Decreased mRNA stability as a mechanism of glucocorticoid-mediated inhibition of vascular endothelial growth factor gene expression by cultured keratinocytes

Staphylococcus aureus Adaptation to the Skin in Health and Persistent/Recurrent Infections

Staphylococcus aureus is a microorganism with an incredible capability to adapt to different niches within the human body. Approximately between 20 and 30% of the population is permanently but asymptomatically colonized with S. aureus in the nose, and another 30% may carry S. aureus intermittently. It has been established that nasal colonization is a risk factor for infection in other body sites, including mild to severe skin and soft tissue infections. The skin has distinct features that make it a hostile niche for many bacteria, therefore acting as a strong barrier against invading microorganisms. Healthy skin is desiccated; it has a low pH at the surface; the upper layer is constantly shed to remove attached bacteria; and several host antimicrobial peptides are produced. However, S. aureus is able to overcome these defenses and colonize this microenvironment. Moreover, this bacterium can very efficiently adapt to the stressors present in the skin under pathological conditions, as it occurs in patients with atopic dermatitis or suffering chronic wounds associated with diabetes. The focus of this manuscript is to revise the current knowledge concerning how S. aureus adapts to such diverse skin conditions causing persistent and recurrent infections.

Topical Anti-Inflammatory Agents for Non-Infectious Uveitis: Current Treatment and Perspectives

Non-infectious uveitis represents a heterogenous group of immune-mediated ocular diseases, which can be associated with underlying systemic disease. While the initial choice of treatment of non-infectious uveitis depends on a number of factors such as anatomical location and degree of inflammation, topical therapies often remain the initial choice of non-invasive therapy. In this narrative review, we aim to describe the literature on non-infectious uveitis, with specific focus on the current perspective on topical anti-inflammatory therapy.

Effects of Glucocorticoids on Postoperative Neurocognitive Disorders in Adult Patients: A Systematic Review and Meta-Analysis

Background

Postoperative neurocognitive disorders (PNDs) is common among surgical patients, however, the effect of glucocorticoids for preventing PNDs is not clear. This review aims to evaluate the effect of glucocorticoids on the incidence of PNDs in adult patients undergoing surgery.

Methods

The databases of PubMed/Medline, Embase, the Cochrane Library, and Web of science were searched for all available randomized controlled trials (RCTs) from inception to April 30, 2022. RCTs comparing the effect of glucocorticoids with placebo on the incidence of PNDs in adult surgical patients (≥18 years old) were eligible. Subgroup analyses and meta-regressions were performed to evaluate sources of clinical heterogeneity. The level of certainty for main outcomes were assessed by the Grading of Recommendations Assessment, Development and Evaluation (GRADE) methodology.

Results

Eleven trials with a total of 10,703 patients were identified. Compared with the control group, glucocorticoids did not reduce the incidence of PNDs (RR: 0.84, 95% CI: 0.67 to 1.06, P = 0.13, GRADE = moderate). Secondary analyses for primary outcome did not change the result. In addition, the length of ICU stay was decreased in glucocorticoids group (RR: −13.58, 95% CI: −26.37 to −0.80, P = 0.04, GRADE = low). However, there were no significant differences between groups with regards to the incidence of postoperative infection (RR: 0.94, 95% CI: 0.84 to 1.06, P = 0.30, GRADE = moderate), blood glucose level (RR: 1.05, 95% CI: −0.09 to 2.19, P = 0.07, GRADE = low), duration of mechanical ventilation (RR: −2.44, 95% CI: −5.47 to 0.59, P = 0.14, GRADE = low), length of hospital stay (RR: −0.09, 95% CI: −0.27 to 0.09, P = 0.33, GRADE = moderate) and 30-day mortality (RR: 0.86, 95% CI: 0.70 to 1.06, P = 0.16, GRADE = moderate).

Conclusions

This meta-analysis suggests that perioperative administration of glucocorticoids may not reduce the incidence of PNDs after surgery. The effect of glucocorticoids on decreased length of ICU stay needs further researches. Future high-quality trials using acknowledged criteria and validated diagnostic tools are needed to determine the influence of glucocorticoids on long-term PNDs.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42022302262, identifier: CRD42022302262.

Dexamethasone Inhibits the Pro-Angiogenic Potential of Primary Human Myoblasts

Tissue regeneration depends on the complex processes of angiogenesis, inflammation and wound healing. Regarding muscle tissue, glucocorticoids (GCs) inhibit pro-inflammatory signalling and angiogenesis and lead to muscle atrophy. Our hypothesis is that the synthetic GC dexamethasone (dex) impairs angiogenesis leading to muscle atrophy or inhibited muscle regeneration. Therefore, this study aims to elucidate the effect of dexamethasone on HUVECs under different conditions in mono- and co-culture with myoblasts to evaluate growth behavior and dex impact with regard to muscle atrophy and muscle regeneration. Viability assays, qPCR, immunofluorescence as well as ELISAs were performed on HUVECs, and human primary myoblasts seeded under different culture conditions. Our results show that dex had a higher impact on the tube formation when HUVECs were maintained with VEGF. Gene expression was not influenced by dex and was independent of cells growing in a 2D or 3D matrix. In co-culture CD31 expression was suppressed after incubation with dex and gene expression analysis revealed that dex enhanced expression of myogenic transcription factors, but repressed angiogenic factors. Moreover, dex inhibited the VEGF mediated pro angiogenic effect of myoblasts and inhibited expression of angiogenic inducers in the co-culture model. This is the first study describing a co-culture of human primary myoblast and HUVECs maintained under different conditions. Our results indicate that dex affects angiogenesis via inhibition of VEGF release at least in myoblasts, which could be responsible not only for the development of muscle atrophy after dex administration, but also for inhibition of muscle regeneration after vascular damage.

