Role of intracellular Ca2+-based mechanotransduction of human periodontal ligament fibroblasts

Piezo1 contributes to alveolar bone remodeling by activating β-catenin under compressive stress

INTRODUCTION

The mechanosensitive ion channel, Piezo1, is responsible for transducing mechanical stimuli into intracellular biochemical signals and has been identified within periodontal ligament cells (PDLCs). Nonetheless, the precise biologic function of Piezo1 in the regulation of alveolar bone remodeling by PDLCs during compressive forces remains unclear. Therefore, this study focused on elucidating the role of the Piezo1 channel in alveolar bone remodeling and uncovering its underlying mechanisms.

METHODS

PDLCs were subjected to compressive force and Piezo1 inhibitors. Piezo1 and β-catenin expressions were quantified by quantitative reverse transcription polymerase chain reaction and Western blot. The intracellular calcium concentration was measured using Fluo-8 AM staining. The osteogenic and osteoclastic activities were assessed using alkaline phosphatase staining, enzyme-linked immunosorbent assay, quantitative reverse transcription polymerase chain reaction, and Western blot. In vivo, orthodontic tooth movement was used to determine the effects of Piezo1 on alveolar bone remodeling.

RESULTS

Piezo1 and activated β-catenin expressions were upregulated under compressive force. Piezo1 inhibition reduced β-catenin activation, osteogenic differentiation, and osteoclastic activities. β-catenin knockdown reversed the increased osteogenic differentiation but had little impact on osteoclastic activities. In vivo, Piezo1 inhibition led to decreased tooth movement distance, accompanied by reduced β-catenin activation and expression of osteogenic and osteoclastic markers on the compression side.

CONCLUSIONS

The Piezo1 channel is a key mechanotransduction component of PDLCs that senses compressive force and activates β-catenin to regulate alveolar bone remodeling.

USP12 regulates ER stress-associated osteogenesis in human periodontal ligament cells under tension stress

The bone formation (osteogenesis) of human periodontal ligament cells (hPDLCs) under tension stress is essential for alveolar bone remodeling during orthodontic tooth movement (OTM). Deubiquitinating enzymes (DUBs) remove ubiquitin from target proteins, affecting their function and mediating cell survival and differentiation. However, whether and how DUBs regulate hPDLC function under tension force is poorly understood. In this study, we first investigated the expression of DUBs in hPDLCs under cyclic tension stimulation (CTS). Up-regulation of USP12 was observed in hPDLCs and at the tension side of molar teeth in OTM C57BL6 mice models. Knockdown (KD) of USP12 led to enhanced osteogenesis of hPDLCs under CTS. RNA-seq analysis suggested that the unfolded protein response (UPR) was the prevailing biological process in hPDLCs with USP12 KD, indicating that USP12 depletion triggered endoplasmic reticulum (ER) stress. The three major UPR-related signaling branches, namely PERK/eIF2α/ATF4, IRE1α/XBP1s, and ATF6 axis, were activated in hPDLCs with USP12 KD. By utilizing specific inhibitors, we proved that the PERK/eIF2α/ATF4 axis predominantly mediated the enhanced osteogenesis in hPDLCs with USP12 KD under CTS. In summary, our study demonstrates that USP12 serves as a key regulator for CTS-induced osteogenesis in hPDLCs, suggesting that USP12 upregulation serves as an adaptive mechanism for hPDLCs to alleviate ER stress during OTM.

Sanhuang decoction inhibits autophagy of periodontal ligament fibroblasts during orthodontic tooth movement by activating PI3K-Akt-mTOR pathway

BACKGROUND

Orthodontic tooth movement (OTM) is a typical treatment that corrects malaligned teeth by applying mechanical forces. However, mechanical overload often leads to damage of PDL fibroblasts. Sanhuang decoction (SHD) is commonly used to inhibit inflammation and oxidative stress. However, the mechanism of SHD for OTM treatment is still unclear. Therefore, this study attempts to explore the underlying mechanism through relevant experiments.

METHODS

In the present paper, we established a OTM rat model and further explored the effects of SHD on the PDL of OTM rats. The OTM model and effects of SHD were determined by micro-CT, and the PDL pathological changes, PDL width and capillaries in PDL were observed by H&E staining. Subsequently, the ROS levels in PDL was determined using flow cytometry analysis with DCFH-DA staining, MDA contents and antioxidative enzymes activities were also measured using commercial kits. Furthermore, the autophagy of PDL fibroblasts and proteins in the PI3K/Akt/mTOR pathway were detected using immunoluminescence, qPCR and western blotting assays.

