Transcriptional changes in the hookworm, Ancylostoma caninum, during the transition from a free-living to a parasitic larva

Characterisation of protective vaccine antigens from the thiol-containing components of excretory/secretory material of Ostertagia ostertagi

Previous vaccination trials have demonstrated that thiol proteins affinity purified from Ostertagia ostertagi excretory-secretory products (O. ostertagi ES-thiol) are protective against homologous challenge. Here we have shown that protection induced by this vaccine was consistent across four independent vaccine-challenge experiments. Protection is associated with reduced cumulative faecal egg counts across the duration of the trials, relative to control animals. To better understand the diversity of antigens in O. ostertagi ES-thiol we used high-resolution shotgun proteomics to identify 490 unique proteins in the vaccine preparation. The most numerous ES-thiol proteins, with 91 proteins identified, belong to the sperm-coating protein/Tpx/antigen 5/pathogenesis-related protein 1 (SCP/TAPS) family. This family includes previously identified O. ostertagi vaccine antigens O. ostertagi ASP-1 and ASP-2. The ES-thiol fraction also has numerous proteinases, representing three distinct classes, including: metallo-; aspartyl- and cysteine proteinases. In terms of number of family members, the M12 astacin-like metalloproteinases, with 33 proteins, are the most abundant proteinase family in O. ostertagi ES-thiol. The O. ostertagi ES-thiol proteome provides a comprehensive database of proteins present in this vaccine preparation and will guide future vaccine antigen discovery projects.

A member of the CAP protein superfamily, Hc-CAP-15, is important for the parasitic-stage development of Haemonchus contortus

BACKGROUND

The CAP superfamily proteins are distributed widely in eukaryotes and play crucial roles in various biological processes. However, very little is known about their functions in parasitic nematodes, including Haemonchus contortus, a socioeconomically important parasitic nematode. We have therefore studied a member of the CAP protein family of H. contortus, named Hc-CAP-15, with the aim to explore its roles in regulating the parasitic developmental process.

METHODS

The conservation and phylogenetic relationships, spatial expression and temporal transcription profiles of Hc-CAP/cap-15, as well its biological function during parasite development were investigated using bioinformatics, immunofluorescence, real-time PCR and RNA interference (RNAi).

RESULTS

Hc-CAP-15 was found to be a single-domain CAP protein consisting of four conserved motifs that is localized in the cuticle, intestine and oocyte of adult worms. Hc-cap-15 was transcribed at all developmental stages of H. contortus, with the highest transcription level in parasitic fourth-stage larvae (L4s). Silencing of Hc-cap-15 resulted in a significant increase in the body length of L4s.

CONCLUSIONS

The results suggested that Hc-CAP-15 is important for the development of H. contortus. Our findings provide a basis for further study of the functions of the CAP family proteins in H. contortus and related parasitic nematodes.

Quantifying metabolic activity of Ascaris suum L3 using resazurin reduction

BACKGROUND

Helminth infections are an important public health problem in humans and have an even greater impact on domestic animal and livestock welfare. Current readouts for anthelmintic drug screening assays are stage development, migration, or motility that can be subjective, laborious, and low in throughput. The aim of this study was to apply and optimize a fluorometric technique using resazurin for evaluating changes in the metabolic activity of Ascaris suum third-stage larvae (L3), a parasite of high economic relevance in swine.

METHODS

Ascaris suum L3 were mechanically hatched from 6- to 8-week embryonated and sucrose-gradient-enriched eggs. Resazurin dye and A. suum L3 were titrated in 96-well microtiter plates, and resazurin reduction activity was assessed by fluorometry after 24 h of incubation. Fluorescence microscopy was used to localize the resazurin reduction site within the larvae. Finally, we exposed A. suum L3 to various stress conditions including heat, methanol, and anthelmintics, and investigated their impact on larval metabolism through resazurin reduction activity.

RESULTS

We show that the non-fluorescent dye resazurin is reduced inside vital A. suum L3 to fluorescent resorufin and released into the culture media. Optimal assay parameters are 100-1000 L3 per well, a resazurin concentration of 7.5 µg/ml, and incubation at 37 °C/5% CO₂ for 24 h. An intact L2 sheath around the L3 of A. suum completely prevents the uptake of resazurin, while in unsheathed L3, the most intense fluorescence signal is observed along the larval midgut. L3 exposed to methanol or heat show a gradually decreased resazurin reduction activity. In addition, 24 h exposure to ivermectin at 0.625 µM, mebendazole at 5 µM, and thiabendazole from 10 to 100 µM significantly decreased larval metabolic activity by 55%, 73%, and 70% to 89%, respectively.

CONCLUSIONS

Together, our results show that both metabolic stressors and anthelmintic drugs significantly and reproducibly reduce the resazurin reduction activity of A. suum L3, making the proposed assay a sensitive and easy-to-use method to evaluate metabolic activity of A. suum L3 in vitro.

Novel antiinflammatory biologics shaped by parasite-host coevolution

Parasitic helminth infections, while a major cause of neglected tropical disease burden, negatively correlate with the incidence of immune-mediated inflammatory diseases such as inflammatory bowel diseases (IBD). To evade expulsion, helminths have developed sophisticated mechanisms to regulate their host's immune responses. Controlled experimental human helminth infections have been assessed clinically for treating inflammatory conditions; however, such a radical therapeutic modality has challenges. An alternative approach is to harness the immunomodulatory properties within the worm's excretory-secretory (ES) complement, its secretome. Here, we report a biologics discovery and validation pipeline to generate and screen in vivo a recombinant cell-free secretome library of helminth-derived immunomodulatory proteins. We successfully expressed 78 recombinant ES proteins from gastrointestinal hookworms and screened the crude in vitro translation reactions for anti-IBD properties in a mouse model of acute colitis. After statistical filtering and ranking, 20 proteins conferred significant protection against various parameters of colitis. Lead candidates from distinct protein families, including annexins, transthyretins, nematode-specific retinol-binding proteins, and SCP/TAPS were identified. Representative proteins were produced in mammalian cells and further validated, including ex vivo suppression of inflammatory cytokine secretion by T cells from IBD patient colon biopsies. Proteins identified herein offer promise as novel, safe, and mechanistically differentiated biologics for treating the globally increasing burden of inflammatory diseases.

Expression of Ascaris lumbricoides putative virulence-associated genes when infecting a human host

BACKGROUND

Ascaris lumbricoides is the most common causative agent of soil-transmitted helminth infections worldwide, with an estimated 450 million people infected with this nematode globally. It is suggested that helminths are capable of evading and manipulating the host immune system through the release of a spectrum of worm proteins which underpins their long-term survival in the host. We hypothesise that the worm overexpresses these proteins when infecting adults compared to children to cirvumvent the more robust defence mechanisms of adults. However, little is known about the parasite's genes and encoded proteins involved during A. lumbricoides infection. Hence, this study was conducted to assess the expression profile of putative virulence-associated genes during an active infection of adults and children.

METHODS

In this study, quantitative PCR was performed to evaluate the expression profile of putative virulence-associated genes in A. lumbricoides isolated from infected children and adults. The study was initiated by collecting adult worms expelled from adults and children following anthelminthic treatment. High-quality RNA was successfully extracted from each of six adult worms expelled by three adults and three children, respectively. Eleven putative homologues of helminth virulence-associated genes reported in previous studies were selected, primers were designed and specific amplicons of A. lumbricoides genes were noted. The expression profiles of these putative virulence-associated genes in A. lumbricoides from infected adults were compared to those in A. lumbricoides from infected children.

RESULTS

The putative virulence-associated genes VENOM, CADHERIN and PEBP were significantly upregulated at 166-fold, 13-fold and fivefold, respectively, in adults compared to children. Conversely, the transcription of ABA-1 (fourfold), CATH-L (threefold) and INTEGRIN (twofold) was significantly suppressed in A. lumbricoides from infected adults.

CONCLUSIONS

On the basis of the expression profile of the putative virulence-associated genes, we propose that the encoded proteins have potential roles in evasion mechanisms, which could guide the development of therapeutic interventions.

