Advanced glycation end‐products and Porphyromonas gingivalis lipopolysaccharide increase calprotectin expression in human gingival epithelial cells

Accumulation of advanced glycation end-products (AGEs) in periodontal tissues of patients with diabetes mellitus aggravates periodontitis, but the mechanisms are unknown. Calprotectin, a heterocomplex of S100A8 and S100A9 proteins, is a constitutive cytoplasmic component of healthy gingival epithelial cells. This study aimed at investigating the effects of AGE and Porphyromonas gingivalis lipopolysaccharide (PgLPS) on calprotectin expression in the human gingival epithelial cell line OBA-9. AGE and PgLPS increased the expression of S100A8 and S100A9 mRNAs, and AGE+PgLPS co-stimulation amplified their expression in OBA-9 cells. A higher concentration of calprotectin in cell lysates was also induced by stimulation with AGE and/or PgLPS. S100A8 was mainly translocated from the nucleus to the cytoplasm by AGE stimulation, while cytoplasmic localization of S100A9 was not altered following stimulation with AGE and/or PgLPS. Calprotectin was found in the cytoplasm of BSA-treated cells, but cytoplasmic and nuclear localization was observed following stimulation with AGE and/or PgLPS. AGE-induced S100A8, and S100A9 mRNA expression was partially suppressed by RAGE-specific siRNA. In contrast, PgLPS-induced S100A8 and S100A9 mRNA expression was strongly suppressed by TLR2-specific siRNA. Furthermore, the inhibition of p38, JNK MAPK, and NF-κB attenuated AGE- and PgLPS-induced S100A8 and S100A9 mRNA expression. Taken together, these results demonstrate that AGE acts in synergy with PgLPS to stimulate RAGE and TLR2 expression and activate p38, JNK MAPK, and NF-κB signaling pathways, resulting in increased activation of calprotectin (S100A8/S100A9) in human gingival epithelial cells. Our results suggest that calprotectin may be involved in the pathogenesis of diabetic periodontitis.