In Vitro Impact of FSH Glycosylation Variants on FSH Receptor-stimulated Signal Transduction and Functional Selectivity

Follicle-stimulating hormone sweetness: How carbohydrate structures impact on the biological function of the hormone

Follicle-stimulating hormone (FSH), or follitropin, exists in multiple molecular forms due largely to its protein-carbohydrate composition and the complexity of the glycans attached to the protein core. The heterogeneity of gonadotropins exists in two forms, macroheterogeneity, which results from the absence of one or two oligosaccharide chains in the ß-subunit, and microheterogeneity which results from variation in the structures and complexity of the glycans attached to the hormone. In the clinical arena, FSH compounds are widely used by fertility specialists to promote ovarian follicle growth and maturation to a preovulatory follicle containing a fertilization-competent oocyte. Several genetically engineered recombinant human FSH preparations have been added to the arsenal of follitropin preparations in several countries for the treatment of infertility, particularly in women attending assisted reproduction clinics. Although the primary structure of these recombinant proteins is identical to that of naturally occurring FSH, the cell context and variations in the production and purification processes may impact the glycosidic profile of the recombinant FSH macro- and micro-heterogeneity, which may potentially influence the pharmacokinetics and pharmacodynamics of the compound. This review concentrates on the structure-function correlates of follitropin, with emphasis on the physiological and biological importance of the carbohydrates attached to its protein core, including its pharmacokinetics and biological activity. Emphasis is placed on pituitary FSH, and the available data on the various recombinant FSH preparations employed in therapeutics are also discussed, considering that this gonadotropin represents the cornerstone for the treatment of infertility in modern assisted reproduction.

Hormonal and Allosteric Regulation of the Luteinizing Hormone/Chorionic Gonadotropin Receptor

Luteinizing hormone (LH) and human chorionic gonadotropin (CG), like follicle-stimulating hormone, are the most important regulators of the reproductive system. They exert their effect on the cell through the LH/CG receptor (LHCGR), which belongs to the family of G protein-coupled receptors. Binding to gonadotropin induces the interaction of LHCGR with various types of heterotrimeric G proteins (Gs, Gq/11, Gi) and β-arrestins, which leads to stimulation (Gs) or inhibition (Gi) of cyclic adenosine monophosphate-dependent cascades, activation of the phospholipase pathway (Gq/11), and also to the formation of signalosomes that mediate the stimulation of mitogen-activated protein kinases (β-arrestins). The efficiency and selectivity of activation of intracellular cascades by different gonadotropins varies, which is due to differences in their interaction with the ligand-binding site of LHCGR. Gonadotropin signaling largely depends on the status of N- and O-glycosylation of LH and CG, on the formation of homo- and heterodimeric receptor complexes, on the cell-specific microenvironment of LHCGR and the presence of autoantibodies to it, and allosteric mechanisms are important in the implementation of these influences, which is due to the multiplicity of allosteric sites in different loci of the LHCGR. The development of low-molecular-weight allosteric regulators of LHCGR with different profiles of pharmacological activity, which can be used in medicine for the correction of reproductive disorders and in assisted reproductive technologies, is promising. These and other issues regarding the hormonal and allosteric regulation of LHCGR are summarized and discussed in this review.

Differential effects of follicle-stimulating hormone glycoforms on the transcriptome profile of cultured rat granulosa cells as disclosed by RNA-seq

