Myeloid HIF1α Is Involved in the Extent of Orthodontically Induced Tooth Movement

During orthodontic tooth movement, transcription factor hypoxia-inducible factor 1α (HIF1α) is stabilised in the periodontal ligament. While HIF1α in periodontal ligament fibroblasts can be stabilised by mechanical compression, in macrophages pressure application alone is not sufficient to stabilise HIF1α. The present study was conducted to investigate the role of myeloid HIF1α during orthodontic tooth movement. Orthodontic tooth movement was performed in wildtype and Hif1αΔmyel mice lacking HIF1α expression in myeloid cells. Subsequently, µCT images were obtained to determine periodontal bone loss, extent of orthodontic tooth movement and bone density. RNA was isolated from the periodontal ligament of the control side and the orthodontically treated side, and the expression of genes involved in bone remodelling was investigated. The extent of tooth movement was increased in Hif1αΔmyel mice. This may be due to the lower bone density of the Hif1αΔmyel mice. Deletion of myeloid Hif1α was associated with increased expression of Ctsk and Acp5, while both Rankl and its decoy receptor Opg were increased. HIF1α from myeloid cells thus appears to play a regulatory role in orthodontic tooth movement.

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Role and Regulation of Mechanotransductive HIF-1α Stabilisation in Periodontal Ligament Fibroblasts

International Journal of Molecular Sciences ◽

10.3390/ijms21249530 ◽

2020 ◽

Vol 21 (24) ◽

pp. 9530

Author(s):

Christian Kirschneck ◽

Magdalena Thuy ◽

Alexandra Leikam ◽

Svenja Memmert ◽

James Deschner ◽

...

Keyword(s):

Periodontal Ligament ◽

Tensile Strain ◽

Tooth Movement ◽

Compressive Strain ◽

Mechanical Strain ◽

Hypoxia Inducible Factor ◽

Orthodontic Tooth Movement ◽

Prostaglandin Synthesis ◽

Vegf Expression ◽

Periodontal Ligament Fibroblasts

Orthodontic tooth movement (OTM) creates compressive and tensile strain in the periodontal ligament, causing circulation disorders. Hypoxia-inducible factor 1α (HIF-1α) has been shown to be primarily stabilised by compression, but not hypoxia in periodontal ligament fibroblasts (PDLF) during mechanical strain, which are key regulators of OTM. This study aimed to elucidate the role of heparan sulfate integrin interaction and downstream kinase phosphorylation for HIF-1α stabilisation under compressive and tensile strain and to which extent downstream synthesis of VEGF and prostaglandins is HIF-1α-dependent in a model of simulated OTM in PDLF. PDLF were subjected to compressive or tensile strain for 48 h. In various setups HIF-1α was experimentally stabilised (DMOG) or destabilised (YC-1) and mechanotransduction was inhibited by surfen and genistein. We found that HIF-1α was not stabilised by tensile, but rather by compressive strain. HIF-1α stabilisation had an inductive effect on prostaglandin and VEGF synthesis. As expected, HIF-1α destabilisation reduced VEGF expression, whereas prostaglandin synthesis was increased. Inhibition of integrin mechanotransduction via surfen or genistein prevented stabilisation of HIF-1α. A decrease in VEGF expression was observed, but not in prostaglandin synthesis. Stabilisation of HIF-1α via integrin mechanotransduction and downstream phosphorylation of kinases seems to be essential for the induction of VEGF, but not prostaglandin synthesis by PDLF during compressive (but not tensile) orthodontic strain.

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Role of Oxygen Supply in Macrophages in a Model of Simulated Orthodontic Tooth Movement

Mediators of Inflammation ◽

10.1155/2020/5802435 ◽

2020 ◽

Vol 2020 ◽

pp. 1-11

Author(s):

Agnes Schröder ◽

Leonie Barschkies ◽

Jonathan Jantsch ◽

Peter Proff ◽

Lina Gölz ◽

...

Keyword(s):

