Fluoride-induced changes to proteoglycan structure synthesised within the dentine–pulp complex in vitro

Modification of gingival proteoglycans by reactive oxygen species: potential mechanism of proteoglycan degradation during periodontal diseases

Reactive oxygen species (ROS) overproduction and oxidative stress are increasingly being implicated in the extracellular matrix (ECM) degradation associated with chronic inflammatory conditions, such as periodontal diseases. The present study investigated the effects of ROS exposure on the proteoglycans of gingival tissues, utilizing an in vitro model system comprised of supra-physiological oxidant concentrations, to ascertain whether gingival proteoglycan modification and degradation by ROS contributed to the underlying mechanisms of ECM destruction during active gingivitis. Proteoglycans were purified from ovine gingival tissues and exposed to increasing H₂O₂ concentrations or a hydroxyl radical (·OH) flux for 1 h or 24 h, and ROS effects on proteoglycan core proteins and sulfated glycosaminoglycan (GAG) chains were assessed. ROS were capable of degrading gingival proteoglycans, with ·OH species inducing greater degradative effects than H₂O₂ alone. Degradative effects were particularly manifested as amino acid modification, core protein cleavage, and GAG chain depolymerization. Proteoglycan core proteins were more susceptible to degradation than GAG chains with H₂O₂ alone, although core proteins and GAG chains were both extensively degraded by ·OH species. Proteoglycan exposure to ·OH species for 24 h induced significant core protein amino acid modification, with decreases in glutamate, proline, isoleucine, and leucine; and concomitant increases in serine, glycine, and alanine residues. As clinical reports have previously highlighted proteoglycan core protein degradation during chronic gingivitis, whereas their sulfated GAG chains remain relatively intact, these findings potentially provide further evidence to implicate ROS in the pathogenesis of active gingivitis, complementing the enzymic mechanisms of periodontal tissue destruction already established.

Fluoride Alters Signaling Pathways Associated with the Initiation of Dentin Mineralization in Enamel Fluorosis Susceptible Mice

Fluoride can alter the formation of mineralized tissues, including enamel, dentin, and bone. Dentin fluorosis occurs in tandem with enamel fluorosis. However, the pathogenesis of dentin fluorosis and its mechanisms are poorly understood. In this study, we report the effects of fluoride on the initiation of dentin matrix formation and odontoblast function. Mice from two enamel fluorosis susceptible strains (A/J and C57BL/6J) were given either 0 or 50 ppm fluoride in drinking water for 4 weeks. In both mouse strains, there was no overall change in dentin thickness, but fluoride treatment resulted in a significant increase in the thickness of the predentin layer. The lightly mineralized layer (LL), which lies at the border between predentin and fully mineralized dentin and is associated with dentin phosphoprotein (DPP), was absent in fluoride exposed mice. Consistent with a possible reduction of DPP, fluoride-treated mice showed reduced immunostaining for dentin sialoprotein (DSP). Fluoride reduced RUNX2, the transcription regulator of dentin sialophosphoprotein (DSPP), that is cleaved to form both DPP and DSP. In fluoride-treated mouse odontoblasts, the effect of fluoride was further seen in the upstream of RUNX2 as the reduced nuclear translocation of β-catenin and phosphorylated p65/NFκB. In vitro, MD10-F2 pre-odontoblast cells showed inhibition of the Dspp mRNA level in the presence of 10 μM fluoride, and qPCR analysis showed a significantly downregulated level of mRNAs for RUNX2, β-catenin, and Wnt10b. These findings indicate that in mice, systemic exposure to excess fluoride resulted in reduced Wnt/β-catenin signaling in differentiating odontoblasts to downregulate DSPP production via RUNX2.

An ex vivo culture model for orthodontically induced root resorption

OBJECTIVES

Root resorption is a ubiquitous although undesirable sequela to orthodontic treatment. Current methods to investigate the pathophysiology have certain limitations. In pursuit to understand and develop treatment modalities for orthodontically induced root resorption, the ability to manipulate cells within their natural extracellular matrix in a three dimensional organotypic model is invaluable. The study aimed to develop a laboratory-based organotypic model to investigate the effect of orthodontic forces on the periodontium.

METHODS

Mandibular slices of male Wistar rats were maintained in Trowel-typed cultures at 37°C in 5% carbon dioxide in air for 7 days with test specimens subjected to compressive forces at 50 g and 100g by stainless steel springs. Tissue architecture and cell viability were maintained under culture conditions.

RESULTS

Osteoclast numbers increased significantly in both test groups whilst odontoclasts increased in the 50 g group. Immunohistochemistry demonstrated increased dentine sialoprotein expression in both test groups, suggesting changes in mineralization-related activity due to mechanical strain.

CONCLUSION

The study showed initial cellular and molecular changes of key markers that relate to root resorption in response to mechanical loading.

CLINICAL SIGNIFICANCE

Severe root resorption may occur when forces applied are heavy or transmitted over an extended period and could lead to mobility and tooth loss. This ex vivo model can be used to investigate cellular and molecular processes during orthodontic tooth movement which may advance the clinical management of root resorption.

