Female sex hormones modulate Porphyromonas gingivalis lipopolysaccharide-induced Toll-like receptor signaling in primary human monocytes

Abstract

Background and objective: Female sex hormones are elevated and are potential host response modifiers during pregnancy. Modulation of immune responses by estrogen and progesterone may be responsible for periodontal inflammation. Therefore, we aimed to investigate the role of β-estradiol and progesterone in human monocyte immune responses, at cellular and molecular levels, to identify their role as a possible immunological link between pregnancy and periodontal disease.

Material and methods: Primary human monocytes were purified from human peripheral blood mononuclear cells by adherent method. Expression of Toll-like receptor (TLR) 2, 4 and CD14 was analyzed by flow cytometry. TLR2, TLR4, cyclooxygenase-2 (COX2), nuclear factor-kappa B (NF-κB) and NF-κB inhibitor-alpha mRNA expressions were measured using real-time reverse transcriptase-polymerase chain reaction and prostaglandin E2 secretion was assayed by enzyme-linked immunosorbent assay. NF-κB expression was also examined by immunofluorescence. Western blotting was performed to determine the activation of mitogen-activated protein kinase pathway.

Results: We report herein that both β-estradiol and progesterone significantly reduced TLR2 expression at both protein and mRNA levels but had less of an effect on TLR4 expression in primary human monocytes. We also found that the hormones decreased monocyte cell surface protein expression of CD14. Significantly, β-estradiol and progesterone dose-dependently downregulated monocyte expression of COX2 mRNA. Pretreatment monocytes with β-estradiol or progesterone reduced effects of Porphyromonas gingivalis lipopolysaccharide (LPS) on COX2 mRNA expression and decreased prostaglandin E2 secretion by the monocytes. Furthermore, we demonstrated that both β-estradiol and progesterone inhibited P. gingivalis LPS-induced NF-κB signaling pathway through the upregulation of NF-κB inhibitor-alpha expression. However, neither β-estradiol nor progesterone altered the phosphorylation of the p38, the extracellular signal-regulated kinase 1/2 and the c-Jun N-terminal activated kinase in P. gingivalis LPS-stimulated monocytes. Thus, the inhibitory effects of these hormones on the response of human monocytes to P. gingivalis LPS appear to be independent on mitogen-activated protein kinase signaling pathway.

Conclusion: The results of the present study suggest that β-estradiol and progesterone could influence the immune response of human monocytes to periodontal pathogens and this process may have a role in the clinical manifestations of periodontal disease associated with pregnancy.

Keywords: Toll-like receptors; cell signaling; cytokine; inflammation; innate immunity; periodontal disease.