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Objective Periodontium regeneration is one of the most important processes for periodontitis therapy. Human periodontal ligament cells (hPDLCs) play a vital role in the repair and regeneration of periodontal tissues. Our study aimed to investigated the mechanisms underlying the promotion of hPLDCs osteogenic differentiation by baicalein. Design hPDLCs were obtained from periodontal ligament (PDL) tissues by primary culture. The MTT assay was used to determine the growth curves of hPDLCs treated with different concentrations of baicalein (1.25, 2.5, 5, or 10 μM). Alkaline phosphatase (ALP) staining and Alizarin red S staining were performed to assess osteogenic differentiation of hPDLCs administered baicalein. Osteogenic differentiation-related gene and protein expression levels and Wnt/β-catenin pathway signal changes were assessed by qRT-PCR and Western blotting analysis. Results The results showed that baicalein decreased the growth of hPDLCs slightly and increased ALP activity and calcium deposition in a dose-dependent manner. The expression of runt-related transcription factor 2 (RUNX2), bone morphogenetic protein 2 (BMP2), Osterix (OSX) and osteocalcin (OCN) were elevated after baicalein administration. Moreover, baicalein strongly activated the Wnt/β-catenin pathway and up-regulated the expression of β-catenin, lymphoid enhancer factor 1 (LEF1) and Cyclin D1. Dickkopf-related protein 1 (DKK-1) significantly reversed the effects of baicalein on hPDLCs. Conclusions Our findings indicated that baicalein enhanced the osteogenic differentiation of hPDLCs via the activation of the Wnt/β-catenin signaling pathway, which may represent a potential candidate for periodontitis therapy.

Mechanical strain plays an important role in bone formation and resorption during orthodontic tooth movement. The mechanism has not been fully studied, and the process becomes complex with increased amounts of periodontal patients seeking orthodontic care. Our aims were to elucidate the combined effects of proinflammatory cytokines and intermittent cyclic strain (ICS) on the osteogenic capacity of human periodontal ligament cells. Cultured human periodontal ligament cells were exposed to proinflammatory cytokines (interleukin-1β 5 ng/mL and tumor necrosis factor-α 10 ng/mL) for 1 and 5 days, and ICS (0.5 Hz, 12% elongation) was applied for 4 h per day. The autocrine of inflammatory cytokines was measured by enzyme-linked immunosorbent assay. The expression of osteoblast markers runt-related transcription factor 2 and rabbit collagen type I was determined using real-time polymerase chain reaction and Western blot. The osteogenic capacity was also detected by alkaline phosphatase (ALP) staining, ALP activity, and alizarin red staining. We demonstrated that ICS impaired the osteogenic capacity of human periodontal ligament cells when incubated with proinflammatory cytokines, as evidenced by the low expression of ALP staining, low ALP activity, reduced alizarin red staining, and reduced osteoblast markers. These data, for the first time, suggest that ICS has a negative effect on the inductive inhibition of osteogenicity in human PDL cells mediated by proinflammatory cytokines.

The present study aimed to investigate the role of orthodontic force in osteogenesis differentiation, matrix deposition and mineralization in periodontal ligament cells (PDLCs) cells in inflammatory microenvironments. The mesenchymal origin of PDLCs was confirmed by vimentin and cytokeratin staining. PDLCs were exposed to inflammatory cytokines (5 ng/ml IL‑1β and 10 ng/ml TNF‑α) and/or tensile strength (0.5 Hz, 12% elongation) for 12, 24 or 48 h. Cell proliferation and tensile strength‑induced cytokine expression were assessed by MTT assay and ELISA, respectively. Runt‑related transcription factor 2 (RUNX2) and type I collagen (COL‑I) expression were analysed by reverse transcription‑quantitative polymerase chain reaction and western blot analysis. Additionally, alkaline phosphatase activity was measured, and the mineralization profile was evaluated by alizarin red S staining. PDLCs exposed to tensile strength in inflammatory microenvironments exhibited reduced proliferation and mineralization potential. Treatment with the inflammatory cytokines IL‑1β and TNF‑α increased RUNX2 expression levels; however, decreased COL‑I expression levels, indicating that bone formation and matrix deposition involve different mechanisms in PDL tissues. Notably, RUNX2 and COL‑I expression levels were decreased in PDLCs exposed to a combination of an inflammatory environment and loading strength. The decreased osteogenic potential in an inflammatory microenvironment under tensile strength suggests that orthodontic force may amplify periodontal destruction in orthodontic patients with periodontitis.

Objective Endogenous hydrogen sulfide (H2S) has recently emerged as an important intracellular gaseous signaling molecule within cellular systems. Endogenous H2S is synthesized from l -cysteine via cystathionine β-synthase and cystathionine γ-lyase and it regulates multiple signaling pathways in mammalian cells. Indeed, aberrant H2S levels have been linked to defects in bone formation in experimental mice. The aim of this study was to examine the potential production mechanism and function of endogenous H2S within primary human periodontal ligament cells (PDLCs). Design Primary human PDLCs were obtained from donor molars with volunteer permission. Immunofluorescent labeling determined expression of the H2S synthetase enzymes. These enzymes were inhibited with D,L-propargylglycine or hydroxylamine to examine the effects of H2S signaling upon the osteogenic differentiation of PDLCs. Gene and protein expression levels of osteogenic markers in conjunction with ALP staining and activity and alizarin red S staining of calcium deposition were used to assay the progression of osteogenesis under different treatment conditions. Cultures were exposed to Wnt3a treatment to assess downstream signaling mechanisms. Results In this study, we show that H2S is produced by human PDLCs via the cystathionine β-synthase/cystathionine γ-lyase pathway to promote their osteogenic differentiation. These levels must be carefully maintained as excessive or deficient H2S levels temper the observed osteogenic effect by inhibiting Wnt/β-catenin signaling. Conclusions These results demonstrate that optimal concentrations of endogenous H2S must be maintained within PDLCs to promote osteogenic differentiation by activating the Wnt/β-catenin signaling cascade.