Regulatory mechanisms of periodontal regeneration

Dynamic analyses of a soft tissue-implant interface: Biological responses to immediate versus delayed dental implants

AIM

To qualitatively and quantitatively evaluate the formation and maturation of peri-implant soft tissues around 'immediate' and 'delayed' implants.

MATERIALS AND METHODS

Miniaturized titanium implants were placed in either maxillary first molar (mxM1) fresh extraction sockets or healed mxM1 sites in mice. Peri-implant soft tissues were evaluated at multiple timepoints to assess the molecular mechanisms of attachment and the efficacy of the soft tissue as a barrier. A healthy junctional epithelium (JE) served as positive control.

RESULTS

No differences were observed in the rate of soft-tissue integration of immediate versus delayed implants; however, overall, mucosal integration took at least twice as long as osseointegration in this model. Qualitative assessment of Vimentin expression over the time course of soft-tissue integration indicated an initially disorganized peri-implant connective tissue envelope that gradually matured with time. Quantitative analyses showed significantly less total collagen in peri-implant connective tissues compared to connective tissue around teeth around implants. Quantitative analyses also showed a gradual increase in expression of hemidesmosomal attachment proteins in the peri-implant epithelium (PIE), which was accompanied by a significant inflammatory marker reduction.

CONCLUSIONS

Within the timeframe examined, quantitative analyses showed that connective tissue maturation never reached that observed around teeth. Hemidesmosomal attachment protein expression levels were also significantly reduced compared to those in an intact JE, although quantitative analyses indicated that macrophage density in the peri-implant environment was reduced over time, suggesting an improvement in PIE barrier functions. Perhaps most unexpectedly, maturation of the peri-implant soft tissues was a significantly slower process than osseointegration.

PSO/SDF-1 composite hydrogel promotes osteogenic differentiation of PDLSCs and bone regeneration in periodontitis rats

Periodontitis is an inflammatory disease characterized by the destruction of periodontal tissues, and the promotion of bone tissue regeneration is the key to curing periodontitis. Psoralen is the main component of Psoralea corylifolia Linn, and has multiple biological effects, including anti-osteoporosis and osteogenesis. We constructed a novel hydrogel loaded with psoralen (PSO) and stromal cell-derived factor-1 (SDF-1) for direct endogenous cell homing. This study aimed to evaluate the synergistic effects of PSO/SDF-1 on periodontal bone regeneration in patients with periodontitis. The results of CCK8, alkaline phosphatase (ALP) activity assay, and Alizarin Red staining showed that PSO/SDF-1 combination treatment promoted cell proliferation, chemotaxis ability, and ALP activity of PDLSCs. qRT-PCR and western blotting showed that the expression levels of alkaline phosphatase (ALP), dwarf-associated transcription factor 2 (RUNX2), and osteocalcin (OCN) gene were upregulated. Rat periodontal models were established to observe the effect of local application of the composite hydrogel on bone regeneration. These results proved that the PSO/SDF-1 combination treatment significantly promoted new bone formation. The immunohistochemical (IHC) results confirmed the elevated expression of ALP, RUNX2, and OCN osteogenic genes. PSO/SDF-1 composite hydrogel can synergistically regulate the biological function and promote periodontal bone formation. Thus, this study provides a novel strategy for periodontal bone regeneration.

Effect of simultaneous and sequential use of TGF-β1 and TGF-β3 with FGF-2 on teno/ligamentogenic differentiation of periodontal ligament stem cells

OBJECTIVE

The periodontal ligament is a crucial part of the periodontium, and its regeneration is challenging. This study compares the effect of simultaneous and sequential use of FGF-2 and TGF-β1 with FGF-2 and TGF-β3 on the periodontal ligament stem cells (PDLSCs) teno/ligamentogenic differentiation.

DESIGN

This study comprises ten different groups. A control group with only PDLSCs; FGF-2 group containing PDLSCs with a medium culture supplemented with FGF-2 (50 ng/mL). In other experimental groups, different concentrations (5 ng/mL or 10 ng/mL) of TGF-β1&-β3 simultaneously or sequentially were combined with FGF-2 on the cultured PDLSCs. TGF-β was added to the medium after day 3 in the sequential groups. Methyl Thiazolyl Tetrazolium (MTT) assay on days 3, 5, and 7 and Quantitative Real-time Polymerase Chain Reaction (RT-qPCR) analysis after day 7 were conducted to investigate PLAP1, SCX, and COL3A1, RUNX2 genes. All experiments were conducted in a triplicate. The One-way and Two-way ANOVA with Tukey post hoc were utilized to analyze the results of the MTT and RT-qPCR tests, respectively. A p-value less than 0.05 is considered significant.

RESULTS

The proliferation of cells on days 3, 5, and 7 was not significantly different among different experimental groups (P > 0.05). A higher expression of the PLAP1, SCX, and COL3A1 have been seen in groups with sequential use of growth factors; among these groups, the group using 5 ng/mL of TGF-β3 led other groups with the most amount of significant upregulation in PLAP1(17.69 ± 1.11 fold; P < 0.0001), SCX (5.71 ± 0.38 fold; P < 0.0001), and COL1A3 (6.35 ± 0.39 fold; P < 0.0001) expression, compared to the control group. The expression of the RUNX2 decreased in all groups compared to the control group; this reduction was more in groups with sequential use of growth factors.

CONCLUSION

The sequential use of growth factors can be more effective than simultaneous use in teno/ligamentogenic differentiation of PDLSCs. Moreover, treatment with 5 ng/mL TGF-β3 after FGF-2 was more effective than TGF-β1.

Wisdom Tooth Autotransplantation for the Missing Maxillary Central Incisors Using a 3D-Printed Replica: A Case Report

In this case report, we describe a 19-year-old man who underwent an autotransplantation of a lower third molar into the extracted region of his upper central incisors. Due to trauma, the patient's upper right and left central incisors had been extracted. He visited our clinic and requested to perform autotransplantation of his own teeth into the upper central incisor part because he wanted to use his natural teeth. So, we decided to extract his lower right third molar and autotransplant it into the extraction part of the upper central incisors. Immediately after extraction of the lower right third molar, the tooth was autotransplanted into the upper anterior region using a 3D-printed resin replica of the donor tooth and artificial sockets of the recipient site. Then, the root canal treatment was performed, and a temporary crown was set. Next, orthodontic treatment was done to flatten the curve of Spee. After completing the orthodontic treatment, a final prosthodontic restoration was set on the autotransplanted tooth. Four years later, the autotransplanted tooth remained stable with a healthy periodontium. This case demonstrates that if a patient has a request to use their natural teeth, autotransplantation of a wisdom tooth into the anterior region can be a useful method to replace the missing teeth.

Entire Dental Arch Mesial Movement after Extraction of Maxillary Right Central Incisor due to Root Fracture Treated with Temporary Anchorage Devices

This case report describes a 19-year-old woman with skeletal Class I crowding and an unsalvageable maxillary right central incisor. She visited our clinic with the chief complaint of mobility of the maxillary right central incisor due to a traffic accident. After extraction of the maxillary right central incisor, the space was closed orthodontically. All the maxillary right teeth were moved mesially with an elastic chain attached to a palatal lever arm which was connected to palatal temporary anchorage devices (TADs). After orthodontic treatment had been completed, the maxillary right lateral incisor and peg-shaped left lateral incisor were restored with a porcelain laminate veneer. The maxillary right canine was morphologically reshaped and built up with composite resin. Consequently, esthetically ideal occlusion and functional lateral guidance with uncontacted molars were obtained. These results show that mesial movement of the entire dental arch with TADs is a useful orthodontic treatment option in patients in whom the maxillary central incisor has been extracted.

Activation of periodontal ligament cell cytodifferentiation by juxtacrine signaling from cementoblasts

BACKGROUND

New cementum forms from existing cementum during periodontal tissue regeneration, indicating that cementoblasts may interact with progenitor cells in the periodontal ligament to enhance cementogenesis. However, the molecular mechanisms of this process are currently unknown. This study aims to clarify the role of cell-cell interactions between cementoblasts and periodontal ligament cells in differentiation into cementoblasts.

METHODS

To analyze the role of human cementoblast-like cells (HCEMs) on human periodontal ligament cells (HPDLs), we mixed cell suspensions of enhanced green fluorescent protein-tagged HPDLs and HCEMs, and then seeded and cultured them in single wells (direct co-cultures). We sorted co-cultured HPDLs and analyzed their characteristics, including the expression of cementum-related genes. In addition, we cultured HPDLs and HCEMs in a non-contact environment using a culture system composed of an upper insert and a lower well separated by a semi-permeable membrane (indirect co-cultures), and similar analysis was performed. Gene expression of integrin-binding sialoprotein (IBSP) in cementoblasts was confirmed in mouse periodontal tissues. We also investigated the effect of Wingless-type (Wnt) signaling on the differentiation of HPDLs into cementoblasts.

RESULTS

Direct co-culture of HPDLs with HCEMs significantly upregulated the expression of cementoblast-related genes in HPDLs, whereas indirect co-culture exerted no effect. Wnt3A stimulation significantly upregulated IBSP expression in HPDLs, whereas inhibition of canonical Wnt signaling suppressed the effects of co-culture.

