Calorie Restriction modulates beta cell IP₃R activity to regulate Ca²⁺ homeostasis and cell network connectivity

Calorie restriction (CR) promotes beta cell longevity by regulating cell identity, organelle and protein homeostasis, and metabolism pathways. CR beta cells have higher cAMP levels and mitochondria with an elevated potential to generate ATP. However, CR beta cells have reduced insulin secretion due to increased peripheral insulin sensitivity. How CR impacts beta cell Ca²⁺ homeostasis to regulate beta cell insulin release remains unknown. We investigated this question using acute pancreatic tissue slices prepared from ad-libitum (AL) or CR mice loaded with a low affinity Ca²⁺ indicator and recorded cytosolic Ca²⁺ gradients with fast confocal imaging. We exposed these slices to increasing glucose concentrations and applied our semi-automatic analysis pipeline to detect thousands of individual beta cells followed by identification of individual Ca²⁺ spiking events. We observed that CR beta cells have fast short-amplitude Ca²⁺ oscillations that correlate with largely disconnected beta cell networks across the islet. Using acetylcholine stimulation, we found that faster IP₃R-driven Ca²⁺ oscillations linked to higher cytosolic cAMP levels protect beta cells against acute depletion of ER Ca²⁺ stress. Therefore, this study provides new mechanistic insight into adaptation of beta cell and of beta cell networks to CR interventions.