Genetics of Host Resistance and Susceptibillity to MTB

描述(申请人提供)：结核病仍然是一个重大的公共卫生问题，尽管近年来在开发新药和疫苗方面做出了大量努力。宿主对感染的易感性的差异是制定普遍有效的预防和治疗战略的主要障碍。这种变异部分是由遗传因素造成的。本研究利用强毒结核分枝杆菌(MTB)感染小鼠模型，剖析宿主对结核分枝杆菌耐药的复杂遗传控制，揭示在体内对结核分枝杆菌感染进程有重要影响的基因。我们的研究表明，两个免疫活性小鼠品系C3HeB/FEJ和C57BL/6J的结核病易感性的显著差异是由于多个遗传位点及其上位性相互作用的影响。到目前为止，我们已经定位了9个结核耐药基因座，解剖了sst1基因座，并通过定位克隆鉴定了Ipr1基因。在我们的模型中，sst1与小鼠7号染色体上一个新的基因座(Chr7)的协同作用是一个主要的遗传成分，它解释了亲本菌株之间约50%的变异。两个B6抗性基因座的累积效应显著强于它们的个体效应之和，首次提供了上位性基因互作控制寄主对MTB抗性的直接实验证据。这两个基因座共同提高了极敏感的C3HeB/FEJ小鼠感染后1个月至5-6个月的存活率，极大地改善了对结核杆菌生长的控制，并减少了肺部炎症。在这一应用中，我们提出了对chr7基因的遗传和功能特征进行定位克隆，以确定致病基因，并揭示其在控制宿主对结核病感染的耐药性中的特殊作用。使用我们开发的一组亚基因菌株，候选区域将减少到0.5-2Mb间隔。将利用单倍型结构、基因表达模式和最小候选区域的序列分析来确定最佳候选基因。将通过体外和体内试验对候选基因进行功能分析，以获得其在宿主对MTB的抗性中所起作用的确凿证据，并在分子、细胞和整个生物水平上表征候选基因控制的途径。这将有助于更好地理解不同途径如何相互作用产生免疫活性宿主的耐药或敏感表型，探索人类的这些途径，并有可能为纠正敏感表型提供分子靶点。公共卫生相关性：结核病仍然是一个重大的公共卫生问题。为了减少疾病负担，我们必须提高对病原体如何破坏具有免疫能力的人的肺的理解，并揭示环境和遗传因素导致个人对结核病的抵抗力存在巨大差异。我们通过对实验性小鼠感染模型的遗传分析，找出了影响肺部结核感染进展的基因，并发现了两个主要的宿主耐药基因，它们的协同作用显著减少了肺组织的病理改变，提高了结核病感染小鼠的存活率。我们之前已经确定了其中一个基因座sst1的特征，并发现了一个候选基因，它介导了对结核病的先天免疫。在这一应用中，我们提出了对7号染色体第二个位点的遗传和功能解剖，以分离新的宿主抗性基因，并揭示其在控制结核病感染中的功能。

DESCRIPTION (provided by applicant): Tuberculosis remains a significant public health problem, despite substantial effort to develop new drugs and vaccines in recent years. Host variation in terms of susceptibility to the infection is a major impediment to the development of universally efficient prevention and treatment strategies. This variation is partially explained by the genetic factors. In our studies mouse model of infection with virulent Mycobacterium tuberculosis (MTB) is used to dissect complex genetic control of host resistance to MTB and reveal genes, which strongly influence progression of tuberculosis infection in vivo. Our studies demonstrate that dramatic differences in tuberculosis susceptibility of two immunocompetent mouse strains C3HeB/FeJ and C57BL/6J mice are due to effects of several genetic loci and their epistatic interactions. To date, we have mapped nine tuberculosis resistance loci, dissected the sst1 locus and identified the Ipr1 gene by positional cloning. Synergisitic interactions of the sst1 with a novel locus on mouse chromosome 7 (Chr7) represent a major genetic component in our model, which accounts for about 50% of the variation between the parental strains. The cumulative effect of the two B6-derived resistance loci was remarkably stronger than the sum of their individual effects, providing the first direct experimental evidence of epistatic gene interactions in control of host resistance to MTB. Together the two loci increased the survival of the extremely susceptible C3HeB/FeJ mice from one month to 5 - 6 months post infection, greatly improved control of MTB growth and decreased lung inflammation. In this application we propose genetic and functional characterization of the Chr7 locus to identify causal gene using positional cloning and reveal its specific role in control of host resistance of tuberculosis infection. The candidate region will be reduced to 0.5 - 2 Mb interval using a set of subcongenic strains that we have developed. Haplotype structure, gene expression pattern and sequence analysis of the minimal candidate region will be used to identify top candidate genes. Functional analysis of the candidate gene will be performed using in vitro and in vivo assays to obtain definitive proof for its role in host resistance to MTB and characterize pathways that the candidate gene controls at molecular, cellular and whole organism levels. This will lead to a better understanding of how different pathways interact to produce resistant or susceptible phenotypes in immunocompetent hosts, an exploration of these pathways in humans and potentially provide molecular targets for correction of the susceptible phenotypes. PUBLIC HEALTH RELEVANCE: Tuberculosis remains a significant public health problem. To reduce the disease burden we must improve our understanding of how the pathogen destroys lungs of immunocompetent individuals and reveal environmental and genetic factors responsible for big differences among individuals in resistance to tuberculosis. We use genetic analysis in experimental mouse model of infection to identify genes, which effects strongly influence progression of tuberculosis infection in the lungs and have found two major host resistance loci, which synergistic effect dramatically reduce lung pathology and increase survival of the tuberculosis infected mice. We have previously characterized one of those loci, sst1, and found a candidate gene, which mediates innate immunity to tuberculosis. In this application we propose genetic and functional dissection of the second locus on chromosome 7 to isolate novel host resistance gene and reveal its function in control of tuberculosis infection.