Genome-wide analysis of two different regions of brain reveals the molecular changes of fertility related genes in rln3a-/- mutants in male Nile tilapia (Oreochromis niloticus)

Relaxin3 (rln3) has been associated with various emotional and cognitive processes, including stress, anxiety, learning, memory, motivational behavior, and circadian rhythm. Notably, previous report revealed that Rln3a played an indispensable role in testicular development and male fertility in Nile tilapia (Oreochromis niloticus). However, the underlying molecular mechanisms remain largely unknown. We found that Rln3a is expressed exclusively in the diencephalon* (Di*) of the brain. Deficiency of Rln3a resulted in a significant increase in serum dopamine level and an upregulation of gene expression of gnrh1 and kisspeptin2. To further elucidate the role of Rln3a in fish fertility, we collected two different regions of Di* and hypothalamus (Hyp) tissues for subsequent RNA-seq analysis of both wild-type (rln3a+/+) and rln3a-/- male tilapia. Upon the transcriptomic data, 1136 and 755 differentially expressed genes (DEGs) were identified in the Di* and Hyp tissues, respectively. In Di*, the up-regulated genes were enriched in circadian rhythm, chemical carcinogenesis, while the down-regulated genes were enriched in type II diabetes mellitus, dopaminergic synapse, and other pathways. In Hyp, the up-regulated genes were enriched in circadian rhythm, pyrimidine metabolism, while the down-regulated genes were enriched in type I diabetes mellitus, autoimmune thyroid disease, and other pathways. Subsequently, the results of both qRT-PCR and FISH assays highlighted a pronounced up-regulation of core circadian rhythm genes, cry1b and per3, whereas genes such as clocka, clockb, and arntl exhibited down-regulation. Furthermore, the genes associated with dopamine biosynthesis were significantly increased in the Hyp. In summary, the mutation of rln3a in male tilapia resulted in notable changes in circadian rhythm and disease-linked signaling pathways in the Di* and Hyp. These changes might account for the fertility defects observed in rln3a-/- male mutants in tilapia.

Identification and Quantification of Human Relaxin Proteins by Immunoaffinity-Mass Spectrometry

The human relaxins belong to the Insulin/IGF/Relaxin superfamily of peptide hormones, and their physiological function is primarily associated with reproduction. In this study, we focused on a prostate tissue-specific relaxin RLN1 (REL1_HUMAN protein) and a broader tissue specificity RLN2 (REL2_HUMAN protein). Due to their structural similarity, REL1 and REL2 proteins were collectively named a 'human relaxin protein' in previous studies and were exclusively measured by immunoassays. We hypothesized that the highly selective and sensitive immunoaffinity-selected reaction monitoring (IA-SRM) assays would reveal the identity and abundance of the endogenous REL1 and REL2 in biological samples and facilitate the evaluation of these proteins for diagnostic applications. High levels of RLN1 and RLN2 transcripts were found in prostate and breast cancer cell lines by RT-PCR. However, no endogenous prorelaxin-1 or mature REL1 were detected by IA-SRM in cell lines, seminal plasma, or blood serum. The IA-SRM assay of REL2 demonstrated its undetectable levels (<9.4 pg/mL) in healthy control female and male sera and relatively high levels of REL2 in maternal sera across different gestational weeks (median 331 pg/mL; N = 120). IA-SRM assays uncovered potential cross-reactivity and nonspecific binding for relaxin immunoassays. The developed IA-SRM assays will facilitate the investigation of the physiological and pathological roles of REL1 and REL2 proteins.

Expression of Relaxin Family Peptide Receptors 1 and 3 in the Ovarian Follicle of Japanese Quail

In our previous studies, we demonstrated that the primary source of relaxin 3 (RLN3) in Japanese quail is ovarian granulosa cells. Although several relaxin family peptide (RXFP) receptors have been sequenced, the intricacies of these receptors in avian species remain insufficiently clarified. Therefore, we assessed the expression of RXFP receptors, RXFP1 and 3, in Japanese quail. Using RT-PCR, we found that both RXFP1 and 3 were ubiquitously expressed. The expression level of RXFP1 is significantly higher in the ovarian theca layer, indicating that it is the primary receptor for RLN3 in the ovary. During follicular development, there was an elevation in thecal RXFP1 expression, but it declined after the luteinizing hormone (LH) surge. We found that the protease activity of the 60 kDa band increased after the LH surge, suggesting the involvement of RLN3 signaling in ovulation. These results suggest a paracrine role of RLN3, involving its binding with RXFP1 in ovarian theca cells. This interaction may elicit biological actions, potentially initiating ovulation after the LH surge.

The Relaxin-3 Receptor, RXFP3, Is a Modulator of Aging-Related Disease

During the aging process our body becomes less well equipped to deal with cellular stress, resulting in an increase in unrepaired damage. This causes varying degrees of impaired functionality and an increased risk of mortality. One of the most effective anti-aging strategies involves interventions that combine simultaneous glucometabolic support with augmented DNA damage protection/repair. Thus, it seems prudent to develop therapeutic strategies that target this combinatorial approach. Studies have shown that the ADP-ribosylation factor (ARF) GTPase activating protein GIT2 (GIT2) acts as a keystone protein in the aging process. GIT2 can control both DNA repair and glucose metabolism. Through in vivo co-regulation analyses it was found that GIT2 forms a close coexpression-based relationship with the relaxin-3 receptor (RXFP3). Cellular RXFP3 expression is directly affected by DNA damage and oxidative stress. Overexpression or stimulation of this receptor, by its endogenous ligand relaxin 3 (RLN3), can regulate the DNA damage response and repair processes. Interestingly, RLN3 is an insulin-like peptide and has been shown to control multiple disease processes linked to aging mechanisms, e.g., anxiety, depression, memory dysfunction, appetite, and anti-apoptotic mechanisms. Here we discuss the molecular mechanisms underlying the various roles of RXFP3/RLN3 signaling in aging and age-related disorders.

