2024 Theses Doctoral

Dynamic duets: Arrestin recruitment to metabotropic glutamate receptor dimers

Rauffenbart, Caroline

Myriad small molecule compounds targeting metabotropic glutamate receptors (mGluRs) have been investigated for the treatment of various neuropsychiatric diseases and displayed promise in preclinical studies. At the clinical level, many of these compounds have been well tolerated by human subjects but have eluded success as promising therapeutics. There are eight subtypes of mGluRs, which express as constitutive dimers.

This dimerization can occur between identical (homodimerization) or different (heterodimerization) mGluR protomer subtypes, which are subject to pairing-specific signaling mechanisms. Subtype expression of mGluRs is heterogenous between brain regions and cell types, yielding probable cell-specific homo- and heterodimer combinations that respond differently to certain drugs. While G protein recruitment to active mGluR dimers has been studied extensively, little is known about arrestin recruitment to these receptors.

I used bioluminescence resonance energy transfer (BRET) assays, which provide a quantitative measure of protein-protein proximity, to observe and quantify arrestin recruitment to specific mGluR subtype pairings upon ligand administration in heterologous cells. I studied how select allosteric ligands affect communication between protomers to enhance arrestin recruitment to dimers. My findings indicate that arrestin recruitment occurs only at select mGluR homodimers upon orthosteric stimulation but is frequently stimulated or enhanced by administration of activating allosteric ligands.

Additionally, I found that trans-protomer communication is highly specific to mGluR protomer subtype pairings, the ligand administered,a nd inter-protomer signal direction. Lastly, my findings reveal a cooperative effect of mGluR2 and 3 heterodimerization on arrestin recruitment that is dependent on the functional ability of each protomer to bind orthosteric agonist and responds distinctively from homodimers to stimulation by certain allosteric ligands. Taken together, this work shows that mGluR signaling can be tuned using strategic pharmacology and energizes hope for future clinical success of mGluR-targeting ligands.