Effect of Mechanical Stress on the Proliferation and Expression of Cell Cycle Regulators in Human Periodontal Ligament Cells

Abstract

Recently, mechanical stress has been found to be associated with the proliferation of human periodontal ligament〔PDL〕cells. Although the detailed mechanism for the proliferation of PDL cells by mechanical stress remains largely unknown, the effect may be due to the increased expression of cell cycle regulatory proteins. To investigate this possibility, we measured the growth pattern and determined the protein levels of cellular p53, p21^WAF1/CIP1, cyclin-dependent kinases〔cdks〕, G_1 cyclins, and proliferating cell nuclear antigen〔PCNA〕expressed by PDL cells exposed to mechanical stress. Human PDL cells of passage number 6 were planted onto 55-mm Petriperm dishes〔1×10^4 cells/dish〕and exposed to mechanical stress〔1kg/dish〕for 12days. Mechanical stress markedly increased the proliferation of the PDL cells exposed to stress for 8-12days, compared to the controls. It also increased the protein level of cellular PCNA in the PDL cells exposed to stress for 6-10days. Mechanical stress also slightly increased the expression of cdks and cyclin D1 in these cells, but the protein levels of p53 and p21^WAF1/CIP1 were unchanged. The increased proliferation of PDL cells by mechanical stress may be due, in part, to the elevated cellular levels of cdks, without corresponding changes in p53 and p21^WAF1/CIP1 levels in human PDL cells.