Relaxin regulates MMP expression and promotes satellite cell mobilization during muscle healing in both young and aged mice

Bioinformatics Analysis Identifies Key Genes in the Effect of Resistance Training on Female Skeletal Muscle Aging

Resistance training is used to combat skeletal muscle function decline in older adults. Few studies have been designed specific for females, resulting in very limited treatment options for skeletal muscle atrophy in aging women. Here, we analyzed the gene expression profiles of skeletal muscle samples from sedentary young women, sedentary older women, and resistance-trained older women, using microarray data from public database. A total of 45 genes that were differentially expressed during female muscle aging and reversed by resistance training were identified. Functional and pathway enrichment analysis, protein-protein interaction network analysis, and receiver operating characteristic analysis were performed to reveal the key genes and pathways involved in the effects of resistance training on female muscle aging. The collagen genes COL1A1, COL3A1, and COL4A1 were identified important regulators of female muscle aging and resistance training, by modulating multiple signaling pathways, such as PI3 kinase-Akt signaling, focal adhesions, extracellular matrix-receptor interactions, and relaxin signaling. Interestingly, the expression of CDKN1A and TP63 were increased during aging, and further upregulated by resistance training in older women, suggesting they may negatively affect resistance training outcomes. Our findings provide novel insights into the molecular mechanisms of resistance training on female muscle aging and identify potential biomarkers and targets for clinical intervention.

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.

FOXO1 regulates bovine skeletal muscle cells differentiation by targeting MYH3

The growth and development of bovine skeletal muscle and beef yield is closely intertwined. Our previous research found that forkhead box O1 (FOXO1) plays an important role in the regulation of beef muscle formation, but its specific mechanism is still unknown. In this study, we aimed to clarify the regulatory mechanism of FOXO1 in proliferation and differentiation of bovine skeletal muscle cells (BSMCs). The results showed that interfering with FOXO1 can promote proliferation and the cell G1/S phase of BSMCs by up-regulating the expression of PCNA, CDK1, CDK2, CCNA2, CCNB1, CCND1 and CCNE2. Besides, interfering with FOXO1 inhibited the apoptosis of BSMCs by up-regulating the expression of anti-apoptosis gene BCL2, while simultaneously down-regulating the expression of the pro-apoptosis genes BAD and BAX. Inversely, interfering with FOXO1 can promote the differentiation of BSMCs by up-regulating the expression of myogenic differentiation marker genes MYOD, MYOG, MYF5, MYF6 and MYHC. Furthermore, RNA-seq combined with western bolt, immunofluorescence and chromatin immunoprecipitation analysis showed that FOXO1 could regulate BSMCs differentiation process by influencing PI3K-Akt, Relaxin and TGF-beta signaling pathways, and target MYH3 for transcriptional inhibition. In conclusion, this study provides a basis for studying the role and molecular mechanism of FOXO1 in BSMCs.

Extraocular muscle stem cells exhibit distinct cellular properties associated with non-muscle molecular signatures

Skeletal muscle stem cells (MuSCs) are recognised as functionally heterogeneous. Cranial MuSCs are reported to have greater proliferative and regenerative capacity when compared with those in the limb. A comprehensive understanding of the mechanisms underlying this functional heterogeneity is lacking. Here, we have used clonal analysis, live imaging and single cell transcriptomic analysis to identify crucial features that distinguish extraocular muscle (EOM) from limb muscle stem cell populations. A MyogeninntdTom reporter showed that the increased proliferation capacity of EOM MuSCs correlates with deferred differentiation and lower expression of the myogenic commitment gene Myod. Unexpectedly, EOM MuSCs activated in vitro expressed a large array of extracellular matrix components typical of mesenchymal non-muscle cells. Computational analysis underscored a distinct co-regulatory module, which is absent in limb MuSCs, as driver of these features. The EOM transcription factor network, with Foxc1 as key player, appears to be hardwired to EOM identity as it persists during growth, disease and in vitro after several passages. Our findings shed light on how high-performing MuSCs regulate myogenic commitment by remodelling their local environment and adopting properties not generally associated with myogenic cells.

Effects of pregnancy and lactation on muscle-tendon morphology

Pregnancy and lactation hormones have been shown to mediate anatomical changes to the musculoskeletal system that generates animal movement. In this study, we characterize changes in the medial gastrocnemius muscle, its tendon and aponeuroses that are likely to have an effect on whole animal movement and energy expenditure, using the rat model system, Rattus norvegicus. We quantified muscle architecture (mass, cross-sectional area, and pennation angle), muscle fiber type and diameter, and Young's modulus of stiffness for the medial gastrocnemius aponeuroses as well as its contribution to Achilles tendon in three groups of three-month-old female rats: virgin, primiparous pregnant, and primiparous lactating animals. We found that muscle mass drops by 23% during lactation but does not change during pregnancy. We also found that during pregnancy muscle fibers switch from Type I to IIa and during lactation from Type IIb to Type I. The stiffness of connective tissues that has a demonstrated role in locomotion, the aponeurosis and tendon, also changed. Pregnant animals had a significantly less stiff aponeurosis. However, tendon stiffness was most affected during lactation, with a significant drop in stiffness and interindividual variation. We propose that the energetic demands of locomotion may have driven the evolution of these anatomical changes in muscle-tendon units during pregnancy and lactation to ensure more energy can be allocated to fetal development and lactation.

Matrix Metalloproteinase-9 is Involved in the Fibrotic Process in Denervated Muscles after Sciatic Nerve Trauma and Recovery

Fibrosis of the injured muscles is a problem of recovery from trauma and denervation. The aim of the work was to investigate the interconnection of matrix metalloproteinase-9 (ММР-9) activity in denervated muscles with fibrosis and to estimate its role in nerve restoration by the epineurial suture, fibrin-based glue, and polyethylene glycol hydrogel. The activity of matrix metalloproteinases was estimated by gelatin zymography. Collagen density in muscles was determined histochemically. An increased level of the active MMP-9 is associated with the fibrous changes in the denervated skeletal muscles and after an epineurial suture. The use of fibrin glue and polyethylene glycol hydrogel resulted in a lower level of collagen and ММР-9 activity, which may be a therapeutic target in the treatment of neuromuscular lesions, and has value in fibrosis analysis following microsurgical intervention for peripheral nerve reconstruction.

