Mutations of gonadotropins and gonadotropin receptors: elucidating the physiology and pathophysiology of pituitary-gonadal function

Follicle-stimulating hormone receptor polymorphisms in women with normogonadotropic anovulatory infertility

OBJECTIVE

To assess the incidence of different FSH receptor genotypes in normogonadotropic anovulatory infertile women (World Health Organization class II) and normo-ovulatory controls and to correlate these genotypes with baseline characteristics and ovarian responsiveness during ovulation induction.

DESIGN

Cross-sectional study.

SETTING

University hospital.

PATIENT(S)

Thirty normo-ovulatory controls and 148 normogonadotropic anovulatory infertile women.

INTERVENTION(S)

All participants underwent a standardized evaluation that included cycle history, body mass index measurement, and transvaginal ultrasonography of ovaries. Fasting blood samples were obtained for endocrine evaluation. Ovarian responsiveness to FSH in normogonadotropic anovulatory infertile women was assessed during ovulation induction, and DNA was analyzed to determine the FSH receptor genotype.

MAIN OUTCOME MEASURE(S)

Prevalence of FSH receptor polymorphisms, baseline serum FSH levels, amount of FSH administered, duration of stimulation, and ovarian response dose.

RESULT(S)

The Thr/Thr 307 genotype was significantly less prevalent (52% vs. 23%) and the Ser/Ser 680 polymorphism was significantly more prevalent (40% vs. 16%) in patients compared with controls. Normogonadotropic anovulatory infertile women with the Ser/Ser 680 polymorphism presented with higher median FSH serum levels (5.2 IU/L [range, 2.4-9.7 IU/L]) than did those with the Asn/Asn 680 (4.6 IU/L [range, 1.4-5.8 IU/L) and Asn/Ser 680 (4.5 IU/L [range, 1.8-9.7 IU/L) variants. However, ovarian responsiveness to FSH was similar among anovulatory women with the various polymorphisms.

CONCLUSION(S)

Normogonadotropic anovulatory infertile patients have a different FSH receptor genotype than do normo-ovulatory controls. Although this characteristic is associated with increased baseline FSH serum levels, altered ovarian sensitivity to exogenous FSH during ovulation induction could not be established.

Hypogonadotropic hypogonadism due to loss of function of the KiSS1-derived peptide receptor GPR54

Hypogonadotropic hypogonadism is defined as a deficiency of the pituitary secretion of follicle-stimulating hormone and luteinizing hormone, which results in the impairment of pubertal maturation and of reproductive function. In the absence of pituitary or hypothalamic anatomical lesions and of anosmia (Kallmann syndrome), hypogonadotropic hypogonadism is referred to as isolated hypogonadotropic hypogonadism (IHH). A limited number of IHH cases are due to loss-of-function mutations of the gonadotropin-releasing hormone receptor. To identify additional gene defects leading to IHH, a large consanguineous family with five affected siblings and with a normal gonadotropin-releasing hormone receptor coding sequence was studied. Homozygosity whole-genome mapping allowed the localization of a new locus within the short arm of chromosome 19 (19p13). Sequencing of several genes localized within this region showed that all affected siblings of the family carried a homozygous deletion of 155 nucleotides in the GPR54 gene. This deletion encompassed the splicing acceptor site of intron 4-exon 5 junction and part of exon 5. The deletion was absent or present on only one allele in unaffected family members. GPR54 has been initially identified as an orphan G protein-coupled receptor with 40% homology to galanin receptors. Recently, a 54-aa peptide derived from the KiSS1 protein was identified as a ligand of GPR54. The present study shows that loss of function of GPR54 is a cause of IHH, and it identifies GPR54 and possibly KiSS1 protein-derived peptide as playing a major and previously unsuspected role in the physiology of the gonadotropic axis.

A constitutively active somatic mutation of the human lutropin receptor found in Leydig cell tumors activates the same families of G proteins as germ line mutations associated with Leydig cell hyperplasia

Using a Leydig tumor cell line (MA-10) transiently transfected with the human lutropin receptor (hLHR) and mutants thereof, we examined the identity of the G proteins activated by the agonist-engaged hLHR-wild type (wt) and by three of its naturally occurring constitutively active mutants. Two of the mutants examined, L457R in transmembrane helix 3 and D578Y in transmembrane helix 6, are germ-line mutations found in boys with Leydig cell hyperplasia and precocious puberty. The third, D578H, is a somatic mutation found in Leydig cell tumors in boys with precocious puberty. We show that the hLHR-wt and the three mutants activate the G(s), G(i/o), and G(q/11), but not the G(12/13), families of G proteins. The activation of these G proteins by the hLHR-wt occurs only when engaged by agonist, but their activation by the L457R, D578Y, and D578H mutants occurs independently of agonist stimulation. We conclude that the G proteins activated by constitutively active mutants of the hLHR associated with Leydig cell hyperplasia or tumors are identical and are the same as those activated by the agonist-engaged hLHR-wt. If there was preferential activation of some G protein families by the somatic D578H mutation found in Leydig cell tumors as opposed to the germ line mutations found in Leydig cell hyperplasia, then one could envision mechanisms by which the D578H mutant would be oncogenic. The data presented here suggest that such mechanisms do not need to be considered.

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.

