An Epilepsy-Associated SV2A Mutation Disrupts Synaptotagmin-1 Expression and Activity-Dependent Trafficking.

The epilepsy-linked gene SV2A, has a number of potential roles in the synaptic vesicle (SV) life cycle. However, how loss of SV2A function translates into presynaptic dysfunction and ultimately seizure activity is still undetermined. In this study, we examined whether the first SV2A mutation identified in human disease (R383Q) could provide information regarding which SV2A-dependent events are critical in the translation to epilepsy. We utilized a molecular replacement strategy in which exogenous SV2A was expressed in mouse neuronal cultures of either sex, which had been depleted of endogenous SV2A to mimic the homozygous human condition. We found that the R383Q mutation resulted in a mislocalization of SV2A from SVs to the plasma membrane, but had no effect on its activity-dependent trafficking. This SV2A mutant displayed reduced mobility when stranded on the plasma membrane and reduced binding to its interaction partner synaptotagmin-1 (Sytl). Furthermore, the R383Q mutant failed to rescue reduced expression and dysfunctional activity-dependent trafficking of Sytl in the absence of endogenous SV2A. This suggests that the inability to control Sytl expression and trafficking at the presynapse may be key in the transition from loss of SV2A function to seizure activity. [ABSTRACT FROM AUTHOR]