Codon Usage Bias and Cluster Analysis of the MMP-2 and MMP-9 Genes in Seven Mammals

Matrix metalloproteinase (MMP)-2 and MMP-9 are a family of Zn²⁺ and Ca²⁺-dependent gelatinase MMPs that regulate muscle development and disease treatment, and they are highly conservative during biological evolution. Despite increasing knowledge of MMP genes, their evolutionary mechanism for functional adaption remains unclear. Moreover, analysis of codon usage bias (CUB) is reliable to understand evolutionary associations. However, the distribution of CUB of MMP-2 and MMP-9 genes in mammals has not been revealed clearly. Multiple analytical software was used to study the genetic evolution, phylogeny, and codon usage pattern of these two genes in seven species of mammals. Results showed that the MMP-2 and MMP-9 genes have CUB. By comparing the content of synonymous codon bases amongst seven mammals, we found that MMP-2 and MMP-9 were low-expression genes in mammals with high codon conservation, and their third codon preferred the G/C base. RSCU analysis revealed that these two genes preferred codons encoding delicious amino acids. Analysing what factors influence CUB showed that the third base distributors of these two genes were C/A and C/T, and GC_3S had a wide distribution range on the ENC plot reference curve under no selection or mutational pressure. Thus, mutational pressure is an important factor in CUB. This study revealed the usage characteristics of the MMP-2 and MMP-9 gene codons in different mammals and provided basic data for further study towards enhancing meat flavour, treating muscle disease, and optimizing codons.

The myokine Fibcd1 is an endogenous determinant of myofiber size and mitigates cancer-induced myofiber atrophy

Decline in skeletal muscle cell size (myofiber atrophy) is a key feature of cancer-induced wasting (cachexia). In particular, atrophy of the diaphragm, the major muscle responsible for breathing, is an important determinant of cancer-associated mortality. However, therapeutic options are limited. Here, we have used Drosophila transgenic screening to identify muscle-secreted factors (myokines) that act as paracrine regulators of myofiber growth. Subsequent testing in mouse myotubes revealed that mouse Fibcd1 is an evolutionary-conserved myokine that preserves myofiber size via ERK signaling. Local administration of recombinant Fibcd1 (rFibcd1) ameliorates cachexia-induced myofiber atrophy in the diaphragm of mice bearing patient-derived melanoma xenografts and LLC carcinomas. Moreover, rFibcd1 impedes cachexia-associated transcriptional changes in the diaphragm. Fibcd1-induced signaling appears to be muscle selective because rFibcd1 increases ERK activity in myotubes but not in several cancer cell lines tested. We propose that rFibcd1 may help reinstate myofiber size in the diaphragm of patients with cancer cachexia.

Enhancement of myogenic potential of muscle progenitor cells and muscle healing during pregnancy

The decline of muscle regenerative potential with age has been attributed to a diminished responsiveness of muscle progenitor cells (MPCs). Heterochronic parabiosis has been used as a model to study the effects of aging on stem cells and their niches. These studies have demonstrated that, by exposing old mice to a young systemic environment, aged progenitor cells can be rejuvenated. One interesting idea is that pregnancy represents a unique biological model of a naturally shared circulatory system between developing and mature organisms. To test this hypothesis, we evaluated the muscle regeneration potential of pregnant mice using a cardiotoxin (CTX) injury mouse model. Our results indicate that the pregnant mice demonstrate accelerated muscle healing compared to nonpregnant control mice following muscle injury based on improved muscle histology, superior muscle regeneration, and a reduction in inflammation and necrosis. Additionally, we found that MPCs isolated from pregnant mice display a significant improvement of myogenic differentiation capacity in vitro and muscle regeneration in vivo when compared to the MPCs from nonpregnant mice. Furthermore, MPCs from nonpregnant mice display enhanced myogenic capacity when cultured in the presence of serum obtained from pregnant mice. Our proteomics data from these studies provides potential therapeutic targets to enhance the myogenic potential of progenitor cells and muscle repair.

Matrix Metalloproteinase 13 from Satellite Cells is Required for Efficient Muscle Growth and Regeneration

BACKGROUND/AIMS

Cell migration and extracellular matrix remodeling underlie normal mammalian development and growth as well as pathologic tumor invasion. Skeletal muscle is no exception, where satellite cell migration replenishes nuclear content in damaged tissue and extracellular matrix reforms during regeneration. A key set of enzymes that regulate these processes are matrix metalloproteinases (MMP)s. The collagenase MMP-13 is transiently upregulated during muscle regeneration, but its contribution to damage resolution is unknown. The purpose of this work was to examine the importance of MMP-13 in muscle regeneration and growth in vivo and to delineate a satellite cell specific role for this collagenase.

METHODS

Mice with total and satellite cell specific Mmp13 deletion were utilized to determine the importance of MMP-13 for postnatal growth, regeneration after acute injury, and in chronic injury from a genetic cross with dystrophic (mdx) mice. We also evaluated insulin-like growth factor 1 (IGF-1) mediated hypertrophy in the presence and absence of MMP-13. We employed live-cell imaging and 3D migration measurements on primary myoblasts obtained from these animals. Outcome measures included muscle morphology and function.

RESULTS

Under basal conditions, Mmp13^-/- mice did not exhibit histological or functional deficits in muscle. However, following acute injury, regeneration was impaired at 11 and 14 days post injury. Muscle hypertrophy caused by increased IGF-1 was blunted with minimal satellite cell incorporation in the absence of MMP-13. Mmp13^-/- primary myoblasts displayed reduced migratory capacity in 2D and 3D, while maintaining normal proliferation and differentiation. Satellite cell specific deletion of MMP-13 recapitulated the effects of global MMP-13 ablation on muscle regeneration, growth and myoblast movement.

CONCLUSION

These results show that satellite cells provide an essential autocrine source of MMP-13, which not only regulates their migration, but also supports postnatal growth and resolution of acute damage.

Doxorubicin induces trans-differentiation and MMP1 expression in cardiac fibroblasts via cell death-independent pathways

Although doxorubicin (DOX)-induced cardiomyopathy causes lethal heart failure (HF), no early detection or effective treatment methods are available. The principal mechanisms of cardiotoxicity are considered to involve oxidative stress and apoptosis of cardiomyocytes. However, the effect of DOX on cardiac fibroblasts at non-lethal concentrations remains unknown. The aim of this study was to investigate the direct effect of doxorubicin on the activation of cardiac fibroblasts independent of cell death pathways. We first found that DOX induced α-SMA expression (marker of trans-differentiation) at a low concentration range, which did not inhibit cell viability. DOX also increased MMP1, IL-6, TGF-β and collagen expression in human cardiac fibroblasts (HCFs). In addition, DOX promoted Akt and Smad phosphorylation. A Smad inhibitor prevented DOX-induced α-SMA and IL-6 protein expression. An PI3K inhibitor also prevented MMP1 mRNA expression in HCFs. These findings suggest that DOX directly induces fibrotic changes in HCFs via cell death-independent pathways. Furthermore, we confirmed that these responses are organ- and species-specific for HCFs based on experiments using different types of human and murine fibroblast cell lines. These results suggest potentially new mechanisms of DOX-induced cardiotoxicity from the viewpoint of fibrotic changes in cardiac fibroblasts.

