Impairment of osteocalcin production in senescent periodontal ligament fibroblasts

Annexin A1 protects periodontal ligament cells against lipopolysaccharide-induced inflammatory response and cellular senescence: An implication in periodontitis

Periodontitis is an inflammatory condition that affects the tooth-supporting structures, triggered by the host's immune response toward the bacterial deposits around the teeth. Annexin A1 (AnxA1), a vital member of the annexin superfamily, is known for its diverse physiological functions, particularly its anti-inflammatory and anti-senescence properties. We hypothesized that AnxA1 has a protective effect against lipopolysaccharide (LPS)-induced inflammatory responses and cellular damage in periodontal ligament cells (PDLCs). In this study, we demonstrate that LPS stimulation significantly reduced telomerase activity in PDLCs, a decline that was dose-dependently reversed by AnxA1. Importantly, AnxA1 protected the cells from LPS-induced cellular senescence and the downregulation of human telomerase reverse transcriptase (hTERT) expression. In line with this, AnxA1 suppressed the LPS-induced expression of p21 and p16 at both the mRNA and protein levels. Furthermore, AnxA1 demonstrated potent anti-inflammatory effects by inhibiting the secretion of interleukin 6 (IL-6), interleukin 8 (IL-8), and monocyte chemoattractant protein-1 (MCP-1). It also mitigated LPS-induced oxidative stress by reducing the levels of phosphorylated Foxo3a (Ser253) and restored sirtuin 1 (SIRT1) expression. Notably, SIRT1 silencing abolished AnxA1's protective effects on Foxo3a phosphorylation and cellular senescence, suggesting that SIRT1 mediates AnxA1's actions. In conclusion, AnxA1 protected PDLCs against LPS-triggered inflammation and cell senescence by activating SIRT1 signal pathway. These findings indicate that AnxA1 could serve as a promising therapeutic strategy for the treatment of periodontitis.

Effect of Different Parameters of In Vitro Static Tensile Strain on Human Periodontal Ligament Cells Simulating the Tension Side of Orthodontic Tooth Movement

This study aimed to investigate the effects of different magnitudes and durations of static tensile strain on human periodontal ligament cells (hPDLCs), focusing on osteogenesis, mechanosensing and inflammation. Static tensile strain magnitudes of 0%, 3%, 6%, 10%, 15% and 20% were applied to hPDLCs for 1, 2 and 3 days. Cell viability was confirmed via live/dead cell staining. Reference genes were tested by reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) and assessed. The expressions of TNFRSF11B, ALPL, RUNX2, BGLAP, SP7, FOS, IL6, PTGS2, TNF, IL1B, IL8, IL10 and PGE2 were analyzed by RT-qPCR and/or enzyme-linked immunosorbent assay (ELISA). ALPL and RUNX2 both peaked after 1 day, reaching their maximum at 3%, whereas BGLAP peaked after 3 days with its maximum at 10%. SP7 peaked after 1 day at 6%, 10% and 15%. FOS peaked after 3 days with its maximum at 3%, 6% and 15%. The expressions of IL6 and PTGS2 both peaked after 1 day, with their minimum at 10%. PGE2 peaked after 1 day (maximum at 20%). The ELISA of IL6 peaked after 3 days, with the minimum at 10%. In summary, the lower magnitudes promoted osteogenesis and caused less inflammation, while the higher magnitudes inhibited osteogenesis and enhanced inflammation. Among all magnitudes, 10% generally caused a lower level of inflammation with a higher level of osteogenesis.