CONCLUSION

Our results suggest that direct cell interactions with cementoblasts promote periodontal ligament cell differentiation into cementoblasts. Juxtacrine signaling via the canonical Wnt pathway plays a role in this interaction.

Cyclic Stretching Triggers Cell Orientation and Extracellular Matrix Remodeling in a Periodontal Ligament 3D In Vitro Model

During orthodontic tooth movement (OTM), the periodontal ligament (PDL) plays a crucial role in regulating the tissue remodeling process. To decipher the cellular and molecular mechanisms underlying this process in vitro, suitable 3D models are needed that more closely approximate the situation in vivo. Here, a customized bioreactor is developed that allows dynamic loading of PDL-derived fibroblasts (PDLF). A collagen-based hydrogel mixture is optimized to maintain structural integrity and constant cell growth during stretching. Numerical simulations show a uniform stress distribution in the hydrogel construct under stretching. Compared to static conditions, controlled cyclic stretching results in directional alignment of collagen fibers and enhances proliferation and spreading ability of the embedded PDLF cells. Effective force transmission to the embedded cells is demonstrated by a more than threefold increase in Periostin protein expression. The cyclic stretch conditions also promote extensive remodeling of the extracellular matrix, as confirmed by increased glycosaminoglycan production. These results highlight the importance of dynamic loading over an extended period of time to determine the behavior of PDLF and to identify in vitro mechanobiological cues triggered during OTM-like stimulus. The introduced dynamic bioreactor is therefore a useful in vitro tool to study these mechanisms.

Evaluation of radiation dose and image quality for dental cone-beam computed tomography in pediatric patients

Children are sensitive to radiation; therefore, it is necessary to reduce radiation dose as much as possible in pediatric patients. In addition, it is crucial to investigate the optimal imaging conditions as they considerably affect the radiation dose. In this study, we investigated the effect of different imaging conditions on image quality and optimized the imaging conditions for dental cone-beam computed tomography (CBCT) examinations to diagnose ectopic eruptions and impacted teeth in children. To achieve our aims, we evaluated radiation doses and subjective and objective image quality. The CBCT scans were performed using 3D Accuitomo F17. All combinations of a tube voltage (90 kV), tube currents (1, 2, 3 mA), fields of view (FOVs) (4 × 4, 6 × 6 cm), and rotation angles (360°, 180°) were used. Dose-area product values were measured. SedentexCT IQ cylindrical phantom was used to physically evaluate the image quality. We used the modulation transfer function as an index of resolution, the noise power spectrum as an index of noise characteristics, and the system performance function as an overall evaluation index of the image. Five dentists visually evaluated the images from the head-neck phantom. The results showed that the image quality tended to worsen, and scores for visual evaluation decreased as tube currents, FOVs and rotation angles decreased. In particular, image noise negatively affected the delineation of the periodontal ligament space. The optimal imaging conditions were 90 kV, 2 mA, 4 × 4 cm FOV and 180° rotation. These results suggest that CBCT radiation doses can be significantly reduced by optimizing the imaging conditions.

Electrospun Poly(L-Lactic Acid)/Gelatin Hybrid Polymer as a Barrier to Periodontal Tissue Regeneration

Poly(L-lactic acid) (PLLA) and PLLA/gelatin polymers were prepared via electrospinning to evaluate the effect of PLLA and gelatin content on the mechanical properties, water uptake capacity (WUC), water contact angle (WCA), degradation rate, cytotoxicity and cell proliferation of membranes. As the PLLA concentration increased from 1 wt% to 3 wt%, the tensile strength increased from 5.8 MPa to 9.1 MPa but decreased to 7.0 MPa with 4 wt% PLLA doping. The WUC decreased rapidly from 594% to 236% as the PLLA content increased from 1 to 4 wt% due to the increased hydrophobicity of PLLA. As the gelatin content was increased to 3 wt% PLLA, the strength, WUC and WCA of the PLLA/gelatin membrane changed from 9.1 ± 0.9 MPa to 13.3 ± 2.3 MPa, from 329% to 1248% and from 127 ± 1.2° to 0°, respectively, with increasing gelatin content from 0 to 40 wt%. However, the failure strain decreased from 3.0 to 0.5. The biodegradability of the PLLA/gelatin blend increased from 3 to 38% as the gelatin content increased to 40 wt%. The viability of L-929 and MG-63 cells in the PLLA/gelatin blend was over 95%, and the excellent cell proliferation and mechanical properties suggested that the tunable PLLA/gelatin barrier membrane was well suited for absorbable periodontal tissue regeneration.

Remodeling of the periodontal ligament and alveolar bone during axial tooth movement in mice with type 1 diabetes

OBJECTIVES

To observe the elongation of the axial tooth movement in the unopposed rodent molar model with type 1 diabetes mellitus and explore the pathological changes of periodontal ligament and alveolar bone, and their correlation with tooth axial movement.

METHODS

The 80 C57BL/6J mice were randomly divided into the streptozotocin(STZ)-injected group (n = 50) and the control group (n = 30). Mice in the streptozotocin(STZ)-injected group were injected intraperitoneal with streptozotocin (STZ), and mice in the control group were given intraperitoneal injection of equal doses of sodium citrate buffer. Thirty mice were randomly selected from the successful models as the T1DM group. The right maxillary molar teeth of mice were extracted under anesthesia, and allowed mandibular molars to super-erupt. Mice were sacrificed at 0, 3, 6,9, and 12 days. Tooth elongation and bone mineral density (BMD) were evaluated by micro-CT analysis(0,and 12 days mice). Conventional HE staining, Masson staining and TRAP staining were used to observe the changes in periodontal tissue(0, 3, 6, 9, and 12 days mice). The expression differences of SPARC, FGF9, BMP4, NOGGIN, and type I collagen were analyzed by RT-qPCR.

RESULTS

After 12 days of tooth extraction, our data showed significant super-eruption of mandibular mouse molars of the two groups. The amount of molar super-eruption in the T1DM group was 0.055mm( ± 0.014mm), and in the control group was 0.157( ± 0.017mm). The elongation of the T1DM mice was less than that of the control mice(P<0.001). It was observed that the osteoclasts and BMD increased gradually in both groups over time. Compared with the control group, the collagen arrangement was more disordered, the number of osteoclasts was higher (P<0.05), and the increase of bone mineral density was lower(2.180 ± 0.007g/cm³ vs. 2.204 ± 0.006g/cm³, P<0.001) in the T1DM group. The relative expression of SPARC, FGF9, BMP4, and type I collagen in the two groups increased with the extension of tooth extraction time while NOGGIN decreased. The relative expression of all of SPARC, FGF9, BMP4, and type I collagen in the T1DM group were significantly lower, and the expression of NOGGIN was higher than that in the control group (P<0.05).

CONCLUSION

The axial tooth movement was inhibited in type 1 diabetic mice. The result may be associated with the changes of periodontal ligament osteoclastogenic effects and alveolar bone remodeling regulated by the extracellular matrix and osteogenesis-related factors.

Junctional epithelium and hemidesmosomes: Tape and rivets for solving the "percutaneous device dilemma" in dental and other permanent implants

The percutaneous device dilemma describes etiological factors, centered around the disrupted epithelial tissue surrounding non-remodelable devices, that contribute to rampant percutaneous device infection. Natural percutaneous organs, in particular their extracellular matrix mediating the "device"/epithelium interface, serve as exquisite examples to inspire longer lasting long-term percutaneous device design. For example, the tooth's imperviousness to infection is mediated by the epithelium directly surrounding it, the junctional epithelium (JE). The hallmark feature of JE is formation of hemidesmosomes, cell/matrix adhesive structures that attach surrounding oral gingiva to the tooth's enamel through a basement membrane. Here, the authors survey the multifaceted functions of the JE, emphasizing the role of the matrix, with a particular focus on hemidesmosomes and their five main components. The authors highlight the known (and unknown) effects dental implant - as a model percutaneous device - placement has on JE regeneration and synthesize this information for application to other percutaneous devices. The authors conclude with a summary of bioengineering strategies aimed at solving the percutaneous device dilemma and invigorating greater collaboration between clinicians, bioengineers, and matrix biologists.

CTGF Promotes the Osteoblast Differentiation of Human Periodontal Ligament Stem Cells by Positively Regulating BMP2/Smad Signal Transduction

Objective

This work is aimed at revealing the role and the molecular mechanism of connective tissue growth factor 2 (CTGF) in the osteoblast differentiation of periodontal ligament stem cells (PDLSCs).

Methods

The osteogenic differentiation of PDLSCs was induced by osteogenic induction medium (OM), and the expression level of osteogenic related proteins ALP, RUNX2, OCN, and CTGF was estimated using quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting analysis. We constructed cell lines with CTGF overexpression or knockdown to verify the role of CTGF in the osteoblast differentiation of PDLSCs. Alkaline phosphatase (ALP) staining was introduced to measure the osteoblasts activity, and alizarin red S (ARS) staining was employed to test matrix mineralization. The interaction between CTGF and bone morphogenetic protein-2 (BMP-2) was determined by endogenous coimmunoprecipitation (Co-IP).

Results

The expression level of CTGF was increased during the osteogenic induction of PDLSCs. Additionally, CTGF overexpression effectively maintained the stemness and facilitated the osteoblast differentiation in PDLSCs, and CTGF knockdown exerted opposite effects. Moreover, at molecular mechanism, CTGF increased the activity of BMP-2/Smad signaling pathway.

