The pro-fibrotic connective tissue growth factor (CTGF/CCN2) correlates with the number of necrotic-regenerative foci in dystrophic muscle

Endothelial-mesenchymal transition in skeletal muscle: Opportunities and challenges from 3D microphysiological systems

Fibrosis is a pathological condition that in the muscular context is linked to primary diseases such as dystrophies, laminopathies, neuromuscular disorders, and volumetric muscle loss following traumas, accidents, and surgeries. Although some basic mechanisms regarding the role of myofibroblasts in the progression of muscle fibrosis have been discovered, our knowledge of the complex cell-cell, and cell-matrix interactions occurring in the fibrotic microenvironment is still rudimentary. Recently, vascular dysfunction has been emerging as a key hallmark of fibrosis through a process called endothelial-mesenchymal transition (EndoMT). Nevertheless, no effective therapeutic options are currently available for the treatment of muscle fibrosis. This lack is partially due to the absence of advanced in vitro models that can recapitulate the 3D architecture and functionality of a vascularized muscle microenvironment in a human context. These models could be employed for the identification of novel targets and for the screening of potential drugs blocking the progression of the disease. In this review, we explore the potential of 3D human muscle models in studying the role of endothelial cells and EndoMT in muscle fibrotic tissues and identify limitations and opportunities for optimizing the next generation of these microphysiological systems. Starting from the biology of muscle fibrosis and EndoMT, we highlight the synergistic links between different cell populations of the fibrotic microenvironment and how to recapitulate them through microphysiological systems.

Imaging mass cytometry analysis of Becker muscular dystrophy muscle samples reveals different stages of muscle degeneration

Becker muscular dystrophy (BMD) is characterised by fiber loss and expansion of fibrotic and adipose tissue. Several cells interact locally in what is known as the degenerative niche. We analysed muscle biopsies of controls and BMD patients at early, moderate and advanced stages of progression using Hyperion imaging mass cytometry (IMC) by labelling single sections with 17 markers identifying different components of the muscle. We developed a software for analysing IMC images and studied changes in the muscle composition and spatial correlations between markers across disease progression. We found a strong correlation between collagen-I and the area of stroma, collagen-VI, adipose tissue, and M2-macrophages number. There was a negative correlation between the area of collagen-I and the number of satellite cells (SCs), fibres and blood vessels. The comparison between fibrotic and non-fibrotic areas allowed to study the disease process in detail. We found structural differences among non-fibrotic areas from control and patients, being these latter characterized by increase in CTGF and in M2-macrophages and decrease in fibers and blood vessels. IMC enables to study of changes in tissue structure along disease progression, spatio-temporal correlations and opening the door to better understand new potential pathogenic pathways in human samples.

Spatial transcriptomics reveal markers of histopathological changes in Duchenne muscular dystrophy mouse models

Duchenne muscular dystrophy is caused by mutations in the DMD gene, leading to lack of dystrophin. Chronic muscle damage eventually leads to histological alterations in skeletal muscles. The identification of genes and cell types driving tissue remodeling is a key step to developing effective therapies. Here we use spatial transcriptomics in two Duchenne muscular dystrophy mouse models differing in disease severity to identify gene expression signatures underlying skeletal muscle pathology and to directly link gene expression to muscle histology. We perform deconvolution analysis to identify cell types contributing to histological alterations. We show increased expression of specific genes in areas of muscle regeneration (Myl4, Sparc, Hspg2), fibrosis (Vim, Fn1, Thbs4) and calcification (Bgn, Ctsk, Spp1). These findings are confirmed by smFISH. Finally, we use differentiation dynamic analysis in the D2-mdx muscle to identify muscle fibers in the present state that are predicted to become affected in the future state.

Multiomic characterization of disease progression in mice lacking dystrophin

Duchenne muscular dystrophy (DMD) is caused by genetic mutations leading to lack of dystrophin in skeletal muscle. A better understanding of how objective biomarkers for DMD vary across subjects and over time is needed to model disease progression and response to therapy more effectively, both in pre-clinical and clinical research. We present an in-depth characterization of disease progression in 3 murine models of DMD by multiomic analysis of longitudinal trajectories between 6 and 30 weeks of age. Integration of RNA-seq, mass spectrometry-based metabolomic and lipidomic data obtained in muscle and blood samples by Multi-Omics Factor Analysis (MOFA) led to the identification of 8 latent factors that explained 78.8% of the variance in the multiomic dataset. Latent factors could discriminate dystrophic and healthy mice, as well as different time-points. MOFA enabled to connect the gene expression signature in dystrophic muscles, characterized by pro-fibrotic and energy metabolism alterations, to inflammation and lipid signatures in blood. Our results show that omic observations in blood can be directly related to skeletal muscle pathology in dystrophic muscle.

Cytokine levels in the aqueous humor of young and senior patients with proliferative diabetic retinopathy

OBJECTIVE

To evaluate the aqueous humor levels of vascular endothelial growth factor (VEGF), connective tissue growth factor (CTGF), and tumor necrosis factor α (TNF-α) as biomarkers of the severity of proliferative diabetic retinopathy (PDR) in young and senior patients.

