Biology subjects

Janse, C. J.

Publications and source records attributed to Janse, C. J..

11 recordsLinked to original sources

bioRxiv2026

Bradykinin Contributes to Vasogenic Edema in Murine Experimental Cerebral Malaria

Cerebral malaria (CM) due to Plasmodium falciparum (Pf) infection is a major cause of death in African children. Bradykinin (BK) is a mediator of vasogenic edema. It could contribute to the pathogenesis of central nervous system malaria in Kenyan children and P. berghei ANKA (PbA) infected C57BL/6J mice with experimental cerebral malaria. Cleaved plasma high molecular weight kininogen (cHK) is a marker for prior BK release. 40% of children with central nervous system malaria had plasma cHK versus 18% of children with uncomplicated malaria. Wild-type PbA-infected mice had circulating plasma cHK, elevated BK levels, and reduced HK and prekallikrein levels. HK null (Kng1-/-), combined BK B1 and B2 receptor null (Bdkrb1-/- / Bdkrb2-/-), BK B2 (Bdkrb2-/-) or BK B1 (Bdkrb1-/-) receptor null mice were protected from neurologic deterioration and brain edema compared to wild-type mice. F12-/-mice were not protected from neurological deterioration. Prekallikrein null (Klkb1-/-), prolylcarboxypeptidase hypomorphs (Prcpgt/gt), and brain endothelial cell conditional knockout of PRCP (Prcpfl/fl Cre) mice had reduced neurologic deterioration and brain edema. Adjuvant plasma kallikrein inhibition combined with artesunate treatment of PbA-infected mice reversed neurologic deterioration and brain edema and prolonged survival relative to artesunate alone. BK-induced vasogenic edema contributes to human and murine CM.

pathology↗

bioRxiv2026

Essential function reflected in the phylodynamics of a multigene family: the pir genes of malaria parasites

The genomes of malaria parasites (Plasmodium spp.) encode many gene families, which are intimately associated with host interactions and disease in these important pathogens. The largest malaria gene family is the Plasmodium interspersed repeat (pir) genes, present in rodent, primate and most human malaria parasites, which are suggested to have originated from one highly conserved gene, which we call pirC1. The precise function(s) of pir is unknown but to determine their potentially multifarious roles we must understand the evolutionary dynamics of pir repertoire to discriminate among the many genes. Here we estimate the global phylogeny for pir genes in 14 Plasmodium species and one Hepatocystis species. We reveal that pirC1 is not the common ancestor but is one of several orthologous genes conserved in multiple species amidst the rapid turnover of species-specific paralogs. We show that the PIRC1 protein is nonetheless essential for blood stage growth of P. berghei, P. chabaudi and P. knowlesi, as parasites lacking the pirC1 gene could not be generated or had severely reduced growth rates. As this effect was observed both in vivo and in vitro, the role of pirC1 is not related to host immune interaction. Rather, P. berghei and P. knowlesi PIRC1 are secreted from the parasite, pointing to a role in parasite interaction with the host cell or nutrient uptake by blood stages. The phylodynamics of pir genes indicate that old orthologs, like pirC1, and younger within-species paralogs could have fundamentally different roles, and emphasize the need to distinguish between them in future. This study is the first to provide evidence for the existence of an essential pir gene and provides a robust rationale for further experimental approaches to pir gene functions. SIGNFICANCEThe genomes of malaria parasites (Plasmodium) contain many different gene families, of which the pir family is the largest, with more than 1000 members in some species. The PIR proteins are likely important for parasite fitness but their precise functions remain unknown - roles in adherence of infected red blood cells to blood vessels, virulence and immune evasion of have been suggested. How, and why, this highly diverse gene family evolved is a significant question both for understanding malaria physiology and pathogenesis. Here we present a comprehensive pir phylogeny, identifying the origins of gene diversity during Plasmodium evolution and a select group of highly conserved genes. We show that one conserved pir gene (pirC1) encodes a protein that is essential for optimal growth of multiple malaria parasites during the asexual blood stage, both in the host and in vitro. This indicates that pirC1 function relates to interaction with the host cell or nutrient acquisition, and not to immune evasion or sequestration, (although this might still be the function of other pir genes). This study provides a robust rationale for the hitherto baffling diversity of pir genes, and shows why it is important to distinguish old orthologs from young paralogs in future studies on pir gene function.

