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 elevated cAMP in CR beta cells causes fast short-amplitude Ca²⁺ oscillations that potentiate insulin release despite a largely disconnected beta cell network landscape. 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⁺. Therefore, this study demonstrates that CR promotes beta cell cAMP and ER Ca²⁺ homeostasis to enhance beta cell secretory function.