Relaxin

Relaxin is one of the 6-kDa peptide hormones, which acts as a pleiotropic endocrine and paracrine factor. Our previous studies revealed that sperm capacitating medium containing relaxin induced capacitation and acrosome reaction (AR) in fresh and frozen-thawed porcine or bovine spermatozoa. However, the intracellular signaling cascades involved with capacitation or AR induced by relaxin was unknown. Therefore, the present study was designed to investigate the intracellular signaling cascades involved with capacitation and AR induced by relaxin in fresh and frozen-thawed bovine spermatozoa. Spermatozoa were incubated in sperm Tyrode's albumin lactate pyruvate (Sp-TALP) medium supplemented with (40 ng ml(-1)) or without relaxin, and subjected to evaluation of chlortetracycline staining pattern, cholesterol efflux, Ca(2+)-influx, intracellular cyclic adenosine monophosphate (cAMP) and protein tyrosine phosphorylation. Capacitation and AR were increased (P<0.05) in both fresh and frozen-thawed spermatozoa incubated with relaxin. Cholesterol effluxes were greater in the fresh (P<0.01) and frozen-thawed (P<0.05) spermatozoa incubated with relaxin than the spermatozoa incubated without relaxin. Ca(2+)-influxes were also significantly stimulated by relaxin in the fresh (P<0.01) and frozen-thawed (P<0.05) spermatozoa. The Sp-TALP medium containing relaxin influenced the generation of intracellular cAMP in the fresh (P<0.01) and frozen-thawed (P<0.05) spermatozoa, and exhibited higher exposure of protein tyrosine phosphorylation in both sperm types than the medium devoid of relaxin. Therefore, the results postulate that relaxin exerts the intracellular signaling cascades involved with capacitation and AR through accelerating the cholesterol efflux, Ca(2+)-influx, intracellular cAMP and protein tyrosine phosphorylation in fresh and frozen-thawed bovine spermatozoa.

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, notabl...

Although originally characterised as a reproductive hormone, relaxin has emerged as a multi-functional endocrine and paracrine factor that plays a number of important roles in several organs, including the normal and diseased cardiovascular system. The recent discovery of the H3/relaxin-3 gene, and the elusive receptors for relaxin (Relaxin family peptide receptor; RXFP1) and relaxin-3 (RXFP3/RXFP4) have led to the re-classification of a distinct relaxin peptide/receptor family. Additionally, the identification of relaxin and RXFP1 mRNA and/or relaxin binding sites in the heart and blood vessels has confirmed that the cardiovascular system is a target for relaxin peptides. While evidence for the production of relaxins within the cardiovascular system is limited, several studies have established that the relaxin genes are upregulated in the diseased human and rodent heart where they likely act as cardioprotective agents. The ability of relaxin to protect the heart is most likely medi...

Relaxin is a polypeptide hormone involved in remod-eling of the birth canal during parturition. It is syn-thesized as a preprohormone precursor, which undergoes specific processing to form the mature two-chain disulfide-linked active species that is se-creted by the cell. A ...

In pregnancy, blood volume increases greatly and plasma osmolality is reduced, due to mild hyponatraemia despite sodium retention. In rats, both vasopressin and oxytocin neurones in the supraoptic nucleus are osmosensitive and have contrasting roles in these adaptations. Increased vasopressin secretion stimulates water retention by renal actions, while oxytocin is natriuretic, partly by stimulating cardiac atrial natriuretic peptide (ANP) secretion. In pregnancy, relaxin from the corpora lutea, acting via the lamina terminalis in the presence of pregnancy levels of oestrogen and progesterone, stimulates vasopressin secretion and drinking, resulting in hypervolaemia and hyponatraemia. Initial stimulation of oxytocin secretion by relaxin is lost in late pregnancy, and oxytocin neurone responses to modest osmotic stimulation are reduced. Consequently, with reduced ANP secretion and action, sodium is retained and hypervolaemia maintained. Oxytocin neurone responses to other inputs, from...

Nanoluciferase (NanoLuc) is a newly developed small luciferase reporter with the brightest bioluminescence to date. In the present work, we developed NanoLuc as a sensitive bioluminescent reporter to measure quantitatively the internalization of cell membrane receptors, based on the pH dependence of the reporter activity. The G protein-coupled receptor RXFP3, the cognate receptor of relaxin-3/INSL7, was used as a model receptor. We first generated stable HEK293T cells that inducibly coexpressed a C-terminally NanoLuc-tagged human RXFP3 and a C-terminally enhanced green fluorescent protein (EGFP)-tagged human RXFP3. The C-terminal EGFP-tag and NanoLuc-tag had no detrimental effects on the ligand-binding potency and intracellular trafficking of RXFP3. Based on the fluorescence of the tagged EGFP reporter, the ligand-induced RXFP3 internalization was visualized directly under a fluorescence microscope. Based on the bioluminescence of the tagged NanoLuc reporter, the ligand-induced RXFP...

