Mitochondrial Networks in Beta Cells of Pancreatic Islet of Langerhans Investigated by Serial Block Face Scanning Electron Microscopy

Abstract

The process whereby mitochondrial tubules fuse to form extended networks within cells has been associated with metabolic activity, and may provide a defense against generation of reactive oxygen species, whereas fission of such mitochondrial networks has been associated with apoptosis. We have used serial block-face scanning electron microscopy (SBF-SEM) to analyze distributions of mitochondrial network lengths in metabolically active insulin secreting beta cells of mouse pancreatic islets of Langerhans, with the aim of quantifying differences between wild type and diabetic disease models (Pfeifer et al., 2015). This technique provides three-dimensional ultrastructure of beta cells at a spatial resolution of about 10 nm in the x-y plane and 25 nm in the z-direction, from which we have been able to obtain cross sectional areas, volumes and network lengths of mitochondrial tubules in a population of beta cells. Blocks of isolated pancreatic islets were prepared by fixation, staining with heavy atoms, and embedding in Epon-Araldite resin, and were imaged at 1.5-keV primary beam energy with the backscattered electron signal. Our results showed that approximately one-third of the total mitochondrial volume originated from short networks less than 10 µm in length, one-third came from tubules of length 10 to 45 µm, and one-third from networks of length 45 to 150 µm. We conclude that SBF-SEM can provide a quantitative characterization of mitochondrial networks in wild type and disease models of endocrine tissues. This research was funded by the intramural program of NIBIB, NIH.C.R. Pfeifer, A. Shomorony, M.A. Aronova, G. Zhang, T. Cai, H. Xu. A.L. Notkins, R.D. Leapman. Quantitative analysis of mouse pancreatic islet architecture by serial block-face SEM. J Struct Biol, 189 (2015) 44-52.