In this study, by using aliskiren to directly inhibit renin enzymatic activity, we demonstrated that renin activity is required for the development of lung fibrosis in this model; by using hydralazine to normalize blood pressure in RenTgMK mice, which does not interfere with the RAS, we showed that the development of lung fibrosis is independent of high blood pressure; and by blocking the AT1 receptor signaling with losartan, we proved that lung fibrosis is at least in part induced by the activation of the AT1 receptor signaling pathway. Here, REN is linked to pulmonary fibrosis.