Corticosteroids induce COX-2 expression in cardiomyocytes: role of glucocorticoid receptor and C/EBP-beta

Network Pharmacology and ­Experimental Analyses of the Mechanism of Analgesic and Glucose Intolerance Through Glucocorticoid Signaling in C57 Mice Treated with Water Extract of Prunella vulgaris L. Spica

The aim of this study was to confirm the anti-inflammatory effect and explore the adverse effects and underlying mechanisms of Prunella vulgaris L., which has been extensively used for hundreds of years in East Asia. Network pharmacology studies predicted that glucocorticoids (GCs), GC-targeting molecules, and brain-derived neurotrophic factor (BDNF) were intensively involved in the anti-inflammation and glucose intolerance. To attest the effects and underlying mechanisms, C57 male mice were randomly divided into 5 groups, control (C), dexamethasone (Dex), water extract of P. vulgaris (PE 35 or 70 mg), and PE (70 mg) + mifepristone (PEM). After a 3-week treatment, acetic acid-induced writhing and hot plate tests confirmed the peripheral and central analgesic effects, respectively. Plasma GCs and BDNF were significantly increased. Coincidently, plasma pro-inflammatory cytokines, including IL1β, IL6, and IL10, were decreased by PE treatment, which were blocked by the application of mifepristone ( P < 0.5). Western blots confirmed GC receptor (GR) translocation, and decreased cyclooxygenase 2 in the lumber spine by PE treatment. Food intake was impeded after a 4-week PE treatment, but the ratio of bodyweight gain to food intake was increased in a time-dependent manner. An intraperitoneal glucose tolerance test disclosed that PE treatment impaired glucose disposal in mice. Quantitative polymerase chain reaction (PCR) showed that hepatic GC-responsive genes such as GC-induced leucine zipper protein and glucose-6-phosphatase catalytic subunit 1 were up-regulated, and hypothalamic neuropeptide Y and agouti-related protein expressions were decreased by PE treatment. Hypothalamic BDNF was up-regulated, whereas hepatic BDNF was down-regulated. The regulation of these genes by PE was reversed by mifepristone administration. In conclusion, PE treatment plays analgesic and glucose regulation roles simultaneously through GC-induced signaling pathways, and P. vulgaris may provide a natural ligand of GR for the treatment of inflammation with glucose dysregulation.

Influence of biological sex and exercise on murine cardiac metabolism

Although the structural and functional effects of exercise on the heart are well established, the metabolic changes that occur in the heart during and after exercise remain unclear. In this study, we used metabolomics to assess time-dependent changes in the murine cardiac metabolome following 1 session of treadmill exercise. After the exercise bout, we also recorded blood lactate, glucose, and ketone body levels and measured cardiac mitochondrial respiration. In both male and female mice, moderate- and high-intensity exercise acutely increased blood lactate levels. In both sexes, low- and moderate-intensity exercise augmented circulating 3-hydroxybutryrate levels immediately after the exercise bout; however, only in female mice did high-intensity exercise increase 3-hydroxybutyrate levels, with significant increases occurring 1 h after the exercise session. Untargeted metabolomics analyses of sedentary female and male hearts suggest considerable sex-dependent differences in basal cardiac metabolite levels, with female hearts characterized by higher levels of pantothenate, pyridoxamine, homoarginine, tryptophan, and several glycerophospholipid and sphingomyelin species and lower levels of numerous metabolites, including acetyl coenzyme A, glucuronate, gulonate, hydroxyproline, prolyl-hydroxyproline, carnosine, anserine, and carnitinylated and glycinated species, as compared with male hearts. Immediately after a bout of treadmill exercise, both male and female hearts had higher levels of corticosterone; however, female mice showed more extensive exercise-induced changes in the cardiac metabolome, characterized by significant, time-dependent changes in amino acids (e.g., serine, alanine, tyrosine, tryptophan, branched-chain amino acids) and the ketone body 3-hydroxybutyrate. Results from experiments using isolated cardiac mitochondria suggest that high-intensity treadmill exercise does not acutely affect respiration or mitochondrial coupling; however, female cardiac mitochondria demonstrate generally higher adenosine diphosphate sensitivity compared with male cardiac mitochondria. Collectively, these findings in mice reveal key sex-dependent differences in cardiac metabolism and suggest that the metabolic network in the female heart is more responsive to physiological stress caused by exercise.

