Mechanisms of FSH synthesis: what we know, what we don't, and why you should care

The expression profiles of cyp19a1, sf-1, esrs and gths in the brain-pituitary during gonadal sex differentiation in juvenile Japanese eels

Eels are gonochoristic species whose gonadal differentiation initiates at the yellow eel stage and is influenced by environmental factors. We revealed some sex-related genes were sex dimorphically expressed in gonads during gonadal sex differentiation of Japanese eel (Anguilla japonica); however, the expression of sex-related genes in the brain-pituitary during gonadal sex differentiation in eels is still unclear. This study aimed to investigate the sex-related gene expressions in the brain-pituitary and tried to clarify their roles in the brain and gonads during gonadal sex differentiation. Based on our previous histological study, the control eels developed as males, and estradiol-17β (E2) was used for feminization. Our results showed that during testicular differentiation, the brain cyp19a1 transcripts and aromatase proteins were increased significantly; moreover, the cyp19a1, sf-1, foxl2s, and esrs (except gperb) transcripts in the midbrain/pituitary also were increased significantly. Forebrain gnrh1 transcripts increased slightly during gonadal differentiation of both sexes, but the gnrhr1b and gnrhr2 transcripts in the midbrain/pituitary were stable during gonadal differentiation. The expression levels of gths and gh in the midbrain/pituitary were significantly increased during testicular differentiation and were much higher in males than in E2-feminized females. These results implied that endogenous estrogens might play essential roles in the brain/pituitary during testicular differentiation, sf-1, foxl2s, and esrs may have roles in cyp19a1 regulation in the midbrain/pituitary of Japanese eels. For the GnRH-GTH axis, gths, especially fshb, may be regulated by esrs and involved in regulating testicular differentiation and development in Japanese eels.

Gonadotropin-Releasing Hormone (GnRH) and Its Agonists in Bovine Reproduction I: Structure, Biosynthesis, Physiological Effects, and Its Role in Estrous Synchronization

GnRH is essential for the regulation of mammalian reproductive processes. It regulates the production and release of pituitary gonadotropins, thereby influencing steroidogenesis and gametogenesis. While primarily produced in the hypothalamus, GnRH is also produced in peripheral organs, such as the gonads and placenta. GnRH analogs, including agonists and antagonists, have been synthesized for the reproductive management of animals and humans. This review focuses on the functions of hypothalamic GnRH in the reproductive processes of cattle. In addition to inducing the surge release of LH, the pulsatile secretion of GnRH stimulates the pituitary gland to release FSH and LH, thereby regulating gonadal function. Various GnRH-based products have been synthesized to increase their potency and efficacy in regulating reproductive functions. This review article describes the chemical structures of GnRH and its agonists. This discussion extends to the gene expression of GnRH in the hypothalamus, highlighting its pivotal role in regulating the reproductive process. Furthermore, GnRH is involved in regulating ovarian follicular development and luteal phase support, and estrus synchronization is involved. A comprehensive understanding of the role of GnRH and its analogs in the modulation of reproductive processes is essential for optimizing animal reproduction.

Changes in pituitary gonadotropin subunits and hypothalamic Kiss-1 gene expression by administration of sex steroids in ovary-intact female rats

OBJECTIVE

We examined how the sex steroids influence the synthesis of gonadotropins.

MATERIALS AND METHODS

The effects of sex steroids estradiol (E2), progesterone (P4), and dihydrotestosterone (DHT) in pituitary gonadotroph cell model (LβT2 cells) in vitro and ovary-intact rats in vivo were examined. The effects of sex steroids on Kiss1 gene expression in the hypothalamus were also examined in ovary-intact rats.

RESULTS

In LβT2 cells, E2 increased common glycoprotein alpha (Cga) and luteinizing hormone beta (Lhb) subunit promoter activity as well as their mRNA expression. Although gonadotropin subunit promoter activity was not modulated by P4, Cga and Lhb mRNA expression was increased by P4. DHT inhibited Cga and Lhb mRNA expression with a concomitant decrease in their promoter activity. During the 2-week administration of exogenous E2 to ovary-intact rats, the estrous cycle determined by vaginal smears was disrupted. P4 or DHT administration completely eliminated the estrous cycle. Protein expression of all three gonadotropin subunits within the pituitary gland was inhibited by E2 or P4 treatment in vivo; however, DHT reduced Cga expression but did not modulate Lhb or follicle-stimulating hormone beta subunit expression. E2 administration significantly repressed Kiss1 mRNA expression in a posterior hypothalamic region that included the arcuate nucleus. P4 and DHT did not modulate Kiss1 mRNA expression in this region. In contrast, P4 administration significantly inhibited Kiss1 mRNA expression in the anterior region of the hypothalamus that included the anteroventral periventricular nucleus. The expression of gonadotropin-releasing hormone (Gnrh) mRNA in the anterior hypothalamic region, where the preoptic area is located, appeared to be decreased by treatment with E2 and P4.

CONCLUSION

Our findings suggest that sex steroids have different effects in the hypothalamus and pituitary gland.

Pre- and postnatal developmental exposure to the polychlorinated biphenyl mixture aroclor 1221 alters female rat pituitary gonadotropins and estrogen receptor alpha levels

Polychlorinated-biphenyls (PCBs) are industrial compounds, which were widely used in manufacturing of electrical parts and transformers. Despite being banned in 1979 due to human health concerns, they persist in the environment. In humans and experimental model systems, PCBs elicit toxicity in part by acting as endocrine-disrupting chemicals (EDCs). Aroclor 1221 (A1221) is a weakly estrogenic PCB mixture known to alter reproductive function in rodents. EDCs can impact hormone signaling at any level of the hypothalamic-pituitary-gonadal (HPG) axis, and we investigated the effects of A1221 exposure during the prenatal and postnatal developmental periods on pituitary hormone and steroid receptor expression in female rats. Examining offspring at 3 ages, postnatal day 8 (P8), P32 and P60, we found that prenatal exposure to A1221 increased P8 neonate pituitary luteinizing hormone beta (Lhb) mRNA and LHβ gonadotrope cell number while decreasing LH serum hormone concentration. No changes in pituitary hormone or hormone receptor gene expression were observed peri-puberty at P32. In reproductively mature rats at P60, we found pituitary follicle stimulating hormone beta (Fshb) mRNA levels increased by prenatal A1221 exposure with no corresponding alterations in FSH hormone or FSHβ expressing cell number. Estrogen receptor alpha (ERα) mRNA and protein levels were also increased at P60, but only following postnatal A1221 dosing. Together, these data illustrate that exposure to the PCB A1221, during critical developmental windows, alters pituitary gonadotropin hormone subunits and ERα levels in offspring at different phases of maturation, potentially impacting reproductive function in concert with other components of the HPG axis.

Activating Transcription Factor 3 Stimulates Follicle-Stimulating Hormone-β Expression In Vitro But Is Dispensable for Follicle-Stimulating Hormone Production in Murine Gonadotropes In Vivo

Follicle-stimulating hormone (FSH), a dimeric glycoprotein produced by pituitary gonadotrope cells, regulates spermatogenesis in males and ovarian follicle growth in females. Hypothalamic gonadotropin-releasing hormone (GnRH) stimulates FSHβ subunit gene (Fshb) transcription, though the underlying mechanisms are poorly understood. To address this gap in knowledge, we examined changes in pituitary gene expression in GnRH-deficient mice (hpg) treated with a regimen of exogenous GnRH that increases pituitary Fshb but not luteinizing hormone β (Lhb) messenger RNA levels. Activating transcription factor 3 (Atf3) was among the most upregulated genes. Activating transcription factor 3 (ATF3) can heterodimerize with members of the activator protein 1 family to regulate gene transcription. Co-expression of ATF3 with JunB stimulated murine Fshb, but not Lhb, promoter-reporter activity in homologous LβT2b cells. ATF3 also synergized with a constitutively active activin type I receptor to increase endogenous Fshb expression in these cells. Nevertheless, FSH production was intact in gonadotrope-specific Atf3 knockout [conditional knockout (cKO)] mice. Ovarian follicle development, ovulation, and litter sizes were equivalent between cKOs and controls. Testis weights and sperm counts did not differ between genotypes. Following gonadectomy, increases in LH secretion were enhanced in cKO animals. Though FSH levels did not differ between genotypes, post-gonadectomy increases in pituitary Fshb and gonadotropin α subunit expression were more pronounced in cKO than control mice. These data indicate that ATF3 can selectively stimulate Fshb expression in vitro but is not required for FSH production in vivo.

Altered GnRH neuron and ovarian innervation characterize reproductive dysfunction linked to the Fragile X messenger ribonucleoprotein (Fmr1) gene mutation

Introduction

Mutations in the Fragile X Messenger Ribonucleoprotein 1 (FMR1) gene cause Fragile X Syndrome, the most common monogenic cause of intellectual disability. Mutations of FMR1 are also associated with reproductive disorders, such as early cessation of reproductive function in females. While progress has been made in understanding the mechanisms of mental impairment, the causes of reproductive disorders are not clear. FMR1-associated reproductive disorders were studied exclusively from the endocrine perspective, while the FMR1 role in neurons that control reproduction was not addressed.

