Differential gene expression and protein-protein interaction networks of human periodontal ligament stromal cells under mechanical tension

Orthodontic treatment is based on complex strategies and takes up to years until a desired therapeutic outcome is accomplished, implying long periods of high costs and discomfort for the patient. Choosing the optimal settings for force intensities in the initial phase of orthodontic tooth movement is the key to successful orthodontic treatment. It is known that orthodontic tooth movement is mainly mediated by tensile and compressive forces that are communicated to the alveolar bone via the periodontal ligament. While the revelation of the complex molecular network was already approached by transcriptomic analysis of compressed periodontal ligament cells, the entity of molecular key players activated by tensile forces remains elusive. Therefore, the aim of this study was to assess the effect of mechanical tensile forces on the gene expression profile of human primary periodontal ligament stromal cells, mimicking the initial phase of orthodontic tooth movement. A transcriptomic analysis of tension-treated and untreated periodontal ligament stromal cells yielded 543 upregulated and 793 downregulated differentially expressed genes. Finally, six highly significant genes were found in the transcriptome that are related to biological processes with relevance to orthodontic tooth movement, including apelin, fibroblast growth factor receptor 2, noggin, sulfatase 1, secreted frizzled-related protein 4 and stanniocalcin 1. Additionally, differences of gene expression profiles between individual cell donors showed a high effect size. Closer understanding of the roles of the identified candidates in the initial phase of orthodontic tooth movement could help to clarify the underlying mechanisms, which will be essential for the development of personalized treatment strategies in orthodontics.

25-hydroxyvitamin D3 generates immunomodulatory plasticity in human periodontal ligament-derived mesenchymal stromal cells that is inflammatory context-dependent

Introduction

Human periodontal ligament-derived mesenchymal stromal cells (hPDL-MSCs) exhibit a tight bi-directional interaction with CD4+ T lymphocytes. The hPDL-MSCs' immunomodulatory abilities are drastically enhanced by pro-inflammatory cytokines via boosting the expression of various immunomediators. 25-hydroxyvitamin D3 (25(OH)D3), the major metabolite of vitamin D3 in the blood, affects both hPDL-MSCs and CD4+ T lymphocytes, but its influence on their interaction is unknown.

Methods

Therefore, primary hPDL-MSCs were stimulated in vitro with tumor necrosis factor (TNF)-α a or interleukin (IL)-1β in the absence and presence of 25(OH)D3 followed by an indirect co-culture with phytohemagglutinin-activated CD4+ T lymphocytes. The CD4+ T lymphocyte proliferation, viability, and cytokine secretion were analyzed. Additionally, the expression of various immunomediators in hPDL-MSCs was investigated, and their implication was verified by using pharmacological inhibitors.

Results

25(OH)D3 significantly counteracted the suppressive effects of IL-1β-treated hPDL-MSCs on CD4+ T lymphocyte proliferation, whereas no effects were observed in the presence of TNF-α. Additionally, 25(OH)D3 significantly increased the percentage of viable CD4+ T lymphocytes via TNF-α- or IL-1β-treated hPDL-MSCs. It also caused a significant decrease in interferon-γ, IL-17A, and transforming growth factor-β productions, which were triggered by TNF-α-treated hPDL-MSCs. 25(OH)D3 significantly decreased the production of various immunomediators in hPDL-MSCs. Inhibition of two of them, prostaglandin E2 and indoleamine-2,3-dioxygenase-1, partially abolished some of the hPDL-MSCs-mediated effects of 25(OH)D3 on CD4+ T lymphocytes.

Conclusion

These data indicate that 25(OH)D3 influences the immunomodulatory activities of hPDL-MSCs. This modulatory potential seems to have high plasticity depending on the local cytokine conditions and may be involved in regulating periodontal tissue inflammatory processes.

Effect of Titanium and Zirconia Nanoparticles on Human Gingival Mesenchymal Stromal Cells

Nano- and microparticles are currently being discussed as potential risk factors for peri-implant disease. In the present study, we compared the responses of human gingival mesenchymal stromal cells (hG-MSCs) on titanium and zirconia nanoparticles (<100 nm) in the absence and presence of Porphyromonas gingivalis lipopolysaccharide (LPS). The primary hG-MSCs were treated with titanium and zirconia nanoparticles in concentrations up to 2.000 µg/mL for 24 h, 72 h, and 168 h. Additionally, the cells were treated with different nanoparticles (25−100 µg/mL) in the presence of P. gingivalis LPS for 24 h. The cell proliferation and viability assay and live−dead and focal adhesion stainings were performed, and the expression levels of interleukin (IL)-6, IL-8, and monocyte chemoattractant protein (MCP)-1 were measured. The cell proliferation and viability were inhibited by the titanium (>1000 µg/mL) but not the zirconia nanoparticles, which was accompanied by enhanced apoptosis. Both types of nanoparticles (>25 µg/mL) induced the significant expression of IL-8 in gingival MSCs, and a slightly higher effect was observed for titanium nanoparticles. Both nanoparticles substantially enhanced the P. gingivalis LPS-induced IL-8 production; a higher effect was observed for zirconia nanoparticles. The production of inflammatory mediators by hG-MSCs is affected by the nanoparticles. This effect depends on the nanoparticle material and the presence of inflammatory stimuli.

