The cloning of the human follicle stimulating hormone receptor and its expression in COS-7, CHO, and Y-1 cells

Peroxiredoxin 4 deficiency induces accelerated ovarian aging through destroyed proteostasis in granulosa cells

Ovarian aging, a complex and challenging concern within the realm of reproductive medicine, is associated with reduced fertility, menopausal symptoms and long-term health risks. Our previous investigation revealed a correlation between Peroxiredoxin 4 (PRDX4) and human ovarian aging. The purpose of this research was to substantiate the protective role of PRDX4 against ovarian aging and elucidate the underlying molecular mechanism in mice. In this study, a Prdx4-/- mouse model was established and it was observed that the deficiency of PRDX4 led to only an accelerated decline of ovarian function in comparison to wild-type (WT) mice. The impaired ovarian function observed in this study can be attributed to an imbalance in protein homeostasis, an exacerbation of endoplasmic reticulum stress (ER stress), and ultimately an increase in apoptosis of granulosa cells. Furthermore, our research reveals a noteworthy decline in the expression of Follicle-stimulating hormone receptor (FSHR) in aging Prdx4-/- mice, especially the functional trimer, due to impaired disulfide bond formation. Contrarily, the overexpression of PRDX4 facilitated the maintenance of protein homeostasis, mitigated ER stress, and consequently elevated E2 levels in a simulated KGN cell aging model. Additionally, the overexpression of PRDX4 restored the expression of the correct spatial conformation of FSHR, the functional trimer. In summary, our research reveals the significant contribution of PRDX4 in delaying ovarian aging, presenting a novel and promising therapeutic target for ovarian aging from the perspective of endoplasmic reticulum protein homeostasis.

Endogenous, tissue-resident stem/progenitor cells in gonads and bone marrow express FSHR and respond to FSH via FSHR-3

Follicle stimulating hormone (FSH) is secreted by the anterior pituitary and acts on the germ cells indirectly through Granulosa cells in ovaries and Sertoli cells in the testes. Extragonadal action of FSH has been reported but is still debated. Adult tissues harbor two populations of stem cells including a reserve population of primitive, small-sized, pluripotent very small embryonic-like stem cells (VSELs) and slightly bigger, tissue-specific progenitors which include ovarian stem cells (OSCs) in ovaries, spermatogonial stem cells (SSCs) in testes, endometrial stem cells (EnSCs) in uterus and hematopoietic stem cells (HSCs) in the bone marrow. Data has accumulated in animal models showing FSHR expression on both VSELs and progenitors in ovaries, testes, uterus and bone marrow and eventually gets lost as the cells differentiate further. FSH exerts a direct action on the stem/progenitor cells via alternatively spliced FSHR-3 rather than the canonical FSHR-1. FSH stimulates VSELs to undergo asymmetrical cell divisions to self-renew and give rise to the progenitors that in turn undergo symmetrical cell divisions and clonal expansions followed by differentiation into specific cell types. Excessive self-renewal of VSELs results in cancer and this explains ubiquitous expression of embryonic markers including nuclear OCT-4 along with FSHR in cancerous tissues. Focus of this review is to compile published data to support this concept. FSHR expression in stem/progenitor cells was confirmed by immuno-fluorescence, Western blotting, in situ hybridization and by quantitative RT-PCR. Two different commercially available antibodies (Abcam, Santacruz) were used to confirm specificity of FSHR expression along with omission of primary antibody and pre-incubation of antibody with immunizing peptide as negative controls. Western blotting allowed detection of alternatively spliced FSHR isoforms. Oligoprobes and primers specific for Fshr-1 and Fshr-3 were used to study these alternately-sliced isoforms by in situ hybridization and their differential expression upon FSH treatment by qRT-PCR. To conclude, stem/progenitor cells in adult tissues express FSHR and directly respond to FSH via FSHR-3. These findings change the field of FSH-FSHR biology, call for paradigm shift, explain FSHR expression on cancer cells in multiple organs and provide straightforward explanations for various existing conundrums including extragonadal expression of FSHR.

A Novel Mutation in the FSH Receptor (I423T) Affecting Receptor Activation and Leading to Primary Ovarian Failure

CONTEXT

Follicle-stimulating hormone (FSH) plays an essential role in gonadal function. Loss-of-function mutations in the follicle-stimulating hormone receptor (FSHR) are an infrequent cause of primary ovarian failure.

OBJECTIVE

To analyze the molecular physiopathogenesis of a novel mutation in the FSHR identified in a woman with primary ovarian failure, employing in vitro and in silico approaches, and to compare the features of this dysfunctional receptor with those shown by the trafficking-defective D408Y FSHR mutant.

METHODS

Sanger sequencing of the FSHR cDNA was applied to identify the novel mutation. FSH-stimulated cyclic adenosine monophosphate (cAMP) production, ERK1/2 phosphorylation, and desensitization were tested in HEK293 cells. Receptor expression was analyzed by immunoblotting, receptor-binding assays, and flow cytometry. Molecular dynamics simulations were performed to determine the in silico behavior of the mutant FSHRs.

RESULTS

A novel missense mutation (I423T) in the second transmembrane domain of the FSHR was identified in a woman with normal pubertal development but primary amenorrhea. The I423T mutation slightly impaired plasma membrane expression of the mature form of the receptor and severely impacted on cAMP/protein kinase A signaling but much less on β-arrestin-dependent ERK1/2 phosphorylation. Meanwhile, the D408Y mutation severely affected membrane expression, with most of the FSH receptor located intracellularly, and both signal readouts tested. Molecular dynamics simulations revealed important functional disruptions in both mutant FSHRs, mainly the loss of interhelical connectivity in the D408Y FSHR.

CONCLUSIONS

Concurrently, these data indicate that conformational differences during the inactive and active states account for the distinct expression levels, differential signaling, and phenotypic expression of the I423T and D408Y mutant FSHRs.

Discovery and Preclinical Development of Orally Active Small Molecules that Exhibit Highly Selective Follicle Stimulating Hormone Receptor Agonism

An orally active follicle stimulating hormone receptor allosteric agonist would provide a preferred treatment for over 16 million infertile women of reproductive age in low complexity methods (ovulation induction-intrauterine insemination) or in high complexity methods (controlled ovarian stimulation-in vitro fertilization). We present two oral follicle stimulating hormone receptor allosteric agonist compounds that have the desired pharmacology, drug metabolism, pharmacokinetics, and safety profile for clinical use. These molecules provide a single agent suitable for ovulation induction-intrauterine insemination or controlled ovarian stimulation-in vitro fertilization that is more convenient for patients and achieves similar preclinical efficacy as rec-hFSH. TOP5668, TOP5300 were evaluated in vitro in Chinese hamster ovary cells transfected with individual glycoprotein receptors measuring cAMP (FSHR, LH/CGR, thyroid stimulating hormone receptor). TOP5668 was found to have solely follicle stimulating hormone receptor allosteric agonist activity while TOP5300 was found to have mixed follicle stimulating hormone receptor allosteric agonist and LHR-AA activity. Both compounds stimulated concentration-dependent increases in estradiol production from cultured rat granulosa cells in the presence or absence of low dose rec-hFSH, while only TOP5300 stimulated testosterone production from rat primary Leydig cells. In pooled human granulosa cells obtained from patients undergoing controlled ovarian stimulation-in vitro fertilization, TOP5300 stimulated 7-fold greater maximal estradiol response than rec-hFSH and TOP5668 was 10-fold more potent than TOP5300. Both TOP5300 and TOP5668 stimulated follicular development in immature rat to the same efficacy as recombinant follicle stimulating hormone. In mice treated with TOP5300, in the presence of low dose of follicle stimulating hormone, there were no differences in oocyte number, fertilization rate, and hatched blastocyst rate in mice with TOP5300 and low dose follicle stimulating hormone vs. reference proteins pregnant mare serum gonadotropin or high dose rec-hFSH. ADME/PK and safety profiles were favorable. In addition, there was no appreciable activity on thyroid hormones by TOP5300 in 14-days toxicological study in rat or dog. The selected lead compound, TOP5300 stimulated a more robust increase in estradiol production from granulosa-lutein cells from women with polycystic ovarian syndrome patient compared to rec-hFSH. Conclusions: Two novel oral FSHR allosteric agonist, TOP5668 and TOP5300, were found to mimic the biological activity of rec hFSH in preclinical studies. Both compounds led to folliculogenesis and superovulation in rat and mice. Specifically, TOP5300 led to a similar number of ovulated oocytes that fertilized and developed into hatched blastocysts in mice when compared to rec-hFSH. The safety profile demonstrated lack of toxicity.

