Delayed tooth eruption and suppressed osteoclast number in the eruption pathway of heterozygous Runx2/Cbfa1 knockout mice

Circ_ST6GAL1-mediated competing endogenous RNA network regulates TGF-β1-stimulated matrix Metalloproteinase-13 expression via Runx2 acetylation in osteoblasts

Transforming growth factor-beta1 (TGF-β1) stimulates matrix metalloproteinase-13 (MMP-13, a bone-remodeling gene) expression, and this effect requires p300-mediated Runx2 (Runt-related transcription factor 2) acetylation in osteoblasts. p300 and Runx2 are transcriptional coactivator and bone transcription factor, respectively, which play key roles in the regulation of bone-remodeling genes. Non-coding ribonucleic acids (ncRNAs), such as long ncRNAs (lncRNAs) and microRNAs (miRNAs), have been linked to both physiological and pathological bone states. In this study, we proposed that TGF-β1-mediated stimulation of MMP-13 expression is due to the downregulation of p300 targeting miRNAs in osteoblasts. We identified miR-130b-5p as one of the miRNAs downregulated by TGF-β1 in osteoblasts. Forced expression of miR-130b-5p decreased p300 expression, Runx2 acetylation, and MMP-13 expression in these cells. Furthermore, TGF-β1 upregulated circ_ST6GAL1, (a circular lncRNA) in osteoblasts; circRNA directly targeted miR-130b-5p. Antisense-mediated knockdown of circ_ST6GAL1 restored the function of miR-130b-5p, resulting in downregulation of p300, Runx2, and MMP-13 in these cells. Hence, our results suggest that TGF-β1 influences circ_ST6GAL1 to sponge and degrade miR-130b-5p, thereby promoting p300-mediated Runx2 acetylation for MMP-13 expression in osteoblasts. Thus, the circ_ST6GAL1/miR-130b-5p/p300 axis has potential significance in the treatment of bone and bone-related disorders.

Effects of antiresorptive medications on tooth root formation and tooth eruption in paediatric patients

Tooth eruption is a pivotal milestone for children's growth and development. This process involves with the formation of the tooth root, the periodontal ligament (PDL) and the alveolar bone, as the tooth crown penetrates the bone and gingiva to enter the oral cavity. This review aims to outline current knowledge of the adverse dental effects of antiresorptive medications. Recently, paediatric indications for antiresorptive medications, such as bisphosphonates (BPs), have emerged, and these agents are increasingly used in children and adolescents to cure pathological bone resorption associated with bone diseases and cancers. Since tooth eruption is accompanied by osteoclastic bone resorption, it is expected that the administration of antiresorptive medications during this period affects tooth development. Indeed, several articles studying human patient cohorts and animal models report the dental defects associated with the use of these antiresorptive medications. This review shows the summary of the possible factors related to tooth eruption and introduces the future research direction to understand the mechanisms underlying the dental defects caused by antiresorptive medications.

Impact of Mechanical Strain and Nicotinamide on RUNX2-Deficient Osteoblast Mimicking Cleidocranial Dysplasia

Cleidocranial dysplasia (CCD) is a rare genetic defect caused by a heterozygous mutation of runt-related transcription factor 2 (RUNX2), which is important for osteoblast and skeletal development. RUNX2-deficiency causes extra- and intra-oral malformations that often require orthodontic treatment. Nicotinamide (NAM) affects bone remodelling processes. As these are crucial for orthodontic therapy, NAM could improve orthodontic treatment in CCD patients. This study investigates the effect of NAM in control and RUNX2-deficient osteoblasts under mechanical strain mimicking orthodontic treatment. First, the optimal NAM concentration and the differences in the expression profile of control and RUNX2-deficient osteoblasts were determined. Subsequently, osteoblasts were exposed to tensile and compressive strain with and without NAM, and the expression of genes critically involved in bone remodelling was investigated. NAM increased the expression of bone remodelling genes. RUNX2-deficient osteoblasts expressed more receptor activator of NFkB ligand (RANKL) and interleukin-6 (IL6), but less colony-stimulating factor-1 (CSF1). Most of the positive effects of NAM on bone remodelling genes were impaired by mechanical loading. In conclusion, NAM stimulated osteoblast differentiation by increasing the expression of RUNX2 and regulated the expression of osteoclastogenic factors. However, the positive effects of NAM on bone metabolism were impaired by mechanical loading and RUNX2 deficiency.

Runx2 and Nell-1 in dental follicle progenitor cells regulate bone remodeling and tooth eruption

Dental follicles are necessary for tooth eruption, surround the enamel organ and dental papilla, and regulate both the formation and resorption of alveolar bone. Dental follicle progenitor cells (DFPCs), which are stem cells found in dental follicles, differentiate into different kinds of cells that are necessary for tooth formation and eruption. Runt‐related transcription factor 2 (Runx2) is a transcription factor that is essential for osteoblasts and osteoclasts differentiation, as well as bone remodeling. Mutation of Runx2 causing cleidocranial dysplasia negatively affects osteogenesis and the osteoclastic ability of dental follicles, resulting in tooth eruption difficulties. Among a variety of cells and molecules, Nel-like molecule type 1 (Nell-1) plays an important role in neural crest-derived tissues and is strongly expressed in dental follicles. Nell-1 was originally identified in pathologically fused and fusing sutures of patients with unilateral coronal synostosis, and it plays indispensable roles in bone remodeling, including roles in osteoblast differentiation, bone formation and regeneration, craniofacial skeleton development, and the differentiation of many kinds of stem cells. Runx2 was proven to directly target the Nell-1 gene and regulate its expression. These studies suggested that Runx2/Nell-1 axis may play an important role in the process of tooth eruption by affecting DFPCs. Studies on short and long regulatory noncoding RNAs have revealed the complexity of RNA-mediated regulation of gene expression at the posttranscriptional level. This ceRNA network participates in the regulation of Runx2 and Nell-1 gene expression in a complex way. However, non-study indicated the potential connection between Runx2 and Nell-1, and further researches are still needed.

A Novel lncRNA Mediates the Delayed Tooth Eruption of Cleidocranial Dysplasia

Delayed eruption of permanent teeth is a common symptom of cleidocranial dysplasia (CCD). Previous studies have focused on the anomaly of osteogenesis resulting from mutations in the Runt-related transcription factor-2 gene (RUNX2). However, deficiencies in osteoclastogenesis and bone resorption, and the epigenetic regulation mediated by long non-coding (lnc)RNAs in CCD remain to be elucidated. Here, a novel osteoclast-specific lncRNA (OC-lncRNA) was identified during the osteoclast differentiation of RAW 264.7 cells transfected with a RUNX2 mutation expression cassette. We further confirmed that OC-lncRNA positively regulated osteoclastogenesis and bone resorption. The OC-lncRNA promoted the expression of CXC chemokine receptor type 3 (CXCR3) by competitively binding to microRNA (miR)-221-5p. The CXCR3–CXC-motif chemokine ligand 10 (CXCL10) interaction and nuclear factor-κB constituted a positive feedback that positively regulated osteoclastogenesis and bone resorption. These results demonstrate that OC-lncRNA-mediated osteoclast dysfunction via the OC-lncRNA–miR-221-5p–CXCR3 axis, which is involved in the process of delayed tooth eruption of CCD.