Insights into glucocorticoid responses derived from omics studies

Glucocorticoid drugs are commonly used in the treatment of several conditions, including autoimmune diseases, asthma and cancer. Despite their widespread use and knowledge of biological pathways via which they act, much remains to be learned about the cell type-specific mechanisms of glucocorticoid action and the reasons why patients respond differently to them. In recent years, human and in vitro studies have addressed these questions with genomics, transcriptomics and other omics approaches. Here, we summarize key insights derived from omics studies of glucocorticoid response, and we identify existing knowledge gaps related to mechanisms of glucocorticoid action that future studies can address.

The Antiangiogenesis Role of Histone Deacetylase Inhibitors: Their Potential Application to Tumor Therapy and Tissue Repair

Angiogenesis, a process of new blood vessel formation from existing blood vessels, plays an important role in tumor growth and the tissue repair process. It is generally acknowledged that angiogenesis might contribute two both processes. In tumor growth, angiogenesis often increases oncogenic signaling, and in tissue repair, it decreases the stiffness of wound tissue and potentially exacerbates scar formation, resulting in pain and poor function. These poor outcomes are due to an increase in the expression of important genes involved in angiogenesis, such as hypoxia-inducible factor-1 alpha (HIF-1α) and its transcriptional target vascular endothelial growth factor (VEGF). Therefore, this adverse effect of angiogenesis should be taken into consideration. Limiting vessel growth instead of boosting growth may be beneficial for favorable long-term healing outcomes. Posttranslational modifications, including acetylation, which is mediated by histone acetyltransferases, and deacetylation, which is mediated by histone deacetylases (HDACs), are critical to HIF-1α function. Most studies have indicated that HDAC inhibitors (HDACIs) show great promise as antiangiogenic agents in the early phase of clinical trials. In this review, we discuss the role of the HDACs HIF-1α and VEGF in angiogenesis. Furthermore, we also discuss the molecular and cellular underpinnings of the effects of HDACIs on antiangiogenesis, which creates new avenues for anticancer therapeutics and the repair of wounded tissue.

Involvement of small G protein RhoB in the regulation of proliferation, adhesion and migration by dexamethasone in osteoblastic cells

Long-term exposure to therapeutic doses of glucocorticoids (GCs) results in bone remodeling, which frequently causes osteoporosis and fracture healing retardation because of the abnormality of osteoblastic proliferation and differentiation. The mechanisms of GCs’ effect on osteoblasts are largely unknown. In this present study, we found that dexamethasone (Dex) could induce the expression of the small G protein, RhoB, in mRNA and protein levels in the osteoblast-derived osteosarcoma cell lines MG-63. The up-regulation of RhoB mRNA by Dex mainly occurs at posttranscriptional level by increasing its mRNA stability through PI-3K/Akt and p38 mitogen-activated protein kinase signaling pathways. Over-expression of RhoB in MG-63 cells magnified while down-regulation of RhoB level by RNA interference impaired Dex-induced growth inhibition but not differentiation. What’s more, over-expression of RhoB mimicked the effect of Dex on cell adhesion and migration. And interfering RhoB expression partially suppressed Dex-induced pro-adhesion and anti-migration in MG-63 cells. In conclusion, these results indicate that RhoB plays an important role in the pathological effect of Dex on osteoblastic growth and migration, which is a part of the mechanisms of GCs’ adverse effect on bone remodeling.

Glucocorticoids suppress inflammation via the upregulation of negative regulator IRAK-M

Glucocorticoids are among the most commonly used anti-inflammatory agents. Despite the enormous efforts in elucidating the glucocorticoid-mediated anti-inflammatory actions, how glucocorticoids tightly control overactive inflammatory response is not fully understood. Here we show that glucocorticoids suppress bacteria-induced inflammation by enhancing IRAK-M, a central negative regulator of Toll-like receptor signalling. The ability of glucocorticoids to suppress pulmonary inflammation induced by non-typeable Haemophilus influenzae is significantly attenuated in IRAK-M-deficient mice. Glucocorticoids improve the survival rate after a lethal non-typeable Haemophilus influenzae infection in wild-type mice, but not in IRAK-M-deficient mice. Moreover, we show that glucocorticoids and non-typeable Haemophilus influenzae synergistically upregulate IRAK-M expression via mutually and synergistically enhancing p65 and glucocorticoid receptor binding to the IRAK-M promoter. Together, our studies unveil a mechanism by which glucocorticoids tightly control the inflammatory response and host defense via the induction of IRAK-M and may lead to further development of anti-inflammatory therapeutic strategies.

