An integrated transcriptomics and proteomics analysis of the secretome of the helminth pathogen Fasciola hepatica: proteins associated with invasion and infection of the mammalian host

The immunoregulatory effects of co-infection with Fasciola hepatica: From bovine tuberculosis to Johne's disease

Fasciola hepatica (liver fluke) is a parasite prevalent in much of the world that causes the economically-important disease of fasciolosis in livestock. The threat that this disease poses extends beyond its direct effects due to the parasite's immunomodulatory effects. Research at this laboratory is focusing on whether this immunoregulation can, in animals infected with liver fluke, exert a bystander effect on concurrent infections in the host. It has already been established that F. hepatica infection reduces cell mediated immune responses to Mycobacterium bovis in cattle, and that the interaction between the two pathogens can be detected on an epidemiological scale. This review explores the immunological consequences of co-infection between F. hepatica and other bacterial infections. Arguments are presented suggesting that immunity of cattle to Mycobacterium avium subsp. paratuberculosis is also likely to be affected.

A parasite-derived 68-mer peptide ameliorates autoimmune disease in murine models of Type 1 diabetes and multiple sclerosis

Helminth parasites secrete molecules that potently modulate the immune responses of their hosts and, therefore, have potential for the treatment of immune-mediated human diseases. FhHDM-1, a 68-mer peptide secreted by the helminth parasite Fasciola hepatica, ameliorated disease in two different murine models of autoimmunity, type 1 diabetes and relapsing-remitting immune-mediated demyelination. Unexpectedly, FhHDM-1 treatment did not affect the proliferation of auto-antigen specific T cells or their production of cytokines. However, in both conditions, the reduction in clinical symptoms was associated with the absence of immune cell infiltrates in the target organ (islets and the brain tissue). Furthermore, after parenteral administration, the FhHDM-1 peptide interacted with macrophages and reduced their capacity to secrete pro-inflammatory cytokines, such as TNF and IL-6. We propose this inhibition of innate pro-inflammatory immune responses, which are central to the initiation of autoimmunity in both diseases, prevented the trafficking of autoreactive lymphocytes from the periphery to the site of autoimmunity (as opposed to directly modulating their function per se), and thus prevented tissue destruction. The ability of FhHDM-1 to modulate macrophage function, combined with its efficacy in disease prevention in multiple models, suggests that FhHDM-1 has considerable potential as a treatment for autoimmune diseases.

Stimulating Neoblast-Like Cell Proliferation in Juvenile Fasciola hepatica Supports Growth and Progression towards the Adult Phenotype In Vitro

Fascioliasis (or fasciolosis) is a socioeconomically important parasitic disease caused by liver flukes of the genus Fasciola. Flukicide resistance has exposed the need for new drugs and/or a vaccine for liver fluke control. A rapidly improving ‘molecular toolbox’ for liver fluke encompasses quality genomic/transcriptomic datasets and an RNA interference platform that facilitates functional genomics approaches to drug/vaccine target validation. The exploitation of these resources is undermined by the absence of effective culture/maintenance systems that would support in vitro studies on juvenile fluke development/biology. Here we report markedly improved in vitro maintenance methods for Fasciola hepatica that achieved 65% survival of juvenile fluke after 6 months in standard cell culture medium supplemented with 50% chicken serum. We discovered that this long-term maintenance was dependent upon fluke growth, which was supported by increased proliferation of cells resembling the “neoblast” stem cells described in other flatworms. Growth led to dramatic morphological changes in juveniles, including the development of the digestive tract, reproductive organs and the tegument, towards more adult-like forms. The inhibition of DNA synthesis prevented neoblast-like cell proliferation and inhibited growth/development. Supporting our assertion that we have triggered the development of juveniles towards adult-like fluke, mass spectrometric analyses showed that growing fluke have an excretory/secretory protein profile that is distinct from that of newly-excysted juveniles and more closely resembles that of ex vivo immature and adult fluke. Further, in vitro maintained fluke displayed a transition in their movement from the probing behaviour associated with migrating stage worms to a slower wave-like motility seen in adults. Our ability to stimulate neoblast-like cell proliferation and growth in F. hepatica underpins the first simple platform for their long-term in vitro study, complementing the recent expansion in liver fluke resources and facilitating in vitro target validation studies of the developmental biology of liver fluke.

Parasitic worms require a host organism in order to survive and reproduce. As such, it is difficult to study them outside of a host. Some parasites can be maintained in vitro using cell culture methods; in the case of F. hepatica, previously-reported methods are unsatisfactory because they are difficult to reproduce and unable to support long term growth and development. Here we have developed a new set of methods for maintaining F. hepatica juveniles in vitro. These methods use simple, commonly available reagents and techniques, enabling us to keep fluke alive in vitro for at least 6 months, as well as stimulating the development of characteristics that resemble adult parasites. Over time, our in vitro fluke show changes in the structure and complexity of individual tissues, and the proteins they produce, such that they are more reminiscent of adult, than juvenile fluke. Additionally, we demonstrate that fluke growth is supported by the division of cells resembling stem cells, which have not been reported previously for F. hepatica. This work will support the study of liver fluke, enabling the development of new drugs and vaccines for the treatment of liver fluke infections of humans and animals.

Conservation and diversification of the transcriptomes of adult Paragonimus westermani and P. skrjabini

Background

Paragonimiasis is an important and widespread neglected tropical disease. Fifteen Paragonimus species are human pathogens, but two of these, Paragonimus westermani and P. skrjabini, are responsible for the bulk of human disease. Despite their medical and economic significance, there is limited information on the gene content and expression of Paragonimus lung flukes.

Results

The transcriptomes of adult P. westermani and P. skrjabini were studied with deep sequencing technology. Approximately 30 million reads per species were assembled into 21,586 and 25,825 unigenes for P. westermani and P. skrjabini, respectively. Many unigenes showed homology with sequences from other food-borne trematodes, but 1,217 high-confidence Paragonimus-specific unigenes were identified. Analyses indicated that both species have the potential for aerobic and anaerobic metabolism but not de novo fatty acid biosynthesis and that they may interact with host signaling pathways. Some 12,432 P. westermani and P. skrjabini unigenes showed a clear correspondence in bi-directional sequence similarity matches. The expression of shared unigenes was mostly well correlated, but differentially expressed unigenes were identified and shown to be enriched for functions related to proteolysis for P. westermani and microtubule based motility for P. skrjabini.

Conclusions

The assembled transcriptomes of P. westermani and P. skrjabini, inferred proteins, and extensive functional annotations generated for this project (including identified primary sequence similarities to various species, protein domains, biological pathways, predicted proteases, molecular mimics and secreted proteins, etc.) represent a valuable resource for hypothesis driven research on these medically and economically important species.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1785-x) contains supplementary material, which is available to authorized users.

Fasciolosis in South America: epidemiology and control challenges

Fasciolosis caused by Fasciola hepatica severely affects the efficiency of livestock production systems worldwide. In addition to the economic impact inflicted on livestock farmers, fasciolosis is an emergent zoonosis. This review emphasizes different aspects of the disease in South America. Available data on epidemiology in bovines and ovines in different countries, as well as a growing body of information on other domestic and wildlife definitive hosts, are summarized. The issue of drug resistance that compromises the long-term sustainability of current pharmacological strategies is examined from a regional perspective. Finally, efforts to develop a single-antigen recombinant vaccine in ruminants are reviewed, focusing on the cases of leucine aminopeptidase or thioredoxin glutathione reductase.

Across intra-mammalian stages of the liver f luke Fasciola hepatica: a proteomic study

Fasciola hepatica is the agent of fasciolosis, a foodborne zoonosis that affects livestock production and human health. Although flukicidal drugs are available, re-infection and expanding resistance to triclabendazole demand new control strategies. Understanding the molecular mechanisms underlying the complex interaction with the mammalian host could provide relevant clues, aiding the search for novel targets in diagnosis and control of fasciolosis. Parasite survival in the mammalian host is mediated by parasite compounds released during infection, known as excretory/secretory (E/S) products. E/S products are thought to protect parasites from host responses, allowing them to survive for a long period in the vertebrate host. This work provides in-depth proteomic analysis of F. hepatica intra-mammalian stages, and represents the largest number of proteins identified to date for this species. Functional classification revealed the presence of proteins involved in different biological processes, many of which represent original findings for this organism and are important for parasite survival within the host. These results could lead to a better comprehension of host-parasite relationships, and contribute to the development of drugs or vaccines against this parasite.

