Human FSH beta subunit gene is highly conserved

Genetic polymorphisms in ESR and FSHβ genes and their association with litter traits in Large White pigs

The estrogen receptor (ESR) gene and follicle-stimulating hormone β (FSHβ) gene are responsible for litter traits. The present study aimed to verify the polymorphisms of ESR and FSHβ and assess their effects on the litter traits in 201 Large White pigs. Four SNPs (g.C669T, g.A1296G, g.C1665T and g.A1755G) were found in ESR. The TT genotype at g.C1665T locus and AA genotype at g.A1755G locus could significantly increase the total litter size of the first litter of American Large White pigs (p < 0.05). Eight SNPs were found in exon 3 of FSHβ. The AA genotype at g.A511G locus, AA and AG genotypes at g.A617G locus, CC and CT genotypes at g.C630T locus, CT and TT genotypes at g.C652T locus, CT and TT genotypes at g.C735T locus, AA and AG genotypes at g.A746G, AA and AG genotypes at g.A921G and CT genotype at g.C678T could significantly increase the litter size of different strains of Large White pigs (p < 0.05). Our study revealed that the genetic variations of ESR and FSHβ were closely related to the litter trait of Large White pigs. Therefore, ESR and FSHβ genes could be used as molecular markers for the genetic selection of Large White pigs.

Identification of common genetic polymorphisms associated with down-regulated gonadotropin levels in an exome-wide association study

OBJECTIVE

To investigate whether common genetic polymorphisms are associated with gonadotropin levels after down-regulation with daily gonadotropin-releasing hormone agonist and whether the polymorphisms of candidate variants influence the ovarian response to exogenous gonadotropins.

DESIGN

Genetic association study.

SETTING

University-affiliated in vitro fertilization center.

PATIENTS

Subjects enrolled in an exploratory exome-wide association study (n = 862), a replication exome-wide association study (n = 86), and a classifier validation study (n = 148) were recruited from September 2016 to October 2018, September 2019 to September 2020, and January 2021 to December 2021, respectively. The included patients were aged ≤40 years and had a basal follicle-stimulating hormone (FSH) ≤12 IU/L.

INTERVENTIONS

All participants received a luteal phase down-regulation long protocol. Genome DNA was extracted from the peripheral blood leukocytes. For the exploratory and replication cohorts, exome sequencing was conducted on a HiSeq 2500 sequencing platform. The multiplex polymerase chain reaction amplification technique and next-generation sequencing also were performed in the exploratory and replication cohorts. For the samples of the validation cohort, Sanger sequencing was performed.

MAIN OUTCOME MEASURES

The primary endpoint was the gonadotropin levels after down-regulation, and the secondary endpoints were hormone levels and follicle diameters during stimulation, the total dose of FSH, duration of FSH stimulation, number of oocytes retrieved, and clinical pregnancy rate.

RESULTS

In the exploratory cohort, we identified that FSHB rs6169 (P=2.71 × 10-24) and its single-nucleotide polymorphisms in high linkage disequilibrium were associated with the down-regulated FSH level. The same locus was confirmed in the replication cohort. Women carrying the C allele of FSHB rs6169 exhibited higher average estradiol level during stimulation (P=6.82 × 10-5), shorter duration of stimulation, and less amount of exogenous FSH (Pduration=0.0002; Pdose=0.0024). In the independent validation set, adding rs6169 genotypes into the prediction model for FSH level after down-regulation enhanced the area under the curve from 0.560 to 0.712 in a logistic regression model, and increased prediction accuracy by 41.05% when a support vector machine classifier was applied.

CONCLUSION

The C allele of FSHB rs6169 is a susceptibility site for the relatively high level of FSH after down-regulation, which may be associated with increased ovarian FSH sensitivity.

