RNA interference of Schistosoma mansoni cathepsin D, the apical enzyme of the hemoglobin proteolysis cascade

A comprehensive exploration of schistosomiasis: Global impact, molecular characterization, drug discovery, artificial intelligence and future prospects

Schistosomiasis, one of the neglected tropical diseases which affects both humans and animals, is caused by trematode worms of the genus Schistosoma. The disease is caused by several species of Schistosoma which affect several organs such as urethra, liver, bladder, intestines, skin and bile ducts. The life cycle of the disease involves an intermediate host (snail) and a mammalian host. It affects people who are in close proximity to water bodies where the intermediate host is abundant. Common clinical manifestations of the disease at various stages include fever, chills, headache, cough, dysuria, hyperplasia and hydronephrosis. To date, most of the control strategies are dependent on effective diagnosis, chemotherapy and public health education on the biology of the vectors and parasites. Microscopy (Kato-Katz) is considered the golden standard for the detection of the parasite, while praziquantel is the drug of choice for the mass treatment of the disease since no vaccines have yet been developed. Most of the previous reviews on schistosomiasis have concentrated on epidemiology, life cycle, diagnosis, control and treatment. Thus, a comprehensive review that is in tune with modern developments is needed. Here, we extend this domain to cover historical perspectives, global impact, symptoms and detection, biochemical and molecular characterization, gene therapy, current drugs and vaccine status. We also discuss the prospects of using plants as potential and alternative sources of novel anti-schistosomal agents. Furthermore, we highlight advanced molecular techniques, imaging and artificial intelligence that may be useful in the future detection and treatment of the disease. Overall, the proper detection of schistosomiasis using state-of-the-art tools and techniques, as well as development of vaccines or new anti-schistosomal drugs may aid in the elimination of the disease.

Peptide-Alkoxyamine Drugs: An Innovative Approach to Fight Schistosomiasis: "Digging Their Graves with Their Forks"

The expansion of drug resistant parasites sheds a serious concern on several neglected parasitic diseases. Our recent results on cancer led us to envision the use of peptide-alkoxyamines as a highly selective and efficient new drug against schistosome adult worms, the etiological agents of schistosomiasis. Indeed, the peptide tag of the hybrid compounds can be hydrolyzed by worm's digestive enzymes to afford a highly labile alkoxyamine which homolyzes spontaneously and instantaneously into radicals-which are then used as a drug against Schistosome adult parasites. This approach is nicely summarized as digging their graves with their forks. Several hybrid peptide-alkoxyamines were prepared and clearly showed an activity: two of the tested compounds kill 50% of the parasites in two hours at a concentration of 100 µg/mL. Importantly, the peptide and alkoxyamine fragments that are unable to generate alkyl radicals display no activity. This strong evidence validates the proposed mechanism: a specific activation of the prodrugs by the parasite proteases leading to parasite death through in situ alkyl radical generation.

Hepatocyte nuclear factor 4 located in different developmental stages in Schistosoma japonicum and involved in important metabolic pathways

BACKGROUND

Nuclear receptors (NRs) are vital for regulating gene expression un organisms. Hepatocyte nuclear factor 4 (HNF4), a class of NRs, participates in blood feeding and intestinal maintenance in schistosomes. However, there is limited research on the molecular and functional characterization of HNF4 in Schistosoma japonicum (S. japonicum).

METHODS

Highly specific polyclonal antibodies were generated to analyze the expression and tissue localization of S. japonicum HNF4 (SjHNF4). The potential biological functions of SjHNF4 were characterized by transcriptome and pull-down analysis. Subsequently, enrichment analysis was performed to identify the specific signaling pathways linked to SjHNF4.

RESULTS

The SjHNF4 protein was expressed heterologously and purified successfully. High purity and high potency polyclonal antibodies were further prepared. The expression of SjHNF4 was higher in female compared to male worms at both transcriptional and protein levels. Female worms expressed SjHNF4 in their perithecium, reproductive system, and certain parts of the intestinal tissues. SjHNF4 was also detected in the perithecium of male worms, as well as in the head, body of cercaria, and eggs. Furthermore, our findings highlighted the potential role of SjHNF4 in blood feeding and its interaction with crucial pathways such as glucose metabolism, lipid metabolism, and nucleotide metabolism.

CONCLUSIONS

This study shed light on the location of SjHNF4 in different life stages of S. japonicum, particularly associated with the female schistosomes. A strong correlation was observed between SjHNF4 and essential metabolic pathways. These findings laid a solid groundwork for the research on the relationship between NRs and schistosomes.

Discovery of new Schistosoma mansoni aspartyl protease inhibitors by structure-based virtual screening

BACKGROUND

Schistosomiasis is a neglected tropical disease caused by trematodes of the genus Schistosoma, with a limited treatment, mainly based on the use of praziquantel (PZQ). Currently, several aspartic proteases genes have already been identified within the genome of Schistosoma species. At least one enzyme encoded from this gene family (SmAP), named SmCD1, has been validated for the development of schistosomicidal drugs, since it has a key role in haemoglobin digestion by worms.

OBJECTIVE

In this work, we integrated a structure-based virtual screening campaign, enzymatic assays and adult worms ex vivo experiments aiming to discover the first classes of SmCD1 inhibitors.

METHODS

Initially, the 3D-structures of SmCD1, SmCD2 and SmCD3 were generated using homology modelling approach. Using these models, we prioritised 50 compounds from 20,000 compounds from ChemBridge database for further testing in adult worm aqueous extract (AWAE) and recombinant SmCD1 using enzymatic assays.

FINDINGS

Seven compounds were confirmed as hits and among them, two compounds representing new chemical scaffolds, named 5 and 19, had IC50 values against SmCD1 close to 100 μM while presenting binding efficiency indexes comparable to or even higher than pepstatin, a classical tight-binding peptide inhibitor of aspartyl proteases. Upon activity comparison against mammalian enzymes, compound 50 was selective and the most potent against the AWAE aspartic protease activity (IC50 = 77.7 μM). Combination of computational and experimental results indicate that compound 50 is a selective inhibitor of SmCD2. Compounds 5, 19 and 50 tested at low concentrations (10 uM) were neither cytotoxic against WSS-1 cells (48 h) nor could kill adult worms ex-vivo, although compounds 5 and 50 presented a slight decrease on female worms motility on late incubations times (48 or 72 h).

MAIN CONCLUSION

Overall, the inhibitors identified in this work represent promising hits for further hit-to-lead optimisation.

Advances in new target molecules against schistosomiasis: A comprehensive discussion of physiological structure and nutrient intake

Schistosomiasis, a severe parasitic disease, is primarily caused by Schistosoma mansoni, Schistosoma japonicum, or Schistosoma haematobium. Currently, praziquantel is the only recommended drug for human schistosome infection. However, the lack of efficacy of praziquantel against juvenile worms and concerns about the emergence of drug resistance are driving forces behind the research for an alternative medication. Schistosomes are obligatory parasites that survive on nutrients obtained from their host. The ability of nutrient uptake depends on their physiological structure. In short, the formation and maintenance of the structure and nutrient supply are mutually reinforcing and interdependent. In this review, we focus on the structural features of the tegument, esophagus, and intestine of schistosomes and their roles in nutrient acquisition. Moreover, we introduce the significance and modes of glucose, lipids, proteins, and amino acids intake in schistosomes. We linked the schistosome structure and nutrient supply, introduced the currently emerging targets, and analyzed the current bottlenecks in the research and development of drugs and vaccines, in the hope of providing new strategies for the prevention and control of schistosomiasis.

