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Nutrient metabolism regulates insulin granule formation in the pancreatic islet β-cell via ER redox homeostasis

By Kristen E Rohli, Cierra K Boyer, Shelby C Bearrows, Marshall R Moyer, Weston S Elison, Casey J Bauchle, Sandra E Blom, Chi-Li Yu, Marshall R Pope, Jianchao Zhang, Yanzhuang Wang, Samuel Stephens

Posted 23 Sep 2021
bioRxiv DOI: 10.1101/2021.09.22.461417

Defects in the {beta}-cells secretion system are well-described in Type 2 diabetes (T2D), including reduced insulin storage and impaired proinsulin processing; however, the cellular mechanisms underlying these secretory defects and the contribution of chronic hyperglycemia to this process remain poorly understood. In this study, we provide evidence that oxidative protein folding in the endoplasmic reticulum (ER) is perturbed in models of {beta}-cell dysfunction, leading to delays in proinsulin trafficking and insulin granule formation. Using an in situ fluorescent pulse-chase labeling strategy and APEX2-based proximity labeling, we demonstrate that enriched interactions of proinsulin with ER oxidoreductases coincides with a delay in proinsulin ER export. Furthermore, our data show that proinsulin ER export can be regulated by metabolically-derived NADPH and reducing equivalent (glutathione) availability. Together, these data highlight an emerging role for nutrient metabolism and mitochondrial dysfunction in the maladaptive remodeling of the {beta}-cells secretory pathway during the decline of {beta}-cell function in T2D.

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