Notch2 protein distribution in human teeth under normal and pathological conditions

Involvement of the Notch signaling system in alveolar bone resorption

The Notch pathway is an evolutionarily preserved signaling pathway involved in a variety of vital cell functions. Additionally, it is one of the key regulators of inflammation, and controls the differentiation and function of different cells. Moreover, it was found to be involved in skeletal development and bone remodeling process. This review provides an overview of the involvement of the Notch signaling pathway in the pathogenesis of alveolar bone resorption in different forms of pathological conditions such as apical periodontitis, periodontal disease, and peri-implantitis. In vitro and in vivo evidence have confirmed the involvement of Notch signaling in alveolar bone homeostasis. Nonetheless, Notch signaling system, along with complex network of different biomolecules are involved in pathological process of bone resorption in apical periodontitis, periodontitis, and peri-implantitis. In this regard, there is a substantial interest to control the activity of this pathway in the treatment of disorders associated with its dysregulation. This review provides knowledge on Notch signaling and outlines its functions in alveolar bone homeostasis and alveolar bone resorption. Further investigations are needed to determine whether inhibition of the Notch signaling pathways might be beneficial and safe as a novel approach in the treatment of these pathological conditions.

The Versatile Roles of Nerve Growth Factor in Neuronal Attraction, Odontoblast Differentiation, and Mineral Deposition in Human Teeth

Nerve growth factor (NGF) is an important molecule for the development and differentiation of neuronal and non-neuronal cells. Here we analyze by immunohistochemistry the distribution of NGF in the dental pulp mesenchyme of embryonic and functional human teeth. In the dental pulp of both embryonic and healthy functional teeth, NGF is mainly expressed in the odontoblasts that are responsible for dentine formation, while in functional teeth NGF is also expressed in nerve fibers innervating the dental pulp. In injured teeth, NGF is expressed in the newly formed odontoblastic-like cells, which replace the dying odontoblasts. In these teeth, NGF expression is also upregulated in the intact odontoblasts, suggesting a role for this molecule in dental tissue repair. Similarly, in cultures of human dental pulp cells, NGF expression is strongly upregulated during their differentiation into odontoblasts as well as during the mineralization process. In microfluidic devices, release of NGF from cultured human dental pulp cells induced neuronal growth from trigeminal ganglia toward the NGF secreting cells. These results show that NGF is closely linked to the various functions of odontoblasts, including secretory and neuronal attraction processes.

Notch signaling in the dynamics of perivascular stem cells and their niches

The Notch signaling pathway is a fundamental regulator of cell fate determination in homeostasis and regeneration. In this work, we aimed to determine how Notch signaling mediates the interactions between perivascular stem cells and their niches in human dental mesenchymal tissues, both in homeostatic and regenerative conditions. By single cell RNA sequencing analysis, we showed that perivascular cells across the dental pulp and periodontal human tissues all express NOTCH3, and that these cells are important for the response to traumatic injuries in vivo in a transgenic mouse model. We further showed that the behavior of perivascular NOTCH3‐expressing stem cells could be modulated by cellular and molecular cues deriving from their microenvironments. Taken together, the present studies, reinforced by single‐cell analysis, reveal the pivotal importance of Notch signaling in the crosstalk between perivascular stem cells and their niches in tissue homeostasis and regeneration.

A single-cell atlas of human teeth

Teeth exert fundamental functions related to mastication and speech. Despite their great biomedical importance, an overall picture of their cellular and molecular composition is still missing. In this study, we have mapped the transcriptional landscape of the various cell populations that compose human teeth at single-cell resolution, and we analyzed in deeper detail their stem cell populations and their microenvironment. Our study identified great cellular heterogeneity in the dental pulp and the periodontium. Unexpectedly, we found that the molecular signatures of the stem cell populations were very similar, while their respective microenvironments strongly diverged. Our findings suggest that the microenvironmental specificity is a potential source for functional differences between highly similar stem cells located in the various tooth compartments and open new perspectives toward cell-based dental therapeutic approaches.

