Antisense inhibition of decorin expression in myoblasts decreases cell responsiveness to transforming growth factor beta and accelerates skeletal muscle differentiation

Integrating miRNA and full-length transcriptome profiling to elucidate the mechanism of muscle growth in Muscovy ducks reveals key roles for miR-301a-3p/ANKRD1

BACKGROUND

The popularity of Muscovy ducks is attributed not only to their conformation traits but also to their slightly higher content of breast and leg meat, as well as their stronger-tasting meat compared to that of typical domestic ducks. However, there is a lack of comprehensive systematic research on the development of breast muscle in Muscovy ducks. In addition, since the number of skeletal muscle myofibers is established during the embryonic period, this study conducted a full-length transcriptome sequencing and microRNA sequencing of the breast muscle. Muscovy ducks at four developmental stages, namely Embryonic Day 21 (E21), Embryonic Day 27 (E27), Hatching Day (D0), and Post-hatching Day 7 (D7), were used to isolate total RNA for analysis.

RESULTS

A total of 68,161 genes and 472 mature microRNAs were identified. In order to uncover deeper insights into the regulation of mRNA by miRNAs, we conducted an integration of the differentially expressed miRNAs (known as DEMs) with the differentially expressed genes (referred to as DEGs) across various developmental stages. This integration allowed us to make predictions regarding the interactions between miRNAs and mRNA. Through this analysis, we identified a total of 274 DEGs that may serve as potential targets for the 68 DEMs. In the predicted miRNA‒mRNA interaction networks, let-7b, miR-133a-3p, miR-301a-3p, and miR-338-3p were the hub miRNAs. In addition, multiple DEMs also showed predicted target relationships with the DEGs associated with skeletal system development. These identified DEGs and DEMs as well as their predicted interaction networks involved in the regulation of energy homeostasis and muscle development were most likely to play critical roles in facilitating the embryo-to-hatchling transition. A candidate miRNA, miR-301a-3p, exhibited increased expression during the differentiation of satellite cells and was downregulated in the breast muscle tissues of Muscovy ducks at E21 compared to E27. A dual-luciferase reporter assay suggested that the ANKRD1 gene, which encodes a transcription factor, is a direct target of miR-301a-3p.

CONCLUSIONS

miR-301a-3p suppressed the posttranscriptional activity of ANKRD1, which is an activator of satellite cell proliferation, as determined with gain- and loss-of-function experiments. miR-301a-3p functions as an inducer of myogenesis by targeting the ANKRD1 gene in Muscovy ducks. These results provide novel insights into the early developmental process of black Muscovy breast muscles and will improve understanding of the underlying molecular mechanisms.

Resistance Exercise-Induced Increases in Muscle Myostatin mRNA and Protein Expression Are Subsequently Decreased in Circulation in the Presence of Increased Levels of the Extracellular Matrix Stabilizing Protein Decorin

Resistance exercise (RE) activates cell signaling pathways associated with myostatin. Decorin is located in the extracellular matrix (ECM) and can block the inhibitory effect of myostatin. This study sought to determine the impact of low-load (LL) and high-load (HL) RE on myostatin mRNA and protein expression along with changes in muscle decorin and circulating follistatin. Ten resistance-trained men performed a LL (50% 1RM) and HL (80% 1RM) RE session using the angled leg press and leg extension with load and volume equated. Venous blood samples and muscle biopsies were obtained prior to and at 3h and 24h following each RE session. Muscle myostatin mRNA expression was increased at 24h post-exercise (p = 0.032) in LL and at 3h (p = 0.044) and 24h (p = 0.003) post-exercise in HL. Muscle decorin was increased at 24h post-exercise (p < 0.001) in LL and HL; however, muscle myostatin was increased at 24h post-exercise (p < 0.001) only in HL. For muscle Smad 2/3, no significant differences were observed (p > 0.05). Serum follistatin was increased and myostatin decreased at 24h post-exercise (p < 0.001) in LL and HL. Muscle myostatin gene and protein expression increased in response to HL RE. However, serum myostatin was decreased in the presence of increases in decorin in muscle and follistatin in circulation. Therefore, our data suggest a possible mechanism may exist where decorin within the ECM is able to bind to, and decrease, myostatin that might otherwise enter the circulation for activin IIB (ACTIIB) receptor binding and subsequent canonical signaling through Smad 2/3.

Decellularized Extracellular Matrix for Cell Biology

The extracellular matrix (ECM) is an architecture that supports the cells in our bodies and regulates various cell functions. The ECM is composed of many proteins and carbohydrates, and these molecules activate various intracellular signaling pathways orchestrated to decide cell fates. Therefore, it is not enough to study the role of single ECM molecules to understand the roles of the ECM in the regulation of cell functions; it is necessary to understand how the ECM, as an assembly of various molecules, regulates cell functions as a whole. For this purpose, in vitro ECM models mimicking native ECM are required. Here, a decellularization technique is presented to reconstitute native ECM in vitro. In this article, methods for preparing decellularized ECM (dECM) are described for use in tumor and stem cell biology. Additionally, a method for confirmation of decellularization and a dECM modification method are described. These dECM types will be useful for comprehensive studies of ECM roles. © 2021 Wiley Periodicals LLC. Basic Protocol 1: Preparation of in vitro extracellular matrix (ECM) models mimicking native ECM in different malignant tumor tissues Basic Protocol 2: Preparation of in vitro ECM models mimicking native ECM surrounding myoblasts differentiating into myotubes at each myogenic stage Support Protocol 1: Confirmation of myogenic stages by myogenic stages by myogenic gene expression analysis Basic Protocol 3: Confirmation of cell removal Basic Protocol 4: Reduction of chondroitin sulfate chains in cultured cell-derived decellularized ECM Support Protocol 2: Quantification of chondroitin sulfate chain amounts in the decellularized ECM.

Myogenic Potential of Extracellular Matrix Derived from Decellularized Bovine Pericardium

Skeletal muscles represent 40% of body mass and its native regenerative capacity can be permanently lost after a traumatic injury, congenital diseases, or tumor ablation. The absence of physiological regeneration can hinder muscle repair preventing normal muscle tissue functions. To date, tissue engineering (TE) represents one promising option for treating muscle injuries and wasting. In particular, hydrogels derived from the decellularized extracellular matrix (dECM) are widely investigated in tissue engineering applications thanks to their essential role in guiding muscle regeneration. In this work, the myogenic potential of dECM substrate, obtained from decellularized bovine pericardium (Tissuegraft Srl), was evaluated in vitro using C2C12 murine muscle cells. To assess myotubes formation, the width, length, and fusion indexes were measured during the differentiation time course. Additionally, the ability of dECM to support myogenesis was assessed by measuring the expression of specific myogenic markers: α-smooth muscle actin (α-sma), myogenin, and myosin heavy chain (MHC). The results obtained suggest that the dECM niche was able to support and enhance the myogenic potential of C2C12 cells in comparison of those grown on a plastic standard surface. Thus, the use of extracellular matrix proteins, as biomaterial supports, could represent a promising therapeutic strategy for skeletal muscle tissue engineering.

