Stem cell regulatory gene expression in human adult dental pulp and periodontal ligament cells undergoing odontogenic/osteogenic differentiation

Evaluation of the Efficacy of Stem Cells Therapy in the Periodontal Regeneration: A Meta-Analysis and Mendelian Randomization Study

Stem cell therapy for periodontal defects has shown good promise in preclinical studies. The purpose of this study was to evaluate the impact of stem cell support on the regeneration of both soft and hard tissues in periodontal treatment. PubMed, Cochrane Library, Embase, and Web of Science were searched and patients with periodontal defects who received stem cell therapy were included in this study. The quality of the included articles was assessed using Cochrane's tool for evaluating bias, and heterogeneity was analyzed using the I2 method. An Mendelian randomization investigation was conducted using abstract data from the IEU public databases obtained through GWAS. Nine articles were included for the meta-analysis. Stem cell therapy effectively rebuilds periodontal tissues in patients with periodontal defects, as evidenced by a reduction in probing depth, clinical attachment level  and bone defect depth . And delta-like homolog 1 is a protective factor against periodontal defects alternative indicator of tooth loosening. The findings of this research endorse the utilization of stem cell treatment for repairing periodontal defects in individuals suffering from periodontitis. It is recommended that additional extensive clinical investigations be carried out to validate the efficacy of stem cell therapy and encourage its widespread adoption.

Network analysis of transcriptomic data uncovers molecular signatures and the interplay of mRNAs, lncRNAs, and miRNAs in human embryonic stem cells

Growing evidence has shown that besides the protein coding genes, the non-coding elements of the genome are indispensable for maintaining the property of self-renewal in human embryonic stem cells and in cell fate determination. However, the regulatory mechanisms and the landscape of interactions between the coding and non-coding elements is poorly understood. In this work, we used weighted gene co-expression network analysis (WGCNA) on transcriptomic data retrieved from RNA-seq and small RNA-seq experiments and reconstructed the core human pluripotency network (called PluriMLMiNet) consisting of 375 mRNA, 57 lncRNA and 207 miRNAs. Furthermore, we derived networks specific to the naïve and primed states of human pluripotency (called NaiveMLMiNet and PrimedMLMiNet respectively) that revealed a set of molecular markers (RPS6KA1, ZYG11A, ZNF695, ZNF273, and NLRP2 for naive state, and RAB34, TMEM178B, PTPRZ1, USP44, KIF1A and LRRN1 for primed state) which can be used to distinguish the pluripotent state from the non-pluripotent state and also to identify the intra-pluripotency states (i.e., naïve and primed state). The lncRNA DANT1 was found to be a crucial as it formed a bridge between the naive and primed state-specific networks. Analysis of the genes neighbouring DANT1 suggested its possible role as a competing endogenous RNA (ceRNA) for the induction and maintenance of human pluripotency. This was computationally validated by predicting the missing DANT1-miRNA interactions to complete the ceRNA circuit. Here we first report that DANT1 might harbour binding sites for miRNAs hsa-miR-30c-2-3p, hsa-miR-210-3p and hsa-let-7b-5p which may influence pluripotency.

Mineralized Microgels via Electrohydrodynamic Atomization: Optimization and In Vitro Model for Dentin-Pulp Complex

There is growing interest in the use of micro-sized hydrogels, including bioactive signals, as efficient platforms for tissue regeneration because they are able to mimic cell niche structure and selected functionalities. Herein, it is proposed to optimize bioactive composite microgels via electrohydrodynamic atomization (EHDA) to regenerate the dentin-pulp complex. The addition of disodium phosphate (Na2HPO4) salts as mineral precursors triggered an in situ reaction with divalent ions in solution, thus promoting the encapsulation of different amounts of apatite-like phases. Morphological analysis via image analysis of optical images confirmed a narrow distribution of perfectly rounded particles, with an average diameter ranging from 223 ± 18 μm to 502 ± 64 μm as a function of mineral content and process parameters used. FTIR, TEM, and EDAX analyses confirmed the formation of calcium phosphates with a characteristic Ca/P ratio close to 1.67 and a needle-like crystal shape. In vitro studies-using dental pulp stem cells (DPSCs) in crown sections of natural teeth slices-showed an increase in cell viability until 14 days, recording a decay of proliferation at 21 days, independent on the mineral amount, suggesting that differentiation is started, as confirmed by the increase of ALP activity at 14 days. In this view, mineralized microgels could be successfully used to support in vitro osteogenesis, working as an interesting model to study dental tissue regeneration.

Functional role of circRNAs in osteogenesis: A review

The extracellular matrixes (ECM), as well as the microenvironmental signals, play an essential role in osteogenesis by regulating intercellular pathways. Recently, it has been demonstrated that a newly identified RNA, circular RNA, contributes to the osteogenesis process. Circular RNA (circRNA), the most recently identified RNA, is involved in the regulation of gene expression at transcription to translation levels. The dysregulation of circRNAs has been observed in several tumors and diseases. Also, various studies have shown that circRNAs expression is changed during osteogenic differentiation of progenitor cells. Therefore, understanding the role of circRNAs in osteogenesis might help the diagnosis as well as treatment of bone diseases such as bone defects and osteoporosis. In this review, circRNA functions and the related pathways in osteogenesis have been discussed.

From Teeth to Therapy: A Review of Therapeutic Potential within the Secretome of Stem Cells from Human Exfoliated Deciduous Teeth

Stem cells derived from human exfoliated deciduous teeth (SHED) have emerged as an alternative stem cell source for cell therapy and regenerative medicine because they are readily available, pose fewer ethical concerns, and have low immunogenicity and tumourigenicity. SHED offer a number of advantages over other dental stem cells, including a high proliferation rate with the potential to differentiate into multiple developmental lineages. The therapeutic effects of SHED are mediated by multiple mechanisms, including immunomodulation, angiogenesis, neurogenesis, osteogenesis, and adipogenesis. In recent years, there is ample evidence that the mechanism of action of SHED is mainly due to its paracrine action, releasing a wide range of soluble factors such as cytokines, chemokines, and trophic factors (also known as 'secretome') into the local tissue microenvironment to promote tissue survival and recovery. This review provides an overview of the secretome derived from SHED and highlights the bioactive molecules involved in tissue regeneration and their potential applications in regenerative medicine.

The Wisdom in Teeth: Neuronal Differentiation of Dental Pulp Cells

Mesenchymal stem/stromal cells (MSCs) are found in almost all postnatal organs. Under appropriate environmental cues, multipotency enables MSCs to serve as progenitors for several lineage-specific, differentiated cell types. In vitro expansion and differentiation of MSCs give the opportunity to obtain hardly available somatic cells, such as neurons. The neurogenic potential of MSCs makes them a promising, autologous source to restore damaged tissue and as such, they have received much attention in the field of regenerative medicine. Several stem cell pool candidates have been studied thus far, but only a few of them showed neurogenic differentiation potential. Due to their embryonic ontology, stem cells residing in the stroma of the dental pulp chamber are an exciting source for in vitro neural cell differentiation. In this study, we review the key properties of dental pulp stem cells (DPSCs), with a particular focus on their neurogenic potential. Moreover, we summarize the various presently available methods used for neural differentiation of human DPSCs also emphasizing the difficulties in reproducibly high production of such cells. We postulate that because DPSCs are stem cells with very close ontology to neurogenic lineages, they may serve as excellent targets for neuronal differentiation in vitro and even for direct reprogramming.

