Pancreatic ß-Cell Adaptive Plasticity in Obesity Increases Insulin Production but Adversely Affects Secretory Function.

Pancreatic ß-cells normally produce adequate insulin to control glucose homeostasis, but in obesity-related diabetes, there is a presumed deficit in insulin production and secretory capacity. In this study, insulin production was assessed directly in obese diabetic mouse models, and proinsulin biosynthesis was found to be contrastingly increased, coupled with a significant expansion of the rough endoplasmic reticulum (without endoplasmic reticulum stress) and Golgi apparatus, increased vesicular trafficking, and a depletion of mature ß-granules. As such, ß-cells have a remarkable capacity to produce substantial quantities of insulin in obesity, which are then made available for immediate secretion to meet increased metabolic demand, but this comes at the price of insulin secretory dysfunction. Notwithstanding, it can be restored. Upon exposing isolated pancreatic islets of obese mice to normal glucose concentrations, ß-cells revert back to their typical morphology with restoration of regulated insulin secretion. These data demonstrate an unrealized dynamic adaptive plasticity of pancreatic ß-cells and underscore the rationale for transient ß-cell rest as a treatment strategy for obesity-linked diabetes.

Illoura: a software tool for analysis, visualization and semantic querying of cellular and other spatial biological data.

UNLABELLED: New high-resolution approaches for mapping ultrastructure of cells in 3D are leading to unprecedented quantities of spatial data. Here we present Illoura, a software tool for the integrated management, analysis and visualization of these data within a semantic context, and illustrate its capability by analysis of spatial relationships in mammalian beta cells. AVAILABILITY: http://www.visiblecell.com/illoura. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

Expedited approaches to whole cell electron tomography and organelle mark-up in situ in high-pressure frozen pancreatic islets.

We have developed a simplified, efficient approach for the 3D reconstruction and analysis of mammalian cells in toto by electron microscope tomography (ET), to provide quantitative information regarding 'global' cellular organization at approximately 15-20 nm resolution. Two insulin-secreting beta cells-deemed 'functionally equivalent' by virtue of their location at the periphery of the same pancreatic islet-were reconstructed in their entirety in 3D after fast-freezing/freeze-substitution/plastic embedment in situ within a glucose-stimulated islet of Langerhans isolated intact from mouse pancreata. These cellular reconstructions have afforded several unique insights into fundamental structure-function relationships among key organelles involved in the biosynthesis and release of the crucial metabolic hormone, insulin, that could not be provided by other methods. The Golgi ribbon, mitochondria and insulin secretory granules in each cell were segmented for comparative analysis. We propose that relative differences between the two cells in terms of the number, dimensions and spatial distribution (and for mitochondria, also the extent of branching) of these organelles per cubic micron of cellular volume reflects differences in the two cells' individual capacity (and/or readiness) to respond to secretagogue stimulation, reflected by an apparent inverse relationship between the number/size of insulin secretory granules versus the number/size of mitochondria and the Golgi ribbon. We discuss the advantages of this approach for quantitative cellular ET of mammalian cells, briefly discuss its application relevant to other complementary techniques, and summarize future strategies for overcoming some of its current limitations.