肠道蛋白质感应系统与肠道内分泌细胞调控研究进展

肠道上皮细胞的感应系统能够感应肠腔营养物质,影响肠道内分泌细胞(EECs)分泌脑肠肽,从而调节机体生理活动。机体对蛋白胨的感应主要通过小肽转运蛋白(Pep T1)和溶血磷脂酸受体5(LPAR5)发挥作用,对氨基酸的感应主要通过G蛋白偶联受体C家族6组a亚型受体(GPRC6A)、1型味觉受体1和3(T1R1/T1R3)以及雷帕霉素靶蛋白复合体1(m TORC1)信号通路发挥作用。文章对动物肠道蛋白质的感应机制及内分泌调控进行综述,旨在为同行提供参考。     

细菌群体感应的抑制及其对肠道健康的调控

细菌群体感应(QS)是细菌用来调节集体行为的细胞间通讯过程。QS依赖于细胞外信号分子动态调节多种代谢和生理活动。研究发现,细菌QS在调控肠道微生物及肠道对营养素的吸收中发挥着重要作用。肠道是营养素主要的吸收器官,也是微生物菌群的聚集地,肠道内的营养素和微生物直接或间接影响着动物机体的健康。有害细菌会通过QS分泌的毒力因子威胁宿主的健康,而益生菌会通过抑制有害细菌QS的发生而达到保护宿主的目的。因此,本文对细菌QS、肠道微生物、营养素三者之间的联系及抑制QS促进肠道健康的对策进行了综述。     

猪的肠道微生物与宿主营养代谢

肠道中栖息着数量庞大复杂多样的微生物菌群,肠道微生物在宿主健康中发挥着重要作用,既影响着饲料消化、营养物质吸收和能量供应,又调控着宿主正常生理功能及疾病的发生与发展.动物胃肠道不仅是消化器官,还是感应器官,肠道对营养物质的感应可以通过脑肠轴调节机体生理活动.肠道微生物还能代谢蛋白质产生宿主细胞不能合成的肽类物质,并通过小肠上皮的肽类转运系统影响机体代谢,因此可能存在微生物-肠道-大脑轴.肠道微生物还可以与机体形成宿主-微生物代谢轴,对动物机体营养物质代谢和免疫稳态起重要作用.饲粮对宿主代谢的改变,常伴随有肠道微生物区系的变化,肠道微生物的代谢可能通过微生物-肠道-大脑轴以及宿主-微生物代谢轴调节宿主很多生理过程,进而影响机体整体代谢.本文概述了猪肠道微生物区系与宿主肠道营养物质代谢的关系,以加深关于肠道微生物对机体代谢贡献的认识.     

肠道微生物-肠-脑轴与猪营养代谢

肠-脑轴是肠道与大脑通过神经和内分泌介导的一种双向应答系统,越来越多的研究表明,肠道菌群在此轴中发挥着关键作用。因此,微生物-肠-脑轴之间的双向交流关系逐渐成为动物营养代谢以至人类健康和疾病中热门的研究方向。肠道微生物群与宿主相互作用,从而控制体内平衡。本文从微生物与宿主肠道以及脑神经系统之间的相互关系入手,综述了微生物-肠-脑轴在猪营养代谢中的研究进展。     

动物消化道脂类物质感应机制及其EECs调控

肠道具有感应功能,能够感应肠腔内的营养物质,通过影响肠道内分泌细胞(EECs)的分泌功能调节营养代谢等生理活动。机体对脂类物质的感应主要通过与游离脂肪酸受体、G-蛋白偶联受体、胆固醇感应蛋白相互作用,影响EECs分泌功能,从而发挥调节作用。     

葡萄糖感应机制与肠道内分泌调控的研究进展

动物肠道具有感应肠腔葡萄糖的功能,机体通过葡萄糖激酶(GCK)、味觉受体、葡萄糖转运蛋白GLUT2、mTORC1信号通路及AMPK等机制感应葡萄糖,影响肠道内分泌细胞(enteroendocrine cells,EECs)分泌激素,形成复杂的内分泌调控网络,调节机体营养物质代谢和采食行为等重要生理活动。文章综述了动物葡萄糖的感应机制及其对肠道内分泌调控的影响。     

