Peptides derived from Plasmodium falciparum leucine-rich repeat 1 bind to serine/threonine phosphatase type 1 and inhibit parasite growth in vitro.

International audienceThe biogenesis of protein phosphatase 1 (PP1) holoenzyme in eukaryotes requires diverse regulatory subunit proteins (RSPs) that bind to the highly conserved PP1 catalytic subunit (PP1c) and direct its spatiotemporal activity as well as its specificity. Several studies demonstrated that most RSPs share a canonical common binding motif, the RVXF motif, which is present in ~85% of RSPs and is considered as the main contributor for the interaction to PP1c.1 In Plasmodium falciparum (Pf), our earlier studies revealed that leucine-rich repeat 1 (LRR1), one of the major RSPs of PfPP1 and an ortholog of human and yeast Sds22, lacks the RVXF motif. The amino acids sequence of PfLRR1 exhibits nine leucine-rich repeats (LRRs) and a hydrophobic region at the C-terminal end, known as the LRR cap motif.2 In this work, we identified the PP1-binding peptides of PfLRR1 and examined their capacity to affect Pf growth

Etudes épigénétiques des stades pré-érythrocytaires de plasmodium falciparum

Epigenetic mechanisms control key processes during Plasmodium falciparum blood stage development such as antigenic variation, malaria pathogenesis and sexual commitment. However, the epigenetic landscape has not been reported for the sporozoites stage. To characterize epigenetic regulation in sporozoites, we tested the major epigenetic regulators P. falciparum Heterochromatin Protein 1 (PfHP1) and the histone lysine methyltransferases (PfSET6 and PfSET7) in P. falciparum sporozoites. I obtained a reliable genome-wide occupancy data for repressive heterochromatin and active euchromatin marks. Notably, I discovered an unprecedented stage specific mechanism of silencing, which represses several hundreds of genes, encoding parasite surface exported proteins. This is based on an expansion of facultative heterochromatin boundaries in sporozoites. Moreover, I demonstrate that a single member of the polymorphic var gene family, encoding the blood stage virulence factor PfEMP1, is expressed at the surface of sporozoites. This is in contrast to blood stages where PfEMP1 is transported to the erythrocyte surface participating in cytoadhesion. Overall, my findings rise new biological questions including what are the factors that regulate heterochromatin boundaries and what is the function of a virulence-associated surface antigen in sporozoites stage. My findings point to a putative function of this adhesion molecule in sporozoites migration. Moreover, the expression of a highly polymporphic and strain-specific antigen on the surface of sporozoites might provide a molecular explanation for the strain-specific protective immune response induced by attenuated sporozoites.L'épigénétique joue un rôle majeur dans le développement érythrocytaire de Plasmodium falciparum, tels que variation antigénique, pathogenèse, différenciation sexuée. Jusqu'à présent, ces éléments n'ont jamais été décrits chez les sporozoïtes. Pour caractériser la régulation épigénétique au niveau des sporozoïtes de P. falciparum, nous avons étudié les principaux régulateurs épigénétiques PfHP1 (P. falciparum hétérochromatine Protein 1) ainsi que PfSET6 et PfSET7 (méthyltransférases histone lysine). J'ai établi une cartographie génomique des marques épigénétiques répressives associées à l'hétérochromatine, et actives associées à l'euchromatine. J'ai identifié un nouveau mécanisme stade-spécifique de contrôle de l'expression génique, qui réprimés plusieurs gènes codant pour des protéines exportées. Ce mécanisme repose sur une expansion d'hétérochromatine. De plus, je démontre qu'un membre de la famille des gènes var, qui code pour le facteur de virulence PfEMP1 des stades sanguins, est exprimé à la surface des sporozoïtes. Cette localisation contraste avec les stades sanguins, où PfEMP1 est transporté à la surface des érythrocytes et participe à cytoadhérence. L'ensemble de ces résultats ouvre de nouvelles questions biologiques: quels sont les facteurs qui régulent la formation d'hétérochromatine chez les sporozoïtes? Quelle est la fonction de PfEMP1 sur la surface d'un sporozoïte? Mes conclusions indiquent un rôle putatif de PfEMP1 lors de la migration des sporozoïtes. En outre, l'expression, à la surface du sporozoïte, d'un antigène polymorphique et spécifique de souche pourrait expliquer la réponse immunitaire souche-spécifique, induite par les sporozoïtes atténués