The functions of CAP superfamily proteins in mammalian fertility and disease

BACKGROUND

Members of the cysteine-rich secretory proteins (CRISPS), antigen 5 (Ag5) and pathogenesis-related 1 (Pr-1) (CAP) superfamily of proteins are found across the bacterial, fungal, plant and animal kingdoms. Although many CAP superfamily proteins remain poorly characterized, over the past decade evidence has accumulated, which provides insights into the functional roles of these proteins in various processes, including fertilization, immune defence and subversion, pathogen virulence, venom toxicology and cancer biology.

OBJECTIVE AND RATIONALE

The aim of this article is to summarize the current state of knowledge on CAP superfamily proteins in mammalian fertility, organismal homeostasis and disease pathogenesis.

SEARCH METHODS

The scientific literature search was undertaken via PubMed database on all articles published prior to November 2019. Search terms were based on following keywords: 'CAP superfamily', 'CRISP', 'Cysteine-rich secretory proteins', 'Antigen 5', 'Pathogenesis-related 1', 'male fertility', 'CAP and CTL domain containing', 'CRISPLD1', 'CRISPLD2', 'bacterial SCP', 'ion channel regulator', 'CatSper', 'PI15', 'PI16', 'CLEC', 'PRY proteins', 'ASP proteins', 'spermatogenesis', 'epididymal maturation', 'capacitation' and 'snake CRISP'. In addition to that, reference lists of primary and review article were reviewed for additional relevant publications.

OUTCOMES

In this review, we discuss the breadth of knowledge on CAP superfamily proteins with regards to their protein structure, biological functions and emerging significance in reproduction, health and disease. We discuss the evolution of CAP superfamily proteins from their otherwise unembellished prokaryotic predecessors into the multi-domain and neofunctionalized members found in eukaryotic organisms today. At least in part because of the rapid evolution of these proteins, many inconsistencies in nomenclature exist within the literature. As such, and in part through the use of a maximum likelihood phylogenetic analysis of the vertebrate CRISP subfamily, we have attempted to clarify this confusion, thus allowing for a comparison of orthologous protein function between species. This framework also allows the prediction of functional relevance between species based on sequence and structural conservation.

WIDER IMPLICATIONS

This review generates a picture of critical roles for CAP proteins in ion channel regulation, sterol and lipid binding and protease inhibition, and as ligands involved in the induction of multiple cellular processes.

Hookworms Evade Host Immunity by Secreting a Deoxyribonuclease to Degrade Neutrophil Extracellular Traps

Hookworms cause a major neglected tropical disease, occurring after larvae penetrate the host skin. Neutrophils are phagocytes that kill large pathogens by releasing neutrophil extracellular traps (NETs), but whether they target hookworms during skin infection is unknown. Using a murine hookworm, Nippostrongylus brasiliensis, we observed neutrophils being rapidly recruited and deploying NETs around skin-penetrating larvae. Neutrophils depletion or NET inhibition altered larvae behavior and enhanced the number of adult worms following murine infection. Nevertheless, larvae were able to mitigate the effect of NETs by secreting a deoxyribonuclease (Nb-DNase II) to degrade the DNA backbone. Critically, neutrophils were able to kill larvae in vitro, which was enhanced by neutralizing Nb-DNase II. Homologs of Nb-DNase II are present in other nematodes, including the human hookworm, Necator americanus, which also evaded NETs in vitro. These findings highlight the importance of neutrophils in hookworm infection and a potential conserved mechanism of immune evasion.

Twenty-five-year research progress in hookworm excretory/secretory products

Hookworm infection is a major public health problem that threatens about 500 million people throughout tropical areas of the world. Adult hookworms survive for many years in the host intestine, where they suck blood, causing iron deficiency anemia and malnutrition. Numerous molecules, named excretory/secretory (ES) products, are secreted by hookworm adults and/or larvae to aid in parasite survival and pathobiology. Although the molecular cloning and characterization of hookworm ES products began 25 years ago, the biological role and molecular nature of many of them are still unclear. Hookworm ES products, with distinct structures and functions, have been linked to many essential events in the disease pathogenesis. These events include host invasion and tissue migration, parasite nourishment and reproduction, and immune modulation. Several of these products represent promising vaccine targets for controlling hookworm disease and therapeutic targets for many inflammatory diseases. This review aims to summarize our present knowledge about hookworm ES products, including their role in parasite biology, host-parasite interactions, and as vaccine and pharmaceutical targets and to identify research gaps and future research directions in this field.

Adaptive Radiation of the Flukes of the Family Fasciolidae Inferred from Genome-Wide Comparisons of Key Species

Liver and intestinal flukes of the family Fasciolidae cause zoonotic food-borne infections that impact both agriculture and human health throughout the world. Their evolutionary history and the genetic basis underlying their phenotypic and ecological diversity are not well understood. To close that knowledge gap, we compared the whole genomes of Fasciola hepatica, Fasciola gigantica, and Fasciolopsis buski and determined that the split between Fasciolopsis and Fasciola took place ∼90 Ma in the late Cretaceous period, and that between 65 and 50 Ma an intermediate host switch and a shift from intestinal to hepatic habitats occurred in the Fasciola lineage. The rapid climatic and ecological changes occurring during this period may have contributed to the adaptive radiation of these flukes. Expansion of cathepsins, fatty-acid-binding proteins, protein disulfide-isomerases, and molecular chaperones in the genus Fasciola highlights the significance of excretory-secretory proteins in these liver-dwelling flukes. Fasciola hepatica and Fasciola gigantica diverged ∼5 Ma near the Miocene-Pliocene boundary that coincides with reduced faunal exchange between Africa and Eurasia. Severe decrease in the effective population size ∼10 ka in Fasciola is consistent with a founder effect associated with its recent global spread through ruminant domestication. G-protein-coupled receptors may have key roles in adaptation of physiology and behavior to new ecological niches. This study has provided novel insights about the genome evolution of these important pathogens, has generated genomic resources to enable development of improved interventions and diagnosis, and has laid a solid foundation for genomic epidemiology to trace drug resistance and to aid surveillance.

Elucidating the molecular and developmental biology of parasitic nematodes: Moving to a multiomics paradigm

In the past two decades, significant progress has been made in the sequencing, assembly, annotation and analyses of genomes and transcriptomes of parasitic worms of socioeconomic importance. This progress has somewhat improved our knowledge and understanding of these pathogens at the molecular level. However, compared with the free-living nematode Caenorhabditis elegans, the areas of functional genomics, transcriptomics, proteomics and metabolomics of parasitic nematodes are still in their infancy, and there are major gaps in our knowledge and understanding of the molecular biology of parasitic nematodes. The information on signalling molecules, molecular pathways and microRNAs (miRNAs) that are known to be involved in developmental processes in C. elegans and the availability of some molecular resources (draft genomes, transcriptomes and some proteomes) for selected parasitic nematodes provide a basis to start exploring the developmental biology of parasitic nematodes. Indeed, some studies have identified molecules and pathways that might associate with developmental processes in related, parasitic nematodes, such as Haemonchus contortus (barber's pole worm). However, detailed information is often scant and 'omics resources are limited, preventing a proper integration of 'omic data sets and comprehensive analyses. Moreover, little is known about the functional roles of pheromones, hormones, signalling pathways and post-transcriptional/post-translational regulations in the development of key parasitic nematodes throughout their entire life cycles. Although C. elegans is an excellent model to assist molecular studies of parasitic nematodes, its use is limited when it comes to explorations of processes that are specific to parasitism within host animals. A deep understanding of parasitic nematodes, such as H. contortus, requires substantially enhanced resources and the use of integrative 'omics approaches for analyses. The improved genome and well-established in vitro larval culture system for H. contortus provide unprecedented opportunities for comprehensive studies of the transcriptomes (mRNA and miRNA), proteomes (somatic, excretory/secretory and phosphorylated proteins) and lipidomes (e.g., polar and neutral lipids) of this nematode. Such resources should enable in-depth explorations of its developmental biology at a level, not previously possible. The main aims of this review are (i) to provide a background on the development of nematodes, with a particular emphasis on the molecular aspects involved in the dauer formation and exit in C. elegans; (ii) to critically appraise the current state of knowledge of the developmental biology of parasitic nematodes and identify key knowledge gaps; (iii) to cover salient aspects of H. contortus, with a focus on the recent advances in genomics, transcriptomics, proteomics and lipidomics as well as in vitro culturing systems; (iv) to review recent advances in our knowledge and understanding of the molecular and developmental biology of H. contortus using an integrative multiomics approach, and discuss the implications of this approach for detailed explorations of signalling molecules, molecular processes and pathways likely associated with nematode development, adaptation and parasitism, and for the identification of novel intervention targets against these pathogens. Clearly, the multiomics approach established recently is readily applicable to exploring a wide range of interesting and socioeconomically significant parasitic worms (including also trematodes and cestodes) at the molecular level, and to elucidate host-parasite interactions and disease processes.

