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

Relaxin as a treatment for musculoskeletal fibrosis: What we know and future directions

Fibrotic changes in musculoskeletal diseases arise from the abnormal buildup of fibrotic tissue around the joints, leading to limited mobility, compromised joint function, and diminished quality of life. Relaxin (RLX) attenuates fibrosis by accelerating collagen degradation and inhibiting excessive extracellular matrix (ECM) production. Further, RLX disrupts myofibroblast activation by modulating the TGF-β/Smads signaling pathways, which reduces connective tissue fibrosis. However, the mechanisms and effects of RLX in musculoskeletal pathologies are emerging as increasing research focuses on relaxin's impact on skin, ligaments, tendons, cartilage, joint capsules, connective tissues, and muscles. This review delineates the actions of relaxin within the musculoskeletal system and the challenges to its clinical application. Relaxin shows significant potential in both in vivo and in vitro studies for broadly managing musculoskeletal fibrosis; however, challenges such as short biological half-life and sex-specific responses may pose hurdles for clinical use.

The involvement of the Wnt/β-catenin signaling cascade in fibrosis progression and its therapeutic targeting by relaxin

Organ scarring, referred to as fibrosis, results from a failed wound-healing response to chronic tissue injury and is characterised by the aberrant accumulation of various extracellular matrix (ECM) components. Once established, fibrosis is recognised as a hallmark of stiffened and dysfunctional tissues, hence, various fibrosis-related diseases collectively contribute to high morbidity and mortality in developed countries. Despite this, these diseases are ineffectively treated by currently-available medications. The pro-fibrotic cytokine, transforming growth factor (TGF)-β1, has emerged as the master regulator of fibrosis progression, owing to its ability to promote various factors and processes that facilitate rapid ECM synthesis and deposition, whilst negating ECM degradation. TGF-β1 signal transduction is tightly controlled by canonical (Smad-dependent) and non-canonical (MAP kinase- and Rho-associated protein kinase-dependent) intracellular protein activity, whereas its pro-fibrotic actions can also be facilitated by the Wnt/β-catenin pathway. This review outlines the pathological sequence of events and contributing roles of TGF-β1 in the progression of fibrosis, and how the Wnt/β-catenin pathway contributes to tissue repair in acute disease settings, but to fibrosis and related tissue dysfunction in synergy with TGF-β1 in chronic diseases. It also outlines the anti-fibrotic and related signal transduction mechanisms of the hormone, relaxin, that are mediated via its negative modulation of TGF-β1 and Wnt/β-catenin signaling, but through the promotion of Wnt/β-catenin activity in acute disease settings. Collectively, this highlights that the crosstalk between TGF-β1 signal transduction and the Wnt/β-catenin cascade may provide a therapeutic target that can be exploited to broadly treat and reverse established fibrosis.

Drugs targeting TGF-β/Notch interaction attenuate hypertrophic scar formation by optic atrophy 1-mediated mitochondrial fusion

Hypertrophic scar (HS) formation is a cutaneous fibroproliferative disease that occurs after skin injuries and results in severe functional and esthetic disability. To date, few drugs have shown satisfactory outcomes for the treatment of HS formation. Transforming growth factor-beta (TGF-β)/Notch interaction via small mothers against decapentaplegic 3 (Smad3) could facilitate HS formation; therefore, targeting TGF-β/ Notch interaction via Smad3 is a potential therapeutic strategy to attenuate HS formation. In addition, optic atrophy 1 (OPA1)-mediated mitochondrial fusion contributes to fibroblast proliferation, and TGF-β/Smad3 axis and the Notch1 pathway facilitate OPA1-mediated mitochondrial fusion. Thus, the aim of this study was to investigate whether drugs targeting TGF-β/Notch interaction via Smad3 suppressed fibroblast proliferation to attenuate HS formation through OPA1-mediated mitochondrial fusion. We found that the TGF-β pathway, Notch pathway, and TGF-β/Notch interaction via Smad3 were inhibited by pirfenidone, the gamma- secretase inhibitor DAPT, and SIS3 in human keloid fibroblasts (HKF) and an HS rat model, respectively. Protein interaction was detected by co-immunoprecipitation, and mitochondrial morphology was determined by electron microscopy. Our results indicated that pirfenidone, DAPT, and SIS3 suppressed the proliferation of HKFs and attenuated HS formation in the HS rat model by inhibiting TGF-β/Notch interaction via Smad3. Moreover, pirfenidone, DAPT, and SIS3 hindered OPA1-mediated mitochondrial fusion through inhibiting TGF-β/Notch interaction, thereby suppressing the proliferation of HS fibroblasts and HS formation. In summary, these findings investigating the effects of drugs targeting TGF-β/Notch interaction on HS formation might lead to novel drugs for the treatment of HS formation.

Serelaxin Alleviates Fibrosis in Thyroid-Associated Ophthalmopathy via the Notch Pathway

Fibrosis is the late stage of thyroid-associated ophthalmopathy (TAO), resulting in serious complications. Effective therapeutic drugs are still lacking. We aimed to explore the mechanism of TAO fibrosis and to find a targeted drug. High-throughput RNA sequencing was performed on orbital connective tissues from twelve patients with TAO and six healthy controls. Protein-protein interaction (PPI) network was constructed using the Search Tool for the Retrieval of Interacting Genes (STRING) database and we identified the hub gene by Cytoscape software. Additionally, the RNA sequencing results were validated by quantitative real-time polymerase chain reaction (qRT-PCR). Bioinformatic prediction identified the functions of differentially expressed genes (DEGs). Further orbital connective tissue and serum samples of the TAO and control groups were collected for subsequent experiments. Histologic staining, Western blotting (WB), qRT-PCR, enzyme-linked immunosorbent assays (ELISAs), gene overexpression through lentiviral infection or silencing gene by short interfering RNA (siRNA) were performed. We found that the relaxin signaling pathway is an important regulatory pathway in TAO fibrosis pathogenesis. Serelaxin exerts antifibrotic and anti-inflammatory effects in TAO. Furthermore, the downstream Notch pathway was activated by serelaxin and was essential to the antifibrotic effect of serelaxin in TAO. The antifibrotic effect of serelaxin is dependent on RXFP1.

Simultaneous late-gadolinium enhancement and T1 mapping of fibrosis and a novel cell-based combination therapy in hypertensive mice

Fibrosis is a hallmark of chronic hypertension and disrupts the viability of human bone marrow-derived mesenchymal stromal cells (BM-MSCs) post-transplantation. This study thus, determined whether the anti-fibrotic drug, serelaxin (RLX), could enhance the therapeutic effects of BM-MSCs or BM-MSC-derived exosomes (BM-MSC-EXO) in hypertensive mice. Left ventricular (LV) fibrosis in particular was assessed using conventional histological staining and non-invasive cardiac magnetic resonance imaging (CMRI). CMRI was employed using a novel magnetisation prepared 2 rapid acquisition gradient echo (MP2RAGE) sequence to simultaneously perform late gadolinium enhancement imaging and T1 mapping. Adult male C57BL/6 mice were uninephrectomised, received deoxycorticosterone acetate and saline to drink (1 K/DOCA/salt) for 21 days, whilst control mice were given normal drinking water for the same time-period. On day 14 post-injury, subgroups of 1 K/DOCA/salt-hypertensive mice were treated with RLX alone or in combination with BM-MSCs or BM-MSC-EXO; or the mineralocorticoid receptor antagonist, spironolactone. At day 21 post-injury, LV and kidney histopathology was assessed, whilst LV fibrosis and function were additionally analysed by CMRI and echocardiography. 1 K/DOCA/salt-hypertensive mice developed kidney tubular injury, inflammation, fibrosis, and more moderate LV hypertrophy, fibrosis and diastolic dysfunction. RLX and BM-MSCs combined provided optimal protection against these pathologies and significantly reduced picrosirius red-stained organ fibrosis and MP2RAGE analysis of LV fibrosis. A significant correlation between MP2RAGE analysis and histologically-stained interstitial LV fibrosis was detected. It was concluded that the MP2RAGE sequence enhanced the non-invasive CMRI detection of LV fibrosis. Furthermore, combining RLX and BM-MSCs may represent a promising treatment option for hypertensive cardiorenal syndrome.

Relaxin in fibrotic ligament diseases: Its regulatory role and mechanism

Fibrotic ligament diseases (FLDs) are diseases caused by the pathological accumulation of periarticular fibrotic tissue, leading to functional disability around joint and poor life quality. Relaxin (RLX) has been reported to be involved in the development of fibrotic lung and liver diseases. Previous studies have shown that RLX can block pro-fibrotic process by reducing the excess extracellular matrix (ECM) formation and accelerating collagen degradation in vitro and in vivo. Recent studies have shown that RLX can attenuate connective tissue fibrosis by suppressing TGF-β/Smads signaling pathways to inhibit the activation of myofibroblasts. However, the specific roles and mechanisms of RLX in FLDs remain unclear. Therefore, in this review, we confirmed the protective effect of RLX in FLDs and summarized its mechanism including cells, key cytokines and signaling pathways involved. In this article, we outline the potential therapeutic role of RLX and look forward to the application of RLX in the clinical translation of FLDs.