In Vitro Analysis of the Interaction between Atovaquone and Proguanil against Liver Stage Malaria Parasites

International audienceThe interaction between atovaquone and proguanil has never been studied against liver stage malaria, which is the main target of this drug combination when used for chemoprevention. Using human hepatocytes lacking cytochrome P450 activity, and thus avoiding proguanil metabolizing into potent cycloguanil, we show in vitro that the atovaquone-proguanil combination synergistically inhibits the growth of rodent Plasmodium yoelii parasites. These results provide a pharmacological basis for the high efficacy of atovaquone-proguanil used as malaria chemoprevention

A Specific PfEMP1 Is Expressed in P. falciparum Sporozoites and Plays a Role in Hepatocyte Infection

Contains fulltext : 190128.pdf (publisher's version ) (Open Access

Original 2-(3-Alkoxy-1H-pyrazol-1-yl)pyrimidine Derivatives as Inhibitors of Human Dihydroorotate Dehydrogenase (DHODH)

International audienceFrom a research program aimed at the design of new chemical entities followed by extensive screening on various models of infectious diseases, an original series of 2-(3-alkoxy-1H-pyrazol-1-yl)pyrimidines endowed with notable antiviral properties were found. Using a whole cell measles virus replication assay, we describe here some aspects of the iterative process that, from 2-(4-benzyl-3-ethoxy-5-methyl-1H-pyrazol-1-yl)pyrimidine, led to 2-(4-(2,6-difluorophenoxy)-3-isopropoxy-5-methyl-1H-pyrazol-1-yl)-5-ethylpyrimidine and a 4000-fold improvement of antiviral activity with a subnanomolar level of inhibition. Moreover, recent precedents in the literature describing antiviral derivatives acting at the level of the de novo pyrimidine biosynthetic pathway led us to determine that the mode of action of this series is based on the inhibition of the cellular dihydroorotate dehydrogenase (DHODH), the fourth enzyme of this pathway. Biochemical studies with recombinant human DHODH led us to measure IC50 as low as 13 nM for the best example of this original series when using 2,3-dimethoxy-5-methyl-6-(3-methyl-2-butenyl)-1,4-benzoquinone (coenzyme Q1) as a surrogate for coenzyme Q10, the cofactor of this enzyme

Malaria blood stage infection suppresses liver stage infection via host-induced interferons but not hepcidin

Abstract Malaria-causing Plasmodium parasites first replicate as liver stages (LS), which then seed symptomatic blood stage (BS) infection. Emerging evidence suggests that these stages impact each other via perturbation of host responses, and this influences the outcome of natural infection. We sought to understand whether the parasite stage interplay would affect live-attenuated whole parasite vaccination, since the efficacy of whole parasite vaccines strongly correlates with their extend of development in the liver. We thus investigated the impact of BS infection on LS development of genetically attenuated and wildtype parasites in female rodent malaria models and observed that for both, LS infection suffered severe suppression during concurrent BS infection. Strikingly and in contrast to previously published studies, we find that the BS-induced iron-regulating hormone hepcidin is not mediating suppression of LS development. Instead, we demonstrate that BS-induced host interferons are the main mediators of LS developmental suppression. The type of interferon involved depended on the BS-causing parasite species. Our study provides important mechanistic insights into the BS-mediated suppression of LS development. This has direct implications for understanding the outcomes of live-attenuated Plasmodium parasite vaccination in malaria-endemic areas and might impact the epidemiology of natural malaria infection

Plasmodium falciparum full life cycle and Plasmodium ovale liver stages in humanized mice.

International audienceExperimental studies of Plasmodium parasites that infect humans are restricted by their host specificity. Humanized mice offer a means to overcome this and further provide the opportunity to observe the parasites in vivo. Here we improve on previous protocols to achieve efficient double engraftment of TK-NOG mice by human primary hepatocytes and red blood cells. Thus, we obtain the complete hepatic development of P. falciparum, the transition to the erythrocytic stages, their subsequent multiplication, and the appearance of mature gametocytes over an extended period of observation. Furthermore, using sporozoites derived from two P. ovale-infected patients, we show that human hepatocytes engrafted in TK-NOG mice sustain maturation of the liver stages, and the presence of late-developing schizonts indicate the eventual activation of quiescent parasites. Thus, TK-NOG mice are highly suited for in vivo observations on the Plasmodium species of humans