Glucocorticoid Receptor Inhibition Research Articles

Circadian Regulation of lncRNAs Connects Per1, Endothelin‐1, and GR

The circadian clock regulates expression of nearly half of all mammalian genes. The mechanism of this regulation involves four core clock proteins: Bmal1, CLOCK, Cry (homologs 1-2) and Per (homologs 1-3). We have demonstrated that Per1 is an aldosterone and glucocorticoid target gene in the kidney. Long, non-coding (lnc)RNAs regulate gene expression via diverse mechanisms and can either activate or silence genes. Growth arrest specific 5 (Gas5) is a lncRNA implicated in inhibition of glucocorticoid receptor (GR) action. We have shown that Gas5 mRNA is acutely upregulated in response to 4 hour aldosterone treatment in a renal collecting duct cell line. Gas5 expression is also affected by Per1 in vivo in the liver and the renal cortex of Per1 KO mice compared to wild type. Potential circadian regulation of Gas5 is further supported by the observation that Gas5 expression oscillates in synchronized human renal proximal tubule cells (HK2). Endothelin-1 (ET-1) production is inhibited by Per1 in the kidney. ET-1 is a peptide hormone that contributes to blood pressure control. We have identified a novel lncRNA transcribed from the human ET-1 gene (EDN1) locus. This antisense lncRNA (EDN1-AS) is expressed in HK2 cells, human umbilical vein endothelial (HUVEC) cells, human bronchoepithelial (S9) cells, human mammary (HMEC) cells and whole human kidney. The EDN1-AS lncRNA was also shown to oscillate over 24 hours in synchronized HK2 cells. Both GR and Per1 were detected at the EDN1-AS promoter. Thus, we have identified two lncRNAs as novel Per1 targets which may have implications for the regulation of ET-1 and GR action by the clock.

Fluocinolone Acetonide Is a Potent Synergistic Factor of TGF-β3-Associated Chondrogenesis of Bone Marrow-Derived Mesenchymal Stem Cells for Articular Surface Regeneration.

Articular cartilage repair remains a challenging problem. Based on a high-throughput screening and functional analysis, we found that fluocinolone acetonide (FA) in combination with transforming growth factor beta 3 (TGF-β3) strongly potentiated chondrogenic differentiation of human bone marrow-derived mesenchymal stem cells (hBMSCs). In an in vivo cartilage defect model in knee joints of immunocompromised mice, transplantation of FA/TGF-β3-treated hBMSCs could completely repair the articular surface. Analysis of the intracellular pathways revealed that FA enhanced TGF-β3-induced phosphorylation of Smad2 and Smad3. Additionally, we performed a pathway array and found that FA activates the mTORC1/AKT pathway. Chemical inhibition of mTORC1 with rapamycin substantially suppressed FA effect, and inhibition of AKT completely repressed chondrogenesis of hBMSCs. Inhibition of glucocorticoid receptor with mifepristone also suppressed FA effect, suggesting that FA involves binding to the glucocorticoid receptor. Comparative analysis with other glucocorticoids (triamcinolone acetonide [TA] and dexamethasone [DEX]) revealed the unique ability of FA to repair articular cartilage surgical defects. Analysis of intracellular pathways showed that the mTORC1/AKT pathway and the glucocorticoid receptor was highly activated with FA and TA, but to a lesser extent with DEX. Collectively, these results show a unique ability of FA to enhance TGF-β3-associated chondrogenesis, and suggest that the FA/TGF-β3 combination may be used as major inducer of chondrogenesis in vitro. Additionally, FA/TGF-β3 could be potentially applied in a clinical setting to increase the efficiency of regenerative approaches based on chondrogenic differentiation of stem cells.

Exercise reverses OVA-induced inhibition of glucocorticoid receptor and increases anti-inflammatory cytokines in asthma.

