Sunday, May 18, 2025
5/18/2025
Regulation of metabotropic glutamate receptor activity by protein/protein interactions - PROJECT SUMMARY Metabotropic glutamate receptors are G Protein-Coupled Receptors (GPCRs) that serve as critical regulators of neurotransmitter release. Within the mGlu family, the three widely expressed members of the group III mGlu receptor subfamily (mGlu4, 7 and 8) modulate glutamate and GABA release from presynaptic terminals throughout the brain. Recently, it has been shown that the group III mGlu receptors are “anchored” at specific presynaptic locations by the postsynaptic expression of laminin proteins termed Extracellular Leucine Rich Repeat and Fibronectin Type III Domain Containing 1 and 2 (Elfn1 and Elfn2). Of the group III receptors, mGlu7 and Elfn1 have been reported to form a critical pairing, as mutations in each protein in humans are correlated with ADHD and seizures. Additionally, both Elfn1 and Grm7 knockout mice exhibit cognitive and motor impairments, blunted responses to amphetamine, and seizures that develop with a similar developmental time course. mGlu7/Elfn1 interactions localize the receptor to the active zones of glutamatergic pyramidal cell synapses onto somatostatin-containing GABAergic interneurons (SST-INs) in the hippocampus and prefrontal cortex (PFC). Dysfunction of SST-INs interneurons has now been described in numerous diseases such as schizophrenia, autism and epilepsy; therefore, the mGlu7/Elfn1 interaction in SST-INs is in a position to fine tune inhibitory synaptic responses onto pyramidal cells to provide distinct circuit-level control of hippocampal and cortical networks. In vitro, Elfn1 allosterically inhibits agonist-mediated activation of the group III mGlu receptors. Using a system in which we have co-cultured cells expressing mGlu7 with cells expressing Elfn1, we have now identified a positive allosteric modulator (PAM) and a negative allosteric modulator (NAM) of mGlu7 that are no longer active when Elfn1 is present; in contrast, other PAMs and NAMs exhibit activity at mGlu7 regardless of the presence of Elfn1. In the current application, we will test a suite of control agonists, PAMs, and NAMs for activity at mGlu7 with and without Elfn1 and perform analogous studies with mGlu4/Elfn1, mGlu8/Elfn1 and mGlu7/Elfn2 to understand compound specificity. We will then prepare the mGlu7/Elfn1 assay for HTS and conduct a pilot screen of an existing 1,000 compound collection of mGlu7 receptor modulators to identify new activators and antagonists to probe this interaction. Finally, we will test the hypothesis that the pharmacological profiles we observe in vitro in the presence and absence of Elfn1 will also be seen in a native tissue preparation at SST-INs. It is anticipated that these small molecules will assist in understanding the basic biology of mGlu7/Elfn1, create novel assays to assess GPCR signal bias, generate highly selective tools to specifically modulate SST-INs versus other types of interneurons, and could eventually represent a highly selective way to modulate mGlu7 activity only at specific synaptic locations.
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