Stathmin inhibits proliferation and differentiation of dental pulp stem cells via sonic hedgehog/Gli

Odontoblasts release exosomes to regulate the odontoblastic differentiation of dental pulp stem cells

BACKGROUND

Dental pulp stem cells (DPSCs) play a crucial role in dentin-pulp complex regeneration. Further understanding of the mechanism by which DPSCs remain in a quiescent state could contribute to improvements in the dentin-pulp complex and dentinogenesis.

METHODS

TSC1 conditional knockout (DMP1-Cre+; TSC1f/f, hereafter CKO) mice were generated to increase the activity of mechanistic target of rapamycin complex 1 (mTORC1). H&E staining, immunofluorescence and micro-CT analysis were performed with these CKO mice and littermate controls. In vitro, exosomes were collected from the supernatants of MDPC23 cells with different levels of mTORC1 activity and then characterized by transmission electron microscopy and nanoparticle tracking analysis. DPSCs were cocultured with MDPC23 cells and MDPC23 cell-derived exosomes. Alizarin Red S staining, ALP staining, qRT‒PCR, western blotting analysis and micro-RNA sequencing were performed.

RESULTS

Our study showed that mTORC1 activation in odontoblasts resulted in thicker dentin and higher dentin volume/tooth volume of molars, and it increased the expression levels of the exosome markers CD63 and Alix. In vitro, when DPSCs were cocultured with MDPC23 cells, odontoblastic differentiation was inhibited. However, the inhibition of odontoblastic differentiation was reversed when DPSCs were cocultured with MDPC23 cells with mTORC1 overactivation. To further study the effects of mTORC1 on exosome release from odontoblasts, MDPC23 cells were treated with rapamycin or shRNA-TSC1 to inactivate or activate mTORC1, respectively. The results revealed that exosome release from odontoblasts was negatively correlated with mTORC1 activity. Moreover, exosomes derived from MDPC23 cells with active or inactive mTORC1 inhibited the odontoblastic differentiation of DPSCs at the same concentration. miRNA sequencing analysis of exosomes that were derived from shTSC1-transfected MDPC23 cells, rapamycin-treated MDPC23 cells or nontreated MDPC23 cells revealed that the majority of the miRNAs were similar among these groups. In addition, exosomes derived from odontoblasts inhibited the odontoblastic differentiation of DPSCs, and the inhibitory effect was positively correlated with exosome concentration.

CONCLUSION

mTORC1 regulates exosome release from odontoblasts to inhibit the odontoblastic differentiation of DPSCs, but it does not alter exosomal contents. These findings might provide a new understanding of dental pulp complex regeneration.

Degradable hydrogel fibers encapsulate and deliver metformin and periodontal ligament stem cells for dental and periodontal regeneration

Human periodontal ligament stem cells (hPDLSCs) are promising cells for dental and periodontal regeneration. This study aimed to develop novel alginate-fibrin fibers that encapsulates hPDLSCs and metformin, to investigate the effect of metformin on the osteogenic differentiation of hPDLSCs, and to determine the regulatory role of the Shh/Gli1 signaling pathway in the metformin-induced osteogenic differentiation of hPDLSCs for the first time. CCK8 assay was used to evaluate hPDLSCs. Alkaline phosphatase (ALP) staining, alizarin red S staining, and the expression of osteogenic genes were evaluated. Metformin and hPDLSCs were encapsulated in alginate-fibrinogen solutions, which were injected to form alginate-fibrin fibers. The activation of Shh/Gli1 signaling pathway was examined using qRT-PCR and western blot. A mechanistic study was conducted by inhibiting the Shh/Gli1 pathway using GANT61. The administration of 50 μM metformin resulted in a significant upregulation of osteogenic gene expression in hPDLSCs by 1.4-fold compared to the osteogenic induction group (P < 0.01), including ALP and runt-related transcription factor-2 (RUNX2). Furthermore, metformin increased ALP activity by 1.7-fold and bone mineral nodule formation by 2.6-fold (P<0.001). We observed that hPDLSCs proliferated with the degradation of alginate-fibrin fibers, and metformin induced their differentiation into the osteogenic lineage. Metformin also promoted the osteogenic differentiation of hPDLSCs by upregulating the Shh/Gli1 signaling pathway by 3- to 6- fold compared to the osteogenic induction group (P<0.001). The osteogenic differentiation ability of hPDLSCs were decreased 1.3- to 1.6-fold when the Shh/Gli1 pathway was inhibited, according to ALP staining and alizarin red S staining (P<0.01). Metformin enhanced the osteogenic differentiation of hPDLSCs via the Shh/Gli1 signaling pathway. Degradable alginate-fibrin hydrogel fibers encapsulating hPDLSCs and metformin have significant potential for use in dental and periodontal tissue engineering applications. Alginate-fibrin fibers encapsulating hPDLSCs and metformin have a great potential for use in the treatment of maxillofacial bone defects caused by trauma, tumors, and tooth extraction. Additionally, they may facilitate the regeneration of periodontal tissue in patients with periodontitis.

