Transcriptomic analysis of male and female Schistosoma mekongi adult worms

A reanalysis and integration of transcriptomics and proteomics datasets unveil novel drug targets for Mekong schistosomiasis

Schistosomiasis, caused by Schistosoma trematodes, is a significant global health concern, particularly affecting millions in Africa and Southeast Asia. Despite efforts to combat it, the rise of praziquantel (PZQ) resistance underscores the need for new treatment options. Protein kinases (PKs) are vital in cellular signaling and offer potential as drug targets. This study focused on focal adhesion kinase (FAK) as a candidate for anti-schistosomal therapy. Transcriptomic and proteomic analyses of adult S. mekongi worms identified FAK as a promising target due to its upregulation and essential role in cellular processes. Molecular docking simulations assessed the binding energy of FAK inhibitors to Schistosoma FAK versus human FAK. FAK inhibitor 14 and PF-03814735 exhibited strong binding to Schistosoma FAK with minimal binding for human FAK. In vitro assays confirmed significant anti-parasitic activity against S. mekongi, S. mansoni, and S. japonicum, comparable to PZQ, with low toxicity in human cells, indicating potential safety. These findings highlight FAK as a promising target for novel anti-schistosomal therapies. However, further research, including in vivo studies, is necessary to validate efficacy and safety before clinical use. This study offers a hopeful strategy to combat schistosomiasis and reduce its global impact.

Mechanisms of Arachidonic Acid In Vitro Schistosomicidal Potential

Arachidonic acid (ARA) was shown to possess safe and effective schistosomicidal impact on larval and adult Schistosoma mansoni and Schistosoma hematobium in vitro and in vivo in laboratory rodents and in children residing in low and high endemicity regions. We herein examine mechanisms underlying ARA schistosomicidal potential over two experiments, using in each pool a minimum of 50 adult male, female, or mixed-sex freshly recovered, ex vivo S. mansoni. Worms incubated in fetal calf serum-free medium were exposed to 0 or 10 mM ARA for 1 h at 37 °C and immediately processed for preparation of surface membrane and whole worm body homogenate extracts. Mixed-sex worms were additionally used for evaluating the impact of ARA exposure on the visualization of outer membrane cholesterol, sphingomyelin (SM), and ceramide in immunofluorescence assays. Following assessment of protein content, extracts of intact and ARA-treated worms were examined and compared for SM content, neutral sphingomyelinase activity, reactive oxygen species levels, and caspase 3/7 activity. Arachidonic acid principally led to perturbation of the organization, integrity, and SM content of the outer membrane of male and female worms and additionally impacted female parasites via stimulating neutral sphingomyelinase activity and oxidative stress. Arachidonic powerful action on female worms combined with its previously documented ovocidal activities supports its use as safe and effective therapy against schistosomiasis, provided implementation of the sorely needed and long waited-for chemical synthesis.

Chromosome-scale genome of the human blood fluke Schistosoma mekongi and its implications for public health

BACKGROUND

Schistosoma mekongi is a human blood fluke causing schistosomiasis that threatens approximately 1.5 million humans in the world. Nonetheless, the limited available S. mekongi genomic resources have hindered understanding of its biology and parasite-host interactions for disease management and pathogen control. The aim of our study was to integrate multiple technologies to construct a high-quality chromosome-level assembly of the S. mekongi genome.

METHODS

The reference genome for S. mekongi was generated through integrating Illumina, PacBio sequencing, 10 × Genomics linked-read sequencing, and high-throughput chromosome conformation capture (Hi-C) methods. In this study, we conducted de novo assembly, alignment, and gene prediction to assemble and annotate the genome. Comparative genomics allowed us to compare genomes across different species, shedding light on conserved regions and evolutionary relationships. Additionally, our transcriptomic analysis focused on genes associated with parasite-snail interactions in S. mekongi infection. We employed gene ontology (GO) enrichment analysis for functional annotation of these genes.

