Eimeria falciformis infection of the mouse caecum identifies opposing roles of IFNγ-regulated host pathways for the parasite development

Quantitative proteomic analysis of local and systemic extracellular vesicles during Eimeria falciformis infectious cycle in the host

BACKGROUND

Extracellular vesicles (EVs) are membranous structures that are formed during pathophysiology, host-parasite interactions and parasite motility. Typically, apicomplexan-infected host cells secrete EVs which traverse local and systemic strata of the host as the parasites develop.

METHODS

Extracellular vesicles were isolated from the caecum and serum of Eimeria falciformis-infected mice during oocyst ingestion (0 h post-infection [0 hpi]), merozont stages 1 and 2 (68 and 116 hpi), oocyst shedding (7 days post-infection [7 dpi]) and host recovery (10 dpi) and subsequently characterized and profiled by tandem mass tag (TMT).

RESULTS

With the progression of E. falciformis life stages, subpopulation of EVs bearing EV biomarkers, including CD9, CD82, heat shock protein 70 (HSP70) and major histocompatibility complex (MHC) molecules, increased. A total of 860 and 1024 differentially expressed proteins were identified in serum EVs (sEVs) and caecum EVs (cEVs), respectively. Identified immune-related molecules (such as cytokines, receptors, immunoglobins, complements, hormones, inflammasomes), ion exchange and cell death-associated proteins were significantly expressed, at least during the E. falciformis first and second merozont stages. Bioinformatics assessment indicated that sEV proteins were at all time points implicated in antigen processing and presentation as well as natural killer cell-mediated cytotoxicity (68 hpi), complement activation/blood coagulation (116 hpi/10 dpi) and catabolic activities (7 dpi). In contrast, cEV proteins were involved in catabolic process, ion transport and antigen presentation (68 and 116 hpi). Host response to E. falciformis infection was similar to intestinal bacterium at 7 dpi and cell adhesion and intercellular protein transport at 10 dpi. In both systems, ferroptosis and necroptosis were common across the parasite's infectious cycle while apoptosis occurred at 68 hpi.

CONCLUSION

The proteomic data indicate that E. falciformis infection co-opts cellular and humoral responses through EV secretions, and that, host cell death and ionic imbalance are associated with E. falciformis infection. This study offers additional insight into host-parasite interactions and host regulatory EV proteins as potential disease indicators or diagnostic molecules.

Eimeria falciformis secretes extracellular vesicles to modulate proinflammatory response during interaction with mouse intestinal epithelial cells

BACKGROUND

Protozoan parasite secretions can be triggered by various modified media and diverse physicochemical stressors. Equally, host-parasite interactions are known to co-opt the exchange and secretion of soluble biochemical components. Analysis of Eimeria falciformis sporozoite secretions in response to interaction with mouse intestinal epithelial cells (MIECs) may reveal parasite secretory motifs, protein composition and inflammatory activities of E. falciformis extracellular vesicles (EVs).

METHODS

Eimeria falciformis sporozoites were allowed to interact with inactivated MIECs. Parasite secretions were separated into EV and vesicle-free (VF) fractions by discontinuous centrifugation and ultracentrifugation. Secreted EVs were purified in an iodixanol density gradient medium and the protein composition of both EV and VF fractions were analyzed by liquid chromatoraphy-tandem mass spectroscopy. The inflammatory activities of E. falciformis sporozoite EV on MIECs were then investigated.

RESULTS

During the interaction of E. falciformis sporozoites with inactivated MIECs, the parasite secreted VF and vesicle-bound molecules. Eimeria falciformis vesicles are typical pathogenic protozoan EVs with a mean diameter of 264 ± 2 nm, and enclosed heat shock protein (Hsp) 70 as classical EV marker. Refractile body-associated aspartyl proteinase (or eimepsin), GAP45 and aminopeptidase were the main components of E. falciformis sporozoite EVs, while VF proteins include Hsp90, actin, Vps54 and kinases, among others. Proteomic data revealed that E. falciformis EV and VF proteins are aggregates of bioactive, antigenic and immunogenic molecules which act in concert for E. falciformis sporozoite motility, pathogenesis and survival. Moreover, in MIECs, E. falciformis EVs induced upregulation of gene expression and secretion of IL-1β, IL-6, IL-17, IL-18, MCP1 as well as pyroptosis-dependent caspase 11 and NLRP6 inflammasomes with the concomitant secretion of lactate dehydrogenase.