CGRP and Shh Mediate the Dental Pulp Cell Response to Neuron Stimulation

Dental pain is a persistent, detrimental public health issue that requires a better understanding of the mechanisms of tooth pain and inflammation in order to develop more effective treatments. Calcitonin gene-related peptide (CGRP) and dental pulp cells are promising candidates for mediating tooth pain and generating reparative dental tissues, respectively, but their behavior in the context of pulpitis remains elusive. The mouse incisor requires Sonic hedgehog (Shh) secreted from sensory nerves to continuously regenerate. However, it is unknown whether sensory nerves also regulate the comparatively nonregenerative mouse molar through CGRP and Shh. This is an important knowledge gap to fill since mouse incisors differ biologically from human teeth, while mouse and human molars are similar. In this work, we identified that molar pulp cells express CGRP receptor and Gli1, a Hedgehog (Hh) signaling protein found to label a dental stem cell population in the mouse incisor. We also observed in a mouse molar injury model that Hh signaling was activated and Shh expression was upregulated in vivo. We then determined in vitro that Shh and CGRP regulate differentiation of primary mouse molar and incisor pulp cells and a human dental pulp stem cell line. Furthermore, conditioned media from stimulated sensory neurons induced Hh signaling activation and inflammatory gene expression in primary molar pulp cells, which was abolished by inhibition of either Shh or CGRP. Our results suggest that CGRP and Shh signaling may promote an inflammatory response after injury in the molar and that activated sensory nerves secrete CGRP and Shh to regulate molar pulp cell expansion and differentiation into odontoblast-like cells for dentin repair. Thus, CGRP/Shh signaling should be considered for new strategies that seek to manage pain or dentin regeneration in the molar.

mTORC1 promotes mineralization via p53 pathway

The objectives of our study were to investigate the roles of mTORC1 in odontoblast proliferation and mineralization and to determine the mechanism by which mTORC1 regulates odontoblast mineralization. In vitro, MDPC23 cells were treated with rapamycin (10 nmol/L) and transfected with a lentivirus for short hairpin (shRNA)-mediated silencing of the tuberous sclerosis complex (shTSC1) to inhibit and activate mTORC1, respectively. CCK8 assays, flow cytometry, Alizarin red S staining, ALP staining, qRT-PCR, and western blot analysis were performed. TSC1-conditional knockout (DMP1-Cre⁺ ; TSC1^f/f , hereafter CKO) mice and littermate control (DMP1-Cre^- ; TSC1^f/f , hereafter WT) mice were generated. H&E staining, immunofluorescence, and micro-CT analysis were performed. Transcriptome sequencing analysis was used to screen the mechanism of this process. mTORC1 inactivation decreased the cell proliferation. The qRT-PCR and western blot results showed that mineralization-related genes and proteins were downregulated in mTORC1-inactivated cells. Moreover, mTORC1 overactivation promoted cell proliferation and mineralization-related gene and protein expression. In vivo, the micro-CT results showed that DV/TV and dentin thickness were higher in CKO mice than in controls and H&E staining showed the same results. Mineralization-related proteins expression was upregulated. Transcriptome sequencing analysis revealed that p53 pathway-associated genes were differentially expressed in TSC1-deficient cells. By inhibiting p53 alone or both mTORC1 and p53 with rapamycin and a p53 inhibitor, we elucidated that p53 acts downstream of mTORC1 and that mTORC1 thereby promotes odontoblast mineralization. Taken together, our findings demonstrate that the role of mTORC1 in odontoblast proliferation and mineralization, and confirm that mTORC1 upregulates odontoblast mineralization via the p53 pathway.

