Immunolocalization of fibroblast growth factor-2 (FGF-2) in the developing root and supporting structures of the murine tooth

A Wnt10a-Notch signaling axis controls Hertwig's epithelial root sheath cell behaviors during root furcation patterning

Human with bi-allelic WNT10A mutations and epithelial Wnt10a knockout mice present enlarged pulp chamber and apical displacement of the root furcation of multi-rooted teeth, known as taurodontism; thus, indicating the critical role of Wnt10a in tooth root morphogenesis. However, the endogenous mechanism by which epithelial Wnt10a regulates Hertwig's epithelial root sheath (HERS) cellular behaviors and contributes to root furcation patterning remains unclear. In this study, we found that HERS in the presumptive root furcating region failed to elongate at an appropriate horizontal level in K14-Cre;Wnt10afl/fl mice from post-natal day 0.5 (PN0.5) to PN4.5. EdU assays and immunofluorescent staining of cyclin D1 revealed significantly decreased proliferation activity of inner enamel epithelial (IEE) cells of HERS in K14-Cre;Wnt10afl/fl mice at PN2.5 and PN3.5. Immunofluorescent staining of E-Cadherin and acetyl-α-Tubulin demonstrated that the IEE cells of HERS tended to divide perpendicularly to the horizontal plane, which impaired the horizontal extension of HERS in the presumptive root furcating region of K14-Cre;Wnt10afl/fl mice. RNA-seq and immunofluorescence showed that the expressions of Jag1 and Notch2 were downregulated in IEE cells of HERS in K14-Cre;Wnt10afl/fl mice. Furthermore, after activation of Notch signaling in K14-Cre;Wnt10afl/fl molars by Notch2 adenovirus and kidney capsule grafts, the root furcation defect was partially rescued. Taken together, our study demonstrates that an epithelial Wnt10a-Notch signaling axis is crucial for modulating HERS cell proper proliferation and horizontal-oriented division during tooth root furcation morphogenesis.

Effects of Growth Factors on the Differentiation of Dental Stem Cells: A Systematic Review and Meta-analysis (Part I)

INTRODUCTION

To evaluate the biological interaction between dental stem cells (DSCs) and different growth factors in the field of regenerative endodontics.

METHODS

A systematic search was conducted in the electronic databases up to October 2021. This study followed the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. Ex vivo studies evaluating the biological interactions of DSCs and growth factors were included. The meta-analysis was performed according to the type of growth factor. The outcomes were cell viability/ proliferation and mineralization. Standardized mean differences (SMDs) were estimated using the random-effect maximum-likelihood method (P < .05). Additional analysis was performed to find any potential source of heterogeneity.

RESULTS

Twenty articles were included in the systematic review; meta-analysis was performed for fibroblast growth factor-2 (FGF-2) and Transforming growth factor-ß1 (TGF-β1) (n = 5). Results showed that use of FGF-2 significantly increased cell proliferation on day 1-(SMD = 3.56, P = 0.00), 3-(SMD = 9.04, P = 0.00), 5-(SMD = 8.37, P = 0.01), and 7 (SMD=8.51, P=0.00) than the control group. TGF-ß1 increased alkaline phosphatase (ALP) activity more than control only on day 3 (SMD = 3.68, P = 0.02). TGF-β1 had no significant effect on cell proliferation on days 1 and 3 (P > 0.05) and on ALP activity on days 5 and 7 (P > 0.05). Meta-regression analysis showed that different covariates (i.e., cell type, passage number, and growth factors' concentration) could significantly influence the effect sizes at different follow- ups (P < 0.05).

CONCLUSION

Specific growth factors might enhance the proliferation and mineralization of DSCs; however, the obtained evidence was weak. Due to the high heterogeneity among the included studies, other growth factors' inhibitory/stimulatory effects on DSCs could not be evaluated.