Cell Culture ◽

Periodontal Ligament ◽

Oxygen Supply ◽

Tooth Movement ◽

Mechanical Strain ◽

Orthodontic Tooth Movement ◽

Hypoxic Cell ◽

Periodontal Ligament Fibroblasts ◽

Hypoxic Conditions ◽

Expression Of Genes

Apart from periodontal ligament fibroblasts, immune cells like macrophages also play an important mediating role in orthodontic tooth movement (OTM). Upon orthodontic force application to malpositioned teeth, macrophages in the periodontal ligament get exposed to both mechanical strain and hypoxic conditions (via a compression of blood vessels). In this study, we assessed the relative impact of orthodontically induced mechanical strain and hypoxic conditions on macrophages for the mediation and regulation of OTM. Macrophages were stimulated with physiological orthodontic compressive forces of 2 g/cm2 for 4 h and 24 h on gas-impermeable or gas-permeable cell culture plates under normoxic or hypoxic cell culture conditions. We quantified expression of genes involved in inflammation (Tnf, Il-6, and Cox-2), extracellular remodelling (Mmp-9), and angiogenesis (Vegf) by RT-qPCR. Furthermore, we analysed HIF-1α, prostaglandin-E2, and VEGF protein expression via immunoblotting or ELISA. Mechanical strain and oxygen supply both differentially affected expression of genes and proteins involved in inflammation and angiogenesis. In this context, we found that HIF-1α protein levels were elevated by combined mechanical strain and hypoxic conditions, whereas gas-permeable plates providing sufficient oxygen supply prevented HIF-1α stabilization at the protein level after pressure application on macrophages. Our results thus indicate that macrophages involved in the mediation of OTM are affected by and respond differently to hypoxic conditions and mechanical compressive strain, which occur concomitantly during OTM, than periodontal ligament fibroblasts (PDLF), thus indicating different roles of these cells in the regulation of OTM at the cellular-molecular level. We further observed that contrary to PDLF HIF-1α stabilization in macrophages is rather induced via the decreased oxygen supply associated with OTM than via mechanotransduction by mechanical strain.

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Effects of mechanical strain on periodontal ligament fibroblasts in presence of Aggregatibacter actinomycetemcomitans lysate

BMC Oral Health ◽

10.1186/s12903-021-01761-3 ◽

2021 ◽

Vol 21 (1) ◽

Author(s):

Agnes Schröder ◽

Julia Stumpf ◽

Eva Paddenberg ◽

Patrick Neubert ◽

Valentin Schatz ◽

...

Keyword(s):

Periodontal Ligament ◽

Tooth Movement ◽

Bone Remodelling ◽

Mechanical Strain ◽

Orthodontic Tooth Movement ◽

Aggregatibacter Actinomycetemcomitans ◽

Periodontal Ligament Fibroblasts ◽

Reduced Pressure ◽

Expression Of Genes ◽

Ros Formation

Abstract Purpose Many adult orthodontic patients suffer from periodontitis, which is caused by oral pathogens such as the gram-negative Aggregatibacter actinomycetemcomitans (Agac). Like orthodontic tooth movement, periodontitis is associated with inflammation and alveolar bone remodelling thereby affecting orthodontic treatment. Interactions of both processes, however, are not sufficiently explored, particularly with regard to oxidative stress. Methods After preincubation with Agac lysate for 24 h periodontal ligament fibroblasts (PDLF) were either stretched or compressed for further 48 h simulating orthodontic forces in vitro. We analysed the expression of genes and proteins involved in the formation of reactive oxygen species (NOX-4, ROS) and nitric oxide (NOS-2), inflammation (TNF, IL-6, PTGS-2) and bone remodelling (OPG, RANKL). Results Agac lysate elevated the expression of NOX-4, NOS-2, inflammatory IL-6 and PTGS-2 and the bone-remodelling RANKL/OPG ratio during compressive, but not tensile mechanical strain. Agac lysate stimulated pressure-induced inflammatory signalling, whereas surprisingly ROS formation was reduced. Pressure-induced downregulation of OPG expression was inhibited by Agac lysate. Conclusions Agac lysate impact on the expression of genes and proteins involved in inflammation and bone remodelling as well as ROS formation, when PDLF were subjected to mechanical forces occurring during orthodontic tooth movement.

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

Biomolecules ◽

10.3390/biom11070932 ◽

2021 ◽

Vol 11 (7) ◽

pp. 932

Author(s):

Julia Brockhaus ◽

Rogerio B. Craveiro ◽

Irma Azraq ◽

Christian Niederau ◽

Sarah K. Schröder ◽

...

Keyword(s):

Cell Cycle ◽

Cell Death ◽

Periodontal Ligament ◽

Environmental Changes ◽

Tooth Movement ◽

Orthodontic Tooth Movement ◽

Compressive Force ◽

Periodontal Ligament Fibroblasts ◽

Human Periodontal Ligament Fibroblasts

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.

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The role of inhibition of osteocyte apoptosis in mediating orthodontic tooth movement and periodontal remodeling: a pilot study

Progress in Orthodontics ◽

10.1186/s40510-021-00366-4 ◽

2021 ◽

Vol 22 (1) ◽

Author(s):

Michele Kaplan ◽

Zana Kalajzic ◽

Thomas Choi ◽

Imad Maleeh ◽

Christopher L. Ricupero ◽

...

