Is endometriosis due to evolutionary maladaptation?

Similar to diabetes and unlike many pathogen-induced diseases, endometriosis is likely a result of maladaptation to the evolutionary heritage of humans. The objective of this article is to review the literature and improve understanding of the evolutionary factors behind endometriosis, leading to more effective prevention and treatment approaches. In primates, spontaneous decidualization of the endometrium evolved to ensure optimal implantation of a limited number of early embryos, unlike many non-primates which depend on early embryos to induce decidualization and subsequent pregnancy. Spontaneous decidualization results in menstrual bleeding when embryo implantation does not occur, and endometriosis is commonly believed to be caused by retrograde menstruation. Although direct evidence is lacking, it is likely that hunter-gatherer women experienced fewer menstrual periods due to pregnancy shortly after menarche, followed by repeated pregnancies and lactation. However, the mismatch between the evolved uterine physiology and rapid societal changes has led to modern women delaying pregnancy and experiencing numerous menstrual periods, potentially increasing the incidence of endometriosis. The symptoms of endometriosis are often managed by suppressing menstruation through systemic hormonal treatments, but these may have side effects. For patients with a family history of endometriosis or in the early stages of the disease, intrauterine devices releasing progesterone locally could prevent uterine bleeding and the development of endometriosis while preserving fertility and minimizing side effects.

Out of step societal and Darwinian adaptation during evolution is the cause of multiple women's health issues

During human evolution, major changes in our societal conditions and environment took place without sufficient time for concomitant genetic alterations, leading to out of step adaptation and diseases in women. We first discuss recent societal adaptation mismatch (menstrual bleeding; increases in cancers of reproductive organs, endometriosis; mother's nursing; polycystic ovarian syndrome; transgenerational epigenetic modifications), followed by Darwinian out of step adaptation (labor difficulties; sex chromosomes, human diseases and sex disparity in genomic DNA). We discuss the evolutionary basis of menstrual bleeding, followed by recent increases in cancers of reproductive organs and endometriosis. The importance of breastfeeding by mothers is also emphasized. Earlier onset of menarche, decreased rates of childbirths and breastfeeding resulted in increased number of menstrual cycles in a lifetime, coupled with excess estrogen exposure and incessant ovulation, conditions that increased the susceptibility to mammary and uterine cancers as well as ovarian epithelial cancer and endometriosis. Shorter lactation duration in mothers also contributed to more menstrual cycles. We further discuss the evolutionary basis of the prevalent polycystic ovary syndrome. During the long-term Darwinian evolution, difficulties in childbirth evolved due to a narrowed pelvis, our upright walking and enlarged fetal brain sizes. Because there are 1.5% genomic DNA differences between woman and man, it is of significance to investigate sex-specific human physiology and diseases. In conclusion, understanding out of step adaptation during evolution could allow the prevention and better management of female reproductive dysfunction and diseases.

Hippo signaling disruption and ovarian follicle activation in infertile patients

The Hippo signaling pathway, which is important in organ size regulation, is present in organisms from the fly to mammals. Disruption of the Hippo signaling pathway leads to increased nuclear translocation of the effector Yes-associated protein (YAP), resulting in the expression of cystein-rich 61, connective tissue growth factor, and nephroblastoma overexpressed (CCN) growth factors and baculoviral inhibitors of apoptosis repeat containing (BIRC) apoptosis inhibitors to increase organ sizes. Furthermore, genome-wide knockdown of genes in insect cells demonstrated that actin polymerization promoted nuclear translocation of YAP. In the mammalian ovary, we demonstrated the expression of Hippo signaling pathway genes and showed that ovarian fragmentation increased actin polymerization, leading to YAP nuclear translocation and increased expression of cystein-rich 61, CCN growth factors and BIRC apoptosis inhibitors, followed by enhanced follicle growth. Here we summarize evidence suggesting the role of mechanical stress on follicle growth in the ovary and describe recent use of ovary-damaging procedures to treat ovarian infertility. Ovarian fragmentation, together with in vitro incubation with Akt-stimulating drugs, formed the basis of an in vitro activation (IVA) therapy to treat patients with premature ovarian insufficiency, whereas ovarian fragmentation alone (drug-free IVA) was successful in treating patients with premature ovarian insufficiency with recent menses cessation. For middle-aged women with poor ovarian responses and diminished ovarian reserve, drug-free IVA was also effective in promoting follicle growth for infertility treatment. In addition, an in vivo follicle activation approach based on laparoscopic ovarian incision showed promise for patients with resistant ovary syndrome. With initial success using mechanical disruption approaches, future investigation could evaluate possibilities to refine mechanical methods and to locally administer actin polymerization-enhancing drugs for ovarian infertility treatment.

Discovery of polypeptide ligand-receptor pairs based on their co-evolution

Sequencing diverse genomes allowed the tracing of orthologous and paralogous genes to understand the co-evolution of polypeptide ligands and receptors. This review documents the discovery of several polypeptide ligands and their cognate receptors mainly expressed in the reproductive tissue using evolutionary genomics. We discussed the sub-functionization of paralogs and co-evolution of ligand-receptor families. Based on the conserved signaling among paralogous receptors and common knock-out phenotypes of ligand-receptor pairs, relationships between relaxin family peptides and leucine-rich repeat-containing, G protein-coupled receptors (LGR) were revealed. We also described the identification of a novel paralogous glycoprotein hormone thyrostimulin and design of a long-acting FSH. Human stresscopin and stresscopin-related peptide, paralogous to CRH, were also identified based on the conserved signaling pathways. Recently, a novel ligand placensin expressed in human placenta was found based on the paralogous relationship with a metabolic hormone asprosin. Placensin likely contributes to stage-dependent increases in insulin resistance during human pregnancy and its elevated secretion was associated with gestational diabetes mellitus. Although many ligands were predicted based on sequence signatures, ligands of shorter sequences have not been identified, together with many "orphan" receptors without known ligands. Future development of tools for predicting ligands and high throughput assays to identify ligand-receptor pairs based on ligand binding and/or signal transduction could advance hormone-based physiology and pathophysiology.

Drug-free in-vitro activation of follicles for infertility treatment in poor ovarian response patients with decreased ovarian reserve

RESEARCH QUESTION

The recently developed in-vitro activation (IVA) approach provides a promising infertility treatment for patients with premature ovarian insufficiency. The IVA method promotes growth of residual ovarian follicles following ovarian tissue fragmentation leading to Hippo signalling disruption, together with in-vitro incubation with Akt stimulators. As poor ovarian response (POR) patients with decreased ovarian reserve (DOR) have multiple secondary follicles, this study tested whether Hippo signalling disruption alone using in-vitro ovarian cortical fragmentation, followed by autologous grafting, was sufficient to promote follicle growth.

DESIGN

A case series study.

RESULTS

In 9 out of 11 POR patients with DOR treated with a simplified IVA procedure, increases in antral follicle numbers in multiple growth waves were detected following FSH treatment. Subsequent injection with human chorionic gonadotrophin allowed retrieval of more mature oocytes for IVF (median antral follicle counts before and after IVA per ovarian stimulation: 1.0 versus 2.6) with 68.7% fertilization rates and 56.9% showing high-quality embryonic development. One natural conception and 16 embryo transfers in five patients resulted in one live birth, two ongoing pregnancies and one miscarriage. Three additional patients and the miscarriage patient have cryopreserved embryos for future transfer.

CONCLUSIONS

The present drug-free IVA approach may be suitable for POR patients with DOR, as it increased the number of antral follicles. The procedure also eliminated the need for 2-day incubation with drugs and required only one surgery. This approach could allow the retrieval of more oocytes in middle-aged women to achieve higher pregnancy rates and deserves proper evaluation in future randomized controlled trials.

Imaging the ovary

During each reproductive cycle, the ovary exhibits tissue remodelling and cyclic vasculature changes associated with hormonally regulated folliculogenesis, follicle rupture, luteal formation and regression. However, the relationships among different types of follicles and corpora lutea are unclear, and the role of ovarian vasculature in folliculogenesis and luteal dynamics has not been extensively investigated. Understanding of ovarian physiology and pathophysiology relies upon elucidation of ovarian morphology and architecture. This paper summarizes the literature on traditional approaches to the imaging of ovarian structures and discusses recent advances in ovarian imaging. Traditional in-vivo ultrasound, together with histological and electron microscopic approaches provide detailed views of the ovary at organ, tissue and molecular levels. However, in-vivo imaging is limited to antral and larger follicles whereas histological imaging is mainly two-dimensional in nature. Also discussed are emerging approaches in the use of near-infrared fluorophores to image follicles in live animals to detect preantral follicles as well as visualizing ovarian structures using CLARITY in fixed whole ovaries to elucidate three-dimensional interrelationships among follicles, corpora lutea and ovarian vasculature. Advances in ovarian imaging techniques provide new understanding of ovarian physiology and allow for the development of better tools to diagnose ovarian pathophysiology.