Screening and analysis of key genes in the biological behavior of bone mesenchymal stem cells seeded on gradient nanostructured titanium compared with native pure Ti

Titanium (Ti) and Ti-based alloy materials are ideal brackets that restore bone defect, and the mechanism of related genes inducing bone mesenchymal stem cells (BMSCs) to osteogenic differentiation is currently a hot research topic. In order to screen key genes of BMSCs during the osteogenic expression process, we acquired data sets (GSE37237 and GSE84500) which were in the database Gene Expression Omnibus (GEO). Investigations on differentially expressed genes (DEGs) and their enrichment of functions were conducted. We constructed relative protein-protein interaction (PPI) network by using Search Tool for the Retrieval of Interacting Genes (STRING) and visualized the expression of DEGs with Cytoscape. A total of 279 DEGs were discerned, which could be divided into 177 down regulated genes and 102 up regulated genes. In addition, the DEGs' enrichment and pathways included regulation of actin cytoskeleton, inflammatory mediator regulation of transient receptor potential (TRP) channels, peroxisome proliferator-activated receptors (PPAR) pathway, cell cycle, Rheumatoid arthritis, mitogen-activated protein kinases (MAPK) signaling pathway and Ras signaling pathway ect. It showed that 10 notable up regulated genes were mainly in AMP-activated protein kinase (AMPK) pathway. Then we used a technology named surface mechanical attrition treatment (SMAT) to prepare gradient nanostructured (GNS) surface Ti and seeded well-growing BMSCs on the surface of SMAT Ti and native pure Ti. Cell Counting Kits-8 (CCK-8), apoptosis experiment, immunofluorescence technology and staining experiments for alka-line phosphatase (ALP) and alizarin red staining (ARS) were used to research the proliferation, adhesion and differentiation ability of BMSCs seeded on SMAT Ti compared with native pure Ti. We used quantitative real-time PCR (qRT-PCR) technology so as to verify the expression of the most significant 5 genes. In summary, these results indicated novel point of views into candidate genes and potential mechanism for the further study of BMSCs' behaviors seeded on SMAT Ti.

Dental-derived cells for regenerative medicine: stem cells, cell reprogramming, and transdifferentiation

Embryonic stem cells have been a popular research topic in regenerative medicine owing to their pluripotency and applicability. However, due to the difficulty in harvesting them and their low yield efficiency, advanced cell reprogramming technology has been introduced as an alternative. Dental stem cells have entered the spotlight due to their regenerative potential and their ability to be obtained from biological waste generated after dental treatment. Cell reprogramming, a process of reverting mature somatic cells into stem cells, and transdifferentiation, a direct conversion between different cell types without induction of a pluripotent state, have helped overcome the shortcomings of stem cells and raised interest in their regenerative potential. Furthermore, the potential of these cells to return to their original cell types due to their epigenetic memory has reinforced the need to control the epigenetic background for successful management of cellular differentiation. Herein, we discuss all available sources of dental stem cells, the procedures used to obtain these cells, and their ability to differentiate into the desired cells. We also introduce the concepts of cell reprogramming and transdifferentiation in terms of genetics and epigenetics, including DNA methylation, histone modification, and non-coding RNA. Finally, we discuss a novel therapeutic avenue for using dental-derived cells as stem cells, and explain cell reprogramming and transdifferentiation, which are used in regenerative medicine and tissue engineering.

The Effect of Diabetes Mellitus on IGF Axis and Stem Cell Mediated Regeneration of the Periodontium

Periodontitis and diabetes mellitus (DM) are two of the most common and challenging health problems worldwide and they affect each other mutually and adversely. Current periodontal therapies have unpredictable outcome in diabetic patients. Periodontal tissue engineering is a challenging but promising approach that aims at restoring periodontal tissues using one or all of the following: stem cells, signalling molecules and scaffolds. Mesenchymal stem cells (MSCs) and insulin-like growth factor (IGF) represent ideal examples of stem cells and signalling molecules. This review outlines the most recent updates in characterizing MSCs isolated from diabetics to fully understand why diabetics are more prone to periodontitis that theoretically reflect the impaired regenerative capabilities of their native stem cells. This characterisation is of utmost importance to enhance autologous stem cells based tissue regeneration in diabetic patients using both MSCs and members of IGF axis.

Dental Pulp Stem Cells Derived From Adult Human Third Molar Tooth: A Brief Review

The fields of regenerative medicine and stem cell-based tissue engineering have the potential of treating numerous tissue and organ defects. The use of adult stem cells is of particular interest when it comes to dynamic applications in translational medicine. Recently, dental pulp stem cells (DPSCs) have been traced in third molars of adult humans. DPSCs have been isolated and characterized by several groups. DPSCs have promising characteristics including self-renewal capacity, rapid proliferation, colony formation, multi-lineage differentiation, and pluripotent gene expression profile. Nevertheless, genotypic, and phenotypic heterogeneities have been reported for DPSCs subpopulations which may influence their therapeutic potentials. The underlying causes of DPSCs’ heterogeneity remain poorly understood; however, their heterogeneity emerges as a consequence of an interplay between intrinsic and extrinsic cellular factors. The main objective of the manuscript is to review the current literature related to the human DPSCs derived from the third molar, with a focus on their physiological properties, isolation procedures, culture conditions, self-renewal, proliferation, lineage differentiation capacities and their prospective advances use in pre-clinical and clinical applications.

The regulation mechanism of LINC00707 on the osteogenic differentiation of human periodontal ligament stem cells

The osteogenic differentiation of periodontal ligament stem cells (PDLSCs) is important for periodontal tissue repair and regeneration. Long non-coding RNAs (lncRNAs) are key regulators of diverse biological processes. However, their roles in PDLSC osteogenic differentiation are still largely unknown. This study explored the effect of LINC00707 and its mechanism on the osteogenic differentiation of human PDLSCs. Results showed an increase in LINC00707 and forkhead box O1 (FOXO1) but a decrease in miR-490-3p during PDLSC osteogenic differentiation. LINC00707 and FOXO1 promoted osteogenic differentiation as evidenced by the formation of calcium nodules and the increase in osteogenic markers such as alkaline phosphatase, osteocalcin (OCN), and runt-related transcription factor 2 (Runx2). LINC00707 and FOXO1 knockdown exhibited opposite effects. Dual-luciferase reporter assay and qRT-PCR showed that LINC00707 can specially bind to miR-490-3p, which reversed the effect of LINC00707 on PDLSCs. MiR-490-3p inhibitor relieved the inhibiting effect of sh-LINC00707 on osteogenic differentiation. Further investigation revealed that LINC00707 can promote osteogenic differentiation by regulating FOXO1 expression through miR-490-3p sponging. Thus, the LINC00707/miR-490-3p/FOXO1 axis modulated PDLSC osteogenic differentiation and might be a promising therapeutic target for periodontal diseases.

Long non-coding RNA potassium voltage-gated channel subfamily Q member 1 overlapping transcript 1 regulates the proliferation and osteogenic differentiation of human periodontal ligament stem cells by targeting miR-24-3p

OBJECTIVES

This study aims to explore the effect and molecular mechanism of long non-coding RNA (lncRNA) potassium voltage-gated channel subfamily Q member 1 overlapping transcript 1 (KCNQ1OT1) on proliferation and osteogenic differentiation in human periodontal ligament stem cells (hPDLSCs).

METHODS

The hPDLSCs of normal periodontal tissues were isolated and cultured. The mineralized solution induced the osteoblast differentiation of hPDLSCs. The down-regulation of lncRNA KCNQ1OT1, the overexpression of anti-miR-24-3p on the proliferation and the levels of osteocalcin (OCN), osteopontin (OPN) and alkaline phosphatase (ALP) of hPDLSCs were investigated. Real-time quantitative polymerase chain reaction (RT-qPCR) was used to detect the levels of lncRNA KCNQ1OT1, miR-24-3p, OCN, OPN, and ALP. Methyl thiazolyl tetrazolium (MTT) method was used to detect cell viability and activity. Cell proliferation was evaluated by MTT. Western blot was used to detect protein expression. The targeted relationship between lncRNA KCNQ1OT1 and miR-24-3p was detected by double-luciferase experiment.

RESULTS

The expression level of lncRNA KCNQ1OT1 increased, and that of miR-24-3p decreased during the osteogenesis of hPDLSCs (P<0.05). The down-regulation of lncRNA KCNQ1OT1 inhibited cell proliferation and reduced the mRNA and protein expression levels of OCN, OPN, and ALP (P<0.05). LncRNA KCNQ1OT1 targeted and regulated miR-24-3p. The overexpression of miR-24-3p inhibited cell proliferation and reduced the mRNA and protein expression levels of OCN, OPN, and ALP (P<0.05). Inhibition of miR-24-3p reversed the effect of the down-regulation of lncRNA KCNQ1OT1 on cell proliferation and mRNA and protein expression levels of OCN, OPN, and ALP (P<0.05).

CONCLUSIONS

Down-regulation of lncRNA KCNQ1OT1 inhibited the proliferation and osteogenic differentiation of hPDLSCs by targeting the up-regulated expression of miR-24-3p.

