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Abstract: Background: Hypoxia‐induced damage is one of the key factors associated with islet graft dysfunction. Mesenchymal stem cells (MSCs) could be used to enhance the therapeutic effect of islet transplantation due to their paracrine potential such as exosomes. In this study, we investigated whether exosomes from human umbilical cord‐derived MSC‐conditioned medium (hu‐MSC‐CM) could increase the survival and function of neonatal porcine islet cell clusters (NICCs) exposed to hypoxia. Methods: Neonatal porcine islet cell clusters were cultured with hu‐MSC‐CM, with or without exosomes, and native medium RPMI‐1640 (Control) under hypoxic conditions (1% O2). The effects of exosomes on NICCs viability and function in vitro were examined by FACS, the Loops system, and the Extracellular Flux assay, respectively. Results: Compared with NICCs cultured in RPMI‐1640 medium and hu‐MSC‐CM without exosomes, the survival ratio, viability, and function increased in NICCs cultured in hu‐MSC‐CM with exosomes. Conclusions: This study found that hu‐MSC‐CM could protect NICCs from hypoxia‐induced dysfunction, and exosomes played an important role in hypoxic resistance, suggesting a potential strategy to improve islet transplantation outcomes. [ABSTRACT FROM AUTHOR]

Background: The dysfunction of islet grafts is generally attributed to hypoxia‐induced damage. Mesenchymal stem cells (MSCs) are currently thought to effectively protect cells from various risk factors via regulating autophagy. In our study, we investigated if human umbilical cord‐derived MSCs could ameliorate hypoxia‐induced apoptosis in porcine islets by modulating autophagy, and we explored the underlying mechanisms. Methods: Neonatal porcine islet cell clusters (NICCs) were cultured with human umbilical cord‐derived MSC conditioned medium (huc‐MSC‐CM) and RPMI‐1640 medium (control) under hypoxic conditions (1% O2) in vitro. NICCs were treated with 3‐methyladenine (3‐MA) and chloroquine (CQ) to examine the role of huc‐MSC‐CM in regulating autophagy. Finally, the levels of several cytokines secreted by huc‐MSCs were detected by ELISAs, and the corresponding inhibitors were applied to investigate which cytokine mediates the protective effects of huc‐MSC‐CM. The effects of huc‐MSC‐CM on NICCs viability and autophagy were examined using AO/PI staining, flow cytometry analysis, transmission electron microscopy (TEM) and confocal fluorescence microscopy analysis. The insulin secretion of NICCs was tested with an insulin immunoradiometric assay kit. Results: Compared to the control, the huc‐MSC‐CM treatment improved the viability of NICCs, inhibited apoptosis, increased autophagic activity and the levels of PI3K class III and phosphorylated Akt, while the ratio of phosphorylated mTOR/mTOR was reduced. These changes were reversed by CQ and 3‐MA treatments. High concentrations of IL‐6 were detected in hu‐MSC‐CM. Furthermore, recombinant IL‐6 pre‐treatment exerted similar effects as huc‐MSC‐CM, and these effects were reversed by a specific inhibitor of IL‐6 (Sarilumab). Conclusions: Our results demonstrated that huc‐MSC‐CM improved islet viability and function by increasing autophagy through the PI3K/Akt/mTOR pathway under hypoxic conditions. Additionally, IL‐6 plays an important role in the function of huc‐MSC‐CM. [ABSTRACT FROM AUTHOR]