The response of periodontal ligament cells to fibronectin

Delivery technologies for therapeutic targeting of fibronectin in autoimmunity and fibrosis applications

Fibronectin (FN) is a critical component of the extracellular matrix (ECM) contributing to various physiological processes, including tissue repair and immune response regulation. FN regulates various cellular functions such as adhesion, proliferation, migration, differentiation, and cytokine release. Alterations in FN expression, deposition, and molecular structure can profoundly impact its interaction with other ECM proteins, growth factors, cells, and associated signaling pathways, thus influencing the progress of diseases such as fibrosis and autoimmune disorders. Therefore, developing therapeutics that directly target FN or its interaction with cells and other ECM components can be an intriguing approach to address autoimmune and fibrosis pathogenesis.

High glucose impairs human periodontal ligament cells migration through lowered microRNAs 221 and 222

OBJECTIVE

To investigate the effects of miR-221 and miR-222 and high glucose on human periodontal ligament (PL) cells morphology, cytoskeleton, adhesion, and migration.

BACKGROUND

Chronic hyperglycemia is common in uncontrolled diabetes mellitus (DM) and plays a central role in long-term DM complications, such as impaired periodontal healing. We have previously shown that high glucose increases apoptosis of human PL cells by inhibiting miR-221 and miR-222 and consequently augmenting their target caspase-3. However, other effects of miR-221/222 downregulation on PL cells are still unknown.

METHODS

Cells from young humans' premolar teeth were cultured for 7 days under 5 or 30 mM glucose. Directional and spontaneous migration on fibronectin were studied using transwell and time-lapse assays, respectively. F-actin staining was employed to study cell morphology and the actin cytoskeleton. MiR-221 and miR-222 were inhibited using antagomiRs, and their expressions were evaluated by real-time RT-PCR.

RESULTS

High glucose inhibited PL cells early adhesion, spreading, and migration on fibronectin. Cells exposed to high glucose showed reduced polarization, velocity, and directionality. They formed several simultaneous unstable and short-lived protrusions, suggesting impairment of adhesion maturation. MiR-221 and miR-222 inhibition also reduced migration, decreasing cell directionality but not significantly cell velocity. After miR-221 and miR-222 downregulation cells showed morphological resemblance with cells exposed to high glucose.

CONCLUSION

High glucose impairs human PL cells migration potentially through a mechanism involving reduction of microRNA-221 and microRNA-222 expression. These effects may contribute to the impairment of periodontal healing, especially after surgery and during guided regeneration therapies.

LncRNA ADAMTS9-AS2 regulates periodontal ligament cell migration under mechanical compression via ADAMTS9/fibronectin

BACKGROUND

Periodontal ligament cells (PDLCs) are key mechanosensory cells involved in extracellular matrix (ECM) remodeling during orthodontic tooth movement (OTM). Mechanical force changes the ECM components, such as collagens and matrix metalloproteinases. However, the associations between the changes in ECM molecules and cellular dynamics during OTM remain largely uncharacterized.

OBJECTIVES

To investigate the influence of mechanical force on the morphology and migration of PDLCs and explore the interaction between ECM remodeling and cellular dynamics, including the detailed mechanisms involved.

METHODS

Human PDLCs (hPDLCs) were subjected to a static mechanical compression to mimic the compression state of OTM in vitro. A mouse OTM model was used to mimic the OTM procedure in vivo. The migration of hPDLCs was compared by wound healing and transwell migration assays. Moreover, expression levels of ADAM metallopeptidase with thrombospondin type 1 motif 9 (ADAMTS9) and fibronectin (FN) in hPDLCs were determined via western blotting, immunofluorescence staining, and enzyme-linked immunosorbent assays. Expression levels of ADAMTS9 and FN in mice were assessed via immunohistochemical staining. Additionally, the relative expression of long non-coding RNA (lncRNA) ADAMTS9-antisense RNA 2 (ADAMTS9-AS2) was assessed via quantitative real-time polymerase chain reaction. ADAMTS9-AS2 knockdown was performed to confirm its function in hPDLCs.

RESULTS

Mechanical compression induced changes in the morphology of hPDLCs. It also promoted migration and simultaneous upregulation of FN and downregulation of ADAMTS9, a fibronectinase. The mouse OTM model showed the same expression patterns of the two proteins on the compression side of the periodontium of the moved teeth. RNA sequencing revealed that lncRNA ADAMTS9-AS2 expression was significantly upregulated in hPDLCs under mechanical compression. After knocking down ADAMTS9-AS2, hPDLCs migration was significantly inhibited. ADAMTS9 expression was increased as FN expression decreased compared to that in the control group. Moreover, knockdown of ADAMTS9-AS2 reduced the effect of mechanical compression on hPDLCs migration and reversed the expression change of ADAMTS9 and FN. RNA immunoprecipitation revealed direct binding between ADAMTS9-AS2 and ADAMTS9 protein.

CONCLUSION

Our study suggests that mechanical compression induces the expression of ADAMTS9-AS2, which directly binds to ADAMTS9 and inhibits its function, leading to the promotion of downstream FN expression and ECM remodeling to facilitate hPDLCs migration and maintain the stability of the periodontium.

3D Bioprinting of Hyaline Articular Cartilage: Biopolymers, Hydrogels, and Bioinks

The musculoskeletal system, consisting of bones and cartilage of various types, muscles, ligaments, and tendons, is the basis of the human body. However, many pathological conditions caused by aging, lifestyle, disease, or trauma can damage its elements and lead to severe disfunction and significant worsening in the quality of life. Due to its structure and function, articular (hyaline) cartilage is the most susceptible to damage. Articular cartilage is a non-vascular tissue with constrained self-regeneration capabilities. Additionally, treatment methods, which have proven efficacy in stopping its degradation and promoting regeneration, still do not exist. Conservative treatment and physical therapy only relieve the symptoms associated with cartilage destruction, and traditional surgical interventions to repair defects or endoprosthetics are not without serious drawbacks. Thus, articular cartilage damage remains an urgent and actual problem requiring the development of new treatment approaches. The emergence of biofabrication technologies, including three-dimensional (3D) bioprinting, at the end of the 20th century, allowed reconstructive interventions to get a second wind. Three-dimensional bioprinting creates volume constraints that mimic the structure and function of natural tissue due to the combinations of biomaterials, living cells, and signal molecules to create. In our case-hyaline cartilage. Several approaches to articular cartilage biofabrication have been developed to date, including the promising technology of 3D bioprinting. This review represents the main achievements of such research direction and describes the technological processes and the necessary biomaterials, cell cultures, and signal molecules. Special attention is given to the basic materials for 3D bioprinting-hydrogels and bioinks, as well as the biopolymers underlying the indicated products.

Establishing a technique for isolation and characterization of human periodontal ligament derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) are extensively used in tissue regenerative procedures. One source of MSCs is the periodontal ligament (PDL) of teeth. Isolation of MSCs from extracted teeth is reasonably simple, being less invasive and presenting fewer ethical concerns than does the harvesting of MSC’s from other sites. The objectives of this study were to isolate and characterize the PDL stem cells (PDLSC) from healthy adults’ extracted teeth and then to characterize them by comparing them with bone-marrow derived MSCs (BMMSC).

Methods

The PDL tissue was scraped from the roots of freshly extracted teeth to enzymatically digest using collagenase. The cells were sub-cultured. Flow-cytometric analysis for the MSC surface-markers CD105, CD73, CD166, CD90, CD34, CD45 and HLA-DR was performed. To confirm the phenotype, total RNA was extracted to synthesize cDNA and which was then subjected to RT-PCR. The gene-expression for Oct4A, Sox2, NANOG and GAPDH was determined by gel-electrophoresis. To assess their multilineage potential, cells were cultured with osteogenic, chondrogenic and adipogenic medium and then stained by Alizarin-red, Alcian-blue and Oil-Red-O respectively. MSCs from the bone-marrow were processed similarly to serve as controls.

