Hypoxia-regulated human periodontal ligament cells via Wnt/β-catenin signaling pathway

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.

Oxygen-Releasing Hyaluronic Acid-Based Dispersion with Controlled Oxygen Delivery for Enhanced Periodontal Tissue Engineering

Periodontitis is a chronic biofilm-associated inflammatory disease of the tooth-supporting tissues that causes tooth loss. It is strongly associated with anaerobic bacterial colonization and represents a substantial global health burden. Due to a local hypoxic environment, tissue regeneration is impaired. Oxygen therapy has shown promising results as a potential treatment of periodontitis, but so far, local oxygen delivery remains a key technical challenge. An oxygen (O₂)-releasing hyaluronic acid (HA)-based dispersion with a controlled oxygen delivery was developed. Cell viability of primary human fibroblasts, osteoblasts, and HUVECs was demonstrated, and biocompatibility was tested using a chorioallantoic membrane assay (CAM assay). Suppression of anaerobic growth of Porphyromonas gingivalis was shown using the broth microdilution assay. In vitro assays showed that the O₂-releasing HA was not cytotoxic towards human primary fibroblasts, osteoblasts, and HUVECs. In vivo, angiogenesis was enhanced in a CAM assay, although not to a statistically significant degree. Growth of P. gingivalis was inhibited by CaO₂ concentrations higher than 256 mg/L. Taken together, the results of this study demonstrate the biocompatibility and selective antimicrobial activity against P. gingivalis for the developed O₂-releasing HA-based dispersion and the potential of O₂-releasing biomaterials for periodontal tissue regeneration.

Canonical Wnt/β-catenin signaling has positive effects on osteogenesis, but can have negative effects on cementogenesis

BACKGROUND

To date, therapeutic approaches for cementum regeneration are limited and outcomes remain unpredictable. A significant barrier to improve therapies for cementum regeneration is that the cementocyte and its intracellular signal transduction mechanisms remain poorly understood. This study aims to elucidate the regulatory mechanism of Wnt pathway in cementogenesis.

METHODS

The effects of canonical Wnt signaling were compared in vitro using immortalized murine cementocyte cell line IDG-CM6 and osteocyte cell line IDG-SW3 by qRT-PCR, Western blot, confocal microscopy, alkaline phosphatase (ALP) assay and Alizarin red S staining. In vivo, histological changes of cementum and bone formation were examined in transgenic mice in which constitutive activation of β-catenin is driven by Dmp1 promoter.

RESULTS

Expression of components of the Wnt/β-catenin pathway were much greater in the IDG-SW3 cells compared to the IDG-CM6 cells resulting in much lower expression of Sost/sclerostin in the IDG-SW3 cells. In the IDG-CM6 cells, low dose Wnt3a (20 ng/ml) had a modest effect while high dose (200 ng/ml) inhibited runt-related transcription factor 2 (Runx2), osterix (Osx), ALP and osteopontin (OPN) in contrast to the IDG-SW3 cells where high dose Wnt3a dramatically increased mRNA expression of these same markers. However, high Wnt3a significantly increased mRNA for components of Wnt/β-catenin signaling pathway in both IDG-CM6 and IDG-SW3 cells. In vivo, constitutive activation of β-catenin in the Dmp1-lineage cells in mice leads to bone hyperplasia and cementum hypoplasia.

CONCLUSION(S)

These findings indicate that Wnt signaling has distinct and different effects on the regulation of long bone as compared to cementum. This article is protected by copyright. All rights reserved.

Dental mesenchymal stromal/stem cells in different microenvironments— implications in regenerative therapy

Current research data reveal microenvironment as a significant modifier of physical functions, pathologic changes, as well as the therapeutic effects of stem cells. When comparing regeneration potential of various stem cell types used for cytotherapy and tissue engineering, mesenchymal stem cells (MSCs) are currently the most attractive cell source for bone and tooth regeneration due to their differentiation and immunomodulatory potential and lack of ethical issues associated with their use. The microenvironment of donors and recipients selected in cytotherapy plays a crucial role in regenerative potential of transplanted MSCs, indicating interactions of cells with their microenvironment indispensable in MSC-mediated bone and dental regeneration. Since a variety of MSC populations have been procured from different parts of the tooth and tooth-supporting tissues, MSCs of dental origin and their achievements in capacity to reconstitute various dental tissues have gained attention of many research groups over the years. This review discusses recent advances in comparative analyses of dental MSC regeneration potential with regards to their tissue origin and specific microenvironmental conditions, giving additional insight into the current clinical application of these cells.

