The role of HIF-1α in nicotine-induced root and bone resorption during orthodontic tooth movement

HIF-1α and periodontitis: Novel insights linking host-environment interplay to periodontal phenotypes

Periodontitis, the sixth most prevalent epidemic disease globally, profoundly impacts oral aesthetics and masticatory functionality. Hypoxia-inducible factor-1α (HIF-1α), an oxygen-dependent transcriptional activator, has emerged as a pivotal regulator in periodontal tissue and alveolar bone metabolism, exerts critical functions in angiogenesis, erythropoiesis, energy metabolism, and cell fate determination. Numerous essential phenotypes regulated by HIF are intricately associated with bone metabolism in periodontal tissues. Extensive investigations have highlighted the central role of HIF and its downstream target genes and pathways in the coupling of angiogenesis and osteogenesis. Within this concise perspective, we comprehensively review the cellular phenotypic alterations and microenvironmental dynamics linking HIF to periodontitis. We analyze current research on the HIF pathway, elucidating its impact on bone repair and regeneration, while unraveling the involved cellular and molecular mechanisms. Furthermore, we briefly discuss the potential application of targeted interventions aimed at HIF in the field of bone tissue regeneration engineering. This review expands our biological understanding of the intricate relationship between the HIF gene and bone angiogenesis in periodontitis and offers valuable insights for the development of innovative therapies to expedite bone repair and regeneration.

RANK-RANKL-OPG expression after gingival mesenchymal stem cell hypoxia preconditioned application in an orthodontic tooth movement animal model

Background

The expression of receptor activator of Nuclear Factor Kappa Beta (RANK) and its ligand (RANKL), as well as osteoprotegrin (OPG), in the alveolar bone (AB), may improve bone remodeling during orthodontic tooth movement (OTM). It is hypothesized that hypoxia-preconditioned gingival mesenchymal stem cells (GMSC) may be more effective than normoxia-preconditioned GMSC in this regard. This study aims to investigate the expression of RANK, RANKL, and OPG in the compression and tension sides of AB after allogeneic administration of GMSC that were normoxia or hypoxia-preconditioned in rabbits (Oryctolagus cuniculus) undergoing OTM.

Methods

Twenty-four healthy young male rabbits were divided into two groups: T1, which underwent OTM and received normoxia-preconditioned GMSC, and T2, which underwent OTM and received hypoxia-preconditioned GMSC. A ligature wire was attached to the mandibular first molar and connected to a 50 g/mm2 closed coil spring, exerting force on the central incisor and left mandibular molar of the experimental animals. After 24 h of OTM, either normoxia- or hypoxia-preconditioned GMSC were injected into the gingiva of the samples in a single dose of 20 μl of phosphate-buffered saline (PBS). All samples were sacrificed on days 7, 14, and 28, and immunohistochemistry was performed to analyze the expression of RANK, RANKL, and OPG on the tension and compression sides.

Results

The expressions of RANK-RANKL-OPG in the alveolar bone of the compression and tension sides were significantly different during the 14-day period of OTM following allogeneic administration of GMSC that were normoxia or hypoxia-preconditioned (p < 0.05).

Conclusion

The expression of RANK-RANKL was significantly increased on the compression side of the alveolar bone during OTM after the administration of hypoxia-preconditioned allogeneic GMSC but not on the tension side. Conversely, RANKL-OPG expression was enhanced on the tension side but not on the compression side, as observed through immunohistochemical analysis in vivo.

Under pressure-mechanisms and risk factors for orthodontically induced inflammatory root resorption: a systematic review

BACKGROUND

The application of orthodontic forces causes root resorption of variable severity with potentially severe clinical ramifications.

OBJECTIVE

To systematically review reports on the pathophysiological mechanisms of orthodontically induced inflammatory root resorption (OIIRR) and the associated risk factors based on in vitro, experimental, and in vivo studies.

SEARCH METHODS

We undertook an electronic search of four databases and a separate hand-search.

