CTGF/Hcs24, hypertrophic chondrocyte-specific gene product, interacts with perlecan in regulating the proliferation and differentiation of chondrocytes

An overview of CCN4 (WISP1) role in human diseases

CCN4 (cellular communication network factor 4), a highly conserved, secreted cysteine-rich matricellular protein is emerging as a key player in the development and progression of numerous disease pathologies, including cancer, fibrosis, metabolic and inflammatory disorders. Over the past two decades, extensive research on CCN4 and its family members uncovered their diverse cellular mechanisms and biological functions, including but not limited to cell proliferation, migration, invasion, angiogenesis, wound healing, repair, and apoptosis. Recent studies have demonstrated that aberrant CCN4 expression and/or associated downstream signaling is key to a vast array of pathophysiological etiology, suggesting that CCN4 could be utilized not only as a non-invasive diagnostic or prognostic marker, but also as a promising therapeutic target. The cognate receptor of CCN4 remains elusive till date, which limits understanding of the mechanistic insights on CCN4 driven disease pathologies. However, as therapeutic agents directed against CCN4 begin to make their way into the clinic, that may start to change. Also, the pathophysiological significance of CCN4 remains underexplored, hence further research is needed to shed more light on its disease and/or tissue specific functions to better understand its clinical translational benefit. This review highlights the compelling evidence of overlapping and/or diverse functional and mechanisms regulated by CCN4, in addition to addressing the challenges, study limitations and knowledge gaps on CCN4 biology and its therapeutic potential.

Porcine nasal septum cartilage-derived decellularized matrix promotes chondrogenic differentiation of human umbilical mesenchymal stem cells without exogenous growth factors

BACKGROUND

In the domain of plastic surgery, nasal cartilage regeneration is of significant importance. The extracellular matrix (ECM) from porcine nasal septum cartilage has shown potential for promoting human cartilage regeneration. Nonetheless, the specific biological inductive factors and their pathways in cartilage tissue engineering remain undefined.

METHODS

The decellularized matrix derived from porcine nasal septum cartilage (PN-DCM) was prepared using a grinding method. Human umbilical cord mesenchymal stem cells (HuMSCs) were cultured on these PN-DCM scaffolds for 4 weeks without exogenous growth factors to evaluate their chondroinductive potential. Subsequently, proteomic analysis was employed to identify potential biological inductive factors within the PN-DCM scaffolds.

RESULTS

Compared to the TGF-β3-cultured pellet model serving as a positive control, the PN-DCM scaffolds promoted significant deposition of a Safranin-O positive matrix and Type II collagen by HuMSCs. Gene expression profiling revealed upregulation of ACAN, COL2A1, and SOX9. Proteomic analysis identified potential chondroinductive factors in the PN-DCM scaffolds, including CYTL1, CTGF, MGP, ITGB1, BMP7, and GDF5, which influence HuMSC differentiation.

CONCLUSION

Our findings have demonstrated that the PN-DCM scaffolds promoted HuMSC differentiation towards a nasal chondrocyte phenotype without the supplementation of exogenous growth factors. This outcome is associated with the chondroinductive factors present within the PN-DCM scaffolds.

Tissue engineering in growth plate cartilage regeneration: Mechanisms to therapeutic strategies

The repair of growth plate injuries is a highly complex process that involves precise spatiotemporal regulation of multiple cell types. While significant progress has been made in understanding the pathological mechanisms underlying growth plate injuries, effectively regulating this process to regenerate the injured growth plate cartilage remains a challenge. Tissue engineering technology has emerged as a promising therapeutic approach for achieving tissue regeneration through the use of functional biological materials, seed cells and biological factors, and it is now widely applied to the regeneration of bone and cartilage. However, due to the unique structure and function of growth plate cartilage, distinct strategies are required for effective regeneration. Thus, this review provides an overview of current research on the application of tissue engineering to promote growth plate regeneration. It aims to elucidates the underlying mechanisms by which tissue engineering promotes growth plate regeneration and to provide novel insights and therapeutic strategies for future research on the regeneration of growth plate.

Perlecan: Roles in osteoarthritis and potential treating target

Osteoarthritis (OA) is the most common joint disease, affecting hundreds of millions of people globally, which leads to a high cost of treatment and further medical care and an apparent decrease in patient prognosis. The recent view of OA pathogenesis is that increased vascularity, bone remodeling, and disordered turnover are influenced by multivariate risk factors, such as age, obesity, and overloading. The view also reveals the gap between the development of these processes and early stage risk factors. This review presents the latest research on OA-related signaling pathways and analyzes the potential roles of perlecan, a typical component of the well-known protective structure against osteoarthritic pericellular matrix (PCM). Based on the experimental results observed in end-stage OA models, we summarized and analyzed the role of perlecan in the development of OA. In normal cartilage, it plays a protective role by maintaining the integrin of PCM and sequesters growth factors. Second, perlecan in cartilage is required to not only activate vascular epithelium growth factor receptor (VEGFR) signaling of endothelial cells for vascular invasion and catabolic autophagy, but also for different signaling pathways for the catabolic and anabolic actions of chondrocytes. Finally, perlecan may participate in pain sensitization pathways.

Molecular and Genetic Interactions between CCN2 and CCN3 behind Their Yin-Yang Collaboration

Cellular communication network factor (CCN) 2 and 3 are the members of the CCN family that conduct the harmonized development of a variety of tissues and organs under interaction with multiple biomolecules in the microenvironment. Despite their striking structural similarities, these two members show contrastive molecular functions as well as temporospatial emergence in living tissues. Typically, CCN2 promotes cell growth, whereas CCN3 restrains it. Where CCN2 is produced, CCN3 disappears. Nevertheless, these two proteins collaborate together to execute their mission in a yin–yang fashion. The apparent functional counteractions of CCN2 and CCN3 can be ascribed to their direct molecular interaction and interference over the cofactors that are shared by the two. Recent studies have revealed the mutual negative regulation systems between CCN2 and CCN3. Moreover, the simultaneous and bidirectional regulatory system of CCN2 and CCN3 is also being clarified. It is of particular note that these regulations were found to be closely associated with glycolysis, a fundamental procedure of energy metabolism. Here, the molecular interplay and metabolic gene regulation that enable the yin–yang collaboration of CCN2 and CCN3 typically found in cartilage development/regeneration and fibrosis are described.

