Autoimmunity to the Follicle-Stimulating Hormone Receptor (FSHR) and Luteinizing Hormone Receptor (LHR) in Polycystic Ovarian Syndrome

Hyperandrogenemia and ovulatory dysfunction are hallmarks of polycystic ovary syndrome (PCOS), pointing to a deranged hypothalamus-pituitary-ovarian (HPO) axis. An autoimmune etiology of PCOS is suspected in a subset of patients due to the relatively high concordance of PCOS with common autoimmune diseases. For this reason, we tested the hypothesis that natural autoantibodies (aAb) to the follicle-stimulating hormone receptor (FSHR) or luteinizing hormone receptor (LHR) are prevalent in PCOS. To this end, new luminometric assays for quantifying aAb to the FSHR (FSHR-aAb) or LHR (LHR-aAb) were developed using full-length recombinant human receptors as fusion proteins with luciferase as reporter. Prevalence of FSHR-aAb and LHR-aAb was determined in serum samples from healthy controls and PCOS patients. Steroid hormone profiles were compared between patients with and without FSHR-aAb or LHR-aAb. Signal linearity and detection ranges were characterized and both methods passed basic performance quality checks. The analysis revealed a relatively low prevalence, with 4 out of 430 samples positive for FSHR-aAb in the control versus 11 out of 550 samples in the PCOS group, i.e., 0.9% versus 2.0%, respectively. Similarly, there were only 5 samples positive for LHR-aAb in the control versus 2 samples in the PCOS group, i.e., 1.2% versus 0.4%, respectively. Samples positive for FSHR-aAb displayed steroid hormones in the typical range of PCOS patients, whereas the two samples positive for LHR-aAb showed relatively elevated free testosterone in relation to total testosterone concentrations with unclear significance. We conclude that the FSHR and LHR constitute potential autoantigens in human subjects. However, the prevalence of specific autoantibodies to these receptors is relatively low, both in control subjects and in women with PCOS. It is therefore unlikely that autoimmunity to the LHR or FSHR constitutes a frequent cause of hyperandrogenemia or ovulatory dysfunction in PCOS.

Three-Dimensional Genome Interactions Identify Potential Adipocyte Metabolism-Associated Gene STON1 and Immune-Correlated Gene FSHR at the rs13405728 Locus in Polycystic Ovary Syndrome

Background

rs13405728 was identified as one of the most prevalent susceptibility loci for polycystic ovary syndrome (PCOS) in Han Chinese and Caucasian women. However, the target genes and potential mechanisms of the rs13405728 locus remain to be determined.

Methods

Three-dimensional (3D) genome interactions from the ovary tissue were characterized via high-through chromosome conformation capture (Hi-C) and Capture Hi-C technologies to identify putative targets at the rs13405728 locus. Combined analyses of eQTL, RNA-Seq, DNase-Seq, ChIP-Seq, and sing-cell sequencing were performed to explore the molecular roles of these target genes in PCOS. PCOS-like mice were applied to verify the expression patterns.

Results

Generally, STON1 and FSHR were identified as potential targets of the rs13405728 locus in 3D genomic interactions with epigenomic regulatory peaks, with STON1 (P=0.0423) and FSHR (P=0.0013) being highly expressed in PCOS patients. STON1 co-expressed genes were associated with metabolic processes (P=0.0008) in adipocytes (P=0.0001), which was validated in the fat tissue (P<0.0001) and ovary (P=0.0035) from fat-diet mice. The immune system process (GO:0002376) was enriched in FSHR co-expressed genes (P=0.0002) and PCOS patients (P=0.0002), with CD4 high expression in PCOS patients (P=0.0316) and PCOS-like models (P=0.0079). Meanwhile, FSHR expression was positively correlated with CD4 expression in PCOS patients (P=0.0252) and PCOS-like models (P=0.0178). Furthermore, androgen receptor (AR) was identified as the common transcription factor for STON1 and FSHR and positively correlated with the expression of STON1 (P=0.039) and FSHR (P=4e-06) in ovary tissues and PCOS-like mice.

Conclusion

Overall, we identified STON1 and FSHR as potential targets for the rs13405728 locus and their roles in the processes of adipocyte metabolism and CD4 immune expression in PCOS, which provides 3D genomic insight into the pathogenesis of PCOS.

Follicle-stimulating hormone receptors: A comparison of commercially-available monoclonal and polyclonal antibodies as immunohistochemical markers for cancer research

PURPOSE

In recent studies, follicle-stimulating hormone receptors (FSHRs) have been reported in a wide range of malignant and benign tumours, depending on the type of antibody used. Using two commercially available antibodies (monoclonal and polyclonal), the current research attempted to demonstrate the usefulness of each antibody for investigating FSHRs in non-canonical tissues. Further, we sought to replicate the results of a major study which demonstrated the presence of FSHRs in the endothelial cells of perineoplastic blood vessels.

METHODS

Immunostaining was performed on 16 surgically excised benign and malignant tumor tissue samples using both monoclonal and polyclonal anti-FSHR antibodies.

RESULTS

Positive staining of FSHRs was heterogeneous among the tissue samples used for analysis, and was confirmed not only in tumour and endothelial cells of perineoplastic blood vessels, but also in benign and normal cells. Based on our findings, FSHR staining using a polyclonal antibody appeared to be highly sensitive, but with a relatively low specificity. Comparatively, immunoreactivity using a monoclonal antibody appeared to show high specificity, but relatively low sensitivity. Although the selected monoclonal antibody for FSHRs seemed to be more specific than the polyclonal variant, neither exhibited a high overall specificity. Neither of the antibodies assessed in the present research could replicate the results of the aforementioned major study.

CONCLUSIONS

In conclusion, neither of the two commercially available antibodies seem to be appropriate for investigating FSHRs in non-canonical tissues and, by extension, their role in carcinogenesis.

