The role of endoplasmic reticulum stress in endothelial dysfunction induced by homocysteine thiolactone.

Our and other studies have reported that homocysteine thiolactone (HTL) could induce endothelial dysfunction. However, the precise mechanism was largely unknown. In this study, we tested the most possible factor-endoplasmic reticulum (ER) stress, which was demonstrated to be involved in endothelial dysfunction in cardiovascular disease. Acetylcholine (Ach)-induced endothelium-dependent relaxation (EDR) and biochemical parameters were measured in rat isolated aorta. The level of reactive oxygen species (ROS) and NO was designed by specific fluorescent probe DCFH-DA and DAF-FM DA separately. The nuclear translocation of the NF-κB was studied by immune-fluorescence. The mRNA expression and protein expression of GRP78--a key indicator for the induction of ER stress--were assessed by real-time PCR and Western blot. Two ER stress inhibitors-4-PBA (5 mm) and Tudca (500 μg/mL)--significantly prevented HTL-impaired EDR and increased NO release, endothelial nitric oxide synthase (eNOS) and SOD activity, decreased ROS production, NADPH activity, NOX-4 mRNA and MDA level. We also found that 4-PBA and Tudca blocked HTL--induced NF-κB activation thus inhibiting the downstream target gene production including TNF-α and ICAM-1. Simultaneously, HTL increased the mRNA and protein level of GRP78. HTL could induce ER stress leading to a downstream enhancement of oxidative stress and inflammation, which finally caused vascular endothelial dysfunction.