Structural features of mammalian gonadotropins

Comparative glycomics of the glycoprotein follicle stimulating hormone: glycopeptide analysis of isolates from two mammalian species

Follicle stimulating hormone (FSH) is one of the important hormones that regulate gonadal functions. This hormone is glycosylated, and the glycans greatly influence the biological properties. In the present study the negatively charged glycopeptides of equine and human pituitary follicle stimulating hormone (eFSH and hFSH) have been characterized in a glycosylation site-specific manner using FT-ICR-MS and Edman sequencing. The characteristic pattern of glycan distribution at each glycosylation site has been deduced and compared between horse and human FSH preparations. The data suggest that site-specific differences exist between glycoforms of human and equine FSH. For instance, except for one site in the beta subunit (Asn7) of hFSH all other sites in both species have sulfated glycoforms. Also, glycoforms at Asn52 of hFSH are all complex type, whereas in eFSH, both complex and hybrid structures exist at this site. There is also a higher percentage of sulfated glycans in the latter site compared to the former. This is the first study that characterizes the glycans from this hormone in a glycosylation site-specific manner, and these data can be used to begin correlative studies between glycosylation structure and hormone function.

Conjugated estrogens and tibolone modify the gonadotrophin glycosylation pattern in postmenopausal women

OBJECTIVE

The purpose of this study was to evaluate the changes in the percentage of glycosylation of FSH and LH when using conjugated estrogens and tibolone as hormonal therapy (HT) in postmenopausal compared with regular menstrual cycles.

DESIGN

The study had three groups, with 10 participants in each group. The control group consisted of 10 women with normal menstrual cycles, a second group with 10 postmenopausal patients who received conjugated estrogens (Premarin 0.625 mg), and a third group had 10 patients who received tibolone (Livial 2.5 mg). All patients had hormonal determinations before and 6 months after the use of HT. Concavalin-A was used to separate the different glycosylated species of gonadotrophins, defined as unbound (UB: triantennary and bisecting oligosaccharides), weakly bound (WB: biantennary and truncated oligosaccharides), and firmly bound isoforms (FB: hybrid- and high-mannose-type oligosaccharides) in patients serum. Elusions containing the fractions with the isoforms were concentrated using Centriprep membranes (Amicon, Beverly, Mass., USA) and the different gonadotrophins isoforms were quantified by chemiluminescence using an automated system Immulite.

RESULTS

The pattern of distribution of gonadotrophins glycosylation in patients treated with conjugated estrogens and tibolone was similar to that observed in the control group with normal menstrual cycles, although with different glycosylation percentage. When the glycosylation percentages were compared for FSH, in the fraction UB the glycosylation did not have significant differences, but the fraction WB that has isoforms with high amounts of oligosaccharides showed a different percentage of glycosylation, where the recovery percentage was bigger with tibolone use (p < 0.05). The FB fraction had similar hormonal glycosylation with estrogens and tibolone use. When compared, LH glycosylation showed significant differences (p < 0.05) in the fraction UB with a bigger glycosylation degree, and in the fraction FB with a smaller glycosylation percentage, both in the tibolone group compared with conjugated estrogens use.

CONCLUSIONS

Our results show that there are different percentages of glycosylation of gonadotrophins depending on type of HT (conjugated estrogens vs tibolone), and this could be of utility in young women with ovarian problem since to know the isoform that more favors to cellular activity could help a better therapeutic.

Germ cell development in equine testis tissue xenografted into mice

Grafting of testis tissue from immature animals to immunodeficient mice results in complete spermatogenesis, albeit with varying efficiency in different species. The objectives of this study were to investigate if grafting of horse testis tissue would result in spermatogenesis, and to assess the effect of exogenous gonadotropins on xenograft development. Small fragments of testis tissue from 7 colts (2 week to 4 years of age) were grafted under the back skin of castrated male immunodeficient mice. For 2 donor animals, half of the mice were treated with gonadotropins. Xenografts were analyzed at 4 and 8 months post-transplantation. Spermatogenic differentiation following grafting ranged from no differentiation to progression through meiosis with appearance of haploid cells. Administration of exogenous gonadotropins appeared to support post-meiotic differentiation. For more mature donor testis samples where spermatogenesis had progressed into or through meiosis, after grafting an initial loss of differentiated germ cells was observed followed by a resurgence of spermatogenesis. However, if haploid cells had been present prior to grafting, spermatogenesis did not progress beyond meiotic division. In all host mice with spermatogenic differentiation in grafts, increased weight of the seminal vesicles compared to castrated mice showed that xenografts were releasing testosterone. These results indicate that horse spermatogenesis occurs in a mouse host albeit with low efficiency. In most cases, spermatogenesis arrested at meiosis. The underlying mechanisms of this spermatogenic arrest require further investigation.