Genotoxic potential of Fasciolagigantica infection in experimentally infected rabbits

A number of parasitic platyhelminthes are known to cause genotoxicity in humans and animals. However no such information is available on tropical liver fluke, Fasciola gigantica, which incurs huge economic losses worldwide. In the present study the genotoxic potential of F. gigantica infection in rabbits, experimentally infected with the metacercarial cysts of this parasite, has been investigated using the standard comet assay and micronucleus (MNi) test on the isolated hepatocytes and the whole blood from the infected rabbits. The tail length of the comet in both hepatocytes and reticulocytes from the infected animals was significantly prominent (p < 0.05) as compared to the controls. About 61.17 % of the hepatocytes from the infected rabbits were positive for MNi formation. A number of blood cells also showed cellular deformities, which were recognised as spicule type, schistocytes, tear drop type, acanthocytes and dumbbell type. It is possible that during the establishment of host-parasite relationship the worms might have released some products which could have contributed to the induction of cellular and DNA damage. However, long term studies are required to understand the serious implications of such an effect caused by F. gigantica, though hepatic carcinoma has not been reported so far due to fasciolosis, however, considering the present results the possibility may not be rule out for the disease progression in this direction.

Cysteine and Aspartyl Proteases Contribute to Protein Digestion in the Gut of Freshwater Planaria

Proteases perform numerous vital functions in flatworms, many of which are likely to be conserved throughout the phylum Platyhelminthes. Within this phylum are several parasitic worms that are often poorly characterized due to their complex life-cycles and lack of responsiveness to genetic manipulation. The flatworm Schmidtea mediterranea, or planaria, is an ideal model organism to study the complex role of protein digestion due to its simple life cycle and amenability to techniques like RNA interference (RNAi). In this study, we were interested in deconvoluting the digestive protease system that exists in the planarian gut. To do this, we developed an alcohol-induced regurgitation technique to enrich for the gut enzymes in S. mediterranea. Using a panel of fluorescent substrates, we show that this treatment produces a sharp increase in proteolytic activity. These enzymes have broad yet diverse substrate specificity profiles. Proteomic analysis of the gut contents revealed the presence of cysteine and metallo-proteases. However, treatment with class-specific inhibitors showed that aspartyl and cysteine proteases are responsible for the majority of protein digestion. Specific RNAi knockdown of the cathepsin B-like cysteine protease (SmedCB) reduced protein degradation in vivo. Immunohistochemistry and whole-mount in situ hybridization (WISH) confirmed that the full-length and active forms of SmedCB are found in secretory cells surrounding the planaria intestinal lumen. Finally, we show that the knockdown of SmedCB reduces the speed of tissue regeneration. Defining the roles of proteases in planaria can provide insight to functions of conserved proteases in parasitic flatworms, potentially uncovering drug targets in parasites.

Controversial aspects of the life cycle of Fasciola hepatica

Fasciola hepatica is a well-known helminth parasite, with significant economic and public health importance all over the world. It has been known since more than 630 years ago and a considerable research work has been carried out on the life cycle of this important parasite. In the hepatic phase of the life cycle of F. hepatica, it is assumed that the young flukes, after about 6-7 weeks of migration in the liver parenchyma, enter into the bile ducts of the definitive hosts and become sexually mature. Even though the secretion of cysteine peptidases including cathepsin L and B proteases by F. hepatica may justify this opinion, because of several scientific reasons and based on the experimental studies conducted in different animals (reviewed in this article), the entry of parasites into the bile ducts, after their migration in the liver parenchyma seems to be doubtful. However, considering all the facts relating to the hepatic and biliary phases of the life cycle of F. hepatica, two alternative ideas are suggested: 1) some of the migrating juvenile flukes may enter into the bile ducts immediately after reaching the liver parenchyma while they are still very small, or 2) when newly excysted juvenile flukes are penetrating into the intestinal wall to reach the liver through the abdominal cavity, a number of these flukes may enter into the choleduct and reach the hepatic bile ducts, where they mature. According to the previously performed natural and experimental studies in different animals and human beings, the supporting and opposing evidences for the current opinion as well as the evidences that might justify the two new ideas are reviewed and discussed briefly. In conclusion, our present knowledge about the time and quality of the entry of F. hepaticas into the bile ducts, seems to be insufficient, therefore, there are still some dark corners and unknown aspects in this field that should be clarified.

Unexpected Activity of a Novel Kunitz-type Inhibitor: INHIBITION OF CYSTEINE PROTEASES BUT NOT SERINE PROTEASES

Kunitz-type (KT) protease inhibitors are low molecular weight proteins classically defined as serine protease inhibitors. We identified a novel secreted KT inhibitor associated with the gut and parenchymal tissues of the infective juvenile stage of Fasciola hepatica, a helminth parasite of medical and veterinary importance. Unexpectedly, recombinant KT inhibitor (rFhKT1) exhibited no inhibitory activity toward serine proteases but was a potent inhibitor of the major secreted cathepsin L cysteine proteases of F. hepatica, FhCL1 and FhCL2, and of human cathepsins L and K (K_i = 0.4-27 nm). FhKT1 prevented the auto-catalytic activation of FhCL1 and FhCL2 and formed stable complexes with the mature enzymes. Pulldown experiments from adult parasite culture medium showed that rFhKT1 interacts specifically with native secreted FhCL1, FhCL2, and FhCL5. Substitution of the unusual P1 Leu¹⁵ within the exposed reactive loop of FhKT1 for the more commonly found Arg (FhKT1Leu¹⁵/Arg¹⁵) had modest adverse effects on the cysteine protease inhibition but conferred potent activity against the serine protease trypsin (K_i = 1.5 nm). Computational docking and sequence analysis provided hypotheses for the exclusive binding of FhKT1 to cysteine proteases, the importance of the Leu¹⁵ in anchoring the inhibitor into the S2 active site pocket, and the inhibitor's selectivity toward FhCL1, FhCL2, and human cathepsins L and K. FhKT1 represents a novel evolutionary adaptation of KT protease inhibitors by F. hepatica, with its prime purpose likely in the regulation of the major parasite-secreted proteases and/or cathepsin L-like proteases of its host.

A prospective view of animal and human Fasciolosis

Fasciolosis, a food-borne trematodiasis, results following infection with the parasites, Fasciola hepatica and Fasciola gigantica. These trematodes greatly affect the global agricultural community, infecting millions of ruminants worldwide and causing annual economic losses in excess of US $3 billion. Fasciolosis, an important zoonosis, is classified by WHO as a neglected tropical disease with an estimated 17 million people infected and a further 180 million people at risk of infection. The significant impact on agriculture and human health together with the increasing demand for animal-derived food products to support global population growth demonstrate that fasciolosis is a major One Health problem. This review details the problematic issues surrounding fasciolosis control, including drug resistance, lack of diagnosis and the threat that hybridization of the Fasciola species poses to future animal and human health. We discuss how these parasites may mediate their long-term survival through regulation and modulation of the host immune system, by altering the host immune homeostasis and/or by influencing the intestinal microbiome particularly in respect to concurrent infections with other pathogens. Large genome, transcriptome and proteomic data sets are now available to support an integrated One Health approach to develop novel diagnostic and control strategies for both animal and human disease.

Identification of Chalcones as Fasciola hepatica Cathepsin L Inhibitors Using a Comprehensive Experimental and Computational Approach

BACKGROUND

Increased reports of human infections have led fasciolosis, a widespread disease of cattle and sheep caused by the liver flukes Fasciola hepatica and Fasciola gigantica, to be considered an emerging zoonotic disease. Chemotherapy is the main control measure available, and triclabendazole is the preferred drug since is effective against both juvenile and mature parasites. However, resistance to triclabendazole has been reported in several countries urging the search of new chemical entities and target molecules to control fluke infections.

METHODOLOGY/PRINCIPLE FINDINGS

We searched a library of forty flavonoid derivatives for inhibitors of key stage specific Fasciola hepatica cysteine proteases (FhCL3 and FhCL1). Chalcones substituted with phenyl and naphtyl groups emerged as good cathepsin L inhibitors, interacting more frequently with two putative binding sites within the active site cleft of the enzymes. One of the compounds, C34, tightly bounds to juvenile specific FhCL3 with an IC50 of 5.6 μM. We demonstrated that C34 is a slow-reversible inhibitor that interacts with the Cys-His catalytic dyad and key S2 and S3 pocket residues, determinants of the substrate specificity of this family of cysteine proteases. Interestingly, C34 induces a reduction in NEJ ability to migrate through the gut wall and a loss of motility phenotype that leads to NEJ death within a week in vitro, while it is not cytotoxic to bovine cells.

CONCLUSIONS/SIGNIFICANCE

Up to date there are no reports of in vitro screening for non-peptidic inhibitors of Fasciola hepatica cathepsins, while in general these are considered as the best strategy for in vivo inhibition. We have identified chalcones as novel inhibitors of the two main Cathepsins secreted by juvenile and adult liver flukes. Interestingly, one compound (C34) is highly active towards the juvenile enzyme reducing larval ability to penetrate the gut wall and decreasing NEJ´s viability in vitro. These findings open new avenues for the development of novel agents to control fluke infection and possibly other helminthic diseases.