METHODS

This was a prospective clinical study. From October 2020 to June 2021, 37 patients (37 eyes) who were diagnosed with PDR and received pars plana vitrectomy (PPV) at Tianjin Medical University Eye Hospital were recruited and allocated to either the young (16 patients, 16 eyes) or senior subgroup (21 patients, 21 eyes). Twelve patients with cataracts (12 eyes) who underwent phacoemulsification combined with intraocular lens (IOL) implantation during the same period were recruited in the control group. The fibrovascular proliferation (FVP) grade and PDR severity scores were recorded during PPV. Enzyme-linked immunosorbent assay was used to detect the levels of VEGF, CTGF, and TNF-α in the aqueous humor.

RESULTS

(1) Young patients with PDR had a higher FVP grade and PDR severity score (P = 0.037, = 0.009); (2) The levels of the three cytokines in the study group were all significantly higher than in the control group (all P < 0.001); (3) The CTGF level in the young subgroup (2239.55 ± 167.32 pg/mL) was significantly higher than that in the senior subgroup (2114.49 ± 102.04 pg/mL) (P = 0.025). The VEGF level in the young subgroup (311.09 ± 10.74 pg/mL) was significantly lower than that in the senior subgroup (324.85 ± 14.97 pg/mL) (P = 0.004). The TNF-α level was not statistically different between the two subgroups (P = 0.382); (4) The CTGF/VEGF ratio in the young subgroup (7.20 ± 0.54) was significantly higher than in the senior subgroup (6.52 ± 0.39) (P < 0.001); (5) The CTGF/VEGF ratio was positively correlated with the FVP grades (R = 0.377, P = 0.022) and with the PDR severity scores (R = 0.354, P = 0.032) in patients with PDR.

CONCLUSION

The aqueous humor CTGF/VEGF ratio was positively correlated with the severity of PDR. A higher CTGF/VEGF ratio in the aqueous humor proved that neovascular fibrosis was more serious in young patients when they received PPV.

Single-Cell RNA Sequencing Reveals Smooth Muscle Cells Heterogeneity in Experimental Aortic Dissection

Purpose: This study aims to illustrate the cellular landscape in the aorta of experimental aortic dissection (AD) and elaborate on the smooth muscle cells (SMCs) heterogeneity and functions among various cell types.

Methods: Male Apolipoprotein deficient (ApoE−/−) mice at 28 weeks of age were infused with Ang II (2,500 ng/kg/min) to induce AD. Aortas from euthanized mice were harvested after 7 days for 10×Genomics single-cell RNA sequencing (scRNA-seq), followed by the identification of cell types and differentially expressed genes (DEGs). Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis was conducted.

Results: AD was successfully induced in ApoE−/− mice. scRNA-seq identified 15 cell clusters and nine cell types, including non-immune cells (endothelials, fibroblasts, and SMCs) and immune cells (B cells, natural killer T cell, macrophages, dendritic cells, neutrophils, and mast cells). The relative numbers of SMCs were remarkably changed, and seven core DEGs (ACTA2,IL6,CTGF,BGN,ITGA8,THBS1, and CDH5) were identified in SMCs. Moreover, we found SMCs can differentiate into 8 different subtypes through single-cell trajectory analysis.

Conclusion: scRNA-seq technology can successfully identify unique cell composition in experimental AD. To our knowledge, this is the first study that provided the complete cellular landscape in AD tissues from mice, seven core DEGs and eight subtypes of SMCs were identified, and the SMCs have evolution from matrix type to inflammatory type.

Paraspinal Muscle Health is Related to Fibrogenic, Adipogenic, and Myogenic Gene Expression in Patients with Lumbar Spine Pathology

BACKGROUND

Lumbar spine pathology is a common feature of lower back and/or lower extremity pain and is associated with observable degenerative changes in the lumbar paraspinal muscles that are associated with poor clinical prognosis. Despite the commonly observed phenotype of muscle degeneration in this patient population, its underlying molecular mechanisms are not well understood. The aim of this study was to investigate the relationships between groups of genes within the atrophic, myogenic, fibrogenic, adipogenic, and inflammatory pathways and multifidus muscle health in individuals undergoing surgery for lumbar spine pathology.

METHODS

Multifidus muscle biopsies were obtained from patients (n = 59) undergoing surgery for lumbar spine pathology to analyze 42 genes from relevant adipogenic/metabolic, atrophic, fibrogenic, inflammatory, and myogenic gene pathways using quantitative polymerase chain reaction. Multifidus muscle morphology was examined preoperatively in these patients at the level and side of biopsy using T2-weighted magnetic resonance imaging to determine whole muscle compartment area, lean muscle area, fat cross-sectional areas, and proportion of fat within the muscle compartment. These measures were used to investigate the relationships between gene expression patterns and muscle size and quality.

RESULTS

Relationships between gene expression and imaging revealed significant associations between decreased expression of adipogenic/metabolic gene (PPARD), increased expression of fibrogenic gene (COL3A1), and lower fat fraction on MRI (r = -0.346, p = 0.018, and r = 0.386, p = 0.047 respectively). Decreased expression of myogenic gene (mTOR) was related to greater lean muscle cross-sectional area (r = 0.388, p = 0.045).