Effect of erythropoietin on angiogenic potential of dental pulp cells

Erythropoietin (EPO) is a 34-kDa glycoprotein that possesses the potential for angiogenesis, as well as anti-inflammatory and anti-apoptotic properties. The present study aimed to examine the effect of EPO on the angiogenesis of dental pulp cells (DPCs) and to explore the underlying mechanisms of these effects. It was demonstrated that EPO not only promoted DPCs proliferation but also induced angiogenesis of DPCs in a paracrine fashion. EPO enhanced the angiogenic capacity by stimulating DPCs to secrete a series of angiogenic cytokines. ELISA confirmed that high concentrations of EPO increased the production of MMP-3 and angiopoietin-1 but decreased the secretion of IL-6. Furthermore, EPO activated the ERK1/2 and p38 signaling pathways in DPCs, while inhibition of these pathways diminished the angiogenesis capacity of DPCs. The present study suggested that EPO may have an important role in the repair and regeneration of dental pulp.

Differential expression of Notch related genes in dental pulp stem cells and stem cells isolated from apical papilla

Although dental pulp and apical papilla are originated from neural crest cells, these tissues exhibit distinct characteristics. Notch signaling is one of the known signaling pathways regulating stemness and behaviors of stem cells. The aim of this study was to examine Notch signaling related gene expression profile comparing between coronal pulp tissues and apical pulp complex. Results demonstrated that coronal pulp tissue had higher expression levels of various genes in Notch pathway. However, NOTCH2, MAML2, DTX4, and NEDD4 mRNA levels were significantly lower in coronal pulp tissue than those of apical pulp complex. Furthermore, dental pulp stem cells (DPSCs) and stem cells isolated from apical papilla (SCAPs) were isolated and characterized. These two cell types exhibited similar mesenchymal stem cell surface markers. DPSCs expressed higher mRNA levels of NOTCH3, NOTCH4, DLL1, and HES1. In addition, SCAPs demonstrated higher colony formation and cell proliferation than DPSCs. In summary, cells and tissues from dental pulp and apical papilla exhibited the distinct gene expression profile of Notch related genes. This could be of one the signaling participated in control of DPSCs and SCAPs cells behaviors.

High concentrations of calcium suppress osteogenic differentiation of human periodontal ligament stem cells in vitro

Background/purpose

Periodontal ligament stem cells (PDLSCs)-based regeneration therapy has received attention for its potential alternative applications in hard tissue and tooth. However, the environmental diversity of oral cavity that regulates PDLSCs differentiation has made it difficult to develop. Therefore, we investigated how high calcium concentrations in the oral environment influence osteogenic differentiation of human PDLSCs (hPDLSCs).

Materials and methods

hPDLSCs collected from human molars were isolated and cultured with CaCl₂. First, multi lineage differentiation potentials to osteogenic, chondrogenic, and adipogenic cells were investigated. Then, the effects of CaCl₂ on both alkaline phosphatase (ALP) activity and bone mineralization were analyzed and the expression of mRNA and protein for osteogenic marker was explored. Further, luciferase assay was performed to evaluate CaCl₂ could regulate the transcriptional activity on osteogenic differentiation in hPDLSCs

Results

CaCl₂ treatment at normal to high concentrations showed similar suppression of ALP activity, while mineralized nodule formation was decreased by CaCl₂ treatment dose-dependently without affecting proliferation or cytotoxicity in hPDLSCs. We also observed that CaCl₂ treatment repressed the mRNA expression and protein abundance of osteogenic genes and transcriptional factors. Notably, repression of the Runx2 level was significant, and CaCl₂ treatment inhibited Runx2-mediated transcriptional activity on the osteoblast-specific element (OSE) and ALP promoters.

Conclusion

High concentrations of calcium negatively regulate osteogenic differentiation of hPDLSCs, by repressing osteogenic gene expressions and transcriptional activity. Therefore, these conditions may be applicable to determine the physiologically appropriate concentration of calcium.

Shared Genetic and Epigenetic Mechanisms between the Osteogenic Differentiation of Dental Pulp Stem Cells and Bone Marrow Stem Cells

OBJECTIVE

To identify the shared genetic and epigenetic mechanisms between the osteogenic differentiation of dental pulp stem cells (DPSC) and bone marrow stem cells (BMSC).

MATERIALS AND METHODS

The profiling datasets of miRNA expression in the osteogenic differentiation of mesenchymal stem cells from the dental pulp (DPSC) and bone marrow (BMSC) were searched in the Gene Expression Omnibus (GEO) database. The differential expression analysis was performed to identify differentially expressed miRNAs (DEmiRNAs) dysregulated in DPSC and BMSC osteodifferentiation. The target genes of the DEmiRNAs that were dysregulated in DPSC and BMSC osteodifferentiation were identified, followed by the identification of the signaling pathways and biological processes (BPs) of these target genes. Accordingly, the DEmiRNA-transcription factor (TFs) network and the DEmiRNAs-small molecular drug network involved in the DPSC and BMSC osteodifferentiation were constructed.

RESULTS

16 dysregulated DEmiRNAs were found to be overlapped in the DPSC and BMSC osteodifferentiation, including 8 DEmiRNAs with a common expression pattern (8 upregulated DEmiRNAs (miR-101-3p, miR-143-3p, miR-145-3p/5p, miR-19a-3p, miR-34c-5p, miR-3607-3p, miR-378e, miR-671-3p, and miR-671-5p) and 1 downregulated DEmiRNA (miR-671-3p/5p)), as well as 8 DEmiRNAs with a different expression pattern (i.e., miR-1273g-3p, miR-146a-5p, miR-146b-5p, miR-337-3p, miR-382-3p, miR-4508, miR-4516, and miR-6087). Several signaling pathways (TNF, mTOR, Hippo, neutrophin, and pathways regulating pluripotency of stem cells), transcription factors (RUNX1, FOXA1, HIF1A, and MYC), and small molecule drugs (curcumin, docosahexaenoic acid (DHA), vitamin D3, arsenic trioxide, 5-fluorouracil (5-FU), and naringin) were identified as common regulators of both the DPSC and BMSC osteodifferentiation.

CONCLUSION

Common genetic and epigenetic mechanisms are involved in the osteodifferentiation of DPSCs and BMSCs.

Pluripotency of Dental Pulp Cells and Periodontal Ligament Cells Was Enhanced through Cell-Cell Communication via STAT3/Oct-4/Sox2 Signaling

Alternation in culture environment due to cell-cell communications can rejuvenate the biological activity of aged/differentiated cells and stimulate the expression of pluripotency markers. Dental pulp cells (DPCs) and periodontal ligament cells (PDLCs) are promising candidates in dental tissue regeneration. However, the molecular network that underlies cell-cell communications between dental-derived cells and the microenvironment remains to be identified. To elucidate the signaling network that regulates the pluripotency of DPCs and PDLCs, proliferation, apoptosis, cell cycle, and the expression of Oct-4/Sox2/c-Myc in DPCs and PDLCs with indirect/direct coculture were examined. PCR arrays were constructed to identify genes that were differentially expressed, and the results were confirmed by a rat model with injury. Further research on the mechanism of the related signaling pathways was investigated by overexpression/silence of STAT3, ChIP, the dual-luciferase reporter assay, and EMSA. We found that the proliferation and apoptosis of DPCs and PDLCs were inhibited, and their cell cycles were arrested at the G0/G1 phase after coculture. Oct-4, Sox2, and STAT3 expression significantly increased and PAX5 expression decreased in the coculture systems. Oct-4/Sox2/STAT3/PAX5 was actively expressed in the rat defect model. Moreover, STAT3 was directly bound to the Oct-4 and Sox2 gene promoter regions and activated the expression of those genes. Our data showed that the pluripotency of DPCs and PDLCs was enhanced through cell-cell communication. STAT3 plays essential roles in regulating the pluripotency of DPCs and PDLCs by targeting Oct-4 and Sox2 both in vitro and in vivo.

