过瘤胃葡萄糖对肉牛皮下与肌内脂肪差异沉积的作用机制研究

Rumen bypass glucose can directly enter the small intestine through the rumen, increasing the total amount of absorbable glucose in the small intestine. Up to now, the studies on rumen bypass glucose of ruminants were mainly focus on alleviating the negative energy balance in postpartum dairy cows, but the effects of rumen bypass glucose on fat deposition of beef cattle were seldom reported. In our previous study, we found that adding rumen bypass glucose to fattening beef cattle diets could control the deposition of subcutaneous fat and promote the deposition of intramuscular fat. However, the mechanism of rumen bypass glucose on the differential deposition of subcutaneous and intramuscular fat of beef cattle is unclear. Therefore, rumen bypass glucose was used to feed beef cattle in our project. The effects of rumen bypass glucose on the morphology of subcutaneous and intramuscular adipocytes, precursors content for fatty acid synthesis，the expression of glucose transporters and key enzymes of glucose and lipid metabolism in beef cattle were studied. The effects of subcutaneous and intramuscular adipocytes on glucose uptake and utilization were studied by adipocyte culture in vitro, the sequential changes in proliferation, differentiation and lipid synthesis metabolism of preadipocytes were observed. The results of this study will lay a theoretical foundation for further understanding the effect and mechanism of rumen bypass glucose on the differential deposition of subcutaneous and intramuscular fat in beef cattle. In addition, it will also provide fundamental knowledge for the effective application of rumen bypass glucose on beef cattle production.

过瘤胃葡萄糖可以通过瘤胃直接进入小肠，增加小肠可吸收葡萄糖的总量。目前，关于过瘤胃葡萄糖在反刍动物方面的研究主要集中在缓解奶牛产后能量负平衡方面，在对肉牛脂肪沉积方面的作用却鲜有报道。项目申请人在前期研究中发现肉牛育肥期日粮中添加过瘤胃葡萄糖可以在控制皮下脂肪沉积的同时显著增加肌内脂肪的含量。然而，有关过瘤胃葡萄糖对肉牛皮下与肌内脂肪差异沉积的作用机制尚不明确。因此，本项目使用过瘤胃葡萄糖饲喂育肥期肉牛。在组织水平上研究过瘤胃葡萄糖对肉牛皮下与肌内脂肪细胞形态、脂肪合成前体物含量、葡萄糖转运蛋白和糖脂代谢关键酶表达的影响；在细胞水平上，通过体外脂肪细胞培养，研究肉牛皮下与肌内脂肪细胞对葡萄糖摄取和利用的差异，观察前脂肪细胞增殖、分化以及脂肪合成代谢的时序性变化。研究结果为深入认识过瘤胃葡萄糖对肉牛皮下与肌内脂肪差异沉积的作用机制奠定理论基础，为过瘤胃葡萄糖在肉牛生产上的应用提供科学依据。

本项目旨在阐明过瘤胃葡萄糖对肉牛不同脂肪组织沉积的作用效果和相关机制，为过瘤胃葡萄糖在肉牛育肥阶段的合理应用提供理论依据。并且对生产高档优质牛肉具有重要的实践意义。. 试验一选择45头肉牛，随机分为3组（1个对照组和2个处理组），每组各15头。对照组不添加过瘤胃葡萄糖（Rumen Protected Glucose, RPG）。试验组分别添加100g和300gRPG。饲喂4个月后进行屠宰，采集样品进行分析。阐明过瘤胃葡萄糖对肉牛脂肪沉积和牛肉品质的影响并探究其分子作用机制。研究结果显示：（1）与对照组相比，添加100gRPG能够显著增加背最长肌内脂肪含量和大理石花纹评分等级（P<0.05）。背膘厚度随着RPG添加量呈现降低趋势，但各组没有显著差异。（2）与对照组相比，试验组肌肉组织中多不饱和脂肪酸C18:2n6c和C18:3n6含量极显著升高（P<0.01），脂肪组织中C18:1n9t和C18:2n6t含量极显著降低。（3）通过转录组测序后，发现与对照组相比，试验组皮下脂肪组织中PRSS2基因表达量显著增加，而MYOM2基因表达量显著降低。肌肉组织中，100gRPG组中PRSS2和LAMA1基因表达量显著增加。表明PRSS2基因可能对肉牛脂肪代谢和肉质性状具有重要调控作用。.试验二培养前脂肪细胞，在诱导分化时使用葡萄糖进行刺激。葡萄糖浓度分别为3.0、3.5和4.0 mmol/L，与脂肪细胞共孵育2、4、8d后终止培养，进行相关指标测定。研究结果显示：（1）葡萄糖转运蛋白GLUT1和GLUT4分布的位置主要在细胞质中，并且随着葡萄糖添加量的增加而变得更加密集。（2）在2 d和4d时，脂肪细胞中甘油三酯的含量随着葡萄糖添加量的增加而增加，在第8d时随着葡萄糖添加量的增加而降低。（3）脂肪细胞中PPARγmRNA和蛋白表达量随着葡萄糖添加量的增加而降低，而ACC1和FASmRNA和蛋白表达量则显著增加。.综上所述，试验日粮中添加100gRPG在不增加皮下脂肪的情况下，对提高肌内脂肪沉积的效果最好，PRSS2基因可能对肉牛脂肪代谢和肉质性状具有重要调控作用。随着葡萄糖添加量增加，脂肪细胞中PPARγ表达量显著下降而ACC1和FAS表达量显著增加。