PAR-1 as a Therapeutic Target for Silica-Induced Pulmonary Fibrosis

Introduction: Silicosis is an occupational lung disease caused by the inhalation of silica particles, characterized by chronic inflammation, granuloma and progressive fibrosis. Protease-activated receptor 1 (PAR-1) has been linked to fibrosis in different organs. We investigated the role of PAR-1 in silica-induced pulmonary inflammation and fibrosis. ​Methods: A549 cells were pretreated with the PAR-1 antagonist, vorapaxar (1 and 100 μM), for 1 h prior to stimulation with silica particles (300 μg/mL) or with the PAR-1 agonist S1820 (30 μg/mL), and analyzed after 24 h. Swiss-Webster mice received an intranasal instillation of silica (10 mg) or saline. Vorapaxar (1.5 or 5 mg/kg, s.c.) was administered daily between days 21 and 27 after instillation, and analyses were performed on day 28 post-silica. Were evaluated radiological lung alterations (micro-CT), histology (H&E and Picrosirius), total collagen content (Sircol), cytokines and chemokines (ELISA), and PAR-1 expression (WB and RT-qPCR). All procedures were approved by the Ethics Committee on Animal Use of the Oswaldo Cruz Foundation (CEUA L-001/19A6). Results: Stimulation of A549 cells with silica or the PAR-1 agonist, S1820, increased the production of IL-8/CXCL8 and MCP-1/CCL2, an effect significantly inhibited by vorapaxar (100 μM). Silica also elevated PAR-1 mRNA expression in these cells. In mice, silica exposure increased pulmonary PAR-1 expression compared to controls. Vorapaxar treatment reversed major silica-induced alterations, including the reduction of normally aerated lung areas, increase of non-aerated areas, granuloma formation, collagen deposition, and the production of inflammatory mediators, such as KC/CXCL1, MCP-1/CCL2, IL-1β, and TNF-α. Conclusion: These findings identify PAR-1 as a potential therapeutic target for the treatment of silicosis and other fibrotic lung diseases. Financial Support: FIOCRUZ, FAPERJ, CNPq, CAPES.