Aquatic high iron induces hepatic ferroptosis in zebrafish (Danio rerio) via interleukin-22 signaling pathway

Iron is one of the indispensable trace elements in living organisms. However, excessive iron deposition in organisms is prone to induce dysfunction of the liver and other vital organs. The present study aimed to investigate the mechanism how aquatic high iron affects iron transport and induces hepatic injury in zebrafish. Our results showed that the iron levels in zebrafish liver and serum were significantly increased after the fish treated with aquatic high iron (200 mg/L ferric ammonium citrate, FAC) for 21 days. Meanwhile, hepatic fibrosis was observed in zebrafish with high iron treatment. Furthermore, the expression of hepcidin, a key factor in the regulation of iron homeostasis, as well as other factors related to iron transport, was significantly influenced by high iron treatment. Nonetheless, different tissues, such as liver, gill and gut, diversely responded to high iron in water. Interestingly, our results identified that the expression of IL-22, instead of IL-6, was significantly elevated after high iron treatment. Moreover, high iron triggered STAT3 phosphorylation via IL-22, leading to the augmented expression of hepcidin and hepatic iron accumulation. As a result, the iron overload in fish liver induced hepatic ferroptosis, marked as the repressed activity of glutathione peroxidase (GPx) and elevated lipid peroxidation. Further studies confirmed that, unlike wild-type (WT) zebrafish, the expression of hepcidin and iron content in the liver of il22-deficient zebrafish was unaffected upon to high iron treatment. At the meantime, hepatic ferroptosis and fibrosis induced by high iron was significantly alleviated in il22-deficient zebrafish. In summary, aquatic high iron induced hepcidin expression in zebrafish by activating the IL-22/STAT3 signaling pathway, which in turn regulated hepatic iron transport and ferroptosis in zebrafish. The present study identified for the first time that IL-22 may be a potential regulatory target for iron overload-induced liver injury.