Résumé :
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We are developing a strategy for the selective engraftment of stem cells in a solid tissue. It is based on the forced expression in transplanted cells of a mutant form of methylguanine methyltransferase [MGMT(P140K)] which can confer resistance to chemotherapeutic drugs, providing a selective advantage to cells in the presence of alkylating agents [Pegg AE Mutat Res 462: 83-100 (2000)]. This strategy was originally developed for bone marrow transplantation [Davis et al. Blood 95: 3078-84 (2000)]. In order to apply this strategy to a solid tissue, we chose regenerating muscle and optimised methods of skeletal muscle injury to mobilize/activate resident stem cells. The regenerating muscle was exposed to BCNU/O6BG and examined 3 months post-treatment. The treated muscle bed lacked muscle fibers indicating sustained ablation of the resident stem cells. CD34+, MGMT(P140K) expressing cells isolated from muscles of a transgenic mouse were injected into the recipient muscle at the time of induction of regeneration and drug administration. The transplanted CD34+, MGMT(P140K) cells resulted in full regeneration of the muscle [Lee AS et al. Stem Cells 27: 1098-108 (2009). However, the engrafted cells contributed only ~12.5% of the total cell number indicating that the engrafted cells in the chemo-ablated muscle elicit a significant recruitment of myogenic progenitor cells from other sites within the host. Furthermore, when the same muscles in both legs of the mouse were chemo-ablated, but CD34+, MGMT(P140K) cells were introduced into the muscle of only one leg, both muscles regenerated fully. This demonstrated that successful regeneration in one muscle can rescue a regeneration-impaired muscle in another region of the body, providing evidence for systemic involvement in muscle stem cell recruitment. To investigate the role of blood borne cells and/or factors in this process, parabiosis pairing was used. A transgenic mouse expressing EGFP ubiquitously and a wild-type mouse were joined surgically in order to track cell movement between mice. One hindlimb muscle in each mouse was injured, chemo-ablated and CD34+, MGMT(P140K) cells injected into the chemo-ablated muscle of the EGFP mouse alone. The chemo-ablated muscles in both mice regenerated; however, no injected CD34+ cells nor EGFP+ cells were observed in the regenerated muscle of the wild-type mouse. These results confirm that the engrafted cells lead to a systemic propagation of a pro-regenerative signal that activates and/or recruits local progenitors for muscle regeneration.
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