RESULTS

In the present study, the S. mekongi genome was both assembled into 8 pseudochromosomes with a length of 404 Mb, with contig N50 and scaffold N50 lengths of 1168 kb and 46,759 kb, respectively. We detected that 43% of the genome consists of repeat sequences and predicted 9103 protein-coding genes. We also focused on proteases, particularly leishmanolysin-like metalloproteases (M8), which are crucial in the invasion of hosts by 12 flatworm species. Through phylogenetic analysis, it was discovered that the M8 gene exhibits lineage-specific amplification among the genus Schistosoma. Lineage-specific expansion of M8 was observed in blood flukes. Additionally, the results of the RNA-seq revealed that a mass of genes related to metabolic and biosynthetic processes were up-regulated, which might be beneficial for cercaria production.

CONCLUSIONS

This study delivers a high-quality, chromosome-scale reference genome of S. mekongi, enhancing our understanding of the divergence and evolution of Schistosoma. The molecular research conducted here also plays a pivotal role in drug discovery and vaccine development. Furthermore, our work greatly advances the understanding of host-parasite interactions, providing crucial insights for schistosomiasis intervention strategies.

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.

Transcriptome profiling of male and female Ascaris lumbricoides reproductive tissues

BACKGROUND

Ascaris lumbricoides causes human ascariasis, the most prevalent helminth disease, infecting approximately 1 billion individuals globally. In 2019 the global disease burden was estimated to be 754,000 DALYs and resulted in 2090 deaths. In the absence of a vaccination strategy, treatment of ascariasis has relied on anthelminthic chemotherapy, but drug resistance is a concern. The propensity for reinfection is also a major challenge to disease control; female worms lay up to 200,000 eggs daily, which contaminate surrounding environments and remain viable for years, resulting in high transmission rates. Understanding the molecular mechanisms of reproductive processes, including control of egg production, spermatogenesis, oogenesis and embryogenesis, will drive the development of new drugs and/or vaccine targets for future ascariasis control.

METHODS

Transcriptome profiles of discrete reproductive and somatic tissue samples were generated from adult male and female worms using Illumina HiSeq with 2 × 150 bp paired-end sequencing. Male tissues included: testis germinal zone, testis part of vas deferens, seminal vesicle and somatic tissue. Female tissues included: ovary germinal zone, ovary part of the oviduct, uterus and somatic tissue. Differentially expressed genes (DEGs) were identified from the fragments per kilobases per million reads (FPKM) profiles. Hierarchical analysis was performed to identify tissue-specific genes. Furthermore, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were employed to identify significant terms and pathways for the DEGs.

RESULTS

DEGs involved in protein phosphorylation and adhesion molecules were indicated to play a crucial role in spermatogenesis and fertilization, respectively. Those genes associated with the G-protein-coupled receptor (GPCR) signaling pathway and small GTPase-mediated signal transduction pathway play an essential role in cytoskeleton organization during oogenesis. Additionally, DEGs associated with the SMA genes and TGF-β signaling pathway are crucial in adult female embryogenesis. Some genes associated with particular biological processes and pathways that were identified in this study have been linked to defects in germline development, embryogenesis and reproductive behavior. In the enriched KEGG pathway analysis, Hippo signaling, oxytocin signaling and tight junction pathways were identified to play a role in Ascaris male and female reproductive systems.

CONCLUSIONS

This study has provided comprehensive transcriptome profiles of discrete A. lumbricoides reproductive tissue samples, revealing the molecular basis of these functionally important tissues. The data generated from this study will provide fundamental knowledge on the reproductive biology of Ascaris and will inform future target identification for anti-ascariasis drugs and/or vaccines.

