Persistently expressed human chorionic gonadotropin induces premature luteinization and progressive alterations on the reproductive axis in female mice

The hypothalamic-pituitary-gonadal axis plays a fundamental role in the endocrine regulation of the reproductive function in mammals. Any change in the function of the participating hormones or their receptors can lead to alterations in sexual differentiation, the onset of puberty, infertility, cancer development, and other dysfunctions. In this study, we analyzed the influence of persistently elevated levels of the human chorionic gonadotropin hormone (hCG), a powerful agonist of pituitary luteinizing hormone (LH), on the reproductive axis of female mice. As a consequence of chronic hCG hypersecretion through a global expression of the hCGbeta-subunit in transgenic (TG) female mice, a series of events perturbed the prepubertal to juvenile transition. The imbalance in gonadotropin action was first manifested by precocious puberty and alterations in gonadal hormone production, with the consequent ovarian function disruption and infertility in adulthood. The expansion of cumulus cells in vivo and in vitro, ovulatory capacity, and gene expression of ovulation-related marker genes after hormone stimulation were normal in 3-week-old TG females. However, the expression of genes related to steroidogenesis and luteinization such as Lhcgr, Prlr, and the steroidogenic enzymes Cyp11a1, Cyp17a1, and Cyp19a1 were significantly elevated in the TG females. This study demonstrates that the excessive secretion of hCG in concert with high prolactin, induced premature luteinization, and enhanced ovarian steroidogenesis, as was shown by the up-regulation of luteal cell markers and progesterone synthesis in the TG mice. Furthermore, progressively impaired reproductive function of the TG females occurred from the peripubertal stage to adulthood, thus culminating in infertility.

Neuroprotective Effects of Testosterone in Male Wobbler Mouse, a Model of Amyotrophic Lateral Sclerosis

Patients suffering of amyotrophic lateral sclerosis (ALS) present motoneuron degeneration leading to muscle atrophy, dysphagia, and dysarthria. The Wobbler mouse, an animal model of ALS, shows a selective loss of motoneurons, astrocytosis, and microgliosis in the spinal cord. The incidence of ALS is greater in men; however, it increases in women after menopause, suggesting a role of sex steroids in ALS. Testosterone is a complex steroid that exerts its effects directly via androgen (AR) or Sigma-1 receptors and indirectly via estrogen receptors (ER) after aromatization into estradiol. Its reduced-metabolite 5α-dihydrotestosterone acts via AR. This study analyzed the effects of testosterone in male symptomatic Wobblers. Controls or Wobblers received empty or testosterone-filled silastic tubes for 2 months. The cervical spinal cord from testosterone-treated Wobblers showed (1) similar androgen levels to untreated control and (2) increased levels of testosterone, and its 5α-reduced metabolites, 5α- dihydrotestosterone, and 3β-androstanediol, but (3) undetectable levels of estradiol compared to untreated Wobblers. Testosterone-treated controls showed comparable steroid concentrations to its untreated counterpart. In testosterone- treated Wobblers a reduction of AR, ERα, and aromatase and high levels of Sigma-1 receptor mRNAs was demonstrated. Testosterone treatment increased ChAT immunoreactivity and the antiinflammatory mediator TGFβ, while it lessened vacuolated motoneurons, GFAP+ astrogliosis, the density of IBA1+ microgliosis, proinflammatory mediators, and oxidative/nitrosative stress. Clinically, testosterone treatment in Wobblers slowed the progression of paw atrophy and improved rotarod performance. Collectively, our findings indicate an antiinflammatory and protective effect of testosterone in the degenerating spinal cord. These results coincided with a high concentration of androgen-reduced derivatives after testosterone treatment suggesting that the steroid profile may have a beneficial role on disease progression.

Mammary gland-specific regulation of GNRH and GNRH-receptor gene expression is likely part of a local autoregulatory system in female vizcachas (Rodentia: Chinchillidae)