Histone Methylation: Achilles Heel and Powerful Mediator of Periodontal Homeostasis

The packaging of DNA around nucleosomes exerts dynamic control over eukaryotic gene expression either by granting access to the transcriptional machinery in an open chromatin state or by silencing transcription via chromatin compaction. Histone methylation modification affects chromatin through the addition of methyl groups to lysine or arginine residues of histones H3 and H4 by means of histone methyl transferases or histone demethylases. Changes in histone methylation state modulate periodontal gene expression and have profound effects on periodontal development, health, and therapy. At the onset of periodontal development, progenitor cell populations such as dental follicle cells are characterized by an open H3K4me3 chromatin mark on RUNX2, MSX2, and DLX5 gene promoters. During further development, periodontal progenitor differentiation undergoes a global switch from the H3K4me3 active methyl mark to the H3K27me3 repressive mark. When compared with dental pulp cells, periodontal neural crest lineage differentiation is characterized by repressive H3K9me3 and H3K27me3 marks on typical dentinogenesis-related genes. Inflammatory conditions as they occur during periodontal disease result in unique histone methylation signatures in affected cell populations, including repressive H3K9me3 and H3K27me3 histone marks on extracellular matrix gene promoters and active H3K4me3 marks on interleukin, defensin, and chemokine gene promoters, facilitating a rapid inflammatory response to microbial pathogens. The inflammation-induced repression of chromatin on extracellular matrix gene promoters presents a therapeutic opportunity for the application of histone methylation inhibitors capable of inhibiting suppressive trimethylation marks. Furthermore, inhibition of chromatin coregulators through interference with key inflammatory mediators such as NF-kB by means of methyltransferase inhibitors provides another avenue to halt the exacerbation of the inflammatory response in periodontal tissues. In conclusion, histone methylation dynamics play an intricate role in the fine-tuning of chromatin states during periodontal development and harbor yet-to-be-realized potential for the treatment of periodontal disease.

Neurotrophic effects of dental pulp stem cells in repair of peripheral nerve after crush injury

BACKGROUND

Nerve diseases and injuries, which are usually accompanied by motor or sensory dysfunction and disorder, impose a heavy burden upon patients and greatly reduce their quality of life. Dental pulp stem cells (DPSCs), derived from the neural crest, have many characteristics that are similar to those of neural cells, indicating that they can be an ideal source for neural repair.

AIM

To explore the potential roles and molecular mechanisms of DPSCs in crushed nerve recovery.

METHODS

DPSCs were isolated, cultured, and identified by multilineage differentiation and flow cytometry. Western blot and immunofluorescent staining were applied to analyze the expression levels of neurotrophic proteins in DPSCs after neural induction. Then, we collected the secretions of DPSCs. We analyzed their effects on RSC96 cell proliferation and migration by CCK8 and transwell assays. Finally, we generated a sciatic nerve crush injury model in vivo and used the sciatic function index, walking track analysis, muscle weight, and hematoxylin & eosin (H&E) staining to further evaluate the nerve repair ability of DPSCs.

RESULTS

DPSCs highly expressed several specific neural markers, including GFAP, S100, Nestin, P75, and NF200, and were inclined toward neural differentiation. Furthermore, neural-induced DPSCs (N-DPSCs) could express neurotrophic factors, including NGF, BDNF, and GDNF. The secretions of N-DPSCs could enhance the proliferation and migration of Schwann cells. In vivo, both DPSC and N-DPSC implants alleviated gastrocnemius muscle atrophy. However, in terms of anatomy and motor function, as shown by H&E staining, immunofluorescent staining, and walking track analyses, the repair effects of N-DPSCs were more sustained, potent, and effective than those of DPSCs and the controls.

CONCLUSION

In summary, this study demonstrated that DPSCs are inclined to differentiate into neural cells. N-DPSCs express neurotrophic proteins that could enhance the proliferation and migration of SCs. Furthermore, our results suggested that N-DPSCs could help crushed nerves with functional recovery and anatomical repair in vivo. Thus, DPSCs or N-DPSCs could be a promising therapeutic cell source for peripheral nerve repair and regeneration.

NOTCH2 participates in Jagged1-induced osteogenic differentiation in human periodontal ligament cells

Jagged1 activates Notch signaling and subsequently promotes osteogenic differentiation in human periodontal ligament cells (hPDLs). The present study investigated the participation of the Notch receptor, NOTCH2, in the Jagged1-induced osteogenic differentiation in hPDLs. NOTCH2 and NOTCH4 mRNA expression levels increased during hPDL osteogenic differentiation. However, the endogenous NOTCH2 expression levels were markedly higher compared with NOTCH4. NOTCH2 expression knockdown using shRNA in hPDLs did not dramatically alter their proliferation or osteogenic differentiation compared with the shRNA control. After seeding on Jagged1-immobilized surfaces and maintaining the hPDLs in osteogenic medium, HES1 and HEY1 mRNA levels were markedly reduced in the shNOTCH2-transduced cells compared with the shControl group. Further, shNOTCH2-transduced cells exhibited less alkaline phosphatase enzymatic activity and in vitro mineralization than the shControl cells when exposed to Jagged1. MSX2 and COL1A1 mRNA expression after Jagged1 activation were reduced in shNOTCH2-transduced cells. Endogenous Notch signaling inhibition using a γ-secretase inhibitor (DAPT) attenuated mineralization in hPDLs. DAPT treatment significantly promoted TWIST1, but decreased ALP, mRNA expression, compared with the control. In conclusion, Notch signaling is involved in hPDL osteogenic differentiation. Moreover, NOTCH2 participates in the mechanism by which Jagged1 induced osteogenic differentiation in hPDLs.

Robust expression of SIRT6 inhibits pulpitis via activation of the TRPV1 channel

Invasion of dentinal tubules and pulp tissue by pathogenic bacteria may cause infection leading to pulpitis. Sirtuin 6 (SIRT6) is a NAD-dependent protein deacetylase encoded by the SIRT6 gene. The effect of SIRT6 on lipopolysaccharide (LPS)-induced pulpitis and its mechanism of action were discussed in this study. Dental pulp cells (DPCs) were extracted from human teeth and injected with LPS to induce inflammation. The cells injected with LPS showed substantially decreased expression of SIRT6. The overexpression of SIRT6, induced by plasmid-transfection of DPCs with SIRT6 overexpressing vector, led to a marked decrease in proinflammatory cytokines (IL-6, IL-1β, and TNF-α) and deactivation of NF kappa B pathway. Additionally, dentin matrix protein-1 (DMP1), a promoter of inflammation in dental pulp tissues, was downregulated. Further investigation revealed that SIRT6 promotes ubiquitination of the transient receptor potential vanilloid 1 (TRPV1) channel, leading to its degradation and deactivation. The role of TRPV1 in the anti-inflammatory effects of SIRT6 was determined through incubation of SIRT6-expressing dental pulp stem cells (DPSCs) with capsaicin. This incubation counteracted the effect of SIRT6 on cytokines and DMP1. The injection of lentivirus-SIRT6 attenuated LPS-induced pulpitis in vivo by suppressing TRPV1 activity. Thus, SIRT6 inhibits the TRPV1 channel during LPS-induced inflammation of dental pulp. SIGNIFICANCE OF THE STUDY: This study discussed the effect of sirtuin 6 (SIRT6) on lipopolysaccharide (LPS)-induced pulpitis as well as its mechanism of action and found that SIRT6 may be a negative regulator of pulpitis. Additionally, low expression of SIRT6 and high expression of transient receptor potential vanilloid 1 (TRPV1) in LPS-treated human dental pulp cells are closely associated with proinflammatory cytokines, dentin matrix protein 1 expression, and activation of the NF-κB pathway, which indicated that TRPV1 may be a biomarker for pulpitis and the SIRT6-TRPV1-CGRP axis maybe a clinical target due to their role regulating inflammation and neuropathic pain.

Effect of puerarin on osteogenic differentiation of human periodontal ligament stem cells

Objective

To investigate the effects of the flavonoid, puerarin, on osteogenic differentiation of human periodontal ligament stem cells (PDLSCs).

Methods

Human PDLSCs were isolated from patients undergoing orthodontic treatment, and the cell surface markers CD146, CD34, CD45, and STRO-1 were identified by immunofluorescence. Cell proliferation was detected by MTT assay; alkaline phosphatase (ALP) activity was measured, and calcium deposition was detected by alizarin red staining. PCR was then used to detect the distributions of COL-I, OPN, Runx2, and OCN, genes related to osteogenic differentiation.

Results

Staining was positive for cytokines CD146, CD34, CD45, and STRO-1 in the experimental group; staining was also positive for silk protein, but negative for keratin. After 7 days of culture, exposure to puerarin significantly promoted the level of intracellular ALP; increased puerarin concentration led to increased intracellular ALP. Red mineralized nodules appeared upon exposure to puerarin and the number of nodules was concentration-dependent. PCR analysis revealed that COL-I, OPN, Runx2, and OCN expression levels increased as puerarin concentration increased.