Lung Lipidomic Alterations in Beagle Dogs Infected with Toxocara canis

Toxocariasis, mainly caused by Toxocara canis, and to a lesser extent, Toxocara cati, is a neglected parasitic zoonosis. The mechanisms that underlie the changes in lipid metabolism of T. canis infection in Beagle dogs' lungs remain unclear. Lipidomics is a rapidly emerging approach that enables the global profiling of lipid composition by mass spectrometry. In this study, we performed a non-targeted lipidomic analysis of the lungs of Beagle dogs infected with the roundworm T. canis using liquid chromatography-tandem mass spectrometry (LC-MS/MS). A total of 1197 lipid species were identified, of which 63, 88, and 157 lipid species were significantly altered at 24 h post-infection (hpi), 96 hpi, and 36 days post-infection (dpi), respectively. This global lipidomic profiling identified infection-specific lipid signatures for lung toxocariasis, and represented a comprehensive comparison between the lipid composition of dogs' lungs in the presence and absence of T. canis infection. The potential roles of the identified lipid species in the pathogenesis of T. canis are discussed, which has important implications for better understanding the interaction mechanism between T. canis and the host lung.

Discovery of Schistosoma mekongi circulating proteins and antigens in infected mouse sera

Schistosomiasis is a neglected tropical disease caused by an infection of the parasitic flatworms schistosomes. Schistosoma mekongi is a restricted Schistosoma species found near the Mekong River, mainly in southern Laos and northern Cambodia. Because there is no vaccine or effective early diagnosis available for S. mekongi, additional biomarkers are required. In this study, serum biomarkers associated with S. mekongi-infected mice were identified at 14-, 28-, 42-, and 56-days post-infection. Circulating proteins and antigens of S. mekongi in mouse sera were analyzed using mass spectrometry-based proteomics. Serine protease inhibitors and macrophage erythroblast attacher were down-regulated in mouse sera at all infection timepoints. In addition, 54 circulating proteins and 55 antigens of S. mekongi were identified. Notable circulating proteins included kyphoscoliosis peptidase and putative tuberin, and antigens were detected at all four infection timepoints, particularly in the early stages (12 days). The putative tuberin sequence of S. mekongi was highly similar to homologs found in other members of the genus Schistosoma and less similar to human and murine sequences. Our study provided the identity of promising diagnostic biomarkers that could be applicable in early schistosomiasis diagnosis and vaccine development.

Untargeted serum metabolomic profiling for early detection of Schistosoma mekongi infection in mouse model

Mekong schistosomiasis is a parasitic disease caused by blood flukes in the Lao People’s Democratic Republic and in Cambodia. The standard method for diagnosis of schistosomiasis is detection of parasite eggs from patient samples. However, this method is not sufficient to detect asymptomatic patients, low egg numbers, or early infection. Therefore, diagnostic methods with higher sensitivity at the early stage of the disease are needed to fill this gap. The aim of this study was to identify potential biomarkers of early schistosomiasis using an untargeted metabolomics approach. Serum of uninfected and S. mekongi-infected mice was collected at 2, 4, and 8 weeks post-infection. Samples were extracted for metabolites and analyzed with a liquid chromatography-tandem mass spectrometer. Metabolites were annotated with the MS-DIAL platform and analyzed with Metaboanalyst bioinformatic tools. Multivariate analysis distinguished between metabolites from the different experimental conditions. Biomarker screening was performed using three methods: correlation coefficient analysis; feature important detection with a random forest algorithm; and receiver operating characteristic (ROC) curve analysis. Three compounds were identified as potential biomarkers at the early stage of the disease: heptadecanoyl ethanolamide; picrotin; and theophylline. The levels of these three compounds changed significantly during early-stage infection, and therefore these molecules may be promising schistosomiasis markers. These findings may help to improve early diagnosis of schistosomiasis, thus reducing the burden on patients and limiting spread of the disease in endemic areas.