胰高血糖素样肽-2的研究进展

胰高血糖素样肽-2(glucagon-like peptide-2,GLP-2)是由肠道内分泌L细胞合成分泌的、胰高血糖素原经转录、翻译后加工处理的33个氨基酸多肽。文章介绍了GLP-2的合成、代谢与生理功能,GLP-2在动物肠道内可促进肠道营养吸收、抗炎、促进肠道损伤修复,在肠道外可以通过脑-肠轴调节食物摄取、血压、胰高血糖素的分泌和骨的重吸收;对GLP-2发挥生物活性的可能作用途径cAMP/蛋白激酶途径、PI-3K/Akt途径、激活ERK1和ERK2途径、刺激生长因子的释放等途径进行阐述;并对GLP-2和GLP-2类似物在人的疾病治疗和动物生产中的应用进行概述。     

短链脂肪酸介导的宿主肠道免疫调控机制

肠道是营养素、微生物群和宿主进行免疫反应的共享场所。肠道稳态失衡、免疫功能失调、环境因素等都可能引发疾病,肠道微生物群是控制机体健康肠道内环境平衡的一个重要因素。短链脂肪酸(SCFAs)主要由细菌发酵产生,是肠道微生物群及宿主肠上皮细胞(IECs)的重要能量来源,能够维持肠道酸碱平衡,抑制有害病原菌生长,调节宿主肠道免疫,降低炎症反应。SCFAs不仅在共生细菌聚居的肠道内起局部作用,而且还影响肠道免疫细胞,调节免疫反应。本文主要概述了SCFAs通过G蛋白偶联受体(GPCRs)激活途径、组蛋白脱乙酰化酶(HDAC)抑制作用改变代谢状态,并将代谢途径与表观遗传修饰联系起来引起宿主免疫应答,降低肠道炎症反应并增强肠道屏障功能。     

色氨酸对肠屏障免疫的调控作用研究进展

肠道是机体重要的代谢场所,也是动物体内最大的免疫器官。肠道屏障维持着肠道内环境的稳定,是动物肠道健康的保障。色氨酸在机体中通过3条途径被代谢,产生的犬尿氨酸、犬尿酸、5-羟色胺、吲哚等代谢产物可通过芳香烃受体途径、旁分泌等途径调控肠道屏障免疫功能的稳定,促进机体肠道健康。本文综述了色氨酸对动物肠屏障免疫的调控作用及其机制,为色氨酸在动物生产中的应用及相关疾病的治疗提供理论依据。     

微生物-肠-脑轴调控蛋鸡应激性异常行为的研究进展

现代养禽业采用的高密度笼养体系、分阶段饲养、断喙等管理措施可引起禽的过度应激,使它们出现啄羽、攻击或同类相食等异常行为。肠道菌群被视为一种跨物种的虚拟内分泌器官,通过肠-脑轴的双向通讯整合来自代谢、免疫、内分泌和神经通路发出的信号,并通过肠神经和迷走神经等外周神经系统、5-羟色胺和短链脂肪酸等微生物代谢产物以及免疫系统等途径调控动物应激反应及相应异常行为。本文系统地总结了蛋鸡饲养管理措施所造成的禽过度应激行为,并对微生物-肠-脑轴对鸡应激及其相关行为调控的可能机制进行论述,旨在为益生菌在蛋鸡饲养管理的推广应用提供参考依据。     

脱氧雪腐镰刀菌烯醇导致厌食和呕吐的机制研究进展

由镰刀菌产生的脱氧雪腐镰刀菌烯醇(DON)广泛存在于谷物及其加工产品中,对动物和人类健康有着潜在的危害。DON具有多方面的毒性作用,而厌食和呕吐是机体摄入DON后出现的最典型症状,厌食和呕吐的产生主要归因于DON对中枢神经系统和胃肠道食欲因子的影响。DON可直接作用于中枢神经系统的呕吐中枢产生呕吐反射,同时激活下丘脑神经元分泌食欲调节因子影响采食;DON可诱导肠内分泌细胞分泌肽YY、胆囊收缩素等食欲调节因子从而引发厌食;DON对中枢神经系统和胃肠道分泌的影响又可通过肠-脑轴产生关联;此外,细胞因子及肠道微生物也部分参与了反应的介导。本文综述了DON诱发机体出现厌食和呕吐的可能机制,以期为找到相应解决措施提供理论指导。     