Hypothetical granulin-like molecule from Fasciola hepatica identified by bioinformatics analysis

Fasciola hepatica is considered an emergent human pathogen, causing liver fibrosis or cirrhosis, conditions that are known to be direct causes of cancer. Some parasites have been categorized by WHO as carcinogenic agents such as Opisthorchis viverrini, a relative of F. hepatica. Although these two parasites are from the same class (Trematoda), the role of F. hepatica in carcinogenesis is unclear. We hypothesized that F. hepatica might share some features with O. viverrini and to be responsible to induce proliferation of host cells. We analyzed the recently released genome of F. hepatica looking for a gene coding a granulin-like growth factor, a protein secreted by O. viverrini (Ov-GRN-1), which is a potent stimulator of proliferation of host cells. Using computational biology tools, we identified a granulin-like molecule in F. hepatica, here termed FhGLM, which has high sequence identity level to Ov-GRN-1 and human progranulin. We found evidence of an upstream promoter compatible with the expression of FhGLM. The FhGLM architecture showed to have five granulin domains, one of them, the domain 3, was homologue to Ov-GRN-1 and human GRNC. The structure of the FhGLM granulin domain 3 resulted to have the overall folding of its homologue the human GRNC. Our findings show the presence of a homologue of a potent modulator of cell growth in F. hepatica that might have, as other granulins, a proliferative action on host cells during fascioliasis. Future experimental assays to demonstrate the presence of FhGLM in F. hepatica are needed to confirm our hypothesis.

Secretome analysis of rice suspension-cultured cells infected by Xanthomonas oryzae pv.oryza (Xoo)

BACKGROUND

Rice bacterial blight (BB) caused by Xanthomonas oryzae pv.oryzae (Xoo) is one of the most devastating bacterial diseases in rice-growing regions worldwide. The rice-Xoo interaction is a classical model for studying the interaction between plants and pathogens. Secreted proteins play important roles in plant-bacterial interactions, but are poorly studied in the rice-Xoo system. Rice cv. Nipponbare is highly susceptible to Xoo. Here, we used two-dimensional difference gel electrophoresis (2D-DIGE) coupled with MALDI-TOF/TOF mass spectrometry (MS), to investigate secreted proteins in Nipponbare embryo cell suspension culture infected by Xoo.

RESULTS

A total of 32 protein spots changed significantly (p < 0.05) by more than 1.5 fold in gel intensity after Xoo inoculation, and were identified by MS. They represent protein products of 11 unique genes, seven from rice and four from Xoo. Of the rice proteins, six up-regulated proteins are involved in cell wall modification, the TCA cycle, glycolysis and redox, while a down-regulated protein, CHIT16, is involved in plant defense. Quantitative Real-Time PCR showed that transcript levels were not correlated with secreted protein levels. Of the Xoo proteins, three of them were possibly located in the extracellular space as shown by transient expression assays in rice protoplasts. Two of the Xoo proteins were previously reported to be likely involved in pathogenicity, and the third gene, Xoo3654, is likely a negative regulator of Xoo virulence as its overexpression reduced Xoo pathogenicity in our study.

CONCLUSION

Among the secreted proteins that responded to Xoo inoculation, we identified rice proteins involved in cell defense and Xoo proteins involved in pathogenicity. Our study also showed that Xoo3654 (X2) protein is likely a novel negative regulator of Xoo virulence. These results not only help us better understand the interaction between susceptible rice and Xoo, but also serve as a reference for studying the interaction between other plants and their pathogens.

Phylogenetic characterization of Clonorchis sinensis proteins homologous to the sigma-class glutathione transferase and their differential expression profiles

Glutathione transferase (GST) is one of the major antioxidant proteins with diverse supplemental activities including peroxidase, isomerase, and thiol transferase. GSTs are classified into multiple classes on the basis of their primary structures and substrate/inhibitor specificity. However, the evolutionary routes and physiological environments specific to each of the closely related bioactive enzymes remain elusive. The sigma-like GSTs exhibit amino acid conservation patterns similar to the prostaglandin D synthases (PGDSs). In this study, we analyzed the phylogenetic position of the GSTs of the biocarcinogenic liver fluke, Clonorchis sinensis. We also observed induction profile of the GSTs in association with the parasite's maturation and in response to exogenous oxidative stresses, with special attention to sigma-class GSTs and PGDSs. The C. sinensis genome encoded 12 GST protein species, which were separately assigned to cytosolic (two omega-, one zeta-, two mu-, and five sigma-class), mitochondrial (one kappa-class), and microsomal (one membrane-associated proteins in eicosanoid and glutathione metabolism-like protein) GST families. Multiple sigma GST (or PGDS) orthologs were also detected in Opisthorchis viverrini. Other trematode species possessed only a single sigma-like GST gene. A phylogenetic analysis demonstrated that one of the sigma GST lineages duplicated in the common ancestor of trematodes were specifically expanded in the opisthorchiids, but deleted in other trematodes. The induction profiles of these sigma GST genes along with the development and aging of C. sinensis, and against various exogenous chemical stimuli strongly suggest that the paralogous sigma GST genes might be undergone specialized evolution to cope with the diverse hostile biochemical environments within the mammalian hepatobiliary ductal system.

Identification and characterization of Clonorchis sinensis cathepsin B proteases in the pathogenesis of clonorchiasis

BACKGROUND

Human clonorchiasis is a prevailing food-borne disease caused by Clonorchis sinensis infection. Functional characterizations of key molecules from C. sinensis could facilitate the intervention of C. sinensis associated diseases.

METHODS

In this study, immunolocalization of C. sinensis cathepsin B proteases (CsCBs) in C. sinensis worms was investigated. Four CsCBs were expressed in Pichia pastoris yeast cells. Purified yCsCBs were measured for enzymatic and hydrolase activities in the presence of various host proteins. Cell proliferation, wound-healing and transwell assays were performed to show the effect of CsCBs on human cells.

RESULTS

CsCBs were localized in the excretory vesicle, oral sucker and intestinal tract of C. sinensis. Recombinant yCsCBs from yeast showed active enzymatic activity at pH 5.0-5.5 and at 37-42 °C. yCsCBs can degrade various host proteins including human serum albumin, human fibronectin, human hemoglobin and human IgG. CsCBs were detected in liver tissues of mice and cancer patients afflicted with clonorchiasis. Various bioassays collectively demonstrated that CsCBs could promote cell proliferation, migration and invasion of human cancer cells.

CONCLUSION

Our results demonstrated that CsCBs can degrade various human proteins and we proved that the secreted CsCBs are involved in the pathogenesis of clonorchiasis.

Development of a versatile in vitro method for understanding the migration of Fasciola hepatica newly excysted juveniles

Fasciola hepatica is a parasitic trematode that causes serious losses to livestock producers, and also zoonotic disease. The limitations of chemotherapy for the control of fasciolosis have led to significant interest in the development of vaccines to protect cattle and sheep from infection. However, relatively few studies have concentrated on the mechanisms of invasion of the gut by newly excysted juvenile liver flukes (NEJ) and the host response triggered by this event. The aim of this work was to develop an in vitro model to study invasion by NEJ, while also reducing the requirement for challenge infections of experimental animals. Fasciola hepatica metacercariae were excysted in vitro and placed into compartments containing rat distal jejunal sheets. Variations in incubation medium, chamber size and incubation temperature were used to identify optimal conditions for NEJ migration across the gut. Histological examination showed increased migration until 120 min post-incubation. The use of RPMI, without gassing at 39 °C, as the incubation medium was found to be optimal, with 40·5% of NEJ migrating after 150 min. This study describes a readily-reproducible method for studying the migration of F. hepatica NEJ within the definitive host. It will be useful for identifying potential drug and vaccine targets.

The Extracellular Vesicles of the Helminth Pathogen, Fasciola hepatica: Biogenesis Pathways and Cargo Molecules Involved in Parasite Pathogenesis

Extracellular vesicles (EVs) released by parasites have important roles in establishing and maintaining infection. Analysis of the soluble and vesicular secretions of adult Fasciola hepatica has established a definitive characterization of the total secretome of this zoonotic parasite. Fasciola secretes at least two subpopulations of EVs that differ according to size, cargo molecules and site of release from the parasite. The larger EVs are released from the specialized cells that line the parasite gastrodermus and contain the zymogen of the 37 kDa cathepsin L peptidase that performs a digestive function. The smaller exosome-like vesicle population originate from multivesicular bodies within the tegumental syncytium and carry many previously described immunomodulatory molecules that could be delivered into host cells. By integrating our proteomics data with recently available transcriptomic data sets we have detailed the pathways involved with EV biogenesis in F. hepatica and propose that the small exosome biogenesis occurs via ESCRT-dependent MVB formation in the tegumental syncytium before being shed from the apical plasma membrane. Furthermore, we found that the molecular “machinery” required for EV biogenesis is constitutively expressed across the intramammalian development stages of the parasite. By contrast, the cargo molecules packaged within the EVs are developmentally regulated, most likely to facilitate the parasites migration through host tissue and to counteract host immune attack.

