Activation of skeletal muscle calpain-3 by eccentric exercise in humans does not result in its translocation to the nucleus or cytosol

J Appl Physiol (1985). 2011 Nov;111(5):1448-58. doi: 10.1152/japplphysiol.00441.2011. Epub 2011 Aug 11.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Autolysis / metabolism
  • Calpain / metabolism*
  • Cell Nucleus / metabolism*
  • Cytosol / metabolism*
  • Exercise / physiology*
  • Humans
  • Male
  • Muscle Proteins / metabolism*
  • Muscle, Skeletal / metabolism*
  • Muscle, Skeletal / physiology
  • Myofibrils / metabolism
  • NF-kappa B / metabolism
  • Protein Transport / physiology*
  • Young Adult


  • Muscle Proteins
  • NF-kappa B
  • CAPN3 protein, human
  • Calpain