Antifibrotic properties of relaxin: in vivo mechanism of action in experimental renal tubulointerstitial fibrosis

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. LINKED ARTICLES: This article is part of a themed issue Therapeutic Targeting of G Protein-Coupled Receptors: hot topics from the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists 2021 Virtual Annual Scientific Meeting. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.14/issuetoc.

Engineering a long acting, non-biased relaxin agonist using Protein-in-Protein technology

The peptide hormone relaxin plays a critical role in tissue remodeling in a variety of tissues through activation of its cognate receptor, RXFP1. Relaxin's ability to modify extracellular matrices has provided a strong rationale for treating fibrosis in a variety of tissues. Treatment with recombinant relaxin peptides in clinical studies of heart failure has not yet proven useful, likely due to the short half-life of infused peptide. To circumvent this particular pharmacokinetic pitfall we have used a Protein-in-Protein (PiP) antibody technology described previously, to insert a single-chain human relaxin construct into the complementarity-determining region (CDR) of an immunoglobulin G (IgG) backbone, creating a relaxin molecule with a half-life of ∼4-5 days in mice. Relaxin-PiP biologics displaced Europium-labeled human relaxin in RXFP1-expressing cells and demonstrated full agonist activity on both human and mouse RXFP1 receptors. Relaxin-PiPs did not show signal transduction bias, as they activated cAMP in THP-1 cells, and cGMP and pERK signaling in primary human cardiac fibroblasts. In an induced carbon tetrachloride mouse model of liver fibrosis one relaxin-PiP, R2-PiP, caused reduction of liver lesions, ameliorated collagen accumulation in the liver with the corresponding reduction of Collagen1a1 gene expression, and increased cell proliferation in hepatic parenchyma. These relaxin biologics represent a novel approach to the design of a long-acting RXFP1 agonist to probe the clinical utility of relaxin/RXFP1 signaling to treat a variety of human fibrotic diseases.

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.

Baicalein improves renal interstitial fibrosis by inhibiting the ferroptosis in vivo and in vitro

Evidence indicates that Baicalein can ameliorate renal interstitial fibrosis by inducing myofibroblast apoptosis and inhibit the RLS3-induced ferroptosis in melanocytes. However, the relationship between renal interstitial fibrosis and anti-ferroptosis affected by Baicalein remains unclear. In our study, the anti-fibrosis and anti-ferroptosis effects of Baicalein were assessed in a rat model induced by the UUO method in vivo, and the effects of Baicalein on Erastin-induced ferroptosis of renal MPC-5 cells were examined by Western blot of fibrosis-related and ferroptosis-related proteins in vitro. In the UUO-induced rat model, Baicalein decreased kidney weight loss, improved renal function assessed the biomarks of urinary albumin excretion, serum creatine, and BUN levels, and reduced renal tubular injury. Furthermore, Baicalein inhibited renal ferroptosis by reducing ROS and MDA levels and increasing SOD and GSH levels in the UUO rat model. In addition, Baicalein potently reduced the expression of fibrosis-related proteins such as TGF-β1, a-SMA, and Smad-2 to prevent renal interstitial fibrosis, and increased the expression of ferroptosis-related proteins such as SLC7A11, GPX4, and FTH to inhibit ferroptosis both in vitro and in vivo. Taken together, Baicalein exerts anti-fibrosis activity by reducing the ferroptosis response on the UUO-induced rat model and renal MPC5 cells. Therefore, Baicalein, as a novel therapeutic method on kidney diseases with strong activity in suppressing ferroptosis, could be a potential alternative treatment for renal interstitial fibrosis.

The protective effects of a novel AT2 receptor agonist, β-Pro7Ang III in ischemia-reperfusion kidney injury

BACKGROUND AND PURPOSE

This study investigated the reno-protective effects of a highly selective AT₂R agonist peptide, β-Pro⁷Ang III in a mouse model of acute kidney injury (AKI).

METHODS

C57BL/6 J mice underwent either sham surgery or unilateral kidney ischemia-reperfusion injury (IRI) for 40 min. IRI mice were treated with either β-Pro⁷Ang III or perindopril and at 7 days post-surgery the kidneys analysed for histopathology and the development of fibrosis and matrix metalloproteinase (MMP)-2 and -9 activity. The association of the therapeutic effects of β-Pro⁷Ang III with macrophage number and phenotype was determined in vivo and in vitro.

KEY RESULTS

Decreased kidney tubular injury, interstitial matrix expansion and reduced interstitial immune cell infiltration in IRI mice receiving β-Pro⁷Ang III treatment was observed at day 7, compared to IRI mice without treatment. This correlated to reduced collagen accumulation and MMP-2 activity in IRI mice following β-Pro⁷Ang III treatment. FACS analysis showed a reduced number and proportion of CD45⁺CD11b⁺F4/80⁺ macrophages in IRI kidneys in response to β-Pro⁷Ang III, correlating with a significant increase in M2 macrophage markers and decreased M1 markers at day 3 and 7 post-IR injury, respectively. In vitro analysis of cultured THP-1 cells showed that β-Pro⁷Ang III attenuated lipopolysaccharide (LPS)-induced tumour necrosis factor-α (TNF-α) and interleukin (IL)- 6 production but increased IL-10 secretion, compared to LPS alone.

CONCLUSION

Administration of β-Pro⁷Ang III via mini-pump improved kidney structure and reduced interstitial collagen accumulation, in parallel with an alteration of macrophage phenotype and anti-inflammatory cytokine release, therefore mitigating the downstream progression of ischemic AKI.

Nicorandil and Bone Marrow-derived Mesenchymal Stem Cells Therapeutic Effect after Ureteral Obstruction in Adult Male Albino Rats

BACKGROUND

Chronic kidney disease is a global health problem for which renal fibrogenesis is the final treatment target.

OBJECTIVE

In our work, we have highlighted two new strategies, nicorandil and Bone marrow-derived mesenchymal stem cells (BM-MSCs), as effective in reversing renal fibrosis induced by partial unilateral ureteral obstruction (PUUO).

METHODS

The current study included 96 male albino rats randomly divided into four groups, with 24 rats per group; Group I, the control group; Group II, PUUO, where two-thirds of the left ureter was entrenched in the psoas muscle; Group III, same surgical procedure as in Group II for 7 days, and then the rats received 15 mg/kg/day nicorandil once daily for 21 days; and Group IV, same surgical procedure as in Group II for 7 days, and then rats were given 3 × 106 of labeled MSCs injected intravenous, and left for 21 days. Blood and kidney tissues were collected for biochemical, histological, and molecular analyses.

RESULTS

Both the nicorandil and BM-MSCs treatment groups could ameliorate kidney damage evidenced by inhibition of MDA elevation and total antioxidant capacity reduction caused by PUUO. Also, there was a significant reduction observed in TNF, TGF, IL6, collagen I, and α-SMA in addition to improvement in histological examination. However, a significant difference was found between the BM-MSCs and nicorandil-treated groups.