Ligand selectivity of gonadotropin receptors. Role of the beta-strands of extracellular leucine-rich repeats 3 and 6 of the human luteinizing hormone receptor

The difference in hormone selectivity between the human follicle-stimulating hormone receptor (hFSH-R) and human luteinizing hormone/chorionic gonadotropin receptor (hLH-R) is determined by their approximately 350 amino acid-long N-terminal receptor exodomains that allow the mutually exclusive binding of human follicle-stimulating hormone (hFSH) and human luteinizing hormone (hLH) when these hormones are present in physiological concentrations. The exodomains of each of these receptors consist of a nine-leucine-rich repeat-containing subdomain (LRR subdomain) flanked by N- and C-terminal cysteine-rich subdomains. Chimeric receptors, in which the structural subdomains of the hFSH-R exodomain were substituted with those of the hLH-R, showed a similar high responsiveness to human chorionic gonadotropin (hCG) and hLH as long as they harbored the LRR subdomain of the hLH-R. In addition, these chimeric receptors showed no responsiveness to hFSH. The LRR subdomains of the gonadotropin receptor exodomains are predicted to adopt a horseshoe-like conformation, of which the hormone-binding concave surface is composed of nine parallel beta-strands. Receptors in which individual beta-strands of the hFSH-R were replaced with the corresponding hLH-R sequences revealed that hCG and hLH selectivity is predominantly determined by hLH-R beta-strands 3 and 6. A mutant receptor in which the hFSH-R beta-strands 3 and 6 were substituted simultaneously with their hLH-R counterparts displayed a responsiveness to hCG and hLH similar to that of the wild type hLH-R. Responsiveness to hFSH was not affected by most beta-strand substitutions, suggesting the involvement of multiple low-impact determinants for this hormone.

Developmental regulation of follicle-stimulating hormone receptor messenger RNA expression in the baboon fetal ovary

In the adult ovary, pituitary FSH via interaction with its receptor (FSHR) is required for follicular maturation and granulosa cell development. In humans and nonhuman primates, the pool of follicles available for adult ovarian function is established in utero. However, our understanding of the ontogeny and developmental regulation of FSHR in the ovary of the primate fetus is incomplete. Our goal was to determine whether the baboon fetal ovary expresses the full-length FSHR mRNA transcript and whether levels are developmentally regulated. Fetal ovaries were obtained at mid (Day 100) and late (Day 165) gestation (term = Day 184) from untreated baboons and on Day 165 from baboons in which fetal estrogen levels were either decreased by >95% by treatment with the aromatase inhibitor CGS 20267 or restored to 30% of normal by treatment with CGS 20267 plus estradiol benzoate administered s.c. to the mother on Days 100-164. The full-length 2088-base pair FSHR mRNA transcript was expressed in ovaries of adult and fetal baboons untreated or treated with CGS 20267 or CGS 20267 and estrogen. Mean (+/-SEM) FSHR mRNA levels (ratio of FSHR mRNA:18S rRNA), quantified by reverse transcription polymerase chain reaction, were increased (P < 0.05) 2-fold between mid (0.34 +/- 0.06) and late gestation (0.76 +/- 0.07), an increase prevented (P < 0.05) in estrogen-depleted baboons (0.44 +/- 0.10) and partially restored by treatment with CGS 20267 and estrogen (0.58 +/- 0.16). We previously showed that the number of follicles/0.33 mm2 in fetal ovaries of untreated baboons in late gestation was reduced 50% by treatment with CGS 20267 and restored to normal in baboons treated with CGS 20267 and estrogen. Thus, when corrected for the number of follicles/0.33 mm2, FSHR mRNA levels were similar in baboon fetal ovaries untreated (0.010 +/- 0.001) or treated with CGS 20267 (0.009 +/- 0.002) or CGS 20267 and estrogen (0.007 +/- 0.003). We conclude that estrogen plays a major role in regulating ovarian FSHR mRNA expression in the primate fetus, and that the developmental increase in FSHR mRNA levels reflects the estrogen-dependent increase in folliculogenesis (i.e., increased number of granulosa cells and oocytes).

Luteinizing hormone signaling and breast cancer: polymorphisms and age of onset

Estrogen exposure has repeatedly been shown to associate with the risk of developing breast cancer. Estrogen synthesis is under the control of LH and FSH, where LH, through its receptor (LHR), stimulates production of ovarian androgens; and FSH, their aromatization to estrogens. Here, we investigated whether functional polymorphic variants in the LH signaling pathway are associated with the risk of breast cancer or its clinical phenotype. A PCR-restriction fragment length polymorphism genotyping approach was used to investigate this in 266 breast cancers. The LHR18insLQ allele does not seem to influence breast cancer risk. However, women who were homozygous for the LHR18insLQ allele were, on average, 8.3 yr younger at diagnosis, compared with those homozygous for the wild-type LHR allele (mean age, 51.9 yr vs. 60.2 yr; P = 0.03). Trends were observed for associations between LHR18insLQ carriers and nodal involvement or larger tumor size. Patients who were LHR18insLQ carriers revealed a significantly worse overall survival, compared with those who were homozygous for LHR [hazard ratio = 2.4; 95% CI (1.3-4.3); P = 0.006]. In contrast, no associations between the LH genotype and any of the clinical parameters were observed. Our findings suggest that the LHR18insLQ gene polymorphism determines an earlier age of disease onset and is prognostic for poor outcome of breast cancer.

Dynamic tests and FSH biological activity in female rats with acute nephrotic syndrome

To investigate the pituitary-ovarian status during the acute state of the nephrotic syndrome, a sequence of experiments were undertaken in adult female rats after a single dose of the puromycin aminonucleoside (PAN). The functional condition of the hypophyseal-ovarian unit was determined in control and nephrotic rats by two dynamic tests. In the first one, 10 days after PAN or placebo administration female rats were stimulated with LHRH (300 ng/100 g body wt) and samples were collected at 0, 20, 40, 60 and 80 min after releasing factor administration. The second dynamic test, which was performed in control and nephrotic rats, consists of one (day 10 after PAN) or four (between days 7-10 after PAN) doses of hCG (8 UI), respectively. In all cases, serum samples were collected on day 10. In addition, the relative in vitro biological activity of FSH from control and nephrotic rats before and after LHRH stimulus was determined. The results reveal that after a stimulatory dose of LHRH the secretion of LH was significantly diminished in nephrotic rats at all registered times. By contrast, normal response was observed in terms of FSH secretion in nephrotic females. On the other hand, no ovarian response, in terms of progesterone or estradiol synthesis, was observed in nephrotic rats after either one or four stimuli with hCG Interestingly, in spite of the normal or high concentrations of FSH, the biological activity of FSH was totally abolished in nephrotic rats. On the whole, the results from this study indicate that the nephrotic syndrome had a harmful effect on the pituitary-ovarian unit, and strongly suggest that the endocrine dysfunction could be initiated at the hypophysial level; even though a specific ovarian damage is also predictable.