浅析反刍动物胃肠道微生物通过肠道－脑轴对宿主的影响

反刍动物胃肠道中存在着众多微生物,如细菌、真菌、原虫和古细菌等。胃肠道微生物对于动物的能量代谢发挥着重要作用,同时对于动物的中枢神经正常功能的发挥也扮演着重要角色。肠道微生物可以与肠道细胞直接接触,不仅产生激活内源性中枢神经系统信号传导机制的代谢物,还可以独立地产生或促成许多神经活性分子的产生。微生物代谢产物和神经活性分子通过神经信号通路、胃肠道内分泌信号通路、免疫系统等关键途径共同形成一个复杂的反射网络,即胃肠道微生物与代谢产物通过传入神经元将信号传导至中枢神经系统。胃肠道微生物与宿主之间通过主要的信号通路相互作用,影响机体胃肠道屏障、营养代谢、免疫应答等生理机能和摄食行为。作者主要从反刍动物胃肠道微生物的种类、微生物通过肠道-脑轴的"自下而上"的传导途径、微生物及其代谢产物通过肠道-脑轴对宿主疾病和行为起到的作用、胃肠道微生物-肠道-脑轴可能的影响因素进行浅析,并对反刍动物胃肠道微生物-肠道-脑轴的研究进行了展望。     

Glucose,epithelium, and enteric nervous system: dialogue in the dark

The gastrointestinal epithelium is in close contact with the various components of the chymus, including nutrients, bacteria and toxins. The epithelial barrier has to decide which components are effectively absorbed and which components are extruded. In the small intestine, a nutrient like glucose is mainly absorbed by the sodium linked glucose cotransporter 1 (SGLT1) and the glucose transporter 2 (GLUT2). The expression and activity of both transport proteins is directly linked to the amount of intraluminal glucose. Besides the direct interaction between glucose and the enterocytes, glucose also stimulates different sensory mechanisms within the intestinal wall. The most important types of cells involved in the sensing of intraluminal contents are enteroendocrine cells and neurones of the enteric nervous system. Regarding glucosensing, a distinct type of enteroendocrine cells, the enterochromaffine (EC) cells are involved. Excitation of EC cells by intraluminal glucose results in the release of serotonin (5‐HT), which modulates epithelial functions and activates enteric secretomotorneurones. Enteric neurones are not only activated by 5‐HT, but also directly by glucose. The activation of different cell types and the subsequent crosstalk between these cells may trigger appropriate absorptive and secretory processes within the intestine.     

Glucagon-like peptide 2 function in domestic animals

Glucagon-like peptide 2 (GLP-2) is a member of family of peptides derived from the proglucagon gene expressed in the intestines, pancreas and brain. Tissue-specific posttranslational processing of proglucagon leads to GLP-2 and GLP-1 secretion from the intestine and glucagon secretion from the pancreas. GLP-2 and GLP-1 are co-secreted from the enteroendocrine L-cells located in distal intestine in response to enteral nutrient ingestion, especially carbohydrate and fat. GLP-2 secretion is mediated by direct nutrient stimulation of the L-cells and indirect action from enteroendocrine and neural inputs, including GIP, gastrin-releasing peptide (GRP) and the vagus nerve. GLP-2 is secreted as a 33-amino acid peptide and is rapidly cleaved by dipeptidylpeptidase IV (DPP-IV) to a truncated peptide which acts as a weak agonist with competitive antagonistic properties. GLP-2 acts to enhance nutrient absorption by inhibiting gastric motility and secretion and stimulating nutrient transport. GLP-2 also suppresses food intake when infused centrally. The trophic actions of GLP-2 are specific for the intestine and occur via stimulation of crypt cell proliferation and suppression of apoptosis in mucosal epithelial cells. GLP-2 reduces gut permeability, bacterial translocation and proinflammatory cytokine expression under conditions of intestinal inflammation and injury. The effects of GLP-2 are mediated by a G-protein-linked receptor that is localized to the intestinal mucosa and hypothalamus. The intestinal localization of the GLP-2R to neural and endocrine cells, but not enterocytes, suggests that its actions are mediated indirectly via a secondary signaling mechanism. The implications of GLP-2 in domestic animal production are largely unexplored. However, GLP-2 may have therapeutic application in treatment of gastrointestinal injury and diarrheal diseases that occur in developing neonatal and weanling animals.     