microbiology↗

bioRxiv2024

Erythrocyte membrane protein 3 (EMAP3) is exposed on the surface of the Plasmodium berghei infected red blood cell

The human malaria parasite Plasmodium falciparum invades red blood cells (RBC) and exports parasite proteins to transform the host cell for its survival. These exported proteins facilitate uptake of nutrients and cytoadherence of the infected RBC (iRBC) to endothelial cells of small blood vessels, thus protecting the iRBC from splenic clearance. The parasite protein PfEMP1 and the host protein CD36 play a major role in P. falciparum iRBC cytoadherence. The murine parasite Plasmodium berghei is a widely used experimental model that combines high genetic tractability with access to in vivo studies. P. berghei iRBC also sequesters in small blood vessels, mediated by binding to CD36. However, the parasite proteins binding to CD36 are unknown and only very few parasite proteins, including EMAP1 and EMAP2, have been identified that are present at the iRBC membrane. We have identified a new protein named EMAP3 and demonstrated its export to the iRBC membrane where it interacts with EMAP1, with only EMAP3 exposed on the outer surface of the iRBC. Parasites lacking EMAP3 display no significant reduction in growth or sequestration, indicating that EMAP3 is not the major CD36-binding protein. The outer-surface location of EMAP3 offers a new scaffold for displaying P. falciparum proteins on the surface of the P. berghei iRBC, providing a platform to screen in vivo putative inhibitors of P. falciparum cytoadherence.

microbiology↗

bioRxiv2023

Vaccination by single dose sporozoite injection of blood stage attenuated malaria parasites

An efficient malaria vaccine remains elusive. As an alternative to malaria subunit vaccines, vaccination approaches are currently explored using live Plasmodium parasites, either attenuated mosquito-derived sporozoites or attenuated blood stage parasites. Both approaches would profit from the availability of attenuated and avirulent parasites with a reduced blood stage multiplication rate. Ideally, such slow growing parasites would proceed normally through the mosquito but cause a self-limiting infection upon transmission. Here we screened gene-deletion mutants of the rodent parasite P. berghei and the human parasite P. falciparum for slow growth. In addition, we tested the P. berghei mutants for avirulence in mice and self-resolving blood stage infections, while preserving sporozoite formation and liver infection. Targeting fifty genes yielded seventeen P. berghei gene-deletion mutants with two mutants causing self-clearing infections in mice while retaining full transmissibility through mosquitoes. For those, infection of mice by a low number of blood stages, infected-mosquito bites or by single injection of sporozoites led to protection from disease after challenge with wild type sporozoites. Two of six generated P. falciparum gene-deletion mutants showed a slow growth rate. Slow growing, avirulent P. falciparum mutants will constitute valuable tools to inform on the induction of immune responses and aid in developing new as well as safeguarding existing attenuated parasite vaccines.

cell biology↗

bioRxiv2022

Downregulation of the secreted protein with an altered thrombospondin repeat (SPATR) impacts the infectivity of malaria sporozoites

The identification of surface proteins of the sporozoite stage of malaria parasites important for sporozoite infectivity could aid in the improvement of the efficacy of vaccines targeting pre-erythrocytic stages. Thus, we set out to disclose the role of the secreted protein with an altered thrombospondin repeat (SPATR), which is highly expressed in sporozoites. Previous studies showed an essential function in blood stages, while no role was detected in sporozoites despite high expression. To achieve downregulation of expression in sporozoites while maintaining blood stage expression, a promoter swap approach was used to generate a mutant where the Plasmodium berghei spatr gene was placed under transcriptional control of the hado gene promoter. Downregulation of expression in oocysts and sporozoites resulted in formation of sporozoites with impaired motility, strongly reduced capacity to invade salivary glands, and decreased infectivity to mice. In conclusion, we revealed a new role for SPATR in sporozoite infectivity, highlighting the importance to use complementary methods in studies on sporozoite biology.

