Hypoglycemia reduces vascular endothelial growth factor A production by pancreatic beta cells as a regulator of beta cell mass

J Biol Chem. 2013 Mar 22;288(12):8636-8646. doi: 10.1074/jbc.M112.422949. Epub 2013 Feb 1.

Abstract

VEGF-A expression in beta cells is critical for pancreatic development, formation of islet-specific vasculature, and Insulin secretion. However, two key questions remain. First, is VEGF-A release from beta cells coupled to VEGF-A production in beta cells? Second, how is the VEGF-A response by beta cells affected by metabolic signals? Here, we show that VEGF-A secretion, but not gene transcription, in either cultured islets or purified pancreatic beta cells, was significantly reduced early on during low glucose conditions. In vivo, a sustained hypoglycemia in mice was induced with Insulin pellets, resulting in a significant reduction in beta cell mass. This loss of beta cell mass could be significantly rescued with continuous delivery of exogenous VEGF-A, which had no effect on beta cell mass in normoglycemic mice. In addition, an increase in apoptotic endothelial cells during hypoglycemia preceded an increase in apoptotic beta cells. Both endothelial and beta cell apoptosis were prevented by exogenous VEGF-A, suggesting a possible causative relationship between reduced VEGF-A and the loss of islet vasculature and beta cells. Furthermore, in none of these experimental groups did beta cell proliferation and islet vessel density change, suggesting a tightly regulated balance between these two cellular compartments. The average islet size decreased in hypoglycemia, which was also prevented by exogenous VEGF-A. Taken together, our data suggest that VEGF-A release in beta cells is independent of VEGF-A synthesis. Beta cell mass can be regulated through modulated release of VEGF-A from beta cells based on physiological need.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism
  • Cell Proliferation
  • Cells, Cultured
  • Gene Expression
  • Hypoglycemia / metabolism*
  • Insulin-Secreting Cells / metabolism*
  • Insulin-Secreting Cells / physiology
  • Intramolecular Transferases / genetics
  • Intramolecular Transferases / metabolism
  • Mice
  • Pancreas / blood supply
  • Pancreas / pathology
  • Vascular Endothelial Growth Factor A / biosynthesis*
  • Vascular Endothelial Growth Factor A / genetics
  • Vascular Endothelial Growth Factor A / metabolism
  • Vascular Endothelial Growth Factor A / physiology

Substances

  • Arabidopsis Proteins
  • Vascular Endothelial Growth Factor A
  • vascular endothelial growth factor A, mouse
  • Intramolecular Transferases
  • marneral synthase, Arabidopsis