Fasciola gigantica cathepsin B5 is an acidic endo- and exopeptidase of the immature and mature parasite

Cysteine proteases of the liver fluke Fasciola have been described as essential molecules in the infection process of the mammalian host. Destinct cathepsin Bs, which are already expressed in the metacercarial stage and released by the newly excysted juvenile are major actors in this process. Following infection their expression is stopped and the proteins will not be detectable any longer after the first month of development. On the contrary, the novel cathepsin B5 of Fasciola gigantica (FgCB5) described in this work was also found expressed in later juvenile stages and the mature worm. Like all previously described Fasciola family members it was located in the cecal epithelium of the parasite. Western blot analysis of adult antigen preparations detected procathepsin B5 in crude worm extract and in small amounts in the ES product. In support of these data, the sera of infected rabbits and mice were reactive with recombinant FgCB5 in Western blot and ELISA. Biochemical analysis of yeast-expressed FgCB5 revealed that it has properties of a lysosomal hydrolase optimized for activity at acid pH and that it is able to efficiently digest a broad spectrum of host proteins. Unlike previously characterized Fasciola family members FgCB5 carries a histidine doublet in the occluding loop equivalent to residues His110 and His111 of human mature cathepsin B and consequently showed substantial carboxydipeptidyl activity which depends on these two residues.

Influence of levamisole and Freund's adjuvant on mouse immunisation with antigens of adults of the liver fluke Fasciola hepatica Linnaeus, 1758

We have studied the influence of both levamisole (AL) and Freund's adjuvant (AF) on the immunisation of mice with the secretory antigens of adults of the liver fluke Fasciola hepatica Linnaeus, 1758. Total IgG antibodies were detected in all groups where the F. hepatica antigen was administered, been levels of IgG1 increased respect to IgG2a antibodies. During immunisation, IL-4 and IFN-γ were only detected in AL and AF groups, but after infection, IL-4 boosted in all groups. IFN-γ increased two fold in AF and AL groups compared to the saline solution (AS) group. Worm recovering was of 32-35% in groups administered without antigen whereas in AS, AL and AF groups recovering was of 25%, 12% and 8%, respectively. Macroscopical lesions in the liver were scarce in AL and AF groups. Our data suggest that immunisation of mice with antigens of F. hepatica enhances the immune response avoiding both liver damage and worm establishment after challenge infection. The murine model of fasciolosis has appeared to be useful to elucidate the mechanism by which the parasite modulates immune responses toward a Th2 type but also the development of Th1 type-inducing vaccines.

Juvenile-specific cathepsin proteases in Fasciola spp.: their characteristics and vaccine efficacies

Fasciolosis, caused by Fasciola hepatica and Fasciola gigantica, is one of the most neglected tropical zoonotic diseases. One sustainable control strategy against these infections is the employment of vaccines that target proteins essential for parasites' invasion and nutrition acquiring processes. Cathepsin proteases are the most abundantly expressed proteins in Fasciola spp. that have been tested successfully as vaccines against fasciolosis in experimental as well as large animals because of their important roles in digestion of nutrients, invasion, and migration. Specifically, juvenile-specific cathepsin proteases are the more effective vaccines because they could block the invasion and migration of juvenile parasites whose immune evasion mechanism has not yet been fully developed. Moreover, because of high sequence similarity and identity of cathepsins from juveniles with those of adults, the vaccines can attack both the juvenile and adult stages. In this article, the characteristics and vaccine potentials of juvenile-specific cathepsins, i.e., cathepsins L and B, of Fasciola spp. were reviewed.

The helminth parasite proteome at the host-parasite interface - Informing diagnosis and control

Helminth parasites are a significant health burden for humans in the developing world and also cause substantial economic losses in livestock production across the world. The combined lack of vaccines for the major human and veterinary helminth parasites in addition to the development of drug resistance to anthelmintics in sheep and cattle mean that controlling helminth infection and pathology remains a challenge. However, recent high throughput technological advances mean that screening for potential drug and vaccine candidates is now easier than in previous decades. A better understanding of the host-parasite interactions occurring during infection and pathology and identifying pathways that can be therapeutically targeted for more effective and 'evolution proof' interventions is now required. This review highlights some of the advances that have been made in understanding the host-parasite interface in helminth infections using studies of the temporal expression of parasite proteins, i.e. the parasite proteome, and discuss areas for potential future research and translation.

Insights into the Interactions of Fasciola hepatica Cathepsin L3 with a Substrate and Potential Novel Inhibitors through In Silico Approaches

Background

Fasciola hepatica is the causative agent of fascioliasis, a disease affecting grazing animals, causing economic losses in global agriculture and currently being an important human zoonosis. Overuse of chemotherapeutics against fascioliasis has increased the populations of drug resistant parasites. F. hepatica cathepsin L3 is a protease that plays important roles during the life cycle of fluke. Due to its particular collagenolytic activity it is considered an attractive target against the infective phase of F. hepatica.

Methodology/Principal Findings

Starting with a three dimensional model of FhCL3 we performed a structure-based design of novel inhibitors through a computational study that combined virtual screening, molecular dynamics simulations, and binding free energy (ΔG_bind) calculations. Virtual screening was carried out by docking inhibitors obtained from the MYBRIDGE-HitFinder database inside FhCL3 and human cathepsin L substrate-binding sites. On the basis of dock-scores, five compounds were predicted as selective inhibitors of FhCL3. Molecular dynamic simulations were performed and, subsequently, an end-point method was employed to predict ΔG_bind values. Two compounds with the best ΔG_bind values (-10.68 kcal/mol and -7.16 kcal/mol), comparable to that of the positive control (-10.55 kcal/mol), were identified. A similar approach was followed to structurally and energetically characterize the interface of FhCL3 in complex with a peptidic substrate. Finally, through pair-wise and per-residue free energy decomposition we identified residues that are critical for the substrate/ligand binding and for the enzyme specificity.

Conclusions/Significance

The present study is the first computer-aided drug design approach against F. hepatica cathepsins. Here we predict the principal determinants of binding of FhCL3 in complex with a natural substrate by detailed energetic characterization of protease interaction surface. We also propose novel compounds as FhCL3 inhibitors. Overall, these results will foster the future rational design of new inhibitors against FhCL3, as well as other F. hepatica cathepsins.

Fascioliosis is considered an emerging disease in humans, causing important losses in global agriculture through the infection of livestock animals. The outcome of resistant parasites has increased the search for new drugs which may contribute to disease control. In recent decades, Fasciola cathepsins (FhCs) have been defined as the principal virulence factors of this parasite. Despite being in the same protein family, they have different specificities and, thus, distinct roles throughout the fluke life cycle. Differences in specificity have been attributed to a few variations in the sequence of key FhCs subsites. Currently, the structure-based drug design of inhibitors against Fasciola cathepsin Ls (FhCLs) with unknown structures is possible due to the availability of the three-dimensional structure of FhCL1. Our detailed structural analysis of the major infective juvenile enzyme (FhCL3) identifies the molecular determinants for protein binding. Also, novel potential inhibitors against FhCL3 are proposed, which might reduce host invasion and penetration processes. These compounds are predicted to interact with the binding site of the enzyme, therefore they could prevent substrate processing by competitive inhibition. The structure-based drug design strategy described here will be useful for the development of new potent and selective inhibitors against other FhCs.

Comparative transcriptome profiling approach to glean virulence and immunomodulation-related genes of Fasciola hepatica

BACKGROUND

Fasciola hepatica causes chronic liver disease, fasciolosis, leading to significant losses in the livestock economy and concerns for human health in many countries. The identification of F. hepatica genes involved in the parasite's virulence through modulation of host immune system is utmost important to comprehend evasion mechanisms of the parasite and develop more effective strategies against fasciolosis. In this study, to identify the parasite's putative virulence genes which are associated with host immunomodulation, we explored whole transcriptome of an adult F. hepatica using current transcriptome profiling approaches integrated with detailed in silico analyses. In brief, the comparison of the parasite transcripts with the specialised public databases containing sequence data of non-parasitic organisms (Dugesiidae species and Caenorhabditis elegans) or of numerous pathogens and investigation of the sequences in terms of nucleotide evolution (directional selection) and cytokine signaling relation were conducted.