Conclusions

Exposure to puerarin can promote proliferation and ALP activity in human PDLSCs, thus promoting both molecular and osteogenic differentiation; these findings may provide a theoretical basis for the clinical treatment of periodontal disease with puerarin.

Identification of Aberrantly Expressed lncRNAs Involved in Orthodontic Force Using a Subpathway Strategy

Background

The aim of the study was to identify key long noncoding RNAs (lncRNA) and related subpathways in the periodontal ligament tissue following orthodontic force.

Methods

We adopt a novelty subpathway strategy to identify lncRNAs competitively regulated functions and the key competitive lncRNAs in periodontal ligament disorders after undergoing orthodontic force. To begin with, patients with orthodontics in our hospital were enrolled in our research. The relationship of lncRNA-mRNA was established through shared predicted miRNA by using the hypergeometric test, Jaccard coefficient standardization, and the Pearson coefficient to determine the valid interaction relationship. After embedding screened lncRNA interactions to pathways, the significant subpathways were recognized by lenient distance and Wallenius approximation methods to calculate the false discovery rate value of each subpathway.

Results

The lncRNA-mRNA intersections including 263 lncRNAs, 1,599 mRNAs, and 3,762 interacting pairs were obtained. The enriched mRNAs were further enriched into various candidate pathways such as the PI3K-Akt signaling pathway. Several subpathways were screened, including the PI3K-Akt signaling pathway, 04510_1 focal adhesion, and p53 signaling pathway, respectively. The network of pathway-lncRNA-mRNA was constructed. Several key lncRNAs including DNAJC3-AS1, WDFY3-AS2, LINC00482, and DLEU2 were screened.

Conclusions

DNAJC3-AS1, WDFY3-AS2, LINC00482, and DLEU2 as aberrantly expressed lncRNAs involved in orthodontic force might play crucial roles in periodontal ligament disease pathogenesis.

Lin28 promotes dental pulp cell proliferation via upregulation of cyclin-dependent proteins and interaction with let-7a/IGF2BP2 pathways

Caries, pulpitis, and trauma are the main causes of dental pulp damage. The regeneration capacity of dental pulp declines with age. Lin28 is a conserved RNA-binding protein in higher eukaryotes that regulates several important cellular functions associated with development, glucose metabolism, differentiation, and pluripotency. Conditional reactivation of Lin28 gene in adult mice markedly accelerates the wound-healing process in injured digits. However, little is known about its functions and molecular mechanism in human dental pulp. The aim of this study was to investigate the effects and mechanism of overexpression of Lin28 gene on the proliferation of human dental pulp cells (HDPCs). For this purpose, a number of molecular and biochemical analytical techniques, including the ethynyl-2'-deoxyuridine (EdU) incorporation assay, RNA-protein immunoprecipitation (RIP) analysis, and luciferase assays, were used for detailed characterization. In addition, factors regulating HDPCs activation were explored through gain-of-function and loss-of-function analyses. The results demonstrate that Lin28 promotes cell proliferation and the S-G2/M transition of HDPCs and directly binds to a group of cell cycle regulatory mRNAs in HDPCs. Through bioinformatics analysis and luciferase assays, we confirmed that let-7a targets IGF2BP2. Silencing of IGF2BP2 showed similar cellular and molecular effects as let-7a. Similarly, restoration of IGF2BP2 counteracted the effects of let-7a expression. In conclusion, Lin28 promotes cell proliferation by regulation of both mRNA translation (let-7-independent) and miRNA biogenesis (let-7-dependent). Lin28 can promote the expression of pro-proliferative genes by directly enhancing their translation to maintain a tight control over HDPC proliferation.

Endothelial cells and endothelin‑1 promote the odontogenic differentiation of dental pulp stem cells

It has been established that dental pulp stem cells (DPSCs) serve an important role in the restoration and regeneration of dental tissues. DPSCs are present in blood vessels and also exist in the vessel microenvironment in vivo and have a close association with endothelial cells (ECs). The present study aimed to evaluate the influence of ECs and their secretory product endothelin-1 (ET-1) on the differentiation of DPSCs. In the present study, cells were divided into four groups: i) a DPSC-only control group; ii) a DPSC with ET-1 administration group; iii) a DPSC and human umbilical vein endothelial cell (HUVEC) direct co-culture group; and iv) a DPSC and HUVEC indirect co-culture group using a Transwell system. Reverse transcription-quantitative polymerase chain reaction was used to detect the expression of the odontoblastic differentiation-associated genes, including dentin sialoprotein (DSP) and dentin matrix acidic phosphoprotein 1 (DMP-1) at days 4, 7, 14 and 21. Alizarin Red S staining, immunofluorescence and western blot analyses were also conducted to assess the differentiation of the DPSCs in each group. The highest expression levels of odontoblastic differentiation-associated genes were observed on day 7 and in the two co-culture groups were increased compared with the DPSC-only and DPSC + ET-1 culture groups at all four time points. However, expression levels in the DPSC + ET-1 group were not downregulated as notably as in the co-culture groups on days 14 and 21. The Transwell group exhibited the greatest ability for odontoblastic differentiation compared with the other groups according to staining with Alizarin Red S, immunofluorescence and western blot analysis results. According to the results of the present study, the culture solution with HUVECs affected the differentiation of DPSCs. In addition, ET-1 may promote the odontoblastic differentiation of DPSCs.

Potential Roles of Dental Pulp Stem Cells in Neural Regeneration and Repair

This review summarizes current advances in dental pulp stem cells (DPSCs) and their potential applications in the nervous diseases. Injured adult mammalian nervous system has a limited regenerative capacity due to an insufficient pool of precursor cells in both central and peripheral nervous systems. Nerve growth is also constrained by inhibitory factors (associated with central myelin) and barrier tissues (glial scarring). Stem cells, possessing the capacity of self-renewal and multicellular differentiation, promise new therapeutic strategies for overcoming these impediments to neural regeneration. Dental pulp stem cells (DPSCs) derive from a cranial neural crest lineage, retain a remarkable potential for neuronal differentiation, and additionally express multiple factors that are suitable for neuronal and axonal regeneration. DPSCs can also express immunomodulatory factors that stimulate formation of blood vessels and enhance regeneration and repair of injured nerve. These unique properties together with their ready accessibility make DPSCs an attractive cell source for tissue engineering in injured and diseased nervous systems. In this review, we interrogate the neuronal differentiation potential as well as the neuroprotective, neurotrophic, angiogenic, and immunomodulatory properties of DPSCs and its application in the injured nervous system. Taken together, DPSCs are an ideal stem cell resource for therapeutic approaches to neural repair and regeneration in nerve diseases.

Dental pulp stem cells in regenerative medicine

The mesenchymal stem cells (dental pulp stem cells; DPSC) found inside teeth represent a significant future source of stem cells for regenerative medicine procedures. This review describes the ontogeny of DPSC; the laboratory processing and collection of DPSC; the immuno-cytochemical characterisation of DPSC; the differentiation between adult DPSC and DPSC obtained from exfoliated deciduous teeth (SHED) and their potential use in regenerative medicine procedures in the future both in dental and general medical applications.

MicroRNA-214 Suppresses Osteogenic Differentiation of Human Periodontal Ligament Stem Cells by Targeting ATF4

Periodontitis is the main cause of adult tooth loss. Stem cell-based tissue engineering has become a promising therapy for periodontitis treatment. To date, human periodontal ligament stem cells (hPDLSCs) have been shown to be a favorable source for tissue engineering, but modulatory mechanisms of hPDLSCs remain unclear. Approximately 60% of mammalian genes are the targets of over 2000 miRNAs in multiple human cell types, and miRNAs are able to influence various biological processes in the human body, including bone formation. In this study, we found that after osteogenic induction, miR-214 was significantly decreased in hPDLSCs; therefore, we examined the effects of miR-214 on osteogenic differentiation. Computational miRNA target prediction analyses and luciferase reporter assays revealed that activating transcription factor 4 (ATF4) is a direct target of miR-214. We prepared cells overexpressing miR-214 and found that miR-214 negatively regulates osteogenic differentiation of hPDLSCs. For the target of miR-214, ATF4 protein expression level was decreased after induction. In conclusion, we found that miR-214-ATF4 axis is a novel pathway for regulating hPDLSC osteogenic differentiation.

