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: 8450086
• 负责人: F. NINA Papavasiliou
• 金额: $ 39.32万
• 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/8450086
• 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.

描述（由申请人提供）：Brucei寄生虫原生动物锥虫是非洲锥虫病的致病药物，可导致人类和农民动物的纳加纳的睡眠。世界卫生组织预测，当前人类非洲锥虫病的疾病负担约为200万“残疾调整后的生命年”（每年有300,000例新病例）。加上对长纳纳（Nagana）造成的经济的深远影响，T。Brucei是非洲大部分地区发展的主要障碍之一。虽然相关的寄生虫在进入哺乳动物宿主后利用受保护的壁ches，但T. Brucei在哺乳动物的血液中繁荣发展，在那里它必须在体液免疫反应的袭击中幸存下来。该寄生虫通过其致密的表面涂层来做到这一点，由〜5 x 106可变的表面糖蛋白（VSG）同型二聚体组成。虽然这种VSG涂层暴露于抗体并识别为抗体，但T. Brucei会定期替换（在称为“ VSG开关”的过程中），使寄生虫的亚群可以通过逃避补体介导的裂解来生存。关于分子水平的VSG切换知之甚少。在过去的25年中的工作已经确定（a）大多数切换是通过重复的基因转换而发生的，并且（b）在感染后与后期相对于早期与后期的VSG类型有关，具有半预测的层次结构。我们最近建立了一个强大的实验系统，我们用来成功地再现体内感染的许多特征。在这里，我们建议将该系统用于两个具体目标：1）确定启动VSG切换的机制。长期存在的假设是，核酸内切酶启动了VSG切换。另外，切换可能是由于染色体末端特有的内源性过程（这是所有表达的VSG所在的地方）可能引起的自发但频繁的DNA断裂的结果。我们提出了评估这两个假设的实验。 2）了解控制捐赠者VSG选择的规则，从而导致观察到的切换层次结构。在VSG切换的早期阶段，在感染过程中引起的新（供体）VSG并非随机。例如，表达VSG221的细胞倾向于切换到体内（Robinson等，1999）和体外（我们的初步数据）。我们将评估可以解释这一一致发现的两种机制：（a）最初的偏好可能是由于表达位点的保守元素（例如70 bp重复区域）的序列相似性所致，并且（b）此偏好可能是两个表达位点附近的结果。除非治疗，否则非洲锥虫病总是致命的。确实存在的少数治疗方法很昂贵，具有严重的副作用，并且随着耐药性T. brucei菌株的出现，越来越效率。我们提出的工作集中于理解并最终破坏这种寄生虫的主要逃避途径，这也是病原体持久性的原因。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防止这种被忽视的疾病。