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Dental atlas of the pulp and periodontal tissues of human teeth

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Identification of three common MSC subclusters between dental pulp and periodontium

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Dental pulp and periodontal MSCs are similar, and their niches diverge

Mutations in COL1A1/A2 and CREB3L1 are associated with oligodontia in osteogenesis imperfecta

Background

Osteogenesis imperfecta (OI) is a heterogeneous connective tissue disorder characterized by an increased tendency for fractures throughout life. Autosomal dominant (AD) mutations in COL1A1 and COL1A2 are causative in approximately 85% of cases. In recent years, recessive variants in genes involved in collagen processing have been found. Hypodontia (< 6 missing permanent teeth) and oligodontia (≥ 6 missing permanent teeth) have previously been reported in individuals with OI. The aim of the present cross-sectional study was to investigate whether children and adolescents with OI and oligodontia and hypodontia also present with variants in other genes with potential effects on tooth development. The cohort comprised 10 individuals (7.7–19.9 years of age) with known COL1A1/A2 variants who we clinically and radiographically examined and further genetically evaluated by whole-genome sequencing. All study participants were treated at the Astrid Lindgren Children’s Hospital at Karolinska University Hospital, Stockholm (Sweden’s national multidisciplinary pediatric OI team). We evaluated a panel of genes that were associated with nonsyndromic and syndromic hypodontia or oligodontia as well as that had been found to be involved in tooth development in animal models.

Results

We detected a homozygous nonsense variant in CREB3L1, p.Tyr428*, c.1284C > A in one boy previously diagnosed with OI type III. COL1A1 and COL1A2 were the only two genes among 9 individuals which carried a pathogenic mutation. We found rare variants with unknown significance in several other genes related to tooth development.

Conclusions

Our findings suggest that mutations in COL1A1, COL1A2, and CREB3L1 may cause hypodontia and oligodontia in OI. The findings cannot exclude additive effects from other modifying or interacting genes that may contribute to the severity of the expressed phenotype. Larger cohorts and further functional studies are needed.

Ameloblastomas Exhibit Stem Cell Potential, Possess Neurotrophic Properties, and Establish Connections with Trigeminal Neurons

Ameloblastomas are locally invasive and aggressive odontogenic tumors treated via surgical resection, which results in facial deformity and significant morbidity. Few studies have addressed the cellular and molecular events of ameloblastoma onset and progression, thus hampering the development of non-invasive therapeutic approaches. Tumorigenesis is driven by a plethora of factors, among which innervation has been long neglected. Recent findings have shown that innervation directly promotes tumor progression. On this basis, we investigated the molecular characteristics and neurotrophic properties of human ameloblastomas. Our results showed that ameloblastomas express dental epithelial stem cell markers, as well as components of the Notch signaling pathway, indicating persistence of stemness. We demonstrated that ameloblastomas express classical stem cell markers, exhibit stem cell potential, and form spheres. These tumors express also molecules of the Notch signaling pathway, fundamental for stem cells and their fate. Additionally, we showed that ameloblastomas express the neurotrophic factors NGF and BDNF, as well as their receptors TRKA, TRKB, and P75/NGFR, which are responsible for their innervation by trigeminal axons in vivo. In vitro studies using microfluidic devices showed that ameloblastoma cells attract and form connections with these nerves. Innervation of ameloblastomas might play a key role in the onset of this malignancy and might represent a promising target for non-invasive pharmacological interventions.

Notch - a possible mediator between Epstein-Barr virus infection and bone resorption in apical periodontitis

Objectives: This study aimed to investigate whether Epstein-Barr virus (EBV) positive periapical lesions exhibited higher mRNA levels of Notch signalling molecules (Notch2 and Jagged1), bone resorption regulators (receptor activator of nuclear factor kappa-β ligand (RANKL) and osteoprotegerin (OPG)), and proinflammatory cytokines (tumour necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β) and IL-6) compared to EBV negative lesions. Additionally, the potential correlation between investigated molecules in periapical lesions was analyzed.Materials and methods: Sixty-four apical periodontitis lesions were obtained subsequent to standard apicoectomy procedure. The presence of EBV was determined using nested PCR. Based on the presence of EBV all periapical lesions were divided into two groups, 29 EBV positive and 35 EBV negative lesions. A reverse transcriptase real-time PCR was used to determine mRNA levels of Notch2, Jagged1, RANKL, OPG, TNF-α, IL-1β and IL-6.Results: Significantly higher mRNA levels of Notch2, Jagged1, RANKL and IL-1β were observed in EBV positive compared to EBV negative lesions. Significant positive correlation was present between Notch2 and Jagged1, Jagged1 and RANKL, and IL-β and TNF-α in EBV positive periapical lesions.Conclusions: Notch signalling pathway may be involved in alveolar bone resorption in apical periodontitis lesions infected by EBV.

