GPR151

GPR151 is a Gi-coupled G protein-coupled receptor with a restricted neuronal expression pattern that functions in pain signaling and habenular reward circuitry (PMID:34244727, PMID:25116430). It is selectively expressed in habenular neurons and their efferent axonal projections to the interpeduncular nucleus, raphe nuclei, and tegmental targets, where its axons overlap with cholinergic, substance P-ergic, and glutamatergic markers (PMID:25116430). The receptor couples specifically to Gαi (and not Gαq, Gα12, or Gα13) and is activated under acidic conditions (~pH 5.8), acting as a proton-sensing receptor (PMID:33239523, PMID:31119277). In nociceptive DRG neurons, GPR151 physically couples to P2X3 ion channels and enhances P2X3-mediated calcium influx and excitability, placing it upstream of a P2X3 → CSF1 → spinal microglial activation cascade in neuropathic pain (PMID:34244727). In trigeminal ganglion neurons it signals through Gβγ to activate ERK, driving upregulation of neuroinflammatory chemokines (CCL5, CCL7, CXCL9, CXCL10) (PMID:33239523). Structural determination revealed activation-resistant features in canonical motifs and an autoinhibitory N-terminal region occupying the orthosteric pocket that governs receptor maturation and trafficking (PMID:42085164). Synthetic psoralen-ring agonists and partial agonists drive GPR151 internalization and signaling and bidirectionally modulate morphine analgesia, while galanin was excluded as an endogenous ligand (PMID:27913310, PMID:42104714). Behaviorally, loss of GPR151 reduces social preference and alters diet-dependent body weight (PMID:36424418, PMID:35381001).

1. 2014 Medium

   Establishing where GPR151 acts: defining its restricted expression resolved the anatomical substrate for the receptor's function before any ligand or signaling mechanism was known.

   Evidence Immunohistochemistry and quantitative confocal colocalization across rat, mouse, and zebrafish

   PMID:25116430

   Open questions at the time

   • Does not establish signaling mechanism or ligand
   • Functional consequence of habenular expression not tested
2. 2016 Medium

   Testing a candidate endogenous ligand: galanin was directly excluded, narrowing the deorphanization search.

   Evidence Calcium signaling assay in GPR151-transfected ND7/23 cells (negative result)

   PMID:27913310

   Open questions at the time

   • Negative result only; does not identify the true ligand
   • Single cell system
3. 2019 Medium

   Defining a stimulus and transducer: GPR151 was shown to be activated by acidic pH and to couple to Gi, providing the first biochemical signaling readout.

   Evidence [35S]GTPγS binding with GPR151-Giα fusion and reporter gene assay in CHO cells

   PMID:31119277

   Open questions at the time

   • Whether protons are the physiological activator in vivo unresolved
   • No structural basis for pH sensing
4. 2021 High

   Connecting the receptor to a pain effector: GPR151 was placed upstream of P2X3 channels via physical coupling and bidirectional functional control of P2X3 activity, defining a neuropathic pain mechanism.

   Evidence Co-IP, calcium imaging, conditional KO and overexpression in DRG neurons, behavioral assays

   PMID:34244727

   Open questions at the time

   • Molecular interface of GPR151-P2X3 coupling not resolved
   • Whether coupling requires G-protein signaling unclear
5. 2021 Medium

   Extending the pathway to neuroinflammation: GPR151 → P2X3 was linked to CSF1 upregulation and spinal microglial activation, and a parallel Gβγ/ERK arm was shown to drive chemokine expression.

   Evidence Conditional KO and knockdown with microglial/chemokine readouts; Co-IP for Gαi selectivity and ERK phosphorylation in WT vs Gpr151-/- mice with PD98059 inhibition

   PMID:33239523 PMID:34244727

   Open questions at the time

   • No in vitro reconstitution of the pathway
   • Single lab for each arm
   • Relationship between P2X3 arm and Gβγ/ERK arm not integrated
6. 2022 Low

   Probing physiological roles beyond pain: KO mice revealed contributions of GPR151 to social reward behavior and diet-dependent metabolism, and human loss-of-function variants were confirmed non-functional.

   Evidence Gpr151-/- mouse behavior, metabolic phenotyping, and in vitro variant loss-of-function assays

   PMID:35381001 PMID:36424418

   Open questions at the time

   • Social preference finding rests on a single behavioral assay with no molecular mechanism
   • Metabolic mechanism not defined
   • Link between habenular circuitry and behavior not mechanistically established
7. 2026 High

   Resolving receptor architecture and pharmacology: structure revealed an autoinhibitory N-terminus controlling maturation/trafficking, and synthetic ligands established GPR151 as a druggable modulator of opioid analgesia.

   Evidence Structure determination with stabilizing mutations/nanobody plus trafficking assays; psoralen-ring agonist/partial agonist characterization with morphine co-administration in rats

   PMID:42085164 PMID:42104714

   Open questions at the time

   • Endogenous ligand still unidentified
   • Mechanism by which N-terminal autoinhibition is relieved unknown
   • How synthetic ligands intersect opioid signaling pathway not resolved

• The endogenous ligand of GPR151 and how its autoinhibited, activation-resistant architecture is physiologically engaged remain unresolved.
• No validated endogenous agonist identified
• Physiological trigger for N-terminal autoinhibition relief unknown
• Mechanistic link between habenular signaling and behavioral phenotypes incomplete