Effects of Cellular Senescence on Dental Follicle Cells

RUNX2 mutation inhibits the cellular senescence of dental follicle cells via ERK signalling pathway

OBJECTIVE

The aim of this study was to explore the regulatory effect of RUNX2 mutation on dental follicle cells (DFCs) senescence and clarify the underlying mechanism. This study aimed to explore the basis for a novel mechanism of delayed permanent tooth eruption in cleidocranial dysplasia (CCD) patients.

MATERIALS AND METHODS

Dental follicles were collected from a CCD patient and healthy controls. Senescence-associated β-galactosidase (SA-β-gal) staining, Ki67 staining, cell cycle assays, and senescence-related gene and protein expression assays were performed to assess DFCs senescence. Western blotting was performed to detect the activation of mitogen-activated protein kinase (MAPK) signalling pathways, and the molecular mechanism underlying RUNX2 regulating in DFCs senescence was explored.

RESULTS

RUNX2 mutation inhibited the cellular senescence of DFCs from the CCD patient compared with healthy controls. Ki67 staining showed that mutant RUNX2 promoted DFCs proliferation, and cell cycle assays revealed that the healthy control-derived DFCs arrested at G1 phase. RUNX2 mutation significantly downregulated senescence-associated gene and protein expression. RUNX2 mutation suppressed ERK signalling pathway activation, an ERK inhibitor decreased healthy control-derived DFCs senescence, and an ERK activator promoted CCD patient-derived DFCs senescence.

CONCLUSIONS

RUNX2 mutation delayed DFCs senescence through the ERK signalling pathway, which may be responsible for delayed permanent tooth eruption in CCD patients.

Mesenchymal Stromal Cells Derived from Dental Tissues: Immunomodulatory Properties and Clinical Potential

Mesenchymal stem/stromal cells (MSCs) are multipotent cells located in different areas of the human body. The oral cavity is considered a potential source of MSCs because they have been identified in several dental tissues (D-MSCs). Clinical trials in which cells from these sources were used have shown that they are effective and safe as treatments for tissue regeneration. Importantly, immunoregulatory capacity has been observed in all of these populations; however, this function may vary among the different types of MSCs. Since this property is of clinical interest for cell therapy protocols, it is relevant to analyze the differences in immunoregulatory capacity, as well as the mechanisms used by each type of MSC. Interestingly, D-MSCs are the most suitable source for regenerating mineralized tissues in the oral region. Furthermore, the clinical potential of D-MSCs is supported due to their adequate capacity for proliferation, migration, and differentiation. There is also evidence for their potential application in protocols against autoimmune diseases and other inflammatory conditions due to their immunosuppressive capacity. Therefore, in this review, the immunoregulatory mechanisms identified at the preclinical level in combination with the different types of MSCs found in dental tissues are described, in addition to a description of the clinical trials in which MSCs from these sources have been applied.

Curcumin attenuates replicative senescence in human dental follicle cells and restores their osteogenic differentiation

OBJECTIVE

This study aimed to examine the therapeutic effects of curcumin against replicative senescence in dental follicle cells (DFCs).

METHODS

Human DFCs were cultured in Dulbecco's Modified Eagle Medium with growth supplements. Replicative senescence in DFCs at different passages was assessed using β-galactosidase activity assay. Cell proliferation and size of DFCs at different passages were determined by CCK-8 kit and microscopy method, respectively. In addition, curcumin's effect on replicative senescence, cell proliferation, and size of DFCs at different passages was analyzed. Using western-blot analysis and siRNA-mediated gene silencing, we determined the molecular mechanisms involved in curcumin's effect against replicative senescence and osteogenic differentiation in DFCs at different passages.

RESULTS

We observed decreased proliferation and increased cell size and replicative senescence in cultured human DFCs at higher passages. Intriguingly, despite not showing any effect on cell size, curcumin (50 μM) significantly restored proliferation ability in DFCs and inhibited their replicative senescence. Concerning mechanisms, we found that curcumin inhibits replicative senescence in DFCs via down-regulation of senescence markers (P16 & P21) and restoration of proliferation markers (E2F1 & P53). Additionally, curcumin also rescued the osteogenic differentiation potential in higher-passage DFCs via restoration of osteogenic markers RUNX2 and OPN.

CONCLUSION

Our findings reveal for the first time that curcumin could act as a potential anti-senescence therapeutic for DFCs via regulation of proliferation, senescence, and osteogenic differentiation markers.

Evaluation of Current Studies to Elucidate Processes in Dental Follicle Cells Driving Osteogenic Differentiation

When research on osteogenic differentiation in dental follicle cells (DFCs) began, projects focused on bone morphogenetic protein (BMP) signaling. The BMP pathway induces the transcription factor DLX3, whichh in turn induces the BMP signaling pathway via a positive feedback mechanism. However, this BMP2/DLX3 signaling pathway only seems to support the early phase of osteogenic differentiation, since simultaneous induction of BMP2 or DLX3 does not further promote differentiation. Recent data showed that inhibition of classical protein kinase C (PKCs) supports the mineralization of DFCs and that osteogenic differentiation is sensitive to changes in signaling pathways, such as protein kinase B (PKB), also known as AKT. Small changes in the lipidome seem to confirm the participation of AKT and PKC in osteogenic differentiation. In addition, metabolic processes, such as fatty acid biosynthesis, oxidative phosphorylation, or glycolysis, are essential for the osteogenic differentiation of DFCs. This review article attempts not only to bring the various factors into a coherent picture of osteogenic differentiation in DFCs, but also to relate them to recent developments in other types of osteogenic progenitor cells.

