Plasmodium yoelii Erythrocyte-Binding-like Protein Modulates Host Cell Membrane Structure, Immunity, and Disease Severity

Gene expression analyses reveal differences in children's response to malaria according to their age

In Bandiagara, Mali, children experience on average two clinical malaria episodes per year. However, even in the same transmission area, the number of uncomplicated symptomatic infections, and their parasitemia, can vary dramatically among children. We simultaneously characterize host and parasite gene expression profiles from 136 Malian children with symptomatic falciparum malaria and examine differences in the relative proportion of immune cells and parasite stages, as well as in gene expression, associated with infection and or patient characteristics. Parasitemia explains much of the variation in host and parasite gene expression, and infections with higher parasitemia display proportionally more neutrophils and fewer T cells, suggesting parasitemia-dependent neutrophil recruitment and/or T cell extravasation to secondary lymphoid organs. The child's age also strongly correlates with variations in gene expression: Plasmodium falciparum genes associated with age suggest that older children carry more male gametocytes, while variations in host gene expression indicate a stronger innate response in younger children and stronger adaptive response in older children. These analyses highlight the variability in host responses and parasite regulation during P. falciparum symptomatic infections and emphasize the importance of considering the children's age when studying and treating malaria infections.

Invasion-inhibitory peptides chosen by natural selection analysis as an antimalarial strategy

Plasmodium vivax's biological complexity has restricted in vitro culture development for characterising antigens involved in erythrocyte invasion and their immunological relevance. The murine model is proposed as a suitable alternative in the search for therapeutic candidates since Plasmodium yoelii uses homologous proteins for its invasion. The AMA-1 protein is essential for parasite invasion of erythrocytes as it is considered an important target for infection control. This study has focused on functional PyAMA-1 peptides involved in host-pathogen interaction; the protein is located in regions under negative selection as determined by bioinformatics analysis. It was found that pyama1 has two highly conserved regions amongst species (>70%) under negative selection. Fourteen synthetic peptides spanning both conserved regions were evaluated; 5 PyAMA-1 peptides having high specific binding (HABP) to murine erythrocytes were identified. The parasite's invasion inhibition capability was analysed through in vitro assays, suggesting that peptides 42681 (43-ENTERSIKLINPWDKYMEKY-62), 42903 (206-RYSSNDANNENQPFSFTPEK-225) and 42904 (221-FTPEKIENYKDLSYLTKNLR-240) had greater than 50% inhibition profile and restricted P. yoelii intra-erythrocyte development. This work proposes that the screening of conserved HABPs under negative selective pressure might be good candidates for developing a synthetic anti-malarial vaccine since they share functionally-relevant characteristics, such as interspecies conservation, specific RBC binding profile, invasion and parasite development inhibition capability, and the predicted B-epitopes within were recognised by sera obtained from experimentally-infected mice.

Gene expression analyses reveal differences in children's response to malaria according to their age

In Bandiagara, Mali, children experience on average two clinical malaria episodes per season. However, even in the same transmission area, the number of uncomplicated symptomatic infections, and their parasitemia, vary dramatically among children. To examine the factors contributing to these variations, we simultaneously characterized the host and parasite gene expression profiles from 136 children with symptomatic falciparum malaria and analyzed the expression of 9,205 human and 2,484 Plasmodium genes. We used gene expression deconvolution to estimate the relative proportion of immune cells and parasite stages in each sample and to adjust the differential gene expression analyses. Parasitemia explained much of the variation in both host and parasite gene expression and revealed that infections with higher parasitemia had more neutrophils and fewer T cells, suggesting parasitemia-dependent neutrophil recruitment and/or T cell extravasation to secondary lymphoid organs. The child's age was also strongly correlated with gene expression variations. Plasmodium falciparum genes associated with age suggested that older children carried more male gametocytes, while host genes associated with age indicated a stronger innate response (through TLR and NLR signaling) in younger children and stronger adaptive immunity (through TCR and BCR signaling) in older children. These analyses highlight the variability in host responses and parasite regulation during P. falciparum symptomatic infections and emphasize the importance of considering the children's age when studying and treating malaria infections.