Runjing Decoction alleviated cyclophosphamide-induced oligoasthenospermia rats by inhibiting cell apoptosis via RXFP1/AKT/FOXO1 pathway

Runjing Decoction (RJD) is a prescription of traditional Chinese medicine for the treatment of oligoasthenospermia. However, the molecular mechanism of RJD on oligoasthenospermia still remains unknown. A model of oligoasthenospermia was induced in 30 Sprague Dawley rats by intraperitoneal injection of cyclophosphamide at 35 mg/kg per day for 5 days and treated by intragastric RJD (13.5 g/kg) or L-carnitine (100 mg/kg) for 14 days. The body weight, testis and epididymis weight, grade A spermatozoa, grade B spermatozoa, the percentage of sperm forward motility (PR%), the sperm activity rate and the sperm density of rats were evaluated before and after RJD treatment. The testis apoptosis was determined by TUNEL staining. The expressions of RXFP1, FoxO1, PI3K, Akt, Bax and Bcl-2 were determined by qRT-PCR and Western blot, respectively. After RJD treatment, the grade A spermatozoa, sperm PR%, sperm activity and sperm density were significantly increased relative to those in model rats. Cell apoptosis of testis tissue was reversed by RJD. RJD suppressed cell apoptosis, inhibited the expression of RXFP1, FOXO1, PI3K, AKT and Bax, and promoted the expression levels of Bcl-2 in testicular tissue of oligoasthenospermia rats. RJD could alleviate sperm quality and testis damage in oligoasthenospermia rats by inhibiting RXFP1/AKT/FOXO1 pathway.

Single-cell transcriptomic analysis of the adult mouse spinal cord reveals molecular diversity of autonomic and skeletal motor neurons

The spinal cord is a fascinating structure that is responsible for coordinating movement in vertebrates. Spinal motor neurons control muscle activity by transmitting signals from the spinal cord to diverse peripheral targets. In this study, we profiled 43,890 single-nucleus transcriptomes from the adult mouse spinal cord using fluorescence-activated nuclei sorting to enrich for motor neuron nuclei. We identified 16 sympathetic motor neuron clusters, which are distinguishable by spatial localization and expression of neuromodulatory signaling genes. We found surprising skeletal motor neuron heterogeneity in the adult spinal cord, including transcriptional differences that correlate with electrophysiologically and spatially distinct motor pools. We also provide evidence for a novel transcriptional subpopulation of skeletal motor neuron (γ*). Collectively, these data provide a single-cell transcriptional atlas ( http://spinalcordatlas.org ) for investigating the organizing molecular logic of adult motor neuron diversity, as well as the cellular and molecular basis of motor neuron function in health and disease.

Mass Spectrometry Supports That the Structure of Circulating Human Insulin-Like Factor 3 Is a Heterodimer

The structure of the testicular peptide hormone insulin-like factor 3 (INSL3) has been the subject of discussion for more than a decade. Some studies support that the central C-domain of INSL3 is proteolytically removed and that INSL3 is secreted by the testicular Leydig cells into circulation as a small heterodimer consisting of an A- and a B-chain linked by two disulfide bridges. Other studies support that the INSL3 peptide remains uncleaved and that the predominant structure of circulating INSL3 is the larger pro-form. Furthermore, the structure of INSL3 could differ between species, and both structural forms of INSL3 could, in principle, be present in circulation. Recently, we have developed a mass spectrometry (MS)-based method for INSL3 in human serum that provides new information about the structure of circulating INSL3. Based on recent and newly presented data, we argue that in healthy men, the common, and probably the only, form of circulating INSL3 is the smaller AB heterodimer. For the first time, we demonstrate that the same analytical principle, with slight modifications, can also be applied to sera from other species, and we show that the INSL3 AB heterodimer is also present in serum from rodents. Improved understanding of the structure and biochemistry of circulating INSL3 could be valuable for the interpretation of INSL3 as a marker for reproductive and developmental disorders in humans and domesticated animals.

Leydig cell tumorigenesis - implication of G-protein coupled membrane estrogen receptor, peroxisome proliferator-activated receptor and xenoestrogen exposure. In vivo and in vitro appraisal

The etiology and molecular characteristics of Leydig cell tumor (LCT) are scarcely known. From the research data stems that estrogen can be implicated in LCT induction and development, however it is not investigated in detail. Considering the above, herein we analyzed the relation between G-protein coupled membrane estrogen receptor, peroxisome proliferator-activated receptor and insulin-like family peptides (insulin-like 3 peptide; INSL3 and relaxin; RLN) expressions as well as estrogen level with impact of xenoestrogen (bisphenol A; BPA, tetrabromobisphenol A; TBBPA, and tetrachlorobisphenol A; TCBPA). While in our previous studies altered GPER-PPAR partnership was found in human LCT being a possible cause and/or additionally effecting on LCT development, here mouse testes with experimentally induced LCT and mouse tumor Leydig cell (MA-10) treated with BPA chemicals were examined. We revealed either diverse changes in expression or co-expression of GPER and PPAR in mouse LCT as well as in MA-10 cells after BPA analogues when compared to human LCT. Relationships between expression of INSL3, RLN, including co-expression, and estrogen level in human LCT, mouse LCT and MA-10 cells xenoestrogen-treated were found. Moreover, involvement of PI3K-Akt-mTOR pathway or only mTOR in the interactions of examined receptors and hormones was showed. Taken together, species, cell of origin, experimental system used and type of used chemical differences may result in diverse molecular characteristics of LCT. Estrogen/xenoestrogen may play a role in tumor Leydig cell proliferation and biochemical nature but this issue requires further studies. Experimentally-induced LCT in mouse testis and MA-10 cells after BPA exposure seem to be additional models for understanding some aspects of human LCT biology.

