Hyperglycemia increases the expression levels of sclerostin in a reactive oxygen species- and tumor necrosis factor-alpha-dependent manner

Purpose: Sclerostin, an inhibitor of Wnt/beta-catenin signaling, exerts negative effects on bone formation and contributes to periodontitis-induced alveolar bone loss. Recent studies have demonstrated that serum sclerostin levels are increased in diabetic patients and that sclerostin expression in alveolar bone is enhanced in a diabetic periodontitis model. However, the molecular mechanism of how sclerostin expression is enhanced in diabetic patients remains elusive. Therefore, in this study, the effect of hyperglycemia on the expression of sclerostin in osteoblast lineage cells was examined. Methods: C2C12 and MLO-Y4 cells were used in this study. In order to examine the effect of hyperglycemia, the glucose concentration in the culture medium was adjusted to a range of levels between 40 and 100 mM. Gene expression levels were examined by quantitative reverse transcription-polymerase chain reaction and Western blot assays. Top-Flash reporter was used to examine the transcriptional activity of the beta-catenin/lymphoid enhanced factor/T-cell factor complex. Tumor necrosis factor-alpha (TNF alpha) protein levels were examined with the enzyme-linked immunosorbent assay. The effect of reactive oxygen species on sclerostin expression was examined by treating cells with 1 mM H2O2 or 20 mM N-acetylcysteine. Results: The high glucose treatment increased the mRNA and protein levels of sclerostin. High glucose suppressed INnt3a-induced Top-Flash reporter activity and the expression levels of osteoblast marker genes. High glucose increased reactive oxygen species production and TNF alpha expression levels. Treatment of cells with H2O2 also enhanced the expression levels of TNF alpha and sclerostin. In addition, N-acetylcysteine treatment or knockdown of TNF alpha attenuated high glucose-induced sclerostin expression. Conclusions: These results suggest that hyperglycemia increases sclerostin expression via the enhanced production of reactive oxygen species and TNF alpha.