Nicotine favors osteoclastogenesis in human periodontal ligament cells co-cultured with CD4(+) T cells by upregulating IL-1β.

Periodontitis, which is the main cause of tooth loss, is one of the most common chronic oral diseases in adults. Tooth loss is mainly a result of alveolar bone resorption, which reflects an increased osteoclast formation and activation. Osteoclast formation in periodontal tissue is a multistep process driven by osteoclastogenesis supporting cells such as human periodontal ligament (PDL) cells and CD4(+) T cells. Inflammatory cytokines, such as interleukin-1β (IL-1β), can induce osteoclastogenesis by affecting the expression of receptor activator of NF-κB ligand (RANKL) and osteoprotegerin (OPG) in human PDL cells. Nicotine, the major component in tobacco smoking and a specific agonist of the α7 nicotinic acetylcholine receptor (α7 nAChR), has been proven to regulate the expression of inflammatory cytokines in smoking-associated periodontitis. In this study, we investigated the mechanism(s) through which nicotine affects osteoclastogenesis in human PDL cells co-cultured/non-co-cultured with CD4(+) T cells. Human PDL cells were stimulated with nicotine (10-5 M) and/or α-bungarotoxin (α-BTX, specific antagonist of α7 nAChR, 10-8 M) before being co-cultured with CD4(+) T cells. Compared with mono-culture systems, stimulation with nicotine caused an increased secretion of IL-1β in serum of human PDL cell-CD4(+) T cell co-culture, and the expression of RANKL in human PDL cells was further upregulated co-cultured with CD4(+) T cells, while no differences were observed in the expression of OPG between the co-culture and mono-culture systems. Our data suggested that nicotine upregulated IL-1β secretion, further upregulated RANKL expression in smoking-associated periodontitis, which may aid in the better understanding of the relationship between nicotine and alveolar bone resorption.