Abstract
Exosomes are small vesicles of endocytic origin, which are released into the extracellular environment and mediate a variety of physiological and pathological conditions. Here we show that Schistosoma mansoni releases exosome-like vesicles in vitro. Vesicles were purified from culture medium by sucrose gradient fractionation and fractions containing vesicles verified by western blot analyses and electron microscopy. Proteomic analyses of exosomal contents unveiled 130 schistosome proteins. Among these proteins are common exosomal markers such as heat shock proteins, energy-generating enzymes, cytoskeletal proteins, and others. In addition, the schistosome extracellular vesicles contain proteins of potential importance for host-parasite interaction, notably peptidases, signaling proteins, cell adhesion proteins (e.g., integrins) and previously described vaccine candidates, including glutathione-S-transferase (GST), tetraspanin (TSP-2) and calpain. S. mansoni exosomes also contain 143 microRNAs (miRNA), of which 25 are present at high levels, including miRNAs detected in sera of infected hosts. Quantitative PCR analysis confirmed the presence of schistosome-derived miRNAs in exosomes purified from infected mouse sera. The results provide evidence of vesicle-mediated secretion in these parasites and suggest that schistosome-derived exosomes could play important roles in host-parasite interactions and could be a useful tool in the development of vaccines and therapeutics.
Highlights
Schistosomiasis is a major parasitic disease, affecting >200 million people in 74 countries, the majority in sub-Saharan Africa[1]
exosome-like vesicles (ELVs) were initially purified from culture medium by differential centrifugation, followed by filtration and sucrose density ultracentrifugation (Fig. 1) to establish the sucrose concentration required for the sedimentation and enrichment of the S. mansoni ELVs
We focused on the abundant S. mansoni exosomal miRNAs from the RNA seq analysis and used a stem-loop RT method[45] combined with TaqMan probe-based qPCR to improve specificity
Summary
Schistosomiasis is a major parasitic disease, affecting >200 million people in 74 countries, the majority in sub-Saharan Africa[1]. Parasitic worms secrete microRNAs (miRNA)[15,16,17,18,19], which could play important roles in modulating host immune responses. Secreted miRNAs are increasingly recognized as mediators of cell communication[20,21] and their regulatory roles in the immune system are well established[22] Despite these advances, and the considerable efforts made to identify schistosome ESPs, very little is known about the mechanisms by which these molecules are released. Leishmania exosomes may be the principal mechanism by which the parasite delivers virulence factors to the host cell[25] These studies clearly implicate EVs as important mediators of the host-parasite interaction and underscore the need for further research into their mode of action
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