The inhibition of mineralisation by fibroblast growth factor 2 is associated with the altered expression of genes regulating phosphate balance

The study aimed to determine whether inhibitory effects of fibroblast growth factor 2 (FGF2) on mineralisation in dental pulp (DP) cultures were associated with changes in the expression of genes regulating phosphate balance (Enpp1, Ank, Slc20a2, Alpl, Phospho1, and Xpr1). DP cultures growing under mineralisation-inducing conditions were exposed to FGF2 and inhibitors of the FGFR and MEK/ERK1/2 signaling pathways. Mineralisation, culture cellularity, and gene expression were examined at various time points. Statistical analysis was performed using analysis of variance followed by the Holm-Šídák test. Control cultures exhibited transient increases in Enpp1 and Ank, continuous increases in Alpl, Phospho1, and Xpr1, and continuous decreases in Slc20a2. FGF2 increased Enpp1, Ank, and Slc20a2 and decreased Alpl, Phospho1, and Xpr1, whereas the FGF2 withdrawal and inhibition of FGFR and MEK/ERK1/2 exerted opposite effects. These changes suggest that FGF2-mediated decreases in mineralisation could be functionally coupled to the altered regulation of phosphate formation and transport.

Transcriptome Analysis Reveals Modulation of Human Stem Cells from the Apical Papilla by Species Associated with Dental Root Canal Infection

Interaction of oral bacteria with stem cells from the apical papilla (SCAP) can negatively affect the success of regenerative endodontic treatment (RET). Through RNA-seq transcriptomic analysis, we studied the effect of the oral bacteria Fusobacterium nucleatum and Enterococcus faecalis, as well as their supernatants enriched by bacterial metabolites, on the osteo- and dentinogenic potential of SCAPs in vitro. We performed bulk RNA-seq, on the basis of which differential expression analysis (DEG) and gene ontology enrichment analysis (GO) were performed. DEG analysis showed that E. faecalis supernatant had the greatest effect on SCAPs, whereas F. nucleatum supernatant had the least effect (Tanimoto coefficient = 0.05). GO term enrichment analysis indicated that F. nucleatum upregulates the immune and inflammatory response of SCAPs, and E. faecalis suppresses cell proliferation and cell division processes. SCAP transcriptome profiles showed that under the influence of E. faecalis the upregulation of VEGFA, Runx2, and TBX3 genes occurred, which may negatively affect the SCAP's osteo- and odontogenic differentiation. F. nucleatum downregulates the expression of WDR5 and TBX2 and upregulates the expression of TBX3 and NFIL3 in SCAPs, the upregulation of which may be detrimental for SCAPs' differentiation potential. In conclusion, the present study shows that in vitro, F. nucleatum, E. faecalis, and their metabolites are capable of up- or downregulating the expression of genes that are necessary for dentinogenic and osteogenic processes to varying degrees, which eventually may result in unsuccessful RET outcomes. Transposition to the clinical context merits some reservations, which should be approached with caution.

Effect of bFGF on the growth and matrix turnover of stem cells from human apical papilla: Role of MEK/ERK signaling

BACKGROUND/PURPOSE

Basic fibroblast growth factor (bFGF) exhibits multiple biological functions in various tissues. Stem cells from apical papilla (SCAP) can be isolated from human apical papilla tissues in developmental teeth of children. The purposes of this study were to investigate the expression of FGF receptors (FGFRs) and the effects of bFGF on SCAP and related MEK/ERK signaling.

METHODS

SCAP cells were treated under different concentrations of bFGF with or without U0126 (an inhibitor of MEK/ERK). Expression of FGFR1 and FGFR2 in SCAP was analyzed by RT-PCR. Cell proliferation was measured by MTT assay. The expressions of type I collagen, cdc 2, cyclin B1, TIMP-1 and p-ERK proteins were examined by Western blot.

RESULTS

SCAP cells expressed FGFR1 and FGFR2. Exposure of SCAP to bFGF enhanced cell proliferation, and the expression cyclinB1, cdc 2, and TIMP-1, but not type I collagen. U0126 pretreatment and co-incubation attenuated the bFGF-induced proliferation, cdc2, cyclin B1 and TIMP-1 proteins' expression, but not type I collagen in SCAP.

CONCLUSION

SCAP cells express FGFRs. bFGF may stimulate proliferation and affect the matrix turnover of SCAP cells, possibly via stimulation of FGFRs and MEK/ERK signaling pathway. These results are useful for clinical therapies for apexogenesis and regeneration of pulpo-dentin complex.

