Egr-1, a master switch coordinating upregulation of divergent gene families underlying ischemic stress

A newly identified microRNA, mmu-miR-7578, functions as a negative regulator on inflammatory cytokines tumor necrosis factor-α and interleukin-6 via targeting Egr1 in vivo

Appropriate innate immune responses are required to protect an organism against foreign pathogens, and the immune response must be tightly controlled. Here, we report a new microRNA (miRNA) identified from a small RNA library from the epididymis, termed miR-7578, that acts as a negative regulator of inflammatory responses. It was abundantly expressed in immune-related organs and induced by lipopolysaccharide in the lung and epididymis, as well as macrophages stimulated with diverse Toll-like receptor ligands, in an NF-κB-dependent manner. mmu-miR-7578 inhibited the release of pro-inflammatory cytokines, including TNFα and IL6, by regulating its target gene Egr1, which encodes a transcription factor that activates TNFα and NF-κB expression. Transgenic mice overexpressing mmu-miR-7578 displayed higher resistance to endotoxin shock and lower plasma levels of TNFα and IL6, indicating that this miRNA acted as a negative molecule of immune response. In sum, we report a previously uncharacterized LPS-responsive miRNA that controls inflammatory response in a feedback loop by fine-tuning a key transcription factor in vivo.

High bias gas flows increase lung injury in the ventilated preterm lamb

BACKGROUND

Mechanical ventilation of preterm babies increases survival but can also cause ventilator-induced lung injury (VILI), leading to the development of bronchopulmonary dysplasia (BPD). It is not known whether shear stress injury from gases flowing into the preterm lung during ventilation contributes to VILI.

METHODS

Preterm lambs of 131 days' gestation (term = 147 d) were ventilated for 2 hours with a bias gas flow of 8 L/min (n = 13), 18 L/min (n = 12) or 28 L/min (n = 14). Physiological parameters were measured continuously and lung injury was assessed by measuring mRNA expression of early injury response genes and by histological analysis. Control lung tissue was collected from unventilated age-matched fetuses. Data were analysed by ANOVA with a Tukey post-hoc test when appropriate.

RESULTS

High bias gas flows resulted in higher ventilator pressures, shorter inflation times and decreased ventilator efficiency. The rate of rise of inspiratory gas flow was greatest, and pulmonary mRNA levels of the injury markers, EGR1 and CTGF, were highest in lambs ventilated with bias gas flows of 18 L/min. High bias gas flows resulted in increased cellular proliferation and abnormal deposition of elastin, collagen and myofibroblasts in the lung.

CONCLUSIONS

High ventilator bias gas flows resulted in increased lung injury, with up-regulation of acute early response genes and increased histological lung injury. Bias gas flows may, therefore, contribute to VILI and BPD.

Purine anti-metabolite attenuates nuclear factor κB and related pro-inflammatory cytokines in experimental vasospasm

BACKGROUND

Increased nuclear factor κB (NF-κB) bioexpression, as well as TNF-α, IL-1β and IL-6 levels, were observed after aneurysmal subarachnoid hemorrhage (SAH). It is of interest to investigate the effect of 6-mercaptopurine (6-mp) on cytokines/NF-κB in this SAH model.

MATERIALS AND METHODS

A rodent double-hemorrhage SAH model was employed. Serum and cerebrospinal fluid (CSF) samples were collected to examine IL-1, IL-6 and TNF-α levels. NF-κB subunit p65 and its inhibitor of nuclear factor κB (IκB) were examined (by Western blot). TNF-α was used to induce the phosphorylation of IκB in the presence or absence of 6-mp.

RESULTS

Nuclear NF-κB subunit p65/IκB kinase in the basilar artery was over-expressed, and cytokines was notably increased in the SAH groups, compared with the controls (P < 0.01). In the 6-mp SAH group, obvious reduction was observed in NF-κB subunit p65 (nuclei) (P < 0.01). Treatment with 6-mp significantly reduced IL-1β and TNF-α levels to those of the healthy control. 6-Mercaptopurine also significantly increased the level of IκB in the TNF-α-stimulated SAH rats.

CONCLUSIONS

Through inhibiting IκB bioexpression, 6-mp decreases NF-κB-related IL-1β, IL-6, and TNF-α in the presence of SAH. The study suggests 6-mp exerts vascular anti-inflammatory properties through inhibiting IκB kinase and subsequently blocks bio-activation of NF-κB and related cytokines, which may contribute to its antivasospastic effect in animals subjected to SAH.

Adaptive and maladaptive cardiorespiratory responses to continuous and intermittent hypoxia mediated by hypoxia-inducible factors 1 and 2

Hypoxia is a fundamental stimulus that impacts cells, tissues, organs, and physiological systems. The discovery of hypoxia-inducible factor-1 (HIF-1) and subsequent identification of other members of the HIF family of transcriptional activators has provided insight into the molecular underpinnings of oxygen homeostasis. This review focuses on the mechanisms of HIF activation and their roles in physiological and pathophysiological responses to hypoxia, with an emphasis on the cardiorespiratory systems. HIFs are heterodimers comprised of an O(2)-regulated HIF-1α or HIF-2α subunit and a constitutively expressed HIF-1β subunit. Induction of HIF activity under conditions of reduced O(2) availability requires stabilization of HIF-1α and HIF-2α due to reduced prolyl hydroxylation, dimerization with HIF-1β, and interaction with coactivators due to decreased asparaginyl hydroxylation. Stimuli other than hypoxia, such as nitric oxide and reactive oxygen species, can also activate HIFs. HIF-1 and HIF-2 are essential for acute O(2) sensing by the carotid body, and their coordinated transcriptional activation is critical for physiological adaptations to chronic hypoxia including erythropoiesis, vascularization, metabolic reprogramming, and ventilatory acclimatization. In contrast, intermittent hypoxia, which occurs in association with sleep-disordered breathing, results in an imbalance between HIF-1α and HIF-2α that causes oxidative stress, leading to cardiorespiratory pathology.

Genes differentially regulated by NKX2-3 in B cells between ulcerative colitis and Crohn's disease patients and possible involvement of EGR1

Ulcerative colitis (UC) and Crohn's disease (CD) are two related yet different forms of chronic intestinal inflammation. We investigated the genes regulated by NKX2-3 in B cells from a UC patient by cDNA microarray and compared the results to those genes regulated by NKX2-3 in B cells from a CD patient. Genes regulated by NKX2-3 in B cells from UC were mainly involved in cell growth, inflammation, and immune response. Among the genes regulated by NKX2-3 in both UC and CD, expression of 145 genes was similarly altered and 34 genes was differentially affected by NKX2-3 knockdown. EGR1 was up-regulated in NKX2-3 knockdown B cells from UC while down-regulated in NKX2-3 knockdown B cells from CD. mRNA expressions of NKX2-3 and EGR1 were increased in diseased intestinal tissues from 19 CD patients. NKX2-3 may play different roles in UC and CD pathogenesis by differential regulation of EGR1.

Time-dependent expression and distribution of Egr-1 during skeletal muscle wound healing in rats

Recent studies have shown that early growth response factor-1 (Egr-1) plays an important role in regulation of inflammation and tissue repair, but little is known about its expression after trauma to skeletal muscles. A preliminary study on time-dependent expression and distribution of Egr-1 was performed by immunohistochemistry, immunofluorescence and Western blotting during skeletal muscle wound healing in rats. An animal model of skeletal muscle contusion was established in 45 Sprague-Dawley male rats. Samples were taken at 6 h, 12 h, 1 day, 3 days, 5 days, 7 days, 10 days, 14 days and 21 days post-injury, respectively (5 rats in each posttraumatic interval). 5 rats were employed as control. In the uninjured controls, Egr-1 positive staining was observed in the sarcoplasm and nuclei of normal myofibers. In wounded specimens, a small number of polymorphonuclear cells (PMNs), a number of mononuclear cells (MNCs), fibroblastic cells (FBCs) and regenerated multinucleated myotubes showed positive reaction for Egr-1 in contused zones. By morphometric analysis, an increase in Egr-1 expression was verified at inflammatory phase after contusion, which reached a peak in the regenerated phase overlapping with the fibrotic phase during skeletal muscle wound healing. The expression tendency was further confirmed by Western blotting assay. By immunofluorescent staining for co-localization, the Egr-1-positive MNCs and FBCs in wounds were identified as macrophages and myofibroblasts. The results demonstrate that the expression of Egr-1 is up-regulated and temporally distributed in certain cell types after trauma to skeletal muscles, which may be closely involved in inflammatory response, fibrotic repair and muscle regeneration during skeletal muscle wound healing.

