Bone morphogenetic protein-7 (osteogenic protein-1, OP-1) and tooth development

BMP Signaling Pathway in Dentin Development and Diseases

BMP signaling plays an important role in dentin development. BMPs and antagonists regulate odontoblast differentiation and downstream gene expression via canonical Smad and non-canonical Smad signaling pathways. The interaction of BMPs with their receptors leads to the formation of complexes and the transduction of signals to the canonical Smad signaling pathway (for example, BMP ligands, receptors, and Smads) and the non-canonical Smad signaling pathway (for example, MAPKs, p38, Erk, JNK, and PI3K/Akt) to regulate dental mesenchymal stem cell/progenitor proliferation and differentiation during dentin development and homeostasis. Both the canonical Smad and non-canonical Smad signaling pathways converge at transcription factors, such as Dlx3, Osx, Runx2, and others, to promote the differentiation of dental pulp mesenchymal cells into odontoblasts and downregulated gene expressions, such as those of DSPP and DMP1. Dysregulated BMP signaling causes a number of tooth disorders in humans. Mutation or knockout of BMP signaling-associated genes in mice results in dentin defects which enable a better understanding of the BMP signaling networks underlying odontoblast differentiation and dentin formation. This review summarizes the recent advances in our understanding of BMP signaling in odontoblast differentiation and dentin formation. It includes discussion of the expression of BMPs, their receptors, and the implicated downstream genes during dentinogenesis. In addition, the structures of BMPs, BMP receptors, antagonists, and dysregulation of BMP signaling pathways associated with dentin defects are described.

Ablation of Fam20c causes amelogenesis imperfecta via inhibiting Smad dependent BMP signaling pathway

BACKGROUND

Amelogenesis imperfecta (AI) is a type of hereditary diseases that manifest defects in the formation or mineralization of enamel. Recently, it is reported that inactivation of FAM20C, a well-known Golgi casein kinase, caused AI. However, the mechanism of it is still unknown. The aim of this study was to explore the molecular mechanism of AI, which caused by ablation of FAM20C.

RESULTS

In the Sox2-Cre;Fam20C^fl/fl (cKO) mouse, we found abnormal differentiation of ameloblasts, improper formation and mineralization of enamel, and downregulation of both mRNA and protein level of enamel matrix proteins, including amelogenin (AMEL), ameloblastin (AMBN) and enamelin (ENAM). The levels of BMP2, BMP4 and BMP7, the ligands of BMP signaling pathway, and phosphorylation of Smad1/5/8, the key regulators of BMP signaling pathway, were all decreased in the enamel matrix and the ameloblast of the cKO mice, respectively. The expression of cyclin-dependent kinase inhibitor (P21), muscle segment homeobox genes 2 (Msx2), which are the target genes of the BMP signaling pathway, and laminin 3, the downstream factor of Msx2, were all significantly decreased in the ameloblasts of the cKO mice compared to the control mice.

CONCLUSION

the results of our study suggest that ablation of FAM20C leads to AI through inhibiting the Smad dependent BMP signaling pathway in the process of amelogenesis.

Mesenchymal Bmp7 Controls Onset of Tooth Mineralization: A Novel Way to Regulate Molar Cusp Shape

Investigating the molecular basis for tooth shape variation provides an important glimpse into the evolution of tooth function. We recently showed that loss of mesenchymal BMP7 is sufficient to alter morphology and function of the toothrow. Here we report on the underlying mechanism. Expression of mesenchymal Bmp7 is observed at sites where mineralization is initiated, in tooth cusps of developing molars. Neural crest-specific deletion of Bmp7 (Bmp7^ncko) resulted in a complete lack of dentin/enamel formation at birth, the time when mineralization is normally initiated in the upper molars, similar to what was observed in Bmp2^ncko mice. Unlike loss of Bmp2, loss of Bmp7 did not affect odontoblast polarization and did not significantly alter the levels of pSmad1/5/8, but almost completely abolished canonical Wnt signaling in (pre)-ameloblasts. Tooth mineralization resumed with a 48-h delay allowing for additional mesenchymal proliferation. Enamel volume was still reduced at P4 and P8, but was comparable in erupted teeth, which were broader and had altered cusp shapes. Tooth eruption was also delayed. Overall, enamel appeared inconspicuous, although some structural changes along with reduced mineral density could be observed. Loss of Bmp7 led to an increase in mesenchymal Bmp6 suggesting an interplay between Bmp6 and Bmp7 in the regulation of mineralization initiation. Our findings show that regulation of the onset of tooth mineralization is a hitherto unsuspected mechanism controlling tooth shape variation. Initiation of tooth mineralization is regulated by a complex epithelial-mesenchymal Bmp/Wnt-signaling network to which Bmp7 contributes. This network is separate and independent of the Bmp2-signaling network regulating odontoblast cell polarization. From an evolutionary perspective, addition of Bmp7 as initiator of tooth mineralization might be akin to an upgrade of an existing computer operating system. While not essential, it provides obviously sufficient advantage warranting its evolutionary incorporation.

Pointing on the early stages of maxillary bone and tooth development - histological findings

Although the morphological stages of tooth development, in parallel with maxillary bone construction, are known for decades, the intimate mechanisms of early development of the oral cavity structures and tooth's proper and associated tissues are still incompletely elucidated. Nowadays, the research in embryology was shifted from the morphological to the molecular and genetic approach. This new approach is accomplished by using in vivo and in vitro experimental studies performed on animal models and cell lines. The interest in the knowledge of these events at gene and molecular level is still current, aiming to sustain the progress in the endorsement of novel regenerative and restorative therapies. However, the morphological standpoint maintains its interest, because the extrapolation of the results of experimental studies in humans requires a strong confirmation. Within this context, our work aims to analyze the histological characteristics of the maxillary bone and integrated tooth germs during the early stages of embryonic development. The study group consisted in mandible fragments obtained by dissection of the cephalic extremities collected from fetuses aged from 10 to 24 weeks, after medical or spontaneous abortions. The tissue specimens were processed for the histological exam. The histoarchitectonic traits of the initial stages of mandibular bone tissue and tooth development were assessed. The results revealed the dynamics of the ossification stages, from stages of early-dispersed intramembranous ossification to the organization of the dental alveoli, incorporated step-by-step in the maxillary body, and the simultaneous presence of tooth germs with different sizes and shapes, in accordance with the development stage. Our study complements the existing data regarding the embryonic period, bringing an important contribution for the enlargement of existing morphological, visual information for maxillary bone and tooth development.

