Stem Cells from the Apical Papilla (SCAPs): Past, Present, Prospects, and Challenges

METTL3-m6A methylase regulates the osteo-/odontogenic potential of stem cells from apical papilla via NFIC in apical periodontitis

Stem cells from the apical papilla (SCAPs) show strong odontogenic ability and can form root dentin. However, the underlying mechanisms that control the odontogenic differentiation of SCAPs in an inflammatory environment need further exploration. In the present study, we explored the regulatory role of METTL3 in the differentiation of SCAPs originating from tooth with apical periodontitis. Stem cells from the apical papilla derived from healthy teeth (SCAPs) and teeth with apical periodontitis (AP-SCAPs) were successfully isolated and cultured. The expressions of tumor necrosis factor-a (TNF-a) and interleukin-6 (IL-6) were higher in AP-SCAPs. A decrease in METTL3 expression accompanied the decreased osteo-/odontogenic differentiation ability of AP-SCAPs. Exploring the role of METTL3 on the osteo-/odontogenic differentiation of AP-SCAPs revealed that overexpression of METTL3 upregulated the odontogenic ability of AP-SCAPs. However, silencing METTL3 exerted the opposite effect. Overexpression of METTL3 suppressed the expression of TNF-α and IL-6 in AP-SCAPs, whereas knockdown of METTL3 in these cells enhanced TNF-α and IL-6 expression. METTL3 regulates the osteo-/odontogenic differentiation of SCAPs and modulates their inflammatory response. Furthermore, overexpression of METTL3 upregulated the methylation level, mRNA, and protein expression of nuclear factor-IC (NFIC) during mineralization induction. NFIC silencing attenuated osteo-/odontogenic differentiation of METTL3-overexpressed AP-SCAPs. In conclusion, METTL3-mediated-m6A upregulated the odontogenic differentiation of AP-SCAPs via NFIC. This paper elucidates a novel mechanism regulating the odontogenic differentiation of AP-SCAPs, and METTL3 may be a new target for regenerative endodontic treatment.

Injectable thermosensitive antibiotic-laden chitosan hydrogel for regenerative endodontics

Injectable biomaterials, such as thermosensitive chitosan (CH)-based hydrogels, present a highly translational potential in dentistry due to their minimally invasive application, adaptability to irregular defects/shapes, and ability to carry therapeutic drugs. This work explores the incorporation of azithromycin (AZI) into thermosensitive CH hydrogels for use as an intracanal medication in regenerative endodontic procedures (REPs). The morphological and chemical characteristics of the hydrogel were assessed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). The thermosensitivity, gelation kinetics, compressive strength, cytocompatibility, and antibacterial efficacy were evaluated according to well-established protocols. An in vivo model of periapical disease and evoked bleeding in rats' immature permanent teeth was performed to determine disinfection, tissue repair, and root formation. AZI was successfully incorporated into interconnected porous CH hydrogels, which retained their thermosensitivity. The mechanical and rheological findings indicated that adding AZI did not adversely affect the hydrogels' strength and injectability. Incorporating 3 % and 5 % AZI into the hydrogels led to minimal cytotoxic effects compared to higher concentrations while enhancing the antibacterial response against endodontic bacteria. AZI-laden hydrogel significantly decreased E. faecalis biofilm compared to the controls. Regarding tissue response, the 3 % AZI-laden hydrogel improved mineralized tissue formation and vascularization compared to untreated teeth and those treated with double antibiotic paste. Our findings demonstrate that adding 3 % AZI into CH hydrogels ablates infection and supports neotissue formation in vivo when applied to a clinically relevant model of regenerative endodontics.

