V.M. Mikhailov, A.V. Sokolova, V.V. Kravtsova, V.V. Zenin, E.V. Kaminskaya, N.A. Timonina and I.I. Krivoi
Background: Mdx mice are experimental model of cureless human monogenic disease Duchenne Muscular Dystrophy (DMD). Hope for а cure is associated with the use of stem cells therapy particular but not exclusively. Analysis of multiple experimental results shows what intramuscularly transplantation of different types of cells of different origins with stem cells properties can’t convert mutant striated muscles fibers (SMF) into wild type SMF. It was concluded that only replacement of mutant bone marrow (BM) by wild type BM cells can convert mutant SMF into SMF of wild type. Unfortunately X-ray irradiation of mdx mice at a lethal dose of 11, 7 or 5 Gy followed by transplantation of wild C57BL/6 mice BM cells did not increase SMF dystrophin synthesis. The aim of this study was to analyse a dystrophin synthesis by mdx mice striated muscles after x-ray irradiation with the dose of 3 Gy followed by C57BL/6 bone marrow cells transplantation. Also we investigate the reparation of structure of diaphragm muscle fibers NMJs. To confirm the functional significance of observed structural changes of NMJs an investigation of resting membrane potential of diaphragm muscle fiber NMJs was also conducted. Methods: 1-1.5 months old mdx mice were irradiated by x-ray at a dose of 3 Gy. Next day freshly prepared BM cells were injected intravenously in the amount of (15-20) x 106 cells per mouse. Animals were studied through 2, 4, and 6 months after transplantation. Each experimental group of mice included 3-8 animals. Mus. quadriceps femoris and diaphragm muscle fibers with their nerve-muscle junctions (NMJs) were under investigation. For chimerism registration a special study was conducted using transplantation of GFP-positive C57BL/6 BM cells to mdx mice after 3 Gy irradiation. Through 6 months BM cells were separated from long bones and smears were prepared. After carbinol fixation smears were stained by propidium iodide and studied on confocal microscope LSM 5 Pascal (Carl Zeiss, Germany) to count the part of GFP-positive cells in relation to whole quantity of nuclear cells. Results: We observed a stable growth of dystrophin synthesis after nonlethal X-ray irradiation at a dose of 3 Gy. The part of dystrophin positive SMF of M. quadriceps femoris increased from 1% up to 4% (2 months), 12% (4 months) and 27% (6 months) after transplantation. Growth of dystrophin synthesis was accompanied by the decrease of SMF death level, by increase of part of SMF without central nuclear up to 22%, by accumulation of MNJ branches and by reparation of resting membrane potentials. The part of GFP-positive cells between all cells with nuclear on the BM smears of chimeric GFP transplanted mdx mice at 6 months after transplantation was 3.3 ± 0.8 % that show for chimeric nature of mice. Conclusion: Non myeloablative bone marrow cell transplantation of mdx mice after X-ray irradiation 3 Gy is accompanied by formation of chimerism, stable growth of dystrophin synthesis and reparation of structure and function of NMJs.