Differentiation Of Dental Follicle Cells Research Articles

Evaluation of Current Studies to Elucidate Processes in Dental Follicle Cells Driving Osteogenic Differentiation.

When research on osteogenic differentiation in dental follicle cells (DFCs) began, projects focused on bone morphogenetic protein (BMP) signaling. The BMP pathway induces the transcription factor DLX3, whichh in turn induces the BMP signaling pathway via a positive feedback mechanism. However, this BMP2/DLX3 signaling pathway only seems to support the early phase of osteogenic differentiation, since simultaneous induction of BMP2 or DLX3 does not further promote differentiation. Recent data showed that inhibition of classical protein kinase C (PKCs) supports the mineralization of DFCs and that osteogenic differentiation is sensitive to changes in signaling pathways, such as protein kinase B (PKB), also known as AKT. Small changes in the lipidome seem to confirm the participation of AKT and PKC in osteogenic differentiation. In addition, metabolic processes, such as fatty acid biosynthesis, oxidative phosphorylation, or glycolysis, are essential for the osteogenic differentiation of DFCs. This review article attempts not only to bring the various factors into a coherent picture of osteogenic differentiation in DFCs, but also to relate them to recent developments in other types of osteogenic progenitor cells.

Curcumin attenuates replicative senescence in human dental follicle cells and restores their osteogenic differentiation

ObjectiveThis study aimed to examine the therapeutic effects of curcumin against replicative senescence in dental follicle cells (DFCs). MethodsHuman DFCs were cultured in Dulbecco's Modified Eagle Medium with growth supplements. Replicative senescence in DFCs at different passages was assessed using β-galactosidase activity assay. Cell proliferation and size of DFCs at different passages were determined by CCK-8 kit and microscopy method, respectively. In addition, curcumin's effect on replicative senescence, cell proliferation, and size of DFCs at different passages was analyzed. Using western-blot analysis and siRNA-mediated gene silencing, we determined the molecular mechanisms involved in curcumin's effect against replicative senescence and osteogenic differentiation in DFCs at different passages. ResultsWe observed decreased proliferation and increased cell size and replicative senescence in cultured human DFCs at higher passages. Intriguingly, despite not showing any effect on cell size, curcumin (50 μM) significantly restored proliferation ability in DFCs and inhibited their replicative senescence. Concerning mechanisms, we found that curcumin inhibits replicative senescence in DFCs via down-regulation of senescence markers (P16 & P21) and restoration of proliferation markers (E2F1 & P53). Additionally, curcumin also rescued the osteogenic differentiation potential in higher-passage DFCs via restoration of osteogenic markers RUNX2 and OPN. ConclusionOur findings reveal for the first time that curcumin could act as a potential anti-senescence therapeutic for DFCs via regulation of proliferation, senescence, and osteogenic differentiation markers.

Energy Metabolism and Lipidome Are Highly Regulated during Osteogenic Differentiation of Dental Follicle Cells.

Dental follicle cells (DFCs) are stem/progenitor cells of the periodontium and give rise to alveolar osteoblasts. However, understanding of the molecular mechanisms of osteogenic differentiation, which is required for cell-based therapies, is delimited. This study is aimed at analyzing the energy metabolism during the osteogenic differentiation of DFCs. Human DFCs were cultured, and osteogenic differentiation was induced by either dexamethasone or bone morphogenetic protein 2 (BMP2). Previous microarray data were reanalyzed to examine pathways that are regulated after osteogenic induction. Expression and activity of metabolic markers were evaluated by western blot analysis and specific assays, relative amount of mitochondrial DNA was measured by real-time quantitative polymerase chain reaction, the oxidative state of cells was determined by a glutathione assay, and the lipidome of cells was analyzed via mass spectrometry (MS). Moreover, osteogenic markers were analyzed after the inhibition of fatty acid synthesis by 5-(tetradecyloxy)-2-furoic acid or C75. Pathway enrichment analysis of microarray data revealed that carbon metabolism was amongst the top regulated pathways after osteogenic induction in DFCs. Further analysis showed that enzymes involved in glycolysis, citric acid cycle, mitochondrial activity, and lipid metabolism are differentially expressed during differentiation, with most markers upregulated and more markedly after induction with dexamethasone compared to BMP2. Moreover, the cellular state was more oxidized, and mitochondrial DNA was distinctly upregulated during the second half of differentiation. Besides, MS of the lipidome revealed higher lipid concentrations after osteogenic induction, with a preference for species with lower numbers of C-atoms and double bonds, which indicates a de novo synthesis of lipids. Concordantly, inhibition of fatty acid synthesis impeded the osteogenic differentiation of DFCs. This study demonstrates that energy metabolism is highly regulated during osteogenic differentiation of DFCs including changes in the lipidome suggesting enhanced de novo synthesis of lipids, which are required for the differentiation process.

