CCN family protein 2 (CCN2) promotes the early differentiation, but inhibits the terminal differentiation of skeletal myoblasts

Senescent adipocytes as potential effectors of muscle cells dysfunction: An in vitro model

Recently, there has been a growing body of evidence showing a negative effect of the white adipose tissue (WAT) dysfunction on the skeletal muscle function and quality. However, little is known about the effects of senescent adipocytes on muscle cells. Therefore, to explore potential mechanisms involved in age-related loss of muscle mass and function, we performed an in vitro experiment using conditioned medium obtained from cultures of mature and aged 3 T3-L1 adipocytes, as well as from cultures of dysfunctional adipocytes exposed to oxidative stress or high insulin doses, to treat C2C12 myocytes. The results from morphological measures indicated a significant decrease in diameter and fusion index of myotubes after treatment with medium of aged or stressed adipocytes. Aged and stressed adipocytes presented different morphological characteristics as well as a different gene expression profile of proinflammatory cytokines and ROS production. In myocytes treated with different adipocytes' conditioned media, we demonstrated a significant reduction of gene expression of myogenic differentiation markers as well as a significant increase of genes involved in atrophy. Finally, a significant reduction in protein synthesis as well as a significant increase of myostatin was found in muscle cells treated with medium of aged or stressed adipocytes compared to controls. In conclusion, these preliminary results suggest that aged adipocytes could influence negatively trophism, function and regenerative capacity of myocytes by a paracrine network of signaling.

Muscle cell-derived cytokines in skeletal muscle regeneration

Regeneration of the mammalian adult skeletal muscle is a well-orchestrated process regulated by multiple proteins and signalling pathways. Cytokines constitute a major class of regulators of skeletal myogenesis. It is well established that infiltrating immune cells at the site of muscle injury secrete cytokines, which play critical roles in the myofibre repair and regeneration process. In the past 10-15 years, skeletal muscle itself has emerged as a prolific producer of cytokines. Much attention in the field has been focused on the endocrine effects of muscle-secreted cytokines (myokines) on metabolic regulation. However, ample evidence suggests that muscle-derived cytokines also regulate myogenic differentiation and muscle regeneration in an autocrine manner. In this review, we survey cytokines that meet two criteria: (a) evidence of expression by muscle cells; (b) evidence demonstrating a myogenic function. Dozens of cytokines representing several major classes make up this group, and together they regulate all steps of the myogenic process. How such a large array of cytokines coordinate their signalling to form a regulatory network is a fascinating, pressing question. Functional studies that can distinguish the source of the cytokines in vivo are also much needed in order to facilitate exploration of their full therapeutic potential.

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.

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.

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.

WISP1 promotes bovine MDSC differentiation via recruitment of ANXA1 for the regulation of the TGF-β signalling pathway

Skeletal muscle is one of the most important tissues of the human body necessary for sporting activities. The differentiation of muscle-derived satellite cells (MDSCs) plays an important role in the development and regeneration of skeletal muscles. Similarly, the Wnt/β-catenin signalling pathway plays an important role in the process of muscle differentiation. Wnt1-inducible signalling pathway protein-1 (WISP1), a downstream protein of the Wnt/β-catenin signalling pathway and a member of the CCN family that also plays an important role in the differentiation process, and its expression increase during the differentiation of bovine MDSCs. However, its role in MDSC differentiation is poorly understood. Therefore, we investigated the mechanisms regulating this process via Western blot and immunofluorescence staining. Immunoprecipitation and mass spectrometry detected annexin A1 (ANXA1), a protein that interacts with WISP1. To determine whether WISP1 influences TGF-β signalling and differentiation independently of ANXA1, the latter was knocked down, while WISP1 was activated. WISP1 expression increased significantly during bovine MDSC differentiation. However, WISP1 did not affect the TGF-β signalling pathway protein marker when ANXA1 was inhibited. Taken together, WISP1 regulates the TGF-β signalling pathway through ANXA1 recruitment, thereby promoting bovine MDSC differentiation, suggesting the Wnt/β-catenin signalling pathway as another target to promote cell differentiation.

WISP1 Predicts Clinical Prognosis and Is Associated With Tumor Purity, Immunocyte Infiltration, and Macrophage M2 Polarization in Pan-Cancer

Cancer is becoming the leading cause of death and a major public health problem. Although many advanced treatment strategies are currently in use, the general prognosis of cancer patients remains dismal due to the high frequency of recurrence, metastasis. The identification of effective biomarkers is important for predicting survival of cancer patients and improving treatment efficacy. In this study, we comprehensively analyzed WNT1-inducible-signaling pathway protein 1 (WISP1) expression and explored its correlation with prognosis in pan-cancer using tumor IMmune Estimation Resource (TIMER) and Gene Expression Profiling Interactive Analysis 2 (GEPIA2). We also examined correlations between WISP1 and immunocyte infiltration using TIMER. We identified genes co-expressed with WISP1 using the LinkedOmics database and analyzed associated gene ontology using Metascape. Finally, we constructed protein-protein interaction networks and examined correlations between genes co-expressed with WISP1 and immunocyte infiltration in pan-cancer. WISP1 level differed between human pan-cancer tissues and normal tissues, indicating its potential as a prognostic biomarker. WISP1 expression was correlated with tumor purity and immunocyte infiltration, especially monocyte-macrophage trafficking and M2 polarization. Genes co-expressed with WISP1 were mainly associated with extracellular matrix organization, with collagen members COL6A3, COL5A1, and COL8A1 being key genes correlated with macrophage infiltration and M2 polarization in pan-cancer. Conversely, in certain types of cancer with better prognoses, WISP1 was associated with low M2 macrophage infiltration. These results suggest that WISP1 affect clinical prognosis through associations with tumor purity, immune cell infiltration, and macrophage M2 polarization in pan-cancer, with collagen member proteins may serving as effector molecules of WISP1.

