Graduate Thesis Or Dissertation

 

Effects of age, castration and gestation on calpains and calpastatin in sheep and rabbit skeletal muscle Public Deposited

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  • Objectives of this study were to examine effects of age, castration and gestation on actvities of calpains and calpastatin in skeletal muscle. Also, the regulation of calpains and calpastatin at the molecular level was investigated. Two experiments were designed. Experiment 1 was designed to evaluate effects of age and castration on calpains and calpastatin in sheep skeletal muscle. Experiment 2 was designed to examine the effects of age and gestation on calpains, calpastatin and their molecular regulation in rabbit skeletal muscle. In Experiment 1, ten newborn male lambs, six weaned wethers (92 days), six weaned rams (92 days), six market weight wethers (89 days post-weaning) and six market weight rams (89 days post-weaning) were slaughtered and gluteobiceps femoris was taken for assay of calpain I, calpain II and calpastatin. Body weights were not different between wethers and rams in weaned animals; however, post-weaning, body weight gain of rams was greater (p < .05) than that of wethers. Ram gluteobiceps femoris weight at market weight was greater than that of wethers (p < .05). Activities of muscle calpain I, calpain II and calpastatin in newborn lambs were higher than those of weaned and market weight lambs. The age-dependent reduction of calpain and calpastatin activities was complete at weaning and may be associated with or cause age-dependent attenuation of muscle protein degradation. Although muscle weights were greater in rams compared to wethers, no differences in activities of muscle calpains and calpastatin were detected between these two groups at weaning and at market weight. Hence, castration does not influence lamb muscle growth by changing muscle total calpain or calpastatin activities. In Experiment 2, biceps femoris muscle was collected from newborn, weaned (1 month), market weight (2 months), non-gestational adults (5 months) and gestational (20 day) adult rabbits and for assay of calpains, calpastatin activities, muscle NI-- methylhistidine (NMH) and mRNA encoding calpains and calpastatin. Muscle protein content (mg/g tissue) increased as animals aged indicating proliferation of myofibrillar protein. Total RNA content and ribosomal capacity (mg/g protein) declined (p < .05) as the rabbits aged; however, no differences in protein content and ribosomal capacity were detected in muscles taken from gestational versus non-gestational adult rabbits. Concentration of muscle NMH decreased as animal aged; however, no differences were detected in 20-day gestational muscle versus non-gestational muscle. Activities of calpains and calpastatin declined (p < .05) as animal aged. Most of the loss of activity occurred before 4 weeks of age (weaning). No differences in calpain and calpastatin activities were detected in gestational versus non-gestational animals. Reductions in activities of calpains and calpastatin were associated with reduced RNA concentration (ribosomal capacity) and reduced concentrations of muscle calpains and calpastatin mRNA (expressed as densitometry units per g tissue protein). The reduction of mRNA appeared to be associated with an overall loss of RNA from skeletal muscle because mRNA/g protein was greatly reduced whereas mRNA/total RNA for both calpains and calpastatin did not change greatly; however, mRNA/total RNA in adult rabbits compared to newborn, weaned and market weight animal declined significantly. In addition, from the Northern blot assay, it was determinated that newborn and weaned rabbits only expressed an intermediate length calpastatin mRNA isoform (II). However, the longest calpastatin mRNA isoform (I) was expressed in market weight and adult rabbits. The reason why muscle cells express different forms of calpastatin mRNA at different ages remains unknown. In pregnant rabbits, neither calpains nor calpastatin changed significantly. Also, muscle NMH concentration did not change. However, at the mRNA level, the steadystate concentration of mRNA encoding calpain II increased and calpastatin band II mRNA decreased in pregnant rabbits. This implies that in late catabolic stage of gestation, increased calpain II activity and decreased calpastatin activity may facilitate proteolysis.
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