RESULTS

The results showed SHD treatment can alleviate the decrease of PDL cells and capillaries induced by OTM, and improve the MDA and ROS levels in PDL, as well as enhance the activities of SOD and GSH-Px. Further experiments indicated SHD decreased the autophagy levels of PDL fibroblasts via promoting the phosphorylation levels of mTOR, PI3K and Akt proteins.

CONCLUSION

SHD inhibited autophagy of periodontal ligament fibroblasts during orthodontic tooth movement by inhibiting oxidative stress via activating PI3K-Akt-mTOR pathway. Our present findings suggested SHD treatment would be useful for management of the possible disorders occurs in orthodontic tooth movement therapy.

Advancements and Future Perspectives in Cell Electrospinning and Bio-Electrospraying

In recent years, researchers have tried to include living cells into electrospun nanofibers or droplets, leading to the field of live cell electrospinning and bio-electrospraying . In live cell electrospinning and bio-electrospraying, cells are embedded in a polymer and subject to the process of mechanical and electrical stimulation of the process. The resulting nanofiber mats or droplets with embedded cells have several potential applications in tissue engineering. The nanofiber structure provides a supportive and porous environment for cells to grow and interact with their surroundings. This can be favorable for tissue regeneration, where the goal is to create functional tissues that closely mimic the extracellular matrix. However, there are also challenges associated with live cell electrospinning and electrospraying, including maintaining cell viability and uniform cell distribution within the nanofiber mat. Additionally, the electrospinning/electrospraying process can have an impact on cell behavior, phenotype, and genotype, which must be cautiously monitored and studied. Overall, the goal of this review paper is to provide a comprehensive and critical analysis of the existing literature on cell electrospinning and bio-electrospraying.

The interaction between the nervous system and the stomatognathic system: from development to diseases

The crosstalk between the nerve and stomatognathic systems plays a more important role in organismal health than previously appreciated with the presence of emerging concept of the "brain-oral axis". A deeper understanding of the intricate interaction between the nervous system and the stomatognathic system is warranted, considering their significant developmental homology and anatomical proximity, and the more complex innervation of the jawbone compared to other skeletons. In this review, we provide an in-depth look at studies concerning neurodevelopment, craniofacial development, and congenital anomalies that occur when the two systems develop abnormally. It summarizes the cross-regulation between nerves and jawbones and the effects of various states of the jawbone on intrabony nerve distribution. Diseases closely related to both the nervous system and the stomatognathic system are divided into craniofacial diseases caused by neurological illnesses, and neurological diseases caused by an aberrant stomatognathic system. The two-way relationships between common diseases, such as periodontitis and neurodegenerative disorders, and depression and oral diseases were also discussed. This review provides valuable insights into novel strategies for neuro-skeletal tissue engineering and early prevention and treatment of orofacial and neurological diseases.

Ribosomal Stress Couples with the Hypoxia Response in Dec1-Dependent Orthodontic Tooth Movement

This study characterized the effects of a deficiency of the hypoxia-responsive gene, differentiated embryonic chondrocyte gene 1 (Dec1), in attenuating the biological function of orthodontic tooth movement (OTM) and examined the roles of ribosomal proteins in the hypoxic environment during OTM. HIF-1α transgenic mice and control mice were used for hypoxic regulation of periodontal ligament (PDL) fibroblasts. Dec1 knockout (Dec1KO) and wild-type (WT) littermate C57BL/6 mice were used as in vivo models of OTM. The unstimulated contralateral side served as a control. In vitro, human PDL fibroblasts were exposed to compression forces for 2, 4, 6, 24, and 48 h. HIF-1α transgenic mice had high expression levels of Dec1, HSP105, and ribosomal proteins compared to control mice. The WT OTM mice displayed increased Dec1 expression in the PDL fibroblasts. Micro-CT analysis showed slower OTM in Dec1KO mice compared to WT mice. Increased immunostaining of ribosomal proteins was observed in WT OTM mice compared to Dec1KO OTM mice. Under hypoxia, Dec1 knockdown caused a significant suppression of ribosomal protein expression in PDL fibroblasts. These results reveal that the hypoxic environment in OTM could have implications for the functions of Dec1 and ribosomal proteins to rejuvenate periodontal tissue homeostasis.