Current and future options for dental pulp therapy

Dental pulp is a connective tissue and has functions that include initiative, formative, protective, nutritive, and reparative activities. However, it has relatively low compliance, because it is enclosed in hard tissue. Its low compliance against damage, such as dental caries, results in the frequent removal of dental pulp during endodontic therapy. Loss of dental pulp frequently leads to fragility of the tooth, and eventually, a deterioration in the patient’s quality of life. With the development of biomaterials such as bioceramics and advances in pulp biology such as the identification of dental pulp stem cells, novel ideas for the preservation of dental pulp, the regenerative therapy of dental pulp, and new biomaterials for direct pulp capping have now been proposed. Therapies for dental pulp are classified into three categories; direct pulp capping, vital pulp amputation, and treatment for non-vital teeth. In this review, we discuss current and future treatment options in these therapies.

The Role of Fibroblast Growth Factors in Tooth Development and Incisor Renewal

The mineralized tissue of the tooth is composed of enamel, dentin, cementum, and alveolar bone; enamel is a calcified tissue with no living cells that originates from oral ectoderm, while the three other tissues derive from the cranial neural crest. The fibroblast growth factors (FGFs) are critical during the tooth development. Accumulating evidence has shown that the formation of dental tissues, that is, enamel, dentin, and supporting alveolar bone, as well as the development and homeostasis of the stem cells in the continuously growing mouse incisor is mediated by multiple FGF family members. This review discusses the role of FGF signaling in these mineralized tissues, trying to separate its different functions and highlighting the crosstalk between FGFs and other signaling pathways.

Cellular and molecular mechanisms of tooth root development

The tooth root is an integral, functionally important part of our dentition. The formation of a functional root depends on epithelial-mesenchymal interactions and integration of the root with the jaw bone, blood supply and nerve innervations. The root development process therefore offers an attractive model for investigating organogenesis. Understanding how roots develop and how they can be bioengineered is also of great interest in the field of regenerative medicine. Here, we discuss recent advances in understanding the cellular and molecular mechanisms underlying tooth root formation. We review the function of cellular structure and components such as Hertwig's epithelial root sheath, cranial neural crest cells and stem cells residing in developing and adult teeth. We also highlight how complex signaling networks together with multiple transcription factors mediate tissue-tissue interactions that guide root development. Finally, we discuss the possible role of stem cells in establishing the crown-to-root transition, and provide an overview of root malformations and diseases in humans.

Optimization of treatment with recombinant FGF-2 for proliferation and differentiation of human dental stem cells, mesenchymal stem cells, and osteoblasts

Basic fibroblast growth factor (bFGF or FGF-2) is widely used to modulate the proliferation and differentiation of certain cell types. An expression and purification system for recombinant human FGF-2 in Escherichia coli was established for the purpose of securing a continuous supply of this protein. The purified recombinant FGF-2 significantly increased the population of human embryonic stem cells. The optimal concentrations of FGF-2 for cell proliferative induction in various adult stem cells including human dental pulp stem cells, full term human periodontal ligament stem cells, human gingival fibroblasts, mesenchymal stem cells, and osteogenic oseosarcoma were established in a dose-dependent manner. When cells were treated with recombinant FGF-2 for 6 days before osteogenic induction, the mRNA expression of the bone markers was upregulated in cells originated from human dental pulp tissue, indicating that pretreatment with FGF-2 during culture increase stem cell/progenitor population and osteogenic potential.

