Cyclic stretch influenced expression of membrane connexin 43 in human periodontal ligament cell

Cyclic stretch-induced exosomes from periodontal ligament cells promote osteoblasts osteogenic differentiation via the miR-181d-5p/TNF signaling pathway

OBJECTIVE

To investigate the effects of cyclic stretch-induced periodontal ligament cell (PDLC) exosomes on osteoblast differentiation, and to explore their regulatory role in mechanical force-related periodontal tissue remodeling.

DESIGN

After applying 20 % cyclic stretch loading to PDLCs, exosomes were extracted from the supernatant and co-cultured with osteoblasts to detect their effects on osteogenic differentiation. Meanwhile, the exosomes were sequenced by high-throughput microRNA sequencing for bioinformatic analysis and validation to explore exosome signaling pathways through miRNAs.

RESULTS

Cyclic stretch-induced PDLC exosomes could be taken up by osteoblasts and promoted osteogenic differentiation of osteoblasts, as demonstrated by the increased expression levels of osteogenesis-related factors and enhanced alkaline phosphatase (Alp) staining. Among the differentially expressed miRNAs between exosomes from cyclic stretch group and control group, miRNA-181d-5p was up-regulated significantly. The expression levels of osteogenesis-related factors and Alp staining were also increased in osteoblasts transfected with miR-181d-5p, and this effect might be related to the inhibitory role of exosomal miR-181d-5p on tumor necrosis factor (TNF).

CONCLUSIONS

Cyclic stretch-induced PDLC exosomes exhibited a promoting effect on osteogenic differentiation, which might result from the inhibition of TNF via exosomal miR-181d-5p.

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.

Impact of phosphorylation of heat shock protein 27 on the expression profile of periodontal ligament fibroblasts during mechanical strain

PURPOSE

Orthodontic tooth movement is a complex process involving the remodeling of extracellular matrix and bone as well as inflammatory processes. During orthodontic treatment, sterile inflammation and mechanical loading favor the production of receptor activator of NF-κB ligand (RANKL). Simultaneously, expression of osteoprotegerin (OPG) is inhibited. This stimulates bone resorption on the pressure side. Recently, heat shock protein 27 (HSP27) was shown to be expressed in the periodontal ligament after force application and to interfere with inflammatory processes.

METHODS

We investigated the effects of phosphorylated HSP27 on collagen synthesis (COL1A2 mRNA), inflammation (IL1B mRNA, IL6 mRNA, PTGS2 protein) and bone remodeling (RANKL protein, OPG protein) in human periodontal ligament fibroblasts (PDLF) without and with transfection of a plasmid mimicking permanent phosphorylation of HSP27 using real-time quantitative polymerase chain reaction (RT-qPCR), western blot and enzyme-linked immunosorbent assays (ELISAs). Furthermore, we investigated PDLF-induced osteoclastogenesis after compressive strain in a co-culture model with human macrophages.

RESULTS

In particular, phosphorylated HSP27 increased gene expression of COL1A2 and protein expression of PTGS2, while IL6 mRNA levels were reduced. Furthermore, we observed an increasing effect on the RANKL/OPG ratio and osteoclastogenesis mediated by PDLF.

CONCLUSION

Phosphorylation of HSP27 may therefore be involved in the regulation of orthodontic tooth movement by impairment of the sterile inflammation response and osteoclastogenesis.

Maintenance of Ligament Homeostasis of Spheroid-Colonized Embroidered and Functionalized Scaffolds after 3D Stretch