Dexamethasone inhibits BMP7-induced osteogenic differentiation in rat dental follicle cells via the PI3K/AKT/GSK-3β/β-catenin pathway

Impacted third molars are commonly seen in teenagers and young adults and can cause considerable suffering. Preventing eruption of the third molars can reduce pain at the source. Our previous study has shown that dexamethasone (DEX) at a certain concentration can prevent the eruption of third molars without damaging alveolar bone in Sprague-Dawley (SD) rats, but the relevant molecular mechanisms need to be explored. This study aimed to explore the effects of high concentrations of DEX on osteogenic signaling pathways, including BMP/Smad and Wnt/β-catenin pathways, in rat dental follicle cells (rDFCs) and to elucidate the possible mechanisms. The results showed that BMP7 induced osteogenic differentiation by increasing the activity of ALP and the protein levels of OPN in rDFCs. DEX decreased endogenous BMP7 and phosphorylated Smad1/5/8 expression as well as BMP7-induced osteogenic differentiation. DEX also reduced the mRNA and protein levels of β-catenin by enhancing the expression of GSK-3β. In addition, regardless of DEX intervention, overexpression of BMP7 promoted the expression of β-catenin, while knockdown of BMP7 attenuated it. Further investigation revealed that overexpression of BMP7 attenuated the DEX-mediated inhibition of AKT and GSK-3β phosphorylation, but knockdown of BMP7 exerted the opposite effects. This study suggests that high concentrations of DEX may inhibit the expression of β-catenin via the PI3K/AKT/GSK-3β pathway in a manner mediated by BMP7. The findings further illustrate the possible molecular mechanisms by which DEX prevents tooth development.

Noggin inhibition of mouse dentinogenesis

OBJECTIVES

The Bone Morphogenetic Proteins (BMPs) direct tooth development and still express in the adult tooth. We hypothesized that inhibition of BMP function would therefore disrupt dentinogenesis by differentiated odontoblasts.

METHODS

We generated mice overexpressing the BMP-inhibitory protein Noggin in differentiated odontoblasts and osteocytes under control of a Dmp1 promoter-driven cre transgene. We compared the dentin phenotype in these mice with that in WT littermates and in mice with a Smad4 odontoblast/osteocyte knockout mediated by the same cre and therefore lacking all BMP and Tgfβ signaling in the same tissues.

RESULTS

Three-month-old first molars from both Noggin-expressing and Smad4-deleted mice showed decreased dentin volume with enlarged pulp cavities, and both displayed less organized and mineralized dentinal tubules compared to WT. The Smad4-ablated phenotype was more severe. While dentin sialophosphoprotein (DSPP) and bone sialoprotein (BSP) were decreased in the dentin of both lines, dentin matrix protein 1 (DMP1) was sharply increased in Noggin-expressing teeth.

CONCLUSIONS

The phenotypes we observed in Noggin-overexpressing and Smad4-conditional knockout teeth resemble the phenotype of Dentinogenesis Imperfecta (DGI) type III. Our results show that BMPs regulate post-natal dentinogenesis and that BMP-inhibitory proteins like Noggin play a role in that regulation. The increased severity of the Smad4 phenotype indicates that Tgfβ ligands, in addition to BMPs, play a crucial role in post-developmental dentinogenesis.

Associations between variants of bone morphogenetic protein 7 gene and growth traits in chickens

1. Enhancing bone strength to solve leg disorders in poultry has become an important goal in broiler production. Bone morphogenetic protein 7 (BMP7), a member of the BMP family, represents an attractive therapeutic target for bone regeneration in humans and plays critical roles in skeletal development. 2. The objective of this study was to investigate the relationship between BMP7 gene expression, single-nucleotide polymorphisms (SNPs) and growth traits in chickens. Here, a SNP (c.1995T>C) in the chicken (Gallus gallus) BMP7 gene was identified, that was associated with growth and carcass traits. 3. Genotyping revealed that the T allele occurred more frequently in breeds with high growth rates, whereas the C allele was predominant in those with low growth rates. The expression level of BMP7 in the thigh bone of birds with the TT genotype was significantly higher than in those with the CC genotype at 21, 42 and 91 d of age. 4. These findings suggest that selecting the birds with the TT genotype of SNP c.1995T>C could improve bone growth, could reduce leg disorders in fast-growing birds. The SNP c.1995T>C may serve as a selective marker for improving bone growth and increasing the consistency of body weights in poultry breeding.

The role of bone morphogenetic proteins 2 and 4 in mouse dentinogenesis

OBJECTIVE

The bone morphogenetic proteins (BMPs) play crucial roles in tooth development. However, several BMPs retain expression in the dentin of the fully patterned and differentiated tooth. We hypothesized that BMP signaling therefore plays a role in the function of the differentiated odontoblast, the job of which is to lay down and mineralize the dentin matrix.

DESIGN

We generated mice deficient in Bmp2 and 4 using a dentin matrix protein 1 (Dmp1) promoter-driven cre recombinase that was expressed in differentiated odontoblasts.

RESULTS

The first and second molars of these Bmp2 and Bmp4 double conditional knockout (DcKO) mice displayed reduced dentin and enlarged pulp chambers compared to cre-negative littermate controls. DcKO mouse dentin in first molars was characterized by small, disorganized dentinal fibers, a wider predentin layer, and reduced expression of dentin sialophosphoprotein (DSPP), dentin matrix protein 1 (DMP1), and bone sialoprotein (BSP). DcKO mouse odontoblasts demonstrated increased type I collagen mRNA production, indicating that the loss of BMP signaling altered the rate of collagen gene expression in these cells. Bmp2 and Bmp4 single Dmp1-cre knockout mice displayed no discernable dentin phenotype.

CONCLUSIONS

These data demonstrate that BMP signaling in differentiated odontoblasts is necessary for proper dentin production in mature teeth.

Tissue engineering: Dentin - pulp complex regeneration approaches (A review)

Dental pulp is a highly specialized tissue that preserves teeth. It is important to maintain the capabilities of dental pulp before a pulpectomy by creating a local restoration of the dentin-pulp complex from residual dental pulp. The articles identified were selected by two reviewers based on entry and exit criteria. All relevant articles indexed in PubMed, Springer, Science Direct, and Scopus with no limitations from 1961 to 2016 were searched. Factors investigated in the selected articles included the following key words: Dentin-Pulp Complex, Regeneration, Tissue Engineering, Scaffold, Stem Cell, and Growth Factors. Of the 233 abstracts retrieved, the papers which were selected had evaluated the clinical aspects of the application of dentin-pulp regeneration. Generally, this study has introduced a new approach to provoke the regeneration of the dentin-pulp complex after a pulpectomy, so that exogenous growth factors and the scaffold are able to induce cells and blood vessels from the residual dental pulp in the tooth root canal. This study further presents a new strategy for local regeneration therapy of the dentin-pulp complex. This review summarizes the current knowledge of the potential beneficial effects derived from the interaction of dental materials with the dentin-pulp complex as well as potential future developments in this exciting field.

