CCN2/Connective Tissue Growth Factor Is Essential for Pericyte Adhesion and Endothelial Basement Membrane Formation during Angiogenesis

CCN2/Connective Tissue Growth Factor (CTGF) is a matricellular protein that regulates cell adhesion, migration, and survival. CCN2 is best known for its ability to promote fibrosis by mediating the ability of transforming growth factor β (TGFβ) to induce excess extracellular matrix production. In addition to its role in pathological processes, CCN2 is required for chondrogenesis. CCN2 is also highly expressed during development in endothelial cells, suggesting a role in angiogenesis. The potential role of CCN2 in angiogenesis is unclear, however, as both pro- and anti-angiogenic effects have been reported. Here, through analysis of Ccn2-deficient mice, we show that CCN2 is required for stable association and retention of pericytes by endothelial cells. PDGF signaling and the establishment of the endothelial basement membrane are required for pericytes recruitment and retention. CCN2 induced PDGF-B expression in endothelial cells, and potentiated PDGF-B-mediated Akt signaling in mural (vascular smooth muscle/pericyte) cells. In addition, CCN2 induced the production of endothelial basement membrane components in vitro, and was required for their expression in vivo. Overall, these results highlight CCN2 as an essential mediator of vascular remodeling by regulating endothelial-pericyte interactions. Although most studies of CCN2 function have focused on effects of CCN2 overexpression on the interstitial extracellular matrix, the results presented here show that CCN2 is required for the normal production of vascular basement membranes

New collagen markers of ‘derepression’ synthesized by rabbit articular chondrocytes in culture

Chondrocytes isolated from rabbit articular cartilage undergo a progressive ‘derepression’ in culture and synthesize Type I, Type III and an unidentified collagen designated Peak ‘X’. In contrast, cartilage slices synthesize predominantly Type II collagen with increasing amounts of Peak ‘X’ during prolonged culture

Transforming growth factor-β type-II receptor signalling : intrinsic/associated casein kinase activity, receptor interactions and functional effects of blocking antibodies

The transforming growth factor β (TGF-β) family of growth factors control proliferation, extracellular matrix synthesis and\ or differentiation in a wide variety of cells. However, the molecular mechanisms governing ligand binding, receptor oligomerization and signal transduction remain incompletely understood. In this study, we utilized a set of antibodies selective for the extracellular and intracellular domains of the TGF-β type-II receptor as probes to investigate the intrinsic kinase activity of this receptor and its physical association in multimeric complexes with type-I and type-III receptors. The type-II receptor immunoprecipitated from human osteosarcoma cells exhibited autophosphorylation and casein kinase activity that was markedly stimulated by polylysine yet was insensitive to heparin. Affinity crosslinking of "#&I-TGF-β1 ligand to cellular receptors followed by specific immunoprecipitation demonstrated that type-II receptors form stable complexes with both type-I and type-III receptors expressed on the surfaces of both human osteosarcoma cells an

CCN2/CTGF is required for matrix organization and to protect growth plate chondrocytes from cellular stress

CCN2 (connective tissue growth factor (CTGF/CCN2)) is a matricellular protein that utilizes integrins to regulate cell proliferation, migration and survival. The loss of CCN2 leads to perinatal lethality resulting from a severe chondrodysplasia. Upon closer inspection of Ccn2 mutant mice, we observed defects in extracellular matrix (ECM) organization and hypothesized that the severe chondrodysplasia caused by loss of CCN2 might be associated with defective chondrocyte survival. Ccn2 mutant growth plate chondrocytes exhibited enlarged endoplasmic reticula (ER), suggesting cellular stress. Immunofluorescence analysis confirmed elevated stress in Ccn2 mutants, with reduced stress observed in Ccn2 overexpressing transgenic mice. In vitro studies revealed that Ccn2 is a stress responsive gene in chondrocytes. The elevated stress observed in Ccn2-/- chondrocytes is direct and mediated in part through integrin α5. The expression of the survival marker NFκB and components of the autophagy pathway were decreased in Ccn2 mutant growth plates, suggesting that CCN2 may be involved in mediating chondrocyte survival. These data demonstrate that absence of a matricellular protein can result in increased cellular stress and highlight a novel protective role for CCN2 in chondrocyte survival. The severe chondrodysplasia caused by the loss of CCN2 may be due to increased chondrocyte stress and defective activation of autophagy pathways, leading to decreased cellular survival. These effects may be mediated through nuclear factor κB (NFκB) as part of a CCN2/integrin/NFκB signaling cascade

Extracellular matrix domain formation as an indicator of chondrocyte dedifferentiation and hypertrophy

Cartilage injury represents one of the most significant clinical conditions. Implantation of expanded autologous chondrocytes from noninjured compartments of the joint is a typical strategy for repairing cartilage. However, two-dimensional culture causes dedifferentiation of chondrocytes, making them functionally inferior for cartilage repair. We hypothesized that functional exclusion of dedifferentiated chondrocytes can be achieved by the selective mapping of collagen molecules deposited by chondrogenic cells in a three-dimensional environment. Freshly isolated and in vitro expanded human fetal or adult articular chondrocytes were cultured in a thermoreversible hydrogel at density of 1 × 10(7) cells/mL for 24 h. Chondrocytes were released from the gel, stained with antibodies against collagen type 2 (COL II) or COL I or COL X and sorted by fluorescence activated cell sorting. Imaging flow cytometry, immunohistochemistry, quantitative polymerase chain reaction, and glycosaminoglycan (GAG) assays were performed to evaluate the differences between COL II domain forming and COL II domain-negative cells. Freshly dissected periarticular chondrocytes robustly formed domains that consisted of the extracellular matrix surrounding cells in the hydrogel as a capsule clearly detectable by imaging flow cytometry (ImageStream) and confocal microscopy. These domains were almost exclusively formed by COL II. In contrast to that, a significant percentage of freshly isolated growth plate pre-hypertrophic and hyperdrophic chondrocytes deposited matrix domains positive for COL II, COL I, and COL X. The proportion of the cells producing COL II domains decreased with the increased passage of in vitro expanded periarticular fetal or adult articular chondrocytes. Sorted COL II domain forming cells deposited much higher levels of COL II and GAGs in pellet assays than COL II domain-negative cells. COL II domain forming cells expressed chondrogenic genes at higher levels than negative cells. We report a novel method that allows separation of functionally active chondrogenic cells, which deposit high levels of COL II from functionally inferior dedifferentiated cells or hypertrophic chondrocytes producing COL X. This approach may significantly improve current strategies used for cartilage repair