shRNA knockdown of integrin-linked kinase on hPDLCs migration, proliferation, and apoptosis under cyclic tensile stress

Investigation of Oxidative-Stress Impact on Human Osteoblasts During Orthodontic Tooth Movement Using an In Vitro Tension Model

In recent years, there has been a growing number of adult orthodontic patients with periodontal disease. The progression of periodontal disease is well-linked to oxidative stress (OS). Nevertheless, the impact of OS on orthodontic tooth movement (OTM) is not fully clarified. Therefore, we applied an OS in vitro-model utilizing H2O2 to study its effect on tension-induced mechanotransduction in human osteoblasts (hOBs). Experimental parameters were established based on cell viability and proliferation. Apoptosis detection was based on caspase-3/7 activity. Gene expression related to bone-remodeling (RUNX2, P2RX7, TNFRSF11B/OPG), inflammation (CXCL8/IL8, IL6, PTRGS2/COX2), autophagy (MAP1LC3A/LC3, BECN1), and apoptosis (CASP3, CASP8) was analyzed by RT-qPCR. IL6 and PGE2 secretion were determined by ELISA. Tension increased the expression of PTRGS2/COX2 in all groups, especially after stimulation with higher H2O2 concentration. This corresponds also to the measured PGE2 concentrations. CXCL8/IL8 was upregulated in all groups. Cells subjected to tension alone showed a general upregulation of osteogenic differentiation-related genes; however, pre-stimulation with OS did not induce significant changes especially towards downregulation. MAP1LC3A/LC3, BECN1 and CASP8 were generally upregulated in cells without OS pre-stimulation. Our results suggest that OS might have considerable impacts on cellular behavior during OTM.

Investigation of Impact of Oxidative Stress on Human Periodontal Ligament Cells Exposed to Static Compression

Oxidative stress (OS) is a common feature of many inflammatory diseases, oral pathologies, and aging processes. The impact of OS on periodontal ligament cells (PDLCs) in relation to oral pathologies, including periodontal diseases, has been investigated in different studies. However, its impact on orthodontic tooth movement (OTM) remains poorly understood. This study used an in vitro model with human PDLCs previously exposed to H2O2 to investigate the effects of OS under a static compressive force which simulated the conditions of OTM. Human PDLCs were treated with varying concentrations of H2O2 to identify sub-lethal doses that affected viability minimally. To mimic compromised conditions resembling OTM under OS, the cells were pretreated with the selected H2O2 concentrations for 24 h. Using an in vitro loading model, a static compressive force (2 g/cm2) was applied for an additional 24 h. The cell viability, proliferation, and cytotoxicity were evaluated using live/dead and resazurin assays. Apoptosis induction was assessed based on caspase-3/7 activity. The gene expression related to bone remodeling (RUNX2, TNFRSF11B/OPG, BGLAP), inflammation (IL6, CXCL8/IL8, PTGS2/COX2), apoptosis (CASP3, CASP8), and autophagy (MAP1LC3A/LC3, BECN1) was analyzed using RT-qPCR. This study suggests an altering effect of previous OS exposure on static-compression-related mechanosensing. Further research is needed to fully elucidate these mechanisms.

Novel Antibacterial and Biocompatible Nanostructured Gels Based on One-step Synthesis as a Potential Disinfectant for Endodontic Infection Control

AIM

The objective of this study was to develop nanostructured gels as biocompatible intracanal disinfectants by one-step microwave radiation-assisted synthesis.

METHODS

Polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP) were used as a support network, and polyethylene glycol (PEG) was used as a reducing agent. The gels were characterized by measuring the swelling ratio (SR) and rheological properties and by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). The antibacterial effects of each gel were evaluated against the endodontic clinical strain Enterococcus faecalis. Then, the viability of the 21-day mature multispecies bacterial biofilm was assessed using confocal microscopy in an ex vivo model, where the biofilm was exposed to the mix of nanogels. The cell proliferation, viability, and morphology of human periodontal ligament (HPDL) cells were quantified using a real-time IncuCyte® S3 Live-Cell System. Viability was measured by confocal microscopy using an ex vivo model exposing a 21-day mature multispecies bacterial biofilm to the mix of nanogels.

