Differential Effects of Amelogenin on Mineralization of Cementoblasts and Periodontal Ligament Cells

Organoids from human tooth showing epithelial stemness phenotype and differentiation potential

Insight into human tooth epithelial stem cells and their biology is sparse. Tissue-derived organoid models typically replicate the tissue’s epithelial stem cell compartment. Here, we developed a first-in-time epithelial organoid model starting from human tooth. Dental follicle (DF) tissue, isolated from unerupted wisdom teeth, efficiently generated epithelial organoids that were long-term expandable. The organoids displayed a tooth epithelial stemness phenotype similar to the DF’s epithelial cell rests of Malassez (ERM), a compartment containing dental epithelial stem cells. Single-cell transcriptomics reinforced this organoid-ERM congruence, and uncovered novel, mouse-mirroring stem cell features. Exposure of the organoids to epidermal growth factor induced transient proliferation and eventual epithelial-mesenchymal transition, highly mimicking events taking place in the ERM in vivo. Moreover, the ERM stemness organoids were able to unfold an ameloblast differentiation process, further enhanced by transforming growth factor-β (TGFβ) and abrogated by TGFβ receptor inhibition, thereby reproducing TGFβ's known key position in amelogenesis. Interestingly, by creating a mesenchymal-epithelial composite organoid (assembloid) model, we demonstrated that the presence of dental mesenchymal cells (i.e. pulp stem cells) triggered ameloblast differentiation in the epithelial stem cells, thus replicating the known importance of mesenchyme-epithelium interaction in tooth development and amelogenesis. Also here, differentiation was abrogated by TGFβ receptor inhibition. Together, we developed novel organoid models empowering the exploration of human tooth epithelial stem cell biology and function as well as their interplay with dental mesenchyme, all at present only poorly defined in humans. Moreover, the new models may pave the way to future tooth-regenerative perspectives.

Analysis of the cells isolated from epithelial cell rests of Malassez through single-cell limiting dilution

The epithelial cell rests of Malassez (ERM) are essential in preventing ankylosis between the alveolar bone and the tooth (dentoalveolar ankylosis). Despite extensive research, the mechanism by which ERM cells suppress ankylosis remains uncertain; perhaps its varied population is to reason. Therefore, in this study, eighteen unique clones of ERM (CRUDE) were isolated using the single-cell limiting dilution and designated as ERM 1-18. qRT-PCR, ELISA, and western blot analyses revealed that ERM-2 and -3 had the highest and lowest amelogenin expression, respectively. Mineralization of human periodontal ligament fibroblasts (HPDLF) was reduced in vitro co-culture with CRUDE ERM, ERM-2, and -3 cells, but recovered when an anti-amelogenin antibody was introduced. Transplanted rat molars grown in ERM-2 cell supernatants produced substantially less bone than those cultured in other cell supernatants; inhibition was rescued when an anti-amelogenin antibody was added to the supernatants. Anti-Osterix antibody staining was used to confirm the development of new bones. In addition, next-generation sequencing (NGS) data were analysed to discover genes related to the distinct roles of CRUDE ERM, ERM-2, and ERM-3. According to this study, amelogenin produced by ERM cells helps to prevent dentoalveolar ankylosis and maintain periodontal ligament (PDL) space, depending on their clonal diversity.

Calcitriol and enamel matrix derivative differentially regulated cementoinduction and mineralization in human periodontal ligament-derived cells

BACKGROUNDS

Alveolar bone and cementum share many biological and developmental similarities. The mineralizing effect of calcitriol has been previously reported. Yet, its cementoinductivity has not been confirmed. This study evaluated the potential cementoinductivity effect of calcitriol and enamel matrix derivative (EMD) on human periodontal ligament-ligament derived cells (hPDCs).

METHODS

Human PDCs obtained from extracted third molars or premolars were cultured with calcitriol, or EMD. Cementogenic gene expression was examined using RT-qPCR. Expression analysis also included cementoblast-specific markers, Cementum Protein 1 (CEMP1), cementum attachment protein (CAP), and recently reported cementoblast-enriched genes, secreted frizzled related protein 1 (SFRP1), and Dickkopf-related protein 1 (DKK1). Mineralization capacities were evaluated by alkaline phosphatase (ALP) activity, Alizarin Red and Von Kossa staining followed by scanning electron microscope imaging and element mapping.

