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

FGF signaling modulates mechanotransduction/WNT signaling in progenitors during tooth root development

Stem/progenitor cells differentiate into different cell lineages during organ development and morphogenesis. Signaling pathway networks and mechanotransduction are important factors to guide the lineage commitment of stem/progenitor cells during craniofacial tissue morphogenesis. Here, we used tooth root development as a model to explore the roles of FGF signaling and mechanotransduction as well as their interaction in regulating the progenitor cell fate decision. We show that Fgfr1 is expressed in the mesenchymal progenitor cells and their progeny during tooth root development. Loss of Fgfr1 in Gli1+ progenitors leads to hyperproliferation and differentiation, which causes narrowed periodontal ligament (PDL) space with abnormal cementum/bone formation leading to ankylosis. We further show that aberrant activation of WNT signaling and mechanosensitive channel Piezo2 occurs after loss of FGF signaling in Gli1-CreER;Fgfr1fl/fl mice. Overexpression of Piezo2 leads to increased osteoblastic differentiation and decreased Piezo2 leads to downregulation of WNT signaling. Mechanistically, an FGF/PIEZO2/WNT signaling cascade plays a crucial role in modulating the fate of progenitors during root morphogenesis. Downregulation of WNT signaling rescues tooth ankylosis in Fgfr1 mutant mice. Collectively, our findings uncover the mechanism by which FGF signaling regulates the fate decisions of stem/progenitor cells, and the interactions among signaling pathways and mechanotransduction during tooth root development, providing insights for future tooth root regeneration.

Regulatory role of N-myc downregulated genes in amelogenesis in rats

Cytodifferentiation of odontogenic cells, a late stage event in odontogenesis is based on gene regulation. However, studies on the identification of the involved genes are scarce. The present study aimed to search for molecules for the cytodifferentiation of ameloblastic cells in rats. Differential display-PCR revealed a differentially expressed gene between cap/early bell stage and hard tissue formation stage in molars. This gene was identified as N-myc Downregulated Gene 1 (Ndrg1), which is the first report in tooth development. Real time PCR and western blotting confirmed that the mRNA level of Ndrg1 was higher during enamel formation than the cap stage. Ndrg1 expression was upregulated in the early bell, crown, and root stages in a time-dependent manner. These patterns of expression were similar in Ndrg2, but Ndrg3 and Ndrg4 levels did not change during the developmental stages. Immunofluorescence revealed that strong immunoreactivity against Ndrg1 were detected in differentiated ameloblasts only, not inner enamel epithelium, odontoblasts and ameloblastic cells in defected enamel regions. Alkaline phosphatase and alizarin red s stains along with real time PCR, revealed that Ndrg1 and Ndrg2 were involved in cytodifferentiation and enamel matrix mineralization by selectively regulating amelogenin and ameloblastin genes in SF2 ameloblastic cells. These results suggest that Ndrg may play a crucial functional role in the cytodifferentiation of ameloblasts for amelogenesis.

Current Trends, Advances, and Challenges of Tissue Engineering-Based Approaches of Tooth Regeneration: A Review of the Literature

INTRODUCTION

Tooth loss is a significant health issue. Currently, this situation is often treated with the use of synthetic materials such as implants and prostheses. However, these treatment modalities do not fully meet patients' biological and mechanical needs and have limited longevity. Regenerative medicine focuses on the restoration of patients' natural tissues via tissue engineering techniques instead of rehabilitating with artificial appliances. Therefore, a tissue-engineered tooth regeneration strategy seems like a promising option to treat tooth loss.

OBJECTIVE

This review aims to demonstrate recent advances in tooth regeneration strategies and discoveries about underlying mechanisms and pathways of tooth formation.

RESULTS AND DISCUSSION

Whole tooth regeneration, tooth root formation, and dentin-pulp organoid generation have been achieved by using different seed cells and various materials for scaffold production. Bioactive agents are critical elements for the induction of cells into odontoblast or ameloblast lineage. Some substantial pathways enrolled in tooth development have been figured out, helping researchers design their experiments more effectively and aligned with the natural process of tooth formation.

CONCLUSION

According to current knowledge, tooth regeneration is possible in case of proper selection of stem cells, appropriate design and manufacturing of a biocompatible scaffold, and meticulous application of bioactive agents for odontogenic induction. Understanding innate odontogenesis pathways play a crucial role in accurately planning regenerative therapeutic interventions in order to reproduce teeth.

