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.

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.

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.

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.

Functions of beta2-adrenergic receptor in human periodontal ligament cells.

Adrenergic receptors (ARs) are receptors of noradrenalin and adrenalin, of which there are nine different subtypes. In particular, ß2 adrenergic receptor (ß2-AR) is known to be related to the restoration and maintenance of homeostasis in bone and cardiac tissues; however, the functional role of signaling through ß2-AR in periodontal ligament (PDL) tissue has not been fully examined. In this report, we investigated that ß2-AR expression in PDL tissues and their features in PDL cells. ß2-AR expressed in rat PDL tissues and human PDL cells (HPDLCs) derived from two different patients (HPDLCs-2G and -3S). Rat PDL tissue with occlusal loading showed high ß2-AR expression, while its expression was downregulated in that without loading. In HPDLCs, ß2-AR expression was increased exposed to stretch loading. The gene expression of PDL-related molecules was investigated in PDL clone cells (2-23 cells) overexpressing ß2-AR. Their gene expression and intracellular cyclic adenosine monophosphate (cAMP) levels were also investigated in HPDLCs treated with a specific ß2-AR agonist, fenoterol (FEN). Overexpression of ß2-AR significantly promoted the gene expression of PDL-related molecules in 2 to 23 cells. FEN led to an upregulation in the expression of PDL-related molecules and increased intracellular cAMP levels in HPDLCs. In both HPDLCs, inhibition of cAMP signaling by using protein kinase A inhibitor suppressed the FEN-induced gene expression of α-smooth muscle actin. Our findings suggest that the occlusal force is important for ß2-AR expression in PDL tissue and ß2-AR is involved in fibroblastic differentiation and collagen synthesis of PDL cells. The signaling through ß2-AR might be important for restoration and homeostasis of PDL tissue.

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.

R-spondin 2 promotes osteoblastic differentiation of immature human periodontal ligament cells through the Wnt/ß-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/ß-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 ß-catenin and expression of active ß-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/ß-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 ß-catenin, activation of ß-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/ß-catenin signaling pathway.

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.

Senescence and odontoblastic differentiation of dental pulp cells.

Cellular senescence has been suggested to be involved in physiological changes of cytokine production. Previous studies showed that the concentration of tumor necrosis factor-α (TNF-α) is higher in the blood of aged people compared with that of young people. So far, the precise effects of TNF-α on the odontoblastic differentiation of pulp cells have been controversial. Therefore, we aimed to clarify how this cytokine affected pulp cells during aging. Human dental pulp cells (HDPCs) were cultured until reaching the plateau of their growth, and the cells were isolated at actively (young HDPCs; yHDPCs) or inactively (senescent HDPCs; sHDPCs) proliferating stages. sHDPCs expressed senescence-related molecules while yHDPCs did not. When these HDPCs were cultured in an odontoblast-inductive medium, both young and senescent cells showed mineralization, but mineralization in sHDPCs was lower compared with yHDPCs. However, the administration of TNF-α to this culture medium altered these responses: yHDPCs showed downregulated mineralization, while sHDPCs exhibited significantly increased mineralization. Furthermore, the expression of tumor necrosis factor receptor 1 (TNFR1), a receptor of TNF-α, was significantly upregulated in sHDPCs compared with yHDPCs. Downregulation of TNFR1 expression led to decreased mineralization of TNF-α-treated sHDPCs, whereas restored the reduction in TNF-α-treated yHDPCs. These results suggested that sHDPCs preserved the odontoblastic differentiation capacity and TNF-α promoted odontoblastic differentiation of HDPCs with the progress of their population doublings through increased expression of TNFR1. Thus, TNF-α might exert a different effect on the odontoblastic differentiation of HDPCs depending on their proliferating activity. In addition, the calcification of pulp chamber with age may be related with increased reactivity of pulp cells to TNF-α.

GDNF From Human Periodontal Ligament Cells Treated With Pro-Inflammatory Cytokines Promotes Neurocytic Differentiation of PC12 Cells.