Metformin prevents against oxidative stress-induced senescence in human periodontal ligament cells

Periodontitis is a chronic infectious disease involving periodontal tissues. Periodontal ligament cells (PDLCs) play an important role in the regeneration of periodontal tissue. However, senescent PDLCs have an impeded regenerative potential. Metformin has been reported to prevent senescence at both the cellular and individual levels. The objectives of the present study were to evaluate the effects of metformin on cellular senescence in human PDLCs (hPDLCs) under oxidative stress. hPDLCs were pretreated with metformin, followed by H₂O₂ exposure. The cell viability, oxidative damage, cellular senescence and osteogenic potential were detected. To inhibit autophagy, hPDLCs were treated with 3-methyladenine before metformin treatment. The present study revealed that H₂O₂ exposure inhibits proliferation, increased lysosomal β-galactosidase activity, augments reactive oxidative species (ROS) accumulation, elevates the oxidative damage, stimulates the expression of senescence-related genes and impedes the activity of the osteogenic differentiation of hPDLCs. Metformin pretreatment could partly reverse the detrimental influences of H₂O₂ on hPDLCs. Moreover, metformin could stimulate autophagy, whereas the inhibition of autophagy with 3-methyladenine reversed the anti-senescence effects of metformin on hPDLCs under oxidative stress. The present study manifested that metformin could alleviate oxidative stress-induced senescence via stimulating autophagy and could partially recover the osteogenic potential of hPDLCs, possibly providing a reference for the discovery of periodontal treatment from the perspective of antisenescence.

Cellular senescence in dental pulp stem cells

OBJECTIVE

This short review summarizes our current knowledge about dental stem cell aging and about possible targets for the regulation of cellular senescence.

DESIGN

A literature search was performed using a combination of keywords, e.g., stem cells, replicative senescence, differentiation potential, dental pulp, dental follicle and periodontal ligament.

RESULTS

Previous studies have shown that cellular senescence occurs while the proliferation of dental stem cells. Moreover, the differentiation potential was significantly decreased in senescent stem cells and senescent cells secrete also factors that are harmful to the adjacent tissue cells. Moreover, many targets for the regulation of cellular senescence are considered; for example pathways related to the nutrient sensing such as the 5' adenosine monophosphate-activated protein kinase (AMPK) pathway.

CONCLUSIONS

The regulation of cellular senescence will play a crucial role in the clinical use of stem cells. However, there is no cell culture protocol available that prevents dental stem cell senescence. Therefore, more knowledge about molecular processes in stem cells is needed before and after the induction of senescence.

3D TECA hydrogel reduces cellular senescence and enhances fibroblasts migration in wound healing

This study was designed to investigate the effect of 3D TECA hydrogel on the inflammatory-induced senescence marker, and to assess the influence of the gel on the periodontal ligament fibroblasts (PDLFs) migration in wound healing in vitro. PDLFs were cultured with 20 ng/ml TNF-α to induce inflammation in the presence and absence of 50 µM 3D TECA gel for 14 d. The gel effect on the senescence maker secretory associated-β-galactosidase (SA-β-gal) activity was measured by a histochemical staining. Chromatin condensation and DNA synthesis of the cells were assessed by 4′,6-diamidino-2-phenylindole and 5-ethynyl-2′-deoxyuridine fluorescent staining respectively. For evaluating fibroblasts migration, scratch wound healing assay and Pro-Plus Imaging software were used. The activity of senescence marker, SA-β-gal, was positive in the samples with TNF-α-induced inflammation. SA-β-gal percentage is suppressed (>65%, P < 0.05) in the treated cells with TECA gel as compared to the non-treated cells. Chromatin foci were obvious in the non-treated samples. DNA synthesis was markedly recognized by the fluorescent staining in the treated compared to non-treated cultures. Scratch wound test indicated that the cells migration rate was significantly higher (14.9 µm²/h, P < 0.05) in the treated versus (11 µm²/h) for control PDLFs. The new formula of 3D TECA suppresses the inflammatory-mediated cellular senescence and enhanced fibroblasts proliferation and migration. Therefore, 3D TECA may be used as an adjunct to accelerate repair and healing of periodontal tissues.