Results

The cells isolated from extracted teeth expanded successfully. On flow-cytometric analysis, the cells were positive for CD73, CD90, CD105, CD166 and negative for CD34, CD45 and HLA-DR. The PDLSCs expressed Oct4A, Sox2, and NANOG mRNA with GAPDH expression. Cells cultured in the osteogenic, chondrogenic and adipogenic media stained positive for Alizarin-red, Alcian-blue and Oil- Red-O respectively. The surface marker expression and the trilineage differentiation characteristics were comparable to those of the BMMSCs.

Conclusions

The periodontal ligament tissue of extracted teeth is a potential source of therapeutically useful MSCs. Harvesting them is not invasive and are a promising source of MSC as the PDLSCs showed characteristics similar to those of the highly regarded MSC’s derived from bone-marrow.

Bioactivity effects of extracellular matrix proteins on apical papilla cells

Potent signaling agents stimulate and guide pulp tissue regeneration, especially in endodontic treatment of teeth with incomplete root formation.

Treponema denticola dentilisin triggered TLR2/MyD88 activation upregulates a tissue destructive program involving MMPs via Sp1 in human oral cells

Periodontal disease is driven by dysbiosis in the oral microbiome, resulting in over-representation of species that induce the release of pro-inflammatory cytokines, chemokines, and tissue-remodeling matrix metalloproteinases (MMPs) in the periodontium. These chronic tissue-destructive inflammatory responses result in gradual loss of tooth-supporting alveolar bone. The oral spirochete Treponema denticola, is consistently found at significantly elevated levels in periodontal lesions. Host-expressed Toll-Like Receptor 2 (TLR2) senses a variety of bacterial ligands, including acylated lipopolysaccharides and lipoproteins. T. denticola dentilisin, a surface-expressed protease complex comprised of three lipoproteins has been implicated as a virulence factor in periodontal disease, primarily due to its proteolytic activity. While the role of acylated bacterial components in induction of inflammation is well-studied, little attention has been given to the potential role of the acylated nature of dentilisin. The purpose of this study was to test the hypothesis that T. denticola dentilisin activates a TLR2-dependent mechanism, leading to upregulation of tissue-destructive genes in periodontal tissue. RNA-sequencing of periodontal ligament cells challenged with T. denticola bacteria revealed significant upregulation of genes associated with extracellular matrix organization and degradation including potentially tissue-specific inducible MMPs that may play novel roles in modulating host immune responses that have yet to be characterized within the context of oral disease. The Gram-negative oral commensal, Veillonella parvula, failed to upregulate these same MMPs. Dentilisin-induced upregulation of MMPs was mediated via TLR2 and MyD88 activation, since knockdown of expression of either abrogated these effects. Challenge with purified dentilisin upregulated the same MMPs while a dentilisin-deficient T. denticola mutant had no effect. Finally, T. denticola-mediated activation of TLR2/MyD88 lead to the nuclear translocation of the transcription factor Sp1, which was shown to be a critical regulator of all T. denticola-dependent MMP expression. Taken together, these data suggest that T. denticola dentilisin stimulates tissue-destructive cellular processes in a TLR2/MyD88/Sp1-dependent fashion.

Fibronectin in development and wound healing

Fibronectin structure and composition regulate contextual cell signaling. Recent advances have been made in understanding fibronectin and its role in tissue organization and repair. This review outlines fibronectin splice variants and their functions, evaluates potential therapeutic strategies targeting or utilizing fibronectin, and concludes by discussing potential future directions to modulate fibronectin function in development and wound healing.

Treatment of Pulpectomized Teeth With Trypsin Prior to Transplantation of Mobilized Dental Pulp Stem Cells Enhances Pulp Regeneration in Aged Dogs

There is an age-dependent decline of pulp regeneration, due to the decline of migration, proliferation, and cell survival of resident stem cells. Trypsin is a proteolytic enzyme clinically used for tissue repair. Here, we investigated the effects of trypsin pretreatment of pulpectomized teeth prior to cell transplantation on pulp regeneration in aged dogs. The amount of regenerated pulp was significantly higher in trypsin-pretreated teeth compared to untreated teeth. Trypsin pretreatment increased the number of cells attached to the dentinal wall that differentiated into odontoblast-like cells. The trypsin receptor, PAR2, was higher in vitro expression in the periodontal ligament cells (PDLCs) from aged dogs compared to those from young. The direct effects of trypsin on aged PDLCs were increased expression of genes related to immunomodulation, cell survival, and extracellular matrix degradation. To examine the indirect effects on microenvironment, highly extracted proteins from aged cementum were identified by proteomic analyses. Western blotting demonstrated that significantly increased fibronectin was released by the trypsin treatment of aged cementum compared to young cementum. The aged cementum extract (CE) and dentin extract (DE) by trypsin treatment increased angiogenesis, neurite extension and migration activities as elicited by fibronectin. Furthermore, the DE significantly increased the mRNA expression of immunomodulatory factors and pulp markers in the aged DPSCs. These results demonstrated the effects of trypsin on the microenvironment in addition to the resident cells including PDLCs in the aged teeth. In conclusion, the potential utility of trypsin pretreatment to stimulate pulp regeneration in aged teeth and the underlying mechanisms were demonstrated.

Induction of migration of periodontal ligament cells by selective regulation of integrin subunits

The recruitment of tissue-resident stem cells is important for wound regeneration. Periodontal ligament cells (PDL cells) are heterogeneous cell populations with stemness features that migrate into wound sites to regenerate periodontal fibres and neighbouring hard tissues. Cell migration is regulated by the local microenvironment, coordinated by growth factors and the extracellular matrix (ECM). Integrin-mediated cell adhesion to the ECM provides essential signals for migration. We hypothesized that PDL cell migration could be enhanced by selective expression of integrins. The migration of primary cultured PDL cells was induced by platelet-derived growth factor-BB (PDGF-BB). The effects of blocking specific integrins on migration and ECM adhesion were investigated based on the integrin expression profiles observed during migration. Up-regulation of integrins α3, α5, and fibronectin was identified at distinct localizations in migrating PDL cells. Treatment with anti-integrin α5 antibodies inhibited PDL cell migration. Treatment with anti-integrin α3, α3-blocking peptide, and α3 siRNA significantly enhanced cell migration, comparable to treatment with PDGF-BB. Furthermore, integrin α3 inhibition preferentially enhanced adhesion to fibronectin via integrin α5. These findings indicate that PDL cell migration is reciprocally regulated by integrin α3-mediated inhibition and α5-mediated promotion. Thus, targeting integrin expression is a possible therapeutic strategy for periodontal regeneration.

Treponema denticola increases MMP-2 expression and activation in the periodontium via reversible DNA and histone modifications

Host-derived matrix metalloproteinases (MMPs) and bacterial proteases mediate destruction of extracellular matrices and supporting alveolar bone in periodontitis. The Treponema denticola dentilisin protease induces MMP-2 expression and activation in periodontal ligament (PDL) cells, and dentilisin-mediated activation of pro-MMP-2 is required for cellular fibronectin degradation. Here, we report that T. denticola regulates MMP-2 expression through epigenetic modifications in the periodontium. PDL cells were treated with epigenetic enzyme inhibitors before or after T. denticola challenge. Fibronectin fragmentation, MMP-2 expression, and activation were assessed by immunoblot, zymography, and qRT-PCR, respectively. Chromatin modification enzyme expression in T. denticola-challenged PDL cells and periodontal tissues were evaluated using gene arrays. Several classes of epigenetic enzymes showed significant alterations in transcription in diseased tissue and T. denticola-challenged PDL cells. T. denticola-mediated MMP-2 expression and activation were significantly reduced in PDL cells treated with inhibitors of aurora kinases and histone deacetylases. In contrast, DNA methyltransferase inhibitors had little effect, and inhibitors of histone acetyltransferases, methyltransferases, and demethylases exacerbated T. denticola-mediated MMP-2 expression and activation. Chronic epigenetic changes in periodontal tissues mediated by T. denticola or other oral microbes may contribute to the limited success of conventional treatment of chronic periodontitis and may be amenable to therapeutic reversal.

Effect of dentin treatment on proliferation and differentiation of human dental pulp stem cells

Objectives

Sodium hypochlorite (NaOCl) is an excellent bactericidal agent, but it is detrimental to stem cell survival, whereas intracanal medicaments such as calcium hydroxide (Ca[OH]₂) promote the survival and proliferation of stem cells. This study evaluated the effect of sequential NaOCl and Ca[OH]₂ application on the attachment and differentiation of dental pulp stem cells (DPSCs).