It has been documented that variations in glycosylation on glycoprotein hormones, confer distinctly different biological features to the corresponding glycoforms when multiple in vitro biochemical readings are analyzed. We here applied next generation RNA sequencing to explore changes in the transcriptome of rat granulosa cells exposed for 0, 6, and 12 h to 100 ng/ml of four highly purified follicle-stimulating hormone (FSH) glycoforms, each exhibiting different glycosylation patterns: a. human pituitary FSH18/21 (hypo-glycosylated); b. human pituitary FSH24 (fully glycosylated); c. Equine FSH (eqFSH) (hypo-glycosylated); and d. Chinese-hamster ovary cell-derived human recombinant FSH (recFSH) (fully-glycosylated). Total RNA from triplicate incubations was prepared from FSH glycoform-exposed cultured granulosa cells obtained from DES-pretreated immature female rats, and RNA libraries were sequenced in a HighSeq 2500 sequencer (2 x 125 bp paired-end format, 10-15 x 106 reads/sample). The computational workflow focused on investigating differences among the four FSH glycoforms at three levels: gene expression, enriched biological processes, and perturbed pathways. Among the top 200 differentially expressed genes, only 4 (0.6%) were shared by all 4 glycoforms at 6 h, whereas 118 genes (40%) were shared at 12 h. Follicle-stimulating hormone glycocoforms stimulated different patterns of exclusive and associated up regulated biological processes in a glycoform and time-dependent fashion with more shared biological processes after 12 h of exposure and fewer treatment-specific ones, except for recFSH, which exhibited stronger responses with more specifically associated processes at this time. Similar results were found for down-regulated processes, with a greater number of processes at 6 h or 12 h, depending on the particular glycoform. In general, there were fewer downregulated than upregulated processes at both 6 h and 12 h, with FSH18/21 exhibiting the largest number of down-regulated associated processes at 6 h while eqFSH exhibited the greatest number at 12 h. Signaling cascades, largely linked to cAMP-PKA, MAPK, and PI3/AKT pathways were detected as differentially activated by the glycoforms, with each glycoform exhibiting its own molecular signature. These data extend previous observations demonstrating glycosylation-dependent distinctly different regulation of gene expression and intracellular signaling pathways triggered by FSH in granulosa cells. The results also suggest the importance of individual FSH glycoform glycosylation for the conformation of the ligand-receptor complex and induced signalling pathways.

Oocyte quality is enhanced by hypoglycosylated FSH through increased cell-to-cell interaction during mouse follicle development

Macroheterogeneity in follicle-stimulating hormone (FSH) β-subunit N-glycosylation results in distinct FSH glycoforms. Hypoglycosylated FSH21 is the abundant and more bioactive form in pituitaries of females under 35 years of age, whereas fully glycosylated FSH24 is less bioactive and increases with age. To investigate whether the shift in FSH glycoform abundance contributes to the age-dependent decline in oocyte quality, the direct effects of FSH glycoforms on folliculogenesis and oocyte quality were determined using an encapsulated in vitro mouse follicle growth system. Long-term culture (10-12 days) with FSH21 (10 ng/ml) enhanced follicle growth, estradiol secretion and oocyte quality compared with FSH24 (10 ng/ml) treatment. FSH21 enhanced establishment of transzonal projections, gap junctions and cell-to-cell communication within 24 h in culture. Transient inhibition of FSH21-mediated bidirectional communication abrogated the positive effects of FSH21 on follicle growth, estradiol secretion and oocyte quality. Our data indicate that FSH21 promotes folliculogenesis and oocyte quality in vitro by increasing cell-to-cell communication early in folliculogenesis, and that the shift in in vivo abundance from FSH21 to FSH24 with reproductive aging may contribute to the age-dependent decline in oocyte quality.

Differential effects of follicle-stimulating hormone glycoforms on the transcriptome profile of cultured rat granulosa cells as disclosed by RNA-seq

It has been documented that variations in glycosylation on glycoprotein hormones, confer distinctly different biological features to the corresponding glycoforms when multiple in vitro biochemical readings are analyzed. We here applied next generation RNA sequencing to explore changes in the transcriptome of rat granulosa cells exposed for 0, 6, and 12 h to 100 ng/ml of four highly purified follicle-stimulating hormone (FSH) glycoforms, each exhibiting different glycosylation patterns: human pituitary FSH18/21 and equine FSH (eqFSH) (hypo-glycosylated), and human FSH24 and chinese-hamster ovary cell-derived human recombinant FSH (recFSH) (fully-glycosylated). Total RNA from triplicate incubations was prepared from FSH glycoform-exposed cultured granulosa cells obtained from DES-pretreated immature female rats, and RNA libraries were sequenced in a HighSeq 2500 sequencer (2 × 125 bp paired-end format, 10-15 × 106 reads/sample). The computational workflow focused on investigating differences among the four FSH glycoforms at three levels: gene expression, enriched biological processes, and perturbed pathways. Among the top 200 differentially expressed genes, only 4 (0.6%) were shared by all 4 glycoforms at 6 h, whereas 118 genes (40%) were shared at 12 h. Follicle-stimulating hormone glycocoforms stimulated different patterns of exclusive and associated up regulated biological processes in a glycoform and time-dependent fashion with more shared biological processes after 12 h of exposure and fewer treatment-specific ones, except for recFSH, which exhibited stronger responses with more specifically associated processes at this time. Similar results were found for down-regulated processes, with a greater number of processes at 6 h or 12 h, depending on the particular glycoform. In general, there were fewer downregulated than upregulated processes at both 6 h and 12 h, with FSH18/21 exhibiting the largest number of down-regulated associated processes at 6 h while eqFSH exhibited the greatest number at 12 h. Signaling cascades, largely linked to cAMP-PKA, MAPK, and PI3/AKT pathways were detected as differentially activated by the glycoforms, with each glycoform exhibiting its own molecular signature. These data extend previous observations demonstrating glycosylation-dependent differential regulation of gene expression and intracellular signaling pathways triggered by FSH in granulosa cells. The results also suggest the importance of individual FSH glycoform glycosylation for the conformation of the ligand-receptor complex and induced signalling pathways.

