Small molecules affect human dental pulp stem cell properties via multiple signaling pathways

Research progress on optimization of in vitro isolation, cultivation and preservation methods of dental pulp stem cells for clinical application

Due to high proliferative capacity, multipotent differentiation, immunomodulatory abilities, and lack of ethical concerns, dental pulp stem cells (DPSCs) are promising candidates for clinical application. Currently, clinical research on DPSCs is in its early stages. The reason for the failure to obtain clinically effective results may be problems with the production process of DPSCs. Due to the different preparation methods and reagent formulations of DPSCs, cell characteristics may be affected and lead to inconsistent experimental results. Preparation of clinical-grade DPSCs is far from ready. To achieve clinical application, it is essential to transit the manufacturing of stem cells from laboratory grade to clinical grade. This review compares and analyzes experimental data on optimizing the preparation methods of DPSCs from extraction to resuscitation, including research articles, invention patents and clinical trials. The advantages and disadvantages of various methods and potential clinical applications are discussed, and factors that could improve the quality of DPSCs for clinical application are proposed. The aim is to summarize the current manufacture of DPSCs in the establishment of a standardized, reliable, safe, and economic method for future preparation of clinical-grade cell products.

Role of alpha smooth muscle actin in odontogenic differentiation of dental pulp stem cells

Pulpotomy is an effective treatment for retaining vital pulp after pulp exposure caused by caries removal and/or trauma. The expression of alpha smooth muscle actin (α-SMA) is increased during the wound-healing process, and α-SMA-positive fibroblasts accelerate tissue repair. However, it remains largely unknown whether α-SMA-positive fibroblasts influence pulpal repair. In this study, we established an experimental rat pulpotomy model and found that the expression of α-SMA was increased in dental pulp after pulpotomy relative to that in normal dental pulp. In vitro results showed that the expression of α-SMA was increased during the induction of odontogenic differentiation in dental pulp stem cells (DPSCs) compared with untreated DPSCs. Moreover, α-SMA overexpression promoted the odontogenic differentiation of DPSCs via increasing mitochondrial function. Mechanistically, α-SMA overexpression activated the mammalian target of rapamycin (mTOR) signaling pathway. Inhibition of the mTOR signaling pathway by rapamycin decreased the mitochondrial function in α-SMA-overexpressing DPSCs and suppressed the odontogenic differentiation of DPSCs. Furthermore, we found that α-SMA overexpression increased the secretion of transforming growth factor beta-1 (TGF-β1). In sum, our present study demonstrates a novel mechanism by which α-SMA promotes odontogenic differentiation of DPSCs by increasing mitochondrial respiratory activity via the mTOR signaling pathway.

Combined GSK-3β and MEK inhibitors modulate the stemness and radiotherapy sensitivity of cervical cancer stem cells through the Wnt signaling pathway

Cancer stem cells (CSCs) are the basis of cancer and lead to the recurrence and metastasis of cervical cancer. The aim of this study was to investigate the effects of antineoplastic agents on the stemness and radiotherapy sensitivity of cervical CSCs. Side population (SP) and non-side population (NSP) cells from the SiHa cervical cancer cell line were separated using flow cytometry. The cell spheroidization, proliferation, and subcutaneous tumor formation abilities of SP cells were stronger than those of NSP cells, and cervical CSC marker expressions increased in SP cells. The proliferation, anti-apoptosis and migration of SP cells under ionizing radiation were higher than those of SiHa cells. GSK-3β and/or MEK inhibitors can increase the proliferation, migration and anti-apoptosis of SP cells, and CSC marker expressions. The Wnt pathway inhibitor decreased CSC stemness maintenance by combination of GSK-3β and MEK inhibitors. Injection of GSK-3β and MEK inhibitors under ionizing radiation promoted tumor growth and activated downstream factor expressions in the Wnt signaling pathway in vivo. This study demonstrated that combining GSK-3β and MEK inhibitors can activate Wnt signaling pathway in cervical CSCs, thereby affecting their stemness maintenance and radiotherapy sensitivity.

