Isolation and partial characterization of mitogenic factors from cementum

Regeneration of rat periodontium by cementum protein 1-derived peptide

BACKGROUND AND OBJECTIVE

Cementum protein 1 (CEMP1) has the capacity to promote differentiation of periodontal ligament (PDL) cells toward a cementoblastic phenotype in vitro and bone regeneration in vivo. In this study, we tested the capabilities of a synthetic cementum protein 1-derived peptide, MGTSSTDSQQAGHRRCSTSN (CEMP1-p1), to promote regeneration of periodontal structures in a periodontal fenestration defect in rats.

MATERIAL AND METHODS

Fenestration defects were created using an extra-oral approach in the buccal aspect of the mandibular first molar roots. Eighteen male Wistar rats were divided into three groups. Two controls (defects non-treated or defects treated with a gelatin matrix scaffold [GMS] only) and the experimental group treated with 5 µg/dose of CEMP1-p1 embedded in GMS. After 28 days, the animals were sacrificed, and the mandibles processed for histopathological examination. Expression of cementum proteins, cementum attachment protein (CAP), CEMP1, integrin binding sialoprotein (IBSP), and osteocalcin (OCN), was assessed using immunofluorescence. The formation of new cementum, bone, and PDL fibers were compared between control and experimental groups.

RESULTS

The histological analysis revealed that the control group without any treatment new cementum or oriented PDL fibers were not observed. However, the presence of newly bone was detected. In the control group treated with GMS, new cementum formation was not detectable, the PDL fibers were oriented parallel to the longitudinal root axis, and new bone formation was observed. The experimental group showed deposit of acellular extrinsic fiber cementum (AEFC) in a lamellae-like feature with inserted Sharpey's fibers, formation of cellular mixed stratified cementum (CMSC) with the presence of cementocytes, and newly formed bone close to the cementum-enamel junction. Cementoblast cells adjacent to new cementum expressed CAP, CEMP1, IBSP, and OCN.

CONCLUSION

These studies show that CEMP1-p1 promotes the formation of AEFC, CMSC, new PDL with Sharpey's fibers inserted in cementum and bone, thus providing strong evidence that the synthetic peptide CEMP1-p1 promotes periodontal regeneration in a rat fenestration model.

Targeting and Immobilization of Bioactive Peptides on Dentin Matrix

The regeneration of structurally/functionally competent tooth root cementum is a critical step for the successful restoration of periodontal attachment. In this study, we tested whether a poly-glutamic acid-rich domain and glutamine-containing transglutaminase substrate can be used to target biologically active peptides to the mineralized root matrix and to bind such peptides covalently to the organic matrix. As a biologically active model molecule, the integrin-binding motif, RGD, was used. The effects of immobilization of such synthetic peptides to the dentin matrix on cementoblastic adhesion in vitro and cementogenesis in vivo were studied. In vitro, cementoblastic adhesion improved significantly when the dentin surface contained covalently bound peptides. In vivo, this bound peptide significantly increased cementum formation compared with that attained in control conditions. Transglutaminase-catalyzed covalent binding of bioactive peptides targeted to mineralized collagenous dentin matrix via the poly-glutamate domain can be readily achieved. This approach offers potential for clinical use in periodontal regeneration.

Redefining the induction of periodontal tissue regeneration in primates by the osteogenic proteins of the transforming growth factor-β supergene family

The molecular bases of periodontal tissue induction and regeneration are the osteogenic proteins of the transforming growth factor-β (TGF-β) supergene family. These morphogens act as soluble mediators for the induction of tissues morphogenesis sculpting the multicellular mineralized structures of the periodontal tissues with functionally oriented ligament fibers into newly formed cementum. Human TGF-β₃ (hTGF-β₃ ) in growth factor-reduced Matrigel^® matrix induces cementogenesis when implanted in class II mandibular furcation defects surgically prepared in the non-human primate Chacma baboon, Papio ursinus. The newly formed periodontal ligament space is characterized by running fibers tightly attached to the cementoid surface penetrating as mineralized constructs within the newly formed cementum assembling and initiating within the mineralized dentine. Angiogenesis heralds the newly formed periodontal ligament space, and newly sprouting capillaries are lined by cellular elements with condensed chromatin interpreted as angioblasts responsible for the rapid and sustained induction of angiogenesis. The inductive activity of hTGF-β₃ in Matrigel^® matrix is enhanced by the addition of autogenous morcellated fragments of the rectus abdominis muscle potentially providing myoblastic, pericytic/perivascular stem cells for continuous tissue induction and morphogenesis. The striated rectus abdominis muscle is endowed with stem cell niches in para/perivascular location, which can be dominant, thus imposing stem cell features or stemness to the surrounding cells. This capacity to impose stemness is morphologically shown by greater alveolar bone induction and cementogenesis when hTGF-β₃ in Matrigel^® matrix is combined with morcellated fragments of autogenous rectus abdominis muscle. The induction of periodontal tissue morphogenesis develops as a mosaic structure in which the osteogenic proteins of the TGF-β supergene family singly, synergistically and synchronously initiate and maintain tissue induction and morphogenesis. In primates, the presence of several homologous yet molecularly different isoforms with osteogenic activity highlights the biological significance of this apparent redundancy and indicates multiple interactions during embryonic development and bone regeneration in postnatal life. Molecular redundancy with associated different biological functionalities in primate tissues may simply represent the fine-tuning of speciation-related molecular evolution in anthropoid apes at the early Pliocene boundary, which resulted in finer tuning of the bone induction cascade.

