Engineered vascular beds provide key signals to pancreatic hormone-producing cells.

The mechanisms underlying early islet graft failure are not entirely clear, but are thought to involve ischemic injury due to delayed vascularization. We hypothesize that blood vessels play an active role in cell-cell communications supporting islet survival and engraftment. To test this hypothesis and to uncouple endothelial cell (EC)-generated signaling stimuli from their nutritional and gas exchange functions, we developed three dimensional (3D) endothelial vessel networks in engineered pancreatic tissues prepared from islets, fibroblasts and ECs. The tri-culture setup, seeded on highly porous biocompatible polymeric scaffolds closely mimics the natural anatomical context of pancreatic vasculature. Enhanced islet survival correlating with formation of functional tube-like endothelial vessels was demonstrated. Addition of foreskin fibroblasts to islet-endothelial cultures promoted tube-like structure formation, which further supported islet survival as well as insulin secretion. Gene expression profiles of EC growth factors, extracellular matrix (ECM), morphogenes and differentiation markers were significantly different in 2D versus 3D culture systems and were further modified upon addition of fibroblasts. Implantation of prevascularized islets into diabetic mice promoted survival, integration and function of the engrafted engineered tissue, supporting the suggested role of ECs in islet survival. These findings present potential strategies for preparation of transplantable islets with increased survival prospects.

Lineage tracing evidence for in vitro dedifferentiation but rare proliferation of mouse pancreatic beta-cells.

Understanding and manipulating pancreatic beta-cell proliferation is a major challenge for pancreas biology and diabetes therapy. Recent studies have raised the possibility that human beta-cells can undergo dedifferentiation and give rise to highly proliferative mesenchymal cells, which retain the potential to redifferentiate into beta-cells. To directly test whether cultured beta-cells dedifferentiate, we applied genetic lineage tracing in mice. Differentiated beta-cells were heritably labeled using the Cre-lox system, and their fate in culture was followed. We provide evidence that mouse beta-cells can undergo dedifferentiation in vitro into an insulin-, pdx1-, and glut2-negative state. However, dedifferentiated beta-cells only rarely proliferate under standard culture conditions and are eventually eliminated from cultures. Thus, the predominant mesenchymal cells seen in cultures of mouse islets are not of a beta-cell origin.