Early growth response gene-1 promotes airway allograft rejection

Role of early growth response 1 in inflammation-associated lung diseases

Early growth response 1 (EGR1), which is involved in cell proliferation, differentiation, apoptosis, adhesion, migration, and immune and inflammatory responses, is a zinc finger transcription factor. EGR1 is a member of the EGR family of early response genes and can be activated by external stimuli such as neurotransmitters, cytokines, hormones, endotoxins, hypoxia, and oxidative stress. EGR1 expression is upregulated during several common respiratory diseases, such as acute lung injury/acute respiratory distress syndrome, chronic obstructive pulmonary disease, asthma, pneumonia, and novel coronavirus disease 2019. Inflammatory response is the common pathophysiological basis of these common respiratory diseases. EGR1 is highly expressed early in the disease, amplifying pathological signals from the extracellular environment and driving disease progression. Thus, EGR1 may be a target for early and effective intervention in these inflammation-associated lung diseases.

Human adipose-derived mesenchymal stem cells alleviate obliterative bronchiolitis in a murine model via IDO

Background

Long-term survival of lung transplantation is hindered by the development of obliterative bronchiolitis (OB). Adipose-derived stem cells (ASCs) were documented to have more potent immunosuppressive ability than mesenchymal stem cells (MSCs) from bone marrow and placenta. The goal of our study is to evaluate the effect of repeated administration of ASCs on OB and the involvement of indoleamine 2,3-dioxygenase (IDO) mediating the protective effect of ASCs in a heterotopic tracheal transplantation (HTT) model.

Methods

For studies in vitro, ASCs were treated with interferon-γ (IFN-γ). For in vivo study, tracheas from BALB/c or C57BL/6 donors were transplanted into C57BL/6 recipients to create a HTT model. On days 0, 1, 3, 5, 8, 12, 15, 20 and 25 post-transplant, the allogeneic recipient mice were administered intravenously with phosphate buffered saline, 1 × 10⁶ human ASCs, or 1 × 10⁶ human ASCs plus 1-methyltryptophan (1-MT), an IDO inhibitor. On days 3, 7, 14 and 28, serum, trachea and spleen samples were harvested for analysis.

Results

ASCs homed to heterotopic tracheal grafts after infusion. Multiple doses of ASCs significantly increased tracheal IDO levels in allografts. There were significant increases in graft and serum IFN-γ levels in allografts compared with isografts. IFN-γ elevated IDO expression and activity in ASCs in vitro. ASCs alleviated OB in allografts as evidenced by reduced epithelial loss, epithelial apoptosis, and intraluminal obstruction. The effects of ASCs on OB were blocked by 1-MT. 1-MT also blocked the alterations in pro and anti-inflammatory cytokines as well as CD3+ T cell infiltration induced by ASCs. ASCs induced not only splenic levels of CD4+CD25+Foxp3+ regulatory T cells (Treg) but also IL-10 and TGF-β-producing Treg. Furthermore, IDO inhibition abolished the changes of splenic Treg induced by ASCs. In addition, Treg reduction by cyclophosphamide treatment did not alter the effects of ASCs on tracheal IDO expression in allografts confirming Treg induction is downstream of IDO.

Conclusions

Repeated doses of ASCs are capable of ameliorating OB. ASCs act at least in part via elevating IDO expression. ASCs promote the generation of Treg and suppress T cell infiltration via an IDO-dependent mechanism.

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 P2X7-Egr pathway regulates nucleotide-dependent inflammatory gene expression in microglia

Microglial hyperactivity contributes to neuronal damage resulting from CNS injury and disease. Therefore, a better understanding of endogenous microglial receptor systems that can be exploited to modulate their inflammatory functions is important if better, neuroprotective therapeutics are to be designed. Previous studies from our lab and others have demonstrated that the P2X7 purinergic receptor agonist BzATP attenuates microglial inflammatory mediator production stimulated by lipopolysaccharide (LPS), suggesting that purinergic receptors may be one such receptor system that can be used for manipulating microglial activation. However, although P2X7 receptor activation is well recognized to regulate processing and release of cytokines, little is known concerning its role in regulating the transcription of inflammatory genes, nor the molecular mechanisms underlying these transcriptional effects. In the present studies, we identify that the transcription factors early growth response (Egr)-1, -2 and -3 are downstream signaling targets of P2X7 receptors in microglia, and that their activation is sensitive to MEK and p38 mitogen-activated protein kinase (MAPK) inhibitors. Moreover, using RNAi, we demonstrate that Egr factors and P2X7 receptors are necessary for BzATP-mediated attenuation of iNOS, and stimulation of TNF-α and IL-6 gene expression. BzATP also attenuates neuronal death induced by LPS conditioned medium, and P2X7 receptors are required for this effect. These studies are the first to identify Egr factors as regulators of inflammatory gene expression following P2X7 receptor activation, and suggest that P2X7 receptors may utilize the MAPK-Egr pathway to exert differential effects on microglial inflammatory activities which are beneficial to neuron survival.

