Conjugated linoleic acid inhibits hyphal growth in Candida albicans by modulating Ras1 cellular levels and down-regulating TEC1 expression

The polymorphic yeast Candida albicans exists in blastospore and filamentous forms. The switch from one morphological state to the other coincides with the expression of virulence factors, which makes the yeast-to-hypha transition an attractive target for the development of new antifungal agents. Because an untapped therapeutic potential resides in small molecules that hinder C. albicans filamentation, we characterized the inhibitory effect of conjugated linoleic acid (CLA) on hyphal growth and addressed its mechanism of action. CLA inhibited hyphal growth in a dose-dependent fashion, in both liquid- and solid-inducing media. The fatty acid blocked germ tube formation and impeded hyphal elongation. Global transcriptional profiling revealed that CLA downregulated the expression of hypha-specific genes and abrogated the induction of several morphogenesis regulators, including RAS1, TEC1 and UME6. CLA’s repressive effect on TEC1 expression was Ras1-dependent, but Efg1-independent. CLA treatment resulted in the delocalization of Ras1 and its degradation, resulting in the downregulation of the Ras1-cAMP-PKA signaling pathway. This study provides the biological and molecular explanations that underlie CLA’s ability to inhibit hyphal growth in C. albicans. Two-color experimental design that consistently used growth in Spider Media at 30℃ as the control. We tested the effect of high temperature as well as the effect of adding 100 mµ CLA at either low or high temperature. RNA from each replicate came from independent cultures.

多形性酵母白色念珠菌（Candida albicans）兼具芽生孢子与丝状两种形态。其从一种形态状态转换为另一种的过程与毒力因子的表达密切同步，因此酵母-菌丝形态转换成为开发新型抗真菌剂的极具吸引力的靶点。由于抑制白色念珠菌丝状生长的小分子尚存在未被发掘的治疗潜力，本研究表征了共轭亚油酸（conjugated linoleic acid，CLA）对菌丝生长的抑制作用，并阐明了其作用机制。CLA在液体及固体诱导培养基中均以剂量依赖性方式抑制菌丝生长：该脂肪酸可阻断芽管形成并阻碍菌丝伸长。全转录组分析显示，CLA下调了菌丝特异性基因的表达，并抑制了包括RAS1、TEC1及UME6在内的多种形态发生调控因子的诱导。CLA对TEC1表达的抑制作用依赖Ras1，但不依赖Efg1。CLA处理会导致Ras1的定位异常及其降解，进而下调Ras1-cAMP-PKA信号通路。本研究阐明了CLA抑制白色念珠菌菌丝生长的生物学与分子机制。本研究采用双色实验设计，以30℃下在Spider培养基（Spider Media）中的生长作为统一对照，分别测试了高温以及在低温或高温条件下添加100 μM CLA的作用。每个重复样本的RNA均来自独立培养的培养物。