The incretin co-agonist tirzepatide requires GIPR for hormone secretion from human islets

Abstract

The incretins glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) mediate insulin responses that are proportionate to nutrient intake to facilitate glucose tolerance¹. The GLP-1 receptor (GLP-1R) is an established drug target for the treatment of diabetes and obesity², whereas the therapeutic potential of the GIP receptor (GIPR) is a subject of debate. Tirzepatide is an agonist at both the GIPR and GLP-1R and is a highly effective treatment for type 2 diabetes and obesity^3,4. However, although tirzepatide activates GIPR in cell lines and mouse models, it is not clear whether or how dual agonism contributes to its therapeutic benefit. Islet beta cells express both the GLP-1R and the GIPR, and insulin secretion is an established mechanism by which incretin agonists improve glycemic control⁵. Here, we show that in mouse islets, tirzepatide stimulates insulin secretion predominantly through the GLP-1R, owing to reduced potency at the mouse GIPR. However, in human islets, antagonizing GIPR activity consistently decreases the insulin response to tirzepatide. Moreover, tirzepatide enhances glucagon secretion and somatostatin secretion in human islets. These data demonstrate that tirzepatide stimulates islet hormone secretion from human islets through both incretin receptors.

Fig. 1. Tirzepatide stimulates insulin secretion in mice predominantly through the GLP-1R.

a, Mouse islets from control mice and mice with beta-cell-specific deletion of the Gipr (Gipr^-β-cell-/-) were perifused with ramping concentrations of tirzepatide (TZP) (0–100 nM) with or without Ex9 at a 1 μM concentration beginning at minute 28. The iAUC was calculated for TZP using the value at minute 42 as the baseline. n = 5 for all groups. b, Mouse islets were perifused with increasing concentrations of TZP (0–100 nM) in the presence of Ex9, a GIPR antagonist (GIPR ant) or a combination of both. All antagonists were used at 1 μM concentrations starting at minute 28. The iAUC was calculated for TZP using the value at minute 42 as the baseline. PBS and GIPR ant, n = 4; Ex9 and Ex9 + GIPR ant, n = 5. c, Glycemia after a 5 h fast, immediately before the administration of glucose. Antagonists were administered 2 h before and TZP was administered 1 h before. n = 8 for all groups. d, Glycemia during the IPGTT. The iAUC was calculated using the fasting glycemia value. PBS, TZP and TZP + GIPR ant, n = 8; TZP + GLP-1R ant and TZP + GLP-1R/GIPR ant, n = 7. All values are mean ± s.e.m. Statistical tests were two-way ANOVA with Tukey’s post-hoc test (a) and one-way ANOVA with Tukey’s post-hoc test (b–d). Source data

Fig. 2. Tirzepatide stimulates insulin secretion through both the GLP-1R and GIPR in human islets.

a, Islet perifusion from one set of human islets. Insulin secretion was measured in response to 30 nM tirzepatide in the presence of Ex9 (1 μM), a GIPR antagonist (GIPR ant) or both. n = 3 per group. b, iAUC values for insulin secretion in response to tirzepatide in eight individual sets of human islets. The dashed line indicates the level of glucose-stimulated insulin secretion before tirzepatide stimulation. n = 3 per group. c, Summary data of all eight experiments in human islets. Each individual experiment was averaged to produce a single data point for each condition and expressed as a relative value to control conditions. Individual experiments have connecting lines. n = 8. All values are mean ± s.e.m. The statistical test was one-way ANOVA with Tukey’s post-hoc test (b,c). Source data

Fig. 3. Tirzepatide stimulates glucagon secretion in human islets.