Shut-Down of Type IX Protein Secretion Alters the Host Immune Response to Tannerella forsythia and Porphyromonas gingivalis

Tannerella forsythia and Porphyromonas gingivalis target distinct virulence factors bearing a structurally conserved C-terminal domain (CTD) to the type IX protein secretion system (T9SS). The T9SS comprises an outer membrane translocation complex which works in concert with a signal peptidase for CTD cleavage. Among prominent T9SS cargo linked to periodontal diseases are the TfsA and TfsB components of T. forsythia’s cell surface (S-) layer, the bacterium’s BspA surface antigen and a set of cysteine proteinases (gingipains) from P. gingivalis. To assess the overall role of the bacterial T9SS in the host response, human macrophages and human gingival fibroblasts were stimulated with T. forsythia and P. gingivalis wild-type bacteria and T9SS signal peptidase-deficient mutants defective in protein secretion, respectively. The immunostimulatory potential of these bacteria was compared by analyzing the mRNA expression levels of the pro-inflammatory mediators IL-6, IL-8, MCP-1 and TNF-α by qPCR and by measuring the production of the corresponding proteins by ELISA. Shot-gun proteomics analysis of T. forsythia and P. gingivalis outer membrane preparations confirmed that several CTD-bearing virulence factors which interact with the human immune system were depleted from the signal peptidase mutants, supportive of effective T9SS shut-down. Three and, more profoundly, 16 hours post stimulation, the T. forsythia T9SS mutant induced significantly less production of cytokines and the chemokine in human cells compared to the corresponding parent strain, while the opposite was observed for the P. gingivalis T9SS mutant. Our data indicate that T9SS shut-down translates into an altered inflammatory response in periodontal pathogens. Thus, the T9SS as a potential novel target for periodontal therapy needs further evaluation.

Toll-Like Receptors and Dental Mesenchymal Stromal Cells

Dental mesenchymal stromal cells (MSCs) are a promising tool for clinical application in and beyond dentistry. These cells possess multilineage differentiation potential and immunomodulatory properties. Due to their localization in the oral cavity, these cells could sometimes be exposed to different bacteria and viruses. Dental MSCs express various Toll-like receptors (TLRs), and therefore, they can recognize different microorganisms. The engagement of TLRs in dental MSCs by various ligands might change their properties and function. The differentiation capacity of dental MSCs might be either inhibited or enhanced by TLRs ligands depending on their nature and concentrations. Activation of TLR signaling in dental MSCs induces the production of proinflammatory mediators. Additionally, TLR ligands alter the immunomodulatory ability of dental MSCs, but this aspect is still poorly explored. Understanding the role of TLR signaling in dental MSCs physiology is essential to assess their role in oral homeostasis, inflammatory diseases, and tissue regeneration.

A Review of Antimicrobial Activity of Dental Mesenchymal Stromal Cells: Is There Any Potential?

Antimicrobial defense is an essential component of host-microbial homeostasis and contributes substantially to oral health maintenance. Dental mesenchymal stromal cells (MSCs) possess multilineage differentiation potential, immunomodulatory properties and play an important role in various processes like regeneration and disease progression. Recent studies show that dental MSCs might also be involved in antibacterial defense. This occurs by producing antimicrobial peptides or attracting professional phagocytic immune cells and modulating their activity. The production of antimicrobial peptides and immunomodulatory abilities of dental MSCs are enhanced by an inflammatory environment and influenced by vitamin D3. Antimicrobial peptides also have anti-inflammatory effects in dental MSCs and improve their differentiation potential. Augmentation of antibacterial efficiency of dental MSCs could broaden their clinical application in dentistry.

MMPs and TIMPs Expression Levels in the Periodontal Ligament during Orthodontic Tooth Movement: A Systematic Review of In Vitro and In Vivo Studies

Background: During orthodontic tooth movement (OTM), applied orthodontic forces cause an extensive remodeling of the extracellular matrix (ECM) in the periodontal ligament (PDL). This is mainly orchestrated by different types of matrix metalloproteinases (MMPs) and their tissue inhibitors of matrix metalloproteinases (TIMPs), which are both secreted by periodontal ligament (PDL) fibroblasts. Multiple in vitro and in vivo studies already investigated the influence of applied orthodontic forces on the expression of MMPs and TIMPs. The aim of this systematic review was to explore the expression levels of MMPs and TIMPs during OTM and the influence of specific orthodontic force-related parameters. Methods: Electronic article search was performed on PubMed and Web of Science until 31 January 2021. Screenings of titles, abstracts and full texts were performed according to PRISMA, whereas eligibility criteria were defined for in vitro and in vivo studies, respectively, according to the PICO schema. Risk of bias assessment for in vitro studies was verified by specific methodological and reporting criteria. For in vivo studies, risk of bias assessment was adapted from the Joanna Briggs Institute Critical Appraisal Checklist for analytical cross-sectional study. Results: Electronic article search identified 3266 records, from which 28 in vitro and 12 in vivo studies were included. The studies showed that orthodontic forces mainly caused increased MMPs and TIMPs expression levels, whereas the exact effect may depend on various intervention and sample parameters and subject characteristics. Conclusion: This systematic review revealed that orthodontic forces induce a significant effect on MMPs and TIMPs in the PDL. This connection may contribute to the controlled depletion and formation of the PDLs' ECM at the compression and tension site, respectively, and finally to the highly regulated OTM.

