猪低蛋白日粮氨基酸代谢节俭机制研究

Amino acids (AA) are the metabolic fuel that most tissue cells prefer, especially for the portal-drained viscera. This is an important reason for high nitrogen emission from pigs, therefore, inhibiting the role of AA as a metabolic fuel is an important strategy to reduce porcine nitrogen excretion. Pyruvate, which occupies a pivotal node in the metabolism of carbon, AA, and lipid, should be a common regulatory target for the metabolism of AA and glucose. In this study, by applying the techniques of blood catheter and stable isotope tracing, the experiments in vitro and vivo will be carried out to investigate the effects of addition of pyruvate to low-protein diets on the release of nitrogen precursors of urea in the portal-drained viscera, urea synthesis in the liver, and nitrogen excretion and reveal the relative regulatory mechanisms. Then, by applying the techniques of RNA interference, chemical inhibitor, and chemical activator, we will study the effects of down-regulating or up-regulating the activity of glucose-pyruvate metabolic enzymes in the porcine jejunal cells on the metabolism of glucose and AA to determine the regulatory target of glucose-pyruvate oxidative metabolism and indentify the regulatory additives that promote the energy supply efficiency of glucose and consequently inhibit the role of AA as metabolic fuel. Based on these studies, low-protein diets, which are characterized by supplementing with the regulatory additives, will be developed, then the experiments of toxicology, nitrogen balance, and growth performance will be carried out to reveal the mechanisms of the AA metabolic thrift in the low-protein diets. The implementation of this study will provide theoretical basis and practical guidance on modifying the technology of low-protein diets for pigs.

氨基酸是多数组织细胞尤其是门静脉回流组织偏好的燃料物质，这是造成猪尿氮和总氮排放量居高不下的重要原因，因此，抑制氨基酸代谢供能是减少猪氮排放的重要策略。丙酮酸作为三大营养物质的代谢中枢，其氧化过程是调控葡萄糖和氨基酸代谢的关键环节。本项目首先利用稳定性同位素示踪、血插管技术，结合体内与体外试验，研究低蛋白日粮添加丙酮酸对生长猪门静脉回流组织尿素前体物释放、肝脏尿素合成以及氮排放的影响，以回答丙酮酸抑制氨基酸代谢供能的作用机制；然后研究激活或抑制葡萄糖-丙酮酸氧化代谢关键酶对猪小肠上皮细胞葡萄糖和氨基酸代谢的影响，以揭示葡萄糖-丙酮酸氧化代谢的调控靶点，并挖掘高效的调控物质；在此基础上进行毒理试验，之后改进猪低蛋白日粮，并开展氮平衡、生长试验以及相关的调控路径研究，最终阐述猪低蛋白日粮氨基酸代谢节俭机制。本项目的实施将提升对猪氮减排机制的认识，为研制高效的猪及其它畜禽低蛋白日粮提供理论指导。

低蛋白质日粮是节约蛋白质饲料资源和减少氮排放最有效的方法，但降低日粮粗蛋白质含量需要补充重要氨基酸，以平衡日粮氨基酸模式，并且在不影响动物生长或生产条件下，日粮粗蛋白质含量的降低幅度通常只有1-2个百分点。此外，饲喂低蛋白质日粮往往会增加生长肥育猪的脂肪沉积。因此，需要对现有低蛋白质日粮进行技术创新，以解决上述技术难题，使低蛋白质日粮能在畜禽生产中得到广泛应用。在前期工作基础上，项目组提出畜禽氮减排新理论，即实现氨基酸代谢节俭是破解低蛋白质日粮技术瓶颈的重要策略。本项目以实现氨基酸代谢节俭为目标，开展了一系列研究，具体如下：（1）丙酮酸对氨基酸代谢供能的影响及其调节机制；（2）低蛋白日粮添加丙酮酸对猪氮代谢的影响；（3）葡萄糖-丙酮酸氧化代谢的调控靶点及调节机制；（4）基于氨基酸代谢节俭的猪新型低蛋白日粮。通过以上研究取得的成果如下：（1）明确了丙酮酸可替代氨基酸的代谢燃料功能；（2）揭示PDK/PDH/PDP是葡萄糖-丙酮酸氧化代谢的调控靶点，并明确二氯乙酸钠能够通过调控PDK/PDH/PDP轴来促进葡萄糖的氧化供能效率，从而减少氨基酸的氧化代谢；（3）研制了基于二氯乙酸钠代谢调节的新型低蛋白质日粮，该日粮能够在不影响生长肥育猪生长性能前体下进一步降低日粮的蛋白质含量，显著提高低蛋白质日粮的生态效益与生态效益。本项目所取得的研究成果对于破解低蛋白质日粮技术瓶颈、促进低蛋白日粮在生产中的广泛应用具有重要理论与实践意义。