Parameters that govern initiation of VSG switching in T.brucei

控制 T.brucei 中 VSG 切换启动的参数

• 批准号: 8066403
• 负责人: F. NINA Papavasiliou
• 金额: $ 41.83万
• 依托单位: ROCKEFELLER UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-05-01 至 2015-04-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8066403
• 关键词: Address; Adverse effects; Africa; Africa South of the Sahara; African Trypanosomiasis; Antibodies; Antigenic Variation; Binding; Biological Assay; Bite; Blood Circulation; Borrelia; Candida albicans; Cattle; Cell Nucleus; Cells; Chromosomes; Chronic; Complement; Coupled; Cytolysis; DNA; DNA Double Strand Break; DNA lesion; Data; Development; Disease; Drug resistance; Elements; Enzymes; Frequencies; Gene Conversion; Genetic Transcription; HO nuclease; Human; Immune; Immune response; Immune system; In Vitro; Infection; Intermediate Variables; Lead; Length; Light; Livestock; Mediating; Membrane Glycoproteins; Membrane Proteins; Methods; Molecular; Molecular Conformation; Neisseria gonorrhoeae; Outcome; Parasites; Pathway interactions; Population; Process; Research; Site; Source; Staging; System; Testing; Therapeutic; Therapeutic Intervention; Tropical Disease; Trypanosoma; Trypanosoma brucei brucei; Variant; Work; World Health Organization; burden of illness; disability-adjusted life years; endonuclease; homologous recombination; in vivo; nagana; neglect; novel; pathogen; preference; public health relevance; research study; surface coating; telomere; tool; vector

DESCRIPTION (provided by applicant): The parasitic protozoan Trypanosoma brucei is the causative agent of African trypanosomiasis which causes sleeping sickness in humans and Nagana in farm animals. The World Health Organization projects that the current disease burden of human African trypanosomiasis is about two million "Disability Adjusted Life Years" (with 300,000 new cases each year). Coupled with the profound effect on the economy caused by Nagana, T. brucei is one of the leading impediments to development in much of Africa. While related parasites utilize protected niches after they enter their mammalian host, T. brucei thrives in the mammalian bloodstream, where it must survive the onslaught of the humoral immune response. The parasite does this by virtue of its dense surface coat, consisting of ~5 x 106 variable surface glycoprotein (VSG) homodimers. While this VSG coat is exposed to and recognized by antibodies, T. brucei periodically replaces it (in a process called "VSG switching") enabling a subpopulation of parasites to survive by evading complement-mediated lysis. Little is known about VSG switching at the molecular level. Work over the last 25 years has determined (a) that the majority of switching occurs by duplicative gene conversion and (b) that there is semi-predictable hierarchy with regard to the types of VSGs that appear early vs. late after infection. We have recently established a robust experimental system, which we have used to successfully reproduce many of the features of in vivo infection. Here, we propose to use this system toward two specific aims: 1) Determine the mechanism that initiates VSG switching. There is a long-standing hypothesis that VSG switching is initiated by an endonuclease. Alternatively, switching could be a result of spontaneous but frequent DNA breaks that can arise from endogenous processes peculiar to chromosome ends (which is where all expressed VSGs are located). We propose experiments to evaluate both hypotheses. 2) Understand the rules that govern choice of donor VSG, leading to the observed hierarchy of switching. In the early stages of VSG switching, the new (donor) VSGs arising in the course of infection are not random. For example, cells expressing VSG221 tend to switch to VSG224, both in vivo (Robinson et al., 1999) and in vitro (our preliminary data). We will evaluate two mechanisms that could explain this consistent finding: (a) initial preference could be due to sequence similarity in conserved elements (such as the 70-bp repeat tracts) of expression sites, and (b) this preference could be the result of proximity of the two expression sites in the context of the nucleus. African trypanosomiasis is always fatal unless treated. The few therapeutic treatment options that do exist are expensive, have serious side effects and are increasingly inefficient as drug resistant T. brucei strains begin to emerge. The work we propose centers upon understanding and eventually disrupting the major known pathway of immune evasion by this parasite which is also the cause of pathogen persistence. As such, in the long term the research we propose could lead to a novel and effective way to protect against this neglected disease. PUBLIC HEALTH RELEVANCE: The parasite Trypanosoma brucei is the causative agent of African sleeping sickness in humans and of Nagana in cattle, and one of the leading impediments to development in much of sub-Saharan Africa. T. brucei is transmitted to the mammalian bloodstream through the bite of the tse-tse vector, and once there, it quickly elicits an antibody mediated immune response which is capable of eliminating the parasite by binding to its exposed surface coat. However, the parasite has evolved a survival strategy that hinges upon its ability to change its surface coat, to evade the host immune response. The work we propose aims to understand the mechanism of T. brucei surface coat switching, which is the sole cause of pathogen persistence and chronic infection.