Molecular dynamics simulation of the follicle-stimulating hormone receptor. Understanding the conformational dynamics of receptor variants at positions N680 and D408 from in silico analysis

Follicle-stimulating hormone receptor (FSHR) is a G-protein coupled receptor (GPCR) and a prototype of the glycoprotein hormone receptors subfamily of GPCRs. Structural data of the FSHR ectodomain in complex with follicle-stimulating hormone suggests a "pull and lift" activation mechanism that triggers a conformational change on the seven α-helix transmembrane domain (TMD). To analyze the conformational changes of the FSHR TMD resulting from sequence variants associated with reproductive impairment in humans, we set up a computational approach combining helix modeling and molecular simulation methods to generate conformational ensembles of the receptor at room (300 K) and physiological (310 K) temperatures. We examined the receptor dynamics in an explicit membrane environment of polyunsaturated phospholipids and solvent water molecules. The analysis of the conformational dynamics of the functional (N680 and S680) and dysfunctional (mutations at D408) variants of the FSHR allowed us to validate the FSHR-TMD model. Functional variants display a concerted motion of flexible intracellular regions at TMD helices 5 and 6. Disruption of side chain interactions and conformational dynamics were detected upon mutation at D408 when replaced with alanine, arginine, or tyrosine. Dynamical network analysis confirmed that TMD helices 2 and 5 may share communication pathways in the functional FSHR variants, whereas no connectivity was detected in the dysfunctional mutants, indicating that the global dynamics of the FSHR was sensitive to mutations at amino acid residue 408, a key position apparently linked to misfolding and variable cell surface plasma membrane expression of FSHRs with distinct mutations at this position.

β-arrestins regulate gonadotropin receptor-mediated cell proliferation and apoptosis by controlling different FSHR or LHCGR intracellular signaling in the hGL5 cell line

Gonadotropin signaling classically involves proliferative, steroidogenic and apoptotic stimuli. In this study, we used the human granulosa cell line hGL5 to demonstrate how follicle-stimulating hormone (FSH) and luteinizing hormone (LH) differently control proliferative or apoptotic signals, revealing novel intrinsic properties of their receptors (FSHR, LHCGR). We found that, in this tumor-like cell line, the expression of endogenous FSHR and LHCGR is serum-dependent, but both receptors were unable to activate the canonical cAMP/PKA pathway upon gonadotropin stimulation, failing to produce cAMP, progesterone and G protein-coupled receptor (GPCR)-mediated apoptosis in vitro. Conversely, ligand treatment resulted in FSHR- and LHCGR-mediated ERK1/2 phosphorylation and cell proliferation due to receptor coupling to β-arrestins. The inactive cAMP/PKA pathway was unlocked by siRNA-mediated knock-down of β-arrestin 1 and 2, leading to progesterone synthesis and apoptosis. Surprisingly, FSH, but not LH treatment accelerated the cAMP/PKA-mediated apoptosis after β-arrestin silencing, an effect which could be reproduced by overexpressing the FSHR, but not the LHCGR. This work demonstrates that the expression of FSHR and LHCGR can be induced in hGL5 cells but that the FSHR-dependent cAMP/PKA pathway is constitutively silenced, possibly to protect cells from FSHR-cAMP-PKA-induced apoptosis. Also, we revealed previously unrecognized features intrinsic to the two structurally similar gonadotropin receptors, oppositely resulting in the regulation of life and death signals in vitro.

Towards a non-animal risk assessment for anti-androgenic effects in humans

Toxicology testing is undergoing a transformation from a system based on high-dose studies in laboratory animals to one founded primarily on in vitro methods that evaluate changes in normal cellular signalling pathways using human-relevant cells or tissues. We review the tools and approaches that could be used to develop a non-animal safety assessment for anti-androgenic effects in humans, with a focus on the molecular initiating events (MIEs) that human disorders indicate critical for normal functioning of the hypothalamus-pituitary-testicular (HPT) axis. In vitro test systems exist which can be used to characterize the effects of test chemicals on some MIEs such as androgen receptor antagonism, inhibition of steroidogenic enzymes or 5α-reductase inhibition. When used alongside information describing the pharmacokinetics of a specific chemical exposure, these could be used to inform a pathways-based safety assessment. However, some parts of the HPT axis such as events occurring in the hypothalamus or pituitary are not well represented by accepted in vitro methods. In vitro tools to characterize perturbations in these events need to be developed before a fully integrated model of the HPT axis can be described. Knowledge gaps also exist which prevent us from using in vitro data to predict the type and severity of in vivo effect(s) that could arise from a given level of in vitro anti-androgenic activity. This means that more work is needed to reliably link an MIE with an adverse outcome. However, especially for chemicals with low anti-androgenic activity, human exposure data can be used to put in vitro mode of action data into context for risk-based safety decision-making.

Gonadotropins in European sea bass: Endocrine roles and biotechnological applications

Follicle stimulating hormone (Fsh) and luteinizing hormone (Lh) are central endocrine regulators of the gonadal function in vertebrates. They act through specific receptors located in certain cell types found in the gonads. In fish, the differential roles of these hormones are being progressively elucidated due to the development of suitable tools for their study. In European sea bass (Dicentrarchus labrax), isolation of the genes coding for the gonadotropin subunits and receptors allowed in first instance to conduct expression studies. Later, to overcome the limitation of using native hormones, recombinant dimeric gonadotropins, which show different functional characteristics depending on the cell system and DNA construct, were generated. In addition, single gonadotropin beta-subunits have been produced and used as antigens for antibody production. This approach has allowed the development of detection methods for native gonadotropins, with European sea bass being one of the few species where both gonadotropins can be detected in their native form. By administering recombinant gonadotropins to gonad tissues in vitro, we were able to study their effects on steroidogenesis and intracellular pathways. Their administration in vivo has also been tested for use in basic studies and as a biotechnological approach for hormone therapy and assisted reproduction strategies. In addition to the production of recombinant hormones, gene-based therapies using somatic gene transfer have been offered as an alternative. This approach has been tested in sea bass for gonadotropin delivery in vivo. The hormones produced by the genes injected were functional and have allowed studies on the action of gonadotropins in spermatogenesis.

Follicle-stimulating hormone receptor (FSHR) alternative skipping of exon 2 or 3 affects ovarian response to FSH

Genes critical for fertility are highly conserved in mammals. Interspecies DNA sequence variation, resulting in amino acid substitutions and post-transcriptional modifications, including alternative splicing, are a result of evolution and speciation. The mammalian follicle-stimulating hormone receptor (FSHR) gene encodes distinct species-specific forms by alternative splicing. Skipping of exon 2 of the human FSHR was reported in women of North American origin and correlated with low response to ovarian stimulation with exogenous follicle-stimulating hormone (FSH). To determine whether this variant correlated with low response in women of different genetic backgrounds, we performed a blinded retrospective observational study in a Turkish cohort. Ovarian response was determined as low, intermediate or high according to retrieved oocyte numbers after classifying patients in four age groups (<35, 35-37, 38-40, >40). Cumulus cells collected from 96 women undergoing IVF/ICSI following controlled ovarian hyperstimulation revealed four alternatively spliced FSHR products in seven patients (8%): exon 2 deletion in four patients; exon 3 and exons 2 + 3 deletion in one patient each, and a retention of an intron 1 fragment in one patient. In all others (92%) splicing was intact. Alternative skipping of exons 2, 3 or 2 + 3 were exclusive to low responders and was independent of the use of agonist or antagonist. Interestingly, skipping of exon 3 occurs naturally in the ovaries of domestic cats--a good comparative model for human fertility. We tested the signaling potential of human and cat variants after transfection in HEK293 cells and FSH stimulation. None of the splicing variants initiated cAMP signaling despite high FSH doses, unlike full-length proteins. These data substantiate the occurrence of FSHR exon skipping in a subgroup of low responders and suggest that species-specific regulation of FSHR splicing plays diverse roles in mammalian ovarian function.

