Direct Actions of Kisspeptins in GnRH Neurons Permit Attainment of Fertility but Are Insufficient to Preserve Full Activity of the Gonadotropic Axis in Mice

Presentation Number: OR16-2
Date of Presentation: March 6th, 2015

Silvia Leon1, Alexia Barroso1, María J. Vázquez1, David Garcia Galiano1, Maria Manfredi-Lozano1, Francisco Ruiz-Pino1, Antonio Romero-Ruiz2, Juan Roa1, Gunther Schutz3, Milen Kirilov3, Leonor Pinilla1 and Manuel Tena-Sempere*1
1University of Cordoba, Cordoba, Spain, 2Department of Cell Biology, Physiology and Immunology, University of Córdoba; CIBER Fisiopatología de la Obesidad y Nutrición, Instituto de Salud Carlos III; Instituto Maimónides de Investigación Biomédica de Córdoba/Hospital Universitario Reina Sofia, Cordoba, Spain, 3German Cancer Research Center, Heidelberg, Germany

Abstract

Kisspeptins, ligands of the receptor, Gpr54, are essential regulators of puberty and fertility that act primarily on GnRH neurons to conduct their potent stimulatory actions on the reproductive axis. Yet, whether direct kisspeptin effects on GnRH can explain the whole repertoire of reproductive effects of kisspeptins is still matter of debate. Recent data using a Gpr54 null mouse model with selective rescue of Gpr54 expression in GnRH cells (Gpr54-/-Tg; rescued) suggest that such direct effects are sufficient to attain fertility in mice. However, indirect actions of kisspeptins via neuronal afferents to GnRH neurons and effects at other levels of the reproductive axis have been proposed also.

We report herein the detailed phenotypic characterization of male and female Gpr54-/-Tg rescued mice, assessing (i) reproductive hormone levels, gonadal histology and other indices of reproductive function; (ii) gonadotropin secretion after elimination of negative feedback by gonadectomy (GNX); and (iii) LH responses to different stimulators of the HPG axis, including kisspeptin-10, NMDA, the antagonist of GABA-A receptors, PHP, and agonists of the three tachykinin receptors (NKR).

The most salient findings of our study are: (a) Despite preserved fertility, adult Gpr54-/-Tg rescued females displayed subtle changes in estrous cycles and ovarian histology, reminiscent of precocious ageing; (b) Gpr54-/-Tg rescued males showed smaller testes and epididymis, overt histological abnormalities in the testis, and elevated LH levels without concomitant increases of testosterone secretion; (c) Feedback responses to GNX were clearly subnormal, for both gonadotropins in male and female Gpr54-/-Tg rescued mice; and (c) Although Gpr54-/-Tg rescued males displayed preserved absolute LH responses to various regulators of the gonadotropic axis, relative responses were variably affected, with fully conserved responses to PHP (GABA-A antagonist) and NK1R and NK3R agonists, and partially blunted responses to kisspeptin-10, NMDA and NK2R agonist.

In conclusion, our data confirm that direct effects of kisspeptins on GnRH cells are sufficient to attain fertility. Yet, such direct actions are not sufficient to allow complete preservation of proper functionality gonadotropic axis, as evidenced by altered gonadotropin secretion, perturbed negative feedback regulation, diminished relative responses to central transmitters and disrupted gonadal histology and possibly function, as revealed by our mouse model with elimination of kisspeptin signaling outside GnRH cells.

 

Nothing to Disclose: SL, AB, MJV, DG, MM, FR, AR, JR, GS, MK, LP, MT