Article

Hostile Takeover by Plasmodium: Reorganization of Parasite and Host Cell Membranes during Liver Stage Egress

Malaria Lab I, Department of Molecular Parasitology, Bernhard Nocht Institute for Tropical Medicine, Hamburg, Germany.
PLoS Pathogens (Impact Factor: 8.06). 09/2011; 7(9):e1002224. DOI: 10.1371/journal.ppat.1002224
Source: PubMed

ABSTRACT The protozoan parasite Plasmodium is transmitted by female Anopheles mosquitoes and undergoes obligatory development within a parasitophorous vacuole in hepatocytes before it is released into the bloodstream. The transition to the blood stage was previously shown to involve the packaging of exoerythrocytic merozoites into membrane-surrounded vesicles, called merosomes, which are delivered directly into liver sinusoids. However, it was unclear whether the membrane of these merosomes was derived from the parasite membrane, the parasitophorous vacuole membrane or the host cell membrane. This knowledge is required to determine how phagocytes will be directed against merosomes. Here, we fluorescently label the candidate membranes and use live cell imaging to show that the merosome membrane derives from the host cell membrane. We also demonstrate that proteins in the host cell membrane are lost during merozoite liberation from the parasitophorous vacuole. Immediately after the breakdown of the parasitophorous vacuole membrane, the host cell mitochondria begin to degenerate and protein biosynthesis arrests. The intact host cell plasma membrane surrounding merosomes allows Plasmodium to mask itself from the host immune system and bypass the numerous Kupffer cells on its way into the bloodstream. This represents an effective strategy for evading host defenses before establishing a blood stage infection.

