Figure 5. PAR-1-induced TGF-β activation on fibroblasts is mediated by FX.

A. Thrombin (FII), FX, Granzyme K (GZMK), MMP1, MMP13, KLK1, KLK4 and KLK6 mRNA levels in RAW264.7 cells as assessed by real-time reverse transcriptase PCR. Data are expressed relative to two housekeeping genes, GAPDH and TBP. Shown is the mean ± SEM, of an experiment performed three times. B. Western blot analysis of SMAD2 phosphorylation in NIH3T3 cells stimulated for 0, 15, 30 and 60 minutes with RAW264.7 CM in the absence or presence of the FXa inhibitor antistasin (40 μM). GAPDH served as loading control. C. Proposed mechanism by which macrophages promote lung fibrosis in a PAR-1 dependent manner. During lung injury, epithelial cells release mediators that potentiate PAR-1 dependent macrophage migration towards the injured site (1). The recruited macrophages subsequently secrete TGF-β and FX. The PAR-1 agonist (FX) than activates PAR-1 on fibroblasts (2) leading to TGF-β production and activation. Finally, TGF-β induces TGFBR signaling (3) on fibroblast thereby inducing their migration, differentiation and ECM deposition.