Mechanical stimulation induces CTGF expression in rat osteocytes

Connective tissue growth factor (CTGF), which is encoded by an immediate early gene and a member of the CCN family, has been shown to be expressed in osteoblasts, fibroblasts, and chondrocytes. Although CTGF is expressed in bone and cartilage tissues, we tested the hypothesis that CTGF is regulated in mechanotransduction. In the alveolar bone during experimental tooth movement, CTGF mRNA was expressed in osteoblasts and in osteocytes localized around the periodontal ligament under control conditions. Interestingly, 12 hrs after the start of experimental tooth movement, the expression of CTGF mRNA in osteocytes and osteoblasts became more intense around the periodontal ligament, and the intense expression of CTGF extended to osteocytes situated deep in alveolar bone matrix apart from periodontal ligament in both tension and compression sides. Our present findings indicate that CTGF could play a role in regulation of osteocyte function during the mechanical stimulation of bone.     

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??Sclerostin/SOST??mainly expressed in osteocytes??is a negative regulator of bone formation and is regulated by mechanical stimulus??which plays an important role in orthodontic tooth movement. Wnt and BMP are two important signaling pathways in bone metabolic regulation. SOST can regulate osteoblastic differentiation and bone formation by binding type ??or??receptors and co-receptor LRP5/6 to inhibit BMP and Wnt signaling pathways. This review covers the effect of Sclerostin/SOST on orthodontic tooth movement after mechanical loading and its mechanism??and the clinical significance as well as prospect of Sclerostin/SOST in clinical application.     

The role of osteocytes during experimental orthodontic tooth movement: A review

ObjectiveTo explore the types of orthodontic force-induced mechanical stimuli that regulate osteocyte function.DesignIn orthodontics, a tooth can be moved through the alveolar bone when an appropriate orthodontic force is applied. These mechanical loads stimulate cells within the bone tissue around the tooth. These cellular responses lead to bone resorption on the side of the tooth where the pressure has been applied and bone deposition on the side of the tooth experiencing tension. Recently, osteocytes were identified to function as mechano-sensory cells in bone tissue that direct bone resorption and bone formation. Based on recent literature, the proposed function of osteocytes during orthodontic tooth movement is explored with better understanding.ResultsSeveral stimuli regulating osteocyte function have been highlighted, and their potential roles in events initiating osteocyte sensing of orthodontic force have been explored in detail. The most popular hypotheses for osteocyte response include stress-induced bone matrix deformation/microcrack formation and fluid-flow shear stress.ConclusionsUnderstanding osteocyte function under mechanical stress may have profound implications in future orthodontic treatments.     

Wnt signaling in the murine diastema

The correct number and shape of teeth are critical factors for an aesthetic and functional dentition. Understanding the molecular mechanisms regulating tooth number and shape are therefore important in orthodontics. Mice have only one incisor and three molars in each jaw quadrant that are divided by a tooth-less region, the diastema. Although mice lost teeth in the diastema during evolution, the remnants of the evolutionary lost teeth are observed as transient epithelial buds in the wild-type diastema during early stages of development. Shh and Fgf signaling pathways that are essential for tooth development have been shown to be repressed in the diastema. It remains unclear however how Wnt signaling, that is also required for tooth development, is regulated in the diastema. In this study we found that in the embryonic diastema, Wnt5a expression was observed in mesenchyme, whereas Wnt4 and Wnt10b were expressed in epithelium. The expression of Wnt6 and Wnt11 was found in both tissues. The Wnt co-receptor, Lrp6, was weakly expressed in the diastema overlapping with weak Lrp4 expression, a co-receptor that inhibits Wnt signaling. Secreted Wnt inihibitors Dkk1, Dkk2, and Dkk3 were also expressed in the diastema. Lrp4 mutant mice develop supernumerary teeth in the diastema that is accompanied by upregulation of Wnt signaling and Lrp6 expression. Wnt signaling is thus usually attenuated in the diastema by these secreted and membrane bound Wnt inhibitors.     

