Crosstalk between extravascular coagulation, chemokine networks and immunity in fibroproliferative lung disease

When the lungs are damaged by pollution, smoke, trauma or infection, the coagulation cascade system of blood clotting proteins (coagulation factors), is activated in order to temporarily plug damaged blood vessels. Aside from their roles in clotting, many of these coagulation factors can also directly affect lung repair mechanisms. In lung disease, this process can snowball - unwarranted activation of the coagulation cascade has been implicated in the excessive scarring known as fibrosis, which leads to the eventual loss of normal lung function in adults, children and premature infants. There are currently no effective therapies, so the insidious progression of fibrosis often results in death of affected individuals. New therapies are therefore urgently required. Encouragingly, the results of a recent clinical trial support the notion that anti-coagulant drugs may be beneficial. Our work has identified a particular coagulation factor which, unusually, is made within the lung itself. This project will begin to identify the mechanisms by which this and other coagulation factors can lead to lung inflammation and scarring, using an experimental model of fibrosis, cultured cells and patient biopsy material. This information will help in the development of more specific and useful therapies for this devastating and fatal disease.

Introduction: Uncontrolled activation of the coagulation cascade contributes to the pathophysiology of several respiratory conditions, including pulmonary fibrosis. Current dogma assumes that coagulation zymogens are derived from the circulation and locally-activated in response to tissue injury. However, my recent data show for the first time that coagulation factor X (FX) gene expression is significantly upregulated in pulmonary fibrosis and that the bronchial/alveolar epithelium represents a prominent cellular source of FX - the activated form of which (FXa) exerts potent pro-inflammatory/pro-fibrotic effects. These findings herald a paradigm shift in our understanding of the tissue origin of excessive procoagulant signaling in lung disease, and are consistent with the existence of an inducible extravascular lung coagulation system. Our work has also highlighted the involvement of proteinase-activated receptor 1 (PAR1) as the major signaling receptor for coagulation proteinases in the injured lung. Hypothesis: Extravascular pro-coagulant activity, signaling via PAR1, influences innate immune mechanisms and chemokine production to drive the development of lung inflammation and fibrosis. Aims: My aims are to determine: a) the relative contribution of locally-produced and activated FX to experimental lung inflammation and fibrosis; b) the mechanisms mediating increased FX gene expression; c) how FXa (via its receptor, PAR1) contributes to the establishment of chemokine networks involved in recruitment of leukocytes and circulating mesenchymal progenitor cells to the injured lung; and d) the significance of extravascular pro-coagulant activity for monocyte/macrophage activation and formation of secondary lymphoid tissue. Methods: These studies will employ an integrated approach involving a well-established animal model of inflammation/fibrosis, in vitro biology and patient material. FX production/activity in vivo will be manipulated using shRNA or a specific FXa inhibitor. Immunohistochemistry, ELISA, flow cytometry and real-time RT-PCR will be used to elucidate effects on inflammation/fibrosis and chemokine networks. In vitro cell biology, including both mono- and co-culture experiments, will be used to investigate FX gene regulation, and determine cross-talk between epithelium and fibroblasts or macrophages. Patient biopsy material and bronchoalveolar lavage fluid will be used to underpin this basic science programme and ensure findings are of human disease relevance. Outcomes: Besides expanding our knowledge of the fundamental crosstalk between the coagulation cascade, inflammation and immunity, this work will provide novel insights into the pathophysiological mechanisms underlying lung inflammation and fibrosis. Interfering with FX production or signaling may represent an extremely attractive target for therapeutic intervention in lung injury and fibrosis, and potentially other lung diseases associated with excessive pro-coagulant activity.