Comparative proteome analysis of the tegument of male and female adult Schistosoma mansoni

The tegument, as the surface layer of adult male and female Schistosoma spp. represents the protective barrier of the worms to the hostile environment of the host bloodstream. Here we present the first comparative analysis of sex-specific tegument proteins of paired or virgin Schistosoma mansoni. We applied a new and highly sensitive workflow, allowing detection of even low abundance proteins. Therefore, a streptavidin–biotin affinity purification technique in combination with single pot solid-phase enhanced sample preparation was established for subsequent LC–MS/MS analysis. We were able to identify 1519 tegument proteins for male and female virgin and paired worms and categorized them by sex. Bioinformatic analysis revealed an involvement of female-specific tegument proteins in signaling pathways of cellular processes and antioxidant mechanisms. Male-specific proteins were found to be enriched in processes linked to phosphorylation and signal transduction. This suggests a task sharing between the sexes that might be necessary for survival in the host. Our datasets provide a basis for further studies to understand and ultimately decipher the strategies of the two worm sexes to evade the immune system.

Comparative transcriptome profiles of Schistosoma japonicum larval stages: Implications for parasite biology and host invasion

Schistosoma japonicum is prevalent in Asia with a wide mammalian host range, which leads to highly harmful zoonotic parasitic diseases. Most previous transcriptomic studies have been performed on this parasite, but mainly focus on stages inside the mammalian host. Moreover, few larval transcriptomic data are available in public databases. Here we mapped the detailed transcriptome profiles of four S. japonicum larval stages including eggs, miracidia, sporocysts and cercariae, providing a comprehensive development picture outside of the mammalian host. By analyzing the stage-specific/enriched genes, we identified functional genes associated with the biological characteristic at each stage: e.g. we observed enrichment of genes necessary for DNA replication only in sporocysts, while those involved in proteolysis were upregulated in sporocysts and/or cercariae. This data indicated that miracidia might use leishmanolysin and neprilysin to penetrate the snail, while elastase (SjCE2b) and leishmanolysin might contribute to the cercariae invasion. The expression profile of stem cell markers revealed potential germinal cell conversion during larval development. Additionally, our analysis indicated that tandem duplications had driven the expansion of the papain family in S. japonicum. Notably, all the duplicated cathepsin B-like proteases were highly expressed in cercariae. Utilizing our 3rd version of S. japonicum genome, we further characterized the alternative splicing profiles throughout these four stages. Taken together, the present study provides compressive gene expression profiles of S. japonicum larval stages and identifies a set of genes that might be involved in intermediate and definitive host invasion.

Metabolomics reveal alterations in arachidonic acid metabolism in Schistosoma mekongi after exposure to praziquantel

BACKGROUND

Mekong schistosomiasis is a parasitic disease caused by the blood-dwelling fluke Schistosoma mekongi. This disease contributes to human morbidity and mortality in the Mekong region, posing a public health threat to people in the area. Currently, praziquantel (PZQ) is the drug of choice for the treatment of Mekong schistosomiasis. However, the molecular mechanisms of PZQ action remain unclear, and Schistosoma PZQ resistance has been reported occasionally. Through this research, we aimed to use a metabolomic approach to identify the potentially altered metabolic pathways in S. mekongi associated with PZQ treatment.

METHODOLOGY/PRINCIPAL FINDINGS

Adult stage S. mekongi were treated with 0, 20, 40, or 100 μg/mL PZQ in vitro. After an hour of exposure to PZQ, schistosome metabolites were extracted and studied with mass spectrometry. The metabolomic data for the treatment groups were analyzed with the XCMS online platform and compared with data for the no treatment group. After low, medium (IC50), and high doses of PZQ, we found changes in 1,007 metabolites, of which phosphatidylserine and anandamide were the major differential metabolites by multivariate and pairwise analysis. In the pathway analysis, arachidonic acid metabolism was found to be altered following PZQ treatment, indicating that this pathway may be affected by the drug and potentially considered as a novel target for anti-schistosomiasis drug development.

CONCLUSIONS/SIGNIFICANCE

Our findings suggest that arachidonic acid metabolism is a possible target in the parasiticidal effects of PZQ against S. mekongi. Identifying potential targets of the effective drug PZQ provides an interesting viewpoint for the discovery and development of new agents that could enhance the prevention and treatment of schistosomiasis.

