Résumé :
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Human skeletal muscle is an essential source of cellular progenitors with potential therapeutic perspectives deserving further identification and characterization. Aldehyde dehydrogenase type 1A1 (ALDH) belongs to a large family of enzymes involved in oxidation and detoxification, and its activity is one hallmark of human primitive progenitors presenting broad regeneration capacities in vivo. We investigated for the presence and capacities of cell populations expressing ALDH in human skeletal muscles. ALDH expression was assessed by immunohistochemistry, and its activity was revealed and quantified using the reliable fluorescent substrate Aldefluor®, which allowed cell sorting by flow cytometry. The phenotypic and differentiation capacities of different sub-populations of ALDH+ cells were assessed in vitro and in vivo upon intramuscular implantation. Immunohistofluorescence study identified rare endomysial cells positively labeled for ALDH1. Using flow cytometry, we described welldefined sub-populations of SSClo/ALDHbr cells isolated from bulk dissociated human skeletal muscle biopsies, that we called SMALD (Skeletal Muscle ALDH-positive cells). Two main sub-populations were discriminated according to CD34 expression, and termed SMALD/34- and SMALD/34+ cells. These sub-populations did not express endothelial (CD31), hematopoietic (CD45) and myogenic (CD56) markers, and could be partly discriminated by the variable expression of associated markers (CD44, CD90, CD105, CD140b). Therefore, these cells may be distinct from satellite cells, pericytes or mesangioblasts, myo-endothelial, or hematopoietic stem cells. Upon sorting, SMALD populations were expanded and their differentiation abilities were compared in vitro. While SMALD/34+ cells developed as an heterogeneous population of CD56- and CD15+ cells able to differentiate in adipoblasts, the SMALD/34- cells developed in vitro as a highly enriched population of CD56+ /CD15- myoblasts able to form myotubes. Interestingly, the initial proportion of SMALD/34- cells in a given biopsy was a predictor of its final yield in myogenic cells. In vivo, FACS-sorted SMALD/34- cells participated efficiently to muscle regeneration upon intramuscular transplantation in SCID mice, while SMALD/34+ cells did not. SMALD cells may thus become a new player in the field of muscle homeostasis or repair in therapeutic perspectives.
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