Transcriptional Regulation of EGR1 by EGF and the ERK Signaling Pathway in Prostate Cancer Cells

The early growth response gene 1, EGR1, is an important transcriptional regulator and acts as the convergent point between a variety of extracellular stimuli and activation of target genes. Unlike other tumor types, prostate tumors express high levels of EGR1 relative to normal tissues. However, the mechanism of EGR1 regulation in prostate tumor cells is unknown. As EGR1 expression and epidermal growth factor (EGF) signaling are frequently upregulated in prostate tumors, we tested the hypothesis that EGF induces EGR1 expression in prostate cancer cells. Using RT-PCR to quantify EGR1 transcripts, we found that EGF induced EGR1 expression in a dose- and time-dependent manner and the ERK pathway inhibitor, PD98059, abrogated the EGF-mediated EGR1 response in LNCaP and PC3 cells. Analysis of the EGR1 promoter using deletion constructs identified an EGF-responsive region in the proximal promoter (-771 to -245 bp) containing 3 potential serum response element (SRE) sites. In vivo chromatin immunoprecipitation assays demonstrated that Elk-1 binding at the SRE sites of the EGR1 promoter was enhanced by EGF treatment in PC3 cells. Overexpression of Elk-1 was sufficient to activate the EGF-responsive region of EGR1 promoter in PC3 cells and, similarly, a dominant-negative Elk-1 suppressed EGR1 promoter activity. Taken together, these results demonstrate for the first time that EGR1 expression in PC3 cells is mediated through an EGF-ERK-Elk-1 signaling cascade.

Pioglitazone, a PPAR-γ activator, attenuates the severity of cerulein-induced acute pancreatitis by modulating early growth response-1 transcription factor

The purpose of this study was to test the hypothesis that activation of endogenous peroxisome proliferator-activated receptor (PPARγ) inhibits induction of early growth response factor-1 (Egr-1), which is rapidly induced in the pancreas following cerulein intraperitoneal injection. Acute pancreatitis was induced in mice by hourly intraperitoneal injection of cerulein. Pioglitazone was administered prophylactically and pancreatic inflammation was assessed. AR42J cells were stimulated with caerulein 10⁻⁸ M co-incubated in presence of different concentration of pioglitazone. The expression of PPARγ, Egr-1, and the target genes of Egr-1 were studied by real-time reverse transcriptase polymerase chain reaction (PCR), Western blot, and immunohistochemistry. In vitro, a PPAR-γ activator (pioglitazone) strikingly diminished Egr-1 mRNA and protein expression corresponding to Egr-1. In vivo, treatment with pioglitazone prior to the intraperitoneal injection of cerulein induction of Egr-1 and its target genes such as, monocyte chemotactic protein-1 (MCP-1) and macrophage inflammatory protein-1 (MIP-1). The inhibitory effect of pioglitazone on Egr-1 expression induced by cerulein was almost fully restored by GW9662. Activation of PPAR-γ suppressed the activation of Egr-1 and its inflammatory gene targets and provided potent protection against pancreas injury. These data suggest a new mechanism in which PPAR-γ activation may decrease tissue inflammation in response to a cerulein insult.

Critical role of Egr transcription factors in regulating insulin biosynthesis, blood glucose homeostasis, and islet size

Expression of early growth response protein (Egr)-1, a protein of the Egr family of zinc finger transcription factors, is stimulated in glucose-treated pancreatic β-cells and insulinoma cells. The purpose of this study was to elucidate the role of Egr transcription factors in pancreatic β-cells in vivo. To overcome the problem associated with redundancy of functions between Egr proteins, conditional transgenic mice were generated expressing a dominant-negative mutant of Egr-1 in pancreatic β-cells. The Egr-1 mutant interferes with DNA binding of all Egr proteins and thus impairs the biological functions of the entire Egr family. Expression of the Egr-1 mutant reduced expression of TGFβ and basic fibroblast growth factor, known target genes of Egr-1, whereas the expression of Egr-1, Egr-3, Ets-like gene-1 (Elk-1), and specificity protein-3 was not changed in the presence of the Egr-1 mutant. Expression of the homeobox protein pancreas duodenum homeobox-1, a major regulator of insulin biosynthesis, was reduced in islets expressing the Egr-1 mutant. Accordingly, insulin mRNA and protein levels were reduced by 75 or 25%, respectively, whereas expression of glucagon and somatostatin was not altered after expression of the Egr-1 mutant in β-cells. Glucose tolerance tests revealed that transgenic mice expressing the Egr-1 mutant in pancreatic β-cells displayed impaired glucose tolerance. In addition, increased caspase-3/7 activity was detected as a result of transgene expression, leading to a 20% decrease of the size of the islets. These results show that Egr proteins play an important role in controlling insulin biosynthesis, glucose homeostasis, and islet size of pancreatic β-cells in vivo.

Real-imaging cDNA-AFLP transcript profiling of pancreatic cancer patients: Egr-1 as a potential key regulator of muscle cachexia

Background

Cancer cachexia is a progressive wasting syndrome and the most prevalent characteristic of cancer in patients with advanced pancreatic adenocarcinoma. We hypothesize that genes expressed in wasted skeletal muscle of pancreatic cancer patients may determine the initiation and severity of cachexia syndrome.

Experimental design

We studied gene expression in skeletal muscle biopsies from pancreatic cancer patients with and without cachexia utilizing Real-Imaging cDNA-AFLP-based transcript profiling for genome-wide expression analysis.

Results

Our approach yielded 183 cachexia-associated genes. Ontology analysis revealed characteristic changes for a number of genes involved in muscle contraction, actin cytoskeleton rearrangement, protein degradation, tissue hypoxia, immediate early response and acute-phase response.

Conclusions

We demonstrate that Real-Imaging cDNA-AFLP analysis is a robust method for high-throughput gene expression studies of cancer cachexia syndrome in patients with pancreatic cancer. According to quantitative RT-PCR validation, the expression levels of genes encoding the acute-phase proteins α-antitrypsin and fibrinogen α and the immediate early response genes Egr-1 and IER-5 were significantly elevated in the skeletal muscle of wasted patients. By immunohistochemical and Western immunoblotting analysis it was shown, that Egr-1 expression is significantly increased in patients with cachexia and cancer. This provides new evidence that chronic activation of systemic inflammatory response might be a common and unifying factor of muscle cachexia.

Asymmetrical roles of zinc fingers in dynamic DNA-scanning process by the inducible transcription factor Egr-1

Egr-1 is an inducible transcription factor that recognizes 9-bp target DNA sites via three zinc finger domains and activates genes in response to cellular stimuli such as synaptic signals and vascular stresses. Using spectroscopic and computational approaches, we have studied structural, dynamic, and kinetic aspects of the DNA-scanning process in which Egr-1 is nonspecifically bound to DNA and perpetually changes its location on DNA. Our NMR data indicate that Egr-1 undergoes highly dynamic domain motions when scanning DNA. In particular, the zinc finger 1 (ZF1) of Egr-1 in the nonspecific complex is mainly dissociated from DNA and undergoes collective motions on a nanosecond timescale, whereas zinc fingers 2 and 3 (ZF2 and ZF3, respectively) are bound to DNA. This was totally unexpected because the previous crystallographic studies of the specific complex indicated that all of Egr-1's three zinc fingers are equally involved in binding to a target DNA site. Mutations that are expected to enhance ZF1's interactions with DNA and with ZF2 were found to reduce ZF1's domain motions in the nonspecific complex suggesting that these interactions dictate the dynamic behavior of ZF1. By experiment and computation, we have also investigated kinetics of Egr-1's translocation between two nonspecific DNA duplexes. Our data on the wild type and mutant proteins suggest that the domain dynamics facilitate Egr-1's intersegment transfer that involves transient bridging of two DNA sites. These results shed light on asymmetrical roles of the zinc finger domains for Egr-1 to scan DNA efficiently in the nucleus.

