TRANSFORMING GROWTH FACTOR-BETA-1 INHIBITS GONADOTROPIN ACTION IN CULTURED PORCINE SERTOLI CELLS

In the present study, we have tested the effects of transforming growth factor beta-1 (TGF-beta-1) on FSH action toward aromatase activity and lactate production in cultured Sertoli cells isolated from immature porcine testes. Whereas treatment of Sertoli cells with FSH resulted in a dose-dependent increase (about 7-fold) in aromatase activity (conversion of testosterone into estradiol) (ED50 = 80 ng/ml FSH), the addition of TGF-beta-1 reduced this gonadotropin action. The inhibitory effect of TGF-beta-1 on FSH aromatase activity was dose dependent (ED50 = 0.1 ng/ml, 4 pm TGF-beta-1) with a maximal decrease (about 40%) observed after a long term (48-h) treatment. TGF-beta-1 exerted its inhibitory effect on FSH action at the level(s) of cAMP accumulation, exerting no apparent effect on the gonadotropin receptor or at a site(s) related to cAMP action. TGF-beta-1 (2 ng/ml) significantly (P < 0.002) reduced (52% decrease) FSH-stimulated cAMP levels in cultured porcine Sertoli cells. However, such an inhibitory effect of the growth factor was no longer observed when stimulation of cAMP accumulation with FSH occurred in the presence of methyl isobutyl xanthine (0.5 mM), an inhibitor of cAMP-phosphodiesterase activity. This observation suggests that TGF-beta-1 decreased cAMP levels by increasing catabolism of the cyclic nucleotide through an enhancement of cAMP-phosphodiesterase activity. The inhibitory effect of TGF-beta-1 was not limited to the action of FSH on aromatase activity but also extended to the gonadotropin action (mediated by cAMP) on lactate production. As for the inhibitory effect of TGF-beta-1 on FSH-induced aromatase activity, the inhibitory effect of the growth factor on FSH-stimulated lactate production was dose and time dependent with a maximal decrease (about 30%) observed in the picomolar range (1 ng/ml, 40 pM) after 48 h treatment with TGF-beta-1. In conclusion, the present study demonstrates that TGF-beta-1 attenuates FSH action on Sertoli cell activity and that such inhibitory action is potentially exerted through a decrease in cAMP levels. Because of the local production of TGF-beta-1, it is suggested that the effects of the growth factor reported here might be exerted in the context of the testicular paracrine mechanisms.