RESULTS

NGS of the whole transcriptome resulted in 19,534,766 sequence reads, yielding a total of 40,260 transcripts (N₅₀ = 522 bp). A number of the parasite transcripts (n = 1,671) were predicted to be virulence-related on the basis of the exclusive homology with the pathogen-associated data, positive selection or relationship with cytokine signaling. Of these, a group of the virulence-related genes (n = 62), not previously described, were found likely to be associated with immunomodulation based on in silico functional categorisation, showing significant sequence similarities with various immune receptors (i.e. MHC I class, TGF-β receptor, toll/interleukin-1 receptor, T-cell receptor, TNF receptor, and IL-18 receptor accessory protein), cytokines (i.e. TGF-β, interleukin-4/interleukin-13 and TNF-α), cluster of differentiations (e.g. CD48 and CD147) or molecules associated with other immunomodulatory mechanisms (such as regulation of macrophage activation). Some of the genes (n = 5) appeared to be under positive selection (Ka/Ks > 1), imitating proteins associated with cytokine signaling (through sequence homologies with thrombospondin type 1, toll/interleukin-1 receptor, TGF-β receptor and CD147).

CONCLUSIONS

With a comparative transcriptome profiling approach, we have identified a number of potential immunomodulator genes of F. hepatica (n = 62), which are firstly described here, could be employed for the development of better strategies (including RNAi) in the battle against both zoonotically and economically important disease, fasciolosis.

The Fasciola hepatica genome: gene duplication and polymorphism reveals adaptation to the host environment and the capacity for rapid evolution

Background

The liver fluke Fasciola hepatica is a major pathogen of livestock worldwide, causing huge economic losses to agriculture, as well as 2.4 million human infections annually.

Results

Here we provide a draft genome for F. hepatica, which we find to be among the largest known pathogen genomes at 1.3 Gb. This size cannot be explained by genome duplication or expansion of a single repeat element, and remains a paradox given the burden it may impose on egg production necessary to transmit infection. Despite the potential for inbreeding by facultative self-fertilisation, substantial levels of polymorphism were found, which highlights the evolutionary potential for rapid adaptation to changes in host availability, climate change or to drug or vaccine interventions. Non-synonymous polymorphisms were elevated in genes shared with parasitic taxa, which may be particularly relevant for the ability of the parasite to adapt to a broad range of definitive mammalian and intermediate molluscan hosts. Large-scale transcriptional changes, particularly within expanded protease and tubulin families, were found as the parasite migrated from the gut, across the peritoneum and through the liver to mature in the bile ducts. We identify novel members of anti-oxidant and detoxification pathways and defined their differential expression through infection, which may explain the stage-specific efficacy of different anthelmintic drugs.

Conclusions

The genome analysis described here provides new insights into the evolution of this important pathogen, its adaptation to the host environment and external selection pressures. This analysis also provides a platform for research into novel drugs and vaccines.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-015-0632-2) contains supplementary material, which is available to authorized users.

Identification and characterization of a member of Rab subfamily, Rab8, from Clonorchis sinensis

The Rabs act as a binary molecular switch that utilizes the conformational changes associated with the GTP/GDP cycle to elicit responses from target proteins. It regulates a broad spectrum of cellular processes including cell proliferation, cytoskeletal assembly, and intracellular membrane trafficking in eukaryotes. The Rab8 from Clonorchis sinensis (CsRab8) was composed of 199 amino acids. The deduced amino acid sequence shared above 50% identities with other species from trematode, tapeworm, mammal, insecta, nematode, and reptile, respectively. The homologous analysis of sequences showed the conservative domains: G1 box (GDSGVGKS), G2 box (T), G3 box (DTAG), G4 box (GNKCDL), and G5 box. In addition, the structure modeling had also shown other functional domains: GTP/Mg(2+) binding sites, switch I region, and switch II region. A phylogenic tree analysis indicated that the CsRab8 was clustered with the Rab from Schistosoma japonicum, and trematode and tapeworm came from the same branch, which was different from an evolutional branch built by other species, such as mammal animal, insecta, nematode, and reptile. The recombinant CsRab8 protein was expressed in Escherichia coli and the purified protein was a soluble molecule by 12% sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis. CsRab8 was identified as a component of excretory/secretory products of C. sinensis by western blot analysis. The transcriptional level of CsRab8 at metacercaria stage was the highest at the four stages and higher by 56.49-folds than that at adult worm, 1.23-folds than that at excysted metacercaria, and 2.69-folds than that at egg stage. Immunohistochemical localization analysis showed that CsRab8 was specifically distributed in the tegument, vitellarium, eggs, and testicle of adult worms, and detected on the vitellarium and tegument of metacercaria. Combined with the results, CsRab8 is indispensable for survival and development of parasites, especially for regulating excretory/secretory products secretion.

Fasciola hepatica fatty acid binding protein inhibits TLR4 activation and suppresses the inflammatory cytokines induced by lipopolysaccharide in vitro and in vivo

TLR4, the innate immunity receptor for bacterial endotoxins, plays a pivotal role in the induction of inflammatory responses. There is a need to develop molecules that block either activation through TLR4 or the downstream signaling pathways to inhibit the storm of inflammation typically elicited by bacterial LPS, which is a major cause of the high mortality associated with bacterial sepsis. We report in this article that a single i.p. injection of 15 μg fatty acid binding protein from Fasciola hepatica (Fh12) 1 h before exposure to LPS suppressed significantly the expression of serum inflammatory cytokines in a model of septic shock using C57BL/6 mice. Because macrophages are a good source of IL-12p70 and TNF-α, and are critical in driving adaptive immunity, we investigated the effect of Fh12 on the function of mouse bone marrow-derived macrophages (bmMΦs). Although Fh12 alone did not induce cytokine expression, it significantly suppressed the expression of IL-12, TNF-α, IL-6, and IL-1β cytokines, as well as inducible NO synthase-2 in bmMΦs, and also impaired the phagocytic capacity of bmMΦs. Fh12 had a limited effect on the expression of inflammatory cytokines induced in response to other TLR ligands. One mechanism used by Fh12 to exert its anti-inflammatory effect is binding to the CD14 coreceptor. Moreover, it suppresses phosphorylation of ERK, p38, and JNK. The potent anti-inflammatory properties of Fh12 demonstrated in this study open doors to further studies directed at exploring the potential of this molecule as a new class of drug against septic shock or other inflammatory diseases.

Transcriptional analysis identifies key genes involved in metabolism, fibrosis/tissue repair and the immune response against Fasciola hepatica in sheep liver

BACKGROUND

Although fascioliasis has been relatively well studied, little is known about the molecular basis of this disease. This is particularly relevant, considering the very different response that sheep have to Fasciola hepatica relative to cattle. The acute phase of this disease is severe in sheep, whereas chronic fascioliasis is more common in cattle.

METHODS

To begin to explore the host-response to Fasciola in sheep and improve the understanding of the host-pathogen interactions during the parasite's migration through liver parenchyma to the bile duct, we used RNA sequencing (RNA-seq) to investigate livers from sheep infected for eight weeks compared with those from uninfected controls.

RESULTS

This study identified 572 and 42 genes that were up- and down-regulated, respectively, in infected livers relative to uninfected controls. Our molecular findings provide significant new insights into the mechanisms linked to metabolism, fibrosis and tissue-repair in sheep, and highlight the relative importance of specific components of immune response pathways, which appear to be driven toward a suppression of inflammation.

CONCLUSIONS

This study is, to our knowledge, the first detailed investigation of the transcriptomic responses in the liver tissue of any host to F. hepatica infection. It defines the involvement of specific genes associated with the host's metabolism, immune response and tissue repair/regeneration, and highlights an apparent overlapping function of many genes involved in these processes.

Protection against Fasciola gigantica infection in mice by vaccination with recombinant juvenile-specific cathepsin L

Fasciola gigantica cathepsin L1H (FgCatL1H) is one of the major cathepsin L released by juveniles of F. gigantica to aid in the invasion of host's tissues. Due to its high sequence similarity with other cathepsin L (CatL) isoforms of late stage F. gigantica, it was considered to be a good vaccine candidate that can block all CatL-mediated protease activities and affect juveniles as well as adult parasites. In this study, recombinant proFgCatL1H protein expressed in yeast, Pichia pastoris, system was mixed with Freund's adjuvants and used to subcutaneously immunize mice that were later challenged with metacercariae of F. gigantica. The percentage of worm protection in the rproFgCatL1H-vaccinated mice compared to the non-immunized and adjuvant control mice were approximately 62.7% and 66.1%, respectively. Anti-rproFgCatL1H antisera collected from vaccinated mice reacted specifically with rproFgCatL1H and other cathepsin L isoforms of F. gigantica, but the antibodies did not cross react with antigens from other trematode and nematode parasites, including Eurytrema pancreaticum, Opisthorchis viverrini, Fischoederius cobboldi, Cotylophoron cotylophorum, Gigantocotyle explanatum, Paramphistomum cervi, and Setaria labiato-papillosa. The levels of IgG1 and IgG2a in mouse sera increased significantly at two weeks after immunization and were highest during the sixth to eighth weeks after immunization. The IgG1 level was higher than IgG2a at all periods of immunization, implicating the dominance of the Th2 response. The levels of IgG1 and IgG2a in the immune sera were shown to be strongly correlated with the numbers of worm recovery, and the correlation coefficient was higher for IgG1. The levels of serum aspartate aminotransferase and alanine transaminase were significantly lower in the sera of rproFgCatL1H-vaccinated mice than in the infected control mice indicating a lower degree of liver damage. This study demonstrated a high potential of FgCatL1H vaccine, and its efficacy is currently being studied in the larger economic animals.

