Decoding Insulin\nSecretory Granule Maturation Using\nGenetically Encoded pH Sensors

Insulin is a peptide hormone secreted from pancreatic\nbeta cells\nto regulate blood glucose homeostasis. Maturation of active insulin\noccurs within insulin secretory granules (ISG) by acidification of\nthe lumen and enzymatic cleavage of insulin before secretion. This\nprocess is dysregulated in diabetes, and many questions remain on\nhow the cell controls insulin maturation. We address this gap in knowledge\nby designing two genetically encoded fluorescence pH sensors and a\nfluorescence lifetime imaging and analysis pipeline to monitor the\npH of individual secretory ISGs within live cells at higher resolution\nand precision than previously possible. We observed different subpopulations\nof ISGs based on their pH and subcellular localization. Signals regulating\nmetabolism vs membrane depolarization mobilize different subpopulations\nof ISGs for secretion, and we confirm that maturation signals acidify\nISGs. We conclude that different signaling networks uniquely impact\nISG mobilization and secretion. Future applications of these tools\nwill be useful for exploring how these processes are dysregulated\nin diabetes and provide new paths for developing more effective treatments.