Search

The protozoan parasites, Theileria annulata and T. parva are unique amongst intracellular eukaryotic pathogens as they induce a transformation‐like phenotype in their bovine host cell. T. annulata causes tropical theileriosis, which is frequently fatal, with infected leukocytes becoming metastatic and forming foci in multiple organs resulting in destruction of the lymphoid system. Exosomes, a sub‐set of extracellular vesicles (EV), are critical in metastatic progression in many cancers. Here we characterised the cargo of EV from a control bovine lymphosarcoma cell line (BL20) and BL20 infected with T. annulata (TBL20) by comparative mass spectrometry and miRNA profiling (data available via ProteomeXchange, identifier PXD010713 and NCBI GEO, accession number GSE118456, respectively). Ingenuity Pathway Analysis that many infection‐associated proteins essential to migration and extracellular matrix digestion were upregulated in EV from TBL20 cells compared to BL20 controls. An altered repertoire of host miRNA, many with known roles in tumor and/or infection biology was also observed. Focusing on the tumor suppressor miRNA, bta‐miR‐181a and bta‐miR‐181b, we identified putative mRNA targets and confirmed the interaction of bta‐miR181a with icam‐1. We propose that EV and their miRNA cargo play an important role in the manipulation of the host cell phenotype and the pathobiology of Theileria infection.

Resistance to anthelmintic drugs is a major problem in the global fight against parasitic nematodes infecting humans and animals. While previous studies have identified mutations in drug target genes in resistant parasites, changes in the expression levels of both targets and transporters have also been reported. The mechanisms underlying these changes in gene expression are unresolved. Here, we take a novel approach to this problem by investigating the role of small regulatory RNAs in drug resistant strains of the important parasite Haemonchus contortus. microRNAs (miRNAs) are small (22 nt) non-coding RNAs that regulate gene expression by binding predominantly to the 3′ UTR of mRNAs. Changes in miRNA expression have been implicated in drug resistance in a variety of tumor cells. In this study, we focused on two geographically distinct ivermectin resistant strains of H. contortus and two lines generated by multiple rounds of backcrossing between susceptible and resistant parents, with ivermectin selection. All four resistant strains showed significantly increased expression of a single miRNA, hco-miR-9551, compared to the susceptible strain. This same miRNA is also upregulated in a multi-drug-resistant strain of the related nematode Teladorsagia circumcincta. hco-miR-9551 is enriched in female worms, is likely to be located on the X chromosome and is restricted to clade V parasitic nematodes. Genes containing predicted binding sites for hco-miR-9551 were identified computationally and refined based on differential expression in a transcriptomic dataset prepared from the same drug resistant and susceptible strains. This analysis identified three putative target mRNAs, one of which, a CHAC domain containing protein, is located in a region of the H. contortus genome introgressed from the resistant parent. hco-miR-9551 was shown to interact with the 3′ UTR of this gene by dual luciferase assay. This study is the first to suggest a role for miRNAs and the genes they regulate in drug resistant parasitic nematodes. miR-9551 also has potential as a biomarker of resistance in different nematode species.

Ivermectin is one of the most important drugs in veterinary and human medicine for the control of parasitic infection and was the joint focus of the 2015 Nobel Prize in Physiology or Medicine, some 35 years after its remarkable discovery. Although best described for its activity on glutamate-gated chloride channels in parasitic nematodes, understanding of its mode of action remains incomplete. In the field of veterinary medicine, resistance to ivermectin is now widespread, but the mechanisms underlying resistance are unresolved. Here we discuss the history of this versatile drug and its use in global health. Based on recent studies in a variety of systems, we question whether ivermectin could have additional modes of action on parasitic nematodes.

HSP90 chaperones are essential regulators of cellular function, as they ensure the appropriate conformation of multiple key client proteins. Four HSP90 isoforms were identified in the protozoan parasite Theileria annulata. Partial characterization was undertaken for three and localization confirmed for cytoplasmic (TA12105), endoplasmic reticulum (TA06470), and apicoplast (TA10720) forms. ATPase activity and binding to the HSP90 inhibitor geldanamycin were demonstrated for recombinant TA12105, and all three native forms could be isolated to varying extents by binding to geldanamycin beads. Because it is essential, HSP90 is considered a potential therapeutic drug target. Resistance to the only specific Theileriacidal drug is increasing, and one challenge for design of drugs that target the parasite is to limit the effect on the host. An in vitro cell culture system that allows comparison between uninfected bovine cells and the T. annulata‐infected counterpart was utilized to test the effects of geldanamycin and the derivative 17‐AAG. T. annulata‐infected cells had greater tolerance to geldanamycin than uninfected cells yet exhibited significantly more sensitivity to 17‐AAG. These findings suggest that parasite HSP90 isoform(s) can alter the drug sensitivity of infected host cells and that members of the Theileria HSP90 family are potential targets worthy of further investigation.

SUMMARYNematodes are amongst the most successful and abundant organisms on the planet with approximately 30 000 species described, although the actual number of species is estimated to be one million or more. Despite sharing a relatively simple and invariant body plan, there is considerable diversity within the phylum. Nematodes have evolved to colonize most ecological niches, and can be free-living or can parasitize plants or animals to the detriment of the host organism. In this review we consider the role of heat shock protein 90 (Hsp90) in the nematode life cycle. We describe studies on Hsp90 in the free-living nematodeCaenorhabditis elegansand comparative work on the parasitic speciesBrugia pahangi, and consider whether a dependence upon Hsp90 can be exploited for the control of parasitic species.