Results

Here, we demonstrate that similar to women with FMR1 mutations, female Fmr1 null mice stop reproducing early. However, young null females display larger litters, more corpora lutea in the ovaries, increased inhibin, progesterone, testosterone, and gonadotropin hormones in the circulation. Ovariectomy reveals both hypothalamic and ovarian contribution to elevated gonadotropins. Altered mRNA and protein levels of several synaptic molecules in the hypothalamus are identified, indicating reasons for hypothalamic dysregulation. Increased vascularization of corpora lutea, higher sympathetic innervation of growing follicles in the ovaries of Fmr1 nulls, and higher numbers of synaptic GABAA receptors in GnRH neurons, which are excitatory for GnRH neurons, contribute to increased FSH and LH, respectively. Unmodified and ovariectomized Fmr1 nulls have increased LH pulse frequency, suggesting that Fmr1 nulls exhibit hyperactive GnRH neurons, regardless of the ovarian feedback.

Conclusion

These results reveal Fmr1 function in the regulation of GnRH neuron secretion, and point to the role of GnRH neurons, in addition to the ovarian innervation, in the etiology of Fmr1-mediated reproductive disorders.

Inhibin Inactivation in Female Mice Leads to Elevated FSH Levels, Ovarian Overstimulation, and Pregnancy Loss

Inhibins are members of the transforming growth factor-β family, composed of a common α-subunit disulfide-linked to 1 of 2 β-subunits (βA in inhibin A or βB in inhibin B). Gonadal-derived inhibin A and B act in an endocrine manner to suppress the synthesis of follicle-stimulating hormone (FSH) by pituitary gonadotrope cells. Roles for inhibins beyond the pituitary, however, have proven difficult to delineate because deletion of the inhibin α-subunit gene (Inha) results in unconstrained expression of activin A and activin B (homodimers of inhibin β-subunits), which contribute to gonadal tumorigenesis and lethal cachectic wasting. Here, we generated mice with a single point mutation (Arg233Ala) in Inha that prevents proteolytic processing and the formation of bioactive inhibin. In vitro, this mutation blocked inhibin maturation and bioactivity, without perturbing activin production. Serum FSH levels were elevated 2- to 3-fold in InhaR233A/R233A mice due to the loss of negative feedback from inhibins, but no pathological increase in circulating activins was observed. While inactivation of inhibin A and B had no discernible effect on male reproduction, female InhaR233A/R233A mice had increased FSH-dependent follicle development and enhanced natural ovulation rates. Nevertheless, inhibin inactivation resulted in significant embryo-fetal resorptions and severe subfertility and was associated with disrupted maternal ovarian function. Intriguingly, heterozygous Inha+/R233A females had significantly enhanced fecundity, relative to wild-type littermates. These studies have revealed novel effects of inhibins in the establishment and maintenance of pregnancy and demonstrated that partial inactivation of inhibin A/B is an attractive approach for enhancing female fertility.

Deletion of Gαq/11 or Gαs Proteins in Gonadotropes Differentially Affects Gonadotropin Production and Secretion in Mice

Gonadotropin-releasing hormone (GnRH) regulates gonadal function via its stimulatory effects on gonadotropin production by pituitary gonadotrope cells. GnRH is released from the hypothalamus in pulses and GnRH pulse frequency differentially regulates follicle-stimulating hormone (FSH) and luteinizing hormone (LH) synthesis and secretion. The GnRH receptor (GnRHR) is a G protein-coupled receptor that canonically activates Gα q/11-dependent signaling on ligand binding. However, the receptor can also couple to Gα s and in vitro data suggest that toggling between different G proteins may contribute to GnRH pulse frequency decoding. For example, as we show here, knockdown of Gα s impairs GnRH-stimulated FSH synthesis at low- but not high-pulse frequency in a model gonadotrope-derived cell line. We next used a Cre-lox conditional knockout approach to interrogate the relative roles of Gα q/11 and Gα s proteins in gonadotrope function in mice. Gonadotrope-specific Gα q/11 knockouts exhibit hypogonadotropic hypogonadism and infertility, akin to the phenotypes seen in GnRH- or GnRHR-deficient mice. In contrast, under standard conditions, gonadotrope-specific Gα s knockouts produce gonadotropins at normal levels and are fertile. However, the LH surge amplitude is blunted in Gα s knockout females and postgonadectomy increases in FSH and LH are reduced both in males and females. These data suggest that GnRH may signal principally via Gα q/11 to stimulate gonadotropin production, but that Gα s plays important roles in gonadotrope function in vivo when GnRH secretion is enhanced.

The Hippo Pathway Effectors YAP and TAZ Regulate LH Release by Pituitary Gonadotrope Cells in Mice

The Hippo transcriptional coactivators YAP and TAZ exert critical roles in morphogenesis, organ size determination and tumorigenesis in many tissues. Although Hippo kinase cascade activity was recently reported in the anterior pituitary gland in mice, the role of the Hippo effectors in regulating gonadotropin production remains unknown. The objective of this study was therefore to characterize the roles of YAP and TAZ in gonadotropin synthesis and secretion. Using a conditional gene targeting approach (cKO), we found that gonadotrope-specific inactivation of Yap and Taz resulted in increased circulating levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) in adult male mice, along with increased testosterone levels and testis weight. Female cKO mice had increased circulating LH (but not FSH) levels, which were associated with a hyperfertility phenotype characterized by higher ovulation rates and larger litter sizes. Unexpectedly, the loss of YAP/TAZ did not appear to affect the expression of gonadotropin subunit genes, yet both basal and GnRH-induced LH secretion were increased in cultured pituitary cells from cKO mice. Likewise, pharmacologic inhibition of YAP binding to the TEAD family of transcription factors increased both basal and GnRH-induced LH secretion in LβT2 gonadotrope-like cells in vitro without affecting Lhb expression. Conversely, mRNA levels of ChgA and SgII, which encode key secretory granule cargo proteins, were decreased following pharmacologic inhibition of YAP/TAZ, suggesting a mechanism whereby YAP/TAZ regulate the LH secretion machinery in gonadotrope cells. Together, these findings represent the first evidence that Hippo signaling may play a role in regulating pituitary LH secretion.

Iodoacetic Acid, a Water Disinfection Byproduct, Disrupts Hypothalamic, and Pituitary Reproductive Regulatory Factors and Induces Toxicity in the Female Pituitary

Iodoacetic acid (IAA) is a water disinfection byproduct (DBP) formed by reactions between oxidizing disinfectants and iodide. In vitro studies have indicated that IAA is one of the most cyto- and genotoxic DBPs. In humans, DBPs have been epidemiologically associated with reproductive dysfunction. In mouse ovarian culture, IAA exposure significantly inhibits antral follicle growth and reduces estradiol production. Despite this evidence, little is known about the effects of IAA on the other components of the reproductive axis: the hypothalamus and pituitary. We tested the hypothesis that IAA disrupts expression of key neuroendocrine factors and directly induces cell damage in the mouse pituitary. We exposed adult female mice to IAA in drinking water in vivo and found 0.5 and 10 mg/l IAA concentrations lead to significantly increased mRNA levels of kisspeptin (Kiss1) in the arcuate nucleus although not affecting Kiss1 in the anteroventral periventricular nucleus. Both 10 mg/l IAA exposure in vivo and 20 μM IAA in vitro reduced follicle stimulating hormone (FSHβ)-positive cell number and Fshb mRNA expression. IAA did not alter luteinizing hormone (LHβ) expression in vivo although exposure to 20 μM IAA decreased expression of Lhb and glycoprotein hormones, alpha subunit (Cga) mRNA in vitro. IAA also had toxic effects in the pituitary, inducing DNA damage and P21/Cdkn1a expression in vitro (20 μM IAA) and DNA damage and Cdkn1a expression in vivo (500 mg/l). These data implicate IAA as a hypothalamic-pituitary-gonadal axis toxicant and suggest the pituitary is directly affected by IAA exposure.

Gonadotropin response to insulin and lipid infusion reproduces the reprometabolic syndrome of obesity in eumenorrheic lean women: a randomized crossover trial

OBJECTIVE

To study the reprometabolic syndrome in normal-weight, eumenorrheic women by infusing a combination of insulin and lipid. Women with obesity have been shown to have reduced gonadotropins and impaired luteinizing hormone (LH) and follicle-stimulating hormone (FSH) response to gonadotropin-releasing hormone (GnRH).

DESIGN

Randomized crossover.

SETTING

Academic medical center.

PARTICIPANT(S)

Fifteen women, median age 32 (interquartile ranged [IQR] 26, 36) years and body mass index 21.9 (IQR 20.2, 22.9) kg/m2 were recruited.

