The permissive role of prolactin as a regulator of luteinizing hormone action in the female mouse ovary and extragonadal tumorigenesis

Elevated chorionic gonadotropic hormone in transgenic mice induces parthenogenetic activation and ovarian teratomas

Both male and female reproductive functions are impacted by altered gonadotrophin secretion and action, which may also influence the development of endocrine tumours. To ascertain if chronic hypersecretion of human chorionic gonadotropin (hCG) contributes to the development of gonadal tumours, double transgenic (TG) mice that overexpress hCGα- and β-subunits were analysed. By the age of two months, ovarian tumours with characteristics of teratomas developed with 100% penetrance. Teratomas were also seen in wild-type ovaries orthotopically transplanted into TG mice, demonstrating an endocrine/paracrine mechanism for the hCG-induced ovarian tumorigenesis. Both in vitro and in vivo experiments showed oocyte parthenogenetic activation in TG females. In addition, ovaries showed reduced ovulatory gene expression, inhibited ERK1/2 phosphorylation, and impaired cumulus cell expansion. Hence, persistently high endocrine hCG activity causes parthenogenetic activation and development of ovarian teratomas, along with altered follicle development and impaired ERK1/2 signalling, offering a novel mechanism associated with the molecular pathogenesis of ovarian teratomas.

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.

Acute Suppression of LH Secretion by Prolactin in Female Mice Is Mediated by Kisspeptin Neurons in the Arcuate Nucleus

Hyperprolactinemia causes infertility, but the specific mechanism is unknown. It is clear that elevated prolactin levels suppress pulsatile release of GnRH from the hypothalamus, with a consequent reduction in pulsatile LH secretion from the pituitary. Only a few GnRH neurons express prolactin receptors (Prlrs), however, and thus prolactin must act indirectly in the underlying neural circuitry. Here, we have tested the hypothesis that prolactin-induced inhibition of LH secretion is mediated by kisspeptin neurons, which provide major excitatory inputs to GnRH neurons. To evaluate pulsatile LH secretion, we collected serial blood samples from diestrous mice and measured LH levels by ultrasensitive ELISA. Acute prolactin administration decreased LH pulses in wild-type mice. Kisspeptin neurons in the arcuate nucleus and in the rostral periventricular area of the third ventricle (RP3V) acutely responded to prolactin, but prolactin-induced signaling in kisspeptin neurons was up to fourfold higher in the arcuate nucleus when compared with the RP3V. Consistent with this, conditional knockout of Prlr specifically in arcuate nucleus kisspeptin neurons prevented prolactin-induced suppression of LH secretion. Our data establish that during hyperprolactinemia, suppression of pulsatile LH secretion is mediated by Prlr on arcuate kisspeptin neurons.

GnRH Receptor Expression and Reproductive Function Depend on JUN in GnRH Receptor‒Expressing Cells

Gonadotropin-releasing hormone (GnRH) from the hypothalamus regulates synthesis and secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from the anterior pituitary gonadotropes. LH and FSH are heterodimers composed of a common α-subunit and unique β-subunits, which provide biological specificity and are limiting components of mature hormone synthesis. Gonadotrope cells respond to GnRH via specific expression of the GnRH receptor (Gnrhr). GnRH induces the expression of gonadotropin genes and of the Gnrhr by activation of specific transcription factors. The JUN (c-Jun) transcription factor binds to AP-1 sites in the promoters of target genes and mediates induction of the FSHβ gene and of the Gnrhr in gonadotrope-derived cell lines. To analyze the role of JUN in reproductive function in vivo, we generated a mouse model that lacks JUN specifically in GnRH receptor‒expressing cells (conditional JUN knockout; JUN-cKO). JUN-cKO mice displayed profound reproductive anomalies such as reduced LH levels resulting in lower gonadal steroid levels, longer estrous cycles in females, and diminished sperm numbers in males. Unexpectedly, FSH levels were unchanged in these animals, whereas Gnrhr expression in the pituitary was reduced. Steroidogenic enzyme expression was reduced in the gonads of JUN-cKO mice, likely as a consequence of reduced LH levels. GnRH receptor‒driven Cre activity was detected in the hypothalamus but not in the GnRH neuron. Female, but not male, JUN-cKO mice exhibited reduced GnRH expression. Taken together, our results demonstrate that GnRH receptor‒expression levels depend on JUN and are critical for reproductive function.

Screening and evaluating of long noncoding RNAs in the puberty of goats

Background

Long noncoding RNAs (lncRNAs) are involved in regulating animal development, however, their function in the onset of puberty in goats remain largely unexplored. To identify the genes controlling the regulation of puberty in goats, we measured lncRNA and mRNA expression levels from the hypothalamus.

Results

We applied RNA sequencing analysis to examine the hypothalamus of pubertal (case; n = 3) and prepubertal (control; n = 3) goats. Our results showed 2943 predicted lncRNAs, including 2012 differentially expressed lncRNAs, which corresponded to 5412 target genes. We also investigated the role of lncRNAs that act cis and trans to the target genes and found a number of lncRNAs involved in the regulation of puberty and reproduction, as well as several pathways related to these processes. For example, oxytocin signaling pathway, sterol biosynthetic process, and pheromone receptor activity signaling pathway were enriched as Kyoto Encyclopedia of Genes and Genomes (KEGG) or gene ontology (GO) analyses showed.