Three-dimensional Reconstruction of the Vascular Architecture of the Passive CLARITY-cleared Mouse Ovary

The ovary is the main organ of the female reproductive system and is essential for the production of female gametes and for controlling the endocrine system, but the complex structural relationships and three-dimensional (3D) vasculature architectures of the ovary are not well described. In order to visualize the 3D connections and architecture of blood vessels in the intact ovary, the first important step is to make the ovary optically clear. In order to avoid tissue shrinkage, we used the hydrogel fixation-based passive CLARITY (Clear Lipid-exchanged Acrylamide-hybridized Rigid Imaging/ Immunostaining/In situ-hybridization-compatible Tissue Hydrogel) protocol method to clear an intact ovary. Immunostaining, advanced multiphoton confocal microscopy, and 3D image-reconstructions were then used for the visualization of ovarian vessels and follicular capillaries. Using this approach, we showed a significant positive correlation (P <0.01) between the length of the follicular capillaries and volume of the follicular wall.

Apela Regulates Fluid Homeostasis by Binding to the APJ Receptor to Activate Gi Signaling

Apela (APJ early endogenous ligand, also known as elabela or toddler) is a recently discovered peptide hormone. Based on genetic studies in zebrafish, apela was found to be important for endoderm differentiation and heart development during embryogenesis. Although common phenotypes of apela and APJ-null zebrafish during embryonic development suggested that apela interacts with the APJ receptor, kinetics of apela binding to APJ and intracellular signaling pathways for apela remain unknown. The role of apela in adults is also uncertain. Using a chimeric apela ligand, we showed direct binding of apela to APJ with high affinity (Kd = 0.51 nm) and the ability of apelin, the known peptide ligand for APJ, to compete for apela binding. Apela, similar to apelin, acts through the inhibitory G protein pathway by inhibiting forskolin-stimulated cAMP production and by inducing ERK1/2 phosphorylation. In adult rats, apela is expressed exclusively in the kidney, unlike the wide tissue distribution of apelin. In vivo studies demonstrated the ability of apela to regulate fluid homeostasis by increasing diuresis and water intake. Dose-response studies further indicated that apela induces 2- and 5-fold higher maximal responses than apelin in ERK1/2 phosphorylation and diuresis/water intake, respectively. After designing an apela antagonist, we further demonstrated the role of endogenous ligand(s) in regulating APJ-mediated fluid homeostasis. Our results identified apela as a potent peptide hormone capable of regulating fluid homeostasis in adult kidney through coupling to the APJ-mediated Gi signaling pathway.

Intraovarian control of early folliculogenesis

Although hormonal regulation of ovarian follicle development has been extensively investigated, most studies concentrate on the development of early antral follicles to the preovulatory stage, leading to the successful use of exogenous FSH for infertility treatment. Accumulating data indicate that preantral follicles are under stringent regulation by FSH and local intraovarian factors, thus providing the possibility to develop new therapeutic approaches. Granulosa cell-derived C-type natriuretic factor not only suppresses the final maturation of oocytes to undergo germinal vesicle breakdown before ovulation but also promotes preantral and antral follicle growth. In addition, several oocyte- and granulosa cell-derived factors stimulate preantral follicle growth by acting through wingless, receptor tyrosine kinase, receptor serine kinase, and other signaling pathways. In contrast, the ovarian Hippo signaling pathway constrains follicle growth and disruption of Hippo signaling promotes the secretion of downstream CCN growth factors capable of promoting follicle growth. Although the exact hormonal factors involved in primordial follicle activation has yet to be elucidated, the protein kinase B (AKT) and mammalian target of rapamycin signaling pathways are important for the activation of dormant primordial follicles. Hippo signaling disruption after ovarian fragmentation, combined with treating ovarian fragments with phosphatase and tensin homolog (PTEN) inhibitors and phosphoinositide-3-kinase stimulators to augment AKT signaling, promote the growth of preantral follicles in patients with primary ovarian insufficiency, leading to a new infertility intervention for such patients. Elucidation of intraovarian mechanisms underlying early folliculogenesis may allow the development of novel therapeutic strategies for patients diagnosed with primary ovarian insufficiency, polycystic ovary syndrome, and poor ovarian response to FSH stimulation, as well as for infertile women of advanced reproductive age.

Actin cytoskeleton regulates Hippo signaling

Hippo pathway controls the organ size by modulating cell proliferation and apoptosis. However, the upstream regulation of hippo signaling by actin cytoskeleton is not clear. To elucidate the role of actin as an upstream regulator of Hippo signaling, the levels of F (filamentous)-actin in cells were elevated using jasplakinolide, an actin-stabilizing drug. Induction of F-actin formation in HeLa cells resulted in decreased phosphorylation of YAP, a key effector molecule for Hippo signaling. The activated YAP is localized to the cell nucleus and YAP increase was associated with increased expression of downstream CCN growth factors CCN1/CYR61 and CCN2/CTGF. The effect of the actin-stabilizing drug was blocked when YAP levels were suppressed in YAP “knock-down” cells. In summary, using an actin-stabilizing drug we show that actin cytoskeleton is one of the upstream regulators of Hippo signaling capable of activating YAP and increasing its downstream CCN growth factors.

Evolution of a potential hormone antagonist following gene splicing during primate evolution

Alternative splicing of genes generates novel mRNAs, leading to the evolution of new functional proteins. Cholecystokinin (CCK) induces the release of pancreatic enzymes and the contraction of the gallbladder to promote the digestion of fat and proteins. CCK activates two G-protein-coupled receptors, CCKA and CCKB. Here, we showed that a CCKsv (splicing variant), originated de novo during Catarrhini evolution by including a portion of intronic sequence of the CCK gene, encodes novel C-terminal peptide sequence followed by a new poly-adenylation signal. CCKsv is expressed in many human tissues and likely a secreted peptide retaining the original signal peptide and the N-terminal proteolytic processing signal, together with novel C-terminal sequences. Although CCKsv cannot activate CCK receptors, it partially inhibits the CRE- or SRF-driven reporter activities stimulated by wide type CCK-8 mediated by both CCK receptors. Co-treatment with CCKsv also partially antagonizes Ewing tumor cell growth stimulated by CCK-8. Our study provides an example of new peptide hormone antagonist evolution in primates.

Multi-functional norrin is a ligand for the LGR4 receptor

Mammalian LGR4, 5 and 6 are seven-transmembrane receptors that are important for diverse physiological processes. These receptors are orthologous to DLGR2, a Drosophila receptor activated by the burs/pburs heterodimer important for morphogenesis. Although recent studies indicated that four R-spondin proteins are cognate ligands for LGR4, 5 and 6 receptors, several BMP antagonists in vertebrates have been postulated to be orthologous to burs and pburs. Using newly available genome sequences, we showed that norrin is a vertebrate ortholog for insect burs and pburs and stimulates Wnt signaling mediated by LGR4, but not by LGR5 and 6, in mammalian cells. Although norrin could only activate LGR4, binding studies suggested interactions between norrin and LGR4, 5 and 6. Norrin, the Norrie disease gene product, is also capable of activating Wnt signaling mediated by the Frizzled4 receptor and serves as a BMP antagonist. Mutagenesis studies indicated that different norrin mutations found in patients with Norrie disease can be categorized into subgroups according to defects for signaling through the three distinct binding proteins. Thus, norrin is a rare ligand capable of binding three receptors/binding proteins that are important for BMP and Wnt signaling pathways.

Oocyte-derived R-spondin2 promotes ovarian follicle development

R-spondin proteins are adult stem cell growth factors capable of stimulating gut development by activating LGR4, 5, and 6 receptors to promote Wnt signaling. Although multiple Wnt ligands and cognate Frizzled receptors are expressed in the ovary, their physiological roles are unclear. Based on bioinformatic and in situ hybridization analyses, we demonstrated the exclusive expression of R-spondin2 in oocytes of ovarian follicles. In cultured somatic cells from preantral follicles, R-spondin2 treatment (ED50: 3 ng/ml) synergized with Wnt3a to stimulate Wnt signaling. In cultured ovarian explants from prepubertal mice containing preantral follicles, treatment with R-spondin2, similar to follicle stimulating hormone, promoted the development of primary follicles to the secondary stage. In vivo administration of an R-spondin agonist stimulated the development of primary follicles to the antral stage in both immature mice and gonadotropin releasing hormone antagonist-treated adult mice. Subsequent treatment with gonadotropins allowed the generation of mature oocytes capable of undergoing early embryonic development and successful pregnancy. Furthermore, R-spondin agonist treatment of immune-deficient mice grafted with human cortical fragments stimulated the development of primary follicles to the secondary stage. Thus, oocyte-derived R-spondin2 is a paracrine factor essential for primary follicle development, and R-spondin agonists could provide a new treatment regimen for infertile women with low responses to the traditional gonadotropin therapy.

