Cyclic strain-induced cytoskeletal rearrangement of human periodontal ligament cells via the Rho signaling pathway

Jaw osteoporosis: Challenges to oral health and emerging perspectives of treatment

Osteoporosis is a prevalent bone metabolic disease that poses a significant challenge to global human health. Jaw osteoporosis, characterized by microstructural damage of the jaw resulting from various factors, is one of the common manifestations of this condition. Recent studies have demonstrated that jaw osteoporosis has multifaceted effects on oral health and can negatively impact conditions such as periodontitis, oral implantation, orthodontic treatment, and wound healing. However, there are still some limitations in the conventional treatment of osteoporosis. For instance, while bisphosphonates can enhance bone quality, they may also lead to osteonecrosis of the jaw, which poses a potential safety hazard in oral diagnosis and treatment. In recent years, considerable attention has been focused on improving the pathological condition of jaw osteoporosis. Treatment strategies such as gut microbial regulation, extracellular vesicles, molecular targeted therapy, herbal medicine, mechanical stimulation are expected to enhance efficacy and minimize adverse reactions. Therefore, understanding these effects and exploring novel treatments for jaw osteoporosis may provide new insights for oral health maintenance and disease treatment. This article reviews the impact of jaw osteoporosis on oral health and describes the limitations associated with current methods. It also discusses emerging perspectives on treatment, offering a comprehensive overview of the challenges and future directions in managing jaw osteoporosis.

Cellular mechanotransduction in health and diseases: from molecular mechanism to therapeutic targets

Cellular mechanotransduction, a critical regulator of numerous biological processes, is the conversion from mechanical signals to biochemical signals regarding cell activities and metabolism. Typical mechanical cues in organisms include hydrostatic pressure, fluid shear stress, tensile force, extracellular matrix stiffness or tissue elasticity, and extracellular fluid viscosity. Mechanotransduction has been expected to trigger multiple biological processes, such as embryonic development, tissue repair and regeneration. However, prolonged excessive mechanical stimulation can result in pathological processes, such as multi-organ fibrosis, tumorigenesis, and cancer immunotherapy resistance. Although the associations between mechanical cues and normal tissue homeostasis or diseases have been identified, the regulatory mechanisms among different mechanical cues are not yet comprehensively illustrated, and no effective therapies are currently available targeting mechanical cue-related signaling. This review systematically summarizes the characteristics and regulatory mechanisms of typical mechanical cues in normal conditions and diseases with the updated evidence. The key effectors responding to mechanical stimulations are listed, such as Piezo channels, integrins, Yes-associated protein (YAP) /transcriptional coactivator with PDZ-binding motif (TAZ), and transient receptor potential vanilloid 4 (TRPV4). We also reviewed the key signaling pathways, therapeutic targets and cutting-edge clinical applications of diseases related to mechanical cues.

Role of noncoding RNAs in orthodontic tooth movement: new insights into periodontium remodeling

Orthodontic tooth movement (OTM) is biologically based on the spatiotemporal remodeling process in periodontium, the mechanisms of which remain obscure. Noncoding RNAs (ncRNAs), especially microRNAs and long noncoding RNAs, play a pivotal role in maintaining periodontal homeostasis at the transcriptional, post-transcriptional, and epigenetic levels. Under force stimuli, mechanosensitive ncRNAs with altered expression levels transduce mechanical load to modulate intracellular genes. These ncRNAs regulate the biomechanical responses of periodontium in the catabolic, anabolic, and coupling phases throughout OTM. To achieve this, down or upregulated ncRNAs actively participate in cell proliferation, differentiation, autophagy, inflammatory, immune, and neurovascular responses. This review highlights the regulatory mechanism of fine-tuning ncRNAs in periodontium remodeling during OTM, laying the foundation for safe, precise, and personalized orthodontic treatment.

LRP6/filamentous-actin signaling facilitates osteogenic commitment in mechanically induced periodontal ligament stem cells

BACKGROUND

Mechanotransduction mechanisms whereby periodontal ligament stem cells (PDLSCs) translate mechanical stress into biochemical signals and thereby trigger osteogenic programs necessary for alveolar bone remodeling are being deciphered. Low-density lipoprotein receptor-related protein 6 (LRP6), a Wnt transmembrane receptor, has been qualified as a key monitor for mechanical cues. However, the role of LRP6 in the mechanotransduction of mechanically induced PDLSCs remains obscure.

