Cellular localization of human relaxin-like factor in the cyclic endometrium and placenta

The effects of mifepristone on the structure of human decidua and chorion and Bax and Bcl-2 expression at early stage of pregnancy

Background

As a progesterone receptor antagonist, mifepristone combined with misoprostol is widely used to terminate early pregnancy in clinical practice. It has also been reported that mifepristone may cause cell death in decidual cells and result in hemorrhage of the decidua and insufficient blood supply. However, little is known about the histological effects of mifepristone on human decidua and chorion.

Methods

Histological and subcellular structural changes of decidua and chorionic villi from women taking mifepristone at early pregnancy times were examined by Hematoxylin and eosin (H&E) staining and transmission Electron microscope. The expression of apoptosis-related proteins Bax/Bcl-2 was examined by immunohistochemistry.

Results

After 48 h of mifepristone administration, the decidua tissue and chorionic villus structures were altered in women within 39–49 days of gestation and displayed varying degrees of degeneration and necrosis-like features. Apoptotic events were observed in the decidua and chorionic villi of early pregnancy, and mifepristone treatment significantly increases the number of apoptotic cells. The increased apoptotic events were concomitant with the increased expression of Bax and decreased expression of Bcl-2.

Conclusion

This study provides evidence that mifepristone induces histological and subcellular changes in decidua and chorionic villi. Mifepristone modulates the relative ratio of Bax/Bcl-2 and the increased apoptosis contributes to the pregnancy termination at early stage of pregnancy.

Evidence for existence of insulin-like factor 3 (INSL3) hormone-receptor system in the ovarian corpus luteum and extra-ovarian reproductive organs during pregnancy in goats

Insulin-like factor 3 (INSL3), initially described as a male hormone, is expressed in female reproductive organs during the estrous cycle and pregnancy but its function has not yet been established. This study explores the function of INSL3 in pregnant Saanen goats by characterizing the expression dynamics of INSL3 and its receptor, relaxin family peptide receptor 2 (RXFP2) and by demonstrating specific INSL3 binding in reproductive organs, using molecular and immunological approaches and ligand-receptor interaction assays. We demonstrate that the corpus luteum (CL) acts as both a source and target of INSL3 in pregnant goats, while extra-ovarian reproductive organs serve as additional INSL3 targets. The expression of INSL3 and RXFP2 in the CL reached maximum levels in middle pregnancy, followed by a decrease in late pregnancy; in contrast, RXFP2 expression levels in extra-ovarian reproductive organs were higher in the mammary glands but lower in the uterus, cervix and placenta and did not significantly change during pregnancy. The functional RXFP2 enabling INSL3 to bind was identified as an ~ 85 kDa protein in both the CL and mammary glands and localized in large and small luteal cells in the CL and in tubuloalveolar and ductal epithelial cells in the mammary glands. Additionally, INSL3 also bound to multiple cell types expressing RXFP2 in the uterus, cervix and placenta in a hormone-specific and saturable manner. These results provide evidence that an active intra- and extra-ovarian INSL3 hormone-receptor system operates during pregnancy in goats.

Functional implications of the utero-placental relaxin (RLN) system in the dog throughout pregnancy and at term

Relaxin (RLN) is a key hormone of pregnancy in mammals best known for its involvement in connective tissue remodeling. In the domestic dog, placental RLN is the only known endocrine marker of pregnancy. However, knowledge is sparse regarding the spatio-temporal expression of RLN and its receptors (RXFP1 and RXFP2) in the canine uterus and placenta. Here, their expression was investigated in the pre-implantation uterus and utero-placental compartments (UtPl) at selected time points during gestation: post-implantation, mid-gestation, and at normal and antigestagen-induced luteolysis/abortion. Immunohistochemistry with newly generated, canine-specific antisera, in situ hybridization and semi-quantitative PCR were applied. In compartmentalization studies, placental and endometrial RLN increased continuously toward prepartum. The placental RXFP1 was time-related and highest during post-implantation and decreased together with RXFP2 at prepartum luteolysis. The endometrial levels of both receptors did not vary greatly, but myometrial RXFP2 decreased from mid-gestation to prepartum luteolysis. Antigestagen treatment resulted in suppression of RLN in UtPl and decreased RXFP1 and RXFP2 in the uterus. The placental RLN was localized mainly in the cytotrophoblast. Additionally, RXFP1 stained strongly in placental endothelial cells while RXFP2 was found mainly in maternal decidual cells. Uterine staining for all targets was found in epithelial cellular constituents and in myometrium. Finally, besides its endocrine functions, RLN seems to be involved in auto-/paracrine regulation of utero-placental functions in dogs in a time-dependent manner. New insights into feto-maternal communication was provided, in particular regarding the localization of RXFP2 in the maternal decidual cells, implying functional roles of RLN during the decidualization process.