Wnt信号通路与骨细胞生物力刺激信号转导间的关系

Wnt信号通路是体内重要的信号调节系统之一,而骨细胞作为骨组织中最主要的应力感受细胞,受载后可引起其内部Wnt信号通路的快速激活,最终调节其基因表达,影响骨改建。该激活过程受诸多调控因子的影响。本文就Wnt信号通路与骨细胞生物力刺激信号转导间的关系,以及该信号转导过程中Wnt信号通路的调控因子等研究进展作一综述。     

In situ hybridization for matrix metalloproteinase-1 and cathepsin K in rat root-resorbing tissue induced by tooth movement

The movement of teeth during orthodontic treatment occasionally induces undesirable root resorption. Although high collagenolytic activity has been detected in resorbing tissue of deciduous teeth, the cellular origin of collagenolytic enzymes in root-resorbing tissue caused by tooth movement has not been identified. Here, rats were subject to 7 days of experimental tooth movement to induce root resorption. In situ hybridization with digoxigenin-labelled RNA probes was performed on sections of the maxillary bone to detect the mRNAs that encode matrix metalloproteinase-1 (MMP-1) and cathepsin K in root-resorbing tissue. MMP-1 mRNA was detected in fibroblastic cells, cementoblasts and osteoblasts, but not in odontoclasts nor osteoclasts. Moreover, MMP-1 mRNA was highly expressed in some cementocytes located near odontoclasts and in many osteocytes. In contrast, cathepsin K mRNA was expressed only in odontoclasts and osteoclasts. These results suggest that MMP-1 and cathepsin K are important in root resorption during tooth movement in a mode similar to bone resorption.     

骨硬化蛋白对牙骨质形成的影响及其机制

骨硬化蛋白是一种含有胱氨酸结的分泌型糖蛋白,可通过骨细胞突触传递至骨表面并作用于周围的成骨细胞,从而降低骨的发生发育速度。其机制在于骨硬化蛋白与无翅型小鼠乳房肿瘤病毒整合位点家族蛋白竞争性地结合辅助受体低密度脂蛋白受体相关蛋白5/6,促进β-连环蛋白磷酸化并降低β-连环蛋白水平,从而抑制成骨细胞的分化及活性。牙骨质为连接牙体和牙周组织间的桥梁,其功能在于维系牙体的稳固和牙周组织的健康。骨硬化蛋白参与并影响牙骨质的发生发育等各种生理性活动,因此进一步深入探讨骨硬化蛋白这一骨形成负性调控因子与牙骨质间的相互作用和机制,将有助于牙骨质相关再生领域的发展。     

Temporal and spatial mRNA expression of bone sialoprotein and type I collagen during rodent tooth movement.

To investigate the mechanism of bone formation during tooth movement, in situ hybridization was performed with digoxigenin-labelled RNA probes to detect bone sialoprotein (BSP) and type I collagen mRNAs in the dentoalveolar tissue of 72 Sprague-Dawley rats. An elastic band was inserted between the first and second right maxillary molars, and the teeth experimentally moved for 1, 3, and 7 days. The left first maxillary molar was used as the control. For the untreated molars, osteoblasts and osteocytes near the distal surface of the interradicular septum (IRS) expressed a high level of both BSP and type I collagen mRNAs, while cells on the mesial side of the IRS showed a low level of these mRNAs. For the first molars subjected to experimental tooth movement, a high level of type I collagen mRNA expression was found in the osteoblasts on the tension side of the IRS after 1 day of experimental tooth movement. A high level of BSP mRNA was detected after 3 days of experimental tooth movement. However, a negligible amount of both mRNAs was found in cells on the compression side. These results support the hypothesis that BSP may be involved in mineralization during physiological bone remodelling. On application of orthodontic force, osteoblasts were activated and induced to express BSP mRNA, which is involved in bone remodelling due to orthodontic force. In addition, response to the orthodontic force was observed in osteocytes.     

Functional analysis of a novel missense mutation in AXIN2 associated with non‐syndromic tooth agenesis

