肌肽对运动受限动物肌纤维类型转化和骨骼肌发育的营养调控作用

The appropriate amount of exercise could improve the development of skeltal muscle and help to construct the meat quality. But for animals in intensive feeding,their excerise intensity are often lower than the threshold to activate the muscle satellite cells,and caused slow development of skeltal muscle and even increased the ratio of Ⅱb type muscle fiber, which means poor growth performance and meat quality.Carnosine is one of the most abundant nitrogenous compounds occurring in the nonproteic fraction of muscle and other tissues. Sports medicine showed that orally supplemented carnosine could improve the susceptibility of muscle to ecercise, but the mechanism is not clear.In this study, firstly, the effects of carnosine on activation and cellular differentiation of different kind satellite cells through NO-HGF-C-met signaling pathways are evaluated by two cell culture trials in vitro，respectively. Then the cooperative effects of dietary supplemented carnosine and exercise loading on pig muscle development and fibre type transition are studied to elucidate the potential signaling pathways including Calcineurin(Cn), Calmodulin-dependent protein kinase-Ⅱ(CaMKⅡ) and AMPK. The results should be help to know better the molecular basis of meat quality development and introduce a new idea for regulation on muscle type transition on the basis of low exercise intensity of intensive feeding animals.

适量运动是刺激骨骼肌生长发育和肉品质形成的必要条件。集约化饲养动物处于运动受限状态，运动量难以激活骨骼肌卫星细胞，瘦肉率降低，肌肉中快白肌纤维比例增加，肉品质降低。肌肽是肌肉等组织中存在的天然二肽。运动医学表明口服肌肽可以提高肌肉对运动刺激的敏感性，但其作用机理尚不清楚。本研究通过离体培养试验，比较研究肌肽通过NO-HGF-C-met信号通路对处于静息态的快、慢肌纤维卫星细胞的激活作用，阐明了肌肽对肌纤维卫星细胞的调控增殖和诱导分化作用；通过在体实验验证了不同强度运动刺激和外源肌肽对猪骨骼肌发育和肌纤维转化的作用效果，解析肌肽通过钙调神经磷酸酶（Cn）信号途径、钙调蛋白依赖性蛋白激酶Ⅱ（CaMKⅡ）信号途径、AMPK信号途径等提高运动刺激敏感性的作用机制。本研究成果有助于加深理解肌肉发育和肉品质形成的分子基础，为集约化养殖和运动受限状态下的畜禽高效优质生产奠定基础。

肌纤维类型是影响肉品质的主要因素。运动医学证实，运动刺激、肌肽含量等可以促进肌纤维类型转化；补充肌肽可以提高运动成绩；大强度运动可以诱导肌纤维类型转换；肌肽及其前体物提高红肌纤维相对表达水平。本研究采用在体饲养试验和离体细胞培养试验相结合，通过11个试验，较为系统的研究了肌肽对运动受限动物肌纤维类型转化和骨骼肌发育的营养调控作用。研究结果表明不同部位骨骼肌在肌肽含量、肌纤维类型、增殖期和分化期细胞因子表达量等方面具有显著差异，而这种差异是构成其对运动刺激敏感度的物质基础。肌纤维类型对运动刺激敏感性的差异与其能量代谢方式有关。饲料或饮水中补充肌肽通过mTOR信号通路促进骨骼肌生长发育，并通过Wnt/β-catenin信号通路调控肌纤维卫星细胞分化过程调控肌纤维类型转化。加强训练可以促进快白肌的氧化代谢、慢红肌酵解型代谢，提高肌肽合成能力。补充肌肽提高运动刺激敏感性和改善锻炼效果的作用机制与其通过钙调神经磷酸酶、CaMKⅡ和AMPK改善肌肉能量代谢密切相关。β-丙氨酸是体内肌肽合成的限制性氨基酸，在饲料或饮水中补充β-丙氨酸具有与补充肌肽相类似的效果。成果有助于理解肉品质形成的分子基础，提出改善肉质的新思路。