Effect of Enamel Matrix Derivatives on Osteoclast Formation from PBMC of Periodontitis Patients and Healthy Individuals after Interaction with Activated Endothelial Cells

Background and objectives: Enamel matrix derivative (EMD) is produced from developing porcine tooth buds and represents a complex of low-molecular-weight hydrophobic enamel proteins. EMD is widely applied in periodontal regeneration. Osteoclasts are multinuclear cells, which are responsible for bone resorption. The precursors of osteoclasts, hematopoietic cells, undergo in vivo the process of transendothelial migration before differentiation. EMD is known to affect the process of osteoclastogenesis, but its effect on human osteoclasts precursors after the interaction with activated endothelium was never studied. Materials and Methods: Human umbilical vein endothelial cells (HUVECs)s were seeded in transwell inserts with a pore size of 8 µm and pre-activated by TNF-α and IL-1β for 18 h. Peripheral blood mononuclear cells (PBMCs), freshly isolated from 16 periodontitis patients and 16 healthy individuals, were added to pre-activated HUVECs. Adherent, non-adherent and transmigrated cells were collected and differentiated to osteoclasts by the standard protocol in the presence or absence of EMD. The number of osteoclasts was determined by tartrate-resistant acid phosphatase staining. Results: PBMCs isolated from periodontitis patients have formed a significantly higher osteoclast number compared to PBMCs isolated from healthy individuals (p < 0.05). EMD induced concentration-dependent inhibition of osteoclast formation from PBMCs. This was true for the different PBMC fractions isolated from both healthy individuals and periodontitis patients. Conclusions: Our data show that EMD inhibits the formation and activity of osteoclasts differentiated from the progenitor cells after the interaction with activated endothelium. This might be associated with bone resorption inhibition and supporting bone regeneration in the frame of periodontal therapy.

Effects of Er:YAG laser irradiation of different titanium surfaces on osteoblast response

The aim of this in vitro study was to evaluate the effects of erbium-doped yttrium aluminum garnet (Er:YAG) laser irradiation on titanium surface topography and the proliferation and differentiation of osteoblasts using standard clinical treatment settings. Er:YAG laser irradiation at two levels ((1): 160 mJ, pulse at 20 Hz; (2): 80 mJ, pulse at 20 Hz) was applied to moderately rough and smooth titanium disks before MG-63 osteoblast-like cells were cultured on these surfaces. Titanium surface and cell morphology were observed by scanning electron microscopy. Cell proliferation/viability was measured by CCK-8 test. Gene expression of alkaline phosphatase (ALP), osteocalcin (OC), osteoprotegerin (OPG), receptor activator of nuclear factor kappa-B ligand (RANKL), and collagen type 1 was measured by qPCR, and OPG and OC protein production was determined by enzyme-linked immunosorbent assay. Treatment with Er:YAG laser at 160 mJ/20 Hz markedly caused heat-induced fusion of titanium and cell condensation on moderately rough surfaces, but not in smooth surfaces. MG-63 proliferation/viability decreased after 5 days in moderately rough surfaces. The expression of ALP, OC, OPG, and collagen type 1 was unaffected by laser treatment at 160 mJ/20. Laser irradiation at 80 mJ/20 Hz enhanced RANKL gene expression after 5 days in moderately rough surfaces. Study results suggest that Er:YAG laser irradiation at clinically relevant setting has no essential effect on osteogenic gene and protein expression of osteoblasts. However, surface structure, cell attachment, and proliferation are influenced by both treatment protocols, which implies that caution should be taken in the clinical treatment of peri-implant diseases when Er:YAG laser is used.

Effect of vitamin D3 on the osteogenic differentiation of human periodontal ligament stromal cells under inflammatory conditions

Objectives

Vitamin D₃ is known to activate osteogenic differentiation of human periodontal ligament stromal cells (hPDLSCs). Recently, inflammatory stimuli were shown to inhibit the transcriptional activity of hPDLSCs, but their effect on vitamin D₃‐induced osteogenic differentiation is not known. The present study aimed to investigate whether the effects of 1,25‐dihydroxvitamin D₃ (1,25(OH)₂D₃) and 25‐hydroxvitamin D₃ (25(OH)D₃) on the osteogenic differentiation of hPDLSCs are also altered under inflammatory conditions. Furthermore, the expression of osteogenesis‐related factors by hPDLSCs under osteogenic conditions was assessed in the presence of inflammatory stimuli.

Materials and Methods

Primary hPDLSCs of six donors were cultured in osteogenic induction medium containing either 1,25(OH)₂D₃ (0‐10 nM) or 25(OH)D₃ (0‐100 nM) in the presence and absence of Porphyromonas gingivalis lipopolysaccharide (LPS) or Pam3CSK4 for 7, 14 and 21 days. Osteogenic differentiation of hPDLSCs was evaluated by analysis of mineralization as assessed by Alizarin Red S staining and gene expression levels of osteogenesis‐related factors osteocalcin, osteopontin and runt‐related transcription factor 2 (RUNX2) were analysed with qPCR.

Results

Treatment with 1,25(OH)₂D₃ significantly enhanced the osteogenic differentiation of hPDLSCs and their expression of osteocalcin and osteopontin. The 1,25(OH)₂D₃‐triggered expression of osteogenesis‐related factors was significantly lower in the presence of Pam3CSK4, but not P. gingivalis LPS. None of the inflammatory stimuli had significant effects on the 1,25(OH)₂D₃‐induced osteogenic differentiation. 25(OH)D₃ neither affected gene expression levels nor osteogenic differentiation of hPDLSCs cultured in osteogenic induction medium.

