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activation enhances the structure and function of regenerating muscles after myotoxic injury
1 Physiology, The University of Melbourne, Melbourne, Victoria, Australia
2 Molecular Biology, University of Texas Southwestern Medical Center, Dallas, Texas, United States
* To whom correspondence should be addressed. E-mail: gsl{at}unimelb.edu.au.
Calcineurin signaling is essential for successful muscle regeneration. Although calcineurin inhibition compromises muscle repair, it is not known whether calcineurin activation can enhance muscle repair after injury. Tibialis anterior (TA) muscles from adult wild-type (WT) and transgenic mice overexpressing the constitutively active calcineurin-A
transgene under the control of the mitochondrial creatine kinase promoter (MCK-CnA
*) were injected with the myotoxic snake venom Notexin to destroy all muscle fibers. The TA muscle of the contralateral limb served as the uninjured control. Muscle structure was assessed at 5 and 9 days post-injury and muscle function was tested in situ at 9 days post-injury. Calcineurin stimulation enhanced muscle regeneration and altered levels of myoregulatory factors (MRFs). Recovery of myofiber size and force producing capacity was hastened in injured muscles of MCK-CnA
* mice compared with control. Myogenin levels were greater 5 days post-injury and myocyte enhancer factor 2a (MEF2a) expression was greater 9 post-injury in muscles of MCK-CnA
* mice than in WT mice. Higher MEF2a expression in regenerating muscles of MCK-CnA
* mice 9 days post-injury may be related to an increase of slow fiber genes. Calcineurin activation in uninjured and injured TA muscles slowed muscle contractile properties, reduced fatigability, and enhanced force recovery after four minutes of intermittent maximal stimulation. Therefore, calcineurin activation can confer structural and functional benefits to regenerating skeletal muscles, which may be mediated in part by differential expression of MRFs.
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