The proteoglycans of human cementum: immunohistochemical localization in healthy, periodontally involved and ageing teeth

Matrix Metalloproteinases in the Periodontium-Vital in Tissue Turnover and Unfortunate in Periodontitis

The extracellular matrix (ECM) is a complex non-cellular three-dimensional macromolecular network present within all tissues and organs, forming the foundation on which cells sit, and composed of proteins (such as collagen), glycosaminoglycans, proteoglycans, minerals, and water. The ECM provides a fundamental framework for the cellular constituents of tissue and biochemical support to surrounding cells. The ECM is a highly dynamic structure that is constantly being remodeled. Matrix metalloproteinases (MMPs) are among the most important proteolytic enzymes of the ECM and are capable of degrading all ECM molecules. MMPs play a relevant role in physiological as well as pathological processes; MMPs participate in embryogenesis, morphogenesis, wound healing, and tissue remodeling, and therefore, their impaired activity may result in several problems. MMP activity is also associated with chronic inflammation, tissue breakdown, fibrosis, and cancer invasion and metastasis. The periodontium is a unique anatomical site, composed of a variety of connective tissues, created by the ECM. During periodontitis, a chronic inflammation affecting the periodontium, increased presence and activity of MMPs is observed, resulting in irreversible losses of periodontal tissues. MMP expression and activity may be controlled in various ways, one of which is the inhibition of their activity by an endogenous group of tissue inhibitors of metalloproteinases (TIMPs), as well as reversion-inducing cysteine-rich protein with Kazal motifs (RECK).

Control of tissue homeostasis by the extracellular matrix: Synthetic heparan sulfate as a promising therapeutic for periodontal health and bone regeneration

Proteoglycans are core proteins associated with carbohydrate/sugar moieties that are highly variable in disaccharide composition, which dictates their function. These carbohydrates are named glycosaminoglycans, and they can be attached to proteoglycans or found free in tissues or on cell surfaces. Glycosaminoglycans such as hyaluronan, chondroitin sulfate, dermatan sulfate, keratan sulfate, and heparin/heparan sulfate have multiple functions including involvement in inflammation, immunity and connective tissue structure, and integrity. Heparan sulfate is a highly sulfated polysaccharide that is abundant in the periodontium including alveolar bone. Recent evidence supports the contention that heparan sulfate is an important player in modulating interactions between damage associated molecular patterns and inflammatory receptors expressed by various cell types. The structure of heparan sulfate is reported to dictate its function, thus, the utilization of a homogenous and structurally defined heparan sulfate polysaccharide for modulation of cell function offers therapeutic potential. Recently, a chemoenzymatic approach was developed to allow production of many structurally defined heparan sulfate carbohydrates. These oligosaccharides have been studied in various pathological inflammatory conditions to better understand their function and their potential application in promoting tissue homeostasis. We have observed that specific size and sulfation patterns can modulate inflammation and promote tissue maintenance including an anabolic effect in alveolar bone. Thus, new evidence provides a strong impetus to explore heparan sulfate as a potential novel therapeutic agent to treat periodontitis, support alveolar bone maintenance, and promote bone formation.

Orthodontic tooth movement alters cementocyte ultrastructure and cellular cementum proteome signature

Cementum is a mineralized tissue that covers tooth roots and functions in the periodontal attachment complex. Cementocytes, resident cells of cellular cementum, share many characteristics with osteocytes, are mechanoresponsive cells that direct bone remodeling based on changes in loading. We hypothesized that cementocytes play a key role during orthodontic tooth movement (OTM). To test this hypothesis, we used 8-week-old male Wistar rats in a model of OTM for 2, 7, or 14 days (0.5 N), whereas unloaded contralateral teeth served as controls. Tissue and cell responses were analyzed by high-resolution micro-computed tomography, histology, tartrate-resistant acid phosphatase staining for odontoclasts/osteoclasts, and transmission electron microscopy. In addition, laser capture microdissection was used to collect cellular cementum, and extracted proteins were identified by liquid chromatography coupled to tandem mass spectrometry. The OTM model successfully moved first molars mesially more than 250 μm by 14 days introducing apoptosis in a small number of cementocytes and areas of root resorption on mesial and distal aspects. Cementocytes showed increased nuclear size and proportion of euchromatin suggesting cellular activity. Proteomic analysis identified 168 proteins in cellular cementum with 21 proteins found only in OTM sites and 54 proteins only present in control samples. OTM-down-regulated several extracellular matrix proteins, including decorin, biglycan, asporin, and periostin, localized to cementum and PDL by immunostaining. Furthermore, type IV collagen (COL14A1) was the protein most down-regulated (-45-fold) by OTM and immunolocalized to cells at the cementum-dentin junction. Eleven keratins were significantly increased by OTM, and a pan-keratin antibody indicated keratin localization primarily in epithelial remnants of Hertwig's epithelial root sheath. These experiments provide new insights into biological responses of cementocytes and cellular cementum to OTM.

Proteoglycans in the periodontium: A review with emphasis on specific distributions, functions, and potential applications

Proteoglycans (PGs) are largely glycosylated proteins, consisting of a linkage sugar, core proteins, and glycosaminoglycans (GAGs). To date, more than 40 kinds of PGs have been identified, and they can be classified as intracellular, cell surface, pericellular, and extracellular PGs according to cellular locations. To illustrate, extracellular PGs are known for regulating the homeostasis of the extracellular matrix; cell-surface PGs play a role in mediating cell adhesion and binding various growth factors. In the field of periodontology, PGs are implicated in cellular proliferation, migration, adhesion, contractility, and anoikis, thereby exerting a profound influence on periodontal tissue development, wound repair, the immune response, biomechanics, and pathological process. Additionally, the expression patterns of some PGs are dynamic and cell-specific. Therefore, determining the roles and spatial-temporal expression patterns of PGs in the periodontium could shed light on treatments for wound healing, tissue regeneration, periodontitis, and gingival overgrowth. In this review, close attention is paid to the distributions, functions, and potential applications of periodontal PGs. Related genetically modified animal experiments and involved signal transduction cascades are summarized for improved understanding of periodontal PGs. To date, however, there is a large amount of speculation on this topic that requires rigorous experiments for validation.

Comparative proteomic analysis of dental cementum from deciduous and permanent teeth

BACKGROUND AND OBJECTIVES

Dental cementum (DC) is a mineralized tissue covering tooth roots that plays a critical role in dental attachment. Differences in deciduous vs. permanent tooth DC have not been explored. We hypothesized that proteomic analysis of DC matrix would identify compositional differences in deciduous (DecDC) vs. permanent (PermDC) cementum that might reflect physiological or pathological differences, such as root resorption that is physiological in deciduous teeth but can be pathological in the permanent dentition.

