Exploring the utility of circulating miRNAs as diagnostic biomarkers of fasciolosis

Effective management and control of parasitic infections on farms depends on their early detection. Traditional serological diagnostic methods for Fasciola hepatica infection in livestock are specific and sensitive, but currently the earliest detection of the parasite only occurs at approximately three weeks post-infection. At this timepoint, parasites have already entered the liver and caused the tissue damage and immunopathology that results in reduced body weight and loss in productivity. Here, we investigated whether the differential abundance of micro(mi)miRNAs in sera of F. hepatica-infected sheep has potential as a tool for the early diagnosis of infection. Using miRNA sequencing analysis, we discovered specific profiles of sheep miRNAs at both the pre-hepatic and hepatic infection phases in comparison to non-infected sheep. In addition, six F. hepatica-derived miRNAs were specifically identified in sera from infected sheep. Thus, a panel of differentially expressed miRNAs comprising four sheep (miR-3231-3p; miR133-5p; 3957-5p; 1197-3p) and two parasite miRNAs (miR-124-3p; miR-Novel-11-5p) were selected as potential biomarkers. The expression of these candidates in sera samples from longitudinal sheep infection studies collected between 7 days and 23 weeks was quantified using RT-qPCR and compared to samples from age-matched non-infected sheep. We identified oar-miR-133-5p and oar-miR-3957-5p as promising biomarkers of fasciolosis, detecting infection as early as 7 days. The differential expression of the other selected miRNAs was not sufficient to diagnose infection; however, our analysis found that the most abundant forms of fhe-miR-124-3p in sera were sequence variants (IsomiRs) of the canonical miRNA, highlighting the critical importance of primer design for accurate diagnostic RT-qPCR. Accordingly, this investigative study suggests that certain miRNAs are biomarkers of F. hepatica infection and validates miRNA-based diagnostics for the detection of fasciolosis in sheep.

Glycan Complexity and Heterogeneity of Glycoproteins in Somatic Extracts and Secretome of the Infective Stage of the Helminth Fasciola hepatica

Fasciola hepatica is a global helminth parasite of humans and their livestock. The invasive stage of the parasite, the newly excysted juvenile (NEJs), relies on glycosylated excreted-secreted (ES) products and surface/somatic molecules to interact with host cells and tissues and to evade the host's immune responses, such as disarming complement and shedding bound antibody. While -omics technologies have generated extensive databases of NEJs' proteins and their expression, detailed knowledge of the glycosylation of proteins is still lacking. Here, we employed glycan, glycopeptide, and proteomic analyses to determine the glycan profile of proteins within the NEJs' somatic (Som) and ES extracts. These analyses characterized 123 NEJ glycoproteins, 71 of which are secreted proteins, and allowed us to map 356 glycopeptides and their associated 1690 N-glycan and 37 O-glycan forms to their respective proteins. We discovered abundant micro-heterogeneity in the glycosylation of individual glycosites and between different sites of multi-glycosylated proteins. The global heterogeneity across NEJs' glycoproteome was refined to 53 N-glycan and 16 O-glycan structures, ranging from highly truncated paucimannosidic structures to complex glycans carrying multiple phosphorylcholine (PC) residues, and included various unassigned structures due to unique linkages, particularly in pentosylated O-glycans. Such exclusive glycans decorate some well-known secreted molecules involved in host invasion, including cathepsin B and L peptidases, and a variety of membrane-bound glycoproteins, suggesting that they participate in host interactions. Our findings show that F. hepatica NEJs generate exceptional protein variability via glycosylation, suggesting that their molecular portfolio that communicates with the host is far more complex than previously anticipated by transcriptomic and proteomic analyses. This study opens many avenues to understand the glycan biology of F. hepatica throughout its life-stages, as well as other helminth parasites, and allows us to probe the glycosylation of individual NEJs proteins in the search for innovative diagnostics and vaccines against fascioliasis.

In vitro evaluation of the potential use of snake-derived peptides in the treatment of respiratory infections using inhalation therapy: A proof of concept study

Inhalation therapy using nebulisers is an attractive non-invasive route for drug delivery, particularly for the treatment of lung infections with anti-inflammatory and anti-microbial compounds. This study evaluated the suitability of three snake-derived peptides (termed Sn1b, SnE1 and SnE1-F), which we have recently shown have potent anti-inflammatory and bacteriostatic activities, for nebulisation using a vibrating mesh nebuliser (VMN). The effect of nebulisation on peptide concentration, stability and function were assessed, prior to progression to aerodynamic particle size distribution, and in vitro drug delivery in simulated adult spontaneous breathing and mechanical ventilated patient models. When nebulised, all three peptides exhibited similar functions to their non-nebulised counterparts and were found to be respirable during simulated mechanical ventilation. Based on the assessment of the droplet distributions of nebulised peptides using a Next Generation Impactor (NGI) demonstrated that if administered in vivo each peptide would likely be delivered to the lower airways. These data suggest that nebulisation using a VMN is a viable means of anti-microbial / anti-inflammatory peptide delivery targeting microbial respiratory infections, and possibly even systemic infections.

A new multiplex SARS-CoV-2 antigen microarray showed correlation of IgG, IgA, and IgM antibodies from patients with COVID-19 disease severity and maintenance of relative IgA and IgM antigen binding over time

Zoonotic spillover of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) to humans in December 2019 caused the coronavirus disease 2019 (COVID-19) pandemic. Serological monitoring is critical for detailed understanding of individual immune responses to infection and protection to guide clinical therapeutic and vaccine strategies. We developed a high throughput multiplexed SARS-CoV-2 antigen microarray incorporating spike (S) and nucleocapsid protein (NP) and fragments expressed in various hosts which allowed simultaneous assessment of serum IgG, IgA, and IgM responses. Antigen glycosylation influenced antibody binding, with S glycosylation generally increasing and NP glycosylation decreasing binding. Purified antibody isotypes demonstrated a binding pattern and intensity different from the same isotype in whole serum, probably due to competition from the other isotypes present. Using purified antibody isotypes from naïve Irish COVID-19 patients, we correlated antibody isotype binding to different panels of antigens with disease severity, with binding to the S region S1 expressed in insect cells (S1 Sf21) significant for IgG, IgA, and IgM. Assessing longitudinal response for constant concentrations of purified antibody isotypes for a patient subset demonstrated that the relative proportion of antigen-specific IgGs decreased over time for severe disease, but the relative proportion of antigen-specific IgA binding remained at the same magnitude at 5 and 9 months post-first symptom onset. Further, the relative proportion of IgM binding decreased for S antigens but remained the same for NP antigens. This may support antigen-specific serum IgA and IgM playing a role in maintaining longer-term protection, important for developing and assessing vaccine strategies. Overall, these data demonstrate the multiplexed platform as a sensitive and useful platform for expanded humoral immunity studies, allowing detailed elucidation of antibody isotypes response against multiple antigens. This approach will be useful for monoclonal antibody therapeutic studies and screening of donor polyclonal antibodies for patient infusions.

Omics tools enabling vaccine discovery against fasciolosis

In the past decade significant advances in our understanding of liver fluke biology have been made through in-depth interrogation and analysis of evolving Fasciola hepatica and Fasciola gigantica omics datasets. This information is crucial for developing novel control strategies, particularly vaccines necessitated by the global spread of anthelmintic resistance. Distilling them down to a manageable number of testable vaccines requires combined rational, empirical, and collaborative approaches. Despite a lack of clear outstanding vaccine candidate(s), we must continue to identify salient parasite-host interacting molecules, likely in the secretory products, tegument, or extracellular vesicles, and perform robust trials especially in livestock, using present and emerging vaccinology technologies to discover that elusive liver fluke vaccine. Omics tools are bringing this prospect ever closer.

Stage-specific miRNAs regulate gene expression associated with growth, development and parasite-host interaction during the intra-mammalian migration of the zoonotic helminth parasite Fasciola hepatica

Background

MiRNAs are small non-coding RNAs that post-transcriptionally regulate gene expression in organisms ranging from viruses to mammals. There is great relevance in understanding how miRNAs regulate genes involved in the growth, development, and maturation of the many parasitic worms (helminths) that together afflict more than 2 billion people.

