Kinetics of RANKL, RANK and OPG expressions in experimentally induced rat periapical lesions

Objective. The object of this study was to elucidate the kinetics of receptor activator of NF kappa B ligand (RANKL), RANK, osteoprotegerin (OPG), and cytokine expressions in experimentally induced rat periapical lesions. Study design. The mRNA expressions of RANKL, RANK, OPG, and cytokines in experimentally induced rat periapical lesions were evaluated by real-time PCR. The lesions were induced in male Wistar rats (n = 48, 5 weeks of age) by unsealed pulp exposure of the lower first molars. Results. Expression of RANKL was up-regulated at the beginning of lesion expansion, and expression ratio of RANKL against OPG, a competitor of RANKL, peaked at 2 and 3 weeks. Expression of inflammatory cytokines, such as TNF-alpha, IL-1 alpha, and IL-1 beta also increased at this stage, suggesting contribution of synergic effects of RANKL and proinflammatory cytokine signaling to lesion expansion. Most of RANKL(+) cells were fibroblastic, but few of them were T cells. Conclusion. Expression of RANKL and proinflammatory cytokines was correlated with periapical lesion expansion.