Brack, Andrew S.Muñoz Cánoves, Pura, 1962-2016-07-112016-07-112016Brack AS, Muñoz-Cánoves P. The ins and outs of muscle stem cell aging. Skeletal muscle. 2016; 6: 1. DOI 10.1186/s13395-016-0072-z2044-5040http://hdl.handle.net/10230/27025Skeletal muscle has a remarkable capacity to regenerate by virtue of its resident stem cells (satellite cells). This capacity declines with aging, although whether this is due to extrinsic changes in the environment and/or to cell-intrinsic mechanisms associated to aging has been a matter of intense debate. Furthermore, while some groups support that satellite cell aging is reversible by a youthful environment, others support cell-autonomous irreversible changes, even in the presence of youthful factors. Indeed, whereas the parabiosis paradigm has unveiled the environment as responsible for the satellite cell functional decline, satellite cell transplantation studies support cell-intrinsic deficits with aging. In this review, we try to shed light on the potential causes underlying these discrepancies. We propose that the experimental paradigm used to interrogate intrinsic and extrinsic regulation of stem cell function may be a part of the problem. The assays deployed are not equivalent and may overburden specific cellular regulatory processes and thus probe different aspects of satellite cell properties. Finally, distinct subsets of satellite cells may be under different modes of molecular control and mobilized preferentially in one paradigm than in the other. A better understanding of how satellite cells molecularly adapt during aging and their context-dependent deployment during injury and transplantation will lead to the development of efficacious compensating strategies that maintain stem cell fitness and tissue homeostasis throughout life.application/pdfeng© 2016 Brack and Muñoz-Cánoves. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.Múscul estriatinfo:eu-repo/semantics/articlehttp://dx.doi.org/10.1186/s13395-016-0072-zinfo:eu-repo/semantics/openAccess