Identification of an astacin-like metallo-proteinase transcript from the infective larvae of Strongyloides stercoralis

Astacin metalloproteases in human-parasitic nematodes

Parasitic nematodes infect over 2 billion individuals worldwide, primarily in low-resource areas, and are responsible for several chronic and potentially deadly diseases. Throughout their life cycle, these parasites are thought to use astacin metalloproteases, a subfamily of zinc-containing metalloendopeptidases, for processes such as skin penetration, molting, and tissue migration. Here, we review the known functions of astacins in human-infective, soil-transmitted parasitic nematodes - including the hookworms Necator americanus and Ancylostoma duodenale, the threadworm Strongyloides stercoralis, the giant roundworm Ascaris lumbricoides, and the whipworm Trichuris trichiura - as well as the human-infective, vector-borne filarial nematodes Wuchereria bancrofti, Onchocerca volvulus, and Brugia malayi. We also review astacin function in parasitic nematodes that infect other mammalian hosts and discuss the potential of astacins as anthelmintic drug targets. Finally, we highlight the molecular and genetic tools that are now available for further exploration of astacin function and discuss how a better understanding of astacin function in human-parasitic nematodes could lead to new avenues for nematode control and drug therapies.

Strongyloidiasis

Strongyloidiasis is a neglected tropical disease caused primarily by the roundworm Strongyloides stercoralis. Strongyloidiasis is most prevalent in Southeast Asia and the Western Pacific. Although cases have been documented worldwide, global prevalence is largely unknown due to limited surveillance. Infection of the definitive human host occurs via direct skin penetration of the infective filariform larvae. Parasitic females reside in the small intestine and reproduce via parthenogenesis, where eggs hatch inside the host before rhabditiform larvae are excreted in faeces to begin the single generation free-living life cycle. Rhabditiform larvae can also develop directly into infectious filariform larvae in the gut and cause autoinfection. Although many are asymptomatic, infected individuals may report a range of non-specific gastrointestinal, respiratory or skin symptoms. Autoinfection may cause hyperinfection and disseminated strongyloidiasis in immunocompromised individuals, which is often fatal. Diagnosis requires direct examination of larvae in clinical specimens, positive serology or nucleic acid detection. However, there is a lack of standardization of techniques for all diagnostic types. Ivermectin is the treatment of choice. Control and elimination of strongyloidiasis will require a multifaceted, integrated approach, including highly sensitive and standardized diagnostics, active surveillance, health information, education and communication strategies, improved water, sanitation and hygiene, access to efficacious treatment, vaccine development and better integration and acknowledgement in current helminth control programmes.

Salmon louse labial gland enzymes: implications for host settlement and immune modulation

Salmon louse (Lepeophtheirus salmonis) is a skin- and blood-feeding ectoparasite, infesting salmonids. While feeding, labial gland proteins from the salmon louse may be deposited on the Atlantic salmon (Salmo salar) skin. Previously characterized labial gland proteins are involved in anti-coagulation and may contribute to inhibiting Atlantic salmon from mounting a sufficient immune response against the ectoparasite. As labial gland proteins seem to be important in the host-parasite interaction, we have, therefore, identified and characterized ten enzymes localized to the labial gland. They are a large group of astacins named L. salmonis labial gland astacin 1-8 (LsLGA 1-8), one serine protease named L. salmonis labial gland serine protease 1 (LsLGSP1), and one apyrase named L. salmonis labial gland apyrase 1 (LsLGAp1). Protein domain predictions showed that LsLGA proteins all have N-terminal ShK domains, which may bind to potassium channels targeting the astacins to its substrate. LsLGA1 and -4 are, in addition, expressed in another gland type, whose secrete also meets the host-parasite interface. This suggests that LsLGA proteins may have an anti-microbial function and may prevent secondary infections in the wounds. LsLGAp1 is predicted to hydrolyze ATP or AMP and is, thereby, suggested to have an immune dampening function. In a knockdown study targeting LsLGSP1, a significant increase in IL-8 and MMP13 at the skin infestation site was seen under LsLGSP1 knockdown salmon louse compared to the control, suggesting that LsLGSP1 may have an anti-inflammatory effect. Moreover, most of the identified labial gland proteins are expressed in mature copepodids prior to host settlement, are not regulated by starvation, and are expressed at similar or higher levels in lice infesting the salmon louse-resistant pink salmon (Oncorhynchus gorbuscha). This study, thereby, emphasizes the importance of labial gland proteins for host settlement and their immune dampening function. This work can further contribute to anti-salmon louse treatment such as vaccine development, functional feed, or gene-edited salmon louse-resistant Atlantic salmon.

Invade or die: behaviours and biochemical mechanisms that drive skin penetration in Strongyloides and other skin-penetrating nematodes

Skin-penetrating nematodes, including the human threadworm Strongyloides stercoralis and hookworms in the genera Necator and Ancylostoma, are gastrointestinal parasites that are a major cause of neglected tropical disease in low-resource settings worldwide. These parasites infect hosts as soil-dwelling infective larvae that navigate towards hosts using host-emitted sensory cues such as odorants and body heat. Upon host contact, they invade the host by penetrating through the skin. The process of skin penetration is critical for successful parasitism but remains poorly understood and understudied. Here, we review current knowledge of skin-penetration behaviour and its underlying mechanisms in the human parasite S. stercoralis, the closely related rat parasite Strongyloides ratti, and other skin-penetrating nematodes such as hookworms. We also highlight important directions for future investigations into this underexplored process and discuss how recent advances in molecular genetic and genomic tools for Strongyloides species will enable mechanistic investigations of skin penetration and other essential parasitic behaviours in future studies. This article is part of the Theo Murphy meeting issue 'Strongyloides: omics to worm-free populations'.