Suppression of transcription factor early growth response 1 reduces herpes simplex virus 1-induced corneal disease in mice

Herpes simplex virus 1 replication initiates angiogenesis and inflammation in the cornea. This can result in herpetic stromal keratitis (HSK), which is a leading cause of infection-induced corneal blindness. Host cellular factors mediate the progression of HSK, but little is known about these cellular factors and their mechanisms of action. We show here that the expression of the cellular transcription factor early growth response 1 (Egr-1) in HSV-1-infected mouse corneas was enhanced. Enhanced Egr-1 expression aggravated HSK by increasing viral replication and subsequent neovascularization with high levels of potent angiogenic factors, fibroblast growth factor 2, and vascular endothelial growth factor. Furthermore, Egr-1 deficiency due to a targeted disruption of the gene or knockdown of Egr-1 expression topically using a DNA-based enzyme significantly reduced HSK by decreasing both viral replication and the angiogenic response. The present study provides the first evidence that endogenous Egr-1 aggravates HSK and that blocking Egr-1 reduces corneal damage.

Egr1: a novel target for ameliorating acute allograft rejection in an experimental lung transplant model

OBJECTIVES

Acute allograft rejection is one of the significant complications occurring in lung transplant recipients. Early growth response-1 (Egr-1), zinc-finger-type transcription factor, is known as a master switch regulator of diverse chemical mediators. We used an orthotopic mouse model of left lung transplant to elucidate the function of Egr-1 in acute pulmonary rejection.

METHODS

Left lung grafts retrieved from C57BL/6 wild mice or C57BL/6 Egr-1-null mice were orthotopically transplanted into BALB/c mice; the lungs were harvested at day 1, 3, 5 or 7 after lung transplantation. The grade of acute rejection was histopathologically evaluated. The intragraft gene expression levels of Egr-1 and downstream target mediators were quantitatively measured by real-time polymerase chain reaction. Immunohistochemical analysis was used to determine the location and distribution of the Egr-1 protein in the pulmonary graft.

RESULTS

Severe acute rejection was observed in allografts from wild-type mice at 5 days after transplantation. Only minimal rejection was seen in the lung graft from Egr-1-null donor mice at 5 days after transplantation. Strong upregulation of Egr-1 mRNA transcripts was observed at day 1, which then decreased during the next 5 days. The mRNA of Egr-1 target mediators [interleukin-1-beta (IL-1β), monocyte chemotactic protein-1 (MCP-1) and plasminogen activator inhibitor-1] reached maximal levels at day 5. Egr-1-null allografts exhibited significantly lower expressions of IL-1β and MCP-1 mRNA (P < 0.05).

CONCLUSIONS

Our study showed that deletion of Egr-1 in lung allografts ameliorates severe acute rejection with the reduction of expression levels of chemical mediators, implying a new possible strategy for treating acute pulmonary allograft rejection.

The sterile immune response during hepatic ischemia/reperfusion

Hepatic ischemia and reperfusion elicits an immune response that lacks a microbial constituent yet poses a potentially lethal threat to the host. In this sterile setting, the immune system is alarmed by endogenous danger signals that are release by stressed and dying liver cells. The detection of these immunogenic messengers by sentinel leukocyte populations constitutes the proximal trigger for a self-perpetuating cycle of inflammation, in which consecutive waves of cytokines and chemokines orchestrate the influx of various leukocyte subsets that ultimately confer tissue destruction. This review focuses on the temporal organization of sterile hepatic inflammation, using surgery-induced trauma as a template disease state.

DNA damage response and inflammatory signaling limit the MLL-ENL-induced leukemogenesis in vivo

Activation of the MLL-ENL-ERtm oncogene initiates aberrant proliferation of myeloid progenitors. Here, we show induction of a fail-safe mechanism mediated by the DNA damage response (DDR) machinery that results in activation of the ATR/ATM-Chk1/Chk2-p53/p21(CIP1) checkpoint and cellular senescence at early stages of cellular transformation caused by a regulatable MLL-ENL-ERtm in mice. Furthermore, we identified the transcription program underlying this intrinsic anticancer barrier, and DDR-induced inflammatory regulators that fine-tune the signaling toward senescence, thereby modulating the fate of MLL-ENL-immortalized cells in a tissue-environment-dependent manner. Our results indicate that DDR is a rate-limiting event for acquisition of stem cell-like properties in MLL-ENL-ERtm-mediated transformation, as experimental inhibition of the barrier accelerated the transition to immature cell states and acute leukemia development.

The anticancer effects of resveratrol: modulation of transcription factors

Resveratrol (3, 4', 5-trihydroxystilbene), a naturally occurring phytoalexin readily available in the diet, is reported to possess both chemopreventive and chemotherapeutic activities in several cancers. However, despite the identification of numerous molecular targets, the underlying mechanisms involved in the anticancer activities of resveratrol are not completely understood. Resveratrol is postulated to function as a potential signaling pathway modulator and, as such, is demonstrated to affect a multitude of signal transduction pathways associated with tumorigenesis and/or carcinogenesis; it is likely that this collective activity, rather than just a single effect, may play an important role in the anticancer properties of resveratrol. Since transcription factors control the expression of many genes, the elucidation of molecular targets of resveratrol involved in transcriptional regulation is necessary to better understand how this dietary phytochemical affects chemopreventive and chemotherapeutic processes. As a result, investigators have increasingly searched for and examined possible targets of resveratrol. In this review, we summarize the current knowledge on molecular targets, specifically transcription factors, that contribute to the observed anticancer effects of resveratrol related to 1) inhibition of carcinogenic activation and induction of carcinogen detoxification, 2) induction of growth arrest and apoptosis, and 3) suppression of proinflammatory signaling pathways related to cancer progression.

Intracoronary delivery of DNAzymes targeting human EGR-1 reduces infarct size following myocardial ischaemia reperfusion

Despite improvements in treatment, myocardial infarction (MI) remains an important cause of morbidity and mortality. Inflammation arising from ischaemic and reperfusion injury is a key mechanism which underpins myocardial damage and impairment of cardiac function. Early growth response-1 (Egr-1) is an early immediate gene and a master regulator that has been implicated in the pathogenesis of ischaemia-reperfusion (IR) injury. This study sought to examine the effect of selective inhibition of Egr-1 using catalytic deoxyribonucleic acid molecules (DNAzymes, DZs) delivered via the clinically relevant coronary route in a large animal model of myocardial IR. It was hypothesized that Egr-1 inhibition with intracoronary DZ would reduce infarction size by modulating its downstream effector molecules. Egr-1 DZs inhibited the adherence of THP-1 monocytes to IL-1β-activated endothelial cells in vitro and retained its catalytic activity up to 225 min after in vivo administration. In a porcine model of myocardial IR (45 min ischaemia/3 h reperfusion), DZ was taken up in the cytoplasm and nuclei of cardiomyocytes and endothelial cells in the myocardium after intracoronary delivery. Egr-1 DZs reduced infarct size and improved cardiac functional recovery following intracoronary delivery at the initiation of IR in this large animal model of MI. This was associated with inhibition of pro-inflammatory Egr-1 and ICAM-1 expression, and the reduced expression of TNF-α, PAI-1, TF, and myocardial MPO activity in tissue derived from the border zone of the infarct. Taken together, these data suggest that strategies targeting Egr-1 via the intracoronary route after IR injury in pigs have potential therapeutic implications in human MI.

Loss of Arnt (Hif1β) in mouse epidermis triggers dermal angiogenesis, blood vessel dilation and clotting defects

Targeted ablation of Aryl hydrocarbon receptor nuclear translocator (Arnt) in the mouse epidermis results in severe abnormalities in dermal vasculature reminiscent of petechia induced in human skin by anticoagulants or certain genetic disorders. Lack of Arnt leads to downregulation of Egln3/Phd3 hydroxylase and concomitant hypoxia-independent stabilization of hypoxia-induced factor 1α (Hif1α) along with compensatory induction of Arnt2. Ectopic induction of Arnt2 results in its heterodimerization with stabilized Hif1α and is associated with activation of genes coding for secreted proteins implicated in control of angiogenesis, coagulation, vasodilation and blood vessel permeability such as S100a8/S100a9, S100a10, Serpine1, Defb3, Socs3, Cxcl1 and Thbd. Since ARNT and ARNT2 heterodimers with HIF1α are known to have different (yet overlapping) downstream targets our findings suggest that loss of Arnt in the epidermis activates an aberrant paracrine regulatory pathway responsible for dermal vascular phenotype in K14-Arnt KO mice. This assumption is supported by a significant decline of von Willebrand factor in dermal vasculature of these mice where Arnt level remains normal. Given the essential role of ARNT in the adaptive response to environmental stress and striking similarity between skin vascular phenotype in K14-Arnt KO mice and specific vascular features of tumour stroma and psoriatic skin, we believe that further characterization of Arnt-dependent epidermal-dermal signalling may provide insight into the role of macro- and micro-environmental factors in control of skin vasculature and in pathogenesis of environmentally modulated skin disorders.

