The role of granulosa and theca cell interactions in ovarian structure and function

The term paracrine control has recently become very fashionable in the field of endocrinology: however, no study has yet clarified directly the role of paracrine activity in the functional and morphological development of endocrine organs. We developed a culture system in which two types of cells were allowed to attach to opposite sides of a collagen membrane in order to observe cellular communication directly and used it to explore the role of granulosa and theca cell interactions in ovarian structure and function. In the first series of the study, we explored the interaction between theca and granulosa cells by investigating the morphology, proliferation, and steroidogenesis of the cells. Granulosa cells cultured alone were flattened and polygonal in shape and formed a monolayer sheet. Granulosa cells cocultured with theca cells formed multilayer sheets. The apical surface of each cell appeared convex. Numerous filopodia spread over the cellular surfaces to connect individual cells. Theca cells cultured alone were thin, flat, and spindle-shaped. Theca cells cocultured with granulosa cells were also spindle-shaped; however, the apical surface appeared convex. The cell numbers of both granulosa and theca cells in the cocultured group increased approximately twofold compared to control cells cultured alone. The progesterone producing activity of granulosa cells in the cocultured group was reduced to 40% of that of cells in the control group. In contrast, the androstenedione producing activity of theca cells in the cocultured group increased approximately threefold compared to that of control group cells. In the second series of experiments, effects of cellular communication on cellular response to gonadotropins were investigated. When granulosa cells were cultured with theca cells, FSH treatment (1 μg/ml) promoted cellular growth: however, LH treatment (1 μg/ml) suppressed cellular growth and augmented their progesterone production. In contrast, such effects of gonadotropins were not detected when granulosa cells were cultured alone. LH induced estradiol production by granulosa cells both cultured alone and cocultured with theca cells: however, FSH-induced estradiol production was not detected in this experimental condition. LH treatment increased androstenedione production of theca cells cocultured with granulosa cells, but no increase was observed for theca cells cultured alone. These results demonstrate that communication between these two types of follicular cells results in reciprocal modulation of their morphology, structure, growth, and function and that the actions of gonadotropins on target cells in the follicular wall can also be modified by the communication between these cells. In contrast to granulosa and theca cells cultured alone, cells in coculture seemed to possess morphological and functional characteristics more similar to those of cells in the growing follicular wall in vivo. Therefore, we speculate that interactions between these two types of follicular cells is essential in the maintenance of original structure and function of the bovine follicular wall. © 1994 Wiley-Liss, Inc.