Results

Here, we describe the miRNAs expressed by each of the predominant intra-mammalian development stages of Fasciola hepatica, a foodborne flatworm that infects a wide range of mammals worldwide, most importantly humans and their livestock. A total of 124 miRNAs were profiled, 72 of which had been previously reported and three of which were conserved miRNA sequences described here for the first time. The remaining 49 miRNAs were novel sequences of which, 31 were conserved with F. gigantica and the remaining 18 were specific to F. hepatica. The newly excysted juveniles express 22 unique miRNAs while the immature liver and mature bile duct stages each express 16 unique miRNAs. We discovered several sequence variant miRNAs (IsomiRs) as well as miRNA clusters that exhibit strict temporal expression paralleling parasite development. Target analysis revealed the close association between miRNA expression and stage-specific changes in the transcriptome; for example, we identified specific miRNAs that target parasite proteases known to be essential for intestinal wall penetration (cathepsin L3). Moreover, we demonstrate that miRNAs fine-tune the expression of genes involved in the metabolic pathways that allow the parasites to move from an aerobic external environment to the anerobic environment of the host.

Conclusions

These results provide novel insight into the regulation of helminth parasite development and identifies new genes and miRNAs for therapeutic development to limit the virulence and pathogenesis caused by F. hepatica.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08644-z.

Tuaimenal A, a Meroterpene from the Irish Deep-Sea Soft Coral Duva florida, Displays Inhibition of the SARS-CoV-2 3CLpro Enzyme

Cold water benthic environments are a prolific source of structurally diverse molecules with a range of bioactivities against human disease. Specimens of a previously chemically unexplored soft coral, Duva florida, were collected during a deep-sea cruise that sampled marine invertebrates along the Irish continental margin in 2018. Tuaimenal A (1), a cyclized merosesquiterpenoid representing a new carbon scaffold with a highly substituted chromene core, was discovered through exploration of the soft coral secondary metabolome via NMR-guided fractionation. The absolute configuration was determined through vibrational circular dichroism. Functional biochemical assays and in silico docking experiments found tuaimenal A selectively inhibits the viral main protease (3CLpro) of SARS-CoV-2.

Targeting Secreted Protease/Anti-Protease Balance as a Vaccine Strategy against the Helminth Fasciola hepatica

The liver fluke Fasciola hepatica is an economically important global pathogen of humans and their livestock. To facilitate host invasion and migration, F. hepatica secretes an abundance of cathepsin peptidases but prevents excessive damage to both parasite and host tissues by co-secreting regulatory peptidase inhibitors, cystatins/stefins and Kunitz-type inhibitors. Here, we report a vaccine strategy aimed at disrupting the parasite’s protease/anti-protease balance by targeting these key inhibitors. Our vaccine cocktail containing three recombinant stefins (rFhStf-1, rFhStf-2, rFhStf-3) and a Kunitz-type inhibitor (rFhKT1) formulated in adjuvant Montanide 61VG was assessed in two independent sheep trials. While fluke burden was not reduced in either trial, in Trial 1 the vaccinated animals showed significantly greater weight gain (p < 0.05) relative to the non-vaccinated control group. In both trials we observed a significant reduction in egg viability (36–42%). Multivariate regression analyses showed vaccination and increased levels of IgG2 antibodies specific for the F. hepatica peptidase inhibitors were positive indicators for increased weight gain and levels of haemoglobin within the normal range at 16 weeks post-infection (wpi; p < 0.05). These studies point to the potential of targeting peptidase inhibitors as vaccine cocktails for fasciolosis control in sheep.

Fasciola hepatica is refractory to complement killing by preventing attachment of mannose binding lectin (MBL) and inhibiting MBL-associated serine proteases (MASPs) with serpins

The complement system is a first-line innate host immune defence against invading pathogens. It is activated via three pathways, termed Classical, Lectin and Alternative, which are mediated by antibodies, carbohydrate arrays or microbial liposaccharides, respectively. The three complement pathways converge in the formation of C3-convertase followed by the assembly of a lethal pore-like structure, the membrane attack complex (MAC), on the pathogen surface. We found that the infectious stage of the helminth parasite Fasciola hepatica, the newly excysted juvenile (NEJ), is resistant to the damaging effects of complement. Despite being coated with mannosylated proteins, the main initiator of the Lectin pathway, the mannose binding lectin (MBL), does not bind to the surface of live NEJ. In addition, we found that recombinantly expressed serine protease inhibitors secreted by NEJ (rFhSrp1 and rFhSrp2) selectively prevent activation of the complement via the Lectin pathway. Our experiments demonstrate that rFhSrp1 and rFhSrp2 inhibit native and recombinant MBL-associated serine proteases (MASPs), impairing the primary step that mediates C3b and C4b deposition on the NEJ surface. Indeed, immunofluorescence studies show that MBL, C3b, C4b or MAC are not deposited on the surface of NEJ incubated in normal human serum. Taken together, our findings uncover new means by which a helminth parasite prevents the activation of the Lectin complement pathway to become refractory to killing via this host response, in spite of presenting an assortment of glycans on their surface.

The Impact of Lung Proteases on Snake-Derived Antimicrobial Peptides

Respiratory infections are a leading cause of global morbidity and mortality and are of significant concern for individuals with chronic inflammatory lung diseases. There is an urgent need for novel antimicrobials. Antimicrobial peptides (AMPs) are naturally occurring innate immune response peptides with therapeutic potential. However, therapeutic development has been hindered by issues with stability and cytotoxicity. Availing of direct drug delivery to the affected site, for example the lung, can reduce unwanted systemic side effects and lower the required dose. As cystic fibrosis (CF) and chronic obstructive pulmonary disease (COPD) lungs typically exhibit elevated protease levels, the aim of this study was to assess their impact on snake-derived AMPs. Peptide cleavage was determined using SDS-PAGE and antimicrobial and anti-inflammatory activities of neutrophil elastase (NE)-incubated peptides were assessed using a radial diffusion assay (RDA) and an in vitro LPS-induced inflammation model, respectively. Although the snake-derived AMPs were found to be susceptible to cleavage by lung proteases including NE, several retained their function following NE-incubation. This facilitated the design of novel truncated derivatives that retained functionality following NE incubation. Snake-derived AMPs are tractable candidate treatments for use in environments that feature elevated NE levels, such as the CF airways.

Antigen-specific response of CD4+ T cells and hepatic lymph node cells to Fasciola hepatica-derived molecules at the early and late stage of the infection in sheep

The immunomodulatory capacity of F. hepatica antigens is probably one of the main reasons for the development of a driven non-protective Th2 immune response. In this study, we analysed the cellular response of hepatic lymph node cells and CD4⁺ T cells in terms of proliferative response, efficiency of antigen presentation and cytokine production, to F. hepatica-derived molecules, at early and late stages of the infection. Thirty-one sheep were allocated into five groups and were slaughtered at 16 dpi and 23 wpi. In order to analyse antigen-specific response, the following F. hepatica recombinant molecules were used: rFhCL1, rFhCL2, rFhCL3, rFhCB1, rFhCB2, rFhCB3, rFhStf-1, rFhStf-2, rFhStf-3 and rFhKT1. A cell proliferation assay using hepatic lymph node cells and an antigen presentation cell assay using CD4⁺ T cells were performed. At 16 dpi, all molecules but rFhStf-2 and rFhKT1 elicited a significant cell proliferative response on hepatic lymph node cells of infected animals. At both early and late stage of the infection, antigen presentation of rFhCB3 and rFhCL2 resulted in higher stimulation index of CD4⁺ T cells which was IL-2 mediated, although no statistically significant when compared to uninfected animals. Significant cytokine production (IL-4, IL-10 and IFN-γ) was conditioned by the antigen-specific cell stimulation. No CD4⁺ T cell exhaustion was detected in infected sheep at the chronic stage of the infection. This study addressed antigen-specific response to F. hepatica-derived molecules that are involved in key aspects of the parasite survival within the host.

Autonomous Non Antioxidant Roles for Fasciola hepatica Secreted Thioredoxin-1 and Peroxiredoxin-1

Trematode parasites of the genus Fasciola are the cause of liver fluke disease (fasciolosis) in humans and their livestock. Infection of the host involves invasion through the intestinal wall followed by migration in the liver that results in extensive damage, before the parasite settles as a mature egg-laying adult in the bile ducts. Genomic and transcriptomic studies revealed that increased metabolic stress during the rapid growth and development of F. hepatica is balanced with the up-regulation of the thiol-independent antioxidant system. In this cascade system thioredoxin/glutathione reductase (TGR) reduces thioredoxin (Trx), which then reduces and activates peroxiredoxin (Prx), whose major function is to protect cells against the damaging hydrogen peroxide free radicals. F. hepatica expresses a single TGR, three Trx and three Prx genes; however, the transcriptional expression of Trx1 and Prx1 far out-weighs (>50-fold) other members of their family, and both are major components of the parasite secretome. While Prx1 possesses a leader signal peptide that directs its secretion through the classical pathway and explains why this enzyme is found freely soluble in the secretome, Trx1 lacks a leader peptide and is secreted via an alternative pathway that packages the majority of this enzyme into extracellular vesicles (EVs). Here we propose that F. hepatica Prx1 and Trx1 do not function as part of the parasite’s stress-inducible thiol-dependant cascade, but play autonomous roles in defence against the general anti-pathogen oxidative burst by innate immune cells, in the modulation of host immune responses and regulation of inflammation.