Hemoglobin uptake and utilization by human protozoan parasites: a review

The protozoan disease is a major global health concern. Amoebiasis, leishmaniasis, Chagas disease, and African sleeping sickness affect several million people worldwide, leading to millions of deaths annually and immense social and economic problems. Iron is an essential nutrient for nearly all microbes, including invading pathogens. The majority of iron in mammalian hosts is stored intracellularly in proteins, such as ferritin and hemoglobin (Hb). Hb, present in blood erythrocytes, is a very important source of iron and amino acids for pathogenic microorganisms ranging from bacteria to eukaryotic pathogens, such as worms, protozoa, yeast, and fungi. These organisms have developed adequate mechanisms to obtain Hb or its byproducts (heme and globin) from the host. One of the major virulence factors identified in parasites is parasite-derived proteases, essential for host tissue degradation, immune evasion, and nutrient acquisition. The production of Hb-degrading proteases is a Hb uptake mechanism that degrades globin in amino acids and facilitates heme release. This review aims to provide an overview of the Hb and heme-uptake mechanisms utilized by human pathogenic protozoa to survive inside the host.

Genetic manipulations in helminth parasites

Screening of vaccine or drug target in parasitic helminth is hindered by lack of robust tool for functional studies of parasite protein which account for the availability of only a few anti-helminthic vaccines, diagnostic assay and slower pace of development of an anthelmintic drug. With the piling up of parasite transcriptomic and genomic data, in silico screening for possible vaccine/drug target could be validated by functional characterization of proteins by RNA interference or CRISPR/Cas9. These reverse genetic engineering tools have opened up a better avenue and opportunity for screening parasitic proteins in vitro as well as in vivo. RNA interference provides a technique for silencing targeted mRNA transcript for understanding a gene function in helminth as evidence by work in Caenorhabditis elegans. Recent genetic engineering tool, CRISPR/Cas9 allows knock-out/deletion of the desired gene in parasitic helminths and the other provision it provides in terms of gene knock-in/insertion in parasite genome is still to be explored in future. This manuscript discussed the work that has been carried out on RNAi and CRISPR/Cas9 for functional studies of helminth parasitic proteins.

Characterization of aspartyl aminopeptidase from Schistosoma japonicum

The tegument of schistosomes is the interface between the worm and the host environment. Some molecules distributed on the tegument participate in host-parasite interactions. Aspartyl aminopeptidase (AAP), identified on the tegument of Schistosoma japonicum (S. japonicum), facilitate protein turnover by acting in concert with other aminopeptidases. In this study, the gene encoding S. japonicum aspartyl aminopeptidase (SjAAP) was cloned, expressed and characterized. Quantitative real-time PCR analysis showed that SjAAP was expressed in all studied developmental stages. The transcript level was higher in 8, 14, 21, and 28 days old worms than the other detected stages. Moreover, the level of expression in 42-day-old male worms was significantly higher than that in females. The recombinant SjAAP (rSjAAP) was expressed as both supernatant and inclusion bodies in Escherichia coli BL21 cells. The enzymatic activity of rSjAAP was 4.45 U/mg. The Km and Vmax values for H-Asp-pNA hydrolysis were discovered to be 5.93 mM and 0.018 mM·min^-1. Immunofluorescence analysis revealed that SjAAP is primarily distributed on the tegument and parenchyma of schistosomes. Western blot showed that rSjAAP possessed good immunogenicity. Although specific antibodies were produced in BALB/c mice vaccinated with rSjAAP emulsified with ISA 206 adjuvant, no significant reduction of worm burden and number of eggs in the liver was observed. Therefore, rSjAAP may not be suitable to act as a potential vaccine candidate against schistosomiasis japonica in mice. However, this study provides some foundation for further exploration of the biological function of this molecule.

Schistosomiasis Drug Discovery in the Era of Automation and Artificial Intelligence

Schistosomiasis is a parasitic disease caused by trematode worms of the genus Schistosoma and affects over 200 million people worldwide. The control and treatment of this neglected tropical disease is based on a single drug, praziquantel, which raises concerns about the development of drug resistance. This, and the lack of efficacy of praziquantel against juvenile worms, highlights the urgency for new antischistosomal therapies. In this review we focus on innovative approaches to the identification of antischistosomal drug candidates, including the use of automated assays, fragment-based screening, computer-aided and artificial intelligence-based computational methods. We highlight the current developments that may contribute to optimizing research outputs and lead to more effective drugs for this highly prevalent disease, in a more cost-effective drug discovery endeavor.

Revisiting the Schistosoma japonicum life cycle transcriptome for new insights into lung schistosomula development

Schistosome parasites are complex trematode blood flukes responsible for the disease schistosomiasis; a global health concern prevalent in many tropical and sub-tropical countries. While established transcriptomic databases are accessed ad hoc to facilitate studies characterising specific genes or gene families, a more comprehensive systematic updating of gene annotation and survey of the literature to aid in annotation and context is rarely addressed. We have reanalysed an online transcriptomic dataset originally published in 2009, where seven life cycle stages of Schistosoma japonicum were examined. Using the online pathway analysis tool Reactome, we have revisited key data from the original study. A key focus of this study was to improve the interpretation of the gene expression profile of the developmental lung-stage schistosomula, since it is one of the principle targets for worm elimination. Highly enriched transcripts, associated with lung schistosomula, were related to a number of important biological pathways including host immune evasion, energy metabolism and parasitic development. Revisiting large transcriptomic databases should be considered in the context of substantial new literature. This approach could aid in the improved understanding of the molecular basis of parasite biology. This may lead to the identification of new targets for diagnosis and therapies for schistosomes, and other helminths.

Adjuvanted Schistosoma mansoni-Cathepsin B With Sulfated Lactosyl Archaeol Archaeosomes or AddaVax™ Provides Protection in a Pre-Clinical Schistosomiasis Model

Schistosomiasis threatens 800 million people worldwide. Chronic pathology manifests as hepatosplenomegaly, and intestinal schistosomiasis caused by Schistosoma mansoni can lead to liver fibrosis, cirrhosis, and blood in the stool. To assist the only FDA-approved drug, praziquantel, in parasite elimination, the development of a vaccine would be of high value. S. mansoni Cathepsin B (SmCB) is a well-documented vaccine target for intestinal schistosomiasis. Herein, we test the increased efficacy and immunogenicity of SmCB when combined with sulfated lactosyl archaeol (SLA) archaeosomes or AddaVax™ (a squalene based oil-in-water emulsion). Both vaccine formulations resulted in robust humoral and cell mediated immune responses. Impressively, both formulations were able to reduce parasite burden greater than 40% (WHO standard), with AddaVax™ reaching 86.8%. Additionally, SmCB with both adjuvants were able to reduce granuloma size and the amount of larval parasite hatched from feces, which would reduce transmission. Our data support SmCB as a target for S. mansoni vaccination; especially when used in an adjuvanted formulation.

