Positive modulation of glucagon‐like peptide 1 (GLP‐1) receptor by endogenous haemorphins with implications in glucose metabolism and diabetes

Abstract Background and Purpose Haemorphins are known to target G protein‐coupled receptors and their reduced serum levels were associated with diabetes and obesity. This is consistent with inhibitory action on dipeptidyl peptidase IV, controlling GLP‐1 levels. The modulation of the GLP‐1 receptor by haemorphins as a mechanism for regulating glucose homeostasis was investigated. Experimental Approach The effect of LVV‐haemorphin 7 (LVV‐H7) on GLP‐1 receptor was assessed in human embryonic kidney (HEK293) and rat insulinoma (INS‐1 832/3) cells using bioluminescence resonance energy transfer, downstream signalling, cell viability, insulin synthesis experimental and computational ligand binding analysis. Key Results LVV‐H7 has positive action on GLP‐1 receptor occurring with GLP‐1 but not orforglipron (LY3502970), indicating a peptide–peptide interaction, causing a left shift in GLP‐1's dose responses. LVV‐H7 also potentiated GLP‐1‐induced insulin expression and its protective effect against glucose‐induced cytotoxicity. Moreover, LVV‐H7 slightly reduced the GLP‐1's association kinetics with no impact on its binding properties. Molecular docking supported by functional analysis showed the existence of a putative ‘allosteric’ binding site at the junction between the helical and the extracellular domains (ECDs) and highlighted the critical role of Trp6 of LVV‐H7 and Ser31 ECD /Glu34 ECD /Arg299 ECL2 /Asp372 ECL3 /Arg380 ECL3/ ™ 7 of GLP‐1 receptor. This also demonstrated that active GLP‐1/GLP‐1 receptor complex is required for the positive action of LVV‐H7. Conclusions and Implications LVV‐H7 is active on the GLP‐1 receptor‐mediated metabolic pathways in pancreatic β‐cells. This is consistent with reduced serum haemorphin levels in diabetes/obesity, suggesting implications in glucose homeostasis. This constitutes the first Class B GPCR modulated by haemorphins, illustrating the role of haemorphin‐GPCR axis in physiology/pathophysiology.