4-META/MMA-TBB resin containing nano hydroxyapatite induces the healing of periodontal tissue repair in perforations at the pulp chamber floor.

We aimed to evaluate the materials based on 4-methacryloxyethyl trimellitate anhydride/methyl methacrylate tri-n-butylborane (Super-bond [SB]) and nano hydroxyapatite (naHAp) for the repair of perforation at pulp chamber floor (PPF) in vitro and in vivo models. SB and naHAp were mixed in the mass ratio of 10% or 30% to produce naHAp/SB. Human periodontal ligament stem cells (HPDLSCs) were cultured on resin discs of SB or naHAp/SB to analyze the effects of naHAp/SB on cell adhesion, proliferation, and cementoblastic differentiation. A rat PPF model was treated with SB or naHAp/SB to examine the effects of naHAp/SB on the healing of defected cementum and periodontal ligament (PDL) at the site of PPF. HPDLSCs were spindle-shaped and adhered to all resin discs. Changing the resin from SB to naHAp/SB did not significantly alter cell proliferation. Both 10% and 30% naHAp/SB were more effective than SB in promoting cementoblastic differentiation of HPDLSCs. In the rat PPF model, 30% naHAp/SB was more effective than SB in promoting the formation Sharpey's fiber-like structures with expression of the PDL-related marker and cementum-like structures with expression of cementum-related markers. In conclusion, 30% naHAp/SB can be the new restorative material for PPF because it exhibited the abilities of adhering to dentin and healing of defected periodontal tissue.

Effect of Fibrillin-2 on Differentiation into Periodontal Ligament Stem Cell-Like Cells Derived from Human-Induced Pluripotent Stem Cells.

Periodontal tissue regeneration is important for preserving teeth. Periodontal ligament stem cells (PDLSCs) are useful in periodontal tissue regeneration; however, tooth extraction is required to obtain these cells. Therefore, we focused on induced pluripotent stem (iPS) cells and established a method to obtain PDLSC-like cells from iPS cells. Specifically, we first differentiated iPS cells into neural crest-like cells (iNCs). Next, we obtained PDLSC-like cells (iPDLSCs) by culturing iNCs on extracellular matrix (ECM) derived from human primary periodontal ligament cells (HPDLCs). This differentiation method suggested that ECM derived from HPDLCs is important for iPDLSC differentiation. Thus, we aimed to identify the PDLSC-inducing factor present in HPDLC-derived ECM in this study. We first performed comprehensive analyses of HPDLC genes and identified fibrillin-2 (FBN2), an ECM-related factor. Furthermore, to clarify the effect of FBN2 on iPDLSC differentiation, we cultured iNCs using ECM derived from HPDLCs with FBN2 knocked down. As a result, expression of PDL-related markers was reduced in iNCs cultured on ECM derived from HPDLCs transfected with FBN2 siRNA (iNC-siFBN2) compared with iPDLSCs. Furthermore, the expression of CD105 (a mesenchymal stem cell marker), proliferation ability, and multipotency of iNC-siFBN2 were lower compared with iPDLSCs. Next, we cultured iNCs on FBN2 recombinant protein; however, expression of PDL-related markers did not increase compared with iPDLSC. The present results suggest the critical involvement of FBN2 in inducing iPDLSCs from iNCs when in fact it does not promote iPDLSC differantiation. Therefore, we need to elucidate the entire HPDLC-ECMs, responsible for iPDLSCs induction.

Dopamine is involved in reparative dentin formation through odontoblastic differentiation of dental pulp stem cells.

Conventional direct pulp-capping materials induce pulp cells to secrete various biomolecules in pulp tissues that promote reparative dentin formation through induction of odontoblastic differentiation of dental pulp stem cells (DPSCs). However, these biomolecules sometimes induce bone-like dentin with poor sealing properties. Therefore, exploration of biomolecules that allow tight sealing by tubular reparative dentin is required. We recently reported that dopamine (DA) is involved in dentinogenesis. Hence, we investigated the effect of DA on odontoblastic differentiation of DPSCs and reparative dentin formation. Both tyrosine hydroxylase (TH), a DA synthetase, and DA were expressed in odontoblast-like cells in vivo. In vitro, their expression was increased during odontoblastic differentiation of DPSCs. Furthermore, TH-overexpressing DPSCs had promoted odontoblastic differentiation and DA production. Moreover, DA stimulation promoted their differentiation and induced tubular reparative dentin. These results suggest that DA produced by TH is involved in odontoblastic differentiation of DPSCs and has an inductive capacity for reparative dentin formation similar to primary dentin. This study may lead to the development of therapy to preserve vital pulp tissues.

Decorin Promotes Osteoblastic Differentiation of Human Periodontal Ligament Stem Cells.