A novel reproductive peptide, phoenixin

Normal anterior pituitary function is essential for fertility. Release from the gland of the reproductive hormones luteinising hormone and follicle-stimulating hormone is regulated primarily by hypothalamically-derived gonadotrophin-releasing hormone (GnRH), although other releasing factors (RF) have been postulated to exist. Using a bioinformatic approach, we have identified a novel peptide, phoenixin, that regulates pituitary gonadotrophin secretion by modulating the expression of the GnRH receptor, an action with physiologically relevant consequences. Compromise of phoenixin in vivo using small interfering RNA resulted in the delayed appearance of oestrus and a reduction in GnRH receptor expression in the pituitary. Phoenixin may represent a new class of hypothalamically-derived pituitary priming factors that sensitise the pituitary to the action of other RFs, rather than directly stimulating the fusion of secretary vesicles to pituitary membranes.

Promotion of human early embryonic development and blastocyst outgrowth in vitro using autocrine/paracrine growth factors

Studies using animal models demonstrated the importance of autocrine/paracrine factors secreted by preimplantation embryos and reproductive tracts for embryonic development and implantation. Although in vitro fertilization-embryo transfer (IVF-ET) is an established procedure, there is no evidence that present culture conditions are optimal for human early embryonic development. In this study, key polypeptide ligands known to be important for early embryonic development in animal models were tested for their ability to improve human early embryo development and blastocyst outgrowth in vitro. We confirmed the expression of key ligand/receptor pairs in cleavage embryos derived from discarded human tri-pronuclear zygotes and in human endometrium. Combined treatment with key embryonic growth factors (brain-derived neurotrophic factor, colony-stimulating factor, epidermal growth factor, granulocyte macrophage colony-stimulating factor, insulin-like growth factor-1, glial cell-line derived neurotrophic factor, and artemin) in serum-free media promoted >2.5-fold the development of tri-pronuclear zygotes to blastocysts. For normally fertilized embryos, day 3 surplus embryos cultured individually with the key growth factors showed >3-fold increases in the development of 6-8 cell stage embryos to blastocysts and >7-fold increase in the proportion of high quality blastocysts based on Gardner's criteria. Growth factor treatment also led to a 2-fold promotion of blastocyst outgrowth in vitro when day 7 surplus hatching blastocysts were used. When failed-to-be-fertilized oocytes were used to perform somatic cell nuclear transfer (SCNT) using fibroblasts as donor karyoplasts, inclusion of growth factors increased the progression of reconstructed SCNT embryos to >4-cell stage embryos. Growth factor supplementation of serum-free cultures could promote optimal early embryonic development and implantation in IVF-ET and SCNT procedures. This approach is valuable for infertility treatment and future derivation of patient-specific embryonic stem cells.

C-type natriuretic peptide stimulates ovarian follicle development

C-type natriuretic peptide (CNP) encoded by the NPPC (Natriuretic Peptide Precursor C) gene expressed in ovarian granulosa cells inhibits oocyte maturation by activating the natriuretic peptide receptor (NPR)B (NPRB) in cumulus cells. RT-PCR analyses indicated increased NPPC and NPRB expression during ovarian development and follicle growth, associated with increases in ovarian CNP peptides in mice. In cultured somatic cells from infantile ovaries and granulosa cells from prepubertal animals, treatment with CNP stimulated cGMP production. Also, treatment of cultured preantral follicles with CNP stimulated follicle growth whereas treatment of cultured ovarian explants from infantile mice with CNP, similar to FSH, increased ovarian weight gain that was associated with the development of primary and early secondary follicles to the late secondary stage. Of interest, treatment with FSH increased levels of NPPC, but not NPRB, transcripts in ovarian explants. In vivo studies further indicated that daily injections of infantile mice with CNP for 4 d promoted ovarian growth, allowing successful ovulation induction by gonadotropins. In prepubertal mice, CNP treatment alone also promoted early antral follicle growth to the preovulatory stage, leading to efficient ovulation induction by LH/human chorionic gonadotropin. Mature oocytes retrieved after CNP treatment could be fertilized in vitro and developed into blastocysts, allowing the delivery of viable offspring. Thus, CNP secreted by growing follicles is capable of stimulating preantral and antral follicle growth. In place of FSH, CNP treatment could provide an alternative therapy for female infertility.

Intraovarian thrombin and activated protein C signaling system regulates steroidogenesis during the periovulatory period

In addition to its role in blood coagulation, thrombin directly stimulates protease-activated receptors (PAR) or interacts with thrombomodulin (THBD) to activate membrane-bound protein C which stimulates PAR1 and PAR4 receptors to promote downstream pleiotropic effects. Our DNA microarray, RT-PCR, and immunostaining analyses demonstrated ovarian expression of THBD, activated protein C (APC) receptor [endothelial protein C receptor (EPCR)], as well as PAR1 and PAR4 receptors in mice. After treatment of gonadotropin-primed immature mice with an ovulatory dose of human chorionic gonadotropin (hCG) (a LH surrogate), major increases in the expression of THBD, EPCR, PAR1, and PAR4 were detected in granulosa and cumulus cells of preovulatory follicles. Immunoassay analyses demonstrated sustained increases in ovarian prothrombin and APC levels after hCG stimulation. We obtained luteinizing granulosa cells from mice treated sequentially with equine CG and hCG. Treatment of these cells with thrombin or agonists for PAR1 or PAR4 decreased basal and forskolin-induced cAMP biosynthesis and suppressed hCG-stimulated progesterone production. In cultured preovulatory follicles, treatment with hirudin (a thrombin antagonist) and SCH79797 (a PAR1 antagonist) augmented hCG-stimulated progesterone biosynthesis, suggesting a suppressive role of endogenous thrombin in steroidogenesis. Furthermore, intrabursal injection with hirudin or SCH79797 led to ipsilateral increases in ovarian progesterone content. Our findings demonstrated increased ovarian expression of key components of the thrombin-APC-PAR1/4 signaling system after LH/hCG stimulation, and this signaling pathway may allow optimal luteinization of preovulatory follicles. In addition to assessing the role of thrombin and associated genes in progesterone production by the periovulatory ovary, these findings provide a model with which to study molecular mechanisms underlying thrombin-APC-PAR1/4 signaling.

Oocyte-expressed interleukin 7 suppresses granulosa cell apoptosis and promotes oocyte maturation in rats

Development of ovarian follicles is regulated by pituitary-derived gonadotropins together with local ovarian paracrine factors. Based on DNA microarray data, we performed RT-PCR and immunostaining to demonstrate the expression of interleukin 7 transcripts in oocytes of preantral, antral, and preovulatory follicles in rats. We also found the expression of interleukin 7 receptor and the coreceptor interleukin 2 receptor gamma in granulosa cells, cumulus cells, and preovulatory oocytes. In cultured rat granulosa cells obtained from early antral and preovulatory follicles, treatment with interleukin 7 stimulated the phosphorylation of AKT, glycogen synthase kinase (GSK3B), and STAT5 proteins in a time- and dose-dependent manner. Furthermore, measurement of mitochondrial reductase activity indicated that treatment with interleukin 7, similar to gonadotropins, increased the number of viable granulosa cells during a 24-h culture period. Furthermore, monitoring of the activities of apoptotic enzymes (caspase 3/7) indicated that treatment with interleukin 7 suppressed apoptosis of cultured granulosa cells from both antral and preovulatory follicles following serum withdrawal. The apoptosis-suppressing actions of interleukin 7 were blocked by an inhibitor of the phosphoinositol-3-kinase (PIK3)/AKT pathway. Furthermore, treatment of cultured preovulatory follicles with interleukin 7, like treatment with human chorionic gonadotropin, induced germinal vesicle breakdown of oocytes. The stimulatory effect of interleukin 7 was also blocked by inhibitors of the PIK3/AKT pathway. The present findings suggest that oocyte-derived interleukin 7 could act on neighboring granulosa cells as a survival factor and promote the nuclear maturation of preovulatory oocytes through activation of the PIK3/AKT pathway.

Autocrine regulation of early embryonic development by the artemin-GFRA3 (GDNF family receptor-alpha 3) signaling system in mice

Development of early embryos is regulated by autocrine/paracrine factors. Analyzing the expression of polypeptide ligand-receptor pairs using DNA microarray datasets, we identified transcripts for artemin, a member of the GDNF (glial cell line-derived neurotrophic factor) family, its receptor GFRA3 (GDNF family receptor-alpha 3) and coreceptor RET. Here we report an autocrine/paracrine role of the artemin-GFRA3 signaling system in regulating early embryonic development and apoptosis. Possible involvement of the MAP kinase signaling pathway was also demonstrated. The genome-wide survey of ligand-receptor pairs and early embryo cultures provided a better understanding of autocrine/paracrine embryonic factors important for optimal blastocyst development.