Low Sensitivity of Real Time PCRs Targeting Retrotransposon Sequences for the Detection of Schistosoma japonicum Complex DNA in Human Serum

While hybridization probe-based real-time PCR assays targeting highly repetitive multi-copy genome sequences for the diagnosis of S. mansoni complex or S. haematobium complex from human serum are well established, reports on the evaluation of respective assays for the identification of S. japonicum complex DNA in human serum are scarce. Here, we assessed the potential use of the retrotransposon sequences SjR2 and SjCHGCS19 from S. japonicum, S. mekongi and S. malayensis for the diagnosis of Asian Schistosoma infections. Based on available S. japonicum sequences and newly provided S. mekongi and S. malayensis sequences, hybridization probe-based real-time PCRs targeting SjR2 and SjCHGCS19 of the S. japonicum complex were designed both as consensus primer assays as well as multi-primer assays for the coverage of multiple variants of the target sequences. The assays were established using plasmids and S. mekongi DNA. While the consensus primer assays failed to detect S. mekongi DNA in human serum samples, the multi-primer assays showed positive or borderline positive results but only in 9.8% (6/61) of serum samples from patients with confirmed S. mekongi infections. Some cross-reactions with samples positive for S. mansoni or S. haematobium were observed but with the SjCHGCS19-PCR only. In spite of the low sensitivity, the presented experience may guide future evaluations of S. japonicum-complex-specific PCRs from human serum.

Identification of Low Molecular Weight Proteins and Peptides from Schistosoma mekongi Worm, Egg and Infected Mouse Sera

Schistosoma mekongi is found in the lower Mekong river region and causes schistosomiasis. Low sensitivity of diagnosis and development of drug resistance are problems to eliminate this disease. To develop novel therapies and diagnostics for S. mekongi, the basic molecular biology of this pathogen needs to be explored. Bioactive peptides have been reported in several worms and play important roles in biological functions. Limited information is available on the S. mekongi peptidome. Therefore, this study aimed to identify S. mekongi peptides using in silico transcriptome mining and mass spectrometry approaches. Schistosoma peptide components were identified in adult worms, eggs, and infected mouse sera. Thirteen neuropeptide families were identified using in silico predictions from in-house transcriptomic databases of adult S. mekongi worms. Using mass spectrometry approaches, 118 peptides (from 54 precursor proteins) and 194 peptides (from 86 precursor proteins) were identified from adult worms and eggs, respectively. Importantly, eight unique peptides of the S. mekongi ubiquitin thioesterase, trabid, were identified in infected mouse sera 14, 28, and 56 days after infection. This protein may be a potential target for diagnosis of schistosomiasis. The S. mekongi peptide profiles determined in this study could be used for further drug and diagnostic development.

Proteomic and deep sequencing analysis of extracellular vesicles isolated from adult male and female Schistosoma japonicum

Schistosomes are the causative agent of schistosomiasis, which affects more than 200 million people worldwide. Unlike other trematode parasites, schistosomes (along with the Didymozoidae) have evolved separate sexes. Pairing of males and females is a prerequisite for female sexual development and subsequent egg production. However, the mechanisms underlying these processes remain poorly understood. Extracellular vesicles (EVs) have been shown to play important roles in many biological processes. In the present study, we characterized EVs isolated from adult male and female Schistosoma japonicum. Proteomic analyses of the isolated EVs revealed that some proteins are significantly enriched in male or female EVs. RNA-sequencing analysis of a small RNA population associated with EVs identified 18 miRNAs enriched in male and female S. japonicum EVs. Among these, miR-750 was specifically enriched in female EVs. Additionally, the inhibition of miR-750 by a miRNA inhibitor led to decreased egg production in female schistosomes cultured in vitro. Collectively, our results suggest that miR-750 within female EV cargo may be involved in regulating ovary development and egg production in S. japonicum females.

