Microvascular development: learning from pancreatic islets

Abstract

Microvascular development is determined by the interplay between tissue cells and microvascular endothelial cells. Because the pancreatic islet is an organ composed mainly of endothelial and endocrine cells, it represents a good model tissue for studying microvascular development in the context of a tissue. In this review, we will describe the special morphology of islet capillaries and its role in the physiologic function of islets: secretion of insulin in response to blood glucose levels. We will speculate on how islet-secreted VEGF-A generates a permeable endothelium that allows insulin to pass quickly into the blood stream. In addition, we speculate on how endothelial cells might form a capillary lumen within the islets. At the end, we look at the islet microvasculature from a medical point of view, thus describing its critical role during type I diabetes and islet transplantation.

Blockade of β1 Integrin–Laminin-5 Interaction Affects Spreading and Insulin Secretion of Rat β-Cells Attached on Extracellular Matrix

“…In humans, collagen IV was detected in association with the islet microvasculature (40). Intimate relationships between individual ␤-cells and islet capillaries, and direct contact between ␤-cells and subendothelial basement membrane, have been confirmed by electron microscopy studies (41,42). In human pancreas, basement membrane of duct cells showed immunoreactivity for ladsin, a homolog of laminin-5, but in this study, islets were not analyzed (43).…”

Impaired insulin secretion in vivo but enhanced insulin secretion from isolated islets in pancreatic beta cell-specific vascular endothelial growth factor-A knock-out mice

“…To achieve normal dynamics of blood insulin levels, both the beta cells and vascular system in islets may play important roles [1]. The islet capillary network is about five times denser than that of the exocrine tissue and the microvasculature of pancreatic islets consists of thin fenestrated endothelial cells separated from beta cells by the basement membrane [1,2]. The islet microvasculature has a unique relationship with beta cells, which are polarised with one domain facing an arterial capillary and another facing a venous capillary [3].…”

Hyperglycemia Induces Apoptosis of Human Pancreatic Islet Endothelial Cells

“…This notion stands against the background that the microvasculature has a key role at the interface between the vascular space and organ parenchymas and participates in numerous pathophysiological processes. Pancreatic islets are one of the most vascularized organs, 1,2 and vascular endothelial growth factor-A secreted by the neighboring ␤ cells is responsible for this strong vascularization and capillary fenestration from organogenesis to adult life. 3 Recent studies indicate that the islet vasculature is likely to play a role in the physiology as well as in the disease of the pancreatic islets.…”