Impacts of sex, biometals homeostasis, and dietary fructose on non-alcoholic fatty liver disease pathogenesis

Abstract

Non-alcoholic fatty liver disease (NAFLD) is a broad-spectrum liver disorder that ranges from simple hepatic steatosis to its more severe form, non-alcoholic steatohepatitis, which is marked by hepatic inflammation and cirrhosis. Estimates indicated NAFLD prevalence is currently between 25-30% of adults worldwide. Currently, there are no treatment options for NAFLD other than weight loss, as the etiology of this disease remains elusive. Prior studies have indicated that NAFLD is likely a multifactorial disease arising from interactions between factors like: genetics, nutrition, age, sex, hormone levels, lipid regulation, and biometals homeostasis. While prior studies have largely done an excellent job at defining the NAFLD landscape there are many factors known to impact NAFLD pathogenesis that remain understudied. This study aimed to examine the impacts of some of these factors; namely, biometals homeostasis, dietary fructose intake, and sex. This study first reviewed prior findings to outline the current understanding of the impacts of biological Cu on lipid metabolism and regulation. Next, we used dietary treatments in an animal model (Wistar rat) to examine the interplay between sex, dietary fructose and biometals homeostasis in NAFLD pathogenesis. Finally, an integrated network analysis of human RNA-Seq data was conducted to identify key genes involved in NALFD pathogenesis that were correlated with our factors of interest. In our review we identified some of the potential mechanisms by which copper (Cu) deficiency may promote NAFLD. These included increased immune cell activation, increased lipid biosynthesis, increased oxidative stress, and alterations to mitochondrial metabolism regulation. 1H nuclear magnetic resonance metabolomics results from the animal model identified distinct metabolic phenotypes that were highly correlated with diet and sex. Additionally, ICP-MS and western blot analysis identified previously unknown sex-specific responses to both fructose supplementation and restricted copper intake. Finally, our RNA-Seq integrated network analysis of human samples identified 66 total and 10 novel hub genes that are likely key regulators of NAFLD-related pathways. Enrichment analysis of the hub genes identified overrepresentation of genes related to the CAMKK2 pathway, oxidative phosphorylation, and regulation of mitochondrial transcription. All of the hub genes correlated with both disease status and sex were found to escape X-inactivation, suggesting XIST escapee genes may disproportionately impact sex-specific mechanisms of NAFLD pathogenesis. These results suggest sex, biometals homeostasis, and dietary fructose all impact NAFLD pathogenesis and further investigation into their roles should be pursued.