CXXC5 mitigates P. gingivalis-inhibited cementogenesis by influencing mitochondrial biogenesis

BACKGROUND

Cementoblasts on the tooth-root surface are responsible for cementum formation (cementogenesis) and sensitive to Porphyromonas gingivalis stimulation. We have previously proved transcription factor CXXC-type zinc finger protein 5 (CXXC5) participates in cementogenesis. Here, we aimed to elucidate the mechanism in which CXXC5 regulates P. gingivalis-inhibited cementogenesis from the perspective of mitochondrial biogenesis.

METHODS

In vivo, periapical lesions were induced in mouse mandibular first molars by pulp exposure, and P. gingivalis was applied into the root canals. In vitro, a cementoblast cell line (OCCM-30) was induced cementogenesis and submitted for RNA sequencing. These cells were co-cultured with P. gingivalis and examined for osteogenic ability and mitochondrial biogenesis. Cells with stable CXXC5 overexpression were constructed by lentivirus transduction, and PGC-1α (central inducer of mitochondrial biogenesis) was down-regulated by siRNA transfection.

RESULTS

Periapical lesions were enlarged, and PGC-1α expression was reduced by P. gingivalis treatment. Upon apical inflammation, Cxxc5 expression decreased with Il-6 upregulation. RNA sequencing showed enhanced expression of osteogenic markers, Cxxc5, and mitochondrial biogenesis markers during cementogenesis. P. gingivalis suppressed osteogenic capacities, mitochondrial biogenesis markers, mitochondrial (mt)DNA copy number, and cellular ATP content of cementoblasts, whereas CXXC5 overexpression rescued these effects. PGC-1α knockdown dramatically impaired cementoblast differentiation, confirming the role of mitochondrial biogenesis on cementogenesis.

CONCLUSIONS

CXXC5 is a P. gingivalis-sensitive transcription factor that positively regulates cementogenesis by influencing PGC-1α-dependent mitochondrial biogenesis. Video Abstract.

REV-ERBs negatively regulate mineralization of the cementoblasts

OBJECTIVE

The role of circadian clock in cementogenesis is unclear. This study examines the role of REV-ERBs, one of circadian clock proteins, in proliferation, migration and mineralization of cementoblasts to fill the gap in knowledge.

METHODS

Expression pattern of REV-ERBα in cementoblasts was investigated in vivo and in vitro. CCK-8 assay, scratch wound healing assay, alkaline phosphatase (ALP) and alizarin red S (ARS) staining were performed to evaluate the effects of REV-ERBs activation by SR9009 on proliferation, migration and mineralization of OCCM-30, an immortalized cementoblast cell line. Furthermore, mineralization related markers including osterix (OSX), ALP, bone sialoprotein (BSP) and osteocalcin (OCN) were evaluated.

RESULTS

Strong expression of REV-ERBα was found in cellular cementum around tooth apex. Rev-erbα mRNA oscillated periodically in OCCM-30 and declined after mineralization induction. REV-ERBs activation by SR9009 inhibited proliferation but promoted migration of OCCM-30 in vitro. Results of ALP and ARS staining suggested that REV-ERBs activation negatively regulated mineralization of OCCM-30. Mechanically, REV-ERBs activation attenuated the expression of OSX and its downstream targets including ALP, BSP and OCN.

CONCLUSIONS

REV-ERBs are involved in cementogenesis and negatively regulate mineralization of cementoblasts via inhibiting OSX expression. Our study provides a potential target regarding periodontal and cementum regeneration.