Effects of recombinant human follicle stimulating hormone on follicle development and ovulation in the mare

The only gonadotrophin preparation shown to stimulate commercially useful multiple ovulation in mares is equine pituitary extract (EPE); even then, the low and inconsistent ovulatory response has been ascribed to the variable, but high, LH content. This study investigated the effects of an LH-free FSH preparation, recombinant human follicle stimulating hormone (rhFSH), on follicle development, ovulation and embryo production in mares. Five mares were treated twice-daily with 450 i.u. rhFSH starting on day 6 after ovulation, coincident with PGF(2alpha) analogue administration; five control mares were treated similarly but with saline instead of rhFSH. The response was monitored by daily scanning of the mares' ovaries and assay of systemic oestradiol-17beta and progesterone concentrations. When the dominant follicle(s) exceeded 35 mm, ovulation was induced with human chorionic gonadotrophin; embryos were recovered on day 7 after ovulation. After an untreated oestrous cycle to 'wash-out' the rhFSH, the groups were crossed-over and treated twice-daily with 900 i.u. rhFSH, or saline. At the onset of treatment, the largest follicle was <25 mm in all mares, and mares destined for rhFSH treatment had at least as many 10-25 mm follicles as controls. However, neither dose of rhFSH altered the number of days before the dominant follicle(s) reached 35 mm, the number of follicles of any size class (10-25, 25-35, >3 mm) at ovulation induction, the pre- or post-ovulatory oestradiol-17beta or progesterone concentrations, the number of ovulations or the embryo yield. It is concluded that rhFSH, at the doses used, is insufficient to stimulate multiple follicle development in mares.

Potential new strategies for the treatment of ovarian infertility and degenerative diseases with autologous ovarian stem cells

The 50-year-old and currently prevailing view that all oocytes in adult human ovaries persist from the fetal period of life is controversial as it clashes with Darwinian evolutionary theory. Studies of oogenesis and follicular renewal in adult human ovaries, and of the role of hormonal signals and third-party cells (tissue macrophages and T cells), could all be helpful in providing better understanding of the causes of ovarian infertility, its prevention and potential therapy. In addition, the authors recently reported differentiation of distinct cell types and the production of new eggs in cultures derived from premenopausal and postmenopausal human ovaries. It is possible that fertilisation of such eggs will open up new opportunities for providing genetically related children to infertile women for whom conventional in vitro fertilisation has failed. As ovarian stem cells appear to represent a new type of totipotent adult stem cell, they could also be utilised for autologous stem cell therapy of degenerative diseases, without any involvement of allogeneic embryonic stem cells and somatic cell nuclear transfer.

A Reference Preparation of Buffalo Pituitary Follicle Stimulating Hormone using Lectin Affinity Chromatography

An improved and cost effective method to isolate FSH from buffalo pituitary glands is described here. The buFSH activity was monitored throughout by a highly sensitive heterologous radioimmunoassay (sensitivity 0.2 ng oFSH/mL) and the in vivo biological activity of the final preparation was also established. A biologically active buFSH-enriched preparation with a moderate recovery (42%) was obtained. The yield of the final buFSH-enriched preparation was 26.5 mg/kg of buffalo pituitary gland. In SDS-PAGE, the purified buFSH resolved as a heterodimer of 30 kDa molecular size, with a 21 kDa presumptive alpha-subunit. This preparation was also characterized in terms of biological and some of its physicochemical properties. A high-titer antiserum to buFSH was also raised in rabbit using this preparation. The reagents generated, buFSH and buFSH-specific polyclonal antisera, have possible diagnostic and therapeutic usage for improvement of reproductive health of water buffaloes.