Mechanisms during Osteogenic Differentiation in Human Dental Follicle Cells.

Human dental follicle cells (DFCs) as periodontal progenitor cells are used for studies and research in regenerative medicine and not only in dentistry. Even if innovative regenerative therapies in medicine are often considered the main research area for dental stem cells, these cells are also very useful in basic research and here, for example, for the elucidation of molecular processes in the differentiation into mineralizing cells. This article summarizes the molecular mechanisms driving osteogenic differentiation of DFCs. The positive feedback loop of bone morphogenetic protein (BMP) 2 and homeobox protein DLX3 and a signaling pathway associated with protein kinase B (AKT) and protein kinase C (PKC) are presented and further insights related to other signaling pathways such as the WNT signaling pathway are explained. Subsequently, some works are presented that have investigated epigenetic modifications and non-coding ncRNAs and their connection with the osteogenic differentiation of DFCs. In addition, studies are presented that have shown the influence of extracellular matrix molecules or fundamental biological processes such as cellular senescence on osteogenic differentiation. The putative role of factors associated with inflammatory processes, such as interleukin 8, in osteogenic differentiation is also briefly discussed. This article summarizes the most important insights into the mechanisms of osteogenic differentiation in DFCs and is intended to be a small help in the direction of new research projects in this area.

Puerarin promotes the osteogenic differentiation of rat dental follicle cells by promoting the activation of the nitric oxide pathway

Puerarin regulates the osteoblast differentiation of umbilical cord mesenchymal stem cells. This study, hereby, explored the effects of puerarin on the osteogenic differentiation of dental follicle cells (DFCs) for the first time. Rat DFCs (rDFCs) were isolated and identified. After the rDFCs were treated by Puerarin and cultured in osteogenic induction medium, the viability, osteogenic differentiation, and the activities of alkaline phosphatase (ALP) and nitric oxide (NO) were detected. Besides, the secretion of cyclic guanosine monophosphate (cGMP) and expressions of collagen I, osteocalcin (OC), osteopontin (OPN), runt-related transcription factor 2 (RUNX2), soluble guanylate cyclase (SGC), and protein kinase G 1 (PKG-1) were further determined or quantified. Puerarin enhanced the viability and osteogenic differentiation, and increased the activities of ALP, NO, and cGMP and the expressions of Collagen I, OC, OPN, RUNX2, SGC, and PKG-1 in rDFCs. After the co-treatment with puerarin and L-NMMA (NO synthase inhibitor), the promotive effects of Puerarin on cell viability, osteogenic differentiation, and the expressions of collagen I, OC, OPN, RUNX2, SGC, and PKG-1 in rDFCs were reversed by L-NMMA. Puerarin boosted the osteogenic differentiation of rDFCs by activating the NO pathway.