Craniofacial sutures: Signaling centres integrating mechanosensation, cell signaling, and cell differentiation

Cranial sutures are dynamic structures in which stem cell biology, bone formation, and mechanical forces interface, influencing the shape of the skull throughout development and beyond. Over the past decade, there has been significant progress in understanding mesenchymal stromal cell (MSC) differentiation in the context of suture development and genetic control of suture pathologies, such as craniosynostosis. More recently, the mechanosensory function of sutures and the influence of mechanical signals on craniofacial development have come to the forefront. There is currently a gap in understanding of how mechanical signals integrate with MSC differentiation and ossification to ensure appropriate bone development and mediate postnatal growth surrounding sutures. In this review, we discuss the role of mechanosensation in the context of cranial sutures, and how mechanical stimuli are converted to biochemical signals influencing bone growth, suture patency, and fusion through mediation of cell differentiation. We integrate key knowledge from other paradigms where mechanosensation forms a critical component, such as bone remodeling and orthodontic tooth movement. The current state of the field regarding genetic, cellular, and physiological mechanisms of mechanotransduction will be contextualized within suture biology.

Mechanical Compression by Simulating Orthodontic Tooth Movement in an In Vitro Model Modulates Phosphorylation of AKT and MAPKs via TLR4 in Human Periodontal Ligament Cells

Mechanical compression simulating orthodontic tooth movement in in vitro models induces pro-inflammatory cytokine expression in periodontal ligament (PDL) cells. Our previous work shows that TLR4 is involved in this process. Here, primary PDL cells are isolated and characterized to better understand the cell signaling downstream of key molecules involved in the process of sterile inflammation via TLR4. The TLR4 monoclonal blocking antibody significantly reverses the upregulation of phospho-AKT, caused by compressive force, to levels comparable to controls by inhibition of TLR4. Phospho-ERK and phospho-p38 are also modulated in the short term via TLR4. Additionally, moderate compressive forces of 2 g/cm², a gold standard for static compressive mechanical stimulation, are not able to induce translocation of Nf-kB and phospho-ERK into the nucleus. Accordingly, we demonstrated for the first time that TLR4 is also one of the triggers for signal transduction under compressive force. The TLR4, one of the pattern recognition receptors, is involved through its specific molecular structures on damaged cells during mechanical stress. Our findings provide the basis for further research on TLR4 in the modulation of sterile inflammation during orthodontic therapy and periodontal remodeling.

O-GlcNAcylation drives calcium signaling toward osteoblast differentiation: A bioinformatics-oriented study

This study aimed to reveal the possible mechanisms by which O-linked-N-acetylglucosaminylation (O-GlcNAcylation) regulates osteoblast differentiation using a series of bioinformatics-oriented experiments. To examine the influence of O-GlcNAcylation levels on osteoblast differentiation, osteoblastic MC3T3-E1 cells were treated with O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) inhibitors. Correlations between the levels of O-GlcNAcylation and the expression of osteogenic markers as well as OGT were evaluated by qPCR and western blotting. The O-GlcNAcylated proteins assumed to correlate with Runx2 expression were retrieved from several public databases and used for further bioinformatics analysis. Following the findings of the bioinformatics analysis, intracellular calcium ([Ca²⁺ ]_i ) was monitored in the cells treated with OGT and OGA inhibitors using a confocal laser-scanning microscope (CLS). The interaction effect between O-GlcNAcylation and [Ca²⁺ ]_i on osteogenic marker expression was determined using stable OGT knockdown MC3T3-E1 cells. O-GlcNAcylation was positively associated with osteoblast differentiation. The time-course profile of global O-GlcNAcylated proteins showed a distinctive pattern with different molecular weights during osteoblast differentiation. The expression pattern of several O-GlcNAcylated proteins was significantly similar to that of Runx2 expression. Bioinformatic analysis of the retrieved Runx2-related-O-GlcNAcylated-proteins revealed the importance of [Ca²⁺ ]_i . CLS showed that alteration of O-GlcNAcylation rapidly changed [Ca²⁺ ]_i in MC3T3-E1 cells. O-GlcNAcylation and [Ca²⁺ ]_i showed an interaction effect on the expression of osteogenic markers. OGT knockdown disrupted the [Ca²⁺ ]_i -induced expression changes of osteogenic markers. O-GlcNAcylation interacts with [Ca²⁺ ]_i and elicits osteoblast differentiation by regulating the expression of osteogenic markers.

Identification osteogenic signaling pathways following mechanical stimulation: A systematic review

INTRODUCTION

It has been shown that mechanical forces can induce or promote osteogenic differentiation as well as remodeling of the new created bone tissues. To apply this characteristic in bone tissue engineering, it is important to know which mechanical stimuli through which signaling pathway has a more significant impact on osteogenesis.

