Anticoagulant heparan sulfate proteoglycans expression in the rat ovary peaks in preovulatory granulosa cells

Ovarian granulosa cells synthesize anticoagulant heparan sulfate proteoglyc ans (aHSPGs), which bind and activate antithrombin III. To determine if aHS PGs could contribute to the control of proteolytic activities involved in f ollicular development and ovulation, we studied the pattern of expression o f these proteoglycans during the ovarian cycle. aHSPGs were localized on ce lls and tissues by I-125-labeled antithrombin III binding followed by micro scopic autoradiography. Localization of aHSPCs has shown that cultured gran ulosa cells, hormonally stimulated by gonadotropins to differentiate in vit ro, up-regulate their synthesis and release of aHSPGs. In vivo, during gona dotropin-stimulated cycle, aHSPGs are present on granulosa cells of antral follicles and are strongly labeled in preovulatory follicles. These data de monstrate that aHSPG expression in the ovarian follicle is hormonally induc ed to culminate in preovulatory follicles. Moreover, we have shown that fiv e heparan sulfate core proteins mRNA (perlecan; syndecan-1, -2, and -4; and glypican-1) are synthesized by granulosa cells, providing attachment for a nticoagulant heparan sulfate chains on the cell surface and in the extracel lular matrix. These core proteins are constantly expressed during the cycle , indicating that modulations of aHSPG levels observed in the ovary are lik ely controlled at the level of the biosynthesis of anticoagulant heparan su lfate glycosaminoglycan chains. This expression pattern enables aHSPGs to f ocus serine protease inhibitors in the developing follicle to control prote olysis and fibrin formation at ovulation.