Phenotypic Switching in Candida albicans and its Role in Pathogenesis

描述（由申请方提供）：白色念珠菌是一种机会致病菌，能够引起衰弱性粘膜感染以及危及生命的全身性感染。感染人类免疫缺陷病毒（HIV）的个体特别容易感染念珠菌，90%的人在疾病的某个阶段经历口咽念珠菌病。C.白色念珠菌普遍存在于人体的天然微生物区系中，并且其作为寄生菌和病原体的成功依赖于其快速适应宿主生理变化的能力。这一建议将确立表型转换在C.白念珠菌生物学，重点是转换在促进免疫受损宿主不同部位的定植和感染中的作用。表型转换是指细胞在集落形态和基因表达方面发生可逆的和可遗传的变化的表观遗传现象。In C.白念珠菌，表型转换率升高与侵袭性生长和耐药性增加有关，特别是在HIV感染个体中，这使得理解转换的机制至关重要。本提案中概述的实验将解决白色和不透明形式的C之间的表型转换机制。白色念珠菌白色不透明开关在C.白念珠菌生物学，指导组织特异性，毒力和生物膜形成，但白色不透明转换的分子机制现在才开始被阐明。初步实验表明，多种明显不同的因素通过对细胞生长的影响间接影响白色-不透明转换的速率。表型转换和细胞生长之间的意想不到的联系将在目标1中进一步研究，因为它代表了细胞可以适应环境应激的新机制。该提案的第二个目的将使用转录因子的过表达筛选来识别白色不透明开关的新调节器。预计过表达文库的构建也将证明是该领域许多研究人员有用的遗传工具。最后，该提案的第三个目的将使用RIVET（重组酶体内表达技术）建立哺乳动物宿主中白色-不透明转换的时间和空间调节。因此，综合考虑，拟议的研究将确定环境和宿主因素对白色不透明开关的体外调节，以及定义发生开关的体内生态位。因此，这些研究的完成将揭示C.白念珠菌，以促进适应宿主，并帮助避免由免疫系统清除。公共卫生相关性：白色念珠菌是人类最常见的真菌病原体，可引起使人衰弱的粘膜感染和危及生命的全身感染。我们的研究主要集中在C.白念珠菌产生表型多样性，以及这些过程如何促进哺乳动物宿主的存活和感染。本研究还探讨了C.白色念珠菌能够从无害的寄生菌转变为机会致病菌，几乎可以侵入身体的所有器官。

DESCRIPTION (provided by applicant): Candida albicans is an opportunistic pathogen capable of causing debilitating mucosal infections as well as life-threatening systemic infections. Individuals infected with Human Immunodeficiency Virus (HIV) are particularly susceptible to Candida infections, with 90% of this population experiencing oropharyngeal candidiasis at some stage of the disease. C. albicans is ubiquitously present in the natural microflora of the body and its success as both a commensal and a pathogen relies on its ability to rapidly adapt to changes in host physiology. This proposal will establish the role of phenotypic switching in C. albicans biology, with emphasis on the role of switching in promoting colonization and infection of distinct sites in the immunocompromised host. Phenotypic switching refers to an epigenetic phenomenon in which cells undergo a reversible and heritable change in colony morphology and gene expression. In C. albicans, elevated rates of phenotypic switching are associated with increased invasive growth and drug resistance, particularly in HIV-infected individuals, making an understanding of the mechanism(s) of switching of paramount importance. Experiments outlined in this proposal will address the mechanism of phenotypic switching between white and opaque forms of C. albicans. The white-opaque switch plays a pleiotropic role in C. albicans biology, directing tissue specificity, virulence, and biofilm formation, yet the molecular mechanism of white-opaque switching is only now beginning to be elucidated. Preliminary experiments indicate that multiple, apparently diverse, factors impact the rate of white-opaque switching indirectly by their effect on cellular growth. The unexpected connection between phenotypic switching and cell growth will be further investigated in Aim 1, as it represents a novel mechanism by which the cell can adapt to environmental stress. The second Aim of the proposal will identify novel regulators of the white-opaque switch using an overexpression screen of transcription factors. It is expected that the construction of an overexpression library will also prove a useful genetic tool for many researchers in the field. Finally, the third Aim of the proposal will establish the temporal and spatial regulation of white- opaque switching in the mammalian host using RIVET (recombinase in vivo expression technology). Thus, taken together, the proposed studies will determine both the in vitro regulation of the white-opaque switch by environmental and host factors, as well as defining the in vivo niche where switching occurs. The completion of these studies will therefore shed light on how phenotypic switching is used by C. albicans to promote adaptation to the host and help avoid clearance by the immune system. PUBLIC HEALTH RELEVANCE: Candida albicans is the most common fungal pathogen in humans, causing both debilitating mucosal infections and life-threatening systemic infections. Our research focuses on the mechanisms used by C. albicans to generate phenotypic diversity and how these processes promote survival and infection in the mammalian host. The research also addresses how C. albicans is able to switch from growing as a harmless commensal to an opportunistic pathogen that can invade virtually all the organs in the body.