Expression and localization of relaxin family peptide receptor 4 in human spermatozoa and impact of insulin-like peptide 5 on sperm functions

Insulin-like peptide 5 (INSL5) is a member of the insulin superfamily peptide that interacts with the relaxin family peptide receptor 4 (RXFP4). Numerous recent studies have focused on the functional effects of INSL5 on fat and glucose metabolism. Although there is no evidence that the human sperm may be a candidate target of INSL5, it has been detected in mice testis and sperm. Therefore, the present study sought to analyze the localization and expression of RXFP4 on human sperm and determine the efficiency of INSL5 in human sperm. Normal semen samples were incubated in different doses and exposure time periods of INSL5. We analyzed sperm motility by computer-assisted sperm analysis (CASA) and ROS levels by flow cytometry using the MitoSOX™ Red probe. Localization and expression of RXFP4 were assayed by immunofluorescence and RT-PCR, respectively. The results confirmed the presence of RXFP4 in human spermatozoa, which localized in the neck and midpiece of sperm. Nested PCR showed the expression of RXFP4 in human sperm. INSL5 could attenuate generation of mitochondrial ROS at the 1, 10, 30, and 100nmol/L doses. This result was particularly noted in the 30nmol/L treated samples after 4h incubation. Total motility of sperm was significantly preserved in the 100nmol/L after 2h and in 30nmol/L after 4h incubation period. This study, for the first time, clarified the expression and localization of RXFP4 on human sperm and revealed the role of INSL5 in sperm motility and mitochondrial ROS generation in a dose-dependent manner.

Neohormones in milk

Neohormone systems evolved specifically to regulate those mammalian traits, such as internal fertilization, pregnancy and lactation, which have proved to be central to the success, environmental independence, and adaptability of mammals as a vertebrate group. Neohormones such as oxytocin or relaxin are not only involved in the regulation of mammary gland development and function, but are also significant components of milk itself. Particularly for the latter hormone, it has been shown for the pig that relaxin in the first milk is taken up by the gastrointestinal tract of the offspring, enters the neonatal circulation and can have specific physiological and epigenetic effects on target organs such as the female reproductive system. Nevertheless, there are large gaps in our knowledge and understanding of such lactocrine systems especially in regard to other neohormones, species, and neonatal organ systems.

Male Seminal Relaxin Contributes to Induction of the Post-mating Cytokine Response in the Female Mouse Uterus

The hormone relaxin is important in female reproduction for embryo implantation, cardiovascular function, and during labor and lactation. Relaxin is also synthesized in males by organs of the male tract. We hypothesized that relaxin might be one component of seminal plasma responsible for eliciting the female cytokine response induced in the uterus at mating. When recombinant relaxin was injected into the uterus of wild-type (Rln^+/+) mice at estrus, it evoked the production of Cxcl1 mRNA and its secreted protein product CXCL1 in four of eight animals. Mating experiments were then conducted using mice with a null mutation in the relaxin gene (Rln^−/− mice). qRT-PCR analysis of mRNA expression in wild-type females showed diminished uterine expression of several cytokine and chemokine genes in the absence of male relaxin. Similar differences were also noted comparing Rln^−/− and Rln^+/+ females mated to wild-type males. Quantification of uterine luminal fluid cytokine content confirmed that male relaxin provokes the production of CXCL10 and CSF3 in Rln^+/+ females. Differences were also seen comparing Rln^−/− and Rln^+/+ females mated with Rln^−/− males for CXCL1, CSF3, and CCL5, implying that endogenous relaxin in females might prime the uterus to respond appropriately to seminal fluid at coitus. Finally, pan-leukocyte CD45 mRNA was increased in wild-type matings compared to other combinations, implying that male and female relaxin may trigger leukocyte expansion in the uterus. We conclude that male and/or female relaxin may be important in activating the uterine cytokine/chemokine network required to initiate maternal immune adaptation to pregnancy.

Relaxin-Family Peptide Receptors 1 and 2 Are Fully Functional in the Bovine

In most mammals the peptide hormone relaxin is a key physiological component regulating early pregnancy and birth. However, synteny analysis shows that the gene encoding ovarian relaxin-2 is deleted in cows and sheep. While, these ruminants appear to exhibit a relaxin-like physiology, as in other mammals, until now a molecular understanding of this has been lacking. Cloning and expression analysis of the cognate bovine receptor for relaxin, RXFP1, as well as of the structurally related receptor, RXFP2, in female tissues, shows that these are expressed in a similar way to other mammals. RXFP1 transcripts are found in ovarian theca cells, endometrium, and myometrium, whereas RXFP2 transcripts are expressed in ovarian theca cells, oocytes, as well as in myometrium. Transfection of receptor-expressing gene constructs into HEK293 cells indicates that bovine RXFP1 has a greater EC50 at 10–50 nM for porcine or human relaxin, compared to human RXFP1. For bovine RXFP2, in contrast, the EC50 is <1 nM for its cognate ligand, bovine INSL3, but also 10–30 nM for porcine or human relaxin. Functional analysis shows that bovine myometrial cells are able to respond to exogenous relaxin and INSL3 with a significant increase in cAMP. Although expressing mRNA for both RXFP1 and RXFP2, bovine follicular theca cells only respond to INSL3 with a dose-dependent increase in cAMP. Altogether the results suggest that the cow is able to compensate for the missing hormone, and moreover imply that relaxin analogs could offer an important therapeutic option in treating female ruminant infertility.