Ligament/Tendon Culture under Hypoxic Conditions: A Systematic Review

The hypoxic environment is a substantial factor in maintenance, proliferation, and differentiation of the cell cultures. Low oxygen is known as a potent chondrogenesis stimulus in stem cells that is important for clinical application and engineering of functional cartilage. Hypoxia can potentially induce angiogenesis process by secretion of cytokines. This systematic review goal is to discover the effect of hypoxic condition on tendon/ ligament culture and the best oxygen level of hypoxia for in vitro and in vivo studies. We included 21 articles. A comprehensive review of this database confirms that the hypoxic condition is a substantial factor in the maintenance, proliferation, and differentiation of ligament/tendon cultures. Cell proliferation in the severe hypoxic (oxygen concentration of 1%) group at 24 h postcultivation was considered significant, but cell proliferation was markedly inhibited in the severe hypoxic group after 48 h.

Wnt signalling in oral and maxillofacial diseases

Wnts include more than 19 types of secreted glycoproteins that are involved in a wide range of pathological processes in oral and maxillofacial diseases. The transmission of Wnt signalling from the extracellular matrix into the nucleus includes canonical pathways and noncanonical pathways, which play an important role in tooth development, alveolar bone regeneration, and related diseases. In recent years, with the in-depth study of Wnt signalling in oral and maxillofacial-related diseases, many new conclusions and perspectives have been reached, and there are also some controversies. This article aims to summarise the roles of Wnt signalling in various oral diseases, including periodontitis, dental pulp disease, jaw disease, cleft palate, and abnormal tooth development, to provide researchers with a better and more comprehensive understanding of Wnts in oral and maxillofacial diseases.

Characterization of stable hypoxia-preconditioned dental pulp stem cells compared with mobilized dental pulp stem cells for application for pulp regenerative therapy

Background

Dental pulp stem cells (DPSCs) have been developed as a potential source of mesenchymal stem cells (MSCs) for regeneration of dental pulp and other tissues. However, further strategies to isolate highly functional DPSCs beyond the colony-forming methods are required. We have demonstrated the safety and efficacy of DPSCs isolated by G-CSF-induced mobilization and cultured under normoxia (mobilized DPSCs, MDPSCs) for pulp regeneration. The device for isolation of MDPSCs, however, is not cost-effective and requires a prolonged cell culture period. It is well known that MSCs cultured under hypoxic-preconditions improved MSC proliferation activity and stemness. Therefore, in this investigation, we attempted to improve the clinical utility of DPSCs by hypoxia-preconditioned DPSCs (hpDPSCs) compared with MDPSCs to improve the potential clinical utility for pulp regeneration in endodontic dentistry.

Methods

Colony-forming DPSCs were isolated and preconditioned with hypoxia in a stable closed cultured system and compared with MDPSCs isolated from the individual dog teeth. We examined the proliferation rate, migration potential, anti-apoptotic activity, and gene expression of the stem cell markers and angiogenic/neurotrophic factors. Trophic effects of the conditioned medium (CM) were also evaluated. In addition, the expression of immunomodulatory molecules upon stimulation with IFN-γ was investigated. The pulp regenerative potential and transplantation safety of hpDPSCs were further assessed in pulpectomized teeth in dogs by histological and immunohistochemical analyses and by chemistry of the blood and urine tests.

