Understanding growth and development in the liver fluke, Fasciola hepatica

: exposing new targets for improved parasite control

Abstract

The liver fluke, Fasciola hepatica, exerts a significant disease burden on ruminant livestock worldwide and is a causative agent of fascioliasis, a neglected tropical zoonosis. Increasing reports of flukicide resistance threatens to undermine F. hepatica control and accentuates the need for both improved diagnostics and novel therapeutic target discovery. Chapter 2 exploited F. hepatica eggs to demonstrate the utility of egg-derived data in the diagnosis of resistance. The WMicroTracker bioassay platform shows promise as an automated, high throughput egg hatch assay. Parallels were also uncovered between the neoblast-like stem cells of eggs and pathogenic juvenile fluke. F. hepatica growth, development and virulence are driven by the proliferation of neoblast-like cells, such that their dysregulation represents an attractive avenue for control. Chapters 3 and 4 exploited available genomic/transcriptomic datasets and an in vitro culture platform to identify and functionally interrogate molecular signalling pathways underpinning growth, development and cell cycle events in growing juveniles. Wnt signalling was found to be conserved in fluke, with both fluorescence in situ hybridisation and RNA interference (RNAi)-induced gene silencing demonstrating the vital roles played by Wnt pathway components in the growth/development of diverse cell/tissue types. Silencing a Fhβ-catenin uncovered a key role for this gene in neuromuscular development and survival, exposing the first gene to be associated with an RNAi-induced lethal phenotype in F. hepatica. “Pro-survival” signalling pathway components were found to be essential in the regulation of the cell cycle, governing the delicate balance between cell proliferation and apoptosis. Indeed, silencing select components profoundly reduced growth, dysregulated neoblast-like cell proliferation, increased apoptosis and proved fatal. The involvement of such pathways in tumourigenesis provides impetus for the repurposing of anti-cancer drugs as novel flukicides. Collectively, these data indicate that targeting developmental pathways represents a novel strategy for F. hepatica control.