Jiangsu Key Laboratory for Microbes and Functional Genomics, College of Life Sciences, Nanjing Normal University, Nanjing, PR China.
The Key Laboratory of Biotechnology for Medicinal Plants of Jiangsu Province and School of Life Science, Jiangsu Normal University, Xuzhou, PR China.
Cell Microbiol. 2019 Dec;21(12):e13092. doi: 10.1111/cmi.13092. Epub 2019 Aug 14.
Previous studies identified that the budding yeast Saccharomyces cerevisiae have two sphingolipid synthesis-related proteins, Orm1p and Orm2p, that negatively regulate the activities of SPT, which is a key rate-limiting enzyme in sphingolipid synthesis. However, little is known about whether sphingolipids in the cell membrane, which are closely related to ergosterols, could affect the efficacy of azole drugs, which target to the ergosterol biosynthesis. In this study, through genome-wide homologue search analysis, we found that the Aspergillus fumigatus genome only contains one Orm homologue, referred to as OrmA for which the protein expression could be induced by azole antifungals in a dose-dependent manner. Deletion of ormA caused hypersensitivity to azoles, and adding the sphingolipid synthesis inhibitor myriocin rescued the azole susceptibility induced by lack of ormA. In contrast, overexpression of OrmA resulted in azole resistance, indicating that OrmA is a positive azole-response regulator. Further mechanism analysis verified that OrmA is related to drug susceptibility by affecting endoplasmic reticulum stress responses in an unfolded protein response pathway-HacA-dependent manner. Lack of ormA led to an abnormal profile of sphingolipid ceramide components accompanied by hypersensitivity to low temperatures. Furthermore, deletion of OrmA significantly reduced virulence in an immunosuppressed mouse model. The findings in this study collectively suggest that the sphingolipid metabolism pathway in A. fumigatus plays a critical role in azole susceptibility and fungal virulence.
先前的研究表明，酿酒酵母（Saccharomyces cerevisiae）有两种与鞘脂合成相关的蛋白，Orm1p 和 Orm2p，它们负调控 SPT 的活性，SPT 是鞘脂合成的关键限速酶。然而，人们对细胞膜中的鞘脂（与麦角固醇密切相关）是否会影响唑类药物的疗效知之甚少，唑类药物是针对麦角固醇生物合成的。在这项研究中，通过全基因组同源物搜索分析，我们发现烟曲霉（Aspergillus fumigatus）基因组只含有一个 Orm 同源物，称为 OrmA，唑类抗真菌药物可以以剂量依赖的方式诱导其蛋白表达。ormA 的缺失导致对唑类药物的敏感性增加，而添加鞘脂合成抑制剂 myriocin 可挽救因缺乏 ormA 而引起的唑类药物敏感性。相比之下，OrmA 的过表达导致唑类药物耐药，表明 OrmA 是一个正向唑类药物反应调节剂。进一步的机制分析证实，OrmA 通过影响未折叠蛋白反应途径中的内质网应激反应-HacA 依赖性方式与药物敏感性有关。缺乏 ormA 会导致鞘脂神经酰胺成分谱异常，并对低温敏感。此外，ormA 的缺失显著降低了免疫抑制小鼠模型中的毒力。本研究的结果表明，烟曲霉中的鞘脂代谢途径在唑类药物敏感性和真菌毒力中起着关键作用。
