Browsing by Subject "Plasmodium"

Now showing 1 - 10 of 15
  • Thumbnail Image
    Item
    Apicoplast Dynamics During Plasmodium Cell Cycle
    (Frontiers Media, 2022-04-29) Elaagip, Arwa; Absalon, Sabrina; Florentin, Anat; Pharmacology and Toxicology, School of Medicine
    The deadly malaria parasite, Plasmodium falciparum, contains a unique subcellular organelle termed the apicoplast, which is a clinically-proven antimalarial drug target. The apicoplast is a plastid with essential metabolic functions that evolved via secondary endosymbiosis. As an ancient endosymbiont, the apicoplast retained its own genome and it must be inherited by daughter cells during cell division. During the asexual replication of P. falciparum inside human red blood cells, both the parasite, and the apicoplast inside it, undergo massive morphological changes, including DNA replication and division. The apicoplast is an integral part of the cell and thus its development is tightly synchronized with the cell cycle. At the same time, certain aspects of its dynamics are independent of nuclear division, representing a degree of autonomy in organelle biogenesis. Here, we review the different aspects of organelle dynamics during P. falciparum intraerythrocytic replication, summarize our current understanding of these processes, and describe the many open questions in this area of parasite basic cell biology.
  • Thumbnail Image
    Item
    Bromodomains in Protozoan Parasites: Evolution, Function, and Opportunities for Drug Development
    (American Society for Microbiology, 2017-01-11) Jeffers, Victoria; Yang, Chunlin; Huang, Sherri; Sullivan, William J., Jr.; Pharmacology and Toxicology, School of Medicine
    Parasitic infections remain one of the most pressing global health concerns of our day, affecting billions of people and producing unsustainable economic burdens. The rise of drug-resistant parasites has created an urgent need to study their biology in hopes of uncovering new potential drug targets. It has been established that disrupting gene expression by interfering with lysine acetylation is detrimental to survival of apicomplexan (Toxoplasma gondii and Plasmodium spp.) and kinetoplastid (Leishmania spp. and Trypanosoma spp.) parasites. As "readers" of lysine acetylation, bromodomain proteins have emerged as key gene expression regulators and a promising new class of drug target. Here we review recent studies that demonstrate the essential roles played by bromodomain-containing proteins in parasite viability, invasion, and stage switching and present work showing the efficacy of bromodomain inhibitors as novel antiparasitic agents. In addition, we performed a phylogenetic analysis of bromodomain proteins in representative pathogens, some of which possess unique features that may be specific to parasite processes and useful in future drug development.
  • Thumbnail Image
    Item
    Characterization of Plasmodium Atg3-Atg8 Interaction Inhibitors Identifies Novel Alternative Mechanisms of Action in Toxoplasma gondii
    (American Society for Microbiology, 2018-01-25) Varberg, Joseph M.; LaFavers, Kaice A.; Arrizabalaga, Gustavo; Sullivan, William J., Jr.; Pharmacology and Toxicology, School of Medicine
    Protozoan parasites, including the apicomplexan pathogens Plasmodium falciparum (which causes malaria) and Toxoplasma gondii (which causes toxoplasmosis), infect millions of people worldwide and represent major human disease burdens. Despite their prevalence, therapeutic strategies to treat infections caused by these parasites remain limited and are threatened by the emergence of drug resistance, highlighting the need for the identification of novel drug targets. Recently, homologues of the core autophagy proteins, including Atg8 and Atg3, were identified in many protozoan parasites. Importantly, components of the Atg8 conjugation system that facilitate the lipidation of Atg8 are required for both canonical and parasite-specific functions and are essential for parasite viability. Structural characterization of the P. falciparum Atg3-Atg8 (PfAtg3-Atg8) interaction has led to the identification of compounds that block this interaction. Additionally, many of these compounds inhibit P. falciparum growth in vitro, demonstrating the viability of this pathway as a drug target. Given the essential role of the Atg8 lipidation pathway in Toxoplasma, we sought to determine whether three PfAtg3-Atg8 interaction inhibitors identified in the Medicines for Malaria Venture Malaria Box exerted a similar inhibitory effect in Toxoplasma While all three inhibitors blocked Toxoplasma replication in vitro at submicromolar concentrations, they did not inhibit T. gondii Atg8 (TgAtg8) lipidation. Rather, high concentrations of two of these compounds induced TgAtg8 lipidation and fragmentation of the parasite mitochondrion, similar to the effects seen following starvation and monensin-induced autophagy. Additionally, we report that one of the PfAtg3-Atg8 interaction inhibitors induces Toxoplasma egress and provide evidence that this is mediated by an increase in intracellular calcium in response to drug treatment.