Relaxin-2 plasma levels in atrial fibrillation are linked to inflammation and oxidative stress markers

Relaxin-2 exerts many favourable cardiovascular effects in pathological circumstances such as atrial fibrillation (AF) and heart failure, but the mechanisms underlying its actions are not completely understood. Since inflammation and fibrosis are pivotal processes in the pathogenesis of AF, our aim was to study the relationship between relaxin-2 plasma levels in left atrium (LA) and peripheral vein with molecules implicated in fibrosis, inflammation and oxidative stress in AF patients, and to evaluate the anti-fibrotic ability of relaxin-2 in normal human atrial cardiac fibroblasts (NHCF-A). Peripheral vein relaxin-2 plasma levels were higher than LA relaxin-2 plasma levels in men while, in women, peripheral vein relaxin-2 levels were increased compared to men. AF patients with higher levels of relaxin-2 exhibited a reduction in H₂O₂ plasma levels and in mRNA levels of alpha-defensin 3 (DEFA3) and IL-6 in leucocytes from LA plasma. Relaxin-2-in-vitro treatment inhibited NHCF-A migration and decreased mRNA and protein levels of the pro-fibrotic molecule transforming growth factor-β1 (TGF-β1). Our results support an association between relaxin-2 and molecules involved in fibrosis, inflammation and oxidative stress in AF patients, and reinforce an anti-fibrotic protective role of this hormone in NHCF-A; strengthening the relevance of relaxin-2 in AF physiopathology, diagnosis and treatment.

Functional crosstalk between angiotensin receptors (types 1 and 2) and relaxin family peptide receptor 1 (RXFP1): Implications for the therapeutic targeting of fibrosis

Class A, rhodopsin-like, G-protein-coupled receptors (GPCRs) are by far the largest class of GPCRs and are integral membrane proteins used by various cells to convert extracellular signals into intracellular responses. Initially, class A GPCRs were believed to function as monomers, but a growing body of evidence has emerged to suggest that these receptors can function as homodimers and heterodimers and can undergo functional crosstalk to influence the actions of agonists or antagonists acting at each receptor. This review will focus on the angiotensin type 1 (AT1 ) and type 2 (AT2 ) receptors, as well as the relaxin family peptide receptor 1 (RXFP1), each of which have their unique characteristics but have been demonstrated to undergo some level of interaction when appropriately co-expressed, which influences the function of each receptor. In particular, this receptor functional crosstalk will be discussed in the context of fibrosis, the tissue scarring that results from a failed wound-healing response to injury, and which is a hallmark of chronic disease and related organ dysfunction.

Minimally invasive, sustained-release relaxin-2 microparticles reverse arthrofibrosis

Substantial advances in biotherapeutics are distinctly lacking for musculoskeletal diseases. Musculoskeletal diseases are biomechanically complex and localized, highlighting the need for novel therapies capable of addressing these issues. All frontline treatment options for arthrofibrosis, a debilitating musculoskeletal disease, fail to treat the disease etiology-the accumulation of fibrotic tissue within the joint space. For millions of patients each year, the lack of modern and effective treatment options necessitates surgery in an attempt to regain joint range of motion (ROM) and escape prolonged pain. Human relaxin-2 (RLX), an endogenous peptide hormone with antifibrotic and antifibrogenic activity, is a promising biotherapeutic candidate for musculoskeletal fibrosis. However, RLX has previously faltered through multiple clinical programs because of pharmacokinetic barriers. Here, we describe the design and in vitro characterization of a tailored drug delivery system for the sustained release of RLX. Drug-loaded, polymeric microparticles released RLX over a multiweek time frame without altering peptide structure or bioactivity. In vivo, intraarticular administration of microparticles in rats resulted in prolonged, localized concentrations of RLX with reduced systemic drug exposure. Furthermore, a single injection of RLX-loaded microparticles restored joint ROM and architecture in an atraumatic rat model of arthrofibrosis with clinically derived end points. Finally, confirmation of RLX receptor expression, RXFP1, in multiple human tissues relevant to arthrofibrosis suggests the clinical translational potential of RLX when administered in a sustained and targeted manner.

Synthetic short-chain peptide analogues of H1 relaxin lack affinity for the RXFP1 receptor and relaxin-like bioactivity. Clues to a better understanding of relaxin agonist design

The peptide hormone relaxin (RLX), also available as clinical-grade recombinant protein (serelaxin), holds great promise as a cardiovascular and anti-fibrotic agent but is limited by the pharmacokinetic issues common to all peptide drugs. In this study, by a computational modelling chemistry approach, we have synthesized and tested a set of low molecular weight peptides based on the putative receptor-binding domain of the B chain of human H1 RLX isoform, with the objective to obtain RLX analogues with improved pharmacokinetic features. Some of them were stabilized to induce the appropriate 3-D conformation by intra-chain tri-azolic staples, which should theoretically enhance their resistance to digestive enzymes making them suited for oral administration. Despite these favourable premises, none of these H1 peptides, either linear or stapled, revealed a sufficient affinity to the specific RLX receptor RXFP1. Moreover, none of them was endowed with any RLX-like biological effects in RXFP1-expressing THP-1 human monocytic cells and mouse NIH-3T3-derived myofibroblasts in in vitro culture, in terms of significantly relevant cAMP elevation and ERK1/2 phosphorylation, which represent two major signal transduction events downstream RXFP1 activation. This was at variance with authentic serelaxin, which induced a clear-cut, significant activation of both these classical RLX signaling pathways. Albeit negative, the results of this study offer additional information about the structural requirements that new peptide therapeutics shall possess to effectively behave as RXFP1 agonists and RLX analogues.

Targeting Myocardial Fibrosis—A Magic Pill in Cardiovascular Medicine?

Fibrosis, characterized by an excessive accumulation of extracellular matrix, has long been seen as an adaptive process that contributes to tissue healing and regeneration. More recently, however, cardiac fibrosis has been shown to be a central element in many cardiovascular diseases (CVDs), contributing to the alteration of cardiac electrical and mechanical functions in a wide range of clinical settings. This paper aims to provide a comprehensive review of cardiac fibrosis, with a focus on the main pathophysiological pathways involved in its onset and progression, its role in various cardiovascular conditions, and on the potential of currently available and emerging therapeutic strategies to counteract the development and/or progression of fibrosis in CVDs. We also emphasize a number of questions that remain to be answered, and we identify hotspots for future research.

Relaxin Inhibits the Cardiac Myofibroblast NLRP3 Inflammasome as Part of Its Anti-Fibrotic Actions via the Angiotensin Type 2 and ATP (P2X7) Receptors

Chronic NLRP3 inflammasome activation can promote fibrosis through its production of interleukin (IL)-1β and IL-18. Conversely, recombinant human relaxin (RLX) can inhibit the pro-fibrotic interactions between IL-1β, IL-18 and transforming growth factor (TGF)-β1. Here, the broader extent by which RLX targeted the myofibroblast NLRP3 inflammasome to mediate its anti-fibrotic effects was elucidated. Primary human cardiac fibroblasts (HCFs), stimulated with TGF-β1 (to promote myofibroblast (HCMF) differentiation), LPS (to prime the NLRP3 inflammasome) and ATP (to activate the NLRP3 inflammasome) (T+L+A) or benzoylbenzoyl-ATP (to activate the ATP receptor; P2X7R) (T+L+Bz), co-expressed relaxin family peptide receptor-1 (RXFP1), the angiotensin II type 2 receptor (AT2R) and P2X7R, and underwent increased protein expression of toll-like receptor (TLR)-4, NLRP3, caspase-1, IL-1β and IL-18. Whilst RLX co-administration to HCMFs significantly prevented the T+L+A- or T+L+Bz-stimulated increase in these end points, the inhibitory effects of RLX were annulled by the pharmacological antagonism of either RXFP1, AT2R, P2X7R, TLR-4, reactive oxygen species (ROS) or caspase-1. The RLX-induced amelioration of left ventricular inflammation, cardiomyocyte hypertrophy and fibrosis in isoproterenol (ISO)-injured mice, was also attenuated by P2X7R antagonism. Thus, the ability of RLX to ameliorate the myofibroblast NLRP3 inflammasome as part of its anti-fibrotic effects, appeared to involve RXFP1, AT2R, P2X7R and the inhibition of TLR-4, ROS and caspase-1.

Relaxin-2 as a Potential Biomarker in Cardiovascular Diseases

The pleiotropic hormone relaxin-2 plays a pivotal role in the physiology and pathology of the cardiovascular system. Relaxin-2 exerts relevant regulatory functions in cardiovascular tissues through the specific receptor relaxin family peptide receptor 1 (RXFP1) in the regulation of cardiac metabolism; the induction of vasodilatation; the reversion of fibrosis and hypertrophy; the reduction of inflammation, oxidative stress, and apoptosis; and the stimulation of angiogenesis, with inotropic and chronotropic effects as well. Recent preclinical and clinical outcomes have encouraged the potential use of relaxin-2 (or its recombinant form, known as serelaxin) as a therapeutic strategy during cardiac injury and/or in patients suffering from different cardiovascular disarrangements, especially heart failure. Furthermore, relaxin-2 has been proposed as a promising biomarker of cardiovascular health and disease. In this review, we emphasize the relevance of the endogenous hormone relaxin-2 as a useful diagnostic biomarker in different backgrounds of cardiovascular pathology, such as heart failure, atrial fibrillation, myocardial infarction, ischemic heart disease, aortic valve disease, hypertension, and atherosclerosis, which could be relevant in daily clinical practice and could contribute to comprehending the specific role of relaxin-2 in cardiovascular diseases.