Conclusion

The results of this study indicate that inflammatory stimuli also diminish the 1,25(OH)₂D₃‐induced expression of osteogenesis‐related factors in hPDLSCs under osteogenic conditions, while having no effect on the osteogenic differentiation.

Interleukin-1β Induced Matrix Metalloproteinase Expression in Human Periodontal Ligament-Derived Mesenchymal Stromal Cells under In Vitro Simulated Static Orthodontic Forces

The periodontal ligament (PDL) responds to applied orthodontic forces by extracellular matrix (ECM) remodeling, in which human periodontal ligament-derived mesenchymal stromal cells (hPDL-MSCs) are largely involved by producing matrix metalloproteinases (MMPs) and their local inhibitors (TIMPs). Apart from orthodontic forces, the synthesis of MMPs and TIMPs is influenced by the aseptic inflammation occurring during orthodontic treatment. Interleukin (IL)-1β is one of the most abundant inflammatory mediators in this process and crucially affects the expression of MMPs and TIMPs in the presence of cyclic low-magnitude orthodontic tensile forces. In this study we aimed to investigate, for the first time, how IL-1β induced expression of MMPs, TIMPs and how IL-1β in hPDL-MSCs was changed after applying in vitro low-magnitude orthodontic tensile strains in a static application mode. Hence, primary hPDL-MSCs were stimulated with IL-1β in combination with static tensile strains (STS) with 6% elongation. After 6- and 24 h, MMP-1, MMP-2, TIMP-1 and IL-1β expression levels were measured. STS alone had no influence on the basal expression of investigated target genes, whereas IL-1β caused increased expression of these genes. In combination, they increased the gene and protein expression of MMP-1 and the gene expression of MMP-2 after 24 h. After 6 h, STS reduced IL-1β-induced MMP-1 synthesis and MMP-2 gene expression. IL-1β-induced TIMP-1 gene expression was decreased by STS after 6- and 24-h. At both time points, the IL-1β-induced gene expression of IL-1β was increased. Additionally, this study showed that fetal bovine serum (FBS) caused an overall suppression of IL-1β-induced expression of MMP-1, MMP-2 and TIMP-1. Further, it caused lower or opposite effects of STS on IL-1β-induced expression. These observations suggest that low-magnitude orthodontic tensile strains may favor a more inflammatory and destructive response of hPDL-MSCs when using a static application form and that this response is highly influenced by the presence of FBS in vitro.

Potential Suppressive Effect of Nicotine on the Inflammatory Response in Oral Epithelial Cells: An In Vitro Study

Smoking is a well-recognized risk factor for oral mucosal and periodontal diseases. Nicotine is an important component of cigarette smoke. This study aims to investigate the impact of nicotine on the viability and inflammatory mediator production of an oral epithelial cell line in the presence of various inflammatory stimuli. Oral epithelial HSC-2 cells were challenged with nicotine (10⁻⁸–10⁻² M) for 24 h in the presence or absence of Porphyromonas gingivalis lipopolysaccharide (LPS, 1 µg/mL) or tumor necrosis factor (TNF)-α (10⁻⁷ M) for 24 h. The cell proliferation/viability was determined by MTT assay. Gene expression of interleukin (IL)-8, intercellular adhesion molecule (ICAM)-1, and β-defensin was assayed by qPCR. The production of IL-8 protein and cell surface expression of ICAM-1 was assessed by ELISA and flow cytometry, respectively. Proliferation/viability of HSC-2 cells was unaffected by nicotine at concentrations up to 10⁻³ M and inhibited at 10⁻² M. Nicotine had no significant effect on the basal expression of IL-8, ICAM-1, and β-defensin. At the same time, it significantly diminished P. gingivalis LPS or the TNF-α-induced expression levels of these factors. Within the limitations of this study, the first evidence was provided in vitro that nicotine probably exerts a suppressive effect on the production of inflammatory mediators and antimicrobial peptides in human oral epithelial cells.

Effect of Multi-Phosphonate Coating of Titanium Surfaces on Osteogenic Potential

The aim of this study was to evaluate the impact of a novel multi-phosphonate (MP) coating strategy of dental implant surfaces on the expression of osteogenesis-related factors in vitro. MG-63 human osteoblast-like cells, bone marrow mesenchymal stem cells (BM-MSCs), and human periodontal ligament stem cells (hPDLSCs) were cultured separately on titanium disks with and without MP coating. Cell attachment was visualized by focal adhesion and actin cytoskeleton staining. The proliferation and gene expression of the markers related to osteogenesis and bone turnover were measured after 48 and 120 h of cell culture. Actin cytoskeleton assembly and focal adhesion were similar between test surfaces within each cell type but differed from those on tissue culture plastic (TCP). The proliferation of MG-63 cells and PDLSCs was comparable on all surfaces, while BM-MSCs showed an increase on tissue culture plastic (TCP) versus titanium. The gene expression of osteoprotegerin and receptor activator of nuclear factor-kappa B ligand was higher in MG-63 cells grown on MP-coated surfaces. At the same time, osteocalcin was decreased compared to the other surfaces. Collagen type I gene expression after 120 h was significantly lower in hPDLSCs cultivated on MP-coated surfaces. Within the limitations of this study, MP coating on titanium surfaces might have a slight beneficial effect on bone turnover in vitro.

