Characterization of the autophagy machinery in Schistosoma mansoni, a parasite of public health relevance
Schistosomiasis is caused by dioecious schistosomes of the genus Schistosoma and is a neglected tropical disease of global importance for human and animal health. Praziquantel represents the only widely used drug to combat schistosomiasis. Due to concerns of developing drug resistance, the search for novel drug and vaccine candidates represents a ... feasible approach to fight schistosomiasis. As a first part, my work focused on autophagy-related genes which, due to highevolutionary conservation, are potential regulators of autophagy. I identified seven autophagy genes (Beclin, Ambra1, Vps34, LC3B, DRAM, DAP1) in S. mansoni by in silico analyses and investigated the influence of in vitro culture conditions on the mRNA transcriptional level of these autophagy genes in male and female adult parasites based on quantitative real-time PCR. Among the autophagy-associated genes, some exhibited sex-dependent expression patterns. For example, the death-associated protein DAP1 in S. mansoni was found to be highly expressed in females compared to males. The opposite applied to the damage-regulated autophagy modulator DRAM. In addition, the effect of in vitro culture conditions significantly changed the mRNA expression level of DAP1 only in female S. mansoni. The conversion of LC3B-I into LC3B-II, a marker for autophagic flux, was increased by rapamycin and blocked by bafilomycin A1 (BA1) treatment of parasites as observed by western blot analyses. Furthermore, all tested autophagy inhibitors, BA1, wortmannin, and spautin-1 affected worm viability and egg production. All inhibitors drastically influenced the intestinal and gonadal morphology as shown by confocal laser scanning microscopy (CLSM). As a second part, I observed an anticancer drug, imatinib drastically affected intestinal morphology and caused the death of adult worms at 50 μM or higher concentrations within 3-4 days in vitro (already published). Adult parasites were co-treated with imatinib and BA1. I identified a significant increase of LC3B protein following imatinib treatment. Of note, the drastic effects induced by imatinib on pairing stability, egg production, gut dilatation were mitigated by BA1. Furthermore, the mRNA levels of cathepsins, genes predominantly expressed in the schistosome gut, were reversed upon BA1 treatment in imatinib-treated male parasites. These results provided a possible explanation for the deleterious gut phenotype caused by imatinib, which might in part be explained by autophagy induction. In general, my results indicated that autophagy regulation in S. mansoni represents not only a defense mechanism regulating cellular homeostasis, but when disrupted by chemical inhibition, can affect parasite viability and reproduction.