Differentiation of hMSC and hPDLSC induced by PGE2 or BMP-7 in 3D models

Regenerative therapies of pathogenic tissue defects are gaining increasing importance in periodontology. Among others, the osteogenic effect of BMP-7 seems to play a major role in the development of teeth and alveolar bone. Human periodontal ligament stem cells (hPDLSC), as well as human mesenchymal stem cells (hMSC), show the ability to differentiate into various types of tissues. Regarding prostaglandin E2, many studies have confirmed that it is involved in the inflammation associated to periodontitis stimulating osteoclasts, which ultimately leads to resorption of tooth supporting bone. Herein, we aimed to investigate how PGE2 influences regenerative processes. The influence of PGE2 and BMP-7 on the osteogenic differentiation of hMSC and hPDLSC was determined in a 3D cell culture model using qRT-PCR, immunocytochemistry and REM. BMP-7 enhanced the expression of osteogenic markers in hMSC and lowered it in hPDLSC-TERT. BMP-7 had a lower osteogenic effect on hPDLSC-hTERT than on hMSC, while PGE2 decreases the osteogenic differentiation in both cell types, thus, inhibiting anabolic processes. Both cell types presented good proliferation and adhesion onto the scaffolds. The well-developed structural morphology and the support of osteogenic differentiation suggest that the scaffolds are potential candidate materials for bone regeneration. The positivity for Cap in hPDLSC and more in hMSC immunostaining samples indicates the initiation of neocementogenesis as part of periodontal regeneration. In conclusion, BMP7, in particular combined with MSC, seems to have a favourable application also in periodontal regeneration. Our results show that inflammation plays an important role in periodontal regeneration. PGE2 is a key mediator, which stimulates bone resorption also via a mechanism involving the inhibition of osteogenic differentiation of MSC as well as PDLSC. Therefore, regenerative approaches should always be conducted in combination with anti-inflammatory measures oriented to control inflammation.

Biological Molecules for the Regeneration of the Pulp-Dentin Complex

Regenerative endodontic treatment has yielded excellent clinical outcomes, but only several animal studies have shown the robust regeneration of the pulp-dentin complex. The biological molecules, if properly delivered, can enkindle regeneration of dental pulp and dentin rather than repair with tissues of periodontal origin. This review details the biological significance of regenerating the pulp-dentin complex, the effects of biological cues in pulp regeneration, and the delivery strategies of biological molecules to enhance the outcomes of regenerative endodontic therapy.

Family-Based Genetic Association for Molar-Incisor Hypomineralization

Despite some evidence of genetic and environmental factors on molar-incisor hypomineralization (MIH), its aetiology remains unclear. This family-based genetic association study aimed more comprehensively to investigate the genetic carriage potentially involved in MIH development. DNA was obtained from buccal cells of 391 individuals who were birth family members of 101 Brazilian nuclear families. Sixty-three single nucleotide polymorphisms (SNPs) were investigated in 21 candidate genes related to amelogenesis using the TaqMan™ OpenArray™ Genotyping platform. All SNPs were genotyped in 165 birth family members unaffected by MIH, 96 with unknown MIH status and 130 affected individuals (50.7% with severe MIH). Association analysis was performed by the transmission/disequilibrium test (TDT), and statistical results were corrected using the false discovery rate. Significant results were obtained for SNPs rs7821494 (FAM83H gene, OR = 3.7; 95% CI = 1.75-7.78), rs34367704 (AMBN gene, OR = 2.7; 95% CI = 1.16-6.58), rs3789334 (BMP2 gene, OR = 2.9; 95% CI = 1.34-6.35), rs6099486 (BMP7 gene, OR = 2.2; 95% CI = 1.14-4.38), rs762642 (BMP4 gene, OR = 2.3; 95% CI = 1.38-3.65), rs7664896 (ENAM gene, OR = 2.1; 95% CI = 1.19-3.51), rs1711399 (MMP20 gene, OR = 0.4; 95% CI = 0.20-0.72), rs1711423 (MMP20 gene, OR = 2.1; 95% CI = 1.18-3.61), rs2278163 (DLX3 gene, OR = 2.8; 95% CI = 1.26-6.41), rs6996321 (FGFR1 gene, OR = 2.7; 95% CI = 1.20-5.88), and rs5979395 (AMELX gene, OR = 11.7; 95% CI = 1.63-84.74). Through this family-based association study, we concluded that variations in genes related to amelogenesis were associated with the susceptibility to develop MIH. This result is in agreement with the multifactorial idea of the MIH aetiology, but further studies are necessary to investigate more thoroughly the factors that could influence MIH.

Mineralization Effect of Hyaluronan on Dental Pulp Cells via CD44

INTRODUCTION

CD44 is a cell-surface glycoprotein involved in various cellular functions. Recent studies have suggested that CD44 is involved in early mineralization of odontoblasts. Hyaluronic acid (HA) is the principal ligand for receptor CD44. Whether and how HA regulated the mineralization process of dental pulp cells were investigated.

METHODS

The effects of high-molecular-weight HA on differentiation and mineral deposition of dental pulp cells were tested by using alkaline phosphatase (ALP) activity assay and alizarin red S staining. Osteogenesis real-time polymerase chain reaction array, quantitative polymerase chain reaction, and Western blotting were performed to identify downstream molecules involved in the mineralization induction of HA. CD44 was knocked down and examined to confirm whether the mineralization effect of HA was mediated by receptor CD44. Immunohistochemistry was used to understand the localization patterns of CD44 and the identified downstream proteins in vivo.

RESULTS

Pulse treatment of HA enhanced ALP activity and mineral deposition in dental pulp cells. Tissue-nonspecific ALP, bone morphogenetic protein 7 (BMP7), and type XV collagen (Col15A1) were upregulated via the HA-CD44 pathway in vitro. Immunohistochemistry of tooth sections showed that the staining pattern of BMP7 was very similar to that of CD44.

CONCLUSIONS

Results of this study indicated that high-molecular-weight HA enhanced early mineralization of dental pulp cells mediated via CD44. The process involved important mineralization-associated molecules including tissue-nonspecific ALP, BMP7, and Col15A1. The findings may help develop new strategies in regenerative endodontics.

Genome-wide association study of dental caries in the Hispanic Communities Health Study/Study of Latinos (HCHS/SOL)

Dental caries is the most common chronic disease worldwide, and exhibits profound disparities in the USA with racial and ethnic minorities experiencing disproportionate disease burden. Though heritable, the specific genes influencing risk of dental caries remain largely unknown. Therefore, we performed genome-wide association scans (GWASs) for dental caries in a population-based cohort of 12 000 Hispanic/Latino participants aged 18-74 years from the HCHS/SOL. Intra-oral examinations were used to generate two common indices of dental caries experience which were tested for association with 27.7 M genotyped or imputed single-nucleotide polymorphisms separately in the six ancestry groups. A mixed-models approach was used, which adjusted for age, sex, recruitment site, five principal components of ancestry and additional features of the sampling design. Meta-analyses were used to combine GWAS results across ancestry groups. Heritability estimates ranged from 20-53% in the six ancestry groups. The most significant association observed via meta-analysis for both phenotypes was in the region of the NAMPT gene (rs190395159; P-value = 6 × 10(-10)), which is involved in many biological processes including periodontal healing. Another significant association was observed for rs72626594 (P-value = 3 × 10(-8)) downstream of BMP7, a tooth development gene. Other associations were observed in genes lacking known or plausible roles in dental caries. In conclusion, this was the largest GWAS of dental caries, to date and was the first to target Hispanic/Latino populations. Understanding the factors influencing dental caries susceptibility may lead to improvements in prediction, prevention and disease management, which may ultimately reduce the disparities in oral health across racial, ethnic and socioeconomic strata.

