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Regulation of satellite cell proliferation and adult skeletal muscle regeneration by the Wnt family of signalling molecules

Satellite cells represent the stem cell population of adult skeletal muscle. These relatively rare cells are normally maintained in a quiescent, mitotically inactive state. However, during phases of muscle growth or regeneration, they start to divide not only give rise to myoblasts that eventually form muscle but also to daughter cells that replenish the stem cell pool. We have a poor understanding of how the small myoblast population that develops after satellite cell activation is expanded to generate numbers required to repair injured tissue. In this study we show that members of the Wnt family of secreted proteins have a profound, identity specific, influence on satellite cell proliferation. Wnt1, 3a, or 5a protein cause a dramatic increase in satellite cell proliferation. In contrast, exposure of satellite cells to Wnt4 or 6 diminishes this process. A key mechanism dictating whether a satellite cell undergoes proliferation or not is the intracellular localisation of Act‐β ‐Cat. We show that proliferation enhancing Wnt proteins induce premature proliferation along with Act‐β ‐Cat nuclear translocation. Finally, we provide evidence that the dynamics of cellular Act‐β ‐Cat translocation observed during in vitro culture are found in cases of either acute or chronic skeletal muscle regeneration in rodents and humans. In summary, we propose that Wnt proteins may be key factors acting to regulate the rate of satellite cell proliferation on adult muscle fibres during the wound healing response.