Secreted venom allergen-like proteins of helminths: Conserved modulators of host responses in animals and plants

Despite causing considerable damage to host tissue at the onset of parasitism, invasive helminths establish remarkably persistent infections in both animals and plants. Secretions released by these obligate parasites during host invasion are thought to be crucial for their persistence in infection. Helminth secretions are complex mixtures of molecules, most of which have unknown molecular targets and functions in host cells or tissues. Although the habitats of animal- and plant-parasitic helminths are very distinct, their secretions share the presence of a structurally conserved group of proteins called venom allergen-like proteins (VALs). Helminths abundantly secrete VALs during several stages of parasitism while inflicting extensive damage to host tissue. The tight association between the secretion of VALs and the onset of parasitism has triggered a particular interest in this group of proteins, as improved knowledge on their biological functions may assist in designing novel protection strategies against parasites in humans, livestock, and important food crops.

Molecular alterations during larval development of Haemonchus contortus in vitro are under tight post-transcriptional control

In this study, we explored the molecular alterations in the developmental switch from the L3 to the exsheathed L3 (xL3) and to the L4 stage of Haemonchus contortus in vitro using an integrated transcriptomic, proteomic and bioinformatic approach. Totals of 9,754 mRNAs, 88 microRNAs (miRNAs) and 1,591 proteins were identified, and 6,686 miRNA-mRNA pairs inferred in all larval stages studied. Approximately 16% of transcripts in the combined transcriptome (representing all three larval stages) were expressed as proteins, and there were positive correlations (r = 0.39-0.44) between mRNA transcription and protein expression in the three distinct developmental stages of the parasite. Of the predicted targets, 1,019 (27.0%) mRNA transcripts were expressed as proteins, and there was a negative correlation (r = -0.60 to -0.50) in the differential mRNA transcription and protein expression between developmental stages upon pairwise comparison. The changes in transcription (mRNA and miRNA) and protein expression from the free-living to the parasitic life cycle phase of H. contortus related to enrichments in biological pathways associated with metabolism (e.g., carbohydrate and lipid degradation, and amino acid metabolism), environmental information processing (e.g., signal transduction, signalling molecules and interactions) and/or genetic information processing (e.g., transcription and translation). Specifically, fatty acid degradation, steroid hormone biosynthesis and the Rap1 signalling pathway were suppressed, whereas transcription, translation and protein processing in the endoplasmic reticulum were upregulated during the transition from the free-living L3 to the parasitic xL3 and L4 stages of the nematode in vitro. Dominant post-transcriptional regulation was inferred to elicit these changes, and particular miRNAs (e.g., hco-miR-34 and hco-miR-252) appear to play roles in stress responses and/or environmental adaptations during developmental transitions of H. contortus. Taken together, these integrated results provide a comprehensive insight into the developmental biology of this important parasite at the molecular level in vitro. The approach applied here to H. contortus can be readily applied to other parasitic nematodes.

Modulation of mitochondrial metabolism as a biochemical trait in blood feeding organisms: the redox vampire hypothesis redux

Hematophagous organisms undergo remarkable metabolic changes during the blood digestion process, increasing fermentative glucose metabolism, and reducing respiratory rates, both consequence of functional mitochondrial remodeling. Here, we review the pathways involved in energy metabolism and mitochondrial functionality in a comparative framework across different hematophagous species, and consider how these processes regulate redox homeostasis during blood digestion. The trend across distinct species indicate that a switch in energy metabolism might represent an important defensive mechanism to avoid the potential harmful interaction of oxidants generated from aerobic energy metabolism with products derived from blood digestion. Indeed, in insect vectors, blood feeding transiently reduces respiratory rates and oxidant production, irrespective of tissue and insect model. On the other hand, a different scenario is observed in several unrelated parasite species when exposed to blood digestion products, as respiratory rates reduce and mitochondrial oxidant production increase. The emerging picture indicates that re-wiring of energy metabolism, through reduced mitochondrial function, culminates in improved tolerance to redox insults and seems to represent a key step for hematophagous organisms to cope with the overwhelming and potentially toxic blood meal.

Recombinant Haemonchus contortus 24 kDa excretory/secretory protein (rHcES-24) modulate the immune functions of goat PBMCs in vitro

A 24 kDa protein is one of the important components in Haemonchus contortus (barber pole worm) excretory/secretory products (HcESPs), which was shown to have important antigenic function. However, little is known about the immunomodulatory effects of this proteinon host cell. In the present study gene encoding 24kDa excretory/secretory protein (HcES-24) was cloned. The recombinant protein of HcES-24 (rHcES-24) was expressed in a histidine-tagged fusion protein soluble form in Escherichia coli. Binding activity of rHcES-24 to goat PBMCs was confirmed by immunofluorescence assay (IFA) and its immunomudulatory effect on cytokine secretion, cell proliferation, cell migration and nitric oxide production were observed by co-incubation of rHcES-24. IFA results revealed that rHcES-24 could bind to the PBMCs. The interaction of rHcES-24 increased the production of IL4, IL10, IL17 and cell migration in dose dependent manner. However, rHcES-24 treatment significantly suppressed the production of IFNγ, proliferation of the PBMC and Nitric oxide (NO) production. Our findings showed that the rHcES-24 played important regulatory effects on the goat PBMCs.

Of dogs and hookworms: man's best friend and his parasites as a model for translational biomedical research

We present evidence that the dog hookworm (Ancylostoma caninum) is underutilised in the study of host-parasite interactions, particularly as a proxy for the human-hookworm relationship. The inability to passage hookworms through all life stages in vitro means that adult stage hookworms have to be harvested from the gut of their definitive hosts for ex vivo research. This makes study of the human-hookworm interface difficult for technical and ethical reasons. The historical association of humans, dogs and hookworms presents a unique triad of positive evolutionary pressure to drive the A. caninum-canine interaction to reflect that of the human-hookworm relationship. Here we discuss A. caninum as a proxy for human hookworm infection and situate this hookworm model within the current research agenda, including the various 'omics' applications and the search for next generation biologics to treat a plethora of human diseases. Historically, the dog hookworm has been well described on a physiological and biochemical level, with an increasing understanding of its role as a human zoonosis. With its similarity to human hookworm, the recent publications of hookworm genomes and other omics databases, as well as the ready availability of these parasites for ex vivo culture, the dog hookworm presents itself as a valuable tool for discovery and translational research.

Tissue-specific transcriptomes of Anisakis simplex (sensu stricto) and Anisakis pegreffii reveal potential molecular mechanisms involved in pathogenicity

Background

Larval stages of the sibling species of parasitic nematodes Anisakis simplex (sensu stricto) (s.s.) (AS) and Anisakis pegreffii (AP) are responsible for a fish-borne zoonosis, known as anisakiasis, that humans aquire via the ingestion of raw or undercooked infected fish or fish-based products. These two species differ in geographical distribution, genetic background and peculiar traits involved in pathogenicity. However, thus far little is known of key molecules potentially involved in host-parasite interactions. Here, high-throughput RNA-Seq and bioinformatics analyses of sequence data were applied to the characterization of the whole sets of transcripts expressed by infective larvae of AS and AP, as well as of their pharyngeal tissues, in a bid to identify transcripts potentially involved in tissue invasion and host-pathogen interplay.