Classical isoforms of protein kinase C (PKC) and Akt regulate the osteogenic differentiation of human dental follicle cells via both \u03b2-catenin and NF-\u03baB

BackgroundHuman dental follicle cells (DFCs) are the precursor cells of the periodontium with a high potential for regenerative therapies of (alveolar) bone. However, the molecular mechanisms of osteogenic differentiation are inadequately understood. Classical isoforms of protein kinase C (PKC) are reported to inhibit osteogenesis of stem/precursor cells. This study evaluated the role of classical PKCs and potential downstream targets on the osteogenic differentiation of DFCs.MethodsDFCs were osteogenic differentiated with dexamethasone or bone morphogenetic protein 2 (BMP2). Expression of PKC and potential upstream/downstream regulators was manipulated using activators, inhibitors, and small interfering ribonucleic acid (siRNA). Expression of proteins was examined by Western blot analysis, while the activation levels of enzymes and transcription factors were examined by their phosphorylation states or by specific activation assays. Expression levels of osteogenic markers were examined by RT-qPCR (reverse transcription-quantitative polymerase chain reaction) analysis. Activity of alkaline phosphatase (ALP) and accumulation of calcium nodules by Alizarin Red staining were measured as indicators of mineralization.ResultsClassical PKCs like PKCα inhibit the osteogenic differentiation of DFCs, but do not interfere with the induction of differentiation. Inhibition of classical PKCs by Gö6976 enhanced activity of Akt after osteogenic induction. Akt was also regulated during differentiation and especially disturbed BMP2-induced mineralization. The PKC/Akt axis was further shown to regulate the canonical Wnt signaling pathway and eventually nuclear expression of active β-catenin during dexamethasone-induced osteogenesis. Moreover, the nuclear factor “kappa-light-chain-enhancer” of activated B cells (NF-κB) pathway is regulated during osteogenic differentiation of DFCs and via the PKC/Akt axis and disturbs the mineralization. Upstream, parathyroid hormone-related protein (PTHrP) sustained the activity of PKC, while Wnt5a inhibited it.ConclusionsOur results demonstrate that classical PKCs like PKCα and Akt regulate the osteogenic differentiation of DFCs partly via both β-catenin and NF-κB.

VPS4B mutation impairs the osteogenic differentiation of dental follicle cells derived from a patient with dentin dysplasia type I

A splicing mutation in VPS4B can cause dentin dysplasia type I (DD-I), a hereditary autosomal-dominant disorder characterized by rootless teeth, the etiology of which is genetically heterogeneous. In our study, dental follicle cells (DFCs) were isolated and cultured from a patient with DD-I and compared with those from an age-matched, healthy control. In a previous study, this DD-I patient was confirmed to have a loss-of-function splicing mutation in VPS4B (IVS7 + 46C > G). The results from this study showed that the isolated DFCs were vimentin-positive and CK14-negative, indicating that the isolated cells were derived from the mesenchyme. DFCs harboring the VPS4B mutation had a significantly higher proliferation rate from day 3 to day 8 than control DFCs, indicating that VPS4B is involved in cell proliferation. The cells were then replenished with osteogenic medium to investigate how the VPS4B mutation affected osteogenic differentiation. Induction of osteogenesis, detected by alizarin red and alkaline phosphatase staining in vitro, was decreased in the DFCs from the DD-I patient compared to the control DFCs. Furthermore, we also found that the VPS4B mutation in the DD-I patient downregulated the expression of osteoblast-related genes, such as ALP, BSP, OCN, RUNX2, and their encoded proteins. These outcomes confirmed that the DD-I-associated VPS4B mutation could decrease the capacity of DFCs to differentiate during the mineralization process and may also impair physiological root formation and bone remodeling. This might provide valuable insights and implications for exploring the pathological mechanisms underlying DD-I root development.