Remodeling of hepatic stellate cells orchestrated the stroma-derived oxaliplatin-resistance through CCN3 paracrine in hepatocellular carcinoma

BACKGROUND

Hepatic stellate cells (HSCs) have a key role in fibrogenesis and in the filtrates of the hepatocellular carcinoma (HCC) stroma, in which they are remodeled and play a critical role in HCC progression. However, the precise role of HSCs trending, infiltration and paracrine in orchestrating the stroma-derived oxaliplatin-resistance in HCC is still vague.

METHODS

The chemo-resistant models were established to explore the correlation between HSC cells and the condition of chemoresistance. The HCC clinical samples were collected to confirm this phenomenon. Then, the relationship between secretory CCN3 from oxaliplatin-resistant HCC and the infiltration of HSCs in associated HCC microenvironment was evaluated. Finally, the role and mechanism of HSCs remodeling in the orchestration of oxaliplatin-resistant HCC were explored.

RESULTS

The increased infiltration of HSCs and collagen accumulation were found in the microenvironment of oxaliplatin-resistant HCC. The cDNA profiles of the oxaliplatin-resistant HCC was reanalyzed, and CCN3 was one of the significantly increased genes. In HCC clinical samples, the levels of CCN3 and α-SMA are positively correlated, and high expression of CCN3 and α-SMA are positively associated with malignant phenotype and poor prognosis. Then the enhanced abilities of migration and proliferation of HSCs, and elevation of the cytokines paracrine from HSCs relating to HCC malignancy were proved in vitro and in vivo, and which were related to CCN3-ERK signaling pathway activation.

CONCLUSIONS

HSCs remodeling are positively related to CCN3 paracrine in hepatocellular carcinoma, which orchestrated the stroma-derived resistance to chemotherapy in HCC.

Toxoplasma gondii Impairs Myogenesis in vitro, With Changes in Myogenic Regulatory Factors, Altered Host Cell Proliferation and Secretory Profile

Toxoplasma gondii is the causative agent of toxoplasmosis, a parasitic disease with a wide global prevalence. The parasite forms cysts in skeletal muscle cells and neurons, although no evident association with inflammatory infiltrates has been typically found. We studied the impact of T. gondii infection on the myogenic program of mouse skeletal muscle cells (SkMC). The C2C12 murine myoblast cell line was infected with T. gondii tachyzoites (ME49 strain) for 24 h followed by myogenic differentiation induction. T. gondii infection caused a general decrease in myotube differentiation, fusion and maturation, along with decreased expression of myosin heavy chain. The expression of Myogenic Regulatory Factors Myf5, MyoD, Mrf4 and myogenin was modulated by the infection. Infected cultures presented increased proliferation rates, as assessed by Ki67 immunostaining, whereas neither host cell lysis nor apoptosis were significantly augmented in infected dishes. Cytokine Bead Array indicated that IL-6 and MCP-1 were highly increased in the medium from infected cultures, whereas TGF-β1 was consistently decreased. Inhibition of the IL-6 receptor or supplementation with recombinant TGF-β failed to reverse the deleterious effects caused by the infection. However, conditioned medium from infected cultures inhibited myogenesis in C2C12 cells. Activation of the Wnt/β-catenin pathway was impaired in T. gondii-infected cultures. Our data indicate that T. gondii leads SkMCs to a pro-inflammatory phenotype, leaving cells unresponsive to β-catenin activation, and inhibition of the myogenic differentiation program. Such deregulation may suggest muscle atrophy and molecular mechanisms similar to those involved in myositis observed in human patients.

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.

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

Connective tissue growth factor (CTGF/CCN2) has strong inflammatory and profibrotic activities. Its expression is enhanced in skeletal muscular dystrophies such as Duchenne muscular dystrophy (DMD), a myopathy characterized by exacerbated inflammation and fibrosis. In dystrophic tissue, necrotic-regenerative foci, myofibroblasts, newly-regenerated muscle fibers and necrosis all occur simultaneously. To determine if CCN2 is involved in the appearance of the foci, we studied their presence and characteristics in mdx mice (DMD mouse model) compared to mdx mice hemizygous for CCN2 (mdx-Ccn2+/-). We used laser capture microdissection followed by gene expression and immunofluorescence analyses to investigate fibrotic, inflammation and regeneration markers in damaged and non-damaged areas in mdx and mdx-Ccn2+/- skeletal muscle. Mdx mice foci express elevated mRNAs levels of transforming growth factor type beta, collagen, fibronectin, the myofribroblast marker α-SMA, and the myogenic transcription factor myogenin. Mdx foci also show elevated levels of MCP-1 and CD-68 positive cells, indicating that CCN2 could be inducing an inflammatory response. We found a significant reduction in the number of foci in mdx-Ccn2+/- mice muscle. Fibrotic and inflammatory markers were also decreased in these foci. We did not observe any difference in Pax7 mRNA levels, a marker for satellite cells, in mdx mice compared to mdx-Ccn2+/- mice. Thus, CCN2 appears to be involved in the fibrotic response as well as in the inflammatory response in the dystrophic skeletal muscle.