Cloning, expression and characterization of protein disulfide isomerase of Schistosoma japonicum

The excretory/secretory (ES) proteins of schistosomes play important roles in modulating host immune systems and are regarded as potential vaccine candidates and drug targets. Protein disulfide isomerase (PDI) is an essential enzyme that is involved in disulfide bond formation and rearrangement. In the present study, SjPDI, a 52.8 kDa protein previously identified in a proteomics analysis as one of the ES proteins of Schistosoma japonicum, was cloned and characterized. Western blot analysis showed that recombinant SjPDI (rSjPDI) was recognized by serum from rabbits vaccinated with schistosome worm antigen. Worm protein extracts and ES protein extracts from S. japonicum could react with anti-rSjPDI mouse serum. Real-time PCR analysis indicated that SjPDI was expressed at all developmental stages tested, and a high expression level was detected in 42-day-old male worms. Immunofluorescence analysis revealed that SjPDI was mainly distributed on the tegument and parenchyma of S. japonicum worms. An enzyme-linked immunosorbent assay (ELISA) demonstrated that rSjPDI could induce a high level of rSjPDI-specific IgG antibodies. The biological activity of purified rSjPDI was confirmed by isomerization and antioxidative activity assays. The 35.32%, 26.19% reduction in the worm burden and 33.17%, 31.7% lower liver egg count were obtained in mice vaccinated with rSjPDI compared with the blank control group in two independent trials. Our preliminary results suggest that rSjPDI plays an important role in the development of the schistosome and is a potential vaccine candidate for schistosomiasis.

Fasciola hepatica vaccine: we may not be there yet but we're on the right road

Major advances have been made in identifying potential vaccine molecules for the control of fasciolosis in livestock but we have yet to reach the level of efficacy required for commercialisation. The pathogenesis of fasciolosis is associated with liver damage that is inflicted by migrating and feeding immature flukes as well as host inflammatory immune responses to parasite-secreted molecules and tissue damage alarm signals. Immune suppression/modulation by the parasites prevents the development of protective immune responses as evidenced by the lack of immunity observed in naturally and experimentally infected animals. In our opinion, future efforts need to focus on understanding how parasites invade and penetrate the tissues of their hosts and how they potentiate and control the ensuing immune responses, particularly in the first days of infection. Emerging 'omics' data employed in an unbiased approach are helping us understand liver fluke biology and, in parallel with new immunological data, to identify molecules that are essential to parasite development and accessible to vaccine-induced immune responses.

Extracellular vesicles in parasitic diseases

Parasitic diseases affect billions of people and are considered a major public health issue. Close to 400 species are estimated to parasitize humans, of which around 90 are responsible for great clinical burden and mortality rates. Unfortunately, they are largely neglected as they are mainly endemic to poor regions. Of relevance to this review, there is accumulating evidence of the release of extracellular vesicles (EVs) in parasitic diseases, acting both in parasite–parasite inter-communication as well as in parasite–host interactions. EVs participate in the dissemination of the pathogen and play a role in the regulation of the host immune systems. Production of EVs from parasites or parasitized cells has been described for a number of parasitic infections. In this review, we provide the most relevant findings of the involvement of EVs in intercellular communication, modulation of immune responses, involvement in pathology, and their potential as new diagnostic tools and therapeutic agents in some of the major human parasitic pathogens.

Transcriptome profiles of the protoscoleces of Echinococcus granulosus reveal that excretory-secretory products are essential to metabolic adaptation

Background

Cystic hydatid disease (CHD) is caused by the larval stages of the cestode and affects humans and domestic animals worldwide. Protoscoleces (PSCs) are one component of the larval stages that can interact with both definitive and intermediate hosts. Previous genomic and transcriptomic data have provided an overall snapshot of the genomics of the growth and development of this parasite. However, our understanding of how PSCs subvert the immune response of hosts and maintains metabolic adaptation remains unclear. In this study, we used Roche 454 sequencing technology and in silico secretome analysis to explore the transcriptome profiles of the PSCs from E. granulosus and elucidate the potential functions of the excretory-secretory proteins (ESPs) released by the parasite.

Methodology/Principal Findings

A large number of nonredundant sequences as unigenes were generated (26,514), of which 22,910 (86.4%) were mapped to the newly published E. granulosus genome and 17,705 (66.8%) were distributed within the coding sequence (CDS) regions. Of the 2,280 ESPs predicted from the transcriptome, 138 ESPs were inferred to be involved in the metabolism of carbohydrates, while 124 ESPs were inferred to be involved in the metabolism of protein. Eleven ESPs were identified as intracellular enzymes that regulate glycolysis/gluconeogenesis (GL/GN) pathways, while a further 44 antigenic proteins, 25 molecular chaperones and four proteases were highly represented. Many proteins were also found to be significantly enriched in development-related signaling pathways, such as the TGF-β receptor pathways and insulin pathways.

Conclusions/Significance

This study provides valuable information on the metabolic adaptation of parasites to their hosts that can be used to aid the development of novel intervention targets for hydatid treatment and control.

The successful infection establishment of parasites depends on their ability to combat their host's immune system while maintaining metabolic adaptation to their hosts. The mechanisms of these processes are not well understood. We used the protoscoleces (PSCs) of E. granulosus as a model system to study this complex host-parasite interaction by investigating the role of excretory-secretory proteins (ESPs) in the physiological adaptation of the parasite. Using Roche 454 sequencing technology and in silico secretome analysis, we predicted 2280 ESPs and analyzed their biological functions. Our analysis of the bioinformatic data suggested that ESPs are integral to the metabolism of carbohydrates and proteins within the parasite and/or hosts. We also found that ESPs are involved in mediating the immune responses of hosts and function within key development-related signaling pathways. We found 11 intracellular enzymes, 25 molecular chaperones and four proteases that were highly represented in the ESPs, in addition to 44 antigenic proteins that showed promise as candidates for vaccine or serodiagnostic development purposes. These findings provide valuable information on the mechanisms of metabolic adaptation in parasites that will aid the development of novel hydatid treatment and control targets.

Production and analysis of immunomodulatory excretory-secretory products from the mouse gastrointestinal nematode Heligmosomoides polygyrus bakeri

Heligmosomoides polygyrus bakeri (Hpb) infection in mice is a convenient model for studying the pathophysiology and immunology of gastrointestinal (GI) helminth infection. Hpb infection suppresses immune responses to bystander antigens and unrelated pathogens, and it slows the progression and modifies the outcome of immune-mediated diseases. Hpb-derived excretory-secretory (ES) products potently modulate CD4(+) helper T cell (TH) responses by inducing regulatory T cells, tolerogenic dendritic cells (DCs) and immunoregulatory cytokines. This observation has spiked interest in identifying the immunomodulatory molecules, especially proteins, in ES products from Hpb and other GI nematodes for development as novel therapies to treat individuals with immune-mediated diseases, such as inflammatory bowel diseases (IBDs). In this protocol, we describe how to (i) maintain Hpb in the laboratory for experimental infections, (ii) collect adult worms from infected mice to generate ES products and (iii) evaluate the modulatory effects of ES products on toll-like receptor (TLR) ligand-induced maturation of CD11c(+) DCs. The three major sections of the PROCEDURE can be used independently, and they require ∼6, 10 and 27 h, respectively. Although other methods use a modified Baermann apparatus to collect Hpb adult worms, we describe a method that involves dissection of adult worms from intestinal tissue. The protocol will be useful to investigators studying the host-parasite interface and identifying and analyzing helminth-derived molecules with therapeutic potential.

Systems biology studies of adult paragonimus lung flukes facilitate the identification of immunodominant parasite antigens

Background

Paragonimiasis is a food-borne trematode infection acquired by eating raw or undercooked crustaceans. It is a major public health problem in the far East, but it also occurs in South Asia, Africa, and in the Americas. Paragonimus worms cause chronic lung disease with cough, fever and hemoptysis that can be confused with tuberculosis or other non-parasitic diseases. Treatment is straightforward, but diagnosis is often delayed due to a lack of reliable parasitological or serodiagnostic tests. Hence, the purpose of this study was to use a systems biology approach to identify key parasite proteins that may be useful for development of improved diagnostic tests.