NFIC promotes the vitality and osteogenic differentiation of rat dental follicle cells

Nuclear factor I-C (NFIC) plays critical roles in the regulation of tooth development by influencing the biological behaviors of stem cells in the dental germ. This study aimed to investigate the effect of NFIC on the vitality and osteogenic/cementogenic differentiation of rat dental follicle cells (DFCs). DFCs were isolated from dental follicles in the first molars of neonatal rats. DFCs expressed mesenchymal stromal cell markers CD29, CD44 and CD90 and had capabilities for self-renewal and multipotent differentiation. Overexpression of NFIC promoted the proliferation of DFCs without markedly influencing the apoptosis of DFCs. Moreover, NFIC increased alkaline phosphatase (ALP) activity in DFCs and upregulated the mRNA levels of osteogenic-related markers, namely, collagen type I (Col I), Runt-related transcription factor 2 (Runx2) and ALP, as well as β-catenin. In contrast, silencing NFIC by siRNA increased the apoptosis of DFCs and downregulated the expression of osteogenic-related markers. In conclusion, these results suggested that upregulation of NFIC may promote the proliferation and osteogenic/cementogenic differentiation of DFCs.

WNT5A supports viability of senescent human dental follicle cells.

The osteogenic differentiation of dental follicle cells (DFCs) is inhibited by the onset of cellular senescence, but the cause for this is largely unknown. Recently it was shown that WNT5a, which is an inductor of the non-canonical WNT pathway, stimulates both cellular senescence and osteogenic differentiation of different cell types. In this study, we investigated the role of WNT5a for viability and osteogenic differentiation in human DFCs after the induction of cellular senescence. DFCs were cultivated until the induction of cellular senescence. The induction of cellular senescence was confirmed by β-galactosidase staining, estimation of population doubling time, and slightly telomere length shortening. After induction of cellular senescence, the expression of WNT5A and the potential to induce the osteogenic differentiation decreased. Inhibition of WNT5A by specific siRNAs had significant effect on the viability of DFCs. Cell proliferation was reduced, whereas both cellular senescence and cell death were increased in DFCs. However, an inhibition of WNT5A did only slightly effect the osteogenic differentiation of DFCs. Our results suggest that WNT5A supports viability during both cell proliferation and osteogenic differentiation of DFCs.

RUNX2 mutation impairs osteogenic differentiation of dental follicle cells

ObjectivesCleidocranial dysplasia (CCD), mainly caused by RUNX2 mutation, is a dominantly inherited skeletal disorder with many dental abnormalities, characterized by delayed permanent tooth eruption. In this study, we explored a novel RUNX2 mutation and the effect of RUNX2 mutation on osteogenic differentiation of dental follicle cells (DFCs). DesignA CCD patient with typical clinical features was involved in this study. Conservation and secondary structural analysis of the RUNX2 mutation was first performed. Then DFCs that stably expressing wild-type or mutant RUNX2 were established using lentiviruses. Cell Counting Kit 8 (CCK8) assays were performed to test the proliferation of DFCs. Measurement of alkaline phosphatase (ALP) activity, ALP staining, alizarin red staining and determination of osteoblast-specific genes expression were performed to assess osteogenic capacity of DFCs. ResultsA missense mutation (c.674 G > T, p. R225 L) of RUNX2 gene was identified in the CCD patient. Conservation and secondary structural analysis revealed that the mutation was located in highly conserved Runt domain and altered secondary structure of RUNX2. CCK8 assays showed that mutant RUNX2 increased the proliferation rate of DFCs compared to wild-type RUNX2. ALP activity, ALP staining and alizarin red staining results indicated that mutant RUNX2 decreased the mineralization ability of DFCs. In addition, mutant RUNX2 significantly down-regulated the expression of osteoblast-associated genes. ConclusionsRUNX2 mutation can reduce the osteogenic capacity of DFCs by inhibiting osteoblast-associated genes and then affecting bone formation, which participates in bone remodeling during tooth eruption. These effects may be partly responsible for the defects in permanent tooth eruption of CCD patients.

RUNX2 mutation reduces osteogenic differentiation of dental follicle cells in cleidocranial dysplasia.