Effect of FGF-2, TGF-β-1, and BMPs on Teno/Ligamentogenesis and Osteo/Cementogenesis of Human Periodontal Ligament Stem Cells

The periodontal ligament (PDL) is the connective tissue between tooth root and alveolar bone containing mesenchymal stem cells (MSC). It has been suggested that human periodontal ligament stem cells (hPDLSCs) differentiate into osteo/cementoblast and ligament progenitor cells. The periodontitis is a representative oral disease where the PDL tissue is collapsed, and regeneration of this tissue is important in periodontitis therapy. Fibroblast growth factor-2 (FGF-2) stimulates proliferation and differentiation of fibroblastic MSCs into various cell lineages. We evaluated the dose efficacy of FGF-2 for cytodifferentiation of hPDLSCs into ligament progenitor. The fibrous morphology was highly stimulated even at low FGF-2 concentrations, and the expression of teno/ligamentogenic markers, scleraxis and tenomodulin in hPDLSCs increased in a dose dependent manner of FGF-2. In contrast, expression of the osteo/cementogenic markers decreased, suggesting that FGF-2 might induce and maintain the ligamentogenic potential of hPDLSCs. Although the stimulation of tenocytic maturation by TGF-β1 was diminished by FGF-2, the inhibition of the expression of early ligamentogenic marker by TGF-β1 was redeemed by FGF-2 treatment. The stimulating effect of BMPs on osteo/cementogenesis was apparently suppressed by FGF-2. These results indicate that FGF-2 predominantly differentiates the hPDLSCs into teno/ligamentogenesis, and has an antagonistic effect on the hard tissue differentiation induced by BMP-2 and BMP-4.

NficGene Disruption Inhibits Differentiation of Odontoblasts Responsible for Root Formation and Results in Formation of Short and Abnormal Roots in Mice

BACKGROUND

Nuclear factor I genes play an important role in the development of the brain, lung, and roots of teeth. We had reported that Nfic-deficient mice form normal crowns, but abnormal roots of molar teeth. However, the mechanism by which the disruption of Nfic gene causes abnormal root formation remains unknown.

METHODS

To understand this mechanism, the root formation in Nfic-deficient mice was examined and compared to that of wild-type mice by morphological, immunohistochemical, and in situ hybridization analyses.

RESULTS

Nfic-deficient mice formed normal Hertwig's epithelial root sheath (HERS) but severely disrupted odontoblast differentiation, leading to the formation of aberrant odontoblasts in the early stage of root formation. They became dissociated and polygonal in shape, lost their orientation and polarity, and did not express dentin sialophosphoprotein. The abnormal roots contained trapped aberrant odontoblasts, thereby resembling osteodentin in overall morphology. No osteoclasts were associated with abnormal roots. Further, the abnormal roots exhibited a decreased number of cementoblasts and cementum formation on the root surface.

CONCLUSIONS

The loss of Nfic did not interfere with the formation of HERS, but it caused disrupted odontoblast differentiation, which resulted in the formation of short and abnormal roots, and decreased cementum. This finding suggests that root dentin is required for normal cementum formation. Therefore, Nfic may be a key regulator of root odontoblast differentiation and root formation.

Extracellular phosphate alters cementoblast gene expression

Genetic data from humans and mice reveal that the formation of cementum is sensitive to intra- and extracellular phosphate/pyrophosphate distribution. The intracellular molecular pathways whereby altered levels of extracellular phosphate concentration may affect cementum formation have not been elucidated. To initiate inquiry, we have studied the temporal effects of extracellular phosphate on global patterns of gene expression in a line of immortalized mouse cementoblasts. Total RNA from cultured cementoblasts treated with 5 mM inorganic phosphate over a designated time period, from 1-48 hrs, was analyzed for global patterns of gene expression by means of DNA microarrays representing the complete mouse genome. Analyses of significant hybridization signals indicated that 5 mM extracellular phosphate alters the expression of genes comprising several gene ontology (GO) groups, including transcription factor activity and Wnt signaling.

