PAR-2 antagonist inhibits bleomycin-induced lung fibrosis

Rationale: Idiopathic interstitial pneumonias are characterized by variable degrees of lung inflammation and fibrosis, and the mechanisms leading to these responses remain unclear. Protease activated receptor (PAR)-2, a G-protein-coupled receptor has been recognized as a key molecule in inflammation and fibrosis. In a previous study, we found that activation of PAR-2 induces transforming growth factor (TGF)-β expression and epithelial-to-mesenchymal transition (EMT) associated with lung fibrosis in vitro. We hypothesized PAR-2 inhibiting peptide (IP) might reduce bleomycin (BLM)-induced lung injury and fibrosis in vivo. Methods: C57BL/6 mice were used in all experiments. BLM was administered by intratracheal injection under anesthesia. PAR-2 IP was intranasally instilled half an hour before BLM injection and once daily until the end of the experiment. Blood sampling and bronchoalveolar lavage (BAL) were performed 7, 14 and 21 days after BLM instillation. The lungs were excised and the samples were used for histological analysis, RT-PCR and ELISA. Results: PAR-2 IP reduced BLM-induced lymphocytes in BAL fluid (BALF). Lung fibrosis was reduced in PAR-2 IP-treated BLM mice. PAR-2 IP downregulated the expression of monocyte chemotactic protein (MCP)-1 and TGF-β, and inhibited profibrotic responses, as seen by reduced collagen induction by BLM. Immunohistochemistry showed PAR-2 IP reduced BLM-induced EMT. Induction of high-mobility group box (HMGB)-1 by BLM which may mediate EMT was reduced by PAR-2 IP treatment. Conclusion: PAR-2 inhibition reduces BLM-induced lung inflammation and fibrosis, suggesting that PAR-2 might play a pivotal role in BLM-induced lung injury. The results could lead to new therapeutic strategies for lung fibrosis.