iTRAQ-based proteomic analysis of myofibrillar contents and relevant synthesis and proteolytic proteins in soleus muscle of hibernating Daurian ground squirrels (Spermophilus dauricus).
BACKGROUND
Daurian ground squirrels (Spermophilus dauricus) deviate from significant increase of protein catabolism and loss of myofibrillar contents during long period of hibernation inactivity.


METHODS
Here we use iTRAQ based quantitative analysis to examine proteomic changes in the soleus of squirrels in pre-hibernation, hibernation and post-hibernation states. The total proteolysis rate of soleus was measured by the release of the essential amino acid tyrosine from isolated muscles. Immunofluorescent analysis was used to determine muscle fiber cross-sectional area. Western blot was used for the validation of the quantitative proteomic analysis.


RESULTS
The proteomic responses to hibernation had a 0.4- to 0.8-fold decrease in the myofibrillar contractile protein levels of myosin-3, myosin-13 and actin, but a 2.1-fold increase in myosin-2 compared to pre-hibernation group. Regulatory proteins such as troponin C and tropomodulin-1 were 1.4-fold up-regulated and 0.7-fold down-regulated, respectively, in hibernation compared to pre-hibernation group. Moreover, 10 proteins with proteolytic function in hibernation, which was less than 14 proteins in the post-hibernation group, were up-regulated relative to the pre-hibernation group. The total proteolysis rates of soleus in hibernation and post-hibernation groups were significantly inhibited as compared with pre-hibernation group.


CONCLUSIONS
These findings suggest that the myofibrillar remodeling and partial suppression of myofibrillar proteolysis were likely responsible for preventing skeletal muscle atrophy during prolonged disuse in hibernation. This is the first study where the myofibrillar contents and relevant synthesis and proteolytic proteins in slow soleus was discussed based on proteomic investigation performed on wild Daurian ground squirrels. Our results lay the foundation for further research in preventing disuse-induced skeletal muscle atrophy in mammals.
Key Laboratory of Resource Biology and Biotechnology in Western China (College of Life Sciences, Northwest University), Ministry of Education, Xi'an, 710069 People's Republic of China.|Shaanxi Key Laboratory for Animal Conservation, Northwest University, Xi'an, 710069 People's Republic of China.
Hui
H
Chang
Key Laboratory of Resource Biology and Biotechnology in Western China (College of Life Sciences, Northwest University), Ministry of Education, Xi'an, 710069 People's Republic of China.
Shan-Feng
SF
Jiang
Key Laboratory of Resource Biology and Biotechnology in Western China (College of Life Sciences, Northwest University), Ministry of Education, Xi'an, 710069 People's Republic of China.
Kai
K
Dang
Key Laboratory of Resource Biology and Biotechnology in Western China (College of Life Sciences, Northwest University), Ministry of Education, Xi'an, 710069 People's Republic of China.
Hui-Ping
HP
Wang
Key Laboratory of Resource Biology and Biotechnology in Western China (College of Life Sciences, Northwest University), Ministry of Education, Xi'an, 710069 People's Republic of China.
Shen-Hui
SH
Xu
Key Laboratory of Resource Biology and Biotechnology in Western China (College of Life Sciences, Northwest University), Ministry of Education, Xi'an, 710069 People's Republic of China.|Shaanxi Key Laboratory for Animal Conservation, Northwest University, Xi'an, 710069 People's Republic of China.
Yun-Fang
YF
Gao
Daurian ground squirrel; Disuse atrophy; Hibernation; Myofibrillar protein; Proteomic; Synthesis and proteolysis