MMP9 and pulmonary fibrosis: It has been described that during the process of fibrosis, MMP-2 and MMP-9 respectively called gelatinase A and gelatinase B are usually up-regulated, which can disrupt basement membranes through degrading Collagen type IV and induce lung tissue remodeling as well as alveolar thickening, resulting in lung fibrosis (Dancer et al., 2011; Van Doren, 2015).