  • Thumbnail Image
    Item
    An ensemble of specifically targeted proteins stabilizes cortical microtubules in the human parasite Toxoplasma gondii
    (American Society for Cell Biology, 2016-02-01) Liu, Jun; He, Yudou; Benmerzouga, Imaan; Sullivan, William J., Jr.; Morrissette, Naomi S.; Murray, John M.; Hu, Ke; Department of Pharmacology and Toxicology, IU School of Medicine
    Although all microtubules within a single cell are polymerized from virtually identical subunits, different microtubule populations carry out specialized and diverse functions, including directional transport, force generation, and cellular morphogenesis. Functional differentiation requires specific targeting of associated proteins to subsets or even subregions of these polymers. The cytoskeleton of Toxoplasma gondii, an important human parasite, contains at least five distinct tubulin-based structures. In this work, we define the differential localization of proteins along the cortical microtubules of T. gondii, established during daughter biogenesis and regulated by protein expression and exchange. These proteins distinguish cortical from mitotic spindle microtubules, even though the assembly of these subsets is contemporaneous during cell division. Finally, proteins associated with cortical microtubules collectively protect the stability of the polymers with a remarkable degree of functional redundancy.
  • Thumbnail Image
    Item
    Expansion Microscopy Reveals Plasmodium falciparum Blood-Stage Parasites Undergo Anaphase with A Chromatin Bridge in the Absence of Mini-Chromosome Maintenance Complex Binding Protein
    (MDPI, 2021-11) Liffner, Benjamin; Absalon, Sabrina; Pharmacology and Toxicology, School of Medicine
    The malaria parasite Plasmodium falciparum undergoes closed mitosis, which occurs within an intact nuclear envelope, and differs significantly from its human host. Mitosis is underpinned by the dynamics of microtubules and the nuclear envelope. To date, our ability to study P. falciparum mitosis by microscopy has been hindered by the small size of the P. falciparum nuclei. Ultrastructure expansion microscopy (U-ExM) has recently been developed for P. falciparum, allowing the visualization of mitosis at the individual nucleus level. Using U-ExM, three intranuclear microtubule structures are observed: hemispindles, mitotic spindles, and interpolar spindles. A previous study demonstrated that the mini-chromosome maintenance complex binding-protein (MCMBP) depletion caused abnormal nuclear morphology and microtubule defects. To investigate the role of microtubules following MCMBP depletion and study the nuclear envelope in these parasites, we developed the first nuclear stain enabled by U-ExM in P. falciparum. MCMBP-deficient parasites show aberrant hemispindles and mitotic spindles. Moreover, anaphase chromatin bridges and individual nuclei containing multiple microtubule structures were observed following MCMBP knockdown. Collectively, this study refines our understanding of MCMBP-deficient parasites and highlights the utility of U-ExM coupled with a nuclear envelope stain for studying mitosis in P. falciparum.
  • Thumbnail Image
    Item
    The gut microbiome, immunity, and Plasmodium severity
    (Elsevier, 2020-12) Waide, Morgan L.; Schmidt, Nathan W.; Pediatrics, School of Medicine
    Malaria continues to pose a severe threat to over half of the world's population each year. With no long-term, effective vaccine available and a growing resistance to antimalarials, there is a need for innovative methods of Plasmodium treatment. Recent evidence has pointed to a role of the composition of the gut microbiota in the severity of Plasmodium infection in both animal models and human studies. Further evidence has shown that the gut microbiota influences the adaptive immune response of the host, the arm of the immune system necessary for Plasmodium clearance, sustained Plasmodium immunity, and vaccine efficacy. Together, this illustrates the future potential of gut microbiota modulation as a novel method of preventing severe malaria.