Conclusion

Our results clearly demonstrate that lncRNAs play an important role in regulating puberty in goats. However, further research is needed to explore the functions of lncRNAs and their predicted targets to provide a detailed expression profile of lncRNAs on goat puberty.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3578-9) contains supplementary material, which is available to authorized users.

Hyperprolactinemia induced by hCG leads to metabolic disturbances in female mice

The metabolic syndrome is a growing epidemic; it increases the risk for diabetes, cardiovascular disease, fatty liver, and several cancers. Several reports have indicated a link between hormonal imbalances and insulin resistance or obesity. Transgenic (TG) female mice overexpressing the human chorionic gonadotropin β-subunit (hCGβ+ mice) exhibit constitutively elevated levels of hCG, increased production of testosterone, progesterone and prolactin, and obesity. The objective of this study was to investigate the influence of hCG hypersecretion on possible alterations in the glucose and lipid metabolism of adult TG females. We evaluated fasting serum insulin, glucose, and triglyceride levels in adult hCGβ+ females and conducted intraperitoneal glucose and insulin tolerance tests at different ages. TG female mice showed hyperinsulinemia, hypertriglyceridemia, and dyslipidemia, as well as glucose intolerance and insulin resistance at 6 months of age. A 1-week treatment with the dopamine agonist cabergoline applied on 5-week-old hCGβ+ mice, which corrected hyperprolactinemia, hyperandrogenism, and hyperprogesteronemia, effectively prevented the metabolic alterations. These data indicate a key role of the hyperprolactinemia-induced gonadal dysfunction in the metabolic disturbances of hCGβ+ female mice. The findings prompt further studies on the involvement of gonadotropins and prolactin on metabolic disorders and might pave the way for the development of new therapeutic strategies.

Core Binding Factor-β Knockdown Alters Ovarian Gene Expression and Function in the Mouse

Core binding factor (CBF) is a heterodimeric transcription factor complex composed of a DNA-binding subunit, one of three runt-related transcription factor (RUNX) factors, and a non-DNA binding subunit, CBFβ. CBFβ is critical for DNA binding and stability of the CBF transcription factor complex. In the ovary, the LH surge increases the expression of Runx1 and Runx2 in periovulatory follicles, implicating a role for CBFs in the periovulatory process. The present study investigated the functional significance of CBFs (RUNX1/CBFβ and RUNX2/CBFβ) in the ovary by examining the ovarian phenotype of granulosa cell-specific CBFβ knockdown mice; CBFβ f/f * Cyp19 cre. The mutant female mice exhibited significant reductions in fertility, with smaller litter sizes, decreased progesterone during gestation, and fewer cumulus oocyte complexes collected after an induced superovulation. RNA sequencing and transcriptome assembly revealed altered expression of more than 200 mRNA transcripts in the granulosa cells of Cbfb knockdown mice after human chorionic gonadotropin stimulation in vitro. Among the affected transcripts are known regulators of ovulation and luteinization including Sfrp4, Sgk1, Lhcgr, Prlr, Wnt4, and Edn2 as well as many genes not yet characterized in the ovary. Cbfβ knockdown mice also exhibited decreased expression of key genes within the corpora lutea and morphological changes in the ovarian structure, including the presence of large antral follicles well into the luteal phase. Overall, these data suggest a role for CBFs as significant regulators of gene expression, ovulatory processes, and luteal development in the ovary.

Effect of intravaginal fluorogestone acetate sponges on prolactin levels of Damascus-local cross breed goats

The effect of intravaginal fluorogestone acetate (FGA) sponges on prolactin levels (PRL) and correlations between PRL and milk somatic cell count (SCC) and steroid hormones levels of Damascus-local cross goats during transitional period to anestrous were investigated in this study. Fifty-six goats were assigned to three groups. Group 1 (FGA, n = 19) was treated with 40 mg FGA and equine chorionic gonadotropin (600 IU, i.m.) at time of sponge withdrawal (day 0). Group 2 (FGA-PGF; n = 19) was treated similar to group 1 but was also injected with dinoprost tromethamine (naturally occurring PGF2α) (10 mg, i.m.) on day 0. Control goats (n = 18) were left untreated. On day 0, five fertile bucks were turned in with all goats. Milk and blood samples were collected on days -13 (day of sponge insertion), -6, 0, 1, 2, 7, 13, and 20. Prolactin levels were at lowest values on day -13 of the study and increased (p < 0.05) from day -6 to day 20 in all groups. A significant positive correlation (p < 0.05) between PRL and progesterone and between PRL and estradiol levels was found in this study. No significant correlation was found between PRL and SCC of all groups during the study except on days 2 and 20 where PRL levels were correlated (p < 0.05) with SCC of left udder halves of FGA group. In conclusion, estrus induction with FGA resulted in significant increase in PRL. A positive correlation was found between PRL and steroid hormones, but there was no correlation between PRL and goat milk SCC.