Vascular Endothelial FSH Receptor, a Target of Interest for Cancer Therapy

Improved molecular understanding of tumor microenvironment has resulted in the identification of various cancer cell targets for diagnostic and therapeutic interventions, including the receptor for the FSH, a glycoprotein hormone responsible for growth, maturation, and function of human reproductive system. The expression and localization of the FSH receptor (FSHR)-protein were associated with the tumor epithelial cells and/or with the peripheral tumor blood vessels. The available evidence indicates that in ovarian cancer, prostate cancer, and breast cancer, the tumor epithelial FSHR promotes proliferation, migration, and invasion of cancer cells. The vascular endothelial FSHR, detected in 11 types of solid tumors and 11 types of sarcomas, is involved in receptor-mediated transendothelial transport of FSH, tumor angiogenesis, and vascular remodeling. In contrast to intratumor vessels, which are abnormal and disorganized, the FSHR-positive blood microvessels are arranged in a hierarchical pattern: arterioles-capillaries-venules. The FSHR-positive blood vessels make connections between the intratumor vessels and the general blood circulation of patients. In this mini-review, I summarize these studies and discuss the rationale for developing a strategy for cancer therapy based on FSHR expressed on the luminal endothelial cell surface of blood vessels located in the peritumoral area rather than endothelial markers expressed in the core of tumors. Because FSHR is a common marker of peritumoral vessels, therapeutic agents coupled to anti-FSHR humanized antibodies should in principle be applicable to a wide range of tumor types.

[Preparation and identification of anti-follicle-stimulating hormone receptor nanobodies]

OBJECTIVE

To prepare camel derived nanobodies which specifically bind to follicle-stimulating hormone receptor (FSHR).

METHODS

The FSHR gene fragment (fshr234) was expressed in E.coli as antigen for affinity screening against VHH phage display library constructed from Xinjiang Bactrian camel. After confirmed by DNA sequencing, the vhh gene fragments of interest were subcloned into pET30a expression vector, and then were used to transform E.coli BL21(DE3). After IPTG induction, 6×His and c-Myc tagged fusion nanobodies were expressed. The nanobodies were purified by Ni-ion affinity chromatography. The binding specificity of nanobodies with His-FSHR234 was determined by ELISA.

RESULTS

By enrichment screening with the antigen His-FSHR234, the 28 clones showed VHH sequence identities in DNA sequencing from 40 randomly selected binding clones. The 4 clones were subcloned into pET30a vector and confirmed as expected size of inserts by PCR and endonuclease digestion. The 4 expressed and affinity purified recombinant nanobodies namely VHHFSHR;-06, VHHFSHR;-25, VHHFSHR;-30 and VHHFSHR;-50 showed single band at Mr; 31 000, 26 000, 25 000 and 26 000 on SDS-PAGE, respectively. ELISA results showed that 4 nanobodies could bind to FSHR234 specifically, in which VHHFSHR;-06 showed the highest antigen binding activity.

CONCLUSION

By screening camel VHH phage display library with His-FSHR234 antigen, one nanobody, VHHFSHR;-06 with relatively high antigen binding activity has been produced and identified.

Expression of follicle-stimulating hormone receptor in tumor blood vessels

BACKGROUND

In adult humans, the follicle-stimulating hormone (FSH) receptor is expressed only in the granulosa cells of the ovary and the Sertoli cells of the testis. It is minimally expressed by the endothelial cells of gonadal blood vessels.

METHODS

We used immunohistochemical and immunoblotting techniques involving four separate FSH-receptor-specific monoclonal antibodies that recognize different FSH receptor epitopes and in situ hybridization to detect FSH receptor in tissue samples from patients with a wide range of tumors. Immunoelectron microscopy was used to detect FSH receptor in mouse tumors.

RESULTS

In all 1336 patients examined, FSH receptor was expressed by endothelial cells in tumors of all grades, including early T1 tumors. The tumors were located in the prostate, breast, colon, pancreas, urinary bladder, kidney, lung, liver, stomach, testis, and ovary. In specimens obtained during surgery performed to remove tumors, the FSH receptor was not expressed in the normal tissues located more than 10 mm from the tumors. The tumor lymphatic vessels did not express FSH receptor. The endothelial cells that expressed FSH receptor were located at the periphery of the tumors in a layer that was approximately 10 mm thick; this layer extended both into and outside of the tumor. Immunoelectron microscopy in mice with xenograft tumors, after perfusion with anti–FSH-receptor antibodies coupled to colloidal gold, showed that the FSH receptor is exposed on the luminal endothelial surface and can bind and internalize circulating ligands.

CONCLUSIONS

FSH receptor is selectively expressed on the surface of the blood vessels of a wide range of tumors. (Funded by INSERM.).

A novel dominant B-cell epitope of FSHR identified by molecular docking induced specific immune response and suppressed fertility

The follicle stimulating hormone (FSH) is of great importance in reproduction modulation of both sexes. The extracellular domain (ECD) of its receptor (FSHR) is crucial for FSH binding and subsequent signal transduction; therefore, it is the potential target for fertility control. To avoid unwanted side-effect when used as immunocontraceptive agent, the ECD was analysed by online prediction combined with molecular docking to identify the candidate B-cell epitopes. Four potential B-cell epitopes were identified and synthesised in tandem with Pan DR epitope. Then the epitope-based peptides were used to boost adult male mice following rhFSHR protein priming, thus to determine their immune responses and fertility inhibition capacity. Three of the four peptides showed suppressed fertility accompanied with small testis and lower serum testosterone level, which was consistent with absolutely lower sperm quantity and poor quality. Among the four epitope peptides, Pep2 displayed the lowest fertility rate of 26.67%, which was similar to that of rhFSHR homologously prime/boost mice (23.30 and 25.00%). Thus, we identified a novel immunodominant B-cell epitope by molecular docking and protein prime/peptide boost strategy.

Identification of the region 285–309 of follicle stimulating hormone receptor as a bioneutralizing epitope

Structure-function relationship studies of the follicle stimulating hormone and its receptor assume importance as this hormone is essential for folliculogenesis and spermatogenesis in females and males, respectively. The interaction between the hormone and the receptor is complex and not well understood. In vitro studies using synthetic peptides from the extracellular domain of the receptor and corresponding antipeptide antibodies have suggested that the 285-309 region is surface-oriented. Antipeptide antibodies to this region also inhibit hormone-receptor interaction in a dose-dependent manner and the mechanism of inhibition appears to be competitive in nature. To test this hypothesis in an animal model, antibodies to peptide 285-309 from rat follicle stimulating hormone receptor (FSHR) were developed and characterized. These antibodies were able to detect FSHR in rat ovaries by immunohistochemistry. Further, these antibodies were administered into adult female rats and their effect on fertility status was monitored. These antibodies were found to neutralize the biological activity of endogenous receptor, which resulted in the induction of infertility in the treated animals. Thus, bioneutralization of FSHR has been achieved by targeting its region 285-309 in an in vivo system.