Cementum and Periodontal Ligament Regeneration

The unique anatomy and composition of the periodontium make periodontal tissue healing and regeneration a complex process. Periodontal regeneration aims to recapitulate the crucial stages of wound healing associated with periodontal development in order to restore lost tissues to their original form and function and for regeneration to occur, healing events must progress in an ordered and programmed sequence both temporally and spatially, replicating key developmental events. A number of procedures have been employed to promote true and predictable regeneration of the periodontium. Principally, the approaches are based on the use of graft materials to compensate for the bone loss incurred as a result of periodontal disease, use of barrier membranes for guided tissue regeneration and use of bioactive molecules. More recently, the concept of tissue engineering has been integrated into research and applications of regenerative dentistry, including periodontics, to aim to manage damaged and lost oral tissues, through reconstruction and regeneration of the periodontium and alleviate the shortcomings of more conventional therapeutic options. The essential components for generating effective cellular based therapeutic strategies include a population of multi-potential progenitor cells, presence of signalling molecules/inductive morphogenic signals and a conductive extracellular matrix scaffold or appropriate delivery system. Mesenchymal stem cells are considered suitable candidates for cell-based tissue engineering strategies owing to their extensive expansion rate and potential to differentiate into cells of multiple organs and systems. Mesenchymal stem cells derived from multiple tissue sources have been investigated in pre-clinical animal studies and clinical settings for the treatment and regeneration of the periodontium.

Stem cells, tissue engineering and periodontal regeneration

The aim of this review is to discuss the clinical utility of stem cells in periodontal regeneration by reviewing relevant literature that assesses the periodontal-regenerative potential of stem cells. We consider and describe the main stem cell populations that have been utilized with regard to periodontal regeneration, including bone marrow-derived mesenchymal stem cells and the main dental-derived mesenchymal stem cell populations: periodontal ligament stem cells, dental pulp stem cells, stem cells from human exfoliated deciduous teeth, stem cells from apical papilla and dental follicle precursor cells. Research into the use of stem cells for tissue regeneration has the potential to significantly influence periodontal treatment strategies in the future.

Clinical utility of stem cells for periodontal regeneration

The aim of this review is to discuss the clinical utility of stem cells in periodontal regeneration by reviewing relevant literature that assesses the periodontal-regenerative potential of stem cells. We considered and described the main stem cell populations that have been utilized with regard to periodontal regeneration, including bone marrow-derived mesenchymal stem cells and the main dental-derived mesenchymal stem cell populations: periodontal ligament stem cells, dental pulp stem cells, stem cells from human exfoliated deciduous teeth, stem cells from apical papilla and dental follicle precursor cells. Research into the use of stem cells for tissue regeneration has the potential to significantly influence periodontal treatment strategies in the future.

Elevated extracellular calcium increases fibroblast growth factor-2 gene and protein expression levels via a cAMP/PKA dependent pathway in cementoblasts

Cementoblasts, tooth root lining cells, are responsible for laying down cementum on the root surface, a process that is indispensable for establishing a functional periodontal ligament. Cementoblasts share phenotypical features with osteoblasts. Elevated levels of extracellular Ca(2+) have been implicated in osteogenesis by stimulating the proliferation and differentiation of osteoblasts; however, the role of extracellular Ca(2+) signaling in cementogenesis has not been examined. Using RT-PCR, we found that elevated levels of extracellular Ca(2+) increase fibroblast growth factor (FGF)-2 gene expression with a peak at 6h. Pretreatment with a protein kinase A (PKA) inhibitor, H89, or an adenylate cyclase inhibitor, MDL-12,330A, inhibited Ca(2+)-stimulated Fgf-2 expression. In contrast, pretreatment with the protein kinase C (PKC) inhibitor GF-109203X or the phospholipase C (PLC) inhibitor U73122 did not affect the expression of Fgf-2 transcripts, suggesting that the increase in Fgf-2 expression was dependent on the PKA but not the PLC/PKC signaling pathway. Treatment with an activator of adenylate cyclase, forskolin, or a cell-permeable analog of cAMP, 8-Br-cAMP, enhanced Ca(2+)-stimulated Fgf-2 expression, but a single treatment with forskolin or 8-Br-cAMP did not, suggesting that cAMP generation is indispensable but not sufficient for Ca(2+)-stimulated FGF2 expression. Next, we examined the cation specificity of the putative receptor and showed that treatment with trivalent/divalent inorganic ions, Ca(2+), Gd(3+), Sr(2+), or Al(3+), caused a dose-dependent increase in Fgf-2 mRNA levels in a cAMP-dependent fashion, whereas Mg(2+) and the organic ions neomycin and spermine had no effect on Fgf-2 gene expression levels. These findings suggest that an extracellular Ca(2+)-sensing mechanism is present in cementoblasts and its activation leads to FGF-2 stimulation in a cAMP/PKA dependent fashion. Understanding the pathway regulating key genes involved in modulating the regeneration of oral tissues will assist in designing regenerative therapies based on reliable biological principles.