Monitoring Notch Signaling-Associated Activation of Stem Cell Niches within Injured Dental Pulp

Dental pulp stem/progenitor cells guarantee tooth homeostasis, repair and regeneration throughout life. The decision between renewal and differentiation of these cells is influenced by physical and molecular interactions with stromal cells and extracellular matrix molecules forming the specialized microenvironment of dental pulp stem cell niches. Here we study the activation of putative pulp niches after tooth injury through the upregulation of Notch signaling pathway. Notch1, Notch2, and Notch3 molecules were used as markers of dental pulp stem/progenitor cells. Upon dental injury, Notch1 and Notch3 are detected in cells related to vascular structures suggesting a role of these proteins in the activation of specific pulpal perivascular niches. In contrast, a population of Notch2-positive cells that are actively proliferative is observed in the apical part of the pulp. Kinetics of these cells is followed up with a lipophilic DiI labeling, showing that apical pulp cells migrate toward the injury site where dynamic regenerative/repair events occur. The knowledge of the activation and regulation of dental pulp stem/progenitor cells within their niches in pathologic conditions may be helpful for the realization of innovative dental treatments in the near future.

Parallels between Tooth Development and Repair: Conserved Molecular Mechanisms following Carious and Dental Injury

The reparative mechanisms that operate following carious and traumatic dental injury are critical for pulp survival and involve a series of highly conserved processes. It appears that these processes share genetic programs—linked to cytoskeletal organization, cell movement, and differentiation—that occur throughout embryogenesis. Reactionary dentin is secreted by surviving odontoblasts in response to moderate stimuli, leading to an increase in metabolic activity. In severe injury, necrotic odontoblasts are replaced by other pulp cells, which are able to differentiate into odontoblast-like cells and produce a reparative dentin. This complex process requires the collaborative efforts of cells of different lineage. The behavior of each of the contributing cell types during the phases of proliferation, migration, and matrix synthesis as well as details of how growth factors control wound cell activities are beginning to emerge. In this review, we discuss what is known about the molecular mechanisms involved in dental repair.

Expression of Nerve Growth Factor (NGF), TrkA, and p75(NTR) in Developing Human Fetal Teeth

Nerve growth factor (NGF) is important for the development and the differentiation of neuronal and non-neuronal cells. NGF binds to specific low- and high-affinity cell surface receptors, respectively, p75^NTR and TrkA. In the present study, we examined by immunohistochemistry the expression patterns of the NGF, p75^NTR, and TrkA proteins during human fetal tooth development, in order to better understand the mode of NGF signaling action in dental tissues. The results obtained show that these molecules are expressed in a wide range of dental cells of both epithelial and mesenchymal origin during early stages of odontogenesis, as well as in nerve fibers that surround the developing tooth germs. At more advanced developmental stages, NGF and TrkA are localized in differentiated cells with secretory capacities such as preameloblasts/ameloblasts secreting enamel matrix and odontoblasts secreting dentine matrix. In contrast, p75^NTR expression is absent from these secretory cells and restricted in proliferating cells of the dental epithelium. The temporospatial distribution of NGF and p75^NTR in fetal human teeth is similar, but not identical, with that observed previously in the developing rodent teeth, thus indicating that the genetic information is well-conserved during evolution. The expression patterns of NGF, p75^NTR, and TrkA during odontogenesis suggest regulatory roles for NGF signaling in proliferation and differentiation of epithelial and mesenchymal cells, as well as in attraction and sprouting of nerve fibers within dental tissues.

Activation and dynamic expression of Notch signalling in dental pulp cells after injury in vitro and in vivo

AIM

To investigate the expression pattern of Notch signalling in odontoblast-like cells stimulated by lipopolysaccharide (LPS) in vitro, and in injured rat dental pulp in vivo.