The control of adenohypophysial hormone secretion by amino acids and peptides in swine

Several different amino acids and peptides control secretion of adenohypophysial hormones and this control may be indirect, via the modulation of hypothalamic hormone secretion. Indeed, classical hypothalamic hormones (e.g., gonadotropin-releasing hormone [GnRH], growth hormone-releasing hormone [GHRH], somatostatin, etc.) may be released into the hypothalamo-hypophysial portal vasculature, travel to the adenohypophysis and there stimulate or inhibit secretion of hormones. Alternatively, some amino acids and peptides exert direct stimulatory or inhibitory effects on the adenohypophysis, thereby impacting hormone secretion. In swine, the most extensively studied modulators of adenohypophysial hormone secretion are the excitatory amino acids (ExAA), namely glutamate and aspartate, and the endogenous opioid peptides (EOP). In general, excitatory amino acids stimulate release of luteinizing hormone (LH), follicle-stimulating hormone (FSH), growth hormone (GH), and prolactin (PRL). Secretion of adenohypophysial hormones induced by ExAA is primarily, but perhaps not exclusively, a consequence of action at the central nervous system. By acting primarily at the level of the central nervous system, EOP inhibit LH secretion, stimulate GH release and depending on the animal model studied, exert either stimulatory or inhibitory influences on PRL secretion. However, the EOP also inhibited LH release by direct action on the adenohypophysis. More recently, peptides such as neuropeptide-Y (NPY), orexin-B, ghrelin, galanin, and substance P have been evaluated for possible roles in controlling adenohypophysial hormone secretion in swine. For example, NPY, orexin-B, and ghrelin increased basal GH secretion and modulated the GH response to GHRH, at least in part, by direct action on the adenohypophysis. Secretion of LH was stimulated by orexin-B, galanin, and substance P from porcine pituitary cells in vitro. Because the ExAA and various peptides modulate secretion of adenohypophysial hormones, these compounds may play an important role in regulating swine growth and reproduction.     

Growth and Development Symposium: Endotoxin, inflammation, and intestinal function in livestock

Endotoxin, also referred to as lipopolysaccharide (LPS), can stimulate localized or systemic inflammation via the activation of pattern recognition receptors. Additionally, endotoxin and inflammation can regulate intestinal epithelial function by altering integrity, nutrient transport, and utilization. The gastrointestinal tract is a large reservoir of both gram-positive and gram-negative bacteria, of which the gram-negative bacteria serve as a source of endotoxin. Luminal endotoxin can enter circulation via two routes: 1) nonspecific paracellular transport through epithelial cell tight junctions, and 2) transcellular transport through lipid raft membrane domains involving receptor-mediated endocytosis. Paracellular transport of endotoxin occurs through dissociation of tight junction protein complexes resulting in reduced intestinal barrier integrity, which can be a result of enteric disease, inflammation, or environmental and metabolic stress. Transcellular transport, via specialized membrane regions rich in glycolipids, sphingolipids, cholesterol, and saturated fatty acids, is a result of raft recruitment of endotoxin-related signaling proteins leading to endotoxin signaling and endocytosis. Both transport routes and sensitivity to endotoxin may be altered by diet and environmental and metabolic stresses. Intestinal-derived endotoxin and inflammation result in suppressed appetite, activation of the immune system, and partitioning of energy and nutrients away from growth toward supporting the immune system requirements. In livestock, this leads to the suppression of growth, particularly suppression of lean tissue accretion. In this paper, we summarize the evidence that intestinal transport of endotoxin and the subsequent inflammation leads to decrease in the production performance of agricultural animals and we present an overview of endotoxin detoxification mechanisms in livestock.     

