Guo, Amin; Zhang, Jianhua; He, Bo; Li, Angdi; Sun, Tianxiao; Li, Weimin; Wang, Jian; Tai, Renzhong; Liu, Yan; Qian, Zhen; Fan, Jiadong; Sali, Andrej; Stevens, Raymond C.; Jiang, Huaidong

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA

2022, 119, 0027-8424

Guo, Amin; Zhang, Jianhua; He, Bo; Li, Angdi; Sun, Tianxiao; Li, Weimin; Wang, Jian; Tai, Renzhong; Liu, Yan; Qian, Zhen; Fan, Jiadong; Sali, Andrej; Stevens, Raymond C.; Jiang, Huaidong

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.