Sphingolipids as Potential Targets for Anti-Giardial Therapy

蓝氏贾第鞭毛虫是一种非侵入性寄生虫，可导致人类通过水传播感染。这 鞭毛原生动物以滋养体和包囊两种形式存在。形态上的 从包囊到滋养体的转变(激发作用)发生在胃部，而体内的因素 小肠触发滋养体向包囊(包囊)的转化。这一行动的主要目标是 建议阐明鞘磷脂在调节肌动蛋白囊化-排泄循环中的新作用。 贾第虫。众所周知，鞘磷脂在信号传导、分化和细胞凋亡中起着重要作用。 在所有真核细胞中。然而，贾第虫合成鞘脂的能力有限，并依赖于 一种用于能量生产和膜生物合成的外源鞘脂供应。我们的研究 表明贾第虫使用肌动蛋白/网状蛋白依赖的途径来输入和靶向神经酰胺，神经酰胺是主要的 神经鞘脂的前体，通向内质网/核周膜。分子分析显示，只有两个 鞘磷脂代谢基因在滋养体和包囊贾第鞭毛虫中表达差异。SPT-2 丝氨酸棕榈酰转移酶-2的mRNA主要在滋养体中表达，而GlcT-1 (神经酰胺-葡萄糖基转移酶)转录本主要在包膜细胞中表达。由于…… SPT-2基因在滋养体中上调，我们推测合成的3-酮-鞘氨酸 通过SPT和肌动蛋白聚合和内吞作用所必需的，增加了细胞内的运输 滋养体。然而，对于囊壁的生物合成，我们假设外源性神经酰胺被吸收了。 由贾第虫制成，并作为支架组装含糖神经酰胺/鞘磷脂 在GlcT-1酶(由GlcT-1基因编码)的帮助下。为了检验这些假设，我们提出了 以下目标，即目标-1：确定SPT-2和GlcT-1基因和酶是否 目的-2：确定是否转录后转录 沉默Spt-2和GlcT-1基因将中断激活-包裹循环；以及Aim-3： 确定SPT-2和GlcT-1mRNA或基因产物是否是神经酰胺内吞所必需的 和滋养体的代谢，以及囊化特异性囊泡和囊壁的合成。 包被细胞。 这些研究将提供有价值的信息，说明鞘脂在调节 心脏的生命周期，并将为未来努力开发新的治疗方法奠定基础 水传播的病原体。

Giardia lamblia is a non-invasive parasite that can cause waterborne infection in humans. This flagellated protozoan exists in two forms, i.e., the trophozoite and the cyst. The morphological transformation from cyst to trophozoite (excystation) takes place in the stomach, while factors in the small intestine trigger the transformation from trophozoite to cyst (encystation). The major goal of this proposal is to elucidate the novel role of sphingolipids in regulating the encystation-excystation cycle of Giardia. It is well known that sphingolipids play an important role in signaling, differentiation and apoptosis in all eukaryotic cells. However, Giardia has a limited ability to synthesize sphingolipids and depends on an exogenous supply of sphingolipids for energy production and membrane biosynthesis. Our studies indicate that Giardia uses actin/clathrin-dependent pathways to import and target ceramide, the major precursor of sphingolipids, to the ER/perinuclear membranes. Molecular analysis revealed that only two sphingolipid metabolic genes are differentially expressed in trophozoites and encysting Giardia. SPT-2 (serine-palmitoyl transferase-2) mRNA is expressed predominantly in trophozoites, while GlcT-1 (ceramide-glucosyl transferase) transcript is expressed predominantly in encysting cells. As a result of SPT-2 gene upregulation in trophozoites, we hypothesize that 3-keto-sphinganine, which is synthesized by SPT and required for actin polymerization and endocytosis, increases the endocytic traffic in trophozoites. For cyst wall biosynthesis, however, we hypothesize that exogenous ceramide is taken up by Giardia and used as a scaffold to assemble complex saccharide-containing ceramide/sphingolipids with the help of the GlcT-1 enzyme (encoded by the GlcT-1 gene). To test these hypotheses we propose the following aims, i.e., Aim-1: Determine whether SPT-2 and GlcT-1 genes and enzymes that are differentially regulated in excysting and encysting Giardia; Aim-2: Determine whether post-transcriptional silencing of SPT-2 and GlcT-1 genes will interrupt the excystation-encystation cycle; and Aim-3: Determine whether SPT-2 and GlcT-1 mRNA or gene products are essential for ceramide endocytosis and metabolism in trophozoites, and synthesis of encystation-specific vesicles and cyst wall in the encysting cell. These studies will yield valuable information regarding the role of sphingolipids in regulating the giardial life cycle, and will lay the foundation for future efforts to develop new therapies against this waterborne pathogen.