Ciliary IFT80 regulates dental pulp stem cells differentiation by FGF/FGFR1 and Hh/BMP2 signaling

Molecular insights into the proteomic composition of porcine treated dentin matrix

Background

Human-treated dentin matrix (hTDM) has recently been studied as a natural extracellular matrix-based biomaterial for dentin pulp regeneration. However, porcine-treated dentin matrix (pTDM) is a potential alternative scaffold due to limited availability. However, there is a dearth of information regarding the protein composition and underlying molecular mechanisms of pTDM.Methods: hTDM and pTDM were fabricated using human and porcine teeth, respectively, and their morphological characteristics were examined using scanning electron microscopy. Stem cells derived from human exfoliated deciduous teeth (SHEDs) were isolated and characterized using flow cytometry and multilineage differentiation assays. SHEDs were cultured in three-dimensional environments with hTDM, pTDM, or biphasic hydroxyapatite/tricalcium phosphate. The expression of odontogenesis markers in SHEDs were assessed using real-time polymerase chain reaction and immunochemical staining. Subsequently, SHEDs/TDM and SHEDs/HA/TCP complexes were transplanted subcutaneously into nude mice. The protein composition of pTDM was analyzed using proteomics and compared to previously published data on hTDM.Results: pTDM and hTDM elicited comparable upregulation of odontogenesis-related genes and proteins in SHEDs. Furthermore, both demonstrated the capacity to stimulate root-related tissue regeneration in vivo. Proteomic analysis revealed the presence of 278 protein groups in pTDM, with collagens being the most abundant. Additionally, pTDM and hTDM shared 58 identical proteins, which may contribute to their similar abilities to induce odontogenesis.

Conclusions

Both hTDM and pTDM exhibit comparable capabilities in inducing odontogenesis, potentially owing to their distinctive bioactive molecular networks.

Mesenchymal stromal cell exosomes enhance dental pulp cell functions and promote pulp-dentin regeneration

Mesenchymal stromal/stem cell (MSC) therapies are currently being explored for dental pulp regeneration. As the therapeutic effects of MSCs in tissue repair are mediated mainly through the release of extracellular vesicles (EVs) including exosomes, we investigated here the cellular processes and molecular mechanisms modulated by MSC exosomes in dental pulp regeneration. Using dental pulp cell (DPC) cultures, we demonstrated that MSC exosomes could increase DPC migration, proliferation, and odontogenic differentiation. The enhancement of these cellular processes was mediated through exosomal CD73-mediated adenosine receptor activation of AKT and ERK signaling. Consistent with these observations, MSC exosomes increased the expression of dentin matrix proteins and promoted the formation of dentin-like tissue and bridge-like structures in a rat pulp defect model. These effects were comparable to that of mineral trioxide aggregate (MTA) treatment. MSC exosomes also yielded recellularized pulp-dentin tissues in the root canal of endodontically-treated human premolars, following subcutaneous implantation in the mouse dorsum. Together, our findings suggest that MSC exosomes could exert a multi-faceted effect on DPC functions including migration, proliferation and odontogenic differentiation to promote dental pulp regeneration. This study provides the basis for development of MSC exosomes as a cell-free MSC therapeutic alternative for pulp-dentin regeneration.

Primary cilia: The central role in the electromagnetic field induced bone healing

Primary cilia have emerged as the cellular “antenna” that can receive and transduce extracellular chemical/physical signals, thus playing an important role in regulating cellular activities. Although the electromagnetic field (EMF) is an effective treatment for bone fractures since 1978, however, the detailed mechanisms leading to such positive effects are still unclear. Primary cilia may play a central role in receiving EMF signals, translating physical signals into biochemical information, and initiating various signalingsignaling pathways to transduce signals into the nucleus. In this review, we elucidated the process of bone healing, the structure, and function of primary cilia, as well as the application and mechanism of EMF in treating fracture healing. To comprehensively understand the process of bone healing, we used bioinformatics to analyze the molecular change and associated the results with other studies. Moreover, this review summarizedsummarized some limitations in EMFs-related research and provides an outlook for ongoing studies. In conclusion, this review illustrated the primary cilia and related molecular mechanisms in the EMF-induced bone healing process, and it may shed light on future research.