Conclusion

This investigation verified that CTGF promotes the osteoblast differentiation in PDLSCs at least partly by activating BMP-2/Smad cascade signal.

Mechanical Compression by Simulating Orthodontic Tooth Movement in an In Vitro Model Modulates Phosphorylation of AKT and MAPKs via TLR4 in Human Periodontal Ligament Cells

Mechanical compression simulating orthodontic tooth movement in in vitro models induces pro-inflammatory cytokine expression in periodontal ligament (PDL) cells. Our previous work shows that TLR4 is involved in this process. Here, primary PDL cells are isolated and characterized to better understand the cell signaling downstream of key molecules involved in the process of sterile inflammation via TLR4. The TLR4 monoclonal blocking antibody significantly reverses the upregulation of phospho-AKT, caused by compressive force, to levels comparable to controls by inhibition of TLR4. Phospho-ERK and phospho-p38 are also modulated in the short term via TLR4. Additionally, moderate compressive forces of 2 g/cm², a gold standard for static compressive mechanical stimulation, are not able to induce translocation of Nf-kB and phospho-ERK into the nucleus. Accordingly, we demonstrated for the first time that TLR4 is also one of the triggers for signal transduction under compressive force. The TLR4, one of the pattern recognition receptors, is involved through its specific molecular structures on damaged cells during mechanical stress. Our findings provide the basis for further research on TLR4 in the modulation of sterile inflammation during orthodontic therapy and periodontal remodeling.

Fibrillin protein, a candidate for creating a suitable scaffold in PDL regeneration while avoiding ankylosis

The tooth is stabilized by fiber-rich tissue called the periodontal ligament (PDL). The narrow space of the PDL does not calcify in the physiological state even thought it exists between two calcified tissues, namely, the cementum of the root and alveolar bone. Two situations that require PDL regeneration are periodontitis and dental trauma. Periodontitis induces the loss of PDL and alveolar bone due to inflammation related to infection. Conversely, in PDLs damaged by dental trauma, accelerating bone formation as an overreaction of the healing process is induced, thereby inducing dentoalveolar ankylosis at the tooth root surface. PDL regeneration following dental trauma must therefore be considered separately from periodontitis. Therefore, PDL regeneration in dental trauma must be considered separately from periodontitis. This review focuses on the components involved in avoiding dentoalveolar ankylosis, including oxytalan fibers, aggregated microfibrils, epithelial cell rests of Malassez (ERM), and TGF-β signaling. During root development, oxytalan fibers produced by PDL cells work in collaboration with the epithelial components in the PDL (e.g., Hertwig's root sheath [HERS] and ERM). We herein describe the functions of oxytalan fibers, ERM, and TGF-β signals which are involved in the avoidance of bone formation.

MZB1 targeted by miR-185-5p inhibits the migration of human periodontal ligament cells through NF-κB signaling and promotes alveolar bone loss

OBJECTIVE

To explore the role of Marginal Zone B and B-1 Cell-Specific Protein (MZB1), a novel molecule associated with periodontitis, in migration of human periodontal ligament cells (hPDLCs) and alveolar bone orchestration.

BACKGROUND

MZB1 is an ER-localized protein and its upregulation has been found to be associated with a variety of human diseases. However, few studies have investigated the effect and mechanism of MZB1 on hPDLCs in periodontitis.

METHODS

Gene expression profiles in human gingival tissues were acquired from the Gene Expression Omnibus (GEO) database, and candidate molecules were then selected through bioinformatic analysis. Subsequently, we identified the localization and expression of MZB1 in human gingival tissues, mice, and hPDLCs by immunofluorescence, RT-qPCR, and Western blot. Dual-luciferase reporter assay was applied to assess the binding of miR-185-5p to MZB1. Furthermore, the effects of MZB1 on cell migration, proliferation, and apoptosis in vitro were investigated by wound-healing assay, transwell assay, CCK-8 assay, and flow cytometry analysis. Finally, Micro-CT analysis and H&E staining were performed to examine the effects of MZB1 on alveolar bone loss in vivo.

RESULTS

Bioinformatic analysis discovered that MZB1 was one of the most significantly increased genes in periodontitis patients. MZB1 was markedly increased in the gingival tissues of periodontitis patients, in the mouse models, and in the hPDLCs treated with lipopolysaccharide of Porphyromonas gingivalis (LPS-PG). Furthermore, in vitro experiments showed that MZB1, as a target gene of miR-185-5p, inhibited migration of hPDLCs. Overexpression of MZB1 specifically upregulated the phosphorylation of p65, while pretreatment of MZB1-overexpressed hPDLCs with PDTC (NF-κB inhibitor) notably reduced the p-p65 level and promoted cell migration. In addition, the mRNA expression levels of alkaline phosphatase (ALP) and Runt-related transcription factor 2 (Runx2) were inhibited in MZB1-overexpressed hPDLCs and miR-185-5p inhibitor treated hPDLCs, respectively. In vivo experiments showed that knockdown of MZB1 alleviated the loss of alveolar bone.

CONCLUSION

As a target gene of miR-185-5p, MZB1 plays a crucial role in inhibiting the migration of hPDLCs through NF-κB signaling pathway and deteriorating alveolar bone loss.

Sclerostin in Periodontal Ligament: Homeostatic Regulator in Biophysical Force-Induced Tooth Movement

AIM

This study elucidates the role of sclerostin in periodontal ligament (PDL) as a homeostatic regulator in biophysical force-induced tooth movement (BFTM).

MATERIALS AND METHODS

BFTM was performed in rats, followed by microarray, immunofluorescence, in situ hybridization, and real-time PCR for detection and identification of the molecules. The periodontal space was analyzed via micro-computed tomography. Effects on osteoclastogenesis and bone resorption were evaluated in mouse bone marrow-derived cells. In vitro human PDL cells were subjected to biophysical forces.

RESULTS

In the absence of BFTM, sclerostin was hardly detected in the periodontium except the PDL and alveolar bone in the furcation region and apex of the molar roots. However, sclerostin was upregulated in the PDL in vivo by adaptable force, which induced typical transfiguration without changes in periodontal space as well as in vitro PDL cells under compression and tension. In contrast, the sclerostin level was unaffected by heavy force, which caused severe degeneration of the PDL and narrowed periodontal space. Sclerostin inhibited osteoclastogenesis and bone resorption, which corroborates the accelerated tooth movement by the heavy force.

CONCLUSIONS

Sclerostin in PDL may be a key homeostatic molecule in the periodontium and a biological target for the therapeutic modulation of BFTM. This article is protected by copyright. All rights reserved.

A Review of Tissue Engineering for Periodontal Tissue Regeneration

Periodontal disease is one of the most common diagnoses in small animal veterinary medicine. This infectious disease of the periodontium is characterized by the inflammation and destruction of the supporting structures of teeth, including periodontal ligament, cementum, and alveolar bone. Traditional periodontal repair techniques make use of open flap debridement, application of graft materials, and membranes to prevent epithelial downgrowth and formation of a long junctional epithelium, which inhibits regeneration and true healing. These techniques have variable efficacy and are made more challenging in veterinary patients due to the cost of treatment for clients, need for anesthesia for surgery and reevaluation, and difficulty in performing necessary diligent home care to maintain oral health. Tissue engineering focuses on methods to regenerate the periodontal apparatus and not simply to repair the tissue, with the possibility of restoring normal physiological functions and health to a previously diseased site. This paper examines tissue engineering applications in periodontal disease by discussing experimental studies that focus on dogs and other animal species where it could potentially be applied in veterinary medicine. The main areas of focus of tissue engineering are discussed, including scaffolds, signaling molecules, stem cells, and gene therapy. To date, although outcomes can still be unpredictable, tissue engineering has been proven to successfully regenerate lost periodontal tissues and this new possibility for treating veterinary patients is discussed.

Activin A Promotes Osteoblastic Differentiation of Human Preosteoblasts through the ALK1-Smad1/5/9 Pathway

Activin A, a member of transforming growth factor-β superfamily, is involved in the regulation of cellular differentiation and promotes tissue healing. Previously, we reported that expression of activin A was upregulated around the damaged periodontal tissue including periodontal ligament (PDL) tissue and alveolar bone, and activin A promoted PDL-related gene expression of human PDL cells (HPDLCs). However, little is known about the biological function of activin A in alveolar bone. Thus, this study analyzed activin A-induced biological functions in preosteoblasts (Saos2 cells). Activin A promoted osteoblastic differentiation of Saos2 cells. Activin receptor-like kinase (ALK) 1, an activin type I receptor, was more strongly expressed in Saos2 cells than in HPDLCs, and knockdown of ALK1 inhibited activin A-induced osteoblastic differentiation of Saos2 cells. Expression of ALK1 was upregulated in alveolar bone around damaged periodontal tissue when compared with a nondamaged site. Furthermore, activin A promoted phosphorylation of Smad1/5/9 during osteoblastic differentiation of Saos2 cells and knockdown of ALK1 inhibited activin A-induced phosphorylation of Smad1/5/9 in Saos2 cells. Collectively, these findings suggest that activin A promotes osteoblastic differentiation of preosteoblasts through the ALK1-Smad1/5/9 pathway and could be used as a therapeutic product for the healing of alveolar bone as well as PDL tissue.