6-Bromoindirubin-3′-Oxime Regulates Colony Formation, Apoptosis, and Odonto/Osteogenic Differentiation in Human Dental Pulp Stem Cells

6-bromoindirubin-3′-oxime (BIO) is a candidate small molecule that effectively modulates Wnt signalling owing to its stable property. The present study investigated the influence of BIO on the odonto/osteogenic differentiation of human dental pulp stem cells (hDPSCs). hDPSCs were treated with 200, 400, or 800 nM BIO, and the effects on hDPSC responses and osteogenic differentiation were assessed. BIO-mediated Wnt activation was confirmed by β-catenin nuclear translocation detected by immunofluorescence staining. BIO attenuated colony formation and cell migration determined by in vitro wound-healing assay. BIO increased early apoptotic cell population evaluated using flow cytometry. For osteogenic induction, BIO promoted alkaline phosphatase (ALP) activity and mineralisation in a dose-dependent manner. ALP, RUNX2, OCN, OSX, ANKH, DMP1, and DSPP mRNA expression were significantly upregulated. The OPG/RANKL expression ratio was also increased. Further, BIO attenuated adipogenic differentiation as demonstrated by decreased lipid accumulation and adipogenic-related gene expression. Bioinformatic analysis of RNA sequencing data from the BIO-treated hDPSCs revealed that BIO modulated pathways related to autophagy and actin cytoskeleton regulation. These findings demonstrated that BIO treatment promoted hDPSC osteogenic differentiation. Therefore, this small molecule is a strong candidate as a bioactive molecule to enhance dentin repair.

Effects of intentionally treated water on the growth of mesenchymal stem cells: An exploratory study

OBJECTIVE

This study explored if human primary mesenchymal stem cells (MSCs), derived from two donors and cultivated in a medium made with intentionally treated water, would exhibit more growth and pluripotency than MSCs from the same source but grown in untreated (control) water.

DESIGN

To create the treated water, three Buddhist monks directed their attention toward commercially bottled water while holding the intention that the water would enhance the growth of MSCs. Under double-blind conditions, cell culture growth mediums were prepared with the treated and untreated water, which was in turn used to grow the primary MSCs. Primary cells obtained from two donors were designated as Cells #1 and Cells #2. The prediction was that treated water would result in increased cell proliferation, that more cells would enter the cell cycle growth phase, and that there would be increased expression of genes (NANOG, OCT4 and SOX2) associated with improved cell growth and decreased expression of genes (p16, p21, and p53) associated with a decline in cell growth. The improved growth hypothesis was directional, thus one-tailed p-values were used to evaluate the results.

RESULTS

Proliferation averaged across Cells #1 and #2 showed overall increased growth in treated as compared to control water (p = 0.0008). Cells #1 and #2 considered separately had differences in the same direction but only Cells #2 showed a significant difference on day 6 (p = 0.01). For cell cycle, there was a significantly greater percentage of Cells #2 in the S interphase with treated vs. control water (p = 0.04). For the gene expression analysis, when considering the average across the two donor cells, only the NANOG gene expression was in the predicted direction (p = 0.01); by contrast, the p16 gene expression was significantly opposite to the predicted direction (p = 0.005, one-tailed, post-hoc). For Cells #1 considered separately, no differences were significant except for p16, which resulted in an effect opposite to the predicted outcome (p = 0.05). For Cells #2, three genes were significantly in the predicted directions: NANOG (p = 0.0008), OCT4 (p = 0.005), and P53 (p = 0.05); p16 was significantly opposite to the prediction (p = 0.001).

CONCLUSION

Intentionally treated water appeared to have some biological effects on the growth, pluripotency and senescence of human MSCs. This was especially the case in one of the two donor cells tested, but the effects were not consistently in the predicted direction. As an exploratory study, caution is warranted in interpreting these outcomes, and adjustment for multiple testing would likely reduce some of the weaker effects to nonsignificant. But given the double-blind protocol, as well as several more significant outcomes in the predicted directions, further research is warranted.

SC1 limits tube formation, branching, migration, expansion and induce apoptosis of endothelial cells

Endothelial cells (ECs) are essential in the growth and progression of the tumor cells by supplying nutrition and angiogenesis factors. Targeting ECs emerged as a major strategy to prevent the growth of tumors. Studies suggest that ERK1/2 signaling is important for endothelial cells, which could be specifically targeted by small molecule SC1. We aimed to study the effects of SC1 treatments on endothelial cell proliferation, angiogenesis, and death. To this end, we performed viability, apoptosis, cell cycle, gene expression, wound closure, tube formation, and western blot analysis in endothelial cells post SC1 treatments. Intriguingly, we found that SC1 has an antiangiogenic effect on endothelial cells, which limits the endothelial cell expansion, tube formation, branching, and migration. The proliferation is especially limited in dose dependent manner by SC1. In addition, we found that SC1 elevates the apoptosis of endothelial cells and associated pathways including BAK1, Stat1, Sox4, and Caspase1. We believe that these findings could contribute to the development of improved therapies based on the SC1 as an attractive candidate for anticancer clinical studies targeted to tumor angiogenesis.

