DIFFERENTIAL EFFECT OF COMPONENTS OF THE EXTRACELLULAR-MATRIX ON DIFFERENTIATION AND APOPTOSIS

Background: Epithelial cells are closely associated with a basement me mbrane, but the intimate relationships that affect growth, differentia tion and survival remain enigmatic, We have previously reported that g ranulosa cells adjacent to the basement membrane of the ovarian follic le have a higher degree of differentiation compared with cells located distal to the basement membrane. By contrast, granulosa cells distal to the basement membrane are the first to undergo apoptosis during fol licular atresia. Moreover, growth of granulosa cells in vitro on a nat urally produced basement-membrane-like extracellular matrix (ECM) enha nces progesterone production and the cellular response to gonadotropic hormones by an undefined mechanism. Results: To investigate the effec t of the ECM on granulosa cell differentiation and death, primary gran ulosa cells were cultured on ECMs that lacked or contained bFGF (basic fibroblast growth factor). These otherwise identical ECMs were deposi ted by HR9 mouse endodermal cells, which do not synthesize bFGF, or by HR9 cells transfected with the bFGF gene. Both ECMs provided protecti on against apoptosis in serum-free medium, but only the bFGF-containin g ECM maintained expression of the steroidogenic P450scc enzyme system and the production of progesterone. Moreover, culturing the cells on this ECM enhanced the expression of the 30 kDa steroid acute regulator y protein which plays a key role in steroid hormone biosynthesis. Lami nin, but not fibronectin, was able to replace the ECM in protecting th e cells from apoptosis, but not in maintaining steroidogenesis, wherea s bFGF was able to enhance steroidogenesis without protecting the cell s against apoptosis. Cells cultured on both ECMs or laminin had a well -developed actin cytoskeleton compared with cells cultured on non-coat ed dishes, which underwent apoptosis. Conclusions: Cellular responses to ECM are mediated by the combined action of macromolecular constitue nts and regulatory molecules, such as bFGF, that are sequestered and s tored in the ECM. ECM or laminin protects against cell death by intera cting with specific integrin receptors and maintaining a well-develope d actin cytoskeleton. ECM-bound bFGF provides differentiation signals for granulosa cells, which are in intimate contact with the ECM. Thus, a clear distinction can be made between the survival activity and the differentiation stimulus exerted by the ECM on epithelial cells.