Improved chemical synthesis and demonstration of the relaxin receptor binding affinity and biological activity of mouse relaxin

Modulation of contextual fear acquisition and extinction by acute and chronic relaxin-3 receptor (RXFP3) activation in the rat retrosplenial cortex

The retrosplenial cortex (RSC) plays a central role in processing contextual fear conditioning. In addition to corticocortical and thalamocortical projections, the RSC receives subcortical inputs, including a substantial projection from the nucleus incertus in the pontine tegmentum. This GABAergic projection contains the neuropeptide, relaxin-3 (RLN3), which inhibits target neurons via its Gi/o-protein-coupled receptor, RXFP3. To assess this peptidergic system role in contextual fear conditioning, we bilaterally injected the RSC of adult rats with an adeno-associated-virus (AAV), expressing the chimeric RXFP3 agonist R3/I5 or a control AAV, and subjected them to contextual fear conditioning. The R3/I5 injected rats did not display any major differences to control-injected and naïve rats but displayed a significantly delayed extinction. Subsequently, we employed acute bilateral injections of the specific RXFP3 agonist peptide, RXFP3-Analogue 2 (A2), into RSC. While the administration of A2 before each extinction trial had no impact on the extinction process, treatment with A2 before each acquisition trial resulted in delayed extinction. In related anatomical studies, we detected an enrichment of RLN3-immunoreactive nerve fibers in deep layers of the RSC, and a higher level of co-localization of RXFP3 mRNA with vesicular GABA transporter (vGAT) mRNA than with vesicular glutamate transporter-1 (vGLUT1) mRNA across the RSC, consistent with an effect of RLN3/RXFP3 signalling on the intrinsic, inhibitory circuits within the RSC. These findings suggest that contextual conditioning processes in the RSC involve, in part, RLN3 afferent modulation of local inhibitory neurons that provides a stronger memory acquisition which, in turn, retards the extinction process.

Cardiomyocyte-specific RXFP1 overexpression protects against pressure overload-induced cardiac dysfunction independently of relaxin

Heart failure (HF) prevalence is rising due to reduced early mortality and demographic change. Relaxin (RLN) mediates protective effects in the cardiovascular system through Relaxin-receptor 1 (RXFP1). Cardiac overexpression of RXFP1 with additional RLN supplementation attenuated HF in the pressure-overload transverse aortic constriction (TAC) model. Here, we hypothesized that robust transgenic RXFP1 overexpression in cardiomyocytes (CM) protects from TAC-induced HF even in the absence of RLN. Hence, transgenic mice with a CM-specific overexpression of human RXFP1 (hRXFP1tg) were generated. Receptor functionality was demonstrated by in vivo hemodynamics, where the administration of RLN induced positive inotropy strictly in hRXFP1tg. An increase in phospholamban-phosphorylation at serine 16 was identified as a molecular correlate. hRXFP1tg were protected from TAC without additional RLN administration, presenting not only less decline in systolic left ventricular (LV) function but also abrogated LV dilation and pulmonary congestion compared to WT mice. Molecularly, transgenic hearts exhibited not only a significantly attenuated fetal and fibrotic gene activation but also demonstrated less fibrotic tissue and CM hypertrophy in histological sections. These protective effects were evident in both sexes. Similar cardioprotective effects of hRXFP1tg were detectable in a RLN-knockout model, suggesting an alternative mechanism of receptor activation through intrinsic activity, alternative endogenous ligands or crosstalk with other receptors. In summary, CM-specific RXFP1 overexpression provides protection against TAC even in the absence of endogenous RLN. This suggests RXFP1 overexpression as a potential therapeutic approach for HF, offering baseline protection with optional RLN supplementation for specific activation.