Pituitary tissue-specific miR-7a-5p regulates FSH expression in rat anterior adenohypophyseal cells

The follicle-stimulating hormone (FSH), which is synthesized and secreted by the anterior pituitary gland, plays an important role in regulating reproductive processes. In this study, using the TargetScan program, we predicted that microRNAs (miRNAs) regulate FSH secretion. Dual-luciferase reporter assays were performed and identified miR-7a-5p. MiR-7a-5p has been reported to regulate diverse cellular functions. However, it is unclear whether miR-7a-5p binds to mRNAs and regulates reproductive functions. Therefore, we constructed a suspension of rat anterior pituitary cells and cultured them under adaptive conditions, transfected miR-7a-5p mimics or inhibitor into the cell suspension and detected expression of the FSHb gene. The results demonstrated that miR-7a-5p downregulated FSHb expression levels, while treatment with miR-7a-5p inhibitors upregulated FSHb expression levels relative to those of negative control groups, as shown by quantitative PCR analysis. The results were confirmed with a subsequent experiment showing that FSH secretion was reduced after treatment with mimics and increased in the inhibitor groups, as shown by enzyme-linked immunosorbent assay. Our results indicated that miR-7a-5p downregulates FSHb expression levels, resulting in decreased FSH synthesis and secretion, which demonstrates the important role of miRNAs in the regulation of FSH and animal reproduction.

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.

Glycosylation Pattern and in vitro Bioactivity of Reference Follitropin alfa and Biosimilars

Recombinant follicle-stimulating hormone (FSH) (follitropin alfa) and biosimilar preparations are available for clinical use. They have specific FSH activity and a unique glycosylation profile dependent on source cells. The aim of the study is to compare the originator (reference) follitropin alfa (Gonal-f®)- with biosimilar preparations (Bemfola® and Ovaleap®)-induced cellular responses in vitro. Gonadotropin N-glycosylation profiles were analyzed by ELISA lectin assay, revealing preparation specific-patterns of glycan species (Kruskal-Wallis test; p < 0.05, n = 6) and by glycotope mapping. Increasing concentrations of Gonal-f® or biosimilar (1 × 10^-3-1 × 10³ ng/ml) were used for treating human primary granulosa lutein cells (hGLC) and FSH receptor (FSHR)-transfected HEK293 cells in vitro. Intracellular cAMP production, Ca²⁺ increase and β-arrestin 2 recruitment were evaluated by BRET, CREB, and ERK1/2 phosphorylation by Western blotting. 12-h gene expression, and 8- and 24-h progesterone and estradiol synthesis were measured by real-time PCR and immunoassay, respectively. We found preparation-specific glycosylation patterns by lectin assay (Kruskal-Wallis test; p < 0.001; n = 6), and similar cAMP production and β-arrestin 2 recruitment in FSHR-transfected HEK293 cells (cAMP EC₅₀ range = 12 ± 0.9-24 ± 1.7 ng/ml; β-arrestin 2 EC₅₀ range = 140 ± 14.1-313 ± 18.7 ng/ml; Kruskal-Wallis test; p ≥ 0.05; n = 4). Kinetics analysis revealed that intracellular Ca²⁺ increased upon cell treatment by 4 μg/ml Gonal-f®, while equal concentrations of biosimilars failed to induced a response (Kruskal-Wallis test; p < 0.05; n = 3). All preparations induced both 8 and 24 h-progesterone and estradiol synthesis in hGLC, while no different EC₅₀s were demonstrated (Kruskal-Wallis test; p > 0.05; n = 5). Apart from preparation-specific intracellular Ca²⁺ increases achieved at supra-physiological hormone doses, all compounds induced similar intracellular responses and steroidogenesis, reflecting similar bioactivity, and overall structural homogeneity.

Regulation of reproduction via tight control of gonadotropin hormone levels

Mammalian reproduction is controlled by the hypothalamic-pituitary-gonadal axis. GnRH from the hypothalamus regulates synthesis and secretion of gonadotropins, LH and FSH, which then control steroidogenesis and gametogenesis. In females, serum LH and FSH levels exhibit rhythmic changes throughout the menstrual or estrous cycle that are correlated with pulse frequency of GnRH. Lack of gonadotropins leads to infertility or amenorrhea. Dysfunctions in the tightly controlled ratio due to levels slightly outside the normal range occur in a larger number of women and are correlated with polycystic ovaries and premature ovarian failure. Since the etiology of these disorders is largely unknown, studies in cell and mouse models may provide novel candidates for investigations in human population. Hence, understanding the mechanisms whereby GnRH regulates gonadotropin hormone levels will provide insight into the physiology and pathophysiology of the reproductive system. This review discusses recent advances in our understanding of GnRH regulation of gonadotropin synthesis.

