幼龄反刍动物瘤胃上皮细胞β-羟基丁酸代谢与调控机制

β-羟基丁酸(β-hydroxybutyric acid,BHBA)是酮体的主要成分之一,在反刍动物瘤胃中由微生物发酵产生的丁酸在瘤胃上皮细胞中氧化生成,BHBA对反刍动物瘤胃上皮细胞的代谢与增殖具有重要调控作用。近年来,有关BHBA研究多集中在肝脏生酮、奶牛酮病及泌乳等方面,关于BHBA与幼龄反刍动物瘤胃上皮细胞生长发育之间的关系及内在机制研究很少。本文重点针对BHBA在瘤胃上皮的生成、转运,以及BHBA作为信号分子调控瘤胃上皮细胞代谢与增殖的分子机制进行综述,这对于丰富瘤胃发育及调控理论与幼龄反刍动物培育营养策略具有重要意义。     

幼龄反刍动物瘤胃上皮细胞β-羟基丁酸代谢与调控机制

β-羟基丁酸（β-hydroxybutyric acid,BHBA）是酮体的主要成分之一,在反刍动物瘤胃中由微生物发酵产生的丁酸在瘤胃上皮细胞中氧化生成,BHBA对反刍动物瘤胃上皮细胞的代谢与增殖具有重要调控作用。近年来,有关BHBA研究多集中在肝脏生酮、奶牛酮病及泌乳等方面,关于BHBA与幼龄反刍动物瘤胃上皮细胞生长发育之间的关系及内在机制研究很少。本文重点针对BHBA在瘤胃上皮的生成、转运,以及BHBA作为信号分子调控瘤胃上皮细胞代谢与增殖的分子机制进行综述,这对于丰富瘤胃发育及调控理论与幼龄反刍动物培育营养策略具有重要意义。     

挥发性脂肪酸在反刍动物瘤胃上皮吸收转运及调节作用

挥发性脂肪酸(VFA)作为瘤胃发酵的重要产物,在瘤胃上皮通过扩散、阴离子交换、VFA硝酸根离子以及电介导途径吸收转运,为反刍动物提供能量;同时作为化学刺激因素,具有促进细胞分化与增殖,增加瘤胃乳头表面积以及调节酶与激素及编码其蛋白的基因表达的作用。本文结合前人研究结果,总结VFA在瘤胃上皮的吸收转运途径,并对瘤胃上皮组织形态结构受VFA刺激发生的变化和瘤胃上皮细胞发育的相关基因及编码蛋白的调控作用进行综述,旨在为进一步研究瘤胃的营养调控提供理论基础。     

过氧化物酶体增殖物激活受体调控幼龄反刍动物瘤胃的生酮作用及其机制

发育良好的瘤胃对于幼龄反刍动物至关重要,不仅关乎其自身的健康,也与其成年后生产性能的发挥息息相关。对于刚出生的幼龄反刍动物,其瘤胃不具有生酮功能,随日龄的增加,瘤胃形态与功能逐渐发育成熟,逐渐具备了该功能。生酮作用是瘤胃发育成熟的关键因素,β-羟丁酸(BHBA)被认为是瘤胃发育成熟的标志。近十几年来,许多学者针对影响瘤胃生酮作用的因素进行了大量研究,发现过氧化物酶体增殖物激活受体(PPARs)对于瘤胃生酮和上皮细胞增殖十分重要,转录因子PPARs可以影响到生酮作用关键酶3-羟基-3-甲基戊二酰辅酶A合成酶2(HMGCS2)的表达。但目前对于PPARs调控瘤胃生酮作用分子机制的了解仍然十分有限,因此本文针对PPARs调控幼龄反刍动物瘤胃发育的研究进展进行了综述。     

