Tumor necrosis factor-α inhibits glutathione S-transferase-α expression in cultured porcine Sertoli cells

Abstract

Glutathione S-transferases (GSTs) are a family of soluble enzymes of detoxification that use reduced glutathione in conjugation and reduction reactions. Toxic electrophiles are substrates for the GSTs. GSTα is expressed at high levels in different tissues such as the testis. Among the different GSTs present in the testis, GSTα is specifically expressed in Leydig and Sertoli cells known to be under the control of hormonal and local regulatory factors. The present study investigated the regulatory action of tumor necrosis factor-α (TNFα) on basal and hormone (FSH and testosterone)-stimulated GSTα expression in cultured Sertoli cells. Treatment with TNFα (0-20 ng/ml, 48 h) induced a decrease in basal GSTα mRNA levels in a dose-dependent manner (fivefold decrease; P<0.001). The maximal and half maximal effects were observed at 20 ng/ml and 7 ng/ml respectively. The inhibitory effect of TNFα was also time-dependent with a maximal inhibitory effect (threefold decrease; P<0.001) observed at 48 h. The inhibitory effect of the cytokine was also observed on basal GSTα protein (28 kDa) levels. TNFα also inhibited the hormone-stimulated GSTα expression in Sertoli cells. The treatment of cultured Sertoli cells with both FSH and TNFα (100 ng/ml and 10 ng/ml respectively, 48 h) resulted in a complete suppression of the stimulatory action of FSH ort GSTα mRNA levels. Similarly, in Sertoli cells treated with testosterone or its non-aromatizable metabolite dihydrotestosterone (100 ng/ml, 24 h), TNFα reduced the hormone-stimulated GSTα mRNA and protein levels. TNFα inhibited basal GSTα expression without affecting mRNA stability. Indeed, the decay curves (mRNA half-life time = 18 h) for the GSTα basal mRNA levels in Sertoli cells was similar in the absence or presence of TNFα (10 ng/ml, 48 h). Testosterone increased GSTα mRNA without affecting the enzyme mRNA stability. TNFα antagonized the androgen-stimulated GSTα mRNA levels without affecting the enzyme mRNA stability, suggesting that the interaction between the androgen and the cytokine is mostly exerted at a transcriptional level. FSH increased GSTα mRNA levels through an increase in mRNA stability (increased mRNA half-life times to 119 h). TNFα antagonized the stimulatory effect of FSH on GSTα mRNA levels by antagonizing the stabilizing effect exerted by the hormone on GSTα mRNA. Together, these results suggest that the increase in the cytokine levels within the testis would alter the detoxification processes against genotoxic products during spermatogenesis.