a, Glucagon secretion from human islets stimulated with either 30 nM hGIP or GLP-1 individually (minutes 8–24) or together (minutes 32–50) under 16 mM glucose conditions. The iAUC was calculated for the individual effects of the peptides (minutes 8–24) and the combined effects (minutes 32–50) using the value of the first time point as the baseline. GIP, n = 4; GLP-1, n = 6; GIP + GLP-1, n = 10. b, Glucagon secretion from human islets treated with 30 nM of either hGIP or tirzepatide (TZP) under 16 mM glucose conditions. The iAUC was calculated using minutes 24 and 54 as the baseline values for the first and second stimulation, respectively. n = 3 for all groups. c, Glucagon secretion in response to 30 nM TZP in eight individual donor sets of human islets under 16 mM glucose conditions. The summary of these experiments is shown as the of the average values from minutes 55–65. The fold induction on the right y axis was calculated using the baseline glucagon values from minutes 35–45. n = 3 for each donor, n = 8 for summary data. d, Glucagon secretion in human islets (donor R464) stimulated with TZP (30 nM) at either 2.7 mM glucose (2.7 G) or 10 mM glucose (10 G), with or without 3 mM alanine. n = 3. e, Somatostatin concentrations from pooled samples taken from baseline samples or during TZP stimulation. n = 3. All values are mean ± s.e.m. Statistical tests were one-way ANOVA with Tukey’s post-hoc test (a), two-way ANOVA with Sidak post-hoc test (b), paired t-test (c,d) and unpaired t-test (e). Source data

Extended Data Fig. 1. Tirzepatide activity in mice.

A) Intraperitoneal glucose tolerance test (IPGTT) in wild-type (WT) mice. Mice were pretreated 2 hours prior to glucose with either PBS or a GIPR antagonist, 1 hour prior to glucose with either PBS or acyl-GIP (3 or 10 nmol/kg dose). Glucose was given after a 5 hour fast at 1.5 mg/kg. The integrated area under the curve (iAUC) was calculated using the glycemia measure immediately before PBS/GIPR antagonist administration. 3 nmol/kg dose: PBS/PBS, n = 7; PBS/Acyl-GIP, n = 6, GIPR Antag/Acyl-GIP, n = 6. 10 nmol/kg dose: PBS/PBS, n = 7; PBS/Acyl-GIP, n = 8, GIPR Antag/Acyl-GIP, n = 7. B) A dose-response curve for tirzepatide during an IPGTT in WT mice. (n = 5/group) B) Tirzepatide during an IPGTT in WT and Glp1r knockout mice. (n = 8/group) C) 30 nmol/kg tirzepatide in WT mice treated with an antagonist for the GLP-1R (Jant-4), GIPR, or both. N = 8/group. All values are mean + /- SEM. The following statistical tests were used: A, B, and D) one-way ANOVA with Tukey’s posthoc test, C) two-way ANOVA with Tukey’s posthoc test. Source data

Extended Data Fig. 2. Tirzepatide stimulated insulin secretion in human islets.

Two independent donor sets of human islets were stimulated with 30 nM tirzepatide (TZP) in the presence of 1μM concentrations of exendin(9-39) (Ex9), hGIP(3-30) (GIPR Ant) or the combination. The integrated area under the curve (iAUC) was calculated for both glucose and tirzepatide stimulated insulin secretion using the value of the first time point as the baseline. All values are mean + /- SEM, n = 3/group. A one-way ANOVA with Tukey’s posthoc test was used. Source data

Extended Data Fig. 3. GIPR but not GLP-1R is needed for tirzepatide-stimulated glucagon secretion.

Human islets were stimulated with either tirzepatide or hGIP in the presence of the GIPR antagonist (GIPR Ant – left panel) or exendin(9-39) (Ex9 – right). Tirzepatide was used at 30 nM and the antagonists were used at 1μM concentrations. All values are mean + /- SEM, n = 3/group for GIPR antagonist and 6/group for Ex9. A two-way ANOVA with Tukey’s posthoc test was used. Source data

Extended Data Fig. 4. GIP and amino acids synergistically increase glucose secretion in human islets.

Human islets were treated with 30 nM hGIP or 3 mM amino acids (combination of glutamine, arginine, alanine, and leucine), individually or in combination. All values are mean ± SEM, n = 3/group. A two-way ANOVA with Tukey’s posthoc test was used. Source data