Eudiplozoon nipponicum (Monogenea, Diplozoidae) and its adaptation to haematophagy as revealed by transcriptome and secretome profiling

Background

Ectoparasites from the family Diplozoidae (Platyhelminthes, Monogenea) belong to obligate haematophagous helminths of cyprinid fish. Current knowledge of these worms is for the most part limited to their morphological, phylogenetic, and population features. Information concerning the biochemical and molecular nature of physiological processes involved in host–parasite interaction, such as evasion of the immune system and its regulation, digestion of macromolecules, suppression of blood coagulation and inflammation, and effect on host tissue and physiology, is lacking. In this study, we report for the first time a comprehensive transcriptomic/secretome description of expressed genes and proteins secreted by the adult stage of Eudiplozoon nipponicum (Goto, 1891) Khotenovsky, 1985, an obligate sanguivorous monogenean which parasitises the gills of the common carp (Cyprinus carpio).

Results

RNA-seq raw reads (324,941 Roche 454 and 149,697,864 Illumina) were generated, de novo assembled, and filtered into 37,062 protein-coding transcripts. For 19,644 (53.0%) of them, we determined their sequential homologues. In silico functional analysis of E. nipponicum RNA-seq data revealed numerous transcripts, pathways, and GO terms responsible for immunomodulation (inhibitors of proteolytic enzymes, CD59-like proteins, fatty acid binding proteins), feeding (proteolytic enzymes cathepsins B, D, L1, and L3), and development (fructose 1,6-bisphosphatase, ferritin, and annexin). LC-MS/MS spectrometry analysis identified 721 proteins secreted by E. nipponicum with predominantly immunomodulatory and anti-inflammatory functions (peptidyl-prolyl cis-trans isomerase, homolog to SmKK7, tetraspanin) and ability to digest host macromolecules (cathepsins B, D, L1).

Conclusions

In this study, we integrated two high-throughput sequencing techniques, mass spectrometry analysis, and comprehensive bioinformatics approach in order to arrive at the first comprehensive description of monogenean transcriptome and secretome. Exploration of E. nipponicum transcriptome-related nucleotide sequences and translated and secreted proteins offer a better understanding of molecular biology and biochemistry of these, often neglected, organisms. It enabled us to report the essential physiological pathways and protein molecules involved in their interactions with the fish hosts.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07589-z.

Biochemical and cellular characterisation of the Plasmodium falciparum M1 alanyl aminopeptidase (PfM1AAP) and M17 leucyl aminopeptidase (PfM17LAP)

The Plasmodium falciparum M1 alanyl aminopeptidase and M17 leucyl aminopeptidase, PfM1AAP and PfM17LAP, are potential targets for novel anti-malarial drug development. Inhibitors of these aminopeptidases have been shown to kill malaria parasites in culture and reduce parasite growth in murine models. The two enzymes may function in the terminal stages of haemoglobin digestion, providing free amino acids for protein synthesis by the rapidly growing intra-erythrocytic parasites. Here we have performed a comparative cellular and biochemical characterisation of the two enzymes. Cell fractionation and immunolocalisation studies reveal that both enzymes are associated with the soluble cytosolic fraction of the parasite, with no evidence that they are present within other compartments, such as the digestive vacuole (DV). Enzyme kinetic studies show that the optimal pH of both enzymes is in the neutral range (pH 7.0-8.0), although PfM1AAP also possesses some activity (< 20%) at the lower pH range of 5.0-5.5. The data supports the proposal that PfM1AAP and PfM17LAP function in the cytoplasm of the parasite, likely in the degradation of haemoglobin-derived peptides generated in the DV and transported to the cytosol.

Complementary transcriptomic and proteomic analyses reveal the cellular and molecular processes that drive growth and development of Fasciola hepatica in the host liver

Background

The major pathogenesis associated with Fasciola hepatica infection results from the extensive tissue damage caused by the tunnelling and feeding activity of immature flukes during their migration, growth and development in the liver. This is compounded by the pathology caused by host innate and adaptive immune responses that struggle to simultaneously counter infection and repair tissue damage.

Results

Complementary transcriptomic and proteomic approaches defined the F. hepatica factors associated with their migration in the liver, and the resulting immune-pathogenesis. Immature liver-stage flukes express ~ 8000 transcripts that are enriched for transcription and translation processes reflective of intensive protein production and signal transduction pathways. Key pathways that regulate neoblast/pluripotent cells, including the PI3K-Akt signalling pathway, are particularly dominant and emphasise the importance of neoblast-like cells for the parasite’s rapid development. The liver-stage parasites display different secretome profiles, reflecting their distinct niche within the host, and supports the view that cathepsin peptidases, cathepsin peptidase inhibitors, saposins and leucine aminopeptidases play a central role in the parasite’s destructive migration, and digestion of host tissue and blood. Immature flukes are also primed for countering immune attack by secreting immunomodulating fatty acid binding proteins (FABP) and helminth defence molecules (FhHDM). Combined with published host microarray data, our results suggest that considerable immune cell infiltration and subsequent fibrosis of the liver tissue exacerbates oxidative stress within parenchyma that compels the expression of a range of antioxidant molecules within both host and parasite.

Conclusions

The migration of immature F. hepatica parasites within the liver is associated with an increase in protein production, expression of signalling pathways and neoblast proliferation that drive their rapid growth and development. The secretion of a defined set of molecules, particularly cathepsin L peptidases, peptidase-inhibitors, saponins, immune-regulators and antioxidants allow the parasite to negotiate the liver micro-environment, immune attack and increasing levels of oxidative stress. This data contributes to the growing F. hepatica -omics information that can be exploited to understand parasite development more fully and for the design of novel control strategies to prevent host liver tissue destruction and pathology.

Regulation of the Fasciola hepatica newly excysted juvenile cathepsin L3 (FhCL3) by its propeptide: a proposed 'clamp-like' mechanism of binding and inhibition

BACKGROUND

The zoonotic worm parasite Fasciola hepatica secretes an abundance of cathepsin L peptidases that are associated with virulence, invasiveness, feeding and migration. The peptidases are produced as inactive zymogens that activate at low pH by autocatalytic removal of their N-terminal pro-domain or propeptide. Propeptides bind to their cognate enzyme with high specificity. Little is known, however, about the mechanism by which the propeptide of FhCL3, a cathepsin L peptidase secreted by the infective newly excysted juveniles (NEJs), regulates the inhibition and activation of the mature enzyme before it is secreted into host tissues.

RESULTS

Immunolocalisation/immunoblotting studies show that the FhCL3 zymogen is produced and secreted by gastrodermal cells of the NEJs gut. A recombinant propeptide of FhCL3 (ppFhCL3) was shown to be a highly potent and selective inhibitor of native and recombinant F. hepatica FhCL3 peptidase, and other members of the cathepsin L family; inhibition constant (K_i) values obtained for FhCL1, FhCL2 and FhCL3 were 0.04 nM, 0.004 nM and < 0.002 nM, respectively. These values are at least 1000-fold lower than those K_i obtained for human cathepsin L (HsCL) and human cathepsin K (HsCK) demonstrating the selectivity of the ppFhCL3 for parasite cathepsins L. By exploiting 3-D structural data we identified key molecular interactions in the specific binding between the ppFhCL3 and FhCL3 mature domain. Using recombinant variants of ppFhCL3 we demonstrated the critical importance of a pair of propeptide residues (Tyr⁴⁶Lys⁴⁷) for the interaction with the propeptide binding loop (PBL) of the mature enzyme and other residues (Leu⁶⁶ and Glu⁶⁸) that allow the propeptide to block the active site.