Schistosomiasis is a neglected tropical disease caused by the genus Schistosoma and affects more than 200 million people worldwide. Previously, we and other groups found that Schistosoma japonicum can secrete extracellular vesicles (EVs) that are taken up by mammalian cells. Here, we characterized EVs isolated from adult male and female S. japonicum and found that some proteins and microRNAs (miRNAs) were significantly enriched in male or female EVs. More importantly, the inhibition of miR-750, which is specifically enriched in female EVs, resulted in decreased egg production. Overall, our study suggests that female EV miRNA cargo may play important roles in regulating female ovary development and egg production during male-female pairing in S. japonicum.

Transcriptomic Features of Echinococcus granulosus Protoscolex during the Encystation Process

Cystic echinococcosis (CE) is a zoonotic infection caused by Echinococcus granulosus larvae. It seriously affects the development of animal husbandry and endangers human health. Due to a poor understanding of the cystic fluid formation pathway, there is currently a lack of innovative methods for the prevention and treatment of CE. In this study, the protoscoleces (PSCs) in the encystation process were analyzed by high-throughput RNA sequencing. A total of 32,401 transcripts and 14,903 cDNAs revealed numbers of new genes and transcripts, stage-specific genes, and differently expressed genes. Genes encoding proteins involved in signaling pathways, such as putative G-protein coupled receptor, tyrosine kinases, and serine/threonine protein kinase, were predominantly up-regulated during the encystation process. Antioxidant enzymes included cytochrome c oxidase, thioredoxin glutathione, and glutathione peroxidase were a high expression level. Intriguingly, KEGG enrichment suggested that differentially up-regulated genes involved in the vasopressin-regulated water reabsorption metabolic pathway may play important roles in the transport of proteins, carbohydrates, and other substances. These results provide valuable information on the mechanism of cystic fluid production during the encystation process, and provide a basis for further studies on the molecular mechanisms of growth and development of PSCs.

Effect of Praziquantel on Schistosoma mekongi Proteome and Phosphoproteome

Schistosoma mekongi causes schistosomiasis in southeast Asia, against which praziquantel (PZQ) is the only treatment option. PZQ resistance has been reported, thus increasing the requirement to understand mechanism of PZQ. Herein, this study aimed to assess differences in proteome and phosphoproteome of S. mekongi after PZQ treatment for elucidating its action. Furthermore, key kinases related to PZQ effects were predicted to identify alternative targets for novel drug development. Proteomes of S. mekongi were profiled after PZQ treatment at half maximal inhibitory concentration and compared with untreated worms. A total of 144 proteins were differentially expressed after treatment. In parallel, immunohistochemistry indicated a reduction of phosphorylation, with 43 phosphoproteins showing reduced phosphorylation, as identified by phosphoproteomic approach. Pathway analysis of mass spectrometric data showed that calcium homeostasis, worm antigen, and oxidative stress pathways were influenced by PZQ treatment. Interestingly, two novel mechanisms related to protein folding and proteolysis through endoplasmic reticulum-associated degradation pathways were indicated as a parasiticidal mechanism of PZQ. According to kinase–substrate predictions with bioinformatic tools, Src kinase was highlighted as the major kinase related to the alteration of phosphorylation by PZQ. Interfering with these pathways or applying Src kinase inhibitors could be alternative approaches for further antischistosomal drug development.

