No abstract

Transcription factor Ets-1 has been reported to regulate angiogenesis in vascular endothelial cells. Here, we investigated a mechanism that may regulate the expression of Ets-1 in vascular endothelial growth factor (VEGF)- and hypoxia-induced retinal neovascularization and that may have potential to inhibit ocular neovascular diseases. VEGF and hypoxia increased Ets-1 expression in cultured bovine retinal endothelial cells. The VEGF-induced mRNA increase of Ets-1 was suppressed by a tyrosine kinase inhibitor (genistein), by inhibitors of MEK (mitogen-activated protein and extracellular signal-regulated kinase kinase) (PD98059 and UO126), and by inhibitors of protein kinase C (GF109203X, staurosporine, and Gö6976). Dominant-negative Ets-1 inhibited VEGF-induced cell proliferation, tube formation, and the expression of neuropilin-1 and angiopoietin-2. In a mouse model of proliferative retinopathy, Ets-1 mRNA was up-regulated. Intravitreal injection of dominant-negative Ets-1 suppressed retinal angiogenesis in a mouse model of proliferative retinopathy. In conclusion, VEGF induces Ets-1 expression in bovine retinal endothelial cells and its expression is protein kinase C/ERK pathway-dependent. Ets-1 up-regulation is involved in the development of retinal neovascularization, and inhibition of Ets-1 may be beneficial in the treatment of ischemic ocular diseases.

The Eph receptor/ephrin system is a recently discovered regulator of vascular development during embryogenesis. Activation of EphA2, one of the Eph receptors, reportedly suppresses cell proliferation and adhesion in a wide range of cell types, including vascular endothelial cells. Vascular endothelial growth factor (VEGF) plays a primary role in both pathological angiogenesis and abnormal vascular leakage in diabetic retinopathy. In the study described herein, we demonstrated that EphA2 stimulation by ephrinA1 in cultured bovine retinal endothelial cells inhibits VEGF-induced VEGFR2 receptor phosphorylation and its downstream signaling cascades, including PKC (protein kinase C)-ERK (extracellular signal-regulated kinase) 1/2 and Akt. This inhibition resulted in the reduction of VEGF-induced angiogenic cell activity, including migration, tube formation, and cellular proliferation. These inhibitory effects were further confirmed in animal models. Intraocular injection of ephrinA1 suppressed ischemic retinal neovascularization in a dose-dependent manner in a mouse model. At a dose of 125 ng/eye, the inhibition was 36.0 ؎ 14.9% (P < 0.001). EphrinA1 also inhibited VEGF-induced retinal vascular permeability in a rat model by 46.0 ؎ 10.0% (P < 0.05). These findings suggest a novel therapeutic potential for EphA2/ephrinA1 in the treatment of neovascularization and vasopermeability abnormalities in diabetic retinopathy.