Effects of a single course versus repeated courses of antenatal corticosteroids on fetal growth, placental morphometry and the differential regulation of vascular endothelial growth factor

AIM

To investigate the impact of antenatal exposure to a single course or repeated courses of dexamethasone (DEX) on neonatal anthropometrics, placental morphometry and potential effect on maternal plasma levels and placental expression of vascular endothelial growth factor (VEGF).

METHODS

Pregnant women between 27 and 32 weeks of gestation who delivered between 28 and 40 weeks and received a single course (n = 38) or repeated courses (n = 33) of DEX were compared to gestational age-matched controls (n = 30). Maternal blood samples were obtained, and placental biopsy was taken. Area percent of VEGF immunostaining and villous capillarization index were evaluated using image analysis.

RESULTS

Infants exposed to repeated courses of DEX were significantly associated with decreased birthweight, body length, head circumference and placental weight compared with controls (P = 0.011, P < 0.001, P = 0.004, P < 0.001, respectively) and with the group that received a single course of DEX (P = 0.021, P = 0.020, P = 0.049, P = 0.010, respectively). There was a significant decrease in maternal VEGF plasma levels and percentage of VEGF immunostained area after repeated courses of DEX compared with controls (P < 0.001 and P = 0.001, respectively) or a single course (P = 0.028 and P = 0.002, respectively). Notably, repeated courses of DEX impaired normal increase in villous capillarization index compared with controls or a single course (P = 0.001 and P = 0.041, respectively).

CONCLUSION

Repeated antenatal courses of DEX compromised fetal and placental growth compared with a single course of DEX, and these effects were potentially mediated by altered maternal plasma levels and placental expression of VEGF with consequent decrease in placental vascularization. Because of continuing uncertainties, several key messages for clinicians are provided.

Targeting Neovascularization in Ischemic Retinopathy: Recent Advances

Pathological retinal neovascularization (RNV) is a common micro-vascular complication in several retinal diseases including retinopathy of prematurity, diabetic retinopathy, age-related macular degeneration and central vein occlusion. The current therapeutic modalities of RNV are invasive and although they may slow or halt the progression of the disease they are unlikely to restore normal acuity. Therefore, there is an urgent need to develop treatment modalities, which are less invasive and therefore associated with fewer procedural complications and systemic side effects. This review article summarizes our understanding of the pathophysiology and current treatment of RNV in ischemic retinopathies; lists potential therapeutic targets; and provides a framework for the development of future treatment modalities.

Early-life glucocorticoid exposure: the hypothalamic-pituitary-adrenal axis, placental function, and long-term disease risk

An adverse early-life environment is associated with long-term disease consequences. Adversity early in life is hypothesized to elicit developmental adaptations that serve to improve fetal and postnatal survival and prepare the organism for a particular range of postnatal environments. These processes, although adaptive in their nature, may later prove to be maladaptive or disadvantageous if the prenatal and postnatal environments are widely discrepant. The exposure of the fetus to elevated levels of either endogenous or synthetic glucocorticoids is one model of early-life adversity that contributes substantially to the propensity of developing disease. Moreover, early-life glucocorticoid exposure has direct clinical relevance because synthetic glucocorticoids are routinely used in the management of women at risk of early preterm birth. In this regard, reports of adverse events in human newborns have raised concerns about the safety of glucocorticoid treatment; synthetic glucocorticoids have detrimental effects on fetal growth and development, childhood cognition, and long-term behavioral outcomes. Experimental evidence supports a link between prenatal exposure to synthetic glucocorticoids and alterations in fetal development and changes in placental function, and many of these alterations appear to be permanent. Because the placenta is the conduit between the maternal and fetal environments, it is likely that placental function plays a key role in mediating effects of fetal glucocorticoid exposure on hypothalamic-pituitary-adrenal axis development and long-term disease risk. Here we review recent insights into how the placenta responds to changes in the intrauterine glucocorticoid environment and discuss possible mechanisms by which the placenta mediates fetal hypothalamic-pituitary-adrenal development, metabolism, cardiovascular function, and reproduction.

Excess maternal glucocorticoids in response to in utero undernutrition inhibit offspring angiogenesis

To test the hypothesis that inhibition of offspring angiogenesis by maternal undernutrition (MUN) is mediated by maternal glucocorticoids, 3 groups of dams were studied: controls received ad libitum food; MUN dams were food restricted by 50% from day 10 of gestation; and metyrapone (MET) dams were food restricted and treated with 0.5 mg/mL of MET, a glucocorticoid synthesis inhibitor. The MUN reduced birth weights, reduced vascular endothelial growth factor (VEGF) abundance in P1 aortas, reduced VEGF and VEGF-R2 abundances in P1 mesenteric arterioles, reduced arteriolar endothelial nitric oxide synthase abundance, reduced microvessel density in the anterior tibialis, reduced endothelial cell branching in culture, reduced arteriolar immunoreactivity for proliferating cell nuclear antigen (PCNA), increased active caspase 3 in P1 mesenteric arterioles, and decreased matrix metalloproteinase (MMP)-2 and MMP-9 abundances in lysates of P1 aortas. All of these effects were prevented by treatment with metyrapone. Collectively, these findings suggest that reduced angiogenesis in MUN offspring involves direct inhibitory effects of maternal glucorticoid on fetal VEGF and its receptors.

