Glicentin identified as a low-potency, cross-reactive agonist for GIPR, GLP-1R, and GCGR
Background
Dual agonism of glucose-dependent insulinotropic polypeptide receptor (GIPR) and glucagon-like peptide-1 receptor (GLP-1R) is a breakthrough for type 2 diabetes and obesity, improving glycemic control and weight loss. While GIPR is expressed in the central nervous system, endogenous GIP expression in the brain is debated, and peripheral GIPR/GLP-1R agonists often localize to circumventricular organs. This suggests a potential lack of GIP-ligand for receptors protected by the blood-brain barrier, prompting a search for alternative endogenous GIPR ligands.
Study Design
Researchers profiled ligand activity at heterologously expressed human GIPR to identify alternative endogenous agonists. They tested 42 ligands using cAMP accumulation, calcium mobilisation, and cAMP inhibition assays. The study also investigated glicentin's activity at human GLP-1R and GCGR, and its conservation at rodent GIPRs. Furthermore, the impact of co-expression with RAMP2 or RAMP3 on GIPR-active ligands, including glicentin, was assessed.
Results
Among 42 ligands tested, glicentin was the only non-proGIP-derived peptide to elicit a cAMP response at human GIPR. Its potency was low, with an EC₅₀ of 877nM. No ligand-induced calcium mobilisation or cAMP inhibition was observed for any tested ligand. Glicentin demonstrated cross-reactivity, also activating human GLP-1R and glucagon receptor (GCGR). Receptor-specific antibody blockade reduced glicentin's potency by 10-20-fold at all three receptors. Glicentin's activity was conserved at rodent GIPRs, albeit with reduced potency. Co-expression with RAMP2 or RAMP3 attenuated cAMP responses to GIPR-active ligands, including glicentin. This indicates high selectivity for GIPR.
Key Findings
- Glicentin was the only non-proGIP-derived peptide among 42 tested to activate human GIPR.
- Glicentin exhibited low potency at GIPR, with an EC₅₀ of 877nM for cAMP accumulation.
- Glicentin cross-activated human GLP-1R and glucagon receptor (GCGR).
- Receptor-specific antibody blockade reduced glicentin's potency by 10-20-fold at all three receptors.
- Co-expression of RAMP2 or RAMP3 attenuated GIPR responses to glicentin and other active ligands.
Why It Matters
This study expands our understanding of potential endogenous ligands for the GIPR, a key target in metabolic disease. While glicentin's high EC₅₀ suggests it's unlikely to be a primary physiological ligand under basal conditions, its cross-reactivity with GLP-1R and GCGR highlights complex incretin system biology. Understanding these interactions could inform the design of novel multi-agonist therapies or strategies to modulate existing incretin-based drugs. For biohackers and clinicians, this finding is more foundational science than immediate protocol change, but it deepens the mechanistic picture of how GIPR signaling might be influenced beyond canonical GIP.
glicentin
gipr
glp-1r
gcgr
incretin
gpcr