[Show abstract][Hide abstract] ABSTRACT: The so-called "matricellular" proteins have recently emerged as important regulators of cell-extracellular matrix (ECM) interactions. These proteins modulate a variety of cell functions through a range of interactions with cell-surface receptors, hormones, proteases and structural components of the ECM. As such, matricellular proteins are crucial regulators of cell phenotype, and consequently tissue function. The distinct cell types and microenvironments that together form the IVD provide an excellent paradigm to study how matricellular proteins mediate communication within and between adjacent tissue types. In recent years, the role of several matricellular proteins in the intervertebral disc has been explored in vivo using mutant mouse models in which the expression of target matricellular proteins was deleted from either one or all compartments of the intervertebral disc. The current review outlines what is presently known about the roles of the matricellular proteins belonging to the CCN family, SPARC (Secreted Protein, Acidic, and Rich in Cysteine), and thrombospondin (TSP) 2 in regulating intervertebral disc cell-ECM interactions, ECM synthesis and disc tissue homeostasis using genetically modified mouse models. Furthermore, we provide a brief overview of recent preliminary studies of other matricellular proteins including, periostin (POSTN) and tenascin (TN). Each specific tissue type of the IVD contains a different matricellular protein signature, which varies based on the specific stage of development, maturity or disease. A growing body of direct genetic evidence links IVD development, maintenance and repair to the coordinate interaction of matricellular proteins within their respective niches and suggest that several of these signalling modulators hold promise in the development of diagnostics and/or therapeutics targeting intervertebral disc aging and/or degeneration.
Matrix biology: journal of the International Society for Matrix Biology 05/2014; · 3.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The potent profibrotic cytokine TGFβ induces connective tissue growth factor (CCN2/CTGF) is induced in fibroblasts in a fashion sensitive to SB-431542, a specific pharmacological inhibitor of TGFβ type I receptor (ALK5). In several cell types, TGFβ induces CCN1 but suppresses CCN3, which opposes CCN1/CCN2 activities. However, whether SB-431542 alters TGFβ-induced CCN1 or CCN3 in human foreskin fibroblasts in unclear. Here we show that TGFβ induces CCN1 but suppresses CCN3 expression in human foreskin fibroblasts in a SB-431542-sensitive fashion. These results emphasize that CCN1/CCN2 and CCN3 are reciprocally regulated and support the notion that blocking ALK5 or addition of CCN3 may be useful anti-fibrotic approaches.
Journal of Cell Communication and Signaling 02/2014;
[Show abstract][Hide abstract] ABSTRACT: Scarring, which occurs in essentially all adult tissue, is characterized by the excessive production and remodeling of extracellular matrix by α-smooth muscle actin (SMA)-expressing myofibroblasts located within connective tissue. Excessive scarring can cause organ failure and death. Oral gingivae do not scar. Compared to dermal fibroblasts, gingival fibroblasts do not respond to transforming growth factor (TGFβ) by inducing α-SMA expression, due to the reduced expression and activity of focal adhesion kinase (FAK) by this cell type. Herein, we show that, compared with dermal fibroblasts, gingival fibroblasts show reduced expression of miR-218. Introduction of pre-miR-218 into gingival fibroblasts elevates FAK expression and, via a FAK/src-dependent mechanism, results in the ability of TGFβ to induce α-SMA. The deubiquitinase cezanne is a direct target of miR-218 and has increased expression in gingival fibroblasts compared with dermal fibroblasts. Knockdown of cezanne in gingival fibroblasts increases FAK expression and causes TGFβ to induce α-SMA. These results suggest that miR-218 regulates the ability of TGFβ to induce myofibroblast differentiation in fibroblasts via cezanne/FAK.
Molecular biology of the cell 02/2014; · 5.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cell-mediated activation of latent TGF-β1 is intimately involved with tissue repair and fibrosis in all organs. Previously, it was shown that the integrin β1 subunit was required for activation of latent TGF-β1 and skin fibrosis. A recent study by Henderson and colleagues (Nature Medicine 19,1617-1624, 2013) used three different in vivo models of fibrosis to show that integrin αv subunit was required for fibrogenesis. Through a process of elimination, the authors conclude that in vivo, the little-studied αvβ1 could be the major integrin responsible for TGF-β activation by myofibroblasts. Thus targeting this integrin might be a useful therapy for fibrosis.