The purpose of this study was to determine the effect of aerobic exercise training (AT) on the expression of glucocorticoid receptors (GR) and anti-inflammatory cytokines in an asthma model. BALB/c mice were divided into groups control (CT; nonsensitized/nontrained), aerobic training (AT; nonsensitized/trained), ovalbumin (OVA; sensitized/not trained), and OVA+AT (sensitized/trained). OVA groups received OVA by inhalation, and the AT groups completed 1, 3, or 7 days of exercise (60 min/session). Expression of GR, IL-4, IL-5, IL-10, IL-1ra, NF-κB, TGF-β, VEGF, ICAM-1, VCAM-1; eosinophils counting; and airway remodeling (AR) features [airway smooth muscle (ASM) and epithelial thickness and collagen fiber deposition] were quantified. OVA sensitization induced a decrease in the expression of GR and increases in the eosinophil, IL-4, IL-5, NF-κB, TGF-β, VEGF, ICAM-1, VCAM-1, and AR features (P < 0.05). After 3 days, AT reversed the OVA-induced reduction in the expression of GR, and subsequently induced increases in the expression of IL-10 and IL-1ra (seventh day). In contrast, the eosinophil migration, the expression of NF-κB, IL-4, IL-5, TGF-β, RANTES, VEGF, ICAM-1, VCAM-1, and the AR features (P < 0.05) were reduced. AT increases the expression of GR and anti-inflammatory cytokines (IL-10 and IL-1ra) and reduces the expression of inflammatory mediators and airway inflammation in an animal model of asthma.

Impaired miR449a-induced downregulation of Crhr1 expression in low-birth-weight rats.

Low birth weight (LBW) is related to increased incidence of common cardiovascular and metabolic disorders, and psychopathologies later in life. Recent studies have suggested that maternal malnutrition affects fetal hypothalamic-pituitary-adrenal (HPA) axis programing although the mechanism is unknown. We demonstrated that LBW offspring delivered from malnourished dams showed prolonged elevated plasma corticosterone concentrations when compared with those of normal-birth-weight (NBW) offspring and impaired downregulation of corticotropin-releasing factor receptor type 1 (CRF-R1, Crhr1) in the anterior pituitary in restraint. Restraint increased expression of miR449a, which we had previously demonstrated to be involved in Crhr1 downregulation, in the anterior pituitary and serum exosomal miR449a contents through glucocorticoids in NBW offspring, but not in LBW offspring. Although plasma corticosterone concentrations were higher at 2000 h than at 0800 h in both LBW and NBW offspring, they were significantly higher in LBW offspring than in NBW offspring at 2000 and 0200 h. There were no significant diurnal changes in miR449a expression levels in the anterior pituitary of either NBW or LBW offspring, but the expression was significantly lower in LBW offspring than in NBW offspring at 1400, 2000, and 0200 h. The expression levels of GAS5, which inhibits glucocorticoid receptor (GR) binding to glucocorticoid-responsive element, in the anterior pituitary of LBW offspring were elevated when compared with those of NBW offspring. The downregulation of GR found in NBW offspring did not occur in restrained LBW offspring. These results indicate that impaired miR449a expression, probably induced by increased GAS5 expression, causes dysregulation of Crhr1 expression in the anterior pituitary, resulting in prolonged HPA axis activation in restrained LBW offspring.

Involvement of Nitric Oxide, Neurotrophins and HPA Axis in Neurobehavioural Alterations Induced by Prenatal Stress.

Several studies suggest that negative emotions during pregnancy generate adverse effects on the cognitive, behavioural and emotional development of the descendants. The psychoneuroendocrine pathways involve the transplacentary passage of maternal glucocorticoids in order to influence directly on fetal growth and brain development.Nitric oxide is a gaseous neurotransmitter that plays an important role in the control of neural activity by diffusing into neurons and participates in learning and memory processes. It has been demonstrated that nitric oxide is involved in the regulation of corticosterone secretion. Thus, it has been found that the neuronal isoform of nitric oxide synthase (nNOS) is an endogenous inhibitor of glucocorticoid receptor (GR) in the hippocampus and that nNOS in the hippocampus may participate in the modulation of hypothalamic-pituitary-adrenal axis activity via GR.Neurotrophins are a family of secreted growth factors consisting of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin 3 (NT3) and NT4. Although initially described in the nervous system, they regulate processes such as cell survival, proliferation and differentiation in several other compartments. It has been demonstrated that the NO-citrulline cycle acts together with BDNF in maintaining the progress of neural differentiation.In the present chapter, we explore the interrelation between nitric oxide, glucocorticoids and neurotrophins in brain areas that are key structures in learning and memory processes. The participation of this interrelation in the behavioural and cognitive alterations induced in the offspring by maternal stress is also addressed.