Gene expression analyses reveal differences in children's response to malaria according to their age

In Bandiagara, Mali, children experience on average two clinical malaria episodes per season. However, even in the same transmission area, the number of uncomplicated symptomatic infections, and their parasitemia, vary dramatically among children. To examine the factors contributing to these variations, we simultaneously characterized the host and parasite gene expression profiles from 136 children with symptomatic falciparum malaria and analyzed the expression of 9,205 human and 2,484 Plasmodium genes. We used gene expression deconvolution to estimate the relative proportion of immune cells and parasite stages in each sample and to adjust the differential gene expression analyses. Parasitemia explained much of the variation in both host and parasite gene expression and revealed that infections with higher parasitemia had more neutrophils and fewer T cells, suggesting parasitemia-dependent neutrophil recruitment and/or T cell extravasation to secondary lymphoid organs. The child's age was also strongly correlated with gene expression variations. Plasmodium falciparum genes associated with age suggested that older children carried more male gametocytes, while host genes associated with age indicated a stronger innate response (through TLR and NLR signaling) in younger children and stronger adaptive immunity (through TCR and BCR signaling) in older children. These analyses highlight the variability in host responses and parasite regulation during P. falciparum symptomatic infections and emphasize the importance of considering the children's age when studying and treating malaria infections.

Dysfunction of CD169+ macrophages and blockage of erythrocyte maturation as a mechanism of anemia in Plasmodium yoelii infection

Plasmodium parasites cause malaria with disease outcomes ranging from mild illness to deadly complications such as severe malarial anemia (SMA), pulmonary edema, acute renal failure, and cerebral malaria. In young children, SMA often requires blood transfusion and is a major cause of hospitalization. Malaria parasite infection leads to the destruction of infected and noninfected erythrocytes as well as dyserythropoiesis; however, the mechanism of dyserythropoiesis accompanied by splenomegaly is not completely understood. Using Plasmodium yoelii yoelii 17XNL as a model, we show that both a defect in erythroblastic island (EBI) macrophages in supporting red blood cell (RBC) maturation and the destruction of reticulocytes/RBCs by the parasites contribute to SMA and splenomegaly. After malaria parasite infection, the destruction of both infected and noninfected RBCs stimulates extramedullary erythropoiesis in mice. The continuous decline of RBCs stimulates active erythropoiesis and drives the expansion of EBIs in the spleen, contributing to splenomegaly. Phagocytosis of malaria parasites by macrophages in the bone marrow and spleen may alter their functional properties and abilities to support erythropoiesis, including reduced expression of the adherence molecule CD169 and inability to support erythroblast differentiation, particularly RBC maturation in vitro and in vivo. Therefore, macrophage dysfunction is a key mechanism contributing to SMA. Mitigating and/or alleviating the inhibition of RBC maturation may provide a treatment strategy for SMA.

A Plasmodium falciparum RING Finger E3 Ubiquitin Ligase Modifies the Roles of PfMDR1 and PfCRT in Parasite Drug Responses

Protein ubiquitination is an important posttranslational regulation mechanism that mediates Plasmodium development and modifies parasite responses to antimalarial drugs. Although mutations in several parasite ubiquitination enzymes have been linked to increased drug tolerance, the molecular mechanisms by which ubiquitination pathways mediate these parasite responses remain largely unknown. Here, we investigate the roles of a Plasmodium falciparum ring finger ubiquitin ligase (PfRFUL) in parasite development and in responses to antimalarial drugs. We engineered a transgenic parasite having the Pfrful gene tagged with an HA-2A-NeoR-glmS sequence to knockdown (KD) Pfrful expression using glucosamine (GlcN). A Western blot analysis of the proteins from GlcN-treated pSLI-HA-NeoR-glmS-tagged (PfRFULg) parasites, relative to their wild-type (Dd2) controls, showed changes in the ubiquitination of numerous proteins. PfRFUL KD rendered the parasites more sensitive to multiple antimalarial drugs, including mefloquine, piperaquine, amodiaquine, and dihydroartemisinin. PfRFUL KD also decreased the protein level of the P. falciparum multiple drug resistance 1 protein (PfMDR1) and altered the ratio of two bands of the P. falciparum chloroquine resistance transporter (PfCRT), suggesting contributions to the changed drug responses by the altered ubiquitination of these two molecules. The inhibition of proteasomal protein degradation by epoxomicin increased the PfRFUL level, suggesting the degradation of PfRFUL by the proteasome pathways, whereas the inhibition of E3 ubiquitin ligase activities by JNJ26854165 reduced the PfRFUL level. This study reveals the potential mechanisms of PfRFUL in modifying the expression of drug transporters and their roles in parasite drug responses. PfRFUL could be a potential target for antimalarial drug development.

