Msx2 mediates the inhibitory action of TNF-α on osteoblast differentiation

Abstract

TNF-α, a proinflammatory cytokine, inhibits osteoblast differentiation under diverse inflammatory conditions; however, the underlying mechanisms in terms of the TNF-α signaling pathway remain unclear. In this study, we examined the role of Msx2 in TNF-α-mediated inhibition of alkaline phosphatase (ALP) expression and the signaling pathways involved. TNF-α down-regulated ALP expression induced by bone morphogenetic protein 2 (BMP2) in C2C12 and Runx2 -/-calvarial cells. Over-expression of Msx2 suppressed BMP2-induced ALP expression. Furthermore, TNF-α induced Msx2 expression, and the knockdown of Msx2 by small interfering RNAs rescued ALP expression, which was inhibited by TNF-α. TNF-α activated the NF-κB and the JNK pathways. Inhibition of NF-κB or JNK activation reduced the inhibitory effect of TNF-α on ALP expression, whereas TNF-α-induced Msx2 expression was only suppressed by the inhibition of the NF-κB pathway. Taken together, these results indicate that Msx2 mediates the inhibitory action of TNF-α on BMP2-regulated osteoblast differentiation and that the TNF-α-activated NF-κB pathway is responsible for Msx2 induction.

Effects of combined mechanical stimulation on the proliferation and differentiation of pre-osteoblasts

“…OC and osteopontin are expressed thereafter when the cell status reaches the calcification step; both are involved in binding calcium ions and hydroxyapatite during the mineralization processes. Additionally, the osteogenic regulators RUNX2 and OSX are indispensable for osteoblastspecific genes including the osteocalcin gene (Ali et al, 2007;Lee et al, 2010).…”

Cyclic AMP Response Element-binding Protein H (CREBH) Mediates the Inhibitory Actions of Tumor Necrosis Factor α in Osteoblast Differentiation by Stimulating Smad1 Degradation

“…TNF␣ inhibits BMP signaling by interfering with the DNA-binding ability of Smads via activation of the nuclear factor-B (NF-B) pathway, regulating Runx2 expression, and inhibiting BMP-induced osteoblast differentiation (18,21,22). In addition, TNF␣ induces the expression of Smad7 and Msx2, which also inhibit BMP signaling and related osteogenesis (23,24). Activation of ERK by TNF␣ results in inhibition of the transcription factor osterix, and TNF␣-mediated induction of Smad ubiquitination regulatory factor 1 (Smurf1) and Smurf2 accelerates the degradation of Runx2 protein through the proteasomal degradation pathway (25).…”

“…To more confirm the involvement of specific IKK/IB␣/ NF-B pathway in the TNF␣-induced CREBH expression, we examined the effects of the dnIB␣ (S32A/S36A) mutant, which is unable to be phosphorylated and proteolytically degraded (23). Transfection of dnIB␣ effectively blocked TNF␣-increased p65 and CREBH protein levels in nucleus and Crebh mRNA expression in the cells (Fig.…”

Sirt1 overexpression protects murine osteoblasts against TNF-α-induced injury in vitro by suppressing the NF-κB signaling pathway

“…TNF-α activates several intracellular signaling pathways, including the AP-1 pathway, the MAPK pathway, and the JNK pathway in osteoblastic cells [28][29][30] . However, to our knowledge, TNF-α exerts deleterious effects primarily through the NF-κB signaling pathway in osteoblastic cells [31][32][33] . Because NF-κB is a molecular target of Sirt1 [34,35] , we investigated the influence of the overexpression of Sirt1 on NF-κB signaling pathways in TNF-α-treated osteoblasts.…”