CONCLUSIONS

The FhCL3 peptidase involved in host invasion by F. hepatica is produced as a zymogen in the NEJs gut. Regulation of its activation involves specific binding sites within the propeptide that are interdependent and act as a "clamp-like" mechanism of inhibition. These interactions are disrupted by the low pH of the NEJs gut to initiate autocatalytic activation. Our enzyme kinetics data demonstrates high potency and selectivity of the ppFhCL3 for its cognate FhCL3 enzyme, information that could be utilised to design inhibitors of parasite cathepsin L peptidases.

Fasciola hepatica-Derived Molecules as Regulators of the Host Immune Response

Helminths (worms) are one of the most successful organisms in nature given their ability to infect millions of humans and animals worldwide. Their success can be attributed to their ability to modulate the host immune response for their own benefit by releasing excretory-secretory (ES) products. Accordingly, ES products have been lauded as a potential source of immunomodulators/biotherapeutics for an array of inflammatory diseases. However, there is a significant lack of knowledge regarding the specific interactions between these products and cells of the immune response. Many different compounds have been identified within the helminth "secretome," including antioxidants, proteases, mucin-like peptides, as well as helminth defense molecules (HDMs), each with unique influences on the host inflammatory response. HDMs are a conserved group of proteins initially discovered in the secretome of the liver fluke, Fasciola hepatica. HDMs interact with cell membranes without cytotoxic effects and do not exert antimicrobial activity, suggesting that these peptides evolved specifically for immunomodulatory purposes. A peptide generated from the HDM sequence, termed FhHDM-1, has shown extensive anti-inflammatory abilities in clinically relevant models of diseases such as diabetes, multiple sclerosis, asthma, and acute lung injury, offering hope for the development of a new class of therapeutics. In this review, the current knowledge of host immunomodulation by a range of F. hepatica ES products, particularly FhHDM-1, will be discussed. Immune regulators, including HDMs, have been identified from other helminths and will also be outlined to broaden our understanding of the variety of effects these potent molecules exert on immune cells.

Fasciola hepatica serine protease inhibitor family (serpins): Purposely crafted for regulating host proteases

Serine protease inhibitors (serpins) regulate proteolytic events within diverse biological processes, including digestion, coagulation, inflammation and immune responses. The presence of serpins in Fasciola hepatica excretory-secretory products indicates that the parasite exploits these to regulate proteases encountered during its development within vertebrate hosts. Interrogation of the F. hepatica genome identified a multi-gene serpin family of seven members that has expanded by gene duplication and divergence to create an array of inhibitors with distinct specificities. We investigated the molecular properties and functions of two representatives, FhSrp1 and FhSrp2, highly expressed in the invasive newly excysted juvenile (NEJ). Consistent with marked differences in the reactive centre loop (RCL) that executes inhibitor-protease complexing, the two recombinant F. hepatica serpins displayed distinct inhibitory profiles against an array of mammalian serine proteases. In particular, rFhSrp1 efficiently inhibited kallikrein (K_i = 40 nM) whilst rFhSrp2 was a highly potent inhibitor of chymotrypsin (K_i = 0.07 nM). FhSrp1 and FhSrp2 are both expressed on the NEJ surface, predominantly around the oral and ventral suckers, suggesting that these inhibitors protect the parasites from the harmful proteolytic effects of host proteases, such as chymotrypsin, during invasion. Furthermore, the unusual inhibition of kallikrein suggests that rFhSrp1 modulates host responses such as inflammation and vascular permeability by interfering with the kallikrein-kinin system. A vaccine combination of rFhSrp1 and rFhSrp2 formulated in the adjuvant Montanide ISA 206VG elicited modest but non-significant protection against a challenge infection in a rat model, but did induce some protection against liver pathogenesis when compared to a control group and a group vaccinated with two well-studied vaccine candidates, F. hepatica cathepsin L2 and L3. This work highlights the importance of F. hepatica serpins to regulate host responses that enables parasite survival during infection and, coupled with the vaccine data, encourages future vaccine trials in ruminants.

Serpins are protease inhibitors that regulate various biological processes, including digestion, blood coagulation, inflammation and immune responses. The liver fluke, Fasciola hepatica, produces an array of inhibitors to regulate proteolytic enzymes they encounter during development within the mammalian host. In this study, we identified seven different serpins that have evolved to inhibit a range of host proteases. In particular, we characterized two representatives, FhSrp1 and FhSrp2, that we found highly expressed on the surface of the invasive newly excysted juvenile (NEJ), suggesting that they protect the parasites from harmful proteolytic effects during invasion. Contrasting inhibitory profiles were observed; while recombinant FhSrp1 inhibited kallikrein, recombinant FhSrp2 was a highly potent inhibitor of chymotrypsin. The unusual inhibition of kallikrein suggests that rFhSrp1 influences host responses such as inflammation and vascular permeability by interfering with the kallikrein-kinin system. Conversely, chymotrypsin is typically inhibited by trematode-specific serpins, implying a conserved mechanism to regulate digestive enzymes. The ability of the liver fluke serpin family to inhibit such an array of proteases highlights the importance of these inhibitors in parasite-host interactions and encourages future investigations of serpins as candidate anti-parasite vaccine targets for the control of fasciolosis in ruminants.

Schistosoma mansoni immunomodulatory molecule Sm16/SPO-1/SmSLP is a member of the trematode-specific helminth defence molecules (HDMs)

BACKGROUND

Sm16, also known as SPO-1 and SmSLP, is a low molecular weight protein (~16kDa) secreted by the digenean trematode parasite Schistosoma mansoni, one of the main causative agents of human schistosomiasis. The molecule is secreted from the acetabular gland of the cercariae during skin invasion and is believed to perform an immune-suppressive function to protect the invading parasite from innate immune cell attack.

METHODOLOGY/PRINCIPAL FINDINGS

We show that Sm16 homologues of the Schistosomatoidea family are phylogenetically related to the helminth defence molecule (HDM) family of immunomodulatory peptides first described in Fasciola hepatica. Interrogation of 69 helminths genomes demonstrates that HDMs are exclusive to trematode species. Structural analyses of Sm16 shows that it consists predominantly of an amphipathic alpha-helix, much like other HDMs. In S. mansoni, Sm16 is highly expressed in the cercariae and eggs but not in adult worms, suggesting that the molecule is of importance not only during skin invasion but also in the pro-inflammatory response to eggs in the liver tissues. Recombinant Sm16 and a synthetic form, Sm16 (34-117), bind to macrophages and are internalised into the endosomal/lysosomal system. Sm16 (34-117) elicited a weak pro-inflammatory response in macrophages in vitro but also suppressed the production of bacterial lipopolysaccharide (LPS)-induced inflammatory cytokines. Evaluation of the transcriptome of human macrophages treated with a synthetic Sm16 (34-117) demonstrates that the peptide exerts significant immunomodulatory effects alone, as well as in the presence of LPS. Pathways most significantly influenced by Sm16 (34-117) were those involving transcription factors peroxisome proliferator-activated receptor (PPAR) and liver X receptors/retinoid X receptor (LXR/RXR) which are intricately involved in regulating the cellular metabolism of macrophages (fatty acid, cholesterol and glucose homeostasis) and are central to inflammatory responses.

CONCLUSIONS/SIGNIFICANCE

These results offer new insights into the structure and function of a well-known immunomodulatory molecule, Sm16, and places it within a wider family of trematode-specific small molecule HDM immune-modulators with immuno-biotherapeutic possibilities.

Complex and dynamic transcriptional changes allow the helminth Fasciola gigantica to adjust to its intermediate snail and definitive mammalian hosts

BACKGROUND

The tropical liver fluke, Fasciola gigantica causes fasciolosis, an important disease of humans and livestock. We characterized dynamic transcriptional changes associated with the development of the parasite in its two hosts, the snail intermediate host and the mammalian definitive host.

RESULTS

Differential gene transcription analysis revealed 7445 unigenes transcribed by all F. gigantica lifecycle stages, while the majority (n = 50,977) exhibited stage-specific expression. Miracidia that hatch from eggs are highly transcriptionally active, expressing a myriad of genes involved in pheromone activity and metallopeptidase activity, consistent with snail host finding and invasion. Clonal expansion of rediae within the snail correlates with increased expression of genes associated with transcription, translation and repair. All intra-snail stages (miracidia, rediae and cercariae) require abundant cathepsin L peptidases for migration and feeding and, as indicated by their annotation, express genes putatively involved in the manipulation of snail innate immune responses. Cercariae emerge from the snail, settle on vegetation and become encysted metacercariae that are infectious to mammals; these remain metabolically active, transcribing genes involved in regulation of metabolism, synthesis of nucleotides, pH and endopeptidase activity to assure their longevity and survival on pasture. Dramatic growth and development following infection of the mammalian host are associated with high gene transcription of cell motility pathways, and transport and catabolism pathways. The intra-mammalian stages temporally regulate key families of genes including the cathepsin L and B proteases and their trans-activating peptidases, the legumains, during intense feeding and migration through the intestine, liver and bile ducts. While 70% of the F. gigantica transcripts share homology with genes expressed by the temperate liver fluke Fasciola hepatica, gene expression profiles of the most abundantly expressed transcripts within the comparable lifecycle stages implies significant species-specific gene regulation.