Results

hpDPSCs demonstrated higher proliferation rate and expression of a major regulator of oxygen homeostasis, HIF-1α, and a stem cell marker, CXCR-4. The direct migratory activity of hpDPSCs in response to G-CSF was significantly higher than MDPSCs. The CM of hpDPSCs stimulated neurite extension. However, there were no changes in angiogenic, migration, and anti-apoptotic activities compared with the CM of MDPSCs. The expression of immunomodulatory gene, PTGE was significantly upregulated by IFN gamma in hpDPSCs compared with MDPSCs. However, no difference in nitric oxide was observed. The regenerated pulp tissue was quantitatively and qualitatively similar in hpDPSC transplants compared with MDPSC transplants in dog teeth. There was no evidence of toxicity or adverse events of the hpDPSC transplantation.

Conclusions

These results demonstrated that the efficacy of hpDPSCs for pulp regeneration was identical, although hpDPSCs improved stem cell properties compared to MDPSCs, suggesting their potential clinical utility for pulp regeneration.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02240-w.

Resveratrol Counteracts Hypoxia-Induced Gastric Cancer Invasion and EMT through Hedgehog Pathway Suppression

BACKGROUND

Gastric Cancer (GC) is one of the most malignant and lethal tumors worldwide. The hypoxic microenvironment is correlated with GC cell invasion, metastasis and Epithelial-Mesenchymal Transition (EMT). Resveratrol is a compound extracted from various plants, including grapes, berries, and some traditional Chinese medicines. Recently, the anticancer properties of resveratrol against many cancers have been reported in a range of studies. However, the exact mechanism through which resveratrol prevents GC invasion and metastasis under hypoxic conditions remains unclear.

OBJECTIVE

The objective of this study is to show to what extent resveratrol could inhibit the hypoxia-induced malignant biological behavior of GC.

METHODS

SGC-7901 cells were cultured in a consistent 3% O2 hypoxic condition or 21% O2 normal condition for 48 hours to establish an in vitro hypoxia model. Western blot and qRT-PCR were used to detect EMT markers of SGC- 7901 cells, including E-cadherin, HIF-1a, Vimentin, etc. Transwell Matrigel Invasion Assays were used to test the invasive ability of SGC-7901 cells. The siRNA targeting Gli-1 showed its role in hypoxia-induced EMT and invasion of SGC-7901 cells.

RESULTS

Resveratrol was found to significantly decrease HIF-1α protein levels induced by hypoxia in SGC-7901 cells. HIF-1α accumulation was found to promote cell proliferation, migration, and invasive capacities in addition to EMT changes through the activation of the Hedgehog pathway. These effects were found to be reversed by resveratrol.

CONCLUSION

Therefore, these data indicate that resveratrol may serve as a potential anticancer agent for the treatment of GC, even in a hypoxic tumor microenvironment.

Fibroblastic differentiation of mesenchymal stem/stromal cells (MSCs) is enhanced by hypoxia in 3D cultures treated with bone morphogenetic protein 6 (BMP6) and growth and differentiation factor 5 (GDF5)

INTRODUCTION

Culture conditions and differentiation cocktails may facilitate cell maturation and extracellular matrix (ECM) secretion and support the production of engineered fibroblastic tissues with applications in ligament regeneration. The objective of this study is to investigate the potential of two connective tissue-related ligands (i.e., BMP6 and GDF5) to mediate collagenous ECM synthesis and tissue maturation in vitro under normoxic and hypoxic conditions based on the hypothesis that BMP6 and GDF5 are components of normal paracrine signalling events that support connective tissue homeostasis.

METHODS

Human adipose-derived MSCs were seeded on 3D-printed medical-grade polycaprolactone (PCL) scaffolds using a bioreactor and incubated in media containing GDF5 and/or BMP6 for 21 days in either normoxic (5% oxygen) or hypoxic (2% oxygen) conditions. Constructs were harvested on Day 3 and 21 for cell viability analysis by live/dead staining, structural analysis by scanning electron microscopy, mRNA levels by RTqPCR analysis, and in situ deposition of proteins by immunofluorescence microscopy.

RESULTS

Pro-fibroblastic gene expression is enhanced by hypoxic culture conditions compared to normoxic conditions. Hypoxia renders cells more responsive to treatment with BMP6 as reflected by increased expression of ECM mRNA levels on Day 3 with sustained expression until Day 21. GDF5 was not particularly effective either in the absence or presence of BMP6.