Determination of Half-lives of Circulating FSH and LH Glycoforms in Women During GnRH Receptor Blockade

CONTEXT

Both FSH and LH circulate as 2 glycoforms, differing in number of glycans: low-N-glycosylated glycoforms, FSHtri and LHdi, and fully N-glycosylated glycoforms, FSHtetra and LHtri.

OBJECTIVES

To determine the half-lives of endogenous circulating gonadotropin glycoforms in women during GnRH receptor blockade.

DESIGN/PARTICIPANTS

Serum samples were collected in 8 healthy women before and up to 20 hours after administration of the NAL-GLU GnRH antagonist. Three women were in early follicular phase, 2 at mid-cycle phase, and 3 were postmenopausal.

MAIN OUTCOME MEASURES

The half-life of each glycoform was estimated by monoexponential decay for FSH (n = 8) and LH (n = 5). Data were analyzed using paired t tests.

RESULTS

Half-lives in the circulation of low-N-glycosylated glycoforms of both FSH and LH were shorter than those of the fully N-glycosylated glycoforms (mean; range, FSHtri 343; 116-686 minutes vs FSHtetra 757; 436-1038, minutes, P = 0.0003; LHdi 125, 84-198 minutes vs LHtri 164, 107-235 minutes, P = 0.004). The half-lives of low-and fully N-glycosylated forms of LH were shorter than the corresponding half-lives of FSH glycoforms, P = 0.0008.

CONCLUSIONS

For both FSH and LH, low-N-glycosylated glycoforms disappeared from the circulation faster than the fully N-glycosylated. The half-lives of low and fully N-glycosylated forms of LH were shorter than the corresponding half-lives of FSH. The estimated values for half-life in the circulation of total FSH and total LH will depend on the relative amounts of the 2 glycoforms of each hormone and their individual disappearance rates in circulation.

Updating the Landscape for Functioning Gonadotroph Tumors

Functioning gonadotroph adenomas (FGAs) are rare tumors, as the overwhelming majority of gonadotroph tumors are clinically silent. Literature is based on case reports and small case series. Gonadotroph tumors are poorly differentiated and produce and secrete hormones inefficiently, but in exceptional cases, they cause clinical syndromes due to hypersecretion of intact gonadotropins. The clinical spectrum of endocrine dysfunction includes an exaggerated response of ovaries characterized as ovarian hyperstimulation syndrome (OHSS) in premenopausal females and adolescent girls, testicular enlargement in males, and isosexual precocious puberty in children. Transsphenoidal surgery and removal of tumor reduces hormonal hypersecretion, improves endocrine dysfunction, and provides tissue for further analysis. Medical therapies (somatostatin analogues, dopamine agonists, GnRH agonists/antagonists) are partially or totally ineffective in many cases, especially with respect to antitumor effect. This review aims to update recent literature on these rare functioning tumors and highlight their therapeutic management.

