Kisspeptins, Estrogens and Male Fertility.

Abstract

The control of male fertility requires accurate endocrine, paracrine and autocrine communications along the hypothalamus-pituitary-gonad (HPG) axis. In this respect, the possible interplay between upcoming/classical modulators of reproductive functions deserves attention in that may be a successful tool for the future exploitation of new potential therapeutic targets in the treatment of fertility disorders. In this review we will discuss upcoming data concerning the role of kisspeptins, the products of the Kiss1 gene, and estrogens - classically considered as female hormones - as well as their possible interplay in testis. Kisspeptins, via the activation of kisspeptin receptor Gpr54 represent the main gatekeeper of the hypothalamic Gonadotropin Releasing Hormone (GnRH) centrally modulating the onset and maintaining reproductive functions. As a consequence, the loss of kisspeptin signalling causes hypogonadotrophic hypogonadism in humans and animal models. In spite of the well recognized functions at hypothalamic levels, recent data strongly support direct production and activity of kisspeptin in testis and its involvement in the control of Leydig cells, germ cells progression and sperm functions. Similarly, estrogens exhibit high impact on proliferative/apoptotic/differentiative events in testis, thus resulting as local key modulators for the production - but also for the release, transport and maturation - of high quality spermatozoa. This review summarizes the upcoming data from experimental models and humans concerning the testicular activity of kisspeptins and estrogens to preserve male fertility. Mutual enhancement of kisspeptin and estradiol signalling for the progression of spermatogenesis has also been discussed.