The long term goals are to elucidate the mechanisms that control new blood vessel growth - a process called angiogenesis - in the ovarian follicle and corpus luteum (CL). In the ovary, blood vessels undergo repeated and rapid growth and involution in conjunction with follicular growth and CL formation and regression. It is likely, that this vessel growth is controlled by the release of angiogenic factors from the granulosa cells of the developing follicle and from the cells of the CL - a mechanism analogous to that by which tumors recruit a blood supply. Rat ovarian tissue, for example, transplanted to the chorioallantoic membrane of the chick embryo induces new blood vessel formation and revascularizes; this revascularization is correlated with the functional status of the tissue, e.g., age of the CL. It was subsequently found that granulosa cells from preovulatory follicles of rats release potent endothelial cell mitogens when cultured in vitro. When cultured under hypoxic conditions, the cells release an additional high-MW factor that causes endothelial cells to lose their normal polygonal shape and assume an elongated morphology, resembling that of migrating endothelial cells. Furthermore, hypoxia induces the synthesis of specific proteins by granulosa cells and other cell types, a novel observation that could rapidly lead to the identification of hypoxia-induced angiogenic factors.
The specific aim of the present grant proposal are to: (I) Separate, characterize, purify, and identify the multiple angiogenic factors (endothelial cell effectors) present in or produced by rat granulosa cells and other ovarian tissues; (II) Evaluate the effects of mediators of ovarian function - gonadotropins, steroids, growth factors, glycosaminoglycans, etc. - on the production of these angiogenic factors; and (III) Determine the role of hypoxia in stimulating angiogenic factor production by granulosa cells. Identification of ovarian angiogenic factors and an understanding of how their production is controlled could lead to a better understanding of normal and abnormal ovarian function, as well as the pathological neovascularization that contributes to tumor growth, heart disease, and diabetic retinopathy.
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