Defining the roots of cementum formation

Significant progress has been seen in research aimed at regeneration of the disease-damaged periodontium. Our own strategy has been to approach periodontal tissue development (i.e. root, cementum, periodontal ligament, and bone) as a source for the identification of key regulators of cellular processes that may be applicable to periodontal tissue repair. Specifically, enamel-like molecules, bone morphogenetic proteins (BMPs), and phosphates have been investigated for their role in altering gene expression and cell functions in follicle cells, periodontal ligament cells, and cementoblasts. Amelogenin, leucine-rich amelogenin peptide, and tyrosine-rich amelogenin peptide have been found to similarly affect cementoblast gene expression and cementoblast-mediated mineralization in vitro; however, these enamel-like factors do not increase cell proliferation as has been observed in cells treated with Emdogain (Biora AB, Malmö, Sweden), an enamel matrix derivative. BMP-2 has been found to promote differentiation of follicle cells into a cementoblast/osteoblast phenotype, and BMP-3 is being investigated as a negative regulator of mineralization. The increased ratio of phosphate to pyrophosphate in the local region during root development has been found to significantly enhance the extent of cementum formation in animal models. Furthermore, phosphate has been identified as a regulator of cementoblast SIBLING (small integrin-binding ligand N-linked glycoprotein) gene expression in vitro. These investigations of candidate factors for periodontal regeneration have uncovered mechanisms regulating gene expression and cell function in cells controlling the behavior of periodontal tissues (i.e. follicle cells, periodontal cells, and cementoblasts) and offer new directions to consider for clinical repair of periodontal defects.

Bone Sialoprotein Gene Transfer to Periodontal Ligament Cells May Not Be Sufficient to Promote Mineralization In Vitro or In Vivo

BACKGROUND

To improve regenerative therapies, it is important to understand the cells and factors modulating periodontal tissues. Our group has focused on bone sialoprotein (BSP), a mineralized tissue-selective protein considered to be involved in the initiation of cementogenesis and osteogenesis. In this study, we examined whether gene transfer of BSP into periodontal ligament (PDL) cells would result in an increased ability of PDL cells to promote mineralization in vitro and in vivo.

METHODS

PDL cells obtained from CD-1 mice were immortalized using simian virus (SV) 40 large T antigen (TAg) and designated SV-PDL cells. SV-PDL cells were infected in vitro with LacZ gene-expressing control adenovirus vector. A 1,000 plaque-forming unit (pfu) titer was selected (based on X-gal staining) and cells were infected with mouse BSP-expressing replication-deficient adenoviral vector to determine the mRNA expression and protein level of BSP. Total RNA was isolated from cells on days 2, 4, and 6. Media were obtained on days 3, 5, and 7 for protein determination. Northern blot analysis was performed for mRNA expression and Western blot analysis for protein expression. To test the effect of BSP gene transfer on the mineralization of PDL cells, in vitro (von Kossa) and in vivo (severe combined immunodeficiency [SCID] mice) experiments were performed.

RESULTS

Under normal conditions, PDL cells do not express BSP transcripts and do not promote significant mineralization. SV-PDL cells infected with a BSP viral vector expressed and secreted substantial levels of BSP as confirmed by Northern and Western blot analysis. BSP mRNA and protein levels were strong on day 2 and still apparent on day 6, although not as great. However, no mineral nodule formation was noted either in vitro or in vivo.

CONCLUSIONS

Although BSP is an important and necessary protein for mineralization, it may not be sufficient for promoting mineralization without the addition or removal of other factors. Further studies will help to clarify the specific factors required for promoting mineralization, a required step for designing predictable periodontal regenerative therapies.

Effect of sustained gene delivery of platelet-derived growth factor or its antagonist (PDGF-1308) on tissue-engineered cementum

BACKGROUND

Cementum, a mineralized tissue lining the tooth root surface, is destroyed during the inflammatory process of periodontitis. Restoration of functional cementum is considered a criterion for successful regeneration of periodontal tissues, including formation of periodontal ligament, cementum, and alveolar bone. Short-term administration of platelet-derived growth factor (PDGF) has been shown to partially regenerate periodontal structures. Nonetheless, the role of PDGF in cementogenesis is not well understood. The aim of the present study was to determine the effect of sustained PDGF gene transfer on cementum formation in an ex vivo ectopic biomineralization model.

