Chapter 4 Diseases Associated with Mutations of the Human Lutropin Receptor

Effect Modification of LHCGR Gene Variant (rs2293275) on Clinico-Biochemical Profile, and Levels of Luteinizing Hormone in Polycystic Ovary Syndrome Patients

 Polycystic ovary syndrome (PCOS) is a common multifaceted endocrine disorder among reproductive-aged women. Deranged luteinizing hormone levels and associated downstream signaling cascade mediated by its receptor luteinizing hormone chorionic gonadotropin receptor (LHCGR) are pivotal in the etiopathogenesis of PCOS. Genetic variations in the LHCGR have been associated with PCOS risk. However, the results are mixed and inconclusive. We evaluated the association of the LHCGR rs2293275 polymorphic variant with PCOS risk and its association with clinico-biochemical features of PCOS. 120 confirmed PCOS cases and an equal number of age-matched controls were subjected to clinical, biochemical, and hormonal investigations. Genotyping for rs2293275 was performed using polymerase chain reaction-restriction fragment length polymorphism. Logistic regression models were used to calculate odds ratios (ORs) at 95% confidence intervals (95% CIs). In the current study, PCOS cases reported a lower number of menstrual cycles per year than respective controls. A significantly higher BMI, Ferriman Galway score, levels of serum testosterone, insulin, TSH, FSH, and fasting glucose were observed in cases than in controls (p < 0.01). Compared to GG carriers, we observed a higher risk of developing PCOS in the subjects who harbored GA (OR 10.4, p < 0.0001) or AA (OR 7.73, p = 0.02) genotype. The risk persisted in the dominant model (GA + AA) as well (OR 10.29, p = 0.01). On stratification, a higher risk of developing PCOS was observed in variant genotype carriers who had a family history of either type two diabetes mellitus (OR 117; p < 0.0001) or hirsutism (OR 79; p < 0.0001). We also found significantly elevated levels of serum LH levels in the subject harboring GA and AA genotypes when compared to GG carriers. In the present study, we report a significant association of the LHCGR rs2293275 variant with the PCOS risk.

Association analysis of LHCGR variants and polycystic ovary syndrome in Punjab: a case-control approach

BACKGROUND

Polycystic ovary syndrome (PCOS) is an endocrine-metabolic disorder that affects women at their child bearing age. The exact etiology is uncertain, however the involvement of multiple genes and environmental interactions has been proposed for the advancement of PCOS. The aim of present study was to evaluate the association of LHCGR variants (rs2293275 and rs12470652) with PCOS in Punjab.

METHODS

The present case-control study comprised a total of 743 women (421 PCOS cases and 322 healthy controls). Genotyping was performed using polymerase chain reaction-restriction fragment length polymorphism technique (PCR-RFLP). Biochemical analysis was carried out to measure the levels of cholesterol, High-density lipoprotein (HDL), Low-density lipoprotein (LDL), Very low-density lipoprotein (VLDL), triglycerides, testosterone, luteinizing hormone (LH) and follicle-stimulating hormone (FSH). All the statistical analysis was done using SPSS (version21, IBM SPSS, NY, USA).

RESULTS

The mutant genotype (AA) and mutant allele (A) of rs2293275 conferred 1.7 and 1.3 fold risk, respectively and mutant allele (C) of rs12470652 conferred 2.3 fold risks towards PCOS progression. Levels of cholesterol and triglycerides were elevated and HDL levels were lower in PCOS cases as compared to controls. Total testosterone and luteinizing hormone levels were also found to be higher in PCOS cases.

CONCLUSION

Our study postulated that LHCGR variants are playing a cardinal role in the progression of PCOS and can be used to assess the risk of PCOS in women of reproductive age.