INTERVENTION(S)

Early follicular phase, 6-hour infusions of insulin (20-40 mU/m2 per minute) and lipid (Intralipid)-insulin/lipid infusion; or saline infusion (controls). The first 4 hours of each study assessed endogenous gonadotropins; at 4 hours, GnRH (75 ng/kg) bolus was administered and sampling continued until 6 hours.

MAIN OUTCOME MEASURE(S)

Linear mixed model analysis was used to determine differences between insulin/lipid and saline influence on endogenous LH pulse amplitude (primary outcome), mean FSH, and area under the curve (AUC) response to GnRH (secondary outcomes).

RESULT(S)

Twelve women completed both intended studies and an additional 3 women completed only 1 of the 2 studies. LH pulse amplitude, mean FSH, and both AUC responses to GnRH were reduced by insulin/lipid, mean FSH and AUC for LH were at or near statistical significance. LH response to GnRH was significantly reduced when 1 participant with very high LH and antimullerian hormone levels was excluded.

CONCLUSION(S)

Acute infusion of insulin/lipid to eumenorrheic, normal-weight women recapitulated the reprometabolic syndrome of obesity. These findings imply that specific circulating factors in obese women contribute to their subfertility and thus may be amenable to discovery and treatment.

CLINICAL TRIAL REGISTRATION NUMBER

NCT02653092.

Distal Enhancer Potentiates Activin- and GnRH-Induced Transcription of FSHB

FSH is critical for fertility. Transcription of FSHB, the gene encoding the beta subunit, is rate-limiting in FSH production and is regulated by both GnRH and activin. Activin signals through SMAD transcription factors. Although the mechanisms and importance of activin signaling in mouse Fshb transcription are well-established, activin regulation of human FSHB is less well understood. We previously reported a novel enhancer of FSHB that contains a fertility-associated single nucleotide polymorphism (rs10031006) and requires a region resembling a full (8 base-pair) SMAD binding element (SBE). Here, we investigated the role of the putative SBE within the enhancer in activin and GnRH regulation of FSHB. In mouse gonadotrope-derived LβT2 cells, the upstream enhancer potentiated activin induction of both the human and mouse FSHB proximal promoters and conferred activin responsiveness to a minimal promoter. Activin induction of the enhancer required the SBE and was blocked by the inhibitory SMAD7, confirming involvement of the classical SMAD signaling pathway. GnRH induction of FSHB was also potentiated by the enhancer and dependent on the SBE, consistent with known activin/GnRH synergy regulating FSHB transcription. In DNA pull-down, the enhancer SBE bound SMAD4, and chromatin immunoprecipitation demonstrated SMAD4 enrichment at the enhancer in native chromatin. Combined activin/GnRH treatment elevated levels of the active transcriptional histone marker, histone 3 lysine 27 acetylation, at the enhancer. Overall, this study indicates that the enhancer is directly targeted by activin signaling and identifies a novel, evolutionarily conserved mechanism by which activin and GnRH can regulate FSHB transcription.

Pituitary response to GnRH stimulation tests in different FSHB-211 G/T genotypes

STUDY QUESTION

Does pituitary response to a GnRH stimulation test differ according to the different FSHB-211 G/T genotypes?

SUMMARY ANSWER

The promoter polymorphism FSHB-211 G > T affects the pituitary response to exogenous GnRH stimulation by reducing FSH and increasing LH outputs.

WHAT IS KNOWN ALREADY

The FSHB-211 G > T single nucleotide polymorphism (SNP) is known to affect pituitary FSH output by impairing the transcriptional activity of FSHB.

STUDY DESIGN, SIZE, DURATION

This was a cross-sectional, retrospective study on 67 male subjects (mean age: 24.6 ± 10.3 years) undergoing a GnRH stimulation test for diagnostic purposes in cases of secondary hypogonadism.

PARTICIPANTS/MATERIALS, SETTING, METHODS

A GnRH stimulation test was performed by administering an i.v. bolus of 100 µg of the GnRH-analogue gonadorelin acetate to all patients, with blood samples drawn from the cubital vein immediately prior to injection (T0) and 30 (T1) and 45 minutes (T2) after. Clinical and genetic data were retrieved from a computerized database. Linear longitudinal mixed-effect models were used to assess the effects of SNP genotype on FSH and LH levels over time via additive and recessive models.

MAIN RESULTS AND THE ROLE OF CHANCE

An overall marked increase in serum FSH and LH following administration i.v. of 100 µg of an LHRH-analogue was found (P < 0.0001 for linear trend, both models). Peak levels of LH were significantly higher in TT carriers than in GT and GG carriers (P = 0.012); no significant between-groups difference was found concerning stimulated FSH levels. In both the additive and recessive model, the main effect of T allele(s) did not reach statistical significance concerning FSH levels (P = 0.9502 and P = 0.8576, respectively), yet interaction effects over time demonstrated an attenuated response in T-allele carriers compared to the GG-allele carriers (P = 0.0219 and P = 0.0276). Main and interaction effects for LH were significant in both the additive (P = 0.0022 and P = 0.0013, respectively) and recessive model (P = 0.0025 and P = 0.0016, respectively).

LIMITATIONS, REASONS FOR CAUTION

Given the retrospective nature of the study and the small number of TT carriers, results should be interpreted with caution.

WIDER IMPLICATIONS OF THE FINDINGS

The FSHB c.-211G>T polymorphism might result in an impaired response to endogenous, as well as exogenous, GnRH stimulation. This finding might contribute to the clinical phenotype of reduced testicular volume and sperm count for patients carrying one or two T alleles.

STUDY FUNDING/COMPETING INTEREST(S)

Parts of the study were supported by the German Research Foundation (CRU326 Male Germ Cells). On behalf of all authors, the corresponding author states that there is no conflict of interest.

TRIAL REGISTRATION NUMBER

NA.

Sequential preovulatory expression of a gonadotropin-releasing hormone-inducible gene, Nr4a3, and its suppressor Anxa5 in the pituitary gland of female rats

Functional relationship between nuclear receptor subfamily 4 group A member 3 (Nr4a3) and annexin A5 (Anxa5), which are two gonadotropin-releasing hormone (GnRH)-inducible genes, has been established while evaluating pituitary gonadotropes in relation to follicle-stimulating hormone beta (Fshb) expression. However, the physiological variations that arise due to the differential expression of these genes in the pituitary gland during rat estrous cycle remain unknown. This study aimed to evaluate the Nr4a3 and Anxa5 mRNA expression during the estrous cycle in rats in comparison with the expression of the gonadotropin subunit genes, luteinizing hormone beta (Lhb) and Fshb. Nr4a3 mRNA expression showed a single peak at 1400 h of proestrus during the 4-d estrous cycle. Anxa5 mRNA level was elevated along with increased Fshb mRNA expression after the decline of Nr4a3 mRNA until 2300 h. Lhb mRNA expression levels were not significantly changed during the estrous cycle. Notably, addition of a GnRH antagonist at 1100 h completely eradicated luteinizing hormone secretion at 1400 h and 1700 h of proestrus, and significantly reduced the Nr4a3 mRNA expression level at both the time points. These results suggest that GnRH is, at least partly, responsible for the increase in pituitary Nr4a3, and that the interaction between NR4A3 and ANXA5 is required to regulate Fshb expression during the preovulatory gonadotropin surge.

FSHB and FSHR gene variants exert mild modulatory effect on reproductive hormone levels and testis size but not on semen quality: A study of 2020 men from the general Danish population

BACKGROUND

Spermatogenesis depends on stimulation by follicle-stimulating hormone (FSH) which binds to FSH receptors (FSHR) on testicular Sertoli cells. Three FSH-related single-nucleotide polymorphisms (SNPs), FSHB -211G>T (rs10835638), FSHR -29G>A (rs1394205) and FSHR 2039A>G (rs6166) affect FSH action, and have been suggested to affect testicular function, but the evidence is uncertain.

OBJECTIVE

To describe the associations between the three SNPs and testicular function in a large and well-characterised cohort of men from the general population.

MATERIALS AND METHODS

A cross-sectional study of 2020 Danish men unselected regarding testicular function. Outcome variables were semen parameters, reproductive hormones and testis size. Genotyping was done by competitive allele-specific quantitative PCR. Differences in genotype frequencies were tested by chi-square test and associations between genotypes and outcomes were assessed by multivariate linear regressions.

RESULTS

The SNPs affected serum FSH; carriers of the variant affecting FSH secretion (FSHB -211G>T) had lower FSH levels while carriers of variants affecting receptor expression (FSHR -29G>A) and receptor sensitivity (FSHR 2039A>G) had higher FSH levels. Carriers of FSHB -211G>T had lower calculated free testosterone/LH ratio. Although both FSHB -211G>T and FSHR 2039A>G were associated with smaller testis size, no clear association was detected in relation to any semen parameters, except a lower total number of morphologically normal spermatozoa in the heterozygous carriers of the FSHB -211G>T DISCUSSION AND CONCLUSION: The studied polymorphisms have only minor modulating influence on testis size and function in healthy men. We detected subtle effects of the three SNPs on FSH levels, but also effects of FSHB -211G>T on calculated free testosterone/LH ratio, compatible with altered Leydig cell function. Thus, the role of these FSH-related polymorphisms is complex and modest in men with normal testicular function, but the possible importance of FSH polymorphisms in men with impaired testicular function should be evaluated in future studies in more detail.

