The distribution pattern of the hyaluronan receptor CD44 during human tooth development

ADAM10 Expression by Ameloblasts Is Essential for Proper Enamel Formation

ADAM10 is a multi-functional proteinase that can cleave approximately 100 different substrates. Previously, it was demonstrated that ADAM10 is expressed by ameloblasts, which are required for enamel formation. The goal of this study was to determine if ADAM10 is necessary for enamel development. Deletion of Adam10 in mice is embryonically lethal and deletion of Adam10 from epithelia is perinatally lethal. We therefore deleted Adam10 from ameloblasts. Ameloblast-specific expression of the Tg(Amelx-iCre)872pap construct was confirmed. These mice were crossed with Adam10 floxed mice to generate Amelx-iCre; Adam10fl/fl mice (Adam10 cKO). The Adam10 cKO mice had discolored teeth with softer than normal enamel. Notably, the Adam10 cKO enamel density and volume were significantly reduced in both incisors and molars. Moreover, the incisor enamel rod pattern became progressively more disorganized, moving from the DEJ to the outer enamel surface, and this disorganized rod structure created gaps and S-shaped rods. ADAM10 cleaves proteins essential for cell signaling and for enamel formation such as RELT and COL17A1. ADAM10 also cleaves cell-cell contacts such as E- and N-cadherins that may support ameloblast movement necessary for normal rod patterns. This study shows, for the first time, that ADAM10 expressed by ameloblasts is essential for proper enamel formation.

From Basic Science to Clinical Practice: A Review of Current Periodontal/Mucogingival Regenerative Biomaterials

Periodontitis is a dysbiosis-driven inflammatory disease affecting the tooth-supporting tissues, characterized by their progressive resorption, which can ultimately lead to tooth loss. A step-wise therapeutic approach is employed for periodontitis. After an initial behavioral and non-surgical phase, intra-bony or furcation defects may be amenable to regenerative procedures. This review discusses the regenerative technologies employed for periodontal regeneration, highlighting the current limitations and future research areas. The search, performed on the MEDLINE database, has identified the available biomaterials, including biologicals (autologous platelet concentrates, hydrogels), bone grafts (pure or putty), and membranes. Biologicals and bone grafts have been critically analyzed in terms of composition, mechanism of action, and clinical applications. Although a certain degree of periodontal regeneration is predictable in intra-bony and class II furcation defects, complete defect closure is hardly achieved. Moreover, treating class III furcation defects remains challenging. The key properties required for functional regeneration are discussed, and none of the commercially available biomaterials possess all the ideal characteristics. Therefore, research is needed to promote the advancement of more effective and targeted regenerative therapies for periodontitis. Lastly, improving the design and reporting of clinical studies is suggested by strictly adhering to the Consolidated Standards of Reporting Trials (CONSORT) 2010 statement.

Chemokine‑like receptor 1‑positive cells are present in the odontoblast layer in tooth tissue in rats and humans

Cluster of differentiation (CD)44 is a marker of dental pulp stem cells and is involved in odontoblast differentiation and calcification. Chemokine-like receptor 1 (CMKLR1), also known as chemerin receptor 23 (ChemR23) is also expressed in odontoblasts and dental pulp stem cells and is involved in inflammation suppression and tooth regeneration. Resolvin E1, a bioactive lipid, is a CMKLR1 ligand that mediates the chemerin-CMKLR1 interaction and suppresses pulpal inflammation. The present study clarified the intracellular and tissue localization of CD44 and CMKLR1 by immunohistochemical staining of normal pulp and pulp with pulpitis from 12-week-old male Wistar rat teeth or human teeth. In addition, the localization of CD44 and CMKLR1 in human dental pulp stem cells was observed by immunofluorescence staining. The present study also examined the involvement of resolvin E1 in inhibiting inflammation and calcification by western blotting. CD44- and CMKLR1-positive cells were confirmed in the odontoblast layer in normal dental pulp of rats and humans. CD44 was mainly localized in the cell membrane and CMKLR1 was mainly found in the cytoplasm of human dental pulp stem cells. CMKLR1 was also confirmed in the odontoblast layer in rats and humans with pulpitis but CD44 was not present. Following treatment of dental pulp stem cells with lipoteichoic acid, which imitates Gram-positive bacterial infection, resolvin E1 did not suppress the expression of cyclooxygenase-2 or of the odontoblast differentiation marker, dentin sialophosphoprotein. Furthermore, resolvin E1 induced the differentiation of dental pulp stem cells into odontoblasts even in the presence of the inflammatory stimulus.

