Objective: Reactive oxygen species (ROS) are generated within the cell and serve as second messengers in fundamental cellular processes under physiologic conditions. Although the deleterious effects of high-level ROS associated with oxidative stress are well established, it is unclear how the developing brain reacts to redox changes. Our aim is to investigate how redox alteration affects neurogenesis and the mechanism that underlies it.
Materials and methods: We investigated in vivo microglial polarization and neurogenesis in zebrafish after hydrogen peroxide (H2O2) incubation. To quantify intracellular H2O2 levels in vivo, a transgenic zebrafish line that expresses Hyper and termed Tg(actb2:hyper3)ka8 was used. Then, in vitro studies with N9 microglial cells, 3-dimensional neural stem cell (NSC)-microglia coculture, and conditioned medium experiments are carried out to comprehend the mechanism underlying the changes in neurogenesis upon redox modulation.
Results: In zebrafish, exposure to H2O2 altered embryonic neurogenesis, induced M1 polarization in microglia, and triggered the Wnt/β-catenin pathway. N9 microglial cell culture experiments revealed that exposure to H2O2 resulted in M1 polarization in microglial cells, and this polarization was mediated by the Wnt/β-catenin pathway. Redox modulation of microglia interfered with NSC differentiation in coculture experiments. Neuronal differentiation was significantly higher in NSCs cocultured with H2O2-treated microglia when compared to control microglia. Wnt inhibition prevented the effects of H2O2-treated microglia on NSCs. No significant alterations were observed in conditioned medium experiments.
Conclusions: Our findings point to a robust interplay between microglia and neural progenitors influenced by the redox state. Intracellular H2O2 levels can interfere with neurogenesis by altering the phenotypic state of the microglia via the Wnt/β-catenin system.