CONCLUSION

Fibrogenic and adipogenic/metabolic genes were related to pre-operative muscle quality, and myogenic genes were related to pre-operative muscle size. These findings provide insight into molecular pathways associated with muscle health in the presence of lumbar spine pathology, establishing a foundation for future research that addresses how these changes impact outcomes in this patient population.

Connective Tissue Growth Factor in Idiopathic Pulmonary Fibrosis: Breaking the Bridge

CTGF is upregulated in patients with idiopathic pulmonary fibrosis (IPF), characterized by the deposition of a pathological extracellular matrix (ECM). Additionally, many omics studies confirmed that aberrant cellular senescence-associated mitochondria dysfunction and metabolic reprogramming had been identified in different IPF lung cells (alveolar epithelial cells, alveolar endothelial cells, fibroblasts, and macrophages). Here, we reviewed the role of the CTGF in IPF lung cells to mediate anomalous senescence-related metabolic mechanisms that support the fibrotic environment in IPF.

Human Myometrial and Uterine Fibroid Stem Cell-Derived Organoids for Intervening the Pathophysiology of Uterine Fibroid

Uterine fibroids (UFs) (leiomyomas or myomas) are the most common clonal neoplasms of the uterus in women of reproductive age worldwide. UFs originate from myometrium consist of smooth muscle and fibroblast components, in addition to a substantial amount of fibrous extracellular matrix which all contribute to the pathogenetic process. Current treatments are primarily limited to surgical and interventional. Here, we have established a novel and promising organoid model from both normal and patient myometrial stem cells (MMSCs). MMSCs embedded in Matrigel in stem cell media swiftly formed organoids which successfully proliferate and self-organized into complex structures developing a sustainable organoid culture that maintain their capacity to differentiate into the different cell types recapitulating their tissue of origin and shows responsiveness to the reproductive hormones (estrogen and progesterone). Gene expression analysis and structural features indicated the early onset of uterine fibrosis led to the accumulation of extracellular matrix suggesting the potential use of this model in better understanding of the pathophysiology associated with UFs and inventing novel therapeutics for the treatment of UFs.

Multifunctional regulatory protein connective tissue growth factor (CTGF): A potential therapeutic target for diverse diseases

Connective tissue growth factor (CTGF), a multifunctional protein of the CCN family, regulates cell proliferation, differentiation, adhesion, and a variety of other biological processes. It is involved in the disease-related pathways such as the Hippo pathway, p53 and nuclear factor kappa-B (NF-κB) pathways and thus contributes to the developments of inflammation, fibrosis, cancer and other diseases as a downstream effector. Therefore, CTGF might be a potential therapeutic target for treating various diseases. In recent years, the research on the potential of CTGF in the treatment of diseases has also been paid more attention. Several drugs targeting CTGF (monoclonal antibodies FG3149 and FG3019) are being assessed by clinical or preclinical trials and have shown promising outcomes. In this review, the cellular events regulated by CTGF, and the relationships between CTGF and pathogenesis of diseases are systematically summarized. In addition, we highlight the current researches, focusing on the preclinical and clinical trials concerned with CTGF as the therapeutic target.

CCN2 participates in overload-induced skeletal muscle hypertrophy

The regulation of skeletal muscle growth following pro-hypertrophic stimuli requires a coordinated response by different cell types that leads to extracellular matrix (ECM) remodeling and increases in muscle cross-sectional area. Indeed, matricellular proteins serve a key role as communication vehicles that facilitate the propagation of signaling stimuli required for muscle adaptation to environmental challenges. We found that the matricellular protein cellular communication network factor 2 (CCN2), also known as connective tissue growth factor (CTGF), is induced during a time course of overload-driven skeletal muscle hypertrophy in mice. To elucidate the role of CCN2 in mediating the hypertrophic response, we utilized genetically engineered mouse models for myofiber-specific CCN2 gain- and loss-of-function and then examined their response to mechanical stimuli through muscle overload. Interestingly, myofiber-specific deletion of CCN2 blunted muscle's hypertrophic response to overload without interfering with ECM deposition. On the other hand, when in excess through transgenic CCN2 overexpression, CCN2 was efficient in promoting overload-induced aberrant ECM accumulation without affecting myofiber growth. Altogether, our genetic approaches highlighted independent ECM and myofiber stress adaptation responses, and positioned CCN2 as a central mediator of both. Mechanistically, CCN2 acts by regulating focal adhesion kinase (FAK) mediated transduction of overload-induced extracellular signals, including interleukin 6 (IL6), and their regulatory impact on global protein synthesis in skeletal muscle. Overall, our study highlights the contribution of muscle-derived extracellular matrix factor CCN2 for proper hypertrophic muscle growth.