CONCLUSIONS

Fibroblastic differentiation of MSCs is selectively enhanced by BMP6 and not GDF5. Environmental factors (i.e., hypoxia) also influenced the responsiveness of cells to this morphogen.

Chemokine C-C motif ligand 8 in periodontal ligament during orthodontic tooth movement

OBJECTIVES

To investigate the roles of chemokine (C-C motif) ligand 8 (CCL8) in periodontal ligament during orthodontic tooth movement (OTM).

METHODS

Bioinformatics analyzed 100 genes in human periodontal ligament cells that were most upregulated after 48 hours of mechanical stress, and these genes were classified through GO and KEGG databases. Nickel-titanium closed-coil springs were placed between right first molar and incisors to produce 20 cN of orthodontic force in eight-week-old male SD rats for 1 and 2 days, followed by immunohistochemical staining of CCL8. Human periodontal ligament fibroblasts (hPDLFs) were stimulated by 14% cyclic tension force (Flexcell FX-5000 T Tension System) or hypoxia conditions to mimic OTM for 1 and 2 days, then the resulting CCL8 were examined through ELISA. Scratching assay was performed by treating hPDLFs with different concentrations of CCL8 (1 ng/ml, 10 ng/ml, 100 ng/ml). The migration, proliferation, and adhesion abilities of 100 ng/ml CCL8-treated hPDLFs were also examined. qRT-PCR and western blot detected matrix metalloproteinase 3, periostin, and osteoprotegrin expressions of hPDLFs under 100 ng/ml CCL8.

RESULTS

Bioinformatic analysis demonstrated that CCL8 was upregulated after applying mechanical stress for 48 hours. CCL8 secretion showed upregulation after 24 hours of OTM applicationsin vivo and in vitro. CCL8-treated hPDLFs showed significant positive effects on cell proliferation and matrix metalloproteinase 3. It also inhibited periostin and osteoprotegrin expressions.

CONCLUSIONS

CCL8 was upregulated in periodontal ligament during initial stage of OTM. Although CCL8 in human periodontal ligaments showed no significant effects on cell migration ability, it did enhance cell proliferation and osteoclastogenesis.

Long non-coding RNA 01126 promotes periodontitis pathogenesis of human periodontal ligament cells via miR-518a-5p/HIF-1α/MAPK pathway

BACKGROUND

Periodontitis is a prevalent oral inflammatory disease, which can cause periodontal ligament to a local hypoxia environment. However, the mechanism of hypoxia associated long non-coding RNAs (lncRNAs) involved in periodontitis is still largely unknown.

METHODS

Microarray was performed to detect the expression patterns of lncRNAs in 3 pairs of gingival tissues from patients with periodontitis and healthy controls. The expression of lncRNA 01126 (LINC01126), miR-518a-5p and hypoxia-inducible factor-1α (HIF-1α) in periodontal tissues and in human periodontal ligament cells (hPDLCs) under hypoxia was measured by quantitative real-time polymerase chain reaction or western blot. Fluorescence in situ hybridization and cell fraction assay were performed to determine the subcellular localization of LINC01126 and miR-518a-5p. Overexpression or knockdown of LINC01126 or HIF-1α was used to confirm their biological roles in hPDLCs. MTT assays were performed to evaluate hPDLCs proliferation ability. Flow cytometry was used to detect apoptosis. ELISA was used to measure the expression levels of interleukin (IL)-1β, IL-6, IL-8 and TNF-α. Dual-luciferase reporter assays were performed to assess the binding of miR-518a-5p to LINC01126 and HIF-1α. RNA immunoprecipitation assay was used to identify whether LINC01126 and miR-518a-5p were significantly enriched in AGO-containing micro-ribonucleoprotein complexes.

RESULTS

We selected LINC01126, which was the most highly expressed lncRNA, to further verify its functions in periodontitis-induced hypoxia. The expression of LINC01126 was increased in periodontal tissues. In vitro experiment demonstrated that LINC01126 suppressed proliferation, promoted apoptosis and inflammation of hPDLCs under hypoxia via sponging miR-518a-5p. Moreover, we identified HIF-1α acted as a direct target of miR-518a-5p in hPDLCs and LINC01126 promoted periodontitis pathogenesis by regulating the miR-518a-5p/HIF-1α/MAPK pathway.