Pro-and anti-inflammatory effects of glucocorticoid Fluticasone on ovarian and immune functions in commercial-aged laying hens

Ovarian chronic inflammation has been created and extended in the laying hen mainly via increasing laying frequency and microbial infection, especially during the late stage of production period. This study was aimed to evaluate glucocorticoid (GC) Fluticasone as an anti-inflammatory agent on the gene expression of the ovarian pro-and anti-inflammatory mediators (follicular cyclooxygenases COX 1, 2, and cytokines), inflammatory responses of the immune system, ovarian functions (ovulation rate and follicular growths), and hormones in the commercial-aged laying hens. White Leghorn hens aged 92-weeks were used for four weeks to be supplemented by 2 ppm Fluticasone as an optimum dose obtained in a pre-trial base on ovulation rate. As compared to control, Fluticasone resulted in a significant decrease in the mRNA expression of COX-1 and pro-and anti-inflammatory cytokines, and increase in COX-2 mRNA expression and heterophil to lymphocyte ratio (P < 0.001). A significant reduction was observed in the ovulation rate, follicular size (P < 0.001), ovarian hormones, immunoglobulins, body weight, and food consummation (P ≤ 0.05) by administering GC Fluticasone. Although a relative anti-inflammatory improvement was created by Fluticasone in the ovarian condition, the administration of this glucocorticoid resulted in a considerable reduction in ovarian hormones and functions of commercial aged laying hens.

Masticatory Myofascial Pain Syndrome: Implications for Endodontists

INTRODUCTION

Masticatory myofascial pain syndrome can present similarly to other dental conditions in odontogenetic structures. Endodontists should be familiar with the symptomology and pathophysiology of masticatory myofascial pain syndrome to avoid misdiagnosis, incorrect treatment, and medicolegal repercussions. The aim of this review was to provide a foundational summary for endodontists to identify and correctly manage masticatory myofascial pain syndrome.

METHODS

A narrative review of the literature was performed through a MEDLINE search and a hand search of the major myofascial pain textbooks.

RESULTS

Masticatory myofascial pain syndrome is a musculoligamentous syndrome that can present similarly to odontogenic pain or refer pain to the eyebrows, ears, temporomandibular joints, maxillary sinus, tongue, and hard palate. Currently, the most comprehensive pathophysiology theory describing masticatory myofascial pain syndrome is the expanded integrated hypothesis. The most widely accepted diagnostic guidelines for masticatory myofascial pain syndrome are the Diagnostic Criteria for Temporomandibular Disorders; however, their diagnostic capability is limited. There is no hierarchy of treatment methods because each patient requires a tailored and multidisciplinary management aimed at regaining the muscle's range of motion, deactivating the myofascial trigger points, and maintaining pain relief.

CONCLUSIONS

The pain patterns for masticatory myofascial pain syndrome are well-known; however, there is a lack of consensus on the most proper method of trigger point diagnosis or pain quantification. The diagnostic strategies for masticatory myofascial pain syndrome vary, and the diagnostic aids are not well developed.

Combined Irradiation by Gamma Rays and Carbon Nuclei Increases the C/EBP-β LIP Isoform Content in the Pituitary Gland of Rats

C/EBP-β, a basic leucine zipper transcription factor, has important roles in the regulation of the body immune and inflammatory responses. Wistar rats subjected to combined irradiation were characterized by an increase in the content of the C/EBP-β LIP isoform in the pituitary gland. The obtained data indicate that moderate doses of ionizing radiation to initiate the endoplasmic reticulum stress response and are likely to initiate C/EBP-β-mediated cell death according to the apoptotic scenario. This study also confirms the earlier hypothesis about the alterations of the hypothalamic-pituitary-adrenocortical axis in response to moderate doses of ionizing radiation.

Glucocorticoid receptor is involved in the differential expression of hepatic 3β-hydroxysteroid dehydrogenase between barrows and boars at finishing stage