The Role of Wnt Signaling in Postnatal Tooth Root Development

Appropriate tooth root formation and tooth eruption are critical for achieving and maintaining good oral health and quality of life. Tooth eruption is the process through which teeth emerge from their intraosseous position to their functional position in the oral cavity. This temporospatial process occurs simultaneously with tooth root formation through a cascade of interactions between the epithelial and adjoining mesenchymal cells. Here, we will review the role of the Wnt system in postnatal tooth root development. This signaling pathway orchestrates the process of tooth root formation and tooth eruption in conjunction with several other major signaling pathways. The Wnt signaling pathway is comprised of the canonical, or Wnt/β-catenin, and the non-Canonical signaling pathway. The expression of multiple Wnt ligands and their downstream transcription factors including β-catenin is found in the cells in the epithelia and mesenchyme starting from the initiation stage of tooth development. The inhibition of canonical Wnt signaling in an early stage arrests odontogenesis. Wnt transcription factors continue to be present in dental follicle cells, the progenitor cells responsible for differentiation into cells constituting the tooth root and the periodontal tissue apparatus. This expression occurs concurrently with osteogenesis and cementogenesis. The conditional ablation of β-catenin in osteoblast and odontoblast causes the malformation of the root dentin and cementum. On the contrary, the overexpression of β-catenin led to shorter molar roots with thin and hypo-mineralized dentin, along with the failure of tooth eruption. Therefore, the proper expression of Wnt signaling during dental development is crucial for regulating the proliferation, differentiation, as well as epithelial-mesenchymal interaction essential for tooth root formation and tooth eruption.

Role of transient receptor potential channel 6 in the osteogenesis of periodontal ligament cells

Transient receptor potential channel 6 (TRPC6) is a receptor-operated Ca2+ channel that plays an important role in Ca2+ influx in the majority of non-excitable cells and influences calcium signalling and cellular responses. Therefore, the purpose of the present study was to gain insight into the role of TRPC6 in the osteogenesis of periodontal ligament cells (PDLCs). By western blot and immunohistochemical staining, the protein level of TRPC6 was found to be increased in a time-dependent manner during osteoblastic differentiation of PDLCs. In addition, the TRPC6 inhibitor SKF96365 was used to block the function of TRPC6 and inhibit osteoblastic differentiation of PDLCs. The TRPC6 activator hyperforin dicyclohexylammonium salt (hyperforin DCHA) was used to activate TRPC6 and promote osteoblastic differentiation of PDLCs. In vivo, wild-type mice showed better bone regeneration than TRPC6-/- mice, suggesting that TRPC6 has notable osteogenic induction properties and is important for bone defect repair. In conclusion, the current data demonstrated that TRPC6 plays a significant role in osteoblastic differentiation of PDLCs, suggesting that it may be a promising therapeutic target in osteogenesis.

Age-related osteogenesis on lateral force application to rat incisor – Part II: Bony recession and cortical remodeling

Objective:

The aim of this study is to analyze the age-related changes in the bony recession and cortical bone remodeling induced by lateral orthodontic tooth movement, using a three-dimensional micro-computed tomography (CT) analysis.

Material and Methods:

A total of 40 male Sprague-Dawley rats were divided into two distinct age groups (young, 10 weeks and adult, 52 weeks). Double-helical springs exerting 40 g of force were applied to central incisors to analysis of changes in lateral cortical bone and tooth movement with age and time. The young and adult rats were divided into four subgroups, T0 (0 week), T1 (1 week), T2 (2 weeks), and T3 (3 weeks), depending on the period of wearing the appliance. Micro-CT image was taken on each dissected pre-maxilla specimen. In each subgroup, distance between the center of teeth, suture width, tooth displacement, bony recession, and bone volume was evaluated.

Results:

The changes in the distance between the center of teeth and the suture width were significantly greater in the young group. However, the change in the tooth displacement showed no significant difference between groups. In the young group, bony recession of outer cortical layer was observed at T1 (P < 0.05), but the amount of recession gradually decreased at T2 and T3. In contrast, in the adult group, bony recession increased gradually over observation period (P < 0.05). The bone volume decreased at T1 (P < 0.05), but recovered at T2 and T3 in both groups.

Conclusion:

The compensatory bone formation occurs in the pressure side of cortical bone more significantly in the young group than in the adult according to the lateral displacement of incisor in rats. The reduced bone reaction in the adult is considered a limiting factor of the excessive tooth movement in the compromised treatment of skeletal malocclusion.

Healing of Experimental Periodontal Defects Following Treatment with Fibroblast Growth Factor-2 and Deproteinized Bovine Bone Mineral

The aim of this study was to investigate the effects of fibroblast growth factor (FGF)-2 used in combination with deproteinized bovine bone mineral (DBBM) on the healing of experimental periodontal defects. Periodontal defects created in rats were treated by FGF-2, DBBM, FGF-2 + DBBM, or left unfilled. Microcomputed tomography, histological, and immunohistochemical examinations were used to evaluate healing. In vitro cell viability/proliferation on DBBM with/without FGF-2 was assessed by WST-1. Cell behavior was analyzed using scanning electron and confocal laser scanning microscopy. Osteogenic differentiation was evaluated by staining with alkaline phosphatase and alizarin red. Bone volume fraction was significantly greater in FGF-2 and FGF-2 + DBBM groups than in other groups at 2 and 4 weeks postoperatively. In histological assessment, newly formed bone in FGF-2 and FGF-2 + DBBM groups appeared to be greater than other groups. Significantly greater levels of proliferating cell nuclear antigen-, vascular endothelial growth factor-, and osterix-positive cells were observed in FGF-2 and FGF-2 + DBBM groups compared to Unfilled group. In vitro, addition of FGF-2 to DBBM promoted cell viability/proliferation, attachment/spreading, and osteogenic differentiation. The combination therapy using FGF-2 and DBBM was similarly effective as FGF-2 alone in the healing of experimental periodontal defects. In certain bone defect configurations, the combined use of FGF-2 and DBBM may enhance healing via promotion of cell proliferation, angiogenesis, and osteogenic differentiation.

Generation of biohybrid implants using a multipotent human periodontal ligament cell line and bioactive core materials

We aimed to generate periodontal ligament (PDL) tissue-like structures from a multipotent human PDL cell line using three-dimensional (3D) bioprinting technology and to incorporate these structures with bioactive core materials to develop a new biohybrid implant system. After 3D bioprinting, single-cell spheroids were able to form 3D tubular structures (3DTBs). We established three types of complexes using 3DTBs and different core materials: 3DTB-titanium core (TIC), 3DTB-hydroxyapatite core (HAC), and 3DTB without a core material (WOC). The expressions of PDL-, angiogenesis-, cementum-, and bone-related genes were significantly increased in the three complexes compared with monolayer-cultured cells. Abundant collagen fibers and cells positive for the above markers were confirmed in the three complexes. However, more positive cells were detected in HAC than in WOC or TIC. The present results suggest that 3D-bioprinted structures and hydroxyapatite core materials can function similarly to the PDL and may be useful for the development of a new biohybrid implant system.

Current Trends in In Vitro Modeling to Mimic Cellular Crosstalk in Periodontal Tissue

Clinical evidence indicates that in physiological and therapeutic conditions a continuous remodeling of the tooth root cementum and the periodontal apparatus is required to maintain tissue strength, to prevent damage, and to secure teeth anchorage. Within the tooth's surrounding tissues, tooth root cementum and the periodontal ligament are the key regulators of a functional tissue homeostasis. While the root cementum anchors the periodontal fibers to the tooth root, the periodontal ligament itself is the key regulator of tissue resorption, the remodeling process, and mechanical signal transduction. Thus, a balanced crosstalk of both tissues is mandatory for maintaining the homeostasis of this complex system. However, the mechanobiological mechanisms that shape the remodeling process and the interaction between the tissues are largely unknown. In recent years, numerous 2D and 3D in vitro models have sought to mimic the physiological and pathophysiological conditions of periodontal tissue. They have been proposed to unravel the underlying nature of the cell-cell and the cell-extracellular matrix interactions. The present review provides an overview of recent in vitro models and relevant biomaterials used to enhance the understanding of periodontal crosstalk and aims to provide a scientific basis for advanced regenerative strategies.

Long non-coding RNA 01126 promotes periodontitis pathogenesis of human periodontal ligament cells via miR-518a-5p/HIF-1α/MAPK pathway

BACKGROUND

Periodontitis is a prevalent oral inflammatory disease, which can cause periodontal ligament to a local hypoxia environment. However, the mechanism of hypoxia associated long non-coding RNAs (lncRNAs) involved in periodontitis is still largely unknown.