Tooth agenesis is a congenital anomaly frequently seen in humans. Several genes have been associated with non‐syndromic tooth agenesis, including msh homeobox 1 (MSX1), paired box 9 (PAX9), axis inhibition protein 2 (AXIN2), ectodysplasin A (EDA), and wingless‐type MMTV integration site family member 10A (WNT10A). In this study, we investigated a Chinese family with non‐syndromic tooth agenesis. A novel missense mutation (c.C1978T) in AXIN2 was identified in affected members. The mutation results in a His660Tyr substitution located between the Axin beta‐catenin binding domain and the DIX domain of the axis inhibition protein 2 (AXIN2). We analysed this novel AXIN2 mutant, together with two reported AXIN2 mutants [c.1966C>T (p.Arg656Stop) and c.1994delG (p.Leu688Stop)] that cause colorectal cancer with and without oligodontia, to study the effect of the mutant p.His660Tyr on the Wnt/β‐catenin signaling pathway and to compare the molecular pathogenesis of different AXIN2 mutants in tooth agenesis and carcinogenesis. Further in vitro experiments indicated that the mutant p.His660Tyr caused inhibition of the Wnt/β‐catenin pathway, and the mutants p.Arg656Stop and p.Leu688Stop resulted in over‐activation of the Wnt/β‐catenin pathway. In line with previous AXIN2 mutation studies, we suggest that AXIN2 mutations with different levels of severity may have distinct effects on the Wnt pathway and the phenotype of disease. Our study provides functional evidence supporting the notion that both inhibition and over‐activation of the Wnt pathway may lead to tooth agenesis.     

Fluid shear stress inhibits TNFalpha-induced osteocyte apoptosis

Bone tissue can adapt to orthodontic load. Mechanosensing in bone is primarily a task for the osteocytes, which translate the canalicular flow resulting from bone loading into osteoclast and osteoblast recruiting signals. Apoptotic osteocytes attract osteoclasts, and inhibition of osteocyte apoptosis can therefore affect bone remodeling. Since TNF-alpha is a pro-inflammatory cytokine with apoptotic potency, and elevated levels are found in the gingival sulcus during orthodontic tooth movement, we investigated if mechanical loading by pulsating fluid flow affects TNF-alpha-induced apoptosis in chicken osteocytes, osteoblasts, and periosteal fibroblasts. During fluid stasis, TNF-alpha increased apoptosis by more than two-fold in both osteocytes and osteoblasts, but not in periosteal fibroblasts. One-hour pulsating fluid flow (0.70 +/- 0.30 Pa, 5 Hz) inhibited (-25%) TNF-alpha-induced apoptosis in osteocytes, but not in osteoblasts or periosteal fibroblasts, suggesting a key regulatory role for osteocyte apoptosis in bone remodeling after the application of an orthodontic load.     

Wnt5a调控牙源性干细胞作用研究进展

Wnt5a是非经典Wnt蛋白中具有代表性的蛋白,其介导的非经典Wnt信号具有调控细胞增殖、分化、迁移和极化的作用。近年来研究发现,Wnt5a及其介导的信号通路在调控牙源性干细胞方面起重要作用,其机制成为牙组织工程学研究热点,也为牙再生提供了新的思路。以下仅对Wnt5a及其介导的信号通路在牙源性干细胞方面的研究进展做一综述。     

Aggregatibacter actinomycetemcomitans,a potent immunoregulator of the periodontal host defense system and alveolar bone homeostasis

Aggregatibacter actinomycetemcomitans is a perio‐pathogenic bacteria that has long been associated with localized aggressive periodontitis. The mechanisms of its pathogenicity have been studied in humans and preclinical experimental models. Although different serotypes of A. actinomycetemcomitans have differential virulence factor expression, A. actinomycetemcomitans cytolethal distending toxin (CDT), leukotoxin, and lipopolysaccharide (LPS) have been most extensively studied in the context of modulating the host immune response. Following colonization and attachment in the oral cavity, A. actinomycetemcomitans employs CDT, leukotoxin, and LPS to evade host innate defense mechanisms and drive a pathophysiologic inflammatory response. This supra‐physiologic immune response state perturbs normal periodontal tissue remodeling/turnover and ultimately has catabolic effects on periodontal tissue homeostasis. In this review, we have divided the host response into two systems: non‐hematopoietic and hematopoietic. Non‐hematopoietic barriers include epithelium and fibroblasts that initiate the innate immune host response. The hematopoietic system contains lymphoid and myeloid‐derived cell lineages that are responsible for expanding the immune response and driving the pathophysiologic inflammatory state in the local periodontal microenvironment. Effector systems and signaling transduction pathways activated and utilized in response to A. actinomycetemcomitans will be discussed to further delineate immune cell mechanisms during A. actinomycetemcomitans infection. Finally, we will discuss the osteo‐immunomodulatory effects induced by A. actinomycetemcomitans and dissect the catabolic disruption of balanced osteoclast–osteoblast‐mediated bone remodeling, which subsequently leads to net alveolar bone loss.     