Insulin-like factor 3 promotes wound healing at the ocular surface

Tear fluid is known to contain many different hormones with relevance for ocular surface homeostasis. We studied the presence and functional role of insulin-like factor 3 (INSL3) and its cognate receptor RXFP2 (relaxin/insulin-like family peptide receptor 2) at the ocular surface and in tears. Expression of human INSL3 and RXFP2 was determined in tissues of the ocular surface and lacrimal apparatus; in human corneal (HCE), conjunctival (HCjE), and sebaceous (SC) epithelial cell lines; and in human tears by RT-PCR and ELISA. We investigated effects of human recombinant INSL3 (hrINSL3) on cell proliferation and cell migration and the influence of hrINSL3 on the expression of MMP2, -9, and -13 and TIMP1 and -2 was quantified by real-time PCR and ELISA in HCE, HCjE, and SC cells. We used a C57BL/6 mouse corneal defect model to elucidate the effect of topical application of hrINSL3 on corneal wound healing. INSL3 and RXFP2 transcripts and INSL3 protein were detected in all tissues and cell lines investigated. Significantly higher concentrations of INSL3 were detected in tears from male vs. female volunteers. Stimulation of HCE, HCjE, and SC with hrINSL3 significantly increased cell proliferation in HCjE and SC and migration of HCjE. Treatment with hrINSL3 for 24 hours regulated MMP2, TIMP1, and TIMP2 expression. The local application of hrINSL3 onto denuded corneal surface resulted in significantly accelerated corneal wound healing in mice. These findings suggest a novel and gender-specific role for INSL3 and cognate receptor RXFP2 signaling in ocular surface homeostasis and determined a novel role for hrINSL3 in corneal wound healing.

Relaxin family peptides and their receptors

There are seven relaxin family peptides that are all structurally related to insulin. Relaxin has many roles in female and male reproduction, as a neuropeptide in the central nervous system, as a vasodilator and cardiac stimulant in the cardiovascular system, and as an antifibrotic agent. Insulin-like peptide-3 (INSL3) has clearly defined specialist roles in male and female reproduction, relaxin-3 is primarily a neuropeptide involved in stress and metabolic control, and INSL5 is widely distributed particularly in the gastrointestinal tract. Although they are structurally related to insulin, the relaxin family peptides produce their physiological effects by activating a group of four G protein-coupled receptors (GPCRs), relaxin family peptide receptors 1-4 (RXFP1-4). Relaxin and INSL3 are the cognate ligands for RXFP1 and RXFP2, respectively, that are leucine-rich repeat containing GPCRs. RXFP1 activates a wide spectrum of signaling pathways to generate second messengers that include cAMP and nitric oxide, whereas RXFP2 activates a subset of these pathways. Relaxin-3 and INSL5 are the cognate ligands for RXFP3 and RXFP4 that are closely related to small peptide receptors that when activated inhibit cAMP production and activate MAP kinases. Although there are still many unanswered questions regarding the mode of action of relaxin family peptides, it is clear that they have important physiological roles that could be exploited for therapeutic benefit.

Human testicular insulin-like factor 3: in relation to development, reproductive hormones and andrological disorders

Knockout of the gene encoding insulin-like factor 3 (INSL3) results in cryptorchidism in mice due to disruption of the transabdominal phase of testicular descent. This finding was essential for understanding the complete course of testis descensus, and wound up years of speculations regarding the endocrine regulation of this process. INSL3 is, along with testosterone, a major secretory product of testicular Leydig cells. In addition to its crucial function in testicular descent, INSL3 is suggested to play a paracrine role in germ cell survival and an endocrine role in bone metabolism. INSL3 is produced in human prenatal and neonatal, and in adult Leydig cells to various extents, and is in a developmental context regulated like testosterone, with production during second trimester, an early postnatal peak and increasing secretion during puberty, resulting in high adult serum levels. INSL3 production is entirely dependent on the state of Leydig cell differentiation, and is stimulated by the long-term trophic effects mediated by luteinizing hormone (LH). Once differentiated, Leydig cells apparently express INSL3 in a constitutive manner, and the hormone is thereby insensitive to the acute, steroidogenic effects of LH, which for example is an important factor in the regulation of testosterone. Clinically, serum INSL3 levels can turn out to be a usable tool to monitor basal Leydig cell function in patients with various disorders affecting Leydig cell function. According to animal studies, foetal INSL3 production is, directly or indirectly, sensitive to oestrogenic or anti-androgenic compounds. This provides important insight into the mechanism by which maternal exposure to endocrine disrupters can result in cryptorchidism in the next generation. Conclusively, INSL3 is an interesting testicular hormone with potential clinical value as a marker for Leydig cell function. It should be considered on a par with testosterone in the evaluation of testicular function and the consequences of Leydig cell dysfunction.

