Spatiotemporal Control of GPR37 Signaling and Its Behavioral Effects by Optogenetics

Abstract

Despite the progress in deorphanization of G Protein-Coupled Receptors (GPCRs), ≈100 GPCRs are still classified as orphan receptors without identified endogenous ligands and with unknown physiological functions. The lack of endogenous ligands triggering GPCR signaling has hampered the study of orphan GPCR functions. Using GPR37 as an example, we provide here the first demonstration of the channelrhodopsin 2 (ChR2)-GPCR approach to bypass the endogenous ligand and selectively activate the orphan GPCR signal by optogenetics. Inspired by the opto-XR approach, we designed the ChR2-GPR37 chimera, in which the corresponding parts of GPR37 replaced the intracellular portions of ChR2. We showed that optogenetic activation of ChR2/opto-GPR37 elicited specific GPR37 signaling, as evidenced by reduced cAMP level, enhanced ERK phosphorylation and increased motor activity, confirming the specificity of opto-GPR37 signaling. Besides, optogenetic activation of opto-GPR37 uncovered novel aspects of GPR37 signaling (such as IP-3 signaling) and anxiety-related behavior. Optogenetic activation of opto-GPR37 permits the causal analysis of GPR37 activity in the defined cells and behavioral responses of freely moving animals. Importantly, given the evolutionarily conserved seven-helix transmembrane structures of ChR2 and orphan GPCRs, we propose that opto-GPR37 approach can be readily applied to other orphan GPCRs for their deorphanization in freely moving animals.

GPR37 and GPR37L1 differently interact with dopamine 2 receptors in live cells

“…Further studies are required to determine whether the observed neuroprotective effect of pramipexole could be due to increased interaction of GPR37 with D2R. From a clinical perspective, the pramipexole induced D2R-mediated G i -signaling in the indirect striatopallidal pathway could be augmented by the GPR37/D2R interaction as GPR37 is also reported to be G i coupled (Meyer et al, 2013; Zheng et al, 2018). Such an increased inhibition of the striatopallidal neurons might improve movements in patients with PD.…”

Accumbal Adenosine A2A Receptors Enhance Cognitive Flexibility by Facilitating Strategy Shifting

“…The sequence of animal entries to each arm and the number of entries were recorded. Correct spontaneous alternation was defined as the continuous entry into three arms (such as 1, 2, 3 or 1, 3, 2) as described previously (Zheng et al, 2018).…”

Orphan G Protein Coupled Receptors in Affective Disorders

“…By replacing the intracellular portions of channelrhodopsin2 (ChR2) with the corresponding amino acid sequences of GPR37, they designed a ChR2-GPR37 chimera, aimed at bypassing the lack of a ligand to activate GPR37. First, they validated the approach by measuring the intracellular decrease in cAMP levels and the augment in ERK phosphorylation in the light-activated transfected HEK293T cells [ 74 ]. Then, the viral delivery of the ChR2-GPR37 chimera in the dorsomedial striatum allowed them to trigger GPR37-driven signaling cascades that resulted in an increased time spent in the center during the OFT, indicating an anxiolytic behavioral response [ 74 ].…”

“…First, they validated the approach by measuring the intracellular decrease in cAMP levels and the augment in ERK phosphorylation in the light-activated transfected HEK293T cells [ 74 ]. Then, the viral delivery of the ChR2-GPR37 chimera in the dorsomedial striatum allowed them to trigger GPR37-driven signaling cascades that resulted in an increased time spent in the center during the OFT, indicating an anxiolytic behavioral response [ 74 ]. Overall, overwhelming evidence from both human and animal studies indicate a modulation of GPR37 expression levels by events that trigger affective disorders, while its role in mediating behavioral consequences is still debated and requires further research.…”