Acidosis promotes cell apoptosis through the G protein-coupled receptor 4/CCAAT/enhancer-binding protein homologous protein pathway

The aim of the present study was to investigate the effects of acidosis on the apoptosis of renal epithelial and endothelial cells, and the molecular pathways responsible for this. A human proximal tubular cell line, HK-2, and human umbilical vein endothelial cells (HUVECs), were transfected with control or G protein-coupled receptor 4 siRNA for 36 h. Cells were exposed to normal (pH 7.4) or acidic (pH 6.4) media. Western blot analysis was used to assess the protein expression levels of G protein-coupled receptor 4 (GPR4), CCAAT/enhancer-binding protein homologous protein (CHOP) and cleaved caspase-3. Cell apoptosis was examined using the TUNEL assay and the lactate dehydrogenase (LDH) release assay. Using these techniques, it was demonstrated that acidosis increased the protein expression levels of GPR4, CHOP, cleaved caspase-3 and intracellular cyclic adenosine monophosphate levels in hypoxia/reoxygenation (HR)-treated cell lines. Knockdown of GPR4 in HK-2 cells and HUVECs markedly reduced the protein expression levels of acidosis-mediated GPR4, CHOP and cleaved caspase-3, as well as the rate of cell apoptosis. Therefore, the results of the present study suggested that acidosis promotes the apoptosis of HK-2 cells and HUVECs by regulating the GPR4/CHOP pathway.