Receptor binding activity and in vitro biological activity of the human FSH charge isoforms as disclosed by heterologous and homologous assay systems: implications for the structure-function relationship of the FSH variants

Molecular cloning, characterization, and function analysis of the AMH gene in Yak (Bos grunniens) Sertoli cells

Sertoli cells (SCs) are important testicular somatic cells that carry out various functions in spermatogenesis. Understanding the biological mechanisms underlying SC development may facilitate the understanding of animal reproduction. Anti-Mullerian hormone (AMH) is a dimeric glycoprotein produced by SCs and plays essential roles in spermatogenesis. In this study, we cloned the coding sequence of the yak AMH, predicated the structure of AMH protein, analyzed AMH expression in the testis at different stages, and studied the functions of AMH in yak SCs. The open reading frame (ORF) of the yak AMH contained 1728 bp and encoded 575 amino acids. Structural analysis revealed that the yak AMH protein had a highly conserved transforming growth factor-β (TGF-β) domain. The mRNA expression level for the AMH gene in yak testis increased significantly from the fetal stage to calf stage, then decreased with the increase of age. The highest expression was found in calf stage. Cell proliferation was depressed in AMH-deficient SCs. Expression of several genes involved in SC proliferation and development, including PCNA, BCL-2, BAX, CASP3, AR and AMHR2 were altered after knockdown of AMH. Also, three SC-secreted factors essential for spermatogenesis, SCF, GDNF and ABP, were repressed at the transcription level after AMH knockdown in yak SCs. Moreover, supplementation with exogenous AMH protein partially rescued SC proliferation, and the expression of PCNA, BCL-2, AR and AMHR2 after AMH gene interference. This research provided theoretical basis for understanding the mechanism by which AMH regulates yak spermatogenesis and might give new insights in improving yak reproductive performance in the future.

Gonadotropins and Their Analogs: Current and Potential Clinical Applications

The gonadotropin receptors LH receptor and FSH receptor play a central role in governing reproductive competency/fertility. Gonadotropin hormone analogs have been used clinically for decades in assisted reproductive therapies and in the treatment of various infertility disorders. Though these treatments are effective, the clinical protocols demand multiple injections, and the hormone preparations can lack uniformity and stability. The past two decades have seen a drive to develop chimeric and modified peptide analogs with more desirable pharmacokinetic profiles, with some displaying clinical efficacy, such as corifollitropin alfa, which is now in clinical use. More recently, low-molecular-weight, orally active molecules with activity at gonadotropin receptors have been developed. Some have excellent characteristics in animals and in human studies but have not reached the market-largely as a result of acquisitions by large pharma. Nonetheless, such molecules have the potential to mitigate risks currently associated with gonadotropin-based fertility treatments, such as ovarian hyperstimulation syndrome and the demands of injection-based therapies. There is also scope for novel use beyond the current remit of gonadotropin analogs in fertility treatments, including application as novel contraceptives; in the treatment of polycystic ovary syndrome; in the restoration of function to inactivating mutations of gonadotropin receptors; in the treatment of ovarian and prostate cancers; and in the prevention of bone loss and weight gain in postmenopausal women. Here we review the properties and clinical application of current gonadotropin preparations and their analogs, as well as the development of novel orally active, small-molecule nonpeptide analogs.

Molecular regulation of follicle-stimulating hormone synthesis, secretion and action

Follicle-stimulating hormone (FSH) plays fundamental roles in male and female fertility. FSH is a heterodimeric glycoprotein expressed by gonadotrophs in the anterior pituitary. The hormone-specific FSHβ-subunit is non-covalently associated with the common α-subunit that is also present in the luteinizing hormone (LH), another gonadotrophic hormone secreted by gonadotrophs and thyroid-stimulating hormone (TSH) secreted by thyrotrophs. Several decades of research led to the purification, structural characterization and physiological regulation of FSH in a variety of species including humans. With the advent of molecular tools, availability of immortalized gonadotroph cell lines and genetically modified mouse models, our knowledge on molecular mechanisms of FSH regulation has tremendously expanded. Several key players that regulate FSH synthesis, sorting, secretion and action in gonads and extragonadal tissues have been identified in a physiological setting. Novel post-transcriptional and post-translational regulatory mechanisms have also been identified that provide additional layers of regulation mediating FSH homeostasis. Recombinant human FSH analogs hold promise for a variety of clinical applications, whereas blocking antibodies against FSH may prove efficacious for preventing age-dependent bone loss and adiposity. It is anticipated that several exciting new discoveries uncovering all aspects of FSH biology will soon be forthcoming.

