The change of HSP47, collagen specific molecular chaperone, expression in rat skeletal muscle may regulate collagen production with gravitational conditions
- Paper number
IAC-05-A1.4.08
- Author
Ms. Asami Oguro, University of Tokyo, Japan
- Coauthor
Mr. Yoriko Atomi, University of Tokyo, Japan
- Year
2005
- Abstract
It is well known that unloading of skeletal muscle with spaceflight leads skeletal muscle atrophy. The decreases of gravitational load such as space flight and bed rest cause the same effect on skeletal muscle, especially soleus muscle composed mainly slow-twitch fibers, with unloading and leads soleus muscle atrophy. Thus the skeletal muscle is highly adaptable to the change of environmental conditions, including gravity. However, it remains unclear how the extracelluar matrix within the muscle and the connective tissues such as tendon and ligament respond to reduced mechanical load including microgravity, although they have been thought to play important roles in both the transmission of force and the signal transduction between cells and tissues. Type-I collagen and Type-IV collagen, both of the major components of extracellular matrix and connective tissues, we focused on the changes of collagen synthesis with mechanical load. To obtain an insight into the effects of gravitational changing on the protein metabolism of collagen in skeletal muscle during mechanical unloading, reloading after unloading, we investigated the changes in the content of Heat Shock Protein 47 (HSP47), which has been postulated to be a collagen-specific molecular chaperone localized in the ER (Nagata et al, 1992). HSP47 is a collagen-binding protein, and assists in the molecular maturation of procollagen. HSP47 can bind to procollagen in vivo and in vitro, and preferentially binds the triple-helical region of procollagen. The crucial role of HSP47 in the collagen biosynthesis is well documented, and HSP47 gene disruption resulted in embryonic lethality in mice with molecular abnormalities in procollagen. The correlation of HSP47 expression with collagen is also reported in pathophysiological conditions. We examined such a hypothesis as HSP47 of skeletal muscle may sensitively change in both directions of unloading by HS and increased loading HG induced by the centrifugation, and confirmed this hypothesis in this study. Western blot analysis revealed that HSP47 in rat soleus muscle decreases at 5 days after Hindlimb suspension (HS). On the other hand, HSP47 in rat soleus muscle increases at 5 days after hypergravity (HG) induced by the centrifugation. RT-PCR analysis showed HSP47 mRNA was decreased with HS earlier, as compared with collagen type-I and type-IV mRNA. From these results, the amount of HSP47 changing by gravitational condition may effect on signal transfers in the primary stage of adaptation. It seems that the changes of HSP47 of soleus muscle may reflect to cellular adaptation for outer environment, resulting in the reorganization of collagen consisting of ECM or basal lamina, and the change of HSP47 expression in skeletal muscle may regulate collagen production with gravitational conditions.
- Abstract document