In Vivo ZIMIR Imaging of Mouse Pancreatic Islet Cells Shows Oscillatory Insulin Secretion.

Shiuhwei Chen,Wen-Hong Li,Ebrahim H Ghazvini Zadeh,Min Kim,Eul Hyun Suh,Yan Xu,Philipp E Scherer,Zhijiang Huang,Harrison Kidd,A Dean Sherry,Shangkui Xie

doi:10.3389/fendo.2021.613964

Abstract

Appropriate insulin secretion is essential for maintaining euglycemia, and impairment or loss of insulin release represents a causal event leading to diabetes. There have been extensive efforts of studying insulin secretion and its regulation using a variety of biological preparations, yet it remains challenging to monitor the dynamics of insulin secretion at the cellular level in the intact pancreas of living animals, where islet cells are supplied with physiological blood circulation and oxygenation, nerve innervation, and tissue support of surrounding exocrine cells. Herein we presented our pilot efforts of ZIMIR imaging in pancreatic islet cells in a living mouse. The imaging tracked insulin/Zn2+ release of individual islet β-cells in the intact pancreas with high spatiotemporal resolution, revealing a rhythmic secretion activity that appeared to be synchronized among islet β-cells. To facilitate probe delivery to islet cells, we also developed a chemogenetic approach by expressing the HaloTag protein on the cell surface. Finally, we demonstrated the application of a fluorescent granule zinc indicator, ZIGIR, as a selective and efficient islet cell marker in living animals through systemic delivery. We expect future optimization and integration of these approaches would enable longitudinal tracking of beta cell mass and function in vivo by optical imaging.

Highlights

The islet of Langerhans plays essential roles in controlling metabolism and glucose homeostasis through the release of peptide hormones
When applied to isolated islets, zinc indicator for monitoring induced exocytotic release (ZIMIR) diffuses through interstitial space to label individual islet cells [4]
To label islet cells with ZIMIR in the intact pancreas, we initially considered a multicell bolus loading method previously developed for loading fluorescent indicators to a population of cells in brain slices [8]

Summary

Introduction

The islet of Langerhans plays essential roles in controlling metabolism and glucose homeostasis through the release of peptide hormones. By sampling the total insulin output from the pancreas, a number of studies have revealed the dynamic feature of insulin release in live animals, including rodents, dogs, and human [1, 2]. The lack of imaging assays capable of tracking insulin release of single cells or individual islets in live animals remains to be a roadblock towards functional analysis of islet beta cells in vivo [3]. Exploiting Zn2+ elevation at the cell surface as a surrogate marker of insulin release, we applied laser scanning confocal microscopy to image ZIMIR and to map the spatiotemporal characteristics of insulin release in isolated islets. Confocal ZIMIR imaging revealed oscillatory and synchronized insulin release among islet beta cells in a living mouse. We presented data to demonstrate the utility of a recently developed granule Zn2+ indicator, ZIGIR, as a selective and efficient marker of islet beta cells in vivo via systemic delivery

Methods

Results

Conclusion