SELECTION CRITERIA

Studies reporting on the effect of orthodontic forces with/without the addition of potential risk factors on OIIRR, including (1) gene expression in in-vitro studies, the incidence root resorption in (2) animal studies, and (3) human studies.

DATA COLLECTION AND ANALYSIS

Potential hits underwent a two-step selection, data extraction, quality assessment, and systematic appraisal performed by duplicate examiners.

RESULTS

One hundred and eighteen articles met the eligibility criteria. Studies varied considerably in methodology, reporting of results, and variable risk of bias judgements.In summary, the variable evidence identified supports the notion that the application of orthodontic forces leads to (1) characteristic alterations of molecular expression profiles in vitro, (2) an increased rate of OIIRR in animal models, as well as (3) in human studies. Importantly, the additional presence of risk factors such as malocclusion, previous trauma, and medications like corticosteroids increased the severity of OIIRR, whilst other factors decreased its severity, including oral contraceptives, baicalin, and high caffeine.

CONCLUSIONS

Based on the systematically reviewed evidence, OIIRR seems to be an inevitable consequence of the application of orthodontic forces-with different risk factors modifying its severity. Our review has identified several molecular mechanisms that can help explain this link between orthodontic forces and OIIRR. Nevertheless, it must be noted that the available eligible literature was in part significantly confounded by bias and was characterized by substantial methodological heterogeneity, suggesting that the results of this systematic review should be interpreted with caution.

REGISTRATION

PROSPERO (CRD42021243431).

Sinomenine Inhibits Orthodontic Tooth Movement and Root Resorption in Rats and Enhances Osteogenic Differentiation of PDLSCs

Purpose

To investigate the effects of sinomenine on orthodontic tooth movement and root resorption in rats, as well as the effect of sinomenine on the osteogenesis of periodontal ligament stem cells (PDLSCs).

Methods

Fifty-four male Wistar rats were randomly divided into 3 groups: control group, 20 mg/kg sinomenine group and 40 mg/kg sinomenine group. Fifty-gram orthodontic force was applied to all groups. Each group was injected intraperitoneally with corresponding concentration of sinomenine every day. After 14 days, all rats were sacrificed. Micro-computed tomography (micro-CT) scan was used to analyze tooth movement, root resorption and alveolar bone changes. The effect on periodontal tissue was analyzed by Masson, tartrate-resistant acid phosphatase (TRAP) and immunohistochemical staining. In vitro, PDLSCs were extracted and identified. The effect of sinomenine on proliferation was determined by cell-counting kit-8. The effect of sinomenine on osteogenesis was investigated by alkaline phosphatase (ALP) activity and alizarin red staining. qPCR and Western blotting were performed to explore the effects of sinomenine on the expression levels of ALP, runt-related transcription factor 2 (RUNX2), receptor activator of nuclear factor kappaB ligand (RANKL) and osteoprotegerin (OPG).

Results

The tooth movement and root resorption of sinomenine groups were reduced. Sinomenine decreased trabecular spacing on compression side and increased alveolar bone volume and trabecular thickness on tension side. TRAP-positive cells in sinomenine groups decreased significantly. The expressions of TNF-α and RANKL were decreased, while the expressions of OPG, RUNX2 and osteocalcin were up-regulated. In vitro, 0.1 M and 0.5 M sinomenine enhanced ALP activity, mineral deposition and the expression of ALP, RUNX2 and OPG, and reduced the expression of RANKL.

Conclusion

Sinomenine could inhibit tooth movement, reduce root resorption, and exert a positive effect on bone formation in rats. Moreover, sinomenine promoted the osteogenesis of PDLSCs.