Primary Cilia: The New Face of Craniofacial Research

The primary cilium is a solitary, sensory organelle that extends from the surface of nearly every vertebrate cell, including craniofacial cells. This organelle converts chemical and physical external stimuli into intracellular signaling cascades and mediates several well-known signaling pathways simultaneously. Thus, the primary cilium is considered a cellular signaling nexus and amplifier. Primary cilia dysfunction directly results in a collection of diseases and syndromes that typically affect multiple organ systems, including the face and teeth. Despite this direct connection, primary cilia are largely unexplored in craniofacial research. In this review, I briefly summarize craniofacial abnormalities tied to the primary cilium and examine the existing information on primary cilia in craniofacial development and repair. I close with a discussion on preliminary studies that motivate future areas of exploration that are further supported by studies performed in long bone and kidney cells.

Pharmacological intervention of the FGF-PTH axis as a potential therapeutic for craniofacial ciliopathies

Ciliopathies represent a disease class characterized by a broad range of phenotypes including polycystic kidneys and skeletal anomalies. Ciliopathic skeletal phenotypes are among the most common and most difficult to treat due to a poor understanding of the pathological mechanisms leading to disease. Using an avian model (talpid2) for a human ciliopathy with both kidney and skeletal anomalies (Orofaciodigital syndrome 14), we identified disruptions in the FGF23-PTH axis that resulted in reduced calcium uptake in the developing mandible and subsequent micrognathia. While pharmacological intervention with the FDA-approved pan-FGFR inhibitor AZD4547 alone rescued expression of the FGF target Sprouty2, it did not significantly rescue micrognathia. In contrast, treatment with a cocktail of AZD4547 and Teriparatide acetate, a PTH agonist and FDA-approved treatment for osteoporosis, resulted in a molecular, cellular, and phenotypic rescue of ciliopathic micrognathia in talpid2 mutants. Together, these data provide novel insight into pathological molecular mechanisms associated with ciliopathic skeletal phenotypes and a potential therapeutic strategy for a pleiotropic disease class with limited to no treatment options.

Type II collagen-positive progenitors are important stem cells in controlling skeletal development and vascular formation

Type II collagen-positive (Col2+) cells have been reported as skeletal stem cells (SSCs), but the contribution of Col2+ progenitors to skeletal development both prenatally and postnatally during aging remains unclear. To address this question, we generated new mouse models with ablation of Col2+ cells at either the embryonic or postnatal stages. The embryonic ablation of Col2+ progenitors resulted in the death of newborn mice due to a decrease in skeletal blood vessels, loss of all vertebral bones and absence of most other bones except part of the craniofacial bone, the clavicle bone and a small piece of the long bone and ribs, which suggested that intramembranous ossification is involved in long bone development but does not participate in spine development. The postnatal ablation of Col2+ cells resulted in mouse growth retardation and a collagenopathy phenotype. Lineage tracing experiments with embryonic or postnatal mice revealed that Col2+ progenitors occurred predominantly in the growth plate (GP) and articular cartilage, but a limited number of Col2+ cells were detected in the bone marrow. Moreover, the number and differentiation ability of Col2+ progenitors in the long bone and knee joints decreased with increasing age. The fate-mapping study further revealed Col2+ lineage cells contributed to, in addition to osteoblasts and chondrocytes, CD31+ blood vessels in both the calvarial bone and long bone. Specifically, almost all blood vessels in calvarial bone and 25.4% of blood vessels in long bone were Col2+ lineage cells. However, during fracture healing, 95.5% of CD31+ blood vessels in long bone were Col2+ lineage cells. In vitro studies further confirmed that Col2+ progenitors from calvarial bone and GP could form CD31+ vascular lumens. Thus, this study provides the first demonstration that intramembranous ossification is involved in long bone and rib development but not spine development. Col2+ progenitors contribute to CD31+ skeletal blood vessel formation, but the percentage differs between long bone and skull bone. The number and differentiation ability of Col2+ progenitors decreases with increasing age.

