ABSTRACT
Liver plays a central role in S-adenosylmethionine (SAMe, the principal methyl donor) metabolism, as this is
where 50% of methionine intake is catabolized to SAMe. In liver, SAMe biosynthesis is mediated by
methionine adenosyltransferase 1A (MAT1A)-encoded enzyme. Patients with advanced non-alcoholic
steatohepatitis (NASH) have reduced MAT1A expression. We developed the Mat1a knockout (KO) mouse
model, which has chronically low hepatic SAMe level, spontaneous development of NASH and hepatocellular
carcinoma (HCC). This grant, currently in its 16th year, has supported 77 original papers plus 27 reviews.
During the past funding period we showed how dysregulation of SAMe leads to NASH, defined the
metabolomic signatures as a function of hepatic SAMe content and found nearly 50% of non-alcoholic fatty
liver disease (NAFLD) patients share the M-subtype metabolomic signature of the Mat1a KO mice. Using this
KO model, we have uncovered two novel SAMe targets, aldolase B (ALDOB) hypomethylation and La
Ribonucleoprotein Domain Family Member 1 (LARP1) hyperphosphorylation, that we hypothesize are linked to
NASH progression during fructose consumption and NASH-HCC, respectively. This renewal application tests
this novel hypothesis in two specific aims. Specific Aim 1 examines the role of ALDOB R173 methylation in
NAFLD progression. Our data support the hypothesis that ALDOB exists in two forms: one that is
unmethylated, enzymatically active and senses fructose 1,6-bisphosphate (FBP) level to regulating AMPK
activity; and a second form that is methylated, enzymatically inactive and does not regulate AMPK activity. We
further hypothesize that in Mat1a KO mice ALDOB hypomethylation (with higher activity and lower FBP)
activates AMPK as an adaptive response to halt further fatty acid accumulation but this will be disrupted by
fructose consumption, which will increase FBP content and accelerate NASH progression. We will define 1)
how SAMe depletion affect glucose/fructose flux, 2) how ALDOB R173 is methylated and how it affects ALDOB
structure, activity, and FBP sensing, 3) whether fructose consumption accelerates NASH progression through
dampening AMPK activation, and 4) relevance to human NAFLD. Specific Aim 2 will examine the role of
LARP1 in NASH-HCC progression. Our data show LARP1 protein level and phosphorylation at multiple sites
(some are novel) are increased under SAMe depletion, leading to enhanced translation of 5’-terminal
oligopyrimidine tract mRNAs, including proteins involved in translation. Overexpressing LARP1 enhanced HCC
cell growth, migration and invasion. We will define 1) how SAMe regulates LARP1 expression, 2) which
kinases are responsible, 3) how phosphorylation affects LARP1 function, 4) whether LARP1 is a driver of
NASH-HCC in SAMe deficiency, and 5) relevance to human NAFLD. Successful completion of these proposed
aims will provide important insights on how fructose consumption accelerates NASH progression and how
LARP1 drives HCC development in patients with NAFLD, topics that are highly relevant to public health.