Estrogen signaling in testicular cells
Résumé
Aromatase transforms irreversibly androgens into estrogens and is present in the endoplasmic reticulum of various tissues including the mammalian testis. In rat all testicular cells except peritubular cells express aromatase. Indeed in adult rat germ cells (pachytene spermatocytes and round spermatids) we have demonstrated the presence of a functional aromatase (transcript, protein and biological activity) and the estrogen output is equivalent to that of Leydig cells. In addition in the adult rat, transcripts of aromatase vary according to the germ cell type and to the stages of seminiferous epithelium. By contrast with the androgen receptors mainly localized in somatic cells, estrogen receptors (ERs) are described in most of the testicular cells including germ cells. Moreover, besides the presence of high affinity ERα and/or ERβ, a rapid membrane effect has been recently reported and we demonstrated that GPR30 (a transmembrane intracellular estrogen receptor) is expressed in adult rat pachytene spermatocytes. Therefore estrogens through both GPR30 and ERα are able to activate the rapid EGFR/ERK/c-jun signaling cascade, which in turn triggers an apoptotic mitochondrial pathway involving an increase in Bax expression and a concomitant reduction of cyclin A1 and B1 gene levels. In another study in round spermatids of adult rat we have shown that the rapid membrane effect of estradiol is also efficient in controlling apoptosis and maturation / differentiation of these haploid germ cells. In man the presence of a biologically active aromatase and of estrogen receptors has been reported in Leydig cells, but also in immature germ cells and ejaculated spermatozoa. Thus the role of estrogen (intracrine, autocrine and / or paracrine) in spermatogenesis (proliferation, apoptosis, survival and maturation) and more generally, in male reproduction is now evidenced taking into account the simultaneous presence of a biologically active aromatase and the widespread distribution of estrogen receptors especially in haploid germ cells.