Relaxin/serelaxin for cardiac dysfunction and heart failure in hypertension

The pregnancy related hormone relaxin is produced throughout the reproductive system. However, relaxin also has important cardiovascular effects as part of the adaptation that the cardiovascular system undergoes in response to the extra demands of pregnancy. These effects are primarily mediated by the relaxin family peptide receptor 1, which is one of four known relaxin receptors. The effects of relaxin on the cardiovascular system during pregnancy, as well as its anti-fibrotic and anti-inflammatory properties, have led to extensive studies into the potential of relaxin therapy as an approach to treat heart failure. Cardiomyocytes, cardiac fibroblasts, and endothelial cells all possess relaxin family peptide receptor 1, allowing for direct effects of therapeutic relaxin on the heart. Many pre-clinical animal studies have demonstrated a beneficial effect of exogenous relaxin on adverse cardiac remodeling including inflammation, fibrosis, cardiomyocyte hypertrophy and apoptosis, as well as effects on cardiac contractile function. Despite this, clinical studies have yielded disappointing results for the synthetic seralaxin, even though seralaxin was well tolerated. This article will provide background on relaxin in the context of normal physiology, as well as the role of relaxin in pregnancy-related adaptations of the cardiovascular system. We will also present evidence from pre-clinical animal studies that demonstrate the potential benefits of relaxin therapy, as well as discussing the results from clinical trials. Finally, we will discuss possible reasons for the failure of these clinical trials as well as steps being taken to potentially improve relaxin therapy for heart failure.

Omega-3 fatty acids impair miR-1-3p-dependent Notch3 down-regulation and alleviate sepsis-induced intestinal injury

Background

Sepsis is a troublesome syndrome that can cause intestinal injury and even high mortality rates. Omega-3 fatty acids (FAs) are known to protect against intestinal damage. Accordingly, the current study set out to explore if omega-3 FAs could affect sepsis-induced intestinal injury with the involvement of the microRNA (miR)-1-3p/Notch3-Smad axis.

Methods

First, cecal ligation and perforation (CLP) was performed to establish septic mouse models in C57BL/6J mice, and mouse intestinal epithelial MODE-K cells were induced by lipopolysaccharide (LPS) to establish sepsis cell models. The CLP-induced septic mice or LPS-exposed cells were subjected to treatment with Omega-3 FAs and activin (Smad signaling activator), miR-1-3p inhibitor and over-expressed/short hairpin RNA (oe-/sh)-Notch3 to explore their roles in inflammation, intestinal oxidative stress and cell apoptosis. A dual-luciferase reporter gene assay was further performed to verify the regulatory relationship between miR-1-3p and Notch3.

Results

Omega-3 FAs inhibited CLP-induced intestinal injury and ameliorated LPS-induced intestinal epithelial cell injury by down-regulating miR-1-3p, as evidenced by decreased levels of tumor necrosis factor-α, interleukin-1β (IL-1β) and IL-6, in addition to diminished levels of reactive oxygen species, malondialdehyde levels and superoxide dismutase activity. Furthermore, miR-1-3p could down-regulate Notch3, which inactivated the Smad pathway.

Conclusion

Collectively, our findings indicated that omega-3 FAs elevate the expression of Notch3 by down-regulating miR-1-3p, and then blocking the Smad pathway to alleviate intestinal epithelial inflammation and oxidative stress injury caused by sepsis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-021-00425-w.

Cardiac Gene Therapy With Relaxin Receptor 1 Overexpression Protects Against Acute Myocardial Infarction

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AAV9 vectors can upregulate Rxfp1 mRNA in murine heart after intravenous injection.

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RXFP1 upregulation sensitizes the left ventricle to relaxin-induced inotropy.

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RXFP1 overexpression protects heart from ischemia-reperfusion injury.

Relaxin is a pleiotropic hormone shown to confer cardioprotection in several preclinical models of cardiac ischemia-reperfusion injury. In the present study, the effects of up-regulating relaxin family peptide receptor 1 (RXFP1) via adeno-associated virus serotype 9 (AAV9) vectors were investigated in a mouse model of myocardial infarction. AAV9-RXFP1 vectors were generated and injected in adult male CD1 mice. Up-regulation of Rxfp1 was confirmed via quantitative polymerase chain reaction, and overexpressing animals showed increased sensitivity to relaxin-induced ventricular inotropic response. Overexpressing animals also demonstrated reduced infarct size and preserved cardiac function 24 hours after ischemia-reperfusion. Up-regulation of RXFP1 via AAV9 vectors has potential therapeutic utility in preventing adverse remodeling after myocardial infarction.

Relaxin as an anti-fibrotic treatment: Perspectives, challenges and future directions

Fibrosis refers to the scarring and hardening of tissues, which results from a failed immune system-coordinated wound healing response to chronic organ injury and which manifests from the aberrant accumulation of various extracellular matrix components (ECM), primarily collagen. Despite being a hallmark of prolonged tissue damage and related dysfunction, and commonly associated with high morbidity and mortality, there are currently no effective cures for its regression. An emerging therapy that meets several criteria of an effective anti-fibrotic treatment, is the recombinant drug-based form of the human hormone, relaxin (also referred to as serelaxin, which is bioactive in several other species). This review outlines the broad anti-fibrotic and related organ-protective roles of relaxin, mainly from studies conducted in preclinical models of ageing and fibrotic disease, including its ability to ameliorate several aspects of fibrosis progression and maturation, from immune cell infiltration, pro-inflammatory and pro-fibrotic cytokine secretion, oxidative stress, organ hypertrophy, cell apoptosis, myofibroblast differentiation and ECM production, to its ability to facilitate established ECM degradation. Studies that have compared and/or combined these therapeutic effects of relaxin with current standard of care medication have also been discussed, along with the main challenges that have hindered the translation of the anti-fibrotic efficacy of relaxin to the clinic. The review then outlines the future directions as to where scientists and several pharmaceutical companies that have recognized the therapeutic potential of relaxin are working towards, to progress its development as a treatment for human patients suffering from various fibrotic diseases.

Simultaneous targeting of oxidative stress and fibrosis reverses cardiomyopathy-induced ventricular remodelling and dysfunction

BACKGROUND AND PURPOSE

Oxidative stress and fibrosis are hallmarks of cardiomyopathy-induced heart failure yet are not effectively targeted by current frontline therapies. Here, the therapeutic effects of the anti-oxidant, N-acetylcysteine (NAC), were compared and combined with an acute heart failure drug with established anti-fibrotic effects, serelaxin (RLX), in a murine model of cardiomyopathy.

EXPERIMENTAL APPROACH

Adult male 129sv mice were subjected to repeated isoprenaline (25 mg·kg^-1 )-induced cardiac injury for five consecutive days and then left to undergo fibrotic healing until Day 14. Subgroups of isoprenaline-injured mice were treated with RLX (0.5 mg·kg^-1 ·day^-1 ), NAC (25 mg·kg^-1 ·day^-1 ) or both combined, given subcutaneously via osmotic minipumps from Day 7 to 14. Control mice received saline instead of isoprenaline.

KEY RESULTS

Isoprenaline-injured mice showed increased left ventricular (LV) inflammation (~5-fold), oxidative stress (~1-2.5-fold), cardiomyocyte hypertrophy (~25%), cardiac remodelling, fibrosis (~2-2.5-fold) and dysfunction by Day 14 after injury. NAC alone blocked the cardiomyopathy-induced increase in LV superoxide levels, to a greater extent than RLX. Additionally, either treatment alone only partly reduced several measures of LV inflammation, remodelling and fibrosis. In comparison, the combination of RLX and NAC prevented the cardiomyopathy-induced LV macrophage infiltration, remodelling, fibrosis and cardiomyocyte size, to a greater extent than either treatment alone after 7 days. The combination therapy also restored the isoprenaline-induced reduction in LV function, without affecting systolic BP.

CONCLUSION AND IMPLICATIONS

These findings demonstrated that the simultaneous targeting of oxidative stress and fibrosis is key to treating the pathophysiology and dysfunction induced by cardiomyopathy.

Human Recombinant Relaxin (Serelaxin) as Anti-fibrotic Agent: Pharmacology, Limitations and Actual Perspectives

Relaxin (recombinant human relaxin-2 hormone; RLX-2; serelaxin) had raised expectations as a new medication for fibrotic diseases. A plethora of in vitro and in vivo studies have offered convincing demonstrations that relaxin promotes remodelling of connective tissue extracellular matrix mediated by inhibition of multiple fibrogenic pathways, especially the downstream signalling of transforming growth factor (TGF)-β1, a major pro-fibrotic cytokine, and the recruitment and activation of myofibroblast, the main fibrosis-generating cells. However, all clinical trials with relaxin in patients with fibrotic diseases gave inconclusive results. In this review, we have summarized the molecular mechanisms of fibrosis, highlighting those which can be effectively targeted by relaxin. Then, we have performed a critical reappraisal of the clinical trials performed to-date with relaxin as anti-fibrotic drug, in order to highlight their key points of strength and weakness and to identify some future opportunities for the therapeutic use of relaxin, or its analogues, in fibrotic diseases and pathologic scarring which, in our opinion, deserve to be investigated.