Injectable platelet-rich fibrin positively regulates osteogenic differentiation of stem cells from implant hole via the ERK1/2 pathway

Bone regeneration in dentistry is a dynamic approach for treating critical size bone defects that are unlikely to self-heal. Human bone marrow stem cell (hBMSCs) therapies are being tested clinically for various disorders and have remarkable clinical advancements in bone regeneration. Injectable platelet-rich fibrin (i-PRF), which is obtained from autologous blood centrifuged at 700 rpm (60 G) for 3 min can promote osteogenic differentiation of this cell, but the mechanism remains unclear. The objectives of this study were to explore the contents of i-PRF further and investigate its effect on the cell behavior of hBMSCs and the underlying molecular mechanisms. The results showed that i-PRF contained 41 cytokines, including macrophage colony-stimulating factor (M-CSF) and β-nerve growth factor (β-NGF), which had not been reported before. The Cell Counting Kit-8 and wound healing assay showed that 10% and 20% i-PRF improved the proliferation rate and the migration capacity of hBMSCs without toxicity to cells. Besides, the expression of osteogenic markers and the capacity to form mineralized nodules of hBMSCs were promoted by 20% i-PRF. Furthermore, i-PRF activated the ERK pathway, and the ERK inhibitor attenuated its effects. In summary, i-PRF promotes hBMSCs proliferation and migration and facilitates cell osteogenesis through the ERK pathway, which has promising potential in bone regeneration.

Infigratinib, a selective FGFR1-3 tyrosine kinase inhibitor, alters dentoalveolar development at high doses

BACKGROUND

Fibroblast growth factor receptor-3 (FGFR3) gain-of-function mutations are linked to achondroplasia. Infigratinib, a FGFR1-3 tyrosine kinase inhibitor, improves skeletal growth in an achondroplasia mouse model. FGFs and their receptors have critical roles in developing teeth, yet effects of infigratinib on tooth development have not been assessed. Dentoalveolar and craniofacial phenotype of Wistar rats dosed with low (0.1 mg/kg) and high (1.0 mg/kg) dose infigratinib were evaluated using micro-computed tomography, histology, and immunohistochemistry.

RESULTS

Mandibular third molars were reduced in size and exhibited aberrant crown and root morphology in 100% of female rats and 80% of male rats at high doses. FGFR3 and FGF18 immunolocalization and extracellular matrix protein expression were unaffected, but cathepsin K (CTSK) was altered by infigratinib. Cranial vault bones exhibited alterations in dimension, volume, and density that were more pronounced in females. In both sexes, interfrontal sutures were significantly more patent with high dose vs vehicle.

CONCLUSIONS

High dose infigratinib administered to rats during early stages affects dental and craniofacial development. Changes in CTSK from infigratinib in female rats suggest FGFR roles in bone homeostasis. While dental and craniofacial disruptions are not expected at therapeutic doses, our findings confirm the importance of dental monitoring in clinical studies.

CRISPR/Cas9-Induced Fam83h Knock-out Leads to Impaired Wnt/β-Catenin Pathway and Altered Expression of Tooth Mineralization Genes in Mice

Background

Dental enamel formation is a complex process that is regulated by various genes. One such gene, Family With Sequence Similarity 83 Member H (Fam83h), has been identified as an essential factor for dental enamel formation. Additionally, Fam83h has been found to be potentially linked to the Wnt/β-catenin pathway.

Objectives

This study aimed to investigate the effects of the Fam83h knockout gene on mineralization and formation of teeth, along with mediators of the Wnt/β-catenin pathway as a development aspect in mice.

Materials and Methods

To confirm the Fam83h-KnockOut mice, both Sanger sequencing and Western blot methods were used. then used qPCR to measure the expression levels of genes related to tooth mineralization and formation of dental root, including Fam20a, Dspp, Dmp1, Enam, Ambn, Sppl2a, Mmp20, and Wnt/β-catenin pathway mediators, in both the Fam83h-Knockout and wild-type mice at 5, 11 and 18 days of age. also the expression level of Fgf10 and mediators of the Wnt/β-catenin pathway was measured in the skin of both Knockout and wild-type mice using qPCR. A histological assessment was then performed to further investigate the results.

Results

A significant reduction in the expression levels of Ambn, Mmp20, Dspp, and Fgf10 in the dental root of Fam83h-Knockout mice compared to their wild-type counterparts was demonstrated by our results, indicating potential disruptions in tooth development. Significant down-regulation of CK1a, CK1e, and β-catenin in the dental root of Fam83h-Knockout mice was associated with a reduction in mineralization and formation-related gene. Additionally, the skin analysis of Fam83h-Knockout mice revealed reduced levels of Fgf10, CK1a, CK1e, and β-catenin. Further histological assessment confirmed that the concurrent reduction of Fgf10 expression level and Wnt/β-catenin genes were associated with alterations in hair follicle maturation.

Conclusions

The concurrent reduction in the expression level of both Wnt/β-catenin mediators and mineralization-related genes, resulting in the disruption of dental mineralization and formation, was caused by the deficiency of Fam83h. Our findings suggest a cumulative effect and multi-factorial interplay between Fam83h, Wnt/Β-Catenin signaling, and dental mineralization-related genes subsequently, during the dental formation process.

