Transcriptomic analysis supports a role for the nervous system in regulating growth and development of Fasciola hepatica juveniles

In vitro co-culture of Fasciola hepatica newly excysted juveniles (NEJs) with 3D HepG2 spheroids permits novel investigation of host-parasite interactions

Fasciola hepatica, or liver fluke, causes fasciolosis in humans and livestock. Following ingestion of vegetation contaminated with encysted parasites, metacercariae, newly excysted juveniles (NEJ) excyst in the small intestine and cross the intestinal wall. After penetrating the liver, the parasite begins an intra-parenchymal migratory and feeding phase that not only drives their rapid growth and development but also causes extensive haemorrhaging and immune pathology. Studies on infection are hindered by the difficulty in accessing these microscopic juvenile parasites in vivo. Thus, a simple and scalable in vitro culture system for parasite development is needed. Here, we find that two-dimensional (2D) culture systems using cell monolayers support NEJ growth to a limited extent. By contrast, co-culture of F. hepatica NEJ with HepG2-derived 3D spheroids, or "mini-livers," that more closely mimic the physiology and microenvironment of in vivo liver tissue, promoted NEJ survival, growth, and development. NEJ grazed on the peripheral cells of the spheroids, and they released temporally regulated digestive cysteine proteases, FhCL3, and FhCL1/2, similar to in vivo parasites. The 3D co-culture induced development of the NEJ gut and body musculature, and stimulated the tegument to elaborate spines and a variety of surface sensory/tango/chemoreceptor papillae (termed S1, S2, and S3); these were especially pronounced around the oral and ventral suckers that sense host chemical cues and secure the parasite in tissue. HepG2 3D spheroid/parasite co-culture methodologies should accelerate investigations into the understanding of F. hepatica NEJ developmental biology and studies on host-parasite interactions, and streamline the search for new anti-parasite interventions.

Wnt/β-catenin signalling underpins juvenile Fasciola hepatica growth and development

Infection by the liver fluke, Fasciola hepatica, places a substantial burden on the global agri-food industry and poses a significant threat to human health in endemic regions. Widespread resistance to a limited arsenal of chemotherapeutics, including the frontline flukicide triclabendazole (TCBZ), renders F. hepatica control unsustainable and accentuates the need for novel therapeutic target discovery. A key facet of F. hepatica biology is a population of specialised stem cells which drive growth and development - their dysregulation is hypothesised to represent an appealing avenue for control. The exploitation of this system as a therapeutic target is impeded by a lack of understanding of the molecular mechanisms underpinning F. hepatica growth and development. Wnt signalling pathways govern a myriad of stem cell processes during embryogenesis and drive tumorigenesis in adult tissues in animals. Here, we identify five putative Wnt ligands and five Frizzled receptors in liver fluke transcriptomic datasets and find that Wnt/β-catenin signalling is most active in juveniles, the most pathogenic life stage. FISH-mediated transcript localisation revealed partitioning of the five Wnt ligands, with each displaying a distinct expression pattern, consistent with each Wnt regulating the development of different cell/tissue types. The silencing of each individual Wnt or Frizzled gene yielded significant reductions in juvenile worm growth and, in select cases, blunted the proliferation of neoblast-like cells. Notably, silencing FhCTNNB1, the key effector of the Wnt/β-catenin signal cascade led to aberrant development of the neuromuscular system which ultimately proved lethal - the first report of a lethal RNAi-induced phenotype in F. hepatica. The absence of any discernible phenotypes following the silencing of the inhibitory Wnt/β-catenin destruction complex components is consistent with low destruction complex activity in rapidly developing juvenile worms, corroborates transcriptomic expression profiles and underscores the importance of Wnt signalling as a key molecular driver of growth and development in early-stage juvenile fluke. The putative pharmacological inhibition of Wnt/β-catenin signalling using commercially available inhibitors phenocopied RNAi results and provides impetus for drug repurposing. Taken together, these data functionally and chemically validate the targeting of Wnt signalling as a novel strategy to undermine the pathogenicity of juvenile F. hepatica.

Spatial transcriptomics of a parasitic flatworm provides a molecular map of drug targets and drug resistance genes

The spatial organization of gene expression dictates tissue functions in multicellular parasites. Here, we present the spatial transcriptome of a parasitic flatworm, the common liver fluke Fasciola hepatica. We identify gene expression profiles and marker genes for eight distinct tissues and validate the latter by in situ hybridization. To demonstrate the power of our spatial atlas, we focus on genes with substantial medical importance, including vaccine candidates (Ly6 proteins) and drug resistance genes (glutathione S-transferases, ABC transporters). Several of these genes exhibit unique expression patterns, indicating tissue-specific biological functions. Notably, the prioritization of tegumental protein kinases identifies a PKCβ, for which small-molecule targeting causes parasite death. Our comprehensive gene expression map provides unprecedented molecular insights into the organ systems of this complex parasitic organism, serving as a valuable tool for both basic and applied research.