Gene expression of peripheral blood cells reveals pathways downstream of glucocorticoid receptor antagonism and nab-paclitaxel treatment.

Whereas paclitaxel treatment is associated with leukopenia, the mechanisms that underlie this effect are not well-characterized. In addition, despite the importance of glucocorticoid signaling in cancer treatment, the genomic effects of glucocorticoid receptor antagonism by mifepristone treatment in primary human cells have never been described. As part of a randomized phase 1 clinical trial, we used microarrays to profile gene expression in peripheral blood cells sampled from each of four patients at baseline, after placebo/nanoparticle albumin-bound paclitaxel (nab-paclitaxel) treatment (cycle 1), and after mifepristone/nab-paclitaxel treatment (cycle 2). We found that 63 genes were differentially expressed following treatment with nab-paclitaxel, including multiple genes in the tubulin pathway. We also found 606 genes that were differentially expressed in response to mifepristone; genes downregulated by mifepristone overlapped significantly with those previously identified as being upregulated by dexamethasone. These results provide insights into the mechanisms of paclitaxel and glucocorticoid receptor inhibition in peripheral blood cells.

Glucocorticoid receptors in the nucleus of the solitary tract (NTS) decrease endocrine and behavioral stress responses.

Stress activates the hypothalamo-pituitary-adrenal (HPA) axis, leading to adrenocortical secretion of glucocorticoids. The magnitude and duration of the HPA axis response is mediated in large part by the glucocorticoid receptor (GR). The nucleus of the solitary tract (NTS) abundantly expresses the GR and is a key brain region for processing autonomic and endocrine stress responses. This study tests the hypothesis that GR within the NTS plays an important role in inhibiting stress-induced endocrine and behavioral responses. Cohorts of rats received bilateral micropellet (30 μg) implantations of crystalline corticosterone, mifepristone (a GR antagonist) or cholesterol (control) directed into the region of the NTS, and were subsequently subjected to either acute psychogenic (restraint) stress or chronic variable stress (CVS). We found that NTS GR antagonism increased acute stress-induced corticosterone levels, whereas GR activation within the NTS attenuated this response. Following CVS, basal and 15 min post-restraint plasma corticosterone levels were increased by NTS GR antagonism, which was associated with an increase in Fos immunoreactivity within the PVN. Using the elevated plus maze (EPM) and forced swim test (FST), we assessed the effect of NTS GR inhibition on anxiety- and depression-like behaviors, respectively. GR inhibition within the NTS decreased open arm exploratory behavior in the EPM and increased immobility in the FST relative to controls. Together, the findings reveal a novel role of NTS GR signaling for inhibiting both endocrine and behavioral responses to stress.

Low-dose anisomycin sensitizes glucocorticoid-resistant T-acute lymphoblastic leukemia CEM-C1 cells to dexamethasone-induced apoptosis through activation of glucocorticoid receptor and p38-MAPK/JNK

Glucocorticoid (GC) resistance in children with acute lymphoblastic leukemia (ALL) usually resulted in the failure of treatment. Exploring new agents to overcome GC resistance is important. Here we reported for the first time that low-dose anisomycin has the potential to sensitize GC-resistant T-ALL CEM-C1 cells to dexamethasone (DEX). Compared with the use of DEX or low-dose anisomycin alone, co-treatment with them resulted in a significant increase of growth inhibition, apoptosis and cell cycle arrest in CEM-C1 cells through induction of activated caspase-3 and up-regulation of Bim, p21and p27, and down-regulation of Mcl-1, Bcl-2, c-myc, cyclin A and cyclin D1. Furthermore, co-treatment remarkably activated glucocorticoid receptor (GR), p38-MAPK and JNK, and all of them were canceled only by the GR inhibitor RU486, indicating GR might be an at the upstream of GR–p38-MAPK/JNK pathway. We conclude that low-dose anisomycin sensitizes GC-resistant CEM-C1 cells to DEX and this effect is mediated, at least in part, by activation of the GR–p38-MAPK/JNK signaling pathway.

