Silencing of the ER and Integrative Stress Responses in the Liver of Mice with Error-Prone Translation

Proteomic analysis of the hepatic response to a pollutant mixture in mice. The protective action of selenium

Metals and pharmaceuticals contaminate water and food worldwide, forming mixtures where they can interact to enhance their individual toxicity. Here we use a shotgun proteomic approach to evaluate the toxicity of a pollutant mixture (PM) of metals (As, Cd, Hg) and pharmaceuticals (diclofenac, flumequine) on mice liver proteostasis. These pollutants are abundant in the environment, accumulate in the food chain, and are toxic to humans primarily through oxidative damage. Thus, we also evaluated the putative antagonistic effect of low-dose dietary supplementation with the antioxidant trace element selenium. A total of 275 proteins were affected by PM treatment. Functional analyses revealed an increased abundance of proteins involved in the integrated stress response that promotes translation, the inflammatory response, carbohydrate and lipid metabolism, and the sustained expression of the antioxidative response mediated by NRF2. As a consequence, a reductive stress situation arises in the cell that inhibits the RICTOR pathway, thus activating the early stage of autophagy, impairing xenobiotic metabolism, and potentiating lipid biosynthesis and steatosis. PM exposure-induced hepato-proteostatic alterations were significantly reduced in Se supplemented mice, suggesting that the use of this trace element as a dietary supplement may at least partially ameliorate liver damage caused by exposure to environmental mixtures.

An integrative approach to assessing effects of a short-term Western diet on gene expression in rat liver

Consumption of a diet rich in saturated fatty acids and carbohydrates contributes to the accumulation of fat in the liver and development of non-alcoholic steatohepatitis (NASH). Herein we investigated the hypothesis that short-term consumption of a high fat/sucrose Western diet (WD) alters the genomic and translatomic profile of the liver in association with changes in signaling through the protein kinase mTORC1, and that such alterations contribute to development of NAFLD. The results identify a plethora of mRNAs that exhibit altered expression and/or translation in the liver of rats consuming a WD compared to a CD. In particular, consumption of a WD altered the abundance and ribosome association of mRNAs involved in lipid and fatty acid metabolism, as well as those involved in glucose metabolism and insulin signaling. Hepatic mTORC1 signaling was enhanced when rats were fasted overnight and then refed in the morning; however, this effect was blunted in rats fed a WD as compared to a CD. Despite similar plasma insulin concentrations, fatty acid content was elevated in the liver of rats fed a WD as compared to a CD. We found that feeding had a significant positive effect on ribosome occupancy of 49 mRNAs associated with hepatic steatosis (e.g., LIPE, LPL), but this effect was blunted in the liver of rats fed a WD. In many cases, changes in ribosome association were independent of alterations in mRNA abundance, suggesting a critical role for diet-induced changes in mRNA translation in the expression of proteins encoded by those mRNAs. Overall, the findings demonstrate that short-term consumption of a WD impacts hepatic gene expression by altering the abundance of many mRNAs, but also causes wide-spread variation in mRNA translation that potentially contribute to development of hepatic steatosis.