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Argininosuccinate synthetase regulates hepatic AMPK linking protein catabolism
and ureagenesis to hepatic lipid metabolism
#MMPMID27247419
Madiraju AK
; Alves T
; Zhao X
; Cline GW
; Zhang D
; Bhanot S
; Samuel VT
; Kibbey RG
; Shulman GI
Proc Natl Acad Sci U S A
2016[Jun]; 113
(24
): E3423-30
PMID27247419
show ga
A key sensor of cellular energy status, AMP-activated protein kinase (AMPK),
interacts allosterically with AMP to maintain an active state. When active, AMPK
triggers a metabolic switch, decreasing the activity of anabolic pathways and
enhancing catabolic processes such as lipid oxidation to restore the energy
balance. Unlike oxidative tissues, in which AMP is generated from adenylate
kinase during states of high energy demand, the ornithine cycle enzyme
argininosuccinate synthetase (ASS) is a principle site of AMP generation in the
liver. Here we show that ASS regulates hepatic AMPK, revealing a central role for
ureagenesis flux in the regulation of metabolism via AMPK. Treatment of primary
rat hepatocytes with amino acids increased gluconeogenesis and ureagenesis and,
despite nutrient excess, induced both AMPK and acetyl-CoA carboxylase (ACC)
phosphorylation. Antisense oligonucleotide knockdown of hepatic ASS1 expression
in vivo decreased liver AMPK activation, phosphorylation of ACC, and plasma
?-hydroxybutyrate concentrations. Taken together these studies demonstrate that
increased amino acid flux can activate AMPK through increased AMP generated by
ASS, thus providing a novel link between protein catabolism, ureagenesis, and
hepatic lipid metabolism.
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