Role of Primary Cilia in Bone and Cartilage

The primary cilium is a nonmotile microtubule-based organelle in most vertebrate cell types. The primary cilium plays a critical role in tissue development and homeostasis by sensing and transducing various signaling pathways. Ciliary proteins such as intraflagellar transport (IFT) proteins as well as ciliary motor proteins, kinesin and dynein, comprise a bidirectional intraflagellar transport system needed for cilia formation and function. Mutations in ciliary proteins that lead to loss or dysfunction of primary cilia cause ciliopathies such as Jeune syndrome and Ellis-van Creveld syndrome and cause abnormalities in tooth development. These diseases exhibit severe skeletal and craniofacial dysplasia, highlighting the significance of primary cilia in skeletal development. Cilia are necessary for the propagation of hedgehog, transforming growth factor β, platelet-derived growth factor, and fibroblast growth factor signaling during osteogenesis and chondrogenesis. Ablation of ciliary proteins such as IFT80 or IFT20 blocks cilia formation, which inhibits osteoblast differentiation, osteoblast polarity, and alignment and reduces bone formation. Similarly, cilia facilitate chondrocyte differentiation and production of a cartilage matrix. Cilia also play a key role in mechanosensing and are needed for increased bone formation in response to mechanical forces.

Differential lncRNA/mRNA Expression Profiling and Functional Network Analyses in Bmp2 Deletion of Mouse Dental Papilla Cells

Bmp2 is essential for dentin development and formation. Bmp2 conditional knock-out (KO) mice display a similar tooth phenotype of dentinogenesis imperfecta (DGI). To elucidate a foundation for subsequent functional studies of cross talk between mRNAs and lncRNAs in Bmp2-mediated dentinogenesis, we investigated the profiling of lncRNAs and mRNAs using immortalized mouse dental Bmp2 flox/flox (iBmp2^fx/fx) and Bmp2 knock-out (iBmp2^ko/ko) papilla cells. RNA sequencing was implemented to study the expression of the lncRNAs and mRNAs. Quantitative real-time PCR (RT-qPCR) was used to validate expressions of lncRNAs and mRNAs. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) databases were used to predict functions of differentially expressed genes (DEGs). Protein-protein interaction (PPI) and lncRNA-mRNA co-expression network were analyzed by using bioinformatics methods. As a result, a total of 22 differentially expressed lncRNAs (16 downregulated vs 6 upregulated) and 227 differentially expressed mRNAs (133 downregulated vs. 94 upregulated) were identified in the iBmp2^ko/ko cells compared with those of the iBmp2^fx/fx cells. RT-qPCR results showed significantly differential expressions of several lncRNAs and mRNAs which were consistent with the RNA-seq data. GO and KEGG analyses showed differentially expressed genes were closely related to cell differentiation, transcriptional regulation, and developmentally relevant signaling pathways. Moreover, network-based bioinformatics analysis depicted the co-expression network between lncRNAs and mRNAs regulated by Bmp2 in mouse dental papilla cells and symmetrically analyzed the effect of Bmp2 during dentinogenesis via coding and non-coding RNA signaling.