反刍动物体内尿素循环及其转运蛋白的分子调控机制研究进展

虽然在哺乳动物体内都存在尿素循环利用机制,但是反刍动物由于瘤胃的存在而使得尿素循环在维系机体氮平衡和提高氮素利用效率等方面发挥着更加重要的生物学意义。通过瘤胃壁扩散或转运,血液中的尿素可进入胃肠道,在脲酶的作用下转化为氨态氮,从而为瘤胃微生物蛋白合成提供氮源。研究表明,尿素在瘤胃上皮的自由扩散速度较慢,而尿素转运蛋白可以介导尿素分子高效地进行跨膜转运,其也被认为是反刍动物尿素循环最重要的调控因子。然而,相关报道已经证实,尿素转运蛋白的表达和功能发挥受到日粮营养水平与结构组成、瘤胃内环境、动物年龄等因素的影响。本文以尿素循环为出发点,重点阐述了反刍动物体内尿素循环的特点、影响因素以及尿素转运蛋白的表达特征及其分子调控过程,以期从分子生物学角度解析反刍动物尿素循环的作用机制,从而为生产实践中动物氮素的精准营养提供理论依据和技术支撑。     

亚急性瘤胃酸中毒对反刍动物瘤胃生理功能及物质吸收转运的影响

畜牧业集约化养殖越来越普遍。为提高反刍动物生产性能,饲喂大量能量饲料,进而引发亚急性瘤胃酸中毒(SARA),导致动物采食量下降、畜产品产出降低以及动物发生炎症反应。近年研究表明,SARA会改变瘤胃生理状态,而瘤胃健康对反刍动物饲养至关重要。本文综述了反刍动物SARA状态下瘤胃生理生化过程变化,结合瘤胃发酵模式变化和瘤胃微生物的改变,重点阐述了SARA引起的瘤胃上皮细胞形态结构变化、屏障功能改变、瘤胃上皮细胞中物质转运及相关载体表达及其引发的瘤胃上皮细胞炎症通路,为更好指导反刍动物饲养及为瘤胃营养生理生化研究提供参考。     

反刍动物瘤胃物质转运系统及其调控的研究

小肽、挥发性脂肪酸（VFA）和葡萄糖是反刍动物体内重要的营养物质．对反刍动物的生产性能和产品质量影响重大。研究发现小肽的主要转运载体有两个．PepT1和PepT2：葡萄糖的转运载体分两大类共16个载体；VFA的瘤胃转运主要受PH、日粮精粗比、分子大小及血液流量的调控。本文对此3种重要营养物质在反刍动物瘤胃内的转运机制和调控因子进行综述．并展望以后的研究动向.     

Research Progress of Effects of Maternal Supplementing Rumen-Protected Methionine during Transition Period on Growth and Development of Young Ruminant and Regulatory Mechanism北大核心CSCD

围产期是反刍动物重要的生理阶段,研究发现反刍动物围产期补饲过瘤胃蛋氨酸(RPM)不仅对母体具有显著的营养调控作用,对幼畜的生长发育、机体健康和产品品质等也有重要影响。因此,本文从RPM的营养调控功能,围产期补饲RPM调控母体、胎儿后期及幼龄阶段的影响及调控机制进行综述,以期进一步为反刍动物围产期营养调控研究提供理论依据。     

多胺跨膜物质转运的机制

多胺具有调控细胞增殖、分化和凋亡的功能,可参与动物繁殖、胚胎发育以及癌症发生发展等多种生物学过程。在动物机体中,多胺稳态是通过多胺跨膜物质转运和多胺代谢途径共同维持的。溶质转运蛋白(SLC)基因家族中的SLC3A2、SLC7A1、SLC12A8、SLC22A16、SLC22A 1、SLC22A 2、SLC22A 3基因及其编码的蛋白质可参与多胺的跨膜物质转运;多胺代谢关键调控基因鸟氨酸脱羧酶(ODC)、鸟氨酸脱羧酶抗酶(OAZ)和鸟氨酸脱羧酶抗酶抑制剂(AZIN)对多胺跨膜物质转运也具有重要的调控功能;此外,金属阳离子、细胞膜跨膜电位和p H等内环境因素也可参与多胺转运的调节。因此,本文就多胺转运蛋白、多胺代谢相关基因和蛋白质以及内环境因素调控多胺跨膜物质转运的分子调控机制作一综述,以期为阐明多胺转运调控机制的研究奠定理论基础。     