ANGPTL4 regulates the osteogenic differentiation of periodontal ligament stem cells

The molecular mechanism of mechanical force regulating the osteogenic differentiation of periodontal ligament stem cells (PDLSCs) has not been clearly elucidated. In this study, two mRNA-seqs, GSE106887 and GSE109167, which contained several samples of PDLSCs under mechanical force, were downloaded from Gene Expression Omnibus. Differential expression analysis was firstly taken between GSE106887 and GSE109167, then the common 84 up-regulated genes and 26 down-regulated genes were selected. Function enrichment analysis was used to identify the key genes and pathways in PDLSCs subjected to the tension and compression force. PDLSCs were isolated from human periodontal ligament tissues. The effects of ANGPTL4 knockdown with shRNA on the osteogenic differentiation of PDLSCs were studied in vitro. Then, the orthodontic tooth movement (OTM) rat model was used to study the expression of HIF-1α and ANGPTL4 in alveolar bone remodeling in vivo. ANGPTL4 and the HIF-1 pathway were identified in PDLSCs subjected to the tension and compression force. alizarin red staining, alcian blue staining, and oil red O staining verified that PDLSCs had the ability of osteogenic, chondrogenic, and adipogenic differentiation, respectively. Verification experiment revealed that the expression of ANGPTL4 in PDLSCs significantly increased when cultured under osteogenic medium in vitro. While ANGPTL4 was knocked down by shRNA, the levels of ALPL, RUNX2, and OCN decreased significantly, as well as the protein levels of COL1A1, ALPL, RUNX2, and OCN. During the OTM, the expression of HIF-1α and ANGPTL4 in periodontal ligament cells increased on the tension and compression sides. We concluded the positive relationship between ANGPTL4 and osteogenic differentiation of PDLSCs.

The Synergistic Effect of Nicotine and Staphylococcus aureus on Peri-Implant Infections

Smoking is considered a key risk factor for implant survival; however, how it interacts with the pathogens in peri-implant infections is not clear. Here, we identified that nicotine, the key component of cigarette smoking, can interact with Staphylococcus aureus and synergistically induce peri-implant infections in a rat osteolysis model. The nicotine–S. aureus combination group increased the gross bone pathology, osteolysis, periosteal reactions, and bone resorption compared to the nicotine or S. aureus single treated group (p < 0.05). Nicotine did not promote the proliferation of S. aureus both in vitro and in vivo, but it can significantly upregulate the expression of staphylococcal protein A (SpA), a key virulence factor of S. aureus. The nicotine–S. aureus combination also synergistically activated the expression of RANKL (receptor activator of nuclear factor-kappa B ligand, p < 0.05) to promote the development of peri-implant infections. The synergistic effects between nicotine and S. aureus infection can be a new target to reduce the peri-implant infections.

Local Vascularization during Orthodontic Tooth Movement in a Split Mouth Rat Model-A MRI Study

Orthodontic tooth movement to therapeutically align malpositioned teeth is supposed to impact blood flow in the surrounding tissues. Here, we evaluated actual vascularization in the tension area of the periodontal ligament during experimental tooth movement in rats (N = 8) with magnetic resonance imaging (MRI). We inserted an elastic band between the left upper first and the second rat molar; the right side was not treated and served as control. After four days of tooth movement, we recorded T1-weighted morphologic and dynamic-contrast-enhanced MRI sequences with an animal-specific 7 Tesla MRI to assess of local vascularization. Furthermore, we quantified osteoclasts and monocytes in the periodontal ligament, which are crucial for orthodontic tooth movement, root resorptions as undesirable side effects, as well as the extent of tooth movement using paraffine histology and micro-CT analysis. Data were tested for normal distribution with Shapiro–Wilk tests followed by either a two-tailed paired t-test or a Wilcoxon matched-pairs signed rank test. Significant orthodontic tooth movement was induced within the four days of treatment, as evidenced by increased osteoclast and monocyte activity in the periodontal ligament as well as by µCT analysis. Contrast enhancement was increased at the orthodontically-treated side distally of the moved upper first left molar, indicating increased vascularization at the tension side of the periodontal ligament. Accordingly, we detected reduced time-to-peak and washout rates. Our study using MRI to directly assess local vascularization thus seems to confirm the hypothesis that perfusion is enhanced in tension zones of the periodontal ligament during orthodontic tooth movement.