Structural and evolutionary insights into astacin metallopeptidases

The astacins are a family of metallopeptidases (MPs) that has been extensively described from animals. They are multidomain extracellular proteins, which have a conserved core architecture encompassing a signal peptide for secretion, a prodomain or prosegment and a zinc-dependent catalytic domain (CD). This constellation is found in the archetypal name-giving digestive enzyme astacin from the European crayfish Astacus astacus. Astacin catalytic domains span ∼200 residues and consist of two subdomains that flank an extended active-site cleft. They share several structural elements including a long zinc-binding consensus sequence (HEXXHXXGXXH) immediately followed by an EXXRXDRD motif, which features a family-specific glutamate. In addition, a downstream SIMHY-motif encompasses a "Met-turn" methionine and a zinc-binding tyrosine. The overall architecture and some structural features of astacin catalytic domains match those of other more distantly related MPs, which together constitute the metzincin clan of metallopeptidases. We further analysed the structures of PRO-, MAM, TRAF, CUB and EGF-like domains, and described their essential molecular determinants. In addition, we investigated the distribution of astacins across kingdoms and their phylogenetic origin. Through extensive sequence searches we found astacin CDs in > 25,000 sequences down the tree of life from humans beyond Metazoa, including Choanoflagellata, Filasterea and Ichtyosporea. We also found < 400 sequences scattered across non-holozoan eukaryotes including some fungi and one virus, as well as in selected taxa of archaea and bacteria that are pathogens or colonizers of animal hosts, but not in plants. Overall, we propose that astacins originate in the root of Holozoa consistent with Darwinian descent and that the latter genes might be the result of horizontal gene transfer from holozoan donors.

Insights into the functional expansion of the astacin peptidase family in parasitic helminths

Helminths secrete a plethora of proteins involved in parasitism-related processes such as tissue penetration, migration, feeding and immunoregulation. Astacins, a family of zinc metalloproteases belonging to the peptidase family M12, are one of the most abundantly represented protein families in the secretomes of helminths. Despite their involvement in virulence, very few studies have addressed the role of this loosely defined protein group in parasitic helminths. Herein, we have analysed the predicted proteomes from 154 helminth species and confirmed the expansion of the astacin family in several nematode taxa. The astacin domain associated with up to 110 other domains into 145 unique domain architectures, where CUB and ShK constitute the principal and nearly independent bi-domain frameworks. The presence of co-existing domains suggests promiscuous adaptable functions to several roles. These activities could be related either to substrate specificity or to higher-order functions, such as anti-angiogenesis and immunomodulation, where the astacin domain would play an accessory role. Furthermore, some phylogenetically restricted mutations in the astacin domain affected residues located at the active cleft and binding sub-pockets, suggesting adaptation to different substrate specificities. Altogether, these findings suggest the astacin domain is a highly adaptable module that fulfils multiple proteolytic needs of the parasitic lifestyle. This study contributes to the understanding of helminth-secreted astacins and, ultimately, provides the foundation to guide future investigations about the role of this diverse family of proteins in host-parasite interactions.

Transcriptional profiles in Strongyloides stercoralis males reveal deviations from the Caenorhabditis sex determination model

The human and canine parasitic nematode Strongyloides stercoralis utilizes an XX/XO sex determination system, with parasitic females reproducing by mitotic parthenogenesis and free-living males and females reproducing sexually. However, the genes controlling S. stercoralis sex determination and male development are unknown. We observed precocious development of rhabditiform males in permissive hosts treated with corticosteroids, suggesting that steroid hormones can regulate male development. To examine differences in transcript abundance between free-living adult males and other developmental stages, we utilized RNA-Seq. We found two clusters of S. stercoralis-specific genes encoding predicted transmembrane proteins that are only expressed in free-living males. We additionally identified homologs of several genes important for sex determination in Caenorhabditis species, including mab-3, tra-1, fem-2, and sex-1, which may have similar functions. However, we identified three paralogs of gld-1; Ss-qki-1 transcripts were highly abundant in adult males, while Ss-qki-2 and Ss-qki-3 transcripts were highly abundant in adult females. We also identified paralogs of pumilio domain-containing proteins with sex-specific transcripts. Intriguingly, her-1 appears to have been lost in several parasite lineages, and we were unable to identify homologs of tra-2 outside of Caenorhabditis species. Together, our data suggest that different mechanisms control male development in S. stercoralis and Caenorhabditis species.

Identification of proteins from the secretory/excretory products (SEPs) of the branchiuran ectoparasite Argulus foliaceus (Linnaeus, 1758) reveals unique secreted proteins amongst haematophagous ecdysozoa

BACKGROUND

It is hypothesised that being a blood-feeding ectoparasite, Argulus foliaceus (Linnaeus, 1758), uses similar mechanisms for digestion and host immune evasion to those used by other haematophagous ecdysozoa, including caligid copepods (e.g. sea louse). We recently described and characterised glands associated with the feeding appendages of A. foliaceus using histological techniques. The work described in the present study is the first undertaken with the objective of identifying and partially characterising the components secreted from these glands using a proteomic approach.

METHODS

Argulus foliaceus parasites were sampled from the skin of rainbow trout (Oncorhynchus mykiss), from Loch Fad on the Isle of Bute, Scotland, UK. The proteins from A. foliaceus secretory/excretory products (SEPs) were collected from the supernatant of artificial freshwater conditioned with active adult parasites (n = 5-9 per ml; n = 560 total). Proteins within the SEPs were identified and characterised using LC-ESI-MS/MS analysis. Data are available via ProteomeXchange with identifier PXD016226.

RESULTS

Data mining of a protein database translated from an A. foliaceus dataset using ProteinScape allowed identification of 27 predicted protein sequences from the A. foliaceus SEPs, each protein matching the criteria of 2 peptides with at least 4 contiguous amino acids. Nine proteins had no matching sequence through OmicsBox (Blast2GO) analysis searches suggesting that Argulus spp. may additionally have unique proteins present in their SEPs. SignalP 5.0 software, identified 13 proteins with a signal sequence suggestive of signal peptides and supportive of secreted proteins being identified. Notably, the functional characteristics of identified A. foliaceus proteins/domains have also been described from the salivary glands and saliva of other blood-feeding arthropods such as ticks. Identified proteins included: transporters, peroxidases, metalloproteases, proteases and serine protease inhibitors which are known to play roles in parasite immune evasion/induction (e.g. astacin), immunomodulation (e.g. serpin) and digestion (e.g. trypsin).

CONCLUSIONS

To our knowledge, the present study represents the first proteomic analysis undertaken for SEPs from any branchiuran fish louse. Here we reveal possible functional roles of A. foliaceus SEPs in digestion and immunomodulation, with a number of protein families shared with other haematophagous ectoparasites. A number of apparently unique secreted proteins were identified compared to other haematophagous ecdysozoa.