Dental pulp cells that express adeno-associated virus serotype 2-mediated BMP-7 gene enhanced odontoblastic differentiation

This present study investigated the potential of adeno-associated virus serotype 2 (AAV2) mediated BMP-7 (AAV2-BMP-7) to induce odontoblastic differentiation of human dental pulp cells (DPCs) in vitro. AAV2-BMP-7 was constructed to overexpress BMP-7, and the biologic effects of BMP-7 on DPCs were investigated by the evaluation of the activity of alkaline phosphatase (ALPase), the detection of the expression of dentin sialophosphoprotein (DSPP) and osteocalcin (OCN) expression and the analysis of the proliferative ability of the cells. DPCs that were infected with AAV2-BMP-7 displayed significantly upregulated ALP activity and formed mineralized nodules. Moreover, AAV2-BMP-7 promoted the expression of mineralization-related genes, which included DSPP and OCN. In addition, there was no significant difference between the proliferative ability of AAV2-BMP-7 and the control group. In conclusion, AAV2-BMP-7 promoted the odontoblastic differentiation in DPCs, a clear indication of the therapeutic potential of AAV2-BMP-7 in dental tissue regeneration.

Distribution of BMP6 in the alveolar bone during mouse mandibular molar eruption

Eruption requires synchrony of the tooth with the surrounding tissues, particularly the bone. One important step during eruption is remodelling of the alveolar bone at the base of the tooth and along the roots. Expression of BMP6 was reported to be increased in the basal half of the dental follicle prior to eruption and inhibition of BMP6 affected bone formation at the base of the alveolar crypt. The aim of this study was to further investigate BMP6 protein in relation to tooth eruption and the corresponding bone remodelling using temporospatial correlations of BMP6 localization with morphogenetic events (proliferation, differentiation, apoptosis and bone apposition/resorption), other BMPs (BMP2 and BMP7) and three-dimensional images of tooth-bone development. BMP6 expression pattern was mapped in the mandibular molar teeth and related structures around eruption. Localization of BMP6 dominated in osteoblasts, in regions of bone formation within the alveolar crypt. These findings positively correlated with proliferation at the tooth base region, osteocalcin expression in the osteoblasts/osteocytes and BMP2 and BMP7 presence in the alveolar bone surrounding the tooth. Osteoclast activity and apoptotic elimination in the root region gradually decreased before eruption and totally ceased at eruption stages. Generally, BMP6 positively correlated with BMP2, BMP7 and osteocalcin-positive osteoblasts, and areas of bone remodelling. Moreover, BMP6 was found in the periodontium and cementoblasts. BMP6 expression in the alveolar bone accompanied tooth eruption. Notably, the expression pattern of BMP6 in the bone did not differ around individual molar teeth at the same stage of development. The expression of BMP6 in periodontal ligaments may contribute to interaction between the tooth and bone during the eruption and anchoring process.

The clinical use of bone morphogenetic proteins revisited: a novel biocompatible carrier device OSTEOGROW for bone healing

PURPOSE

The purpose of this study was to revise the clinical use of commercial BMP2 (Infuse) and BMP7 (Osigraft) based bone devices and explore the mechanism of action and efficacy of low BMP6 doses in a novel whole blood biocompatible device OSTEOGROW.

METHODS

Complications from the clinical use of BMP2 and BMP7 have been systemically reviewed in light of their role in bone remodeling. BMP6 function has been assessed in Bmp6-/- mice by μCT and skeletal histology, and has also been examined in mesenchymal stem cells (MSC), hematopoietic stem cells (HSC) and osteoclasts. Safety and efficacy of OSTEOGROW have been assessed in rats and rabbits.

RESULTS

Clinical use issues of BMP2 and BMP7 have been ascribed to the limited understanding of their role in bone remodeling at the time of device development for clinical trials. BMP2 and BMP7 in bone devices significantly promote bone resorption leading to osteolysis at the endosteal surfaces, while in parallel stimulating exuberant bone formation in surrounding tissues. Unbound BMP2 and BMP7 in bone devices precipitate on the bovine collagen and cause inflammation and swelling. OSTEOGROW required small amounts of BMP6, applied in a biocompatible blood coagulum carrier, for stimulating differentiation of MSCs and accelerated healing of critical size bone defects in animals, without bone resorption and inflammation. BMP6 decreased the number of osteoclasts derived from HSC, while BMP2 and BMP7 increased their number.

CONCLUSIONS

Current issues and challenges with commercial bone devices may be resolved by using novel BMP6 biocompatible device OSTEOGROW, which will be clinically tested in metaphyseal bone fractures, compartments where BMP2 and BMP7 have not been effective.

Genome-wide association study (GWAS) for molar-incisor hypomineralization (MIH)

OBJECTIVES

This genome-wide association study (GWAS) investigated the relationship between molar-incisor hypomineralization (MIH) and possible genetic loci. Clinical and genetic data from the 10-year follow-up of 668 children from the Munich GINI-plus and LISA-plus birth cohort studies were analyzed.

MATERIAL AND METHODS

The dental examinations included the diagnosis of MIH according to the criteria of the European Academy of Paediatric Dentistry (EAPD). Children with MIH were categorized as those with a minimum of one hypomineralized first permanent molar. A GWAS was implemented following a quality-control step and an additive genetic effect was assumed.

RESULTS

A total of 2,013,491 single-nucleotide polymorphisms (SNPs) were available for analysis. Rs13058467, which is located near the SCUBE1 gene on chromosome 22 (p < 3.72E-7), was identified as a possible locus linked to MIH when using a threshold of p value <1E-6.

CONCLUSIONS

After considering the limitations of the present study (e.g., limited sample size and lack of an independent replication sample), it can be concluded that (1) replication analyses in an independent cohort study are strongly recommended and (2) large-scale and well-powered studies are needed to investigate a possible genetic link to MIH.

Chitosan/collagen scaffold containing bone morphogenetic protein-7 DNA supports dental pulp stem cell differentiation in vitro and in vivo

In this study, porous chitosan/collagen scaffolds were prepared through a freeze-drying process, and loaded with the plasmid vector encoding human bone morphogenetic protein-7 (BMP-7) gene. To investigate the feasibility and efficacy of this gene-activated scaffold on dental tissue engineering, human dental pulp stem cells (DPSCs) were seeded in this scaffold for in vitro and in vivo study. In vitro results indicated that cells can be transfected successfully by loaded plasmid and secrete BMP-7 until day 24. Evaluation of DNA content, ALP activity, calcium content, SEM, and real-time PCR revealed that cells on gene-activated scaffold showed better proliferation properties and odontoblastic differentiation behaviors than cells on pure scaffolds. Then, these cell-scaffold complexes were implanted subcutaneously and retrieved after 4 weeks for histology evaluation. In vivo results that gene-activated scaffold group could still trace the existence of tranfected cells at week 4 and showed the upregulated expression of DSPP compared to pure scaffold groups. On the basis of our results, chitosan/collagen-loaded BMP-7 DNA appears to be an effective substrate candidate for gene delivery and indeed enhanced DPSCs differentiation toward an odontoblast-like phenotype in vitro and in vivo. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A:, 2012.