Detailed analysis of the region 9-30 of rat follicle stimulating hormone receptor: identification of peptide 20-30 as a potential hormone binding inhibitor

The extracellular domain (ECD) of the follicle stimulating hormone receptor (FSHR) has been shown to be a major determinant of hormone selectivity. The N-terminal 9-30 region, the sequence of which is unique to FSHR, has been extensively studied earlier and has been proposed to be an FSHR neutralizing epitope. In this study antipeptide antibodies specific to the peptide 9-30 were generated and used for identifying a specific immunodominant region within it. Overlapping peptides corresponding to the regions 9-19, 15-25 and 20-30 were synthesized. The ability of the antipeptide antibodies to 9-30 of FSHR to bind to different peptides was checked. The results indicated that the antibodies mainly recognized the peptide 20-30 and not the other two overlapping peptides. Further, the effect of the peptide 20-30 on the binding of radiolabeled FSH to its receptor was monitored. This peptide showed FSH-binding inhibitory activity with an IC(50) value of 0.598 x 10(-4)M and was more effective than the peptide 9-30 itself. Binding kinetics revealed that the observed effect of the peptide 20-30 is due to mixed type of inhibitory mechanism. This is the smallest peptide from the rat FSHR sequence having ability to inhibit FSH binding to its receptor by more than 90%.

Effects of a thyroid-stimulating human monoclonal autoantibody (M22) on functional activity of LH and FSH receptors

OBJECTIVE

The glycoprotein hormones luteinizing hormone (LH), follicle-stimulating hormone (FSH), and thyrotropin (TSH) show low-level cross-reactivity between their respective receptors (R). Patient serum autoantibodies to the thyrotropin receptor (TSHR) do not appear to cross-react with the luteinizing hormone receptor (LHR) or follicle-stimulating hormone receptor (FSHR), although the concentrations of autoantibody with which it is feasible to carry out experiments of this type are limited. Consequently, we have studied the effects of high doses of the thyroid-stimulating human monoclonal autoantibody (M22) on the LHR and FSHR.

DESIGN

Chinese Hamster ovary (CHO) cells stably expressing the TSHR, LHR, and FSHR and purified M22 IgG preparations were used in the study.

METHODS

CHO-TSHR, CHO-LHR, and CHO-FSHR cells were incubated with bovine TSH (0.1-25mU/mL), human recombinant chorionic gonadotropin (hCG; 0.5-10mU/mL) or human recombinant FSH (100-5000mU/mL) or with M22 IgG (0.001-5.0 microg/mL), and the extracellular cyclic AMP was measured by radioimmunoassay.

RESULTS

Cyclic AMP levels increased in a dose-dependent manner after incubation of CHO-TSHR cells with TSH or M22 IgG, and on a molar basis the effects of TSH and M22 were similar. Cyclic AMP stimulation was not detectable in CHO-LHR and CHO-FSHR cells after incubation with M22 IgG, whereas incubation with hCG or FSH, respectively, caused dose-dependent cyclic AMP stimulation. On a molar basis, concentrations of M22 IgG approximately 100x those of FSH causing clear stimulation were ineffective with CHO-FSHR cells. Similarly, molar concentration of M22 IgG 20,000x those of hCG causing clear stimulation had no effect on CHO-LHR cells.

CONCLUSIONS

This study shows that at relatively high concentrations, M22 IgG is unable to stimulate cyclic AMP levels in CHO-LHR or CHO-FSHR cells, suggesting that TSHR autoantibodies have greater specificity for the TSHR than TSH itself.

Follicle-stimulating hormone receptor in felids: intra- and interspecies variation

Assisted reproductive technologies are increasingly applied to support breeding efforts for many endangered felids. To explain the highly variable responses among felids to exogenous gonadotropins (FSH, eCG), we analyzed a 567bp fragment spanning a hyper-variable region of the FSH receptor in the domestic cat (catFSHR) and nine wild felid species/subspecies (felFSHR). Phylogenetic analysis indicated that the newly sequenced felFSHRs, together with the bear FSHR, belong to the carnivore group closely related to the ungulate clade. Within Felidae, genetic distances were 0.0089 +/- 0.0018 for nucleotide and 0.0183 +/- 0.0044 for amino acid (aa) sequences. In pairwise comparisons among catFSHR and all new felFSHRs, similarity ranged from 98.6 to 99.5% for nucleotides and from 97.4 to 98.9% for aa. Besides interspecies variability, intraspecies variation was also detected on both the cDNA and the protein level. There were no indications for an expression of tissue-specific isoforms of FSHR in testis and ovary.

Evaluation of the role of FSH in regulation of Leydig cell function during different stages of its differentiation

The role of follicle stimulating hormone (FSH) in Leydig cell function was evaluated by a passive neutralization approach at different stages of Leydig cell development. Neutralization of endogenous FSH in neonatal rats (10-day-old) resulted in reduction of testes weight, however the testicular testosterone levels and in vitro testosterone production by purified Leydig cells were elevated. Administration of FSH antiserum to immature (25-28-day-old) and adult (90-day-old) rats did not have any effect on testes weight, serum testosterone and testicular testosterone. Interestingly, there was a significant reduction in testosterone production by isolated Leydig cells under hCG stimulated and 22-R-hydroxycholesterol (22-R-OH CHOL) saturated conditions. In support of this observation administration of recombinant FSH to immature and adult rats resulted in significant increase in testosterone production by Leydig cells following incubations in presence of hCG and saturating concentrations of 22-R-OH CHOL, although there was no change in serum and testicular testosterone levels. The role of FSH in immature rats was also confirmed employing FSH receptor antiserum which was raised against the unique domains of FSH receptor. RT-PCR analysis revealed a significant reduction in the mRNA levels of StAR and IGF-1 following blockade of FSH action by FSH receptor antiserum. The results of our studies suggest a stage specific function for FSH in regulation of Leydig cell development by modulating the LH responsiveness and steroidogenesis.

