The Effects of Reactive Oxygen and Nitrogen on Gene Regulation in B. Burgdorferi

活性氧和氮对伯氏疏螺旋体基因调控的影响

• 批准号: 8156936
• 负责人: Frank Gherardini
• 金额: $ 51.97万
• 依托单位: NATIONAL INSTITUTE OF ALLERGY AND INFECTIOUS DISEASES
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/8156936
• 关键词: Affect; Bacteria sigma factor KatF protein; Borrelia burgdorferi; DNA; DNA Damage; Data; Electrons; Environment; Enzymes; Escherichia coli; Eukaryotic Cell; Fatty Acids; Free Radicals; Gene Expression; Gene Expression Regulation; Homologous Gene; Nitrogen; O-(biotinylcarbazoylmethyl)hydroxylamine; Oxygen; Peroxonitrite; Process; Proliferating; Reactive Oxygen Species; Transcription Coactivator; Virulence Factors; biological adaptation to stress; defense response; in vivo; transmission process

Borrelia burgdorferi, the causative agent of Lyme disease, survives and proliferates in both an arthropod vector and various mammalian hosts. During its transmission/infective cycle, B. burgdorferi encounters environmental challenges specific to those hosts. One such challenge comes from reactive oxygen species (ROS) e.g. superoxide radicals (O2.-), hydrogen peroxide (H2O2) and hydroxyl radicals (OH.) and reactive nitrogen species (RNS) e.g. nitric oxide (NO), N2O3 and peroxynitrite. There are two stages in the infective cycle when B. burgdorferi is exposed to ROS/RNS. The first is during the initial stages of infection of the mammalian host when cells of the immune system attempt to limit and eliminate B. burgdorferi using several mechanisms including the production of ROS and RNS. Surprisingly, the second ROS/RNS challenge occurs as the bacteria migrate through the salivary glands during transmission. Our lab, in collaboration with Dr. Tom Schwan, has demonstrated that the salivary glands of Ixodes scapularis contain significant levels of ROS. Therefore, our current working model is that as B. burgdorferi migrates from the anaerobic midgut (containing no ROS) to the salivary glands, ROS act as a signal to induce the expression of ROS defense enzymes and key virulence factors that promote the survival and successful colonization of a new host. Cellular defenses against the damaging effects of ROS involve both enzymatic and nonenzymatic components. B. burgdorferi has a limited number of enzymes that could potentially be involved in this defense response. Those identified include a Mn-dependent superoxide dismutase (SOD), a Dps/Dpr homologue (NapA), thioredoxin (Trx), thioredoxin reductase (TrxR) and a Coenzyme-A disulfide reductase (CoADR). To date the Mn-SOD, CoADR, and NapA (unpublished data) have been characterized experimentally. Because these enzymes would promote the in vivo survival of B. burgdorferi cells when challenged by O2.