Obesity and insulin resistance lead to islet hyperplasia. However, how the islet remodeling influences the pancreatic environment and the associated neurovascular networks is largely unknown. The lack of information is primarily due to the difficulty of global visualization of the hyperplasic islet (>200 μm) and the neurovascular environment with high definition.
We modulated the pancreatic optical property to achieve 3-dimensional (3-D) whole-islet histology and to integrate transmitted light microscopy (which provides the ground-truth tissue information) with confocal fluorescence imaging. The new optical and imaging conditions were used to globally examine the hyperplastic islets of the young (2 months) obese db/db and ob/ob mice, which otherwise cannot be easily portrayed by the standard microtome-based histology. The voxel-based islet micrographs were digitally processed for stereo projection and qualitative and quantitative analyses of the islet tissue networks.
Paired staining and imaging of the pancreatic islets, ducts and neurovascular networks reveal the unexpected formation of the ‘neuro-insular-ductal complex’ in the young obese mice. The complex consists of the peri- and/or intra-islet ducts and prominent peri-ductal sympathetic nerves; the latter contributes to a marked increase in islet sympathetic innervation. In vascular characterization, we identify a decreased perivascular density of the ob/ob islet pericytes, which adapt to ensheathing the dilated microvessels with hypertrophic processes.
Modulation of pancreatic optical property enables 3-D panoramic examination of islets in the young hyperphagic mice to reveal the formation of the islet–duct complex and neurovascular remodeling. On the basis of the morphological proximity of the remodeled tissue networks, we propose a reactive islet microenvironment consisting of the endocrine cells, ductal epithelium and neurovascular tissues in response to the metabolic challenge that is experienced early in life.
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We thank the Brain Research Center in National Tsing Hua University for technical support of confocal imaging. This work was supported in part by grants from the Chang Gung Memorial Hospital (CMRP G3C0191 and CMRPG3D0601) to JHJ, and Taiwan National Health Research Institutes (NHRI-EX102-10044EI and NHRI-EX103-10332EI) and National Science Council (NSC 102-2628-B-007-002-MY2) to SCT.
All authors contributed to experimental design, data analysis and interpretation of data. HJC, SJP and TEH contributed to specimen preparation and data collection. CHK and JHJ contributed to the islet transplantation experiment. SCT directed the imaging project and contributed to the writing of the paper. All the authors approved the final version of the paper.
The authors declare no conflict of interest.
Supplementary Information accompanies this paper on International Journal of Obesity website
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