CONCLUSIONS

Eimeria falciformis sporozoite interaction with MIECs triggered the secretion of immunogenic and antigenic proteins. In addition, E. falciformis sporozoite EVs constitute parasite-associated molecular pattern that induced inflammatory response and cell death. This study offers additional insight in the secretion and protein composition of E. falciformis secretomes as well as the proinflammatory functions of E. falciformis sporozoite EVs.

Shifting focus from resistance to disease tolerance: A review on hybrid house mice

Parasites have been proposed to modulate the fitness of hybridizing hosts in part based on observations in the European house mouse hybrid zone (HMHZ), a tension zone in which hybrids show reduced fitness. We here review evidence (1) for parasite load differences in hybrid versus parental mice and (2) for health and fitness effects of parasites promoting or preventing introgression and hybridization. The question of relative resistance or susceptibility of hybrids to parasites in the HMHZ has long been controversial. Recent field studies found hybrids to be more resistant than mice from parental subspecies against infections with pinworms and protozoans (Eimeria spp.). We argue that the field studies underlying the contradictory impression of hybrid susceptibility have limitations in sample size, statistical analysis and scope, focusing only on macroparasites. We suggest that weighted evidence from field studies indicate hybrid resistance. Health is a fitness component through which resistance can modulate overall fitness. Resistance, however, should not be extrapolated directly to a fitness effect, as the relationship between resistance and health can be modulated by tolerance. In our own recent work, we found that the relationship between health and resistance (tolerance) differs between infections with the related species E. falciformis and E. ferrisi. Health and tolerance need to be assessed directly and the choice of parasite has made this difficult in previous experimental studies of house mice. We discuss how experimental Eimeria spp. infections in hybrid house mice can address resistance, health and tolerance in conjunction.

Eimeria proteins: order amidst disorder

Apicomplexans are important pathogens that cause severe infections in humans and animals. The biology and pathogeneses of these parasites have shown that proteins are intrinsically modulated during developmental transitions, physiological processes and disease progression. Also, proteins are integral components of parasite structural elements and organelles. Among apicomplexan parasites, Eimeria species are an important disease aetiology for economically important animals wherein identification and characterisation of proteins have been long-winded. Nonetheless, this review seeks to give a comprehensive overview of constitutively expressed Eimeria proteins. These molecules are discussed across developmental stages, organelles and sub-cellular components vis-à-vis their biological functions. In addition, hindsight and suggestions are offered with intention to summarise the existing trend of eimerian protein characterisation and to provide a baseline for future studies.

From celiac disease to coccidia infection and vice-versa: The polyQ peptide CXCR3-interaction axis

Zonulin is a physiological modulator of intercellular tight junctions, which upregulation is involved in several diseases like celiac disease (CeD). The polyQ gliadin fragment binds to the CXCR3 chemokine receptor that activates zonulin upregulation, leading to increased intestinal permeability in humans. Here, we report a general hypothesis based on the structural connection between the polyQ sequence of the immunogenic CeD protein, gliadin, and enteric coccidian parasites proteins. Firstly, a novel interaction pathway between the parasites and the host is described based on the structural similarities between polyQ gliadin fragments and the parasite proteins. Secondly, a potential connection between coccidial infections as a novel environmental trigger of CeD is hypothesized. Therefore, this report represents a promising breakthrough for coccidian research and points out the potential role of coccidian parasites as a novel trigger of CeD that might define a preventive strategy for gluten-related disorders in general. Also see the video abstract here: https://youtu.be/oMaQasStcFI.