Total Chemical Synthesis of Aggregation-Prone Disulfide-Rich Starfish Peptides

A relaxin-like gonad-stimulating peptide (RGP), Aso-RGP, featuring six cysteine residues, was identified in the Crown-of-Thorns Starfish (COTS, Acanthaster cf. solaris) and initially produced through recombinant yeast expression. This method yielded a single-chain peptide with an uncleaved C-peptide (His Tag) and suboptimal purity. Our objective was to chemically synthesize Aso-RGP in its mature form, comprising two chains (A and B) and three disulfide bridges, omitting the C-peptide. Furthermore, we aimed to synthesize a newly identified relaxin-like peptide, Aso-RLP2, from COTS, which had not been previously synthesized. This paper reports the first total chemical synthesis of Aso-RGP and Aso-RLP2. Aso-RGP synthesis proceeded without major issues, whereas the A-chain of Aso-RLP2, in its reduced and unfolded state with two free thiols, presented considerable challenges. These were initially marked by "messy" RP-HPLC profiles, typically indicative of synthesis failure. Surprisingly, oxidizing the A-chain significantly improved the RP-HPLC profile, revealing the main issue was not synthesis failure but the peptide's aggregation tendency, which initially obscured analysis. This discovery highlights the critical need to account for aggregation in peptide synthesis and analysis. Ultimately, our efforts led to the successful synthesis of both peptides with purities exceeding 95 %.

Developing insulin-like peptide 5-based antagonists for the G protein-coupled receptor, RXFP4

Human insulin-like peptide 5 (INSL5) is a gut hormone produced by colonic L-cells, and its biological functions are mediated by Relaxin Family Peptide Receptor 4 (RXFP4). Our preliminary data indicated that RXFP4 agonists are potential drug leads for the treatment of constipation. More recently, we designed and developed a novel RXFP4 antagonist, A13-nR that was shown to block agonist-induced activity in cells and animal models. We showed that A13-nR was able to block agonist-induced increases in colon motility in mice of both genders that express the receptor, RXFP4. Our data also showed that colorectal propulsion induced by intracolonic administration of short-chain fatty acids was antagonized by A13-nR. Therefore, A13-nR is an important research tool and potential drug lead for the treatment of colon motility disorders, such as bacterial diarrhea. However, A13-nR acted as a partial agonist at high concentrations in vitro and demonstrated modest antagonist potency (∼35 nM). Consequently, the primary objective of this study is to pinpoint novel modifications to A13-nR that eliminate partial agonist effects while preserving or augmenting antagonist potency. In this work, we detail the creation of a series of A13-nR-modified analogues, among which analogues 3, 4, and 6 demonstrated significantly improved RXFP4 affinity (∼3 nM) with reduced partial agonist activity, enhanced antagonist potency (∼10 nM) and maximum agonist inhibition (∼80 %) when compared with A13-nR. These compounds have potential as candidates for further preclinical evaluations, marking a significant stride toward innovative therapeutics for colon motility disorders.

Development of a synthetic relaxin-3/INSL5 chimeric peptide ligand for NanoBiT complementation binding assays

INSL5 and relaxin-3 are relaxin family peptides with important roles in gut and brain function, respectively. They mediate their actions through the class A GPCRs RXFP4 and RXFP3. RXFP4 has been proposed to be a therapeutic target for colon motility disorders whereas RXFP3 targeting could be effective for neurological conditions such as anxiety. Validation of these targets has been limited by the lack of specific ligands and the availability of robust ligand-binding assays for their development. In this study, we have utilized NanoBiT complementation to develop a SmBiT-conjugated tracer for use with LgBiT-fused RXFP3 and RXFP4. The low affinity between LgBiT:SmBiT should result in a low non-specific luminescence signal and enable the quantification of binding without the tedious separation of non-bound ligands. We used solid-phase peptide synthesis to produce a SmBiT-labelled RXFP3/4 agonist, R3/I5, where SmBiT was conjugated to the B-chain N-terminus via a PEG12 linker. Both SmBiT-R3/I5 and R3/I5 were synthesized and purified in high purity and yield. Stable HEK293T cell lines expressing LgBiT-RXFP3 and LgBiT-RXFP4 were produced and demonstrated normal signaling in response to the synthetic R3/I5 peptide. Binding was first characterized in whole-cell binding kinetic assays validating that the SmBiT-R3/I5 bound to both cell lines with nanomolar affinity with minimal non-specific binding without bound and free SmBiT-R3/I5 separation. We then optimized membrane binding assays, demonstrating easy and robust analysis of both saturation and competition binding from frozen membranes. These assays therefore provide an appropriate rigorous binding assay for the high-throughput analysis of RXFP3 and RXFP4 ligands.