Single-cell-resolution transcriptome map revealed novel genes involved in testicular germ cell progression and somatic cells specification in Chinese tongue sole with sex reversal

Female-to-male sex reversals (pseudomales) are common in lower vertebrates and have been found in natural populations, which is a concern under rapid changes in environmental conditions. Pseudomales can exhibit altered spermatogenesis. However, the regulatory mechanisms underlying pseudomale spermatogenesis remain unclear. Here, we characterized spermatogenesis in Chinese tongue sole (Cynoglossus semilaevis), a species with genetic and environmental sex determination, based on a high-resolution single-cell RNA-seq atlas of cells derived from the testes of genotypic males and pseudomales. We identified five germ cell types and six somatic cell types and obtained a single-cell atlas of dynamic changes in gene expression during spermatogenesis in Chinese tongue sole, including alterations in pseudomales. We detected decreased levels of Ca²⁺ signaling pathway-related genes in spermatogonia, insufficient meiotic initiation in spermatocytes, and a malfunction of somatic niche cells in pseudomales. However, a cluster of CaSR genes and MAPK signaling factors were upregulated in undifferentiated spermatogonia of pseudomales. Additionally, we revealed that Z chromosome-specific genes, such as piwil2, dhx37, and ehmt1, were important for spermatogenesis. These results improve our understanding of reproduction after female-to-male sex-reversal and provide new insights into the adaptability of reproductive strategies in lower vertebrates.

Familial Male-limited Precocious Puberty (FMPP) and Testicular Germ Cell Tumors

OBJECTIVE

The purpose of this study is to report development of a malignant testicular germ cell tumor (GCT) in 2 young adult males with familial male-limited precocious puberty (FMPP) because of LHCGR pathogenic variants in 2 families. Secondarily, to study the possible relation between FMPP and testicular tumors and to investigate whether FMPP might predispose to development of malignant testicular tumors in adulthood a literature review is conducted.

METHODS

Data on 6 cases in 2 families are obtained from the available medical records. In addition, a database search is performed in Cochrane, PubMed, and Embase for studies that report on a possible link between FMPP and testicular tumors.

RESULTS

The characteristics of 6 males with FMPP based on activating LH receptor (LHCGR) germline pathogenic variants are described, as are details of the testicular GCTs. Furthermore, a literature review identified 4 more patients with signs of FMPP and a (precursor of) testicular GCT in adolescence or adulthood (age 15-35 years). Additionally, 12 patients with signs of precocious puberty and, simultaneously, occurrence of a Leydig cell adenoma or Leydig cell hyperplasia are reported.

CONCLUSION

There is a strong suggestion that FMPP might increase the risk of development of testicular GCTs in early adulthood compared with the risk in the general population. Therefore, prolonged patient monitoring from mid-pubertal age onward including instruction for self-examination and periodic testicular ultrasound investigation in patients with a germline LHCGR pathogenic variant might contribute to early detection and thus early treatment of testicular GCT.

Novel homozygous inactivating mutation in the luteinizing hormone receptor gene (LHCGR) associated with 46, XY DSD in a Moroccan family

OBJECTIVES

We present the first cases of two male brothers with Leydig cell hypoplasia secondary to a novel mutation in the LHCGR gene that has never been described before.

CASE PRESENTATION

We report the case of two brothers with Leydig cell hypoplasia (LCH) type II caused by novel homozygous inactivating mutation of the LHCGR gene, located in exon 10 in c 947 position. The two patients presented at 11 years 7 months and 1 year 6 months, respectively, with abnormal sexual development, micropenis and cryptorchidism. Genetic analysis revealed a homozygous deletion of approximately 4 bp encompassing exon 10 of the LHR gene in the two brothers indicating autosomal recessive inheritance. An hCG stimulation test induced testosterone secretion within the normal range. Subsequently, a treatment with enanthate of testosterone was started, with an increase in the length of the penis.

CONCLUSIONS

Leydig cell hypoplasia is a rare form of disorder of sex development. We report the occurrence of a new mutation of the LHCGR gene in two Moroccan brothers in whom the clinical features and the molecular diagnosis were correlated.