CO metabolism, sensing, and signaling

CO is a colorless and odorless gas produced by the incomplete combustion of hydrocarbons, both of natural and anthropogenic origin. Several microorganisms, including aerobic and anaerobic bacteria and anaerobic archaea, use exogenous CO as a source of carbon and energy for growth. On the other hand, eukaryotic organisms use endogenous CO, produced during heme degradation, as a neurotransmitter and as a signal molecule. CO sensors act as signal transducers by coupling a "regulatory" heme-binding domain to a "functional" signal transmitter. Although high CO concentrations inhibit generally heme-protein actions, low CO levels can influence several signaling pathways, including those regulated by soluble guanylate cyclase and/or mitogen-activated protein kinases. This review summarizes recent insights into CO metabolism, sensing, and signaling.

Paradoxical exacerbation of neuronal injury in reperfused stroke despite improved blood flow and reduced inflammation in early growth response-1 gene-deleted mice

OBJECTIVES

Early growth response gene-1 (Egr-1) coordinates the rapid upregulation of diverse inflammatory and coagulation-related genes following ischemia/reperfusion. Genetic deletion of Egr-1 results in attenuated post-ischemic injury in diverse tissue systems. In the present study, we utilized a murine model of transient middle cerebral artery occlusion to probe the functional effects of Egr-1 deletion following cerebral ischemia/reperfusion.

METHODS

The time course of Egr-1 expression was established by Northern/Western blot analysis, and immunocytochemistry localized Egr-1 to specific cell populations. Flow cytometry was then employed to characterize the ischemic cellular infiltrate of both wild-type (+/+) and Egr-1-null (-/-) mice. Next, the functional effect of Egr-1 deletion was investigated in Egr-1-deficient mice and their wild-type littermates subjected to middle cerebral artery occlusion. Infarct volumes, neurological scores, and reperfusion cerebral blood flow were compared between cohorts.

RESULTS

Rapid upregulation of Egr-1 was observed in the ischemic hemisphere, and localized primarily to neurons and mononuclear cells. Egr-1 deletion led to a suppression of infiltrating neutrophils and activated microglia/macrophages (P<0.001). Additionally, although Egr-1 deletion enhanced post-ischemic cerebral blood flow, Egr-1-deficient mice suffered larger infarcts (P=0.01) and demonstrated a trend towards worse neurological scores (P=0.06) than wild-type controls.

DISCUSSION

Despite a reduction in the proportion of infiltrating inflammatory cells/activated microglia and improvement in post-ischemic reperfusion, Egr-1-deficient animals suffer larger infarcts in our model. Therefore, cerebral Egr-1 expression may function to protect neurons despite its adverse modulatory consequences for inflammation and thrombosis.

Loss of transcription factor early growth response gene 1 results in impaired endochondral bone repair

Transcription factors that play a role in ossification during development are expected to participate in postnatal fracture repair since the endochondral bone formation that occurs in embryos is recapitulated during fracture repair. However, inherent differences exist between bone development and fracture repair, including a sudden disruption of tissue integrity followed by an inflammatory response. This raises the possibility that repair-specific transcription factors participate in bone healing. Here, we assessed the consequence of loss of early growth response gene 1 (EGR-1) on endochondral bone healing because this transcription factor has been shown to modulate repair in vascularized tissues. Model fractures were created in ribs of wild type (wt) and EGR-1(-/-) mice. Differences in tissue morphology and composition between these two animal groups were followed over 28 post fracture days (PFDs). In wt mice, bone healing occurred in healing phases characteristic of endochondral bone repair. A similar healing sequence was observed in EGR-1(-/-) mice but was impaired by alterations. A persistent accumulation of fibrin between the disconnected bones was observed on PFD7 and remained pronounced in the callus on PFD14. Additionally, the PFD14 callus was abnormally enlarged and showed increased deposition of mineralized tissue. Cartilage ossification in the callus was associated with hyper-vascularity and -proliferation. Moreover, cell deposits located in proximity to the callus within skeletal muscle were detected on PFD14. Despite these impairments, repair in EGR-1(-/-) callus advanced on PFD28, suggesting EGR-1 is not essential for healing. Together, this study provides genetic evidence that EGR-1 is a pleiotropic regulator of endochondral fracture repair.

Diurnal regulation of the early growth response 1 (Egr-1) protein expression by hepatocyte nuclear factor 4alpha (HNF4alpha) and small heterodimer partner (SHP) cross-talk in liver fibrosis

Early growth response 1 (Egr-1) protein is a critical regulator of genes contributing to liver fibrosis; however, little is known about the upstream transcriptional factors that control its expression. Here we show that Egr-1 expression is tightly regulated by nuclear receptor signaling. Hepatocyte nuclear factor 4α (HNF4α) activated the Egr-1 promoter through three DR1 response elements as identified by trans-activation assays. Deletion of these response elements or knockdown of HNF4α using siRNA largely abrogated Egr-1 promoter activation. HNF4α activity, as well as its enrichment on the Egr-1 promoter, were markedly repressed by small heterodimer partner (SHP) co-expression. Egr-1 mRNA and protein were transiently induced by HNF4α. On the contrary, HNF4α siRNA reduced Egr-1 expression at both the mRNA and protein levels, and overexpression of SHP reversed these effects. Conversely, knockdown of SHP by siRNA elevated Egr-1 protein. Interestingly, Egr-1 mRNA exhibited diurnal fluctuation, which was synchronized to the cyclic expression of SHP and HNF4α after cells were released from serum shock. Unexpectedly, the levels of Egr-1 mRNA and protein were highly up-regulated in Hnf4α(-/-) mice. Both HNF4α and Egr-1 expression were dramatically increased in SHP(-/-) mice with bile duct ligation and in human cirrhotic livers, which was inversely correlated with diminished SHP expression. In conclusion, our study revealed control network for Egr-1 expression through a feedback loop between SHP and HNF4α.

Venous valvular stasis-associated hypoxia and thrombosis: what is the link?

This review focuses on the role of the venous valves in the genesis of thrombus formation in venous thromboembolic disease (VTE). Clinical VTE and the evidence for the valvular origin of venous thrombosis are reviewed. Virchow's triad is then used as a framework for discussion to approach the question posed regarding the link between venous valvular stasis-associated hypoxia and thrombosis. Thus, the effects of blood flow stasis, hypercoagulability of blood, and the characteristics of the vessel wall within the venous valvular sinus are assessed in turn.

Resveratrol-induced apoptosis is mediated by early growth response-1, Krüppel-like factor 4, and activating transcription factor 3

Resveratrol, a dietary phytoalexin readily available in the diet, is reported to possess antitumorigenic properties in several cancers, including colorectal. However, the underlying mechanism(s) involved is not completely understood. In the present study, we investigated the effect of resveratrol treatment on gene modulation in human colorectal cancer cells and identified activating transcription factor 3 (ATF3) as the most highly induced gene after treatment. We confirmed that resveratrol upregulates ATF3 expression, both at the mRNA and protein level, and showed resveratrol involvement in ATF3 transcriptional regulation. Analysis of the ATF3 promoter revealed the importance of early growth response-1 (Egr-1; located at -245 to -236) and Krüppel-like factor 4 (KLF4; located at -178 to -174) putative binding sites in resveratrol-mediated ATF3 transactivation. Specificity of these sites to the Egr-1 and KLF4 protein was confirmed by electrophoretic mobility shift and chromatin immunoprecipitation assays. Resveratrol increased Egr-1 and KLF4 expression, which preceded ATF3 expression, and further suggests Egr-1 and KLF4 involvement in resveratrol-mediated activity. We provide evidence for Egr-1 and KLF4 interaction in the presence of resveratrol, which may facilitate ATF3 transcriptional regulation by this compound. Furthermore, we demonstrate that induction of apoptosis by resveratrol is mediated, in part, by increased ATF3 expression. Taken together, these results provide a novel mechanism by which resveratrol induces ATF3 expression and represent an additional explanation of how resveratrol exerts its antitumorigenic effects in human colorectal cancer cells.