Bone Morphogenetic Protein-9 Enhances Osteogenic Differentiation of Human Periodontal Ligament Stem Cells via the JNK Pathway

Bone morphogenetic protein-9 (BMP9) shows great osteoinductive potential in bone regeneration. Periodontal ligament stem cells (PDLSCs) with multi-differentiation capability and low immunogenicity are increasingly used as seed cells for periodontal regenerative therapies. In the present study, we investigated the potent osteogenic activity of BMP9 on human PDLSCs (hPDLSCs), in which the c-Jun N-terminal kinase (JNK) pathway is possibly involved. Our results showed that JNK inhibition by the specific inhibitor SP600125 or adenovirus expressing small interfering RNA (siRNA) targeting JNK (AdR-si-JNK) significantly decreased BMP9-induced gene and protein expression of early and late osteogenic markers, such as runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP), osteopontin (OPN), and osteocalcin (OCN), in hPDLSCs. We also confirmed the in-vivo positive effect of JNKs on ectopic bone formation induced by hPDLSCs injected into the musculature of athymic nude mice and BMP9 ex vivo gene delivery. For the cellular mechanism, we found that BMP9 activated the phosphorylation of JNKs and Smad2/3, and that JNKs may engage in cross-talk with the Smad2/3 pathway in BMP9-mediated osteogenesis.

Comparative In Vitro Evaluation of Human Dental Pulp and Follicle Stem Cell Commitment

Objective

Pulp and periodontal tissues are well-known sources of mesenchymal stem cells (MSCs) that provide a promising place in tissue engineering and regenerative medicine. The molecular mechanisms underlying commitment and differentiation of dental stem cells that originate from different dental tissues are not fully understood. In this study, we have compared the expression levels of pluripotency factors along with immunological and developmentally-related markers in the culture of human dental pulp stem cells (hDPSCs), human dental follicle stem cells (hDFSCs), and human embryonic stem cells (hESCs).

Materials and Methods

In this experimental study, isolated human dental stem cells were investigated using quantitative polymerase chain reaction (qPCR), immunostaining, and fluorescence-activated cell sorting (FACS). Additionally, we conducted gene ontology (GO) analysis of differentially expressed genes and compared them between dental stem cells and pluripotent stem cells.

Results

The results demonstrated that pluripotency (OCT4 and SOX2) and immunological (IL-6 and TLR4) factors had higher expressions in hDFSCs, with the exception of the JAGGED-1/NOTCH1 ratio, c-MYC and NESTIN which expressed more in hDPSCs. Immunostaining of OCT4, SOX2 and c-MYC showed cytoplasmic and nucleus localization in both groups at similar passages. GO analysis showed that the majority of hDFSCs and hDPSCs populations were in the synthesis (S) and mitosis (M) phases of the cell cycle, respectively.

Conclusion

This study showed different status of heterogeneous hDPSCs and hDFSCs in terms of stemness, differentiation fate, and cell cycle phases. Therefore, the different behaviors of dental stem cells should be considered based on clinical treatment variations.

XPC Promotes Pluripotency of Human Dental Pulp Cells through Regulation of Oct-4/Sox2/c-Myc

Introduction. Xeroderma pigmentosum group C (XPC), essential component of multisubunit stem cell coactivator complex (SCC), functions as the critical factor modulating pluripotency and genome integrity through interaction with Oct-4/Sox2. However, its specific role in regulating pluripotency and multilineage differentiation of human dental pulp cells (DPCs) remains unknown. Methods. To elucidate the functional role XPC played in pluripotency and multilineage differentiation of DPCs, expressions of XPC in DPCs with long-term culture were examined by real-time PCR and western blot. DPCs were transfected with lentiviral-mediated human XPC gene; then transfection rate was investigated by real-time PCR and western blot. Cell cycle, apoptosis, proliferation, senescence, multilineage differentiation, and expression of Oct-4/Sox2/c-Myc in transfected DPCs were examined. Results. XPC, Oct-4, Sox2, and c-Myc were downregulated at P7 compared with P3 in DPCs with long-term culture. XPC genes were upregulated in DPCs at P2 after transfection and maintained high expression level at P3 and P7. Cell proliferation, PI value, and telomerase activity were enhanced, whereas apoptosis was suppressed in transfected DPCs. Oct-4/Sox2/c-Myc were significantly upregulated, and multilineage differentiation in DPCs with XPC overexpression was enhanced after transfection. Conclusions. XPC plays an essential role in the modulation of pluripotency and multilineage differentiation of DPCs through regulation of Oct-4/Sox2/c-Myc.

Proinflammatory Cytokines Regulate Cementogenic Differentiation of Periodontal Ligament Cells by Wnt/Ca(2+) Signaling Pathway

Periodontal inflammation can inhibit cell differentiation of periodontal ligament cells (PDLCs), resulting in decreased bone/cementum regeneration ability. The Wnt signaling pathway, including canonical Wnt/β-catenin signaling and noncanonical Wnt/Ca(2+) signaling, plays essential roles in cell proliferation and differentiation during tooth development. However, little is still known whether noncanonical Wnt/Ca(2+) signaling cascade could regulate cementogenic/osteogenic differentiation capability of PDLCs within an inflammatory environment. Therefore, in this study, human PDLCs (hPDLCs) and their cementogenic differentiation potential were investigated in the presence of cytokines. The data demonstrated that both cytokines interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-α) inhibited cell proliferation, relative alkaline phosphatase activity, bone/cementum-related gene/protein expression, and canonical Wnt pathway-related gene/protein expression in hPDLCs. Interestingly, both cytokines upregulated the noncanonical Wnt/Ca(2+) signaling-related gene and protein expression in hPDLCs. When the Wnt/Ca(2+) pathway was blocked by Ca(2+)/calmodulin-dependent protein kinase II inhibitor KN93, even in the presence of IL-6 and TNF-α, cementogenesis could be stimulated in hPDLCs. Our data indicate that the Wnt/Ca(2+) pathway plays an inhibitory role on PDLC cementogenic differentiation in inflammatory microenvironments. Therefore, targeting the Wnt/Ca(2+) pathway may provide a novel therapeutic approach to improve periodontal regeneration for periodontal diseases.

Effect of Jagged-1 and Dll-1 on osteogenic differentiation by stem cells from human exfoliated deciduous teeth

OBJECTIVE

The aim of the present study was to determine the influence of Notch ligands, Jagged-1 and Dll-1, on osteogenic differentiation by stem cells from human exfoliated deciduous teeth.

DESIGN

Notch ligands were immobilized on tissue culture surface using an indirect affinity immobilization technique. Cells from the remaining of dental pulp tissues from human deciduous teeth were isolated and characterized using flow cytometry and differentiation assay. Alkaline phosphatase (ALP) enzymatic activity, osteogenic marker gene expression, and mineralization were determined using ALP assay, real-time polymerase chain reaction, and alizarin red staining, respectively.

RESULTS

The isolated cells exhibited CD44, CD90, and CD105 expression but lack of CD45 expression. Further, these cells were able to differentiate toward osteogenic lineage. The upregulation of HES-1 and HEY-1 was observed in those cells on Dll-1 and Jagged-1 coated surface. The significant increase of ALP activity and mineralization was noted in those cells seeded on Jagged-1 surface and these results were attenuated when cells were pretreated with gamma secretase inhibitor. The significant upregulation of ALP and collagen type I gene expression was also observed in those cells seeded on Jagged-1 surface. The inconsistent Dll-1 induced osteogenic differentiation was found and high Dll-1 immobilized dose (50 nM) slightly enhanced alkaline phosphatase enzymatic activity. However, the statistical significant difference was not obtained as compared to the hFc control.

CONCLUSION

The surface immobilization of Notch ligands, Jagged-1 and Dll-1, likely to enhance osteogenic differentiation of SHEDs. However, Jagged-1 had more ability in enhancing osteogenic differentiation than Dll-1 in our model.

Mesenchymal Stem Cells Derived from Dental Pulp: A Review

The mesenchymal stem cells of dental pulp (DPSCs) were isolated and characterized for the first time more than a decade ago as highly clonogenic cells that were able to generate densely calcified colonies. Now, DPSCs are considered to have potential as stem cell source for orthopedic and oral maxillofacial reconstruction, and it has been suggested that they may have applications beyond the scope of the stomatognathic system. To date, most studies have shown that, regardless of their origin in third molars, incisors, or exfoliated deciduous teeth, DPSCs can generate mineralized tissue, an extracellular matrix and structures type dentin, periodontal ligament, and dental pulp, as well as other structures. Different groups worldwide have designed and evaluated new efficient protocols for the isolation, expansion, and maintenance of clinically safe human DPSCs in sufficient numbers for various therapeutics protocols and have discussed the most appropriate route of administration, the possible contraindications to their clinical use, and the parameters to be considered for monitoring their clinical efficacy and proper biological source. At present, DPSC-based therapy is promising but because most of the available evidence was obtained using nonhuman xenotransplants, it is not a mature technology.

