白念珠菌灰菌细胞的菌丝生长调控机制研究

Candida albicans is an important and opportunistic fungal pathogen of humans. It has a number of morphological forms. The ability to switching among different forms is related to its pathogenesis. White-opaque switching and yeast-filamentous growth transitions are two typical phenotypic switching systems in C. albicans. Under regular inducing conditions such as the presence of serum, increased temperature, and nutrient starvation, white cells can undergo filamentation, while opaque cells do not. Based on the importance of filamentation in virulence of C. albicans, in this project, we are going to study the environmental and genetic regulatory mechanisms of opaque cell filamentation using RNA-Seq, gene deletion, and library screening assays. We are going to identify several environmental factors and key regulatory genes involved in this biological process. The study will focus on the roles of transcription factors Bcr1, War1, and Mnl1, and the related pathways in filamentation and pathogenesis. Moreover, we will study the regulatory mechanisms of opaque cell filamentation in microenvironmental adaptation and Candida-host interactions. This project will find potential antifungal targets and provide new insights into the mechanisms of pathogenesis of C. albicans and the evolution of biological complexity in fungal species as well.

白念珠菌是人体内一种重要的机会性致病真菌。该菌能以多种形态存在，不同形态间的转换能力与致病性密切相关。白菌-灰菌转换和酵母-菌丝转换是白念珠菌中两种典型的形态转换系统。在常规诱导条件下（如血清、中性pH和营养饥饿条件等），白菌细胞能形成菌丝，而灰菌细胞不能。本项目着眼于菌丝生长在白念珠菌致病性中的重要性，将利用RNA-Seq、基因敲除和文库筛选等技术研究灰菌细胞菌丝生长的环境和遗传调控机制。鉴定参与调控灰菌菌丝生长的宿主环境因子和关键的转录因子，揭示该生物学过程的调控通路。着重研究Bcr1、War1和Mnl1等转录因子及其上下游调控元件在菌丝生长和致病性中的作用机制；解析灰菌细胞菌丝生长在白念珠菌微环境适应和宿主互作中的功能。本项目将有助于提升对白念珠菌致病机理的认识和发现潜在药物靶标，也将为其它真菌中复杂生物表型的进化和调控研究提供参考。

微生物在自然环境中很少以单个种群存在，白色念珠菌作为一种重要的机会性致病真菌，广泛分布于人体口腔、胃肠道、生殖道等部位。白色念珠菌通过何种策略来适应这些富含多种微生物及压力的宿主微环境，目前对其机制研究较少。我们研究发现白色念珠菌利用其形态的可塑性对宿主微环境中乳酸菌等细菌分泌的乳酸、丁酸产生应答。乳酸菌分泌的乳酸能诱导灰菌发育成菌丝，而对白菌则没有诱导作用。白念珠菌的菌丝形成能力是其重要的毒力因子之一，菌丝态的细胞有着更强的粘附与侵入能力。进一步研究发现，环腺苷酸cAMP信号为核心的正调控途径（cAMP-PKA pathway）在乳酸菌诱导灰菌菌丝中起着主要作用。该途径RAS1(RAS signal transduction GTPase)、CDC35(Class III adenylyl cyclase)，HGC1，FLO8等基因敲除后灰菌细胞不能被乳酸菌诱导出菌丝。而BCR1（Biofilm and Cell wall Regulator）、RFG1（Repressor of Filamentous Growth）、CUP9等转录因子在此过程中起负调控的作用。经文库筛选，我们发现受BCR1调控的热激蛋白HSP90以及热激转录因子HSF1也参与调控白念珠菌细胞菌丝的生长，有趣的是，当白念珠菌受到营养饥饿压力时，热激蛋白Hsp90与Hsf1还参与调控白念珠菌同性生殖过程。进一步的实验表明营养匮乏压力可提升细胞内活性氧的产生，这些氧化物能够过载Hsf1与Hsp90介导的压力应答途径。该途径通过下游的Cwt1，Cta4调控MTLa2以及MFα基因的转录来调节同性生殖。白念珠菌巧妙的利用形态转换（white-opaque转换与酵母-菌丝形态的转换）以及有性生殖来对宿主微环境产生适应性的应答，从而提高其在宿主体内的生存能力。该研究增强了我们对白念珠菌宿主环境适应及致病机理的认识。