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.

3D Structure and Processing Methods Direct the Biological Attributes of ECM-Based Cardiac Scaffolds

High hopes are held for cardiac regenerative therapy, driving a vast research effort towards the development of various cardiac scaffolds using diverse technologies and materials. Nevertheless, the role of factors such as fabrication process and structure in determining scaffold's characteristics is yet to be discovered. In the present study, the effects of 3D structure and processing method on cardiac scaffolds are addressed using three distinct scaffolds made through different production technologies from the same biomaterial: decellularized porcine cardiac extracellular matrix (pcECM). pcECM patch, injectable pcECM hydrogel, and electrospun pcECM scaffolds were all proven as viable prospective therapies for MI, thus generally preserving pcECM beneficial properties. Yet, as we demonstrate, minor differences in scaffolds composition and micro-morphology as well as substantial differences in their mechanical properties, which arise from their production process, highly affect the interactions of the scaffold with both proliferating cells and functional cells. Hence, the rates of cell attachment, survival, and proliferation significantly vary between the different scaffolds. Moreover, major differences in cell morphology and alignment as well as in matrix remodeling are obtained. Overall, the effects revealed herein can guide a more rational scaffold design for the improved cellular or acellular treatment of different cardiac disease scenarios.

Peimine suppresses interleukin‑1β‑induced inflammation via MAPK downregulation in chondrocytes

Osteoarthritis (OA) is the most common type of degenerative joint disease and secreted inflammatory molecules serve a pivotal role in it. Peimine has been reported to have anti‑inflammatory activity. In order to investigate the potential therapeutic role of Peimine in OA, mouse articular chondrocytes were treated with IL‑1β and different doses of Peimine in vitro. The data revealed that Peimine not only suppressed IL‑1β‑induced production of nitric oxide (NO) and prostaglandin E2, but also reduced the protein levels of inducible NO synthase (iNOS) and cyclooxygenase‑2 (COX‑2). In addition, Peimine inhibited the IL‑1β‑induced mRNA expression of matrix metalloproteinase (MMP)‑1, MMP‑3, MMP‑9, MMP‑13, a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS)‑4 and ADAMTS‑5. Furthermore, Peimine inhibited IL‑1β‑induced activation of the mitogen‑activated protein kinase (MAPK) pathway. The protective effect of Peimine on IL‑1β‑treated chondrocytes was attenuated following activation of the MAPK pathway, as demonstrated by the increased expression levels of MMP‑3, MMP‑13, ADAMTS‑5, iNOS and COX‑2 compared with the Peimine group. The in vivo data suggested that Peimine limited the development of OA in the mouse model. In general, the data indicate that Peimine suppresses IL‑1β‑induced inflammation in mouse chondrocytes by inhibiting the MAPK pathway, suggesting a promising therapeutic role for Peimine in the treatment of OA.

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

PURPOSE

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

The Molecular Mechanisms and Prevention Principles of Muscle Atrophy in Aging

Muscle atrophy in aging is characterized by progressive loss of muscle mass and function. Muscle mass is determined by the balance of synthesis and degradation of protein, which are regulated by several signaling pathways such as ubiquitin-proteasome system, autophagy-lysosome systems, oxidative stress, proinflammatory cytokines, hormones, and so on. Sufficient nutrition can enhance protein synthesis, while exercise can improve the quality of life in the elderly. This chapter will discuss the epidemiology, pathogenesis, as well as the current treatment for aging-induced muscular atrophy.

Abnormal extracellular matrix remodelling in the cervix of pregnant relaxin-deficient mice is not associated with reduced matrix metalloproteinase expression or activity

Relaxin regulates cervical extracellular matrix (ECM) remodelling during pregnancy by modifying collagen and other ECM molecules by unknown mechanisms. We hypothesised that abnormal collagen remodelling in the cervix of pregnant relaxin-deficient (Rln1−/−) mice is due to excessive collagen (Col1a1 and Col3a1) and decreased matrix metalloproteinases (Mmp2, Mmp9, Mmp13 and Mmp7) and oestrogen receptors (Esr1 and Esr2). Quantitative polymerase chain reaction, gelatinase zymography, MMP activity assays and histological staining evaluated changes in ECM in pregnant wildtype (Rln1+/+) and Rln1−/− mice. Cervical Col1a1, Col3a1 and total collagen increased in Rln1−/− mice and were higher at term compared with Rln1+/+ mice. This was not correlated with a decrease in gelatinase (Mmp2, Mmp9) expression or activity, Mmp7 or Mmp13 expression, which were all significantly higher in Rln1−/− mice. In late pregnancy, circulating MMP2 and MMP9 were unchanged. Esr1 expression was highest in Rln1+/+ and Rln1−/− mice in late pregnancy, coinciding with a decrease in Esr2 in Rln1+/+ but not Rln1−/− mice. The relaxin receptor (Rxfp1) decreased slightly in late-pregnant Rln1+/+ mice, but was significantly higher in Rln1−/− mice. In summary, relaxin deficiency results in increased cervical collagen in late pregnancy, which is not explained by a reduction in Mmp expression or activity or decreased Rxfp1. However, an imbalance between Esr1 and Esr2 may be involved.

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.

Biohybrid cardiac ECM-based hydrogels improve long term cardiac function post myocardial infarction

Injectable scaffolds for cardiac tissue regeneration are a promising therapeutic approach for progressive heart failure following myocardial infarction (MI). Their major advantage lies in their delivery modality that is considered minimally invasive due to their direct injection into the myocardium. Biomaterials comprising such scaffolds should mimic the cardiac tissue in terms of composition, structure, mechanical support, and most importantly, bioactivity. Nonetheless, natural biomaterial-based gels may suffer from limited mechanical strength, which often fail to provide the long-term support required by the heart for contraction and relaxation. Here we present newly-developed injectable scaffolds, which are based on solubilized decellularized porcine cardiac extracellular matrix (pcECM) cross-linked with genipin alone or engineered with different amounts of chitosan to better control the gel's mechanical properties while still leveraging the ECM biological activity. We demonstrate that these new biohybrid materials are naturally remodeled by mesenchymal stem cells, while supporting high viabilities and affecting cell morphology and organization. They exhibit neither in vitro nor in vivo immunogenicity. Most importantly, their application in treating acute and long term chronic MI in rat models clearly demonstrates the significant therapeutic potential of these gels in the long-term (12weeks post MI). The pcECM-based gels enable not only preservation, but also improvement in cardiac function eight weeks post treatment, as measured using echocardiography as well as hemodynamics. Infiltration of progenitor cells into the gels highlights the possible biological remodeling properties of the ECM-based platform.