Immortalized cell lines derived from dental/odontogenic tissue

Stem cells derived from dental/odontogenic tissue have the property of multiple differentiation and are prospective in tooth regenerative medicine and cellular and molecular studies. However, in the face of cellular senescence soon in vitro, the proliferation ability of the cells is limited, so studies are hindered to some extent. Fortunately, immortalization strategies are expected to solve the above issues. Cellular immortalization is that cells are immortalized by introducing oncogenes, human telomerase reverse transcriptase genes (hTERT), or miscellaneous immortalization genes to get unlimited proliferation. At present, a variety of immortalized stem cells from dental/odontogenic tissue has been successfully generated, such as dental pulp stem cells (DPSCs), periodontal ligament cells (PDLs), stem cells from human exfoliated deciduous teeth (SHEDs), dental papilla cells (DPCs), and tooth germ mesenchymal cells (TGMCs). This review summarized establishment and applications of immortalized stem cells from dental/odontogenic tissues and then discussed the advantages and challenges of immortalization.

DNA protein kinase promotes cellular senescence in dental follicle cells

OBJECTIVE

Short telomeres and genomic DNA damage are causes of cellular senescence in dental follicle cells (DFCs).

DESIGN

This study examined the role of the DNA damage response (DDR) during cellular senescence of DFCs by β-galactosidase activity and DNA damage by comet assay. Expression of genes/proteins was determined by Western Blots and reverse transcription-quantitative polymerase chain reaction, while glycolysis was enzymatically estimated. Cell cycle stages and reactive oxygen species (ROS) were investigated by flow cytometry.

RESULTS

During the induction of cellular senescence gene expression of DDR genes were down-regulated, while DNA double-strand breaks occurred at the same time. Furthermore, inhibition of DNA protein kinase (DNA-PK) reduced senescence and ROS, both of which are associated with cellular senescence. In contrast, while these data suggest that inhibition of DDR is associated with the induction of cellular senescence, inhibition of DNA-PK did not result in renewal of DFCs, as inhibition resulted in typical features of depleted cells such as increased cell size and reduced cell proliferation rate. DNA-PK repression inhibited both osteogenic differentiation potential and glycolysis, which are typical features of cellular exhaustion. Moreover, DNA-PK affects cellular senescence via activation of AKT1 (protein kinase B).

CONCLUSION

Our results suggest that DNA-PK promotes cellular senescence, but DFCs may control the induction of cellular senescence via down-regulation of DDR genes. However, we also showed that inhibition of DNA-PK cannot renew senescent DFCs.

Changes in AMPK activity induces cellular senescence in human dental follicle cells

Dental Follicle Cells (DFCs) are somatic stem cells with a limited lifespan, but little is known about a possible mechanism of cellular senescence. Previous studies have shown that cellular senescence is associated with increased demand of glycolsis or the "glycolytic metabotype", which can be induced by activation of 5' adenosine monophosphate-activated protein kinase (AMPK), and decreased autophagy. This study examined the role of AMPK in inducing senescence in DFCs. During the induction of cellular senescence, AMPK activity was impaired, suggesting a negative impact on senescence induction. In line with this assumption, cellular senescence was induced upon inhibition of AMPK with a specific siRNA. In addition, after this inhibition, autophagy was also inhibited. Moreover, specific inhibition of autophagy promoted cellular senescence. However, inducers of AMPK such as metformin or AICAR surprisingly increased senescence in DFCs. Interestingly, autophagy was impaired after long-term induction of AMPK with AICAR and metformin. Moreover, activation of AMPK induces the consumption of glucose but decreases NAD/NADH ratio in DFCs that suggest not only "glycolytic metabotype" of DFCs but also Mitochondrial Dysfunction Associated Senescence (MiDAS). Both changes are highly associated with the induction of cellular senescence. Hence, both AMPK activation and inhibition promote the induction of cellular senecence of DFCs.

Senescence-associated secretory phenotype and its impact on oral immune homeostasis

The senescence-associated secretory phenotype (SASP), which accumulates over the course of normal aging and in age-related diseases, is a crucial driver of chronic inflammation and aging phenotypes. It is also responsible for the pathogenesis of multiple oral diseases. However, the pathogenic mechanism underlying SASP has not yet been fully elucidated. Here, relevant articles on SASP published over the last five years (2017-2022) were retrieved and used for bibliometric analysis, for the first time, to examine SASP composition. More than half of the relevant articles focus on various cytokines (27.5%), growth factors (20.9%), and proteases (20.9%). In addition, lipid metabolites (13.1%) and extracellular vesicles (6.5%) have received increasing attention over the past five years, and have been recognized as novel SASP categories. Based on this, we summarize the evidences demonstrating that SASP plays a pleiotropic role in oral immunity and propose a four-step hypothetical framework for the progression of SASP-related oral pathology-1) oral SASP development, 2) SASP-related oral pathological alterations, 3) pathological changes leading to oral immune homeostasis disruption, and 4) SASP-mediated immune dysregulation escalating oral disease. By targeting specific SASP factors, potential therapies can be developed to treat oral and age-related diseases.