c-JUN Dimerization Protein 2 (JDP2) Is a Transcriptional Repressor of Follicle-stimulating Hormone β (FSHβ) and Is Required for Preventing Premature Reproductive Senescence in Female Mice

Follicle-stimulating hormone (FSH) regulates follicular growth and stimulates estrogen synthesis in the ovaries. FSH is a heterodimer consisting of an α subunit, also present in luteinizing hormone, and a unique β subunit, which is transcriptionally regulated by gonadotropin-releasing hormone 1 (GNRH). Because most FSH is constitutively secreted, tight transcriptional regulation is critical for maintaining FSH levels within a narrow physiological range. Previously, we reported that GNRH induces FSHβ (Fshb) transcription via induction of the AP-1 transcription factor, a heterodimer of c-FOS and c-JUN. Herein, we identify c-JUN-dimerization protein 2 (JDP2) as a novel repressor of GNRH-mediated Fshb induction. JDP2 exhibited high basal expression and bound the Fshb promoter at an AP-1-binding site in a complex with c-JUN. GNRH treatment induced c-FOS to replace JDP2 as a c-JUN binding partner, forming transcriptionally active AP-1. Subsequently, rapid c-FOS degradation enabled reformation of the JDP2 complex. In vivo studies revealed that JDP2 null male mice have normal reproductive function, as expected from a negative regulator of the FSH hormone. Female JDP2 null mice, however, exhibited early puberty, observed as early vaginal opening, larger litters, and early reproductive senescence. JDP2 null females had increased levels of circulating FSH and higher expression of the Fshb subunit in the pituitary, resulting in elevated serum estrogen and higher numbers of large ovarian follicles. Disruption of JDP2 function therefore appears to cause early cessation of reproductive function, a condition that has been associated with elevated FSH in women.

FOXO1 is regulated by insulin and IGF1 in pituitary gonadotropes

The FOXO1 transcription factor is important for multiple aspects of reproductive function. We previously reported that FOXO1 functions as a repressor of gonadotropin hormone synthesis, but how FOXO1 is regulated in pituitary gonadotropes is unknown. The growth factors, insulin and insulin-like growth factor I (IGF1), function as key regulators of cell proliferation, metabolism and apoptosis in multiple cell types through the PI3K/AKT signaling pathway. In this study, we found that insulin and IGF1 signaling in gonadotropes induced FOXO1 phosphorylation through the PI3K/AKT pathway in immortalized and primary cells, resulting in FOXO1 relocation from the nucleus to the cytoplasm. Furthermore, insulin administration in vivo induced phosphorylation of FOXO1 and AKT in the pituitary. Thus, insulin and IGF1 act as negative regulators of FOXO1 activity and may serve to fine-tune gonadotropin expression.

Rapid communication: A microRNA-132/212 pathway mediates GnRH activation of FSH expression

GnRH plays a key role in the vertebrate reproductive system by stimulating biosynthesis and secretion of pituitary gonadotropins. However, the potential involvement of microRNAs (miRNAs) on this activation has still to be explored. In this study, we investigated the role of miRNA-132 and miRNA-212, two tandemly expressed miRNAs that target the same transcripts, on GnRH-induced FSH expression. We first showed that the GnRH stimulation of FSH secretion was reduced and Fshb mRNA abolished by blocking miR-132/212 action in rat pituitary cells. In mouse LβT2 gonadotrope cells, the GnRH stimulation of Fshb mRNA was also demonstrated to be dependent on miR-132/212 and reproduced by overexpressing one or both miRNAs. We then showed that the miR-132/212-mediated action of GnRH involved a posttranscriptional decrease of sirtuin 1 (SIRT1) deacetylase. The lower level of SIRT1 deacetylase correlated with an increase in the acetylated form of Forkhead Box O1 (FOXO1), a transcriptional repressor of Fshb. Interestingly, we show that the acetylated mimicking mutant of FOXO1 was localized outside the nucleus, thus alleviating its repressive effect on Fshb transcription. Overall, we demonstrate that the GnRH stimulation of Fshb expression is dependent on miR-132/212 and involves a SIRT1-FOXO1 pathway. This is the first demonstration of an obligatory microRNA pathway in the GnRH-regulated expression of a gonadotropin gene.

