Effects of gravitational loading levels on protein expression related to metabolic and/or morphologic properties of mouse neck muscles

Abstract

The effects of 3 months of spaceflight (SF), hindlimb suspension, or exposure to 2G on the characteristics of neck muscle in mice were studied. Three 8‐week‐old male C57BL/10J wild‐type mice were exposed to microgravity on the International Space Station in mouse drawer system (MDS) project, although only one mouse returned to the Earth alive. Housing of mice in a small MDS cage (11.6 × 9.8‐cm and 8.4‐cm height) and/or in a regular vivarium cage was also performed as the ground controls. Furthermore, ground‐based hindlimb suspension and 2G exposure by using animal centrifuge (n = 5 each group) were performed. SF‐related shift of fiber phenotype from type I to II and atrophy of type I fibers were noted. Shift of fiber phenotype was related to downregulation of mitochondrial proteins and upregulation of glycolytic proteins, suggesting a shift from oxidative to glycolytic metabolism. The responses of proteins related to calcium handling, myofibrillar structure, and heat stress were also closely related to the shift of muscular properties toward fast‐twitch type. Surprisingly, responses of proteins to 2G exposure and hindlimb suspension were similar to SF, although the shift of fiber types and atrophy were not statistically significant. These phenomena may be related to the behavior of mice that the relaxed posture without lifting their head up was maintained after about 2 weeks. It was suggested that inhibition of normal muscular activities associated with gravitational unloading causes significant changes in the protein expression related to metabolic and/or morphological properties in mouse neck muscle.

Macrophage deficiency in osteopetrotic (op/op) mice inhibits activation of satellite cells and prevents hypertrophy in single soleus fibers

“…Exposure to microgravity or hind limb unloading of rodents causes passive shortening of soleus muscle due to ankle plantarflexion (20,39,59), which reduces the mechanical stress (20) and neural activity (19,20,39,43). Even though it is well-reported that muscles composed predominantly of slowtwitch fibers are more susceptible to unloading-related atrophy (6,41,42,(45)(46)(47)59), atrophy in soleus muscle of mice composed of fast-twitch fibers mainly was also observed in all types of mice, as was reported elsewhere (40,48,55). The unloading-related decreases in fiber length and sarcomere number may be associated with the remodeling of muscle fibers and sarcomeres, as was reported before (20,59).…”

Isoform Composition and Gene Expression of Thick and Thin Filament Proteins in Striated Muscles of Mice after 30-Day Space Flight

“…It is well known that disuse of muscles under conditions of both simulated and real microgravity leads to the development of atrophic changes in them [ 3 , 41 ]. In particular, following 91 days of long-term exposure to real microgravity in space (MDS Mission), atrophy was evident in soleus and neck muscles of mice [ 41 , 42 ]. It has been shown that hindlimb unloading causes atrophy of soleus, plantaris, gastrocnemius, and tibialis anterior muscles in mice [ 43 , 44 ].…”

Effects of long time exposure to simulated micro- and hypergravity on skeletal architecture

“…During the first experimental week a body weight decrement for both groups (HLU and 2 g) was recorded, probably due to stress and consequent decreased food intake. However, the weight eventually increased gradually, particularly in 2 g animals (Ohira et al, 2014). It would be interesting to evaluate shorter time exposition in 2 g in mice in term of body mass and bone phenotype.…”

“…The dimension of the cages were 25.0 Â 29.5 Â 20.0 (height) cm inserted in a gondola of 29.0 Â 35.0 Â 35.0 cm 3 (height) at the end of the centrifuge arms. Animals were exposed to 2g continuously, except 30 min per day for cleaning and feeding (Ohira et al, 2014). In the second group (n¼7), the unloading microgravity condition was achieved by the hindlimb unloading (HLU) suspension mode.…”