METHODS

Protein extracts from deciduous (n = 25) and permanent (n = 12) teeth were pooled (five pools of DecDC, five teeth each; four pools of PermDC, three teeth each). Samples were denatured, and proteins were extracted, reduced, alkylated, digested, and analyzed by liquid chromatography-mass spectrometry (LC-MS/MS). The beta-binomial statistical test was applied to normalized spectrum counts with 5% significance level to determine differentially expressed proteins. Immunohistochemistry was used to validate selected proteins.

RESULTS

A total of 510 proteins were identified: 123 (24.1%) exclusive to DecDC; 128 (25.1%) exclusive to PermDC; 259 (50.8%) commonly expressed in both DecDC and PermDC. Out of 60 differentially expressed proteins, 17 (28.3%) were detected in DecDC, including myeloperoxidase (MPO), whereas 43 (71.7%) were detected in PermDC, including decorin (DCN) and osteocalcin (BGLAP). Overall, Gene Ontology (GO) analysis indicated that all expressed proteins were related to GO biological processes that included localization and response to stress, and the GO molecular function of differentially expressed proteins was enriched in cell adhesion, molecular binding, cytoskeletal protein binding, structural molecular activity, and macromolecular complex binding. Immunohistochemistry confirmed the trends for selected differentially expressed proteins in human teeth.

CONCLUSIONS

Clear differences were found between the proteomes of DecDC and PermDC. These findings may lead to new insights into developmental differences between DecDC and PermDC, as well as to a better understanding of physiological/pathological events such as root resorption.

Glycosaminoglycans accelerate biomimetic collagen mineralization in a tissue-based in vitro model

Mammalian teeth are attached to the jawbone through an exquisitely controlled mineralization process: unmineralized collagen fibers of the periodontal ligament anchor directly into the outer layer of adjoining mineralized tissues (cementum and bone). The sharp interface between mineralized and nonmineralized collagenous tissues makes this an excellent model to study the mechanisms by which extracellular matrix macromolecules control collagen mineralization. While acidic phosphoproteins, localized in the mineralized tissues, play key roles in control of mineralization, the role of glycosaminoglycans (GAGs) is less clear. As several proteoglycans are found only in the periodontal ligament, it has been hypothesized that these inhibit mineralization of collagen in this tissue. Here we used an in vitro model based on remineralization of mouse dental tissues to determine the role of matrix GAGs in control of mineralization. GAGs were selectively removed from demineralized mouse periodontal sections via enzymatic digestion. Proteomic analysis confirmed that enzymatic GAG removal does not significantly alter protein content. Analysis of remineralized tissue sections by transmission electron microscopy (TEM) shows that GAG removal reduced the rate of remineralization in mineralized tissues compared to the untreated control, while the ligament remained unmineralized. Protein removal with trypsin also reduced the rate of mineralization, but to a lesser extent than GAG removal, despite a much larger effect on protein content. These results indicate that GAGs promote mineralization in mineralized dental tissues rather than inhibiting mineral formation in the ligament, which may have broader implications for understanding control of collagen mineralization in connective tissues.

Incremental distribution of strontium and zinc in great ape and fossil hominin cementum using synchrotron X-ray fluorescence mapping

Cementum and the incremental markings it contains have been widely studied as a means of ageing animals and retrieving information about diet and nutrition. The distribution of trace elements in great ape and fossil hominin cementum has not been studied previously. Synchrotron X-ray fluorescence (SXRF) enables rapid scanning of large tissue areas with high resolution of elemental distributions. First, we used SXRF to map calcium, phosphorus, strontium and zinc distributions in great ape dentine and cementum. At higher resolution, we compared zinc and strontium distributions in cellular and acellular cementum in regions where clear incremental markings were expressed. We then mapped trace element distributions in fossil hominin dentine and cementum from the 1.55-1.65 million year old site of Koobi Fora, Kenya. Zinc, in particular, is a precise marker of cementum increments in great apes, and is retained in fossil hominin cementum, but does not correspond well with the more diffuse fluctuations observed in strontium distribution. Cementum is unusual among mineralized tissues in retaining so much zinc. This is known to reduce the acid solubility of hydroxyapatite and so may confer resistance to resorption by osteoclasts in the dynamic remodelling environment of the periodontal ligament and alveolar bone.

Are Cementoblasts a Subpopulation of Osteoblasts or a Unique Phenotype?

Experimental studies have shown a great potential for periodontal regeneration. The limitations of periodontal regeneration largely depend on the regenerative potential at the root surface. Cellular intrinsic fiber cementum (CIFC), so-called bone-like tissue, may form instead of the desired acellular extrinsic fiber cementum (AEFC), and the interfacial tissue bonding may be weak. The periodontal ligament harbors progenitor cells that can differentiate into periodontal ligament fibroblasts, osteoblasts, and cementoblasts, but their precise location is unknown. It is also not known whether osteoblasts and cementoblasts arise from a common precursor cell line, or whether distinct precursor cell lines exist. Thus, there is limited knowledge about how cell diversity evolves in the space between the developing root and the alveolar bone. This review supports the hypothesis that AEFC is a unique tissue, while CIFC and bone share some similarities. Morphologically, functionally, and biochemically, however, CIFC is distinctly different from any bone type. There are several lines of evidence to propose that cementoblasts that produce both AEFC and CIFC are unique phenotypes that are unrelated to osteoblasts. Cementum attachment protein appears to be cementum-specific, and the expression of two proteoglycans, fibromodulin and lumican, appears to be stronger in CIFC than in bone. A theory is presented that may help explain how cell diversity evolves in the periodontal ligament. It proposes that Hertwig’s epithelial root sheath and cells derived from it play an essential role in the development and maintenance of the periodontium. The role of enamel matrix proteins in cementoblast and osteoblast differentiation and their potential use for tissue engineering are discussed.

Histology of human cementum: Its structure, function, and development

Cementum was first demonstrated by microscopy, about 180 years ago. Since then the biology of cementum has been investigated by the most advanced techniques and equipment at that time in various fields of dental sciences. A great deal of data on cementum histology have been accumulated. These data have been obtained from not only human, but also non-human animals, in particular, rodents such as the mouse and rat. Although many dental histologists have reviewed histology of human cementum, some descriptions are questionable, probably due to incorrect comparison of human and rodent cementum. This review was designed to introduce current histology of human cementum, i.e. its structure, function, and development and to re-examine the most questionable and controversial conclusions made in previous reports.