The Luteinizing Hormone Receptor Knockout Mouse as a Tool to Probe the In Vivo Actions of Gonadotropic Hormones/Receptors in Females

Mouse models with altered gonadotropin functions have provided invaluable insight into the functions of these hormones/receptors. Here we describe the repurposing of the infertile and hypogonadal luteinizing hormone receptor (LHR) knockout mouse model (LuRKO), to address outstanding questions in reproductive physiology. Using crossbreeding strategies and physiological and histological analyses, we first addressed the physiological relevance of forced LHR homomerization in female mice using BAC expression of 2 ligand-binding and signaling deficient mutant LHR, respectively, that have previously shown to undergo functional complementation and rescue the hypogonadal phenotype of male LuRKO mice. In female LuRKO mice, coexpression of signaling and binding deficient LHR mutants failed to rescue the hypogonadal and anovulatory phenotype. This was apparently due to the low-level expression of the 2 mutant LHR and potential lack of luteinizing hormone (LH)/LHR-dependent pleiotropic signaling that has previously been shown at high receptor densities to be essential for ovulation. Next, we utilized a mouse model overexpressing human chorionic gonadotropin (hCG) with increased circulating "LH/hCG"-like bioactivity to ~40 fold higher than WT females, to determine if high circulating hCG in the LuRKO background could reveal putative LHR-independent actions. No effects were found, thus, suggesting that LH/hCG mediate their gonadal and non-gonadal effects solely via LHR. Finally, targeted expression of a constitutively active follicle stimulating hormone receptor (FSHR) progressed antral follicles to preovulatory follicles and displayed phenotypic markers of enhanced estrogenic activity but failed to induce ovulation in LuRKO mice. This study highlights the critical importance and precise control of functional LHR and FSHR for mediating ovarian functions and of the potential repurposing of existing genetically modified mouse models in answering outstanding questions in reproductive physiology.

A novel variant in LCHGR gene in 3 siblings with type 1 Leydig cell hypoplasia

INTRODUCTION

Leydig cell hypoplasia (LCH) is an autosomal recessive disease that causes 46, XY sex development disorder. The patients with LCH are usually in the female phenotype and are presented with the complaints of no breast development and primary amenorrhea. In this article, the cases of three siblings who presented with primary amenorrhea and who had LCH were presented.

CASE

A 16-year-old patient with female phenotype is presented with primary amenorrhea. Breast development was at Tanner stage 1, the external genitalia were completely in female phenotype. The karyotype was determined as 46, XY. The hormonal analyses revealed that the testosterone synthesis was insufficient despite the high level of luteinizing hormone (LH). Cortisol, ACTH, 17-Hydroxyprogesterone, and AMH levels were normal. LCH diagnosis was considered in the patient with elevated LH and no testosterone synthesis. A new mutation of homozygous c.161 + 4A > G was detected in LHCGR gene. The same mutation was detected in the patient's two siblings with female phenotype and 46, XY karyotype.

CONCLUSION

In patients presenting with primary amenorrhea and karyotype 46, XY, there is no testosterone synthesis and if there is LH elevation, LCH should be considered. We found a novel variant in the LHCGR gene in three siblings with karyotype 46, XY and female phenotype.

Spontaneous fertility in a male patient with testotoxicosis despite suppression of FSH levels

Testotoxicosis is a rare cause of peripheral precocious puberty in boys caused by constitutively activating mutations of the LHCG receptor. Affected males usually have normal gonadotropin profiles and fertility in their adult life. Here, we described the long-term follow-up of a 24-year-old young man with severe testotoxicosis due to a de novo activating mutation in the third transmembrane helix of the LHCGR (p.Leu457Arg). This patient was treated with different medications, including medroxyprogesterone acetate, ketoconazole, cyproterone acetate and aromatase inhibitor from age 2.5 to 9.5 years. His basal and GnRH-stimulated gonadotropin levels were continually suppressed during and after medical treatment. At adulthood, extremely high serum testosterone levels (>35 nmol/L), undetectable gonadotropin levels (LH < 0.15 IU/L and FSH < 0.6 IU/L) and oligozoospermia were evidenced. Despite his suppressed FSH levels and an unfavorable spermogram, the patient fathered a healthy girl and biological paternity was confirmed through analysis of microsatellites. Spontaneous fertility in a young man with severe testotoxicosis and chronic suppression of FSH levels reinforces the key role of high intratesticular testosterone levels in human spermatogenesis.