Selection of fewer dominant follicles in Trio carriers given GnRH antagonist and luteinizing hormone action replaced by nonpulsatile human chorionic gonadotropin†

Studying selection of multiple dominant follicles (DFs) in monovulatory species can advance our understanding of mechanisms regulating selection of single or multiple DFs. Carriers of the bovine high fecundity Trio allele select multiple DFs, whereas half-sib noncarriers select a single DF. This study compared follicle selection during endogenous gonadotropin pulses versus during ablation of pulses with Acyline (GnRH antagonist) and luteinizing hormone (LH) action replaced with nonpulsatile human chorionic gonadotropin (hCG) treatment in Trio carriers (n = 28) versus noncarriers (n = 32). On Day 1.5 (Day 0 = ovulation), heifers were randomized: (1) Control, untreated; (2) Acyline, two i.m. doses (Days 1.5 and D3) of 3 μg/kg; (3) hCG, single i.m. dose of 50 IU hCG on Day 1.5 followed by daily doses of 100 IU; and (4) Acyline + hCG. Treatments with nonpulsatile hCG were designed to replace LH action in heifers treated with Acyline. Acyline treatment resulted in cessation of follicle growth on Day 3 with smaller (P < 0.0001) maximum follicle diameter in Trio carriers (6.6 ± 0.2 mm) than noncarriers (8.7 ± 0.4 mm). Replacement of LH action (hCG) reestablished follicle diameter deviation and maximum diameter of DFs in both genotypes (8.9 ± 0.3 mm and 13.1 ± 0.5 mm; P < 0.0001). Circulating follicle stimulating hormone (FSH) was greater in Acyline-treated than in controls. Finally, Acyline + hCG decreased (P < 0.0001) the number of DFs from 2.7 ± 0.2 to 1.3 ± 0.2 in Trio carriers, with most heifers having only one DF. This demonstrates the necessity for LH in acquisition of dominance in Trio carriers (~6.5 mm) and noncarriers (~8.5 mm) and provides evidence for a role of GnRH-induced FSH/LH pulses in selection of multiple DFs in Trio carriers and possibly other physiologic situations with increased ovulation rate.

Androgen-dependent sexual dimorphism in pituitary tryptophan hydroxylase expression: relevance to sex differences in pituitary hormones

Serotonin is a biogenic monoamine conserved across phyla that is implicated in diverse physiological and behavioural functions. On examining the expression of the rate-limiting enzymes in serotonin synthesis, tryptophan hydroxylases (TPHs), in the teleost medaka (Oryzias latipes), we found that males have much higher levels of tph1 expression as compared with females. This robust sexual dimorphism was found to probably result from the direct stimulation of tph1 transcription by androgen/androgen receptor binding to canonical bipartite androgen-responsive elements in its proximal promoter region. Our results further revealed that tph1 expression occurs exclusively in pro-opiomelanocortin (pomc)-expressing cells and that the resulting serotonin and its derivative melatonin inhibit the expression of the pituitary hormone genes, fshb, sl and tshb. This suggests that serotonin and/or melatonin synthesized in pomc-expressing cells act in a paracrine manner to suppress pituitary hormone levels. Consistent with these findings and the male-biased expression of tph1, the expression levels of fshb, sl and tshb were all higher in females than in males. Taken together, the male bias in tph1 expression and consequent serotonin/melatonin production presumably contribute to sex differences in the expression of pituitary hormones and ultimately in the physiological functions mediated by them.

Human Follicle-Stimulating Hormone ß Subunit Expression Depends on FOXL2 and SMAD4

Follicle-stimulating hormone (FSH), an essential regulator of mammalian fertility, is synthesized by pituitary gonadotrope cells in response to activins. In mice, activins signal via SMAD3, SMAD4, and FOXL2 to regulate transcription of the FSHβ subunit (Fshb) gene. Gonadotrope-specific deletion of Foxl2, alone or in combination with Smad4, renders mice FSH-deficient. Whether human FSHB expression is similarly regulated is not known. Here, we used a combination of transgenic and conditional knockout mouse strains to assess the roles of activins, FOXL2, and SMAD4 in regulation of the human FSHB gene. First, we cultured pituitaries from mice harboring a human FSHB transgene (hFSHB mice) and measured both murine Fshb and human FSHB messenger ribonucleic acid (mRNA) expression in response to exogenous activins or two antagonists of endogenous activin-like signaling (follistatin-288 and SB431542). Both murine Fshb and human FSHB expression were stimulated by activins and reduced by the inhibitors. Next, we analyzed human FSHB expression in hFSHB mice carrying floxed Foxl2 and Smad4 alleles. Cre-mediated ablation of FOXL2 and SMAD4 strongly reduced basal and activin-stimulated murine Fshb and human FSHB expression in cultured pituitaries. Finally, the hFSHB transgene was previously shown to rescue FSH production and fertility in Fshb knockout mice. However, gonadotrope-specific Foxl2/Smad4 knockout females carrying the hFSHB transgene have significantly reduced murine Fshb and human FSHB pituitary mRNA levels and are hypogonadal. Collectively, these data suggest that similar to Fshb regulation in mice, FOXL2 and SMAD4 play essential roles in human FSHB expression.

Neuroendocrine, autocrine, and paracrine control of follicle-stimulating hormone secretion

Follicle-stimulating hormone (FSH) is a glycoprotein hormone produced by gonadotropes in the anterior pituitary that plays a central role in controlling ovarian folliculogenesis and steroidogenesis in females. Moreover, recent studies strongly suggest that FSH exerts extragonadal actions, particularly regulating bone mass and adiposity. Despite its crucial role, the mechanisms regulating FSH secretion are not completely understood. It is evident that hypothalamic, ovarian, and pituitary factors are involved in the neuroendocrine, paracrine, and autocrine regulation of FSH production. Large animal models, such as the female sheep, represent valuable research models to investigate specific aspects of FSH secretory processes. This review: (i) summarizes the role of FSH controlling reproduction and other biological processes; (ii) discusses the hypothalamic, gonadal, and pituitary regulation of FSH secretion; (iii) considers the biological relevance of the different FSH isoforms; and (iv) summarizes the distinct patterns of FSH secretion under different physiological conditions.

Nr5a1b promotes and Nr5a2 inhibits transcription of lhb in the orange-spotted grouper, Epinephelus coioides†

Nr5a1 (Sf-1) up-regulates lhb expression across vertebrates; however, its regulatory roles on fshb remain to be defined. Moreover, the involvement of Nr5a2 in the regulation of gonadotropin expression is not clear either. In the present study, the involvement of Nr5a1b (a homologue of Nr5a1) and Nr5a2 in the regulation of lhb and fshb expression in the orange-spotted grouper was examined. Dual fluorescent immunohistochemistry using homologous antisera showed that in the pituitary of orange-spotted groupers, Lh cells contain both immunoreactive Nr5a1b and Nr5a2 signals, whereas Fsh cells contain neither of them. In LβT2 cells, Nr5a1b up-regulated basal activities of lhb and fshb promoters possibly via Nr5a sites, and synergistically (on lhb promoter) or additively (on fshb promoter) with forskolin. Surprisingly, Nr5a2 inhibited basal activities of lhb promoter possibly via Nr5a sites and attenuated the stimulatory effects of both forskolin and Nr5a1b. In contrast, Nr5a2 had no effects on fshb promoter. Chromatin immunoprecipitation analysis showed that both Nr5a1b and Nr5a2 bound to lhb promoter, but not fshb promoter in the pituitary of the orange-spotted grouper. The abundance of Nr5a1b bound to lhb promoter was significantly higher at the vitellogenic stage than the pre-vitellogenic stage, whereas that of Nr5a2 exhibited an opposite trend. Taken together, data of the present study demonstrated antagonistic effects of Nr5a1b and Nr5a2 on lhb transcription in the orange-spotted grouper and revealed novel regulatory mechanisms of differential expression of lhb and fshb genes through Nr5a homologues in vertebrates.