Novel drugs are required for the elimination of infections caused by filarial worms, as most commonly used drugs largely target the microfilariae or first stage larvae of these infections. Previous studies, conducted in vitro, have shown that inhibition of Hsp90 kills adult Brugia pahangi. As numerous small molecule inhibitors of Hsp90 have been developed for use in cancer chemotherapy, we tested the activity of several novel Hsp90 inhibitors in a fluorescence polarization assay and against microfilariae and adult worms of Brugia in vitro. The results from all three assays correlated reasonably well and one particular compound, NVP-AUY922, was shown to be particularly active, inhibiting Mf output from female worms at concentrations as low as 5.0 nanomolar after 6 days exposure to drug. NVP-AUY922 was also active on adult worms after a short 24 h exposure to drug. Based on these in vitro data, NVP-AUY922 was tested in vivo in a mouse model and was shown to significantly reduce the recovery of both adult worms and microfilariae. These studies provide proof of principle that the repurposing of currently available Hsp90 inhibitors may have potential for the development of novel agents with macrofilaricidal properties.

Lymphatic filarial worms are mosquito borne parasites which cause chronic disease in humans. Infection is characterized by proliferative suppression of T cells in the host and a skewing of the immune response, away from an IFN-gamma producing Th1 response, towards a Th2 or regulatory phenotype, with production of IL-4 and IL-10. In this study, a mouse model was used to investigate the role of the infective form of the parasite (the third stage larvae, L3) in regulating immune responses. BALB/c mice were infected by the subcutaneous route to mimic the natural transmission of the parasite, and immune responses generated by the L3 were analysed. Experiments carried out in the intact BALB/c mouse showed that infection with L3 results in increased IL-4, IL-10 and IL-5 with no IL-2 or IFN-gamma, a similar situation to that observed in infected humans. In order to investigate the key components in this skewing of the immune response, experiments were carried out using IL-4-/- mice. IL-4 was shown to have a role in down-regulating Th1 responses in wild type mice, as knock-out animals produced elevated levels of IL-2 and IFN-gamma. However these mice still had the capacity to produce IL-5, IL-13 and IL-10, suggesting that although IL-4 is an important Th2 cytokine, it may be dispensable in the initiation of such a response. In addition, reduced levels of proliferation of CD4+ and B220+ cells were observed in infected IL-4-/- mice. Despite elevated levels of IFN-gamma, this reduction in proliferation was not associated with increased production of NO, and neutralizing IFN-gamma itself did not restore proliferative responses. Addition of rIL-4 to cultures of splenocytes from these mice had a mild effect but did not result in a significant increase in proliferation. Treatment of splenocytes from intact mice with anti-IL-10 MAb in vitro resulted in increased levels of IL-2 and IFN-gamma, but no significant effect on Ag-specific proliferation was observed. However, when mice were treated with an anti-IL-10R MAb the opposite effect was seen, with a significant increase in levels of proliferation and no alteration in cytokines. When examined by FACS it was shown that CD4+ cells were the major population which expanded during IL-10R blockade. In addition, CD4+ cells were found to be the major source of IL-10 post-infection with L3, suggesting these cells may modulate their own proliferation, or perhaps these cells were of a regulatory nature. Experiments were also carried out to determine the effect of natural transmission on host immune responses. L3 were administered via syringe inoculation or via mosquito transmission. Splenocytes from mice infected via syringe inoculation had an increased capacity to produce cytokines and displayed higher levels of proliferation. Further experiments demonstrated that cytokine and proliferative responses were not dose- dependant therefore there may be factors within mosquito saliva which down-regulate immune responses in the mouse model.

Graphical abstract, Highlights • MicroRNAs and siRNAs in helminth post-transcriptional gene regulation are reviewed. • Many parasitic helminth miRNAs are unique and developmentally expressed. • miRNAs released by parasites have diagnostic potential, particularly for filarial and schistosome spp. • Parasite and host miRNAs may regulate immune responses. • Improvements to siRNA-mediated gene silencing are important for functional genomics., Over the last decade microRNAs (miRNAs) and small interfering RNAs (siRNAs) have emerged as important regulators of post-transcriptional gene expression. miRNAs are short, non-coding RNAs that regulate a variety of processes including cancer, organ development and immune function. This class of small RNAs bind with partial complementarity to their target mRNA sequences, most often in the 3′UTR, to negatively regulate gene expression. In parasitic helminths, miRNAs are being increasingly studied for their potential roles in development and host-parasite interactions. The availability of genome data, combined with small RNA sequencing, has paved the way to profile miRNAs expressed at particular developmental stages for many parasitic helminths. While some miRNAs are conserved across species, others appear to be unique to specific parasites, suggesting important roles in adaptation and survival in the host environment. Some miRNAs are released from parasites, in exosomes or in protein complexes, and the potential effects of these on host immune function are being increasingly studied. In addition, release of miRNAs from schistosome and filarial parasites into host plasma can be exploited for the development of specific and sensitive diagnostic biomarkers of infection. Interfering with miRNA function, as well as silencing key components of the pathways they regulate, will progress our understanding of parasite development and provide a novel approach to therapeutic control. RNA interference (RNAi) by siRNAs has proven to be inconsistent in parasitic nematodes. However, the recent successes reported for schistosome and liver fluke RNAi, encourage further efforts to enhance delivery of RNA and improve in vitro culture systems and assays to monitor phenotypic effects in nematodes. These improvements are important for the establishment of reliable functional genomic platforms for novel drug and vaccine development. In this review we focus on the important roles of miRNAs and siRNAs in post-transcriptional gene regulation in veterinary parasitic helminths and the potential value of these in parasite diagnosis and control.