title: Role of AMPK in regulation of LC3 lipidation as a marker of autophagy in skeletal muscle.
abstract: During induction of the autophagosomal degradation process, LC3-I is lipidated to LC3-II and associates to the cargo isolation membrane allowing for autophagosome formation. Lipidation of LC3 results in an increased LC3-II/LC3-I ratio, and this ratio is an often used marker for autophagy in various tissues, including skeletal muscle. From cell studies AMPK has been proposed to be necessary and sufficient for LC3 lipidation. The aim of the present study was to investigate the role of AMPK in regulation of LC3 lipidation as a marker of autophagy in skeletal muscle. We observed an increase in the LC3-II/LC3-I ratio in skeletal muscle of AMPKα2 kinase-dead (KD) (p<0.001) and wild type (WT) (p<0.05) mice after 12h of fasting, which was greater (p<0.05) in AMPKα2 KD mice than in WT. The fasting-induced increase in the LC3-II/LC3-I ratio in both genotypes coincided with an initial decrease (p<0.01) in plasma insulin concentration, a subsequent decrease in muscle mTORC1 signaling and increased (p<0.05) levels of the autophagy-promoting proteins, FoxO3a and ULK1. Furthermore, a higher (p<0.01) LC3-II/LC3-I ratio was observed in old compared to young mice. We were not able to detect any change in LC3 lipidation with either in vivo treadmill exercise or in situ contractions. Collectively, these findings suggest that AMPKα2 is not necessary for induction of LC3 lipidation with fasting and aging. Furthermore, LC3 lipidation is increased in muscle lacking functional AMPKα2 during fasting and aging. Moreover, LC3 lipidation seems not to be a universal response to muscle contraction in mice.
authors.affiliation: Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, the August Krogh Centre, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Andreas Mæchel
authors.initials: AM
authors.lastname: Fritzen
authors.affiliation: Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, the August Krogh Centre, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Christian
authors.initials: C
authors.lastname: Frøsig
authors.affiliation: Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, the August Krogh Centre, Faculty of Science, University of Copenhagen, Copenhagen, Denmark; Incretin and Obesity Pharmacology, Novo Nordisk A/S, Maaloev, Denmark.
authors.forename: Jacob
authors.initials: J
authors.lastname: Jeppesen
authors.affiliation: Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, the August Krogh Centre, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Thomas Elbenhardt
authors.initials: TE
authors.lastname: Jensen
authors.affiliation: Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, the August Krogh Centre, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Lundsgaard
authors.affiliation: Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, the August Krogh Centre, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Annette Karen
authors.initials: AK
authors.lastname: Serup
authors.affiliation: Institute of Sports Medicine, Department of Orthopedic Surgery M, Bispebjerg Hospital and Center for Healthy Aging, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Peter
authors.initials: P
authors.lastname: Schjerling
authors.affiliation: South Australian Health and Medical Research Institute and University of Adelaide, Adelaide, Australia.
authors.forename: Chris G
authors.initials: CG
authors.lastname: Proud
authors.affiliation: Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, the August Krogh Centre, Faculty of Science, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Erik A
authors.initials: EA
authors.lastname: Richter
authors.affiliation: Section of Molecular Physiology, Department of Nutrition, Exercise and Sports, the August Krogh Centre, Faculty of Science, University of Copenhagen, Copenhagen, Denmark. Electronic address: bkiens@nexs.ku.dk.
authors.forename: Bente
authors.initials: B
authors.lastname: Kiens
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D000375:Aging / Q000502:physiology; D000818:Animals; D001343:Autophagy; D015415:Biomarkers; D005260:Female; D055879:Gene Knock-In Techniques; D050356:Lipid Metabolism; D008810:Mice, Inbred C57BL; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000201:enzymology / Q000378:metabolism* / Q000502:physiology; D020652:Peptide Elongation Factor 2 / Q000235:genetics; D010805:Physical Conditioning, Animal; D015398:Signal Transduction
chemical_list: D015415:Biomarkers; C480860:Map1lc3b protein, mouse; D008869:Microtubule-Associated Proteins; D020652:Peptide Elongation Factor 2; D055372:AMP-Activated Protein Kinases
keywords: AMPK; Aging; Autophagy; Exercise and eEF2K; Fasting; LC3 lipidation