Results

Approximately 34,000,000 single-end reads were generated from cDNA libraries for each species. Transcripts identified in AS and AP encoded 19,403 and 10,424 putative peptides, respectively, and were classified based on homology searches, protein motifs, gene ontology and biological pathway mapping. Differential gene expression analysis yielded 226 and 339 transcripts upregulated in the pharyngeal regions of AS and AP, respectively, compared with their corresponding whole-larvae datasets. These included proteolytic enzymes, molecules encoding anesthetics, inhibitors of primary hemostasis and virulence factors, anticoagulants and immunomodulatory peptides.

Conclusions

This work provides the scientific community with a list of key transcripts expressed by AS and AP pharyngeal tissues and corresponding annotation information which represents a ready-to-use resource for future functional studies of biological pathways specifically involved in host-parasite interplay.

Electronic supplementary material

The online version of this article (10.1186/s13071-017-2585-7) contains supplementary material, which is available to authorized users.

Ancylostoma ceylanicum infective third-stage larvae are activated by co-culture with HT-29-MTX intestinal epithelial cells

Background

Human hookworm larvae arrest development until they enter an appropriate host. This makes it difficult to access the larvae for studying larval development or host-parasite interactions. While there are in vivo and in vitro animal models of human hookworm infection, there is currently no human, in vitro model. While animal models have provided much insight into hookworm biology, there are limitations to how closely this can replicate human infection. Therefore, we have developed a human, in vitro model of the initial phase of hookworm infection using intestinal epithelial cell culture.

Results

Co-culture of the human hookworm Ancylostoma ceylanicum with the mucus-secreting, human intestinal epithelial cell line HT-29-MTX resulted in activation of infective third-stage larvae, as measured by resumption of feeding. Larvae were maximally activated by direct contact with fully differentiated HT-29-MTX intestinal epithelial cells. HT-29-MTX cells treated with A. ceylanicum larvae showed differential gene expression of several immunity-related genes.

Conclusions

Co-culture with HT-29-MTX can be used to activate A. ceylanicum larvae. This provides an opportunity to study the interaction of activated larvae with the human intestinal epithelium.

Exploiting Helminth-Host Interactomes through Big Data

Helminths facilitate their parasitic existence through the production and secretion of different molecules, including proteins. Some helminth proteins can manipulate the host's immune system, a phenomenon that is now being exploited with a view to developing therapeutics for inflammatory diseases. In recent years, hundreds of helminth genomes have been sequenced, but as a community we are still taking baby steps when it comes to identifying proteins that govern host-helminth interactions. The information generated from genomic, immunomic, and proteomic studies, as well as from cutting-edge approaches such as proteogenomics, is leading to a substantial volume of big data that can be utilised to shed light on fundamental biology and provide solutions for the development of bioactive-molecule-based therapeutics.

CAP protein superfamily members in Toxocara canis

BACKGROUND

Proteins of the cysteine-rich secretory proteins, antigen 5 and pathogenesis-related 1 (CAP) superfamily are recognized or proposed to play roles in parasite development and reproduction, and in modulating host immune attack and infection processes. However, little is known about these proteins for most parasites.

RESULTS

In the present study, we explored CAP proteins of Toxocara canis, a socioeconomically important zoonotic roundworm. To do this, we mined and curated transcriptomic and genomic data, predicted and curated full-length protein sequences (n = 28), conducted analyses of these data and studied the transcription of respective genes in different developmental stages of T. canis. In addition, based on information available for Caenorhabditis elegans, we inferred that selected genes (including lon-1, vap-1, vap-2, scl-1, scl-8 and scl-11 orthologs) of T. canis and their interaction partners likely play central roles in this parasite's development and/or reproduction via TGF-beta and/or insulin-like signaling pathways, or via host interactions.

CONCLUSION

In conclusion, this study could provide a foundation to guide future studies of CAP proteins of T. canis and related parasites, and might assist in finding new interventions against diseases caused by these parasites.

Understanding Haemonchus contortus Better Through Genomics and Transcriptomics

Parasitic roundworms (nematodes) cause substantial mortality and morbidity in animals globally. The barber's pole worm, Haemonchus contortus, is one of the most economically significant parasitic nematodes of small ruminants worldwide. Although this and related nematodes can be controlled relatively well using anthelmintics, resistance against most drugs in common use has become a major problem. Until recently, almost nothing was known about the molecular biology of H. contortus on a global scale. This chapter gives a brief background on H. contortus and haemonchosis, immune responses, vaccine research, chemotherapeutics and current problems associated with drug resistance. It also describes progress in transcriptomics before the availability of H. contortus genomes and the challenges associated with such work. It then reviews major progress on the two draft genomes and developmental transcriptomes of H. contortus, and summarizes their implications for the molecular biology of this worm in both the free-living and the parasitic stages of its life cycle. The chapter concludes by considering how genomics and transcriptomics can accelerate research on Haemonchus and related parasites, and can enable the development of new interventions against haemonchosis.

Expression profile of heat shock response factors during hookworm larval activation and parasitic development

When organisms are exposed to an increase in temperature, they undergo a heat shock response (HSR) regulated by the transcription factor heat shock factor 1 (HSF-1). The heat shock response includes the rapid changes in gene expression initiated by binding of HSF-1 to response elements in the promoters of heat shock genes. Heat shock proteins function as molecular chaperones to protect proteins during periods of elevated temperature and other stress. During infection, hookworm infective third stage larvae (L3) undergo a temperature shift from ambient to host temperature. This increased temperature is required for the resumption of feeding and activation of L3, but whether this increase initiates a heat shock response is unknown. To investigate the role of the heat shock in hookworm L3 activation and parasitic development, we identified and characterized the expression profile of several components of the heat shock response in the hookworm Ancylostoma caninum. We cloned DNAs encoding an hsp70 family member (Aca-hsp-1) and an hsp90 family member (Aca-daf-21). Exposure to a heat shock of 42°C for one hour caused significant up-regulation of both genes, which slowly returned to near baseline levels following one hour attenuation at 22°C. Neither gene was up-regulated in response to host temperature (37°C). Conversely, levels of hsf-1 remained unchanged during heat shock, but increased in response to incubation at 37°C. During activation, both hsp-1 and daf-21 are down regulated early, although daf-21 levels increase significantly in non-activated control larvae after 12h, and slightly in activated larvae by 24h incubation. The heat shock response modulators celastrol and KNK437 were tested for their effects on gene expression during heat shock and activation. Pre-incubation with celastrol, an HSP90 inhibitor that promotes heat shock gene expression, slightly up-regulated expression of both hsp-1 and daf-21 during heat shock. KNK437, an inhibitor of heat shock protein expression, slightly down regulated both genes under similar conditions. Both modulators inhibited activation-associated feeding, but neither had an effect on hsp-1 levels in activated L3 at 16h. Both celastrol and KNK437 prevent the up-regulation of daf-21 and hsf-1 seen in non-activated control larvae during activation, and significantly down regulated expression of the HSF-1 negative regulator Aca-hsb-1 in activated larvae. Expression levels of heat shock response factors were examined in developing Ancylostoma ceylanicum larvae recovered from infected hosts and found to differ significantly from the expression profile of activated L3, suggesting that feeding during in vitro activation is regulated differently than parasitic development. Our results indicate that a classical heat shock response is not induced at host temperature and is suppressed during larval recovery and parasitic development in the host, but a partial heat shock response is induced after extended incubation at host temperature in the absence of a developmental signal, possibly to protect against heat stress.

