Hyperglycemia-induced alteration of ER redox homeostasis delays ER export of proinsulin
Defects in the pancreatic {beta}-cells secretion system are well-described in Type 2 diabetes (T2D) and include impaired proinsulin processing and a deficit in mature insulin-containing secretory granules; however, the cellular mechanisms underlying these defects and the contribution of hyperglycemia to this process remain poorly understood. Here, we used an in situ fluorescent pulse-chase strategy and proximity labeling-based quantitative proteomics analysis to study proinsulin trafficking and demonstrate a direct link to glucose metabolism via the production of redox intermediates that facilitate proinsulin export from the ER. We show that ER export of proinsulin is delayed in T2D models resulting in decreased insulin granule formation and further demonstrate this process can be regulated by NADPH and reducing equivalent availability. Together, these data highlight a critical role for nutrient metabolism and mitochondrial dysfunction in the maladaptive remodeling of the {beta}-cells secretory pathway in the decline of {beta}-cell function in T2D.