Adaptations in Hippo-Yap signaling and myofibroblast fate underlie scar-free ear appendage wound healing in spiny mice

Spiny mice (Acomys cahirinus) are terrestrial mammals that evolved unique scar-free regenerative wound-healing properties. Myofibroblasts (MFs) are the major scar-forming cell type in skin. We found that following traumatic injury to ear pinnae, MFs appeared rapidly in both Acomys and mouse yet persisted only in mouse. The timing of MF loss in Acomys correlated with wound closure, blastema differentiation, and nuclear localization of the Hippo pathway target protein Yap. Experiments in vitro revealed an accelerated PP2A-dependent dephosphorylation activity that maintained nuclear Yap in Acomys dermal fibroblasts (DFs) and was not detected in mouse or human DFs. Treatment of Acomys in vivo with the nuclear Yap-TEAD inhibitor verteporfin prolonged MF persistence and converted tissue regeneration to fibrosis. Forced Yap activity prevented and rescued TGF-β1-induced human MF formation in vitro. These results suggest that Acomys evolved modifications of Yap activity and MF fate important for scar-free regenerative wound healing in vivo.

Driving fibrosis in neuromuscular diseases: Role and regulation of Connective tissue growth factor (CCN2/CTGF)

Connective tissue growth factor or cellular communication network 2 (CCN2/CTGF) is a matricellular protein member of the CCN family involved in several crucial biological processes. In skeletal muscle, CCN2/CTGF abundance is elevated in human muscle biopsies and/or animal models for diverse neuromuscular pathologies, including muscular dystrophies, neurodegenerative disorders, muscle denervation, and muscle overuse. In this context, CCN2/CTGF is deeply involved in extracellular matrix (ECM) modulation, acting as a strong pro-fibrotic factor that promotes excessive ECM accumulation. Reducing CCN2/CTGF levels or biological activity in pathological conditions can decrease fibrosis, improve muscle architecture and function. In this work, we summarize information about the role of CCN2/CTGF in fibrosis associated with neuromuscular pathologies and the mechanisms and signaling pathways that regulate their expression in skeletal muscle.

Current Pharmacological Strategies for Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is a lethal, X-linked neuromuscular disorder caused by the absence of dystrophin protein, which is essential for muscle fiber integrity. Loss of dystrophin protein leads to recurrent myofiber damage, chronic inflammation, progressive fibrosis, and dysfunction of muscle stem cells. There is still no cure for DMD so far and the standard of care is principally limited to symptom relief through glucocorticoids treatments. Current therapeutic strategies could be divided into two lines. Dystrophin-targeted therapeutic strategies that aim at restoring the expression and/or function of dystrophin, including gene-based, cell-based and protein replacement therapies. The other line of therapeutic strategies aims to improve muscle function and quality by targeting the downstream pathological changes, including inflammation, fibrosis, and muscle atrophy. This review introduces the important developments in these two lines of strategies, especially those that have entered the clinical phase and/or have great potential for clinical translation. The rationale and efficacy of each agent in pre-clinical or clinical studies are presented. Furthermore, a meta-analysis of gene profiling in DMD patients has been performed to understand the molecular mechanisms of DMD.

CCN proteins in the musculoskeletal system: current understanding and challenges in physiology and pathology

The acronym for the CCN family was recently revised to represent “cellular communication network”. These six, small, cysteine-enriched and evolutionarily conserved proteins are secreted matricellular proteins, that convey and modulate intercellular communication by interacting with structural proteins, signalling factors and cell surface receptors. Their role in the development and physiology of musculoskeletal system, constituted by connective tissues where cells are interspersed in the cellular matrix, has been broadly studied. Previous research has highlighted a crucial balance of CCN proteins in mesenchymal stem cell commitment and a pivotal role for CCN1, CCN2 and their alter ego CCN3 in chondrogenesis and osteogenesis; CCN4 plays a minor role and the role of CCN5 and CCN6 is still unclear. CCN proteins also participate in osteoclastogenesis and myogenesis. In adult life, CCN proteins serve as mechanosensory proteins in the musculoskeletal system providing a steady response to environmental stimuli and participating in fracture healing. Substantial evidence also supports the involvement of CCN proteins in inflammatory pathologies, such as osteoarthritis and rheumatoid arthritis, as well as in cancers affecting the musculoskeletal system and bone metastasis. These matricellular proteins indeed show involvement in inflammation and cancer, thus representing intriguing therapeutic targets. This review discusses the current understanding of CCN proteins in the musculoskeletal system as well as the controversies and challenges associated with their multiple and complex roles, and it aims to link the dispersed knowledge in an effort to stimulate and guide readers to an area that the writers consider to have significant impact and relevant potentialities.

Platelet Derived Growth Factor-AA Correlates With Muscle Function Tests and Quantitative Muscle Magnetic Resonance in Dystrophinopathies

Introduction: Duchenne (DMD) and Becker (BMD) muscular dystrophy are X-linked muscular disorders produced by mutations in the DMD gene which encodes the protein dystrophin. Both diseases are characterized by progressive involvement of skeletal, cardiac, and respiratory muscles. As new treatment strategies become available, reliable biomarkers and outcome measures that can monitor disease progression are needed for clinical trials.

