Reducing endoplasmic reticulum stress does not improve steatohepatitis in mice fed a 1 methionine - and choline - deficient diet

21 Background: Endoplasmic reticulum (ER) stress has been implicated in the pathogenesis of nonalcoholic 22 steatohepatitis. The ER stress response is activated in the livers of mice fed a methionineand choline23 deficient (MCD) diet yet the role of ER stress in the pathogenesis of MCD diet-induced steatohepatitis is 24 unknown. We aim to determine the effects of reducing ER stress using chemical chaperones on hepatic 25 steatosis and markers of inflammation and fibrosis in mice fed a MCD diet. Methods: C57BL/6J mice 26 were fed a MCD diet with or without the ER chemical chaperones, 4-phenylbutyric acid (PBA) or 27 tauroursodeoxycholic acid (TUDCA), for 2 weeks. Results: TUDCA and PBA effectively attenuated the 28 ER stress response in MCD-fed mice as evidenced by reduced protein levels of phosphorylated eIF229 alpha and phosphorylated JNK and suppression of mRNA levels of CHOP, GRP78, and XBP1. 30 However, PBA and TUDCA did not decrease MCD diet-induced hepatic steatosis. MCD diet-induced 31 hepatic inflammation, as evidenced by increased plasma ALT and induction of hepatic tumor necrosis 32 factor (TNF) alpha expression, was also not reduced by PBA or TUDCA. PBA and TUDCA did not 33 attenuate MCD diet-induced upregulation of the fibrosis-associated genes, TIMP-1 or MMP-9. 34 Conclusions: ER chemical chaperones reduce MCD diet-induced ER stress, yet do not improve MCD 35 diet-induced hepatic steatosis, inflammation, or activation of genes associated with fibrosis. These data 36 suggest that although the ER stress response is activated by the MCD diet, it does not have a primary role 37 in the pathogenesis of MCD diet-induced steatohepatitis. 38 39