Role of SAMe in Pathogenesis and Treatment of Non-Alcholic Fatty Liver Disease

Cedars-Sinai Medical Center, West Hollywood CA

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Abstract

DESCRIPTION (provided by applicant):-Adenosylmethionine (SAMe) is the principal biological methyl donor, precursor of polyamines and GSH. Liver plays a central role in SAMe metabolism, as this is where the bulk of SAMe is generated as the product of methionine catabolism. This reaction is catalyzed by methionine adenosyltransferase (MAT), encoded by MAT1A in liver. In liver, SAMe homeostasis is controlled by MAT-mediated biosynthesis and utilization, largely accomplished by glycine N-methyltransferase (GNMT). We developed the MAT1A knockout (KO) mouse model, which exhibits chronic hepatic SAMe deficiency, development of non-alcoholic steatohepatitis (NASH) and hepatocellular carcinoma (HCC). This model recapitulates the situation in many patients with chronic liver disease, as hepatic SAMe biosynthesis is impaired. We also developed the GNMT KO mouse model, where hepatic SAMe accumulates to supraphysiological level and the mice develop liver injury, NASH, fibrosis and also HCC. This model is relevant to human disease as children with GNMT mutations have liver injury. These models have been instrumental in teaching us about the various functions of SAMe in the liver. This grant is currently in its 10th year and we have published 63 original papers plus 23 reviews. During the past funding period we showed how dysregulation of SAMe could lead to liver injury and malignant degeneration. We also found that chronically high and low hepatic SAMe levels lead to NASH via different alterations in lipid metabolism that is reflected in their lipidomic profiles. Our finding led us to hypothesize that altered hepatic SAMe level is an important determinant in the progression of steatosis to NASH. In addition, we hypothesize that lipidomic profiling from the two KO models can help categorize NASH patients and personalize NASH treatment. Four specific aims are proposed to test these hypotheses: 1. Examine the influence of SAMe level on personalized NASH treatment. We will test different proposed NASH treatment protocols in the two KO models to see how they affect their lipidomics and NASH progression. 2. Examine the influence of SAMe level on progression from steatosis to NASH. We will test the hypothesis that when hepatic SAMe level is altered by reducing either MAT1A or GNMT expression, this will convert animal models of simple steatosis to NASH. 3. Examine the influence of SAMe level on serum lipid signature. We will examine and compare serum lipidomics in MAT1A KO to GNMT KO mice to generate M-type (for MAT1A) and G-type (for GNMT) serum lipid signatures. We will examine serum lipid profiles from 467 patients to see if they can be categorized into these types. 4. Validate lipid signatures in NASH patients. We will prospectively validate both liver and serum lipid signatures in a group of NASH patients and compare the lipid profiles to hepatic SAMe metabolite levels, expression of MAT1A, GNMT and genes involved in lipid metabolism. Successful completion of these proposed aims will further enhance our knowledge of how altered SAMe metabolism affects NAFLD progression and help personalize NASH treatment, which are highly relevant to public health.