Multiple roles of Runt-related transcription factor-2 in tooth eruption: bone formation and resorption

OBJECTIVE

The aim was to provide a comprehensive review of the current knowledge of the multiple roles of Runt-related transcription factor-2 (RUNX2) in regulating tooth eruption, focusing on the molecular mechanisms regarding tooth eruption mediated by RUNX2.

DESIGN

Relevant literatures in PubMed, Medline, and Scopus database were searched, and a narrative review was performed. The multiple roles of RUNX2 in regulating tooth eruption was reviewed and discussed.

RESULTS

Aberrant RUNX2 expression leads to disturbed or failed tooth eruption. Tooth eruption involves both the process of bone formation and bone resorption. RUNX2 promotes osteogenesis around the radicular portion of the dental follicle that provides the biological force for tooth eruption through inducing the expression of osteogenesis-related genes in dental follicle cells/osteoblasts. On the other hand, through indirect and direct pathways, RUNX2 regulates osteoclastogenesis and the formation of the eruption pathway.

CONCLUSION

RUNX2 exerts a pivotal and complex influence in regulating tooth eruption. This review provides a better understanding of the function of RUNX2 in tooth eruption, which is beneficial to illuminate the precise molecular mechanism of osteogenesis and bone resorption, aiding the development of effective therapy for the failure of tooth eruption.

Genetic Pattern, Orthodontic and Surgical Management of Multiple Supplementary Impacted Teeth in a Rare, Cleidocranial Dysplasia Patient: A Case Report

Background: Cleidocranial dysplasia (CCD) is a rare, autosomal dominant skeletal dysplasia with a prevalence of one per million births. The main causes of CCD are mutations in the core-binding factor alpha-1 (CBFA1) or runt-related transcription factor-2 (RUNX2), located at the 6p21 chromosomal region. RUNX2 plays important roles in osteoblast differentiation, chondrocyte proliferation and differentiation, and tooth formation. The disease is characterized by clavicular aplasia or hypoplasia, Wormian bones, delayed closure of cranial suture, brachycephalic head, maxillary deficiency, retention of primary teeth, inclusion of permanent teeth, and multiple supernumerary teeth. Materials and Methods: A 22-year-old girl suffering from cleidocranial dysplasia with short stature, narrow shoulders, craniofacial manifestations (short face, broad forehead, etc.) and dental anomalies (different lower dental elements under eruption, supernumerary and impacted multiple teeth, etc.) was examined at our service (Complex Operative Unit of Odontostomatology of Policlinico of Bari). RX Orthopantomography (OPG) and cone beam computed tomography (CBCT) were requested to better assess the position of the supernumerary teeth and their relationships with others and to evaluate the bone tissue. Results: Under eruption was probably caused by dental interferences with supernumerary teeth; hence, extractions of supernumerary upper canines and lower premolars were performed under general anaesthesia. Surgery outcome was excellent with good tissue healing and improvements in the therapeutic possibilities with future orthodontics. Conclusions: The objective of this article is to give an update about radiological, clinical, and molecular features of CCD and to alert the health team about the importance of establishing an early diagnosis and an appropriate treatment in these patients to prevent impacted teeth complications and to offer them a better quality of life.

Nicotinamide Improves Delayed Tooth Eruption in Runx2+/- Mice

Patients with cleidocranial dysplasia (CCD) caused by mutations in RUNX2 have severe dental anomalies, including delayed or absent eruption of permanent teeth. This requires painful and expensive surgical/orthodontic intervention because of the absence of medicine for this condition. Here, we demonstrate that nicotinamide, a vitamin B3 and class III histone deacetylase inhibitor, significantly improves delayed tooth eruption in Runx2^+/- mice, a well-known CCD animal model, through the restoration of decreased osteoclastogenesis. We also found that Csf1 mRNA and protein levels were significantly reduced in Runx2^+/- osteoblasts as compared with wild type whereas RANKL and OPG levels had no significant difference between wild type and Runx2^+/- osteoblasts. The nicotinamide-induced restoration of osteoclastogenesis of bone marrow-derived macrophages in Runx2^+/- mice was due to the increased expression of RUNX2 and CSF1 and increased RANKL/OPG ratio. RUNX2 directly regulated Csf1 mRNA expression via binding to the promoter region of the Csf1 gene. In addition, nicotinamide enhanced the RUNX2 protein level and transacting activity posttranslationally with Sirt2 inhibition. Taken together, our study shows the potential and underlying molecular mechanism of nicotinamide for the treatment of delayed tooth eruption by using the Runx2^+/- murine model, suggesting nicotinamide as a candidate therapeutic drug for dental abnormalities in patients with CCD.

The Characteristics of Adjacent Anatomy of Mandibular Third Molar Germs: A CBCT Pilot Study in Patients with Osteogenesis Imperfecta

(1) Objectives: The aim of our study was to investigate the anatomical features of lower third molar and its adjacent anatomical connections in type I Osteogenesis Imperfecta (OI) patients through cone beam computed tomography (cbct). (2) Methods: The study was conducted among 25 patients, 13 patients with type I OI and 12 control patients (individuals with no disorders and no treatment); average age was 15.44 ± 2.06, 23 third molar germs for each group. The germs have been compared to the parameters using the Mann-Whitney test. A chi-square test was also used to investigate the correlation between the status case/control and tooth development stage. (3) Results: Mann-Whitney test showed significant differences between cases and controls: diameter of the tooth germ in toto (U = 93.5; p < 0.001), tooth development stage, (U = 145; p < 0.01), roots length (U = 44.5; p < 0.01), cementoenamel junction diameter (U = 157.5; p < 0.05), size of the pulp chamber (U = 95.5; p < 0.05). Type I OI is not associated with the relationship between the germ of mandibular third molar and alveolar canal on axial plane (χ² = 4.095; p = 0.129), and parasagittal (χ² = 4.800; p = 0.091). The association between type I OI and relationship with the germ of mandibular third molar and alveolar canal on the coronal plane has been significant (χ² = 9.778; p < 0.05) as the perforation of the lingual cortical bone in the region of mandibular third molar tooth germ (χ² = 11.189; p < 0.01). (4) Conclusions: The results confirm the cbct accuracy in the evaluation of bone density in type I OI patients giving also the opportunity to study the tridimensional anatomy of germs and the adjacent anatomical structures in order to avoid any perioperative complications.

MSX1 is differentially expressed in the deepest impacted maxillary third molars

An impacted third molar is one of the most common dental abnormalities. Among the reasons for impaction the most common are: insufficient space, time of eruption, improper position of the tooth bud, and genetic disruptions. To investigate if runt-related transcription factor 2 (RUNX2), bone morphogenetic protein 2 (BMP2), and msh homeobox 1 (MSX1) are differently expressed depending on the position of the molar, we studied 32 patients who had been referred for surgical removal. An orthopantomogram was used to separate them according to Winter's, and Pell & Gregory's, classifications. Bone samples were harvested during the operation for gene expression assay. The Kruskal-Wallis, Dunn's post hoc, and Spearman's correlation, tests were used to assess the significance of differences. No correlations were found in expression of the genes, and no differences between expression in maxillary and mandibular third molars, nor were they expressed differently according to Winter's or Pell and Gregory's classifications or in relation to impaction of the mandibular ramus. However, MSX1 was expressed differently when account was taken of the depth of impaction in maxillary third molars (p = 0.029), but there was no difference in expression of RUNX2, BMP2, and MSX1 for the Pell and Gregory classification of depth of impaction (p > 0.05). We conclude that MSX1 is expressed differently depending on the depth of maxillary impaction phenotypes.