The barber's pole worm CAP protein superfamily--A basis for fundamental discovery and biotechnology advances

Parasitic worm proteins that belong to the cysteine-rich secretory proteins, antigen 5 and pathogenesis-related 1 (CAP) superfamily are proposed to play key roles in the infection process and the modulation of immune responses in host animals. However, there is limited information on these proteins for most socio-economically important worms. Here, we review the CAP protein superfamily of Haemonchus contortus (barber's pole worm), a highly significant parasitic roundworm (order Strongylida) of small ruminants. To do this, we mined genome and transcriptomic datasets, predicted and curated full-length amino acid sequences (n=45), undertook systematic phylogenetic analyses of these data and investigated transcription throughout the life cycle of H. contortus. We inferred functions for selected Caenorhabditis elegans orthologs (including vap-1, vap-2, scl-5 and lon-1) based on genetic networking and by integrating data and published information, and were able to infer that a subset of orthologs and their interaction partners play pivotal roles in growth and development via the insulin-like and/or the TGF-beta signalling pathways. The identification of the important and conserved growth regulator LON-1 led us to appraise the three-dimensional structure of this CAP protein by comparative modelling. This model revealed the presence of different topological moieties on the canonical fold of the CAP domain, which coincide with an overall charge separation as indicated by the electrostatic surface potential map. These observations suggest the existence of separate sites for effector binding and receptor interactions, and thus support the proposal that these worm molecules act in similar ways as venoms act as ligands for chemokine receptors or G protein-coupled receptor effectors. In conclusion, this review should guide future molecular studies of these molecules, and could support the development of novel interventions against haemonchosis.

The structure of hookworm platelet inhibitor (HPI), a CAP superfamily member from Ancylostoma caninum

Secreted protein components of hookworm species include a number of representatives of the cysteine-rich/antigen 5/pathogenesis-related 1 (CAP) protein family known as Ancylostoma-secreted proteins (ASPs). Some of these have been considered as candidate antigens for the development of vaccines against hookworms. The functions of most CAP superfamily members are poorly understood, but one form, the hookworm platelet inhibitor (HPI), has been isolated as a putative antagonist of the platelet integrins αIIbβ3 and α2β1. Here, the crystal structure of HPI is described and its structural features are examined in relation to its possible function. The HPI structure is similar to those of other ASPs and shows incomplete conservation of the sequence motifs CAP1 and CAP2 that are considered to be diagnostic of CAP superfamily members. The asymmetric unit of the HPI crystal contains a dimer with an extensive interaction interface, but chromatographic measurements indicate that it is primarily monomeric in solution. In the dimeric structure, the putative active-site cleft areas from both monomers are united into a single negatively charged depression. A potential Lys-Gly-Asp disintegrin-like motif was identified in the sequence of HPI, but is not positioned at the apex of a tight turn, making it unlikely that it interacts with the integrin. Recombinant HPI produced in Escherichia coli was found not to inhibit the adhesion of human platelets to collagen or fibrinogen, despite having a native structure as shown by X-ray diffraction. This result corroborates previous analyses of recombinant HPI and suggests that it might require post-translational modification or have a different biological function.

Impact of next-generation technologies on exploring socioeconomically important parasites and developing new interventions

High-throughput molecular and computer technologies have become instrumental for systems biological explorations of pathogens, including parasites. For instance, investigations of the transcriptomes of different developmental stages of parasitic nematodes give insights into gene expression, regulation and function in a parasite, which is a significant step to understanding their biology, as well as interactions with their host(s) and disease. This chapter (1) gives a background on some key parasitic nematodes of socioeconomic importance, (2) describes sequencing and bioinformatic technologies for large-scale studies of the transcriptomes and genomes of these parasites, (3) provides some recent examples of applications and (4) emphasizes the prospects of fundamental biological explorations of parasites using these technologies for the development of new interventions to combat parasitic diseases.

Apoplastic venom allergen-like proteins of cyst nematodes modulate the activation of basal plant innate immunity by cell surface receptors

Despite causing considerable damage to host tissue during the onset of parasitism, nematodes establish remarkably persistent infections in both animals and plants. It is thought that an elaborate repertoire of effector proteins in nematode secretions suppresses damage-triggered immune responses of the host. However, the nature and mode of action of most immunomodulatory compounds in nematode secretions are not well understood. Here, we show that venom allergen-like proteins of plant-parasitic nematodes selectively suppress host immunity mediated by surface-localized immune receptors. Venom allergen-like proteins are uniquely conserved in secretions of all animal- and plant-parasitic nematodes studied to date, but their role during the onset of parasitism has thus far remained elusive. Knocking-down the expression of the venom allergen-like protein Gr-VAP1 severely hampered the infectivity of the potato cyst nematode Globodera rostochiensis. By contrast, heterologous expression of Gr-VAP1 and two other venom allergen-like proteins from the beet cyst nematode Heterodera schachtii in plants resulted in the loss of basal immunity to multiple unrelated pathogens. The modulation of basal immunity by ectopic venom allergen-like proteins in Arabidopsis thaliana involved extracellular protease-based host defenses and non-photochemical quenching in chloroplasts. Non-photochemical quenching regulates the initiation of the defense-related programmed cell death, the onset of which was commonly suppressed by venom allergen-like proteins from G. rostochiensis, H. schachtii, and the root-knot nematode Meloidogyne incognita. Surprisingly, these venom allergen-like proteins only affected the programmed cell death mediated by surface-localized immune receptors. Furthermore, the delivery of venom allergen-like proteins into host tissue coincides with the enzymatic breakdown of plant cell walls by migratory nematodes. We, therefore, conclude that parasitic nematodes most likely utilize venom allergen-like proteins to suppress the activation of defenses by immunogenic breakdown products in damaged host tissue.

Plant-parasitic nematodes have a major impact on global food security, as they reduce the annual yield of food crops by approximately 10 percent. For decades, the application of non-selective toxic chemicals to infested soils controlled outbreaks of plant-parasitic nematodes. The recent bans on most of these chemicals has redirected attention towards a wider use of basal, broad-spectrum immunity to nematodes in crop cultivars. However, it is currently not known if this most ancient layer of immunity affects host invasion by plant-parasitic nematodes at all. Basal immunity in plants relies on the detection of molecular patterns uniquely associated with infections in the apoplast by surface-localized receptors. Here, we demonstrate that venom allergen-like proteins in secretions of soil-borne cyst nematodes suppress immune responses mediated by surface-localized pattern recognition receptors. Migratory stages of cyst nematodes most likely deliver venom allergen-like proteins together with a range of plant cell wall-degrading enzymes into the apoplast of host cells. We therefore conclude that these nematodes most likely secrete venom allergen-like proteins to modulate host responses triggered by the release of immunogenic fragments of damaged plant cell walls.

The Relevance of Structural Biology in Studying Molecules Involved in Parasite–Host Interactions: Potential for Designing New Interventions

New interventions against infectious diseases require a detailed knowledge and understanding of pathogen–host interactions and pathogeneses at the molecular level. The combination of the considerable advances in systems biology research with methods to explore the structural biology of molecules is poised to provide new insights into these areas. Importantly, exploring three-dimensional structures of proteins is central to understanding disease processes, and establishing structure–function relationships assists in identification and assessment of new drug and vaccine targets. Frequently, the molecular arsenal deployed by invading pathogens, and in particular parasites, reveals a common theme whereby families of proteins with conserved three-dimensional folds play crucial roles in infectious processes, but individual members of such families show high levels of specialisation, which is often achieved through grafting particular structural features onto the shared overall fold. Accordingly, the applicability of predictive methodologies based on the primary structure of proteins or genome annotations is limited, particularly when thorough knowledge of molecular-level mechanisms is required. Such instances exemplify the need for experimental three-dimensional structures provided by protein crystallography, which remain an essential component of this area of research. In the present article, we review two examples of key protein families recently investigated in our laboratories, which could represent intervention targets in the metabolome or secretome of parasites.

