First insights into the autophagy machinery of adult Schistosoma mansoni

Autophagy in hepatic progenitor cells modulates exosomal miRNAs to inhibit liver fibrosis in schistosomiasis

Schistosoma infection is one of the major causes of liver fibrosis. Emerging roles of hepatic progenitor cells (HPCs) in the pathogenesis of liver fibrosis have been identified. Nevertheless, the precise mechanism underlying the role of HPCs in liver fibrosis in schistosomiasis remains unclear. This study examined how autophagy in HPCs affects schistosomiasis-induced liver fibrosis by modulating exosomal miRNAs. The activation of HPCs was verified by immunohistochemistry (IHC) and immunofluorescence (IF) staining in fibrotic liver from patients and mice with Schistosoma japonicum infection. By coculturing HPCs with hepatic stellate cells (HSCs) and assessing the autophagy level in HPCs by proteomic analysis and in vitro phenotypic assays, we found that impaired autophagy degradation in these activated HPCs was mediated by lysosomal dysfunction. Blocking autophagy by the autophagy inhibitor chloroquine (CQ) significantly diminished liver fibrosis and granuloma formation in S. japonicum-infected mice. HPC-secreted extracellular vehicles (EVs) were further isolated and studied by miRNA sequencing. miR-1306-3p, miR-493-3p, and miR-34a-5p were identified, and their distribution into EVs was inhibited due to impaired autophagy in HPCs, which contributed to suppressing HSC activation. In conclusion, we showed that the altered autophagy process upon HPC activation may prevent liver fibrosis by modulating exosomal miRNA release and inhibiting HSC activation in schistosomiasis. Targeting the autophagy degradation process may be a therapeutic strategy for liver fibrosis during Schistosoma infection.

Salmonella Typhimurium expressing chromosomally integrated Schistosoma mansoni Cathepsin B protects against schistosomiasis in mice

Schistosomiasis threatens hundreds of millions of people worldwide. The larval stage of Schistosoma mansoni migrates through the lung and adult worms reside adjacent to the colonic mucosa. Several candidate vaccines are in preclinical development, but none is designed to elicit both systemic and mucosal responses. We have repurposed an attenuated Salmonella enterica Typhimurium strain (YS1646) to express Cathepsin B (CatB), a digestive enzyme important for the juvenile and adult stages of the S. mansoni life cycle. Previous studies have demonstrated the prophylactic and therapeutic efficacy of our plasmid-based vaccine. Here, we have generated chromosomally integrated (CI) YS1646 strains that express CatB to produce a viable candidate vaccine for eventual human use (stability, no antibiotic resistance). 6-8-week-old C57BL/6 mice were vaccinated in a multimodal oral (PO) and intramuscular (IM) regimen, and then sacrificed 3 weeks later. The PO + IM group had significantly higher anti-CatB IgG titers with greater avidity and mounted significant intestinal anti-CatB IgA responses compared to PBS control mice (all P < 0.0001). Multimodal vaccination generated balanced T_H1/T_H2 humoral and cellular immune responses. Production of IFNγ by both CD4⁺ and CD8⁺ T cells was confirmed by flow cytometry (P < 0.0001 & P < 0.01). Multimodal vaccination reduced worm burden by 80.4%, hepatic egg counts by 75.2%, and intestinal egg burden by 78.4% (all P < 0.0001). A stable and safe vaccine that has both prophylactic and therapeutic activity would be ideal for use in conjunction with praziquantel mass treatment campaigns.

The anticancer drug imatinib induces autophagy in Schistosoma mansoni

Schistosomiasis, caused by schistosome parasites, is a neglected tropical disease affecting humans and animals. There is no vaccine available yet, and fear of upcoming resistance against the only widely used drug, praziquantel, is omnipresent. Previously, we showed that imatinib (Gleevec), an anticancer drug, affected schistosome physiology and caused the death of adult Schistosoma mansoni in vitro. Here, we present the first known evidence that one effect of imatinib is the induction of autophagy in S. mansoni. Furthermore, worms co-treated with imatinib and bafilomycin A1, a late-phase autophagy inhibitor, reversed imatinib-induced autophagy and its antischistosomal effects as revealed by phenotypic and molecular analyses.

Rhesus macaques self-curing from a schistosome infection can display complete immunity to challenge

The rhesus macaque provides a unique model of acquired immunity against schistosomes, which afflict >200 million people worldwide. By monitoring bloodstream levels of parasite-gut-derived antigen, we show that from week 10 onwards an established infection with Schistosoma mansoni is cleared in an exponential manner, eliciting resistance to reinfection. Secondary challenge at week 42 demonstrates that protection is strong in all animals and complete in some. Antibody profiles suggest that antigens mediating protection are the released products of developing schistosomula. In culture they are killed by addition of rhesus plasma, collected from week 8 post-infection onwards, and even more efficiently with post-challenge plasma. Furthermore, cultured schistosomula lose chromatin activating marks at the transcription start site of genes related to worm development and show decreased expression of genes related to lysosomes and lytic vacuoles involved with autophagy. Overall, our results indicate that enhanced antibody responses against the challenge migrating larvae mediate the naturally acquired protective immunity and will inform the route to an effective vaccine.

To date there is only one single drug with modest efficacy and no vaccine available to protect from schistosomiasis. Here, Amaral et al. characterize the self-cure process of rhesus macaques following primary infection and secondary challenge with Schistosoma mansoni to inform future vaccine development studies.