Journal of Cell Communication and Signaling 01/2014;
[Show abstract][Hide abstract] ABSTRACT: The CCN family of matricellular proteins, which includes CCN2 and CCN1, is believed to have a major in vivo role in controlling tissue morphogenesis and repair. In adult skin, the proadhesive matricellular protein connective tissue growth factor (CTGF/CCN2) is specifically up-regulated in fibrosis and wound healing. In mice, CCN2 is required for dermal fibrogenesis, but whether CCN2 is required for cutaneous tissue repair is unknown. To address this question, in this report we subjected adult mice bearing a fibroblast-specific deletion of CCN2 to the dermal punch model of cutaneous tissue repair. Loss of CCN2 did not appreciably affect the kinetics of tissue repair, collagen content, or the number of α-smooth muscle actin-positive cells. CCN1 (cyr61), which has in vitro effect similar to CCN2, is also induced in cutaneous tissue repair. Fibroblast-specific CCN1/CCN2 double knockout mice were also generated; loss of both CCN1 and CCN2 together did not appreciably affect cutaneous tissue repair. However, loss of CCN2 resulted in impaired recruitment of NG2-positive pericyte-like cells to the wound area. Collectively, these results indicate that neither CCN2 nor CCN1 is essential for cutaneous tissue repair; CCN2 appears to be required for recruitment of pericyte-like cells and may represent a specific antifibrotic target.
Wound Repair and Regeneration 01/2014; 22(1):119-24. · 2.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The so-called “matricellular” proteins have recently emerged as important regulators of cell-extracellular matrix (ECM) interactions. These proteins modulate a variety of cell functions through a range of interactions with cell-surface receptors, hormones, proteases and structural components of the ECM. As such, matricellular proteins are crucial regulators of cell phenotype, and consequently tissue function. The distinct cell types and microenvironments that together form the IVD provide an excellent paradigm to study how matricellular proteins mediate communication within and between adjacent tissue types. In recent years, the role of several matricellular proteins in the intervertebral disc has been explored in vivo using mutant mouse models in which the expression of target matricellular proteins was deleted from either one or all compartments of the intervertebral disc. The current review outlines what is presently known about the roles of the matricellular proteins belonging to the CCN family, SPARC (Secreted Protein, Acidic, and Rich in Cysteine), and thrombospondin (TSP) 2 in regulating intervertebral disc cell-ECM interactions, ECM synthesis and disc tissue homeostasis using genetically modified mouse models. Furthermore, we provide a brief overview of recent preliminary studies of other matricellular proteins including, periostin (POSTN) and tenascin (TN). Each specific tissue type of the IVD contains a different matricellular protein signature, which varies based on the specific stage of development, maturity or disease. A growing body of direct genetic evidence links IVD development, maintenance and repair to the coordinate interaction of matricellular proteins within their respective niches and suggest that several of these signalling modulators hold promise in the development of diagnostics and/or therapeutics targeting intervertebral disc aging and/or degeneration.
[Show abstract][Hide abstract] ABSTRACT: It is critical to understand how stem cell activity is regulated during regeneration. Hair follicles are considered to be an important model for organ regeneration as, throughout adult life, they undergo cyclical regeneration. Hair follicle stem cells, epithelial cells located in the follicle bulge, are activated by periodic β-catenin activity which is regulated not only by epithelial-derived wnt but also, through as yet undefined mechanisms, by the surrounding dermal microenvironment. The matricellular protein CCN2 (connective tissue growth factor) is secreted into the microenvironment and acts as a multifunctional signaling modifier. In adult skin, CCN2 is largely absent but is unexpectedly restricted to the dermal papillae. Deletion of CCN2 in dermal papillae fibroblasts results in a shortened telogen phase length and elevated numbers of hair follicles. Recombinant CCN2 causes decreased β-catenin stability in keratinocytes. In vivo, loss of CCN2 results in elevated numbers of K15-positive epidermal stem cells that possess elevated β-catenin levels and β-catenin-dependent reporter gene expression. These results indicate that CCN2 expression by dermal papillae cells is a physiologically relevant suppressor of hair follicle formation through its destabilization of β-catenin, and suggest that CCN2 normally acts to maintain stem cell quiescence.