METHODS

Osteocalcin (OC) promoter-driven SV40 transgenic mice were used to obtain immortalized cementoblasts (OCCM). The OCCM cells were transduced with adenoviruses (Ad) encoding either PDGF-A, an antagonist of PDGF signaling (PDGF-1308), a control virus (green fluorescent protein, GFP), or no treatment (NT). The transduced cells were incorporated into polymer scaffolds and implanted subcutaneously into severe combined immunodeficient (SCID) mice. The implants were harvested at 3 and 6 weeks for histomorphometric analysis of the newly formed mineralized tissues. Northern blot analysis was performed to determine the expression levels of mineral-associated genes including bone sialoprotein (BSP), OC, and osteopontin (OPN) in the cell-implant specimens at 3 and 6 weeks.

RESULTS

The results indicated mineralization was significantly reduced in both the Ad/PDGF-A and Ad/PDGF-1308 treated specimens when compared to the NT or Ad/GFP groups at 3 and 6 weeks (P<0.01). In addition, the size of the implants treated with Ad/PDGF-A and Ad/PDGF-1308 was significantly reduced compared to implants from Ad/GFP and NT groups at 3 weeks (P<0.05). At 6 weeks, the size of implants and mineral formation increased in NT, Ad/GFP, and Ad/PDGF-A groups, while the Ad/PDGF-1308 treated implants continued to decrease in size and mineral formation (P<0.01). Northern blot analysis revealed that in the Ad/PDGF-A treated implants OPN was increased, whereas OC gene expression was downregulated at 3 weeks. In the Ad/PDGF-1308 treated implants, BSP, OC, and OPN were all downregulated at 3 weeks. At 3 weeks, the Ad/PDGF-A treated implants contained significantly higher multinucleated giant cell (MNGC) density compared to NT, Ad/GFP, and Ad/PDGF-1308 specimens. The MNGC density in NT, Ad/GFP, and Ad/PDGF-A treated groups reduced over time, while the Ad/PDGF-1308 transduced implants continued to exhibit significantly higher MNGC density compared with the other treatment groups at 6 weeks.

CONCLUSIONS

The results showed that continuous exposure to PDGF-A had an inhibitory effect on cementogenesis, possibly via the upregulation of OPN and subsequent enhancement of MNGCs at 3 weeks. On the other hand, Ad/PDGF-1308 inhibited mineralization of tissue-engineered cementum possibly due to the observed downregulation of BSP and OC and a persistence of stimulation of MNGCs. These findings suggest that continuous exogenous delivery of PDGF-A may delay mineral formation induced by cementoblasts, while PDGF is clearly required for mineral neogenesis.

Amelogenin: A Potential Regulator of Cementum-Associated Genes

BACKGROUND

Studies suggest that enamel matrix proteins induce differentiation and mineralization of a variety of mesenchymal cells, including odontoblasts, osteoblasts, and cementoblasts. It has been postulated that this activity could be due to amelogenin-like proteins, known to be present in some mixtures of enamel matrix derivatives. Amelogenins have been reported to induce expression of a mineralized tissue-specific marker, bone sialoprotein (BSP), indicating that epithelial products can regulate the activity of mesenchyme-derived cells.

METHODS

To explore the molecular mechanisms involved in BSP regulation, a clonal population of immortalized murine cementoblasts (OCCM-30) was exposed to full-length murine amelogenin protein (rp(H)M180), 0.1 microg/ml to 10.0 microg/ml, for 8 days in vitro. To further investigate the potential epithelial-mesenchymal interaction, an amelogenin knockout mouse model was used to examine expression of BSP and other markers, including Type I collagen, in tissue samples.

RESULTS

The lowest dose of amelogenin slightly enhanced BSP expression, whereas at the highest dose, a dramatic decrease (three-fold) in BSP expression was observed. Parallel experiments showed a corresponding decrease in mineral nodule formation in vitro for cells treated with the higher dose of rp(H)M180. In situ hybridization and immunohistochemical analysis of sections from amelogenin null mice revealed a dramatic reduction in expression of BSP mRNA and protein in cementoblasts and surrounding osteoblasts in comparison to age-matched controls. In contrast, the expression of Type I collagen was not significantly different from controls.

CONCLUSION

These data suggest that amelogenin may be a critical signaling molecule required for appropriate development of the periodontium.