CONCLUSION

Our results suggest that BM-MSCs and nicorandil improved renal fibrosis progression through their antiapoptotic, anti-inflammatory, and antifibrotic effects in male albino rats subjected to PUUO, with BM-MSCs being more effective compared to nicorandil.

Porcine Relaxin but Not Serelaxin Shows Residual Bioactivity after In Vitro Simulated Intestinal Digestion-Clues for the Development of New Relaxin Peptide Agonists Suitable for Oral Delivery

Despite human recombinant H2 relaxin or serelaxin holding promise as a cardiovascular drug, its actual efficacy in chronic treatment of heart failure patients was hampered by the need to be administered by multiple daily IV injections for a long time, with obvious drawbacks in terms of patients' compliance. This in vitro study aimed at exploring the molecular background for a possible administration of the peptide hormone relaxin by the oral route. Serelaxin and purified porcine relaxin (pRLX) were subjected to simulated intestinal fluid (SIF) enzymatic digestion in vitro to mimic the behavior of gastroprotective formulations. The digestion time course was studied by HPLC, and the relative bio-potency of the intact molecules and their proteolytic fragments was assessed by second messenger (cAMP) response in RXFP1 relaxin receptor-bearing THP-1 human monocytic cells. Both intact proteins (100 ng/mL) induced a significant cAMP rise in THP-1 cells. Conversely, SIF-treated serelaxin showed a brisk (30 s) bioactivity decay, dropping down to the levels of the unstimulated controls at 120 s, whereas SIF-treated pRLX retained significant bioactivity for up to 120 s. After that, it progressively declined to the levels of the unstimulated controls. HPLC analysis indicates that this bioactivity could be ascribed to a minor component of the pRLX sample more resistant to proteolysis. When identified and better characterized, this peptide could be exploited for the development of synthetic relaxin agonists suitable for oral formulations.

Identification of hub ferroptosis-related genes and immune infiltration in lupus nephritis using bioinformatics

Lupus nephritis (LN) is one of the most severe and more common organ manifestations of the autoimmune disease, systemic lupus erythematosus. Ferroptosis, a novel type of programmed cell death, so far its role in LN remains uncertain. In the present study, we explored the role of ferroptosis in LN and its relationship with the immune response. The GSE112943 LN dataset was downloaded from the Gene Expression Omnibus database. Ferroptosis-Related Genes (FRGs) that drive, suppress or mark ferroptosis were retrieved from the public FerrDb database. The gene expression matrix of the GSE112943 dataset was analyzed with the "limma" package in R to obtain differentially expressed genes (DEGs) between LN and healthy samples. Subsequently, the crossover genes between DEGs and FRGs were identified as differentially expressed ferroptosis-related genes (DE-FRGs). Protein-protein interaction (PPI) network analysis, visualization, and identification of hub lupus nephritis ferroptosis-related genes (LN-FRGs) were performed with STRING and Cytoscape, while their Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were determined with the clusterProfiler package. Immune cell infiltration was calculated with CIBERSORT. The relationship between hub LN-FRGs and immune-infiltrated cells in LN was determined by Pearson correlation. A total of 96 DE-FRGs and 8 hub LN-FRGs (KRAS, PIK3CA, EGFR, MAPK14, SRC, MAPK3, VEGFA, and ATM) were identified. GO and KEGG functional classification indicated these genes enrichment in apoptotic process, programmed cell death, autophagy-animal, FoxO signaling pathway, relaxin signaling pathway, and VEGF signaling pathway. Infiltration matrix analysis of immune cells showed abundant Monocytes and M0/M1/M2 macrophages in LN kidney tissues. Correlation analysis revealed 8 hub LN-FRGs associated with immune-infiltrated cells in LN. In summary, overproduction of ROS and abnormal infiltration of immune cells would be implicated in the LN caused by ferroptosis. 8 hub lupus nephritis ferroptosis-related genes (LN-FRGs) which might be good biomarkers of ferroptosis in LN were identified in this study. These findings point to the immune response playing an important role in LN caused by ferroptosis via mutual regulation between hub LN-FRGs and immune-infiltrated cells.

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.

Comparing the renoprotective effects of BM-MSCs versus BM-MSC-exosomes, when combined with an anti-fibrotic drug, in hypertensive mice

Fibrosis, a hallmark of chronic kidney disease (CKD), impairs the viability of human bone marrow derived-mesenchymal stromal cells (BM-MSCs) post-transplantation. To address this, we demonstrated that combining BM-MSCs with the anti-fibrotic drug, serelaxin (RLX), enhanced BM-MSC-induced renoprotection in preclinical CKD models. Given the increased interest and manufacturing advantages to using stem cell-derived exosomes (EXO) as therapeutics, this study determined whether RLX could enhance the therapeutic efficacy of BM-MSC-EXO, and compared the renoprotective effects of RLX and BM-MSC-EXO versus RLX and BM-MSCs in mice with hypertensive CKD. Adult male C57BL/6 mice were uninephrectomised, received deoxycorticosterone acetate and given saline to drink (1K/DOCA/salt) for 21 days. Control mice were uninephrectomised and given normal drinking water for the same time-period. Subgroups of 1K/DOCA/salt-hypertensive mice were then treated with either RLX (0.5 mg/kg/day) or BM-MSC-EXO (25 μg/mouse; equivalent to 1-2 × 106 BM-MSCs/mouse) alone; combinations of RLX and BM-MSC-EXO or BM-MSCs (1 × 106/mouse); or the mineralocorticoid receptor antagonist, spironolactone (20 mg/kg/day), from days 14-21. 1K/DOCA/salt-hypertensive mice developed kidney tubular damage, inflammation and fibrosis, and impaired kidney function 21 days post-injury. Whilst RLX alone attenuated the 1K/DOCA/salt-induced fibrosis, BM-MSC-EXO alone only diminished measures of tissue inflammation post-treatment. Comparatively, the combined effects of RLX and BM-MSC-EXO or BM-MSCs demonstrated similar anti-fibrotic efficacy, but RLX and BM-MSCs offered broader renoprotection over RLX and/or BM-MSC-EXO, and comparable effects to spironolactone. Only RLX and BM-MSCs, but not RLX and/or BM-MSC-EXO, also attenuated the 1K/DOCA/salt-induced hypertension. Hence, although RLX improved the renoprotective effects of BM-MSC-EXO, combining RLX with BM-MSCs provided a better therapeutic option for hypertensive CKD.

