ER stress-mediated cell damage contributes to the release of EDA+ fibronectin from hepatocytes in nonalcoholic fatty liver disease.

Fibronectin containing extra domain A (EDA+ FN), a functional glycoprotein participating in several cellular processes, correlates with chronic liver disease. Herein, we aim to investigate the expression and secretion of EDA+ FN from hepatocytes in nonalcoholic fatty liver disease (NAFLD) and the underlying mechanisms. Circulating levels of EDA+ FN were determined by ELISA in clinical samples. Western blotting and flow cytometry were performed on L02 and HepG2 cell lines to analyze whether the levels of EDA+ FN were associated with endoplasmic reticulum (ER) stress-related cell death. Circulating levels of EDA+ FN in NAFLD patients were significantly higher than those in control subjects, and positively related with severity of ultrasonographic steatosis score. In cultured hepatocytes, palmitate up-regulated the expression of EDA+ FN in a dose-dependent manner. Conversely, when the cells were pretreated with 4-phenylbutyrate, a specific inhibitor of ER stress, up-regulation of EDA+ FN could be abrogated. Moreover, silencing CHOP by shRNA enhanced the release of EDA+ FN from hepatocytes following palmitate treatment, which was involved in ER stress-related cell damage. These findings suggest that the up-regulated level of EDA+ FN is associated with liver damage in NAFLD, and ER stress-mediated cell damage contributes to the release of EDA+ FN from hepatocytes.