Production of Recombinant CCN2 Protein by Mammalian Cells

Recombinant CCN2 protein (rCCN2) is available from many companies; however, most of them are produced in E. coli. To investigate true functions of rCCN2, glycosylated protein with proper folding needs to be used. Therefore, we use rCCN2 produced by mammalian cells. Conditioned medium (CM) of HeLa cells stably transfected with a CCN2 expression vector are collected, and the recombinant CCN2 protein produced and secreted into the CM is purified by two-step chromatography, first with a heparin affinity column and then with an anti-CCN2 affinity column prepared with a monoclonal antibody against CCN2. The purified rCCN2 shows the bands of 36-38 kDa with sliver staining after gel electrophoresis, which can be confirmed by Western blotting. This chapter describes these methods in detail.

Extracellular Matrix Regulation of Stem Cell Behavior

Stem cells hold great promise in treating many diseases either through promoting endogenous cell repair or through direct cell transplants. In order to maximize their potential, understanding the fundamental signals and mechanisms that regulate their behavior is essential. The extracellular matrix (ECM) is one such component involved in mediating stem cell fate. Recent studies have made significant progress in understanding stem cell-ECM interactions. Technological developments have provided greater clarity in how cells may sense and respond to the ECM, in particular the physical properties of the matrix. This review summarizes recent developments, providing illustrative examples of the different modes with which the ECM controls both embryonic and adult stem cell behavior.

CCN: core regulatory proteins in the microenvironment that affect the metastasis of hepatocellular carcinoma?

Hepatocellular carcinoma (HCC) results from an underlying chronic liver inflammatory disease, such as chronic hepatitis B or C virus infections, and the general prognosis of patients with HCC still remains extremely dismal because of the high frequency of HCC metastases. Throughout the process of tumor metastasis, tumor cells constantly communicate with the surrounding microenvironment and improve their malignant phenotype. Therefore, there is a strong rationale for targeting the tumor microenvironment as primary treatment of HCC therapies. Recently, CCN family proteins have emerged as localized multitasking signal integrators in the inflammatory microenvironment. In this review, we summarize the current knowledge of CCN family proteins in inflammation and the tumor. We also propose that the CCN family proteins may play a central role in signaling the tumor microenvironment and regulating the metastasis of HCC.

Bioinformatic identification of connective tissue growth factor as an osteogenic protein within skeletal muscle

Aging is associated with increasing incidence of osteoporosis; a skeletal disorder characterized by compromised bone strength that may predispose patients to an increased risk of fracture. It is imperative to identify novel ways in which to attenuate such declines in the functional properties of bone. The purpose of this study was to identify, through in silico, in vitro, and in vivo approaches, a protein secreted from skeletal muscle that is putatively involved in bone formation. We performed a functional annotation bioinformatic analysis of human skeletal muscle‐derived secretomes (n = 319) using DAVID software. Cross‐referencing was conducted using OMIM, Unigene, UniProt, GEO, and CGAP databases. Signal peptides and transmembrane residues were analyzed using SignalP and TMHMM software. To further investigate functionality of the identified protein, L6 and C2C12 myotubes were grown for in vitro analysis. C2C12 myotubes were subjected to 16 h of glucose deprivation (GD) prior to analysis. In vivo experiments included analysis of 6‐week calorie restricted (CR) rat muscle samples. Bioinformatic analysis yielded 15 genes of interest. GEO dataset analysis identified BMP5, COL1A2, CTGF, MGP, MMP2, and SPARC as potential targets for further processing. Following TMHMM and SignalP processing, CTGF was chosen as a candidate gene. CTGF expression level was increased during L6 myoblast differentiation (P <0.01). C2C12 myotubes showed no change in response to GD. Rat soleus muscle samples exhibited an increase in CTGF expression (n = 16) in response to CR (35%) (P <0.05). CTGF was identified as a skeletal muscle expressed protein through bioinformatic analysis of skeletal muscle‐derived secretomes and in vitro/in vivo analysis. Future study is needed to determine the role of muscle‐derived CTGF in bone formation and remodeling processes.

In this study, we explore the method of bioinformatic analysis, coupled with in vitro and in vivo investigation, to identify a new skeletal muscle‐derived protein with osteogenic properties. CTGF is expressed in young, healthy skeletal muscle, and this expression is increased with calorie restriction. Muscular secretion of CTGF might play an osteogenic role in maintaining bone health.