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Transforming growth factor beta inhibits Leydig cell functions
Abstract:
The role of transforming growth factor beta (TGF-beta) on the functions of pig Leydig cells cultured in a chemically defined medium was investigated. TGF-beta reduced the number of hCG receptors, without modification of the binding affinity, and reduced the cAMP and testosterone response to this hormone. These effects were dose-dependent. The minimal effective dose was 10 pg/ml (4 X 10(-13) M) and half-maximal inhibition for the three effects was observed at about 100 pg/ml. At maximal effective concentration (1 ng/ml), the inhibitory effect was time-dependent, the first effects were observed after a lag period of 12 h and the maximal effect after 72 h. At maximal concentrations TGF-beta reduced by 70% the number of hCG receptors and the steroidogenic response to this hormone and reduced by 50% the cAMP response to hCG. Moreover, TGF-beta also reduced the cAMP response to forskolin and the steroidogenic effects of this diterpene and 8-Bromo-cAMP. In contrast, the conversion of exogenous pregnenolone to testosterone was increased in TGF-beta-treated cells. The inhibition of Leydig cell steroidogenesis can be dissociated from any effect on cell proliferation and is related to modifications located at the membrane level and beyond cAMP formation, but before pregnenolone formation. The results suggest that in the testis, as in other steroidogenic tissues, TGF-beta may play a role in the development and maintenance of differentiated function.
Insights
Transforming growth factor beta (TGF-beta) inhibits pig Leydig cell function by reducing hCG receptors and steroid production. This suggests TGF-beta regulates testicular cell differentiation and function.
Area of Science:
- Reproductive Endocrinology
- Molecular Endocrinology
- Cell Biology
Background:
- Leydig cells are crucial for testosterone production in the testis.
- Transforming growth factor beta (TGF-beta) is a key regulator of cellular functions.
- The specific role of TGF-beta in Leydig cell function requires further elucidation.
Purpose of the Study:
- To investigate the effects of TGF-beta on pig Leydig cell function in vitro.
- To determine the impact of TGF-beta on hCG receptor expression and signaling pathways.
- To understand TGF-beta's role in regulating steroidogenesis and Leydig cell differentiation.
Main Methods:
- Primary pig Leydig cells were cultured in a chemically defined medium.
- Cells were treated with varying concentrations and durations of TGF-beta.
- Hormone receptor binding, cAMP production, and steroidogenesis were measured.
- Effects on cell proliferation and precursor conversion were also assessed.
Main Results:
- TGF-beta dose-dependently reduced hCG receptor number and affinity, decreasing testosterone and cAMP response to hCG.
- Inhibitory effects were time-dependent, with maximal inhibition after 72 hours.
- TGF-beta reduced cAMP and steroidogenic responses to forskolin and 8-Bromo-cAMP, indicating effects beyond cAMP formation.
- TGF-beta increased pregnenolone conversion to testosterone, suggesting a specific site of action before pregnenolone synthesis.
Conclusions:
- TGF-beta inhibits pig Leydig cell steroidogenesis by affecting membrane-level events and post-cAMP signaling.
- The findings suggest TGF-beta plays a role in maintaining Leydig cell differentiated function.
- TGF-beta's actions are dissociated from effects on cell proliferation.