Methods: We collected clinical and functional data and blood samples from 19 DMD patients, 13 BMD patients, and 66 healthy controls (8 pediatric and 58 adult controls), and blood samples from 15 patients with dysferlinopathy (DYSF) and studied the serum concentration of 4 growth factors involved in the process of muscle fibrosis. We correlated the serum concentration of these growth factors with several muscle function tests, spirometry results and fat fraction identified by quantitative Dixon muscle MRI.

Results: We found significant differences in the serum concentration of Platelet Derived Growth Factor-AA (PDGF-AA) between DMD patients and pediatric controls, in Connective Tissue Growth Factor (CTGF) between BMD patients and adult controls, and in and Transforming Growth Factor- β1 (TGF-β1) between BMD and DYSF patients. PDGF-AA showed a good correlation with several muscle function tests for both DMD and BMD patients and with thigh fat fraction in BMD patients. Moreover, PDGF-AA levels were increased in muscle biopsies of patients with DMD and BMD as was demonstrated by immunohistochemistry and Real-Time PCR studies.

Conclusion: Our study suggests that PDGF-AA should be further investigated in a larger cohort of DMD and BMD patients because it might be a good biomarker candidate to monitor the progression of these diseases.

Role of Matricellular CCN Proteins in Skeletal Muscle: Focus on CCN2/CTGF and Its Regulation by Vasoactive Peptides

The Cellular Communication Network (CCN) family of matricellular proteins comprises six proteins that share conserved structural features and play numerous biological roles. These proteins can interact with several receptors or soluble proteins, regulating cell signaling pathways in various tissues under physiological and pathological conditions. In the skeletal muscle of mammals, most of the six CCN family members are expressed during embryonic development or in adulthood. Their roles during the adult stage are related to the regulation of muscle mass and regeneration, maintaining vascularization, and the modulation of skeletal muscle fibrosis. This work reviews the CCNs proteins' role in skeletal muscle physiology and disease, focusing on skeletal muscle fibrosis and its regulation by Connective Tissue Growth factor (CCN2/CTGF). Furthermore, we review evidence on the modulation of fibrosis and CCN2/CTGF by the renin-angiotensin system and the kallikrein-kinin system of vasoactive peptides.

The linkage between inflammation and fibrosis in muscular dystrophies: The axis autotaxin-lysophosphatidic acid as a new therapeutic target?

Muscular dystrophies (MDs) are a diverse group of severe disorders characterized by increased skeletal muscle feebleness. In many cases, respiratory and cardiac muscles are also compromised. Skeletal muscle inflammation and fibrosis are hallmarks of several skeletal muscle diseases, including MDs. Until now, several keys signaling pathways and factors that regulate inflammation and fibrosis have been identified. However, no curative treatments are available. Therefore, it is necessary to find new therapeutic targets to fight these diseases and improve muscle performance. Lysophosphatidic acid (LPA) is an active glycerophospholipid mainly synthesized by the secreted enzyme autotaxin (ATX), which activates six different G protein-coupled receptors named LPA₁ to LPA₆ (LPARs). In conjunction, they are part of the ATX/LPA/LPARs axis, involved in the inflammatory and fibrotic response in several organs-tissues. This review recapitulates the most relevant aspects of inflammation and fibrosis in MDs. It analyzes experimental evidence of the effects of the ATX/LPA/LPARs axis on inflammatory and fibrotic responses. Finally, we speculate about its potential role as a new therapeutic pharmacological target to treat these diseases.

Potential cross-talk between muscle and tendon in Duchenne muscular dystrophy

PURPOSE

To describe potential signaling (cross-talk) between dystrophic skeletal muscle and tendon in Duchenne muscular dystrophy.

MATERIALS AND METHODS

Review of Duchenne muscular dystrophy and associated literature relevant to muscle-tendon cross-talk.

RESULTS AND CONCLUSIONS

Duchenne muscular dystrophy results from the absence of the protein dystrophin and the associated dystrophin - glycoprotein complex, which are thought to provide both structural support and signaling functions for the muscle fiber. In addition, there are other potential signal pathways that could represent cross-talk between muscle and tendon, particularly at the myotendinous junction. Duchenne muscular dystrophy is characterized by multiple pathophysiologic mechanisms. Herein, we explore three of these: (1) the extracellular matrix, fibrosis, and fat deposition; (2) satellite cells; and (3) tensegrity. A key signaling protein that emerged in each was transforming growth factor - beta one (TGF-β1).].

Connective Tissue Growth Factor: From Molecular Understandings to Drug Discovery

Connective tissue growth factor (CTGF) is a key signaling and regulatory molecule involved in different biological processes, such as cell proliferation, angiogenesis, and wound healing, as well as multiple pathologies, such as tumor development and tissue fibrosis. Although the underlying mechanisms of CTGF remain incompletely understood, a commonly accepted theory is that the interactions between different protein domains in CTGF and other various regulatory proteins and ligands contribute to its variety of functions. Here, we highlight the structure of each domain of CTGF and its biology functions in physiological conditions. We further summarized main diseases that are deeply influenced by CTGF domains and the potential targets of these diseases. Finally, we address the advantages and disadvantages of current drugs targeting CTGF and provide the perspective for the drug discovery of the next generation of CTGF inhibitors based on aptamers.

