Expression of the mRNA for types I and II interleukin-1 receptors in dental tissues of mice during tooth development

IL-1α Regulates Osteogenesis and Osteoclastic Activity of Dental Follicle Cells Through JNK and p38 MAPK Pathways

Inflammatory cytokines such as interleukin-1α (IL-1α) are increased in teeth with periapical lesions. Primary teeth with periapical lesions have a propensity for accelerated eruption of the successors. In this study, we asked whether increased levels of IL-1α in the dental follicle (DF) occurring as the result of periapical lesions promote tooth eruption, possibly due to enhanced osteoclastic remodeling of DF cells (DFCs). To this end, we studied the effect and possible mechanism of IL-1α on osteogenic differentiation, osteoclastogenic activity, and matrix remodeling of DFCs. Results demonstrated that DFCs cultured with IL-1α exhibited reduced osteogenic capacity, higher osteoclastogenic activity, and stronger invasive ability. Phosphorylation of JNK and p38 was upregulated, and pretreatment with SB203580 and SP600125 reversed the effect of IL-1α on DFCs. Neonatal rats subjected to subcutaneous injection of an IL-1 receptor antagonist exhibited a reduced number in activated osteoclasts, increased expression of alkaline phosphatase and osteopontin, and delayed tooth eruption. These data support our hypothesis that increased IL-1α cytokine levels as they occur during periodontal and periapical inflammation cause osteoclastic remodeling of the alveolar socket as a requirement for tooth eruption and thus may indirectly promote the vertical eruption of teeth toward the occlusal plane.

Extremely High Expression of Antisense RNA for Wilms' Tumor 1 in Active Osteoclasts: Suppression of Wilms' Tumor 1 Protein Expression during Osteoclastogenesis

Wilms' tumor 1 (WT1), a zinc-finger transcription regulator of the early growth response family, identified as the product of a tumor suppressor gene of Wilms' tumors, bears potential ability to induce macrophage differentiation in blood cell differentiation. Herein, we examined the involvement of WT1 in the regulation of osteoclastogenesis. We detected a high level of WT1 protein expression in osteoclast precursors; however, WT1 expression was markedly suppressed during osteoclastogenesis. We examined expression of WT1 transcripts in bone tissue by RNA in situ hybridization. We found a high level of antisense transcripts in osteoclasts actively resorbing bone in mandible of newborn rats. Expression of antisense WT1 RNA in mandible was also confirmed by Northern blot analysis and strand-specific RT-PCR. Overexpression of antisense WT1 RNA in RAW-D cells, an osteoclast precursor cell line, resulted in a marked enhancement of osteoclastogenesis, suggesting that antisense WT1 RNA functions to suppress expression of WT1 protein in osteoclastogenesis. High level expression of antisense WT1 RNA may contribute to commitment to osteoclastogenesis, and may allow osteoclasts to maintain or stabilize their differentiation state.

Immunolocalization of TAK1, TAB1, and p38 in the developing rat molar

In tooth development, transforming growth factor beta (TGF-β) and bone morphogenetic protein (BMP) are involved in cell differentiation and matrix protein production. TGF-β and BMP have two signaling pathways: the Smad pathway and the non-Smad pathway. However, only a few studies have focused on the non-Smad pathway in tooth development. TGF-β-activated kinase 1 (TAK1) is activated by TGF-β or BMP and binds to TAK1-binding protein (TAB1), activating p38 or c-Jun N-terminal kinase (JNK), forming the non-Smad signaling pathway. In this study, we examined the distribution of these kinases, TGF-β receptor 1 (TGF-β-R1), BMP receptor-1B (BMPR-1B) and Smad4 in cells of the rat molar germ histochemically, in order to investigate the signaling pathway in each type of cell. Immunostaining for TGF-β-R1, BMPR-1B, Smad4, TAK1, TAB1 and phosphorylated-p38 (p-p38) showed similar reactions. In the cervical loop, reactions were clearer than in other enamel epithelium. In the inner enamel epithelium, signal increased with differentiation into ameloblasts, became strongest in the secretory stage, and decreased rapidly in the maturation stage. Signal also increased upon differentiation from preodontoblasts to odontoblasts. In Hertwig's epithelial sheath, with the exception of BMPR-1B, reactions were stronger in the later stage, showing more enamel protein secretion than in the early stage. However, no clear reaction corresponding to phosphorylated-JNK was observed in any type of cell. These results suggest that TGF-β or BMP is involved in the induction of differentiation of inner enamel epithelium cells into ameloblasts, and preodontoblast differentiation into odontoblasts, the regulation of cervical loop cell proliferation, the elongation or regulation of the epithelial sheath, and the secretion of enamel protein and dentin matrix protein through the non-Smad signaling pathway via TAK1, TAB1 and p38 as well as Smad signaling pathways in the rat molar germ.