Sertoli and germ cell development in hypogonadal (hpg) mice expressing transgenic follicle-stimulating hormone alone or in combination with testosterone

We recently created a novel transgenic (tg) model to examine the specific gonadal actions of FSH, distinct from LH effects, by expressing tg-FSH in gonadotropin-deficient hypogonadal (hpg) mice. Using this unique in vivo paradigm, we now describe the postnatal cellular development in seminiferous tubules selectively stimulated by tg-FSH alone or combined with testosterone (T). In the alphabeta.6 line, tg-FSH stimulated the maturation and proliferation ( approximately 2-fold) of Sertoli cells in hpg testes. Total Sertoli cell numbers were also significantly increased (1.5-fold) independently of FSH effects by T treatment alone. Selective FSH activity in alphabeta.6 hpg testes increased total spermatogonia numbers 3-fold, which established a normal spermatogonia/Sertoli cell ratio. FSH also elevated meiotic spermatocyte numbers 7-fold, notably at pachytene (28-fold), but induced only limited numbers of postmeiotic haploid cells (absent in hpg controls) that arrested during spermatid elongation. In contrast, T treatment alone had little effect on postnatal spermatogonial proliferation but greatly enhanced meiotic progression with total spermatocytes increased 12-fold (pachytene 53-fold) relative to hpg testes, and total spermatid numbers 11-fold higher than tg-FSH hpg testes. Combining tg-FSH and T treatment had no further effect on Sertoli or spermatogonia numbers relative to FSH alone but had marked additive and synergistic effects on meiotic cells, particularly pachytene (107-fold more than hpg), to establish normal meiotic germ cell/Sertoli cell ratios. Furthermore, tg-FSH had a striking synergistic effect with T treatment on total spermatid numbers (19-fold higher than FSH alone), although spermatid to Sertoli cell ratios were not fully restored to normal, indicating elevated Sertoli cell numbers alone are insufficient to establish a maximal postmeiotic germ cell capacity. This unique model has allowed a detailed dissection of FSH in vivo activity alone or with T and provided compelling evidence that FSH effects on spermatogenesis are primarily via Sertoli and spermatogonial proliferation and the stimulation of meiotic and postmeiotic germ cell development in synergy with and dependent on T actions.

Inhibin B: a novel marker of spermatogenesis

Subfertility affects about 15% of all couples. Assessment of spermatogenesis has a central role in the evaluation of the subfertile couple. Classical markers of spermatogenesis, such as semen analysis, testicular biopsy and endocrine evaluation all have their diagnostic limitations. There is a clear need for accurate additional markers of spermatogenesis. Recently, the serum inhibin B level has emerged as a sensitive endocrine marker of spermatogenesis. This paper summarises the pros and cons of different markers of spermatogenesis, with specific focus on serum inhibin B. The serum inhibin B level has been shown to be associated with classical markers of spermatogenesis, particularly testicular histology, and to be the most accurate endocrine marker of spermatogenesis. A subnormal serum inhibin B level clearly reflects disturbed spermatogenesis. Before puberty, when no spermatogenesis takes place, inhibin B is a marker of testicular integrity. Clinical applications of serum inhibin B in childhood and adulthood are given, and a view on future directions and research is presented. The serum inhibin B level has proven to be valuable in the evaluation of spermatogenesis, and holds a promise for further research.

Cloning and functional characterization of a gonadal luteinizing hormone receptor complementary DNA from the African catfish (Clarias gariepinus)

A cDNA encoding a putative African catfish (Clarias gariepinus) gonadal LH receptor (cfLH-R) has been cloned. Multiple sequence alignment of the deduced amino acid sequence revealed that the cfLH-R had the highest identity with vertebrate LH receptors (>50%). Overall sequence identity between the cfLH-R and the African catfish FSH receptor (cfFSH-R) is 47%. Sequence analysis of part of the cfLH-R gene revealed the presence of an intron typically found in other vertebrate LH-R genes. Abundant cfLH-R mRNA expression was detected in ovary and testis as well as in head-kidney (the adrenal homologue in fish). Other tissues, such as muscle, brain, cerebellum, stomach, heart, and seminal vesicles, also contained detectable cfLH-R mRNA. Transient expression of the cfLH-R in HEK-T 293 cells resulted in significantly increased basal cAMP levels in the absence of gonadotropic hormone. The cAMP levels could be further elevated in response to catfish LH, salmon LH, human LH, human choriogonadotropin, and human FSH. Salmon FSH and human TSH, however, were inactive. We conclude that we have cloned a cDNA encoding the LH-R of the African catfish. This receptor displays constitutive activity but is still responsive to additional ligand-induced activation.

Male contraception

The provision of safe, effective contraception has been revolutionized in the past 40 yr following the development of synthetic steroids and the demonstration that administration of combinations of sex steroids can be used to suppress ovulation and, subsequently, other reproductive functions. This review addresses the current standing of male contraception, long the poor relation in family planning but currently enjoying a resurgence in both scientific and political interest as it is recognized that men have a larger role to play in the regulation of fertility, whether seen in geopolitical or individual terms. Condoms and vasectomy continue to be popular at particular phases of the reproductive lifespan and in certain cultures. Although not perfect contraceptives, condoms have the additional advantage of offering protection from sexually transmitted infection. The hormonal approach may have acquired the critical mass needed to make the transition from academic research to pharmaceutical development. Greatly increased understanding of male reproductive function, partly stimulated by interest in ageing and the potential benefits of androgen replacement, is opening up other avenues for investigation taking advantage of nonhormonal regulatory pathways specific to spermatogenesis and the reproductive tract.