Role of FSH glycan structure in the regulation of Sertoli cell inhibin production

Variations in follicle-stimulating hormone (FSH) carbohydrate composition and structure are associated with important structural and functional changes in Sertoli cells (SCs) during sexual maturation. The aim of the present study was to investigate the impact of FSH oligosaccharide structure and its interaction with gonadal factors on the regulation of monomeric and dimeric inhibin production at different maturation stages of the SC. Recombinant human FSH (rhFSH) glycosylation variants were isolated according to their sialylation degree (AC and BA) and complexity of oligosaccharides (CO and HY). Native rhFSH stimulated inhibin α-subunit (Pro-αC) but did not show any effect on inhibin B (INHB) production in immature SCs isolated from 8-day-old rats. Activin A stimulated INHB and had a synergistic effect on FSH to stimulate Pro-αC. The less acidic/sialylated rhFSH charge analogues, BA, were the only charge analogue mix that stimulated INHB as well as the most potent stimulus for Pro-αC production. Native rhFSH stimulated both Pro-αC and INHB in SCs at a more advanced maturation stage, isolated from 20-day-old rats. In these cells, all rhFSH glycosylation variants increased INHB and Pro-αC production, even in the presence of growth factors. The BA preparation exerted a more marked stimulatory effect on INHB and Pro-αC than the AC. Glycoforms bearing high mannose and hybrid-type oligosaccharides, HY, stimulated INHB and Pro-αC more effectively than those bearing complex oligosaccharides, CO, even in the presence of gonadal growth factors. These findings demonstrate the modulatory effect of FSH oligosaccharide structure on the regulation of inhibin production in the male gonad.

Dose-exposure proportionality of a novel recombinant follicle-stimulating hormone (rFSH), FE 999049, derived from a human cell line, with comparison between Caucasian and Japanese women after subcutaneous administration

Background and Objectives

FE 999049 is a novel recombinant follicle-stimulating hormone (rFSH) preparation expressed by a human cell line (PER.C6^®), in contrast to existing rFSH preparations expressed by Chinese hamster ovary (CHO) cell lines. Since the individual dose of rFSH may be altered depending on the response in women undergoing assisted reproductive technologies, knowledge on the dose-exposure linearity and proportionality is important. The purpose of these studies was to investigate the dose-exposure linearity and proportionality properties of FE 999049 with a comparison between Caucasian and Japanese women. This is the first study in Japanese women regarding pharmacokinetics of rFSH.

Methods

Forty-eight Caucasian and 31 Japanese healthy women of reproductive age were pituitary down-regulated to suppress endogenous FSH. Following single subcutaneous administration of 37.5, 75, 150, 225, or 450 IU (Steelman–Pohley assay), the serum FSH concentration was followed over 10 days.

Results

The dose-dependent pharmacokinetic parameters of FE 999049, area under the serum concentration-time curve (AUC) and maximum serum concentration (C_max), showed dose-exposure linearity and proportionality over 150–450 IU in Caucasian women, the dose interval available for analysis, and 75–450 IU in Japanese women, which was the dose interval investigated. Comparison between Caucasian and Japanese women showed no differences between the populations. The dose-independent parameters were similar over all doses in both populations. FE 999049 was safe and well tolerated at all doses in both populations with few, mostly mild, adverse events.

Conclusion

The results demonstrate dose-exposure proportionality and a predictable dose-dependent exposure of FE 999049, with no differences in Caucasian and Japanese women of reproductive age.

Biosimilars entering the clinic without animal studies. A paradigm shift in the European Union

The concept of biosimilars has spread from Europe to other regions throughout the world, and many regions have drafted regulatory guidelines for their development. Recently, a paradigm shift in regulatory thinking on the non-clinical development of biosimilars has emerged in Europe: In vivo testing should follow a step-wise approach rather than being performed by default. To not require animal testing at all in some instances can well be seen as a revolutionary, but science-based, step. Here, we describe the internal discussions that led to this paradigm shift. The mainstay for the establishment of biosimilarity is the pharmaceutical comparability based on extensive physicochemical and biological characterization. Pharmacodynamic comparability can be evaluated in in vitro assays, whereas pharmacokinetic comparability is best evaluated in clinical studies. It is considered highly unlikely that new safety issues would arise when comparability has been demonstrated based on physicochemical and in vitro comparative studies.