Transcriptomic Network Regulation of Rat Tooth Germ from Bell Differentiation Stage to Secretory Stage: MAPK Signaling Pathway Is Crucial to Extracellular Matrix Remodeling

Hard tissues make up the vast majority of teeth and are mineralized from the surrounding matrix. If the development of tooth germ is affected during mineralization, hypoplasia of the tooth tissue can occur. To better understand the mechanisms mediating hypoplasia, we need to first study normal development. Using a rodent model, we highlight the transcriptomic changes that occur from the differentiation to secretion stages of mandibular molar germs. The tooth germ was dissected from rats at postnatal day 1.5 or 3.5 for high-throughput sequencing. Combining transcriptome analysis and DNA methylation, we identified 590 differentially expressed genes (436 upregulated and 154 downregulated) and 551 differentially expressed lncRNAs (long noncoding RNA; 369 upregulated and 182 downregulated) which were linked to the biological processes of odontogenesis, amelogenesis, tooth mineralization, and the alteration of extracellular matrix (ECM), especially matrix metalloproteinases (MMPs) and elastin. We found DNA methylation changes in 32 selected fragments involved in 5 chromosomes, 26 targets, and 2 haplotypes. Finally, three novel genes were identified: MMP20, Tgfb3, and Dusp1. Further analysis revealed that MMP20 has a role in odontogenesis and amelogenesis by influencing Slc24a4 and DSPP; Tgfb3 is involved in epithelial cell proliferation, cellular component disassembly process, ECM cellular component, and decomposition of cell components. But lncRNA expression could affect DNA methylation and mRNA expression. Moreover, the degree of DNA methylation could also affect the transcriptome level. Thus, Tgfb3 had no difference in DNA methylation, and Dusp1 conferred no difference at the transcriptome level. These three genes were all enriched in the MAPK pathway and played an important role in ECM remodeling. These data suggest that during the period of the bell differentiation stage to the secretory stage, along with enamel/dentin matrix secretion and hard tissue occurrence, the ECM is remodeled via MAPK signaling.

KDF1 Novel Variant Causes Unique Dental and Oral Epithelial Defects

Keratinocyte differentiation factor 1 (KDF1) is a recently identified and rare candidate gene for human tooth agenesis; however, KDF1-related morphological characteristics and pathological changes in dental tissue and the oral epithelium remain largely unknown. Here, we employed whole-exome sequencing (WES) and Sanger sequencing to screen for the suspected variants in a cohort of 151 tooth agenesis patients, and we segregated a novel KDF1 heterozygous missense variation, c.920G>C (p.R307P), in a non-syndromic tooth agenesis family. Essential bioinformatics analyses and tertiary structural predictions were performed to analyze the structural changes and functional impacts of the novel KDF1 variant. The subsequent functional assessment using a TOP-flash/FOP-flash luciferase reporter system demonstrated that KDF1 variants suppressed the activation of canonical Wnt signaling in 293T cells. To comprehensively investigate the KDF1-related oral morphological anomalies, we performed scanning electron microscopy and ground section of the lower right lateral deciduous incisor extracted from #285 proband, and histopathological assessment of the gingiva. The phenotypic analyses revealed a series of tooth morphological anomalies related to the KDF1 variant R307P, including a shovel-shaped lingual surface of incisors and cornicione-shaped marginal ridges with anomalous morphological occlusal grooves of premolars and molars. Notably, keratinized gingival epithelium abnormalities were revealed in the proband and characterized by epithelial dyskeratosis with residual nuclei, indistinct stratum granulosum, epithelial hyperproliferation, and impaired epithelial differentiation. Our findings revealed new developmental anomalies in the tooth and gingival epithelium of a non-syndromic tooth agenesis individual with a novel pathogenic KDF1 variant, broadening the phenotypic spectrum of KDF1-related disorders and providing new evidence for the crucial role of KDF1 in regulating human dental and oral epithelial development.

Establishment of inclusive single-cell transcriptome atlases from mouse and human tooth as powerful resource for dental research

Single-cell (sc) omics has become a powerful tool to unravel a tissue’s cell landscape across health and disease. In recent years, sc transcriptomic interrogation has been applied to a variety of tooth tissues of both human and mouse, which has considerably advanced our fundamental understanding of tooth biology. Now, an overarching and integrated bird’s-view of the human and mouse tooth sc transcriptomic landscape would be a powerful multi-faceted tool for dental research, enabling further decipherment of tooth biology and development through constantly progressing state-of-the-art bioinformatic methods as well as the exploration of novel hypothesis-driven research. To this aim, we re-assessed and integrated recently published scRNA-sequencing datasets of different dental tissue types (healthy and diseased) from human and mouse to establish inclusive tooth sc atlases, and applied the consolidated data map to explore its power. For mouse tooth, we identified novel candidate transcriptional regulators of the ameloblast lineage. Regarding human tooth, we provide support for a developmental connection, not advanced before, between specific epithelial compartments. Taken together, we established inclusive mouse and human tooth sc atlases as powerful tools to potentiate innovative research into tooth biology, development and disease. The maps are provided online in an accessible format for interactive exploration.