描述（由申请方提供）：寄生原生动物布氏锥虫是非洲锥虫病的病原体，非洲锥虫病导致人类昏睡病和农场动物的Nagana病。世界卫生组织预测，目前非洲锥虫病的疾病负担约为200万“残疾调整生命年”（每年有30万新病例）。再加上长名事件对经济的深刻影响，T。在非洲大部分地区，布鲁塞是发展的主要障碍之一。虽然相关寄生虫在进入哺乳动物宿主后利用受保护的小生境，但T。布氏杆菌在哺乳动物的血液中繁殖，它必须在体液免疫反应的冲击下存活。寄生虫通过其致密的表面被膜（由约5 x 106个可变表面糖蛋白（VSG）同源二聚体组成）来实现这一点。当这种VSG被暴露于抗体并被抗体识别时，T。布氏杆菌周期性地替换它（在称为“VSG转换”的过程中），使得寄生虫亚群通过逃避补体介导的裂解而存活。关于分子水平上的VSG开关知之甚少。过去25年的工作已经确定：（a）大多数转换是通过重复基因转换发生的;（B）关于感染后早期与晚期出现的VSG类型，存在半可预测的等级。我们最近建立了一个强大的实验系统，我们已经成功地再现了体内感染的许多功能。在这里，我们建议使用这个系统对两个特定的目标：1）确定启动VSG切换的机制。有一个长期存在的假设，即VSG开关是由核酸内切酶启动的。或者，转换可能是自发但频繁的DNA断裂的结果，所述DNA断裂可能由染色体末端特有的内源性过程（其是所有表达的VSG所在的地方）引起。我们提出实验来评估这两种假设。2)理解支配供体VSG选择的规则，从而导致观察到的切换层次。在VSG转换的早期阶段，在感染过程中产生的新的（供体）VSG不是随机的。例如，表达VSG 221的细胞倾向于在体内转换为VSG 224（罗宾逊等人，1999）和体外（我们的初步数据）。我们将评估两种机制，可以解释这一一致的发现：（a）最初的偏好可能是由于序列相似性的保守元件（如70 bp的重复序列）的表达位点，和（B）这种偏好可能是两个表达位点在核的背景下接近的结果。非洲锥虫病除非得到治疗，否则总是致命的。目前仅有的几种治疗方法都很昂贵，有严重的副作用，而且随着耐药T。布氏菌株开始出现。我们提出的工作集中在理解并最终破坏这种寄生虫的免疫逃避的主要已知途径，这也是病原体持续存在的原因。因此，从长远来看，我们提出的研究可能会导致一种新颖有效的方法来预防这种被忽视的疾病。 公共卫生相关性：布氏锥虫是人类非洲昏睡病和牛Nagana病的病原体，也是撒哈拉以南非洲大部分地区发展的主要障碍之一。T.布氏杆菌通过tse-tse载体的叮咬传播到哺乳动物的血液中，一旦到达那里，它迅速激发抗体介导的免疫应答，该抗体能够通过结合到其暴露的表面涂层来消除寄生虫。然而，这种寄生虫已经进化出一种生存策略，这种策略取决于它改变其表面涂层的能力，以逃避宿主的免疫反应。我们提出的工作旨在了解T.布氏杆菌表面被毛交换，这是病原体持续存在和慢性感染的唯一原因。