Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2009
Publication Date: 8/20/2009
Citation: Kemp, C.M., King, D.A., Shackelford, S.D., Wheeler, T.L., Koohmaraie, M. 2009. The Caspase Proteolytic System in Callipyge and Normal Lambs in Longissimus, Semimembranosus, and Infraspinatus Muscles During Postmortem Storage. Journal of Animal Science. 87:2943-2951. Interpretive Summary: Meat tenderness is a complex trait controlled by many factors, some of which are still poorly understood. One of those factors is the amount of degradation of proteins during aging of meat. The calpain enzyme system has the primary control over the extent of protein degradation during the aging process. Recent evidence indicates the caspase enzyme system also may have a role in the tenderization process. This experiment utilized control and callipyge lamb to characterize the activities of these enzyme systems in several muscles at different aging times. Results suggest that the caspase proteolytic system could contribute to postmortem tenderization through its actions on calpastatin, which is the inhibitor of the calpain system.
Technical Abstract: The objective of this experiment was to determine whether the caspase proteolytic system has a role in postmortem tenderization. Six ewes and six wethers that were non-carriers and six ewes and six wethers that were expressing the callipyge gene were used for this study. Caspase activities were determined in LM at seven different time points during the postmortem storage period: 0 h, 4 h, 8 h, 24 h, 2 d, 7 d, and 21 d and in semimembranosus (SM) and infraspinatus (IS) muscles at 0 h, 8 h, 24 h, and 7 d from callipyge and non-callipyge (normal) lambs. Calpastatin activity was determined at 0 h, 2 d, 7 d, and 21 d and slice shear force measured at 2, 7, and 21 d in the LM. Calpastatin activity and slice shear force were higher in LM from callipyge lambs than normal lambs at each time point (P < 0.001 and P < 0.0001, respectively). Caspases 3 and 7 are executioner caspases and their combined activity was found to decrease during the postmortem storage period in LM, SM, and IS muscles from both callipyge and normal lambs. Similarly, activity of the initiator caspase, (caspase 9) decreased (P < 0.05) in all three muscles across the postmortem storage period in both callipyge and normal lambs and its decrease in activity preceded that of the executioner caspases 3/7. A positive relationship also was detected between caspase 9 and caspase 3/7 in LM, SM, and IS muscles (P < 0.0001, r = 0.85, r = 0.86, r = 0.84, respectively) which is consistent with caspase 9 being responsible for the cleavage and activation of the executioner caspases (caspase 3/7) downstream. Caspase 3/7 and caspase 9 activities at 8 h in SM were higher in normal lamb than callipyge lamb (P < 0.05), with a trend for caspase 3/7 activity to be higher at 24 h postmortem (P = 0.0841). There also was a trend for caspase 3/7 activity to be higher in LM at 21 d in normal lamb than in callipyge lamb (P = 0.053), although there were no differences detected in caspase activities between genotypes in the IS muscle, which is not affected by the callipyge gene. A negative relationship also was detected between peak caspase 3/7 activity at 8 h in LM from normal lambs and calpastatin activity at 0 d and 2 d (r = -0.65, r = -0.68, respectively, P < 0.05). This relationship was not observed in LM from callipyge lambs, suggesting that caspase 3/7 may be cleaving calpastatin in normal lambs but the level of calpastatin in callipyge lambs is such that caspase 3/7 cannot degrade it sufficiently to overcome the high levels of calpastatin and, thus, calpastatin activity is the over-riding factor in postmortem proteolysis in these animals. There was no direct evidence from this study that caspases have a significant role in postmortem tenderization, but they may have some role through calpastatin degradation.