Protective effect of conditioned medium derived from melatonin-stimulated stem cells from the apical papilla on glutamate-induced neurotoxicity in PC12 cells

Glutamate-induced neurotoxicity can be attenuated via paracrine mechanisms involving mesenchymal stem cells (MSCs). Conditioned medium (CM) from dental MSCs stimulates neuroprotective effects through trophic factors, and melatonin is a known enhancer of the efficacy of conditional media. Here, we investigated the protective effect of CM derived from stem cells from the apical papilla (SCAPs), supplemented without and with melatonin CM (SCAP-CM and Mel-CM), against glutamate-induced PC12 cell apoptosis via the inhibition of intracellular calcium influx and reactive oxygen species (ROS) production. The results showed that CM effectively reduced glutamate-induced intracellular calcium ion concentration, ROS production, and LDH levels in PC12 cells, elevated mitochondrial membrane potential, and inhibited Bax and Cytochrome c protein expression while increasing Bcl-2 protein expression. Moreover, CM significantly reduced the expression of caspase-9 and caspase-3 to inhibit glutamate-induced PC12 cell apoptosis. Notably, Mel-CM outperformed SCAP-CM in all aspects. This study demonstrates that melatonin can enhance the paracrine effects of stem cells and that Mel-CM mediates neuroprotection by inhibiting neuronal cell damage and apoptosis induced by glutamate-induced neurotoxicity.

m6A-Modified GATA2 Enhances Odontogenic Differentiation in Stem Cells from the Apical Papilla

Epigenetic modifications play a crucial role in regulating stem cell differentiation. Among these, N6-methyladenosine (m6A) modification significantly impacts mRNA stability and translation. However, its role in dental stem cell differentiation remains largely unexplored. Functional assays, including ALP activity, alizarin red S staining, qPCR, and Western blot, were conducted to assess odontogenic differentiation. Then, an in vivo dentin formation model was used to validate our findings. Additionally, we employed RNA stability assays and m6A site mutagenesis to investigate the regulatory mechanism of m6A modification in GATA2-mediated differentiation. Our results demonstrated that overexpression of GATA2 significantly promoted SCAP odontogenic differentiation. Moreover, in vivo studies confirmed that GATA2 overexpression enhances dentin formation in mouse models. Conversely, knockdown of GATA2 or mutation of its m6A sites led to reduced mRNA stability and decreased odontogenic differentiation. m6A modification is enriched in the 3' untranslated region (3'UTR) of GATA2 mRNA, regulating its stability and expression. Our findings indicate that m6A modification contributes to the post-transcriptional regulation of GATA2, enhancing its stability and promoting SCAP-mediated odontogenic differentiation and dentin formation. This study provides new insights into the epigenetic regulation of dental stem cells and suggests a potential molecular target for dental tissue regeneration.

The potential role of chromodomain helicase DNA-binding protein 3 in defining the cervical width by regulating the early growth stage of the apical papilla during tooth development

OBJECTIVE

This study aimed to evaluate the role of the chromodomain helicase DNA-binding protein 3 (CHD3) in tooth morphogenesis in Chd3 knockout mice.

METHODS

Chd3 knockout mice were generated using the CRISPR-Cas9 method. Mandibular first molars were extracted from the mice and their littermates and morphometrically analyzed. Subsequent histological and immunohistochemical analyses of teeth were performed at each developmental stage. Chd3 knockdown in mesenchymal cells from the dental papilla (mDP) and Hertwig's epithelial root sheath (HERS) was performed by Chd3 shRNA transduction or a control using an adenoviral vector. These effects were examined using cell proliferation assays and quantitative real-time polymerase chain reaction.

RESULTS

Narrowing of tooth cervical width was observed in mandibular first molars of Chd3 knockout mice. On postnatal day (PN) 8, the cervical width was narrow before root formation in tooth germs. The number of Ki-67-positive cells decreased in the dental mesenchyme at PN1 and apical papilla at PN8. Chd3 promoted the proliferation of dental mesenchymal cells, but no significant changes were observed in HERS epithelial cells. Chd3 maintained sonic hedgehog (Shh) expression and inhibited that of bone morphogenetic protein (Bmp)4 in dental mesenchymal cells, maintaining Shh and Wnt3a expression and inhibited that of Bmp2 in HERS epithelial cells.

CONCLUSION

Chd3 may regulate tooth cervical width during the early growth stage of the apical papilla via Shh, Bmp, and Wnt signaling.