Integration of multimodal data in the developing tooth reveals candidate regulatory loci driving human odontogenic phenotypes

Human odontogenic aberrations such as abnormal tooth number and delayed tooth eruption can occur as a symptom of rare syndromes or, more commonly, as nonsyndromic phenotypes. These phenotypes can require extensive and expensive dental treatment, posing a significant burden. While many dental phenotypes are heritable, most nonsyndromic cases have not been linked to causal genes. We demonstrate the novel finding that common sequence variants associated with human odontogenic phenotypes are enriched in developmental craniofacial enhancers conserved between human and mouse. However, the bulk nature of these samples obscures if this finding is due to the tooth itself or the surrounding tissues. We therefore sought to identify enhancers specifically active in the tooth anlagen and quantify their contribution to the observed genetic enrichments. We systematically identified 22,001 conserved enhancers active in E13.5 mouse incisors using ChIP-seq and machine learning pipelines and demonstrated biologically relevant enrichments in putative target genes, transcription factor binding motifs, and in vivo activity. Multi-tissue comparisons of human and mouse enhancers revealed that these putative tooth enhancers had the strongest enrichment of odontogenic phenotype-associated variants, suggesting a role for dysregulation of tooth developmental enhancers in human dental phenotypes. The large number of these regions genome-wide necessitated prioritization of enhancer loci for future investigations. As enhancers modulate gene expression, we prioritized regions based on enhancers' putative target genes. We predicted these target genes and prioritized loci by integrating chromatin state, bulk gene expression and coexpression, GWAS variants, and cell type resolved gene expression to generate a prioritized list of putative odontogenic phenotype-driving loci active in the developing tooth. These genomic regions are of particular interest for downstream experiments determining the role of specific dental enhancer:gene pairs in odontogenesis.

Extracellular hyaluronate pressure shaped by cellular tethers drives tissue morphogenesis

How tissues acquire complex shapes is a fundamental question in biology and regenerative medicine. Zebrafish semicircular canals form from invaginations in the otic epithelium (buds) that extend and fuse to form the hubs of each canal. We find that conventional actomyosin-driven behaviors are not required. Instead, local secretion of hyaluronan, made by the enzymes uridine 5'-diphosphate dehydrogenase (ugdh) and hyaluronan synthase 3 (has3), drives canal morphogenesis. Charged hyaluronate polymers osmotically swell with water and generate isotropic extracellular pressure to deform the overlying epithelium into buds. The mechanical anisotropy needed to shape buds into tubes is conferred by a polarized distribution of actomyosin and E-cadherin-rich membrane tethers, which we term cytocinches. Most work on tissue morphogenesis ascribes actomyosin contractility as the driving force, while the extracellular matrix shapes tissues through differential stiffness. Our work inverts this expectation. Hyaluronate pressure shaped by anisotropic tissue stiffness may be a widespread mechanism for powering morphological change in organogenesis and tissue engineering.

Facilitated and Controlled Strontium Ranelate Delivery Using GCS-HA Nanocarriers Embedded into PEGDA Coupled with Decortication Driven Spinal Regeneration

BACKGROUND AND PURPOSE

Strontium ranelate (SrR) is an oral pharmaceutical agent for osteoporosis. In recent years, numerous unwanted side effects of oral SrR have been revealed. Therefore, its clinical administration and applications are limited. Hereby, this study aims to develop, formulate, and characterize an effective SrR carrier system for spinal bone regeneration.

METHODS

Herein, glycol chitosan with hyaluronic acid (HA)-based nanoformulation was used to encapsulate SrR nanoparticles (SrRNPs) through electrostatic interaction. Afterward, the poly(ethylene glycol) diacrylate (PEGDA)-based hydrogels were used to encapsulate pre-synthesized SrRNPs (SrRNPs-H). The scanning electron microscope (SEM), TEM, rheometer, Fourier-transform infrared spectroscopy (FTIR), and dynamic light scattering (DLS) were used to characterize prepared formulations. The rabbit osteoblast and a rat spinal decortication models were used to evaluate and assess the developed formulation biocompatibility and therapeutic efficacy.