CYP2S1 is negatively regulated by corticosteroids in human cell lines

Cytochrome P450s are monooxygenase proteins involved in the metabolism of both exogenous and endogenous compounds. CYP2S1 can metabolize eicosanoids in the absence of both NADPH and NADPH cytochrome P450 reductase, and can also activate the anticancer agent 1 AQ4N [1,4-bis{[2-(dimethylamino-N-oxide)ethyl]amino}-5,8-dihydroxy anthracene-9,10-dione]. CYP2S1 is mainly expressed in extrahepatic tissues such as the trachea, lung, stomach, small intestine, spleen, skin, breast, kidney and placenta. Furthermore, increased expression of CYP2S1 occurs in several tumors of epithelial origin, making the characterization of CYP2S1 regulation relevant to the treatment of disease. We report that the synthetic glucocorticoid receptor ligand dexamethasone (DEX) represses CYP2S1 expression. The ED(50) is between 1 nM and 3 nM and maximal repression is reached by 48 h. Other corticosteroids are also effective at repressing CYP2S1. We show that repression by DEX is mediated by the glucocorticoid receptor and requires histone deacetylase activity.

Case study: Using microbe molecular biology for Gulf oil spill clean up

This case has the student actively investigate the regulation of expression of a novel bacterial gene in the context of attempts to solve a real world problem, clean up of the April 2010 Deep Water Horizon oil spill in the Gulf of Mexico. Although the case is fictitious, it is based on factual gene regulatory characteristics of oil-degrading microbes. The case is written for a sophomore Cell Biology lecture course at Indiana Wesleyan University that is taught to Biology/Pre-Med majors. This study is also appropriate for use in undergraduate microbiology, biochemistry, molecular biology, and molecular genetics courses. The case is intended to enhance coverage of transcription, translation, control of gene expression, and selected molecular biology techniques. Opportunities to practice critical thinking skills and to a lesser extent an introduction to the paradigm of life science research at the industry level are provided.

Dexamethasone and betamethasone for prenatal lung maturation: differences in vascular endothelial growth factor expression and alveolarization in rats

BACKGROUND

Fetal and postnatal lung development is regulated by glucocorticoids. The use of antenatal corticosteroids is reported to produce effects on vascular endothelial growth factor (VEGF), which plays a crucial role in pulmonary development.

OBJECTIVES

The purpose of this study was to compare pulmonary VEGF expression in newborn rats that were exposed to antenatal betamethasone versus dexamethasone and to evaluate its impact on the alveolarization period of rats (0-14 days of life).

METHODS

Betamethasone, dexamethasone or equivalent saline solution (control group) was administered to pregnant rats on 20th and 21st days of gestation. Pulmonary VEGF mRNA, VEGF protein expression, and alveolarization changes were evaluated at birth and at 14 days of life.

RESULTS

Betamethasone and dexamethasone were observed to have different actions on VEGF expression with a correlation with alveolarization on both days of study. Antenatal dexamethasone decreased VEGF expression, betamethasone tended to produce the induction of the expression of VEGF, and moreover, betamethasone did not produce a decrease in alveolarization as seen in the animals that received dexamethasone.

CONCLUSIONS

Our results support the notion that betamethasone could be a better choice than dexamethasone for antenatal lung maturation.

Glucocorticoid-mediated inhibition of angiogenic changes in human endothelial cells is not caused by reductions in cell proliferation or migration

Background

Glucocorticoid-mediated inhibition of angiogenesis is important in physiology, pathophysiology and therapy. However, the mechanisms through which glucocorticoids inhibit growth of new blood vessels have not been established. This study addresses the hypothesis that physiological levels of glucocorticoids inhibit angiogenesis by directly preventing tube formation by endothelial cells.

Methodology/Principal Findings

Cultured human umbilical vein (HUVEC) and aortic (HAoEC) endothelial cells were used to determine the influence of glucocorticoids on tube-like structure (TLS) formation, and on cellular proliferation (5-bromo-2′-deoxyuridine (BrdU) incorporation), viability (ATP production) and migration (Boyden chambers). Dexamethasone or cortisol (at physiological concentrations) inhibited both basal and prostaglandin F_2α (PGF_2α)-induced and vascular endothelial growth factor (VEGF) stimulated TLS formation in endothelial cells (ECs) cultured on Matrigel, effects which were blocked with the glucocorticoid receptor antagonist RU38486. Glucocorticoids had no effect on EC viability, migration or proliferation. Time-lapse imaging showed that cortisol blocked VEGF-stimulated cytoskeletal reorganisation and initialisation of tube formation. Real time PCR suggested that increased expression of thrombospodin-1 contributed to glucocorticoid-mediated inhibition of TLS formation.

Conclusions/Significance

We conclude that glucocorticoids interact directly with glucocorticoid receptors on vascular ECs to inhibit TLS formation. This action, which was conserved in ECs from two distinct vascular territories, was due to alterations in cell morphology rather than inhibition of EC viability, migration or proliferation and may be mediated in part by induction of thrombospodin-1. These findings provide important insights into the anti-angiogenic action of endogenous glucocorticoids in health and disease.