Adipose-derived stromal/stem cells are verified to be potential seed candidates for bio-root regeneration in three-dimensional culture

BACKGROUND

Bio-root regeneration is a promising treatment for tooth loss. It has been reported that dental-derived stem cells are effective seed cells for bio-root construction, but further applications are limited by their few sources. Human adipose tissues have a wide range of sources and numerous studies have confirmed the ability of adipose-derived stromal/stem cells (ASCs) in regenerative medicine. In the current study, the odontogenic capacities of ASCs were compared with dental-derived stem cells including dental follicle cells (DFCs), and stem cells from human exfoliated deciduous teeth (SHEDs).

METHODS

The biological characteristics of ASCs, DFCs, and SHEDs were explored in vitro. Two-dimensional (2D) and three-dimensional (3D) cultures were compared in vitro. Odontogenic characteristics of porcine-treated dentin matrix (pTDM) induced cells under a 3D microenvironment in vitro were compared. The complexes (cell/pTDM) were transplanted subcutaneously into nude mice to verify regenerative potential. RNA sequencing (RNA-seq) was used to explore molecular mechanisms of different seed cells in bio-root regeneration.

RESULTS

3D culture was more efficient in constructing bio-root complexes. ASCs exhibited good biological characteristics similar to dental-derived stem cells in vitro. Besides, pTDM induced ASCs presented odontogenic ability similar to dental-derived stem cells. Furthermore, 3D cultured ASCs/pTDM complex promoted regeneration of dentin-like, pulp-like, and periodontal fiber-like tissues in vivo. Analysis indicated that PI3K-Akt, VEGF signaling pathways may play key roles in the process of inducing ASCs odontogenic differentiation by pTDM.

CONCLUSIONS

ASCs are potential seed cells for pTDM-induced bio-root regeneration, providing a basis for further research and application.

Spatiotemporal Expression Patterns of Critical Genes Involved in FGF Signaling During Morphogenesis and Odontogenesis of Deciduous Molars in Miniature Pigs

The fibroblast growth factor (FGF) pathway plays an important role in epithelial-mesenchymal interactions during tooth development. Nevertheless, how the ligands, receptors, and antagonists of the FGF pathway are involved in epithelial-mesenchymal interactions remains largely unknown. Miniature pigs exhibit tooth anatomy and replacement patterns like those in humans and hence can serve as large animal models. The present study investigated the spatiotemporal expression patterns of critical genes encoding FGF ligands (FGF3, FGF4, FGF7, and FGF9), antagonists (SPRY2 and SPRY4) and receptors (FGFR1, FGFR2, and FGFR3) in the third deciduous molars of miniature pigs at the cap (embryonic day 40, E40), early bell (E50), and late bell (E60) stages. The results of in situ hybridization (ISH) with tyramide signal amplification and of qRT-PCR analysis revealed increased expression of FGF7, FGFR1, FGFR2, and SPRY4 in dental epithelium and of FGF7 and FGFR1 in mesenchyme from E40 to E50. In contrast, the results revealed decreased expression of FGF3, FGF4, FGF9, and FGFR3 in dental epithelium and of FGF4, FGF9, FGFR2, and FGFR3 in the mesenchyme from E40 to E60. Mesenchyme signals of FGF3, FGF4, FGF7, SPRY2, FGFR2, and FGFR3 were concentrated in the odontoblast layer from E50 to E60. The distinct expression patterns of these molecules indicated elaborate regulation during dental morphogenesis. Our results provide a foundation for further investigation into fine-tuning dental morphogenesis and odontogenesis by controlling interactions between dental epithelium and mesenchyme, thus promoting tooth regeneration in large mammals.

Ckip-1 Mediates P. gingivalis-Suppressed Cementoblast Mineralization

Porphyromonas gingivalis is responsible for the destruction of cementum in patients with periodontitis and periapical periodontitis. However, research about the effects of P. gingivalis on cementoblast mineralization and the underlying mechanism is still lacking. Casein kinase 2 interacting protein 1 (Ckip-1) is a scaffold protein that interacts with various proteins and signals to regulate different cell functions, such as cell morphology, apoptosis, and differentiation. In this study, we verified the suppressive effects of P. gingivalis and lipopolysaccharide (Pg-LPS) on OCCM-30 mineralization. We also showed that Ckip-1 gradually decreased during OCCM-30 mineralization but increased with the aggravation of Pg-induced inflammation. However, it remained unchanged when cells were stimulated with Pg-LPS, regardless of the concentration and incubation time. Then, more cellular cementum and enhanced Osterix expression were observed in Ckip-1 knockout mice when compared with the wild-type mice. Meanwhile, Ckip-1 silencing significantly enhanced cementoblast mineralization with or without P. gingivalis-associated inflammation. The trend was opposite when Ckip-1 was overexpressed. Finally, we found that the p38, Akt, and Wnt pathways were activated, while the Erk1/2 pathway was inhibited when Ckip-1 was silenced. The opposite results were also observed in the Ckip-1 overexpression group. Furthermore, we proved that cell mineralization was weakened when p38, Akt inhibitors were applied and strengthened when the Erk1/2 pathway was inhibited. In summary, Ckip-1 is upregulated underP. gingivalis-induced inflammation and negatively regulates cementoblast mineralization partially through mitogen-activated protein kinases and Akt signaling pathways, which may contribute to the restoration of cementum destroyed by P. gingivalis.

