Aromatase expression in the human male

The role of estrogens produced by the testis may involve negative feedback regulation of androgen biosynthesis. Estrogens are also associated with contractile processes of seminiferous tubules, and might have mitogenic effects on Sertoli and Leydig cells. To investigate the location of aromatase (estrogen synthetase) in the testes, tissue from normal human subjects, aged 3 months to 72 years were studied using immunocytochemistry. In mature testes, aromatase immunostain was always associated with Leydig cells and was absent from Sertoli cells. Aromatase activity ranged from 0.014-0.55 pmol estrogen per mg/h and was significantly correlated with the immunostain intensity (P<0.02). Activity and immunostain intensity did not correlate with increasing age. Rather, the highest levels were measured in four of six testes of men aged 18-20 years, three of whom also had the strongest immunostain in larger and more prominent Leydig cell clusters than those in the other specimens. A low level of aromatase activity but no immunostain was detected in prepubertal testes. However, in several prepubertal patients with Peutz-Jegher's Syndrome (PJS) with bilateral multifocal sex cord tumors and enlarged seminiferous tubules and Sertoli cells, aromatase was expressed in these Sertoli cells, but absent from normal Sertoli and Leydig cells. Increased aromatase expression in these tissues involved activation of upstream regulatory elements of the gonadal P II promoter of P-450(arom). In a prepubertal boy with gynecomastia but without PJS, aromatase excess appeared to be due to increased aromatization in skin fibroblasts and lymphocytes. Several members of the patient's family including his sister also expressed high levels of aromatase. This condition appears to be inherited in an autosomal dominant manner.