Osterix Controls Cementoblast Differentiation through Downregulation of Wnt-signaling via Enhancing DKK1 Expression

Abstract

Osterix (Osx), a transcriptional factor essential for osteogenesis, is also critical for in vivo cellular cementum formation. However, the molecular mechanism by which Osx regulates cementoblasts is largely unknown. In this study, we initially demonstrated that overexpression of Osx in a cementoblast cell line upregulated the expression of markers vital to cementogenesis such as osteopontin (OPN), osteocalcin (OCN), and bone sialoprotein (BSP) at both mRNA and protein levels, and enhanced alkaline phosphatase (ALP) activity. Unexpectedly, we demonstrated a sharp increase in the expression of DKK1 (a potent canonical Wnt antagonist), and a great reduction in protein levels of β-catenin and its nuclear translocation by overexpression of Osx. Further, transient transfection of Osx reduced protein levels of TCF1 (a target transcription factor of β-catenin), which were partially reversed by an addition of DKK1. We also demonstrated that activation of canonical Wnt signaling by LiCl or Wnt3a significantly enhanced levels of TCF1 and suppressed the expression of OPN, OCN, and BSP, as well as ALP activity and formation of extracellular mineralized nodules. Importantly, we confirmed that there were a sharp reduction in DKK1 and a concurrent increase in β-catenin in Osx cKO mice (crossing between the Osx loxP and 2.3 Col 1-Cre lines), in agreement with the in vitro data. Thus, we conclude that the key role of Osx in control of cementoblast proliferation and differentiation is to maintain a low level of Wnt-β-catenin via direct up-regulation of DKK1.

ISLET1-Dependent β-Catenin/Hedgehog Signaling Is Required for Outgrowth of the Lower Jaw

“…Together with the reduced nuclear accumulation of ␤-catenin in the Isl1 mutant ( Fig. 6B and C), these data suggest that ISL1 may partially sustain epithelial WNT/␤-catenin signaling through regulation of the expression of WNT antagonists (30).…”

Overlapping functions of bone sialoprotein and pyrophosphate regulators in directing cementogenesis

“…These changes are intriguing, especially because Wnt and TGFβ signaling have both been implicated in cementogenesis [80–84]. However, like the changes in PP i -associated genes, these were not identified until 26 dpn, after the primary cementum defect in Bsp −/− had been evident for some time.…”

Soybean isoflavone treatment induces osteoblast differentiation and proliferation by regulating analysis of Wnt/β-catenin pathway

“…The membrane association of Axin and GSK3b disrupts the β-catenin destruction complex, resulting in accumulation of β-catenin in the nucleus, where it triggers target gene activation by displacing transcriptional repressors from DNA-bound LEF/ TCF (Behrens et al, 1996;Brunner et al, 1997). In recent years, canonical Wnt signaling pathway is identified to be crucial for bone formation and bone homeostasis Cao et al, 2015). Fujita et al reported that deactivation of Wnt signaling pathway will decrease OPG expression, increase RANKL expression, and inhibit osteoblastic differentiation (Fujita and Janz, 2007).…”