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

Abstract

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.

CCN2 in orofacial tissue development and remodeling

“…As described in a previous section, CCN2 is produced by osteoblasts at early stages of differentiation and promotes their proliferation and osteoblastic differentiation [28]. Moreover, our recent study revealed that the same CCN2 molecule enhances osteoclastogenesis via interaction with dendritic cell-specific transmembrane protein (DC-STAMP), which is a cell-surface molecule playing a role in the cell fusion events that occur upon the maturation of osteoclasts [43]. In that report, the production of CCN2 by osteoclast progenitors was confirmed as well.…”

Osteoclastos: mucho más que células remodeladoras del hueso

“…In these mice there persisted a moderate degree of resorptive activity in the mature cells, which indicates that their fundamental role is performed at fusion 85 . The regulation of DC-STAMP is complex and depends not only on the RANKL/RANK pathway but also on other independent factors, such as IL-32 86 , Tal1 (T-cell acute lymphocytic leukemia 1) 87 , LDLR (low-density lipoprotein receptor) 88 , CCN2/CTGF (CCN family 2/connective tissue growth factor) 89 and vitamin E 90 , among others, whose role is even less well known but which could be future targets of therapeutic interest. OC fusion is promoted by other molecules such as the inflammatory cytokines.…”

The skeleton: a multi-functional complex organ. The role of key signalling pathways in osteoclast differentiation and in bone resorption

“…CCN1 inhibits osteoclast formation in vitro (Crockett et al 2007) via a mechanism that may involve a paracrine effect of osteoblast-derived CCN1 (Wang & Crockett, unpublished observations) whereas CCN2 has been shown to be elevated in the serum and synovium of patients with rheumatoid arthritis where it is expressed in the synovial macrophages and is associated with increased osteoclast formation and activity (Nozawa et al 2009), possibly as a consequence of regulating DC-STAMP expression (Nishida et al 2011).…”