Diseases caused by mutations in luteinizing hormone/chorionic gonadotropin receptor

Accumulating evidence showed that the luteinizing hormone/chorionic gonadotropin receptor (LHCGR) is an essential regulator of sexual development and reproduction from zebrafish to human. Activating and inactivating mutations of LHCGR gene have been identified from patients of different phenotypes. Familial male-limited precocious puberty, Leydig cell hypoplasia, and empty follicle syndrome are caused by LHCGR mutations. More than 50 mutations have been reported from subjects of different ethnic backgrounds. Functional analyses of the mutant LHCGR revealed multiple defects, including cell surface expression, ligand binding, and signaling. The difference of the two native ligands and signaling pathway activated by LHCGR are illustrated. Potential therapeutic implications from the analyses of the naturally occurring LHCGR mutations, such as pharmacological chaperones, are highlighted.

GATA4 Variants in Individuals With a 46,XY Disorder of Sex Development (DSD) May or May Not Be Associated With Cardiac Defects Depending on Second Hits in Other DSD Genes

Disorders of sex development (DSD) consist of a wide range of conditions involving numerous genes. Nevertheless, about half of 46,XY individuals remain genetically unsolved. GATA4 gene variants, mainly related to congenital heart defects (CHD), have also been recently associated with 46,XY DSD. In this study, we characterized three individuals presenting with 46,XY DSD with or without CHD and GATA4 variants in order to understand the phenotypical variability. We studied one patient presenting CHD and 46,XY gonadal dysgenesis, and two patients with a history of genetically unsolved 46,XY DSD, also known as male primary hypogonadism. Mutation analysis was carried out by candidate gene approach or targeted gene panel sequencing. Functional activity of GATA4 variants was tested in vitro on the CYP17 promoter involved in sex development using JEG3 cells. We found two novel and one previously described GATA4 variants located in the N-terminal zinc finger domain of the protein. Cys238Arg variant lost transcriptional activity on the CYP17 promoter reporter, while Trp228Cys and Pro226Leu behaved similar to wild type. These results were in line with bioinformatics simulation studies. Additional DSD variations, in the LRP4 and LHCGR genes, respectively, were identified in the two 46,XY individuals without CHD. Overall, our study shows that human GATA4 mutations identified in patients with 46,XY DSD may or may not be associated with CHD. Possible explanations for phenotypical variability may comprise incomplete penetrance, variable sensitivity of partner genes, and oligogenic mechanisms.

Mouse Models for the Study of Synthesis, Secretion, and Action of Pituitary Gonadotropins

Gonadotropins play fundamental roles in reproduction. More than 30years ago, Cga transgenic mice were generated, and more than 20years ago, the phenotypes of Cga null mice were reported. Since then, numerous mouse strains have been generated and characterized to address several questions in reproductive biology involving gonadotropin synthesis, secretion, and action. More recently, extragonadal expression, and in some cases, functions of gonadotropins in nongonadal tissues have been identified. Several genomic and proteomic approaches including novel mouse genome editing tools are available now. It is anticipated that these and other emerging technologies will be useful to build an integrated network of gonadotropin signaling pathways in various tissues. Undoubtedly, research on gonadotropins will continue to provide new knowledge and allow us transcend from benchside to the bedside.

The expression of several reproductive hormone receptors can be modified by perfluorooctane sulfonate (PFOS) in adult male rats

This study was undertaken to evaluate the possible role of several reproductive hormone receptors on the disruption of the hypothalamic-pituitary-testis (HPT) axis activity induced by perfluorooctane sulfonate (PFOS). The studied receptors are the gonadotropin-releasing hormone receptor (GnRHr), luteinizing hormone receptor (LHr), follicle-stimulating hormone receptor (FSHr), and the androgen receptor (Ar). Adult male rats were orally treated with 1.0; 3.0 and 6.0 mg of PFOS kg(-1) d(-1) for 28 days. In general terms, PFOS can modify the relative gene and protein expressions of these receptors in several tissues of the reproductive axis. At the testicular level, apart from the expected inhibition of both gene and protein expressions of FSHr and Ar, PFOS also stimulates the GnRHr protein and the LHr gene expression. The receptors of the main hormones involved in the HPT axis may have an important role in the disruption exerted by PFOS on this axis.