Construction and Analysis of Coexpression Network to Understand Biological Responses in Chickens Infected by Eimeria tenella

Coccidiosis, caused by various Eimeria species, is a major parasitic disease in chickens. Our understanding of how chickens respond to coccidian infections is highly limited at both the molecular and cellular levels. In this study, coexpression modules were identified by weighted gene coexpression network analysis in chickens infected with Eimeria tenella. A total of 15 correlation modules were identified using 5,175 genes with 24 chicken samples, 12 with primary and 12 with secondary E. tenella infection. The analysis of the interactions between these modules showed a high degree of scale independence. Gene Ontology and Kyoto Encyclopedia of Gene and Genomes enrichment analyses revealed that genes in these functional modules were involved in a broad categories of functions, such as immune response, amino acid metabolism, cellular responses to lipids, sterol biosynthetic processes, and RNA transport. Two modules viz yellow and magenta were identified significantly associating with infection status. Preservation analysis showed that most of the modules identified in E. tenella infections were highly or moderately preserved in chickens infected with either Eimeria acervulina or Eimeria maxima. These analyses outline a biological responses landscape for chickens infected by E. tenella, and also indicates that infections with these three Eimeria species elicit similar biological responses in chickens at the system level. These findings provide new clues and ideas for investigating the relationship between parasites and host, and the control of parasitic diseases.

Toxoplasma and Eimeria co-opt the host cFos expression for intracellular development in mammalian cells

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Gene expression profiles differ significantly between Toxoplasma and Eimeria-infected host cells.

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Several distinct and shared host-signaling cascades are regulated by coccidian parasites.

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cFos is one of the few host transcripts mutually regulated during infection by both pathogens.

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Host cFos is required for optimal in vitro development of E. falciformis and T. gondii.

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Transcriptomics of parasitized wild-type and cFos^-/- host cells reveals a perturbation of cFos network.

Successful asexual reproduction of intracellular pathogens depends on their potential to exploit host resources and subvert antimicrobial defense. In this work, we deployed two prevalent apicomplexan parasites of mammalian cells, namely Toxoplasma gondii and Eimeria falciformis, to identify potential host determinants of infection. Expression analyses of the young adult mouse colonic (YAMC) epithelial cells upon infection by either parasite showed regulation of several distinct transcripts, indicating that these two pathogens program their intracellular niches in a tailored manner. Conversely, parasitized mouse embryonic fibroblasts (MEFs) displayed a divergent transcriptome compared to corresponding YAMC epithelial cells, suggesting that individual host cells mount a fairly discrete response when encountering a particular pathogen. Among several host transcripts similarly altered by T. gondii and E. falciformis, we identified cFos, a master transcription factor, that was consistently induced throughout the infection. Indeed, asexual growth of both parasites was strongly impaired in MEF host cells lacking cFos expression. Last but not the least, our differential transcriptomics of the infected MEFs (parental and cFos^-/- mutant) and YAMC epithelial cells disclosed a cFos-centered network, underlying signal cascades, as well as a repertoire of nucleotides- and ion-binding proteins, which presumably act in consort to acclimatize the mammalian cell and thereby facilitate the parasite development.

Phosphatidylinositol synthesis, its selective salvage, and inter-regulation of anionic phospholipids in Toxoplasma gondii

Phosphatidylinositol (PtdIns) serves as an integral component of eukaryotic membranes; however, its biosynthesis in apicomplexan parasites remains poorly understood. Here we show that Toxoplasma gondii-a common intracellular pathogen of humans and animals-can import and co-utilize myo-inositol with the endogenous CDP-diacylglycerol to synthesize PtdIns. Equally, the parasite harbors a functional PtdIns synthase (PIS) containing a catalytically-vital CDP-diacylglycerol phosphotransferase motif in the Golgi apparatus. Auxin-induced depletion of PIS abrogated the lytic cycle of T. gondii in human cells due to defects in cell division, gliding motility, invasion, and egress. Isotope labeling of the PIS mutant in conjunction with lipidomics demonstrated de novo synthesis of specific PtdIns species, while revealing the salvage of other lipid species from the host cell. Not least, the mutant showed decline in phosphatidylthreonine, and elevation of selected phosphatidylserine and phosphatidylglycerol species, indicating a rerouting of CDP-diacylglycerol and homeostatic inter-regulation of anionic phospholipids upon knockdown of PIS. In conclusion, strategic allocation of own and host-derived PtdIns species to gratify its metabolic demand features as a notable adaptive trait of T. gondii. Conceivably, the dependence of T. gondii on de novo lipid synthesis and scavenging can be exploited to develop new anti-infectives.

Susceptibility to Various Coccidiostats in the Murine Coccidian Parasite Eimeria krijgsmanni

INTRODUCTION

Murine Eimeria spp. have been used as effective experimental models of disease instead of large mammalian hosts such as cattle. We here examine drug susceptibility of the uncharacterized murine intestinal protozoan parasite, Eimeria krijgsmanni.