Continuing Effect of Cytokines and Toll-Like Receptor Agonists on Indoleamine-2,3-Dioxygenase-1 in Human Periodontal Ligament Stem/Stromal Cells

Transplanted mesenchymal stem/stromal cells (MSCs) are a promising and innovative approach in regenerative medicine. Their regenerative potential is partly based upon their immunomodulatory activities. One of the most investigated immunomediators in MSCs, such as in periodontal ligament-derived MSCs (hPDLSCs), is indoleamine-2,3-dioxygenase-1 (IDO-1) which is upregulated by inflammatory stimuli, like cytokines. However, there are no data concerning continuing IDO-1 expression in hPDLSCs after the removal of inflammatory stimuli, such as cytokines and toll-like receptor (TLR) agonist-2 and TLR-3. Hence, primary hPDLSCs were stimulated with interleukin (IL)-1β, tumor necrosis factor (TNF)-α, interferon (IFN)-γ, TLR-2 agonist Pam3CSK4 or TLR-3 agonist Poly I/C. IDO-1 gene and protein expression and its enzymatic activity were measured up to five days after removing any stimuli. IL-1β- and TNF-α-induced IDO-1 expression and enzymatic activity decreased in a time-dependent manner after cessation of stimulation. IFN-γ caused a long-lasting effect on IDO-1 up to five days after removing IFN-γ. Both, TLR-2 and TLR-3 agonists induced a significant increase in IDO-1 gene expression, but only TLR-3 agonist induced significantly higher IDO-1 protein expression and enzymatic activity in conditioned media (CM). IDO-1 activity of Poly I/C- and Pam3CSK4-treated hPDLSCs was higher at one day after removal of stimuli than immediately after stimulation and declined to basal levels after five days. Among all tested stimuli, only IFN-γ was able to induce long-lasting IDO-1 expression and activity in hPDLSCs. The high plasticity of IDO-1 expression and its enzymatic activity in hPDLSCs due to the variable cytokine and virulence factor milieu and the temporal-dependent responsiveness of hPDLSCs may cause a highly dynamic potential of hPDLSCs to modulate immune responses in periodontal tissues.

Salivary MRP-8/14 and the presence of periodontitis-associated bacteria in children with bonded maxillary expansion treatment

OBJECTIVES

The aim of this study was to investigate changes in saliva concentration of the inflammatory marker MRP-8/14 and the presence of some periodontitis-associated bacteria in patients with mixed dentition treated with a rigid acrylic, bonded maxillary expander.

METHODS

Fifteen patients in mixed dentition treated with a bonded palatal expander were enrolled in this longitudinal study. Saliva samples were taken before the therapy, as well as in 2 weeks and 3, 6, 9, and 12 months after the beginning of the therapy. In each sample, the levels of MRP-8/14 were determined by ELISA and the presence of 11 bacteria was detected by PCR followed by DNA-DNA hybridization.

RESULTS

Salivary concentration of MRP-8/14 and the amount of Tannerella forsythia, Treponema denticola, and Eikenella corrodens were significantly increased during treatment with bonded maxillary expander. These changes were transient and the maximal levels of MRP-8/14 and periodontitis-associated pathogens were observed 6-9 months after the beginning of the therapy.

CONCLUSION

Therapy with bonded maxillary results in higher MRP-8/14 levels and increased prevalence of some periodontitis-associated bacteria, namely T. forsythia, T. denticola, and E. corrodens. The results suggest the detection of salivary MRP-8/14 levels may be a potential tool to reflect the oral health status in children with fixed orthodontic treatment.

CLINICAL RELEVANCE

Our data suggest that the treatment with bonded maxillary expander might influence the oral health status and should be accompanied by the careful control of the oral health during the therapy.

Response of Human Mesenchymal Stromal Cells from Periodontal Tissue to LPS Depends on the Purity but Not on the LPS Source

Human periodontal ligament stromal cells (hPDLSCs) and gingival mesenchymal stromal cells (hGMSCs) are resident mesenchymal stromal cells (MSCs) of the periodontal tissue. The lipopolysaccharide (LPS) from Porphyromonas gingivalis is structurally distinct from that of other Gram-negative bacteria, and earlier studies linked this structural difference to a distinct virulence activity and the ability to activate toll-like receptor 2 (TLR-2), besides TLR-4 as commonly occurring upon LPS challenge. Later studies, in contrast, argue that TLR-2 activation by P. gingivalis LPS is due to lipoprotein contamination. In the present study, we aimed to define the influence of structure versus purity of P. gingivalis LPS on the immune response of hPDLSCs and hGMSCs. Cells were stimulated with commercially available "standard" P. gingivalis LPS, "ultrapure" P. gingivalis LPS, or "ultrapure" Escherichia coli LPS, and the expression of interleukin- (IL-) 8, IL-6, monocyte chemoattractant protein- (MCP-) 1, TLR-2, and TLR-4 was evaluated. The contribution of TLR-4 to the LPS-induced response was assessed using the specific TLR-4 inhibitor TAK-242. "Standard" P. gingivalis LPS induced significantly higher IL-8, IL-6, and MCP-1 production compared to the "ultrapure" LPS preparations, with no significant difference detectable for "ultrapure" LPS from P. gingivalis and E. coli. By using TAK-242, the response of hPDLSCs and hGMSCs to "ultrapure" LPS preparations was effectively inhibited to the levels comparable to those of nonstimulated controls. In contrast, high levels of response to "standard" LPS were observed, even in the presence of TAK-242. Our data show that the response of MSCs from periodontal tissue to LPS depends more on the purity of the LPS preparation than on the LPS source. Even a small amount of contaminating lipoproteins can drastically enhance the hPDLSCs' and hGMSCs; responsiveness to P. gingivalis LPS, which might also contribute to the progression of periodontal disease.