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??Wnt5a is a representative noncanonical Wnt molecule and the nocanonical Wnt signalling pathway induced by it regulates a variety of cellular functions??such as proliferation??differentiation??migration?? adhesion and polarity. Recent studies have shown that Wnt5a and its signaling pathways play a pivotal role in the regulation of dental mesenchymal stem cells??DMSCs???? whose mechanism has become a hot topic for tooth tissue engineering??providing a new way of thinking for dental tissue regeneration. In this paper??the new researches on Wnt5a and its mediated signaling pathways in terms of dental stem cells were overviewed.     

Bone modeling: biomechanics, molecular mechanisms, and clinical perspectives

Bone modeling is a mechanically mediated adaptive process for changing a bone’s size, shape, or position. Site specific, anabolic and catabolic modeling events are manifestations of overload hypertrophy and disuse atrophy, respectively. Catabolic bone modeling at the periodontal ligament (PDL) surface is the rate-limiting step in tooth movement. In initiating tooth movement, connective tissue growth factor (CTGF) is expressed in osteoblasts and osteocytes, and osteopontin (Opn) is expressed by osteoclasts and osteocytes. Undermining resorption occurs by recruiting osteoclasts to the site of maximal PDL compression and a paravascular osteogenic response is initiated in widened areas of the PDL: (1) preosteoblast formation at 10 hours, (2) peak DNA synthesis at 20 hours, (3) maximum rate of mitosis at 30 hours, and (4) initiation of bone formation at 48 hours. At other skeletal sites, additional genes have been linked to mechanical activation of bone: glutamate/aspartate transporter (GLAST), nitric oxide synthetase (NOS), prostaglandin G/H synthetase (PGHS-2), Msx1, and c-fos. An intricate series of endocrine, paracrine, and autocrine factors has been described. Parathyroid hormone (PTH) enhances expression of insulin-like growth factor I (IGF-I) and the estrogen receptor beta (ER-β), which are both modulators of mechanical loading. Transforming growth factor beta (TGF-β) and the related bone morphogenetic proteins (BMPs) help control anabolic modeling. Catabolic modeling is mediated by PGE2, IL-1β, and other inflammatory cytokines. Osteoclast differentiation and activation is controlled by genes related to tumor necrosis factor (TNF) and its receptor (TNFR): colony stimulating factor 1 (CSF-1), osteoprotegerin (OPG), receptor activator of nuclear factor (RANK), and RANK ligand (RANKL). Orthodontic aspects of bone modeling are reviewed relative to morphology, biomechanics, neurology, molecular control mechanisms, and the periodontal adaptation to loading. Clinical correlations discussed are orthodontic analgesics, inflammatory cytokines, surgical enhancement of tooth movement, distraction osteogenesis, closure of atrophic defects, periodontal compromise, traumatized periodontium, and systemic disease.     

大鼠正畸牙移动中牙周组织Wnt10b和β-catenin的表达研究

［摘要］目的：通过观察Wnt10b和β-catenin在大鼠正畸牙齿移动牙周组织中的表达,初步探讨Wnt10b和β-catenin在正畸牙齿移动牙周组织改建中的作用。方法：建立30只雄性SD大鼠左侧上颌第一磨牙近中移动模型。右侧上颌第一磨牙不加力作为自身对照。分别在牙齿移动1d、3d、5d、7d、10d、14d时处死动物,制取上颌标本。进行免疫组织化学分析。结果：对照组大鼠牙周组织中,Wnt10b和β-catenin低表达。实验组牙周组织中,β-catenin表达增加在各时间点均有显著差异,Wnt10b仅在5d、7d、10d时有显著差异。结论：Wnt10b和β-catenin参与了正畸牙齿移动中牙周组织改建。     

Low‐energy laser irradiation accelerates the velocity of tooth movement via stimulation of the alveolar bone remodeling