The enzyme 3β-hydroxysteroid dehydrogenase (3β-HSD) plays an important role in androstenone metabolism in pig liver, and its defective expression is related to the development of boar taint. Early age castration is a common practice in many countries to avoid boar taint, yet whether and how castration affects porcine hepatic 3β-HSD expression are still poorly understood. In this study, we aimed to compare the expression of 3β-HSD between intact (boars) and castrated (barrows) male pigs, and to explore the potential factors regulating 3β-HSD transcription. Compared to barrows, boars showed worse carcass quality. Boars had significantly higher levels of serum androstenone (P < 0.01), testosterone (P < 0.01) and hepatic cortisol (P < 0.05), which were contrary to significantly lower expression of 3β-HSD messenger RNA (P < 0.01) and protein (P < 0.01) in the liver. Significant differences were detected for the hepatic expression of androgen receptor (AR) and CCAAT/enhancer binding protein β (C/EBPβ). Chromatin immunoprecipitation (ChIP) assay demonstrated reduced histone H3 acetylation (P < 0.05) but increased glucocorticoid receptor (GR) binding to 3β-HSD gene promoter in boars (P < 0.05). These results indicate that GR binding to 3β-HSD promoter is involved in the differential hepatic 3β-HSD expression between boars and barrows.

Differential Regulation of Bcl-xL Gene Expression by Corticosterone, Progesterone, and Retinoic Acid

Corticosterone (CT), progesterone (PG), and retinoic acid (RA) are capable of inhibiting Doxorubicin (Dox) from inducing apoptosis in rat cardiomyocytes. Mechanistically, CT, PG, and RA induce increases of Bcl-xL protein and mRNA, and activate a 3.2 kb bcl-x gene promoter. CT and RA, but not PG, induced the activity of a 0.9 kb bcl-x promoter, containing sequences for AP-1 and NF-kB binding. RA, but not CT or PG, induced NF-kB activation. CT, but not PG or RA, induced AP-1 activation, and induction of the 0.9 kb bcl-x reporter by CT was inhibited by dominant negative c-Jun TAM-67 or removal of AP-1 binding site. Therefore, although CT, PG, and RA all induce Bcl-xL mRNA and protein, three independent mechanisms are in operation: while CT induces Bcl-xL via AP-1 transcription factor, and RA induces NF-kB activation and bcl-x promoter activity, PG induces Bcl-xL via a mechanism independent of NF-kB or AP-1.

A simplified protocol for the isolation and culture of cardiomyocytes and progenitor cells from neonatal mouse ventricles

The neonatal heart is a very useful tool for the study of biochemical pathways and properties of cardiomyocytes and as it has the potential to regenerate for a brief period of time from birth; it is also useful to study cardiac regeneration. However, as the heart matures, this proficiency for regeneration is reduced. This regenerative potential may be influenced by the microenvironment of the heart in the early stages of postnatal development and therefore, cell cultures derived at this stage may contain functional cardiomyocytes and progenitor cells. The aim of this study was to identify key steps in the isolation and culture of such early stage-neonatal mouse hearts to allow maximum migration of cardiomyocytes from the explant and their maintenance as functional, long term cultures. Explant cultures of mouse ventricles preserved 3-dimensional structure and generated migrating layers of cardiomyocytes that expressed alpha sarcomeric actin which could be further sub-cultured by enzymatic dissociation. Western blotting demonstrated expression of c-KIT, GATA4, alpha sarcomeric actin and connexin43 proteins after 20 days of explant culture. ACTA1, GATA4, and CX43 continued to express in five weeks old explant cultures while the c-KIT protein was expressed up to two passages during sub-culture. Real time PCR and SQRT PCR also demonstrated gene expression of cardiomyocyte markers in long term cultures. Migrating cells from the explants assembled into contracting spheroids after subculture and expressed the c-KIT protein. Progenitor markers CD44, CD90, and extracellular proteins, periostin and vimentin demonstrated the preservation of cellular heterogeneity in such cultures. Supplementation with Hydrocortisone maintained a cardioprotective environment and reduced the non-myocyte population. This is an optimized and efficient method for the generation of neonatal heart cultures that is not labor intensive and does not require supplementation with cytokines.

Glucocorticoid receptor is involved in the breed-dependent transcriptional regulation of 3β-hydroxysteroid dehydrogenase in the liver of preweaning piglets

Background

Hepatic 3β-hydroxysteroid dehydrogenase (3β-HSD) plays an important role in steroid inactivation and catabolism. Serum concentrations of steroid hormones differ significantly between breeds in pigs, however the molecular mechanism regulating hepatic 3β-HSD expression in different breeds of pigs is poorly understood. In the present study, we used preweaning purebred male Large White (LW) and Erhualian (EHL) piglets as model to investigate the breed difference in the expression and regulation of 3β-HSD gene in porcine liver.