Relaxin-like peptides in male reproduction - a human perspective

The relaxin family of peptide hormones and their cognate GPCRs are becoming physiologically well-characterized in the cardiovascular system and particularly in female reproductive processes. Much less is known about the physiology and pharmacology of these peptides in male reproduction, particularly as regards humans. H2-relaxin is involved in prostate function and growth, while insulin-like peptide 3 (INSL3) is a major product of the testicular Leydig cells and, in the adult, appears to modulate steroidogenesis and germ cell survival. In the fetus, INSL3 is a key hormone expressed shortly after sex determination and is responsible for the first transabdominal phase of testicular descent. Importantly, INSL3 is becoming a very useful constitutive biomarker reflecting both fetal and post-natal development. Nothing is known about roles for INSL4 in male reproduction and only very little about relaxin-3, which is mostly considered as a brain peptide, or INSL5. The former is expressed at very low levels in the testes, but has no known physiology there, whereas the INSL5 knockout mouse does exhibit a testicular phenotype with mild effects on spermatogenesis, probably due to a disruption of glucose homeostasis. INSL6 is a major product of male germ cells, although it is relatively unexplored with regard to its physiology or pharmacology, except that in mice disruption of the INSL6 gene leads to a disruption of spermatogenesis. Clinically, relaxin analogues may be useful in the control of prostate cancer, and both relaxin and INSL3 have been considered as sperm adjuvants for in vitro fertilization.

LINKED ARTICLES

This article is part of a themed section on Recent Progress in the Understanding of Relaxin Family Peptides and their Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.10/issuetoc.

A common effect of angiotensin II and relaxin 2 on the PNT1A normal prostate epithelial cell line

The prostate gland is a part of the male reproductive tract which produces both angiotensin II (Ang II) and relaxin 2 (RLN2). The present study analyzes the effect of both these peptide hormones at concentration 10(-8)M on viability, proliferation, adhesion, migration, and invasion of normal prostate epithelial cells (PNT1A). Improved survival in two- and three-dimensional cell cultures was noted as well as visual changes in colony size and structure in Geltrex™. Stimulatory influence on cell viability of each peptide applied single was lower than in combination. Enhanced survival of PNT1A cells appears to be associated with increased BCL2/BAX messenger RNA (mRNA) expression ratio. Modulation of cell spreading and cell-extracellular matrix adhesion dynamics were also altered as an influence of tested hormone application. However, long-term Ang II and RLN2 effects may lead to an increase of normal prostate cell migration and invasion abilities. Moreover, gelatin zymography revealed that both gelatinases A and B were augmented by Ang II treatment, whereas RLN2 significantly stimulated only MMP-9 secretion. These results support the hypothesis that deregulation of locally secreted peptide hormones such as Ang II and RLN2 may take part in the development of certain cancers, including prostate cancer. Moreover, the observed ability of relaxin 2 to act as a regulator of mRNA expression levels not only LGR7 but also classic angiotensin receptors suggested that renin-angiotensin system and relaxin family peptide system are functionally linked.

Sex-specific regulation of Lgr3 in Drosophila neurons

The development of sexually dimorphic morphology and the potential for sexually dimorphic behavior in Drosophila are regulated by the Fruitless (Fru) and Doublesex (Dsx) transcription factors. Several direct targets of Dsx have been identified, but direct Fru targets have not been definitively identified. We show that Drosophila leucine-rich repeat G protein-coupled receptor 3 (Lgr3) is regulated by Fru and Dsx in separate populations of neurons. Lgr3 is a member of the relaxin-receptor family and a receptor for Dilp8, necessary for control of organ growth. Lgr3 expression in the anterior central brain of males is inhibited by the B isoform of Fru, whose DNA binding domain interacts with a short region of an Lgr3 intron. Fru A and C isoform mutants had no observed effect on Lgr3 expression. The female form of Dsx (Dsx(F)) separately up- and down-regulates Lgr3 expression in distinct neurons in the abdominal ganglion through female- and male-specific Lgr3 enhancers. Excitation of neural activity in the Dsx(F)-up-regulated abdominal ganglion neurons inhibits female receptivity, indicating the importance of these neurons for sexual behavior. Coordinated regulation of Lgr3 by Fru and Dsx marks a point of convergence of the two branches of the sex-determination hierarchy.

Relaxin in Obstructive Sleep Apnea: Relationship with Blood Pressure and Inflammatory Mediators

BACKGROUND

Obstructive sleep apnea (OSA) is associated with nocturnal intermittent hypoxia, which may be responsible for increased circulating levels of vascular endothelial growth factor (VEGF) and inflammatory mediators, such as metalloproteinases (MMPs), and which contributes to the pathogenesis of systemic hypertension. Why some OSA patients remain normotensive is poorly understood. Relaxin-2, a pregnancy hormone, may sometimes circulate in men and could increase in hypoxic conditions. It exerts a vasodilatory activity and can modulate the release of molecules, such as MMPs and VEGF.

OBJECTIVES

The objective of this study was to explore if circulating relaxin-2 in male OSA subjects may be related to OSA severity, to circulating levels of MMPs, of their inhibitors (tissue inhibitors of metalloproteinases; TIMPs), and of VEGF, and if it may protect from hypertension.

PATIENTS AND METHODS

Fifty untreated male subjects with suspected OSA were recruited. After nocturnal polysomnography, a morning venous blood sample was withdrawn. Then, 24-hour ambulatory blood pressure (BP) monitoring was performed.

RESULTS

The respiratory disturbance index in the sample was 30.4 [interquartile range (IQR) 15.6-55.2]. Relaxin-2 was detectable in 20 subjects. These subjects did not differ in OSA severity or diurnal and nocturnal BP from subjects with undetectable relaxin-2, but they showed lower TIMP-1 (126.8 ± 29.1 vs. 156.9 ± 41.7 pg/ml, respectively; p = 0.007) and a marginally higher MMP-9/TIMP-1 molar ratio [0.58 (IQR 0.23-1.35) vs. 0.25 (IQR 0.15-0.56); p = 0.052].

CONCLUSIONS

Relaxin-2 in male subjects was not related to OSA severity, but it was associated with lower TIMP-1. As it was often undetectable, even when BP values were normal, it is unlikely that it plays a role as a major factor protecting from hypertension in OSA.