microbiology↗

bioRxiv2021

Malaria parasite evades mosquito immunity by glutaminyl cyclase mediated protein modification

Glutaminyl cyclase (QC) modifies N-terminal glutamine or glutamic acid residues of target proteins into cyclic pyroglutamic acid (pGlu). Here, we report the biochemical and functional analysis of Plasmodium QC. We show that Plasmodium sporozoites of QC-null mutants are recognized by the mosquito immune system and melanized when they reach the hemocoel. Sporozoite numbers in salivary glands are also reduced in mosquitoes infected with QC-null or QC catalytically-dead mutants. This phenotype can be rescued by genetic complementation or by disrupting mosquito hemocytes or melanization immune responses. Mutation of a single QC-target glutamine of the major sporozoite surface protein (CSP) also results in immune recognition of sporozoites. These findings reveal QC-mediated post-translational modification of surface proteins as a major mechanism of mosquito immune evasion by Plasmodium sporozoites.

microbiology↗

bioRxiv2021

Suppression of Plasmodium MIF-CD74 Signaling Protects Against Severe Malaria

Malaria begins when mosquito-borne Plasmodium sporozoites invade hepatocytes and usurp host pathways to support the differentiation and multiplication of erythrocyte-infective merozoite progeny. The deadliest complication of infection, cerebral malaria, accounts for the majority of malarial fatalities. Although our understanding of the cellular and molecular mechanisms underlying the pathology remains incomplete, recent studies support the contribution of systemic and neuroinflammation as the cause of cerebral edema and blood-brain barrier (BBB) dysfunction. All Plasmodium species encode an orthologue of the innate cytokine, Macrophage Migration Inhibitory Factor (MIF), which functions in mammalian biology to regulate innate responses. Plasmodium MIF (PMIF) similarly signals through the host MIF receptor CD74, leading to an enhanced inflammatory response. We investigated the PMIF-CD74 interaction in the onset of experimental cerebral malaria (ECM) using CD74 deficient (Cd74-/-) mice, which were found to be protected from ECM. The protection was associated with the inability of brain microvessels from Cd74-/- hosts to present parasite antigen to sequestered Plasmodium-specific CD8+ T cells. Infection of mice with PMIF-deficient sporozoites (PbAmif-) also protected mice from ECM, highlighting the pivotal role of PMIF in the pre-erythrocytic stage of the infection. A novel pharmacologic PMIF-selective antagonist reduced PMIF/CD74 signaling and fully protected mice from ECM. These findings reveal a conserved mechanism for Plasmodium usurpation of host CD74 signaling and suggest a tractable approach for new pharmacologic intervention.

microbiology↗

bioRxiv2020

Dissection-independent production of a protective whole-sporozoite malaria vaccine

Complete protection against human malaria challenge has been achieved using infected mosquitoes as the delivery route for immunization with Plasmodium parasites. Strategies seeking to replicate this efficacy with either a manufactured whole-parasite or subunit vaccine, however, have shown only limited success. A major roadblock to whole parasite vaccine progress and understanding of the human infective sporozoite form in general, is reliance on manual dissection for parasite isolation from infected mosquitoes. We report here the development of a four-step process based on whole mosquito homogenization, slurry and density-gradient filtration, combined with free-flow electrophoresis that is able to rapidly produce a pure, aseptic sporozoite inoculum from hundreds of mosquitoes. Murine P. berghei or human-infective P. falciparum sporozoites produced in this way are 2-3-fold more infective with in vitro hepatocytes and can confer sterile protection when immunized intravenously with subsequent challenge using a mouse malaria model. Critically, we can also demonstrate for the first time 60-70% protection when the same parasites are administered via intramuscular (i.m.) route. In developing a process amenable to industrialisation and demonstrating efficacy by i.m. route these data represent a major advancement in capacity to produce a whole parasite malaria vaccine at scale. One-Sentence SummaryA four-step process for isolating pure infective malaria parasite sporozoites at scale from homogenized whole mosquitoes, independent of manual dissection, is able to produce a whole parasite vaccine inoculum that confers sterilizing protection.