CGFe and TGF-β1 enhance viability and osteogenic differentiation of human dental pulp stem cells through the MAPK pathway

The present study aimed to evaluate the effects of concentrated growth factor exudate (CGFe) and TGF-β1 on the viability and osteogenic differentiation of human dental pulp stem cells (hDPSCs). CGFe was prepared from the peripheral blood of healthy donors (obtained with informed consent). STRO-1⁺ hDPSCs were isolated from dental pulp tissues and treated in four groups: i) Control; ii) TGF-β1 (1 ng/ml); iii) 100% CGFe; and iv) TGF-β1 (1 ng/ml) + 100% CGFe group. hDPSC viability was measured via MTT assay. The osteogenic differentiation of hDPSCs was quantified via alkaline phosphatase (ALP) activity, western blotting and reverse transcription-quantitative PCR assays. CGFe and TGF-β1 enhanced hDPSC viability, upregulated ALP activity, upregulated the expression of phosphorylated (p)-ERK1/2, p-JNK and p-p38 in hDPSCs, and promoted transcription and protein expression of osteogenic-related genes (bone sialoprotein, Runt-related transcription factor 2 and osteocalcin) in hDPSCs. The present study demonstrated that CGFe and TGF-β1 facilitated the viability and osteogenic differentiation of hDPSCs potentially through activation of the MAPK signaling pathway.

Potential of tailored amorphous multiporous calcium silicate glass for pulp capping regenerative endodontics-A preliminary assessment

INTRODUCTION/OBJECTIVE

The tailored amorphous multi-porous (TAMP) material fabrication technology has led to a new class of bioactive materials possessing versatile characteristics. It has not been tested for dental applications. Thus, we aimed to assess its biocompatibility and ability to regenerate dental mineral tissue.

METHODS

30CaO-70SiO₂ model TAMP discs were fabricated by a sol-gel method followed by in vitro biocompatibility testing with isolated human or mini-swine dental pulp stem cells (DPSCs). TAMP scaffolds were tested in vivo as a pulp exposure (pin-point, 1 mm, 2 mm, and entire pulp chamber roof) capping material in the molar teeth of mini-swine.

RESULTS

The in vitro assays showed that DPSCs attached well onto the TAMP discs with comparable viability to those attached to culture plates. Pulp capping tests on mini-swine showed that after 4.5 months TAMP material was still present at the capping site, and mineral tissue (dentin bridge) had formed in all sizes of pulp exposure underneath the TAMP material.

CONCLUSIONS

TAMP calcium silicate is biocompatible with both human and swine DPSCs in vitro and with pulp in vivo, it may help regenerate the dentin bridge after pulp exposure.

6-Bromoindirubin-3'-oxime Promotes Osteogenic Differentiation of Periodontal Ligament Stem Cells and Facilitates Bone Regeneration in a Mouse Periodontitis Model

Effective bone tissue engineering is important to overcome the unmet clinical challenges of periodontal tissue regeneration. Successful bone tissue engineering comprises three key factors: stem cells, growth factors, and scaffolds. 6-Bromoindirubin-3'-oxime (BIO) is an inhibitor of glycogen synthase kinase-3 (GSK-3) that can activate the Wnt signaling pathway by enhancing β-catenin activity. In this study, the effects of BIO on the proliferation, migration, and osteogenic differentiation of periodontal ligament stem cells (PDLSCs) were investigated. Poly(lactic-co-glycolic acid) (PLGA) and hyaluronic acid (HA) emerged as promising biomaterials; thus, we developed a novel HA hydrogel embedded with BIO-encapsulated PLGA microspheres and injected the formulation into the gingival sulcus of mice with experimental periodontitis. The release speed of this system was fast in the first week and followed a sustained release phase until week 4. In vivo experiments showed that this PLGA-BIO-HA hydrogel system can inhibit periodontal inflammation, promote bone regeneration, and induce the expression of bone-forming markers alkaline phosphatase (ALP), runt-related transcription factor 2 (Runx2), and osteocalcin (OCN) in a mouse periodontitis model. Therefore, this PLGA-BIO-HA hydrogel system provides a promising therapeutic strategy for periodontal bone regeneration.

