OXYGEN SENSING AND ADAPTATION TO HOST TISSUE HYPOXIA IN C. NEOFORMANS

描述(申请人提供)：艾滋病毒大流行和因癌症或器官移植而导致免疫功能受损的患者增加，导致被包裹的致病真菌新生隐球菌感染的人数急剧上升。这种无处不在的担子菌通过肺部进入免疫受损的人，通常感染大脑，如果不治疗，会导致脑膜脑炎和死亡。艾滋病在美国和发展中国家的流行使得清楚地了解隐球菌的发病机制和改进治疗方法成为公共卫生的当务之急。感染哺乳动物宿主并不是新生弧菌生命周期中的必经步骤，但这种真菌已经进化出在宿主环境中生存的机制。宿主组织的含氧量平均为3%，远低于大气中21%的水平，而大脑中的含氧量可能低至1%。因此，新生葡萄球菌在宿主中的生长需要适应低氧。虽然对环境信号转导途径的毒力要求，如耐热性和营养饥饿，已经在新生葡萄球菌中进行了研究，但关于这种专性需氧菌如何对环境氧气的变化做出反应尚不清楚。在这里，我们将确定新生葡萄球菌感知氧气的机制，以及允许感染进展的适应性基因表达程序。初步实验表明，在哺乳动物中控制胆固醇稳态的膜结合SREBP转录因子Sre1在氧感应途径中发挥作用，是新生隐孢子虫低氧生长所必需的。鉴于受感染的宿主组织是低氧的，我们假设SRE1是新生葡萄球菌毒力所必需的。为了支持这一假设，初步研究表明，Sre1在低氧(1%-3%)时被激活，并且在感染的小鼠模型中，缺乏SRE1的新生葡萄球菌菌株显示出毒力降低。因此，新生葡萄球菌中的SREBP通路是治疗这种致命的机会性感染的潜在治疗靶点。我们的具体目标是：目的1.确定新生葡萄球菌SRE1对毒力的要求。目的2.检测Sre1激活蛋白水解酶Zmp1的毒力要求。目的3.分离新生隐球菌低氧生长所需的额外基因。通过结合基因表达谱、基因筛选和小鼠体内毒力研究，我们将识别新生弧菌的新毒力因子。我们的研究将提供有关新生葡萄球菌如何适应低氧的第一批信息。艾滋病毒大流行和因癌症或器官移植而导致的免疫功能受损患者数量的增加，导致致病真菌新生隐球菌造成的致命感染数量急剧上升。在这个项目中，我们将确定这种病原体适应宿主低氧环境和真菌感染进展所需的基因。这些基因代表了未来抗真菌治疗的候选靶点。

DESCRIPTION (provided by applicant): The HIV pandemic and increases in immunocompromised patients due to cancer or organ transplants have led to a sharp rise in the number of infections by the encapsulated pathogenic fungus, Cryptococcus neoformans. This ubiquitous basidiomycete fungus enters immunocompromised individuals via the lungs and commonly infects the brain, causing meningoencephalitis and death if untreated. The prevalence of AIDS in the United States and developing countries makes a clear understanding of cryptococcal pathogenesis and improved therapeutics a public health imperative. Infection of a mammalian host is not an obligate step in the lifecycle of C. neoformans, yet this fungus has evolved mechanisms to survive in the host environment. Host tissue oxygen averages 3%, far below atmospheric levels of 21%, and levels in the brain can be as low as 1%. Thus, growth of C. neoformans in the host necessitates adaptation to low oxygen. While the requirement for virulence of environmental signal transduction pathways such as thermotolerance and nutrient starvation has been examined in C. neoformans, nothing is known about how this obligate aerobe responds to changes in environmental oxygen . Here, we will identify mechanisms by which C. neoformans senses oxygen and the adaptive gene expression programs that allow infection to progress. Preliminary experiments indicate that the membrane-bound SREBP transcription factor Sre1, which controls cholesterol homeostasis in mammals, functions in an oxygen sensing pathway and is required for low oxygen growth in C. neoformans. Given that infected host tissues are hypoxic, we hypothesize that SRE1 is required for virulence of C. neoformans. In support of this hypothesis, preliminary studies indicate that Sre1 is activated in response to low oxygen (1% - 3%) and that a C. neoformans strain lacking SRE1 shows decreased virulence in a mouse model of infection. Thus, the SREBP pathway in C. neoformans represents a potential therapeutic target for the treatment of this lethal opportunistic infection. Our specific aims are: AIM 1. To determine the requirement of C. neoformans SRE1 for virulence. AIM 2. To test the requirement of the Sre1 activating protease, Zmp1, for virulence. AIM 3. To isolate additional genes required for low oxygen growth in C. neoformans. Using a combination of gene expression profiling, genetic screening, and in vivo virulence studies in mice, we will identify novel virulence factors in C. neoformans. Our studies will provide the first information about how C. neoformans adapts to low oxygen. The HIV pandemic and increases in the number of immunocompromised patients due to cancer or organ transplants have led to a sharp rise in the number of lethal infections due to the pathogenic fungus, Cryptococcus neoformans. In this project, we will identify genes required for adaptation of this pathogen to the low oxygen environment of the host and for progression of fungal infection. These genes represent candidate targets for future anti-fungal therapy.