Substance P participates in periodontitis by upregulating HIF-1α and RANKL/OPG ratio

Background Both substance P and hypoxia-inducible factor 1 alpha (HIF-1 alpha) are involved in inflammation and angiogenesis. However, the relationship between substance P and HIF-1 alpha in rat periodontitis is still unknown. Methods Ligation-induced rat periodontitis was established to observe the distribution and expression of substance P and HIF-1 alpha by immunohistochemistry. Rat gingival fibroblasts were cultured and stimulated with Porphyromonas gingivalis lipopolysaccharide (LPS). Recombinant substance P was applied to elaborate the relationship between substance P and HIF-1 alpha in gingival fibroblasts in vitro. Primary mouse bone marrow-derived macrophages (BMMs) were isolated and cultured to observe the effect of substance P on receptor activator of NF-kappa B ligand (RANKL)-induced osteoclastogenesis by TRAP staining. Western blotting was used to investigate the expression of HIF-1 alpha, osteoprotegerin (OPG) and RANKL. Results Rat experimental periodontitis was successfully established 6 weeks after ligation. Gingival inflammatory infiltration and alveolar bone loss were observed. Positive expression of substance P was found in the infiltrating cells. Higher HIF-1 alpha levels were observed in periodontitis compared to that of normal tissues. Substance P upregulated the level of HIF-1 alpha in gingival fibroblasts with or without 1 mu g/ml LPS in vitro (*P < 0.05). Substance P upregulated the expression of HIF-1 alpha in RANKL-stimulated BMMs in vitro. Substance P also increased the RANKL/OPG ratio in gingival fibroblasts (*P < 0.05). Both 10nM and 50nM substance P promoted RANKL-induced osteoclast differentiation (*P < 0.05).ConclusionSubstance P participates in periodontitis by upregulating HIF-1 alpha and the RANKL/OPG ratio.