Characterising the complexity of endocannabinoid signalling pathways in parasitic helminths

Abstract

Parasitic helminths represent a significant threat to human, animal and plant health, serving as the causative agents of several Neglected Tropical Diseases and economically important livestock infections. Over-reliance on a limited portfolio of frontline anthelmintics is exacerbating the development of parasite drug resistance, therefore identifying, and validating novel anti- parasite chemotherapeutics is essential. To identify and validate appealing novel drug targets, a robust understanding of the functional significance of chemotherapeutically unexploited facets of parasitic helminth biology is required. The endocannabinoid signalling (ECS) pathway is a significant area of interest in mammalian medicine, offering attractive treatment options for a variety of conditions including anorexia, obesity, schizophrenia, and cardiac disease. Comparatively, our understanding of the helminth ECS pathway is significantly limited. Available data are primarily derived from the model free-living nematode Caenorhabditis elegans where the ECS pathway appears to modulate several key aspects of neurobiology (including motility, lifespan, fertility, growth, and axon regeneration). In addition, understanding of flatworm ECS pathways is sparse, with only a handful of studies demonstrating the presence of EC ligands and associated-pathway enzymes however, the complexity and conservation of the flatworm ECS system remains almost entirely uncharacterised. This study: (a) employed an in silico bioinformatics pipeline to examine the conservation, expression and phylogenetic relationships of EC-effectors in phylum Nematoda and phylum Platyhelminthes; (b) translated in situ hybridisation approaches to the model animal parasitic nematodes Strongyloides ratti and Strongyloides stercoralis to facilitate future EC-effector localisation efforts and, (c) exploited CRISPR/cas-9 mediated genome editing in S. stercoralis for mutagenesis of the putative EC-GPCR npr-19. These studies demonstrate that (i) helminth ECS pathways exhibit increased complexity in comparison to vertebrate ECS pathways; (ii) EC-effectors exhibit broad pan-phylum conservation in nematodes and flatworms; (iii) flatworms encode a novel, putative, cannabinoid-like receptor denoted here as FwCB1/2; (iv) EC-effectors are expressed in therapeutically relevant helminth life stages, including infective larvae, suggesting that ECS pathways may be involved in key parasite behaviours; (v) EC-GPCR knockout mutants are achievable in S. stercoralis via CRISPR-mediated targeted mutagenesis. Collectively, these data advance our understanding of ECS pathway complexity in helminths and will inform the identification and validation of putative novel drug targets in parasitic helminths.

Thesis is embargoed until 31 December 2024.

Date of Award	Dec 2023
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Northern Ireland Department for the Economy
Supervisor	Louise Atkinson (Supervisor), Angela Mousley (Supervisor) & Aaron Maule (Supervisor)