Novel homozygous nonsense mutations in the luteinizing hormone receptor (LHCGR) gene associated with 46,XY primary amenorrhea

OBJECTIVE

To determine the genetic cause of 46,XY primary amenorrhea in three 46,XY girls.

DESIGN

Whole exome sequencing.

SETTING

University cytogenetics center.

PATIENT(S)

Three patients with unexplained 46,XY primary amenorrhea were included in the study.

INTERVENTION(S)

Potentially pathogenic variants were confirmed by Sanger sequencing, and familial segregation was determined where parents' DNA was available.

MAIN OUTCOME MEASURE(S)

Exome sequencing was performed in the three patients, and the data were analyzed for potentially pathogenic mutations. The functional consequences of mutations were predicted.

RESULT(S)

Three novel homozygous nonsense mutations in the luteinizing hormone receptor (LHCGR) gene were identified:c.1573 C→T, p.Gln525Ter, c.1435 C→T p.Arg479Ter, and c.508 C→T, p.Gln170Ter.

CONCLUSION(S)

Inactivating mutations of the LHCGR gene may be a more common cause of 46,XY primary amenorrhea than previously considered.

Misfolding Ectodomain Mutations of the Lutropin Receptor Increase Efficacy of Hormone Stimulation

We demonstrate 2 novel mutations of the LHCGR, each homozygous, in a 46,XY patient with severe Leydig cell hypoplasia. One is a mutation in the signal peptide (p.Gln18_Leu19ins9; referred to here as SP) that results in an alteration of the coding sequence of the N terminus of the mature mutant receptor. The other mutation (p.G71R) is also within the ectodomain. Similar to many other inactivating mutations, the cell surface expression of recombinant human LHR(SP,G71R) is greatly reduced due to intracellular retention. However, we made the unusual discovery that the intrinsic efficacy for agonist-stimulated cAMP in the reduced numbers of receptors on the cell surface was greatly increased relative to the same low number of cell surface wild-type receptor. Remarkably, this appears to be a general attribute of misfolding mutations in the ectodomains, but not serpentine domains, of the gonadotropin receptors. These findings suggest that there must be a common, shared mechanism by which disparate mutations in the ectodomain that cause misfolding and therefore reduced cell surface expression concomitantly confer increased agonist efficacy to those receptor mutants on the cell surface. Our data further suggest that, due to their increased agonist efficacy, extremely small changes in cell surface expression of misfolded ectodomain mutants cause larger than expected alterations in the cellular response to agonist. Therefore, for inactivating LHCGR mutations causing ectodomain misfolding, the numbers of cell surface mutant receptors on fetal Leydig cells of 46,XY individuals exert a more exquisite effect on the relative severity of the clinical phenotypes than already appreciated.

Perspectives in Pediatric Pathology, Chapter 6. Male Undermasculinization

Normal male development requires three conditions: (1) adequate differentiation of the fetal testis; (2) synthesis and secretion of testicular hormones; and (3) effective action of these hormones on target organs. This requires the combined action of the inhibitory anti-müllerian hormone (AMH, secreted by Sertoli cells) to block the development of the uterus and fallopian tubes from the müllerian duct, together with the trophic stimulus of testosterone (a Leydig cell product), which leads to virilization of the wolffian ducts. Additionally, the development of external genitalia depends on the conversion of testosterone to dihydrotestosterone by the enzyme 5-α-reductase. Failure of any of these mechanisms leads to deficient virilization or the so-called "male pseudohermaphroditism" syndromes.

A novel compound heterozygous mutation of the luteinizing hormone receptor -implications for fertility

The luteinizing hormone/chorionic gonadotropin receptor (LHCGR) belongs to the family of G-protein coupled receptors and binds both luteinizing hormone (LH) and human chorionic gonadotropin (hCG). Ligand-receptor interaction mediates a downstream cascade of events which is essential for ovulation in women, and expression of the male phenotype in men. The human LHCGR gene consists of 11exons and 10 introns. Homozygous and compound heterozygous mutations may inactivate the receptor by altering its structure and subsequent function. Herein we reported a novel, compound heterozgygous inactivating LHCGR mutation in a woman who presented with secondary infertility, having previously carried to term a donor oocyte pregnancy. A 27 bp deletion was detected in exon I at amino acid number 12. This mutation involved the signal peptide region, which is important for protein targeting, maturation and cellular expression. Another mutation involving a 2 base pair (thymine and cytosine) deletion was detected in exon 11 at amino acid number 586. This deletion produced a frameshift resulting in a premature stop codon and a truncated protein. An XY sibling with the same mutations was phenotypically female and misdiagnosed as complete androgen insensitivity syndrome. Other unaffected family members were genetically tested and carried one of the two mutations.

