Superoxide generation via the NR2B-NMDAR/RasGRF1/NOX2 pathway promotes dendritogenesis.

N-methyl-D-aspartate receptors (NMDARs) that contain the NR2A and NR2B subunits play a critical role in neuronal plasticity and dendritogenesis. Gain-and-loss-of function studies indicate that NR2B, but not NR2A, promotes dendritic branching. Accumulating evidence indicates that stimulation of NMDARs activates NADPH oxidase (NOX2), thereby generating superoxide. However, the molecular underpinnings of this process are not understood. RasGRF1, a guanine nucleotide exchange factor, is key for several forms of neuronal plasticity and interacts directly with the tail of NR2B. We investigated whether the NR2B-NMDAR/RasGRF1 pathway regulates the activity of NOX2 and whether superoxide production is required for dendritogenesis. We measured superoxide production in developing primary cultures of hippocampal neurons from 3 to 25 days in vitro (DIV) with the probe dihydroethidium (dHE). We found the highest dHE levels at early and intermediate developmental stages (3-15 DIV), when the NR2B-NMDAR expression is abundant. During these early/intermediate developmental stages, but not in mature neurons (>15 DIV), NMDAR activity is required for superoxide production. We also found that disrupting the NR2B-RasGRF1 interaction led to reduced dHE fluorescence intensity and moreover inhibited dendritic branching in hippocampal neurons. Together, our data indicate that superoxide production is induced by the NR2B-NMDARs/RasGRF1/NOX2 pathway and promotes dendritogenesis.

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