Aromatase and estrogen receptors in male reproduction

Aromatase is a terminal enzyme which transforms irreversibly androgens into estrogens and it is present in the endoplasmic reticulum of numerous tissues. We have demonstrated that mature rat germ cells express a functional aromatase with a production of estrogens equivalent to that of Leydig cells. In humans in addition to Leydig cells, we have shown the presence of aromatase in ejaculated spermatozoa and in immature germ cells. In most tissues, high affinity estrogen receptors, ER alpha and/or ER beta, mediate the role of estrogens. Indeed, in human spermatozoa, we have successfully amplified ER beta mRNA but the protein was not detectable. Using ERa antibody we have detected two proteins ill human immature at 46 kDa likely corresponding to the ER alpha isoform lacking exon 1. In spermatozoa only germ cells: one at the expected size 66 kDa and another the 46 kDa isoform was present, and we suggest that it may be located oil the membrane. In addition, in men genetically deficient in aromatase, it is reported that alterations of spermatogenesis occur both in terms of the number and motility of spermatozoa. All together, these observations suggest that endogenous estrogens are important in male reproduction. (c) 2005 Elsevier Ireland Ltd. All rights reserved.