Modulatory mechanisms of TARP γ8-selective AMPA receptor therapeutics

Abstract

AMPA glutamate receptors (AMPARs) mediate excitatory neurotransmission throughout the brain. Their signalling is uniquely diversified by brain region-specific auxiliary subunits, providing an opportunity for the development of selective therapeutics. AMPARs associated with TARP γ8 are enriched in the hippocampus, and are targets of emerging anti-epileptic drugs. To understand their therapeutic activity, we determined cryo-EM structures of the GluA1/2-γ8 receptor associated with three potent, chemically diverse ligands. We find that despite sharing a lipid-exposed and water-accessible binding pocket, drug action is differentially affected by binding-site mutants. Together with patch-clamp recordings and MD simulations we also demonstrate that ligand-triggered reorganisation of the AMPAR-TARP interface contributes to modulation. Unexpectedly, one ligand (JNJ-61432059) acts bifunctionally, negatively affecting GluA1 but exerting positive modulatory action on GluA2-containing AMPARs, in a TARP stoichiometry-dependent manner. These results further illuminate the action of TARPs, demonstrate the sensitive balance between positive and negative modulatory action, and provide a mechanistic platform for development of both positive and negative selective AMPAR modulators.

Structure of Transmembrane AMPA Receptor Regulatory Protein Subunit γ2

“…Previously determined structures of TARPs are overall like our structure of TARPg2 (Fig. 2b), and the loop anchor DSB is within structures of TARPg3 18 and TARPg8 11,12,19 , and even previously published structures of TARPg2 6 . However, it is absent, as expected, in the structure of the type-II TARP, TARPg5 20,21 (Fig.…”

“…2c). In contrast, the TARP cleat motif is conserved in all TARPg3, g5, and g8 subunit structures as well as GSG1L 11,18,20 (Fig. 2d).…”

“…Cryo-EM studies of TARP subunits have advanced our understanding of TARP structure in the context of AMPAR complexes, but intermediate resolution has historically precluded de novo building of TARP structures [5][6][7][8][9][10][11][12][13][14] . X-ray crystallography structures of TARP homologs, such as claudins, have been indispensable for modeling TARPs 15 .…”

Roles of AMPA receptors in social behaviors

“…TARPs have been shown to modulate the trafficking and gating properties of AMPARs ( Milstein and Nicoll, 2008 ). Recent findings have shown that injecting TARP γ8 ligand JNJ-61432059 into mouse BLA or ventral hippocampus could reduce and enhance GluA1- and GluA2-containing AMPARs, respectively ( Zhang et al, 2023 ), and reduce repetitive alcohol self-administration, in an animal model of addiction ( Hoffman et al, 2021 ) (for review, see ( Brogi et al, 2019 )). Taken together, these AMPAR-modulating reagents could be promising therapeutics for restoring normal social functioning in brain diseases.…”