Global proteome profiling of dental cementum under experimentally-induced apposition

Dental cementum (DC) covers the tooth root and has important functions in tooth attachment and position. DC can be lost to disease, and regeneration is currently unpredictable due to limited understanding of DC formation. This study used a model of experimentally-induced apposition (EIA) in mice to identify proteins associated with new DC formation. Mandibular first molars were induced to super-erupt for 6 and 21days after extracting opposing maxillary molars. Decalcified and formalin-fixed paraffin-embedded mandible sections were prepared for laser capture microdissection. Microdissected protein extracts were analyzed by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS), and the data submitted to repeated measure ANOVA test (RM-ANOVA, alpha=5%). A total of 519 proteins were identified, with 97 (18.6%) proteins found exclusively in EIA sites and 50 (9.6%) proteins exclusively expressed in control sites. Fifty six (10.7%) proteins were differentially regulated by RM-ANOVA (p<0.05), with 24 regulated by the exclusive effect of EIA (12 proteins) or the interaction between EIA and time (12 proteins), including serpin 1a, procollagen C-endopeptidase enhancer, tenascin X (TNX), and asporin (ASPN). In conclusion, proteomic analysis demonstrated significantly altered protein profile in DC under EIA, providing new insights on DC biology and potential candidates for tissue engineering applications.

SIGNIFICANCE

Dental cementum (DC) is a mineralized tissue that covers the tooth root surface and has important functions in tooth attachment and position. DC and other periodontal tissues can be lost to disease, and regeneration is currently unpredictable due to lack of understanding of DC formation. This study used a model of experimentally-induced apposition (EIA) in mice to promote new cementum formation, followed by laser capture microdissection (LCM) and liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) proteomic analysis. This approach identified proteins associated with new cementum formation that may be targets for promoting cementum regeneration.

Effect of proteoglycans at interfaces as related to location, architecture, and mechanical cues

INTRODUCTION

Covalently bound functional GAGs orchestrate tissue mechanics through time-dependent characteristics.

OBJECTIVE

The role of specific glycosaminoglycans (GAGs) at the ligament-cementum and cementum-dentin interfaces within a human periodontal complex were examined. Matrix swelling and resistance to compression under health and modeled diseased states was investigated.

MATERIALS AND METHODS

The presence of keratin sulfate (KS) and chondroitin sulfate (CS) GAGs at the ligament-cementum and cementum-dentin interfaces in human molars (N=5) was illustrated by using enzymes, atomic force microscopy (AFM), and AFM-based nanoindentation. The change in physical characteristics of modeled diseased states through sequential digestion of keratin sulfate (KS) and chondroitin sulfate (CS) GAGs was investigated. One-way ANOVA tests with P<0.05 were performed to determine significant differences between groups. Additionally, the presence of mineral within the seemingly hygroscopic interfaces was investigated using transmission electron microscopy.

RESULTS

Immunohistochemistry (N=3) indicated presence of biglycan and fibromodulin small leucine rich proteoglycans at the interfaces. Digestion of matrices with enzymes confirmed the presence of KS and CS GAGs at the interfaces by illustrating a change in tissue architecture and mechanics. A significant increase in height (nm), decrease in elastic modulus (GPa), and tissue deformation rate (nm/s) of the PDL-C attachment site (215±63-424±94nm; 1.5±0.7-0.4±0.2GPa; 21±7-48±22nm/s), and cementum-dentin interface (122±69-360±159nm; 2.9±1.3-0.7±0.3GPa; 18±4-30±6nm/s) was observed.

CONCLUSIONS

The sequential removal of GAGs indicated loss in intricate structural hierarchy of hygroscopic interfaces. From a mechanics perspective, GAGs provide tissue recovery/resilience. The results of this study provide insights into the role of GAGs toward conserved tooth movement in the socket in response to mechanical loads, and modulation of potentially deleterious strain at tissue interfaces.

Fibromodulin and Biglycan Modulate Periodontium through TGFβ/BMP Signaling

A full understanding of the key regulators controlling periodontal development and homeostasis is necessary for the design of improved periodontal regenerative therapies. Small leucine-rich proteoglycans (SLRPs) are extracellular matrix molecules suggested to regulate collagen organization and cell signaling. Mice with double-deficiency of 2 SLRPs, fibromodulin and biglycan (dKO), acquire skeletal abnormalities, but their roles in regulating the periodontium remain undefined and were the focus of our studies. Transmission electron microscopy studies showed abnormal collagen fibrils in the periodontal ligament (PDL) and altered remodeling of alveolar bone in dKO mice. Immunohistochemistry (IHC) revealed increased staining of SLRPs (asporin, lumican, and decorin) and dentin matrix protein-1 (DMP1, a mechanosensory/osteocyte marker), while osteoblast markers, bone sialoprotein and osteopontin, remained unchanged. Disruption of homeostasis was further evidenced by increased expression of receptor-activator of nuclear factor-κB ligand (RANKL) and elevated numbers of osteoclasts, especially noted around the alveolar bone of molars (buccal side) and incisors. Polymerase chain reaction (PCR) array revealed hyperactive transforming growth factors beta/bone morphogenetic protein (TGFβ/BMP) signaling in dKO PDL tissues, which was further confirmed by elevated expression of phosphorylated Smad5 (p-Smad5) by IHC in dKO PDL. These studies highlight the importance of SLRPs in maintaining periodontal homeostasis through regulation of TGFβ/BMP signaling, matrix turnover, and collagen organization.

Biomechanical adaptation of the bone-periodontal ligament (PDL)-tooth fibrous joint as a consequence of disease

In this study, an in vivo ligature-induced periodontitis rat model was used to investigate temporal changes to the solid and fluid phases of the joint by correlating shifts in joint biomechanics to adaptive changes in soft and hard tissue morphology and functional space. After 6 and 12 weeks of ligation, coronal regions showed a significant decrease in alveolar crest height, increased expression of TNF-α, and degradation of attachment fibers as indicated by decreased collagen birefringence. Cyclical compression to peak loads of 5-15N at speeds of 0.2-2.0mm/min followed by load relaxation tests showed decreased stiffness and reactionary load rate values, load relaxation, and load recoverability, of ligated joints. Shifts in joint stiffness and reactionary load rate increased with time while shifts in joint relaxation and recoverability decreased between control and ligated groups, complementing measurements of increased tooth displacement as evaluated through digital image correlation. Shifts in functional space between control and ligated joints were significantly increased at the interradicular (Δ10-25μm) and distal coronal (Δ20-45μm) regions. Histology revealed time-dependent increases in nuclei elongation within PDL cells and collagen fiber alignment, uncrimping, and directionality, in 12-week ligated joints compared to random orientation in 6-week ligated joints and to controls. We propose that altered strains from tooth hypermobility could cause varying degrees of solid-to-fluid compaction, alter dampening characteristics of the joint, and potentiate increased adaptation at the risk of joint failure.