PACAP induces FSHβ gene expression via EPAC

Gonadotropins, luteinizing hormone (LH) and follicle-stimulating hormone (FSH), are heterodimers of a common α subunit and unique β subunits. Regulation of their levels, primarily by GnRH, is critical for reproductive function. Several other hormones modulate gonadotropin expression, either independently or by modifying the responsiveness to GnRH. Pituitary adenylate cyclase activating peptide (PACAP) is one such hormone. Four-hour treatment of female mouse primary pituitary cells by either GnRH or PACAP induced FSHβ expression, while 24-h treatment repressed FSHβ. Both PACAP and GnRH caused FSH secretion into the medium. In the gonadotropes, PACAP activates primarily Gαs and increases concentration of cAMP, while GnRH primarily functions via Gαq and increases calcium concentration. Herein, we compared PACAP and GnRH signaling pathways that lead to the induction of FSHβ expression. Interestingly, constitutively active Gαs represses LHβ and induces FSHβ expression, while Gαq induces both β-subunits. We determined that FSHβ induction by PACAP requires functional EPAC, a cAMP sensor protein that serves as a guanine exchange factors for small G proteins that then bridges cAMP signaling to MAPK pathway. We further demonstrate that in addition to the prototypical small G protein Ras, two members of the Rho subfamily, Rac and CDC42 are also necessary for PACAP induction of FSHβ, likely via activation of p38 MAPK that leads to induction of cFOS, a critical transcription factor that is necessary and sufficient for FSHβ induction. Therefore, PACAP-induced cAMP pathway leads to MAPK activation that stimulates cFOS induction, to induce the expression of FSHβ subunit and increase FSH concentration.

Cytogenetic, Genomic, and Functional Characterization of Pituitary Gonadotrope Cell Lines

LβT2 and αT3-1 are important, widely studied cell line models for the pituitary gonadotropes that were generated by targeted tumorigenesis in transgenic mice. LβT2 cells are more mature gonadotrope precursors than αT3-1 cells. Microsatellite authentication patterns, chromosomal characteristics, and their intercellular variation have not been reported. We performed microsatellite and cytogenetic analysis of both cell types at early passage numbers. Short tandem repeat (STR) profiling was consistent with a mixed C57BL/6J × BALB/cJ genetic background, with distinct patterns for each cell type. Spectral karyotyping in αT3-1 cells revealed cell-to-cell variation in chromosome composition and pseudodiploidy. In LβT2 cells, chromosome counting and karyotyping demonstrated pseudotriploidy and high chromosomal variation among cells. Chromosome copy number variation was confirmed by single-cell DNA sequencing. Chromosomal compositions were consistent with a male sex for αT3-1 and a female sex for LβT2 cells. Among LβT2 stocks used in multiple laboratories, we detected two genetically similar but distinguishable lines via STR authentication, LβT2a and LβT2b. The two lines differed in morphological appearance, with LβT2a having significantly smaller cell and nucleus areas. Analysis of immediate early gene and gonadotropin subunit gene expression revealed variations in basal expression and responses to continuous and pulsatile GnRH stimulation. LβT2a showed higher basal levels of Egr1, Fos, and Lhb but lower Fos induction. Fshb induction reached significance only in LβT2b cells. Our study highlights the heterogeneity in gonadotrope cell line genomes and provides reference STR authentication patterns that can be monitored to improve experimental reproducibility and facilitate comparisons of results within and across laboratories.

GnRH-A Key Regulator of FSH

The hypothalamic decapeptide, GnRH, is the gatekeeper of mammalian reproductive development and function. Activation of specific, high-affinity cell surface receptors (GnRH receptors) on gonadotropes by GnRH triggers signal transduction cascades to stimulate the coordinated synthesis and secretion of the pituitary gonadotropins FSH and LH. These hormones direct gonadal steroidogenesis and gametogenesis, making their tightly regulated production and secretion essential for normal sexual maturation and reproductive health. FSH and LH are glycoprotein heterodimers comprised of a common α-subunit and a unique β-subunit (FSHβ and LHβ, respectively), which determines the biological specificity of the gonadotropins. The unique β-subunit is the rate-limiting step for the production of the mature gonadotropins. Therefore, FSH synthesis is regulated at the transcriptional level by Fshb gene expression. The overarching goal of this review is to expand our understanding of the mechanisms and pathways underlying the carefully orchestrated control of FSH synthesis and secretion by GnRH, focusing on the transcriptional regulation of the Fshb gene. Identification of these regulatory mechanisms is not only fundamental to our understanding of normal reproductive function but will also provide a context for the elucidation of the pathophysiology of reproductive disorders and infertility to lead to potential new therapeutic approaches.

Gain-of-Function Genetic Models to Study FSH Action

Follicle-stimulating hormone (FSH) is a pituitary-derived gonadotropin that plays key roles in male and female reproduction. The physiology and biochemistry of FSH have been extensively studied for many years. Beginning in the early 1990s, coincident with advances in the then emerging transgenic animal technology, and continuing till today, several gain-of-function (GOF) models have been developed to understand FSH homeostasis in a physiological context. Our group and others have generated a number of FSH ligand and receptor GOF mouse models. An FSH GOF model when combined with Fshb null mice provides a powerful genetic rescue platform. In this chapter, we discuss different GOF models for FSH synthesis, secretion and action and describe additional novel genetic models that could be developed in the future to further refine the existing models.

Pharmacogenetics of FSH Action in the Male

Male infertility is a major contributor to couple infertility, however in most cases it remains "idiopathic" and putative treatment regimens are lacking. This leads to a scenario in which intra-cytoplasmic spermatozoa injection (ICSI) is widely used in idiopathic male infertility, though the treatment burden is high for the couple and it entails considerable costs and risks. Given the crucial role of the Follicle-stimulating hormone (FSH) for spermatogenesis, FSH has been used empirically to improve semen parameters, but the response to FSH varied strongly among treated infertile men. Single nucleotide polymorphisms (SNPs) within FSH ligand/receptor genes (FSHB/FSHR), significantly influencing reproductive parameters in men, represent promising candidates to serve as pharmacogenetic markers to improve prediction of response to FSH. Consequently, several FSH-based pharmacogenetic studies have been conducted within the last years with unfortunately wide divergence concerning selection criteria, treatment and primary endpoints. In this review we therefore outline the current knowledge on single nucleotide polymorphisms (SNPs) in the FSH and FSH receptor genes and their putative functional effects. We compile and critically assess the previously performed pharmacogenetic studies in the male and propose a putative strategy that might allow identifying patients who could benefit from FSH treatment.

Ca2+ Channels in Anterior Pituitary Somatotrophs: A Therapeutic Perspective

Ca2+ influx through voltage-gated Ca2+ channels (VGCCs) plays a key role in GH secretion. In this review, we summarize the current state of knowledge regarding the physiology and molecular machinery of VGCCs in pituitary somatotrophs. We next discuss the possible involvement of Ca2+ channelopathies in pituitary disease and the potential use of Ca2+ channel blockers to treat pituitary disease. Various types of VGCCs exist in pituitary cells. However, because L-type Ca2+ channels (LTCCs) contribute the major component to Ca2+ influx in somatotrophs, lactotrophs, and corticotrophs, we focused on these channels. An increasing number of studies in recent years have linked genetic missense mutations in LTCCs to diseases of the human cardiovascular, nervous, and endocrine systems. These disease-associated genetic mutations occur at homologous functional positions (activation gates) in LTCCs. Thus, it is plausible that similar homologous missense mutations in pituitary LTCCs can cause abnormal hormone secretion and underlying pituitary disorders. The existence of LTCCs in pituitary cells opens questions about their sensitivity to dihydropyridines, a group of selective LTCC blockers. The dihydropyridine sensitivity of pituitary cells, as with any other excitable cell, depends primarily on two parameters: the pattern of their electrical activity and the dihydropyridine sensitivity of their LTCC isoforms. These two parameters are discussed in detail in relation to somatotrophs. These discussions are also relevant to lactotrophs and corticotrophs. High dihydropyridine sensitivity may facilitate their use as drugs to treat pituitary oversecretion disorders such as acromegaly, hyperprolactinemia, and Cushing disease.

MiR-7 Mediates the Zearalenone Signaling Pathway Regulating FSH Synthesis and Secretion by Targeting FOS in Female Pigs

Zearalenone (ZEA) acts as an environmental endocrine disruptor (EED) to cause health detriments. miRNAs were reported to influence the synthesis and secretion of pituitary hormones. However, the interactions between ZEA and miRNAs and related mechanisms remain unclear. The aims of this study were to determine whether and how miR-7 affects animal reproduction by its interactions with ZEA in the pig pituitary, which is sensitive to ZEA and has been used as an important animal model in medical research. Expressions of miRNA were detected by real-time PCR, in situ hybridization, and immunohistochemistry. The effects of ZEA, miR-7, and their interactions in the pituitary gland were identified by using an ovariectomized pig model, transfecting miR-7 mimics and inhibitor, radioimmunoassay, luciferase reporter assay, and Western blotting. The ZEA dosage was 7.5 mg/kg body weight in vivo and 1 μM in vitro. Our results demonstrate miR-7 acts to regulate gonadotropin synthesis and secretion. Furthermore, we found that ZEA leads to reproductive defects by enhancing miR-7 expression, which subsequently inhibits FSH synthesis and secretion. In vitro and in vivo experiments revealed that the effects of ZEA rely on G protein-coupled estrogen receptor 1, and miR-7 functions by mediating ZEA signaling pathway and targeting the Finkel-Biskis-Jinkins murine osteosarcoma viral oncogene homolog (FOS) gene. These findings show that miRNAs are key intrinsic factors regulating pituitary gonadotropins by mediating EED signaling in pituitary glands, and the actions of miRNAs and EEDs should be seriously considered in related studies about medical practice and animal production.

