No increase in the expression of key unfolded protein response genes in HCV genotype 3 patients with severe steatosis

Naringenin inhibits alcoholic injury by improving lipid metabolism and reducing apoptosis in zebrafish larvae

Alcoholic liver disease (ALD) includes a spectrum of hepatic abnormalities that range from isolated alcoholic steatosis to steatohepatitis and cirrhosis. Naringenin, a predominant flavanone in grapefruit, increases resistance to oxidative stress and inflammation and protects against multiple organ injury in various animal models. However, the specific mechanisms responsible for protection against alcoholic injury are poorly understood. In the present study, we aimed to investigate the effect of naringenin on alcoholic events and the molecular regulatory mechanisms of naringenin in the liver and whole body of zebrafish larvae following exposure to 350 mmol/l ethanol for 32 h. Zebrafish larvae {4 days post‑fertilization (dpf); wild-type (WT) and a transgenic line with liver-specific eGFP expression [Tg(lfabp10α-eGFP)]} were used to establish an alcoholic fatty liver model in order to evaluate the effects of naringenin treatment on anti-alcoholic injury. Naringenin significantly reduced alcoholic liver morphological phenotypes and the expression of alcohol and lipid metabolism-related genes, including cyp2y3, cyp3a65, hmgcra, hmgcrb, fasn, fabp10α, fads2 and echs1, in zebrafish larvae. Naringenin also attenuated hepatic apoptosis in larvae as detected by TUNEL staining, consistent with the expression of critical biomarkers of endoplasmic reticulum stress and of DNA damage genes (chop, gadd45αa and edem1). The present study showed that naringenin inhibited alcohol-induced liver steatosis and injury in zebrafish larvae by reducing apoptosis and DNA damage and by harmonizing alcohol and lipid metabolism.

Molecularly defined unfolded protein response subclasses have distinct correlations with fatty liver disease in zebrafish

The unfolded protein response (UPR) is a complex network of sensors and target genes that ensure efficient folding of secretory proteins in the endoplasmic reticulum (ER). UPR activation is mediated by three main sensors, which regulate the expression of hundreds of targets. UPR activation can result in outcomes ranging from enhanced cellular function to cell dysfunction and cell death. How this pathway causes such different outcomes is unknown. Fatty liver disease (steatosis) is associated with markers of UPR activation and robust UPR induction can cause steatosis; however, in other cases, UPR activation can protect against this disease. By assessing the magnitude of activation of UPR sensors and target genes in the liver of zebrafish larvae exposed to three commonly used ER stressors (tunicamycin, thapsigargin and Brefeldin A), we have identified distinct combinations of UPR sensors and targets (i.e. subclasses) activated by each stressor. We found that only the UPR subclass characterized by maximal induction of UPR target genes, which we term a stressed-UPR, induced steatosis. Principal component analysis demonstrated a significant positive association between UPR target gene induction and steatosis. The same principal component analysis showed significant correlation with steatosis in samples from patients with fatty liver disease. We demonstrate that an adaptive UPR induced by a short exposure to thapsigargin prior to challenging with tunicamycin reduced both the induction of a stressed UPR and steatosis incidence. We conclude that a stressed UPR causes steatosis and an adaptive UPR prevents it, demonstrating that this pathway plays dichotomous roles in fatty liver disease.