New Function of RUNX2 in Regulating Osteoclast Differentiation via the AKT/NFATc1/CTSK Axis

Cleidocranial dysplasia is an autosomal dominant skeletal disorder resulting from RUNX2 mutations. The influence of RUNX2 mutations on osteoclastogenesis and bone resorption have not been reported. To investigate the role of RUNX2 in osteoclast, RUNX2 expression in macrophages (RAW 264.7 cells) was detected. Stable RAW 264.7 cell lines expressing wild-type RUNX2 or mutated RUNX2 (c.514delT, p.172 fs) were established, and their functions in osteoclasts were investigated. Wild-type RUNX2 promoted osteoclast differentiation, formation of F-actin ring, and bone resorption, while mutant RUNX2 attenuated the positive differentiation effect. Wild-type RUNX2 increased the expression and activity of mTORC2. Subsequently, mTORC2 specifically promoted phosphorylation of AKT at the serine 473 residue. Activated AKT improved the nuclear translocation of NFATc1 and increased the expression of downstream genes, including CTSK. Inhibition of AKT phosphorylation abrogated the osteoclast formation of wild-type macrophages, whereas constitutively activated AKT rescued the osteoclast formation of mutant macrophages. The present study suggested that RUNX2 promotes osteoclastogenesis and bone resorption through the AKT/NFATc1/CTSK axis. Mutant RUNX2 lost the function of regulating osteoclast differentiation and bone remodeling, resulting in the defective formation of the tooth eruption pathway and impaction of permanent teeth in cleidocranial dysplasia. This study, for the first time, verifies the effect of RUNX2 on osteoclast differentiation and bone resorption and provides new insight for the explanation of cleidocranial dysplasia.

Mesenchymal Progenitor Regulation of Tooth Eruption: A View from PTHrP

Tooth eruption is a unique biological process by which highly mineralized tissues emerge into the outer world, and it occurs concomitantly with tooth root formation. These 2 processes have been considered independent phenomena; however, recent studies support the theory that they are indeed intertwined. Dental mesenchymal progenitor cells in the dental follicle lie at the heart of the coupling of these 2 processes, providing a source for diverse mesenchymal cells that support formation of the highly functional tooth root and the periodontal attachment apparatus, while facilitating formation of osteoclasts. These cells are regulated by autocrine signaling by parathyroid hormone-related protein (PTHrP) and its parathyroid hormone/PTHrP receptor PPR. This PTHrP-PPR signaling appears to crosstalk with other signaling pathways and regulates proper cell fates of mesenchymal progenitor cell populations. Disruption of this autocrine PTHrP-PPR signaling in these cells leads to defective formation of the periodontal attachment apparatus, tooth root malformation, and failure of tooth eruption in molars, which essentially recapitulate primary failure of eruption in humans, a rare genetic disorder exclusively affecting tooth eruption. Diversity and distinct functionality of these mesenchymal progenitor cell populations that regulate tooth eruption and tooth root formation are beginning to be unraveled.

SP1 regulates KLF4 via SP1 binding motif governed by DNA methylation during odontoblastic differentiation of human dental pulp cells

OBJECTIVE

DNA methylation is a critical epigenetic modulation in regulating gene expression in cell differentiation process, however, its detailed molecular mechanism during odontoblastic differentiation remains elusive. We aimed to study the global effect of DNA methylation on odontoblastic differentiation and how DNA methylation affects the transactivation of transcription factor (TF) on its target gene.

METHODS

DNA methyltransferase (DNMTs) inhibition assay and following odontoblastic differentiation assay were performed to evaluate the effect of DNA methylation inhibition on odontoblastic differentiation. Promoter DNA methylation microarray and motif enrichment assay were performed to predict the most DNA-methylation-affected TF motifs during odontoblastic differentiation. The enriched target sites and motifs were further analyzed by methylation-specific polymerase chain reaction (MS-PCR) and sequencing. The functional target sites were validated in vitro with Luciferase assay. The regulatory effect of DNA methylation on the enriched target sites in primary human dental pulp cells and motifs were confirmed by in vitro methylation assay.

RESULTS

Inhibition of DNMTs in preodontoblast cells increased the expression level of Klf4 as well as marker genes of odontoblastic differentiation including Dmp1 and Dspp, and enhanced the efficiency of odontoblastic differentiation. SP1/KLF4 binding motifs were found to be highly enriched in the promoter regions and showed demethylation during odontoblastic differentiation. Mutation of SP1 binding site at -75 within KLF4's promoter region significantly decreased the luciferase activity. The in vitro methylation of KLF4's promoter decreased the transactivation of SP1 on KLF4.

CONCLUSION

We confirmed that SP1 regulates KLF4 through binding site lying in a CpG island in KLF4's promoter region which demethylated during odontoblastic differentiation thus enhancing the efficiency of SP1's binding and transcriptional regulation on KLF4.

Abnormal bone remodelling activity of dental follicle cells from a cleidocranial dysplasia patient

OBJECTIVES

To explore the role of dental follicle cells (DFCs) with a novel cleidocranial dysplasia (CCD) causative gene RUNX2 mutation (DFCs^RUNX2+/m ) in delayed permanent tooth eruption.

MATERIALS AND METHODS

A CCD patient with typical clinical features was involved in this study. DFCs^RUNX2+/m were cultured and DNA was extracted for RUNX2 mutation screening. Measurements of cell proliferation, alkaline phosphatase (ALP) activity, alizarin red staining and osteoblast-specific genes expression were performed to assess osteogenesis of DFCs^RUNX2+/m . Co-culture of DFCs and peripheral blood mononuclear cells (PBMCs), followed tartrate-resistant acid phosphatase (TRAP) staining, real-time PCR and western blot were performed to evaluate osteoclast-inductive capacity of DFCs^RUNX2+/m .

RESULTS

A missense RUNX2 mutation (c. 557G>C) was found in DFCs^RUNX2+/m from the CCD patient. Compared with normal controls, this mutation did not affect the proliferation of DFCs^RUNX2+/m , but down-regulated the expression of osteogenesis-related genes, leading to a decrease in ALP activity and mineralisation. Co-culture results showed that DFCs^RUNX2+/m reduced the formation of TRAP⁺ multinucleated cells and the expression of osteoclastogenesis-associated genes. Furthermore, the mutation reduced the ratio of RANKL/OPG in DFCs^RUNX2+/m .

CONCLUSIONS

DFCs^RUNX2+/m disturbs bone remodelling activity during tooth eruption through RANK/RANKL/OPG signalling pathway and may thus be responsible for impaired permanent tooth eruption in CCD patients.

