DS0401 -

Identification of virulence factors mediating hepatocyte invasion in the malaria parasite – MALINV

Malaria invasion of the liver

Malaria is caused by Plasmodium parasites and begins with the inoculation of sporozoites into the host skin by infected Anopheles mosquitoes. The sporozoites rapidly migrate to the liver and actively invade hepatocytes, where they differentiate into thousands of merozoites. In this project, we propose to employ a multidisciplinary approach to investigate the role, at the cellular and molecular levels, of parasite and host cell factors involved during parasite entry.

Objectives

A potent strategy to prevent the initial liver stage infection is to interfere with host-parasite molecular interactions to prevent sporozoite entry into hepatocytes. We believe that elucidating the molecular interplay involved during Plasmodium sporozoite entry into hepatocytes is an absolute requirement towards the development of effective antimalarial strategies against the liver stages. The purpose of our proposal is to contribute filling this gap. <br /> <br />We had previously identified the tetraspanin CD81 as a critical host entry factor for P. falciparum and P. yoelii sporozoites in hepatocytes. More recently, we found that the Scavenger Receptor B1 (SRB1) mediates CD81-independent invasion of P. vivax and P. berghei sporozoites. Our most recent work allowed us to identify sporozoite proteins of the so-called 6-cys protein family as major parasite determinants of host cell invasion. Parasites lacking the 6-cys proteins P52 and P36 fail to productively invade cells, reproducing the phenotype of CD81 and/or SRB1 inhibition. Using an original genetic strategy, we identified P36 as a major parasite determinant that mediates CD81-independent entry via SRB1. For the first time, we could establish a functional link between parasite and host cell entry factors, which opens the way towards the identification of ligand-receptor interactions mediating Plasmodium sporozoite entry into hepatocytes and the identification of novel vaccine targets. <br /> <br />The aim of this proposal is to investigate the nature of the link between the sporozoite 6-cys proteins and the hepatocyte receptors SRB1 and CD81, and provide an in-depth characterization of these proteins at the molecular level.

In this project, we will combine genetic and functional assays in rodent malaria models to analyze in details the contribution of the putative ligands and receptors during host cell invasion by Plasmodium sporozoites. We will explore at the molecular level the interactions between sporozoite and host cell entry factors, and characterize the structural determinants involved. Our ultimate goal is to identify sporozoite proteins that are potential targets of neutralizing antibodies. For this purpose, we will translate the findings made in the rodent malaria models to human parasites, and analyze candidate P. falciparum and P. vivax targets using in vitro cellular models and innovative in vivo animal models.

This proposal aims at elucidating the molecular interactions resulting in sporozoite entry into hepatocytes, with the objective to identify novel vaccine targets. We should also gain information on how Plasmodium spp have evolved different strategies to infect their hosts. Until now, the molecular mechanisms of malaria sporozoite entry into hepatocytes remained elusive. We have now uncovered a role of host SRB1 in sporozoite entry, especially for the human parasite P. vivax, and identified putative parasite factors associated with host entry pathway. This breakthrough offers unique opportunities to elucidate ligand-receptor interactions involved in host cell invasion. With this project we will gain new insights into the biology of sporozoite infection and identify new parasite targets, paving the way towards the rational design of novel antimalarial strategies. We thus expect this project to generate conceptual advances with high translational potential.
In particular, we expect to gain novel insights into the function of the sporozoite 6-cys proteins, their organization in complexes and most importantly their interaction properties with host cell surface receptors. We will not only improve our understanding of the molecular mechanisms of parasite invasion during malaria liver infection, but also bring novel insights on the function of important host cell molecules. During the course of the project, we will generate a body of reagents, parasites and methods that may benefit to other researchers of the malaria research community.

By addressing the role of parasite putative ligands and host cell receptors, this project will generate a body of data and tools and improve our knowledge of the enigmatic sporozoite entry process. Beyond the fundamental aspects that we expect to uncover, this project may also contribute to antigen discovery for the development of next generation malaria vaccines. The international community has now committed itself to the eventual eradication of malaria, an ambitious goal that will be difficult to achieve with the currently available anti-malarial tools. Novel drugs will be needed, and an efficacious and affordable vaccine will likely be instrumental for successful and sustainable control of malaria transmission. A better understanding of the mechanisms of infection and the identification of optimal targets are clearly required for the rational design of next generation malaria vaccines. Efficacious malaria vaccines would have tremendous positive effects on global health, not only against P. falciparum, which continues to kill nearly half a million people every year in endemic areas, but also against P. vivax, which is widely distributed around the world and poses major challenges for malaria elimination due to persistence of the parasite in the liver of infected individuals. By providing novel insights into the molecular mechanisms of sporozoite invasion, this project will contribute to identifying and validating novel targets to be included in the vaccine development pipeline, accelerating the development of novel vaccine strategies to prevent the very first stage of the malaria infection.

