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Islet beta cells in situ express intracellular heparan sulfate (HS), a property previously shown in vitro to be important for their survival. We report that HS levels inside islet beta cells correlate with the novel intracellular localization of the HSPG core proteins for collagen type XVIII (Col18), a conventional extracellular matrix component. Syndecan-1 (Sdc1) and CD44 core proteins were similarly localized inside beta cells. During isolation, mouse islets selectively lose HS to 11-27% of normal levels but retain their HSPG core proteins. Intra-islet HS failed to recover substantially during culture for 4 days and was not reconstituted in vitro using HS mimetics. In contrast, significant recovery of intra-islet HS to ∼40-50% of normal levels occurred by 5-10 days after isotransplantation. Loss of islet HS during the isolation procedure is independent of heparanase (a HS-degrading endoglycosidase) and due, in part, to oxidative damage. Treatment with antioxidants reduced islet cell death by ∼60% and increased the HS content of isolated islets by ∼twofold compared to untreated islets, preserving intra-islet HS to ∼60% of the normal HS content of islets in situ. These findings suggest that the preservation of islet HS during the islet isolation process may optimize islet survival posttransplant., (© Copyright 2015 The American Society of Transplantation and the American Society of Transplant Surgeons.)

The isolation of islets by collagenase digestion can cause damage and impact the efficiency of islet engraftment and function. In this study, we assessed the basement membranes (BMs) of mouse pancreatic islets as a molecular biomarker for islet integrity, damage after isolation, and islet repair in vitro as well as in the absence or presence of an immune response after transplantation. Immunofluorescence staining of BM matrix proteins and the endothelial cell marker platelet endothelial cell adhesion molecule-1 (PECAM-1) was performed on pancreatic islets in situ, isolated islets, islets cultured for 4 days, and islet grafts at 3-10 days posttransplantation. Flow cytometry was used to investigate the expression of BM matrix proteins in isolated islet β-cells. The islet BM, consisting of collagen type IV and components of Engelbreth-Holm-Swarm (EHS) tumor laminin 111, laminin α2, nidogen-2, and perlecan in pancreatic islets in situ, was completely lost during islet isolation. It was not reestablished during culture for 4 days. Peri- and intraislet BM restoration was identified after islet isotransplantation and coincided with the migration pattern of PECAM-1(+) vascular endothelial cells (VECs). After islet allotransplantation, the restoration of VEC-derived peri-islet BMs was initiated but did not lead to the formation of the intraislet vasculature. Instead, an abnormally enlarged peri-islet vasculature developed, coinciding with islet allograft rejection. The islet BM is a sensitive biomarker of islet damage resulting from enzymatic isolation and of islet repair after transplantation. After transplantation, remodeling of both peri- and intraislet BMs restores β-cell-matrix attachment, a recognized requirement for β-cell survival, for isografts but not for allografts. Preventing isolation-induced islet BM damage would be expected to preserve the intrinsic barrier function of islet BMs, thereby influencing both the effector mechanisms required for allograft rejection and the antirejection strategies needed for allograft survival.