Biological role and clinical significance of insulin-like peptide 3

PURPOSE OF REVIEW

Insulin-like peptide 3 (INSL3) is the subject of a fast expanding literature reflecting increasing clinical application, particularly as a diagnostic parameter. This review summarizes the recent INSL3 literature published within the last 12-18 months.

RECENT FINDINGS

Significant inroads have been made to understand how INSL3 is working in testicular descent. It also has other functions in the adult, for example in bone metabolism, extending its role as a largely gender-specific hormone. Advances in molecular pharmacology have increased our understanding of INSL3 interaction with its specific receptor, RXFP2, and delivered new high-affinity antagonists. INSL3 is increasingly being used to assess Leydig cell functional capacity within the testis, independently of factors affecting the hypothalamic-pituitary-gonadal axis, being a robust parameter by comparison with testosterone. Particularly in the aging male, metabolic syndrome, and the effects of adiposity on testis function, INSL3 is a valuable adjunct to the standard clinical repertoire.

SUMMARY

The Leydig cell hormone INSL3 is responsible for the first phase of testicular descent during pregnancy and may have multiple roles as a gender-specific circulating hormone in the adult reflecting Leydig cell functional capacity. In women, INSL3 is a paracrine factor within the ovary and probably placenta, in which it may have a fetal gender-specific role.

INSL3 in the ruminant: a powerful indicator of gender- and genetic-specific feto-maternal dialogue

The hormone Insulin-like peptide 3 (INSL3) is a major secretory product of the Leydig cells from both fetal and adult testes. Consequently, it is a major gender-specific circulating hormone in the male fetus, where it is responsible for the first phase of testicular descent, and in the adult male. In most female mammals, circulating levels are very low, corresponding to only a small production of INSL3 by the mature ovaries. Female ruminants are exceptional in exhibiting high INSL3 gene expression by the thecal cells of antral follicles and by the corpora lutea. We have developed a specific and sensitive immunoassay to measure ruminant INSL3 and show that, corresponding to the high ovarian gene expression, non-pregnant adult female sheep and cows have up to four times the levels observed in other female mammals. Significantly, this level declines during mid-pregnancy in cows carrying a female fetus, in which INSL3 is undetectable. However, in cows carrying a male fetus, circulating maternal INSL3 becomes elevated further, presumably due to the transplacental transfer of fetal INSL3 into the maternal circulation. Within male fetal blood, INSL3 is high in mid-pregnancy (day 153) corresponding to the first transabdominal phase of testicular descent, and shows a marked dependence on paternal genetics, with pure bred or hybrid male fetuses of Bos taurus (Angus) paternal genome having 30% higher INSL3 levels than those of Bos indicus (Brahman) paternity. Thus INSL3 provides the first example of a gender-specific fetal hormone with the potential to influence both placental and maternal physiology.

Relaxin signalling in primary cultures of human myometrial cells

In myometrium of pigs and rats, though not humans, relaxin appears to mediate an inhibition of spontaneous and oxytocin-induced contractility, presumably acting through a G-protein coupled receptor (RXFP1) to generate cAMP. In humans, circulating relaxin is highest in the first trimester, including the time of implantation, when transitory uterine quiescence could help a blastocyst to implant. We investigated whether relaxin can activate adenylate cyclase in primary human myometrial cells from non-pregnant tissue, and we show that relaxin is able to stimulate the generation of cAMP in a manner, which is dependent upon a tyrosine phosphorylation activity, as in the endometrium. We identified transcripts for the relaxin receptor RXFP1 as full-length variants, though a minor splice variant missing exon 2 was also present in low amounts. These cells also express transcripts encoding RXFP2, the receptor for the closely related hormone, INSL3. Although able to respond to relaxin at high concentrations, this receptor does not appear to function by contributing to the cAMP production in human myometrial cells, nor does INSL3 act as a functional agonist or antagonist of relaxin action. In conclusion, the inability of relaxin to inhibit contractility in human myometrial cells would appear to be due to events downstream of simple cAMP generation.

