SPP1 and pulmonary fibrosis: Studies in murine models of bleomycin-induced IPF demonstrated that Spp1−/− mice are characterized by the development of pulmonary fibrosis due to cystic dilatation of the distal airways, accompanied by the reduced expression of type I collagen, TGF-β, and matrix metalloproteinase-2 compared to wild-type (WT) control mice; on the other hand, the administration of Spp1 siRNA protects mice against bleomycin-induced pulmonary fibrosis [54,56].