Mapping the global mRNA transcriptome during development of the murine first molar

The main objective of this study was to map global gene expression in order to provide information about the populations of mRNA species participating in murine tooth development at 24 h intervals, starting at the 11th embryonic day (E11.5) up to the 7th post-natal day (P7). The levels of RNA species expressed during murine tooth development were mesured using a total of 58 deoxyoligonucleotide microarrays. Microarray data was validated using real-time RT-PCR. Differentially expressed genes (p < 0.05) were subjected to bioinformatic analysis to identify cellular activities significantly associated with these genes. Using ANOVA the microarray data yielded 4362 genes as being differentially expressed from the 11th embryonic day (E11.5) up to 7 days post-natal (P7), 1921 of these being genes without known functions. The remaining 2441 genes were subjected to further statistical analysis using a supervised procedure. Bioinformatic analysis results for each time-point studied suggests that the main molecular functions associated with genes expressed at the early pre-natal stages (E12.5–E18.5) were cell cycle progression, cell morphology, lipid metabolism, cellular growth, proliferation, senescence and apoptosis, whereas most genes expressed at post-natal and secretory stages (P0–P7) were significantly associated with regulation of cell migration, biosynthesis, differentiation, oxidative stress, polarization and cell death. Differentially expressed genes (DE) not described earlier during murine tooth development; Inositol 1, 4, 5-triphosphate receptor 3 (Itpr3), metallothionein 1(Mt1), cyclin-dependent kinase 4 (Cdk4), cathepsin D (Ctsd), keratin complex 2, basic, gene 6a (Krt2-6a), cofilin 1, non-muscle (Cfl1), cyclin 2 (Ccnd2), were verified by real-time RT-PCR.

Induced overexpression of Oct4A in human dental pulp cells enhances pluripotency and multilineage differentiation capability

Octamer-binding transcription factor 4A (Oct4A), one of the three spliced variants of the class V of POU transcription factor family, is mainly expressed in the nucleus of undifferentiated cells and serves as the key regulator for the maintenance of pluripotency and self-renewal. However, its specific role in regulating pluripotency and multilineage differentiation potential of dental pulp cells (DPCs) remains unknown. To explore the effect of Oct4A on pluripotency and multilineage differentiation capability of DPCs, expression of Oct4A in human dental pulp tissue and pluripotent markers Oct4A, Sox2, c-Myc, Nanog, and Klf4 in DPCs with prolonged in vitro culture were examined by immunohistochemistry and immunofluorescent staining. Oct4A transfection rate in DPCs with lentivirus was evaluated by real-time polymerase chain reaction (PCR) and western blot. Cell proliferation, multilineage differentiation, and the expression of Oct4B1, Sox2, Nanog, Klf4, c-Myc, and Utf1 in DPCs after Oct4A transfection were detected by cell counting kit-8, Alizarin red/Oil red O staining, immunofluorescent staining, alkaline phosphatase analysis, and real-time PCR. We demonstrated that Oct4A was mainly expressed in the nucleus of odontoblasts in dental pulp tissue. Oct4A, Sox2, c-Myc, Nanog, and Klf4 were primarily located in the nucleus of DPCs at early passage (passage 1) and translocated to cytoplasm at late passage (passage 7). In DPCs with Oct4A overexpression, Oct4A, Oct4B1, Sox2, Nanog, Klf4, c-Myc, and Utf1 were significantly upregulated (p<0.05) and the cell proliferation (p<0.05), odontogenic and adipogenic differentiation were significantly enhanced. Taken together, Oct4A plays a critical role in regulation of cell proliferation, pluripotency, and multilineage differentiation potential of DPCs.

Coculture of stem cells from apical papilla and human umbilical vein endothelial cell under hypoxia increases the formation of three-dimensional vessel-like structures in vitro

The success of bioengineered dental pulp depends on two principles, (1) whether the transplanted tissue can develop its own vascular endothelial tubule network and (2) whether the host vasculature can be induced to penetrate the bioengineered pulp replacement and conjoin. Major inductive molecules that participate in laying down blood vessels include vascular endothelial growth factor (VEGF), ephrinB2, and hypoxia-inducible factor 1α (HIF-1α). Being able to modulate the genes encoding these angiogenic molecules is a therapeutic target in pulp regeneration for endogenous blood vessel formation, prevention of graft rejection, and exclusion of infection. Once implanted inside the root canal, bioengineered pulp is subjected to severe hypoxia that causes tissue degeneration. However, short-term hypoxia is known to stimulate angiogenesis. Thus, it may be feasible to prime dental cells for angiogenic activity before implantation. Stem cells from apical papilla (SCAP) are arguably one of the most potent and versatile dental stem cell populations for bioengineering pulp in vitro. Our study aimed to investigate whether coculture of SCAP and human umbilical vein endothelial cells (HUVECs) under hypoxia promotes the formation of endothelial tubules and a blood vessel network. In addition, we clarified the interplay between the genes that orchestrate these important angiogenic molecules in SCAP under hypoxic conditions. We found that SCAP cocultured with HUVEC at a 1:5 ratio increased the number of endothelial tubules, tubule lengths, and branching points. Fluorescence staining showed that HUVEC formed the trunk of tubular structures, whereas SCAP located adjacent to the endothelial cell line, resembling the pericyte location. When we used CoCl2 (0.5 mM) to induce hypoxic environment, the expression of proteins, HIF-1α and VEGF, and transcript of ephrinB2 in SCAP was upregulated. However, minimal VEGF levels in supernatants of HUVEC and coculture Petri dishes were detected, suggesting that VEGF secreted by SCAP might be used by HUVEC to accelerate the formation of vessel-like structures. Taken together, we revealed that artificial hypoxia stimulates angiogenic responses in SCAP for possible use in engineering dental pulp replacements. Our results may help to delineate the optimal therapeutic target to promote angiogenesis so that future bioengineered pulp replacements integrate faster and permanently within the host.

Dental pulp stem cells: state of the art and suggestions for a true translation of research into therapy

OBJECTIVES

Stem cells have the ability to rescue and/or repair injured tissue. In humans, it is possible to isolate different types of stem cells from the body. Among these, dental pulp stem cells (DPSCs) are relatively easily obtainable and exhibit high plasticity and multipotential capabilities. In particular they represent a gold standard for neural-crest-derived bone reconstruction in humans and can be used for the repair of body defects in low-risk autologous therapeutic strategies.

SOURCES

An electronic search was conducted on PubMed databases and supplemented with a manual study of relevant references.

RESULTS

All research described in this review highlight that DPSCs are mesenchymal stem cells that could be used in clinical applications. Unfortunately, very few clinical trials have been reported. Major obstacles imposed on researchers are hindering the translation of potentially effective therapies to the clinic. Both researchers and regulatory institutions need to develop a new approach to this problem, drawing up a new policy for good manufacturing practice (GMP) procedures. We strongly suggest that only general rules be standardized rather than everything. Importantly, this would not have an effect on the safety of patients, but may very well affect the results, which cannot be identical for all patients, due to physiological diversity in the biology of each patient. Alternatively, it would be important to study the role of specific molecules that recruit endogenous stem cells for tissue regeneration. In this way, the clinical use of stem cells could be successfully developed.

CONCLUSIONS

DPSCs are mesenchymal stem cells that differentiate into different tissues, maintain their characteristics after cryopreservation, differentiate into bone-like tissues when loaded on scaffolds in animal models, and regenerate bone in human grafts. In summary, all data reported up to now should encourage the development of clinical procedures using DPSCs.