Glial cell line-derived neurotrophic factor (GDNF) is known to mediate multiple biological activities such as promotion of cell motility and proliferation, and morphogenesis. However, little is known about its effects on periodontal ligament (PDL) cells. Recently, we reported that GDNF expression is increased in wounded rat PDL tissue and human PDL cells (HPDLCs) treated with pro-inflammatory cytokines. Here, we investigated the associated expression of GDNF and the pro-inflammatory cytokine interleukin-1 beta (IL-1ß) in wounded PDL tissue, and whether HPDLCs secrete GDNF which affects neurocytic differentiation. Rat PDL cells near the wounded area showed intense immunoreactions against an anti-GDNF antibody, where immunoreactivity was also increased against an anti-IL-1ß antibody. Compared with untreated cells, HPDLCs treated with IL-1ß or tumor necrosis factor-alpha showed an increase in the secretion of GDNF protein. Conditioned medium of IL-1ß-treated HPDLCs (IL-1ß-CM) increased neurite outgrowth of PC12 rat adrenal pheochromocytoma cells. The expression levels of two neural regeneration-associated genes, growth-associated protein-43 (Gap-43), and small proline-rich repeat protein 1A (Sprr1A), were also upregulated in IL-1ß-CM-treated PC12 cells. These stimulatory effects of IL-1ß-CM were significantly inhibited by a neutralizing antibody against GDNF. In addition, U0126, a MEK inhibitor, inhibited GDNF-induced neurite outgrowth of PC12 cells. These findings suggest that an increase of GDNF in wounded PDL tissue might play an important role in neural regeneration probably via the MEK/ERK signaling pathway. J. Cell. Biochem. 118: 699-708, 2017. © 2016 Wiley Periodicals, Inc.

Effect of CTGF/CCN2 on osteo/cementoblastic and fibroblastic differentiation of a human periodontal ligament stem/progenitor cell line.

Appropriate mechanical loading during occlusion and mastication play an important role in maintaining the homeostasis of periodontal ligament (PDL) tissue. Connective tissue growth factor (CTGF/CCN2), a matricellular protein, is known to upregulate extracellular matrix production, including collagen in PDL tissue. However, the underlying mechanisms of CTGF/CCN2 in regulation of PDL tissue integrity remain unclear. In this study, we investigated the effect of CTGF/CCN2 on osteo/cementoblastic and fibroblastic differentiation of human PDL stem cells using the cell line 1-11. CTGF/CCN2 expression in rat PDL tissue and human PDL cells (HPDLCs) was confirmed immunohisto/cytochemically. Mechanical loading was found to increase gene expression and secretion of CTGF/CCN2 in HPDLCs. CTGF/CCN2 upregulated the proliferation and migration of 1-11 cells. Furthermore, increased bone/cementum-related gene expression in this cell line led to mineralization. In addition, combined treatment of 1-11 cells with CTGF/CCN2 and transforming growth factor-ß1 (TGF-ß1) significantly promoted type I collagen and fibronectin expression compared with that of TGF-ß1 treatment alone. Thus, these data suggest the underlying biphasic effects of CTGF/CCN2 in 1-11 cells, inducible osteo/cementoblastic, and fibroblastic differentiation dependent on the environmental condition. CTGF/CCN2 may contribute to preservation of the structural integrity of PDL tissue, implying its potential use as a therapeutic agent for PDL regeneration.

Wnt5a Induces Collagen Production by Human Periodontal Ligament Cells Through TGFß1-Mediated Upregulation of Periostin Expression.

Wnt5a, a member of the noncanonical Wnt proteins, is known to play important roles in the development of various organs and in postnatal cell functions. However, little is known about the effects of Wnt5a on human periodontal ligament (PDL) cells. In this study, we examined the localization and potential function of Wnt5a in PDL tissue. Immunohistochemical analysis revealed that Wnt5a was expressed predominantly in rat PDL tissue. Semi-quantitative reverse-transcription polymerase chain reaction and Western blotting analysis demonstrated that human PDL cells (HPDLCs) expressed Wnt5a and its receptors (Ror2, Fzd2, Fzd4, and Fzd5). Removal of occlusal pressure by extraction of opposing teeth decreased Wnt5a expression in rat PDL tissue, and the expression of Wnt5a and its receptors in HPDLCs was upregulated by exposure to mechanical stress. Stimulation with Wnt5a significantly enhanced the proliferation and migration of HPDLCs. Furthermore, Wnt5a suppressed osteoblastic differentiation of HPDLCs cultivated in osteogenic induction medium, while it significantly enhanced the expression of PDL-related genes, such as periostin, type-I collagen, and fibrillin-1 genes, and the production of collagen in HPDLCs cultivated in normal medium. Both knockdown of periostin gene expression by siRNA and inhibition of TGFß1 function by neutralizing antibody suppressed the Wnt5a-induced PDL-related gene expression and collagen production in HPDLCs. Interestingly, in HPDLCs cultured with Wnt5a, TGFß1 neutralizing antibody significantly suppressed periostin expression, while periostin siRNA had no effect on TGFß1 expression. These results suggest that Wnt5a expressed in PDL tissue plays specific roles in inducing collagen production by PDL cells through TGFß1-mediated upregulation of periostin expression.

