Non_coding_extracellular_RNA_signatures_of_the_cestode_parasite_Echinococcus_multilocularis

Extracellular RNAs (ex-RNAs) are secreted by cells through different means that may involve association with proteins, lipoproteins or extracellular vesicles (EV). In the context of parasitism, ex-RNAs represent new and exciting communication intermediaries with promising potential as novel biomarkers. In the last years, it was shown that helminth parasites secrete ex-RNAs, however, most works have mainly focused on small RNA secretion mediated by EV. In this work, we have characterised the ex-RNA profile secreted in vitro by Echinococcus multilocularis metacestodes. The cestodes of the genus Echinococcus are the aetiological agents of echinococcosis or hydatid disease, a neglected zoonotic disease with global distribution. In this way, we have used high throughput RNA-sequencing together with RT-qPCR to characterise the ex-RNA profile secreted towards the extra- and intra-parasite milieus in EV-enriched and EV-depleted fractions. We show that a polarized secretion of small RNAs takes place, with microRNAs mainly secreted to the extra-parasite milieu and rRNA- and tRNA-derived sequences secreted to the intra-parasite milieu. In addition, we show by nanoparticle tracking analyses that viable metacestodes secrete EV mainly towards the hydatid fluid, however, the number of nanoparticles in culture medium and hydatid fluid increases > 10-fold when metacestodes show signs of tegument impairment. Interestingly, we confirm the presence of host miRNAs in the intra-parasite milieu, implying their internalization and transport through the tegument towards the hydatid fluid. Finally, our assessment of the detecion of Echinococcus miRNAs in patients samples by RT-qPCR rendered negative results suggesting the tested miRNAs may not be good biomarkers for this disease. A comprehensive study of the secretion mechanisms throughout the life cycle of these parasites will help to understand parasite interaction with the host and also, improve current diagnostic tools.