Role of 6-phosphogluconate dehydrogenase enzyme 1 in growth and virulence of Toxoplasma gondii and development of attenuated live vaccine

Evaluation of the toxoplasma Urm1 gene deletion mutant (PruΔUrm1) as a promising vaccine candidate against toxoplasmosis in mice

Toxoplasmosis is a significant zoonotic disease that poses a serious threat to both human and animal health. Despite ongoing research, developing an effective vaccine for toxoplasmosis remains a challenge. In this study, we evaluated the vaccine potential of the Toxoplasma Urm1 gene deletion mutant (PruΔUrm1) by assessing its pathogenicity and protective efficacy in mice. Using CRISPR/Cas9 technology, we successfully created a type II Toxoplasma gondii Pru mutant strain with a deleted Urm1 gene. Compared to the wild-type parasite, the PruΔUrm1 strain exhibited significantly reduced invasive and proliferative abilities in vitro. In in vivo studies, mice intraperitoneally infected with the parental Pru strain showed severe symptoms including emaciation, hunching, and high mortality rates. In contrast, mice infected with PruΔUrm1 tachyzoites demonstrated a 100 % survival rate, no overt symptoms, and a markedly reduced parasite burden in the liver, spleen, and lungs, indicating reduced pathogenicity. Notably, PruΔUrm1 vaccination triggered a strong immune response, characterized by significantly elevated cytokine levels, including TNF-α, IFN-γ and IL-10. Furthermore, we assessed the immunoprotective efficacy of PruΔUrm1 vaccination in mice against type I strains. Mice immunized with PruΔUrm1 were able to resist the tachyzoites of type I RH wild-type parasites, achieving a 100 % survival rate and significantly reduced parasite loads in the liver, spleen and lungs. These data demonstrate that PruΔUrm1 immunization provides effective protection against acute Toxoplasma infections and holds promise as a potential vaccine candidate for toxoplasmosis.

Metabolic plasticity, essentiality and therapeutic potential of ribose-5-phosphate synthesis in Toxoplasma gondii

Ribose-5-phosphate (R5P) is a precursor for nucleic acid biogenesis; however, the importance and homeostasis of R5P in the intracellular parasite Toxoplasma gondii remain enigmatic. Here, we show that the cytoplasmic sedoheptulose-1,7-bisphosphatase (SBPase) is dispensable. Still, its co-deletion with transaldolase (TAL) impairs the double mutant's growth and increases 13C-glucose-derived flux into pentose sugars via the transketolase (TKT) enzyme. Deletion of the latter protein affects the parasite's fitness but is not lethal and is correlated with an increased carbon flux via the oxidative pentose phosphate pathway. Further, loss of TKT leads to a decline in 13C incorporation into glycolysis and the TCA cycle, resulting in a decrease in ATP levels and the inability of phosphoribosyl-pyrophosphate synthetase (PRPS) to convert R5P into 5'-phosphoribosyl-pyrophosphate and thereby contribute to the production of AMP and IMP. Likewise, PRPS is essential for the lytic cycle. Not least, we show that RuPE-mediated metabolic compensation is imperative for the survival of the ΔsbpaseΔtal strain. In conclusion, we demonstrate that multiple routes can flexibly supply R5P to enable parasite growth and identify catalysis by TKT and PRPS as critical enzymatic steps. Our work provides novel biological and therapeutic insights into the network design principles of intracellular parasitism in a clinically-relevant pathogen.