天然草地牧草营养品质的高光谱遥感研究进展

天然草地牧草营养品质的优劣不仅影响家畜的生长发育,同时也影响畜产品的品质,对草牧业的发展具有至关重要的意义。高光谱遥感技术的飞速发展使深入研究天然草地牧草品质的动态变化成为可能。本研究综述了目前可利用的高光谱遥感数据以及天然草地牧草营养品质遥感反演的主要成果、常用方法和最新研究动态,分析了我国在天然草地牧草营养品质监测与评价方面尚存在数据获取困难、相关研究缺乏、软硬件性能不足等问题;在多种观测平台及相关技术不断革新背景下,探索星载、机载和地面高光谱数据的有机结合,强化高光谱遥感仪器性能,提高关键营养成分的反演精度是未来研究的重点。     

Effects of Amino Acids on Inflammatory Bowel Disease and Its Signaling Pathways

The intestine is the primary organ responsible for digestion and absorption of nutrients and is frequently subjected to external environmental stimulations leading to the development of inflammatory bowel disease (IBD), which can cause serious harm to intestinal health in animals. Dietary amino acids play important roles in promoting intestinal development and maintaining intestinal health and exert diverse effects through multiple signaling pathways on the prevention and treatment of IBD, including affecting the physiological activities of intestinal epithelial cells, improving intestinal barrier function, reducing intestinal oxidative damage, regulating the production of inflammatory cytokines, and promoting the expression of endogenous antimicrobial peptides, and involved in main signaling pathways including AMP-activated kinase (AMPK), mammalian target of rapamycin (mTOR), mitogen-activated protein kinase (MAPK), Toll-like receptors (TLRs), nucleotide binding oligomerization domain (NOD)/nuclear factor kappa-B (NF-κB). In this review, basic characteristics of IBD, effects and involved signaling pathways of the amino acids on IBD, and effects and applications of amino acids in maintaining intestinal health in livestock and poultry production were reviewed, so as to provide effective clues and strategies for dietary nutrients in the prevention and treatment of IBD.     

氨基酸在炎症性肠病中的作用及其信号通路

肠道是营养物质消化、吸收的主要器官，但易受外界环境刺激，导致炎症性肠病（inflammatory bowel disease，IBD）的发生，严重危害动物肠道健康。膳食氨基酸在促进肠道发育、维持肠道健康方面发挥重要作用，其主要通过调控腺苷酸活化蛋白激酶（AMP-activated kinase，AMPK）、雷帕霉素靶蛋白（mammalian target of rapamycin，mTOR）、丝裂原活化蛋白激酶（mitogen-activated protein kinase，MAPK）、Toll样受体（Toll-like receptors，TLRs）、核苷酸结合寡聚化结构域（nucleotide binding oligomerization domain，NOD）/核因子-κB（nuclear factor kappa-B，NF-κB）等信号通路影响肠上皮细胞生理活动、改善肠道屏障功能、减轻肠道氧化损伤、调节炎性因子的产生、提高内源抗菌肽表达，进而预防和治疗IBD。本文综述了IBD的基本特征、氨基酸在IBD中的作用及其信号通路，以及氨基酸在畜禽生长中维持肠道健康的作用与应用，为膳食营养素防治IBD提供有效线索与策略。     

日粮膳食纤维与猪肠道健康调控

日粮纤维目前基本认定为第七大营养素,在猪体内中虽然消化率不高,甚至会影响其他营养素消化吸收,但能发酵产生短链脂肪酸,具有改善肠道微生物环境、调控母猪生理行为、调控猪肠道健康等作用。文章综述了日粮纤维在猪体内的营养特性和对肠道的调控作用,为日粮纤维在猪生产中的应用提供参考。