The hedgehog-patched signaling pathway and function in the mammalian ovary: a novel role for hedgehog proteins in stimulating proliferation and steroidogenesis of theca cells

The expression of hedgehog (Hh) genes, their receptor, and the co-receptor in mice, rat, and bovine ovaries were investigated. RT-PCR of ovarian transcripts in mice showed amplification of transcripts for Indian (Ihh) and desert (Dhh) Hh, patched 1 (Ptch1), and smoothened (Smo) genes. Semi-quantitative RT-PCR and northern blot analyses showed that whole ovarian Ihh and Dhh transcripts decreased 4-24 h after hCG versus 0-48 h after pregnant mares serum gonadotrophin treatment in mice, whereas mouse Ptch1 and Smo transcripts were expressed throughout the gonadotropin treatments. Quantitative real-time RT-PCR (qRT-PCR) revealed that the expression of the Hh-patched signaling system with Ihh mRNA abundance in granulosa cells was greater, whereas Smo and Ptch1 mRNA abundance was less in theca cells of small versus large follicles of cattle. In cultured rat and bovine theca-interstitial cells, qRT-PCR analyses revealed that the abundance of Gli1 and Ptch1 mRNAs were increased (P<0.05) with sonic hedgehog (SHH) treatment. Additional studies using cultured bovine theca cells indicated that SHH induces proliferation and androstenedione production. IGF1 decreased Ihh mRNA abundance in bovine granulosa cells. The expression and regulation of Ihh transcripts in granulosa cells and Ptch1 mRNA in theca cells suggest a potential paracrine role of this system in bovine follicular development. This study illustrates for the first time Hh activation of Gli1 transcriptional factor in theca cells and its stimulation of theca cell proliferation and androgen biosynthesis.

Paracrine regulation of the resumption of oocyte meiosis by endothelin-1

Mammalian oocytes remain dormant in the diplotene stage of prophase I until the resumption of meiosis characterized by germinal vesicle breakdown (GVBD) following the preovulatory gonadotropin stimulation. Based on genome-wide analysis of peri-ovulatory DNA microarray to identify paracrine hormone-receptor pairs, we found increases in ovarian transcripts for endothelin-1 and endothelin receptor type A (EDNRA) in response to the preovulatory luteinizing hormone (LH)/human chorionic gonadotropin (hCG) stimulation. Immunohistochemical analyses demonstrated localization of EDNRA in granulosa and cumulus cells. In cultured preovulatory follicles, treatment with endothelin-1 promoted oocyte GVBD. The stimulatory effect of endothelin-1 was blocked by cotreatment with antagonists for the type A, but not related type B, receptor. The stimulatory effect of hCG on GVBD was partially blocked by the same antagonist. The endothelin-1 promotion of GVBD was found to be mediated by the MAPK/ERK pathway but not by the inhibitory G protein. Studies using cumulus-oocyte complexes and denuded oocytes demonstrated that the endothelin-1 actions are mediated by cumulus cells. Furthermore, intrabursal administration with endothelin-1 induced oocyte GVBD in preovulatory follicles. Our findings demonstrate a paracrine role of endothelin-1 in the induction of the resumption of meiosis and provide further understanding on the molecular mechanisms underlying the nuclear maturation of oocytes induced by the preovulatory LH surge.

Neuronostatin encoded by the somatostatin gene regulates neuronal, cardiovascular, and metabolic functions

Somatostatin is important in the regulation of diverse neuroendocrine functions. Based on bioinformatic analyses of evolutionarily conserved sequences, we predicted another peptide hormone in pro-somatostatin and named it neuronostatin. Immuno-affinity purification allowed the sequencing of an amidated neuronostatin peptide of 13 residues from porcine tissues. In vivo treatment with neuronostatin induced c-Fos expression in gastrointestinal tissues, anterior pituitary, cerebellum, and hippocampus. In vitro treatment with neuronostatin promoted the migration of cerebellar granule cells and elicited direct depolarizing actions on paraventricular neurons in hypothalamic slices. In a gastric tumor cell line, neuronostatin induced c-Fos expression, stimulated SRE reporter activity, and promoted cell proliferation. Furthermore, intracerebroventricular treatment with neuronostatin increased blood pressure but suppressed food intake and water drinking. Our findings demonstrate diverse neuronal, neuroendocrine, and cardiovascular actions of a somatostatin gene-encoded hormone and provide the basis to investigate the physiological roles of this endogenously produced brain/gut peptide.

Hormonal regulation of proprotein convertase subtilisin/kexin type 5 expression during ovarian follicle development in the rat

The proprotein convertase subtilisin/kexin (PCSKs), a family of subtilisin-like proteases, is the processing enzymes for the activation of many hormone precursors. The present study was designed to identify the PCSK isoform expressed in the ovary and to examine its expression in gonadotropin-stimulated rat ovary. Northern blot analysis of ovaries obtained from prepubertal rats revealed an increased expression of Pcsk5 messenger RNA (mRNA) during development with the highest levels at 21 days of age. Treatment of immature rats with PMSG further increased ovarian Pcsk5 expression, and in situ hybridization analysis revealed the localization of Pcsk5 mRNA in theca-interstitial cells of follicles in different sizes. Interestingly, treatment of PMSG-primed rats with hCG resulted in a transient stimulation of ovarian Pcsk5 mRNA levels within 3-6 h. In addition to theca-interstitial cells, hCG treatment induced the expression of Pcsk5 in granulosa cells of preovulatory follicles. Pcsk1, 2 and 4 mRNAs were not detected whereas Pcsk7 mRNA was slightly expressed. Injection of a progestin antagonist RU486 or an inhibitor of 3beta-hydroxysteroid dehydrogenase epostane at 1h before hCG treatment inhibited hCG-induced Pcsk5 mRNA levels. Treatment with LH stimulated both Pcsk5 mRNA and protein levels in preovulatory follicles cultured in vitro. In addition, forskolin but not TPA stimulated Pcsk5 mRNA levels. RNase protection assay revealed that the soluble Pcsk5A variant was the predominant form stimulated by gonadotropins in the ovary. Finally, the predicted proprotein substrates cleaved by PCSK5 were analyzed in preovulatory follicles using regular expressions. The present study demonstrates PCSK5A as the gonadotropin-regulated PCSK isoform in the ovary, and its possible contribution to ovulation by processing pro-TGFbeta and matrix metalloproteinase family.

Gonadotropin stimulation of ovarian fractalkine expression and fractalkine augmentation of progesterone biosynthesis by luteinizing granulosa cells

Recent studies indicated that ovarian functions are regulated by diverse paracrine factors induced by the preovulatory increases in circulating LH. Based on DNA microarray analyses and real-time RT-PCR, we found a major increase in the transcript levels of a chemokine fractalkine after human chorionic gonadotropin (hCG) treatment during the preovulatory period in gonadotropin-primed immature mice and rats. Although CX3CR1, the seven-transmembrane receptor for fractalkine, was also found in murine ovaries, its transcripts displayed minimal changes. Using tandem RT-PCR and immunohistochemistry, fractalkine transcripts and proteins were localized in cumulus, mural granulosa, and theca cells as well as the oocytes, whereas CX3CR1 was found in the same cells except the oocyte. Real-time RT-PCR further indicated the hCG induction of fractalkine transcripts in different ovarian compartments, with the highest increases found in granulosa cells. In cultured granulosa cells, treatment with fractalkine augmented hCG stimulation of progesterone but not estradiol and cAMP biosynthesis with concomitant increases in transcript levels for key steroidogenic enzymes (steroidogenic acute regulatory protein, CYP11A, and 3beta-hydroxysteroid dehydrogenase). In cultured preovulatory follicles, treatment with fractalkine also augmented progesterone production stimulated by hCG. Furthermore, treatment with fractalkine augmented the phosphorylation of P38 MAPK in cultured granulosa cells. The present data demonstrated that increases in preovulatory LH/hCG induce the expression of fractalkine to augment the luteinization of preovulatory granulosa cells and suggest the fractalkine/CX3CR1 signaling system plays a potential paracrine/autocrine role in preovulatory follicles.

Obestatin induction of early-response gene expression in gastrointestinal and adipose tissues and the mediatory role of G protein-coupled receptor, GPR39

Obestatin was identified as a brain/gut peptide hormone encoded by the ghrelin gene and found to interact with the G protein-coupled receptor, GPR39. We investigated target cells for obestatin based on induction of an early-response gene c-fos in different tissues. After ip injection of obestatin, c-fos staining was found in the nuclei of gastric mucosa, intestinal villi, white adipose tissues, hepatic cords, and kidney tubules. Immunohistochemical analyses using GPR39 antibodies further revealed cytoplasmic staining in these tissues. In cultured 3T3-L1 cells, treatment with obestatin, but not motilin, induced c-fos expression. In these preadipocytes, treatment with obestatin also stimulated ERK1/2 phosphorylation. Because phenotypes of GPR39 null mice are partially consistent with a role of GPR39 in mediating obestatin actions, we hypothesized that inconsistencies on the binding of iodinated obestatin to GPR39 are due to variations in the bioactivity of iodinated obestatin. We obtained monoiodoobestatin after HPLC purification and demonstrated its binding to jejunum, stomach, ileum, pituitary, and white adipose tissue. Furthermore, human embryonic kidney 293T cells transfected with plasmids encoding human or mouse GPR39 or a human GPR39 isoform, but not the ghrelin receptor, exhibited high-affinity binding to monoiodoobestatin. Binding studies using jejunum homogenates and recombinant GPR39 revealed obestatin-specific displacement curves. Furthermore, treatment with obestatin induced c-fos expression in gastric mucosa of wild-type, but not GPR39 null, mice, underscoring a mediating role of this receptor in obestatin actions. The present findings indicate that obestatin is a metabolic hormone capable of binding to GPR39 to regulate the functions of diverse gastrointestinal and adipose tissues.

