Effects of different signaling pathways on odontogenic differentiation of dental pulp stem cells: a review

Cellular dynamics and signalling mechanisms in dentine repair: A narrative review

BACKGROUND

Bioactive molecules have gained significant attention in regenerative medicine due to their ability to boost the reparative properties of stem cells, including those in the dental pulp. This narrative review aims to deepen our understanding of the dynamics of bioactive molecules in the dental pulp and their role in enhancing hard tissue reparative processes.

OBJECTIVES

(i) To discuss the role of different cells and the critical pathways involved in dentine formation through direct (reparative) or indirect (infection control and immunomodulatory) mechanisms. (ii) To highlight how innovative therapeutic strategies could be employed to target key molecules for successful dentine repair and regeneration.

METHODS

The review encompassed all years up to the search period. Databases such as PubMed, Scopus and Medline were utilized to gather relevant studies. The search strategy involved specific signalling molecules such as Transforming growth factor-β1 (TGF-β), Bone Morphogenetic Proteins (BMP), Small Integrin Binding Ligand N-linked Glycoproteins (SIBLING) and growth factors. Cell types including odontoblasts, fibroblasts, immune cells and dental pulp stem cells (DPSCs) were of interest. Additionally, signalling pathways like Wnt, Notch, Shh, amongst others, were investigated for their roles in repair mechanisms. Key terms were combined using Boolean operators [Cell type] AND [signalling molecules] AND/OR [dentine], [Cell type] AND/OR [signalling pathways] AND/OR [dentine] to include studies addressing the interaction of these components in enhancing repair processes.

DISCUSSION

Key molecules such as TGF-β1, BMP and SIBLING proteins effectively enhance the dentine reparative response, whilst other molecules such as complement proteins and antimicrobial peptides primarily activate immune cells and facilitate pathogen clearance to promote the regenerative capabilities of DPSCs. This well-orchestrated interaction emphasizes the need to investigate the effects of these molecules on all cells within the dental pulp. Morphogenic signalling molecules such as BMP-2, -4 and -7, and Wnt show temporal, yet significant regenerative properties, whilst Shh and Notch present inconsistent effects on dentine regeneration, and a consensus on their roles and properties in dentine repair has yet to be reached.

CONCLUSIONS

This review highlights the critical role of bioactive molecules in dentine repair to guide the development of next-generation bioinspired therapeutics for vital pulp therapy.

FoxO1 mediates odontoblast differentiation of hDPSCs via B cell-derived ANGPTL1 in dental caries: A laboratory investigation

AIM

Clinical and in vitro evidence indicates that chronic inflammatory responses initiated by dental caries can persist in the dental pulp even after treatment, necessitating the formation of reparative dentin to restore tissue homeostasis and health. Human dental pulp stem cells (hDPSCs) serve as crucial precursors in this reparative process. This study explores the role of B cells and their secreted factor, Angiopoietin Like 1 (ANGPTL1), in promoting hDPSCs differentiation into odontoblasts under carious conditions, with a particular focus on the activation of Forkhead box O1 (FoxO1).

METHODOLOGY

Single-cell RNA sequencing (scRNA-Seq) data from the GEO database were analysed to explore cellular interactions and molecular mechanisms in dental pulp. Immunofluorescence staining was used to investigate the expression patterns of B cells or hDPSCs in dental pulp and hydroxyapatite/tricalcium phosphate (HA/TCP) scaffolds. The expression levels of ANGPTL1 were quantified using enzyme-linked immunosorbent assay (ELISA). Odontoblast differentiation capacity was assessed by alkaline phosphatase activity, alizarin red S staining, and western blotting analysis. hDPSCs were overexpressed or knocked down FoxO1 with lentiviruses. The regulatory interaction between FoxO1 and the DSPP promoter was evaluated through dual-luciferase reporter assay and chromatin immunoprecipitation assay. Statistical analyses were conducted using Student's t-test or one-way analysis of variance (anova) with a p-value of <.05 considered statistically significant.