NOTCH1 is critical for fibroblast-mediated induction of cardiomyocyte specialization into ventricular conduction system-like cells in vitro

Cardiac fibroblasts are present throughout the myocardium and are enriched in the microenvironment surrounding the ventricular conduction system (VCS). Several forms of arrhythmias are linked to VCS abnormalities, but it is still unclear whether VCS malformations are cardiomyocyte autonomous or could be linked to crosstalk between different cell types. We reasoned that fibroblasts influence cardiomyocyte specialization in VCS cells. We developed 2D and 3D culture models of neonatal rat cardiac cells to assess the influence of cardiac fibroblasts on cardiomyocytes. Cardiomyocytes adjacent to cardiac fibroblasts showed a two-fold increase in expression of VCS markers (NAV1.5 and CONTACTIN 2) and calcium transient duration, displaying a Purkinje-like profile. Fibroblast-conditioned media (fCM) was sufficient to activate VCS-related genes (Irx3, Scn5a, Connexin 40) and to induce action potential prolongation, a hallmark of Purkinge phenotype. fCM-mediated response seemed to be spatially-dependent as cardiomyocyte organoids treated with fCM had increased expression of connexin 40 and NAV1.5 primarily on its outer surface. Finally, NOTCH1 activation in both cardiomyocytes and fibroblasts was required for connexin 40 up-regulation (a proxy of VCS phenotype). Altogether, we provide evidence that cardiac fibroblasts influence cardiomyocyte specialization into VCS-like cells via NOTCH1 signaling in vitro.

Mechanisms of diabetic cardiomyopathy and potential therapeutic strategies: preclinical and clinical evidence

The pathogenesis and clinical features of diabetic cardiomyopathy have been well-studied in the past decade, but effective approaches to prevent and treat this disease are limited. Diabetic cardiomyopathy occurs as a result of the dysregulated glucose and lipid metabolism associated with diabetes mellitus, which leads to increased oxidative stress and the activation of multiple inflammatory pathways that mediate cellular and extracellular injury, pathological cardiac remodelling, and diastolic and systolic dysfunction. Preclinical studies in animal models of diabetes have identified multiple intracellular pathways involved in the pathogenesis of diabetic cardiomyopathy and potential cardioprotective strategies to prevent and treat the disease, including antifibrotic agents, anti-inflammatory agents and antioxidants. Some of these interventions have been tested in clinical trials and have shown favourable initial results. In this Review, we discuss the mechanisms underlying the development of diabetic cardiomyopathy and heart failure in type 1 and type 2 diabetes mellitus, and we summarize the evidence from preclinical and clinical studies that might provide guidance for the development of targeted strategies. We also highlight some of the novel pharmacological therapeutic strategies for the treatment and prevention of diabetic cardiomyopathy.

Relaxin Can Mediate Its Anti-Fibrotic Effects by Targeting the Myofibroblast NLRP3 Inflammasome at the Level of Caspase-1

Introduction

The NLRP3 inflammasome produces interleukin (IL)-1β and IL-18, which when chronically activated by transforming growth factor (TGF)-β1, contribute to fibrosis. The recombinant form of the anti-fibrotic hormone, relaxin (RLX), suppresses the pro-fibrotic influence of TGF-β1 and toll-like receptor (TLR)-4 on NLRP3 inflammasome priming and activity in human cardiac myofibroblasts and mice with cardiomyopathy. However, whether RLX also modulates components of the myofibroblast NLRP3 inflammasome remains unknown.

Methods and Results

Stimulation of a human dermal fibroblast (HDF) cell line with TGF-β1 [5 ng/ml; to promote myofibroblast (HDMF) differentiation], LPS (100 ng/ml; to prime the NLRP3 inflammasome) and ATP (5 mM; to activate the NLPR3 inflammasome) (T+L+A) significantly increased NLRP3 inflammasome priming and activity after 8 and 72 h; and α-SMA expression (myofibroblast differentiation) and collagen-I deposition after 72 h. siRNA-induced knock-down of NLRP3 inflammasome priming components (NLRP3, ASC, caspase-1) in T+L+A-stimulated HDMFs for 24 h, completely knocked-down each component after 72 h. RLX (100 ng/ml) administration to T+L+A-stimulated HDMFs after control, NLRP3 or ASC siRNA transfection, equivalently suppressed IL-1β, pro-IL-18, α-SMA, and collagen-I protein levels (by 40%–50%; all p<0.05 vs. T+L+A) after 72 h, as determined by Western blotting. These RLX-induced effects were abrogated by siRNA knock-down of caspase-1.

Conclusion

The anti-fibrotic actions of RLX appear to require modulation of caspase-1 within the myofibroblast NLRP3 inflammasome.

Platelet-Rich Plasma Modulates Gap Junction Functionality and Connexin 43 and 26 Expression During TGF-β1-Induced Fibroblast to Myofibroblast Transition: Clues for Counteracting Fibrosis

Skeletal muscle repair/regeneration may benefit by Platelet-Rich Plasma (PRP) treatment owing to PRP pro-myogenic and anti-fibrotic effects. However, PRP anti-fibrotic action remains controversial. Here, we extended our previous researches on the inhibitory effects of PRP on in vitro transforming growth factor (TGF)-β1-induced differentiation of fibroblasts into myofibroblasts, the effector cells of fibrosis, focusing on gap junction (GJ) intercellular communication. The myofibroblastic phenotype was evaluated by cell shape analysis, confocal fluorescence microscopy and Western blotting analyses of α-smooth muscle actin and type-1 collagen expression, and electrophysiological recordings of resting membrane potential, resistance, and capacitance. PRP negatively regulated myofibroblast differentiation by modifying all the assessed parameters. Notably, myofibroblast pairs showed an increase of voltage-dependent GJ functionality paralleled by connexin (Cx) 43 expression increase. TGF-β1-treated cells, when exposed to a GJ blocker, or silenced for Cx43 expression, failed to differentiate towards myofibroblasts. Although a minority, myofibroblast pairs also showed not-voltage-dependent GJ currents and coherently Cx26 expression. PRP abolished the TGF-β1-induced voltage-dependent GJ current appearance while preventing Cx43 increase and promoting Cx26 expression. This study adds insights into molecular and functional mechanisms regulating fibroblast-myofibroblast transition and supports the anti-fibrotic potential of PRP, demonstrating the ability of this product to hamper myofibroblast generation targeting GJs.

Recombinant human H2 relaxin (serelaxin) as a cardiovascular drug: aiming at the right target

Serelaxin (recombinant human relaxin-2 hormone; RLX-2) had raised expectations as a new medication for cardiovascular diseases. Evidence from preclinical studies indicated that serelaxin has chronotropic, inotropic, and anti-arrhythmic actions on the myocardium and cardioprotective effects mediated by vasodilation, angiogenesis, and inhibition of inflammation and fibrosis. However, clinical trials with serelaxin in patients with acute heart failure (AHF) gave inconclusive results. A critical reappraisal of the comprehensive cardiovascular actions of serelaxin clearly delineates acute myocardial infarction (AMI) as a feasible therapeutic target. Serelaxin acts at multiple levels on the pathogenic mechanisms of AMI and previous in vivo studies suggest that its administration at reperfusion affords myocardial salvage. Thus, serelaxin could be an effective adjunctive medical therapy to coronary angioplasty.

Characterizing relaxin receptor expression and exploring relaxin's effect on tissue remodeling/fibrosis in the human bladder

Background

Relaxin is an endogenous protein that has been shown to have antifibrotic properties in various organ systems. There has been no characterization of relaxin’s role in the human bladder. Our objective was to characterize relaxin receptor expression in the human bladder and assess relaxin’s effect on tissue remodeling/fibrosis pathways in bladder smooth muscle cells.

Methods

Relaxin family peptide receptor 1 (RXFP1) and RXFP2 expression was assessed using quantitative reverse transcriptase-PCR (qRT-PCR) and immunohistochemistry (IHC) on primary bladder tissue. Primary human smooth muscle bladder cells were cultured and stimulated with various concentrations of relaxin. Western blot, qRTPCR, ELISA, and zymogram assays were used to analyze fibrosis/tissue remodeling pathway proteins.

Results

There was universal mRNA transcript detection and protein expression of relaxin receptors in primary bladder specimens. Immunohistochemistry demonstrated RXFP1 and RXFP2 localizing to both urothelial and smooth muscle cell layers of the bladder. 24 h of in vitro relaxin stimulation did not affect mRNA expression of selected proteins in human bladder smooth muscle cells. However, 48 h of in vitro relaxin stimulation resulted in upregulation of active (p = 0.004) and latent (p = 0.027) MMP-2 in cell lysate, and upregulation of active MMP-2 in supernatant (p = 0.04). There was a dose dependent relationship with increasing expression of MMP-2 with increasing relaxin concentration. Relaxin stimulation resulted in decreased levels of active and total TGF-β1 in supernatant and extracellular matrix (p < 0.005 with 100 ng/mL relaxin stimulation).