- and H2O2 from host cells, we are particularly interested in the process and how it is regulated. The Borrelia oxidative stress regulator, BosR, acts as a transcriptional activator of oxidative stress genes. Although there is no apparent amino acid homology (>15%), BosR appears to be functionally similar to OxyR from E. coli. In addition, we have shown that BosR regulates sodA (Mn-SOD), the gene encoding NapA (an AhpR homolog), and cdr (CoADR). The effects of ROS/RNS on cells have been extensively investigated. These highly reactive compounds have been shown to damage cellular macromolecules including DNA, proteins, and membrane lipids. In eukaryotes, membrane lipids are a major target of reactive oxygen species. Free radicals attack polyunsaturated fatty acids in membranes and initiate lipid peroxidation. A primary effect is a decrease in membrane fluidity which affects the physical properties of the membrane altering the function of membrane-associated proteins. Once lipid peroxides form, they react with adjacent polyunsaturated lipids causing an amplification of the damage. Lipid peroxides undergo further oxidation to a variety of products, including aldehydes, which subsequently react with and damage membrane proteins. However, in bacteria, it is assumed that lipids are not subject to the oxidative damage observed in eukaryotic cells. Only certain polyunsaturated lipids, such as linoleic and linolenic acid, are susceptible to oxidation and it is clear that most bacteria do not synthesize or incorporate these types of lipids in their cell membranes. Two notable exceptions are the photosynthetic bacteria and Borrelia species who synthesize or incorporate significant levels of linoleic and linolenic acid in their membranes. Instead, it has been shown that the most damaging effects of ROS in bacteria result from the interactions of radicals (H2O2) with "free" Fe2+ generating very reactive OH- (Fenton reaction).Because of this reactivity, its effect on any given biomolecule will depend largely upon proximity to the target. Because Fe2+ localizes along the phosphodiester backbone of nucleic acid, DNA is a major target of OH-.This reactive species can pull electrons from either the base and sugar moieties producing a varety of lesions including single and double strand breaks in the backbone and chemical crosslinks to other molecules. These strand breaks, and other lesions that block DNA replication, contribute to OH.- toxicity and cell death. Other base damage, that does not hinder replication, contributes to a significant increase in mutation rates. The intracellular biochemistry of B. burgdorferi suggest that the primary intracellular target of ROS may not be DNA as described in other bacteria such as E. coli. In E.coli, the extent of DNA damage due to H2O2 and Fenton chemistry is directly proportional to Fe metabolism and the free Fe concentration within the cell.(5-100 nM) Since the intracellular Fe concentrations of B. burgdorferi are estimated to be <10 atoms per cell, it seems unlikely that DNA is a primary target for ROS in B. burgdorferi. In support of this, growth of B. burgdorferi in the presence of 5mM H2O2 had little to no effect on the DNA mutation rate (spontaneous coumermycin A1 resistance). Also, when cells were treated with various oxidants (t-butyl peroxide or H2O2) no increase in DNA damage was detected in comparison to untreated cells as determined by calculating the number of DNA base lesions using an aldehyde reactive probe. As previously mentioned, B. burgdorferi incorporates polyunsaturated fatty