Dissection of signaling pathways regulating TrkB-dependent gephyrin clustering

Introduction The TrkB receptor is known for its role in regulating excitatory neuronal plasticity. However, accumulating evidence over the past decade has highlighted the involvement of TrkB in regulating inhibitory synapse stability and plasticity, particularly through regulation of the inhibitory scaffold protein gephyrin, although with contradicting results.Methods In this study, we extended on these findings by overexpressing rat TrkB mutants deficient in either Shc-or PLC gamma-dependent signaling, as well as a kinase-dead mutant, to dissect the contributions of specific TrkB-dependent signaling pathways to gephyrin clustering.Results Our results demonstrate that TrkB signaling is required for gephyrin clustering on the perisomatic area of granule cells in the dentate gyrus in vivo. To further investigate, we expressed TrkB wild-type and mutants in hippocampal neurons in vitro.Discussion Under basal conditions, TrkB-Shc signaling was important for the reduction of gephyrin cluster size, while TrkB-PLC gamma signaling accounts for gephyrin clustering specifically at synaptic sites. Concomitant, impaired PLC gamma signaling was associated with disinhibition of transduced neurons. Moreover, chemically induced inhibitory long-term potentiation (chem iLTP) depended on TrkB signaling and the activation of both Shc and PLC gamma pathways.Conclusion Our findings suggest a complex, pathway-specific regulation of TrkB-dependent gephyrin clustering, both under basal conditions and during chem iLTP.