Human FSH Glycoform α-Subunit Asparagine52 Glycans: Major Glycan Structural Consistency, Minor Glycan Variation in Abundance

Follicle-stimulating hormone (FSH), an α/β heterodimeric glycoprotein hormone, consists of functionally significant variants resulting from the presence or absence of either one of two FSHβ subunit N-glycans. The two most abundant variants are fully-glycosylated FSH24 (based on 24 kDa FSHβ band in Western blots) and hypo-glycosylated FSH21 (21 kDa band, lacks βAsn²⁴ glycans). Due to its ability to bind more rapidly to the FSH receptor and occupy more FSH binding sites than FSH24, hypo-glycosylated FSH21 exhibits greater biological activity. Endoglycosidase F1-deglycosylated FSH bound to the complete extracellular domain of the FSH receptor crystallized as a trimeric complex. It was noted that a single biantennary glycan attached to FSHα Asn⁵² might preemptively fill the central pocket in this complex and prevent the other two FSH ligands from binding the remaining ligand-binding sites. As the most active FSH21 preparations possessed more rapidly migrating α-subunit bands in Western blots, we hypothesized that Asn⁵² glycans in these preparations were small enough to enable greater FSH21 receptor occupancy in the putative FSHR trimer model. Highly purified hFSH oligosaccharides derived from each FSH subunit, were characterized by electrospray ionization-ion mobility-collision-induced dissociation (ESI-IM-CID) mass spectrometry. FSHβ glycans typically possessed core-linked fucose and were roughly one third bi-antennary, one third tri-antennary and one third tetra-antennary. FSHα oligosaccharides largely lacked core fucose and were bi- or tri-antennary. Those αAsn⁵² glycans exhibiting tetra-antennary glycan m/z values were found to be tri-antennary, with lactosamine repeats accounting for the additional mass. Selective αAsn⁵² deglycosylation of representative pituitary hFSH glycoform Superdex 75 gel filtration fractions followed by ESI-IM-CID mass spectrometry revealed tri-antennary glycans predominated even in the lowest molecular weight FSH glycoforms. Accordingly, the differences in binding capacity of the same receptor preparation to different FSH glycoforms are likely the organization of the FSH receptor in cell membranes, rather than the αAsn⁵² oligosaccharide.

Purification Process of a Recombinant Human Follicle Stimulating Hormone Biosimilar (Primapur®) to Yield a Pharmaceutical Product with High Batch-to-Batch Consistency

Recombinant human follicle stimulating hormone (r-hFSH) is widely used for infertility treatment and is subject to the development of biosimilars. There are different purification strategies that can yield r-hFSH of pharmaceutical quality from Chinese hamster ovary cell culture broth. We developed a purification process for r-hFSH centered on immunoaffinity chromatography with single-domain recombinant camelid antibodies. The resulting downstream process is simple and devoid of ultrafiltration operations. Studies on chromatography resin resource and ligand leakage showed that the immunoaffinity matrix employed was suitable for industrial use and stable for at least 40 full chromatography cycles, and the leaked single-domain antibody ligand was completely removed by subsequent purification steps. All chromatography resins employed withstood the same 40 cycles of use without significant changes in separation efficiency and product binding capacity. The resulting industrial purification process yielded batches of r-hFSH with consistent levels of purity and bioactivity.

Hypo-glycosylated hFSH drives ovarian follicular development more efficiently than fully-glycosylated hFSH: enhanced transcription and PI3K and MAPK signaling

STUDY QUESTION

Does hypo-glycosylated human recombinant FSH (hFSH18/21) have greater in vivo bioactivity that drives follicle development in vivo compared to fully-glycosylated human recombinant FSH (hFSH24)?

SUMMARY ANSWER

Compared with fully-glycosylated hFSH, hypo-glycosylated hFSH has greater bioactivity, enabling greater follicular health and growth in vivo, with enhanced transcriptional activity, greater activation of receptor tyrosine kinases (RTKs) and elevated phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT) and Mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) signaling.

WHAT IS KNOWN ALREADY

Glycosylation of FSH is necessary for FSH to effectively activate the FSH receptor (FSHR) and promote preantral follicular growth and formation of antral follicles. In vitro studies demonstrate that compared to fully-glycosylated recombinant human FSH, hypo-glycosylated FSH has greater activity in receptor binding studies, and more effectively stimulates the PKA pathway and steroidogenesis in human granulosa cells.