Conditional Deletion of FOXL2 and SMAD4 in Gonadotropes of Adult Mice Causes Isolated FSH Deficiency

The glycoprotein FSH, a product of pituitary gonadotrope cells, regulates ovarian follicle development in females and spermatogenesis in males. FSH is a heterodimer of the common α gonadotropin subunit and the hormone-specific FSHβ subunit (a product of the Fshb gene). Using a conditional knockout approach (Cre-lox), we previously demonstrated that Fshb expression in mice depends on the transcription factors forkhead box L2 (FOXL2) and SMAD4. Deletion of Foxl2 or Smad4 alone led to FSH deficiency, female subfertility, and oligozoospermia in males. Simultaneous deletion of the two genes yielded a greater suppression of FSH and female sterility. The Cre-driver used previously was first active during embryonic development. Therefore, it is unclear whether FOXL2 and SMAD4 play important roles in the development or adult function of gonadotropes, or both. To address this question, we developed a tamoxifen-inducible Cre-driver line, which enabled Foxl2 and Smad4 gene deletions in gonadotropes of adult mice. After tamoxifen treatment, females with previously demonstrated fertility exhibited profound reductions in FSH levels, arrested ovarian follicle development, and sterility. FSH levels were comparably reduced in males 1 or 2 months after treatment; however, spermatogenesis was unaffected. These data indicate that (1) FOXL2 and SMAD4 are necessary to maintain FSH synthesis in gonadotrope cells of adult mice, (2) FSH is essential for female reproduction but appears to be unnecessary for the maintenance of spermatogenesis in adult male mice, and (3) the inducible Cre-driver line developed here provides a powerful tool to interrogate gene function in gonadotrope cells of adult mice.

Mouse models for the analysis of gonadotropin secretion and action

Gonadotropins are pituitary gonadotrope-derived glycoprotein hormones. They act by binding to G-protein coupled receptors on gonads. Gonadotropins play critical roles in reproduction by regulating both gametogenesis and steroidogenesis. Although biochemical and physiological studies provided a wealth of knowledge, gene manipulation techniques using novel mouse models gave new insights into gonadotropin synthesis, secretion and action. Both gain of function and loss of function mouse models for understanding gonadotropin action in a whole animal context have already been generated. Moreover, recent studies on gonadotropin actions in non-gonadal tissues challenged the central dogma of classical gonadotropin actions in gonads and revealed new signaling pathways in these non-gonadal tissues. In this Chapter, we have discussed our current understanding of gonadotropin synthesis, secretion and action using a variety of genetically engineered mouse models.

Regulation of FSH expression by differentially expressed miR-186-5p in rat anterior adenohypophyseal cells

Follicle-stimulating hormone (FSH) has key roles in animal reproduction, including spermatogenesis and ovarian maturation. Many factors influence FSH secretion. However, despite the broad functions of microRNAs (miRNAs) via the regulation of target genes, little is known about their roles in FSH secretion. Our previous results suggested that miR-186-5p targets the 3′ UTR of FSHb; therefore, we examined whether miR-186-5p could regulate FSH secretion in rat anterior adenohypophyseal cells. miR-186-5p was transfected into rat anterior pituitary cells. The expression of FSHb and the secretion of FSH were examined by RT-qPCR and ELISA. A miR-186-5p mimic decreased the expression of FSHb compared with expression in the control group and decreased FSH secretion. In contrast, both the mRNA levels and secretion of FSH increased in response to miR-186-5p inhibitors. Our results demonstrate that miR-186-5p regulates FSH secretion by directly targeting the FSHb 3′ UTR, providing additional functional evidence for the importance of miRNAs in the regulation of animal reproduction.

Gonadotropin regulation by pulsatile GnRH: Signaling and gene expression

The precise orchestration of hormonal regulation at all levels of the hypothalamic-pituitary-gonadal axis is essential for normal reproductive function and fertility. The pulsatile secretion of hypothalamic gonadotropin-releasing hormone (GnRH) stimulates the synthesis and release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) by pituitary gonadotropes. GnRH acts by binding to its high affinity seven-transmembrane receptor (GnRHR) on the cell surface of anterior pituitary gonadotropes. Different signaling cascades and transcriptional mechanisms are activated, depending on the variation in GnRH pulse frequency, to stimulate the synthesis and release of FSH and LH. While changes in GnRH pulse frequency may explain some of the differential regulation of FSH and LH, other factors, such as activin, inhibin and sex steroids, also contribute to gonadotropin production. In this review, we focus on the transcriptional regulation of the gonadotropin subunit genes and the signaling pathways activated by pulsatile GnRH.

Zearalenone and alpha-zearalenol inhibit the synthesis and secretion of pig follicle stimulating hormone via the non-classical estrogen membrane receptor GPR30

Zearalenone (ZEA) is one of the most popular endocrine-disrupting chemicals and is mainly produced by fungi of the genus Fusarium. The excessive intake of ZEA severely disrupts human and animal fertility by affecting the reproductive axis. However, most studies on the effects of ZEA and its metabolite α-zearalenol (α-ZOL) on reproductive systems have focused on gonads. Few studies have investigated the endocrine-disrupting effects of ZEA and α-ZOL on pituitary gonadotropins, including follicle-stimulating hormone (FSH) and luteinizing hormone (LH). The present study was designed to investigate the effects of ZEA and α-ZOL on the synthesis and secretion of FSH and LH and related mechanisms in female pig pituitary. Our in vivo and in vitro results demonstrated that ZEA significantly inhibited the synthesis and secretion of FSH in the pig pituitary gland, but ZEA and α-ZOL had no effects on LH. Our study also showed that ZEA and α-ZOL decreased FSH synthesis and secretion through non-classical estrogen membrane receptor GPR30, which subsequently induced protein kinase cascades and the phosphorylation of PKC, ERK and p38MAPK signaling pathways in pig pituitary cells. Furthermore, our study showed that the LIM homeodomain transcription factor LHX3 was involved in the mechanisms of ZEA and α-ZOL actions on gonadotropes in the female pig pituitary. These findings elucidate the mechanisms behind the physiological alterations resulting from endocrine-disrupting chemicals and further show that the proposed key molecules of the α-ZOL signaling pathway could be potential pharmacological targets.

Extra-pituitary expressed follicle-stimulating hormone: Is it physiologically important?

Pituitary gonadotropes synthesize and secrete follicle-stimulating hormone (FSH). FSH is a heterodimer that consists of an α- and β-subunit. The α-subunit is common to other pituitary and placental glycoprotein hormones, and the β-subunit is the hormone/receptor-specific subunit. Although the pituitary is the main tissue that accounts for circulating hormone, previous and recent reports indicate extra-pituitary sources of FSH production including mouse gonads, human stomach, prostate, umbilical cord vein endothelial cells, uterine myometrium, placenta, and chicken abdominal adipose tissue. Whether extra-pituitary derived FSH exerts any physiologically significant actions is not known. In this review, we have comprehensively analyzed the expression of mRNAs that encode mouse and human FSH subunits and also their corresponding expressed sequence tags in normal tissues, cancer cell lines, and primary tumors by public database mining. We propose criteria to assess the significance of individual FSH subunit or FSH dimer expression as well as genetic approaches to unambiguously define the physiological relevance of extra-pituitary FSH expression.

The increased expression of follicle-stimulating hormone leads to a decrease of fecundity in transgenic Large White female pigs

Follicle-stimulating hormone (FSH) is a pituitary gonadotropin regulating reproduction in mammals. Overexpression of the exogenous FSHα/β genes from Chinese Erhualian pigs improved female fecundity of transgenic (TG) mice and male spermatogenesis ability of Large White TG boars. Here, we investigated the impact of the exogenous FSHα/β genes on female reproductive performance of Large White TG pigs. First, we identified the integration site of the exogenous FSHα/β genes at 140,646,456 bp on chromosome 9 in these TG pigs using whole-genome sequencing. Then, we showed that TG gilts had higher levels of serum FSH and FSHβ protein in pituitary while had a potentially lower number of born piglets than their wild-type half sibs. TG gilts grew healthily and normally without significant difference in growth and health parameters as compared to WT gilts. The expression levels of FSHR, LHR, ESR1 and ESR2 were significantly lower in TG gilts than in WT gilts at the age of 300 days. Taken together, we proposed that the overexpressed FSHα/β transgenes could cause deteriorate fecundity via disturbing the normal expression of the endogenous reproduction-related genes in female pigs. Our findings provide insight into the effect of overexpression of FSHα/β on female reproduction performance in pigs.

