Ferroptosis is important for <i>Toxoplasma gondii</i> replication and virulence <i>in vitro</i> and <i>in vivo</i>

The protozoan parasite <i>T. gondii</i> employs intricate mechanisms to exploit host cells while sustaining their viability, yet its interaction with ferroptosis - an iron-dependent cell death driven by lipid peroxidation - remains poorly defined. Here, we show <i>T. gondii</i> infection induces ferroptotic hallmarks in RAW264.7 macrophages, including elevated lactate dehydrogenase release, labile Fe^{2 +} accumulation, reactive oxygen species (ROS) generation, and lipid peroxidation. Molecular analyses revealed infection-induced downregulation of ferroptosis suppressor GPX4 and upregulation of pro-ferroptotic ACSL4 in macrophages and mice. Mechanistically, the SLC7A11/GPX4 axis governed parasite growth: knockdown of these genes promoted <i>T. gondii</i> replication, whereas overexpression restricted proliferation. Pharmacological studies showed ferroptosis inhibitor Fer-1 suppressed intracellular parasite proliferation. Notably, GPX4 inhibitor RSL3 exhibited context-dependent effects: pre-infection treatment enhanced replication, while post-infection administration inhibited growth. Direct RSL3 exposure induced time-dependent growth arrest in extracellular tachyzoites, associated with disrupted transcriptomes, increased lipid ROS, and downregulated parasite antioxidant genes (<i>TgPRX2</i>, <i>TgTPX1/2</i>, <i>TgNXN</i>), indicating redox homoeostasis impairment. In vivo murine studies corroborated this biphasic effect: therapeutic RSL3 administration post-infection significantly reduced parasite burdens across multiple organs (spleen, liver, kidney, brain) and improved survival rates, while prophylactic pretreatment exacerbated disease progression. We propose RSL3 exerts direct parasiticidal effects via oxidative damage but also enables early nutrient acquisition from ferroptosis-compromised host cells. These findings establish ferroptosis as a critical node in <i>T. gondii</i> pathogenesis, highlighting the parasite's hijacking of host iron-lipid metabolism. The dual role of ferroptosis regulators underscores the host-pathogen metabolic complexity and positions the SLC7A11/GPX4 axis as a promising therapeutic target.