Recapitulating Development: A Template for Periodontal Tissue Engineering

The induction of bone formation by the soluble osteogenic molecular signals of the transforming growth factor-beta (TGF-beta) superfamily is a critical issue to periodontologists, molecular biologists, and tissue engineers alike, because preclinical studies in primates and clinical trials have demonstrated the bone induction capacity of bone morphogenetic and osteogenic proteins (BMPs/OPs) in clinical context. BMPs/OPs, pleiotropic members of the TGF-beta superfamily, induce de novo endochondral bone formation as a recapitulation of embryonic development and act as soluble signals for tissue morphogenesis sculpting the multicellular mineralized structures of the periodontal tissues with functionally oriented periodontal ligament fibers inserting into newly formed cementum. This paper reviews the induction of the complex tissue morphologies of the periodontal tissues in the nonhuman primate Papio ursinus with furcation defects treated with doses of naturally derived and recombinantly produced human BMPs/OPs. Periodontal tissue regeneration develops as a mosaic structure in which the OPs of the TGF-beta superfamily singly, synergistically, and synchronously initiate and maintain tissue induction and morphogenesis.

The effect of basic fibroblast growth factor on delayed-replanted monkey teeth

BACKGROUND

Basic fibroblast growth factor (bFGF; FGF-2) has been reported to facilitate wound healing and periodontal regeneration in experimental alveolar bone defects. The purpose of this study was to evaluate histologically the effect of topically applied bFGF with or without fibrin glue on delayed-replanted monkey teeth prone to replacement resorption.

METHODS

Forty-five roots from five monkeys were endodontically treated aseptically and then extracted as atraumatically as possible. Ten negative control roots were replanted immediately, while 12 positive control roots were allowed to bench dry for 1 hour prior to replantation, both without further treatment. Roots in the two experimental groups were bench dried for 1 hour, rinsed with saline, and then replanted into sockets filled with bFGF with (11 roots) or without (12 roots) fibrin glue. After 12 weeks, histological sections were prepared and evaluated according to morphometric analysis as complete healing or unfavorable healing composed of inflammatory resorption and replacement resorption.

RESULTS

Kruskal-Wallis and Mann-Whitney U tests showed teeth in the negative control group to have significantly higher complete healing (98.88% +/- 2.30%) and significantly lower unfavorable healing (1.12% +/- 2.30%) than the positive control group and the experimental groups. bFGF/fibrin glue group showed higher occurrence of complete healing (39.06% +/- 41.62%) compared to the bFGF group (25.28% +/- 28.85%) and the positive control group (16.58% +/- 19.60%), although the differences were not significant. Comparing the complete and unfavorable healing, there was no significant difference in the bFGF/fibrin glue group (P = 0.47), but the differences were significant in the other groups (P < 0.05).

CONCLUSION

Topical application of bFGF with fibrin glue showed an insignificantly higher occurrence of complete healing in delayed-replanted monkey teeth.

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.

Role of Hertwig's epithelial root sheath cells in tooth root development

During tooth development, after the completion of crown formation, the apical mesenchyme forms the developing periodontium while the inner and outer enamel epithelia fuse below the level of the crown cervical margin to produce a bilayered epithelial sheath termed Hertwig's epithelial root sheath (HERS). The role of HERS cells in root formation is widely accepted; however, the precise function of these cells remains controversial. Functions suggested have ranged from structural (subdivide the dental ectomesenchymal tissues into dental papilla and dental follicle), regulators of timing of root development, inducers of mesenchymal cell differentiation into odontoblasts and cementoblasts, to cementoblast cell precursors. The characterization of the HERS phenotype has been hindered by the small amount of tissue present at a given time during root formation. In this study, we report the establishment of an immortal HERS-derived cell line that can be maintained in culture and then induced to differentiate in vitro. Characterization of the HERS phenotype using reverse transcriptase-polymerase chain reaction and Western blot immunostaining suggests that HERS cells initially synthesize and secrete some enamel-related proteins such as ameloblastin, and then these cells appear to change their morphology and produce a mineralized extracellular matrix resembling acellular cementum. These studies suggest that the acellular and cellular cementum are synthesized by two different types of cells, the first one by HERS-derived cementoblasts and the later by neural crest-derived cementoblasts.

Intrinsic Cytotoxicity and Chemomodulatory Actions of Novel Phenethylisothiocyanate Sphingoid Base Derivatives in HL-60 Human Promyelocytic Leukemia Cells

The protein kinase C (PKC) isoenzyme superfamily represents a popular target in pharmacological interventions designed to elicit apoptosis directly in tumor cells or to potentiate the lethal effects of antineoplastic agents. Numerous observations support the clinical utility of PKC inhibition by experimental sphingolipid derivatives such as safingol. The present studies document the cytotoxicity and chemomodulatory capacity of phenethylisothiocyanate derivatives of sphinganine and sphingosine (PEITC-Sa and PEITC-So) in the human myeloid leukemia cell line HL-60. The biological actions of these novel derivatives were compared directly with those of the parent compounds sphinganine and sphingosine. Exposure to natural and modified sphingoid bases promoted extensive apoptotic cell death. The PEITC-sphingoid base derivatives exhibited higher cytotoxicity than their natural counterparts and were also distinctly superior to the clinically relevant sphingoid base analog safingol. In each instance, lethality was shown to correlate with inhibition of conventional and novel PKC isoforms and downstream loss of extracellular signal-regulated kinase (ERK)1/ERK2. The involvement of these signaling systems in potentiating the lethal actions of 1-(beta-D-arabinofuranosyl)cytosine (araC) was also examined with regard to the differential actions of PEITC-Sa and PEITC-So to that of the parent compounds as well as safingol. Exposure to araC alone rapidly increased PKC activity. In the presence of PEITC-Sa or PEITC-So, the therapeutic efficacy of araC increased markedly; moreover, potentiation was directly related to the loss of araC-stimulated PKC activity. These findings demonstrate that PEITC-substituted sphingoid base analogs exert potent antineoplastic effects in human leukemia cells. We suggest that these synthetic lipids represent potentially useful agents in the development of conventional PKC/novel PKC-directed chemotherapeutic strategies.

