Although insulin-like growth factor 1 (IGF-1) has been associated with retinopathy, proof of a direct relationship has been lacking. Here we show that an IGF-1 receptor antagonist suppresses retinal neovascularization in vivo, and infer that interactions between IGF-1 and the IGF-1 receptor are necessary for induction of maximal neovascularization by vascular endothelial growth factor (VEGF). IGF-1 receptor regulation of VEGF action is mediated at least in part through control of VEGF activation of p44/42 mitogen-activated protein kinase, establishing a hierarchical relationship between IGF-1 and VEGF receptors. These findings establish an essential role for IGF-1 in angiogenesis and demonstrate a new target for control of retinopathy. They also explain why diabetic retinopathy initially increases with the onset of insulin treatment. IGF-1 levels, low in untreated diabetes, rise with insulin therapy, permitting VEGF-induced retinopathy.

E-selectin, an endothelial-specific adhesion molecule best known for its role in leukocyte adhesion, is not detected in quiescent endothelial cells, but is induced by inflammatory stimuli. However, E-selectin is also expressed in proliferating endothelial cells under noninflammatory conditions in vivo and in vitro, suggesting that E-selectin is also regulated by growth signals. To investigate E-selectin expression in lipopolysaccharide-stimulated versus nonstimulated proliferating cells, we analyzed the distribution of E-selectin-positive human microvascular endothelial cells in G0/G1, S, and G2/M phases of the cell cycle under both conditions. Lipopolysaccharide treatment resulted in uniformly increased E-selectin expression in cells in G0/G1, S, and G2/M. In contrast, levels of E-selectin in nonstimulated proliferating cells showed a linear correlation with the percentage of cells in G2/M. E-selectin in proliferating endothelial cells was not reduced by addition of soluble tumor necrosis factor-alpha-receptor or soluble interleukin-1-receptor indicating that its expression was not due to endogenous production of either cytokine. In addition, E-selectin was increased in cells stimulated with basic fibroblast growth factor, a well-known mitogen for endothelial cells. E-selectin in proliferating endothelial cells is functional, as shown by E-selectin-dependent adhesion of the promyelocytic leukemia cell line HL-60 to subconfluent human microvascular endothelial cells. In summary, these studies indicate that E-selectin can be regulated by a non-inflammatory pathway that is related to the proliferative state of the endothelium.