RESULTS

In vitro and in vivo studies for cytotoxicity and bone regeneration were conducted. The cell viability test showed that SrRNPs exerted no cytotoxic effects in osteoblast in vitro. Furthermore, in vivo analysis for new bone regeneration mechanism was carried out on rat decortication models. Radiographical and histological analysis suggested a higher level of bone regeneration in the SrRNPs-H-implanted groups than in the other experimental groups.

CONCLUSION

Local administration of the newly developed formulated SrR could be a promising alternative therapy to enhance bone regeneration in bone-defect sites in future clinical applications.

Balance Between Tooth Size and Tooth Number Is Controlled by Hyaluronan

While the function of proteins and genes has been widely studied during vertebrate development, relatively little work has addressed the role of carbohydrates. Hyaluronan (HA), also known as hyaluronic acid, is an abundant carbohydrate in embryonic tissues and is the main structural component of the extracellular matrix of epithelial and mesenchymal cells. HA is able to absorb large quantities of water and can signal by binding to cell-surface receptors. During organ development and regeneration, HA has been shown to regulate cell proliferation, cell shape, and migration. Here, we have investigated the function of HA during molar tooth development in mice, in which, similar to humans, new molars sequentially bud off from a pre-existing molar. Using an ex vivo approach, we found that inhibiting HA synthesis in culture leads to a significant increase in proliferation and subsequent size of the developing molar, while the formation of sequential molars was inhibited. By cell shape analysis, we observed that inhibition of HA synthesis caused an elongation and reorientation of the major cell axes, indicating that disruption to cellular orientation and shape may underlie the observed phenotype. Lineage tracing demonstrated the retention of cells in the developing first molar (M1) at the expense of the generation of a second molar (M2). Our results highlight a novel role for HA in controlling proliferation, cell orientation, and migration in the developing tooth, impacting cellular decisions regarding tooth size and number.

Expression of Different Isoforms of Versican During the Development of Mouse Mandibular First Molars

Versican is a large chondroitin sulfate proteoglycan enriched in the extracellular matrix, and it has at least four different isoforms, termed V0, V1, V2, and V3. Although several studies have demonstrated that versican is stably expressed in various developing organs, the expression of versican isoforms during tooth development has not been elucidated yet. Therefore, the present study was to investigate the expression of versican isoforms in the developing mouse molars. The mandibular first molars from embryonic day (E) 11.5 to postnatal day (PN) 21 were used to investigate the expression of versican isoforms by immunohistochemistry, and the gene expressions of versican (Vcan) isoforms from E13.5 to PN7 were analyzed by quantitative real-time PCR. The results exhibited different expressing patterns of versican isoforms-the stellate reticulum (SR) and the dental mesenchymal cells adjacent to Hertwig's Epithelial Root Sheath (HERS) only expressed V1 and the mature odontoblasts mainly expressed V2, while the dental papilla and the ameloblasts might both express V0/V1/V2. These results suggested that different versican isoforms may act different roles in the tooth development, and we speculated that V0/V1 might be intimately involved in the cell proliferation while V2 was associated in the cytodifferentiation.

Hyaluronan and hyaluronan synthases expression and localization in embryonic mouse molars

Hyaluronan (HA) and hyaluronan synthases (HASs) have been shown to play critical roles in embryogenesis and organ development. However, there have not been any studies examining HA and HAS expression and localization during tooth development. The present study was designed to investigate the expression of HA and three isoforms of HASs (HAS1, 2, 3) in embryonic mouse molars. The first mandibular embryonic mouse molars were examined by immunohistochemistry at E11.5, E13.5, E14.5, E16.5, and E18.5. PCR and western blot analyses were performed on RNA and proteins samples from E13.5 to E18.5 tooth germs. At the initial stage (E11.5), HA and HASs were expressed in the dental epithelium but not the underlying dental mesenchyme. HA immunostaining gradually increased in the enamel organ from the bud stage (E13.5) to the late bell stage (E18.5), and HA and HASs were highly expressed in the stellate reticulum and stratum intermedium. HA immunostaining was also enhanced in the dental mesenchyme and its derived tissues, but it was not expressed in the ameloblast and odontoblast regions. The three HAS isoforms had distinct expression patterns, and they were expressed in the dental mesenchyme and odontoblast at various levels. Furthermore, HAS1 and HAS2 expression decreased, while HAS3 expression increased from E13.5 to E18.5. These results suggested that HA synthesized by different HASs is involved in embryonic mouse molar morphogenesis and cytodifferentiation.