Aromatase (CYP19) gene variants influence ovarian response to standard gonadotrophin stimulation

PURPOSE

The association of cytochrome P450 aromatase gene CYP19(TTTA) ( n ) polymorphism with ovarian response to FSH stimulation was explored.

METHODS

Three hundred women undergoing medically assisted reproduction and 300 women with at least one spontaneous pregnancy participated in the study. CYP19(TTTA) ( n ) polymorphism was genotyped, while serum hormones were determined. During oocyte retrieval, the follicular size, the follicle and oocyte numbers were recorded.

RESULTS

Six CYP19(TTTA) ( n ) alleles with 7 to 12 repeats were revealed. Women homozygous for long CYP19(TTTA) ( n ) alleles presented with lower serum FSH levels at the third day of the menstrual cycle (p < 0.001) and higher large follicle numbers (p < 0.01), compared to women homozygous for short CYP19(TTTA) ( n ) alleles. The CYP19(TTTA) ( 7 ) allele was associated with higher serum FSH levels (p < 0.003), with lower total follicle (p < 0.02) and large follicle numbers (p < 0.03), while CYP19(TTTA) ( 7 ) allele-carriers presented more frequently with small follicles than CYP19(TTTA) ( 7 ) allele-non carriers (p < 0.01).

CONCLUSIONS

CYP19 genetic variants were associated with ovarian reserve and response to standard gonadotrophin stimulation of women undergoing in vitro fertilization.

Assessment of the quality and structural integrity of a complex glycoprotein mixture following extraction from the formulated biopharmaceutical drug product

Biological drugs represent an important and rapidly growing class of therapeutics useful in the treatment of a variety of disorders ranging from cancer to inflammation to infectious diseases. Unlike single chemical entities, the recombinant production of these drugs in living cells confers considerable structural and chemical heterogeneity to the biologically derived protein product that constitutes the active pharmaceutical ingredient (API). In mammalian based expression systems, much of this diversity is conferred through heterogeneous protein glycosylation. These post-translational modifications can have significant effects on the structure, biological function, and pharmacological properties of the API. In addition, the bulk proteins that comprise the API are further formulated through the use of multiple excipients designed to ensure product stability, solubility, and lot-to-lot consistency. Unfortunately, these matrices can interfere with commonly available analytical methods used in the thorough chemical characterization of the biological drug product. At the same time, a demonstration of the suitable extraction of the bulk drug substance in a manner and form that does not destabilize the active ingredient or introduce any structural bias with direct reference to the original drug product is both critical and necessary. Here, we use recombinant human follicle stimulating hormone (follitropin alpha for injection) from a pharmaceutical source as an example to illustrate a suitable purification strategy to effectively extract the bulk drug substance from the formulated drug product with high purity and yield. We assess the suitability of this extraction method in preserving the structural integrity and overall quality of the drug substance relative to the formulated drug product, placing a particular emphasis on glycosylation as a key product attribute. In so doing, we demonstrate that it is possible to effectively extract the active pharmaceutical ingredient from a formulated biological drug product in a manner that is consequently sufficient for its use in comparability studies.

In vitro biological-to-immunological ratio of serum gonadotropins throughout male puberty in children with insulin-dependent diabetes mellitus

Information on the impact of prolonged deficient glycemic control in the quality of the gonadotropin signal delivered by the pituitary gland during puberty in children with insulin-dependent diabetes mellitus (IDDM) is scarce. In the present study, we examined the impact of deficient glycemic control on bioactive LH and FSH concentrations and their corresponding biological-to-immunological (B:I) ratio in boys with poorly controlled, but systemically uncomplicated IDDM. Dual control groups comprising patients with well-controlled IDDM and healthy boys of comparable age and body mass index were included for appropriate comparisons within and between each pubertal stage. Patients with poorly controlled and well-controlled IDDM exhibited serum bioactive FSH levels and B:I FSH ratio similar to those showed by the healthy control group. In contrast, in early and mid-pubertal boys with poorly controlled IDDM bioactive LH levels were normal, but its B:I LH relationship was significantly (P < 0.05) decreased. This attenuation in the quality of the LH signal did not affect total serum T concentrations, and apparently, progression of puberty. Long-standing uncontrolled diabetes and the consequent metabolic disturbances and/or complications may aggravate the reproductive axis dysfunction and eventually provoke pubertal arrest.

