A search for the mechanism of the stretch-induced activation of human periodontal ligament cells

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The present study was carried out to clarify how the human periodontal ligament (hPDL) cells respond to the cyclic stretching. We focused on the role of the stretched hPDL cells for the differentiation of osteoclasts and on the production of vascular endothelial growth factor in the stretched hPDL cells. The results are summarized as follows.1)It was shown by RT-PCR and Northern blotting that cultured hPDL cells express mRNAs of receptor activator of NF-kappa B ligand (RANKL) and its decoy receptor osteoprotegerin (OPG) in αMEM supplemented with 10% FCS in the presence of 1 alpha, 25(OH)__2 vitamin D__3(1, 25-(OH)__2D__3)and dexamethasone(Dex).2)When the coculture of hPDL cells and mouse bone marrow cells (BMCs) were treated with 1, 25-(OH)__2D__3 and Dex, Tartrate-resistant acid phosphatase (TRAP)-positive multinuclear cells were induced in the BMC-rich culture but not induced in the low BMC-density culture. However, osteoclasts were induced when the low BMC-density culture was treate … More d with an anti-OPG antibody.3)We found that RANKL mRNA was reduced while OPG mRNA was increased markedly by stretching in the hPDL cells by using Real-time RT-PCR The concentration of OPG in the culture media was increased when the hPDL cells were stretched in situ, suggesting that stretching of the hPDL cells acts to suppress induction of osteoclastogenesis in the BMCs.4)When the stretched hPDL cells and BMCs were cocultured in the presence of 1, 25-(OH)__2D__3 and Dex, TRAP-positive multinuclear cells were induced but the number was smaller than that induced in the conculture of unstreched hPDL cells and BMCs.5)It was demonstrated that cultured hPDL cells express vascular endothelial growth factor (VEGF) mRNA in αMEM supplemented with 10% FCS by using RT-PCR, and that the synthesized VEGF was released in the culture media by using ELISA.6)The expression of VEGF mRNA in cultured hPDL cells was increased by stretching and the concentration of VEGF in the media was higher in stretched culture than in unstretched culture. Thus, stretching stimuli enhance production of VEGF in hPDL cells and may further facilitate angiogenesis in the PDL tissue. Less