Primary cilia regulate GLP-1 signaling in pancreatic β cells

Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are mainstay therapies for diabetes and obesity, acting in part by enhancing glucose-dependent insulin secretion. While the primary cilium is a known signaling compartment for certain G-protein coupled receptors (GPCRs), its role in the β-cell response to incretins remains undefined. Here, we show that primary cilia are essential for full GLP-1R signaling. Loss of β-cell cilia in mouse and human islets severely impaired GLP-1-potentiated insulin secretion, an effect preceded by blunted whole-cell cAMP and Ca²⁺ responses. Immunofluorescence and immunogold scanning electron microscopy revealed endogenous GLP-1R localized to the primary cilium. Adenylyl cyclase immunostaining was also enriched within cilia, and targeted inhibition of ciliary PKA reduced insulin secretion. Critically, disrupting ciliary GPCR trafficking via Tulp3 knockdown - while preserving cilia structure - recapitulated the signaling and secretory deficits, demonstrating a specific requirement for the ciliary receptor pool. These findings establish the primary cilium as a non-redundant signaling compartment for GLP-1R and uncover a new layer of subcellular organization in incretin action in β cells.