Assessment of renal fibrosis and anti-fibrotic agents using a novel diagnostic and stain-free second-harmonic generation platform

Current histological measurement techniques for interstitial collagen, the basis of interstitial fibrosis, are semi-quantitative at best and only provide a ratio of collagen levels within tissues. The Genesis200 imaging system and supplemental image analysis software, FibroIndex from HistoIndex, is a novel, automated platform that uses second-harmonic generation (SHG) for imaging and characterization of interstitial collagen deposition and additional characteristics, in the absence of any staining. However, its ability to quantify renal fibrosis requires investigation. This study compared SHG imaging of renal fibrosis in mice with unilateral ureteric obstruction (UUO), to that of Masson's trichrome staining (MTS) and immunohistochemistry (IHC) of collagen I. Additionally, the platform generated data on collagen morphology and distribution patterns. While all three methods determined that UUO-injured mice underwent significantly increased renal fibrosis after 7 days, the HistoIndex platform additionally determined that UUO-injured mice had a significantly increased collagen-to-tissue cross reticulation ratio (all P < .001 vs sham group). Furthermore, in UUO-injured mice treated with the relaxin family peptide receptor-1 agonists, relaxin (0.5 mg/kg/day) or B7-33 (0.25 mg/kg/day), or angiotensin converting enzyme-inhibitor, perindopril (1 mg/kg/day) over the 7-day period, only the HistoIndex platform determined that the drug-induced prevention of renal fibrosis correlated with significantly reduced collagen fiber thickness and collagen-to-tissue cross reticulation ratio, but increased collagen fiber counts. Relaxin or B7-33 treatment also increased renal matrix metalloproteinase-2 and reduced tissue inhibitor of metalloproteinase-1 levels (all P < .01 vs UUO alone). This study demonstrated the diagnostic value of the HistoIndex platform over currently used staining techniques.

Anti-apoptotic and Matrix Remodeling Actions of a Small Molecule Agonist of the Human Relaxin Receptor, ML290 in Mice With Unilateral Ureteral Obstruction

Diseases, such as diabetes and hypertension, often lead to chronic kidney failure. The peptide hormone relaxin has been shown to have therapeutic effects in various organs. In the present study, we tested the hypothesis that ML290, a small molecule agonist of the human relaxin receptor (RXFP1), is able to target the kidney to remodel the extracellular matrix and reduce apoptosis induced by unilateral ureteral obstruction (UUO). UUO was performed on the left kidney of humanized RXFP1 mice, where the right kidneys served as contralateral controls. Mice were randomly allocated to receive either vehicle or ML290 (30 mg/kg) via daily intraperitoneal injection, and kidneys were collected for apoptosis, RNA, and protein analyses. UUO significantly increased expression of pro-apoptotic markers in both vehicle- and ML290-treated mice when compared to their contralateral control kidneys. Specifically, Bax expression and Erk1/2 activity were upregulated, accompanied by an increase of TUNEL-positive cells in the UUO kidneys. Additionally, UUO induced marked increase in myofibroblast differentiation and aberrant remodeling on the extracellular matrix. ML290 suppressed these processes by promoting a reduction of pro-apoptotic, fibroblastic, and inflammatory markers in the UUO kidneys. Finally, the potent effects of ML290 to remodel the extracellular matrix were demonstrated by its ability to reduce collagen gene expression in the UUO kidneys. Our data indicate that daily administration of ML290 has renal protective effects in the UUO mouse model, specifically through its anti-apoptotic and extracellular matrix remodeling properties.

Combining mesenchymal stem cells with serelaxin provides enhanced renoprotection against 1K/DOCA/salt-induced hypertension

BACKGROUND AND PURPOSE

Fibrosis is a hallmark of chronic kidney disease (CKD) that significantly contributes to renal dysfunction, and impairs the efficacy of stem cell-based therapies. This study determined whether combining bone marrow-derived mesenchymal stem cells (BM-MSCs) with the renoprotective effects of recombinant human relaxin (serelaxin) could therapeutically reduce renal fibrosis in mice with one kidney/deoxycorticosterone acetate/salt (1K/DOCA/salt)-induced hypertension, compared with the effects of the ACE inhibitor, perindopril.

EXPERIMENTAL APPROACH

Adult male C57BL/6 mice were uni-nephrectomised and received deoxycorticosterone acetate and saline to drink (1K/DOCA/salt) for 21 days. Control mice were uni-nephrectomised but received water over the same time period. Sub-groups of 1K/DOCA/salt-injured mice (n = 5-8 per group) were treated with either serelaxin (0.5 mg·kg^-1 ·day^-1 ) or BM-MSCs (1 × 10⁶ per mouse) alone; both treatments combined (with 0.5 × 10⁶ or 1 × 10⁶ BM-MSCs per mouse); or perindopril (2 mg·kg^-1 ·day^-1 ) from days 14-21.

KEY RESULTS

1K/DOCA/salt-injured mice developed elevated BP and hypertension-induced renal damage, inflammation and fibrosis. BM-MSCs alone reduced the injury-induced fibrosis and attenuated BP to a similar extent as perindopril. Serelaxin alone modestly reduced renal fibrosis and effectively reduced tubular injury. Strikingly, the combined effects of BM-MSCs (at both doses) with serelaxin significantly inhibited renal fibrosis and proximal tubular epithelial injury while restoring renal architecture, to a greater extent than either therapy alone, and over the effects of perindopril.

CONCLUSION AND IMPLICATIONS

Combining BM-MSCs and serelaxin provided broader renoprotection over either therapy alone or perindopril and might represent a novel treatment for hypertensive CKD.

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.

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.

AT1R-AT2R-RXFP1 Functional Crosstalk in Myofibroblasts: Impact on the Therapeutic Targeting of Renal and Cardiac Fibrosis

BACKGROUND

Recombinant human relaxin-2 (serelaxin), which has organ-protective actions mediated via its cognate G protein-coupled receptor relaxin family peptide receptor 1 (RXFP1), has emerged as a potential agent to treat fibrosis. Studies have shown that serelaxin requires the angiotensin II (AngII) type 2 receptor (AT₂R) to ameliorate renal fibrogenesis in vitro and in vivo. Whether its antifibrotic actions are affected by modulation of the AngII type 1 receptor (AT₁R), which is expressed on myofibroblasts along with RXFP1 and AT₂R, is unknown.

METHODS

We examined the signal transduction mechanisms of serelaxin when applied to primary rat renal and human cardiac myofibroblasts in vitro, and in three models of renal- or cardiomyopathy-induced fibrosis in vivo.

RESULTS

The AT₁R blockers irbesartan and candesartan abrogated antifibrotic signal transduction of serelaxin via RXFP1 in vitro and in vivo. Candesartan also ameliorated serelaxin's antifibrotic actions in the left ventricle of mice with cardiomyopathy, indicating that candesartan's inhibitory effects were not confined to the kidney. We also demonstrated in a transfected cell system that serelaxin did not directly bind to AT₁Rs but that constitutive AT₁R-RXFP1 interactions could form. To potentially explain these findings, we also demonstrated that renal and cardiac myofibroblasts expressed all three receptors and that antagonists acting at each receptor directly or allosterically blocked the antifibrotic effects of either serelaxin or an AT₂R agonist (compound 21).