Specificity Protein 7 Is Required for Proliferation and Differentiation of Ameloblasts and Odontoblasts

The Sp7/Osterix transcription factor is essential for bone development. Mutations of the Sp7 gene in humans are associated with craniofacial anomalies and osteogenesis imperfecta. However, the role of Sp7 in embryonic tooth development remains unknown. Here we identified the functional requirement of Sp7 for dentin synthesis and tooth development. Sp7-null mice exhibit craniofacial dysmorphogenesis and are completely void of alveolar bone. Surprisingly, initial tooth morphogenesis progressed normally in Sp7-null mice. Thus the formation of alveolar bone is not a prerequisite for tooth morphogenesis. Sp7 is required for mineralization of palatal tissue but is not essential for palatal fusion. The reduced proliferative capacity of Sp7-deficient ectomesenchyme results in small and misshapen teeth with randomly arranged cuboidal preodontoblasts and preameloblasts. Sp7 promotes functional maturation and polarization of odontoblasts. Markers of mature odontoblast (Col1a, Oc, Dspp, Dmp1) and ameloblast (Enam, Amelx, Mmp20, Amtn, Klk4) are barely expressed in incisors and molar tissues of Sp7-null mice. Consequently, dentin and enamel matrix are absent in the Sp7-null littermates. Interestingly, the Sp7 expression is restricted to cells of the dental mesenchyme indicating the effect on oral epithelium-derived ameloblasts is cell-nonautonomous. Abundant expression of Fgf3 and Fgf8 ligand was noted in the developing tooth of wild-type mice. Both ligands were remarkably absent in the Sp7-null incisor and molar, suggesting cross-signaling between mesenchyme and epithelium is disrupted. Finally, promoter-reporter assays revealed that Sp7 directly controls the expression of Fgf-ligands. Together, our data demonstrate that Sp7 is obligatory for the differentiation of both ameloblasts and odontoblasts but not for the initial tooth morphogenesis. © 2018 American Society for Bone and Mineral Research.

A novel RUNX2 mutation in exon 8, G462X, in a patient with Cleidocranial Dysplasia

To identify a novel mutation of Runx2 gene in Cleidocranial Dysplasia (CCD) patients and to characterize the functional consequences of this mutation. The subjects consisted of 12 Korean CCD patients. After oral epithelial cells were collected using a mouthwash technique, genomic DNA was extracted. Screening for Runx2 mutation was performed using direct sequencing of polymerase chain reaction (PCR) products for exons 1-8. Restriction fragment length polymorphism (RFLP) analysis was performed to confirm the novel mutation. For functional studies, we performed luciferase assay for Runx2 transacting activity, cyclohexamide chase assay for Runx2 protein stability, real-time PCR for mRNA level of Runx2 downstream bone marker genes, and alkaline phosphatase (ALP) staining assay in mesenchymal stem cells for osteoblast differentiation. Of the 12 patients, seven showed Runx2 mutations reported previously and four showed no mutation. A novel mutation, G462X in exon 8, which was located in the C-terminus of proline/serine/threonine-rich (PST) domain, was found in one patient. In the luciferase assay, Runx2 transacting activity was decreased in Runx2-G462X transfected cells. In the cyclohexamide chase assay, Runx2-G462X mutation reduced the stability of Runx2 protein. Expression of the bone marker genes (osteocalcin, ALP, Type I collagen αI, matrix metalloproteinase-13, bone sialoprotein, and osteopontin) decreased in G462X-transfected cells. In the ALP staining assay, osteoblast differentiation was reduced in Runx2-G462X overexpressed cell. The G462X mutation might reduce the Runx2 transacting activity, lower the protein stability, downgrade the expression of bone marker genes, and eventually diminish osteoblast differentiation in CCD patients.

RUNX2 mutation impairs bone remodelling of dental follicle cells and periodontal ligament cells in patients with cleidocranial dysplasia

RUNX2 is an important osteo-specific factor with crucial functions in bone formation and remodelling as well as resorption of teeth. Heterozygous mutation of RUNX2 can cause cleidocranial dysplasia (CCD), a systemic disease with extensive skeletal dysplasia and abnormality of tooth growth. In our study, dental follicle cells (DFCs) and periodontal ligament cells (PDLCs) were isolated, cultured and identified from one patient with CCD and compared with normal controls. This CCD patient was confirmed to have a heterozygous frameshift mutation of RUNX2 (c.514delT, p.Ser172fs) in the previous study. The results showed that the proliferation abilities of DFCs and PDLCs were both disturbed by the RUNX2 mutation in the CCD patient compared with the normal control. A co-culture system of these cells with human peripheral blood mononuclear cells was then used to investigate the effect of RUNX2 mutation on osteoclastogenesis. We found that the RUNX2 mutation in CCD reduced the expression of osteoclast-related genes, such as RUNX2, CTR, CTSK, RANKL and OPG The ability of osteoclastogenesis in DFCs and PDLCs detected by tartrate-resistant acid phosphatase staining in the co-culture system was also reduced by the RUNX2 mutation compared with the normal control. These outcomes indicate that the RUNX2 mutation disturbs the modulatory effects of DFCs and PDLCs on the differentiation of osteoclasts and osteoblasts, thereby interfering with bone remodelling. These effects may contribute in part to the pathological manifestations of retention of primary teeth and delayed eruption of permanent teeth in patients with CCD.

RUNX2 Mutation Impairs 1α,25-Dihydroxyvitamin D3 mediated Osteoclastogenesis in Dental Follicle Cells

Cleidocranial dysplasia (CCD), a skeletal disorder characterized by delayed permanent tooth eruption and other dental abnormalities, is caused by heterozygous RUNX2 mutations. As an osteoblast-specific transcription factor, RUNX2 plays a role in bone remodeling, tooth formation and tooth eruption. To investigate the crosstalk between RUNX2 and 1α,25-dihydroxyvitamin D3 (1α,25-(OH)₂D₃) in human dental follicle cells (hDFCs) during osteoclast formation, we established a co-culture system of hDFCs from CCD patient and healthy donors with peripheral blood mononuclear cells (PBMCs). Expression of the osteoclast-associated genes and the number of TRAP⁺ cells were reduced in CCD hDFCs, indicating its suppressed osteoclast-inductive ability, which was reflected by the downregulated RANKL/OPG ratio. In addition, 1α,25-(OH)₂D₃-stimulation elevated the expression of osteoclast-related genes, as well as RANKL mRNA levels and RANKL/OPG ratios in control hDFCs. Conversely, RUNX2 mutation abolished this 1α,25-(OH)₂D₃-induced RANKL gene activation and osteoclast formation in CCD hDFCs. Therefore, RUNX2 haploinsufficiency impairs dental follicle-induced osteoclast formation capacity through RANKL/OPG signaling, which may be partially responsible for delayed permanent tooth eruption in CCD patients. Furthermore, this abnormality was not rescued by 1α,25-(OH)₂D₃ application because 1α,25-(OH)₂D₃-induced RANKL activation in hDFCs is mediated principally via the RUNX2-dependent pathway.

