Disabling the Gβγ-SNARE interaction disrupts GPCR-mediated presynaptic inhibition, leading to physiological and behavioral phenotypes

Abstract

Genetic ablation of Gβγ-SNARE signaling produces stress- and depression-related behaviors. Gβγ ensnares neurotransmitter vesicles The exocytosis of neurotransmitter-containing vesicles requires the SNARE protein complex to mediate vesicle fusion with the plasma membrane. The Gβγ subunit activated by Gi/o-coupled GPCRs can inhibit this process by interacting with the SNARE protein SNAP25. Zurawski et al. generated mice that expressed a mutant form of SNAP25 that could not interact with Gβγ. These mice showed defects in nociception, stress responses, motor coordination, affect, and spatial learning. These results provide in vivo evidence of the importance of the association between presynaptic Gβγ and SNARE proteins in presynaptically inhibiting neurotransmitter release. G protein–coupled receptors (GPCRs) that couple to Gi/o proteins modulate neurotransmission presynaptically by inhibiting exocytosis. Release of Gβγ subunits from activated G proteins decreases the activity of voltage-gated Ca2+ channels (VGCCs), decreasing excitability. A less understood Gβγ-mediated mechanism downstream of Ca2+ entry is the binding of Gβγ to SNARE complexes, which facilitate the fusion of vesicles with the cell plasma membrane in exocytosis. Here, we generated mice expressing a form of the SNARE protein SNAP25 with premature truncation of the C terminus and that were therefore partially deficient in this interaction. SNAP25Δ3 homozygote mice exhibited normal presynaptic inhibition by GABAB receptors, which inhibit VGCCs, but defective presynaptic inhibition by receptors that work directly on the SNARE complex, such as 5-hydroxytryptamine (serotonin) 5-HT1b receptors and adrenergic α2a receptors. Simultaneously stimulating receptors that act through both mechanisms showed synergistic inhibitory effects. SNAP25Δ3 homozygote mice had various behavioral phenotypes, including increased stress-induced hyperthermia, defective spatial learning, impaired gait, and supraspinal nociception. These data suggest that the inhibition of exocytosis by Gi/o-coupled GPCRs through the Gβγ-SNARE interaction is a crucial component of numerous physiological and behavioral processes.