Results

The hepatic expression of 3β-HSD mRNA was significantly lower (P < 0.01) in EHL piglets compared to that in LW piglets. Significant breed differences were detected for the hepatic expression of transcription factors such as androgen receptor (AR), glucocorticoid receptor (GR), and CCAAT/enhancer binding protein β (C/EBPβ). The nucleoprotein contents of AR (P < 0.05), GR (P < 0.01) and phospho-Ser²¹¹GR (P < 0.01) were significantly higher in the liver of EHL piglets. Chromatin immunoprecipitation (ChIP) assay demonstrated significantly lower binding of GR, but not AR or C/EBPβ, to 3β-HSD gene promoter in EHL piglets (P < 0.05). GR was not detected to interact with C/EBPβ or AR in the co-immunoprecipitation analysis.

Conclusions

These results indicate that GR binding to 3β-HSD promoter is involved in the breed-dependent 3β-HSD expression in the liver of piglets.

Inhibition of corticosteroid-binding globulin gene expression by glucocorticoids involves C/EBPβ

Corticosteroid-binding globulin (CBG), a negative acute phase protein produced primarily in the liver, is responsible for the transport of glucocorticoids (GCs). It also modulates the bioavailability of GCs, as only free or unbound steroids are biologically active. Fluctuations in CBG levels therefore can directly affect GC bioavailability. This study investigates the molecular mechanism whereby GCs inhibit the expression of CBG. GCs regulate gene expression via the glucocorticoid receptor (GR), which either directly binds to DNA or acts indirectly via tethering to other DNA-bound transcription factors. Although no GC-response elements (GRE) are present in the Cbg promoter, putative binding sites for C/EBPβ, able to tether to the GR, as well as HNF3α involved in GR signaling, are present. C/EBPβ, but not HNF3α, was identified as an important mediator of DEX-mediated inhibition of Cbg promoter activity by using specific deletion and mutant promoter reporter constructs of Cbg. Furthermore, knockdown of C/EBPβ protein expression reduced DEX-induced repression of CBG mRNA, confirming C/EBPβ’s involvement in GC-mediated CBG repression. Chromatin immunoprecipitation (ChIP) after DEX treatment indicated increased co-recruitment of C/EBPβ and GR to the Cbg promoter, while C/EBPβ knockdown prevented GR recruitment. Together, the results suggest that DEX repression of CBG involves tethering of the GR to C/EBPβ.

Albumin-induced podocyte injury and protection are associated with regulation of COX-2

Albuminuria is both a hallmark and a risk factor for progressive glomerular disease, and results in increased exposure of podocytes to serum albumin with its associated factors. Here in vivo and in vitro models of serum albumin overload were used to test the hypothesis that albumin-induced proteinuria and podocyte injury directly correlate with COX-2 induction. Albumin induced COX-2, MCP-1, CXCL1 and the stress protein HSP25 in both rat glomeruli and cultured podocytes, while B7-1 and HSP70i were also induced in podocytes. Podocyte exposure to albumin induced both mRNA and protein and enhanced the mRNA stability of COX-2, a key regulator of renal hemodynamics and inflammation, which renders podocytes susceptible to injury. Podocyte exposure to albumin also stimulated several kinases (p38 MAPK, MK2, JNK/SAPK and ERK1/2), inhibitors of which (except JNK/SAPK) down-regulated albumin-induced COX-2. Inhibition of AMPK, PKC and NFκB also down-regulated albumin-induced COX-2. Critically, albumin-induced COX-2 was also inhibited by glucocorticoids and thiazolidinediones, both of which directly protect podocytes against injury. Furthermore, specific albumin-associated fatty acids were identified as important contributors to COX-2 induction, podocyte injury and proteinuria. Thus, COX-2 is associated with podocyte injury during albuminuria, as well as with the known podocyte protection imparted by glucocorticoids and thiazolidinediones. Moreover, COX-2 induction, podocyte damage and albuminuria appear mediated largely by serum albumin-associated fatty acids.