Conclusions

In the human bladder, relaxin receptors are expressed at the dome and trigone and localize to the urothelium and smooth muscle cell layers. Stimulation of human bladder SMCs with relaxin in vitro affects expression of MMP-2 and TGF-β1.

The anti-fibrotic actions of relaxin are mediated through AT2 R-associated protein phosphatases via RXFP1-AT2 R functional crosstalk in human cardiac myofibroblasts

Fibrosis is a hallmark of several cardiovascular diseases. The relaxin family peptide receptor 1 (RXFP1) agonist, relaxin, has rapidly occurring anti-fibrotic actions which are mediated through RXFP1 and angiotensin II receptor crosstalk on renal and cardiac myofibroblasts. Here, we investigated whether this would allow relaxin to indirectly activate angiotensin II type 2 receptor (AT₂ R)-specific signal transduction in primary human cardiac myofibroblasts (HCMFs). The anti-fibrotic effects of recombinant human relaxin (RLX; 16.8 nM) or the AT₂ R-agonist, Compound 21 (C21; 1 μM), were evaluated in TGF-β1-stimulated HCMFs, in the absence or presence of an RXFP1 antagonist (1 μM) or AT₂ R antagonist (0.1 μM) to confirm RXFP1-AT₂ R crosstalk. Competition binding for RXFP1 was determined. Western blotting was performed to determine which AT₂ R-specific protein phosphatases were expressed by HCMFs; then, the anti-fibrotic effects of RLX and/or C21 were evaluated in the absence or presence of pharmacological inhibition (NSC95397 (1 μM) for MKP-1; okadaic acid (10 nM) for PP2A) or siRNA-knockdown of these phosphatases after 72 hours. The RLX- or C21-induced increase in ERK1/2 and nNOS phosphorylation, and decrease in α-SMA (myofibroblast differentiation) and collagen-I expression by HCMFs was abrogated by pharmacological blockade of RXFP1 or the AT₂ R, confirming RXFP1-AT₂ R crosstalk in these cells. HCMFs were found to express AT₂ R-dependent MKP-1 and PP2A phosphatases, while pharmacological blockade or siRNA-knockdown of either phosphatase also abolished RLX and/or C21 signal transduction in HCMFs (all P < .05 vs RLX or C21 alone). These findings demonstrated that RLX can indirectly activate AT₂ R-dependent phosphatase activity in HCMFs by signaling through RXFP1-AT₂ R crosstalk, which have important therapeutic implications for its anti-fibrotic actions.

B7-33, a Functionally Selective Relaxin Receptor 1 Agonist, Attenuates Myocardial Infarction-Related Adverse Cardiac Remodeling in Mice

Background

Human relaxin‐2 is a peptide hormone capable of pleiotropic effects in several organ systems. Its recombinant formulation (serelaxin) has been demonstrated to reduce infarct size and prevent excessive scar formation in animal models of cardiac ischemia‐reperfusion injury. B7‐33, a synthetically designed peptide analogous to B‐chain of relaxin‐2, invokes signaling at relaxin family peptide receptor 1 (cognate receptor for relaxin‐2) by preferentially phosphorylating the mitogen‐activated protein kinase extracellular signal‐regulated kinase 1/2. We sought to investigate the effects of B7‐33 treatment post ischemia‐reperfusion injury in mice.

Methods and Results

Adult male CD1 mice were subjected to ischemia‐reperfusion via ligation of left anterior descending artery for 30 minutes, followed by 24 hours or 7 days of reperfusion. Echocardiography was performed to assess cardiac function, and cardiac tissue was stained to determine infarct size at 24 hours. B7‐33 significantly reduced infarct size (21.99% versus 45.32%; P=0.02) and preserved fractional shortening (29% versus 23%; P=0.02) compared with vehicle. The difference in fractional shortening further increased at 7 days post myocardial infarction (29% versus 20% for B7‐33 and vehicle groups, respectively). In vitro, primary cardiomyocytes were isolated from adult hearts and subjected to simulated ischemia‐reperfusion injury (simulated ischemia reoxygenation). B7‐33 (50 and 100 nmol/L) improved cell survival and reduced the expression of GRP78 (glucose regulated protein), an endoplasmic reticulum stress marker. Subsequently, B7‐33 (100 nmol/L) reduced tunicamycin (2.5 μg/mL) induced upregulation of GRP78 in an extracellular signal‐regulated kinase 1/2–dependent manner.

Conclusions

B7‐33 confers acute cardioprotection and limits myocardial infarction–related adverse remodeling in mice by attenuating cardiomyocyte death and endoplasmic reticulum stress as well as preserving cardiac function.

Serelaxin alleviates cardiac fibrosis through inhibiting endothelial-to-mesenchymal transition via RXFP1

Rationale: Cardiac fibrosis is an integral constituent of every form of chronic heart disease, and persistence of fibrosis reduces tissue compliance and accelerates the progression to heart failure. Relaxin-2 is a human hormone, which has various physiological functions such as mediating renal vasodilation in pregnancy. Its recombinant form Serelaxin has recently been tested in clinical trials as a therapy for acute heart failure but did not meet its primary endpoints. The aim of this study is to examine whether Serelaxin has an anti-fibrotic effect in the heart and therefore could be beneficial in chronic heart failure. Methods: We utilized two different cardiac fibrosis mouse models (ascending aortic constriction (AAC) and Angiotensin II (ATII) administration via osmotic minipumps) to assess the anti-fibrotic potential of Serelaxin. Histological analysis, immunofluorescence staining and molecular analysis were performed to assess the fibrosis level and indicate endothelial cells which are undergoing EndMT. In vitro TGFβ1-induced endothelial-to-mesenchymal transition (EndMT) assays were performed in human coronary artery endothelial cells and mouse cardiac endothelial cells (MCECs) and were examined using molecular methods. Chromatin immunoprecipitation-qPCR assay was utilized to identify the Serelaxin effect on chromatin remodeling in the Rxfp1 promoter region in MCECs. Results: Our results demonstrate a significant and dose-dependent anti-fibrotic effect of Serelaxin in the heart in both models. We further show that Serelaxin mediates this effect, at least in part, through inhibition of EndMT through the endothelial Relaxin family peptide receptor 1 (RXFP1). We further demonstrate that Serelaxin administration is able to increase its own receptor expression (RXFP1) through epigenetic regulation in form of histone modifications by attenuating TGFβ-pSMAD2/3 signaling in endothelial cells. Conclusions: This study is the first to identify that Serelaxin increases the expression of its own receptor RXFP1 and that this mediates the inhibition of EndMT and cardiac fibrosis, suggesting that Serelaxin may have a beneficial effect as anti-fibrotic therapy in chronic heart failure.

Relaxin reverses maladaptive remodeling of the aged heart through Wnt-signaling

Healthy aging results in cardiac structural and electrical remodeling that increases susceptibility to cardiovascular diseases. Relaxin, an insulin-like hormone, suppresses atrial fibrillation, inflammation and fibrosis in aged rats but the mechanisms-of-action are unknown. Here we show that relaxin treatment of aged rats reverses pathological electrical remodeling (increasing Nav1.5 expression and localization of Connexin43 to intercalated disks) by activating canonical Wnt signaling. In isolated adult ventricular myocytes, relaxin upregulated Nav1.5 (EC₅₀ = 1.3 nM) by a mechanism inhibited by the addition of Dickkopf-1. Furthermore, relaxin increased the levels of connexin43, Wnt1, and cytosolic and nuclear β-catenin. Treatment with Wnt1 or CHIR-99021 (a GSK3β inhibitor) mimicked the relaxin effects. In isolated fibroblasts, relaxin blocked TGFβ-induced collagen elevation in a Wnt dependent manner. These findings demonstrate a close interplay between relaxin and Wnt-signaling resulting in myocardial remodeling and reveals a fundamental mechanism of great therapeutic potential.

Fibrosis and the bladder, implications for function ICI-RS 2017

AIMS

Most benign bladder pathologies are associated with an increase of extracellular matrix (ECM-fibrosis) and may progress from formation of stiffer matrix to a more compliant structure. The aims were to summarize current knowledge of the origins of bladder fibrosis and consequences in bladder function.

METHODS

A meeting at the International Consultation on Incontinence Research Society 2017 congress discussed the above aims and considered paradigms to reduce the extent of fibrosis. Discussants based their arguments on the basis of their own expertise, supplemented by review of the literature through PubMed. Proposals for future work were derived from the discussion.

RESULTS

Altered urodynamic compliance when ECM deposition is increased is mirrored by changes in the elastic modulus of isolated tissue, whether compliance is decreased or increased. No changes to compliance or fibrosis have been reported after botulinum toxin injections. Several paracrine and autocrine agents increase ECM deposition, the role of TGF-β was particularly emphasized. None of these agents has a net long-term effect on detrusor contractility and the reduction of contractile performance with increased ECM is due solely to a loss of detrusor mass. Several strategies to reduce fibrosis were described, ranging from potential therapeutic roles for vitamin-D or endostatin, manipulation of intracellular pathways that mediate myofibroblast differentiation and the potential role of the anti-fibrotic hormone relaxin. An understanding of epigenetic regulation of ECM deposition was also considered.

CONCLUSIONS

The conclusion that reduced bladder contractile function with increased fibrosis is due largely to the replacement of detrusor with ECM offers a way forward for future research to consider approaches that will restore bladder function by reducing ECM deposition.