Methodology/Principal Findings

The transcriptome of adult Paragonimus kellicotti was sequenced with Illumina technology. Raw reads were pre-processed and assembled into 78,674 unique transcripts derived from 54,622 genetic loci, and 77,123 unique protein translations were predicted. A total of 2,555 predicted proteins (from 1,863 genetic loci) were verified by mass spectrometric analysis of total worm homogenate, including 63 proteins lacking homology to previously characterized sequences. Parasite proteins encoded by 321 transcripts (227 genetic loci) were reactive with antibodies from infected patients, as demonstrated by immunoaffinity purification and high-resolution liquid chromatography-mass spectrometry. Serodiagnostic candidates were prioritized based on several criteria, especially low conservation with proteins in other trematodes. Cysteine proteases, MFP6 proteins and myoglobins were abundant among the immunoreactive proteins, and these warrant further study as diagnostic candidates.

Conclusions

The transcriptome, proteome and immunolome of adult P. kellicotti represent a major advance in the study of Paragonimus species. These data provide a powerful foundation for translational research to develop improved diagnostic tests. Similar integrated approaches may be useful for identifying novel targets for drugs and vaccines in the future.

Paragonimiasis is a food-borne trematode infection that people acquire when they eat raw or undercooked crustaceans. Disease symptoms (including cough, fever, blood in sputum, etc.) can be similar to those observed in patients with tuberculosis or bacterial pneumonia, frequently resulting in misdiagnosis. Although the infection is relatively easy to treat, diagnosis is complicated. Available diagnostic assays rely on total parasite homogenate to facilitate the detection of Paragonimus-specific antibodies in patients. Though these blot-based assays have shown high sensitivity and specificity, they are inconvenient because total parasite homogenate is not readily available. This study used next generation genomic and proteomic methods to identify transcripts and proteins expressed in adult Paragonimus flukes. We then used sera from patients infected with P. kellicotti to isolate immunoreactive proteins, and these were analyzed by mass spectrometry. The annotated transcriptome and the associated proteome of the antibody immune response represent a significant advance in research on Paragonimus. This information will be a valuable resource for further research on Paragonimus and paragonimiasis. Thus this project illustrates the potential power of employing systems biology for translational research in parasitology.

RNAi dynamics in Juvenile Fasciola spp. Liver flukes reveals the persistence of gene silencing in vitro

Background

Fasciola spp. liver fluke cause pernicious disease in humans and animals. Whilst current control is unsustainable due to anthelmintic resistance, gene silencing (RNA interference, RNAi) has the potential to contribute to functional validation of new therapeutic targets. The susceptibility of juvenile Fasciola hepatica to double stranded (ds)RNA-induced RNAi has been reported. To exploit this we probe RNAi dynamics, penetrance and persistence with the aim of building a robust platform for reverse genetics in liver fluke. We describe development of standardised RNAi protocols for a commercially-available liver fluke strain (the US Pacific North West Wild Strain), validated via robust transcriptional silencing of seven virulence genes, with in-depth experimental optimisation of three: cathepsin L (FheCatL) and B (FheCatB) cysteine proteases, and a σ-class glutathione transferase (FheσGST).

Methodology/Principal Findings

Robust transcriptional silencing of targets in both F. hepatica and Fasciola gigantica juveniles is achievable following exposure to long (200–320 nt) dsRNAs or 27 nt short interfering (si)RNAs. Although juveniles are highly RNAi-susceptible, they display slower transcript and protein knockdown dynamics than those reported previously. Knockdown was detectable following as little as 4h exposure to trigger (target-dependent) and in all cases silencing persisted for ≥25 days following long dsRNA exposure. Combinatorial silencing of three targets by mixing multiple long dsRNAs was similarly efficient. Despite profound transcriptional suppression, we found a significant time-lag before the occurrence of protein suppression; FheσGST and FheCatL protein suppression were only detectable after 9 and 21 days, respectively.

Conclusions/Significance

In spite of marked variation in knockdown dynamics, we find that a transient exposure to long dsRNA or siRNA triggers robust RNAi penetrance and persistence in liver fluke NEJs supporting the development of multiple-throughput phenotypic screens for control target validation. RNAi persistence in fluke encourages in vivo studies on gene function using worms exposed to RNAi-triggers prior to infection.

RNA interference (RNAi) is a method for selectively silencing (or reducing expression of) mRNA transcripts, an approach which can be used to interrogate the function of genes and proteins, and enables the validation of potential targets for anthelmintic drugs or vaccines, by investigating the impact of silencing a particular gene on parasite survival or behaviour. This study focuses on liver fluke parasites, which cause serious disease in both humans and animals. We have only a handful of drugs with which to treat these infections, to which flukes are developing resistance, and no anti-fluke vaccines have yet been developed. New options for treatment and control of liver fluke parasites are sorely needed, and RNAi is a powerful tool in the development of such treatments. This study developed a set of simple methods for triggering RNAi in juvenile liver fluke, which show that although robust transcriptional suppression can be readily achieved across all targets tested, protein suppression occurs only after a target-specific lag period (likely related to protein half-life), which may require >25 days under current in vitro maintenance conditions. These findings are important for researchers aiming to employ RNAi in investigations of liver fluke biology and target validation.

Fasciola hepatica fatty acid binding protein induces the alternative activation of human macrophages

The liver fluke Fasciola hepatica is a highly evolved parasite that uses sophisticated mechanisms to evade the host immune response. The immunosuppressive capabilities of the parasite have been associated with antigens secreted through the parasite's tegument, called excretory-secretory products (ESPs). Proteomic studies have identified the fatty acid binding protein (FABP) as one of molecules present in the parasite ESPs. Although FABP has been investigated for potential use in the development of vaccines against fascioliasis, its direct interaction with cells of immune system has not been studied. In this study, FABP was purified in native form from soluble extracts of F. hepatica adult flukes using a combination of molecular sieving chromatography and preparative isoelectric focusing. The immunological effect of the purified protein, termed Fh12, was assayed in vitro using monocyte-derived macrophages (MDM) obtained from healthy human donors. Results from the assay indicate that Fh12 produced a significantly increased arginase expression and activity and induced the expression of chitinase-3-like protein (CHI3L1). The assay also showed that Fh12 downregulated the production of nitric oxide (NO) and the expression of nitric oxide synthase (NOS2). This indicates that Fh12 induced the production of alternatively activated macrophages (AAMϕ). The results also demonstrated the ability of Fh12 to downregulate the secretion of the proinflammatory and inflammatory cytokines tumor necrosis factor alpha (TNF-α), interleukin-12 (IL-12), and IL-1βB, even after stimulation with lipopolysaccharide (LPS), as well as its ability to stimulate the overexpression of IL-10. These results suggest a potent anti-inflammatory role for Fh12, which could occur via targeting of Toll-like receptor 4 (TLR4).

Harnessing the helminth secretome for therapeutic immunomodulators

Helminths are the largest and most complex pathogens to invade and live within the human body. Since they are not able to outpace the immune system by rapid antigen variation or faster cell division or retreat into protective niches not accessible to immune effector mechanisms, their long-term survival depends on influencing and regulating the immune responses away from the mode of action most damaging to them. Immunologists have focused on the excretory and secretory products that are released by the helminths, since they can change the host environment by modulating the immune system. Here we give a brief overview of the helminth-associated immune response and the currently available helminth secretome data. We introduce some major secretome-derived immunomodulatory molecules and describe their potential mode of action. Finally, the applicability of helminth-derived therapeutic proteins in the treatment of allergic and autoimmune inflammatory disease is discussed.

