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The role of amino acids in liver protein metabolism under a high protein diet : identification of amino acids signal and associated transduction pathways

Abstract : High Protein (HP) intake improves glucose homeostasis and reduces weight gain, body fat mass, white adipose tissue and adipocyte size in rats. The metabolic adaptation is characterized by at least a decrease in hepatic lipogenesis and an increase in hepatic amino acid (AA) conversion into glycogen. However, the role of amino acids (AAs) in the control of these metabolic adaptations has not been studied, and the transduction pathways involved in the sensing of the increase in AA supply remain unclear. Therefore, the aim of our study was to understand the effect of AAs on translation and on proteolysis, to identify the transduction pathways involved in AA signaling and the AA or the groups of AAs involved in these effects, using both in vivo and in vitro approaches. Western blot analysis was performed on protein extracts to examine the phosphorylation state of the mammalian target of rapamycin (mTOR), adenosine monophosphate-activated protein kinase (AMPK) and general control non-depressible kinase 2 (GCN2) transduction pathways which may be involved in AA sensing and in the control of translation in liver. This study demonstrated that adaptation to HP diet was characterized by the stimulation of translation, at least for the initiation step in the liver. Using primary culture of hepatocytes, we showed that this activation required both high AA levels (at least for leucine alone or a branched-chain AA mixture) and insulin, as indicated by the increase of mTOR, 4E-BP1 and S6 phosphorylation and the decrease of AMPK and GCN2 phosphorylation. Using AICAR (AMPK activator) and rapamycin (mTOR inhibitor), we demonstrated that mTOR might not be the only regulator of 4E-BP1 and S6K1 (downstream targets of mTOR) in high AA conditions and that AMPK may also play an important role in their control. Moreover, the HP diet induced the inhibition of protein breakdown in the liver and these results were concomitant with a decrease of gene expression of the major components for both autophagy and the ubiquitin-proteasome system in liver. Subsequently, ubiquitinated protein in the liver was lower and both AAs and insulin were required for the down-regulation of ubiquitination. Indeed, mTOR and AMPK were also involved in the control of the ubiquitin proteasome system in the liver in response to the increase in AA and insulin concentrations. These results suggested that the control of the catabolic and anabolic pathways of protein metabolism was regulated by the same set of signals and mediated by the same transduction signaling pathways.
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https://pastel.archives-ouvertes.fr/pastel-00610998
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Submitted on : Monday, July 25, 2011 - 1:57:19 PM
Last modification on : Tuesday, March 17, 2020 - 3:14:08 AM
Long-term archiving on: : Wednesday, October 26, 2011 - 2:21:50 AM

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  • HAL Id : pastel-00610998, version 1

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Nattida Chotechuang. The role of amino acids in liver protein metabolism under a high protein diet : identification of amino acids signal and associated transduction pathways. Food and Nutrition. AgroParisTech, 2010. English. ⟨NNT : 2010AGPT0026⟩. ⟨pastel-00610998⟩

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