STUDY DESIGN, SIZE, DURATION

This is a cross-sectional study evaluating the actions of purified recombinant human FSH glycoforms on parameters of follicular development, gene expression and cell signaling in immature postnatal day (PND) 17 female CD-1 mice. To stimulate follicle development in vivo, PND 17 female CD-1 mice (n = 8-10/group) were treated with PBS (150 µl), hFSH18/21 (1 µg/150 µl PBS) or hFSH24 (1 µg/150 µl PBS) by intraperitoneal injection (i.p.) twice daily (8:00 a.m. and 6:00 p.m.) for 2 days. Follicle numbers, serum anti-Müllerian hormone (AMH) and estradiol levels, and follicle health were quantified. PND 17 female CD-1 mice were also treated acutely (2 h) in vivo with PBS, hFSH18/21 (1 µg) or hFSH24 (1 µg) (n = 3-4/group). One ovary from each mouse was processed for RNA sequencing analysis and the other ovary processed for signal transduction analysis. An in vitro ovary culture system was used to confirm the relative signaling pathways.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The purity of different recombinant hFSH glycoforms was analyzed using an automated western blot system. Follicle numbers were determined by counting serial sections of the mouse ovary. Real-time quantitative RT-PCR, western blot and immunofluorescence staining were used to determine growth and apoptosis markers related with follicle health. RNA sequencing and bioinformatics were used to identify pathways and processes associated with gene expression profiles induced by acute FSH glycoform treatment. Analysis of RTKs was used to determine potential FSH downstream signaling pathways in vivo. Western blot and in vitro ovarian culture system were used to validate the relative signaling pathways.

MAIN RESULTS AND THE ROLE OF CHANCE

Our present study shows that both hypo- and fully-glycosylated recombinant human FSH can drive follicular growth in vivo. However, hFSH18/21 promoted development of significantly more large antral follicles compared to hFSH24 (P < 0.01). In addition, compared with hFSH24, hFSH18/21 also promoted greater indices of follicular health, as defined by lower BAX/BCL2 ratios and reduced cleaved Caspase 3. Following acute in vivo treatment with FSH glycoforms RNA-sequencing data revealed that both FSH glycoforms rapidly induced ovarian transcription in vivo, but hypo-glycosylated FSH more robustly stimulated Gαs and cAMP-mediated signaling and members of the AP-1 transcription factor complex. Moreover, hFSH18/21 treatment induced significantly greater activation of RTKs, PI3K/AKT and MAPK/ERK signaling compared to hFSH24. FSH-induced indices of follicle growth in vitro were blocked by inhibition of PI3K and MAPK.

LARGE SCALE DATA

RNA sequencing of mouse ovaries. Data will be shared upon reasonable request to the corresponding author.

LIMITATIONS, REASONS FOR CAUTION

The observations that hFSH glycoforms have different bioactivities in the present study employing a mouse model of follicle development should be verified in nonhuman primates. The gene expression studies reflect transcriptomes of whole ovaries.

WIDER IMPLICATIONS OF THE FINDINGS

Commercially prepared recombinant human FSH used for ovarian stimulation in human ART is fully-glycosylated FSH. Our findings that hypo-glycosylated hFSH has greater bioactivity enabling greater follicular health and growth without exaggerated estradiol production in vivo, demonstrate the potential for its development for application in human ART.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by NIH 1P01 AG029531, NIH 1R01 HD 092263, VA I01 BX004272, and the Olson Center for Women's Health. JSD is the recipient of a VA Senior Research Career Scientist Award (1IK6 BX005797). This work was also partially supported by National Natural Science Foundation of China (No. 31872352). The authors declared there are no conflicts of interest.

Reduced FSH and LH action: implications for medically assisted reproduction

Luteinizing hormone (LH) and follicle-stimulating hormone (FSH) play complementary roles in follicle development and ovulation via a complex interaction in the hypothalamus, anterior pituitary gland, reproductive organs, and oocytes. Impairment of the production or action of gonadotropins causes relative or absolute LH and FSH deficiency that compromises gametogenesis and gonadal steroid production, thereby reducing fertility. In women, LH and FSH deficiency is a spectrum of conditions with different functional or organic causes that are characterized by low or normal gonadotropin levels and low oestradiol levels. While the causes and effects of reduced LH and FSH production are very well known, the notion of reduced action has received less attention by researchers. Recent evidence shows that molecular characteristics, signalling as well as ageing, and some polymorphisms negatively affect gonadotropin action. These findings have important clinical implications, in particular for medically assisted reproduction in which diminished action determined by the afore-mentioned factors, combined with reduced endogenous gonadotropin production caused by GnRH analogue protocols, may lead to resistance to gonadotropins and, thus, to an unexpected hypo-response to ovarian stimulation. Indeed, the importance of LH and FSH action has been highlighted by the International Committee for Monitoring Assisted Reproduction Technologies (ICMART) in their definition of hypogonadotropic hypogonadism as gonadal failure associated with reduced gametogenesis and gonadal steroid production due to reduced gonadotropin production or action. The aim of this review is to provide an overview of determinants of reduced FSH and LH action that are associated with a reduced response to ovarian stimulation.