Glucocorticoids induce the production of the chemoattractant CCL20 in airway epithelium

Th17-mediated neutrophilic airway inflammation has been implicated in decreased response to glucocorticoids in asthma. We aimed to investigate the effect of glucocorticoids on the airway epithelial release of the neutrophilic and Th17-cell chemoattractant CCL20. We studied CCL20 and CXCL8 sputum levels in asthmatic subjects using inhaled glucocorticoids or not, and the effect of budesonide on CCL20 and CXCL8 production in primary bronchial epithelial cells. The mechanism behind the effect of budesonide-induced CCL20 production was studied in 16HBE14o- cells using inhibitors for the glucocorticoid receptor, intracellular pathways and metalloproteases. We observed higher levels of CCL20, but not CXCL8, in the sputum of asthmatics who used inhaled glucocorticoids. CCL20 levels correlated with inhaled glucocorticoid dose and sputum neutrophils. Budesonide increased tumour necrosis factor (TNF)-α-induced CCL20 by primary bronchial epithelium, while CXCL8 was suppressed. In 16HBE14o- cells, similar effects were observed at the CCL20 protein and mRNA levels, indicating transcriptional regulation. Although TNF-α-induced CCL20 release was dependent on the ERK, p38 and STAT3 pathways, the increase by budesonide was not. Inhibition of glucocorticoid receptor or ADAM17 abrogated the budesonide-induced increase in CCL20 levels. We show that glucocorticoids enhance CCL20 production by bronchial epithelium, which may constitute a novel mechanism in Th17-mediated glucocorticoid-insensitive inflammation in asthma.

Rapid induction of the Growth Hormone Gene Transcription by Glucocorticoids In Vitro: Possible Involvement of Membrane Glucocorticoid Receptors and Phosphatidylinositol 3‐Kinase Activation

The regulation of transcription of the growth hormone (GH) gene by glucocorticoids was studied in MtT/S cells, a cell line derived from an oestrogen-induced mammotrophic tumour in the rat, and in the primary culture of the anterior pituitary gland of adult mice. The levels of the GH heteronuclear RNA (GH hnRNA), which are mainly determined by the transcription rate, increased by 25-fold during 24 h in response to dexamethasone (DEX; 1 μM) in MtT/S cells that were cultured in the medium containing charcoal-stripped serum for 7 days. The stimulatory effect of DEX on the GH hnRNA levels was detectable as early as 30 min. This rapid effect of DEX did not require on-going protein synthesis, whereas it was considered that DEX requires the presence of unknown cellular proteins produced independently of DEX stimulation. By contrast, on-going protein synthesis was required for DEX action when incubated for 6 h, as has been observed in the previous studies. The specific inhibitor of glucocorticoid receptor, RU486, inhibited both rapid (30 min) and delayed (6 h) the effects of glucocorticoids on GH hnRNA levels. Membrane impermeable glucocorticoid, corticosterone-bovine serum albumin conjugate (CSBSA), was found to have effects similar to those of DEX and free corticosterone (CS), suggesting that glucocorticoids regulate GH gene transcription at least in part through the membrane bound receptors. From pharmacological studies, it was suggested that phosphatidylinositol 3-kinase (PI3K) activation is involved in the rapid effects but not in the delayed effects of glucocorticoids. This also suggests that the delayed effects of glucocorticoids depend on mechanisms other than the activation of PI3-kinase. Finally, both rapid and delayed effects of CS and CSBSA were observed not only in MtT/S cells, but also in the mouse pituitary cells in primary culture. Therefore, it is possible that the membrane initiated action of glucocorticoids is involved in the regulation of GH transcription in normal pituitary cells, as well as in pituitary tumour cells.

Abstract P2-16-21: A randomized phase I trial of nanoparticle albumin bound paclitaxel (nab-paclitaxel, Abraxane®) with or without mifepristone for advanced breast cancer