Effects of metformin on inappropriate LH release in women with polycystic ovarian syndrome and insulin resistance

The role of hyperinsulinaemia in neuroendocrine abnormalities in polycystic ovarian syndrome (PCOS) is controversial. The present study applied frequent blood sampling to assess the response of LH to metformin treatment in insulin-resistant women with PCOS. Thirteen predominantly overweight women with PCOS were studied before and after treatment with 1.5 g/day metformin for 3 months. Serum LH and testosterone were measured every 10 min for 10 h; LH was measured for an additional 2 h after gonadotrophin-releasing hormone (GnRH) administration. LH pulses were characterized by cluster analysis, secretory LH episodes by a deconvolution procedure, and synchronicity of paired LH-testosterone concentrations by lag-specific cross-correlation. After treatment, basal LH concentrations, amplitude of LH pulses, LH secretory amplitude, response to exogenous GnRH, and basal testosterone concentrations significantly decreased in seven patients, whereas in the remaining women these parameters remained unaltered. Before treatment, decreased coordinate LH and testosterone release was manifested by all patients; metformin treatment led to re-establishment of the feed-back control of testosterone on LH secretory rates by -20 to 0 min. Treatment did not modify the glucose:insulin ratio or serum insulin concentrations. In conclusion, administration of metformin allowed the identification of two subsets of PCOS women in whom neuroendocrine abnormalities may improve independently of the presence of insulin resistance or hyperinsulinaemia.

Follicle-stimulating hormone receptor gene polymorphism and ovarian responses to controlled ovarian hyperstimulation for IVF-ET

This study was performed to investigate the association between FSH receptor (FSHR) gene polymorphism at position 680 and the outcomes of controlled ovarian hyperstimulation (COH) for in vitro fertilization and embryo transfer (IVF-ET) in Korean women. Two hundred and sixty-three patients under 40 years of age who underwent IVF-ET procedures were included in this study. Patients with polycystic ovary syndrome, endometriosis, or a previous history of ovarian surgery were excluded. Following extraction of genomic DNA, the FSHR polymorphism at position 680 was determined by polymerase chain reaction and restriction fragment length polymorphism analysis. The FSHR genotype distribution was 41.8% for Asn/Asn, 45.6% for Asn/Ser, and 12.5% for Ser/Ser FSHR genotype groups. Although there was no difference among the three genotype groups in terms of the age and infertility diagnosis of study subjects, the basal levels of FSH (day 3) were significantly different [5.7 +/- 0.3 IU/l (mean+/-SEM), 6.0 +/- 0.3 IU/l, and 8.2 +/- 0.9 IU/l for Asn/Asn, Asn/Ser, and Ser/Ser groups, respectively. The Ser/Ser group tended to require a higher dose of gonadotropins for COH, and tended to show lower serum estradiol levels at the time of hCG administration than the other two groups, though these differences did not reach statistical significance. The numbers of oocytes retrieved tended to be different for the three groups (9.6 +/- 0.6, 10.2 +/- 0.6, and 7.9 +/- 0.8 for Asn/Asn, Asn/Ser, and Ser/Ser groups, respectively). Clinical pregnancy rate was significantly higher in Asn/Asn, compared to the others (45.7 vs. 30.5%, P=0.013). The homozygous Ser/Ser genotype of FSHR polymorphism at position 680 may be associated with a reduced ovarian response to COH for IVF-ET, while Asn/Asn genotypes showed a higher pregnancy rate.

Effects of human pituitary FSH isoforms on mouse follicles in vitro

The effects of human FSH glycoforms on mouse follicle development and function in vitro were analysed, and an attempt was made to relate markers of follicular maturation to the expression of immunolocalized connexin (Cx) 43 and Cx26-based gap junctions. Three FSH fractions comprising discrete pI ranges [7.10-5.99 (pool I), pI 5.62-4.95 (pool II) and <3.75 (pool III)] were studied. Pool I produced the strongest effect on preantral granulosa cell proliferation and oestradiol production, and was highly effective for stimulating antral formation; this isoform also evoked a peripheral distribution of Cx43-containing gap junctions. Pool II was effective in promoting preantral granulosa cell proliferation but required higher FSH doses. This particular isoform provoked a more central distribution of Cx43-containing gap junctions, which was associated with a lower oestradiol production and less effective antral formation. Pool III was the least active for all markers of follicle development, and this was associated with minimal induction of Cx43-based gap junctions. The effects of the three FSH isoform pools on Cx26 expression were similar. The pattern of differences strongly suggests that FSH isoforms have complementary and specific actions on developing follicles, and that a shifting stage specific balance of isoforms is required for optimal follicle development.