Transcriptional regulation of follicle-stimulating hormone β-subunit in marmoset by an alternate distal promoter

Follicle-stimulating hormone (FSH) is essential for mammalian folliculogenesis and spermatogenesis. Common marmoset (Callithrix jacchus) is a New World primate which exhibits an unusual FSH profile across the ovarian cycle with a mid-follicular FSH peak that is not observed in Catarrhini primates like humans. Since transcription of FSH β-subunit gene (FSHβ) is a rate-limiting step in the production of mature FSH, this study aimed to investigate the regulation of marmoset FSHβ gene expression in comparison to human. In silico analysis of the FSHβ promoter sequences identified a TATA box element upstream of the conventional TATA box element in marmoset but not in human sequence. FSHβ mRNA transcript longer than the conventional transcript was detected in marmoset pituitary implying presence of a distal transcription start site. In luciferase reporter assays, the marmoset putative distal promoter had higher activity than the corresponding human region even in absence of the conventional proximal promoter. Indeed higher affinity binding of TATA box-binding protein to the putative distal TATA box element was obtained in electrophoretic mobility shift assay. This suggests existence of a differential regulation of FSHβ transcription in marmoset compared to humans.

Modeling and high-throughput experimental data uncover the mechanisms underlying Fshb gene sensitivity to gonadotropin-releasing hormone pulse frequency

Neuroendocrine control of reproduction by brain-secreted pulses of gonadotropin-releasing hormone (GnRH) represents a longstanding puzzle about extracellular signal decoding mechanisms. GnRH regulates the pituitary gonadotropin's follicle-stimulating hormone (FSH) and luteinizing hormone (LH), both of which are heterodimers specified by unique β subunits (FSHβ/LHβ). Contrary to Lhb, Fshb gene induction has a preference for low-frequency GnRH pulses. To clarify the underlying regulatory mechanisms, we developed three biologically anchored mathematical models: 1) parallel activation of Fshb inhibitory factors (e.g. inhibin α and VGF nerve growth factor-inducible), 2) activation of a signaling component with a refractory period (e.g. G protein), and 3) inactivation of a factor needed for Fshb induction (e.g. growth differentiation factor 9). Simulations with all three models recapitulated the Fshb expression levels obtained in pituitary gonadotrope cells perifused with varying GnRH pulse frequencies. Notably, simulations altering average concentration, pulse duration, and pulse frequency revealed that the apparent frequency-dependent pattern of Fshb expression in model 1 actually resulted from variations in average GnRH concentration. In contrast, models 2 and 3 showed "true" pulse frequency sensing. To resolve which components of this GnRH signal induce Fshb, we developed a high-throughput parallel experimental system. We analyzed over 4,000 samples in experiments with varying near-physiological GnRH concentrations and pulse patterns. Whereas Egr1 and Fos genes responded only to variations in average GnRH concentration, Fshb levels were sensitive to both average concentration and true pulse frequency. These results provide a foundation for understanding the role of multiple regulatory factors in modulating Fshb gene activity.

A model of ovulatory regulation examining the effects of insulin-mediated testosterone production on ovulatory function

Polycystic ovary syndrome (PCOS), a common cause of infertility in women, is often accompanied by abnormal reproductive and metabolic hormone levels. Specifically, androgens such as testosterone are elevated in many PCOS women, and the syndrome itself is frequently associated with insulin resistance, which leads to hyperinsulinemia, i.e., elevated insulin. Although the precise role of insulin in ovulatory function is unclear, its role in ovulatory dysfunction is often linked to the effects of increased ovarian androgen production. We present a mathematical model of the menstrual cycle that incorporates regulation by the pituitary-ovarian axis and mechanisms of ovarian testosterone production. We determine a physiological role for testosterone in the normal ovulatory cycle and study the role of hyperinsulinemia in pathological regulation of the cycle. Model results indicate increased ovulatory disruption with elevated insulin-mediated testosterone production and suggest that variations in the response of ovarian follicles to essential signals can alter the degree to which hyperinsulinemia disrupts the ovulatory cycle. The model also provides insight into the various PCOS phenotypes and the severity of ovulatory dysfunction.

miR-361-3p regulates FSH by targeting FSHB in a porcine anterior pituitary cell model

FSH plays an essential role in processes involved in human reproduction, including spermatogenesis and the ovarian cycle. While the transcriptional regulatory mechanisms underlying its synthesis and secretion have been extensively studied, little is known about its posttranscriptional regulation. A bioinformatics analysis from our group indicated that a microRNA (miRNA; miR-361-3p) could regulate FSH secretion by potentially targeting the FSHB subunit. Herein, we sought to confirm these findings by investigating the miR-361-3p-mediated regulation of FSH production in primary pig anterior pituitary cells. Gonadotropin-releasing hormone (GnRH) treatment resulted in an increase in FSHB synthesis at both the mRNA, protein/hormone level, along with a significant decrease in miR-361-3p and its precursor (pre-miR-361) levels in time- and dose-dependent manner. Using the Dual-Luciferase Assay, we confirmed that miR-361-3p directly targets FSHB. Additionally, overexpression of miR-361-3p using mimics significantly decreased the FSHB production at both the mRNA and protein levels, with a reduction in both protein synthesis and secretion. Conversely, both synthesis and secretion were significantly increased following miR-361-3p blockade. To confirm that miR-361-3p targets FSHB, we designed FSH-targeted siRNAs, and co-transfected anterior pituitary cells with both the siRNA and miR-361-3p inhibitors. Our results indicated that the siRNA blocked the miR-361-3p inhibitor-mediated upregulation of FSH, while no significant effect on non-target expression. Taken together, our results demonstrate that miR-361-3p negatively regulates FSH synthesis and secretion by targeting FSHB, which provides more functional evidence that a miRNA is involved in the direct regulation of FSH.

SMAD3 Regulates Follicle-stimulating Hormone Synthesis by Pituitary Gonadotrope Cells in Vivo

Pituitary follicle-stimulating hormone (FSH) is an essential regulator of fertility in females and of quantitatively normal spermatogenesis in males. Pituitary-derived activins are thought to act as major stimulators of FSH synthesis by gonadotrope cells. In vitro, activins signal via SMAD3, SMAD4, and forkhead box L2 (FOXL2) to regulate transcription of the FSHβ subunit gene (Fshb). Consistent with this model, gonadotrope-specific Smad4 or Foxl2 knock-out mice have greatly reduced FSH and are subfertile. The role of SMAD3 in vivo is unresolved; however, residual FSH production in Smad4 conditional knock-out mice may derive from partial compensation by SMAD3 and its ability to bind DNA in the absence of SMAD4. To test this hypothesis and determine the role of SMAD3 in FSH biosynthesis, we generated mice lacking both the SMAD3 DNA binding domain and SMAD4 specifically in gonadotropes. Conditional knock-out females were hypogonadal, acyclic, and sterile and had thread-like uteri; their ovaries lacked antral follicles and corpora lutea. Knock-out males were fertile but had reduced testis weights and epididymal sperm counts. These phenotypes were consistent with those of Fshb knock-out mice. Indeed, pituitary Fshb mRNA levels were nearly undetectable in both male and female knock-outs. In contrast, gonadotropin-releasing hormone receptor mRNA levels were significantly elevated in knock-outs in both sexes. Interestingly, luteinizing hormone production was altered in a sex-specific fashion. Overall, our analyses demonstrate that SMAD3 is required for FSH synthesis in vivo.

Polygenic sex determination in the cichlid fish Astatotilapia burtoni

BACKGROUND

The East African riverine cichlid species Astatotilapia burtoni serves as an important laboratory model for sexually dimorphic physiology and behavior, and also serves as an outgroup species for the explosive adaptive radiations of cichlid species in Lake Malawi and Lake Victoria. An astounding diversity of genetic sex determination systems have been revealed within the adaptive radiation of East African cichlids thus far, including polygenic sex determination systems involving the epistatic interaction of multiple, independently segregating sex determination alleles. However, sex determination has remained unmapped in A. burtoni. Here we present mapping results supporting the presence of multiple, novel sex determination alleles, and thus the presence of polygenic sex determination in A. burtoni.

RESULTS

Using mapping in small families in conjunction with restriction-site associated DNA sequencing strategies, we identify associations with sex at loci on linkage group 13 and linkage group 5-14. Inheritance patterns support an XY sex determination system on linkage group 5-14 (a chromosome fusion relative to other cichlids studied), and an XYW system on linkage group 13, and these associations are replicated in multiple families. Additionally, combining our genetic data with comparative genomic analysis identifies another fusion that is unassociated with sex, with linkage group 8-24 and linkage group 16-21 fused in A. burtoni relative to other East African cichlid species.

