Effect of genotype and nutrition on calpastatin inhibitory activity and mRNA abundance in milk-fed lambs

Abstract

Muscle proteolysis is controlled by a wide range of enzyme systems. The reported effects of the calcium dependent proteinases (calpain I and II) and its specific inhibitor (calpastatin) on myofibrillar structure, has led to the speculation that this system may have a pivotal role in regulating protein turnover and muscle growth. The present study highlights the possibility of protein degradation being subject to genetic variation. The relationship between genotype, level of nutrition, muscle protein turnover and the calpain system in young milk-fed lambs was assessed. Male lambs which had been selected for 10 generations for high (W+) and low (W-) weight at weaning were used in the study. Lambs were removed from their mothers 4 days after birth and surgically fitted with abomasal catheters and infused with reconstituted milk replacer at a high or a low rate. At 8 weeks of age, measurements of muscle protein gain, synthesis and degradation were performed, the animals were slaughtered and samples rapidly removed for subsequent chemical analysis. The liveweight gain and weight of the m vastus lateralis was reflected ( P < 0.001) in the designed differences in nutrient supply. The weight of the m vastus lateralis was greater ( P < 0.01) in the W+ compared to the W- lambs. The rate of protein synthesis and calculated degradation were greater ( P < 0.05) in W+ than W- lambs. Calpain I and II and calpastatin activity were not significantly altered by genotype or nutrition. Calpastatin mRNA abundance increased significantly ( P < 0.05) between 1 and 8 weeks of age. Regression analysis revealed genotype-specific responses with respect to calpastatin activity and mRNA abundance. The results suggest that in sheep lines genetically divergent for growth potential, differences in the rate of protein gain were associated with alterations in muscle protein degradation and its sensitivity to nutrient supply. The differences may in part be explained by differences in the calpain system, including the specific inhibitor calpastatin between the genotypes.