Endocrine Abstracts

Introduction: Glucagon-like peptide-1 receptor (GLP-1R) agonists are highly effective anti-obesity therapeutics that are thought to primarily enact appetite suppression via action on central nervous system (CNS) appetite centres. However, their therapeutic potential can be limited by side effects and variable efficacy. Biased agonism, which selectively modulates downstream signalling pathways such as G-protein activation versus β-arrestin-mediated receptor internalisation, offers a promising strategy for refining these therapies. We hypothesised that biased GLP-1R agonists may cause differential receptor desensitisation in key CNS regions, providing a mechanism for improving therapeutic outcomes.

Methods: To investigate this in vivo, mice were pre-treated with vehicle or one of two biased GLP-1R agonists: ExD3, which promotes receptor internalisation, or ExF1, which is internalisation-resistant. The functional consequence of this pre-treatment was assessed by measuring the physiological response to a subsequent challenge with the conventional GLP-1R agonist Exendin-4 (Ex-4). To visualise the underlying mechanism, we used light-sheet microscopy on cleared brains to quantify available surface GLP-1R in pre-treated mice via injection of a fluorescently conjugated agonist, Ex-4-Cy5.

Results: Pre-treatment with the pro-internalisation agonist ExD3 significantly attenuated the response to the Ex-4 rechallenge compared to vehicle controls. In contrast, pre-treatment with the internalisation-resistant agonist ExF1 preserved the physiological response to Ex-4. Light-sheet imaging data directly corroborated these findings, revealing that ExD3 pre-treatment caused a marked reduction in available surface GLP-1R in key appetite-regulating nuclei. Conversely, ExF1 pre-treatment did not reduce surface receptor availability.

Conclusion: These findings provide direct in vivo evidence that biased agonism at neuronal GLP-1R critically modulates receptor surface availability and functional desensitisation. This mechanism likely contributes to the differential efficacy observed among new GLP-1R therapeutics. Targeting GLP-1R bias to minimise receptor internalisation presents a key strategy for developing more potent and sustained therapies for obesity.