Mammalian-like nonsialyl complex-type N-glycosylation of equine gonadotropins in Mimic™ insect cells

Recombinant equine luteinizing hormone/chorionic gonadotropin (eLH/CG) was expressed in Mimic insect cells, that are commercial stably transformed Spodoptera frugiperda (Sf9) cells expressing five mammalian genes encoding glycosyltransferases involved in the synthesis of complex-type monosialylated N-glycans. We previously showed that it exhibited no in vivo bioactivity although expressing full in vitro bioactivity, and it was suspected that this was because of insufficient sialylation of eLH/CG N-glycans. Lectin binding analyses were performed with recombinant dimeric eLH/CG or its alpha subunit, secreted in the serum-containing supernatant of infected Sf9 and Mimic cells. Two types of specific lectin affinity assays (blot analyses and enzyme-linked immunosorbent assay) were used to compare the ability or inability of natural and recombinant gonadotropins to bind to various lectins. In natural equine chorionic gonadotropin (eCG), complex-type N-glycans terminating with both Siaalpha2,3Gal (based on Maackia amurensis agglutinin [MAA] binding) and Siaalpha2,6Gal (based on Sambucus nigra agglutinin [SNA] binding) were found, but in the alpha subunit dissociated from natural eCG, we only detected Siaalpha2-6Gal. In eLH/CG and its alpha subunit produced by Sf9 cells, N-glycans were found to be terminated by mannosyl residues (based on Galanthus nivalis agglutinin [GNA] binding), whereas those produced in Mimic cells were terminated by galactoses (based on binding to Ricinus communis agglutinin I [RCA I] , but not to SNA or MAA). This is in agreement with the fact that the nucleotide donor substrate of sialic acid is not naturally synthesized in insect cells. On the basis of binding to Arachis Hypogaea agglutinin [PNA], O-glycans exhibited the Galbeta1-3GalNAc structure in recombinant-free alpha and eLH/CG from both Sf9 and Mimic cell lines. Both N- and O-linked carbohydrate side chains synthesized in Mimic cells should thus be amenable to further acellular sialylation.

Oogenesis in adult mammals, including humans: a review

The origin of oocytes and primary follicles in ovaries of adult mammalian females has been a matter of dispute for over 100 yr. The prevailing belief that all oocytes in adult mammalian females must persist from the fetal period of life seems to be a uniquely retrogressive reproductive mechanism requiring humans to preserve their gametes from the fetal period for several decades. The utilization of modern techniques during last 10 yr clearly demonstrates that mammalian primordial germ cells originate from somatic cell precursors. This indicates that if somatic cells are precursors of germ cells, then somatic mutations can be passed on to progeny. Mitotically active germline stem cells have been described earlier in ovaries of adult prosimian primates and recently have been reported to also be present in the ovaries of adult mice. We have earlier shown that in adult human females, mesenchymal cells in the ovarian tunica albuginea undergo a mesenchymal-epithelial transition into ovarian surface epithelium cells, which differentiate sequentially into primitive granulosa and germ cells. Recently, we have reported that these structures assemble in the deeper ovarian cortex and form new follicles to replace earlier primary follicles undergoing atresia (follicular renewal). Our current observations also indicate that follicular renewal exists in rat ovaries, and human oocytes can differentiate from ovarian surface epithelium in fetal ovaries in vivo and from adult ovaries in vitro. These reports challenge the established dogma regarding the fetal origin of eggs and primary follicles in adult mammalian ovaries. Our data indicate that the pool of primary follicles in adult human ovaries does not represent a static but a dynamic population of differentiating and regressing structures. Yet, the follicular renewal may cease at a certain age, and this may predetermine the onset of the natural menopause or premature ovarian failure. A lack of follicular renewal in aging ovaries may cause an accumulation of spontaneously arising or environmentally induced genetic alterations of oocytes, and that may be why aging females have a much higher chance of having oocytes with more mutations in persisting primary follicles.

Two-step chromatographic purification of recombinant human thyrotrophin and its immunological, biological, physico-chemical and mass spectral characterization