Circulating relaxin levels have repeatedly been associated with preterm birth (PTB). Our aim was to investigate if mothers carrying promoter single nucleotide polymorphisms (SNPs) in one of the three relaxin genes (RLN1, RLN2, RLN3) are predisposed for PTB. Maternal DNA from 80 preterm cases (40 very preterm births (24-34 weeks) and 40 moderate preterm (34-36 weeks) and 40 controls (term delivery)) nested in the Danish National Birth Cohort were examined for nine SNPs. Maternal homozygosity of the rarer allele in the relaxin 2 gene (RLN2, rs10115467 and rs4742076) had an increased risk of moderate PTB (odds ratio 4.1 [95% CI 1.4-12] and 8.8 [95% CI 1.03-75] respectively). Only rs10115467 remained significant after correction for multiple testing. Women homozygous for prevalent SNPs in the RLN2 gene may have a genetic susceptibility for PTB.

Serelaxin is a promising therapy for acute heart failure. The renal hemodynamic effects of serelaxin in patients with chronic heart failure are unknown. In this double-blind, randomized, placebo-controlled, multicenter study, patients with New York Heart Association Class II to III chronic heart failure, left ventricular ejection fraction ≤45%, and estimated glomerular filtration rate (GFR) 30 to 89 mL/min per 1.73 m(2) received intravenous serelaxin 30 μg/kg per day or placebo for 24 hours. Primarily, we assessed the difference between serelaxin and placebo on renal plasma flow (para-aminohippuric acid clearance) and GFR (iothalamate clearance) over 8 to 24 hours. All 22 patients from 1 clinical site were excluded from primary analyses before unblinding because of implausible measurements. The primary analysis comprised 65 patients, mean age was 68 (±10) years, 89% were male, mean estimated GFR was 64 (±19) mL/min per 1.73 m(2), and 34% had New York Heart Association Class III symp...

Relapse and hazardous drinking represent the most difficult clinical problems in treating patients with alcohol use disorders. Using a rat model of alcohol use and alcohol-seeking, we demonstrated that central administration of peptide antagonists for relaxin family peptide 3 receptor (RXFP3), the cognate receptor for the highly conserved neuropeptide, relaxin-3, decreased self-administration of alcohol in a dose-related manner and attenuated cue- and stress-induced reinstatement following extinction. By comparison, RXFP3 antagonist treatment did not significantly attenuate self-administration or reinstatement of sucrose-seeking, suggesting a selective effect for alcohol. RXFP3 is densely expressed in the stress-responsive bed nucleus of the stria terminalis, and bilateral injections of RXFP3 antagonist into the bed nucleus of the stria terminalis significantly decreased self-administration and stress-induced reinstatement of alcohol, suggesting that this brain region may, at least ...

Relaxin is a pleiotropic hormone with actions in reproductive and non-reproductive tissues, and has a role in tumor biology. It can promote growth, differentiation and invasiveness of different tumors, especially those that give bone metastases, and relaxin serum concentrations are increased in patients with bone metastasis. In osteolytic metastasis the destruction of bone is mediated by osteoclasts that are multinucleated cells derived from hematopoietic progenitors. We found that human hematopoietic precursors and mature osteoclasts express the relaxin receptor RXFP1. Then, we investigated the effects of relaxin on the differentiation, activation and gene expression of osteoclasts during in vitro osteoclastogenesis from human hematopoietic progenitor cells. Relaxin alone was able to induce the multistep differentiation process of human osteoclastogenesis with timing similar to that obtained with the classical stimulators of osteoclastogenesis RANKL, M-CSF and PTH. The expression profile of several osteoclast genes was studied with quantitative RT-PCR during the entire process of osteoclastogenesis. This analysis showed that relaxin induced genes that are implicated in the differentiation, survival and activation of osteoclasts. Relaxin-induced osteoclasts were fully differentiated, positive for tartrate resistant acid phosphatase and vitronectin receptor, expressing a typical F-actin ring and able to resorb the bone. Furthermore, relaxin induced the expression of its specific receptor RXFP1 in osteoclasts. This study demonstrates for the first time that relaxin is a potent stimulator of osteoclastogenesis from hematopoietic precursors and regulates the activity of mature osteoclasts, opening new perspectives on the role of this hormone in bone physiology, diseases and metastasis.