Current status and future prospects of protein vaccine candidates against Schistosoma mansoni infection

Schistosomiasis is an acute and chronic tropical parasitic disease caused by blood dwelling worm of the genus Schistosoma. It is the most destructive disease globally and is a major cause of morbidity and mortality for developing countries. Three main species of schistosomes infect human beings from which S. mansoni is the most common and widespread. Over the last several decades, chemotherapy using praziquantel has been a commonly used strategy for the treatment and control of schistosomiasis. However, control programs focused exclusively on chemotherapy have been challenging because of the frequency and rapidity of reinfection and these programs were expensive. Thus, new schistosomiasis control strategies will be needed. Vaccination strategy would be an ideal tool for a significant and sustainable reduction in the transmission and disease burden of schistosomiasis. An effective anti schistosome vaccine would greatly contribute to decreasing schistosomiasis-associated morbidity via protective immune responses leading to reduced worm burdens and decreased egg production. Vaccine development is a long process that can take decades. There have been three candidate vaccines that have been produced by Good Manufacturing Procedure and entered human clinical trials for S. mansoni are Sm14, SmTSP-2, and Sm-p80. Other candidates that are in pre-clinical trials at various stages include paramyosin, Sm29, SmKI-1, and Sm23. Since the growth of several new technologies, including genomics, transcriptomics, microarrays, immunomic profiling, and proteomics, have helped in the identification of promising new target schistosome antigens. Therefore, this review considers the present status of protein vaccine candidates against Schistosoma mansoni and provides some insight on prospects vaccine design and discovery.

Molecular characterization of a Trichinella spiralis aspartic protease and its facilitation role in larval invasion of host intestinal epithelial cells

BACKGROUND

T. spiralis aspartic protease has been identified in excretion/secretion (ES) proteins, but its roles in larval invasion are unclear. The aim of this study was to characterize T. spiralis aspartic protease-2 (TsASP2) and assess its roles in T. spiralis invasion into intestinal epithelial cells (IECs) using RNAi.

METHODOLOGY/PRINCIPAL FINDINGS

Recombinant TsASP2 (rTsASP2) was expressed and purified. The native TsASP2 of 43 kDa was recognized by anti-rTsASP2 serum in all worm stages except newborn larvae (NBL), and qPCR indicated that TsASP2 transcription was highest at the stage of intestinal infective larvae (IIL). IFA results confirmed that TsASP2 was located in the hindgut, midgut and muscle cells of muscle larvae (ML) and IIL and intrauterine embryos of the female adult worm (AW), but not in NBL. rTsASP2 cleaved several host proteins (human hemoglobin (Hb), mouse Hb, collagen and IgM). The proteolytic activity of rTsASP2 was host-specific, as it hydrolyzed mouse Hb more efficiently than human Hb. The enzymatic activity of rTsASP2 was significantly inhibited by pepstatin A. The expression levels of TsASP2 mRNA and protein were significantly suppressed by RNAi with 5 μM TsASP2-specific siRNA. Native aspartic protease activity in ML crude proteins was reduced to 54.82% after transfection with siRNA. Larval invasion of IECs was promoted by rTsASP2 and inhibited by anti-rTsASP2 serum and siRNA. Furthermore, cell monolayer damage due to larval invasion was obviously alleviated when siRNA-treated larvae were used. The adult worm burden, length of adult worms and female fecundity were clearly reduced in mice challenged using siRNA-treated ML relative to the PBS group.

CONCLUSIONS

rTsASP2 possesses the enzymatic activity of native aspartic protease and facilitates T. spiralis invasion of host IECs.

Investigation of three enzymes and their roles in the embryonic development of parthenogenetic Haemaphysalis longicornis

BACKGROUND

The tick Haemaphysalis longicornis exhibits two separate reproductive populations: bisexual and parthenogenetic, which have diploid and triploid karyotypes, respectively. The parthenogenetic population can undergo engorgement without copulation and produce viable female-only offspring with a longer incubation period than the bisexual population. Three enzymes, cathepsin B, cathepsin D and acid phosphatase, were found to be involved in vitellin degradation during the embryonic development of bisexual H. longicornis. However, the expression and activity profiles of these enzymes during the embryonic development of parthenogenetic ticks remain unknown. In the present study, the transcriptional expression profile, enzyme activity and roles in embryogenesis of the three enzymes during the embryonic development of parthenogenetic H. longicornis were investigated.

METHODS

Quantitative real-time polymerase chain reaction (qPCR) and fluorescence detection were used to analyze the dynamic changes in the three enzymes during embryogenesis. The roles of the three enzymes during embryogenesis were also explored using RNA interference (RNAi).

RESULTS

The three enzymes were all expressed during embryonic development in parthenogenetic H. longicornis. The expression of cathepsin B was highest on day 15, whereas that of cathepsin D was highest on day 3 and the peak of acid phosphatase expression occurred on day 9. The activity of cathepsin B was highest on day 3 and lowest on day 5, then gradually increased and remained stable. Cathepsin D activity was highest on day 1 and showed a gradually decreasing trend, whereas acid phosphatase showed the opposite trend and reached a peak on day 23. RNA interference experiments in engorged female ticks revealed that there was no significant difference in the number of eggs laid, but the hatching rate of the eggs was significantly decreased.

CONCLUSION

The three enzymes all play important roles in embryonic development of H. longicornis, but the expression patterns and changes in the activity of the enzymes in the bisexual and parthenogenetic populations are different. The results will help a better understanding of the similarities and differences underlying embryonic development in the bisexual and parthenogenetic populations and contribute to the future exploration of the development of the parthenogenetic population of H. longicornis.

Gene Silencing in the Liver Fluke Fasciola hepatica: RNA Interference

The chronic infection with the liver fluke of the genus Fasciola spp. is the most prevalent foodborne trematodiasis, affecting at least one-fourth of the world livestock grazing in areas where the parasite is present. Moreover, fascioliasis is considered a major zoonosis mainly in rural areas of central South America, Northern Africa, and Central Asia. Increasing evidences of resistance against triclabendazole may compromise its use as drug of choice; thus, novel control strategies are desperately needed. Functional genomic approaches play a key role in the validation and characterization of new targets for drug and vaccine development. So far, RNA interference has been the only gene silencing approach successfully employed in liver flukes of the genus Fasciola spp. Herein, we describe a detailed step-by-step protocol to perform gene silencing mediated by RNAi in Fasciola hepatica.

Schistosoma mansoni cathepsin D1: Biochemical and biophysical characterization of the recombinant enzyme expressed in HEK293T cells

Schistosomes express a variety of aspartyl proteases (APs) with distinct roles in the helminth pathophysiology, among which degradation of host haemoglobin is key, since it is the main amino acid source for these parasites. A cathepsin D-like AP from Schistosoma mansoni (SmCD1) has been used as a model enzyme for vaccine and drug development studies in schistosomes and yet a reliable expression system for readily producing the recombinant enzyme in high yield has not been reported. To contribute to further advancing the knowledge about this valuable antischistosomal target, we developed a transient expression system in HEK 293T mammalian cells and performed a biochemical and biophysical characterization of the recombinant enzyme (rSmCD1). It was possible to express a recombinant C-terminal truncated form of SmCD1 (rSmCD1ΔCT) and purify it with high yield (16 mg/L) from the culture supernatant. When analysed by Size-Exclusion Chromatography and multi-angle laser light scattering, rSmCD1ΔCT behaved as a dimer at neutral pH, which is unusual for cathepsins D, turning into a monomer after acidification of the medium. Through analytical ultrancentrifugation, the dimer was confirmed for free rSmCD1ΔCT in solution as well as stabilization of the monomer during interaction with pepstatin. The mammalian cell expression system used here was able to produce rSmCD1ΔCT with high yields allowing for the first time the characterization of important kinetic parameters as well as initial description of its biophysical properties.

