Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, fatal lung disorder characterized by aberrant extracellular matrix deposition in the interstitium. Pirfenidone is an antifibrotic agent used to treat patients with IPF. Pirfenidone shows a pleiotropic mode of action, but its underlying antifibrotic mechanism is unclear. Transient receptor potential vanilloid 4 (TRPV4), which is a mechanosensitive calcium channel, was recently shown to be related to pulmonary fibrosis. To clarify the antifibrotic mechanisms of pirfenidone, we investigated whether TRPV4 blockade has a pharmacological effect in a murine model of pulmonary fibrosis and whether pirfenidone contributes to suppression of TRPV4. Our synthetic TRPV4 antagonist and pirfenidone treatment attenuated lung injury in the bleomycin mouse model. TRPV4-mediated increases in intracellular calcium were inhibited by pirfenidone. In addition, TRPV4-stimulated interleukin-8 release from cells was reduced and a delay in cell migration was abolished by pirfenidone. Furthermore, pirfenidone decreased TRPV4 endogenous ligands in bleomycin-administered mouse lungs and their production by microsomes of human lungs. We found TRPV4 expression in the bronchiolar and alveolar epithelium and activated fibroblasts of the lungs in patients with IPF. Finally, we showed that changes in forced vital capacity of patients with IPF treated with pirfenidone were significantly correlated with metabolite levels of TRPV4 endogenous ligands in bronchoalveolar lavage fluid. These results suggest that the antifibrotic action of pirfenidone is partly mediated by TRPV4 and that TRPV4 endogenous ligands in bronchoalveolar lavage fluid may be biomarkers for distinguishing responders to pirfenidone.
Keywords: biomarker; bleomycin; idiopathic pulmonary fibrosis (IPF); pirfenidone; transient receptor potential vanilloid 4 (TRPV4).