Structural biology of glycoprotein hormones and their receptors: insights to signaling

This article reviews the progress made in the field of glycoprotein hormones (GPH) and their receptors (GPHR) by several groups of structural biologists including ourselves aiming to gain insight into GPH signaling mechanisms. The GPH family consists of four members, with follicle-stimulating hormone (FSH) being the prototypic member. GPH members belong to the cystine-knot growth factor superfamily, and their receptors (GPHR), possessing unusually large N-terminal ectodomains, belong to the G-protein coupled receptor Family A. GPHR ectodomains can be divided into two subdomains: a high-affinity hormone binding subdomain primarily centered on the N-terminus, and a second subdomain that is located on the C-terminal region of the ectodomain that is involved in signal specificity. The two subdomains unexpectedly form an integral structure comprised of leucine-rich repeats (LRRs). Following the structure determination of hCG in 1994, the field of FSH structural biology has progressively advanced. Initially, the FSH structure was determined in partially glycosylated free form in 2001, followed by a structure of FSH bound to a truncated FSHR ectodomain in 2005, and the structure of FSH bound to the entire ectodomain in 2012. Comparisons of the structures in three forms led a proposal of a two-step monomeric receptor activation mechanism. First, binding of FSH to the FSHR high-affinity hormone-binding subdomain induces a conformational change in the hormone to form a binding pocket that is specific for a sulfated-tyrosine found as sTyr 335 in FSHR. Subsequently, the sTyr is drawn into the newly formed binding pocket, producing a lever effect on a helical pivot whereby the docking sTyr provides as the 'pull & lift' force. The pivot helix is flanked by rigid LRRs and locked by two disulfide bonds on both sides: the hormone-binding subdomain on one side and the last short loop before the first transmembrane helix on the other side. The lift of the sTyr loop frees the tethered extracellular loops of the 7TM domain, thereby releasing a putative inhibitory influence of the ectodomain, ultimately leading to the activating conformation of the 7TM domain. Moreover, the data lead us to propose that FSHR exists as a trimer and to present an FSHR activation mechanism consistent with the observed trimeric crystal form. A trimeric receptor provides resolution of the enigmatic, but important, biological roles played by GPH residues that are removed from the primary FSH-binding site, as well as several important GPCR phenomena, including negative cooperativity and asymmetric activation. Further reflection pursuant to this review process revealed additional novel structural characteristics such as the identification of a 'seat' sequence in GPH. Together with the 'seatbelt', the 'seat' enables a common heteodimeric mode of association of the common α subunit non-covalently and non-specifically with each of the three different β subunits. Moreover, it was possible to establish a dimensional order that can be used to estimate LRR curvatures. A potential binding pocket for small molecular allosteric modulators in the FSHR 7TM domain has also been identified.

Identification of two novel, alternatively spliced mRNA transcripts of the human follicle-stimulating hormone receptor

Glycoprotein hormone receptors contain large extracellular domains encoded by multiple exons that can be alternatively spliced. Using human ovarian surface epithelium, we cloned two new splice variants of the human follicle-stimulating hormone receptor (FSH-R) gene, hFSH-R2 and hFSH-R3. The hFSH-R2 splice variant differed from the full-length FSH-R mRNA by the deletion of exon 10 and inclusion of two small exons after exon 9 whereas the hFSH-R3 splice variant retained only exons 1-6 of the full-length transcript. Both variants were expressed at low levels, but were detected in cells from follicular fluid derived from 30 different subjects. Transfection of these two variants individually into KGN cells, an ovarian cancer cell line that expresses wild-type FSH-R, reduced FSH-mediated phosphorylation of ERK(1/2), Akt, and p38/MAPK. Furthermore, in vitro co-expression of either hFSH-R2 or hFSH-R3 and full-length FSH-R in HEK293T cells reduced signal transduction through full-length FSH-R. Further studies are needed to fully elucidate the functions of these receptor isoforms.

Serum follicle-stimulating hormone level is associated with human epidermal growth factor receptor type 2 and Ki67 expression in post-menopausal females with breast cancer

The present study aimed to determine the association between levels of the gender hormones, follicle-stimulating hormone (FSH), luteinizing hormone (LH), progesterone (P) and prolactin (PRL), and two breast cancer molecular markers, human epidermal growth factor receptor 2 (Her-2) and Ki67, in post-menopausal patients with breast cancer. A retrospective study of the serum hormone levels of FSH, LH, P and PRL and the expression status of Her-2 and Ki67 was performed using 187 post-menopausal females with breast cancer. Her-2⁺ breast cancer patients exhibited higher serum FSH levels compared with Her-2⁻ patients (69.47±3.219 vs. 58.56±1.516 IU/l). The patients with high Ki67 expression [immunohistochemistry (IHC), 3+] displayed higher FSH (72.51±4.616 vs. 60.53±1.476 IU/l) and LH (32.33±1.916 vs. 26.98±0.8852 IU/l) levels than those with lower Ki67 expression. No correlation was identified between the FSH, LH, P and PRL hormone levels, tumor stages and lymphovascular invasion (LVI). In conclusion, a higher serum FSH level was identified in Her-2⁺ post-menopausal patients with breast cancer. Higher serum FSH and LH levels were also observed in breast cancer patients with high Ki67 expression. FSH and LH may function in the progression of breast cancer.

Ectopic expression of FSH receptor isoforms in neoplastic but not in endothelial cells from pancreatic neuroendocrine tumors

FSH receptor (FSHR) expression is restricted to gonads, where it drives FSH-dependent cell differentiation; in addition, FSHR plays an important role in the regulation of ovarian angiogenesis. Recently, FHSR expression has been shown in blood vessels of various tumors. However, pancreatic neuroendocrine tumors (p-NET), which have high-degree blood supply, were not included in that study. The aim of this study was to evaluate FSHR expression in p-NET. FSHR expression was evaluated in tumor samples from 30 patients with p-NET by immunohistochemistry and Western blot; fluorescence microscopy was used to localize FSHR in specific cells from tissue samples. von Willebrand factor (vWF) and chromograninA (chrA) was used as blood vessel and NET cells marker, respectively, to co-localize FSHR. FSHR expression was detected in all p-NET by immunohistochemistry. Western blot confirmed FSHR expression on p- NET although different FSHR isoforms, ranging from 240 kD to 55 kD were found in the samples studied. Surprisingly, FSHR co-localized with chrA but not with vWF, suggesting that neoplastic cells of neuroendocrine origin rather than blood vessels expressed FSHR. No relationship was found between degree of FSHR expression and histology of p-NET. FSHR may be aberrantly expressed in neoplastic cells from p-NET and not in tumor blood vessels; however, its biological significance as well as its clinical relevance remains to be elucidated.

The molecular basis of impaired follicle-stimulating hormone action: evidence from human mutations and mouse models

The pituitary gonadotropin follicle-stimulating hormone (FSH) interacts with its membrane-bound receptor to produce biologic effects. Traditional functions of FSH include follicular development and estradiol production in females, and the regulation of Sertoli cell action and spermatogenesis in males. Knockout mice for both the ligand (Fshb) and the receptor (Fshr) serve as models for FSH deficiency, while Fshb and Fshr transgenic mice manifest FSH excess. In addition, inactivating mutations of both human orthologs (FSHB and FSHR) have been characterized in a small number of patients, with phenotypic effects of the ligand disruption being more profound than those of its receptor. Activating human FSHR mutants have also been described in both sexes, leading to a phenotype of normal testis function (male) or spontaneous ovarian hyperstimulation syndrome (females). As determined from human and mouse models, FSH is essential for normal puberty and fertility in females, particularly for ovarian follicular development beyond the antral stage. In males, FSH is necessary for normal spermatogenesis, but there are differences in human and mouse models. The FSHB mutations in humans result in azoospermia; while FSHR mutations in humans and knockouts of both the ligand and the receptor in mice affect testicular function but do not result in absolute infertility. Available evidence also indicates that FSH may also be necessary for normal androgen synthesis in males and females.

Bioassay for follicle stimulating activity of equine gonadotropic hormone in mare serum using frozen/thawed transiently transfected reporter cells

The objective was to establish a cell line-based bioassay for FSH in horse serum for screening samples with high eCG bioactivity. A cell line (HEK293) was transiently cotransfected with an FSH reporter expression plasmid and a cAMP-responsive β-galactosidase reporter plasmid. Cells were bulk frozen, and thawed for assay purposes. This assay was specific for FSH, with no cross-reaction with LH or insulin-like growth factor-1. Standard curves (eCG) and serum samples from pregnant mares passed parallel line bioassay validity tests (linearity and parallelism). Estimates of bioactivity with this bioassay were highly correlated with estimates obtained with the Steelman-Pohley hCG augmentation assay. The colorimetric end point permitted the use of this assay as a rapid screen for FSH bioactivity without the need for animal use or complex cell culture facilities.

