AMPK promotes skeletal muscle autophagy through activation of forkhead FoxO3a and interaction with Ulk1

Authors

  • Anthony MJ Sanchez,

    Corresponding author
    1. INRA, UMR866 Dynamique Musculaire et Métabolisme, 2 Place Viala, F-34060 Montpellier, France
    2. Université de Montpellier 1, Faculté des Sciences du Sport, 700 av du Pic Saint-Loup, F-34090 Montpellier, France
    • INRA, UMR866 Dynamique Musculaire et Métabolisme, Faculté des Sciences du Sport, Université Montpellier 1, 2 place Viala, F-34060 Montpellier, France.
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  • Alfredo Csibi,

    1. Université de Montpellier 1, Faculté des Sciences du Sport, 700 av du Pic Saint-Loup, F-34090 Montpellier, France
    Current affiliation:
    1. Harvard Medical School, Boston.
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  • Audrey Raibon,

    1. Université de Montpellier 1, Faculté des Sciences du Sport, 700 av du Pic Saint-Loup, F-34090 Montpellier, France
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  • Karen Cornille,

    1. Université de Montpellier 1, Faculté des Sciences du Sport, 700 av du Pic Saint-Loup, F-34090 Montpellier, France
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  • Stéphanie Gay,

    1. Université de Montpellier 1, Faculté des Sciences du Sport, 700 av du Pic Saint-Loup, F-34090 Montpellier, France
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  • Henri Bernardi,

    1. Université de Montpellier 1, Faculté des Sciences du Sport, 700 av du Pic Saint-Loup, F-34090 Montpellier, France
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  • Robin Candau

    1. INRA, UMR866 Dynamique Musculaire et Métabolisme, 2 Place Viala, F-34060 Montpellier, France
    2. Université de Montpellier 1, Faculté des Sciences du Sport, 700 av du Pic Saint-Loup, F-34090 Montpellier, France
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  • Conflicts of interest: None.

  • Henri Bernardi and Robin Candau contributed equally to this work.

Abstract

In skeletal muscle, protein levels are determined by relative rates of protein synthesis and breakdown. The balance between synthesis and degradation of intracellular components determines the overall muscle fiber size. AMP-activated protein kinase (AMPK), a sensor of cellular energy status, was recently shown to increase myofibrillar protein degradation through the expression of MAFbx and MuRF1. In the present study, the effect of AMPK activation by AICAR on autophagy was investigated in muscle cells. Our results show that FoxO3a transcription factor activation by AMPK induces the expression of the autophagy-related proteins LC3B-II, Gabarapl1, and Beclin1 in primary mouse skeletal muscle myotubes and in the Tibialis anterior (TA) muscle. Time course studies reveal that AMPK activation by AICAR leads to a transient nuclear relocalization of FoxO3a followed by an increase of its cytosolic level. Moreover, AMPK activation leads to the inhibition of mTORC1 and its subsequent dissociation of Ulk1, Atg13, and FIP200 complex. Interestingly, we identify Ulk1 as a new interacting partner of AMPK in muscle cells and we show that Ulk1 is associated with AMPK under normal conditions and dissociates from AMPK during autophagy process. Moreover, we find that AMPK phosphorylates FoxO3a and Ulk1. In conclusion, our data show that AMPK activation stimulates autophagy in skeletal muscle cells through its effects on the transcriptional function of FoxO3a and takes part in the initiation of autophagosome formation by interacting with Ulk1. Here, we present new evidences that AMPK plays a crucial role in the fine tuning of protein expression programs that control skeletal muscle mass. J. Cell. Biochem. 113: 695–710, 2012. © 2011 Wiley Periodicals, Inc.

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