Myasthenia gravis and premature ovarian failure

We describe a patient who developed seropositive myasthenia gravis 16 years after she was diagnosed with autoimmune premature ovarian failure with antibodies to the receptor for follicle-stimulating hormone (FSH). Although thymectomy led to improvement of her myasthenic symptoms, menses did not resume. Such combined seropositivity for antibodies to acetylcholine and ovarian hormone receptors in a patient with myasthenia gravis and premature ovarian failure may reflect common disease mechanisms, although the precise pathogenesis of these disorders remains ill-defined.

TSH receptor antibodies do not alter the function of gonadotropin receptors stably expressed in eukaryotic cells

OBJECTIVE

TSH receptor (TSHr) mediates the activating action of TSH on the thyroid gland resulting in the growth and proliferation of thyrocytes and thyroid hormone production. TSHr is a major autoantigen in Graves' disease (GD) and is the target for TSHr antibodies. In GD, thyroid-stimulating antibodies (TSAb) are competitive agonists of TSH. In atrophic thyroiditis (AT), thyroid-stimulating blocking antibodies (TSHBAb) are TSH antagonists. The TSHr together with the LH receptor (LHr) and FSH receptor (FSHr) are G-protein-coupled receptors with considerable amino acid homologies in the extracellular domain. We studied the cross-reactivity of the antibodies measured in sera from patients with GD or AT on the LHr and FSHr function.

METHODS

We tested the activity of TSAb and TSHBAb in cell lines expressing the LHr and the FSHr. To this purpose a pSVL-FSHr construct was transfected in CHO cells and one clone was used.

RESULTS

Twenty-eight sera from patients with GD and four from patients with AT, known to contain TSHr antibodies measured with a radioreceptor assay, were selected. TSAb and TSHBAb activities were measured in CHO cells expressing the TSHr (CHO-TSHr). TSAb and TSHBAb were then tested with the cell lines expressing the LHr and the FSHr for their ability to elicit cAMP accumulation or inhibit FSH/LH-induced cAMP production. None of the TSAb identified was able to stimulate cAMP increase in CHO-LHr or CHO-FSHr. Similarly, none of the TSHBAb was able to block the cAMP response induced by FSH or LH in the respective cell lines.

CONCLUSIONS

Our results confirm the notion of the organ-specific nature of the TSHr antibodies.

Peptide vaccines in immunocontraception

Vaccines have been used successfully to treat and eradicate infectious diseases; this has encouraged a major drive towards development of contraceptive vaccines (immunocontraception) as an additional method against rising human and animal populations. Despite three decades worth of research in this field, there are no licensed human contraceptive vaccines and less than ten for use in animals. The development of peptide antifertility vaccines has had a substantial impact on improving safety and specificity of immunogens, but has resulted in efficacy problems. Innovative strategies have been developed to overcome these problems.

Induction of infertility in adult male bonnet monkeys by immunization with phage-expressed peptides of the extracellular domain of FSH receptor

Active immunization of proven fertile adult male bonnet monkeys (Macaca radiata) with phage-expressed follicle-stimulating hormone receptor (FSHR)-specific peptides from the extracellular domain resulted in a progressive drop in sperm count with all animals becoming azoospermic by day 100. However, serum testosterone concentrations were unaltered during the entire course of study and animals exhibited normal mating behaviour. Breeding studies with proven fertile female monkeys revealed that all the immunized males were infertile. Following interruption of immunization on day 225, sperm counts returned to normal with restoration of fertility. These results indicate that infertility can be induced in adult male monkeys by interfering with the action of FSH using specific peptides of the extracellular domain of FSHR as antigens, without the risk of producing cross-reacting antibodies to the other glycoprotein hormones.

Maintenance of sexual immaturity in male mice and bucks by immunization against N-terminal peptides of the follicle-stimulating hormone receptor

The follicle-stimulating hormone is one of the two pituitary hormones that control fertility in both sexes. In the male, receptors for FSH (FSHR) are only expressed on testicular Sertoli cells. FSH plays different roles during the male life; it functions as a growth factor during development and sustains spermatogenesis in adults. However, the exact role of this hormone as an initiator of male fertility is not fully understood and few data are available concerning its involvement during the peripubertal period. We recently produced filamentous phages displaying FSHR fragments overlapping residues 18-38, which, if injected in animals, induced anti-FSH receptor immunity capable of inhibiting hormone binding. We employed this strategy to transiently inhibit FSH activity in male mice and male goats of the Saanen and the Mongolian Alpas Cashmere breeds at the prepubertal stage. Anti-FSHR peptide immunization from the age of 3 wk delayed the acquisition of fecundity in male mice by up to 1 wk. Once fertile, progeny sizes produced by mating immunized males and untreated females were found to be reduced by up to 60%. In two different breeds of goats, FSHR peptide vaccines were able to maintain circulating testosterone at low prepubertal levels for several months despite no alteration in LH levels, reflecting their ability to delay the onset of puberty. These results support the conclusion that FSH may play a central role in the male at puberty through the control of testosterone production.

Hormone-induced conformational change of the purified soluble hormone binding domain of follitropin receptor complexed with single chain follitropin

Human follicle-stimulating hormone receptor (hFSHR) belongs to family I of G protein-coupled receptors. FSHR extracellular domain (ECD) is predicted to have 8-9 alphabeta or leucine-rich repeat motif elements. The objective of this study was to identify elements of the FSHR ECD involved in ligand binding. Preincubation of recombinant hFSHR ECD with rabbit antisera raised against synthetic peptides of hFSHR ECD primary sequence abolished follitropin binding primarily in the region of amino acids 150-254. Accessibility of hFSHR ECD after hormone binding, captured by monoclonal antibodies against either ECD or FSH, was decreased for the region of amino acids 150-220 but additionally for amino acids 15-100. Thus, when hFSH bound first, accessibility of antibody binding was decreased to a much larger extent than if antibody was bound first. This suggestion of a conformational change upon binding was examined further. Circular dichroism spectra were recorded for purified single chain hFSH, hFSHR ECD, and hFSHR ECD-single chain hFSH complex. A spectral change indicated a small but consistent conformational change in the ECD.FSH complex after hormone binding. Taken together, these data demonstrate that FSH binding requires elements within the leucine-rich repeat motifs that form a central region of hFSHR ECD, and a conformational change occurs upon hormone binding.