Molecular biology of the cell 10/2013; · 5.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Objective
Currently, our ability to treat intervertebral disc (IVD) degeneration is hampered by an incomplete understanding of disc development and aging. The specific function of matricellular proteins, including CCN2, during these processes remains an enigma. The aim of this study was to determine the tissue-specific localization of CCN proteins and to characterize their role in IVD tissues during embryonic development and age-related degeneration by using a mouse model of notochord-specific CCN2 deletion. Methods
Expression of CCN proteins was assessed in IVD tissues from wild-type mice beginning on embryonic day 15.5 to 17 months of age. Given the enrichment of CCN2 in notochord-derived tissues, we generated notochord-specific CCN2–null mice to assess the impact on the IVD structure and extracellular matrix composition. Using a combination of histologic evaluation and magnetic resonance imaging (MRI), IVD health was assessed. ResultsLoss of the CCN2 gene in notochord-derived cells disrupted the formation of IVDs in embryonic and newborn mice, resulting in decreased levels of aggrecan and type II collagen and concomitantly increased levels of type I collagen within the nucleus pulposus. CCN2-knockout mice also had altered expression of CCN1 (Cyr61) and CCN3 (Nov). Mirroring its role during early development, notochord-specific CCN2 deletion accelerated age-associated degeneration of IVDs. Conclusion
Using a notochord-specific gene targeting strategy, this study demonstrates that CCN2 expression by nucleus pulposus cells is essential to the regulation of IVD development and age-associated tissue maintenance. The ability of CCN2 to regulate the composition of the intervertebral disc suggests that it may represent an intriguing clinical target for the treatment of disc degeneration.
[Show abstract][Hide abstract] ABSTRACT: Introduction: Prior attempts at developing anti-fibrotic therapies have focused on using growth factors and cytokines as targets. However, growth factors and cytokines have effects on normal physiology as well as fibrosis, making effective drug development difficult. Areas covered: Matricellular proteins alter the cellular microenvironment and hence cellular signaling responses to cytokines and growth factors. A survey of Pubmed reveals that the expression pattern of matricellular proteins notably that of CCN2 (connective tissue growth factor) is often altered in pathophysiological conditions such as fibrosis. Moreover, data presented in recent publications suggests that CCN2 directly mediates fibrosis. Expert opinion: As a result of these features, matricellular proteins such as CCN2, a member of the CCN family of matricellular proteins, might be ideal targets against which to develop novel therapeutic strategies.
Expert Opinion on Therapeutic Targets 07/2013; · 4.90 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Tensegrity (tensional integrity) is an emerging concept governing the structure of the body. Integrin-mediated mechanical tension is essential for connective tissue function in vivo. For example, in adult skin fibroblasts, the integrin β1 subunit mediates adhesion to collagen and fibronectin. Moreover, integrin β1, through its abilities to activate latent TGFβ1 and promote collagen production through focal adhesion kinase/rac1/nicotinamide adenine dinucleotide phosphate oxidase (NOX)/reactive oxygen species (ROS), is essential for dermal homeostasis, repair and fibrosis. The integrin β1-interacting protein CCN2, a member of the CCN family of proteins, is induced by TGFβ1; yet, CCN2 is not a simple downstream mediator of TGFβ1, but instead synergistically promote TGFβ1-induced adhesive signaling and fibrosis. Due to its selective ability to sense mechanical forces in the microenvironment, CCN2 may represent an exquisitely precise target for therapeutic intervention.
Journal of Cell Communication and Signaling 06/2013;
[Show abstract][Hide abstract] ABSTRACT: There is no effective drug therapy for scarring and fibrotic disease. The cytokine transforming growth factor beta (TGF-β) promotes tissue repair, but its excessive action can lead to over exuberant scarring and fibrotic disease. However, owing to the multifunctional nature of TGF-β, broad targeting of the canonical Smad-TGF-β signaling pathway in vivo is likely to have unintended, deleterious consequences.
