# PI3K/Akt/mTOR signaling pathway mediates energy metabolic reprogramming and regulates mitochondrial homeostasis in host cells exposed to Toxoplasma gondii

## TL;DR

This study shows that Toxoplasma gondii manipulates host cell energy metabolism and mitochondria via the PI3K/Akt/mTOR pathway, offering a new therapeutic target.

## Contribution

The study identifies the PI3K/Akt/mTOR pathway as a novel mediator of T. gondii-induced metabolic reprogramming and mitochondrial dysfunction in host cells.

## Key findings

- T. gondii infection alters mitochondrial morphology and impairs oxidative phosphorylation while boosting glycolysis.
- Activation of the PI3K/Akt/mTOR pathway is critical for T. gondii-induced metabolic changes and can be inhibited to reduce parasite proliferation.
- Inhibiting PI3K/Akt/mTOR with LY294002 significantly reduces intracellular T. gondii proliferation.

## Abstract

Toxoplasma gondii (T. gondii) relies on host cells for energy and nutrition. Our previous studies showed that T. gondii regulates host cell apoptosis via the mitochondrial pathway, highlighting the essential role of mitochondria in its parasitism. In this study, T. gondii infection was found to significantly affect mitochondrial morphology and dynamic homeostasis in porcine kidney-15 (PK-15) cells, characterized by aggregated, swollen, fragmented, and oval-shaped mitochondria with disappearing cristae, accompanied by increased fusion and decreased fission. Additionally, the energy metabolic reprogramming of PK-15 cells exposed to T. gondii was affirmed from the perspectives of glucose consumption; changes in NAD+/NADH, lactate, pyruvate, and ATP production; and expressions of proteins related to glycolysis and oxidative phosphorylation (OXPHOS). T. gondii-induced mitochondrial damage impaired the OXPHOS process; however, the glycolysis level was significantly increased. Mechanistically, we demonstrated that activation of phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) signaling pathway played a critical role in energy metabolic reprogramming and mitochondrial damage induced by T. gondii, and this effect could be attenuated by LY294002 (a PI3K inhibitor), which significantly reduced intracellular proliferation of T. gondii through inhibiting PI3K/Akt/mTOR signaling pathway. These findings highlight the PI3K/Akt/mTOR pathway as a key mediator of T. gondii-induced cellular metabolic reprogramming and mitochondrial dysfunction; however, its potential as a therapeutic target remains to be validated in vivo.

Toxoplasma gondii, a globally distributed obligate intracellular protozoan parasite, poses severe health risks to immunocompromised individuals and pregnant women, causing miscarriage and fetal abnormalities. Current therapies suffer from high toxicity and limited targets, with unclear mechanisms underlying host-parasite interactions. This study reveals a novel parasitic strategy: T. gondii hijacks host mitochondrial dynamics and energy metabolism. Infection disrupts mitochondrial morphology and suppresses oxidative phosphorylation while activating the PI3K/Akt/mammalian target of rapamycin (mTOR) pathway to drive metabolic reprogramming, enhancing glycolysis to meet energy demands. Critically, inhibiting PI3K/Akt/mTOR with LY294002 reduces intracellular parasite proliferation, validating this pathway as a therapeutic target. Conventional antiparasitic drugs targeting the parasite directly face resistance challenges. By focusing on host metabolic regulation via PI3K/Akt/mTOR, this work advances understanding of parasitism and proposes host-directed therapies to disrupt parasite proliferation by modulating the metabolic microenvironment, highlighting its therapeutic potential against toxoplasmosis.