Regulation of tissue factor and inflammatory mediators by Egr-1 in a mouse endotoxemia model

Abstract

In septic shock, tissue factor (TF) activates blood coagulation, and cytokines and chemokines orchestrate an inflammatory response. In this study, the role of Egr-1 in lipopolysaccharide (LPS) induction of TF and inflammatory mediators in vivo was evaluated using Egr-1 ؉/؉ and Egr-1 ؊/؊ mice. Administration of LPS transiently increased the steady-state levels of Egr-1 mRNA in the kidneys and lungs of Egr-1 ؉/؉ mice with maximal induction at one hour. Egr-1 was expressed in epithelial cells in the kidneys and lungs in untreated and LPS-treated mice. LPS induction of monocyte chemoattractant protein mRNA in the kidneys and lungs of Egr-1 ؊/؊ mice was not affected at 3 hours, but its expression was significantly reduced at 8 hours compared with the expression observed in Egr-1 ؉/؉ mice. Similarly, LPS induction of TF mRNA expression in the kidneys and lungs at 8 hours was reduced in Egr-1 ؊/؊ mice. However, Egr-1 deficiency did not affect plasma levels of tumor necrosis factor ␣ in endotoxemic mice. Moreover, Egr-1 ؉/؉ and Egr-1 ؊/؊ mice exhibited similar survival times in a model of acute endotoxemia. These data indicate that Egr-1 does not contribute to the early inflammatory response in the kidneys and lungs or the early systemic inflammatory response in endotoxemic mice. However, Egr-1 does contribute to the sustained expression of inflammatory mediators and to the maximal expression of TF at 8 hours in the kidneys and lungs. IntroductionSeptic shock is induced in humans by the presence of pathogenic bacteria or fungi in the blood and is associated with a high mortality. 1 In Gram-negative sepsis, lipopolysaccharide (LPS [endotoxin]) is released from Gram-negative bacteria and activates monocytes, endothelial cells, and epithelial cells. In sepsis, the procoagulant molecule tissue factor (TF) is expressed by circulating monocytes, vascular endothelial cells in the spleen, and epithelial cells in the lungs and kidneys. 2-7 TFdependent activation of coagulation and the resulting intravascular fibrin deposition contributes to multiorgan failure. 8 Administration of anti-TF antibodies reduced mortality in baboon and mouse models of septic shock. 9,10 In addition, administration of other coagulation inhibitors, such as antithrombin III, protein C, and tissue factor pathway inhibitor in various animal models of sepsis, reduced mortality. [11][12][13] Plasminogen activator inhibitor type 1 (PAI-1) inhibits both types of plasminogen activators and reduces fibrinolysis. 14 PAI-1 activity is increased in the plasma of patients with Gram-negative sepsis 15 and is likely to contribute to intravascular fibrin deposition. Indeed, inhibition of PAI-1 prevents renal fibrin deposition in endotoxemic rabbits. 16 In a mouse model of endotoxemia, maximal levels of TF mRNA are observed at 8 hours, and induction is observed in bronchial and tubular epithelial cells in the lungs and kidneys, respectively. 2,[5][6][7] In contrast, LPS treatment of mice induces maximal PAI-1 mRNA expression at 3 hours, and PAI-1 is expressed by endot...

Early Growth Response-1 Regulates Lipopolysaccharide-induced Suppressor of Cytokine Signaling-1 Transcription

“…In contrast to these results, macrophage differentiation appears normal in Egr-1 Ϫ/Ϫ mice (39). Further, many of the target genes of Egr-1 have additional regulatory mechanisms, because the Egr-1 Ϫ/Ϫ mice demonstrate only slightly reduced levels of MCP-1, tissue factor, intercellular adhesion molecule-1, and interleukin-6 at certain time points following LPS challenge (26).…”

“…The phenotype of the Egr-1 Ϫ/Ϫ mice suggests that other regulatory factors are involved in the induction of SOCS-1 because animals from an acute model of endotoxemia demonstrate only slightly reduced survival rates (26). If the regulation of SOCS-1 were entirely dependent upon Egr-1, the Egr-1 Ϫ/Ϫ mice would demonstrate a dramatic susceptibility to endotoxin challenge, a phenotype displayed by both the SOCS-1 ϩ/Ϫ and SOCS-1 Ϫ/Ϫ animals.…”

“…Egr-1 is an immediate early gene that is up-regulated by a multitude of growth factors, cytokines, and environmental stresses such as hypoxia (24), vascular injury (25), and septic shock (26). Specifically, the induction of Egr-1 in response to LPS has been shown to be mediated by the activation and subsequent binding of Elk-1 to a number of serum response elements present within the Egr-1 promoter (27)(28)(29).…”

Overexpression of Notch1 Ectodomain in Myeloid Cells Induces Vascular Malformations through a Paracrine Pathway

“…In particular, MCP-5 was increased ϳ40-fold (range, 10 to 150) ( Figure 8). Because MCP-1 30 and FIII [31][32][33] genes have been described as targets of the transcription factor Egr-1, expression of the latter was measured and found to be increased ϳ4-fold in Tg macrophages relative to non-Tg ones (Figure 8). Together, these results indicate that N1 EC -expressing macrophages produce enhanced levels of pro-angiogenic molecules.…”

“…This activation is also supported by the increased expression of the Egr-1 transcription factor in Tg macrophages. Egr-1 seems to be a stress-responsive gene, 55 and its activation regulates the expression of several proangiogenic genes, 56 -58 including MCP-1 30 and FIII [31][32][33]59 (see below). The reprogramming of macrophages by N1 EC must be unique, because no other signaling molecule has yet been described, to our knowledge, as being able to confer to macrophages the angiogenic properties observed in these Tg mice.…”