Transplanted islets undergo cell death immediately after transplantation due to poor blood supply to inner core. Islet isolation process severs existing peri-islet vascular connections.  Stimulation of intraislet endothelial cells to form peri-islet vessels (PIV’s) in vitro prior to transplantation may accelerate post-implant islet revascularization. Intra-pancreatic microvascular fragments are known to create microvascular networks and release angiogenic tropic factors. However, for the first time, we evaluated the effect peripancreatic fat-derived microvascular fragments (PPMVF) cells on PIV formation in a 3D-culture system.

Human islets were isolated from brain-dead donor pancreases (n=15) according to our laboratory protocol. Peripancreatic fat was collected around the pancreas and PPMVF cells were isolated using MVF cell isolation method.
 
Isolated human islets were cultured in a 3D collagen gel (rat tail collagen-1) for 14 days with PPMVF cells (250,000 cells). Confocal microscopy and Time-lapse microscopy (Cytation 5) was used to monitor islet-derived PIV growth every day for 14 days. 

Human islets co-cultured with PPMVF cells induced cellular sprouting within 7 days. Many of these sprouts appeared to be PIV since they resembled a vasculature that arose from the islets. Our labeling indicated that several of these sprouts were endothelial. Intraislet endothelial cells were stained with UEA-1 and we speculate these cells were the source of the peri-islet sprouts. 3D-cultured islets maintained >90% cellular viability after 14 days, whereas 2D-cultured islets displayed disintegration of their borders as well as reduced viability. Statistically significant difference (P<0.05) was observed in number of sprouts when islets were cultured in 3D environment without PPMVF cells. 

We have successfully stimulated the formation of peri-islet vessels from human islets with PPMVF cells in 3D matrix support. PPMVF with 3D culture may provide unique avenues to accelerate islet neovascularization following transplantation.