The malaria digestive vacuole: its role in parasite development

疟原虫恶性疟原虫是一种单细胞微生物，具有复杂的生命周期，可侵入宿主肝细胞和红细胞 (RBC)。它生命周期的很大一部分是在红细胞（RBC）中度过的，红细胞主要由血红蛋白组成，缺乏细胞核和细胞器。红细胞的入侵和随后的修饰是这种致病性致命寄生虫生存的关键步骤。 为了支持疟疾寄生虫的动态繁殖，疟原虫将大量的红细胞胞质溶胶吸收到一​​种称为消化液泡（DV）的特殊酸性细胞器中。该细胞器分解红细胞胞质的主要成分血红蛋白，为其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被认为与液泡膜（植物细胞的酸性细胞内液泡）和哺乳动物细胞的溶酶体有相似之处。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降解血红蛋白。重要的是，正如线粒体和顶质体等其他细胞器所见，DV 不会在整个血液阶段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；一旦新的红细胞侵入并且寄生虫在其中发育，DV 就会被重新形成。因此，寄生虫的 DV 执行各种专门和关键的功能，以确保寄生虫的生存，包括血红蛋白降解、氧自由基解毒、离子稳态以及营养物和/或溶质跨膜运输。 这种复杂细胞器的基础生物学不完整且知之甚少，可能是由于过去的实验主要使用固定的寄生虫样本。因此，该研究计划的长期目标是利用我们实验室现有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 提案，我们着手更好地表征 PfMDR1 转运蛋白，并能够量化该转运蛋白的动力学。这项工作发表在多种期刊上。我们还发现了一种新的表型，即当用抗疟药氯喹治疗寄生虫感染的红细胞时，就会形成含有 Hz 的区室。我们实现了一个重要目标，并将其发表在《科学报告》的工作中。 目前的提案将侧重于更好地理解用某些抗疟药治疗寄生虫时出现的含有赫兹的隔室。我们将继续使用活细胞成像技术来更好地了解原位寄生虫动态。这将使我们能够更好地实时了解活寄生虫中的这些过程。

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.