人核糖核酸酶A超家族抗微生物活性及其作用机制

人核糖核酸酶A(human RNase A)超家族包含13个具有不同生物活性的成员(RNase 1～RNase 13),其蛋白质结构除具有催化保守序列外，还具有显著多样性的序列，决定了人类核糖核酸酶A可发挥核糖核酸酶活性之外的生物学功能。人核糖核酸酶A超家族成员在多种免疫细胞例如嗜酸性粒细胞、中性粒细胞、单核细胞和巨噬细胞中表达，并可被分泌以发挥多种多样的生物学功能，包括抗微生物活性、促进宿主防御、参与血管生成及精子成熟等。其中，人核糖核酸酶A超家族部分成员，可通过水解病毒RNA、抑制病毒复制、破坏细菌细胞壁、促进微生物凝集、损伤寄生虫细胞膜和线粒体膜等直接作用，以及通过宿主天然免疫细胞介导的间接作用，发挥抗微生物及寄生虫活性，参与宿主防御。本文对人核糖核酸酶A的抗微生物(包括病毒、细菌、真菌)和抗寄生虫活性及其作用机制进行综述，并对人核糖核酸酶A作为抗微生物活性物质和天然免疫分子，用于治疗严重和耐药微生物感染的前景进行展望。     

核糖核酸酶基因超家族分子进化

核糖核酸酶基因(Ribonuclease A, RNASE A)超家族是进化生物学中研究新基因起源及新功能演变的重要模式系统之一。RNASE A超家族中的很多成员表现出基因复制的进化模式, 而且在适应性(正)选择的驱动下, 发生了功能分化。文章综述了RNASE A超家族成员在不同动物类群中进化模式的研究进展, 包括近年来越来越多在基因组水平上开展的相关研究, 显示该基因超家族可能具有比人们以往认识的更为复杂的基因进化模式。随着越来越多动物基因组数据的产生, 对更多动物代表类群进行RNASE A超家族研究, 将有望揭示新的进化机制和功能分化, 为系统认识动物适应进化的遗传机制奠定基础。     

微生物-肠-脑轴的研究进展

肠道微生物群能够调节宿主肠道稳态,同时参与调节宿主神经系统功能和行为。肠道菌群失调可能导致宿主神经系统功能障碍,从而引发神经退行性疾病。因此,研究微生物在肠?脑轴中发挥的作用及其机制,靶向调控肠道微生物菌群结构和功能,将为神经系统疾病的诊断与治疗提供新的手段。近年来,有关肠道微生物与机体神经系统间的互作研究受到了广泛关注,然而其具体的调控机制还未明晰。因此,本文综述了肠道微生物对宿主神经健康的调节作用,以及肠道微生物与宿主间的互作在调节神经功能、行为的潜力等研究进展,为更好地了解肠道微生物在调控宿主神经系统功能和行为的作用机制提供参考。     

黑色素与常见病原真菌致病性的关系

黑色素是一类广泛存在于微生物及动植物的生物大分子聚合体,被认为是多数病原真菌的毒力因子,具有抗氧化、吸收紫外线、抵御外界不良环境及宿主免疫等作用.本文就黑色素的生物学特点、作用及其与常见病原真菌致病性的关系等方面作一综述.     

食源性肠道疾病的微生态防治进展

肠道是一个复杂的微生态系统,其中存在着数以万亿计的微生物以及丰富的营养物质,微生物群依赖肠道营养物质生长并经长期的进化适应而特异性地存在于宿主肠道,通过其代谢活动及其产物维持宿主的微生态稳态。肠道微生物可抵抗外来病原微生物的入侵和定植,预防肠道疾病的发生,其作用机制包括竞争营养物质和生态位、产生拮抗细菌素、干扰群体感应和免疫介导等。饮食和药物等外界因素与遗传因素均可改变宿主的肠道环境,从而影响机体对入侵病原微生物的抵抗。本文就肠道食源性疾病的微生态防治研究进行综述,为预防和治疗肠道感染性疾病提供参考。     

丛枝菌根真菌对植物根腐病的抑制效应及其机制

根腐病是一类危害严重的土传病害,常常导致作物产量和品质降低。丛枝菌根(AM)真菌是一类重要的土壤微生物,通过与植物根系建立共生体而发挥重要的生理生态功能。研究表明,AM真菌通过调节宿主植物一系列生理生化响应,诱导植物增强根腐病抗性。当前,利用AM真菌开展根腐病等土传病害的生物防治是植物与微生物互作领域的研究热点。本文全面梳理了AM真菌对宿主植物根腐病病原物的抑制效应,系统总结了AM真菌改变宿主植物根系形态结构、改善植物营养水平、与病原物竞争生态位点、激活植物防御体系、调节根系分泌物等方面的研究结果,分析了AM真菌抑制根腐病危害的作用机制,展望了AM真菌抑制根腐病危害的潜在机制和AM真菌高效利用面临的现实问题,旨在为利用AM真菌开展植物根腐病的生物防治提供理论依据。     

