In vitro maturation of Toxoplasma gondii bradyzoites in human myotubes and their metabolomic characterization

The apicomplexan parasite Toxoplasma gondii forms bradyzoite-containing tissue cysts that cause chronic and drug-tolerant infections. However, current in vitro models do not allow long-term culture of these cysts to maturity. Here, we developed a human myotube-based in vitro culture model of functionally mature tissue cysts that are orally infectious to mice and tolerate exposure to a range of antibiotics and temperature stresses. Metabolomic characterization of purified cysts reveals global changes that comprise increased levels of amino acids and decreased abundance of nucleobase- and tricarboxylic acid cycle-associated metabolites. In contrast to fast replicating tachyzoite forms of T. gondii these tissue cysts tolerate exposure to the aconitase inhibitor sodium fluoroacetate. Direct access to persistent stages of T. gondii under defined cell culture conditions will be essential for the dissection of functionally important host-parasite interactions and drug evasion mechanisms. It will also facilitate the identification of new strategies for therapeutic intervention. Bradyzoites are a quiescent form of Toxoplasma gondii enclosed in cysts during chronic infections. Here, Christiansen et al. develop a human myotube-based in vitro culture model of cysts that are infectious to mice and characterize their metabolism in comparison to fast replicating tachyzoites.

Automated summary

In this study, a human myotube-based in vitro culture model was developed to successfully culture functionally mature tissue cysts of Toxoplasma gondii, the parasites that cause chronic infections. The cultured cysts were orally infectious to mice and tolerant to various antibiotics and temperature stresses. Metabolomic analysis revealed significant changes in the metabolism of the cysts compared to the fast replicating tachyzoite forms, including increased levels of amino acids and decreased abundance of nucleobase- and tricarboxylic acid cycle-associated metabolites. This study provides a crucial tool for dissecting important host-parasite interactions and drug evasion mechanisms, as well as identifying new therapeutic strategies.