Quantitative, in situ visualization of intracellular insulin vesicles in pancreatic beta cells

Proc Natl Acad Sci U S A. 2022 Aug 9;119(32):e2202695119. doi: 10.1073/pnas.2202695119. Epub 2022 Aug 3.


Characterizing relationships between Zn2+, insulin, and insulin vesicles is of vital importance to the study of pancreatic beta cells. However, the precise content of Zn2+ and the specific location of insulin inside insulin vesicles are not clear, which hinders a thorough understanding of the insulin secretion process and diseases caused by blood sugar dysregulation. Here, we demonstrated the colocalization of Zn2+ and insulin in both single extracellular insulin vesicles and pancreatic beta cells by using an X-ray scanning coherent diffraction imaging (ptychography) technique. We also analyzed the elemental Zn2+ and Ca2+ contents of insulin vesicles using electron microscopy and energy dispersive spectroscopy (EDS) mapping. We found that the presence of Zn2+ is an important characteristic that can be used to distinguish insulin vesicles from other types of vesicles in pancreatic beta cells and that the content of Zn2+ is proportional to the size of insulin vesicles. By using dual-energy contrast X-ray microscopy and scanning transmission X-ray microscopy (STXM) image stacks, we observed that insulin accumulates in the off-center position of extracellular insulin vesicles. Furthermore, the spatial distribution of insulin vesicles and their colocalization with other organelles inside pancreatic beta cells were demonstrated using three-dimensional (3D) imaging by combining X-ray ptychography and an equally sloped tomography (EST) algorithm. This study describes a powerful method to univocally describe the location and quantitative analysis of intracellular insulin, which will be of great significance to the study of diabetes and other blood sugar diseases.

Keywords: STXM images stack; X-ray diffraction imaging; Zn2+ content; dual-energy abstract X-ray imaging; insulin vesicles.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Blood Glucose
  • Cell Line
  • Insulin* / analysis
  • Insulin* / metabolism
  • Insulin-Secreting Cells* / metabolism
  • Insulin-Secreting Cells* / ultrastructure
  • Rats
  • Secretory Vesicles* / chemistry
  • Secretory Vesicles* / metabolism
  • Spectrometry, X-Ray Emission
  • X-Ray Diffraction
  • Zinc* / analysis


  • Blood Glucose
  • Insulin
  • Zinc