Pituitary–ovarian axis during lactational amenorrhoea. II. Longitudinal assessment of serum FSH polymorphism before and after recovery of menstrual cycles

BACKGROUND

The association of normal serum levels of immunoassayable gonadotrophins with anovulation during lactational amenorrhoea (LA) has not been fully explained.

METHODS

Serum FSH polymorphism was analysed in 10 women during LA between days 60 and 70 post-partum and again, in the mid-follicular phase (MFP), after resuming menstrual cyclicity. FSH microheterogeneity was characterized according to charge, using preparative isoelectric focusing, and according to the inner structure of carbohydrate chains, using lectin chromatography.

RESULTS

A significantly higher proportion of FSH charge isoforms isolated below pH 4.10 and a lower proportion of FSH isoforms bearing highly branched oligosaccharides were observed during LA when compared to MFP. Further analysis with higher resolution showed that FSH charge isoforms, isolated in the lower pH range in LA, corresponded to FSH molecules bearing highly branched and biantennary oligosaccharides. FSH isoforms bearing hybrid-type oligosaccharides were only present during LA. The circulating FSH isoform mix was significantly less bioactive in LA than in MFP. LA is characterized by a more acidic mix of FSH isoforms, containing hormone bearing less processed oligosaccharides, with decreased biopotency in comparison with the follicular phase.

CONCLUSIONS

This FSH microheterogeneity may be one of the critical factors contributing to incomplete follicular development and anovulation during LA.

Impact of carbohydrate heterogeneity in function of follicle-stimulating hormone: studies derived from in vitro and in vivo models

Carbohydrates attached to the protein core of glycoprotein hormones influence a number of intracellular and extracellular processes. As with other members of the glycoprotein hormone family, FSH is produced and released as an array of isoforms that differ from each other in the structure of their oligosaccharide attachments. In this review, we discuss how carbohydrate heterogeneity can impact on FSH action in different in vitro and in vivo systems. We present evidence for diverse effects of distinct charge isoforms at the target cell level, including differential and unique effects on various end responses, and discuss how the use of multiple cell-type assays has allowed identification of some specific effects of FSH isoforms on different cell populations and follicle compartments as well as oocyte maturation. Finally, we discuss recent information on the ability of naturally occurring and laboratory manufactured FSH isoforms to evoke particular effects on granulosa cell function and ovarian follicular maturation in vivo. Such studies have provided evidence that the type(s) of FSH signal delivered may in fact regulate distinct biological outcomes irrespective or in addition to outcomes dictated solely by clearance rate differences.

Glycosylation of an N-terminal extension prolongs the half-life and increases the in vivo activity of follicle stimulating hormone

FSH is a key component in assisted reproductive technologies. Because of rapid clearance of the hormone, patients have to be treated with daily injections. To address this problem, a long-acting FSH mutein was created by introduction of additional N-linked glycosylation into the molecule. New glycosylation sites were introduced by two different approaches: structure-aided, site-directed introduction of sites within the FSH molecule and addition of N-terminal extensions. A mutein with the extension sequence ANITVNITV at the N terminus of the alpha-chain (FSH1208) was efficiently glycosylated at both new sites. This resulted in a molecule with increased size and charge, factors known to reduce renal clearance of proteins. FSH1208 was found to have a 3- to 4-fold increased serum half-life, compared with wild-type recombinant FSH. Furthermore, in spite of a lower in vitro activity, FSH1208 had a markedly increased in vivo potency, as shown by increased ability to augment the ovarian weight and stimulate the serum estradiol levels in rats. These characteristics make FSH1208 a possible candidate for improved infertility treatment.

Glycosylation of erythropoietin affects receptor binding kinetics: role of electrostatic interactions

Erythropoietin (EPO) is a cytokine produced by the kidney whose function is to stimulate red blood cell production in the bone marrow. Previously, it was shown that the affinity of EPO for its receptor, EPOR, is inversely related to the sialylation of EPO carbohydrate. To better understand the properties of EPO that modulate its receptor affinity, various glycoforms were analyzed using surface plasmon resonance. The system used has been well characterized and is based on previous reports employing an EPOR-Fc chimera captured on a Protein A surface. Using three variants of EPO containing different levels of sialylation, we determined that sialic acid decreased the association rate constant (k(on)) about 3-fold. Furthermore, glycosylated EPO had a 20-fold slower k(on) than nonglycosylated EPO, indicating that the core carbohydrate also negatively impacted k(on). The effect of electrostatic forces on EPO binding was studied by measuring binding kinetics in varying NaCl concentrations. Increasing NaCl concentration resulted in a slower k(on) while having little impact on k(off), suggesting that long-range electrostatic interactions are primarily important in determining the rate of association between EPO and EPOR. Furthermore, the glycosylation content (i.e., nonglycosylated vs glycosylated, sialylated vs desialylated) affected the overall sensitivities of k(on) to [NaCl], indicating that sialic acid and the glycan itself each impact the overall effect of these electrostatic forces.