Materials and Methods

DPSCs were obtained from human third molars. All dentin specimens were treated with 5.25% NaOCl for 30 min. DPSCs were seeded on the dentin specimens and processed with additional 1 mg/mL Ca[OH]₂, 17% ethylenediaminetetraacetic acid (EDTA) treatment, file instrumentation, or a combination of these methods. After 7 day of culture, we examined DPSC morphology using scanning electron microscopy and determined the cell survival rate with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. We measured cell adhesion gene expression levels after 4 day of culture and odontogenic differentiation gene expression levels after 4 wk using quantitative real-time polymerase chain reaction.

Results

DPSCs did not attach to the dentin in the NaOCl-treated group. The gene expression levels of fibronectin-1 and secreted phosphoprotein-1 gene in both the Ca[OH]₂- and the EDTA-treated groups were significantly higher than those in the other groups. All Ca[OH]₂-treated groups showed higher expression levels of dentin matrix protein-1 than that of the control. The dentin sialophosphoprotein level was significantly higher in the groups treated with both Ca[OH]₂ and EDTA.

Conclusions

The application of Ca[OH]₂ and additional treatment such as EDTA or instrumentation promoted the attachment and differentiation of DPSCs after NaOCl treatment.

The extended tentacles of laser - From diagnosis to treatment in orthodontics: An overview

Since the introduction of lasers in dentistry in the mid-1990's, research in laser supported dental therapies is progressing at a rapid pace. Orthodontics is no exception. In orthodontics, lasers have many diagnostic, therapeutic, and biomodulating applications. To update the various applications of lasers in orthodontics. Lasers work by delivering energy in the form of light. Laser, striking the biological tissues can either get reflected, absorbed or scattered depending on several factors. Depending on the fate of the emitted laser, it can be applied for different diagnostic, therapeutic and surgical procedures. The knowledge and understanding of different types of lasers and its specific applications is a prerequisite before it can be applied beneficially. In Orthodontics, the versatility of laser has expanded into bonding, curing, debonding, imaging, growth modification, pain reduction, etc. Definitely laser has extended its tentacles from diagnosis to treatment in orthodontics.

Resistance to cigarette smoke is increased in periodontal ligament cells by attachment to collagen and fibronectin

BACKGROUND

The toxic effects of cigarette smoke often presents in smokers as increased incidence and severity of periodontal disease. These patients demonstrate symptomatic inflammation, increased probing depth, and tooth loss likely attributable to the direct effects of cigarette smoke on periodontal ligament (PDL) fibroblasts. The goal of this in vitro study is to investigate the direct effects of smoking on PDL fibroblasts, focusing on cell-extracellular matrix (ECM) interactions and cell survival.

METHODS

PDL cells were plated for various times on tissue culture plastic, PDL-derived ECMs, collagen Type I, or fibronectin. Cells were exposed to various concentrations of cigarette smoke extract (CSE) at different times during the cell attachment process. Subsequently, cell survival was quantified using calcein-acetoxymethyl ester compound and a fluorescent plate reader.

RESULTS

After exposure to CSE, PDL cell survival increased with increased cell attachment time to plastic. These observations were independent of soluble factors present in PDL cell-conditioned media. PDL-derived ECMs and collagen Type I-pretreated plates promoted increased cell survival after 1 day of cell attachment. Fibronectin-pretreated plates demonstrated increased cell survival after 3 days of cell attachment.

CONCLUSIONS

Cell-ECM interactions increase survival of PDL cells exposed to CSE. It is suggested that the increased survival is attributable to PDL cells altering their ECM, potentially by depositing collagen and fibronectin. This may imply that cells embedded in an ECM would be more resistant to the toxic effects of cigarette smoke, leading to increased cell death near the exposed edges of a wound.

Scaffold-free cell pellet transplantations can be applied to periodontal regeneration

Cell transplantation has emerged as a novel therapeutic strategy for periodontitis, and the adoption of cell pellet offers advantages by secreting abundant extracellular matrix (ECM) and eliminating the adverse effect of cell carriers. This study aimed to fabricate scaffold-free periodontal ligament stem cell (PDLSC) pellets (MUCPs) and to evaluate their regeneration potential. We constructed monolayer cell pellets (MCPs) by fabricating and culturing multilayered cell sheets (MUCS) and constructed MUCPs from the MUCS. Immunochemistry, scanning electron microscope, real-time PCR, and Western blot analysis showed higher levels of COL-I, COL-III, fibronectin, and laminin in the MUCPs. Furthermore, the massive increase in ECM secretion improved cell adhesion, migration, and proliferation. Finally, upon transplantation into the omentum sac and periodontal defects, all the transplants formed regular aligned cementum/PDL-like complex, but the mineral deposit and fiber alignment were more obvious in the MUCPs than in the MCPs. Altogether, our results suggest that MUCPs may be a promising alternative to periodontal repair for future clinical application.

Prospective potency of TGF-β1 on maintenance and regeneration of periodontal tissue

Periodontal ligament (PDL) tissue, central in the periodontium, plays crucial roles in sustaining tooth in the bone socket. Irreparable damages of this tissue provoke tooth loss, causing a decreased quality of life. The question arises as to how PDL tissue is maintained or how the lost PDL tissue can be regenerated. Stem cells included in PDL tissue (PDLSCs) are widely accepted to have the potential to maintain or regenerate the periodontium, but PDLSCs are very few in number. In recent studies, undifferentiated clonal human PDL cell lines were developed to elucidate the applicable potentials of PDLSCs for the periodontal regenerative medicine based on cell-based tissue engineering. In addition, it has been suggested that transforming growth factor-beta 1 is an eligible factor for the maintenance and regeneration of PDL tissue.

Periodontal tissue engineering with stem cells from the periodontal ligament of human retained deciduous teeth

BACKGROUND AND OBJECTIVE

Periodontal ligament stem cells from human permanent teeth (PePDLSCs) have been investigated extensively in periodontal tissue engineering and regeneration. However, little knowledge is available on the periodontal ligament stem cells from human retained deciduous teeth (DePDLSCs). This study evaluated the potential of DePDLSCs in periodontal tissue regeneration.

MATERIAL AND METHODS

DePDLSCs were isolated and purified by limited dilution. The characteristics of DePDLSCs were evaluated and compared with PePDLSCs both in vitro and in vivo.

RESULTS

DePDLSCs presented a higher proliferation rate and colony-forming capacity than PePDLSCs in vitro. During the osteogenic induction, alkaline phosphatase (ALP) activity, mineralized matrix formation and expression of mineralization-related genes, including runt-related transcription factor 2 (RUNX2), ALP, collagen type I (COLI) and osteocalcin (OCN) were significantly enhanced in DePDLSCs compared with PePDLSCs. Furthermore, DePDLSC cell sheets showed a stronger synthesis of collagen type I in the extracellular matrix than did PePDLSC cell sheets. After in vivo transplantation, DePDLSC cell sheets recombined with human dentin blocks were able to generate new cementum/periodontal ligament-like tissues.

CONCLUSION

Our findings suggest that DePDLSCs can be used as a promising candidate for periodontal tissue engineering.

Implications of cultured periodontal ligament cells for the clinical and experimental setting: a review

The periodontal ligament (PDL) is a key contributor to the process of regeneration of the periodontium. The heterogeneous nature of the PDL tissue, its development during early adulthood, and the different conditions to which the PDL tissue is exposed to in vivo impart on the PDL unique characteristics that may be of consequence during its cultivation in vitro. Several factors affecting the in vivo setting influence the behaviour of PDL fibroblasts in culture. The purpose of this review is to address distinct factors that influence the behaviour of PDL fibroblasts in culture -in vivo-in vitro transitions, cell identification/isolation markers, primary PDL cultures and cell lines, tooth-specific factors, and donor-specific factors. Based on the reviewed studies, the authors recommendations include the use of several identification markers to confirm cell identity, use of primary cultures at early passage to maintain unique PDL heterogeneic characteristics, and noting donor conditions such as age, systemic health status, and tooth health status. Continued efforts will expand our understanding of the in vitro and in vivo behaviour of cells, with the goal of orchestrating optimal periodontal regeneration. This understanding will lead to improved evidence-based rationales for more individualized and predictable periodontal regenerative therapies.