METHODS

Microarray was performed to detect the expression patterns of lncRNAs in 3 pairs of gingival tissues from patients with periodontitis and healthy controls. The expression of lncRNA 01126 (LINC01126), miR-518a-5p and hypoxia-inducible factor-1α (HIF-1α) in periodontal tissues and in human periodontal ligament cells (hPDLCs) under hypoxia was measured by quantitative real-time polymerase chain reaction or western blot. Fluorescence in situ hybridization and cell fraction assay were performed to determine the subcellular localization of LINC01126 and miR-518a-5p. Overexpression or knockdown of LINC01126 or HIF-1α was used to confirm their biological roles in hPDLCs. MTT assays were performed to evaluate hPDLCs proliferation ability. Flow cytometry was used to detect apoptosis. ELISA was used to measure the expression levels of interleukin (IL)-1β, IL-6, IL-8 and TNF-α. Dual-luciferase reporter assays were performed to assess the binding of miR-518a-5p to LINC01126 and HIF-1α. RNA immunoprecipitation assay was used to identify whether LINC01126 and miR-518a-5p were significantly enriched in AGO-containing micro-ribonucleoprotein complexes.

RESULTS

We selected LINC01126, which was the most highly expressed lncRNA, to further verify its functions in periodontitis-induced hypoxia. The expression of LINC01126 was increased in periodontal tissues. In vitro experiment demonstrated that LINC01126 suppressed proliferation, promoted apoptosis and inflammation of hPDLCs under hypoxia via sponging miR-518a-5p. Moreover, we identified HIF-1α acted as a direct target of miR-518a-5p in hPDLCs and LINC01126 promoted periodontitis pathogenesis by regulating the miR-518a-5p/HIF-1α/MAPK pathway.

CONCLUSION

LINC01126 promotes periodontitis pathogenesis of hPDLCs via miR-518a-5p/HIF-1α/MAPK pathway, providing a possible clue for LINC01126-based periodontal therapeutic approaches.

Biomimetic Properties of Engineered Periodontal Ligament/Cementum in Dental Implants

The conventional concept of osseointegrated dental implants based on direct connection to alveolar bone lacks a structured periodontal ligament (PDL) as in natural tooth. This limits the physiologic and functional efficiency of the implant in cushioning occlusal overload, orthodontic tooth movement, and proprioception. Development of bio-mimetic implants that can satisfy the bio-functional requirements of the natural tooth will be an innovative approach and preliminary researches in this area has been reported. This review includes in vivo studies which reported structural features and functional efficiency of an artificial PDL or cementum developed around dental implants. The electronic search identified 12 animal studies and one human trial which utilized retained or adjacent natural tooth roots, exogenous scaffold materials, dental progenitor cells derived from PDL of extracted tooth root as PDL substitutes. The result of the review is dominated by bio-hybrid implants that used dental follicles separated on the particular embryonic day and cell sheets from immortalized human cells. A summary of the currently available research on artificial PDL/cementum around dental implants highlights the potential need of autologous cell-derived tissues to bioengineer a fully functional implant design

Formation and regeneration of a Wnt-responsive junctional epithelium

AIM

To identify the molecular mechanisms mediating the persistent defensive functions of the self-renewing junctional epithelium (JE).

MATERIALS AND METHODS

Two strains of Wnt reporter mice, Axin2^{CreErt2 /+} ;R26R^{mTmG /+} and Axin2^{LacZ /+} , were employed, along with three clinically relevant experimental scenarios where the function of the JE is disrupted: after tooth extraction, after a partial gingivectomy, and after a complete circumferential gingivectomy.

RESULTS

Using transgenic Wnt reporter strains of mice, we established the JE is a Wnt-responsive epithelium beginning at the time of its formation and that it maintains this status into adulthood. After tooth extraction, progeny of the initial Wnt-responsive JE population directly contributed to healing and ultimately adopted an oral epithelium (OE) phenotype. In the traditional partial gingivectomy model, the JE completely regenerated and did so via progeny of the original Wnt-responsive population. However, following circumferential gingivectomy, the OE was incapable of re-establishing a functional JE.

CONCLUSIONS

A Wnt-responsive niche at the interface between tooth and oral epithelia is required for a functional JE.

Role of YAP1 gene in proliferation, osteogenic differentiation, and apoptosis of human periodontal ligament stem cells induced by TNF-α

BACKGROUND

Periodontitis is a chronic inflammatory disease that occurs in periodontal tissues and can cause tooth loosening and loss in severe cases. As the main effector of downstream of Hippo signaling pathway, yes-related protein 1 (YAP1) plays an important role in cell proliferation and differentiation. However, the role of YAP1 in periodontitis has not been reported.

METHODS

Cell activity was detected by Cell Counting Kit-8 (CCK-8). YAP1 was overexpressed by cell transfection, and then RT-qPCR and western blot were used to detect the expression of YAP1. The cell proliferation was determined by clone formation assay, and the expression of proliferation-related proteins was determined by western blot. The cell differentiation was detected by ELISA kit of alkaline phosphatase activity (ALP) and alizarin red staining. Finally, western blot was used to detect the expression of differentiation-related protein and Hippo signaling pathway-related proteins. Apoptosis was detected by flow cytometry.

RESULTS

With the increase of concentration induced by TNF-α, the cell survival rate of human periodontal ligament stem cells (HPDLSCs) decreased significantly. After the overexpression of YAP1, cell proliferation and proliferation-related protein expression increased. Overexpression of YAP1 can improve the differentiation and the formation of osteoblasts of HPDLSCs induced by TNF-α. The expression of Hippo signaling pathway-related proteins transcriptional coactivators with PDZ binding domains (TAZ), TEA domain family member (TRED) increased and proliferation-related protein P27 decreased, whereas there was no significant change in the expression of MST1.

CONCLUSION

TNF-α can inhibit proliferation and osteogenic differentiation of HPDLSCs, which can be ameliorated by the YAP1 gene through the Hippo signaling pathway. Our paper suggested that YAP1 may be a potential therapeutic target for periodontitis.

Curcumin promotes osteogenic differentiation of human periodontal ligament stem cells by inducting EGR1 expression

OBJECTIVE

Human periodontal ligament stem cells (hPDLSCs) attract attention for the periodontal regeneration therapy. Curcumin may promote osteogenic differentiation of hPDLSCs. This research aims to elucidate whether Curcumin displays promoting osteogenic differentiation and its mechanism.

METHODS

The hPDLSCs were isolated from human periodontal ligament by immunomagnetic beads, identified with immumofluorescence. hPDLSCs were treated with 0, 5, 10, 20, 50, 100 μmol/L Curcumin. The early growth response gene 1 (EGR1) siRNA or plasmind were tranfected into the hPDLSCs. The viability, Alkaline Phosphatase (ALP) activity and mineralizaiton level of hPDLSCs were measured with 3-(4,5)-dimethylthiahiazo(-z-y1)-3,5-di-phenytetrazoliumromide (MTT) assay, ALP Assay Kit or Alizarin Red staining. The expression of EGR1, RUNX family transcription factor 2 (Runx2), bone gamma-carboxyglutamate protein (OC), secreted phosphoprotein 1 (OPN) and collagen type I alpha 1 chain (Collagen I), in hPDLSC were determined by Western blotting and quantitative reverse transcription-polymerase chain reaction.

RESULTS

The isolated hPDLSCs were spindle or irregular, arranged in radial shape and shown positive expression of STRO-1, CD146 and Vimentin. Curcumin 10 μmol/L treatment maximal promoting the cells viability, ALP activities, mineralization, and levels of Runx2, OC, OPN, Collagen I and EGR-1 in hPDLSCs. EGR-1 siRNA transfection inversed Curcumin's promoting effect on ALP activities, mineralization, and levels of Runx2, OC, OPN, Collagen I and EGR-1 in hPDLSCs. While the EGR-1 plasmid transfection enhanced Curcumin's promoting effect on these parameters of hPDLSCs.

CONCLUSION

Curcumin promotes the osteogenic differentiation of hPDLSCs, which may work through the EGR1. Curcumin may be a promising medicine for periodontitis treatment and periodontal regeneration.

Cellular network across cementum and periodontal ligament elucidated by FIB/SEM tomography

Cementocytes in cementum form a lacuna-canalicular network. However, the 3D ultrastructure and range of the cementocyte network are unclear. Here, the 3D ultrastructure of the cementocyte network at the interface between cementum and periodontal ligament (PDL) was investigated on the mesoscale using FIB/SEM tomography. The results revealed a cellular network of cementocytes and PDL cells. A previous histomorphological study revealed the osteocyte-osteoblast-PDL cellular network. We extended this knowledge and revealed the cementum-PDL-bone cellular network, which may orchestrate the remodeling and modification of periodontal tissue, using a suitable method for imaging of complex tissue.

MEST Regulates the Stemness of Human Periodontal Ligament Stem Cells

Periodontal ligament (PDL) stem cells (PDLSCs) have been reported as a useful cell source for periodontal tissue regeneration. However, one of the issues is the difficulty of obtaining a sufficient number of PDLSCs for clinical application because very few PDLSCs can be isolated from PDL tissue of donors. Therefore, we aimed to identify a specific factor that converts human PDL cells into stem-like cells. In this study, microarray analysis comparing the gene profiles of human PDLSC lines (2-14 and 2-23) with those of a cell line with a low differentiation potential (2-52) identified the imprinted gene mesoderm-specific transcript (MEST). MEST was expressed in the cytoplasm of 2-23 cells. Knockdown of MEST by siRNA in 2-23 cells inhibited the expression of stem cell markers, such as CD105, CD146, p75NTR, N-cadherin, and NANOG; the proliferative potential; and multidifferentiation capacity for osteoblasts, adipocytes, and chondrocytes. On the other hand, overexpression of MEST in 2-52 cells enhanced the expression of stem cell markers and PDL-related markers and the multidifferentiation capacity. In addition, MEST-overexpressing 2-52 cells exhibited a change in morphology from a spindle shape to a stem cell-like round shape that was similar to 2-14 and 2-23 cell morphologies. These results suggest that MEST plays a critical role in the maintenance of stemness in PDLSCs and converts PDL cells into PDLSC-like cells. Therefore, this study indicates that MEST may be a therapeutic factor for periodontal tissue regeneration by inducing PDLSCs.

