Short telomeres correlate with a strong induction of cellular senescence in human dental follicle cells

Regulation of self-renewal and senescence in primitive mesenchymal stem cells by Wnt and TGFβ signaling

BACKGROUND

The therapeutic application of multipotent mesenchymal stem cells (MSCs) encounters significant challenges, primarily stemming from their inadequate growth and limited self-renewal capabilities. Additionally, as MSCs are propagated, their ability to self-renew declines, and the exact cellular and molecular changes responsible for this are poorly understood. This study aims to uncover the complex molecular mechanisms that govern the self-renewal of primitive (p) MSCs.

METHODS

We grew pMSCs using two types of medium, fetal bovine serum (FM) and xeno-free (XM), at both low passage (LP, P3) and high passage (HP, P20). To evaluate LP and HP pMSCs, we examined their physical characteristics, cell surface markers, growth rate, colony-forming ability, BrdU assays for proliferation, telomerase activity, and potential to differentiate into three lineages. Moreover, we conducted RNA-seq to analyze their transcriptome and MNase-seq analysis to investigate nucleosome occupancies.

RESULTS

When grown in FM, pMSCs underwent changes in their cellular morphology, becoming larger and elongated. This was accompanied by a decrease in the expression of CD90 and CD49f, as well as a reduction in CFE, proliferation rate, and telomerase activity. In addition, these cells showed an increased tendency to differentiate into the adipogenic lineage. However, when grown in XM, pMSCs maintained their self-renewal capacity and ability to differentiate into multiple lineages while preserving their fibroblastoid morphology. Transcriptomic analysis showed an upregulation of genes associated with self-renewal, cell cycle regulation, and DNA replication in XM-cultured pMSCs, while senescence-related genes were upregulated in FM-cultured cells. Further analysis demonstrated differential nucleosomal occupancies in self-renewal and senescence-related genes for pMSCs grown in XM and FM, respectively. These findings were confirmed by qRT-PCR analysis, which revealed alterations in the expression of genes related to self-renewal, cell cycle regulation, DNA replication, differentiation, and senescence. To understand the underlying mechanisms, we investigated the involvement of Wnt and TGFβ signaling pathways by modulating them with agonists and antagonists. This experimental manipulation led to the upregulation and downregulation of self-renewal genes in pMSCs, providing further insights into the signaling pathways governing the self-renewal and senescence of pMSCs.

CONCLUSION

Our study shows that the self-renewal potential of pMSCs is associated with the Wnt pathway, while senescence is linked to TGFβ.

WNT and VEGF/PDGF signaling regulate self-renewal in primitive mesenchymal stem cells

Background

Therapeutic use of multipotent mesenchymal stem cells (MSCs) is hampered due to poor growth and limited self-renewal potential. The self-renewal potential of MSCs is also affected during propagation and changes are poorly understood. This study investigated the molecular mechanism involved in the self-renewal of primitive (p) MSCs.

Methods

pMSCs were cultured to low passage (LP), P3, and high passage (HP), P20, in fetal bovine serum medium (FM) and xeno-free medium (XM). The characteristics of LP and HP pMSCs were evaluated for morphology, expression of cell surface markers, doubling time (DT), colony forming efficiency (CFE), proliferation by BrdU assay, telomerase activity and trilineage differentiation. We then examined transcriptome and nucleosome occupancies using RNA-seq and MNase-seq, respectively analyses.

Results

pMSCs grown in FM gradually changed morphology to large elongated cells and showed a significant reduction in the expression of CD90 and CD49f, CFE, proliferation, and telomerase activity. In addition, cells had a greater propensity to differentiate into the adipogenic lineage. In contrast, pMSCs grown in XM maintained small fibroblastoid morphology, self-renewal, and differentiation potential. Transcriptomic analysis showed upregulation of genes involved in self-renewal, cell cycle, and DNA replication in XM-grown pMSCs. Whereas senescence genes were upregulated in cells in FM. MNase-seq analysis revealed less nucleosomal occupancies in self-renewal genes and senescence genes in pMSCs grown in XM and FM, respectively. The expression of selected genes associated with self-renewal, cell cycle, DNA replication, differentiation, and senescence was confirmed by qRT-PCR. These results led us to propose signaling pathways involved in the self-renewal and senescence of pMSCs.