Anoikis triggers Mdm2-dependent p53 degradation

The extracellular matrix (ECM) plays a key role in cell-cell communication and signaling, and the signals it propagates are important for tissue remodeling and survival. However, signals from disease-altered ECM may lead to anoikis-apoptotic cell death triggered by loss of ECM contacts. Previously, we found that an altered fibronectin matrix triggers anoikis in human primary ligament cells via a pathway that requires p53 transcriptional downregulation. Here we show that this p53 reduction is suppressed by transfecting cells with Mdm2 antisense oligonucleotides or small interfering RNA. Similar results were found in cells treated to prevent p53 and Mdm2 interactions. When p53 was overexpressed in cells lacking Mdm2 and p53, p53 levels were unaffected by anoikis conditions. However, cells cotransfected with p53 and wild type Mdm2, but not a mutant Mdm2, exhibited decreased p53 levels in response to anoikis conditions. Thus, cells under anoikis conditions undergo p53 degradation that is mediated by Mdm2.

Proapoptotic fibronectin fragment induces the degradation of ubiquitinated p53 via proteasomes in periodontal ligament cells

BACKGROUND AND OBJECTIVE

The extracellular matrix (ECM) plays a key role in signaling necessary for tissue remodeling and cell survival. However, signals from the ECM altered by disease, e.g. inflammatory diseases such as periodontitis and arthritis, may lead to apoptosis or programmed cell death of resident cells. Previously, we found that a disease-associated fibronectin fragment triggers apoptosis of primary human periodontal ligament cells via a novel apoptotic pathway in which the tumor suppressor, p53, is transcriptionally downregulated.

MATERIAL AND METHODS

We used immunofluorescence, transfection assays, western blotting and ELISAs to show that p53 is degraded by a proteasomal pathway in response to a proapoptotic disease-associated fibronectin fragment.

RESULTS

We found that in these apoptotic conditions, p53 is further downregulated by post-translational ubiquitination and subsequent targeting to proteasomes for degradation. Pretreatment of cells with the proteasomal inhibitors MG132 and lactacystin rescued the cells from apoptosis. The p53 levels in cells transfected with ubiquitin small interfering RNA were resistant to degradation induced by the proapoptotic fibronectin fragment, showing that ubiquitination is important for the proapoptotic fibronectin fragment-induced degradation of p53.

CONCLUSION

These data show that a proapoptotic fibronectin matrix induces ubiquitination and degradation of p53 in the proteasome as part of a novel mechanism of apoptosis associated with inflammatory diseases.

Tissue engineering of cementum/periodontal-ligament complex using a novel three-dimensional pellet cultivation system for human periodontal ligament stem cells

Limitations of conventional regeneration modalities underscore the necessity of recapitulating development for periodontal tissue engineering. In this study, we proposed a novel three-dimensional pellet cultivation system for periodontal ligament stem cells (PDLSCs) to recreate the biological microenvironment similar to those of a regenerative milieu. Monodispersed human PDLSCs were cultured in medium with ascorbic acid and conditioned medium from developing apical tooth germ cells and were subsequently harvested from culture plate as a contiguous cell sheet with abundant extracellular matrix. The detached cell-matrix membrane spontaneously contracted to produce a single-cell pellet. The PDLSCs embedded within this cell-matrix complex exhibited several phenotypic characteristics of cementoblast lineages, as indicated by upregulated alkaline phosphatase activity, accelerated mineralization, and the expression of bone sialoprotein and osteocalcin genes. When this PDLSC pellets were transplanted into immunocompromised mice, a regular aligned cementum/PDL-like complex was formed. These results suggest that the combination of apical tooth germ cell-conditioned medium and endogenous extracellular matrix could maximally mimic the microenvironment of root/periodontal tissue development and enhance the reconstruction of physiological architecture of a cementum/PDL-like complex in a tissue-mimicking way; on the other hand, such PDLSC pellet may also be a promising alternative to promote periodontal defect repair for future clinical applications.

Low-level laser irradiation facilitates fibronectin and collagen type I turnover during tooth movement in rats

The aim of this study was to investigate the effects of low-level laser (LLL) irradiation on the turnover of fibronectin and collagen type I in periodontal tissue during tooth movement in rats by immunohistochemistry. Thirty male Sprague-Dawley rats aged 15 weeks were assigned to either an experimental group (n = 15) that underwent LLL irradiation during tooth movement, or a control group (n = 15). In the experimental group, the gallium-aluminum-arsenide (Ga-Al-As) diode LLL (wavelength 808 nm; output 96 mW) was used to irradiate three areas on both the palatal side and the labial side of the maxillary incisor. The radiation was administered by the contact method for 10 s at 0.83 J/cm(2) energy dose, once a day for 7 days. Total energy dose over the complete schedule was 34.86 J/cm(2). The animals were killed on days 1, 3, 7, 14 and 21. There was no difference between the two groups in the amount of tooth movement. The immunohistochemistry results showed that the expression of fibronectin and collagen type I in the experimental group had significantly increased from day 1, with a more even distribution than in the control group, and that this difference was maintained until the end of the experiment. These results suggest that LLL irradiation facilitates the reorganization of the connective tissues during tooth movement in rats.

Fibronectin fragmentation is a feature of periodontal disease sites and diabetic foot and leg wounds and modifies cell behavior

BACKGROUND

Fibronectin (FN) undergoes fragmentation in periodontal disease sites and in poorly healing diabetic wounds. The biologic effects of FN fragments on wound healing remain unresolved. This study characterized the pattern of FN fragmentation and its effects on cellular behavior compared to intact FN.

METHODS

Polyclonal antibodies were raised against FN and three defined recombinant segments of FN and used to analyze gingival crevicular fluid from periodontal disease sites in systemically healthy subjects and in subjects with diabetes, as well as chronic leg and foot wound exudates from subjects with diabetes. Subsequently, the behavior of human gingival fibroblasts (hGFs) and HT1080 reference cells were analyzed by measuring cell attachment, migration, and chemotaxis in the presence of intact FN or recombinant FN fragments.

RESULTS

FN fragmentation was evident in fluids from periodontal disease sites and diabetic leg and foot wounds. However, no fragmentation pattern distinguished systemically healthy subjects from subjects with diabetes. hGFs and HT1080 cells required significantly higher concentrations of FN fragments to achieve attachment comparable to intact FN. Cells cultured on FN fragments also were morphologically different from cells cultured on full-length FN. Migration was reduced for hGFs cultured on FN fragments relative to full-length FN. In contrast, FN fragments increased HT1080 fibrosarcoma cell migration over intact FN.

CONCLUSIONS

FN fragmentation is a prominent feature of periodontal and chronic leg and foot wounds in diabetes. Furthermore, cell culture assays confirmed the hypothesis that exposure to defined FN fragments significantly alters cell behavior.

An altered fibronectin matrix induces anoikis of human squamous cell carcinoma cells by suppressing integrin alpha v levels and phosphorylation of FAK and ERK

Fibronectin regulates many cellular processes, including migration, proliferation, differentiation, and survival. Previously, we showed that squamous cell carcinoma (SCC) cell aggregates escape suspension-induced, p53-mediated anoikis by engaging in fibronectin-mediated survival signals through focal adhesion kinase (FAK). Here we report that an altered matrix, consisting of a mutated, nonfunctional high-affinity heparin-binding domain and the V region of fibronectin (V+H-), induced anoikis in human SCC cells; this response was blocked by inhibitors of caspase-8 and caspase-3. Anoikis was mediated by downregulation of integrin alpha v in a panel of SCC cells and was shown to be proteasome-dependent. Overexpression of integrin alpha v or FAK inhibited the increase in caspase-3 activation and apoptosis, whereas suppression of alpha v or FAK triggered a further significant increase in apoptosis, indicating that the apoptosis was mediated by suppression of integrin alpha v levels and dephosphorylation of FAK. Treatment with V+H- decreased the phosphorylation of extracellular signal-regulated kinase (ERK) 1 and 2, and direct activation of ERK by constitutively active MEK1, an ERK kinase, increased ERK1 and ERK2 phosphorylation and inhibited the increase in apoptosis induced by V+H-. ERK acted downstream from alpha v and FAK signals, since alpha v and FAK overexpression inhibited both the decrease in ERK phosphorylation and the increase in anoikis triggered by V+H-. These findings provide evidence that mutations in the high-affinity heparin-binding domain in association with the V region of fibronectin, or altered fibronectin matrices, induce anoikis in human SCC cells by modulating integrin alpha v-mediated phosphorylation of FAK and ERK.

