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MUSCLE CELL BIOLOGY AND CELL MOTILITY

Differential localization of autolyzed calpains 1 and 2 in slow and fast skeletal muscles in the early phase of atrophy

¹Institut National de la Santé et de la Recherche Médicale (INSERM), ERI 25; ²Université Montpellier1, UFR de Médecine, EA 701; ³INSERM, U637; ⁴Université Montpellier1, UFR de Médecine; ⁵Centre National de la Recherche Scientifique, UMR 5539, Université de Montpellier2; and ⁶UPRES-EA 3799 "Approche bio-psycho-sociale du dopage," Université de Montpellier1, Faculté des Science du Sport, Montpellier, France

Submitted 21 July 2006 ; accepted in final form 15 December 2006

Calpains have been proposed to be involved in the cytoskeletal remodeling and wasting of skeletal muscle. However, limited data are available about the specific involvement of each calpain in the early stages of muscle atrophy. The aims of this study were to determine whether calpains 1 and 2 are autolyzed after a short period of muscle disuse, and, if so, where in the myofibers the autolyzed products are localized. In the rat soleus muscle, 5 days of immobilization increased autolyzed calpain 1 in the particulate and not the soluble fraction. Conversely, autolyzed calpain 2 was not found in the particulate fraction, whereas it was increased in the soluble fraction after immobilization. In the less atrophied plantaris muscle, no difference was noted between the control and immobilized groups whatever the fraction or calpain. Other proteolytic pathways were also investigated. The ubiquitin-proteasome pathway was activated in both skeletal muscles, and caspase 3 was activated only in the soleus muscle. Taken together, our data suggest that calpains 1 and 2 are involved in atrophy development in slow type muscle exclusively and that they have different regulation and protein targets. Moreover, the activation of proteolytic pathways appears to differ in slow and fast muscles, and the proteolytic mechanisms involved in fast-type muscle atrophy remain unclear.

Ca²⁺-dependent proteases; wasting; skeletal muscle; soluble and particulate fractions; immobilization

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