Impact of perlecan, a core component of basement membrane, on regeneration of cartilaginous tissues

As an indispensable component of the extracellular matrix, perlecan (Pln) plays an essential role in cartilaginous tissue function. Although there exist studies suggesting that Pln expressed by cartilaginous tissues is critical for chondrogenesis, few papers have discussed the potential impact Pln may have on cartilage regeneration. In this review, we delineate Pln structure, biomechanical properties, and interactive ligands-which together contribute to the effect Pln has on cartilaginous tissue development. We also review how the signaling pathways of Pln affect cartilage development and scrutinize the potential application of Pln to divisions of cartilage regeneration, spanning vascularization, stem cell differentiation, and biomaterial improvement. The aim of this review is to deepen our understanding of the spatial and temporal interactions that occur between Pln and cartilaginous tissue and ultimately apply Pln in scaffold design to improve cell-based cartilage engineering and regeneration. STATEMENT OF SIGNIFICANCE: As a key component of the basement membrane, Pln plays a critical role in tissue development and repair. Recent findings suggest that Pln existing in the pericellular matrix surrounding mature chondrocytes is actively involved in cartilage regeneration and functionality. We propose that Pln is essential to developing an in vitro matrix niche within biological scaffolds for cartilage tissue engineering.

The CCN2/CTGF interactome: an approach to understanding the versatility of CCN2/CTGF molecular activities

Cellular communication network 2 (CCN2), also known as connective tissue growth factor (CTGF) regulates diverse cellular processes, some at odds with others, including adhesion, proliferation, apoptosis, and extracellular matrix (ECM) protein synthesis. Although a cause-and-effect relationship between CCN2/CTGF expression and local fibrotic reactions has initially been established, CCN2/CTGF manifests cell-, tissue-, and context-specific functions and differentially affects developmental and pathological processes ranging from progenitor cell fate decisions and angiogenesis to inflammation and tumorigenesis. CCN2/CTGF multimodular structure, binding to and activation or inhibition of multiple cell surface receptors, growth factors and ECM proteins, and susceptibility for proteolytic cleavage highlight the complexity to CCN2/CTGF biochemical attributes. CCN2/CTGF expression and dosage in the local environment affects a defined community of its interacting partners, and this results in sequestration of growth factors, interference with or potentiation of ligand-receptor binding, cellular internalization of CCN2/CTGF, inhibition or activation of proteases, and generation of CCN2/CTGF degradome products that add molecular diversity and expand the repertoire of functional modules in the cells and their microenvironment. Through these interactions, different intracellular signals and cellular responses are elicited culminating into physiological or pathological reactions. Thus, the CCN2/CTGF interactome is a defining factor of its tissue- and context-specific effects. Mapping of new CCN2/CTGF binding partners might shed light on yet unknown roles of CCN2/CTGF and provide a solid basis for tissue-specific targeting this molecule or its interacting partners in a therapeutic context.

CCN2 (Cellular Communication Network factor 2) in the bone marrow microenvironment, normal and malignant hematopoiesis

CCN2, formerly termed Connective Tissue Growth Factor, is a protein belonging to the Cellular Communication Network (CCN)-family of secreted extracellular matrix-associated proteins. As a matricellular protein it is mainly considered to be active as a modifier of signaling activity of several different signaling pathways and as an orchestrator of their cross-talk. Furthermore, CCN2 and its fragments have been implicated in the regulation of a multitude of biological processes, including cell proliferation, differentiation, adhesion, migration, cell survival, apoptosis and the production of extracellular matrix products, as well as in more complex processes such as embryonic development, angiogenesis, chondrogenesis, osteogenesis, fibrosis, mechanotransduction and inflammation. Its function is complex and context dependent, depending on cell type, state of differentiation and microenvironmental context. CCN2 plays a role in many diseases, especially those associated with fibrosis, but has also been implicated in many different forms of cancer. In the bone marrow (BM), CCN2 is highly expressed in mesenchymal stem/stromal cells (MSCs). CCN2 is important for MSC function, supporting its proliferation, migration and differentiation. In addition, stromal CCN2 supports the maintenance and longtime survival of hematopoietic stem cells, and in the presence of interleukin 7, stimulates the differentiation of pro-B lymphocytes into pre-B lymphocytes. Overexpression of CCN2 is seen in the majority of B-acute lymphoblastic leukemias, especially in certain cytogenetic subgroups associated with poor outcome. In acute myeloid leukemia, CCN2 expression is increased in MSCs, which has been associated with leukemic engraftment in vivo. In this review, the complex function of CCN2 in the BM microenvironment and in normal as well as malignant hematopoiesis is discussed. In addition, an overview is given of data on the remaining CCN family members regarding normal and malignant hematopoiesis, having many similarities and some differences in their function.

CTGF/CCN2 facilitates LRP4-mediated formation of the embryonic neuromuscular junction

At the neuromuscular junction (NMJ), lipoprotein-related receptor 4 (LRP4) mediates agrin-induced MuSK phosphorylation that leads to clustering of acetylcholine receptors (AChRs) in the postsynaptic region of the skeletal muscle. Additionally, the ectodomain of LRP4 is necessary for differentiation of the presynaptic nerve terminal. However, the molecules regulating LRP4 have not been fully elucidated yet. Here, we show that the CT domain of connective tissue growth factor (CTGF/CCN2) directly binds to the third beta-propeller domain of LRP4. CTGF/CCN2 enhances the binding of LRP4 to MuSK and facilitates the localization of LRP4 on the plasma membrane. CTGF/CCN2 enhances agrin-induced MuSK phosphorylation and AChR clustering in cultured myotubes. Ctgf-deficient mouse embryos (Ctgf^-/- ) have small AChR clusters and abnormal dispersion of synaptic vesicles along the motor axon. Ultrastructurally, the presynaptic nerve terminals have reduced numbers of active zones and mitochondria. Functionally, Ctgf^-/- embryos exhibit impaired NMJ signal transmission. These results indicate that CTGF/CCN2 interacts with LRP4 to facilitate clustering of AChRs at the motor endplate and the maturation of the nerve terminal.

TGF-β Initiates β-Catenin-Mediated CTGF Secretory Pathway in Old Bovine Nucleus Pulposus Cells: A Potential Mechanism for Intervertebral Disc Degeneration

We have recently demonstrated that overexpression of Smurf2 under the control of type II collagen alpha 1 (Col2a1) promoter induces an intervertebral disc degeneration phenotype in Col2a1‐Smurf2 transgenic mice. The chondrocyte‐like cells that express type II collagen and Smurf2 in the transgenic mouse discs are prone to degenerate. However, how the chondrocyte‐like cells contribute to disc degeneration is not known. Here, we utilized primary old bovine nucleus pulposus (NP) cells as substitutes for the chondrocyte‐like cells in Col2a1‐Smurf2 transgenic mouse discs to identify mechanism. We found that 35% of the cells were senescent; TGF‐β treatment of the cells induced a rapid moderate accumulation of β‐catenin, which interacted with connective tissue growth factor (CTGF/CCN2) in the cytoplasm and recruited it to the membrane for secretion. The TGF‐β‐initiated β‐catenin‐mediated CTGF secretory cascade did not occur in primary young bovine NP cells; however, when Smurf2 was overexpressed in young bovine NP cells, the cells became senescent and allowed this cascade to occur. These results suggest that Smurf2‐induced disc degeneration in Col2a1‐Smurf2 transgenic mice occurs through activation of CTGF secretory pathway in senescent disc cells. © 2018 The Authors JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

The in vitro effects of CCN2 on odontoblast-like cells

OBJECTIVE

To investigate the in vitro effects of CCN2 on odontoblast-like cells proliferation and differentiation.

