Dkk-1–TNF-α crosstalk regulates MC3T3E1 pre-osteoblast proliferation and differentiation under mechanical stress through the ERK signaling pathway

The study aims to explore the role of the ERK signaling pathway in the crosstalk between Dkk-1 and TNF-α in MC3T3E1 pre-osteoblasts under cyclic tensile/compressive stress. A forced four-point bending system was used to apply cyclic uniaxial tensile/compressive strain (2000 μ, 0.5 Hz) to MC3T3E1 cells. Dkk-1 and TNF-α expression were upregulated in MC3T3E1 cells under compressive strain. Cell proliferation, the cell cycle, osteogenesis-related gene (Wnt5a, Runx2, Osterix) expression, β-catenin expression, and the p-ERK/ERK ratio were significantly enhanced, whereas apoptosis, the RANKL/OPG ratio, and TNF-α expression were significantly attenuated, by Dkk-1 silencing. Dkk-1 expression increased and the effects of Dkk-1 silencing were reversed when exogenous TNF-α was added. Mechanically, TNF-α crosstalked with Dkk-1 through ERK signaling in MC3T3E1 cells. ERK signaling blockade impaired Dkk-1-induced TNF-α expression and TNF-α-mediated Dkk-1 expression. Dkk-1 and TNF-α crosstalked, partially through ERK signaling, in MC3T3E1 cells under compressive/tensile strain, synergistically modulating various biological behaviors of the cells. These findings not only provide mechanical insight into the cellular events and molecular regulation of orthodontic tooth movement (OTM), but also aid the development of novel strategies to accelerate OTM.