Proteomic analysis of human dental cementum and alveolar bone

Dental cementum (DC) is a bone-like tissue covering the tooth root and responsible for attaching the tooth to the alveolar bone (AB) via the periodontal ligament (PDL). Studies have unsuccessfully tried to identify factors specific to DC versus AB, in an effort to better understand DC development and regeneration. The present study aimed to use matched human DC and AB samples (n=7) to generate their proteomes for comparative analysis. Bone samples were harvested from tooth extraction sites, whereas DC samples were obtained from the apical root portion of extracted third molars. Samples were denatured, followed by protein extraction reduction, alkylation and digestion for analysis by nanoAcquity HPLC system and LTQ-FT Ultra. Data analysis demonstrated that a total of 318 proteins were identified in AB and DC. In addition to shared proteins between these tissues, 105 and 83 proteins exclusive to AB or DC were identified, respectively. This is the first report analyzing the proteomic composition of human DC matrix and identifying putative unique and enriched proteins in comparison to alveolar bone. These findings may provide novel insights into developmental differences between DC and AB, and identify candidate biomarkers that may lead to more efficient and predictable therapies for periodontal regeneration.

BIOLOGICAL SIGNIFICANCE

Periodontal disease is a highly prevalent disease affecting the world population, which involves breakdown of the tooth supporting tissues, the periodontal ligament, alveolar bone, and dental cementum. The lack of knowledge on specific factors that differentiate alveolar bone and dental cementum limits the development of more efficient and predictable reconstructive therapies. In order to better understand cementum development and potentially identify factors to improve therapeutic outcomes, we took the unique approach of using matched patient samples of dental cementum and alveolar bone to generate and compare a proteome list for each tissue. A potential biomarker for dental cementum was identified, superoxide dismutase 3 (SOD3), which is found in cementum and cementum-associated cells in mouse, pig, and human tissues. These findings may provide novel insights into developmental differences between alveolar bone and dental cementum, and represent the basis for improved and more predictable therapies.

Ultrastructural immunolocalization of dentin matrix protein 1 on Sharpey's fibers in monkey tooth cementum

Despite the importance of dentin matrix protein 1 (DMP1) in the formation of mineralized tissue, including dentinogenesis and osteogenesis, its precise role in cementogenesis remains to be clarified fully. The purpose of our study was to demonstrate the ultrastructural immunolocalization of DMP1 in monkey molar tooth cementum. Japanese Macaca fuscata monkeys were fixed by perfusion. The upper molar teeth and accompanying periodontium then were dissected and demineralized with EDTA. Cryosections were obtained, incubated in anti-DMP1 polyclonal antibody, and processed by immunoperoxidase and immunogold labeling. Intense immunoperoxidase staining for DMP1 was observed in acellular extrinsic fiber cementum, particularly in Sharpey's fibers. Cementocyte lacunae with canaliculi showed DMP1 staining in the apical region of the tooth root. Electron immunomicroscopy revealed the close proximity of DMP1 to collagen fibrils in Sharpey's fibers at the mineralization front. Intense immunogold labeling was localized on the walls of the cementocyte lacunae in cellular cementum. These results should contribute to better understanding of the role of DMP1, not only in Sharpey's fiber biomineralization, but also in the maintenance of the cementocyte lacunar space in cementum.

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.

An immunohistochemical study of the extracellular matrix of entheses associated with the human pisiform bone

The immunohistochemical labelling patterns of the extracellular matrix at the insertion of the flexor carpi ulnaris tendon and the entheses at both ends of the pisometacarpal and pisohamate ligaments were compared in order to relate the molecular composition of the attachment sites to their mechanical environment. Tissue was obtained from elderly dissecting room cadavers and labelled with a panel of monoclonal antibodies directed against collagens, glycosaminoglycans, proteoglycans and matrix proteins. All entheses were fibrocartilaginous and labelled positively for molecules typically associated with articular cartilage (type II collagen, chondroitin 6 sulphate, aggrecan and link protein). Labelling for type II collagen was most conspicuous at the attachment of the flexor carpi ulnaris tendon. In the ligaments, type II collagen labelling was always greater at the pisiform end. Matrilin 1 was universally present at all five entheses examined and fibromodulin labelling was most intense around the tidemark. Fibromodulin may thus be involved in anchorage and/or the control of mineralization at the hard-soft tissue interface of entheses. The greater prominence of fibrocartilage at the pisiform enthesis of the flexor carpi ulnaris tendon than at any ligament attachment may relate to the marked change in the tendon insertional angle that occurs with wrist movements. We also suggest that the more fibrocartilaginous character of the proximal compared with the distal ends of the ligaments relates to the fact that the pisiform is anchored in position and is thus at the centre of rotation of any movement of ligaments attached to it.

Confocal laser scanning microscopy of human cementocytes: Analysis of three-dimensional image reconstruction

In order to define a practical method for a quantitative-qualitative analysis of dental hard tissue cells, we have studied cementocytes of human teeth using Confocal Laser Scanning Microscopy (CLSM), a research technique based on laser light microscopic analysis of biological samples stained for fluorescence observation. One thousand and eight hundred cementocyte images were analyzed. CLSM allowed improved tissue imaging, bi-dimensional pictures with better resolution at cellular level and, in particular, the possibility of a three-dimensional image reconstruction, thus providing a dynamic view of the cell under different situations. CLSM allowed a careful morphological observation and dimensional analysis of cementocytes at cellular resolution: cementocyte dimensional parameters like cell body without cell processes, cell dimensions with cell processes, and the number of cellular processes could be obtained. In conclusion, this study reports the fine definition of cementocytes at microscopic level by CSLM and the results warrant the use of this technique for further comparative analyses between normal and pathological cementocyte cells, e.g. cementum neoplasia and periodontal disease which still await a clear analytical description at cellular level.