Luteinizing hormone and human chorionic gonadotropin: distinguishing unique physiologic roles

Luteinizing hormone (LH) and human chorionic gonadotropin (hCG) are integral components of the hypothalamic-pituitary-gonadal axis, which controls sexual maturation and functionality. In the absence of signaling through their shared receptor, fetal sexual differentiation and post-natal development cannot proceed normally. Although they share a high degree of homology, the physiologic roles of these hormones are unique, governed by differences in expression pattern, biopotency and regulation. Whereas LH is a key regulator of gonadal steroidogenesis and ovulation, hCG is predominantly active in pregnancy and fetal development. Emerging evidence has revealed endogenous functions not previously ascribed to hCG, including participation in ovulation and fertilization, implantation, placentation and other activities in support of successful pregnancy. Spontaneous and induced mutations in LH, hCG and their mutual receptor have contributed substantially to our understanding of reproductive development and function. The lack of naturally occurring, functionally significant mutations in the β-subunit of hCG reinforce its putative role in establishment of pregnancy. Rescue of reproductive abnormalities resulting from aberrant gonadotropin signaling is possible in certain clinical contexts, depending on the nature of the underlying defect. By understanding the physiologic roles of LH and hCG in normal and pathologic states, we may better harness their diagnostic, prognostic and therapeutic potential.

Association between the luteinizing hormone/chorionic gonadotropin receptor (LHCGR) rs4073366 polymorphism and ovarian hyperstimulation syndrome during controlled ovarian hyperstimulation

BACKGROUND

The aim of this study was to determine the relationship between a purported luteinizing hormone/chorionic gonadotropin (LHCGR) high function polymorphism (rs4539842/insLQ) and outcome to controlled ovarian hyperstimulation (COH).

METHODS

This was a prospective study of 172 patients undergoing COH at the Fertility and IVF Center at GWU. DNA was isolated from blood samples and a region encompassing the insLQ polymorphism was sequenced. We also investigated a polymorphism (rs4073366 G > C) that was 142 bp from insLQ. The association of the insLQ and rs4073366 alleles and outcome to COH (number of mature follicles, estradiol level on day of human chorionic gonadotropin (hCG) administration, the number of eggs retrieved and ovarian hyperstimulation syndrome (OHSS)) was determined.

RESULTS

Increasing age and higher day 3 (basal) FSH levels were significantly associated with poorer response to COH. We found that both insLQ and rs4073366 were in linkage disequilibrium (LD) and no patients were homozygous for both recessive alleles (insLQ/insLQ; C/C). The insLQ variant was not significantly associated with any of the main outcomes to COH. Carrier status for the rs4073366 C variant was associated (P = 0.033) with an increased risk (OR 2.95, 95% CI = 1.09-7.96) of developing OHSS.

CONCLUSIONS

While age and day 3 FSH levels were predictive of outcome, we found no association between insLQ and patient response to COH. Interestingly, rs4073366 C variant carrier status was associated with OHSS risk. To the best of our knowledge, this is the first report suggesting that LHCGR genetic variation might function in patient risk for OHSS.

