Leptin regulates OPG and RANKL expression in Gingival Fibroblasts and Tissues of Chronic Periodontitis Patients

Objective: Chronic periodontitis is a bone-destructive disease affecting periodontal support structures. Although leptin has a protective effect against periodontitis, the underlying mechanism remains unclear. Therefore, this study aimed to investigate the possible role of leptin by examining its relationship with OPG and RANKL in human gingival tissues obtained from patients with chronic periodontitis. Method: Twenty-two patients with chronic periodontitis were enrolled (10 with moderate periodontitis and 12 with severe periodontitis) in the experimental group, and 12 healthy individuals were enrolled in the control group. Gingival tissue samples were collected, and the protein levels and localization of leptin, OPG, and RANKL were studied using immunohistochemistry (IHC). The staining intensities of leptin, OPG, and RANKL were correlated with the periodontal clinical index. Moreover, real-time quantitative PCR (RT-qPCR) was used to determine OPG and RANKL mRNA levels in gingival fibroblasts stimulated with gradient concentrations of leptin protein in vitro. Result: Leptin, OPG, and RANKL were located in the cytoplasm of gingival epithelial cells and the connective tissue. Leptin was widely and significantly expressed in the control group, whereas it was lightly stained in the severe group. RANKL was lightly stained in the control group, whereas it was widely and significantly expressed in the severe group. The control and the moderate groups had similar OPG levels, which were significantly higher than that in the severe group. Leptin was positively correlated with OPG (r = 0.905, p < 0.01) and negatively correlated with RANKL (r = -0.635, p < 0.01). In vitro low concentrations of leptin led to an increased OPG/RANKL mRNA ratio, whereas the opposite effect was observed at high concentrations. Conclusion: Leptin can regulate OPG and RANKL expression in gingival fibroblasts and may thus play a role in the development of chronic periodontitis by modulating the OPG/RANKL ratio.