Contribution of p38 MAPK to Endoplasmic Reticulum Stress-Mediated Apoptosis in Cardiomyocytes

Unfolded protein response (UPR) of prolonged endoplasmic reticulum (ER) stress-mediated apoptosis is known to be involved in various diseases. However, the signaling mechanism linking UPR and p38 mitogen-activated protein kinase (MAPK) to apoptosis still remains uncertain. This study was to investigate the role of p38 MAPK-C/EBP homologous protein (CHOP) signaling in ER stress-mediated apoptosis. ER stress was induced by thapsigargin (TG) in H9c2 cells, with or without treatment of SB203580 (SB). It was randomly assigned for H9c2 cells as the control group, the TG group, the SB group and the TG + SB group, receiving designating treatment respectively. Cells of different groups were studied for cell viability by CCK8, apoptotic rate by TUNEL, protein expression by western blot or immunofluorescence staining, and mRNA expression by qRT-PCR. Results showed that TG significantly decreased cell viability and increased apoptosis, with increase of mRNA expression of CHOP, cleavage of caspase-3, and increase of protein expressions of p-p38 MAPK, p-PERK, p-eIF2α, ATF4, and CHOP. Compared with the TG group, SB significantly improved cell viability and decreased apoptosis in the TG + SB group, with inhibition of CHOP mRNA and protein expression. However, there was no significant difference in protein expressions of p‑PERK, p-eIF2α, and ATF4 between the TG group and the TG + SB group. In summary, p38 MAPK-CHOP signaling plays an important role in ER stress-mediated apoptosis independent of PERK-activated pathway, and may be a potential therapeutic target for ER stress-related diseases.