Epithelial and interstitial Notch1 activity contributes to the myofibroblastic phenotype and fibrosis

Background

Notch1 signalling is a stem-cell-related pathway that is essential for embryonic development, tissue regeneration and organogenesis. However, the role of Notch1 in the formation of myofibroblasts and fibrosis in kidneys following injury remains unknown.

Methods

The activity of Notch1 signalling was evaluated in fibrotic kidneys in CKD patients and in ureteral obstructive models in vivo and in cultured fibroblasts and TECs in vitro. In addition, the crosstalk of Notch1 with TGF-β1/Smad2/3 signalling was also investigated.

Results

Notch1 activity was elevated in fibrotic kidneys of rat models and patients with chronic kidney disease (CKD). Further study revealed that epithelial and interstitial Notch1 activity correlated with an α-SMA-positive myofibroblastic phenotype. In vitro, injury stimulated epithelial Notch1 activation and epithelial-mesenchymal transition (EMT), resulting in matrix deposition in tubular epithelial cells (TECs). Additionally, interstitial Notch1 activation in association with fibroblast-myofibroblast differentiation (FMD) in fibroblasts mediated a myofibroblastic phenotype. These TGF-β1/Smad2/3-dependent phenotypic transitions were abolished by Notch1 knockdown or a specific antagonist, DAPT, and were exacerbated by Notch1 overexpression or an activator Jagged-1-Fc chimaera protein. Interestingly, as a major driving force behind the EMT and FMD, TGF-β1, also induced epithelial and interstitial Notch1 activity, indicating that TGF-β1 may engage in crosstalk with Notch1 signalling to trigger fibrogenesis.

Conclusion

These findings suggest that epithelial and interstitial Notch1 activation in kidneys following injury contributes to the myofibroblastic phenotype and fibrosis through the EMT in TECs and to the FMD in fibroblasts by targeting downstream TGF-β1/Smad2/3 signalling.

Microvascular Dysfunction in Heart Failure With Preserved Ejection Fraction

Heart failure with preserved ejection fraction (HFpEF) is an increasingly studied entity accounting for 50% of all diagnosed heart failure and that has claimed its own dignity being markedly different from heart failure with reduced EF in terms of etiology and natural history (Graziani et al., 2018). Recently, a growing body of evidence points the finger toward microvascular dysfunction as the major determinant of the pathological cascade that justifies clinical manifestations (Crea et al., 2017). The high burden of comorbidities such as metabolic syndrome, hypertension, atrial fibrillation, chronic kidney disease, obstructive sleep apnea, and similar, could lead to a systemic inflammatory state that impacts the physiology of the endothelium and the perivascular environment, engaging complex molecular pathways that ultimately converge to myocardial fibrosis, stiffening, and dysfunction (Paulus and Tschope, 2013). These changes could even self-perpetrate with a positive feedback where hypoxia and locally released inflammatory cytokines trigger interstitial fibrosis and hypertrophy (Ohanyan et al., 2018). Identifying microvascular dysfunction both as the cause and the maintenance mechanism of this condition has opened the field to explore specific pharmacological targets like nitric oxide (NO) pathway, sarcomeric titin, transforming growth factor beta (TGF-β) pathway, immunomodulators or adenosine receptors, trying to tackle the endothelial impairment that lies in the background of this syndrome (Graziani et al., 2018;Lam et al., 2018). Yet, many questions remain, and the new data collected still lack a translation to improved treatment strategies. To further elaborate on this tangled and exponentially growing topic, we will review the evidence favoring a microvasculature-driven etiology of this condition, its clinical correlations, the proposed diagnostic workup, and the available/hypothesized therapeutic options to address microvascular dysfunction in the failing heart.

Serelaxin inhibits the profibrotic TGF-β1/IL-1β axis by targeting TLR-4 and the NLRP3 inflammasome in cardiac myofibroblasts

The recombinant form of the peptide hormone relaxin, serelaxin (RLX), mediates its anti-fibrotic actions by impeding the profibrotic activity of cytokines including TGF-β1 and IL-1β. As IL-1β can be produced by the nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domains-containing protein 3 (NLRP3) inflammasome, this study determined whether RLX targeted the inflammasome to inhibit the profibrotic TGF-β1/IL-1β axis in primary human cardiac myofibroblasts (HCMFs) in vitro and in mice with isoproterenol (ISO)-induced cardiomyopathy in vivo. HCMFs stimulated with TGF-β1 (5 ng/ml), LPS (100 ng/ml), and ATP (5 mM) (T+L+A) for 8 h, to induce the NLRP3 inflammasome, demonstrated significantly increased protein expression of markers of NLRP3 priming (NLRP3, apoptosis-associated speck-like protein containing a C-terminal caspase-recruitment domain, procaspase-1) and activity (IL-1β, IL-18). After 72 h, there was significantly increased neuronal NOS (nNOS), TLR-4, procaspase-1, myofibroblast differentiation, and collagen-I deposition. These measures, along with interstitial TGF-β1 expression and collagen deposition, were also increased in the left ventricle (LV) of ISO-injured mice 14 d postinjury. RLX [16.8 nM (100 ng/ml) in vitro; 0.5 mg/kg per day in vivo] inhibited T+L+A- and ISO-induced TLR-4 expression, NLRP3 priming, IL-1β, IL-18, myofibroblast differentiation, and interstitial collagen deposition at the time points studied, via the promotion of nNOS; with the NLRP3- and IL-1β-inhibitory effects of RLX in HCMFs being abrogated by pharmacological blockade of nNOS or TLR-4. Comparatively, the small molecule NLRP3 inhibitor, N-{[(1,2,3,5,6,7-hexahydro-s-indacen-4-yl)amino]carbonyl}-4-(1-hydroxy-1-methylethyl)-2-furansulfonamide (1 μM in vitro, 10 mg/kg/d in vivo), inhibited components of the NLRP3 inflammasome in vitro and in vivo and ISO-induced interstitial LV fibrosis in vivo but did not affect nNOS, TLR-4, myofibroblast differentiation, or myofibroblast-induced collagen deposition. Hence, RLX can inhibit the TGF-β1/IL-1β axis via a nNOS-TLR-4-NLRP3 inflammasome-dependent mechanism on cardiac myofibroblasts.-Cáceres, F. T., Gaspari, T. A., Samuel, C. S., Pinar, A. A. Serelaxin inhibits the profibrotic TGF-β1/IL-1β axis by targeting TLR-4 and the NLRP3 inflammasome in cardiac myofibroblasts.

Platelet-Rich Plasma and Bone Marrow-Derived Mesenchymal Stromal Cells Prevent TGF-β1-Induced Myofibroblast Generation but Are Not Synergistic when Combined: Morphological in vitro Analysis

The persistence of activated myofibroblasts is a hallmark of fibrosis of many organs. Thus, the modulation of the generation/functionality of these cells may represent a strategical anti-fibrotic therapeutic option. Bone marrow-derived mesenchymal stromal cell (MSC)-based therapy has shown promising clues, but some criticisms still limit the clinical use of these cells, including the need to avoid xenogeneic compound contamination for ex vivo cell amplification and the identification of appropriate growth factors acting as a pre-conditioning agent and/or cell delivery vehicle during transplantation, thus enabling the improvement of cell survival in the host tissue microenvironment. Many studies have demonstrated the ability of platelet-rich plasma (PRP), a source of many biologically active molecules, to positively influence MSC proliferation, survival, and functionality, as well as its anti-fibrotic potential. Here we investigated the effects of PRP, murine and human bone marrow-derived MSCs, and of the combined treatment PRP/MSCs on in vitro differentiation of murine NIH/3T3 and human HDFα fibroblasts to myofibroblasts induced by transforming growth factor (TGF)-β1, a well-known pro-fibrotic agent. The myofibroblastic phenotype was evaluated morphologically (cell shape and actin cytoskeleton assembly) and immunocytochemically (vinculin-rich focal adhesion clustering, α-smooth muscle actin and type-1 collagen expression). We found that PRP and MSCs, both as single treatments and in combination, were able to prevent the TGF-β1-induced fibroblast-myofibroblast transition. Unexpectedly, the combination PRP/MSCs had no synergistic effects. In conclusion, within the limitations related to an in vitro experimentation, our study may contribute to providing an experimental background for supporting the anti-fibrotic potential of the combination PRP/MSCs which, once translated "from bench to bedside," could potentially offer advantages over the single treatments.

The Notch pathway: a novel therapeutic target for cardiovascular diseases?

Introduction: The Notch pathway is involved in determining cell fate during development and postnatally in continuously renewing tissues, such as the endothelium, the epithelium, and in the stem cells pool. The dysregulation of the Notch pathway is one of the causes of limited response, or resistance, to available cancer treatments and novel therapeutic strategies based on Notch inhibition are being investigated in preclinical and clinical studies in oncology. A large body of evidence now shows that the dysregulation of the Notch pathway is also involved in the pathophysiology of cardiovascular diseases (CVDs). Areas covered: This review discusses the molecular mechanisms involving Notch which underlie heart failure, aortic valve calcification, and aortic aneurysm. Expert opinion: Despite the existence of preventive, pharmacological and surgical interventions approaches, CVDs are the first causes of mortality worldwide. The Notch pathway is becoming increasingly recognized as being involved in heart failure, aortic aneurysm and aortic valve calcification, which are among the most common global causes of mortality due to CVDs. As already shown in cancer, the dissection of the biological processes and molecular mechanisms involving Notch should pave the way for new strategies to prevent and cure these diseases.

