Proliferative retinopathy is one of the most common and serious vascular complications of diabetes. The major pathological finding in the eye results form proliferation of retinal capillary endothelial cells, causing new and aberrant capillary growth on the surface of the retina. It is thought that growth hormone may be one of several important causes of this condition. However, many actions previously attributed to growth hormone are now known to be mediated by insulin-like growth factors (IFG). I will concentrate on determining the role of insulin-like growth factor I in the development of retinal neovascularization, with emphasis on its interactions with other angiogenic agents. I will use in vitro methods to study three key aspects of neovascularization: 1) production by the endothelial cell of enzymes which cause proteolysis of the extracellular matrix, 2) migration of the endothelial cell, and 3) proliferation of the endothelial cell. Human endothelial cell cultures derived from both diabetic retinas and non- diabetic retinas will be used. The use of diabetic endothelial cell cultures will enable me to also test whether an inherent defect exists in the diabetic endothelial cell. Both diabetic and non-diabetic cells will be studied under conditions of altered pH, varying glucose and insulin concentrations. These cell cultures will be compared with regard to ultrastructure, growth capacity and ability to release proteases. IGF I will be characterized along with established angiogenic factors on growth, movement, and enzyme production by these cells. I will test whether IGF I can induce the endothelial cells to invade a three-dimensional collagen matrix and form a network of capillary-like tubular structures. Also, the degradative potential of growth factor stimulated endothelial cells will be investigated using radiolabeled extracellular matrices. An in vivo model for studying angiogenesis has also been developed. When Elvax 4 pellets are placed in the cornea of rabbit eyes, IGF I induces vessels from the limbus to grow toward the pellet and surround it. The protocols of this proposal provide for the experimental dissection of the biochemical steps involved in neovascularization. A better understanding of how these phenomena are regulated at the cellular level could allow for the identification of specific inhibitors of neovascularization.
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