Editorial: Frontiers in skeletal muscle wasting, regeneration and stem cells

" Frontiers in Skeletal Muscle Wasting, Regeneration and Stem Cells " is a Frontiers Research Topic aimed to highlight the available knowledge regarding skeletal muscle and stem cell biology in the context of both physiological and pathological conditions. In the last decades we have many advances in the understating of muscle biology and pathophysiology of myopathies. Herein we presented articles focused in skeletal muscle biology and both pathophysiology and treatment of skeletal muscle disorders. Animal models are frequently used in the study of muscle atrophy, focusing on its molecular mechanisms or on the search for strategies of muscle atrophy attenuation. On this regard, Baldwin et al. (2013) presented a review on the effect of unloading on the muscle phenotype mostly based on the extensive work carried out by the authors over the last 25 years using different experimental models as microgravity and hindlimb suspension, among others. Brooks and Myburgh (2014) also discuss the skeletal muscle atrophy, focusing on the interplay between myonuclei, satellite cells and signaling pathways, highlighting the multi-dimensional feature of skeletal muscle wasting. Still regarding skeletal muscle atrophy, Koopman et al. (2014) discuss recent findings linking changes in metabolism to changes in muscle stem cell function and skeletal muscle mass, discussing the " metabolic reprogramming " concept and Manring et al. (2014) address the roles of modulatory genes of the skeletal muscle excitation-contraction coupling process on muscle wasting, bringing new possibilities for the treatment of muscle diseases. The misposition of myonuclei is a common feature of myopathies. In these conditions, nuclei are localized within the center of the muscle fiber. For decades, the centralized myonuclei was used as an evaluative parameter of regeneration in skeletal muscle. In this special issue, Dr Folker and Dr Baylies presented an interesting review regarding a possible role of myonuclei mispositioning in pathophysiology of muscle disorders (Folker and Baylies, 2013). Regarding the treatment of muscle disorders and cachexia, Berardi et al. (2014) discussed the effect of many interventions including stem cell and gene therapies, myostatin inhibition, tumor necrosis factor alpha (TNF-alpha) and interleukin-6 (IL-6) pharmacologic antagonism and microRNAs (miRNAs). Muscle gene therapy is a very actual issue for discussion in scientific community. Where we are on this way and where we should go? Beyond the correction of gene defects in muscle cells, the therapy should consider improve capillarity and reduce fibrosis to improve muscle environment and the stem cells engraftment. On this way, …