BACKGROUND Several mechanisms have been proposed to account for diabetes-induced microvasculopathy (DMV). Although Notch signaling was reported to be affected by glucose metabolism in endothelial cells during developmental angiogenesis, it has not been investigated in vascular remodeling of adult capillaries in relation to diabetes mellitus.

METHODS We induced diabetes mellitus in 8-week-old adult mice by intravenously administering streptozotocin. After 6 weeks, we harvested organs, including retina, heart, and skeletal muscle, and evaluated the capillaries with immunofluorescence and confocal microscopy. We modulated endothelial Notch signaling using chemical inhibitors in wild-type mice or transgenic mice, inducing conditional knockout of Jagged1 or Mib1.

RESULTS DMV was characterized by capillary remodeling, regression, and decreased density. Notch ligand Jagged1, but not δ-like ligand 4, was markedly increased in endothelial cells of diabetic mice. Using endothelium-specific Jagged1 knockdown mice, we found that blocking Jagged1 prevented DMV even under diabetic conditions. Furthermore, in the inducible endothelium-specific Jagged1 knockdown mice, blocking Jagged1 even at 4 weeks after the establishment of DMV could reverse it, leading to normalization of retinal vasculature. A search for downstream signals revealed that diabetes mellitus decreased the nuclear localization of Notch1 intracellular domain and reduced the expression of VE-cadherin and N-cadherin in endothelial cells. Chemical Notch inhibition phenocopied DMV in normal mice.

CONCLUSIONS Our findings indicate that diabetes mellitus induces Jagged1 overexpression and suppresses Notch signaling in endothelial cells, leading to DMV in adult mice. We conclude that dysregulated intercellular Notch signaling may be a novel mechanism of DMV.