Completion of Meiosis I of preovulatory oocytes and facilitation of preimplantation embryo development by glial cell line-derived neurotrophic factor

Optimal maturation of oocytes and successful development of preimplantation embryos is essential for reproduction. We performed DNA microarray analyses of ovarian transcripts and identified glial cell line-derived neurotrophic factor (GDNF) secreted by cumulus, granulosa, and theca cells as an ovarian factor stimulated by the preovulatory LH/hCG surge. Treatment of cumulus-oocyte complexes with GDNF enhanced first polar body extrusion with increase in cyclin B1 synthesis and the GDNF actions are likely mediated by its receptor GDNF family receptor-alpha1 (GFRA1) and a co-receptor ret proto-oncogene (Ret), both expressed in oocytes. However, treatment with GDNF did not affect germinal vesicle breakdown and cytoplasmic maturation of oocytes. During the preimplantation stages, GDNF was expressed in pregnant oviducts and uteri, whereas GFRA1 and Ret were expressed in embryos throughout early development with an increase after the early blastocyst stage. In blastocysts, both GDNF and GFRA1 were exclusively localized in trophectoderm cells, whereas Ret was detected in both cell lineages. Treatment with GDNF promoted the development of two-cell-stage embryos into blastocysts showing increased cell proliferation and decreased apoptosis mainly in trophectoderm cells. Our findings suggest potential paracrine roles of GDNF in the promotion of completion of meiosis I and the development of early embryos.

Regulation of preimplantation embryo development by brain-derived neurotrophic factor

Hormonal factors secreted by embryos and reproductive tracts are important for successful development of preimplantation embryos. We found expression of brain-derived neurotrophic factor (BDNF) and neurotrophin-4/5 (NT-4/5) transcripts at its highest levels in the blastocyst stages. The transcripts for their receptor, TrkB, were detectable throughout the early embryonic stages with an increase after the early blastocyst stage. Both BDNF and TrkB are expressed in trophectoderm cells, whereas ligand-binding studies indicated specific binding of BDNF to trophectoderm cells. Furthermore, BDNF and NT-4/5 were produced in pregnant oviducts and uteri. Treatment with BDNF promoted the development of two-cell-stage embryos into blastocysts showing increased proliferation and decreased apoptosis. The effects of BDNF were blocked by the TrkB ectodomain or a Trk receptor inhibitor, K252a. Studies using specific inhibitors demonstrated the roles of the PI3K, but not the ERK, pathway in mediating BDNF actions. Under high-density embryo cultures, treatment with the TrkB ectodomain or K252a alone also inhibited embryonic development and survival, suggesting potential autocrine actions of BDNF produced by the embryo. In vivo experiments further demonstrated that K252a treatment suppressed early embryo development by inhibiting blastocyst cell numbers, and increasing blastocyst apoptosis. Our findings suggested that BDNF signaling plays important paracrine roles during blastocyst development by promoting the development of preimplantation embryos.

Matching receptome genes with their ligands for surveying paracrine/autocrine signaling systems

Sequencing of genomes from diverse organisms facilitates studies on the repertoire of genes involved in intercellular signaling. Extending previous efforts to annotate most human plasma membrane receptors in the Human Plasma Membrane Receptome database, we matched cognate ligands with individual receptors by surveying the published literature. In the updated online database we called "liganded receptome," users can search for individual ligands or receptors to reveal their pairing partners and browse through receptor or ligand families to identify relationships between ligands and receptors in their respective families. Because local signaling systems are prevalent in diverse normal and diseased tissues, we used the liganded receptome knowledgebase to interrogate DNA microarray datasets for genome-wide analyses of potential paracrine/autocrine signaling systems. In addition to viewing ligand-receptor coexpression based on precomputed DNA microarray data, users can submit their own microarray data to perform online genome-wide searches for putative paracrine/autocrine signaling systems. Investigation of transcriptome data based on liganded receptome allows the discovery of paracrine/autocrine signaling for known ligand-receptor pairs in previously uncharacterized tissues or developmental stages. The present annotation of ligand-receptor pairs also identifies orphan receptors and ligands without known interacting partners in select families. Because hormonal ligands within the same family usually interact with paralogous receptors, this genomic approach could also facilitate matching of orphan receptors and ligands. The liganded receptome is accessible at http://receptome.stanford.edu.

Characterization of Novel Splice Variants of LGR7 and LGR8 Reveals That Receptor Signaling Is Mediated by Their Unique Low Density Lipoprotein Class A Modules

The relaxin and insulin-like peptide 3 receptors, LGR7 and LGR8, respectively, are unique members of the leucine-rich repeat-containing G-protein-coupled receptor (LGR) family, because they possess an N-terminal motif with homology to the low density lipoprotein class A (LDLa) modules. By characterizing several LGR7 and LGR8 splice variants, we have revealed that the LDLa module directs ligand-activated cAMP signaling. The LGR8-short variant encodes an LGR8 receptor lacking the LDLa module, whereas LGR7-truncate, LGR7-truncate-2, and LGR7-truncate-3 all encode truncated secreted proteins retaining the LGR7 LDLa module. LGR8-short and an engineered LGR7 variant missing its LDLa module, LGR7-short, bound to their respective ligands with high affinity but lost their ability to signal via stimulation of intracellular cAMP accumulation. Conversely, secreted LGR7-truncate protein with the LDLa module was able to block relaxin-induced LGR7 cAMP signaling and did so without compromising the ability of LGR7 to bind to relaxin or be expressed on the cell membrane. Although the LDLa module of LGR7 was N-glycosylated at position Asn-14, an LGR7 N14Q mutant retained relaxin binding affinity and cAMP signaling, implying that glycosylation is not essential for optimal LDLa function. Using real-time PCR, the expression of mouse LGR7-truncate was detected to be high in, and specific to, the uterus of pregnant mice. The differential expression and evolutionary conservation of LGR7-truncate further suggests that it may also play an important role in vivo. This study highlights the essential role of the LDLa module in LGR7 and LGR8 function and introduces a novel model of GPCR regulation.

Intraovarian tumor necrosis factor-related weak inducer of apoptosis/fibroblast growth factor-inducible-14 ligand-receptor system limits ovarian preovulatory follicles from excessive luteinization

In addition to gonadotropins, many ovarian paracrine factors are crucial for optimal follicle rupture, oocyte maturation, and luteinization. Based on DNA microarray analyses, we found that transcripts for the fibroblast growth factor-inducible-14 (Fn14) receptor are increased after LH/human chorionic gonadotropin (hCG) treatment of gonadotropin-primed immature mice or rats. Fn14 is the cognate receptor for TNF-related weak inducer of apoptosis (TWEAK), a TNF superfamily member. TWEAK transcripts also were detected in the ovary; however, their levels were not regulated by gonadotropins. In situ hybridization analyses indicated that the Fn14 receptor is expressed in the granulosa and cumulus cells of preovulatory follicles and, to a lesser extent, in theca cells. In contrast, in situ hybridization analyses revealed that TWEAK is primarily expressed in theca cells. In cultured granulosa cells pretreated with hCG to induce Fn14 receptor expression, treatment with TWEAK suppressed progesterone synthesis without accompanying changes in cAMP production. Furthermore, intrabursal injection of TWEAK suppressed ovarian progesterone content in gonadotropin-primed rats. In contrast, preovulatory follicles cultured in the presence of the Fn14 decoy, a recombinant protein containing the ligand-binding domain of Fn14, led to increases in progesterone production, presumably by antagonizing the actions of endogenous TWEAK. Likewise, ip injection of the Fn14 decoy enhanced serum progesterone levels with accompanying increases in transcript levels for several key steroidogenic enzymes. The present findings demonstrate a suppressive role of the TWEAK/Fn14 signaling system in the ovary. Following gonadotropin induction of ovulation, Fn14 is induced and could protect preovulatory follicles from excessive luteinization.