CONCLUSIONS

These findings have significant implications for the concomitant use of RXFP1 or AT₂R agonists with AT₁R blockers, and suggest that functional interactions between the three receptors on myofibroblasts may represent new targets for controlling fibrosis progression.

Profiling histone modifications in the normal mouse kidney and after unilateral ureteric obstruction

Posttranslational modification of nucleosomal histones is a major determinant of chromatin structure and gene activity. In the present study, we hypothesized that unilateral ureteric obstruction (UUO), a widely used model of tubulointerstitial injury, would be associated with a distinct pattern of histone modifications (marks) in the kidney. Mass spectrometry was used to profile 63 different histone marks in normal mouse kidneys and those after 10 days of UUO. A subsequent histochemical analysis further examined examples of specific marks that changed significantly after UUO for which antisera are available. Histone marks were much more widely distributed and abundant in the normal kidney than is usually appreciated. Although aggregate analysis of the mass spectrometry results revealed net differences between control and UUO groups, residue-specific variations were subtle. Of the 16/63 significant changes ( P < 0.05), only 8 changes were quantitatively different by >5%. Nevertheless, we identified several that are not usually examined in the kidney, including marks in the globular domain of core histones (H3:K79), linker histones (H1.4), and histone variants (H3.1:K27 and H3.3:K27). In several cases, there were complementary changes in different marks on the same amino acid. Using H3:K79ME2 as an example, mark enrichment was heterogeneous but largely colocalized with active transcription in a subset of tubular pathology. In conclusion, our study highlights the importance of unbiased screening in examining histone marks. Simultaneous changes in multiple marks on the same amino acid indicate a coordinated histone mark signature. The heterogeneous enrichment of marks, even within the same tubule, highlights the importance of regulatory context.

Therapeutic effects of a small molecule agonist of the relaxin receptor ML290 in liver fibrosis

Fibrosis is an underlying cause of cirrhosis and hepatic failure resulting in end stage liver disease with limited pharmacological options. The beneficial effects of relaxin peptide treatment were demonstrated in clinically relevant animal models of liver fibrosis. However, the use of relaxin is problematic because of a short half-life. The aim of this study was to test the therapeutic effects of recently identified small molecule agonists of the human relaxin receptor, relaxin family peptide receptor 1 (RXFP1). The lead compound of this series, ML290, was selected based on its effects on the expression of fibrosis-related genes in primary human stellate cells. RNA sequencing analysis of TGF-β1-activated LX-2 cells showed that ML290 treatment primarily affected extracellular matrix remodeling and cytokine signaling, with expression profiles indicating an antifibrotic effect of ML290. ML290 treatment in human liver organoids with LPS-induced fibrotic phenotype resulted in a significant reduction of type I collagen. The pharmacokinetics of ML290 in mice demonstrated its high stability in vivo, as evidenced by the sustained concentrations of compound in the liver. In mice expressing human RXFP1 gene treated with carbon tetrachloride, ML290 significantly reduced collagen content, α-smooth muscle actin expression, and cell proliferation around portal ducts. In conclusion, ML290 demonstrated antifibrotic effects in liver fibrosis.-Kaftanovskaya, E. M., Ng, H. H., Soula, M., Rivas, B., Myhr, C., Ho, B. A., Cervantes, B. A., Shupe, T. D., Devarasetty, M., Hu, X., Xu, X., Patnaik, S., Wilson, K. J., Barnaeva, E., Ferrer, M., Southall, N. T., Marugan, J. J., Bishop, C. E., Agoulnik, I. U., Agoulnik, A. I. Therapeutic effects of a small molecule agonist of the relaxin receptor ML290 in liver fibrosis.

Human recombinant relaxin-2 does not attenuate hypertension or renal injury but exacerbates vascular dysfunction in a female mouse model of SLE

Systemic lupus erythematosus (SLE) is an autoimmune disease that disproportionately affects women of reproductive age and increases their risk for developing hypertension, vascular, and renal disease. Relaxin has potential beneficial therapeutic effects in cardiovascular disease through direct actions on the vasculature. The potential therapeutic benefit of relaxin on SLE-associated cardiovascular and renal risk factors like hypertension has not previously been tested. We hypothesized that relaxin would attenuate hypertension, renal injury, and vascular dysfunction in an established female mouse model of SLE (NZBWF1 mice). Serelaxin (human recombinant relaxin-2, 0.5 mg·kg^-1·day^-1) or vehicle was administered via osmotic mini-pump for 4 wk in female control (NZW) or SLE mice between 28 and 31 wk of age. Serelaxin treatment increased uterine weights in both groups, suggesting that the Serelaxin was bioactive. Mean arterial pressure, measured by carotid artery catheter, was significantly increased in vehicle-treated SLE mice compared with vehicle-treated controls, but was not changed by Serelaxin treatment. Albumin excretion rate, measured by ELISA, was similar between vehicle- and Serelaxin-treated SLE mice and between vehicle- and Serelaxin-treated control mice. Wire myography was performed using isolated carotid arteries to assess endothelial-independent and -dependent vasodilation, and data confirm that SLE mice have impaired endothelium-independent and -dependent relaxation compared with control mice. Serelaxin treatment did not affect endothelium-independent vasodilation, but exacerbated the endothelium-dependent dysfunction. These data suggest that, contrary to our hypothesis, Serelaxin infusion does not attenuate hypertension, renal injury, or vascular dysfunction in SLE, but worsens underlying vascular endothelial dysfunction in this experimental model of SLE. These data do not support the use of human recombinant relaxin-2 as an antihypertensive in the SLE patient population. NEW & NOTEWORTHY Relaxin is a peptide hormone commonly known for its role in pregnancy and for its use in recent clinical trials for the treatment of heart failure. Evidence suggests that relaxin has immunomodulatory effects; however, the potential therapeutic impact of relaxin in chronic immune mediated disease is unclear. This study tests whether recombinant human relaxin (Serelaxin) attenuates the progression of autoimmunity, and the associated cardiovascular consequences, in an experimental model of systemic lupus erythematosus.

Human umbilical cord-derived mesenchymal stem cells conditioned medium attenuate interstitial fibrosis and stimulate the repair of tubular epithelial cells in an irreversible model of unilateral ureteral obstruction

AIM

The growing number of patients suffering from chronic renal disease (CKD) is a challenge for the development of innovative therapies. Researchers have studied the therapeutic effects of cell therapy in acute kidney injury (AKI). However, the therapeutic effect of conditional medium (CM) in the CKD models have been rarely reported. Here, we examined the effects of umbilical cord derived-mesenchymal stem cells (hUC-MSCs) CM on renal fibrosis in a rat model of unilateral ureteral obstruction (UUO).