Abstract Up to 40% of breast cancers have been shown to express the glucocorticoid receptor (GR), and activation of the GR is associated with poor prognosis in ER-negative breast cancer. We hypothesize that GR activation in breast cancer cells initiates anti-apoptotic signaling contributing to chemotherapy resistance. Based on our compelling preclinical data demonstrating that GR antagonism with mifepristone (mif) increases paclitaxel (pac) induced breast cancer cell death in vitro and in vivo, we conducted the first clinical trial of the combination of anti-GR therapy and chemotherapy in patients (pts) with metastatic breast cancer (MBC). Because the combination of mif and nab-paclitaxel (nab) had not previously been administered to pts, and because nab can result in cumulative neurotoxicity, a randomized, placebo-controlled, phase I design was used. Mif is known to inhibit CYP2C8, an enzyme involved in the metabolism of pac, thus plasma pac levels were monitored to evaluate for significant changes in clearance. A 3+3 dose escalation scheme was planned, with an initial nab dose of 100mg/m2 weekly and a mif dose of 300 mg/d for 2 days (day prior to and of nab infusion). For each dose level (DL), patients were randomized 3:2 to mif:placebo (p) for cycle 1 (C1). After C1, pts randomized to p were crossed over to receive mif at their assigned DL for the duration of study treatment. DL1 was deemed intolerable due to neutropenia, so the nab dose was decreased to 80 mg/m2 for DL2, and dose escalation of mif beyond 300 mg was halted. Serum cortisol and ACTH levels—biomarkers of effective GR blockade—were measured before and after mif treatment. Archival tumor was collected to determine tumor GR expression, and peripheral blood lymphocytes (PBLs) were collected to evaluate GR-target gene expression after mif. 9 pts were enrolled. Median age was 56 yrs (range 47-74). Median number of prior therapies for MBC was 2 (range 0-3). 8 pts had triple-negative breast cancer (TNBC), and 1 had ER+ disease. 8 of 9 pts had recurred after taxane-based therapy. 1 pt had a CR, 4 pts a PR, and 4 pts POD. 4 of 5 pts who responded to nab plus mif had previously relapsed after taxane-based therapy. 4 pts were treated at DL1 (2 mif, 2 p). Both pts randomized to mif experienced a dose-limiting toxicity (DLT) of neutropenia during C1. 5 pts were treated at DL2 (3 mif, 2 p), and 2 of the 3 pts randomized to mif for C1 experienced a DLT (neutropenia). Plasma pac levels were consistent with delayed clearance of nab when co-administered with mif for most pts. All pts were found to have a 2-fold or greater rise in their serum cortisol levels, demonstrating effective adrenal GR inhibition. Mif delays clearance of nab in most pts, and results in DLT. Given the inter-patient variability in delay of nab clearance by mif, co-administration produces unpredictable toxicity. However, given the responses seen in taxane-pretreated TNBC pts, GR antagonism is a promising approach for treating aggressive TNBCs. As neither carboplatin nor gemcitabine are metabolized, mif is unlikely to affect clearance of these agents. As they are widely used for advanced TNBC, both agents represent attractive chemotherapy partners for future clinical investigation. Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P2-16-21.

Lose dose genistein inhibits glucocorticoid receptor and ischemic brain injury in female rats

Although acute bolus of genistein treatment has been shown to protect against neuronal damage in experimental brain injury animal models, chronic continuous low dose treatment of genistein on ischemic brain injury has not been well elucidated. In the present study, female rats were received either pure genistein (0.1mg/kg/day via osmotic minipumps) or placebo at the time of ovariectomy, and transient forebrain ischemia was induced 7days later. Results demonstrated that genistein treatment for 14days significantly improved ischemic neuronal survival in hippocampal CA1 region of ovariectomized rats. Glucocorticoid receptor (GR) is a member of the adrenal steroid hormone receptor, which is highly expressed in the rat hippocampus. Activation of the GR plays a critical role in the neuronal stress responses, including ischemic brain damage. This study therefore examined the potential mechanisms by which genistein regulates GR signaling, including the protein distribution and receptor activation in hippocampus following ischemic reperfusion (I/R). Results showed that GR expression in the ovariectomized rats was excessively increased both in neurons (I/R 6h) and activated microglial cells (I/R 7d) in hippocampal CA1 region. Genistein treatment significantly attenuated GR induction and the enhanced GR nuclear translocation and DNA-binding capacity. The effects of genistein on the GR levels was accompanied with decreased blood plasma levels of corticosterone (primary glucocorticoid in rodents) and coupled to an E3 ubiquitin ligase Mdm2 targeted proteasomal degradation of GR, because genistein treatment could enhance the GR–Mdm2 interaction and the ubiquitination level of GR protein. In addition, our results indicated that genistein markedly prevented the excessive activation of microglia in CA1 sector. These results demonstrate the neuroprotective action of chronic low dose genistein replacement against ischemic brain damage, and a potential mechanism associated with the inhibition of both neuronal and microglial GR signaling following ischemic stress.

