CCN2 (Connective Tissue Growth Factor) is essential for extracellular matrix production and integrin signaling in chondrocytes

Abstract

The matricellular protein CCN2 (Connective Tissue Growth Factor; CTGF ) is an essential mediator of ECM composition, as revealed through analysis of Ccn2 deficient mice. These die at birth due to complications arising from impaired endochondral ossification. However, the mechanism(s) by which CCN2 mediates its effects in cartilage are unclear. We investigated these mechanisms using Ccn2−/− chondrocytes. Expression of type II collagen and aggrecan were decreased in Ccn2 −/− chondrocytes, confirming a defect in ECM production. Ccn2 −/− chondrocytes also exhibited impaired DNA synthesis and reduced adhesion to fibronectin. This latter defect is associated with decreased expression of α5 integrin. Moreover, CCN2 can bind to integrin α5β1 in chondrocytes and can stimulate increased expression of integrin α5. Consistent with an essential role for CCN2 as a ligand for integrins, immunofluorescence and Western blot analysis revealed that levels of focal adhesion kinase (FAK) and extracellular signalregulated kinase (ERK)1/2 phosphorylation were reduced in Ccn2 −/− chondrocytes. These findings argue that CCN2 exerts major effects in chondrocytes through its ability to (1) regulate ECM production and integrin α5 expression, (2) engage integrins and (3) activate integrin-mediated signaling pathways.

The effects of qindan-capsule-containing serum on the TGF-β1/ERK signaling pathway, matrix metalloproteinase synthesis and cell function in adventitial fibroblasts

“…In chondrocytes, CTGF regulates ECM via ERK1/2 signaling (Nishida et al, 2007). Our study shows that QC reduces TGFb1-induced effects; the expression of MMPs and ERK is down-regulated.…”

CCN2 Suppresses Catabolic Effects of Interleukin-1β through α5β1 and αVβ3 Integrins in Nucleus Pulposus Cells

“…Next, we determined whether the binding of CCN2 to cognate integrin receptors explains its anti-catabolic effects. We used disintegrins ECH and VLO4 to inhibit CCN2-specific, RGD-dependent integrins ␣v␤3 and ␣5␤1, respectively (10,12,26). First, we confirmed that these disintegrins block CCN2 function by measuring aggrecan expression with or without ECH and VLO4 in NP cells following CCN2 treatment.…”

“…Thus, given that the NF-B is a major downstream effector of inflammatory stimuli; it is likely that in the healthy NP, in contrast to other cell types, CCN2 is primarily anabolic and unlikely to play an inflammatory role (19,44). Next, we investigated the possibility that the anti-catabolic effects of CCN2 are mediated through cognate integrin receptors, ␣5␤1 and ␣V␤3 (10,12,41). We tested this possibility using the disintegrins ECH and VLO4 to inhibit ␣v␤3 and ␣5␤1, respectively.…”

“…By promoting cellular adhesion, proliferation, migration, and extracellular matrix synthesis, CCN2 plays a role in a range of processes, including wound healing and inflammation (9,10,(12)(13)(14)(15)(16)(17). The multimodular domain structure of CCN2 allows it to interact with growth factors and matrix molecules, whereas the outside-in signal-ing of CCN2 is mediated through interaction with integrins and heparan sulfate proteoglycans (10,12,14,18). Relating to the normal physiology of intervertebral disc and cartilage, we and others have shown that CCN2 is anabolic and promotes the synthesis of aggrecan (14,17,19).…”

CTGF disrupts alveolarization and induces pulmonary hypertension in neonatal mice: implication in the pathogenesis of severe bronchopulmonary dysplasia

“…Upon stimulation, CTGF is secreted into the extracellular environment, where it interacts with distinct cell surface receptors, growth factors, and the extracellular matrix (ECM) (34). The principal CTGF receptor is the heterodimeric cell surface integrin complex whereas integrin-linked kinase (ILK) is a key mediator of integrin signaling that interacts with the cytoplasmic domain of ␤ integrins (22,25,40). Activated ILK subsequently phosphorylates AKT, also known as protein kinase B and glucose synthesis kinase-3 ␤ (GSK-3␤) thus leading to activation of a diverse array of cellular processes (22,37,45).…”