Effects of Extreme Heat Exposure on Heatstroke and Liver Injury in Mice: The Role of PPARα

BACKGROUND: Liver injury is a frequent complication of heatstroke and constitutes a direct cause of death. However, only a few studies examined the mechanism underlying heatstroke-induced liver injury. OBJECTIVE: We aimed to evaluate the role of peroxisome proliferator-activated receptor α (PPARα) in heatstroke-induced liver injury and to explore the potential mechanisms. METHODS: Male C57BL/6N mice were subjected to a control (22 ± 1 °C) or extreme heat temperature (39.5 ± 0.5 °C) to induce a heatstroke-associated liver injury animal model. PPARα agonist, ferroptosis inhibitor, and AAV8-mediated PPARα overexpression were administered to the mice to investigate the role of PPARα and ferroptosis in the heatstroke-induced liver injury. Serum was collected for liver function evaluation. Liver tissues were applied for morphological observation, staining detection, ferroptosis examination, and mechanistic exploration. RESULTS: Compared with the control group, extreme heat exposure-induced temperature dysregulation, impaired liver function, and morphological damage in mice. Proteomics screened PPARα as a protein of interest, with its level being significantly decreased in response to extreme heat exposure. Both PPARα activation and overexpression attenuated extreme heat-induced heatstroke and liver injury. Hmox1 was next screened and higher Hmox1 expression was identified, accompanied by elevated markers of ferroptosis including prostaglandin-endoperoxide synthase 2 (Ptgs2), malondialdehyde (MDA), lipid peroxidation (LPO) and Fe2+ levels. Ferroptosis inhibition mitigated heatstroke and liver injury induced by heat exposure. In the setting of extreme heat exposure, PPARα activation suppressed Hmox1 expression and the levels of ferroptosis markers. It not only induced differences in the expression of members of iron generation, efflux and uptake process and reduced hepatic intracellular Fe2+ accumulation, but also stimulated expression of molecules for countering lipid peroxidation including Nrf2-SLC7A11-GPX4 axis and FSP1 signaling. DISCUSSION: PPARα played an essential role in extreme heat exposure-induced heatstroke and liver injury, and PPARα intervention conferred protection against it via inhibition of ferroptosis.