MATERIALS AND METHODS

The effectiveness of different treatments against infection of E. krijgsmanni was examined for suppression of oocyst shedding: ST mixture ST mixture, pyrimethamine, Ektecin and toltrazuril.

RESULTS

ST mixture and pyrimethamine did not suppress oocyst shedding effectively. Although therapeutic efficacy of Ektecin was demonstrated, the dose required was larger than that for cattle and chickens. Oocyst shedding was only completely suppressed completely by continuous administration of toltrazuril. Furthermore, it was confirmed through morphological examination that early developmental stage zoites appeared in host epithelial cells during and following treatment by toltrazuril, and toltrazuril could not eliminate residual zoites in epithelial cells.

CONCLUSION

E. krijgsmanni may be relatively resistant to these anti-coccidian agents and might therefore have different characteristics that differ from other coccidia with regard to drug susceptibility.

Effects of host fatty acid-binding protein 4 on Eimeria tenella sporozoites invasion of cells

In our previous study, proteomics analyses of host cells infected with Eimeria tenella sporozoites coupled with isobaric tags for relative and absolute quantitation, identified several host proteins related to Eimeria invasion. In this study, A 458-bp Gallus gallus fatty acid-binding protein 4 (FABP4) gene was cloned and subcloned to pET-28c(+) vector to construct the prokaryotic recombinant expression plasmid pET-28c(+)-FABP4. The 18.5 kDa recombinant FABP4 protein (rFABP4) was expressed and identified by western blotting. Expression of FABP4 in E. tenella sporozoite-infected DF-1 cells was downregulated significantly than in non-infected cells detected by western blotting and immunohistochemistry. The antibody inhibition assay showed that antibodies against FABP4 at 50, 100, 200, 300, and 400 μg/mL had no significant effect on sporozoite invasion. BMS-309403 and transforming growth factor-β3 (TGF-β3) was used to inhibit and improve the expression of FABP4 in DF-1 cells, respectively, and their effect on the sporozoite invasion of cells was detected by flow cytometry. Sporozoite invasion rate in the BMS-309403-treated group was not significantly affected; however, the invasion rate in the TGF-β3-treated group declined significantly. These results show that host FABP4 plays a negative role in Eimeria invasion. However, further studies are needed to elucidate the exact mechanism of how FABP4 negatively regulates Eimeria invasion.

iTRAQ-based comparative proteomic analysis of cells infected with Eimeria tenella sporozoites

Eimeria tenella is an obligate intracellular parasite that actively invades cecal epithelial cells of chickens. When E. tenella infects a host cell, the host produces a corresponding change to deal with damage caused by this infection. To date, our knowledge on the mechanism of how the host cell responds to E. tenella infection is highly limited at both the molecular and cellular levels. In this study, isobaric tags for relative and absolute quantitation (iTRAQ) coupled with LC-MS/MS was used to screen the differentially expressed proteins (DEPs) in BHK-21 cells infected with E. tenella sporozoites for 24 h post infection. In total, 6139 non-redundant distinct proteins were identified and 195 of these were found to have a fold change ratio ≥1.3 or ≤0.7 and p < 0.05, including 151 up-regulated proteins and 44 down-regulated proteins. The reliability of the proteomic data was further validated with qPCR and western blot. Gene Ontology enrichment indicated that the up-regulated DEPs were mainly involved in binding and catalytic activity, whereas the down-regulated DEPs were catalytic activity and molecular function regulators. Furthermore, KEGG pathway analysis showed that the DEPs participated in the PI3K-Akt, chemokine, Ras, Wnt, and p53 signaling pathways and so on, and the up-regulated and down-regulated DEPs mainly related to the ribosome and mRNA surveillance pathway, respectively. The data in this study provide an important basis to further analyze E. tenella host cell interactions.

