Mami Shimizu

Notch Signaling Induces Root Resorption via RANKL and IL-6 from hPDL Cells

In this study, we first investigated the expressions of Jagged1, Notch2, the receptor activator of nuclear factor–kappa B ligand (RANKL), and interleukin (IL)-6 in areas of root resorption during experimental tooth movement in rats in vivo. We then assessed the effects of compression force (CF) with or without GSI (an inhibitor of Notch signaling) on Jagged1, RANKL, and IL-6 release from human periodontal ligament (hPDL) cells. Twelve male 6-wk-old Wistar rats were subjected to an orthodontic force of 50 g to induce mesially tipping movement of the upper first molars for 7 d. The expression levels of tartrate-resistant acid phosphatase, Jagged1, Notch2, IL-6, and RANKL proteins in the dental root were determined using an immunohistochemical analysis. Furthermore, the effects of the CF on Jagged1, IL-6, and RANKL production were investigated using hPDL cells in vitro. The effects of the cell-conditioned medium obtained from the hPDL cells subjected to CF (CFM) and Jagged 1 on osteoclastogenesis of human osteoclast precursor cells (hOCPs) were also investigated. Under the conditions of experimental tooth movement in vivo, resorption lacunae with multinucleated cells were observed in the 50 g group. In addition, immunoreactivity for Jagged1, Notch2, IL-6, and RANKL was detected on day 7 in the PDL tissue subjected to the orthodontic force. In the in vitro study, the compression force increased the production of Jagged1, IL-6, and RANKL from the hPDL cells, whereas treatment with GSI inhibited the production of these factors in vitro. The osteoclastogenesis increased with the CFM and rhJagged1, and the increase in the osteoclastogenesis was almost inhibited by GSI. These results suggest that the Notch signaling response to excessive orthodontic forces stimulates the process of root resorption via RANKL and IL-6 production from hPDL cells.

Interleukin-17/T-helper 17 cells in an atopic dermatitis mouse model aggravate orthodontic root resorption in dental pulp.

Interleukin (IL)-17 is an important mediator of orthodontically induced inflammatory root resorption (OIIRR). However, its role in the dental pulp (DP) has not been studied. The aim of this study was to investigate, using an atopic dermatitis (AD) model, how IL-17 contributes to OIIRR in DP. Atopic dermatitis is the most common IL-17-associated allergic disease. Atopic dermatitis model mice (AD group) and wild-type mice (control group) were subjected to an excessive orthodontic force. The localization of T-helper (Th)17 cells, IL-17, IL-6, and keratinocyte chemoattractant (KC; an IL-8-related protein in rodents) were determined in DP. In addition, CD4+ T cells, including IL-17 production cells, were obtained from patients with AD and from healthy donors, and the effects of IL-17 on the production of IL-6 and IL-8 were investigated using a co-culture of CD4+ T cells with human dental pulp (hDP) cells stimulated with substance P (SP). Immunoreactivity for Th17 cells, IL-17, IL-6, and KC was increased in DP tissue subjected to orthodontic force in the AD group compared with DP tissue subjected to orthodontic force in the control group. The cells obtained from the AD patients displayed increased IL-6 and IL-8 production. These results suggest that IL-17 may aggravate OIIRR in DP.

Interleukin-17 is involved in orthodontically induced inflammatory root resorption in dental pulp cells

INTRODUCTION The objectives of this study were (1) to investigate the expressions of interleukin (IL)-17, RANKL (the receptor activator of NF-kappaB ligand), and osteoprotegerin (OPG) in root resorption areas during experimental tooth movement in rats, and (2) to determine the effect of IL-17 on the expressions of RANKL and OPG mRNA from human dental pulp cells. METHODS Twelve male 6-week-old Wistar rats were subjected to an orthodontic force of 50 g to induce a mesially tipping movement of the maxillary first molars for 7 days. The expression levels of tartrate resistant acid phosphatase (TRAP), interleukin (IL)-17, IL-17 receptor (IL-17R), receptor activator of nuclear factor-kappa B ligand (RANKL), and OPG proteins were determined in dental pulp by immunohistochemical analysis. Furthermore, the effects of IL-17 on the expressions of RANKL and OPG mRNA were investigated using human dental pulp cells in vitro. RESULTS In the experimental tooth movements in vivo, resorption lacunae with multinucleated cells were observed in the 50-g group. The immunoreactivities for IL-17, IL-17R, and RANKL were detected in dental pulp tissues subjected to the orthodontic force on day 7. Moreover, IL-17 increased the mRNA expression of RANKL from human dental pulp cells in vitro. CONCLUSIONS The results of this study suggest that IL-17 and RANKL may be involved in the process of orthodontically induced inflammatory root resorption in dental pulp cells.