METHODS

Animals were randomly divided into three groups: sham-operated, UUO, UUO + CM. CM was administered via the left renal artery after total ligation of the left ureter. Rats were killed after 14 days of obstruction. Histological changes and oxidative stress parameters were assessed. Western blotting and immunohistochemistry analysis were used to measure epithelial-mesenchymal transition (EMT) markers, including epithelial cadherin (E-cadherin), α-smooth muscle actin (α-SMA), tumour necrosis factor-α (TNF-α), Collagen-I, and transforming growth factor β1 (TGF-β1). Proliferation and apoptosis of renal tubular epithelial cells (RTEs) were also measured.

RESULTS

HucMSC-CM significantly reduced the levels of malondialdehyde (MDA) and reactive oxygen species (ROS), and increased the activity of glutathione (GSH) induced by UUO. Moreover, CM significantly reduced the expression of TGF-β1, α-SMA, TNF-α and Collagen-I in UUO kidney, promoted the proliferation of RTEs and inhibited its apoptosis. In addition, the increased expression of E-cadherin also reflects the effective improvement of renal interstitial fibrosis.

CONCLUSION

This study shows that CM protects UUO-induced kidney damage and therefore could be a potential tool to prevent CKD progression.

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.

Telbivudine attenuates UUO-induced renal fibrosis via TGF-β/Smad and NF-κB signaling

Renal fibrosis yields decreased renal function and is a potent contributor to chronic kidney disease (CKD). Telbivudine (LdT) is an anti-hepatitis B virus (HBV) drug that has been found to steadily improve renal function, but the mechanism of drug action is unclear. One explanation is that LdT impacts inflammatory or fibrotic pathways. In this study, we investigated renal protection by LdT in a rat model of unilateral ureteral obstruction (UUO). UUO rats received oral gavage of LdT (1, 1.5, or 2g/kg/day) for 5weeks. Kidney tissues were examined histopathologically with hematoxylin and eosin and Masson's trichrome stain. To assess proliferation of myofibroblasts and matrix accumulation, α-smooth muscle actin (α-sma) and collagen type I and III were detected. Interleukin-1 (IL-1) and tumor necrosis factor (TNF)-α were evaluated as a measure of proinflammatory cytokines. Transforming growth factor (TGF)-β and nuclear factor-κB (NF-κB) were considered the canonical signaling components in our investigation of the underlying mechanism of LdT action. Histopathology results indicated that LdT ameliorates renal injury and matrix accumulation. Expression of α-sma and collagen I/III as well as key fibrotic signaling factors in the TGF-β/Smad pathway were downregulated. In addition, LdT suppressed the release of IL-1 and TNF-α and decreased the expression of NF-κB by inhibiting toll-like receptor 4. Taken together, these findings indicate that LdT can attenuate renal fibrosis and inflammation via TGF-β/Smad and NF-κB pathways in UUO.

FGF23 is synthesised locally by renal tubules and activates injury-primed fibroblasts

In kidney disease, higher circulating levels of the mineral-regulating hormone fibroblast growth factor (FGF)-23 are predictive of disease progression but direct pathogenic effects on the kidney are unknown. We sought evidence of local renal synthesis in response to unilateral ureteric obstruction in the mouse, and pro-fibrotic actions of FGF23 on the fibroblast in vitro. Acute tubulointerstitial injury due to unilateral ureteric obstruction stimulated renal FGF23 synthesis by tubules, and downregulated inactivating proprotein convertases, without effects on systemic mineral metabolism. In vitro, FGF23 had divergent effects on fibroblast activation in cells derived from normal and obstructed kidneys. While FGF23 failed to stimulate fibrogenesis in normal fibroblasts, in those primed by injury, FGF23 induced pro-fibrotic signalling cascades via activation of TGF-β pathways. Effects were independent of α-klotho. Tubule-derived FGF23 may amplify myofibroblast activation in acute renal injury, and might provide a novel therapeutic target in renal fibrosis.

Maternal lactocrine programming of porcine reproductive tract development

The lactocrine hypothesis for maternal programming of female reproductive tract development is based on the idea that non-nutritive, milk-borne bioactive factors (MbFs), delivered from mother to offspring during nursing, play a role in determining the trajectory of development with long-term consequences in the adult. Porcine female reproductive tract development is completed postnatally, and the period during which maternal support of neonatal growth derives exclusively from colostrum/milk defines a window of opportunity for lactocrine programming of reproductive tissues. Beyond nutrition, milk serves as a delivery system for a variety of bioactive factors. Porcine relaxin is a prototypical MbF. Present in colostrum at highest concentrations at birth, relaxin is transmitted into the circulation of nursing piglets where it can act on Relaxin receptors found in neonatal female reproductive tract tissues. This process is facilitated by the physiology of the maternal-neonatal dyad and the fact that the neonatal gastrointestinal tract is open to absorb macromolecules for a period of time postnatally. Age at first nursing and duration of nursing from birth are also important for porcine female reproductive tract development. These parameters affect both the quality and quantity of colostrum consumed. Disruption of lactocrine signaling by feeding milk replacer from birth altered porcine uterine, cervical, and testicular development by postnatal Day 2. Moreover, insufficient colostrum consumption in nursing piglets can impair uterine capacity to support viable litters of optimal size in adulthood. In the pig, lactocrine signaling supports neonatal organizational events associated with normal reproductive development and may program adult uterine capacity.

Novel Anti-fibrotic Therapies

Fibrosis is a major player in cardiovascular disease, both as a contributor to the development of disease, as well as a post-injury response that drives progression. Despite the identification of many mechanisms responsible for cardiovascular fibrosis, to date no treatments have emerged that have effectively reduced the excess deposition of extracellular matrix associated with fibrotic conditions. Novel treatments have recently been identified that hold promise as potential therapeutic agents for cardiovascular diseases associated with fibrosis, as well as other fibrotic conditions. The purpose of this review is to provide an overview of emerging antifibrotic agents that have shown encouraging results in preclinical or early clinical studies, but have not yet been approved for use in human disease. One of these agents is bone morphogenetic protein-7 (BMP7), which has beneficial effects in multiple models of fibrotic disease. Another approach discussed involves altering the levels of micro-RNA (miR) species, including miR-29 and miR-101, which regulate the expression of fibrosis-related gene targets. Further, the antifibrotic potential of agonists of the peroxisome proliferator-activated receptors will be discussed. Finally, evidence will be reviewed in support of the polypeptide hormone relaxin. Relaxin is long known for its extracellular remodeling properties in pregnancy, and is rapidly emerging as an effective antifibrotic agent in a number of organ systems. Moreover, relaxin has potent vascular and renal effects that make it a particularly attractive approach for the treatment of cardiovascular diseases. In each case, the mechanism of action and the applicability to various fibrotic diseases will be discussed.

Epigenetic Modifications to H3K9 in Renal Tubulointerstitial Cells after Unilateral Ureteric Obstruction and TGF-β1 Stimulation

Introduction: Epigenetic regulation of fibrogenesis through post-translational histone modifications (marks) may be a key determinant of progression in renal disease. In this study, we examined the distribution and acquisition of histone 3 Lysine 9 (H3K9) marks after injury and stimulation with the pro-fibrotic cytokine TGF-β1. Our focus was on their presence in activated fibroblasts (myofibroblasts) and epithelial cells (epithelial-mesenchymal transition).