METHODOLOGY

Mouse odontoblast-like cells (MDPC-23) were exposed to LPS. Expression of Notch-related genes was detected by real-time PCR. A rat pulpitis model was established by mechanical injury and LPS plus mechanical injury was followed by the analysis of expression of Notch2 by immunohistochemical staining. One-way analysis of variance (anova) was performed to examine the effect of differing concentrations of LPS on cell proliferation, and least significant difference test was used for paired comparisons. For independent sample, t-test was performed to compare the expression of Notch signalling genes between LPS group and control group in vitro.

RESULTS

The in vitro study revealed the proliferation of MDPC-23 cells on exposure to 10 ng mL^-1 to 1 μg mL^-1 LPS. Expression of Notch1 and Notch2 was significantly higher in the LPS group than that in the control group on day 1 and day 3 (P ˂ 0.05). The levels of both Delta1 and Jagged1 were higher in the study group than in the control group on day 3 (P = 0.019 and P = 0.034) and day 5 (P ˂ 0.001 and P = 0.046), respectively. In addition, Hes1 levels were significantly higher in the study group than in the control group on day 5 (P = 0.005). The in vivo study demonstrated positive staining for Notch2, both in the mechanical injury (MI) group and in the LPS plus mechanical injury (LMI) group from day 3 to day 7, which showed very weak or absent staining on day 14, thereby demonstrating the dynamic nature of the change.

CONCLUSIONS

Both in vitro and in vivo activation and dynamic expression of Notch signalling in dental pulp cells after injury were found. Notch signalling activation by LPS stimulation or mechanical injury showed a similar pattern in vivo.

Elucidating the cellular actions of demineralised dentine matrix extract on a clonal dental pulp stem cell population in orchestrating dental tissue repair

Bioactive growth factors identified within the extracellular matrix of dentine have been proposed roles in regulating the naturally inherent regenerative dentine formation seen in teeth in response to trauma and infection, which may also be harnessed for novel clinical treatments in augmenting mineralised tissue repair. This study examined the specific biological action of demineralised dentine matrix extract on a clonal population of dental pulp stem cells in stimulating the prerequisite stages of wound healing associated with mineralised tissue repair. A clonal dental pulp stem cell population with sustained proliferative capacity and multi-potentiality towards osteogenic, adipogenic and chondrogenic lineages was isolated from the pulp of human third molars. Dentine was collected from human healthy teeth, powdered and treated with ethylenediaminetetraacetic acid to obtain a solubilised DDM protein extract. The influence of DDM on the DPSC clonal population was assessed in vitro. Exposure of cells to proteolytically degraded DDM or unsupplemented media served as controls. Compared to controls, DDM stimulated cell expansion, reduced apoptotic marker caspase 3, increased cell survival marker Akt1 and enhanced mineralised matrix deposition as determined by mineral deposition and increased expression of bone-related markers, alkaline phosphatase and osteopontin. Dental pulp stem cells successfully migrated into collagen gels supplemented with demineralised dentine matrix, with cells remaining viable and expanding in numbers over a 3-day period. Collectively, the results provide evidence that soluble proteins extracted from dentine matrix are able to exert a direct biological effect on dental pulp stem cells in promoting mineralised tissue repair mechanisms.

Distribution of the amelogenin protein in developing, injured and carious human teeth

Amelogenin is the major enamel matrix protein with key roles in amelogenesis. Although for many decades amelogenin was considered to be exclusively expressed by ameloblasts, more recent studies have shown that amelogenin is also expressed in other dental and no-dental cells. However, amelogenin expression in human tissues remains unclear. Here, we show that amelogenin protein is not only expressed during human embryonic development but also in pathological conditions such as carious lesions and injuries after dental cavity preparation. In developing embryonic teeth, amelogenin stage-specific expression is found in all dental epithelia cell populations but with different intensities. In the different layers of enamel matrix, waves of positive vs. negative immunostaining for amelogenin are detected suggesting that the secretion of amelogenin protein is orchestrated by a biological clock. Amelogenin is also expressed transiently in differentiating odontoblasts during predentin formation, but was absent in mature functional odontoblasts. In intact adult teeth, amelogenin was not present in dental pulp, odontoblasts, and dentin. However, in injured and carious adult human teeth amelogenin is strongly re-expressed in newly differentiated odontoblasts and is distributed in the dentinal tubuli under the lesion site. In an in vitro culture system, amelogenin is expressed preferentially in human dental pulp cells that start differentiating into odontoblast-like cells and form mineralization nodules. These data suggest that amelogenin plays important roles not only during cytodifferentiation, but also during tooth repair processes in humans.