The roles of calcium-sensing receptor and calcium channel in osteogenic differentiation of undifferentiated periodontal ligament cells.

Elevated extracellular calcium has been shown to promote the differentiation of osteoblasts. However, the way that calcium affects the osteogenic differentiation of human periodontal ligament stem/progenitor cells (PDLSCs) remains unclear. Our aim has been to investigate the proliferation and osteogenic differentiation of a calcium-exposed human PDLSC line (cell line 1-17) that we have recently established and to elucidate the roles of the calcium-sensing receptor (CaSR) and L-type voltage-dependent calcium channel (L-VDCC) in this process. Proliferation activity was investigated by WST-1 assay, and gene and protein expression was examined by quantitative reverse transcriptase plus the polymerase chain reaction and immunostaining, respectively. Calcification assay was performed by von Kossa and Alizarin red staining. Treatment with 5 mM CaCl2 significantly induced proliferation, bone-related gene expression, and calcification in cell line 1-17. During culture with 5 mM CaCl2, this cell line up-regulated the gene expression of CaSR, which was reduced after 7 days. Simultaneous treatment with NPS2143, a CaSR inhibitor, and calcium significantly further increased bone-related gene expression and calcification as compared with CaCl2 exposure alone. The L-VDCC inhibitor, nifedipine, significantly suppressed osteogenic differentiation of cell line 1-17 treated with 5 mM CaCl2 and promoted the expression of CaSR, as compared with calcium treatment alone. Thus, elevated extracellular calcium promotes the proliferation and osteogenic differentiation of a PDLSC line. Antagonizing CaSR further enhances the effect of calcium on osteogenic differentiation, with CaSR expression being regulated by L-VDCC under extracellular calcium. Extracellular calcium might therefore modulate the osteogenic differentiation of PDLSCs through reciprocal adjustments of CaSR and L-VDCC.

Expression and effects of epidermal growth factor on human periodontal ligament cells.

Repair of damaged periodontal ligament (PDL) tissue is an essential challenge in tooth preservation. Various researchers have attempted to develop efficient therapies for healing and regenerating PDL tissue based on tissue engineering methods focused on targeting signaling molecules in PDL stem cells and other mesenchymal stem cells. In this context, we investigated the expression of epidermal growth factor (EGF) in normal and surgically wounded PDL tissues and its effect on chemotaxis and expression of osteoinductive and angiogenic factors in human PDL cells (HPDLCs). EGF as well as EGF receptor (EGFR) expression was observed in HPDLCs and entire PDL tissue. In a PDL tissue-injured model of rat, EGF and IL-1ß were found to be upregulated in a perilesional pattern. Interleukin-1ß induced EGF expression in HPDLCs but not EGFR. It also increased transforming growth factor-α (TGF-α) and heparin-binding EGF-like growth factor (HB-EGF) expression. Transwell assays demonstrated the chemotactic activity of EGF on HPDLCs. In addition, EGF treatment significantly induced secretion of bone morphogenetic protein 2 and vascular endothelial growth factor, and gene expression of interleukin-8 (IL-8), and early growth response-1 and -2 (EGR-1/2). Human umbilical vein endothelial cells developed well-formed tube networks when cultured with the supernatant of EGF-treated HPDLCs. These results indicated that EGF upregulated under inflammatory conditions plays roles in the repair of wounded PDL tissue, suggesting its function as a prospective agent to allow the healing and regeneration of this 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.

Exposure to transforming growth factor-ß1 after basic fibroblast growth factor promotes the fibroblastic differentiation of human periodontal ligament stem/progenitor cell lines.