大肠杆菌核糖核酸酶调控机制研究

核糖核酸酶参与体内多种RNA代谢反应,对细菌生理功能调节起重要作用。细菌需要进化出多种策略来对体内核糖核酸酶进行调节,以避免对RNA进行不必要地降解。目前对大肠杆菌核糖核酸酶调节机制的研究包括转录后调控、翻译后修饰、细胞定位及相关抑制剂等。本文系统性地阐述了大肠杆菌核糖核酸酶的分类、功能及其体内调控机制,总结了不同环境压力下大肠杆菌对自身核糖核酸酶进行适应性调节的响应机制及存在的问题。     

动物肠道菌群与宿主肠道免疫系统相互作用的研究进展

作为动物机体中最大的免疫器官之一,动物肠道是机体阻止外源病原体入侵的重要防线。动物肠道中定殖的微生物与宿主的营养物代谢,疾病和免疫系统发育等密切相关。该文主要综述了肠道微生物对于维持肠道屏障完整性的作用、诱导机体T、B淋巴细胞的发育和分化的分子机制及与一些代谢类疾病发生的关系等内容。尽管如此,肠道微生物与宿主免疫系统相互作用的机制还有待深入研究。随着免疫学、微生物学及分子生物学等学科的发展,对动物肠道菌群与宿主免疫系统互作机制的研究也得到快速发展,并为临床上预防和治疗人类疾病提供理论支撑。     

病毒感染对宿主肠道微生态的影响

肠道菌群对宿主免疫系统的建立和发育起着重要的作用,与宿主的生理、病理等密切相关,对机体抗病毒作用具有一定的影响。病毒感染影响宿主肠道微生物群落,进而影响宿主机体营养物质的代谢及细胞免疫功能。本研究着重综述病毒感染对宿主肠道微生态及免疫的影响。     

念珠菌适应宿主环境压力的共生机制研究进展

作为人体微生物菌群中真菌菌群的一个重要组成部分,念珠菌通常定植于人体的众多生态位,在免疫系统功能正常的健康人群中与宿主保持共生状态。为适应宿主体内复杂多变的环境,拮抗宿主免疫系统的攻击,以及应对其他微生物菌群的竞争等诸多生存压力,念珠菌进化出一系列极为有效的应对机制以维持其在宿主体内的共生。本文总结了念珠菌通过形态转换、环境适应、免疫调节以及与其他微生物菌群相互作用等策略应对宿主环境生存压力的分子机制,重点阐述了念珠菌、宿主免疫系统以及微生物菌群三者之间的相互作用和相互平衡对于念珠菌实现成功定植和共生的重要意义。     

The porcine <Emphasis Type="Italic">ANG</Emphasis>, <Emphasis Type="Italic">RNASE1</Emphasis> and <Emphasis Type="Italic">RNASE6</Emphasis> genes: molecular cloning,polymorphism detection and the association with haematological parameters

Angiogenin (ANG) [also known as ribonuclease, RNase A family, 5 (RNASE5)], ribonuclease, RNase A family, 1 (pancreatic) (RNASE1) and ribonuclease, RNase A family, k6 (RNASE6) are three members of the RNase A superfamily. It has been suggested that these three genes play important roles in host defense. In this study, we obtained the whole open reading frame (ORF) of each gene and found the deduced proteins contain some similar structures harboring a catalytic triad and an invariant “CKXXNTF” signature motif. One single nucleotide polymorphism (SNP) was detected in each gene (g. 149G>T polymorphism in the porcine ANG gene, which resulted in an amino acid change from glycine to valine, g. 296A>G polymorphism in the porcine RNASE1 gene and g. 389C>T polymorphism in the porcine RNASE6 gene). Association analyses revealed the significant associations (P < 0.05) between the porcine ANG g. 149G>T polymorphism and mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean platelet volume (MPV) and platelet-large cell ratio (P-LCR) measured on 0-day-old pigs and MCV measured at 32 days after birth. The porcine RNASE6 g. 389C>T polymorphism was significantly associated (P < 0.05) with MCV, MCH and neutrophil percentage (NEI %) measured on 0-day-old pigs, respectively. Our current findings, if confirmed by other studies, might shed some light on the roles of the investigated genes in host defense.     