The ERK1/2 pathway regulates testosterone synthesis by coordinately regulating the expression of steroidogenic genes in Leydig cells

Adult mice with a Leydig cell specific deletion of MAPK kinase (MEK) 1 and 2 (Mek1(f)(/)(f);Mek2(-/-);Cre(+)) mice display Leydig cell hypoplasia and hypergonadotropic hypogonadism. We used radioimmunoassays and quantitative PCR to evaluate the function and expression of the Leydig cell genes involved in the conversion of cholesterol to testosterone (Star, Cyp11a1, Hsd3b6, Cyp17a1 and Hsd17b3), androgen metabolism (Srda1 and Dhrs9), and four transcription factors (Creb1, Nr5a1, Nr4a1 and Nr0b1) that regulate the expression of steroidogenic genes. We show that Star, Hsd3b6, Cyp17a1 and Hsd17b3 are downregulated in Ledyig cells of adult Mek1(f)(/)(f);Mek2(-/-);Cre(+) mice whereas Srda1 and Dhrs9 are upregulated and Creb1, Nr5a1, Nr4a1 and Nr0b1 are unchanged or upregulated. Functionally, all the downregulated genes but none of the upregulated genes contribute to the decrease in testosterone synthesis in Leydig cells of adult Mek1(f)(/)(f);Mek2(-/-);Cre(+) mice because they produce low testosterone and dihydrotestosterone when stimulated with hCG or when incubated with testosterone precursors such as progesterone or androstenedione.

Structure, function and regulation of gonadotropin receptors - a perspective

Luteinizing hormone receptor and follicle stimulating hormone receptor play a crucial role in female and male reproduction. Significant new information has emerged about the structure, mechanism of activation, and regulation of expression of these receptors. Here we provide an overview of the current information on those aspects with an in-depth discussion of the recent developments in the post-transcriptional mechanism of LH receptor expression mediated by a specific LH receptor mRNA binding protein, designated as LRBP. LRBP was identified by electrophoretic gel mobility shift assay using cytosolic fractions from ovaries in the down regulated state. LRBP was purified, its binding site on LH receptor mRNA was identified and characterized. During ligand-induced down regulation, LRBP expression is increased through the cAMP/PKA and ERK signaling pathway, is translocated to translating ribosomes, binds LH receptor mRNA and forms an untranslatable ribonucleoprotein complex. This complex is then routed to the mRNA degradation machinery resulting in diminished levels of both LHR mRNA and cell surface expression of LH receptor. The studies leading to these conclusions are presented.

Association of the genetic variants of luteinizing hormone, luteinizing hormone receptor and polycystic ovary syndrome

BACKGROUND

High circulating luteinizing hormone (LH) level is a typical biochemical feature of polycystic ovary syndrome (PCOS) whose pathophysiology is still unclear. Certain mutations of LH and LH receptor (LHR) may lead to changes in bioactivity of these hormones. The aim of this study was determine the role of the LH and LHR polymorphisms in the pathogenesis of PCOS using a genetic approach.

METHODS

315 PCOS women and 212 controls were screened for the gene variants of LH G1052A and LHR rs61996318 polymorphisms by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP).

RESULTS

PCOS patients had significantly more A allele frequency of LH G1052A mutations than controls (p=0.001). Within PCOS group, carriers of LH 1052A allele had lower LH (p=0.05) and higher fasting glucose levels (p=0.04). No subjects were identified with LHR rs61996318 polymorphisms. A new LHR single nucleotide polymorphism (SNP) was found without clear association with PCOS.

CONCLUSIONS

Results suggested LH G1052A mutation might influence PCOS susceptibility and phenotypes.

Regulatory processes governing the cell surface expression of LH and FSH receptors

The LH receptor (LHR) and FSH receptor (FSHR), collectively termed the gonadotropin receptors, are members of the Family A of GPCRs. The gonadotropin receptors each contain N-linked carbohydrates that are not directly involved in hormone binding, but contribute to the proper folding, and therefore, cell surface expression of the receptor. Loss-of-function mutations of an LHR or FSHR results in decreased target cell responsiveness. Most inactivating mutations cause receptor misfolding, resulting in the retention of the mutant in its immature form in the endoplasmic reticulum. A membrane-permeable allosteric agonist of the LHR has been shown to serve as a pharmacological chaperone for misfolded and intracellularly retained LHRs by promoting their cell surface expression. Wild-type LHR and FSHR each form homodimers and heterodimers while in the ER. Therefore, when wild-type receptor is co-expressed with a misfolded mutant, the misfolded receptor dimerizes with immature wild-type receptor in the ER, causing a dominant-negative effect on cell surface expression of the mature wild-type receptor. Notably, the propensity for homodimerization is not affected by the activation status of the receptor. However, within a receptor dimer, the activity of one protomer may allosterically regulate the other protomer. Therefore, the dimerization of the gonadotropin receptors appears to be an obligate process that is part of the normal itinerary for trafficking to the cell surface and, once there, the dimerized receptors allow for additional modulations of cell signaling.