Crosstalk between miR-34a and Notch Signaling Promotes Differentiation in Apical Papilla Stem Cells (SCAPs)

Stem cells from the apical papilla (SCAPs) are important for the formation and regeneration of root dentin. Here, we examined the expression of Notch signaling components in SCAPs and investigated crosstalk between microRNA miR-34aand Notch signaling during cell differentiation. We found that human SCAPs express NOTCH2, NOTCH3, JAG2, DLL3, and HES1, and we tested the relationship between Notch signaling and both cell differentiation and miR-34a expression. NOTCH activation in SCAPs inhibited cell differentiation and up-regulated the expression of miR-34a, whereas miR-34a inhibited Notch signaling in SCAPs by directly targeting the 3'UTR of NOTCH2 and HES1 mRNA and suppressing the expression of NOTCH2, N2ICD, and HES1. DSPP, RUNX2, OSX, and OCN expression was consequently up-regulated. Thus, Notch signaling in human SCAPs plays a vital role in maintenance of these cells. miR-34a interacts with Notch signaling and promotes both odontogenic and osteogenic differentiation of SCAPs.

Promotion of dentin regeneration via CCN3 modulation on Notch and BMP signaling pathways

Dentin regeneration remains a great challenge in clinic. Dental pulp stem cells (DPSCs) actively contribute to dentinogenesis, which is orchestrated by a spectrum of signaling factors. However, the exact mechanism underlying the reparative dentin regeneration process is largely unknown and the application of DPSCs in the repair of dentin defect is thus limited. Here, using a rat reparative dentin regeneration model, we observed that DPSCs underwent a proliferation phase followed by a differentiation phase after dental injury. A transient elevation of nephroblastoma overexpressed (NOV, or CCN3) expression correlated with this progressive dental tissue restoration process. Further studies revealed that over-expression of CCN3 promoted human DPSCs proliferation via activation of Notch. Moreover, using cocultured cells (DPSCs/CCN3 and DPSCs) in vitro and the cocultured cells-poly (lactic-co-glycolic acid) (PLGA) scaffold complex in vivo, we demonstrated that CCN3 was capable of promoting mineralization in a non-cell autonomous manner through promoting secretion of BMP2. CCN3 can promote dentinogenesis by coordinating proliferation and odontoblastic differentiation of DPSCs via modulating Notch and BMP2 signaling pathways and CCN3 is a promising therapeutic target in dentin tissue engineering.

Dental pulp stem cells, niches, and notch signaling in tooth injury

Stem cells guarantee tissue repair and regeneration throughout life. The decision between cell self-renewal and differentiation is influenced by a specialized microenvironment called the 'stem cell niche'. In the tooth, stem cell niches are formed at specific anatomic locations of the dental pulp. The microenvironment of these niches regulates how dental pulp stem cell populations participate in tissue maintenance, repair, and regeneration. Signaling molecules such as Notch proteins are important regulators of stem cell function, with various capacities to induce proliferation or differentiation. Dental injuries often lead to odontoblast apoptosis, which triggers activation of dental pulp stem cells followed by their proliferation, migration, and differentiation into odontoblast-like cells, which elaborate a reparative dentin. Better knowledge of the regulation of dental pulp stem cells within their niches in pathological conditions will aid in the development of novel treatments for dental tissue repair and regeneration.

Notch signalling pathway in tooth development and adult dental cells

Notch signalling is a highly conserved intercellular signal transfer mechanism that includes canonical and non-canonical pathways. It regulates differentiation and proliferation of stem/progenitor cells by means of para-inducing effects. Expression and activation of Notch signalling factors (receptors and ligands) are critical not only for development of the dental germ but also for regeneration of injured tissue associated with mature teeth. Notch signalling plays key roles in differentiation of odontoblasts and osteoblasts, calcification of tooth hard tissue, formation of cusp patterns and generation of tooth roots. After tooth eruption, Notch signalling can also be triggered in dental stem cells of the pulp, where it induces them to differentiate into odontoblasts, thus generating fresh dentine tissue. Other signalling pathways, such as TGFβ, NF-κB, Wnt, Fgf and Shh also interact with Notch signalling during tooth development.

