Pulmonary fibrosis is a major and common medical condition, characterized by progressive scaring and decline in lung function. Persistent inflammation and acute lung injury in response to sepsis are potential triggers of the fibrotic response. Recently, we have reported that Escherichia coli sepsis in baboons strongly induces procoagulant responses and affects the integrity of the lung. These effects are diminished by the treatment with compstatin, a C3 convertase complement inhibitor .
Here we used the baboon model described  in conjunction with detailed gene expression analysis, as well as biochemical and histological assays to determine if E. coli sepsis triggered metabolic and signaling pathways related to lung remodeling and fibrosis, and whether complement inhibition could attenuate these pathways.
Microarray gene expression analysis shows that sepsis augments several fibrotic gene clusters in the lung as early as 24 hours post E. coli challenge. Immunochemical and biochemical analysis reveals enhanced collagen synthesis, induction of profibrotic factors and increased cell recruitment and proliferation. Compstatin treatment decreases sepsis-induced expression of extracellular matrix genes, including eight collagen genes. Sirius Red and immunofluorescence staining for procollagens 1 and 3 confirms the collagen deposition in the lung. Ingenuity® pathway analysis of transcriptomics data shows that compstatin treatment reduces sepsis-induced expression of genes involved in fibroblast transformation and connective tissue production, cell chemotaxis, migration and proliferation (see Table 1). Immunocytochemistry and pathway-oriented transcriptomics and phospho-proteomics analysis reveal changes of multiple processes mediated by transforming growth factor beta (TGF-β), connective tissue growth factor and other TGF-β controlled proteins. Immunostaining for cell proliferation markers demonstrates that compstatin treatment strongly reduces cell proliferation in fibroblastic foci. Moreover, biochemical analysis shows decreased production in the compstatin-treated group of two chemokines responsible for fibrocyte recruitment (CCL2 and CXCL12) and of the type 1 tissue inhibitor of metalloproteases that controls extracellular matrix remodeling.
Our data demonstrate that bacterial sepsis initiates pulmonary collagen deposition, and complement inhibition effectively attenuates the fibrotic response. This suggests that complement inhibitors could be used for prevention of sepsis-induced pulmonary fibrosis.
The authors thank Dr Bart Frank (OMRF) for help with protein array scanning and quantitation. This work was supported by grants from the National Institutes of Health (GM097747-01 to FL and JL; 2P20RR018758-06A2 and 1RC1GM09739-02 to FL; AI068730 and GM062134 to JL).
Silasi-Mansat R, Zhu H, Popescu NI, Peer G, Sfyroera G, Magotti P, Ivanciu L, Lupu C, Mollnes TE, Taylor FB, et al.: Complement inhibition decreases the procoagulant response and confers organ protection in a baboon model of Escherichia coli sepsis.