Mechanical force modulates periodontal ligament stem cell characteristics during bone remodelling via TRPV4

PGC-1α inhibits NLRP3 signaling through transcriptional activation of POP1 to alleviate inflammation and strengthen osteogenic differentiation of lipopolysaccharide-induced human periodontal stem cells

Periodontitis is a chronic infectious disease that affects the oral health of adults. Periodontal stem cells (PDLSCs) have good self-renewal and multipotential differentiation abilities to maintain the integrity of periodontal support structure and repair defects. This study aimed to elucidate the role of peroxisome proliferator activated receptor-γ co-activator 1-α (PGC-1α) in lipopolysaccharide (LPS)-induced PDLSCs and the underlying mechanisms related to predicated that pyrin domain (PYD)-only protein 1 (POP1). Notably downregulated PGC-1α and POP1 expression was observed in LPS-induced PDLSCs. PGC-1α or POP1 overexpression significantly reduced the inflammation and enhanced the osteogenic differentiation of LPS-treated PDLSCs. Particularly, PGC-1 bound to POP1 promoter region and upregulated POP1 expression. Moreover, POP1 knockdown ameliorated the impacts of PGC-1α overexpression on the inflammation and osteogenic differentiation in LPS-induced PDLSCs. Besides, PGC-1α inactivated NLRP3 signaling in LPS-treated PDLSCs, which was reversed by POP1 knockdown. Taken together, PGC-1α inhibits NLRP3 signaling through transcriptional activation of POP1, thereby alleviating inflammation and strengthening osteogenic differentiation of LPS-induced PDLSCs.

Effects of mechanical loading on matrix homeostasis and differentiation potential of periodontal ligament cells: A scoping review

Various mechanical loadings, including mechanical stress, orthodontics forces, and masticatory force, affect the functions of periodontal ligament cells. Regulation of periodontal tissue destruction, formation, and differentiation functions are crucial processes for periodontal regeneration therapy. Numerous studies have reported that different types of mechanical loading play a role in maintaining periodontal tissue matrix homeostasis, and osteogenic differentiation of the periodontal ligament cells. This scoping review aims to evaluate the studies regarding the effects of various mechanical loadings on the secretion of extracellular matrix (ECM) components, regulation of the balance between formation and destruction of periodontal tissue matrix, osteogenic differentiation, and multiple differentiation functions of the periodontal ligament. An electronic search for this review has been conducted on two databases; MEDLINE via PubMed and SCOPUS. Study selection criteria included original research written in English that reported the effects of different mechanical loadings on matrix homeostasis and differentiation potential of periodontal ligament cells. The final 204 articles were mainly included in the present scoping review. Mechanical forces of the appropriate magnitude, duration, and pattern have a positive influence on the secretion of ECM components such as collagen, as well as regulate the secretion of matrix metalloproteinases and tissue inhibitors of matrix metalloproteinases. Additionally, these forces regulate a balance between osteoblastic and osteoclast differentiation. Conversely, incorrect mechanical loadings can lead to abnormal formation and destruction of both soft and hard tissue. This review provides additional insight into how mechanical loadings impact ECM homeostasis and multiple differentiation functions of periodontal ligament cells (PDLCs), thus making it valuable for regenerative periodontal treatment. In combination with advancing technologies, the utilization of ECM components, application of different aspects of mechanical force, and differentiation potential of PDLCs could bring potential benefits to future periodontal regeneration therapy.

The role of photobiomodulation in accelerating bone repair

Bone repair is faced with obstacles such as slow repair rates and limited bone regeneration capacity. Delayed healing even nonunion could occur in bone defects, influencing the life quality of patients severely. Photobiomodulation (PBM) utilizes different light sources to derive beneficial therapeutic effects with the advantage of being non-invasive and painless, providing a promising strategy for accelerating bone repair. In this review, we summarize the parameters, mechanisms, and effects of PBM regulating bone repair, and further conclude the current clinical application of PBM devices in bone repair. The wavelength of 635-980 nm, the output power of 40-100 mW, and the energy density of less than 100 J/cm2 are the most commonly used parameters. New technologies, including needle systems and biocompatible and implantable optical fibers, offer references to realize an efficient and safe strategy for bone repair. Further research is required to establish the reliability of outcomes from in vivo and in vitro studies and to standardize clinical trial protocols.

Static magnetic field-induced IL-6 secretion in periodontal ligament stem cells accelerates orthodontic tooth movement

Static magnetic field (SMF) promoting bone tissue remodeling is a potential non-invasive therapy technique to accelerate orthodontic tooth movement (OTM). The periodontal ligament stem cells (PDLSCs), which are mechanosensitive cells, are essential for force-induced bone remodeling and OTM. However, whether and how the PDLSCs influence the process of inflammatory bone remodeling under mechanical force stimuli in the presence of SMFs remains unclear. In this study, we found that local SMF stimulation significantly enhanced the OTM distance and induced osteoclastogenesis on the compression side of a rat model of OTM. Further experiments with macrophages cultured with supernatants from force-loaded PDLSCs exposed to an SMF showed enhanced osteoclast formation. RNA-seq analysis showed that interleukin-6 (IL-6) was elevated in force-loaded PDLSCs exposed to SMFs. IL-6 expression was also elevated on the pressure side of a rat OTM model with an SMF. The OTM distance induced by an SMF was significantly decreased after injection of the IL-6 inhibitor tocilizumab. These results imply that SMF promotes osteoclastogenesis by inducing force-loaded PDLSCs to secrete the inflammatory cytokine IL-6, which accelerates OTM. This will help to reveal the mechanism of SMF accelerates tooth movement and should be evaluated for application in periodontitis patients.

CircPRKD3/miR-6783-3p responds to mechanical force to facilitate the osteogenesis of stretched periodontal ligament stem cells

BACKGROUND

The mechanotransduction mechanisms by which cells regulate tissue remodeling are not fully deciphered. Circular RNAs (circRNAs) are crucial to various physiological processes, including cell cycle, differentiation, and polarization. However, the effects of mechanical force on circRNAs and the role of circRNAs in the mechanobiology of differentiation and remodeling in stretched periodontal ligament stem cells (PDLSCs) remain unclear. This article aims to explore the osteogenic function of mechanically sensitive circular RNA protein kinase D3 (circPRKD3) and elucidate its underlying mechanotransduction mechanism.

MATERIALS AND METHODS

PDLSCs were elongated with 8% stretch at 0.5 Hz for 24 h using the Flexcell® FX-6000™ Tension System. CircPRKD3 was knockdown or overexpressed with lentiviral constructs or plasmids. The downstream molecules of circPRKD3 were predicted by bioinformatics analysis. The osteogenic effect of related molecules was evaluated by quantitative real-time PCR (qRT-PCR) and western blot.

RESULTS

Mechanical force enhanced the osteogenesis of PDLSCs and increased the expression of circPRKD3. Knockdown of circPRKD3 hindered PDLSCs from osteogenesis under mechanical force, while overexpression of circPRKD3 promoted the early osteogenesis process of PDLSCs. With bioinformatics analysis and multiple software predictions, we identified hsa-miR-6783-3p could act as the sponge of circPRKD3 to indirectly regulate osteogenic differentiation of mechanically stimulated PDLSCs.