CONCLUSIONS

We identify genetic signals supporting the presence of three previously unidentified sex determination alleles at two loci in the species A. burtoni, strongly supporting the presence of polygenic sex determination system in the species. These results provide a foundation for future mapping of multiple sex determination genes and their interactions. A better understanding of sex determination in A. burtoni provides important context for their use in behavioral studies, as well as studies of the evolution of genetic sex determination and sexual conflicts in East African cichlids.

Mouse Models for the Study of Synthesis, Secretion, and Action of Pituitary Gonadotropins

Gonadotropins play fundamental roles in reproduction. More than 30years ago, Cga transgenic mice were generated, and more than 20years ago, the phenotypes of Cga null mice were reported. Since then, numerous mouse strains have been generated and characterized to address several questions in reproductive biology involving gonadotropin synthesis, secretion, and action. More recently, extragonadal expression, and in some cases, functions of gonadotropins in nongonadal tissues have been identified. Several genomic and proteomic approaches including novel mouse genome editing tools are available now. It is anticipated that these and other emerging technologies will be useful to build an integrated network of gonadotropin signaling pathways in various tissues. Undoubtedly, research on gonadotropins will continue to provide new knowledge and allow us transcend from benchside to the bedside.

Sphingosine-1-phosphate, regulated by FSH and VEGF, stimulates granulosa cell proliferation

Sphingosine-1-phosphate (S1P) is a bioactive polar sphingolipid which stimulates proliferation, growth and survival in various cell types. In the ovary S1P has been shown protect the granulosa cells and oocytes from insults such as oxidative stress and radiotherapy, and S1P concentrations are greater in healthy than atretic large follicles. Hence, we postulate that S1P is fundamental in follicle development and that it is activated in ovarian granulosa cells in response to FSH and VEGF. To test this hypothesis we set out: i) to evaluate the effect of FSH and VEGF on S1P synthesis in cultured bovine granulosa cells and ii) to analyse the effect of S1P on proliferation and survival of bovine granulosa cells in vitro. Seventy five thousand bovine granulosa cells from healthy medium-sized (4-7mm) follicles were cultured in 96-well plates in McCoy's 5a medium containing 10ng/mL of insulin and 1ng/mL of LR-IGF-I at 37°C in a 5% CO2/air atmosphere at 37°C. Granulosa cell production of S1P was tested in response to treatment with FSH (0, 0.1, 1 and 10ng/mL) and VEGF (0, 0.01, 0.1, 1, 10 and 100ng/mL) and measured by HPLC. Granulosa cells produced S1P at 48 and 96h, with the maximum production observed with 1ng/mL of FSH. Likewise, 0.01ng/mL of VEGF stimulated S1P production at 48, but not 96h of culture. Further, the granulosa cell expression of sphingosine kinase-1 (SK1), responsible for S1P synthesis, was demonstrated by Western blot after 48h of culture. FSH increased the expression of phosphorylated SK1 (P<0.05) and the addition of a SK1 inhibitor reduced the constitutive and FSH-stimulated S1P synthesis (P<0.05). Sphingosine-1-phosphate had a biphasic effect on granulosa cell number after culture. At low concentration S1P (0.1μM) increased granulosa cell number after 48h of culture (P<0.05) and the proportion of cells in the G2 and M phase of the cell cycle (P<0.05), whereas higher concentrations decreased cell number (10μM; P<0.05) by an increase (P<0.05) in the proportion of cells in apoptosis (hypodiploid cells). In addition, treatment with SK-178 suppressed the FSH- and VEGF-stimulated rise of the granulosa cells number (P<0.05). Interestingly, the effect of 0.1μM S1P on granulosa cell number and their proportion in G2/M phases is similar to that observed with 1ng/mL FSH. The results of this study are the first to demonstrate sphingosine-1-phosphate (S1P) synthesis in granulosa cells under the control of FSH and VEGF. The later achieved through the regulation of sphingosine kinase 1 expression. This S1P augments the proportion of cells in the G2/M phase of the cell cycle that translates in increased granulosa cell proliferation.

Clinical Applications of Gonadotropins in the Male

The pituitary gonadotropins, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) play a pivotal role in reproduction. The synthesis and secretion of gonadotropins are regulated by complex interactions among several endocrine, paracrine, and autocrine factors of diverse chemical structure. In men, LH regulates the synthesis of androgens by the Leydig cells, whereas FSH promotes Sertoli cell function and thereby influences spermatogenesis. Gonadotropins are complex molecules composed of two subunits, the α- and β-subunit, that are noncovalently associated. Gonadotropins are decorated with glycans that regulate several functions of the protein including folding, heterodimerization, stability, transport, conformational maturation, efficiency of heterodimer secretion, metabolic fate, interaction with their cognate receptor, and selective activation of signaling pathways. A number of congenital and acquired abnormalities lead to gonadotropin deficiency and hypogonadotropic hypogonadism, a condition amenable to treatment with exogenous gonadotropins. Several natural and recombinant preparations of gonadotropins are currently available for therapeutic purposes. The difference between natural and the currently available recombinant preparations (which are massively produced in Chinese hamster ovary cells for commercial purposes) mainly lies in the abundance of some of the carbohydrates that conform the complex glycans attached to the protein core. Whereas administration of exogenous gonadotropins in patients with isolated congenital hypogonadotropic hypogonadism is a well recognized therapeutic approach, their role in treating men with normogonadotropic idiopathic infertility is still controversial. This chapter concentrates on the main structural and functional features of the gonadotropin hormones and how basic concepts have been translated into the clinical arena to guide therapy for gonadotropin deficit in males.

Characterization of Gonadotrope Secretoproteome Identifies Neurosecretory Protein VGF-derived Peptide Suppression of Follicle-stimulating Hormone Gene Expression

Reproductive function is controlled by the pulsatile release of hypothalamic gonadotropin-releasing hormone (GnRH), which regulates the expression of the gonadotropins luteinizing hormone and FSH in pituitary gonadotropes. Paradoxically, Fshb gene expression is maximally induced at lower frequency GnRH pulses, which provide a very low average concentration of GnRH stimulation. We studied the role of secreted factors in modulating gonadotropin gene expression. Inhibition of secretion specifically disrupted gonadotropin subunit gene regulation but left early gene induction intact. We characterized the gonadotrope secretoproteome and global mRNA expression at baseline and after Gα_s knockdown, which has been found to increase Fshb gene expression (1). We identified 1077 secreted proteins or peptides, 19 of which showed mRNA regulation by GnRH or/and Gα_s knockdown. Among several novel secreted factors implicated in Fshb gene regulation, we focused on the neurosecretory protein VGF. Vgf mRNA, whose gene has been implicated in fertility (2), exhibited high induction by GnRH and depended on Gα_s In contrast with Fshb induction, Vgf induction occurred preferentially at high GnRH pulse frequency. We hypothesized that a VGF-derived peptide might regulate Fshb gene induction. siRNA knockdown or extracellular immunoneutralization of VGF augmented Fshb mRNA induction by GnRH. GnRH stimulated the secretion of the VGF-derived peptide NERP1. NERP1 caused a concentration-dependent decrease in Fshb gene induction. These findings implicate a VGF-derived peptide in selective regulation of the Fshb gene. Our results support the concept that signaling specificity from the cell membrane GnRH receptor to the nuclear Fshb gene involves integration of intracellular signaling and exosignaling regulatory motifs.

Normal gonadotropin production and fertility in gonadotrope-specific Bmpr1a knockout mice

Pituitary follicle-stimulating hormone (FSH) synthesis is regulated by transforming growth factorβsuperfamily ligands, most notably the activins and inhibins. Bone morphogenetic proteins (BMPs) also regulate FSHβ subunit (Fshb) expression in immortalized murine gonadotrope-like LβT2 cells and in primary murine or ovine primary pituitary cultures. BMP2 signals preferentially via the BMP type I receptor, BMPR1A, to stimulate murine Fshb transcription in vitro Here, we used a Cre-lox approach to assess BMPR1A's role in FSH synthesis in mice in vivo Gonadotrope-specific Bmpr1a knockout animals developed normally and had reproductive organ weights comparable with those of controls. Knockouts were fertile, with normal serum gonadotropins and pituitary gonadotropin subunit mRNA expression. Cre-mediated recombination of the floxed Bmpr1a allele was efficient and specific, as indicated by PCR analysis of diverse tissues and isolated gonadotrope cells. Furthermore, BMP2 stimulation of inhibitor of DNA binding 3 expression was impaired in gonadotropes isolated from Bmpr1a knockout mice, confirming the loss of functional receptor protein in these cells. Treatment of purified gonadotropes with small-molecule inhibitors of BMPR1A (and the related receptors BMPR1B and ACVR1) suppressed Fshb mRNA expression, suggesting that an autocrine BMP-like molecule might regulate FSH synthesis. However, deletion of Bmpr1a and Acvr1 in cultured pituitary cells did not alter Fshb expression, indicating that the inhibitors had off-target effects. In sum, BMPs or related ligands acting via BMPR1A or ACVR1 are unlikely to play direct physiological roles in FSH synthesis by murine gonadotrope cells.