Stage-specific effects of fibroblast growth factor 2 on the differentiation of dental pulp cells

Dentinogenesis is a complex and multistep process, which is regulated by various growth factors, including members of the fibroblast growth factor (FGF) family. Both positive and negative effects of FGFs on dentinogenesis have been reported, but the underlying mechanisms of these conflicting results are still unclear. To gain a better insight into the role of FGF2 in dentinogenesis, we used dental pulp cells from various transgenic mice, in which fluorescent protein expression identifies cells at different stages of odontoblast differentiation. Our results showed that the continuous exposure of pulp cells to FGF2 inhibited mineralization and revealed both the stimulatory and inhibitory effects of FGF2 on the expression of markers of dentinogenesis and various transgenes. During the proliferation phase of in vitro growth, FGF2 increased the expression of markers of dentinogenesis and the percentages of dentin matrix protein 1/green fluorescent protein (DMP1-GFP)-positive functional odontoblasts and dentin sialophosphoprotein (DSPP)-Cerulean-positive odontoblasts. Additional exposure to FGF2 during the differentiation/mineralization phase of in vitro growth decreased the extent of mineralization and the expression of markers of dentinogenesis and of the DMP1-GFP and DSPP-Cerulean transgenes. Recovery experiments showed that the inhibitory effects of FGF2 on dentinogenesis were related to the blocking of the differentiation of cells into mature odontoblasts. These observations together showed the stage-specific effects of FGF2 on dentinogenesis by dental pulp cells, and they provide critical information for the development of improved treatments for vital pulp therapy and dentin regeneration.

Molecular regulatory mechanism of tooth root development

The root is crucial for the physiological function of the tooth, and a healthy root allows an artificial crown to function as required clinically. Tooth crown development has been studied intensively during the last few decades, but root development remains not well understood. Here we review the root development processes, including cell fate determination, induction of odontoblast and cementoblast differentiation, interaction of root epithelium and mesenchyme, and other molecular mechanisms. This review summarizes our current understanding of the signaling cascades and mechanisms involved in root development. It also sets the stage for de novo tooth regeneration.

Promotional effects of vasoactive intestinal peptide on the development of rodent Hertwig's epithelial root sheath

Hertwig's epithelial root sheath (HERS), a bilayered epithelial cell sheath located at the cervical loop of the enamel organ in a developing tooth, is at the forefront of root formation. However, little is known about the exact mechanisms that regulate the development of HERS. The neuropeptide vasoactive intestinal peptide (VIP) is involved in the development of various tissues and cells. In this study, we investigated the roles of VIP in HERS development. VIP-immunoreactive nerve fibers were found in the dental pulp and around the root apex of the tooth, while the expression of VIP receptor 1 (VPAC1) was observed in HERS. The expression level of VPAC1 correlated with the development of HERS and was elevated at postnatal days 14 and 21. Using ex vivo cultures of neonatal tooth germs, VIP enhanced the elongation and proliferation of HERS. In vitro, VIP also promoted the proliferation of cells from the HERS-derived cell line, HERS01a cells, and upregulated the mRNA expression of cytokeratin 14 and vimentin (typical molecular markers of HERS) in these cells. These results suggest that VIP may be an essential factor for HERS development.

Basic fibroblast growth factor enhances stemness of human stem cells from the apical papilla

INTRODUCTION

Stem cells from the apical papilla (SCAP) are a type of mesenchymal stem cells found in the developing tissue, apical papilla, of immature permanent teeth. Studies have shown that SCAP are likely to be a source of primary odontoblasts that are responsible for the formation of root dentin. Basic fibroblast growth factor (bFGF) is a signaling molecule and pleiotropic growth factor involved in tooth root development, and it promotes proliferation of a variety of cell types. The effects of bFGF on SCAP, however, have not been examined.

METHODS

We investigated the regulatory effects of bFGF on the proliferation and differentiation potential of human SCAP in vitro. Changes in the cell cycle and proliferation, colony-forming unit-fibroblastic formation, alkaline phosphatase (ALP) activity, osteogenic/dentinogenic differentiation, and stem cell gene makers of SCAP, cultured in the presence or absence of bFGF, were evaluated.

RESULTS

Treatment with 5 ng/mL bFGF significantly increased SCAP proliferation and their colony-forming unit-fibroblastic formation efficiency. The growth factor also increased the expression of STRO-1 and the stem cell gene makers Nanog, Oct4, Sox2, and Rex1 in SCAP. In contrast, bFGF reduced the ALP activity, mineral nodule formation, and the expression of ALP, osteocalcin, bone sialoprotein, and dentin sialophosphoprotein. When SCAP cultures were expanded in the presence of bFGF for 1 week, subsequent stimulation of the osteogenic/dentinogenic condition resulted in enhanced differentiation.

