iturelix and Hypogonadism

The gonadotropin-releasing hormone (GnRH) is the master regulator of fertility and kisspeptin (KP) is a potent trigger of GnRH secretion from GnRH neurons. KP signals via KISS1R, a Gαq/11-coupled receptor, and mice bearing a global deletion of Kiss1r (Kiss1r(-/-)) or a GnRH neuron-specific deletion of Kiss1r (Kiss1r(d/d)) display hypogonadotropic hypogonadism and infertility. KISS1R also signals via β-arrestin, and in mice lacking β-arrestin-1 or -2, KP-triggered GnRH secretion is significantly diminished. Based on these findings, we hypothesized that ablation of Gαq/11 in GnRH neurons would diminish but not completely block KP-triggered GnRH secretion and that Gαq/11-independent GnRH secretion would be sufficient to maintain fertility. To test this, Gnaq (encodes Gαq) was selectively inactivated in the GnRH neurons of global Gna11 (encodes Gα11)-null mice by crossing Gnrh-Cre and Gnaq(fl/fl);Gna11(-/-) mice. Experimental Gnaq(fl/fl);Gna11(-/-);Gnrh-Cre (Gnaq(d/d)) and control Gnaq(fl/fl);Gna11(-/-) (Gnaq(fl/fl)) littermate mice were generated and subjected to reproductive profiling. This process revealed that testicular development and spermatogenesis, preputial separation, and anogenital distance in males and day of vaginal opening and of first estrus in females were significantly less affected in Gnaq(d/d) mice than in previously characterized Kiss1r(-/-) or Kiss1r(d/d) mice. Additionally, Gnaq(d/d) males were subfertile, and although Gnaq(d/d) females did not ovulate spontaneously, they responded efficiently to a single dose of gonadotropins. Finally, KP stimulation triggered a significant increase in gonadotropins and testosterone levels in Gnaq(d/d) mice. We therefore conclude that the milder reproductive phenotypes and maintained responsiveness to KP and gonadotropins reflect Gαq/11-independent GnRH secretion and activation of the neuroendocrine-reproductive axis in Gnaq(d/d) mice.. The gonadotropin-releasing hormone (GnRH) is the master regulator of fertility. Over the last decade, several studies have established that the KISS1 receptor, KISS1R, is a potent trigger of GnRH secretion and inactivation of KISS1R on the GnRH neuron results in infertility. While KISS1R is best understood as a Gαq/11-coupled receptor, we previously demonstrated that it could couple to and signal via non-Gαq/11-coupled pathways. The present study confirms these findings and, more importantly, while it establishes Gαq/11-coupled signaling as a major conduit of GnRH secretion, it also uncovers a significant role for non-Gαq/11-coupled signaling in potentiating reproductive development and function. This study further suggests that by augmenting signaling via these pathways, GnRH secretion can be enhanced to treat some forms of infertility.

Topics: Animals; Blastocyst; Embryonic Development; Female; Gene Expression Profiling; Genitalia, Female; Genitalia, Male; Gonadal Steroid Hormones; Gonadotropin-Releasing Hormone; Gonadotropins, Pituitary; GTP-Binding Protein alpha Subunits; Hypogonadism; Hypothalamo-Hypophyseal System; Hypothalamus; Infertility, Female; Infertility, Male; Kisspeptins; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Neurons; Oligopeptides; Ovariectomy; Ovulation; Peptide Fragments; Peptides; Phenotype; Receptors, G-Protein-Coupled; Receptors, Kisspeptin-1; Spermatogenesis

Little is known of the cell biology of Leydig cells during the neonatal activation of the hypothalamic-pituitary-testicular (HPT) axis. The current study examined the effect of blockade of the HPT axis with a GnRH antagonist (antide) on the neonatal population of Leydig cells in the new world primate, the common marmoset. Three sets of twins, age 7 weeks, were studied: in each pair one twin was used as a control, while the other received treatment with GnRH antagonist from the day of birth to suppress pituitary gonadotrophin secretion. Leydig cells of treated animals were dramatically different from those of controls. The cells were atrophic and exhibited very irregular nuclei. The organelles involved in steroid synthesis were reduced to the extent to being barely evident. The smooth endoplasmic reticulum (SER) was greatly diminished in quantity and distribution. The usual form of the SER (anastomosing tubules) was not evident, but, instead, the SER was relatively unbranched. Peroxisomes, organelles involved in transfer of cholesterol to the mitochondria, were greatly reduced in number. Mitochondria were relatively sparse and exhibited a non-typical morphology, as tubular elements of the cristae were rarely evident. Thus, the central apparatus in steroid production, the SER, mitochondria and peroxisomes, was essentially shut down in the GnRH-antagonist-treated animals. Storage of cholesterol, the precursor of steroid biosynthesis, was also not in evidence, as lipid droplets were extremely rare. Two prominent features of control in neonatal marmoset Leydig cells, the membranofibrillar inclusion (MFI) and basal laminae, remain prominent in the Leydig cells of treated animals. Evidence of apoptosis was not observed. These results provide strong support that the gonadotrophic hormones are the primary regulator of neonatal Leydig cell development in primates, and also suggest cell regression, rather than apoptosis, being the mechanism of this inhibition.

Topics: Animals; Animals, Newborn; Atrophy; Callithrix; Cholesterol; Endoplasmic Reticulum, Smooth; Gonadotropin-Releasing Hormone; Gonadotropins, Pituitary; Hypogonadism; Hypothalamo-Hypophyseal System; Leydig Cells; Male; Microbodies; Microscopy, Electron; Mitochondria; Oligopeptides; Testis; Testosterone