Absence of seasonal changes in FSHR gene expression in the cat cumulus-oocyte complex in vivo and in vitro

Domestic cat oocytes are seasonally sensitive to FSH. Compared with those collected during the breeding season, oocytes from the nonbreeding (NB) season require more FSH during in vitro maturation to achieve comparable developmental competence. This study tested the hypothesis that this seasonal variation was due to altered expression of FSH receptors (FSHR) and/or FSH-induced genes. Relative expression levels of FSHR mRNA and FSH-enhanced gene estrogen receptor β (ESR2) were measured by qPCR in whole ovaries and immature cumulus-oocyte complexes (COCs) isolated from cat ovaries during the natural breeding vs NB seasons. Expression levels of FSH-induced genes prostaglandin-endoperoxide synthase 2 (PTGS2), early growth response protein-1 (EGR1), and epidermal growth factor receptor (EGFR) were examined in mature COCs from both seasons that were a) recovered in vivo or b) matured in vitro with conventional (1 μg/ml) or high (10 μg/ml) FSH concentrations. Overall, FSHR mRNA levels were lower in whole ovaries during the NB compared with breeding season but were similar in immature COCs, whereas ESR2 levels did not differ in either group between intervals. We observed changes in PTGS2, EGR1, and EGFR mRNA expression patterns across maturation in COCs within but not between the two seasons. The lack of seasonal differentiation in FSH-related genes was not consistent with the decreased developmental capacity of oocytes fertilized during the NB season. These findings reveal that the seasonal decrease in cat oocyte sensitivity to FSH occurs both in vivo and in vitro. Furthermore, this decline is unrelated to changes in expression of FSHR mRNA or mRNA of FSH-induced genes in COCs from antral follicles.

The adapter protein APPL1 links FSH receptor to inositol 1,4,5-trisphosphate production and is implicated in intracellular Ca(2+) mobilization

FSH binds to its receptor (FSHR) on target cells in the ovary and testis, to regulate oogenesis and spermatogenesis, respectively. The signaling cascades activated after ligand binding are extremely complex and have been shown to include protein kinase A, mitogen-activated protein kinase, phosphatidylinositol 3-kinase/protein kinase B, and inositol 1,4,5-trisphosphate-mediated calcium signaling pathways. The adapter protein APPL1 (Adapter protein containing Pleckstrin homology domain, Phosphotyrosine binding domain and Leucine zipper motif), which has been linked to an assortment of other signaling proteins, was previously identified as an interacting protein with FSHR. Thus, alanine substitution mutations in the first intracellular loop of FSHR were generated to determine which residues are essential for FSHR-APPL1 interaction. Three amino acids were essential; when any one of them was altered, APPL1 association with FSHR mutants was abrogated. Two of the mutants (L377A and F382A) that displayed poor cell-surface expression were not studied further. Substitution of FSHR-K376A did not affect FSH binding or agonist-stimulated cAMP production in either transiently transfected human embryonic kidney cells or virally transduced human granulosa cells (KGN). In the KGN line, as well as primary cultures of rat granulosa cells transduced with wild type or mutant receptor, FSH-mediated progesterone or estradiol production was not affected by the mutation. However, in human embryonic kidney cells inositol 1,4,5-trisphosphate production was curtailed and KGN cells transduced with FSHR-K376A evidenced reduced Ca(2+) mobilization from intracellular stores after FSH treatment.

Expression of lrwd1 in mouse testis and its centrosomal localization

The mouse leucine-rich repeats and WD repeat domain containing 1 (lrwd1) gene is located on chromosome 5qG2 and spans over 13 kilobases. It encodes a novel protein of 648-amino acid protein that shares 78.3% amino acid sequence identity with the human LRWD1 protein. We used an oligopeptide as immunogen to generate an anti-lrwd1 antibody in rabbits. Both Northern and Western blot results indicated that the expression of lrwd1 is testis specific. Immunostaining of mouse testis sections detected high levels of lrwd1 signals in the cytoplasm of primary spermatocytes to mature spermatozoa and much weaker signals in spermatogonia. On mature spermatozoa, the anti-lrwd1 antibody stained strongly the connection region between the head and the neck where the centrosome is located. Additional immunostaining and immunoprecipitation showed colocalization and interaction between lrwd1 and γ-tubulin respectively, implicating lrwd1 as a candidate centrosomal protein. These results suggest that lrwd1 may play an important role in spermatogenesis.

Decreased degradation of internalized follicle-stimulating hormone caused by mutation of aspartic acid 6.30(550) in a protein kinase-CK2 consensus sequence in the third intracellular loop of human follicle-stimulating hormone receptor

A naturally occurring mutation in follicle-stimulating hormone receptor (FSHR) gene has been reported: an amino acid change to glycine occurs at a conserved aspartic acid 550 (D550, D567, D6.30(567)). This residue is contained in a protein kinase-CK2 consensus site present in human FSHR (hFSHR) intracellular loop 3 (iL3). Because CK2 has been reported to play a role in trafficking of some receptors, the potential roles for CK2 and D550 in FSHR function were evaluated by generating a D550A mutation in the hFSHR. The hFSHR-D550A binds hormone similarly to WT-hFSHR when expressed in HEK293T cells. Western blot analyses showed lower levels of mature hFSHR-D550A. Maximal cAMP production of both hFSHR-D550A as well as the naturally occurring mutation hFSHR-D550G was diminished, but constitutive activity was not observed. Unexpectedly, when (125)I-hFSH bound to hFSHR-D550A or hFSHR-D550G, intracellular accumulation of radiolabeled FSH was observed. Both sucrose and dominant-negative dynamin blocked internalization of radiolabeled FSH and its commensurate intracellular accumulation. Accumulation of radiolabeled FSH in cells transfected with hFSHR-D550A is due to a defect in degradation of hFSH as measured in pulse chase studies, and confocal microscopy imaging revealed that FSH accumulated in large intracellular structures. CK2 kinase activity is not required for proper degradation of internalized FSH because inhibition of CK2 kinase activity in cells expressing hFSHR did not uncouple degradation of internalized radiolabeled FSH. Additionally, the CK2 consensus site in FSHR iL3 is not required for binding because CK2alpha coimmunoprecipitated with hFSHR-D550A. Thus, mutation of D550 uncouples the link between internalization and degradation of hFSH.

Dominant negative effects of human follicle-stimulating hormone receptor expression-deficient mutants on wild-type receptor cell surface expression. Rescue of oligomerization-dependent defective receptor expression by using cognate decoys

Current evidence indicates that G protein-coupled receptors form dimers that may affect biogenesis and membrane targeting of the complexed receptors. We here analyzed whether expression-deficient follicle-stimulating hormone receptor (FSHR) mutants exert dominant negative actions on wild-type FSHR cell surface membrane expression. Co-transfection of constant amounts of wild-type receptor cDNA and increasing quantities of mutant (R556A or R618A) FSHR cDNAs progressively decreased agonist-stimulated cAMP accumulation, [(125)I]-FSH binding, and plasma membrane expression of the mature wild-type FSHR species. Co-transfection of wild-type FSHR fragments involving transmembrane domains 5-6, or transmembrane domain 7 and/or the carboxyl-terminus specifically rescued wild-type FSHR expression from the transdominant inhibition by the mutants. Mutant FSHRs also inhibited function of the luteinizing hormone receptor but not that of the thyrotropin receptor or non-related receptors. Defective intracellular transport and/or interference with proper maturation due to formation of misfolded mutant:wild-type receptor complexes may explain the negative effects provoked by the altered FSHRs.

Selective modulation of follicle-stimulating hormone signaling pathways with enhancing equine chorionic gonadotropin/antibody immune complexes

The injection of equine chorionic gonadotropin (eCG) in dairy goats induces the production of anti-eCG antibodies (Abs) in some females. We have previously shown that Abs negatively modulate the LH and FSH-like bioactivities of eCG, in most cases, compromising fertility in treated females. Surprisingly, we found out that some anti-eCG Abs improved fertility and prolificity of the treated females, in vivo. These Abs, when complexed with eCG, enhanced LH and FSH ability to induce steroidogenesis on specific target cells, in vitro. In the present study, we analyzed the impact of three eCG/anti-eCG Ab-enhancing complexes on two transduction mechanisms triggered by the FSH receptor: guanine nucleotide-binding protein alphaS-subunit/cAMP/protein kinase A (PKA) and beta-arrestin-dependent pathways, respectively. In all cases, significant enhancing effects were observed on ERK phosphorylation compared with eCG alone. However, cAMP production and PKA activation induced by eCG could be differently modulated by Abs. By using a pharmacological inhibitor of PKA and small interfering RNA-mediated knock-down of endogenous beta-arrestin 1 and 2, we demonstrated that signaling bias was induced and was clearly dependent on the complexed Ab. Together, our data show that eCG/anti-eCG Ab-enhancing complexes can differentially modulate cAMP/PKA and beta-arrestin pathways as a function of the complexed Ab. We hypothesize that enhancing Abs may change the eCG conformation, the immune complex acquiring new "biased" pharmacological properties ultimately leading to the physiological effects observed in vivo. The modulation of ligand pharmacological properties by Abs opens promising research avenues towards the optimization of glycoprotein hormone biological activities and, more generally, the development of new therapeutics.