Identification of clam plasma proteins that bind its pathogen Quahog Parasite Unknown

The hard clam (Mercenaria mercenaria) is among the most economically-important marine species along the east coast of the United States, representing the first marine resource in several Northeastern states. The species is rather resilient to infections and the only important disease of hard clams results from an infection caused by Quahog Parasite Unknown (QPX), a protistan parasite that can lead to significant mortality events in wild and aquacultured clam stocks. Though the presence of QPX disease has been documented since the 1960s, little information is available on cellular and molecular interactions between the parasite and the host. This study examined the interactions between the clam immune system and QPX cells. First, the effect of clam plasma on the binding of hemocytes to parasite cells was evaluated. Second, clam plasma proteins that bind QPX cells were identified through proteomic (LC-MS/MS) analyses. Finally, the effect of prior clam exposure to QPX on the abundance of QPX-reactive proteins in the plasma was evaluated. Results showed that plasma factors enhance the attachment of hemocytes to QPX. Among the proteins that specifically bind to QPX cells, several lectins were identified, as well as complement component proteins and proteolytic enzymes. Furthermore, results showed that some of these lectins and complement-related proteins are inducible as their abundance significantly increased following QPX challenge. These results shed light on plasma proteins involved in the recognition and binding of parasite cells and provide molecular targets for future investigations of factors involved in clam resistance to the disease, and ultimately for the selection of resistant clam stocks.

Duplications and Positive Selection Drive the Evolution of Parasitism-Associated Gene Families in the Nematode Strongyloides papillosus

Gene duplication is a major mechanism playing a role in the evolution of phenotypic complexity and in the generation of novel traits. By comparing parasitic and nonparasitic nematodes, a recent study found that the evolution of parasitism in Strongyloididae is associated with a large expansion in the Astacin and CAP gene families.To gain novel insights into the developmental processes in the sheep parasite Strongyloides papillosus, we sequenced transcriptomes of different developmental stages and sexes. Overall, we found that the majority of genes are developmentally regulated and have one-to-one orthologs in the diverged S. ratti genome. Together with the finding of similar expression profiles between S. papillosus and S. ratti, these results indicate a strong evolutionary constraint acting against change at sequence and expression levels. However, the comparison between parasitic and free-living females demonstrates a quite divergent pattern that is mostly due to the previously mentioned expansion in the Astacin and CAP gene families. More detailed phylogenetic analysis of both gene families shows that most members date back to single expansion events early in the Strongyloides lineage and have undergone subfunctionalization resulting in clusters that are highly expressed either in infective larvae or in parasitic females. Finally, we found increased evidence for positive selection in both gene families relative to the genome-wide expectation.In summary, our study reveals first insights into the developmental transcriptomes of S. papillosus and provides a detailed analysis of sequence and expression evolution in parasitism-associated gene families.

Proteolytic activity of excretory/secretory products of Cochliomyia hominivorax larvae (Diptera: Calliphoridae)

Abstract: The protein profiles and proteolytic activity of the excretory secretory products (E/SP) of the first (L1), second (L2) and third (L3) larval stages of Cochliomyia hominivorax were studied in the laboratory. Analysis on the E/SP protein profile was carried out using polyacrylamide gel containing sodium dodecyl sulfate (SDS-PAGE). The E/SP of each larval stage (L1, L2 and L3) treated with protease inhibitors, containing 30μg, 40μg and 50μg of protein, was applied to the 10% polyacrylamide gel. The proteolytic activity of the crude E/SP was analyzed in gels copolymerized with gelatin and by colorimetric assays using azocasein as a substrate, with the characterization of the proteases using synthetic inhibitors. Different protein profiles were observed for the larval instars, with L1 presenting the most complex profile. Nevertheless, various protein bands were observed that were common to all the larval instars. The E/SP of all the instars showed proteolytic activity on gelatin, evidenced by proteolysis zones, predominantly with apparently higher molecular masses in L1, while for L2 and L3 the proteolysis zones could also be observed in regions with lower masses. Tests with protease inhibitors using gelatin as substrate showed that the E/SP of larvae were mainly composed of serine proteases. Additionally, inhibition was observed in L2 E/SP treated previously with EDTA, an inhibitor of metalloproteases. The assays with azocasein revealed a gradual increase of proteolytic activity on this substrate with larval development progress, with the strongest inhibitions being observed after treatments with 3,4-dichloroisocoumarin (DCI) for E/SP of L1, L2 and L3. These results suggest that C. hominivorax larvae produce different proteases, a fact that can be related to the parasite's vital processes for survival, such as penetration into the host's tissues and nutrition during the larval stage.

The genomic basis of parasitism in the Strongyloides clade of nematodes

Soil-transmitted nematodes, including the Strongyloides genus, cause one of the most prevalent neglected tropical diseases. Here we compare the genomes of four Strongyloides species, including the human pathogen Strongyloides stercoralis, and their close relatives that are facultatively parasitic (Parastrongyloides trichosuri) and free-living (Rhabditophanes sp. KR3021). A significant paralogous expansion of key gene families--families encoding astacin-like and SCP/TAPS proteins--is associated with the evolution of parasitism in this clade. Exploiting the unique Strongyloides life cycle, we compare the transcriptomes of the parasitic and free-living stages and find that these same gene families are upregulated in the parasitic stages, underscoring their role in nematode parasitism.

Onchocerca volvulus Molting Inhibitors Identified through Scaffold Hopping

The anthelmintic closantel has shown promise in abrogating the L3 molting of Onchocerca volvulus, the causative agent of the infectious disease onchocerciasis. In our search for alternative scaffolds, we utilized a fragment replacement/modification approach to generate novel chemotypes with improved chitinase inhibitory properties. Further evaluation of the compounds unveiled the potential of urea-tropolones as potent inhibitors of O. volvulus L3 molting.