Specificity protein 7 is not essential for tooth morphogenesis

Tooth formation is a multifaceted process involving numerous interactions between oral epithelium and neural crest derived ecto-mesenchyme from morphogenesis to cyto-differentiation. The precise molecular regulator that drives the cyto-differentiation and dynamic cross-talk between the two cell types has yet to be fully understood. Runx2 along with its downstream target Sp7 are essential transcription factors for development of the mineralizing cell types. Global knockout of the Runx2 gene results in an arrest of tooth morphogenesis at the late bud stage. Like Runx2, Sp7-null mutants exhibit peri-natal lethality and are completely devoid of alveolar bone. However, the role of Sp7 in tooth development remains elusive. Here, we report the effects of Sp7 deletion on tooth formation. Surprisingly, tooth morphogenesis progresses normally until the mid bell stage in Sp7-homozygous mutants. Incisors and multi-cusped first and second molars were noted in both littermates. Thus, formation of alveolar bone is not a prerequisite for tooth morphogenesis. Tooth organs of Sp7-null however, were significantly smaller in size when compared to WT. Differentiation of both ameloblasts and odontoblasts was disrupted in Sp7-null mice. Only premature and disorganized ameloblasts and odontoblasts were noted in mutant mice. These data indicate that Sp7 is not required for tooth morphogenesis but is obligatory for the functional maturation of both ameloblasts and odontoblasts.

Osteoclastogenic potential of peripheral blood mononuclear cells in cleidocranial dysplasia

Cleidocranial dysplasia (CCD) is an autosomal dominant skeletal dysplasia characterized by hypoplastic or aplastic clavicles, dental abnormalities, and delayed closure of the cranial sutures. In addition, mid-face hypoplasia, short stature, skeletal anomalies and osteoporosis are common. We aimed to evaluate osteoclastogenesis in a child (4 years old), who presented with clinical signs of CCD and who have been diagnosed as affected by deletion of RUNX2, master gene in osteoblast differentiation, but also affecting T cell development and indirectly osteoclastogenesis. The results of this study may help to understand whether in this disease is present an alteration in the bone-resorptive cells, the osteoclasts (OCs). Unfractionated and T cell-depleted Peripheral Blood Mononuclear Cells (PBMCs) from patient were cultured in presence/absence of recombinant human M-CSF and RANKL. At the end of the culture period, OCs only developed following the addition of M-CSF and RANKL. Moreover, real-time PCR experiment showed that freshly isolated T cells expressed the osteoclastogenic cytokines (RANKL and TNFα) at very low level, as in controls. This is in accordance with results arising from flow cytometry experiments demonstrating an high percentage of circulating CD4(+)CD28(+) and CD4(+)CD27(+) T cells, not able to produce osteoclastogenic cytokines. Also RANKL, OPG and CTX serum levels in CCD patient are similar to controls, whereas QUS measurements showed an osteoporotic status (BTT-Z score -3.09) in the patient. In conclusions, our findings suggest that the heterozygous deletion of RUNX2 in this CCD patient did not alter the osteoclastogenic potential of PBMCs in vitro.

Low osteogenic differentiation potential of placenta-derived mesenchymal stromal cells correlates with low expression of the transcription factors Runx2 and Twist2

Recent studies indicated that mesenchymal stromal cells from bone marrow (bmMSC) differ in their osteogenic differentiation capacity compared to MSC from term placenta (pMSC). We extended these studies and investigated the expression of factors involved in regulation of bone metabolism in both cell types. To this end, MSC were expanded in vitro and characterized. The total transcriptome was investigated by microarrays, and for selected genes, the differences in gene expression were explored by quantitative reverse transcriptase-polymerase chain reaction, immunocytochemistry, and flow cytometry. We report that bmMSC and pMSC share expression of typical lineage surface markers, including CD73, CD90, CD105, and lack of CD14, CD34, and CD45. However, according to transcriptome analyses, they differ significantly in their expression of more than 590 genes. Factors involved in bone metabolism, including alkaline phosphatase (P<0.05), osteoglycin (P<0.05), osteomodulin (P<0.05), runt-related transcription factor 2 (Runx2) (P<0.04), and WISP2 (P<0.05), were expressed at significantly lower levels in pMSC, but twist-related protein 2 (Twist2) (P<0.0002) was expressed at significantly higher levels. The osteogenic differentiation capacity of pMSC was very low. The adipogenic differentiation was somewhat more prominent in bmMSC, while the chondrogenic differentiation seemed not to differ between bmMSC and pMSC, as determined by histochemical staining. However, expression and induction of peroxisome proliferator-activated receptor gamma-2 (PPARγ2) and Sox9, factors involved in early adipogenesis and chondrogenesis, respectively, were higher in bmMSC. We conclude that despite many similarities between bmMSC and pMSC, when expanded under identical conditions, they vary considerably with respect to their in vitro differentiation potential. For regenerative purposes, the choice of MSC may therefore influence the outcome of a treatment considerably.

A 13-year-old Caucasian boy with cleidocranial dysplasia: a case report

Background

Cleidocranial dysplasia (CCD) is a rare congenital autosomal dominant skeletal disorder. The disorder is caused by heterozygosity of mutations in human RUNX2, which is present on the short arm of chromosome 6p21. The incidence of CCD is one per million births. CCD appears spontaneously with no apparent genetic cause in approximately 40% of affected patients, and one in three patients has unaffected parents. The most prevalent features associated with CCD are aplastic or hypoplastic clavicles, supernumerary teeth, failed eruption of permanent teeth, and a hypoplastic maxilla.

Case presentation

A 13-year-old Caucasian boy presented with a chief complaint of delayed eruption of the permanent anterior teeth. The patient was subsequently diagnosed with CCD based on the clinical examination, panoramic X-ray, anterior-posterior and lateral cephalogram, and chest radiograph findings. The details of this case are herein reported because of the extremely low incidence of this disorder.

Conclusions

CCD is of clinical importance in dentistry and medicine because it affects the bones and teeth and is characterized by many changes in skeletal patterning and growth. Particularly in dentistry, CCD is of great clinical significance because is associated with delayed ossification of the skull sutures, delayed exfoliation of the primary teeth, lack of permanent teeth eruption, multiple supernumerary teeth, and morphological abnormalities of the maxilla and mandible. Patients with CCD seek treatment mainly for dental problems. Knowledge of the pathogenesis, clinical characteristics, and diagnostic tools of CCD will enable clinicians to render the appropriate treatment to improve function and aesthetics. Early diagnosis of CCD is crucial for timely initiation of an appropriate treatment approach.

Cleidocranial dysplasia: a review of the dental, historical, and practical implications with an overview of the South African experience

Cleidocranial dysplasia (CCD) is an uncommon but well-known genetic skeletal condition. Several hundred affected persons are members of a large extended family in the Cape Town Mixed Ancestry community of South Africa. The clinical manifestations are often innocuous, but hyperdontia and other developmental abnormalities of the teeth are a major feature and may require special dental management. Over the past 40 years, the authors have encountered more than 100 affected persons in Cape Town. Emphasis has been on dental management, but medical, genetic, and social problems have also been addressed. In this article, we have reviewed the manifestations of the disorder in the light of our own experience, and performed a literature search with emphasis on the various approaches to dental management and treatment options in CCD. Advances in the understanding of the biomolecular pathogenesis of CCD are outlined and the international and local history of the disorder is documented.

