Abstract
Mechanical force regulates periodontal ligament cell (PDL) behavior. However, different force types lead to distinct PDL responses. Here, we report that pretreatment with an intermittent compressive force (ICF), but not a continuous compressive force (CCF), promoted human PDL (hPDL) osteogenic differentiation as determined by osteogenic marker gene expression and mineral deposition in vitro. ICF-induced osterix (OSX) expression was inhibited by cycloheximide and monensin. Although CCF and ICF significantly increased extracellular adenosine triphosphate (ATP) levels, pretreatment with exogenous ATP did not affect hPDL osteogenic differentiation. Gene-expression profiling of hPDLs subjected to CCF or ICF revealed that extracellular matrix (ECM)-receptor interaction, focal adhesion, and transforming growth factor beta (TGF-β) signaling pathway genes were commonly upregulated, while calcium signaling pathway genes were downregulated in both CCF- and ICF-treated hPDLs. The TGFB1 mRNA level was significantly increased, while those of TGFB2 and TGFB3 were decreased by ICF treatment. In contrast, CCF did not modify TGFB1 expression. Inhibiting TGF-β receptor type I or adding a TGF-β1 neutralizing antibody attenuated the ICF-induced OSX expression. Exogenous TGF-β1 pretreatment promoted hPDL osteogenic marker gene expression and mineral deposition. Additionally, pretreatment with ICF in the presence of TGF-β receptor type I inhibitor attenuated the ICF-induced mineralization. In conclusion, this study reveals the effects of ICF on osteogenic differentiation in hPDLs and implicates TGF-β signaling as one of its regulatory mechanisms.
Highlights
The periodontal ligament (PDL) is a connective tissue that links the tooth root to alveolar bone[1,2]
intermittent compressive force (ICF) pretreatment-induced human PDL (hPDL) osteogenic differentiation Cells were pretreated with continuous compressive force (CCF) or ICF for 24 h in serum-free culture medium and subsequently maintained in osteogenic medium for 21 days (Fig. 1a)
Reduced BMP4 and DSPP mRNA levels were observed at day 3 and 7 in osteogenic medium, respectively. hPDLs pretreated with ICF significantly upregulated OSX, COL1A1, DSPP, BMP2, and BMP7 mRNA expression at day 3 of osteogenic induction (Fig. 1e)
Summary
The periodontal ligament (PDL) is a connective tissue that links the tooth root to alveolar bone[1,2]. Fibroblasts are the main cell type residing in the PDL3. The PDL functions to resist occlusal forces, to transmit forces from the teeth to alveolar bone, to secure the teeth in the alveolar socket, and as a protective scaffold for cells, vessels, and nerves[6,7]. The PDL is exposed to various mechanical stimuli in both physiological and pathological conditions. The PDL is subjected to various force types. The PDL fibers are arranged in several orientations, generating resistance to chewing forces from various directions. During orthodontic tooth movement (OTM), the PDL normally
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