Multidifferentiation potential of dental-derived stem cells

Tooth-related diseases and tooth loss are widespread and are a major public health issue. The loss of teeth can affect chewing, speech, appearance and even psychology. Therefore, the science of tooth regeneration has emerged, and attention has focused on tooth regeneration based on the principles of tooth development and stem cells combined with tissue engineering technology. As undifferentiated stem cells in normal tooth tissues, dental mesenchymal stem cells (DMSCs), which are a desirable source of autologous stem cells, play a significant role in tooth regeneration. Researchers hope to reconstruct the complete tooth tissues with normal functions and vascularization by utilizing the odontogenic differentiation potential of DMSCs. Moreover, DMSCs also have the ability to differentiate towards cells of other tissue types due to their multipotency. This review focuses on the multipotential capacity of DMSCs to differentiate into various tissues, such as bone, cartilage, tendon, vessels, neural tissues, muscle-like tissues, hepatic-like tissues, eye tissues and glands and the influence of various regulatory factors, such as non-coding RNAs, signaling pathways, inflammation, aging and exosomes, on the odontogenic/osteogenic differentiation of DMSCs in tooth regeneration. The application of DMSCs in regenerative medicine and tissue engineering will be improved if the differentiation characteristics of DMSCs can be fully utilized, and the factors that regulate their differentiation can be well controlled.

Exosomes from LPS-Stimulated hDPSCs Activated the Angiogenic Potential of HUVECs In Vitro

Background

Exosomes from human dental pulp stem cells (hDPSCs) were indicated to play a positive role in vascular regeneration processes. But the angiogenic capabilities of exosomes from inflammatory hDPSCs and the underlying mechanism remain unknown. In this study, the inflammatory factor lipopolysaccharide (LPS) was used to stimulate hDPSCs, and exosomes were extracted from these hDPSCs. The proangiogenic potential of exosomes was examined, and the underlying mechanism was studied.

Method

Exosomes were isolated from hDPSCs with or without LPS stimulation (N-EXO and LPS-EXO) and cocultured with human umbilical vein endothelial cells (HUVECs). The proangiogenic potential of exosomes was evaluated by endothelial cell proliferation, migration, and tube formation abilities in vitro. To investigate the proangiogenic mechanism of LPS-EXO, microRNA sequencing was performed to explore the microRNA profile of N-EXO and LPS-EXO. Gene Ontology (GO) analysis was used to study the functions of the predicted target genes. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis was used to estimate the signaling pathways associated with the inflammation-induced angiogenesis process.

Result

Compared to the uptake of N-EXO, uptake of LPS-EXO activated the angiogenic potential of HUVECs by promoting the proliferation, migration, and tube formation abilities in vitro. The mRNA expression levels of vascular endothelial growth factor (VEGF) and kinase-insert domain-containing receptor (KDR) in the LPS-EXO group were significantly higher than those in the N-EXO group. MicroRNA sequencing showed that 10 microRNAs were significantly changed in LPS-EXO. Pathway analysis showed that the genes targeted by differentially expressed microRNAs were involved in multiple angiogenesis-related pathways.

Conclusion

This study revealed that exosomes derived from inflammatory hDPSCs possessed better proangiogenic potential in vitro. This is the first time to explore the role of exosomal microRNA from hDPSCs in inflammation-induced angiogenesis. This finding sheds new light on the effect of inflammation-stimulated hDPSCs on tissue regeneration.

Long non-coding RNA maternally expressed gene 3 inhibits osteogenic differentiation of human dental pulp stem cells via microRNA-543/smad ubiquitin regulatory factor 1/runt-related transcription factor 2 axis

OBJECTIVE

The aim of the present study was to investigate the biological roles and underlying mechanism of the long non-coding RNA maternally expressed gene 3 (MEG3) on osteogenic differentiation of human dental pulp stem cells (hDPSCs).

METHODS

The expression levels of MEG3, microRNA-543 (miR-543), osterix, osteopontin, osteocalcin and runt-related transcription factor 2 (RUNX2) were measured by quantitative real-time PCR (qRT-PCR). Alkaline phosphatase (ALP) activity assay and alizarin red S staining (ARS) were used to measure the impacts exerted by MEG3, miR-543 on osteogenic differentiation. Cell proliferation was measured by MTT assay. In addition, the targeted relationships between miR-543, MEG3, and Smad ubiquitin regulatory factor 1 (SMURF1) were assessed through dual luciferase reporter assay.

RESULTS

During osteogenic induction, the expression of MEG3 was gradually reduced, whereas the expression of miR-543, osterix, osteopontin, osteocalcin and RUNX2 were gradually increased. Functional analysis implied that MEG3 overexpression or miR-543 inhibition reduced the cell proliferation, ALP activity, ARS levels, and decreased the expression of osteoblast-related proteins. Moreover, MEG3 promoted SMURF1 expression by directly targeting miR-543 as a competing endogenous RNA. Furthermore, overexpression of miR-543 or silencing SMURF1 could reverse the inhibitory effects of MEG3 on the osteogenic differentiation of hDPSCs.

CONCLUSIONS

In conclusion, our study revealed that overexpression of MEG3 inhibited hDPSCs osteogenic differentiation via miR-543/SMURF1/RUNX2 regulatory network, which may contribute to the functional regulation and clinical applications of hDPSCs.