RESULTS

The antibacterial activity of the gels coincided with the superficial characterization and the solubility of the gel in the growth medium. Gels with higher viscosity (327.85-980.58 Pa s), higher dissolution (42-70%SR), and lower porosity (no porosity and 611.63 nm) showed excellent antibacterial activity against E. faecalis. Despite their physicochemical characteristics, CuNPs gels showed greater effectiveness against E. faecalis.These nanostructured gels with high PVA concentrations promote HPDL cells proliferation while still exerting antibacterial properties. Mix of nanogels showed an increase non-viable cells biomass from at of application.

CONCLUSIONS

The use of biocompatible polymers influences the physicochemical, bactericidal, and cytotoxic response, making these materials potential disinfectant agents against resistant bacteria with good biocompatibility and improved HPDL cells proliferation.

Programmed cell death of periodontal ligament cells

The periodontal ligament is a crucial tissue that provides support to the periodontium. Situated between the alveolar bone and the tooth root, it consists primarily of fibroblasts, cementoblasts, osteoblasts, osteoclasts, periodontal ligament stem cells (PDLSCs), and epithelial cell rests of Malassez. Fibroblasts, cementoblasts, osteoblasts, and osteoclasts are functionally differentiated cells, whereas PDLSCs are undifferentiated mesenchymal stem cells. The dynamic development of these cells is intricately linked to periodontal changes and homeostasis. Notably, the regulation of programmed cell death facilitates the clearance of necrotic tissue and plays a pivotal role in immune response. However, it also potentially contributes to the loss of periodontal supporting tissues and root resorption. These findings have significant implications for understanding the occurrence and progression of periodontitis, as well as the mechanisms underlying orthodontic root resorption. Further, the regulation of periodontal ligament cell (PDLC) death is influenced by both systemic and local factors. This comprehensive review focuses on recent studies reporting the mechanisms of PDLC death and related factors.

Real-time evaluation of the biocompatibility of calcium silicate-based endodontic cements: An in vitro study

INTRODUCTION

An ideal filling material should hermetically seal the communication pathways between the canal system and surrounding tissues. Therefore, during the last few years, the development of obturation materials and techniques to create optimal conditions for the proper healing of apical tissues has been a focus of interest. The effects of calcium silicate-based cements (CSCs) on periodontal ligament cells have been investigated, and promising results have been obtained. To date, there are no reports in the literature that have evaluated the biocompatibility of CSCs using a real-time live cell system. Therefore, this study aimed to evaluate the real-time biocompatibility of CSCs with human periodontal ligament cells (hPDLCs).

METHODOLOGY

hPDLC were cultured with testing media of endodontic cements for 5 days: TotalFill-BC Sealer, BioRoot RCS, Tubli-Seal, AH Plus, MTA ProRoot, Biodentine, and TotalFill-BC RRM Fast Set Putty. Cell proliferation, viability, and morphology were quantified using real-time live cell microscopy with the IncuCyte S3 system. Data were analyzed using the one-way repeated measures (RM) analysis of variance multiple comparison test (p < .05).

RESULTS

Compared to the control group, cell proliferation in the presence of all cements was significantly affected at 24 h (p < .05). ProRoot MTA and Biodentine lead to an increase in cell proliferation; there were no significant differences with the control group at 120 h. In contrast, Tubli-Seal and TotalFill-BC Sealer inhibited cell growth in real-time and significantly increased cell death compared to all groups. hPDLC co-cultured with sealer and repair cements showed a spindle-shaped morphology except with cements Tubli-Seal and TotalFill-BC Sealer where smaller and rounder cells were obtained.

CONCLUSIONS

The biocompatibility of the endodontic repair cements performed better than the sealer cements, highlighting the cell proliferation of the ProRoot MTA and Biodentine in real-time. However, the calcium silicate-based TotalFill-BC Sealer presented a high percentage of cell death throughout the experiment similar to that obtained.

Substrate Stiffness Regulates the Proliferation and Apoptosis of Periodontal Ligament Cells through Integrin-Linked Kinase ILK

The hallmark of orthodontic tooth movement (OTM) is time-consuming during clinical treatments. The acceleration of OTM through modulating proliferation and apoptosis of periodontal ligament cells (PDLCs) possesses the potential application in clinical treatments. Here, we established an in vitro model with a graded increase in substrate stiffness to investigate the underlying mechanism of proliferation and apoptosis of PDLCs. The role of the integrin-linked kinase (ILK) in response to substrate stiffness was investigated by the depletion model of PDLCs. We found that the proliferation and apoptosis of PDLCs show a stiffness-dependent property with stiffer substrates favoring increased bias at the transcript level. Depleting integrin-linked kinase diluted the correlation between PDLCs behaviors and substrate stiffness. Our results suggest that ILK plays a significant role in modulating PDLC proliferation and apoptosis and can serve as a potential target for accelerating OTM.