Gene Expression in Developmental Stages of Schistosoma japonicum Provides Further Insight into the Importance of the Schistosome Insulin-Like Peptide

We showed previously that the Schistosoma japonicum insulin-like peptide (SjILP) binds the worm insulin receptors, thereby, activating the parasite’s insulin pathway and emphasizing its important role in regulating uptake of glucose, a nutrient essential for parasite survival. Here we show that SjILP is differentially expressed in the schistosome life cycle and is especially highly transcribed in eggs, miracidia, and adult female worms. RNA inference was employed to knockdown SjILP in adults in vitro, with suppression confirmed by significantly reduced protein production, declined adenosine diphosphate levels, and reduction in glucose consumption. Immunolocalization showed that SjILP is located to lateral gland cells of mature intra-ovular miracidia in the schistosome egg, and is distributed on the ciliated epithelium and internal cell masses of newly transformed miracidia. In schistosomula, SjILP is present on the tegument in two antero-lateral points, indicating highly polarized expression during cercarial transformation. Analysis of serum from S. japonicum-infected mice by ELISA using a recombinant form of SjILP as an antigen revealed IgG immunoreactivity to this molecule at 7 weeks post-infection indicating it is likely secreted from mature eggs into the host circulation. These findings provide further insights on ILP function in schistosomes and its essential roles in parasite survival and growth in different development stages.

Suppression of Schistosoma japonicum Acetylcholinesterase Affects Parasite Growth and Development

To further investigate the importance of Schistosoma japonicum acetylcholinesterase (SjAChE) in cholinergic signaling for parasite growth and development, we used RNA interference (RNAi) to knock-down its expression in adults and eggs in vitro. This resulted in its reduced transcription but also expression of other important genes involved both in cholinergic signaling and glucose uptake were impacted substantially. Significant decreases in AChE protein expression, AChE enzymatic activity, and glucose uptake were observed in the SjAChE-knockdown parasites compared with luciferase controls. In vaccine/challenge experiments, we found that immunization of mice with recombinant SjAChE (rSjAChE) expressed in Escherichia coli elicited reductions in male worm numbers (33%), liver granuloma density (41%), and reduced numbers of mature intestinal eggs (73%) in the vaccinated group compared with the control group. These results indicate AChE plays an important role in the metabolism of male worms, and impacts indirectly on female fecundity leading to increased numbers of immature eggs being released and reduced sizes of liver granulomas. Furthermore, cytokine analysis showed that immunization of mice with rSjAChE elicited a predominantly Th1-type immune response characterized by increased production of IFNγ in splenic CD4⁺ T cells of vaccinated mice. The study confirms the potential of SjAChE as a vaccine/drug candidate against zoonotic schistosomiasis japonica.

Nanomedicine Approaches Against Parasitic Worm Infections

Nanomedicine approaches have the potential to transform the battle against parasitic worm (helminth) infections, a major global health scourge from which billions are currently suffering. It is anticipated that the intersection of two currently disparate fields, nanomedicine and helminth biology, will constitute a new frontier in science and technology. This progress report surveys current innovations in these research fields and discusses research opportunities. In particular, the focus is on: (1) major challenges that helminth infections impose on mankind; (2) key aspects of helminth biology that inform future research directions; (3) efforts to construct nanodelivery platforms to target drugs and genes to helminths hidden in their hosts; (4) attempts in applying nanotechnology to enable vaccination against helminth infections; (5) outlooks in utilizing nanoparticles to enhance immunomodulatory activities of worm-derived factors to cure allergy and autoimmune diseases. In each section, achievements are summarized, limitations are explored, and future directions are assessed.

Serine/threonine protein phosphatase 1 (PP1) controls growth and reproduction in Schistosoma japonicum

Schistosomiasis is a human parasitic disease caused by flatworms of the genus Schistosoma. Adult female schistosomes produce numerous eggs that are responsible for the pathogenesis and transmission of the disease, and the maturation of female gonads depends on the permanent pairing of females and males. Signaling protein kinases have been proven to control female gonad differentiation after pairing; however, little is known about the roles of protein phosphatases in the developmental and reproductive biology of schistosomes. Here we explored 3 genes encoding catalytic subunits of serine/threonine protein phosphatase 1 (PP1c) that were structurally and evolutionarily conserved in Schistosoma japonicum. In situ hybridization showed transcripts of 3 Sj-pp1c genes mainly localized in the reproductive organs and tissues. Triple knockdown of Sj-pp1c genes by RNA interference caused stunted growth and decreased pairing stability of worm pairs, as well as a remarkable reduction in cell proliferation activity and defects in reproductive maturation and fecundity. Transcriptomic analysis post-RNA interference suggested that Sj-pp1c genes are involved in controlling worm development and maturation mainly by regulating cell proliferation, eggshell synthesis, nutritional metabolism, cytoskeleton organization, and neural process. Our study provides the first insight into the fundamental contribution of Sj-PP1c to molecular mechanisms underlying the reproductive biology of schistosomes.-Zhao, L., Lu, Z., He, X., Mughal, M. N., Fang, R., Zhou, Y., Zhao, J., Gasser, R. B., Grevelding, C. G., Ye, Q., Hu, M. Serine/threonine protein phosphatase 1 (PP1) controls growth and reproduction in Schistosoma japonicum.

A novel blood-feeding detoxification pathway in Nippostrongylus brasiliensis L3 reveals a potential checkpoint for arresting hookworm development

As part of on-going efforts to control hookworm infection, the "human hookworm vaccine initiative" has recognised blood feeding as a feasible therapeutic target for inducing immunity against hookworm infection. To this end, molecular approaches have been used to identify candidate targets, such as Necator americanus (Na) haemoglobinase aspartic protease-1 (APR-1), with immunogenicity profiled in canine and hamster models. We sought to accelerate the immune analysis of these identified therapeutic targets by developing an appropriate mouse model. Here we demonstrate that Nippostrongylus brasiliensis (Nb), a phylogenetically distant strongylid nematode of rodents, begins blood feeding early in its development and that immunisation with Na-APR-1 can block its growth and completion of its life cycle. Furthermore, we identify a new haem detoxification pathway in Nb required for blood feeding that can be blocked by drugs of the quinolone family, reducing both infection burden and the associated anaemia in rodents. Collectively, our findings show that haem metabolism has potential as a checkpoint for interrupting hookworm development in early stages of the hookworm life cycle and that the Nippostrongylus brasiliensis rodent model is relevant for identifying novel therapeutic targets against human hookworm.