A purification strategy for rapidly obtaining recombinant human thyrotropin (rhTSH) was designed based on size exclusion and reversed-phase high-performance liquid chromatographic (HPLC) analysis, carried out on hTSH-secreting CHO cell conditioned medium. These analyses permitted the identification of the main contaminants to be eliminated. Considering that hTSH is highly hydrophobic and elutes only with the addition of organic solvents, hydrophobic interaction chromatography was adopted as the first purification step; this resulted in the elimination of, among others, the major contaminant. A second purification step, based on size exclusion chromatography, was then utilized, being effective in the elimination of other previously identified contaminating proteins. Useful purity, as high as 99% at the chemical reagent level, and recoveries (37%) were obtained by adopting this two step strategy, which also provided adequate material for physico-chemical, immunological and biological characterization. This included matrix-assisted laser desorption ionization time-of-flight mass spectral analysis (MALDI-TOF-MS), Western blotting analysis, in vivo biological assay, size-exclusion HPLC (HPSEC) and reversed-phase HPLC (RP-HPLC) analysis, which confirmed the integrity and bioactivity of our rhTSH in comparison with the only two reference preparations available at the milligram level of native (hTSH-NIDDK) and recombinant (Thyrogen) hTSH. Thyrogen and rhTSH-IPEN, when compared to pit-hTSH-NIDDK, presented more than twice as much biological activity and about 7% increased molecular mass by MALDI-TOF-MS analysis, an accurate heterodimer mass determination providing the Mr values of 29,611, 29,839 and 27,829, respectively. The increased molecular mass of the two recombinant preparations was also confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and HPSEC analysis. Comparing the two recombinant preparations, minor though interesting physico-chemical and biological differences were also observed.

Generation and purification of recombinant bovine pregnancy associated glycoprotein

Bovine pregnancy-associated glycoprotein-1 (bPAG-1) is predicted to play an essential role during pregnancy and is labelled as a potential biochemical marker of pregnancy in ungulates. We have compared the generation of the glycosylated form of recombinant bPAG-1 (rbPAG-1) by human embryonic kidney 293 (HEK 293) and Chinese hamster ovary (CHO) cells in attached cultures and evaluated the adaptation of the rbPAG-1 transfected cell line to suspension culture. The PAG cDNA was cloned from placental RNA obtained from a slaughtered cow on day 55 of pregnancy. The PAG-pRcRSV expression vector was transfected into HEK 293 and CHO cells. Western blot analysis showed that clonal HEK 293 cells expressed rbPAG-1 better than CHO cells in attached cultures. Transfected HEK 293 cells were adapted to suspension culture in spinner flasks and the rbPAG-1 purified to homogeneity using ion-exchange, pepstatin-sepharose affinity chromatographies and preparative SDS-PAGE. The expression of rbPAG-1 was immunocharacterised using a polyclonal antibody. Our findings indicated that 293 cells are suitable for production of glycosylated form of rbPAG-1 and that the availability of the recombinant glycoprotein will aid in further studies to elucidate the function and structure of the protein.

Multiple and overlapping combinatorial codes orchestrate hormonal responsiveness and dictate cell-specific expression of the genes encoding luteinizing hormone

Normal reproductive function in mammals requires precise control of LH synthesis and secretion by gonadotropes of the anterior pituitary. Synthesis of LH requires expression of two genes [alpha-glycoprotein subunit (alphaGSU) and LHbeta] located on different chromosomes. Hormones from the hypothalamus and gonads modulate transcription of both genes as well as secretion of the biologically active LH heterodimer. In males and females, the transcriptional tone of the genes encoding alphaGSU and LHbeta reflects dynamic integration of a positive signal provided by GnRH from hypothalamic neurons and negative signals emanating from gonadal steroids. Although alphaGSU and LHbeta genes respond transcriptionally in the same manner to changes in hormonal input, different combinations of regulatory elements orchestrate their response. These hormone-responsive regulatory elements are also integral members of much larger combinatorial codes responsible for targeting expression of alphaGSU and LHbeta genes to gonadotropes. In this review, we will profile the genomic landscape of the promoter-regulatory region of both genes, depicting elements and factors that contribute to gonadotrope-specific expression and hormonal regulation. Within this context, we will highlight the different combinatorial codes that control transcriptional responses, particularly those that mediate the opposing effects of GnRH and one of the sex steroids, androgens. We will use this framework to suggest that GnRH and androgens attain the same transcriptional endpoint through combinatorial codes unique to alphaGSU and LHbeta. This parallelism permits the dynamic and coordinate regulation of two genes that encode a single hormone.