CONCLUSIONS

Our results first suggested that both circPRKD3 and hsa-miR-6783-3p could enhance osteogenesis of stretched PDLSCs. Furthermore, hsa-miR-6783-3p could sponge circPRKD3 to indirectly regulate RUNX2 during the periodontal tissue remodeling process in orthodontic treatment.

Low-intensity pulsed ultrasound promotes the osteogenesis of mechanical force-treated periodontal ligament cells via Piezo1

Background

Low-intensity pulsed ultrasound (LIPUS) can accelerate tooth movement and preserve tooth and bone integrity during orthodontic treatment. However, the mechanisms by which LIPUS affects tissue remodeling during orthodontic tooth movement (OTM) remain unclear. Periodontal ligament cells (PDLCs) are pivotal in maintaining periodontal tissue equilibrium when subjected to mechanical stimuli. One notable mechano-sensitive ion channel, Piezo1, can modulate cellular function in response to mechanical cues. This study aimed to elucidate the involvement of Piezo1 in the osteogenic response of force-treated PDLCs when stimulated by LIPUS.

Method

After establishing rat OTM models, LIPUS was used to stimulate rats locally. OTM distance and alveolar bone density were assessed using micro-computed tomography, and histological analyses included hematoxylin and eosin staining, tartrate-resistant acid phosphatase staining and immunohistochemical staining. GsMTx4 and Yoda1 were respectively utilized for Piezo1 functional inhibition and activation experiments in rats. We isolated human PDLCs (hPDLCs) in vitro and evaluated the effects of LIPUS on the osteogenic differentiation of force-treated hPDLCs using real-time quantitative PCR, Western blot, alkaline phosphatase and alizarin red staining. Small interfering RNA and Yoda1 were employed to validate the role of Piezo1 in this process.

Results

LIPUS promoted osteoclast differentiation and accelerated OTM in rats. Furthermore, LIPUS alleviated alveolar bone resorption under pressure and enhanced osteogenesis of force-treated PDLCs both in vivo and in vitro by downregulating Piezo1 expression. Subsequent administration of GsMTx4 in rats and siPIEZO1 transfection in hPDLCs attenuated the inhibitory effect on osteogenic differentiation under pressure, whereas LIPUS efficacy was partially mitigated. Yoda1 treatment inhibited osteogenic differentiation of hPDLCs, resulting in reduced expression of Collagen Ⅰα1 and osteocalcin in the periodontal ligament. However, LIPUS administration was able to counteract these effects.

Conclusion

This research unveils that LIPUS promotes the osteogenesis of force-treated PDLCs via downregulating Piezo1.

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.

Mechanisms of mechanical force aggravating periodontitis: A review

Periodontitis is a widespread oral disease accompanied by uncontrolled inflammation-related tissue destruction. Periodontitis is related to various factors. Among them, occlusal trauma can aggravate the severity of periodontitis and has been attracting a great deal of attention. We systematically searched PubMed and Web of Science databases for related articles. Keywords for the search were "mechanical force", "mechanical stress", "occlusal trauma" and "periodontitis". This review focuses on the effect of mechanical forces on periodontitis and discusses the possible pivotal targets participating in this process. We elucidated and summarized 21 articles that reported on our topic. Several biological processes and pathways that participate in enhancing the inflammatory response to mechanical stress have been studied, including the regulation of osteogenesis and osteoclastic resorption balance, Yes-associated protein signaling, induction of collagen destruction, and regulation of programmed cell death. Mechanical force enhances the process of periodontitis in multiple ways. However, currently, no studies have further examined its underlying mechanism. Understanding the specific roles of mechanical forces may assist in the treatment of periodontitis with traumatic occlusal trauma.

Mechanical overload induces TMJ disc degeneration via TRPV4 activation

OBJECTIVE

The temporomandibular joint (TMJ) disc cushions intraarticular stress during mandibular movements. While mechanical overloading is related to cartilage degeneration, the pathogenesis of TMJ disc degeneration is unclear. Here, we determined the regulatory role of mechanoinductive transient receptor potential vanilloid 4 (TRPV4) in mechanical overload-induced TMJ disc degeneration.

METHODS

We explored the effect of mechanical overload on the TMJ discs in a rat occlusal interference model in vivo, and by applying sustained compressive force in vitro. TRPV4 inhibition was delivered by small interfering RNA or GSK2193874; TRPV4 activation was delivered by GSK1016790A. The protective effect of TRPV4 inhibition was validated in the rat occlusal interference model.

RESULTS

Occlusal interference induced TMJ disc degeneration with enhanced extracellular matrix degradation in vivo and mechanical overload promoted inflammatory responses in the TMJ disc cells via Ca2+ influx with significantly upregulated TRPV4. TRPV4 inhibition reversed mechanical overload-induced inflammatory responses; TRPV4 activation simulated mechanical overload-induced inflammatory responses. Moreover, TRPV4 inhibition alleviated TMJ disc degeneration in the rat occlusal interference model.

CONCLUSION

Our findings suggest TRPV4 plays a pivotal role in the pathogenesis of mechanical overload-induced TMJ disc degeneration and may be a promising target for the treatment of degenerative changes of the TMJ disc.

Micro/nano topological modification of TiO2 nanotubes activates Thy-1 signaling to control osteogenic differentiation of stem cells

Micro/nano topological modification is critical for improving the in vivo behaviors of bone implants, regulating multiple cellular functions. Titania (TiO2) nanotubes show the capacity of promoting osteoblast-related cell differentiation and induce effective osseointegration, serving as a model material for studying the effects of micro/nano-topological modifications on cells. However, the intracellular signaling pathways by which TiO2 nanotubes regulate the osteogenic differentiation of stem cells are not fully defined. Thy-1 (CD90), a cell surface glycoprotein anchored by glycosylphosphatidylinositol, has been considered a key molecule in osteoblast differentiation in recent years. Nevertheless, whether the micro/nano topology of the implant surface leads to changes in Thy-1 is unknown, as well as whether these changes promote osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). Here, TiO2 nanotubes of various diameters were prepared by adjusting the anodizing voltage. qPCR and immunoblot were carried out to assess the mechanism by which TiO2 nanotubes regulate Thy-1. The results revealed Ti plates harboring TiO2 nanotubes ∼100-nm diameter (TNT-100) markedly upregulated Thy-1. Subsequently, upregulated Thy-1 promoted the activation of Fyn/RhoA/MLC Ⅱ/F-actin axis, which enhanced the nuclear translocation of YAP. After Thy-1 knockdown by siRNA, the Fyn/RhoA/MLC Ⅱ/F-actin axis was significantly inhibited and TiO2 nanotubes showed decreased effects on osteogenic differentiation. Therefore, Thy-1 upregulation might be a major mechanism by which micro/nano-topological modification of TiO2 nanotubes promotes osteogenic differentiation in BMSCs. This study provides novel insights into the molecular mechanism of TiO2 nanotubes, which may help design improved bone implants for clinical application.