Intraarticular injection of relaxin-2 alleviates shoulder arthrofibrosis

Arthrofibrosis is a prevalent condition affecting greater than 5% of the general population and leads to a painful decrease in joint range of motion (ROM) and loss of independence due to pathologic accumulation of periarticular scar tissue. Current treatment options are limited in effectiveness and do not address the underlying cause of the condition: accumulation of fibrotic collagenous tissue. Herein, the naturally occurring peptide hormone relaxin-2 is administered for the treatment of adhesive capsulitis (frozen shoulder) and to restore glenohumeral ROM in shoulder arthrofibrosis. Recombinant human relaxin-2 down-regulates type I collagen and α smooth muscle actin production and increases intracellular cAMP concentration in human fibroblast-like synoviocytes, consistent with a mechanism of extracellular matrix degradation and remodeling. Pharmacokinetic profiling of a bolus administration into the glenohumeral joint space reveals the brief systemic and intraarticular (IA) half-lives of relaxin-2: 0.96 h and 0.62 h, respectively. Furthermore, using an established, immobilization murine model of shoulder arthrofibrosis, multiple IA injections of human relaxin-2 significantly improve ROM, returning it to baseline measurements collected before limb immobilization. This is in contrast to single IA (sIA) or multiple i.v. (mIV) injections of relaxin-2 with which the ROM remains constrained. The histological hallmarks of contracture (e.g., fibrotic adhesions and reduced joint space) are absent in the animals treated with multiple IA injections of relaxin-2 compared with the untreated control and the sIA- and mIV-treated animals. As these findings show, local delivery of relaxin-2 is an innovative treatment of shoulder arthrofibrosis.

Circulating Relaxin-1 Level Is a Surrogate Marker of Myocardial Fibrosis in HFrEF

Introduction: Relaxin-1 (RLN1) has emerged as a possible therapeutic target in myocardial fibrosis due to its anti-fibrotic effects. Previous randomized clinical trials investigated therapeutic role of exogenous relaxin in patients with acute-on-chronic heart failure (HF) and failed to meet clinical endpoints. Here, we aimed to assess endogenous, circulating RLN1 levels in patients with heart failure with reduced ejection fraction (HFrEF) of ischemic origin. Furthermore, we analyzed relation of RLN1 and left ventricular diastolic function, left and right ventricular fibrosis, and invasive hemodynamic measurements. Unique feature of our study is the availability of ex vivo human myocardial tissue.

Methods: Human myocardial samples were available from the Transplantation Biobank of the Heart and Vascular Center at Semmelweis University after local ethical approval and informed consent of all participants (n = 47). Tissue was collected immediately after heart explantations; peripheral blood was collected before induction of anesthesia. Myocardial sections were stained for Masson’s trichrome and Picrosirius red staining to quantify fibrosis. Medical records were analyzed (ECG, anthropometry, blood tests, medication, echocardiography, and invasive hemodynamic measurements).

Results: Average RLN1 levels in HFrEF population were significantly higher than measured in age and gender matched healthy control human subjects (702 ± 283 pg/ml in HFrEF vs. 44 ± 27 pg/ml in control n = 47). We found a moderate inverse correlation between RLN1 levels and degree of myocardial fibrosis in both ventricles (r = −0.357, p = 0.014 in the right ventricle vs. r = −0.321, p = 0.028 in the left ventricle with Masson’s trichrome staining). Parallel, a moderate positive correlation was found in left ventricular diastolic function (echocardiography, E/A wave values) and RLN1 levels (r = 0.456, p = 0.003); a negative correlation with RLN1 levels and left ventricular end-systolic diameter (r = −0.373, p = 0.023), and diastolic pulmonary artery pressure (r = −0.894, p < 0.001). RLN1 levels showed moderate correlation with RLN2 levels (r = 0.453, p = 0.0003).

Conclusion: Increased RLN1 levels were accompanied by lower myocardial fibrosis rate, which is a novel finding in our patient population with coronary artery disease and HFrEF. RLN1 can have a biomarker role in ventricular fibrosis; furthermore, it may influence hemodynamic and vasomotor activity via neurohormonal mechanisms of action. Given these valuable findings, RLN1 may be targeted in anti-fibrotic therapeutics and in perioperative care of heart transplantation.

Understanding relaxin signalling at the cellular level

The peptide hormone relaxin mediates many biological actions including anti-fibrotic, vasodilatory, angiogenic, anti-inflammatory, anti-apoptotic, and organ protective effects across a range of tissues. At the cellular level, relaxin binds to the G protein-coupled receptor relaxin family peptide receptor 1 (RXFP1) to activate a variety of downstream signal transduction pathways. This signalling cascade is complex and also varies in diverse cellular backgrounds. Moreover, RXFP1 signalling shows crosstalk with other receptors to mediate some of its physiological functions. This review summarises known signalling pathways induced by acute versus chronic treatment with relaxin across a range of cell types, it describes RXFP1 crosstalk with other receptors, signalling pathways activated by other ligands targeting RXFP1, and it also outlines physiological relevance of RXFP1 signalling outputs. Comprehensive understanding of the mechanism of relaxin actions in fibrosis, vasodilation, as well as organ protection, will further support relaxin's clinical potential.

Relaxin and extracellular matrix remodeling: Mechanisms and signaling pathways

Fibrosis is associated with accumulation of excess fibrillar collagen, leading to tissue dysfunction. Numerous processes, including inflammation, myofibroblast activation, and endothelial-to-mesenchymal transition, play a role in the establishment and progression of fibrosis. Relaxin is a peptide hormone with well-known antifibrotic properties that result from its action on numerous cellular targets to reduce fibrosis. Relaxin activates multiple signal transduction pathways as a mechanism to suppress inflammation and myofibroblast activation in fibrosis. In this review, the general mechanisms underlying fibrotic diseases are described, along with the current state of knowledge regarding cellular targets of relaxin. Finally, an overview is presented summarizing the signaling pathways activated by relaxin and other relaxin family peptide receptor agonists to suppress fibrosis.

Cardioprotective actions of relaxin

Relaxin is a hormone of pregnancy first discovered for its ability to induce ligament relaxation in nonpregnant guinea pig and is important for softening of the birth canal during parturition, decidualization, implantation, nipple development and increased maternal renal perfusion, glomerular filtration, and cardiac output. Subsequently, relaxin has been shown to exert multiple beneficial cardiovascular effects during pathological events such as hypertension, atrial fibrillation, heart failure and myocardial infarction, including suppression of arrhythmia and inflammation, and reversal of fibrosis. Despite extensive studies, the mechanisms underlying relaxin's effects are not well understood. Relaxin signals primarily through its G protein coupled receptor, the relaxin family peptide receptor-1, to activate multiple signaling pathways and this review summarizes our understanding of these pathways as they relate to the cardioprotective actions of relaxin, focusing on relaxin's anti-fibrotic, anti-arrhythmic and anti-inflammatory properties. Further, this review includes a brief overview of relaxin in clinical trials for heart failure and progress in the development of relaxin mimetics.

Effect of integrin β1 in the treatment of stress urinary incontinence by electrical stimulation

The aim of the present study was to investigate the protective effect of integrin β1 in the treatment of stress urinary incontinence (SUI) by electrical stimulation, and the underlying mechanisms by which electrical stimulation regulates the collagen metabolism of female vaginal wall fibroblasts (FVWFs). FVWFs obtained from the vaginal wall tissue of patients with (Ingelman-Sundberg scale; grade II, n=8; grade III, n=10) or without (n=8) SUI during gynecological operations were isolated by enzymatic digestion and subsequently identified by immunocytochemistry. Following this, cultured FVWFs were treated with an inhibitor of integrin β1, recombinant human integrin β1 and electrical stimulation (100 mv/mm, 2 h, 20 Hz), followed by total mRNA and protein extraction. mRNA and protein expression levels of integrin β1, transforming growth factor (TGF)-β1 and collagen (COL) I and III in FVWFs were quantified by reverse transcription-quantitative PCR (RT-qPCR) and western blot analysis respectively. Integrin β1, TGF-β1 and COL I and III expression levels were decreased in patients with SUI compared with healthy controls, and the grade III group had lower levels than the grade II group. Following electrical stimulation treatment, the expression levels of TGF-β1, COL I and III were enhanced in the grade II group, but not in the grade III group. Nevertheless, the inhibitor of integrin β1 reduced the protective effect of electrical stimulation in the grade II group. In addition, electrical stimulation combined with recombinant human integrin β1 could also protect cells from SUI in the grade III group. The present study provides evidence for the increased degradation of the extracellular matrix and integrin β1 in the vaginal wall tissues of patients with SUI, and the protective effect of electrical stimulation against SUI via integrin β1. These results provide a novel mechanism for the treatment of SUI using electrical stimulation.