DESIGN

MDPC-23 cells were cultured in DMEM supplemented with 5% FBS. CCN2 was either added to culture media or coated onto culture polystyrene, addition or coating of dH2O was served as control. In the addition group, CCN2 (100 ng/mL) was added into culture media. In the coating group, CCN2 at the concentration of 1000 ng/mL was employed. Cell proliferation was performed using CCK-8 assay. Cell differentiation and mineralization were analyzed by ALPase activity assay, real time RT-PCR and alizarin red staining. One-way ANOVA with post-hoc tukey HSD test was used for statistical analysis.

RESULTS

MDPC-23 cells exhibited robust proliferative activity upon exposure to either soluble or immobilized CCN2. ALP activity of cells cultured on CCN2-modified surface was continuously strengthened from day six (0.831 ± 0.024 units/μg protein versus 0.563 ± 0.006 units/μg protein of control) till day eight (1.035 ± 0.139 units/μg protein versus 0.704 ± 0.061 units/μg protein of control). Gene expression of BSP, OCN and OPN were promoted by soluble CCN2 after 48 h exposure. Moreover, gene expression of BSP, OCN, OPN, ALP, COL1 A1, Runx-2, DSPP and DMP-1 was significantly enhanced by immobilized CCN2. Finally, mineralization of MDPC-23 cells was accelerated by both soluble and immobilized CCN2 to different extent.

CONCLUSIONS

The findings indicate that CCN2 promoted proliferation, odontogenic gene expression and mineralization of MDPC-23 cells. It is proposed that CCN2 may be a promising adjunctive formula for dentin regeneration.

Effects of connective tissue growth factor (CTGF/CCN2) on condylar chondrocyte proliferation, migration, maturation, differentiation and signalling pathway

CCN2, also known as connective tissue growth factor (CTGF), is a 38 kDa cysteine-rich extracellular matrix protein that regulates a sequence of cellular functions and participates in multiple complex biological processes, such as chondrogenesis and osteogenesis. In the present study, we provided the first evidence describing the physiological role of CCN2 in condylar chondrocyte proliferation, migration, maturation and differentiation. CCN2 was widely expressed throughout the whole layers of condylar cartilage and predominantly distributed in the proliferative zone. Recombinant CCN2 promoted the proliferation, migration, proteoglycan synthesis and differentiation capacity of isolated condylar chondrocytes. The stimulatory effect of CCN2 on chondrocyte proliferation was associated with the activation of phosphatidylinositol 3-kinase/Akt signalling pathway. The blocking of this pathway by its inhibitor LY294002 impaired the proliferative effect of CCN2 on chondrocytes. These results suggested a novel physiological role of CCN2 in the development of condylar cartilage.

Regulatory mechanism of CCN2 production by serotonin (5-HT) via 5-HT2A and 5-HT2B receptors in chondrocytes

Serotonin (5-hydroxytryptamine: 5-HT) is recognized as a neurotransmitter in the central nerve system and as a regulator of systemic blood pressure in the peripheral tissues. Recently, it was reported that 5-HT2 receptors (5-HT2Rs) were expressed in cartilage tissues lacking both vessels and neurons, suggesting possible novel functions of 5-HT during cartilage development and regeneration. Our previous data indicated that CCN family protein 2/connective tissue growth factor (CCN2/CTGF) plays a central role in cartilage development and regeneration. Therefore, the aim of this study was to investigate the effect of 5-HT on the production of CCN2 in chondrocytes. Firstly, we showed that the mRNAs of 5-HT2R subtypes 5-HT2AR and 5-HT2BR, were expressed in a human chondrocytic cell line, HCS-2/8; however, 5-HT2CR mRNA was not detected. In addition, exogenously added 5-HT did not affect the 5-HT2AR and 5-HT2BR expressions. Next, we demonstrated that CCN2 production was increased by treatment with a 5-HT2AR agonist and the combination of 5-HT and 5-HT2BR antagonist. In contrast, treatment with a 5-HT2BR agonist and the combination of 5-HT and 5-HT2AR antagonist decreased CCN2 production. Furthermore, we showed that phosphorylation of Akt and p38 MAPK were increased by treatment with 5-HT2AR agonist, and that phosphorylation of PKCε, PKCζ, ERK1/2 and JNK were increased by treatment with 5-HT2BR agonist. Finally, we found that 5-HT2AR was localized in the growth plate, whereas 5-HT2BR was localized in the articular cartilage. These findings suggest that 5-HT promotes CCN2 production through the 5-HT2AR in growth plates, and that it represses CCN2 production through the 5-HT2BR in articular cartilage for harmonized development of long bones.

An early history of CCN2/CTGF research: the road to CCN2 via hcs24, ctgf, ecogenin, and regenerin

The principal aim of this historical review is to present the processes by which the different aspects of CCN2/CTGF/Hcs24 were discovered by different groups and how much CCN2/CTGF, by being integrated into CCN family, has contributed to the establishment of the basic concepts regarding the role and functions of this new class of proteins. This review should be particularly useful to new investigators who have recently entered this exciting field of study and also provides a good opportunity to acknowledge the input of those individuals who participated in the development of this scientific field.

Smad3-dependent CCN2 mediates fibronectin expression in human skin dermal fibroblasts

The potential involvement of connective tissue growth factor (CCN2/CTGF) in extracellular matrix (ECM) production is recognized. However, the role CCN2 in fibronectin (FN) gene expression has remained incompletely understood and even controversial. Here we report that CCN2 is absolutely necessary for FN expression in primary human skin dermal fibroblasts, the major cells responsible for ECM production in skin. Gain- and loss-of-function approaches demonstrate that CCN2 is an essential component of FN expression in both basal and stimulation by TGF-β signaling, the major regulator of FN expression. CCN2 is significantly induced by Smad3, a critical mediator of TGF-β signaling. CCN2 acts as a downstream mediator of TGF-β/Smad signaling and acting synergistically with TGF-β to regulate FN gene expression. Finally, we observed that CCN2 and FN predominantly expressed in the dermis of normal human skin, stromal tissues of skin squamous cell carcinoma (SCC), and simultaneously induced in wounded human skin in vivo. These findings provide evidence that CCN2 is responsible for mediating the stimulatory effects of TGF-β/Smad on FN gene expression, and attenuation of CCN2 expression may benefit to reduce fibrotic ECM microenvironment in disease skin.

