Muscle regeneration: cellular and molecular events.

Muscle injury induces strong changes in muscle cells and extracellular matrix. Muscle regeneration after injury has similarities to muscle development during embryogenesis and seems to follow the same procedure. The initial phase of muscle repair is characterized by inflammation and degeneration of the damaged tissue. Almost simultaneously, previous quiescent myogenic cells, called satellite cells, are activated, proliferate, differentiate and fuse to form multinucleated myofibers. Other non-muscle stem cells may also take part in this process. Secreted factors, such as hepatocyte growth factor (HGF), fibroblast growth factors (FGFs), transforming growth factor-betas (TGF-betas), insulin-like growth factors (IGFs), tumour necrosis factor alpha (TNFalpha) and others, are released during muscle repair and guide muscle regeneration, however, their exact functions and effects on muscle remodeling remain unknown. Intensive research is currently addressing the regenerative mechanisms which are involved in acute muscle injuries and chronic muscle diseases.