CTHRC1 expressed in periodontitis and human periodontal fibroblasts exposed to inflammatory stimuli

OBJECTIVES

Collagen triple helix repeat containing-1 (CTHRC1) is a glycoprotein that can be secreted extracellularly and is involved in the regulation of collagen matrix in a variety of diseases. The expression level of CTHRC1 in periodontitis was detected in the present study.

MATERIALS AND METHODS

The gingival tissues from clinically healthy subjects (15 cases) and those with periodontitis (30 cases) were taken for immunohistochemical staining. Lipopolysaccharide of the Porphyromonas gingivalis was added in the periodontal ligament fibroblast culture in vitro. Cells were collected and the mRNA levels of the intracellular CTHRC1 and protein expression of the extracellular CTHRC1 were detected.

RESULTS

The protein expression of CTHRC1 in the periodontitis group was higher than that of the clinically healthy group. The in vitro cell experiments showed that 10 μg/mL of P.g LPS could induce a significant increase in protein secretion of CTHRC1, and 5 μg/mL P.g LPS had a significant effect on promoting the mRNA expression of CTHRC1.

CONCLUSION

CTHRC1 might be involved in the development of periodontitis and the expression level might be significantly correlated with the stimulation of P.g LPS on fibroblasts. Different stimulation intensities of P.g LPS might result in different expression patterns of CTHRC1.

ILK regulates osteogenic differentiation of Human Periodontal Ligament Stem Cells through YAP-mediated Mechanical Memory

Mechanical memory meant the mechanical properties of the matrix could influence the cell fate even after the matrix was changed and has been justified in many kinds of cells. To utilize the phenomenon to improve periodontal tissue engineering, we studied whether mechanical memory existed in human periodontal ligament stem cells and testified if ILK plays a role in this process. The substrate of different stiffness was fabricated by gelatin methacrylate hydrogel. Two groups of hPDLSCs with stiff (St) and soft (So) matrix respectively were cultivated. Then half of the cells exchanged their matrix stiffness in the fourth passage and therefore So, St, So-St and St-So were formed. Morphology of hPDLSCs and intracellular location of YAP was observed via fluorescence staining, osteogenic differentiation of hPDLSCs was assessed by Real-Time PCR, ALP staining and western blot. Then all these were reassessed after the ILK gene had been knocked down. The results showed that morphology and YAP location of hPDLSCs were different between matrix changed and unchanged groups; osteogenic genes expression, ALP staining and western blot also varied. After the ILK gene had been knocked down, the YAP location and osteogenic activity of hPDLSCs were significantly influenced. Thus, it could be concluded that mechanical memory exists in hPDLSCs; ILK is involved in this process.

Role of integrin‑linked kinase in static compressive stress‑induced autophagy via phosphatidylinositol 3 kinase in human periodontal ligament cells

Orthodontic tooth movement (OTM) is achieved by using mechanical stimuli, which lead to the remodeling of periodontal tissues. Previous findings have demonstrated that autophagy may be one of the cell responses to mechanical stress. As a key structure in the integrin pathway, integrin linked‑kinase (ILK) may play a role in the transmission of these mechanical signals. In addition, ILK is an important upstream molecule that regulates autophagy, under the influence of phosphatidylinositol 3 kinase (PI3K). Therefore, exploring the effect of mechanical stress on autophagy and the associated role of ILK/PI3K is of utmost significance to understanding the mechanism behind OTM. In the present study, human periodontal ligament cells (hPDLCs) were embedded into a collagen‑alginate complex hydrogel for three‑dimensional (3D) culturing. Static compressive stress (2.5 g/cm²) was loaded using the uniform weight method for 5, 15, 30, and 60 min. The autophagy of hPDLCs was detected by the expression of Beclin‑1 (BECN1) and ATG‑5 using RT‑qPCR and LC3, respectively, using immunofluorescence. The results showed that the level of autophagy and gene expression of ILK increased significantly under static compressive stress. In ILK‑silenced cells, static compressive stress could also upregulate ILK expression and increase the levels of autophagy. After PI3K inhibition, the increase in the autophagy level and the upregulation of ILK expression disappeared. These findings suggest that static compressive stress can induce autophagy in hPDLCs in a rapid, transient process, regulated by ILK and PI3K. Moreover, this static stress can upregulate ILK expression in a PI3K‑dependent manner.