CCN2 and idiopathic pulmonary fibrosis: Repetitive injury to the alveolar epithelium, failure to reepithelization, increased AEC apoptosis, and induction of growth factors and profibrotic cytokines such as transforming growth factor-β1 (TGF-β1), TNF-α, platelet-derived growth factor, and connective tissue growth factor (CTGF) are implicated in the progression of IPF (54).