Immunohistochemical Study of Bone Sialoprotein and Osteopontin in Healthy and Diseased Root Surfaces

BACKGROUND

Periodontal disease is marked by inflammation and damage to tooth-supporting tissues. In particular, damage occurs to factors present in cementum that are thought to have the ability to influence the regeneration of surrounding tissues. Bone sialoprotein and osteopontin are major non-collagenous proteins in mineralized connective tissues associated with precementoblast chemo-attraction, adhesion to the root surface, and cell differentiation. The purpose of this investigation was to determine whether the expression and distribution of bone sialoprotein and osteopontin on root surfaces affected by periodontitis are altered compared to healthy, non-diseased root surfaces.

METHODS

Thirty healthy and 30 periodontitis-affected teeth were collected. Following fixation and demineralization, specimens were embedded in paraffin, sectioned, and exposed to antibodies against bone sialoprotein and osteopontin. Stained sections were assessed using light microscopy.

RESULTS

Bone sialoprotein was not detected in the exposed cementum (absence of overlying periodontal ligament) of diseased teeth. In most areas where the periodontal ligament was intact, bone sialoprotein was detected for healthy and diseased teeth. For teeth reactive for bone sialoprotein, the matrix of the cementum just below the periodontal ligament was moderately stained. A similar immunoreactivity pattern for osteopontin was observed.

CONCLUSIONS

The absence of bone sialoprotein and osteopontin staining along exposed cementum surfaces may be due to structural and compositional changes in matrix components associated with periodontal disease. This may influence the ability for regeneration and new connective tissue attachment onto previously diseased root surfaces.

Periodontal healing may be affected by aging: a histologic study in rats

BACKGROUND AND OBJECTIVE

Although wound healing has been reported to be impaired with aging, very little is known about its effect on periodontal tissues. Therefore, the aim of this study was to evaluate, histologically in rats, the influence of aging on a spontaneous periodontal healing model.

MATERIAL AND METHODS

Twenty-four male Wistar rats were used and assigned to the following groups: control (n = 12; 2 mo old) and aged (n = 12; 18 mo old). Fenestration defects (4 x 3 x 1 mm) were created bilaterally at the buccal aspect of the distal root of the first mandibular molars, and the mandibulae were retrieved 3 and 6 wk postoperatively. The percentage of bone fill and density of newly formed bone, new cementum formation (NC), and the extension of the remaining defect (ERD) were histometrically obtained.

RESULTS

Intragroup analysis demonstrated that, except for cementum, all histological parameters significantly improved over time (p < 0.05). Intergroup analysis additionally showed that the defects were initially similar in size, and that at 3 wk aging negatively influenced newly formed bone (86.38 +/- 2.99% and 73.06 +/- 3.21%, p < 0.001, for groups control and aged, respectively), BF (75.84 +/- 16.53% and 57.70 +/- 22.28%, p = 0.014) and ERD (0.41 +/- 0.20 mm and 1.17 +/- 0.37 mm, p < 0.001). At 6 wk, aging negatively influenced newly formed bone (88.12 +/- 2.90% and 78.19 +/- 5.35%, p < 0.001, for groups control and aged, respectively) and ERD (0.01 +/- 0.006 mm and 0.34 +/- 0.18 mm, p = 0.003), but not BF (98.15 +/- 2.43% and 87.87 +/- 11.63%, p > 0.05). No new cementum was formed along the root surface in the above groups.

CONCLUSION

Within the limits of the present study, data analysis suggests that aging may impair, but not prevent, periodontal healing.

Effect of Interleukin-1β on Transforming Growth Factor-Beta and Bone Morphogenetic Protein-2 Expression in Human Periodontal Ligament and Alveolar Bone Cells in Culture: Modulation by Avocado and Soybean Unsaponifiables

BACKGROUND

In periodontal disease, interleukin-1beta (IL-1beta) is responsible for the matrix breakdown through excessive production of degrading enzymes by periodontal ligament fibroblasts and osteoblasts. Transforming growth factor-beta (TGF-beta) plays an important role in tissue regeneration as one of the factors capable of counteracting IL-1beta effects. In this study, we investigated the in vitro effect of avocado and soya unsaponifiables (ASU) on the expression of TGF-beta1, TGF-beta2, and bone morphogenetic protein-2 (BMP-2) by human periodontal ligament (HPL) and human alveolar bone (HAB) cells in the presence of IL-1beta.

METHODS

HPL and HAB cells were incubated for 48 hours with ASU (10 microg/ml) in the presence or absence of IL-1beta (10 ng/ml). The steady-state levels of TGF-beta1, TGF-beta2, and BMP-2 mRNAs were determined by Northern blot or reverse transcription-polymerase chain reaction (RT-PCR). The amounts of TGF-beta1 and TGF-beta2 proteins were measured by enzyme-linked immunosorbent assay (ELISA).

RESULTS

The data indicated that IL-1beta strongly decreases the expression of TGF-beta1 and TGF-beta2 by HPL cells. ASU were capable of opposing the cytokine effect. In HAB cells, TGF-beta1 and BMP-2 mRNA levels were downregulated by the cytokine. ASU were found to reverse the IL-1beta-inhibiting effect. In contrast, the cytokine stimulated the production of TGF-beta2 in alveolar bone cells, with no significant effect of ASU.

CONCLUSIONS

The results indicate that the IL-1beta-driven erosive effect in periodontitis could be enhanced by a decreased expression of members of the TGF-beta family. The ASU stimulation of TGF-beta1, TGF-beta2, and BMP-2 expression may explain their promoting effects in the treatment of periodontal disorders, at least partly. These findings support the hypothesis that ASU could exert a preventive action on the deleterious effects exerted by IL-1beta in periodontal diseases.

Immunohistochemical localization of components of the insulin-like growth factor system in human permanent teeth

There is growing evidence that the insulin-like growth factor (IGF) system plays an important role in the biology of oro-dento-facial tissues and organs, including the development, homeostasis and regeneration of the periodontium. To obtain basic data on the occurrence and distribution of IGF components in human permanent teeth we immunohistochemically investigated 25 extracted, decalcified and paraffin-embedded teeth using mono and polyclonal antibodies against the ligands IGF-I and -II, the IGF1 receptor (IGF1R) and all six IGF binding proteins (IGFBP-1 to -6). In the extracellular matrix (ECM) of the adhering periodontal ligament (PDL), immunoreactivity for IGF-I, -II and IGFBP-1 and -6 was observed. PDL fibroblasts showed immunostaining for the IGF1R. For the cementum, in the acellular cementum only IGF-II could be detected, while outer cementum layers with inserting Sharpey's fibers reacted with all antibodies applied except for IGFBP-4 and -6. In the pulp, mainly fibrotic areas and areas around denticles were immunoreactive for IGF-I, IGFBP-1, -3, -5 and -6. Predentin and odontoblastic processes were stained for IGF-I and IGFBP-3. The spatially oriented occurrence of components of the IGF system in human permanent teeth indicates that specific functions of the IGFs may be localized in particular tissue compartments. In the cementum, several IGF components were found indicating roles in tissue homeostasis or attachment. The PDL may function as a reservoir for IGFs probably bound to ECM components. PDL fibroblasts could then respond in a paracrine manner. In the pulp, the IGF system may be involved in odontoblast biology, fibrosis and denticle formation.