Identification and in vitro characterization of follicle stimulating hormone (FSH) receptor variants associated with abnormal ovarian response to FSH

CONTEXT

FSH mediates cyclic follicle growth and development and is widely used for controlled ovarian stimulation in women undergoing infertility treatment. The ovarian response of women to FSH is variable, ranging from poor response to ovarian hyperstimulation.

OBJECTIVE

We investigated whether genetic alterations of the FSH receptor (FSHR) contribute to this variability.

DESIGN AND PATIENTS

Our approach was to study women undergoing treatment with in vitro fertilization falling into the edges of the normal distribution of ovarian response to FSH, with respect to age.

SETTING

We conducted the study at the Yale Fertility Clinic.

METHODS

We extracted RNA from cumulus cells surrounding the oocytes of women undergoing in vitro fertilization and analyzed the FSHR mRNA by RT-PCR and sequencing.

RESULTS

We identified four abnormal FSHR splicing products (three exon deletions and one intron insertion) in the FSHR mRNA in 37% (13 of 35) of women tested. All alterations affected the extracellular ligand-binding portion of the receptor without causing a frameshift. When transfected in HEK293T cells, all four splicing variants showed markedly decreased cAMP activation compared to controls. Untransfected cells showed no response to FSH, whereas all the cell lines showed normal cAMP activation when treated with forskolin, a nonreceptor-mediated cAMP stimulant. None of the normal or mutant forms showed any response to LH or TSH.

CONCLUSIONS

Our findings strongly indicate FSHR variants as being an intrinsic genetic cause of some forms of infertility and identify a need for functional characterization of these variants and the investigation of more individualized ovarian stimulation protocols.

Toward gene therapy of premature ovarian failure: intraovarian injection of adenovirus expressing human FSH receptor restores folliculogenesis in FSHR(-/-) FORKO mice

A homozygous missense mutation, C566T, in the follicle stimulation hormone receptor (FSHR) gene has been linked to premature ovarian failure. The disease leads to infertility in a normal karyotype female with an elevated follicle stimulating hormone (FSH) and decreased serum estrogen level. Female mice carrying mutated FSHR gene, called follitropin receptor knockout (FORKO), display similar phenotype and are sterile because of a folliculogenesis block at a primary stage. We investigated the effects of bilateral intra-ovarian injection of an adenovirus expressing a normal copy of human FSHR on the reproductive system of 6-10 weeks female FORKO mice. Ad-LacZ was injected directly into each ovary of the control group. Animals were sacrificed at 2, 4, 8 and 12 weeks post-injection and tissues collected for evaluation. Treated mice showed estrogenic changes in daily vaginal smear whereas control animals remained fixated in the diestrus stage. Histological evaluation showed on average 26 +/- 4 follicles/ovary in treated group with 8 +/- 2 follicles at the antral stage compared with only 5 +/- 2 with zero follicles at antral stage in Ad-LacZ control mice. There was no significant change in serum level of progesterone, however, estrogen level increased 2-3-fold (P < 0.02) and FSH decreased by up to 50% (P < 0.04) in treated animals. FSHR mRNA was detected in the ovaries of the treated group. In conclusion, intra-ovarian injection of an adenovirus expressing human FSHR gene is able to restore FSH responsiveness and reinitiate ovarian folliculogenesis as well as resume estrogen production in female FORKO mice. Ad-LacZ injections indicate the absence of systemic viral dissemination or germ line transmission of adenovirus DNA to offspring.

No activating mutations of FSH receptor in four children with ovarian juvenile granulosa cell tumors and the association of these tumors with central precocious puberty

STUDY OBJECTIVE

The stimulation of the follicle-stimulating hormone receptor (FSHR) by circulating FSH or some activating mutations of the FSHR may play a causal role in the development of granulosa cell tumors of ovaries.

STUDY DESIGN

We evaluated four patients with ovarian juvenile granulosa cell tumors (age range, 2.4 to 7.2; median, 2.9 years) and five healthy pubertal girls (age range, 16 to 18.5; median, 16.8 years) for activating mutations in exon 10 of the FSHR. The patients were followed and evaluated clinically. Genomic DNA was extracted from the peripheral blood. Exon10 of the FSHR was evaluated for mutations.

RESULTS

All four patients presented with signs of precocious puberty. One patient, who had markedly accelerated growth velocity and advanced bone age, developed central precocious puberty after the removal of her tumor. Another patient was diagnosed to have a left ovarian cyst without tumor recurrence approximately 3.3 years after the removal of the tumor. Activating mutations were not found, but previously reported polymorphisms (Ser680Asn and Ala307Thr) of the FSHR were detected in three of four patients and in three of five controls. The follow-up period of these four patients ranged from 4.5 to 8.8 years, with a median value of 6.7 years.

CONCLUSIONS

We did not find any activating mutation in exon 10 of the FSHR in our patients, and one patient developed precocious puberty after removal of her tumor. The development of ovarian tumors in these patients may have been caused by mutations at other exons of the FSHR and G protein subunits, so the association noted between central precocious puberty and granulosa cell tumors might not be coincidental.

Sex change in the Gobiid fish is mediated through rapid switching of gonadotropin receptors from ovarian to testicular portion or vice versa

Sex-changing fish Trimma okinawae can change its sex back and forth from male to female and then to male serially, depending on the social status in the harem. T. okinawae is well equipped to respond to its social status by possessing both ovarian and testicular tissues even though only one gonad remains active at one time. Here we investigated the involvement of gonadotropins in sex change by determining the changes in gonadotropin receptor (GtHR) gene expression during the onset of sex change from female to male and male to female. The expression of the GtHR was found to be confined to the active gonad of the corresponding sexual phase. During the sex-change from female to male, initially the ovary had high levels of FSHR and LHR, which eventually went up in the testicular tissue if the fish was bigger. Changing of the gonads started with switching of GtHR expression discernible within 8-12 h of the visual cue. Further in vitro culture of the transitional gonads with a supply of exogenous gonadotropin (human chorionic gonadotropin) revealed that the to-be-active gonad acquired the ability to produce the corresponding sex hormone within 1 d of the activation of GtHR. Conversely, the to-be-regressed gonad did not respond to the exogenous gonadotropin. Our findings show that the gonads of successive sex-changing fish possess the intrinsic mechanism to respond to the social cue differentially. Additionally, this location switching of GtHR expression also could substantiate the importance of the hypothalamo-pituitary-gonadotropic axis.

Functional and structural roles of conserved cysteine residues in the carboxyl-terminal domain of the follicle-stimulating hormone receptor in human embryonic kidney 293 cells

The carboxyl-terminal segment of G protein-coupled receptors has one or more conserved cysteine residues that are potential sites for palmitoylation. This posttranslational modification contributes to membrane association, internalization, and membrane targeting of proteins. In contrast to other members of the glycoprotein hormone receptor family (the LH and thyroid-stimulating hormone receptors), it is not known whether the follicle-stimulating hormone receptor (FSHR) is palmitoylated and what are the effects of abolishing its potential palmitoylation sites. In the present study, a functional analysis of the FSHR carboxyl-terminal segment cysteine residues was carried out. We constructed a series of mutant FSHRs by substituting cysteine residues with alanine, serine, or threonine individually and together at positions 629 and 655 (conserved cysteines) and 627 (nonconserved). The results showed that all three cysteine residues are palmitoylated but that only modification at Cys629 is functionally relevant. The lack of palmitoylation does not appear to greatly impair coupling to G(s) but, when absent at position 629, does significantly impair cell surface membrane expression of the partially palmitoylated receptor. All FSHR Cys mutants were capable of binding agonist with the same affinity as the wild-type receptor and internalizing on agonist stimulation. Molecular dynamics simulations at a time scale of approximately 100 nsec revealed that replacement of Cys629 resulted in structures that differed significantly from that of the wild-type receptor. Thus, deviations from wild-type conformation may potentially contribute to the severe impairment in plasma membrane expression and the modest effects on signaling exhibited by the receptors modified in this particular position.