Schistosome infectivity in the snail, Biomphalaria glabrata, is partially dependent on the expression of Grctm6, a Guadeloupe Resistance Complex protein

Schistosomiasis is one of the most important neglected tropical diseases. Despite effective chemotherapeutic treatments, this disease continues to afflict hundreds of millions of people. Understanding the natural intermediate snail hosts of schistosome parasites is vital to the suppression of this disease. A recently identified genomic region in Caribbean Biomphalaria glabrata snails strongly influences their resistance to infection by Schistosoma mansoni. This region contains novel genes having structural similarity to known pathogen recognition proteins. Here we elaborate on the probable structure and role of one of these genes, grctm6. We characterised the expression of Grctm6 in a population of Caribbean snails, and performed a siRNA knockdown of Grctm6. We show that this protein is not only expressed in B. glabrata hemolymph, but that it also has a role in modulating the number of S. mansoni cercariae released by infected snails, making it a possible target for the biological control of schistosomiasis.

Parasite Cathepsin D-Like Peptidases and Their Relevance as Therapeutic Targets

Inhibition of aspartic cathepsin D-like peptidases (APDs) has been often discussed as an antiparasite intervention strategy. APDs have been considered as virulence factors of Trypanosoma cruzi and Leishmania spp., and have been demonstrated to have important roles in protein trafficking mechanisms of apicomplexan parasites. APDs also initiate blood digestion as components of multienzyme proteolytic complexes in malaria, platyhelminths, nematodes, and ticks. Increasing DNA and RNA sequencing data indicate that parasites express multiple APD isoenzymes of various functions that can now be specifically evaluated using new functional-genomic and biochemical tools, from which we can further assess the potential of APDs as targets for novel effective intervention strategies against parasitic diseases that still pose an alarming threat to mankind.

Proteomic Analysis of the Schistosoma mansoni Miracidium

Despite extensive control efforts, schistosomiasis continues to be a major public health problem in developing nations in the tropics and sub-tropics. The miracidium, along with the cercaria, both of which are water-borne and free-living, are the only two stages in the life-cycle of Schistosoma mansoni which are involved in host invasion. Miracidia penetrate intermediate host snails and develop into sporocysts, which lead to cercariae that can infect humans. Infection of the snail host by the miracidium represents an ideal point at which to interrupt the parasite’s life-cycle. This research focuses on an analysis of the miracidium proteome, including those proteins that are secreted. We have identified a repertoire of proteins in the S. mansoni miracidium at 2 hours post-hatch, including proteases, venom allergen-like proteins, receptors and HSP70, which might play roles in snail-parasite interplay. Proteins involved in energy production and conservation were prevalent, as were proteins predicted to be associated with defence. This study also provides a strong foundation for further understanding the roles that neurohormones play in host-seeking by schistosomes, with the potential for development of novel anthelmintics that interfere with its various life-cycle stages.

Molecular cloning and characterization of a phospholipid hydroperoxide glutathione peroxidase gene from a blood fluke Schistosoma japonicum

Phospholipid hydroperoxide glutathione peroxidase (PHGPx) is a major antioxidant enzyme and plays critical roles in the protection of cells against oxidative stress by catalysing reduction of lipid hydroperoxides. A full-length cDNA sequence corresponding to GPx gene from Schistosoma japonicum (designated SjGPx) was isolated and characterized. SjGPx contained an in-frame TGA codon for selenocysteine (Sec) and a concurrent Sec insertion sequence in its 3'-untranslated region. Protein encoded by SjGPx demonstrated a primary structure characteristic to the PHGPx family, including preservation of catalytic domains and absence of the subunit interaction domains. Phylogenetic analysis revealed that the SjGPx was highly related to the other PHGPx-related members, and clustered into the trematode subclade II. Semi-quantitative reverse transcription PCR and western blotting showed that the SjGPx was mainly expressed in the female adults and eggs. RNA interference was employed to investigate the effects of knockdown of SjGPx. SjGPx expression level was significantly reduced on the 5th day post-RNAi. We observed a 53.86% reduction in total GPx activity and the eggs severely deformed. Oxidative stimulation of viable worms with H2O2 or paraquat resulted in 1.6- to 2.1-fold induction of the GPx activity. Our results revealed that the SjGPx protein is selenium-dependent PHGPx, which might actively participate in the detoxification of oxidative damage during egg production.

Excretion/secretion products from Schistosoma mansoni adults, eggs and schistosomula have unique peptidase specificity profiles

Schistosomiasis is one of a number of chronic helminth diseases of poverty that severely impact personal and societal well-being and productivity. Peptidases (proteases) are vital to successful parasitism, and can modulate host physiology and immunology. Interference of peptidase action by specific drugs or vaccines can be therapeutically beneficial. To date, research on peptidases in the schistosome parasite has focused on either the functional characterization of individual peptidases or their annotation as part of global genome or transcriptome studies. We were interested in functionally characterizing the complexity of peptidase activity operating at the host-parasite interface, therefore the excretory-secretory products of key developmental stages of Schistosoma mansoni that parasitize the human were examined. Using class specific peptidase inhibitors in combination with a multiplex substrate profiling assay, a number of unique activities derived from endo- and exo-peptidases were revealed in the excretory-secretory products of schistosomula (larval migratory worms), adults and eggs. The data highlight the complexity of the functional degradome for each developmental stage of this parasite and facilitate further enquiry to establish peptidase identity, physiological and immunological function, and utility as drug or vaccine candidates.

Expression and characterization of a phospholipid hydroperoxide glutathione peroxidase gene in Schistosoma japonicum

Phospholipid hydroperoxide glutathione peroxidase (PHGPx, GPx4) is a major antioxidant enzyme, which plays unique roles in the protection of cells against oxidative stress by catalysing reduction of lipid hydroperoxides. We isolated and characterized a full-length cDNA sequence encoding GPx gene from a blood fluke, Schistosoma japonicum (designated SjGPx), which contained an in-frame TGA codon for selenocysteine (Sec) and a concurrent Sec insertion sequence in its 3'-untranslated region. Protein encoded by SjGPx demonstrated a primary structure characteristic to the PHGPx family, including preservation of catalytic domains and absence of the subunit interaction domains. Semi-quantitative reverse transcription PCR and Western blotting showed that the SjGPx was mainly expressed in the female adults and eggs. RNA interference approach was employed to investigate the effects of knockdown of SjGPx. SjGPx expression level was significantly reduced on the 5th day post-RNAi. Significantly reduction in GPx enzyme activities, as well as obvious changes in morphology of intrauterine eggs followed the reduction in SjGPx transcript level. We observed a 63·04% reduction in GPx activity and the eggs severely deformed. Our results revealed that SjGPx protein might be involved in the provision of enzyme activity during egg production.

Transfection of Platyhelminthes

Flatworms are one of the most diverse groups within Lophotrochozoa with more than 20,000 known species, distributed worldwide in different ecosystems, from the free-living organisms in the seas and lakes to highly specialized parasites living in a variety of hosts, including humans. Several infections caused by flatworms are considered major neglected diseases affecting countries in the Americas, Asia, and Africa. For several decades, a particular interest on free-living flatworms was due to their ability to regenerate considerable portions of the body, implying the presence of germ cells that could be important for medicine. The relevance of reverse genetics for this group is clear; understanding the phenotypic characteristics of specific genes will shed light on developmental traits of free-living and parasite worms. The genetic manipulation of flatworms will allow learning more about the mechanisms for tissue regeneration, designing new and more effective anthelmintic drugs, and explaining the host-parasite molecular crosstalk so far partially inaccessible for experimentation. In this review, availability of transfection techniques is analyzed across flatworms, from the initial transient achievements to the stable manipulations now developed for free-living and parasite species.