Mechanosensitive TRPV4 channel guides maturation and organization of the bilayered mammary epithelium

Biophysical cues from the cell microenvironment are detected by mechanosensitive components at the cell surface. Such machineries convert physical information into biochemical signaling cascades within cells, subsequently leading to various cellular responses in a stimulus-dependent manner. At the surface of extracellular environment and cell cytoplasm exist several ion channel families that are activated by mechanical signals to direct intracellular events. One of such channel is formed by transient receptor potential cation channel subfamily V member, TRPV4 that is known to act as a mechanosensor in wide variaty of tissues and control ion-influx in a spatio-temporal way. Here we report that TRPV4 is prominently expressed in the stem/progenitor cell populations of the mammary epithelium and seems important for the lineage-specific differentiation, consequently affecting mechanical features of the mature mammary epithelium. This was evident by the lack of several markers for mature myoepithelial and luminal epithelial cells in TRPV4-depleted cell lines. Interestingly, TRPV4 expression is controlled in a tension-dependent manner and it also impacts differentation process dependently on the stiffness of the microenvironment. Furthermore, such cells in a 3D compartment were disabled to maintain normal mammosphere structures and displayed abnormal lumen formation, size of the structures and disrupted cellular junctions. Mechanosensitive TRPV4 channel therefore act as critical player in the homeostasis of normal mammary epithelium through sensing the physical environment and guiding accordingly differentiation and structural organization of the bilayered mammary epithelium.

The role of mechanically sensitive ion channel Piezo1 in bone remodeling

Piezo1 (2010) was identified as a mechanically activated cation channel capable of sensing various physical forces, such as tension, osmotic pressure, and shear force. Piezo1 mediates mechanosensory transduction in different organs and tissues, including its role in maintaining bone homeostasis. This review aimed to summarize the function and possible mechanism of Piezo1 in the mechanical receptor cells in bone tissue. We found that it is a potential therapeutic target for the treatment of bone diseases.

Force-induced Caspase-1-dependent pyroptosis regulates orthodontic tooth movement

Pyroptosis, an inflammatory caspase-dependent programmed cell death, plays a vital role in maintaining tissue homeostasis and activating inflammatory responses. Orthodontic tooth movement (OTM) is an aseptic force-induced inflammatory bone remodeling process mediated by the activation of periodontal ligament (PDL) progenitor cells. However, whether and how force induces PDL progenitor cell pyroptosis, thereby influencing OTM and alveolar bone remodeling remains unknown. In this study, we found that mechanical force induced the expression of pyroptosis-related markers in rat OTM and alveolar bone remodeling process. Blocking or enhancing pyroptosis level could suppress or promote OTM and alveolar bone remodeling respectively. Using Caspase-1-/- mice, we further demonstrated that the functional role of the force-induced pyroptosis in PDL progenitor cells depended on Caspase-1. Moreover, mechanical force could also induce pyroptosis in human ex-vivo force-treated PDL progenitor cells and in compressive force-loaded PDL progenitor cells in vitro, which influenced osteoclastogenesis. Mechanistically, transient receptor potential subfamily V member 4 signaling was involved in force-induced Caspase-1-dependent pyroptosis in PDL progenitor cells. Overall, this study suggested a novel mechanism contributing to the modulation of osteoclastogenesis and alveolar bone remodeling under mechanical stimuli, indicating a promising approach to accelerate OTM by targeting Caspase-1.

Fluid flow-induced modulation of viability and osteodifferentiation of periodontal ligament stem cell spheroids-on-chip

Developing physiologically relevant in vitro models for studying periodontitis is crucial for understanding its pathogenesis and developing effective therapeutic strategies. In this study, we aimed to integrate the spheroid culture of periodontal ligament stem cells (PDLSCs) within a spheroid-on-chip microfluidic perfusion platform and to investigate the influence of interstitial fluid flow on morphogenesis, cellular viability, and osteogenic differentiation of PDLSC spheroids. PDLSC spheroids were seeded onto the spheroid-on-chip microfluidic device and cultured under static and flow conditions. Computational analysis demonstrated the translation of fluid flow rates of 1.2 μl min-1 (low-flow) and 7.2 μl min-1 (high-flow) to maximum fluid shear stress of 59 μPa and 360 μPa for low and high-flow conditions, respectively. The spheroid-on-chip microfluidic perfusion platform allowed for modulation of flow conditions leading to larger PDLSC spheroids with improved cellular viability under flow compared to static conditions. Modulation of fluid flow enhanced the osteodifferentiation potential of PDLSC spheroids, demonstrated by significantly enhanced alizarin red staining and alkaline phosphatase expression. Additionally, flow conditions, especially high-flow conditions, exhibited extensive calcium staining across both peripheral and central regions of the spheroids, in contrast to the predominantly peripheral staining observed under static conditions. These findings highlight the importance of fluid flow in shaping the morphological and functional properties of PDLSC spheroids. This work paves the way for future investigations exploring the interactions between PDLSC spheroids, microbial pathogens, and biomaterials within a controlled fluidic environment, offering insights for the development of innovative periodontal therapies, tissue engineering strategies, and regenerative approaches.

NTRK1 knockdown induces mouse cognitive impairment and hippocampal neuronal damage through mitophagy suppression via inactivating the AMPK/ULK1/FUNDC1 pathway

Hippocampal neuronal damage may induce cognitive impairment. Neurotrophic tyrosine kinase receptor 1 (NTRK1) reportedly regulates neuronal damage, although the underlying mechanism remains unclear. The present study aimed to investigate the role of NTRK1 in mouse hippocampal neuronal damage and the specific mechanism. A mouse NTRK1-knockdown model was established and subjected to pre-treatment with BAY-3827, followed by a behavioral test, Nissl staining, and NeuN immunofluorescence (IF) staining to evaluate the cognitive impairment and hippocampal neuronal damage. Next, an in vitro analysis was conducted using the CCK-8 assay, TUNEL assay, NeuN IF staining, DCFH-DA staining, JC-1 staining, ATP content test, mRFP-eGFP-LC3 assay, and LC3-II IF staining to elucidate the effect of NTRK1 on mouse hippocampal neuronal activity, apoptosis, damage, mitochondrial function, and autophagy. Subsequently, rescue experiments were performed by subjecting the NTRK1-knockdown neurons to pre-treatment with O304 and Rapamycin. The AMPK/ULK1/FUNDC1 pathway activity and mitophagy were detected using western blotting (WB) analysis. Resultantly, in vivo analysis revealed that NTRK1 knockdown induced mouse cognitive impairment and hippocampal tissue damage, in addition to inactivating the AMPK/ULK1/FUNDC1 pathway activity and mitophagy in the hippocampal tissues of mice. The treatment with BAY-3827 exacerbated the mouse depressive-like behavior induced by NTRK1 knockdown. The results of in vitro analysis indicated that NTRK1 knockdown attenuated viability, NeuN expression, ATP production, mitochondrial membrane potential, and mitophagy, while enhancing apoptosis and ROS production in mouse hippocampal neurons. Conversely, pre-treatment with O304 and rapamycin abrogated the suppression of mitophagy and the promotion of neuronal damage induced upon NTRK1 silencing. Conclusively, NTRK1 knockdown induces mouse hippocampal neuronal damage through the suppression of mitophagy via inactivating the AMPK/ULK1/FUNDC1 pathway. This finding would provide insight leading to the development of novel strategies for the treatment of cognitive impairment induced due to hippocampal neuronal damage.