Strongyloidiasis with emphasis on human infections and its different clinical forms

Strongyloidiasis (caused by Strongyloides stercoralis, and to a lesser extent by Strongyloides fuelleborni) is one of the most neglected tropical diseases with endemic areas and affecting more than 100 million people worldwide. Chronic infections in endemic areas can be maintained for decades through the autoinfective cycle with the L3 filariform larvae. In these endemic areas, misdiagnosis, inadequate treatment and the facilitation of the hyperinfection syndrome by immunosuppression are frequent and contribute to a high mortality rate. Despite the serious health impact of strongyloidiasis, it is a neglected disease and very little is known about this parasite and the disease when compared to other helminth infections. Control of the disease is difficult because of the many gaps in our knowledge of strongyloidiasis. We examine the recent literature on different aspects of strongyloidiasis with emphasis in those aspects that need further research.

A highly conserved, inhibitable astacin metalloprotease from Teladorsagia circumcincta is required for cuticle formation and nematode development

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Astacin metalloprotease, DPY-31, is conserved throughout the nematode phylum.

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DPY-31 is crucial to Teladorsagia circumcincta cuticle formation.

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Matrix metalloprotease inhibitors are efficacious against recombinant DPY-31.

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Novel hydroxamate inhibitors caused Dumpy and Moult defects in nematodes.

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DPY-31 is a potential target for future nematode control.

Parasitic nematodes cause chronic, debilitating infections in both livestock and humans worldwide, and many have developed multiple resistance to the currently available anthelmintics. The protective collagenous cuticle of these parasites is required for nematode survival and its synthesis has been studied extensively in the free-living nematode, Caenorhabditis elegans. The collagen synthesis pathway is a complex, multi-step process involving numerous key enzymes, including the astacin metalloproteases. Nematode astacinsare crucial for C. elegans development, having specific roles in hatching, moulting and cuticle synthesis. NAS-35 (also called DPY-31) is a homologue of a vertebrate procollagen C-proteinase and performs a central role in cuticle formation of C. elegans as its mutation causes temperature-sensitive lethality and cuticle defects. The characterisation of DPY-31 from the ovine gastrointestinal nematode Teladorsagia circumcincta and its ability to rescue the C. elegans mutant is described. Compounds with a hydroxamate functional group have previously been shown to be potent inhibitors of procollagen C-proteinases and were therefore examined for inhibitory activity against the T. circumcincta enzyme. Phenotypic screening against T. circumcincta, Haemonchus contortus and C. elegans larval stages identified compounds that caused body morphology phenotypes consistent with the inhibition of proteases involved in cuticle collagen synthesis. These compounds correspondingly inhibited the activity of recombinant T. circumcincta DPY-31, supporting the hypothesis that this enzyme may represent a potentially novel anthelmintic drug target.

Secreted proteomes of different developmental stages of the gastrointestinal nematode Nippostrongylus brasiliensis

Hookworms infect more than 700 million people worldwide and cause more morbidity than most other human parasitic infections. Nippostrongylus brasiliensis (the rat hookworm) has been used as an experimental model for human hookworm because of its similar life cycle and ease of maintenance in laboratory rodents. Adult N. brasiliensis, like the human hookworm, lives in the intestine of the host and releases excretory/secretory products (ESP), which represent the major host-parasite interface. We performed a comparative proteomic analysis of infective larval (L3) and adult worm stages of N. brasiliensis to gain insights into the molecular bases of host-parasite relationships and determine whether N. brasiliensis could indeed serve as an appropriate model for studying human hookworm infections. Proteomic data were matched to a transcriptomic database assembled from 245,874,892 Illumina reads from different developmental stages (eggs, L3, L4, and adult) of N. brasiliensis yielding∼18,426 unigenes with 39,063 possible isoform transcripts. From this analysis, 313 proteins were identified from ESPs by LC-MS/MS-52 in the L3 and 261 in the adult worm. Most of the proteins identified in the study were stage-specific (only 13 proteins were shared by both stages); in particular, two families of proteins-astacin metalloproteases and CAP-domain containing SCP/TAPS-were highly represented in both L3 and adult ESP. These protein families are present in most nematode groups, and where studied, appear to play roles in larval migration and evasion of the host's immune response. Phylogenetic analyses of defined protein families and global gene similarity analyses showed that N. brasiliensis has a greater degree of conservation with human hookworm than other model nematodes examined. These findings validate the use of N. brasiliensis as a suitable parasite for the study of human hookworm infections in a tractable animal model.

Proteolytic activity in the adult and larval stages of the human roundworm parasite Angiostrongylus costaricensis

Angiostrongylus costaricensis is a nematode that causes abdominal angiostrongyliasis, a widespread human parasitism in Latin America. This study aimed to characterize the protease profiles of different developmental stages of this helminth. First-stage larvae (L1) were obtained from the faeces of infected Sigmodon hispidus rodents and third-stage larvae (L3) were collected from mollusks Biomphalaria glabrata previously infected with L1. Adult worms were recovered from rodent mesenteric arteries. Protein extraction was performed after repeated freeze-thaw cycles followed by maceration of the nematodes in 40 mM Tris base. Proteolysis of gelatin was observed by zymography and found only in the larval stages. In L3, the gelatinolytic activity was effectively inhibited by orthophenanthroline, indicating the involvement of metalloproteases. The mechanistic class of the gelatinases from L1 could not be precisely determined using traditional class-specific inhibitors. Adult worm extracts were able to hydrolyze haemoglobin in solution, although no activity was observed by zymography. This haemoglobinolytic activity was ascribed to aspartic proteases following its effective inhibition by pepstatin, which also inhibited the haemoglobinolytic activity of L1 and L3 extracts. The characterization of protease expression throughout the A. costaricensis life cycle may reveal key factors influencing the process of parasitic infection and thus foster our understanding of the disease pathogenesis.