Expression of the full-length and alternatively spliced equine luteinizing hormone/chorionic gonadotropin receptor mRNAs in the primary corpus luteum and fetal gonads during pregnancy

The full-length equine luteinizing hormone/chorionic gonadotropin (LH/CG) receptor (eLH/CG-RA) cDNA and two alternatively spliced isoforms (eLH/CG-RB,C) were isolated from luteal tissue and characterized using a combination of reverse transcription-polymerase chain reaction (RT-PCR) and 5'-rapid amplification of cDNA ends. The 680-amino acid full sequence of eLH/CG-RA displayed 87-92% homology with other mammalian LH/CG-Rs. The eLH/CG-RB and eLH/CG-RC cDNA isoforms were truncated from the 3'-end of exon X: eLH/CG-RB spliced out of frame into the last exon whereas eLH/CG-RC contained an in-frame stop codon within a divergent sequence. Consequently, both eLH/CG-RB and eLH/CG-RC cDNA isoforms encoded putative proteins without transmembrane and intracellular domains. In order to study the responsiveness of the primary corpus luteum (CL) and fetal gonads to eCG, the expression of eLH/CG-R mRNAs was examined by RT-PCR and Northern blot analysis during early and mid-pregnancy. All three eLH/CG-R cDNA isoforms (eLH/CG-RA,B,C) were expressed from day 14 to day 83 of pregnancy in the primary CL and from day 44 to day 222 in fetal gonads. Interestingly, the primary CL at days 89 and 151 expressed only truncated eLH/CG-R cDNA isoforms. The relative values of Northern hybridized major 7, 5.7, 3.9 and 1.8 kb eLH/CG-R mRNA transcripts tended to decrease in the primary CL whereas the unique major 1.8 kb eLH/CG-R mRNA was steadily expressed in fetal gonads during pregnancy. These results show that the expression of eLH/CG-R mRNAs occurs in the fetal gonads before ceasing in the primary CL and suggest that eCG may be involved in the gradual transition from a luteal to a feto-placental output of steroids during equine pregnancy.

Expression and binding activity of luteinizing hormone/chorionic gonadotropin receptors in the primary corpus luteum during early pregnancy in the mare

Luteal steroids are necessary to maintain the first 70-90 days of pregnancy in the mare. At 35 days postovulation, the resurgence of the primary corpus luteum (CL) coincides with the secretion of the fetal hormone eCG. In order to study the responsiveness of the primary CL to eCG, we have examined levels of luteal equine LH/CG receptors (eLH/CG-R) mRNAs by Northern blot analysis and measured concentrations of eLH/CG binding sites on luteal membranes using 125I-eLH saturation binding assays at three stages of gestation: before the onset of eCG secretion (Days 14-31), from onset to maximum eCG secretion (Days 38-62), and during decline of eCG secretion (Days 83-101). Multiple transcripts of eLH/CG-R (7, 5.7, 4.9, 3.9, 2.8, 1.8, 0.6 kilobase [kb]) were identified in the primary CL at all stages examined. Three of them (5.7, 2.8, 0.6 kb) coded for truncated eLH/CG-R lacking the transmembrane domain. The relative intensities of the four major transcripts tended to decrease (5.7 and 3.9 kb) or were steadily expressed (7 and 1.8 kb) during pregnancy. The affinity of eLH/CG binding sites did not change during pregnancy whereas the number of eLH/CG binding sites decreased significantly after the onset of eCG secretion. Nevertheless, levels of binding sites were still at 44.6% (Days 38-62) to 24.7% (Days 83-101) of those measured before the onset of eCG secretion. Taken together, the presence of eLH/CG-R mRNAs and of a substantial part of eLH/CG binding sites with high affinity suggest that the primary CL still expresses a high number of eLH/CG-R and remains responsive to eCG during early pregnancy.

Biochemical and functional aspects of gonadotrophin-releasing hormone and gonadotrophins

Reproductive function in mammals is governed by the hypothalamic-pituitary-gonadal axis, which conforms a functional unit. Sexual maturation and the subsequent development of reproductive competence depend on the precise and coordinated function of this axis. The components of the reproductive axis communicate each other through endocrine signals. The hypothalamus synthesizes gonadotrophin-releasing hormone or GnRH, which in turn stimulates synthesis and secretion of the pituitary gonadotrophins, follicle-stimulating hormone (FSH) and luteinizing hormone (LH). The ovarian follicles and the interstitial and Sertoli cells of the testis are the targets for these pituitary signals. Under gonadotrophic stimulation, the gonads produce and secrete several steroid and non-steroid (polypeptide) factors, which in turn regulate in different ways the function of the hypothalamic-pituitary axis. An episodic and pulsatile mode of secretion of hormonal signals characterize (as in other endocrine systems) the function of the reproductive axis, particularly that of the hypothalamic-pituitary unit. The target cell response, and consequently the harmonic function of the corresponding gland, will depend on the adequate dynamics of this pulsatile secretion. The function of each component of the reproductive axis is strongly influenced by locally-produced signals acting either in a paracrine or autocrine manner; these particular signals represent fine-tuning regulation systems that eventually amplify or restrain the magnitude of response to a particular endocrine signal, providing additional mechanisms for tissue homeostasis and a better functional plasticity of the target gland. The design and rational use of novel therapeutic strategies for an optimal exogenously-controlled reproductive function largely depend on the detailed knowledge of the hypothalamic-pituitary-gonadal axis function and the structure and mechanism of action of those factors and signals involved in its regulation.