Lepr-Expressing PDLSCs Contribute to Periodontal Homeostasis and Respond to Mechanical Force by Piezo1

Periodontium supports teeth in a mechanically stimulated tissue environment, where heterogenous stem/progenitor populations contribute to periodontal homeostasis. In this study, Leptin receptor+ (Lepr+) cells are identified as a distinct periodontal ligament stem cell (PDLSC) population by single-cell RNA sequencing and lineage tracing. These Lepr+ PDLSCs are located in the peri-vascular niche, possessing multilineage potential and contributing to tissue repair in response to injury. Ablation of Lepr+ PDLSCs disrupts periodontal homeostasis. Hyper-loading and unloading of occlusal forces modulate Lepr+ PDLSCs activation. Piezo1 is demonstrated that mediates the mechanosensing of Lepr+ PDLSCs by conditional Piezo1-deficient mice. Meanwhile, Yoda1, a selective activator of Piezo1, significantly accelerates periodontal tissue growth via the induction of Lepr+ cells. In summary, Lepr marks a unique multipotent PDLSC population in vivo, to contribute toward periodontal homeostasis via Piezo1-mediated mechanosensing.

Hierarchically Porous Implants Orchestrating a Physiological Viscoelastic and Piezoelectric Microenvironment for Bone Regeneration

The extracellular matrix microenvironment of bone tissue comprises several physiological cues. Thus, artificial bone substitute materials with a single cue are insufficient to meet the demands for bone defect repair. Regeneration of critical-size bone defects remains challenging in orthopedic surgery. Intrinsic viscoelastic and piezoelectric cues from collagen fibers play crucial roles in accelerating bone regeneration, but scaffolds or implants providing integrated cues have seldom been reported. In this study, it is aimed to design and prepare hierarchically porous poly(methylmethacrylate)/polyethyleneimine/poly(vinylidenefluoride) composite implants presenting a similar viscoelastic and piezoelectric microenvironment to bone tissue via anti-solvent vapor-induced phase separation. The viscoelastic and piezoelectric cues of the composite implants for human bone marrow mesenchymal stem cell line stimulate and activate Piezo1 proteins associated with mechanotransduction signaling pathways. Cortical and spongy bone exhibit excellent regeneration and integration in models of critical-size bone defects on the knee joint and femur in vivo. This study demonstrates that implants with integrated physiological cues are promising artificial bone substitute materials for regenerating critical-size bone defects.

Mechanical stretch promotes apoptosis and impedes ciliogenesis of primary human airway basal stem cells

BACKGROUND

Airway basal stem cells (ABSCs) have self-renewal and differentiation abilities. Although an abnormal mechanical environment related to chronic airway disease (CAD) can cause ABSC dysfunction, it remains unclear how mechanical stretch regulates the behavior and structure of ABSCs. Here, we explored the effect of mechanical stretch on primary human ABSCs.

METHODS

Primary human ABSCs were isolated from healthy volunteers. A Flexcell FX-5000 Tension system was used to mimic the pathological airway mechanical stretch conditions of patients with CAD. ABSCs were stretched for 12, 24, or 48 h with 20% elongation. We first performed bulk RNA sequencing to identify the most predominantly changed genes and pathways. Next, apoptosis of stretched ABSCs was detected with Annexin V-FITC/PI staining and a caspase 3 activity assay. Proliferation of stretched ABSCs was assessed by measuring MKI67 mRNA expression and cell cycle dynamics. Immunofluorescence and hematoxylin-eosin staining were used to demonstrate the differentiation state of ABSCs at the air-liquid interface.

RESULTS

Compared with unstretched control cells, apoptosis and caspase 3 activation of ABSCs stretched for 48 h were significantly increased (p < 0.0001; p < 0.0001, respectively), and MKI67 mRNA levels were decreased (p < 0.0001). In addition, a significant increase in the G0/G1 population (20.2%, p < 0.001) and a significant decrease in S-phase cells (21.1%, p < 0.0001) were observed. The ratio of Krt5+ ABSCs was significantly higher (32.38% vs. 48.71%, p = 0.0037) following stretching, while the ratio of Ac-tub+ cells was significantly lower (37.64% vs. 21.29%, p < 0.001). Moreover, compared with the control, the expression of NKX2-1 was upregulated significantly after stretching (14.06% vs. 39.51%, p < 0.0001). RNA sequencing showed 285 differentially expressed genes, among which 140 were upregulated and 145 were downregulated, revealing that DDIAS, BIRC5, TGFBI, and NKX2-1 may be involved in the function of primary human ABSCs during mechanical stretch. There was no apparent difference between stretching ABSCs for 24 and 48 h compared with the control.

CONCLUSIONS

Pathological stretching induces apoptosis of ABSCs, inhibits their proliferation, and disrupts cilia cell differentiation. These features may be related to abnormal regeneration and repair observed after airway epithelium injury in patients with CAD.

Mechanical force induces mitophagy-mediated anaerobic oxidation in periodontal ligament stem cells

BACKGROUND

The preference for glucose oxidative mode has crucial impacts on various physiological activities, including determining stem cell fate. External mechanical factors can play a decisive role in regulating critical metabolic enzymes and pathways of stem cells. Periodontal ligament stem cells (PDLSCs) are momentous effector cells that transform mechanical force into biological signals during the reconstruction of alveolar bone. However, mechanical stimuli-induced alteration of oxidative characteristics in PDLSCs and the underlying mechanisms have not been fully elucidated.

METHODS

Herein, we examined the expression of LDH and COX4 by qRT-PCR, western blot, immunohistochemistry and immunofluorescence. We detected metabolites of lactic acid and reactive oxygen species for functional tests. We used tetramethylrhodamine methyl ester (TMRM) staining and a transmission electron microscope to clarify the mitochondrial status. After using western blot and immunofluorescence to clarify the change of DRP1, we further examined MFF, PINK1, and PARKIN by western blot. We used cyclosporin A (CsA) to confirm the regulation of mitophagy and ceased the stretching as a rescue experiment.

RESULTS

Herein, we ascertained that mechanical force could increase the level of LDH and decrease the expression of COX4 in PDLSCs. Simultaneously, the yield of reactive oxygen species (ROS) in PDLSC reduced after stretching, while lactate acid augmented significantly. Furthermore, mitochondrial function in PDLSCs was negatively affected by impaired mitochondrial membrane potential (MMP) under mechanical force, and the augment of mitochondrial fission further induced PRKN-dependent mitophagy, which was confirmed by the rescue experiments via blocking mitophagy. As a reversible physiological stimulation, the anaerobic preference of PDLSCs altered by mechanical force could restore after the cessation of force stimulation.