Authors – Yoshida T, Yamaguchi M, Utsunomiya T, Kato M, Arai Y, Kaneda T, Yamamoto H, Kasai K Introduction – Previously, the authors have reported the acceleration of tooth movement and osteoclastogenesis on the pressure site in an experimental tooth movement model by low‐energy laser irradiation (LELI), which stimulated the RANK/RANKL system and c‐fms/macrophage colony‐stimulating factor system. However, the effect of LELI on osteogenesis on the tension site is not known clearly. Moreover, the temporal changes in alveolar bone during tooth movement have not been investigated as yet. Therefore, the present study was designed to examine the effects of LELI on alveolar bone remodeling during experimental tooth movement, and observe the temporal bone mineral density (BMD) using micro‐computed tomography (μCT). Materials and methods – To induce experimental tooth movement in rats, 10 g force was applied to the upper right first molar with Nickel titanium closed‐coil. Next, a gallium‐aluminum‐arsenide (Ga‐Al‐As) diode laser was used to irradiate the area around the moved tooth, and BMD and the amount of tooth movement were measured by μCT scanning for 21 days. Histopathological examination was also performed. Results – The amount of tooth movement in the LELI group was significantly greater than in the non‐irradiation group by the end of the experimental period. Further, compared with the non‐irradiation group, the fall of BMD was less in the LELI group. Conclusion – These findings suggest that LELI accelerates the velocity of tooth movement via stimulation of the alveolar bone remodeling.     

大鼠正畸牙齿移动过程中Wnt3a和DKK1的表达

目的:观察Wnt3a和DKK1在大鼠正畸牙移动时牙周组织中的表达变化。方法:将30只健康雄性SD大鼠随机分为6组,即正畸加力1,3,5,7,10,14 d组。使用镍钛拉簧施加50 g力近中移动左侧上颌第一磨牙,以右侧上颌第一磨牙不加力为自身对照。通过免疫组化方法检测牙周组织中Wnt3a和DKK1蛋白的表达。结果:Wnt3a和DKK1在加力组和未加力组的牙周膜中都有表达。在张力区,Wnt3a和DKK1都先增加后减少,分别在第5天和第10天达到高峰;在压力区,Wnt3a先减少后增加,DKK1先增加后减少,分别在第5天和第10天达峰值。结论:Wnt3a和DKK1参与牙周组织的改建,提示Wnt信号通路可能是正畸牙周改建的调控途径之一。[关键词] Wnt3a DKK1 正畸牙齿移动 牙周组织改建     

Sclerostin and its role as a bone modifying agent in periodontal disease

BackgroundPeriodontitis is a highly prevalent inflammatory disease affecting the periodontium that results from an imbalance between periodontopathogens and host mechanisms. Continuous progression of the disease may lead to tissue and bone destruction, eventually resulting in tooth loss. The extent of bone loss depends on the dysregulated host immune response. Various host-elicited molecules play a major role in disease progression. The discovery of the glycoprotein sclerostin and its role as a regulator of bone mass has led to a better understanding of bone metabolism.HighlightSclerostin, which is primarily expressed by osteocytes, is a negative regulator of bone formation. It is a potent antagonist of the canonical Wingless-related integration site (Wnt) pathway, which is actively involved in bone homeostasis. Sclerostin is known to stimulate bone resorption by altering the osteoprotegerin (OPG)/receptor activator of nuclear factor kappa- β ligand (RANKL) balance. Additionally, in periodontitis, activation of the inflammatory cascade also increases the synthesis of sclerostin.ConclusionThe recently discovered sclerostin antibody has emerged as a positive therapeutic tool for the treatment of metabolic bone diseases. It has been reported to improve bone strength, bone formation, osseointegration around implants and lower the risk of bone fractures in various animal and human models. This review describes the properties and action of sclerostin, its role in periodontal diseases, and the advent and efficacy of sclerostin antibodies.     

Osteoimmunology in orthodontic tooth movement

The skeletal and immune systems share a multitude of regulatory molecules, including cytokines, receptors, signaling molecules, and signaling transducers, thereby mutually influencing each other. In recent years, several novel insights have been attained that have enhanced our current understanding of the detailed mechanisms of osteoimmunology. In orthodontic tooth movement, immune responses mediated by periodontal tissue under mechanical force induce the generation of inflammatory responses with consequent alveolar bone resorption, and many regulators are involved in this process. In this review, we take a closer look at the cellular/molecular mechanisms and signaling involved in osteoimmunology and at relevant research progress in the context of the field of orthodontic tooth movement.