Multiple luteinizing hormone receptor (LHR) protein variants, interspecies reactivity of anti-LHR mAb clone 3B5, subcellular localization of LHR in human placenta, pelvic floor and brain, and possible role for LHR in the development of abnormal pregnancy, pelvic floor disorders and Alzheimer's disease

Distinct luteinizing hormone receptor (LHR) protein variants exist due to the posttranslational modifications. Besides ovaries, LHR immunoreactivity (LHRI) was also found in other tissues, such as the brain, fallopian tube, endometrium, trophoblast and resident tissue macrophages. The 3B5 mouse monoclonal antibody was raised against purified rat LHR. In rat, porcine and human ovaries, the 3B5 identified six distinct LHR bands migrating at approximately 92, 80, 68, 59, 52 and 48 kDa. Characteristic LHRI was detected in rat, human and porcine corpora lutea. During cellular differentiation, subcellular LHR distribution changed from none to granular cytoplasmic, perinuclear, surface, nuclear and no staining. There were also differences in vascular LHR expression--lack of LHRI in ovarian vessels and strong staining of vessels in other tissues investigated. In normal human term placentae, villous LHRI was associated with blood sinusoids and cytotrophoblast cells, and rarely detected in trophoblastic syncytium. In all abnormal placentae, the LHRI of sinusoids was absent, and syncytium showed either enhanced (immature placental phenotypes) or no LHRI (aged placental phenotype). LHRI in human brain was identified in microglial cells (CD68+ resident macrophages). Protein extracts from human vaginal wall and levator ani muscle and fascia showed strong approximately 92 and 68 kDa species, and LHRI was detected in smooth muscle cells, fibroblasts, resident macrophages and nuclei of skeletal muscle fibers. Our observations indicate that, in contrast to the theory on the role of vascular hormone receptors in preferential pick up of circulating hormones, there is no need to enhance selective pick up rather only prevent LH/CG transport to inappropriate sites. Abnormal placental LHR expression may play a role in the development of abnormal pregnancy. Expression of LHR in the pelvic floor compartments suggests that high LH levels in postmenopausal women may contribute to the pelvic floor relaxation and increased incidence of pelvic floor disorders. Since chorionic gonadotropin increases secretion of a variety of cytokines by monocytes, and induces their inflammatory reaction and phagocytic activity, high LH levels in aging individuals may also activate microglia (mononuclear phagocyte system in the central nervous system) and contribute to the development of Alzheimer's disease and other inflammation-mediated neurodegenerative diseases.

Inositol phosphate stimulation by LH requires the entire alpha Asn56 oligosaccharide

Lentil lectin-bound, fucose-enriched hTSH was reported to stimulate both cAMP and inositol phosphate (IP) intracellular signalling pathways, whereas fucose-depleted hTSH stimulated only the cAMP pathway. Gonadotropins activate the cAMP pathway and in several studies higher concentrations activate the IP pathway. Since only the 10% of alpha subunit Asn(56) oligosaccharides (Asn(52) in humans) are fucosylated, the higher glycoprotein hormone concentrations required for IP pathway activation might be related to the abundance of competent hormone isoforms. Lentil lectin-fractionated equine (e)LHalpha and eFSHalpha preparations were combined with a truncated, des(121-149)eLHbeta preparation. All four hybrid hormone preparations induced IP accumulation in porcine theca cells, suggesting that activation of the IP pathway was not dependent on fucosylation at alpha subunit Asn(56). However, the presence of Asn(56) carbohydrate was necessary for increased IP accumulation. Intact, rather than Asn(56)-deglycosylated eLH preparations provoked a biphasic steroidogenic response by rat testis Leydig cells, suggesting that Galpha(i) stimulation was also sensitive to loss of Asn(56) carbohydrate. While rat granulosa cells responded to human FSH preparations in a biphasic manner, a classical sigmoidal response was obtained to eFSH and Asn(56)-deglycosylated eFSH, suggesting that the equine preparations did not activate Galpha(i). Purified oLHalpha Asn(56) oligosaccharides inhibited FSH-stimulated steroidogenesis in rat granulosa cell cultures indicating a direct role for carbohydrate in FSH action. The same carbohydrate preparation inhibited hCG-stimulated fluorescence energy transfer suggesting oligosaccharide involvement in activated LH receptor self-association.

