title: Nerve activity-dependent modulation of calcineurin signaling in adult fast and slow skeletal muscle fibers.
abstract: This study tested the hypothesis that calcineurin signaling is modulated in skeletal muscle cells by fluctuations in nerve-mediated activity. We show that dephosphorylation of NFATc1, MEF2A, and MEF2D transcription factors by calcineurin in all muscle types is dependent on nerve activity and positively correlated with muscle usage under normal weightbearing conditions. With increased nerve-mediated activity, calcineurin dephosphorylation of these targets was found to be potentiated in a way that paralleled the higher muscle activation profiles associated with functional overload or nerve electrical stimulation conditions. We also establish that muscle activity must be sustained above native levels for calcineurin-dependent dephosphorylation of MEF2A and MEF2D to be transduced into an increase in MEF2 transcriptional function, suggesting that calcineurin cooperates with other activity-linked events to signal via these proteins. Finally, examination of individual fiber responses to overload and nerve electrical stimulation revealed that calcineurin-MEF2 signaling occurs in all fiber types but most readily in fibers that are normally least active (i.e. those expressing IIx and IIb myosin heavy chain (MHC)), suggesting that signaling via this phosphatase is also dependent upon the activation history of the muscle cell.
authors.affiliation: Neuromuscular Research Laboratory, Department of Chemistry and Biochemistry, Laurentian University, Sudbury, Ontario P3E 2C6, Canada.
authors.forename: S E
authors.initials: SE
authors.lastname: Dunn
authors.forename: A R
authors.initials: AR
authors.lastname: Simard
authors.forename: R
authors.initials: R
authors.lastname: Bassel-Duby
authors.forename: R S
authors.initials: RS
authors.lastname: Williams
authors.forename: R N
authors.initials: RN
authors.lastname: Michel
mesh_terms: D000818:Animals; D015153:Blotting, Western; D019703:Calcineurin / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D016572:Cyclosporine / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D017930:Genes, Reporter; D005838:Genotype; D049452:Green Fluorescent Proteins; D007150:Immunohistochemistry; D007166:Immunosuppressive Agents / Q000494:pharmacology; D008164:Luminescent Proteins / Q000378:metabolism; D064326:MEF2 Transcription Factors; D051379:Mice; D008810:Mice, Inbred C57BL; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism*; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism*; D009132:Muscles / Q000166:cytology; D018006:Myogenic Regulatory Factors; D050778:NFATC Transcription Factors; D009474:Neurons / Q000378:metabolism*; D009687:Nuclear Proteins; D010641:Phenotype; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction; D016559:Tacrolimus / Q000494:pharmacology; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D007166:Immunosuppressive Agents; D008164:Luminescent Proteins; D064326:MEF2 Transcription Factors; C578036:Mef2a protein, mouse; C578044:Mef2d protein, mouse; D018006:Myogenic Regulatory Factors; D050778:NFATC Transcription Factors; C494005:Nfatc1 protein, mouse; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D049452:Green Fluorescent Proteins; D016572:Cyclosporine; D019703:Calcineurin; D001616:beta-Galactosidase; D016559:Tacrolimus