Low- and Fully N-Glycosylated Gonadotropins Circulating in Women With Polycystic Ovary Syndrome

Context

A preponderance of basic luteinizing hormone (LH) molecules having elevated bioactivity was detected in the circulation of women with polycystic ovary syndrome (PCOS). Subsequent studies have shown that LH and follicle-stimulating hormone (FSH) both circulate as glycoforms differing in number of glycans: low-N-glycosylated glycoforms, LHdi and FSHtri, with high in vitro bioactivity, and fully glycosylated glycoforms, LHtri and FSHtetra, with high in vivo bioactivity.

Objective

This work aims to characterize the glycosylation patterns on circulating gonadotropin glycoforms in women with PCOS.

Methods

Serum samples, collected from 8 women with PCOS were included. The concentration, sulfonation, and sialylation of each glycoform were determined and compared with values of serum samples from healthy women: 22 women at follicular phase, 16 at midcycle, and 15 after menopause.

Results

All the women with PCOS had higher LHdi serum levels compared with those in the follicular-phase group. Median LHdi and median LHtri levels were significantly elevated in PCOS women. The percentage of LHdi was increased from 37 to 49 and that of FSHtri was decreased from 41 to 33. The LHdi, LHtri, and FSHtetra glycoforms were more sialylated and both LH glycoforms less sulfonated in women with PCOS.

Conclusion

All women with PCOS had increased serum levels of LHdi, compared with those in the follicular phase. The percentage of LHdi was increased and that of FSHtri decreased in women with PCOS. The increased LHdi leads to maintenance of the abnormal early follicular development of the polycystic ovary, and the decreased FSHtri contributes to the arrested follicle growth.

Recent advances in understanding gonadotropin signaling

Gonadotropins are glycoprotein sex hormones regulating development and reproduction and bind to specific G protein–coupled receptors expressed in the gonads. Their effects on multiple signaling cascades and intracellular events have recently been characterized using novel technological and scientific tools. The impact of allosteric modulators on gonadotropin signaling, the role of sugars linked to the hormone backbone, the detection of endosomal compartments supporting signaling modules, and the dissection of different effects mediated by these molecules are areas that have advanced significantly in the last decade. The classic view providing the exclusive activation of the cAMP/protein kinase A (PKA) and the steroidogenic pathway by these hormones has been expanded with the addition of novel signaling cascades as determined by high-resolution imaging techniques. These new findings provided new potential therapeutic applications. Despite these improvements, unanswered issues of gonadotropin physiology, such as the intrinsic pro-apoptotic potential to these hormones, the existence of receptors assembled as heteromers, and their expression in extragonadal tissues, remain to be studied. Elucidating these issues is a challenge for future research.

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

CONTEXT

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

New Human Follitropin Preparations: How Glycan Structural Differences May Affect Biochemical and Biological Function and Clinical Effect

It is well accepted that pituitary follitropin is secreted into the circulation as a mixture of variants, which differ not in primary structure but rather at the level of glycosylation. These glycosidic forms vary in the number of glycosylation sites filled, complexity of glycosidic chains, and sialylation and sulfation. It is generally agreed that high sialylation, 2,3 sialic acid capping of terminal N-acetyl galactosamine or galactose leads to longer circulating half-life, by blocking binding of asialoglycoprotein receptor (ASGPR) in the liver. In contrast, 2,6 sialic acid found in humans does not prevent recognition of galactose and N-acetyl galactosamine by ASGPR. Few studies on clinical outcomes comparing differences in sialylation of follitropin found in commercially available preparations are available. Thus, there is a clear need for a consortium of open data to address this unmet need. Recently, FSH glycosylation, primarily on the β-subunit, which varies as women age, has emerged as a key modifier of follitropin action, with profound biological effects in vivo in animal models. To date, limited information of recombinant follitropin hormone preparations is available. Thus, most of the studies with FSH that is well characterized biochemically have been done in vitro, with engineered non gonadal host cells bearing recombinant receptors or in animal models. Since limited studies in human granulosa cells are available, a question is whether structural differences in glycosylation in commercially available follitropin affects biological function and clinical effect in humans. The presence of fucose, for example, has not been studied greatly even though, in the case of antibody therapy it has been shown to have a large effect on antibody targeting. This review on glycosidic variability of follitropin from the biochemical/structural point of view reflects on this question and presents an assessment in the context of available published data. If clinical differences are to be expected or not, the readers will have a better understanding of the evidence for and limitations of such expectations.

