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: 7.56). 09/2011; 7(9):e1002224. DOI: 10.1371/journal.ppat.1002224
Source: PubMed


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.

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Available from: Christine Lehmann, Oct 04, 2015
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    • "To access the bloodstream, liver-stage merozoites must leave hepatocytes and cross both the Disse and sinusoid spaces, where they are vulnerable to be attacked by phagocytes including KCs and DCs. To avoid host cell defense mechanisms, merozoites bud from detached hepatocytes in merosomes [4, 47], which are covered with host cell-derived membranes [48]. During this process, the infected hepatocyte dies, but merozoites uptake Ca2+ and maintain low Ca2+ levels in the host cell to block the exposure of PS (phosphatidylserine) on the outer leaflet of the dying cells [4, 47]. "
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    ABSTRACT: Malaria is a mosquito-borne infectious disease of humans. It begins with a bite from an infected female Anopheles mosquito and leads to the development of the pre-erythrocytic and blood stages. Blood-stage infection is the exclusive cause of clinical symptoms of malaria. In contrast, the pre-erythrocytic stage is clinically asymptomatic and could be an excellent target for preventive therapies. Although the robust host immune responses limit the development of the liver stage, malaria parasites have also evolved strategies to suppress host defenses at the pre-erythrocytic stage. This paper reviews the immune evasion strategies of malaria parasites at the pre-erythrocytic stage, which could provide us with potential targets to design prophylactic strategies against malaria.
    Mediators of Inflammation 05/2014; 2014:362605. DOI:10.1155/2014/362605 · 3.24 Impact Factor
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    • "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. "
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    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 · 4.92 Impact Factor
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    • "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). "
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    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 · 4.97 Impact Factor
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