Molecular cloning and characterisation of in vitro immune response against astacin-like metalloprotease Ace-MTP-2 from Ancylostoma ceylanicum

Ancylostoma ceylanicum belongs to the group of parasites commonly known as hookworms, blood-sucking nematodes which infect around 576 million people and hundreds of millions of animals. The interactions between these parasites and host immune systems are complicated and yet to be determined. Hookworm infections are usually long lasting and recurrent, due in part to their ability to synthesize macromolecules capable of modulating the host immune response. The interaction of parasite proteins with host immune systems has been proven, but so far there is no data describing the influence of astacin-like metalloproteases (expressed among different parasitic nematodes) on the human immune system. The cDNA encoding A. ceylanicum metalloprotease 2 (Ace-mtp-2) was cloned using RACE-PCR. Computational analysis was used to examine the immunogenicity and recombinant Ace-MTP-2 was used to investigate its influence on human THP-1 monocytes and macrophages. The Ace-mtp-2 gene encodes an astascin-like metalloprotease, with a theoretical molecular mass of 26.7 kDa. The protease has a putative signal peptide, 11 potential phosphorylation sites, and two disulfide bridges revealed by computational analysis. Maximal expression of Ace-mtp-2 by A. ceylanicum occurs in the adult stage of the parasite, and Western blot indicates the secretory nature of the protease. This suggests the protease is working at the host-parasite interface and would likely be exposed to the hosts immune response. Recombinant protein were expressed in Escherichia coli and Pichia pastoris. Recombinant Ace-MTP-2 amplified the in vitro release of TNFα and induced release of IFNγ by lipopolysaccharide activated THP-1 macrophages. The presence of Ace-MTP-2 in secretory products of the adult parasite and the induction of IFNγ release may suggest an important role for Ace-MTP-2 in host-parasite interactions since IFNγ is suggested to be responsible for the protective immune response against adult hookworms.

Transcriptomic analysis of four developmental stages of Strongyloides venezuelensis

Strongyloides venezuelensis is one of some 50 species of genus Strongyloides, obligate gastrointestinal parasites of vertebrates, responsible for strongyloidiasis in humans and other domestic/companion animals. Although S. venezuelensis has been widely used as a model species for studying human/animal strongyloidiasis, the sequence information for this species has been quite limited. To create a more comprehensive catalogue of expressed genes for identification of genes potentially involved in animal parasitism, we conducted a de novo sequencing analysis of the transcriptomes from four developmental stages of S. venezuelensis, using a Roche 454 GS FLX Titanium pyrosequencing platform. A total of 14,573 contigs were produced after de novo assemblies of over 2 million sequencing reads and formed a dataset "Vene454". BLAST homology search of Vene454 against proteome and transcriptome data from other animal-parasitic and non-animal-parasitic nematode species revealed several interesting genes, which may be potentially related to animal parasitism, including nicotinamide phosphoribosyltransferase and ferrochelatase. The Vene454 dataset analysis also enabled us to identify transcripts that are specifically enriched in each developmental stage. This work represents the first large-scale transcriptome analysis of S. venezuelensis and the first study to examine the transcriptome of the lung L3 developmental stage of any Strongyloides species. The results not only will serve as valuable resources for future functional genomics analyses to understand the molecular aspects of animal parasitism, but also will provide essential information for ongoing whole genome sequencing efforts in this species.

Metal accumulation from dietary exposure in the sea urchin, Strongylocentrotus droebachiensis

Metal contamination is a common problem in aquatic environments and may result in metal bioaccumulation and toxicity in aquatic biota. Recent studies have reported the significance of dietary metal accumulation in aquatic food chains, particularly in species of lower trophic levels. This research investigated the accumulation and effects of dietary metals in a macroinvertebrate. The seaweed species Ulva lactuca and Enteromorpha prolifera were concurrently exposed to five metals (copper, nickel, lead, cadmium, and zinc) and then individually fed to the green sea urchin Strongylocentrotus droebachiensis for a period of 2 weeks. Body mass, test length, total length, and coelomic fluid ion concentration and osmolality were measured. The sea urchins were also dissected and their organs (esophagus, stomach, intestine, gonads, and rectum) digested and analyzed for metals. The results demonstrated that metal accumulation and distribution varied between seaweed species and among metals. In general, there were greater concentrations of metals within the sea urchins fed E. prolifera compared with those fed U. lactuca. All of the metals accumulated within at least one organ of S. droebachiensis, with Cu being most significant. These results indicate that E. prolifera may accumulate metals in a more bioavailable form than within U. lactuca, which could impact the grazer. In this study, no significant differences in body length, growth, or coelomic fluid ion concentration and osmolality were detected between the control and metal-exposed sea urchins after the 2-week testing period. This research presents new data concerning metal accumulation in a marine herbivore after dietary metal exposure.

The transcriptome analysis of Strongyloides stercoralis L3i larvae reveals targets for intervention in a neglected disease

Background

Strongyloidiasis is one of the most neglected diseases distributed worldwide with endemic areas in developed countries, where chronic infections are life threatening. Despite its impact, very little is known about the molecular biology of the parasite involved and its interplay with its hosts. Next generation sequencing technologies now provide unique opportunities to rapidly address these questions.

Principal Findings

Here we present the first transcriptome of the third larval stage of S. stercoralis using 454 sequencing coupled with semi-automated bioinformatic analyses. 253,266 raw sequence reads were assembled into 11,250 contiguous sequences, most of which were novel. 8037 putative proteins were characterized based on homology, gene ontology and/or biochemical pathways. Comparison of the transcriptome of S. strongyloides with those of other nematodes, including S. ratti, revealed similarities in transcription of molecules inferred to have key roles in parasite-host interactions. Enzymatic proteins, like kinases and proteases, were abundant. 1213 putative excretory/secretory proteins were compiled using a new pipeline which included non-classical secretory proteins. Potential drug targets were also identified.

Conclusions

Overall, the present dataset should provide a solid foundation for future fundamental genomic, proteomic and metabolomic explorations of S. stercoralis, as well as a basis for applied outcomes, such as the development of novel methods of intervention against this neglected parasite.

Strongyloides stercoralis (Nematoda) is an important parasite of humans, causing Strongyloidiasis, considered as one of the most neglected diseases, affecting more than 100 million people worldwide. Chronic infections in endemic areas can be maintained for decades through the autoinfective cycle with the L3 filariform larvae. In these areas, misdiagnosis, inadequate treatment and the facilitation of hyperinfection syndrome by immunosupression are frequent and contribute to a high mortality rate. Among the affected areas, chronic patients have been described in the Valencian Mediterranean coastal region of Spain. Despite its serious impact, very little is known about this parasite and its relationship with its hosts at the molecular level, and more effective diagnostic tests and treatments are needed. Next generation sequencing technologies now provide unique opportunities to rapidly advance in these areas. In this study, we present the first transcriptome of S. stercoralis L3i using 454 sequencing followed by semi-automated bioinformatic analyses. Our study identifies 8037 putative proteins based on homology, gene ontology, and/or biochemical pathways, including putative excretory/secretory proteins as well as potential drug targets. The present dataset provides a useful resource and adds greatly to our understanding of a human parasite affecting both developed and developing countries.