Proteomic analysis of adult Schistosoma mekongi somatic and excretory-secretory proteins

Schistosoma mekongi is a causative agent of human schistosomiasis. There is limited knowledge of the molecular biology of S. mekongi and very few studies have examined drug targets, vaccine candidates and diagnostic biomarkers for S. mekongi. To explore the biology of S. mekongi, computational as well as experimental approaches were performed on S. mekongi males and females to identify excretory-secretory (ES) proteins and proteins that are differentially expressed between genders. According to bioinformatic prediction, the S. mekongi ES product was approximately 4.7% of total annotated transcriptome sequences. The classical secretory pathway was the main process to secrete proteins. Mass spectrometry-based quantification of male and female adult S. mekongi proteins was performed. We identified 174 and 156 differential expression of proteins in male and female worms, respectively. The dominant male-biased proteins were involved in actin filament-based processes, microtubule-based processes, biosynthetic processes and homeostatic processes. The major female-biased proteins were related to biosynthetic processes, organelle organization and signal transduction. An experimental approach identified 88 proteins in the S. mekongi secretome. The S. mekongi ES proteins mainly contributed to nutrient uptake, essential substance supply and host immune evasion. This research identifies proteins in the S. mekongi secretome and provides information on ES proteins that are differentially expressed between S. mekongi genders. These findings will contribute to S. mekongi drug and vaccine development. In addition, the study enhances our understanding of basic S. mekongi biology.

Recent advances in Schistosoma mekongi ecology, transcriptomics and proteomics of relevance to snail control

Mekong schistosomiasis caused by Schistosoma mekongi is a public health problem that occurs along the border between southern Laos and northern Cambodia. Given its restricted distribution and low prevalence, eventual eradication via an effective control program can be expected to be successful. To achieve this goal detailed knowledge of its basic biology, molecular biology, biochemistry, and pathology is urgently required. In this regard, recent studies on transcriptome analysis of adult male and female S. mekongi worms, and proteome analysis of developmental stages have been reported and are discussed here. The biology, habitat, and distribution of the snail intermediate host Neotricula aperta, which are factors in disease transmission, are discussed in this review. These have initiated renewed interest in S. mekongi research and contributed promising data that will be utilized in the generation of effective control and prevention strategies.

Molecular characterization and functional analysis of the Schistosoma mekongi Ca2+-dependent cysteine protease (calpain)

Background

Schistosoma mekongi, which causes schistosomiasis in humans, is an important public health issue in Southeast Asia. Treatment with praziquantel is the primary method of control but emergence of praziquantel resistance requires the development of alternative drugs and vaccines. Calcium-dependent cysteine protease (calpain) is a novel vaccine candidate that has been studied in S. mansoni, S. japonicum, and protozoans including malaria, leishmania and trypanosomes. However, limited information is available on the properties and functions of calpain in other Schistosoma spp., including S. mekongi. In this study, we functionally characterized calpain 1 of S. mekongi (SmeCalp1).

Results

Calpain 1 of S. mekongi was obtained from transcriptomic analysis of S. mekongi; it had the highest expression level of all isoforms tested and was predominantly expressed in the adult male. SmeCalp1 cDNA is 2274 bp long and encodes 758 amino acids, with 85% to 90% homology with calpains in other Schistosoma species. Recombinant SmeCalp1 (rSmeCalp1), with a molecular weight of approximately 86.7 kDa, was expressed in bacteria and stimulated a marked antibody response in mice. Native SmeCalp1 was detected in crude worm extract and excretory-secretory product, and it was mainly localized in the tegument of the adult male; less signal was detected in the adult female worm. Thus, SmeCalp1 may play a role in surface membrane synthesis or host–parasite interaction. We assessed the protease activity of rSmeCalp1 and demonstrated that rSmeCalp1 could cleave the calpain substrate N-succinyl-Leu-Leu-Val-Tyr-7-amino-4-methylcoumarin, that was inhibited by calpain inhibitors (MDL28170 and E64c). Additionally, rSmeCalp1 could degrade the biological substrates fibronectin (blood clotting protein) and human complement C3, indicating important roles in the intravascular system and in host immune evasion.

Conclusions

SmeCalp1 is expressed on the tegumental surface of the parasite and can cleave host defense molecules; thus, it might participate in growth, development and survival during the entire life-cycle of S. mekongi. Information on the properties and functions of SmeCalp1 reported herein will be advantageous in the development of effective drugs and vaccines against S. mekongi and other schistosomes.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3639-9) contains supplementary material, which is available to authorized users.

