The malaria digestive vacuole: its role in parasite development

恶性疟原虫是一种单细胞微生物，具有复杂的生命周期，同时入侵宿主肝细胞和红细胞(RBC)。它生命周期的很大一部分时间是在红细胞(RBC)内度过的，红细胞是一种主要由血红蛋白组成的细胞，缺乏细胞核和细胞器。RBC的入侵和随后的修饰是这种致病和致命寄生虫生存的关键一步。 为了支持疟疾寄生虫的动态繁殖，这种寄生虫将大量的红细胞胞浆转化为一种特殊的酸性细胞器，称为消化液泡(DV)。这种细胞器分解红细胞胞浆的主要成分血红蛋白，为自身提供对其发育和生长至关重要的营养物质(即氨基酸)。 DV被认为与植物细胞的液泡膜和哺乳动物细胞的溶酶体都有相似之处。然而，典型的溶酶体酸性磷酸酶和糖苷酶的缺失表明，疟原虫的DV是一种特殊的细胞器，最有可能进化为有效地降解血红蛋白。重要的是，DV并不像线粒体和质外体等其他细胞器那样在整个血液阶段的生命周期中持续存在。一旦裂殖子寄生虫从红细胞中释放出来，DV就会被丢弃，一旦新的红细胞入侵，寄生虫在体内发育，DV就会重新形成。因此，寄生虫的DV执行各种特殊和关键的功能来确保寄生虫的生存，包括血红蛋白降解、氧自由基的解毒、离子稳态以及营养物质和/或溶质的跨膜运输。 这种复杂细胞器的基本生物学还不完整，也不太清楚，这可能是因为过去的实验大多使用了固定的寄生虫样本。因此，这项研究计划的长期目标是利用我们实验室提供的现代成像技术深入了解寄生虫消化液泡的分子和细胞过程。根据我们之前的NSERC建议，我们开始更好地描述PfMDR1转运体的特征，并能够量化该转运体的动力学。这项研究发表在几种期刊上。我们还发现了一种新的表型，当被寄生虫感染的红细胞用抗疟药氯喹处理时，形成了含有赫兹的隔室。我们完成了一个重要目标，并将其发表在《科学报告》工作中。 目前的提案将侧重于更好地了解在用某些抗疟疾药物治疗寄生虫时出现的含有赫兹的间隔。我们将继续使用活细胞成像技术，以更好地了解寄生虫的原位动态。这将使我们能够更好地实时了解活体寄生虫内的这些过程。

The malaria parasite Plasmodium falciparum is a single-celled microorganism with a complex life cycle that invades both host hepatocytes and red blood cells (RBCs). It spends a great proportion of its life cycle within the red blood cell (RBC), a cell comprised mostly of hemoglobin and lacking in nuclei and organelles. The invasion and subsequent modification of the RBC is a crucial step for the survival of this pathogenic and lethal parasite. To support the dynamic multiplication of malaria parasites, the parasite takes up large amounts of RBC cytosol into a specialized acidic organelle called the digestive vacuole (DV). This organelle breaks down the RBC cytosol's primary constituent hemoglobin to provide itself with nutrients (i.e. amino acids) that are crucial for its development and growth. The DV has been thought to have similarities to both tonoplasts, an acidic intracellular vacuole of plant cells, and lysosomes of mammalian cells. However, the absence of the typical lysosomal acid phosphatase and glycosidase indicates that the DV of Plasmodium is a specialized organelle that most likely evolved to efficiently degrade hemoglobin. Importantly, the DV does not persist throughout the complete blood stage life cycle, as is seen for other organelles such as the mitochondrion and the apicoplast. The DV is discarded once the merozoite parasites are released from the RBC and is reformed once a new RBC is invaded and the parasite develops within. Consequently, the parasite's DV carries out a variety of specialized and critical functions to ensure the survival of the parasite, including hemoglobin degradation, detoxification of oxygen radicals, ion homeostasis, and nutrient and/or solute transport across its membrane. The underlying biology of this complex organelle is incomplete and poorly understood, possibly due to past experiments that mostly used fixed samples of parasites. Therefore, the long-term objective of this research program is the development of an in-depth understanding of the molecular and cellular processes of the parasite's digestive vacuole using modern imaging techniques available in our lab. With our previous NSERC proposal, we set out to better characterize the PfMDR1 transporter and were able to quantify the kinetics of this transporter. This work was published in several journals. We also discovered a new phenotype, the formation of Hz-containing compartments that form when the parasite infected RBCs are treated with the antimalarial chloroquine. We accomplished an important objective and published this in work in Scientific Reports. The present proposal will focus on a better understanding of the Hz-containing compartments that arise when parasites are treated with certain antimalarials. We will continue to use live cell imaging techniques to get a better understanding of parasite dynamics in situ. This will allow us to better understand these processes in real time within the live parasite.