Genetic reduction of the extracellular matrix protein versican attenuates inflammatory cell infiltration and improves contractile function in dystrophic mdx diaphragm muscles

There is a persistent, aberrant accumulation of V0/V1 versican in skeletal muscles from patients with Duchenne muscular dystrophy and in diaphragm muscles from mdx mice. Versican is a provisional matrix protein implicated in fibrosis and inflammation in various disease states, yet its role in the pathogenesis of muscular dystrophy is not known. Here, female mdx and male hdf mice (haploinsufficient for the versican allele) were bred. In the resulting F1 mdx-hdf male pups, V0/V1 versican expression in diaphragm muscles was decreased by 50% compared to mdx littermates at 20-26 weeks of age. In mdx-hdf mice, spontaneous physical activity increased by 17% and there was a concomitant decrease in total energy expenditure and whole-body glucose oxidation. Versican reduction improved the ex vivo strength and endurance of diaphragm muscle strips. These changes in diaphragm contractile properties in mdx-hdf mice were associated with decreased monocyte and macrophage infiltration and a reduction in the proportion of fibres expressing the slow type I myosin heavy chain isoform. Given the high metabolic cost of inflammation in dystrophy, an attenuated inflammatory response may contribute to the effects of versican reduction on whole-body metabolism. Altogether, versican reduction ameliorates the dystrophic pathology of mdx-hdf mice as evidenced by improved diaphragm contractile function and increased physical activity.

Increased Fibrogenic Gene Expression in Multifidus Muscles of Patients With Chronic Versus Acute Lumbar Spine Pathology

STUDY DESIGN

Prospective observational study-basic science (Level 1).

OBJECTIVE

The aim of this study was to compare expression of functional groups of genes within the atrophic, myogenic, fibrogenic, adipogenic, and inflammatory pathways between paraspinal muscle biopsies from individuals with acute and chronic lumbar spine pathology.

SUMMARY OF BACKGROUND DATA

Low back pain is a complex and multifactorial condition that affects a majority of the general population annually. Changes in muscle tissue composition (i.e., fatty and fibrotic infiltration) are a common feature in individuals with lumbar spine pathology associated with low back pain, which often results in functional loss. Understanding the molecular underpinnings of these degenerative changes in different phases of disease progression may improve disease prevention and treatment specificity.

METHODS

Intraoperative biopsies of the multifidus muscle were obtained from individuals undergoing surgery for acute (<6-month duration) or chronic (>6-month duration) lumbar spine pathology. Expression of 42 genes related to myogenesis, atrophy, adipogenesis, metabolism, inflammation, and fibrosis were measured in 33 samples (eight acute, 25 chronic) using qPCR, and tissue composition of fat, muscle, and fibrosis was quantified using histology.

RESULTS

We found that tissue composition of the biopsies was heterogeneous, resulting in a trend toward lower RNA yields in biopsies with higher proportions of fat (r <-0.39, P < 0.1). There were no significant differences in gene expression patterns for atrophy (P > 0.635), adipogenesis (P > 0.317), myogenesis (P > 0.320), or inflammatory (P > 0.413) genes after adjusting for the proportion of muscle, fat, and connective tissue. However, in the fibrogenesis pathway, we found significant upregulation of CTGF (P = 0.046), and trends for upregulation of COL1A1 (P = 0.061), and downregulation of MMP1 and MMP9 (P = 0.061) in the chronic group.

CONCLUSION

There is increased fibrogenic gene expression in individuals with chronic disease when compared to acute disease, without significant differences in atrophic, myogenic, adipogenic, or inflammatory pathways, suggesting increased efforts should be made to prevent or reverse fibrogenesis to improve patient function in this population.

LEVEL OF EVIDENCE

N/A.

Role of hypoxia in skeletal muscle fibrosis: Synergism between hypoxia and TGF-β signaling upregulates CCN2/CTGF expression specifically in muscle fibers

Several skeletal muscle diseases are characterized by fibrosis, the excessive accumulation of extracellular matrix. Transforming growth factor-β (TGF-β) and connective tissue growth factor (CCN2/CTGF) are two profibrotic factors augmented in fibrotic skeletal muscle, together with signs of reduced vasculature that implies a decrease in oxygen supply. We observed that fibrotic muscles are characterized by the presence of positive nuclei for hypoxia-inducible factor-1α (HIF-1α), a key mediator of the hypoxia response. However, it is not clear how a hypoxic environment could contribute to the fibrotic phenotype in skeletal muscle. We evaluated the role of hypoxia and TGF-β on CCN2 expression in vitro. Fibroblasts, myoblasts and differentiated myotubes were incubated with TGF-β1 under hypoxic conditions. Hypoxia and TGF-β1 induced CCN2 expression synergistically in myotubes but not in fibroblasts or undifferentiated muscle progenitors. This induction requires HIF-1α and the Smad-independent TGF-β signaling pathway. We performed in vivo experiments using pharmacological stabilization of HIF-1α or hypoxia-induced via hindlimb ischemia together with intramuscular injections of TGF-β1, and we found increased CCN2 expression. These observations suggest that hypoxic signaling together with TGF-β signaling, which are both characteristics of a fibrotic skeletal muscle environment, induce the expression of CCN2 in skeletal muscle fibers and myotubes.