RNase 7, a novel innate immune defense antimicrobial protein of healthy human skin

We analyzed healthy human skin for the presence of endogenous antimicrobial proteins that might explain the unusually high resistance of human skin against infections. A novel 14.5-kDa antimicrobial ribonuclease, termed RNase 7, was isolated from skin-derived stratum corneum. RNase 7 exhibited potent ribonuclease activity and thus may contribute to the well known ribonuclease activity of human skin. RNase 7 revealed broad spectrum antimicrobial activity against many pathogenic microorganisms and remarkably potent activity (lethal dose of 90% < 30 nm) against a vancomycin-resistant Enterococcus faecium. Molecular cloning from skin-derived primary keratinocytes and purification of RNase 7 from supernatants of cultured primary keratinocytes indicate that keratinocytes represent the major cellular source in skin and that RNase 7 is secreted. RNase 7 mRNA expression was detected in various epithelial tissues including skin, respiratory tract, genitourinary tract, and at a low level, in the gut. In addition to a constitutive expression, RNase 7 mRNA was induced in cultured primary keratinocytes by interleukin-1beta, interferon-gamma, and bacterial challenge. This is the first report demonstrating RNases as a novel class of epithelial inducible antimicrobial proteins, which may play an important role in the innate immune defense system of human epithelia.     

Insights into the role of ribonuclease 4 polymorphisms in amyotrophic lateral sclerosis

Mutations in certain genes of the Ribonuclease (RNASE) superfamily can cause amyotrophic lateral sclerosis (ALS) through altered RNA processing mechanisms. About 30 of these missense mutations in RNASE5/ANG gene have already been reported in ALS patients. In another gene of the ribonuclease superfamily, ribonuclease 4 (RNASE4), missense mutations and single nucleotide polymorphisms have been identified in patients suffering from ALS. However, their plausible molecular mechanisms of association with ALS are not known. Here, we present the molecular mechanisms of RNASE4 polymorphisms with ALS using all-atom molecular dynamics (MD) simulations followed by functional assay experiments. As most ALS causing mutations in RNASE superfamily proteins affect either the ribonucleolytic or nuclear translocation activity, we examined these functional properties of wild-type and known RNASE4 variants, R10W, A98V, E48D and V75I, using MD simulations. Our simulation predicted that these variants would retain nuclear translocation activity and that E48D would exhibit loss of ribonucleolytic activity, which was subsequently validated by ribonucleolytic assay. Our results give a mechanistic insight into the association of RNASE4 polymorphisms with ALS and show that E48D-RNASE4 would probably be deleterious and cause ALS in individuals harbouring this polymorphism.     

Cutting edge: the toll pathway is required for resistance to gram-positive bacterial infections in Drosophila

In Drosophila, the response against various microorganisms involves different recognition and signaling pathways, as well as distinct antimicrobial effectors. On the one hand, the immune deficiency pathway regulates the expression of antimicrobial peptides that are active against Gram-negative bacteria. On the other hand, the Toll pathway is involved in the defense against filamentous fungi and controls the expression of antifungal peptide genes. The gene coding for the only known peptide with high activity against Gram-positive bacteria, Defensin, is regulated by both pathways. So far, survival experiments to Gram-positive bacteria have been performed with Micrococcus luteus and have failed to reveal the involvement of one or the other pathway in host defense against such infections. In this study, we report that the Toll pathway, but not that of immune deficiency, is required for resistance to other Gram-positive bacteria and that this response does not involve Defensin.     

Fungal Chitin Induces Trained Immunity in Human Monocytes during Cross-talk of the Host with Saccharomyces cerevisiae

The immune system is essential to maintain the mutualistic homeostatic interaction between the host and its micro- and mycobiota. Living as a commensal, Saccharomyces cerevisiae could potentially shape the immune response in a significant way. We observed that S. cerevisiae cells induce trained immunity in monocytes in a strain-dependent manner through enhanced TNFα and IL-6 production upon secondary stimulation with TLR ligands, as well as bacterial and fungal commensals. Differential chitin content accounts for the differences in training properties observed among strains, driving induction of trained immunity by increasing cytokine production and direct antimicrobial activity both in vitro and in vivo. These chitin-induced protective properties are intimately associated with its internalization, identifying a critical role of phagosome acidification to facilitate microbial digestion. This study reveals how commensal and passenger microorganisms could be important in promoting health and preventing mucosal diseases by modulating host defense toward pathogens and thus influencing the host microbiota-immune system interactions.     