CONCLUSIONS

Under certain conditions, bFGF enhances SCAP stemness by up-regulating stem cell gene expression, increasing proliferation ability, and potentiating differentiation potency.

Response to intracanal medication in immature teeth with pulp necrosis: an experimental model in rat molars

INTRODUCTION

The present study aimed at developing an experimental model in rat molars for evaluating treatment strategies in necrotic immature teeth.

METHODS

To define the periods to be adopted in the experimental procedures and to confirm induction of periapical lesions and interruption of root embryogenesis, the left lower first molars of 4-weeks-old Wistar rats underwent pulpectomy and were left open to the oral environment. Comparisons with the right lower first molars (vital teeth) were performed in animals with ages of 7, 10, 13, and 16 weeks. In another group of animals the teeth were left open for 3 weeks, and then interventions for disinfection including the use of an antibiotic paste were carried out. Root formation was then assessed after 3 and 6 weeks on the basis of radiographic and histologic evaluation.

RESULTS

Vital teeth showed increase of root length and hard tissue thickness throughout the experimental periods. On the other hand, induction of necrosis arrested root formation. Teeth subjected to disinfection with sodium hypochlorite associated with the triple antibiotic paste showed significant reduction of periapical lesions, gain in root length, and increased wall thickness compared with the control (P < .05).

CONCLUSIONS

The root canal disinfection protocol used was able to reduce periapical lesion size and improve root development. The experimental model presented should contribute to studies that aim at improving therapeutic strategies for necrotic immature teeth by using a rat model.

Local regeneration of dentin-pulp complex using controlled release of fgf-2 and naturally derived sponge-like scaffolds

Restorative and endodontic procedures have been recently developed in an attempt to preserve the vitality of dental pulp after exposure to external stimuli, such as caries infection or traumatic injury. When damage to dental pulp is reversible, pulp wound healing can proceed, whereas irreversible damage induces pathological changes in dental pulp, eventually requiring its removal. Nonvital teeth lose their defensive abilities and become severely damaged, resulting in extraction. Development of regeneration therapy for the dentin-pulp complex is important to overcome limitations with presently available therapies. Three strategies to regenerate the dentin-pulp complex have been proposed; regeneration of the entire tooth, local regeneration of the dentin-pulp complex from amputated dental pulp, and regeneration of dental pulp from apical dental pulp or periapical tissues. In this paper, we focus on the local regeneration of the dentin-pulp complex by application of exogenous growth factors and scaffolds to amputated dental pulp.

Incisor degeneration in rats induced by vascular endothelial growth factor/fibroblast growth factor receptor tyrosine kinase inhibition

BMS-645737, an inhibitor of vascular endothelial growth factor (VEGF) receptor-2 and fibroblast growth factor (FGF) receptor-1, has anti-angiogenic activity and was evaluated in nonclinical studies as a treatment for cancer. This article characterizes the BMS-645737-induced clinical, gross, and histologic lesions of incisor teeth in Sprague-Dawley (SD) rats. Rats received 0 800 mg/kg BMS-645737 in a single-dose study or consecutive daily doses of 0 20 mg/kg/day in a 1-month study. The reversibility of these effects was assessed in the 1-month study. White discoloration and fracture of incisors were observed clinically and grossly in the 1-month study. In both studies, dose-dependent histopathologic lesions of incisors were degeneration and/or necrosis of odontoblasts and ameloblasts; decreased mineralization of dentin; inflammation and necrosis of the dental pulp; and edema, congestion, and hemorrhage in the pulp and periodontal tissue adjacent to the enamel organ. Partial recovery was observed at lower doses after a two-week dose-free period in the one-month study. Drug-induced incisor lesions were considered to be related to the pharmacologic inhibitory effects on VEGF and FGF signaling, that is, inhibition of growth and maintenance of small-diameter vessels that support the formation of dentin and enamel in growing teeth and/or to perturbances of function of odontoblasts and ameloblasts or their precursors.

