Molecular and in vivo phenotyping of missense variants of the human glucagon receptor

Abstract

Naturally occurring missense variants of G protein–coupled receptors with loss of function have been linked to metabolic disease in case studies and in animal experiments. The glucagon receptor, one such G protein–coupled receptor, is involved in maintaining blood glucose and amino acid homeostasis; however, loss-of-function mutations of this receptor have not been systematically characterized. Here, we observed fewer glucagon receptor missense variants than expected, as well as lower allele diversity and fewer variants with trait associations as compared with other class B1 receptors. We performed molecular pharmacological phenotyping of 38 missense variants located in the receptor extracellular domain, at the glucagon interface, or with previously suggested clinical implications. These variants were characterized in terms of cAMP accumulation to assess glucagon-induced Gα s coupling, and of recruitment of β-arrestin-1/2. Fifteen variants were impaired in at least one of these downstream functions, with six variants affected in both cAMP accumulation and β-arrestin-1/2 recruitment. For the eight variants with decreased Gα s signaling (D63 ECD N, P86 ECD S, V96 ECD E, G125 ECD C, R225 3.30 H, R308 5.40 W, V368 6.59 M, and R378 7.35 C) binding experiments revealed preserved glucagon affinity, although with significantly reduced binding capacity. Finally, using the UK Biobank, we found that variants with wildtype-like Gα s signaling did not associate with metabolic phenotypes, whereas carriers of cAMP accumulation-impairing variants displayed a tendency toward increased risk of obesity and increased body mass and blood pressure. These observations are in line with the essential role of the glucagon system in metabolism and support that Gα s is the main signaling pathway effecting the physiological roles of the glucagon receptor.

Acute pharmacodynamic responses to exenatide: Drug-induced increases in insulin secretion and glucose effectiveness

“…Furthermore, this genetic variant in GIPR has been reported to be associated with increased plasma levels of GIP as well as various anthropometric and glycemic traits 38 . The p.G40S variant in GCGR has been reported to impair signaling through β-arrestin-1 23 . This p.G40S variant in GCGR has been reported to be associated with diabetes 22 , but this finding seems not to be reproducible 39 .…”

“…This pilot study was designed to test the hypothesis that missense variants in two candidate genes (GCGR and GIPR) might be associated with pharmacodynamic responses to GLP1 receptor agonists. Table S3 compares pharmacodynamic responses to exenatide among three groups of people: (a) individuals who are homozygous for the major alleles of both genes; (b) homozygotes for the G40S variant of GCGR (rs1801483) 22,23 ; and (c) homozygotes for the E354Q variant of GIPR (rs1800437) [24][25][26] (Table S3). Four co-primary endpoints were prespecified: association of genotype (either G40S-GCGR or E354Q-GIPR) with the magnitude of drug effect (i.e., either exenatide-induced augmentation of first phase insulin secretion or exenatide-induced acceleration of the rate of glucose disappearance).…”

Acute pharmacodynamic responses to exenatide: Drug‐induced increases in insulin secretion and glucose effectiveness

“…This pilot study was designed to test the hypothesis that missense variants in two candidate genes (GCGR and GIPR) might be associated with pharmacodynamic responses to GLP-1R agonists. Table S3 compares pharmacodynamic responses to exenatide among three groups of people: (a) individuals who are homozygous for the major alleles of both genes; (b) homozygotes for the G40S variant of GCGR (rs1801483) 11,19 ; and (c) homozygotes for the E354Q variant of GIPR (rs1800437) 10,20,21 (Table S3). Four co-primary endpoints were prespecified: association of genotype (either G40S-GCGR or E354Q-GIPR) with the magnitude of drug effect (i.e.…”

“…We focused on two variants (rs1800437 and rs850763), which have been reported to alter the function of GIPR and GCGR, respectively. 10,11 2 | METHODS…”

Role of Glucagon and Its Receptor in the Pathogenesis of Diabetes

“…For example, in addition to Gly40Ser, homozygous missense mutations (P86S) have been found in GCGR ; these mutations contribute to the formation of an ineffective GCGR, resulting in hyperglycemia and extreme α-cell proliferation ( 65 ). Recent studies have reported 250 missense variants in human GCGR ( 66 , 67 ). GCGR shows lower allelic diversity and fewer missense variants and variants with trait associations than the other class B1 GPCRs.…”