Ciliary GPCRs Regulate Glucose-Stimulated Insulin Secretion

Defects in primary cilia result in syndromes collectively called “ciliopathies”, which often present with obesity and diabetes. Although glucose is the primary mediator of GSIS, circulating factors including free fatty acids, amino acids, and various hormones also play critical roles. At the interface between these circulating factors and GSIS, GPCR signaling is often central. The primary cilium is a membrane and microtubule-based sensory organelle and is highly enriched with specialized GPCRs. Cilia are present on pancreatic β-cells, but the role of cilia in β-cell function remains unclear. To discover ciliary GPCRs important for β-cell function, we compiled a list of candidate β-cell specific or highly expressed GPCRs based on human pancreatic gene expression profiles. We identified 66 β-cell specific GPCRs comparing with α-cells and acinar-cells. These 66 candidate GPCRs was expressed as C-terminally tagged GFP fusion proteins and screened for ciliary localization in a mouse pancreatic β-cell line, MIN6. To date, we have identified the following GPCRs localize to cilia in MIN6 cells: FFAR4, PTGER4, ADRB2, KISS1R, and P2RY14. To validate ciliary localization of GPCRs, we also used antibodies against the endogenous GPCRs. We have confirmed that the free fatty acid receptor 4 (Ffar4) and the prostaglandin E receptor 4 (Ptger4) are localized to the primary cilium of mouse and human β-cells. In addition, the treatment of each of agonists of these receptors promote glucose-stimulated insulin secretion (GSIS) in mouse and human islet. Tulp3 is required for transporting GPCRs into the primary cilium. We used shRNA targeting Tulp3 delivered by lentivirus to knock-down Tulp3 in mouse and human islet cells. Tulp3 depletion leaves ciliary structure intact but impairs the localization of Ffar4 and Ptger4 in cilia and disrupts agonist-stimulated GSIS in mouse and human pseudo-islets. Together, these data suggest that primary cilia and ciliary GPCRs are important for the circulating factors-regulated GSIS in β-cell. Disclosure C. Wu: None. K. Hilgendorf: None. Y. Hang: None. R.J. Bevacqua: None. C.T. Johnson: None. C.A. Chang: None. S. Park: None. K. Tellez: None. S. Kim: None. P.K. Jackson: None. Funding Stanford Diabetes Research Center