Applications of the regenerative capacity of platelets in modern medicine

Platelets produce platelet growth factors such as PDGF, IGF-1, EGF-, HGF, TGFβ, bFGF, and VEGF, which are crucial in regulating all stages of the wound healing process. The source of these substances is platelet-rich plasma (PRP). Over the past five decades, the interest and use of the regenerative properties of platelets have increased significantly in many different fields of medicine around the world. PRP and PRF plate preparations are used in: 1. Dentistry (they reduce bleeding, facilitate and accelerate soft tissue healing and bone regeneration - FGF 2, IGF-1, IGF-2, TGF-β1, and PDGF); 2. Sports medicine - IGF-1, IGF-2, TGF-β, VEGF, PDGF and bFGF, EGF); 3. dermatology and cosmetology (treatment of alopecia, hair reconstruction - FGF-7, HGF, acne scars, skin rejuvenation and regeneration, treatment of chronic and poorly healing wounds, burns, and acquired vitiligo); 4. Gynecology and reproductive medicine (treatment of infertility, erectile dysfunction - PDGF-β, TGF-β, IGF-1, in sexual dysfunction - PDGF, in vaginal atrophy); 5 Ophthalmology (in the healing of corneal epithelial wounds, in the treatment of dormant corneal ulcers, dry eye syndrome and the reconstruction of the corneal surface; 6. Neurology (regeneration of neurons, pain alleviation, and clinical symptoms - TGF-β 1, IGF-1, PDGF, VEGF) and FGF). Platelet-rich plasma therapy is a very interesting alternative and complement to traditional methods of treatment. However, the potential for using platelets is still not fully understood. The composition of platelet-rich plasma depends on many factors that may affect its use's efficacy and clinical benefits. Further research is necessary to standardize PRP delivery's preparation procedures and methods for a specific disease entity or clinical case.

Revitalizing mouse diphyodontic dentition formation by inhibiting the sonic hedgehog signaling pathway

BACKGROUND

Tooth regeneration depends on the longevity of the dental epithelial lamina. However, the exact mechanism of dental lamina regression has not yet been clarified. To explore the role of the Sonic hedgehog (Shh) signaling pathway in regression process of the rudimentary successional dental lamina (RSDL) in mice, we orally administered a single dose of a Shh signaling pathway inhibitor to pregnant mice between embryonic day 13.0 (E13.0) and E17.0.

RESULTS

We observed that the Shh signaling pathway inhibitor effectively inhibited the expression of Shh signaling pathway components and revitalized RSDL during E15.0-E17.0 by promoting cell proliferation. In addition, mRNA-seq, reverse transcription plus polymerase chain reaction (RT-qPCR), and immunohistochemical analyses indicated that diphyodontic dentition formation might be related to FGF signal up-regulation and the Sostdc1-Wnt negative feedback loop.

CONCLUSIONS

Overall, our results indicated that the Shh signaling pathway may play an initial role in preventing further development of mouse RSDL in a time-dependent manner.

A single-cell interactome of human tooth germ from growing third molar elucidates signaling networks regulating dental development

Background

Development of dental tissue is regulated by extensive cell crosstalk based on various signaling molecules, such as bone morphogenetic protein (BMP) and fibroblast growth factor (FGF) pathways. However, an intact network of the intercellular regulation is still lacking.

Result

To gain an unbiased and comprehensive view of this dental cell interactome, we applied single-cell RNA-seq on immature human tooth germ of the growing third molar, discovered refined cell subtypes, and applied multiple network analysis to identify the central signaling pathways. We found that immune cells made up over 80% of all tooth germ cells, which exhibited profound regulation on dental cells via Transforming growth factor-β, Tumor necrosis factor (TNF) and Interleukin-1. During osteoblast differentiation, expression of genes related to extracellular matrix and mineralization was continuously elevated by signals from BMP and FGF family. As for the self-renewal of apical papilla stem cell, BMP-FGFR1-MSX1 pathway directly regulated the G0-to-S cell cycle transition. We also confirmed that Colony Stimulating Factor 1 secreted from pericyte and TNF Superfamily Member 11 secreted from osteoblast regulated a large proportion of genes related to osteoclast transformation from macrophage and monocyte.