ZFP36L1 is regulated by growth factors and cytokines in keratinocytes and influences their VEGF production

Keratinocyte-derived growth factors and cytokines play an important role in epidermal homeostasis and particularly in cutaneous wound repair. Thus, we analyzed a potential role of the ZFP36/tristetraprolin family of zinc finger proteins, which are targets of these factors, but also regulate their production, in keratinocytes. We show that expression of ZFP36, ZFP36L1, and ZFP36L2 is induced by a broad variety of growth factors and cytokines, and by scratch wounding. Since ZFP36L1 is a modulator of vascular endothelium growth factor (VEGF) mRNA stability, we subsequently used siRNA technology to inhibit ZFP36L1 gene expression. Notably, this treatment resulted in prolonged maintenance of elevated VEGF levels in HaCaT keratinocytes upon epidermal growth factor stimulation of these cells. Taken together, our results suggest an important role of ZFP36L1 in wound healing.

Uteroplacental insufficiency affects kidney VEGF expression in a model of IUGR with compensatory glomerular hypertrophy and hypertension

Low nephron endowment secondary to intrauterine growth restriction (IUGR) results in compensatory hypertrophy of the remaining glomeruli, which in turn is associated with hypertension. However, gender differences exist in the response of the kidney to injury, and IUGR female offspring seems protected from an unfavorable outcome. We previously reported differences in gender-specific gene expression in the IUGR kidney as well as increased circulating corticosterone levels following uteroplacental insufficiency (UPI). Vascular endothelial growth factor (VEGF), which is critical for renal development, is an important candidate in the IUGR kidney since its expression can be regulated by sex-steroids and glucocorticoids. We hypothesize that IUGR leads to altered kidney VEGF expression in a gender-specific manner. Following uterine ligation in the pregnant rat, UPI decreases renal VEGF levels in male and female IUGR animals at birth and through postnatal day 21. However, by day 120 of life, IUGR females have increased kidney VEGF expression, not present in the IUGR males. In addition, IUGR males exhibit increased serum testosterone levels as well as proteinuria. These findings are intriguing in light of the difference in glomerular hypertrophy observed: IUGR males show increased glomerular area when compared to IUGR females. In this model characterized by decreased nephron number and adult onset hypertension, UPI decreases renal VEGF expression during nephrogenesis. Our most intriguing finding is the increased renal VEGF levels in adult IUGR females, associated with a more benign phenotype. We suggest that the mechanisms underlying renal disease in response to IUGR are most likely regulated in a gender specific manner.

Dexamethasone coordinately regulates angiopoietin-1 and VEGF: a mechanism of glucocorticoid-induced stabilization of blood-brain barrier

Glucocorticoids stabilize the blood-brain barrier (BBB), leading to attenuation of vasogenic brain edema. However, the action mechanism of glucocorticoids has been poorly elucidated. To elucidate the mechanism, we investigated whether dexamethasone (Dex), a synthetic glucocorticoid hormone, regulates the levels of key permeability regulating factors such as angiopoietin-1, angiopoietin-2, and vascular endothelial growth factor (VEGF) in the three types of cells comprising BBB. Dex increased the level of angiopoietin-1 mRNA and protein and decreased VEGF mRNA and protein in brain astrocytes and pericytes, but not in endothelial cells. The mRNA and protein of angiopoietin-2 were detected only in endothelial cells and not regulated by Dex. The Dex-induced regulation of angiopoietin-1 and VEGF was inhibited by RU486, suggestive of glucocorticoid receptor mediation. The mRNA stability of angiopoietin-1 and VEGF was not changed by Dex treatment, implying that Dex increases angiopoietin-1 and decreases VEGF through transcriptional regulation. This is the first study showing the coordinate regulation of angiopoietin-1 and VEGF by glucocorticoids, suggesting a novel mechanism underlying glucocorticoids-induced stabilization of BBB.

Anti-inflammatory functions of glucocorticoid-induced genes

There is a broad consensus that glucocorticoids (GCs) exert anti-inflammatory effects largely by inhibiting the function of nuclear factor kappaB (NFkappaB) and consequently the transcription of pro-inflammatory genes. In contrast, side effects are thought to be largely dependent on GC-induced gene expression. Biochemical and genetic evidence suggests that the positive and negative effects of GCs on transcription can be uncoupled from one another. Hence, novel GC-related drugs that mediate inhibition of NFkappaB but do not activate gene expression are predicted to retain therapeutic effects but cause fewer or less severe side effects. Here, we critically re-examine the evidence in favor of the consensus, binary model of GC action and discuss conflicting evidence, which suggests that anti-inflammatory actions of GCs depend on the induction of anti-inflammatory mediators. We propose an alternative model, in which GCs exert anti-inflammatory effects at both transcriptional and post-transcriptional levels, both by activating and inhibiting expression of target genes. The implications of such a model in the search for safer anti-inflammatory drugs are discussed.

The macrophage migration inhibitory factor-glucocorticoid dyad: regulation of inflammation and immunity

The cytokine macrophage migration inhibitory factor (MIF) occupies a unique position in physiology by its ability to directly regulate the immunosuppressive actions of glucocorticoids. We review herein the interactions between MIF and glucocorticoids within the immune system and discuss the relevance of the MIF-glucocorticoid regulatory dyad in physiology and immunopathology. Therapeutic antagonism of MIF may be an effective approach for steroid-sparing therapies in patients with refractory autoimmune or inflammatory diseases.

