Cysteine proteases as digestive enzymes in parasitic helminths

Caffrey, Conor R.; Goupil, Louise S.; Rebello, Karina M.; Dalton, John P.; Smith, David W.

doi:10.1371/journal.pntd.0005840

Cited by 84 publications

(68 citation statements)

References 151 publications

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“…As for them, the major attention has been paid especially to the NO-related inhibition of schistosomula aerobic metabolism [11,13,15,16]. Other mechanisms, including the effect of NO on cysteine peptidases, have not been evaluated yet even though these enzymes play a crucial role in schistosome biology [77,79]. This might be due to the generally accepted view that the host immunity against schistosomes shifts from initial Th1 (targeting schistosomula aerobic metabolism by NO) to Th2/Treg which are not associated with NO production harmful to adults [80,81].…”

Section: Discussionmentioning

confidence: 99%

Nitric oxide debilitates the neuropathogenic schistosome Trichobilharzia regenti in mice, partly by inhibiting its vital peptidases

et al. 2020

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Background: Avian schistosomes, the causative agents of human cercarial dermatitis (or swimmer's itch), die in mammals but the mechanisms responsible for parasite elimination are unknown. Here we examined the role of reactive nitrogen species, nitric oxide (NO) and peroxynitrite, in the immune response of mice experimentally infected with Trichobilharzia regenti, a model species of avian schistosomes remarkable for its neuropathogenicity. Methods: Inducible NO synthase (iNOS) was localized by immunohistochemistry in the skin and the spinal cord of mice infected by T. regenti. The impact of iNOS inhibition by aminoguanidine on parasite burden and growth was then evaluated in vivo. The vulnerability of T. regenti schistosomula to NO and peroxynitrite was assessed in vitro by viability assays and electron microscopy. Additionally, the effect of NO on the activity of T. regenti peptidases was tested using a fluorogenic substrate. Results: iNOS was detected around the parasites in the epidermis 8 h post-infection and also in the spinal cord 3 days post-infection (dpi). Inhibition of iNOS resulted in slower parasite growth 3 dpi, but the opposite effect was observed 7 dpi. At the latter time point, moderately increased parasite burden was also noticed in the spinal cord. In vitro, NO did not impair the parasites, but inhibited the activity of T. regenti cathepsins B1.1 and B2, the peptidases essential for parasite migration and digestion. Peroxynitrite severely damaged the surface tegument of the parasites and decreased their viability in vitro, but rather did not participate in parasite clearance in vivo. Conclusions: Reactive nitrogen species, specifically NO, do not directly kill T. regenti in mice. NO promotes the parasite growth soon after penetration (3 dpi), but prevents it later (7 dpi) when also suspends the parasite migration in the CNS. NO-related disruption of the parasite proteolytic machinery is partly responsible for this effect.

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Section: Discussionmentioning

confidence: 99%

Nitric oxide debilitates the neuropathogenic schistosome Trichobilharzia regenti in mice, partly by inhibiting its vital peptidases

et al. 2020

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“…These data suggest a decrease in the blood ingestion and digestion capacity of the hnf4(RNAi) animals but does not address the mechanism of any digestive defects. Because we measured a decrease in the expression of many proteolytic enzymes in our RNAseq experiment (Supplementary Table 2), we next asked whether there was a loss in the hnf4(RNAi) parasites of those cysteine (cathepsin) proteases that contribute to hemoglobin digestion 31 . Accordingly, we measured the cathepsin activity of lysates from control(RNAi) and hnf4(RNAi) parasites using the fluorogenic peptidyl substrate, z-Phe-Arg-AMC (Z-FR-AMC) 32 .…”

Section: Figmentioning

confidence: 99%

A single-cell RNAseq atlas of the pathogenic stage of Schistosoma mansoni identifies a key regulator of blood feeding