Conclusions

We constructed the intercellular signaling networks that regulated the essential developmental process of human tooth, which served as a foundation for future dental regeneration engineering and the understanding of oral pathology.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-021-00691-5.

Spontaneous calcium responses of SF2 rat dental epithelial cells stably expressing the calcium sensor G-GECO

Genetically-encoded calcium indicators such as G-GECO are useful for studying Ca²⁺ responses during long-term processes. In this study, we employed a lentiviral vector and established a rat dental epithelial cell line that stably expressed G-GECO (SF2-G-GECO). Ca²⁺ imaging analysis under cell culture conditions revealed that SF2-G-GECO cells exhibited spontaneous Ca²⁺ responses, which could be classified into the following three major patterns depending on the cell density: localized Ca²⁺ responses at cell protrusions at a low density, a cell-wide spread of Ca²⁺ responses at a medium density, and Ca²⁺ responses in clusters of 3-20 cells at a high density. The P2Y receptor inhibitor suramin (10 μM), the ATP-degrading enzyme apyrase (5 units/mL), and the fibroblast growth factor (FGF) receptor inhibitor FIIN-2 (1 μM) decreased the frequency of spontaneous Ca²⁺ responses. These results indicate that ATP and FGF are involved in the spontaneous Ca²⁺ responses. SF2 cells differentiate into ameloblasts via interactions with mesenchymal cells. Therefore, SF2-G-GECO cells are expected to be a useful tool for studying the functions of Ca²⁺ responses in regulating gene expression during tooth development.

Fibroblastic Growth Factor as a Diagnostic and Prognostic Marker in Odontogenic Cysts and Tumors: A Systematic Review

Cellular signaling proteins maintain the basic activities of cell and communication, between the cells for normal growth and development and pathological situation as well. Fibroblast growth factor (FGF) and fibroblast growth factor receptors (FGFRs) have a comparatively huge part to play in the cellular communication processes. Human FGF has 22 members, 18 ligands, and 4 tyrosine kinase receptors for binding and is expressed in a wide range of cells. Any alteration in these factors would disrupt their normal function, leading to various abnormalities. The aim of this systematic analysis, is to understand the FGFs, the physiological and pathological role of FGF in oral diseases, and to predict the use of FGF in the predilection toward odontogenic cyst and tumors. This review helps confer the role of FGF in various physiological and pathological aspects in systemic diseases and analyzes its role in diagnosis and prognosis of odontogenic cysts and tumors.

Hypoxia-Responsive Oxygen Nanobubbles for Tissues-Targeted Delivery in Developing Tooth Germs

Hypoxia is a state of inadequate supply of oxygen. Increasing evidence indicates that a hypoxic environment is strongly associated with abnormal organ development. Oxygen nanobubbles (ONBs) are newly developed nanomaterials that can deliver oxygen to developing tissues, including hypoxic cells. However, the mechanisms through which nanobubbles recover hypoxic tissues, such as developing tooth germs remain to be identified. In this study, tooth germs were cultured in various conditions: CO₂ chamber, hypoxic chamber, and with 20% ONBs for 3 h. The target stages were at the cap stage (all soft tissue) and bell stage (hard tissue starts to form). Hypoxic tooth germs were recovered with 20% ONBs in the media, similar to the tooth germs incubated in a CO₂ chamber (normoxic condition). The tooth germs under hypoxic conditions underwent apoptosis both at the cap and bell stages, and ONBs rescued the damaged tooth germs in both the cap and bell stages. Using kidney transplantation for hard tissue formation in vivo, amelogenesis and dentinogenesis imperfecta in hypoxic conditions at the bell stage were rescued with ONBs. Furthermore, glucose uptake by tooth germs was highly upregulated under hypoxic conditions, and was restored with ONBs to normoxia levels. Our findings indicate that the strategies to make use of ONBs for efficient oxygen targeted delivery can restore cellular processes, such as cell proliferation and apoptosis, glucose uptake, and hypomineralization in hypoxic environments.

Expression of fibroblast growth factor receptor1, -2c, and -3c transcripts in mouse molars after tooth eruption

A previous study suggested that fibroblast growth factor (FGF) signaling plays an important role in dentin formation during tooth development. In this study, to examine dentin formation after tooth eruption involving secondary and tertiary dentin, we analyzed the expression patterns and expressing cells of Fgfr1, -2c, and -3c in mouse maxillary first molars (M₁). Since it is difficult to recover the mRNAs from mineralized tissues, we tested methods for extraction after fixation and decalcification of teeth. We successfully obtained consistent results with quantitative real-time PCR (qPCR) using β-actin transcripts for validation. qPCR for Dentin sialo phosphoprotein (Dspp), Fgfr1, -2c, and -3c transcripts was performed on mice at ages of 2-20 weeks. The results showed that the highest expression levels of Dspp and Fgfr2c occurred at 2 weeks old followed by lower expression levels after 4 weeks old. However, the expression levels of Fgfr1 and Fgfr3c were constant throughout the experimental period. By in situ hybridization, Dspp, Fgfr1, and Fgfr3c transcripts were detected in odontoblasts at ages of 2 and 4 weeks. In addition, Dspp and Fgfr1 transcripts were detected in odontoblasts facing reactionary dentin at 8 weeks old. These results suggest that FGF-FGFR signaling might be involved in the regulation of odontoblasts even after tooth eruption, including secondary and tertiary dentin formation. Moreover, our modified method for extracting mRNA from mineralized tissues after fixation and decalcification successfully produced consistent results.

