Genetic and mechanistic analysis of carbon dioxide tolerance in Cryptococcus pathogenesis

摘要 隐球菌脑膜脑炎（CME）是影响人群的最重要的机会性感染之一 艾滋病毒/艾滋病。这种疾病的重要性不仅在于它在这一地区的高发病率和死亡率， 其他患者人群，而且CME的症状是一种常见的哨兵事件， 艾滋病毒/艾滋病的诊断。因此，许多患者必须首先在CME中存活，然后才能从CME中获益。 艾滋病治疗的进展。不幸的是，CME治疗的结果远不能接受，特别是在 资源有限、疾病负担重的地区。因此，有效和广泛可用的治疗方法 是一个未满足的全球重要临床需求。隐球菌属是担子菌酵母 其主要生态位是外部环境。因此，只有菌株和物种的隐球菌， 转移到人类宿主并在人类宿主内复制，能够引起疾病。我们的中心前提是， 了解隐球菌在人类中生存所需的生物学机制， 为治疗提供新的靶点，就像研究肿瘤生物学为设计新的抗肿瘤药物提供信息一样。 抗癌药人类宿主和自然生态位之间的一个重要环境区别是， 隐球菌是二氧化碳（CO2）的浓度。我们假设，对宿主水平的适应 CO2可能是隐球菌致病的关键步骤。为了验证这个假设，我们 比较了C.新形变种Grubii菌株在仅浓度变化的条件下， 二氧化碳。与我们的假设一致，生长速率在经历的CO2浓度下降低， 主持人接下来，我们测试了一组具有已知毒力特性的环境菌株的CO2耐受性 在小鼠模型中;在宿主浓度的CO2存在下生长减少的菌株是无毒的 而那些具有与来自人类患者的临床分离株相匹配的生长速率的菌株是有毒的。因此， 我发现，CO2耐受性是一种以前未被认识到的与宿主环境相关的 C.毒力特性新人类因此，这项建议的目标是确定遗传， 转录和调节反应，使特定菌株的C.新形动物对宿主的反应 CO2的浓度，从而导致CME。为实现这些目标，我们提出以下建议 具体目标：目标1。表征CO2-之间的毒力，转录和基因组差异 宽容和非宽容C.新型菌株; Aim 2.确定CO2耐受性所需的基因， 有针对性的大规模遗传筛查;以及目标3。确定基因的分子机制 需要C。CO2反应。成功实现这些目标不仅将进一步推动我们的 理解C。新形式的发病机制和宿主的生存，但也确定了新的分子靶点，为未来 探索药物靶点。

Abstract Cryptococcal meningoencephalitis (CME) is one of the most important opportunistic infections affecting people with HIV/AIDS. The importance of this disease is due not only to its high incidence and mortality in this and other patient populations but also to the fact that symptoms of CME are a common sentinel event leading to the diagnosis of HIV/AIDS. Thus, many patients must first survive CME before they can benefit from the advances in HIV therapy. Unfortunately, the outcomes for CME therapy are far from acceptable, particularly in resource-limited regions with high burdens of disease. Consequently, effective and widely available therapies for CME are an unmet clinical need of global importance. Cryptococcus spp. are basidiomycetous yeasts whose primary niche is the external environment. As such, only strains and species of Cryptococcus that can transition to, and replicate within, the human host are able to cause disease. Our central premise is that an understanding of the biological mechanisms required for Cryptococcus to survive in human beings could provide new targets for therapy in the same way as studying tumor biology informs the design of new anti- cancer drugs. An important environmental distinction between the human host and the natural niche of Cryptococcus is the concentration of carbon dioxide (CO2). We hypothesized that adaptation to host levels of CO2 may represent a critical step in Cryptococcus pathogenesis. To specifically test this hypothesis, we compared the growth of C. neoformans var. grubii strains under conditions that varied only in the concentration of CO2. Consistent with our hypothesis, the growth rate was reduced at concentrations of CO2 experienced in the host. Next, we tested the CO2 tolerance of a set of environmental strains with known virulence properties in a mouse model; strains with reduced growth in the presence of host concentrations of CO2 were avirulent while those with growth rates that matched clinical isolates from human patients were virulent. We, therefore, have discovered that CO2 tolerance is a previously unrecognized host environment-associated virulence attribute of C. neoformans. Accordingly, the goal of this proposal is to identify the genetic, transcriptional, and regulatory responses that allow specific strains of C. neoformans to respond to host concentrations of CO2 and, thereby, cause CME. To accomplish these goals, we propose the following specific aims: Aim 1. Characterize the virulence, transcriptional, and genomic distinctions between CO2- tolerant and -non-tolerant C. neoformans strains; Aim 2. Identify genes required for CO2 tolerance through targeted and large-scale genetic screening; and Aim 3. Determine the molecular mechanisms of genes required for C. neoformans CO2 response. Successful execution of these aims will not only further our understanding C. neoformans pathogenesis and host survival but also identify new molecular targets for future exploration as drug targets.