反刍动物瘤胃发育规律及其调控机制研究进展

瘤胃是反刍动物至关重要的消化吸收器官,部分降解的营养物质可直接通过瘤胃上皮被机体吸收和利用。因此,瘤胃的发育程度与反刍动物的生产性能密切相关,而瘤胃发育充分且功能健全是反刍动物最佳生产性能得以发挥的前提条件。然而,幼龄反刍动物瘤胃的生理结构及其功能均发育不完善,需在固体饲料、断母乳等外界刺激下完成经由非反刍阶段向反刍阶段转变的复杂过程,进而才可发挥其重要功能。目前,如何掌握并遵循瘤胃的发育规律,在保证瘤胃充分发育且功能完善的情况下,对幼龄反刍动物实施早期断奶技术,已成为现代反刍动物养殖生产中亟需解决的问题之一。作者就反刍动物瘤胃发育进程中瘤胃微生物菌群的时空演变、瘤胃组织形态学发育和代谢改变及瘤胃发育调控机制进行综述,由生理结构至功能逐层对反刍动物瘤胃的发育规律进行全面总结,阐明影响反刍动物瘤胃发育的相关因素及其可能的调控机制。本文旨在进一步丰富与瘤胃发育相关的理论基础,以期为利用瘤胃发育规律开发促进反刍动物瘤胃发育的营养调控策略提供科学支撑,为挖掘幼龄反刍动物的生产潜力提供新思路。     

日粮添加尿素对瘤胃上皮细胞增殖、凋亡以及吸收转运能力的影响

本研究探讨了在日粮中添加尿素替代部分豆粕对山羊瘤胃发酵、上皮细胞增殖、凋亡和吸收转运能力的影响。将18 只波杂山羊随机分为3 组（n=6）,分别饲喂3 种日粮：LC组（纯粗料）、MC组（30%精料）以及Urea组（1%DM缓释尿素替代部分豆粕+30%精料）。饲喂Urea组和MC组的山羊瘤胃中短链脂肪酸（SCFA）浓度、pH值均显著高于LC组,而该两组之间无显著差异;但Urea组在MC组的基础上进一步显著提高了瘤胃NH₃和血浆尿素氮（BUN）浓度。因此日粮添加尿素对于瘤胃上皮中受瘤胃SCFA浓度、pH值调节的上皮生长、细胞周期、增殖凋亡相关基因和SCFA转运载体mRNA表达的影响与MC组相似,但对受瘤胃NH₃调节的尿素转运、细胞内pH（pHi）调节相关蛋白mRNA表达则有显著的抑制效果,即显著高于LC组,但低于MC组。     

浏阳黑山羊瘤胃上皮细胞周期分布、增殖和凋亡特点

本研究旨在建立浏阳黑山羊瘤胃上皮细胞的体外培养模型,并对其周期分布、增殖和凋亡特点进行研究。试验采集60日龄浏阳黑山羊的瘤胃上皮组织,应用0.25%胰蛋白酶+0.02%乙二胺四乙酸(EDTA)消化法对山羊瘤胃上皮组织进行消化,得到单个的山羊瘤胃上皮原代细胞进行体外培养。通过倒置显微镜对原代和传代培养阶段细胞形态进行观察,采用细胞计数法检测细胞的生长活性,应用细胞免疫组化学方法对传代细胞进行鉴定,并用流式细胞术检测山羊瘤胃上皮传代细胞周期分布情况和凋亡比率。结果显示:1)经0.25%胰蛋白酶+0.02%EDTA消化获得的山羊瘤胃上皮原代细胞,培养1 d开始贴壁生长,2 d开始生长较快(对数期),呈典型的"波峰"状生长,3~4 d生长最为迅速,7 d生长速度平稳(平台期)。2)经细胞免疫组化学方法的鉴定,细胞胞浆为黄褐色,即细胞角蛋白19呈阳性表达。3)膜联蛋白-V/碘化丙啶联合染色显示,随着培养时间的延长,细胞凋亡比率显著增加(P0.01)。结果表明,通过0.25%胰蛋白酶+0.02%EDTA的消化方法成功得到了浏阳黑山羊瘤胃上皮细胞,可为今后研究反刍动物瘤胃相关机制与功能提供模型。     