Hormonal therapy for non-obstructive azoospermia: basic and clinical perspectives

Microdissection testicular sperm extraction (micro-TESE) combined with intracytoplasmic sperm injection is a standard therapeutic option for patients with non-obstructive azoospermia (NOA). Hormonal treatment has been believed to be ineffective for NOA because of high gonadotropin levels; however, several studies have stimulated spermatogenesis before or after micro-TESE by using anti-estrogens, aromatase inhibitors, and gonadotropins. These results remain controversial; however, it is obvious that some of the patients showed a distinct improvement in sperm retrieval by micro-TESE, and sperm was observed in the ejaculates of a small number of NOA patients. One potential way to improve spermatogenesis is by optimizing the intratesticular testosterone (ITT) levels. ITT has been shown to be increased after hCG-based hormonal therapy. The androgen receptor that is located on Sertoli cells plays a major role in spermatogenesis, and other hormonal and non-hormonal factors may also be involved. Before establishing a new hormonal treatment protocol to stimulate spermatogenesis in NOA patients, further basic investigations regarding the pathophysiology of spermatogenic impairment are needed. Gaining a better understanding of this issue will allow us to tailor a specific treatment for each patient.

Forkhead box O1 is a repressor of basal and GnRH-induced Fshb transcription in gonadotropes

Synthesis of the gonadotropin β-subunits is tightly controlled by a complex network of hormonal signaling pathways that may be modulated by metabolic cues. Recently, we reported that insulin regulates FOXO1 phosphorylation and cellular localization in pituitary gonadotropes and that FOXO1 overexpression inhibits Lhb transcription. In the current study, we investigated whether FOXO1 modulates Fshb synthesis. Here, we demonstrate that FOXO1 represses basal and GnRH-induced Fshb transcription in LβT2 cells. In addition, we show that PI3K inhibition, which increases FOXO1 nuclear localization, results in decreased Fshb mRNA levels in murine primary pituitary cells. FOXO1 also decreases transcription from the human FSHB promoter, suggesting that FOXO1 regulation of FSHB transcription may be conserved between rodents and humans. Although the FOXO1 DNA-binding domain is necessary for suppression of Fshb, we do not observe direct binding of FOXO1 to the Fshb promoter, suggesting that FOXO1 exerts its effect through protein-protein interactions with transcription factors required for Fshb synthesis. FOXO1 suppression of basal Fshb transcription may involve PITX1 because PITX1 interacts with FOXO1, FOXO1 repression maps to the proximal Fshb promoter containing a PITX1-binding site, PITX1 induction of Fshb or a PITX1 binding element in CV-1 cells is decreased by FOXO1, and FOXO1 suppresses Pitx1 mRNA and protein levels. GnRH induction of an Fshb promoter containing a deletion at -50/-41 or -30/-21 is not repressed by FOXO1, suggesting that these two regions may be involved in FOXO1 suppression of GnRH-induced Fshb synthesis. In summary, our data demonstrate that FOXO1 can negatively regulate Fshb transcription and suggest that FOXO1 may relay metabolic hormonal signals to modulate gonadotropin production.

GnRH increases c-Fos half-life contributing to higher FSHβ induction

GnRH is a potent hypothalamic regulator of gonadotropin hormones, LH and FSH, which are both expressed within the pituitary gonadotrope and are necessary for the stimulation of gametogenesis and steroidogenesis in the gonads. Differential regulation of LH and FSH, which is essential for reproductive fitness, is achieved, in part, through the varying of GnRH pulse frequency. However, the mechanism controlling the increase in FSH during the periods of low GnRH has not been elucidated. Here, we uncover another level of regulation by GnRH that contributes to differential expression of the gonadotropins and may play an important role for the generation of the secondary rise of FSH that stimulates folliculogenesis. GnRH stimulates LHβ and FSHβ subunit transcription via induction of the immediate early genes, Egr1 and c-Fos, respectively. Here, we determined that GnRH induces rapidly both Egr1 and c-Fos, but specifically decreases the rate of c-Fos degradation. In particular, GnRH modulates the rate of c-Fos protein turnover by inducing c-Fos phosphorylation through the ERK1/2 pathway. This extends the half-life of c-Fos, which is normally rapidly degraded. Confirming the role of phosphorylation in promoting increased protein activity, we show that a c-Fos mutant that cannot be phosphorylated by GnRH induces lower expression of the FHSβ promoter than wild-type c-Fos. Our studies expand upon the role of GnRH in the regulation of gonadotropin gene expression by highlighting the role of c-Fos posttranslational modification that may cause higher levels of FSH during the time of low GnRH pulse frequency to stimulate follicular growth.