The cementum-dentin junction also contains glycosaminoglycans and collagen fibrils

The presence of glycosaminoglycans (GAGs) and their contribution to mechanical properties of the cementum-dentin junction (CDJ) were investigated using nanometer scale characterization techniques. Five to two millimeter thick transverse sections from the apical ends of human molars were ultrasectioned at room temperature under wet conditions using a diamond knife and an ultramicrotome. The structure of the CDJ under dry and wet conditions before and after digestion of GAGs and collagen fibrils was studied using an atomic force microscope (AFM). The mechanical properties of the untreated and enzyme treated CDJ under wet conditions were studied using an AFM-based nanoindenter. GAG digestion was performed for 1, 3, and 5 h at 37 degrees C using chondroitinase-ABC. Collagen fibril digestion was performed for 24 and 48 h at 37 degrees C using collagenase. As reported previously, AFM scans of dry untreated CDJ (control) revealed a valley, which transformed into a peak under wet conditions. The height differences relative to cementum and dentin of untreated and treated CDJ were determined by measuring the CDJ profile under dry and wet conditions. The depth of the valley of GAG and collagen-digested CDJ was greater than that of undigested CDJ under dry conditions. The height of the peak of GAG-digested CDJ was significantly higher than that of the undigested CDJ under wet conditions. The collagen-digested CDJ under wet conditions is assumed to form a valley because of the removal of collagen fibrils from the CDJ. However, the depth of the valley was lower compared to the depth under dry conditions. Wet AFM-based nanoindentation showed that the elastic modulus and hardness of control (3.3+/-1.2 and 0.08+/-0.03 GPa) were significantly higher (ANOVA & SNK, P < 0.05) than chondroitinase-ABC treated CDJ (0.9+/-0.4 and 0.02+/-0.004 GPa) and collagenase treated CDJ (1.5+/-0.6 and 0.04+/-0.01 GPa). No significant difference in mechanical properties between chondroitinase-ABC and collagenase treated CDJ was observed. Based on the results it was concluded that the 10-50 microm wide CDJ is a composite that includes, chondroitin-4-sulfate, chondroitin-6-sulfate, and possibly dermatan sulfate, and collagen fibrils. The association of GAGs with the collagen fibrils provides the observed controlled hydration and partially contributes toward the stiffness of the CDJ under wet conditions.

Distinctive localization and function for lumican, fibromodulin and decorin to regulate collagen fibril organization in periodontal tissues

BACKGROUND

Small leucine-rich proteoglycans (SLRPs) decorin, biglycan, fibromodulin and lumican are secreted extracellular matrix molecules that associate with fibrillar collagens and regulate collagen fibrillogenesis. Collagens are the major extracellular matrix components of periodontal connective tissues where they provide mechanical attachment of the tooth to the bone and gingiva and mediate signals that regulate cell functions, including remodeling of the periodontal ligament and bone. Structural organization of collagen may also be important for the defense against periodontal disease, because in certain conditions abnormal collagen fibrils associate with increased susceptibility to periodontal disease.

OBJECTIVES

The purpose of this study was to find out the role of SLRPs to regulate collagen fibril and fibril bundle formation in periodontal tissues.

METHODS

The localization of SLRPs in human and mouse periodontal tissues was studied using immunohistochemical methods. To assess the function of SLRPs we studied periodontal tissues of mice harboring targeted deletions of decorin, fibromodulin or lumican genes and lumican and fibromodulin double knockout mice using histological and electronmicroscopical methods.

RESULTS

The SLRPs were coexpressed in human and mouse gingival and periodontal ligament connective tissues where they colocalized with collagen fibril bundles. Teeth in the knockout animals were fully erupted and showed normal gross morphology. Targeted deletion of decorin, fibromodulin, lumican or both lumican and fibromodulin resulted in abnormal collagen fibril and fibril bundle morphology that was most evident in the periodontal ligament. Each of the gene deletions resulted in a unique fibril and fibril bundle phenotype.

CONCLUSIONS

These findings indicate that decorin, fibromodulin and lumican coordinately regulate the fibrillar and suprafibrillar organization of collagen in the periodontal ligament.

Transcript Profiling of Periodontal Fibroblasts and Osteoblasts

BACKGROUND

Fibroblasts are critical to the establishment and maintenance of the periodontal attachment apparatus (cementum, periodontal ligament [PDL], and bone). In order to characterize the cellular changes that accompany periodontal regeneration, better tools are necessary to distinguish periodontal ligament fibroblasts (PDLF), gingival fibroblasts, and osteoblasts. Our goal is to identify gene markers to better characterize and identify these cell types.

METHODS

We chose to examine and compare the expression of numerous gene transcripts by semiquantitative reverse transcriptase-polymerase chain reaction using primers specific for 44 different gene transcripts in order to better characterize the identity of these cells.

RESULTS

Several transcripts were cell-type specific. Specifically, fibromodulin was expressed only in PDL fibroblasts, while osteopontin was expressed only in dermal fibroblasts. In addition, lumican was expressed by all three types of fibroblasts (PDL, gingival, and dermal), while alkaline phosphatase was expressed by osteoblasts as well as PDL and gingival fibroblasts.

CONCLUSIONS

Our results indicate that PDL fibroblasts are distinct from either gingival or dermal fibroblasts or osteoblasts. In general, PDL and gingival fibroblasts displayed greater similarity to each other than either displayed toward dermal fibroblasts. Furthermore, both gingival and PDL fibroblasts displayed greater similarity to osteoblasts than to dermal fibroblasts, possibly reflecting their common origin (the neural crest).