In addition to key mammotrophic hormones such as the pituitary prolactin (PRL) and the ovarian steroids progesterone and estradiol, there are local factors that modulate the tissue dynamics of the mammary glands during pregnancy and lactation. By immunohistochemistry and RT-PCR, we found local transcription and translation of gonadotropin-releasing hormone (GNRH), GNRH receptor (GNRHR), PRL and PRL receptor (PRLR) in mammary glands of adult vizcachas during pregnancy and lactation. Both GNRH and GNRHR showed a lag between protein expression and gene transcription throughout the gestational period: while the highest transcription levels of these genes were recorded at early-pregnancy, the epithelial immunoexpressions of both showed their maximum during lactation. RIA results corroborated the presence of GNRH in mammary glands at all the analyzed stages and confirmed the maximum amount of this peptide in the lactating group. Significant amounts of GNRH were detected in milk samples as well. Conversely, PRL and PRLR shared similar protein and gene expression profiles, all exhibiting maximum values during lactation. GNRH peptide content in mammary glands of females with sulpiride-induced hyperprolactinemia (HP) was significantly lower than that of control females (CT). Although PRL mRNA levels remained unchanged, there was a marked increase in theα-lactalbumin (LALBA) transcription in mammary glands of HP- vs CT-females. These results suggest that after targeting mammary glands, PRL stimulates the expression of milk protein genes, but also, tempers the local expression of GNRH. Mammary gland-explantssupplemented with a GNRH analogue (GN-explants) had no differences in terms of PRLR orLALBA transcription levels compared to CT-explants, so the mammary PRLR signaling would not appear to be modulated by GNRH. Yet, mRNA expression levels of both GNRH and the GNRHR-downstream factor, EGR1, were significantly higher in GN-explants compared to that of CT which would point to a GNRH-positive feedback mechanism. In summary, the local coupled expression of GNRH, GNRHR and EGR1 in the mammary gland throughout pregnancy of vizcachas, the PRL-dependent mammary GNRH secretion as well as the GNRH positive feedback on its own transcription suggest an autocrine-paracrine regulatory mechanism and propose an active role for GNRH in mammary gland tissue remodeling.

SAT-409 A Novel Population of Kisspeptin Neurons in the Medial Tuberal Nucleus of the Hypothalamus in Mice

Kisspeptin, encoded by Kiss1, stimulates GnRH release and is required for puberty onset and reproduction. Kiss1 neurons primarily reside in the hypothalamus, in the AVPV/PeN and ARC nuclei; however, smaller Kiss1 neuronal populations exist in other regions such as the medial amygdala, bed nucleus of the stria terminalis, and lateral septum. We identified a novel population of Kiss1 neurons in the lateral hypothalamus, specifically in the medial tuberal nucleus (MTu), in mice. A similar, small population of Kiss1 neurons in this lateral hypothalamic region was also newly identified in sheep (Moore et al., 2018), but nothing is known about the regulation or function of these Kiss1 neurons. Using both in situ hybridization in normal mice and fluorescent TdTomato expression in KissCre+/TdTomato+ mice, we confirmed the presence of Kiss1 neurons in the MTu of adult mice. Next, we examined the developmental time course of Kiss1 expression in the MTu by looking at TdTomato expression in KissCre+/TdTomato+ mice at different developmental ages (prepubertal, pubertal, and adult). We found that TdTomato expression in the MTu increased around puberty, perhaps as a result of increasing gonadal sex steroids. Estradiol (E₂) regulates Kiss1 expression in all previously-identified Kiss1 neuronal populations and thus, we next examined whether E₂ regulates MTu Kiss1 expression. We found that like the AVPV and extra-hypothalamic Kiss1 populations, Kiss1 expression in the MTu is upregulated by E₂. In addition to E₂, GABA_BR signaling is known to regulate extra-hypothalamic Kiss1 expression, while having no impact on AVPV/PeN and ARC Kiss1 expression. We examined if GABA_BR signaling regulates MTu Kiss1 expression by comparing Kiss1 expression in WT and GABA_BR KO mice. Like the other hypothalamic Kiss1 populations in the AVPV and ARC, Kiss1 expression in the MTu does not appear to be strongly regulated by GABA_BR signaling in male mice. Additional research is ongoing to further characterize these E₂-regulated MTu Kiss1 neurons and elucidate their function(s).

MON-222 Blocking GABAB Receptors (GABABR) from Birth to Weaning in Mice Induces Profound Changes in the Gonadotropic Axis