Predominant suppression of follicle-stimulating hormone β-immunoreactivity after long-term treatment of intact and castrate adult male rats with the gonadotrophin-releasing hormone agonist deslorelin

Gonadotrophin-releasing hormone (GnRH) agonists are used to treat gonadal steroid-dependent disorders in humans and to contracept animals. These agonists are considered to work by desensitising gonadotrophs to GnRH, thereby suppressing follicle-stimulating hormone (FSH) and luteinising hormone (LH) secretion. It is not known whether changes occur in the cellular composition of the pituitary gland after chronic GnRH agonist exposure. Adult male Sprague-Dawley rats were treated with a sham, deslorelin, or deslorelin plus testosterone implant for 41.0 ± 0.6 days. In a second experiment, rats were castrated and treated with deslorelin and/or testosterone. Pituitary sections were labelled immunocytochemically for FSHβ and LHβ, or gonadotrophin α subunit (αGSU). Deslorelin suppressed testis weight by two-thirds and reduced plasma FSH and LH in intact rats. Deslorelin decreased the percentage of gonadotrophs, although the effect was specific to the FSHβ-immunoreactive (-ir) cells. Testosterone did not reverse the deslorelin-induced reduction in the overall gonadotroph population. However, in the presence of testosterone, the proportion of gonadotrophs that was FSHβ-ir increased in the remaining gonadotrophs. There was no effect of treatment on the total LHβ-ir cell population, although the loss of FSHβ in bi-hormonal cells increased the proportion of mono-hormonal LHβ-ir gonadotrophs. The castration-induced plasma LH and FSH increases were suppressed by deslorelin, testosterone or both. Castration increased both LH-ir and FSH-ir without increasing the overall gonadotroph population, thus increasing the proportion of bi-hormonal cells. Deslorelin suppressed these increases. Testosterone increased FSH-ir in deslorelin-treated castrate rats. Deslorelin did not affect αGSU immunoreactivity, suggesting that the gonadotroph population per se is not eliminated by deslorelin, although the ability of gonadotrophs to synthesise FSHβ is compromised. We hypothesise that the FSH dominant suppression may be central to the long-term contraceptive efficacy of deslorelin in the male.

Effects of polymorphisms in gonadotropin and gonadotropin receptor genes on reproductive function

Gonadotropins, the action of which is mediated at the level of their gonadal receptors, play a key role in sexual development, reproductive functions and in metabolism. The involvement of the gonadotropins and their receptor genotypes on reproductive function are widely studied. A large number of gonadotropins and their receptors gene polymorphisms are known, but the only one considerable as a clear, absolute genetic marker of reproductive features or disfunctions is the FSHR Asn680Ser polymorphism, since it modulates ovarian response to FSH. The aim of these studies would to be the prediction of the genetic causes of sex-related diseases to enable a customized clinical setting based on individual response of patients undergoing gonadotropin stimulation. In this review we discuss the latest information about the effects of polymorphisms of the gonadotropins and their receptor genes on reproductive functions of both male and female, and discuss their patho-physiological implications.

Investigating the association between polymorphism of follicle-stimulating hormone receptor gene and ovarian response in controlled ovarian hyperstimulation

AIM

The aim of the study was to investigate the association between follicle-stimulating hormone receptor (FSHR) gene polymorphism at Position 680 and the outcomes of controlled ovarian hyperstimulation for in vitro fertilization and embryo transfer (IVF-ET) in infertile women.

MATERIALS AND METHODS

One hundred and eight patients under 35 years of age who underwent IVF-ET procedures were included in this study. The hormonal profile and treatment of all patients were analyzed and FSHR polymorphism was examined by polymerase chain reaction-restriction fragment length polymorphism. Women from all groups were classified based on polymorphisms at Position 680, occupied either by asparagines (Asn) or serine (Ser) as Asn/Asn, Asn/Ser, and Ser/Ser genotype.

