This project aims to study muscle development and complementation mechanisms after normal myoblasts are transplanted into a growing and regenerating dystrophic muscle. Applicability of this new transplant technique to alleviate muscle weakness in hereditary myopathies will be tested in dystrophic mice. We have shown that surgically transplanted mesenchymal cells from normal mouse embryos improve the structure and function of dystrophic mouse muscles. The present myoblast transplantation is an extension designed to mimic future development in humans. Dystrophic cells degenerate because of the lack of the normal genome. The normal genome may become incorporated when normal donor myoblasts fuse with satellite cells of dystrophic hosts to form mosaic myofibers. In myopathies of recessive inheritance, gene products from the normal nuclei may restore the phenotype of these heterokaryotes to normal. Furthermore, surviving donor cells will develop and replace the myopathic tissue. They may further donate a diffusible gene product to supplement neighboring dystrophic fibers. These three mechanisms of complementation will be investigated. Cultured myoblasts from genetically normal mouse embryos will be transplanted into the right soleus of 20-day-old normal or dystrophic mice. Hosts and donors are of C57BL/6J background, and are immunocompatible. Survival and development of donor myoblasts in host muscles will be analyzed with electrophoresis of muscle isozymes of glucose phosphate isomerase (GPI). Donor cells carry the gpi-1b allele and produce GPI-1B. Host cells carry the gpi-1c allele and produce GPI-1C. Presence of the heterodimer, GPI-1BC, will substantiate intracellular mosaicism. Different groups of test and control solei will be compared before transplantation, and at 2, 4 and 6 months after transplantation. Muscle mechanophysiology, cellular resting potential and histology will be examined to determine if test muscles exhibit improved structure and function. Genetic mosaicism quantified each time with GPI electrophoresis will be correlated to phenotype indicated by physiology and histology. The effects of variation on donor cell number will be compared. The optimal quantity of donor cells for obtaining normal muscle function will be determined. The effects of transplanting myoblasts vs. fibroblasts will be compared. Dystrophic myoblasts will be transplanted into normal or dystrophic hosts and the results compared. Sham control for surgery will also be studied.