Methods and Results: Immunofluorescent microscopy was used to examine global H3K9 acetylation (H3K9Ac) and tri-methylation (H3K9Me3) after unilateral ureteric obstruction (UUO) in mice. Confocal, super resolution microscopy and flow cytometry were used to determine the in vitro effect of TGF-β1 on structural arrangement of these marks, and their relationship with α-smooth muscle actin (αSMA) expression, a marker of myofibroblasts and early EMT. The number of individual histone marks was increased 10 days after UUO (p < 0.05 vs. control), with both marks clearly seen in various cell types including proximal tubules and myofibroblasts. Sub-nuclear microscopy in primary rat renal fibroblasts and a proximal tubule cell line (NRK-52e) showed that H3K9Ac was co-localized with phosphorylated-Ser2 RNA polymerase II (pRNAPol II), while H3K9Me3 was not, consistent with permissive and repressive effects on gene expression respectively. In both cell types H3K9Ac was diffusely distributed throughout the nucleus, while H3K9Me3 was found in compartments resembling the nucleolus, and in the case of the fibroblast, also juxtapositioned with the nuclear membrane. TGF-β1 had no effect on H3K9Ac marks in either cell, but resulted in a redistribution of H3K9Me3 within the fibroblast nucleus. This was unrelated to any change in mitogenesis, but was associated with increased αSMA expression.

Conclusion: These findings highlight why it is important to consider the epigenetics of each cell individually, because whilst no overall enrichment occurred, renal myofibroblast differentiation was accompanied by distinct changes in histone mark arrangements.

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.

Involvement of Cyclic Guanosine Monophosphate-Dependent Protein Kinase I in Renal Antifibrotic Effects of Serelaxin

Introduction: Kidney fibrosis has shown to be ameliorated through the involvement of cyclic guanosine monophosphate (cGMP) and its dependent protein kinase I (cGKI). Serelaxin, the recombinant form of human relaxin-II, increases cGMP levels and has shown beneficial effects on kidney function in acute heart failure patients. Antifibrotic properties of serelaxin are supposed to be mediated via relaxin family peptide receptor 1 and subsequently enhanced nitric oxide/cGMP to inhibit transforming growth factor-β (TGF-β) signaling. This study examines the involvement of cGKI in the antifibrotic signaling of serelaxin.

Methods and Results: Kidney fibrosis was induced by unilateral ureteral obstruction in wildtype (WT) and cGKI knock-out (KO) mice. After 7 days, renal antifibrotic effects of serelaxin were assessed. Serelaxin treatment for 7 days significantly increased cGMP in the kidney of WT and cGKI-KO. In WT, renal fibrosis was reduced through decreased accumulation of collagen1A1, total collagen, and fibronectin. The profibrotic connective tissue growth factor as well as myofibroblast differentiation were reduced and matrix metalloproteinases-2 and -9 were positively modulated after treatment. Moreover, Smad2 as well as extracellular signal-regulated kinase 1 (ERK1) phosphorylation were decreased, whereas phosphodiesterase (PDE) 5a phosphorylation was increased. However, these effects were not observed in cGKI-KO.

Conclusion: Antifibrotic renal effects of serelaxin are mediated via cGMP/cGKI to inhibit Smad2- and ERK1-dependent TGF-β signaling and increased PDE5a phosphorylation.

The Anti-fibrotic Actions of Relaxin Are Mediated Through a NO-sGC-cGMP-Dependent Pathway in Renal Myofibroblasts In Vitro and Enhanced by the NO Donor, Diethylamine NONOate

INTRODUCTION

The anti-fibrotic hormone, relaxin, has been inferred to disrupt transforming growth factor (TGF)-β1/Smad2 phosphorylation (pSmad2) signal transduction and promote collagen-degrading gelatinase activity via a nitric oxide (NO)-dependent pathway. Here, we determined the extent to which NO, soluble guanylate cyclase (sGC) and cyclic guanosine monophosphate (cGMP) were directly involved in the anti-fibrotic actions of relaxin using a selective NO scavenger and sGC inhibitor, and comparing and combining relaxin's effects with that of an NO donor.

METHODS AND RESULTS

Primary renal cortical myofibroblasts isolated from injured rat kidneys were treated with human recombinant relaxin (RLX; 16.8 nM), the NO donor, diethylamine NONOate (DEA/NO; 0.5-5 μM) or the combined effects of RLX (16.8 nM) and DEA/NO (5 μM) over 72 h. The effects of RLX (16.8 nM) and DEA/NO (5 μM) were also evaluated in the presence of the NO scavenger, hydroxocobalamin (HXC; 100 μM) or sGC inhibitor, ODQ (5 μM) over 72 h. Furthermore, the effects of RLX (30 nM), DEA/NO (5 μM) and RLX (30 nM) + DEA/NO (5 μM) on cGMP levels were directly measured, in the presence or absence of ODQ (5 μM). Changes in matrix metalloproteinase (MMP)-2, MMP-9 (cell media), pSmad2 and α-smooth muscle actin (α-SMA; a measure myofibroblast differentiation) (cell layer) were assessed by gelatin zymography and Western blotting, respectively. At the highest concentration tested, both RLX and DEA/NO promoted MMP-2 and MMP-9 levels by 25-33%, while inhibiting pSmad2 and α-SMA expression by up to 50% (all p < 0.05 vs. untreated and vehicle-treated cells). However, 5μM of DEA/NO was required to produce the effects seen with 16.8 nM of RLX over 72 h. The anti-fibrotic effects of RLX or DEA/NO alone were completely abrogated by HXC and ODQ (both p < 0.01 vs. RLX alone or DEA/NO alone), but were significantly enhanced when added in combination (all p < 0.05 vs. RLX alone). Additionally, the direct cGMP-promoting effects of RLX, DEA/NO and RLX+DEA/NO (which all increased cGMP levels by 12-16-fold over basal levels; all p < 0.01 vs. vehicle-treated cells) were significantly inhibited by pre-treatment of ODQ (all p < 0.05 vs. the respective treatments alone).

CONCLUSION

These findings confirmed that RLX mediates its TGF-β1-inhibitory and gelatinase-promoting effects via a NO-sGC-cGMP-dependent pathway, which was additively augmented by co-administration of DEA/NO.

Relaxin-2 does not ameliorate nephropathy in an experimental model of type-1 diabetes

BACKGROUND/AIMS

In diabetic nephropathy (DN), the current angiotensin-II-blocking pharmacotherapy is frequently failing. For diabetic cardiomyopathy (DC), there is no specific remedy available. Relaxin-2 (Rlx) - an anti-fibrotic, anti-inflammatory, and vasoprotecting peptide – is a candidate drug for both.

