Long-term exposure of human gingival fibroblasts to cigarette smoke condensate reduces cell growth by modulating Bax, caspase-3 and p53 expression

Abstract

Background and objective: Smoking cigarettes increases the risk of oral tissue damage leading to periodontal disease. Gingival fibroblasts, the predominant cell type inhabiting gingival connective tissue, play a critical role in remodeling and maintaining gingival structure. The objective of this study was to investigate the effect of long-term exposure to cigarette smoke on human gingival fibroblast survival/apoptosis and the molecular pathways involved in these cell responses.

Material and methods: Human gingival fibroblasts were extracted from healthy non-smokers and cultured in the presence of cigarette smoke condensate (CSC). At the end of each time point, cell growth was evaluated by means of MTT assay. Apoptotic and necrotic gene's expression was investigated by polymerase chain reaction array and by annexin V/propidium iodide staining and cell cycle assays. Western blot was used to investigate Bax and p53 proteins. These tests were supported by caspase 3 activity analyses.

Results: High levels of CSC decreased cell growth and deregulated cell cycle progression by increasing the G(0)/G(1) and reducing the S and G(2)/M phases of the gingival fibroblasts. Polymerase chain reaction arrays revealed the activation of several apoptotic genes by CSC, including TNF receptors, caspases, Bax and p53. This was supported by increases in the Bax and p53 protein levels as well as by an elevated activity of caspase-3 in the CSC-exposed cells. Immunofluorescence staining demonstrated that both Bax and caspase-3 displayed a cytosolic and mitochondrial distribution in the CSC-exposed gingival fibroblasts, compared to controls. The damaging effect of CSC on gingival fibroblast growth was also supported by the decrease in interleukin 6 and 8 secretion by the gingival fibroblasts.

Conclusion: These results suggest that CSC may contribute to deregulating fibroblast functions. This can compromise fibroblast-epithelial cell interactions, which ultimately increases the risk of gingival tissue damage and the onset of periodontitis.

Keywords: IL-6; IL-8; PCR arrays; apoptosis; bax; caspase; cigarette smoke; human cells; inflammation; p53.