Expression of Versican and ADAMTS During Rat Tooth Eruption

A disintegrin and metalloprotease with thrombospondin type 1 motifs (ADAMTS) is a family of extracellular proteases and implicated in cleaving proteoglycans, such as aggrecan, versican and brevican. No information is available about expression or localization of these ADAMTSs in teeth. Versican is a large chondroitin sulfate proteoglycan that is present in a variety of connective tissue including dental pulp, dentin, cementum and periodontal ligaments. The present study was designed to investigate expression of ADAMTSs and versican during rat tooth eruption. Rat maxillary first molars in weeks 1, 2, 3, 4 and 6 were examined. The mRNA expression of ADAMTS1, ADAMTS4, ADAMTS5 and versican was localized using in situ hybridization. ADAMTS1, ADAMTS4, ADAMTS5 and versican were expressed in dental pulp cells, odontoblasts, cementoblasts, cementocytes, periodontal ligament cells, osteoblasts and osteocytes. The temporal and spatial expression pattern in these cellular phenotypes was comparable among ADAMTSs and versican. The present study suggests that dental pulp cells, odontoblasts, cementoblasts, cementocytes, periodontal ligament cells, osteoblasts and osteocytes may be involved in both production and degradation of versican with secreting ADAMTS1, ADAMTS4 and ADAMTS5.

GLUT1 is highly expressed in cementoblasts but not in osteoblasts

Cementum is a specialized mineralized tissue covering root surface of the tooth. Although the tissue's composition resembles bone, there are distinct structural and functional differences between the two mineralized tissues. In this study, the genes that are differentially expressed in putative cementoblasts (human cementum-derived cells [HCDCs]) compared with preosteoblastic cells (human bone marrow stromal cells [BMSCs]) were screened by two independent microarray systems, and some of the selected genes were further analyzed by quantitative real-time RT-PCR. The gene encoding glucose transporter 1 [GLUT1], which showed the greatest difference between the two groups by the latter analysis, was subjected to further analyses. High levels of the GLUT1 protein in HCDCs, but not in BMSCs, were detected by Western blotting and immunocytochemistry. Furthermore, intense immunoreactivities for GLUT1 were observed in cementoblasts and cementocytes but not in osteoblasts or osteocytes in human periodontal tissues. These results indicate that GLUT1 may play a role in cementogenesis and could serve as a biomarker to differentiate between cells of cementoblastic and osteoblastic lineage.

Immunohistochemical localization and expression of fibromodulin in adult rat periodontium and inflamed human gingiva

OBJECTIVE

The aim of this study was to determine the distribution and expression of fibromodulin in adult rat periodontal tissues and inflamed human gingiva.

MATERIALS AND METHODS

The distribution of fibromodulin in rat molar periodontium and human gingival tissue was studied by immunohistochemistry. The expression of fibromodulin mRNA from human gingival fibroblasts, periodontal ligament fibroblasts and osteoblasts was studied by reverse transcription-polymerase chain reaction (RT-PCR). For comparative purposes, the distribution and mRNA expression of collagen types I and III, as well as the two small leucine-rich proteoglycans decorin and biglycan were also studied.

RESULTS

In the adult rat periodontium, fibromodulin was distributed in the suprabasal gingival epithelium, gingival and periodontal fibroblasts as well as their surrounding extracellular matrices. Strong expression was noted in the palatal gingival tissues and the interfaces of the periodontal ligament with alveolar bone and cementum. In human gingival tissues, staining of fibromodulin was detected in the connective tissue of inflamed gingiva associated with both gingivitis and periodontitis; whereas, weak staining for this molecule was noted in healthy gingival tissues. The expression of mRNA for fibromodulin was strongest in the cultured osteoblasts. Periodontal ligament fibroblasts showed only a weak level of expression for fibromodulin mRNA.

CONCLUSIONS

Fibromodulin is differentially expressed throughout the periodontium being primarily associated with collagen type I in non-mineralized sites. In addition fibromodulin showed an upregulation in inflamed gingival tissue.

The effect of sample preparation technique on determination of structure and nanomechanical properties of human cementum hard tissue

The mechanical properties of a tissue can be evaluated by determining the response of the structure to mechanical loading. This can be accomplished only when the tissue has been prepared with minimum to no artifacts, thus preserving its structure. In this study it was hypothesized that the structure of cementum is inhomogeneous, contributing to a significant variation in mechanical properties of cementum. Therefore, the goals of the study were to identify potential artifacts generated by conventional sample preparation techniques such as polishing and ultrasectioning and subsequently characterize the prepared specimens using an atomic force microscope (AFM) and an AFM-nanoindenter. Comparisons between cryofractured, ultrasectioned and polished specimens concluded that ultrasectioned surfaces have significantly lower average surface roughness 'R(a)' (p<0.05). Microstructure of ultrasectioned specimens characterized using an AFM illustrated Sharpey's fibers (SF) and intrinsic fibers (IF) running perpendicular and parallel to the root surface similar to the observed microstructure of cryofractured cementum. In addition, a 10-50 microm wide cementum dentin junction (CDJ) was distinctly observed in the ultrasectioned specimens but not in polished specimens. The SF and CDJ illustrated relatively higher levels of hydrophilicity under wet conditions. The observed inhomogeneous microstructure of the ultrasectioned specimens led to a broader range of nanomechanical properties (modulus: 14.2-25.9 GPa; hardness: 0.48-1.09 GPa). However, masking of the same regions such as SF and CDJ due to smeared cementum in polished specimens resulted in a narrower range of nanomechanical properties (modulus: 18.2-20.8 GPa; hardness: 0.79-0.89 GPa). This effect is most noticeable under wet conditions for ultrasectioned specimens (modulus 2.6-10.9 GPa; hardness 0.05-0.30 GPa) compared to the polished specimens (modulus 12.2-14.5 GPa; hardness 0.33-0.45 GPa). Cementum also was shown to be highly viscoelastic, especially when hydrated. The results suggest ultrasectioning of cementum was superior to polishing preparation technique since it allowed visualization of cementum structures similar to cryofractured specimens while providing a flat surface necessary for AFM-based nanoindentation techniques. Additionally, the structural inhomogeneity observed within ultrasectioned cementum contributed to a broader range of mechanical properties.

Immunohistochemical localization of fibromodulin in the periodontium during cementogenesis and root formation in the rat molar

BACKGROUND

Cementum is essential for periodontal regeneration, as it provides anchorage between the root surface and the periodontal ligament. A variety of macromolecules present in the extracellular matrix of the periodontium, including proteoglycans, are likely to play a regulatory role in cementogenesis. Recently, the small leucine-rich proteoglycan, fibromodulin, has been isolated from bovine periodontal ligament and localized in bovine cementum, as well as in human periodontal ligament.

OBJECTIVE

The aim of this study was to examine the distribution of fibromodulin during cementogenesis and root formation.