Cell Biological Assays for Measuring Chondrogenic Activities of CCN2 Protein

Growth-plate chondrocytes undergo proliferation, maturation, hypertrophic differentiation, and calcification; and these processes can be reproduced in vitro in a chondrocyte culture system. Using this system, we have shown that CCN family protein 2/connective tissue growth factor (CCN2/CTGF) promotes all stages of proliferation, maturation, hypertrophic differentiation, and calcification, thus suggesting that CCN2 is a multifunctional growth factor for chondrocytes and plays important roles in chondrocyte proliferation and differentiation. In this chapter, we describe how to evaluate CCN2 functions in these processes occurring in cultured chondrocytes. Evaluation strategies for cell proliferation include measuring DNA synthesis by [³H]-thymidine incorporation, cellular metabolic activity, and cell number with a hemocytometer. Next, evaluation strategies to assess maturation are analysis of the gene expression of markers of mature chondrocytes, and examination of proteoglycan and collagen synthesis by using radioactive compounds. In addition, cytohistochemical detection of glycosaminoglycans (GAGs), such as chondroitin sulfate, by use of alcian blue and toluidine blue staining is useful to evaluate chondrocyte maturation. These methods can be also used for evaluation of physiological functions of CCN2 in permanent chondrocytes such as articular and auricular chondrocytes, which do not calcify under physiological conditions. Next, evaluation of hypertrophic differentiation is performed by detecting type X collagen, which is specific marker of hypertrophic chondrocytes, and by measuring alkaline phosphatase (ALP) activity. Finally, evaluation of calcification is performed by detecting matrix calcification by use of alizarin red staining and by examining the incorporation of ⁴⁵Ca into cartilaginous matrix. These methods would be useful for the evaluation not only of CCN2 but also of its derivatives and other CCN proteins.

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.

Engineered Tissue Inhibitor of Metalloproteinases-3 Variants Resistant to Endocytosis Have Prolonged Chondroprotective Activity

Tissue inhibitor of metalloproteinases-3 (TIMP-3) is a central inhibitor of matrix-degrading and sheddase families of metalloproteinases. Extracellular levels of the inhibitor are regulated by the balance between its retention on the extracellular matrix and its endocytic clearance by the scavenger receptor low density lipoprotein receptor-related protein 1 (LRP1). Here, we used molecular modeling to predict TIMP-3 residues potentially involved in binding to LRP1 based on the proposed LRP1 binding motif of 2 lysine residues separated by about 21 Å and mutated the candidate lysine residues to alanine individually and in pairs. Of the 22 mutants generated, 13 displayed a reduced rate of uptake by HTB94 chondrosarcoma cells. The two mutants (TIMP-3 K26A/K45A and K42A/K110A) with lowest rates of uptake were further evaluated and found to display reduced binding to LRP1 and unaltered inhibitory activity against prototypic metalloproteinases. TIMP-3 K26A/K45A retained higher affinity for sulfated glycosaminoglycans than K42A/K110A and exhibited increased affinity for ADAMTS-5 in the presence of heparin. Both mutants inhibited metalloproteinase-mediated degradation of cartilage at lower concentrations and for longer than wild-type TIMP-3, indicating that their increased half-lives improved their ability to protect cartilage. These mutants may be useful in treating connective tissue diseases associated with increased metalloproteinase activity.

Genetics of Common Antipsychotic-Induced Adverse Effects

The effectiveness of antipsychotic drugs is limited due to accompanying adverse effects which can pose considerable health risks and lead to patient noncompliance. Pharmacogenetics (PGx) offers a means to identify genetic biomarkers that can predict individual susceptibility to antipsychotic-induced adverse effects (AAEs), thereby improving clinical outcomes. We reviewed the literature on the PGx of common AAEs from 2010 to 2015, placing emphasis on findings that have been independently replicated and which have additionally been listed to be of interest by PGx expert panels. Gene-drug associations meeting these criteria primarily pertain to metabolic dysregulation, extrapyramidal symptoms (EPS), and tardive dyskinesia (TD). Regarding metabolic dysregulation, results have reaffirmed HTR2C as a strong candidate with potential clinical utility, while MC4R and OGFR1 gene loci have emerged as new and promising biomarkers for the prediction of weight gain. As for EPS and TD, additional evidence has accumulated in support of an association with CYP2D6 metabolizer status. Furthermore, HSPG2 and DPP6 have been identified as candidate genes with the potential to predict differential susceptibility to TD. Overall, considerable progress has been made within the field of psychiatric PGx, with inroads toward the development of clinical tools that can mitigate AAEs. Going forward, studies placing a greater emphasis on multilocus effects will need to be conducted.

Emerging role of CCN family proteins in tumorigenesis and cancer metastasis (Review)

The CCN family of proteins comprises the members CCN1, CCN2, CCN3, CCN4, CCN5 and CCN6. They share four evolutionarily conserved functional domains, and usually interact with various cytokines to elicit different biological functions including cell proliferation, adhesion, invasion, migration, embryonic development, angiogenesis, wound healing, fibrosis and inflammation through a variety of signalling pathways. In the past two decades, emerging functions for the CCN proteins (CCNs) have been identified in various types of cancer. Perturbed expression of CCNs has been observed in a variety of malignancies. The aberrant expression of certain CCNs is associated with disease progression and poor prognosis. Insight into the detailed mechanisms involved in CCN-mediated regulation may be useful in understanding their roles and functions in tumorigenesis and cancer metastasis. In this review, we briefly introduced the functions of CCNs, especially in cancer.

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

Many studies have reported that CCN family protein 2 (also known as connective tissue growth factor) induces fibrotic response in skeletal muscle, thus emphasizing the pathological role of CCN2 in muscle tissues. However, the physiological role of CCN2 in myogenesis is still unknown. This study clarified the CCN2 functions during myogenesis. Recombinant CCN2 (rCCN2) promoted proliferation and MyoD production in C2C12 cells and primary myoblasts, but inhibited myogenin production. In accordance with these findings, the gene expression levels of myosin heavy chain, which is a marker of terminally differentiated myoblasts and desmin, which is the main intermediate filament protein of muscle cells, were decreased by rCCN2 treatment. In vivo analyses with Ccn2-deficient skeletal muscle revealed decreased proliferating cell nuclear antigen (PCNA)/MyoD double positive cells and muscle hypoplasia. Consistent with this finding, myogenic marker genes and myotube formation were repressed in Ccn2-deficient myoblasts. The protein production of CCN2 was increased in C2C12 myoblasts treated with tumor necrosis factor-α, which is a pro-inflammatory cytokine, suggesting its role in muscle regeneration after inflammation. These findings indicate that CCN2 promotes proliferation and early differentiation but inhibits the terminal differentiation of myoblasts, thus suggesting that CCN2 plays a physiological role in myogenesis.

New strategy to control cell migration and metastasis regulated by CCN2/CTGF

Connective tissue growth factor (CTGF)/CCN family member 2 (CCN2) is a CCN family member of matricellular signaling modulators. It has been shown that CCN2/CTGF mediates cell adhesion, aggregation and migration in a large variety of cell types, including vascular endothelial cells, fibroblasts, epithelial cells, aortic smooth muscle and also pluripotent stem cells. Others matricellular proteins are capable of interacting with CCN2/CTGF to mediate its function. Cell migration is a key feature for tumor cell invasion and metastasis. CCN2/CTGF seems to be a prognostic marker for cancer. In addition, here we intend to discuss recent discoveries and a new strategy to develop therapies against CCN2/CTGF, in order to treat cancer metastasis.

