The PERK/Nrf2 pathway mediates endoplasmic reticulum stress-induced injury by upregulating endoplasmic reticulophagy in H9c2 cardiomyoblasts

Endoplasmic reticulum stress (ERS) is an evolutionarily conserved cell stress response. Recently, it was found that ERS induces not only apoptosis but also endoplasmic reticulophagy (ER-phagy). A previous study demonstrated that inhibition of ER-phagy alleviates cell injury. The purpose of this study was to investigate the involvement of the protein kinase R-like ER kinase (PERK)/nuclear factor erythroid 2-related factor 2 (Nrf2) pathway in ERS-induced ER-phagy in H9c2 cardiomyoblasts. To address this aim, cells were treated with ERS inhibitors and a Nrf2 inhibitor before establishment of thapsigargin (TG)- or tunicamycin (TM)-induced ERS models in H9c2 cardiomyoblasts.Transmission electron microscopy and immunofluorescence staining were used to detect ER-phagy. Western blotting was employed to detect the levels of calreticulin (CRT), total and phosphorylated PERK, nuclear Nrf2, activated transcription factor 4 (ATF4), light chain 3B (LC3B)-II and Beclin 1. Immunofluorescence staining was used to assess subcellular location of Nrf2.TG or TM induced H9c2 cell injury and ER-phagy and upregulated CRT expression, PERK phosphorylation, Nrf2 nuclear translocation, and expression of ATF4, Beclin 1, and LC3B-II compared with control cells. Treatment with ERS inhibitors decreased TG- or TM-induced ER-phagy, downregulated CRT expression, PERK phosphorylation, Nrf2 nuclear translocation and the expression of ATF4, Beclin 1 and LC3B-II. Moreover, a Nrf2 inhibitor downregulated the expression of ATF4, Beclin 1 and LC3B-II and alleviated TG- or TM-induced ER-phagy and H9c2 cell injury.These findings suggest that the PERK/Nrf2 pathway mediates upregulation of ER-phagy, thereby inducing cell injury in H9c2 cardiomyoblasts.