Specificity of the cyclic adenosine 3',5'-monophosphate signal in granulosa cell function

Cyclic AMP signaling is involved in most aspects of differentiation and maturation of the granulosa cells in the ovarian follicle. As the genetic programs activated at different stages of follicle growth maturation are being elucidated, it is becoming increasingly difficult to reconcile the simplicity of the cAMP cascade with the complexity and the divergent patterns of gene expression activated in these cells. To account for these divergent outcomes of the cAMP signal, three aspects of this signaling cascade in granulosa cells will be reviewed. We will discuss the evidence for gonadotropin receptors coupling to different G proteins and effectors. Next, we will explore the possibility that the temporal and spatial dimensions of the cAMP signal itself may contribute to the diverse outcomes. Finally, we will summarize available data showing that the cAMP signal is distributed through several cascades of kinase activation. It is hoped this compendium will provide a framework with which to understand how the initial signals activated by gonadotropins control the complex patterns of gene expression that are required for follicle maturation and ovulation.

Reproductive disturbances, pituitary lactotrope adenomas, and mammary gland tumors in transgenic female mice producing high levels of human chorionic gonadotropin

To assess the consequences of prolonged exposure to elevated levels of LH/human chorionic gonadotropin (hCG) in the female, we developed a transgenic (TG) mouse model (hCGbeta+) that overexpresses the hCGbeta-subunit cDNA. Because of the promoter used, ubiquitin C, the transgene is expressed in multiple tissues, including the pituitary gland, in which coupling with the endogenous common alpha-subunit results in synthesis of high levels of bioactive hCG. The TG females presented with precocious puberty, infertility, enhanced ovarian steroidogenesis, and abnormal uterine structure. Pituitary enlargement was evident from the age of 2 months, which progressed to adenomas by the age of 10-12 months. Immunohistochemical studies and electron microscopy demonstrated lactotrope origin for the adenomas, associated with severe hyperprolactinemia. The mammary glands of TG females showed marked lobuloalveolar development followed by mammary tumors with characteristics of adenocarcinoma at the age of 9-12 months. More than 90% of penetrance and high frequency of metastasis (47%) was observed. Formation of the pituitary and mammary gland tumors was totally abolished by ovariectomy despite persistently elevated hCG levels. Taken together, these findings suggest that the hCG-induced aberrations of ovarian function are clearly responsible for the extragonadal tumors observed in these TG mice.

Human chorionic gonadotropin inhibits Kaposi's sarcoma associated angiogenesis, matrix metalloprotease activity, and tumor growth

Kaposi's sarcoma is a highly angiogenic, AIDS-associated neoplasm that is more frequent in male than in female patients. Cases of spontaneous regression during pregnancy have been reported and the pregnancy hormone human chorionic gonadotropin (hCG) has shown anti-Kaposi's sarcoma activity in several, but not all, clinical trials. Antiproliferative and proapoptotic activities specific for Kaposi's sarcoma (KS) cells have been shown. We report here further analyses of the anti-KS activity of the hormone and show that urinary hCG, the hCG beta-subunit, the hCG beta-core, and to a lesser extent a recombinant hCG, directly inhibit the activity of matrix metalloproteases of different origin. The hCG hormone also inhibited angiogenesis in vivo in the matrigel sponge assay as well as growth of KS cell xenografts in nude mice. The effect of the pure recombinant hormone dimer on xenograft growth was transient, indicating that the activity of intact hCG alone is not sufficient to overcome the growth potential of this tumor and suggesting that active hCG fragments or other anti-KS activities contribute to the activity of urinary hCG.

Structural aspects of luteinizing hormone receptor: information from molecular modeling and mutagenesis

The luteinizing hormone receptor (LHR) is a member of the superfamily of G protein-coupled receptors and, in humans, binds two closely related ligands, members of the heterodimeric glycoprotein hormone family. This receptor is an essential component of the reproductive axis in males and females, and a number of naturally occurring pathophysiologic activating and inactivating mutations have been described. This review deals with the current state of knowledge of the structure of LHR based on molecular modeling and the supporting experimental data from engineered and naturally occurring mutations.

Evolution of glycoprotein hormone subunit genes in bilateral metazoa: identification of two novel human glycoprotein hormone subunit family genes, GPA2 and GPB5

The canonical members of the human glycoprotein hormone subunit family of cystine knot-forming polypeptides include the common alpha-subunit, and four beta-subunit genes, FSHbeta, LHbeta, TSHbeta, and hCGbeta. Using pairwise sequence analysis of the complete human genome, we have identified two novel glycoprotein hormone subunit-related genes. Based on unique sequence similarity to the alpha- and beta-subunits of glycoprotein hormones, they were named glycoprotein-alpha2 (GPA2) and glycoprotein-beta5 (GPB5), respectively. PCR analysis using a panel of human cDNAs from 14 different tissues demonstrated that GPB5 is similar to other beta-subunits showing restricted tissue expression, mainly in pituitary and brain. In contrast, the GPA2 transcript is found in diverse tissues. Furthermore, immunoreactive GPA2 and GPB5 were detected in the anterior pituitary of mouse and frog, whereas the expression of GPA2 and GPB5 in transfected cells resulted in the secretion of recombinant polypeptides in conditioned medium. After GenBank searches in lower organisms, glycoprotein hormone beta-subunit-related genes were identified from the genome of nematode Caenorhabditis elegans, hookworm Ancylostoma caninum, and Drosophila melanogaster. The evolutionary conservation of these invertebrate homologs can be seen in several key sequence characteristics, and the data suggest that the glycoprotein hormone beta-subunit gene ancestor evolved before the emergence of bilateral metazoa, thus providing a better understanding of the evolution of this group of classic polypeptide hormones and their receptors. Studies of the complete inventory of genes homologous to glycoprotein hormone subunits in the human genome and lower organisms will allow future functional characterization and identification of their respective receptors.