Vitamin D3 and Dental Mesenchymal Stromal Cells

Vitamin D3 is a hormone involved in the regulation of bone metabolism, mineral homeostasis, and immune response. Almost all dental tissues contain resident mesenchymal stromal cells (MSCs), which are largely similar to bone marrow-derived MSCs. In this narrative review, we summarized the current findings concerning the physiological effects of vitamin D3 on dental MSCs. The existing literature suggests that dental MSCs possess the ability to convert vitamin D3 into 25(OH)D3 and subsequently to the biologically active 1,25(OH)2D3. The vitamin D3 metabolites 25(OH)D3 and 1,25(OH)2D3 stimulate osteogenic differentiation and diminish the inflammatory response of dental MSCs. In addition, 1,25(OH)2D3 influences the immunomodulatory properties of MSCs in different dental tissues. Thus, dental MSCs are both producers and targets of 1,25(OH)2D3 and might regulate the local vitamin D3-dependent processes in an autocrine/paracrine manner. The local vitamin D3 metabolism is assumed to play an essential role in the local physiological processes, but the mechanisms of its regulation in dental MSCs are mostly unknown. The alteration of the local vitamin D3 metabolism may unravel novel therapeutic modalities for the treatment of periodontitis as well as new strategies for dental tissue regeneration.

Transcriptional activity of vitamin D receptor in human periodontal ligament cells is diminished under inflammatory conditions

Background

Although vitamin D₃ deficiency is considered as a risk factor for periodontitis, supplementation during periodontal treatment has not been shown to be beneficial to date. Human periodontal ligament cells (hPDLCs) are regulated by vitamin D₃ and play a fundamental role in periodontal tissue homeostasis and inflammatory response in periodontitis. The aim of this study is to investigate possible alterations of the vitamin D₃ activity in hPDLCs under inflammatory conditions.

Methods

Cells isolated from six different donors were treated with either 1,25(OH)₂D₃ (0 to 10 nM) or 25(OH)D₃ (0 to 100 nM) in the presence and absence of ultrapure or standard Porphyromonas gingivalis lipopolysaccharide (PgLPS), Pam3CSK4, or interferon‐γ for 48 hours. Additionally, nuclear factor (NF)‐κB inhibition was performed with BAY 11‐7082. The bioactivity of vitamin D in hPDLCs was assessed based on the gene expression levels of vitamin D receptor (VDR)‐regulated genes osteocalcin and osteopontin. Additionally, VDR and CYP27B1 expression levels were measured.

Results

The vitamin D₃‐induced increase of osteocalcin and osteopontin expression was significantly decreased in the presence of standard PgLPS and Pam3CSK4, which was not observed by ultrapure PgLPS. Interferon‐y had diverse effects on the response of hPDLCs to vitamin D₃ metabolites. NF‐kB inhibition abolished the effects of standard PgLPS and Pam3CSK4. Standard PgLPS and Pam3CSK4 increased VDR expression in the presence of vitamin D₃. CYP27B1 expression was not affected by vitamin D₃ and inflammatory conditions.

Conclusions

This study indicates that the transcriptional activity of VDR is diminished under inflammatory conditions, which might mitigate the effectiveness of vitamin D₃ supplementation during periodontal treatment.

Cytokines Differently Define the Immunomodulation of Mesenchymal Stem Cells from the Periodontal Ligament

Human periodontal ligament stem cells (hPDLSCs) play an important role in periodontal tissue homeostasis and regeneration. The function of these cells in vivo depends largely on their immunomodulatory ability, which is reciprocally regulated by immune cells via cytokines, particularly interferon (IFN)-γ, tumor necrosis factor (TNF)-α, and interleukin (IL)-1β. Different cytokines activate distinct signaling pathways and might differently affect immunomodulatory activities of hPDLSCs. This study directly compared the effect of IFN-γ, TNF-α, or IL-1β treated primary hPDLSCs on allogenic CD4⁺ T lymphocyte proliferation and apoptosis in an indirect co-culture model. The effects of IFN-γ, TNF-α, and IL-1β on the expression of specific immunomodulatory factors such as intoleamine-2,3-dioxygenase-1 (IDO-1), prostaglandin E₂ (PGE₂), and programmed cell death 1 ligand 1 (PD-L1) and ligand 2 (PD-L2) in hPDLSCs were compared. The contribution of different immunomodulatory mediators to the immunomodulatory effects of hPDLSCs in the indirect co-culture experiments was assessed using specific inhibitors. Proliferation of CD4⁺ T lymphocytes was inhibited by hPDLSCs, and this effect was strongly enhanced by IFN-γ and IL-1β but not by TNF-α. Apoptosis of CD4⁺ T lymphocytes was decreased by hPDLSCs per se. This effect was counteracted by IFN-γ or IL-1β. Additionally, IFN-γ, TNF-α, and IL-1β differently regulated all investigated immunomediators in hPDLSCs. Pharmacological inhibition of immunomediators showed that their contribution in regulating CD4⁺ T lymphocytes depends on the cytokine milieu. Our data indicate that inflammatory cytokines activate specific immunomodulatory mechanisms in hPDLSCs and the expression of particular immunomodulatory factors, which underlies a complex reciprocal interaction between hPDLSCs and CD4⁺ T lymphocytes.