Critical role for αvβ6 integrin in enamel biomineralization

Tooth enamel has the highest degree of biomineralization of all vertebrate hard tissues. During the secretory stage of enamel formation, ameloblasts deposit an extracellular matrix that is in direct contact with ameloblast plasma membrane. Although it is known that integrins mediate cell-matrix adhesion and regulate cell signaling in most cell types, the receptors that regulate ameloblast adhesion and matrix production are not well characterized. Thus, we hypothesized that αvβ6 integrin is expressed in ameloblasts where it regulates biomineralization of enamel. Human and mouse ameloblasts were found to express both β6 integrin mRNA and protein. The maxillary incisors of Itgb6−/− mice lacked yellow pigment and their mandibular incisors appeared chalky and rounded. Molars of Itgb6−/− mice showed signs of reduced mineralization and severe attrition. The mineral-to-protein ratio in the incisors was significantly reduced in Itgb6−/− enamel, mimicking hypomineralized amelogenesis imperfecta. Interestingly, amelogenin-rich extracellular matrix abnormally accumulated between the ameloblast layer of Itgb6−/− mouse incisors and the forming enamel surface, and also between ameloblasts. This accumulation was related to increased synthesis of amelogenin, rather than to reduced removal of the matrix proteins. This was confirmed in cultured ameloblast-like cells, which did not use αvβ6 integrin as an endocytosis receptor for amelogenins, although it participated in cell adhesion on this matrix indirectly via endogenously produced matrix proteins. In summary, integrin αvβ6 is expressed by ameloblasts and it plays a crucial role in regulating amelogenin deposition/turnover and subsequent enamel biomineralization.

The proteome and gene expression profile of cementoblastic cells treated by bone morphogenetic protein-7 in vitro

AIM

Regenerative periodontal therapy is often unpredictable and limited. Cementum regeneration is necessary for the proper repair of a periodontal ligament. The precise mechanism how bone morphogenetic protein-7 (BMP7) induces differentiation and mineralization of cementoblasts remains undetermined. The purpose of this study was to evaluate the effect of BMP7 on early proteome and gene expression profile of cementoblastic OCCM.30 cells in vitro.

MATERIALS AND METHODS

Immortalized murine cementoblasts (OCCM.30) were exposed to BMP7 and evaluated for: (1) proliferation; (2) mineralization; (3) early proteome profile using liquid chromatography-mass spectrometry (LC-MS); and (4) gene expression by quantitative RT-PCR.

RESULTS

Bone morphogenetic protein-7 increased the cell proliferation at 24 h and 48 h, while higher doses suppressed the cell proliferation at 48 h. BMP7 induced the mineralization of cementoblasts following 8 days of therapy. Using LC-MS we identified 1117 proteins from the cell lysate. Many belonged to extracellular matrix formation such as PCPE1, collagens, annexins and integrin receptors. RT-PCR analyses revealed a BMP7 dose-dependent upregulation of BMP1, TGFβ1, osterix, osteoprotegerin, procollagen I and II, PCPE1, and noggin, while BMP6 and chordin expression were decreased. The high BMP7 dose down regulated most of the genes 24 h following therapy.

CONCLUSION

Bone morphogenetic protein-7 promotes differentiation and mineralization of cementoblasts via inducing PCPE1 and BMP1 responsible for processing of type I collagen.

Mechanical loading stimulates BMP7, but not BMP2, production by osteocytes

Bone mechanical adaptation is a cellular process that allows bones to adapt their mass and structure to mechanical loading. This process is governed by the osteocytes, which in response to mechanical loading produce signaling molecules that affect osteoblasts and osteoclasts. Bone morphogenic proteins (BMPs) are excellent candidates as signaling molecules, but it is unknown whether mechanically stimulated osteocytes affect bone adaptation through BMP production. Therefore, the aim of this study was to assess whether osteocytes produce BMPs in response to mechanical loading. In addition, since BMP7 has a vitamin D receptor (VDR) response element in the promoter region, we also investigated whether VDR is involved in the BMP7 response to mechanical loading. Human or VDR(-/-) mouse primary bone cells were submitted in vitro to 1 h pulsating fluid flow (PFF) and postincubated without PFF (PI) for 1-24 h, and gene and protein expression of BMP2 and BMP7 were quantified. In human bone cells, PFF did not change BMP2 gene expression, but it upregulated BMP7 gene expression by 4.4- to 5.6-fold at 1-3 h PI and stimulated BMP7 protein expression by 2.4-fold at 6 h PI. PFF did not stimulate BMP7 gene expression in VDR(-/-) mouse bone cells. These results show for the first time that mechanical loading upregulates BMP7, likely via the VDR, but not BMP2, gene and protein expression in osteocytes in vitro. Since BMP7 plays a major role in bone development and remodeling, these data might contribute to a better understanding of the mechanism leading to the mechanical adaptation of bone.

Expression of mineralized tissue associated proteins: dentin sialoprotein and phosphophoryn in rodent hair follicles

BACKGROUND

Mammalian hair development and tooth development are controlled by a series of reciprocal epithelial-mesenchymal interactions. Similar growth factors and transcription factors, such as fibroblast growth factor (FGF), sonic hedgehog homolog (SHH), bone morphogenetic proteins (BMPs) and Wnt10a, were reported to be involved in both of these interactions. Dentin sialoprotein (DSP) and phosphophoryn (PP) are the two major non-collagenous proteins secreted by odontoblasts that participate in dentin mineralization during tooth development. Because of striking similarities between tooth development and hair follicle development, we investigated whether DSP and/or PP proteins may also play a role in hair follicle development.

OBJECTIVE

In this study, we examined the presence and location of DSP/PP proteins during hair follicle development.

METHODS

Rat PP proteins were detected using immunohistochemical/immunofluorescent staining. DSP-PP mRNAs were detected by in situ hybridization with riboprobes. LacZ expression was detected in mouse tissues using a DSP-PP promoter-driven LUC in transgenic mice.

RESULTS

We found that PP proteins and DSP-PP mRNAs are present in rat hair follicles. We also demonstrate that an 8 kb DSP-PP promoter is able to drive lacZ expression in hair follicles.

CONCLUSION

We have firmly established the presence of DSP/PP in mouse and rat hair follicles by immunohistochemical/immunofluorescent staining, in situ hybridization with riboprobes and transgenic mice studies. The expression of DSP/PP in hair follicles is the first demonstration that major mineralization proteins likely may also contribute to soft tissue development. This finding opens a new avenue for future investigations into the molecular-genetic management of soft tissue development.