Anterior cruciate ligament (ACL) ruptures are usually treated with autograft implantation to prevent knee instability. Tissue engineered ACL reconstruction is becoming promising to circumvent autograft limitations. The aim was to evaluate the influence of cyclic stretch on lapine (L) ACL fibroblasts on embroidered scaffolds with respect to adhesion, DNA and sulphated glycosaminoglycan (sGAG) contents, gene expression of ligament-associated extracellular matrix genes, such as type I collagen, decorin, tenascin C, tenomodulin, gap junctional connexin 43 and the transcription factor Mohawk. Control scaffolds and those functionalized by gas phase fluorination and cross-linked collagen foam were either pre-cultured with a suspension or with spheroids of LACL cells before being subjected to cyclic stretch (4%, 0.11 Hz, 3 days). Stretch increased significantly the scaffold area colonized with cells but impaired sGAGs and decorin gene expression (functionalized scaffolds seeded with cell suspension). Stretching increased tenascin C, connexin 43 and Mohawk but decreased decorin gene expression (control scaffolds seeded with cell suspension). Pre-cultivation of functionalized scaffolds with spheroids might be the more suitable method for maintaining ligamentogenesis in 3D scaffolds compared to using a cell suspension due to a significantly higher sGAG content in response to stretching and type I collagen gene expression in functionalized scaffolds.

Mechanistic Insight into Orthodontic Tooth Movement Based on Animal Studies: A Critical Review

Alveolar bone remodeling in orthodontic tooth movement (OTM) is a highly regulated process that coordinates bone resorption by osteoclasts and new bone formation by osteoblasts. Mechanisms involved in OTM include mechano-sensing, sterile inflammation-mediated osteoclastogenesis on the compression side and tensile force-induced osteogenesis on the tension side. Several intracellular signaling pathways and mechanosensors including the cilia and ion channels transduce mechanical force into biochemical signals that stimulate formation of osteoclasts or osteoblasts. To date, many studies were performed in vitro or using human gingival crevicular fluid samples. Thus, the use of transgenic animals is very helpful in examining a cause and effect relationship. Key cell types that participate in mediating the response to OTM include periodontal ligament fibroblasts, mesenchymal stem cells, osteoblasts, osteocytes, and osteoclasts. Intercellular signals that stimulate cellular processes needed for orthodontic tooth movement include receptor activator of nuclear factor-κB ligand (RANKL), tumor necrosis factor-α (TNF-α), dickkopf Wnt signaling pathway inhibitor 1 (DKK1), sclerostin, transforming growth factor beta (TGF-β), and bone morphogenetic proteins (BMPs). In this review, we critically summarize the current OTM studies using transgenic animal models in order to provide mechanistic insight into the cellular events and the molecular regulation of OTM.

Gap junction-mediated cell-to-cell communication in oral development and oral diseases: a concise review of research progress

Homoeostasis depends on the close connection and intimate molecular exchange between extracellular, intracellular and intercellular networks. Intercellular communication is largely mediated by gap junctions (GJs), a type of specialized membrane contact composed of variable number of channels that enable direct communication between cells by allowing small molecules to pass directly into the cytoplasm of neighbouring cells. Although considerable evidence indicates that gap junctions contribute to the functions of many organs, such as the bone, intestine, kidney, heart, brain and nerve, less is known about their role in oral development and disease. In this review, the current progress in understanding the background of connexins and the functions of gap junctions in oral development and diseases is discussed. The homoeostasis of tooth and periodontal tissues, normal tooth and maxillofacial development, saliva secretion and the integrity of the oral mucosa depend on the proper function of gap junctions. Knowledge of this pattern of cell-cell communication is required for a better understanding of oral diseases. With the ever-increasing understanding of connexins in oral diseases, therapeutic strategies could be developed to target these membrane channels in various oral diseases and maxillofacial dysplasia.

Transcriptional Expression in Human Periodontal Ligament Cells Subjected to Orthodontic Force: An RNA-Sequencing Study

This study was performed to investigate the changes in gene expression in periodontal ligament (PDL) cells following mechanical stimulus through RNA sequencing. In this study, premolars extracted for orthodontic treatment were used. To stimulate the PDL cells, an orthodontic force of 100× g was applied to the premolar (experimental group; n = 11), whereas the tooth on the other side was left untreated (control group; n = 11). After the PDL cells were isolated from the extracted teeth, gene set enrichment analysis (GSEA), differentially expressed gene (DEG) analysis, and real-time PCR were performed to compare the two groups. GSEA demonstrated that gene sets related to the cell cycle pathway were upregulated in PDL. Thirteen upregulated and twenty downregulated genes were found through DEG analysis. Real-time PCR results confirmed that five upregulated genes (CC2D1B, CPNE3, OPHN1, TANGO2, and UAP-1) and six downregulated genes (MYOM2, PPM1F, PCDP1, ATP2A1, GPR171, and RP1-34H18.1-1) were consistent with RNA sequencing results. We suggest that, from among these eleven genes, two upregulated genes, CPNE3 and OPHN1, and one downregulated gene, PPM1F, play an important role in PDL regeneration in humans when orthodontic force is applied.