Silvie O, Amino R, Hafalla JC. Tissue-specific cellular immune responses to malaria pre-erythrocytic stages. Curr Op Microbiol 2017, 40 :160-167.

Malaria is caused by Plasmodium parasites and remains a major health and socio-economic problem in developing countries. The international community has now committed itself to the eventual eradication of malaria, an ambitious goal that will be difficult to achieve without an efficacious and affordable vaccine. Malaria begins with the inoculation of sporozoites into the host skin by infected Anopheles mosquitoes. The sporozoites rapidly migrate to the liver and actively invade hepatocytes, where they differentiate into thousands of merozoites. Once released in the blood, merozoites invade and multiply inside erythrocytes, causing the malaria disease. Infection of the liver is an essential, initial and clinically silent phase of the malaria life cycle, and therefore constitutes an ideal target for a malaria vaccine.
A potent strategy to prevent the initial liver stage infection is to interfere with host-parasite molecular interactions to prevent sporozoite entry into hepatocytes. Apicomplexan parasites such as Plasmodium invade host cells using a unique mechanism that involves the sequential secretion of apical organelles, called micronemes and rhoptries, and the formation of a junction through which the parasite glides to enter the cell and form a parasitophorous vacuole where it further replicates. Proteins released from micronemes onto the parasite surface are prime candidates to interact with host cell surface receptors, triggering subsequent secretion of the rhoptry content, formation of the moving junction and commitment to productive invasion. However, until now the ligand-receptor interactions mediating Plasmodium sporozoite invasion have remained totally enigmatic.
We have previously identified the hepatocyte protein CD81 as an essential host entry factor for human-infective P. falciparum and rodent-infective P. yoelii sporozoites. CD81 acts at an early step of invasion, possibly before moving junction formation by providing signals that trigger rhoptry secretion. Importantly, P. vivax and P. berghei sporozoites can infect cells lacking CD81, indicative of alternative entry pathways depending on parasite species. Our most recent work allowed us to make two important discoveries. First, we identified a host surface protein involved in CD81-independent entry. Secondly, by employing a genetic approach, we have identified sporozoite proteins that are required for parasite entry and are key determinants of the host cell entry pathway used by the parasite. For the first time, we could establish a functional link between parasite and host cell entry factors, which are potentially involved in ligand-receptor interactions. These exciting new results open novel perspectives to elucidate the molecular interactions involved in sporozoite host cell entry during malaria liver infection.
In this project, we propose to employ a multidisciplinary approach to investigate the role, at the cellular and molecular levels, of the parasite and host cell entry factors that we have identified. We will combine genetic and functional assays in rodent malaria models to analyze in details the contribution of the putative ligands and receptors during host cell invasion by Plasmodium sporozoites. We will explore at the molecular level the interactions between sporozoite and host cell entry factors, and characterize the structural determinants involved. Our ultimate goal is to identify sporozoite proteins that are potential targets of neutralizing antibodies. For this purpose, we will translate the findings made in the rodent malaria models to human parasites, and analyze candidate P. falciparum and P. vivax targets using in vitro cellular models and innovative in vivo animal models.
By providing novel insights into the molecular mechanisms of sporozoite invasion, this project may contribute to accelerating the development of novel vaccine strategies to prevent the very first stage of the malaria infection.

Project coordinator

Monsieur Olivier Silvie (Institut National de la Santé et de la Recherche Médicale, Délégation Régionale Paris 6)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

INSERM DR Paris 6 Institut National de la Santé et de la Recherche Médicale, Délégation Régionale Paris 6

Help of the ANR 137,772 euros
Beginning and duration of the scientific project: September 2016 - 36 Months

Useful links

Explorez notre base de projets financés

 

 

ANR makes available its datasets on funded projects, click here to find more.

Sign up for the latest news:
Subscribe to our newsletter