Genomic analyses facilitate identification of receptors and signalling pathways for growth differentiation factor 9 and related orphan bone morphogenetic protein/growth differentiation factor ligands

Recent advances in genomic sequencing allow a new paradigm in hormonal research, and a comparative genomic approach facilitates the identification of receptors and signalling mechanisms for orphan ligands of the transforming growth factor beta (TGFbeta) superfamily. Instead of purifying growth differentiation factor 9 (GDF9) receptor proteins for identification, we hypothesized that GDF9, like other ligands in the TGFbeta family, activates type II and type I serine/threonine kinase receptors. Because searches of the human genome for genes with sequence homology to known serine/threonine kinase receptors failed to reveal uncharacterized receptor genes, GDF9 likely interacts with the known type II and type I activin receptor-like kinase (ALK) receptors in granulosa cells. We found that co-treatment with the bone morphogenetic protein (BMP) type II receptor (BMPRII) ectodomain blocks GDF9 activity. Likewise, in a GDF9-non-responsive cell line, overexpression of ALK5, but none of the other six type I receptors, conferred GDF9 responsiveness. The roles of BMPRII and ALK5 as receptors for GDF9 were validated in granulosa cells using gene "knock-down" approaches. Furthermore, we demonstrated the roles of BMPRII, ALK3 and ALK6 as the receptors for the orphan ligands GDF6, GDF7 and BMP10. Thus, evolutionary tracing of polypeptide ligands, receptors and downstream signalling molecules in their respective 'subgenomes' facilitates a new approach for hormonal research.

Relaxin Research in the Postgenomic Era

Because of the coevolution of ligands and their cognate receptors, analysis of human genomic sequences allows prediction of the pairing of these elements. Initially, we identified a group of five human leucine-rich repeat-containing G-protein-coupled receptor (LGR) genes homologous to LH, FSH, and TSH receptors. Based on common phenotypes of INSL3 null mice and transgenic mice with LGR8 gene deletion, we hypothesized that INSL3, relaxin, and related genes are likely ligands for the paralogous LGR7 and LGR8 genes. Matching the relaxin family peptides with these two orphan LGRs led to the finding that relaxin is capable of activating LGR7 and LGR8 through the Gs pathway. In addition, INSL3 and relaxin 3 were found to be specific ligands for LGR8 and LGR7, respectively. Based on the known production of INLS3 by testicular Leydig cells and ovarian theca cells, we demonstrated the expression of the INSL3 receptor LGR8 in oocytes in ovary and in male germ cells in the testis. Furthermore, we found that LH stimulates INSL3 transcripts in ovarian theca and testicular Leydig cells. INSL3, in turn, binds LGR8 expressed in germ cells to initiate the meiotic progression of arrested oocytes in preovulatory follicles in vitro and in vivo and to suppress male germ cell apoptosis in vivo. INSL3 interacts with germ cells to activate the inhibitory G protein, thus leading to decreases in cAMP production. Our data demonstrate the importance of the INSL3-LGR8 paracrine system in mediating gonadotropic actions in both ovary and testis.

Genomic analyses of the evolution of LGR genes

Recent completion of the sequencing of genomes from several mammals, teleosts and invertebrates has shown that G protein-coupled receptors (GPCRs) are one of the conserved groups of cell surface receptors with an ancient origin. GPCRs play important roles in diverse physiological functions and are the most important targets for pharmaceutical discoveries. Recent work based on the search for gene with structural similarity to LH, FSH and thyroid-stimulating hormone (TSH) receptors in diverse genomes has led to the identification of a group of GPCRs called Leucine-rich repeat-containing, G protein-coupled Receptor (LGR). We present the genomic analyses of the evolution of LGR genes in the literature.

Obestatin, a peptide encoded by the ghrelin gene, opposes ghrelin's effects on food intake

Ghrelin, a circulating appetite-inducing hormone, is derived from a prohormone by posttranslational processing. On the basis of the bioinformatic prediction that another peptide also derived from proghrelin exists, we isolated a hormone from rat stomach and named it obestatin-a contraction of obese, from the Latin "obedere," meaning to devour, and "statin," denoting suppression. Contrary to the appetite-stimulating effects of ghrelin, treatment of rats with obestatin suppressed food intake, inhibited jejunal contraction, and decreased body-weight gain. Obestatin bound to the orphan G protein-coupled receptor GPR39. Thus, two peptide hormones with opposing action in weight regulation are derived from the same ghrelin gene. After differential modification, these hormones activate distinct receptors.

Hormonology: a genomic perspective on hormonal research

Recent advances in comparative genomics allow a new paradigm for hormonal research. At the centennial of the first use of the term hormone by Ernest Starling, we reflected on the changing approaches in elucidating hormonal signaling mechanisms and highlighted the inadequacy of the term endocrinology, implying remote activation, to describe the diverse modes of hormone actions. Several examples were presented to underscore the power of comparative genomics in the identification of new polypeptide hormones, receptors, and signaling pathways. We propose the use of the term hormonology to more accurately reflect the expanding boundaries of the discipline.

Heterodimeric fly glycoprotein hormone-alpha2 (GPA2) and glycoprotein hormone-beta5 (GPB5) activate fly leucine-rich repeat-containing G protein-coupled receptor-1 (DLGR1) and stimulation of human thyrotropin receptors by chimeric fly GPA2 and human GPB5

Glycoprotein hormones play important roles in thyroid and gonadal function in vertebrates. The glycoprotein hormone alpha-subunit forms heterodimers with different beta-subunits to activate TSH or gonadotropin (LH and FSH) receptors. Recent genomic analyses allowed the identification of another alpha-subunit, GPA2, and another beta-subunit, GPB5, in human, capable of forming heterodimers to activate TSH receptors. Based on comparative genomic searches, we isolated the fly orthologs for human GPA2 and GPB5, each consisting of 10 cysteine residues likely involved in cystine-knot formation. RT-PCR analyses in Drosophila melanogaster demonstrated the expression of GPA2 and GPB5 at different developmental stages. Immunoblot analyses further showed that fly GPA2 and GPB5 subunit proteins are of approximately 16 kDa, and coexpression of these subunits yielded heterodimers. Purified recombinant fly GPA2/GPB5 heterodimers were found to be glycoproteins with N-linked glycosylated alpha-subunits and nonglycosylated beta-subunits, capable of stimulating cAMP production mediated by fly orphan receptor DLGR1 but not DLGR2. Although the fly GPA2/GPB5 heterodimers did not activate human TSH or gonadotropin receptors, chimeric fly GPA2/human GPB5 heterodimers stimulated human TSH receptors. These findings indicated that fly GPA2/GPB5 is a ligand for DLGR1, thus showing the ancient origin of this glycoprotein hormone-seven transmembrane receptor-G protein signaling system. The fly GPA2 also could form heterodimers with human GPB5 to activate human TSH receptors, indicating the evolutionary conservation of these genes and suggesting that the GPA2 subunit may serve as a scaffold for the beta-subunit to activate downstream G protein-mediated signaling.

Identification of receptors and signaling pathways for orphan bone morphogenetic protein/growth differentiation factor ligands based on genomic analyses

There are more than 30 human transforming growth factor beta/bone morphogenetic protein/growth differentiation factor (TGFbeta/BMP/GDF)-related ligands known to be important during embryonic development, organogenesis, bone formation, reproduction, and other physiological processes. Although select TGFbeta/BMP/GDF proteins were found to interact with type II and type I serine/threonine receptors to activate downstream Smad and other proteins, the receptors and signaling pathways for one-third of these TGFbeta/BMP/GDF paralogs are still unclear. Based on a genomic analysis of the entire repertoire of TGFbeta/BMP/GDF ligands and serine/threonine kinase receptors, we tested the ability of three orphan BMP/GDF ligands to activate a limited number of phylogenetically related receptors. We characterized the dimeric nature of recombinant GDF6 (also known as BMP13), GDF7 (also known as BMP12), and BMP10. We demonstrated their bioactivities based on the activation of Smad1/5/8-, but not Smad2/3-, responsive promoter constructs in the MC3T3 cell line. Furthermore, we showed their ability to induce the phosphorylation of Smad1, but not Smad2, in these cells. In COS7 cells transfected with the seven known type I receptors, overexpression of ALK3 or ALK6 conferred ligand signaling by GDF6, GDF7, and BMP10. In contrast, transfection of MC3T3 cells with ALK3 small hairpin RNA suppressed Smad signaling induced by all three ligands. Based on the coevolution of ligands and receptors, we also tested the role of BMPRII and ActRIIA as the type II receptor candidates for the three orphan ligands. We found that transfection of small hairpin RNA for BMPRII and ActRIIA in MC3T3 cells suppressed the signaling of GDF6, GDF7, and BMP10. Thus, the present approach provides a genomic paradigm for matching paralogous polypeptide ligands with a limited number of evolutionarily related receptors capable of activating specific downstream Smad proteins.

Ovarian brain-derived neurotrophic factor (BDNF) promotes the development of oocytes into preimplantation embryos

Optimal development of fertilized eggs into preimplantation embryos is essential for reproduction. Although mammalian oocytes ovulated after luteinizing hormone (LH) stimulation can be fertilized and promoted into early embryos in vitro, little is known about ovarian factors important for the conditioning of eggs for early embryo development. Because LH interacts only with ovarian somatic cells, its potential regulation of oocyte functions is presumably mediated by local paracrine factors. We performed DNA microarray analyses of ovarian transcripts and identified brain-derived neurotrophic factor (BDNF) secreted by granulosa and cumulus cells as an ovarian factor stimulated by the preovulatory LH surge. Ovarian BDNF acts on TrkB receptors expressed exclusively in oocytes to enhance first polar body extrusion of oocytes and to promote the in vitro development of zygotes into preimplantation embryos. Furthermore, in vivo treatment with a Trk receptor inhibitor suppressed first polar body extrusion and the progression of zygotes into blastocysts. Thus, ovarian BDNF is important to nuclear and cytoplasmic maturation of the oocyte, which is essential for successful oocyte development into preimplantation embryos. Treatment with BDNF could condition the cultured oocytes for optimal progression into the totipotent blastocysts.