Expression profiles of relaxin family peptides and their receptors indicate their influence on spermatogenesis in the domestic cat (Felis catus)

Disturbed spermatogenesis is a common problem in felines. Studying spermatogenesis in the domestic cat can improve the understanding of the biological background and help to counteract fertility problems in other feline species. Here, we analyzed 3 relaxin family peptides (relaxin, relaxin-3, and INSL3) and their receptors (RXFP1, RXFP2, and RXFP3) as potential spermatogenic factors involving their expression in the testis at different stages of its development. It may be concluded from its stage-dependent expression that relaxin, together with RXFP1, appears to be involved in the first stage of spermatogenesis, whereas relaxin-3 via binding to RXFP3 influences spermiogenesis. Furthermore, correlations were observed between relaxin, relaxin-3, RXFP1, RXFP2 and RXFP3 messenger RNA expression, and the relative numbers of haploid cells in testes. The peptide INSL3 was highly expressed at all testis development stages. Because of the low and stage-independent expression of its receptor RXFP2, an auto- and/or paracrine function of INSL3 in spermatogenesis seems unlikely. In the adult testis, messenger RNA expression of relaxin, RXFP1, and RXFP3 predominantly occurs in the tubular testis compartment, whereas INLS3 is mainly expressed in the interstitium.

Profiling of relaxin and its receptor proteins in boar reproductive tissues and spermatozoa

BACKGROUND

Relaxin levels in seminal plasma have been associated with positive effects on sperm motility and quality, and thus having potential roles in male fertility. However, the origin of seminal relaxin, within the male reproductive tract, and the moment of its release in the vicinity of spermatozoa remain unclear. Here, we assessed the longitudinal distribution of relaxin and its receptors RXFP1 and RXFP2 in the reproductive tract, sex accessory glands, and spermatozoa of adult boars.

METHODS

Spermatozoa were harvested from three fertile boars and reproductive tract (testes and epididymis) and sex accessory gland (prostate and seminal vesicles) tissues were collected post-mortem from each boar. Epididymis ducts were sectioned into caput, corpus, and cauda regions, and spermatozoa were mechanically collected. All samples were subjected to immunofluorescence and/or western immunoblotting for relaxin, RXFP1, and RXFP2 detection. Immunolabeled-spermatozoa were submitted to flow cytometry analyses and data were statistically analyzed with ANOVA.

RESULTS

Both receptors were detected in all tissues, with a predominance of mature and immature isoforms of RXFP1 and RXFP2, respectively. Relaxin signals were found in the testes, with Leydig cells displaying the highest intensity compared to other testicular cells. The testicular immunofluorescence intensity of relaxin was greater than that of other tissues. Epithelial basal cells exhibited the highest relaxin immunofluorescence intensity within the epididymis and the vas deferens. The luminal immunoreactivity to relaxin was detected in the seminiferous tubule, epididymis, and vas deferens ducts. Epididymal and ejaculated spermatozoa were immunopositive to relaxin, RXFP1, and RXFP2, and epididymal corpus-derived spermatozoa had the highest immunoreactivities across epididymal sections. Both vas deferens-collected and ejaculated spermatozoa displayed comparable, but lowest immunofluorescence signals among groups. The entire sperm length was immunopositive to both relaxin and receptors, with relaxin signal being robust in the acrosome area and RXFP2, homogeneously distributed than RXFP1 on the head of ejaculated spermatozoa.

CONCLUSIONS

Immunolocalization indicates that relaxin-receptor complexes may have important roles in boar reproduction and that spermatozoa are already exposed to relaxin upon their production. The findings suggest autocrine and/or paracrine actions of relaxin on spermatozoa, either before or after ejaculation, which have possible roles on the fertilizing potential of spermatozoa.

Beneficial effects of relaxin on motility characteristics of stored boar spermatozoa

BACKGROUND

Relaxin is detected in seminal plasma of many species and its association with sperm motility may be beneficial in some aspects of assisted reproduction. Here, we immunolocalized relaxin receptors and investigated the effects of exogenous relaxin on motility characteristics, viability, and cAMP content of boar spermatozoa after storage.

METHODS

Commercial doses of boar semen were obtained on the collection day (Day 0) and kept in shipping containers at room temperature for up to 4 days (Day 4). On Day 0, spermatozoa were fixed for immunofluorescence detection of relaxin receptors RXFP1 and RXFP2 (Experiment 1). Semen aliquots were taken from the same dose at Day 0, Day 1, and Day 2 (Experiment 2a), and Day 2 and Day 4 (Experiment 2b) for analyses. Alive spermatozoa were purified and incubated (1 h-37°C) with 0, 50, or 100 ng relaxin/ml (Experiment 2a) and 0, 100, or 500 ng relaxin/ml (Experiment 2b). Afterward, aliquots of each treatment group were subjected to motility (Experiments 2), viability (Experiment 3) analyses, and cAMP quantification (Experiment 4). Data (3-4 independent replicates) were statistically analyzed (ANOVA followed by pairwise comparisons) and p values less or equal to 0.05 was set for significant difference.

RESULTS

Both RXFP1 and RXFP2 receptors were immunolocalized on the entire spermatozoon. Relaxin concentration of 100 ng/ml significantly improved the proportions of motile, progressive, and rapid spermatozoa up to Day 2. Only 500 ng relaxin/ml provided beneficial effects on Day 4. The viability of spermatozoa was not affected by relaxin (100 ng/ml) during storage, but the extent of mitochondria membrane damages was significantly decreased. Furthermore, relaxin did not affect the cAMP contents of spermatozoa during storage, in our conditions.

CONCLUSIONS

Relaxin could be a valuable motility booster of stored- or aged-spermatozoa for assisted reproduction techniques. However, the related-intracellular signaling cascades of relaxin in boar spermatozoa remain undetermined.