METHODS

The Tension System and tooth movement model were established to determine the expression profile of LRP6. The loss-of-function assay was used to investigate the role of LRP6 on force-regulated osteogenic commitment in PDLSCs. The ability of osteogenic differentiation and proliferation was estimated by alkaline phosphatase (ALP) staining, ALP activity assay, western blotting, quantitative real-time PCR (qRT-PCR), and immunofluorescence. Crystalline violet staining was used to visualize cell morphological change. Western blotting, qRT-PCR, and phalloidin staining were adopted to affirm filamentous actin (F-actin) alteration. YAP nucleoplasmic localization was assessed by immunofluorescence and western blotting. YAP transcriptional response was evaluated by qRT-PCR. Cytochalasin D was used to determine the effects of F-actin on osteogenic commitment and YAP switch behavior in mechanically induced PDLSCs.

RESULTS

LRP6 was robustly activated in mechanically induced PDLSCs and PDL tissues. LRP6 deficiency impeded force-dependent osteogenic differentiation and proliferation in PDLSCs. Intriguingly, LRP6 loss caused cell morphological aberration, F-actin dynamics disruption, YAP nucleoplasmic relocation, and subsequent YAP inactivation. Moreover, disrupted F-actin dynamics inhibited osteogenic differentiation, proliferation, YAP nuclear translocation, and YAP activation in mechanically induced PDLSCs.

CONCLUSIONS

We identified that LRP6 in PDLSCs acted as the mechanosensor regulating mechanical stress-inducible osteogenic commitment via the F-actin/YAP cascade. Targeting LRP6 for controlling alveolar bone remodeling may be a prospective therapy to attenuate relapse of orthodontic treatment.

CPNE7 regenerates periodontal ligament via TAU-mediated alignment and cementum attachment protein-mediated attachment

AIM

Once the periodontal ligament (PDL) is damaged, it is difficult to regenerate its characteristic structure. Copine7 (CPNE7) reportedly plays a functional role in supporting periodontal attachment and PDL alignment. Here we demonstrate the regulatory mechanism of CPNE7 coordination with cytoskeleton reorganization and cementum attachment protein (CAP)-mediated attachment in PDL regeneration.

MATERIALS AND METHODS

The expression and localization of CPNE7, α-TUBULIN, ACTIN, and microtubule associated protein tau (TAU) were investigated in vitro. The effects of recombinant CPNE7 (rCPNE7) and CPNE7-derived peptides (CPNE7-DP) on the regulation of CAP were analysed in vitro, and PDL repair capacity was analysed in vivo.

RESULTS

CPNE7 co-localized with F-ACTIN and induced α-TUBULIN expansion to the edge of human PDL cells (hPDLCs). ACTIN and α-TUBULIN protein expressions were not elevated in rCPNE7-treated hPDLCs. rCPNE7 elevated the protein expression of TAU, which co-localized with F-ACTIN and α-TUBULIN. Replantation studies on mice revealed that well-attached and well-aligned PDLs were repaired in the rCPNE7 group. CPNE7-DP directly up-regulate the expression of CAP in vitro and promote PDL regeneration in three-wall defect canine models in vivo.

CONCLUSIONS

Our findings suggest that CPNE7 helps in PDL repair by supporting PDL alignment through TAU-mediated cytoskeleton reorganization and direct regulation of CAP-mediated PDL attachments of PDLCs.

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.

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.

Roles and mechanisms of YAP/TAZ in orthodontic tooth movement

Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are transcriptional coactivators encoded by paratactic homologous genes, shuttle-crossing between cytoplasm and nucleus to regulate the gene expression and cell behavior and standing at the center place of the sophisticated regulatory networking of mechanotransduction. Orthodontic tooth movement (OTM) is a process in which extracellular mechanical stimuli are transformed into intracellular biochemical signals to regulate cellular responses and tissue remodeling. Literature studies have confirmed that YAP/TAZ plays an important role not only in embryonic development, homeostasis and tumorigenesis, but also in mechanical-biochemical signal transduction of periodontal tissues under the mediation of various signal molecules in its upstream and downstream. Herein, we review the advances in the roles and mechanisms of YAP/TAZ in OTM to provide insights for better understanding and further study of the OTM and possible targeted clinical intervention in orthodontic treatment.

