Opposing TNF-α/IL-1β- and BMP-2-activated MAPK signaling pathways converge on Runx2 to regulate BMP-2-induced osteoblastic differentiation

Abstract

In patients who were treated with exogenous BMP-2 to repair bone fractures or defects, the levels of the inflammatory cytokines such as TNF-α and IL-1β in sera are significantly elevated, which may affect the outcome of bone regeneration. Mitogen-activated protein kinase (MAPK) cascades such as extracellular signal-regulated kinase 1/2 (ERK1/2), p38, and c-Jun NH2-terminal kinase 1/2 (JNK1/2) have a crucial role in osteogenic differentiation and are activated by both BMP-2 and TNF-α/IL-1β. However, previous studies suggested that the effects of BMP-2 and TNF-α/IL-1β in osteoblastic differentiation are opposite. Here, we investigated the exact role of MAPKs in a BMP-2 and TNF-α/IL-1β co-existed condition. Treatment with TNF-α/IL-1β inhibited BMP-2-induced alkaline phosphatase activity, calcium deposition, osteogenic transcriptional factor Runx2, and the expression of osteogenic markers in C2C12 and MC3T3-E1 cells. This inhibitory effect was independent of the canonical BMP/Smad pathway, suggesting the presence of an alternate regulatory pathway for BMP-2-induced Runx2 activity and subsequent osteoblastic differentiation. We then confirmed that BMP-2, TNF-α, and IL-1β alone can activate p38, ERK1/2, and JNK1/2, respectively. However, only inhibition of p38 and ERK1/2 signaling were required to modulate BMP-2-induced Runx2 expression. Finally, we determined that TNF-α/IL-1β decreased BMP-2-induced Runx2 expression through the activation of p38 and ERK1/2 signaling. Furthermore, strong activation of p38 and ERK1/2 signaling by transfection with CA-MKK3 or CA-MEK1 inhibited BMP-2-induced Runx2 expression and osteoblastic differentiation in C2C12 and MC3T3-E1 cells. Based on these results, we conclude that TNF-α/IL-1β- and BMP-2-activated p38 and ERK1/2 signaling have opposing roles that converge on Runx2 to regulate osteoblastic differentiation. The elucidation of these mechanisms may hasten the development of new strategies and improve the osteoinductive efficacy of BMP-2 in the clinic to enhance osteoblastic differentiation and bone formation.

Pro-Inflammatory Cytokine TNF-α Attenuates BMP9-Induced Osteo/ Odontoblastic Differentiation of the Stem Cells of Dental Apical Papilla (SCAPs)

“…Similarly, it was reported that the BMP2-induced osteoblastic differentiation of MSCs was inhibited by TNF-α through activation of MAPK signaling pathway [19, 44, 45], while other studies suggest that TNF-α inhibited BMP/Smads signaling through the activation of NF-κB signaling pathway[46-48]. Nonetheless, the molecular mechanisms underlying such inhibition remain to be thoroughly investigated.…”

“…Similarly, an earlier study reported that TNF-α and BMP2 had opposing effects on osteoblastic differentiation of C2C12 and MC3T3-E1 cells [19]. While the exact mechanisms need to be understood, it offers a promise that exogenous BMP9 may be used to promote the bone defect repair and bone regeneration in the presence of high doses of TNF-α or under chronic inflammation conditions.…”

“…It was shown that high dose of TNF-α suppressed the osteogenic differentiation of MSC-like cells by decreased levels of alkaline phosphatase (ALP), osteocalcin (OCN), and Runx2 [16-18]. On the other hand, several studies suggest that TNF-α may have an inhibitory effect on BMP-induced osteoblast differentiation of MSCs or preosteoblastic cells [19-21]. …”

MMP‑2 silencing reduces the osteogenic transformation of fibroblasts by inhibiting the activation of the BMP/Smad pathway in ankylosing spondylitis

“…It was also found that MMP-2 inhibition by siRNA technique resulted in decreased expression of BMP-2, which in turn reduced the levels of Smad signalling protein levels remarkably. BMP molecules induce ligand-dependent type I and type II receptor heterodimerization, which activates p-Smad1/5/8 that bind Smad4 (32). The inhibition of BMP/Smad signalling by siRNA-MMP-2 was also associated with the inhibition of Cbfa-1 expression.…”

Role of mesenchymal stem cells on differentiation in steroid-induced avascular necrosis of the femoral head

“…Glucocorticoid serves a crucial regulatory function in the proliferation and differentiation of MSCs (13). Under certain conditions, hormones are able to induce MSC proliferation, differentiation and differentiation direction changes, potentially causing bone necrosis (14). The limited self-repair capacity associated with SANFH may be associated with the limited number and the weak proliferative activity of MSCs in femoral neck and femoral metaphyseal bone marrow of these patients (15).…”