热应激对肉牛骨骼肌纤维类型的影响及其葛根素调控机理

Muscle fibers of beef are divided into four types, and their composition and proportion is a key factor to affect meat quality. Previous research has indicated that heat stress damaged muscle fiber structure, decreased carcass performance and meat tenderness of beef cattle, and lead to PSE meat. There is an important relationship between PSE meat and II b type contents in skeletal muscle fibers, but no report was noticed about how does heat stress influence muscle fiber types of beef cattle..This project will be conducted to study the change of muscle fiber composition of Jinjiang yellow cattle under heat stress, and discuss the intervening effect of Puerarin on them from the perspective of AMPK signaling pathways . The study consists of three details as follows..1) Effect of heat stress on the activity of AMPK, muscle fiber types, glycolysis metabolic and meat quality in beef cattle..2) Effect of different levels Puerarin as feed additive on antioxidant function, meat quality, AMPK activity, glycolysis potential, glycolytic enzyme, muscle fiber types and the expression of AMPK pathway upstream and downstream information factors of beef cattle under heat stress..3) Skeletal muscle satellite cells is cultured in vitro, and the cell model of AMPK activation and inhibition are set up under AICAR and compound C. In these models, the effect of AMPK signaling pathway in Puerarin regulating muscle fiber type transformation are investigated in vivo..This project will be investigated with the aim to clarity the effect of heat stress and Puerarin on beef muscle fiber types by AMPK signaling pathway, and the results will provide scientific basis for improving meat quality and carcass performance of beef cattle in South summer.

肉牛骨骼肌纤维分四种类型，其含量和比例是影响肉品质的关键。前期研究表明，热应激可降低肉牛产肉性能，使宰后牛肉出现色白、质软、嫩度差的类PSE肉。PSE肉的发生与骨骼肌中II b型肌纤维比例增加有重要关系，但有关热应激对肉牛肌纤维类型的影响未见报道。本项目拟以锦江黄牛为对象，从AMPK信号通路，探讨热应激对肉牛肌纤维类型的影响及葛根素调控机理。内容如下：1）观测热应激对肉牛AMPK活性、肌纤维类型、糖酵解代谢及肉品质的影响；2）研究添加不同水平葛根素对热应激肉牛抗氧化功能、肉品质、肌纤维结构、肌纤维类型及AMPK信号通路中上游、下游信息因子表达量的调控；3）体外培养骨骼肌卫星细胞，建立AMPK激活和抑制模型，研究AMPK信号通路在葛根素调控肌纤维类型转化中的作用。通过以上研究，将阐明热应激对肉牛肌纤维类型的影响，揭示葛根素调控肉质的机理，为改善牛肉品质、提高南方夏季肉牛养殖效益提供理论依据。

肉牛骨骼肌纤维分四种类型，其含量和比例是影响肉品的关键。肌纤维的数量在动物出生后便已固定，但不同类型之间受动物年龄、饲料营养、应激等因素影响可能发生转化。南方夏季高温高湿环境可诱发肉牛热应激反应，导致产肉性能降低，宰后牛肉嫩度变差，肉品下降。有研究显示，热应激可引起猪和家禽肌纤维类型发生转化，进而影响肉质，但热应激对肉牛肌纤维类型的影响未见报道。为了缓解热应激对牛肉品质的负面影响，改善夏季牛肉品质，本项目选用江西省本地黄牛——锦江牛为对象，利用春、夏季不同的环境气候及实验肉牛生理表现，确立热应激条件，研究了热应激对肉牛宰后肌肉能量代谢、肉品质、肌纤维类型的影响；并在此基础上，比较了日粮中添加不同水平的葛根素对热应激条件下肉牛育肥性能、屠宰性能、肉品质、肌纤维形态、肌纤维类型的影响，从AMPK信号通路入手，探讨了葛根素对热应激肉牛肌纤维类型的影响机制。主要结果如下：（1）夏季热应激导致肉牛宰后肌肉能量代谢异常，大量ATP转化为AMP，p-AMPK活性升高，肌纤维I型比例下降、IIb型比例升高；背膘厚下降，肉的pH异常，嫩度变差。（2）日粮中添加200~800mg/kg葛根素可降低热应激肉牛的体温和呼吸频率，提高肉牛的抗氧化酶活性和免疫功能；其中，400mg/kg的葛根素改善了热应激肉牛生产性能，下调了p-AMPK的活性，提高AMPK及其信号通路下游信息分子（PGC-1α、Nrf1）的mRNA表达量，促进肌纤维类型由IIb型向I型转化，改善了牛肉的嫩度。（3）通过对小鼠成肌细胞（C2C12）建立体外氧化应激模型，并使用CC抑制剂抑制AMPK活性，研究葛根素对应激细胞肌纤维类型的影响及其对AMPK信号通路的依赖性。结果表明，葛根素可降低应激肌细胞p-AMPK活性，提高AMPKα2 及其下游信号因子的mRNA表达量，促进肌纤维类型由IIB型向I型的转化。