Tooth eruption: altered gene expression in the dental follicle of patients with cleidocranial dysplasia

OBJECTIVES

The dental follicle plays an important role in tooth eruption by providing key regulators of osteogenesis and bone resorption. Patients with cleidocranial dysplasia (CCD) exhibit delayed tooth eruption in combination with increased bone density in the maxilla and mandible, suggesting disturbances in bone remodeling. The aim of this study was to determine the expression of genes relevant for tooth eruption and bone remodeling in the dental follicles of patients with CCD and normal subjects.

MATERIAL AND METHODS

Thirteen dental follicles were isolated from five unrelated patients with CCD, and fourteen dental follicles were obtained from 10 healthy individuals. All teeth were in the intraosseous phase of eruption. The expression of RANK, RANKL, OPG, and CSF-1 was determined by quantitative RT-PCR.

RESULTS

In patients with CCD, the mRNA levels of RANK, OPG, and CSF-1 were significantly elevated compared with the control group. Accordingly, the ratios of RANKL/OPG and RANKL/RANK mRNAs were significantly decreased in patients with CCD.

CONCLUSION

The observed alterations in the expression and ratios of the aforementioned factors in the dental follicle of CCD individuals suggest a disturbed paracrine signaling for bone remodeling that could be responsible for the impaired tooth eruption seen in these patients.

Cleidocranial dysplasia: oral features and genetic analysis of 11 patients

BACKGROUND

Cleidocranial dysplasia (CCD) is a dominantly inherited autosomal disease characterized by typical bone defects including short stature, persistently open or delayed closure of the cranial sutures, and hypoplastic or aplastic clavicles. Oral features are frequent and include supernumerary teeth, delayed eruption or impaction of the permanent teeth, and malocclusion. Heterozygous mutations in RUNX2 gene, which encodes a transcription factor essential for osteoblast differentiation, were identified as the etiological cause of CCD.

OBJECTIVE AND METHODS

Herein, we performed physical and radiographic examination and screening for RUNX2 mutations in 11 patients from five families with CCD.

RESULTS

All patients demonstrated the classical phenotypes related to CCD. Families whose affected members had several dental alterations such as multiple impacted and supernumerary teeth demonstrated heterozygous missense mutations (R190Q and R225Q) that impair the runt domain of RUNX2. On the other hand, CCD patients from families with low frequency of dental abnormalities showed no mutation in RUNX2 or mutation outside of the runt domain (Q292fs→X299).

CONCLUSION

The current findings suggest a correlation between dental alterations and mutations in the runt domain of RUNX2 in CCD patients. Further clinical and genetic studies are needed to clarify the relationship between phenotypes and genotypes in CCD and to identify other factors that might influence the clinical features of this uncommon disease.

Osteoclasts and odontoclasts: signaling pathways to development and disease

Osteoclasts are cells essential for physiologic remodeling of bone and also play important physiologic and pathologic roles in the dentofacial complex. Osteoclasts and odontoclasts are necessary for tooth eruption yet result in dental compromise when associated with permanent tooth internal or external resorption. The determinants that separate their physiologic and pathologic roles are not well delineated. Clinical cases of primary eruption failure and root resorption are challenging to treat. Mineralized tissue resorbing cells undergo a fairly well characterized series of differentiation stages driven by transcriptional mediators. Signal transduction via cytokines and integrin-mediated events comprise the detailed pathways operative in osteo/odontoclastic cells and may provide insights to their targeted regulation. A better understanding of the unique aspects of osteoclastogenesis and osteo/odontoclast function will facilitate effective development of new therapeutic approaches. This review presents the clinical challenges and delves into the cellular and biochemical aspects of the unique cells responsible for resorption of mineralized tissues of the craniofacial complex.

Immunolocalization and expression of Runx2 in tertiary dentinogenesis

Runx2 is a new transcription factor that takes part in odontoblast differentiation. This study is aimed at investigating the immunolocalization and expression of Runx2 in the process of dental pulp injury and repair using immunohistochemical technique. In normal dental pulp, positive staining can hardly be detected. In experimental groups, strong positive staining was detected at the site of the impaired pulp after 1 day, while only weak Runx2 staining was detected 3 days after operation. Five days later, a large number of stellate cells in the root apex expressed Runx2, and after 7 days, followed by the reparative dentinogenesis, Runx2 expression vanished slowly, then totally disappeared. Taken together, the expression of Runx2 has temporal and spatial specificity during different phases in rat tertiary dentinogenesis.

Dilated capillaries, disorganized collagen fibers and differential gene expression in periodontal ligaments of hypomorphic fibrillin-1 mice

The periodontal ligaments (PDLs) are soft connective tissue between the cementum covering the tooth root surface and alveolar bone. PDLs are composed of collagen and elastic system fibers, blood vessels, nerves, and various types of cells. Elastic system fibers are generally formed by elastin and microfibrils, but PDLs are mainly composed of the latter. Compared with the well-known function of collagen fibers to support teeth, little is known about the role of elastic system fibers in PDLs. To clarify their role, we examined PDLs of mice under-expressing fibrillin-1 (mgR mice), which is one of the major microfibrillar proteins. The PDLs of homozygous mgR mice showed one-quarter of the elastic system fibers of wild-type (WT) mice. A close association between the elastic system fibers and the capillaries was noted in WT, homozygous and heterozygous mgR mice. Interestingly, capillaries in PDLs of homozygous mice were dilated or enlarged compared with those of WT mice. A comparable level of type I collagen, which is the major collagen in PDLs, was expressed in PDL-cells of mice with three genotypes. However, multi-oriented collagen fiber bundles with a thinner appearance were noted in homozygous mice, whereas well-organized collagen fiber bundles were seen in WT mice. Moreover, there was a marked decrease in periostin expression, which is known to regulate the fibrillogenesis and crosslinking of collagen. These observations suggest that the microfibrillar protein, fibrillin-1, is indispensable for normal tissue architecture and gene expression of PDLs.

The significance of RUNX2 in postnatal development of the mandibular condyle

OBJECTIVE

RUNX2, in the Runt gene family, is one of the most important transcription factors in the development of the skeletal system. Research in recent decades has shown that this factor plays a major role in the development, growth and maturation of bone and cartilage. It is also important in tooth development, mechanotransduction and angiogenesis, and plays a significant role in various pathological processes, i.e. tumor metastasization. Mutations in the RUNX2 gene correlate with the cleidocranial dysplasia (CCD) syndrome, important to dentistry, particularly orthodontics because of its dental and orofacial symptoms. Current research on experimentally-induced mouse mutants enables us to study the etiology and pathogenesis of these malformations at the cellular and molecular biological level. This study's aim is to provide an overview of the RUNX2 gene's function especially in skeletal development, and to summarize our research efforts to date, which has focused on investigating the influence of RUNX2 on mandibular growth, which is slightly or not at all altered in many CCD patients.

MATERIALS AND METHODS

Immunohistochemical analyses were conducted to reveal RUNX2 in the condylar cartilage of normal mice and of heterozygous RUNX2 knockout mice in early and late growth phases; we also performed radiographic and cephalometric analyses.