Download full-text

Full-text

Available from: Christine Lehmann, Aug 25, 2015
0 Followers
 · 
180 Views
  • Source
    • "Several recent publications provided increasing evidence for an inside-out egress of the malaria parasite from the erythrocyte, during which the breakdown of the PVM precedes rupture of the EM (Glushakova et al., 2010; Chandramohanadas et al., 2011; Graewe et al., 2011; Sologub et al., 2011; reviewed in Wirth and Pradel, 2012). However, the molecular mechanisms of the inside-out egress are not fully known yet. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Egress of malaria parasites from the host cell requires the concerted rupture of its enveloping membranes. Hence, we investigated the role of the plasmodial perforin-like protein PPLP2 in the egress of Plasmodium falciparum from erythrocytes. PPLP2 is expressed in blood stage schizonts and mature gametocytes. The protein localizes in vesicular structures, which in activated gametocytes discharge PPLP2 in a calcium-dependent manner. PPLP2 comprises a MACPF domain and recombinant PPLP2 has hemolytic activities towards erythrocytes. PPLP2-deficient (PPLP2(-)) merozoites show normal egress dynamics during the erythrocytic replication cycle, but activated PPLP2(-) gametocytes were unable to leave erythrocytes and stayed trapped within these cells. While the parasitophorous vacuole membrane ruptured normally, the activated PPLP2(-) gametocytes were unable to permeabilize the erythrocyte membrane and to release the erythrocyte cytoplasm. In consequence, transmission of PPLP2(-) parasites to the Anopheles vector was reduced. Pore-forming equinatoxin II rescued both PPLP2(-) gametocyte exflagellation and parasite transmission. The pore sealant Tetronic 90R4, on the other hand, caused trapping of activated wild-type gametocytes within the enveloping erythrocytes, thus mimicking the PPLP2(-) loss-of-function phenotype. We propose that the hemolytic activity of PPLP2 is essential for gametocyte egress due to permeabilization of the erythrocyte membrane and depletion of the erythrocyte cytoplasm.
    Cellular Microbiology 03/2014; 16(5). DOI:10.1111/cmi.12288 · 4.82 Impact Factor
  • Source
    • "Hypoxia-treated hepatocytes exhibited a similar increase in susceptibility to P. yoelii infection (Fig. 2B,D,F; supplementary material Fig. S1B), suggesting that the observed effect of hypoxia is not restricted to a particular Plasmodium spp. Because P. berghei liver-stage infections mature at 55-65 hours post-infection in vitro (Graewe et al., 2011), P. berghei EEF sizes were quantified at 56 hours and 65 hours post-infection to address the possibility that hypoxia could be speeding up parasite development instead of increasing the potential for parasite growth. P. berghei EEFs were larger in hypoxic cultures at 48, 56 and 65 hours post-infection (supplementary material Fig. S1F). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Homeostasis of mammalian cell function strictly depends on balancing oxygen exposure to maintain energy metabolism without producing excessive reactive oxygen species. In vivo, cells in different tissues are exposed to a wide range of oxygen concentrations, and yet in vitro models almost exclusively expose cultured cells to higher, atmospheric oxygen levels. Existing models of liver stage malaria that utilize primary human hepatocytes typically exhibit low in vitro infection efficiencies, possibly due to missing microenvironmental support signals. One cue that may influence the infection capacity of cultured human hepatocytes is the dissolved oxygen concentration. We developed a microscale human liver platform comprised of precisely patterned primary human hepatocytes and nonparenchymal cells (MPCC) to model liver stage malaria, but the oxygen concentrations are typically higher in the in vitro liver platform than anywhere along the hepatic sinusoid. Indeed, we observed that liver stage Plasmodium parasite development in vivo correlates with hepatic sinusoidal oxygen gradients. Therefore, we hypothesized that in vitro liver stage malaria infection efficiencies may improve under hypoxia. Using the infection of MPCCs with P. berghei or P. yoelii as a model, we observed that ambient hypoxia resulted in increased survival of exo-erythrocytic forms (EEFs) in hepatocytes, and improved parasite development in a subset of surviving EEFs, based on EEF size. Further, the effective cell surface oxygen tensions (pO2) experienced by the hepatocytes, as predicted by a mathematical model, were systematically perturbed by varying culture parameters like hepatocyte density and media height, uncovering an optimal cell surface pO2 to maximize the number of mature EEFs. Initial mechanistic experiments reveal that treatment of primary human hepatocytes with the hypoxia mimetic, cobalt (II) chloride, as well as a HIF-1α activator, dimethyloxalylglycine, also enhance P. berghei infection, suggesting that the effect of hypoxia on infection is mediated in part by host-dependent HIF-1α mechanisms.
    Disease Models and Mechanisms 11/2013; 7(2). DOI:10.1242/dmm.013490 · 5.54 Impact Factor
  • Source
    • "Further work is required to understand how the parasite triggers the induction of this enzyme. Finally, in vitro and in vivo studies have shown that developing parasites evade the attack of immune cells by inhibiting host cell apoptosis (Leiriao et al., 2005; van de Sand et al., 2005) and by generating merozoites that are covered by the host cell membrane (Sturm et al., 2006; Graewe et al., 2011). Interestingly, merozoite-filled merosomes budding off from infected hepatocytes inhibit the exposure of phosphatidylserine, a phagocyte ligand, on their membrane. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Innate immunity plays a central role in combating infections. However, the importance of innate immune sensors in detecting intracellular parasites, such as Plasmodium spp., has only recently emerged as a central topic in the field of host-pathogen interactions. Genetic dissection of innate immune pathways has uncovered a complex relationship between the host innate immune system and Plasmodium blood-stage parasites. In fact, recognition molecules of the innate immune system, such as toll-like receptors, might not only be implicated in host defense but also in the pathogenesis of the disease. Whether Plasmodium liver stage parasites are recognised and controlled by the host innate immune system remains to be discovered. In this review we discuss recent findings on how the host innate immune system may sense and fight the different forms of Plasmodium and how the latter may have evolved mechanisms to escape host detection and/or to manipulate the defensive reaction of the host.
    International journal for parasitology 04/2012; 42(6):557-66. DOI:10.1016/j.ijpara.2012.04.006 · 3.40 Impact Factor
Show more