Possible function of GDNF and Schwann cells in wound healing of periodontal tissue

OBJECTIVE

The purpose of this study was to evaluate the function of Schwann cells in wound healing of periodontal tissue.

BACKGROUND

In our previous study, glial cell line-derived neurotrophic factor (GDNF) promoted the migration of human periodontal ligament (PDL) cells and that GDNF expression increased in wounded periodontal tissue. GDNF reportedly induces the migration of Schwann cell precursors. Schwann cells play a crucial role in the regeneration of peripheral tissues, including bone tissue. However, the role of Schwann cells on periodontal tissue regeneration remains unclear.

METHODS

A transwell assay and a WST-1 (water-soluble tetrazolium compound-1) proliferation assay were used to determine whether GDNF promotes the migration and proliferation of Schwann cells, respectively. Quantitative RT-PCR and Alizarin Red S staining were performed to examine the effect of these cells on the differentiation of human preosteoblast (Saos2 cells) using conditioned medium from YST-1 (YST-1-CM). Western blotting analysis was performed to determine whether YST-1-CM activates ERK signaling pathway in Saos2 cells. The expression of Schwann cell markers, S100 calcium-binding protein B (S100-B) and growth associated protein 43 (GAP-43), was determined in normal and wounded periodontal tissue by immunofluorescent staining.

RESULTS

Glial cell line-derived neurotrophic factor promoted the migration of YST-1 cells but did not affect the proliferation of YST-1 cells. Saos2 cells cultured with YST-1-CM increased the expression of osteoblastic markers and mineralization. YST-1-CM also induced phosphorylation of ERK1/2 in Saos2 cells. The number of S100-B-immunoreactive cells which also expressed GAP-43 was increased in rat wounded periodontal tissue during healing process.

CONCLUSION

The accumulation of Schwann cells in wounded periodontal tissue suggests that they play a significant role in wound healing of this tissue, especially alveolar bone tissue.

Inhibitory effect of C-X-C motif chemokine ligand 14 on the osteogenic differentiation of human periodontal ligament cells through transforming growth factor-beta1

OBJECTIVE

This study aimed to determine the expression of chemokine (C-X-C motif) ligand 14 (CXCL14) in pulpal and periodontal cells in vivo and in vitro, and investigate function of CXCL14 and its underlying mechanism in the proliferation and osteogenic differentiation of human periodontal ligament (hPDL) cells.

METHODS

To determine the expression level of CXCL14 in adult rat oral tissues and in hPDL cells after application of biophysical forces, RT-PCR, western blot, and histological analyses were performed. The role of CXCL14 in proliferation and osteogenic differentiation of PDL cells was evaluated by measuring dehydrogenase activity and Alizarin red S staining.

RESULTS

Strong immunoreactivity against CXCL14 was observed in the PDL tissues and pulpal cells of rat molar, and attenuated apparently by orthodontic biophysical forces. As seen in rat molar, highly expressed CXCL14 was observed in human dental pulp and hPDL cells, and attenuated obviously by biophysical tensile force. CXCL14 expression in hPDL cells was increased in incubation time-dependent manner. Proliferation of hPDL cells was inhibited dramatically by small interfering (si) RNA against CXCL14. Furthermore, dexamethasone-induced osteogenic mineralization was inhibited by recombinant human (rh) CXCL14, and augmented by CXCL14 siRNA. rhCXCL14 increased transforming growth factor-beta1 (TGF- β1) in hPDL cells. Inhibition of the cell proliferation and osteogenic differentiation of hPDL cells by CXCL14 siRNA and rhCXCL14 were restored by rhTGF-β1 and SB431542, respectively.

CONCLUSION

These results suggest that CXCL14 may play roles as a growth factor and a negative regulator of osteogenic differentiation by increasing TGF-β1 expression in hPDL cells.

Transcriptome analysis of ankylosed primary molars with infraocclusion

Primary molar ankylosis with infraocclusion can retard dental arch development and cause dental asymmetry. Despite its widespread prevalence, little is known about its molecular etiology and pathogenesis. To address this, RNA sequencing was used to generate transcriptomes of furcal bone from infraoccluded (n = 7) and non-infraoccluded (n = 9) primary second molars, all without succeeding biscuspids. Of the 18 529 expressed genes, 432 (2.3%) genes were differentially expressed between the two groups (false discovery rate < 0.05). Hierarchical clustering and principal component analysis showed clear separation in gene expression between infraoccluded and non-infraoccluded samples. Pathway analyses indicated that molar ankylosis is associated with the expression of genes consistent with the cellular inflammatory response and epithelial cell turnover. Independent validation using six expressed genes by immunohistochemical analysis demonstrated that the corresponding proteins are strongly expressed in the developing molar tooth germ, in particular the dental follicle and inner enamel epithelium. The descendants of these structures include the periodontal ligament, cementum, bone and epithelial rests of Malassez; tissues that are central to the ankylotic process. We therefore propose that ankylosis involves an increased inflammatory response associated with disruptions to the developmental remnants of the dental follicle and epithelial rests of Malassez.

Three-dimensional periodontal tissue regeneration using a bone-ligament complex cell sheet

Periodontal tissue is a distinctive tissue structure composed three-dimensionally of cementum, periodontal ligament (PDL) and alveolar bone. Severe periodontal diseases cause fundamental problems for oral function and general health, and conventional dental treatments are insufficient for healing to healthy periodontal tissue. Cell sheet technology has been used in many tissue regenerations, including periodontal tissue, to transplant appropriate stem/progenitor cells for tissue regeneration of a target site as a uniform tissue. However, it is still difficult to construct a three-dimensional structure of complex tissue composed of multiple types of cells, and the transplantation of a single cell sheet cannot sufficiently regenerate a large-scale tissue injury. Here, we fabricated a three-dimensional complex cell sheet composed of a bone-ligament structure by layering PDL cells and osteoblast-like cells on a temperature responsive culture dish. Following ectopic and orthotopic transplantation, only the complex cell sheet group was demonstrated to anatomically regenerate the bone-ligament structure along with the functional connection of PDL-like fibers to the tooth root and alveolar bone. This study represents successful three-dimensional tissue regeneration of a large-scale tissue injury using a bioengineered tissue designed to simulate the anatomical structure.

Long non-coding RNA FER1L4 promotes osteogenic differentiation of human periodontal ligament stromal cells via miR-874-3p and vascular endothelial growth factor A

Background

Periodontal ligament stromal cells (PDLSCs) are ideal cell sources for periodontal tissue repair and regeneration, but little is known about what determines their osteogenic capacity. Long non-coding RNAs (lncRNAs) are important regulatory molecules at both transcriptional and post-transcriptional levels. However, their roles in the osteogenic differentiation of PDLSCs are still largely unknown.

Methods

The expression of lncRNA Fer-1-like family member 4 (FER1L4) during the osteogenic differentiation of PDLSCs was detected by quantitative reverse transcription polymerase chain reaction. Overexpression or knockdown of FER1L4 was used to confirm its regulation of osteogenesis in PDLSCs. Alkaline phosphatase and Alizarin red S staining were used to detect mineral deposition. Dual luciferase reporter assays were used to analyze the binding of miR-874-3p to FER1L4 and vascular endothelial growth factor A (VEGFA). Bone regeneration in critical-sized calvarial defects was assessed in nude mice. New bone formation was analyzed by micro-CT, hematoxylin and eosin staining, Masson’s trichrome staining, and immunohistochemical analyses.

Results

FER1L4 levels increased gradually during consecutive osteogenic induction of PDLSCs. Overexpression of FER1L4 promoted the osteogenic differentiation of PDLSCs, as revealed by alkaline phosphatase activity, Alizarin red S staining, and the expression of osteogenic markers, whereas FER1L4 knockdown inhibited these processes. Subsequently, we identified a predicted binding site for miR-874-3p on FER1L4 and confirmed a direct interaction between them. Wild-type FER1L4 reporter activity was significantly inhibited by miR-874-3p, whereas mutant FER1L4 reporter was not affected. MiR-874-3p inhibited osteogenic differentiation and reversed the promotion of osteogenesis in PDLSCs by FER1L4. Moreover, miR-874-3p targeted VEGFA, a crucial gene in osteogenic differentiation, whereas FER1L4 upregulated the expression of VEGFA. In vivo, overexpression of FER1L4 led to more bone formation compared to the control group, as demonstrated by micro-CT and the histologic analyses.

Conclusion

FER1L4 positively regulates the osteogenic differentiation of PDLSCs via miR-874-3p and VEGFA. Our study provides a promising target for enhancing the osteogenic potential of PDLSCs and periodontal regeneration.