Vesicular nucleotide transporter mediates adenosine triphosphate release in compressed human periodontal ligament fibroblast cells and participates in tooth movement-induced nociception in rats

OBJECTIVE

Pain control is imperative in orthodontic treatment. Adenosine triphosphate (ATP) is a key mediator released from periodontal ligament cells that excites nociceptive nerve endings. Vesicular nucleotide transporter (VNUT), encoded by the Solute carrier family 17 member 9 (SLC17A9) gene, participates in ATP uptake into secretory vesicles; thus, it may mediate tooth movement-induced pain. In the present study, we examined whether VNUT in periodontal ligament cells participates in tooth movement-induced nociception.

DESIGN

Expression levels of SLC17A9, connexin 43, and pannexin 1 in human periodontal ligament fibroblasts (HPDLFs) were examined by quantitative reverse transcription-polymerase chain reaction. Mechanical force via centrifugation-induced ATP release was measured using an ATP bioluminescence assay. Inhibitors were used to evaluate the role of ATP transporters. Face-grooming behaviors were assessed as indicators of nociceptive responses after experimental tooth movement in rats, as well as the effects of drugs for the pain-like behavior.

RESULTS

After HPDLFs underwent mechanical stimulation by centrifugation, SLC17A9 mRNA expression in the cells was significantly upregulated. Increased ATP release from HPDLFs after mechanical stimulation was suppressed by treatment with clodronic acid, a VNUT inhibitor, at concentrations of 0.1 and 1.0 μM. In rats, face-grooming behaviors (indicators of nociception) were significantly increased on day 1 after experimental tooth movement. Increased face-grooming behaviors were suppressed by systemic administration of clodronic acid (0.1 mg/kg).

CONCLUSIONS

These results indicate that release of ATP from periodontal ligament cells via VNUT is important for nociceptive transduction during orthodontic treatment. Thus, VNUT may provide a novel drug target for tooth movement-induced pain.

Effect of ILK on small-molecule metabolism of human periodontal ligament fibroblasts with mechanical stretching

BACKGROUND

Mechanical stimuli can cause periodontal tissue reconstruction. Studies have found that changes in metabolites can be the terminal effect of integrin-mediated mechanical signaling. As a key kinase in integrin regulation, integrin-linked kinase (ILK) mediates mechanical signal transduction, which may contribute to metabolite changes. Defining the components of small-molecule metabolites can optimize mechanical stimuli and periodontal tissue reconstruction. Our purpose is to detect the effect of ILK-mediated mechanical signaling on intracellular small-molecule metabolites (amino acids and organic acids) in human periodontal ligament fibroblasts (HPDLFs).

METHODS

Primary HPDLFs were isolated by enzyme digestion method. Tensile stresses were applied on HPDLFs in vitro using a Flexcell system. ILK gene in HPDLFs was knocked down by RNA interference (RNAi). Twenty common amino acids and seven organic acids in HPDLFs were analyzed by gas chromatography/mass spectrometry technique.

RESULTS

Five amino acids (ie, alanine, glutamine, glutamate, glycine, and threonine) and three organic acids (ie, pyruvate, lactate, and citric acid) were found to be changed remarkably after mechanical stretching. In addition, baseline levels of four amino acids (ie, glutamate, glutamine, threonine, and glycine) and two organic acids (ie, lactate and citric acid) were significantly different in ILK knockdown compared with wild-type HPDLFs.

CONCLUSION

This study suggests that five amino acids (ie, alanine, glutamine, glutamate, glycine, and threonine) and three organic acids (ie, pyruvate, lactate, and citric acid) may act as cellular mediators for mechanical signals in HPDLFs. Among them, four amino acids (ie, glutamate, glutamine, threonine, and glycine) and two organic acids (ie, lactate and citric acid) may be closely linked to ILK.