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.

Norethisterone is bioconverted to oestrogenic compounds that activate both the oestrogen receptor alpha and oestrogen receptor beta in vitro

In the present study, we used [3H]norethisterone to explore the bioconversion of this compound to A-ring reduced metabolites in African Green Monkey Kidney CV-1 cells and breast cancer T-47D cells. Additionally, we analyzed the capability of each norethisterone tetrahydro-reduced compound to bind the human oestrogen receptors alpha and beta and transactivate an oestrogen-sensitive reporter gene. The results showed that norethisterone is mainly metabolized to 3 alpha,5 alpha-norethisterone (>85% of total [3H]norethisterone added) by CV-1 and T-47D cells, and that both A-ring tetrahydro-reduced metabolites exhibit different capabilities to displace [3H]17beta-oestradiol from the oestrogen receptor alpha and beta, being 3 alpha,5 alpha-norethisterone the weakest competitor. We also found that 3 alpha,5 alpha-norethisterone and 3beta,5 alpha-norethisterone activate both oestrogen receptors at nanomolar concentrations and that the transactivation induced by the oestrogen receptor alpha was generally higher (1.7- to 4.0-fold) than that provoked by the beta receptor isoform. In oestrogen receptor alpha-transfected CV-1 and T-47 D cells, the oestrogenic-like potency of the 3beta,5 alpha-tetrahydro-reduced form was similar to that exhibited by 17beta-oestradiol and 2.5- to 4.0-fold higher than that shown by the 3 alpha,5 alpha-reduced compound; conversely, in the oestrogen receptor beta system the potency of the natural ligand was higher than that presented by the 3beta,5 alpha-tetrahydro-reduced metabolite. In CV-1 cells expressing the oestrogen receptor beta, the transactivation potency of 3beta,5 alpha-norethisterone was approximately 2-fold higher than that exhibited by its 3 alpha,5 alpha-tetrahydro-reduced isomer, whereas in T-47D cells the potency of the 3 alpha,5 alpha-tetrahydro-reduced compound was slightly higher than that shown by the 3beta,5 alpha A-ring reduced norethisterone metabolite. These results demonstrate that CV-1 and T-47D cells possess the enzymatic machinery to bioconvert norethisterone into the 5 alpha-reduced, 3 alpha-hydroxylated form and that neither 3 alpha,5 alpha- or 3beta,5 alpha-norethisterone exhibit preference or selectivity towards a particular oestrogen receptor isoform to induce a particular oestrogenic effect in these cell lines.

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.

Thyroid-stimulating hormone and thyroid-stimulating hormone receptor structure-function relationships

This review focuses on recent advances in the structure-function relationships of thyroid-stimulating hormone (TSH) and its receptor. TSH is a member of the glycoprotein hormone family constituting a subset of the cystine-knot growth factor superfamily. TSH is produced by the pituitary thyrotrophs and released to the circulation in a pulsatile manner. It stimulates thyroid functions using specific membrane TSH receptor (TSHR) that belongs to the superfamily of G protein-coupled receptors (GPCRs). New insights into the structure-function relationships of TSH permitted better understanding of the role of specific protein and carbohydrate domains in the synthesis, bioactivity, and clearance of this hormone. Recent progress in studies on TSHR as well as studies on the other GPCRs provided new clues regarding the molecular mechanisms of receptor activation. Such advances are a result of extensive site-directed mutagenesis, peptide and antibody approaches, detailed sequence analyses, and molecular modeling as well as studies on naturally occurring gain- and loss-of-function mutations. This review integrates expanding information on TSH and TSHR structure-function relationships and summarizes current concepts on ligand-dependent and -independent TSHR activation. Special emphasis has been placed on TSH domains involved in receptor recognition, constitutive activity of TSHR, new insights into the evolution of TSH bioactivity, and the development of high-affinity TSH analogs. Such structural, physiological, pathophysiological, evolutionary, and therapeutic implications of TSH-TSHR structure-function studies are frequently discussed in relation to concomitant progress made in studies on gonadotropins and their receptors.