Cementum and periodontal wound healing and regeneration

The extracellular matrix (ECM) of cementum resembles other mineralized tissues in composition; however, its physiology is unique, and it contains molecules that have not been detected in other tissues. Cementum components influence the activities of periodontal cells, and they manifest selectivity toward some periodontal cell types over others. In light of emerging evidence that the ECM determines how cells respond to environmental stimuli, we hypothesize that the local environment of the cementum matrix plays a pivotal role in maintaining the homeostasis of cementum under healthy conditions. The structural integrity and biochemical composition of the cementum matrix are severely compromised in periodontal disease, and the provisional matrix generated during periodontal healing is different from that of cementum. We propose that, for new cementum and attachment formation during periodontal regeneration, the local environment must be conducive for the recruitment and function of cementum-forming cells, and that the wound matrix is favorable for repair rather than regeneration. How cementum components may regulate and participate in cementum regeneration, possible new regenerative therapies using these principles, and models of cementoblastic cells are discussed.

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.

Biological effects of cementum and bone extracts on human periodontal fibroblasts

BACKGROUND

Non-collagenous proteins of mineralized tissues play important roles in bone induction during mineralization and in regulating the activity of many types of mesenchymal cells. This study was conducted to determine the effects of acetic acid extracts of bone and cementum on alkaline phosphatase (ALPase) activity and in vitro mineralization of cultured human periodontal fibroblasts (hPF).

METHODS

Alveolar bone and cementum obtained from clinically healthy subjects were extracted by a solution containing 0.5 M acetic acid and enzyme inhibitors. Osteoblastic phenotypes of hPF were assayed by ALPase activity, gene expression of bone marker proteins, and the ability to produce in vitro mineralization in culture media containing 50 microg/ml ascorbic acid, 10 mM sodium beta-glycerophosphate, and 10(-7) M dexamethasone. The effects of cementum and bone extracts on the expression of osteoblastic phenotypes in hPF were also determined.

RESULTS

Many protein components, varying in molecular weight from 10 to 14 to 120 kDa, were detectable in 10% SDS-PAGE of both cementum and alveolar bone extracts. The hPF cells were found to exhibit a moderate ALPase activity when compared with rat osteosarcoma (ROS) 17/2.8 cells under the same experimental conditions. Gene expression for ALPase, osteocalcin bone sialoprotein, osteopontin, and BMP-7 at mRNA message was detected by RT-PCR in hPF and ROS 17/2.8 cells. The confluent hPF and ROS 17/2.8 cells showed evidence of calcium deposition in the extracellular milieu at 30 and 15 to 30 days' cultures, respectively, under a mineralization medium. The hPF appeared to form mineralized foci with morphological characteristics different from the mineralized nodules produced by ROS 17/2.8 cells. The addition of low concentrations (5 microg/ml) of either cementum or bone extract produced an increase in the size and number of mineralization spots, as well as greater ALPase activity in both hPF and ROS 17/2.8 cultures during the observation periods.

CONCLUSIONS

These results suggest that hPF possess certain mineralizing phenotypes, and that acetic acid extracts of bone and cementum contain components capable of stimulating osteogenic differentiation of hPF.

Blood circulation as source for osteopontin in acellular extrinsic fiber cementum and other mineralizing tissues

Osteopontin (OPN) is one of the major non-collagenous proteins in root cementum and other mineralized tissues. Although most of this mineral-seeking protein is thought to be produced by local tissue cells, some of it might enter the mineralizing matrix from the blood. To test this hypothesis, we followed the distribution of a single dose of purified porcine or rat 125I-labeled OPN injected i.v. in rats, in mineralizing and non-mineralizing tissues and in subcutaneously implanted collagenous implants. The animals were killed 30 or 48 hrs after injection. Tissues (calvaria, tibia, lower and upper jaws) were harvested and processed for radioautography and biochemical analysis. Tissues as well as calcifying collagenous implants proved to have taken up radiolabel. In EDTA extracts of long bones, the majority of the radiolabel was demonstrated to be associated with intact OPN. The iodinated protein was also found in the acellular extrinsic fiber cementum (acellular cementum) layer investing the continuously growing incisors, in laminae limitantes, cement lines, and in forming bone near the mineralization front. Further, the label was present in the circumpulpal dentin of the incisors, and some of it appeared to have been incorporated into developing enamel. It is concluded that OPN in acellular cementum and other mineralizing tissues may-at least partially-originate from sources outside the direct environment following its transportation via serum.