Reversible immunoneutralization of human follitropin receptor

Investigations of the human Follitropin receptor (hFSHR) have failed to identify the tertiary structure that forms the active hormone-receptor interaction site which is essential to develop an immunocontraceptive based upon the receptor. To identify such a domain of hFSHR, an immunoneutralizing monoclonal antibody (mAb) 106-105 (IgG2b) was generated. Flow cytometry tested whether mAb 106-105 recognized native hFSHR. The epitope of mAb 106-105 was mapped by Western blot and by peptide ELISA. Inhibition of hFSH binding and bioactivity was determined by radioreceptor assay and by cAMP production, respectively. MAb 106-105 bound native hFSHR through an epitope including residues 300-315. MAb 106-105 completely blocked hormone binding to receptor and cAMP production by Y1-R cells expressing hFSHR. These effects were completely reversible by increasing the concentration of hFSH. Coincubation of this antibody with peptide D300-F315 blocked antibody activity. These data demonstrate that a discrete linear hFSHR epitope is a target for interference with hormone activity. These results further demonstrate that antibody binding to the extracellular domain (ECD) of hFSHR and subsequent bioactivation can be modulated through a domain specific hindrance, offering a reversible immunoneutralizing target.

A follicle-stimulating hormone receptor ecto-domain epitope that is a target for receptor immunoneutralization yet does not affect ligand contact and activation

The follicle-stimulating hormone receptor (FSHR) large extracellular domain suggests that interaction of ligand with receptor is likely to be complex. Residues 265-296 of the FSHR are part of a sequence primarily nonhomologous with other glycoprotein hormone receptors. A reasonable hypothesis is that this sequence of the FSHR plays a role in binding FSH. Flow cytometry studies of this region revealed that antibody X179 against peptide R265-S296 binds to human FSHR expressed by CHO cells and can be competed against by preincubating the cells with hFSH. These results suggested that the region corresponding to residues 265-296 in the extracellular domain of the FSHR is involved in binding to hormone. To test this hypothesis 10 scanning alanine mutants of rFSHR at the 265-296 epitope were generated, and the binding characteristics of these mutants were studied. Their affinity constants for 125I-hFSH did not deviate greatly from that of wild-type FSHR, in which some mutants exhibited an approximately two- to threefold reduction in Ka compared to wild-type receptor, and no mutation abolished signal transduction. These results lead to rejection of the hypothesis that this region contains residues critical for conveying hormone specificity and receptor-dependent hormone action.

Structural features and expression of an alternatively spliced growth factor type I receptor for follitropin signaling in the developing ovary

The pleiotropic actions of pituitary follitropin (FSH), regulate the expression of many cell cycle genes controlling ovarian follicular development and differentiation. In this study we asked the question whether different receptor motifs are created by the alternative splicing of the single large 80-100 Kb receptor gene. A 1.2 Kb transcript identified from a cDNA library of hormone primed (immature) sheep ovaries, codes for a putative protein lacking the seven transmembrane segment. The receptor of 259 amino acids designated FSH-R3 is derived from a transcript comprising the first eight exons of the Gs coupled larger FSH receptor (R1) spliced to another DNA segment. This event produces a different carboxyl terminus at the junction creating a novel receptor motif with a single membrane spanning domain, assigning it to the growth factor type I receptor family. In transfected cells the expressed receptor localizes on the cell surface and specific antibodies directed against the unique C-terminal portion (residues 242-259) of FSH-R3 demonstrate the presence of the receptor protein in solubilized ovarian and testicular membrane preparations. FSH binding to the transfected cells induced [Ca2+]i identifying coupling of the R3 receptor to calcium signaling pathways. Thus, a growth factor type I receptor for FSH may be implicated in the growth promoting actions of FSH in the ovary. This is the first documentation of alternative splicing of a G protein coupled receptor gene creating a different signaling motif for cellular signaling.

Generating FSH antagonists and agonists through immunization against FSH receptor N-terminal decapeptides

Follicle-stimulating hormone (FSH) via interaction with G-protein coupled specific receptors plays a central role in the control of gametogenesis in mammals of both sexes. In females, FSH is crucial for follicle growth, follicle maturation and ovulation. FSH receptors, together with luteinizing hormone-chorionic gonadotropin and thyrotropin receptors belong to a subfamily of structurally related receptors within the seven transmembrane receptor family. Among several other regions, the N-terminus of these receptors is believed to be responsible for important specific hormone-receptor contact sites. Recombinant filamentous phages displaying at their surface three overlapping N-terminal decapeptides of the FSH receptor, peptides A18-27, B25-34 and C29-38 were constructed. Ewes and female mice were immunized against the three FSH receptor (FSHR) recombinant phages. Immunoglobulins purified from immunized animals were analyzed for their biochemical properties on a Chinese hamster ovary cell line expressing the porcine FSH receptor. AntiA and antiB immunoglobulins (IgGs) behave as antagonists for 125I-FSH binding and for FSH-dependent cAMP production, while antiC IgGs did not compete for hormone binding. By contrast, antibodies against the C29-38 peptide displayed FSH agonist activity and stimulated the FSH receptor, whereas antiA and antiB IgGs did not. Furthermore, when the FSHR phages were used as peptidic vaccines, they induced a reversible inhibition of ovulation rate in ewes, and impaired fertility in female mice.