RESULTS

Among tested conditions, 10 nM calcitriol enhanced most cementogenic gene expression, Trans-forming growth factor-β1 (TGF-β1), bone morphogenetic proteins (BMP-2 and BMP-4), Core-binding factor subunit alpha-1/Runt-related transcription factor 2 (Cbfa1/RUNX2), Type I collagen (Col-1), Alkaline phosphatase (ALP), Bone sialoprotein (BSP), osteopontin (OPN/SPP1), osteocalcin (OCN), CEMP1 and CAP, and Wnt signaling negative modulators, SFRP1 and DKK1, along with highest ALP activity and mineralization formation in hPDCs. However, only moderate CEMP-1 protein was observed. In contrast, EMD stimulated stronger CEMP-1 and CAP protein, but presented weaker mineralization capacity, hinting at the possibility that strong stimulation of mineralization might dominate cemetogenic specific factors and vice versa.

CONCLUSION

Calcitriol demonstrated not only great osteoinductivity, but also the potential to induce cementogenic gene expression by initiating hPDC differentiation and promoting mineralization. Compared to calcitriol, EMD promoted cementoinductivity in hPDCs at a later time point via highly expressed CEMP1 and CAP protein, but with less mineralization. Thus, calcitriol and EMD could provide differential enhancement of cementoinduction and mineralization, likely acting at various differentiation stages. This article is protected by copyright. All rights reserved.

Treatment of intrabony periodontal defects in controlled diabetic patients with an enamel matrix derivative: a split-mouth randomized clinical trial

OBJECTIVE

This split-mouth randomized controlled trial aimed to evaluate the effect of enamel matrix derivative (EMD) associated with a simplified papilla preservation flap (SPPF) compared to SPPF alone in the surgical treatment of intrabony defects (ID) in type 2 diabetic mellitus (T2DM) patients.

MATERIAL AND METHODS

Thirteen patients with controlled T2DM presenting with ID in at least two quadrants were included. In each patient, the test site (TS) was treated with SPPF plus EMD, whereas the control site (CS) was treated only with SPPF. Prior to surgery and at 6 months after intervention, the following parameters were evaluated: clinical attachment level (CAL), probing pocket depth (PPD), and gingival recession (GR).

RESULTS

The TS and CS demonstrated a mean CAL gain of 3.31 ± 0.96 mm and 1.61 ± 1.12 mm, and a PPD reduction from 8.15 ± 0.98 to 3.00 ± 0.57 mm and 7.53 ± 0.96 to 4.69 ± 0.63 mm after 6 months, respectively. In both sites, the mean CAL gain and PPD reduction improved significantly after 6 months compared to baseline; however, the improvement was higher in the TS (p < 0.001).

CONCLUSIONS

Both surgical procedures presented with clinical improvements in controlled T2DM patients. However, the additional use of EMD showed enhanced clinical results after 6 months with regard to CAL gain and PPD reduction.

CLINICAL RELEVANCE

This study showed a better PPD reduction and CAL gain when an EMD was applied in addition to SPPF. Therefore, EMD may be used to enhance clinical outcomes in periodontal ID of controlled T2DM patients.

Amelogenin-Derived Peptides in Bone Regeneration: A Systematic Review

Amelogenins are enamel matrix proteins currently used to treat bone defects in periodontal surgery. Recent studies have highlighted the relevance of amelogenin-derived peptides, named LRAP, TRAP, SP, and C11, in bone tissue engineering. Interestingly, these peptides seem to maintain or even improve the biological activity of the full-length protein, which has received attention in the field of bone regeneration. In this article, the authors combined a systematic and a narrative review. The former is focused on the existing scientific evidence on LRAP, TRAP, SP, and C11's ability to induce the production of mineralized extracellular matrix, while the latter is concentrated on the structure and function of amelogenin and amelogenin-derived peptides. Overall, the collected data suggest that LRAP and SP are able to induce stromal stem cell differentiation towards osteoblastic phenotypes; specifically, SP seems to be more reliable in bone regenerative approaches due to its osteoinduction and the absence of immunogenicity. However, even if some evidence is convincing, the limited number of studies and the scarcity of in vivo studies force us to wait for further investigations before drawing a solid final statement on the real potential of amelogenin-derived peptides in bone tissue engineering.