The relaxin family peptide receptors and their ligands: new developments and paradigms in the evolution from jawless fish to mammals

Relaxin family peptide receptors (Rxfps) and their ligands, relaxin (Rln) and insulin-like (Insl) peptides, are broadly implicated in the regulation of reproductive and neuroendocrine processes in mammals. Most placental mammals harbour genes for four receptors, namely rxfp1, rxfp2, rxfp3 and rxfp4. The number and identity of rxfps in other vertebrates are immensely variable, which is probably attributable to intraspecific variation in reproductive and neuroendocrine regulation. Here, we highlight several interesting, but greatly overlooked, aspects of the rln/insl-rxfp evolutionary history: the ancient origin, recruitment of novel receptors, diverse roles of selection, differential retention and lineage-specific loss of genes over evolutionary time. The tremendous diversity of rln/insl and rxfp genes appears to have arisen from two divergent receptors and one ligand that were duplicated by whole genome duplications (WGD) in early vertebrate evolution, although several genes, notably relaxin in mammals, were also duplicated via small scale duplications. Duplication and loss of genes have varied across lineages: teleosts retained more WGD-derived genes, dominated by those thought to be involved in neuroendocrine regulation (rln3, insl5 and rxfp 3/4 genes), while eutherian mammals witnessed the diversification and rapid evolution of genes involved in reproduction (rln/insl3). Several genes that arose early in evolutionary history were lost in most mammals, but retained in teleosts and, to a lesser extent, in early diverging tetrapods. To elaborate on their evolutionary history, we provide updated phylogenies of the Rxfp1/2 and Rxfp3/4 receptors and their ligands, including new sequences from early diverging vertebrate taxa such as coelacanth, skate, spotted gar, and lamprey. We also summarize the recent progress made towards understanding the functional biology of Rxfps in non-mammalian taxa, providing a new conceptual framework for research on Rxfp signaling across vertebrates.

Evolution of the relaxin/insulin-like gene family in anthropoid primates

The relaxin/insulin-like gene family includes signaling molecules that perform a variety of physiological roles mostly related to reproduction and neuroendocrine regulation. Several previous studies have focused on the evolutionary history of relaxin genes in anthropoid primates, with particular attention on resolving the duplication history of RLN1 and RLN2 genes, which are found as duplicates only in apes. These studies have revealed that the RLN1 and RLN2 paralogs in apes have a more complex history than their phyletic distribution would suggest. In this regard, alternative scenarios have been proposed to explain the timing of duplication, and the history of gene gain and loss along the organismal tree. In this article, we revisit the question and specifically reconstruct phylogenies based on coding and noncoding sequence in anthropoid primates to readdress the timing of the duplication event giving rise to RLN1 and RLN2 in apes. Results from our phylogenetic analyses based on noncoding sequence revealed that the duplication event that gave rise to the RLN1 and RLN2 occurred in the last common ancestor of catarrhine primates, between ∼44.2 and 29.6 Ma, and not in the last common ancestor of apes or anthropoids, as previously suggested. Comparative analyses based on coding and noncoding sequence suggests an event of convergent evolution at the sequence level between co-ortholog genes, the single-copy RLN gene found in New World monkeys and the RLN1 gene of apes, where changes in a fraction of the convergent sites appear to be driven by positive selection.

Targeting the relaxin hormonal pathway in prostate cancer

Targeting the androgen signalling pathway has long been the hallmark of anti-hormonal therapy for prostate cancer. However, development of androgen-independent prostate cancer is an inevitable outcome to therapies targeting this pathway, in part, owing to the shift from cancer dependence on androgen signalling for growth in favor of augmentation of other cellular pathways that provide proliferation-, survival- and angiogenesis-promoting signals. This review focuses on the role of the hormone relaxin in the development and progression of prostate cancer, prior to and after the onset of androgen independence, as well as its role in cancers of other reproductive tissues. As the body of literature expands, examining relaxin expression in cancerous tissues and its role in a growing number of in vitro and in vivo cancer models, our understanding of the important involvement of this hormone in cancer biology is becoming clearer. Specifically, the pleiotropic functions of relaxin affecting cell growth, angiogenesis, blood flow, cell migration and extracellular matrix remodeling are examined in the context of cancer progression. The interactions and intercepts of the intracellular signalling pathways of relaxin with the androgen pathway are explored in the context of progression of castration-resistant and androgen-independent prostate cancers. We provide an overview of current anti-hormonal therapeutic treatment options for prostate cancer and delve into therapeutic approaches and development of agents aimed at specifically antagonizing relaxin signalling to curb tumor growth. We also discuss the rationale and challenges utilizing such agents as novel anti-hormonals in the clinic, and their potential to supplement current therapeutic modalities.

Relaxin protects astrocytes from hypoxia in vitro

The peptide relaxin has recently been shown to protect brain tissues from the detrimental effects of ischemia. To date, the mechanisms for this remain unclear. In order to investigate the neuroprotective mechanisms by which relaxin may protect the brain, we investigated the possibility that relaxin protects astrocytes from hypoxia or oxygen/glucose deprivation (OGD). Cultured astrocytes were pre-treated with either relaxin-2 or relaxin-3 and exposed to OGD for 24 or 48 hours. Following OGD exposure, viability assays showed that relaxin-treated cells exhibited a higher viability when compared to astrocytes that experienced OGD-alone. Next, to test whether relaxin reduced the production of reactive oxygen species (ROS) astrocytes were exposed to the same conditions as the previous experiment and a commercially available ROS detection kit was used to detect ROS production. Astrocytes that were treated with relaxin-2 and relaxin-3 showed a marked decrease in ROS production when compared to control astrocytes that were exposed only to OGD. Finally, experiments were performed to determine whether or not the mitochondrial membrane potential was affected by relaxin treatment during 24 hour OGD. Mitochondrial membrane potential was higher in astrocytes that were treated with relaxin-2 and relaxin-3 compared to untreated OGD-alone astrocytes. Taken together, these data present novel findings that show relaxin protects astrocytes from ischemic conditions through the reduction of ROS production and the maintenance of mitochondrial membrane potential.