Effects of uteroplacental restriction on the relaxin-family receptors, Lgr7 and Lgr8, in the uterus of late pregnant rats

The peptide hormone relaxin stimulates uterine growth and endometrial angiogenesis and inhibits myometrial contractions in a variety of species. The receptor for relaxin is a leucine-rich repeat containing G-protein-coupled receptor Lgr7 (RXFP1) that is highly expressed in the myometrium of late pregnant mice, with a significant decrease in receptor density observed at term. The present study first compared the expression of Lgr7 with another relaxin-family receptor Lgr8 (RXFP2) in the uterus and placenta of late pregnant rats. The uterus was separated into endometrial and myometrial components, and the myometrium into fetal and non-fetal sites, for further analysis. We then assessed the response of these receptors to uteroplacental restriction (UPR). Expression of the Lgr7 gene was significantly higher in the uterus compared with the placenta. Within the uterus, on Day 20 of gestation, there was equivalent expression of Lgr7 in fetal and non-fetal sites of the myometrium, as well as in the endometrium v. myometrium. The second receptor investigated, Lgr8, was also expressed in the endometrium and myometrium, but at significantly lower levels than Lgr7. Bilateral ligation of the maternal uterine blood vessels on Day 18 of gestation resulted in uteroplacental restriction, a decrease in fetal weight and litter size, and a significant upregulation in uterine, but not placental, Lgr7 and Lgr8 gene expression in UPR animals compared with controls. These data suggest that both relaxin family receptors are upregulated in response to a reduction in uteroplacental blood flow in rats.

International Union of Pharmacology LVII: recommendations for the nomenclature of receptors for relaxin family peptides

Although the hormone relaxin was discovered 80 years ago, only in the past 5 years have the receptors for relaxin and three other receptors that respond to related peptides been identified with all four receptors being G-protein-coupled receptors. In this review it is suggested that the receptors for relaxin (LGR7) and those for the related peptides insulin-like peptide 3 (LGR8), relaxin-3 (GPCR135), and insulin-like peptide 5 (LGPCR142) be named the relaxin family peptide receptors 1 through 4 (RXFP1-4). RXFP1 and RXFP2 are leucine-rich repeat-containing G-protein-coupled receptors with complex binding characteristics involving both the large ectodomain and the transmembrane loops. RXFP1 activates adenylate cyclase, protein kinase A, protein kinase C, phosphatidylinositol 3-kinase, and extracellular signaling regulated kinase (Erk1/2) and also interacts with nitric oxide signaling. RXFP2 activates adenylate cyclase in recombinant systems, but physiological responses are sensitive to pertussis toxin. RXFP3 and RXFP4 resemble more conventional peptide liganded receptors and both inhibit adenylate cyclase, and in addition RXFP3 activates Erk1/2 signaling. Physiological studies and examination of the phenotypes of transgenic mice have established that relaxin has roles as a reproductive hormone involved in uterine relaxation (some species), reproductive tissue growth, and collagen remodeling but also in the cardiovascular and renal systems and in the brain. The connective tissue remodeling properties of relaxin acting at RXFP1 receptors have potential for the development of agents effective for the treatment of cardiac and renal fibrosis, asthma, and scleroderma and for orthodontic remodelling. Agents acting at RXFP2 receptors may be useful for the treatment of cryptorchidism and infertility, whereas antagonists may be used as contraceptives. The brain distribution of RXFP3 receptors suggests that actions at these receptors have the potential for the development of antianxiety and antiobesity drugs.

Influence of the menstrual cycle on aminolevulinic acid induced protoporphyrin IX fluorescence in the endometrium: In vivo study

BACKGROUND AND OBJECTIVES

In vitro studies indicated that compared to postmenopausal women, premenopausal women had increased aminolevulinic acid induced protoporphyrin IX (ALA-induced PpIX) fluorescence expression in the endometrium. The aim of this study was to evaluate menstrual cycle dependency of ALA-induced PpIX fluorescence in the endometrium in vivo.