Combined application of geranylgeranylacetone and amelogenin promotes angiogenesis and wound healing in human periodontal ligament cells

Amelogenin directly binds to glucose-regulated protein 78 (Grp78). Cell migration activity is expected to increase when human periodontal ligament cells (hPDLCs) overexpressing Grp78 are treated with amelogenin. Geranylgeranylacetone (GGA) is a drug that induces the expression of heat shock protein and is routinely used to treat gastric ulcers. Here, we investigated the changes in the properties and behavior of hPDLCs in response to treatment with GGA and the synergistic effects of amelogenin stimulation in hPDLCs pretreated with GGA for the establishment of a novel periodontal tissue regenerative therapy. We observed that GGA treatment increased Grp78 protein expression in hPDLCs and enhanced cell migration. Microarray analysis demonstrated that increased Grp78 expression triggered the production of angiopoietin-like 4 and amphiregulin, which are involved in the enhancement of angiogenesis and subsequent wound healing via the activation of hypoxia-inducible factor 1α and peroxisome proliferator-activated receptors as well as the phosphorylation of cAMP response element-binding protein and protein kinase A. Moreover, the addition of recombinant murine amelogenin (rM180) further accelerated hPDLC migration and tube formation of human umbilical vein endothelial cells due to the upregulation of interleukin-8 (IL-8), monocyte chemotactic protein 1, and IL-6, which are also known as angiogenesis-inducing factors. These findings suggest that the application of GGA to gingival tissue and alveolar bone damaged by periodontal disease would facilitate the wound healing process by inducing periodontal ligament cells to migrate to the root surface and release cytokines involved in tissue repair. Additionally, supplementation with amelogenin synergistically enhanced the migratory capacity of these cells while actively promoting angiogenesis. Therefore, the combined application of GGA and amelogenin may establish a suitable environment for periodontal wound healing and further drive the development of novel therapeutics for periodontal tissue regeneration.

TVH-19, a synthetic peptide, induces mineralization of dental pulp cells in vitro and formation of tertiary dentin in vivo

Functional peptides derived from the active domains of odontogenesis-related proteins have been reported to promote dental hard tissue regeneration. The purpose of this study was to evaluate the effects of an artificially synthesized peptide, TVH-19, on odontoblast differentiation and tertiary dentin formation in indirect pulp capping (IPC) using in vitro and in vivo experiments. TVH-19 did not exhibit any effect on the proliferation of human dental pulp cells (hDPCs) but significantly promoted cell migration, compared with the control (p < 0.05). TVH-19-treated hDPCs showed significantly higher alkaline phosphatase (ALP) activity and stronger alizarin red staining (ARS) reactivity than the control group (p < 0.05). TVH-19 also upregulated the mRNA and protein expression levels of odontogenic genes. After generating IPC in rats, the samples of teeth were studied using micro-computed tomography (Micro-CT), hematoxylin & eosin (HE) staining, and immunohistochemical staining to investigate the functions of TVH-19. The in vivo results showed that TVH-19 induced the formation of tertiary dentin, and reduced inflammation and apoptosis, as evident from the downregulated expression of interleukin 6 (IL-6) and cleaved-Caspase-3 (CL-CASP3). Overall, the results of our study suggest that TVH-19 induces differentiation of hDPCs, promotes tertiary dentin formation, relieves inflammation, and reduces apoptosis, indicating the potential applications of TVH-19 in IPC.

Recent advances in periodontal regeneration: A biomaterial perspective

Periodontal disease (PD) is one of the most common inflammatory oral diseases, affecting approximately 47% of adults aged 30 years or older in the United States. If not treated properly, PD leads to degradation of periodontal tissues, causing tooth movement, and eventually tooth loss. Conventional clinical therapy for PD aims at eliminating infectious sources, and reducing inflammation to arrest disease progression, which cannot achieve the regeneration of lost periodontal tissues. Over the past two decades, various regenerative periodontal therapies, such as guided tissue regeneration (GTR), enamel matrix derivative, bone grafts, growth factor delivery, and the combination of cells and growth factors with matrix-based scaffolds have been developed to target the restoration of lost tooth-supporting tissues, including periodontal ligament, alveolar bone, and cementum. This review discusses recent progresses of periodontal regeneration using tissue-engineering and regenerative medicine approaches. Specifically, we focus on the advances of biomaterials and controlled drug delivery for periodontal regeneration in recent years. Special attention is given to the development of advanced bio-inspired scaffolding biomaterials and temporospatial control of multi-drug delivery for the regeneration of cementum-periodontal ligament-alveolar bone complex. Challenges and future perspectives are presented to provide inspiration for the design and development of innovative biomaterials and delivery system for new regenerative periodontal therapy.