METHODS

A standard indirect immunoperoxidase technique was employed, using an antifibromodulin polyclonal antibody on sections of molar teeth from rats aged 3, 5 and 8 weeks.

RESULTS

Immunoreactivity to fibromodulin was evident in the periodontal ligament in all sections. An intense positive stain was observed in the extracellular matrix where the periodontal ligament fibers insert into the alveolar bone and where the Sharpey's fibers insert into the cementum. There was no staining evident in the mineralized cellular and acellular cementum. The intensity of immunoreactivity to the antifibromodulin antibody increased proportionally with increasing tissue maturation.

CONCLUSION

The results from this study suggest that fibromodulin is a significant component of the extracellular matrix in the periodontal ligament during development, and may play a regulatory role in the mineralization process or maintaining homeostasis at the hard-soft tissue interface during cementogenesis.

Dentin proteoglycans: an immunocytochemical FEISEM study

Dentin proteoglycans are fundamental constituents of the dentin matrix and are distributed ubiquitously both in dentin and cement. They have several important functional properties; in particular, they have a fundamental role in the maintenance and the correct stabilization of collagen fibers. The use of phosphoric acid on dentin, as proposed in most common dental adhesive systems to establish a reliable bond, may affect the molecular structure of proteoglycans. The aim of this study was to evaluate, after the application of EDTA or phosphoric acid on dentin, the dentin proteoglycans with an immunocytochemical approach with high resolution SEM. For this purpose, dentin disks obtained from recently extracted human molars were etched with a 35% water solution of phosphoric acid for 15 s, 30 s, and 60 s. Control specimens were conditioned with EDTA. Specimens were immunolabeled with a monoclonal antibody antichondroitin sulfate and visualized with a gold-conjugated secondary antibody. Conditioning dentin with EDTA resulted in a distinct labeling of the proteoglycans, as visualized on branching fibrillar structures in the order of 10-20 nm. The use of 35% phosphoric acid on dentin revealed a coagulation of proteoglycans after etching for 15 s while a very low labeling signal was detectable after 30 s. No labeling was obtained after etching dentin with phosphoric acid for 60 s. These results suggest that the use of 35% phosphoric acid on dentin is able to produce significant structural modifications of the dentin proteoglycans even after short application times. Additionally, when applied on the dentin surface for more than 30 s, phosphoric acid produces a dramatic decrease in proteoglycans' antigenicity, probably due to structural modifications of the three-dimensional conformation of these molecules.

Immunohistochemical localization of components of the insulin-like growth factor-system in human deciduous teeth

To investigate the occurrence of components of the insulin-like growth factor (IGF) system during the resorption process of shedding human deciduous teeth, we investigated sections of 13 decalcified and paraffin-embedded deciduous teeth immunohistochemically with antibodies against IGF-I and -II, six IGF binding proteins (IGFBPs 1-6) and the IGF receptors IGF1R and IGF2R. The teeth were in different stages of resorption and all showed reparative cementum formation. It was found that acellular extrinsic fiber cementum, reversal lines and reparative cellular intrinsic fiber cementum were immunoreactive for both IGFs and various IGFBPs. Therefore, in human deciduous teeth, all subgroups of cementum, but not dentine, may represent sources of components of the IGF system. Odontoclasts did not carry IGFs or the IGF1R, but IGFBPs and the IGF2R. Therefore, these cells, in contrast to osteoclasts, may not respond to IGFs, but may be involved in the release and sequestration of IGFs from cementum during the resorption process. In contrast to odontoclasts, cementoblasts and periodontal ligament (PDL) fibroblasts carried IGF1R. The influence of the IGF system on the function of these cells with respect to periodontal matrix turnover and cementogenesis is discussed. On the behalf of the IGFBP immunoreactivities found, the PDL extracellular matrix can be considered to be a reservoir for IGF system components, where binding proteins may regulate IGF distribution and activity.

Proteoglycans and orthodontic tooth movement

Proteoglycans represent an important and diverse family of extracellular matrix components within the connective tissues of the periodontium. This review focuses on the function and metabolism of the various proteoglycans in periodontal tissues, such as alveolar bone and periodontal ligament, and considers their potential fate in response to an orthodontic force. Such considerations provide an important background in evaluating the potential for proteoglycan metabolites, alongside other connective tissue metabolites, as biomarkers for assessing the deep-seated metabolic changes and as a diagnostic tool in monitoring orthodontic tooth movement.

Differential expression of decorin and biglycan genes during mouse tooth development

Small leucine-rich proteoglycans (SLRPs) have a number of biological functions and some of them are thought to regulate collagen mineralizaton in bone and tooth. We have previously identified and immunolocalized two members of the SLRPs family, decorin and biglycan, in bovine tooth/periodontium. To investigate their potential roles in tooth development, we examined the mRNA expression patterns of decorin, biglycan and type I collagen in newborn (day 19) mice tooth germs by in situ hybridization. At this developmental stage, the first maxillary and mandibular molars include stages before and after secretion of the predentin matrix, respectively. The expression of decorin mRNA coincided with that of type I collagen mRNA and was mostly observed in secretory odontoblasts, while the biglycan mRNA was expressed throughout the tooth germ, including pre-secretory odontoblasts/ameloblasts, dental papilla and stellate reticulum. However, its signal in secretory odontoblasts was not as evident as that of decorin. In mandibular incisors, where a significant amount of predentin matrix and a small amount of enamel matrix were already secreted, a similar differential expression pattern was observed. In secretory ameloblasts the biglycan mRNA expression was apparent, while that of decorin was not. These differential expression patterns suggest the distinct roles of biglycan and decorin in the process of tooth development.

Collagen XII mutation disrupts matrix structure of periodontal ligament and skin

Collagen XII has been postulated to organize the extracellular matrix (ECM) architecture of dense connective tissues such as the periodontal ligament (PDL) and skin. The objective of this study was to test this hypothesis in transgenic mice carrying a dominant interference mutation of collagen XII. The truncated alpha1(XII) collagen minigene construct MXIINC3(-), driven by the mouse alpha2(I) collagen promoter, was prepared and used to generate transgenic mouse lines. The PDL matrix fibers of molar teeth lost the ordered architecture characteristic of ligament tissue without noticeable inflammation. Cellular cement appeared to be disrupted at the PDL insertion. By confocal laser scanning microscopy, the PDL of transgenic mice demonstrated swollen and irregularly arranged collagen fibers associated with internal porosity. The skin of transgenic mice revealed the lack of matrix fiber structure in the papillary dermis. These results indicated that the dominant interference mutation of collagen XII disorganized the ECM architecture of PDL and skin.