STUDY DESIGN/PATIENTS AND METHODS

Thirteen patients were included for in vivo spectrofluorometric measurements of ALA-induced PpIX in the endometrium and 51 patients for fluorescence hysteroscopy. Two milliliter of a 2% 5-ALA-solution at pH = 4.0 (ASAT AG/Zug, Switzerland) was topically administrated just before spectrofluorometry and 4 hours before hysteroscopy. Spectrofluorometry: Optical fiber based. Fluorescence hysteroscopy: STORZ-D-Light system (Storz, Tuttlingen, Germany). Histological classification of curettage and bioptic endometrial tissue stained with hematoxylin and eosin (H&E).

RESULTS

Hysteroscopic and in vivo spectrofluorometric measurements showed an increase of ALA-induced PpIX fluorescence in the secretory and hyperplastic endometrium compared to proliferative and atrophic endometrium.

CONCLUSIONS

The accuracy of fluorescence hysteroscopy and the success of the photodynamic endometrial ablation using ALA-induced PpIX may depend on the hormonal influence of the menstrual cycle. The mechanisms responsible for the increased ALA-induced PpIX fluorescence in the secretory versus proliferative phase of the menstrual cycle deserve further studies.

INSL3 ligand-receptor system in the equine testis

We employed molecular and immunological techniques to investigate the expression of INSL3, a member of the insulin-like superfamily, in prepubertal testis, postpubertal testes exhibiting normal and disturbed spermatogenesis, and cryptorchid testes of male horses. In addition, the partial cDNA coding sequences of the equine homologue of the human relaxin/INSL3-receptor Lgr8 were determined. Nonradioactive in-situ hybridization with a cRNA probe for equine Insl3 and immunohistochemistry with a specific rabbit INSL3 antiserum localized Insl3 transcripts and immunoreactive INSL3 ligand to Leydig cells in all types of testes investigated. Quantitative polymerase chain reaction analysis revealed a down-regulation of Insl3 and an up-regulation of the relaxin/INSL3-receptor expression in unilateral cryptorchid versus descended testes. Western blot analysis of protein extracts from adult normal and cryptorchid testes and prepubertal testes showed a single immunoreactive band at 14.5 kDa, which correlates with the predicted size of equine proINSL3. Densitometric analysis of Western blot data of adult normal testes revealed significantly stronger expression of immunoreactive proINSL3 as compared to extracts derived from cryptorchid or prepubertal testes. Thus, decreased expression of immunoreactive INSL3 in cryptorchid and prepubertal equine testis is transcriptionally regulated. The detection of transcripts for equine Lgr8 in the testis has identified the testis as a potential target of INSL3.

Relaxin peptides are new global players

Relaxin (RLX) has come of age. From being one of the earliest hormones described with a very specific function in parturition, recent research has now shown that it is involved in a variety of roles, from endometrial differentiation during embryo implantation, to being a response factor in infarct and wound situations. It ameliorates fibrosis, and might also be involved in tumour growth and progression. And it is not alone: two other closely related peptide hormones have recently been identified, one specific for the brain, the other with roles in testicular descent and ovarian apoptosis. Finally, the recent cloning of the RLX receptors now provides the basis for a new molecular pharmacology for these peptide hormones, and preliminary studies suggest that their signal transduction is both interesting and unusual.

Reproductive biology of the relaxin-like factor (RLF/INSL3)

The relaxin-like factor (RLF), which is the product of the insulin-like factor 3 (INSL3) gene, is a new circulating peptide hormone of the relaxin-insulin family. In male mammals, it is a major secretory product of the testicular Leydig cells, where it appears to be expressed constitutively but in a differentiation-dependent manner. In the adult testis, RLF expression is a good marker for fully differentiated adult-type Leydig cells, but it is only weakly expressed in prepubertal immature Leydig cells or in Leydig cells that have become hypertrophic or transformed. It is also an important product of the fetal Leydig cell population, where it has been demonstrated using knockout mice to be responsible for the second phase of testicular descent acting on the gubernaculum. INSL3 knockout mice are cryptorchid, and in estrogen-induced cryptorchidism, RLF levels in the testis are significantly reduced. RLF is also made in female tissues, particularly in the follicular theca cells of small antral follicles and in the corpus luteum of the cycle and pregnancy. The ruminant ovary has a very high level of RLF expression, and analysis of primary cultures of ovarian theca-lutein cells indicated that, as in the testis, expression is probably constitutive but differentiation dependent. Female INSL3 knockout mice have altered estrous cycles, where RLF may be involved in follicle selection, an idea strongly supported by observations on bovine secondary follicles. Recently, a novel 7-transmembrane domain receptor (LGR8 or Great) has been tentatively identified as the RLF receptor, and its deletion in mice leads also to cryptorchidism.