STATEMENT OF SIGNIFICANCE

This work describes the development of new injectable scaffolds for cardiac tissue regeneration that are based on solubilized porcine cardiac extracellular matrix (ECM), combined with natural biomaterials: genipin, and chitosan. The design of such scaffolds aims at leveraging the natural bioactivity and unique structure of cardiac ECM, while overcoming its limited mechanical strength, which may fail to provide the long-term support required for heart contraction and relaxation. Here, we present a biocompatible gel-platform with custom-tailored mechanical properties that significantly improve cardiac function when injected into rat hearts following acute and chronic myocardial infarction. We clearly demonstrate the substantial therapeutic potential of these scaffolds, which not only preserved heart functions but also alleviated MI damage, even after the formation of a mature scar tissue.

Matrix metalloproteinase and tissue inhibitor of metalloproteinase responses to muscle damage after eccentric exercise

High-intensity eccentric exercise is known to induce muscle damage leading to inflammatory responses and extracellular matrix (ECM) degradation. These degradation processes involve enzymes such as matrix metalloproteinases (MMPs) and tissue inhibitor of metalloproteinases (TIMPs). MMPs are calcium and zinc-dependent proteolytic enzymes that play a role in ECM degradation and recruitment of inflammatory and myogenic cells into the damaged site. In contrast, TIMPs inhibit MMP-induced ECM degradation to maintain normal homeostasis in ECM. Recently, several studies have examined the process of muscle remodeling and the roles of ECM, MMPs, and TIMPs in exercise-induced muscle damage. However, the results of these studies are not inconsistent. In the present mini-review, we will discuss the responses of MMP and TIMP to eccentric exercise based on the literature review.

MMP1 gene expression enhances myoblast migration and engraftment following implanting into mdx/SCID mice

Myoblast transplantation (MT) is a method to introduce healthy genes into abnormal skeletal muscle. It has been considered as a therapeutic modality in the last few decades for diseases such as Duchenne Muscular Dystrophy (DMD). However, challenges including cell death and poor graft engraftment have limited its application. The current experiment utilizes MMP1 gene transfer to improve the efficacy of myoblast transplantation into the diseased dystrophic skeletal muscle of mdx mice. Our results indicated that MMP1 expression can promote myogenic differentiation and fusion capacities, increase migration of MMP1 expressing myoblasts in vitro, as well as improve engraftment of dystrophin positive myofibers in vivo. Taken together, our observation suggests that the addition of MMP1 can overcome limitations in MT and improve its clinical efficacy.

Combining an epithelial repair factor and anti-fibrotic with a corticosteroid offers optimal treatment for allergic airways disease

BACKGROUND AND PURPOSE

We evaluated the extent to which individual versus combination treatments that specifically target airway epithelial damage [trefoil factor-2 (TFF2)], airway fibrosis [serelaxin (RLX)] or airway inflammation [dexamethasone (DEX)] reversed the pathogenesis of chronic allergic airways disease (AAD).

EXPERIMENTAL APPROACH

Following induction of ovalbumin (OVA)-induced chronic AAD in 6–8 week female Balb/c mice, animals were i.p. administered naphthalene (NA) on day 64 to induce epithelial damage, then received daily intranasal administration of RLX (0.8 mg·mL(−1)), TFF2 (0.5 mg·mL(−1)), DEX (0.5 mg·mL(−1)), RLX + TFF2 or RLX + TFF2 + DEX from days 67–74. On day 75, lung function was assessed by invasive plethysmography, before lung tissue was isolated for analyses of various measures. The control group was treated with saline + corn oil (vehicle for NA).

KEY RESULTS

OVA + NA-injured mice demonstrated significantly increased airway inflammation, airway remodelling (AWR) (epithelial damage/thickness; subepithelial myofibroblast differentiation, extracellular matrix accumulation and fibronectin deposition; total lung collagen concentration), and significantly reduced airway dynamic compliance (cDyn). RLX + TFF2 markedly reversed several measures of OVA + NA-induced AWR and normalized the reduction in cDyn. The combined effects of RLX + TFF2 + DEX significantly reversed peribronchial inflammation score, airway epithelial damage, subepithelial extracellular matrix accumulation/fibronectin deposition and total lung collagen concentration (by 50–90%) and also normalized the reduction of cDyn.

CONCLUSIONS AND IMPLICATIONS

Combining an epithelial repair factor and anti-fibrotic provides an effective means of treating the AWR and dysfunction associated with AAD/asthma and may act as an effective adjunct therapy to anti-inflammatory corticosteroids

Relaxin and insulin-like peptide 3 in the musculoskeletal system: from bench to bedside

Skeletal muscles and bones form a joined functional unit sharing a complex mechanical, biochemical and hormonal crosstalk. A number of factors, including sex hormones, physiologically regulate the musculoskeletal system. Striking gender differences in muscle and bone mass, and function are mainly caused by distinct actions exerted by oestrogens and androgens. However, relaxin and relaxin-related peptides, such as insulin-like peptide 3 (INSL3), might contribute to these sex-associated differences in physiological and pathological conditions (such as osteoporosis and sarcopenia). Relaxin is a 'pregnancy' hormone, but it is also produced from the prostate gland, and has recently attracted attention as a potential drug for cardiovascular disorders and fibrosis. In contrast, INSL3 is a male-specific hormone produced by the Leydig cells of the testis with a fundamental role in testicular descent during fetal life. Recent evidence suggests that both hormones have interesting roles in the musculoskeletal system. Relaxin and INSL3, by finely tuning bone formation and resorption, are involved in bone remodelling processes, and relaxin contributes to the healing of injured ligaments and promotes skeletal muscle regeneration. Here, we review the most recent findings on the effects of relaxin and INSL3 on skeletal muscle and the cell components of bone. In the light of the experimental evidence available and animal models, their clinical implications are also discussed.

