Hypoxia Regulates Osteogenic Differentiation of Human Periodontal Ligament Stem Cells

Objectives: Periodontitis is an inflammatory disease that results in the loss of connective tissue attachment and alveolar bone. A hypoxic gradient develops in deep periodontal pockets which may potentially affect periodontal ligament stem cells (PDLSCs) which are essential for periodontal regeneration. The purpose of this study was to investigate the effects of hypoxia on isolated human PDLSCs (hPDLSCs) in vitro. Methods: hPDLSCs were exposed to normoxia (O2=20%) and hypoxia (O22%). Total cellular RNA and protein were collected at 1, 2, 4, and 6 day. Western analysis and Semi-quantitative RT-PCR were used to analyze osteogenic differentiation (ALPase, OCN, SPARC, BMP-2 and Runx2) of hPDLSCs. Results: In the first two days hypoxia slightly increased the growth of hPDLSCs and after the third day hypoxia dramatically decreased the growth of the hPDLSCs. Upto 90% reduction of ALPase activity decreased by hypoxia observed in hPDLSCs at 4 and 6 day. Hypoxia decreased SPARC expression at protein level and down regulated ALPase, OCN, BMP2 and Runx2 expression at mRNA level in comparison with nomoxia. Conclusions: Taken together, our findings indicate that hypoxia inhibited proliferation of hPDLSCs and downregulated BMP2 and Runx2 expression, then down-regulated their target genes such as ALPase, OCN, and SPARC, thus inhibiting critical steps in osteogenic differentiation of hPDLSCs. (This study was supported by Lee Hysan Foundation Dental Scholars program and Natural Science Foundation of China #30600705)