Vinyl chloride (VC) is a chemical toxicant and an important occupational/environmental pollutant. VC exposure is linked with an increased risk of cancer. We have developed a new animal model of VC inhalation at concentrations relevant to human health. Although high occupational exposures to VC can directly cause toxicant-associated steatohepatitis, these studies have not considered interactions (of low conc. VC) with risk- modifying factors such as diet. Importantly, cumulative VC exposure may be an independent risk factor for cirrhosis and liver cancer caused by other hepatic ?hits.? Indeed, our recent studies suggest that obesity and hepatic steatosis increase susceptibility to VC, making them vulnerable to worse hepatic pathology. Since non- alcoholic fatty liver disease (NAFLD) is highly prevalent in the developed world, we intend to define the interactions between these two insults. We hypothesize that VC exposure may alter the epitranscriptome by altering mRNA levels post-transcriptionally, e.g., via impacting writer/reader/eraser activity.
Aim 1. Determine if VC exposure alters the hepatic epitranscriptome to contribute to worse phenotype associated with VC+HFD. A well-known effect of VC exposure is the formation of protein and nucleic acid adducts. Indeed, VC- DNA adducts are hypothesized to contribute to its carcinogenicity. Recent findings demonstrate that mRNA modifications have functional consequences that impact translation, without affecting steady-state levels (i.e., epitranscriptomics). In our studies, we observed several proteins/pathways that were impacted by VC exposure in vivo that did not directly impact mRNA expression levels. Given VC?s known ability to adduct nucleic acids, we propose the novel hypothesis that VC is impacting the epitranscriptome. We will therefore directly assess changes in epitranscriptomics in our experimental groups.
Aim 2. Evaluate the tumorigenic basis of VC at sub-OSHA level concentrations when co-exposed with the HFD. Current evidence suggests that misbalanced expression of enzymes (readers, writers and erasers) responsible for modulating RNA modifications are considered a possible signature for specific types of cancer. Considering the broad effect of RNA modifications on tumor cell biology, epitranscriptomic studies may shed light on those relatively unexplored epitranscriptomic mechanisms in tumors. Recent studies suggest positive interactions between VC exposure and known risk factors for liver cancer. Exciting new preliminary findings show enhanced tumorigenesis in mice exposed to VC and HFD as compared to VC or HFD alone. This observation mandates a more in-depth molecular characterization of these tumors. Here, tumor bearing livers from VC+HFD, or livers from VC alone, HFD alone and control groups will be utilized to compare and contrast changes in RNA expression and RNA modification. Associations between epitranscriptomic and gene expression changes in the various groups will be identified using standard computational biology methods. This is expected to yield novel insights into the basis of tumorigenesis in combined toxicant- and diet-induced HCC model.
We propose that vinyl chloride exposure, even below levels that are overtly hepatotoxic, may increase the stimulated inflammatory response in the liver via changes in the epitranscriptome, potentially adding another risk factor to the development of liver disease associated with diet-induced obesity (i.e., non-alcoholic fatty liver disease). The project will focus on the epitranscriptomic mechanisms of liver injury caused by the interaction of VC and diet in experimental NAFLD.