LINKED ARTICLES

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

Relaxin Level in Patients With Atrial Fibrillation and Association with Heart Failure Occurrence: A STROBE Compliant Article

Atrial fibrillation (AF) is the most common arrhythmia requiring medical treatment and has been associated with enhanced atrial fibrosis and heart failure (HF). Relaxin (RLX), an antifibrosis and antiinflammatory peptide hormone, may be used to evaluate atrial fibrosis and is associated with HF occurrence in AF. We aimed to clarify the clinical significance of RLX level in patients with AF.We measured circulating levels of RLX and other fibrosis-related factors in 311 patients with sinus rhythm (SR; n = 116) or AF (n = 195). All discharged AF patients were followed up for the occurrence of HF for a mean of 6 months.Circulating levels of RLX were significantly different in patients with AF as compared with SR (P < 0.001), and in the subgroup analysis of AF. RLX level was correlated with left atrial diameter (LAD; R = 0.358, P < 0.001). Among followed up AF patients, on Kaplan-Meier curve analysis, patients with the third RLX tertile (T3) had a significantly higher HF rate than those with the 1st tertile (T1) (P = 0.002) and the cut-off value was 294.8 ng/L (area under the ROC curve [AUC] = 0.723). On multivariable analysis, HF occurrence with AF was associated with increased tertile of serum RLX level (odds ratio [OR] 2.659; confidence interval [95% CI] 1.434-4.930; P = 0.002).RLX is associated with fibrosis-related biomarkers and significantly elevated in AF. RLX was related to the HF occurrence in patients with AF.

Role of Growth Factors in Modulation of the Microvasculature in Adult Skeletal Muscle

Post-natal skeletal muscle is a highly plastic tissue that has the capacity to regenerate rapidly following injury, and to undergo significant modification in tissue mass (i.e. atrophy/hypertrophy) in response to global metabolic changes. These processes are reliant largely on soluble factors that directly modulate muscle regeneration and mass. However, skeletal muscle function also depends on an adequate blood supply. Thus muscle regeneration and changes in muscle mass, particularly hypertrophy, also demand rapid changes in the microvasculature. Recent evidence clearly demonstrates a critical role for soluble growth factors in the tight regulation of angiogenic expansion of the muscle microvasculature. Furthermore, exogenous modulation of these factors has the capacity to impact directly on angiogenesis and thus, indirectly, on muscle regeneration, growth and performance. This chapter reviews recent developments in understanding the role of growth factors in modulating the skeletal muscle microvasculature, and the potential therapeutic applications of exogenous angiogenic and anti-angiogenic mediators in promoting effective growth and regeneration, and ameliorating certain diseases, of skeletal muscle.

Serum and tissue biomarkers in aortic stenosis

Background: Calcific aortic valve stenosis (CAVS) is seen in a large proportion of individuals over 60 years. It is an active process, influenced by lipid accumulation, mechanical stress, inflammation, and abnormal extracellular matrix turnover. Various biomarkers (BMs) are studied, as regards mechanisms, diagnosis and prognosis. Methods: In the calcified valves calcium deposition, elastin fragmentation and disorganization of cellular matrix were assessed, together with expression of OPN, OPG, osteocalcin (OCN) and RL2.

We prospectively studied the following serum BMs in 60 patients with CAVS and compared them to 20 healthy controls, free from any cardiac disease: Matrix metalloproteinases (MMP) 2 and 9 and tissue inhibitor of metalloproteinase 1 (TIMP1), which regulate collagen turnover, inflammatory factors, i.e. tumor necrosis factor a (TNFa), interleukin 2 (IL2), transforming growth factor β1 (TGF-β1) which regulates fibrosis, fetuin-A (fet-A), osteopontin (OPN), osteoprotegerin (OPG), sclerostin (SOST), and relaxin-2 (RL2) which positively or negatively regulate calcification. Monocyte chemoattractant protein 1 (MCP-1) which regulates migration and infiltration of monocytes/macrophages was also studied as well as malondialdehyde (MDA) an oxidative marker. Results: Extent of tissue valve calcification (Alizarin Red stain) was negatively correlated with tissue elastin, and RL2, and positively correlated with tissue OCN and serum TIMP1 and MCP-1 and negatively with MMP9.

Tissue OCN was positively correlated with OPN and negatively with the elastin. Tissue OPN was negatively correlated with elastin and OPG. Tissue OPN OPG and RL2 were not correlated with serum levels In the serum we found in patients statistically lower TIMP1, fet-A and RL2 levels, while all other BMs were higher compared to the healthy group. Positive correlations between SOST and IL2, OPG and MDA but negative with TNFa and OPN were found; also MMP9 was negatively correlated with TNFa and MCP-1 was negatively correlated with TIMP1. Conclusion: We found that many BMs expressing calcification, collagen breakdown, or formation, and inflammation are increased in the valve tissue and in the serum of patients with CAVS as compared with healthy group. Our findings may give new insights towards diagnosis but also therapy. Thus antisclerostin, and antiflammatory agents could be tried for preventing aortic calcification progression.

The strategy and method in modulating finger regeneration

The tip of the human finger can regenerate if the amputation is distal to the nail bed, usually in young children. Studies in regeneration of rodent digits have shown that regeneration occurs if the amputation is distal to the mid-third phalanx for certain ages. The digit contains many different components, such as muscle, tendon, bone, skin, nerves and blood vessels, which must all be regrown in the proper location in order to restore functionality. The mechanism behind the complex healing/regeneration processes is still under investigation; however, improvements in injured finger regeneration have been gradually developing in animal models over the past few years. This review discusses a few strategies and methods to possibly enhance digit regeneration beyond current natural limits, focusing on aspects including scarless wound healing, cell-based treatments, tissue engineering and electrical stimulation.

Possible local stem cells activation by microcurrent application in experimentally injured soleus muscle

BACKGROUND

Severe injuries in skeletal muscle result in muscle weakness that delays recovery and contribute to progressive decline in muscle function. Microcurrent therapy (MCT) is a novel treatment method used in soft tissue injury and tissue regeneration therapy. The regenerative capacity of skeletal muscle tissue resides in satellite cells, the quiescent adult stem cells.

AIM

The present work aimed at investigating the relation between microcurrent therapy and local stem cells in regeneration of induced skeletal muscle injury in albino rat.

MATERIALS AND METHODS

Twenty six adult male albino rats were divided into Sham group, Injury group (I): subjected to soleus muscle injury and subdivided into subgroups I1 & I2 sacrificed 2 and 4 weeks after injury respectively. Microcurrent group (M): subjected to muscle injury and micro-current was applied. The animals were subdivided into subgroups M1 and M2 sacrificed 2 and 4 weeks after injury. Histological, immunohistochemical and morphometric studies were performed.

RESULTS

Atypical fibers widely separated by infiltrating cells and strong acidophilic sarcoplasm with focal vacuolations were found in injury group. In M1 subgroup few atypical fibers were found. In M2 subgroup multiple typical fibers were detected. A significant decrease in the mean area of atypical fibers, a significant increase in the mean area% of alpha SMA+ve cells and that of CD34+ve cells were found in microcurrent group compared to injury group.