Toward gene therapy of primary ovarian failure: adenovirus expressing human FSH receptor corrects the Finnish C566T mutation

Resistance ovarian syndrome is a heterogeneous disorder inherited as a Mendelian recessive trait and characterized by infertility, primary amenorrhea, normal karyotype and elevated serum FSH and LH levels. An inactivating mutation, C566T, in FSH receptor gene (FSHR) has been identified initially in Finland. We investigated if an adenovirus expressing a normal copy of human FSHR (Ad-hFSHR) has the ability to: (i) transfect granulosa cell lines, (ii) render the transfected cell lines responsive to FSH stimulation and (iii) transcomplement the malfunctioning form of human FSHR gene with C566T mutation. COS-7, JC-410, JC-410-P450-scc-luc and JC-410-StAR-luc cell lines were infected by Ad-hFSHR followed by treatment with FSH. Functional activity of the Ad-hFSHR was tested by measuring cyclic adenosine monophosphate (cAMP) or luciferase activity in response to FSH stimulation, and showed 2-4.6-fold increases in Ad-hFSHR transfected cells compared with untransfected or Ad-LacZ transfected cells, indicating that Ad-hFSHR is functionally active and expressing hFSHR. Generation of cAMP in cells expressing only mutated hFSHR-T566 showed minimal increase after FSH stimulation. Co-transfection of Ad-hFSHR in these cells carrying the malfunction form of human FSHR caused significant increases of 2.2-7.4-fold in FSH dependent cAMP generation (P = 0.0007). We concluded that adenovirus expressing a normal human FSHR can compensate the inactivating human FSHR-C566T mutation and restore FSH responsiveness.

Tumor Necrosis Factor (TNF)-Soluble High-Affinity Receptor Complex as a TNF Antagonist

A novel high-affinity inhibitor of tumor necrosis factor (TNF) is described, which is created by the fusion of the extracellular domains of TNF-binding protein 1 (TBP-1) to both the alpha and beta chains of an inactive version of the heterodimeric protein hormone, human chorionic gonadotropin. The resulting molecule, termed TNF-soluble high-affinity receptor complex (SHARC), self-assembles into a heterodimeric protein containing two functional TBP-1 moieties. The TNF-SHARC is a potent inhibitor of TNF-alpha bioactivity in vitro and has a prolonged pharmacokinetic profile compared with monomeric TBP-1 in vivo. Consistent with the long half-life, the duration of action in an lipopolysaccharide-mediated proinflammatory mouse model is prolonged similarly. In a collagen-induced arthritis mouse model, this molecule demonstrates improved efficacy over monomeric TBP-1. Based on these results, we demonstrated that inactivated heterodimeric protein hormones are flexible and efficient scaffolds for the creation of soluble high-affinity receptor complexes.

The gonadotropins: tissue-specific angiogenic factors?

The gonadotropins, whose members are human chorionic gonadotropin (hCG), lutenizing hormone (LH) and follicle-stimulating hormone (FSH) are a well characterized hormone family known to regulate reproductive functions in both females and males. Recent studies indicate that they can modulate the vascular system of reproductive organs. It was shown that gonadotropins not only influence the expression of vascular endothelial growth factor (VEGF) and both its receptors VEGFR-1 and -2, but also modulate other ubiquitously expressed angiogenic factors like the angiopoietins and their receptor Tie-2, basic fibroblast growth factor or placental-derived growth factor. Some recent data indicates a possible direct action of gonadotropins on endothelial cells. Thus, the gonadotropins act as tissue-specific angiogenic factors providing an optimal vascular supply during the menstrual cycle and early pregnancy in the female reproductive tract as well as in testis. In pathological conditions (e.g. preeclampsia, intrauterine growth restriction, ovarian hyperstimulation or endometriosis), these tightly regulated interactions between the gonadotropins and the ubiquitous angiogenic factors appear to be disturbed. The intent of this short manuscript is to review the current knowledge of the regulatory role of the gonadotropins in vasculo- and angiogenesis. We also review angiogenic actions of thyroid-stimulating hormone (TSH), a glycoprotein closely related to gonadotropins, which display strong gonodal actions.

The tale of follitropin receptor diversity: a recipe for fine tuning gonadal responses?

The original concept (dogma) of a single FSH receptor entity coupling to G(s) protein to activate adenylate cyclase and producing cAMP as second messenger appears inadequate to explain pleiotropic actions of the hormone. The identification and expression of alternatively spliced gonadotropin receptors, suggest that alternative splicing could serve as a mechanism for creating receptor diversity. Studies focused on sheep and mouse gonadal tissues show that the single large gene of approximately 250kb is a modular structure whose pre-mRNA undergoes alternative splicing creating several subtypes (at least four FSH-R1 to R4 identified to date). With segments of the N-terminus that are identical different topographies are generated by differing carboxyl termini. The same gene thus produces receptor types with different motifs that can display dominant positive, dominant negative, growth factor/cytokine type and potentially soluble binding protein features. Functional relevance is shown by modulation of receptor variants during hormonal stimulation. Presence of equivalent segments of the gene in the human and bovine suggests conservation and predicts similarity in structures and function. Thus, the complex cellular biology of follitropin receptors that may interact differently with polymorphic forms (glycosylation variants) of FSH represents an intricate scheme to regulate hormone signaling.

Biological properties of a novel follicle-stimulating hormone/human chorionic gonadotropin chimeric gonadotropin

A chimeric recombinant human gonadotropin, termed C3, demonstrates both follitropic and lutropic bioactivities. The alpha-subunit construct for C3 is comprised of the recombinant wild-type human glycoprotein hormone alpha-subunit. The beta-subunit DNA construct for C3 encodes residues 1-145 from human chorionic gonadotropin (hCG)-beta with the exceptions that FSH beta amino acid 88 (D) is substituted for hCG beta amino acid 94 (R) and FSH beta amino acids 95-108 (TVRGLGPSYCSFGE) are substituted for hCG beta amino acids 101-114 (GGPKDHPLTCDDPR). C3 is a potent FSH and LH agonist able to bind and to signal through FSH and LH receptors in vitro. In in vivo bioassays optimized to quantify each type of activity, C3 was found to have lutropin and follitropin potencies at levels similar to those of recombinant human LH and recombinant human FSH, respectively. In immature rats, C3 was sufficient to support the maturation of normal ovarian follicles. Moreover, a significant portion of follicles matured by C3 ruptured in response to an ovulatory hCG stimulus and gave rise to morphologically normal oocytes. Furthermore, a low dose of C3 promoted weight gain in the rodent uterus, suggesting it also supported preparation for implantation without histological evidence of excessive luteinization of the ovary. In summary, the biological properties of C3 indicate that its chimeric nature has resulted in a fully functional, dual-acting human gonadotropin.

SCREENING OF FSH RECEPTOR GENE MUTATION (C566T) IN AZOOSPERMIC MEN IN JAPAN

To study the genetic mutation, which could cause problems in spermatogenesis, we screened the point mutations of the FSH receptor gene (C566T) in idiopathic azoospermic men in Japan. We performed mutational analysis of the FSH receptor in 54 Japanese patients diagnosed for azoospermia with Sertoli cell-only (SCO) syndrome (n = 33), hypospermatogenesis (n = 11) and maturation arrest (n = 10). For mutation screening of the FSH receptor, polymerase chain reaction (PCR) amplification from genomic DNA with flanking intronic primers were used. On BsmI digestion, all patients demonstrated homozygous, normal exon 7 alleles with 51 and 27 bp fragments. The absence of any 78 bp fragments demonstrated that no heterozygous or homozygous mutant alleles were present in any patients. None of the 54 patients showed a C566T FSH receptor mutation. We could not confirm that the genomic mutation of the FSH receptor (C566T) is a common cause in Japanese azoospermic patients.

Follicle-stimulating hormone receptor gene mutations are not evident in Greek women with premature ovarian failure and poor responders

BACKGROUND/AIMS

This clinical and molecular study aimed to investigate the presence of follicle-stimulating hormone (FSH) receptor gene mutations in women with premature ovarian failure (POF) and poor responders to in vitro fertilization treatment.

METHODS

DNA was extracted from blood samples for subsequent polymerase chain reaction (PCR). PCR was followed by restriction fragment length polymorphism and direct sequencing.

RESULTS

No inactivating mutations reported so far were identified in exons 6, 7, and 10 in women with POF and poor responders.

CONCLUSION

FSH receptor gene mutations are not frequent in Greek patients with POF as is the case in the rest of the world except for cases with ovarian dysgenesis in Finland.