METHODS

In this systematic study, an electronic search was conducted using PubMed and Google Scholar databases. This study has been prepared and organized according to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. Included studies were first categorized according to the in vivo and in vitro studies.

RESULTS

Six types of mechanical stresses were used in these articles and the most commonly used mechanical force and cell source were tension and bone marrow-derived mesenchymal stem cells (BMMSCs), respectively. These forces were able to trigger twelve signaling pathways in which Wnt pathway was so prominent.

CONCLUSION

1) Although specific signaling pathways are induced through specific mechanical forces, Wnt signaling pathways are predominantly activated by almost all types of force/stimulation, 2) All signaling pathways regulate expression of RUNX2, which is known as a master regulator of osteogenesis, 3) In Tension force, the mode of force administration, i.e, continuous or non-continuous tension is more important than the percentage of elongation.

Gli1+ Cells Residing in Bone Sutures Respond to Mechanical Force via IP3R to Mediate Osteogenesis

Early orthodontic correction of skeletal malocclusion takes advantage of mechanical force to stimulate unclosed suture remodeling and to promote bone reconstruction; however, the underlying mechanisms remain largely unclear. Gli1⁺ cells in maxillofacial sutures have been shown to participate in maxillofacial bone development and damage repair. Nevertheless, it remains to be investigated whether these cells participate in mechanical force-induced bone remodeling during orthodontic treatment of skeletal malocclusion. In this study, rapid maxillary expansion (RME) mouse models and mechanical stretch loading cell models were established using two types of transgenic mice which are able to label Gli1⁺ cells, and we found that Gli1⁺ cells participated in mechanical force-induced osteogenesis both in vivo and in vitro. Besides, we found mechanical force-induced osteogenesis through inositol 1,4,5-trisphosphate receptor (IP₃R), and we observed for the first time that inhibition of Gli1 suppressed an increase in mechanical force-induced IP3R overexpression, suggesting that Gli1⁺ cells participate in mechanical force-induced osteogenesis through IP₃R. Taken together, this study is the first to demonstrate that Gli1⁺ cells in maxillofacial sutures are involved in mechanical force-induced bone formation through IP₃R during orthodontic treatment of skeletal malocclusion. Furthermore, our results provide novel insights regarding the mechanism of orthodontic treatments of skeletal malocclusion.

Biomechanical and biological responses of periodontium in orthodontic tooth movement: up-date in a new decade

Nowadays, orthodontic treatment has become increasingly popular. However, the biological mechanisms of orthodontic tooth movement (OTM) have not been fully elucidated. We were aiming to summarize the evidences regarding the mechanisms of OTM. Firstly, we introduced the research models as a basis for further discussion of mechanisms. Secondly, we proposed a new hypothesis regarding the primary roles of periodontal ligament cells (PDLCs) and osteocytes involved in OTM mechanisms and summarized the biomechanical and biological responses of the periodontium in OTM through four steps, basically in OTM temporal sequences, as follows: (1) Extracellular mechanobiology of periodontium: biological, mechanical, and material changes of acellular components in periodontium under orthodontic forces were introduced. (2) Cell strain: the sensing, transduction, and regulation of mechanical stimuli in PDLCs and osteocytes. (3) Cell activation and differentiation: the activation and differentiation mechanisms of osteoblast and osteoclast, the force-induced sterile inflammation, and the communication networks consisting of sensors and effectors. (4) Tissue remodeling: the remodeling of bone and periodontal ligament (PDL) in the compression side and tension side responding to mechanical stimuli and root resorption. Lastly, we talked about the clinical implications of the updated OTM mechanisms, regarding optimal orthodontic force (OOF), acceleration of OTM, and prevention of root resorption.

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

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

The expression and regulation of Wnt1 in tooth movement-initiated mechanotransduction

INTRODUCTION

The Wnt signaling pathway acts as a key regulator of skeletal development and its homeostasis. However, the potential role of Wnt1 in the mechanotransduction machinery of orthodontic tooth movement-initiated bone remodeling is still unclear. Hence, this study focused on the regulatory dynamics of the Wnt1 expression in both the periodontal ligament (PDL) and osteocytes in vivo and in vitro.

METHODS

The Wnt1 expression in the orthodontically moved maxillary first molar in mice was assessed at 0, 1, and 5 days, on both the compression and tension sides. Primary isolated human PDL (hPDL) fibroblasts, as well as murine long-bone osteocyte-Y4 (MLO-Y4) cells, were exposed to continuous compressive force and static tensile force.