CONCLUSION

LINC01126 promotes periodontitis pathogenesis of hPDLCs via miR-518a-5p/HIF-1α/MAPK pathway, providing a possible clue for LINC01126-based periodontal therapeutic approaches.

Wnt signaling: An attractive target for periodontitis treatment

Periodontitis is the most common chronic inflammatory disease, and a leading cause of tooth loss. Characterized by resorption of alveolar process and destruction of periodontal ligaments, periodontitis can impact not only periodontal tissues but also systemic diseases, such as diabetes, cardiovascular diseases, and respiratory infections. Currently, it is a hotspot to manage destruction and gain regeneration of periodontal tissues. Increasing evidence indicates that the Wnt signaling plays an important role in homeostasis of periodontal tissues, functions of periodontal derived cells, and progression of periodontitis. Its molecule expressions were abnormal in periodontitis. As such, modulators targeting the Wnt signaling may be an adjuvant therapy for periodontitis treatment. This review elucidates the role of Wnt signaling and its molecules, with a view to develop a potential application of drugs targeting the Wnt signaling for periodontitis treatment.

Histological evaluation of peri-implant mucosal and gingival tissues in peri-implantitis, peri-implant mucositis and periodontitis patients: a cross-sectional clinical study

Objective: Aim of present study was to evaluate gingival tissue samples obtained from healthy and diseased sites of teeth and dental implants in terms of hypoxia and collagenase activity.Methods: Four study groups were created as Group-1; healthy individuals (H), Group-2; periodontitis patients with stage 3 grade B (P), Group-3; patients with peri-implant mucositis. Group-4; patients with peri-implantitis (P-IMP). Plaque index (PI), gingival index (GI) and probing pocket depth (PPD) were recorded. Gingival and peri-implant mucosal biopsies were obtained. Fibroblast and inflammatory cells were counted. Hypoxia-inducible factor (HIF)-1α, prolyl hydroxylase (PH), matrix metalloproteinase (MMP)-8, tissue inhibitor of MMPs (TIMP)-1, cyclooxygenase (COX)-2 and inducible nitric oxide synthase (iNOS) levels were determined via immunohistochemistry.Results: Healthy controls had highest fibroblast cell counts and lowest inflammatory cell counts compared to other groups. Peri-implantitis and periodontitis samples had similar fibroblast and inflammatory cell counts, while peri-implant mucositis had higher fibroblast cells and lowered inflammatory cells compared to periodontitis and peri-implantitis samples. HIF-1α, COX-2 and iNOS levels were lowest in healthy controls and increased in other groups. Peri-implant mucositis samples had significantly lower expressions of HIF-1α, COX-2 and iNOS compared to peri-implantitis and periodontitis groups. PH expressions were lower in periodontitis and peri-implantitis groups compared to healthy controls and peri-implant mucositis groups. MMP-8 levels were lower in healthy group compared to other groups while levels were similar in periodontitis, peri-implant mucositis and peri-implantitis groups. TIMP levels were similar in groups.Conclusion: Periodontitis, peri-implantitis, and peri-implant mucositis samples exhibited higher inflammation and lower fibroblast cell counts and tend to have increased tissue collagenase activity, hypoxia and inflammation compared to healthy samples.

Salvianolic acid B promotes the osteogenic differentiation of human periodontal ligament cells through Wnt/β-catenin signaling pathway

BACKGROUND

Osteogenic differentiation of human periodontal ligament cells (hPDLCs) is crucial for regenerate periodontal tissues. In this study, we investigated the function of salvianolic acid B (Sal B) in osteogenesis of hPDLCs.

