Vascular endothelial growth factor increases functional β-cell mass by improvement of angiogenesis of isolated human and murine pancreatic islets

Background. Blood flow is impaired in islet transplants, but there is conflicting evidence on improving the outcome by promoting vascularization. We previously reported that islet endothelial cells (EC) possess significant angiogenic capacity. Methods. To further address this issue, we studied human islets in culture under hypoxic conditions. Moreover, we used a transgene mouse model with human vascular endothelial growth factor (VEGF) production in beta-cells under the control of the rat insulin promoter (RIP) to stimulate islet EC proliferation. Results. Subsequent to a hypoxic stimulus, islets responded with specific expression patterns of VEGF and fibroblast growth factor; however, this was not sufficient to prevent the decay of islet EC. VEGF release of RIP-VEGF transgenic islets was controlled by glucose and resulted in the formation of sprouts. When transplanted to the kidney capsule of diabetic mice, RIP-VEGF islets significantly enhanced microvascular density and functional blood flow to the graft compared with controls. Conclusions. Optimized angiogenesis of islet transplants resulted in greater availability of insulin caused by beta-cell proliferation and a significantly higher percentage (90% versus 20%) of mice cured from diabetes.