Hypertrophic effects of urocortin homologous peptides are mediated via activation of the Akt pathway

The UCN homologues SCP and SRP bind specifically to the CRFR2 receptor, whereas UCN binds to both CRFR1 and CRFR2. We have previously demonstrated that all three peptides are cardioprotective, and both the Akt and MAPK p42/44 pathways are essential for this effect. Here we tested the hypertrophic effects of these peptides. We examined the effects of the peptides on cell area, protein synthesis, and induction of the natriuretic peptides ANP and BNP. All three peptides were able to increase all the markers of hypertrophy examined, with SCP being the most potent of the three, followed by UCN and SRP last. In addition, we provide a mechanism of action for the three peptides and show that Akt phosphorylation is important for their hypertrophic action, whereas MAPK p42/44 is not involved in this effect.

Bursicon, the insect cuticle-hardening hormone, is a heterodimeric cystine knot protein that activates G protein-coupled receptor LGR2

All arthropods periodically molt to replace their exoskeleton (cuticle). Immediately after shedding the old cuticle, the neurohormone bursicon causes the hardening and darkening of the new cuticle. Here we show that bursicon, to our knowledge the first heterodimeric cystine knot hormone found in insects, consists of two proteins encoded by the genes burs and pburs (partner of burs). The pburs/burs heterodimer from Drosophila melanogaster binds with high affinity and specificity to activate the G protein-coupled receptor DLGR2, leading to the stimulation of cAMP signaling in vitro and tanning in neck-ligated blowflies. Native bursicon from Periplaneta americana is also a heterodimer. In D. melanogaster the levels of pburs, burs, and DLGR2 transcripts are increased before ecdysis, consistent with their role in postecdysial cuticle changes. Immunohistochemical analyses in diverse insect species revealed the colocalization of pburs- and burs-immunoreactivity in some of the neurosecretory neurons that also express crustacean cardioactive peptide. Forty-three years after its initial description, the elucidation of the molecular identity of bursicon and the verification of its receptor allow for studies of bursicon actions in regulating cuticle tanning, wing expansion, and as yet unknown functions. Because bursicon subunit genes are homologous to the vertebrate bone morphogenetic protein antagonists, our findings also facilitate investigation on the function of these proteins during vertebrate development.

Three's company: two or more unrelated receptors pair with the same ligand

Intercellular communication relies on signal transduction mediated by extracellular ligands and their receptors. Although the ligand-receptor interaction is usually a two-player event, there are selective examples of one polypeptide ligand interacting with more than one phylogenetically unrelated receptor. Likewise, a few receptors interact with more than one polypeptide ligand, and sometimes with more than one coreceptor, likely through an interlocking of unique protein domains. Phylogenetic analyses suggest that for certain triumvirates, the matching events could have taken place at different evolutionary times. In contrast to a few polypeptide ligands interacting with more than one receptor, we found that many small nonpeptide ligands have been paired with two or more plasma membrane receptors, nuclear receptors, or channels. The observation that many small ligands are paired with more than one receptor type highlights the utilitarian use of a limited number of cellular components during metazoan evolution. These conserved ligands are ubiquitous cell metabolites likely favored by natural selection to establish novel regulatory networks. They likely possess structural features useful for designing agonistic and antagonistic drugs to target diverse receptors.

Identification of a stanniocalcin paralog, stanniocalcin-2, in fish and the paracrine actions of stanniocalcin-2 in the mammalian ovary

Stanniocalcin is a glycoprotein hormone important in the maintenance of calcium and phosphate homeostasis in fish. Two related mammalian stanniocalcin genes, STC1 and STC2, were found to be expressed in various tissues as paracrine regulators. We have demonstrated the existence of a second stanniocalcin gene in fish, designated fish STC2, with only 30% identity to fish STC1. However, phylogenetic analysis and comparison of the genomic structure of STC genes in vertebrates indicated that STC1 and STC2 genes were probably derived from a common ancestor gene. Based on the prominent expression of mammalian STC1 in the ovary, we tested STC2 expression in rat ovary and the regulation of STC2 expression by gonadotropins. Treatment of immature rats with pregnant mare serum gonadotropin increased STC2 transcripts, whereas subsequent treatment with human chorionic gonadotropin suppressed STC2 expression. Real-time PCR analyses also demonstrated that STC2 is expressed mainly in thecal layers. In situ hybridization studies also revealed that STC2 is expressed in thecal cell layers of antral and preovulatory follicles after gonadotropin stimulation. To elucidate the physiological functions of STC2, recombinant human and fish STC2 proteins were generated and found to be N-glycosylated homodimers. In cultured granulosa cells, treatment with human or fish STC2 suppressed FSH-induced progesterone, but not estradiol or cAMP, production. The STC2 suppression of progesterone production was associated with the inhibition of FSH-induced CYP11A and 3beta-hydroxysteroid dehydrogenase expression. Thus, STC2 is a functional homodimeric glycoprotein, and thecal cell-derived STC2 could play a paracrine role during follicular development.

Neonatal lethality of LGR5 null mice is associated with ankyloglossia and gastrointestinal distension

The physiological role of an orphan G protein-coupled receptor, LGR5, was investigated by targeted deletion of this seven-transmembrane protein containing a large N-terminal extracellular domain with leucine-rich repeats. LGR5 null mice exhibited 100% neonatal lethality characterized by gastrointestinal tract dilation with air and an absence of milk in the stomach. Gross and histological examination revealed fusion of the tongue to the floor of oral cavity in the mutant newborns and immunostaining of LGR5 expression in the epithelium of the tongue and in the mandible of the wild-type embryos. The observed ankyloglossia phenotype provides a model for understanding the genetic basis of this craniofacial defect in humans and an opportunity to elucidate the physiological role of the LGR5 signaling system during embryonic development.

Forkhead l2 is expressed in the ovary and represses the promoter activity of the steroidogenic acute regulatory gene

Premature ovarian failure in a subgroup of women with blepharophimosis-ptosis-epicanthus inversus type 1 syndrome has been associated with nonsense mutations in the gene encoding a Forkhead transcription factor, Forkhead L2 (FOXL2). However, the exact function of FOXL2 in the ovary is unclear. We investigated the expression of FOXL2 in the mouse ovary during follicular development and maturation by RT-PCR and in situ hybridization. The FOXL2 mRNA is expressed in ovaries throughout development and adulthood and is localized to the undifferentiated granulosa cells in small and medium follicles as well as cumulus cells of preovulatory follicles. FOXL2 belongs to a group of transcription factors capable of interacting with specific DNA sequences in diverse gene promoters. With the presence of multiple putative forkhead DNA consensus sites, the promoter of the human steroidogenic acute regulatory (StAR) gene was used to test for regulation by FOXL2. Cotransfection studies revealed that wild-type FOXL2 represses the activity of the StAR promoter, and the first 95 bp upstream of the transcriptional start site of the StAR gene is sufficient for FOXL2 repression. EMSAs confirmed that FOXL2 interacts directly with this region. Analyses using FOXL2 mutants also demonstrated the importance of the entire alanine/proline-rich carboxyl terminus of FOXL2 for transcriptional repression. Furthermore, these mutations produce a protein with a dominant-negative effect that disables the transcriptional repressor activity of wild-type FOXL2. Dominant-negative mutations of FOXL2 could increase expression of StAR and other follicle differentiation genes in small and medium follicles to accelerate follicle development, resulting in increased initial recruitment of dormant follicles and thus the premature ovarian failure phenotype.

Lack of LGR8 gene mutation in Finnish patients with a family history of cryptorchidism

Cryptorchidism is the most frequent congenital anomaly of the urogenital tract in the male. Although in Western countries 1-2% of males at the age of 3 months are diagnosed with this condition, its aetiology is still unknown. Animal models suggest a possible genetic basis for this disorder. Recently, the INSL3 (Leydig insulin-like peptide) gene and its cognate receptor, LGR8, were found to be important in testicular descent by regulating gubernacular development. Male mice null for either INSL3 or LGR8 genes exhibited bilateral cryptorchidism. Because earlier studies indicated that mutation of the INSL3 gene is not associated with the development of human cryptorchidism, this study analysed whether mutations in the LGR8 gene could be associated with this disorder. Sequencing of 18 exons of the LGR8 gene in 23 cryptorchid Finnish patients and a group of 33 control subjects allowed the identification of three nucleotide changes in exons 12 and 17, showing single base substitutions from A to G at positions 957, 993, and 1810 of LGR8. Among the three changes, only the 1810 A to G substitution is associated with an amino acid change from isoleucine to valine (Ile604Val) located in the fifth transmembrane domain of this seven-transmembrane receptor. This change was more frequent in a control group of normal fertile adult males and infant boys than in the group of cryptorchid males. The change is not associated with altered receptor signalling, thus suggesting the presence of a polymorphism unrelated to the cryptorchid phenotype. These data indicate that mutations involving the human LGR8 gene do not represent a frequent cause of cryptorchidism in the Finnish population.

