Age-dependent changes in the distribution of BrdU- and TUNEL-positive cells in the murine gingival tissue

Background: Age-dependent morphological and cell kinetic changes of the gingival tissue seem to be related to the occurrence of periodontal disease. The purpose of this study was to investigate the age-dependent changes in the distribution of BrdU-and TUNEL-positive cells in murine gingival tissue. Methods: Gingival tissue of the lower first molar region of 2-, 3-, 5-, 7-, 10-, 15-, 20-, 30-, 40-, 50-, 60-, 70-and 80-week-old mice was used in this study. BrdU-and TUNEL-positive cells were evaluated at the following 4 sites: 1) gingival epithelium (GE); 2) junctional epithelium (JE); 3) submucosal connective tissue of the gingival epithelium (GECT); and 4) submucosal connective tissue of the junctional epithelium (JECT). Results: No significant differences in the mean number of BrdU-positive cells at each site were demonstrated among the various age groups. No significant change in the mean number of TUNEL-positive cells was demonstrated in either the GE or JE groups among the various age groups. Meanwhile, a significant increase in the TUNEL-positive cells was observed in the GECT of mice 40 weeks or older, and in the JECT of mice 20 weeks or older. Conclusions: These results indicate that no age-dependent change in the cell proliferation or cell death occurred in the gingival and junctional epithelial layers as well as in the cell proliferation in the submucosal connective tissue. Meanwhile, a significant decrease in the cellular component of the submucosal connective tissue of both gingival and junctional epithelial layers caused by apoptosis occurred with aging. The decreased cellular component in the submucosal connective tissue thus seems to be related to either gingival recession or to the apical migration of the JE with aging. These morphological changes with aging possibly occur in humans and may be related to the susceptibility to periodontal disease in aged individuals.