Direct interaction between CCN family protein 2 and fibroblast growth factor 1

In an attempt to find out a new molecular counterpart of CCN family protein 2 (CCN2), a matricellular protein with multiple functions, we performed an interactome analysis and found fibroblast growth factor (FGF) -1 as one of the candidates. Solid-phase binding assay indicated specific binding between CCN2 and FGF-1. This binding was also confirmed by surface plasmon resonance (SPR) analysis that revealed a dissociation constant (Kd) of 3.98 nM indicating strong molecular interaction between the two. RNA analysis suggested that both FGF-1 and CCN2 could be produced by chondrocytes and thus their interaction in the cartilage is possible. These findings for the first time indicate the direct interaction of CCN2 and FGF-1 and suggest the co-presence of these molecules in the cartilage microenvironment. CCN2 is a well-known promoter of cartilage development and regeneration, whereas the physiological and pathological role of FGF-1 in cartilage mostly remains unclear. Biological role of FGF-1 itself in cartilage is also suspected.

The CCN family proteins: modulators of bone development and novel targets in bone-associated tumors

The CCN family of proteins is composed of six extracellular matrix-associated proteins that play crucial roles in skeletal development, wound healing, fibrosis, and cancer. Members of the CCN family share four conserved cysteine-rich modular domains that trigger signal transduction in cell adhesion, migration, proliferation, differentiation, and survival through direct binding to specific integrin receptors and heparan sulfate proteoglycans. In the present review, we discuss the roles of the CCN family proteins in regulating resident cells of the bone microenvironment. In vertebrate development, the CCN family plays a critical role in osteo/chondrogenesis and vasculo/angiogenesis. These effects are regulated through signaling via integrins, bone morphogenetic protein, vascular endothelial growth factor, Wnt, and Notch via direct binding to CCN family proteins. Due to the important roles of CCN family proteins in skeletal development, abnormal expression of CCN proteins is related to the tumorigenesis of primary bone tumors such as osteosarcoma, Ewing sarcoma, and chondrosarcoma. Additionally, emerging studies have suggested that CCN proteins may affect progression of secondary metastatic bone tumors by moderating the bone microenvironment. CCN proteins could therefore serve as potential therapeutic targets for drug development against primary and metastatic bone tumors.

CCN2: a master regulator of the genesis of bone and cartilage

CCN family member 2 (CCN2), also known as connective tissue growth factor (CTGF), has been suggested to be an endochondral ossification genetic factor that has been termed “ecogenin”, because in vitro studies revealed that CCN2 promotes the proliferation and differentiation of growth-plate chondrocytes, osteoblasts, and vascular endothelial cells, all of which play important roles in endochondral ossification. In addition to its action toward these three types of cells, CCN2 was recently found to promote the formation of osteoclasts in vitro, which cells play an important role in the replacement of cartilage by bone during endochondral ossification, thus strengthening the “ecogenin” hypothesis. For confirmation of this hypothesis, transgenic mice over-expressing CCN2 in cartilage were generated. The results proved the hypothesis; i.e., the over-expression of CCN2 in cartilage stimulated the proliferation and differentiation of growth-plate chondrocytes, resulting in the promotion of endochondral ossification. In addition to its “ecogenin” action, CCN2 had earlier been shown to promote the differentiation of various cartilage cells including articular cartilage cells. In accordance with these findings, cartilage-specific overexpression of CCN2 in the transgenic mice was shown to protect against the development of osteoarthritic changes in aging articular cartilage. Thus, CCN2 may also play a role as an anti-aging (chondroprotective) factor, stabilizing articular cartilage. CCN2 also had been shown to promote intramembranous ossification, regenerate cartilage and bone, and induce angiogenesis in vivo. For understanding of the molecular mechanism underlying such multifunctional actions, yeast two-hybrid analysis, protein array analysis, solid-phase binding assay, and surface plasmon resonance (SPR) analysis have been used to search for binding partners of CCN2. ECMs such as fibronectin and aggrecan, growth factors including BMPs and FGF2 and their receptors such as FGFR1 and 2 and RANK, as well as CCN family members themselves, were shown to bind to CCN2. Regarding the interaction of CCN2 with some of them, various binding modules in the CCN2 molecule have been identified. Therefore, the numerous biological actions of CCN2 would depend on what kinds of binding partners and what levels of them are present in the microenvironment of different types of cells, as well as on the state of differentiation of these cells. Through this mechanism, CCN2 would orchestrate various signaling pathways, acting as a signal conductor to promote harmonized skeletal growth and regeneration.

Cartilage-specific over-expression of CCN family member 2/connective tissue growth factor (CCN2/CTGF) stimulates insulin-like growth factor expression and bone growth

Previously we showed that CCN family member 2/connective tissue growth factor (CCN2) promotes the proliferation, differentiation, and maturation of growth cartilage cells in vitro. To elucidate the specific role and molecular mechanism of CCN2 in cartilage development in vivo, in the present study we generated transgenic mice overexpressing CCN2 and analyzed them with respect to cartilage and bone development. Transgenic mice were generated expressing a ccn2/lacZ fusion gene in cartilage under the control of the 6 kb-Col2a1-enhancer/promoter. Changes in cartilage and bone development were analyzed histologically and immunohistologically and also by micro CT. Primary chondrocytes as well as limb bud mesenchymal cells were cultured and analyzed for changes in expression of cartilage-related genes, and non-transgenic chondrocytes were treated in culture with recombinant CCN2. Newborn transgenic mice showed extended length of their long bones, increased content of proteoglycans and collagen II accumulation. Micro-CT analysis of transgenic bones indicated increases in bone thickness and mineral density. Chondrocyte proliferation was enhanced in the transgenic cartilage. In in vitro short-term cultures of transgenic chondrocytes, the expression of col2a1, aggrecan and ccn2 genes was substantially enhanced; and in long-term cultures the expression levels of these genes were further enhanced. Also, in vitro chondrogenesis was strongly enhanced. IGF-I and IGF-II mRNA levels were elevated in transgenic chondrocytes, and treatment of non-transgenic chondrocytes with recombinant CCN2 stimulated the expression of these mRNA. The addition of CCN2 to non-transgenic chondrocytes induced the phosphorylation of IGFR, and ccn2-overexpressing chondrocytes showed enhanced phosphorylation of IGFR. Our data indicates that the observed effects of CCN2 may be mediated in part by CCN2-induced overexpression of IGF-I and IGF-II. These findings indicate that CCN2-overexpression in transgenic mice accelerated the endochondral ossification processes, resulting in increased length of their long bones. Our results also indicate the possible involvement of locally enhanced IGF-I or IGF-II in this extended bone growth.

