Selection and validation of reference genes by RT-qPCR for murine cementoblasts in mechanical loading experiments simulating orthodontic forces in vitro

Effect of the antirheumatic medication methotrexate (MTX) on biomechanical compressed human periodontal ligament fibroblasts (hPDLFs)

BACKGROUND

The aim of this study was to investigate the in vitro effect of the antirheumatic drug methotrexate (MTX) on biomechanically compressed human periodontal ligament fibroblasts (hPDLFs), focusing on the expression of interleukin 6 (IL-6), as its upregulation is relevant to orthodontic tooth movement.

METHODS

Human PDLFs were subjected to pressure and simultaneously treated with MTX. Cell proliferation, viability and morphology were studied, as was the gene and protein expression of IL-6.

RESULTS

Compared with that in untreated fibroblasts, IL-6 mRNA expression in mechanically compressed ligament fibroblasts was increased (two to sixfold; ****p < 0.0001). Under compression, hPDLFs exhibited a significantly more expanded shape with an increase of cell extensions. MTX with and without pressure did not affect IL-6 mRNA expression or the morphology of hPDLFs.

CONCLUSION

MTX has no effect on IL-6 expression in compressed ligament fibroblasts.

Development, Establishment, and Validation of a Model for the Mineralization of Periodontium Remodelling Cells: Cementoblasts

Chronic kidney disease (CKD) patients undergoing dialysis are at high risk of bone fractures. CKD-induced mineral and bone disorder is extended to periodontal disease due to changes in the ionic composition of saliva in CKD patients, dysregulating mineralization, hindering regeneration and thereby promoting the progression of dental complications. Despite the importance of cementum for overall oral health, the mechanisms that regulate its development and regeneration are not well comprehended, and a lack of sufficient in vitro experimental models has hindered research progress. In this study, the impact of experimental conditions on the calcification of cementoblasts was systematically investigated, aimed at establishing a standardized and validated model for the calcification of cementoblasts. The effects of phosphate, calcium, ascorbic acid, β-glycerolphosphate, dexamethasone, and fetal calf serum on the calcification process of cementoblasts were analyzed over a wide range of concentrations and time points by investigating calcium content, cell viability, gene expression and kinase activity. Cementoblasts calcified in a concentration- and time-dependent manner with higher concentrations of supplements cause a higher degree of calcification but decreased cell viability. Phosphate and calcium have a significantly stronger effect on cementoblast calcification processes compared to osteogenic supplements: ascorbic acid, β-glycerolphosphate, and dexamethasone induce calcification over a wide range of osteogenic signalling pathways, with osteopontin being a central target of gene regulation. Conversely, treatment with ascorbic acid, β-glycerolphosphate, and dexamethasone leads to activating only selected pathways, especially promoting bone sialoprotein expression. The developed and validated cementoblast calcification protocol, incubating up to 60% confluent cementoblasts with 1.9 mmol L-1 of phosphate supplementation for a reasonable, multi-pathway calcification induction and 10 mmol L-1 β-glycerolphosphate, 75 µmol L-1 ascorbic acid and 10 nmol L-1 dexamethasone for a reasonable osteogenic differentiation-based calcification induction, provides standard in vitro experimental models for better understanding cementoblast function and regeneration.

Xanthohumol exerts anti-inflammatory effects in an in vitro model of mechanically stimulated cementoblasts

Xanthohumol (XN) is a prenylated plant polyphenol that naturally occurs in hops and its products, e.g. beer. It has shown to have anti-inflammatory and angiogenesis inhibiting effects and it prevents the proliferation of cancer cells. These effects could be in particular interesting for processes within the periodontal ligament, as previous studies have shown that orthodontic tooth movement is associated with a sterile inflammatory reaction. Based on this, the study evaluates the anti-inflammatory effect of XN in cementoblasts in an in vitro model of the early phase of orthodontic tooth movement by compressive stimulation. XN shows a concentration-dependent influence on cell viability. Low concentrations between 0.2 and 0.8 µM increase viability, while high concentrations between 4 and 8 µM cause a significant decrease in viability. Compressive force induces an upregulation of pro-inflammatory gene (Il-6, Cox2, Vegfa) and protein (IL-6) expression. XN significantly reduces compression related IL-6 protein and gene expression. Furthermore, the expression of phosphorylated ERK and AKT under compression was upregulated while XN re-established the expression to a level similar to control. Accordingly, we demonstrated a selective anti-inflammatory effect of XN in cementoblasts. Our findings provide the base for further examination of XN in modulation of inflammation during orthodontic therapy and treatment of periodontitis.

Selection and validation of reference gene for RT-qPCR studies in co-culture system of mouse cementoblasts and periodontal ligament cells

Objective

RT-qPCR is a reliable method for gene expression analysis, but the accuracy of the quantitative data depends on the appropriate selection of reference genes. A Co-culture system consisting of periodontal ligament cells (SV-PDL) and cementoblasts (OCCM-30) to investigate the crosstalk between these two cell lines under orthodontic condition is essential for experimental orthodontic setups in-vitro. Therefore, we aimed to identify a set of reliable reference genes suitable for RT-qPCR studies for prospective co-culture systems of OCCM-30 and SV-PDL cells.