METHODS

HPDLCs were isolated from healthy third molar roots. HPDLCs at passage 3 were identified by morphological observation and immunohistochemistry of vimentin. The viability of hPDLCs incubated with Sal B at concentrations of 0μM, 0.1μM, 0.5μM, 1μM and 5μM were measured by CCK-8 assay. To evaluate the effect of Sal B on osteogenic differentiation of hPDLCs, the alkaline phosphatase (ALP) activity, osteogenic differentiation markers, and mineralized nodules were determined by ALP kit, qRT-PCR and alizarin red S staining, respectively. To confirm the function of Sal B in hPDLCs involved in Wnt/β-catenin signaling pathway, hPDLCs were incubated with Sal B or co-incubated with Sal B and DKK-1 (a inhibitor of Wnt/β-catenin). The levels of Wnt/β-catenin signaling pathway and osteogenic differentiation-associated indicators were then determined.

RESULTS

HPDLCs showed a typical fibroblast-like and spindle-shaped, with vimentin-positive. The viability of hPDLCs had no obvious change with stimulation of Sal B at various doses. Sal B promoted the increase of ALP activity, osteogenic differentiation markers levels, mineralized nodules and activation of Wnt/β-catenin signaling pathway, and DKK-1 could block those effects of Sal B on hPDLCs.

CONCLUSION

Sal B promoted osteogenesis of hPDLCs through Wnt/β-catenin signaling pathway, which providing a potential drug for periodontitis treatment.

Hypoxia and collagen crosslinking in the healthy and affected sites of periodontitis patients

Present study suggests that diseased sites of periodontitis with stage 3 grade B and C had decreased fibroblast cell density, hypoxia-inducible factor (HIF) and vascular endothelial growth factor (VEGF) expressions while increased inflammatory cell counts compared to both healthy sites of the periodontitis patients and healthy controls. Collagen maturation enzymes also decreased in the diseased sites. Objective: The present study aimed at determining markers of hypoxia and collagen crosslinking in healthy and diseased gingiva from healthy individuals and periodontitis patients. Methods: Group-1; healthy individuals, Group-2; healthy sites of periodontitis patients-stage 3 grade B, (H-GradeB) Group-3; diseased sites of periodontitis patients-stage 3 grade B, (D-GradeB). Group-4; healthy sites of periodontitis patients-stage 3 grade C, (H-GradeC). Group-5; diseased sites of periodontitis patients-stage 3 grade C, (D-GradeC). Plaque index (PI), gingival index (GI) and clinical attachment levels (CALs) were recorded. Gingival biopsies were obtained. Fibroblast and inflammatory cells were counted. HIF-1α, prolyl hydroxylase (PH), VEGF, lysyl oxidase (LOX) and lysyl hydroxylase (LH) levels were determined via immunohistochemistry. Results: Fibroblast cell counts were lower in D-GradeC and D-GradeB than other groups. C group had highest fibroblast cell counts. Inflammatory cell counts were highest in the D-GradeC and lowest in C group. HIF-1α levels were highest in C group and decreased in diseased sites. Lowest value was observed in D-GradeC group. VEGF, PH, and LH levels were higher in the control group compared to other groups. LOX levels were similar in the groups except for D-GradeC. LOX levels were similar in the groups except for D-GradeC which is significantly lower than those of the control group and healthy sites. Conclusions: The results revealed that diseased sites of periodontitis patients had decreased fibroblast cells, HIF and VEGF expressions while increased inflammatory cells. Collagen crosslinking tend to decrease with disease regardless of stage and grade of disease.

Luteolin supports osteogenic differentiation of human periodontal ligament cells

Background

Previous research revealed that luteolin could improve the activation of alkaline phosphatase (ALP) and osteocalcin in mouse osteoblasts. We aimed to determine the effect of luteolin on osteogenic differentiation of periodontal ligament cells (PDLCs).

Methods

Cultured human PDLCs (HPDLCs) were treated by luteolin at 0.01, 0.1, 1, 10, 100 μmol/L, Wnt/β-catenin pathway inhibitor (XAV939, 5 μmol/L) alone or in combination with 1 μmol/L luteolin. Immunohistochemical staining was performed to ensure cells source. Cell activity and the ability of osteogenic differentiation in HPDLCs were determined by MTT, ALP and Alizarin Red S staining. Real-time Quantitative PCR Detecting System (qPCR) and Western blot were performed to measure the expressions of osteogenic differentiation-related genes such as bone morphogenetic protein 2 (BMP2), osteocalcin (OCN), runt-related transcription factor 2 (RUNX2), Osterix (OSX) and Wnt/β-catenin pathway proteins members cyclin D1 and β-catenin.

