The malaria digestive vacuole: its role in parasite development

疟疾寄生虫恶性疟原虫是一种单细胞微生物，具有复杂的生命周期，侵入宿主肝细胞和红细胞（RBC）。它的生命周期中有很大一部分是在红细胞（RBC）中度过的，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。红细胞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步骤。 为了支持疟疾寄生虫的动态繁殖，寄生虫将大量的RBC胞质溶胶吸收到称为消化泡（DV）的专门酸性细胞器中。这种细胞器分解红细胞胞质溶胶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被认为与植物细胞的液泡膜（一种酸性细胞内液泡）和哺乳动物细胞的溶酶体具有相似性。然而，典型的溶酶体酸性磷酸酶和糖苷酶的缺乏表明，疟原虫DV是一个专门的细胞器，最有可能进化到有效地降解血红蛋白。重要的是，DV不会在整个血液阶段的生命周期中持续存在，如在其他细胞器中所看到的，如细胞器和顶质体。一旦裂殖子寄生虫从RBC中释放，DV就被丢弃，并且一旦新的RBC侵入并且寄生虫在其内发育，DV就被重新形成。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、离子稳态以及营养和/或溶质跨膜转运。 这种复杂细胞器的基础生物学是不完整的，也很难理解，可能是由于过去的实验主要使用固定的寄生虫样本。因此，本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泡的分子和细胞过程。通过我们之前的NSERC提案，我们着手更好地表征PfMDR 1转运蛋白，并能够量化该转运蛋白的动力学。这项工作发表在几个期刊上。我们还发现了一种新的表型，当用抗疟氯喹处理寄生虫感染的红细胞时，形成了含Hz的隔室。我们完成了一个重要的目标，并将其发表在《科学报告》中。 目前的建议将集中在更好地了解含赫兹车厢时出现的寄生虫与某些抗疟药物治疗。我们将继续使用活细胞成像技术，以更好地了解寄生虫的动态原位。这将使我们能够更好地了解这些过程在真实的时间内活的寄生虫。

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.