Tissue Factor Maintains Lung Epithelial Barrier Integrity in Acute Lung Injury Through Cell Adhesion

Abstract

Background. Acute Respiratory Distress Syndrome (ARDS) is a common cause of acute respiratory failure. While loss of lung epithelial barrier integrity is a pathologic mechanism of ARDS, little is known about the factors that regulate epithelial barrier integrity in the lung. Our previously published mouse studies showed that deletion of alveolar type II epithelial cell Tissue Factor (TF) caused impaired lung barrier integrity in models of Acute Lung Injury (ALI). TF is an integral membrane protein that both initiates the extrinsic coagulation cascade and serves several non-coagulant functions. Notably, TF promotes cell adhesion through interactions with cell surface integrin heterodimers, comprised of individual α and β integrin subunits. As such, we hypothesize that epithelial TF is necessary for maintaining lung barrier integrity and that its overexpression is protective in ALI through increased cell adhesion. Methods. To determine whether supraphysiologic overexpression of TF in the lung epithelium can enhance barrier integrity we created a novel transgenic mouse in which TF was inducibly overexpressed in the lung epithelium (TFEpi+) using a CMV-TetO promoter and crossed with SPC-rtTA59 mice. High alveolar epithelial TF expression compared to wild-type littermates (WT) was confirmed through immunohistochemistry and western blot analysis after one week of doxycycline in drinking water. To induce ALI, mice were intranasally infected with 2000 colony forming units of Klebsiella pneumoniae (KP) or PBS control. At 24-hours post infection, mice were euthanized, lung tissue was collected, and a bronchoalveolar lavage (BAL) was performed. BAL protein, clot time, and leukocyte influx were measured. Lung wet-to-dry weight ratios and bacterial burden were measured. To better understand TF regulation of β1 integrin function, TF-knockout A549 cells were created using CRISPR and cultured on specific β1 integrin ligands (Collagen I, IV, Laminin-511, and Fibronectin). On-cell western blots and crystal violet were used to assess cell surface β1 integrin expression and cell adhesion. Results. TFEpi+ mice showed higher lung TF protein expression (median 38031 [IQR 25033, 57948] vs 1801 [IQR 804.3, 2083] expression normalized to total protein; p=0.0016) compared to WT. TFEpi+ mice infected with KP showed lower BAL protein (mean 248.51 [SD 98.03] vs 366.3 [SD 159.8] μg/ml; p=0.0035) and lung wet-to-dry weight ratios (mean 4.27 [SD 0.37] vs 5.29 [SD 0.75]; p=0.0152) compared to WT. Bacterial burden and BAL inflammatory cell counts were higher, while BAL clot time was lower in infected WT mice compared to control. However, these outcomes did not differ between infected TFEpi+ and WT mice. Loss of TF in alveolar epithelial cells reduced cell surface β1 integrin expression and cell adhesion to Laminin-511. Conclusion: Alveolar epithelial TF overexpression is protective for maintaining lung barrier integrity independent of coagulation and inflammation. Further, cell adhesion studies suggest that this is potentially mediated through increased a6β1 epithelial cell adhesion. AHA Postdoctoral Fellowship, National Institute of Health Grants (HL150783, I01BX002288). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.