RESULT

Our study showed that all patients in the Asn/Asn group were normal responders and in the Asn/Ser group 64.8% were normal responders and 21.1% and 14.1% were poor and hyper responders respectively. In the Ser/Ser group we did not have normal responders and 46.7% of these patients were poor responders and 53.3% were hyper responders.

CONCLUSION

FSH receptor polymorphism is correlated with response to ovarian stimulation.

Genomics and genetics of gonadotropin beta-subunit genes: Unique FSHB and duplicated LHB/CGB loci

The follicle stimulating hormone (FSH), luteinizing hormone (LH) and chorionic gonadotropin (HCG) play a critical role in human reproduction. Despite the common evolutionary ancestry and functional relatedness of the gonadotropin hormone beta (GtHB) genes, the single-copy FSHB (at 11p13) and the multi-copy LHB/CGB genes (at 19q13.32) exhibit locus-specific differences regarding their genomic context, evolution, genetic variation and expressional profile. FSHB represents a conservative vertebrate gene with a unique function and it is located in a structurally stable gene-poor region. In contrast, the primate-specific LHB/CGB gene cluster is located in a gene-rich genomic context and demonstrates an example of evolutionary young and unstable genomic region. The gene cluster is shaped by a constant balance between selection that acts on specific functions of the loci and frequent gene conversion events among duplicons. As the transcription of the GtHB genes is rate-limiting in the assembly of respective hormones, the genomic and genetic context of the FSHB and the LHB/CGB genes largely affects the profile of the hormone production.

An association study between the genetic polymorphisms within GnRHI, LHβ and FSHβ genes and central precocious puberty in Chinese girls

OBJECTIVES

Gonadotropin-releasing hormone (GnRH), luteinizing hormone (LH) and follicle-stimulating hormone (FSH) are three hypothalamic-pituitary-gonadal axis expressing hormones. They play critical roles in the onset of puberty. Here we report the relationship between the three hormones and Central Precocious Puberty (CPP) in Chinese Han girls.

METHODS

We analyzed the single nucleotide polymorphisms (SNPs) of 5'-flanking regions of these genes by DNA sequencing in 27 CPP samples. Then the SNPs sites were genotyped by ligase detection reaction in a total of 283 Chinese Han CPP cases and 284 matched controls. Distributions of the polymorphisms and haplotypes were calculated for statistical evaluation.

RESULTS

Nine SNPs (One in GnRHI gene: -2003 C/T; Five in LHβ gene: -1456 C/G, -1424 C/G, -238 G/A, -164 G/A and -34 T/A; Three in FSHβ gene: -1825 T/C, -261 G/T and -132 T/A.) were found. A quantitative genetic association study was made. -1825 T/C in FSHβ gene was related with CPP with a weak effect (P=0.025). A haplotype in the 5'-flanking region of LHβ gene was significantly associated with CPP in Chinese Han girls (P=8.25×10(-09)). However, analysis software showed that none of SNP was found in the regulating control element of these genes.

CONCLUSIONS

Our finding implies that the polymorphisms in the 5'-flanking regions of FSHβ gene and LHβ gene probably were related to the puberty onset time of these girls. Further studies on the polymorphisms are needed for the exact mechanism.

FoxL2 Is required for activin induction of the mouse and human follicle-stimulating hormone beta-subunit genes

