Genetics of Host Resistance and Susceptibillity to MTB

描述（由申请人提供）：尽管近年来在开发新药和疫苗方面做出了巨大努力，但结核病仍然是一个重大的公共卫生问题。宿主在感染易感性方面的差异是制定普遍有效的预防和治疗战略的主要障碍。这种变异部分可以用遗传因素来解释。在我们的研究中，使用小鼠感染毒力结核分枝杆菌（MTB）模型来解剖宿主对MTB耐药性的复杂遗传控制，并揭示在体内强烈影响结核感染进展的基因。我们的研究表明，C3HeB/FeJ和C57BL/6J两种免疫能力小鼠的结核病易感性的显著差异是由于几个遗传位点及其相互作用的影响。迄今为止，我们已经绘制了9个结核耐药位点，解剖了sst1位点，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号染色体上的一个新位点（Chr7）的协同相互作用是一个主要的遗传成分，它占亲本菌株之间变异的50%左右。两个b6衍生的耐药位点的累积效应明显强于其个体效应的总和，为上位性基因相互作用控制宿主对MTB的抗性提供了第一个直接的实验证据。这两个基因座共同提高了极易感C3HeB/FeJ小鼠在感染后1个月至5 - 6个月的存活率，极大地改善了对MTB生长的控制，减少了肺部炎症。在本应用中，我们提出了Chr7基因座的遗传和功能特征，利用定位克隆技术鉴定致病基因，并揭示其在控制宿主结核病感染抗性中的具体作用。使用我们开发的一组亚同源菌株，候选区域将减少到0.5 - 2mb的间隔。单倍型结构、基因表达模式和最小候选区域的序列分析将用于确定顶级候选基因。候选基因的功能分析将通过体外和体内试验进行，以获得其在宿主对MTB抗性中的作用的明确证据，并表征候选基因在分子、细胞和整个生物体水平上控制的途径。这将有助于更好地理解不同的途径如何相互作用，在免疫能力强的宿主中产生抗性或易感表型，探索人类中的这些途径，并可能为纠正易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。为了减轻疾病负担，我们必须提高我们对病原体如何破坏免疫正常个体肺部的理解，并揭示导致个体之间结核病耐药性巨大差异的环境和遗传因素。我们通过对实验小鼠感染模型的遗传分析，确定了对肺部结核感染进展有强烈影响的基因，并发现了两个主要的宿主耐药位点，它们的协同作用显著降低了肺部病理，提高了结核感染小鼠的存活率。我们之前已经对其中一个基因座sst1进行了表征，并发现了一个候选基因，该基因介导对结核病的先天免疫。在本应用中，我们提出对7号染色体上的第二个位点进行遗传和功能解剖，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.