acids from the environment into the cells membrane lipids and lipoproteins suggesting that Borrelia membranes could be a target for lipid peroxidation. Analyses of t-butyl peroxide treated B. burgdorferi cells by electron microscopy showed significant irregularities indicative of membrane damage. Fatty acid analysis of cells treated with t-butyl peroxide and lipoxidase indicated that host-derived linoleic acid had been dramatically reduced (10- and 50-fold, respectively) in these cells, with a subsequent increase in the levels of malondialdehyde (MDA) and 4-hydroxyalkenals (HAE) aldehyde(4- and 10-fold respectively),the toxic by-products of lipid peroxidation. These data, taken together, suggest that B. burgdorferi membrane lipids and lipoproteins are the primary targets for attack by ROS encountered in the various stages of the infective cycle, that NapA and CoADR rid the cells of oxidized lipids, and that the genes encoding these proteins are regulated by BosR.

莱姆病的病因伯格多尔菲里（Borrelia burgdorferi）在节肢动物载体和各种哺乳动物宿主中均能生存和增殖。在其传播/感染周期中，B。Burgdorferi遇到了特定于这些宿主的环境挑战。一个这样的挑战来自活性氧（ROS），例如超氧化物自由基（O2.-），过氧化氢（H2O2）和羟基自由基（OH。）和反应性氮种（RNS），例如一氧化氮（NO），N2O3和过氧亚硝酸盐。 在感染周期中，B. burgdorferi暴露于ROS/RN时，有两个阶段。第一个是在免疫系统的细胞试图使用多种机制（包括ROS和RNS的产生）限制和消除B. burgdorferi时，在哺乳动物宿主感染的初始阶段。 令人惊讶的是，第二次ROS/RNS挑战发生在传播过程中细菌通过唾液腺迁移。我们的实验室与汤姆·施旺（Tom Schwan）博士合作，证明了ixodes的唾液腺包含大量的ROS。因此，我们当前的工作模型是，由于B. burgdorferi从厌氧中肠（无ROS）迁移到唾液腺时，ROS充当诱导ROS防御酶的表达和关键的毒力因子的表达，从而促进新宿主的存活和成功定殖。对ROS的破坏作用的细胞防御措施涉及酶促和非酶成分。 B. Burgdorferi的酶数量有限，有可能参与这种国防反应。 确定的包括Mn依赖性的超氧化物歧化酶（SOD），DPS/DPR同源物（NAPA），硫氧还蛋白（TRX），硫氧还蛋白还原酶（TRXR）和辅酶-A二硫化物还原酶（COADR）。 迄今为止，MN-SOD，COADR和NAPA（未发表的数据）已通过实验表征。 由于这些酶会在受宿主细胞的O2.-和H2O2挑战时促进爆发芽孢杆菌细胞的体内存活，因此我们对这一过程及其调节方式特别感兴趣。 BOSR的伯罗氏氧化应激调节剂BOSR充当氧化应激基因的转录激活因子。 尽管没有明显的氨基酸同源性（> 15％），但BOSR似乎在功能上与大肠杆菌的Oxyr相似。 此外，我们已经表明，BOSR调节苏打（MN-SOD），编码NAPA（AHPR同源物）和CDR（COADR）的基因。 ROS/RNS对细胞的影响已得到广泛研究。 这些高反应性化合物已被证明会损害包括DNA，蛋白质和膜脂质在内的细胞大分子。在真核生物中，膜脂质是活性氧的主要靶标。 自由基在膜中攻击多不饱和脂肪酸并启动脂质过氧化。 主要效果是膜流动性的降低，影响膜的物理特性改变了与膜相关蛋白的功能。一旦形成脂质过氧化物，它们就会与相邻的多不饱和脂质反应，从而导致损伤的扩增。 脂质过氧化物将进一步氧化对包括醛在内的多种产物，随后与醛反应并损害膜蛋白。然而，在细菌中，假定脂质不受真核细胞中观察到的氧化损伤的影响。 只有某些多不饱和脂质（例如亚油酸和亚麻酸）易于氧化，很明显，大多数细菌不会合成或掺入这些类型的脂质中。 两个值得注意的例外是光合细菌和伯罗利种类，它们在其膜中合成或结合了大量的亚油酸和亚麻酸。 取而代之的是，已经表明，ROS在细菌中最大的破坏作用是由自由基（H2O2）与“ Free” Fe2+产生非常反应性的OH-的相互作用引起的。 由于Fe2+沿核酸的磷酸二酯主链定位，因此DNA是OH-的主要靶标。这种反应性物种可以从碱基和糖部分中汲取电子，以及产生各种病变的差异，包括单链和双重链断裂，包括单链和双链断裂，在骨架和化学交叉链路上脱离了其他分子。 这些链断裂和其他阻断DNA复制的病变会导致OH.-毒性和细胞死亡。其他基本损害（不会阻碍复制）导致突变率的显着增加。 B. burgdorferi的细胞内生物化学表明，ROS的主要细胞内靶标可能不是其他细菌（例如大肠杆菌）中所述的DNA。在大肠杆菌中，H2O2和Fenton化学造成的DNA损伤程度与FE代谢和细胞内的Fe代谢和自由Fe浓度成正比。（5-100 nm），因为伯格多代芽孢杆菌的细胞内Fe浓度估计是每个细胞<10个原子<10个原子，这似乎是无效的，DNA似乎是dna的主要目标。 为了支持这一点，在5mm H2O2存在下，B. burgdorferi的生长对DNA突变速率（自发的香豆素A1抗性）几乎没有影响。 同样，当细胞用各种氧化剂处理（T丁基过氧化丁基或H2O2）时，与未经处理的细胞相比，未检测到DNA损伤的增加，这是通过使用醛反应性探针计算DNA碱基损伤的数量来确定的。 如前所述，B。burgdorferi将环境中的多不饱和脂肪酸纳入细胞膜脂质和脂蛋白，这表明硼酸毛膜可能是脂质过氧化的靶标。 通过电子显微镜分析通过电子显微镜分析了经过的T叔丁基处理的爆发芽孢杆菌细胞，表明了明显的不规则性，表明膜损伤。 在这些细胞中，用T丁基过氧化丁基和脂蛋白酶处理的细胞对细胞的脂肪酸分析表明，宿主衍生的亚油酸已大大降低（分别为10倍和50倍），随后马长甲基（MDA）（MDA）和4-Hydroxyalkenals（MDA）和4-羟基（Hydroxyalkenals）（4-羟基甲基（Hydroxyalkenals）（4-羟基）（4-- hyde）（4-- hyde）（4-）脂质过氧化的副产品。 这些数据共同表明，B。burgdorferi膜脂质和脂蛋白是在感染周期的各个阶段遇到的ROS攻击的主要目标，即NAPA和COADR消除了氧化脂质的细胞，并且BOSR调节了这些蛋白质的基因。