Extracellular vesicles from human umbilical cord mesenchymal stem cells protect grafted islets against endoplasmic reticulum stress-induced mitochondrial dysfunction by modulating XBP1-based calcium homeostasis

Islet transplantation is an ideal option for diabetes while early graft lose serves as a major obstacle. Human umbilical cord mesenchymal stem cells (hucMSC) have multiple functions including the maintenance of cellular homeostasis. However, it is unknown whether extracellular vesicles (EVs) derived from hucMSC (hucMSC-EVs) provide protective effects against transplant-related trauma-induced islet injury. Here, we isolated and purified hucMSC-EVs, and found that hucMSC-EVs promoted grafted islet survival, and enhanced glycemic control following co-transplantation in a syngeneic streptozotocin (STZ)-induced mouse model of diabetes. After co-cultured for 12 h or 24 h, labelled hucMSC-EVs with PKH67 were readily internalized by NIT-1 β cells and islets. In tunicamycin (Tm) and thapsigargin (Tg) induced specific endoplasmic reticulum stress (ERS) cell injury models, hucMSC-EVs treatment improved cell viability and β cells function both in NIT-1 cells and ex vivo primary islets. Bulk RNA-seq demonstrated that hucMSC-EVs treatment significantly involved in ERS and the negative regulated mitochondrial apoptotic pathway. While ERS promoted interactions between endoplasmic reticulum (ER) and mitochondria, hucMSC-EVs alleviated ERS, maintained calcium homeostasis, and improved mitochondrial energy metabolism. Notably, the downregulation of XBP1 by hucMSC-EVs fine-tuned ER-mitochondria communication via reducing inositol-1,4,5-trisphosphate receptors at mitochondria-associated membranes (MAMs). Reduced XBP1 also activated Nrf2, restoring mitochondrial calcium homeostasis under ERS. miRNA analysis identified miR-182-5p enriched in hucMSC-EVs that specifically targeted XBP1 mRNA, leading to its degradation and downregulation. These findings demonstrate that hucMSC-EVs protect grafted islets by blocking XBP1 and restoring calcium homeostasis, thus suggesting their potential as a cell-free therapy for improving islet transplantation outcomes.