Total Chemical Synthesis of Palmitoyl-Conjugated Insulin

Commercially available insulins are manufactured by recombinant methods for the treatment of diabetes. Long-acting insulin drugs (e.g., detemir and degludec) are obtained by fatty acid conjugation at LysB29 ε-amine of insulin via acid-amide coupling. There are three amine groups in insulin, and they all react with fatty acids in alkaline conditions. Due to the lack of selectivity, such conjugation reactions produce non-desired byproducts. We designed and chemically synthesized a novel thiol-insulin scaffold (CysB²⁹-insulin II), by replacing the Lys^B29 residue in insulin with the Cys^B29 residue. Then, we conjugated a fatty acid moiety (palmitic acid, C16) to CysB²⁹-insulin II by a highly efficient and selective thiol-maleimide conjugation reaction. We obtained the target peptide (palmitoyl-insulin) rapidly within 5 min without significant byproducts. The palmitoyl-insulin is shown to be structurally similar to insulin and biologically active both in vitro and in vivo. Importantly, unlike native insulin, palmitoyl-insulin is slow and long-acting.

Single-Shot Solid-Phase Synthesis of Full-Length H2 Relaxin Disulfide Surrogates

Chemical synthesis of insulin superfamily proteins (ISPs) has recently been widely studied to develop next-generation drugs. Separate synthesis of multiple peptide fragments and tedious chain-to-chain folding are usually encountered in these studies, limiting accessibility to ISP derivatives. Here we report the finding that insulin superfamily proteins (e.g. H2 relaxin, insulin itself, and H3 relaxin) incorporating a pre-made diaminodiacid bridge at A-B chain terminal disulfide can be easily and rapidly synthesized by a single-shot automated solid-phase synthesis and expedient one-step folding. Our new H2 relaxin analogues exhibit almost identical structures and activities when compared to their natural counterparts. This new synthetic strategy will expediate production of new ISP analogues for pharmaceutical studies.

Regulation of MMP and TIMP expression in synovial fibroblasts from knee osteoarthritis with flexion contracture using adenovirus-mediated relaxin gene therapy

PURPOSE

The aim of this study was to investigate the effects of relaxin (RLN) expression on fibrosis inhibition in synovial fibroblasts.

MATERIALS AND METHODS

Tissue cells from patients with knee osteoarthritis and >30° flexion contractures were utilised. Synovial fibroblasts were activated by TGF-β1 (two nanograms per millilitre) and then exposed to Ad-RLN as a therapeutic gene, adenovirus-lacZ construct as a marker gene, and SB505124 as an inhibitor for TGF-β1 signal for 48 h. The mRNA expression levels of collagens and MMPs were analysed by reverse transcription-polymerase chain reaction. Also, fibronectin, phosphorylation of Smad2 and ERK1/2, alpha smooth muscle actin, TIMP-1, TIMP-2, MMP-1 and MMP-13 levels were estimated using western blotting, and the total collagen synthesis was assayed.

RESULTS

Ad-RLN-transduced synovial fibroblasts demonstrated 17%, 13%, and 48% reduction in collagen I, III and IV mRNA expression levels, respectively, and a 40% decrease in MMP-3, MMP-8, 20% decrease in MMP-9, MMP-13 mRNA expression, compared to non-Ad-RLN-transduced cells. In protein expression, Ad-RLN-transduced synovial fibroblasts demonstrated 46% increase in MMP-1, 5% decrease in MMP-2, 51% increase in MMP-9, and 22% increase in MMP-13, compared to non-Ad-RLN-transduced cells. Ad-RLN-transduced synovial fibroblasts showed a 25% decrease in TIMP-1 and 65% decrease in TIMP-2 protein expression at 48h, compared to non-Ad-RLN-transduced cells. Ad-RLN-transduced synovial fibroblasts demonstrated a 45% inhibition of fibronectin in protein expression level and 38% decrease in total collagen synthesis at 48h, compared to non-Ad-RLN-transduced cells.

CONCLUSION

Relaxin expression exerted anti-fibrogenic effects on synovial fibroblasts from patients with knee osteoarthritis and flexion contractures. Therefore, relaxin could be an alternative therapeutic agent during the initial stage of osteoarthritis with flexion contracture by exerting its anti-fibrogenic effects.