Glucocorticoid-induced reversal of interleukin-1β-stimulated inflammatory gene expression in human oviductal cells

Studies indicate that high-grade serous ovarian carcinoma (HGSOC), the most common epithelial ovarian carcinoma histotype, originates from the fallopian tube epithelium (FTE). Risk factors for this cancer include reproductive parameters associated with lifetime ovulatory events. Ovulation is an acute inflammatory process during which the FTE is exposed to follicular fluid containing both pro- and anti-inflammatory molecules, such as interleukin-1 (IL1), tumor necrosis factor (TNF), and cortisol. Repeated exposure to inflammatory cytokines may contribute to transforming events in the FTE, with glucocorticoids exerting a protective effect. The global response of FTE cells to inflammatory cytokines or glucocorticoids has not been investigated. To examine the response of FTE cells and the ability of glucocorticoids to oppose this response, an immortalized human FTE cell line, OE-E6/E7, was treated with IL1β, dexamethasone (DEX), IL1β and DEX, or vehicle and genome-wide gene expression profiling was performed. IL1β altered the expression of 47 genes of which 17 were reversed by DEX. DEX treatment alone altered the expression of 590 genes, whereas combined DEX and IL1β treatment altered the expression of 784 genes. Network and pathway enrichment analysis indicated that many genes altered by DEX are involved in cytokine, chemokine, and cell cycle signaling, including NFκΒ target genes and interacting proteins. Quantitative real time RT-PCR studies validated the gene array data for IL8, IL23A, PI3 and TACC2 in OE-E6/E7 cells. Consistent with the array data, Western blot analysis showed increased levels of PTGS2 protein induced by IL1β that was blocked by DEX. A parallel experiment using primary cultured human FTE cells indicated similar effects on PTGS2, IL8, IL23A, PI3 and TACC2 transcripts. These findings support the hypothesis that pro-inflammatory signaling is induced in FTE cells by inflammatory mediators and raises the possibility that dysregulation of glucocorticoid signaling could contribute to increased risk for HGSOC.

CCAAT/enhancer-binding protein β is involved in the breed-dependent transcriptional regulation of 3β-hydroxysteroid dehydrogenase/Δ(5)-Δ(4)-isomerase in adrenal gland of preweaning piglets

The enzyme 3β-hydroxysteroid dehydrogenase/Δ(5)-Δ(4)-isomerase (3β-HSD) catalyzes the biosynthesis of all steroid hormones. The molecular mechanisms regulating porcine adrenal 3β-HSD expression in different breeds are still poorly understood. In this study, we aimed to compare the expression of 3β-HSD between preweaning purebred Large White (LW) and Erhualian (EHL) piglets and to explore the potential factors regulating 3β-HSD transcription. EHL had significantly higher serum levels of cortisol (P<0.01) and testosterone (P<0.01), which were associated with significantly higher expression of 3β-HSD mRNA (P<0.01) and protein (P<0.05) in the adrenal gland, compared with LW piglets. The 5' flanking region of the porcine 3β-HSD gene showed significant sequence variations between breeds, and the sequence of EHL demonstrated an elevated promoter activity (P<0.05) in luciferase reporter gene assay. Higher adrenal expression of 3β-HSD in EHL was accompanied with higher CCAAT/enhancer binding protein β (C/EBPβ) expression (P<0.05), enriched histone H3 acetylation (P<0.05) and C/EBPβ binding to 3β-HSD promoter (P<0.05). In addition, higher androgen receptor (AR) (P=0.06) and lower glucocorticoid receptor (GR) (P<0.05) were detected in EHL. Co-immunoprecipitation analysis revealed interactions of C/EBPβ with both AR and GR. These results indicate that the C/EBPβ binding to 3β-HSD promoter is responsible, at least in part, for the breed-dependent 3β-HSD expression in adrenal gland of piglets. The sequence variations of 3β-HSD promoter and the interactions of AR and/or GR with C/EBPβ may also participate in the regulation.

Endogenous prostaglandin D2 and its metabolites protect the heart against ischemia-reperfusion injury by activating Nrf2