RESULTS

scRNA-Seq data indicated a significant increase in B cells and ANGPTL1 expression in carious dental pulp. Functional analyses confirmed that ANGPTL1 secreted by B cells activated FoxO1 expression in hDPSCs, enhancing their differentiation into odontoblast-like cells. Blocking ANGPTL1 signalling with a specific antibody reduced FoxO1 expression, indicating a regulatory link between ANGPTL1 and FoxO1. Overexpression of FoxO1 in hDPSCs promoted their differentiation into odontoblasts and facilitated mineralized matrix formation. Mechanistic studies revealed that FoxO1 directly binds to the DSPP promoter, thereby inducing its expression.

CONCLUSIONS

Our study reveals a novel mechanism in which ANGPTL1 secreted by B cells in a carious environment promotes the odontoblast differentiation of hDPSCs by upregulating FoxO1. This finding highlights a potential therapeutic target for enhancing dental pulp repair and regeneration.

Three-dimensional matrix stiffness-based stem cell soil: Tri-phase biomechanical structure promoted human dental pulp stem cells to achieve pulpodentin regeneration

The regeneration of the pulp-dentine complex is characterized by organizational diversity, with both dentine and pulp being essential for regenerating a complete tooth-like structure. Matrix stiffness plays a crucial role in guiding the multi-lineage differentiation of stem cells during the regeneration process. However, human dental pulp stem cell (HDPSCs) differentiation via three-dimensional (3D) matrix stiffness is still ambiguous. This study employed gelatin methacryloyl hydrogels of varying stiffness to investigate their effects on HDPSCs differentiation, and constructing a Tri-Phase Biomechanical Structure. The effects of 3D stiffness on HDPSCs proliferation, morphology, differentiation, and biomineralization were examined. The underlying mechanisms were analyzed by RNA sequencing (RNA-seq). At the same time, the comprehensive effects of 3D matrix stiffness-induced HDPSCs paracrine signals on periapical cells (endothelial cells, macrophages and fibroblasts) were evaluated. In vitro, high stiffness promoted dentin differentiation, medium stiffness supported vascular differentiation, and low stiffness enhanced vascularization of peri-apical cells through paracrine signals. In vivo, treated dentin matrixes implanted in nude mice further confirmed that this Tri-Phase Biomechanical Structure effectively promoted crownward dentin formation, pulp-like regeneration within root canals, and integration with periapical tissues. These findings highlight that understanding HDPSCs responses to 3D matrix stiffness is crucial for guiding targeted, efficient regeneration of a tooth-like pulpodentin complex.

Cannabidiol alleviates LPS-inhibited odonto/osteogenic differentiation in human dental pulp stem cells in vitro

AIM

Cannabidiol (CBD), derived from the Cannabis sativa plant, exhibits benefits in potentially alleviating a number of oral and dental pathoses, including pulpitis and periodontal diseases. This study aimed to explore the impact of CBD on several traits of human dental pulp stem cells (hDPSC), such as their proliferation, apoptosis, migration and odonto/osteogenic differentiation.

METHODOLOGY

hDPSCs were harvested from human dental pulp tissues. The cells were treated with CBD at concentrations of 1.25, 2.5, 5, 10, 25 and 50 μg/mL. Cell responses in terms of cell proliferation, colony-forming unit, cell cycle progression, cell migration, apoptosis and odonto/osteogenic differentiation of hDPSCs were assessed in the normal culture condition and P. gingivalis lipopolysaccharide (LPS)-induced 'inflammatory' milieus. RNA sequencing and proteomic analysis were performed to predict target pathways impacted by CBD.

RESULTS

CBD minimally affects hDPSCs' behaviour under normal culture growth milieu in normal conditions. However, an optimal concentration of 1.25 μg/mL CBD significantly countered the harmful effects of LPS, indicated by the promoting cell proliferation and restoring the odonto/osteogenic differentiation potential of hDPSCs under LPS-treated conditions. The proteomic analysis demonstrated that several proteins involved in cell proliferation and differentiation were upregulated following CBD exposure, including CCL8, CDC42 and KFL5. RNA sequencing data indicated that CBD upregulated the Notch signalling pathway. In an inhibitory experiment, DAPT, a Notch inhibitor, reduced the effect of CBD-rescued LPS-attenuated mineralization in hDPSCs, suggesting that CBD potentially mediates Notch activation to exert its impact on odonto/osteogenic differentiation of hDPSCs.