Proliferation and adhesion of periodontal ligament cells on synthetic biominerals

OBJECTIVE

Hydroxiapatite (HA) has been suggested as a useful biomaterial to support the regeneration of tissues. In this study, we investigated the adhesion of periodontal ligament (PDL) cells on octacalcium phosphate (OCP) and its hydrolyzed apatitic product (HL), which are known precursors of HA.

METHODS

Rat PDL cells were cultured on OCP or HL-coated dishes. Cell proliferation and adhesion and mRNA expression of collagen I, fibronectin integrin subunits were examined. Cell adhesion inhibition assays were carried out by GRGDSPK (Gly-Arg-Gly-Asp-Ser-Pro-Lys).

RESULTS

In early culture period, the cell number of PDL cells was lower on OCP and HL than that on control without any coating. However, the cell number on OCP or HL caught up with control later period. mRNA expression level of collagen I and fibronectin on OCP and HL were similar among OCP HL and control, although they differed early in the culture period. Integrin subunits were expressed on both OCP and HL as well as on control. Cell adhesion was inhibited by RGD inhibitor peptide.

CONCLUSION

Our findings indicated that rat PDL cells produce collagen I and fibronectin on OCP and HL, and then show increased cell numbers depending on adhesion to the matrices through integrins.

Extracellular matrix expression and periodontal wound-healing dynamics following guided tissue regeneration therapy in canine furcation defects

AIM

Temporal and spatial expression pattern of extracellular matrix (ECM) components in furcation defects following guided tissue regeneration (GTR) compared with open-flap debridement (OFD).

MATERIAL AND METHODS

In 21 dogs, mandibular second and fourth pre-molars were treated with one non-resorbable and three different resorbable membranes. Third pre-molars were treated by OFD. After 2, 4, 8 weeks and 3, 6, and 12 months, tissues were analysed by immunohistochemistry for collagen I (Col-I) and III (Col-III), fibronectin (FN), bone sialoprotein (BSP), and osteopontin (OPN).

RESULTS

At 2 weeks, the defect was mainly occupied by FN+ granulation tissue (GT), which was sequentially replaced by new connective tissue expressing FN, Col-I, and increasingly Col-III. Following superficial resorptions by OPN+ osteoclasts and odontoclasts, cementum and bone formation ensued with strong expression of BSP and OPN along bone and tooth surfaces. Deposition of Col-I, FN, BSP and OPN+ cementoid and osteoid became evident after 4 weeks. Extrinsic fibres of cementum and bone stained intensely for Col-III. The newly formed periodontal ligament expressed FN, Col-I, and Col-III, but no BSP or OPN.

CONCLUSIONS

The spatial ECM expression was similar for OFD and the different GTR methods, although the timing and quantity of ECM expression were influenced by wound stabilization and inflammatory reactions.

In vitro models of periodontal cells: a comparative study of long-term gingival, periodontal ligament and alveolar bone cell cultures in the presence of beta-glycerophosphate and dexamethasone

Human gingival (HG), periodontal ligament (HPL) and alveolar bone (HAB) cells (first subculture) were cultured (10(4) cells/cm2) for 35 days in alpha-Minimal Essential Medium supplemented with 10% fetal bovine serum in the presence of (i) ascorbic acid (AA, 50 microg/mL), (ii) AA + beta-glycerophosphate (betaGP, 10 mM) and (iii) AA + betaGP + dexamethasone (Dex, 10 nM). Cultures were assessed for cell attachment and spreading, cell proliferation, alkaline phosphatase (ALP) and acid phosphatase (ACP) activities and matrix mineralization. HG cell cultures presented a high proliferation rate, a low ability to synthesize ALP and ACP and the formation of a non-mineralized extracellular matrix, regardless the experimental situation. HPL cell cultures were very sensitive to the culture conditions and showed a high proliferation rate, synthesis of moderate levels of ALP and ACP and a modest matrix mineralization in the presence of AA + betaGP + Dex. HAB cell cultures presented a growth rate lower than that of HG and HPL cells, a high ALP activity and comparatively low levels of ACP, and the ready formation of a heavy mineralized matrix in the presence of betaGP. In the three periodontal cell cultures, Dex enhanced cell proliferation and expression of osteoblastic markers. Results showed that betaGP and Dex allowed the modulation of the cell proliferation/differentiation behavior within the proposed physiological and regenerative capabilities of these periodontal cells.

Disease-associated fibronectin matrix fragments trigger anoikis of human primary ligament cells: p53 and c-myc are suppressed

Inflammation in periodontal disease is characterized by the breakdown of the extracellular matrix. This study shows that an inflammation-associated matrix breakdown fragment of fibronectin (FN) induces anoikis of human periodontal ligament (PDL) cells. This 40 kDa fragment was identified in human inflammatory crevicular fluid and is associated with disease status. Previously, we reported that a similar recombinant FN fragment triggered apoptosis of PDL cells by an alternate apoptotic signaling pathway that requires transcriptional downregulation of p53 and c-myc. Thus, to determine whether the physiologically relevant 40 kDa fragment triggers apoptosis in these cells, the 40 kDa fragment was generated and studied for its apoptotic properties. The 40 kDa fragment induces apoptosis of PDL cells, and preincubation of cells with intact vitronectin, FN, and to a limited extent collagen I, rescue this apoptotic phenotype. These data suggest that the 40 kDa fragment prevents PDL cell spreading, thereby inducing anoikis. The signaling pathway also involves a downregulation in p53 and c-myc, as determined by Western blotting and real time quantitative PCR. These data indicate that an altered FN matrix as is elaborated in inflammation induces anoikis of resident cells and thus may contribute to disease progression.

JNK1 and JNK2 oppositely regulate p53 in signaling linked to apoptosis triggered by an altered fibronectin matrix: JNK links FAK and p53

The extracellular matrix regulates many cellular processes, including survival, and alterations in the matrix or in matrix survival signals can trigger apoptosis. Previously, we showed that an altered fibronectin matrix triggers apoptosis in primary cells via a novel pathway regulated by transcriptionally mediated decreases in p53 and c-Myc levels. Here we report that this apoptotic mechanism is propagated by decreased phosphorylation of focal adhesion kinase (FAK), which is linked to increased phosphorylation of c-Jun N-terminal kinase (JNK) and to decreased levels of p53. FAK is physically and spatially linked to JNK and p53, which relocalize from the nucleus to the cell membrane to mediate this interaction. Further, p53 participates in a feedback mechanism with JNK to regulate this apoptotic process and is oppositely regulated by JNK1 and JNK2.

Human Periodontal Ligament Cell Sheets Can Regenerate Periodontal Ligament Tissue in an Athymic Rat Model

Conventional periodontal regeneration methods remain insufficient to attain complete and reliable clinical regeneration of periodontal tissues. We have developed a new method of cell transplantation using cell sheet engineering and have applied it to this problem. The purpose of this study was to investigate the characteristics of human periodontal ligament (HPDL) cell sheets retrieved from culture on unique temperature-responsive culture dishes, and to examine whether these cell sheets can regenerate periodontal tissues. The HPDL cell sheets were examined histologically and biochemically, and also were transplanted into a mesial dehiscence model in athymic rats. HPDL cells were harvested from culture dishes as a contiguous cell sheet with abundant extracellular matrix and retained intact integrins that are susceptible to trypsin-EDTA treatment. In the animal study, periodontal ligament-like tissues that include an acellular cementum-like layer and fibrils anchoring into this layer were identified in all the athymic rats transplanted with HPDL cell sheets. This fibril anchoring highly resembles native periodontal ligament fibers; such regeneration was not observed in nontransplanted controls. These results suggest that this technique, based on the concept of cell sheet engineering, can be useful for periodontal tissue regeneration.

