MOLECULAR DRIVERS OF DISEASE PATHOGENESIS IN NONALCOHOLIC STEATOHEPATITIS

Abstract

Non-alcoholic fatty liver disease (NAFLD) is the number one cause of chronic liver disease worldwide, with 25% of these patients developing nonalcoholic steatohepatitis (NASH). NASH is characterized by steatosis, inflammation, cell death, and liver fibrosis and significantly increases the risk of cirrhosis and decompensated liver failure. There are currently no approved drugs on the market for treating NASH leaving a major unmet medical need for drug discovery research. The aim of this dissertation is to better understand the pathophysiology of NASH and elucidate disease driving molecular mechanisms that can be used for drug targeting. Analysis of human liver samples using state of the art mass spectrometry proteomics identified dysregulation of one-carbon metabolism in NASH. This dissertation details the molecular mechanisms for how these proteomic changes can drive NASH pathogenesis and be targeted for therapeutic purposes. Chapter 1 provides an extensive background on NASH prevalence and pathophysiology and the association of one-carbon metabolism and NASH. Chapter 2 presents the identification of reduced glycine N-methyltransferase, a key regulator of one-carbon metabolism, in human NASH patients. Using a diet-induced animal model of NASH and targeted proteomics and metabolomics it was found glycine N-methyltransferase reduction in NASH leads to an accumulation of S-adenosylmethionine, activation of polyamine metabolism, and production of oxidative stress. Oxidative stress is a key component to NASH pathogenesis and this work identifies a novel mechanism for how oxidative stress is produced during NASH. Chapter 3 covers the discovery of increased folate receptor gamma (FOLR3) specifically in the liver of NASH patients. Initially, FOLR3 was predicted to impact one-carbon metabolism through folate metabolism, but molecular characterization found FOLR3 drives liver fibrogenesis independent of one-carbon metabolism. Chapter 3 details the molecular mechanism for how FOLR3 drives liver fibrosis by enhancing transforming growth factor beta activation of hepatic stellate cells through its interaction with serine protease HTRA1. The effect of FOLR3 was then validated in an in vivo model of NASH showing FOLR3 treatment can induce severe liver fibrosis in mice comparable to human liver fibrosis. These findings provide a translational animal model that can be used for NASH drug development and introduce a novel drug target in FOLR3. Chapter 4 discusses the innovation and translational impact of these findings and Chapter 5 summarizes the main results of this dissertation.