Co-culture with periodontal ligament stem cells enhances osteogenic gene expression in de-differentiated fat cells

In recent decades, de-differentiated fat cells (DFAT cells) have emerged in regenerative medicine because of their trans-differentiation capability and the fact that their characteristics are similar to bone marrow mesenchymal stem cells. Even so, there is no evidence to support the osteogenic induction using DFAT cells in periodontal regeneration and also the co-culture system. Consequently, this study sought to evaluate the DFAT cells co-culture with periodontal ligament stem cells (PDLSCs) in vitro in terms of gene expression by comparing runt-related transcription factor 2 (RUNX2) and Peroxisome proliferator-activated receptor gamma 2 (PPARγ2) genes. We isolated DFAT cells from mature adipocytes and compared proliferation with PDLSCs. After co-culture with PDLSCs, we analyzed transcriptional activity implying by DNA methylation in all adipogenic gene promoters using combined bisulfite restriction analysis. We compared gene expression in RUNX2 gene with the PPARγ2 gene using quantitative RT-PCR. After being sub-cultured, DFAT cells demonstrated morphology similar to fibroblast-like cells. At the same time, PDLSCs established all stem cell characteristics. Interestingly, the co-culture system attenuated proliferation while enhancing osteogenic gene expression in RUNX2 gene. Using the co-culture system, DFAT cells could trans-differentiate into osteogenic lineage enhancing, but conversely, their adipogenic characteristic diminished. Therefore, DFAT cells and the co-culture system might be a novel cell-based therapy for promoting osteogenic differentiation in periodontal regeneration.

The effect of hypoxia on the stemness and differentiation capacity of PDLC and DPC

Introduction. Stem cells are regularly cultured under normoxic conditions. However, the physiological oxygen tension in the stem cell niche is known to be as low as 1-2% oxygen, suggesting that hypoxia has a distinct impact on stem cell maintenance. Periodontal ligament cells (PDLCs) and dental pulp cells (DPCs) are attractive candidates in dental tissue regeneration. It is of great interest to know whether hypoxia plays a role in maintaining the stemness and differentiation capacity of PDLCs and DPCs. Methods. PDLCs and DPCs were cultured either in normoxia (20% O₂) or hypoxia (2% O₂). Cell viability assays were performed and the expressions of pluripotency markers (Oct-4, Sox2, and c-Myc) were detected by qRT-PCR and western blotting. Mineralization, glycosaminoglycan (GAG) deposition, and lipid droplets formation were assessed by Alizarin red S, Safranin O, and Oil red O staining, respectively. Results. Hypoxia did not show negative effects on the proliferation of PDLCs and DPCs. The pluripotency markers and differentiation potentials of PDLCs and DPCs significantly increased in response to hypoxic environment. Conclusions. Our findings suggest that hypoxia plays an important role in maintaining the stemness and differentiation capacity of PDLCs and DPCs.

A stimulatory effect of Ca3ZrSi2O9 bioceramics on cementogenic/osteogenic differentiation of periodontal ligament cells

Ca₃ZrSi₂O₉ bioceramics promote the cementogenic/osteogenic differentiation of PDLCs.

Role of miR-424 on angiogenic potential in human dental pulp cells

INTRODUCTION

Growing evidence shows microRNAs (miRNAs) regulate numerous cellular processes. The purpose of this study was to investigate whether miRNAs can regulate the commitment of human dental pulp cells (hDPCs) to the angiogenic fate.

METHODS

The hDPCs were induced to differentiate into the vascular lineage. Gene expression of endothelial markers (vWF and CD31) on day 7 after induction was analyzed by using quantitative reverse transcription-polymerase chain reaction (qRT-PCR).The miRNA expression profiling of endothelial differentiation was performed by microarray and was validated by qRT-PCR analysis. The hDPCs were infected by recombinant lentivirus to overexpress or knock down miR-424 stably, and the biological effects of miR-424 on the endothelial differentiation of hDPCs were further investigated. The tube formation ability and the amount of endothelial markers (vWF and KDR) were evaluated by Matrigel assay and Western blotting. Target genes of miR-424 were further determined by bioinformatic algorithms and Western blotting.

RESULTS

After endothelial differentiation, the expression of vWF and CD31 increased significantly in hDPCs. Microarray data showed that the miR-424 expression level was down-regulated on day 7. The qRT-PCR revealed a time-dependent decrease, with significant differences detected on day 1 and day 7 (P < .05). Knockdown of miR-424 expression in hDPCs promoted endothelial differentiation, with increased tube formation and up-regulated expression of vWF and KDR. In contrast, overexpression of miR-424 inhibited their differentiation. In addition, miR-424 was predicted to target vascular endothelial growth factor and KDR. Overexpression of miR-424 decreased vascular endothelial growth factor and KDR protein levels, whereas miR-424 inhibition significantly elevated them.

CONCLUSIONS

This study demonstrated that miR-424 may play a negative role in regulating endothelial differentiation of hDPCs, and inhibition of miR-424 may contribute to dental pulp repair and regeneration.

Adenosine A1 receptor stimulation enhances osteogenic differentiation of human dental pulp-derived mesenchymal stem cells via WNT signaling

In this study, mesenchymal stem cells deriving from dental pulp (DPSCs) of normal human impacted third molars, previously characterized for their ability to differentiate into osteoblasts, were used. We observed that: i) DPSCs, undifferentiated or submitted to osteogenic differentiation, express all four subtypes of adenosine receptors (AR) and CD73, corresponding to 5'-ecto-nucleotidase; and ii) AR stimulation with selective agonists elicited a greater osteogenic cell differentiation consequent to A1 receptor (A1R) activation. Therefore, we focused on the activity of this AR. The addition of 15-60nM 2-chloro-N(6)-cyclopentyl-adenosine (CCPA), A1R agonist, to DPSCs at each change of the culture medium significantly increased the proliferation of cells grown in osteogenic medium after 8days in vitro (DIV) without modifying that of undifferentiated DPSCs. Better characterizing the effect of A1R stimulation on the osteogenic differentiation capability of these cells, we found that CCPA increased the: i) expression of two well known and early osteogenic markers, RUNX-2 and alkaline phosphatase (ALP), after 3 and 7DIV; ii) ALP enzyme activity at 7DIV and iii) mineralization of extracellular matrix after 21DIV. These effects, abolished by cell pre-treatment with the A1R antagonist 8-cyclopentyl-1,3-dipropyl-xanthine (DPCPX), involved the activation of the canonical Wnt signaling as, in differentiating DPSCs, CCPA significantly increased dishevelled protein and inhibited glycogen synthase kinase-3β, both molecules being downstream of Wnt receptor signal pathway. Either siRNA of dishevelled or cell pre-treatment with Dickkopf-1, known inhibitor of Wnt signaling substantially reduced either DPSC osteogenic differentiation or its enhancement promoted by CCPA. Summarizing, our findings indicate that the stimulation of A1R may stimulate DPSC duplication enhancing their osteogenic differentiation efficiency. These effects may have clinical implications possibly facilitating bone tissue repair and remodeling.

Effect of bone morphogenetic protein-4 on the expression of Sox2, Oct-4, and c-Myc in human periodontal ligament cells during long-term culture

Recent studies demonstrated that the endogenous expression level of Sox2, Oct-4, and c-Myc is correlated with the pluripotency and successful induction of induced pluripotent stem cells. Periodontal ligament cells (PDLCs) have a multilineage differentiation capability and ability to maintain the undifferentiated stage, which makes PDLCs a suitable cell source for tissue repair and regeneration. To elucidate the effect of an in vitro culture condition on the stemness potential of PDLCs, we explored the cell growth, proliferation, cell cycle, and the expression of Sox2, Oct-4, and c-Myc in PDLCs from the passage 1 to 7 with or without the addition of recombinant human bone morphogenetic protein-4 (rhBMP4). Our results revealed that BMP-4 promoted cell growth and proliferation, arrested PDLCs in the S phase of cell cycle, and upregulated the propidium iodinate value. It was revealed that without the addition of rhBMP4, the expression of Sox2, Oct-4, and c-Myc in PDLCs only maintained the nucleus location until passage 3, and then lost the nucleus location subsequently. The mRNA expression in PDLCs further confirmed that the level of Sox2 and Oct-4 peaked at passage 3 and then decreased afterward, whereas c-Myc maintained consistently the upregulation along the passages. After the treatment with rhBMP4, the expression of Sox2, Oct-4, and c-Myc in PDLCs maintained the nucleus location even at passage 7, and the mRNA expression of Sox2 and Oct-4 significantly upregulated at the passages 5 and 7. These results demonstrated that addition of rhBMP-4 in the culture medium could improve the current culture condition for PDLCs to maintain in an undifferentiated stage.