In vitro inhibition of the bioactivity of follicle-stimulating hormone by antisera against a peptide representing part of the FSH-receptor

The aim of the present work was to define an FSH receptor (FSHR) peptide that can induce antibodies that will inhibit the bioactivity of FSH. Therefore, the hFSHR sequence was aligned with that of all other known G-protein coupled receptors. An area with increased sequence homology was identified between the FSH-, LH-, TSH receptors, the C5a receptor and the IL8 receptor. The similarity consists of a richness in acidic (D and E) and hydrophobic (Y and F) residues. In hFSHR the sequence is EDNESSYSRGFDMTYTEFDYDLCNEVVD (amino acid 299-326). Research on both the C5a- and IL8-receptor has indicated that this part is responsible for hormone binding but not for signal transduction. Protamine. an antagonist for both the C5a- and IL8 receptor also inhibited the bioactivities of FSH and LH when tested in a bioassay. This suggests that in the hFSHR this region might also be involved in hormone binding. Specificity of this region towards the diverse ligands all binding to the C5a or to the IL8 receptor might be attributed to differences in the profile of alternating basic and hydrophobic residues. Therefore, the hypothesis was tested as to whether antisera raised against peptides of this FSHR-domain would inhibit FSH-bioactivity but not LH-bioactivity. Indeed antisera were found (anti-hFSHR 309-322) that inhibited the biological activity of FSH in a bioassay. These antisera proved to be specific since they did not inhibit the bioactivity of LH. These data suggest that the core sequence (hFSHR 309-322) of the aligned domain of the hFSHR, in analogy to the IL8- and C5a receptors, is involved in hormone binding and ligand specificity. This domain therefore forms a valuable tool in FSH- and FSHR research for scientific and medical purposes.

Recognition of follicle stimulating hormone (alpha-subunit) by a recombinant receptor protein domain coded by an alternately spliced mRNA and expressed in Escherichia coli

To assess the functional significance of putative proteins encoded by alternately spliced mRNA of the sheep testicular FSH receptor, a short form cDNA comprising of the first four exons (117 residues mature protein) was engineered for expression in Escherichia coli. The expressed protein of molecular mass 15 kDa was purified to homogeneity and verified by reaction with an antibody against a synthetic peptide sequence unique to the amino (N)-terminal region FSH receptor. The purified FSH receptor domain protein bound 125I-labeled hFSH in a ligand blot on polyvinylidine difluoride membranes. Further analyses by slot blot revealed high affinity of the immobilized protein with significant reaction at 10 pmol. As the immobilized receptor protein also reacted with structurally related hormones (125I-labeled LH/125I-labeled human chorionic gonadotropin), we confirmed that interaction most probably occurred via the common alpha-subunit of these glycoprotein hormones. Our results reveal that this N-terminal portion of the FSH receptor contain(s) major site(s) for hormone recognition that could be mediated via the alpha-subunit. A rabbit antibody to the receptor inhibited FSH action in receptor bearing cells, revealing the utility of such recombinant FSH receptor protein(s) for modulation of hormone action.

Immunization of male bonnet monkeys (M. radiata) with a recombinant FSH receptor preparation affects testicular function and fertility

Immunization of proven fertile adult male monkeys (n=3) with a recombinant FSH receptor protein preparation (oFSHR-P) (representing amino acids 1-134 of the extracellular domain of the receptor Mr approximately 15KDa) resulted in production of receptor blocking antibodies. The ability of the antibody to bind a particulate FSH receptor preparation and receptors in intact granulosa cells was markedly (by 30-80%) inhibited by FSH. Serum T levels and LH receptor function following immunization remained unchanged. The immunized monkeys showed a 50% reduction (p<0.001) in transformation of spermatogonia(2C) to primary spermatocytes (4C) as determined by flow cytometry and the 4C:2C ratio showed a correlative change (R 0.81, p<0.0007) with reduction in fertility index (sperm counts X motility score). Breeding studies indicated that monkeys became infertile between 242-368 days of immunization when the fertility index was in the range of 123+/-76 to 354+/-42 (compared to a value of 1602+/-384 on day 0). As the effects observed are near identical to that seen following immunization with FSH it is suggestive that oFSHR-P can substitute for FSH in the development of a contraceptive vaccine.

Decreased spermatogenesis as the result of an induced autoimmune reaction directed against the gonadotropin receptors in male rats

The presence of luteinizing hormone (LH) and testosterone is considered critical for the maintenance of spermatogenesis in the rat. However, the role and importance of follicle-stimulating hormone (FSH) in the initiation and maintenance of spermatogenesis has been a subject of debate for some time. The objective of this study was to examine the role of FSH and LH in vivo in the developing and adult rat by inducing an autoimmune reaction against the receptors to these gonadotropins. Sperm numbers were reduced in animals immunized against either the FSH or LH receptor (FSHR/LHR). In animals immunized against both FSHR and LHR there was also a significant reduction in sperm number although spermatogenesis was never completely ablated. These results were seen in male rats immunized either prepubertally (18 days of age) or as adults (80 days of age). To examine the requirements for FSH in early postnatal-testicular development, pregnant females were also immunized against either FSHR, LHR, or both of the receptors, and the male offspring were examined at 30 days of age. Again, germ-cell number was decreased with the greatest effect in those pups whose mothers were immunized against both FSHR and LHR. Radioligand-receptor-binding assays revealed that the antibody produced in the rats against FSHR was able to compete with FSH for binding sites in receptor-membrane preparations. Therefore, the mechanism of disruption of spermatogenesis is probably due to suppression of hormone to receptor binding. The results of this study support a role for FSH in spermatogenesis not only during neonatal and early postnatal development but also in the adult animal.

Immunization against exon 1 decapeptides from the lutropin/choriogonadotropin receptor or the follitropin receptor as potential male contraceptive

Pituitary gonadotropin hormones lutropin (LH) and follitropin (FSH) control steroidogenesis and gametogenesis in male and female gonads through interaction with G protein-coupled receptors, LHR and FSHR. In the male, LH acts on leydig cells and is mostly responsible for the acquisition of puberty and the production of androgens while FSH, together with androgens, regulates spermatogenesis within Sertoli cells. We have engineered filamentous phages displaying mouse LHR and human FSHR decapeptides chosen in hormone binding regions. Peptides from both receptors displayed on phages belong either to the receptor specific exon 1 (amino acids 18-27) or to the homologous exon 4 (amino acids 98-107). Vaccination of prepubertal BALB/c male mice with hybrid phages using sub-cutaneous or intraperitoneal injections induced immunity against receptors. Anti-receptor immunization produced agonist or antagonist effects depending only on the circulating levels of the antibodies. Both anti-LHR and anti-FSHR vaccines induced efficient as well as reversible male contraception, through different mechanisms: targeting LH receptors inhibited or hyperstimulated Leydig cell testosterone production while targeting FSH receptors did not affect testosterone levels.