Dual roles of TGF-β signaling in the regulation of dental epithelial cell proliferation

The purpose of this study is to investigate the molecular mechanisms and biological function of TGF-β-activated Smad1/5 in dental epithelium. Immunohistochemistry was used to detect the expressions of TGF-β signaling-related gene in mice molar germ. Primary dental epithelial cells were cultured and treated with TGF-β1 at a concentration of 0.5 or 5 ng/mL. Small molecular inhibitors, SB431542 and ML347, was used to inhibite ALK5 and ALK1/2, respectively. Small interfering RNA was used to knock down Smad1/5 or Smad2/3. The proliferation rate of cells was evaluated by EdU assay. In the basal layer of dental epithelial bud TGF-β1 and p-Smad1/5 were highly expressed, and in the interior of the epithelial bud TGF-β1 was lowly expressed, whereas p-Smad2/3 was highly expressed. In primary cultured dental epithelial cells, low concentration of TGF-β1 activated Smad2/3 but not Smad1/5, while high concentration of TGF-β1 was able to activate both Smad2/3 and Smad1/5. SB431542 but not ML347 was able to block the phosphorylation of Smad2/3 by TGF-β1. Either SB431542 or ML347 was able to block the phosphorylation of Smad1/5 by TGF-β1. EdU staining showed that high concentration of TGF-β1 promoted dental epithelial cell proliferation, which was reversed by silencing Smad1/5, whereas low concentration of TGF-β1 inhibited cell proliferation, which was reversed by silencing Smad2/3. In conclusions, TGF-β exhibits dual roles in the regulation of dental epithelial cell proliferation through two pathways. On the one hand, TGF-β activates canonical Smad2/3 signaling through ALK5, inhibiting the proliferation of internal dental epithelial cells. On the other hand, TGF-β activates noncanonical Smad1/5 signaling through ALK1/2-ALK5, promoting the proliferation of basal cells in the dental epithelial bud.

FAM20B-catalyzed glycosaminoglycans control murine tooth number by restricting FGFR2b signaling

BACKGROUND

The formation of supernumerary teeth is an excellent model for studying the molecular mechanisms that control stem/progenitor cell homeostasis needed to generate a renewable source of replacement cells and tissues. Although multiple growth factors and transcriptional factors have been associated with supernumerary tooth formation, the regulatory inputs of extracellular matrix in this regenerative process remains poorly understood.

RESULTS

In this study, we present evidence that disrupting glycosaminoglycans (GAGs) in the dental epithelium of mice by inactivating FAM20B, a xylose kinase essential for GAG assembly, leads to supernumerary tooth formation in a pattern reminiscent of replacement teeth. The dental epithelial GAGs confine murine tooth number by restricting the homeostasis of Sox2(+) dental epithelial stem/progenitor cells in a non-autonomous manner. FAM20B-catalyzed GAGs regulate the cell fate of dental lamina by restricting FGFR2b signaling at the initial stage of tooth development to maintain a subtle balance between the renewal and differentiation of Sox2(+) cells. At the later cap stage, WNT signaling functions as a relay cue to facilitate the supernumerary tooth formation.

CONCLUSIONS

The novel mechanism we have characterized through which GAGs control the tooth number in mice may also be more broadly relevant for potentiating signaling interactions in other tissues during development and tissue homeostasis.

Association between craniofacial morphological patterns and tooth agenesis-related genes

Background

The aim of the present study was to assess if genetic polymorphisms in tooth agenesis (TA)-related genes are associated with craniofacial morphological patterns.

Methods

This cross-sectional, multi-center, genetic study evaluated 594 orthodontic Brazilians patients. The presence or absence of TA was determined by analysis of panoramic radiography. The patients were classified according to their skeletal malocclusion and facial growth pattern by means of digital cephalometric analysis. Genomic DNA was extracted from squamous epithelial cells of buccal mucosa and genetic polymorphisms in MSX1 (rs1042484), PAX9 (rs8004560), TGF-α (rs2902345), FGF3 (rs1893047), FGF10 (rs900379), and FGF13 (rs12838463, rs5931572, and rs5974804) were genotyped by polymerase chain reaction using TaqMan chemistry and end-point analysis.