Effects of follicle-stimulating hormone (FSH) and human chorionic gonadotropin in individuals with an inactivating mutation of the FSH receptor

OBJECTIVE

To study the gonadal steroid responses to FSH and hCG in individuals with the inherited Finnish-type inactivating Ala189Val mutation of the FSH receptor gene.

DESIGN

Prospective clinical and descriptive study.

SETTING

University hospital.

PATIENT(S)

Two women and one man homozygous for the Ala189Val mutation of the FSH receptor gene, and ovarian biopsies from four affected and four healthy women, and four normal fetuses.

INTERVENTION(S)

Individuals were treated with increasing doses of recombinant FSH (300 IU/day start, 900 IU/day final) and/or a single dose of hCG (5000 IU). Ovarian biopsies were used in immunohistochemical analyses for detection of aromatase cytochrome P450 and transcription factor GATA-4. In situ 3'-end labeling analyses were used for detection of apoptosis.

MAIN OUTCOME MEASURE(S)

Measurements of serum concentrations of follicle-stimulating hormone, leuteinizing hormone, inhibin A and B, estradiol, testosterone (T), androstenedione, and prolactin, immunostaining for ovarian aromatase, GATA-4, and apoptosis.

RESULT(S)

Administration of FSH had no effect on production of the steroids. Similarly, human chorionic gonadotropin (hCG) treatment, alone or after FSH administration, failed to raise serum steroid concentrations. Ovarian apoptosis was absent, and the expression of transcription factor GATA-4 and aromatase was negligible in the ovarian biopsies from Ala189Val homozygous individuals.

CONCLUSION(S)

The Ala189Val mutation of the FSH receptor gene results in a complete block of FSH action in vivo. Furthermore, the failure of hCG to increase both ovarian estradiol and testosterone secretion emphasizes the possible contribution of FSH in regulating ovarian androgen synthesis, and supports the concept that both gonadotropins are necessary for appropriate ovarian steroidogenesis in humans.

Absence of activating mutations in the hot spots of the LH receptor and Gs-alpha genes in Leydig cell tumors

Leydig-cell tumors are functioning endocrine tumors that produce T autonomously leading to isosexual precocity in boys and virilization in female patients. Molecular abnormalities such as activating mutations of the luteinizing hormone receptor (LHR), a G protein-coupled receptor, and of the Gs-alpha subunit of G protein have recently been described in these tumors. Both mutations cause continuous activation of the cAMP signaling cascade, autonomous production of T and cell proliferation. We searched for activating mutations in exon 11 of the LHR gene and in exons 8 and 9 of the Gs-a gene, which contain all hot spots for those mutations, in 4 Leydig cell tumors obtained from 4 patients (one boy with LH-independent precocious puberty and 3 women with virilization). DNA was extracted from paraffin-embedded neoplastic and non-neoplastic tissues and from peripheral lymphocytes. Hot spot regions of exons 11 of LHR and exons 8 and 9 of Gs-alpha genes were amplified by PCR and the purified PCR products were directly sequenced. No LHR or Gs-alpha gene mutations were found in the 4 tumors studied. Considering the previously reported mutations found in Leydig cell tumors, the absence of activating mutations in the hot spot regions for activating mutations in these tumors indicate molecular heterogeneity among Leydig cell tumors.

Autoimmune adrenal insufficiency and autoimmune polyendocrine syndromes: autoantibodies, autoantigens, and their applicability in diagnosis and disease prediction

Recent progress in the understanding of autoimmune adrenal disease, including a detailed analysis of a group of patients with Addison's disease (AD), has been reviewed. Criteria for defining an autoimmune disease and the main features of autoimmune AD (history, prevalence, etiology, histopathology, clinical and laboratory findings, cell-mediated andhumoral immunity, autoantigens and their autoepitopes, genetics, animal models, associated autoimmune diseases, pathogenesis, natural history, therapy) have been described. Furthermore, the autoimmune polyglandular syndromes (APS) associated with AD (revised classification, animal models, genetics, natural history) have been discussed. Of Italian patients with primary AD (n = 317), 83% had autoimmune AD. At the onset, all patients with autoimmune AD (100%) had detectable adrenal cortex and/or steroid 21-hydroxylase autoantibodies. In the course of natural history of autoimmune AD, the presence of adrenal cortex and/or steroid 21-hydroxylase autoantibodies identified patients at risk to develop AD. Different risks of progression to clinical AD were found in children and adults, and three stages of subclinical hypoadrenalism have been defined. Normal or atrophic adrenal glands have been demonstrated by imaging in patients with clinical or subclinical AD. Autoimmune AD presented in four forms: as APS type 1 (13% of the patients), APS type 2 (41%), APS type 4 (5%), and isolated AD (41%). There were differences in genetics, age at onset, prevalence of adrenal cortex/21-hydroxylase autoantibodies, and associated autoimmune diseases in these groups. "Incomplete" forms of APS have been identified demonstrating that APS are more prevalent than previously reported. A varied prevalence of hypergonadotropic hypogonadism in patients with AD and value of steroid-producing cells autoantibodies reactive with steroid 17alpha-hydroxylase or P450 side-chain cleavage enzyme as markers of this disease has been discussed. In addition, the prevalence, characteristic autoantigens, and autoantibodies of minor autoimmune diseases associated with AD have been described. Imaging of adrenal glands, genetic tests, and biochemical analysis have been shown to contribute to early and correct diagnosis of primary non-autoimmune AD in the cases of hypoadrenalism with undetectable adrenal autoantibodies. An original flow chart for the diagnosis of AD has been proposed.

Micropenis with testicular regression, low LH levels, and poor androgen and HCG responses: a distinct syndrome?