Disturbed permanent tooth eruption is common in cleidocranial dysplasia (CCD), a skeletal disorder caused by heterozygous mutation of RUNX2, but the mechanism underlying is still unclear. As it is well known that dental follicle cells (DFCs) play a critical role in tooth eruption, the changed biological characteristics of DFCs might give rise to disturbance of permanent tooth eruption in CCD patients. Thus, primary DFCs from one CCD patient and normal controls were collected to investigate the effect of RUNX2 mutation on the bone remodeling activity of DFCs and explore the mechanism of impaired permanent tooth eruption in this disease. Conservation and secondary structure analysis revealed that the RUNX2 mutation (c.514delT, p.172fs) found in the present CCD patient was located in the highly conserved RUNT domain and converted the structure of RUNX2. After osteogenic induction, we found that the mineralised capacity of DFCs and the expression of osteoblast-related genes, including RUNX2, ALP, OSX, OCN and Col Iα1, in DFCs was severely interfered by the RUNX2 mutation found in CCD patients. To investigate whether the osteogenic deficiency of DFCs from the CCD patient can be rescued by RUNX2 restoration, we performed 'rescue' experiments. Surprisingly, the osteogenic deficiency and the abnormal expression of osteoblast-associated genes in DFCs from the CCD patient were almost rescued by overexpression of wild-type RUNX2 using lentivirus. All these findings indicate that RUNX2 mutation can reduce the osteogenic capacity of DFCs through inhibiting osteoblast-associated genes, thereby disturbing alveolar bone formation, which serves as a motive force for tooth eruption. This effect may provide valuable explanations and implications for the mechanism of delayed permanent tooth eruption in CCD patients.

Are Hertwig’s epithelial root sheath cells necessary for periodontal formation by dental follicle cells?

ObjectiveThe role of Hertwig’s epithelial root sheath (HERS) cells in periodontal formation has been controversial. This study aimed to further clarify whether HERS cells participate in formation of the periodontium, and the necessity of HERS cells in differentiation of dental follicle cells (DFCs) for periodontal regeneration. DesignHERS cells and DFCs were isolated and identified from post-natal 7-day Sprauge-Dawley rats. In vitro, direct co-culture of HERS cells and DFCs as well as the individual culture of HERS and DFCs were performed and followed by alizarin red staining and the quantitative real-time polymerase chain reaction analysis. For in vivo evaluation, the inactivated dentin matrix (iTDM) was fabricated. HERS cells and DFCs were seeded in combination or alone on iTDM and then transplanted into the rat omentum. Scanning electron microscope and further histological analysis were carried out. ResultsIn vitro, mineral-like nodules were found in the culture of HERS cells alone or HERS + DFCs either by alizarin red staining or scanning electronic microscope. The mineralization and fiber-forming relevant mRNA expressions, such as bone sialoprotein, osteopontin, collagen I and collagen III in HERS + DFCs were significantly higher than that of the HERS or DFCs alone group. After transplantation in vivo, cementum and periodontal ligament-like tissues were formed in groups of HERS + DFCs and HERS alone, while no evident hard tissues and attached fibers were found in DFCs alone. ConclusionsHertwig’s epithelial root sheath cells directly participate in the formation of the periodontium, and they are essential for the differentiation of dental follicle cells to form periodontal structures. The combination use of Hertwig’s epithelial root sheath cells and dental follicle cells is a promising approach for periodontal regeneration.

Naked cuticle homolog 2 positively regulates the osteogenic differentiation of rat dental follicle cells