Early growth response transcription factors: key mediators of fibrosis and novel targets for anti-fibrotic therapy

Fibrosis is a deregulated and ultimately defective form of tissue repair that underlies a large number of chronic human diseases, as well as obesity and aging. The pathogenesis of fibrosis involves multiple cell types and extracellular signals, of which transforming growth factor-ß (TGF-ß) is pre-eminent. The prevalence of fibrosis is rising worldwide, and to date no agents has shown clinical efficacy in the attenuating or reversing the process. Recent studies implicate the immediate-early response transcription factor Egr-1 in the pathogenesis of fibrosis. Egr-1 couples acute changes in the cellular environment to sustained alterations in gene expression, and mediates a broad spectrum of biological responses to injury and stress. In contrast to other ligand-activated transcription factors such as NF-κB, c-jun and Smad2/3 that undergo post-translational modification such as phosphorylation and nuclear translocation, Egr-1 activity is regulated via its biosynthesis. Aberrant Egr-1 expression or activity is implicated in cancer, inflammation, atherosclerosis, and ischemic injury and recent studies now indicate an important role for Egr-1 in TGF-ß-dependent profibrotic responses. Fibrosis in various animal models and human diseases such as scleroderma (SSc) and idiopathic pulmonary fibrosis (IPF) is accompanied by aberrant Egr-1 expression. Moreover Egr-1 appears to be required for physiologic and pathological connective tissue remodeling, and Egr-1-null mice are protected from fibrosis. As a novel profibrotic mediator, Egr-1 thus appears to be a promising potential target for the development of anti-fibrotic therapies.

Early growth response 1 (Egr-1) regulates phosphorylation of microtubule-associated protein tau in mammalian brain

In the normal brain, tau protein is phosphorylated at a number of proline- and non-proline directed sites, which reduce tau microtubule binding and thus regulate microtubule dynamics. In Alzheimer disease (AD), tau is abnormally hyperphosphorylated, leading to neurofibrillary tangle formation and microtubule disruption, suggesting a loss of regulatory mechanisms controlling tau phosphorylation. Early growth response 1 (Egr-1) is a transcription factor that is significantly up-regulated in AD brain. The pathological significance of this up-regulation is not known. In this study, we found that lentivirus-mediated overexpression of Egr-1 in rat brain hippocampus and primary neurons in culture activates proline-directed kinase Cdk5, inactivates PP1, promotes tau phosphorylation at both proline-directed Ser(396/404) and non-proline-directed Ser(262) sites, and destabilizes microtubules. Furthermore, in Egr-1(-/-) mouse brain, Cdk5 activity was decreased, PP1 activity was increased, and tau phosphorylation was reduced at both proline-directed and non-proline-directed sites. By using nerve growth factor-exposed PC12 cells, we determined that Egr-1 activates Cdk5 to promote phosphorylation of tau and inactivates PP1 via phosphorylation. When Cdk5 was inhibited, tau phosphorylation at both proline- and non-proline directed sites and PP1 phosphorylation were blocked, indicating that Egr-1 acts through Cdk5. By using an in vitro kinase assay and HEK-293 cells transfected with tau, PP1, and Cdk5, we found that Cdk5 phosphorylates Ser(396/404) directly. In addition, by phosphorylating and inactivating PP1, Cdk5 promotes tau phosphorylation at Ser(262) indirectly. Our results indicate that Egr-1 is an in vivo regulator of tau phosphorylation and suggest that in AD brain increased levels of Egr-1 aberrantly activate an Egr-1/Cdk5/PP1 pathway, leading to accumulation of hyperphosphorylated tau, thus destabilizing the microtubule cytoskeleton.

6-Mercaptopurine reverses experimental vasospasm and alleviates the production of endothelins in NO-independent mechanism-a laboratory study

INTRODUCTION

Increased endothelin-1 (ET-1) production and diminished nitric oxide synthase (NOS) bioavailability has been observed in aneurysmal subarachnoid hemorrhage (SAH). The authors previously found that 6-mercaptopurine (6-mp) is effective in preventing and reversing arterial narrowing in a rodent SAH model. This present study is of interest to examine the effect of 6-mp on ET-1/endothelial nitric oxide synthase (eNOS) in this animal model.

METHODS

A rodent double hemorrhage SAH model was employed. Animals were randomly assigned to six groups (sham, SAH only, vehicle, 0.5, 1.0 and 2 mg kg(-1) day(-1) 6-mp treatment). Monoclonal CD45 immunostaining was utilized to evaluate monocytes and microglia. The level of pro-inflammatory cytokines, such as IL-1, IL-6 and TNF-α(RT-PCR), and ET-1 (ELISA) was measured. The basilar arteries (BAs) were harvested and sliced, and their cross-sectional areas were determined. Radiolabeled NOS assay kit was applied to detect eNOS.

RESULTS

Morphologically, convolution of internal elastic lamina, endothelial cells distortion, and necrotic smooth muscle were prevalently present in the basilar artery of SAH groups, which was absent in the 1 and 2 mg kg(-1) day(-1) 6-mp plus SAH group or the healthy controls. Significant vasospasm was noted in the vehicle group (lumen patency, 54.6%, p ≤ 0.01 compared with the sham group), but it was less prominent in the 2 mg kg(-1) day(-1) 6-mp treatment group (lumen patency, 87.6%, p < 0.05). In addition, administration with 2 mg kg(-1) day(-1) 6-mp reduced cytokine levels by 11%, 47%, and 34% for IL-1, IL-6, and TNF-α, respectively, and increased ET-1 levels were found in all the animals subject to SAH (SAH only, SAH plus vehicle, SAH plus 0.5 and 1.0 mg kg(-1) day(-1) 6-mp) except in the 2 mg kg(-1) day(-1) 6-mp SAH group, when compared with the healthy controls (no SAH). Meanwhile, treatment with 6-mp did not induce the levels of expressed eNOS in BAs in the 6-mp groups (0.5, 1.0, and 2 mg kg(-1) day(-1) 6-mp plus SAH) when compared with that in the SAH groups (p > 0.1).

CONCLUSION

In summary, treatment with 6-mp decreased the release of pro-inflammatory cytokines and diminished experimental vasospasm. This study offered first evidence that 6-mp dose-dependently reduces the level of ET-1 in a NO-independent mechanism, which corresponds to its antivasospastic effect in the condition of chronic vasospasm.

Oxygen homeostasis

Metazoan life is dependent upon the utilization of O(2) for essential metabolic processes and oxygen homeostasis is an organizing principle for understanding metazoan evolution, ontology, physiology, and pathology. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that is expressed by all metazoan species and functions as a master regulator of oxygen homeostasis. Recent studies have elucidated complex mechanisms by which HIF-1 activity is regulated and by which HIF-1 regulates gene expression, with profound consequences for prenatal development, postnatal physiology, and disease pathogenesis.

Gene expression associated with an enriched environment after transient focal ischemia

Recent studies have demonstrated that animals housed in an enriched environment after an experimental stroke obtained a better functional outcome than those housed in a standard cage; however, little is known about the gene expression associated with this functional recovery. The purpose of the present study was to elucidate the expression of genes in an enriched environment after experimental stroke in the ischemic and non-ischemic sides of the cortices. Transient focal brain ischemia was produced by the occlusion of the right middle cerebral artery (t-MCAO) in male Sprague-Dawley rats. The rats were divided into 3 groups: ischemic rats housed in the enriched environment, ischemic rats housed in standard cages, and non-ischemic rats in standard cages. Four weeks after t-MCAO, the rats were sacrificed and gene expression was examined. Motor function was improved in ischemic rats housed in the enriched environment compared with those in standard cages; however, there were no significant differences in the size of the infarct area between the ischemic rats in the enriched environment and those in standard cages. Decreases in the expression of Egr-1, -2, and BDNF mRNA in both sides of the cortices were detected in rats housed in the enriched environment, indicating that gene expression was altered throughout the brain at 4 weeks after transient focal ischemia.

