Inflammatory response during slow- and fast-twitch muscle regeneration

Skeletal muscles are characterized by their unique ability to regenerate. Injury of a so-called fast-twitch muscle, extensor digitorum longus (EDL), results in efficient regeneration and reconstruction of the functional tissue. In contrast, slow-twitch muscle (soleus) fails to properly reconstruct and develops fibrosis. This study focuses on soleus and EDL muscle regeneration and associated inflammation.We determined differences in the activity of neutrophils and M1 and M2 macrophages using flow cytometry and differences in the levels of proinflammatory cytokines using Western blotting and immunolocalization at different times after muscle injury.Soleus muscle repair is accompanied by increased and prolonged inflammation, as compared to EDL. The proinflammatory cytokine profile is different in the soleus and ED muscles.Muscle repair efficiency differs by muscle fiber type. The inflammatory response affects the repair efficiency of slow- and fast-twitch muscles. Muscle Nerve 55: 400-409, 2017.