Glucocorticosteroids as antioxidants in treatment of asthma and COPD. New application for an old medication?

Inhaled corticosteroids (ICS) are the standard of care in asthma and are widely used in the treatment of patients with COPD. The influence of steroids on inflammatory processes has long been established since glucocorticoids and their receptor belong to the regulatory network involved in inhibition of several inflammatory pathways. Inflammatory processes are usually accompanied by an increased oxidative burden followed by a depletion of antioxidants. Therefore, the effects of steroids on antioxidant status have been investigated revealing possible positive effects on the reduced antioxidant enzyme activity. Nevertheless, the mechanisms of this modulation have not been fully elucidated yet. It is possible that antioxidant enzyme activity is regulated at the level of transcription. Additionally, because of the fact that antioxidant enzymes are trace element dependent, steroids may affect their activity through influence on trace element accumulation. This review summarizes the effects of steroids on the antioxidant enzymes activity in vitro and in vivo in relation to asthma and COPD.

Potentiation of glucocorticoid activity in hypoxia through induction of the glucocorticoid receptor

Tissue hypoxia is intimately associated with chronic inflammatory disease and may signal to the resolution of inflammatory processes. Glucocorticoid signaling through the glucocorticoid receptor (GR) represents a clinically important endogenous anti-inflammatory pathway. Microarray analysis reveals that the GR is transcriptionally up-regulated by hypoxia in human renal proximal tubular epithelial cells. Hypoxic up-regulation of the GR was confirmed at the level of promoter activity, mRNA, and protein expression. Furthermore, functional potentiation of glucocorticoid activity in hypoxia was observed as an enhancement of dexamethasone-induced glucocorticoid response element promoter activity and enhanced dexamethasone-mediated inhibition of IL-1beta-stimulated IL-8 expression and hypoxia-induced vascular endothelial growth factor expression. Knockdown of enhanced GR gene expression in hypoxia using specific GR small inhibitory RNA (siRNA) resulted in an attenuation of the enhanced glucocorticoid sensitivity. A role for the hypoxia-inducible transcription factor, HIF-1alpha, in the regulation of GR expression and the associated potentiation of glucocorticoid activity in hypoxia was also demonstrated. These results reveal a novel signaling aspect responsible for the incorporation of hypoxic and glucocorticoid stimuli, which we hypothesize to be an important co-operative pathway for the control of gene expression observed in complex tissue microenvironments in inflamed states.

Corticosteroids inhibit VEGF-induced vascular leakage in a rabbit model of blood-retinal and blood-aqueous barrier breakdown

PURPOSE

Recent clinical studies show that a single intravitreal injection of the corticosteroid triamcinolone acetonide (TAA) may reduce edematous retinal swelling and improve visual acuity in patients with diabetic macular edema (DME). In addition, clinical and experimental studies strongly suggest that blood-retinal barrier breakdown in diabetes is induced by vascular endothelial growth factor (VEGF). These results suggest that corticosteroids may modulate VEGF-mediated responses in vivo. To test this hypothesis directly, the current study evaluated the effects of TAA and dexamethasone (DEX) in a newly developed rabbit model of VEGF-induced blood-retinal barrier and blood-aqueous (iris) barrier breakdown.

METHODS

VEGF165 or vehicle was injected intravitreally in female Dutch Belt rabbits, and scanning ocular fluorophotometry was used to non-invasively measure fluorescein leakage from retinal and iris vasculature. VEGF-induced retinal vasculopathy was further assessed with fundus imaging, fluorescein angiography, and ocular coherence tomography. For pharmacologic studies, rabbits were treated with either DEX (2 mg kg(-1) daily, s.c.), TAA (2 or 4 mg, intravitreal), indomethacin (20 mg kg(-1) daily, s.c.), or vehicle (s.c. or intravitreal). Human umbilical vein endothelial cells (HUVEC) were loaded with the fluorescent Ca2+ indicator dye fluo-4 and treated with dexamethasone (0.1-10 microM) or vehicle for either 2 or 24 hr prior to stimulation with 10 ng ml(-1) VEGF165.

RESULTS

VEGF injected intravitreally induced a time and dose-dependent breakdown of the blood-retinal and blood-aqueous barriers. Maximal vascular leakage was measured at 48 hr after intravitreal injection with a dose of 500 ng VEGF. Other effects of VEGF included prominent retinal vasodilation, vessel tortuousity, fluorescein leakage from retinal vessels, and inner retinal edema. These VEGF-mediated responses are transient and approach baseline by 1 week. VEGF-induced blood-retinal and blood-aqueous barrier breakdown was completely blocked by the corticosteroid DEX administered systemically for 3 days. In contrast, the non-steroidal anti-inflammatory drug, indomethacin, had no effect. In a separate study with VEGF injected intravitreally at six different time points over 5 months, a single intravitreal 2 mg dose of TAA completely blocked VEGF-induced retinal and iris leakage for 45 days. VEGF/VEGF receptor-2-mediated Ca2+ mobilization in endothelial cells was not affected by 2 or 24 hr pretreatment with dexamethasone.

