| 1. |
|
|
| 2. |
|
|
| 3. |
- Bernhold Brechter, Anna, 1971-
(författare)
-
Kinins : important regulators in inflammation induced bone resorption
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Inflammatory processes in, or in close vicinity of, the skeleton often lead to loss of bone tissue. Different cytokines have been shown to be involved as stimulators of inflammatory induced osteoclastic bone resorption. During inflammatory processes also the kallikrein-kinin system is activated, leading to production of kinins that can cause pain, vasodilation and increased permeability of vessels. Kinins can also induce bone resorption in vitro. All cytokines and kinins that stimulate bone resorption stimulate in parallell prostaglandin synthesis, and prostaglandins, per se, have also been shown to induce bone resorption. The aim of this project was to increase the knowledge about the mechanisms involved in the interactions between different inflammatory mediators (i.e. kinins, cytokines and prostaglandins) suggested to be involved in the pathogenesis of inflammatory bone resorbing diseases. Human osteoblasts (MG-63) are equipped with both kinin B1 and B2 receptors linked to prostaglandin release and the stimulation of prostaglandin release are likely mediated via separate molecular mechanisms (Paper I). Activation of B1 or B2 receptors causes synergistic stimulation of PGE2 synthesis induced by either interleukin-1b (IL-1b) or tumour necrosis factor-a (TNF-a) (Paper II). The molecular mechanism involves increased expression of cyclooxygenase-2 (COX-2) and results in synergistic potentiation of receptor activator of NF-kB ligand (RANKL) protein expression. The synergistic interaction is dependent on the activation of NF-kB and the mitogen-activated protein kinases (MAPK) p38 and JNK (Paper II). The synergistic increase in RANKL expression might be an explanation why kinins potentiate IL-1b induced bone resorption, a mechanism likely to be important in inflammation induced bone resorption in diseases such as periodontal disease and rheumatoid arthritis. The synergism between kinins and IL-1b or TNF-a might also be dependent on regulation of kinin receptors, since both IL-1b and TNF-a markedly upregulated B1 and B2 receptors, both at the mRNA level and protein level (Paper III). This upregulation is not further potentiated by the kinins, and different kinin receptor agonists do not regulate the receptors for IL-1b or TNF-a, in MG-63 cells. No other cytokines known to stimulate bone resorption regulates the expressions of B1 and B2 receptors. The IL-1b- or TNF-a-induced enhancements of B1 and B2 receptor expressions involve activation of NF-kB and MAPK. The enhancement of kinin receptors may also be an important mechanism in the synergistic interactions between the two pro-inflammatory cytokines and kinins (paper III). IL-4 and IL-13 are two cytokines that have been shown to inhibit bone resorption. We have shown that COX-2 and both B1 and B2 receptors are down-regulated by IL-4 and IL-13, via a ‘signal transducer and activator of transcription6’ (STAT6) dependent pathway, which might be an important regulatory mechanism in inflammation induced bone resorption (paper IV). In conclusion, the mechanisms behind the synergistic potentiation of prostaglandin formation and increased bone resorption caused by co-stimulation with kinins and IL-1b or TNF-a seem to involve both potentiation of COX-2 and subsequently increased levels of RANKL, as well as upregulation of B1 and B2 kinin receptors. Interestingly, IL-4 and IL-13 decreased the expressions of COX-2 and both B1 and B2 receptors. These events might be important in the regulation of inflammation induced bone resorption in diseases such as periodontitis and rheumatoid arthritis.
|
|
| 4. |
- Brechter, Anna Bernhold, et al.
(författare)
-
Kinin B1 and B2 receptor expression in osteoblasts and fibroblasts is enhanced by interleukin-1 and tumour necrosis factor-alpha. Effects dependent on activation of NF-kappaB and MAP kinases.
- 2008
-
Ingår i: Bone. - : Elsevier BV. - 8756-3282 .- 1873-2763. ; 43:1, s. 72-83
-
Tidskriftsartikel (refereegranskat)abstract
- 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-Arg10-Lys-BK (DALBK), IL-1beta and TNF-alpha have been investigated. IL-1beta 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-1beta and TNF-alpha activated NF-kappaB and AP-1 in MG-63 cells. IL-1beta stimulated NF-kappaB 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-1beta and TNF-alpha stimulated cells, but c-Fos only in TNF-alpha stimulated cells. Phospho-ELISA and Western blots showed that IL-1beta activated JNK and p38, but not ERK 1/2 MAP kinase. Pharmacological inhibitors showed that NF-kappaB, p38 and JNK were important for IL-1beta induced stimulation of B1 receptors, and NF-kappaB and p38 for B2 receptors. p38 and JNK were important for TNF-alpha induced stimulation of B1 receptors, whereas NF-kappaB, p38 and JNK were involved in TNF-alpha induced expression of B2 receptors. These data show that IL-1beta and TNF-alpha upregulate B1 and B2 receptor expression by mechanisms involving activation of both NF-kappaB and MAP kinase pathways, but that signal transduction pathways are different for IL-1beta and TNF-alpha. The enhanced kinin receptor expression induced by the pro-inflammatory cytokines IL-1beta 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.
|
|