Notch signaling may negatively regulate neonatal rat cardiac fibroblast-myofibroblast transformation

Cardiac fibroblast-myofibroblast transformation (CMT) is a critical event in the initiation of myocardial fibrosis. Notch signaling has been shown to regulate myofibroblast transformation from other kinds of cells. However, whether Notch signaling is also involved in CMT remains unclear. In the present study, expressions of Notch receptors in cardiac fibroblasts (CFs) were examined, effects of Notch signaling inhibitor N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester (DAPT) and transforming growth factor-beta1 (TGF-beta1) on CMT were determined by increasing alpha-smooth muscle actin (alpha-SMA) expression and collagen synthesis, and Notch signaling was examined by analyzing expressions of Notch receptors. The results showed that: (1) Notch receptor 1, 2, 3 and 4 were all expressed in CFs; (2) DAPT promoted CMT in a time-dependent manner; (3) During the period of CMT induced by TGF-beta1, expressions of Notch receptor 1, 3 and 4 in CFs were down-regulated, whereas there was no change for Notch receptor 2. Moreover, the downtrends of Notch 1, 3 and 4 were corresponding to the trend growth of alpha-SMA expression and collagen synthesis. These results suggested that inhibiting of Notch signaling might promote CMT. The down-regulations of Notch receptor 1, 3 and 4 induced by TGF-beta1 may facilitate CMT. In conclusion, inhibition of Notch signaling might be a novel mechanism of CMT in myocardial fibrosis.

Notch signaling activated by replication stress-induced expression of midkine drives epithelial-mesenchymal transition and chemoresistance in pancreatic cancer

The incidence of pancreatic ductal adenocarcinoma (PDAC) nearly equals its mortality rate, partly because most PDACs are intrinsically chemoresistant and thus largely untreatable. It was found recently that chemoresistant PDAC cells overexpress the Notch-2 receptor and have undergone epithelial-mesenchymal transition (EMT). In this study, we show that these two phenotypes are interrelated by expression of Midkine (MK), a heparin-binding growth factor that is widely overexpressed in chemoresistant PDAC. Gemcitabine, the front-line chemotherapy used in PDAC treatment, induced MK expression in a dose-dependent manner, and its RNAi-mediated depletion was associated with sensitization to gemcitabine treatment. We identified an interaction between the Notch-2 receptor and MK in PDAC cells. MK-Notch-2 interaction activated Notch signaling, induced EMT, upregulated NF-κB, and increased chemoresistance. Taken together, our findings define an important pathway of chemoresistance in PDAC and suggest novel strategies for its clinical attack.

Notch 1 Receptor, Delta 1 Ligand and HES 1 Transcription Factor are Expressed in the Lining Epithelium of Periapical Cysts (Preliminary Study)

Periapical cyst is a chronic inflammatory disorder of periradicular tissues. The precise pathological mechanisms involved in periapical cyst enlargement remain unclear. Notch signaling is an evolutionarily conserved pathway with a regulatory role in cell fate decisions during development and in carcinogenesis. To date, there are no published data available on the expression of Notch signaling components in periapical cysts or any other jaw cyst. In this immunohistochemical study we have examined the expression of the receptor Notch 1, the ligand Delta 1 and the transcription factor HES 1 in the epithelium of well defined periapical cysts. Immunostaining reaction of Notch 1, Delta 1 and HES 1 was observed in the cytoplasm and/or the cytoplasmic membrane and occasionally in the nucleus in the majority of epithelial cells of all periapical cysts. The present observations indicate that Notch pathway is active in the epithelium of periapical cysts. It can be speculated that activation of epithelial cells of periapical cysts is associated with activation of Notch pathway and imply involvement of this pathway in periapical cyst growth and expansion.