Wendt

Zhao

Chen

et al. 2020

Preprint

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Schistosomiasis is an ancient and chronic neglected tropical disease that infects over 240 million people and kills over 200,000 of the world’s poorest people every year1, 2. There are no vaccines and because there is only one drug available, the need for new therapeutics is great. The causative agents of this disease are flatworm parasites that dwell inside the host’s circulation, often for decades, where they feed on blood and lay eggs which are primarily responsible for disease pathology. As metazoans comprised of multiple tissue types, understanding the schistosome’s tissues on a molecular level and their functions during what can be decades of successful parasitism could suggest novel therapeutic strategies. Here, we employ single-cell RNAseq to characterize 43,642 cells from the pathogenic (adult) stage of the schistosome lifecycle. From these data, we characterize 68 molecularly distinct cell populations that comprise nearly all tissues described morphologically, including the nervous and reproductive systems. We further uncover a lineage of somatic stem cells responsible for producing and maintaining the parasite’s gut – the primary tissue responsible for digestion of host blood. Finally, we show that a homologue of hepatocyte nuclear factor 4 (hnf4) is expressed in this gut lineage and required for gut maintenance, blood feeding and inducing egg-associated pathology in vivo. Together, the data highlight the utility of this single-cell RNAseq atlas to understand schistosome biology and identify potential therapeutic interventions.

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“…Limiting parasite access to essential nutrients by blocking protein turnover has become a major focus of anti-parasite drug development (33)(34)(35). In P. falciparum, the hydrolysis of hemoglobin involves the cooperative action of two classes of proteases.…”

Section: Mcdonald Et Almentioning

confidence: 99%

Toxoplasma Cathepsin Protease B and Aspartyl Protease 1 Are Dispensable for Endolysosomal Protein Digestion

McDonald

Smith

Cristina

et al. 2020

mSphere

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The lysosome-like vacuolar compartment (VAC) is a major site of proteolysis in the intracellular parasite Toxoplasma gondii. Previous studies have shown that genetic ablation of a VAC-residing cysteine protease, cathepsin protease L (CPL), resulted in the accumulation of undigested protein in the VAC and loss of parasite viability during the chronic stage of infection. However, since the maturation of another VAC localizing protease, cathepsin protease B (CPB), is dependent on CPL, it remained unknown whether these defects result directly from ablation of CPL or indirectly from a lack of CPB maturation. Likewise, although a previously described cathepsin D-like aspartyl protease 1 (ASP1) could also play a role in proteolysis, its definitive residence and function in the Toxoplasma endolysosomal system were not well defined. Here, we demonstrate that CPB is not necessary for protein turnover in the VAC and that CPB-deficient parasites have normal growth and viability in both the acute and chronic stages of infection. We also show that ASP1 depends on CPL for correct maturation, and it resides in the T. gondii VAC, where, similar to CPB, it plays a dispensable role in protein digestion. Taken together with previous work, our findings suggest that CPL is the dominant protease in a hierarchy of proteolytic enzymes within the VAC. This unusual lack of redundancy for CPL in T. gondii makes it a single exploitable target for disrupting chronic toxoplasmosis. IMPORTANCE Roughly one-third of the human population is chronically infected with the intracellular single-celled parasite Toxoplasma gondii, but little is known about how this organism persists inside people. Previous research suggested that a parasite proteolytic enzyme, termed cathepsin protease L, is important for Toxoplasma persistence; however, it remained possible that other associated proteolytic enzymes could also be involved in the long-term survival of the parasite during infection. Here, we show that two proteolytic enzymes associated with cathepsin protease L play dispensable roles and are dependent on cathepsin L to reach maturity, which differs from the corresponding enzymes in humans. These findings establish a divergent hierarchy of proteases and help focus attention principally on cathepsin protease L as a potential target for interrupting Toxoplasma chronic infection.

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Cysteine proteases as digestive enzymes in parasitic helminths

Cited by 84 publications

References 151 publications

Nitric oxide debilitates the neuropathogenic schistosome Trichobilharzia regenti in mice, partly by inhibiting its vital peptidases

Nitric oxide debilitates the neuropathogenic schistosome Trichobilharzia regenti in mice, partly by inhibiting its vital peptidases

A single-cell RNAseq atlas of the pathogenic stage of Schistosoma mansoni identifies a key regulator of blood feeding

Toxoplasma Cathepsin Protease B and Aspartyl Protease 1 Are Dispensable for Endolysosomal Protein Digestion

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