SNARE protein SNAP25 regulates the chloride-transporter KCC2 in neurons

Inhibitory synaptic neurotransmission mediated by GABA requires a low concentration of chloride ions (Cl^-) in neurons, which is established and maintained by the potassium-chloride co-transporter 2 (KCC2). While KCC2-interacting proteins are known to regulate KCC2 protein level and function, specific KCC2-interacting partners are still being identified and characterized. We asked whether SNAP25, an integral component of the SNARE-complex and a novel KCC2 interactor, regulates KCC2 protein and function in mice. We demonstrated that SNAP25 interacts with KCC2, and that this interaction is regulated by protein kinase C (PKC)-mediated phosphorylation. We also discovered that SNAP25 knockdown decreases total KCC2 in cortical neurons, and reduces the strength of synaptic inhibition, as demonstrated through a depolarization of the reversal potential for GABA (E_GABA), indicating reduced KCC2 function. Our biochemical and electrophysiological data combined demonstrate that SNAP25 regulates KCC2 membrane expression and function, and in doing so, regulates inhibitory synaptic transmission.