Kinin B1 and B2 receptor expression in osteoblasts and fibroblasts is enhanced by interleukin-1 and tumour necrosis factor-α.: Effects dependent on activation of NF-κB and MAP kinases

Pro-inflammatory mediators formed by the kallikrein-kinin system can stimulate bone resorption and synergistically potentiate bone resorption induced by IL-1 and TNF-alpha. We have shown that the effect is associated with synergistically enhanced RANKL expression and enhanced prostaglandin biosynthesis, due to increased cyclooxygenase-2 expression. In the present study, the effects of osteotropic cytokines and different kinins on the expression of receptor subtypes for bradykinin (BK), des-Arg(10)-Lys-BK (DALBK), IL-1 beta and TNF-alpha have been investigated. IL-1 beta and TNF-alpha enhanced kinin B1 and B2 receptor binding in the human osteoblastic cell line MG-63 and the mRNA expression of B1 and B2 receptors in MG-63 cells, human gingival fibroblasts and intact mouse calvarial bones. Kinins did not affect mRNA expression of IL-1 or TNF receptors. EMSA showed that IL-1 beta and TNF-alpha activated NF-kappa B and AP-1 in MG-63 cells. IL-1 beta stimulated NF-kappa B via a non-canonical pathway (p52/p65) and TNF-alpha via the canonical pathway (p50/p65). Activation of AP-1 involved c-Jun in both IL-1 beta and TNF-alpha stimulated cells, but c-Fos only in TNF-alpha stimulated cells. Phospho-ELISA and Western blots showed that IL-1 beta activated JNK and p38, but not ERK 1/2 MAP kinase. Pharmacological inhibitors showed that NF-kappa B, p38 and JNK were important for IL-1 beta induced stimulation of B1 receptors, and NF-kappa B and p38 for B2 receptors. p38 and JNK were important for TNF-alpha induced stimulation of B1 receptors, whereas NF-kappa B, p38 and JNK were involved in TNF-alpha induced expression of B2 receptors. These data show that IL-1 beta and TNF-alpha upregulate B1 and B2 receptor expression by mechanisms involving activation of both NF-kappa B and MAP kinase pathways, but that signal transduction pathways are different for IL-1 beta and TNF-alpha. The enhanced kinin receptor expression induced by the pro-inflammatory cytokines IL-1 beta and TNF-alpha might be one important mechanism involved in the synergistic enhancement of prostaglandin formation caused by co-treatment with kinins and one of the two cytokines. These mechanisms might help to explain the enhanced bone resorption associated with inflammatory disorders, including periodontitis and rheumatoid arthritis. (C) 2008 Elsevier Inc. All rights reserved.