Endocrine regulation of gonadotropin glycosylation

The pituitary gonadotropins--luteinizing hormone and follicle-stimulating hormone--as well as the placental choriogonadotropin belong to the family of glycoprotein hormones. These structurally related hormones, which regulate several major reproductive functions of the body, are heterodimers consisting of a common alpha-subunit noncovalently bound to a beta-subunit. The N- and O-linked oligosaccharide chains of these gonadotropins play an important role in intracellular folding, assembly, secretion, metabolic clearance, and biological activity of the hormone. Gonadotropin glycosylation is a highly complex process; within the gonadotropes it is modulated by a variety of extrapituitary factors of hypothalamic and gonadal origin. In particular, estrogens and androgens appear to regulate terminal sialylation and/or sulfation of the oligosaccharide attachments and hence some functional properties of the gonadotropin molecule determined by these residues, i.e., metabolic clearance and in vivo biopotency. Through these extrapituitary inputs, the anterior pituitary may not only regulate the quantity but also the quality of the gonadotropin signal delivered to the gonads in a given physiologic or pathologic condition.

Immunochemical measurement of early pregnancy isoforms of HCG: potential applications to fertility research, prenatal diagnosis, and cancer

Human chorionic gonadotropin, the glycoprotein hormone of pregnancy, is found naturally in blood and urine in a variety of isoforms. These variants are related to both peptide bond cleavages (such as the nicked forms of hCG) and the beta core fragment urinary metabolite, as well as the larger variety of species resulting from carbohydrate heterogeneity. We have recently developed immunoassay systems that can measure nicked forms of hCG (antibody B151) as well as particular high carbohydrate variants (hyperglycosylated forms) of hCG (B152), which are associated with cancers producing hCG. Using the assay system for nicked hCG, we found that nicked hCG does not appear to be present as a significant hCG isoform during normal pregnancies if the urine specimens are well preserved. Applying the assay for hyperglycosylated hCG isoforms, we discovered that these forms are prevalent during very early pregnancy and decline rapidly to low concentration after the first 6 weeks of pregnancy. Persistence of these early pregnancy forms does not bode well for the pregnancy. Other investigators report that measurement of such hCG isoforms may aid in diagnosis of Down syndrome pregnancies. In summary, measurement of the hyperglycosylated hCG isoforms are useful for evaluation of healthy progress of normal pregnancy, as an additional detection marker for Down syndrome pregnancies, and as a potential new marker of trophoblastic malignancy. New reference preparations will soon be available for the calibration of assay systems for measurement of many of these hCG variants and metabolites.

Interrelationships of porcine X and Y chromosomes with pituitary gonadotropins and testicular size

Endocrine and testicular responses to unilateral castration on 1, 10, 56, or 112 days of age were characterized in 132 Chinese Meishan (MS) x White composite (WC) crossbred boars in which testicular size associates with a quantitative trait locus (QTL) on X chromosome. At 220 days of age, testicles of boars unilaterally castrated on Day 1 or 10 weighed more and had greater total daily sperm production (DSP) than one testicle of bilaterally intact boars (P < 0.05); compensation did not double these two responses. Boars with MS alleles at the X chromosome QTL had smaller testicles, darker colored parenchyma, and lower total DSP than boars with WC alleles (P < 0.05). The MS alleles engendered greater (P < 0.05) plasma FSH and LH during puberty than WC alleles. Plasma FSH increased (P < 0.05) within 48 h of unilateral castration on Days 1, 10, and 56. Subsequent increases occurred earlier during puberty (P < 0.05) after unilateral castration at younger ages than after unilateral castration at older ages. Pubertal increases in plasma FSH and LH were greater (P < 0.05) in boars with MS alleles than in those with WC alleles for the X chromosome QTL. Breed of Y chromosome had no effect on testicular traits, FSH, testosterone, or estrone. For LH, boars with an MS Y chromosome had greater (P < 0.01) plasma LH across all ages than boars with a WC Y chromosome. We conclude that a gene or groups of genes that reside on the porcine X chromosome regulate testicular development and pubertal gonadotropin concentrations.