Effect of implant surface material and roughness to the susceptibility of primary gingival fibroblasts to inflammatory stimuli

OBJECTIVES

The impact of the implant surface material and roughness on inflammatory processes in peri-implantitis is not entirely clear. Hence, we investigated how titanium and zirconia surfaces with different roughness influence the susceptibility of primary human gingival fibroblasts to different inflammatory stimuli.

METHODS

Primary human gingival fibroblasts were isolated from 8 healthy individuals and cultured on following surfaces: smooth titanium machined surface (TiM), smooth zirconia machined surface (ZrM), moderately rough titanium surface (SLA), or moderately rough zirconia surface (ZLA). Subsequently, stimulation with one of the following stimuli was performed: Porphyromonas gingivalis lipopolysaccharide (LPS), tumor necrosis factor (TNF)-α, interleukin (IL)-1β. The resulting production of IL-6, IL-8, and monocyte chemoattractant protein (MCP)-1 was measured by qPCR and ELISA.

RESULTS

P. gingivalis LPS induced IL-6 and MCP-1 production was slightly higher on titanium surfaces compared to zirconia surfaces. IL-1β induced IL-6 production was not affected by any surface characteristic. The production of MCP-1 in response to IL-1β was higher on smooth compared to rough surfaces and was not affected by the material. The production of IL-6 and MCP-1 in response to TNF-α was most strongly affected by surface characteristics. Higher production of these cytokine was observed on smooth compared to rough surfaces and on titanium compared to zirconia surfaces. Surface characteristics had only minor effects on IL-8 production.

SIGNIFICANCE

The susceptibility of primary gingival fibroblasts to inflammation depends on various factors, such as surface material, surface roughness and the nature of inflammatory stimuli. All these factors might determine susceptibility to peri-implantitis.

Effect of bisphosphonate treatment of titanium surfaces on alkaline phosphatase activity in osteoblasts: a systematic review and meta-analysis

BACKGROUND

Bisphosphonate coating of dental implants is a promising tool for surface modification aiming to improve the osseointegration process and clinical outcome. The biological effects of bisphosphonates are thought to be mainly associated with osteoclasts inhibition, whereas their effects on osteoblast function are unclear. A potential of bisphosphonate coated surfaces to stimulate osteoblast differentiation was investigated by several in vitro studies with contradictory results. The purpose of this systematic review and meta-analysis was to evaluate the effect of bisphosphonate coated implant surfaces on alkaline phosphatase activity in osteoblasts.

METHODS

In vitro studies that assessed alkaline phosphatase activity in osteoblasts following cell culture on bisphosphonate coated titanium surfaces were searched in electronic databases PubMed/MEDLINE, Scopus and ISI Web of Science. Animal studies and clinical trials were excluded. The literature search was restricted to articles written in English and published up to August 2019. Publication bias was assessed by the construction of funnel plots.

RESULTS

Eleven studies met the inclusion criteria. Meta-analysis showed that coating of titanium surfaces with bisphosphonates increases alkaline phosphatase activity in osteoblasts after 3 days (n = 1), 7 (n = 7), 14 (n = 6) and 21 (n = 3) days. (7 days beta coefficient = 1.363, p-value = 0.001; 14 days beta coefficient = 1.325, p-value < 0.001; 21 days beta coefficient = 1.152, p-value = 0.159).

CONCLUSIONS

The meta-analysis suggests that bisphosphonate coatings of titanium implant surfaces may have beneficial effects on osteogenic behaviour of osteoblasts grown on titanium surfaces in vitro. Further studies are required to assess to which extent bisphosphonates coating might improve osseointegration in clinical situations.

Methanandamide diminish the Porphyromonas gingivalis lipopolysaccharide induced response in human periodontal ligament cells

BACKGROUND

The endocannabinoid system is involved in the regulation of periodontal tissue homeostasis. Synthetic cannabinoid methanandamide (Meth-AEA) has improved stability and affinity to cannabinoid receptors compared to its endogenous analog anandamide. In the present study, we investigated the effect of methanandamide on the production of pro-inflammatory mediators in primary human periodontal ligament cells (hPdLCs).

METHODS

hPdLCs were treated with Meth-AEA for 24 h, and the resulting production of interleukin (IL)-6, IL-8, and monocyte chemotactic protein (MCP)-1 was measured in the absence or the presence of Porphyromonas gingivalis lipopolysaccharide (LPS). Additionally, the effect of Meth-AEA on the proliferation/viability of hPdLCs was measured by the MTT method.

RESULTS

Methanandamide at a concentration of 10 μM significantly inhibited P. gingivalis LPS induced production of IL-6, IL-8, and MCP-1. Basal production of IL-6 and IL-8 was slightly enhanced by 10 μM Meth-AEA. No effect of Meth-AEA on the basal production of MCP-1 was observed. Meth-AEA in concentrations up to 10 μM did not affect the proliferation/viability of hPdLCs, but significantly inhibited it at a concentration of 30 μM.