瘤胃微生物与宿主的互作及其对瘤胃上皮发育的影响

瘤胃上皮在挥发性脂肪酸的吸收和代谢中发挥着重要作用，但瘤胃上皮发育的机制尚不清楚。近年来研究报道，瘤胃微生物与宿主存在互作关系，瘤胃微生物可以通过与宿主的相互作用，在瘤胃上皮发育和代谢中发挥作用。然而，瘤胃微生物与宿主相互作用的调节机制在很大程度上是未知的。因此，本文总结了瘤胃微生物与宿主互作以及其促进瘤胃上皮发育的最新研究成果，以期从瘤胃微生物与宿主互作角度，分析瘤胃上皮发育机制，为进一步了解瘤胃上皮发育过程中瘤胃微生物与宿主之间的关系研究提供理论依据。     

Cell deletion as a factor in the regulation of rumen epithelial populations

When the feed of sheep was changed from hay to barley, there were hyperplastic changes in the ruminal epithelium. These were characterised by an increase in the rate of mitosis and by a very low incidence of single cell death (apoptosis). A subsequent abrupt change of diet from barley to hay resulted in atrophy of the ruminal epithelium. Atrophy was associated with a fall in the rate of mitosis, and a rise in the incidence of apoptosis which together caused regression of epithelial pegs. It is suggested that apoptosis may play an important role in the regulation of rumen epithelial cell populations and in the control of epithelial cell kinetics.     

Ruminant Nutrition Symposium: Role of fermentation acid absorption in the regulation of ruminal pH

Highly fermentable diets are rapidly converted to organic acids [i.e., short-chain fatty acids (SCFA) and lactic acid] within the rumen. The resulting release of protons can constitute a challenge to the ruminal ecosystem and animal health. Health disturbances, resulting from acidogenic diets, are classified as subacute and acute acidosis based on the degree of ruminal pH depression. Although increased acid production is a nutritionally desired effect of increased concentrate feeding, the accumulation of protons in the rumen is not. Consequently, mechanisms of proton removal and their quantitative importance are of major interest. Saliva buffers (i.e., bicarbonate, phosphate) have long been identified as important mechanisms for ruminal proton removal. An even larger proportion of protons appears to be removed from the rumen by SCFA absorption across the ruminal epithelium, making efficiency of SCFA absorption a key determinant for the individual susceptibility to subacute ruminal acidosis. Proceeding initially from a model of exclusively diffusional absorption of fermentation acids, several protein-dependent mechanisms have been discovered over the last 2 decades. Although the molecular identity of these proteins is mostly uncertain, apical acetate absorption is mediated, to a major degree, via acetate-bicarbonate exchange in addition to another nitrate-sensitive, bicarbonate-independent transport mechanism and lipophilic diffusion. Propionate and butyrate also show partially bicarbonate-dependent transport modes. Basolateral efflux of SCFA and their metabolites has to be mediated primarily by proteins and probably involves the monocarboxylate transporter (MCT1) and anion channels. Although the ruminal epithelium removes a large fraction of protons from the rumen, it also recycles protons to the rumen via apical sodium-proton exchanger, NHE. The latter is stimulated by ruminal SCFA absorption and salivary Na(+) secretion and protects epithelial integrity. Finally, SCFA absorption also accelerates urea transport into the rumen, which via ammonium recycling, may remove protons from rumen to the blood. Ammonium absorption into the blood is also stimulated by luminal SCFA. It is suggested that the interacting transport processes for SCFA, urea, and ammonia represent evolutionary adaptations of ruminants to actively coordinate energy fermentation, protein assimilation, and pH regulation in the rumen.     