Effect of caspases and RANKL induced by heavy force in orthodontic root resorption

Objective Orthodontic root resorption (ORR) due to orthodontic tooth movement is a difficult treatment-related adverse event. Caspases are important effector molecules for apoptosis. At present, little is known about the mechanisms underlying ORR and apoptosis in the cementum. The aim of the present in vivo study was to investigate the expression of tartrate-resistant acid phosphatase (TRAP), caspase 3, caspase 8, and receptor activator of nuclear factor kappa-B ligand (RANKL) in the cementum in response to a heavy or an optimum orthodontic force. Methods The maxillary molars of male Wistar rats were subjected to an orthodontic force of 10 g or 50 g using a closed coil spring. The rats were sacrificed each experimental period on days 1, 3, 5, and 7 after orthodontic force application. And the rats were subjected to histopathological and immunohistochemical analyses. Results On day 7 for the 50-g group, hematoxylin and eosin staining revealed numerous root resorption lacunae with odontoclasts on the root, while immunohistochemistry showed increased TRAP- and RANKL-positive cells. Caspase 3- and caspase 8-positive cells were increased on the cementum surfaces in the 50-g group on days 3 and 5. Moreover, the number of caspase 3- and caspase 8-positive cells and RANKL-positive cells was significantly higher in the 50-g group than in the 10-g group. Conclusions In our rat model, ORR occurred after apoptosis was induced in the cementum by a heavy orthodontic force. These findings suggest that apoptosis of cementoblasts is involved in ORR.

Relationship between root resorption and individual variation in the calcium/phosphorous ratio of cementum

Introduction The purpose of this study was to investigate whether individual variation in the hardness and chemical composition of the cementum in the root apex affects the degree of root resorption. Methods In a previous study, we evaluated the Vickers hardness scale of 50 extracted teeth. For this study, we classified the 50 extracted teeth into soft, moderate, and hard groups according to the Vickers hardness scale. Then, we randomly selected 7 teeth from each group and measured the resorbed areas of the apical cementum in vitro using human osteoclast precursor cells. We also investigated the calcium/phosphorous (Ca/P) and magnesium/calcium ratios of these 21 extracted teeth using energy‐dispersive x‐ray microanalysis studies to determine the chemical composition of the cementum in the root apex. Results In the pit formation assay, the resorbed area in the soft group showed a greater extent than it did in the moderate and hard groups (P < 0.01). A correlation was noted between the Vickers hardness and the resorbed area of the cementum in the root apex (r = −0.714; P < 0.01). The Ca/P ratios in the soft and moderate groups were lower than the ratio in the hard group (P < 0.01 and P < 0.05, respectively). A correlation was noted between the Vickers hardness and the Ca/P ratio of the cementum in the root apex (r = 0.741; P < 0.01). Conclusions These results suggest that the hardness and Ca/P ratio of the cementum may be involved in root resorption caused by orthodontic forces. HighlightsHardness and chemical composition were assayed in the cementum of extracted teeth.The resorbed area was greater in the soft group than in the moderate and hard groups.Ca/P ratio of the apical cementum was lower in the soft and moderate groups.Hardness and Ca/P ratio of the cementum may be involved in root resorption.

Notch signaling induces root resorption via RANKL and IL-6 from hPDL cells

The Notch signaling plays an important role in osteoblast and osteoclast differentiation. However, the role of Notch signaling in root resorption during orthodontic treatment is not yet fully understood. In this study, we first investigated the expressions of Jagged1, RANKL and IL-6 in areas of root resorption during experimental tooth movement in rats in vivo. We then assessed the effects of compression forces (CF) with/without GSI (an inhibitor of Notch signaling)on Jagged1,RANKL, and IL-6release from human periodontal ligament (hPDL) cells. Twelve male Wistar rats were subjected to an orthodontic force of 50 g in order to induce mesially tipping movement of the upper first molars for 7 days. The expression levels of TRAP, Jagged1, Notch2, RANKL and IL-6 proteins in the dental root were determined using an immunohistochemical analysis. Furthermore, the effects of the CF on Jagged1, RANKL and IL-6 production were investigated using hPDL cells in vitro. The effects of the cell-conditioned medium obtained from the hPDL cells subjected to CF (CFM) and Jagged1 (rhJagged1) on osteoclastogenesis of human osteoclast precursor cells (hOCPs) also investigated. Under theconditions of experimental tooth movement in vivo, resorption lacunae with multinucleated cells were observed in the 50 g group. In addition, immunoreactivity for TRAP, Jagged1, Notch2, RANKL and IL-6 was detected on day 7 in the PDL tissue subjected to the orthodontic force. In the in vitro study, the compression force increased the production of Jagged1, RANKL and IL-6 from the hPDL cells, while treatment with GSI inhibited the production of RANKL and IL-6 in vitro. The osteoclastogenesis increased by the CFM and rhJagged1, and the increase in the osteoclastogenesis was almost inhibited by GSI. These results suggest that the Notch signaling response to excessive orthodontic forces stimulates the process of root resorption via RANKL and IL-6 production from hPDL cells.