title: Autophagy and protein turnover signaling in slow-twitch muscle during exercise.
abstract: OBJECTIVE
  The aim of this study was to characterize skeletal muscle protein breakdown and mitochondrial dynamics markers at different points of endurance exercise.
  
  
  METHODS
  Mice run at 10 m·min(-1) during 1 h, and running speed was increased by 0.5 m·min(-1) every minute during 40 min and then by 1 m·min(-1) until exhaustion. Animals were killed by cervical dislocation at 30, 60, 90, and 120 min; at time to exhaustion (Te); and at 3 and 24 h during recovery. The soleus and the deep red regions of the quadriceps muscles were pooled.
  
  
  RESULTS
  AMPK phosphorylation (Thr172) increased from 30 min to Te, and FoxO3a phosphorylation (Thr32 and Ser253) decreased from 120 min to 3 h after exercise. FoxO3a-dependent E3 ligases Mul1 and MuRF1 proteins increased from 30 min to Te and at Te and 3 h after exercise, respectively, whereas MAFbx/atrogin-1 protein expression did not change significantly. The autophagic markers LC3B-II increased at 120 min and Te, and p62 significantly decreased at Te. The AMPK-dependent phosphorylation of Ulk1 at Ser317 and Ser555 increased from 60 min to Te and at 30 and 60 min, respectively. Akt (Ser473), MTOR (Ser2448), and 4E-BP1 (Thr37/46) phosphorylation decreased from 90 min to Te, and the MTOR-dependent phosphorylation of Ulk1 (Ser757) decreased from 120 min to Te. Ser616 phosphorylation of the mitochondrial fission marker DRP1 increased from 60 min to Te, but protein expression of the fusion markers mitofusin-2, a substrate of Mul1, and OPA1 did not significantly change.
  
  
  CONCLUSIONS
  These results fit with a regulation of protein breakdown triggered by FoxO3a and Ulk1 pathways after AMPK activation and Akt/MTOR inhibition. Furthermore, our data suggest that mitochondrial fission is quickly increased, and mitochondrial fusion is unchanged during exercise.
authors.affiliation: 1Faculty of Sport Sciences, University of Montpellier 1, Montpellier, FRANCE; and 2INRA, UMR866 Dynamique Musculaire Et Métabolisme, University of Montpellier 1, Montpellier, FRANCE.
authors.forename: Allan F
authors.initials: AF
authors.lastname: Pagano
authors.forename: Guillaume
authors.initials: G
authors.lastname: Py
authors.forename: Henri
authors.initials: H
authors.lastname: Bernardi
authors.forename: Robin B
authors.initials: RB
authors.lastname: Candau
authors.forename: Anthony M J
authors.initials: AM
authors.lastname: Sanchez
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism; D000818:Animals; D001343:Autophagy; D015415:Biomarkers / Q000378:metabolism; D051543:Hepatocyte Nuclear Factor 3-gamma / Q000378:metabolism; D008810:Mice, Inbred C57BL; D008931:Mitochondria, Muscle / Q000378:metabolism; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism*; D009124:Muscle Proteins / Q000096:biosynthesis / Q000378:metabolism*; D010766:Phosphorylation; D010805:Physical Conditioning, Animal / Q000502:physiology*; D010807:Physical Endurance / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism
chemical_list: D015415:Biomarkers; C496506:Foxa3 protein, mouse; D009124:Muscle Proteins; D012333:RNA, Messenger; D051543:Hepatocyte Nuclear Factor 3-gamma; D044767:Ubiquitin-Protein Ligases; D055372:AMP-Activated Protein Kinases