Novel LRAP-binding partner revealing the plasminogen activation system as a regulator of cementoblast differentiation and mineral nodule formation in vitro

Amelogenin isoforms, including full-length amelogenin (AMEL) and leucine-rich amelogenin peptide (LRAP), are major components of the enamel matrix, and are considered as signaling molecules in epithelial-mesenchymal interactions regulating tooth development and periodontal regeneration. Nevertheless, the molecular mechanisms involved are still poorly understood. The aim of the present study was to identify novel binding partners for amelogenin isoforms in the cementoblast (OCCM-30), using an affinity purification assay (GST pull-down) followed by mass spectrometry and immunoblotting. Protein-protein interaction analysis for AMEL and LRAP evidenced the plasminogen activation system (PAS) as a potential player regulating OCCM-30 response to amelogenin isoforms. For functional assays, PAS was either activated (plasmin) or inhibited (ε-aminocaproic acid [aminocaproic]) in OCCM-30 cells and the cell morphology, mineral nodule formation, and gene expression were assessed. PAS inhibition (EACA 100 mM) dramatically decreased mineral nodule formation and expression of OCCM-30 differentiation markers, including osteocalcin (Bglap), bone sialoprotein (Ibsp), osteopontin (Spp1), tissue-nonspecific alkaline phosphatase (Alpl) and collagen type I (Col1a1), and had no effect on runt-related transcription factor 2 (Runx2) and Osterix (Osx) mRNA levels. PAS activation (plasmin 5 µg/µl) significantly increased Col1a1 and decreased Bglap mRNA levels (p < .05). Together, our findings shed new light on the potential role of plasminogen signaling pathway in the control of the amelogenin isoform-mediated response in cementoblasts and provide new insights into the development of targeted therapies.

Recombinant amelogenin regulates the bioactivity of mouse cementoblasts in vitro

Amelogenin (AMG) is a cell adhesion molecule that has an important role in the mineralization of enamel and regulates events during dental development and root formation. The purpose of the present study was to investigate the effects of recombinant human AMG (rhAMG) on mineralized tissue-associated genes in cementoblasts. Immortalized mouse cementoblasts (OCCM-30) were treated with different concentrations (0.1, 1, 10, 100, 1000, 10,000, 100,000 ng · mL^-1) of recombinant human AMG (rhAMG) and analyzed for proliferation, mineralization and mRNA expression of bone sialoprotein (BSP), osteocalcin (OCN), collagen type I (COL I), osteopontin (OPN), runt-related transcription factor 2 (Runx2), cementum attachment protein (CAP), and alkaline phosphatase (ALP) genes using quantitative RT-PCR. The dose response of rhAMG was evaluated using a real-time cell analyzer. Total RNA was isolated on day 3, and cell mineralization was assessed using von Kossa staining on day 8. COL I, OPN and lysosomal-associated membrane protein-1 (LAMP-1), which is a cell surface binding site for amelogenin, were evaluated using immunocytochemistry. F-actin bundles were imaged using confocal microscopy. rhAMG at a concentration of 100,000 ng · mL^-1 increased cell proliferation after 72 h compared to the other concentrations and the untreated control group. rhAMG (100,000 ng · mL^-1) upregulated BSP and OCN mRNA expression levels eightfold and fivefold, respectively. rhAMG at a concentration of 100,000 ng · mL^-1 remarkably enhanced LAMP-1 staining in cementoblasts. Increased numbers of mineralized nodules were observed at concentrations of 10,000 and 100,000 ng · mL^-1 rhAMG. The present data suggest that rhAMG is a potent regulator of gene expression in cementoblasts and support the potential application of rhAMG in therapies aimed at fast regeneration of damaged periodontal tissue.