Characterization of human FSH isoforms reveals a nonglycosylated beta-subunit in addition to the conventional glycosylated beta-subunit

Human FSH consists of a mixture of isoforms that can be separated on the basis of differences in negative charge conferred by variations in the numbers of sialic acid residues that terminate oligosaccharide branches. Western analysis of human FSH isoforms separated by chromatofocusing revealed the presence of two human FSHbeta isoforms that differed in size. A low mol wt human FSHbeta isoform was associated with all FSH isoform fractions. A high mol wt human FSHbeta isoform was associated with the more acidic fractions and increased in relative abundance as the pI decreased. Characterization of representative human FSHbeta isoforms by mass spectrometry and automated Edman degradation revealed a low mol wt isoform that was not glycosylated. A high mol wt isoform was N-glycosylated at Asn residues 7 and 24. These results indicate that pituitary human FSH consists of two classes of molecules: those that possess a nonglycosylated beta-subunit and those that possess a glycosylated beta-subunit. Glycoprotein hormones are known to be elliptical molecules, and the beta-subunit oligosaccharides project outward from the short diameter, thereby increasing it. It is interesting to speculate that this change in shape might affect ultrafiltration rates, leading to differences in delivery rates to target tissues and elimination by filtration in the kidney.

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.

Identification of twelve O-glycosylation sites in equine chorionic gonadotropin beta and equine luteinizing hormone ss by solid-phase Edman degradation

The O-glycosylation sites for equine LHss (eLHss) and eCGss were identified by solid-phase Edman degradation of four glycopeptides derived from the C-terminal region. Both subunits were O-glycosylated at the same 12 positions, rather than the 4-6 sites anticipated. These sites were partially glycosylated, with carbohydrate attachment ranging from 20% to 100% for eCGss and from 10% to 100% for eLHss. When the C-terminal peptide containing all but one of the O-linked oligosaccharides was removed by mild acid hydrolysis of either eLHss or eCGss, hybrid hormones could be obtained by reassociating eLHalpha,eFSHalpha, or eCGalpha with the truncated ss subunit derivatives. These hybrid hormones were identical in LH receptor-binding activity when des(121-149)eLHss or des(121-149)eCGss were combined with the same alpha subunit preparation. Thus, O-glycosylation appears to be responsible for the ss subunit contribution to the substantial difference in LH receptor-binding activity between eLH and eCG. Comparison of the equid LH/CGss sequences with those available for the primate CGss subunits indicated a greater conservation of glycosylation patterns in the former.

Carbohydrate analysis of glycoprotein hormones

Complete carbohydrate composition analysis of glycoprotein hormones, their subunits, and oligosaccharides isolated from individual glycosylation sites can be accomplished using high-pH anion-exchange chromatography combined with pulsed amperometric detection. Neutral and amino sugars are analyzed from the same hydrolyzate by isocratic chromatography on a Dionex CarboPAC PA1 column in 16 mM NaOH. Sialic acid is quantified following mild hydrolysis conditions on the same column in 150 mM sodium acetate in 150 mM NaOH. Ion chromatography on a Dionex AS4A column in 1.8 mM Na(2)CO(3)/1.7 mM NaHCO(3); postcolumn, in-line anion micromembrane suppression; and conductivity detection can be used to quantify sulfate, a common component of pituitary glycoprotein hormone oligosaccharides. Mass spectrometric analysis before and after elimination of oligosaccharides from a single glycosylation site can provide an estimate of the average oligosaccharide mass, which facilitates interpretation of oligosaccharide composition data. Following release by peptide N-glycanase (PNGase) digestion and purification by ultrafiltration, oligosaccharides can be characterized by a high-resolution oligosaccharide mapping technique using the same equipment employed for composition analysis. Oligosaccharide mapping can be applied to the entire hormone, individual subunits, or individual glycosylation sites by varying PNGase digestion conditions or substrates. Oligosaccharide release by PNGase is readily monitored by SDS-PAGE. Site-specific deglycosylation can be confirmed by amino acid sequence analysis. For routine isolation of oligosaccharides, addition of 2-aminobenzamide at the reducing terminus facilitates detection; however, the oligosaccharide retention times are altered. Composition analysis is also affected as the 2-aminobenzamide-modified GlcNAc peak overlaps the fucose peak.