Keyword(s):

Bone Density ◽

Alveolar Bone ◽

Tooth Movement ◽

Orthodontic Tooth Movement ◽

Tartrate Resistant Acid Phosphatase ◽

Osteocyte Apoptosis ◽

Saline Administration ◽

Group 2 ◽

Group 1

Abstract Background Orthodontic tooth movement (OTM) has been shown to induce osteocyte apoptosis in alveolar bone shortly after force application. However, how osteocyte apoptosis affects orthodontic tooth movement is unknown. The goal of this study was to assess the effect of inhibition of osteocyte apoptosis on osteoclastogenesis, changes in the alveolar bone density, and the magnitude of OTM using a bisphosphonate analog (IG9402), a drug that affects osteocyte and osteoblast apoptosis but does not affect osteoclasts. Material and methods Two sets of experiments were performed. Experiment 1 was used to specifically evaluate the effect of IG9402 on osteocyte apoptosis in the alveolar bone during 24 h of OTM. For this experiment, twelve mice were divided into two groups: group 1, saline administration + OTM24-h (n=6), and group 2, IG9402 administration + OTM24-h (n=6). The contralateral unloaded sides served as the control. The goal of experiment 2 was to evaluate the role of osteocyte apoptosis on OTM magnitude and osteoclastogenesis 10 days after OTM. Twenty mice were divided into 4 groups: group 1, saline administration without OTM (n=5); group 2, IG9402 administration without OTM (n=5); group 3, saline + OTM10-day (n=6); and group 4, IG9402 + OTM10-day (n=4). For both experiments, tooth movement was achieved using Ultra Light (25g) Sentalloy Closed Coil Springs attached between the first maxillary molar and the central incisor. Linear measurements of tooth movement and alveolar bone density (BVF) were assessed by MicroCT analysis. Cell death (or apoptosis) was assessed by terminal dUTP nick-end labeling (TUNEL) assay, while osteoclast and macrophage formation were assessed by tartrate-resistant acid phosphatase (TRAP) staining and F4/80+ immunostaining. Results We found that IG9402 significantly blocked osteocyte apoptosis in alveolar bone (AB) at 24 h of OTM. At 10 days, IG9402 prevented OTM-induced loss of alveolar bone density and changed the morphology and quality of osteoclasts and macrophages, but did not significantly affect the amount of tooth movement. Conclusion Our study demonstrates that osteocyte apoptosis may play a significant role in osteoclast and macrophage formation during OTM, but does not seem to play a role in the magnitude of orthodontic tooth movement.

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Dietary Salt Accelerates Orthodontic Tooth Movement by Increased Osteoclast Activity

International Journal of Molecular Sciences ◽

10.3390/ijms22020596 ◽

2021 ◽

Vol 22 (2) ◽

pp. 596

Author(s):

Agnes Schröder ◽

Joshua Gubernator ◽

Alexandra Leikam ◽

Ute Nazet ◽

Fabian Cieplik ◽

...

Keyword(s):

Bone Density ◽

Bone Loss ◽

Bone Metabolism ◽

Tooth Movement ◽

Orthodontic Tooth Movement ◽

Dietary Salt ◽

Osteoclast Activity ◽

Salt Uptake ◽

Periodontal Bone Loss ◽

The Impact

Dietary salt uptake and inflammation promote sodium accumulation in tissues, thereby modulating cells like macrophages and fibroblasts. Previous studies showed salt effects on periodontal ligament fibroblasts and on bone metabolism by expression of nuclear factor of activated T-cells-5 (NFAT-5). Here, we investigated the impact of salt and NFAT-5 on osteoclast activity and orthodontic tooth movement (OTM). After treatment of osteoclasts without (NS) or with additional salt (HS), we analyzed gene expression and the release of tartrate-resistant acid phosphatase and calcium phosphate resorption. We kept wild-type mice and mice lacking NFAT-5 in myeloid cells either on a low, normal or high salt diet and inserted an elastic band between the first and second molar to induce OTM. We analyzed the expression of genes involved in bone metabolism, periodontal bone loss, OTM and bone density. Osteoclast activity was increased upon HS treatment. HS promoted periodontal bone loss and OTM and was associated with reduced bone density. Deletion of NFAT-5 led to increased osteoclast activity with NS, whereas we detected impaired OTM in mice. Dietary salt uptake seems to accelerate OTM and induce periodontal bone loss due to reduced bone density, which may be attributed to enhanced osteoclast activity. NFAT-5 influences this reaction to HS, as we detected impaired OTM and osteoclast activity upon deletion.

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