Objective: To examine the expression of naked cuticle homolog 2 (Nkd2) in the process of root development and osteogenic differentiation of dental follicle cells of rat (rDFC), in order to explore the molecular mechanisms of Nkd2 on the osteoblast differentiation of rDFCs. Methods: Immunohistochemical analysis was used to detect the expression of Nkd2 in the base dental follicle of the mandibular first molar of rat at 1, 3, 5, 7, 9, 11 and 13 days postnatal. Mineralization nodule formation of rDFCs was detected by alizarin red staining and cetylpyridine. The change of Nkd2 during osteogenic differentiation of rDFCs was evaluated by Western blotting and the associations between Nkd2 and osteogenic cytokines of alkaline phosphatase (ALP), Runt-related transcription factor-2 (RUNX2) and osteocalcin (OCN) were examined. The rDFCs were transfected with small interfering RNA (siRNA) to knock down the expression of Nkd2 and Western blotting and quantitative real-time PCR (qPCR) were adopted to explore the effects of Nkd2 on osteogenic differentiation by detecting variations of Nkd2 and osteogenic factors ALP, RUNX2, OCN among silencing group (Si), negative control RNA group (Nc) and mock control group (Mock), respectively. Results: The expression of Nkd2 in the base dental follicle of the mandibular first molar of rat was time dependent. Mineralization nodules of rDFCs and absorbance of cetylpyridine after osteogenic induction increased gradually (the absorbances of cetylpyridine were 0 week: 0.017±0.005, 1 week: 0.702±0.044, 2 weeks: 1.812±0.531, 3 weeks: 2.767±0.253, respectively). Results of Western blotting showed that Nkd2 (1.60±0.23) of mineralization group was significantly higher than that of control group (1) (P<0.05) at the early stage of osteogenic differentiation along with the expression of other osteogenic factors. The protein and mRNA of Nkd2 and osteogenic factors were significantly decreased in Si group compared with Nc and Mock groups (P<0.05), and no changes between Nc and Mock groups were observed. The changes of protein in Si, Nc and Mock groups were Nkd2: 0.42±0.10, 1.12±0.07, 1, ALP: 0.70±0.15, 1.11±0.14, 1, RUNX2: 0.58±0.08, 0.93±0.08, 1 and OCN: 0.64±0.06, 0.99±0.02, 1, respectively. The mRNA variances in Si, Nc and Mock groups were Nkd2: 0.39±0.05, 0.96±0.10, 1, ALP: 0.15±0.13, 1.01±0.07, 1, RUNX2: 0.39±0.31, 0.97±0.13, 1, OCN: 0.17±0.08, 1.08±0.21, 1, respectively. Conclusions: Nkd2 participates in the root development process in rat and may acts as a positive role in the early stage of osteogenic differentiation of rDFCs in rat.

F-spondin negatively regulates dental follicle differentiation through the inhibition of TGF-β activity

ObjectiveF-spondin is an extracellular matrix (ECM) protein that belongs to the thrombospondin type I repeat superfamily and is a negative regulator of bone mass. We have previously shown that f-spondin is specifically expressed in the dental follicle (DF), which gives rise to the periodontal ligament (PDL) during the tooth root formation stage. To investigate the molecular mechanism of PDL formation, we investigated the function of f-spondin in DF differentiation. DesignThe expression patterning of f-spondin in the developing tooth germ was compared with that of periodontal ligament-related genes, including runx2, type I collagen and periostin, by in situ hybridization analysis. To investigate the function of f-spondin during periodontal ligament formation, an f-spondin adenovirus was infected into the bell stage of the developing tooth germ, and the effect on dental differentiation was analyzed. ResultsF-spondin was specifically expressed in the DF of the developing tooth germ; by contrast, type I collagen, runx2 and periostin were expressed in the DF and in the alveolar bone. F-spondin-overexpresssing tooth germ exhibited a reduction in gene expression of periostin and type I collagen in the DF. By contrast, the knockdown of f-spondin in primary DF cells increased the expression of these genes. Treatment with recombinant f-spondin protein functionally inhibited periostin expression induced by transforming growth factor-β (TGF-β). ConclusionOur data indicated that f-spondin inhibits the differentiation of DF cells into periodontal ligament cells by inhibiting TGF-β. These data suggested that f-spondin negatively regulates PDL differentiation which may play an important role in the immature phenotype of DF.

The hedgehog-signaling pathway is repressed during the osteogenic differentiation of dental follicle cells.