Primary cilia in hard tissue development and diseases

Bone and teeth are hard tissues. Hard tissue diseases have a serious effect on human survival and quality of life. Primary cilia are protrusions on the surfaces of cells. As antennas, they are distributed on the membrane surfaces of almost all mammalian cell types and participate in the development of organs and the maintenance of homeostasis. Mutations in cilium-related genes result in a variety of developmental and even lethal diseases. Patients with multiple ciliary gene mutations present overt changes in the skeletal system, suggesting that primary cilia are involved in hard tissue development and reconstruction. Furthermore, primary cilia act as sensors of external stimuli and regulate bone homeostasis. Specifically, substances are trafficked through primary cilia by intraflagellar transport, which affects key signaling pathways during hard tissue development. In this review, we summarize the roles of primary cilia in long bone development and remodeling from two perspectives: primary cilia signaling and sensory mechanisms. In addition, the cilium-related diseases of hard tissue and the manifestations of mutant cilia in the skeleton and teeth are described. We believe that all the findings will help with the intervention and treatment of related hard tissue genetic diseases.

The Regenerative Potential of bFGF in Dental Pulp Repair and Regeneration

Regenerative endodontic therapy intends to induce the host’s natural wound-healing process, which can restore the vitality, immunity, and sensitivity of the inflammatory or necrotic pulp tissue destroyed by infection or trauma. Myriads of growth factors are critical in the processes of pulp repair and regeneration. Among the key regulatory factors are the fibroblast growth factors, which have turned out to be the master regulators of both organogenesis and tissue homeostasis. Fibroblast growth factors, a family composed of 22 polypeptides, have been used in tissue repair and regeneration settings, in conditions as diverse as burns, ulcers, bone-related diseases, and spinal cord injuries. Meanwhile, in dentistry, the basic fibroblast growth factor is the most frequently investigated. Thereby, the aim of this review is 2-fold: 1) foremost, to explore the underlying mechanisms of the bFGF in dental pulp repair and regeneration and 2) in addition, to shed light on the potential therapeutic strategies of the bFGF in dental pulp–related clinical applications.

Oncogenic FGFR Fusions Produce Centrosome and Cilia Defects by Ectopic Signaling

A single primary cilium projects from most vertebrate cells to guide cell fate decisions. A growing list of signaling molecules is found to function through cilia and control ciliogenesis, including the fibroblast growth factor receptors (FGFR). Aberrant FGFR activity produces abnormal cilia with deregulated signaling, which contributes to pathogenesis of the FGFR-mediated genetic disorders. FGFR lesions are also found in cancer, raising a possibility of cilia involvement in the neoplastic transformation and tumor progression. Here, we focus on FGFR gene fusions, and discuss the possible mechanisms by which they function as oncogenic drivers. We show that a substantial portion of the FGFR fusion partners are proteins associated with the centrosome cycle, including organization of the mitotic spindle and ciliogenesis. The functions of centrosome proteins are often lost with the gene fusion, leading to haploinsufficiency that induces cilia loss and deregulated cell division. We speculate that this complements the ectopic FGFR activity and drives the FGFR fusion cancers.

Characterization of Dental Pulp Stem Cell Responses to Functional Biomaterials Including Mineralized Trioxide Aggregates

INTRODUCTION

Many studies in stem cell biology have demonstrated that dental pulp stem cells (DPSC) may be highly proliferative and capable of pluripotent differentiation into many different tissue types. Recent advances in stem cell research have outlined methods for directing in vitro or in vivo growth, viability, and proliferation, as well as differentiation of DPSC-although much remains to be discovered. Based upon this information, the primary objective of this study was to understand the functional biomaterials needed to more effectively direct DPSC viability, growth, and proliferation.

METHODS

Using an approved protocol, previously collected and isolated samples of DPSC from an existing repository were used. Previously established stem cell biomarkers (Sox-2, Oct-4, NANOG) from each isolate were correlated with their proliferation rates or doubling times to categorize them into rapid, intermediate, or slow-dividing multipotent DPSC. Growth factors and other functional dental biomaterials were subsequently tested to evaluate DPSC responses in proliferation, viability, and morphology.

RESULTS

Differential responses were observed among DPSC isolates to growth factors, including vascular endothelial growth factor (VEGF) and bone morphogenic protein (BMP-2), and functional biomaterials such as mineralized trioxide aggregates (MTA). The responsiveness of DPSC isolates did not correlate with any single factor but rather with a combination of proliferation rate and biomarker expression.

