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Contribution of the calpain system to muscle protein accretion and growth in cattle and swine models
The calpain system plays a regulatory role in skeletal muscle proteolysis in the live animal under normal conditions. Reduced muscle proteolysis as a result of decreased calpain activity or increased calpastatin activity will result in less net protein turnover, all other factors being equal. This may lead to an animal which is more efficient, grows faster, is more heavily muscled, or simply better maintains its current muscle size (i.e., prevention of atrophy). The objective of this work was to examine the skeletal muscle calpain system in two growth models.
The first model compared the longissimus, triceps brachii, and semimembranosus muscles from young, growing cattle (7.3 ± 0.5 mo) and older, mature cows (106.7 ± 43.1 mo; n=6). Calpains and calpastatin were isolated from prerigor sarcoplasmic extracts at 0 d postmortem using ion exchange chromatography and assayed for activity using casein as a substrate. Calpastatin activity was also determined from a crude heated extract at 0, 1, and 6 d postmortem. Muscle from mature cattle tended to have a lower calpain-1:calpastatin activity ratio (P = 0.08). Additionally, less calpastatin activity was lost during postmortem aging of mature muscle, indicating that some mechanism exists which keeps calpastatin more stable in these animals. Overall, the calpain system is more conducive to protein turnover in young, growing cattle compared to older, mature cows.
The second model compared growing gilts (68.4 ± 3.5 kg, n=11) selected for reduced or increased residual feed intake (RFI). More efficient low RFI animals typically have greater lean accretion during growth compared to their less efficient high RFI counterparts. Calpain and calpastatin were isolated from prerigor longissimus and red and white semitendinosus muscle and assayed as described above. In our study, muscle from low RFI pigs had less (P = 0.04) calpastatin activity and a lower (P = 0.04) calpain-1:calpastatin activity ratio. These activities indicate less potential protein degradation in muscle from low RFI animals, which could explain increased lean accretion and some of the increased efficiency observed in low RFI pigs.
These data indicate that, based on the relative activities of skeletal muscle calpains and calpastatin, it is likely that more proteolysis occurs during growth as compared to a mature state. However, given similar growth stage, greater calpastatin activity may be more conducive to lean accretion and efficiency.
Supported by Wise Burroughs Memorial Endowment in Animal Sciences and USDA AFRI Grant no. 2010-65206-20670.
Keywords: calpain calpastatin growth