Allergic airway inflammation inhibits pulmonary antibacterial host defense

The innate immune system of the lung is a multicomponent host defense system and in addition has an instructing role in regulating the quality and quantity of the adaptive immune response. When the interaction between innate and adaptive immunity is disturbed, pathological conditions such as asthma can develop. It was the aim of the study to investigate the effect of the allergic inflammation of the lung on the innate host defense during bacterial infection. Human bronchial epithelial cells were preincubated with Th2 cytokines and infected with Pseudomonas aeruginosa. The effect of the Th2 cytokines on the mRNA levels of antimicrobial peptides and the antimicrobial activity of HBEC was determined. To investigate the influence of an allergic inflammation on pulmonary host defense in vivo, mice sensitized and challenged with OVA were infected with P. aeruginosa, and the number of viable bacteria in the lungs was determined together with markers of inflammation like cytokines and antimicrobial peptides. Exposure of airway epithelial cells to Th2 cytokines resulted in a significantly decreased antimicrobial activity of the cells and in suppressed mRNA levels of the antimicrobial peptide human beta-defensin 2. Furthermore, mice with allergic airway inflammation had significantly more viable bacteria in their lungs after infection. This was consistent with reduced levels of proinflammatory cytokines and of the antimicrobial peptide cathelin-related antimicrobial peptide. These results show that an allergic airway inflammation suppresses the innate antimicrobial host defense. The adaptive immune system modulates the functions of the pulmonary innate immune system.     

A Novel Cationic Ribonuclease with Antimicrobial Activity from Rana dybowskii

A novel ribonuclease (RNase) A superfamily gene (Rdronc) has been cloned from the frog Rana dybowskii. The deduced amino acid sequence shows that it belongs to the ribonuclease A superfamily, with the highest identity, 73%, to Rana pipiens onconase. Adaptive evolution analysis based on maximum likelihood models of codon substitution has been conducted on 10 members of the Rana RNases of subcluster B. Rapid adaptive evolution and multiple positive selection sites have been detected, which indicates that these genes may be evolving under positive selection pressure. Functional assay demonstrates that the recombinant Rdronc protein possesses antimicrobial activity against Gram-negative Escherichia coli and Pseudomonas aeruginosa and weaker antimicrobial activity against Gram-positive Staphylococcus aureus and yeast Candida albicans. Our findings support the hypothesis that ribonuclease A superfamily members may function in host defense of early-diversified vertebrates.     

Immune response of Drosophila melanogaster to infection with the flagellate parasite Crithidia spp

Insects are able to recognize invading microorganisms and to mount an immune response to bacterial and fungal infections. Recently, the fruitfly Drosophila melanogaster has emerged as a promising invertebrate model to investigate innate immunity because of its well-characterized genetics. Insects are also vectors of numerous parasites which can trigger an immune response. We have investigated the interaction of Drosophila melanogaster with the flagellate protozoan Crithidia spp. We show that a per os parasitic infection triggers the synthesis of several antimicrobial peptides. By reverse phase HPLC and mass spectrometry, peptides were shown to be present in the hemolymph and not in the gut tissue, suggesting the presence of immune messengers between the site of the infection, namely the gut, and the fat body, the main site of synthesis for antimicrobial peptides. Interestingly, we have identified one molecule which is specifically induced in the hemolymph after infection with Crithidia, but not with bacteria, suggesting that Drosophila can discriminate between pathogens. When flagellates were injected into the hemolymph, a low synthesis of antimicrobial peptides was observed together with phagocytosis of parasites by circulating hemocytes. The data presented here suggest that Drosophila-Crithidia spp. represents an interesting model to study host defense against protozoan parasites.     

Coral mucus-associated bacteria: a possible first line of defense

Interactions among microorganisms found in coral mucus can be either symbiotic or competitive. It has been hypothesized that microbial communities found on the surface of coral play a role in coral holobiont defense, possibly through production of antimicrobial substances. Selected microorganisms isolated from the mucus layer of a number of coral species were grown using agar-plating techniques. Screening for antimicrobial substances was performed using overlay and drop techniques, employing several indicator microorganisms. Between 25% and 70% of cultivable mucus-associated bacteria from scleractinian corals demonstrated bioactivity. Higher percentages of activity were evident in mucus-associated cultivable bacteria from massive and solitary corals, as compared with bacteria from branching or soft corals. Isolates related to the genera Vibrio and Pseudoalteromonas demonstrated high activity against both Gram-positive and Gram-negative bacteria. Gram-positive bacteria ( Bacillus, Planomicrobium ) demonstrated lower levels of activity, primarily against other Gram-positive bacteria. In some cases, inhibitory effects were confined to the cell fraction, suggesting the involvement of a cell-bound molecule, sensitive to temperature and most likely proteinaceous in nature. These results demonstrate the existence of microorganisms with antimicrobial activity on the coral surface, possibly acting as a first line of defense to protect the coral host against pathogens.