Regulation of the reproductive cycle and early pregnancy by relaxin family peptides

The relaxin family of peptide hormones are structurally closely related to one another sharing a heterodimeric A-B structure, like that of insulin. They may also be active as unprocessed B-C-A pro-forms. Relaxin has been shown to pay a key role within the ovary, being involved in follicle growth, and ovulation. Relaxin is produced in large amounts also by the corpus luteum where it acts as an endocrine hormone positively affecting implantation, placentation and vascularization during the all-important first trimester phase of pregnancy establishment. Relaxin exerts its functions via the receptor RXFP1. Insulin-like peptide 3 (INSL3) in contrast acts through the related receptor RXFP2, and plays an essential role in the production of androgens within growing antral follicles. INSL3 is also produced in large amounts by the male fetus shortly after sex determination, where it controls the first transabdominal phase of testicular descent. However, this fetal INSL3 is also able to influence placental and maternal physiology, indicating associations with later preeclampsia and/or fetal growth restriction. Other members of this relaxin-like family of peptides, such as INSL4, INSL5 and INSL6 are less well studied, though all suggest modulatory roles in ovarian and/or placental function.

Insulin-Like Factor 3 and the HPG Axis in the Male

The hypothalamic-pituitary-gonadal (HPG) axis comprises pulsatile GnRH from the hypothalamus impacting on the anterior pituitary to induce expression and release of both LH and FSH into the circulation. These in turn stimulate receptors on testicular Leydig and Sertoli cells, respectively, to promote steroidogenesis and spermatogenesis. Both Leydig and Sertoli cells exhibit negative feedback to the pituitary and/or hypothalamus via their products testosterone and inhibin B, respectively, thereby allowing tight regulation of the HPG axis. In particular, LH exerts both acute control on Leydig cells by influencing steroidogenic enzyme activity, as well as chronic control by impacting on Leydig cell differentiation and gene expression. Insulin-like peptide 3 (INSL3) represents an additional and different endpoint of the HPG axis. This Leydig cell hormone interacts with specific receptors, called RXFP2, on Leydig cells themselves to modulate steroidogenesis, and on male germ cells, probably to synergize with androgen-dependent Sertoli cell products to support spermatogenesis. Unlike testosterone, INSL3 is not acutely regulated by the HPG axis, but is a constitutive product of Leydig cells, which reflects their number and/or differentiation status and their ability therefore to produce various factors including steroids, together this is referred to as Leydig cell functional capacity. Because INSL3 is not subject to the acute episodic fluctuations inherent in the HPG axis itself, it serves as an excellent marker for Leydig cell differentiation and functional capacity, as in puberty, or in monitoring the treatment of hypogonadal patients, and at the same time buffering the HPG output.

Antibody selection for immunocytochemical characterization of the male reproductive system in Psittaciformes

The success of breeding programs is limited by the sparse knowledge about endocrine regulation and biochemical reactions in the psittacine male tract. The immunocytochemical analysis of parrots' testicular tissues provides an insight into their reproductive system but is often hampered by the lack of reliable antibodies. In the present study, we tested a large panel of antibodies raised against steroid receptors, steroidogenic enzymes, relaxin peptides including their receptors, and proliferation markers on paraffin sections of testicular tissue from eight psittacine genera representing three continents. All investigated species displayed the tested markers in somatic and germ cells of testis and epididymis, even though cell distribution was partly heterogenous and in species-specific patterns. The 17β-hydroxysteroid-dehydrogenase-2, 3β-hydroxysteroid-dehydrogenase, and smooth muscle actin allowed the cross-species differentiation between active and nonactive gonads. The remaining steroidogenic enzymes, steroid receptors, relaxin peptides, and Ki67 proved to be suitable to define reproductive activity depending on the parrot species. Adapting immunocytochemical methods to different psittacines was successful, though various cellular expression patterns do not allow the transfer of results among different parrot species. However, the availability of a reliable repertory of sexual markers is important to examine reproductive biology of psittacine birds.

The active form of goat insulin-like peptide 3 (INSL3) is a single-chain structure comprising three domains B-C-A, constitutively expressed and secreted by testicular Leydig cells

Relaxin-like factor (RLF), also called insulin-like peptide 3 (INSL3), is a member of the insulin/relaxin gene family and is produced by testicular Leydig cells. While the understanding of its effects is growing, very little is known about the structural and functional properties of native INSL3. Here, we demonstrate that native INSL3 isolated from goat testes is a single-chain structure with full biological activity, and is constitutively expressed and secreted by Leydig cells. Using a series of chromatography steps, native INSL3 was highly purified as a single 12-kDa peak as revealed by SDS-PAGE. MS/MS analysis provided 81% sequence coverage and revealed a distinct single-chain structure consisting of the B-, C-, and A-domains deduced previously from the INSL3 cDNA sequence. Moreover, the N-terminal peptide was six amino acid residues longer than predicted. Native INSL3 exhibited full bioactivity in HEK-293 cells expressing the receptor for INSL3. Immunoelectron microscopy and Western blot analysis revealed that INSL3 was secreted by Leydig cells through the constitutive pathway into blood and body fluids. We conclude, therefore, that goat INSL3 is constitutively secreted from Leydig cells as a B-C-A single-chain structure with full biological activity.

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.