CONCLUSIONS

These data strongly suggest that some, but not all, DPSC isolates are capable of a robust and significant in vitro response to differentiation stimuli, although this response is not universal. Although some biomarkers and phenotypes that distinguish and characterize these DPSC isolates may facilitate the ability to predict growth, viability, and differentiation potential, more research is needed to determine the other intrinsic and extrinsic factors that may contribute to and modulate these DPSC responses to these functional biomaterials for biotechnology and bioengineering applications.

RICK regulates the odontogenic differentiation of dental pulp stem cells through activation of TNF-α via the ERK and not through NF-κB signaling pathway

Dental pulp stem cells (DPSCs) are capable of both self-renewal and multilineage differentiation, which play a positive role in dentinogenesis. Studies have shown that tumor necrosis factor-α (TNF-α) is involved in the differentiation of DPSCs under pro-inflammatory stimuli, but the mechanism of action of TNF-α is unknown. Rip-like interacting caspase-like apoptosis-regulatory protein kinase (RICK) is a biomarker of an early inflammatory response that plays a key role in modulating cell differentiation, but the role of RICK in DPSCs is still unclear. In this study, we identified that RICK regulates TNF-α-mediated odontogenic differentiation of DPSCs via the ERK signaling pathway. The expression of the biomarkers of odontogenic differentiation dental matrix protein-1 (DMP-1), dentin sialophosphoprotein (DSPP), biomarkers of odontogenic differentiation, increased in low concentration (1-10 ng/ml) of TNF-α and decreased in high concentration (50-100 ng/ml). Odontogenic differentiation increased over time in the odontogenic differentiation medium. In the presence of 10 ng/L TNF-α, the expression of RICK increased gradually over time, along with odontogenic differentiation. Genetic silencing of RICK expression reduced the expression of odontogenic markers DMP-1 and DSPP. The ERK, but not the NF-κB signaling pathway, was activated during the odontogenic differentiation of DPSCs. ERK signaling modulators decreased when RICK expression was inhibited. PD98059, an ERK inhibitor, blocked the odontogenic differentiation of DPSCs induced by TNF-α. These results provide a further theoretical and experimental basis for the potential use of RICK in targeted therapy for dentin regeneration.

Stem Cell-based Dental Pulp Regeneration: Insights From Signaling Pathways

Deep caries, trauma, and severe periodontitis result in pulpitis, pulp necrosis, and eventually pulp loss. However, no clinical therapy can regenerate lost pulp. A novel pulp regeneration strategy for clinical application is urgently needed. Signaling transduction plays an essential role in regulating the regenerative potentials of dental stem cells. Cytokines or growth factors, such as stromal cell-derived factor (SDF), fibroblast growth factor (FGF), bone morphogenetic protein (BMP), vascular endothelial growth factor (VEGF), WNT, can promote the migration, proliferation, odontogenic differentiation, pro-angiogenesis, and pro-neurogenesis potentials of dental stem cells respectively. Using the methods of signaling modulation including growth factors delivery, genetic modification, and physical stimulation has been applied in multiple preclinical studies of pulp regeneration based on cell transplantation or cell homing. Transplanting dental stem cells and growth factors encapsulated into scaffold regenerated vascularized pulp-like tissue in the root canal. Also, injecting a flowable scaffold only with chemokines recruited endogenous stem/progenitor cells for pulp regeneration. Notably, dental pulp regeneration has gradually developed into the clinical phase. These findings enlightened us on a novel strategy for structural and functional pulp regeneration through elaborate modulation of signaling transduction spatially and temporally via clinically applicable growth factors delivery. But challenges, such as the adverse effects of unphysiological signaling activation, the controlled drug release system, and the safety of gene modulation, are necessary to be tested in future works for promoting the clinical translation of pulp regeneration.