CONCLUSION

These results indicate that one mechanism by which corticosteroids block blood-ocular barrier breakdown and edema is via their modulation of signaling or effector proteins downstream of the VEGF receptor.

Aspects of human fetoplacental vasculogenesis and angiogenesis. I. Molecular regulation

Patterns of fetoplacental angiogenesis vary during gestation and in association with certain pregnancy pathologies. In a set of three linked reviews, we provide a survey of current knowledge about the molecular regulation, cellular players, qualitative and quantitative morphological features of the vascularization of human placental villi. Here, an account is given of the role played by hypoxia-inducible factor in mediating the effects of oxygen on production of growth factor ligands and receptors which regulate angiogenesis and vessel maturation. However, it should be noted that, for the human placenta early in gestation, the normal (i.e. physiological) partial pressure of O(2)is low but this does not mean that the tissue is hypoxic. Thus, the mechanisms of regulating angiogenic growth factor production may differ at this time in comparison to those found later in gestation or in other tissues or organs. The vasculature in the placenta is plastic and changes markedly as gestation progresses. This is controlled by the complex interplay between physical factors and chemical factors including oxygen, growth factors and growth inhibitors. The companion reviews describe morphological features of normal and pathological development of the human placenta in the context of the factors discussed here.

On the link between Bcl-2 family proteins and glucocorticoid-induced apoptosis

As immunosuppressive agents, glucocorticoids (GCs) act by inhibiting the expression of cytokines and adhesion molecules at the transcriptional and post-transcriptional levels. In addition, GCs exerted their effects by modulating apoptosis. In view of the central role of the Bcl-2 family protein in regulating apoptosis, it was tempting to speculate that GCs modulated apoptosis through modulation of the expression of proapoptotic (Bax, Bcl-X(S), Bak) and prosurvival (Bcl-2, Bcl-X(L), Bcl-w) Bcl-2 family members. Prosurvival Bcl-2 family members in various cell types antagonized GC-induced apoptosis, thereby suggesting a causal relationship between GC-induced apoptosis and Bcl-2 proteins. The antagonism of apoptosis afforded by prosurvival Bcl-2 proteins appeared to be specific for the GCs, as Bcl-2 and Bcl-x(L) blocked GC-induced apoptosis in T cell hybridomas but did not affect Fas or activation-induced apoptosis. Although it is speculated that GC-induced apoptosis may be mediated through the activation of proapoptotic Bcl-2 proteins, recent findings suggest that this may vary depending on the conditions and the cell types used. The mechanism by which Bcl-2 inhibited GC-induced apoptosis remains uncertain. It was suggested that Bcl-2 acted on outer mitochondrial membranes to preserve their function. Bcl-2 overexpression also inhibited GC-induced apoptotic events, including caspase activation and mitochondrial dysfunction. The cross-talk of the GC receptors with other secondary messengers could lead to modulation of the activity of Bcl-2 proteins through modification of their phosphorylation status, without ruling out the possibility of a physical interaction between activated GR with Bcl-2 proteins.

Post-transcriptional regulation of gene expression by mitogen-activated protein kinase p38

The mitogen-activated protein kinase p38 pathway was originally identified as a signalling cascade activated by pro-inflammatory stimuli and cellular stresses, and playing a critical role in the translational regulation of pro-inflammatory cytokine synthesis. In almost a decade since this discovery, a great deal has been learned about the role of the p38 pathway in the post-transcriptional regulation of pro-inflammatory gene expression. However, important questions remain to be answered concerning the specificity and mechanism or mechanisms of action of p38. This review describes recent progress and remaining puzzles in the field of post-transcriptional regulation by p38.

Changes in cytoskeletal and tight junctional proteins correlate with decreased permeability induced by dexamethasone in cultured rat brain endothelial cells

The blood-brain barrier (BBB) plays an important role in controlling the passage of molecules from the blood to the extracellular fluid environment of the brain. An immortalised rat brain endothelial cell line (GPNT) was used to investigate the mechanisms underlying dexamethasone-induced decrease in paracellular permeability. Following treatment with 1 microM dexamethasone there was a decrease in transmonolayer paracellular permeability mainly to sucrose, fluorescein and dextrans of up to 20 KDa. According to pore theory, these differences in permeability were consistent with a decrease in the number of pores between brain endothelial cells. This effect was accompanied by a concentration of filamentous actin and cortactin to the cell periphery. Concomitantly, the continuity of the tight junctional protein ZO-1 at the cell borders was improved and was associated with an increase in both ZO-1 and occludin expression. By contrast, the expression and distribution of adherens junctional proteins such as beta-catenin and p100/p120 remained unchanged. These observations suggest that glucocorticoids induce a more differentiated BBB phenotype in cultured brain endothelial cells through modification of tight junction structure.