Biased signaling in naturally occurring mutations of G protein-coupled receptors associated with diverse human diseases

G protein-coupled receptors (GPCRs) play critical roles in transmitting a variety of extracellular signals into the cells and regulate diverse physiological functions. Naturally occurring mutations that result in dysfunctions of GPCRs have been known as the causes of numerous diseases. Significant progresses have been made in elucidating the pathophysiology of diseases caused by mutations. The multiple intracellular signaling pathways, such as G protein-dependent and β-arrestin-dependent signaling, in conjunction with recent advances on biased agonism, have broadened the view on the molecular mechanism of disease pathogenesis. This review aims to briefly discuss biased agonism of GPCRs (biased ligands and biased receptors), summarize the naturally occurring GPCR mutations that cause biased signaling, and propose the potential pathophysiological relevance of biased mutant GPCRs associated with various endocrine diseases.

Differential FSH Glycosylation Modulates FSHR Oligomerization and Subsequent cAMP Signaling

Follicle-stimulating hormone (FSH) and its target G protein-coupled receptor (FSHR) are essential for reproduction. Recent studies have established that the hypo-glycosylated pituitary FSH glycoform (FSH21/18), is more bioactive in vitro and in vivo than the fully-glycosylated variant (FSH24). FSH21/18 predominates in women of reproductive prime and FSH24 in peri-post-menopausal women, suggesting distinct functional roles of these FSH glycoforms. The aim of this study was to determine if differential FSH glycosylation modulated FSHR oligomerization and resulting impact on cAMP signaling. Using a modified super-resolution imaging technique (PD-PALM) to assess FSHR complexes in HEK293 cells expressing FSHR, we observed time and concentration-dependent modulation of FSHR oligomerization by FSH glycoforms. High eFSH and FSH21/18 concentrations rapidly dissociated FSHR oligomers into monomers, whereas FSH24 displayed slower kinetics. The FSHR β-arrestin biased agonist, truncated eLHβ (Δ121-149) combined with asparagine56-deglycosylated eLHα (dg-eLHt), increased FSHR homomerization. In contrast, low FSH21/18 and FSH24 concentrations promoted FSHR association into oligomers. Dissociation of FSHR oligomers correlated with time points where higher cAMP production was observed. Taken together, these data suggest that FSH glycosylation may modulate the kinetics and amplitude of cAMP production, in part, by forming distinct FSHR complexes, highlighting potential avenues for novel therapeutic targeting of the FSHR to improve IVF outcomes.

Follicle-Stimulating Hormone Induces Lipid Droplets via Gαi/o and β-Arrestin in an Endometrial Cancer Cell Line