Immunohistochemical and biochemical assay of versican in human sound predentine/dentine matrix

Aim of this study was to investigate the distribution of versican proteoglycan within the human dentine organic matrix by means of a correlative immunohistochemical analysis with field emission in-lens scanning electron microscope (FEI-SEM), transmission electron microscope (TEM), fluorescence microscope (FM) and biochemical assay. Specimens containing dentine and predentine were obtained from non carious human teeth and divided in three groups: 1) FEI-SEM group: sections were exposed to a pre-embedding immunohistochemical procedure; 2) TEM group: specimens were fixed, demineralised, embedded and submitted to a post-embedding immunohistochemical procedure; 3) FM group: sections mineralised and submitted to a pre-embedding immunohistochemical procedure with fluorescence labelling. Specimens were exposed to two different antibodies to assay distribution of versican fragments and whole versican molecule.Western Blotting analysis of dentine and pulp extracts was also performed. The correlative FEI-SEM,TEM and FM analysis revealed positive immunoreaction for versican fragments both in predentine and dentine, while few gold particles identifying the whole versican molecule were found in predentine only under TEM. No labelling of versican whole molecule was detected by FEI-SEM and FM analysis. The immunoblotting analysis confirmed the morphological findings. This study suggests that in fully developed human teeth versican fragments are significant constituents of the human dentine and predentine organic matrix, while versican whole molecule can be visualised in scarce amount within predentine only. The role of versican fragments within human dentine organic matrix should be further elucidated.

Fluoride at non-toxic dose affects odontoblast gene expression in vitro

Elevated fluoride intake may lead to local tissue disturbances, known as fluorosis. Towards an understanding of this effect, fluoride-induced molecular responses were analyzed in MO6-G3 cultured odontoblasts cells. NaF at 1mM changed expression of genes implicated in tissue formation and growth, without affecting cell proliferation or inducing stress factor RNAs. Up to 1mM NaF, DNA accumulation was not inhibited, whereas at 3mM, cells detached from their support and did not proliferate. Intracellular structures, characterized by EM, were normal up to 1mM, but at 3mM, necrotic features were evident. No sign of apoptotic transformation appeared at any NaF concentration. Fluoride-sensitive genes were identified by microarray analysis; expression levels of selected RNAs were determined by conventional and real-time RT-PCR. At 1mM fluoride, RNAs encoding the extracellular matrix proteins asporin and fibromodulin, and the cell membrane associated proteins periostin and IMT2A were 10-fold reduced. RNA coding for signaling factor TNF-receptor 9 was diminished to one-third, whereas that for the chemokine Scya-5 was enhanced 2.5-fold. These RNAs are present in vivo in tooth forming cells. This was demonstrated by in situ hybridization and RT-PCR on RNA from dissected tissue samples; for the presence and functioning of fibromodulin in dentin matrix, a more comprehensive study has earlier been performed by others [Goldberg, M., Septier, D., Oldberg, A., Young, M.F., Ameye, L.G., 2006. Fibromodulin deficient mice display impaired collagen fibrillogenesis in predentin as well as altered dentin mineralization and enamel formation. J. Histochem. Cytochem. 54, 525-537]. Expression of most other RNA species, in particular of stress factor coding RNAs, was not altered. It was concluded that fluoride could influence the transcription pattern without inducing cell stress or apoptosis. In odontoblasts in vivo, aberrant expression of these fluoride-sensitive genes may impair the formation of the extracellular matrix and influence cell communication, with the possible consequence of fluorotic patterns of normal and deviant dentin.

Dentin in severe fluorosis: a quantitative histochemical study

Dentin responds to different alterations in the enamel with hypermineralization, and is a biomarker of fluoride exposure. We hypothesized that severe fluorosis would lead to hypermineralization of the dentin when the enamel was severely affected. We used scanning electron microscopy and quantitative electron-probe microanalysis to compare dentin and enamel from healthy and fluorotic teeth. The dentin in fluorotic teeth was characterized by a highly mineralized sclerotic pattern, in comparison with control teeth (p < 0.001) and fluorotic enamel lesions (p < 0.001). Enamel near the lesions showed hypercalcification in comparison with dentin (p < 0.001). In response to the effects of severe fluorosis in the enamel, the dentin showed hypermineralization, as found in other enamel disorders. The hypermineralization response of the dentin in our samples suggests that the mechanism of the response should be taken into account in dental caries and other dental disorders associated with severe fluorosis.

Immunohistochemical identification of decorin and biglycan in human dentin: a correlative field emission scanning electron microscopy/transmission electron microscopy study

Decorin and biglycan, two small leucine-rich proteoglycans, have been proposed to play important roles in matrix-mediated formation of mineralized tissues, and their three-dimensional arrangement in human dentin is still not completely understood. The aim of this study was to immunohistochemically analyze the distribution of decorin and biglycan in human predentin/dentin organic matrix under a high-resolution field emission in-lens scanning electron microscope (FEI-SEM) and a transmission electron microscope (TEM). Tooth dentin specimens were submitted to either a preembedding or a postembedding immunolabeling technique using primary antibodies antidecorin and antibiglycan and gold-conjugated secondary antibodies. Correlative FEI-SEM/TEM observations showed that the two antibodies yielded a similar labeling pattern over the processes of odontoblasts and the predentin. Decorin and biglycan were mainly associated with the collagen fibers within the predentin layer, revealing a moderate immunoreaction that was significantly higher compared to the one observed on dentin. Thus, a generally weak labeling for decorin was found in dentin, which, however, was significantly higher on odontoblast processes within dentinal tubules than in intertubular dentin. On the other hand, biglycan immunolocalization on dentin revealed few gold particles rather uniformly distributed, without showing significant differences between tubular and intertubular regions. In conclusion, this study reveals distinct distribution patterns of decorin and biglycan and their relation with collagen. Decorin's and biglycan's precise roles within prematrix and mineralized matrix in human teeth should be further clarified.