CONCLUSION

A definite therapeutic effect of the microcurrent was found on induced skeletal muscle injury. This effect was proved to be related to satellite cell activation.

The injury-induced myokine insulin-like 6 is protective in experimental autoimmune myositis

Background

The idiopathic inflammatory myopathies represent a group of autoimmune diseases that are characterized by lymphocyte infiltration of muscle and muscle weakness. Insulin-like 6 (Insl6) is a poorly characterized member of the insulin-like/relaxin family of secreted proteins, whose expression is upregulated upon acute muscle injury.

Methods

In this study, we employed Insl6 gain or loss of function mice to investigate the role of Insl6 in a T cell-mediated model of experimental autoimmune myositis (EAM). EAM models in rodents have involved immunization with human myosin-binding protein C with complete Freund’s adjuvant (CFA) emulsions and pertussis toxin.

Results

Insl6-deficiency in mice led to a worsened myositis phenotype including increased infiltration of CD4 and CD8 T cells and the elevated expression of inflammatory cytokines. Insl6-deficient mice show significant motor function impairment when tested with treadmill or Rotarod devices. Conversely, muscle-specific overexpression of Insl6 protected against the development of myositis as indicated by reduced lymphocyte infiltration in muscle, diminished inflammatory cytokine expression and improved motor function. The improvement in myositis by Insl6 could also be demonstrated by acute hydrodynamic delivery of a plasmid encoding murine Insl6. In cultured cells, Insl6 inhibits Jurkat cell proliferation and activation in response to phytohemagglutinin/phorbol 12-myristate 13-acetate stimulation. Insl6 transcript expression in muscle was reduced in a cohort of dermatomyositis and polymyositis patients.

Conclusions

These data suggest that Insl6 may have utility for the treatment of myositis, a condition for which few treatment options exist.

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. 

The effect of relaxin on the musculoskeletal system

Relaxin is a hormone structurally related to insulin and insulin-like growth factor, which exerts its regulatory effect on the musculoskeletal and other systems through binding to its receptor in various tissues, mediated by different signaling pathways. Relaxin alters the properties of cartilage and tendon by activating collagenase. This hormone is also involved in bone remodeling and healing of injured ligaments and skeletal muscle. In this review, we have summarized the literature on the effect of relaxin in musculoskeletal system to provide a broad perspective for future studies in this field.

The time course effects of electroacupuncture on promoting skeletal muscle regeneration and inhibiting excessive fibrosis after contusion in rabbits

The aim of this study was to investigate the longitudinal effects of electroacupuncture (EA) on Zusanli (ST36) and Ashi acupoints in promoting skeletal muscle regeneration and inhibiting excessive fibrosis after contusion in rabbits. Sixty rabbits were randomly divided into four groups: normal, contusion, EA, and recombinant human insulin-like growth factor-I (rhIGF-I). An acute skeletal muscle contusion was produced on the right gastrocnemius (GM) by an instrument-based drop-mass technique. EA was performed for 15 minutes every two days with 0.4 mA (2 Hz), and GM injections were executed with rhIGF-I (0.25 mL once a week). Rabbits treated with EA had a higher T-SOD and T-AOC serum activities and lower MDA serum level, the blood perfusion of which was also significantly higher. In the EA group, the diameter of the myofibril was uniform and the arrangement was regular, contrary to the contusion group. The number and diameter of regenerative myofibers and MHC expression were increased in the EA group. EA treatment significantly decreased fibrosis formation and reduced both GDF-8 and p-Smad2/3 expressions in injured muscle. Our data indicate that EA may promote myofiber regeneration and reduce excessive fibrosis by improving blood flow and antioxidant capacities. Additionally, EA may regulate signaling factor expression after contusion.

Notch Signaling is Associated with ALDH Activity and an Aggressive Metastatic Phenotype in Murine Osteosarcoma Cells

Osteosarcoma (OS) is the most common primary malignancy of bone, and pulmonary metastatic disease accounts for nearly all mortality. However, little is known about the biochemical signaling alterations that drive the progression of metastatic disease. Two murine OS cell populations, K7M2 and K12, are clonally related but differ significantly in their metastatic phenotypes and therefore represent excellent tools for studying metastatic OS molecular biology. K7M2 cells are highly metastatic, whereas K12 cells display limited metastatic potential. Here we report that the expression of Notch genes (Notch1, 2, 4) are up-regulated, including downstream targets Hes1 and Stat3, in the highly metastatic K7M2 cells compared to the less metastatic K12 cells, indicating that the Notch signaling pathway is more active in K7M2 cells. We have previously described that K7M2 cells exhibit higher levels of aldehyde dehydrogenase (ALDH) activity. Here we report that K7M2 cell ALDH activity is reduced with Notch inhibition, suggesting that ALDH activity may be regulated in part by the Notch pathway. Notch signaling is also associated with increased resistance to oxidative stress, migration, invasion, and VEGF expression in vitro. However, Notch inhibition did not significantly alter K7M2 cell proliferation. In conclusion, we provide evidence that Notch signaling is associated with ALDH activity and increased metastatic behavior in OS cells. Both Notch and ALDH are putative molecular targets for the treatment and prevention of OS metastasis.

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

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

MMP inhibition as a potential method to augment the healing of skeletal muscle and tendon extracellular matrix

The extracellular matrix (ECM) of skeletal muscle and tendon is composed of different types of collagen molecules that play important roles in the transmission of forces throughout the body, and in the repair and regeneration of injured tissues. Fibroblasts are the primary cells in muscle and tendon that maintain, repair, and modify the ECM in response to mechanical loading, injury, and inactivity. Matrix metalloproteinases (MMPs) are enzymes that digest collagen and other structural molecules, which are synthesized and excreted by fibroblasts. MMPs are required for baseline ECM homeostasis, but disruption of MMP regulation due to injury or disease can alter the normal ECM architecture and prevent proper force transmission. Chronic injuries and diseases of muscles and tendons can be severely debilitating, and current therapeutic modalities to enhance healing are quite limited. This review will discuss the mechanobiology of MMPs, and the potential use of MMP inhibitors to improve the treatment of injured and diseased skeletal muscle and tendon tissue.