Anti-human FSH receptor monoclonal antibodies: immunochemical and immunocytochemical characterization of the receptor

The extracellular domain of the human FSH receptor was expressed in Escherichia coli as a fusion protein with ubiquitin. It was tagged with a poly-His tract which was used for its purification. Immunization of mice allowed the preparation of high affinity antireceptor monoclonal antibodies. The latter fell into two categories: some of them were inhibited hormone binding and adenylate cyclase activation whereas others were devoid of these properties. None of the antibodies had agonistic activity (i.e., stimulated adenylate cyclase). Immunoaffinity chromatography allowed us to purify the native receptor in a single step either from a permanently transfected L cell line (75% recovery) or from human ovaries (33% recovery). Immunoblotting of the receptor in human ovaries showed the presence of a major band of 87 kDa and of a minor band of 81 kDa. Endoglycosidase digestion and pulse-chase experiments showed the former to be the mature receptor and the latter the precursor containing mannose-rich carbohydrates. Thus, as in the case for the LH receptor, there was an accumulation (albeit to a lower degree) of the precursor in target cells. We did not detect variant forms of the protein corresponding to the alternative mRNA transcripts previously described. Additive binding to the receptor of several antibodies, but not of the same antibody, allowed us to establish a sandwich-type ELISA for the receptor (sensitivity approximately 1 fmol) and to obtain evidence against the existence of previously described oligomeric forms of the protein. All monoclonal antibodies were able to label the receptor immunocytochemically in transfected cells, and two of them were also able to detect it at the markedly lower physiological concentrations, i.e., in human Sertoli and granulosa cells.

Identification in human ovarian follicular fluid of proteins that share an epitope region unique to the extracellular domain of the follicle-stimulating hormone receptor

Recently we identified a unique region, residues 9-30 in the extracellular domain of the FSH receptor, capable of binding FSH but not LH or TSH. We have shown that polyclonal antibodies raised against this region specifically recognized intact FSH receptors present on plasma membranes of cultured rat Sertoli cells. In the present study, plasma membranes from human granulosa-lutein cells were solubilized and subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis, followed by Western blot analysis. Antireceptor peptide antibody, but not preimmune serum control, recognized intact human FSH receptors, suggesting that human and rat FSH receptors share this unique N-terminus epitope region. Recent cloning studies have identified, in addition to full length receptor, the presence of FSH receptor-spliced messenger RNA variants, which encode receptor proteins with variable lengths of hydrophilic extracellular domains, but lacking transmembrane domains. Such proteins could theoretically represent secreted forms of the receptor. In this study, we used a polyclonal anti-FSH receptor (residues 9-30) peptide antibody to investigate whether FSH receptor-related soluble proteins might also be present in human ovarian follicular fluid (FF). In an enzyme-linked immunosorbent assay specific for the FSH receptor, antireceptor peptide antibody, but not preimmune serum serving as control, identified significant immunoreactivity in several human ovarian FF samples, suggesting that protein(s) present in FF share a common epitope with the extracellular domain of the FSH receptor. The apparent levels of FSH receptor-related activity in FF samples, expressed relative to the FSH receptor (residues 9-30) peptide, ranged from 31-55 ng/mL. Passing of the samples through 0.22-micron filters or subjecting the samples to high speed centrifugation did not alter the activity profiles of the samples ruling out effects due to contamination with plasma membranes from granulosa cells. When human FF samples were subjected to gel permeation chromatography, at least four distinct protein peaks were resolved, in the molecular mass range between 70-460 kilodaltons, each of which was recognized by the FSH receptor 9-30 peptide antibodies. Our results provide initial evidence for the presence in human ovarian FF of proteins sharing epitope with the extracellular domain of the FSH receptor and presumably derived from the granulosa cell. Since we have previously shown that the epitope region, represented by residues 9-30 in the extracellular domain of the FSH receptor specifically binds FSH, the proteins in human FF sharing this epitope may have functional significance.

A polyclonal antibody to a synthetic peptide derived from the rat follicle-stimulating hormone receptor reveals the recombinant receptor as a 74-kilodalton protein

We have prepared a polyclonal antibody (AntiF) against a synthetic peptide comprising residues 19-29 of the rat FSH receptor. The specificity of this antibody was documented using human embryonic kidney (293) cells and stable transfectants of 293 cells expressing the recombinant LH/CG and FSH receptors. The data presented show that AntiF inhibits the binding of FSH, but not that of LH/CG, to their cognate receptors. AntiF also recognizes a specific protein(s) representing the FSH receptor in Western blots or by immunoprecipitation of cells transfected with the FSH receptor. This protein(s) is not present in untransfected 293 cells or in 293 cells permanently transfected with the LH/CG receptor. Finally, addition of the 19-29 peptide prevents immunoprecipitation of the FSH receptor by AntiF, whereas an unrelated peptide corresponding to residues 637-647 has no effect. In Western blots of 293 cells transfected with the FSH receptor, AntiF reveals the recombinant receptor as a heterogenous glycoprotein with a molecular mass of 58,000-83,000 daltons (in the absence of thiol-reducing agents) or 69,000-81,000 (in the presence of thiol reducing agents). Pulse-chase experiments with metabolically labeled cells show that the mature FSH receptor is a 74-kilodalton protein derived from 67- and 72-kilodalton precursors.

Functional properties of polyclonal antibodies raised against the N-terminus region (residues 9-30) of the follicle-stimulating hormone (FSH) receptor: significance of this receptor region in FSH recognition and signal transduction

