肠道氨基酸感知受体介导支链氨基酸调控仔猪采食量的机制研究

Reduction of feed intake contributes to the decrease of growth performance in pigs. Our Previous studies demonstrated that supplementation of branched chain amino acids (BCAA) in low protein diet significantly increased the feed intake of piglets. However, the underlying mechanism is still largely unknown. Recent study found, except brain, gut is a major organ participating in food intake regulation. To identify to role of amino acid receptors involved in regulation of pig appetite, we firstly detected the distribution of amino acid receptors (CaSR, GPC6A, T1R1 and mGluR4) of GI tract in piglets. Then, we design two animal studies (long-term feeding and short-term feeding) to uncover the expression of amino acid receptors and concentrations of gastrointestinal hormone (CCK, GLP-1 and PYY). Finally, STC-1 cells and pig intestinal tissues were chosen as in vitro models to study the effects of BCAA on expression of amino acid receptors, gastrointestinal hormone concentrations in medium (when receptors were inhibited or not). Collectively, this study reveals the mechanisms of branched-chain amino acids in regulating feed intake through intestinal and brain nutrient receptors in piglets, and lay a foundation for the application and extension of low protein diet in pig industry.

采食量下降是限制猪生产性能的重要因素之一。给猪饲喂低氮排放日粮可减少氮排放污染，但其采食量受到抑制。申请者前期研究工作发现，低氮排放日粮中添加支链氨基酸可提显著高猪采食量，改善其生产性能，但机制尚不清楚。最新报道称，除大脑外，胃肠道在采食调控中也扮演重要角色。本项目拟以仔猪小肠为靶点，首先确定不同氨基酸感知受体（CaSR、GPC6A、T1R1和mGluR4）在仔猪肠道的分布；进而分别在仔猪上建立长期和短期采食调控两个体内模型，研究支链氨基酸对肠道氨基酸感知受体表达和胃肠道激素分泌的影响；最后以肠道内分泌细胞STC-1和仔猪肠道组织块为体外模型，研究氨基酸感知受体正常表达和受抑制时，支链氨基酸对胃肠道激素的分泌作用；进一步明确肠道氨基酸感知受体为仔猪食欲调控靶点。该研究结果不仅可以从理论上阐述支链氨基酸通过肠道感知对仔猪采食调控的作用机制，还可以为低氮排放日粮的进一步推广和应用打下夯实基础。

支链氨基酸（BCAAs）是调节动物采食的重要氨基酸。目前，关于BCAAs通过中枢神经系统对采食调控的研究已经很广泛，但是BCAAs是否能够通过肠道氨基酸受体感知，调节肠道饱感激素释放，调控仔猪采食，尚不明确。在本研究中，我们首先通过对氨基酸感知受体和肠道食欲肽在仔猪肠道各肠段的表达进行分析，发现胆囊收缩素（CCK）和鲜味受体二聚体1/3（T1R1/T1R3）主要在空肠中表达并且两者在功能上相互关联，并确定了空肠是氨基酸感知受体和肠道食欲肽表达的关键部位。通过体外试验，建立了空肠组织模型，并以此探究了BCAAs介导T1R1和T1R3调控仔猪肠道激素CCK分泌的机制。体外试验结果表明，L-亮氨酸、L-异亮氨酸和支链氨基酸混合物可能通过空肠受体T1R1/T1R3诱导肠道饱感激素CCK的分泌，最后调控动物的采食。通过动物试验以验证在仔猪日粮中补充支链氨基酸（BCAA）是否可通过氨基酸感知受体调控仔猪的采食量。试验结果证实了BCAAs缺乏可以通过肠道受体T1R1/T1R3的感知，促进CCK的分泌，并激活GCN2-eIF2α信号通路，抑制仔猪的采食量，最终抑制仔猪的生长性能。