Effect of hypoxia-inducible VEGF gene expression on revascularization and graft function in mouse islet transplantation

Abstract

Summary For gene transfer strategies to improve islet engraftment, vascular endothelial growth factor (VEGF) expression should be regulated in a way that matches the transient nature of revascularization with simultaneously avoiding undesirable effects of overexpression. The aim of this study was to investigate the effects of hypoxia‐inducible VEGF gene transfer using the RTP801 promoter on islet grafts. We implanted pSV‐hVEGF transfected, pRTP801‐hVEGF transfected or nontransfected mouse islets under the kidney capsule of streptozotocin‐induced diabetic syngeneic mice. Human VEGF immunostaining of day 3 grafts revealed that the pRTP801‐hVEGF transfected group had higher hVEGF expression compared with the pSV‐hVEGF transfected group. BS‐1 staining of day 3 grafts from the pRTP801‐hVEGF transfected group showed the highest vascular density, which was comparable with day 6 grafts from the nontransfected group. In 360 islet equivalent (IEQ)‐transplantation which reverted hyperglycemia in all mice, the area under the curve of glucose levels during intraperitoneal glucose tolerance test 7 weeks post‐transplant was lower in mice transplanted with pRTP801‐hVEGF transfected grafts compared with mice transplanted with nontransfected grafts. In 220 IEQ‐transplantations, diabetic mice transplanted with pRTP801‐hVEGF islets became normoglycemic more rapidly compared with mice transplanted with pSV‐hVEGF or nontransfected islets, and diabetes reversal rate after 50 days was 90%, 68%, and 50%, respectively. In conclusion, our results indicate that regulated overexpression of hVEGF in a hypoxia‐inducible manner enhances islet vascular engraftment and preserves islet function overtime in transplants.

Beneficial effects of growth hormone-releasing hormone agonists on rat INS-1 cells and on streptozotocin-induced NOD/SCID mice

“…It has been reported that administration of GH increases proliferation of β cells in transplanted islets (49). Nerve growth factor (NGF) and VEGFs play a critical role in development of β cells and are also associated with the survival of islets in vivo following transplantation (50)(51)(52). GHRH(1-29)NH 2 was reported to stimulate the expression of VEGF in vitro (53), and, correspondingly, GHRH antagonists strongly inhibited the expression of VEGF in tumor (54).…”

Myeloid-derived suppressor cells in transplantation and cancer

“…HIF-1 α is transcriptional factor involved in VEGF expression and regulates the development of MDSC [89]. In transplantation, hypoxia-induced VEGF enhances engraftment and prolongs islet allograft survival [90, 91]. Anti-VEGF treatment has shown promising results in tumor-bearing mice by reducing MDSC accumulation and preventing T-cell anergy and Treg development [92].…”

Nerve growth factor is associated with islet graft failure following intraportal transplantation

“…Insulin staining, TUNEL method and H&E staining were performed using the same procedure as above. Specimens were stained by immunohistochemistry for VEGF for vascularization 50,51 and HIF-1a to determine hypoxia. 11,12 Primary antibodies were goat anti-VEGF antibody (Santa Cruz Biotechnology Inc., sc-1836) diluted 1:50, and goat anti-HIF-1a antibody (Santa Cruz Biotechnology Inc., sc-12542) diluted 1:25.…”