Extracellular matrix-mediated differentiation of periodontal progenitor cells

The periodontal ligament (PDL) is a specialized connective tissue that connects the surface of the tooth root with the bony tooth socket. The healthy PDL harbors stem cell niches and extracellular matrix (ECM) microenvironments that facilitate periodontal regeneration. During periodontal disease, the PDL is often compromised or destroyed, reducing the life-span of the tooth. In order to explore new approaches toward the regeneration of diseased periodontal tissues, we have tested the effect of periodontal ECM signals, fibroblast growth factor 2 (FGF2), connective tissue growth factor (CTGF), and the cell adhesion peptide Arg-Gly-Asp (RGD) on the differentiation of two types of periodontal progenitor cells, PDL progenitor cells (PDLPs) and dental follicle progenitor cells (DFCs). Our studies documented that CTGF and FGF2 significantly enhanced the expression of collagens I & III, biglycan and periostin in tissue engineered regenerates after 4 weeks compared to untreated controls. Specifically, CTGF promoted mature PDL-like tissue regeneration as demonstrated by dense periostin localization in collagen fiber bundles. CTGF and FGF2 displayed synergistic effects on collagen III and biglycan gene expression, while effects on mineralization were antagonistic to each other: CTGF promoted while FGF2 inhibited mineralization in PDL cell cultures. Incorporation of RGD peptides in hydrogel matrices significantly enhanced attachment, spreading, survival and mineralization of the encapsulated DFCs, suggesting that RGD additives might promote the use of hydrogels for periodontal mineralized tissue engineering. Together, our studies have documented the effect of three key components of the periodontal ECM on the differentiation of periodontal progenitor populations.

Formation of dentin-like particles in dentin defects above exposed pulp by controlled release of fibroblast growth factor 2 from gelatin hydrogels

The induction of dentin formation on exposed dental pulp is a major challenge in research on the regeneration of the dentin-pulp complex. We examined the effects of fibroblast growth factor 2 (FGF2), which was delivered in either a collagen sponge (noncontrolled release) or incorporated into gelatin hydrogels (controlled release), on the formation of dentin in exposed rat molar pulps. During the early phase of pulp wound healing, pulp cell proliferation and invasion of vessels into dentin defects above exposed pulp were induced in both groups. In the late phase, the induction of dentin formation was distinctly different between the 2 types of FGF2 release. The noncontrolled release of free FGF2 from collagen sponge induced excessive reparative dentin formation in the residual dental pulp, although dentin defects were not noted. In contrast, controlled release of FGF2 from gelatin hydrogels induced the formation of dentin-like particles with dentin defects above exposed pulp. These results suggest the possibility of a novel therapeutic approach for dentin-pulp complex by controlled release of bioactive FGF2.

Pattern of FGF-2 isoform expression correlated with its biological action in experimental prolactinomas

Fibroblast growth factor-2 (FGF-2) synthesized in the pituitary is involved in the formation and progression of pituitary tumors. The aim of this study was to analyze the pattern expression of two FGF-2 isoforms at different subcellular levels and to determine its correlation with prolactinoma development. Estrogen administration to male rats for 7, 20, and 60 days generated pituitary tumors, with lactotrophs being the prevalent cell type. Ultrastructural immunolabeling showed FGF-2 in the cytosolic and nuclear compartments of somatotrophs, lactotrophs and gonadotrophs, as well as in folliculo-stellate cells of normal rats. Estrogen stimulation increased FGF-2 immunoreactivity in various tumors and enhanced the expression of two FGF-2 isoforms, 18 and 22 kDa, as quantified by western blot. The 18 kDa isoform observed in cytosol extracts reached the highest levels after 60 days of hormonal stimulation and this was related to lactotroph proliferation. However, the 22 kDa FGF-2 isoform was only detected in the nuclear compartment and achieved the maximum expression at 7 days of estrogen treatment, without any correlation with lactotroph proliferation. These results suggest that the 18 kDa FGF-2 may play a role in the modulation of lactotroph proliferation in prolactinomas induced by estrogen. The overproduction of both FGF-2 isoforms appears to be implicated in autocrine-paracrine-intracrine mitogenic loops; this FGF-2 activity could lead to uncontrolled cell growth, angiogenesis, and tumor formation.