The aim of this study is to clarify the biological functions of decorin (DCN) in the healing and regeneration of wounded periodontal tissue. We investigated the expression pattern of DCN during the healing of wounded periodontal tissue in rats by immunohistochemistry and the effects of DCN on the osteoblastic differentiation of human periodontal ligament (PDL) stem cells (HPDLSCs) and preosteoblasts by Alizarin red S staining, quantitative reverse transcription-polymerase chain reactions, and western blotting. The expression of DCN was increased around the wounded PDL tissue on day 5 after surgery compared with the nonwounded PDL tissue, whereas its expression was not changed in the osteoblastic layer around the wounded alveolar bone. Furthermore, DCN promoted the osteoblastic differentiation of HPDLSCs, but it did not affect the osteoblastic differentiation of preosteoblasts. ERK1/2 phosphorylation was upregulated during the DCN-induced osteoblastic differentiation of HPDLSCs. DCN did not affect proliferation, migration, or the PDL-related gene expression of HPDLSCs. In conclusion, this study demonstrates that DCN has a role in the healing of wounded periodontal tissue. Furthermore, DCN secreted from PDL cells may contribute to bone healing by upregulating osteoblastic differentiation through ERK1/2 signaling in HPDLSCs, indicating a therapeutic effect of DCN in periodontal tissue regeneration.

Involvement of M1/M2 Macrophage Polarization in Reparative Dentin Formation.

In cases in which dental pulp tissue is accidentally exposed, direct pulp capping is often performed to induce reparative dentin formation. Although macrophages are essential for the inflammatory response and tissue repair, the emergence pattern and the role of macrophages in dental pulp tissue have not been clarified. Here, we investigated the emergence of M1/M2 macrophages in dental pulp tissue after a direct pulp capping and the effects of M2 macrophages on odontoblastic differentiation of the dental pulp stem cell (DPSC) clones. The emergence of macrophages in dental pulp tissue was investigated using a rat direct pulp capping model. Alizarin Red S staining and quantitative RT-PCR was performed to examine the effect of M2 macrophages on the mineralization and odontoblastic differentiation of DPSC clones. Immunohistochemical staining revealed that M1 macrophages were detected in dental pulp tissue after treatment and increased in number at three days after treatment. However, M2 macrophages gradually increased in number in dental pulp tissue after treatment, with the highest level recorded at seven days post-operation. Additionally, conditioned medium from M2 macrophages induced odontoblast-like differentiation of DPSC clones. These results suggest that macrophages play a role in the inflammatory response and reparative dentin formation after dental pulp exposure.

Inhibition of c-Jun N-terminal kinase signaling promotes osteoblastic differentiation of periodontal ligament stem cells and induces regeneration of periodontal tissues.

OBJECTIVES: Few clinical treatments to regenerate periodontal tissue lost due to severe endodontic and periodontal disease have yet been developed. Therefore, the development of new treatment methods for the regeneration of periodontal tissue is expected. The purpose of this study was to investigate the effects of a c-Jun N-terminal kinase (JNK) inhibitor, SP600125, on the osteoblastic differentiation of periodontal ligament stem cells (PDLSCs) in vitro, and the function of SP600125 on the regeneration of alveolar bone in vivo. DESIGN: Alizarin red S staining, quantitative RT-PCR, and western blotting analysis was performed to determine whether SP600125 affects osteoblastic differentiation of human PDLSCs (HPDLSCs) and bone-related intracellular signaling. The effect of SP600125 on the regeneration of alveolar bone was assessed by using a rat periodontal defect model. The healing of periodontal defects was evaluated using micro-CT scans and histological analysis. RESULTS: SP600125 promoted the osteoblastic differentiation such as Alizarin red S-positive mineralized nodule formation and the expression of osteoblast-related genes in HPDLSCs under osteogenic conditions. In addition, this inhibitor upregulated the BMP2 expression and the phosphorylation of Smad1/5/8 in HPDLSCs under the same conditions. The inhibition of Smad1/5/8 signaling by LDN193189 suppressed the SP600125-induced osteoblastic differentiation of HPDLSCs. Furthermore, the application of SP600125 promoted the regeneration of not only alveolar bone but also PDL tissue in periodontal defects. CONCLUSION: This study suggested that inhibition of JNK signaling promotes the osteoblastic differentiation of HPDLSCs through BMP2-Smad1/5/8 signaling, leading to the regeneration of periodontal tissues such as alveolar bone and PDL tissue.

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

Activin A, a member of transforming growth factor-ß 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.

Mineral trioxide aggregate immersed in sodium hypochlorite reduce the osteoblastic differentiation of human periodontal ligament stem cells.

White mineral trioxide aggregate (WMTA) is a root canal treatment material, which is known to exhibit a dark brown color when in contact with sodium hypochlorite solution (NaOCl). This study aimed to investigate the effects of NaOCl on the surface properties of WMTA discs and WMTA-induced osteoblastic differentiation of periodontal ligament stem cells (PDLSCs). Mixed WMTA (ProRoot MTA) was filled into the molds to form WMTA discs. These discs were immersed in distilled water (D-WMTA) or 5% NaOCl (Na-WMTA). Their surface structures and Ca2+ release level was investigated. Moreover, they were cultured with a clonal human PDLSC line (line 1-17 cells). The main crystal structures of Na-WMTA were identical to the structures of D-WMTA. Globular aggregates with polygonal and needle-like crystals were found on D-WMTA and Na-WMTA, which included Ca, Si, Al, C and O. However, many amorphous structures were also identified on Na-WMTA. These structures consisted of Na and Cl, but did not include Ca. NaOCl immersion also reduced Ca2+ release level from whole WMTA discs. Line 1-17 cells cultured with D-WMTA formed many mineralized nodules and exhibited high expression levels of osteoblast-related genes. However, cells incubated with Na-WMTA generated a small number of nodules and showed low expression levels of osteoblast-related genes. These results indicated that NaOCl reduced Ca2+ release from WMTA by generating amorphous structures and changing its elemental distribution. NaOCl may also partially abolish the ability of WMTA to stimulate osteoblastic differentiation of PDLSCs.