In this study, we raised polyclonal antibodies in rabbits against a synthetic peptide corresponding to a unique region of the FSH receptor, residues 9-30, with no sequence homology to receptors for LH and TSH, and examined their characteristics relevant to receptor function. Binding of [125I]human (h) FSH to membrane-bound receptors was inhibited in a concentration-dependent manner by the anti-FSH receptor-(9-30) peptide antibody. Preimmune serum had no effect. Lineweaver-Burke plot analysis of [125I]hFSH binding to membrane receptors in the presence or absence of antireceptor peptide antibody indicated that the antibody effectively competed with FSH at a hormone-binding site on the receptor. Also, antireceptor peptide antibody, but not preimmune serum, inhibited the ability of FSH to stimulate the conversion of androstenedione to estradiol in cultured immature rat Sertoli cells. Stimulation of estradiol synthesis by Sertoli cells caused by cholera toxin or forskolin (which are known to act through the Gs-protein and catalytic unit of adenylate cyclase, respectively) was not inhibited by antireceptor peptide antibody. Indirect immunofluorescence staining of cultured rat Sertoli cells showed binding of antibody to plasma membrane receptor. No fluorescent staining of receptor was observed when cells were incubated with preimmune serum or antireceptor peptide antibody in the presence of excess receptor-(9-30) peptide or hFSH. These results were consistent with specific labeling of membrane-bound FSH receptors by anti-receptor-(9-30) peptide antibody. When detergent-solubilized membrane preparations from rat Sertoli cells were fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions and then subjected to Western blot analysis, antireceptor peptide antibody, but not preimmune rabbit serum, specifically recognized intact FSH receptor. Although the antireceptor peptide antibody occupied the N-terminus 9-30 epitope region in the FSH receptor, it did not induce postbinding events, such as receptor patching (aggregation), as shown by indirect immunofluorescence staining of rat Sertoli cells and the estradiol response. In contrast, a polyclonal antibody against the FSH holoreceptor capable of interacting with multiple epitopes on the receptor could induce FSH-like effects, such as receptor patching and estradiol response in Sertoli cells. In conclusion, antibody raised against the N-terminus region (9-30) of the FSH receptor recognized intact FSH receptor, inhibited FSH binding, and behaved as an antagonist, suggesting that this N-terminus epitope region of the receptor is involved in hormone binding.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of regions of the follitropin (FSH) beta-subunit that interact with the N-terminus region (residues 9-30) of the FSH receptor

We have recently identified a region, N-terminus residues 9-30, in the extracellular domain of the follicle-stimulating hormone (FSH) receptor capable of binding FSH, but not luteinizing hormone (LH) or thyroid-stimulating hormone (FSH) (Dattatreyamurty and Reichert (1992) Mol. Cell. Endocrinol. 87, 9-17). The objectives of the present study were to examine the interaction between a synthetic peptide corresponding to this receptor sequence and the beta-subunit of FSH, and to identify which FSH-beta regions are involved in the interaction. FSH-beta subunit and synthetic FSH-beta peptides 1-15, 71-85 and 101-111 effectively bound 125I-labeled FSH rec-(9-30) peptide, and binding was inhibited by excess unlabeled FSH receptors. Scatchard analysis indicated that the synthetic FSH-beta peptides had affinities for FSH rec-(9-30) peptide in the order of 10(6) M-1 (Ka), with the sum of individual peptide affinities (Ka = 1.21 x 10(7) M-1) closely approximating that of the intact beta-subunit (1.02 x 10(7) M-1). Polyclonal antibodies raised against FSH rec-(9-30) peptide completely inhibited the binding of 125I-labeled receptor peptide to hFSH, hFSH-beta, and hFSH-beta peptides 1-15, 71-85 and 101-111. Our results indicate that recognition of FSH-beta by N-terminus region (9-30) of the FSH receptor involves contact with residues in three discontinuous binding regions on FSH-beta.(ABSTRACT TRUNCATED AT 250 WORDS)

A search for circulating immunoglobulins blocking follicle-stimulating hormone action in male idiopathic infertility

In this study, patients with idiopathic infertility were investigated for the presence of circulating antibodies which interfered with follicle-stimulating hormone (FSH) activity. A retrospective search for autoantibodies was undertaken using single plasma samples obtained from 29 infertile men with azoo/oligo/asthenoteratozoospermia and eight controls with normozoospermia and normal blood FSH levels. Plasma levels of immunoactive FSH, bioactive FSH, immunoactive luteinizing hormone and testosterone were measured in the individual samples. Plasma immunoglobulin G (IgG) was isolated using protein-A chromatography and tested at different dose levels for its ability to inhibit and/or stimulate basal and FSH-induced aromatase activity in immature rat Sertoli cells in vitro. In the first set of trials, IgGs isolated from three infertile patients showed apparent inhibition of FSH-stimulated aromatase activity, two showed further stimulation and five showed irregular fluctuations beyond the normal range of stimulation. When reanalysed at different doses, none of the IgG fractions exhibited abnormal interference with FSH action. It is concluded that, unlike many other endocrine disorders characterized by autoimmunity, the occurrence of autoantibodies of the IgG class blocking FSH action in male infertility is improbable.

Polyclonal antibodies against follitropin (FSH) receptor interfere with hormone binding, but mimic the effects of FSH

We have raised polyclonal antibodies in rabbits against the FSH receptor, purified from calf testis and isolated the IgG fraction from the immune serum (immune IgG) by protein A affinity chromatography. When the immune IgG was incubated with purified, radioiodinated FSH receptor, the resulting complex could be immunoprecipitated by goat anti-rabbit gamma globulin. The immunoprecipitate, after dissociation of receptor from antibody, separation by SDS-PAGE under reducing conditions, and autoradiography, showed the presence of a approximately 60 kDa protein previously identified as a component of the FSH receptor. Binding of 125I-hFSH to membrane-bound receptors was inhibited in a concentration-dependent manner by immune IgG (Ed50 = 90 micrograms/ml). Nonimmune serum or IgM/IgA fractions from immune serum had no effect. 125I-labeled immune IgG bound specifically to testis membranes and the binding could be inhibited in a concentration-dependent manner by ovine FSH. These results suggest that the FSH-binding site and the antibody-binding site on the receptor are proximate or identical. Immune IgG mimicked the ability of FSH to stimulate basal adenylate cyclase activity and conversion of androstenedione to estradiol in cultured immature rat Sertoli cells. Stimulatory but submaximal effects of FSH were augmented by immune IgG. Rat Sertoli cells treated with IgG fractions from immune serum showed an intense fluorescent staining of plasma membrane receptor. No fluorescent staining of receptor was seen when preimmune IgG was used or in the presence of excess ovine FSH. These observations suggest that the polyclonal receptor antibody capable of recognizing FSH receptor behaved as an FSH binding competitor, but was also active as an agonist producing the biological effect of FSH in vitro. The effectiveness of antibodies against FSH receptor in stimulating estradiol synthesis suggests that the information needed for FSH signal transduction resides in the membrane receptor rather than in the hormone molecule. Such antibodies may offer a useful probe for further study of FSH receptor structure and mechanism of hormone action.