V. Q, Sun L, Yang Y, Liu M, Liu X, Li C, Tang B. Revealing the dynamic whole transcriptome landscape of Clonorchis sinensis: Insights into the regulatory roles of noncoding RNAs and microtubule-related genes in development

Clonorchis sinensis is a significant zoonotic food-borne parasite that causes a range of hepatobiliary diseases, which in severe cases can even lead to cholangiocarcinoma. To explore new diagnostic and treatment strategies, the dynamic RNA regulatory processes across different developmental stages of C. sinensis were analyzed by using whole-transcriptome sequencing. The chromosomal-level genome of C. sinensis was used for sequence alignment and annotation. In this study, we identified a total of 59,103 RNAs in the whole genome, including 2,384 miRNAs, 25,459 mRNAs, 27,564 lncRNAs and 3,696 circRNAs. Differential expression analysis identified 6,556 differentially expressed mRNAs, 2,231 lncRNAs, 877 miRNAs and 20 circRNAs at different developmental stages. Functional enrichment analysis highlighted the critical role of microtubule-related biological processes in the growth and development of C. sinensis. And coexpression analysis revealed 97 lncRNAs and 85 circRNAs that were coexpressed with 42 differentially expressed mRNAs that associated with microtubules at different developmental stages of C. sinensis. The expression of the microtubule-related genes dynein light chain 2 (DLC2) and dynein light chain 4 (DLC4) increased with C. sinensis development, and DLC2/4 could be inhibited by albendazole. Finally, by constructing competing endogenous RNA (ceRNA) networks, the lncRNA-miRNA-mRNA and circRNA-miRNA-mRNA regulatory relationships were constructed, and the ceRNA networks of MSTRG.14258.5-novel_miR_2287-newGene_28215 and MSTRG.14258.5-novel_miR_2216-CSKR_109340 were verified. This study suggests, through whole transcriptome sequencing, that the context of microtubule regulation may play an essential role in the development and growth of C. sinensis.

Neoblast-like stem cells of Fasciola hepatica

The common liver fluke (Fasciola hepatica) causes the disease fasciolosis, which results in considerable losses within the global agri-food industry. There is a shortfall in the drugs that are effective against both the adult and juvenile life stages within the mammalian host, such that new drug targets are needed. Over the last decade the stem cells of parasitic flatworms have emerged as reservoirs of putative novel targets due to their role in development and homeostasis, including at host-parasite interfaces. Here, we investigate and characterise the proliferating cells that underpin development in F. hepatica. We provide evidence that these cells are capable of self-renewal, differentiation, and are sensitive to ionising radiation- all attributes of neoblasts in other flatworms. Changes in cell proliferation were also noted during the early stages of in vitro juvenile growth/development (around four to seven days post excystment), which coincided with a marked reduction in the nuclear area of proliferating cells. Furthermore, we generated transcriptomes from worms following irradiation-based ablation of neoblasts, identifying 124 significantly downregulated transcripts, including known stem cell markers such as fgfrA and plk1. Sixty-eight of these had homologues associated with neoblast-like cells in Schistosoma mansoni. Finally, RNA interference mediated knockdown of histone h2b (a marker of proliferating cells), ablated neoblast-like cells and impaired worm development in vitro. In summary, this work demonstrates that the proliferating cells of F. hepatica are equivalent to neoblasts of other flatworm species and demonstrate that they may serve as attractive targets for novel anthelmintics.

Trematode Genomics and Proteomics

Trematode infections stand out as one of the frequently overlooked tropical diseases, despite their wide global prevalence and remarkable capacity to parasitize diverse host species and tissues. Furthermore, these parasites hold significant socio-economic, medical, veterinary and agricultural implications. Over the past decades, substantial strides have been taken to bridge the information gap concerning various "omic" tools, such as proteomics and genomics, in this field. In this edition of the book, we highlight recent progress in genomics and proteomics concerning trematodes with a particular focus on the advances made in the past 5 years. Additionally, we present insights into cutting-edge technologies employed in studying trematode biology and shed light on the available resources for exploring the molecular facets of this particular group of parasitic helminths.

Form and Function in the Digenea, with an Emphasis on Host-Parasite and Parasite-Bacteria Interactions

This review covers the general aspects of the anatomy and physiology of the major body systems in digenetic trematodes, with an emphasis on new knowledge of the area acquired since the publication of the second edition of this book in 2019. In addition to reporting on key recent advances in the morphology and physiology of tegumentary, sensory, neuromuscular, digestive, excretory, and reproductive systems, and their roles in host-parasite interactions, this edition includes a section discussing the known and putative roles of bacteria in digenean biology and physiology. Furthermore, a brief discussion of current trends in the development of novel treatment and control strategies based on a better understanding of the trematode body systems and associated bacteria is provided.