Leucine-rich repeat-containing, G protein-coupled receptor 4 null mice exhibit intrauterine growth retardation associated with embryonic and perinatal lethality

Leucine-rich repeat-containing, G protein-coupled receptors (LGRs) belong to the largest mammalian superfamily of proteins with seven-transmembrane domains. LGRs can be divided into three subgroups based on their unique domain arrangement. Although two subgroups have been found to be receptors for glycoprotein hormones and relaxin-related ligands, respectively, the third LGR subgroup, consisting of LGR4-6, are orphan receptors with unknown physiological roles. To elucidate the functions of this subgroup of LGRs, LGR4 null mice were generated using a secretory trap approach to delete the majority of the LGR4 gene after the insertion of a beta-galactosidase reporter gene immediately after exon 1. Tissues expressing LGR4 were analyzed based on histochemical staining of the transgene driven by the endogenous LGR4 promoter. LGR4 was widely expressed in kidney, adrenal gland, stomach, intestine, heart, bone/cartilage, and other tissues. The expression of LGR4 in these tissues was further confirmed by immunohistochemical studies in wild-type animals. Analysis of the viability of 250 newborn animals suggested a skewed inheritance pattern, indicating that only 40% of the expected LGR4 null mice were born. For the LGR4 null mice viable at birth, most of them died within 2 d. Furthermore, the LGR4 null mice showed intrauterine growth retardation as reflected by a 14% decrease in body weight at birth, together with 30% and 40% decreases in kidney and liver weights, respectively. The present findings demonstrate the widespread expression of LGR4, and an essential role of LGR4 for embryonic growth, as well as kidney and liver development. The observed pre- and postnatal lethality of LGR4 null mice illustrates the importance of the LGR4 signaling system for the survival and growth of animals during the perinatal stage.

Paracrine regulation of ovarian granulosa cell differentiation by stanniocalcin (STC) 1: mediation through specific STC1 receptors

Stanniocalcin (STC) in fish maintains calcium and phosphate homeostasis, whereas mammalian STC1 shows a diverse tissue expression pattern with ovary exhibiting the highest level. Based on the known expression of STC1 in theca/interstitial cells of the ovary, we generated recombinant N-glycosylated STC1 protein and tested its ability to modulate granulosa cell differentiation. In cultured rat granulosa cells obtained from early antral follicles, treatment with STC1 suppressed FSH-stimulated progesterone biosynthesis with minimal effects on estradiol and cAMP production. In mature granulosa cells, treatment with STC1 also suppressed human chorionic gonadotropin-induced progesterone production. The inhibitory effect of STC1 was accompanied by a pronounced suppression of the CYP11A transcripts and the FSH induction of functional LH receptors. In addition, STC1 was found to act downstream of adenyl cyclases in suppressing progesterone biosynthesis. We also tested the regulation of STC1 gene expression by gonadotropins. Treatment with pregnant mare serum gonadotropin decreased STC1 transcript levels in theca cells of maturing follicles, whereas subsequent treatment with human chorionic gonadotropin led to sustained suppression in the corpora lutea. Using radiolabeled recombinant STC1, receptor assays showed specific STC1 binding with a high affinity to granulosa cells. Because STC1 is expressed in ovarian theca/interstitial cells, the present demonstration of receptor binding and the specific actions of STC1 in granulosa cells suggest the existence of a follicular paracrine system in which theca cell-derived STC1 dampens the gonadotropin stimulation of granulosa cell differentiation. The observed STC1 suppression of progesterone, but not estradiol, production further suggests the potential role of this paracrine hormone as a luteinization inhibitor.

Paracrine regulation of mammalian oocyte maturation and male germ cell survival

Mammalian oocytes are arrested at the prophase of meiosis before induction of maturation by the preovulatory luteinizing hormone (LH) surge. LH also promotes the survival of meiotic male germ cells in the testis. Because LH binds somatic cells, the mechanism underlying its regulation of germ cell function is unclear. We found that LH stimulates Leydig insulin-like 3 (INSL3) transcripts in ovarian theca and testicular Leydig cells. INSL3, in turn, binds a G protein-coupled receptor, LGR8 (leucine-rich repeat-containing G protein-coupled receptor 8), expressed in germ cells to activate the inhibitory G protein, thus leading to decreases in cAMP production. Treatment with INSL3 initiates meiotic progression of arrested oocytes in preovulatory follicles in vitro and in vivo and suppresses male germ cell apoptosis in vivo, thus demonstrating the importance of the INSL3-LGR8 paracrine system in mediating gonadotropin actions.

Protein Related to DAN and Cerberus Is a Bone Morphogenetic Protein Antagonist That Participates in Ovarian Paracrine Regulation

Bone morphogenetic proteins (BMPs) are important for body patterning and morphogenesis, whereas several BMP antagonists regulate the functions of BMPs during embryonic development and tissue differentiation. Protein related to DAN and cerberus (PRDC) is a secreted protein with a cystine knot structure identified by gene trapping in embryonic stem cells. Although PRDC shows sequence homology with proteins of the BMP antagonist family, its biological activity and physiological functions are unclear. We generated recombinant PRDC and its paralog, gremlin, and tested their ability to suppress actions initiated by diverse BMP proteins. Similar to the known BMP antagonist, gremlin, PRDC blocked ligand signaling induced by BMP2 and BMP4 but had minimal effects on reporter gene activation induced by GDF-9, activin, or transforming growth factor-beta. Co-precipitation assays further demonstrated the direct protein-protein interactions between PRDC and BMP2 or BMP4. Reverse transcriptase-PCR analyses indicated that PRDC transcripts are widely expressed showing higher levels in ovary, brain, and spleen. In mouse ovary, PRDC transcripts were increased following gonadotropin treatment. In situ hybridization analyses further indicated that ovarian PRDC transcripts are localized in granulosa cells of selective follicles. In addition, co-treatment with PRDC antagonized the inhibitory effects of BMP4 on the follicle-stimulating hormone stimulation of progesterone production by cultured rat granulosa cells. Thus, PRDC is a potent BMP antagonist with a wide tissue expression pattern, and ovarian PRDC expressed in granulosa cells could be involved in follicular development by antagonizing the actions of theca cell-derived BMPs.

Growth differentiation factor-9 signaling is mediated by the type I receptor, activin receptor-like kinase 5

Growth differentiation factor-9 (GDF-9) is an oocyte-derived growth factor and a member of the TGF-beta superfamily that includes TGF-beta, activin, and bone morphogenetic proteins (BMPs). GDF-9 is indispensable for the development of ovarian follicles from the primary stage, and treatment with GDF-9 enhances the progression of early follicles into small preantral follicles. Similar to other TGF-beta family ligands, GDF-9 likely initiates signaling mediated by type I and type II receptors with serine/threonine kinase activity, followed by the phosphorylation of intracellular transcription factors named Smads. We have shown previously that GDF-9 interacts with the BMP type II receptor (BMPRII) in granulosa cells, but the type I receptor involved is unknown. Using P19 cells, we now report that GDF-9 treatment stimulated the CAGA-luciferase reporter known to be responsive to TGF-beta mediated by the type I receptor, activin receptor-like kinase (ALK)5. In contrast, GDF-9 did not stimulate BMP-responsive reporters. In addition, treatment with GDF-9 induced the phosphorylation of Smad2 and Smad3 in P19 cells, and the stimulatory effect of GDF-9 on the CAGA-luciferase reporter was blocked by the inhibitory Smad7, but not Smad6. We further reconstructed the GDF-9 signaling pathway using Cos7 cells that are not responsive to GDF-9. After overexpression of ALK5, with or without exogenous Smad3, the Cos7 cells gained GDF-9 responsiveness based on the CAGA-luciferase reporter assay. The roles of ALK5 and downstream pathway genes in mediating GDF-9 actions were further tested in ovarian cells. In cultured rat granulosa cells from early antral follicles, treatment with GDF-9 stimulated the CAGA-luciferase reporter activity and induced the phosphorylation of Smad3. Furthermore, transfection with small interfering RNA for ALK5 or overexpression of the inhibitory Smad7 resulted in dose-dependent suppression of GDF-9 actions. In conclusion, although GDF-9 binds to the BMP-activated type II receptor, its downstream actions are mediated by the type I receptor, ALK5, and the Smad2 and Smad3 proteins. Because ALK5 is a known receptor for TGF-beta, diverse members of the TGF-beta family of ligands appear to interact with a limited number of receptors in a combinatorial manner to activate two downstream Smad pathways.