Role of Myokines in Myositis Pathogenesis and Their Potential to be New Therapeutic Targets in Idiopathic Inflammatory Myopathies

Idiopathic inflammatory myopathies (IIM) represent a heterogeneous group of autoimmune diseases whose treatment is often a challenge. Many patients, even after immunosuppressive therapy, do not respond to treatment, so new alternatives have been sought for this. Therefore, other signaling pathways that could contribute to the pathogenesis of myositis have been investigated, such as the expression of myokines in skeletal muscle in response to the inflammatory process. In this review, we will refer to these muscle cytokines that are overexpressed or downregulated in skeletal muscle in patients with various forms of IIM, thus being able to contribute to the maintenance of the autoimmune process. Some muscle cytokines, through their antagonistic action, may be a helpful contributor to the disease modulation, and thus, they could represent personalized treatment targets. Here, we consider the main myokines involved in the pathogenesis of myositis, expressing our view on the possibility of using them as potential therapeutic targets: interleukins IL-6, IL-15, and IL-18; chemokines CXCL10, CCL2, CCL3, CCL4, CCL5, and CCL20; myostatin; follistatin; decorin; osteonectin; and insulin-like 6. An interesting topic regarding the complex connection between myokines and noninflammatory pathways implied in IIM has also been briefly described, because it is an important scientific approach to the pathogenesis of IIM and can be a therapeutic alternative to be considered, especially for the patients who do not respond to immunosuppressive treatment.

TGF-β-driven downregulation of the Wnt/β-Catenin transcription factor TCF7L2/TCF4 in PDGFRα+ fibroblasts

Mesenchymal stromal/stem cells (MSCs) are multipotent progenitors essential for organogenesis, tissue homeostasis, regeneration, and scar formation. Tissue injury upregulates TGF-β signaling, which modulates myofibroblast fate, extracellular matrix remodeling, and fibrosis. However, the molecular determinants of MSCs differentiation and survival remain poorly understood. The canonical Wnt Tcf/Lef transcription factors regulate development and stemness, but the mechanisms by which injury-induced cues modulate their expression remain underexplored. Here, we studied the cell-specific gene expression of Tcf/Lef and, more specifically, we investigated whether damage-induced TGF-β impairs the expression and function of TCF7L2, using several models of MSCs, including skeletal muscle fibro-adipogenic progenitors. We show that Tcf/Lefs are differentially expressed and that TGF-β reduces the expression of TCF7L2 in MSCs but not in myoblasts. We also found that the ubiquitin-proteasome system regulates TCF7L2 proteostasis and participates in TGF-β-mediated TCF7L2 protein downregulation. Finally, we show that TGF-β requires HDACs activity to repress the expression of TCF7L2. Thus, our work found a novel interplay between TGF-β and Wnt canonical signaling cascades in PDGFRα+ fibroblasts and suggests that this mechanism could be targeted in tissue repair and regeneration.

Role of the LDL Receptor-Related Protein 1 in Regulating Protease Activity and Signaling Pathways in the Vasculature

Aortic aneurysms represent a significant clinical problem as they largely go undetected until a rupture occurs. Currently, an understanding of mechanisms leading to aneurysm formation is limited. Numerous studies clearly indicate that vascular smooth muscle cells play a major role in the development and response of the vasculature to hemodynamic changes and defects in these responses can lead to aneurysm formation. The LDL receptor-related protein 1 (LRP1) is major smooth muscle cell receptor that has the capacity to mediate the endocytosis of numerous ligands and to initiate and regulate signaling pathways. Genetic evidence in humans and mouse models reveal a critical role for LRP1 in maintaining the integrity of the vasculature. Understanding the mechanisms by which this is accomplished represents an important area of research, and likely involves LRP1's ability to regulate levels of proteases known to degrade the extracellular matrix as well as its ability to modulate signaling events.

The Muscle Stem Cell Niche in Health and Disease

The regulation of stem cells that maintain and regenerate postnatal tissues depends on extrinsic signals originating from their microenvironment, commonly referred to as the stem cell niche. Complex higher-order regulatory interrelationships with the tissue and factors in the systemic circulation are integrated and propagated to the stem cells through the niche. The stem cell niche in skeletal muscle tissue is both a paradigm for a structurally and functionally relatively static niche that maintains stem cell quiescence during tissue homeostasis, and a highly dynamic regenerative niche that is subject to extensive structural remodeling and a flux of different support cell populations. Conditions ranging from aging to chronically degenerative skeletal muscle diseases affect the composition of the niche and thereby impair the regenerative potential of muscle stem cells. A holistic and integrative understanding of the extrinsic mechanisms regulating muscle stem cells in health and disease in a broad systemic context will be imperative for the identification of regulatory hubs in the niche interactome that can be targeted to maintain, restore, or enhance the regenerative capacity of muscle tissue. Here, we review the microenvironmental regulation of muscle stem cells, summarize how niche dysfunction can contribute to disease, and discuss emerging therapeutic implications.

Effects of Dermatopontin gene silencing on apoptosis and proliferation of osteosarcoma MG‑63 cells

The present study aimed to investigate the effect of Dermatopontin (DPT) gene silencing on the apoptosis and proliferation of osteosarcoma MG‑63 cells. Three eukaryotic expression vectors of short hairpin (sh)RNA fragments targeting different loci of DPT were designed and transfected into an osteosarcoma cell line MG‑63. The cells were assigned to a blank, shRNA‑control, DPT‑shRNA‑a, DPT‑shRNA‑b or DPT‑shRNA‑c group. The shRNA with the highest silencing efficiency was screened using reverse transcription‑quantitative polymerase chain reaction and western blotting. The screened shRNA was transfected into MG‑63 cells. The proliferation, cell cycle and apoptosis of MG‑63 cells were measured using a Cell Counting Kit‑8 assay, flow cytometry and Annexin V‑fluorescein isothiocyanate assay. The recombinant plasmids containing DPT shRNA were successfully constructed. DPT gene silencing was able to significantly reduce the proliferation rate of MG‑63 cells (P<0.05). The proportion of cells in the G0/G1 phase and in the G2/M phase increased significantly (both P<0.05), while the proportion of cells in the S phase decreased (P<0.05). Furthermore, the cell apoptosis rate increased significantly (P<0.05). These results demonstrate that DPT gene silencing is able to reduce the proliferation of MG‑63 cells, slow down cell cycle progression and promote apoptosis, hence may become a novel target for the treatment of osteosarcoma.

The extracellular matrix regulates the effect of decorin and transforming growth factor beta-2 (TGF-β2) on myoblast migration

Muscular injuries that destroy the basal lamina result in poor functional recovery of skeletal muscle. This is due, in part, to the deposition of structural fibrotic proteins such as fibronectin and collagen by fibroblasts and other cells. Transforming growth factor-β (TGF-β) promotes fibrosis, whereas the proteoglycan decorin is known to act as an anti-fibrotic agent, in part via the binding and neutralization of TGF-β. We have previously established that decorin can alter the migratory response of skeletal muscle myoblasts to the extracellular matrix (ECM) factor collagen, but not fibronectin. We have also shown that TGF-β reduces myoblast migration. In the current study we demonstrate that decorin can dramatically alter the inhibitory role of TGF-β on human myoblast migration and go on to shown that the extracellular matrix can significantly modify this effect. Decorin and TGF-β2 in combination were observed to significantly increase the rate of human myoblast migration, despite the inhibitory effect of TGF-β2 on its own. Furthermore, in the presence of fibronectin, TGF-β2 and decorin no longer acted synergistically to promote migration; while in the presence of collagen I, TGF-β2 failed to inhibit migration. These studies show, for the first time, that decorin can alter the bioactivity of TGF-β2 on human myoblast migration and emphasize the crucial regulatory role of the extracellular matrix in determining the response of skeletal muscle myoblasts to migratory cues.