CONCLUSIONS

CBD recovers the proliferation and survival of hDPSCs following exposure to LPS. Additionally, we report that CBD-mediated Notch activation effectively restores the odonto/osteogenic differentiation ability of hDPSCs under inflamed conditions. These results underscore the potential role of CBD as a therapeutic option to enhance dentine regeneration.

Gene expression profiles in human dental pulp stem cells treated short-term with lipopolysaccharides before and after osteoinduction

OBJECTIVES

Dental pulp stem cells (DPSCs) are essential for reparative dentinogenesis following damage or infection. DPSCs surrounding theblood vessels in the central region of the dental pulp actively proliferate after tooth injury and differentiate into new odontoblast-like cells or odontoblasts to form reparative dentin. However, the signaling pathways involved in undifferentiated and osteodifferentiated DPSCs under inflammatory conditions remain unclear. This study aimed to compare the expression profiles of immortalized undifferentiated and osteo-differentiated human DPSCs (hDPSCs) treated with and without lipopolysaccharide (LPS) to elucidate the molecular regulatory mechanisms involved in inflammatory conditions.

METHODS

We investigated the differences between undifferentiated and osteodifferentiated hDPSCs in response to LPS. RNA-seq analyses of undifferentiated and osteodifferentiated hDPSCs were performed with and without LPS.

RESULTS

Whole-transcriptome profiling revealed distinct differences in the expression patterns of LPS-treated undifferentiated and osteodifferentiated DPSCs. Death-associated protein kinase 1 levels downregulated in LPS-treated osteodifferentiated cells, inhibiting apoptosis and enhancing cell survival After LPS treatment, osteodifferentiated DPSCs exhibited higher expression levels of various inflammatory cytokines and chemokines than undifferentiated DPSCs.

CONCLUSION

This study provides valuable transcriptomic data as a critical resource for uncovering potential therapeutic targets to enhance cell survival and regulate inflammation within the dental pulp. By elucidating the key molecular mechanisms and identifying specific gene expression changes linked to inflammatory and immune responses, these findings provide significant insights into osteo-differentiated hDPSCs.

Adrenomedullin-loaded Gelatin Methacryloyl Hydrogel Promotes Endogenous Dental Pulp Regeneration: An In Vitro and In Vivo Study

INTRODUCTION

To prepare a gelatin methacryloyl (GelMA) hydrogel scaffold embedded with adrenomedullin (ADM) and investigate its impact and underlying mechanisms in endogenous pulp regeneration.

METHODS

ADM was evenly distributed within the GelMA hydrogel through a simple and conventional physical mixing technique. The scaffold underwent characterization via scanning electron microscopy, alongside assessments of swelling, degradation, and release properties. Biocompatibility was evaluated using cytoskeletal and live-dead staining techniques. The hydrogel's influence on dental pulp stem cells' proliferation, migration, and differentiation was assessed with CCK-8 assays, Transwell assays, and alizarin red and alkaline phosphatase staining. Transcriptomics provided insights into potential mechanisms. The angiogenic effects on umbilical vein endothelial cells were examined using scratch and tube formation assays. In vivo, the composite hydrogel's regenerative capacity was tested in a rat model of pulp regeneration. Statistical analysis involved Student's t-test and one-way analysis of variance, with significance set at P < .05.

RESULTS

The ADM-loaded GelMA (GelMA@ADM) hydrogel displayed a porous architecture under electron microscopy conducive to cell adhesion and demonstrated excellent biocompatibility. In vitro experiments showed that GelMA@ADM significantly boosted dental pulp stem cells' migration, proliferation, and differentiation, and enhanced the angiogenic activity of umbilical vein endothelial cells after one week of treatment. Corresponding in vivo experiments revealed that GelMA@ADM facilitated the formation of new vascularized pulp tissue after 2 weeks of treatment.

CONCLUSIONS

The GelMA@ADM hydrogel effectively promotes dental pulp stem cells' proliferation and differentiation, augments vascularization by umbilical vein endothelial cells, and fosters the creation of new vascularized pulp tissue. These findings underscore the potential of GelMA@ADM hydrogel for endogenous pulp regeneration.