Inhibitory effects of Porphyromonas gingivalis fimbriae on interactions between extracellular matrix proteins and cellular integrins

Porphyromonas gingivalis is a predominant periodontal pathogen, whose fimbriae are considered to be a major virulence factor, especially for bacterial adherence and invasion of host cells. In the present study, we investigated the influence of fimbriae on the interactions between alphavbeta3- and alpha5beta1-integrins and their ligand extracellular matrix (ECM) proteins (vitronectin and fibronectin), using human alphavbeta3- and alpha5beta1-integrin-overexpressing CHO cell lines (CHOalphavbeta3 and CHOalpha5beta1, respectively). P. gingivalis was found to have significantly greater binding to CHOalphavbeta3 and CHOalpha5beta1 than to control cells, whereas a fimbria-deficient mutant showed negligible binding to any of the tested cell lines. CHOalphavbeta3 and CHOalpha5beta1 cells attached to the polystyrene culture dishes in the presence of their ligand ECM proteins, while fimbriae markedly inhibited those attachments in a dose-dependent manner, with the highest dose of fimbriae achieving complete inhibition. In addition, the binding of vitronectin and fibronectin to CHOalphavbeta3 and CHOalpha5beta1 was inhibited by P. gingivalis cells. These results suggest that P. gingivalis fimbriae compete with ECM proteins for alphavbeta3- and alpha5beta1-integrins, and inhibit integrin/ECM protein-related cellular functions.

Cytotoxic effects of dental resin liquids on primary gingival fibroblasts and periodontal ligament cellsin vitro

Cytotoxic effects of resin liquids of three in situ relining dental polymers, Alike, Kooliner, and Tokuso Rebase, and their major components, methyl methacrylate (MMA), isobutyl methacrylate (IBMA), and 1,6-hexanediol dimethacrylate (1,6-HDMA) were investigated. The concentrations of major monomers in these resin liquids were determined by high-performance liquid chromatography. Cellular viability of human gingival fibroblasts (GF) and periodontal ligament (PDL) cells were evaluated by the 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide assay. Moreover, patterns of cell death were analysed using annexin V/propidium iodide staining with flow cytometry. The results indicated that Alike liquid contained 91.3% MMA, Kooliner liquid contained 94.5% IBMA, and Tokuso Rebase liquid contained 65.8% 1,6-HDMA. All materials examined had cytotoxic effects on GF and PDL cells in dose-dependent manners. Tokuso Rebase liquid appeared to be the most cytotoxic among the various resin liquids examined. The effects of Kooliner and Tokuso Rebase liquids may have resulted from IBMA and 1,6-HDMA, respectively. Furthermore, the majority of treated cells died from necrosis; whereas a small portion of cells died from apoptosis. In conclusion, the results demonstrated that these liquid forms of dental polymers and their major monomers cause cytotoxic reactions. The direct relining procedure that cures these materials in situ should be used cautiously.

Biomimetic approach on human periodontal ligament cells using synthetic oligopeptides

BACKGROUND

Periodontal ligament (PDL) cells, connecting root cementum with alveolar bone, are important for periodontal wound healing. In order to obtain a predictable periodontal regeneration, selective adhesion and proliferation of PDL cells are essential. The purpose of this study was to investigate the effects of synthetic peptides mimicking cell-binding domain of fibronectin (FN) on human PDL cells.

METHODS

Two types of oligopeptides, Gly3-Pro-His-Ser-Arg-Asn-Gly6-Arg-Gly-Asp-Gly (G3PHSRNG6RGDG) and Gly3-His-Pro-Asn-Arg-Ser-Gly6-Arg-Gly-Asp-Gly (G3HPNRSG6RGDG), were constructed using a solid-phase peptide synthesizer. Fibronectin type III ninth to tenth domain (FN III 9-10) and Arg-Gly-Asp-Ser (RGDS) were prepared for comparison with the effects of synthetic peptides. These peptides were coated onto 96-well cell culture plates with 0.001 approximately 100 microM concentrations. Cultured human PDL cells were then applied to the peptide-coated wells at a density of 1 x 10(4)/well. After 1 hour incubation at 37 degrees C, adhered cells were fixed, stained, and examined by phase contrast microscopy for cell spreading assay. Attached PDL cells were solubilized with 2% sodium dodecyl sulfate (SDS) for the cell attachment assay by measuring absorbance at 595 nm in microplate reader. Western blot analysis was performed to determine extracellular signal-regulated kinase (ERK1/2) activity.

RESULTS

Cell attachment and spreading assays revealed that G3PHSRNG6RGDG (> or = 10 microM) possesses similar adhesive behavior to FN III 9-10. G3PHSRNG6RGDG showed a comparable ERK1/2 activity when compared to FN III 9-10.

CONCLUSIONS

G3PHSRNG6RGDG enhanced an attachment and spreading of human PDL cells thereby increasing ERK1/2 activity. Taken together, it is anticipated that this peptide might be a potential tool for arranging a biologically attractive environment for PDL cells, which would enhance periodontal regeneration efficacy.

Effect of enamel matrix derivative on periodontal ligament cells in vitro is diminished by Porphyromonas gingivalis

BACKGROUND

Enamel matrix derivative (EMD) has been shown to possess a mitogenic effect to induce effective periodontal regeneration, however, it is unclear whether periodontal pathogens can modulate the effect of EMD. The present study examined the influence of Porphyromonas gingivalis on EMD-stimulated periodontal ligament (PDL) cells.

METHODS

P. gingivalis ATCC33277 and its mutants deficient in fimbriae (delta fimA) or gingipains (delta rgpA delta rgpB, delta kgp, and delta rgpA delta rgpB delta kgp) were employed. PDL cells were grown on EMD-coated dishes and infected with P. gingivalis wild strain or a mutant. Cell migration and proliferation were then evaluated with an in vitro wound healing assay. The expression of transforming growth factor-beta1 (TGF-beta1) and insulin-like growth factor I (IGF-I) mRNA by PDL cells was examined. Further, the degradation and phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) as well as paxillin in infected PDL cells were estimated using Western blot analysis.

RESULTS

P. gingivalis ATCC33277 inhibited the migration and proliferation of PDL cells on EMD-coated dishes, and the mutants delta fimA, delta rgpA delta rgpB, and delta kgp showed the same effects. Further, each of these organisms diminished the expression of TGF-beta1 and IGF-I mRNA, as well as the phosphorylation of ERK1/2 from EMD-stimulated PDL cells. In addition, total paxillin protein was markedly degraded by both the wild-type strain and each of the mutants except for delta rgpA delta rgpB delta kgp, which showed a negligible effect in all of the assays with EMD-stimulated PDL cells.

CONCLUSION

These results suggest that P. gingivalis diminishes the effect of EMD on PDL cells in vitro through a cooperative action of gingipains.

Establishment of Periodontal Ligament Cell Lines from Temperature-Sensitive Simian Virus 40 Large T-antigen Transgenic Rats

Orthodontic tooth movement is controlled by various cell types in the periodontal ligament (PDL). Mechanical stresses, such as orthodontic force, are thought to induce differentiation of the mesenchymal cells in the PDL into osteoblasts and cementoblasts. The details of the process of differentiation, however, are not known, in part because adequate in vitro systems for their study do not yet exist. The purpose of this study was to establish and characterize immortalized PDL cell lines derived from the PDL of transgenic rats harboring the temperature-sensitive simian virus 40 T-antigen gene (TG rats). The PDL was removed from the molar roots of TG rats and incubated in tissue culture. Outgrowth cells from the PDL explant were passaged and cloned, depending on the shape of the colonies formed. The cell lines thus established were analyzed by reverse transcription-polymerase chain reaction for expression of type-I collagen, osteopontin, fibronectin, alkaline phosphatase (bone type), bone sialoprotein, the receptor activator of NF-kappa B ligand, and osteoprotegerin. In addition, the capacity for formation of mineralized nodules was assessed by incubating cells in calcification-promoting medium at 37 degrees C. A total of 15 stable cell lines were successfully established and characterized. These cell lines were classified into six groups based on their pattern of gene expression at 33 degrees C. Moreover, three of these clones were capable of forming calcified nodules. In conclusion, differential gene expression was demonstrated in 15 established PDL cell lines. Some cells had the potential to differentiate into cell types found in mineralized tissues, such as osteoblasts and cementoblasts, as well as cells expressing molecules that regulate osteoclast differentiation.

