Inverse Trends in Expression of Promoters and Inhibitors of Angiogenesis at E15, PN5, and PN7 During Normal Retinal Development

Abstract

Abstract: : Purpose: Proangiogenic and antiangiogenic factors control the growth and stability of blood vessels throughout life. VEGF is one of the strongest stimulators and PEDF the strongest inhibitor of angiogenesis in the retina. While several studies show a relationship between these two factors in the adult neovascular retina, there is no evidence to show the balance between these molecules in the developing retina. The purpose of this study is to establish the relationship between PEDF and other factors that control angiogenesis during normal retinal development. Methods: C57 B/L6 mouse retinas were dissected at developmental stages E13, E15, E17, PN3, PN7, PN14 and PN21 and processed for RNA extraction. The expression of various angiogenic and antiangiogenic factors during each stage of development was determined using RT–PCR. Results: The inhibitors of angiogenesis, PEDF, TSP1, TSP2, TIMP2, and TIMP3 were present at all stages of development, peaked at E15, and strongly decreased at PN3 developmental stages of the mouse retina. The levels of all the inhibitors, except TSP2, increased again at PN7 and decreased thereafter. The proangiogenic factors VEGF–A₁₆₅, VEGF–A₁₂₁, and VEGF–R2 increased in expression at E15 peaked at PN3, when the antiangiogenic factors are at their lowest levels, and decreased again at PN7. VEGFR1 followed the pattern of expression of the angiogenesis inhibitors but peaked at PN14 instead of E15. Conclusions: These results indicate that the expression of key angiogenesis inhibitors show a similar pattern of expression during early development of the retina with the highest levels at E15 and PN7 and the lowest levels at PN3. Their expression is inversely related to the expression profile of proangiogenic factors at those key time points. PN3 marks the beginning of a second wave of vascularization in deep retinal layers and PN7, the beginning of a capillary network of radial vessels in the nerve fiber layer.

Keywords: gene/expression • retinal development • retinal neovascularization