (GR) cDNA and gene sequences were reported, the existence of two highly homologous GR isoforms was predicted. These were the classic human ligand-binding GRalpha, and a slightly smaller protein, termed GRbeta. Although the mechanism of action of GRbeta has been studied extensively, the role of GRbeta in the modulation of glucocorticoid actions remains uncertain.

Glucocorticoid Receptor beta: View II

There is a clear role for mechanisms that modulate glucocorticoid receptor (GR) function. The non-steroid-binding GRbeta isoform has been proposed to play a role in this modulation but the published data are contradictory. The relative levels of this isoform appear to be low. Alternative mechanisms for the modulation of glucocorticoid action are described and contrasted with the proposed role for GRbeta.