The protective role of Schwann cells in bladder smooth muscle cell fibrosis

Bladder fibrosis is characterized by collagen deposition within bladder walls. Neurogenic lesions are an important contributor to this balder dysfunction. Schwann cells are a kind of glial cell in the peripheral nervous system. However, the role of the cells in bladder fibrosis has received little attention among researchers. Female SD rats were employed in this study to establish a fibrosis model using denervation. Histologically, the fibrosis was evaluated using H&E staining and Masson's staining. CTGF expression was evaluated using immunohistochemistry. Subsequently, the role of Schwann cells in fibrosis was evaluated using a co-culture with bladder smooth cells and exposure to CTGF. After denervation, the bladder fibrosis was observed in a time-dependent manner, and this was accompanied by an increase in CTGF and a decrease in BDNF. After exposure to CTGF, α-SMA, and collagen I and III were significantly increased in the bladder smooth muscle cells. These were significantly inhibited after co-culture with Schwann cells. Furthermore, a significant increase in BDNF was observed in the co-culture. Schwann cells significantly ameliorated the fibrosis of the bladder smooth muscle cells, and this might be associated with the secretion of BDNF.

Mitochondrial Dysfunction in Skeletal Muscle of a Fibromyalgia Model: The Potential Benefits of Melatonin

Fibromyalgia syndrome (FMS) is considered a musculoskeletal disorder associated to other symptoms including chronic pain. Since the hypothesis of FMS etiogenesis is consistent with mitochondrial dysfunction and oxidative stress, we evaluated the pathophysiological correlation among these factors studying some proteins involved in the mitochondrial homeostasis. We focused our attention on the roles of peroxisome proliferator activated receptor gamma coactivator-1alpha (PGC-1α), mitofusin2 (Mfn2), and coenzyme Q10 (CoQ10) in reserpine-induced myalgic (RIM) rats that manifest fibromyalgia-like chronic pain symptoms. First, we underlined that RIM rats are a good model for studying the pathophysiology of FMS and moreover, we found that PGC-1α, Mfn2, and CoQ10 are involved in FMS. In fact, their expressions were reduced in gastrocnemius muscle determining an incorrect mitochondrial homeostasis. Today, none of the currently available drugs are fully effective against the symptoms of this disease and they, often, induce several adverse events; hence, many scientists have taken on the challenge of searching for non-pharmacological treatments. Another goal of this study was therefore the evaluation of the potential benefits of melatonin, an endogenous indoleamine having several functions including its potent capacity to induce antioxidant enzymes and to determine the protective or reparative mechanisms in the cells. We observed that melatonin supplementation significantly preserved all the studied parameters, counteracting oxidative stress in RIM rats and confirming that this indoleamine should be taken in consideration for improving health and/or counteract mitochondrial related diseases.

Genetic manipulation of CCN2/CTGF unveils cell-specific ECM-remodeling effects in injured skeletal muscle

In skeletal muscle, extracellular matrix (ECM) remodeling can either support the complete regeneration of injured muscle or facilitate pathologic fibrosis and muscle degeneration. Muscular dystrophy (MD) is a group of genetic disorders that results in a progressive decline in muscle function and is characterized by the abundant deposition of fibrotic tissue. Unlike acute injury, where ECM remodeling is acute and transient, in MD, remodeling persists until fibrosis obstructs the regenerative efforts of diseased muscles. Thus, understanding how ECM is deposited and organized is critical in the context of muscle repair. Connective tissue growth factor (CTGF or CCN2) is a matricellular protein expressed by multiple cell types in response to tissue injury. Although used as a general marker of fibrosis, the cell type-dependent role of CTGF in dystrophic muscle has not been elucidated. To address this question, a conditional Ctgf myofiber and fibroblast-knockout mouse lines were generated and crossed to a dystrophic background. Only myofiber-selective inhibition of CTGF protected δ-sarcoglycan-null ( Sgcd-/-) mice from the dystrophic phenotype, and it did so by affecting collagen organization in a way that allowed for improvements in dystrophic muscle regeneration and function. To confirm that muscle-specific CTGF functions to mediate collagen organization, we generated mice with transgenic muscle-specific overexpression of CTGF. Again, genetic modulation of CTGF in muscle was not sufficient to drive fibrosis, but altered collagen content and organization after injury. Our results show that the myofibers are critical mediators of the deleterious effects associated with CTGF in MD and acutely injured skeletal muscle.-Petrosino, J. M., Leask, A., Accornero, F. Genetic manipulation of CCN2/CTGF unveils cell-specific ECM-remodeling effects in injured skeletal muscle.

