ATF4 and idiopathic pulmonary fibrosis: Nevertheless, the association of mitochondrial dysfunction with ER stress was not clear until a research group demonstrated that in ATII mice cells, an unfolded protein response in the ER (UPRER) generates a similar response at the mitochondrial level through an ATF4-dependent pathway in aged mice with bleomycin-induced lung injury as well as human cells from subjects with IPF [72].