Ecto-5'-nucleotidase (CD73) attenuates allograft airway rejection through adenosine 2A receptor stimulation

There are multiple drivers of leukocyte recruitment in lung allografts that contribute to lymphocytic bronchitis (LB) and bronchiolitis obliterans (BO). The innate mechanisms driving (or inhibiting) leukocyte trafficking to allografts remain incompletely understood. This study tested the hypothesis that CD73 (ecto-5'nucleotidase), an enzyme that catalyzes the conversion of AMP to adenosine, is a critical negative regulator of LB and BO. Implantation of tracheal allografts from wild type (WT) mice into CD73(-/-) recipients revealed a striking increase in airway luminal obliteration at 7 d (62 +/- 4% and 47 +/- 5% for CD73(-/-) and WT allograft recipients, respectively; p = 0.046). There was also a concordant increase in CD3(+) lymphocytic infiltration (523 +/- 41 cells and 313 +/- 43 cells for CD73(-/-) and WT allograft recipients, respectively; p = 0.013). Because real-time PCR revealed a 43-fold upregulation of mRNA for the adenosine A2A receptor (A2AR) in WT allografts compared with WT isografts (p = 0.032), additional experiments were performed to determine whether the protective effect of CD73 was due to generation of adenosine and its stimulation of the A2AR. Treatment of WT recipients with an A2AR agonist significantly reduced CD3(+) lymphocyte infiltration and airway luminal obliteration; similar treatment of CD73(-/-) recipients rescued them from LB and airway obliteration. These data implicate CD73 acting through adenosine generation and its stimulation of the A2AR as a critical negative modulator of lymphocyte recruitment into airway allografts. The CD73/adenosine axis might be a new therapeutic target to prevent BO.

Transforming growth factor beta1-mediated activation of the smooth muscle alpha-actin gene in human pulmonary myofibroblasts is inhibited by tumor necrosis factor-alpha via mitogen-activated protein kinase kinase 1-dependent induction of the Egr-1 transcriptional repressor

Transforming growth factor (TGF) beta1 is a mediator of myofibroblast differentiation in healing wounds in which it activates transcription of the smooth muscle alpha-actin (SMalphaA) gene via dynamic interplay of nuclear activators and repressors. Targeting components of TGFbeta1 signaling may be an effective strategy for controlling myofibroblasts in chronic fibrotic diseases. We examined the ability of proinflammatory tumor necrosis factor (TNF)-alpha to antagonize TGFbeta1-mediated human pulmonary myofibroblast differentiation. TNF-alpha abrogated TGFbeta1-induced SMalphaA gene expression at the level of transcription without disrupting phosphorylation of regulatory Smads. Intact mitogen-activated protein kinase kinase (Mek)-extracellular signal-regulated kinase (Erk) kinase signaling was required for myofibroblast repression by TNF-alpha via induction of the early growth response factor-1 (Egr-1) DNA-binding protein. Egr-1 bound to the GC-rich SPUR activation element in the SMalphaA promoter and potently suppressed Smad3- and TGFbeta1-mediated transcription. Reduction in Smad binding to the SMalphaA promoter in TNF-alpha-treated myofibroblasts was accompanied by an increase in Egr-1 and YB-1 repressor binding, suggesting that the molecular mechanism underlying repression may involve competitive interplay between Egr-1, YB-1, and Smads. The ability of TNF-alpha to attenuate myofibroblast differentiation via modulation of a Mek1/Erk/Egr-1 regulatory axis may be useful in designing new therapeutic targets to offset destructive tissue remodeling in chronic fibrotic disease.

Lung EC-SOD overexpression attenuates hypoxic induction of Egr-1 and chronic hypoxic pulmonary vascular remodeling

Although production of reactive oxygen species (ROS) such as superoxide (O(2)(.-)) has been implicated in chronic hypoxia-induced pulmonary hypertension (PH) and pulmonary vascular remodeling, the transcription factors and gene targets through which ROS exert their effects have not been completely identified. We used mice overexpressing the extracellular antioxidant enzyme extracellular superoxide dismutase (EC-SOD TG) to test the hypothesis that O(2)(.-) generated in the extracellular compartment under hypoxic conditions contributes to PH through the induction of the transcription factor, early growth response-1 (Egr-1), and its downstream gene target, tissue factor (TF). We found that chronic hypoxia decreased lung EC-SOD activity and protein expression in wild-type mice, but that EC-SOD activity remained five to seven times higher in EC-SOD TG mice under hypoxic conditions. EC-SOD overexpression attenuated chronic hypoxic PH, and vascular remodeling, measured by right ventricular systolic pressures, proliferation of cells in the vessel wall, muscularization of small pulmonary vessels, and collagen deposition. EC-SOD overexpression also prevented the early hypoxia-dependent upregulation of the redox-sensitive transcription factor Egr-1 and the procoagulant protein TF. These data provide the first evidence that EC-SOD activity is disrupted in chronic hypoxia, and increased EC-SOD activity can attenuate chronic hypoxic PH by limiting the hypoxic upregulation of redox-sensitive genes.