Bile acids induce inflammatory genes in hepatocytes: a novel mechanism of inflammation during obstructive cholestasis

Inflammation contributes to liver injury during cholestasis. The mechanism by which cholestasis initiates an inflammatory response in the liver, however, is not known. Two hypotheses were investigated in the present studies. First, activation of Toll-like receptor 4 (TLR4), either by bacterial lipopolysaccharide or by damage-associated molecular pattern molecules released from dead hepatocytes, triggers an inflammatory response. Second, bile acids act as inflammagens, and directly activate signaling pathways in hepatocytes that stimulate production of proinflammatory mediators. Liver inflammation was not affected in lipopolysaccharide-resistant C3H/HeJ mice after bile duct ligation, indicating that Toll-like receptor 4 is not required for initiation of inflammation. Treatment of hepatocytes with bile acids did not directly cause cell toxicity but increased the expression of numerous proinflammatory mediators, including cytokines, chemokines, adhesion molecules, and other proteins that influence immune cell levels and function. Up-regulation of several of these genes in hepatocytes and in the liver after bile duct ligation required early growth response factor-1, but not farnesoid X receptor. In addition, early growth response factor-1 was up-regulated in the livers of patients with cholestasis and correlated with levels of inflammatory mediators. These data demonstrate that Toll-like receptor 4 is not required for the initiation of acute inflammation during cholestasis. In contrast, bile acids directly activate a signaling network in hepatocytes that promotes hepatic inflammation during cholestasis.

Activation of peroxisome-proliferator-activated receptors α and γ mediates remote ischemic preconditioning against myocardial infarction in vivo

Remote ischemic preconditioning (remote IPC) elicits a protective cardiac phenotype against myocardial ischemic injury. The remote stimulus has been hypothesized to act on major signaling pathways; however, its molecular targets remain largely undefined. We hypothesized that remote IPC exerts its effects by activating the peroxisome-proliferator-activated receptors (PPARs) α and γ, which have been previously implicated in cardioprotective signaling. Male New Zealand white rabbits (n = 78) were subjected to a 30-min coronary artery occlusion followed by three hours of reperfusion. Three cycles of remote IPC consisting of 10-min renal ischemia/reperfusion were performed. The animals either received the PPARα-antagonist GW6471 or the PPARγ-antagonist GW9662 alone or combined with remote IPC. Infarct size was determined gravimetrically. Tissue levels of 15d-prostaglandin J(2) (15d-PGJ(2)), as well as the PPAR DNA binding were measured using specific assays. Reverse transcriptase polymerase chain reaction was used to analyze changes in endothelial nitric oxide synthase or inducible nitric oxide synthase (iNOS) mRNA expression in relative quantity (RQ). Data are mean ± SD. As a result, remote IPC significantly reduced the myocardial infarct size (42.2 ± 4.9%* versus 61 ± 1.9%), accompanied by an increased PPAR DNA-binding (189.6 ± 19.8RLU* versus 44.4 ± 9RLU), increased iNOS expression (3.5 ± 1RQ* versus 1RQ), as well as 15d-PGJ(2) levels (179.7 ± 7.9 pg/mL* versus 127.9 ± 7.6 pg/mL). The protective response elicited by remote IPC, as well as the accompanying molecular changes were abolished by inhibiting PPARα (56.8 ± 4.7%; 61.1 ± 14.2RLU; and 1.91 ± 0.96RQ, respectively) or PPARγ (57.4 ± 3.3%; 52.7 ± 16.9RLU; and 1.54 ± 0.25RQ, respectively). (*Significantly different from control P < 0.05). In conclusion, the obtained results indicate that both PPARα and PPARγ play an essential role in remote IPC against myocardial infarction, impinging on the transcriptional control of iNOS expression.

Molecular mechanisms underlying hypothermia-induced neuroprotection

Stroke is a dynamic event in the brain involving heterogeneous cells. There is now compelling clinical evidence that prolonged, moderate cerebral hypothermia initiated within a few hours after severe ischemia can reduce subsequent neuronal death and improve behavioral recovery. The neuroprotective role of hypothermia is also well established in experimental animals. However, the mechanism of hypothermic neuroprotection remains unclear, although, presumably involves the ability of hypothermia to suppress a broad range of injurious factors. In this paper, we addressed this issue by utilizing comprehensive gene and protein expression analyses of ischemic rat brains. To predict precise target molecules, we took advantage of the therapeutic time window and duration of hypothermia necessary to exert neuroprotective effects. We proposed that hypothermia contributes to protect neuroinflammation, and identified candidate molecules such as MIP-3α and Hsp70 that warrant further investigation as targets for therapeutic drugs acting as “hypothermia-like neuroprotectants.”

Hypoxia-regulated angiogenic inhibitors

The regulation of angiogenesis by hypoxia is an essential homeostatic mechanism that depends on a precise balance between positive and negative angiogenic regulatory molecules. Proangiogenic factors are well characterized; however, several in vivo and in vitro studies indicate that there are feedback mechanisms in place to inhibit angiogenesis during hypoxia. Understanding the signaling pathways leading to the negative feedback of angiogenesis will undoubtedly provide important tools to develop novel therapeutic strategies not only to enhance the angiogenic response in coronary artery disease but also to hinder deregulated angiogenesis in tumorigenesis.

6-Mercaptopurine exerts an immunomodulatory and neuroprotective effect on permanent focal cerebral occlusion in rats

BACKGROUND

A bursting cascade of inflammation imposes progressive neurological deterioration after experimental stroke has been demonstrated. In our study, 6-mercaptopurine (6-mp) has been successful in alleviating cerebral infarct in a rodent permanent middle cerebral artery occlusion (pMCAO) model. The present study was aimed to examine the effect of 6-mp on cytokine levels in experimental stroke.

METHODS

The rodent pMCAO model was employed. A dose of 2 mg/kg 6-mp or vehicle (0.1 mol/L PBS) was administered intraperitoneally 30 min after the induction of pMCAO. Neurological score, serum, and cerebrospinal fluid (CSF) cytokines such as IL-1beta, IL-6, and TNF-alpha and infarct volume were determined 48 h after pMCAO.

RESULTS

Cerebral infarction volume was significantly decreased in animals treated with 6-mp (74.3%, p < 0.01), and the ratio of tissue edema was also decreased in 6-mp-treated groups (71%). Animals receiving 6-mp thus showed a significant decrease in IL-1 and TNF-alpha (18/43% and 48/64% in CSF/serum, respectively) when compared with the pMCAO groups (p < 0.01).

CONCLUSION

This study demonstrates that 6-mp interposes the production of IL-1 and TNF-alpha in CSF and serum, attenuates ischemic brain injury, and thus alleviates neurological deficits in the pMCAO animals. These findings also offer first evidence that 6-mp may attenuate TNF-alpha-related neuron apoptosis and also support the notion that 6-mp and other anti-inflammatory agents could potentially have therapeutic uses in cases of cerebral infarct.

The protective effects of Egr-1 antisense oligodeoxyribonucleotide on cardiac microvascular endothelial injury induced by hypoxia-reoxygenation

Early growth response 1 (Egr-1) over-expression has been demonstrated in myocardial ischemia-reperfusion injury, which is closely associated with endothelial dysfunction. In the present study we investigated the expression of Egr-1 on cultured cardiac microvascular endothelial cells (CMECs) to help define the mechanism of myocardial ischemia-reperfusion injury. A model of cultured CMECs exposed to hypoxia-reoxygenation was developed in which synthesized Egr-1 sense and antisense oligodeoxyribonucleotide were transfected into the cells. The expression of Egr-1 was examined by Western blot analysis. Lactate dehydrogenase, malondialdehyde, superoxide dismutase, tumor necrosis factor alpha, and intercellular adhesion molecule 1 were measured after hypoxia-reoxygenation to assess cell function and injury. Cell morphology, cell viability, and neutrophil adhesion to the CMECs were measured to assess the degree of injury and inflammation. Only cells transfected with Egr-1 antisense oligodeoxyribonucleotide showed a significant reduction in Egr-1 protein expression following hypoxia-reoxygenation. Consistent with the down-regulation of Egr-1 expression, other forms of cell injury were significantly reduced in this group of cells, as evidenced by less alteration in cell morphology, a decrease in expression of tumor necrosis factor alpha and intercellular adhesion molecule 1, improved cell survival, and reduced neutrophil adhesion.