Agonists and Antagonists of TGF-β Family Ligands

The discovery of the transforming growth factor β (TGF-β) family ligands and the realization that their bioactivities need to be tightly controlled temporally and spatially led to intensive research that has identified a multitude of extracellular modulators of TGF-β family ligands, uncovered their functions in developmental and pathophysiological processes, defined the mechanisms of their activities, and explored potential modulator-based therapeutic applications in treating human diseases. These studies revealed a diverse repertoire of extracellular and membrane-associated molecules that are capable of modulating TGF-β family signals via control of ligand availability, processing, ligand-receptor interaction, and receptor activation. These molecules include not only soluble ligand-binding proteins that were conventionally considered as agonists and antagonists of TGF-β family of growth factors, but also extracellular matrix (ECM) proteins and proteoglycans that can serve as "sink" and control storage and release of both the TGF-β family ligands and their regulators. This extensive network of soluble and ECM modulators helps to ensure dynamic and cell-specific control of TGF-β family signals. This article reviews our knowledge of extracellular modulation of TGF-β growth factors by diverse proteins and their molecular mechanisms to regulate TGF-β family signaling.

Spanish Consensus Statement: The Treatment of Muscle Tears in Sport

On the 21st of March, 2015, experts met at Clínica CEMTRO in Madrid, Spain, under the patronage of The Spanish Society for Sports Traumatology (SETRADE), The Spanish Federation of Sports Medicine (FEMEDE), The Spanish Association of Medical Services for Football Clubs (AEMEF), and The Spanish Association of Medical Services for Basketball Clubs (AEMB) with the aim of establishing a round table that would allow specialists to consider the most appropriate current general actions to be taken when treating muscle tears in sport, based on proven scientific data described in the medical literature. Each expert received a questionnaire prior to the aforementioned meeting comprising a set of questions concerning therapeutic indications generally applied in the different stages present during muscle repair. The present Consensus Document is the result of the answers to the questionnaire and resulting discussion and consensus over which are the best current indications in the treatment of muscle tears in sport. Avoiding immobilization, not taking nonsteroidal anti-inflammatory drugs (NSAIDs) randomly, fostering early mobilization, increasing vascularization of injured, site and regulating inflammatory mechanisms—without inhibiting these from the early stages of the recovery period—all stood out as main points of the Consensus Document. Additionally, there is controversy concerning cell stimulation techniques and the use of growth factors or cell inhibitors. The decision concerning discharge was unanimous, as was the criteria considered when it came to performing sport techniques without pain.

Restoration of mesenchymal retinal pigmented epithelial cells by TGFβ pathway inhibitors: implications for age-related macular degeneration

BACKGROUND

Age-related macular degeneration (AMD) is a leading cause of blindness. Most vision loss occurs following the transition from a disease of deposit formation and inflammation to a disease of neovascular fibrosis and/or cell death. Here, we investigate how repeated wound stimulus leads to seminal changes in gene expression and the onset of a perpetual state of stimulus-independent wound response in retinal pigmented epithelial (RPE) cells, a cell-type central to the etiology of AMD.

METHODS

Transcriptome wide expression profiles of human fetal RPE cell cultures as a function of passage and time post-plating were determined using Agilent 44 K whole genome microarrays and RNA-Seq. Using a systems level analysis, differentially expressed genes and pathways of interest were identified and their role in the establishment of a persistent mesenchymal state was assessed using pharmacological-based experiments.

RESULTS

Using a human fetal RPE cell culture model that considers monolayer disruption and subconfluent culture as a proxy for wound stimulus, we show that prolonged wound stimulus leads to terminal acquisition of a mesenchymal phenotype post-confluence and altered expression of more than 40 % of the transcriptome. In contrast, at subconfluence fewer than 5 % of expressed transcripts have two-fold or greater expression differences after repeated passage. Protein-protein and pathway interaction analysis of the genes with passage-dependent expression levels in subconfluent cultures reveals a 158-node interactome comprised of two interconnected modules with functions pertaining to wound response and cell division. Among the wound response genes are the TGFβ pathway activators: TGFB1, TGFB2, INHBA, INHBB, GDF6, CTGF, and THBS1. Significantly, inhibition of TGFBR1/ACVR1B mediated signaling using receptor kinase inhibitors both forestalls and largely reverses the passage-dependent loss of epithelial potential; thus extending the effective lifespan by at least four passages. Moreover, a disproportionate number of RPE wound response genes have altered expression in neovascular and geographic AMD, including key members of the TGFβ pathway.

CONCLUSIONS

In RPE cells the switch to a persistent mesenchymal state following prolonged wound stimulus is driven by lasting activation of the TGFβ pathway. Targeted inhibition of TGFβ signaling may be an effective approach towards retarding AMD progression and producing RPE cells in quantity for research and cell-based therapies.

Role of extracellular matrix in development of skeletal muscle and postmortem aging of meat

The integrity of skeletal muscle is maintained by the intramuscular connective tissues (IMCTs) that are composed of extracellular matrix (ECM) molecules such as collagens, proteoglycans, and glycoproteins. The ECM plays an important role not only in providing biomechanical strength of the IMCT, but also in regulating muscle cell behavior. Some ECM molecules, such as decorin and laminin, modulate the activity of myostatin that regulates skeletal muscle mass. Furthermore, it has been shown that decorin activates Akt downstream of insulin-like growth factor-I receptor (IGF-IR) and enhances the differentiation of myogenic cells, suggesting that decorin acts as a signaling molecule to myogenic cells. With animal growth, the structural integrity of IMCT increases; collagen fibrils within the endomysium associate more closely with each other, and the collagen fibers in the perimysium become increasingly thick and their wavy pattern grows more regular. These changes increase the mechanical strength of IMCT, contributing to the toughening of meat. However, in highly marbled beef cattle like Wagyu, intramuscular fat deposits mainly in the perimysium between muscle fiber bundles during the fattening period. The development of adipose tissues appears to disorganize the structure of IMCT and contributes to the tenderness of Wagyu beef. The IMCT was considered to be rather immutable compared to myofibrils during postmortem aging of meat. However, several studies have shown that collagen networks in the IMCT are disintegrated and proteoglycan components are degraded during postmortem aging. These changes in ECM appear to reduce the mechanical strength of IMCT and contribute to the tenderness of uncooked meat or cooked meat at low temperature. Thus, the ECM plays a multifunctional role in skeletal muscle development and postmortem aging of meat.