(1) The myofibroblast is the essential cell type that mediates tissue repair and fibrosis. (2) TGF-β is an essential contributor to myofibroblast differentiation and activity. (3) TGF-β selectively promotes tissue repair and fibrosis via the noncanonical focal adhesion kinase (FAK) pathway; FAK mediates myofibroblast differentiation, and hence may represent a novel intervention point for drugs treating fibrotic disease.
Excessive scarring (e.g., in hypertrophic scars, keloids, and scleroderma) is characterized by enhanced TGF-β signaling and is a major clinical problem. Drugs that selectively and effectively control the profibrotic action of TGF-β is therefore of clinical relevance.
FAK inhibition may represent a novel therapy for scarring disorders.
[Show abstract][Hide abstract] ABSTRACT: There is no effective drug treatment for fibrosis (i.e., pathological scarring). Identifying the fundamental mechanisms responsible for normal and pathological connective tissue deposition is likely to yield novel insights into how to control fibrotic conditions.
An increasing body of evidence suggests a link between mechanical tension and the development of scar tissue. Integrins are the cell surface receptors that mediate interactions between the cell and the surrounding extracellular matrix (ECM). Recent evidence has suggested that, in fibroblasts, the integrin β1-subunit plays an essential role in mechanosignaling and in dermal homeostasis, repair, and fibrosis. The mechanism underlying these activities of integrin β1 appears to involve its ability to (1) mediate activation of latent transforming growth factor beta-1 via ECM contraction and (2) modulate collagen production via a focal adhesion kinase/rac1/nicotinamide adenine dinucleotide phosphate oxidase (NOX)/reactive oxygen species (ROS) pathway. Moreover, the integrin β1-binding protein CCN2, a secreted matricellular protein located within the cellular microenvironment, is required for dermal fibrogenesis.
Mechanical tension is a key feature underlying the development of scar tissue. The mechanosignaling sensor integrin β1 is an essential, central mediator of dermal fibrosis, wound healing, and homeostasis.
Drugs targeting the molecular mechanism underlying integrin β1-mediated signaling may represent a novel therapeutic approach for treating fibroproliferative disorders. Clinical trials directly testing this hypothesis are warranted.
[Show abstract][Hide abstract] ABSTRACT: Cutaneous tissue repair involves an initial inflammatory phase, followed by a fibroproliferative phase and finally by a resolution phase. Failure to initiate fibroblast recruitment during the fibroproliferative phase results in chronic wounds, whereas failure to terminate the fibroproliferative phase results in fibroproliferative disorders. Thus, understanding how to regulate the fibroproliferative phase of tissue repair is, therefore, of high clinical relevance. Controlling the rate of the fibroproliferative response is essential to promote proper wound repair.
(1) The myofibroblast is essential for mediating the fibroproliferative phase of tissue repair. (2) The potent profibrotic cytokine transforming growth factor beta (TGF-β) is a major in vivo contributor to myofibroblast differentiation and activity in vivo.
An increasing body of evidence indicates that the transcription factor peroxisome proliferator-activated receptor gamma (PPAR-γ) plays a key in vivo role in suppressing the fibrogenic response by antagonizing TGF-β signaling. Excessive scarring and/or chronic wounds, caused by a dysregulated fibroproliferative phase, are major clinical problems in response to tissue injury.
The development of drugs to control the rate of the fibroproliferative response are clinically relevant. Controlling PPAR-γ activity may be useful for prevention of scarring as well as for promoting the closure of chronic wounds.
