Transforming growth factor β1 inhibits steroidogenesis in dispersed fetal testicular cells in culture

Abstract

TGF β1 has been detected by immunohistochemistry in the rat fetal testis. Therefore, we attempted to determine whether this factor can act as a local regulator of Leydig cell function during fetal development. An inhibitory effect of TGF β1 on basal and luteinizing hormone (LH)-stimulated testosterone secretion by fetal testes in vitro was observed only with testes from 13.5 day-old fetuses and not with testes from older stages. The lack of effect of exogenous TGF β1 in organ culture after day 13.5 might be related to an elevated intratesticular concentration that would already exert maximal biological effect. On the contrary, in a model of dispersed testicular cells in culture, TGF β1 was able to inhibit LH-stimulated testosterone production by fetal Leydig cells from 16.5 and 20.5 day-old fetuses. This inhibition of LH-stimulated testosterone production was dose- and time-dependent and was maximal after 48 h of treatment with 1 ng/ml TGF β1, with testosterone secretion being reduced to 25% of control values. Inhibition of testosterone secretion was also observed in basal and dbcAMP-stimulated conditions, suggesting that one site of action of TGF β1 is located after the production of cAMP. However, TGF β1 was also able to inhibit LH-induced cAMP production. As demonstrated by the transformation of steroidogenic precursors into testosterone, TGF β1 did not significantly alter 3 β-hydroxysteroid dehydrogenase (3 βHSD) activity but induced a strong inhibition of cytochrome P450 17 α-hydroxylase/C17–20 lyase (P450C17) activity which was associated with a marked diminution of cytochrome P450C17 mRNA levels (26% of control values) but not of cytochrome P450scc mRNA. In addition to its effect on steroidogenesis, TGF β1 exhibited morphogenic actions on the fetal testicular cells, inducing spreading when the cells were adherent and aggregation when the cells were cultured in conditions of lesser adherence and without any significant effect on either total cell number or 3 βHSD positive cells. Taken together these results suggest that TGF β1 likely plays a morphogenic and physiological role very early in the fetal testis via paracrine/autocrine mechanisms.