Eph/ephrinB Mediate Dental Pulp Stem Cell Mobilization and Function

Damage to the dentin matrix instigates the proliferation and mobilization of dental progenitor cells to the injury site, the mechanisms of which are not defined. EphB receptors and ephrin-B ligands expressed within the perivascular niche of dental pulp have been implicated following tooth injury. We propose that elevated levels of ephrin-B1 following injury may prevent the proliferation and migration of dental pulp stem cell (DPSC), while EphB/ephrin-B interaction facilitates odontoblastic differentiation. The migration, proliferation, and differentiation of DPSC in response to Eph/ephrin-B molecules was assessed in an established ex vivo tooth injury model and by in vitro assays for the assessment of colony formation and differentiation. Analysis of our data demonstrated that EphB forward signaling promoted DPSC proliferation, while inhibiting migration. Conversely, reverse signaling enhanced DPSC mineral production. These observations suggest that EphB/ephrin-B molecules are important for perivascular DPSC migration toward the dentin surfaces and differentiation into functional odontoblasts, following damage to the dentin matrix.

Inhibition of human dental pulp stem cell differentiation by Notch signaling

Notch signaling plays a critical role in development and cell fate specification. Notch receptors and ligands have been found to be expressed in dental epithelium or mesenchyme in the developing tooth, suggesting that Notch signaling may regulate odontogenesis. Post-natal human dental pulp stem cells (DPSCs) isolated from the dental pulp have characteristics of mesenchymal stem cells and can differentiate into odontoblasts. In this study, we examined whether Notch signaling regulated the odontoblastic differentiation of DPSCs. We found that over-expression of the Notch ligand, Jagged-1, activated the Notch signaling pathway in DPSCs. Jagged-1 inhibited the odontoblastic differentiation of DPSCs in vitro. Jagged-1-expressing DPSCs could not form mineralized tissues in vivo. Moreover, over-expression of the constitutively activated Notch1 intracellular domain (Notch-ICD) also inhibited odontoblastic differentiation of DPSCs. Taken together, our results demonstrate that Notch signaling can inhibit the odontoblastic differentiation of DPSCs.

FOXC1 is required for cell viability and resistance to oxidative stress in the eye through the transcriptional regulation of FOXO1A

Mutations in the human FOXC1 transcription factor gene underlie Axenfeld-Rieger (AR) syndrome, a disorder characterized by anterior segment malformations in the eye and glaucoma. Through the use of an inducible FOXC1 protein, along with an intermediate protein synthesis blocker, we have determined direct targets of FOXC1 transcriptional regulation. FOXC1 regulates the expression of FOXO1A and binds to a conserved element in the FOXO1A promoter in vivo. The zebrafish foxO1a orthologs exhibit a robust expression pattern in the periocular mesenchyme. Furthermore, FOXO1A expression is reduced in cultured human trabecular meshwork (TM) cells and in the zebrafish developing eye when FOXC1 expression is knocked down by siRNAs and morpholino antisense oliognucleotides, respectively. We also demonstrate that reduced FOXC1 expression increases cell death in cultured TM cells in response to oxidative stress, and increases cell death in the developing zebrafish eye. These studies have uncovered a novel role for FOXC1 as an essential mediator of cellular homeostasis in the eye and indicate that a decreased resistance to oxidative stress may underlie AR-glaucoma pathogenesis. Given that FOXO1A influences cellular homeostasis when positively or negatively regulated; the dysregulation of FOXO1A activities in the eye through FOXC1 loss of function mutations and FOXC1 gene duplications provides an explanation into how seemingly similar human disorders can arise from both increases and decreases in FOXC1 gene dose.

Influence of extended operation time and of occlusal force on determination of pulpal healing pattern in replanted mouse molars

The mechanism regulating the divergent healing processes following tooth replantation is unclear. This study clarifies the relationship between the healing pattern, the time taken for tooth replantation, and the influence of occlusal force. We investigated the pulpal healing process after tooth replantation by immunohistochemistry for 5-bromo-2'-deoxyuridine and nestin and by histochemistry for tartrate-resistant acid phosphatase. The upper right first molar of 3-week-old mice was extracted and repositioned in the original socket immediately or 30 min to 6 h after the operation. We divided the animals into a non-occluded group in which the lower right first molar was extracted and an occluded group without extraction of the counterpart tooth. In control teeth (upper left first molar), the periphery of the coronal dental pulp showed intense nestin-positive reaction. Tooth replantation weakened the nestin-positive reaction in the pulp tissue. On postoperative days 5-7, tubular dentin formation commenced next to preexisting dentin in which nestin-positive odontoblast-like cells were arranged in successful cases. In other cases, bone-like tissue formation occurred in the pulp chamber until day 14. The ratio of tertiary dentin formation was significantly higher in the non-occluded group. The intentionally prolonged time for the completion of tooth replantation induced bone-like tissue formation, expanded inflammatory reaction, or fibrous tissue formation in pulp tissue. Thus, the lack of a proper oxygenated medium is probably decisive for the survival of odontoblast-lineage cells, and occlusal force during and/or after operation worsens the fate of these cells.