Effect of the peptides Relaxin, Neuregulin, Ghrelin and Glucagon-like peptide-1, on cardiomyocyte factors involved in the molecular mechanisms leading to diastolic dysfunction and/or heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) represents an important cardiac condition because of its increasing prevalence, resistance to treatment and high associated morbidity and mortality. Two of the major mechanisms responsible for HFpEF are impaired cardiomyocyte sarcoplasmic reticulum (SR) Ca²⁺ ATPase (SERCA2a), which is responsible for calcium reuptake into the SR, and cardiac fibroblasts/myofibroblasts that produce collagen or myocardial fibrosis. Phospholamban (PLB), in the SR and endoplasmic reticulum, is the primary regulator of SERCA2a in the heart and acts as a reversible inhibitor of SERCA2a. Glucagon-like peptide-1, a 30 amino acid peptide, improves diastolic function through increasing SERCA2a expression and activity as well as by decreasing phosphorylation of Ryanodine receptors. It also enhances collagen production through enhanced procollagen IalphaI/IIIalphaI, connective tissue growth factor, fibronectin, TGF-β3 as well as Interleukin -10, -1beta, and -6 gene expression. Relaxin-2, a two chain, 53 amino acid peptide, increases Ser16- and Thr17-phosphorylation levels of PLB, thereby relieving SERCA2a of its inhibition. H3 Relaxin inhibits TGF-β1-stimulated collagen deposition through H3 relaxin-induced increases in pSmad2. Neuregulin-1, an epidermal growth factor, induces nitric oxide and PI-3 kinase activation that enhance SERCA2 activity. Neuregulin-1 was associated with less myocardial macrophage infiltration and cytokine expression reducing collagen deposition. Ghrelin, a 28 amino acid peptide, improves SERCA2a function by inducing PLB phosphorylation. Ghrelin also reduces cardiac fibrosis. In summary, Glucagon-like peptide-1, Relaxin-2, Neuregulin-1, and Ghrelin each modify calcium dynamics, collagen expression, and myocardial fibrosis through attenuation of deleterious signaling cascades, and induction of adaptive pathways, representing potential therapeutic targets for HFpEF.

Therapeutic approaches for cardiac regeneration and repair

Ischaemic heart disease is a leading cause of death worldwide. Injury to the heart is followed by loss of the damaged cardiomyocytes, which are replaced with fibrotic scar tissue. Depletion of cardiomyocytes results in decreased cardiac contraction, which leads to pathological cardiac dilatation, additional cardiomyocyte loss, and mechanical dysfunction, culminating in heart failure. This sequential reaction is defined as cardiac remodelling. Many therapies have focused on preventing the progressive process of cardiac remodelling to heart failure. However, after patients have developed end-stage heart failure, intervention is limited to heart transplantation. One of the main reasons for the dramatic injurious effect of cardiomyocyte loss is that the adult human heart has minimal regenerative capacity. In the past 2 decades, several strategies to repair the injured heart and improve heart function have been pursued, including cellular and noncellular therapies. In this Review, we discuss current therapeutic approaches for cardiac repair and regeneration, describing outcomes, limitations, and future prospects of preclinical and clinical trials of heart regeneration. Substantial progress has been made towards understanding the cellular and molecular mechanisms regulating heart regeneration, offering the potential to control cardiac remodelling and redirect the adult heart to a regenerative state.

Platelet-Rich Plasma Prevents In Vitro Transforming Growth Factor-β1-Induced Fibroblast to Myofibroblast Transition: Involvement of Vascular Endothelial Growth Factor (VEGF)-A/VEGF Receptor-1-Mediated Signaling †

The antifibrotic potential of platelet-rich plasma (PRP) is controversial. This study examined the effects of PRP on in vitro transforming growth factor (TGF)-β1-induced differentiation of fibroblasts into myofibroblasts, the main drivers of fibrosis, and the involvement of vascular endothelial growth factor (VEGF)-A in mediating PRP-induced responses. The impact of PRP alone on fibroblast differentiation was also assessed. Myofibroblastic phenotype was evaluated by confocal fluorescence microscopy and western blotting analyses of α-smooth muscle actin (sma) and type-1 collagen expression, vinculin-rich focal adhesion clustering, and stress fiber assembly. Notch-1, connexin 43, and VEGF-A expression were also analyzed by RT-PCR. PRP negatively regulated fibroblast-myofibroblast transition via VEGF-A/VEGF receptor (VEGFR)-1-mediated inhibition of TGF-β1/Smad3 signaling. Indeed TGF-β1/PRP co-treated fibroblasts showed a robust attenuation of the myofibroblastic phenotype concomitant with a decrease of Smad3 expression levels. The VEGFR-1 inhibition by KRN633 or blocking antibodies, or VEGF-A neutralization in these cells prevented the PRP-promoted effects. Moreover PRP abrogated the TGF-β1-induced reduction of VEGF-A and VEGFR-1 cell expression. The role of VEGF-A signaling in counteracting myofibroblast generation was confirmed by cell treatment with soluble VEGF-A. PRP as single treatment did not induce fibroblast myodifferentiation. This study provides new insights into cellular and molecular mechanisms underpinning PRP antifibrotic action.

Relaxin induces up-regulation of ADAM10 metalloprotease in RXFP1-expressing cells by PI3K/AKT signaling

ADAM10 metalloprotease is required for activation of Notch-1, a transmembrane receptor regulating cell differentiation, proliferation and apoptosis, whose intracellular proteolytic fragment NICD mediates some key cardiovascular effects of the hormone relaxin (RLX). This study demonstrates the involvement of ADAM10 and PI3K/Akt signaling in mediating RLX-induced Notch-1 activation. H9c2 cardiomyocytes and NIH3T3 fibroblasts were incubated with human RLX-2 (17 nmol/l, 24 h) in presence or absence of the PI3K or Akt inhibitors wortmannin (WT, 100 nmol/l) and triciribine (TCN, 1 μmol/l). Cyclohexanedione-inactivated RLX (iRLX) served as negative control. RLX significantly increased Akt phosphorylation, ADAM10 and NICD expression, which were abolished by WT or TCN and did not occur with iRLX. These findings highlight a new receptor-specific signal transduction pathway of RLX.

Serelaxin induces Notch1 signaling and alleviates hepatocellular damage in orthotopic liver transplantation

Liver ischemia-reperfusion injury (IRI) represents a risk factor for early graft dysfunction and an obstacle to expanding donor pool in orthotopic liver transplantation (OLT). We have reported on the crucial role of macrophage Notch1 signaling in mouse warm hepatic IRI model. However, its clinical relevance or therapeutic potential remain unknown. Here, we used Serelaxin (SER), to verify Notch1 induction and putative hepatoprotective function in ischemia-reperfusion-stressed OLT. C57BL/6 mouse livers subjected to extended (18-hour) cold storage were transplanted to syngeneic recipients. SER treatment at reperfusion ameliorated IRI, improved post-OLT survival, decreased neutrophil/macrophage infiltration, and suppressed proinflammatory cytokine programs, while simultaneously increasing Notch intracellular domain (NICD) and hairy and enhancer of split 1 (Hes1) target genes. In bone marrow-derived macrophage cultures, SER suppressed proinflammatory while enhancing antiinflammatory gene expression concomitantly with increased NICD and Hes1. Hepatic biopsies from 21 adult primary liver transplant patients (2 hours postreperfusion) were divided into low-NICD (n = 11) and high-NICD (n = 10) expression groups (western blots). Consistent with our murine findings, human livers characterized by high NICD were relatively IRI resistant, as shown by serum alanine aminotransferase (ALT) levels at day 1 post-OLT. Our study documents the efficacy of SER-Notch1 signaling in mouse OLT and highlights the protective function of Notch1 in liver transplant patients.

Relaxin as a Therapeutic Target for the Cardiovascular Complications of Diabetes

Cardiovascular complications are the major cause of mortality in patients with diabetes. This is closely associated with both macrovascular and microvascular complications of diabetes, which lead to organ injuries in diabetic patients. Previous studies have consistently demonstrated the beneficial effects of relaxin treatment for protection of the vasculature, with evidence of antioxidant and anti-remodeling actions. Relaxin enhances nitric oxide, prostacyclin and endothelium-derived hyperpolarization (EDH)-type-mediated relaxation in various vascular beds. These effects of relaxin on the systemic vasculature, coupled with its cardiac actions, reduce pulmonary capillary wedge pressure and pulmonary artery pressure. This results in an overall decrease in systemic and pulmonary vascular resistance in heart failure patients. The anti-fibrotic actions of relaxin are well established, a desirable property in the context of diabetes. Further, relaxin ameliorates diabetic wound healing, with accelerated angiogenesis and vasculogenesis. Relaxin-mediated stimulation of vascular endothelial growth factor (VEGF) and stromal cell-derived factor 1-α, as well as regulation of metalloproteinase expression, ameliorates cardiovascular fibrosis in diabetic mice. In the heart, relaxin is a cardioprotective molecule in several experimental animal models, exerting anti-fibrotic, anti-hypertrophy and anti-apoptotic effects in diabetic pathologies. Collectively, these studies provide a foundation to propose the therapeutic potential for relaxin as an adjunctive agent in the prevention or treatment of diabetes-induced cardiovascular complications. This review provides a comprehensive overview of the beneficial effects of relaxin, and identifies its therapeutic possibilities for alleviating diabetes-related cardiovascular injury.