Toxoplasma depends on lysosomal consumption of autophagosomes for persistent infection

Abstract

Globally, nearly 2 billion people are infected with the intracellular protozoan Toxoplasma gondii1. This persistent infection can cause severe disease in immunocompromised people and is epidemiologically linked to major mental illnesses2 and cognitive impairment3. There are currently no options for curing this infection. The lack of effective therapeutics is due partly to a poor understanding of the essential pathways that maintain long-term infection. Although it is known that Toxoplasma replicates slowly within intracellular cysts demarcated with a cyst wall, precisely how it sustains itself and remodels organelles in this niche is unknown. Here, we identify a key role for proteolysis within the parasite lysosomal organelle (the vacuolar compartment or VAC) in turnover of autophagosomes and persistence during neural infection. We found that disrupting a VAC-localized cysteine protease compromised VAC digestive function and markedly reduced chronic infection. Death of parasites lacking the VAC protease was preceded by accumulation of undigested autophagosomes in the parasite cytoplasm. These findings suggest an unanticipated function for parasite lysosomal degradation in chronic infection, and identify an intrinsic role for autophagy in the T. gondii parasite and its close relatives. This work also identifies a key element of Toxoplasma persistence and suggests that VAC proteolysis is a prospective target for pharmacological development.

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Figure 1: VAC proteolytic activity is required for Toxoplasma viability and persistence in vitro.
Figure 2: VAC proteolytic function is required for Toxoplasma persistence in infected mice.
Figure 3: CPL-deficient bradyzoites develop Atg8-positive autophagosomes associated with the VAC.
Figure 4: CPL-deficient bradyzoites develop undigested autophagosomes containing organellar remnants.

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Acknowledgements

This work was supported by National Institutes of Health grants R01AI120627 (to V.B.C. and M.D.C.), R01GM111703 (to M.B.) and R01AI060767 (to I.C.). Z.D. and A.J.S. received fellowship support from the American Heart Association. B.M.H. and G.K. were supported by National Institutes of Health training grant T32AI007528. O.L.M. was supported by a National Institutes of Health Ruth Kirschstein National Research Service Award F31AI118274. The authors thank S. Meshinchi and J. Whitfield at the University of Michigan for help with electron microscopy and cytokine analysis, respectively, as well as the Johns Hopkins University Microscopy facility. The authors thank L. Weiss, W. Sullivan Jr and L.D. Sibley for the provision of antibodies for this study.

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M.D.C., Z.D., M.L., O.L.M., G.K., M.-H.H., A.J.M., B.M.H., C.E. and V.B.C. designed the experiments. M.D.C., A.J.S., A.J.M., B.M.H. and V.B.C. wrote the manuscript. W.v.d.L. performed chemical synthesis. M.D.C., Z.D., M.L., O.L.M., G.K., M.H.-H., T.L.S., A.J.S., A.J.M., B.M.H. and I.C. performed the experiments. C.E., M.B. and S.B. provided advice or reagents that were essential for completion of the study. All authors discussed the findings and commented on the manuscript.

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Correspondence to Manlio Di Cristina or Vern B. Carruthers.

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The authors declare no competing financial interests.

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Supplementary Figures 1–11 and Supplementary Table 1. (PDF 42826 kb)

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Di Cristina, M., Dou, Z., Lunghi, M. et al. Toxoplasma depends on lysosomal consumption of autophagosomes for persistent infection. Nat Microbiol 2, 17096 (2017). https://doi.org/10.1038/nmicrobiol.2017.96

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