Impact of Sustained Transforming Growth Factor-β Receptor Inhibition on Chromatin Accessibility and Gene Expression in Cultured Human Endometrial MSC

Endometrial mesenchymal stem cells (eMSC) drive the extraordinary regenerative capacity of the human endometrium. Clinical application of eMSC for therapeutic purposes is hampered by spontaneous differentiation and cellular senescence upon large-scale expansion in vitro. A83-01, a selective transforming growth factor-β receptor (TGFβ-R) inhibitor, promotes expansion of eMSC in culture by blocking differentiation and senescence, but the underlying mechanisms are incompletely understood. In this study, we combined RNA-seq and ATAC-seq to study the impact of sustained TGFβ-R inhibition on gene expression and chromatin architecture of eMSC. Treatment of primary eMSC with A83-01 for 5 weeks resulted in differential expression of 1,463 genes. Gene ontology analysis showed enrichment of genes implicated in cell growth whereas extracellular matrix genes and genes involved in cell fate commitment were downregulated. ATAC-seq analysis demonstrated that sustained TGFβ-R inhibition results in opening and closure of 3,555 and 2,412 chromatin loci, respectively. Motif analysis revealed marked enrichment of retinoic acid receptor (RAR) binding sites, which was paralleled by the induction of RARB, encoding retinoic acid receptor beta (RARβ). Selective RARβ inhibition attenuated proliferation and clonogenicity of A83-01 treated eMSC. Taken together, our study provides new insights into the gene networks and genome-wide chromatin changes that underpin maintenance of an undifferentiated phenotype of eMSC in prolonged culture.

Human Dental Pulp Stem Cells and Gingival Mesenchymal Stem Cells Display Action Potential Capacity In Vitro after Neuronogenic Differentiation

The potential of human mesenchymal stromal/stem cells (MSCs) including oral stem cells (OSCs) as a cell source to derive functional neurons has been inconclusive. Here we tested a number of human OSCs for their neurogenic potential compared to non-OSCs and employed various neurogenic induction methods. OSCs including dental pulp stem cells (DPSCs), gingiva-derived mesenchymal stem cells (GMSCs), stem cells from apical papilla and non-OSCs including bone marrow MSCs (BMMSCs), foreskin fibroblasts and dermal fibroblasts using non-neurosphere-mediated or neurosphere-mediated methods to guide them toward neuronal lineages. Cells were subjected to RT-qPCR, immunocytofluorescence to detect the expression of neurogenic genes or electrophysiological analysis at final stage of maturation. We found that induced DPSCs and GMSCs overall appeared to be more neurogenic compared to other cells either morphologically or levels of neurogenic gene expression. Nonetheless, of all the neural induction methods employed, only one neurosphere-mediated method yielded electrophysiological properties of functional neurons. Under this method, cells expressed increased neural stem cell markers, nestin and SOX1, in the first phase of differentiation. Neuronal-like cells expressed βIII-tubulin, CNPase, GFAP, MAP-2, NFM, pan-Nav, GAD67, Nav1.6, NF1, NSE, PSD95, and synapsin after the second phase of differentiation to maturity. Electrophysiological experiments revealed that 8.3% of DPSC-derived neuronal cells and 21.2% of GMSC-derived neuronal cells displayed action potential, although no spontaneous excitatory/inhibitory postsynaptic action potential was observed. We conclude that DPSCs and GMSCs have the potential to become neuronal cells in vitro, therefore, these cells may be used as a source for neural regeneration.

Dental Mesenchymal Stem Cells: Dental Pulp Stem Cells, Periodontal Ligament Stem Cells, Apical Papilla Stem Cells, and Primary Teeth Stem Cells-Isolation, Characterization, and Expansion for Tissue Engineering

Dental stem cells (DSCs) have been shown to possess great potential for multiple biomedical applications, especially for dental tissue regeneration. They are a special type of subpopulation of mesenchymal stem/stromal cells (MSCs) and present subtle differences from other types of MSCs. Therefore, it requires a specialized expertise to isolate, culture, and characterize these cells in vitro and in vivo. The purpose of this chapter is to share our experience in studying these cells. We will describe in detail laboratory protocols outlining how the cells are isolated, cultured, expanded, and characterized using various in vitro cellular and biochemical analyses, as well as an in vivo study model using immunocompromised mice to observe tissue regeneration after transplantation of these DSCs.