ARHGAP17 inhibits pathological cyclic strain-induced apoptosis in human periodontal ligament fibroblasts via Rac1/Cdc42

Rho GTPase-activating protein (Rho-GAP) and Rho GDP dissociation inhibitor (Rho- GDI) are two main negative regulators of Rho GTPase. Our previous work has found that Rho-GDI and Rho GTPase are involved in the response of human periodontal ligament (PDL) cells to mechanical stress. However, whether Rho-GAP also has a role in this process remains unknown. Here, we attempted to find the Rho-GAP gene that may be involved in pathological stretch-induced apoptosis of PDL cells. Human PDL fibroblasts were exposed to 20% cyclic strain for 6 hours or 24 hours, after which the expression levels of ARHGAP10, ARHGAP17, ARHGAP21, ARHGAP24 and ARHGAP28 were determined. Results showed that ARHGAP17 expression decreased the most obviously after treatment of stretch. In addition, ARHGAP17 overexpression abolished 20% cyclic strain-induced apoptosis. Therefore, ARHGAP17 has an important role in pathological stretch-induced apoptosis of human PDL fibroblasts. Moreover, we found that ARHGAP17 overexpression also alleviated cyclic strain-induced activation of Rac1/Cdc42, a major downstream target of ARHGAP17. Furthermore, two Rac1 inhibitors, NSC23766 and EHT 1864, both attenuated ARHGAP17 knockdown-mediated apoptosis in human PDL fibroblasts. Collectively, our data demonstrate that ARHGAP17 inhibits pathological cyclic strain-induced apoptosis in human PDL fibroblasts through inactivating Rac1/Cdc42. This study highlights the importance of Rho signalling in the response of human PDL fibroblasts to mechanical stress.

Differential phosphorylation regulates the shear stress-induced polar activity of Rho-specific guanine nucleotide dissociation inhibitor α

The activity of Rho-specific guanine nucleotide dissociation inhibitor α (RhoGDIα) is regulated by its own phosphorylation at different amino acid sites. These phosphorylation sites may have a crucial role in local Rho GTPases activation during cell migration. This paper is designed to explore the influence of phosphorylation on shear stress-induced spatial RhoGDIα activation. Based on the fluorescence resonance energy transfer biosensor sl-RhoGDIα, which was constructed to test the RhoGDIα activity in living cells, new RhoGDIα phosphomimetic mutation (sl-S101E/S174E, sl-Y156E, sl-S101E, sl-S174E) and phosphorylation-deficient mutation (sl-S101A/S174A, sl-Y156A, sl-S101A, sl-S174A) biosensors were designed to test their effects on RhoGDIα activation upon shear stress application in human umbilical vein endothelial cells (HUVECs). The results showed lower RhoGDIα activity at the downstream of HUVECs (the region from the edge of the nucleus to the edge of the cell along with the flow). The overall decrease in RhoGDIα activity was inhibited by Y156A-mutant, whereas the polarized RhoGDIα and Rac1 activity were blocked by S101A/S174A mutant. It is concluded that the Tyr156 phosphorylation mainly mediates shear stress-induced overall RhoGDIα activity, while Ser101/Ser174 phosphorylation mediates its polarization. This study demonstrates that differential phosphorylation of RhoGDIα regulates shear stress-induced spatial RhoGDIα activation, which could be a potential target to control cell migration.

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.

TAZ contributes to osteogenic differentiation of periodontal ligament cells under tensile stress

BACKGROUND AND OBJECTIVE

Bone remodeling during orthodontic treatment is achieved by the osteogenesis of human periodontal ligament cells (PDLCs) subjected to mechanical loadings. Transcriptional co-activator with PDZ-binding motif (TAZ) mediates bone remodeling in response to extracellular mechanical signals. This study aims to investigate the role of TAZ in osteogenesis of PDLCs under tensile strain.

MATERIALS AND METHODS

A uniaxial cyclic tensile stress (CTS) at 12% elongation and 6 cycles/min (5 s on and 5 s off) was applied to PDLCs. The osteogenic differentiation was determined by the protein and gene expressions of osteogenic markers using qRT-PCR and Western blot, respectively, and further by alkaline phosphatase (ALP) activity and Alizarin Red S staining. The interaction of TAZ with core-binding factor α1 (Cbfα1) was examined by co-immunoprecipitation. The immunofluorescence histochemistry was used to examine the nucleus aggregation of TAZ and the reorganization of actin filaments. Moreover, small interfering RNA-targeting TAZ (TAZsiRNA) was used for TAZ inhibition and Y-27632 was employed for Ras homologue-associated coiled-coil protein kinase (ROCK) signaling blockage.