CTGF is a central mediator of tissue remodeling and fibrosis and its inhibition can reverse the process of fibrosis

CTGF is a secreted matricellular protein with very complex biology. It has been shown to modulate many signaling pathways leading to cell adhesion and migration, angiogenesis, myofibroblast activation, and extracellular matrix deposition and remodeling, which together lead to tissue remodeling and fibrosis. It has been reported in the literature that inhibition of CTGF expression by siRNA prevents CCl4-induced liver fibrosis and can reverse fibrosis when administered after significant collagen deposition is observed. A monoclonal antibody to CTGF that is currently in clinical development (FG-3019) has demonstrated the ability to reverse vascular stiffening and improve cardiac function in a rat model of diabetic complications. FG-3019 has also exhibited activity in a murine radiation-induced pulmonary fibrosis model. When FG-3019 was administered to mice after a significant radiation-induced increase in lung density could be observed by CT imaging, the density of the lungs was observed to decrease over the period during which the antibody was administered and to remain stable after therapy had ceased. When considered together, these data indicate that inhibition of CTGF can prevent and reverse the process of fibrosis.

The Wnt antagonist Wif-1 interacts with CTGF and inhibits CTGF activity

Wnt inhibitory factor 1 (Wif-1) is a secreted antagonist of Wnt signalling. We recently demonstrated that this molecule is expressed predominantly in superficial layers of epiphyseal cartilage but also in bone and tendon. Moreover, we showed that Wif-1 is capable of binding to several cartilage-related Wnt ligands and interferes with Wnt3a-dependent Wnt signalling in chondrogenic cells. Here we provide evidence that the biological function of Wif-1 may not be confined to the modulation of Wnt signalling but appears to include the regulation of other signalling pathways. Thus, we show that Wif-1 physically binds to connective tissue growth factor (CTGF/CCN2) in vitro, predominantly by interaction with the C-terminal cysteine knot domain of CTGF. In vivo such an interaction appears also likely since the expression patterns of these two secreted proteins overlap in peripheral zones of epiphyseal cartilage. In chondrocytes CTGF has been shown to induce the expression of cartilage matrix genes such as aggrecan (Acan) and collagen2a1 (Col2a1). In this study we demonstrate that Wif-1 is capable to interfere with CTGF-dependent induction of Acan and Col2a1 gene expression in primary murine chondrocytes. Conversely, CTGF does not interfere with Wif-1-dependent inhibition of Wnt signalling. These results indicate that Wif-1 may be a multifunctional modulator of signalling pathways in the cartilage compartment.

Taking aim at the extracellular matrix: CCN proteins as emerging therapeutic targets

Members of the CCN family of matricellular proteins are crucial for embryonic development and have important roles in inflammation, wound healing and injury repair in adulthood. Deregulation of CCN protein expression or activities contributes to the pathobiology of various diseases - many of which may arise when inflammation or tissue injury becomes chronic - including fibrosis, atherosclerosis, arthritis and cancer, as well as diabetic nephropathy and retinopathy. Emerging studies indicate that targeting CCN protein expression or signalling pathways holds promise in the development of diagnostics and therapeutics for such diseases. This Review summarizes the biology of CCN proteins, their roles in various pathologies and their potential as therapeutic targets.

Effect of CCN2 on FGF2-induced proliferation and MMP9 and MMP13 productions by chondrocytes

CCN2 (also known as connective tissue growth factor) interacts with several growth factors involved in endochondral ossification via its characteristic four modules and modifies the effect of such growth factors. Presently we investigated whether CCN2 interacts with fibroblast growth factor 2 (FGF2). Solid-phase binding assay, immunoprecipitation-Western blot analysis, and surface plasmon resonance (SPR) spectroscopy revealed that the C-terminal module of CCN2 (CT) directly bound to FGF2 with a dissociation constant of 5.5 nm. Next, we examined the combinational effects of CCN2 and FGF2 on the proliferation of and matrix metalloproteinase (MMP)-9 and -13 productions by cultured chondrocytes. FGF2 promoted not only the proliferation but also the production of MMP9 and -13, however, combined of FGF2 with CT module nullified the enhancement of both MMP productions and proliferation. To clarify the mechanism, we investigated the binding of CCN2 or its CT module to FGF receptor 1. As a result, we found that CCN2 bound to FGF receptor 1 with a dissociation constant of 362 nm, whereas the CT module did not. In addition, when we tested FGF signaling in chondrocytic HCS-2/8 cells stimulated by the combination of FGF2 with CT module, the level of ERK1/2, p38 MAPK, and c-Jun N-terminal kinase phosphorylation was decreased compared with that found with FGF2 alone. These findings suggest that CCN2 may regulate the proliferation and matrix degradation of chondrocytes by forming a complex with FGF2 as a novel modulator of FGF2 functions.

Differential roles of CCN family proteins during osteoblast differentiation: Involvement of Smad and MAPK signaling pathways

CCN family proteins play diverse roles in many aspects of cellular processes such as proliferation, differentiation, adhesion, migration, angiogenesis and survival. In the bone tissue of vertebrate species, the expression of most CCN family members has been observed in osteoblasts. However, their spatial and temporal distributions, as well as their functions, are still only partially understood. In this study, we evaluated the localization of CCN family members in skeletal tissue in vivo and comparatively analyzed the gene expression patterns and functions of the members in murine osteoblasts in primary culture. Immunofluorescent analyses revealed that the CCN family members were differentially produced in osteoblasts and osteocytes. The presence of all Ccn transcripts was confirmed in those osteoblasts. Among the members, CCN1, CCN2, CCN4 and CCN5 were found in osteocytes. CCN4 and CCN5 were distributed in osteocytes located inside of bone matrix as well. Next, we investigated the expression pattern of Ccn family members during osteoblast differentiation. Along with differentiation, most of the members followed proper gene expression patterns; whereas, Ccn4 and Ccn5 showed quite similar patterns. Furthermore, we evaluated the effects of CCN family members on the osteoblastic activities by using recombinant CCN proteins and RNA interference method. Five members of this family displayed positive effects on osteoblast proliferation or differentiation. Of note, CCN3 drastically inhibited the osteoblast activities. Each Ccn specific siRNA could modulate osteoblast activities in a manner expected by the observed effect of respective recombinant CCN protein. In addition, we found that extracellular signal-regulated kinase1/2 and p38 mitogen-activated protein kinase pathways were critically involved in the CCN family member-mediated modification of osteoblast activities. Collectively, all Ccn family members were found to be differentially expressed along with differentiation and therefore could participate in progression of the osteoblast lineage.