Structure of Ostertagia ostertagi ASP-1: insights into disulfide-mediated cyclization and dimerization

The cysteine-rich secretory/antigen 5/pathogenesis-related 1 (CAP) protein superfamily is composed of a functionally diverse group of members that are found in both eukaryotes and prokaryotes. The excretome/secretome of numerous helminths (parasitic nematodes) contains abundant amounts of CAP members termed activation-associated secreted proteins (ASPs). Although ASPs are necessary for the parasitic life cycle in the host, the current lack of structural and functional information limits both understanding of their actual role in host-parasite interactions and the development of new routes in controlling parasitic infections and diseases. Alleviating this knowledge gap, a 1.85 Å resolution structure of recombinantly produced Oo-ASP-1 from Ostertagia ostertagi, which is one of the most prevalent gastrointestinal parasites in cattle worldwide, was solved. Overall, Oo-ASP-1 displays the common hallmark architecture shared by all CAP-superfamily members, including the N-terminal CAP and C-terminal cysteine-rich domains, but it also reveals a number of highly peculiar features. In agreement with studies of the natively produced protein, the crystal structure shows that Oo-ASP-1 forms a stable dimer that has been found to be primarily maintained via an intermolecular disulfide bridge, hence the small interaction surface of only 306.8 Å(2). Moreover, unlike any other ASP described to date, an additional intramolecular disulfide bridge links the N- and C-termini of each monomer, thereby yielding a quasi-cyclic molecule. Taken together, the insights presented here form an initial step towards a better understanding of the actual biological role(s) that this ASP plays in host-parasite interactions. The structure is also essential to help to define the key regions of the protein suitable for development of ASP-based vaccines, which would enable the current issues surrounding anthelmintic resistance in the treatment of parasitic infections and diseases to be circumvented.

Venom proteome of the box jellyfish Chironex fleckeri

The nematocyst is a complex intracellular structure unique to Cnidaria. When triggered to discharge, the nematocyst explosively releases a long spiny, tubule that delivers an often highly venomous mixture of components. The box jellyfish, Chironex fleckeri, produces exceptionally potent and rapid-acting venom and its stings to humans cause severe localized and systemic effects that are potentially life-threatening. In an effort to identify toxins that could be responsible for the serious health effects caused by C. fleckeri and related species, we used a proteomic approach to profile the protein components of C. fleckeri venom. Collectively, 61 proteins were identified, including toxins and proteins important for nematocyte development and nematocyst formation (nematogenesis). The most abundant toxins identified were isoforms of a taxonomically restricted family of potent cnidarian proteins. These toxins are associated with cytolytic, nociceptive, inflammatory, dermonecrotic and lethal properties and expansion of this important protein family goes some way to explaining the destructive and potentially fatal effects of C. fleckeri venom. Venom proteins and their post-translational modifications (PTMs) were further characterized using toxin-specific antibodies and phosphoprotein/glycoprotein-specific stains. Results indicated that glycosylation is a common PTM of the toxin family while a lack of cross-reactivity by toxin-specific antibodies infers there is significant divergence in structure and possibly function among family members. This study provides insight into the depth and diversity of protein toxins produced by harmful box jellyfish and represents the first description of a cubozoan jellyfish venom proteome.

The hookworm pharmacopoeia for inflammatory diseases

In the developed world, declining prevalence of parasitic infections correlates with increased incidence of allergic and autoimmune disorders. Current treatments for these chronic inflammatory conditions have little to no effect on their prevalence and are referred to as "controllers" rather than cures. There has been limited success in therapeutically targeting allergic and autoimmune pathways, leaving an unmet need for development of effective anti-inflammatories. We discuss the benefit of hookworm infections and the parasite's ability to condition the immune system to prevent allergic asthma and inflammatory bowel diseases. We then examine the immunomodulatory properties of selected hookworm-derived proteins in these two models of inflammation. While hookworm protein therapy has yet to be fully exploited, the identification of these proteins and the mechanisms by which they skew the immune system will provide new avenues for controlling and optimally reversing key pathological processes important in allergic and inflammatory bowel diseases.

Molecular mechanisms of hookworm disease: stealth, virulence, and vaccines

Hookworms produce a vast repertoire of structurally and functionally diverse molecules that mediate their long-term survival and pathogenesis within a human host. Many of these molecules are secreted by the parasite, after which they interact with critical components of host biology, including processes that are key to host survival. The most important of these interactions is the hookworm's interruption of nutrient acquisition by the host through its ingestion and digestion of host blood. This results in iron deficiency and eventually the microcytic hypochromic anemia or iron deficiency anemia that is the clinical hallmark of hookworm infection. Other molecular mechanisms of hookworm infection cause a systematic suppression of the host immune response to both the parasite and to bystander antigens (eg, vaccines or allergens). This is achieved by a series of molecules that assist the parasite in the stealthy evasion of the host immune response. This review will summarize the current knowledge of the molecular mechanisms used by hookworms to survive for extended periods in the human host (up to 7 years or longer) and examine the pivotal contributions of these molecular mechanisms to chronic hookworm parasitism and host clinical outcomes.

Genes of the bovine lungworm Dictyocaulus viviparus associated with transition from pasture to parasitism

Genes necessary to enable nematode parasitic life after free-living larval life are of substantial interest to understand parasitism. We investigated transcriptional changes during transition to parasitism in the bovine lungworm Dictyocaulus viviparus, one of the most important parasites in cattle farming due to substantial economic losses. Upregulated transcripts in either free-living, developmentally arrested L3 or parasitic immature L5 were identified by suppression subtractive hybridization (SSH) followed by differential screening and subsequent virtual Northern blot verification. From 400 sequenced clones of parasitic L5, 372 (93.0%) upregulated high quality ESTs were obtained clustering into 30 contigs and 38 singletons. Most conceptual translated peptides were SCP/TAPS "family" members also known as pathogenesis-related protein (PRP) superfamily (28.5% of total ESTs), cysteine proteases (24.5%), and H-gal-GP orthologues (9.9%). These proteins are predicted to play key roles in fundamental biological processes such as nutrition and development but also parasite-host interactions and immune defense mechanisms. Increased energy requirement of the rapidly developing L5 lungworm stage was obvious in a proportion of 12.2% upregulated ESTs being components of the respiratory chain. From the developmentally arrested L3 stage sequencing of 200 clones resulted in 195 high quality ESTs (97.0%) clustering into 7 contigs and 3 singletons only. Besides a hypothetical protein (70.1% of total ESTs) most transcripts encoded the cleavage stimulation factor subunit 2 (17.5%), which is a component of the poly(A(+)) machinery and found to be involved in gene silencing. Obtained data provide the basis for future fundamental research into genes associated with parasitic lifestyle but also applied research like vaccine and/or drug development.

Insights into SCP/TAPS proteins of liver flukes based on large-scale bioinformatic analyses of sequence datasets

BACKGROUND

SCP/TAPS proteins of parasitic helminths have been proposed to play key roles in fundamental biological processes linked to the invasion of and establishment in their mammalian host animals, such as the transition from free-living to parasitic stages and the modulation of host immune responses. Despite the evidence that SCP/TAPS proteins of parasitic nematodes are involved in host-parasite interactions, there is a paucity of information on this protein family for parasitic trematodes of socio-economic importance.

METHODOLOGY/PRINCIPAL FINDINGS

We conducted the first large-scale study of SCP/TAPS proteins of a range of parasitic trematodes of both human and veterinary importance (including the liver flukes Clonorchis sinensis, Opisthorchis viverrini, Fasciola hepatica and F. gigantica as well as the blood flukes Schistosoma mansoni, S. japonicum and S. haematobium). We mined all current transcriptomic and/or genomic sequence datasets from public databases, predicted secondary structures of full-length protein sequences, undertook systematic phylogenetic analyses and investigated the differential transcription of SCP/TAPS genes in O. viverrini and F. hepatica, with an emphasis on those that are up-regulated in the developmental stages infecting the mammalian host.

CONCLUSIONS

This work, which sheds new light on SCP/TAPS proteins, guides future structural and functional explorations of key SCP/TAPS molecules associated with diseases caused by flatworms. Future fundamental investigations of these molecules in parasites and the integration of structural and functional data could lead to new approaches for the control of parasitic diseases.

