Effects of tri-iodothyronine on alternative splicing events in the coding region of cytochrome P450 aromatase in immature rat Sertoli cells

Abstract

Transient postnatal hypothyroidism in male rats induces a prolonged proliferation of immature Sertoli cells. This change in Sertoli cell replication at young ages is coincident with enhanced and prolonged aromatase activity that leads to a marked increase in the conversion of androgens into estrogens. Both events are drastically inhibited by tri-iodothyronine (T 3 ) replacement either in vivo or in vitro. This study, after the immunolocalization of aromatase in cultured rat Sertoli cells, examined the effects elicited by T 3 on this enzyme, by simultaneously investigating three functional levels of aromatase: mRNA expression, protein content, and enzymatic activity. The immunolocalization of cytochrome P450 aromatase (P450 arom) was shown in the cytoplasm of cultured Sertoli cells from 15-and 21-day-old rats. Western blot analysis revealed an enhancement of aromatase protein content upon stimulation with N 6 ,2 -O-dibutyryladenosine-3 :5 -cyclic monophosphate ((Bu) 2 cAMP) that was clearly downregulated by T 3 . The presence of a functional P450 arom protein in purified Sertoli cells was confirmed by the measurement of [ H]androst-4-ene-3,17-dione. With 100 nM T3, a decrease in both P450 arom mRNA levels and aromatase activity was observed. The aromatase enzymatic activity was strongly stimulated by (Bu) 2 cAMP and markedly down-regulated by T 3 . In contrast, the strong increase in aromatase mRNA upon (Bu) 2 cAMP stimulation was apparently unaffected by T 3 administration. This paper shows how the identification of an altered transcript induced by T 3 coding for putative truncated and inactive aromatase protein might explain such a decrease in aromatase activity in T 3 -treated cells. On the basis of these results, it is concluded that at least two mechanisms could be involved in the down-regulatory effect of T 3 on aromatase activity in prepuberal Sertoli cells. The first mechanism is linked to a possible direct modulatory role for T 3 in the regulation of the aromatase promoter, whilst the second one is represented by the induction of altered transcripts coding for truncated and inactive aromatase proteins.

Effect of neonatal or adult heat acclimation on plasma fT3 level, testicular thyroid receptors expression in male rats and testicular steroidogenesis in vitro in response to triiodothyronine treatment

“…In response to T3, testicular expression of Star and Cyp19a1 was up-and down-regulated, respectively in the most of the studied groups (except Star expression in AHA rats). Similar effects of T3 on the testicular Star and Cyp19a1 expression were observed by others (Manna et al 1999, Pezzi et al 2001, Catalano et al 2003. It is also worth to note that inhibition of Cyp19a1 expression by T3 was weaker in NHA compared to that found in the other groups.…”

“…However, we were not able to determine any extra nuclear effects of T3 in testes of the studied rats. It cannot be excluded that the effect of T3 on testicular steroidogenesis in heat-acclimated rats would occur using extended tissue incubation with the treatment (Manna et al 1999, Pezzi et al 2001, Catalano et al 2003, Park et al 2014). This notion is supported by observed differences in E2 secretion in response to T3 between the neonatally heat-acclimated (NHA and DA) and the other studied groups (CR and AHA).…”

Differential Expression of Steroidogenic Factor-1/Adrenal 4 Binding Protein and Liver Receptor Homolog-1 (LRH-1)/Fetoprotein Transcription Factor in the Rat Testis: LRH-1 as a Potential Regulator of Testicular Aromatase Expression

“…In fact, toward the end of the period of Sertoli cell proliferation, FSH-induced aromatase activity begins to decline. Thyroid hormone, which stimulates Sertoli cell differentiation (47), decreases aromatase activity (48,49). We have recently demonstrated that the molecular mechanisms by which this inhibition occurs is through a competition of thyroid receptor ␤ and SF-1 for the same regulatory site NRE (20), demonstrating the crucial role of this site in regulating aromatase expression.…”

Effect of Thyroid Hormone on CYP19 Expression in Ovarian Granulosa Cells From Gonadotropin-Treated Immature Rats

“…T 3 inhibits CYP19 activity in rat Sertoli cells (28). Pezzi et al (29) suggested that in rat Sertoli cells, T 3 plays a direct role in the regulation of CYP19 promoter activity and induction of altered transcripts coding for truncated and inactive CYP19 protein. It should be interesting to determine whether T 3 influences the promoter activity of CYP19 gene in rat GCs.…”