Transforming growth factor type beta 1 increases the expression of angiotensin II receptor type 2 by a SMAD- and p38 MAPK-dependent mechanism in skeletal muscle

Excessive deposition of extracellular matrix (ECM) proteins, a condition known as fibrosis, is a hallmark of Duchenne muscular dystrophy. Among the factors that trigger muscle fibrosis are transforming growth factor beta (TGF-β) and angiotensin II (Ang-II). Ang-II belongs to the renin-angiotensin system, and its biological effects are exerted by Ang-II receptors type 1 and type 2 (AT-1 and AT-2, respectively). This study aims to determine the effect of TGF-β1 on the expression of AT-1 and AT-2 receptor in skeletal muscle. C2 C12 myoblasts exposed to TGF-β1 showed a dose-dependent increase in AT-2 expression but with no effect on AT-1 levels. Injection of TGF-β1 in the skeletal muscle of mice increased the levels of AT-2 and ECM protein but unchanged AT-1 levels. We also detected higher expression levels of AT-2 receptor in dystrophic skeletal muscle of mdx mice than in normal mice. The induction of AT-2 was mediated by the canonical TGF-β pathway because under the inhibitory conditions of the kinase activity of TGFβ receptor I or the knockdown of Smad2/3 levels, TGF-β-induced AT-2 receptor increase was strongly inhibited. Furthermore, we demonstrated that p38MAPK activity in response to TGF-β is also required for AT-2 increase as evaluated by a p38MAPK inhibitor. Our results show that the levels of AT-2 but not AT-1 receptor are modulated by the pro-fibrotic factor TGF-β1 in myoblasts and mouse skeletal muscle. This finding suggests that AT-2 might be involved in the physiopathology of fibrosis in dystrophic skeletal muscle.

Role of proteoglycans in the regulation of the skeletal muscle fibrotic response

Myogenesis consists of a highly organized and regulated sequence of cellular processes aimed at forming or repairing muscle tissue. Several processes occur during myogenesis, including cell proliferation, migration, and differentiation. Cytokines, proteinases, cell adhesion molecules and growth factors are involved, either activating or inhibiting these events, and are modulated by a group of molecules called proteoglycans (PGs), which play critical roles in skeletal muscle physiology. Particularly interesting are some of the factors responsible for the fibrotic response associated with skeletal muscular dystrophies. Transforming growth factor-β and connective tissue growth factor have gained great attention as factors participating in the fibrotic response in skeletal muscle. This review is focused on the advances achieved in understanding the roles of proteoglycans as modulators of profibrotic growth factors in fibrosis associated with diseases such as skeletal muscle dystrophies.

Role of skeletal muscle proteoglycans during myogenesis

Skeletal muscle formation during development and the adult mammal consists of a highly organised and regulated the sequence of cellular processes intending to form or repair muscle tissue. This sequence includes, cell proliferation, migration, and differentiation. Proteoglycans (PGs), macromolecules formed by a core protein and glycosaminoglycan chains (GAGs) present a great diversity of functions explained by their capacity to interact with different ligands and receptors forming part of their signalling complex and/or protecting them from proteolytic cleavage. Particularly attractive is the function of the different types of PGs present at the neuromuscular junction (NMJ). This review is focussed on the advances reached to understand the role of PGs during myogenesis and skeletal muscular dystrophies.

Decorin activates Akt downstream of IGF-IR and promotes myoblast differentiation

Decorin, a small leucine-rich proteoglycan, plays an important role in cellular activities through modification of growth factors. It also acts as a signaling molecule to non-muscle cells through epidermal growth factor receptor or insulin-like growth factor I receptor (IGF-IR). However, it is unclear if decorin acts as a signaling molecule to myogenic cells. In this study, we investigated the effect of decorin on the differentiation of myoblasts and the signaling via IGF-IR to myogenic cells. C2C12 myoblasts cultured in media containing decorin for 72 h showed more extensive formation of multinucleated myotubes than control cells cultured in the same media without decorin. The protein expressions of myogenin and myosin heavy chian were higher in decorn-treated cells than in control cells. These results suggest that decorin enhances the differentiation of myoblasts. Western blot analysis and immunocytochemistry showed that IGF-IR was expressed in myoblasts and myotubes. Furthermore, Akt, which is downstream of IGF-IR, was more phosphorylated in myoblasts cultured in media containing decorin than those in media without decorin. These results suggest that decorin activates Akt downstream of IGF-IR and enhances the differentiation of myogenic cells.

The biology of small leucine-rich proteoglycans in bone pathophysiology

The class of small leucine-rich proteoglycans (SLRPs) is a family of homologous proteoglycans harboring relatively small (36-42 kDa) protein cores compared with the larger cartilage and mesenchymal proteoglycans. SLRPs have been localized to most skeletal regions, with specific roles designated during all phases of bone formation, including periods relating to cell proliferation, organic matrix deposition, remodeling, and mineral deposition. This is mediated by key signaling pathways regulating the osteogenic program, including the activities of TGF-β, bone morphogenetic protein, Wnt, and NF-κB, which influence both the number of available osteogenic precursors and their subsequent development, differentiation, and function. On the other hand, SLRP depletion is correlated with degenerative diseases such as osteoporosis and ectopic bone formation. This minireview will focus on the SLRP roles in bone physiology and pathology.

Wild type N-ras displays anti-malignant properties, in part by downregulating decorin

Previously, we have shown that wild type N-ras (wt N-ras) harbors an anti-malignant effect against mutated Ras and in tumors without Ras mutations. To investigate the molecular bases of this anti-malignant activity, we have studied the potency of this anti-malignant effect in a model system against SV40 large T antigen (SV40T). We show that wild-type N-ras (wt N-ras) counteracts the effects of SV40T in NIH3T3 cells as seen by a decrease in proliferation, anchorage independence and changes in migration. We also show that wt N-ras elicits the same anti-malignant effects in some human tumor cell lines (HT1080 and MDA-MB-231). Through mRNA and microRNA (miRNAs) expression profiling we have identified genes (decorin) and miRNAs (mir-29A, let-7b) modulated by wt N-ras potentially responsible for the anti-malignant effect. Wt N-ras appears to mediate its anti-malignant effect by downregulating some of the targets of the TGFβ pathway and decorin, which are able to reverse the inhibition of migration induced by wt N-ras. Our experiments show that the molecules that mediate the anti-malignant effect by wt N-ras appear to be different from those modulated by transforming N-ras. The components of the pathways modulated by wt N-ras mediating its anti-malignant effects are potential targets for therapeutic intervention in cancer.

Review: The skeletal muscle extracellular matrix: Possible roles in the regulation of muscle development and growth

Velleman, S. G., Shin, J., Li, X. and Song, Y. 2012. Review: The skeletal muscle extracellular matrix: Possible roles in the regulation of muscle development and growth. Can. J. Anim. Sci. 92: 1–10. Skeletal muscle fibers are surrounded by an extrinsic extracellular matrix environment. The extracellular matrix is composed of collagens, proteoglycans, glycoproteins, growth factors, and cytokines. How the extracellular matrix influences skeletal muscle development and growth is an area that is not completely understood at this time. Studies on myogenesis have largely been directed toward the cellular components and overlooked that muscle cells secrete a complex extracellular matrix network. The extracellular matrix modulates muscle development by acting as a substrate for muscle cell migration, growth factor regulation, signal transduction of information from the extracellular matrix to the intrinsic cellular environment, and provides a cellular structural architecture framework necessary for tissue function. This paper reviews extracellular matrix regulation of muscle growth with a focus on secreted proteoglycans, cell surface proteoglycans, growth factors and cytokines, and the dynamic nature of the skeletal muscle extracellular matrix, because of its impact on the regulation of muscle cell proliferation and differentiation during myogenesis.