Novel Methods for the Chemical Synthesis of Insulin Superfamily Peptides and of Analogues Containing Disulfide Isosteres

The insulin superfamily of peptides is ubiquitous within vertebrates and invertebrates and is characterized by the presence of a set of three disulfide bonds in a unique disposition. With the exception of insulin-like growth factors I and II, which are single chain peptides, the remaining 8 members of the human insulin superfamily are two-chain peptides containing one intramolecular and two intermolecular disulfide bridges. These structural features have long made the chemical synthesis of the peptides a considerable challenge, in particular, including their correct disulfide bond pairing and formation. However, they have also afforded the opportunity to develop modern solid phase synthesis methods for the preparation of such peptides that incorporate novel or improved chemical methods for the controlled introduction of both disulfide bonds and their surrogates, both during and after peptide chain assembly. In turn, this has enabled a detailed probing of the structure and function relationship of this small but complex superfamily of peptides. After initially using and subsequently identifying significant limitations of the approach of simultaneous random chain combination and oxidative folding, our laboratory undertook to develop robust chemical synthesis strategies in concert with orthogonal cysteine S-protecting groups and corresponding regioselective disulfide bond formation. These have included the separate synthesis of each of the two chains or of the two chains linked by an artificial C-peptide that is removed following postoxidative folding. These, in turn, have enabled an increased ease of acquisition in a good yield of not only members of human insulin superfamily but other insulin-like peptides. Importantly, these successful methods have enabled, for the first time, a detailed analysis of the role that the disulfide bonds play in the structure and function of such peptides. This was achieved by selective removal of the disulfide bonds or by the judicious insertion of disulfide isosteres that possess structurally subtle variations in bond length, hydrophobicity, and angle. These include lactam, dicarba, and cystathionine, each of which has required modifications to the peptide synthesis protocols for their successful placement within the peptides. Together, these synthesis improvements and the novel chemical developments of cysteine/cystine analogues have greatly aided in the development of novel insulin-like peptide (INSL) analogues, principally with intra-A-chain disulfide isosteres, possessing not only improved functional properties such as increased receptor selectivity but also, with one important and unexpected exception, greater in vivo half-lives due to stability against disulfide reductases. Such analogues greatly will aid further biochemical and pharmacological analyses to delineate the structure-function relationships of INSLs and also future potential drug development.

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.

Anti-fibrotic actions of relaxin

Fibrosis refers to the hardening or scarring of tissues that usually results from aberrant wound healing in response to organ injury, and its manifestations in various organs have collectively been estimated to contribute to around 45-50% of deaths in the Western world. Despite this, there is currently no effective cure for the tissue structural and functional damage induced by fibrosis-related disorders. Relaxin meets several criteria of an effective anti-fibrotic based on its specific ability to inhibit pro-fibrotic cytokine and/or growth factor-mediated, but not normal/unstimulated, fibroblast proliferation, differentiation and matrix production. Furthermore, relaxin augments matrix degradation through its ability to up-regulate the release and activation of various matrix-degrading matrix metalloproteinases and/or being able to down-regulate tissue inhibitor of metalloproteinase activity. Relaxin can also indirectly suppress fibrosis through its other well-known (anti-inflammatory, antioxidant, anti-hypertrophic, anti-apoptotic, angiogenic, wound healing and vasodilator) properties. This review will outline the organ-specific and general anti-fibrotic significance of exogenously administered relaxin and its mechanisms of action that have been documented in various non-reproductive organs such as the cardiovascular system, kidney, lung, liver, skin and tendons. In addition, it will outline the influence of sex on relaxin's anti-fibrotic actions, highlighting its potential as an emerging anti-fibrotic therapeutic.

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.

Relaxin Modulates the Expression of MMPs and TIMPs in Fibroblasts of Patients with Carpal Tunnel Syndrome

PURPOSE

The aim of this study was to investigate the anti-fibrotic effect of relaxin in subsynovial fibroblasts activated by transforming growth factor beta (TGF-β).

MATERIALS AND METHODS

To test the anti-fibrotic effect of an adenovirus-relaxin construct (Ad-RLN) on subsynovial fibroblasts in vitro, cells from subsynovial connective tissue of patients with carpal tunnel syndrome were activated with TGF-β1 and exposed to Ad-RLN (as a therapeutic gene) or adenovirus-lacZ construct (as a marker gene) for four hours. Subsynovial fibroblast cultures without adenoviral exposure served as controls.

RESULTS

We observed induction of gene expressions of collagen I, III and IV, as well as the abatement of alpha-smooth muscle actin (a-SMA) synthesis, Smad2 phosphorylation, and fibronectin at the protein level, in comparison to controls. In addition, protein expressions of matrix metalloproteinase (MMP) I was significantly induced, whereas the protein expressions of tissue inhibitor of metalloproteinases (TIMP) I and IV were reduced due to relaxin expression.