Betaine enhances SCAPs chondrogenic differentiation and promotes cartilage repair in TMJOA through WDR81

BACKGROUND

The cartilage tissue regeneration mediated with mesenchymal stem cells (MSCs) is considered as a viable strategy for temporomandibular joint osteoarthritis (TMJOA). Betaine has been confirmed to modulate the multidirectional differentiation of MSCs, while its effect on chondrogenic differentiation of Stem Cells from the Apical Papilla (SCAPs) is unknown. Here, we explored the effects and underlying mechanisms of betaine on chondrogenic differentiation of SCAPs.

METHODS

Betaine was added for SCAPs chondrogenic induction. The chondrogenic differentiation potential was assessed using Alcian Blue staining, Sirius Red staining and the main chondrogenic markers. In vivo cartilage regeneration effects were evaluated by the rat TMJOA model. RNA-sequencing and biological analyses were performed to select target genes and biological processes involved. The mechanism betaine acts on chondrogenic differentiation of SCAPs was further explored.

RESULTS

Betain-treated SCAPs demonstrated stronger cartilage regeneration in vitro and promoted cartilage repair of TMJOA in vivo. Betaine enhanced the expression of WDR81 in SCAPs during chondrogenesis. WDR81 overexpression promoted chondrogenic differentiation of SCAPs, while WDR81 depletion inhibited chondrogenic differentiation. In addition, both betaine treatment and WDR81 overexpression reduced intracellular reactive oxygen species levels and increased mitochondrial membrane potential in SCAPs.

CONCLUSION

Betaine promotes SCAPs chondrogenic differentiation and provided an effective candidate for TMJOA treatment. WDR81 may serve as the potential drug target through mitophagy.

Cell Homing Strategies in Regenerative Endodontic Therapy

Cell homing, a process that leverages the body's natural ability to recruit cells and repair damaged tissues, presents a promising alternative to cell transplantation methods. Central to this approach is the recruitment of endogenous stem/progenitor cells-such as those from the apical papilla, bone marrow, and periapical tissues-facilitated by chemotactic biological cues. Moreover, biomaterial scaffolds embedded with signaling molecules create supportive environments, promoting cell migration, adhesion, and differentiation for the regeneration of the pulp-dentin complex. By analyzing in vivo animal studies using cell homing strategies, this review explores how biomolecules and scaffold materials enhance the recruitment of endogenous stem cells to the site of damaged dental pulp tissue, thereby promoting repair and regeneration. It also examines the key principles, recent advancements, and current limitations linked to cell homing-based regenerative endodontic therapy, highlighting the interplay of biomaterials, signaling molecules, and their broader clinical implications.

Bone morphogenetic protein-4 induced matrix turnover and osteogenic differentiation-related molecules of stem cells from apical papilla and its associated ALK/Smad signaling

Background/purpose

Revascularization procedures are used over apexification to treat teeth with necrotic pulp tissues and incomplete root formation. Clinically, inducing proliferation, migration, matrix deposition, and differentiation of stem cells from apical papilla (SCAPs) are critical for pulp regeneration. The study aimed to elucidate the impact of bone morphogenetic protein-4 (BMP-4) on plasminogen activation molecules and the osteogenic/odontogenic differentiation of SCAPs, as well as understand the related signaling mechanisms.

Materials and methods

SCAPs were exposed to BMP-4 with or without signal transduction inhibitors. Cell viability was assessed using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. mRNA levels were quantified using real-time PCR. Protein expression in SCAPs was analyzed through immunofluorescent staining or western blotting. Cellular protein production was measured with enzyme-linked immunosorbent assay.