Relaxin: new pathophysiological aspects and pharmacological perspectives for an old protein

Human relaxin-2 (hereafter simply defined as "relaxin") is a 6-kDa peptidic hormone best known for the physiological role played during pregnancy in the growth and differentiation of the reproductive tract and in the renal and systemic hemodynamic changes. This factor can also be involved in the pathophysiology of arterial hypertension and heart failure, in the molecular pathways of fibrosis and cancer, and in angiogenesis and bone remodeling. It belongs to the relaxin peptide family, whose members comprehensively exert numerous effects through interaction with different types of receptors, classified as relaxin family peptide (RXFP) receptors (RXFP1, RXFP2, RXFP3, RXFP4). Research looks toward the in-depth examination and complete understanding of relaxin in its various pleiotropic actions. The intent is to evaluate the likelihood of employing this substance for therapeutic purposes, for instance in diseases where a deficit could be part of the underlying pathophysiological mechanisms, also avoiding any adverse effect. Relaxin is already being considered as a promising drug, especially in acute heart failure. A careful study of the different RXFPs and their receptors and the comprehension of all biological activities of these hormones will probably provide new drugs with a potential wide range of therapeutic applications in the near future.

Matrix metalloproteinase inhibition negatively affects muscle stem cell behavior

Skeletal muscle is a large and complex system that is crucial for structural support, movement and function. When injured, the repair of skeletal muscle undergoes three phases: inflammation and degeneration, regeneration and fibrosis formation in severe injuries. During fibrosis formation, muscle healing is impaired because of the accumulation of excess collagen. A group of zinc-dependent endopeptidases that have been found to aid in the repair of skeletal muscle are matrix metalloproteinases (MMPs). MMPs are able to assist in tissue remodeling through the regulation of extracellular matrix (ECM) components, as well as contributing to cell migration, proliferation, differentiation and angiogenesis. In the present study, the effect of GM6001, a broad-spectrum MMP inhibitor, on muscle-derived stem cells (MDSCs) is investigated. We find that MMP inhibition negatively impacts skeletal muscle healing by impairing MDSCs in migratory and multiple differentiation abilities. These results indicate that MMP signaling plays an essential role in the wound healing of muscle tissue because their inhibition is detrimental to stem cells residing in skeletal muscle.

Modelling in vivo skeletal muscle ageing in vitro using three-dimensional bioengineered constructs

Degeneration of skeletal muscle (SkM) with age (sarcopenia) is a major contributor to functional decline, morbidity and mortality. Methodological implications often make it difficult to embark on interventions in already frail and diseased elderly individuals. Using in vitro three-dimensional (3D) bioengineered skeletal muscle constructs that model aged phenotypes and incorporate a representative extracellular matrix (collagen), are under tension, and display morphological and transcript expression of mature skeletal muscle may more accurately characterize the SkM niche. Furthermore, an in vitro model would provide greater experimental manipulation with regard to gene, pharmacological and exercise (mechanical stretch/electrical stimulation) therapies and thus strategies for combating muscle wasting with age. The present study utilized multiple population-doubled (MPD) murine myoblasts compared with parental controls (CON), previously shown to have an aged phenotype in monolayer cultures (Sharples et al., 2011), seeded into 3D type I collagen matrices under uniaxial tension. 3D bioengineered constructs incorporating MPD cells had reduced myotube size and diameter vs. CON constructs. MPD constructs were characterized by reduced peak force development over 24 h after cell seeding, reduced transcript expression of remodelling matrix metalloproteinases, MMP2 and MMP9, with reduced differentiation/hypertrophic potential shown by reduced IGF-I, IGF-IR, IGF-IEa, MGF mRNA. Increased IGFBP2 and myostatin in MPD vs. CON constructs also suggested impaired differentiation/reduced regenerative potential. Overall, 3D bioengineered skeletal muscle constructs represent an in vitro model of the in vivo cell niche with MPD constructs displaying similar characteristics to ageing/atrophied muscle in vivo, thus potentially providing a future test bed for therapeutic interventions to contest muscle degeneration with age.

The origin and fate of muscle satellite cells

Satellite cells represent the primary population of stem cells resident in skeletal muscle. These adult muscle stem cells facilitate the postnatal growth, remodeling, and regeneration of skeletal muscle. Given the remarkable regenerative potential of satellite cells, there is great promise for treatment of muscle pathologies such as the muscular dystrophies with this cell population. Various protocols have been developed which allow for isolation, enrichment, and expansion of satellite cell derived muscle stem cells. However, isolated satellite cells have yet to translate into effective modalities for therapeutic intervention. Broadening our understanding of satellite cells and their niche requirements should improve our in vivo and ex vivo manipulation of these cells to expedite their use for regeneration of diseased muscle. This review explores the fates of satellite cells as determined by their molecular signatures, ontogeny, and niche dependent programming.

Relaxin signals through a RXFP1-pERK-nNOS-NO-cGMP-dependent pathway to up-regulate matrix metalloproteinases: the additional involvement of iNOS

The hormone, relaxin, inhibits aberrant myofibroblast differentiation and collagen deposition by disrupting the TGF-β1/Smad2 axis, via its cognate receptor, Relaxin Family Peptide Receptor 1 (RXFP1), extracellular signal-regulated kinase (ERK)1/2 phosphorylation (pERK) and a neuronal nitric oxide (NO) synthase (nNOS)-NO-cyclic guanosine monophosphate (cGMP)-dependent pathway. However, the signalling pathways involved in its additional ability to increase matrix metalloproteinase (MMP) expression and activity remain unknown. This study investigated the extent to which the NO pathway was involved in human gene-2 (H2) relaxin's ability to positively regulate MMP-1 and its rodent orthologue, MMP-13, MMP-2 and MMP-9 (the main collagen-degrading MMPs) in TGF-β1-stimulated human dermal fibroblasts and primary renal myofibroblasts isolated from injured rats; by gelatin zymography (media) and Western blotting (cell layer). H2 relaxin (10-100 ng/ml) significantly increased MMP-1 (by ~50%), MMP-2 (by ~80%) and MMP-9 (by ~80%) in TGF-β1-stimulated human dermal fibroblasts; and MMP-13 (by ~90%), MMP-2 (by ~130%) and MMP-9 (by ~115%) in rat renal myofibroblasts (all p<0.01 vs untreated cells) over 72 hours. The relaxin-induced up-regulation of these MMPs, however, was significantly blocked by a non-selective NOS inhibitor (L-nitroarginine methyl ester (hydrochloride); L-NAME; 75-100 µM), and specific inhibitors to nNOS (N-propyl-L-arginine; NPLA; 0.2-2 µM), iNOS (1400W; 0.5-1 µM) and guanylyl cyclase (ODQ; 5 µM) (all p<0.05 vs H2 relaxin alone), but not eNOS (L-N-(1-iminoethyl)ornithine dihydrochloride; L-NIO; 0.5-5 µM). However, neither of these inhibitors affected basal MMP expression at the concentrations used. Furthermore, of the NOS isoforms expressed in renal myofibroblasts (nNOS and iNOS), H2 relaxin only stimulated nNOS expression, which in turn, was blocked by the ERK1/2 inhibitor (PD98059; 1 µM). These findings demonstrated that H2 relaxin signals through a RXFP1-pERK-nNOS-NO-cGMP-dependent pathway to mediate its anti-fibrotic actions, and additionally signals through iNOS to up-regulate MMPs; the latter being suppressed by TGF-β1 in myofibroblasts, but released upon H2 relaxin-induced inhibition of the TGF-β1/Smad2 axis.

