Retinal neovascularization (NV) is a major cause of blindness in the United States and developed countries. Vascular endothelial growth factor (VEGF) plays a major role in stimulating retinal neovascularization. Although much is known about the upstream signaling mechanisms in retinal angiogenesis, relatively less is known about the regulation and role of transcription factors in this process. Our laboratory is very interested in elucidating important transcription factors that mediate VEGF's effect on retinal NV. Myocyte enhancer factor 2C (MEF2C) is a MADS-box (MCM1, Agamous, Deficiens, serum response factor-box) transcription factor which is required for vascular development. Targeted deletion of MEF2C results in severe vascular abnormalities and embryonic lethality in mice. Preliminary data in our lab suggests an important role for MEF2C in VEGF function and retinal angiogenesis: (1) VEGF strongly increases MEF2C expression in human retinal endothelial cells (HRECs) in a protein kinase C (PKC)-dependent manner;(2) VEGF activates MEF2C function in HRECs;and (3) inhibition of MEF2C significantly blocks retinal endothelial cell migration in a VEGF-induced chemotaxis assay. Our overall hypothesis is that MEF2C is induced in retinal angiogenesis both at the level of gene expression and functional activity, and that MEF2C plays an important role in mediating retinal angiogenesis. In order to test our hypothesis, we will use purified human retinal endothelial cells and a well-characterized mouse model of retinal NV (the oxygen-induced retinopathy model). We will sequentially examine the regulation of MEF2C gene expression, regulation of MEF2C's activity, and the functional effect of MEF2C in retinal angiogenesis. Accordingly, we propose the following three specific aims: Specific Aim 1. Test the hypothesis that MEF2C gene expression is regulated during retinal NV by angiogenic growth factors. Specific Aim 2. Test the hypothesis that VEGF regulates MEF2C activity by promoting MEF2C nuclear translocation, DNA binding, and transcriptional activation. Specific Aim 3. Test the hypothesis that MEF2C plays an important functional role in retinal NV. The targeting of transcription factors is receiving increasing attention as a therapeutic approach for disease processes including cancer and heart failure. Further understanding of the regulation and role of MEF2C could similarly lead to new therapeutic strategies for treating retinal NV and other ocular angiogenic disorders.