Connective Tissue Growth Factor (CTGF/CCN2) Negatively Regulates BMP‐2 Induced Osteoblast Differentiation and Signaling

Abstract

Connective tissue growth factor (CTGF/CCN2) and bone morphogenetic protein (BMP)-2 are both produced and secreted by osteoblasts. Both proteins have been shown to have independent effects in regulating osteoblast proliferation, maturation and mineralization. However, how these two proteins interact during osteoblast differentiation remains unknown. In this study, we utilized two cell culture model systems, osteoblasts derived from CTGF knockout (KO) mice and osteoblasts infected with an adenovirus which over-expresses CTGF (Ad-CTGF), to investigate the effects of CTGF and BMP-2 on osteoblast development and function in vitro. Contrary to a previously published report, osteoblast maturation and mineralization were similar in osteogenic cultures derived from KO and WT calvaria in the absence of BMP-2 stimulation. Interestingly, in KO and WT osteoblast cultures stimulated with BMP-2, the KO osteoblasts exhibited enhanced osteoblast differentiation. This increase in osteoblast differentiation was accompanied by increased protein levels of phosphorylated Smad 1/5/8 and mRNA expression levels of bone morphogenetic protein receptor Ib. We also examined osteoblast differentiation in cultures that were infected with an adenoviral-CTGF vector (Ad-CTGF) and in controls. Continuous over-expression of CTGF resulted in decreased osteoblast maturation and mineralization in both unstimulated and BMP-2 stimulated cultures. Impaired osteoblast differentiation in cultures over-expressing CTGF was accompanied by decreased protein levels of phosphorylated Smad 1/5/8. Collectively, the data from these studies demonstrate that CTGF acts to negatively regulate BMP-2 induced signaling and osteoblast differentiation, and warrant additional studies to determine the precise mechanism(s) responsible for this effect.

Fibulin-1 is required for bone formation and Bmp-2-mediated induction of Osterix

“…Bone morphogenetic protein-2 (Bmp-2) is an ECM growth factor in the TGFβ super-family [5] that stimulates mesenchymal cells to differentiate into osteoblasts [6,7] and promotes differentiation of osteoclast precursors into mature osteoclasts [8,9]. A relatively large number of ECM proteins negatively regulate Bmp-2-mediated osteoblast differentiation including Noggin (Nog) [10,11], Twisted gastrulation (Twsg1) [10,12], Connective tissue growth factor (CCN2/Ctgf) [13], Nephroblastoma overexpressed (CCN3/Nov) [14], and Fibrillin-2 (Fbn2) [15]. By contrast, a small number of ECM proteins have been defined as positive modulators of Bmp-2 signaling in bone formation ( e.g.…”

CTGF Positively Regulates BMP12 Induced Tenogenic Differentiation of Tendon Stem Cells and Signaling

“…Antagonism between BMP and Fibroblast Growth Factor (FGF) signaling pathways regulates diversification of cartilage and tendon cells from a common precursor [27,28]. Connective Tissue Growth Factor (CTGF) is a cysteine-rich secreted protein characterized in 1991 by several groups [29,30,31], which has been shown to negatively regulate BMP2-stimulated osteoblast differentiation [32]. CTGF belongs to the CCN gene family of early-growth response genes which regulate proliferation and differentiation of connective tissue cells [33,34].…”

Osteocrin, a peptide secreted from the heart and other tissues, contributes to cranial osteogenesis and chondrogenesis in zebrafish

“…While Ctgf-deficient mice show impaired chondrocyte proliferation and matrix composition in the hypertrophic chondrocytes (Ivkovic et al, 2003), overexpression of CTGF from the osteocalcin promoter results in impairment of osteoblast activity due to decreased mineral apposition (Smerdel-Ramoya et al, 2008). However, another study reports that CTGF-deficient osteoblasts exhibit reduced proliferation but normal mineralization (Mundy et al, 2014). These results suggest that CTGF expression promoted by YAP1/WWTR1 might function in bone formation in a stagedependent and cell-dependent manner.…”