Dental follicle stem cells (DFCs) are precursor cells of alveolar osteoblasts, and previous studies have shown that the growth factor bone morphogenetic protein (BMP)2 induces the osteogenic differentiation of DFCs. However, the molecular mechanism down-stream of the induction of the osteogenic differentiation by BMP2 remains elusive. We investigated therefore the phosphoproteome of DFCs after the induction of the osteogenic differentiation with BMP2. In this study, phosphoproteins of the hedgehog "off" state were differentially expressed. Further analyses revealed that BMP2 induced the expression of repressors of the hedgehog-signaling pathway such as Patched 1 (PTCH1), Suppressor of Fused (SUFU), and Parathyroid Hormone-Related Peptide (PTHrP). Previous studies suggested that hedgehog proteins induce the osteogenic differentiation of mesenchymal stem cells via a paracrine pathway. Indian hedgehog (IHH) induced the expression of the osteogenic transcription factor RUNX2. However, a supplementation of the BMP2-based osteogenic differentiation medium with IHH did not induce the expression of RUNX2. Moreover, IHH inhibited slightly the ALP activity and the mineralization of osteogenic-differentiated DFCs. In conclusion, our results suggest that BMP2 inhibits the hedgehog signaling after the induction of the osteogenic differentiation in DFCs.

MiRNA-101 supports the osteogenic differentiation in human dental follicle cells

ObjectiveHuman dental follicle cells (DFCs) are genuine precursor cells of cementoblasts and alveolar bone osteoblasts. MicroRNAs (miRNAs) represent a class of non-coding endogenous RNAs that silence gene expression post-transcriptionally. miRNA101 actively regulates the osteogenic differentiation of periodontal ligament cells. Therefore the aim of this study was to investigate the role of miRNA101 during the osteogenic differentiation in DFCs. Materials and methodsDFCs were isolated, cultivated and osteogenic differentiated in differentiation medium. Total RNA including miRNAs was isolated and the expression of miRNA101 was examined by real-time RT-PCRs. The expression of miRNA101 was induced by miRNA101-mimic transfection and the gene expression of osteogenic transcription factors was obtained by real-time RT-PCRs. Moreover the induction of the osteogenic differentiation was evaluated by the activity of alkaline phosphatase. ResultsmiRNA101 was regulated in DFCs during the osteogenic differentiation. After miRNA101-mimic transfection the alkaline phosphatase was increased and the gene expression of typical osteogenic transcription factors such as SP7 (osterix) was up-regulated. ConclusionOur results suggest that miRNA101 sustains the osteogenic differentiation of DFCs.

The induction of cellular senescence in dental follicle cells inhibits the osteogenic differentiation.

Dental stem cells such as human dental follicle cells (DFCs) have opened new promising treatment alternatives for today's dental health issues such as periodontal tissue regeneration. However, cellular senescence represents a restricting factor to cultured stem cells, resulting in limited lifespan and reduced cell differentiation potential. Therefore, this study evaluated if and how DFCs exhibit features of cellular senescence after being expanded in cell culture. The cell proliferation of DFCs decreased, while the cell size increased during prolonged cell culture. Moreover, DFCs expressed the senescence-associated β-galactosidase after a prolonged cell culture. The onset of senescence inhibited both the induction of osteoblast markers RUNX2 and osteopontin and the biomineralization of DFCs after stimulation of the osteogenic differentiation. In conclusion, we showed that a prolonged cell culture induces cellular senescence and inhibits the osteogenic differentiation in DFCs.

Wnt5a attenuates Wnt3a-induced alkaline phosphatase expression in dental follicle cells

