SNAP47 Silencing Impairs the Morphology and Neurotransmission of Hippocampal GABAergic Neurons

Abstract Synaptosomal-associated protein 47 (SNAP47), a non-canonical SNARE (soluble N-ethylmaleimide-sensitive-factor attachment receptor) protein, is highly expressed in neuronal tissue and exhibits broad cytoplasmic distribution at the cellular level. However, SNAP47 does not directly participate in exocytosis or the recycling of synaptic vesicles (SVs), and its precise physiological function remains elusive. Our previous study revealed that SNAP47 is strongly expressed in GABAergic interneurons (INs) in the hippocampus. Therefore, we created a lentiviral vector carrying a small hairpin RNA (shRNA) to knockdown (KD) SNAP47 and applied this virus to autaptic hippocampal neuronal cultures. To identify GABAergic INs, cultures were prepared using transgenic mice expressing yellow fluorescent protein (YFP)-Venus under the control of the vesicular GABA transporter (VGAT) promoter. SNAP47 KD efficiently reduced the expression of the endogenous SNAP47 in the majority of neurons in autaptic cultures, significantly decreasing the somatic level of the protein. Morphological analysis of INs revealed that SNAP47 KD impacted the morphology with significant reduction in dendrite length. Furthermore, expression of both pre- and postsynaptic markers, was reduced in these neurons. Convergent to these morphological finding, physiological changes were also observed in whole-cell recordings, in particular a decrease in the amplitude and frequency of miniature inhibitory postsynaptic currents (mIPSCs), indicating an alteration in inhibitory synaptic transmission. In contrast, the somato-dendritic morphology and synaptic transmission of YFP-Venus-negative, putative glutamatergic excitatory neurons appeared to remain unaffected. In summary, our results demonstrate that reduced SNAP47 protein expression directly impacts the morphology of GABAergic neurons and their synaptic physiology.