title: Muscle immobilization activates mitophagy and disrupts mitochondrial dynamics in mice.
abstract: Skeletal muscle atrophy following prolonged immobilization (IM) is a catabolic state characterized by increased proteolysis and functional deterioration. Previous research indicates that discord of mitochondrial homoeostasis plays a critical role in muscle atrophy. We hypothesized that muscle IM would activate the ubiquitin-proteolysis, autophagy-lysosome (mitophagy) pathway, mitochondrial dynamics remodelling and apoptosis partially controlled by the FoxO signalling pathway.
  
  
  
  Female FVB/N mice were randomly divided into five groups (n = 8 each): control (CON), IM with banding of one of the hindlimbs for 1, 2 and 3 weeks (1w-, 2w- and 3w-IM) and 2w-IM followed by 1 week of remobilization (RM).
  
  
  
  Mitochondrial density and DNA copies in tibialis anterior (TA) muscle were reduced by approx. 80% (P < 0.05 for 2w-IM; P < 0.01 for 3w-IM), along with activation of FoxO3a, atrogin-1 and MuRF1 following 2w- and 3w-IM (P < 0.01). Protein markers of autophagy/mitophagy, such as beclin 1 (approx. 2.7-fold; P < 0.01), LC3, ubiquitin-binding adaptor (approx. 1.47-fold; P < 0.01), Rheb (approx. 1.9-fold; P < 0.05) and parkin (approx. 70%; P < 0.05), were all increased by IM and remained activated after RM, whereas BNIP3 and PINK1 levels were decreased by IM (P < 0.05), but elevated upon RM (P < 0.01). IM decreased Mfn2 expression (approx. 50%; P < 0.01) and increased Fis-1 expression (approx. 2.4-fold; P < 0.05). Muscle apoptosis indicator Bax/Bcl2 ratio was elevated at 2w- to 3w-IM (approx. 3.7-fold; P < 0.01), whereas caspase-3 activity was five- to sixfold higher (P < 0.01) and remained threefold higher above CON (P < 0.05).
  
  
  
  Our data indicate that IM-induced mitochondrial deterioration is associated with altered protein expressions in the autophagic/mitophagic pathway, more fragmented mitochondrial network and activation of apoptosis partly under the influence of FoxO3 activation.
authors.affiliation: Laboratory of Physiological Hygiene and Exercise Science, School of Kinesiology, University of Minnesota at Twin Cities, Minneapolis, MN, USA.
authors.forename: C
authors.initials: C
authors.lastname: Kang
authors.affiliation: Laboratory of Physiological Hygiene and Exercise Science, School of Kinesiology, University of Minnesota at Twin Cities, Minneapolis, MN, USA.
authors.forename: D
authors.initials: D
authors.lastname: Yeo
authors.affiliation: Laboratory of Physiological Hygiene and Exercise Science, School of Kinesiology, University of Minnesota at Twin Cities, Minneapolis, MN, USA. llji@umn.edu.
authors.forename: L L
authors.initials: LL
authors.lastname: Ji
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D001343:Autophagy / Q000502:physiology; D000071186:Beclin-1 / Q000378:metabolism; D053148:Caspase 3 / Q000378:metabolism; D005260:Female; D000071316:Forkhead Box Protein O3 / Q000378:metabolism; D007103:Immobilization; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008928:Mitochondria / Q000378:metabolism*; D063154:Mitochondrial Dynamics / Q000502:physiology*; D024101:Mitochondrial Proteins / Q000378:metabolism; D063306:Mitophagy / Q000502:physiology*; D009124:Muscle Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000473:pathology; D009133:Muscular Atrophy / Q000378:metabolism* / Q000473:pathology; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D044843:SKP Cullin F-Box Protein Ligases / Q000378:metabolism; D000070584:Tripartite Motif Proteins / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D000099202:PTEN-Induced Putative Kinase
chemical_list: D000071186:Beclin-1; D053148:Caspase 3; D000071316:Forkhead Box Protein O3; D008565:Membrane Proteins; D024101:Mitochondrial Proteins; D009124:Muscle Proteins; D011494:Protein Kinases; D044843:SKP Cullin F-Box Protein Ligases; D000070584:Tripartite Motif Proteins; D044767:Ubiquitin-Protein Ligases; D000099202:PTEN-Induced Putative Kinase; C508686:BNip3 protein, mouse; C474033:FoxO3 protein, mouse; C486691:Fbxo32 protein, mouse; C499084:Trim63 protein, mouse
keywords: FoxO3; atrophy; immobilization; mitochondrial dynamics; mitophagy; skeletal muscle