We report three boys, including two brothers, with micropenis and poor phallic growth in response to both exogenous human chorionic gonadotropin (HCG) and testosterone therapy in the newborn period. They exhibited low neonatal testosterone levels that failed to respond to HCG stimulation. These boys displayed a unique gonadotropin profile with reduced luteinizing hormone levels and elevated follicle-stimulating hormone levels. They had small, cryptorchid testes with subsequent testicular regression and atrophy. Moreover, all three boys have developed microcephaly and mild learning delays. We review the hormonal profiles and phenotypes of known causes of micropenis, and compare them to the features of our three patients. Although individuals with similar features may have been described in past series of males with micropenis, the data presented previously were insufficient for classification; thus, we propose that our patients may represent a distinct, not previously recognized, syndrome with either X-linked recessive inheritance or autosomal recessive inheritance with male sex limitation.

A conserved Asn in TM7 of the thyrotropin receptor is a common requirement for activation by both mutations and its natural agonist

The wide spectrum of naturally occurring mutations able to activate the thyrotropin (TSH) receptor provides a useful tool to approach the structure of the active state(s) of the glycoprotein hormone receptors. Here we show that the side-chain of the highly conserved N7.49 (Asn 674) in TM7 is mandatory for activation of the TSH receptor, not only by TSH, but also by a panel of eight natural and two artificial activating mutations. Basal activity levels of the mutants were significantly decreased by suppression of the side-chain of N7.49 (N7.49A double mutants). In addition, comparative effects of the N7.49A substitution on the ten mutants demonstrate that basal activity and agonist- or mutation-stimulated activity might involve different structural changes.

Ligands act as pharmacological chaperones and increase the efficiency of delta opioid receptor maturation

The endoplasmic reticulum (ER) is recognized as an important site for regulating cell surface expression of membrane proteins. We recently reported that only a fraction of newly synthesized delta opioid receptors could leave the ER and reach the cell surface, the rest being degraded by proteasomes. Here, we demonstrate that membrane-permeable opioid ligands facilitate maturation and ER export of the receptor, thus acting as pharmacological chaperones. We propose that these ligands stabilize the newly synthesized receptor in the native or intermediate state of its folding pathway, possibly by inducing stabilizing conformational constrains within the hydrophobic core of the protein. The receptor precursors that are retained in the ER thus represent fully competent folding intermediates that can be targets for pharmacological intervention aimed at regulating receptor expression and cellular responsiveness. The pharmacological chaperone action is independent of the intrinsic signaling efficacy of the ligand, since both agonists and antagonists were found to promote receptor maturation. This novel property of G protein-coupled receptor ligands may have important implications when considering their effects on cellular responsiveness during therapeutic treatments.

Lysine 183 and glutamic acid 157 of the TSH receptor: two interacting residues with a key role in determining specificity toward TSH and human CG

A naturally occurring mutation in the ectodomain of the TSH receptor (TSHr), K183R, has been described recently in a familial case of gestational hyperthyroidism. Hyperthyroidism was explained by the widening of the specificity of the mutant receptor toward human CG (hCG). In the present study, we attempted to understand in molecular terms the structure-phenotype relationships of this mutant in light of the available structural model of TSHr ectodomain established on the template of the atomic structure of the porcine ribonuclease inhibitor. To this aim, we studied by site-directed mutagenesis and functional assays in transfected COS cells the effects of substituting amino acids with different physicochemical properties for lysine 183. Unexpectedly, all TSHr mutants displayed widening of their specificity toward hCG. Molecular dynamics simulations suggested that the gain of function would be secondary to the release of a nearby glutamate residue (E157) from a salt bridge with K183. This hypothesis was supported by further site-directed mutagenesis experiments showing that the presence of an acidic residue in position 157, or in its vicinity, was required to observe the increase in sensitivity to hCG (an acidic residue in position 183 can partially fulfill the role of a free acidic residue in position 157 when tested on the background of a E157A mutant). Our results suggest also that additional natural mutations (especially K183M, N, or Q) in position 183 of TSHr are expected to be found in gestational hyperthyroidism.

The lutropin/choriogonadotropin receptor, a 2002 perspective

Reproduction cannot take place without the proper functioning of the lutropin/choriogonadotropin receptor (LHR). When the LHR does not work properly, ovulation does not occur in females and Leydig cells do not develop normally in the male. Also, because the LHR is essential for sustaining the elevated levels of progesterone needed to maintain pregnancy during the first trimester, disruptions in the functions of the LHR during pregnancy have catastrophic consequences. As such, a full understanding of the biology of the LHR is essential to the survival of our species. In this review we summarize our current knowledge of the structure, functions, and regulation of this important receptor.

The role of mutations affecting gonadotrophin secretion and action in disorders of pubertal development

A number of mutations that disturb the development and function of the hypothalamic-pituitary-gonadal (HPG) axis and cause disturbances in pubertal development are known today. These mutations have effects at all levels of the HPG axis, from the migration of gonadotrophin releasing hormone (GnRH) neurones from the nasal cavity to the hypothalamus, GnRH secretion, GnRH action, pituitary gonadotroph differentiation, gonadotrophin synthesis and secretion, right through to gonadotrophin action. Most of the mutations are inactivating, thus causing hypogonadism and arrest or delay of pubertal development. One exception is the activating mutations of the LH receptor, which causes the male-limited gonadotrophin-independent precocious puberty. The human mutations and animal models with disrupted function of orthologous genes have clarified the molecular pathogenesis of hypogonadism and disturbances of pubertal development. The correct diagnosis of these disorders using molecular biological techniques is now possible. This allows the selection of specific treatments and correct counselling of the patients and their families.