Distinct protein kinase C isoforms mediate regulation of vascular endothelial growth factor expression by A2A adenosine receptor activation and phorbol esters in pheochromocytoma PC12 cells

Vascular endothelial growth factor (VEGF) stimulates angiogenesis during development and in disease. In pheochromocytoma (PC12) cells, VEGF expression is regulated by A(2A) adenosine receptor (A(2A)AR) activation. The present work examines the underlying signaling pathway. The adenylyl cyclase-protein kinase A cascade has no role in the down-regulation of VEGF mRNA induced by the A(2A)AR agonist, 2-[4-[(2-carboxyethyl)phenyl]ethylamino]-5'-N-ethylcarboxamidoadenosine (CGS21680). Conversely, 6-h exposure of cells to either phorbol 12-myristate 13-acetate (PMA) or protein kinase C (PKC) inhibitors mimicked the CGS21680-induced down-regulation. PMA activated PKCalpha, PKCepsilon, and PKCzeta, and CGS21680 activated PKCepsilon and PKCzeta as assessed by cellular translocation. By 6 h, PMA but not CGS21680 decreased PKCalpha and PKCepsilon expression. Neither compound affected PKCzeta levels. Following prolonged PMA treatment to down-regulate susceptible PKC isoforms, CGS21680 but not PMA inhibited the cobalt chloride induction of VEGF mRNA. The proteasome inhibitor, MG-132, abolished PMA- but not CGS21680-induced down-regulation of VEGF mRNA. Phorbol 12,13-diacetate reduced VEGF mRNA levels while down-regulating PKCepsilon but not PKCalpha expression. In cells expressing a dominant negative PKCzeta construct, CGS21680 was unable to reduce VEGF mRNA. Together, the findings suggest that phorbol ester-induced down-regulation of VEGF mRNA occurs as a result of a reduction of PKCepsilon activity, whereas that mediated by the A(2A)AR occurs following deactivation of PKCzeta.

HGF-, EGF-, and dexamethasone-induced gene expression patterns during formation of tissue in hepatic organoid cultures

Corticosteroids, hepatocyte growth factor (HGF), and epidermal growth factor (EGF) play important roles in hepatic biology. We have previously shown that these molecules are required for formation of tissue with specific histology in complex organoid cultures. Dexamethasone suppresses growth and induces hepatocyte maturation; HGF and EGF are needed for formation of the nonepithelial elements. All three are needed for formation of the biliary epithelium. The gene expression patterns by which corticosteroids, HGF, and EGF mediate their effects in hepatic tissue formation are distinct. These patterns affect many gene families and are described in detail. In terms of main findings, dexamethasone induces expression of both HNF4 and C/EBPalpha, essential transcription factors for hepatocyte differentiation. It suppresses hepatocyte growth by suppressing many molecules associated with growth in liver and other tissues, including IL-6, CXC-chemokine receptor, amphiregulin, COX-2, HIF, etc. HGF and EGF induce all members of the TGF-beta family. They also induced multiple CNS-related genes, probably associated with stellate cells. Dexamethasone, as well as HGF and EGF, induces expression of HNF6-beta, associated with biliary epithelium formation. Combined addition of all three molecules is associated with mature histology in which hepatocyte and biliary lineages are separate and HNF4 is expressed only in hepatocyte nuclei. In conclusion, the results provide new and surprising information on the gene expression alterations by which corticosteroids, HGF, and EGF exert their effects on formation of hepatic tissue. The results underscore the usefulness of the organoid cultures for generating information on histogenesis, which cannot be obtained by other culture or whole animal models.

Dexamethasone causes sustained expression of mitogen-activated protein kinase (MAPK) phosphatase 1 and phosphatase-mediated inhibition of MAPK p38

The stress-activated protein kinase p38 stabilizes a number of mRNAs encoding inflammatory mediators, such as cyclooxygenase 2 (Cox-2). In HeLa cells the anti-inflammatory glucocorticoid dexamethasone destabilizes Cox-2 mRNA by inhibiting p38 function. Here we demonstrate that this effect is phosphatase dependent. Furthermore, in HeLa cells dexamethasone induced the sustained expression of mitogen-activated protein kinase phosphatase 1 (MKP-1), a potent inhibitor of p38 function. The inhibition of p38 and the induction of MKP-1 by dexamethasone occurred with similar dose dependence and kinetics. No other known p38 phosphatases were induced by dexamethasone, and other cell types which failed to express MKP-1 also failed to inhibit p38 in response to dexamethasone. The proinflammatory cytokine interleukin 1 (IL-1) induced MKP-1 expression in a p38-dependent manner and acted synergistically with dexamethasone to induce MKP-1 expression. In HeLa cells treated with IL-1 or IL-1 and dexamethasone, the dynamics of p38 activation mirrored the expression of MKP-1. These observations suggest that MKP-1 participates in a negative-feedback loop which regulates p38 function and that dexamethasone may inhibit proinflammatory gene expression in part by inducing MKP-1 expression.

Angiogenesis as a target for cancer therapy

Antiangiogenic drugs are unique for having highly specific targets while carrying the potential to be effective against a wide variety of tumors. Moreover, some of the major limitations of cytotoxic therapies likely will be avoided by this entirely new class of anticancer weapons. After the realization of the potential advantages of antiangiogenic therapy, the field of angiogenesis research is growing exponentially. Still, there is much to learn about the machinery that tumors use to recruit new blood vessels, and the results of the clinical trials will show the best way to apply that knowledge for cancer therapy.