CONCLUSION

RLN prevents excessive synthesis of extracellular matrix by reducing the expressions of its components, such as fibronectin, a-SMA, and phosphorylated Smad2, by increasing the expression of MMPs; and by decreasing the expression of TIMPs.

Chemical synthesis of peptides within the insulin superfamily

The synthesis of insulin has inspired fundamental advances in the art of peptide science while simultaneously revealing the structure-function relationship of this centrally important metabolic hormone. This review highlights milestones in the chemical synthesis of insulin that can be divided into two separate approaches: (i) disulfide bond formation driven by protein folding and (ii) chemical reactivity-directed sequential disulfide bond formation. Common to the two approaches are the persistent challenges presented by the hydrophobic nature of the individual A-chain and B-chain and the need for selective disulfide formation under mildly oxidative conditions. The extension and elaboration of these synthetic approaches have been ongoing within the broader insulin superfamily. These structurally similar peptides include the insulin-like growth factors and also the related peptides such as relaxin that signal through G-protein-coupled receptors. After a half-century of advances in insulin chemistry, we have reached a point where synthesis is no longer limiting structural and biological investigation within this family of peptide hormones. The future will increasingly focus on the refinement of structure to meet medicinal purposes that have long been pursued, such as the development of a glucose-sensitive insulin. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.

International Union of Basic and Clinical Pharmacology. XCV. Recent advances in the understanding of the pharmacology and biological roles of relaxin family peptide receptors 1-4, the receptors for relaxin family peptides

Relaxin, insulin-like peptide 3 (INSL3), relaxin-3, and INSL5 are the cognate ligands for the relaxin family peptide (RXFP) receptors 1-4, respectively. RXFP1 activates pleiotropic signaling pathways including the signalosome protein complex that facilitates high-sensitivity signaling; coupling to Gα(s), Gα(i), and Gα(o) proteins; interaction with glucocorticoid receptors; and the formation of hetero-oligomers with distinctive pharmacological properties. In addition to relaxin-related ligands, RXFP1 is activated by Clq-tumor necrosis factor-related protein 8 and by small-molecular-weight agonists, such as ML290 [2-isopropoxy-N-(2-(3-(trifluoromethylsulfonyl)phenylcarbamoyl)phenyl)benzamide], that act allosterically. RXFP2 activates only the Gα(s)- and Gα(o)-coupled pathways. Relaxin-3 is primarily a neuropeptide, and its cognate receptor RXFP3 is a target for the treatment of depression, anxiety, and autism. A variety of peptide agonists, antagonists, biased agonists, and an allosteric modulator target RXFP3. Both RXFP3 and the related RXFP4 couple to Gα(i)/Gα(o) proteins. INSL5 has the properties of an incretin; it is secreted from the gut and is orexigenic. The expression of RXFP4 in gut, adipose tissue, and β-islets together with compromised glucose tolerance in INSL5 or RXFP4 knockout mice suggests a metabolic role. This review focuses on the many advances in our understanding of RXFP receptors in the last 5 years, their signal transduction mechanisms, the development of novel compounds that target RXFP1-4, the challenges facing the field, and current prospects for new therapeutics.

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.

Synthetic covalently linked dimeric form of H2 relaxin retains native RXFP1 activity and has improved in vitro serum stability

Human (H2) relaxin is a two-chain peptide member of the insulin superfamily and possesses potent pleiotropic roles including regulation of connective tissue remodeling and systemic and renal vasodilation. These effects are mediated through interaction with its cognate G-protein-coupled receptor, RXFP1. H2 relaxin recently passed Phase III clinical trials for the treatment of congestive heart failure. However, its in vivo half-life is short due to its susceptibility to proteolytic degradation and renal clearance. To increase its residence time, a covalent dimer of H2 relaxin was designed and assembled through solid phase synthesis of the two chains, including a judiciously monoalkyne sited B-chain, followed by their combination through regioselective disulfide bond formation. Use of a bisazido PEG7 linker and "click" chemistry afforded a dimeric H2 relaxin with its active site structurally unhindered. The resulting peptide possessed a similar secondary structure to the native monomeric H2 relaxin and bound to and activated RXFP1 equally well. It had fewer propensities to activate RXFP2, the receptor for the related insulin-like peptide 3. In human serum, the dimer had a modestly increased half-life compared to the monomeric H2 relaxin suggesting that additional oligomerization may be a viable strategy for producing longer acting variants of H2 relaxin.