A Novel mutation in the FSH receptor inhibiting signal transduction and causing primary ovarian failure

Inactivating mutations of the FSH receptor (FSHR) are known to cause ovarian failure with amenorrhea and infertility in women. The first mutation identified in the FSHR gene was a missense mutation (566C-->T, predicting Ala189Val transition) found in several Finnish patients with primary amenorrhea due to ovarian failure. Only five additional, partially or totally inactivating, mutations of the FSHR have been reported. Here, we report a novel FSHR mutation, 1255G-->A, in a Finnish female with primary amenorrhea. The patient was a compound heterozygote for two mutations in the FSHR gene: 566C-->T, the Finnish founder mutation, and 1255G-->A, a previously unidentified mutation. The new mutation is located in exon 10 in the second transmembrane stretch of the FSHR, and it predicts an Ala419Thr change in the protein structure. In functional testing, the mutation was shown to have minimal effect on ligand binding capacity and affinity, but it almost totally abolished the cAMP second messenger response. Neither of the two FSHR mutations (566C-->T or1255G-->A) was identified in 40 other Finnish patients with premature ovarian failure. Based on this and previous studies, FSHR mutations remain a rare cause of ovarian failure.

MA-10 cells transfected with the human lutropin/choriogonadotropin receptor (hLHR): a novel experimental paradigm to study the functional properties of the hLHR

MA-10 cells are a clonal strain of mouse Leydig tumor cells that retain many of the properties of Leydig cells including expression of the endogenous lutropin/choriogonadotropin receptor (LHR) and the ability to respond to LH/CG with increased steroidogenesis. Recently we noted a dramatic decrease in expression of the endogenous LHR. Although we do not have an explanation for this decline, we took advantage of it to devise a method that allows for the expression of the recombinant human LHR (hLHR) in a Leydig cell model that is now practically devoid of endogenous LHR. We show that the recombinant hLHR can be expressed at variable densities in MA-10 cells and that it can stimulate cAMP and steroid synthesis as well as activate the inositol phosphate and MAPK cascades. We also show that two naturally occurring mutants of the hLHR associated with Leydig cell hyperplasia and one mutant associated with Leydig cell adenomas are constitutively active when assayed for activation of cAMP, inositol phosphate, progesterone, and MAPK. Our ability to express the hLHR in MA-10 cells (now practically devoid of endogenous LHR) provides a novel paradigm to study the cellular and molecular basis of the functions of the LHR in Leydig cells.

Tyrosine sulfation is required for agonist recognition by glycoprotein hormone receptors

The glycoprotein hormone receptors (thyrotrophin receptor, TSHr; luteinizing hormone/chorionic gonadotrophin receptor, LH/CGr; follicle-stimulating hormone receptor, FSHr) constitute a subfamily of rhodopsin-like G protein-coupled receptors (GPCRs) with a long N-terminal extracellular extension responsible for high-affinity hormone binding. These ectodomains contain two cysteine clusters flanking nine leucine-rich repeats (LRR), a motif found in several protein families involved in protein-protein interactions. Similar to the situation described recently in CCR5, we demonstrate here that the TSHr, as it is present at the cell surface, is sulfated on tyrosines in a motif located downstream of the C-terminal cysteine cluster. Sulfation of one of the two tyrosines in the motif is mandatory for high-affinity binding of TSH and activation of the receptor. Site-directed mutagenesis experiments indicate that the motif, which is conserved in all members of the glycoprotein hormone receptor family, seems to play a similar role in the LH/CG and FSH receptors.

Leydig cell hypoplasia: cases with new mutations, new polymorphisms and cases without mutations in the luteinizing hormone receptor gene

BACKGROUND

Defective male sex differentiation in patients with hypoplasia of Leydig cells (LCH) is caused by deficient LH receptor signal transduction. To further investigate the variety of LH receptor gene mutations present in LCH patients and their influence on the phenotype, we examined 10 nonrelated patients with the clinical presentation of LCH.

PATIENTS AND METHODS

Ten patients with a clinical phenotype of LCH were analysed for mutations in the complete coding region of the LH receptor gene. Exons 1-10 and two overlapping fragments of exon 11 of the LH receptor gene including all intron-exon boundaries were amplified by polymerase chain reaction and sequenced. To screen for frequencies of DNA changes, mutation analysis was performed on 45-59 healthy persons using denaturation high-performance liquid chromatography.

RESULTS

Six new DNA alterations were identified. Three of them appear to be new polymorphisms. A G to C change at the 28th nucleotide of intron 1 on one allele and a heterozygous CGA to CAA transition at codon 124 (R124Q) were found. Both findings in these two patients are polymorphisms that occur with a frequency of 17% and 1.7%, respectively. A silent heterozygous CTA to TTA change at codon 204 was identified. In a patient with micropenis, the analysis revealed a homozygous missense mutation at codon 625 (I625K). As reported previously, this alteration significantly impaired signal transduction and explains the partial phenotype. Finally, in one compound heterozygous patient, two different mutations were discovered. At the polymorphic site in exon 1, a 27-bp insertion (CTG)2 AAG (CTG)5 CAG and a premature stop codon in the transmembrane segment 4 (W491*) were found. Both mutations disrupt signal transduction and explain the complete phenotype of this patient. In five patients, no DNA alterations could be identified.

CONCLUSIONS

Three mutations (33 bp insertion in exon 1; W491* and I625K) were identified that explain the phenotype in two patients. In addition, most of the patients with the clinical phenotype of LCH did not have causative mutations, suggesting that changes in other regions of the LH receptor gene, such as the large introns or the promoter region, may be responsible for the majority of cases. Alternatively, the displayed phenotype may be the result of other genetic defects. Our work further underscores the importance of thorough clinical analysis of patients before molecular analysis of a particular gene is performed.

The genetics of male undermasculinization

A review of the genetics of male undermasculinization must encompass a description of the embryology of the genital system. The dimorphism of sex development consequent upon the formation of a testis and the subsequent secretion of hormones to impose a male phenotype is highlighted. Thus, an understanding of the causes of male undermasculinization (manifest as XY sex reversal, complete and partial) includes reviewing the genetic factors which control testis determination and the production and action of testicular hormones. The study of disorders of male sex development has contributed substantially to knowledge of normal male development before birth. This knowledge has been complimented in recent years by the use of targeted murine gene disruption experiments to study the sex phenotype, although murine and human phenotypes are not always concordant. The investigation of disorders associated with male undermasculinization of prenatal onset is described briefly to complete the review.