TGF-β enhances deposition of perlecan from COPD airway smooth muscle

Chronic obstructive pulmonary disease (COPD) and asthma are characterized by irreversible remodeling of the airway walls, including thickening of the airway smooth muscle layer. Perlecan is a large, multidomain, proteoglycan that is expressed in the lungs, and in other organ systems, and has been described to have a role in cell adhesion, angiogenesis, and proliferation. This study aimed to investigate functional properties of the different perlecan domains in relation to airway smooth muscle cells (ASMC). Primary human ASMC obtained from donors with asthma (n = 13), COPD (n = 12), or other lung disease (n = 20) were stimulated in vitro with 1 ng/ml transforming growth factor-β(1) (TGF-β(1)) before perlecan deposition and cytokine release were analyzed. In some experiments, inhibitors of signaling molecules were added. Perlecan domains I-V were seeded on tissue culture plates at 10 μg/ml with 1 μg/ml collagen I as a control. ASM was incubated on top of the peptides before being analyzed for attachment, proliferation, and wound healing. TGF-β(1) upregulated deposition of perlecan by ASMC from COPD subjects only. TGF-β(1) upregulated release of IL-6 into the supernatant of ASMC from all subjects. Inhibitors of SMAD and JNK signaling molecules decreased TGF-β(1)-induced perlecan deposition by COPD ASMC. Attachment of COPD ASMC was upregulated by collagen I and perlecan domains IV and V, while perlecan domain II upregulated attachment only of asthmatic ASMC. Seeding on perlecan domains did not increase proliferation of any ASMC type. TGF-β(1)-induced perlecan deposition may enhance attachment of migrating ASMC in vivo and thus may be a mechanism for ASMC layer hypertrophy in COPD.

Roles for CCN2 in normal physiological processes

CCN2, also known as connective tissue growth factor, is a member of the CCN (CCN1-6) family of modular matricellular proteins. Analysis of CCN2 function in vivo has focused primarily on its key role as a mediator of excess ECM synthesis in multiple fibrotic diseases. However, CCN2 and related family members are widely expressed during development. Recent studies using new genetic models are revealing that CCN2 has essential roles in the development of many tissues. This review focuses on current and emerging data on CCN2 and its functions in chondrogenesis and angiogenesis, and on new studies showing that CCN2 has essential functions during embryonic and postnatal development in a number of epithelial tissues.

Modulating endochondral ossification of multipotent stromal cells for bone regeneration

For years it has been recognized that engineering of large bone constructs will be feasible only if the hurdle of vascularization is overcome. Attempts to engineer bone tissue have predominantly focused on intramembranous (direct) bone formation. A relatively new and most likely more physiological approach in this line is endochondral bone formation, comprising an intermediate cartilaginous stage. Cartilage in nature is an avascular tissue and its cells are equipped to survive the poor oxygenation and nutritional conditions inherent to implanted tissues. Subsequent terminal differentiation (hypertrophy) of the chondrocytes initiates the formation of a mineralized matrix that will then be converted into bone. Through this mechanism, our long bones grow and most fractures heal through the process of secondary fracture healing. The feasibility of the attractive concept of endochondral bone tissue engineering has already been shown. Most emphasis has gone to the multipotent stromal cells because of their great potential for expansion and differentiation and immunoprivileged nature. This review will focus on the promises and current status of this new field. Further, potent modulators of endochondral bone tissue engineering, including oxygen tension and mechanical stimuli, will be discussed.

The role of CCN2 in cartilage and bone development

CCN2, a classical member of the CCN family of matricellular proteins, is a key molecule that conducts cartilage development in a harmonized manner through novel molecular actions. During vertebrate development, all cartilage is primarily formed by a process of mesenchymal condensation, while CCN2 is induced to promote this process. Afterwards, cartilage develops into several subtypes with different fates and missions, in which CCN2 plays its proper roles according to the corresponding microenvironments. The history of CCN2 in cartilage and bone began with its re-discovery in the growth cartilage in long bones, which determines the skeletal size through the process of endochondral ossification. CCN2 promotes physiological developmental processes not only in the growth cartilage but also in the other types of cartilages, i.e., Meckel's cartilage representing temporary cartilage without autocalcification, articular cartilage representing hyaline cartilage with physical stiffness, and auricular cartilage representing elastic cartilage. Together with its significant role in intramembranous ossification, CCN2 is regarded as a conductor of skeletogenesis. During cartilage development, the CCN2 gene is dynamically regulated to yield stage-specific production of CCN2 proteins at both transcriptional and post-transcriptional levels. New functional aspects of known biomolecules have been uncovered during the course of investigating these regulatory systems in chondrocytes. Since CCN2 promotes integrated regeneration as well as generation (=development) of these tissues, its utility in regenerative therapy targeting chondrocytes and osteoblasts is indicated, as has already been supported by experimental evidence obtained in vivo.

CCN family 2/connective tissue growth factor (CCN2/CTGF) promotes osteoclastogenesis via induction of and interaction with dendritic cell-specific transmembrane protein (DC-STAMP)

CCN family 2/connective tissue growth factor (CCN2/CTGF) promotes endochondral ossification. However, the role of CCN2 in the replacement of hypertrophic cartilage with bone is still unclear. The phenotype of Ccn2 null mice, having an expanded hypertrophic zone, indicates that the resorption of the cartilage extracellular matrix is impaired therein. Therefore, we analyzed the role of CCN2 in osteoclastogenesis because cartilage extracellular matrix is resorbed mainly by osteoclasts during endochondral ossification. Expression of the Ccn2 gene was upregulated in mouse macrophage cell line RAW264.7 on day 6 after treatment of glutathione S transferase (GST) fusion mouse receptor activator of NF-κB ligand (GST-RANKL), and a combination of recombinant CCN2 (rCCN2) and GST-RANKL significantly enhanced tartrate-resistant acid phosphatase (TRACP)-positive multinucleated cell formation compared with GST-RANKL alone. Therefore, we suspected the involvement of CCN2 in cell-cell fusion during osteoclastogenesis. To clarify the mechanism, we performed real-time PCR analysis of gene expression, coimmunoprecipitation analysis, and solid-phase binding assay of CCN2 and dendritic cell-specific transmembrane protein (DC-STAMP), which is involved in cell-cell fusion. The results showed that CCN2 induced and interacted with DC-STAMP. Furthermore, GST-RANKL-induced osteoclastogenesis was impaired in fetal liver cells from Ccn2 null mice, and the impaired osteoclast formation was rescued by the addition of exogenous rCCN2 or the forced expression of DC-STAMP by a retroviral vector. These results suggest that CCN2 expressed during osteoclastogenesis promotes osteoclast formation via induction of and interaction with DC-STAMP.

Role of c-Maf in Chondrocyte Differentiation: A Review

Chondrocyte differentiation in the growth plate is an important process for the longitudinal growth of endochondral bones. Sox9 and Runx2 are the most often-studied transcriptional regulators of the chondrocyte differentiation process, but the importance of additional factors is also becoming apparent. Mafs are a subfamily of the basic ZIP (bZIP) transcription factor superfamily, which act as key regulators of tissue-specific gene expression and terminal differentiation in many tissues. There is increasing evidence that c-Maf and its splicing variant Lc-Maf play a role in chondrocyte differentiation in a temporal-spatial manner. This review summarizes the functions of c-Maf in chondrocyte differentiation and discusses the possible role of c-Maf in osteoarthritis progression.