Implications of cultured periodontal ligament cells for the clinical and experimental setting: a review

The periodontal ligament (PDL) is a key contributor to the process of regeneration of the periodontium. The heterogeneous nature of the PDL tissue, its development during early adulthood, and the different conditions to which the PDL tissue is exposed to in vivo impart on the PDL unique characteristics that may be of consequence during its cultivation in vitro. Several factors affecting the in vivo setting influence the behaviour of PDL fibroblasts in culture. The purpose of this review is to address distinct factors that influence the behaviour of PDL fibroblasts in culture -in vivo-in vitro transitions, cell identification/isolation markers, primary PDL cultures and cell lines, tooth-specific factors, and donor-specific factors. Based on the reviewed studies, the authors recommendations include the use of several identification markers to confirm cell identity, use of primary cultures at early passage to maintain unique PDL heterogeneic characteristics, and noting donor conditions such as age, systemic health status, and tooth health status. Continued efforts will expand our understanding of the in vitro and in vivo behaviour of cells, with the goal of orchestrating optimal periodontal regeneration. This understanding will lead to improved evidence-based rationales for more individualized and predictable periodontal regenerative therapies.

Effects of human aging on periodontal tissues

Loss of teeth is frequently associated with periodontal disease in older adults. The aim of this review was to present the effects of aging on the periodontal tissues. Aging alone does not lead to critical loss of periodontal attachment in healthy elderly persons. The effects of aging on periodontal tissues are based on molecular changes in the periodontal cells, which intensify bone loss in elderly patients with periodontitis. These effects may be associated with (1) alterations in differentiation and proliferation of osteoblasts and osteoclasts; (2) an increase in periodontal cell response to the oral microbiota and mechanical stress leading to the secretion of cytokines involved in osseous resorption; and (3) systemic endocrine alterations in the elderly people.

Production of colony-stimulating factor in human dental pulp fibroblasts

Class II major histocompatilibity complex (MHC)-expressing cells are usually distributed in dental pulp, and it was postulated that the colony-stimulating factor (CSF) derived from dental pulp fibroblasts contributes to the migration of class II MHC-expressing cells into pulp tissue. This study aimed to investigate the CSF production of human dental pulp fibroblasts. In pulp tissue sections, granulocyte (G)-CSF was detected from normal teeth, while G-CSF, macrophage (M)-CSF, and granulocyte-macrophage (GM)-CSF were detected from teeth with dentinal caries. In cultured dental pulp fibroblasts, G-CSF was detected by immunostaining, immunoprecipitation, and ELISA, and mRNAs of G-CSF, M-CSF, and GM-CSF were detected by RT-PCR. The dental pulp fibroblasts cultured with TNF-alpha were found to increase the G-CSF expression and to produce M-CSF and GM-CSF. These findings suggest that dental pulp fibroblasts usually produce G-CSF. In the presence of TNF-alpha, dental pulp fibroblast express M-CSF and GM-CSF.

Cultured periodontal ligament fibroblasts express diverse connexins

Recent studies have suggested multiple functions of periodontal ligament fibroblasts (PDLFs) which may relate to the permeability of gap junctions composed of various types of connexins (Cxs). At present, 15 types of Cxs are known to exist, and six of their antibodies, anti-Cx26, Cx32, Cx37, Cx40, Cx43, and Cx45 are commercially available. This study aims to examine which types of Cxs are expressed in cultured PDLFs by an immunohistochemical method, western blotting, and RT-PCR. The study confirmed the expressions of Cx32, Cx40, Cx43, and Cx45 in PDLFs, while Cx26 and Cx37 were not detected. Considering previous reports, Cx32 may relate to the secretory function, and Cx40 and Cx45 to the contractile function of PDLFs, however, a function for Cx43 has not been specified. In the immunohistochemical examination, different localizations of Cx40/43 and Cx32/45 were established. The former were observed punctately, suggesting that a large part of Cx40/43 may exist in the cell membrane and construct gap junctions. In contrast, the latter were observed uniformly in all the cells, indicating that they are present both in the cell membrane and in the cytoplasm of the cells.