Effects of adenoviral-mediated coexpression of bone morphogenetic protein-7 and insulin-like growth factor-1 on human periodontal ligament cells

BACKGROUND AND OBJECTIVE

Bone morphogenetic protein-7 (BMP-7) and insulin-like growth factor-1 (IGF-1) are important in periodontal reconstruction. However, their synergistic effect in periodontal regeneration by gene delivery has not been reported. In this study, gene delivery of these two growth factors to human periodontal ligament cells (hPDLCs) was examined for its effects on cell proliferation and differentiation.

MATERIAL AND METHODS

Recombinant adenoviruses containing both human BMP-7 and IGF-1 cDNA created by introducing the internal ribosome entry site (IRES) sequence were used to transfer the genes into hPDLCs. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and cell cycle analysis were used to observe their effects on cell proliferation, while alkaline phosphatase activity measurement, RT-PCR and in vivo tests were conducted to investigate their effects on cell differentiation.

RESULTS

The proliferation of hPDLCs transduced by adenoviruses coexpressing BMP-7 and IGF-1 was suppressed while their differentiation ability was enhanced. There was a synergism of BMP-7 and IGF-1 in up-regulating alkaline phosphatase activity and mRNA levels of collagen type I and Runx2. Implantation in vivo with scaffolds illustrated that the transduced cells exhibited osteogenic differentiation and formed bone-like structures.

CONCLUSION

The combined delivery of BMP-7 and IGF-1 genes using an IRES-based strategy synergistically enhanced differentiation of hPDLCs. It is suggested that this could be a new potential method in gene therapy for periodontal reconstruction.

Toxicity of Flow Line, Durafill VS, and Dycal to dental pulp cells: effects of growth factors

INTRODUCTION

The objective was to determine the effects of growth factor treatment on dental pulp cell sensitivity to toxicity of 2 composite restoration materials, Flow Line and Durafill VS, and a calcium hydroxide pulp capping material, Dycal.

METHODS

Toxicity of the dental materials to cultures of primary dental pulp cells was determined by the MTT metabolism assay. The ability of 6 different growth factors to influence the toxicity was tested.

RESULTS

A 24-hour exposure to either Flow Line or Durafill VS caused approximately 40% cell death, whereas Dycal exposure caused approximately 80% cell death. The toxicity of Flow Line and Durafill VS was mediated by oxidative stress. Four of the growth factors tested (bone morphogenetic protein [BMP]-2, BMP-7, epidermal growth factor [EGF], and transforming growth factor [TGF]-beta) decreased the basal MTT values while making the cells resistant to Flow Line and Durafill VS toxicity except BMP-2, which made the cells more sensitive to Flow Line. Treatment with fibroblast growth factor-2 caused no change in basal MTT metabolism, prevented the toxicity of Durafill VS, but increased the toxicity of Flow Line. Treatment with insulin-like growth factor-I (IGF-I) increased basal MTT metabolism and made the cells resistant to Flow Line and Durafill VS toxicity. None of the growth factors made the cells resistant to Dycal toxicity.

CONCLUSIONS

The results indicated that growth factors can be used to alter the sensitivity of dental pulp cells to commonly used restoration materials. The growth factors BMP-7, EGF, TGF-beta, and IGF-I provided the best profile of effects, making the cells resistant to both Flow Line and Durafill VS toxicity.

Scube1 is expressed during facial development in the mouse

Scube1 encodes a secreted plasma membrane-associated protein characterized by a N-terminal signal peptide sequence, multiple EGF domains, a N-linked glycosylated spacer region and a C-terminal CUB region. Here, we describe expression of the mouse Scube1 gene during early craniofacial development. Transcripts were identified in the nervous system, within the ventral neural tube, telencephalon and trigeminal ganglion. In addition, strong regionally restricted expression was found in the facial processes, including the medial and lateral nasal processes, maxilla and mandible, and caudal pharyngeal arches. During tooth development, Scube1 localized to the dental papilla of both incisor and molar teeth. Together, these data suggest a potential role for Scube1 during early craniofacial development.

Transgenic overexpression of gremlin results in developmental defects in enamel and dentin in mice

Bone morphogenetic proteins (BMPs) and BMP antagonists play a crucial role in the regulation of tooth development. One of the BMP extracellular antagonists, gremlin, is a highly conserved 20.7-kDa glycoprotein. Previously, researchers reported that transgenic mice overexpressing gremlin under the control of the osteocalcin promoter (gremlin OE) exhibit a skeletal phenotype and tooth fragility. To further define the tooth phenotype, teeth and surrounding supporting tissues, obtained from gremlin OE at ages of 4 weeks, 2 months, and 4 months, were examined. The histological results demonstrate that gremlin OE exhibit an enlarged pulp chamber with ectopic calcification and thinner dentin and enamel compared with wild-type control. In vitro studies using murine pulp cells revealed that gremlin inhibited BMP-4 mediated induction of Dspp. These data provide evidence that balanced interactions between BMP agonists/antagonists are required for proper development of teeth and surrounding tissues. It is clear that these interactions require further investigation to better define the mechanisms controlling tooth root formation (pulp, dentin, cementum, and surrounding tissue) to provide the information needed to successfully regenerate these tissues.

Interaction of bone morphogenetic proteins with cells of the osteoclast lineage: review of the existing evidence

The present review evaluates the existing scientific proofs of this supplementary role of the BMPs and summarises its clinical implications. Bone regeneration is a process consisting of bone formation and bone resorption, two different but closely coupling pathways, which in most circumstances proceed simultaneously. Plenty of evidence has also characterised the bone morphogenetic proteins (BMPs) as inducing factors of bone formation. However, there is also evidence that these multifunctioning proteins affect bone resorption and the osteoclast homeostasis utilising various pathways. The present review evaluates the existing scientific evidence of this supplementary role of the BMPs, and summarises its clinical implications.

Localization of STRO-1, BMP-2/-3/-7, BMP receptors and phosphorylated Smad-1 during the formation of mouse periodontium

Bone morphogenetic proteins (BMPs) and BMP receptors (BMPRs) are known to regulate the development of calcified tissues by directing mesenchymal precursor cells differentiation. However, their role in the formation of tooth-supporting tissues remains unclear. We investigated the distribution pattern of STRO-1, a marker of mesenchymal progenitor cells and several members of the BMP pathway during the development of mouse molar periodontium, from the post-natal days 6 to 23 (D6 to D23). STRO-1 was mainly localized in the dental follicle (DF) at D6 and 13 then in the periodontal ligament (PDL) at D23. BMP-2 and -7 were detected in Hertwig's epithelial root sheath (HERS) and in DF, then later in differentiated periodontal cells. BMP-3 was detected after D13 of the periodontal development. BMPRs-Ib, -II, the activin receptor-1 (ActR-1) and the phosphorylated Smad1 were detected in DF and HERS at D6 and later more diffusely in the periodontium. BMPR-Ia detection was restricted to alveolar bone. These findings were in agreement with others data obtained with mouse immortalized DF cells. These results suggest that STRO-1 positive DF cells may be target of BMPs secreted by HERS. BMP-3 might be involved in the arrest of this process by inhibiting the signaling provided by cementogenic and osteogenic BMPs.