Histopathological Evaluation of Human Placental Extract as a Direct Pulp-Capping Material in Dogs' Teeth

OBJECTIVE

 The current research aimed to evaluate the histopathological pulpal alterations in dogs' teeth following direct pulp capping using either mineral trioxide aggregate (MTA) or human placenta extract (HPE).

MATERIALS AND METHODS

 Forty-eight incisors with mature apices from four dogs were involved. The teeth were randomly allocated to three groups (n = 16) based on the material utilized for direct pulp capping: MTA, HPE, and Teflon as the negative control group. All involved teeth were capped and restored at the same session. Each group was subsequently divided into two subgroups (n = 8) based on the post treatment evaluation period: 2 and 4 weeks. The histopathologic changes in each specimen's pulp tissues, including pulp inflammation, hyperemia, necrosis, and dentin bridge development, were assessed. Then, all the data were statistically analyzed using chi-square, t-test, and one-way analysis of variance (p < 0.05).

RESULTS

 At 2 weeks, chronic inflammation was observed in 100% of MTA and 50% of HPE subgroups with a significant difference between them whereas the remaining 50% exhibited no inflammation. In contrast to Teflon that showed acute inflammation, remission of inflammation was time-dependent at both MTA and HPE subgroups as there was a substantial difference between the 2- and 4-weeks evaluation periods within the same group. However, throughout the initially observed 2 weeks, all subgroups exhibited essentially no complete calcified bridge; at 4 weeks, all MTA and HPE subgroups developed dentin bridge formation, with a significant difference between them regarding its thickness.

CONCLUSION

 HPE is a promising pulp-capping material inducing less intense chronic inflammation accompanied with thicker dentine bridge formation in comparison to MTA.

Calcium-sensing receptor regulates the angiogenic differentiation of LPS-treated human dental pulp cells via the phosphoinositide 3-kinase/Akt pathway in vitro

AIM

The purpose of this study was to investigate the role of calcium-sensing receptor (CaSR) in the angiogenic differentiation of lipopolysaccharide (LPS)-treated human dental pulp cells (hDPCs).

METHODOLOGY

The LPS-induced hDPCs were cultured in the medium with different combinations of CaSR agonist R568 and antagonist Calhex231. The cell proliferation, migration, and angiogenic capacity were measured by Cell Counting Kit-8 (CCK-8), scratch wound healing, and tube formation assays, respectively. Enzyme-linked immunosorbent assay (ELISA), quantitative real-time polymerase chain reaction (qRT-PCR), and western blot were conducted to determine the gene/protein expression of CaSR, inflammatory mediators, and angiogenic-associated markers. The activation of phosphoinositide 3-kinase (PI3K) and protein kinase B (Akt) was assessed by western blot analysis.

RESULTS

The cell proliferation was elevated in response to R568 or Calhex231 exposure, but an enhanced cell migration was only found in cultures supplemented with Calhex231. Furthermore, R568 was found to potentiate the formation of vessel-like structure, up-regulated the protein expression of tumour necrosis factor (TNF)-α, vascular endothelial growth factor (VEGF), and stromal cell-derived factor (SDF)-1; comparable influences were also observed in R568-stimulated cells in the presence of PI3K inhibitor LY294002. In contrast, Calhex231 obviously inhibited the tube formation and VEGF protein level, whereas promoted the production of IL-6, TNF-α, and eNOS; however, in the presence of LY294002, Calhex231 showed a significant promotion on the protein expression of CaSR, VEGF, and SDF-1. In addition, R568 exhibited a promotive action on the Akt phosphorylation, which can be reversed by LY294002.

CONCLUSIONS

Our results demonstrated that CaSR can regulate the angiogenic differentiation of LPS-treated hDPCs with an involvement of the PI3K/Akt signalling pathway.