METHODS

Low-dose (32 μg/kg/day) and high-dose (320 μg/kg/day) Rlx were tested against vehicle (n = 20 each) and non-diabetic controls (n = 14) for 12 weeks in a model of type-1 diabetes induced in endothelial nitric oxide synthase knock-out (eNOS-KO) mice by intraperitoneal injection of streptozotocin.

RESULTS

Diabetic animals showed normal plasma creatinine, markedly increased albuminuria and urinary malonyldialdehyde, elevated relative kidney weight, glomerulosclerosis, and increased glomerular size, but no relevant interstitial fibrosis. Neither dose of Rlx affected these changes although the drug was active and targeted plasma levels were achieved. Of note, we found no activation of the renal TGF-β pathway in this model. In the hearts of diabetic animals, no fibrotic alterations indicative of DC could be determined which precluded testing of the initial hypothesis.

CONCLUSIONS

We investigated a model showing early DN without overt tubulointerstitial fibrosis and activation of the TGF-β-Smad-2/3 pathway. In this model, Rlx proved ineffective; however, the same may not apply to other models and types of diabetes.

Mesenchymal stem cells and serelaxin synergistically abrogate established airway fibrosis in an experimental model of chronic allergic airways disease

This study determined if the anti-fibrotic drug, serelaxin (RLN), could augment human bone marrow-derived mesenchymal stem cell (MSC)-mediated reversal of airway remodeling and airway hyperresponsiveness (AHR) associated with chronic allergic airways disease (AAD/asthma). Female Balb/c mice subjected to the 9-week model of ovalbumin (OVA)-induced chronic AAD were either untreated or treated with MSCs alone, RLN alone or both combined from weeks 9-11. Changes in airway inflammation (AI), epithelial thickness, goblet cell metaplasia, transforming growth factor (TGF)-β1 expression, myofibroblast differentiation, subepithelial and total lung collagen deposition, matrix metalloproteinase (MMP) expression, and AHR were then assessed. MSCs alone modestly reversed OVA-induced subepithelial and total collagen deposition, and increased MMP-9 levels above that induced by OVA alone (all p<0.05 vs OVA group). RLN alone more broadly reversed OVA-induced epithelial thickening, TGF-β1 expression, myofibroblast differentiation, airway fibrosis and AHR (all p<0.05 vs OVA group). Combination treatment further reversed OVA-induced AI and airway/lung fibrosis compared to either treatment alone (all p<0.05 vs either treatment alone), and further increased MMP-9 levels. RLN appeared to enhance the therapeutic effects of MSCs in a chronic disease setting; most likely a consequence of the ability of RLN to limit TGF-β1-induced matrix synthesis complemented by the MMP-promoting effects of MSCs.

Relaxin inhibits cardiac fibrosis and endothelial-mesenchymal transition via the Notch pathway

BACKGROUND

Relaxin (RLX) can prevent cardiac fibrosis. We aimed to investigate the possible mechanism and signal transduction pathway of RLX inhibiting cardiac fibrosis.

METHODS

Isoproterenol (5 mg·kg(-1)·d(-1)) was used to establish the cardiac fibrosis model in rats, which were administered RLX. The cardiac function, related targets of cardiac fibrosis, and endothelial-mesenchymal transition (EndMT) were measured. Transforming growth factor β (TGF-β) was used to induce EndMT in human umbilical vein endothelial cells, which were pretreated with RLX, 200 ng·mL(-1), then with the inhibitor of Notch. Transwell cell migration was used to evaluate cell migration. CD31 and vimentin content was determined by immunofluorescence staining and Western blot analysis. Notch protein level was examined by Western blot analysis.

RESULTS

RLX improved cardiac function in rats with cardiac fibrosis; it reduced the content of collagen I and III, increased the microvascular density of the myocardium, and suppressed the EndMT in heart tissue. In vitro, RLX decreased the mobility of human umbilical vein endothelial cells induced by TGF-β, increased the expression of endothelial CD31, and decreased vimentin content. Compared to TGF-β and RLX co-culture alone, TGF-β + RLX + Notch inhibitor increased cell mobility and the EndMT, but decreased the levels of Notch-1, HES-1, and Jagged-1 proteins.

CONCLUSION

RLX may inhibit the cardiac fibrosis via EndMT by Notch-mediated signaling.

Effect of erythropoietin on the expression of dynamin-related protein-1 in rat renal interstitial fibrosis

This study aimed to observe the expression of dynamin-related protein-1 (Drp-1) in the renal interstitium in a rat model of renal interstitial fibrosis induced by unilateral ureteral obstruction (UUO). In addition, the renoprotective effect of erythropoietin in this model was investigated. A total of 81 rats were randomly assigned to sham surgery, UUO model and treatment groups. Following surgery, the rats in the treatment group were subcutaneously administered erythropoietin at a dose of 3,000 IU/kg once a week until the time of sacrifice. Rats in the sham surgery and UUO model groups were administered an identical volume of normal saline. In each group, nine rats were chosen randomly for sacrifice on days 7, 14 and 21 after surgery for histological examination of renal tissue. Renal tissue specimens were examined by hematoxylin and eosin and Masson's trichrome staining. Immunohistochemical analysis was performed to determine the expression of Drp-1 in the renal interstitium. Renal function damage, as evaluated by the measurement of serum creatinine (Cr) and blood urea nitrogen (BUN) levels, was less severe in the treatment group compared with that in the model group at day 21 (P<0.01). Compared with the UUO model group, the renal interstitial injury score and fibrotic area of the treatment group were decreased markedly at the three time points (P<0.05). The expression level of Drp-1 in the treatment group was decreased markedly at the three time points compared with that in the model group (P<0.05). In conclusion, the expression of Drp-1 is increased in rat renal interstitial fibrosis, and erythropoietin may alleviate the degree of renal interstitial fibrosis by downregulating the expression of Drp-1.

Combination therapy of mesenchymal stem cells and serelaxin effectively attenuates renal fibrosis in obstructive nephropathy

Chronic kidney disease (CKD) results from the development of fibrosis, ultimately leading to end-stage renal disease (ESRD). Although human bone marrow-derived mesenchymal stem cells (MSCs) can accelerate renal repair following acute injury, the establishment of fibrosis during CKD may affect their potential to influence regeneration capacity. Here we tested the novel combination of MSCs with the antifibrotic serelaxin to repair and protect the kidney 7 d post-unilateral ureteral obstruction (UUO), when fibrosis is established. Male C57BL6 mice were sham-operated or UUO-inured (n = 4-6) and received vehicle, MSCs (1 × 10(6)), serelaxin (0.5 mg/kg per d), or the combination of both. In vivo tracing studies with luciferin/enhanced green fluorescent protein (eGFP)-tagged MSCs showed specific localization in the obstructed kidney where they remained for 36 h. Combination therapy conferred significant protection from UUO-induced fibrosis, as indicated by hydroxyproline analysis (P < 0.001 vs. vehicle, P < 0.05 vs. MSC or serelaxin alone). This was accompanied by preserved structural architecture, decreased tubular epithelial injury (P < 0.01 vs. MSCs alone), macrophage infiltration, and myofibroblast localization in the kidney (both P < 0.01 vs. vehicle). Combination therapy also stimulated matrix metalloproteinase (MMP)-2 activity over either treatment alone (P < 0.05 vs. either treatment alone). These results suggest that the presence of an antifibrotic in conjunction with MSCs ameliorates established kidney fibrosis and augments tissue repair to a greater extent than either treatment alone.

