In vitro evaluation of the antimicrobial properties of terpinen-4-ol on apical periodontitis-associated bacteria

Manuka oil and tea tree oil are essential oils with known antibacterial properties that are believed to be caused by one main component: terpinen-4-ol. Terpinen-4-ol has potent antibacterial activity against caries-related microorganisms. However, few studies have investigated the antimicrobial effects of terpinen-4-ol on bacteria in apical periodontitis. Thus, the objective of the present study was to evaluate the antibacterial and antibiofilm potential of terpinen-4-ol against Enterococcus faecalis, Porphyromonas gingivalis, Prevotella intermedia, and Fusobacterium nucleatum, which have all been detected in apical periodontitis. The minimum inhibitory and minimum bactericidal concentrations of terpinen-4-ol were determined to assess its activity against biofilms. The minimum inhibitory concentration of terpinen-4-ol was 0.25% against E. faecalis and F. nucleatum, 0.05% against P. gingivalis, and 0.1% against P. intermedia. The minimum bactericidal concentration of terpinen-4-ol was 1.0% against E. faecalis, 0.2% against P. gingivalis and P. intermedia, and 0.5% against F. nucleatum. In the biofilm evaluations, all terpinen-4-ol-treated bacteria had significant reductions in biofilm viability compared with controls in experiments assessing attachment inhibitory activity. Furthermore, structural alterations and decreased bacterial cell clumping were observed under scanning electron microscopy, and significantly decreased cell survival was noted using fluorescence microscopy. Together, these results suggest that terpinen-4-ol is a potential antibacterial agent with bactericidal properties, and can also act on established biofilms.

Actin alpha 2, smooth muscle, a transforming growth factor-β1-induced factor, regulates collagen production in human periodontal ligament cells via Smad2/3 pathway

Background/purpose

Actin alpha 2, smooth muscle (ACTA2) is an actin isoform that forms the cytoskeleton. Actin plays a crucial role in numerous cellular functions. ACTA2 is a marker of functional periodontal ligament (PDL) fibroblasts and is upregulated by transforming growth factor-β1 (TGF-β1); however, the underlying function of ACTA2 in PDL tissue is unknown. We aimed to examine the localization and potential function of ACTA2 in PDL tissues and cells.

Materials and methods

RNA expression was determined using semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) and quantitative RT-PCR. Protein expression was determined using immunofluorescence staining and Western blot analysis. Soluble and insoluble collagen production was examined using the Sircol collagen assay and picrosirius red staining, respectively. Small interfering RNA (siRNA) was used for knockdown assay to examine the effect of ACTA2 in human PDL cells.

Results

ACTA2 expression was observed in human primary PDL cells and PDL cell line (2-23 cells). TGF-β1 upregulated ACTA2, collagen type Ⅰ alpha1 chain (COL1A1), periostin (POSTN), and fibrillin-Ⅰ(FBN1) expression and soluble and insoluble collagen production in 2-23 cells. However, ACTA2 depletion by siRNA strongly suppressed PDL-related gene expression and collagen production compared with those of TGF-β1-stimulated control cells. Furthermore, ACTA2 knockdown significantly suppressed the phosphorylation of Smad2 and Smad3.

Conclusion

ACTA2 plays a crucial role in PDL-related marker expression and collagen production via Smad2/3 phosphorylation. Our findings might contribute to the development of novel and effective periodontal therapies.

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, β2 adrenergic receptor (β2-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 β2-AR in periodontal ligament (PDL) tissue has not been fully examined. In this report, we investigated that β2-AR expression in PDL tissues and their features in PDL cells. β2-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 β2-AR expression, while its expression was downregulated in that without loading. In HPDLCs, β2-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 β2-AR. Their gene expression and intracellular cyclic adenosine monophosphate (cAMP) levels were also investigated in HPDLCs treated with a specific β2-AR agonist, fenoterol (FEN). Overexpression of β2-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 β2-AR expression in PDL tissue and β2-AR is involved in fibroblastic differentiation and collagen synthesis of PDL cells. The signaling through β2-AR might be important for restoration and homeostasis of PDL tissue.

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.