RESULTS

CTS clearly stimulated the nucleus accumulation of TAZ and its interaction with Cbfα1. CTS-induced osteogenesis in PDLCs was significantly abrogated by the infection with TAZsiRNA, as shown by the decreased stained nodules and protein expressions of Cbfα1, collagen type I, osterix, and osteocalcin, along with the inhibition of β-catenin signaling. Moreover, ROCK inhibition by Y-27632 hindered TAZ nucleus aggregation and its binding with Cbfα1, which subsequently lead to the decreased osteoblastic differentiation of PDLCs.

CONCLUSIONS

Taken together, we propose that TAZ nucleus localization and its interaction with Cbfα1 are essential for the CTS-induced osteogenic differentiation in PDLCs. And such TAZ activation by CTS could be mediated by ROCK signaling, indicating the pivot role of ROCK-TAZ pathway for PDLCs differentiation.

Closer to Nature Through Dynamic Culture Systems

Mechanics in the human body are required for normal cell function at a molecular level. It is now clear that mechanical stimulations play significant roles in cell growth, differentiation, and migration in normal and diseased cells. Recent studies have led to the discovery that normal and cancer cells have different mechanosensing properties. Here, we discuss the application and the physiological and pathological meaning of mechanical stimulations. To reveal the optimal conditions for mimicking an in vivo microenvironment, we must, therefore, discern the mechanotransduction occurring in cells.

Rho GDP dissociation inhibitor α silencing attenuates silicosis by inhibiting RhoA/Rho kinase signalling

Transforming growth factor-β1 (TGF-β1) alters the fibroblast phenotype by promoting transdifferentiation into myofibroblasts, which exhibit the ability to promote collagen synthesis and extracellular matrix (ECM) deposition, thereby playing a significant role in the pathology of silicosis. In this study, we investigated the regulatory mechanisms involved in myofibroblast transdifferentiation. Two-dimensional gel electrophoresis showed that Rho GDP-dissociation inhibitor α (RhoGDIα) was upregulated following myofibroblast transdifferentiation stimulated by TGF-β1. We hypothesised that RhoGDIα may induce myofibroblast transdifferentiation and thus result in silicosis. Accordingly, the biological significance of RhoGDIα in cell proliferation and apoptosis was investigated by deletion of RhoGDIα in MRC-5 cells. In addition, a mechanistic study showed that fasudil, an inhibitor of the RhoA/Rho kinase (ROCK) signalling pathway, reduced the levels of RhoGDIα, RhoA, and phospho-myosin phosphatase （phospho-MYPT） in MRC-5 cells and silicosis model rats. Knockdown of RhoGDIα inhibited myofibroblast transdifferentiation and collagen deposition through RhoGDIα/RhoA/ROCK signalling in silicosis model mice. Overall, downregulation of RhoGDIα may significantly promote cell apoptosis and inhibit cell growth, resulting in reversal of myofibroblast transdifferentiation by RhoA/ROCK in vitro and in vivo. These data will facilitate further exploration of the potential use of RhoGDIα as a target for silicosis therapy.

Periodontal cell mechanotransduction

The periodontium is a structurally and functionally complex tissue that facilitates the anchorage of teeth in jaws. The periodontium consists of various cell types including stem cells, fibroblasts and epithelial cells. Cells of the periodontium are constantly exposed to mechanical stresses generated by biological processes such as the chewing motions of teeth, by flows generated by tongue motions and by forces generated by implants. Mechanical stresses modulate the function of cells in the periodontium, and may play a significant role in the development of periodontal disease. Here, we review the literature on the effect of mechanical forces on periodontal cells in health and disease with an emphasis on molecular and cellular mechanisms.