Notch2 negatively regulates myofibroblastic differentiation of myoblasts

Myofibroblasts are one of the key cellular components involved in fibrosis of skeletal muscle as well as in other tissues. Transforming growth factor-beta1 (TGF-beta1) stimulates differentiation of mesenchymal cells into myofibroblasts, but little is known about the regulatory mechanisms of myofibroblastic differentiation. Since Notch2 was shown to be downregulated in TGF-beta1-induced non-muscle fibrogenic tissue, we investigated whether Notch2 also has a distinctive role in myofibroblastic differentiation of myogenic cells induced by TGF-beta1. TGF-beta1 treatment of C2C12 myoblasts led to expression of myofibroblastic marker alpha-smooth muscle actin (alpha-SMA) and collagen I with concomitant downregulation of Notch2 expression. Overexpression of active Notch2 inhibited TGF-beta1-induced expression of alpha-SMA and collagen I. Interestingly, transient knockdown of Notch2 by siRNA in C2C12 myoblasts and primary cultured muscle-derived progenitor cells resulted in differentiation into myofibroblastic cells expressing alpha-SMA and collagen I without TGF-beta1 treatment. Furthermore, we found Notch3 was counter-regulated by Notch2 in C2C12 cells. These findings suggest that Notch2 is inhibiting differentiation of myoblasts into myofibroblasts with downregulation of Notch3 expression.

Activation of the Notch signaling pathway in response to pulp capping of rat molars

Notch signaling is an evolutionarily conserved pathway that controls the developmental choices made by individual cells. Cells communicate via Notch receptors and their ligands, which direct decisions on the fate of stem cells according to the states of their neighbors. In this study we explored Notch signaling after the pulp capping of adult first upper rat molars. The wound was capped with calcium hydroxide. In situ hybridization revealed an increased expression of Notch signaling genes on day 1, which showed a tendency to decrease on day 3. Notch1 increased in the subodontoblast zone and close to the lesion limited to a few cells. Notch2 increased in pulp stroma surrounded by coronal odontoblasts. Notch1 and, especially, Notch3 expression increased, corresponding to perivascular cell groups. A low increase of ligand expression was observed near the injury with Delta1 expression along the dentin wall and Jagged1 in the stroma. Expression of the downstream target, Hes1, was observed along the lesion and adjacent dentin walls. Hes5 expression was not observed. The results indicate that Notch signaling is activated in response to injury and associated with the differentiation of pulp cells into perivascular cells and odontoblasts. The findings are consistent with the concept that the Notch pathway controls stem cell fate during pulp regeneration.

Analysis of gene and protein expression in healthy and carious tooth pulp with cDNA microarray and two-dimensional gel electrophoresis

Complementary DNA (cDNA) microarray and two-dimensional (2-D) gel electrophoresis, combined with mass spectrometry, enable simultaneous analysis of expression patterns of thousands of genes, but their use in pulp biology has been limited. Here we compared gene and protein expression of pulp tissues from sound and carious human teeth using cDNA microarray and 2-D gel electrophoresis to evaluate their usefulness in pulp biology research and to identify the genes with changes in carious teeth. The cDNA microarray revealed several differentially expressed genes and genes with a high expression in both tissues. These genes have various functions, e.g. effects on vascular and nerve structures, inflammation, and cell differentiation. Variability between cDNA hybridizations indicates that the overall gene expression pattern may vary significantly between individual teeth. The 2-D gel electrophoresis revealed no change between healthy and diseased tissue. The identification of 96 proteins in the pulp tissue revealed none of the gene products with corresponding high/different mRNA expression in cDNA microarray. Interestingly, we detected also a hypothetical protein (putative nucleoside diphosphate kinase), and present therefore the first evidence for the existence of this protein. Even though the methods reveal potentially important gene expression, they may currently have only limited value in in vivo pulp biology research.