Tooth Formation: Are the Hardest Tissues of Human Body Hard to Regenerate?

With increasing life expectancy, demands for dental tissue and whole-tooth regeneration are becoming more significant. Despite great progress in medicine, including regenerative therapies, the complex structure of dental tissues introduces several challenges to the field of regenerative dentistry. Interdisciplinary efforts from cellular biologists, material scientists, and clinical odontologists are being made to establish strategies and find the solutions for dental tissue regeneration and/or whole-tooth regeneration. In recent years, many significant discoveries were done regarding signaling pathways and factors shaping calcified tissue genesis, including those of tooth. Novel biocompatible scaffolds and polymer-based drug release systems are under development and may soon result in clinically applicable biomaterials with the potential to modulate signaling cascades involved in dental tissue genesis and regeneration. Approaches for whole-tooth regeneration utilizing adult stem cells, induced pluripotent stem cells, or tooth germ cells transplantation are emerging as promising alternatives to overcome existing in vitro tissue generation hurdles. In this interdisciplinary review, most recent advances in cellular signaling guiding dental tissue genesis, novel functionalized scaffolds and drug release material, various odontogenic cell sources, and methods for tooth regeneration are discussed thus providing a multi-faceted, up-to-date, and illustrative overview on the tooth regeneration matter, alongside hints for future directions in the challenging field of regenerative dentistry.

microRNA-143-3p regulates odontogenic differentiation of human dental pulp stem cells through regulation of the osteoprotegerin-RANK ligand pathway by targeting RANK

NEW FINDINGS

What is the central question of this study? What is the role of miR-143-3p during human dental pulp stem cell (hDPSC) differentiation. What is the main finding and its importance? miR-143-3p negatively regulates receptor activator of nuclear factor-κB (RANK). RANK ligand (RANKL) binds to RANK and stimulates the development of osteoclasts. Osteoprotegerin (OPG) inhibits the interaction between RANK and RANKL. The OPG-RANKL signalling pathway regulates odontogenic differentiation of hDPSCs.

ABSTRACT

Human dental pulp stem cells (hDPSCs) are capable of differentiating into odontoblast-like cells, which secrete reparative dentin after injury, in which the role of microRNA-143-3p (miR-143-3p) has been identified. Therefore, we investigated the mechanism by which miR-143-3p influences odontoblastic differentiation of hDPSCs. The relationship between miR-143-3p and receptor activator of nuclear factor-κB (RANK) was initially identified by bioinformatics prediction and further verified by dual luciferase reporter gene assay. Gain- and loss-of-function analysis with miR-143-3p mimic and miR-143-3p inhibitor was subsequently conducted. Dentin sialophosphoprotein (DSPP), bone sialoprotein (BSP), alkaline phosphatase (ALP), osteocalcin (OCN) and osteopontin (OPN) mRNA levels were then evaluated by RT-qPCR. Osteoprotegerin (OPG), RANK ligand (RANKL), nuclear factor-κB (NF-κB) p65 protein levels and the extent of NF-κB p65 phosphorylation were examined by western blot analysis. Alizarin red staining was performed to assess the mineralization of hDPSCs. Cell apoptosis and cell cycle distribution were determined using flow cytometry. During odontoblastic differentiation of hDPSC, miR-143-3p had high expression, but RANK expression was low. miR-143-3p was found to target RANK, and its inhibition enhanced mineralization and hDPSC apoptosis, while blocking cell cycle entry. At the same time, miR-143-3p inhibition elevated the extent of NF-κB p65 phosphorylation, as well as the expression of RANK, RANKL, DSPP, BSP, ALP, OCN and OPN, while decreasing the OPG level. Silencing RANK had opposite effects on these markers. miR-143-3p regulates odontoblastic differentiation of hDPSCs via the OPG-RANKL pathway that targets RANK. The elucidation of the mechanisms of odontogenic differentiation of hDPSCs may contribute to the development of effective dental pulp repair therapies for the clinical setting.