ATF4 and pulmonary fibrosis: Jiang et al.[36] have shown that activating transcription factor 4 (ATF4) is a key regulator of mitochondrial unfolded protein response (UPRmt) both in experimental pulmonary fibrosis and in IPF, and that this signalling cascade is induced by ER stress, indicating a novel mechanism by which ER stress may contribute to the pathogenesis of IPF.