Advanced glycation end product (AGE)-receptor for AGE (RAGE) signaling and up-regulation of Egr-1 in hypoxic macrophages

Receptor for advanced glycation end product (RAGE)-dependent signaling has been implicated in ischemia/reperfusion injury in the heart, lung, liver, and brain. Because macrophages contribute to vascular perturbation and tissue injury in hypoxic settings, we tested the hypothesis that RAGE regulates early growth response-1 (Egr-1) expression in hypoxia-exposed macrophages. Molecular analysis, including silencing of RAGE, or blockade of RAGE with sRAGE (the extracellular ligand-binding domain of RAGE), anti-RAGE IgG, or anti-AGE IgG in THP-1 cells, and genetic deletion of RAGE in peritoneal macrophages, revealed that hypoxia-induced up-regulation of Egr-1 is mediated by RAGE signaling. In addition, the observation of increased cellular release of RAGE ligand AGEs in hypoxic THP-1 cells suggests that recruitment of RAGE in hypoxia is stimulated by rapid production of RAGE ligands in this setting. Finally, we show that mDia-1, previously shown to interact with the RAGE cytoplasmic domain, is essential for hypoxia-stimulated regulation of Egr-1, at least in part through protein kinase C betaII, ERK1/2, and c-Jun NH(2)-terminal kinase signaling triggered by RAGE ligands. Our findings highlight a novel mechanism by which an extracellular signal initiated by RAGE ligand AGEs regulates Egr-1 in a manner requiring mDia-1.

Placenta growth factor-induced early growth response 1 (Egr-1) regulates hypoxia-inducible factor-1alpha (HIF-1alpha) in endothelial cells

Leukotrienes, the lipid inflammatory products derived from arachidonic acid, are involved in the pathogenesis of respiratory and cardiovascular diseases and reactive airway disease in sickle cell disease. Placenta growth factor (PlGF), elaborated from erythroid cells, increased the mRNA expression of 5-lipoxygenase and 5-lipoxygenase-activating protein (FLAP) in human pulmonary microvascular endothelial cells. PlGF-induced both promoter activity and mRNA expression of hypoxia-inducible factor-1alpha (HIF-1alpha), which was abrogated by early growth response-1 (EGR-1) small interfering RNA. PlGF showed a temporal reciprocal relationship in the mRNA levels of EGR-1 and NAB2, the latter a repressor of Egr-1. Moreover, Nab2, but not mutant Nab2, significantly reduced promoter activity and mRNA expression of HIF-1alpha and also reduced expression of the HIF-1alpha target gene FLAP. Furthermore, overexpression of Egr-1 led to increased promoter activities for both HIF-1alpha and FLAP in the absence of PlGF. Additionally, the Egr-1-mediated induction of HIF-1alpha and FLAP promoters was reduced to basal levels by EGR-1 small interfering RNA. The binding of Egr-1 to HIF-1alpha promoter was corroborated by electrophoretic mobility shift assay and chromatin immunoprecipitation assay, which showed increased Egr-1 binding to the HIF-1alpha promoter in response to PlGF stimulation. These studies provide a novel mechanism for PlGF-mediated regulation of HIF-1alpha via Egr-1, which results in increased FLAP expression. This study provides a new therapeutic target, namely Egr-1, for attenuation of elevated leukotriene levels in patients with sickle cell disease and other inflammatory diseases.

Hepatic fibrosis is enhanced and accompanied by robust oval cell activation after chronic carbon tetrachloride administration to Egr-1-deficient mice

The transcription factor early growth response (Egr)-1 regulates the expression of genes required for execution of the wound healing response. Multiple cycles of injury, coupled to incomplete wound healing, lead to fibrosis. Therefore, we hypothesized that Egr-1 is required for the development of hepatic fibrosis. To test this hypothesis, we exposed wild-type and egr-1(-/-) mice to acute or chronic carbon tetrachloride (CCl(4)). Acute CCl(4) exposure established a profibrotic milieu in the liver, including activation of hepatic stellate cells as well as expression of type 1 collagen genes and tissue inhibitor of matrix metalloproteinase 1 in both wild-type and egr-1(-/-) mice. This response was exacerbated in egr-1(-/-) mice. After chronic CCl(4) exposure, hepatic fibrosis was established in both genotypes; however, the fibrotic response was profoundly worsened in Egr-1-deficient mice. Importantly, enhanced fibrosis in egr-1(-/-) mice was accompanied by a robust activation of the oval cell response, suggesting more severe liver injury and/or reduced hepatocyte proliferation when compared with wild-type mice. Hepatic expression of genes indicative of oval cell activation, as well as the number of cells expressing A6, a mouse oval cell marker, was greater in egr-1(-/-) mice. Taken together, these data reveal novel roles for Egr-1 as a negative regulator of both CCl(4)-induced hepatic fibrosis and the oval cell response.

Response network analysis of differential gene expression in human epithelial lung cells during avian influenza infections

BACKGROUND

The recent emergence of the H5N1 influenza virus from avian reservoirs has raised concern about future influenza strains of high virulence emerging that could easily infect humans. We analyzed differential gene expression of lung epithelial cells to compare the response to H5N1 infection with a more benign infection with Respiratory Syncytial Virus (RSV). These gene expression data are then used as seeds to find important nodes by using a novel combination of the Gene Ontology database and the Human Network of gene interactions. Additional analysis of the data is conducted by training support vector machines (SVM) with the data and examining the orientations of the optimal hyperplanes generated.

RESULTS

Analysis of gene clustering in the Gene Ontology shows no significant clustering of genes unique to H5N1 response at 8 hours post infection. At 24 hours post infection, however, a number of significant gene clusters are found for nodes representing "immune response" and "response to virus" terms. There were no significant clusters of genes in the Gene Ontology for the control (Mock) or RSV experiments that were unique relative to the H5N1 response. The genes found to be most important in distinguishing H5N1 infected cells from the controls using SVM showed a large degree of overlap with the list of significantly regulated genes. However, though none of these genes were members of the GO clusters found to be significant.

CONCLUSIONS

Characteristics of H5N1 infection compared to RSV infection show several immune response factors that are specific for each of these infections. These include faster timescales within the cell as well as a more focused activation of immunity factors. Many of the genes that are found to be significantly expressed in H5N1 response relative to the control experiments are not found to cluster significantly in the Gene Ontology. These genes are, however, often closely linked to the clustered genes through the Human Network. This may suggest the need for more diverse annotations of these genes and verification of their action in immune response.

Gene expression profile in flow-associated pulmonary arterial hypertension with neointimal lesions

Pulmonary arterial hypertension (PAH) is a pulmonary angioproliferative disease with high morbidity and mortality, characterized by a typical pattern of pulmonary vascular remodeling including neointimal lesions. In congenital heart disease, increased pulmonary blood flow has appeared to be a key mediator in the development of these characteristic lesions, but the molecular mechanisms underlying the pulmonary vascular lesions are largely unknown. We employed a rat model of flow-associated PAH, which induced specific pulmonary neointimal lesions. We identified gene expression profiles in rats specifically related to the addition of increased pulmonary blood flow to monocrotaline and the associated occurrence of neointimal lesions. Increased pulmonary blood flow induced the expression of the transcription factors activating transcription factor-3 (ATF3) and early growth response factor-1 (EGR-1), for which presence was confirmed in neointimal lesions. Monocrotaline alone induced increased numbers of activated mast cells and their products. We further identified molecular pathways that may be involved in treatment with the prostacyclin analog iloprost, a vasoactive compound with clinically beneficial effects in patients with PAH, which were similar to pathways described in samples from patient studies. These pathways, associated with the development of angioproliferative lesions as well as with the response to therapy in PAH, may provide new therapeutic targets.

Egr-1-A Ca(2+)-regulated transcription factor

The biosynthesis of the zinc finger transcription factor Egr-1 is stimulated by many extracellular signaling molecules including hormones, neurotransmitters, growth and differentiation factors. The Egr-1 gene represents a convergence point for many intracellular signaling cascades. An increase of the intracellular Ca(2+) concentration, by activating ionotropic or Galpha(q/11)-coupled receptors or voltage-gated L-type Ca(2+) channels, is often the prerequisite for enhanced Egr-1 gene transcription. This increase has been observed following stimulation with extracellular signaling molecules including ATP, glutamate, thrombin, carbachol, gonadotropin-releasing hormone, or glucose. Egr-1 is thus a Ca(2+) regulated transcription factor - similar to CREB, NFAT, NF-kappaB and others. This review also discusses the importance of the cytoplasmic and nuclear Ca(2+) concentration in transcriptional regulation of the Egr-1 gene.