Development of a novel direct dental pulp-capping material using 4-META/MMA-TBB resin with nano hydroxyapatite.

In the case of dental pulp exposure, direct pulp capping is often performed to preserve vital dental pulp tissue. Numerous studies regarding the development of direct pulp-capping materials have been conducted, but materials with an appropriate sealing ability, which induce dense reparative dentin formation, have not been developed. Although nano hydroxyapatite (naHAp) is a bone-filling material with bioactivity and biocompatibility, the inductive effects of naHAp on reparative dentin formation remain unclear. In the present study, the effects of dental adhesive material 4-methacryloxyethyl trimellitate anhydride/methyl methacrylate tri-n-butylborane [4-META/MMA-TBB or Super-bond (SB)], which included 10%, 30%, and 50% naHAp (naHAp/SB) on odontoblastic differentiation of dental pulp stem cells (DPSCs) and reparative dentin formation were investigated. Scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer analysis were performed to verify the existence of naHAp particles on the surface of naHAp/SB discs. The tensile adhesive strength of naHAp/SB was measured using a universal testing machine. As a result, 10% naHAp/SB and 30% naHAp/SB showed almost the same tensile adhesive strength as SB but 50% naHAp/SB showed significantly lower than the other experimental group. WST-1 proliferation assay and SEM analysis revealed that naHAp/SB did not affect the proliferation of DPSCs. Calcium release assay, quantitative RT-PCR, and western blotting analysis demonstrated that naHAp/SB did not release calcium ion but 30% naHAp/SB increased the expression of calcium-sensing receptor (CaSR) in DPSCs. Additionally, quantitative RT-PCR, western blotting analysis, Alizarin Red S- and von Kossa staining revealed that 30% naHAp/SB induced odontoblastic differentiation of DPSCs, which was inhibited by a MEK/ERK inhibitor and CaSR antagonist. Furthermore, 30% naHAp/SB promoted dense reparative dentin formation in an experimentally-formed rat dental pulp exposure model. These findings suggest that 30% naHAp/SB can be used as an ideal direct pulp capping material.

Secreted Frizzled-Related Protein 1 Promotes Odontoblastic Differentiation and Reparative Dentin Formation in Dental Pulp Cells.

Direct pulp capping is an effective treatment for preserving dental pulp against carious or traumatic pulp exposure via the formation of protective reparative dentin by odontoblast-like cells. Reparative dentin formation can be stimulated by several signaling molecules; therefore, we investigated the effects of secreted frizzled-related protein (SFRP) 1 that was reported to be strongly expressed in odontoblasts of newborn molar tooth germs on odontoblastic differentiation and reparative dentin formation. In developing rat incisors, cells in the dental pulp, cervical loop, and inner enamel epithelium, as well as ameloblasts and preodontoblasts, weakly expressed Sfrp1; however, Sfrp1 was strongly expressed in mature odontoblasts. Human dental pulp cells (hDPCs) showed stronger expression of SFRP1 compared with periodontal ligament cells and gingival cells. SFRP1 knockdown in hDPCs abolished calcium chloride-induced mineralized nodule formation and odontoblast-related gene expression and decreased BMP-2 gene expression. Conversely, SFRP1 stimulation enhanced nodule formation and expression of BMP-2. Direct pulp capping treatment with SFRP1 induced the formation of a considerable amount of reparative dentin that has a structure similar to primary dentin. Our results indicate that SFRP1 is crucial for dentinogenesis and is important in promoting reparative dentin formation in response to injury.

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.

Expression and function of dopamine in odontoblasts.

Dopamine (DA) is produced from tyrosine by tyrosine hydroxylase (TH). A recent study has reported that DA promotes the mineralization of murine preosteoblasts. However, the role of DA in odontoblasts has not been examined. Therefore, in this investigation, we researched the expression of TH and DA in odontoblasts and the effects of DA on the differentiation of preodontoblasts (KN-3 cells). Immunostaining showed that TH and DA were intensely expressed in odontoblasts and preodontoblasts of rat incisors and molars. KN-3 cells expressed D1-like and D2-like receptors for DA. Furthermore, DA promoted odontoblastic differentiation of KN-3 cells, whereas an antagonist of D1-like receptors and a PKA signaling blocker, inhibited such differentiation. However, antagonists of D2-like receptors promoted differentiation. These results suggested that DA in preodontoblasts and odontoblasts might promote odontoblastic differentiation through D1-like receptors, but not D2-like receptors, and PKA signaling in an autocrine or paracrine manner and plays roles in dentinogenesis.