Lipid analysis of Eimeria sporozoites reveals exclusive phospholipids, a phylogenetic mosaic of endogenous synthesis, and a host-independent lifestyle

Successful inter-host transmission of most apicomplexan parasites requires the formation of infective sporozoites within the oocysts. Unlike all other infective stages that are strictly intracellular and depend on host resources, the sporozoite stage develops outside the host cells, but little is known about its self-governing metabolism. This study deployed Eimeria falciformis, a parasite infecting the mouse as its natural host, to investigate the process of phospholipid biogenesis in sporozoites. Lipidomic analyses demonstrated the occurrence of prototypical phospholipids along with abundant expression of at least two exclusive lipids, phosphatidylthreonine (PtdThr) and inositol phosphorylceramide with a phytosphingosine backbone, in sporozoites. To produce them de novo, the parasite harbors nearly the entire biogenesis network, which is an evolutionary mosaic of eukaryotic-type and prokaryotic-type enzymes. Notably, many have no phylogenetic counterpart or functional equivalent in the mammalian host. Using Toxoplasma gondii as a gene-tractable surrogate to examine Eimeria enzymes, we show a highly compartmentalized network of lipid synthesis spread primarily in the apicoplast, endoplasmic reticulum, mitochondrion, and Golgi complex. Likewise, trans-genera complementation of a Toxoplasma mutant with the PtdThr synthase from Eimeria reveals a convergent role of PtdThr in fostering the lytic cycle of coccidian parasites. Taken together, our work establishes a model of autonomous membrane biogenesis involving significant inter-organelle cooperation and lipid trafficking in sporozoites. Phylogenetic divergence of certain pathways offers attractive drug targets to block the sporulation and subsequent transmission. Not least, our results vindicate the possession of an entire de novo lipid synthesis network in a representative protist adapted to an obligate intracellular parasitic lifestyle.

Influence of Eimeria falciformis Infection on Gut Microbiota and Metabolic Pathways in Mice

Coccidiosis, caused by different species of Eimeria parasites, is an economically important disease of poultry and livestock worldwide. Here we report previously unknown alterations in the gut microbes and metabolism of BALB/c mice infected with Eimeria falciformis Specifically, we observed a significant shift in the abundance of cecal bacteria and disrupted metabolism in parasitized animals. The relative abundances of Lachnospiraceae bacterium NK4A136, Ruminiclostridium, Alistipes, and Lactobacillus declined in response to E. falciformis infection, whereas Escherichia, Shigella, Helicobacter, Klebsiella, and Bacteroides were increased. Carbohydrate and amino acid metabolites in the serum samples of infected mice were significantly altered compared to naïve controls. Levels of amino acids, including asparagine, histidine, l-cysteine, tryptophan, lysine, glycine, serine, alanine, proline, ornithine, methionine, and valine, decreased on day 7 postinfection before returning to baseline on day 14. In addition, increased levels of indolelactate and mannitol and a reduced amount of oxalic acid indicated impaired carbon metabolism upon parasitic infection. These data demonstrate that intestinal coccidial infection perturbs the microbiota and disrupts carbon and nitrogen metabolism.

Dual RNA-seq reveals no plastic transcriptional response of the coccidian parasite Eimeria falciformis to host immune defenses

Background

Parasites can either respond to differences in immune defenses that exist between individual hosts plastically or, alternatively, follow a genetically canalized (“hard wired”) program of infection. Assuming that large-scale functional plasticity would be discernible in the parasite transcriptome we have performed a dual RNA-seq study of the lifecycle of Eimeria falciformis using infected mice with different immune status as models for coccidian infections.

Results

We compared parasite and host transcriptomes (dual transcriptome) between naïve and challenge infected mice, as well as between immune competent and immune deficient ones. Mice with different immune competence show transcriptional differences as well as differences in parasite reproduction (oocyst shedding). Broad gene categories represented by differently abundant host genes indicate enrichments for immune reaction and tissue repair functions. More specifically, TGF-beta, EGF, TNF and IL-1 and IL-6 are examples of functional annotations represented differently depending on host immune status. Much in contrast, parasite transcriptomes were neither different between Coccidia isolated from immune competent and immune deficient mice, nor between those harvested from naïve and challenge infected mice. Instead, parasite transcriptomes have distinct profiles early and late in infection, characterized largely by biosynthesis or motility associated functional gene groups, respectively. Extracellular sporozoite and oocyst stages showed distinct transcriptional profiles and sporozoite transcriptomes were found enriched for species specific genes and likely pathogenicity factors.