CONCLUSIONS

Altogether, our study demonstrates that PDLSCs under mechanical force preferred anaerobic oxidation induced by the affected mitochondrial dynamics, especially mitophagy. Our findings support an association between mechanical stimulation and the oxidative profile of stem cells, which may shed light on the mechanical guidance of stem cell maintenance and commitment, and lay a molecular foundation for periodontal tissue regeneration.

The role of integrin family in bone metabolism and tumor bone metastasis

Integrins have been the research focus of cell-extracellular matrix adhesion (ECM) and cytokine receptor signal transduction. They are involved in the regulation of bone metabolism of bone precursor cells, mesenchymal stem cells (MSCs), osteoblasts (OBs), osteoclasts (OCs), and osteocytes. Recent studies expanded and updated the role of integrin in bone metabolism, and a large number of novel cytokines were found to activate bone metabolism pathways through interaction with integrin receptors. Integrins act as transducers that mediate the regulation of bone-related cells by mechanical stress, fluid shear stress (FSS), microgravity, hypergravity, extracellular pressure, and a variety of physical factors. Integrins mediate bone metastasis of breast, prostate, and lung cancer by promoting cancer cell adhesion, migration, and survival. Integrin-mediated targeted therapy showed promising prospects in bone metabolic diseases. This review emphasizes the latest research results of integrins in bone metabolism and bone metastasis and provides a vision for treatment strategies.

Immunomodulatory properties of mesenchymal stem cells/dental stem cells and their therapeutic applications

Mesenchymal stem/stromal cells (MSCs) are widely distributed in the body and play essential roles in tissue regeneration and homeostasis. MSCs can be isolated from discarded tissues, expanded in vitro and used as therapeutics for autoimmune diseases and other chronic disorders. MSCs promote tissue regeneration and homeostasis by primarily acting on immune cells. At least six different types of MSCs have been isolated from postnatal dental tissues and have remarkable immunomodulatory properties. Dental stem cells (DSCs) have been demonstrated to have therapeutic effects on several systemic inflammatory diseases. Conversely, MSCs derived from nondental tissues such as the umbilical cord exhibit great benefits in the management of periodontitis in preclinical studies. Here, we discuss the main therapeutic uses of MSCs/DSCs, their mechanisms, extrinsic inflammatory cues and the intrinsic metabolic circuitries that govern the immunomodulatory functions of MSCs/DSCs. Increased understanding of the mechanisms underpinning the immunomodulatory functions of MSCs/DSCs is expected to aid in the development of more potent and precise MSC/DSC-based therapeutics.

CYLD inhibits osteoclastogenesis to ameliorate alveolar bone loss in mice with periodontitis

Periodontitis is a chronic immune inflammatory disease that can lead to the destruction and loss of the tooth-supporting apparatus. During this process, the balance between bone absorption mediated by osteoclasts and bone formation mediated by osteoblasts is damaged. Consistent with previous studies, we observed that depletion of cylindromatosis (CYLD) resulted in an osteoporotic bone phenotype. However, the effect of CYLD deficiency on periodontitis is undetermined. Here, we investigated whether CYLD affects periodontal tissue homeostasis in experimental periodontitis in Cyld knockout (KO) mice, and we explored the underlying mechanisms. Interestingly, we discovered significant alveolar bone density loss and severely reduced alveolar bone height in Cyld KO mice with experimentally induced periodontitis. We observed increased osteoclast number and activity in both the femurs and alveolar bones, accompanied by the downregulation of osteogenesis genes and upregulation of osteoclastogenesis genes of alveolar bones in ligatured Cyld KO mice. Taken together, our findings demonstrate that the deletion of CYLD in mice plays a vital role in the pathogenesis of periodontal bone loss and suggest that CYLD might exert an ameliorative effect on periodontal inflammatory responses.

Dental Pulp Stem Cell-Derived Exosomes Alleviate Mice Knee Osteoarthritis by Inhibiting TRPV4-Mediated Osteoclast Activation

Osteoarthritis (OA) is a degenerative disease that causes chronic pain and joint swelling and even disables millions of patients. However, current non-surgical treatment for OA can only relieve pain without obvious cartilage and subchondral bone repair. Mesenchymal stem cell (MSC)-secreted exosomes have promising therapeutic effects on knee OA, but the efficacy of MSC-exosome therapy is not well determined, and the mechanisms involved are still unclear. In this study, we isolated dental pulp stem cell (DPSC)-derived exosomes by ultracentrifugation and determined the therapeutic effects of a single intra-articular injection of DPSC-derived exosomes in a mice knee OA model. The results showed that the DPSC-derived exosomes effectively improved abnormal subchondral bone remodeling, inhibited the occurrence of bone sclerosis and osteophytes, and alleviated cartilage degradation and synovial inflammation in vivo. Moreover, transient receptor potential vanilloid 4 (TRPV4) was activated during the progression of OA. Enhanced TRPV4 activation facilitated osteoclast differentiation, and TRPV4 inhibition blocked this process in vitro. DPSC-derived exosomes repressed osteoclast activation in vivo by inhibiting TRPV4 activation. Our findings demonstrated that a topical, single injection of DPSC-derived exosomes is a potential strategy for knee OA treatment, and that the exosomes regulated osteoclast activation by TRPV4 inhibition, which may act as a promising target for clinical OA treatment.

Periodontal ligament-associated protein-1 engages in teeth overeruption and periodontal fiber disorder following occlusal hypofunction

BACKGROUND AND OBJECTIVE

Teeth overeruption is a problem of clinical significance, but the underlying mechanism how changes in external occlusal force convert to the periodontium remodeling signals has been a largely under explored domain. And recently, periodontal ligament-associated protein-1 (PLAP-1)/asporin was found to play a pivotal role in maintaining periodontal homeostasis. The aim of this study was to explore the function of PLAP-1 in the periodontally hypofunctional tissue turnover.

METHODS

After extracting left maxillary molars in mice, the left and right mandibular molars were distributed into hypofunction group (HG) and control group (CG), respectively. Mice were sacrificed for radiographic, histological, and molecular biological analyses after 1, 4 and 12 weeks. In vitro, dynamic compression was applied using Flexcell FX-5000 Compression System to simulate intermittent occlusal force. The expression of PLAP1 in loaded and unloaded human periodontal ligament cells (hPDLCs) was compared, and its molecular biological effects were further explored by small interfering RNA (siRNA) targeting PLAP1.

RESULTS

In vivo, fiber disorder in periodontal ligament (PDL), bone apposition at furcation regions, and bone resorption in alveolar bone were illustrated in the HG compared with the CG. In addition, PLAP-1 positive area decreased significantly in PDL following occlusal unloading. In vitro, the loss of compressive loading relatively downregulated PLAP1 expression, which was essential to promote collagen I but inhibit osterix and osteocalcin expression in hPDLCs.

CONCLUSIONS

PLAP-1 presumably plays a pivotal role in occlusal force-regulated periodontal homeostasis by facilitating collagen fiber synthesis in hPDLCs and suppressing excessive osteoblast differentiation, further preventing teeth from overeruption. Further evidence in PLAP-1 conditional knockout mice is needed.