Extracellular Matrix from Periodontal Ligament Cells Could Induce the Differentiation of Induced Pluripotent Stem Cells to Periodontal Ligament Stem Cell-Like Cells

The periodontal ligament (PDL) plays an important role in anchoring teeth in the bone socket. Damage to the PDL, such as after severe inflammation, can be treated with a therapeutic strategy that uses stem cells derived from PDL tissue (PDLSCs), a strategy that has received intense scrutiny over the past decade. However, there is an insufficient number of PDLSCs within the PDL for treating such damage. Therefore, we sought to induce the differentiation of induced pluripotent stem (iPS) cells into PDLSCs as an initial step toward PDL therapy. To this end, we first induced iPS cells into neural crest (NC)-like cells. We then captured the p75 neurotrophic receptor-positive cells (iPS-NC cells) and cultured them on an extracellular matrix (ECM) produced by human PDL cells (iPS-NC-PDL cells). These iPS-NC-PDL cells showed reduced expression of embryonic stem cell and NC cell markers as compared with iPS and iPS-NC cells, and enrichment of mesenchymal stem cell markers. The cells also had a higher proliferative capacity, multipotency, and elevated expression of PDL-related markers than iPS-NC cells cultured on fibronectin and laminin (iPS-NC-FL cells) or ECM produced by human skin fibroblast cells (iPS-NC-SF cells). Overall, we present a culture method to produce high number of PDLSC-like cells from iPS cells as a first step toward a strategy for PDL regeneration.

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.

Calcium-sensing receptor-ERK signaling promotes odontoblastic differentiation of human dental pulp cells

Activation of the G protein-coupled calcium-sensing receptor (CaSR) has crucial roles in skeletal development and bone turnover. Our recent study has identified a role for activated CaSR in the osteogenic differentiation of human periodontal ligament stem cells. Furthermore, odontoblasts residing inside the tooth pulp chamber play a central role in dentin formation. However, it remains unclear how CaSR activation affects the odontoblastic differentiation of human dental pulp cells (HDPCs). We have investigated the odontoblastic differentiation of HDPCs exposed to elevated levels of extracellular calcium (Ca) and strontium (Sr), and the contribution of CaSR and the L-type voltage-dependent calcium channel (L-VDCC) to this process. Immunochemical staining of rat dental pulp tissue demonstrated that CaSR was expressed at high levels in the odontoblastic layer, moderate levels in the sublayer, and low levels in the central pulp tissue. Although normal HDPCs expressed low levels of CaSR, stimulation with Ca or Sr promoted both CaSR expression and odontoblastic differentiation of HDPCs along with increased expression of odontoblastic makers. These effects were inhibited by treatment with a CaSR antagonist, whereas treatment with an L-VDCC inhibitor had no effect. Additionally, knockdown of CaSR with siRNA suppressed odontoblastic differentiation of Ca- and Sr-treated HDPCs. ERK1/2 phosphorylation was observed in Ca- and Sr-treated HDPCs, whereas CaSR antagonist treatment or CaSR knockdown blocked ERK1/2 phosphorylation. Furthermore, inhibition of ERK1/2 suppressed mineralization of Ca- and Sr-treated HDPCs. These results suggest that elevated concentrations of extracellular Ca and Sr induce odontoblastic differentiation of HDPCs through CaSR activation and the ERK1/2 phosphorylation.

Transgelin mediates transforming growth factor-β1-induced proliferation of human periodontal ligament cells

BACKGROUND AND OBJECTIVE

Human periodontal ligament cells (HPDLCs) express transforming growth factor-β1 (TGF-β1) that regulates differentiation and proliferation, and plays key roles in homeostasis of PDL tissue. Transgelin is a cytoskeleton-associated protein with an Smad-binding element in its gene promoter region. In this study, we examined the localization and potential function of transgelin in PDL tissue and cells.

MATERIAL AND METHODS

Microarray analysis of HPDLC lines (2-14, 2-23 and 2-52) was performed. Expression of transgelin in HPDLCs was examined by quantitative reverse transcription-polymerase chain reaction, immunofluorescence staining and western blot analysis. Effects of TGF-β1 and its signaling inhibitor, SB431542, on transgelin expression in HPDLCs were examined by western blot analysis. The effects of transgelin knockdown by small interfering RNA (siRNA) on HPDLC proliferation stimulated by TGF-β1 were assessed by WST-1 assay.