Histone Methylation Mechanisms Modulate the Inflammatory Response of Periodontal Ligament Progenitors

Inflammatory conditions affect periodontal ligament (PDL) homeostasis and diminish its regenerative capacity. The complexity of biological activities during an inflammatory response depends on genetic and epigenetic mechanisms. To characterize the epigenetic changes in response to periodontal pathogens we have focused on histone lysine methylation as a relatively stable chromatin modification involved in the epigenetic activation and repression of transcription and a prime candidate mechanism responsible for the exacerbated and prolonged response of periodontal cells and tissues to dental plaque biofilm. To determine the effect of inflammatory conditions on histone methylation profiles, related gene expression and cellular functions of human periodontal ligament (hPDL) progenitor cells, a hPDL cell culture system was subjected to bacterial cell wall toxin exposure [lipopolysaccharide (LPS)]. Chromatin immunoprecipitation-on-chip analysis revealed that healthy PDL cells featured high enrichment levels for the active H3K4me3 mark at COL1A1, COL3, and RUNX2 gene promoters, whereas there were high occupancy levels for the repressive H3K27me3 marks at DEFA4, CCL5, and IL-1β gene promoters. In response to LPS, H3K27me3 enrichment increased on extracellular matrix and osteogenesis lineage gene promoters, whereas H3K4me3 enrichment increased on the promoters of inflammatory response genes, suggestive of an involvement of epigenetic mechanisms in periodontal lineage differentiation and in the coordination of the periodontal inflammatory response. On a gene expression level, LPS treatment downregulated COL1A1, COL3A1, and RUNX2 expression and upregulated CCL5, DEFA4, and IL-1β gene expression. LPS also greatly affected PDL progenitor function, including a reduction in proliferation and differentiation potential and an increase in cell migration capacity. Confirming the role of epigenetic mechanisms in periodontal inflammatory conditions, our studies highlight the significant role of histone methylation mechanisms and modification enzymes in the inflammatory response to LPS bacterial cell wall toxins and periodontal stem cell function.

Three-dimensional ultrastructural and histomorphological analysis of the periodontal ligament with occlusal hypofunction via focused ion beam/scanning electron microscope tomography

The periodontal ligament (PDL) maintains the environment and function of the periodontium. The PDL has been remodelled in accordance with changes in mechanical loading. Three-dimensional (3D) structural data provide essential information regarding PDL function and dysfunction. However, changes in mechanical loading associated with structural changes in the PDL are poorly understood at the mesoscale. This study aimed to investigate 3D ultrastructural and histomorphometric changes in PDL cells and fibres associated with unloading condition (occlusal hypofunction), using focused ion beam/scanning electron microscope tomography, and to quantitatively analyse the structural properties of PDL cells and fibres. PDL cells formed cellular networks upon morphological changes induced via changes in mechanical loading condition. Drastic changes were observed in a horizontal array of cells, with a sparse and disorganised area of collagen bundles. Furthermore, collagen bundles tended to be thinner than those in the control group. FIB/SEM tomography enables easier acquisition of serial ultrastructural images and quantitative 3D data. This method is powerful for revealing 3D architecture in complex tissues. Our results may help elucidate architectural changes in the PDL microenvironment during changes in mechanical loading condition and regeneration, and advance a wide variety of treatments in dentistry.

Influence of chemical fixation process on primary mesenchymal stem cells evidenced by Raman spectroscopy

In investigation of (patho)physiological processes, cells represent frequently used analyte as an exceptional source of information. However, spectroscopic analysis of live cells is still very seldom in clinics, as well as in research studies. Among others, the reasons are long acquisition time during which autolysis process is activated, necessity of specified technical equipment, and inability to perform analysis in a moment of sample preparation. Hence, an optimal method of preserving cells in the existing state is of extreme importance, having in mind that selection of fixative is cell lineage dependent. In this study, two commonly used chemical fixatives, formaldehyde and methanol, are used for preserving primary mesenchymal stem cells extracted from periodontal ligament, which are valuable cell source for reconstructive dentistry. By means of Raman spectroscopy, cell samples were probed and the impact of these fixatives on their Raman response was analyzed and compared. Different chemical mechanisms are the core processes of formaldehyde and methanol fixation and certain Raman bands are shifted and/or of changed intensity when Raman spectra of cells fixed in that manner are compared. In order to get clearer picture, comprehensive statistical analysis was performed.

Probing primary mesenchymal stem cells differentiation status by micro-Raman spectroscopy

We have employed micro-Raman spectroscopy to get insight into intrinsic biomolecular profile of individual mesenchymal stem cell isolated from periodontal ligament. Furthermore, these cells were stimulated towards adipogenic, chondrogenic, and osteogenic lineages and their status of differentiation was assessed using micro-Raman spectroscopy. In both cases, glass coverslips were used as substrates, due to their wide availability and cost effectiveness. In all sample groups, the same type of behavior was observed, manifested as changes in Raman spectra: the increase of relative intensity of protein/lipid bands and decrease of nucleic acid bands. Comprehensive statistical analysis in the form of principal component analysis was performed, which revealed noticeable grouping of cells with the similar features. Despite the inhomogeneity of primary stem cells and their differentiated lineages, we demonstrated that micro-Raman spectroscopy is sufficient for distinguishing cells' status, which can be valuable for medical and clinical application.

Downregulation of miR-24-3p promotes osteogenic differentiation of human periodontal ligament stem cells by targeting SMAD family member 5

Osteogenic differentiation is a complicated process that depends on various regulatory factors and signal pathways. In our research, the osteogenic differentiation capacity was analyzed by alizarin red staining, alkaline phosphatase activity, and protein levels of osteogenic differentiation markers including runt-related transcription factor 2, bone morphogenetic protein 2, and osteocalcin (OCN). We observed a notable decrease of miR-24-3p level in osteogenic-differentiated human periodontal ligament stem cells (hPDLSCs) by microarray analysis. In our gain- and loss-of-function experiments, we discovered that miR-24-3p has a suppression effect on hPDLSCs osteogenic differentiation. Moreover, SMAD family member 5 (Smad5), the critical osteogenic differentiation transcription factors, was predicted to be targets of miR-24-3p. In addition, luciferase reporter assay further proved that miR-24-3p directly targeted the 3'-untranslated region of Smad5. Similarly, we found that the overexpression of miR-24-3p significantly decreased the Smad5 messenger RNA level in hPDLSCs, which was detected by real-time quantitative polymerase chain reaction. Then hPDLSCs were transfected with miR-24-3p mimics to inhibit Smad5 expression; meanwhile, Smad5 RNA interference could significantly reverse the osteogenic differentiation inhibition effect of miR-24-3p. In brief, a series of data showed that miR-24-3p is a regulator of Smad5, playing an important role in osteogenic differentiation.

R-spondin 2 promotes osteoblastic differentiation of immature human periodontal ligament cells through the Wnt/β-catenin signaling pathway

OBJECTIVE

In this study, we measured the expression of R-spondin 2 (RSPO2) in periodontal ligament (PDL) tissue and cells. Further, we examined the effects of RSPO2 on osteoblastic differentiation of immature human PDL cells (HPDLCs).

BACKGROUND

R-spondin (RSPO) family proteins are secreted glycoproteins that play important roles in embryonic development and tissue homeostasis through activation of the Wnt/β-catenin signaling pathway. RSPO2, a member of the RSPO family, has been reported to enhance osteogenesis in mice. However, little is known regarding the roles of RSPO2 in PDL tissues.

METHODS

Expression of RSPO2 in rat PDL tissue and primary HPDLCs was examined by immunohistochemical and immunofluorescence staining, as well as by semiquantitative RT-PCR. The effects of stretch loading on the expression of RSPO2 and Dickkopf-related protein 1 (DKK1) were assessed by quantitative RT-PCR. Expression of receptors for RSPOs, such as Leucine-rich repeat-containing G-protein-coupled receptors (LGRs) 4, 5, and 6 in immature human PDL cells (cell line 2-14, or 2-14 cells), was investigated by semiquantitative RT-PCR. Mineralized nodule formation in 2-14 cells treated with RSPO2 under osteoblastic inductive condition was examined by Alizarin Red S and von Kossa stainings. Nuclear translocation of β-catenin and expression of active β-catenin in 2-14 cells treated with RSPO2 were assessed by immunofluorescence staining and Western blotting analysis, respectively. In addition, the effect of Dickkopf-related protein 1 (DKK1), an inhibitor of Wnt/β-catenin signaling, was also examined.

RESULTS

Rat PDL tissue and HPDLCs expressed RSPO2, and HPDLCs also expressed RSPO2, while little was found in 2-14 cells. Expression of RSPO2 as well as DKK1 in HPDLCs was significantly upregulated by exposure to stretch loading. LGR4 was predominantly expressed in 2-14 cells, which expressed low levels of LGR5 and LGR6. RSPO2 enhanced the Alizarin Red S and von Kossa-positive reactions in 2-14 cells. In addition, DKK1 suppressed nuclear translocation of β-catenin, activation of β-catenin, and increases of Alizarin Red S and von Kossa-positive reactions in 2-14 cells, all of which were induced by RSPO2 treatment.

CONCLUSION

RSPO2, which is expressed in PDL tissue and cells, might play an important role in regulating the osteoblastic differentiation of immature human PDL cells through the Wnt/β-catenin signaling pathway.

