The Establishment And Application Of The Platform For Detecting Skeletal Contractive Function In Mice

It has identified major adaptive changes with weightlessness in a variety of organ systems. Exposure to microgravity during space flights induces atrophy, slow-fast muscle fiber transition, reduced functional capacity, and increased fatigue in limb skeletal muscles, with the greatest changes observed in anti-gravity skeletal muscle. The changing of skeletal muscle functions contains muscle weakness, reduced muscle tensity and endurance capacity, work capacity, which affects the working capacity during space flying and the crews'ability to readjust to 1G. Therefore, it is significantly that special emphasis will be placed on the cellular and molecular mechanisms of the microgravity-induced muscle atrophy and the potential countermeasures.The research to mimic the weightlessness muscle atrophy was focused on hindlimb unloading rat model. Little is known about the disuse-induced alterations of skeletal muscle when hindlimb unloading is applied to mice. Recently, due to the possibility to easily manipulate mouse genome as well as to include mice in future space missions, there has been s growing advantage toward the murine hindlimb unloading model. So we constructed unloaded muscle atrophy mice model in domestic to mimic the effects of weightlessness on lower limb muscle. Using histology immunohistochemistry, Western blot and Real-time PCR, we dynamically analyzed the changes of muscle weight, cross-sectional area, atrophy-specific proteins, slow and fast myofiber specific proteins, and the transition between MHC subtypes at 0,14,28 day after hindlimb unloading. The results showed that HU affects in adult mice are very similar to those previously observed in HU rats, which confirmed the validity of the mice model.To explore the changes in skeletal muscle contractibility and fatigue after hind-limb unloading-induced muscle atrophy of mice, we established the platform for detecting skeletal contractive function in mice and exerted some applications. After 14-day and 28-day hind-limb unloading and muscle atrophy, we used the method of isolated muscle perfusion with different stimulated protocols to determine the changes in contractile characteristics including the isometric twitch force and tetanus force and fatigue index of slow twitch muscle and fast twitch muscle. We found that the mass of hind-limb skeletal muscle lost significantly after 14-day and 28-day hind-limb unloading with mice, indicating the development of atrophy. The isometric twitch force and the tetanus force of isolated slow and fast twitch muscle were decreased progressively after 14-day and 28-day hind-limb unloading with mice. The tetanus force of isolated slow twitch muscle was decreased significantly in 14-day HU, but the conspicuous decrease of the fast twitch muscle was observed only in 28-day HU. The significant decrease of fatigue index was observed only in soleus with 14-day HU. We concluded that the isometric twitch force and the tetanus force of slow and fast twitch muscle in hind-limb skeletal muscle were decreased progressively in unloaded mice, which were significantly in slow muscle, but the fatigue index was changed only in slow twitch muscle. We also detected the changes in contractile characteristics including the isometric twitch force and tetanus force and fatigue ability of slow twitch muscle and fast twitch muscle with PGC-1αtransgenic mice and wild type mice in same brood. We found that the anti-fatigue capacity was increased in PGC-1αtransgenic mice compared with wild type mice, without the significant difference in the isometric twitch force and tetanus force. It was confirmed that PGC-1αwas principal factor regulating muscle fiber type determination, which sustaind a much longer duration of continuous contraction than wild type controls. After 14-day HU with PGC-1αtransgenic mice and wild type mice in same brood, we found that the isometric twitch force and tetanus force of PGC-1αtransgenic mice was stronger than wild type mice, which was probably the role of PGC-1αin energy metabolism. The C57BL/6 mice were given compound 1010 everyday during 14-day HU. We found that the isometric twitch force and tetanus force of the soleus were stronger than the control with saline. It indicated that the compound proberbly effected muscle mechanics through energy metabolism.