Results

Luteolin at concentrations of 0.01, 0.1, 1, 10, 100 μmol/L promoted cell viability, ALP activity and increased calcified nodules content in HPDLCs. The expressions of BMP2, OCN, OSX, RUNX2, β-catenin and cyclin D1 were increased by luteolin at concentrations of 0.01, 0.1, 1 μmol/L, noticeably, 1 μmol/L luteolin produced the strongest effects. In addition, XAV939 inhibited the expressions of calcification and osteogenic differentiation-related genes in HPDLCs, and 1 μmol/L luteolin availably decreased the inhibitory effect.

Conclusion

1 μmol/L luteolin accelerated osteogenic differentiation of HPDLCs via activating the Wnt/β-catenin pathway, which could be clinically applied to treat periodontal disease.

The Process of Acclimation to Chronic Hypoxia Leads to Submandibular Gland and Periodontal Alterations: An Insight on the Role of Inflammatory Mediators

The exposition to hypoxia is a stressful stimulus, and the organism develops acclimation mechanisms to ensure homeostasis, but if this fails, it leads to the development of pathological processes. Considering the large number of people under hypoxic conditions, it is of utmost importance to study the mechanisms implicated in hypoxic acclimation in oral tissues and the possible alteration of some important inflammatory markers that regulate salivary and periodontal function. It is the aim of the present study to analyze submandibular (SMG) and periodontal status of animals chronically exposed to continuous (CCH) or intermittent (CIH) hypoxia in order to elucidate the underlying molecular mechanisms that may lead to hypoxic acclimation. Adult Wistar rats were exposed to CCH or CIH simulating 4200 meters of altitude during 90 days. Salivary secretion was decreased in animals exposed to hypoxia, being lower in CIH, together with increased prostaglandin E₂ (PGE₂) content, TBARS concentration, and the presence of apoptotic nuclei and irregular secretion granules in SMG. AQP-5 mRNA levels decreased in both hypoxic groups. Only the CCH group showed higher HIF-1α staining, while CIH alone exhibited interradicular bone loss and increased concentration of the bone resorption marker CTX-I. In summary, animals exposed to CIH show a worse salivary secretion rate, which related with higher levels of PGE₂, suggesting a negative role of this inflammatory mediator during hypoxia acclimation. We link the weak immunorreactivity of HIF-1α in CIH with improper hypoxia acclimation, which is necessary to sustaining SMG physiology under this environmental condition. The alveolar bone loss observed in CIH rats could be due mainly to a direct effect of PGE₂, as suggested by its higher content in gingival tissue, but also to the indirect effect of hyposalivation. This study may eventually contribute to finding therapeutics to treat the decreased salivary flow, improving in that way oral health.

Evaluation of Hypoxia on the Expression of miR-646/IGF-1 Signaling in Human Periodontal Ligament Cells (hPDLCs)

Background

This study aims to investigate the role of miR-646 in hypoxia conditions in human periodontal ligament cells (hPDLCs), exploring the effect of hypoxia on hPDLCs proliferation and apoptosis. In addition, this study aimed to explore the potential mechanism of miR-646/IGF-1 signaling in hPDLCs in hypoxia conditions.

Material/Methods

hPDLCs (fifth passage) cultured by the tissue culture method were randomly assigned to the severe hypoxia (1% O₂) group, the slight hypoxia (5% O₂) group or the control (21% O₂) group. Then reverse transcription quantitative real-time polymerase chain reaction and western blot analysis were used to detect the mRNA and protein expression of miR-646 and IGF-1. hPDLCs infected with lentivirus (LV)-pre-miR-646 or LV-anti-mR-646, and negative controls were cultured. MTT assay, caspase-3 ELISA assay, and wound healing assay were performed to evaluate how miR-646 was influenced by hypoxia. In addition, the relationship between miR-646 and IGF-1 was explored.

