ZIGIR, a Granule-Specific Zn²⁺ Indicator, Reveals Human Islet α Cell Heterogeneity.

Area of Science:

• Cell Biology
• Biochemistry
• Neuroendocrinology

Background:

• Mammalian cells store significant amounts of Zn²⁺ in secretory granules.
• Existing Zn²⁺ sensors lack the specificity and sensitivity required for imaging granular Zn²⁺.
• Accurate imaging of granular Zn²⁺ is crucial for understanding cellular processes and diseases.

Purpose of the Study:

• To develop a highly specific and sensitive fluorescent sensor for imaging granular Zn²⁺ in live cells.
• To utilize the sensor for cell sorting and characterization of pancreatic islet cells.
• To explore the role of Zn²⁺ in various cell types and its potential therapeutic implications.

Main Methods:

• Development of a fluorescent zinc granule indicator (ZIGIR) with enhanced fluorescence and membrane permeability.
• Selective enrichment of ZIGIR to acidic granules for improved targeting.
• Application of ZIGIR for live-cell imaging, cell separation, and analysis of pancreatic islets.

Main Results:

• ZIGIR demonstrated >100-fold fluorescence enhancement and selective targeting to acidic granules.
• ZIGIR enabled precise separation of heterogeneous β cells based on insulin content and sorting of mouse islets.
• In human islets, ZIGIR facilitated sorting of α and β cells, revealed high Zn²⁺ in δ cell granules, and showed glucagon variation in α cells.

Conclusions:

• ZIGIR is a superior tool for sensitive and specific imaging of granular Zn²⁺ in live cells.
• ZIGIR facilitates cell sorting and provides novel insights into Zn²⁺ biology within pancreatic islets.
• ZIGIR holds promise for studying Zn²⁺-rich secretory granules and engineering insulin-producing β cells for diabetes therapy.