In silico secretome analysis approach for next generation sequencing transcriptomic data

BACKGROUND

Excretory/secretory proteins (ESPs) play a major role in parasitic infection as they are present at the host-parasite interface and regulate host immune system. In case of parasitic helminths, transcriptomics has been used extensively to understand the molecular basis of parasitism and for developing novel therapeutic strategies against parasitic infections. However, none of transcriptomic studies have extensively covered ES protein prediction for identifying novel therapeutic targets, especially as parasites adopt non-classical secretion pathways.

RESULTS

We developed a semi-automated computational approach for prediction and annotation of ES proteins using transcriptomic data from next generation sequencing platforms. For the prediction of non-classically secreted proteins, we have used an improved computational strategy, together with homology matching to a dataset of experimentally determined parasitic helminth ES proteins. We applied this protocol to analyse 454 short reads of parasitic nematode, Strongyloides ratti. From 296231 reads, we derived 28901 contigs, which were translated into 20877 proteins. Based on our improved ES protein prediction pipeline, we identified 2572 ES proteins, of which 407 (1.9%) proteins have classical N-terminal signal peptides, 923 (4.4%) were computationally identified as non-classically secreted while 1516 (7.26%) were identified by homology to experimentally identified parasitic helminth ES proteins. Out of 2572 ES proteins, 2310 (89.8%) ES proteins had homologues in the free-living nematode Caenorhabditis elegans and 2220 (86.3%) in parasitic nematodes. We could functionally annotate 1591 (61.8%) ES proteins with protein families and domains and establish pathway associations for 691 (26.8%) proteins. In addition, we have identified 19 representative ES proteins, which have no homologues in the host organism but homologous to lethal RNAi phenotypes in C. elegans, as potential therapeutic targets.

CONCLUSION

We report a comprehensive approach using freely available computational tools for the secretome analysis of NGS data. This approach has been applied to S. ratti 454 transcriptomic data for in silico excretory/secretory proteins prediction and analysis, providing a foundation for developing new therapeutic solutions for parasitic infections.

Expression profiling, gene silencing and transcriptional networking of metzincin metalloproteases in the cattle tick, Rhipicephalus (Boophilus) microplus

Tick proteins functioning in vital physiological processes such as blood meal uptake, digestion and reproduction are potential targets for anti-tick vaccines, since vaccination could inhibit these essential functions and ultimately affect tick survival. In this study we identified metzincin metalloproteases from Rhipicephalus microplus as potential vaccine candidates since they are implicated as essential to blood-cavity formation, bloodmeal digestion and reproduction in ixodid ticks. Eight transcripts encoding proteins that contain the characteristic metzincin zinc-binding motif HEXXHXXG/NXXH/D and a unique methionine containing "methionine-turn" were identified from native and in-house assembled R. microplus expressed sequence tag (EST) databases. These were representative of five reprolysin-like and three astacin-like metzincin metalloproteases. Reverse transcription-PCR analysis indicated that the reprolysins were most abundantly expressed in the salivary glands, whereas the astacins were most abundant in the midgut and ovaries. In vivo gene silencing was performed to assess a possible phenotype of these metalloproteases during adult female R. microplus blood feeding and reproduction. RNA interference (RNAi) against two of the reprolysins and one of the astacins significantly affected the average egg weight and oviposition rate. Evidently, this reverse genetic approach enabled the evaluation of the overall vital impact of tick proteins. Finally, integrated real time-PCR studies also revealed an extensive cross organ network between the R. microplus metzincin transcripts, supporting the use of a combinatorial metzincin-based anti- R. microplus vaccine.

Life cycle stage-resolved proteomic analysis of the excretome/secretome from Strongyloides ratti--identification of stage-specific proteases

A wide range of biomolecules, including proteins, are excreted and secreted from helminths and contribute to the parasite's successful establishment, survival, and reproduction in an adverse habitat. Excretory and secretory proteins (ESP) are active at the interface between parasite and host and comprise potential targets for intervention. The intestinal nematode Strongyloides spp. exhibits an exceptional developmental plasticity in its life cycle characterized by parasitic and free-living generations. We investigated ESP from infective larvae, parasitic females, and free-living stages of the rat parasite Strongyloides ratti, which is genetically very similar to the human pathogen, Strongyloides stercoralis. Proteomic analysis of ESP revealed 586 proteins, with the largest number of stage-specific ESP found in infective larvae (196), followed by parasitic females (79) and free-living stages (35). One hundred and forty proteins were identified in all studied stages, including anti-oxidative enzymes, heat shock proteins, and carbohydrate-binding proteins. The stage-selective ESP of (1) infective larvae included an astacin metalloproteinase, the L3 Nie antigen, and a fatty acid retinoid-binding protein; (2) parasitic females included a prolyl oligopeptidase (prolyl serine carboxypeptidase), small heat shock proteins, and a secreted acidic protein; (3) free-living stages included a lysozyme family member, a carbohydrate-hydrolyzing enzyme, and saponin-like protein. We verified the differential expression of selected genes encoding ESP by qRT-PCR. ELISA analysis revealed the recognition of ESP by antibodies of S. ratti-infected rats. A prolyl oligopeptidase was identified as abundant parasitic female-specific ESP, and the effect of pyrrolidine-based prolyl oligopeptidase inhibitors showed concentration- and time-dependent inhibitory effects on female motility. The characterization of stage-related ESP from Strongyloides will help to further understand the interaction of this unique intestinal nematode with its host.

