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

Although islet transplantation is an ideal option for individuals with diabetes, early graft failure due to beta cell apoptosis and stress-induced dysfunction severely limits long-term efficacy. Human umbilical cord mesenchymal stem cells (hucMSCs) have multiple functions including maintaining cellular homeostasis. However, it remains unknown as to whether extracellular vesicles (EVs) derived from hucMSCs (hucMSC-EVs) provide protective effects against transplant-related trauma-induced islet injury. This study aimed to investigate the effects of hucMSC-EVs on islet graft survival in a syngeneic mouse model of islet transplantation and to examine the mechanism of protection.

EVs were isolated from cultured hucMSCs and characterised by transmission electron microscopy, nanoparticle tracking and western blotting. The effects of hucMSC-EVs on islet graft function were evaluated in a mouse model of streptozocin-induced diabetes via co-transplantation under the kidney capsule. Beta cell survival and function were assessed by immunofluorescence, TUNEL staining, insulin secretion assays and in vivo imaging. Endoplasmic reticulum stress (ERS) and mitochondrial dysfunction were further analysed in primary islets and NIT-1 beta cells under thapsigargin- or tunicamycin-stimulated ERS models. Further calcium imaging, JC-1 staining, western blotting and Seahorse assays were performed. microRNA sequencing was conducted and the role of miR-182-5p and XBP1 in mediating hucMSC-EV function was verified using knockdown, overexpression and dual-luciferase assays.

Co-transplantation of hucMSC-EVs with 250 islet equivalents significantly improved glycaemic control (p<0.01) and glucose tolerance (p<0.01) in diabetic mice. Apoptotic beta cells were significantly reduced in grafts receiving EVs, as shown by TUNEL assays (p<0.05) and cleaved caspase 3 staining (p<0.05). Ex vivo, hucMSC-EVs were internalised by beta cells and protected against tunicamycin-induced apoptosis (p<0.01), preserved insulin expression and restored glucose-stimulated insulin secretion. While ERS enhanced interactions between endoplasmic reticulum and mitochondria, hucMSC-EVs maintained calcium homeostasis, improved mitochondrial energy metabolism and alleviated ERS. Small RNA sequencing and functional analysis identified that XBP1-targeted miR-182-5p was enriched in hucMSC-EVs, which further fine-tuned endoplasmic reticulum-mitochondria communication via reducing inositol-1,4,5-trisphosphate receptors at mitochondria-associated membranes and activated Nrf2 to restore mitochondrial calcium homeostasis under ERS. miR-182-5p inhibition reversed the protective effects of EVs on beta cell calcium homeostasis and viability. In vivo, depletion of miR-182-5p in hucMSC-EVs abolished the ability to prevent beta cell apoptosis and improve glycaemic control in diabetic mice.

hucMSC-EVs significantly improved the survival and function of islet grafts by delivering miR-182-5p, which targeted XBP1 to modulate mitochondria-associated membranes, attenuate ERS and restore mitochondrial calcium homeostasis. These findings highlight a novel cell-free EV-based therapeutic strategy for improving the outcome of islet transplantation.