CONCLUSIONS

Transcriptional profiling of the F. gigantica lifecycle identified key metabolic, growth and developmental processes the parasite undergoes as it encounters vastly different environments within two very different hosts. Comparative analysis with F. hepatica provides insight into the similarities and differences of these parasites that diverged > 20 million years ago, crucial for the future development of novel control strategies against both species.

Sea snake cathelicidin (Hc-cath) exerts a protective effect in mouse models of lung inflammation and infection

We investigated the anti-inflammatory and antibacterial activities of Hc-cath, a cathelicidin peptide derived from the venom of the sea snake, Hydrophis cyanocyntus, using in vivo models of inflammation and infection. Hc-cath function was evaluated in in vitro, in vivo in the wax moth, Galleria mellonella, and in mouse models of intraperitoneal and respiratory Pseudomonas aeruginosa infection. Hc-Cath downregulated LPS-induced pro-inflammatory responses in macrophages and significantly improved the survival of P. aeruginosa infected G. mellonella over a 5-day period. We also demonstrated, for the first time, that Hc-cath can modulate inflammation in a mouse model of LPS-induced lung inflammation by significantly reducing the release of the pro-inflammatory cytokine and neutrophil chemoattractant, KC, resulting in reduced cellular infiltration into the lungs. Moreover, Hc-cath treatment significantly reduced the bacterial load and inflammation in mouse models of P. aeruginosa intraperitoneal and respiratory infection. The effect of Hc-cath in our studies highlights the potential to develop this peptide as a candidate for therapeutic development.

The cathepsin-like cysteine peptidases of trematodes of the genus Fasciola

Fasciolosis caused by trematode parasites of the genus Fasciola is a global disease of livestock, particularly cattle, sheep, water buffalo and goats. It is also a major human zoonosis with reports suggesting that 2.4-17 million people are infected worldwide, and 91.1 million people currently living at risk of infection. A unique feature of these worms is their reliance on a family of developmentally-regulated papain-like cysteine peptidases, termed cathepsins. These proteolytic enzymes play central roles in virulence, infection, tissue migration and modulation of host innate and adaptive immune responses. The availability of a Fasciola hepatica genome, and the exploitation of transcriptomic and proteomic technologies to probe parasite growth and development, has enlightened our understanding of the cathepsin-like cysteine peptidases. Here, we clarify the structure of the cathepsin-like cysteine peptidase families and, in this context, review the phylogenetics, structure, biochemistry and function of these enzymes in the host-parasite relationship.

Surface molecules of extracellular vesicles secreted by the helminth pathogen Fasciola hepatica direct their internalisation by host cells

Helminth parasites secrete extracellular vesicles (EVs) that can be internalised by host immune cells resulting in modulation of host immunity. While the molecular cargo of EVs have been characterised in many parasites, little is known about the surface-exposed molecules that participate in ligand-receptor interactions with the host cell surface to initiate vesicle docking and subsequent internalisation. Using a membrane-impermeable biotin reagent to capture proteins displayed on the outer membrane surface of two EV sub-populations (termed 15k and 120k EVs) released by adult F. hepatica, we describe 380 surface proteins including an array of virulence factors, membrane transport proteins and molecules involved in EV biogenesis/trafficking. Proteomics and immunohistochemical analysis show that the 120k EVs have an endosomal origin and may be released from the parasite via the protonephridial (excretory) system whilst the larger 15k EVs are released from the gastrodermal epithelial cells that line the fluke gut. A parallel lectin microarray strategy was used to profile the topology of major surface oligosaccharides of intact fluorogenically-labelled EVs as they would be displayed to the host. Lectin profiles corresponding to glycoconjugates exposed on the surface of the 15 K and 120K EV sub-populations are practically identical but are distinct from those of the parasite surface tegument, although all are predominated by high mannose sugars. We found that while the F. hepatica EVs were resistant to exo- and endo-glycosidases, the glyco-amidase PNGase F drastically remodelled the surface oligosaccharides and blocked the uptake of EVs by host macrophages. In contrast, pre-treatment with antibodies obtained from infected hosts, or purified antibodies raised against the extracellular domains of specific EV surface proteins (DM9-containing protein, CD63 receptor and myoferlin), significantly enhanced their cellular internalisation. This work highlights the diversity of EV biogenesis and trafficking pathways used by F. hepatica and sheds light on the molecular interaction between parasite EVs and host cells.

Over the last decade, it has become recognised that extracellular vesicles (EVs) are important mediators of communication by transferring molecular signals (including proteins, lipids, complex carbohydrates, mRNA, microRNA and other non-coding RNA species), between cells. Variously described as exosomes or microvesicles depending on their cellular origin and mode of biogenesis, EVs perform a variety of roles in the maintenance of normal physiology but also participate in pathological settings. EVs also play an important role in host-pathogen interactions, with recent work suggesting that they contribute to helminth immunomodulatory strategies. Here we have identified the proteins and sugars displayed on the outer surface of two sub-types of EVs released by the helminth pathogen Fasciola hepatica. We show that the proteins are antigenic and direct EV internalisation by host macrophages. Our study provides a better understanding of how parasite-derived EVs interact with host cells which is important for future development of therapeutics/vaccines that target this interface.

A secreted schistosome cathepsin B1 cysteine protease and acute schistosome infection induce a transient T helper 17 response

The natural history of schistosome infection in the mammalian host is determined by CD4⁺ T helper responses mounted against different parasite life cycle stages. A T helper 2 (T_H2) response to schistosome eggs is required for host survival and establishment of chronic infection. However, a T_H2 cell-derived cytokine also contributes to an immune milieu that is conducive to schistosome growth and development. Thus, the same responses that allow for host survival have been co-opted by schistosomes to facilitate parasite development and transmission, underscoring the significance of CD4⁺ T cell responses to both worms and eggs in the natural history of schistosome infection. Here we show that a cathepsin B1 cysteine protease secreted by schistosome worms not only induces T_H2 responses, but also T_H1 and T_H17 responses, by a mechanism that is dependent on the proteolytic activity of the enzyme. Further investigation revealed that, in addition to the expected T_H1 and T_H2 responses, acute schistosome infection also induces a transient T_H17 response that is rapidly down-regulated at the onset of oviposition. T_H17 responses are implicated in the development of severe egg-induced pathology. The regulation of worm-induced T_H17 responses during acute infection could therefore influence the expression of high and low pathology states as infection progresses.

Schistosomiasis, a neglected tropical disease caused by parasites of the genus Schistosoma, is prevalent throughout the developing world, with more than 230 million people infected. Left untreated, schistosome infection may cause relatively mild disease with some morbidity, or, in a minority of cases, result in severe pathology and death. These variable outcomes are recapitulated in animal models, where the natural history of schistosome infection is profoundly influenced by the responses of host CD4⁺ T helper cells. Type 2 CD4⁺ T cell (T_H2) responses, which allow for host survival by limiting pathology, have ironically also been co-opted by schistosomes to promote parasite development. On the other hand, T_H17 responses have been implicated in the development of severe pathology, in both experimentally infected animals and naturally infected humans. Here we show that a schistosome proteolytic enzyme (SmCB1), produced in the parasite gut and released into the bloodstream, induces both T_H2 and T_H17 responses by a mechanism that requires the enzyme’s inherent proteolytic activity. Further investigation revealed that acute schistosome infection also induces a transient T_H17 response that is rapidly down-regulated once parasite egg-laying commences. Regulation of T_H17 responses during early infection may help determine whether mild or severe pathology develops as the infection progresses.