TGF-β signaling in Duchenne muscular dystrophy

The TGF-β protein family consists of secreted multifunctional cytokines that control diverse processes, such as cell growth and differentiation. Aberrant expression and downstream signaling of these growth factors have been associated with multiple diseases, including muscle wasting disorders, such as Duchenne muscular dystrophy. In this review we discuss recent advances in understanding the role of TGF-β family members during normal skeletal muscle biology/regeneration and their role in muscle pathology, with a special focus on Duchenne muscular dystrophy. In addition, we will highlight progress in the development of potential therapeutics for Duchenne muscular dystrophy based on intervention of TGF-β signaling.

The internal region leucine-rich repeat 6 of decorin interacts with low density lipoprotein receptor-related protein-1, modulates transforming growth factor (TGF)-β-dependent signaling, and inhibits TGF-β-dependent fibrotic response in skeletal muscles

Decorin is a small proteoglycan, composed of 12 leucine-rich repeats (LRRs) that modulates the activity of transforming growth factor type β (TGF-β) and other growth factors, and thereby influences proliferation and differentiation in a wide array of physiological and pathological processes, such as fibrosis, in several tissues and organs. Previously we described two novel modulators of the TGF-β-dependent signaling pathway: LDL receptor-related protein (LRP-1) and decorin. Here we have determined the regions in decorin that are responsible for interaction with LRP-1 and are involved in TGF-β-dependent binding and signaling. Specifically, we used decorin deletion mutants, as well as peptides derived from internal LRR regions, to determine the LRRs responsible for these decorin functions. Our results indicate that LRR6 and LRR5 participate in the interaction with LRP-1 and TGF-β as well as in its dependent signaling. Furthermore, the internal region (LRR6i), composed of 11 amino acids, is responsible for decorin binding to LRP-1 and subsequent TGF-β-dependent signaling. Furthermore, using an in vivo approach, we also demonstrate that the LRR6 region of decorin can inhibit TGF-β mediated action in response to skeletal muscle injury.

Extracellular matrix modulates insulin production during differentiation of AR42J cells: functional role of Pax6 transcription factor

Extracellular matrix (ECM) modulates differentiation of pancreatic β-cells during development. However, the mechanism by which ECM proteins modulate differentiation is not totally clear. We investigated the effect of ECM proteins on differentiation β-cells in vitro. We investigated the effect of basement membrane ECM on differentiation of AR42J cells and rat ductal cells. First, we examined the effect of reconstituted basement membrane, Matrigel on differentiation of AR42J cells induced by activin and betacellulin. Matrigel augmented insulin production and increased the expression of GLUT2, SUR1, and glucokinase. Among various transcription factors investigated, Matrigel markedly upregulated the expression of Pax6. When Pax6 was overexpressed in cells treated with activin and betacellulin, the expression of insulin was upregulated. Conversely, knockdown of Pax6 significantly reduced the insulin expression in cells cultured on Matrigel. The effects of Matrigel on insulin-production and induction of Pax6 were reproduced partially by laminin-1, a major component of Matrigel, and inhibited by anti-integrin-β1 antibody. Matrigel also enhanced the activation of p38 mitogen-activated kinase induced by activin and betacellulin, which was inhibited by anti-β1 antibody. Finally, the effect of Matrigel on differentiation was reproduced in rat cultured ductal cells, and Matrigel also increased the expression of Pax6. These results indicate that basement membrane ECM augments differentiation of pancreatic progenitor cells to insulin-secreting cells by upregulating the expression of Pax6. .

Decorin interacts with connective tissue growth factor (CTGF)/CCN2 by LRR12 inhibiting its biological activity

Fibrotic disorders are the end point of many chronic diseases in different tissues, where an accumulation of the extracellular matrix occurs, mainly because of the action of the connective tissue growth factor (CTGF/CCN2). Little is known about how this growth factor activity is regulated. We found that decorin null myoblasts are more sensitive to CTGF than wild type myoblasts, as evaluated by the accumulation of fibronectin or collagen III. Decorin added exogenously negatively regulated CTGF pro-fibrotic activity and the induction of actin stress fibers. Using co-immunoprecipitation and in vitro interaction assays, decorin and CTGF were shown to interact in a saturable manner with a K(d) of 4.4 nM. This interaction requires the core protein of decorin. Experiments using the deletion mutant decorin indicated that the leucine-rich repeats (LRR) 10-12 are important for the interaction with CTGF and the negative regulation of the cytokine activity, moreover, a peptide derived from the LRR12 was able to inhibit CTGF-decorin complex formation and CTGF activity. Finally, we showed that CTGF specifically induced the synthesis of decorin, suggesting a mechanism of autoregulation. These results suggest that decorin interacts with CTGF and regulates its biological activity.

In vitro expression profiling of myostatin, follistatin, decorin and muscle-specific transcription factors in adult caprine contractile myotubes

Skeletal muscle is one of the several adult postmitotic tissues that retain the capacity to regenerate, which relies on a population of quiescent precursors, termed satellite cells. Proliferation and differentiation of myoblasts to form mature myotubes in vitro has been a valuable tool in the characterization of the cellular events during myogenesis, which is a multistep process starting with progenitor cell proliferation, followed by their exit from the cell cycle, differentiation, alignment, and fusion to form multinucleated myotubes. A typical feature during muscle differentiation is the variation in expression of various genes along with myogenic factors. In this experiment, mRNA level of myostatin, follistatin, decorin and three muscle-specific transcription factors in adult caprine contractile myotubes have been studied through quantitative real time PCR. We observed that the expression level of myostatin, decorin, Myf5 and myogenin transcripts were significantly higher in contractile myotubes compared to myoblast monolayer (P < 0.05), and follistatin level was similar in both types of cells, whereas MyoD transcript level was significantly high in monolayer culture which might be due heterogeneity of myoblast population. It is concluded that the information generated would provide the base line information as well as monitoring markers to undertake experiments aimed at modulating muscle growth.

A maternally inherited chromosome 18q22.1 deletion in a male with late-presenting diaphragmatic hernia and microphthalmia-evaluation of DSEL as a candidate gene for the diaphragmatic defect

Using an Affymetrix GeneChip(R) Human Mapping 100K Set to study a patient with a late-presenting, right-sided diaphragmatic hernia and microphthalmia, we found a maternally inherited deletion that was 2.7 Mb in size at chromosome 18q22.1. Mapping of this deletion using fluorescence in situ hybridization revealed three deleted genes-CDH19, DSEL, and TXNDC10, and one gene that contained the deletion breakpoint, CCDC102B. We selected DSEL for further study in 125 patients with diaphragmatic hernias, as it is involved in the synthesis of decorin, a protein that is required for normal collagen formation and that is upregulated during myogenesis. We found p.Met14Ile in an unrelated patient with a late-presenting, anterior diaphragmatic hernia. In the murine diaphragm, Dsel was only weakly expressed at the time of diaphragm closure and its expression in C2C12 myoblast cells did not change significantly during myoblast differentiation, thus reducing the likelihood that the gene is involved in myogenesis of the diaphragm. Although it is possible that the 18q22.1 deletion and haploinsufficiency for DSEL contributed to the diaphragmatic defect in the patient, a definite role for DSEL and decorin in the formation of the collagen-containing, central tendon of the diaphragm has not yet been established.