Down-regulation of collagen synthesis and matrix metalloproteinase expression in myofibroblasts from Dupuytren nodule using adenovirus-mediated relaxin gene therapy

Dupuytren's disease is a fibroproliferative connective tissue disorder characterized by contracture of the palmer fascia of the hand. Relaxin (RLN) is a multifunctional factor which contributes to the remodeling of the pelvic ligament by inhibiting fibrosis and inflammatory activities. The aim of this study was to investigate the effect of the RLN gene on the inhibition of fibrosis in myofibroblastic cells. Myofibroblast cells with adenovirus LacZ (Ad-LacZ) as a marker gene or adenovirus relaxin (Ad-RLN) as therapeutic gene showed transgene expressions in beta-galactosidase assay and Western blot analysis. Myofibroblastic cells with Ad-RLN demonstrated a 22% and 48% reduction in collagen I and III mRNA expressions respectively, a 50% decrease in MMP-1, 70% decrease in MMP-2, 80% decrease in MMP-9, and a 15% reduction in MMP-13 protein expression compared with cultures with viral control and saline control. In addition, myofibroblastic cells with Ad-RLN showed a 40% decrease in TIMP 1 and a 15% increase in TIMP 3 protein expression at 48 h compared to cultures with viral control and saline control. Also, myofibroblastic cell with Ad-RLN demonstrated a 74% inhibition of fibronectin and a 52% decrease in total collagen synthesis at 48 h compared with cultures with viral control and saline control. In conclusion, the RLN gene render antifibrogenic effect on myofibroblastic cells from Dupuytren's nodule via direct inhibition of collagen synthesis not through collagenolytic pathway such as MMP-1, -13, TIMP 1, and 3. Therefore relaxin can be an alternative therapeutic strategy in initial stage of Dupuytren's disease by its antifibrogenic effect.

Relaxin decreases the severity of established hepatic fibrosis in mice

BACKGROUND & AIMS

Hepatic fibrosis is characterized by excess collagen deposition, decreased extracellular matrix degradation and activation of the hepatic stellate cells. The hormone relaxin has shown promise in the treatment of fibrosis in a number of tissues, but the effect of relaxin on established hepatic fibrosis is unknown. The aim of this study was to determine the effect of relaxin on an in vivo model after establishing hepatic fibrosis

METHODS

Male mice were made fibrotic by carbon tetrachloride treatment for 4 weeks, followed by treatment with two doses of relaxin (25 or 75 μg/kg/day) or vehicle for 4 weeks, with continued administration of carbon tetrachloride.

RESULTS

Relaxin significantly decreased total hepatic collagen and smooth muscle actin content at both doses, and suppressed collagen I expression at the higher dose. Relaxin increased the expression of the matrix metalloproteinases MMP13 and MMP3, decreased the expression of MMP2 and tissue inhibitor of metalloproteinase 2 (TIMP2) and increased the overall level of collagen-degrading activity. Relaxin decreased TGFβ-induced Smad2 nuclear localization in mouse hepatic stellate cells.

CONCLUSIONS

The results suggest that relaxin reduced collagen deposition and HSC activation in established hepatic fibrosis despite the presence of continued hepatic insult. This reduced fibrosis was associated with increased expression of the fibrillar collagen-degrading enzyme MMP13, decreased expression of TIMP2, and enhanced collagen-degrading activity, and impaired TGFβ signalling, consistent with relaxin's effects on activated fibroblastic cells. The results suggest that relaxin may be an effective treatment for the treatment of established hepatic fibrosis.

Therapeutic effects of serelaxin in acute heart failure

Over the past few decades, research on the peptide hormone, relaxin, has significantly improved our understanding of its biological actions under physiological and diseased conditions. This has facilitated the conducting of clinical trials to explore the use of serelaxin (human recombinant relaxin). Acute heart failure (AHF) is a very difficult to treat clinical entity, with limited success so far in developing new drugs to combat it. A recent phase-III RELAX-AHF trial using serelaxin therapy given during hospitalization revealed acute (ameliorated dyspnea) and chronic (improved 180-day survival) effects. Although these findings support a substantial improvement by serelaxin therapy over currently available therapies for AHF, they also raise key questions and stimulate new hypotheses. To facilitate the development of serelaxin as a new drug for heart disease, joint efforts of clinicians, research scientists and pharmacological industries are necessary to study these questions and hypotheses. In this review, after providing a brief summary of clinical findings and the pathophysiology of AHF, we present a working hypothesis of the mechanisms responsible for the observed efficacy of serelaxin in AHF patients. The existing clinical and preclinical data supporting our hypotheses are summarized and discussed. The development of serelaxin as a drug provides an excellent example of the bilateral nature of translational research. 

