Association of IGF-I and IGF-II with myofiber regeneration in vivo

This study examined expression of insulinlike growth factor (IGF) in the my ofibers and nonmyofibrillar structures of murine soleus muscle following co ntraction-induced damage. Identifying the cellular sources of this myogenic growth factor could improve muscle rehabilitation strategies. Immunohistoc hemical analysis of muscle sections indicated that the number of myofibers expressing both IGF-I and IGF-II increased significantly at 4, 7, and 10 da ys following injury, compared with control. Muscle spindles and vascular ti ssue expressed only IGF-II, and staining intensity did not change following injury, The number of fibers expressing developmental myosin heavy chain i ncreased significantly at 7 and 10 days postinjury, and these usually coexp ressed IGF, No IGF-specific staining of interstitial/inflammatory cells was observed. Therefore, expression of IGF after mechanically induced fiber da mage occurs exclusively within regenerating fibers without supplemental del ivery of IGF to the tissue by inflammatory cells or changes in constitutive expression of IGF-II in vascular tissue. (C) 1999 John Wiley & Sons, Inc.