Tooth eruption and cementum formation in the Runx2/Cbfa1 heterozygous mouse

Cleidocranial dysplasia (CCD) is an autosomal dominant human disorder that affects development of bones and teeth. The dental disorders in CCD patients include formation of supernumerary teeth, delayed tooth eruption, and lack of formation of cellular cementum in permanent teeth. This disorder involves a mutation in the osteoblast-specific transcription factor Runx2/Cbfa1, leading to haploinsufficiency of the Runx2/Cbfa1 protein. Here, we examined if Runx2/Cbfa1 heterozygous mice (with one functional allele for Runx2/Cbfa1) exhibit similar changes in tooth eruption, and dental cementum formation as in CCD patients. Heads of Runx2/Cbfa1 heterogeneous and wildtype mice aged days 16-35 postnatally were serially sectioned and stained with hematoxylin-eosin or for tartrate resistant acid phosphatase (TRAP) to identify osteoclasts. The results showed that the eruption pattern of the first and second molars in maxilla and mandible in Runx2/Cbfa1 +/- mice was the same as in wildtype animals. No clear difference in distribution or in the (estimated) number of osteoclasts was found. Cellular cement at the apical portions of the molar roots was present in both groups. The data suggests that in the mouse one allele for Runx2/Cbfa1 is sufficient for an undisturbed tooth eruption and an apparently normal formation of the periodontium.

Gene expression of growth differentiation factors in the developing periodontium of rat molars

Growth and differentiation factors (GDF) 5, 6, and 7 are known to play roles in tendon and ligament formation, and are therefore probably involved in the formation of periodontal ligament. In this study, we sought to determine temporal and spatial expression of GDF-5, -6, and -7 mRNA in developing periodontal tissue of rat molars using in situ hybridization. GDF gene expression in the periodontal ligament was first detected in cells associated with the initial process of periodontal ligament fiber bundle formation. Gene signals were also detected in cells located along the alveolar bone and cementum surfaces, the insertion sites of periodontal ligaments, during the course of root formation. GDF expression in these cells were down-regulated after completion of root formation. Our results appeared to suggest the involvement of GDF-5, -6, and -7 in the formation of the dental attachment apparatus.

Expression of bone morphogenetic proteins and Msx genes during root formation

Like crown development, root formation is also regulated by interactions between epithelial and mesenchymml tissues. Bone morphogenetic proteins (BMPs), together with the transcription factors Msx1 and Msx2, play important roles in these interactions during early tooth morphogenesis. To investigate the involvement of this signaling pathway in root development, we analyzed the expression patterns of Bmp2, Bmp3, Bmp4, and Bmp7 as well as Msx1 and Msx2 in the roots of mouse molars. Bmp4 was expressed in the apical mesenchyme and Msx2 in the root sheath. However, Bmps were not detected in the root sheath epithelium, and Msx transcripts were absent from the underlying mesenchyme. These findings indicate that this Bmp signaling pathway, required for tooth initiation, does not regulate root development, but we suggest that root shape may be regulated by a mechanism similar to that regulating crown shape in cap-stage tooth germs. Msx2 expression continued in the epithelial cell rests of Malassez, and the nearby cementoblasts intensely expressed Bmp3, which may regulate some functions of the fragmented epithelium.

Cementum: a phosphate-sensitive tissue

Ectopic calcification within joints has been reported in humans and rodents exhibiting mutations in genes that regulate the level of extracellular pyrophosphate, e.g., ank and PC-1; however, periodontal effects of these mutations have not previously been examined. These initial studies using ank and PC-1 mutant mice were done to see if such mineral deposition and resulting ankylosis were occurring in the periodontium as well. Surprisingly, results indicated the absence of ankylosis; however, a marked increase in cementum formation on the root surfaces of fully developed teeth of these mutant mice was noted. Examination of ank mutant mice at earlier ages of tooth root formation indicated that this striking observation is apparent from the onset of cementogenesis. These findings suggest that cells within the periodontal region are highly responsive to changes in phosphate metabolism. This information may prove valuable in attempts to design successful therapies for regenerating periodontal tissues.