Ectophosphatase activities and phosphate transport mechanisms in Tritrichomonas foetus and their impact on parasite proliferation

Abstract

Tritrichomonas foetus is the etiological agent of bovine trichomoniasis, a sexually transmitted disease that causes early embryonic loss, infertility, and endometritis, leading to significant economic losses in the cattle industry. Understanding its phosphate metabolism may reveal novel targets for therapeutic intervention. Phosphate metabolism plays a central role in T. foetus by supporting energy production, cell signaling, and macromolecule synthesis, all essential for the survival and proliferation of this parasitic protozoan. In this study, we demonstrate that T. foetus has at least two distinct ectophosphatases on its cell surface. One hydrolyzing p-nitrophenyl phosphate (p-NPP) under acidic conditions, and another acting on β-glycerophosphate hydrolysis under alkaline conditions. Both ectophosphatase activities were inhibited by sodium orthovanadate, however the inhibition of p-NPP hydrolysis was irreversible, whereas inhibition of β-glycerophosphate hydrolysis was reversible. These enzymes exhibit other differential biochemical properties and anchoring mechanisms, with the latter being glycosylphosphatidylinositol (GPI)-anchored and sensitive to phosphatidylinositol-specific phospholipase C (PI-PLC). The inhibition caused by sodium orthovanadate significantly impaired parasite proliferation. Furthermore, we show that T. foetus can internalize the inorganic phosphate (P_i) released extracellularly by these enzymes, linking surface phosphatase activities and intracellular phosphate availability. P_i limitation in the culture medium drastically reduced ATP levels and parasite proliferation. The addition of β-glycerophosphate partially restored both, indicating that the parasite can hydrolyze this substrate and use the released P_i for ATP synthesis. However, this effect was abolished by phosphonoacetic acid (PAA), a P_i transport inhibitor, confirming the critical role of phosphate uptake on the parasite metabolism. Similarly, ATP production was enhanced by exposure to p-NPP or β-glycerophosphate and suppressed by sodium orthovanadate and PAA, confirming the integration of ectophosphatase activity, phosphate transport, and energy metabolism. Together, our findings demonstrated the relationship between ectophosphatase-mediated P_i release, P_i transport, and ATP synthesis in T. foetus and highlight the importance of these processes for parasite growth and survival. These results suggest that interfering with phosphate acquisition mechanisms may represent a promising strategy for the development of novel antiparasitic therapies.