In a bleomycin-induced model of fibrosis, the adoptive transfer of mesenchymal stem cells reduced airway fibrosis and attenuated ER stress through PERK-Nrf2, but not the PERK-eIF2α-ATF4-CHOP pathway, suggesting that the ER stress-induced activation of the non-canonical PERK-Nrf2 pathway of the UPR may have a protective role in complex airway diseases (Ono et al., 2015; Lee et al., 2020). Here, DDIT3 is linked to fibrosis.