  • Thumbnail Image
    Item
    Gut Microbiota Composition Modulates the Magnitude and Quality of Germinal Centers during Plasmodium Infections
    (Cell Press, 2020-12-15) Waide, Morgan L.; Polidoro, Rafael; Powell, Whitney L.; Denny, Joshua E.; Kos, Justin; Tieri, David A.; Watson, Corey T.; Schmidt, Nathan W.; Pediatrics, School of Medicine
    Gut microbiota composition is associated with human and rodent Plasmodium infections, yet the mechanism by which gut microbiota affects the severity of malaria remains unknown. Humoral immunity is critical in mediating the clearance of Plasmodium blood stage infections, prompting the hypothesis that mice with gut microbiota-dependent decreases in parasite burden exhibit better germinal center (GC) responses. In support of this hypothesis, mice with a low parasite burden exhibit increases in GC B cell numbers and parasite-specific antibody titers, as well as better maintenance of GC structures and a more targeted, qualitatively different antibody response. This enhanced humoral immunity affects memory, as mice with a low parasite burden exhibit robust protection against challenge with a heterologous, lethal Plasmodium species. These results demonstrate that gut microbiota composition influences the biology of spleen GCs as well as the titer and repertoire of parasite-specific antibodies, identifying potential approaches to develop optimal treatments for malaria.
  • Thumbnail Image
    Item
    Hypertension Increases Susceptibility to Experimental Malaria in Mice
    (Oxford University Press, 2024-02-28) Kandalgaonkar, Mrunmayee R.; Yeoh, Beng San; Joe, Bina; Schmidt, Nathan W.; Vijay-Kumar, Matam; Saha, Piu; Pediatrics, School of Medicine
    Global prevalence of hypertension is on the rise, burdening healthcare, especially in developing countries where infectious diseases, such as malaria, are also rampant. Whether hypertension could predispose or increase susceptibility to malaria, however, has not been extensively explored. Previously, we reported that hypertension is associated with abnormal red blood cell (RBC) physiology and anemia. Since RBC are target host cells for malarial parasite, Plasmodium, we hypothesized that hypertensive patients with abnormal RBC physiology are at greater risk or susceptibility to Plasmodium infection. To test this hypothesis, normotensive (BPN/3J) and hypertensive (BPH/2J) mice were characterized for their RBC physiology and subsequently infected with Plasmodium yoelii (P. yoelii), a murine-specific non-lethal strain. When compared to BPN mice, BPH mice displayed microcytic anemia with RBC highly resistant to osmotic hemolysis. Further, BPH RBC exhibited greater membrane rigidity and an altered lipid composition, as evidenced by higher levels of phospholipids and saturated fatty acid, such as stearate (C18:0), along with lower levels of polyunsaturated fatty acid like arachidonate (C20:4). Moreover, BPH mice had significantly greater circulating Ter119+ CD71+ reticulocytes, or immature RBC, prone to P. yoelii infection. Upon infection with P. yoelii, BPH mice experienced significant body weight loss accompanied by sustained parasitemia, indices of anemia, and substantial increase in systemic pro-inflammatory mediators, compared to BPN mice, indicating that BPH mice were incompetent to clear P. yoelii infection. Collectively, these data demonstrate that aberrant RBC physiology observed in hypertensive BPH mice contributes to an increased susceptibility to P. yoelii infection and malaria-associated pathology.
  • Thumbnail Image
    Item
  • Thumbnail Image
    Item
    Inhibiting the Plasmodium eIF2α Kinase PK4 Prevents Artemisinin-Induced Latency
    (Elsevier, 2017-12) Zhang, Min; Gallego-Delgado, Julio; Fernandez-Arias, Cristina; Waters, Norman C.; Rodriguez, Ana; Tsu, Moriya; Wek, Ronald C.; Nussenzweig, Victor; Sullivan, William J., Jr.; Pharmacology and Toxicology, School of Medicine
    Artemisinin and its derivatives (ARTs) are frontline antimalarial drugs. However, ART monotherapy is associated with a high frequency of recrudescent infection, resulting in treatment failure. A subset of parasites is thought to undergo ART-induced latency, but the mechanisms remain unknown. Here, we report that ART treatment results in phosphorylation of the parasite eukaryotic initiation factor-2α (eIF2α), leading to repression of general translation and latency induction. Enhanced phosphorylated eIF2α correlates with high rates of recrudescence following ART, and inhibiting eIF2α dephosphorylation renders parasites less sensitive to ART treatment. ART-induced eIF2α phosphorylation is mediated by the Plasmodium eIF2α kinase, PK4. Overexpression of a PK4 dominant-negative or pharmacological inhibition of PK4 blocks parasites from entering latency and abolishes recrudescence after ART treatment of infected mice. These results show that translational control underlies ART-induced latency and that interference with this stress response may resolve the clinical problem of recrudescent infection.