GluN2A-NMDA receptors mediate the effect of BDNF on network hyperexcitability in hippocampal neurons

Brain-derived neurotrophic factor (BDNF) modulates synaptic plasticity via activation of TrkB receptors and plays a key role in epileptogenesis, though its molecular mechanisms remain incompletely understood. Here, we examined how BDNF-TrkB signaling regulates synaptic GluN2A-containing NMDA receptors (NMDARs) and impacts network synchronization in cultured hippocampal neurons. BDNF increased synaptic surface expression of GluN2A-NMDARs in rat hippocampal synaptoneurosomes and cultured neurons in a time- and protein synthesis-dependent manner. Mechanistically, we identified a signaling cascade involving hnRNPK, Pyk2, and protein kinase C (PKC) as critical for this effect. Knockdown of hnRNPK or Pyk2, PKC inhibition, or expression of a phosphorylation-deficient Pyk2 mutant prevented BDNF-induced GluN2A synaptic accumulation. Pyk2 phosphorylation at Y402 was required for both basal and BDNF-induced GluN2A expression. Multielectrode array recordings demonstrated that BDNF and GluN2A-NMDARs contribute to enhanced network activity following stimulation. In vivo, BDNF-TrkB signaling mediated increased synaptic GluN2A expression in the hippocampus of rats subjected to the pilocarpine model of temporal lobe epilepsy, confirming a TrkB-dependent mechanism. These findings reveal a BDNF/TrkB-PKC-Pyk2-hnRNPK pathway that regulates GluN2A synaptic expression and neuronal excitability, offering new insights into the molecular basis of synaptic plasticity and epilepsy.