Role of cyclin E and cyclin E-dependent kinase in mitogenic stimulation by cementum-derived growth factor in human fibroblasts

Cementum-derived growth factor (CGF) is a 14 kDa polypeptide sequestered in tooth cementum. It is an IGF-I like molecule that is weakly mitogenic to fibroblasts, but its mitogenic action is synergistically potentiated in the presence of epidermal growth factor (EGF) or serum. We have examined whether the CGF affects cyclin E levels and the activity of cyclin-dependent kinase (Cdk) associated with this cyclin, and whether these changes contribute to the synergism in mitogenic activity between CGF and EGF. Optimal DNA synthesis by serum-starved human gingival fibroblasts required the presence of CGF for 0-12 h and EGF for 0-3 h. Therefore, cells were serum starved for 48 h and then exposed to CGF, EGF, or CGF + EGF. Cells incubated with 10% fetal bovine serum (FBS) served as positive controls. At various time points after the addition of growth factors, cyclin E levels were examined by Western analysis. Cdk associated with cyclin E was immunoprecipitated with anti-cyclin E antibody and kinase activity was measured using H1 histone as substrate. Cyclin E and the H1 kinase activity levels increased after 8-12 h in cells exposed to CGF and in positive controls exposed to 10% FBS. They returned to basal level 4 h later in cells exposed to CGF alone, whereas in the presence of CGF + EGF and FBS they remained elevated for up to 20 h. The cyclin E levels did not increase in the presence of EGF alone. Cyclin-dependent kinase inhibitors p21cip1 and p27kip1 were barely detectable in these cells. Fibroblasts transfected with LXSN-cyclin E, a retroviral vector containing cyclin E cDNA, overexpressed cyclin E and their steady-state cyclin E-Cdk activity was higher than control cells. DNA synthesis by cyclin E overexpressing cells was higher, but optimal DNA synthesis by these cells required the presence of CGF and EGF. These results show that CGF action involves an increase in the levels of cyclin E and E-Cdk activity and that the higher levels are maintained in the presence of both CGF and EGF. They also indicate that sustained high cyclin E levels and Cdk2 activity during G1 phase are necessary, but not sufficient, for optimal mitogenic response in human fibroblasts.

Expression of receptors for basic fibroblast growth factor on human periodontal ligament cells

Basic fibroblast growth factor (FGF-2; bFGF) is a major mitogen for connective tissue cells, and participates in the healing process. It has already been reported that FGF-2 could be applicable to enhance periodontal regeneration. In the present study, we examined FGF receptor (FGFR) expression on human periodontal ligament (PDL) cells. The binding of [125I]-labeled FGF-2 to human PDL cells was studied by radioreceptor assay. The binding of [125I]-FGF-2 to PDL cells reached a plateau after 2.5 h incubation at 4 degrees C and was inhibited by the addition of unlabeled FGF-2 and acidic FGF (FGF-1; aFGF), but not insulin-like growth factor-I, platelet-derived growth factor and transforming growth factor-beta 1. Scatchard analysis revealed the presence of approximately 1.0 x 10(5) FGF-2 binding sites per cell with an apparent Kd of 1.2 x 10(-10) M. Interestingly, the binding of [125I]-FGF-2 on PDL cells reached its maximum at d 6 of the culture and then gradually decreased. Scatchard analysis also demonstrated that the number of FGFRs on a PDL cell was altered during the course of the culture, while the affinity between FGF-2 and its receptor was not. The responsiveness of PDL cells to FGF-2, which was monitored by the inhibitory effect on alkaline phosphatase activity, was reduced in proportion to the decrease in the number of FGFRs on the PDL cells. The present study suggests that PDL cells alter the responsiveness to FGF-2 during the course of the culture by changing the density of its receptor, and that the density of FGFR expression might be a marker of the cytodifferentiation of PDL cells into mineralized tissue forming cells.

Characterization of cementum derived growth factor as an insulin-like growth factor-I like molecule

Cementum is the thin calcified outer layer through which tooth-root surfaces are anchored to soft periodontal connective tissues. A variety of growth factors and adhesion molecules are sequestered in the extracellular matrix of cementum, and we have purified and characterized one of the growth factors. This growth factor, the cementum derived growth factor (CGF), was purified from bovine cementum by acetic acid extraction followed by heparin affinity chromatography and HPLC using cation exchange, molecular sieve, and reverse-phase columns. NaDodSO4-polyacrylamide gel electrophoresis of purified CGF preparation revealed the presence of two major protein bands migrating with Mr 18,000-22,000 and 14,000-16,000. The latter was associated with the major part of the mitogenic activity. The activity of CGF was inhibited by antibodies to insulin-like growth factor-I (IGF-I) and IGF-I receptor. Both CGF and IGF-I were mitogenic to human gingival fibroblasts and alveolar bone cells, but the bone cells responded better to CGF than to IGF-I. The IGF-I did not bind to heparin-sepharose, while CGF bound to it and was eluted with 0.6M NaCl from heparin-sepharose columns. Heparin-sepharose 0.2M NaCl fractions of cementum extracts contained IGF-I migrating with Mr 7,500, but its mobility was not affected by N-glycosidase treatment. Western analysis using anti-IGF-I antibodies showed that CGF preparations contained cross-reacting species migrating with Mr 18,000-22,000, 14,000-16,000 and 11,000-12,000, however after treatment with N-glycosidase the Mr 18,000-22,000 component was absent. Internal amino acid sequences of six tryptic peptides of CGF were determined by microsequencing. The sequence of one 15-amino acid long peptide was the same as the receptor binding domain of IGF-I, and another 9-amino acid peptide had 78 % homology to a sequence derived from an untranslated region of sheep IGF-I exon 1. Four other peptides had no apparent homology with IGF-I. From these results we conclude that the CGF is an IGF-I like molecule.

