Toxoplasma gondii-Derived Soluble Factors Induce G2/M Phase Accumulation and p53-Associated Mitochondrial Apoptosis in Human Umbilical Cord Mesenchymal Stem Cells.

Toxoplasma gondii infection poses potential risks to stem cell-based therapeutic applications; however, the effects of parasite-derived soluble factors on mesenchymal stem cells remain unclear. Here, we investigated the impact of T. gondii-derived soluble factors (Tg-SFs) on human umbilical cord-derived mesenchymal stem cells (hUC-MSCs). hUC-MSCs were exposed to Tg-SFs generated in a Transwell co-culture system, and cellular phenotypes and p53 signalling were analysed using integrated functional and molecular approaches. Tg-SFs induced upper-chamber multiplicity of infection (MOI)-dependent cytotoxicity in hUC-MSCs, accompanied by cytoskeletal remodelling and nuclear condensation. Tg-SFs exposure caused marked G2/M phase accumulation, which was accompanied by reduced expression of Cyclin A2, Cyclin B1, and Cyclin E2 and increased p21 expression. In addition, Tg-SFs exposure reduced phosphorylation of CDK1 at Thr161. Tg-SFs-exposed hUC-MSCs underwent significant apoptosis, as evidenced by PARP and Caspase-3 cleavage. Mechanistically, Tg-SFs promoted accumulation of total p53 protein and selective phosphorylation of p53 at Ser15 and Ser392, and modulated Bcl-2 family proteins by upregulating Bax, BID, Bak, Bad, and Puma while downregulating Bcl-xL and Mcl-1. Pharmacological inhibition of p53 with PFT-α and siRNA-mediated p53 knockdown partially reversed these effects, indicating that p53 signalling contributes substantially, but not exclusively, to Tg-SFs-induced mitochondrial apoptosis. These findings indicate that T. gondii-derived soluble factors impair hUC-MSC viability through G2/M phase accumulation and p53-associated mitochondrial apoptosis, highlighting a potential safety consideration for MSC-based applications under parasite-associated conditions.