Interaction between caspase-3 and caspase-5 in the stretch-induced programmed cell death in the human periodontal ligament cells

In our previous studies, programmed cell death (PCD) was induced in human periodontal ligament (PDL) cells, through activation of caspase-3 and upregulation of CASP5 gene (encoding caspase-5 protein), in response to mechanical stretch loading. The aim of this study is to explore the relationship between the inflammatory caspase, caspase-5, and the apoptotic executioner protein, caspase-3, in human PDL cells. Here, we found that cyclic stretching upregulated the activity and the protein expression level of caspase-3 and -5 and the addition of the caspase-3 inhibitor or caspase-5 inhibitor significantly inhibited the stretch-induced PCD. Meanwhile, the inhibition of caspase-5 inhibited the activation of caspase-3 and vice versa. The result of coimmunoprecipitation also demonstrated that the expression of caspase-3 was immunoprecipitated with caspase-5. Thus, our study revealed that the in vitro application of cyclic stretching induced PCD by activation of caspase-3 and -5 in human PDL cells, and these two caspases could interact with each other after mechanical stretch loading. The study may facilitate further studies on the mechanism of stretch-induced PCD and help us understand the force-related periodontal homeostasis and remodeling better.

Activation of NLRP1 and NLRP3 inflammasomes contributed to cyclic stretch-induced pyroptosis and release of IL-1β in human periodontal ligament cells

Inflammasomes have been reported to be present in periodontal inflammatory tissue, but the exact role of inflammasomes in periodontal inflammatory reactions especially those related to mechanical stimulations has not been clarified. In this study, it was shown that cyclic stretch activated the nucleotide-binding oligomerization domain-like receptor containing pyrin domain 1 and 3 (NLRP1 and NLRP3) inflammasomes and induced the release of IL-1β and pyroptosis via a caspase-1-related mechanism in human periodontal ligament cells (HPDLCs). This study firstly demonstrated that activation of NLRP inflammasomes contributed to the stretch-induced inflammatory response in HPDLCs. As inflammasomes have been reported to be involved in both programmed cell death and inflammation, further studies are required to elucidate the exact roles and signaling pathway of inflammasomes in stretch-induced periodontal inflammation.

Cyclic stretch-induced the cytoskeleton rearrangement and gene expression of cytoskeletal regulators in human periodontal ligament cells

OBJECTIVE

This study aimed to explore the mechanism of the stretch-induced cell realignment and cytoskeletal rearrangement by identifying several mechanoresponsive genes related to cytoskeletal regulators in human PDL cells.

MATERIAL AND METHODS

After the cells were stretched by 1, 10 and 20% strains for 0.5, 1, 2, 4, 6, 12 or 24 h, the changes of the morphology and content of microfilaments were recorded and calculated. Meanwhile, the expression of 84 key genes encoding cytoskeletal regulators after 6 and 24 h stretches with 20% strain was detected by using real-time PCR array. Western blot was applied to identify the protein expression level of several cytoskeletal regulators encoded by these differentially expressed genes.

RESULTS

The confocal fluorescent staining results confirmed that stretch-induced realignment of cells and rearrangement of microfilaments. Among the 84 genes screened, one gene was up-regulated while two genes were down-regulated after 6 h stretch. Meanwhile, three genes were up-regulated while two genes were down-regulated after 24 h stretch. These genes displaying differential expression included genes regulating polymerization/depolymerization of microfilaments (CDC42EP2, FNBP1L, NCK2, PIKFYVE, WASL), polymerization/depolymerization of microtubules (STMN1), interacting between microfilaments and microtubules (MACF1), as well as a phosphatase (PPP1R12B). Among the proteins encoded by these genes, the protein expression level of Cdc42 effector protein-2 (encoded by CDC42EP2) and Stathmin-1 (encoded by STMN1) was down-regulated, while the protein expression level of N-WASP (encoded by WASL) was up-regulated.

