Cultured adult muscle fibers in the microgravity environment. The MYO experiment in the Foton-M3 space flight mission

Loss of skeletal muscle mass and force occurs in situations of altered use such as denervation, immobilization, aging and microgravity. The atrophy program induced under these conditions leads to an enhanced muscle protein degradation mainly via the ubiquitinproteasome and the autophagy-lysosome systems. The aim of our work is the definition of signaling pathways involved in muscle atrophy during space flights, that were never explored so far. As cellular model, we used cultured single skeletal muscle fibers isolated from adult mice. On September 2007, we had the unique opportunity to expose skeletal muscle fibers to microgravity condition during the unmanned Russian Foton-M3 mission, sponsored by Italian Space Agency (ASI) LIFE program. We utilized six pre-existing STROMA bioreactors (produced by Kayser Italia), four of which were for molecular analyses and two for morphology. Here we report the results of this space flight experience whose specific objective was to determine the effects of launch mechanical solicitations and four days space flight on single muscle fibers. Electron microscopy and gene expression analyses showed that space flight caused only minor modifications to cultured muscle fibers. Importantly, Foton-M3 mission provided useful indications on the requirements necessary to develop a novel bioreactor to be used in microgravity environment as well as in on ground experiments.