Compartment- and cell-specific expression of coagulation and fibrinolysis factors in the murine lung undergoing inhalational versus intravenous endotoxin application

Abstract

Intraalveolar and intravascular fibrin formation are typical hallmarks of acute inflammatory lung diseases, and may foster subsequent fibroproliferative events. We investigated the regulation and cellular sources of key coagulation and fibrinolysis factors in lungs undergoing compartmentalized challenge with endotoxin (LPS). BALB/c mice received 15 ng LPS either by intravenous injection or by inhalation. Quantitative gene expression analysis (real-time RT-PCR) was performed for tissue factor (TF), TF pathway inhibitor (TFPI), tissue-type plasminogen activator (t-PA), urokinase-type-PA (u-PA), PA inhibitor-1 (PAI-1), and PAI-2 in peripheral white blood cells (PBC) as well as in alveolar macrophages (AM), type-II pneumocytes (ATII), endothelial cells (EC) and smooth muscle cells (SMC), all obtained by laser microdissection. Neither route of LPS administration caused substantial protein leakage or leukocyte recruitment into the alveolar space. Compartmentalized upregulation of procoagulant and downregulation of fibrinolytic activities was, however, observed in response to both modes of LPS challenge. Intraalveolar endotoxin, in particular, caused strong upregulation of TF ( approximately 20-fold increase in gene expression) and PAI-2 (225-fold increase) in microdissected AM, upregulation of PAI-1 in microdissected ATII (300-fold increase) and EC (180-fold increase), upregulation of t-PA in EC (40-fold), and downregulation of u-PA in vascular smooth muscle cells. TFPI was largely unchanged in all cell types, and PBC showed no major gene regulatory response to inhaled endotoxin. We conclude that the lung possesses a cell-specific alveolar coagulation and fibrinolysis system, being independent of the vascular coagulation cascade and responding readily with enhanced procoagulant and anti-fibrinolytic activities to LPS challenge.

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

“…The majority of the abnormalities that we previously observed in LTF mice after LPS-mediated injury (2) are recapitulated by absence of TF on the lung epithelium. These findings add to a growing literature showing that coagulation in the airspace is regulated by lung epithelial cells rather than inflammatory cells (3,9,29,31). Our group has previously reported increased levels of TF in pulmonary edema fluid of patients with acute respiratory distress syndrome compared with patients with hydrostatic pulmonary edema (3).…”

“…The cellular sources of TF that drive the protective effects of TF during direct ALI, and the mechanisms of the protective effects of TF in the airspace, are currently unknown. Several previous studies suggested that inflammatory cells, specifically alveolar macrophages, have intense up-regulation of TF protein and activity in LPS models, bleomycin-induced lung injury, and human ALI (8,9,17). However, emerging data point to the alveolar epithelium as a critical mediator of intraalveolar coagulation (3,6,9,18,19).…”

“…Several previous studies suggested that inflammatory cells, specifically alveolar macrophages, have intense up-regulation of TF protein and activity in LPS models, bleomycin-induced lung injury, and human ALI (8,9,17). However, emerging data point to the alveolar epithelium as a critical mediator of intraalveolar coagulation (3,6,9,18,19). We hypothesized that TF expression on the alveolar epithelium is a critical mediator of coagulation, inflammation, and permeability during direct lung injury caused by LPS.…”

“…In the lung of both humans and mice, TF is expressed by the lung epithelium and by inflammatory cells (3,(6)(7)(8)(9), including myeloid cells. In addition, TF can be strongly induced on epithelial cells, macrophages, and other cell types in vitro (10)(11)(12)(13)(14)(15)(16).…”

Intracellular and extracellular serpins modulate lung disease

“…50 These findings supported the hypothesis that PAI-1 is a critical regulator of fibrin deposition in the alveolar space in response to ALI. Further support for this theory was gained from animal models of lung injury, including bacterial endotoxin, 51 and bleomycin 52 models of ALI. These studies established PAI-1, its activity and its regulation, as a critical target for therapies treating the family of diseases displaying poor lung function associated with fibrin deposition including ALI, ARDS and COPD.…”