We have previously shown that the administration of a GABAB antagonist (CGP55845) to neonatal BALB/C mice from postnatal day (PND) 2-6 significantly decreased arcuate nucleus (ARC) kisspeptin (Kiss1) expression in both sexes. Furthermore, this neonatal CGP55845 treatment delayed puberty onset in females and altered gonadotropin secretion in both sexes in adulthood. Here our aim was to induce a more sustained inhibition of GABABR signaling and evaluate its effects on the gonadotropic axis. Neonatal Balb/c male (M) and female (F) mice were injected with CGP55845 (1 mg/kg, sc, CGP) or saline (CTRL) from PND2-21, three times/day (8AM, 1PM, 6PM) and sacrificed at 3PM (after two injections on the last day). Serum samples and gonads were collected for hormonal measurements by RIA. Brains were frozen and 500 µm slices were obtained on a cryostat. ARC and antero ventral periventricular nucleus (AVPV) micropunches were obtained. Kiss1, kisspeptin receptor (Kiss1r), prodynorfin (Pdyn), neurokinin B (Tac2), tyrosine hydrolxylase (TH), progesterone receptor (Pgr), GABAB1 and GABAB2 subunits of the GABABR (GABAB1, GABAB2) mRNA expression was assessed in the micropunches by qPCR (control gene: Cyclophilin B). Body weight (BW) and AGI (anogenital distance/BW) were evaluated on PND 7, 14 and 21. In the ARC CGP induced a significant decrease in Kiss1 expression (FCTRL: 1,16±0.24 vs FCGP: 0,67±0.16 vs MCTRL: 1,22±0.24 vs MCGP: 0,70±0.13, CGP vs CTRL p<0,04) and an increase in Pdyn (FCTRL: 0,97±0.26 vs FCGP: 1,77±0,49 vs MCTRL: 1,37±0.32 vs MCGP: 3,01±0.85, CGP vs CTRL: p<0,02) and GABAB1 (FCTRL: 0,42±0.08 vs FCGP: 1,37±0.43 vs MCTRL: 0,74±0.13 vs MCGP: 1,38±0.46, CGP vs CTRL: p<0,04) in both sexes, while a decrease in Tac2 was only observed in males (MCTRL: 1,01±0.14 vs MCGP: 0,45±0.045: p<0,02); no changes were observed in Kiss1r or Pgr expression. In AVPV no CGP-induced changes in Kiss1,Kiss1r, TH, Pgr, GABABR expression were detected. FSH was significantly decreased in CGP-treated males (FSH (ng/ml): MCTRL: 9,3±1,28 vs MCGP: 5,78±0.9: p<0,003). BW was significantly decreased by CGP on PND21 in females while this parameter was decreased at all ages studied in males. CGP significantly decreased AGI in both sexes. These results demonstrate that sustained inhibition of GABABR signaling during the critical postnatal period of development and maturation of the gonadotropic axis profoundly alters key ARC gene expression such as Kiss1, Pdyn, Tac2, altering sexual differentiation (AGI) and BW. In addition, in males FSH levels are decreased to female levels in agreement with feminization of AGI. (Supported by CONICET, ANPCYT, UBA, Fundación René Barón, Fundación Williams).

Lack of functional GABA(B) receptors alters GnRH physiology and sexual dimorphic expression of GnRH and GAD-67 in the brain

GABA, the main inhibitory neurotransmitter, acts through GABA(A/C) and GABA(B) receptors (GABA(B)Rs); it is critical for gonadotropin regulation. We studied whether the lack of functional GABA(B)Rs in GABA(B1) knockout (GABA(B1)KO) mice affected the gonadotropin axis physiology. Adult male and female GABA(B1)KO and wild-type (WT) mice were killed to collect blood and tissue samples. Gonadotropin-releasing hormone (GnRH) content in whole hypothalami (HT), olfactory bulbs (OB), and frontoparietal cortexes (CT) were determined (RIA). GnRH expression by quantitative real-time PCR (qRT-PCR) was evaluated in preoptic area-anterior hypothalamus (POA-AH), medial basal-posterior hypothalamus (MBH-PH), OB, and CT. Pulsatile GnRH secretion from hypothalamic explants was measured by RIA. GABA, glutamate, and taurine contents in HT and CT were determined by HPLC. Glutamic acid decarboxylase-67 (GAD-67) mRNA was measured by qRT-PCR in POA-AH, MBH-PH, and CT. Gonadotropin content, serum levels, and secretion from adenohypophyseal cell cultures (ACC) were measured by RIA. GnRH mRNA expression was increased in POA-AH of WT males compared with females; this pattern of expression was inversed in GABA(B1)KO mice. MBH-PH, OB, and CT did not follow this pattern. In GABA(B1)KO females, GnRH pulse frequency was increased and GABA and glutamate contents were augmented. POA-AH GAD-67 mRNA showed the same expression pattern as GnRH mRNA in this area. Gonadotropin pituitary contents and serum levels showed no differences between genotypes. Increased basal LH secretion and decreased GnRH-stimulated gonadotropin response were observed in GABA(B1)KO female ACCs. These results support the hypothesis that the absence of functional GABA(B)Rs alters GnRH physiology and critically affects sexual dimorphic expression of GnRH and GAD-67 in POA-AH.