Abstract
Satellite cells, localized within muscles in vivo, are Pax7+ muscle stem cells supporting skeletal muscle growth and regeneration. Unfortunately, their amplification in vitro, required for their therapeutic use, is associated with reduced regenerative potential. In the present study, we investigated if human myogenic reserve cells (MRC) obtained in vitro, represented a reliable cell source for muscle repair. For this purpose, primary human myoblasts were freshly isolated and expanded. After 2 days of differentiation, 62 ± 2.9% of the nuclei were localized in myotubes and 38 ± 2.9% in the mononucleated non-fusing MRC. Eighty percent of freshly isolated human MRC expressed a phenotype similar to human quiescent satellite cells (CD56+/Pax7+/MyoD−/Ki67− cells). Fourteen days and 21 days after cell transplantation in immunodeficient mice, live human cells were significantly more numerous and the percentage of Pax7+/human lamin A/C+ cells was 2 fold higher in muscles of animals injected with MRC compared to those injected with human myoblasts, despite that percentage of spectrin+ and lamin A/C+ human fibers in both groups MRC were similar. Taken together, these data provide evidence that MRC generated in vitro represent a promising source of cells for improving regeneration of injured skeletal muscles.
Highlights
Satellite cells (SC) are muscle stem cells located between the plasma membrane of the muscle fibers and the surrounding basal lamina and are essential for muscle regeneration[1, 2]
We demonstrated that 80% of human myogenic reserve cells (MRC) were quiescent Pax7+/MyoD− cells, and importantly, that human MRC exhibited an enhanced survival and an enhanced potency to generate Pax7+ cells after transplantation in immunodeficient mice compared to human myoblasts
CD56+/CD146+/CD45−/CD34−/CD144− human myoblasts were obtained after flow cytometry cell sorting
Summary
Satellite cells (SC) are muscle stem cells located between the plasma membrane of the muscle fibers and the surrounding basal lamina and are essential for muscle regeneration[1, 2]. We generated and characterized human MRC and assessed their potential as a source of myogenic stem cells able to improve muscle regeneration in vivo. For this purpose, we generated high amounts of human MRC from freshly isolated primary human myoblast cultures and transplanted them in immunodeficient mice. We demonstrated that 80% of human MRC were quiescent Pax7+/MyoD− cells, and importantly, that human MRC exhibited an enhanced survival and an enhanced potency to generate Pax7+ cells after transplantation in immunodeficient mice compared to human myoblasts These data highlight a potential role of human MRC in improving muscle healing and in the maintenance of a pool of SC in vivo
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