Follicular Stage-Dependent Regulation of Rat Granulosa Cell Plasminogen Activator System by Transforming Growth Factor-Alpha in Vitro1

In the present study, we have examined the influence of transforming growth factor-alpha (TGFα) and FSH in vitro on the granulosa cell plasminogen activator (PA) system accompanying cell proliferation and differentiation during follicular development. Undifferentiated and differentiated rat granulosa cells from diethylstilbestrol (DES)- and eCG-treated immature rats, respectively, were cultured in medium containing FSH (400 ng/ml), TGFα (0.5−50 ng/ml), and/or transforming growth factor-beta (TGFβ; 25−100 ng/ml). Net secreted PA (PAs) and cell-associated PA (PAc) activities were higher in differentiated cells and were stimulated by TGFα (but not by TGFβ) in a concentration-dependent manner. Basal and FSH-stimulated PAs was higher than PAc and accounted for 70-80% of the total PA activity in both cell preparations. FSH-stimulated PA activities increased in undifferentiated granulosa cells but decreased in differentiated cells with increased duration of culture. A biphasic effect (stimulatory in the first 24 h and inhibitory thereafter) of TGFα on FSH-induced PA activities was observed in the cultures of undifferentiated granulosa cells. Whereas both urokinase (uPA) and tissue (tPA) PA appeared to be present in cultures of granulosa cells from DES-treated rats, only tPA could be detected in those from eCG-treated animals. TGFα increased basal tPA activity at both stages of follicular development but inhibited activities of uPA in undifferentiated granulosa cells, irrespective of the presence of FSH. This growth factor stimulated basal progesterone (P) and 20α-dihydroprogesterone (20α-OH-P) secretion (an index of granulosa cell differentiation), the effect being more pronounced at the late stage of follicular development. Although ineffective with respect to FSH-stimulated total progestin (P + 20α-OH-P) production in both cell preparations, TGFα inhibited the gonadotropin- induced P secretion in undifferentiated cells during 72 h of culture. In addition, the growth factor alone increased the DNA synthetic capacity (an index of cell proliferation) in undifferentiated granulosa cells but acted synergistically with FSH to inhibit DNA synthesis at both stages of follicular maturation. These findings suggest that during follicular maturation, the cytodifferentiative influence of FSH on granulosa cells is modulated by TGFα. Thus, this growth factor may control the programming of the cells from a proliferative to a differentiated state and may determine the fate of the follicle (i.e., atresia vs. growth).