Conclusion

We conclude that the self-renewal potential of pMSCs is controlled by WNT and VEGF/PDGF, but TGFβ and PI3K signaling induce senescence.

Comparative characterization and analysis of telomere length in stem cells derived from deciduous and permanent teeth

Background

Understanding the influence of age on growth kinetics and telomere length in dental stem cells is essential for the successful development of cell therapies. Hence, the present study compared the basic cellular and phenotypical characteristics of stem cells from human exfoliated deciduous teeth (SHEDs) and dental pulp stem cells (DPSCs) of permanent teeth and their telomere lengths using quantitative real-time polymerase chain reaction.

Materials and Methods

The study is an in vitro original research article. Primary cultures of SHED and DPSCs (n = 6 each) were successfully established in vitro, and the parameters analyzed were the morphology, viability, proliferation rate, population doubling time (PDT), phenotypic markers expression, and the relative telomere lengths. Data were analyzed by analysis of variance and P < 0.05 was considered statistically significant.

Results

SHED and DPSCs exhibited a small spindle-shaped fibroblast-like morphology with >90% viability. The proliferation assay showed that the cells had a typical growth pattern. The PDT values of SHED and DPSCs were 29.03 ± 9.71 h and 32.05 ± 9.76 h, respectively. Both cells were positive for surface markers CD29, CD44, and CD90. However, they were negative for CD45 and human leukocyte antigen DR. Although the differences in relative telomere lengths between the individual cell lines of SHED and DPSCs were observed, no significant (P > 0.05) variations were found for the mean T/S ratios of both the cells.

Conclusion

SHED and DPSCs displayed similar morphology, proliferation rates, and phenotypic features. The relative telomere lengths were slightly shorter in DPSCs than SHED, but the values were not significantly different. Thus, SHED and DPSCs can be considered as recognized sources for regenerative applications in dentistry.

Investigation of the expression level of long non-coding RNAs in dental follicles of impacted mandibular third molars

OBJECTIVES

Dental follicle (DF) is made up of mesenchymal cells and fibers surrounding the enamel organ of a developing tooth. It has been shown that cystic and neoplastic lesions can develop from the pericoronal follicles of impacted third molars (ITMs). But the molecular transformation of DF tissues has not yet been uncovered and remains elusive. Accordingly, in the present study, we aimed to investigate the differential expression of lncRNA genes in DF tissues associated with asymptomatic impacted mandibular third molars (IMTMs) that do not show pathological pericoronal radiolucency in radiographic examination.

MATERIAL AND METHODS

A total of 30 patients with unilateral mesioangular IMTMs were enrolled for the study. The expressions of lncRNA genes were determined in the DF and healthy gingival tissues obtained from study patients. For the determination of lncRNA expression levels, RNA was isolated from the obtained tissues, converted to cDNA samples, and analyzed by quantitative real-time PCR method.

RESULTS

As a result, we found that the gene expression of MEG3 was increased about 10-fold in DF tissues compared to healthy gingival tissues (p < 0.0001). In addition, NORAD expression was found to be upregulated 4.2-fold (p = 0.0002) in DF tissues. Also, expression level of MALAT1 was found to be decreased 1.24-fold (p = 0.584) and TP73-AS1 increased 2.6-fold (p = 0.093) in DF tissues compared to healthy gingival tissues.

CONCLUSIONS

Consequently, present findings suggest that differentially expressed lncRNAs in DFs might be associated with the various levels of cellular events including osteogenic differentiation, DNA damage, and the transformation into odontogenic pathology.

CLINICAL RELEVANCE

Expression levels of MEG3 and NORAD lncRNA molecules may guide clinicians in the evaluation of asymptomatic ITM dental follicles that cannot be determined radiologically and during extraction of these teeth for prophylactic purposes.