CONCLUSION

Our study suggests that the inflammatory response in periodontal ligament cells could be influenced by the activation of the cannabinoid system, which might be potentially involved in the progression of periodontal disease.

Pleiotropic effects of vitamin D3 on CD4+ T lymphocytes mediated by human periodontal ligament cells and inflammatory environment

Aims

Both, vitamin D₃ and human periodontal ligament cells (hPDLCs) possess immunosuppressive properties, but their combined effect on immune cells has never been investigated. Here, we analysed the impact of vitamin D₃ on the immunosuppressive properties of hPDLCs towards CD4⁺ T lymphocytes.

Material and Methods

Allogenic CD4⁺ T lymphocytes were activated by phytohemagglutinin either in monoculture or co‐culture with hPDLCs, in the presence or absence of IFN‐γ and 1,25(OH)₂D₃. After 5 days, CD4⁺ T‐lymphocyte proliferation, CD4⁺ CD25⁺ FoxP3⁺ regulatory T lymphocytes (T_regs) proportion and IL‐10, TGF‐β1 and IL‐17A production were analysed.

Results

In monoculture, 1,25(OH)₂D₃ suppressed CD4⁺ T‐lymphocyte proliferation, increased the percentage of CD4⁺ FoxP3⁺ CD25⁺ FoxP3⁺ T_regs and enhanced IL‐10 and TGF‐β1 production. In the presence of IFN‐γ treated hPDLCs, 1,25(OH)₂D₃ significantly increased CD4⁺ T‐lymphocyte proliferation and decreased the percentage of CD4⁺ CD25⁺ FoxP3⁺ T_regs. IL‐10 and IL‐17A expression was significantly diminished by 1,25(OH)₂D₃, whereas TGF‐β1 was slightly increased. The effects of 1,25(OH)₂D₃ in co‐culture were reversed by inhibition of indoleamine‐2,3‐dioxygenase‐1, prostaglandin‐endoperoxide synthase and programmed cell death 1 ligand 1. 1,25(OH)₂D₃ also suppressed the expression of these proteins in hPDLCs.

Conclusion

Effects of vitamin D₃ on CD4⁺ T lymphocyte are modified by hPDLCs depending on the microenvironment.

1,25(OH)2D3 Differently Affects Immunomodulatory Activities of Mesenchymal Stem Cells Depending on the Presence of TNF-α, IL-1β and IFN-γ

Periodontal ligament-derived mesenchymal stem cells (hPDLSCs) possess immunomodulatory abilities which are strongly enhanced by various inflammatory cytokines. Vitamin D₃ has anti-inflammatory effects on hPDLSCs and immune cells. However, no study to date has directly compared the influence of 1,25(OH)₂D₃ on the immunomodulatory activities of hPDLSCs in the presence of different cytokines. In the present study, the effects of hPDLSCs treated with tumor necrosis factor (TNF)-α, interleukin (IL)-1β, or interferon (IFN)-γ in the presence of 1,25(OH)₂D₃ on the proliferation of allogenic CD4⁺ T lymphocyte or on the functional status of primary CD68⁺ macrophages were analyzed in coculture models. Additionally, the effects of 1,25(OH)₂D₃ on TNF-α-, IL-1β-, and IFN-γ-induced gene expression of some immunomodulatory factors in hPDLSCs were compared. Under coculture conditions, 1,25(OH)₂D₃ increased or decreased CD4⁺ T lymphocyte proliferation via hPDLSCs, depending on the cytokine. hPDLSCs primed with 1,25(OH)₂D₃ and different cytokines affected pro- and anti-inflammatory cytokine expression in macrophages variably, depending on the priming cytokine. With one exception, 1,25(OH)₂D₃ significantly reduced TNF-α-, IL-1β-, and IFN-γ-induced expression of all the investigated immunomediators in hPDLSCs, albeit to different extents. These results suggest that 1,25(OH)₂D₃ influences the immunomodulatory activities of hPDLSCs depending qualitatively and quantitatively on the presence of certain inflammatory cytokines.

Immunomodulatory properties of dental tissue-derived mesenchymal stem cells: Implication in disease and tissue regeneration

Mesenchymal stem cells (MSCs) are considered as an attractive tool for tissue regeneration and possess a strong immunomodulatory ability. Dental tissue-derived MSCs can be isolated from different sources, such as the dental pulp, periodontal ligament, deciduous teeth, apical papilla, dental follicles and gingiva. According to numerous in vitro studies, the effect of dental MSCs on immune cells might depend on several factors, such as the experimental setting, MSC tissue source and type of immune cell preparation. Most studies have shown that the immunomodulatory activity of dental MSCs is strongly upregulated by activated immune cells. MSCs exert mostly immunosuppressive effects, leading to the dampening of immune cell activation. Thus, the reciprocal interaction between dental MSCs and immune cells represents an elegant mechanism that potentially contributes to tissue homeostasis and inflammatory disease progression. Although the immunomodulatory potential of dental MSCs has been extensively investigated in vitro, its role in vivo remains obscure. A few studies have reported that the MSCs isolated from inflamed dental tissues have a compromised immunomodulatory ability. Moreover, the expression of some immunomodulatory proteins is enhanced in periodontal disease and even shows some correlation with disease severity. MSC-based immunomodulation may play an essential role in the regeneration of different dental tissues. Therefore, immunomodulation-based strategies may be a very promising tool in regenerative dentistry.