Low-Dose Ionizing γ-Radiation Promotes Proliferation of Human Mesenchymal Stem Cells and Maintains Their Stem Cell Characteristics

Mesenchymal stem cells (MSCs), which are multipotent and have self-renewal ability, support the regeneration of damaged normal tissue. A number of external stimuli promote migration of MSCs into peripheral blood and support their participation in wound healing. In an attempt to harness the potential beneficial effects of such external stimuli, we exposed human MSCs (hMSCs) to one such stimulus-low-dose ionizing radiation (LDIR)-and examined their biological properties. To this end, we evaluated differences in proliferation, cell cycle, DNA damage, expression of surface markers (CD29, CD34, CD90, and CD105), and differentiation potential of hMSCs before and after irradiation with γ-rays generated using a 137CS irradiator. At doses less than 50 mGy, LDIR had no significant effect on the viability or apoptosis of hMSCs. Interestingly, 10 mGy of LDIR increased hMSC viability by 8% (p < 0.001) compared with non-irradiated hMSCs. At doses less than 50 mGy, LDIR did not induce DNA damage, including DNA strand breaks, or cause cellular senescence or cell-cycle arrest. Surface marker expression and in vitro differentiation potential of hMSCs were maintained after two exposures to LDIR at 10 mGy per dose. In conclusion, a two-dose exposure to LDIR at 10 mGy per dose not only facilitates proliferation of hMSCs, it also maintains the stem cell characteristics of hMSCs without affecting their viability. These results provide evidence for the potential of LDIR as an external stimulus for in vitro expansion of hMSCs and application in tissue engineering and regenerative medicine.

Combined Effects of Vascular Endothelial Growth Factor and Bone Morphogenetic Protein 2 on Odonto/Osteogenic Differentiation of Human Dental Pulp Stem Cells In Vitro

INTRODUCTION

The purpose of this study was to investigate whether combined and concerted delivery of vascular endothelial growth factor (VEGF) and bone morphogenetic protein 2 (BMP-2) enhances odonto/osteogenic differentiation of human dental pulp stem cells (DPSCs) in vitro.

METHODS

Various concentrations of VEGF and/or BMP-2 with or without the presence of odonto/osteogenic medium (OM) were added into DPSC cultures for 21 days. The mineral formation in cultures was evaluated using alizarin red stain (ARS). Optimal concentrations of VEGF and BMP-2 were codelivered to DPSCs for total of 21 days with the following experimental groups: (1) group 1: OM only, (2) group 2: OM + VEGF, (3) group 3: OM + BMP-2, and (4) group 4: OM + VEGF + BMP-2 (subgroup 4a: VEGF present the first 7 days, 4b: BMP-2 present the last 14 days, and 4c, both present for 21 days). Cultures were then subjected to quantitative ARS analysis or harvested for quantitative polymerase chain reaction analysis for the expression of core-binding factor alpha 1 (CBFA1), alkaline phosphatase (ALP), and dentin matrix protein 1 (DMP-1).

RESULTS

No mineral formation was detected by ARS when VEGF and/or BMP-2 were used without OM. OM + VEGF, but not OM + BMP-2, formed more mineralization than OM (P < .05). In the codelivery groups, the highest mineralization was observed in OM + VEGF and subgroup 4a compared with OM or the other groups (P < .05). Quantitative polymerase chain reaction analysis showed that CBFA1, ALP, and DMP-1 levels were higher in groups 2, 3, and 4a compared with 4b and 4c (P < .05). CBFA1 expressed higher in groups 2, 3, and 4a compared with OM (P < .05). For ALP expression, only subgroup 4a expressed higher than OM (P < .05). No difference was detected between groups 2 and 3 (P > .05) in the expression of the 3 genes.

CONCLUSIONS

VEGF addition in the early phase rather than a continuous presence of both VEGF and BMP-2 enhances odonto/osteogenic differentiation of DPSCs.

Differential Properties of Human ALP+ Periodontal Ligament Stem Cells vs Their ALP- Counterparts

Characterizing subpopulations of stem cells is important to understand stem cell properties. Tissue-nonspecific alkaline phosphatase (ALP) is associated with mineral tissue forming cells as well as stem cells. Information regarding ALP subpopulation of human periodontal ligament stem cells (hPDLSCs) is limited. In the present study, we examined ALP⁺ and ALP⁻ hPDLSC subpopulations, their surface markers STRO-1 and CD146, and the expression of stemness genes at various cell passages. We found that ALP⁺ subpopulation had higher levels of STRO-1 (30.6 ± 5.6%) and CD146 (90.4 ± 3.3%) compared to ALP⁻ (STRO-1: 0.5 ± 0.1%; CD146: 75.3 ± 7.2%). ALP⁺ cells expressed significantly higher levels of stemness associated genes, NANOG, OCT4 and SOX than ALP⁻ cells at low cell passages of 2-3 (p<0.05). ALP⁺ and ALP⁻ cells had similar osteogenic, chondrogenic and neurogenic potential while ALP⁻, not ALP⁺ cells, lacked adipogenic potential. Upon continuous culturing and passaging, ALP⁺ continued to express higher stemness genes and STRO-1 and CD146 than ALP⁻ cells at ≥passage 19. Under conditions (over-confluence and vitamin C treatment) when ALP⁺ subpopulation was increased, the stemness gene levels of ALP⁺ was no longer significantly higher than those in ALP⁻ cells. In conclusion, ALP⁺ hPDLSCs possess differential properties from their ALP⁻ counterparts.

