Regeneration Capabilities of Rat Rectus Abdominis Muscle

In human diseases, skeletal muscle regeneration is a powerful, naturally-occurring process of tissue reconstruction that follows upon myofiber damage secondary to injury, which does not affect the tissue circulation and scaffold. On the other hand, the ablated tissue, in traumatology and free muscle grafting, is commonly seen to be replaced by scars. The final outcome is poor even after in situ myoblast seeding of the harvested muscle when larger amount of muscle tissue is grafted. Attempts of full-thickness auto-grafting of the rat rectus abdominis also result in a scar. In a rat model of full-thickness 24-mm-long ablation of the medial third of rectus abdominis the harvested muscle was auto-grafted in situ. We compared regenerative myogenesis in 24and 8-mm-wide lesions. We show that all the patches were well integrated with the abdominal wall and that neovascularization from the peritoneum was usually present. In the case of the 8 x 24-mm the healing process ended in scar, since the full cell population of the auto-graft (satellite cells included) initially underwent ischemic necrosis. On the other hand, in the 2and 4 x 24 mm lesion the healing process is almost completely due to myofiber regeneration. A full-thickness RA crush injury, which extends 24 x 8 mm, that was, the maximal size of the harvested muscle in the ablation experiments, also shown full regeneration of the injured myofibers. All together, our observations strongly witness that the satellite cells of the abdominal wall muscles behave like those of any other rat muscle. When occurring, muscle regeneration seems to be the result of one wave of migration of angioblasts and then satellite cell–derived myoblasts from the muscle tissue that surrounds the graft. The spontaneous regenerative process seems to be limited to about 2 mm of damaged tissue. These volume-related constrains clearly contribute to the high rate of success in mice experiments and to the frustrating negative results of myogenic stem cell seeding into acellular patches in larger animals.