Selective modulation through the glucocorticoid receptor ameliorates muscle pathology inmdxmice

The over-expression of NF-κB signalling in both muscle and immune cells contribute to the pathology in dystrophic muscle. The anti-inflammatory properties of glucocorticoids, mediated predominantly through monomeric glucocorticoid receptor inhibition of transcription factors such as NF-κB (transrepression), are postulated to be an important mechanism for their beneficial effects in Duchenne muscular dystrophy. Chronic glucocorticoid therapy is associated with adverse effects on metabolism, growth, bone mineral density and the maintenance of muscle mass. These detrimental effects result from direct glucocorticoid receptor homodimer interactions with glucocorticoid response elements of the relevant genes. Compound A, a non-steroidal selective glucocorticoid receptor modulator, is capable of transrepression without transactivation. We confirm the in vitro NF-κB inhibitory activity of compound A in H-2K(b) -tsA58 mdx myoblasts and myotubes, and demonstrate improvements in disease phenotype of dystrophin deficient mdx mice. Compound A treatment in mdx mice from 18 days of post-natal age to 8 weeks of age increased the absolute and normalized forelimb and hindlimb grip strength, attenuated cathepsin-B enzyme activity (a surrogate marker for inflammation) in forelimb and hindlimb muscles, decreased serum creatine kinase levels and reduced IL-6, CCL2, IFNγ, TNF and IL-12p70 cytokine levels in gastrocnemius (GA) muscles. Compared with compound A, treatment with prednisolone, a classical glucocorticoid, in both wild-type and mdx mice was associated with reduced body weight, reduced GA, tibialis anterior and extensor digitorum longus muscle mass and shorter tibial lengths. Prednisolone increased osteopontin (Spp1) gene expression and osteopontin protein levels in the GA muscles of mdx mice and had less favourable effects on the expression of Foxo1, Foxo3, Fbxo32, Trim63, Mstn and Igf1 in GA muscles, as well as hepatic Igf1 in wild-type mice. In conclusion, selective glucocorticoid receptor modulation by compound A represents a potential therapeutic strategy to improve dystrophic pathology.

A membrane glucocorticoid receptor mediates the rapid/non-genomic actions of glucocorticoids in mammalian skeletal muscle fibres.

Glucocorticoids (GCs) are steroid hormones released from the adrenal gland in response to stress. They are also some of the most potent anti-inflammatory and immunosuppressive drugs currently in clinical use. They exert most of their physiological and pharmacological actions through the classical/genomic pathway. However, they also have rapid/non-genomic actions whose physiological and pharmacological functions are still poorly understood. Therefore, the primary aim of this study was to investigate the rapid/non-genomic effects of two widely prescribed glucocorticoids, beclomethasone dipropionate (BDP) and prednisolone acetate (PDNA), on force production in isolated, intact, mouse skeletal muscle fibre bundles. The results show that the effects of both GCs on maximum isometric force (Po) were fibre-type dependent. Thus, they increased Po in the slow-twitch fibre bundles without significantly affecting that of the fast-twitch fibre bundles. The increase in Po occurred within 10 min and was insensitive to the transcriptional inhibitor actinomycin D. Also, it was maximal at ∼250 nM and was blocked by the glucocorticoid receptor (GCR) inhibitor RU486 and a monoclonal anti-GCR, suggesting that it was mediated by a membrane (m) GCR. Both muscle fibre types expressed a cytosolic GCR. However, a mGCR was present only in the slow-twitch fibres. The receptor was more abundant in oxidative than in glycolytic fibres and was confined mainly to the periphery of the fibres where it co-localised with laminin. From these findings we conclude that the rapid/non-genomic actions of GCs are mediated by a mGCR and that they are physiologically/therapeutically beneficial, especially in slow-twitch muscle fibres.

