Regulation of Alveolar Procoagulant Activity and Permeability in Direct Acute Lung Injury by Lung Epithelial Tissue Factor

Abstract

Tissue factor (TF) initiates the extrinsic coagulation cascade in response to tissue injury, leading to local fibrin deposition. Low levels of TF in mice are associated with increased severity of acute lung injury (ALI) after intratracheal LPS administration. However, the cellular sources of the TF required for protection from LPS-induced ALI remain unknown. In the current study, transgenic mice with cell-specific deletions of TF in the lung epithelium or myeloid cells were treated with intratracheal LPS to determine the cellular sources of TF important in direct ALI. Cell-specific deletion of TF in the lung epithelium reduced total lung TF expression to 39% of wild-type (WT) levels at baseline and to 29% of WT levels after intratracheal LPS. In contrast, there was no reduction of TF with myeloid cell TF deletion. Mice lacking myeloid cell TF did not differ from WT mice in coagulation, inflammation, permeability, or hemorrhage. However, mice lacking lung epithelial TF had increased tissue injury, impaired activation of coagulation in the airspace, disrupted alveolar permeability, and increased alveolar hemorrhage after intratracheal LPS. Deletion of epithelial TF did not affect alveolar permeability in an indirect model of ALI caused by systemic LPS infusion. These studies demonstrate that the lung epithelium is the primary source of TF in the lung, contributing 60-70% of total lung TF, and that lung epithelial, but not myeloid, TF may be protective in direct ALI.Keywords: coagulation; fibrin; pulmonary; acute respiratory distress syndrome; alveolar capillary barrier permeability Clinical RelevanceThis study evaluates the role of tissue factor (TF) in direct acute lung injury using cell-specific genetic approaches. We identify the lung epithelium as the major source of TF in the airspace. Loss of epithelial TF increases lung injury, impairs coagulation, results in lung hemorrhage, and disrupts alveolar-capillary barrier permeability. These findings identify a potential new target for treatment of severe lung injury in humans.A pathologic hallmark of severe acute lung injury (ALI) in humans is intra-alveolar fibrin deposition, forming hyaline membranes lining the airspace (1). Activation of the tissue factor (TF) pathway is a major driver of coagulation in the airspace (2-5). We previously demonstrated a critical role for TF in protection from ALI caused by intratracheal LPS administration (2). LTF mice, which lack murine TF and express 1% of endogenous levels of human TF to overcome embryonic lethality, developed more severe ALI in response to intratracheal LPS than littermate controls. LTF mice had a local coagulation defect in the airspace, increased histologic lung injury, increased alveolar-capillary

Myeloid tissue factor does not modulate lung inflammation or permeability during experimental acute lung injury

“…In contrast, other studies using animal models of indirect ALI have suggested that TF deficiency or systemic TF inhibition reduced tissue injury12131415. We recently identified that TF expressed on the lung epithelium was the predominant source of TF in the lung during direct LPS-induced ALI16, with no significant contribution of TF from myeloid cells in this model. This finding was in contrast to prior data showing that TF expressed on cells in the circulation was critical for the systemic response to LPS in a model of endotoxemia17.…”

ICAM-1–targeted thrombomodulin mitigates tissue factor–driven inflammatory thrombosis in a human endothelialized microfluidic model

“…19,60,61 In fact, the difference in potency between these 2 agents may be more significant than their relative concentrations would suggest, as only a fraction of hTM/R6.5 molecules would have bound to the cell membrane. While ICAM-1 targeting of hTM/R6.5 was limited to hematopoietic and ECs in these studies, other cell types, such as epithelium, express ICAM-1, and may be both an important source of TF 24 and a valuable target of this approach. 62 There are several reasons why binding of TM to cell membranes may enhance its antithrombotic activity.…”

“…It is challenging to discern the contribution of endothelial TF from other sources such as hematopoietic cells, epithelium, fibroblasts, pericytes, and smooth muscle. [22][23][24] While ECs express TF under inflammatory stimuli in vitro, studies have failed to (E) hTM/R6.5 binds strongly to TNF-a-stimulated HUVEC but only minimally to nonstimulated ECs. Cell-based enzyme-linked immunosorbent assays were performed on live cells as previously described 19 using anti-FLAG-HRP to probe for cell-bound fusion protein.…”

“…22,24 TM itself demonstrates species-specific differences in the balance between anti-inflammatory and antithrombotic activity. 26,27 Finally, translation to human pathologies has been limited by the absence of species cross-reactivity of the murine therapeutic.…”

An Inhaled Inhibitor of Myristoylated Alanine-Rich C Kinase Substrate Reverses LPS-Induced Acute Lung Injury in Mice

“…As illustrated in Figure 3C, treatment with BIO-11006 provoked a significant decrease in mRNA expression of these cytokines in the lung, suggesting effects at the message level. MARCKS also has been shown to be involved in activation of NF-kB in different cells (19)(20)(21), perhaps through a protein kinase C d-related mechanism (22), and it is known that KC and TNF-a-contain NF-kB-binding sites in their promoter regions, so a logical next step was to look at whether or not BIO-11006 could affect NF-kB. Using phosphorylation of the p65 subunit of NF-kB in lung cytoplasmic extracts as an indicator of NF-kB activation, inhalation of BIO-11006 at any of the time points in this study inhibited LPS-induced NF-kB activation (Figure 4).…”