Heparan sulfate mimetics modulate calpain activity during rat soleus muscle regeneration

Skeletal muscle regenerates after injury. Tissue remodelling, which takes p lace during muscle regeneration, is a complex process involving proteolytic enzymes. it is inferred that micro and milli calpains are involved in the protein turnover and structural adaptation associated with muscle myolysis and reconstruction. Using a whole-crush injured skeletal muscle, we previou sly have shown that in vivo muscle treatment with synthetic heparan sulfate mimetics, called RGTAs (for ReGeneraTing Agents), greatly accelerates and improves muscle regeneration after crushing. This effect was particularly s triking in the case of the slow muscle Soleus that otherwise would be atrop hied. Therefore, we used this regeneration model to study milli and micro c alpain expressions in the regenerating Soleus muscle and to address the que stion of a possible effect of RGTAs treatment on calpain levels. Micro and milli calpain contents increased by about five times to culminate at days 7 and 14 after crushing respectively, thus during the phases of fibre recons truction and reinnervation. After 64 days of regeneration, muscles still di splayed higher levels of both calpains than an intact uninjured muscle. Mil li calpain detected by immunocytochemistry was shown in the cytoplasm where as micro calpain was in both nuclei and cytoplasm in small myofibres but ap peared almost exclusively in nuclei of more mature fibres. Interestingly, t he treatment of muscles with RGTA highly reduced the increase of both milli and micro calpain contents in Soleus regenerating muscles. These results s uggest that the improvement of muscle regeneration induced by RGTA may be p artly mediated by minimising the consequences of calpain activity.(C) 2001 Wiley-Liss, inc.