Hyperparathyroid genes: sequences reveal answers and questions

OBJECTIVE

To review hyperparathyroid syndromes and genes.

METHODS

Pertinent original studies from the literature are discussed.

RESULTS

Six main hyperparathyroid syndromes are recognized; 5 are from germline mutations in 4 genes-CASR, MEN1, RET, and HRPT2. Each hyperparathyroid syndrome was first described around 1965; the main gene for each syndrome was identified about 30 years later. Gene identification addressed clinical issues. (1) Testing for mutation carriers among affected probands or among unaffected relatives is more robust than prior methods, which were based on syndromal traits such as serum calcium. (2) Interpreting a gene test (RET) could guide an important intervention; other gene tests could yield useful information for patients and physicians. (3) Proving the roles of each gene (in particular, MEN1 somatic mutations) provided insights about contributions to many common tumors. (4) Clarifying molecular pathways and drugs led, for example, to the CASR-aided development of calcimimetic and calcilytic drugs. (5) Explaining novel features, such as the CASR gene encoding a membrane calcium-sensing receptor and its mutations resulting in nonsuppressed parathyroid hormone secretion uncoupled from proliferation, characterized familial hypocalciuric hypercalcemia. (6) Disclosing probands without an identifiable mutation promoted searches for other syndromal genes. Subsequently, rare multiple endocrine neoplasia type 1-like families were shown to have inactivating germline mutations, first of p27 and subsequently of p15, p18, or p21.

CONCLUSION

The next frontier in mutation detection is arriving, with possible sequencing of the whole exome or even the whole genome for 1 case or 1 tumor at an affordable cost.

Constitutive activity of the lutropin receptor and its allosteric modulation by receptor heterodimerization

The lutropin receptor (LHR) is a G protein-coupled receptor (GPCR) that mediates the actions of pituitary LH in males and females and that of placental hCG in pregnant women and, therefore, plays an essential role in reproductive physiology. Mutations of the lhcgr gene that result in constitutive activation of the LHR have been shown to be causative of gonadotropin-independent precocious puberty in young boys. Studies on constitutively active mutants (CAMs) of the LHR have been extremely informative in elucidating the roles of the LHR in reproductive physiology as well as in understanding the molecular basis underlying activation of this GPCR. The constitutive activities of hLHR CAMs can be attenuated by introducing mutations into the CAMs that stabilize the resting state of the hLHR or by coexpressing the hLHR CAMs with an hLHR mutant that is stabilized in the resting state, allowing the two forms of the hLHR to heterodimerize. This chapter describes the experimental methods and strategies underlying studies of hLHR CAMs.

The luteinizing hormone receptor: insights into structure-function relationships and hormone-receptor-mediated changes in gene expression in ovarian cancer cells

The luteinizing hormone receptor (LHR), one of the three glycoprotein hormone receptors, is necessary for critical reproductive processes, including gonadal steroidogenesis, oocyte maturation and ovulation, and male sex differentiation. Moreover, it has been postulated to contribute to certain neoplasms, particularly ovarian cancer. A member of the G protein-coupled receptor family, LHR contains a relatively large extracellular domain responsible for high affinity hormone binding; transmembrane activation then leads to G protein coupling and subsequent second messenger production. This review deals with recent advances in our understanding of LHR structure and structure-function relationships, as well as hormone-mediated changes in gene expression in ovarian cancer cells expressing LHR. Suggestions are also made for critical gaps that need to be filled as the field advances, including determination of the three-dimensional structure of inactive and active receptor, elucidation of the mechanism by which hormone binding to the extracellular domain triggers the activation of Gs, clarification of the putative roles of LHR in non-gonadal tissues, and the role, if any, of activated receptor in the development or progression of ovarian cancer.