Abstract Alcoholic liver disease (ALD) remains an important health problem in the United States. It ranks among the major causes of morbidity and mortality in the world, and affects millions of patients worldwide each year. The disease process is characterized by early steatosis, steatohepatitis, with some individuals ultimately progressing to fibrosis. Currently, there is no accepted therapy available to halt or reverse this process in humans. Nicotinamide N-methyltransferase (NNMT) catalyzes nicotinamide degradation via a SAM-dependent methylation reaction. Emerging evidence supports that NNMT is a novel regulator of metabolism. The very recent studies in our laboratory demonstrated for the first time that chronic alcohol exposure increases hepatic NNMT expression. Using both animal models and in vitro cell culture system, we identified NNMT as a pivotal regulator of cellular and mitochondrial NAD+ homeostasis and mitochondrial function. Specifically, we found that NNMT overexpression in hepatocytes decreased NAD content in both cytosol and mitochondrial and impair mitophagy induction, a protective mechanism in ALD. In this proposal, we will explore the mechanistic implication of NNMT in the pathogenesis of ALD. Successful performance of the studies proposed in this proposal will not only shed new light on the pathogenesis of this disease, but also pave the way for novel therapeutic interventions for ALD. The aims are: AIM 1: AIM 1: To determine the pathological role of NNMT upregulation in ALD and explore therapeutic potential of targeting NNMT for the treatment of the disease. We hypothesize that NNMT inhibition, via either genetic (shRNA administration) or pharmacological (1-MNA, a potent NNMT inhibitor) approach, can prevent and even reverse ALD development/progression. AIM 2: To delineate mechanisms involved in NNMT-induced cellular dysfunction in ALD. Both in vivo (alcohol feeding vs. NAD+ precursor supplementation) and in vitro (NNMT overexpression) experiments will be conducted to test our hypothesis that alcohol-induced NNMT overexpression contribute to ALD via decreasing cellular and mitochondrial NAD+ levels in both the liver and adipose tissue. AIM 3: To elucidate mechanisms underlying alcohol-induced NNMT overexpression. Hif-1alpha knockout mice will be employed to test our hypothesis that Hif-1alpha activation contributes to NNMT upregulation in both the liver and adipose tissue in response to chronic alcohol consumption.