Agarose-based spheroid culture enhanced stemness and promoted odontogenic differentiation potential of human dental follicle cells in vitro

Human dental follicle cells (HDFCs) are an ideal cell source of stem cells for dental tissue repair and regeneration and they have great potential for regenerative medicine applications. However, the conventional monolayer culture usually reduces cell proliferation and differentiation potential due to the continuous passage during in vitro expansion. In this study, primary HDFC spheroids were generated on 1% agarose, and the HDFCs spontaneously formed cell spheroids in the agarose-coated dishes. Compared with monolayer culture, the spheroid-derived HDFCs exhibited increased proliferative ability for later passage HDFCs as analysed by Cell Counting Kit-8 (CCK-8). The transcription-quantitative polymerase chain reaction (qRT-PCR), western blot and immunofluorescence assay showed that the expression of stemness marker genes Sox2, Oct4 and Nanog was increased significantly in the HDFC spheroids. Furthermore, we found that the odontogenic differentiation capability of HDFCs was significantly improved by spheroid culture in the agarose-coated dishes. On the other hand, the osteogenic differentiation capability was weakened compared with monolayer culture. Our results suggest that spheroid formation of HDFCs in agarose-coated dishes partially restores the proliferative ability of HDFCs at later passages, enhances their stemness and improves odontogenic differentiation capability in vitro. Therefore, spheroid formation of HDFCs has great therapeutic potential for stem cell clinical therapy.

Effects of Cellular Senescence on Dental Follicle Cells

The dental follicle is part of the tooth germ, and isolated stem cells from this tissue (dental follicle cells; DFCs) are considered, for example, for regenerative medicine and immunotherapies. However somatic stem cells can also improve pharmaceutical research. Cell proliferation is limited by the induction of senescence, which, while reducing the therapeutic potential of DFCs for cell therapy, can also be used to study aging processes at the cellular level that can be used to test anti-aging pharmaceuticals. Unfortunately, very little is known about cellular senescence in DFCs. This review presents current knowledge about cellular senescence in DFCs.

High endogenous expression of parathyroid hormone-related protein (PTHrP) supports osteogenic differentiation in human dental follicle cells

Dental follicle cells (DFCs) are progenitor cells for mineralizing cells such as alveolar osteoblasts, but little is known about the mechanisms of the differentiation. Interestingly, different cell lines sometimes have different potentials to differentiate into mineralizing cells. In this study, we compared two different DFC lines, with one cell line (DFC_B) showing a high alkaline phosphatase (ALP) activity in long-term cultures with standard medium and a reliable mineralizing potential. However, the other cell line DFC_A shows low ALP activity in standard medium and almost no mineralization. Known osteogenic markers such as RUNX2 were similarly expressed in both cell lines. However, the proosteogenic signaling pathway of the bone morphogenetic protein (BMP) is induced in DFC_B, and the parathyroid hormone-related protein (PTHrP), which is involved in tooth root development, was also expressed more strongly. Previous studies have shown that the secreted PTHrP negatively regulate the transition from pre-osteoblastic progenitors to osteoblasts, but we showed that an inhibition of PTHrP gene expression reduced the ALP activity and the BMP-signaling pathway. In addition, endogenously expressed PTHrP is located in the cell nucleus. In contrast, supplementation of PTHrP or an inhibitor for the PTHrP receptor did not affect the ALP activity of DFC_B. In conclusion, our data suggest that a high endogenous expression of PTHrP in DFCs supports the induction of osteogenic differentiation via an intracrine mode.

Dental Follicle Cells: Roles in Development and Beyond

Dental follicle cells (DFCs) are a group of mesenchymal progenitor cells surrounding the tooth germ, responsible for cementum, periodontal ligament, and alveolar bone formation in tooth development. Cascades of signaling pathways and transcriptional factors in DFCs are involved in directing tooth eruption and tooth root morphogenesis. Substantial researches have been made to decipher multiple aspects of DFCs, including multilineage differentiation, senescence, and immunomodulatory ability. DFCs were proved to be multipotent progenitors with decent amplification, immunosuppressed and acquisition ability. They are able to differentiate into osteoblasts/cementoblasts, adipocytes, neuron-like cells, and so forth. The excellent properties of DFCs facilitated clinical application, as exemplified by bone tissue engineering, tooth root regeneration, and periodontium regeneration. Except for the oral and maxillofacial regeneration, DFCs were also expected to be applied in other tissues such as spinal cord defects (SCD), cardiomyocyte destruction. This article reviewed roles of DFCs in tooth development, their properties, and clinical application potentials, thus providing a novel guidance for tissue engineering.