Intake of Erythrocytes Required for Reproductive Development of Female Schistosoma japonicum

The reproductive development and maturation of female schistosomes are crucial since their released eggs are responsible for the host immunopathology and transmission of schistosomiasis. However, little is known about the nutrients required by female Schistosoma japonicum during its sexual maturation. We evaluated the promoting effect of several nutrients (calf serum, red blood cells (RBCs), ATP and hypoxanthine) on the reproductive development of pre-adult females at 18 days post infection (dpi) from mixed infections and at 50 dpi from unisexual infections of laboratory mice in basic medium RPMI-1640. We found RBCs, rather than other nutrients, promoted the female sexual maturation and egg production with significant morphological changes. In 27% of females (18 dpi) from mixed infections that paired with males in vitro on day 14, vitelline glands could be positively stained by Fast Blue B; and in 35% of females (50 dpi) from unisexual infections on day 21, mature vitelline cells were observed. Infertile eggs were detected among both groups. To analyze which component of mouse RBCs possesses the stimulating effect, RBCs were fractionated and included in media. However, the RBC fractions failed to stimulate development of the female reproductive organs. In addition, bovine hemoglobin hydrolysate, digested by neutral protease, was found to exhibit the promoting activity instead of untreated bovine hemoglobin. The other protein hydrolysate, lactalbumin hydrolysate, exhibited a similar effect with bovine hemoglobin hydrolysate. Using quantitative RT-PCR, we found the expression levels of four reproduction-related genes were significantly stimulated by RBCs. These data indicate that RBCs provide essential nutrients for the sexual maturation of female S. japonicum and that the protein component of RBCs appeared to constitute the key nutrient. These findings would improve laboratory culture of pre-adult schistosomes to adult worms in medium with well-defined components, which is important to investigate the function of genes related to female sexual maturation.

Suppression of the Insulin Receptors in Adult Schistosoma japonicum Impacts on Parasite Growth and Development: Further Evidence of Vaccine Potential

To further investigate the importance of insulin signaling in the growth, development, sexual maturation and egg production of adult schistosomes, we have focused attention on the insulin receptors (SjIRs) of Schistosoma japonicum, which we have previously cloned and partially characterised. We now show, by Biolayer Interferometry, that human insulin can bind the L1 subdomain (insulin binding domain) of recombinant (r)SjIR1 and rSjIR2 (designated SjLD1 and SjLD2) produced using the Drosophila S2 protein expression system. We have then used RNA interference (RNAi) to knock down the expression of the SjIRs in adult S. japonicum in vitro and show that, in addition to their reduced transcription, the transcript levels of other important downstream genes within the insulin pathway, associated with glucose metabolism and schistosome fecundity, were also impacted substantially. Further, a significant decrease in glucose uptake was observed in the SjIR-knockdown worms compared with luciferase controls. In vaccine/challenge experiments, we found that rSjLD1 and rSjLD2 depressed female growth, intestinal granuloma density and faecal egg production in S. japonicum in mice presented with a low dose challenge infection. These data re-emphasize the potential of the SjIRs as veterinary transmission blocking vaccine candidates against zoonotic schistosomiasis japonica in China and the Philippines.

Schistosomiasis affects over 200 million people globally. An anti-schistosome vaccine is not currently available. Schistosome eggs play a critical role in host pathology and the transmission of schistosomiasis; thus a vaccine targeting parasite fecundity and/or egg viability represents a realistic strategy for blocking transmission, promoting disease control in endemic areas. Based on our previous studies on the insulin receptors (SjIRs) of Schistosoma japonicum, as potential vaccine candidates, we have now further investigated the impact of insulin signaling on the growth, development, sexual maturation and egg production of adult schistosomes. Protein binding assays and RNAi strongly support our hypothesis that the insulin pathway in schistosomes is activated by the binding between host insulin and the parasite IRs, regulating the transcription of downstream genes integrally involved in glucose uptake and fecundity in these parasites. This feature was reflected in the striking decreased glucose levels of worms when the SjIRs were knocked down. Furthermore, the importance of the SjIRs in the growth and fecundity of adult S. japonicum was further demonstrated in murine vaccine trials using a low dose cercarial challenge which resulted in depressed female growth and faecal egg production in mice vaccinated with the recombinant L1 subdomains of SjIR1 and SjIR2.

Knocking down schistosomes - promise for lentiviral transduction in parasites

Underpinned by major advances in our understanding of the genomes of schistosomes, progress in the development of functional genomic tools is providing unique prospects to gain insights into the intricacies of the biology of these blood flukes, their host relationships, and the diseases that they cause. This article reviews some key applications of double-stranded RNA interference (RNAi) in Schistosoma mansoni, appraises delivery systems for transgenesis and stable gene silencing, considers ways of increasing efficiency and specificity of gene silencing, and discusses the prospects of using a lentivirus delivery system for future functional genomic-phenomic explorations of schistosomes and other parasites. The ability to achieve effective and stable gene perturbation in parasites has major biological implications and could facilitate the development of new interventions.

Prospects for Vector-Based Gene Silencing to Explore Immunobiological Features of Schistosoma mansoni

Schistosomiasis is a prevalent, socioeconomically important disease of humans caused by parasites of the genus Schistosoma (schistosomes or blood flukes). Currently, more than 200 million people worldwide are infected with schistosomes. Despite major research efforts, there is only one drug routinely used for effective treatment, and no vaccine is available to combat schistosomiasis. The purpose of the present article is to (1) provide a background on the parasites and different forms of disease; (2) describe key immunomolecular aspects of disease induced in the host; and (3) critically appraise functional genomic methods employed to explore parasite biology, parasite-host interactions and disease at the molecular level. Importantly, the article also describes the features and advantages of lentiviral delivery of artificial microRNAs to silence genes. It also discusses the first successful application of such an approach in schistosomes, in order to explore the immunobiological role of selected target proteins known to be involved in egg-induced disease. The lentiviral transduction system provides exciting prospects for future, fundamental investigations of schistosomes, and is likely to have broad applicability to other eukaryotic pathogens and infectious diseases. The ability to achieve effective and stable gene perturbation in parasites has major biotechnological implications, and might facilitate the development of radically new methods for the treatment and control of parasitic diseases.

Kicking in the Guts: Schistosoma mansoni Digestive Tract Proteins are Potential Candidates for Vaccine Development

Schistosomiasis is a debilitating disease that represents a major health problem in at least 74 tropical and subtropical countries. Current disease control strategies consist mainly of chemotherapy, which cannot prevent recurrent re-infection of people living in endemic area. In the last decades, many researchers made a remarkable effort in the search for an effective vaccine to provide long-term protection. Parasitic platyhelminthes of Schistosoma genus, which cause the disease, live in the blood vessels of definitive hosts where they are bathed in host blood for many years. Among the most promising molecules as vaccine candidates are the proteins present in the host–parasite interface, so numerous tegument antigens have been assessed and the achieved protection never got even close to 100%. Besides the tegument, the digestive tract is the other major site of host–parasite interface. Since parasites feed on blood, they need to swallow a considerable amount of blood for nutrient acquisition. Host blood ingested by schistosomes passes through the esophagus and reaches the gut where many peptidases catalyze the proteolysis of blood cells. Recent studies show the emergence of antigens related to the parasite blood feeding, such as esophageal gland proteins, proteases, and other proteins related to nutrient uptake. Herein, we review what is known about Schistosoma mansoni digestive tract proteins, emphasizing the ones described as potential vaccine candidates.

