Fasting increases human skeletal muscle net phenylalanine release and this is associated with decreased mTOR signaling

Mikkel Holm Vendelbo, Andreas Buch Møller, Britt Christensen, Birgitte Nellemann, Berthil Frederik Forrest Clasen, K Sreekumaran Nair, Jens Otto Lunde Jørgensen, Niels Jessen, Niels Møller

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

Aim: Fasting is characterised by profound changes in energy metabolism including progressive loss of body proteins. The underlying mechanisms are however unknown and we therefore determined the effects of a 72-hour-fast on human skeletal muscle protein metabolism and activation of mammalian target of rapamycin (mTOR), a key regulator of cell growth. Methods: Eight healthy male volunteers were studied twice: in the postabsorptive state and following 72 hours of fasting. Regional muscle amino acid kinetics was measured in the forearm using amino acid tracers. Signaling to protein synthesis and breakdown were assessed in skeletal muscle biopsies obtained during non-insulin and insulin stimulated conditions on both examination days. Results: Fasting significantly increased forearm net phenylalanine release and tended to decrease phenylalanine rate of disappearance. mTOR phosphorylation was decreased by ∼50% following fasting, together with reduced downstream phosphorylation of 4EBP1, ULK1 and rpS6. In addition, the insulin stimulated increase in mTOR and rpS6 phosphorylation was significantly reduced after fasting indicating insulin resistance in this part of the signaling pathway. Autophagy initiation is in part regulated by mTOR through ULK1 and fasting increased expression of the autophagic marker LC3B-II by ∼30%. p62 is degraded during autophagy but was increased by ∼10% during fasting making interpretation of autophagic flux problematic. MAFbx and MURF1 ubiquitin ligases remained unaltered after fasting indicating no change in protesomal protein degradation. Conclusions: Our results show that during fasting increased net phenylalanine release in skeletal muscle is associated to reduced mTOR activation and concomitant decreased downstream signaling to cell growth.

Original languageEnglish (US)
Article numbere102031
JournalPLoS One
Volume9
Issue number7
DOIs
StatePublished - Jul 14 2014

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Sirolimus
Phenylalanine
phenylalanine
fasting
Muscle
skeletal muscle
Fasting
Skeletal Muscle
Phosphorylation
Cell growth
Insulin
Chemical activation
phosphorylation
Amino Acids
autophagy
Autophagy
Proteins
Muscle Proteins
Biopsy
Forearm

ASJC Scopus subject areas

  • Agricultural and Biological Sciences(all)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Medicine(all)

Cite this

Vendelbo, M. H., Møller, A. B., Christensen, B., Nellemann, B., Clasen, B. F. F., Nair, K. S., ... Møller, N. (2014). Fasting increases human skeletal muscle net phenylalanine release and this is associated with decreased mTOR signaling. PLoS One, 9(7), [e102031]. https://doi.org/10.1371/journal.pone.0102031

Fasting increases human skeletal muscle net phenylalanine release and this is associated with decreased mTOR signaling. / Vendelbo, Mikkel Holm; Møller, Andreas Buch; Christensen, Britt; Nellemann, Birgitte; Clasen, Berthil Frederik Forrest; Nair, K Sreekumaran; Jørgensen, Jens Otto Lunde; Jessen, Niels; Møller, Niels.

In: PLoS One, Vol. 9, No. 7, e102031, 14.07.2014.

Research output: Contribution to journalArticle

Vendelbo, MH, Møller, AB, Christensen, B, Nellemann, B, Clasen, BFF, Nair, KS, Jørgensen, JOL, Jessen, N & Møller, N 2014, 'Fasting increases human skeletal muscle net phenylalanine release and this is associated with decreased mTOR signaling', PLoS One, vol. 9, no. 7, e102031. https://doi.org/10.1371/journal.pone.0102031
Vendelbo, Mikkel Holm ; Møller, Andreas Buch ; Christensen, Britt ; Nellemann, Birgitte ; Clasen, Berthil Frederik Forrest ; Nair, K Sreekumaran ; Jørgensen, Jens Otto Lunde ; Jessen, Niels ; Møller, Niels. / Fasting increases human skeletal muscle net phenylalanine release and this is associated with decreased mTOR signaling. In: PLoS One. 2014 ; Vol. 9, No. 7.
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