Results

BMP-4 induced suppressor of mother against decapentaplegic (Smad)1/5/8 and Smad2/3 phosphorylation and activation. It also promoted higher expression of osteogenic and odontogenic markers, including Osterix, N-cadherin, and secreted protein acidic and rich in cysteine (SPARC), in SCAPs. Additionally, BMP-4 stimulated connective tissue growth factor (CTGF), plasminogen activator inhibitor-1 (PAI-1), and urokinase plasminogen activator receptor (uPAR) expression, but inhibited uPA expression and production in SCAPs, indicating its role in matrix remodeling and cell migration. Inhibition of Smad2/3 with SB431542 and Smad1/5/8 with LDN193189 attenuated the BMP-4-induced expression Osx, N-cadherin, CTGF, SPARC, uPAR and PAI-1.

Conclusion

These results indicate that BMP-4 stimulates the osteogenic and odontogenic differentiation of SCAPs by regulating matrix turnover and mineralization-related proteins. Furthermore, these processes are associated with the induction of Smad2/3 and Smad1/5/8 of SCAPs by BMP-4.

Fabrication and characterization of nanocomposite scaffold containing zinc-doped mesoporous bioglass: Evaluation of the antioxidant properties, hemocompatibility and proliferation of apical papilla stem cells

Introduction

Nanocomposite scaffolds comprising mesoporous bioactive glass (MBG) were able to increase the viability, proliferation, and growth of stem cells in vitro, rendering them promising candidates for dental root tissue regeneration.

Methods

The Sol-Gel process was utilized for the synthesis of MBG and zinc-doped MBG (Zn-MBG), the latter being integrated into alginate/chitosan scaffolds which in turn were cross-linked to strengthen mechanical properties, followed by freeze-drying. The scaffold's physicochemical characterizations were evaluated, followed by investigations of its antioxidant properties, swelling behavior, mechanical properties, and porosity. The capacity of these biomaterials to increase cell viability and growth of apical papilla stem cells (SCAPs) and hemocompatibility was assessed as a final step.

Results

All fabricated scaffolds demonstrated proper porosity, biocompatibility, and hemocompatibility. Nanocomposite scaffolds with Zn-MBG presented a significant enhancement in cell viability for SCAPs compared to alginate/chitosan scaffolds. DPPH tests indicated that the Zn-MBG-alginate/chitosan scaffold showed the highest antioxidant properties.

Conclusion

Zn-MBG-alginate/chitosan nanocomposite scaffolds demonstrated great physicochemical characteristics and biological and mechanical properties, marking them as suitable candidates for dental root tissue engineering.

The effect of citric acid on mineralisation and vascular endothelial growth factor secretion from apical papilla stem cells

OBJECTIVE

To investigate the influence of citric acid on the osteogenic and angiogenic potential of stem cells from apical papillae (SCAPs).

MATERIALS AND METHODS

Stem cells from apical papillae were isolated from freshly extracted third permanent molars. These cells were treated with 20 and 100 μM citric acid. Alizarin red staining was used to evaluate mineral deposition. The secreted levels of vascular endothelial growth factor (VEGF) were assessed by ELISA on days 18, 24 and 28. Immunofluorescence analysis was performed to assess the expression of surface markers after exposure to 20 and 100 μM citric acid.

RESULTS

Different mineralisation patterns were observed. Supplemented with citric acid, media showed more diffuse and less dense crystals. On day 18, most VEGF was secreted from the cells with no added citric acid. On day 24, there was a significant increase (p < 0.05) in the levels of VEGF secreted from cells treated with 20 μM citric acid. On day 28, cells from the control group did not secrete VEGF. There was a reduction in the levels of VEGF secreted by cells treated with 20 μM citric acid and a significant increase in the cells exposed to 100 μM citric acid (p < 0.05).

CONCLUSION

Citric acid can promote the differentiation of SCAPs and angiogenesis.

Recent adavances of functional modules for tooth regeneration

Dental diseases, such as dental caries and periodontal disorders, constitute a major global health challenge, affecting millions worldwide and often resulting in tooth loss. Traditional dental treatments, though beneficial, typically cannot fully restore the natural functions and structures of teeth. This limitation has prompted growing interest in innovative strategies for tooth regeneration methods. Among these, the use of dental stem cells to generate functional tooth modules represents an emerging and promising approach in dental tissue engineering. These modules aim to closely replicate the intricate morphology and essential physiological functions of dental tissues. Recent advancements in regenerative research have not only enhanced the assembly techniques for these modules but also highlighted their therapeutic potential in addressing various dental diseases. In this review, we discuss the latest progress in the construction of functional tooth modules, especially on regenerating dental pulp, periodontal tissue, and tooth roots.

