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.