Relaxin induces matrix-metalloproteinases-9 and -13 via RXFP1: induction of MMP-9 involves the PI3K, ERK, Akt and PKC-ζ pathways

We determined the precise role of relaxin family peptide (RXFP) receptors-1 and -2 in the regulation of MMP-9 and -13 by relaxin, and delineated the signaling cascade that contributes to relaxin's modulation of MMP-9 in fibrocartilaginous cells. Relaxin treatment of cells in which RXFP1 was silenced resulted in diminished induction of MMP-9 and -13 by relaxin, whereas overexpression of RXFP1 potentiated the relaxin-induced expression of these proteinases. Suppression or overexpression of RXFP2 resulted in no changes in the relaxin-induced MMP-9 and -13. Studies using chemical inhibitors and siRNAs to signaling molecules showed that PI3K, Akt, ERK and PKC-ζ and the transcription factors Elk-1, c-fos and, to a lesser extent, NF-κB are involved in relaxin's induction of MMP-9. Our findings provide the first characterization of signaling cascade involved in the regulation of any MMP by relaxin and offer mechanistic insights on how relaxin likely mediates extracellular matrix turnover.

New insights into ligand-receptor pairing and coevolution of relaxin family peptides and their receptors in teleosts

Relaxin-like peptides (RLN/INSL) play diverse roles in reproductive and neuroendocrine processes in placental mammals and are functionally associated with two distinct types of receptors (RXFP) for each respective function. The diversification of RLN/INSL and RXFP gene families in vertebrates was predominantly driven by whole genome duplications (2R and 3R). Teleosts preferentially retained duplicates of genes putatively involved in neuroendocrine regulation, harboring a total of 10-11 receptors and 6 ligand genes, while most mammals have equal numbers of ligands and receptors. To date, the ligand-receptor relationships of teleost Rln/Insl peptides and their receptors have largely remained unexplored. Here, we use selection analyses based on sequence data from 5 teleosts and qPCR expression data from zebrafish to explore possible ligand-receptor pairings in teleosts. We find support for the hypothesis that, with the exception of RLN, which has undergone strong positive selection in mammalian lineages, the ligand and receptor genes shared between mammals and teleosts appear to have similar pairings. On the other hand, the teleost-specific receptors show evidence of subfunctionalization. Overall, this study underscores the complexity of RLN/INSL and RXFP ligand-receptor interactions in teleosts and establishes theoretical background for further experimental work in nonmammals.

Intracellular signaling pathways involved in the relaxin-induced proliferation of rat Sertoli cells

Regulation of Sertoli cell number is a key event to determine normal spermatogenesis. We have previously shown that relaxin and its G-protein coupled receptor RXFP1 are expressed in rat Sertoli cells, and that relaxin stimulates Sertoli cell proliferation. This study examined the mechanisms underlying the mitogenic effect of relaxin in a primary culture of Sertoli cells removed from testes of immature rats. Stimulation with exogenous relaxin increased Sertoli cell number and the expression of the proliferating cell nuclear antigen (PCNA), but did not affect the mRNA level of the differentiation markers cadherins 1 and 2. Relaxin-induced Sertoli cell proliferation was blocked by inhibition of MEK/ERK1/2 or PI3K/AKT pathways, but not by inhibition of PKC or EGFR activity. Relaxin induced a rapid and transient activation of ERK1/2 phosphorylation, which was MEK and SRC-dependent, and involved upstream activation of G(i). AKT activation could be detected 5 min after relaxin stimulation, and was still detected after 24h of stimulation with relaxin. Relaxin-induced AKT phosphorylation was G(i)- but not PKA-dependent, and it was blocked by both PI3K and MEK inhibitors. In conclusion, the mitogenic effect of relaxin in Sertoli cell involves coupling to G(i) and activation of both MEK/ERK1/2 and PI3K/AKT pathways.

Heterozygous deletion at the RLN1 locus in a family with testicular germ cell cancer identified by integrating copy number variation data with phenome and interactome information

To search for disease-related copy number variations (CNVs) in families with a high frequency of germ cell tumours (GCT), we analysed 16 individuals from four families by array comparative genomic hybridization (aCGH) and applied an integrative systems biology algorithm that prioritizes risk-associated genes among loci targeted by CNVs. The top-ranked candidate, RLN1, encoding a Relaxin-H1 peptide, although only detected in one of the families, was selected for further investigations. Validation of the CNV at the RLN1 locus was performed as an association study using qPCR with 106 sporadic testicular GCT patients and 200 healthy controls. Observed CNV frequencies of 1.9% among cases and 1.5% amongst controls were not significantly different and this was further confirmed by CNV data extracted from a genome-wide analysis of 189 cases and 380 controls, where similar frequencies of 2.2% were observed in both groups (p=1). Immunohistochemistry for Relaxin-H1 (RLN1), Relaxin-H2 (RLN2) and their cognate receptor, RXFP1, detected one, and in some cases both, of the relaxins in Leydig cells, Sertoli cells and a subset of neoplastic germ cells, whereas the receptor was present in Leydig cells and spermatids. Collectively, the findings show that a heterozygous loss at the RLN1 locus is not a genetic factor mediating high population-wide risk for testicular germ cell tumour, but do not exclude a contribution of this aberration in some cases of cancer. The preliminary expression data suggest a possible role of the relaxin peptides in spermatogenesis and warrant further studies.

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.

R171H missense mutation of INSL6 in a patient with spermatogenic failure

Insulin-like peptide 6 (INSL6) is a newly identified insulin/relaxin family peptide hormone that is predominantly expressed by the male germ cells in testes. A recent murine study demonstrated that INSL6-knockout results in spermatogenic failure. In the present study, human INSL6 gene was screened for mutations that may contribute to human spermatogenic failure. Of 249 patients and 249 healthy control subjects, a heterozygous R171H missense mutation was found in one patient. The R171H mutation probably disturbed the in vivo processing of the INSL6 prohormone because it was located at the absolutely conserved tetrabasic cleavage site between the C-peptide and the A-chain, therefore the R171H missense mutation might be responsible for human spermatogenic failure.