Steered molecular dynamics simulations reveal critical residues for (un)binding of substrates, inhibitors and a product to the malarial M1 aminopeptidase

Malaria is a life-threatening disease spread by mosquitoes. Plasmodium falciparum M1 alanyl aminopeptidase (PfM1-AAP) is a promising target for the treatment of malaria. The recently solved crystal structures of PfM1-AAP revealed that the buried active site can be accessed through two channel openings: a short N-terminal channel with the length of 8 Å and a long C-terminal channel with the length of 30 Å. It is unclear, however, how substrates and inhibitors migrate to the active site and a product of cleavage leaves. Here, we study the molecular mechanism of substrate and inhibitor migration to the active site and the product release using steered molecular dynamics simulations. We identified a stepwise passage of substrates and inhibitors in the C-terminal channel of PfM1-AAP, involving (I) ligand recognition at the opening of the channel, (II) ionic translation to the 'water reservoir', (III) ligand reorientation in the 'water reservoir' and (IV) passage in a suitable conformation into the active site. Endorsed by enzymatic analysis of functional recombinant PfM1-AAP and mutagenesis studies, our novel ligand-residue binding network analysis has identified the functional residues controlling ligand migration within the C-terminal channel of PfM1-AAP. Furthermore, from unbinding simulations of the Arg product we propose a charge repulsion as the driving force to expel the product out from the N-terminal channel of PfM1-AAP. Our work paves the way towards the design of a novel class of PfM1-AAP inhibitors based on preventing substrate entry to the active site.

Cysteine proteases during larval migration and development of helminths in their final host

Neglected tropical diseases caused by metazoan parasites are major public health concerns, and therefore, new methods for their control and elimination are needed. Research over the last 25 years has revealed the vital contribution of cysteine proteases to invasion of and migration by (larval) helminth parasites through host tissues, in addition to their roles in embryogenesis, molting, egg hatching, and yolk degradation. Their central function to maintaining parasite survival in the host has made them prime intervention targets for novel drugs and vaccines. This review focuses on those helminth cysteine proteases that have been functionally characterized during the varied early stages of development in the human host and embryogenesis.

Cysteine proteases as digestive enzymes in parasitic helminths

We briefly review cysteine proteases (orthologs of mammalian cathepsins B, L, F, and C) that are expressed in flatworm and nematode parasites. Emphasis is placed on enzyme activities that have been functionally characterized, are associated with the parasite gut, and putatively contribute to degrading host proteins to absorbable nutrients [1–4]. Often, gut proteases are expressed as multigene families, as is the case with Fasciola [5] and Haemonchus [6], presumably expanding the range of substrates that can be degraded, not least during parasite migration through host tissues [5]. The application of the free-living planarian and Caenorhabditis elegans as investigative models for parasite cysteine proteases is discussed. Finally, because of their central nutritive contribution, targeting the component gut proteases with small-molecule chemical inhibitors and understanding their utility as vaccine candidates are active areas of research [7].

In silico analyses of protein glycosylating genes in the helminth Fasciola hepatica (liver fluke) predict protein-linked glycan simplicity and reveal temporally-dynamic expression profiles

Glycoproteins secreted by helminth parasites are immunogenic and represent appealing components of vaccine preparations. Our poor knowledge of the pathways that mediate protein glycosylation in parasitic flatworms hinders our understanding of how proteins are synthesised and modified, and our ability to target these pathways for parasite control. Here we provide the first detailed description of genes associated with protein glycosylation in a parasitic flatworm, focusing on the genome of the liver fluke (Fasciola hepatica), which is a globally important trematode parasite of humans and their livestock. Using 190 human sequences as search queries against currently available F. hepatica genomes, we identified 149 orthologues with putative roles in sugar uptake or nucleotide sugar synthesis, and an array of glycosyltransferase and glycosidase activities required for protein N- and O-glycosylation. We found appreciable duplication within these orthologues, describing just 87 non-redundant genes when paralogues were excluded. F. hepatica lacks many of the enzymes required to produce complex N- and O-linked glycans, which explains the genomic basis for the structurally simple glycans described by F. hepatica glycomic datasets, and predicts pervasive structural simplicity in the wider glycome. These data provide a foundation for functional genomic interrogation of these pathways with the view towards novel parasite intervention strategies.

Immune Mechanisms Involved in Schistosoma mansoni-Cathepsin B Vaccine Induced Protection in Mice

A vaccine against schistosomiasis would contribute to a long-lasting decrease in disease spectrum and transmission. Our previous protection studies in mice using Schistosoma mansoni Cathepsin B (Sm-Cathepsin B) resulted in 59 and 60% worm burden reduction with CpG oligodeoxynucleotides and Montanide ISA720 VG as adjuvants, respectively. While both formulations resulted in significant protection in a mouse model of schistosomiasis, the elicited immune responses differed. Therefore, in this study, we aimed to decipher the mechanisms involved in Sm-Cathepsin B vaccine-mediated protection. We performed in vitro killing assays using schistosomula stage parasites as targets for lung-derived leukocytes and serum obtained from mice immunized with Sm-Cathepsin B adjuvanted with either Montanide ISA 720 VG or CpG and from non-vaccinated controls. Lung cells and immune sera from the Sm-Cathepsin B + Montanide group induced the highest killing (63%) suggesting the importance of antibodies in cell-mediated parasite killing. By contrast, incubation with lung cells from Sm-Cathepsin B + CpG immunized animals induced significant parasite killing (53%) independent of the addition of immune serum. Significant parasite killing was also observed in the animals immunized with Sm-Cathepsin B alone (41%). For the Sm-Cathepsin B + Montanide group, the high level killing effect was lost after the depletion of CD4⁺ T cells or natural killer (NK) cells from the lung cell preparation. For the Sm-Cathepsin B + CpG group, high parasite killing was lost after CD8⁺ T cell depletion, and a reduction to 39% was observed upon depletion of NK cells. Finally, the parasite killing in the Sm-Cathepsin B alone group was lost after the depletion of CD4⁺ T cells. Our results demonstrate how the different Sm-Cathepsin B formulations influence the immune mechanisms involved in parasite killing and protection against schistosomiasis.

Low allelic diversity in vaccine candidates genes from different locations sustain hope for Fasciola hepatica immunization

Fasciola hepatica is a trematode parasite that causes fasciolosis in animals and humans. Fasciolosis is usually treated with triclabendazole, although drug-resistant parasites have been described in several geographical locations. An alternative to drug treatment would be the use of a vaccine, although vaccination studies that have been performed mainly in ruminants over the last 30 years, show high variability in the achieved protection and are not yet ready for commercialisation. Since F. hepatica exhibits a high degree of genomic polymorphism, variation in vaccine efficacy could be attributed, at least partially, to phenotypic differences in vaccine candidate sequences amongst parasites used in the challenge infections. To begin to address this issue, a collection of F. hepatica isolates from geographically dispersed regions, as well as parasites obtained from vaccination trials performed against a field isolate from Uruguay and the experimentally maintained South Gloucester isolate (Ridgeway Research, UK), were compiled to establish a F. hepatica Biobank. These collected isolates were used for the genetic analysis of several vaccine candidates that are important in host-parasite interactions and are the focus of the H2020 PARAGONE vaccine project (https://www.paragoneh2020.eu/), namely FhCL1, FhCL2, FhPrx, FhLAP and FhHDM. Our results show that F. hepatica exhibits a high level of conservation in the sequences encoding each of these proteins. The consequential low variability in these vaccine candidates amongst parasites from different geographical regions reinforces the idea that they would be suitable immunogens against liver fluke isolates worldwide.

Advances in Fasciola hepatica research using 'omics' technologies

The liver fluke Fasciola hepatica is an economically important pathogen of livestock worldwide, as well as being an important neglected zoonosis. Parasite control is reliant on the use of drugs, particularly triclabendazole, which is effective against multiple parasite stages. However, the spread of parasites resistant to triclabendazole has intensified the pursuit for novel control strategies. Emerging 'omics' technologies are helping advance our understanding of liver fluke biology, specifically the molecules that act at the host-parasite interface and are central to infection, virulence and long-term survival within the definitive host. This review discusses the technological sequencing advances that have facilitated the unbiased analysis of liver fluke biology, resulting in an extensive range of 'omics' datasets. In addition, we highlight the 'omics' studies of host responses to F. hepatica infection that, when combined with the parasite datasets, provide the opportunity for integrated analyses of host-parasite interactions. These extensive datasets will form the foundation for future in-depth analysis of F. hepatica biology and development, and the search for new drug or vaccine interventions.