Changes in satellite cell proliferation and differentiation during turkey muscle development

Posthatch muscle growth is determined by the activation, differentiation, and fusion of satellite cells. Satellite cells composing an individual muscle are heterogeneous, which will differentially affect muscle growth. The proliferation and differentiation of turkey primary pectoralis major muscle cells were investigated in vitro at 1 d of age and at 4, 8, 16, 26, 35, 45, and 54 wk of age. The turkey was selected for these studies because turkey skeletal muscle fibroblasts do not grow in primary muscle cell cultures. Results from the proliferation analysis showed a decrease in proliferation by 8 wk of age. Differentiation into myotubes was significantly decreased by 4 wk of age and myotube diameter was decreased. The changes in muscle weight relative to total BW were measured for the anterior latissimus dorsi, biceps brachii, pectoralis major, sartorius, biceps femoris, and gastrocnemius muscles to compare the relative growth of different muscles. The age at which the muscles reached their maximum relative weight was muscle-dependent, with the biceps brachii plateauing the earliest at 4 wk and the sartorius the latest at 45 wk of age. These data suggested that changes in myogenic cells begin to occur early in muscle development and the activity of the satellite cells during these initial stages of posthatch growth is critical in overall muscle mass accumulation.

TGF-beta receptors, in a Smad-independent manner, are required for terminal skeletal muscle differentiation

Skeletal muscle differentiation is strongly inhibited by transforming growth factor type beta (TGF-beta), although muscle formation as well as regeneration normally occurs in an environment rich in this growth factor. In this study, we evaluated the role of intracellular regulatory Smads proteins as well as TGF-beta-receptors (TGF-beta-Rs) during skeletal muscle differentiation. We found a decrease of TGF-beta signaling during differentiation. This phenomenon is explained by a decline in the levels of the regulatory proteins Smad-2, -3, and -4, a decrease in the phosphorylation of Smad-2 and lost of nuclear translocation of Smad-3 and -4 in response to TGF-beta. No change in the levels and inhibitory function of Smad-7 was observed. In contrast, we found that TGF-beta-R type I (TGF-beta-RI) and type II (TGF-beta-RII) increased on the cell surface during skeletal muscle differentiation. To analyze the direct role of the serine/threonine kinase activities of TGF-beta-Rs, we used the specific inhibitor SB 431542 and the dominant-negative form of TGF-beta-RII lacking the cytoplasmic domain. The TGF-beta-Rs were important for successful muscle formation, determined by the induction of myogenin, creatine kinase activity, and myosin. Silencing of Smad-2/3 expression by specific siRNA treatments accelerated myogenin, myosin expression, and myotube formation; although when SB 431542 was present inhibition in myosin induction and myotube formation was observed, suggesting that these last steps of skeletal muscle differentiation require active TGF-beta-Rs. These results suggest that both down-regulation of Smad regulatory proteins and cell signaling through the TGF-beta receptors independent of Smad proteins are essential for skeletal muscle differentiation.

Novel SNPs in the caprine stearoyl-CoA desaturase (SCD) and decorin (DCN) genes that are associated with growth traits in Chinese goat breeds

Stearoyl-CoA desaturase (SCD) is an iron-containing enzyme involving in the biosynthesis of monounsaturated fatty acids (MUFA) in mammary gland and adipose tissue, while decorin (DCN) consists of a protein core and a single dermatan or chondroitin sulfate glycosaminoglycan chain, contributing multifunctionally to matrix assembly, modulation of the activity of growth factors and cell migration and proliferation. However, few studies have focused on the genetic variability of them in goat. Herein, five Chinese goat breeds (1229 animals) were analyzed. Based on DNA pooling and PCR-RFLP, three nucleotide substitutions, one of which caused a amino acid substitution, were detected in SCD gene and three haploids (A, B, C) were constructed. According to SSCP analysis and DNA sequencing methods, a 2-bp deletion and two other SNPs were found existing in another analyzed gene DCN, and three haploids (X, Y, Z) were built. Associations between the genotypes and the growth traits (body length, body height, chest circumference, cannon circumference) were also analyzed. For SCD gene, genotype CC individuals had significant greater body height in Guanzhong and body length in both Guanzhong and Xinong saanen than genotype BC individuals (P < 0.05). For DCN gene, individuals with genotype XX was obviously higher than that with genotype XY (P < 0.05). These results indicated that genotype CC of SCD gene and genotype XX of DCN gene could be used for the breeding of new breeds of goat in China.

A novel mechanism of sequestering fibroblast growth factor 2 by glypican in lipid rafts, allowing skeletal muscle differentiation

Heparan sulfate proteoglycans (HSPGs) are critical modulators of growth factor activities. Skeletal muscle differentiation is strongly inhibited by fibroblast growth factor 2 (FGF-2). We have shown that HSPGs present at the plasma membrane are expressed in myoblasts and are downregulated during muscle differentiation. An exception is glypican-1, which is present throughout the myogenic process. Myoblasts that do not express glypican-1 exhibit defective differentiation, with an increase in the receptor binding of FGF-2, concomitant with increased signaling. Glypican-1-deficient myoblasts show decreased expression of myogenin, the master gene that controls myogenesis, myosin, and the myoblast fusion index. Reversion of these defects was induced by expression of rat glypican-1. Glypican-1 is the only HSPG localized in lipid raft domains in myoblasts, resulting in the sequestration of FGF-2 away from FGF-2 receptors (FGFRs) located in nonraft domains. A chimeric glypican-1, containing syndecan-1 transmembrane and cytoplasmic domains, is located in nonraft domains interacting with FGFR-IV- and enhanced FGF-2-dependent signaling. Thus, glypican-1 acts as a positive regulator of muscle differentiation by sequestering FGF-2 in lipid rafts and preventing its binding and dependent signaling.

Development of stepwise osteogenesis-mimicking matrices for the regulation of mesenchymal stem cell functions

An extracellular microenvironment, including an extracellular matrix (ECM), is an important factor in regulating stem cell differentiation. During tissue development, the ECM is dynamically remodeled to regulate stem cell functions. Here, we developed matrices mimicking ECM remodeling during the osteogenesis of mesenchymal stem cells (MSCs). The matrices were prepared from cultured MSCs controlled at different stages of osteogenesis and referred to as "stepwise osteogenesis-mimicking matrices." The matrices supported the adhesion and proliferation of MSCs and showed different effects on the osteogenesis of MSCs. On the matrices mimicking the early stage of osteogenesis (early stage matrices), the osteogenesis occurred more rapidly than did that on the matrices mimicking undifferentiated stem cells (stem cell matrices) and the late stage of osteogenesis (late stage matrices). RUNX2 was similarly expressed when MSCs were cultured on both the early stage and late stage matrices but decreased on the stem cell matrices. PPARG expression in the MSCs cultured on the late stage matrices was higher than for those cultured on the stem cell and early stage matrices. This increase of PPARG expression was caused by the suppression of the amount of beta-catenin and downstream signal transduction. These results demonstrate that the osteogenesis-mimicking matrices had different effects on the osteogenesis of MSCs, and the early stage matrices provided a favorable microenvironment for the osteogenesis.

