CCN2 and pulmonary fibrosis: In addition to common molecular signaling pathways such as TGF-β, CTGF, Hedgehog, Notch, and fibroblast growth factor (FGF) [187], recent studies have shown that fibroblasts, alveolar epithelial cells, macrophages, Clara cells, and lung resident mesenchymal stem cell (LR-MSC) can been implicated in lung fibrosis through various mechanisms [14, 52, 188–191].