Conclusion

We propose that the niche and host-specific parasite E. falciformis uses a genetically canalized program of infection. This program is likely fixed in an evolutionary process rather than employing phenotypic plasticity to interact with its host. This in turn might limit the potential of the parasite to adapt to new host species or niches, forcing it to coevolve with its host.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4095-6) contains supplementary material, which is available to authorized users.

Course of induced infection by Eimeria krijgsmannni in immunocompetent and immunodeficient mice

Recently, we have demonstrated the utility of Eimeria krijgsmanni as a novel mouse eimerian parasite for elucidating the biological diversity. The parasite showed notable infectivity to mice with various levels of immune status and susceptibility to antimicrobial agents including coccidiostat. However, the detailed lifecycle of E. krijgsmanni had not yet been determined and this information was lacking in discussion of previous findings. In the present study, we clarified the morphological characteristics of E. krijgsmanni and its lifecycle in normal mice, and examined the effects in immunodeficient mice and lifecycle stage for challenge infections after the primary inoculation. In immunocompetent mice, the lifecycle consisted of four asexual stages and the sexual sages followed by formation of oocysts during the prepatent periods. Interestingly, the second-generation meronts were detected in all observation periods after the disappearance of the other stages. For the challenge infection of immunodeficient mice, all developmental stages except for the second generation meronts were temporarily vanished. This finding suggests a "rest" or marked delay in development and a "restart" of the promotion toward the next generations. The second generation meronts may play an important role in the lifecycle of E. krijgsmanni.

Host specificity of turkey and chicken Eimeria: controlled cross-transmission studies and a phylogenetic view

Protozoan parasites of the Eimeria genus have undergone extensive speciation and are now represented by a myriad of species that are specialised to different hosts. These species are highly host-specific and usually parasitise single host species, with only few reported exceptions. Doubts regarding the strict host specificity were frequent in the original literature describing coccidia parasitising domestic turkeys. The availability of pure characterised lines of turkey and chicken Eimeria species along with the recently developed quantitative PCR identification of these species allowed to investigate the issue of host specificity using well-controlled cross-transmission experiments. Seven species of gallinaceous birds (Gallus gallus, Meleagris gallopavo, Alectoris rufa, Perdix perdix, Phasianus colchicus, Numida meleagris and Colinus virginianus) were inoculated with six species and strains of turkey Eimeria and six species of chicken coccidia and production of oocysts was monitored. Turkey Eimeria species E. dispersa, E. innocua and E. meleagridis could complete their development in the hosts from different genera or even different families. Comparison of phylogenetic positions of these Eimeria species according to 18S rDNA and COI showed that the phylogeny cannot explain the observed patterns of host specificity. These findings suggest that the adaptation of Eimeria parasites to foreign hosts is possible and might play a significant role in the evolution and diversification of this genus.

The genome of Eimeria falciformis--reduction and specialization in a single host apicomplexan parasite

BACKGROUND

The phylum Apicomplexa comprises important unicellular human parasites such as Toxoplasma and Plasmodium. Eimeria is the largest and most diverse genus of apicomplexan parasites and some species of the genus are the causative agent of coccidiosis, a disease economically devastating in poultry. We report a complete genome sequence of the mouse parasite Eimeria falciformis. We assembled and annotated the genome sequence to study host-parasite interactions in this understudied genus in a model organism host.

RESULTS

The genome of E. falciformis is 44 Mb in size and contains 5,879 predicted protein coding genes. Comparative analysis of E. falciformis with Toxoplasma gondii shows an emergence and diversification of gene families associated with motility and invasion mainly at the level of the Coccidia. Many rhoptry kinases, among them important virulence factors in T. gondii, are absent from the E. falciformis genome. Surface antigens are divergent between Eimeria species. Comparisons with T. gondii showed differences between genes involved in metabolism, N-glycan and GPI-anchor synthesis. E. falciformis possesses a reduced set of transmembrane transporters and we suggest an altered mode of iron uptake in the genus Eimeria.

CONCLUSIONS

Reduced diversity of genes required for host-parasite interaction and transmembrane transport allow hypotheses on host adaptation and specialization of a single host parasite. The E. falciformis genome sequence sheds light on the evolution of the Coccidia and helps to identify determinants of host-parasite interaction critical for drug and vaccine development.