Ammonia and urea transport across the rumen epithelium: a review

The transport of nitrogen across the rumen epithelium is characterized by absorption of ammonia from the rumen and by an influx of urea into the rumen. The transport rates of both compounds are large and exhibit wide variation. The transport of ammonia occurs in two forms: in the lipophilic form as NH3, the magnitude of which is linearly related to the pH in the ruminal fluid at pH values above 7, while at a physiological pH of 6.5 or lower, ammonia is predominantly absorbed as NH4+ via putative potassium channels in the apical membrane. The uptake of NH4+ depends on the potential difference of the apical membrane, Pda, and shows competition with K uptake. The pathway for basolateral exit of NH4+ is unknown. Hence, the relative transport rates of NH3 or NH4+ are determined by the ruminal pH according to the Henderson-Hasselbalch equation. Transport of ammonia interacts with the transport of Na and Mg mainly via changes of the intracellular pH. Urea recycling into the rumen has been known for many years and the transport across the rumen epithelium is mediated via urea transporters in the luminal and basolateral membrane of the epithelium. Transport of urea occurs by simple diffusion, but is highly variable. A significant increase of urea influx is caused by the fermentation products CO2 and short-chain fatty acids. Conversely, there is some evidence of inhibition of urea influx by ruminal ammonia. The underlying mechanisms of this modulation of urea transport are unknown, but of considerable nutritional importance, and future research should be directed to this aspect of ruminal transport.     

Characterization of bovine ruminal epithelial bacterial communities using 16S rRNA sequencing, PCR-DGGE, and qRT-PCR analysis

Currently, knowledge regarding the ecology and function of bacteria attached to the epithelial tissue of the rumen wall is limited. In this study, the diversity of the bacterial community attached to the rumen epithelial tissue was compared to the rumen content bacterial community using 16S rRNA gene sequencing, PCR-DGGE, and qRT-PCR analysis. Sequence analysis of 2785 randomly selected clones from six 16S rDNA (～1.4kb) libraries showed that the community structures of three rumen content libraries clustered together and were separated from the rumen tissue libraries. The diversity index of each library revealed that ruminal content bacterial communities (4.12/4.42/4.88) were higher than ruminal tissue communities (2.90/2.73/3.23), based on 97% similarity. The phylum Firmicutes was predominant in the ruminal tissue communities, while the phylum Bacteroidetes was predominant in the ruminal content communities. The phyla Fibrobacteres, Planctomycetes, and Verrucomicrobia were only detected in the ruminal content communities. PCR-DGGE analysis of the bacterial profiles of the rumen content and ruminal epithelial tissue samples from 22 steers further confirmed that there is a distinct bacterial community that inhibits the rumen epithelium. The distinctive epimural bacterial communities suggest that Firmicutes, together with other epithelial-specific species, may have additional functions other than food digestion.     

离体瘤胃上皮细胞在瘤胃代谢中的研究进展

反刍动物瘤胃上皮由基底层、棘层、粒层和角质层等四层组成,在瘤胃发酵终产物的代谢中具有重要作用,但其形态学受动物本身及饲喂制度等诸多因素的影响,造成细胞代谢活性上的差异。现在,应用离体瘤胃上皮细胞,使研究其组织形态学和代谢成为可能。     

Urea transport and hydrolysis in the rumen: A review

Inefficient dietary nitrogen (N) conversion to microbial proteins, and the subsequent use by ruminants, is a major research focus across different fields. Excess bacterial ammonia (NH₃) produced due to degradation or hydrolyses of N containing compounds, such as urea, leads to an inefficiency in a host's ability to utilize nitrogen. Urea is a non-protein N containing compound used by ruminants as an ammonia source, obtained from feed and endogenous sources. It is hydrolyzed by ureases from rumen bacteria to produce NH₃ which is used for microbial protein synthesis. However, lack of information exists regarding urea hydrolysis in ruminal bacteria, and how urea gets to hydrolysis sites. Therefore, this review describes research on sites of urea hydrolysis, urea transport routes towards these sites, the role and structure of urea transporters in rumen epithelium and bacteria, the composition of ruminal ureolytic bacteria, mechanisms behind urea hydrolysis by bacterial ureases, and factors influencing urea hydrolysis. This review explores the current knowledge on the structure and physiological role of urea transport and ureolytic bacteria, for the regulation of urea hydrolysis and recycling in ruminants. Lastly, underlying mechanisms of urea transportation in rumen bacteria and their physiological importance are currently unknown, and therefore future research should be directed to this subject.