Cell autonomous requirement for TGF-beta signaling during odontoblast differentiation and dentin matrix formation

TGF-beta subtypes are expressed in tissues derived from cranial neural crest cells during early mouse craniofacial development. TGF-beta signaling is critical for mediating epithelial-mesenchymal interactions, including those vital for tooth morphogenesis. However, it remains unclear how TGF-beta signaling contributes to the terminal differentiation of odontoblast and dentin formation during tooth morphogenesis. Towards this end, we generated mice with conditional inactivation of the Tgfbr2 gene in cranial neural crest derived cells. Odontoblast differentiation was substantially delayed in the Tgfbr2(fl/fl);Wnt1-Cre mutant mice at E18.5. Following kidney capsule transplantation, Tgfbr2 mutant tooth germs expressed a reduced level of Col1a1 and Dspp and exhibited defects including decreased dentin thickness and absent dentinal tubules. In addition, the expression of the intermediate filament nestin was decreased in the Tgfbr2 mutant samples. Significantly, exogenous TGF-beta2 induced nestin and Dspp expression in dental pulp cells in the developing tooth organ. Our data suggest that TGF-beta signaling controls odontoblast maturation and dentin formation during tooth morphogenesis.

Buonocore Memorial Lecture

For many years, operative dentistry has been using regenerative approaches to treat dental disease. The use of calcium hydroxide to stimulate reparative or reactionary dentin is clearly an example of such a therapeutic strategy. The advent of tissue engineering is allowing dentistry to move forward in the use of regeneration as an underlying principle for the treatment of dental disease. Tissue engineering is a multi-disciplinary science that brings together biology, engineering and clinical sciences with developing new tissues and organs. It is based on fundamental principles that involve the identification of appropriate cells, the development of conducive scaffolds and an understanding of the morphogenic signals required to induce cells to regenerate the tissues that were lost. This review is focused on the presentation and discussion of existing literature that covers the engineering of enamel, dentin and pulp, as well on the engineering of entire teeth. There are clearly major roadblocks to overcome before such strategies move to the clinic and are used regularly to treat patients. However, existing evidence strongly suggests that the engineering of new dental structures to replace tissues lost during the process of caries or trauma will have a place in the future of operative dentistry.

Gene-enhanced tissue engineering for dental hard tissue regeneration: (2) dentin-pulp and periodontal regeneration

Potential applications for gene-based tissue engineering therapies in the oral and maxillofacial complex include the delivery of growth factors for periodontal regeneration, pulp capping/dentin regeneration, and bone grafting of large osseous defects in dental and craniofacial reconstruction. Part 1 reviewed the principals of gene-enhanced tissue engineering and the techniques of introducing DNA into cells. This manuscript will review recent advances in gene-based therapies for dental hard tissue regeneration, specifically as it pertains to dentin regeneration/pulp capping and periodontal regeneration.

Evolution of novelty in the cichlid dentition

The shape of teeth occupies a central position in various biological disciplines, from paleo-ecology to molecular biology to cosmetic and reconstructive dentistry. Despite a long tradition of study in mammals, important questions remain regarding the genetic and developmental basis of differences in tooth shape. Here, we use natural mutants of cichlid fish from East Africa, which exhibit tremendous dental diversity, to help fill the gaps in our understanding of vertebrate odontogenesis. We employ an expanded genetic linkage map to demonstrate that cusp number segregates as a gene of major effect, which explains approximately 40% of the phenotypic variance, on cichlid chromosome 5. Furthermore, we examine patterns of Bmp4 expression in early odontogenesis to address and refine predictions of models linking tooth shape and tooth number. Mutations in the Bmp4 cistron do not control tooth shape in this mapping cross. Our data suggest that the evolution of novelty in the cichlid dentition is galvanized by a small number of genetic changes, echoing similar conclusions from recent studies of other vertebrate adaptive morphologies.

Expression patterns of BMPRs in the developing mouse molar

During development, Bone Morphogenetic Proteins (BMPs) can induce apoptosis, cell growth or differentiation. These different effects are mediated by dimers of two types of BMP-receptors (BMPRs). To identify the responding cells during tooth development and search for possible tissue-or stage-specificities in the receptors involved, the distribution patterns of BMPR-IA, -IB and -II were investigated in the mouse molar, from bud to bell stage. At the bud stage, BMP-2 was suggested to be involved in the formation of an epithelial signaling center, the primary enamel knot (PEK), while BMP-4 would mediate the condensation of the mesenchyme. Immunostaining showed the presence of BMPR-IA and -II in the epithelium instead of BMPR-IB and -II in the mesenchyme. At the cap stage, BMPR-IB was detected in the epithelium but not BMPR-II, suggesting the existence of another type II receptor to form a functional dimer. At the late cap stage in the epithelium, BMP-4, BMPR-IA and -II were restricted to the internal part of the PEK and the stalk: two apoptotic areas. The three proteins were detected in the mesenchyme, showing a strong staining where cusps were about to form. At the late bell stage, BMP-2 or -4 may induce cell differentiation. BMPR-IB and -II were detected in odontoblasts instead of BMPR-IA and -II in ameloblasts. These results provide the first evidence of multiple type I and type II BMP-receptors, expressed in the dental epithelium and mesenchyme at different stages of development, to signal different cellular activities in a time- and tissue-specific way.

Bone morphogenetic proteins in craniofacial and periodontal tissue engineering: Experimental studies in the non-human primate Papio ursinus

The bone morphogenetic and osteogenic proteins (BMPs/OPs), pleiotropic members of the transforming growth factor-beta (TGF-beta) supergene family act as soluble signals for the de novo initiation of bone formation, sculpting the multicellular mineralized structures of the bone-bone marrow organ. The strikingly pleiotropic effects of BMPs/OPs spring from amino acid sequence variations in the carboxy-terminal domain and in the transduction of distinct signalling pathways by individual Smad proteins after transmembrane serine/threonine kinase complexes of type I and II receptors. BMPs/OPs are the common molecular initiators deployed for embryonic development and the induction of bone formation and regeneration in postnatal osteogenesis. Naturally derived BMPs/OPs extracted and purified from baboon and bovine bone matrices induce complete regeneration of non-healing calvarial defects in the non-human primate Papio ursinus as well as the induction of cementogenesis and the morphogenesis of a periodontal ligament system with a faithful insertion of Sharpey's fibers into the newly formed cementum. gamma-Irradiated recombinant human osteogenic protein-1 (hOP-1) delivered by xenogeneic bovine collagenous bone matrices completely regenerated and maintained the architecture of the induced bone after treatment of calvarial defects with single applications of doses of 0.1, 0.5 and 2.5mg hOP-1 per gram of carrier matrix. The long-term implantation of hOP-1 delivered by gamma-irradiated bovine bone matrices induced the regeneration of the three essential components of the periodontium, i.e. cementum, periodontal ligament and alveolar bone. The osteogenic proteins of the TGF-beta superfamily are sculpting tissue constructs that engineer skeletal tissue regeneration in molecular terms. The pleiotropy of the signalling molecules of the TGF-beta superfamily is highlighted by the redundancy of molecular signals initiating bone formation, including the TGF-beta isoforms per se, powerful inducers of endochondral bone formation but in the primate only. The induction of bone develops a mosaic structure in which members of the TGF-beta superfamily singly, synergistically and synchronously initiate and maintain tissue induction and morphogenesis.