Assessment of the in vitro and in vivo biological activities of the human follicle-stimulating isohormones

Gonadotropins are synthesized and released in different molecular forms. In this article, we present evidence that the glycosylation variants of human pituitary FSH exhibit differential and divergent effects at the target cell level and that less sialylated, short-lived variants may exert significant effects in in vivo conditions. Less acidic/sialylated glycoforms (elution pH value 6.60-4.60 as disclosed by high resolution chromatofocusing of anterior glycoprotein extracts), induced higher cAMP release, estrogen production and tissue-type plasminogen activator (tPA) enzyme activity as well as cytochrome P450 aromatase and tPA mRNA expression in cultured rat granulosa cells than the more acidic analogs (pH<4.76). By contrast, the more acidic/sialylated glycoforms induced higher alpha-inhibin subunit mRNA expression than their less acidic counterparts. In cumulus enclosed oocytes isolated from mice ovaries, addition of less acidic isoforms induced resumption of meiosis more efficiently than the more acidic analogs. Interestingly, the least acidic isoform (pH>7.10) behave as a strong antagonist of several FSH-mediated effects. Assessment of the in vivo effects of the isoforms on granulosa cell proliferation in follicles from immature rats, revealed that short-lived isoforms were equally or even more efficient than their more acidic counterparts in maintaining granulosa cell proliferation when administered immediately after hypophysectomy. These results show that the naturally occurring human FSH isoforms may exhibit differential or even unique effects at the target cell level and that factors other than the metabolic clearance rate of the molecule (including receptor-binding affinity and capability of the ligand to activate its receptor and trigger intracellular signaling) also play an important role in determining the net in vivo effects of a particular FSH variant.

Embryonic development after follicle culture is influenced by follicle-stimulating hormone isoelectric point range

We evaluated the effects of follicular exposure in vitro to either of two mutually exclusive isoforms of FSH (least acidic and acid) on the subsequent capacity of oocytes for embryonic development. The effects of dose and follicle culture duration were examined. At the threshold dose (that required to produce antra) and at one subthreshold dose, the major difference between the two isoform fractions was the timing and effectiveness of acquisition of two-cell embryonic developmental capacity. With the least-acidic fraction, the highest rate of two-cell development (approximately 80%) occurred after 3 days of follicle culture only at the threshold dose (2.5 ng/ml). With the acid fraction, the highest two-cell rate (approximately 60%) occurred after 5 days of culture but at equivalent rates over a range of doses between 10 ng/ml and 100 ng/ml (threshold dose was 50 ng/ml). At threshold dose or below, the capacity for two-cell embryo production appeared not to be influenced by antral status for either isoform. At above threshold doses, the least-acidic fraction induced an increasing proportion of antral follicles with increasing dose, but this increase was associated with a progressive decrease in embryo production. This relationship was more extreme after longer culture and was due to degeneration of the cumulus-oocyte complex associated with apparently increased differentiation of the mural granulosa cells. The acid fraction was by comparison less bioactive and insensitive to overdosing. The broader isoform mix of the unfractionated FSH provided a measure of protection against overdosing characteristic of the acid fraction while retaining the capacity of the least-acidic fraction to induce antral formation at a low dose.

Is there any physiological role for gonadotrophin oligosaccharide heterogeneity in humans? I. Gondatrophins are synthesized and released in multiple molecular forms. A matter of fact

Carbohydrates attached to the protein core of all glycoprotein hormones play an essential role in the function of the molecule, influencing a number of intracellular and extracellular processes. As with other members of the glycoprotein hormone family, pituitary gonadotrophins are not produced as single or unique molecules but rather as arrays of isoforms that differ from each other mainly in the structure of their oligosaccharide attachments. In both experimental animals and in humans, the abundance of the different isoforms varies depending on the endocrine status of the donor present at the time of collection of the tissue or sample. Conditions characterized by an oestrogen-enriched hormonal milieu (eg. the preovulatory phase of the menstrual cycle) promote the formation and secretion of variants with relatively low sialic acid and/or sulphate content, whereas physiological deficiency of this sex steroid (as in the postmenopause) favours the production of highly sialylated, long-lived gonadotrophin variants. When tested individually, less sialylated isoforms exhibit higher receptor-binding and in-vitro biological activity but shorter plasma half-life than their more sialylated counterparts. Both the hormonal regulation and the functional differences among the naturally occurring isoforms strongly suggest that gonadotrophin heterogeneity represents a distinctly different mechanism through which the pituitary gland may regulate the intensity and duration of the gonadotrophic stimulus. Nevertheless, whereas the existence of the alternatively glycosylated variants of gonadotrophins in both the pituitary and in serum is currently without doubt, the physiological role of this phenomenon is still a controversial issue and a matter of debate.

