Effects Of Adiponectin On Skeletal Muscle Growth And Types Of Muscle Fibers Of Wannanhua Pigs

Three experiments for this thesis were conducted to study the effects of adiponectin on skeletal muscle growth and muscle fiber types at different age of Wannanhua pigs.1. The developmental change of the area and proportion of different muscle fiber types at the age of 0,30,45,90 and 180 days in longissimus dorsi muscle of Wannanhua pigs were investigated with conventional mATPase staining method. In addition, differences of the area and proportion of different muscle fiber types between sex were analyzed.The results showed that:(1) Longissimus dorsi muscle fiber area increased with age, and the most significiant increase was observed in 90~180d, except 2a and 2b muscle fibers area in 30~45d.(2) The proportion of longissimus dorsi muscle fibers had significant developmental of changes with age. The proportion of muscle fiber typeⅠwas significantly decreased, but the proportion of muscle fiber type 2b was significantly increased in 0~30d. The proportion of muscle fiber type2a had no significant changes in 0~90d. The proportion of muscle fiber type2a was significantly increased, but the proportion of muscle fiber type2b had no significant changes in 90~180d.(3)The area and proportion of the longissimus dorsi muscle fibers had no significant differences between sex in general, that there was no significant effects of sex on growth and composition of longissimus dorsi muscle fibers of Wannanhua pigs.2. The developmental patterns of Adipor1, Adipor2 and four specific MyHC isoforms: MyHCI,MyHC2a,MyHC2x, and MyHC2b genes at the age of 0,30,45,90 and 180 days in longissimus dorsi muscle and semitendinosus muscle of Wannanhua pigs were investigated with Real-time fluorescence quantitative PCR(SYBR Green I)method.In addition, the genes expression differences between sex and muscle types were analyzed.The results showed that:(1) AdipoR1 mRNA expression levels in longissimus dorsi and semitendinosus increased with age. AdipoR2 mRNA expression were significantly decreased in 0~30d, and maintained a relatively stable level in 30~180d.(2) During 0~30d, MyHCI and MyHC 2x mRNA expression in longissimus dorsi and semitendinosus had no significant change, however, MyHC2a mRNA expression were significantly decreased, and MyHC2b mRNA expression increased significantly in longissimus dordi muscle. During 90~180d, MyHC2a, MyHC2x and MyHC2b mRNA expressions in longissimus dordi muscle, but not in semitendinosus muscle, were increased significantly. In general, four specific MyHC isoforms gene expression in longissimus dordi muscle and semitendinosus muscle of Wannanhua pigs had significant developmental changes with age. The expression of oxidized muscle fibers decreased, while the expression of glycolysis muscle fibers increased with the growth of Wannanhua pigs.(3) MyHCI mRNA expression in semitendinosus muscle was significantly higher than those in longissimus dorsi muscle in all ages, especially in 180 days of age. Overall, MyHC2a and MyHC2x, MyHC2b mRNA expression in longissimus dorsi muscle was significantly higher than that in semitendinosus muscle.(4) At birth, MyHC2b mRNA expression in longissimus dorsi muscle of gilts was significantly higher than that in boars. In 30 days of age, MyHCI mRNA expression in boars'longissimus dorsi muscle and MyHC2a mRNA expression in boars' semitendinosus muscle were significantly higher than those in gilts. In 45 days of age, MyHCI, MyHC2x, MyHC2b mRNA expression in semitendinosus muscle of gilts was all significantly higher than those in boars. MyHC2a and MyHC2x mRNA expression in gilts'semitendinosus were significantly higher than boars' in 90 days of age. Overall, there was little effect of gender on the composition of four muscle fiber types, that is, there was no significant difference in growth patterns of four specific MyHC isoforms gene expression between Wannanhua gilts and boars.3. To investigate the signaling pathways of adiponectin and the effects of different recombinant adiponectin(rADP) levels(0,1,5,10μg/ml) on the composition of muscle fibers by determining the genes expression of four isoforms of myosin heavy chain(MyHCI,MyHC2a, MyHC2b and MyHC2x), ADP, Adipor1, Adipor2, AMPK, and PPARa in skeletal muscle cells of Wannanhua pigs after 12 h and 24 h culture time with Real-time fluorescence quantitative PCR(SYBR Green I). The results showed that:(1) ADP and AdipoR1 gene expression was significantly increased with 1μg/ml rADP treatment for 12 and 24 h, but AdipoR2 gene expression was significantly increased only at 24 h treated with ADP. In addition, ADP, AdipoR1 and AdipoR2 gene expression were lower with 5 and 10μg/ml rADP treatment than with 1μg/ml rADP treatment.(2) The MyHCI and MyHC2x gene expression significantly increased with 1μg/ml rADP treatment for 12 and 24 h. MyHC2a gene expression was no significant increase. MyHC2b gene expression were significantly decresed with treatment by 1μg/ml rADP for 24 h. MyHC1, MyHC2a, MyHC2b gene expression were lower in 5 and 10μg/ml rADP treatment groups than in 1μg/ml rADP treatment group. MyHC2x gene expression was significantly higher treated by 5μg/ml rADP than treated by 1μg/ml rADP for 12 h. (3) AMPK gene expression was significantly increased when treated with rADP for 12 h. However, the low rADP doseage group had higher AMPK gene expression. PPARa gene expression was significantly higher than control with 1μg/ml rADP treatment for 12 and 24 h. But high rADP doseage groups had no this effects. These results suggest that the role of adiponectin in skeletal muscle, may be related to activating both AMPK and PPARa signaling pathways by binding adiponectin receptor. Adiponectin can change the composition of muscle fibers by increasing MyHCI, MyHC2a, MyHC2x and decreasing MyHC2b gene expression, thus achieve the purpose of improving the carcass quality.