Time-Dependent Response of Human Deciduous Tooth-Derived Dental Pulp Cells Treated with TheraCal LC: Functional Analysis of Gene Interactions Compared to MTA

Pulp capping material should facilitate hard tissue regeneration on the injured pulp tissue. TheraCal LC (TC) was recently developed. Although TC has shown reliable clinical outcomes after direct pulp capping, there are still remaining concerns regarding its detrimental effect on pulp cells. Therefore, this study aimed to identify the gene expression of human deciduous tooth-derived dental pulp cells exposed to TC compared to mineral trioxide aggregate (MTA). The cells were cultured and exposed to TC and MTA for 24 and 72 h. Next, total RNA was isolated. QuantSeq 3′ mRNA-sequencing was used to examine differentially expressed genes (DEGs) in exposed to TC and MTA. Functional analysis of DEGs was performed using bioinformatics analysis. In gene ontology (GO) functional enrichment analysis, cells in TC for 24 h presented significantly enriched immune response (p < 0.001) and inflammatory response (p < 0.01) compared to MTA. TC showed enriched positive regulation of cell migration at 72 h (p < 0.001). In Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, neuroactive ligand–receptor interaction (p = 1.19 × 10⁻⁷) and calcium signaling pathway (p = 2.96 × 10⁻⁵) were confirmed in the shared DEGs in TC. In conclusion, DEGs in TC may be involved in pathways associated with osteoclastogenesis and osteoclastic differentiation.

Vacuolar protein sorting 4B regulates the proliferation and odontoblastic differentiation of human dental pulp stem cells through the Wnt-β-catenin signalling pathway

Our previous studies have revealed that a dominant mutation in vacuolar protein sorting 4B (VPS4B), a member of the AAA ATPase family, causes dentin dysplasia type I. The purpose of the present study was to investigate the roles of VPS4B in human dental pulp stem cells (hDPSCs) and to elucidate the underlying molecular mechanisms. In this study, we found that VPS4B was highly expressed in the dental pulp cells of the mouse molar tooth germ, and the expression of VPS4B increased significantly during the odontoblastic differentiation of hDPSCs. VPS4B downregulation inhibited the proliferation, migration, and odontoblastic differentiation of hDPSCs. Moreover, treatment with lithium chloride, an agonist of the Wnt-β-catenin signalling pathway, partially reversed the VPS4B knockdown-driven suppression of proliferation and of odontoblastic differentiation of hDPSCs. Collectively, our findings indicate that VPS4B, via Wnt-β-catenin signalling, acts as a regulator of the proliferation and differentiation of hDPSCs. Our results suggest potential therapeutic avenues for dentin formation and regenerative endodontics in patients with dentin dysplasia type I.

Stathmin inhibits proliferation and differentiation of dental pulp stem cells via sonic hedgehog/Gli

The mineralization of dental pulp stem cells is an important factor in the tissue engineering of teeth, but the mechanism is not yet obvious. This study aimed to identify the effect of Stathmin on the proliferation and osteogenic/odontoblastic differentiation of human dental pulp stem cells (hDPSCs) and to explore whether the Shh signalling pathway was involved in this regulation. First, Stathmin was expressed in the cytoplasm and on the cell membranes of hDPSCs by cell immunofluorescence. Then, by constructing a lentiviral vector, the expression of Stathmin in hDPSCs was inhibited. Treatment with Stathmin shRNA (shRNA‐Stathmin group) inhibited the ability of hDPSCs to proliferate, as demonstrated by a CCK8 assay and flow cytometry analysis, and suppressed the osteogenic/odontoblastic differentiation ability, as demonstrated by alizarin red S staining and osteogenic/odontoblastic differentiation‐related gene (ALP, BSP, OCN, DSPP) activity, compared to that of hDPSCs from the control shRNA group. Molecular analyses showed that the Shh/GLI1 signalling pathway was inhibited when Stathmin was silenced, and purmorphamine, the Shh signalling pathway activator, was added to hDPSCs in the shRNA‐Stathmin group, real‐time PCR and Western blotting confirmed that expression of Shh and its downstream signalling molecules PTCH1, SMO and GLI1 increased significantly. After activating the Shh signalling pathway, the proliferation of hDPSCs increased markedly, as demonstrated by a CCK8 assay and flow cytometry analysis; osteogenic/odontoblastic differentiation‐related gene (ALP, BSP, OCN, DSPP) expression also increased significantly. Collectively, these findings firstly revealed that Stathmin‐Shh/GLI1 signalling pathway plays a positive role in hDPSC proliferation and osteogenic/odontoblastic differentiation.