Heat shock proteins in the human parasite Schistosoma mansoni

Heat shock proteins (HSPs) are evolutionarily conserved proteins, often produced by cells in response to hostile environmental conditions, that are vital to organism homeostasis. Because schistosomes encounter changes in their local environment during their life cycle and development, HSPs might play a vital role in helping the parasite survive. This thesis reports the first detailed molecular analysis of these important proteins and their tissue expression in the human parasitic blood fluke, Schistosoma mansoni, one of the causative agents of human schistosomiasis. Using bioinformatic tools, 55 HSPs were identified across five HSP families (HSPs 10, 40, 60, 70 and 90); high conservation of HSP sequences was apparent across S. mansoni, Schistosoma haematobium and Schistosoma japonicum, with S. haematobium HSPs showing greater similarity to S. mansoni. For S. mansoni, differential HSP gene expression was evident across the various parasite life stages, supporting varying roles for the HSPs in the different stages, and suggesting that they might confer some degree of protection during life stage transitions. Using confocal laser scanning microscopy, HSPs were demonstrated in the tegument, cephalic ganglia, tubercles, testes, ovaries as well as other important organs in cercariae, somules, adult male and female worms. Focusing further on HSP 90, the HSP 90 inhibitors 17-AAG and EC-144 profoundly reduced the viability of S. mansoni somules, restricted somule development, inhibited daily egg output from female worms and, reduced stem cell proliferation in somules and adult worms. Furthermore, suppression of HSP 90 by RNA interference attenuated somule survival and caused a decrease in somule size during development to later developmental stages. Decreased stem cell activity was also demonstrated following 17-AAG or EC-144 treatment in the planarian, Schmidtea mediterranea, a free-living flatworm model organism for stem cell studies. The involvement of HSP 90 in certain protein kinase signalling pathways was confirmed by the decreased levels of phosphorylated Akt, ERK1/2 and p38 MAPK in 24 h somules following treatment with 17-AAG and EC-144. To our knowledge, this study is the first to report the schistosomicidal activity of EC-144. This detailed analysis highlights the fascinating biology of S. mansoni HSPs and their likely importance to schistosome function, offering a valuable and novel framework for future physiological investigations into the roles of HSPs in schistosomes and their evaluation as anti schistosomal agents.