A protein with its roots in dental development stimulates the proliferation and gene expression of cells linked to regeneration. Amelogenin is a mediator of enamel and tooth root formation, and the main component of a recently-developed medicine for periodontal regeneration. An international research group led by Sema Hakki, of Selcuk University, Turkey, has now elucidated the effects of amelogenin on cementoblasts, a type of cell responsible for producing the vital, mineralized layer on surface of the tooth root. Hakki’s team found that the bacteria-derived amelogenin increased the rate of mouse cementoblast proliferation and mineralization in vitro, and increased the expression of genes related to bone and tissue generation. The team also demonstrated the presence of a likely amelogenin receptor on the cells used in their study. These findings support further investigation into amelogenin’s therapeutic potential.

Effect of EMD on the orthodontically induced root resorption repair process in rats

BACKGROUND

While different levels of root resorption may occur in orthodontic treatment, several preventive approaches have been reported. Nevertheless, little is known about the effect of enamel matrix derivative (EMD) on root repair during orthodontic tooth movement.

OBJECTIVE

To evaluate the effect of EMD on root resorption repair following the application of orthodontic force.

MATERIALS AND METHODS

A force of 100 g was exerted for 14 days on the left maxillary first molars of twenty 10-week-old Sprague-Dawley rats divided into the EMD and control groups (n = 10 per group). In the EMD group, repeatedly injection of Emdogain® was administered after the appliance was removed, while phosphate-buffered saline was administered in the control group. In vivo microcomputed tomography (CT), haematoxylin and eosin (H&E) staining, and immunohistochemistry were then used to evaluate the effect of EMD on the process of root repair.

RESULTS

In the EMD group, the observed decrease in root resorption crater volume and increase in both the bone volume fraction and trabecular thickness were significantly greater than those in the control group. H&E staining showed that the periodontal fibres were relatively regular in arrangement and that the surface of the cementum was smooth in the EMD group. Immunohistochemical analysis showed higher bone morphogenetic protein 2 (BMP-2) and bone sialoprotein (BSP) expression levels in the EMD group than in the control group. In addition, the osteoprotegerin (OPG) and receptor activator of NF-κB ligand (RANKL) expression levels were similar in both groups.

CONCLUSION

EMD enhanced the repair process following orthodontically induced root resorption in rats.

In vitro models for evaluation of periodontal wound healing/regeneration

Periodontal wound healing and regeneration are highly complex processes, involving cells, matrices, molecules and genes that must be properly choreographed and orchestrated. As we attempt to understand and influence these clinical entities, we need experimental models to mimic the various aspects of human wound healing and regeneration. In vivo animal models that simulate clinical situations of humans can be costly and cumbersome. In vitro models have been devised to dissect wound healing/regeneration processes into discrete, analyzable steps. For soft tissue (e.g. gingival) healing, in vitro models range from simple culture of cells grown in monolayers and exposed to biological modulators or physical effectors and materials, to models in which cells are 'injured' by scraping and subsequently the 'wound' is filled with new or migrating cells, to three-dimensional models of epithelial-mesenchymal recombination or tissue explants. The cells employed are gingival keratinocytes, fibroblasts or endothelial cells, and their proliferation, migration, attachment, differentiation, survival, gene expression, matrix production or capillary formation are measured. Studies of periodontal regeneration also include periodontal ligament fibroblasts or progenitors, osteoblasts or osteoprogenitors, and cementoblasts. Regeneration models measure cellular proliferation, attachment and migration, as well as gene expression, transfer and differentiation into a mineralizing phenotype and biomineralization. Only by integrating data from models on all levels (i.e. a single cell to the whole organism) can various critical aspects of periodontal wound healing/regeneration be fully evaluated.

Full-length amelogenin influences the differentiation of human dental pulp stem cells

Background

Amelogenin is an extracellular matrix protein well known for its role in the organization and mineralization of enamel. Clinically, it is used for periodontal regeneration and, due to its finding also in predentin and intercellular spaces of dental pulp cells, it has recently been suggested for pulp capping procedures. The aim of this study was to analyse in vitro the effect of the recombinant human full-length amelogenin on the growth and differentiation of human dental pulp stem cells (hDPSCs).

