Aromatase, oestrogens and human male reproduction

Abstract

In most mammalian species aromatase is encoded by a single gene (Cyp19), which contains 18 exons, nine of them being translated. In man, the presence of a biologically active aromatase and oestrogen receptors (ERalpha and ERbeta) has been reported in Leydig cells, and also in immature germ cells and ejaculated spermatozoa. Concerning aromatase, the amount of transcript and enzymatic activity are decreased in immotile compared with motile sperm. We have amplified aromatase mRNA by real-time polymerase chain reaction in spermatozoa from asthenospermic, teratospermic and asthenoteratospermic men and recorded, respectively, 44, 52 and 67 per cent decreases of the amount of transcripts compared with fertile donors. A high degree of correlation (r = -0.64) between the abnormal spermatozoa (especially microcephaly and acrosome malformations) and aromatase/GAPDH transcript ratio has been observed. Idiopathic infertility is a wide health problem and no treatment is currently available. In humans, even if the role of oestrogens in spermatogenesis is still a matter of debate, the observations of decreased sperm number and motility in men genetically deficient in aromatase, together with our data and those reported in the literature, may suggest a role for aromatase/oestrogens not only during the development and maintenance of spermatogenesis but also in the final maturation of spermatozoa.

Figure 1.

Localization of aromatase in ejaculated human spermatozoa using confocal microscopy. CD 46: specific marker of inner acrosomal membrane; chromatin is localized with DAPI and the aromatase is revealed by a polyclonal antibody. Specific antibodies targeted to specific markers of either the acrosome (CD46), or nucleus (DAPI) or mid-piece (Mitotracker Green) or tail (Tubulin) have been used.

Figure 2.

Putative role(s) of oestrogens in the male gamete.