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.

Schistosome feeding and regurgitation

Schistosomes are parasitic flatworms that infect >200 million people worldwide, causing the chronic, debilitating disease schistosomiasis. Unusual among parasitic helminths, the long-lived adult worms, continuously bathed in blood, take up nutrients directly across the body surface and also by ingestion of blood into the gut. Recent proteomic analyses of the body surface revealed the presence of hydrolytic enzymes, solute, and ion transporters, thus emphasising its metabolic credentials. Furthermore, definition of the molecular mechanisms for the uptake of selected metabolites (glucose, certain amino acids, and water) establishes it as a vital site of nutrient acquisition. Nevertheless, the amount of blood ingested into the gut per day is considerable: for males ∼100 nl; for the more actively feeding females ∼900 nl, >4 times body volume. Ingested erythrocytes are lysed as they pass through the specialized esophagus, while leucocytes become tethered and disabled there. Proteomics and transcriptomics have revealed, in addition to gut proteases, an amino acid transporter in gut tissue and other hydrolases, ion, and lipid transporters in the lumen, implicating the gut as the site for acquisition of essential lipids and inorganic ions. The surface is the principal entry route for glucose, whereas the gut dominates amino acid acquisition, especially in females. Heme, a potentially toxic hemoglobin degradation product, accumulates in the gut and, since schistosomes lack an anus, must be expelled by the poorly understood process of regurgitation. Here we place the new observations on the proteome of body surface and gut, and the entry of different nutrient classes into schistosomes, into the context of older studies on worm composition and metabolism. We suggest that the balance between surface and gut in nutrition is determined by the constraints of solute diffusion imposed by differences in male and female worm morphology. Our conclusions have major implications for worm survival under immunological or pharmacological pressure.

Gaining biological perspectives from schistosome genomes

Characterization of the genomic basis underlying schistosome biology is an important strategy for the development of future treatments and interventions. Genomic sequence is now available for the three major clinically relevant schistosome species, Schistosoma mansoni, S. japonicum and S. haematobium, and this information represents an invaluable resource for the future control of human schistosomiasis. The identification of a biologically important, but distinct from the host, schistosome gene product is the ultimate goal for many research groups. While the initial elucidation of the genome of an organism is critical for most biological research, continued improvement or curation of the genome construction should be an ongoing priority. In this review we will discuss prominent recent findings utilizing a systems approach to schistosome biology, as well as the increased use of interference RNA (RNAi). Both of these research strategies are aiming to place parasite genes into a more meaningful biological perspective.

Reversible paralysis of Schistosoma mansoni by forchlorfenuron, a phenylurea cytokinin that affects septins

Septins are guanosine-5'-triphosphate-binding proteins involved in wide-ranging cellular processes including cytokinesis, vesicle trafficking, membrane remodelling and scaffolds, and with diverse binding partners. Precise roles for these structural proteins in most processes often remain elusive. Identification of small molecules that inhibit septins could aid in elucidating the functions of septins and has become increasingly important, including the description of roles for septins in pathogenic phenomena such as tumorigenesis. The plant growth regulator forchlorfenuron, a synthetic cytokinin known to inhibit septin dynamics, likely represents an informative probe for septin function. This report deals with septins of the human blood fluke Schistosoma mansoni and their interactions with forchlorfenuron. Recombinant forms of three schistosome septins, SmSEPT5, SmSEPT7.2 and SmSEPT10, interacted with forchlorfenuron, leading to rapid polymerization of filaments. Culturing developmental stages (miracidia, cercariae, adult males) of schistosomes in FCF at 50-500 μM rapidly led to paralysis, which was reversible upon removal of the cytokinin. The reversible paralysis was concentration-, time- and developmental stage-dependent. Effects of forchlorfenuron on the cultured schistosomes were monitored by video and/or by an xCELLigence-based assay of motility, which quantified the effect of forchlorfenuron on fluke motility. The findings implicated a mechanism targeting a molecular system controlling movement in these developmental stages: a direct effect on muscle contraction due to septin stabilization might be responsible for the reversible paralysis, since enrichment of septins has been described within the muscles of schistosomes. This study revealed the reversible effect of forchlorfenuron on both schistosome motility and its striking impact in hastening polymerization of septins. These novel findings suggested routes to elucidate roles for septins in this pathogen, and exploitation of derivatives of forchlorfenuron for anti-schistosomal drugs.

Inhibitory effects and analysis of RNA interference on thioredoxin glutathione reductase expression in Schistosoma japonicum

Schistosomes infect around 280 million people worldwide. The worms survive in the veins of the final host, where thioredoxin glutathione reductase (TGR) activity helps the parasites to survive in the aerobic environment. In the present study, we synthesized 4 small interfering RNAs (siRNA S1, S2, S3, and S4) targeting the Schistosoma japonicum (Sj) TGR gene and used them to knockdown the TGR gene. The knockdown effects of the siRNAs on SjTGR, and the thioredoxin reductase (TrxR) activity of SjTGR, were evaluated in vitro. The results of transfection with the siRNAs via the soaking method in vitro were confirmed by flow cytometry. S2 siRNA at a final concentration of 200 nM partially inhibited the expression of SjTGR at both the transcript and protein levels in vitro. TrxR-activity was lower in worms in the S2 siRNA-treated group compared with the control groups. Further analysis revealed that purified recombinant SjTGR could remove oxygen free radicals but not H(2)O(2) directly, which may explain the incomplete effects of RNA interference on SjTGR. The results of this study indicate that SjTGR may play an important role in the clearance of oxygen free radicals and protection of S. japonicum parasites against oxidative damage.

Lipid core peptide targeting the cathepsin D hemoglobinase of Schistosoma mansoni as a component of a schistosomiasis vaccine

The self-adjuvanting lipid core peptide (LCP) system offers a safe alternative vaccine delivery strategy, eliminating the need for additional adjuvants such as CpG Alum. In this study, we adopted the LCP as a scaffold for an epitope located on the surface of the cathepsin D hemoglobinase (Sm-CatD) of the human blood fluke Schistosoma mansoni. Sm-CatD plays a pivotal role in digestion of the fluke's bloodmeal and has been shown to be efficacious as a subunit vaccine in a murine model of human schistosomiasis. Using molecular modeling we showed that S. mansoni cathepsin D possesses a predicted surface exposed α-helix (A₂₆₃K) that corresponds to an immunodominant helix and target of enzyme-neutralizing antibodies against Necator americanus APR-1 (Na-APR-1), the orthologous protease and vaccine antigen from blood-feeding hookworms. The A₂₆₃K epitope was engineered as two peptide variants, one of which was flanked at both termini with a coil maintaining sequence, thereby promoting the helical characteristics of the native A₂₆₃K epitope. Some of the peptides were fused to a self-adjuvanting lipid core scaffold to generate LCPs. Mice were vaccinated with unadjuvanted peptides, peptides formulated with Freund's adjuvants, or LCPs. Antibodies generated to LCPs recognized native Sm-CatD within a soluble adult schistosome extract, and almost completely abolished its enzymatic activity in vitro. Using immunohistochemistry we showed that anti-LCP antibodies bound to the native Sm-CatD protein in the esophagus and anterior regions of the gastrodermis of adult flukes. Vaccines offer an alternative control strategy in the fight against schistosomiasis, and further development of LCPs containing multiple epitopes from this and other vaccine antigens should become a research priority.