We recently demonstrated that glucocorticoids markedly upregulate the expression of cyclooxygenase-2 in cardiomyocytes and protect hearts from ischemia-reperfusion (I/R) injury by activating lipocalin-type prostaglandin D (PGD) synthase (L-PGDS)-derived PGD(2) biosynthesis. We examined a downstream mechanism of cardioprotection elicited by PGD(2) biosynthesis. Acute PGD(2) treatment did not protect hearts against I/R injury. We then speculated that PGD(2) and its metabolite 15-deoxy-Δ12,14-PGJ(2) activate gene expression networks to mediate the glucocorticoid-mediated cardioprotection. Using an unbiased approach, we identified that glucocorticoids induce a number of well-known erythroid-derived 2-like 2 (Nrf2) target genes in the heart in an L-PGDS-dependent manner and that the cardioprotective effect of glucocorticoids against I/R injury was not seen in Nrf2-knockout hearts. We showed relatively low expression of PGD(2) receptors (ie, DP1 and DP2) in the heart but abundant expression of PGF(2α) receptor (FP), which binds PGF(2α) and PGD(2) with equal affinity. Glucocorticoids also failed to induce the expression of L-PGDS-dependent Nrf2 target genes in FP-knockout hearts. PGD(2) acted through its metabolite 15-deoxy-Δ12,14-PGJ(2) in the heart as evidenced by the glucocorticoid-mediated activation of peroxisome proliferator-activated receptor-γ. In turn, glucocorticoids failed to induce the expression of L-PGDS-dependent Nrf2 target genes in hearts pretreated with peroxisome proliferator-activated receptor-γ antagonist GW9662, and glucocorticoid-mediated cardioprotection against I/R injury was compromised in FP-knockout mice and GW9662-treated mice. In conclusion, PGD(2) protects heart against I/R injury by activating Nrf2 predominantly via FP receptor. In addition, we propose activation of peroxisome proliferator-activated receptor-γ by the dehydrated metabolite of PGD(2) (15-deoxy-Δ12,14-PGJ(2)) as another mechanism by which glucocorticoids induce cardioprotection.

C/EBP maintains chromatin accessibility in liver and facilitates glucocorticoid receptor recruitment to steroid response elements

Mechanisms regulating transcription factor interaction with chromatin in intact mammalian tissues are poorly understood. Exploiting an adrenalectomized mouse model with depleted endogenous glucocorticoids, we monitor changes of the chromatin landscape in intact liver tissue following glucocorticoid injection. Upon activation of the glucocorticoid receptor (GR), proximal regions of activated and repressed genes are remodelled, and these remodelling events correlate with RNA polymerase II occupancy of regulated genes. GR is exclusively associated with accessible chromatin and 62% percent of GR-binding sites are occupied by C/EBPβ. At the majority of these sites, chromatin is preaccessible suggesting a priming function of C/EBPβ for GR recruitment. Disruption of C/EBPβ binding to chromatin results in attenuation of pre-programmed chromatin accessibility, GR recruitment and GR-induced chromatin remodelling specifically at sites co-occupied by GR and C/EBPβ. Collectively, we demonstrate a highly cooperative mechanism by which C/EBPβ regulates selective GR binding to the genome in liver tissue. We suggest that selective targeting of GR in other tissues is likely mediated by the combined action of cell-specific priming proteins and chromatin remodellers.

The influence of dexamethasone administration on the protection against doxorubicin-induced cardiotoxicity in purified embryonic stem cell-derived cardiomyocytes

Embryonic stem cells (ESCs) have various uses in drug toxicity, as they can be easily differentiated in vitro. However, one of the major obstacles in the assessment of these differentiated cells is the presence of a heterogeneous cell population. To circumvent this problem, purified ESC-derived desired cells by means of the tissue-specific GFP and/or antibiotic resistance gene expression has been proposed. Therefore, this study aimed to assess the role of doxorubicin (DOX) in cardiotoxicity by using genetically engineered purified ESC-derived cardiomyocytes under the control alpha-myosin heavy chain promoter. The results revealed that ESCs are suitable for evaluation of DOX cardiotoxicity. This study showed that DOX cardiotoxicity was reduced as detected by beating cardiomyocytes and caspase activity only by pretreatment with dexamethasone (DEX), not during or post-DOX treatment. DEX influence appears to be mediated via glucocorticoid receptor and enhances cardiomyocyte-specific gene expression. Therefore, for the general assessment of cytotoxicity, non-genetically engineered ESC-derived cardiomyocytes are sufficient but for the molecular assessment of DOX-induced toxicity, genetically engineered purified ESC-derived cardiomyocytes are necessary.

The emerging role of C/EBPs in glucocorticoid signaling: lessons from the lung

Glucocorticoids (GCs) have been successfully used in the treatment of inflammatory diseases for decades. However, there is a relative GC resistance in several inflammatory lung disorders, such as chronic obstructive pulmonary disease (COPD), but still the mechanism(s) behind this unresponsiveness remains unknown. Interaction between transcription factors and the GC receptor contribute to GC effects but may also provide mechanisms explaining steroid resistance. CCAAT/enhancer-binding protein (C/EBP) transcription factors are important regulators of pulmonary gene expression and have been implicated in inflammatory lung diseases such as asthma, pulmonary fibrosis, cystic fibrosis, sarcoidosis, and COPD. In addition, several studies have indicated a role for C/EBPs in mediating GC effects. In this review, we discuss the different mechanisms of GC action as well as the function of the lung-enriched members of the C/EBP transcription factor family. We also summarize the current knowledge of the role of C/EBP transcription factors in mediating the effects of GCs, with emphasis on pulmonary effects, and their potential role in mediating GC resistance.