Epitranscriptome profiling of spleen mRNA m6A methylation reveals pathways of host responses to malaria parasite infection

N6 -Methyladenosine (m6A), the most abundant mammalian mRNA modification, has been reported to modulate various viral infections. Although it has been confirmed that RNA modifications can also modulate the replication and development of different parasites, the role of the RNA epitranscriptome in the regulation of host response post parasite infection remains to be elucidated. Here we report host spleen m6A epitranscriptome landscapes induced by different strains of the malaria parasite Plasmodium yoelii. We found that malaria parasite infection dramatically changes host spleen m6A mRNA modification and gene expression. Additionally, malaria parasite infection reprograms host immune response pathways by regulating the m6A modification enzymes. Collectively, our study is the first characterization of host spleen m6A methylome triggered by malaria parasite infections, and our data identify m6A modifications as significant transcriptome-wide marks during host-parasite interactions. We demonstrate that host mRNA methylation machinery can sense and respond to malaria parasite infections, and provide new insights into epitranscriptomic mechanisms underlying parasite-induced pathogenesis.

Signaling Pathway in the Osmotic Resistance Induced by Angiotensin II AT2 Receptor Activation in Human Erythrocytes

Background

Angiotensin II regulates blood volume via AT1 (AT1R) and AT2 (AT2R) receptors. As cell integrity is an important feature of mature erythrocyte, we sought to evaluate, in vitro, whether angiotensin II modulates resistance to hemolysis and the signaling pathway involved.

Methods

Human blood samples were collected and hemolysis assay and angiotensin II signaling pathway profiling in erythrocytes were done.

Results

Hemolysis assay created a hemolysis curve in presence of Ang II in several concentrations (10^-6 M, 10^-8 M, 10^-10 M, 10^-12 M). Angiotensin II demonstrated protective effect, both in osmotic stressed and physiological situations, by reducing hemolysis in NaCl 0.4% and 0.9%. By adding receptors antagonists (losartan, AT1R antagonist and PD 123319, AT2R antagonist) and/or signaling modulators for AMPK, Akt/PI3K, p38 and PKC we showed the protective effect was enhanced with losartan and abolished with PD 123319. Also, we showed activation of p38 as well as PI3K/Akt pathways in this system.

Conclusion

Ang II protects human erythrocytes from hypo-osmotic conditions-induced hemolysis by activating AT2 receptors and triggering intracellular pathways.

Genome sequence, transcriptome, and annotation of rodent malaria parasite Plasmodium yoelii nigeriensis N67

Background

Rodent malaria parasites are important models for studying host-malaria parasite interactions such as host immune response, mechanisms of parasite evasion of host killing, and vaccine development. One of the rodent malaria parasites is Plasmodium yoelii, and multiple P. yoelii strains or subspecies that cause different disease phenotypes have been widely employed in various studies. The genomes and transcriptomes of several P. yoelii strains have been analyzed and annotated, including the lethal strains of P. y. yoelii YM (or 17XL) and non-lethal strains of P. y. yoelii 17XNL/17X. Genomic DNA sequences and cDNA reads from another subspecies P. y. nigeriensis N67 have been reported for studies of genetic polymorphisms and parasite response to drugs, but its genome has not been assembled and annotated.

Results

We performed genome sequencing of the N67 parasite using the PacBio long-read sequencing technology, de novo assembled its genome and transcriptome, and predicted 5383 genes with high overall annotation quality. Comparison of the annotated genome of the N67 parasite with those of YM and 17X parasites revealed a set of genes with N67-specific orthology, expansion of gene families, particularly the homologs of the Plasmodium chabaudi erythrocyte membrane antigen, large numbers of SNPs and indels, and proteins predicted to interact with host immune responses based on their functional domains.

Conclusions

The genomes of N67 and 17X parasites are highly diverse, having approximately one polymorphic site per 50 base pairs of DNA. The annotated N67 genome and transcriptome provide searchable databases for fast retrieval of genes and proteins, which will greatly facilitate our efforts in studying the parasite biology and gene function and in developing effective control measures against malaria.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07555-9.