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.

Self-renewal and multilineage differentiation of mouse dental epithelial stem cells

Understanding the cellular and molecular mechanisms underlying the self-renewal and differentiation of dental epithelial stem cells (DESCs) that support the unlimited growth potential of mouse incisors is critical for developing novel tooth regenerative therapies and unraveling the pathogenesis of odontogenic tumors. However, analysis of DESC properties and regulation has been limited by the lack of an in vitro assay system and well-documented DESC markers. Here, we describe an in vitro sphere culture system to isolate the DESCs from postnatal mouse incisor cervical loops (CLs) where the DESCs are thought to reside. The dissociated cells from CLs were able to expand and form spheres for multiple generations in the culture system. Lineage tracing indicated that DESC within the spheres were epithelial in origin as evident by lineage tracing. Upon stimulation, the sphere cells differentiated into cytokeratin 14- and amelogenin-expressing and mineral material-producing cells. Compared to the CL tissue, sphere cells expressed high levels of expression of Sca-1, CD49f (also designated as integrin α6), and CD44. Fluorescence-activated cell sorting (FACS) analyses of mouse incisor CL cells further showed that the CD49f(Bright) population was enriched in sphere-forming cells. In addition, the CD49f(Bright) population includes both slow-cycling and Lgr5(+) DESCs. The in vitro sphere culture system and identification of CD49f(Bright) as a DESC marker provide a novel platform for enriching DESCs, interrogating how maintenance, cell fate determination, and differentiation of DESCs are regulated, and developing tooth regenerative therapies.

Morphogenetic roles of perlecan in the tooth enamel organ: an analysis of overexpression using transgenic mice

Perlecan, a heparan sulfate proteoglycan, is enriched in the intercellular space of the enamel organ. To understand the role of perlecan in tooth morphogenesis, we used a keratin 5 promoter to generate transgenic (Tg) mice that over-express perlecan in epithelial cells, and examined their tooth germs at tissue and cellular levels. Immunohistochemistry showed that perlecan was more strongly expressed in the enamel organ cells of Tg mice than in wild-type mice. Histopathology showed wider intercellular spaces in the stellate reticulum of the Tg molars and loss of cellular polarity in the enamel organ, especially in its cervical region. Hertwig's epithelial root sheath (HERS) cells in Tg mice were irregularly aligned due to excessive deposits of perlecan along the inner, as well as on the outer sides of the HERS. Tg molars had dull-ended crowns and outward-curved tooth roots and their enamel was poorly crystallized, resulting in pronounced attrition of molar cusp areas. In Tg mice, expression of integrin β1 mRNA was remarkably higher at E18, while expression of bFGF, TGF-β1, DSPP and Shh was more elevated at P1. The overexpression of perlecan in the enamel organ resulted in irregular morphology of teeth, suggesting that the expression of perlecan regulates growth factor signaling in a stage-dependent manner during each step of the interaction between ameloblast-lineage cells and mesenchymal cells.

Effects of hyaluronic acid sponge as a scaffold on odontoblastic cell line and amputated dental pulp

It is important to develop a suitable three-dimensional scaffold for the regeneration therapy of dental pulp. In the present study, the effects of hyaluronic acid (HA) sponge on responses of the odontoblastic cell line (KN-3 cells) in vitro, as well as responses of amputated dental pulp of rat molar in vivo, were examined. In vitro, KN-3 cells adhered to the stable structure of HA sponge and that of collagen sponge. In vivo, dental pulp proliferation and vessel invasion were observed in both sponges implanted at dentin defect area above amputated dental pulp, and the cell-rich reorganizing tissue was observed in the dentin defect when HA sponge was implanted as compared with collagen sponge. Expression levels of IL-6 and TNF-alpha in KN-3 cells seeded in HA sponge were nearly the same with those in the cells seeded in collagen sponge, while the numbers (0.67 x 10(3) at 1 week and 0.7 x 10(3) at 3 weeks) of granulated leukocytes that invaded into HA sponge from amputated dental pulp was significantly lower than those (1.22 x 10(3) at 1 week and 1.1 x 10(3) at 3 weeks) of collagen sponge (p < 0.01 at 1 week and p < 0.05 at 3 weeks). These results suggest that HA sponge has an appropriate structure, biocompatibility, and biodegradation for use as a scaffold for dental pulp regeneration.