Neuronal gene expression in two generations of the marine parasitic worm, Cryptocotyle lingua

Trematodes, or flukes, undergo intricate anatomical and behavioral transformations during their life cycle, yet the functional changes in their nervous system remain poorly understood. We investigated the molecular basis of nervous system function in Cryptocotyle lingua, a species of relevance for fisheries. Transcriptomic analysis revealed a streamlined molecular toolkit with the absence of key signaling pathways and ion channels. Notably, we observed the loss of nitric oxide synthase across the Platyhelminthes. Furthermore, we identified upregulated neuronal genes in dispersal larvae, including those involved in aminergic pathways, synaptic vesicle trafficking, TRPA channels, and surprisingly nitric oxide receptors. Using neuronal markers and in situ hybridization, we hypothesized their functional relevance to larval adaptations and host-finding strategies. Additionally, employing a behavior quantification toolkit, we assessed cercaria motility, facilitating further investigations into the behavior and physiology of parasitic flatworms. This study enhances our understanding of trematode neurobiology and provides insights for targeted antiparasitic strategies.

Discovery of long non-coding RNAs in the liver fluke, Fasciola hepatica

Long non-coding (lnc)RNAs are a class of eukaryotic RNA that do not code for protein and are linked with transcriptional regulation, amongst a myriad of other functions. Using a custom in silico pipeline we have identified 6,436 putative lncRNA transcripts in the liver fluke parasite, Fasciola hepatica, none of which are conserved with those previously described from Schistosoma mansoni. F. hepatica lncRNAs were distinct from F. hepatica mRNAs in transcript length, coding probability, exon/intron composition, expression patterns, and genome distribution. RNA-Seq and digital droplet PCR measurements demonstrated developmentally regulated expression of lncRNAs between intra-mammalian life stages; a similar proportion of lncRNAs (14.2%) and mRNAs (12.8%) were differentially expressed (p<0.001), supporting a functional role for lncRNAs in F. hepatica life stages. While most lncRNAs (81%) were intergenic, we identified some that overlapped protein coding loci in antisense (13%) or intronic (6%) configurations. We found no unequivocal evidence for correlated developmental expression within positionally correlated lncRNA:mRNA pairs, but global co-expression analysis identified five lncRNA that were inversely co-regulated with 89 mRNAs, including a large number of functionally essential proteases. The presence of micro (mi)RNA binding sites in 3135 lncRNAs indicates the potential for miRNA-based post-transcriptional regulation of lncRNA, and/or their function as competing endogenous (ce)RNAs. The same annotation pipeline identified 24,141 putative lncRNAs in F. gigantica. This first description of lncRNAs in F. hepatica provides an avenue to future functional and comparative genomics studies that will provide a new perspective on a poorly understood aspect of parasite biology.

Fasciola hepatica juveniles interact with the host fibrinolytic system as a potential early-stage invasion mechanism

BACKGROUND

The trematode Fasciola hepatica is the most widespread causative agent of fasciolosis, a parasitic disease that mainly affects humans and ruminants worldwide. During F. hepatica infection, newly excysted juveniles (FhNEJ) emerge in the duodenum of the mammalian host and migrate towards their definitive location, the intra-hepatic biliary ducts. Understanding how F. hepatica traverses the intestinal wall and migrates towards the liver is pivotal for the development of more successful strategies against fasciolosis. The central enzyme of the mammalian fibrinolytic system is plasmin, a serine protease whose functions are exploited by a number of parasite species owing to its broad spectrum of substrates, including components of tissue extracellular matrices. The aim of the present work is to understand whether FhNEJ co-opt the functions of their host fibrinolytic system as a mechanism to facilitate trans-intestinal migration.

METHODOLOGY/PRINCIPAL FINDINGS

A tegument-enriched antigenic extract of FhNEJ (FhNEJ-Teg) was obtained in vitro, and its capability to bind the zymogen plasminogen (PLG) and enhance its conversion to the active protease, plasmin, were analyzed by a combination of enzyme-linked immunosorbent, chromogenic and immunofluorescence assays. Additionally, PLG-binding proteins in FhNEJ-Teg were identified by bidimensional electrophoresis coupled to mass spectrometry analysis, and the interactions were validated using FhNEJ recombinant proteins.

CONCLUSIONS/SIGNIFICANCE

Our results show that FhNEJ-Teg contains proteins that bind PLG and stimulate its activation to plasmin, which could facilitate the traversal of the intestinal wall by FhNEJ and contribute to the successful establishment of the parasite within its mammalian host. Altogether, our findings contribute to a better understanding of host-parasite relationships during early fasciolosis and may be exploited from a pharmacological and/or immunological perspective for the development of treatment and control strategies against this global disease.