First insight into CD59-like molecules of adult Fasciola hepatica

The present study focussed on investigating CD59-like molecules of Fasciola hepatica. A cDNA encoding a CD59-like protein (termed FhCD59-1) identified previously in the membrane fraction of the F. hepatica tegument was isolated. This homologue was shown to encode a predicted open reading frame (ORF) of 122 amino acids (aa) orthologous to human CD59 with a 25 aa signal peptide, a mature protein containing 10 cysteines and a conserved CD59/Ly-6 family motif "CCXXXXCN". An analysis of cDNAs from two different adult specimens of F. hepatica revealed seven variable types of FhCD59-1 sequences, designated FhCD59-1.1 to FhCD59-1.7, which had 94.3-99.7% amino acid sequence identity upon pairwise comparison. Molecular modeling of FhCD59-1.1 with human CD59 confirmed the presence of the three-finger protein domain found in the CD59 family and predicted three disulphide bonds in the F. hepatica sequence. The interrogation of F. hepatica databases identified two additional sequences, designated FhCD59-2 and FhCD59-3, which had only 23.4-29.5% amino acid identity to FhCD59-1.1. Orthologues of the inferred CD59 protein sequences of F. hepatica were also identified in other flatworms, including Fasciola gigantica, Fascioloides magna, Schistosoma haematobium, Schistosoma japonicum, Schistosoma mansoni, Clonorchis sinensis, Opisthorchis viverrini, Taenia solium, Echinococcus granulosus and the free living Schmidtea mediterannea. The results revealed a considerable degree of sequence complexity in the CD59-like sequence families in F. hepatica and flatworms. Phylogenetic analysis of CD59-like aa sequences from F. hepatica and flatworms showed that FhCD59-2 clustered with the known surface-associated protein SmCD59-2 of S. mansoni. Relatively well-supported clades specific to schistosomes, fasciolids and opisthorchiids were identified. The qPCR analysis of gene transcription showed that the relative expression of these 3 FhCD59-like sequences varied by 11-47-fold during fluke maturation, from the newly excysted juvenile (NEJ) to the adult stage. These findings suggest that different FhCD59-like sequences play distinct roles during the development of F. hepatica.

Exploring the antigenic features of Fasciola hepatica rediae (Trematoda: Digenea) through the evaluation of different antigenic candidates for further monoclonal antibody generation

The control of fasciolosis, as that of other vector-borne diseases, must be related to the control of the lymnaeid snails, the intermediate hosts of the parasite. Thus, an accurate epidemiological surveillance of the transmission foci where the infected mollusks occur is essential. For this purpose, immunoassays could be a useful tool. However, information regarding specific proteins of intramolluscan larvae and previous studies concerning monoclonal antibody generation against asexual stages of trematodes are scarce. Therefore, we explored the antigenic features of intramolluscan rediae of Fasciola hepatica to evaluate three antigenic preparations in order to use the most promising one for developing specific monoclonal antibodies. Mouse antiserum was generated against each antigen for assessing the polyclonal antibody response against the crude extract of rediae and the cross-reactivity against lymnaeids. The specific C-terminal of F. hepatica cytochrome c oxidase subunit I (first antigen), selected by in silico analyses, might not be the appropriate target for immunoassay detection of infected snails, due to its low representation in the total extract of rediae. The majoritarian mixture of low-molecular-weight proteins (<30 kDa) from the rediae homogenate (second antigen) revealed a significant cross-reactivity with lymnaeids. Evidence of the existence of mimetic immunogenic epitopes in this fraction of F. hepatica rediae was achieved. High immunogenicity of the crude extract of rediae (third antigen), mainly related to parasite's specific epitopes, was regarded. Therefore, the rediae homogenate is stated as the most promising antigen from those evaluated, for monoclonal antibody development with potentialities for detecting F. hepatica-infected snails.

Proteomic identification of potential Clonorchis sinensis excretory/secretory products capable of binding and activating human hepatic stellate cells

Epidemiological and experimental evidence demonstrated that Clonorchis sinensis is an important risk factor of hepatic fibrosis and cholangiocarcinoma. C. sinensis excretory/secretory products (CsESPs) are protein complex including proteases, antioxidant enzymes, and metabolic enzymes, which may contribute to pathogenesis of liver fluke-associated hepatobiliary diseases. However, potential CsESP candidates involved into hepatic fibrosis and cholangiocarcinoma still remain to be elucidated. In the present study, we performed proteomic identification of CsESP candidates capable of binding and activating human hepatic stellate cell line LX-2. Immunofluorescence analysis confirmed the interaction of CsESPs with LX-2 cell membrane. LX-2 cells could be stimulated by CsESPs from 24 h post incubation (p < 0.05). Specifically, 50 μg/ml of CsESPs showed the strongest effect on cell proliferation in methyl thiazolyl tetrazolium (MTT) assay which could also be demonstrated by flow cytometry analysis (p < 0.01). Furthermore, expression level of human type III collagen in LX-2 cells treated with CsESPs was significantly higher than that in control cells measured by molecular beacon and semiquantitative reverse transcription (RT)-PCR approaches (p < 0.01). Finally, CsESPs before and after incubation with LX-2 cells were subjected to two-dimensional gel electrophoresis (2-DE) analysis and matrix associated laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry analysis. Nine proteins with abundance change above threefold were Rho GTPase-activating protein, mitochondrial cytochrome c oxidase subunit Va, α-enolase, phospholipase C, interleukin-15, insect-derived growth factor, cytochrome c oxidase subunit VI, DNAH1 protein, and kinesin light chain. Taken together, we identified potential CsESP candidates capable of binding and activating human hepatic stellate cells, providing more direct evidences that are previously unknown to accelerate strategies for C. sinensis prevention.

Biochemical and immunological characterization of annexin B30 from Clonorchis sinensis excretory/secretory products

Clonorchis sinensis has been classified as group I biological carcinogen for cholangiocarcinoma by the World Health Organization. Biological studies on excretory/secretory products (ESPs) enabled us to understand the pathogenesis mechanism of C. sinensis and develop new strategies for the prevention of clonorchiasis. In this study, sequence analysis showed that annexin B30 from C. sinensis (CsANXB30) is composed of four annexin repeats which were characterized by type II and III Ca(2+)-binding sites or KGD motif with the capability of Ca(2+)-binding. In addition, immunoblot assay revealed that recombinant CsANXB30 (rCsANXB30) could be recognized by the sera from rats infected with C. sinensis and the sera from rats immunized by CsESPs. Real-time PCR showed that its transcriptional level was the highest at the stage of metacercaria. Immunofluorescence assay was employed to confirm that CsANXB30 was distributed in the tegument, intestine, and egg of adult worms, as well as the tegument and vitellarium of metacercaria. rCsANXB30 was able to bind phospholipid in a Ca(2+)-dependent manner and human plasminogen in a dose-dependent manner. Moreover, cytokine and antibody measurements indicated that rats subcutaneously immunized with rCsANXB30 developed a strong IL-10 production in spleen cells and a high level of IgG1 isotype, indicating that rCsANXB30 could trigger specific humoral and cellular immune response in rats. The present results implied that CsANXB30 might be involved in a host-parasite interaction and affected the immune response of the host during C. sinensis infection.

Generating a detailed protein profile of Fasciola hepatica during the chronic stage of infection in cattle

Fasciola hepatica is a trematode helminth causing a damaging disease, fasciolosis, in ruminants and humans. Comprehensive proteomic studies broaden our knowledge of the parasite's protein profile, and provide new insights into the development of more effective strategies to deal with fasciolosis. The objective of this study was to generate a comprehensive profile of F. hepatica proteins expressed during the chronic stage of infection in cattle by building on previous efforts in this area. The approach included an improved sample preparation procedure for surface and internal layers of the parasite, the application of nano-UPLC-ESI-qTOF-MS (nano-ultra-performance LC and ESI quadrupole TOF MS) integrated with different acquisition methods and in silico database search against various protein databases and a transcript database including a new assembly of publically available EST. Of a total of 776 identified proteins, 206 and 332 were specific to the surface and internal layers of the parasite, respectively. Furthermore, 238 proteins were common to both layers, with comparative differences of 172 proteins detected. Specific proteins not previously identified in F. hepatica, but shown to be immunomodulatory or potential drug targets for other parasites, are discussed.

Discovery of novel genes and gene isoforms by integrating transcriptomic and proteomic profiling from mouse liver

Comprehensively identifying gene expression in both transcriptomic and proteomic levels of one tissue is a prerequisite for a deeper understanding of its biological functions. Alternative splicing and RNA editing, two main forms of transcriptional processing, play important roles in transcriptome and proteome diversity and result in multiple isoforms for one gene, which are hard to identify by mass spectrometry (MS)-based proteomics approach due to the relative lack of isoform information in standard protein databases. In our study, we employed MS and RNA-Seq in parallel into mouse liver tissue and captured a considerable catalogue of both transcripts and proteins that, respectively, covered 60 and 34% of protein-coding genes in Ensembl. We then developed a bioinformatics workflow for building a customized protein database that for the first time included new splicing-derived peptides and RNA-editing-caused peptide variants, allowing us to more completely identify protein isoforms. Using this experimentally determined database, we totally identified 150 peptides not present in standard biological databases at false discovery rate of <1%, corresponding to 72 novel splicing isoforms, 43 new genetic regions, and 15 RNA-editing sites. Of these, 11 randomly selected novel events passed experimental verification by PCR and Sanger sequencing. New discoveries of gene products with high confidence in two omics levels demonstrated the robustness and effectiveness of our approach and its potential application into improve genome annotation. All the MS data have been deposited to the iProx ( http://ww.iprox.org ) with the identifier IPX00003601.