Extrinsic regulation of domestic animal-derived myogenic satellite cells II

The existence of myogenic satellite cells was reported some 47 years ago, and, since that time, satellite cell research has flourished. So much new information is generated (daily) on these cells that it can be difficult for individuals to keep abreast of important issues related to their activation and proliferation, the modulation of the activity of other cell types, the differentiation of the cells to facilitate normal skeletal muscle growth and development, or to the repair of damaged myofibers. The intent of this review is to summarize new information about the extrinsic regulation of myogenic satellite cells and to provide specific mechanisms involved in altering satellite cell physiology. Where possible, examples from agriculturally important animals are used for illustrative purposes.

Effect of transforming growth factor-beta1 on decorin expression and muscle morphology during chicken embryonic and posthatch growth and development

During skeletal muscle development, transforming growth factor-beta1 (TGF-beta1) is a potent inhibitor of muscle cell proliferation and differentiation, as well as a regulator of extracellular matrix (ECM) production. Decorin, a member of the small leucine-rich ECM proteoglycans, binds to TGF-beta1 and modulates TGF-beta1-dependent cell growth stimulation or inhibition. The expression of decorin can be regulated by TGF-beta1 during muscle proliferation and differentiation. How TGF-beta1 affects decorin and muscle growth, however, has not been well documented in vivo. The present study investigated the effect of TGF-beta1 on decorin expression and intracellular connective tissue development during skeletal muscle growth. Exogenous TGF-beta1 significantly decreased the number of myofibers in a given area at both 1 d and 6 wk posthatch. The TGF-beta1-treated muscle had a significant decrease in decorin mRNA expression at embryonic day (ED) 10, whereas protein amounts decreased at 17 ED and 1 d posthatch compared to the control muscle. Decorin was localized in both the endomysium and perimysium in the control pectoralis major muscle. Transforming growth factor-beta1 reduced decorin in both the endomysium and perimysium from 17 ED to 6 wk posthatch. Compared to the control muscle, the perimysium space in the pectoralis major muscle was dramatically decreased by TGF-beta1 during embryonic development through posthatch growth. Because decorin regulates collagen fibrillogenesis, a major component of the ECM, the reduction of decorin by TGF-beta1 treatment may cause the irregular formation of collagen fibrils, leading to the decrease in endomysium and perimysium space. The results from the current study suggest that the effect of TGF-beta1 on decorin expression and localization was likely associated with altered development of the perimysium and the regulation of muscle fiber development.

Lysyl oxidase binds transforming growth factor-beta and regulates its signaling via amine oxidase activity

Lysyl oxidase (LOX), an amine oxidase critical for the initiation of collagen and elastin cross-linking, has recently been shown to regulate cellular activities possibly by modulating the functions of growth factors. In this study, we investigated the interaction between LOX and transforming growth factor-beta1 (TGF-beta1), a potent growth factor abundant in bone, the effect of LOX on TGF-beta1 signaling, and its potential mechanism. The specific binding between mature LOX and mature TGF-beta1 was demonstrated by immunoprecipitation and glutathione S-transferase pulldown assay in vitro. Both proteins were colocalized in the extracellular matrix in an osteoblastic cell culture system, and the binding complex was identified in the mineral-associated fraction of bone matrix. Furthermore, LOX suppressed TGF-beta1-induced Smad3 phosphorylation likely through its amine oxidase activity. The data indicate that LOX binds to mature TGF-beta1 and enzymatically regulates its signaling in bone and thus may play an important role in bone maintenance and remodeling.

Extracellular matrix proteoglycan decorin-mediated myogenic satellite cell responsiveness to transforming growth factor-beta1 during cell proliferation and differentiation Decorin and transforming growth factor-beta1 in satellite cells

Transforming growth factor-beta1 (TGF-beta1) is a potent inhibitor of muscle cell proliferation and differentiation. Decorin, a small proteoglycan in the extracellular matrix, binds to TGF-beta1 and modulates the activity of TGF-beta1 during muscle cell growth and development. However, its interaction with TGF-beta1 and involvement in myogenesis is not well characterized. In the present study, chicken myogenic satellite cells, myogenic precursors for muscle growth and repair, were isolated from the pectoralis major muscle and used to investigate the biological function of TGF-beta1 and decorin during myogenesis. The over-expression of decorin in satellite cells significantly increased cell proliferation, compared to the control cells. Consistent with this result, reducing decorin expression decreased cell proliferation, which suggests a decorin-mediated mechanism is involved in the regulation of myogenic satellite cell proliferation. Satellite cells over-expressing decorin were less sensitive to TGF-beta1 during proliferation, which indicates that decorin may sequester TGF-beta1 leading to increased proliferation. During satellite cell differentiation, the over-expression of decorin induced differentiation by increasing the muscle specific creatine kinase concentration. However, the addition of TGF-beta1 diminished decorin-mediated cell responsiveness to TGF-beta1 during differentiation. Taken together, these results suggest that decorin induces myogenic satellite cell proliferation and differentiation by regulating cellular responsiveness to TGF-beta1. An alternative TGF-beta1-independent pathway may be involved in the regulation of satellite cells by decorin.

Decorin enhances the proliferation and differentiation of myogenic cells through suppressing myostatin activity

Decorin, a small leucine-rich proteoglycan, plays an important role in the regulation of cell growth. Our recent study has shown that immobilized decorin in the collagen matrix sequesters myostatin into the extracellular matrix and prevents its inhibitory action to myoblast proliferation in vitro. However, it still remains unclear whether free decorin could affect the proliferation and differentiation of myogenic cells by regulating myostatin activity. In the present study, we generated stable clonal C2C12 myoblasts that were over-expressing decorin, and showed that decorin over-expressing cells had an increased rate of proliferation as compared to control cells. Decorin over-expressing cells formed multi-giant hypertrophic myotubes with an elongated morphology and larger size as compared to control cells, although the initiation of differentiation in decorin over-expressing cells was somewhat delayed as compared to control cells. Western blot analysis demonstrated that MyoD expression in decorin over-expressing cells was lower than that in control cells until 12 h after induction to differentiate. At 48-h differentiation, the expressions of MyoD, p21 and myogenin were dramatically increased in cells that over-expressed decorin. Furthermore, we revealed that over-expression of decorin suppressed the activity of myostatin endogenously synthesized in C2C12 myoblasts and attenuated the signaling of exogenous myostatin. Consistent with these results, knock-down of decorin impairs C2C12 myoblast growth by increasing the sensitivity to exogenous myostatin. These results clearly show that decorin enhances the proliferation and differentiation of C2C12 myoblasts through suppressing myostatin activity.