Circular RNA CDR1as regulates osteoblastic differentiation of periodontal ligament stem cells via the miR-7/GDF5/SMAD and p38 MAPK signaling pathway

Background

Periodontal ligament stem cells (PDLSCs) are considered as candidate cells for the regeneration of periodontal and alveolar bone tissues. Antisense to the cerebellar degeneration-related protein 1 transcript (CDR1as), which is a newly discovered circular RNA (circRNA), has been reported to act as an miR-7 sponge and to be involved in many biological processes. Here, we investigated the potential roles of CDR1as and miR-7 in the osteogenic differentiation of PDLSCs.

Methods

The expression pattern of CDR1as and miR-7 in PDLSCs during osteogenesis was detected by quantitative reverse-transcription polymerase chain reaction (qRT-PCR). Then we overexpressed or knocked down CDR1as or miR-7 to confirm whether they were involved in the regulation of osteoblast differentiation in PDLSCs. Alkaline phosphatase (ALP) and alizarin red S (ARS) staining were used to detect the activity of osteoblasts and mineral deposition. Furthermore, a dual luciferase reporter assay was conducted to analyze the binding of miR-7 to growth differentiation factor (GDF)5. To further verify the role of CDR1as in osteoblast differentiation, we conducted animal experiments in vivo. New bone formation in specimens was analyzed by microcomputed tomography (micro-CT), hematoxylin and eosin staining, and immunofluorescence staining.

Results

We observed that CDR1as was significantly upregulated during the osteogenic differentiation, whereas miR-7 was significantly downregulated. Moreover, knockdown of CDR1as and overexpression of miR-7 inhibited the ALP activity, ARS staining, and expression of osteogenic genes. Overexpression of miR-7 significantly reduced the activity of luciferase reporter vectors containing the wild-type, but not the mutant, 3’ untranslated region (UTR) sequence of GDF5. Furthermore, knockdown of GDF5 partially reversed the effects of miR-7 inhibitor on osteoblast differentiation. Downregulation of CDR1as or GDF5 subsequently inhibited phosphorylation of Smad1/5/8 and p38 mitogen-activated protein kinases (MAPK), while upregulation of miR-7 decreased the level of phosphorylated Smad1/5/8 and p38 MAPK. In vivo, CDR1as knockdown lead to less bone formation compared with the control group as revealed by micro-CT and the histological analysis.

Conclusions

Our results demonstrated that CDR1as acts as a miR-7 inhibitor, triggering the upregulation of GDF5 and subsequent Smad1/5/8 and p38 MAPK phosphorylation to promote osteogenic differentiation of PDLSCs. This study provides a novel understanding of the mechanisms of osteogenic differentiation, and suggests a potential method for promoting bone formation.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-0976-0) contains supplementary material, which is available to authorized users.

Periodontal wound healing following reciprocal autologous root transplantation in class III furcation defects

Purpose

Furcation involvement in the molars is difficult to treat, and has been recognized as a risk factor for tooth loss. Although periodontal regenerative therapies, including guided tissue regeneration and various types of bone grafts, have been applied to furcation defects, the effects of these treatments are limited, especially in large class III furcation defects. The purpose of this pilot study was to investigate the effect of reciprocal autologous root transplantation on periodontal wound healing and regeneration in class III furcation defects in dogs.

Methods

Furcation defects (7 mm wide and 6 mm high) were surgically created after root separation of the unilateral third and fourth premolars in 4 dogs. Eight furcation defects were randomized to receive either reciprocal autologous root transplantation (test) or no further treatment (control). In the test group, the mesial and distal roots were transplanted into the distal and mesial extraction sockets, respectively. The animals were sacrificed 10 weeks after surgery for histologic evaluation.

Results

The healing pattern in the control group was characterized by extensive collapse of the flap and limited periodontal regeneration. New bone formation in the test group (3.56±0.57 mm) was significantly greater than in the control group (0.62±0.21 mm). Dense collagen fibers inserting into the residual cementum on the transplanted root surfaces were observed in the test group. Slight ankylosis was observed in 2 of the 4 specimens in the test group on the mesiodistal sides where the root-planed surfaces faced the existing bone. Root resorption (RR) was detected in both the control and test groups.

Conclusions

Within the limits of this study, it can be concluded that reciprocal autologous root transplantation was effective for bone regeneration in class III furcation defects in dogs. However, further studies are required to standardize the approach in order to prevent unwanted RR prior to clinical application.

Static magnetic fields promote osteoblastic/cementoblastic differentiation in osteoblasts, cementoblasts, and periodontal ligament cells

Purpose

Although static magnetic fields (SMFs) have been used in dental prostheses and osseointegrated implants, their biological effects on osteoblastic and cementoblastic differentiation in cells involved in periodontal regeneration remain unknown. This study was undertaken to investigate the effects of SMFs (15 mT) on the osteoblastic and cementoblastic differentiation of human osteoblasts, periodontal ligament cells (PDLCs), and cementoblasts, and to explore the possible mechanisms underlying these effects.

Methods

Differentiation was evaluated by measuring alkaline phosphatase (ALP) activity, mineralized nodule formation based on Alizarin red staining, calcium content, and the expression of marker mRNAs assessed by reverse transcription polymerase chain reaction (RT-PCR). Signaling pathways were analyzed by western blotting and immunocytochemistry.

Results

The activities of the early marker ALP and the late markers matrix mineralization and calcium content, as well as osteoblast- and cementoblast-specific gene expression in osteoblasts, PDLCs, and cementoblasts were enhanced. SMFs upregulated the expression of Wnt proteins, and increased the phosphorylation of glycogen synthase kinase-3β (GSK-3β) and total β-catenin protein expression. Furthermore, p38 and c-Jun N-terminal kinase (JNK) mitogen-activated protein kinase (MAPK), and nuclear factor-κB (NF-κB) pathways were activated.

Conclusions

SMF treatment enhanced osteoblastic and/or cementoblastic differentiation in osteoblasts, cementoblasts, and PDLCs. These findings provide a molecular basis for the beneficial osteogenic and/or cementogenic effect of SMFs, which could have potential in stimulating bone or cementum formation during bone regeneration and in patients with periodontal disease.

Response of porcine epithelial rests of Malassez to stimulation by interleukin-6

AIM

To investigate the proliferation and migration of epithelial cell rests of Malassez (ERM) after stimulation with IL-6.

METHODOLOGY

Porcine-derived ERM were seeded on Dulbecco's modified Eagle's Medium, and IL-6 (100 pg mL^-1 ) was incorporated into the culture medium. The WST-1 assay was performed to evaluate cell proliferation, and absorption was measured at 450 nm. A wound-healing assay and immunofluorescence assay for integrin α₃ were conducted to investigate migration. The Kruskal-Wallis test and the Mann-Whitney U-test with Bonferroni correction were used to analyse data of WST-1 and wound-healing assays.

RESULTS

Cell proliferation following the stimulation by IL-6 increased over time, with a significant increase being observed at 6 h (P < 0.05), but not in a concentration-dependent manner. Cell proliferation was significantly greater in IL-6-treated ERM than in nontreated ERM (P < 0.05). The results of the wound-healing assay revealed earlier closure in IL-6-treated ERM (P < 0.05). In the immunofluorescence assay, integrin α₃ was detected at the edge of cell processes adjacent to the wound area. A neutralized antibody abrogated the effects of the IL-6 stimulation in cell proliferation and migration.

CONCLUSION

IL-6 promoted the proliferation and migration of porcine ERM in vitro.

Wnt5a suppresses osteoblastic differentiation of human periodontal ligament stem cell-like cells via Ror2/JNK signaling

Wnt5a, a non-canonical Wnt protein, is known to play important roles in several cell functions. However, little is known about the effects of Wnt5a on osteoblastic differentiation of periodontal ligament (PDL) cells. Here, we examined the effects of Wnt5a on osteoblastic differentiation and associated intracellular signaling in human PDL stem/progenitor cells (HPDLSCs). We found that Wnt5a suppressed expression of bone-related genes (ALP, BSP, and Osterix) and alizarin red-positive mineralized nodule formation in HPDLSCs under osteogenic conditions. Immunohistochemical analysis revealed that a Wnt5a-related receptor, receptor tyrosine kinase-like orphan receptor 2 (Ror2), was expressed in rat PDL tissue. Interestingly, knockdown of Ror2 by siRNA inhibited the Wnt5a-induced downregulation of bone-related gene expression in HPDLSCs. Moreover, Western blotting analysis showed that phosphorylation of the intracellular signaling molecule, c-Jun N-terminal kinase (JNK) was upregulated in HPDLSCs cultured in osteoblast induction medium with Wnt5a, but knockdown of Ror2 by siRNA downregulated the phosphorylation of JNK. We also examined the effects of JNK inhibition on Wnt5a-induced suppression of osteoblastic differentiation of HPDLSCs. The JNK inhibitor, SP600125 inhibited the Wnt5a-induced downregulation of bone-related gene expression in HPDLSCs. Additionally, SP600125 inhibited the Wnt5a-induced suppression of the alizarin red-positive reaction in HPDLSCs. These results suggest that Wnt5a suppressed osteoblastic differentiation of HPDLSCs through Ror2/JNK signaling. Non-canonical Wnt signaling, including Wnt5a/Ror2/JNK signaling, may function as a negative regulator of mineralization, preventing the development of non-physiological mineralization in PDL tissue.