Recombinant human relaxin-2: (how) can a pregnancy hormone save lives in acute heart failure?

Acute heart failure (AHF) syndrome, characterized by pulmonary and/or venous congestion owing to increased cardiac filling pressures with or without diminished cardiac output, is still associated with high post-discharge mortality and hospitalization rates. Many novel and promising therapeutic approaches, among them endothelin-1, vasopressin and adenosine antagonists, calcium sensitization, and recombinant B-type natriuretic hormone, have failed in large studies. Likewise, the classic drugs, vasodilators, diuretics, and inotropes, have never been shown to lower mortality.The phase III trial RELAX-AHF tested recombinant human relaxin-2 (rhRlx) and found it to improve clinical symptoms moderately, to be neutral regarding the combination of death and hospitalization at day 60, to be safe, and to lower mortality at day 180. This review focuses on basic research and pre-clinical findings that may account for the benefit of rhRlx in AHF. The drug combines short-term hemodynamic advantages, such as moderate blood pressure decline and functional endothelin-1 antagonism, with a wealth of protective effects harboring long-term benefits, such as anti-inflammatory, anti-fibrotic, and anti-oxidative actions. These pleiotropic effects are exerted through a complex and intricate signaling cascade involving the relaxin-family peptide receptor-1, the glucocorticoid receptor, nitric oxide, and a cell type-dependent variety of kinases and transcription factors.

Relaxin does not improve Angiotensin II-induced target-organ damage

Relaxin is a corpus-luteum produced protein hormone with vasodilatatory, anti-fibrotic, and angiogenic properties that are opposite to angiotensin (Ang) II. We investigated whether or not relaxin ameliorates Ang II-induced target-organ damage. We used double transgenic rats harboring both human renin and angiotensinogen genes (dTGR) that develop severe hypertension, target-organ damage, and die untreated within 7–8 weeks. Recombinant relaxin at a low (26 μg/kg/d) and a high dose (240 μg/kg/d) was given to 4 week-old dTGR and age-matched Sprague-Dawley rats (SD). Systolic blood pressure increased progressively in untreated dTGRs from 162±3 mmHg at week 5 to 225±5 mmHg at week 7. Relaxin had no effect on blood pressure whereas SD rats were normotensive (106±1 mmHg). Untreated and relaxin-treated dTGR had similarly severe cardiac hypertrophy indices. Relaxin did not ameliorate albuminuria and did not prevent matrix-protein deposition in the heart and kidney in dTGR. Finally, relaxin treatment did not reduce mortality. These data suggest that pharmacological doses of relaxin do not reverse severe effects of Ang II.

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. 

Relaxin treatment reverses insulin resistance in mice fed a high-fat diet

The endogenous hormone relaxin increases vascular reactivity and angiogenesis. We demonstrate that acute relaxin infusion in lean C57BL/6J mice enhances skeletal muscle perfusion and augments muscle glucose uptake during a hyperinsulinemic-euglycemic clamp. However, an acute effect was absent in mice fed a high-fat (HF) diet for 13 weeks. In contrast, mice fed an HF diet for 13 weeks and continuously treated with relaxin for the final 3 weeks of the diet exhibited decreased fasting blood glucose. Insulin-stimulated whole-body glucose disappearance and percent suppression of hepatic glucose production are corrected by chronic relaxin. The increase in peripheral glucose utilization is a result of augmented in vivo skeletal muscle glucose uptake. Relaxin intervention improves endothelial-dependent vascular reactivity and induces a two-fold proliferation in skeletal muscle capillarity. The metabolic effects of the treatment are not attributed to changes in myocellular insulin signaling. Relaxin intervention reverses the accumulation of collagen III in the liver and collagen III and collagen IV in the heart; this is induced by HF feeding. These studies show the potential of relaxin in the treatment of diet-induced insulin resistance and vascular dysfunction. Relaxin provides a novel therapeutic approach targeting the extramyocellular barriers to insulin action, which are critical to the pathogenesis of insulin resistance.

The emerging role of relaxin as a novel therapeutic pathway in the treatment of chronic kidney disease

Emerging evidence supports a potential therapeutic role of relaxin in fibrotic diseases, including chronic kidney disease. Relaxin is a pleiotropic hormone, best characterized for its role in the reproductive system; however, recent studies have demonstrated a role of relaxin in the cardiorenal system. Both relaxin and its receptor, RXFP1, are expressed in the kidney, and relaxin has been shown to play a role in renal vasodilation, in sodium excretion, and as an antifibrotic agent. Together, these findings suggest that the kidney is a target organ of relaxin. Therefore, the purpose of this review is to describe the functional and structural impacts of relaxin treatment on the kidney and to discuss evidence that relaxin prevents disease progression in several experimental models of kidney disease. In addition, this review will present potential mechanisms that are involved in the therapeutic actions of relaxin.

Animal models of chronic kidney disease: useful but not perfect

Animal models of chronic kidney disease (CKD) approximate the human condition and are keys to understanding its pathogenesis and to developing rational treatment strategies. The ethical use of animals requires a detailed understanding of the strengths and limitations of each species and the disease model, and the way in which findings can be translated from animals to humans. While not perfect, the careful use of animal experiments offers the opportunity to examine individual mechanisms in an accelerated time frame.

Therapeutic effects of human amniotic fluid-derived stem cells on renal interstitial fibrosis in a murine model of unilateral ureteral obstruction

Interstitial fibrosis is regarded as the main pathway for the progression of chronic kidney disease (CKD) and is often associated with severe renal dysfunction. Stem cell-based therapies may provide alternative approaches for the treatment of CKD. Human amniotic fluid-derived stem cells (hAFSCs) are a novel stem cell population, which exhibit both embryonic and mesenchymal stem cell characteristics. Herein, the present study investigated whether the transplantation of hAFSCs into renal tissues could improve renal interstitial fibrosis in a murine model of unilateral ureteral obstruction (UUO). We showed that hAFSCs provided a protective effect and alleviated interstitial fibrosis as reflected by an increase in microvascular density; additionally, hAFSCs treatment beneficially modulated protein levels of vascular endothelial growth factor (VEGF), hypoxia inducible factor-1α (HIF-1α) and transforming growth factor-β1 (TGF-β1). Therefore, we hypothesize that hAFSCs could represent an alternative, readily available source of stem cells that can be applied for the treatment of renal interstitial fibrosis.