The ER stress-mediated decrease in DDAH1 expression is involved in formaldehyde-induced apoptosis in lung epithelial cells

Formaldehyde (FA) is toxic to the respiratory system, and nitric oxide (NO) dysfunction stimulates the onset of respiratory diseases. The involvement of dimethylarginine dimethylaminohydrolase (DDAH), the l-arginine analogue asymmetric dimethylarginine (ADMA) degrading enzyme, in FA-induced cell death in lung epithelial cells has not been investigated. In this study, we assessed the effect of FA on DDAH expression and endoplasmic reticulum (ER) stress in A549 cells. We also investigated the preventive effect of DDAH overexpression on ER stress and apoptosis in FA-induced cell death. FA decreased viability in A549 cells and decreased DDAH1 and DDAH2 mRNA and protein expression in a time-dependent manner (>4 h). This coincided with increased phosphorylation of the ER stress proteins IRE1α, PERK, and eIF-2α, as well as increased expression of pro-apoptotic proteins such as Bax, C/EPB homologous protein (CHOP), cleaved PARP, and cleaved caspase-3, but decreased expression of the anti-apoptotic protein Bcl-2. ADMA treatment mimicked the effect of FA. Overexpression of DDAH1, but not DDAH2, prevented FA-induced decreases in cell viability, phosphorylation of IRE1α, PERK, and eIF2α, and expression of CHOP. Effects of DDAH1 overexpression, but not DDAH2 overexpression, restored FA-induced increases in Bax, CHOP, cleaved PARP, cleaved caspase-3 and decreases in Bcl-2. In conclusion, FA induces apoptosis of lung epithelial cells via a decrease of DDAH1 through ER stress.