Results

The results demonstrated that PPIB, GUSB and RPLP0 turned out to be the three most stable reference genes for OCCM-30 in the co-culture system, while PPIB, POLR2A and RPLP0 have the three highest rankings for SV-PDL cells in the co-culture system. The most stable gene combination were PPIB and POLR2A in the co-culture system. In conclusion, PPIB is overall the most stably expressed reference gene for OCCM-30 or SV-PDL cell line in the system. The combination of PPIB and POLR2A as reference genes are indicated to be the potential and mandatory to obtain accurate quantification results for normalizing RT-qPCR data in genes of interest expression in these two cell lines co-culture systems.

Impact of FGF1 on human periodontal ligament fibroblast growth, osteogenic differentiation and inflammatory reaction in vitro

PURPOSE

To investigate in vitro the impact of fibroblast growth factor 1 (FGF1) in comparison to ascorbic acid (AscA) on human periodontal ligament fibroblast (HPdLF) growth, their osteogenic differentiation, and modulation of their inflammatory reaction to mechanical stress.

METHODS

The influence of different concentrations of FGF1 (12.5-200 ng/mL) on growth and proliferation of HPdLF cells was analyzed over 20 days by counting cell numbers and the percentage of Ki67-positive cells. Quantitative expression analysis of genes encoding the osteogenic markers alkaline phosphatase (ALPL), Runt-related transcription factor 2 (RUNX2), osteocalcin (OCN), and osteopontin (OSP), as well as the fibroblast markers vimentin (VIM) and fibroblast-specific protein 1 (FSP1), was performed after 2 and 20 days of cultivation. Metabolic activity was determined by MTT assay. For comparison with AscA, 50 ng/mL FGF1 was used for stimulation for 2 and 20 days. Cell number, percentage of Ki67-positive cells, and expression of osteoblast- and fibroblast-specific genes were examined. Alkaline phosphatase activity was visualized by NBT/BCIP and calcium deposits were stained with alizarin red. Cytokine (IL‑6, IL‑8, COX2/PGE2) expression and secretion were analyzed by qPCR and ELISA in 6 h mechanically compressed HPdLF cultured for 2 days with FGF1 or ascorbic acid.

RESULTS

Higher concentrations of FGF1 promoted cell proliferation upon short-term stimulation, whereas prolonged treatment induced the expression of osteogenic markers even with low concentrations. AscA promotes cell growth more markedly than FGF1 in short-term cultures, whereas FGF1 induced osteogenic cell fate more strongly in long-term culture. Both factors induced an increased inflammatory response of HPdLF to mechanical compression.

CONCLUSION

Our data suggest that FGF1 promotes an osteogenic phenotype of HPdLF and limits inflammatory response to mechanical forces compared to AscA.

In Vitro Compression Model for Orthodontic Tooth Movement Modulates Human Periodontal Ligament Fibroblast Proliferation, Apoptosis and Cell Cycle

Human Periodontal Ligament Fibroblasts (hPDLF), as part of the periodontal apparatus, modulate inflammation, regeneration and bone remodeling. Interferences are clinically manifested as attachment loss, tooth loosening and root resorption. During orthodontic tooth movement (OTM), remodeling and adaptation of the periodontium is required in order to enable tooth movement. hPDLF involvement in the early phase-OTM compression side was investigated for a 72-h period through a well-studied in vitro model. Changes in the morphology, cell proliferation and cell death were analyzed. Specific markers of the cell cycle were investigated by RT-qPCR and Western blot. The study showed that the morphology of hPDLF changes towards more unstructured, unsorted filaments under mechanical compression. The total cell numbers were significantly reduced with a higher cell death rate over the whole observation period. hPDLF started to recover to pretreatment conditions after 48 h. Furthermore, key molecules involved in the cell cycle were significantly reduced under compressive force at the gene expression and protein levels. These findings revealed important information for a better understanding of the preservation and remodeling processes within the periodontium through Periodontal Ligament Fibroblasts during orthodontic tooth movement. OTM initially decelerates the hPDLF cell cycle and proliferation. After adapting to environmental changes, human Periodontal Ligament Fibroblasts can regain homeostasis of the periodontium, affecting its reorganization.

Gene expression and phosphorylation of ERK and AKT are regulated depending on mechanical force and cell confluence in murine cementoblasts

Cementoblasts, located on the tooth root surface covered with cementum, are considered to have tooth protecting abilities. They prevent tissue damage and secure teeth anchorage inside the periodontal ligament during mechanical stress. However, the involvement of cementoblasts in mechanical compression induced periodontal remodeling needs to be identified and better understood. Here, we investigated the effect of static compressive stimulation, simulating the compression side of orthodontic force and cell confluence on a murine cementoblast cell line (OC/CM). The influence of cell confluence in cementoblast cells was analyzed by MTS assay and immunostaining. Furthermore, mRNA and protein expression were investigated by real-time RT-PCR and western blotting at different confluence grades and after mechanical stimulation. We observed that cementoblast cell proliferation increases with increasing confluence grades, while cell viability decreases in parallel. Gene expression of remodeling markers is regulated by compressive force. In addition, cementoblast confluence plays a crucial role in this regulation. Confluent cementoblasts show a significantly higher basal expression of Bsp, Osterix, Alpl, Vegfa, Mmp9, Tlr2 and Tlr4 compared to sub-confluent cells. After compressive force of 48 h at 60% confluence, an upregulation of Bsp, Osterix, Alpl, Vegf and Mmp9 is observed. In contrast, at high confluence, all analyzed genes were downregulated through mechanical stress. We also proved a regulation of ERK, phospho-ERK and phospho-AKT dependent on compressive force. In summary, our findings provide evidence that cementoblast physiology and metabolism is highly regulated in a cell confluence-dependent manner and by mechanical stimulation.