Table_3_A Targeted Mass Spectrometric Analysis Reveals the Presence of a Reduced but Dynamic Sphingolipid Metabolic Pathway in an Ancient Protozoan, Giardia lamblia.XLS

Giardia lamblia, a single-celled eukaryote, colonizes and thrives in the small intestine of humans. Because of its compact and reduced genome, Giardia has adapted a “minimalistic” life style, as it becomes dependent on available resources of the small intestine. Because Giardia expresses fewer sphingolipid (SL) genes—and glycosphingolipids are critical for encystation—we investigated the SL metabolic cycle in this parasite. A tandem mass spectrometry (MS/MS) analysis reveals that major SLs in Giardia include sphingomyelins, sphingoid bases, ceramides, and glycosylceramides. Many of these lipids are obtained by Giardia from the growth medium, remodeled at their fatty acyl chains and end up in the spent medium. For instance, ceramide-1-phosphate, a proinflammatory molecule that is not present in the culture medium, is generated from sphingosine (abundant in the culture medium) possibly by remodeling reactions. It is then subsequently released into the spent medium. Thus, the secretion of ceramide-1-phospate and other SL derivatives by Giardia could be associated with inflammatory bowel disease observed in acute giardiasis. Additionally, we found that the levels of SLs increase in encysting Giardia and are differentially regulated throughout the encystation cycle. We propose that SL metabolism is important for this parasite and, could serve as potential targets for developing novel anti-giardial agents.

蓝氏贾第鞭毛虫（Giardia lamblia）是一种单细胞真核生物，可定植并繁衍于人类小肠内。因其基因组紧凑且简化，该寄生虫演化出了“极简”的生活方式，完全依赖小肠内可获取的营养物质生存。由于蓝氏贾第鞭毛虫的鞘脂（sphingolipid, SL）编码基因数量较少，而糖鞘脂对其包囊形成至关重要，我们针对该寄生虫的鞘脂代谢循环展开了研究。串联质谱（tandem mass spectrometry, MS/MS）分析结果显示，蓝氏贾第鞭毛虫体内的主要鞘脂类物质包括鞘磷脂、鞘氨醇碱基、神经酰胺与糖基神经酰胺。这类脂质中有许多可从培养介质中摄取，并在其脂肪酰基链处发生结构重塑，最终被排出至废弃培养基中。例如，培养介质中本不存在的促炎分子1-磷酸神经酰胺，可由培养基中丰度较高的鞘氨醇通过重塑反应生成，随后被释放至废弃培养基内。由此可见，蓝氏贾第鞭毛虫分泌的1-磷酸神经酰胺与其他鞘脂衍生物，可能与急性贾第虫病患者观察到的炎症性肠病存在关联。此外，我们发现正在进行包囊形成的贾第鞭毛虫体内鞘脂水平有所上升，且在整个包囊形成周期中呈现差异调控模式。我们据此提出，鞘脂代谢对该寄生虫至关重要，或可作为开发新型抗贾第虫剂的潜在靶点。