NOX4 and idiopathic pulmonary fibrosis: These results indicate that HDAC4 is widely expressed in IPF fibroblasts and shows an array of intracellular signal transduction pathways, including but not limited to HDAC4/AKT/α-SMA, HDAC4/TGIF/α-SMA, and HDAC4/NOX4/α-SMA, depending on its subcellular localization.