A collagenous cementum-derived attachment protein is a marker for progenitors of the mineralized tissue-forming cell lineage of the periodontal ligament

The periodontal ligament (PDL) is a fibrous and cellular connective tissue that mediates tooth attachment to bone, and it comprises fibroblastic and mineralized tissue-forming (MTF) progenitors. The MTF progenitors are believed to give rise to the cementoblastic and osteoblastic lineages. Cementum attachment protein (CAP) is a collagenous cementum-derived protein which binds strongly to osteoblasts, moderately to PDL cells, and weakly to gingival fibroblasts. The aim of the present study was to determine the relationship between the capacity of PDL progenitors to bind CAP and their potential to express alkaline phosphatase (ALP) and form mineralized-like tissue in culture. Cloned human PDL progenitor populations obtained from nine human donors were assayed for their constitutive capacity to bind CAP and express ALP, and for the dexamethasone-induced potential to form mineralized-like tissue in culture in the presence of ascorbic acid and beta-glycerophosphate. Forty percent of the progenitor clones produced mineralized-like tissue. Two patterns of mineralization were observed: a spread and flat pattern similar to that produced by human bone cells in culture and a nodular ridge-like type resembling that formed by human cementoma-derived cells. A direct correlation was found between the percentage of ALP positive cells in each progenitor clone and the amount of mineralized-like tissue formed (r = 0.565). Similar correlations were found between the number of ALP positive cells and the binding capacity of each clone (r = 0.392) and between the CAP binding capacity and mineralized-like tissue formation (r = 0.584). Multiple regression analysis indicated that the constitutive capacity of a clone to bind CAP and express ALP is directly correlated to its dexamethasone-induced potential to form mineralized tissue (r = 0.675). These results indicate that CAP binding and ALP expression can serve as markers for the identification of MTF progenitors in the heterogeneous cultured population of the human periodontal ligament. These data show for the first time that binding capacity to extracellular components of mineralized tissues can be a marker for mineralized tissue-forming progenitors.

Characterization of a collagenous cementum-derived attachment protein

We report further characterization of a cementum-derived protein that promotes the adhesion and spreading of periodontal cells. The cementum attachment protein (CAP) was extracted from bovine cementum, separated by diethylamino ethyl (DEAE)-cellulose chromatography, and purified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and C18 reverse phase high performance liquid chromatography. The purified preparation contained a single protein band migrating with M(r) 56,000. It did not cross-react with polyclonal antibodies to osteopontin, vitronectin, or other attachment proteins. The attachment activity was resistant to chondroitinase ABC digestion. An internal amino acid sequence of six peptides was determined by microsequencing, and the peptide sequences were not present in other attachment proteins described in cementum. Four sequences contained Gly-X-Y repeats typical of collagen helix. One 17 amino acid peptide had 82% homology with a type XII collagen domain. However, bovine type XII collagen did not promote fibroblast attachment. Although another 19-amino-acid-long peptide had 95% homology to bovine alpha 1 [I], two other peptides were only 74% and 68% homologous, and the CAP was not recognized by anti-type I collagen antibody. The attachment activity of CAP was susceptible to bacterial collagenase. The CAP did not cross-react with antibodies to type V, XII, and XIV collagens. These data and our previous immunostaining data indicate that the CAP is not related to other collagens or attachment proteins and that it is a collagenous attachment protein localized in cementum.

Turnover in periodontal connective tissues: dynamic homeostasis of cells, collagen and ground substances

The connective tissues of the periodontium are composed of two soft tissues and two hard tissues--each of which has unique features. This review considers the constituents of normal, healthy periodontal connective tissues together with an appraisal of the changes in the connective tissue matrices of the periodontium which occur during the development of periodontitis. Recent developments in this field have paved the way for new and exciting vistas in periodontal diagnosis and regeneration which, ultimately, are two important goals in periodontal therapy.

Specific cementum attachment protein enhances selectively the attachment and migration of periodontal cells to root surfaces

A specific cementum attachment protein (CAP) was identified in human cementum and found to bind with high affinity to non-demineralized root surfaces, hydroxyapatite and fibronectin. Attempting to elucidate the biological function of this protein and its possible role in cementogenesis the capacity of CAP to promote selective cell migration towards and attachment of various periodontal derived cell populations to root surfaces in vitro was assessed. Human gingival fibroblasts (HGF), periodontal ligament cells (HPC), and alveolar bone cells (HABC) were labeled with [3H]Thymidine during their exponential growth phase. Root slices, 300 microns thick, were incubated with increasing concentrations of CAP. Untreated and fibronectin (FN) treated root slices served as negative and positive controls, respectively. Migration was assessed by placing root slices on confluent layers of labeled cells maintained in serum free medium and determining the number of cells migrated onto the root surface 3 days thereafter. Attachment was assessed by incubating root slices with labeled cell suspensions for 2 h and determining the number of attached cells. CAP promoted both cell migration and attachment dose dependently. HABC responded better than HPC and HGF to CAP treated root slices, and HPC response was higher than that of HGF. Cell attachment was dose dependently inhibited by synthetic RGD peptides. FN did not affect the migration of HGF, barely enhanced that of HABC, and was less potent than CAP at enhancing the migration of HPC. FN was more effective than CAP in promoting the attachment of HGF to root slices, but it was as potent as CAP in supporting the attachment of HPC and HABC.(ABSTRACT TRUNCATED AT 250 WORDS)