Activin is a major physiological regulator of FSH. We identify FoxL2 as a critical component in activin induction of FSHbeta, both for the mouse gene, induction of which is Sma- and Mad-related protein (Smad) dependent, and for the human gene that is Smad independent. FoxL2 has been shown to regulate gonadotrope gene expression (GnRH receptor, alpha-glycoprotein subunit, porcine FSHbeta, and follistatin), but the mechanisms of action are not well understood. We identify novel sites required for activin action in both the mouse and human FSHbeta promoters, some of which bind FoxL2, and show that the FoxL2-binding element encompasses a larger region (12 bp) than the previously identified forkhead-binding consensus (7 bp). Remarkably, although required for activin induction, FoxL2 sites neither contribute to basal FSHbeta promoter activity nor confer activin response to a heterologous promoter; thus, they are neither classical activin-response elements nor is their role solely to recruit Smads to the promoter. FoxL2 overexpression can potentiate activin induction in gonadotropes and can confer activin responsiveness to FSHbeta in heterologous cells where this promoter is normally refractory to activin induction. Although Smad3 requires the presence of FoxL2 sites to induce mouse FSHbeta, even through its consensus Smad-binding element; the human promoter, which is induced by activin independently of Smad3, also requires FoxL2 sites for its induction by activin; thus the actions of FoxL2 are not exclusively through interactions with the Smad pathway. Thus, FoxL2 plays a key role in activin induction of the FSHbeta gene, by binding to sites conserved across multiple species.

Hormones in synergy: regulation of the pituitary gonadotropin genes

The precise interplay of hormonal influences that governs gonadotropin hormone production by the pituitary includes endocrine, paracrine and autocrine actions of hypothalamic gonadotropin-releasing hormone (GnRH), activin and steroids. However, most studies of hormonal regulation of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in the pituitary gonadotrope have been limited to analyses of the isolated actions of individual hormones. LHbeta and FSHbeta subunits have distinct patterns of expression during the menstrual/estrous cycle as a result of the integration of activin, GnRH, and steroid hormone action. In this review, we focus on studies that delineate the interplay among these hormones in the regulation of LHbeta and FSHbeta gene expression in gonadotrope cells and discuss how signaling cross-talk contributes to differential expression. We also discuss how recent technological advances will help identify additional factors involved in the differential hormonal regulation of LH and FSH.

Increased Prevalance of the -211 T allele of follicle stimulating hormone (FSH) beta subunit promoter polymorphism and lower serum FSH in infertile men

CONTEXT

The human FSHB promoter polymorphism (rs10835638; -211 G/T) has been associated with serum FSH in a cohort of young Estonian men. The minor allele carriers had reduced serum FSH (15.7% in GT heterozygotes; 40% in TT homozygotes) compared with GG homozygotes.

OBJECTIVE

Because FSH is essential for normal spermatogenesis and fertility, we speculated that abnormalities in FSH action could contribute to male infertility. We sought to study whether genetically inherited constitutively reduced FSH levels may affect male reproduction and replicate the association between rs10835638 and serum FSH among infertile male patients.

DESIGN

Genotyping of rs10835638 in a cohort of infertile men (n = 1029; Andrology Center of the Tartu University Clinics, Estonia), including idiopathic infertility cases (IIFC; n = 750).

PATIENTS

Patients included male partners (sperm concentration <20 x 10(6)/ml) of infertile couples failing to conceive a child for 12 months or longer.

RESULTS

A significant excess of TT homozygotes (1.1 vs. 2.4%) as well as GT heterozygotes (22.4 vs. 25.1%) was detected among infertile men compared with the young male cohort (chi(2) test, P < 0.05). The T allele of rs10835638 was associated with reduced serum FSH (analysis of covariance; full cohort: P = 1.20 x 10(-6), F = 13.8; IIFC: P = 7.70 x 10(-7), F = 14.3) as well as with low FSH to LH ratio (full cohort: P = 1.52 x 10(-11), F = 25.6; IIFC: P = 3.25 x 10(-9), F = 20.4). The median serum FSH levels differed between the GG and TT carriers by 48.5%. All IIFC with TT genotype exhibited low (<1.8) FSH to LH ratio.

CONCLUSIONS

In perspective, this genetic marker may have clinical significance in molecular diagnostics of male reproductive success and a potential to identify positive responders to FSH treatment.

