期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2022
卷号：119
期号：32
DOI：10.1073/pnas.2202695119
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance
This work accurately quantified the Zn
2+ content of insulin using energy dispersive spectroscopy (EDS) mapping and explored the precise position of insulin in insulin vesicles using dual-energy X-ray contrast microscopy and scanning transmission X-ray microscopy (STXM) image stacks. X-ray ptychography and equally sloped tomography (EST) were combined to perform three-dimensional (3D) structural mapping and reveal the distribution of insulin vesicles in pancreatic beta cells. The method described here fills a gap in the quantitative analysis of insulin and describes a unique approach for exploring the process of insulin secretion in pancreatic beta cells. This study describes an application of advanced X-ray imaging in the exploration of cell structures and provides an approach to the analysis of intracellular microstructures.
Characterizing relationships between Zn
2+, insulin, and insulin vesicles is of vital importance to the study of pancreatic beta cells. However, the precise content of Zn
2+ 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 Zn
2+ 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 Zn
2+ and Ca
2+ contents of insulin vesicles using electron microscopy and energy dispersive spectroscopy (EDS) mapping. We found that the presence of Zn
2+ 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 Zn
2+ 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.