Synthesis of noncollagenous extracellular matrix proteins during development of mineralized nodules by rat periodontal ligament cells in vitro

To characterize the mineralized nodules produced by rat periodontal ligament (PDL) cells in vitro, we have studied the synthesis and distribution of mineralized tissue proteins at various stages of nodule formation. PDL cells were obtained from coagulum in the socket at 2 days after tooth extraction and cultured in Dulbecco's Modified Eagles Medium (DMEM) containing 10% fetal bovine serum and antibiotics. Confluent cells were grown in the presence of ascorbic acid (50 micrograms/ml), dexamethasone (5 microM), and beta-glycerophosphate (10 mM) for 3 weeks. Four stages showing distinct morphological characteristics during development of mineralized nodules were identified. Protein synthesis and deposition of proteins into the matrix were studied during these stages by metabolic labeling with [35S]methionine for 24 hours. Large quantities of SPARC (secreted protein, acidic and rich in cysteine) were synthesized by confluent cells but decreased during the progress of mineralized nodule formation. Two forms of osteopontin (OPN) (67 kDa and 61 kDa) were synthesized in comparable quantities by confluent cells; OPN and bone sialoprotein (BSP) were induced by dexamethasone and represented the major proteins in the mineralized matrix. The 67 kDa form of OPN was the predominant species in the mineralized matrix. Both OPN and BSP were localized by immunogold electron microscopy on globular as well as fused electron-dense structures at sites of tissue mineralization.

Regulation of bone sialoprotein gene transcription by steroid hormones

During the initial formation of bone, dentine and cementum in tooth morphogenesis, fully differentiated osteoblasts, odontoblasts and cementoblasts express bone sialoprotein (BSP), a mineralized tissue-specific acidic glycoprotein that has been implicated in the nucleation of hydroxyapatite crystal growth. The expression of BSP is regulated by steroid hormones that modulate mineralized tissue formation. Thus, the transcription of the BSP gene is induced by glucocorticoids in association with osteoblast differentiation and glucocorticoids also stimulate the expression of BSP in differentiated osteoblasts. In contrast, however, vitamin D3 suppresses bone formation and abrogates the expression of BSP. Our studies, using the osteoblastic cell lines ROS 17/2.8 and UMR 106-06, have revealed that the glucocorticoid (10(-8) M dexamethasone; dex) effect on BSP mRNA involves both direct and indirect pathways. To determine the molecular basis of the direct pathway on transcriptional regulation of the BSP we have isolated and characterized the promoter regions of both the human and rat BSP genes. The promoters are characterized by a highly conserved region (BSP box) encompassing the immediate promoter region, which includes a unique inverted TATA box overlapped by a putative (DR3) vitamin D3 response element (VDRE). Possible glucocorticoid response elements are present approximately 1 kb and approximately 1.4 kb further upstream. Transient transfection analysis of chimeric constructs linked to a luciferase reporter gene have shown Dex-stimulated expression in constructs that include one or both GREs, whereas vit D3 suppresses expression in a short construct that includes the VDRE.(ABSTRACT TRUNCATED AT 250 WORDS)

Cementum specific components which influence periodontal connective tissue cells

We have isolated two polypeptides from cementum one of which promotes the growth and the other the attachment of periodontal cells. One polypeptide, the cementum derived growth factor (CGF), was extracted from healthy human and bovine teeth by 1 M CH3COOH and purified by heparin-affinity chromatography and HPLC. The CGF is a 23 kDa polypeptide which is mitogenic to fibroblasts and smooth muscle cells. It is active alone, but its activity is highly potentiated by plasma-derived serum or EGF. It induces classical mitogenic signaling events, which include Ca++ mobilization, inositol phosphate hydrolysis, activation of phosphokinase C (PKC) and transcription of cellular protooncogenes c-fos and jun-B. The magnitude and pattern of activation of signaling events and their susceptibility to PKC inhibitors and pertussis toxin indicated that the CGF may be a distinct molecular species. The CAP is a 55 kDa polypeptide which promotes the attachment and spreading of fibroblasts, smooth muscle cells, bone cells and endothelial cells, but not epithelial cells. Antibodies to CAP immunostain cementum, but not other tissues. Root surfaces bind CAP. The CGF and CAP do not appear to be present in adjacent periodontal structures. Our data show that the CAP and CGF selectively interact with periodontal cell populations and affect their biological activities, and thus may influence the formation and regeneration of periodontal connective tissues.

