Chemical chaperone 4-phenylbutyric acid protects H9c2 cardiomyocytes from ischemia/reperfusion injury by attenuating endoplasmic reticulum stress-induced apoptosis

Myocardial ischemia/reperfusion (I/R) is a potential contributor to high rates of mortality in several cardiovascular diseases. I/R initiates the unfolded protein response and endoplasmic reticulum (ER) stress, which may lead to apoptotic pathways and exaggerate I/R injury. 4-phenylbutyric acid (4-PBA), a low molecular weight, terminal aromatic substituted fatty acid, has been reported to function as an ER chaperone. The aim of the present study was to investigate whether 4-PBA is able to reduce ER stress-induced apoptosis and prevent cardiomyocyte damage during the process of I/R in vitro. Accordingly, the rat cardiomyocyte line, H9c2, was treated with hypoxia/reoxygenation as an I/R model in vitro. Myocardium apoptosis was determined with TUNEL staining. The expression of ER stress-related proteins were examined by western blotting. The resulting data showed that I/R activates the ER stress proteins, glucose-regulated protein 78, activating transcription factor 6 and protein kinase RNA-like endoplasmic reticulum kinase, which were all reduced by pretreatment with 4-PBA. In addition, pretreatment with 4-PBA significantly inhibited the expression levels of pro-apoptotic proteins, C/EBP homologous protein, B cell lymphoma (Bcl-2)-associated X protein and phosphorylated c-Jun N-terminal kinase, and enhanced the expression of the anti-apoptotic protein Bcl-2 (n=3; P<0.05). The data demonstrated that I/R initiates ER stress-associated apoptotic pathways, and 4-PBA pretreatment protected the cardiomyocytes from I/R-induced cell death. To the best of our knowledge, the present study is the first to report on the cell repair mechanism of 4-PBA against I/R damage in cardiomyocytes based on ER stress-associated apoptotic pathways.