Effects of novel single nucleotide polymorphisms of the FSH beta-subunit gene on semen quality and fertility in bulls

The follicle-stimulating hormone (FSH) acts on the Sertoli cells in the seminiferous tubules of the testis and regulates spermatogenesis up to the secondary spermatocyte stage. This study aimed to investigate molecular genetic characteristics of the bovine FSH beta-subunit gene (FSHB) and elucidate the effects of single nucleotide polymorphisms (SNPs) of FSHB on the quality of fresh and frozen semen and on fertility in bulls. We used polymerase chain reaction single-strand conformation polymorphism (PCR-SSCP) and sequencing of the FSHB gene in 56 bulls belonging to three breeds. We identified 13 substitutions and 1 insertion in the upstream regulation region and in the coding region of exon 3, which were all linked together. Bioinformatics analysis suggested that mutations of the 5'-upstream regulation region altered the binding sites for transcription factors, and radioimmunoassay demonstrated that mutations may result in alterations in the serum FSH concentrations. The least-squares analysis revealed that bulls with this genotype exhibited a significantly lower sperm concentration in fresh semen and a lower percentage of acrosome integrity in both fresh and frozen semen (P<0.05). These bulls also exhibited a significantly higher percentage of sperm deformity in fresh semen (P<0.05), which was more pronounced in frozen semen (P<0.01), and a significantly lower sperm motility in frozen semen (P<0.05). For fertility evaluation, the nonreturn rates obtained from 14,416 inseminations with the analyzed batches revealed that bulls with this genotype showed significantly lower nonreturn rates (P<0.05). In other words, bulls with this genotype exhibited lower semen quality, poor freeze resistance, and lower fertility. These results suggest that the SNPs in bovine FSHB are associated with semen quality and fertility in bulls.

FSHB promoter polymorphism within evolutionary conserved element is associated with serum FSH level in men

BACKGROUND

No polymorphisms affecting serum FSH levels have been described in the human FSHB gene. We have identified a potential regulatory single nucleotide polymorphism (SNP, rs10835638; G/T) 211 bp upstream from the FSHB mRNA transcription start-site, located within a highly conserved region among placental mammals. We aimed to determine the correlation of carrier status of rs10835638 alternative alleles with serum FSH level in men, and testicular and hormonal parameters.

METHODS

A quantitative genetic association study using a cohort of healthy men (n = 554; age 19.2 ± 1.7 years) visiting the Centre of Andrology, Tartu University Hospital, Estonia.

RESULTS

Rs10835638 (allele frequencies: G 87.6%, T 12.4%) was significantly associated with serum FSH level (analysis of variance: F = 13.0, P = 0.0016, df = 1; regression testing for a linear trend: P = 0.0003). Subjects with the GG genotype exhibited higher FSH levels (3.37 ± 1.79 IU/l, n = 423) compared with heterozygotes (2.84 ± 1.54 IU/l, n = 125) (P = 0.0005), the group of T-allele carriers (GT+TT, 2.78 ± 1.51 IU/l, n = 131) (P = 0.0005) and TT-homozygotes (2.02 ± 0.81 IU/L, n = 6) (P = 0.031). Rs10835638 was also associated with significant (P < 0.05) reduction in free testosterone index and testes volume, but increased semen volume, sex hormone-binding globulin, serum testosterone and estradiol. LH and inhibin-B levels did not differ significantly between groups.

CONCLUSIONS

The identification of a regulatory SNP in FSHB promoter paves the way to study the effect of constitutively low FSH on male health and fertility. As FSH contributes to follicular development and sex steroid production in women, the role of this FSHB variant in female reproductive success is still to be addressed.

Haplotype structure of FSHB, the beta-subunit gene for fertility-associated follicle-stimulating hormone: possible influence of balancing selection

Follicle-stimulating hormone (FSH) is essential for human reproduction. The unique functions of this hormone are provided by the FSH receptor-binding beta-subunit encoded by the FSHB gene. Resequencing and genotyping of FSHB in three European, two Asian and one African population, as well as in the great apes (chimpanzee, gorilla, orangutan), revealed low diversity and significant excess of polymorphisms with intermediate frequency alleles. Statistical tests for FSHB showed deviations from neutrality in all populations suggesting a possible effect of balancing selection. Two core haplotypes were identified (carried by 76-96.6% of each population's sample), the sequences of which are clearly separated from each other. As fertility most directly affects an organism's fitness, the carriers of these haplotypes have apparently had more success in human history to contribute to the next generation. There is a preliminary observation suggesting that the second most frequent FSHB haplotype may be associated with rapid conception success in females. Interestingly, the same haplotype is related to an ancestral FSHB variant shared with the ancestor of the great apes. The determination of the functional consequence of the two core FSHB variants may have implications for understanding and regulating human fertility, as well as in assisting infertility treatments.