Résumé :
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Cell therapy has been envisaged for some genetic muscular disorders using myoblasts in order to deliver the missing protein. Although pre-clinical trials in the mouse were promising, therapeutic trials using local injection of myoblasts failed to bring clinical benefit to the patients, with the injected cells presenting a poor survival and migration within the muscle, limiting the efficacy of transplantation. It is known that macrophages (MPs) participate to skeletal muscle regeneration in vivo and may exert specific effects on myoblasts. Macrophages consist of 3 main distinct polarized populations of cells (in the inflammatory infiltrate): M1, M2a, and M2c, which are characterized by distinct phenotypes. Recent studies have shown that M1/pro-inflammatory MPs promote myoblast proliferation in vitro, whereas M2c/anti-inflammatory MPs promote differentiation. Whether the same effects occur in vivo has yet to be demonstrated.In order to investigate in vivo the influence of distinct MPs subpopulations on myoblast behavior during regeneration, we have co-injected human myoblasts together with human Pro or Anti-inflammatory MPs into cryodamaged Tibialis Anterior muscles from immunodeficient RAG-/- C-/- mice. We analyzed the participation of the human transplanted myoblasts by quantifying the expression of human proteins (lamin A/C for human nuclei, and spectrin for fibres expressing human proteins) along the entire injected muscle.Our results show that the presence of pro-inflammatory MPs at the injection site improves dispersion and thus the participation of human myoblasts to host regeneration: the number of muscle fibers that express human muscle proteins is increased one month post-injury, while anti-inflammatory MPs did not have any effect. We observed that pro-inflammatory MPs delay myoblast differentiation both in vitro (MP plus myoblast co-cultures) and in vivo (analysis at early time points after co-injection). This proliferative effect increases the number of injected muscular progenitors that can participate to regeneration and increases the period of migration within the host muscle by delaying differentiation. These data underline the importance of the inflammatory niche on myoblast behavior during muscle regeneration. Conceptually, our data reinforce the notion that pro-inflammatory MPs represent a cellular micro-environmental support for myoblasts in vivo.
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