Effect of stretch frequency on osteogenesis of periodontium during periodontal ligament distraction

OBJECTIVES

Periodontal ligament distraction (PDLD) can accelerate orthodontic tooth movement (OTM). However, the effect of stretch frequency on osseous formation during PDLD remains unclear. Here, we sought to identify the effect of PDLD frequency on the osteogenic remodelling of the periodontium.

MATERIALS AND METHODS

(i) In vitro, five human periodontal ligament stem cell (PDLSC) cultures were randomized to either static conditions or exposure to a cyclic stretch force involving 12% deformation at frequencies of 0.3, 0.5, 0.7 or 1.0 Hz for 12 h, and the osteogenic differentiation of PDLSCs was assessed using Western blotting. (ii) In vivo, 18 beagle dogs underwent orthodontic distalization of bilateral maxillary first premolars. In the test groups, PDLD was performed at a frequency of two or six times/day, while Ni-Ti coil springs were applied to mimic traditional OTM in the control group. The amount of OTM and histological staining was estimated after force loading for 5, 10 and 15 days.

RESULTS

(i) In vitro, the expression of osteogenic-specific markers (runt-related transcription factor 2 [Runx2], type I collagen [COL-I] and osteocalcin [OCN]) increased with the frequency of tensile force, to a peak at 0.7 Hz. (ii) In vivo, both PDLD groups displayed a greater rate of OTM and a higher bone metabolism than the control group. The expression of COL-I and OCN was significantly reinforced in the six times/day-PDLD group in comparison to the two times/day-PDLD group.

CONCLUSIONS

The cyclic stretch force enhances osteogenesis of the periodontium in a frequency-dependent manner.

Differentiation ability of Gli1+ cells during orthodontic tooth movement

Orthodontic tooth movement (OTM) induces bone formation on the alveolar bone of the tension side; however, the mechanism of osteoblast differentiation is not fully understood. Gli1 is an essential transcription factor for hedgehog signaling and functions in undifferentiated cells during embryogenesis. In this study, we examined the differentiation of Gli1⁺ cells in the periodontal ligament (PDL) during OTM using a lineage-tracing analysis. After the final administration of tamoxifen for 2 days to 8-week-old Gli1-Cre^ERT2/ROSA26-loxP-stop-loxP-tdTomato (iGli1/Tomato) mice, Gli1/Tomato⁺ cells were rarely observed near endomucin⁺ blood vessels in the PDL. Osteoblasts lining the alveolar bone did not exhibit Gli1/Tomato fluorescence. To move the first molar of iGli1/Tomato mice medially, nickel-titanium closed-coil springs were attached between the upper anterior alveolar bone and the first molar. Two days after OTM initiation, the number of Gli1/Tomato⁺ cells increased along with numerous PCNA⁺ cells in the PDL of the tension side. As some Gli1/Tomato⁺ cells exhibited positive expression of osterix, an osteoblast differentiation marker, Gli1⁺ cells probably differentiated into osteoblast progenitor cells. On day 10, the newly formed bone labeled by calcein administration during OTM was detected on the surface of the original alveolar bone of the tension side. Gli1/Tomato⁺ cells expressing osterix localized to the surface of the newly formed bone. In contrast, in the PDL of the compression side, Gli1/Tomato⁺ cells proliferated before day 10 and expressed type I collagen, suggesting that the Gli1⁺ cells also differentiated into fibroblasts. Collectively, these results demonstrate that Gli1⁺ cells in the PDL can differentiate into osteoblasts at the tension side and may function in bone remodeling as well as fibril formation in the PDL during OTM.

Piezo1-mediated fluid shear stress promotes OPG and inhibits RANKL via NOTCH3 in MLO-Y4 osteocytes

Piezo1, a mechanosensitive ion channel, participates in a variety of biological processes in maintaining bone homeostasis. As the most abundant cells in bones of the mammals, osteocytes play an essential role in bone formation, remodeling, and bone mass maintenance. Here, by exposing MLO-Y4 osteocytes to the fluid shear stress (FSS) microenvironment, we explored the effect of Piezo1-mediated FSS on the expression of the molecules critical to the process of bone formation and resorption, Receptor Activator of Nuclear Factor-Kappa-B Ligand (RANKL) and Osteoprotegerin (OPG). It was found that 9 dyne/cm² loading for 30 minutes showed an upregulation trend on Piezo1 when MLO-Y4 osteocytes were exposed to an FSS microenvironment. FSS promotes the expression of OPG and inhibits the expression of RANKL. The blocker of Piezo1, GsMTx4, downregulates the effect of FSS on the expression of these two molecules. In addition, NOTCH3 was involved in this process. Thus, the results demonstrated that Piezo1-mediated FSS promotes the expression of OPG and inhibits the expression of RANKL via NOTCH3 in MLO-Y4 osteocytes.

Compressive force regulates orthodontic tooth movement via activating the NLRP3 inflammasome

Mechanical stress regulates various cellular functions like cell inflammation, immune responses, proliferation, and differentiation to maintain tissue homeostasis. However, the impact of mechanical signals on macrophages and the underlying mechanisms by which mechanical force regulates bone remodeling during orthodontic tooth movement remain unclear. NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome has been reported to promote osteoclastic differentiation to regulate alveolar bone resorption. But the relationship between the compressive force and NLRP3 inflammasome in macrophages remains unknown. In this study, immunohistochemical staining results showed elevated expression of NLRP3 and interleukin-1β, as well as an increased number of macrophages expressing NLRP3, on the compression side of the periodontal tissues, after force application for 7 days. Furthermore, the number of tartrate-resistant acid phosphatase-positive osteoclasts, and the mRNA and protein expression levels of osteoclast-related genes in the periodontal tissue decreased in the Nlrp3^-/- mice compared to the WT mice group after orthodontic movement. In vitro mechanical force activates the NLRP3 inflammasome and inhibits autophagy. Intraperitoneal injection of the autophagy inhibitor 3-methyladenine in Nlrp3^-/- mice promoted orthodontic tooth movement. This result indicates that the absence of NLRP3 inflammasome activation can be partially compensated for by autophagy inhibitors. Mechanistically, force-induced activation of the NLRP3 inflammasome in macrophages via the cGAS/P2X7R axis. In conclusion, compressive force regulates orthodontic tooth movement via activating the NLRP3 inflammasome.

Challenges of Periodontal Tissue Engineering: Increasing Biomimicry through 3D Printing and Controlled Dynamic Environment

In recent years, tissue engineering studies have proposed several approaches to regenerate periodontium based on the use of three-dimensional (3D) tissue scaffolds alone or in association with periodontal ligament stem cells (PDLSCs). The rapid evolution of bioprinting has sped up classic regenerative medicine, making the fabrication of multilayered scaffolds-which are essential in targeting the periodontal ligament (PDL)-conceivable. Physiological mechanical loading is fundamental to generate this complex anatomical structure ex vivo. Indeed, loading induces the correct orientation of the fibers forming the PDL and maintains tissue homeostasis, whereas overloading or a failure to adapt to mechanical load can be at least in part responsible for a wrong tissue regeneration using PDLSCs. This review provides a brief overview of the most recent achievements in periodontal tissue engineering, with a particular focus on the use of PDLSCs, which are the best choice for regenerating PDL as well as alveolar bone and cementum. Different scaffolds associated with various manufacturing methods and data derived from the application of different mechanical loading protocols have been analyzed, demonstrating that periodontal tissue engineering represents a proof of concept with high potential for innovative therapies in the near future.