Infection by the Helminth Parasite Fasciola hepatica Requires Rapid Regulation of Metabolic, Virulence, and Invasive Factors to Adjust to Its Mammalian Host

The parasite Fasciola hepatica infects a broad range of mammals with impunity. Following ingestion of parasites (metacercariae) by the host, newly excysted juveniles (NEJ) emerge from their cysts, rapidly penetrate the duodenal wall and migrate to the liver. Successful infection takes just a few hours and involves negotiating hurdles presented by host macromolecules, tissues and micro-environments, as well as the immune system. Here, transcriptome and proteome analysis of ex vivo F. hepatica metacercariae and NEJ reveal the rapidity and multitude of metabolic and developmental alterations that take place in order for the parasite to establish infection. We found that metacercariae despite being encased in a cyst are metabolically active, and primed for infection. Following excystment, NEJ expend vital energy stores and rapidly adjust their metabolic pathways to cope with their new and increasingly anaerobic environment. Temperature increases induce neoblast proliferation and the remarkable up-regulation of genes associated with growth and development. Cysteine proteases synthesized by gastrodermal cells are secreted to facilitate invasion and tissue degradation, and tegumental transporters, such as aquaporins, are varied to deal with osmotic/salinity changes. Major proteins of the total NEJ secretome include proteases, protease inhibitors and anti-oxidants, and an array of immunomodulators that likely disarm host innate immune effector cells. Thus, the challenges of infection by F. hepatica parasites are met by rapid metabolic and physiological adjustments that expedite tissue invasion and immune evasion; these changes facilitate parasite growth, development and maturation. Our molecular analysis of the critical processes involved in host invasion has identified key targets for future drug and vaccine strategies directed at preventing parasite infection.

Proteomic Analysis of Extracellular HMGB1 Identifies Binding Partners and Exposes Its Potential Role in Airway Epithelial Cell Homeostasis

The release of damage-associated molecular patterns (DAMPs) by airway epithelial cells is believed to play a crucial role in the initiation and development of chronic airway conditions such as asthma and chronic obstructive pulmonary disease (COPD). Intriguingly, the classic DAMP high-mobility group box-1 (HMGB1) is detected in the culture supernatant of airway epithelial cells under basal conditions, indicating a role for HMGB1 in the regulation of epithelial cellular and immune homeostasis. To gain contextual insight into the potential role of HMGB1 in airway epithelial cell homeostasis, we used the orthogonal and complementary methods of high-resolution clear native electrophoresis, immunoprecipitation, and pull-downs coupled to liquid chromatography-tandem mass spectrometry (LC-MS/MS) to profile HMGB1 and its binding partners in the culture supernatant of unstimulated airway epithelial cells. We found that HMGB1 presents exclusively as a protein complex under basal conditions. Moreover, protein network analysis performed on 185 binding proteins revealed 14 that directly associate with HMGB1: amyloid precursor protein, F-actin-capping protein subunit alpha-1 (CAPZA1), glyceraldehyde-3 phosphate dehydrogenase (GAPDH), ubiquitin, several members of the heat shock protein family (HSPA8, HSP90B1, HSP90AA1), XRCC5 and XRCC6, high mobility group A1 (HMGA1), histone 3 (H3F3B), the FACT (facilitates chromatin transcription) complex constituents SUPT1H and SSRP1, and heterogeneous ribonucleoprotein K (HNRNPK). These studies provide a new understanding of the extracellular functions of HMGB1 in cellular and immune homeostasis at the airway mucosal surface and could have implications for therapeutic targeting.

Immune signatures of pathogenesis in the peritoneal compartment during early infection of sheep with Fasciola hepatica

Immune signatures of sheep acutely-infected with Fasciola hepatica, an important pathogen of livestock and humans were analysed within the peritoneal compartment to investigate early infection. Within the peritoneum, F. hepatica antibodies coincided with an intense innate and adaptive cellular immune response, with infiltrating leukocytes and a marked eosinophilia (49%). However, while cytokine qPCR analysis revealed IL-10, IL-12, IL-13, IL-23 and TGFβ were elevated, these were not statistically different at 18 days post-infection compared to uninfected animals indicating that the immune response is muted and not yet skewed to a Th2 type response that is associated with chronic disease. Proteomic analysis of the peritoneal fluid identified infection-related proteins, including several structural proteins derived from the liver extracellular matrix, connective tissue and epithelium, and proteins related to the immune system. Periostin and vascular cell adhesion protein 1 (VCAM-1), molecules that mediate leukocyte infiltration and are associated with inflammatory disorders involving marked eosinophilia (e.g. asthma), were particularly elevated in the peritoneum. Immuno-histochemical studies indicated that the source of periostin and VCAM-1 was the inflamed sheep liver tissue. This study has revealed previously unknown aspects of the immunology and pathogenesis associated with acute fascioliasis in the peritoneum and liver.

The development of sexual stage malaria gametocytes in a Wave Bioreactor

Background

Blocking malaria gametocyte development in RBCs or their fertilization in the mosquito gut can prevent infection of the mosquito vector and passage of disease to the human host. A ‘transmission blocking’ strategy is a component of future malaria control. However, the lack of robust culture systems for producing large amounts of Plasmodium falciparum gametocytes has limited our understanding of sexual-stage malaria biology and made vaccine or chemotherapeutic discoveries more difficult.

Methods

The Wave Bioreactor^TM 20/50 EHT culture system was used to develop a convenient and low-maintenance protocol for inducing commitment of P. falciparum parasites to gametocytogenesis. Culture conditions were optimised to obtain mature stage V gametocytes within 2 weeks in a large-scale culture of up to a 1 l.

Results

We report a simple method for the induction of gametocytogenesis with N-acetylglucosamine (10 mM) within a Wave Bioreactor. By maintaining the culture for 14–16 days as many as 100 million gametocytes (stage V) were produced in a 1 l culture. Gametocytes isolated using magnetic activated cell sorting (MACS) columns were frozen in aliquots for storage. These were revitalised by thawing and shown to retain their ability to exflagellate and infect mosquitoes (Anopheles stephansi).

Conclusions

The production of gametocytes in the Wave Bioreactor under GMP-compliant conditions will not only facilitate cellular, developmental and molecular studies of gametocytes, but also the high-throughput screening for new anti-malarial drugs and, possibly, the development of whole-cell gametocyte or sporozoite-based vaccines.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2155-z) contains supplementary material, which is available to authorized users.

Recombinant vacuolar iron transporter family homologue PfVIT from human malaria-causing Plasmodium falciparum is a Fe2+/H+exchanger

Vacuolar iron transporters (VITs) are a poorly understood family of integral membrane proteins that can function in iron homeostasis via sequestration of labile Fe²⁺ into vacuolar compartments. Here we report on the heterologous overexpression and purification of PfVIT, a vacuolar iron transporter homologue from the human malaria-causing parasite Plasmodium falciparum. Use of synthetic, codon-optimised DNA enabled overexpression of functional PfVIT in the inner membrane of Escherichia coli which, in turn, conferred iron tolerance to the bacterial cells. Cells that expressed PfVIT had decreased levels of total cellular iron compared with cells that did not express the protein. Qualitative transport assays performed on inverted vesicles enriched with PfVIT revealed that the transporter catalysed Fe^2+/H⁺ exchange driven by the proton electrochemical gradient. Furthermore, the PfVIT transport function in this system did not require the presence of any Plasmodium-specific factor such as post-translational phosphorylation. PfVIT purified as a monomer and, as measured by intrinsic protein fluorescence quenching, bound Fe²⁺ in detergent solution with low micromolar affinity. This study of PfVIT provides material for future detailed biochemical, biophysical and structural studies to advance understanding of the vacuolar iron transporter family of membrane proteins from important human pathogens.

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

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

Screening of anti-mycobacterial compounds in a naturally infected zebrafish larvae model

OBJECTIVES

Mycobacterium tuberculosis is a deadly human pathogen that causes the lung disease TB. M. tuberculosis latently infects a third of the world's population, resulting in ∼1.5 million deaths per year. Due to the difficulties and expense of carrying out animal drug trials using M. tuberculosis and rodents, infections of the zebrafish Danio rerio with Mycobacterium marinum have become a useful surrogate. However, the infection methods described to date require specialized equipment and a high level of operator expertise.

METHODS

We investigated whether zebrafish larvae could be naturally infected with bioluminescently labelled M. marinum by immersion, and whether infected larvae could be used for rapid screening of anti-mycobacterial compounds using bioluminescence. We used rifampicin and a variety of nitroimidazole-based next-generation and experimental anti-mycobacterial drugs, selected for their wide range of potencies against M. tuberculosis, to validate this model for anti-mycobacterial drug discovery.

