ORF27-04 - GIPR-Dependent Action of Anti-Obesity Medications in Human White and Brown Adipocytes

Recently developed incretin mimetic anti-obesity medications (AOMs), including semaglutide (GLP-1 receptor agonist), tirzepatide (GLP-1/GIP receptor dual agonist), and retatrutide (GLP-1/GIP/GCG receptor tri-agonist) have shown to be highly effective in facilitating weight-loss and improving insulin sensitivity in individuals with obesity. However, their specific molecular actions in adipose tissue and potential to directly influence adipocyte metabolism are not yet determined. RNA sequencing of differentiated human white and brown adipocytes revealed expression of the GIP receptor (GIPR), but not GLP-1 or GCG receptors (GLP-1R, GCGR), we hypothesized that only the AOMs that target GIPR (tirzepatide and retatrutide) would affect adipocyte function and metabolism, while AOMs that exclusively target GLP-1R (semaglutide) would not.

We used in vitro models of differentiated human white (WA) and brown (BA) adipocytes to study the effects of semaglutide, tirzepatide, and retatrutide on adipose tissue. Bupropion was used as a non-incretin AOM negative control. Acute activation of adipocyte signaling was evaluated after 45 minutes of incubation with AOMs via western blot analysis of phosphorylation events indicative of the activation or modulation of adipocyte signaling pathways. Bioenergetics, including real-time oxygen consumption and extracellular acidification rates, were assessed throughout the 45-minute AOM exposure window via Seahorse XFe Extracellular Flux Analyzer.

The expression of GIPR, and absence of GLP-1R and GCGR expression in BA and WA was confirmed via qPCR. The acute upregulation of PKA signaling and subsequent phosphorylation of hormone-sensitive lipase (HSL) was observed in both BA and WA after 45-minute incubation with tirzepatide and retatrutide, where tirzepatide was over two orders of magnitude more potent than retatrutide in directing HSL phosphorylation. Both semaglutide and bupropion failed to induce such a response. Similarly, only tirzepatide and retatrutide increased oxygen consumption and extracellular acidification rates, where tirzepatide was sufficient to enhance BA oxygen consumption to a rate comparable with the positive control forskolin, which directly activates adenylyl cyclase.

Clinical studies have shown an enhanced efficacy of GIP/GLP1 dual agonism over GLP1 agonism alone. Our results provide what may be an essential component of the mechanistic basis for this difference by demonstrating that incretin mimetic peptide AOMs directly influence human adipocyte metabolism in a GIPR-dependent manner. This work also provides additional understanding of incretin mimetic drug action. Besides their primary role in the central nervous system, AOM’s that target adipocyte GIPR may increase PKA-driven WA lipolysis and BA thermogenesis that could contribute to the improved weight loss and maintenance.