Phenotypic Switching in Candida albicans and its Role in Pathogenesis

描述(申请人提供)：白色念珠菌是一种条件致病菌，能够引起衰弱的粘膜感染以及危及生命的系统性感染。感染人类免疫缺陷病毒(HIV)的人特别容易受到念珠菌的感染，90%的人在疾病的某个阶段经历了口咽念珠菌病。白念珠菌普遍存在于人体的自然微生物区系中，其作为共生菌和病原菌的成功依赖于其快速适应宿主生理变化的能力。这项建议将确定表型转换在白念珠菌生物学中的作用，重点是转换在促进免疫受损宿主中不同部位的定植和感染方面的作用。表型转换是指细胞在菌落形态和基因表达方面经历可逆和可遗传的变化的表观遗传现象。在白色念珠菌中，表型转换率的增加与侵袭性生长和耐药性的增加有关，特别是在感染艾滋病毒的人中，这使得对转换的机制的理解变得至关重要(S)。这项提案中概述的实验将解决白色和不透明白色念珠菌之间的表型转换机制。白色-不透明开关在白念珠菌生物学中起着多效性的作用，指导组织特异性、毒力和生物膜的形成，然而，白色-不透明开关的分子机制直到现在才开始被阐明。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了白色-不透明转换的速度。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，因为它代表了细胞能够适应环境压力的新机制。该提案的第二个目标是利用转录因子的过度表达筛选来识别白色不透明开关的新调节因子。预计超表达文库的构建也将为该领域的许多研究人员提供有用的遗传工具。最后，该提案的第三个目标将利用RIVET(活体表达重组酶技术)建立哺乳动物宿主中白色-不透明切换的时间和空间调节。因此，综上所述，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，以及定义发生切换的体内生态位。因此，这些研究的完成将阐明白念珠菌如何利用表型转换来促进对宿主的适应，并帮助避免免疫系统的清除。公共卫生相关性：白色念珠菌是人类最常见的真菌病原体，可引起衰弱的粘膜感染和危及生命的系统性感染。我们的研究重点是白色念珠菌产生表型多样性的机制，以及这些过程如何促进哺乳动物宿主的生存和感染。这项研究还讨论了白色念珠菌是如何从无害的共生菌转变为一种可以入侵人体几乎所有器官的机会性病原体的。

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.