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Insulin granule morphology and crinosome formation in mice lacking the pancreatic β cell-specific phogrin (PTPRN2) gene

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Abstract

We recently reported that phogrin, also known as IA-2β or PTPRN2, forms a complex with the insulin receptor in pancreatic β cells upon glucose stimulation and stabilizes insulin receptor substrate 2. In β cells of systemic phogrin gene knockout (IA-2β−/−) mice, impaired glucose-induced insulin secretion, decreased insulin granule density, and an increase in the number and size of lysosomes have been reported. Since phogrin is expressed not only in β cells but also in various neuroendocrine cells, the precise impact of phogrin expressed in β cells on these cells remains unclear. In this study, we performed a comprehensive analysis of morphological changes in RIP-Cre+/−Phogrinflox/flox (βKO) mice with β cell-specific phogrin gene knockout. Compared to control RIP-Cre+/− Phogrin+/+ (Ctrl) mice, aged βKO mice exhibited a decreased density of insulin granules, which can be categorized into three subtypes. While no differences were observed in the density and size of lysosomes and crinosomes, organelles involved in insulin granule reduction, significant alterations in the regions of lysosomes responding positively to carbohydrate labeling were evident in young βKO mice. These alterations differed from those in Ctrl mice and continued to change with age. These electron microscopic findings suggest that phogrin expression in pancreatic β cells plays a role in insulin granule homeostasis and crinophagy during aging, potentially through insulin autocrine signaling and other mechanisms.

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The datasets generated and analyzed during the current study are available from the corresponding author on reasonable request.

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Acknowledgements

The authors thank Mrs. Mari Hosoi (Gunma University, Maebashi, Japan) for her assistance in mouse breeding.

Funding

This study was supported by Grants-in-Aid from the Japan Society for the Promotion of Science (JSPS) #25450471, #16K08078, #20K06418 (to HG), #24390050, #17K08528, and #20H05310 (to ST). It was also supported in part by the joint research program of the Institute for Molecular and Cellular Regulation, Gunma University (No. 15012 and 18015; to HG and ST) and the Nihon University College of Bioresource Sciences Research Grant for 2019–2022 (to HG and TY).

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TY, HG, MM, AO, HM, MI-M, HH, SK, and CK performed the histological experiments and analyzed the histological image data. HG and ST designed and conducted this study. CK and ST prepared anti-phogrin mouse monoclonal antibody, generated phogrin βKO mice, and fixed the tissue specimens obtained from mice. HG, CK, and ST performed biochemical analyses. HG prepared the original draft of the manuscript. MH contributed to experimental design and reviewed the manuscript. ST and HG revised and edited the draft. The final manuscript has been read and approved by all authors.

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Correspondence to Hiroshi Gomi.

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Yasui, T., Mashiko, M., Obi, A. et al. Insulin granule morphology and crinosome formation in mice lacking the pancreatic β cell-specific phogrin (PTPRN2) gene. Histochem Cell Biol 161, 223–238 (2024). https://doi.org/10.1007/s00418-023-02256-8

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  • DOI: https://doi.org/10.1007/s00418-023-02256-8

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