Strongyloides papillosus: changes in transcript levels of lysozyme and aspartic protease 2 in percutaneously migrated larvae

The infection of the host is the crucial event in the life-cycle of parasites. To understand the molecular mechanisms of this important step, different methods are used in present studies. For analysis of changes in transcript levels the most sensitive method is the quantitative real-time PCR (qPCR). For an accurate analysis the evaluation of a set of adequate reference genes is necessary. The present study aimed to analyse the transcriptional levels of two genes of interest, the putative aspartic protease Spa-asp-2 and the putative lysozyme Spa-lys, in infective, free-living larvae of Strongyloides papillosus at different ages and from long-term and short-term infections and percutaneously migrated ("parasitic") larvae. Percutaneously migrated larvae were collected using the PERL chamber system and ovine skin in vitro. Reference genes identified as most suitable for transcriptional analysis according to geNorm analysis were genes for the eukaryotic translation elongation factor 1 alpha (Spa-eft-2), actin variation 2 (Spa-act-v2) and beta tubulin (Spa-tbb-1). Transcriptional analysis of the genes in percutaneously migrated larvae showed an upregulation of Spa-asp-2, while Spa-lys was downregulated. Data from the presented study provide a first glance into the changes of transcript levels of S. papillosus induced by percutaneous migration.

Hookworm SCP/TAPS protein structure--A key to understanding host-parasite interactions and developing new interventions

SCP/TAPS proteins are a diverse family of molecules in eukaryotes, including parasites. Despite their abundant occurrence in parasite secretomes, very little is known about their functions in parasitic nematodes, including blood-feeding hookworms. Current information indicates that SCP/TAPS proteins (called Ancylostoma-secreted proteins, ASPs) of the canine hookworm, Ancylostoma caninum, represent at least three distinct groups of proteins. This information, combined with comparative modelling, indicates that all known ASPs have an equatorial groove that binds extended structures, such as peptides or glycans. To elucidate structure-function relationships, we explored the three-dimensional crystal structure of an ASP (called Ac-ASP-7), which is highly up-regulated in expression in the transition of A. caninum larvae from a free-living to a parasitic stage. The topology of the N-terminal domain is consistent with pathogenesis-related proteins, and the C-terminal extension that resembles the fold of the Hinge domain. By anomalous diffraction, we identified a new metal binding site in the C-terminal extension of the protein. Ac-ASP-7 is in a monomer-dimer equilibrium, and crystal-packing analysis identified a dimeric structure which might resemble the homo-dimer in solution. The dimer interaction interface includes a novel binding site for divalent metal ions, and is proposed to serve as a binding site for proteins involved in the parasite-host interplay at the molecular level. Understanding this interplay and the integration of structural and functional data could lead to the design of new approaches for the control of parasitic diseases, with biotechnological outcomes.

SCP/TAPS proteins in helminths--where to from now?

A diverse array of proteins belonging to the SCP/TAPS 'family' has been described for various eukaryotic organisms, including parasites. Although SCP/TAPS proteins have been hypothesized to play key roles in various fundamental biological processes, such as host-pathogen interactions and defence mechanisms, there is still a limited understanding of the precise roles of these proteins. Here, we review current knowledge of key SCP/TAPS proteins of helminths and their proposed roles in parasite-host interactions. Molecular investigations of these molecules in parasites and the integration of structural and functional data could lead to new and innovative approaches for the treatment and control of parasitic diseases, with important biotechnological outcomes.

Vaccinomics for the major blood feeding helminths of humans

Approximately one billion people are infected with hookworms and/or blood flukes (schistosomes) in developing countries. These two parasites are responsible for more disability adjusted life years lost than most other neglected tropical diseases (NTDs), and together, are second only to malaria. Although anthelmintic drugs are effective and widely available, they do not protect against reinfection, resistant parasites are likely to emerge, and mass drug administration programs are unsustainable. Therefore, there is a pressing need for the development of vaccines against these parasites. In recent years, there have been major advances in our understanding of hookworms and schistosomes at the molecular level through the use of "omics" technologies. The secretomes of these parasites have been characterized using transcriptomics, genomics, proteomics, and newly developed gene manipulation and silencing techniques, and the proteins of interest are now the target of novel antigen discovery approaches, notably immunomics. This research has resulted in the discovery, development, and early stage clinical trials of subunit vaccines against hookworms and schistosomes.

RNA and protein synthesis is required for Ancylostoma caninum larval activation

The developmentally arrested infective larva of hookworms encounters a host-specific signal during invasion that initiates the resumption of suspended developmental pathways. The resumption of development during infection is analogous to recovery from the facultative arrested dauer stage in the free-living nematode Caenorhabditis elegans. Infective larvae of the canine hookworm Ancylostoma caninum resume feeding and secrete molecules important for infection when exposed to a host mimicking signal in vitro. This activation process is a model for the initial steps of the infective process. Dauer recovery requires protein synthesis, but not RNA synthesis in C. elegans. To determine the role of RNA and protein synthesis in hookworm infection, inhibitors of RNA and protein synthesis were tested for their effect on feeding and secretion by A. caninum infective larvae. The RNA synthesis inhibitors α-amanitin and actinomycin D inhibit feeding dose-dependently, with IC(50) values of 30 and 8 μM, respectively. The protein synthesis inhibitors puromycin (IC(50)=110 μM), cycloheximide (IC(50)=50 μM), and anisomycin (IC(50)=200 μM) also displayed dose-dependent inhibition of larval feeding. Significant inhibition of feeding by α-amanitin and anisomycin occurred when the inhibitors were added before 12h of the activation process, but not if the inhibitors were added after 12h. None of the RNA or protein synthesis inhibitors prevented secretion of the activation-associated protein ASP-1, despite nearly complete inhibition of feeding. The results indicate that unlike dauer recovery in C. elegans, de novo gene expression is required for hookworm larval activation, and the critical genes are expressed within 12h of exposure to activating stimuli. However, secretion of infection-associated proteins is independent of gene expression, indicating that the proteins are pre-synthesized and stored for rapid release during the initial stages of infection. The genes that are inhibited represent a subset of those required for the transition to parasitism, and therefore represent interesting targets for further investigation. Furthermore, while dauer recovery provides a useful model for hookworm infection, the differences identified here highlight the importance of exercising caution before making generalizations about parasitic nematodes based on C. elegans biology.

Larval migration in PERL chambers as an in vitro model for percutaneous infection stimulates feeding in the canine hookworm Ancylostoma caninum

Background

Ancylostoma caninum third-stage larvae are the non-feeding infective stage of this parasite and are able to infect potential hosts via different infection routes. Since percutaneous infection is one of the most important routes and skin penetration is the first step into parasitic life, an existing in vitro model for percutaneous migration was modified and evaluated. The main parameter used to evaluate migration was the migration ratio (migrated larvae as a percentage of total number of larvae recovered). Additionally, the skin lag was calculated, expressing the percentage of larvae remaining in the skin and therefore not being recovered. Since initiation of feeding is proposed to be an important step in the transition from free-living to parasitic A. caninum larvae, feeding assays were performed with in vitro percutaneously migrated larvae. Additionally, infective larvae of A. caninum were activated via serum-stimulation and feeding behaviour was analysed and compared between percutaneously migrated and serum-stimulated larvae.

Results

Maximum skin migration levels of infective larvae were observed at temperatures above 32°C when larvae were placed on the epidermal side of skin for more than 12 hours. The medium beneath the skin had no effect on migration ratio, and no significant difference between the migration ratios through fresh and frozen/thawed skin was observed.

Maximum feeding levels of 93.2% were observed for percutaneously migrated larvae after 48 h incubation, whereas serum-stimulated larvae reached the maximum of 91.0% feeding larvae after 24 h.

Conclusions

The PERL chamber system was optimised and standardised as an in vitro model for percutaneous migration. The larvae recovered after percutaneous migration showed characteristic signs of activation similar to that of serum-stimulated larvae. The observed difference in time course of resumption of feeding indicates that percutaneously migrated larvae are not identical to serum-stimulated larvae, which are currently representing the model for early parasitic stages.