microbiology↗

bioRxiv2020

Exposure to artemisinin at the trophozoite stage increases sexual conversion rates in the malaria parasite Plasmodium falciparum

Malaria transmission is dependent on formation of gametocytes in the human blood. The sexual conversion rate, the proportion of asexual parasites that convert into gametocytes at each multiplication cycle, is variable and reflects the relative parasite investment between transmission and maintaining the infection. The impact of environmental factors such as drugs on sexual conversion rates is not well understood. We developed a robust assay using gametocyte-reporter parasite lines to accurately measure the impact of drugs on conversion rates, independently from their gametocytocidal activity. We found that exposure to subcurative doses of the frontline antimalarial drug dihydroartemisinin (DHA) at the trophozoite stage resulted in a ~4-fold increase in sexual conversion. In contrast, no increase was observed when ring stages were exposed or in cultures in which sexual conversion was stimulated by choline depletion. Our results reveal a complex relationship between antimalarial drugs and sexual conversion, with potential public health implications.

microbiology↗

bioRxiv2019

Transcriptome analysis of Plasmodium berghei during exo-erythrocytic development

The complex life cycle of malaria parasites requires well-orchestrated stage specific gene expression. In the vertebrate host the parasites grow and multiply by schizogony in two different environments: within erythrocytes and within hepatocytes. Whereas erythrocytic parasites are rather well-studied in this respect, relatively little is known about the exo-erythrocytic stages. In an attempt to fill this gap, we performed genome wide RNA-seq analyses of various exo-erythrocytic stages of Plasmodium berghei including sporozoites, samples from a time-course of liver stage development and detached cells, which contain infectious merozoites and represent the final step in exo-erythrocytic development. The analysis represents the completion of the transcriptome of the entire life cycle of P. berghei parasites with temporal detailed analysis of the liver stage allowing segmentation of the transcriptome across the progression of the life cycle. We have used these RNA-seq data from different developmental stages to cluster genes with similar expression profiles, in order to infer their functions. A comparison with published data of other parasite stages confirmed stage-specific gene expression and revealed numerous genes that are expressed differentially in blood and exo-erythrocytic stages. One of the most exo-erythrocytic stage-specific genes was PBANKA_1003900, which has previously been annotated as a "gametocyte specific protein". The promoter of this gene drove high GFP expression in exo-erythrocytic stages, confirming its expression profile seen by RNA-seq. The comparative analysis of the genome wide mRNA expression profiles of erythrocytic and different exo-erythrocytic stages improves our understanding of gene regulation of Plasmodium parasites and can be used to model exo-erythrocytic stage metabolic networks and identify differences in metabolic processes during schizogony in erythrocytes and hepatocytes.

microbiology↗

bioRxiv2017

Probabilistic data integration identifies reliable gametocyte-specific proteins and transcripts in malaria parasites

Plasmodium gametocytes are the sexual forms of the malaria parasite essential for transmission to mosquitoes. To better understand how gametocytes differ from asexual blood-stage parasites, we performed a systematic analysis of available omics data for P. falciparum and other Plasmodium species. 18 transcriptomic and proteomic data sets were evaluated for the presence of curated \"gold standards\" of 41 gametocyte-specific versus 46 non-gametocyte genes and integrated using Bayesian probabilities, resulting in gametocyte-specificity scores for all P. falciparum genes.\n\nTo illustrate the utility of the gametocyte score, we explored newly predicted gametocyte-specific genes as potential biomarkers of gametocyte carriage and exposure. We analyzed the humoral immune response in field samples against 30 novel gametocyte-specific antigens and found five antigens to be differentially recognized by gametocyte carriers as compared to malaria-infected individuals without detectable gametocytes. We also validated the gametocyte-specificity of 15 identified gametocyte transcripts on culture material and samples from naturally infected individuals, resulting in eight transcripts that were >1000-fold higher expressed in gametocytes compared to asexual parasites and whose transcript abundance allowed gametocyte detection in naturally infected individuals. Our integrated genome-wide gametocyte-specificity scores provide a comprehensive resource to identify targets and monitor P. falciparum gametocytemia.

microbiology↗