PROJECT SUMMARY/ABSTRACT Excess fatty acids promote oxidative stress, cell death, and tissue dysfunction through a process called lipotoxicity. In the liver, lipotoxicity contributes to nonalcoholic fatty liver disease, a disorder that can progress from simple steatosis to nonalcoholic steatohepatitis (NASH), cirrhosis, or liver failure. The mechanisms that connect lipid accumulation to cellular injury in NASH are not fully understood, but have been proposed to involve lipid-induced oxidative stress. To uncover novel genes involved in lipotoxicity, our group conducted a promoter trap mutagenesis screen in Chinese Hamster Ovary cells and selected for mutants resistant to palmitate-induced cell death. Lines harboring loss-of-function mutations in the small nucleolar RNA hosting gene 3 (Snhg3) locus were isolated and shown to be resistant to palmitate-induced oxidative stress, raising the possibility that this locus may regulate the transition from steatosis to hepatitis in NASH. Snhg3 produces a long noncoding RNA, SNHG3, and the U17 small nucleolar RNAs. I hypothesize that RNAs encoded by the Snhg3 locus regulate lipotoxicity through interactions with other RNAs and proteins involved in cell metabolism, and that Snhg3 regulates the pathogenesis of NASH. In Specific Aim 1, I will determine the RNA element(s) of Snhg3 that mediates lipotoxicity and identify its associated RNAs and proteins. This work will provide mechanistic information regarding Snhg3 regulation of lipid-induced cell death. In Specific Aim 2, novel mouse models of liver-specific Snhg3 knockout or overexpression will be used to examine the role of this locus in diet-induced NASH. The overall goal of this research is to elucidate mechanisms of lipotoxicity in nonalcoholic fatty liver disease, which could lead to new therapeutic strategies for targeting of noncoding RNAs that precipitate metabolic stress.