Glucocorticoid receptor antagonist and siRNA prevent senescence of human bone marrow mesenchymal stromal cells in vitro

We investigate the effects mediated by glucocorticoid (GC) receptor (GR) blockage by using RU486, a GR antagonist and GR short interfering RNA (GR siRNA) on the proliferative and differentiation capabilities of human bone marrow mesenchymal stromal/stem cells (MSCs) and on their senescence and antioxidant levels during extended in vitro culture. Treatment with either RU486 or GR siRNA for a 7-day period significantly increased the proliferation of MSCs and their osteogenic capabilities, as reflected by an increase in alkaline phosphatase (ALP) levels after differentiation. Following 4 weeks of treatment, MSCs improved or maintained their proliferation rates, whereas control MSCs exhibited decreased proliferation. Although all MSCs exhibited reduced osteogenic potential after 4 weeks of in vitro culture, the MSCs treated with GR inhibitors showed higher ALP levels than untreated MSCs on being subjected to osteogenic differentiation. Such treatment also significantly down-regulated the adipogenic capabilities of MSCs. Telomere lengths and the activities of telomerase and superoxide dismutase of MSCs treated with either RU486 or GR siRNA appeared to be higher than those detected in controls. These results demonstrate that the blockage of effects mediated by the GCs normally found in fetal bovine serum might postpone senescence of these cells by up-regulating their antioxidant levels. Our data suggest that the blocking of the effects mediated by GCs might extend the lifespan of endogenous MSCs in patients who have elevated GC levels as a consequence of advancing age or estrogen depletion.

The role of endogenous glucocorticoids in glucose metabolism and immune status of MIF-deficient mice

Macrophage migration inhibitory factor (MIF)-deficient mice develop glucose intolerance and hyperglycemia, but remain entirely responsive to exogenous insulin in adult age. Furthermore, as a consequence of MIF deficiency, the immune response in these mice is predominantly anti-inflammatory. Since MIF is a natural counter-regulator of glucocorticoid action, and it is known that excessive concentration of glucocorticoids contribute both to beta cell dysfunction and immunosuppression, we hypothesized that MIF absence enables elevation of glucocorticoids which in turn caused the observed condition. Our results confirm that MIF-knockout (MIF-KO) mice possess higher levels of circulating corticosterone, but lower expression of glucocorticoid receptor in pancreatic islets, liver and adipose tissue to the one observed in wild type (WT) mice. A significant up-regulation of glucocorticoid receptor expression was however noticed in MIF-deficient lymph node cells. The inhibition of glucocorticoid receptor by RU486 improved tolerance to glucose in MIF-KO mice and restored euglycemia. Although RU486 treatment did not alter the level of glucose receptor GLUT2, it enhanced insulin secretion and up-regulated insulin-triggered Akt phosphorylation within hepatic tissue. Finally, inhibition of glucocorticoid receptor changed anti-inflammatory phenotype of MIF-KO lymphocytes toward a physiological profile. Our results indicate that deregulated glucocorticoid secretion and glucocorticoid receptor expression in the absence of MIF possibly contributes to the development of glucose intolerance and immunosuppression in MIF-KO mice. However, since MIF-KO mice respond normally to insulin and their beta cell function is within physiological range, additional cause for glucose intolerance could be sought in the possible malfunction of their insulin.

Poly I:C and respiratory syncytial virus (RSV) inhibit glucocorticoid receptor (GR)-mediated transactivation in lung epithelial, but not monocytic, cell lines

Respiratory syncytial virus (RSV)-induced bronchiolitis in infants is not responsive to glucocorticoids. We have recently shown that RSV infection of lung epithelial cells impairs glucocorticoid receptor (GR) function. In this current study, we have shown that the viral mimic poly I:C also represses GR-mediated gene activation in lung epithelial cells, suggesting that this might be a common phenomenon of other viral infections. However, we also show that neither RSV infection nor poly I:C affect GR-mediated gene activation in the monocytic cell line THP-1, suggesting that these effects on GR function may be cell-type specific.

Aldosterone regulates Na+, K+ ATPase activity in human renal proximal tubule cells through mineralocorticoid receptor