Deep insights into Dictyocaulus viviparus transcriptomes provides unique prospects for new drug targets and disease intervention

The lungworm, Dictyocaulus viviparus, causes parasitic bronchitis in cattle, and is responsible for substantial economic losses in temperate regions of the world. Here, we undertake the first large-scale exploration of available transcriptomic data for this lungworm, examine differences in transcription between different stages/both genders and identify and prioritize essential molecules linked to fundamental metabolic pathways, which could represent novel drug targets. Approximately 3 million expressed sequence tags (ESTs), generated by 454 sequencing from third-stage larvae (L3s) as well as adult females and males of D. viviparus, were assembled and annotated. The assembly of these sequences yielded ~61,000 contigs, of which relatively large proportions encoded collagens (4.3%), ubiquitins (2.1%) and serine/threonine protein kinases (1.9%). Subtractive analysis in silico identified 6928 nucleotide sequences as being uniquely transcribed in L3, and 5203 and 7889 transcripts as being exclusive to the adult female and male, respectively. Most peptides predicted from the conceptual translations were nucleoplasmins (L3), serine/threonine protein kinases (female) and major sperm proteins (male). Additional analyses allowed the prediction of three drug target candidates, whose Caenorhabditis elegans homologues were linked to a lethal RNA interference phenotype. This detailed exploration, combined with future transcriptomic sequencing of all developmental stages of D. viviparus, will facilitate future investigations of the molecular biology of this parasitic nematode as well as genomic sequencing. These advances will underpin the discovery of new drug and/or vaccine targets, focused on biotechnological outcomes.

Characterisation of hookworm heat shock factor binding protein (HSB-1) during heat shock and larval activation

When hookworm infective L3s infect their mammalian host, they undergo a temperature shift from that of the ambient environment to that of their endothermic host. Additionally, L3s living in the environment can be exposed to temperature extremes associated with weather fluctuations. The heat shock response (HSR) is a conserved response to heat shock and other stress that involves the expression of protective heat shock proteins (HSPs). The HSR is controlled by heat shock factor-1 (HSF-1), a conserved transcription factor that binds to a heat shock element in the promoter of HSPs, causing their expression. HSF-1 is negatively regulated in part by a HSF binding protein (HSB-1) that binds to and removes HSF-1 trimers bound to HSP gene promoters, resulting in attenuation of the HSR. Herein we describe an HSB-1 orthologue, Ac-HSB-1, from the hookworm Ancylostoma caninum. The Ac-hsb-1 cDNA encodes a 79 amino acid protein that is 71% identical to the Caenorhabditis elegans HSB-1, and is predicted to share the characteristic coiled-coil structural motif comprised of two interacting alpha helices. Recombinant Ac-HSB-1 immunoprecipitated Ce-HSF-1 expressed in mammalian cells that had been heat shocked for 1h at 42°C, but not from cells incubated at 37°C, indicating that HSB-1 only bound to the active DNA binding form of HSF-1. Expression of Ac-hsb-1 transcripts decreased following 1h of heat shock, but increased when L3s were incubated at 37°C for 1h. Activation of hookworm L3s induces a five-sixfold increase in Ac-hsb-1 expression that peaks at 12h, coincident with L3 feeding, but that subsequently decreases to two-threefold above control at 24h. Recombinant Ac-HSB-1 immunoprecipitates greater amounts of 70 and 40kDa proteins from extracts of activated L3s than from non-activated L3s. We propose that an increase in Ac-hsb-1 levels early in activation allows feeding to resume, but that a subsequent decrease in expression permits a HSR that protects non-developing L3s at host-like temperatures. Further investigations of the HSR will clarify the role of HSB-1 and HSF-1 in hookworm infection.

First transcriptomic analysis of the economically important parasitic nematode, Trichostrongylus colubriformis, using a next-generation sequencing approach

Trichostrongylus colubriformis (Strongylida), a small intestinal nematode of small ruminants, is a major cause of production and economic losses in many countries. The aims of the present study were to define the transcriptome of the adult stage of T. colubriformis, using 454 sequencing technology and bioinformatic analyses, and to predict the main pathways that key groups of molecules are linked to in this nematode. A total of 21,259 contigs were assembled from the sequence data produced from a normalized cDNA library; 7876 of these contigs had known orthologues in the free-living nematode Caenorhabditis elegans, and encoded, amongst others, proteins with 'transthyretin-like' (8.8%), 'RNA recognition' (8.4%) and 'metridin-like ShK toxin' (7.6%) motifs. Bioinformatic analyses inferred that relatively high proportions of the C. elegans homologues are involved in biological pathways linked to 'peptidases' (4%), 'ribosome' (3.6%) and 'oxidative phosphorylation' (3%). Highly represented were peptides predicted to be associated with the nervous system, digestion of host proteins or inhibition of host proteases. Probabilistic functional gene networking of the complement of C. elegans orthologues (n=2126) assigned significance to particular subsets of molecules, such as protein kinases and serine/threonine phosphatases. The present study represents the first, comprehensive insight into the transcriptome of adult T. colubriformis, which provides a foundation for fundamental studies of the molecular biology and biochemistry of this parasitic nematode as well as prospects for identifying targets for novel nematocides. Future investigations should focus on comparing the transcriptomes of different developmental stages, both genders and various tissues of this parasitic nematode for the prediction of essential genes/gene products that are specific to nematodes.

A practical, bioinformatic workflow system for large data sets generated by next-generation sequencing

Transcriptomics (at the level of single cells, tissues and/or whole organisms) underpins many fields of biomedical science, from understanding the basic cellular function in model organisms, to the elucidation of the biological events that govern the development and progression of human diseases, and the exploration of the mechanisms of survival, drug-resistance and virulence of pathogens. Next-generation sequencing (NGS) technologies are contributing to a massive expansion of transcriptomics in all fields and are reducing the cost, time and performance barriers presented by conventional approaches. However, bioinformatic tools for the analysis of the sequence data sets produced by these technologies can be daunting to researchers with limited or no expertise in bioinformatics. Here, we constructed a semi-automated, bioinformatic workflow system, and critically evaluated it for the analysis and annotation of large-scale sequence data sets generated by NGS. We demonstrated its utility for the exploration of differences in the transcriptomes among various stages and both sexes of an economically important parasitic worm (Oesophagostomum dentatum) as well as the prediction and prioritization of essential molecules (including GTPases, protein kinases and phosphatases) as novel drug target candidates. This workflow system provides a practical tool for the assembly, annotation and analysis of NGS data sets, also to researchers with a limited bioinformatic expertise. The custom-written Perl, Python and Unix shell computer scripts used can be readily modified or adapted to suit many different applications. This system is now utilized routinely for the analysis of data sets from pathogens of major socio-economic importance and can, in principle, be applied to transcriptomics data sets from any organism.

A suite of genes expressed during transition to parasitic lifestyle in the trichostrongylid nematode Haemonchus contortus encode potentially secreted proteins conserved in Teladorsagia circumcincta

The control of gastro-intestinal nematodes remains largely based on anthelminthic treatments, however spreading of anthelmintic resistance has reduced their efficacy. The genes involved in the transition to parasitic lifestyle could constitute targets of interest to develop alternative control strategies. In the trichostrongylid nematode Haemonchus contortus, we have used a SSH (Suppressive Subtractive Hybridization) based approach to generate two distinct subtracted cDNA libraries specifically enriched in cDNA expressed during the early parasitic fourth stage larvae L4 (5 days post-infection). A total of 200 clones were subjected to dot-blot experiments and 46 clones were selected for further characterization. The 46 corresponding expressed sequence tags (EST) were found to cluster into nine contigs. The corresponding full-length cDNA was obtained for all candidates. The genes encoding potentially secreted proteins were investigated in more detail. RT-PCR experiments confirmed their specific expression or over expression from the early L4 larvae to the adult stages and search for homologs in the trichostrongylid species T. circumcincta was performed in order to investigate whether they may be novel cross-specific targets.