Functional significance of the BBXXB motif reversed present in the cytoplasmic domains of the human follicle-stimulating hormone receptor

The minimal structural motif, BBXXB (where B represents a basic amino acid residue and X a non-basic residue), located in particular regions of the intracellular domains of cell surface membrane receptors is involved in the G protein-activating activity of a number of G protein-coupled receptors. The human FSH receptor (hFSHR) exhibits a reversed BBXXB motif (BXXBB) in the juxtamembrane region of the third intracellular loop (IL3) and the carboxyl terminus (Ctail) of the receptor; however the importance of this sequence on receptor function remains unclear. In the present study, we analyzed the effects of mutations in this structural motif on hFSHR expression, receptor-mediated effector activation and agonist-provoked receptor internalization. Human embryonic kidney 293 cells were transiently transfected with plasmids containing the cDNA of the wild-type (Wt) hFSHR or several hFSHR mutants in which basic amino acids of the minimal structural motif at the IL3 and Ctail were replaced with alanine (i.e. AXXAA, AXXBB, BXXAB and BXXBA mutants). Alanine substitution of the three basic residues present in the IL3-BXXBB (IL3-AXXAA mutant) yielded a < or =60 kDa possibly under-glycosylated form of the FSHR, whereas the same substitutions in the Ctail resulted in the immature >62 kDa form of the receptor; both AXXAA hFSHR mutants completely failed to bind agonist and activate effector. Individual substitutions resulted in different cAMP responses to agonist stimulation: the IL3-AXXBB and IL3-BXXBA mutant hFSHRs failed to evoke Gs protein activation, whereas agonist-stimulated cAMP production was completely normal when the IL3-BXXAB mutant was expressed. All three IL3 mutants bound [125I]-labelled FSH in a similar fashion to the Wt hFSHR. Ligand-binding, cell surface membrane receptor expression and agonist-provoked effector activation were significantly affected by the individual substitutions at the Ctail-BXXBB motif: the Ctail-AXXBB variant exhibited reduced (approximately 50%) maximal cAMP response and ability to bind ligand, whereas both ligand binding and effector activation was severely reduced or abolished by expression of the Ctail-BXXBA and -BXXAB hFSHR mutants; the expression levels of the 80 kDa form of the receptor correlated with the magnitude of ligand-provoked cAMP production and binding capability of the mutant receptors. Upon stimulation by agonist, all mutants with detectable ligand-binding activity internalized following the pattern exhibited by the Wt hFSHR species. These results indicate that the BXXBB motif at the IL3 of the hFSHR is essential for coupling the activated receptor to the Gs protein, whereas the same motif in the Ctail is apparently more important for membrane expression.

Human follitropin receptor (FSHR) interacts with the adapter protein 14-3-3tau

The human follitropin (follicle stimulating hormone, FSH) receptor (FSHR) is a G protein-coupled receptor (GPCR). To identify cytoplasmic proteins that may regulate FSHR function, a yeast-based interaction trap was performed. A linked construct of the first and second intracellular loops (iL1-iL2 bait) of FSHR was used as bait and a human ovarian cDNA library was used as prey. Among the proteins identified that interacted with the bait was 14-3-3tau, a member of a family of homodimeric cytoplasmic adapter proteins. Human granulosa cells, the site of FSHR expression in the ovary, were found to contain 14-3-3tau. Importantly, 14-3-3tau co-immunoprecipitated with FSHR stably expressed in HEK 293 cells. Its association with FSHR was follitropin-dependent. Over-expression of 14-3-3tau resulted in a modest decrease of follitropin-induced cAMP accumulation. Collectively, these data support a role for 14-3-3tau in follitropin action. The finding that 14-3-3tau interacts with FSHR is novel and should lead to new insights into the regulation of GPCR in general and FSHR specifically.

Antiequine chorionic gonadotropin (eCG) antibodies generated in goats treated with eCG for the induction of ovulation modulate the luteinizing hormone and follicle-stimulating hormone bioactivities of eCG differently

In dairy goats, treatments associating a progestogen and the equine chorionic gonadotropin (eCG) are the easiest way to induce and synchronize estrus and ovulation and to permit artificial insemination (AI) and/or out of season breeding. From the first treatment, the injection of eCG induces, in some females, the production of anti-eCG antibodies (Abs) that will interfere with the effectiveness of subsequent treatments. These anti-eCG Abs delay the preovulatory LH surge and the ovulation time, leading to poor fertility of the treated females. In this study, by in vitro bioassays, we show that anti-eCG Abs can positively or negatively modulate the LH and/or FSH bioactivities of eCG. Moreover, the modulation level of eCG bioactivity does not depend on the anti-eCG Ab affinity for eCG, as shown by surface plasmon resonance technology. The specificity of anti-eCG Abs tested by competitive ELISA highlighted the importance of a glycan environment in the recognition mechanism, especially the sialic acids specific to eCG. The different effects of anti-eCG Abs on eCG bioactivities could be explained by two hypotheses. First, steric hindrance preventing the interaction of eCG with its receptors would explain the inhibitory effect of some anti-eCG Abs; second, a conformational change in eCG by anti-eCG Abs could induce inhibition or potentiation of eCG bioactivities. It is significant that these modulations of eCG bioactivities by anti-eCG Abs impact mainly on the FSH bioactivity of eCG, which is essential for ovarian stimulation and subsequent fertility after treatment and AI, and to a lesser extent on LH bioactivity.

Point mutations in follitropin receptor result in ER retention

Accumulating evidence suggests that the human follitropin receptor is unusually sensitive to mutation. Previous results (Mol. Cell. Endo. 166 (2000) 101) determined that scanning mutations in a.a. 12-14 and 22-30 neither bound follitropin nor were present on the cell surface, suggesting that these regions are involved in either hormone binding or trafficking. To distinguish between these hypotheses, single alanine substitutions in a.a. 12-14 and 22-30 were generated, all of which appeared to bind 125I-follitropin with an affinity constant similar to wild type (wt) follitropin receptor. However, the level of receptor on the cell surface varied widely, in some cases 100-fold lower than wt. Expression on the cell surface corresponded to expression of the mature 80 kD follitropin receptor. An accumulation of the ER-resident 62 kD band of follitropin receptor was observed in mutants that had low surface expression of receptor, suggesting that misfolded protein was trapped in the ER by a quality control mechanism.

Signal transduction pathways activated by chorionic gonadotropin in the primate endometrial epithelial cells

Successful implantation requires synergism between the developing embryo and the receptive endometrium. In the baboon, infusion of chorionic gonadotropin (CG) modulates both morphology and physiology of the epithelial and stromal cells of the receptive endometrium. This study explored the signal transduction pathways activated by CG in endometrial epithelial cells from baboon (BE) and human (HES). Incubations of BE and HES cells with CG did not significantly alter adenylyl cyclase activity or increase intracellular cAMP when compared with Chinese hamster ovarian cells stably transfected with the full-length human CG/luteinizing hormone (LH) receptor (CHO-LH cells). However, in BE and HES cells, CG induced the phosphorylation of several proteins, among them, extracellular signal-regulated protein kinases 1 and 2 (ERK 1/2). Phosphorylation of ERK 1/2 in uterine epithelial cells was protein kinase A (PKA) independent. This novel signaling pathway is functional because, in response to CG stimulation, prostaglandin E(2) (PGE(2)) was released into the media and increased significantly 2 h following CG stimulation. CG-stimulated PGE(2) synthesis in epithelial cells was inhibited by a specific mitogen-activated protein kinase (MEK 1/2) inhibitor, PD 98059. In conclusion, immediate signal transduction pathways induced by CG in endometrial epithelial cells are cAMP independent and stimulate phosphorylation of ERK 1/2 via a MEK 1/2 pathway, leading to an increase in PGE(2) release as the possible result of cyclooxygenase-2 activation.

Development and characterization of a long-acting recombinant hFSH agonist

BACKGROUND

Fusion of the carboxyterminal peptide (CTP) of hCG to FSH results in a follitropin agonist with an extended half-life, presumably due to the four O-oligosaccharides on the CTP. Alternatively, an rhFSH analogue containing additional N-linked carbohydrate is described in this report.

METHODS

A DNA sequence containing two N-oligosaccharide signal sequences was ligated into a vector containing hFSHbeta- and alpha-subunit encoding cDNA, and expressed in CHO-K1 cells. In-vitro bioactivity of the single-chain hormone was assessed in CHO cells expressing the hFSH receptor. Pharmacokinetic values were derived from serial serum assays of the analogue in immature female rats following a single i.v. injection. In-vivo bioactivity was assessed by measuring ovarian weight gain 3 days post-injection.