The functional significance of FSH in spermatogenesis and the control of its secretion in male primates

The aim of this review is to provide an integrative analysis of the role of FSH in the control of testicular function in higher primates, including man. Attention is focused on the action of FSH during neonatal development, puberty, and adulthood. Whether FSH is the major determinant of the adult complement of Sertoli cells and whether FSH is obligatory for the initiation, maintenance, and restoration of spermatogenesis is evaluated. The mechanism whereby the circulating concentration of FSH regulates spermatogonial proliferation to dictate the sperm production rate under physiological conditions in the adult is discussed in detail. Inhibin B is the major component of the testicular negative feedback signal governing FSH beta gene expression and FSH secretion, and the evidence for this view is presented. The review concludes with the presentation of a model for the operation of the FSH-inhibin B feedback control system regulating sperm production postpubertally in monkey and man, and with speculation on issues of clinical interest.

Ovarian pathology and high incidence of sex cord tumors in follitropin receptor knockout (FORKO) mice

In this investigation we describe our observations of the status of the aging ovary in mice with disruption of the receptor for FSH. Knockout mice at 3-5 months of age are acyclic and sterile, with very small, underdeveloped ovaries. Thus, they exhibit hypergonadotropic-hypogonadism with high levels of circulating FSH similar to the postmenopausal state in women. By 12 months more than 92% of these animals developed various kinds of ovarian pathology, including neoplasms of sex cord-stromal type as well as cysts. Interestingly, the majority of tumors were located in the right ovary, with the contralateral ovary remaining unaffected but atrophic. The ovary from heterozygotes also showed pathology after 15 months. None of the age-matched wild-type mice that remained fertile developed any sign of ovarian tumors. Circulating LH and FSH levels were increased in follitropin receptor knockout mice and remained severalfold higher in tumor-bearing animals. The histological appearances of ovarian tumors were similar to the pathology observed in some types of sex cord-stromal neoplasms in women. The tumor burden caused weight loss and cachexia in follitropin receptor knockout mice. Based on these characteristics as well as the high incidence of ovarian pathology in the aging mutant, we propose that the loss of the FSH receptor signaling mechanisms predispose the ovary to molecular and structural changes leading to tumor formation. Hence, in the intact and fertile animal, FSH receptor signaling offers a protective mechanism that is lost upon reproductive senescence (menopause in women). Further studies are warranted in this genetic model to explore the molecular changes underlying the development of ovarian neoplasia.

Minireview: sex differentiation

Mammalian sex differentiation is a hormone-dependent process in the male following the determination of a testis from the indifferent gonad through a cascade of genetic events. Female sex differentiation is not dependent on ovarian hormones, yet there is evidence that members of the Wnt family of developmental signaling molecules play a role in Müllerian duct development and in suppressing Leydig cell differentiation in the ovary. The testis induces male sex differentiation (including testis descent) through a time-dependent production of optimal concentrations of anti-Müllerian hormone, insulin-like factor(s) and androgens. Observations in several human syndromes of disordered fetal sex development corroborate findings in murine embryo studies, although there are exceptions in some gene knockout models. The ubiquitously expressed AR interacts in a ligand-dependent manner with coregulators to control the expression of androgen-responsive genes. Preliminary studies suggest the possibility of hormone resistance syndromes associated with coregulator dysfunction. Polymorphic variants in genes controlling androgen synthesis and action may modulate androgenic effects on sex differentiation.

A conserved Asn in transmembrane helix 7 is an on/off switch in the activation of the thyrotropin receptor

The thyrotropin (TSH) receptor is an interesting model to study G protein-coupled receptor activation as many point mutations can significantly increase its basal activity. Here, we identified a molecular interaction between Asp(633) in transmembrane helix 6 (TM6) and Asn(674) in TM7 of the TSHr that is crucial to maintain the inactive state through conformational constraint of the Asn. We show that these residues are perfectly conserved in the glycohormone receptor family, except in one case, where they are exchanged, suggesting a direct interaction. Molecular modeling of the TSHr, based on the high resolution structure of rhodopsin, strongly favors this hypothesis. Our approach combining site-directed mutagenesis with molecular modeling shows that mutations disrupting this interaction, like the D633A mutation in TM6, lead to high constitutive activation. The strongly activating N674D (TM7) mutation, which in our modeling breaks the TM6-TM7 link, is reverted to wild type-like behavior by an additional D633N mutation (TM6), which would restore this link. Moreover, we show that the Asn of TM7 (conserved in most G protein-coupled receptors) is mandatory for ligand-induced cAMP accumulation, suggesting an active role of this residue in activation. In the TSHr, the conformation of this Asn residue of TM7 would be constrained, in the inactive state, by its Asp partner in TM6.

Hypomorphic phenotype in mice with pituitary-specific knockout of steroidogenic factor 1

The bacteriophage Cre recombinase provides a powerful approach for tissue-specific gene inactivation. Using a Cre transgene driven by the common alpha subunit of glycoprotein hormones (alphaGSU-Cre), we have previously inactivated steroidogenic factor 1 (SF-1) in the anterior pituitary, causing hypogonadotropic hypogonadism with sexual infantilism, sterility, and severe gonadal hypoplasia. We now explore the molecular mechanisms underlying a hypomorphic gonadal phenotype in mice carrying two floxed SF-1 alleles (F/F) relative to mice carrying one recombined and one floxed allele (F/R). Because their Cre-mediated disruption of the locus encoding SF-1 was less efficient, alphaGSU-Cre, F/F mice retained some gonadotropin-expressing cells in the anterior pituitary, thereby stimulating some gonadal function. This novel in vivo model for exploring the effects of differing levels of gonadotropins on gonadal development highlights the need for careful genotype-phenotype comparisons in studies using Cre recombinase to produce tissue-specific knockouts.