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Tumor necrosis factor-alpha inhibits leydig cell steroidogenesis through a decrease in steroidogenic acute regulatory
1INSERM U407, Centre Hospitalier Lyon-Sud, Pierre Bénite, France. mauduit@lsgrisn1.univ-lyon1.fr
Abstract:
The aim of the present study was to identify the sites of the inhibitory action of TNFalpha (tumor necrosis factor alpha) on LH/hCG-stimulated testosterone formation. By using cultured porcine Leydig cells as a model, TNFalpha was shown to inhibit testosterone secretion when testicular cells were stimulated with hCG but not when incubated with 22R-hydroxycholesterol (a cholesterol substrate derivative that readily passes through cell and mitochondrial membranes). Such an observation suggested that the cytokine may affect cholesterol transport and/or availability to cytochrome P450scc in the mitochondria. Specifically, we report here that TNFalpha reduced in a dose- and time-dependent manner hCG-induced StAR (steroidogenic acute regulatory protein) levels. The maximal and half-maximal effects were obtained with 20 ng/ml (1.2 nM) and 1.6 ng/ml (0.09 nM) of TNFalpha, respectively. Maximal inhibitory effects of TNFalpha on StAR messenger RNA and protein levels were obtained after 48 h of treatment. Additionally, the presence of TNFalpha receptors P55 in terms of protein (identified through cross-linking experiments) and messenger RNA (identified through RT-PCR analysis) suggested that the effects of the cytokine are directly exerted on the testicular steroidogenic cell type.
Insights
Tumor necrosis factor alpha (TNFalpha) inhibits testosterone production by affecting steroidogenic acute regulatory protein (StAR) levels in testicular cells. This suggests TNFalpha directly impacts Leydig cells, influencing cholesterol transport for steroidogenesis.
Area of Science:
- Endocrinology
- Molecular Biology
- Cell Biology
Background:
- Testosterone production is regulated by luteinizing hormone (LH) and human chorionic gonadotropin (hCG).
- Tumor necrosis factor alpha (TNFalpha) is a cytokine implicated in inflammatory processes and cellular regulation.
Purpose of the Study:
- To pinpoint the inhibitory mechanism of TNFalpha on LH/hCG-stimulated testosterone formation.
- To investigate TNFalpha's effect on cholesterol metabolism and steroidogenic acute regulatory protein (StAR) in Leydig cells.
Main Methods:
- Cultured porcine Leydig cells were used as an in vitro model.
- Cells were stimulated with hCG or 22R-hydroxycholesterol in the presence of varying TNFalpha concentrations.
- StAR mRNA and protein levels were quantified using RT-PCR and cross-linking experiments.
Main Results:
- TNFalpha inhibited hCG-stimulated testosterone secretion but not that induced by 22R-hydroxycholesterol.
- TNFalpha dose-dependently reduced hCG-induced StAR levels, with maximal inhibition at 20 ng/ml.
- Maximal inhibition of StAR mRNA and protein by TNFalpha occurred after 48 hours.
- TNFalpha receptors (P55) were detected on Leydig cells, indicating direct action.
Conclusions:
- TNFalpha's inhibitory effect on testosterone production likely involves the disruption of cholesterol transport to mitochondria.
- TNFalpha directly acts on testicular Leydig cells by downregulating StAR expression.
- This study elucidates a novel mechanism by which TNFalpha modulates steroidogenesis.