title: Activation of the MEF2 transcription factor in skeletal muscles from myotonic mice.
abstract: Becker syndrome, a recessive nondystrophic myotonia caused by mutations in the chloride channel 1 gene (CLCN1), is characterized by delayed muscle relaxation after contraction. The ADR (arrested development of righting response) mouse is an animal model for Becker syndrome. Skeletal muscles from ADR myotonic animals show an increased number of oxidative fibers with a lack of glycolytic fibers as well as signs of muscle hypertrophy. Through breeding ADR myotonic mice with mice harboring a MEF2-dependent reporter gene, we found that the transcriptional activity of MEF2 was dramatically enhanced in myotonic muscles. Post-translational induction of MEF2 transcriptional activity correlated with the activation of p38 MAPK and did not affect MEF2 DNA-binding affinity. Expression of class II histone deacetylases (HDACs), which repress MEF2-dependent gene expression, was significantly reduced in skeletal muscles from myotonic mice. These findings suggest that the combined effects of class II HDAC deficiency and p38 MAPK activation lead to potent upregulation of MEF2 transcriptional activity, which contributes to the long-term changes in gene expression and fiber-type transformation observed in myotonic skeletal muscles. These findings provide new molecular targets for potential treatment of congenital myotonia.
authors.affiliation: Department of Molecular Biology, University of Texas Southwestern Medical Center at Dallas 75390-9148, USA.
authors.forename: Hai
authors.initials: H
authors.lastname: Wu
authors.forename: Eric N
authors.initials: EN
authors.lastname: Olson
mesh_terms: D000818:Animals; D018118:Chloride Channels / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D064326:MEF2 Transcription Factors; D051379:Mice; D008822:Mice, Transgenic; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism; D009154:Mutation; D018006:Myogenic Regulatory Factors; D009224:Myotonia Congenita / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D015398:Signal Transduction / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D015533:Transcriptional Activation; D048051:p38 Mitogen-Activated Protein Kinases
chemical_list: C086321:CLC-1 channel; D018118:Chloride Channels; D004268:DNA-Binding Proteins; D064326:MEF2 Transcription Factors; D018006:Myogenic Regulatory Factors; D014157:Transcription Factors; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases