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Am J Physiol Endocrinol Metab. 2017 Jan 1;312(1):E27-E36. doi: 10.1152/ajpendo.00203.2016. Epub 2016 Nov 8.

Citrulline directly modulates muscle protein synthesis via the PI3K/MAPK/4E-BP1 pathway in a malnourished state: evidence from in vivo, ex vivo, and in vitro studies.

Author information

1
Laboratoire de Biologie de la Nutrition, EA4466, Faculté de Pharmacie, Université Paris Descartes, Sorbonne-Paris-Cité, Paris, France; servane.le-plenier@parisdescartes.fr.
2
Laboratoire de Biologie de la Nutrition, EA4466, Faculté de Pharmacie, Université Paris Descartes, Sorbonne-Paris-Cité, Paris, France.
3
Centre National de la Recherche Scientifique UMR 8104, Institut Cochin, Université Paris Descartes, Sorbonne-Paris-Cité, Paris, France.
4
Laboratoire d'épidémiologie environnementale, EA 4064, Faculté de Pharmacie, Université Paris Descartes, Sorbonne-Paris-Cité, Paris, France.
5
Unité de Nutrition humaine, UMR 1019, Institut National de la Recherche Agronomique/Université d'Auvergne, Centre de Recherche en Nutrition Humaine, Auvergne, Clermont-Ferrand, France; and.
6
Service de Biochimie interhospitalier Cochin et Hôtel-Dieu, GH Hôpitaux universitaire Paris Centre, AP-HP, Paris, France.

Abstract

Citrulline (CIT) is an endogenous amino acid produced by the intestine. Recent literature has consistently shown CIT to be an activator of muscle protein synthesis (MPS). However, the underlying mechanism is still unknown. Our working hypothesis was that CIT might regulate muscle homeostasis directly through the mTORC1/PI3K/MAPK pathways. Because CIT undergoes both interorgan and intraorgan trafficking and metabolism, we combined three approaches: in vivo, ex vivo, and in vitro. Using a model of malnourished aged rats, CIT supplementation activated the phosphorylation of S6K1 and 4E-BP1 in muscle. Interestingly, the increase in S6K1 phosphorylation was positively correlated (P < 0.05) with plasma CIT concentration. In a model of isolated incubated skeletal muscle from malnourished rats, CIT enhanced MPS (from 30 to 80% CIT vs. Ctrl, P < 0.05), and the CIT effect was abolished in the presence of wortmannin, rapamycin, and PD-98059. In vitro, on myotubes in culture, CIT led to a 2.5-fold increase in S6K1 phosphorylation and a 1.5-fold increase in 4E-BP1 phosphorylation. Both rapamycin and PD-98059 inhibited the CIT effect on S6K1, whereas only LY-294002 inhibited the CIT effect on both S6K1 and 4E-BP1. These findings show that CIT is a signaling agent for muscle homeostasis, suggesting a new role of the intestine in muscle mass control.

KEYWORDS:

amino acids; eukaryotic initiation factor 4E-binding protein 1; mammalian target of rapamycin; mitogen-activated protein kinase; muscle; myotube; phosphatidylinositol 3-kinase; protein synthesis

PMID:
27827806
DOI:
10.1152/ajpendo.00203.2016
[Indexed for MEDLINE]
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