Methods

Human DPSCs were treated with a supplement of amelogenin at a concentration of 10 ng/ml, 100 ng/ml and 1000 ng/ml. The groups were compared to the unstimulated control in terms of cell morphology and proliferation, mineralization and gene expression for ALP (alkaline phosphatase), DMP1 (dentin matrix protein-1) and DSPP (dentin sialophosphoprotein).

Results

Amelogenin affects hDPSCs differently than PDL (periodontal ligament) cells and other cell lines. The proliferation rate at two weeks is significantly reduced in presence of the highest concentration of amelogenin as compared to the unstimulated control. hDPSCs treated with low concentrations present a downregulation of DMP1 and DSPP, which is significant for DSPP (p = 0.011), but not for DMP1 (p = 0.395).

Conclusions

These finding suggest that the role of full-length amelogenin is not restricted to participation in tooth structure. It influences the differentiation of hDPSC according to various concentrations and this might impair the clinical results of pulp capping.

Expression of amelogenin and effects of cyclosporin A in developing hair follicles in rats

Amelogenin, an enamel matrix protein has been considered to be exclusively expressed by ameloblasts during odontogenesis. However, burgeoning evidence indicates that amelogenin is also expressed in non-mineralizing tissues. Under the hypothesis that amelogenin may be a functional molecule in developing hair follicles which share developmental features with odontogenesis, this study for the first time elucidated the presence and functional changes of amelogenin and its receptors during rat hair follicle development. Amelogenin was specifically localized in the outer epithelial root sheath of hair follicles. Its expression appeared in the deeper portion of hair follicles, i.e. the bulbar and suprabulbar regions rather than the superficial region. Lamp-1, an amelogenin receptor, was localized in either follicular cells or outer epithelial sheath cells, reflecting functional changes during development. The expression of amelogenin splicing variants increased in a time-dependent manner during postnatal development of hair follicles. Amelogenin expression was increased by treatment with cyclosporin A, which is an inducer of anagen in the hair follicle, whereas the level of Lamp-1 and -2 was decreased by cyclosporin A treatment. These results suggest that amelogenin may be a functional molecule involved in the development of the hair follicle rather than an inert hair shaft matrix protein.

Effects of enamel matrix derivative on the proliferation and osteogenic differentiation of human gingival mesenchymal stem cells

INTRODUCTION

Gingiva-derived mesenchymal stem cells (GMSCs) have recently been harvested and applied for rebuilding lost periodontal tissue. Enamel matrix derivative (EMD) has been used for periodontal regeneration and the formation of new cementum with inserting collagen fibers; however, alveolar bone formation is minimal. Recently, EMD has been shown to enhance the proliferation and mineralization of human bone marrow mesenchymal stem cells. Because the gingival flap is the major component to cover the surgical wound, the effects of EMD on the proliferation and mineralization of GMSCs were evaluated in the present study.

METHODS

After single cell suspension, the GMSCs were isolated from the connective tissues of human gingiva. The colony forming unit assay of the isolated GMSCs was measured. The expression of stem cell markers was examined by flow cytometry. The cellular telomerase activity was identified by polymerase chain reaction (PCR). The osteogenic, adipogenic and neural differentiations of the GMSCs were further examined. The cell proliferation was determined by MTS assay, while the expression of mRNA and protein for mineralization (including core binding factor alpha, cbfα-1; alkaline phosphatase, ALP; and osteocalcin, OC; ameloblastin, AMBN) were analyzed by real time-PCR, enzyme activity and confocal laser scanning microscopy.

RESULTS

The cell colonies could be easily identified and the colony forming rates and the telomerase activities increased after passaging. The GMSCs expressed high levels of surface markers for CD73, CD90, and CD105, but showed low expression of STRO-1. Osteogenic, adipogenic and neural differentiations were successfully induced. The proliferation of GMSCs was increased after EMD treatment. ALP mRNA was significantly augmented by treating with EMD for 3 hours, whereas AMBN mRNA was significantly increased at 6 hours after EMD treatment. The gene expression of OC was enhanced at the dose of 100 μg/ml EMD at day 3. Increased protein expression for cbfα-1 at day 3, for ALP at day 5 and 7, and for OC at week 4 after the EMD treatments were observed.

CONCLUSIONS

Human GMSCs could be successfully isolated and identified. EMD treatments not only induced the proliferation of GMSCs but also enhanced their osteogenic differentiation after induction.