RESULTS

We observed that RUNX2 is involved in normal condylar growth in the mouse and probably plays a significant role in osteogenesis and angiogenesis. The RUNX2 also has a biomechanical correlation in relation to cartilage compartmentalization. At the protein level, we noted no differences in the occurrence and distribution of RUNX2 in the condyle, except for a short phase during the 4th and 6th postnatal weeks, so that one allele might suffice for largely normal growth; other biological factors may have compensatory effects. However, we did observe small changes in a few cephalometric parameters concerning the mandibles of heterozygous knockout animals. We discuss potential correlations to our findings by relating them to the most current knowledge about the RUNX2 biology.

The role of periodontal ligament cells in delayed tooth eruption in patients with cleidocranial dysostosis

OBJECTIVE

The clinical appearance of patients with cleidocranial dysplasia (CCD), which is caused by mutations in the RUNX2 gene, is characterized by anomalies of the clavicles, thorax, spine, pelvis and extremities and by disturbances of the skull and tooth development. Of orthodontic relevance are multiple supernumerary teeth associated with delayed tooth eruption. The present investigation is based on the hypothesis that an altered phenotypic expression of periodontal ligament (PDL) cells from CCD patients and a reduced ability of those cells to support the differentiation of bone-resorbing osteoclasts might contribute to delayed tooth eruption.

MATERIALS AND METHODS

To test this hypothesis, PDL cells from healthy donors and from two patients with clinically and molecular biologically diagnosed CCD were characterized for the basal and induced mRNA expression of osteoblast marker genes. The physiological relevance of the findings for the differentiation of osteoclasts was examined in an osteoclast assay, as well as in a co-culture model of PDL cells and osteoclast precursors.

RESULTS

Both CCD patients displayed missense mutations of the RUNX2 gene. The in vitro experiments revealed an unaltered expression of RUNX2 mRNA, however especially in CCD patient 2 there was a reduced basal expression of mRNA for the key regulatory gene for bone remodeling RANKL. Furthermore, compared to the control cells from healthy donors, these factors were less inducible by stimulation of the cultures with 1alpha,25(OH)(2)D(3). In the osteoclast assays as well as in the co-culture experiments, PDL cells from the CCD patients showed a reduced capacity to induce the differentiation of active osteoclasts.

CONCLUSIONS

These data indicate that PDL cells from CCD patients express a less distinctive osteoblastic phenotype resulting in an impaired ability to support osteoclastogenesis which might, in part, account for the delayed tooth eruption that can be observed clinically.

Novel RUNX2 Mutations in Chinese Individuals with Cleidocranial Dysplasia

Cleidocranial dysplasia (CCD) is an inherited autosomal-dominant skeletal disease caused by heterozygous mutations in the osteoblast-specific transcription factor, RUNX2. We performed mutation analysis of RUNX2 on four unrelated Chinese individuals with CCD. Three novel distinct mutations were detected in the coding region of RUNX2: two missense and one frameshift. These mutations were exclusively clustered within the Runt domain. One missense mutation converts threonine to isoleucine at codon 200 (T200I). The other one substitutes leucine for arginine at codon 225 (R225L), which affects many family members. The frame-shift mutation (214fs) in exon3 leads to the introduction of a translational stop codon at codon 221, resulting in a truncated RUNX2 protein. The reporter gene assays revealed that all the mutants exhibited significantly reduced transactivation activities on the osteocalcin promoter. Our results provide new genetic evidence that mutations involved in RUNX2 contribute to CCD. Abbreviations: AML3, gene encoding acute myeloid leukemia protein 3; bp, base pair; CBFA1, gene encoding core-binding factor 1; CBFβ, gene encoding core-binding factor β; CCD, cleidocranial dysplasia; NLS, nuclear localization signal; OSE2, osteoblast-specific cis-acting element 2; PEBP2A, gene encoding polyoma enhancer binding protein 2A; PST, proline/serine/ threonine-rich domain; Q/A, glutamine-alanine repeat domain; Runt, Runt Homology Domain; RUNX2, the mammalian runt-related genes 2; RUNX2, Runt-related protein 2.

RUNX2 mutations in Chinese patients with cleidocranial dysplasia

Cleidocranial dysplasia (CCD) is an autosomal dominant bone disease in humans caused by haploinsufficiency of the RUNX2 gene. The RUNX2 has two major isoforms derived from P1 and P2 promoters. Over 90 mutations of RUNX2 have been reported associated with CCD. In our study, DNA samples of nine individuals from three unrelated CCD families were collected and screened for all exons of RUNX2 and 2 kb of P1 and P2 promoters. We identified two point mutations in the RUNX2 gene in Case 1, including a nonsense mutation (c.577C>T) that has been reported previously and a silent substitution (c.240G>A). In vitro studies demonstrated that c.577C>T mutation led to truncated RUNX2 protein production and diminished stimulating effects on mouse osteocalcin promoter activity when compared with full-length Runx2-II and Runx2-I isoforms. These results confirm that loss of function RUNX2 mutation (c.577C>T) in Case 1 family is responsible for its CCD phenotype.

Haploinsufficiency of Runx2 results in bone formation decrease and different BSP expression pattern changes in two transgenic mouse models

Runx2 has been identified as "a master gene" for the differentiation of osteoblasts and Runx2-deficient mice has demonstrated a complete absence of mature osteoblast and ossification. To further characterize the Runx2 responsive elements within the bone sialoprotein (BSP) promoter and further investigate into the role of Runx2 haploinsufficiency in osteoblast differentiation, mBSP9.0Luc mice and mBSP4.8Luc mice were crossed with Runx2-deficient mice respectively. Luciferase assay, micro CT scan, and histological analysis were performed using tissues isolated from mBSP9.0luc/Runx2+/- mice, mBSP4.8luc/Runx2+/- mice and their corresponding Runx2+/+ littermates. Alkaline phosphatase activity, mineralization assays and RT-PCR analysis using calvarial osteoblasts isolated from these transgenic mice were also performed. Luciferase assay demonstrated an early increase in luciferase expression in mBSP9.0luc/Runx2+/- mice before the expression level of luciferase dramatically decreased and turned lower than that in their control littermates in later stages. In contrast, luciferase expression in mBSP4.8luc/Runx2+/- failed to show such an early increase. Micro CT scan and histological analysis showed that BMD and trabecular bone volume were decreased and bone formation was delayed in Runx2+/- mice. Furthermore, mineralization assay and semi-quantitative RT-PCR assay demonstrated a gene-dose-dependent decrease in bone nodule formation and bone marker genes expression levels in cultured calvarial osteoblasts derived from Runx2 knockout mice. Reconstitution of Runx2-null cells with Runx2 vector partially rescued the osteoblast function defects. In conclusion, the 9.0 kb BSP promoter demonstrated a higher tissue-specific regulation of the BSP gene by Runx2 in vivo and full Runx2 gene dose is essential for osteoblast differentiation and normal bone formation.