The mechanisms by which aldosterone increases Na+, K+ ATPase and sodium channel activity in cortical collecting duct and distal nephron have been extensively studied. Recent investigations demonstrate that aldosterone increases Na–H exchanger-3 (NHE-3) activity, bicarbonate transport, and H+ ATPase in proximal tubules. However, the role of aldosterone in regulation of Na+, K+ ATPase in proximal tubules is unknown. We hypothesize that aldosterone increases Na+, K+ ATPase activity in proximal tubules through activation of the mineralocorticoid receptor (MR). Immunohistochemistry of kidney sections from human, rat, and mouse kidneys revealed that the MR is expressed in the cytosol of tubules staining positively for Lotus tetragonolobus agglutinin and type IIa sodium-phosphate cotransporter (NpT2a), confirming proximal tubule localization. Adrenalectomy in Sprague–Dawley rats decreased expression of MR, ENaC α, Na+, K+ ATPase α1, and NHE-1 in all tubules, while supplementation with aldosterone restored expression of above proteins. In human kidney proximal tubule (HKC11) cells, treatment with aldosterone resulted in translocation of MR to the nucleus and phosphorylation of SGK-1. Treatment with aldosterone also increased Na+, K+ ATPase-mediated 86Rb uptake and expression of Na+, K+ ATPase α1 subunits in HKC11 cells. The effects of aldosterone on Na+, K+ ATPase-mediated 86Rb uptake were prevented by spironolactone, a competitive inhibitor of aldosterone for the MR, and partially by Mifepristone, a glucocorticoid receptor (GR) inhibitor. These results suggest that aldosterone regulates Na+, K+ ATPase in renal proximal tubule cells through an MR-dependent mechanism.

Dexamethasone induces caveolin-1 in vascular endothelial cells: implications for attenuated responses to VEGF

Steroids exert direct actions on cardiovascular cells, although underlying molecular mechanisms remain incompletely understood. We examined if steroids modulate abundance of caveolin-1, a regulatory protein of cell-surface receptor pathways that regulates the magnitudes of endothelial response to vascular endothelial growth factor (VEGF). Dexamethasone, a synthetic glucocorticoid, induces caveolin-1 at both levels of protein and mRNA in a time- and dose-dependent manner in pharmacologically relevant concentrations in cultured bovine aortic endothelial cells. Aldosterone, a mineralocorticoid, but not the sex steroids 17β-estradiol, testosterone, or progesterone, elicits similar caveolin-1 induction. Caveolin-1 induction by dexamethasone and that by aldosterone were abrogated by RU-486, an inhibitor of glucocorticoid receptor, and by spironolactone, a mineralocorticoid receptor inhibitor, respectively. Dexamethasone attenuates VEGF-induced responses at the levels of protein kinases Akt and ERK1/2, small-G protein Rac1, nitric oxide production, and migration. When induction of caveolin-1 by dexamethasone is attenuated either by genetically by transient transfection with small interfering RNA or pharmacologically by RU-486, kinase responses to VEGF are rescued. Dexamethasone also increases expression of caveolin-1 protein in cultured human umbilical vein endothelial cells, associated with attenuated tube formation responses of these cells when cocultured with normal fibroblasts. Immunohistochemical analyses revealed that intraperitoneal injection of dexamethasone induces endothelial caveolin-1 protein in thoracic aorta and in lung artery in healthy male rats. Thus steroids functionally attenuate endothelial responses to VEGF via caveolin-1 induction at the levels of signal transduction, migration, and tube formation, identifying a novel point of cross talk between nuclear and cell-surface receptor signaling pathways.

Systems Biology and Birth Defects Prevention: Blockade of the Glucocorticoid Receptor Prevents Arsenic-Induced Birth Defects

Background: The biological mechanisms by which environmental metals are associated with birth defects are largely unknown. Systems biology–based approaches may help to identify key pathways that mediate metal-induced birth defects as well as potential targets for prevention.Objectives: First, we applied a novel computational approach to identify a prioritized biological pathway that associates metals with birth defects. Second, in a laboratory setting, we sought to determine whether inhibition of the identified pathway prevents developmental defects.Methods: Seven environmental metals were selected for inclusion in the computational analysis: arsenic, cadmium, chromium, lead, mercury, nickel, and selenium. We used an in silico strategy to predict genes and pathways associated with both metal exposure and developmental defects. The most significant pathway was identified and tested using an in ovo whole chick embryo culture assay. We further evaluated the role of the pathway as a mediator of metal-induced toxicity using the in vitro midbrain micromass culture assay.Results: The glucocorticoid receptor pathway was computationally predicted to be a key mediator of multiple metal-induced birth defects. In the chick embryo model, structural malformations induced by inorganic arsenic (iAs) were prevented when signaling of the glucocorticoid receptor pathway was inhibited. Further, glucocorticoid receptor inhibition demonstrated partial to complete protection from both iAs- and cadmium-induced neurodevelopmental toxicity in vitro.Conclusions: Our findings highlight a novel approach to computationally identify a targeted biological pathway for examining birth defects prevention.