Attachment of Periodontal Ligament Cells to Chlorhexidine-Loaded Guided Tissue Regeneration Membranes

BACKGROUND

Early exposure of a guided tissue regeneration (GTR) membrane in the oral cavity results in bacterial contamination, which may lead to failure or incomplete regeneration. Incorporation of antimicrobial agents in GTR membranes may be valuable to control membrane-associated infection during GTR therapy. The purpose of this study was to evaluate whether the incorporation of chlorhexidine into various GTR membranes improves the attachment of periodontal ligament cells in the presence of Actinobacillus actinomycetemcomitans.

METHODS

The possible effects of chlorhexidine on the viability of primary human periodontal ligament (PDL) cells were determined using 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyltetrazolium bromide (MTT), which measures cellular metabolic activity. An expanded polytetrafluoroethylene (ePTFE) membrane, glycolide fiber membrane, and collagen membrane were loaded with chlorhexidine and characterized. Attachment of PDL cells to the chlorhexidine-loaded membranes with or without A. actinomycetemcomitans was examined using scanning electron microscopy (SEM) analysis.

RESULTS

Relative cellular viability of PDL cells was reduced to approximately 50% when 15 microg/ml (0.0015%) of chlorhexidine was used. Chlorhexidine released from the coated GTR membranes inhibited the growth of A. actinomycetemcomitans. At the concentration used in this study, chlorhexidine incorporated into the GTR membranes did not interfere with the attachment of PDL cells. The inhibitory effects of A. actinomycetemcomitans on cellular attachment were reduced using chlorhexidine-loaded membranes, including ePTFE, glycolide fiber, and collagen membranes.

CONCLUSIONS

These results suggest that incorporation of chlorhexidine into GTR membranes is beneficial in reducing bacterial effects on cellular attachment. The future application of chlorhexidine-loaded membranes during GTR therapy may be of value.

Quantitative evaluation of the vasculature and fibronectin localization in gingival connective tissue of smokers and non-smokers

BACKGROUND

It has been shown that tobacco is a significant risk factor for periodontal disease. The reason for decreased gingival bleeding in smokers is not known. The aim of the present study was to demonstrate the localization of fibronectin in the extracellular matrix of the inflamed gingiva of smokers and non-smokers and to evaluate the chronic effect of smoking on the gingival microvessel number (NVES) and vascular surface density (VSD).

METHODS

Seventy-four (74) adult patients with periodontitis were included in this investigation. Of these patients, 38 were smokers and 36 were non-smokers. Probing depths (PD), papillary bleeding index (PBI) of both groups, and the smoking habits of the smokers were recorded. Biopsy specimens obtained during periodontal surgery were prepared to evaluate fibronectin distribution and to quantitate the vasculature.

RESULTS

The mean VSD values of smokers and non-smokers were 6.721 +/- 1.845 and 5.721 +/- 3.118 (mean +/- SD), and the mean NVES of smokers and non-smokers was 31.582 +/- 11.810 and 30.145 +/- 15.442, respectively. The difference between the mean PD and PBI values of the 2 groups was not statistically significant. The location of the biopsy specimen, whether in the anterior or posterior area of the mouth, did not lead to any statistically significant differences between the groups. In addition, the number of years smoked and the tobacco brand used did not result in statistically significant differences. The most intense staining of fibronectin was observed beneath the epithelium around the blood vessels of the uppermost region of the connective tissue, showing a fibrillar and diffuse distribution; however, there was no significant difference between smokers and non-smokers.

CONCLUSION

The results of the present study indicate that smoking does not affect the vascular surface density, number of vessels per mm2 stroma, or fibronectin distribution in subepithelial gingival connective tissue.

Molecular interaction of Porphyromonas gingivalis with host cells: implication for the microbial pathogenesis of periodontal disease

Porphyromonas gingivalis is a predominant periodontal pathogen, which expresses a number of potential virulence factors involved in the pathogenesis of periodontitis. Among them, fimbriae are a critical factor to mediate the bacterial interaction with host tissues, which promotes the bacterial adhesion to and invasion of the targeted sites. Fimbriae are capable of binding to human salivary components, commensal bacteria, and a variety of host cells including macrophages, epithelial cells, and fibroblasts. Human extracellular matrix (ECM) proteins such as vitronectin and fibronectin play important roles in cellular signal transduction via binding to receptor integrins. Fimbriae showed significant binding affinity to ECM proteins and clearly inhibited the molecular interactions between vitronectin/fibronectin and their receptor alphavbeta3 and alpha5beta1 integrins overexpressed on Chinese hamster ovary (CHO) cell strain. P. gingivalis fimbriae are likely to interrupt the cellular signaling via ECM proteins/integrins in periodontal regions. Fimbriae are also thought to be critically important in invasive events of the organism to host cells. The fimA genes, encoding FimA (a subunit of fimbriae), of P. gingivalis strains are classified into 5 types, I to V. Recent clinical investigations demonstrated the close relationship between the organisms with type II fimA and periodontitis development. Recombinant FimA (rFimA) proteins of types I to V were generated to compare their adhesion/invasion abilities to human gingival fibroblasts (HGF) and a human epithelial cell line (HEp-2 cells), respectively. There were no significant differences in the adhesion ability of microspheres (MS) coated with these rFimAs to HGF; however, the adhesion of type II rFimA-MS to HEp-2 cells was significantly greater than that of other rFimA types. It was also observed that the type II rFimA-MS markedly invaded the epithelial cells and accumulated around the nuclei. Collectively, these findings suggest that fimbriae of P. gingivalis, especially type II, are involved in the initiation and progression of human periodontitis.

Ascorbic acid induces collagenase-1 in human periodontal ligament cells but not in MC3T3-E1 osteoblast-like cells: potential association between collagenase expression and changes in alkaline phosphatase phenotype

Ascorbic acid (AA) enhances osteoblastic differentiation by increasing collagen accumulation, which in turn, results in increased alkaline phosphatase (AP) expression in some osteogenic cells. However, in other cells, including human periodontal ligament (PDL) cells, additional osteoinductive agents are required for this response. To understand the potential basis for the maintenance of the AP phenotype of PDL cells exposed to AA, we examined the modulation of the tissue-degrading matrix metalloproteinases (MMPs) and their inhibitors by AA in short-term cell cultures. Early passage PDL cells in serum-free medium were exposed to AA for 5 days. The samples were analyzed for MMPs and their inhibitors, the tissue inhibitors of metalloproteinases (TIMPs), AP, collagen I(alpha1), and osteocalcin. We found that AA dose-dependently increased the expression of collagenase-1, and minimally TIMP-1, but not stromelysin-1 or TIMP-2. Additionally, AA caused substantial increases in levels of type I collagen. AA was unable to increase AP activity or osteocalcin messenger RNA in PDL cells. However, the cells retained the ability to show a significantly greater AP expression in high- versus low-density cultures, and increased osteocalcin as well as AP levels when cultured in the presence of dexamethasone. Moreover, in cells exposed to dexamethasone, increases in AP and osteocalcin were accompanied by a repression of collagenase-1 expression. In contrast to PDL cells, AA did not induce collagenase but produced a significant increase in AP expression in MC3T3-E1 cells. These findings provide the first evidence that AA, by modulating both collagen and collagenase-1 expression in PDL cells, most likely contributes to a net matrix remodeling response in these cells. Furthermore, the relationship between changes in collagenase expression and alterations in AP activity in PDL and MC3T3-E1 cells suggests a potential role for collagenase in modulating the AP phenotype of cells with osteoblastic potential.