Dexamethasone-induced up-regulation of the human norepinephrine transporter involves the glucocorticoid receptor and increased binding of C/EBP-β to the proximal promoter of norepinephrine transporter

Previously, we have found glucocorticoids up-regulate norepinephrine (NE) transporter (NET) expression in vitro. However, the underlying transcriptional mechanism is poorly understood. In this study, the role of glucocorticoids on the transcriptional regulation of NET was investigated. Exposure of neuroblastoma SK-N-BE(2)M17 cells to dexamethasone (Dex) significantly increased NET mRNA and protein levels in a time- and dose-dependent manner. This effect was attenuated by glucocorticoid receptor (GR) antagonist mifepristone, suggesting that up-regulation of NET by Dex was mediated by the GR. In reporter gene assays, exposure of cells to Dex resulted in dose-dependent increases of luciferase activity that were also prevented by mifepristone. Serial deletions of the NET promoter delineated Dex-responsiveness to a -301 to -148 bp region containing a CCAAT/enhancer binding protein-β (C/EBP-β) response element. Co-immunoprecipitation experiments demonstrated that Dex treatment caused the interaction of the GR with C/EBP-β. Chromatin immunoprecipitation (ChIP) assay revealed that Dex exposure resulted in binding of both GR and C/EBP-β to the NET promoter. Further experiments showed that mutation of the C/EBP-β response element abrogated C/EBP-β- and GR-mediated transactivation of NET. These findings demonstrate that Dex-induced increase in NET expression is mediated by the GR via a non-conventional transcriptional mechanism involving interaction of C/EBP-β with a C/EBP-β response element.

Dexamethasone induces transcriptional activation of Bcl-xL gene and inhibits cardiac injury by myocardial ischemia

Psychological or physical stress causes an elevation of glucocorticoids in the circulating system. Glucocorticoids regulate a variety of physiological functions, from energy metabolism and biochemical homeostasis to immune response. Synthetic steroids are among the most prescribed drugs for immune suppression and chemotherapy. While glucocorticoids are best known for inducing apoptosis in a number of cell types, we have found that corticosteroids at stress relevant levels protect cardiomyocytes from apoptosis. Current study addresses whether glucocorticoids inhibit cardiac injury in vivo. Adult male C57BL6 mice were administered with dexamethasone (20mg/kg, i.p.) or vehicle control 20 h prior to left anterior descending coronary artery occlusion surgery. Myocardial infarction was measured by triphenyl tetrazoliumchloride staining in tissue slices and by levels of cardiac Troponin (cTn I) in the blood. Treatment of dexamethasone markedly reduced infarct size (19.6 ± 4.3%, vs. 29.2 ± 4.9%, p<0.01) and cTn I level in the blood (3.83 ± 0.66 ng/ml vs. 5.62 ± 0.37 ng/ml, p<0.01). In studying the mechanism of such protection, we found that dexamethasone induces the expression of Bcl-xL gene in the myocardium. With cardiomyocytes in culture, glucocorticoids increased transcription of Bcl-xL gene as evidenced by Bcl-xL mRNA increase and promoter activation. The glucocorticoid receptor antagonist mifepristone prevented dexamethasone from inducing cardiac protection or Bcl-xL expression. Our data suggest that activation of glucocorticoid receptor can prevent cardiac injury through transcriptional activation of Bcl-xL gene.

Corticosterone mediates reciprocal changes in CB 1 and TRPV1 receptors in primary sensory neurons in the chronically stressed rat

BACKGROUND & AIMS

Chronic stress is associated with visceral hyperalgesia in functional gastrointestinal disorders. We investigated whether corticosterone plays a role in chronic psychological stress-induced visceral hyperalgesia.