Role of TRPC6 in periodontal tissue reconstruction mediated by appropriate stress

INTRODUCTION

The basis of orthodontic tooth movement (OTM) is the reconstruction of periodontal tissue under stress. Increasing the speed of OTM has always been the focus of attention.

OBJECTIVES

Periodontal ligament stem cells (PDLSCs) are direct effector cells of mechanical force, but the mechanism by which PDLSCs sense mechanical stimuli is unclear.

METHODS

Human PDLSCs (hPDLSCs) were analyzed in the presence or absence of force loading with the Flexcell loading system in vitro. Then, periodontal tissues were analyzed after mechanical stimulation in vivo. In addition, cells in a confined microenvironment were analyzed to observe changes in the cytoskeleton and migration. Finally, TRPC6^-/- mice were used to further verify the effect of TRPC6. After force application, the OTM distance, bone marrow density (BMD), TRPC6 and COL1 expression, and TRAP staining were evaluated in periodontal tissues.

RESULTS

RNA sequencing (RNA-seq) and western blot analyses revealed that TRPC6 was important during mechanical force application to hPDLSCs. Appropriate mechanical force application also induced TRPC6 activation in the OTM model and the confined microenvironment. Under a slightly confined microenvironment, treatment with the TRPC6 inhibitor SKF96365 and TRPC6 knockout decreased the migration speed of hPDLSCs and mouse bone marrow mesenchymal stem cells (mBMSCs). In addition, TRPC6^-/- mice showed lower OTM distances and reduced osteogenic and osteoclastic differentiation.

CONCLUSION

In summary, TRPC6 activation in PDLSCs mediated by appropriate mechanical force application contributes to periodontal tissue reconstruction. PDLSCs modulate periodontal tissue remodeling under appropriate mechanical stimulation through TRPC6; however, under excessive stress, alveolar bone and tooth roots are readily absorbed. Under this condition, environmental factors play a leading role, and the regulatory effect of TRPC6 is not obvious.

New Insights into TRP Ion Channels in Stem Cells

Transient receptor potential (TRP) ion channels are cationic permeable proteins located on the plasma membrane. TRPs are cellular sensors for perceiving diverse physical and/or chemical stimuli; thus, serving various critical physiological functions, including chemo-sensation, hearing, homeostasis, mechano-sensation, pain, taste, thermoregulation, vision, and even carcinogenesis. Dysregulated TRPs are found to be linked to many human hereditary diseases. Recent studies indicate that TRP ion channels are not only involved in sensory functions but are also implicated in regulating the biological characteristics of stem cells. In the present review, we summarize the expressions and functions of TRP ion channels in stem cells, including cancer stem cells. It offers an overview of the current understanding of TRP ion channels in stem cells.

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.

Effect of Tensile Frequency on the Osteogenic Differentiation of Periodontal Ligament Stem Cells

Purpose

The role of periodontal ligament stem cells (PDLSCs) in mediating osteogenesis involved in orthodontic tooth movement (OTM) is well established. However, various relevant in vitro studies vary in the frequency of tension. The effect of tensile frequency on the mechanotransduction of PDLSCs is not clear. The current study aimed to determine the effect of different tensile frequencies on the osteogenic differentiation of PDLSCs and to identify important mechano-sensitivity genes.

Methods

Human PDLSCs were isolated, identified, and subjected to cyclic equibiaxial tensile strain of 12% at different frequencies of 0.1 Hz, 0.5 Hz, 0.7 Hz, or static cultures. Osteogenic differentiation of PDLSCs was assessed by using Western blotting. High-throughput sequencing was used to identify differential mRNA expression. Short time-series expression miner (STEM) was utilized to describe the frequency patterns of the mRNAs. The functions and enriched pathways were identified, and the hub genes were identified and validated.

Results

We found that the osteoblastic differentiation capacity of PDLSCs increased with tensile frequency in the range of 0.1–0.7 Hz. Eight frequency-tendency gene expression profiles were identified to be statistically significant. Tensile frequency-specific expressed genes, such as SALL1 and EYA1, which decreased with the increase in tensile frequency, were found.

Conclusion

The osteoblastic differentiation of PDLSCs under mechanical tensile force is frequency dependent. EYA1 and SALL1 were identified as potential important tensile frequency-sensitive genes, which may contribute to the cyclic tension-induced osteogenic differentiation of PDLSCs in a frequency-dependent manner.

Comparative proteomics analysis of human stem cells from dental gingival and periodontal ligament

Dental stem cells isolated from oral tissues have been shown to provide with high proliferation ability and multilineage differentiation potential. Gingival mesenchymal stem cells (GMSCs) and periodontal ligament stem cells (PDLSCs), kinds of dental stem cells, can be used as substitutes for tissue repair materials because of their similar regenerative functions. In this study, we aim to explore the similarities and differences between the protein profiles of GMSCs and PDLSCs through quantitative proteomics. A total of 2821 proteins were identified and retrieved, of which 271 were up-regulated and 57 were down-regulated in GMSCs compared to PDLSCs. GO analysis demonstrated that the 328 differentially abundant proteins (DAPs) were involved in the regulation of gene expression, metabolism and signal transduction in biological process, mainly distributed in organelles related to vesicle transport, and involved in the molecular function of binding protein. And KEGG analysis showed that the DAPs were committed to regulating the synthesis of proteasome and spliceosome. RT-qPCR results showed that ARPC1B, PDAP1 and SEC61B can be used as special markers to distinguish GMSCs from PDLSCs. This research contributes to explaining the molecular mechanism and promoting the clinical application of tissue regeneration of GMSCs and PDLSCs. This article is protected by copyright. All rights reserved.

Ion channels in stem cells and their roles in stem cell biology and vascular diseases

Stem cell therapy may be a promising option for the treatment of vascular diseases. In recent years, significant progress has been made in stem cell research, especially in the mechanism of stem cell activation, homing and differentiation in vascular repair and reconstruction. Current research on stem cells focuses on protein expression and transcriptional networks. Ion channels are considered to be the basis for the generation of bioelectrical signals, which control the proliferation, differentiation and migration of various cell types. Although heterogeneity of multiple ion channels has been found in different types of stem cells, it is unclear whether the heterogeneous expression of ion channels is related to different cell subpopulations and/or different stages of the cell cycle. There is still a long way to go in clinical treatment by using the regulation of stem cell ion channels. In this review, we reviewed the main ion channels found on stem cells, their expression and function in stem cell proliferation, differentiation and migration, and the research status of stem cells' involvement in vascular diseases.