Results

The expression of miR-646 was downregulated and IGF-1 was upregulated in hypoxia conditions. MiR-646 was able to suppress hPDLCs proliferation and promote apoptosis in hypoxia conditions. The mRNA and protein expressions of IGF-1 were downregulated when miR-646 was overexpressed and upregulated when miR-646 was downregulated.

Conclusions

This finding identified a significant role of miR-646 in hPDLCs in suppressing cell proliferation and promoting apoptosis by inversely regulating IGF-1 expression. Meanwhile, the regulation of hPDLCs in hypoxia may be through the miR-646/IGF-1 signaling pathway, probably serving as a promising therapeutic target for periodontal diseases.

Porous lithium-doped hydroxyapatite scaffold seeded with hypoxia-preconditioned bone-marrow mesenchymal stem cells for bone-tissue regeneration

Hydroxyapatite (HA) is a commonly used biomaterial in bone-tissue engineering, but pure HA is deficient in osteoinduction. In this study, we fabricated scaffolds of lithium-doped HA (Li-HA) and assess the bone generation enhancement of Li-HA scaffolds seeded with hypoxia-preconditioned bone-marrow mesenchymal stem cells (BMMSCs). We found that 1.5%Li-HA obtained optimal cell proliferation activity in vitro. In an in vivo study, Li-HA/BMSCs enhanced new bone formation, reducing the GSK-3β and increasing the β-catenin, but the angiogenic effect was not modified significantly. However, when the seeded BMMSCs had been preconditioned in hypoxia condition, the new bone formation was increased, with lower GSK-3β and higher β-catenin amounts detected. The HIF-1α secretion was up-regulated, and the vascular endothelial growth factor and CD31 expression increased. In conclusion, the bone scaffold developed from Li-doped HA seeded with hypoxia-preconditioned BMMSCs exerted positive effect on activating the Wnt and HIF-1α signal pathway, and showed good osteogenesis and angiogenesis potential. The composited scaffold contributed to an encouraging result in bone regeneration.

Activated Yes-Associated Protein Accelerates Cell Cycle, Inhibits Apoptosis, and Delays Senescence in Human Periodontal Ligament Stem Cells

Objectives: To provide insight into the biological effects of activated Yes-associated protein (YAP) on the proliferation, apoptosis, and senescence of human periodontal ligament stem cells (h-PDLSCs). Methods: h-PDLSCs were isolated by the limiting dilution method, and their surface markers were quantified by flow cytometry. Enhanced green fluorescence protein (EGFP)-labeled lentiviral vector was used to activate YAP in h-PDLSCs, then qRT-PCR and Western blotting were used to evaluate the expression level of YAP. Immunofluorescence was used to detect the location of YAP in h-PDLSCs. The proliferation activity was detected by cell counting kit-8 (CCK-8) and 5-ethynyl-2'-deoxyuridine (EdU), and the cell cycle was determined by flow cytometry. Apoptosis was analyzed by Annexin V-APC staining. Cell senescence was detected by β-galactosidase staining. Proteins in ERK, Bcl-2, and p53 signaling pathways were detected by Western blotting. Results: h-PDLSCs were isolated successfully and were positive for human mesenchymal stem cell surface markers. After YAP was activated by lentiviral vector, the mRNA and protein of YAP were highly expressed, and more YAP translocated into the nucleus. When YAP was overexpressed in h-PDLSCs, proliferation activity was improved; early and late apoptosis rates decreased (P<0.05); the proportion of cells in G2/M phases increased (P<0.05), while that in G0/G1 phase decreased (P<0.05); cellular senescence was delayed (P<0.01); the expression of P-MEK, P-ERK, P-P90RSK and P-Msk increased, while the expression of Bcl-2 family members (Bak, Bid and Bik) decreased. Conclusions: Activated YAP promotes proliferation, inhibits apoptosis, and delays senescence of h-PDLSCs. The Hippo-YAP signaling pathway can influence ERK and Bcl-2 signaling pathways.