Cellular origins and differentiation control mechanisms during periodontal development and wound healing

In the context of cellular origins, odontogenic epithelium and oral epithelium are the sources for junctional epithelium during development and during wound healing respectively. In contrast, both odontogenic and non-odontogenic mesenchyme contain the progenitors for gingival fibroblasts in developing tissues while in wounded tissues, gingival fibroblasts are derived from gingival connective tissues and comprise a heterogeneous population of cells with diverse properties and functions. Periodontal ligament, bone and cementum cell populations apparently originate from dental follicle progenitor cells during development, but during wound healing derive from ancestral cells in periodontal ligament and bone. Cellular differentiation in developing periodontium is governed in part by epithelial-mesenchymal interactions that generate specific signals which regulate selective cell populations in time and space. On the other hand, differentiation during wound healing and regeneration is regulated by a vast array of extracellular matrix informational molecules and by cytokines that induce both selective and non-selective responses in the different cell lineages and their precursors. Further, several important signalling systems are irretrievably lost after development is complete. Thus, in the context of cellular origins and differentiation, developing and wounded periodontal tissues exhibit fundamental differences. Future prospects for improved healing and regeneration of periodontal tissues may derive from identification and isolation of informational molecules that are stored in connective tissue matrices. These molecules and elucidation of their functions may open new perspectives in our understanding of the biology of periodontal wound healing and may provide novel approaches to periodontal regeneration.

Platelet-derived growth factor stimulates hyaluronate but not proteoglycan synthesis by human gingival fibroblasts in vitro

The effect of PDGF-BB on human gingival fibroblasts was monitored in an in vitro system. PDGF was found to be mitogenic for these cells, although it required the presence of low concentrations of fetal calf serum to be active. Proteoglycan and hyaluronate synthesis was analyzed by labeling newly synthesized macromolecules with [35S]-sulfate or [3H]-glucosamine, respectively. Identification of specific glycosaminoglycans was achieved by selective enzymatic or chemical degradations. It was found that cells cultured in the presence of PDGF showed no discernible differences in proteoglycan synthesis relative to the control cultures. There were no alterations in amounts of proteoglycans synthesized, types of sulfated glycosaminoglycans synthesized, or relative hydrodynamic sizes of the proteoglycans. In contrast to the proteoglycans, hyaluronate synthesis was significantly increased in the presence of PDGF. The increase in [3H]-glucosamine incorporation into newly synthesized hyaluronate correlated with an increase in the activity of the enzyme hyaluronate synthetase but could not be accounted for entirely by changes in the specific activity of sugar nucleotide precursors, which did alter slightly under differing culture conditions. It is concluded from these results that PDGF stimulates gingival fibroblasts to proliferate and is associated with a differential effect of proteoglycan and hyaluronate synthesis. These observations may correlate with the observed early events associated with wound healing and repair.

Isolation and partial characterization of a growth factor from human cementum

Cementum is the mineralized interface through which collagen fibers of periodontal connective tissues are anchored onto the tooth surface. We have isolated and partially characterized a mitogenic factor from human cementum which has properties different from other growth factors. Cementum was harvested from healthy human teeth, extracted in 1.0 M CH3COOH and mitogenic activities were fractionated by heparin-affinity chromatography. Proteins eluted by 0.4-0.6 M NaCl, which contained most of the cementum mitogenic activity, were precipitated by trichloroacetic acid and resolved by HPLC through ion-exchange and reverse-phase columns. NaDodSO4-polyacrylamide gel electrophoresis revealed that the purified preparation contained a M(r) 23,000 protein and this protein was associated with mitogenic activity. The purified cementum-derived growth factor (CGF) was active alone, but at suboptimal concentrations its activity was potentiated by small quantities of plasma-derived serum and epidermal growth factor (EGF). The activity was resistant to heat, but it was destroyed by trypsin digestion. Reduction and alkylation destroyed the mitogenic activity, however electrophoretic mobility was not affected. Binding of EGF to fibroblast membranes was not affected by the CGF and assays to detect platelet-derived growth factor were negative. These characteristics indicated that CGF is a distinct molecular species. Our data show that cementum contains several mitogenic factors and that CGF is the major cementum mitogen.

Isolation of human tumor cells that produce cementum proteins in culture

We have cultured cells from explants of a human cementum tumor. The cells obtained were multipolar, they formed network-like structures and they were alkaline-phosphatase positive. Immunostaining and Western blots using specific antibodies revealed that these cells produced bone sialoprotein and collagen types I and V, and they also mineralized in vitro. Conditioned medium was mitogenic to fibroblasts and mitogens present were separated by heparin-affinity chromatography. Based on affinity to heparin and antibody-inhibition studies, the heparin fractions were shown to contain cementum-derived growth factor, platelet-derived growth factor and fibroblast growth factors. The cementum tumor cells, but not gingival fibroblasts, were stained positively by an antibody to cementum-derived attachment protein. The attachment protein was separated by immunoaffinity chromatography, and Western blots revealed that the preparation contained 56-kDa and 43-kDa proteins as major bands. Cells pulse-labeled with radioactive amino acids contained a 43-kDa protein as the major component; however, this protein was absent after a cold chase in the presence of cycloheximide, but 56-kDa, 39-kDa and 26-kDa species became prominent. These data indicated that the 56-kDa cementum attachment protein is derived from a 43-kDa precursor. Our data show that the cells cultured from the cementum tumor represent cementum cells capable of synthesizing and secreting cementum proteins in culture.