Wnt signaling regulates multiple cellular events such as cell proliferation, differentiation, and apoptosis through β-catenin-dependent canonical and β-catenin-independent noncanonical pathways. Canonical Wnt/β-catenin signaling can promote the differentiation of dental follicle cells, putative progenitor cells for cementoblasts, osteoblasts, and periodontal ligament cells, toward a cementoblast/osteoblast phenotype during root formation, but little is known about the biological significance of noncanonical Wnt signaling in this process. We identified the expression of Wnt5a, a representative noncanonical Wnt ligand, in tooth root lining cells (i.e. precementoblasts/cementoblasts) and dental follicle cells during mouse tooth root development, as assessed by immunohistochemistry. Silencing expression of the Wnt5a gene in a dental follicle cell line resulted in enhancement of the Wnt3a (a representative canonical Wnt ligand)-mediated increase in alkaline phosphatase (ALP) expression. Conversely, treatment with recombinant Wnt5a inhibited the increase in ALP expression, suggesting that Wnt5a signaling functions as a negative regulator of canonical Wnt-mediated ALP expression of dental follicle cells. Wnt5a did not affect the nuclear translocation of β-catenin as well as β-catenin-mediated transcriptional activation of T-cell factor (Tcf) triggered by Wnt3a, suggesting that Wnt5a inhibits the downstream part of the β-catenin-Tcf pathway. These findings suggest the existence of a feedback mechanism between canonical and noncanonical Wnt signaling during the differentiation of dental follicle cells.

Wnt3a signaling induces murine dental follicle cells to differentiate into cementoblastic/osteoblastic cells via an osterix-dependent pathway.

Dental follicle cells, putative progenitor cells for cementoblasts, osteoblasts and periodontal ligament cells, interplay with Hertwig's epithelial root sheath (HERS) cells during tooth root formation, in which HERS is considered to have an inductive role in initiating cementogenesis by epithelial-mesenchymal interaction. However, the specific mechanisms controlling the cementoblast/osteoblast differentiation of dental follicle cells are not fully understood. Canonical Wnt signaling has been implicated in increased bone formation by controlling mesenchymal stem cell or osteoblastic cell functions. This study examined the possible expression of canonical Wnt ligand in HERS and the role of Wnt signaling during the cementoblast/osteoblast differentiation of dental follicle cells. The expression of Wnt3a, a representative canonical Wnt ligand, in HERS was assessed by immunohistochemistry. The differentiation and function of immortalized murine dental follicle cells were evaluated by measuring alkaline phosphatase (ALP, Alpl) activity and osteogenic gene expression. We identified the expression of Wnt3a in HERS during mouse tooth root development by immunohistochemistry as well as in cultured human epithelial rest cells of Malassez by real-time polymerase chain reaction, while no expression of Wnt3a was detected in cultured dental mesenchymal cells. Exposure of immortalized murine dental follicle cells to Wnt3a-induced ALP activity as well as expression of the Alpl gene. Pretreatment of cells with Dickkopf-1, a potent canonical Wnt antagonist, markedly attenuated the effect of Wnt3a on ALP expression. Furthermore, Wnt3a induced transcriptional activity of runt-related transcription factor 2 (Runx2) and expression of osterix at gene and/or protein levels. Treatment with osterix-small interfering RNA significantly inhibited Wnt3a-induced ALP expression at gene and protein levels. These findings suggest that HERS has a potential role in stimulating cementoblast/osteoblast differentiation of dental follicle cells via the Wnt/β-catenin signaling pathway.

The WNT inhibitor APCDD1 sustains the expression of β-Catenin during the osteogenic differentiation of human dental follicle cells

In hair follicle cells APCDD1 inhibits the canonical WNT/β-Catenin pathway and its inactivation is associated with an autosomal dominant form of hair loss. We analyzed the role of APCDD1 for the osteogenic differentiation in dental follicle cells (DFCs) and identified a new and surprising function. Contrarily to hair follicle cells APCDD1 was crucial for the expression of β-Catenin and for the activity of the TCF/LEF reporter assay in DFCs. In addition, a depletion of APCDD1 inhibits the expression of osteogenic markers such as RUNX2 and decreased the matrix mineralization. However, similar to hair follicle cells in previous studies a control cell culture with oral squamous carcinoma cells showed that APCDD1 inhibits the expression of β-Catenin and of typical target genes of the canonical WNT/β-Catenin pathway. In conclusion, our data disclosed an unusual role of APCDD1 in DFCs during the osteogenic differentiation. APCDD1 sustains the expression and activation of β-Catenin.