Plasmodium yoelii Erythrocyte Binding Like Protein Interacts With Basigin, an Erythrocyte Surface Protein

Erythrocyte recognition and invasion is critical for the intra-erythrocytic development of Plasmodium spp. parasites. The multistep invasion process involves specific interactions between parasite ligands and erythrocyte receptors. Erythrocyte-binding-like (EBL) proteins, type I integral transmembrane proteins released from the merozoite micronemes, are known to play an important role in the initiation and formation of tight junctions between the apical end of the merozoite and the erythrocyte surface. In Plasmodium yoelii EBL (PyEBL), a single amino acid substitution in the putative Duffy binding domain dramatically changes parasite growth rate and virulence. This suggests that PyEBL is important for modulating the virulence of P. yoelii parasites. Based on these observations, we sought to elucidate the receptor of PyEBL that mediates its role as an invasion ligand. Using the eukaryotic wheat germ cell-free system, we systematically developed and screened a library of mouse erythrocyte proteins against native PyEBL using AlphaScreen technology. We report that PyEBL specifically interacts with basigin, an erythrocyte surface protein. We further confirmed that the N-terminal cysteine-rich Duffy binding-like region (EBL region 2), is responsible for the interaction, and that the binding is not affected by the C351Y mutation, which was previously shown to modulate virulence of P. yoelii. The identification of basigin as the putative PyEBL receptor offers new insights into the role of this molecule and provides an important base for in-depth studies towards developing novel interventions against malaria.

Type I Interferons and Malaria: A Double-Edge Sword Against a Complex Parasitic Disease

Type I interferons (IFN-Is) are important cytokines playing critical roles in various infections, autoimmune diseases, and cancer. Studies have also shown that IFN-Is exhibit 'conflicting' roles in malaria parasite infections. Malaria parasites have a complex life cycle with multiple developing stages in two hosts. Both the liver and blood stages of malaria parasites in a vertebrate host stimulate IFN-I responses. IFN-Is have been shown to inhibit liver and blood stage development, to suppress T cell activation and adaptive immune response, and to promote production of proinflammatory cytokines and chemokines in animal models. Different parasite species or strains trigger distinct IFN-I responses. For example, a Plasmodium yoelii strain can stimulate a strong IFN-I response during early infection, whereas its isogenetic strain does not. Host genetic background also greatly influences IFN-I production during malaria infections. Consequently, the effects of IFN-Is on parasitemia and disease symptoms are highly variable depending on the combination of parasite and host species or strains. Toll-like receptor (TLR) 7, TLR9, melanoma differentiation-associated protein 5 (MDA5), and cyclic GMP-AMP synthase (cGAS) coupled with stimulator of interferon genes (STING) are the major receptors for recognizing parasite nucleic acids (RNA/DNA) to trigger IFN-I responses. IFN-I levels in vivo are tightly regulated, and various novel molecules have been identified to regulate IFN-I responses during malaria infections. Here we review the major findings and progress in ligand recognition, signaling pathways, functions, and regulation of IFN-I responses during malaria infections.

Host-Malaria Parasite Interactions and Impacts on Mutual Evolution

Malaria is the most deadly parasitic disease, affecting hundreds of millions of people worldwide. Malaria parasites have been associated with their hosts for millions of years. During the long history of host-parasite co-evolution, both parasites and hosts have applied pressure on each other through complex host-parasite molecular interactions. Whereas the hosts activate various immune mechanisms to remove parasites during an infection, the parasites attempt to evade host immunity by diversifying their genome and switching expression of targets of the host immune system. Human intervention to control the disease such as antimalarial drugs and vaccination can greatly alter parasite population dynamics and evolution, particularly the massive applications of antimalarial drugs in recent human history. Vaccination is likely the best method to prevent the disease; however, a partially protective vaccine may have unwanted consequences that require further investigation. Studies of host-parasite interactions and co-evolution will provide important information for designing safe and effective vaccines and for preventing drug resistance. In this essay, we will discuss some interesting molecules involved in host-parasite interactions, including important parasite antigens. We also discuss subjects relevant to drug and vaccine development and some approaches for studying host-parasite interactions.