Basic fibroblast growth factor (bFGF) is a cytokine that promotes the regeneration of the periodontium, the specialized tissues supporting the teeth. bFGF, does not, however, induce the synthesis of smooth muscle actin alpha 2 (ACTA2), type I collagen (COL1), or COL3, which are principal molecules in periodontal ligament (PDL) tissue, a component of the periodontium. We have suggested the feasibility of using transforming growth factor-ß1 (TGFß1) to induce fibroblastic differentiation of PDL stem/progenitor cells (PDLSCs). Here, we investigated the effect of the subsequent application of TGFß1 after bFGF (bFGF/TGFß1) on the differentiation of PDLSCs into fibroblastic cells. We first confirmed the expression of bFGF and TGFß1 in rat PDL tissue and primary human PDL cells. Receptors for both bFGF and TGFß1 were expressed in the human PDLSC lines 1-11 and 1-17. Exposure to bFGF for 2 days promoted vascular endothelial growth factor gene and protein expression in both cell lines and down-regulated the expression of ACTA2, COL1, and COL3 mRNA in both cell lines and the gene fibrillin 1 (FBN1) in cell line 1-11 alone. Furthermore, bFGF stimulated cell proliferation of these cell lines and significantly increased the number of cells in phase G2/M in the cell lines. Exposure to TGFß1 for 2 days induced gene expression of ACTA2 and COL1 in both cell lines and FBN1 in cell line 1-11 alone. BFGF/TGFß1 treatment significantly up-regulated ACTA2, COL1, and FBN1 expression as compared with the group treated with bFGF alone or the untreated control. This method might thus be useful for accelerating the generation and regeneration of functional periodontium.

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.

Hyaluronic Acid Induction Promotes the Differentiation of Human Neural Crest-like Cells into Periodontal Ligament Stem-like Cells.

Periodontal ligament (PDL) stem-like cells (PDLSCs) are promising for regeneration of the periodontium because they demonstrate multipotency, high proliferative capacity, and the potential to regenerate bone, cementum, and PDL tissue. However, the transplantation of autologous PDLSCs is restricted by limited availability. Since PDLSCs are derived from neural crest cells (NCs) and NCs persist in adult PDL tissue, we devised to promote the regeneration of the periodontium by activating NCs to differentiate into PDLSCs. SK-N-SH cells, a neuroblastoma cell line that reportedly has NC-like features, seeded on the extracellular matrix of PDL cells for 2 weeks, resulted in the significant upregulation of PDL marker expression. SK-N-SH cell-derived PDLSCs (SK-PDLSCs) presented phenotypic characteristics comparable to induced pluripotent stem cell (iPSC)-derived PDLSCs (iPDLSCs). The expression levels of various hyaluronic acid (HA)-related genes were upregulated in iPDLSCs and SK-PDLSCs compared with iPSC-derived NCs and SK-N-SH cells, respectively. The knockdown of CD44 in SK-N-SH cells significantly inhibited their ability to differentiate into SK-PDLSCs, while low-molecular HA (LMWHA) induction enhanced SK-PDLSC differentiation. Our findings suggest that SK-N-SH cells could be applied as a new model to induce the differentiation of NCs into PDLSCs and that the LMWHA-CD44 relationship is important for the differentiation of NCs into PDLSCs.

Current Application of iPS Cells in the Dental Tissue Regeneration.

When teeth and periodontal tissues are severely damaged by severe caries, trauma, and periodontal disease, such cases may be subject to tooth extraction. As tooth loss leads to the deterioration of quality of life, the development of regenerative medicine for tooth and periodontal tissue is desired. Induced pluripotent stem cells (iPS cells) are promising cell resources for dental tissue regeneration because they offer high self-renewal and pluripotency, along with fewer ethical issues than embryonic stem cells. As iPS cells retain the epigenetic memory of donor cells, they have been established from various dental tissues for dental tissue regeneration. This review describes the regeneration of dental tissue using iPS cells. It is important to mimic the process of tooth development in dental tissue regeneration using iPS cells. Although iPS cells had safety issues in clinical applications, they have been overcome in recent years. Dental tissue regeneration using iPS cells has not yet been established, but it is expected in the future.

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.