SPP1 and idiopathic pulmonary fibrosis: The profibrotic mediators that contribute to the progression of IPF are represented by transforming growth factor beta-1 (TGF-β1), platelet-derived growth factor (PDGF), tumor necrosis factor (TNF), endothelin-1 (EDN1), connective tissue growth factor (CTGF), osteopontin (OPN), and CXC chemokine ligand 12 (CXCL12).