1767-P: “Leader” ß-Cells within the Pancreatic Islet Are a Functionally Stable Subpopulation In Vitro and In Vivo

β-cell coordination within the islet is critical for normal glucose-stimulated insulin secretion. Recently, we and others have identified a subpopulation of β-cells termed “leaders” which are the first cells to show an increase intracellular Ca²⁺ during glucose-induced Ca²⁺ waves. In the Zebrafish, photo ablation of leader cells disrupts pan-islet coordination identifying these as likely pacemakers alongside connected “hub” cells. Our earlier studies were conducted over relatively short time windows (~1hr), leaving open the possibility that leader cells may simply reflect the emergence of a transient functional state rather than a stable subpopulation. To address this question, we used islets from Ins1Cre:GCaMP6f^fl/fl transgenic mice which express the Ca²⁺ sensor GCaMP6f selectively in β-cells. Fast (3-6 Hz) confocal imaging and cell-tracking were used to record calcium dynamics with cellular resolution during stimulation in vitro at 11 mM glucose. Adenoviral delivery of photo-activable PA-mCherry, and excitation with UV light, allowed the identification and labelling of leader cells. Re-imaged 24 h later, 80% (8/10; 4 mice in 2 separate experiments) of islets had the same leader cell as in the earlier session. Correspondingly, after islet engraftment into the anterior chamber (ACE) of the mouse eye, and revascularization, multi-photon imaging revealed calcium waves that were initiated from the same region of the islet in vivo in imaging sessions 24 h apart. These findings establish leader β-cells as a stable subpopulation in vitro and in vivo whose dysfunction may contribute to defective insulin secretion in some forms of diabetes.