Cascades of transcription regulation during liver regeneration

An increasing demand for new strategies in cancer prevention and regenerative medicine requires a better understanding of molecular mechanisms that control cell proliferation in tissue-specific manner. Regenerating liver is a unique model allowing use of biochemical, genetic, and engineering tools to uncover molecular mechanisms and improve treatment of hepatic cancers, liver failure, and fibrotic disease. Molecular mechanisms of liver regeneration involve extra- and intracellular factors to activate transcription of genes normally silenced in quiescent liver. While many upstream signaling pathways of the regenerating liver have been extensively studied, our knowledge of the downstream effectors, transcription factors (TFs), remains limited. This review describes consecutive engagement of pre-existing and de novo synthesized TFs, as cascades that regulate expression of growth-related and metabolic genes during liver regeneration after partial hepatectomy in mice. Several previously recognized regulators of regenerating liver are described in the light of recently identified co-activator and co-repressor complexes that interact with primary DNA-binding TFs. Published results of gene expression and chromatin immunoprecipitation analyses, as well as studies of transgenic mouse models, are used to emphasize new potential regulators of transcription during liver regeneration. Finally, a more detailed description of newly identified transcriptional regulators of liver regeneration illustrates the tightly regulated balance of proliferative and metabolic responses to partial hepatectomy.

Venous thromboembolism in malignant gliomas

Malignant gliomas are associated with a very high risk of venous thromboembolism (VTE). While many clinical risk factors have previously been described in brain tumor patients, the risk of VTE associated with newer anti-angiogenic therapies such as bevacizumab in these patients remains unclear. When VTE occurs in this patient population, concern regarding the potential for intracranial hemorrhage complicates management decisions regarding anticoagulation, and these patients have a worse prognosis than their VTE-free counterparts. Risk stratification models identifying patients at high risk of developing VTE along with predictive plasma biomarkers may guide the selection of eligible patients for primary prevention with pharmacologic thromboprophylaxis. Recent studies exploring disordered coagulation, such as increased expression of tissue factor (TF), and tumorigenic molecular signaling may help to explain the increased risk of VTE in patients with malignant gliomas.

Airway injury from initiating ventilation in preterm sheep

Premature infants exposed to ventilation are at risk of developing bronchopulmonary dysplasia and persistent lung disease in childhood. We report where injury occurred within the lung after brief ventilation at birth. Preterm sheep (129 d gestation) were ventilated with an escalating tidal volume to 15 mL/kg by 15 min to injure the lungs, with the placental circulation intact (fetal) or after delivery (newborn). Fetal lambs were returned to the uterus for 2 h 45 min, whereas newborn lambs were maintained with gentle ventilatory support for the same period. The control group was not ventilated. Bronchoalveolar lavage fluid (BALF) and lung tissue were analyzed. In both fetal and newborn lambs, ventilation caused bronchial epithelial disruption in medium-sized airways. Early growth response protein 1 (Egr-1), monocyte chemotactic protein 1 (MCP-1), IL-6, and IL-1beta mRNA increased in the lung tissue from fetal and newborn lambs. Egr-1, MCP-1, and IL-6 mRNA were induced in mesenchymal cells surrounding small airways, whereas IL-1beta mRNA localized to the epithelium of medium/small airways. Ventilation caused loss of heat shock protein 70 (HSP70) mRNA from the bronchial epithelium, but induced mRNA in the smooth muscle surrounding large airways. HSP70 protein decreased in the lung tissue and increased in BALF with ventilation. Initiation of ventilation induced a stress response and inflammatory cytokines in small and medium-sized airways.

N-n-butyl haloperidol iodide protects cardiac microvascular endothelial cells from hypoxia/reoxygenation injury by down-regulating Egr-1 expression

AIMS

Our previous studies have shown that N-n-butyl haloperidol iodide (F2) can antagonize myocardial ischemia/reperfusion (I/R) injury by down-regulating the early growth response (Egr)-1 expression, but the molecular mechanisms are not well understood. Because there is evidence implicating myocardial I/R injury is closely associated with endothelial dysfunction. The present study is to test the hypothesis that the protective effects of F2 on myocardial I/R injury is related closely with down-regulating Egr-1 expression on cardiac microvascular endothelial cells (CMECs).

METHODS

A model of cultured CMECs exposed to hypoxia/reoxygenation (H/R) was developed. With antisense Egr-1 oligodeoxyribonucleotide (ODN), the relationship between Egr-1 expression and endothelial H/R injury was investigated. Egr-1 mRNA and protein expression were examined by real-time fluorescent quantitative PCR, immunocytochemical staining and Western-blot analysis. Lactate dehydrogenase (LDH), malondialdehyde (MDA), superoxide dismutase (SOD), intercellular adhesion molecule-1 (ICAM-1), adherence of neutrophil and platelets, and cell viability were measured after H/R to evaluate the degree of endothelial injury.

RESULTS

Pretreatment with antisense Egr-1 ODN significantly reduced Egr-1 protein expression and attenuated injury of CMECs. Consistent with down-regulation of Egr-1 expression by F2, inflammation and other damage were significantly reduced as evidenced by a decrease of ICAM-1 expression, reduction of neutrophil and platelets adherence, increase in SOD, and decreases in MDA and LDH levels, resulting in the rise of cell viability.

CONCLUSIONS

We demonstrate a protective effect of F2 in CMECs against H/R injury by down-regulating Egr-1 expression, which might be play a vital role in the pathogenesis of myocardial I/R injury.

Vascular endothelial growth factor activation of endothelial cells is mediated by early growth response-3

Endothelial cell activation and dysfunction underlie many vascular disorders, including atherosclerosis, tumor growth, and sepsis. Endothelial cell activation, in turn, is mediated primarily at the level of gene transcription. Here, we show that in response to several activation agonists, including vascular endothelial growth factor (VEGF), tumor necrosis factor-alpha, and thrombin, endothelial cells demonstrate rapid and profound induction of the early growth response (Egr) genes egr-1 and egr-3. In VEGF-treated endothelial cells, induction of Egr-3 was far greater and more prolonged compared with Egr-1. VEGF-mediated stimulation of Egr-3 involved the inducible binding of NFATc, serum response factor, and CREB to their respective consensus motifs in the upstream promoter region of Egr-3. Knockdown of Egr-3 markedly impaired VEGF-mediated proliferation, migration, and tube formation of endothelial cells and blocked VEGF-induced monocyte adhesion. Egr-3 knockdown abrogated VEGF-mediated vascular outgrowth from ex vivo aortic rings and attenuated Matrigel plug vascularization and melanoma tumor growth in vivo. Together, these findings suggest that Egr-3 is a critical determinant of VEGF signaling in activated endothelial cells. Thus, Egr-3 represents a potential therapeutic target in VEGF-mediated vasculopathic diseases.

Immunological considerations of modern animal models of malignant primary brain tumors

Recent advances in animal models of glioma have facilitated a better understanding of biological mechanisms underlying gliomagenesis and glioma progression. The limitations of existing therapy, including surgery, chemotherapy, and radiotherapy, have prompted numerous investigators to search for new therapeutic approaches to improve quantity and quality of survival from these aggressive lesions. One of these approaches involves triggering a tumor specific immune response. However, a difficulty in this approach is the the scarcity of animal models of primary CNS neoplasms which faithfully recapitulate these tumors and their interaction with the host's immune system. In this article, we review the existing methods utilized to date for modeling gliomas in rodents, with a focus on the known as well as potential immunological aspects of these models. As this review demonstrates, many of these models have inherent immune system limitations, and the impact of these limitations on studies on the influence of pre-clinical therapeutics testing warrants further attention.

Role of alveolar epithelial early growth response-1 (Egr-1) in CD8+ T cell-mediated lung injury

Influenza infection of the distal airways results in severe lung injury, a considerable portion of which is immunopathologic and attributable to the host responses. We have used a mouse model to specifically investigate the role of antiviral CD8(+) T cells in this injury, and have found that the critical effector molecule is TNF-alpha expressed by the T cells upon antigen recognition. Interestingly, the immunopathology which ensues is characterized by significant accumulation of host inflammatory cells, recruited by chemokines expressed by the target alveolar epithelial cells. In this study we analyzed the mechanisms involved in the induction of epithelial chemokine expression triggered by antigen-specific CD8(+) T cell recognition, and demonstrate that the early growth response-1 (Egr-1) transcription factor is rapidly induced in epithelial cells, both in vitro and ex vivo, and that this is a critical regulator of a host of inflammatory chemokines. Genetic deficiency of Egr-1 significantly abrogates both the chemokine expression and the immunopathologic injury associated with T cell recognition, and it directly regulates transcriptional activity of a model CXC chemokine, MIP-2. We further demonstrate that Egr-1 induction is triggered by TNF-alpha-dependent ERK activation, and inhibition of this pathway ablates Egr-1 expression. These findings suggest that Egr-1 may represent an important target in mitigating the immunopathology of severe influenza infection.