Strongyloides stercoralis excretory/secretory protein strongylastacin specifically recognized by IgE antibodies in infected human sera

The infective, microscopic Strongyloides stercoralis larvae in contaminated soil can penetrate human skin with the help of excretory/secretory proteases. These proteases play a critical role in infection and transmigration of the parasite to the intestines. Strongylastacin is similar to astacin (from the digestive gland of the crayfish Astacus astacus), a multi-domain protein with a signal peptide, a pro-enzyme, a catalytic domain containing the zinc binding consensus astacin family signature sequence HEXXHXXGFXHEXXRXDR, and a second conserved zinc binding motif SIMHY at N- terminal region. An EGF-1 like domain and a CUB domain are located at the COOH- terminal. In this study, the excretory/secretory Strongylastacin gene from S. stercoralis infective larval stage was cloned and expressed as a 45 kDa in Escherichia coli. Immunoblot analysis showed the presence of natural IgG antibodies against strongylastacin in six infected and six non-endemic normal sera. These findings were confirmed in an ELISA of 32 S. stercoralis infected and 32 presumed normal human sera; all contained natural anti-strongylastacin IgG antibodies. By contrast, IgE antibodies specific to strongylastacin were present in sera from individuals infected with S. stercoralis but not in uninfected control sera. Moreover, recombinant strongylastacin did not cross-react with IgE antibodies either from patients infected with filaria or patients with tropical pulmonary eosinophilic (TPE) who had increased IgE antibodies. The present authors conclude that strongylastacin, an excretory/secretory antigen, elicits specific IgE antibodies in S. stercoralis infected humans. Non-specific IgG antibodies to strongylastacin are present in both infected and normal humans. Further investigation is needed to understand the role of the host protective response against strongylastacin.

Transcripts analysis of infective larvae of an intestinal nematode, Strongyloides venezuelensis

Free-living infective larvae of Strongyloides nematodes fulfill a number of requirements for the successful infection. They need to endure a long wait in harsh environmental conditions, like temperature, salinity, and pH, which might change drastically from time to time. Infective larvae also have to deal with pathogens and potentially hazardous free-living microbes in the environment. In addition, infective larvae must recognize the adequate host properly, and start skin penetration as quickly as possible. All these tasks are essentially important for the survival of Strongyloides nematodes, however, our knowledge is extremely limited in any one of these aspects. In order to understand how Strongyloides infective larvae meet these requirements, we examined transcripts of infective larvae by randomly sequencing cDNA clones constructed from S. venezuelensis infective larvae. After assembling successfully sequenced clones, we obtained 162 unique singletons and contigs, of which 84 had been significantly annotated. Annotated genes included those for respiratory enzymes, heat-shock proteins, neuromuscular proteins, proteases, and immunodominant antigens. Genes for lipase, small heat-shock protein, globin-like protein and cytochrome c oxidase were most abundantly transcribed, though genes of unknown functions were also abundantly transcribed. There were no hits found against NCBI or NEMABASE4 for 37 (22.3%) EST out of the total 162 EST. Although most of the transcripts were not infective larva-specific, the expression of respiration related proteins was most actively transcribed in the infective larva stage. The expression of astacin-like metalloprotease, small heat-shock protein, S. stercoralis L3Nie antigen homologue, and one unannotated and 2 novel genes was highly specific for the infective larva stage.

The astacin metalloprotease moulting enzyme NAS-36 is required for normal cuticle ecdysis in free-living and parasitic nematodes

Nematodes represent one of the most abundant and species-rich groups of animals on the planet, with parasitic species causing chronic, debilitating infections in both livestock and humans worldwide. The prevalence and success of the nematodes is a direct consequence of the exceptionally protective properties of their cuticle. The synthesis of this cuticle is a complex multi-step process, which is repeated 4 times from hatchling to adult and has been investigated in detail in the free-living nematode, Caenorhabditis elegans. This process is known as moulting and involves numerous enzymes in the synthesis and degradation of the collagenous matrix. The nas-36 and nas-37 genes in C. elegans encode functionally conserved enzymes of the astacin metalloprotease family which, when mutated, result in a phenotype associated with the late-stage moulting defects, namely the inability to remove the preceding cuticle. Extensive genome searches in the gastrointestinal nematode of sheep, Haemonchus contortus, and in the filarial nematode of humans, Brugia malayi, identified NAS-36 but not NAS-37 homologues. Significantly, the nas-36 gene from B. malayi could successfully complement the moult defects associated with C. elegans nas-36, nas-37 and nas-36/nas-37 double mutants, suggesting a conserved function for NAS-36 between these diverse nematode species. This conservation between species was further indicated when the recombinant enzymes demonstrated a similar range of inhibitable metalloprotease activities.

Serine protease-mediated host invasion by the parasitic nematode Steinernema carpocapsae

Steinernema carpocapsae is an insect parasitic nematode used in biological control, which infects insects penetrating by mouth and anus and invading the hemocoelium through the midgut wall. Invasion has been described as a key factor in nematode virulence and suggested to be mediated by proteases. A serine protease cDNA from the parasitic stage was sequenced (sc-sp-1); the recombinant protein was produced in an Escherichia coli system, and a native protein was purified from the secreted products. Both proteins were confirmed by mass spectrometry to be encoded by the sc-sp-1 gene. Sc-SP-1 has a pI of 8.7, a molecular mass of 27.3 kDa, a catalytic efficiency of 22.2 × 10(4) s(-1) m(-1) against N-succinyl-Ala-Ala-Pro-Phe-pNA, and is inhibited by chymostatin (IC 0.07) and PMSF (IC 0.73). Sc-SP-1 belongs to the chymotrypsin family, based on sequence and biochemical analysis. Only the nematode parasitic stage expressed sc-sp-1. These nematodes in the midgut lumen, prepared to invade the insect hemocoelium, expressed higher levels than those already in the hemocoelium. Moreover, parasitic nematode sense insect peritrophic membrane and hemolymph more quickly than they do other tissues, which initiates sc-sp-1 expression. Ex vivo, Sc-SP-1 was able to bind to insect midgut epithelium and to cause cell detachment from basal lamina. In vitro, Sc-SP-1 formed holes in an artificial membrane model (Matrigel), whereas Sc-SP-1 treated with PMSF did not, very likely because it hydrolyzes matrix glycoproteins. These findings highlight the S. carpocapsae-invasive process that is a key step in the parasitism thus opening new perspectives for improving nematode virulence to use in biological control.