Bone morphogenetic proteins in dentin regeneration for potential use in endodontic therapy

The human dentition is indispensable for nutrition and physiology. The teeth have evolved for mastication of food. Caries is a common dental problem in which the dentin matrix is damaged. When the caries is deep and the dental pulp is exposed, the pulp has to be removed in many cases, resulting ultimately in loss of the tooth. Therefore, the regeneration of dentin-pulp complex is the long-term goal of operative dentistry and endodontics. The key elements of dentin regeneration are stem cells, morphogens such as bone morphogenetic proteins (BMPs) and a scaffold of extracellular matrix. The dental pulp has stem/progenitor cells that have the potential to differentiate into dentin-forming odontoblasts in response to BMPs. Pulpal wound healing consists of stem/progenitor cells release from dental pulp niche after noxious stimuli such as caries, migration to the injured site, proliferation and differentiation into odontoblasts. There are two main strategies for pulp therapy to regenerate dentin: (1) in vivo method of enhancing the natural healing potential of pulp tissue by application of BMP proteins or BMP genes, (2) ex vivo method of isolation of stem/progenitor cells, differentiation with BMP proteins or BMP genes and transplantation to the tooth. This review summarizes recent advances in application of BMPs for dentin regeneration and possible use in endodotic therapy.

BMPs and BMPRs in chicken ovary and effects of BMP-4 and -7 on granulosa cell proliferation and progesterone production in vitro

Bone morphogenetic proteins (BMPs) and their receptors (BMPRs) are now known to have important roles in mammalian ovarian folliculogenesis. This study determined the expression of the mRNA encoding for BMPs and their receptors in the chicken ovary and explored possible roles for them. The expression of the mRNA for BMP-2, -4, -6, -7, and BMPR-IA, -IB, and -II was determined and quantified by a semiquantitative RT-PCR. The mRNAs for all the BMPs and receptors determined were present in both the granulosa (G) and theca (T) cells of the F1, F2, and F3 follicles. All BMP mRNAs increased in G cells with follicular development, whereas only BMP-7 mRNA had this trend in the T cells. BMP-2, -4, and -6 mRNAs in T were similar between follicles. BMPR-IA mRNA was similar in F2G and F3G but lower in F1G. BMPR-IB mRNA was similar in G of all follicles, and BMPR-II mRNA increased with development. In the T, each receptor subtype showed equal distribution between follicles. mRNA levels for BMPR-IB and -II were higher in G than in T, suggesting that the G is a major target for BMPs. BMP-4 and -7 stimulated basal, IGF-I-, and gonadotropin-stimulated progesterone production by cultured G cells, with differential responses between cells from the F1 and F3/4. This suggests involvement in follicular differentiation. BMP-4 and -7 reversed the inhibitory effects of transforming growth factor (TGF)-alpha on basal and gonadotropin-stimulated G cell progesterone production, with greater effect in the F1 than in the F3/4. This effect suggests an important role for BMPs interacting with TGF-alpha in modulating the effects of gonadotropins and IGF-I on follicular differentiation. Finally, BMP-7 stimulated G cell proliferation, but BMP-4 inhibited TGF-alpha+ IGF-I- and/or FSH-stimulated G cell proliferation, suggesting a role in the control of follicular growth during development. These effects of BMP-4 and -7 on the G cell function showed relationships with the expression levels of the BMPs and the BMPR-II.

The application of bone morphogenetic proteins to dental tissue engineering

Progress in understanding the role of bone morphogenetic proteins (BMPs) in craniofacial and tooth development, the demonstration of stem cells in dental pulp and accumulating knowledge on biomaterial scaffolds have set the stage for tissue engineering and regenerative therapy of the craniofacial complex. Furthermore, the recent approval by the US Food and Drug Administration (FDA; Rockville, MD, USA) of recombinant human BMPs for accelerating bone fusion in slow-healing fractures indicates that this protein family may prove useful in designing regenerative treatments in dental applications. In the near term, these advances are likely to be applied to endodontics and periodontal surgery; ultimately, they may facilitate approaches to regenerating whole teeth for use in tooth replacement.

Genetically altered mouse models: the good, the bad, and the ugly

Targeted gene disruption in mice is a powerful tool for generating murine models for human development and disease. While the human genome program has helped to generate numerous candidate genes, few genes have been characterized for their precise in vivo functions. Gene targeting has had an enormous impact on our ability to delineate the functional roles of these genes. Many gene knockout mouse models faithfully mimic the phenotypes of the human diseases. Because some models display an unexpected or no phenotype, controversy has arisen about the value of gene-targeting strategies. We argue in favor of gene-targeting strategies, provided they are used with caution, particularly in interpreting phenotypes in craniofacial and oral biology, where many genes have pleiotropic roles. The potential pitfalls are outweighed by the unique opportunities for developing and testing different therapeutic strategies before they are introduced into the clinic. In the future, we believe that genetically engineered animal models will be indispensable for gaining important insights into the molecular mechanisms underlying development, as well as disease pathogenesis, diagnosis, prevention, and treatment.

Expression of bone morphogenetic proteins and cartilage-derived morphogenetic proteins during osteophyte formation in humans

Bone- and cartilage-derived morphogenetic proteins (BMPs and CDMPs), which are TGFbeta superfamily members, are growth and differentiation factors that have been recently isolated, cloned and biologically characterized. They are important regulators of key events in the processes of bone formation during embryogenesis, postnatal growth, remodelling and regeneration of the skeleton. In the present study, we used immunohistochemical methods to investigate the distribution of BMP-2, -3, -5, -6, -7 and CDMP-1, -2, -3 in human osteophytes (abnormal bony outgrowths) isolated from osteoarthritic hip and knee joints from patients undergoing total joint replacement surgery. All osteophytes consisted of three different areas of active bone formation: (1) endochondral bone formation within cartilage residues; (2) intramembranous bone formation within the fibrous tissue cover and (3) bone formation within bone marrow spaces. The immunohistochemistry of certain BMPs and CDMPs in each of these three different bone formation sites was determined. The results indicate that each BMP has a distinct pattern of distribution. Immunoreactivity for BMP-2 was observed in fibrous tissue matrix as well as in osteoblasts; BMP-3 was mainly present in osteoblasts; BMP-6 was restricted to young osteocytes and bone matrix; BMP-7 was observed in hypertrophic chondrocytes, osteoblasts and young osteocytes of both endochondral and intramembranous bone formation sites. CDMP-1, -2 and -3 were strongly expressed in all cartilage cells. Surprisingly, BMP-3 and -6 were found in osteoclasts at the sites of bone resorption. Since a similar distribution pattern of bone morphogenetic proteins was observed during embryonal bone development, it is suggested that osteophyte formation is regulated by the same molecular mechanism as normal bone during embryogenesis.