[Show abstract][Hide abstract] ABSTRACT: Dermal connective tissue is a supportive structure required for skin's barrier function; dysregulated dermal homeostasis results in chronic wounds and fibrotic diseases. The multifunctional cytokine transforming growth factor (TGF) β promotes connective tissue deposition, repair and fibrosis. TGFβ acts through well-defined canonical pathways; however, the non-canonical pathways through which TGFβ selectively promotes connective tissue deposition are unclear. In dermal fibroblasts, we show that inhibition of the non-canonical TGFβ-activated kinase 1 (TAK1) selectively reduced the ability of TGFβ to induce expression of a cohort of wound healing genes such as collagens, CCN2, TGFβ1 and IL-6. Fibroblast-specific TAK1-knockout mice showed impaired cutaneous tissue repair and decreased collagen deposition, α-smooth muscle actin and CCN2 expression, PCNA staining, and JNK and p38, but not Smad3, phosphorylation. TAK1-deficient fibroblasts showed reduced cell proliferation, migration, cell attachment/spreading and contraction of a floating collagen gel matrix. TAK1-deficient mice also showed progressively reduced skin thickness and collagen deposition. Thus TAK1 is essential for connective tissue deposition in the dermis; controlling TAK1 activity may lead to new therapies for chronic connective tissue disease.Journal of Investigative Dermatology accepted article preview online, 22 January 2013; doi:10.1038/jid.2013.28.
Journal of Investigative Dermatology 01/2013; · 6.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: It is well-established that the expression of CCN family of matricellular proteins is altered in essentially all cancers and, hence, targeting these proteins may be a novel therapeutic approach to treating these diseases. For example, CCN6 (WISP3) is downregulated in aggressive breast cancers, and this phenomenon appears to result in the tumor survival by promoting Akt phosphorylation. In a recent report by Pal et al. (Cancer Res 72(18):4818-4828, 2012), CCN6 knockdown was shown to promote BMP4-mediated activation of the Smad-independent TAK1 and p38 kinases. CCN6 expression was inversely associated with BMP4 and phospho-p38 levels in 69 % of invasive breast carcinomas. TAK1 inhibition has been previously shown to decrease tumor progression in preclinical models of TAK1-dependent cancers. These data are consistent with the idea that CCN6 may represent a novel therapeutic approach, as compared to attacking TAK1 directly, to selectively target breast cancers.
Journal of Cell Communication and Signaling 01/2013;
[Show abstract][Hide abstract] ABSTRACT: Pancreatic ductal adenocarcinoma (PDAC) is the fifth leading cause of cancer internationally. As the precise molecular pathways that regulate pancreatic cancer are incompletely understood, appropriate targets for drug intervention remain elusive. It is being increasingly appreciated that the cellular microenvironment plays an important role in driving tumor growth and metastasis. CCN1, a member of the CCN family of secreted matricellular proteins, is overexpressed in pancreatic cancer, and may represent a novel target for therapy. Sonic hedgehog (SHh) is responsible for PDAC cell proliferation, epithelial-mesenchymal transition (EMT), maintenance of cancer stemness, migration, invasion, and metastatic growth; in a recent report, it was shown that CCN1 is a potent regulator of SHh expression via Notch-1. CCN1 activity was mediated, at least in part, through altering proteosome activity. These results suggest that CCN1 may be an ideal target for treating PDAC.
Journal of Cell Communication and Signaling 12/2012;
[Show abstract][Hide abstract] ABSTRACT: Integrins are heterodimers that mediate cell attachment to the extracellular matrix. Previously, we used fibroblast-specific knockout mice to show that the integrin β1 subunit was required in vivo for dermal fibrogenesis and cutaneous tissue repair. Here, we show that integrin β1 expression by fibroblasts is required for dermal homeostasis; at 8 weeks after deletion of integrin β1, the dermis is significantly thinner, expressing less collagen and displaying reduced generation of reactive oxygen species (ROS). Cultured integrin β1-deficient fibroblasts show reduced rac1 activation and ROS generation. Overexpressing rac1 in integrin β1-deficient fibroblasts restored ROS generation; adding hydrogen peroxide to integrin β1-deficient fibroblasts restored Col1a2 (collagen, type I, α2) and α-smooth muscle actin (α-SMA) mRNA expression and α-SMA protein expression and stress fiber formation. Thus integrin β1 expression by fibroblasts is required for the maintenance of dermal connective tissue via a rac/ROS pathway.Journal of Investigative Dermatology advance online publication, 29 November 2012; doi:10.1038/jid.2012.438.
Journal of Investigative Dermatology 11/2012; · 6.19 Impact Factor