Comparison of dentoalveolar morphology in WT and P2X7R KO mice for the development of biomechanical orthodontic models

It has been suggested that the absence of the P2X7 receptor affects long bone morphology, and that one of the cytokines dependent on its activation may also affect tooth morphology. P2X7R KO (knockout) were compared with C57B/6 WT mice (background strain) to identify differences in a maxillary molar and surrounding bone. Nineteen WT and 12 KO mouse maxillae were scanned and 3D-reconstructed using microCT. Tooth dimensions were measured and 3D bone morphometry was conducted. A finite element model was constructed based on the results. No statistically significant differences were found in dentoalveolar characteristics between the two mouse types. A single finite element model of the tooth can be used to mechanically represent both strains. P2X7R does not have a major effect on alveolar bone or tooth morphology. The P2X7R effects are site-specific.

Effect of soluble receptors to interleukin-1 and tumor necrosis factor alpha on experimentally induced root resorption in rats

OBJECTIVE

In this study, the role of the inflammatory cytokines interleukin-1 (IL-1) and tumor necrosis factor alpha (TNFalpha) in the course of mechanically induced root resorption was investigated.

METHODS

Mechanical induction of root resorption was performed on the upper left first molars in 18 male Wistar rats according to the method of Nakane and Kameyama. Starting on day minus 1, six animals received daily intraperitoneal injections of 2 ml of 1 micro g/ml soluble receptors to IL-1 (sIL-1RII) and another six animals were administered the same dose of soluble receptors to TNFalpha (sTNFalpha-RI). Six animals served as a control. On d 7 the left maxillae were prepared for histological and morphometric analysis of the extent of the root resorption that had developed.

RESULTS

The qualitative and quantitative results demonstrated that in both receptor groups the amount of root resorption was significantly reduced. Especially following systemic application of sTNFalpha-RI, root resorption was nearly completely prevented.

CONCLUSIONS

Our results indicate that IL-1 and more particularly TNFalpha are important for the induction and the further process of mechanically induced root resorption in the rat.

Bone loss. Therapeutic approaches for preventing bone loss in inflammatory arthritis

Inflammatory arthritides are commonly characterized by localized and generalized bone loss. Localized bone loss in the form of joint erosions and periarticular osteopenia is a hallmark of rheumatoid arthritis, the prototype of inflammatory arthritis. Recent studies have highlighted the importance of receptor activator of nuclear factor-kappa B ligand (RANKL)-dependent osteoclast activation by inflammatory cells and subsequent bone loss. In this article, we review the pathogenesis of inflammatory bone loss and explore the possible therapeutic interventions to prevent it.

Activation of osteoclasts by interleukin-1: divergent responsiveness in osteoclasts formed in vivo and in vitro

Recently, it has been found that osteoclasts are induced and activated by osteoblastic cells through expression of receptor activator NF-kB ligand (RANKL), and that soluble recombinant RANKL, with M-CSF, can replace the need for osteoblastic cells in osteoclast formation. We exploited this opportunity to compare the responsiveness of osteoclast-like cells (OCL) formed in vitro in the absence of osteoblasts, with that of osteoclasts ex vivo. We found that while OCL responded to several hormones and cytokines like ex vivo osteoclasts, their responsiveness to interleukin-1 (IL-1) was fundamentally different: IL1 directly stimulated actin ring formation in OCL, but had no effect on actin rings or survival in osteoclasts ex vivo unless osteoblastic cells were present. This difference could not be attributed to the use of plastic culture substrates for OCL formation, nor to osteoblastic contamination, and did not seem to be mediated by the macrophages that form in OCL cultures. To understand the mechanisms by which IL-1 induces bone loss, it will need to be determined whether or not IL-1-responsive OCLs have a counterpart in vivo. Whichever is the case, our data suggest that the behavior of osteoclasts formed in culture will not always predict that of osteoclasts in vivo.