Immunolocalization of CD44s in human teeth

CD44s (standard form) is an integral membrane glycoprotein, which plays an important role in both cell-cell and cell-substrate adhesion. Few studies have demonstrated that CD44s and its isoforms are involved in mediating cell-cell and cell-substrate interactions in the periodontium and surrounding tissues. The present study was undertaken as so little data are available on its presence in human adult hard dental structures. Six extracted premolars from children, aged 10-12 years, were used in the present study. They were fixed in 10% neutral buffered formalin and decalcified in 7.5% EDTA for 2 weeks. Immunohistochemistry to reveal binding of a monoclonal mouse anti-CD44s was used for the localization of CD44s. The antibody was applied directly onto the tissue section and the slides incubated overnight (4 degrees C) in a humidified chamber. In serial sagittal sections of teeth, binding of anti-CD44s was seen in odontoblasts, periodontal ligament fibroblasts and cementoblasts. Our findings present evidence that CD44s is localized in periodontal ligament fibroblasts, cementocytes and odontoblasts of mature human teeth. CD44s may be involved in tooth cell differentiation and later in cell-matrix interaction and in the accumulation of inflammatory cells in the extravascular connective tissue in these sites.

The expression pattern of hyaluronan synthase during human tooth development

In previous studies, hyaluronan (HA) and its major cell surface receptor CD44 have been suggested to play an important role during tooth development. HA synthases (HASs) are the enzymes that polymerize hyaluronan. Data on the expression pattern of HASs during tooth development is lacking and the aim of the present study was to investigate the localisation of HAS by immunohistochemistry in human tooth germs from different developmental stages. The distribution pattern of HAS in the various tissues of the "bell stage" tooth primordia corresponded to that of hyaluronan in most locations: positive HAS immunoreactivity was observed in the dental lamina cells, inner- and outer-enamel epithelium. On the stellate reticulum cells, moderate HAS signal was observed, similar to the layers of the oral epithelium, where faint HAS immunoreactivity was detected. At the early phase of dental hard tissues mineralization, strong HAS immunoreactivity was detected in the odontoblasts and their processes, as well as in the secretory ameloblasts and their apical processes and also, the pulpal mesenchymal cells. The HAS signals observed in odontoblasts and ameloblasts gradually decreased with age. Our results demonstrate that hyaluronan synthesised locally by different dental cells and these results provide additional indirect support to the suggestion that HA may contribute both to the regulation of tooth morphogenesis and dental hard tissue formation.

Distribution patterns of the membrane glycoprotein CD44 during the foreign-body reaction to a degradable biomaterial in rats and mice

Although biomaterials have been used in the clinical setting for a long time, little is known of the molecular mechanisms underlying the foreign-body reaction (FBR). A good understanding of these mechanisms is requisite for the controlled regulation of the FBR needed to prevent adverse tissue reactions and thus to improve the function of the biomaterial. Macrophages are essential in the inflammatory reaction in, as well as around, the implants, and they also are believed to initiate most of the adverse responses. Typically, during the FBR macrophages become activated and fuse into multinucleated giant cells (MnGCs). CD44, an integral membrane glycoprotein expressed on a broad spectrum of cell types, is involved in MnGC formation in vitro and in inflammation processes in general. In vivo it is not known whether CD44 is part of a specific protein machinery that enables macrophage fusion or whether it has additional functions in the FBR. In the present in vivo study, CD44 expression patterns were followed in rats and mice during the FBR to a degradable collagen type I biomaterial. We found that CD44 is upregulated on all migrating cells and on newly formed blood vessels at the onset of the FBR and that MnGCs, up to week 15 postimplantation, expressed CD44. Although no evidence was found that CD44 participates in macrophage fusion leading to multinucleation, it nevertheless may be an interesting target molecule for modulating the FBR in vivo, possibly by affecting cell activation, cell migration towards the biomaterial, vascularization, and MnGC formation.