Proteomic analysis of Strongyloides stercoralis L3 larvae

Strongyloidiasis can be perpetuated by autoinfection with the filariform larvae L3, causing asymptomatic chronic infections and creating a population of carriers, affecting not only developing countries. So far, very little is known about the proteins that interact with the human host, and few proteins from the infective Strongyloides stercoralis L3 have been characterized. Here, we report results obtained from a proteomic analysis of the proteins from S. stercoralis L3 larvae obtained from patients. Since the genome of S. stercoralis is not yet available, we used proteomic analysis to identify 26 different proteins, 13 of them released by short digestion with trypsin, which could represent surface-associated proteins. The present work extends our knowledge of host-parasite interactions by identifying proteins that could be of interest in the development of diagnostic tools, vaccines, or treatments for a neglected disease like strongyloidiasis.

Collagen processing and cuticle formation is catalysed by the astacin metalloprotease DPY-31 in free-living and parasitic nematodes

The exoskeleton or cuticle performs many key roles in the development and survival of all nematodes. This structure is predominantly collagenous in nature and requires numerous enzymes to properly fold, modify, process and cross-link these essential structural proteins. The cuticle structure and its collagen components are conserved throughout the nematode phylum but differ from the collagenous matrices found in vertebrates. This structure, its formation and the enzymology of nematode cuticle collagen biogenesis have been elucidated in the free-living nematode Caenorhabditis elegans. The dpy-31 gene in C. elegans encodes a procollagen C-terminal processing enzyme of the astacin metalloprotease or bone morphogenetic protein class that, when mutated, results in a temperature-sensitive lethal phenotype associated with cuticle defects. In this study, orthologues of this essential gene have been identified in the phylogenetically diverse parasitic nematodes Haemonchus contortus and Brugia malayi. The DPY-31 protein is expressed in the gut and secretory system of C. elegans, a location also confirmed when a B. malayi transcriptional dpy-31 promoter-reporter gene fusion was expressed in C. elegans. Functional conservation between the nematode enzymes was supported by the fact that heterologous expression of the H. contortus dpy-31 orthologue in a C. elegans dpy-31 mutant resulted in the full rescue of the mutant body form. This interspecies conservation was further established when the recombinant nematode enzymes were found to have a similar range of inhibitable protease activities. In addition, the recombinant DPY-31 enzymes from both H. contortus and B. malayi were shown to efficiently process the C. elegans cuticle collagen SQT-3 at the correct C-terminal procollagen processing site.

Identification and characterization of onchoastacin, an astacin-like metalloproteinase from the filaria Onchocerca volvulus

The tissue-invasive nematode Onchocerca volvulus causes skin and eye pathology in human onchocerciasis. While the adult females reside sessile in subcutaneous nodules, the microfilariae are abundantly released from the nodules, males and juvenile worms migrate through the host tissue. Matrix-degrading metallo- and serine proteinases have been detected in excretory-secretory worm products that may be essential for migration of the mobile stages. In this study, a 1713bp long cDNA encoding for a putative proteinase of O. volvulus has been isolated. The predicted protein sequence includes a signal peptide indicating secretion to the extracellular space, a propeptide, an astacin-like protease domain, an EGF-like and a CUB-domain, thereby identifying the protein as a member of the astacin family of zinc endopeptidases. Onchoastacin, Ov-AST-1, is most closely related to a subfamily comprising nematode astacins including Caenorhabditis and Ancylostoma. Ov-AST-1 was expressed as a recombinant protein in baculovirus-infected insect cells and exhibited enzymatic activity. The exposure of onchoastacin to the host immune system is indicated by demonstration of IgG reacting with the recombinant Ov-AST-1 and with two peptides of the protein. Since a homologous metalloproteinase is part of a promising hookworm vaccine, Ov-AST-1 may be a candidate for intervention strategies in filarial infections.

Ancylostoma caninum MTP-1, an astacin-like metalloprotease secreted by infective hookworm larvae, is involved in tissue migration

Infective larvae (L3) of nematodes secrete macromolecules that are critical to infection and establishment of the parasite in the host. The dog hookworm Ancylostoma caninum secretes an astacin-like metalloprotease, Ac-MTP-1, upon activation in vitro with host serum. Recombinant Ac-MTP-1 was expressed in the baculovirus/insect cell system as a secreted protein and was purified from culture medium by two separate methods, cation-exchange fast-performance liquid chromatography and gelatin-affinity chromatography. Recombinant MTP-1 was catalytically active and digested a range of native and denatured connective tissue substrates, including gelatin, collagen, laminin, and fibronectin. A dog was immunized with recombinant Ac-MTP-1 formulated with AS03 adjuvant, and the antiserum was used to immunolocalize the anatomic sites of expression within A. caninum L3 to secretory granules in the glandular esophagus and the channels that connect the esophagus to the L3 surface and to the cuticle. Antiserum inhibited the ability of recombinant MTP-1 to digest collagen by 85% and inhibited larval migration through tissue in vitro by 70 to 75%, in contrast to just 5 to 10% inhibition obtained with preimmunization serum. The metalloprotease inhibitors EDTA and 1,10-phenanthroline also reduced the penetration of L3 through skin in vitro by 43 to 61%. The data strongly suggest that Ac-MTP-1 is critical for the invasion process of hookworm larvae, and moreover, that antibodies against the enzyme can neutralize its function and inhibit migration.

Successive changes in tissue migration capacity of developing larvae of an intestinal nematode, Strongyloides venezuelensis

Infective larvae of an intestinal nematode, Strongyloides venezuelensis, enter rodent hosts percutaneously, and migrate through connective tissues and lungs. Then they arrive at the small intestine, where they reach maturity. It is not known how S. venezuelensis larvae develop during tissue migration. Here we demonstrate that tissue invasion ability of S. venezuelensis larvae changes drastically during tissue migration, and that the changes are associated with stage-specific protein expression. Infective larvae, connective tissue larvae, lung larvae, and mucosal larvae were used to infect mice by various infection methods, including percutaneous, subcutaneous, oral, and intraduodenal inoculation. Among different migration stages, only infective larvae penetrated mouse skin. Larvae, once inside the host, quickly lost skin penetration ability, which was associated with the disappearance of an infective larva-specific metalloprotease. Migrating larvae had connective tissue migration ability until in the lungs, where larvae became able to settle down in the intestinal mucosa. Lung larvae and mucosal larvae were capable of producing and secreting adhesion molecules.