Synaptic Proteomes of Cortical Interneuron Classes Revealed by Antibody Directed Proximity Labeling.

Subtypes of inhibitory interneurons play diverse roles within neural circuits in cerebral cortex. Defining the molecular underpinnings of interneuron functions within cortical circuits will require identification of interneuron synaptic proteomes. In this study, we first combined genetically directed expression of tdTomato-synaptophysin with antibody-directed proximity labeling and tandem mass spectrometry to identify synaptic proteomes of three major interneuron classes in mouse cortex: parvalbumin (PV), somatostatin (SS), and vasoactive intestinal peptide (VIP). After stringent filtering we identified 581 proteins: 228 identified in all cell classes and 353 in one or two of three classes. The PV class had the largest number of uniquely identified proteins (141), followed by VIP (30) and SST (20). Consistent with previously reported electrophysiological evidence, PV presynaptic proteomes were enriched for NMDA receptor subunits and scaffolding proteins. We used antibodies against synaptotagmin 2 (Syt2), a presynaptic protein present at PV synapses, to confirm NMDAR localization, and to find that the mu-opioid receptor agonist buprenorphine rapidly caused reorganization of the PV presynaptic proteome. Overall, our results reveal proteomes of PV, SST, and VIP interneurons in cortex that likely underlie distinct and dynamic interneuron synaptic properties.