In idiopathic pulmonary fibrosis, OPN induces fibrosis by increasing the expression of tissue inhibitor of metalloproteinase (TIMP) and type 1 collagen in fibroblasts and increasing the expression of the OPN activating protein matrix metallopretease 7 (MMP7) in alveolar epithelial cells [81]. Here, SPP1 is linked to idiopathic pulmonary fibrosis.