RESULTS

In microarray and quantitative reverse transcription-polymerase chain reaction analyses, the expression levels of transgelin (TAGLN) in 2-14 and 2-23 cells, which highly expressed PDL markers such as periostin (POSTN), tissue non-specific alkaline phosphatase (ALPL), α-smooth muscle actin (ACTA2) and type I collagen A1 (COL1A1), was significantly higher than those in 2-52 cells that expressed PDL markers weakly. Immunohistochemical and immunofluorescence staining revealed expression of transgelin in rat PDL tissue and HPDLCs. In HPDLCs, TGF-β1 treatment upregulated transgelin expression, whereas inhibition of the type 1 TGF-β1 receptor by SB431542 suppressed this upregulation. Furthermore, TAGLN siRNA transfection did not promote the proliferation of HPDLCs treated with TGF-β1. The expression levels of CCNA2 and CCNE1, which regulate DNA synthesis and mitosis through the cell cycle, were also not upregulated in HPDLCs transfected with TAGLN siRNA.

CONCLUSION

Transgelin is expressed in PDL tissue and might have a role in HPDLC proliferation induced by TGF-β1 stimulation.

Transforming growth factor-β-induced gene product-h3 inhibits odontoblastic differentiation of dental pulp cells

OBJECTIVE

The aim of this study was to investigate transforming growth factor-β-induced gene product-h3 (βig-h3) expression in dental pulp tissue and its effects on odontoblastic differentiation of dental pulp cells (DPCs).

DESIGN

A rat direct pulp capping model was prepared using perforated rat upper first molars capped with mineral trioxide aggregate cement. Human DPCs (HDPCs) were isolated from extracted teeth. βig-h3 expression in rat dental pulp tissue and HDPCs was assessed by immunostaining. Mineralization of HDPCs was assessed by Alizarin red-S staining. Odontoblast-related gene expression in HDPCs was analyzed by quantitative RT-PCR.

RESULTS

Expression of βig-h3 was detected in rat dental pulp tissue, and attenuated by direct pulp capping, while expression of interleukin-1β and tumor necrosis factor-α was increased in exposed pulp tissue. βig-h3 expression was also detected in HDPCs, with reduced expression during odontoblastic differentiation. The above cytokines reduced βig-h3 expression in HDPCs, and promoted their mineralization. Recombinant βig-h3 inhibited the expression of odontoblast-related genes and mineralization of HDPCs, while knockdown of βig-h3 gene expression promoted the expression of odontoblast-related genes in HDPCs.

CONCLUSIONS

The present findings suggest that βig-h3 in DPCs may be involved in reparative dentin formation and that its expression is likely to negatively regulate this process.

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-1β) 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-1β antibody. Compared with untreated cells, HPDLCs treated with IL-1β or tumor necrosis factor-alpha showed an increase in the secretion of GDNF protein. Conditioned medium of IL-1β-treated HPDLCs (IL-1β-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-1β-CM-treated PC12 cells. These stimulatory effects of IL-1β-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.

Semaphorin 3A Induces Odontoblastic Phenotype in Dental Pulp Stem Cells

In cases of pulp exposure due to deep dental caries or severe traumatic injuries, existing pulp-capping materials have a limited ability to reconstruct dentin-pulp complexes and can result in pulpectomy because of their low potentials to accelerate dental pulp cell activities, such as migration, proliferation, and differentiation. Therefore, the development of more effective therapeutic agents has been anticipated for direct pulp capping. Dental pulp tissues are enriched with dental pulp stem cells (DPSCs). Here, the authors investigated the effects of semaphorin 3A (Sema3A) on various functions of human DPSCs in vitro and reparative dentin formation in vivo in a rat dental pulp exposure model. Immunofluorescence staining revealed expression of Sema3A and its receptor Nrp1 (neuropilin 1) in rat dental pulp tissue and human DPSC clones. Sema3A induced cell migration, chemotaxis, proliferation, and odontoblastic differentiation of DPSC clones. In addition, Sema3A treatment of DPSC clones increased β-catenin nuclear accumulation, upregulated expression of the FARP2 gene (FERM, RhoGEF, and pleckstrin domain protein 2), and activated Rac1 in DPSC clones. Furthermore, in the rat dental pulp exposure model, Sema3A promoted reparative dentin formation with dentin tubules and a well-aligned odontoblast-like cell layer at the dental pulp exposure site and with novel reparative dentin almost completely covering pulp tissue at 4 wk after direct pulp capping. These findings suggest that Sema3A could play an important role in dentin regeneration via canonical Wnt/β-catenin signaling. Sema3A might be an alternative agent for direct pulp capping, which requires further study.