Scientists at the Harvard Department of Ophthalmology's Schepens Eye Research Institute and Massachusetts Eye and Ear Infirmary (MEEI) are the first to learn why the cornea, the clear window of the eye, is free of blood vessels--a unique phenomenon that makes vision possible. The key, say the researchers, is the unexpected presence of large amounts of the protein VEGFR-3 (vascular endothelial growth factor receptor-3) on the top epithelial layer of normal healthy corneas.
Diabetes can cause blood vessels to collapse, creating a hypoxic environment that generates vascular endothelial growth factor (VEGF) and triggers angiogenesis. Pericytes (diamonds) detach, destabilizing vessels. Kazlauskas and Im hypothesize that endothelial cells (rectangles) receive specific instructions during this unstable state that dictate whether the vessels should grow or regress. In the case of diabetic retinopathy, too many vessels grow, eventually obscuring vision. According to their findings, VEGFR-3 halts angiogenesis (blood vessel growth) by acting as a "sink" to bind or neutralize the growth factors sent by the body to stimulate the growth of blood vessels. The cornea has long been known to have the remarkable and unusual property of not having blood vessels, but the exact reasons for this had remained unknown.
These results, published in the July 25, 2006 issue of the Proceedings of the National Academy of Sciences and in the July 17 online edition, not only solve a profound scientific mystery, but also hold great promise for preventing and curing blinding eye disease and illnesses such as cancer, in which blood vessels grow abnormally and uncontrollably, since this phenomenon, present in the cornea normally, can be used therapeutically in other tissues.
Complete article is available at http://www.sciencedaily.com/releases/2006/07/060718073307.htm