Regenerative application of oral and maxillofacial 3D organoids based on dental pulp stem cell

Dental pulp stem cells (DPSCs) originate from the neural crest and the present mesenchymal phenotype showed self-renewal capabilities and can differentiate into at least three lineages. DPSCs are easily isolated with minimal harm, no notable ethical constraints, and without general anesthesia to the donor individuals. Furthermore, cryopreservation of DPSCs provides this opportunity for autologous transplantation in future studies without fundamental changes in stemness, viability, proliferation, and differentiating features. Current approaches for pulp tissue regeneration include pulp revascularization, cell-homing-based regenerative endodontic treatment (RET), cell-transplantation-based regenerative endodontic treatment, and allogeneic transplantation. In recent years, a novel technology, organoid, provides a mimic physiological condition and tissue construct that can be applied for tissue engineering, genetic manipulation, disease modeling, single-cell high throughput analysis, living biobank, cryopreserving and maintaining cells, and therapeutic approaches based on personalized medicine. The organoids can be a reliable preclinical prediction model for evaluating cell behavior, monitoring drug response or resistance, and comparing healthy and pathological conditions for therapeutic and prognostic approaches. In the current review, we focused on the promising application of 3D organoid technology based on DPSCs in oral and maxillofacial tissue regeneration. We discussed encountering challenges and limitations, and found promising solutions to overcome obstacles.

Providing biomimetic microenvironment for pulp regeneration via hydrogel-mediated sustained delivery of tissue-specific developmental signals

Regenerative endodontic therapy is a promising approach to restore the vitality of necrotic teeth, however, pulp regeneration in mature permanent teeth remains a substantial challenge due to insufficient developmental signals. The dentin is embryologically and histologically similar to the pulp, which contains a cocktail of pulp-specific structural proteins and growth factors, thus we proposed an optimizing strategy to obtain dentin matrix extracted proteins (DMEP) and engineered a DMEP functionalized double network hydrogel, whose physicochemical property was tunable by adjusting polymer concentrations to synchronize with regenerated tissues. In vitro models showed that the biomimetic hydrogel with sustained release of DMEP provided a beneficial microenvironment for the encapsulation, propagation and migration of human dental pulp stem cells (hDPSCs). The odontogenic and angiogenic differentiation of hDPSCs were enhanced as well. To elicit the mechanism hidden in the microenvironment to guide cell fate, RNA sequencing was performed and 109 differential expression of genes were identified, the majority of which enriched in cell metabolism, cell differentiation and intercellular communications. The involvement of ERK, p38 and JNK MAPK signaling pathways in the process was confirmed. Of note, in vivo models showed that the injectable and in situ photo-crosslinkable hydrogel was user-friendly for root canal systems and was capable of inducing the regeneration of highly organized and vascularized pulp-like tissues in root segments that subcutaneously implanted into nude mice. Taken together, this study reported a facile and efficient way to fabricate a cell delivery hydrogel with pulp-specific developmental cues, which exhibited promising application and translation potential in future regenerative endodontic fields.

[Advances in Molecular Regulatory Mechanisms of Jaw Repair and Reconstruction]

Jawbone injuries resulting from trauma, diseases, and surgical resections are commonly seen in clinical practice, necessitating precise and effective strategies for repair and reconstruction to restore both function and aesthetics. The precise and effective repair and the reconstruction of jawbone injuries pose a significant challenge in the field of oral and maxillofacial surgery, owing to the unique biomechanical characteristics and physiological functions of the jawbone. The natural repair process following jawbone injuries involves stages such as hematoma formation, inflammatory response, ossification, and bone remodeling. Bone morphogenetic proteins (BMPs), transforming growth factor beta (TGF-β), vascular endothelial growth factor (VEGF), and other growth factors play crucial roles in promoting jawbone regeneration. Cytokines such as interleukins and tumor necrosis factor play dual roles in regulating inflammatory response and bone repair. In recent years, significant progress in molecular biology research has been made in the field of jawbone repair and reconstruction. Tissue engineering technologies, including stem cell therapy, bioactive scaffolds, and growth factor delivery systems, have found important applications in jawbone repair. However, the intricate molecular regulatory mechanisms involved in the complex jawbone repair and reconstruction methods are not fully understood and still require further research. Future research directions will be focused on the precise control of these molecular processes and the development of more efficient combination therapeutic strategies to promote the effective and functional reconstruction of the jawbone. This review aims to examine the latest findings on the molecular regulatory mechanisms of the repair and reconstruction of jawbone injuries and the therapeutic strategies. The conclusions drawn in this article provide a molecular-level understanding of the repair of jawbone injuries and highlight potential directions for future research.