Retention of the stemness of mouse adipose-derived stem cells by their expansion on human bone marrow stromal cell-derived extracellular matrix

Mesenchymal stem cells (MSCs) usually lose their stemness during in vitro expansion as they are deprived of their niche environment. Cell-extracellular matrix (ECM) interaction is known to play important roles in preserving the stemness of the cells in their stem cell niche environment. Previously, coating with bone marrow MSC (BMSC)-derived ECM was found able to maintain the differentiation potential of in vitro cultured MSCs. This study aimed to determine if this ECM coating could also maintain the stemness of cultured murine adipose-derived stem cells (ASCs) using a regular culture flask as a control. Cells were expanded in ECM-coated and ECM-noncoated flasks for two and four passages and then harvested for various analyses. The results showed that ASCs exhibited fibroblast-like spindle morphology in ECM-coated flasks, whereas ASCs gradually spread and enlarged in the ECM-noncoated flasks. After three and five passages, both groups of cells exhibited similar cytokinetics in the MSC culture medium (MesenPRO RS™ Medium). However, when cultured in Dulbecco's modified Eagles medium (DMEM) plus 10% fetal bovine serum, coating group cells exhibited more potent proliferation than control group cells with a significant difference in both passages 3 and 5 (p<0.01). When seeded at low density (500 cells/10-cm dish), coating group cells formed significantly more and larger sized cell colonies than control group cells with significant difference in cell colony numbers between two groups (p<0.05). In addition, coated colony cells were much smaller and more compactly arranged compared to control colony cells. Furthermore, ASCs expanded in coated flasks exhibited greater potentials for adipogenic, osteogenic, and chondrogenic differentiations than the cells expanded in regular flasks. Quantitatively, the Oil Red O staining area, Alizarin staining area, and Toluidine Blue staining area were all significantly larger than the respective staining areas of control cells (p<0.05). Real-time polymerase chain reaction also revealed significantly higher gene expression levels of peroxisome proliferator-activated receptor gamma (PPARγ), adipocyte protein 2 (aP2), CCAAT/enhancer-binding protein (C/EBP), Runx2, osteocalcin, Sox9, collagen II, and aggrecan in ECM-coated group cells than in control group cells (p<0.05). Collectively, these results suggest that human BMSC decellular ECM coating helps to preserve the stemness of cultured murine ASCs.

Effect of luteolin and apigenin on the expression of Oct-4, Sox2, and c-Myc in dental pulp cells with in vitro culture

Introduction. Dental pulp cells (DPCs) are promising cell source for dental tissue regeneration. Recently, small molecules which optimize microenvironment or activate the reprogramming network provide a new way to enhance the pluripotency. Two promising bioflavonoids luteolin and apigenin were reported to enhance reprogramming efficiency in mouse embryonic fibroblast (MEF). However, their effect and underlying mechanism in cell fate determination of human DPCs remain unclear. Methods. To elucidate the effect of luteolin and apigenin on the cell fate determination of DPCs, we explored the cell proliferation, cell cycle, senescence, apoptosis, expression of pluripotency markers Oct-4, Sox2, and c-Myc, and multilineage differentiation capability of DPCs with luteolin or apigenin treatment. Results. We demonstrated that luteolin and apigenin inhibited cell proliferation, arrested DPCs in G2/M and S phase, and upregulated PI value and apoptosis. Moreover, luteolin and apigenin increased telomerase activity, maintained DPCs in a presenescent state, and activated the expression of Oct-4, Sox2, and c-Myc at a dose- and time-dependent pattern in DPCs even at late passages, albeit repressed lineage-specific differentiation. Conclusions. Addition of luteolin and apigenin in the culture medium might provide an effective way to maintain DPCs in an undifferentiated stage and inhibit lineage-specific differentiation.

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.