Human FSH isoforms: carbohydrate complexity as determinant of in-vitro bioactivity

Differences in sialic acid content of the hormone have been considered the main determinant of FSH polymorphism. The aim of the present study was to investigate the effect of variations in the oligosaccharide structure of the intrapituitary human FSH (hFSH) glycosylation variants on their intrinsic biological activity. FSH charge isoforms obtained after chromatofocusing were further separated by lectin affinity chromatography [Concanavalin A (ConA), Wheat germ agglutinin (WGA), Lentil lectin (LcH)]. Isolated isoforms were separately tested for in-vitro bioactivity in a rat Sertoli cell aromatization bioassay. Our results show that: (1) FSH microheterogeneity is due not only to variations in the sialic acid content of the hormone but also to differences in the internal structure of the carbohydrate chains, and (2) variations in the sialic acid content as well as differences in the complexity of the glycans determine the full biological expression of FSH glycosylation variants.

Ovarian response to follicle-stimulating hormone (FSH) stimulation depends on the FSH receptor genotype

Because the ovarian response to FSH stimulation in assisted reproduction is variable, ranging from hyporesponse to hyperresponse, with the possible complication of ovarian hyperstimulation, it would be of great benefit to predict the response of the patients to FSH. To date, no clear-cut predictors of ovarian responsiveness to FSH have been identified. In this study, we investigated the role of two distinct FSH receptor (FSHR) variants, Thr307/Asn680 and Ala307/Ser680, in the response to FSH in women undergoing controlled ovarian stimulation. The FSHR polymorphism at position 680 was analyzed by restriction-fragment-length polymorphism in 161 ovulatory women below the age of 40 yr. With reference to the couple, infertility has been diagnosed as being attributable to male causes (76%), tubal factor (11%), or both (13%). The distribution was 29% for the Asn/Asn, 45% for the Asn/Ser, and 26% for the Ser/Ser FSHR variant. Peak estradiol levels, number of preovulatory follicles, and number of retrieved oocytes were similar in the 3 groups. However, basal FSH levels were significantly different among the 3 groups (6.4 +/- 0.4 IU/L, 7.9 +/- 0.3 IU/L, and 8.3 +/- 0.6 IU/L for the Asn/Asn, Asn/Ser, and Ser/Ser groups, respectively, P < 0.01). The number of FSH ampoules required for successful stimulation was significantly different among the 3 groups (31.8 +/- 2.4, 40.7 +/- 2.3, and 46.8 +/- 5.0 for the Asn/Asn, Asn/Ser, and Ser/Ser groups, respectively, P < 0.05). According to multiple linear regression analysis, the number of ampoules needed could be predicted from a linear combination of both the type of polymorphism and basal FSH levels (P < 0.001). These clinical findings demonstrate that the ovarian response to FSH stimulation depends on the FSHR genotype.

Role of glycosylation in function of follicle-stimulating hormone

The oligosaccharide structures of heterodimeric glycoprotein hormones, such as follicle-stimulating hormone (FSH), have been shown to play an important role in the biosynthesis, secretion, metabolic fate, and regulation of potency of the hormone. The oligosaccharide structures attached to each subunit of the protein seem to exhibit distinct roles in some of these functions. Glycans attached to the alpha-subunit are critical for dimer assembly, integrity, and secretion, as well as for signal transduction; although beta-subunit glycans are also important for dimer assembly and secretion, they play a crucial role in clearance of the dimer from the circulation. Alternative glycosylation on FSH and other glycoprotein hormones not only may affect the metabolic clearance and net in vivo biopotency of the hormone, but also offers the interesting possibility that some glycosylation variants of the hormone may provoke differential or even unique effects at the target cell level. Glycosylation of FSH is regulated by hypothalamic and/or end products from the glands under the control of this hormone. In particular, estrogens regulate terminal sialylation and thus some functional properties of the gonadotropin influenced by sialic acid. Through these extrapituitary inputs, the gonadotroph may regulate not only the amount but also the intensity of the gonadotropin signal to be secreted by the pituitary in a given physiological condition.