FTO Positively Regulates Odontoblastic Differentiation via SMOC2 in Human Stem Cells from the Apical Papilla under Inflammatory Microenvironment

Odontoblastic differentiation of human stem cells from the apical papilla (hSCAPs) is crucial for continued root development and dentin formation in immature teeth with apical periodontitis (AP). Fat mass and obesity-associated protein (FTO) has been reported to regulate bone regeneration and osteogenic differentiation profoundly. However, the effect of FTO on hSCAPs remains unknown. This study aimed to identify the potential function of FTO in hSCAPs' odontoblastic differentiation under normal and inflammatory conditions and to investigate its underlying mechanism preliminarily. Histological staining and micro-computed tomography were used to evaluate root development and FTO expression in SD rats with induced AP. The odontoblastic differentiation ability of hSCAPs was assessed via alkaline phosphatase and alizarin red S staining, qRT-PCR, and Western blotting. Gain- and loss-of-function assays and online bioinformatics tools were conducted to explore the function of FTO and its potential mechanism in modulating hSCAPs differentiation. Significantly downregulated FTO expression and root developmental defects were observed in rats with AP. FTO expression notably increased during in vitro odontoblastic differentiation of hSCAPs, while lipopolysaccharide (LPS) inhibited FTO expression and odontoblastic differentiation. Knockdown of FTO impaired odontoblastic differentiation, whereas FTO overexpression alleviated the inhibitory effects of LPS on differentiation. Furthermore, FTO promoted the expression of secreted modular calcium-binding protein 2 (SMOC2), and the knockdown of SMOC2 in hSCAPs partially attenuated the promotion of odontoblastic differentiation mediated by FTO overexpression under LPS-induced inflammation. This study revealed that FTO positively regulates the odontoblastic differentiation ability of hSCAPs by promoting SMOC2 expression. Furthermore, LPS-induced inflammation compromises the odontoblastic differentiation of hSCAPs by downregulating FTO, highlighting the promising role of FTO in regulating hSCAPs differentiation under the inflammatory microenvironment.

A Potential Intracanal Medicament, 2-Hydroxyisocaproic Acid (HICA): Cytotoxicity, Genotoxicity, and Its Effect on SCAP Differentiation

Intracanal medicaments with maximal antimicrobial efficacy and minimal damage to resident stem cells are essential for successful regenerative endodontic procedures. 2-Hydroxyisocaproic acid (HICA) could have the attributes of a potential intracanal medicament. This study evaluates its cytotoxicity, genotoxicity, and effects on the odontogenic and osteogenic differentiation of the stem cells of the apical papilla (SCAP). Cytotoxicity and cell viability assays were performed on cells treated for 24, 48, and 72 h with varying concentrations of HICA and compared to the standard intracanal medicament, calcium hydroxide. The genotoxicity was assessed via immunofluorescence for two markers of DNA double-strand breaks: phosphorylated γH2AX and 53BP1. The SCAP differentiation was evaluated based on the alkaline phosphatase activity, Alizarin Red staining, and expression of odontogenic and osteogenic genes (DSPP1, BSP1, OCN, RUNX2) in the presence of selected HICA concentrations. HICA was not cytotoxic at concentrations up to 10 mg/mL, regardless of the exposure time, although it was cytostatic at all tested concentrations. HICA was not genotoxic at concentrations below 5 mg/mL. No difference in cytotoxicity or genotoxicity was found between HICA and calcium hydroxide at 1 mg/mL. HICA retained about 70% of the osteogenic differentiation potential at 1 mg/mL. Within the limitations of this in vitro study, we show that HICA at 1 mg/mL could be a potential intracanal medicament for REPs.