Microscopy is of paramount importance in diabetes research: Paul Langerhans was the first to describe (1869) Islets based on a light microscopic (LM) evaluation of the pancreas. (Immuno-)EM-analysis of the Islets of Langerhans is an outstanding way to discriminate beta-cells from other endocrine cells: The crystalline appearance of insulin granules makes beta-cells readily distinguishable from other cells, allowing to assess total insulin content. In addition, analysis of environmental factors hypothesized to caused diabetes, e.g. viral infection, can be directly visualised. Ultrastructural analysis by EM reveals beta-cell condition, ER stress, abnormalities in mitochondria, fibrosis, as well as apoptosis, necrosis, macro- and micro-autophagy. EM can be used to follow the etiology of T1DM, the fate of transplanted Islets in both human as well as animal models and to assess the success of cellular trans differentiation to create insulin-producing cells. Moreover, EM allows other cell-types to be recognized in the Islet that affect the functioning of beta-cells, including immune cells attacking beta-cells, duct cells, endothelial cells and nerve cells. Our proposed approach enables identification of morphological and macromolecular characteristics in different cell-types within the Islets in a quantitative and high-throughput manner. A single dataset could resolve most of the features raised above. So why is EM-analysis not standard included? Traditionally, EM data-interpretation is mainly done by the publishing scientist(s). EM-examination is hampered by the laborious procedure that requires technical expertise and expensive equipment. In addition, data-sharing is limited, the field of view of the area inspected at high magnification is traditionally very small, the data is noisy making it difficult to objectively quantify and segment the greyscale EM-images. Without the knowledge of how Islets of Langerhans look like, it will remain cumbersome to establish the cause and solution to diabetes. Implementation of computational science has now revolutionized EM, paving the path for routine EM-analysis of complete Islets, as we have pioneered.

We are creating and analyzing high-resolution EM-maps of cross-sections of Islets of Langerhans in health and diabetes, which we term Nanotomy of Islets. The datasets allow to determine many aspects, including leukocyte infiltration, insulin content and cellular stress. Importantly, small particles such as viruses will also be detectable. The data first will be shared with nPOD co-investigators and at a later stage will be made publically available. (adopted by nPOD staff)