RESULTS

The relative quantification of immunodetection showed that orthodontic tooth movement significantly stimulated the Wnt1 expression in both the PDL and alveolar osteocytes on the tension side on day 5, whereas the expression on the compression side did not change. This increase in the Wnt1 expression, shown in vivo, was also noted after the application of 12% static tensile force in isolated hPDL fibroblasts and 20% in MLO-Y4 cells. In contrast, a compressive force led to the attenuation of the Wnt1 gene expression in both hPDL fibroblasts and MLO-Y4 cells in a force-dependent manner. In the osteocyte-PDL coculture system, recombinant sclerostin attenuated Wnt1 in PDL, whereas the antisclerostin antibody upregulated its gene expression, indicating that mechanically-driven Wnt1 signaling in PDL might be regulated by osteocytic sclerostin.

CONCLUSIONS

Our findings provide that Wnt1 signaling plays a vital role in tooth movement-initiated bone remodeling via innovative mechanotransduction approaches.

Identification of cell-to-cell interactions by ligand-receptor pairs in human fetal heart

The heart is the first organ to form during embryogenesis and its development is a complex process. In this study, we identified 120 ligand-receptor pairs including 65 ligands and 58 receptors specifically expressed in one of the nine cell types. The correlation analysis of the cell proportions revealed that the cell-to-cell contact exhibited spatial patterns in human fetal heart. Specifically, the cardiomyocytes (CMs) proportion might have negative correlation with proportion of endothelial cell in left atrium and ventricle during the heart development. In contrast, fibroblast-like cells and macrophages were jointly increased with the gestation. Furthermore, the ligand in CM, NPPA (Natriuretic Peptide A), and receptor in endothelial cell (EC), NPR3 (Natriuretic Peptide Receptor 3), were specifically expressed in atrial CM and endocardial cells, respectively, indicating that the atrial CM might communicate with endocardial cells via NPPA-NRP3 interaction. Moreover, the interplay between fibroblast-like cell and macrophage was observed in both left and right atriums via the ligand-receptor interactions of COL1A1/COL1A2 (Collagen Type I Alpha 1/2 Chain)-CD36 and CTGF (connective tissue growth factor)-ITGB2 (Integrin Subunit Beta 2). Functional enrichment analysis revealed that the ligand-receptor interactions might be associated with the intracellular activation of cGMP-PKG signaling pathway in ECs, PDGF-beta signaling pathway in fibroblast-like cell, and Toll-like receptor signaling in macrophage, respectively. Collectively, the present study unveiled the potential cell-cell communication and underlying mechanism involved in cardiac development, which broadened our insights into developmental biology of heart.

Tensile force-induced PDGF-BB/PDGFRβ signals in periodontal ligament fibroblasts activate JAK2/STAT3 for orthodontic tooth movement

Orthodontic force-induced osteogenic differentiation and bone formation at tension side play a pivotal role in orthodontic tooth movement (OTM). Platelet-derived growth factor-BB (PDGF-BB) is a clinically proven growth factor during bone regeneration process with unclear mechanisms. Fibroblasts in periodontal ligament (PDL) are considered to be mechanosensitive under orthodontic force. Thus, we established OTM model to investigate the correlation between PDGF-BB and fibroblasts during bone regeneration at tension side. We confirmed that tensile force stimulated PDL cells to induce osteogenic differentiation via Runx-2, OCN up-regulation, and to accelerate new bone deposition along the periodontium and the alveolar bone interface. Interestingly, PDGF-BB level was remarkably enhanced at tension side during OTM in parallel with up-regulated PDGFRβ+/α-SMA+ fibroblasts in PDL by immunohistochemistry. Moreover, orthodontic force-treated primary fibroblasts from PDL were isolated and, cultured in vitro, which showed similar morphology and phenotype with control fibroblasts without OTM treatment. PDGFRβ expression was confirmed to be increased in orthodontic force-treated fibroblasts by immunofluorescence and flow cytometry. Bioinformatics analysis identified that PDGF-BB/PDGFRβ signals were relevant to the activation of JAK/STAT3 signals. The protein expression of JAK2 and STAT3 was elevated in PDL of tension side. Importantly, in vivo, the treatment of the inhibitors (imatinib and AG490) for PDGFRβ and JAK-STAT signals were capable of attenuating the tooth movement. The osteogenic differentiation and bone regeneration in tension side were down-regulated upon the treatment of inhibitors during OTM. Meanwhile, the expressions of PDGFRβ, JAK2 and STAT3 were inhibited by imatinib and AG490. Thus, we concluded that tensile force-induced PDGF-BB activated JAK2/STAT3 signals in PDGFRβ⁺ fibroblasts in bone formation during OTM.