A role for Toxoplasma gondii chloroquine resistance transporter in bradyzoite digestive vacuole maintenance and viability

Toxoplasma gondii (T. gondii) is a ubiquitous pathogen that can cause encephalitis‚ congenital defects‚ and ocular disease‚ and has been implicated as a risk factor for mental illness in humans. The parasite persists in the brain as slow growing bradyzoites cysts. No treatments exist to eliminate this form of parasite. Although proteolytic degradation within the parasite’s lysosomal-like vacuolar compartment (VAC) is critical for bradyzoite viability‚ whether other aspects of the VAC are important for parasite persistence remains unknown. An ortholog of Plasmodium falciparum CRT has previously been identified in T. gondii (TgCRT). To interrogate the function of TgCRT in chronic stage bradyzoites and its role in persistence‚ we knocked out TgCRT in a cystogenic strain and assessed VAC digestion of autophagosomes‚ host- derived proteins‚ VAC size‚ and viability of in vitro and in vivo bradyzoites. We found that whereas bradyzoites deficient in TgCRT exhibit near normal digestion of autophagosomes‚ they display a markedly distended VAC and their viability is compromised both in vitro and in vivo. Interestingly‚ impairing VAC proteolysis in TgCRT deficient bradyzoites restored VAC size‚ consistent with a role for TgCRT in mobilizing products of digestion from the VAC. In conjunction with earlier studies‚ our current findings suggest a functional link between TgCRT and VAC proteolysis. This work provides further evidence of a crucial role for the VAC in bradyzoite persistence and a new potential VAC target to abate chronic Toxoplasma infection.