Follicle-stimulating hormone (FSH) and its G protein-coupled receptor, FSHR, represents a paradigm for receptor signaling systems that activate multiple and complex pathways. Classically, FSHR activates Gαs to increase intracellular levels of cAMP, but its ability to activate other G proteins, and β-arrestin-mediated signaling is well documented in many different cell systems. The pleiotropic signal capacity of FSHR offers a mechanism for how FSH drives multiple and dynamic downstream functions in both gonadal and non-gonadal cell types, including distinct diseases, and how signal bias may be achieved at a pharmacological and cell system-specific manner. In this study, we identify an additional mechanism of FSH-mediated signaling and downstream function in the endometrial adenocarcinoma Ishikawa cell line. While FSH did not induce increases in cAMP levels, this hormone potently activated pertussis toxin sensitive Gαi/o signaling. A selective allosteric FSHR ligand, B3, also activated Gαi/o signaling in these cells, supporting a role for receptor-mediated activation despite the low levels of FSHR mRNA. The low expression levels may attribute to the lack of Gαs/cAMP signaling as increasing FSHR expression resulted in FSH-mediated activation of the Gαs pathway. Unlike prior reports for FSH-mediated Gαs/cAMP signaling, FSH-mediated Gαi/o signaling was not affected by inhibition of dynamin-dependent receptor internalization. While chronic FSH did not alter cell viability, FSH was able to increase lipid droplet size. The β-arrestins are key adaptor proteins known to regulate FSHR signaling. Indeed, a rapid, FSH-dependent increase in interactions between β-arrestin1 and Gαi1 was observed via NanoBiT complementation in Ishikawa cells. Furthermore, both inhibition of Gαi/o signaling and siRNA knockdown of β-arrestin 1/2 significantly reduced FSH-induced lipid droplet accumulation, implying a role for a Gαi/o/β-arrestin complex in FSH functions in this cell type. As FSH/FSHR has been implicated in distinct hormone-dependent cancers, including endometrial cancer, analysis of the cancer genome database from 575 human endometrial adenocarcinoma tumors revealed that a subpopulation of samples expressed FSHR. Overall, this study highlights a novel mechanism for FSHR signal pleiotropy that may be exploited for future personalized therapeutic approaches.

Gonadotropin Glycoforms Circulating in Women Using Progestins of the Levonorgestrel Family for Contraception

Context

The progestins of the levonorgestrel family are 13-ethylgonane progestins, commonly used for contraception in women. One contraceptive effect of these progestins is inhibition of ovulation, which may be a result of changes in gonadotropin glycosylation patterns. Gonadotropin glycoforms differ in number of glycans and bioactivity: more bioactive low-N-glycosylated glycoforms, diglycosylated luteinizing hormone (LHdi) and triglycosylated follicle-stimulating hormone (FSHtri), and less bioactive fully N-glycosylated glycoforms, LHtri and FSHtetra.

Objective

Characterize the glycosylation patterns on the circulating gonadotropin glycoforms in women using 13-ethylgonane progestins for contraception.

Design, Subjects, Main Outcome Measures

Serum samples, collected from 92 healthy women using 13-ethylgonane progestins for contraception, were included. Forty women used progestin-only continuously and 52 used progestins combined with ethinylestradiol (EE) for 3 weeks followed by a hormone-free week. Concentration, sulfonation, and sialylation of each glycoform were determined and compared with follicular phase values of normal menstrual cycles.

Results

The progestin-only group had significantly increased serum levels, decreased sulfonation, and increased sialylation of LHdi. The LHdi/FSHtri ratio was increased. The progestin+EE group had significantly decreased gonadotropin glycoform concentrations and decreased sialylation of FSHtri. The progestin+EE effect on sialylation of FSHtri occurred later during the treatment cycle in contrast to the effect on FSHtri concentration.

Conclusions

The 2 different progestin treatments induced different effects on the glycan synthesis and concentrations of more bioactive low-glycosylated gonadotropins. Progestin-only treatment increased sialylation and decreased sulfonation of LHdi molecules, contributing to sustained higher levels of bioactive LHdi molecules. Progestin+EE treatment decreased sialylation of FSHtri, contributing to a shorter half-life and decreased levels of bioactive FSHtri.

Bioactivity of recombinant hFSH glycosylation variants in primary cultures of porcine granulosa cells

Previous studies have reported hypo-glycosylated FSH and fully-glycosylated FSH to be naturally occurring in humans, and these glycoforms exist in changing ratios over a woman's lifespan. The precise cellular and molecular effects of recombinant human FSH (hFSH) glycoforms, FSH21 and FSH24, have not been documented in primary granulosa cells. Herein, biological responses to FSH21 and FSH24 were compared in primary porcine granulosa cells. Hypo-glycosylated hFSH21 was significantly more effective than fully-glycosylated hFSH24 at stimulating cAMP accumulation and protein kinase A (PKA) activity, leading to the higher phosphorylation of CREB and β-Catenin. Compared to fully-glycosylated hFSH24, hypo-glycosylated hFSH21 also induced greater levels of transcripts for HSD3B, STAR and INHA, and higher progesterone production. Our results demonstrate that hypo-glycosylated hFSH21 exerts more robust activation of intracellular signals associated with steroidogenesis than fully-glycosylated hFSH24 in primary porcine granulosa cells, and furthers our understanding of the differing bioactivities of FSH glycoforms in the ovary.