Phosphoproteomics analysis of male and female Schistosoma mekongi adult worms

Schistosoma mekongi is one of the major causative agents of human schistosomiasis in Southeast Asia. Praziquantel is now the only drug available for treatment and there are serious concerns about parasite resistance to it. Therefore, a dataset of schistosome targets is necessary for drug development. Phosphorylation regulates signalling pathways to control cellular processes that are important for the parasite's growth and reproduction. Inhibition of key phosphoproteins may reduce the severity of schistosomiasis. In this research, we studied the phosphoproteomes of S. mekongi male and female adult worms by using computational and experimental approaches. Using a phosphoproteomics approach, we determined that 88 and 44 phosphoproteins were male- and female-biased, respectively. Immunohistochemistry using anti-phosphoserine antibodies demonstrated phosphorylation on the tegument and muscle of male S. mekongi worms and on the vitelline gland and gastrointestinal tract of female worms. This research revealed S. mekongi sex-dependent phosphoproteins. Our findings provide a better understanding of the role of phosphorylation in S. mekongi and could be integrated with information from other Schistosoma species to facilitate drug and vaccine development.

In-depth proteomic characterization of Schistosoma haematobium: Towards the development of new tools for elimination

BACKGROUND

Schistosomiasis is a neglected disease affecting hundreds of millions worldwide. Of the three main species affecting humans, Schistosoma haematobium is the most common, and is the leading cause of urogenital schistosomiasis. S. haematobium infection can cause different urogenital clinical complications, particularly in the bladder, and furthermore, this parasite has been strongly linked with squamous cell carcinoma. A comprehensive analysis of the molecular composition of its different proteomes will contribute to developing new tools against this devastating disease.

METHODS AND FINDINGS

By combining a comprehensive protein fractionation approach consisting of OFFGEL electrophoresis with high-throughput mass spectrometry, we have performed the first in-depth characterisation of the different discrete proteomes of S. haematobium that are predicted to interact with human host tissues, including the secreted and tegumental proteomes of adult flukes and secreted and soluble egg proteomes. A total of 662, 239, 210 and 138 proteins were found in the adult tegument, adult secreted, soluble egg and secreted egg proteomes, respectively. In addition, we probed these distinct proteomes with urine to assess urinary antibody responses from naturally infected human subjects with different infection intensities, and identified adult fluke secreted and tegument extracts as being the best predictors of infection.

CONCLUSION

We provide a comprehensive dataset of proteins from the adult and egg stages of S. haematobium and highlight their utility as diagnostic markers of infection intensity. Protein composition was markedly different between the different extracts, highlighting the distinct subsets of proteins that different development stages present in their different niches. Furthermore, we have identified adult fluke ES and tegument extracts as best predictors of infection using urine antibodies of naturally infected people. This study provides the first steps towards the development of novel tools to control this important neglected tropical disease.

Unpacking the Pathogen Box-An Open Source Tool for Fighting Neglected Tropical Disease

The Pathogen Box is a 400-strong collection of drug-like compounds, selected for their potential against several of the world's most important neglected tropical diseases, including trypanosomiasis, leishmaniasis, cryptosporidiosis, toxoplasmosis, filariasis, schistosomiasis, dengue virus and trichuriasis, in addition to malaria and tuberculosis. This library represents an ensemble of numerous successful drug discovery programmes from around the globe, aimed at providing a powerful resource to stimulate open source drug discovery for diseases threatening the most vulnerable communities in the world. This review seeks to provide an in-depth analysis of the literature pertaining to the compounds in the Pathogen Box, including structure-activity relationship highlights, mechanisms of action, related compounds with reported activity against different diseases, and, where appropriate, discussion on the known and putative targets of compounds, thereby providing context and increasing the accessibility of the Pathogen Box to the drug discovery community.