C-terminus of the B-chain of relaxin-3 is important for receptor activity

Human relaxin-3 is a neuropeptide that is structurally similar to human insulin with two chains (A and B) connected by three disulfide bonds. It is expressed primarily in the brain and has modulatory roles in stress and anxiety, feeding and metabolism, and arousal and behavioural activation. Structure-activity relationship studies have shown that relaxin-3 interacts with its cognate receptor RXFP3 primarily through its B-chain and that its A-chain does not have any functional role. In this study, we have investigated the effect of modification of the B-chain C-terminus on the binding and activity of the peptide. We have chemically synthesised and characterized H3 relaxin as C-termini acid (both A and B chains having free C-termini; native form) and amide forms (both chains’ C-termini were amidated). We have confirmed that the acid form of the peptide is more potent than its amide form at both RXFP3 and RXFP4 receptors. We further investigated the effects of amidation at the C-terminus of individual chains. We report here for the first time that amidation at the C-terminus of the B-chain of H3 relaxin leads to significant drop in the binding and activity of the peptide at RXFP3/RXFP4 receptors. However, modification of the A-chain C-terminus does not have any effect on the activity. We have confirmed using circular dichroism spectroscopy that there is no secondary structural change between the acid and amide form of the peptide, and it is likely that it is the local C-terminal carboxyl group orientation that is crucial for interacting with the receptors.

Relaxin prevents cardiac fibroblast-myofibroblast transition via notch-1-mediated inhibition of TGF-β/Smad3 signaling

The hormone relaxin (RLX) is produced by the heart and has beneficial actions on the cardiovascular system. We previously demonstrated that RLX stimulates mouse neonatal cardiomyocyte growth, suggesting its involvement in endogenous mechanisms of myocardial histogenesis and regeneration. In the present study, we extended the experimentation by evaluating the effects of RLX on primary cultures of neonatal cardiac stromal cells. RLX inhibited TGF-β1-induced fibroblast-myofibroblast transition, as judged by its ability to down-regulate α-smooth muscle actin and type I collagen expression. We also found that the hormone up-regulated metalloprotease (MMP)-2 and MMP-9 expression and downregulated the tissue inhibitor of metalloproteinases (TIMP)-2 in TGF-β1-stimulated cells. Interestingly, the effects of RLX on cardiac fibroblasts involved the activation of Notch-1 pathway. Indeed, Notch-1 expression was significantly decreased in TGF-β1-stimulatedfibroblasts as compared to the unstimulated controls; this reduction was prevented by the addition of RLX to TGF-β1-stimulated cells. Moreover, pharmacological inhibition of endogenous Notch-1 signaling by N-3,5-difluorophenyl acetyl-L-alanyl-2-phenylglycine-1,1-dimethylethyl ester (DAPT), a γ-secretase specific inhibitor, as well as the silencing of Notch-1 ligand, Jagged-1, potentiated TGF-β1-induced myofibroblast differentiation and abrogated the inhibitory effects of RLX. Interestingly, RLX and Notch-1 exerted their inhibitory effects by interfering with TGF-β1 signaling, since the addition of RLX to TGF-β1-stimulated cells caused a significant decrease in Smad3 phosphorylation, a typical downstream event of TGF-β1 receptor activation, while the treatment with a prevented this effect. These data suggest that Notch signaling can down-regulate TGF-β1/Smad3-induced fibroblast-myofibroblast transition and that RLX could exert its well known anti-fibrotic action through the up-regulation of this pathway. In conclusion, the results of the present study beside supporting the role of RLX in the field of cardiac fibrosis, provide novel experimental evidence on the molecular mechanisms underlying its effects.

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.

Synthesis of a dicarba analogue of human β-defensin-1 using a combined ring closing metathesis--native chemical ligation strategy

We herein describe the first synthesis of the native antimicrobial protein HBD-1 making use of an orthogonal thiol protection strategy and a novel dicarba analogue thereof. The robust hydrocarbon linkage was installed by replacement of one disulfide bond using on-resin ring closing metathesis. The unprecedented 59-membered C-terminal cysteine macrocyclic fragment thus formed then engages in native chemical ligation allowing convergent access to this unique synthetic protein analogue.

