Chronic GIPR agonism mediates weight-independent insulin sensitization by tirzepatide in obese insulin resistant mice

Tirzepatide (LY3298176), a dual GIP and GLP-1 receptor agonist, has been shown to deliver enhanced glycemic control and superior weight loss compared to a selective GLP-1 receptor (GLP-1R) agonist in patients with type 2 diabetes mellitus. However, the mechanism by which tirzepatide improves efficacy and how GIP receptor (GIPR) agonism contributes to the therapy is not fully understood. Here, hyperinsulinemic-euglycemic clamp studies were used to show that tirzepatide is a highly effective insulin sensitizer, improving insulin sensitivity in obese mice to a greater extent than GLP-1R agonism. To determine if GIPR agonism contributes to the insulin sensitization, we compared the effect of tirzepatide in obese wild-type and Glp-1r null mice. In the absence of GLP-1R induced weight loss, tirzepatide improved systemic insulin sensitivity by enhancing glucose disposal in WAT. To corroborate these results, chronic treatment with a long-acting GIPR agonist (LAGIPRA) was also found to enhance insulin sensitivity by increasing insulin stimulated glucose uptake in WAT. Interestingly, the effect of tirzepatide and LAGIPRA on insulin sensitivity was associated with reduced branched chain amino and keto acids in the circulation. Whole-body insulin sensitization was associated with pronounced upregulation of genes associated with the catabolism of glucose, lipid and BCAAs in brown adipose tissue. Together, our studies show that tirzepatide improved insulin sensitivity in a weight-dependent and -independent manner. These results highlight how GIPR agonism contributes to the therapeutic profile of dual GIP and GLP-1 receptor agonism, offering mechanistic insights into the clinical efficacy of tirzepatide. 24 total samples. Treatments include Vehicle, LAGIPRA, TZP, PairFed groups. N = 6 for each treatment group.