CTGF/CCN2 from Skeletal Muscle to Nervous System: Impact on Neurodegenerative Diseases

Connective tissue growth factor (CTGF/CCN2) is a matricellular protein that belongs to the CCN family of proteins. Since its discovery, it has been linked to cellular processes such as cell proliferation, differentiation, adhesion, migration, and synthesis of extracellular matrix (ECM) components, among others. The pro-fibrotic role of CTGF/CCN2 has been well-studied in several pathologies characterized by the development of fibrosis. Reduction of CTGF/CCN2 levels in mdx mice, a murine model for Duchenne muscular dystrophy (DMD), decreases fibrosis and improves skeletal muscle phenotype and function. Recently, it has been shown that skeletal muscle of symptomatic hSOD1^G93A mice, a model for Amyotrophic lateral sclerosis (ALS), shows up-regulation of CTGF/CCN2 accompanied by excessive deposition ECM molecules. Elevated levels of CTGF/CCN2 in spinal cord from ALS patients have been previously reported. However, there is no evidence regarding the role of CTGF/CCN2 in neurodegenerative diseases such as ALS, in which alterations in skeletal muscle seem to be the consequence of early pathological denervation. In this regard, the emerging evidence shows that CTGF/CCN2 also exerts non-fibrotic roles in the central nervous system (CNS), specifically impairing oligodendrocyte maturation and regeneration, and inhibiting axon myelination. Despite these striking observations, there is no evidence showing the role of CTGF/CCN2 in peripheral nerves. Therefore, even though more studies are needed to elucidate its precise role, CTGF/CCN2 is starting to emerge as a novel therapeutic target for the treatment of neurodegenerative diseases where demyelination and axonal degeneration occurs.

Identification of potential markers of fatal hypothermia by a body temperature-dependent gene expression assay

Diagnosis of fatal hypothermia is considered to be difficult in forensic practice and even if findings due to cold exposure are evident, cold exposure is not necessarily a direct cause of death. Identification of useful molecular markers for the diagnosis of fatal hypothermia has not been successful. In this study, to identify novel molecular markers that inform the diagnosis of fatal hypothermia, we focused on skeletal muscle, which plays a role in cold-induced thermogenesis in mammals. We made rat models of mild, moderate, and severe hypothermia and performed body temperature-dependent gene expression analysis in the iliopsoas muscle using next-generation sequencing (NGS). NGS showed that after severe hypothermia, the expression levels of 91 mRNAs were more than double those in mild and moderate hypothermia and control animals. Gene ontology (GO) analysis indicated that these mRNAs are involved in a number of biological processes, including response to stress and lipids, and cellular response to hypoxia. The expression of four genes [connective tissue growth factor (Ctgf), JunB proto-oncogene, AP-1 transcription factor subunit (Junb), nuclear receptor subfamily 4, group A, member 1 (Nr4a1), and Syndecan 4 (Sdc4)] and the level of one protein (CTGF) were induced only by severe hypothermia. These genes and protein are involved in muscle regeneration, tissue repair, and lipid metabolism. These results indicate that heat production to maintain body temperature in a process leading to fatal hypothermia might be performed by the iliopsoas muscle, and that Ctgf, Junb, Nr4a1, and Sdc4 genes are potential diagnostic markers for fatal hypothermia.

Effects of Geniposide from Gardenia Fruit Pomace on Skeletal-Muscle Fibrosis

Geniposide is the main bioactive constituent of gardenia fruit. Skeletal-muscle fibrosis is a common and irreversibly damaging process. Numerous studies have shown that geniposide could improve many chronic diseases, including metabolic syndrome and tumors. However, the effects of geniposide on skeletal-muscle fibrosis are still poorly understood. Here, we found that crude extracts of gardenia fruit pomace could significantly decrease the expression of profibrotic genes in vitro. Moreover, geniposide could also reverse profibrotic-gene expression induced by TGF-β and Smad4, a regulator of skeletal-muscle fibrosis. In addition, geniposide treatment could significantly downregulate profibrotic-gene expression and improve skeletal-muscle injuries in a mouse model of contusion. These results together suggest that geniposide has an antifibrotic effect on skeletal muscle through the suppression of the TGF-β-Smad4 signaling pathway.

Blockade of Bradykinin receptors worsens the dystrophic phenotype of mdx mice: differential effects for B1 and B2 receptors

The Kallikrein Kinin System (KKS) is a vasoactive peptide system with known functions in the maintenance of tissue homeostasis, renal function and blood pressure. The main effector peptide of KKS is Bradykinin (BK). This ligand has two receptors: a constitutive B2 receptor (B2R), which has been suggested to have anti-fibrotic effects in renal and cardiac models of fibrosis; and the inducible B1 receptor (B1R), whose expression is induced by damage and inflammation. Inflammation and fibrosis are hallmarks of Duchenne muscular dystrophy (DMD), therefore we hypothesized that the KKS may play a role in this disease. To evaluate this hypothesis we used the mdx mouse a model for DMD. We blocked the endogenous activity of the KKS by treating mdx mice with B2R antagonist (HOE-140) or B1R antagonist (DesArgLeu⁸BK (DALBK)) for four weeks. Both antagonists increased damage, fibrosis, TGF-β and Smad-dependent signaling, CTGF/CCN-2 levels as well as the number of CD68 positive inflammatory cells. B2R blockade also reduced isolated muscle contraction force. These results indicate that the endogenous KKS has a protective role in the dystrophic muscle. The KKS may be a new target for future therapies to reduce inflammation and fibrosis in dystrophic muscle.