Effects of relaxin on relapse and periodontal tissue remodeling after experimental tooth movement in rats

The relapse of teeth that have moved during orthodontic treatment is a major clinical issue with respect to the goals of successful treatment. Relaxin has an influence on many physiologic processes, such as collagen turnover. In this study, we determined the effects of relaxin on the relapse and remodeling of periodontal tissue after experimental tooth movement in rats, and we explored the molecular mechanism underlying these processes. To induce experimental tooth movement in rats, 10 g of orthodontic force was applied to the molars. After 14 days, the spring was removed, and then animals began receiving relaxin at a dose of 500 ng/ml for 1 week. The results were evaluated by micro-computed tomography and immunofluorescence staining. In addition, the effects of matrix metalloproteinase (MMP)-1 and MMP-8 production were investigated in human periodontal ligament (hPDL) cells in vitro. The expression of MMP-1 and MMP-8 was analyzed by real-time polymerase chain reaction and enzyme-linked immunosorbent assay. Furthermore, we demonstrated the signaling pathways involved in relaxin-regulated MMPs expression. The relapse distances and percentages were significantly decreased in the experimental group compared with the controls in vivo. A double-immunofluorescence analysis for Col-I/MMP-1 and Col-I/MMP-8 detected the expression of relaxin in the PDL. Relaxin significantly increased the MMP-1 and MMP-8 expression in a time-dependent manner in hPDL cells in vitro. Furthermore, a p38 inhibitor (SB203580) significantly inhibited the MMP-1 and MMP-8 expression. Our results indicated that relaxin modulates the collagen metabolism, and this hormone may therefore be useful to prevent orthodontic relapse following orthodontic treatment.

Total synthesis of desB30 insulin analogues by biomimetic folding of single-chain precursors

Insulin is a peptide hormone consisting of 51 amino acids in two chains with three disulfide bridges. Human insulin and various analogues are used for the treatment of diabetes and are produced recombinantly at ton scale. Herein, we report the chemical synthesis of insulin by the step-wise, Fmoc-based, solid-phase synthesis of single-chain precursors with solubilising extensions, which under redox conditions, spontaneously fold with the correct pairing of the three disulfide bridges. The folded, single-chain, insulin precursors can be transformed into bioactive two-chain desB30 insulin by the simultaneous removal of the solubilising extension (4-5 residues) and the chain-bridging C-peptide (3-5 residues) by employing Achromobacter lyticus protease--a process well-known from the yeast-based recombinant production of insulin. The overall yields of synthetic insulins were as much as 6 %, and the synthetic process was straightforward and not labour intensive.

Synthesis, conformation, and activity of human insulin-like peptide 5 (INSL5)

Insulin-like peptide 5 (INSL5) was first identified through searches of the expressed sequence tags (EST) databases. Primary sequence analysis showed it to be a prepropeptide that was predicted to be processed in vivo to yield a two-chain sequence (A and B) that contained the insulin-like disulfide cross-links. The high affinity interaction between INSL5 and the receptor RXFP4 (GPCR142) coupled with their apparent coevolution and partially overlapping tissue expression patterns strongly suggest that INSL5 is an endogenous ligand for RXFP4. Given that the primary function of the INSL5–RXFP4 pair remains unknown, an effective means of producing sufficient quantities of this peptide and its analogues is needed to systematically investigate its structural and biological properties. A combination of solid-phase peptide synthesis methods together with regioselective disulfide bond formation were used to obtain INSL5. Both chains were unusually resistant to standard synthesis protocols and required highly optimized conditions for their acquisition. In particular, the use of a strong tertiary amidine, DBU, as N^α-deprotection base was required for the successful assembly of the B chain; this highlights the need to consider incomplete deprotection rather than acylation as a cause of failed synthesis. Following sequential disulfide bond formation and chain combination, the resulting synthetic INSL5, which was obtained in good overall yield, was shown to possess a similar secondary structure to human relaxin-3 (H3 relaxin). The peptide was able to inhibit cAMP activity in SK-N-MC cells that expressed the human RXFP4 receptor with a similar activity to H3 relaxin. In contrast, it had no activity on the human RXFP3 receptor. Synthetic INSL5 demonstrates equivalent activity to the recombinant-derived peptide, and will be an important tool for the determination of its biological function.