Hydrogen peroxide signaling modulates neuronal differentiation via microglial polarization and Wnt/ß-catenin pathway.

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/ß-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/ß-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/ß-catenin system.

Impact of postnatal nutrition on neurodevelopmental outcome in rat model of intrauterine growth restriction.

OBJECTIVE: There are limited data on nutritional management of infants with intrauterine growth restriction (IUGR). Postnatal protein supplementation for promoting growth is a common clinical practice in neonatology. The present study aims to investigate the consequences of protein supplementation on long-term growth, brain and body weight, brain histology and behavioral outcome in a rat model of IUGR. MATERIALS AND METHODS: Twenty-four IUGR-formed rat puppies and 12 healthy puppies were included in the study. IUGR model was established by low (10%) protein diet throughout pregnancy together with intraperitoneal injection of lipopolysaccharide (LPS). Pups were started to be fed with either standard protein (SP), or high protein (HP) diet until postnatal day (PN) 35. Puppies in the control group were given SP diet for 35 days. Six pups from each group were sacrificed at PN7, remaining six were evaluated by Morris water maze test between PN 30 to 35 days and then sacrificed at PN35. Histologic evaluation of brain tissue was performed at PN7 and PN35. RESULTS: IUGR group displayed lower body and brain weights at PN7 when compared with control. At PN35, SP group achieved similar brain/body weight ratios with control, whereas HP group displayed lowest brain/body weight ratio. The number of TUNEL positive cells was significantly higher and myelin basic protein and oligodendrocyte marker O4 immunoreactivity were significantly lower in HP group when compared with SP at PN35. Neuronal density in prefrontal cortex and hippocampus at PN7 were similar among SP and HP groups, but significantly lower in HP group when compared with SP at PN35. SP group displayed better results in the Morris water maze test when compared with HP group. CONCLUSIONS: Although postnatal HP support is associated with increase in body weight at PN35, it did not result in better brain/body weight ratios in the rat model of IUGR. In IUGR rats, HP diet was associated with increased apoptosis in brain tissue with lower neuronal density and decreased myelination when compared to SP. Furthermore, better neurodevelopmental scores were achieved by SP diet rather than HP support in IUGR.