CONCLUSION

The present study confirmed the cyclic stretch-induced cellular realignment and rearrangement of microfilaments in the human PDL cells and indicated several force-sensitive genes with regard to cytoskeletal regulators.

Caspase-8 and Caspase-9 Functioned Differently at Different Stages of the Cyclic Stretch-Induced Apoptosis in Human Periodontal Ligament Cells

Background

Human periodontal ligament (PDL) cells underwent apoptosis after mechanical stretch loading. However, the exact signalling pathway remains unknown. This study aimed to elucidate how the apoptotic caspases functioned in the cyclic stretch-induced apoptosis in human PDL cells.

Materials and Methods

In the present study, 20% cyclic stretch was selected to load the cells for 6 or 24 h. The following parameters were analyzed: apoptotic rates, the protein levels of caspase-3, -7, -8 and -9 and the activities of caspase-8 and -9. Subsequently, the influences of caspase-8 and caspase-9 inhibitors on the apoptotic rate and the protein level of the activated caspase-3 were assessed as well.

Results

The apoptotic rates increased in response to cyclic stretch, but the cells entered different apoptotic stages after 6 and 24 h stretches. Caspase-3, -7, -8 and -9 were all activated after stretch loading. The stretch-induced apoptosis and the protein level of the activated caspase-3 were inhibited after inhibiting both caspase-8 and caspase-9 in both 6 and 24 h stretched cells and after inhibiting caspase-9 in 24 h stretched cells.

Conclusion

Caspase-8 and -9 functioned differently at different apoptotic stages in human PDL cells after cyclic stretch.

Connexins and pannexins in the skeleton: gap junctions, hemichannels and more

Regulation of bone homeostasis depends on the concerted actions of bone-forming osteoblasts and bone-resorbing osteoclasts, controlled by osteocytes, cells derived from osteoblasts surrounded by bone matrix. The control of differentiation, viability and function of bone cells relies on the presence of connexins. Connexin43 regulates the expression of genes required for osteoblast and osteoclast differentiation directly or by changing the levels of osteocytic genes, and connexin45 may oppose connexin43 actions in osteoblastic cells. Connexin37 is required for osteoclast differentiation and its deletion results in increased bone mass. Less is known on the role of connexins in cartilage, ligaments and tendons. Connexin43, connexin45, connexin32, connexin46 and connexin29 are expressed in chondrocytes, while connexin43 and connexin32 are expressed in ligaments and tendons. Similarly, although the expression of pannexin1, pannexin2 and pannexin3 has been demonstrated in bone and cartilage cells, their function in these tissues is not fully understood.

Connexin 43 and ERK regulate tension-induced signal transduction in human periodontal ligament fibroblasts

Periodontal ligament (PDL) fibroblasts play an important role in preserving periodontal homeostasis and transmitting mechanical signals to alveolar bone. Connexin 43 (Cx43), a gap junction protein, is essential for bone homeostasis and regulates bone remodeling. However, the function of Cx43 in human PDL fibroblast-regulated bone remodeling has not yet been elucidated. In this study, human PDL fibroblasts were exposed to cyclic mechanical tension with a maximum 5% elongation for different durations. We then examined the expression of signaling molecules related to osteogenesis and osteoclastogenesis at both the mRNA and protein levels as well as the activity of extracellular signal-regulated kinase (ERK) in human PDL fibroblasts after loading. We found that mechanical tension increased Cx43, which further upregulated osteogenic (e.g., RUNX2, Osterix, and OPG) and down-regulated osteoclastogenic (e.g., RANKL) signaling molecules. Suppressing Cx43 gene (Gja1) by siRNA inhibited the increase in osteogenesis-related molecules but enhanced RANKL expression. Similar to Cx43, activated ERK1/2 was also enhanced by mechanical tension and suppressed by Cx43 siRNA. Inhibition of ERK1/2 signaling using PD98059 reduced the tension-regulated increase in osteogenesis-related molecules but enhanced that of osteoclastogenesis-related ones. These findings suggest that cyclic tension may involve into the osteogenic or osteoclastogenetic differentiation potential of human PDL fibroblasts via the Cx43-ERK1/2 signaling pathway.