Mechanisms during Osteogenic Differentiation in Human Dental Follicle Cells

Human dental follicle cells (DFCs) as periodontal progenitor cells are used for studies and research in regenerative medicine and not only in dentistry. Even if innovative regenerative therapies in medicine are often considered the main research area for dental stem cells, these cells are also very useful in basic research and here, for example, for the elucidation of molecular processes in the differentiation into mineralizing cells. This article summarizes the molecular mechanisms driving osteogenic differentiation of DFCs. The positive feedback loop of bone morphogenetic protein (BMP) 2 and homeobox protein DLX3 and a signaling pathway associated with protein kinase B (AKT) and protein kinase C (PKC) are presented and further insights related to other signaling pathways such as the WNT signaling pathway are explained. Subsequently, some works are presented that have investigated epigenetic modifications and non-coding ncRNAs and their connection with the osteogenic differentiation of DFCs. In addition, studies are presented that have shown the influence of extracellular matrix molecules or fundamental biological processes such as cellular senescence on osteogenic differentiation. The putative role of factors associated with inflammatory processes, such as interleukin 8, in osteogenic differentiation is also briefly discussed. This article summarizes the most important insights into the mechanisms of osteogenic differentiation in DFCs and is intended to be a small help in the direction of new research projects in this area.

Dental Pulp Stem Cell-Derived Secretome and Its Regenerative Potential

The therapeutic potential of the dental pulp stem (DSC) cell-derived secretome, consisting of various biomolecules, is undergoing intense research. Despite promising in vitro and in vivo studies, most DSC secretome-based therapies have not been implemented in human medicine because the paracrine effect of the bioactive factors secreted by human dental pulp stem cells (hDPSCs) and human exfoliated deciduous teeth (SHEDs) is not completely understood. In this review, we outline the current data on the hDPSC- and SHED-derived secretome as a potential candidate in the regeneration of bone, cartilage, and nerve tissue. Published reports demonstrate that the dental MSC-derived secretome/conditional medium may be effective in treating neurodegenerative diseases, neural injuries, cartilage defects, and repairing bone by regulating neuroprotective, anti-inflammatory, antiapoptotic, and angiogenic processes through secretome paracrine mechanisms. Dental MSC-secretomes, similarly to the bone marrow MSC-secretome activate molecular and cellular mechanisms, which determine the effectiveness of cell-free therapy. Many reports emphasize that dental MSC-derived secretomes have potential application in tissue-regenerating therapy due to their multidirectional paracrine effect observed in the therapy of many different injured tissues.

Stem Cells and Their Derivatives-Implications for Alveolar Bone Regeneration: A Comprehensive Review

Oral and craniofacial bone defects caused by congenital disease or trauma are widespread. In the case of severe alveolar bone defect, autologous bone grafting has been considered a “gold standard”; however, the procedure has several disadvantages, including limited supply, resorption, donor site morbidity, deformity, infection, and bone graft rejection. In the last few decades, bone tissue engineering combined with stem cell-based therapy may represent a possible alternative to current bone augmentation techniques. The number of studies investigating different cell-based bone tissue engineering methods to reconstruct alveolar bone damage is rapidly rising. As an interdisciplinary field, bone tissue engineering combines the use of osteogenic cells (stem cells/progenitor cells), bioactive molecules, and biocompatible scaffolds, whereas stem cells play a pivotal role. Therefore, our work highlights the osteogenic potential of various dental tissue-derived stem cells and induced pluripotent stem cells (iPSCs), the progress in differentiation techniques of iPSCs into osteoprogenitor cells, and the efforts that have been made to fabricate the most suitable and biocompatible scaffold material with osteoinductive properties for successful bone graft generation. Moreover, we discuss the application of stem cell-derived exosomes as a compelling new form of “stem-cell free” therapy.

Angiogenesis in Regenerative Dentistry: Are We Far Enough for Therapy?

Angiogenesis is a broad spread term of high interest in regenerative medicine and tissue engineering including the dental field. In the last two decades, researchers worldwide struggled to find the best ways to accelerate healing, stimulate soft, and hard tissue remodeling. Stem cells, growth factors, pathways, signals, receptors, genetics are just a few words that describe this area in medicine. Dental implants, bone and soft tissue regeneration using autologous grafts, or xenografts, allografts, their integration and acceptance rely on their material properties. However, the host response, through its vascularization, plays a significant role. The present paper aims to analyze and organize the latest information about the available dental stem cells, the types of growth factors with pro-angiogenic effect and the possible therapeutic effect of enhanced angiogenesis in regenerative dentistry.