RESULTS

rhFSH-N2 and native rhFSH induced comparable levels of cAMP in vitro. t(1/2) for native rhFSH, rhFSH-CTP and rhFSH-N2 were 3.7, 7.1 and 7.3 h respectively. Rats receiving rhFSH-N2 had a mean +/- SD ovarian weight 3 days post-i.v. injection (22 +/- 3.6 mg) significantly greater than rats receiving rhFSH and saline (16.7 +/- 1.5 and 15.3 +/- 0.47 mg respectively, P < 0.05).

CONCLUSIONS

rhFSH-N2 has prolonged half-life and increased bioactivity compared with native rhFSH. This rhFSH agonist, and other analogues containing additional N-oligosaccharides may have important clinical applications.

Intact follicle culture: what it can tell us about the roles of FSH glycoforms during follicle development

An important limiting factor in assisted reproduction treatment success rates is oocyte quality. In spite of improved results through several important innovations, the pregnancy rate per collected oocyte remains far too low. In order to improve this situation, it is necessary to learn more about fundamental factors modulating follicular development patterns. FSH is known to be the driving force for follicle development, but it is not yet understood how its multifarious functions are controlled and modulated. Evidence is accumulating that FSH glycoforms may be the key to this mystery. Intact follicle culture is a useful tool for the clarification of the actions of the different isoforms because the follicle unit is maintained and allowed to develop through several critical stages. Additionally important is the availability of the oocyte for functional evaluation. Because of these features, relationships can be uncovered that are not revealed with single cell test systems. The results so far obtained with this system suggest that follicle development pattern and oocyte quality is strongly influenced by FSH glycoform range, and that the requirements of the follicle may shift during progress through different stages of development. More studies are required, but these findings already suggest that the physiological shifts of circulating FSH glycoforms may indeed be important, and that attention should be paid to the glycoform distribution of exogenously applied FSH.

Structure and expression of the follicle-stimulating hormone receptor gene in a marsupial, Macropus eugenii

Follicle stimulating hormone (FSH) is essential for folliculogenesis. The function of FSH is mediated through its receptor (FSHr) and modulation of the receptor is thought to be the mechanism by which the responsiveness of follicles to gonadotrophins is regulated. FSHr is alternatively spliced to produce several transcripts in all eutherian species studied. However, controversy exists over the significance of alternatively spliced transcripts. In this study, we cloned and characterised the tammar wallaby (Macropus eugenii) FSHr gene and examined its expression. Comparison of gene structure and function between marsupials and eutherians enables identification of conserved features that are likely to be of functional significance. Tammar FSHr shares 94% amino acid similarity with human FSHr and is expressed in both the adult testis and ovary suggesting a similar function for this gene in both marsupials and eutherians. Tammar FSHr undergoes alternate splicing to produce four transcripts consistent with the splice variants seen in eutherians. These results strongly suggest that alternate splicing is of functional significance in the ovary since it has remained a highly conserved character of this gene for over 100 million years of divergent evolution.

Ovarian expression of messenger RNA encoding the receptors for luteinizing hormone and follicle-stimulating hormone in a marsupial, the brushtail possum (Trichosurus vulpecula)

Both LH and FSH play a central role in controlling ovarian function in mammals. However, little is known about the type of ovarian cells that are responsive to LH and FSH in marsupials. We determined, using in situ hybridization, the localization of mRNA encoding the receptors (R) for LH and FSH in ovaries of brushtail possums. The mRNA encoding FSH-R was observed in granulosa cells of healthy follicles containing at least two complete layers of cells. The mRNA encoding LH-R was first observed in granulosa cells at the time of antrum formation. Cells of the theca interna expressed LH-R mRNA but not FSH-R mRNA. Neither FSH-R nor LH-R mRNA was detected in atretic follicles. Both FSH-R and LH-R mRNAs were observed in luteal tissue, but only LH-R mRNA was observed in interstitial cells. Granulosa cells from follicles of various sizes (0.5 to >2 mm in diameter) responded to LH and FSH treatment with an increase in cAMP synthesis. In contrast, luteal tissue did not respond to either FSH or LH treatment. In conclusion, expression of FSH-R in the brushtail possum ovary was similar to that observed in many eutherian mammals. However, active LH-R was expressed in granulosa cells much earlier in follicular development than has been previously observed. In addition, although mRNAs for both FSH-R and LH-R were observed, neither FSH nor LH treatment stimulated cAMP synthesis in luteal tissue.

Molecular, structural, and cellular biology of follitropin and follitropin receptor

Follitropin and the follitropin receptor are essential for normal gamete development in males and females. This review discusses the molecular genetics and structural and cellular biology of the follitropin/follitropin receptor system. Emphasis is placed on the human molecules when possible. The structure and regulation of the genes for the follitropin beta subunit and the follitropin receptor is discussed. Control of systemic and cellular protein levels is explained. The structural biology of each protein is described, including protein structure, motifs, and activity relationships. Finally, the follitropin/follitropin receptor signal transduction system is discussed.

Structural determinants in the second intracellular loop of the human follicle-stimulating hormone receptor are involved in G(s) protein activation

In the present study, we analyzed the structural determinants present in the second intracellular loop (IL-2) of the human follicle-stimulating hormone (FSH) receptor (R) involved in G(s) protein-mediated signal transduction. Human embryonic kidney 293 (HEK-293) cells, stably expressing wild-type (Wt) human FSHR (HEK-293((+))), were transiently transfected with plasmids containing cDNAs encoding the entire IL-2 or several IL-2 sequences mutated in R467 (a residue located at the center of the conserved ERW motif in the glycoprotein hormone receptors), T470 (a potential site for phosphorylation by protein kinase-A and -C) or L477 (a residue conserved in all glycoprotein hormone receptors). Expression of the IL-2 Wt in HEK-293((+)) cells reduced the maximum FSH-stimulated cAMP production significantly by approximately 40%; similar results were observed with the R467A and R467K IL-2 mutants. The IL-2(R467H), IL-2(T470A), the triple R467A/T470A/L477A IL-2 mutant and the IL-2 of the oxytocin receptor (G(q/11)-coupled) had no effects on Wt FSHR-mediated intracellular signaling whereas the L477A mutation provoked a higher ( approximately 55%) inhibition of FSH-stimulated cAMP than the free, Wt IL-2. These results suggested a specific role of IL-2 residues in FSHR function. Site directed mutagenesis of the FSHR and the expression of resulting mutants in HEK-293 cells were performed in order to corroborate the effects of these substitutions. Expression of FSHR(R467H), FSHR(R467A) and FSHR(T470A) failed to mediate ligand-provoked G(s) protein activation, whereas the R467K mutant behaved as the Wt receptor. Interestingly, the expression of L477A, L477D and L477P FSHR mutants conferred elevated basal cAMP levels to HEK-293 cells. This study indicates that the IL-2 of the human FSHR possesses amino acid residues that are important for both coupling the receptor to the G(s) protein (R467 and T470) and maintaining the receptor molecule in an inactive conformation (L477). It appears that this particular intracellular domain may act as a conformational switch to produce the activation of G proteins as has been reported for the IL-2 of other G protein-coupled receptors.

Synthesis of (bis)sulfonic acid, (bis)benzamides as follicle-stimulating hormone (FSH) antagonists

Screening efforts identified (bis)sulfonic acid, (bis)benzamides (1-3) as compounds that interact with the follicle stimulating-hormone receptor (FSHR) and inhibit FSH-stimulated cAMP accumulation with IC(50) values in the low micromolar range. Structure-activity relationship studies using novel analogues of 1-3 revealed that two phenylsulfonic acid moieties were necessary for activity and that the carbon-carbon double bond of the stilbene sub-series was the optimum spacer connecting these groups. Selected analogues (2, 14, and 50) were also able to block FSHR-dependent estradiol production in rat primary ovarian granulosa cells and progesterone secretion in a clonal mouse adrenal Y1 cell line. IC(50) values for these compounds in these assays were in the low micromolar range. Optimization of the benzoic acid side chains of 1-3 led to gains in selectivity versus activity at the thyroid stimulating hormone (TSH) receptor (TSHR). For instance, while stilbene (bis)sulfonic acid congener 2 was only 10-fold selective for FSHR over TSHR, analogue 50 with an IC(50) value of 0.9 microM in the FSHR-cAMP assay was essentially inactive at 30 microM in the TSHR-cAMP assay.