Results

Genotypes (p = 0.038) and allele (p = 0.037) distributions for the FGF3 rs1893047 were significantly different according to the skeletal malocclusion. Carrying at least one G allele increased in more than two times the chance of presenting skeletal class III malocclusion (OR = 2.21, CI 95% = 1.14–4.32; p = 0.017). There was no association between another skeletal craniofacial pattern and some polymorphism assessed in the present study.

Conclusion

Our results suggest that the genetic polymorphism rs1893047 in FGF3 might contribute to variations in the craniofacial sagittal pattern.

Opposite Expression Patterns of Spry3 and p75NTR in Cerebellar Vermis Suggest a Male-Specific Mechanism of Autism Pathogenesis

Autism is a genetically complex neurobehavioral disorder with a population prevalence of more than 1%. Cerebellar abnormalities, including Purkinje cell deficits in the vermis, are consistently reported, and rodent models of cerebellar dysfunction exhibit features analogous to human autism. We previously analyzed the regulation and expression of the pseudoautosomal region 2 gene SPRY3, which is adjacent to X chromosome-linked TMLHE, a known autism susceptibility gene. SPRY3 is a regulator of branching morphogenesis and is strongly expressed in Purkinje cells. We previously showed that mouse Spry3 is not expressed in cerebellar vermis lobules VI-VII and X, regions which exhibit significant Purkinje cell loss or abnormalities in autism. However, these lobules have relatively high expression of p75NTR, which encodes a neurotrophin receptor implicated in autism. We propose a mechanism whereby inappropriate SPRY3 expression in these lobules could interact with TrkB and p75NTR signaling pathways resulting in Purkinje cell pathology. We report preliminary characterization of X and Y chromosome-linked regulatory sequences upstream of SPRY3, which are polymorphic in the general population. We suggest that an OREG-annotated region on chromosome Yq12 ∼60 kb from SPRY3 acts as a silencer of Y-linked SPRY3 expression. Deletion of a β-satellite repeat, or alterations in chromatin structure in this region due to trans-acting factors, could affect the proposed silencing function, leading to reactivation and inappropriate expression of Y-linked SPRY3. This proposed male-specific mechanism could contribute to the male bias in autism prevalence.

Generation and Characterization of Fibroblast-Specific Basigin Knockout Mice

Basigin is a well-known extracellular stimulator of fibroblasts and may confer resistance to apoptosis of fibroblasts in vitro under some pathological status, but its exact function in fibroblasts and the underlying mechanism remain poorly understood. The systematic Basigin gene knockout leads to the perinatal lethality of mice, which limits the delineation of its function in vivo. In this study, we generated a fibroblast-specific Basigin knock-out mouse model and demonstrated the successful deletion of Basigin in fibroblasts. The fibroblast-specific deletion of Basigin did not influence the growth, fertility and the general condition of the mice. No obvious differences were found in the size, morphology, and histological structure of the major organs, including heart, liver, spleen, lung and kidney, between the knockout mice and the control mice. The deletion of Basigin in fibroblasts did not induce apoptosis in the tissues of the major organs. These results provide the first evidence that the fibroblast-specific Basigin knock-out mice could be a useful tool for exploring the function of Basigin in fibroblasts in vivo.

The in vitro effects of CCN2 on odontoblast-like cells

OBJECTIVE

To investigate the in vitro effects of CCN2 on odontoblast-like cells proliferation and differentiation.

DESIGN

MDPC-23 cells were cultured in DMEM supplemented with 5% FBS. CCN2 was either added to culture media or coated onto culture polystyrene, addition or coating of dH2O was served as control. In the addition group, CCN2 (100 ng/mL) was added into culture media. In the coating group, CCN2 at the concentration of 1000 ng/mL was employed. Cell proliferation was performed using CCK-8 assay. Cell differentiation and mineralization were analyzed by ALPase activity assay, real time RT-PCR and alizarin red staining. One-way ANOVA with post-hoc tukey HSD test was used for statistical analysis.

RESULTS

MDPC-23 cells exhibited robust proliferative activity upon exposure to either soluble or immobilized CCN2. ALP activity of cells cultured on CCN2-modified surface was continuously strengthened from day six (0.831 ± 0.024 units/μg protein versus 0.563 ± 0.006 units/μg protein of control) till day eight (1.035 ± 0.139 units/μg protein versus 0.704 ± 0.061 units/μg protein of control). Gene expression of BSP, OCN and OPN were promoted by soluble CCN2 after 48 h exposure. Moreover, gene expression of BSP, OCN, OPN, ALP, COL1 A1, Runx-2, DSPP and DMP-1 was significantly enhanced by immobilized CCN2. Finally, mineralization of MDPC-23 cells was accelerated by both soluble and immobilized CCN2 to different extent.

CONCLUSIONS

The findings indicate that CCN2 promoted proliferation, odontogenic gene expression and mineralization of MDPC-23 cells. It is proposed that CCN2 may be a promising adjunctive formula for dentin regeneration.