Background: When cells are damaged by nicotine, cellular senescence due to oxidative stress accelerates. In addition, stress-induced inflammatory response and cellular senescence cause the accumulation of damaged organelles in cells, and autophagy appears to remove them. Conversely, when autophagy is reduced, harmful cell components accumulate, and aging is accelerated. This study aimed to determine the association between nicotine-induced cellular senescence and autophagy expression patterns in human gingival fibroblasts. Methods: Cells were treated with various concentrations of nicotine (0, 0.1, 0.5, 1, 2, and 5 mM) and 10 nM rapamycin was added to 1 mM nicotine to investigate the relationship between autophagy and cellular senescence. Cell viability was confirmed using WST-8 and the degree of cellular senescence was measured by SA--gal staining. The expression of the inflammatory proteins (COX-2 and iNOS) and autophagy markers (LC3-II, p62, and Beclin-1) was analyzed by western blotting. Results: The cell viability tended to decrease in a concentration-dependent manner. COX-2 showed no concentration-dependent expression and iNOS increased in the 0.5 mM nicotine treated group. The degree of cellular senescence was the highest in the 1 mM nicotine treatment group. In the group treated with rapamycin and nicotine, the conversion ratio of LC3-II to LC3-I was the highest, that of p62 was the lowest, and the level of Beclin-1 proteins was significantly increased. Furthermore, the degree of cellular senescence was reduced in the group in which rapamycin was added to nicotine compared to that in the group treated with nicotine alone. Conclusion: This study provides evidence that autophagy activated in an aging environment reduces cellular senescence to a certain some extent.

Background: Although microbial infection is direct cause of periodontal disease, various environmental factors influence the disease severity. Aging is considered a risk factor for oral diseases, with the prevalence of periodontal diseases increasing with age. Moreover, senescence-associated secretory phenotype (SASP) expressed in age-related diseases is a key marker of chronic inflammation and aging phenotypes. Therefore, this study aimed to understand the relevance of senescent cells to periodontal health and disease, investigate the possibility of regulating the expression of aging-and osteolysis-related factors in gingival fibroblasts, and investigate the effect of senescence induction in gingival fibroblasts on osteoclast differentiation in mouse bone marrow-derived macrophages (BMMs). Methods: After stimulation with 400 nM hydrogen peroxidase, human gingival fibroblasts (HGFs) were examined for senescenceassociated -galactosidase. Western blot and enzyme-linked immunosorbent assays were performed to assess the expression of SASP. Osteoclast formation was assessed in BMMs using a conditioned medium (CM) from hydrogen peroxide-stimulated HGFs. Osteoclastic differentiation was investigated using tartrate-resistant acid phosphatase (TRAP) staining and activity. Data analysis was performed using SPSS version 25.0. Results: The expression of senescence-related molecules, including p53, p16, and p21, and the expression of osteolytic factors, including IL-6, IL-8, and IL-17, were found to be significantly higher in the hydrogen peroxide-stimulated HGF than in the control group. Regarding the indirect effects of senescent gingival cells, the number of osteoclasts and TRAP activity increased according to the differentiation of BMM cultured in CM. Conclusion: Our results on the of between osteolytic factors and cellular senescence in gingival fibroblast cells helped to reveal evidence of pathological aging mechanisms. Furthermore, our results suggest that the development of novel therapies that target specific SASP factors could be an effective treatment strategy for periodontal disease.