Treatment of human schistosomiasis relies mainly on one drug, praziquantel, which raises concerns for drug resistance, therefore there is urgent need to better understand schistosome biology to identify molecular targets for the development of novel therapeutics. Heat shock proteins (HSPs) are evolutionarily conserved stress response proteins that play an important role in a variety of cellular processes essential to cell survival. Schistosomes are exposed to strikingly different environmental conditions, especially during cercarial to schistosomulum (somule) transition which involves increase in temperature and salt concentration. It is therefore likely that the parasite triggers a cellular response that involves the augmented expression of HSPs. However, a thorough analysis of HSPs in schistosomes and their importance to parasite homeostasis has not been reported.
Here, a bioinformatic analysis was carried out to identify HSP family (HSP 10, 40, 60, 70, and 90) members present in Schistosoma mansoni using human HSPs as query; a total of 47 HSPs were identified across the five HSP families in S. mansoni. Comparison with those seen in free-living flatworms and other Schistosoma species, including S. japonicum and S. haematobium, revealed that HSP members in each of the families were broadly similar in all eight schistosome species analysed. However, a greater number of HSPs were observed in the free-living flatworms. Comparative analysis of quantitative normalised data on HSP gene expression revealed differential HSP expression in the various life stages of the parasite with most HSPs being highly expressed in the miracidium and sporocysts and few in the somule and adult worm. The in-situ distribution of HSPs in S. mansoni was determined using immunofluorescence and confocal microscopy which revealed that HSPs localised mainly in the tegument, sub-tegument, acetabulum and, in some cases, in the cephalic ganglia and the head-tail junction of 3 h and 24 h in vitro transformed somules. In adult S. mansoni, HSP 10 and HSP 90 were localised in the female ovary, and male testes and tubercles, whereas HSP 40, HSP 60 and HSP 70 were mainly localised in the tegument and tubercles. These findings provide a framework for our further work on schistosome HSPs that aims to study their importance to schistosome growth and survival.
