title: Failed reinnervation in aging skeletal muscle.
abstract: Skeletal muscle displays a marked accumulation of denervated myofibers at advanced age, which coincides with an acceleration of muscle atrophy.
  
  
  
  In this study, we evaluated the hypothesis that the accumulation of denervated myofibers in advanced age is due to failed reinnervation by examining muscle from young adult (YA) and very old (VO) rats and from a murine model of sporadic denervation secondary to neurotrypsin over-expression (Sarco mouse).
  
  
  
  Both aging rat muscle and Sarco mouse muscle exhibited marked fiber-type grouping, consistent with repeating cycles of denervation and reinnervation, yet in VO muscle, rapsyn at the endplate increased and was associated with only a 10 % decline in acetylcholine receptor (AChR) intensity, whereas in Sarco mice, there was a decline in rapsyn and a 25 % decrease in AChR intensity. Transcripts of muscle-specific kinase (21-fold), acetylcholine receptor subunits α (68-fold), ε (threefold) and γ (47-fold), neural cell adhesion molecule (66-fold), and runt-related transcription factor 1 (33-fold) were upregulated in VO muscle of the rat, consistent with the marked persistent denervation evidenced by a large proportion of very small fibers (>20 %). In the Sarco mice, there were much smaller increases in denervation transcripts (0-3.5-fold) and accumulation of very small fibers (2-6 %) compared to the VO rat, suggesting a reduced capacity for reinnervation in aging muscle. Despite the marked persistent denervation in the VO rat muscle, transcripts of neurotrophins involved in promoting axonal sprouting following denervation exhibited no increase, and several miRNAs predicted to suppress neurotrophins were elevated in VO rat.
  
  
  
  Our results support the hypothesis that the accumulation of denervated fibers with aging is due to failed reinnervation and that this may be affected by a limited neurotrophin response that mediates axonal sprouting following denervation.
authors: Research Institute of the McGill University Health Centre, EM2.2232, RI MUHC, 1001 Decarie Blvd, Montreal, QC Canada H4A 3J1 ; McGill Research Centre for Physical Activity and Health, McGill University, Montreal, QC Canada.
authors: Sudhakar
authors: S
authors: Aare
authors: Research Institute of the McGill University Health Centre, EM2.2232, RI MUHC, 1001 Decarie Blvd, Montreal, QC Canada H4A 3J1 ; McGill Research Centre for Physical Activity and Health, McGill University, Montreal, QC Canada.
authors: Sally
authors: S
authors: Spendiff
authors: Research Institute of the McGill University Health Centre, EM2.2232, RI MUHC, 1001 Decarie Blvd, Montreal, QC Canada H4A 3J1 ; McGill Research Centre for Physical Activity and Health, McGill University, Montreal, QC Canada.
authors: Madhusudanarao
authors: M
authors: Vuda
authors: Research Institute of the McGill University Health Centre, EM2.2232, RI MUHC, 1001 Decarie Blvd, Montreal, QC Canada H4A 3J1 ; McGill Research Centre for Physical Activity and Health, McGill University, Montreal, QC Canada ; Department of Kinesiology and Physical Education, McGill University, Montreal, QC Canada.
authors: Daren
authors: D
authors: Elkrief
authors: Research Institute of the McGill University Health Centre, EM2.2232, RI MUHC, 1001 Decarie Blvd, Montreal, QC Canada H4A 3J1.
authors: Anna
authors: A
authors: Perez
authors: Research Institute of the McGill University Health Centre, EM2.2232, RI MUHC, 1001 Decarie Blvd, Montreal, QC Canada H4A 3J1 ; McGill Research Centre for Physical Activity and Health, McGill University, Montreal, QC Canada.
authors: Qinghua
authors: Q
authors: Wu
authors: Research Institute of the McGill University Health Centre, EM2.2232, RI MUHC, 1001 Decarie Blvd, Montreal, QC Canada H4A 3J1.
authors: Dominique
authors: D
authors: Mayaki
authors: Research Institute of the McGill University Health Centre, EM2.2232, RI MUHC, 1001 Decarie Blvd, Montreal, QC Canada H4A 3J1.
authors: Sabah N A
authors: SN
authors: Hussain
authors: Neurotune, Zurich, Switzerland.
authors: Stefan
authors: S
authors: Hettwer
authors: Research Institute of the McGill University Health Centre, EM2.2232, RI MUHC, 1001 Decarie Blvd, Montreal, QC Canada H4A 3J1 ; McGill Research Centre for Physical Activity and Health, McGill University, Montreal, QC Canada ; Department of Kinesiology and Physical Education, McGill University, Montreal, QC Canada.
authors: Russell T
authors: RT
authors: Hepple
mesh_terms: D000818:Animals; D050676:Core Binding Factor Alpha 2 Subunit / Q000235:genetics / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018482:Muscle, Skeletal / Q000254:growth & development / Q000294:innervation* / Q000378:metabolism / Q000502:physiology; D009414:Nerve Growth Factors / Q000235:genetics / Q000378:metabolism; D054510:Phospholipases A2, Cytosolic / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D011950:Receptors, Cholinergic / Q000235:genetics / Q000378:metabolism; D055948:Sarcopenia / Q000378:metabolism / Q000503:physiopathology*
chemical_list: D050676:Core Binding Factor Alpha 2 Subunit; D009414:Nerve Growth Factors; D011950:Receptors, Cholinergic; C511695:MuSK protein, mouse; D020794:Receptor Protein-Tyrosine Kinases; D054510:Phospholipases A2, Cytosolic
keywords: Aging; Denervation; MicroRNA; Muscle atrophy; Neurotrophins; Reinnervation; Sarcopenia; Skeletal muscle