The effect of physiological stimuli on sarcopenia; impact of Notch and Wnt signaling on impaired aged skeletal muscle repair

The age-related loss of skeletal muscle mass and function that is associated with sarcopenia can result in ultimate consequences such as decreased quality of life. The causes of sarcopenia are multifactorial and include environmental and biological factors. The purpose of this review is to synthesize what the literature reveals in regards to the cellular regulation of sarcopenia, including impaired muscle regenerative capacity in the aged, and to discuss if physiological stimuli have the potential to slow the loss of myogenic potential that is associated with sarcopenia. In addition, this review article will discuss the effect of aging on Notch and Wnt signaling, and whether physiological stimuli have the ability to restore Notch and Wnt signaling resulting in rejuvenated aged muscle repair. The intention of this summary is to bring awareness to the benefits of consistent physiological stimulus (exercise) to combating sarcopenia as well as proclaiming the usefulness of contraction-induced injury models to studying the effects of local and systemic influences on aged myogenic capability.

Maternal obesity enhances collagen accumulation and cross-linking in skeletal muscle of ovine offspring

Maternal obesity (MO) has harmful effects on both fetal development and subsequent offspring health. We previously demonstrated that MO enhances collagen accumulation in fetal skeletal muscle, but its impact on mature offspring muscle collagen accumulation is unknown. Ewes were fed either a control diet (Con, fed 100% of NRC nutrient recommendations) or obesogenic diet (OB, fed 150% of NRC nutrient recommendations) from 60 days before conception to birth. All ewes received the Con diet during lactation. Male offspring were euthanized at 2.5 years (mean) and the left Longissimus dorsi (LD) muscle and semitendinosus (ST) muscle were sampled. Collagen concentration increased by 37.8±19.0% (P<0.05) in LD and 31.2±16.0% (P<0.05) in ST muscle of OB compared to Con offspring muscle. Mature collagen cross-linking (pyridinoline concentration) was increased for 22.3±7.4% and 36.3±9.9% (P<0.05) in LD and ST muscle of OB group respectively. Expression of lysyl oxidase, lysyl hydroxylase-2b (LH2b) and prolyl 4-hydroxylase (P4HA) was higher in OB LD and ST muscle. In addition, the expression of metalloproteinases (MMPs) was lower but tissue inhibitor of metalloproteinases (TIMPs) was higher in OB offspring muscle, indicating reduced collagen remodeling. MO enhanced collagen content and cross-linking in offspring muscle, which might be partially due to reduced collagen remodeling. Our observation that the collagen content and cross-linking are enhanced in MO offspring muscle is significant, because fibrosis is known to impair muscle functions and is a hallmark of muscle aging.

Adenosine A3 receptor stimulation reduces muscle injury following physical trauma and is associated with alterations in the MMP/TIMP response

We have previously demonstrated that in response to traumatic injury in skeletal muscle, there is a dysregulation of the matrix metalloproteases (MMPs) and their inhibitors (TIMPs), a response hypothesized to interfere with proper skeletal muscle regeneration. Moreover, we have shown that pharmacological activation of the adenosine A(3) receptor by Cl-IBMECA in skeletal muscle can protect against ischemia-reperfusion and eccentric exercise injury. However, the mechanism by which Cl-IBMECA protects muscle tissue is poorly defined. This study evaluated the effects of Cl-IBMECA on MMP/TIMP expression in skeletal muscle and tested the hypothesis that adenosine A(3) receptor-stimulated protection of skeletal muscle following traumatic injury is associated with a blunting of MMPs involved in inflammatory processes and collagen degradation, and an increase in MMPs associated with extracellular matrix remodeling. Sixty C57BL/6J male mice were injected with Cl-IBMECA (n = 30) or a vehicle (n = 30), and Evans blue dye. Injury was induced by applying a cold steel probe (-79°C) to the tibialis anterior (TA) muscle for 10 s. TA muscles from uninjured and injured legs were collected 3, 10, and 24 h postinjury for analysis of muscle injury and MMP/TIMP mRNA and protein levels. Twenty-four hours postinjury, 56.8% of the fibers were damaged in vehicle-treated mice vs. 35.4% in Cl-IBMECA-treated mice (P = 0.02). Cl-IBMECA treatment reduced membrane type 1 (MT1)-MMP, MMP-3, MMP-9, and TIMP-1 mRNA expression 2- to 20-fold compared with vehicle-treated mice (P < 0.05). Cl-IBMECA decreased protein levels of latent/shed MT1-MMP 23-2,000%, respectively, 3-10 h postinjury. In Cl-IBMECA-treated mice, latent MMP-2 was decreased 20% 3 h postinjury, active MMP-3 was decreased 64% 3 h postinjury, and latent/active MMP-9 was decreased 417,631% 3 h postinjury and 20% 10 h postinjury. Protein levels of active MMP-2 and latent MMP-3 were increased 25% and 74% 3 h postinjury, respectively. The present study elucidates a new protective role of adenosine A(3) receptor stimulation in posttraumatic skeletal muscle injury.

Slow-adhering stem cells derived from injured skeletal muscle have improved regenerative capacity

A wide variety of myogenic cell sources have been used for repair of injured and diseased muscle including muscle stem cells, which can be isolated from skeletal muscle as a group of slow-adhering cells on a collagen-coated surface. The therapeutic use of muscle stem cells for improving muscle regeneration is promising; however, the effect of injury on their characteristics and engraftment potential has yet to be described. In the present study, slow-adhering stem cells (SASCs) from both laceration-injured and control noninjured skeletal muscles in mice were isolated and studied. Migration and proliferation rates, multidifferentiation potentials, and differences in gene expression in both groups of cells were compared in vitro. Results demonstrated that a larger population of SASCs could be isolated from injured muscle than from control noninjured muscle. In addition, SASCs derived from injured muscle demonstrated improved migration, a higher rate of proliferation and multidifferentiation, and increased expression of Notch1, STAT3, Msx1, and MMP2. Moreover, when transplanted into dystrophic muscle in MDX/SCID mice, SASCs from injured muscle generated greater engraftments with a higher capillary density than did SASCs from control noninjured muscle. These data suggest that traumatic injury may modify stem cell characteristics through trophic factors and improve the transplantation potential of SASCs in alleviating skeletal muscle injuries and diseases.