METHODS

Male rats were subjected to 1-hour water avoidance (WA) stress or subcutaneous corticosterone injection daily for 10 consecutive days in the presence or absence of corticoid-receptor antagonist RU-486 and cannabinoid-receptor agonist WIN55,212-2. The visceromotor response to colorectal distension was measured. Receptor protein levels were measured and whole-cell patch-clamp recordings were used to assess transient receptor potential vanilloid type 1 (TRPV1) currents in L6-S2 dorsal root ganglion (DRG) neurons. Mass spectrometry was used to measure endocannabinoid anandamide content.

RESULTS

Chronic WA stress was associated with visceral hyperalgesia in response to colorectal distension, increased stool output and reciprocal changes in cannabinoid receptor 1 (CB1) (decreased) and TRPV1 (increased) receptor expression and function. Treatment of WA stressed rats with RU-486 prevented these changes. Control rats treated with serial injections of corticosterone in situ showed a significant increase in serum corticosterone associated with visceral hyperalgesia, enhanced anandamide content, increased TRPV1, and decreased CB1 receptor protein levels, which were prevented by co-treatment with RU-486. Exposure of isolated control L6-S2 DRGs in vitro to corticosterone reproduced the changes in CB1 and TRPV1 receptors observed in situ, which was prevented by co-treatment with RU-486 or WIN55,212-2.

CONCLUSIONS

These results support a novel role for corticosterone to modulate CB1 and TRPV1-receptor pathways in L6-S2 DRGs in the chronic WA stressed rat, which contributes to visceral hyperalgesia observed in this model.

Inhibition of apoptosis by progesterone in cardiomyocytes

While gender-based differences in heart disease have raised the possibility that estrogen (ES) or progesterone (PG) may have cardioprotective effects, recent controversy regarding hormone replacement therapy has questioned the cardiac effects of these steroids. Using cardiomyocytes, we tested whether ES or PG has protective effects at the cellular level. We found that PG but not ES protects cardiomyocytes from apoptotic cell death induced by doxorubicin (Dox). PG inhibited apoptosis in a dose-dependent manner, by 12 ± 4.0% at 1 μm and 60 ± 1.0% at 10 μm. The anti-apoptotic effect of PG was also time dependent, causing 18 ± 5% or 62 + 2% decrease in caspase-3 activity within 1 h or 72 h of pretreatment. While PG causes nuclear translocation of its receptor within 20 min, the cytoprotective effect of PG was canceled by mifepristone (MF), a PG receptor antagonist. Analyses using Affymetrix high-density oligonucleotide array and RT-PCR found that PG induced Bcl-xL, metallothionine, NADPH quinone oxidoreductase 1, glutathione peroxidase-3, and four isoforms of glutathione S-transferase. Western blot analyses revealed that PG indeed induced an elevation of Bcl-xL protein in a dose- and time-dependent manner. Nuclear run-on assay indicated that PG induced Bcl-xL gene transcription. Inhibiting the expression of Bcl-xL using siRNA reduced the cytoprotective effect of PG. Our data suggests that PG induces a cytoprotective effect in cardiomyocytes in association with induction of Bcl-xL gene.

Inhibitors of GSK-3 prevent corticosterone from inducing COX-1 expression in cardiomyocytes

Our recent study has demonstrated that glucocorticoids (GCs) induce cyclooxygenase-1 (COX-1) gene expression in rat cardiomyocytes. While investigating the mechanism underlying corticosterone (CT) induced COX-1, we found that three structurally and mechanistically distinct GSK-3 inhibitors, LiCl, SB216763, and (2'Z,3'E)-6-Bromoindirubin-3'-oxime (BIO), inhibited COX-1 transcription and protein induction. A genetic approach of expressing wild type GSK-3beta increased COX-1 promoter activity, which was abolished by LiCl. LiCl increased inhibitory GSK-3alpha/beta phosphorylation at Ser21/Ser9, while BIO or SB216763 prevented stimulatory phosphorylation at Tyr279/Tyr216 of GSK-3alpha/beta. GSK inhibitors failed to block nuclear translocation of glucocorticoid receptor (GR) or activation of glucocorticoid response element (GRE) by CT treatment. While Sp3 transcription factor mediates CT induced COX-1 expression, GSK inhibitors did not change the level of Sp3 protein or binding of Sp3 transcription factor to COX-1 promoter. The observed effect of GSK-3 inhibitors appears to be unique to COX-1 since LiCl or BIO does not prevent CT from inducing COX-2 gene. We conclude that GSK-3 inhibitors block CT from inducing COX-1 gene expression via a mechanism beyond GR and Sp3 transcription factor.