RESULTS

We observed that five of the six treatments (rifampicin, pretomanid, delamanid, SN30488 and SN30527) significantly reduced the bioluminescent signal from M. marinum within naturally infected zebrafish larvae. Importantly, these same five treatments also retarded the growth of M. tuberculosis in vitro. In contrast, only three of the six treatments tested (rifampicin, delamanid and SN30527) retarded the growth of M. marinum in vitro.

CONCLUSIONS

We have demonstrated that zebrafish larvae naturally infected with bioluminescent M. marinum M can be used for the rapid screening of anti-mycobacterial compounds with readily available equipment and limited expertise. The result is an assay that can be carried out by a wide variety of laboratories for minimal cost and without high levels of zebrafish expertise.

The immune modulatory peptide FhHDM-1 secreted by the helminth Fasciola hepatica prevents NLRP3 inflammasome activation by inhibiting endolysosomal acidification in macrophages

The NLRP3 inflammasome is a multimeric protein complex that controls the production of IL-1β, a cytokine that influences the development of both innate and adaptive immune responses. Helminth parasites secrete molecules that interact with innate immune cells, modulating their activity to ultimately determine the phenotype of differentiated T cells, thus creating an immune environment that is conducive to sustaining chronic infection. We show that one of these molecules, FhHDM-1, a cathelicidin-like peptide secreted by the helminth parasite, Fasciola hepatica, inhibits the activation of the NLRP3 inflammasome resulting in reduced secretion of IL-1β by macrophages. FhHDM-1 had no effect on the synthesis of pro-IL-1β. Rather, the inhibitory effect was associated with the capacity of the peptide to prevent acidification of the endolysosome. The activation of cathepsin B protease by lysosomal destabilization was prevented in FhHDM-1-treated macrophages. By contrast, peptide derivatives of FhHDM-1 that did not alter the lysosomal pH did not inhibit secretion of IL-1β. We propose a novel immune modulatory strategy used by F. hepatica, whereby secretion of the FhHDM-1 peptide impairs the activation of NLRP3 by lysosomal cathepsin B protease, which prevents the downstream production of IL-1β and the development of protective T helper 1 type immune responses that are detrimental to parasite survival.-Alvarado, R., To, J., Lund, M. E., Pinar, A., Mansell, A., Robinson, M. W., O'Brien, B. A., Dalton, J. P., Donnelly, S. The immune modulatory peptide FhHDM-1 secreted by the helminth Fasciola hepatica prevents NLRP3 inflammasome activation by inhibiting endolysosomal acidification in macrophages.

Fasciola hepatica Surface Tegument: Glycoproteins at the Interface of Parasite and Host

Fasciola hepatica, commonly known as liver fluke, is a trematode that causes Fasciolosis in ruminants and humans. The outer tegumental coat of F. hepatica (FhTeg) is a complex metabolically active biological matrix that is continually exposed to the host immune system and therefore makes a good vaccine target. F. hepatica tegumental coat is highly glycosylated and helminth-derived immunogenic oligosaccharide motifs and glycoproteins are currently being investigated as novel vaccine candidates. This report presents the first systematic characterization of FhTeg glycosylation using lectin microarrays to characterize carbohydrates motifs present, and lectin histochemistry to localize these on the F. hepatica tegument. We discovered that FhTeg glycoproteins are predominantly oligomannose oligosaccharides that are expressed on the spines, suckers and tegumental coat of F. hepatica and lectin blot analysis confirmed the abundance of N- glycosylated proteins. Although some oligosaccharides are widely distributed on the fluke surface other subsets are restricted to distinct anatomical regions. We selectively enriched for FhTeg mannosylated glycoprotein subsets using lectin affinity chromatography and identified 369 proteins by mass spectrometric analysis. Among these proteins are a number of potential vaccine candidates with known immune modulatory properties including proteases, protease inhibitors, paramyosin, Venom Allergen-like II, Enolase and two proteins, nardilysin and TRIL, that have not been previously associated with F. hepatica. Furthermore, we provide a comprehensive insight regarding the putative glycosylation of FhTeg components that could highlight the importance of further studies examining glycoconjugates in host-parasite interactions in the context of F. hepatica infection and the development of an effective vaccine.

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

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

A prospective view of animal and human Fasciolosis

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

A vaccine consisting of Schistosoma mansoni cathepsin B formulated in Montanide ISA 720 VG induces high level protection against murine schistosomiasis

Background

Schistosomiasis is the most important human helminth infection due to its impact on public health. The clinical manifestations are chronic and significantly decrease an individual’s quality of life. Infected individuals suffer from long-term organ pathologies including fibrosis which eventually leads to organ failure. The development of a vaccine against this parasitic disease would contribute to a long-lasting decrease in disease spectrum and transmission.

Method

Our group has chosen Schistosoma mansoni (Sm) cathepsin B, a peptidase involved in parasite feeding, as a prospective vaccine candidate. Our experimental formulation consisted of recombinant Sm-cathepsin B formulated in Montanide ISA 720 VG, a squalene based adjuvant containing a mannide mono-oleate emulsifier. Parasitological burden was assessed by determining adult worm, hepatic egg, and intestinal egg numbers in each mouse. Serum was used in ELISAs to evaluate production of antigen-specific antibodies, and isolated splenocytes were stimulated with the antigen for the analysis of cytokine secretion levels.

Results

The Sm-cathepsin B and Montanide formulation conferred protection against a challenge infection by significantly reducing all forms of parasitological burdens. Worm burden, hepatic egg burden and intestinal egg burden were decreased by 60 %, 62 %, and 56 %, respectively in immunized animals compared to controls (P = 0.0002, P < 0.0001, P = 0.0009, respectively). Immunizations with the vaccine elicited robust production of Sm-cathepsin B specific antibodies (endpoint titers = 122,880). Both antigen-specific IgG1 and IgG2c titers were observed, with the former having more elevated titers. Furthermore, splenocytes isolated from the immunized animals, compared to control animals, secreted higher levels of key Th1 cytokines, IFN-γ, IL-12, and TNF-α, as well as the Th2 cytokines IL-5 and IL-4 when stimulated with recombinant Sm-cathepsin B. The Th17 cytokine IL-17, the chemokine CCL5, and the growth factor GM-CSF were also significantly increased in the immunized animals compared to the controls.

Conclusion

The formulation tested in this study was able to significantly reduce all forms of parasite burden, stimulate robust production of antigen-specific antibodies, and induce a mixed Th1/Th2 response. These results highlight the potential of Sm-cathepsin B/Montanide ISA 720 VG as a vaccine candidate against schistosomiasis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-016-1444-z) contains supplementary material, which is available to authorized users.

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

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

Induction of Protective Immune Responses Against Schistosomiasis haematobium in Hamsters and Mice Using Cysteine Peptidase-Based Vaccine

One of the major lessons we learned from the radiation-attenuated cercariae vaccine studies is that protective immunity against schistosomiasis is dependent on the induction of T helper (Th)1-/Th2-related immune responses. Since most schistosome larval and adult-worm-derived molecules used for vaccination uniformly induce a polarized Th1 response, it was essential to include a type 2 immune response-inducing molecule, such as cysteine peptidases, in the vaccine formula. Here, we demonstrate that a single subcutaneous injection of Syrian hamsters with 200 μg active papain, 1 h before percutaneous exposure to 150 cercariae of Schistosoma haematobium, led to highly significant (P < 0.005) reduction of >50% in worm burden and worm egg counts in intestine. Immunization of hamsters with 20 μg recombinant glyceraldehyde 3-phosphate dehydrogenase (rSG3PDH) and 20 μg 2-cys peroxiredoxin-derived peptide in a multiple antigen peptide construct (PRX MAP) together with papain (20 μg/hamster), as adjuvant led to considerable (64%) protection against challenge S. haematobium infection, similar to the levels reported with irradiated cercariae. Cysteine peptidases-based vaccination was also effective in protecting outbred mice against a percutaneous challenge infection with S. haematobium cercariae. In two experiments, a mixture of Schistosoma mansoni cathepsin B1 (SmCB1) and Fasciola hepatica cathepsin L1 (FhCL1) led to highly significant (P < 0.005) reduction of 70% in challenge S. haematobium worm burden and 60% reduction in liver egg counts. Mice vaccinated with SmCB1/FhCL1/rSG3PDH mixture and challenged with S. haematobium cercariae 3 weeks after the second immunization displayed highly significant (P < 0.005) reduction of 72% in challenge worm burden and no eggs in liver of 8-10 mice/group, as compared to unimmunized mice, associated with production of a mixture of type 1- and type 2-related cytokines and antibody responses.

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

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