Genetische Störungen der Zahnentwicklung und Dentition

Die Zähne sind Organe, die aus ektodermalen epithelialen Aussackungen im Bereich des 1. Kiemenbogens entstehen, gesteuert von epitheliomesenchymalen Interaktionen. Dabei spielen zahlreiche Signalmoleküle speziell der 4 großen Familien TGF-β, FGF, Hedgehog und WNT sowie diverse Transkriptionsfaktoren eine Rolle. Eine Beteiligung der Retinoide an der Odontogenese ist durch umfangreiche Befunde belegt, auch wenn die Inaktivierung relevanter Gene in Mausmodellen meist keine Zahnanomalien verursacht. Die Zahnentwicklung wird klassischerweise in verschiedene Stadien eingeteilt: Entstehung der Zahnleiste, der Zahnknospe, der Schmelzkappe, der Schmelzglocke, die Wurzelbildung und der Zahndurchbruch. Anomalien der Zahnentwicklung können isoliert oder gemeinsam mit anderen Symptomen im Zusammenhang mit Syndromen auftreten. Sie können genetisch bedingt sein oder unter Einwirkung teratogener Stoffe während der Bildung und Mineralisierung der Zahnkeime zustande kommen. Dentibukkale Entwicklungsanomalien treten im Kontext seltener Erkrankungen auf und finden zunehmend Beachtung, da sie bei bestimmten Erkrankungen in der Diagnostik und als prädikative Faktoren wichtige Anhaltspunkte geben können. Allerdings ist hierfür eine interdisziplinäre und internationale Kooperation notwendig, die bislang erst in Ansätzen verwirklicht wurde.

Diverse effects of c-src deficiency on molar tooth development and eruption in mice

C-src deficiency is characterized by osteopetrosis due to impaired bone resorption by hypofunctional osteoclasts and the resultant failure of tooth eruption. In preliminary observations, we frequently encountered erupted molars in c-src deficient mice unlike in other osteopetrotic animals. Here we examine the effects of c-src deficiency on the development of molar teeth with an emphasis on the spatial relation of growing teeth with the surrounding bones. In c-src deficient mice, the magnitude of tooth impaction differed considerably among the types of molars; all maxillary 1st molars were totally impacted deep in the alveolar sockets, whereas most mandibular 1st molars fully erupted into oral cavity. Distribution of osteoclasts in the alveolar bone was identical among all types of molars, and electron microscopy revealed signs of bone resorbing activity in these osteoclasts despite the absence of a ruffled border. From early development, the alveolar space was much narrower in the upper molar tooth germs than in the lower ones in both wild type and homozygous animals, and particularly so in the upper 1st molars. Current observations thus indicate a significant contribution of "hypofunctional osteoclasts" in c-src deficient mice in molar tooth development except for the upper 1st molars, which appear to require highly functional osteoclasts to gain sufficient space for them to grow normally. Taken together, these findings on the seemingly tooth-type specific effects of c-src deficiency on the development and eruption of molar teeth in c-src deficient mice can be attributed to the given differential spatial relation of the respective tooth germs with the surrounding bones in the presence of hypofunctional osteoclasts.

Runx2 and dental development

The Runx2 gene is a master transcription factor of bone and plays a role in all stages of bone formation. It is essential for the initial commitment of mesenchymal cells to the osteoblastic lineage and also controls the proliferation, differentiation, and maintenance of these cells. Control is complex, with involvement of a multitude of factors, thereby regulating the expression and activity of this gene both temporally and spatially. The use of multiple promoters and alternative splicing of exons further extends its diversity of actions. RUNX2 is also essential for the later stages of tooth formation, is intimately involved in the development of calcified tooth tissue, and exerts an influence on proliferation of the dental lamina. Furthermore, RUNX2 regulates the alveolar remodelling process essential for tooth eruption and may play a role in the maintenance of the periodontal ligament. In this article, the structure of Runx2 is described. The control and function of the gene and its product are discussed, with special reference to developing tooth tissues, in an attempt to elucidate the role of this gene in the development of the teeth and supporting structures.

Cranioplasty for midline metopic suture defects in adults with cleidocranial dysplasia

OBJECTIVE

Patients with cleidocranial dysplasia often express concerns related to their perception of an undesirable esthetic appearance of their forehead and skull because of a combination of the persistence of metopic suture defects and frontal bossing. This case series reviews the use of a cranioplasty technique that has been developed to address such concerns.

STUDY DESIGN

A series of 7 adult patients with cleidocranial dysplasia were treated using a cranioplasty technique to correct visible metopic suture defects in the forehead region. The patients were 4 males and 3 females with a mean age of 29.0 years. All 7 patients underwent identical cranioplasty procedures.

RESULTS

The metopic suture cranial defects were found to range in size from 0.6 to 2.4 cm in diameter and were present as full-thickness osseous defects in 4 of the 7 patients. All postoperative complications resolved spontaneously. Inpatient admission times ranged from 1 to 3 days. Follow-up ranged from 9 to 48 months with satisfactory subjective esthetic outcomes. The patients were content in all cases.

CONCLUSION

This cranioplasty procedure successfully addresses the specific esthetic concerns of a rare and unique group of individuals. The procedure can be offered to cleidocranial dysplasia patients as part of their overall comprehensive craniomaxillofacial management.

Selective Runx2-II deficiency leads to low-turnover osteopenia in adult mice

Runx2 transcribes Runx2-II and Runx2-I isoforms with distinct N-termini. Deletion of both isoforms results in complete arrest of bone development, whereas selective loss of Runx2-II is sufficient to form a grossly intact skeleton with impaired endochondral bone development. To elucidate the role of Runx2-II in osteoblast function in adult mice, we examined heterozygous Runx2-II (Runx2-II(+/-)) and homozygous Runx2-II (Runx2-II(-/-))-deficient mice, which, respectively, lack one or both copies of Runx2-II but intact Runx2-I expression. Compared to wild-type mice, 6-week-old Runx2-II(+/-) had reduced trabecular bone volume (BV/TV%), cortical thickness (Ct.Th), and bone mineral density (BMD), decreased osteoblastic and osteoclastic markers, lower bone formation rates, impaired osteoblast maturation of BMSCs in vitro, and significant reductions in mechanical properties. Homozygous Runx2-II(-/-) mice had a more severe reduction in BMD, BV/TV%, and Ct.Th, and greater suppression of osteoblastic and osteoclastic markers than Runx2-II(+/-) mice. Non-selective Runx2(+/-) mice, which have an equivalent reduction in Runx2 expression due to the lack one copy of Runx2-I and II, however, had an intermediate reduction in BMD. Thus, selective Runx2-II mutation causes diminished osteoblastic function in an adult mouse leading to low-turnover osteopenia and suggest that Runx2-I and II have distinct functions imparted by their different N-termini.

Osteoclast diseases and dental abnormalities

Tooth eruption depends on the presence of osteoclasts to create an eruption pathway through the alveolar bone. In diseases where osteoclast formation, or function is reduced, such as the various types of osteopetrosis, tooth eruption is affected. Diseases in which osteoclast formation or activity is increased, such as familiar expansile osteolysis and Paget's disease, are associated with dental abnormalities such as root resorption and premature tooth loss. Less is known about the origin of the dental problems in these conditions as there are no rodent models of these diseases as yet. In this short review, the genes currently known to be mutated in human osteoclast diseases will be reviewed and, where known, the effect of osteoclast dysfunction on dental development described. It will focus on human conditions and only mention rodent disease where no clear data in the human are available.