Materials for Dentoalveolar Bioprinting: Current State of the Art

Although current treatments can successfully address a wide range of complications in the dentoalveolar region, they often still suffer from drawbacks and limitations, resulting in sub-optimal treatments for specific problems. In recent decades, significant progress has been made in the field of tissue engineering, aiming at restoring damaged tissues via a regenerative approach. Yet, the translation into a clinical product is still challenging. Novel technologies such as bioprinting have been developed to solve some of the shortcomings faced in traditional tissue engineering approaches. Using automated bioprinting techniques allows for precise placement of cells and biological molecules and for geometrical patient-specific design of produced biological scaffolds. Recently, bioprinting has also been introduced into the field of dentoalveolar tissue engineering. However, the choice of a suitable material to encapsulate cells in the development of so-called bioinks for bioprinting dentoalveolar tissues is still a challenge, considering the heterogeneity of these tissues and the range of properties they possess. This review, therefore, aims to provide an overview of the current state of the art by discussing the progress of the research on materials used for dentoalveolar bioprinting, highlighting the advantages and shortcomings of current approaches and considering opportunities for further research.

Mechanosensitive Piezo1 in Periodontal Ligament Cells Promotes Alveolar Bone Remodeling During Orthodontic Tooth Movement

Orthodontic tooth movement (OTM) is a process depending on the remodeling of periodontal tissues surrounding the roots. Orthodontic forces trigger the conversion of mechanical stimuli into intercellular chemical signals within periodontal ligament (PDL) cells, activating alveolar bone remodeling, and thereby, initiating OTM. Recently, the mechanosensitive ion channel Piezo1 has been found to play pivotal roles in the different types of human cells by transforming external physical stimuli into intercellular chemical signals. However, the function of Piezo1 during the mechanotransduction process of PDL cells has rarely been reported. Herein, we established a rat OTM model to study the potential role of Piezo1 during the mechanotransduction process of PDL cells and investigate its effects on the tension side of alveolar bone remodeling. A total of 60 male Sprague-Dawley rats were randomly assigned into three groups: the OTM + inhibitor (INH) group, the OTM group, and the control (CON) group. Nickel-titanium orthodontic springs were applied to trigger tooth movement. Mice were sacrificed on days 0, 3, 7, and 14 after orthodontic movement for the radiographic, histological, immunohistochemical, and molecular biological analyses. Our results revealed that the Piezo1 channel was activated by orthodontic force and mainly expressed in the PDL cells during the whole tooth movement period. The activation of the Piezo1 channel was essential for maintaining the rate of orthodontic tooth movement and facilitation of new alveolar bone formation on the tension side. Reduced osteogenesis-associated transcription factors such as Runt-related transcription factor 2 (RUNX2), Osterix (OSX), and receptor activator of nuclear factor-kappa B ligand (RANKL)/osteoprotegerin (OPG) ratio were examined when the function of Piezo1 was inhibited. In summary, Piezo1 plays a critical role in mediating both the osteogenesis and osteoclastic activities on the tension side during OTM.

Osteoclastic effects of mBMMSCs under compressive pressure during orthodontic tooth movement

Background

During orthodontic tooth movement (OTM), alveolar bone remodelling is closely related to mechanical force. It is unclear whether stem cells can affect osteoclastogenesis to promote OTM. This study aimed to investigate the role of mouse bone marrow mesenchymal stem cells (mBMMSCs) under compression load in OTM.

Methods

A mouse OTM model was established, and GFP-labelled mBMMSCs and normal saline were injected into different groups of mice by tail vein injection. OTM distance was measured using tissue specimens and micro-computed tomography (micro-CT). The locations of mBMMSCs were traced using GFP immunohistochemistry. Haematoxylin-eosin staining, tartrate-resistant acid phosphate (TRAP) staining and immunohistochemistry of Runx2 and lipoprotein lipase were used to assess changes in the periodontal ligament during OTM. mBMMSCs under compression were co-cultured with mouse bone marrow-derived macrophages (mBMMs), and the gene expression levels of Rankl, Mmp-9, TRAP, Ctsk, Alp, Runx2, Ocn and Osterix were determined by RT-PCR.

Results

Ten days after mBMMSCs were injected into the tail vein of mice, the OTM distance increased from 176 (normal saline) to 298.4 μm, as determined by tissue specimen observation, and 174.2 to 302.6 μm, as determined by micro-CT metrological analysis. GFP-labelled mBMMSCs were mostly located on the compressed side of the periodontal ligament. Compared to the saline group, the number of osteoclasts in the alveolar bone increased significantly (P < 0.01) on the compressed side in the mBMMSC group. Three days after mBMMSC injection, the number of Runx2-GFP double-positive cells on the tension side was significantly higher than that on the compression side. After applying compressive force on the mBMMSCs in vitro for 2 days, RANKL expression was significantly higher than in the non-compression cells, but expression of Alp, Runx2, Ocn and Osterix was significantly decreased (P < 0.05). The numbers of osteoclasts differentiated in response to mBMMs co-cultured with mBMMSCs under pressure load and expression of osteoclast differentiation marker genes (Mmp-9, TRAP and Ctsk) were significantly higher than those in mBMMs stimulated by M-CSF alone (P < 0.05).

Conclusions

mBMMSCs are not only recruited to the compressed side of the periodontal ligament but can also promote osteoclastogenesis by expressing Rankl, improving the efficiency of OTM.

Mechanical force modulates periodontal ligament stem cell characteristics during bone remodelling via TRPV4

OBJECTIVES

Mechanical force plays an important role in modulating stem cell fate and behaviours. However, how periodontal ligament stem cells (PDLSCs) perceive mechanical stimulus and transfer it into biological signals, and thereby promote alveolar bone remodelling, is unclear.

MATERIALS AND METHODS

An animal model of force-induced tooth movement and a compressive force in vitro was used. After force application, tooth movement distance, mesenchymal stem cell and osteoclast number, and proinflammatory cytokine expression were detected in periodontal tissues. Then, rat primary PDLSCs with or without force loading were isolated, and their stem cell characteristics including clonogenicity, proliferation, multipotent differentiation and immunoregulatory properties were evaluated. Under compressive force in vitro, the effects of the ERK signalling pathway on PDLSC characteristics were evaluated by Western blotting.

RESULTS

Mechanical force in vivo induced PDLSC proliferation, which was accompanied with inflammatory cytokine accumulation, osteoclast differentiation and TRPV4 activation; the force-stimulated PDLSCs showed greater clonogenicity and proliferation, reduced differentiation ability, improved induction of macrophage migration, osteoclast differentiation and proinflammatory factor expression. The biological changes induced by mechanical force could be partially suppressed by TRPV4 inhibition. Mechanistically, force-induced activation of TRPV4 in PDLSCs regulated osteoclast differentiation by affecting the RANKL/OPG system via ERK signalling.

CONCLUSIONS

Taken together, we show here that TRPV4 activation in PDLSCs under mechanical force contributes to changing their stem cell characteristics and modulates bone remodelling during tooth movement.