Constitutively activated dystrophic muscle fibroblasts show a paradoxical response to TGF-beta and CTGF/CCN2

Transforming growth factor beta (TGF-beta) and connective tissue growth factor (CTGF) have been described to induce the production of extracellular matrix (ECM) proteins and have been reported to be increased in different fibrotic disorders. Skeletal muscle fibrosis is a common feature of Duchenne muscular dystrophy (DMD). The mdx mouse diaphragm is a good model for DMD since it reproduces the muscle degenerative and fibrotic changes. Fibronectin (FN) and proteoglycans (PG) are some of the ECM proteins upregulated in dystrophic conditions. In view of understanding the fibrotic process involved in DMD we have isolated fibroblasts from dystrophic mdx diaphragms. Here we report that regardless of the absence of degenerative myofibers, adult mdx diaphragm fibroblasts show increased levels of FN and condroitin/dermatan sulfate PGs synthesis. Fibroblasts isolated from non fibrotic tissue, such as 1 week old mice diaphragms or skin, do not present elevated FN levels. Furthermore, mdx fibroblast conditioned media is able to stimulate FN synthesis in control fibroblasts. Autocrine TGF-beta signaling was unaltered in mdx cells. When control fibroblasts are exposed to TGF-beta and CTGF, FN increases as expected. Paradoxically, in mdx cells it decreases in a concentration dependent manner and this decrease is not due to a downregulation of FN synthesis. According to this data we hypothesize that a pathological environment is able to reprogram fibroblasts into an activated phenotype which can be maintained through generations.

Skeletal muscle cells express the profibrotic cytokine connective tissue growth factor (CTGF/CCN2), which induces their dedifferentiation

Fibrotic disorders are typified by excessive connective tissue and extracellular matrix (ECM) deposition that precludes normal healing processes of different tissues. Connective tissue growth factor (CTGF) seems to be involved in the fibrotic response. Several muscular dystrophies are characterized by a progressive weakness and wasting of the musculature, and by extensive fibrosis. However, the exact role of CTGF in skeletal muscle is unknown. Here we show that myoblasts and myotubes are able to synthesize CTGF in response to transforming growth factor type-beta (TGF-beta) and lysophosphatidic acid (LPA). CTGF induced several ECM constituents such as fibronectin, collagen type I and alpha4, 5, 6, and beta1 integrin subunits in myoblasts and myotubes. CTGF had an important inhibitory effect on muscle differentiation evaluated by the decrease in the nuclear translocation of the early muscle regulatory factor myogenin and myosin. Remarkable, CTGF treatment of myoblasts induced their dedifferentiation, characterized by down regulating MyoD and desmin, two markers of committed myoblasts, together with a strong reorganization of cytoskeletal filaments. These results provide novel evidence for the underlying mechanisms and participation of skeletal muscle cells in the synthesis and role of CTGF inducing fibrosis, inhibiting myogenesis and dedifferentiating myoblasts.

Spatiotemporal expression of decorin and myostatin during rat skeletal muscle development

Decorin, a small leucine-rich proteoglycans, plays an important role in tissue morphogenesis through the regulation of collagen fibrillogenesis and the modulation of some growth factors. Our recent study has shown that decorin binds to myostatin, a negative regulator of skeletal muscle mass, and modulates its inhibitory action to myogenic cell growth in vitro. However, it still remains unclear whether decorin binds to myostatin in vivo during the development of skeletal muscle. To clarify this, we investigated the spatiotemporal expression of decorin and myostatin in rat skeletal muscle by RT-PCR and immunohistochemistry. Decorin mRNA abundance in fetal skeletal muscle was significantly higher than those in neonates and adults (P<0.05). Decorin mRNA expression decreased drastically at birth, and thereafter gradually up to 9 weeks of age. The mRNA expression pattern of myostatin was quite similar to that of decorin during prenatal and postnatal development of rat skeletal muscle. Immunohistochemical analysis demonstrated that myostatin was located in the muscle fibers, and that decorin was located in the periphery of muscle fibers in fetal rat skeletal muscle. Taken together with our previous data, these results suggest that decorin binds myostatin and sequesters it in the ECM during the development of rat skeletal.

A novel modulatory mechanism of transforming growth factor-beta signaling through decorin and LRP-1

Transforming growth factor-beta (TGF-beta) is a multifunctional cytokine that signals to the nucleus through cell surface transmembrane receptors with serine/threonine kinase activity and cytoplasmic effectors, including Smad proteins. Here we describe two novel modulators of this pathway, lipoprotein-receptor related protein (LRP-1) and decorin. Decorin null (Dcn null) myoblasts showed a diminished TGF-beta response that is restored by decorin re-expression. Importantly, this reactivation occurs without changes in the binding to TGF-beta receptors, Smad protein phosphorylation, or Smad-4 nuclear translocation. In wild type myoblasts, inhibition of decorin binding to LRP-1 and depletion of LRP-1 inhibited TGF-beta response to levels similar to those observed in Dcn null myoblasts. Re-expression of decorin in Dcn null myoblasts cannot restore TGF-beta response if the Smad pathway or phosphatidylinositol 3-kinase activity is inhibited, suggesting that this LRP-1-decorin modulatory pathway requires activation of the Smad pathway by TGF-beta and involves phosphatidylinositol 3-kinase activity. This work unveils a new regulatory mechanism for TGF-beta signaling by decorin and LRP-1.

Profiling of CD4+, CD8+, and CD4+CD25+CD45RO+FoxP3+ T cells in patients with malignant glioma reveals differential expression of the immunologic transcriptome compared with T cells from healthy volunteers

PURPOSE

Analyses of T-cell mRNA expression profiles in glioblastoma multiforme has not been previously reported but may help to define and characterize the immunosuppressed phenotype in patients with this type of cancer.

EXPERIMENTAL DESIGN

We did microarray studies that have shown significant and fundamental differences in the expression profiles of CD4(+) and CD8(+) T cells and immunosuppressive CD4(+)CD25(+)CD45RO(+)FoxP3(+) regulatory T cells (T(reg)) from normal healthy volunteers compared with patients with newly diagnosed glioblastoma multiforme. For these investigations, we isolated total RNA from enriched CD4(+) and CD8(+) T cell or T(reg) cell populations from age-matched individuals and did microarray analyses.

RESULTS

ANOVA and principal components analysis show that the various T cell compartments exhibit consistently similar mRNA expression profiles among individuals within either healthy or brain tumor groups but reflect significant differences between these groups. Compared with healthy volunteers, CD4(+) and CD8(+) T cells from patients with glioblastoma multiforme display coordinate down-regulation of genes involved in T cell receptor ligation, activation, and intracellular signaling. In contrast, T(regs) from patients with glioblastoma multiforme exhibit increased levels of transcripts involved in inhibiting host immunity.

CONCLUSION

Our findings support the notion that key differences between expression profiles in T-cell populations from patients with glioblastoma multiforme results from differential expression of the immunologic transcriptome, such that a limited number of genes are principally important in producing the dysregulated T-cell phenotype.