Cyr61/CCN1 displays high-affinity binding to the somatomedin B(1-44) domain of vitronectin

Background

Cyr61 is a member of the CCN (Cyr61, connective tissue growth, NOV) family of extracellular-associated (matricellular) proteins that present four distinct functional modules, namely insulin-like growth factor binding protein (IGFBP), von Willebrand factor type C (vWF), thrombospondin type 1 (TSP), and C-terminal growth factor cysteine knot (CT) domain. While heparin sulphate proteoglycans reportedly mediate the interaction of Cyr61 with the matrix and cell surface, the role of other extracellular associated proteins has not been revealed.

Methods and Findings

In this report, surface plasmon resonance (SPR) experiments and solid-phase binding assays demonstrate that recombinant Cyr61 interacts with immobilized monomeric or multimeric vitronectin (VTNC) with K_D in the nanomolar range. Notably, the binding site for Cyr61 was identified as the somatomedin B domain (SMTB ^1–44) of VTNC, which mediates its interaction with PAI-1, uPAR, and integrin αvβ3. Accordingly, PAI-1 outcompetes Cyr61 for binding to immobilized SMTB ^1–44, and Cyr61 attenuates uPAR-mediated U937 adhesion to VTNC. In contrast, isothermal titration calorimetry shows that Cyr61 does not display high-affinity binding for SMTB ^1-44 in solution. Nevertheless, competitive ELISA revealed that multimeric VTNC, heat-modified monomeric VTNC, or SMTB ^1–44 at high concentrations attenuate Cyr61 binding to immobilized VTNC, while monomeric VTNC was ineffective. Therefore, immobilization of VTNC exposes cryptic epitopes that recognize Cyr61 with high affinity, as reported for a number of antibodies, β-endorphin, and other molecules.

Conclusions

The finding that Cyr61 interacts with the SMTB ^1–44 domain suggests that VTNC represent a point of anchorage for CCN family members to the matrix. Results are discussed in the context of the role of CCN and VTNC in matrix biology and angiogenesis.

Connective tissue growth factor promotes fibrosis downstream of TGFbeta and IL-6 in chronic cardiac allograft rejection

Cardiac transplantation is an effective treatment for multiple types of heart failure refractive to therapy. Although immunosuppressive therapeutics have increased survival rates within the first year posttransplant, chronic rejection (CR) remains a significant barrier to long-term graft survival. Indicators of CR include patchy interstitial fibrosis, vascular occlusion and progressive loss of graft function. Multiple factors have been implicated in the onset and progression of CR, including TGFbeta, IL-6 and connective tissue growth factor (CTGF). While associated with CR, the role of CTGF in CR and the factors necessary for CTGF induction in vivo are not understood. To this end, we utilized forced expression and neutralizing antibody approaches. Transduction of allografts with CTGF significantly increased fibrotic tissue development, though not to levels observed with TGFbeta transduction. Further, intragraft CTGF expression was inhibited by IL-6 neutralization whereas TGFbeta expression remained unchanged, indicating that IL-6 effects may potentiate TGFbeta-mediated induction of CTGF. Finally, neutralizing CTGF significantly reduced graft fibrosis without reducing TGFbeta and IL-6 expression levels. These findings indicate that CTGF functions as a downstream mediator of fibrosis in CR, and that CTGF neutralization may ameliorate fibrosis and hypertrophy associated with CR.

Involvement of matrix metalloproteinases in the growth plate response to physiological mechanical load

Enzymes from the matrix metalloproteinase (MMP) family play a crucial role in growth-plate vascularization and ossification via proteolytic cleavage and remodeling of the extracellular matrix. Their regulation in the growth plate is crucial for normal matrix assembly. Endochondral ossification, which takes place at the growth plates, is influenced by mechanical loading. Using an in vivo avian model for mechanical loading, we have found increased blood penetration into the growth plates of loaded chicks. The purpose of this work was to study the involvement of MMP-2, -3, -9, -13, and -16 in the growth plate's response to loading and in the catch-up growth resulting from load release. We found that mechanical loading, as well as release from load, upregulated MMP-2, -9, and -13 expressions. In contrast, MMP-3, associated with cartilage injuries, and its associated protein connective tissue growth factor (CTGF), were downregulated by the load. However, after release from load, MMP-3 was upregulated and CTGF levels were elevated and caught up with the control. MMP-3 and CTGF were also downregulated after 60 min of mechanical stretching in vitro. These results demonstrate the central role of MMPs in the growth plate's response to mechanical loading, as well as in the catch-up growth followed load release.

Defining elastic fiber interactions by molecular fishing: an affinity purification and mass spectrometry approach

Deciphering interacting networks of the extracellular matrix is a major challenge. We describe an affinity purification and mass spectrometry strategy that has provided new insights into the molecular interactions of elastic fibers, essential extracellular assemblies that provide elastic recoil in dynamic tissues. Using cell culture models, we defined primary and secondary elastic fiber interaction networks by identifying molecular interactions with the elastic fiber molecules fibrillin-1, MAGP-1, fibulin-5, and lysyl oxidase. The sensitivity and validity of our method was confirmed by identification of known interactions with the bait proteins. Our study revealed novel extracellular protein interactions with elastic fiber molecules and delineated secondary interacting networks with fibronectin and heparan sulfate-associated molecules. This strategy is a novel approach to define the macromolecular interactions that sustain complex extracellular matrix assemblies and to gain insights into how they are integrated into their surrounding matrix.

Reduced expression of connective tissue growth factor (CTGF/CCN2) mediates collagen loss in chronologically aged human skin

Reduced production of type I procollagen is a prominent feature of chronologically aged human skin. Connective tissue growth factor (CTGF/CCN2), a downstream target of the transforming growth factor-beta (TGF-beta)/Smad pathway, is highly expressed in numerous fibrotic disorders, in which it is believed to stimulate excessive collagen production. CTGF is constitutively expressed in normal human dermis in vivo, suggesting that CTGF is a physiological regulator of collagen expression. We report here that the TGF-beta/Smad/CTGF axis is significantly reduced in dermal fibroblasts, the major collagen-producing cells, in aged (> or = 80 years) human skin in vivo. In primary human skin fibroblasts, neutralization of endogenous TGF-beta or knockdown of CTGF substantially reduced the expression of type I procollagen mRNA, protein, and promoter activity. In contrast, overexpression of CTGF stimulated type I procollagen expression, and increased promoter activity. Inhibition of TGF-beta receptor kinase, knockdown of Smad4, or overexpression of inhibitory Smad7 abolished CTGF stimulation of type I procollagen expression. However, CTGF did not stimulate Smad3 phosphorylation or Smad3-dependent transcriptional activity. These data indicate that in human skin fibroblasts, type I procollagen expression is dependent on endogenous production of both TGF-beta and CTGF, which act through interdependent yet distinct mechanisms. Downregulation of the TGF-beta/Smad/CTGF axis likely mediates reduced type I procollagen expression in aged human skin in vivo.