title: Activation of skeletal muscle calpain-3 by eccentric exercise in humans does not result in its translocation to the nucleus or cytosol.
abstract: The skeletal muscle-specific calpain-3 protease is likely involved in muscle repair, although the mechanism is not known. Physiological activation of calpain-3 occurs 24 h following eccentric exercise in humans. Functional consequences of calpain-3 activation are not known; however, calpain-3 has been suggested to be involved in nuclear signaling via NF-κB. To test this and help identify how/where calpain-3 acts, we investigated whether calpain-3 autolysis (hence, activation) following eccentric exercise results in translocation from its normal myofibrillar location to the nucleus or the cytosol. In resting human skeletal muscle, the majority (87%) of calpain-3 was present in myofibrillar fractions, with only a small proportion (<10%) in an autolyzed state. Enriched nuclear fractions contained ∼8% of the total calpain-3, which was present in a predominantly (>80%) autolyzed state. Using freshly dissected human muscle fibers to identify freely diffusible proteins, we showed that only ∼5% of the total calpain-3 pool was cytosolic. At 3 and 24 h following eccentric step exercise, there was an ∼70% increase in autolysis in whole muscle samples (n = 11, P < 0.05, by 1-way ANOVA with repeated measures and Newman-Keuls post hoc analysis). This exercise-induced autolysis was attributed to myofibrillar-bound calpain-3, since neither the amount of calpain-3 nor the proportion autolyzed was significantly changed in enriched nuclear or cytosolic fractions following the exercise intervention. We present a model for calpain-3 localization at rest and following activation in human skeletal muscle and suggest that the functional importance of calpain-3 remains predominantly tightly associated with its localization within the myofibrillar compartment.
authors.affiliation: Dept. of Zoology, La Trobe Univ., VIC 3086, Australia. r.murphy@latrobe.edu.au
authors.forename: Robyn M
authors.initials: RM
authors.lastname: Murphy
authors.forename: Kristian
authors.initials: K
authors.lastname: Vissing
authors.forename: Heidy
authors.initials: H
authors.lastname: Latchman
authors.forename: Cedric
authors.initials: C
authors.lastname: Lamboley
authors.forename: Michael J
authors.initials: MJ
authors.lastname: McKenna
authors.forename: Kristian
authors.initials: K
authors.lastname: Overgaard
authors.forename: Graham D
authors.initials: GD
authors.lastname: Lamb
mesh_terms: D000328:Adult; D001329:Autolysis / Q000378:metabolism; D002154:Calpain / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism*; D015444:Exercise / Q000502:physiology*; D006801:Humans; D008297:Male; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism* / Q000502:physiology; D009210:Myofibrils / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology*; D055815:Young Adult
chemical_list: D009124:Muscle Proteins; D016328:NF-kappa B; C105884:CAPN3 protein, human; D002154:Calpain