Possible involvement of extracellular signal-regulated kinases 1/2 in mitogenic response of periodontal ligament cells to enamel matrix derivative

The efficacy of enamel matrix derivative (EMD) as an adjunct to periodontal regenerative therapy has been demonstrated in recent clinical studies, however, little is known about its molecular mechanism (s). We examined the mitogenic response of cultured periodontal ligament (PDL) cells to EMD and characterized associated changes in proliferation-related intracellular signaling molecules, including mitogen-activated protein kinases (MAPK) and Akt kinases/protein kinase B (Akt/PKB) kinases. The DNA synthesis of PDL cells increased following treatment with EMD at concentrations higher than 1 microg ml(-1). This mitogenic response to EMD was associated with the selective activation of extracellular signal-regulated kinase (ERK) 1/2. No other MAPKs, or Akt/PKB kinases, responded to EMD stimulation. The EMD induction of DNA synthesis and activation of ERK 1/2 were diminished by pretreatment with suramin, an inhibitor of receptor tyrosine kinases (RTK). The signaling pathway induced by EMD from RTK to ERK 1/2 was similar to that activated by epidermal growth factor (EGF), although the specific binding of 125I-EGF to PDL cells was not affected by pretreatment or concomitant treatment with EMD. These findings suggest that EMD elicits its mitogenic signal through an EMD-specific RTK towards ERK 1/2.

Expression of integrins by human periodontal ligament and gingival fibroblasts and their involvement in fibroblast adhesion to enamel matrix-derived proteins

We showed recently that human periodontal ligament (PDL) and gingival fibroblasts adhere and spread on enamel matrix protein (EMP) coatings. In the present study, we investigated whether this interaction can be attributed to integrin expression. Human PDL and gingival fibroblasts were cultured for periods up to 24 h on EMP coatings, in the presence of synthetic RGD-containing peptide or an antibody against the beta1 integrin subunit. The cells were first cultured for 24 h under serum-free conditions and then cultured on EMP coatings for 48 h. Integrin expression levels were assessed by flow cytometry analysis. It was found that attachment and spreading on EMP was inhibited by the synthetic RGD-containing peptide, but not by a synthetic RGE-peptide. Both PDL and gingival fibroblasts showed expression of the integrin subunits, alpha2, alpha5, beta1, and the integrin, alphavbeta3. Incubation with an antibody against the beta1 subunit significantly inhibited the attachment and spreading of PDL and gingival fibroblasts on EMP coatings. We conclude that integrins are involved in the interaction of PDL and gingival fibroblasts with EMP.

Specific fibronectin fragments as markers of periodontal disease status

BACKGROUND

The diagnosis of progressing periodontal disease typically relies on retrospective methods that detect changes in the amount of periodontal breakdown. Fibronectin (FN) fragments are found in vivo in association with periodontal disease, and specific FN fragments compromise periodontal ligament cell functions in vitro. The overall goal of this cross-sectional study was to determine whether specific FN fragments are present in gingival crevicular fluid (GCF) and can be used as markers for periodontal disease status. The eventual goal is to test these FN fragments in a longitudinal study as potential markers of disease activity.

METHODS

GCF was collected from 94 subjects with untreated periodontitis from clinically healthy, mild/moderate periodontitis, and severe periodontitis sites. Sites were defined on the basis of clinical criteria, including gingival bleeding index, probing depth, and clinical attachment level. Western immunoblotting was used to detect FN fragments in GCF using antibodies to specific FN domains, including the collagen/gelatin-, central cell-, and carboxyl terminal heparin-binding domains, plus the CS-1 site on the alternatively spliced V region and the EIIIA region. FN fragments identified by immunoblotting and analyzed by NIH image software were scored based on pixel intensity and an ordinal grade scale.

RESULTS

We identified several fragments highly associated with severe periodontitis sites, including 40-kDa, 120-kDa, and 68-kDa fragments.

CONCLUSIONS

This study demonstrates that specific FN fragments are markers for periodontal disease status and supports the role of FN fragments as potential components in the pathogenesis of periodontal disease.

Permeability of Streptococcus mutans and Actinobacillus actinomycetemcomitans Through guided tissue regeneration membranes and their effects on attachment of periodontal ligament cells

BACKGROUND

Microbial colonization on barrier materials used in guided tissue regeneration (GTR) may adversely affect treatment outcomes. The purposes of this study were: 1) to compare the invasion of Streptococcus mutans and Actinobacillus actinomycetemcomitans through 3 GTR membranes, composed of expanded polytetrafluoroethylene (ePTFE; non-resorbable), a glycolide fiber composite, and type I collagen (both bioabsorbable), and 2) to explore the effects of bacteria on the attachment of periodontal ligament (PDL) fibroblasts onto these membranes.

METHODS

Bacterial permeability was analyzed using a tube capped with a GTR membrane as a septum and filled with media. The tube was then placed in a bigger tube inoculated with S. mutans or A. actinomycetemcomitans. The passage of bacteria through the membranes into the inner tube was monitored. For cellular attachment experiments, primary human PDL cells were placed onto the GTR membranes with or without bacteria. Attached cells were analyzed by scanning electron microscopy (SEM) analysis.

RESULTS

The ePTFE membrane had the best barrier effects followed by the collagen membrane and then the glycolide fiber composite membrane. Moreover, S. mutans passed through these membranes faster than A. actinomycetemcomitans. The attachment of PDL cells on the 3 membranes was also varied. The ePTFE membrane was the worst substrate for PDL fibroblast attachment. Moreover, both bacteria influenced the cellular attachment on the GTR membranes.

CONCLUSIONS

Differences in the behavior of 3 GTR membranes penetrated by S. mutans and A. actinomycetemcomitans were demonstrated. The results suggest that attachment of PDL cells was affected on bacterial-contaminated GTR membranes, which may alter healing following membrane exposure.

Proteolytic events of wound-healing--coordinated interactions among matrix metalloproteinases (MMPs), integrins, and extracellular matrix molecules

During wound-healing, cells are required to migrate rapidly into the wound site via a proteolytically generated pathway in the provisional matrix, to produce new extracellular matrix, and, subsequently, to remodel the newly formed tissue matrix during the maturation phase. Two classes of molecules cooperate closely to achieve this goal, namely, the matrix adhesion and signaling receptors, the integrins, and matrix-degrading and -processing enzymes, the matrix metalloproteinases (MMPs). There is now substantial experimental evidence that blocking key molecules of either group will prevent or seriously delay wound-healing. It has been known for some time now that cell adhesion by means of the integrins regulates the expression of MMPs. In addition, certain MMPs can bind to integrins or other receptors on the cell surface involved in enzyme activation, thereby providing a mechanism for localized matrix degradation. By proteolytically modifying the existing matrix molecules, the MMPs can then induce changes in cell behavior and function from a state of rest to migration. During wound repair, the expression of integrins and MMPs is simultaneously up-regulated. This review will focus on those aspects of the extensive knowledge of fibroblast and keratinocyte MMPs and integrins in biological processes that relate to wound-healing.

Morphology, chemical structure and diffusion processes of root surface after Er:YAG and Nd:YAG laser irradiation

OBJECTIVES

The aim of this in vitro study was to evaluate the effects of Er:YAG and Nd:YAG lasers on morphology, chemical structure and diffusion processes of the root surface.

MATERIAL AND METHODS

60 root samples were irradiated for 1 min each either with 60 mJ/p, 80 mJ/p and 100 mJ/p using Er:YAG laser or with 0.5W, 1.0W and 1.5W using Nd:YAG laser. Scanning electron microscopy (SEM) was used to determine the morphology, infrared (IR) spectroscopy to assess the alterations in chemical structure and one dimensional electron paramagnetic resonance imaging (1-D EPRI) was used to estimate the diffusion coefficients in dental root samples.

RESULTS

Er:YAG laser treatment resulted in deep crater formation with exposed dentin. Morphological alterations of root surface after Nd:YAG laser irradiation included cracks, crater formation, meltdown of the root mineral and resolidified porous globules formation. Er:YAG laser failed to alter the intensity of Amide peaks I, II or III. In contrast, treatment with Nd:YAG laser, using the highest power setting of 1.5W, reduced the intensity of Amide peak II and III in comparison to the control. The diffusion coefficients were increased significantly in all Er:YAG and Nd:YAG treated root samples.

CONCLUSION

This study demonstrated that Er:YAG laser influences only on morphology and diffusion processes of root surfaces, while Nd:YAG laser also alters the chemical structure of root proteins.