Proteomic analysis of tegument-exposed proteins of female and male Schistosoma japonicum worms

The interplay between sexes is a prerequisite for female growth, reproductive maturation, and egg production, and the basis of schistosome pathopoiesis and propagation. The tegument is in direct contact with the host environment and its surface membranes are particularly crucial for schistosome survival in the definitive host. In this study, a streptavidin-biotin affinity purification technique combined with LC-MS/MS was used to analyze putative tegument-exposed proteins in female and male adult Schistosoma japonicum worms. In total, 179 proteins were identified in females and 300 in males, including 119 proteins common to both sexes, and 60 female biased and 181 male biased proteins. Some (e.g., serpin and CD36-like class B scavenger receptor) were involved in host-schistosome interactions, while some (e.g., gynecophoral canal protein) were important in the interplay between sexes. Gene Ontology analysis revealed that proteins involved in protein glycosylation and lysosome were highly expressed in females, while proteins involved in intracellular signal transduction, regulation of actin filament polymerization, and proteasome core complex were highly expressed in males. These results might elucidate physiological differences between the sexes. Our study provides new insights into schistosome growth and sexual maturity in the final host and permits the screening of vaccine candidates or drug targets for schistosomiasis.

RNA-mediated gene suppression and in vitro culture in Hymenolepis microstoma

Hymenolepis microstoma, the mouse bile-duct tapeworm, is a classical rodent-hosted model that provides easy laboratory access to all stages of the life cycle. Recent characterisation of its genome has greatly advanced its utility for molecular research, albeit contemporary techniques such as those for assaying gene function have yet to be developed in the system. Here we present research on the development of RNA-mediated gene suppression via RNA interference (RNAi), and on in vitro culture of the enteric, adult phase of the life cycle to support this work. We demonstrate up to 80% quantitative suppression of a Hox transcript via soaking activated juvenile worms with double-stranded RNAs. However, we were unable to achieve segmentation of the worms in culture despite extensive manipulations of the culture media and supplements, preventing functional interpretation. An alternative, in vivo approach to RNAi was also tested by exposing cysticercoids prior to inoculation in mice, but fluorescent labelling showed that the RNAs did not sufficiently penetrate the cyst body and no difference in expression was found between exposed and control groups grown in vivo. Genomic and transcriptomic data revealed that H. microstoma has two orthologs each of Dicer, Drosha and Ago-1-like genes and that expression of one of the Ago-1 genes appears exclusive to germline development, suggesting that two or more independent RNA-mediated pathways are in operation. These studies demonstrate the viability of RNAi in H. microstoma and extend the utility of the model for research in the genomic era.

Molecular and functional characterization of a putative PA28γ proteasome activator orthologue in Schistosoma mansoni

PA28γ is a proteasome activator involved in the regulation of the cellular proliferation, differentiation and growth. In the present study, we identified and characterized a cDNA from Schistosoma mansoni exhibiting significant homology to PA28γ of diverse taxa ranging from mammals (including humans) to simple invertebrates. Designated SmPA28γ, this transcript has a 753bp predicted ORF encoding a protein of 250 amino acid residues. Alignment of SmPA28γ with multiple PA28γ orthologues revealed an average similarity of ~40% among the investigated organisms, and 90% similarity with PA28γ from Schistosoma japonicum. In addition, phylogenetic analysis demonstrated a close linkage between SmPA28γ to its sister group that contains well-characterized PA28γ sequences from Drosophila spp., as well as sharing the same branch with PA28γ from S. japonicum. Gene expression profiling of SmPA28γ using real-time quantitative PCR revealed elevated steady-state transcript levels in the eggs, miracidia and paired adult worms compared to other stages. In parallel with gene expression profiles, an affinity-purified anti-SmPA28γ antibody produced against recombinant protein exhibited strongest reactivity in Western blot analyses to endogenous SmPA28γ from miracidia, sporocysts and paired adult worms. Given its known regulatory function in other organisms, we hypothesized that the high level of SmPA28γ transcript and protein in these stages may be correlated with an important role of the PA28γ in the cellular growth and/or development of this parasite. To address this hypothesis, miracidia were transformed in vitro to sporocysts in the presence of SmPA28γ double-stranded RNAs (dsRNAs) and cultivated for 4 days, after which time steady-state transcript and protein levels, and phenotypic changes were evaluated. SmPA28γ dsRNA treatment resulted in gene and protein knockdown of ~60% and ~80%, respectively, which were correlated with a significant decrease in larval length compared to its controls. These findings are consistent with a putative role of SmPA28γ in larval growth/development of the S. mansoni.

Transcriptional responses of in vivo praziquantel exposure in schistosomes identifies a functional role for calcium signalling pathway member CamKII

Treatment for clinical schistosomiasis has relied centrally on the broad spectrum anthelmintic praziquantel; however, there is limited information on its mode of action or the molecular response of the parasite. This paper presents a transcriptional and functional approach to defining the molecular responses of schistosomes to praziquantel. Differential gene expression in Schistosoma japonicum was investigated by transcriptome-wide microarray analysis of adult worms perfused from infected mice after 0.5 to 24 hours after oral administration of sub-lethal doses of praziquantel. Genes up-regulated initially in male parasites were associated with "Tegument/Muscle Repair" and "Lipid/Ion Regulation" functions and were followed by "Drug Resistance" and "Ion Regulation" associated genes. Prominent responses induced in female worms included up-regulation of "Ca(2+) Regulation" and "Drug Resistance" genes and later by transcripts of "Detoxification" and "Pathogen Defense" mechanisms. A subset of highly over-expressed genes, with putative drug resistance/detoxification roles or Ca(2+)-dependant/modulatory functions, were validated by qPCR. The leading candidate among these was CamKII, a putative calcium/calmodulin-dependent protein kinase type II delta chain. RNA interference was employed to knockdown CamKII in S. japonicum to determine the role of CamKII in the response to praziquantel. After partial-knockdown, schistosomes were analysed using IC50 concentrations (50% worm motility) and quantitative monitoring of parasite movement. When CamKII transcription was reduced by 50-69% in S. japonicum, the subsequent effect of an IC50 dosage of praziquantel was exacerbated, reducing motility from 47% to 27% in female worms and from 61% to 23% in males. These observations indicated that CamKII mitigates the effects of praziquantel, probably through stabilising Ca(2+) fluxes within parasite muscles and tegument. Together, these studies comprehensively charted transcriptional changes upon exposure to praziquantel and, notably, identified CamKII as potentially central to the, as yet undefined, mode of action of praziquantel.