The<i>in vivo</i>Hyperglycemic Microenvironment Disrupts Human Islet Identity and Function After Transplantation

Pancreatic islet transplantation is an established approach for β-cell replacement in insulin-deficient diabetes. Recent advancements in islet isolation, culture, and transplantation have improved metabolic outcomes and patient safety. However, preserving islet viability and functionality after transplantation continues to be a significant challenge. Previous studies have demonstrated that a supportive microenvironment—characterized by effective vascularization, paracrine-autocrine signaling, and normoxia—plays a critical role in promoting islet survival and proliferation. Understanding how the in vivo microenvironment affects transplanted islets and identifying strategies to enhance long-term β-cell function and to preserve β-cell mass are key objectives of this study. We hypothesize that human islets from non-diabetic donors, when transplanted into diabetic mice, will lose β-cell identity and function due to glucotoxicity and an unfavorable microenvironment. To test this, varying numbers of non-diabetic human islets (250, 400, or 600) were transplanted under the kidney capsule of either euglycemic or streptozotocin (STZ)-induced diabetic immunodeficient NSG mice. As anticipated, islets from non-diabetic donors exhibited normal levels of C-peptide, insulin, and the β-cell identity marker NKX6.1 prior to transplantation. Transplantation of 400 or 600 islets into STZ-diabetic mice occasionally reduced hyperglycemia, dependent on blood glucose prior to transplantation, with the 600-islet group showing better kidney engraftment and more robust graft staining. Immunostaining of kidney sections from control mice revealed the presence of insulin (INS) and NKX6.1 within the grafts, indicating that islet identity was preserved in the euglycemic environment. Furthermore, STZ-induced diabetic mice that achieved euglycemia after transplantation exhibited improved β-cell marker expression compared to those in the transplanted hyperglycemic group. Conversely, STZ-treated diabetic mice transplanted with 250, 400, or 600 islets that fail to recover from hyperglycemia showed no improvement in islet function, likely due to glucotoxicity. Immunostaining of endogenous pancreas tissue revealed a nearly 40% loss of NKX6.1+/Ins+ cells compared to the euglycemic group. Notably, STZ-diabetic mice that did not achieve euglycemia showed no reduction in hyperglycemia post-transplantation and failed to recover mature β-cell markers in the transplanted islets. These findings offer valuable insights into the mechanisms of β-cell dysfunction in transplanted islets, highlighting the critical role of the in vivo microenvironment. They could also inform the development of strategies to enhance both the survival and function of transplanted islets, potentially improving outcomes for individuals undergoing islet transplantation. 5T32DK007120-49 (RW), R01 DK123163 (MR), R01 DK133838 (MR) This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.