YAP regulates periodontal ligament cell differentiation into myofibroblast interacted with RhoA/ROCK pathway

During orthodontic tooth movement (OTM), periodontal ligament cells (PDLCs) receive the mechanical stimuli and transform it into myofibroblasts (Mfbs). Indeed, previous studies have demonstrated that mechanical stimuli can promote the expression of Mfb marker α-smooth muscle actin (α-SMA) in PDLCs. Transforming growth factor β1 (TGF-β1), as the target gene of yes-associated protein (YAP), has been proven to be involved in this process. Here, we sought to assess the role of YAP in Mfbs differentiation from PDLCs. The time-course expression of YAP and α-SMA was manifested in OTM model in vivo as well as under tensional stimuli in vitro. Inhibition of RhoA/Rho-associated kinase (ROCK) pathway using Y27632 significantly reduced tension-induced Mfb differentiation and YAP expression. Moreover, overexpression of YAP with lentiviral transfection in PDLCs rescued the repression effect of Mfb differentiation induced by Y27632. These data together suggest a crucial role of YAP in regulating tension-induced Mfb differentiation from PDLC interacted with RhoA/ROCK pathway.

Atorvastatin inhibits osteoclastogenesis and arrests tooth movement

INTRODUCTION

In addition to their cholesterol-lowering effects, the statin class of drugs appears to enhance osteogenesis and suppress bone resorption, which could be a clinical concern during orthodontic treatment. In this animal study, we aimed to determine whether atorvastatin (ATV) affects orthodontic tooth movement (OTM) through osteoclast inhibition. Furthermore, we analyzed the potential adverse effects of ATV on long-bone turnover and endochondral ossification.

METHODS

Rats were administered ATV (15 mg/kg) or saline solution via gavage (n = 12 animals/group), starting 2 weeks before initial OTM. Tooth displacement was measured after 7, 14, and 21 days. Histologic sections of the maxilla and femur were obtained after 14 and 21 days of OTM and stained (hematoxylin and eosin; TRAP assay) for histomorphometric analysis.

RESULTS

ATV was associated with significant (P <0.05) reductions in OTM and osteoclast counts. Independently of drug administration, OTM increased the number of osteoclasts and reduced the bone-volume ratio compared with the control maxillae without OTM. Long-term statin administration did not appear to affect femoral endochondral ossification.

CONCLUSIONS

This experimental study showed that the long-term use of ATV can significantly promote osteoclast inhibition and slow the OTM in the first week in rats. Under physiologic conditions, the drug did not affect bone turnover and endochondral ossification.

Modulation of microenvironment for controlling the fate of periodontal ligament cells: the role of Rho/ROCK signaling and cytoskeletal dynamics

Cells behave in a variety of ways when they perceive changes in their microenvironment; the behavior of cells is guided by their coordinated interactions with growth factors, niche cells, and extracellular matrix (ECM). Modulation of the microenvironment affects the cell morphology and multiple gene expressions. Rho/Rho-associated coiled-coil-containing protein kinase (ROCK) signaling is one of the key regulators of cytoskeletal dynamics and actively and/or passively determines the cell fate, such as proliferation, migration, differentiation, and apoptosis, by reciprocal communication with the microenvironment. During periodontal wound healing, it is important to recruit the residential stem cells into the defect site for regeneration and homeostasis of the periodontal tissue. Periodontal ligament (PDL) cells contain a heterogeneous fibroblast population, including mesenchymal stem cells, and contribute to the reconstruction of tooth-supporting tissues. Therefore, bio-regeneration of PDL cells has been the ultimate goal of periodontal therapy for decades. Recent stem cell researches have shed light on intrinsic ECM properties, providing paradigm shifts in cell fate determination. This review focuses on the role of ROCK activity and the effects of Y-27632, a specific inhibitor of ROCK, in the modulation of ECM-microenvironment. Further, it presents the current understanding of how Rho/ROCK signaling affects the fate determination of stem cells, especially PDL cells. In addition, we have also discussed in detail the underlying mechanisms behind the reciprocal response to the microenvironment.

Degree of endplate chondrocyte degeneration in different tension regions during mechanical stimulation

The aim of this study was to explore the degree of degeneration of endplate chondrocytes in different tension regions induced by intermittent cyclic mechanical tension (ICMT) in vitro. Rat endplate chondrocytes were harvested and treated with 10% ICMT for 8 h/day with a frequency of 0.5 Hz. A cartilage degeneration model was induced using an FX‑5000T cell strain‑loading system. The experiment was divided into the central region and the peripheral region, according to the contact area between the loading post and the six‑well flexible silicone rubber BioFlex plates. Toluidine blue and phalloidin staining were used to observe the morphological changes of cells following mechanical stimulation. Apoptosis was detected by flow cytometry and the mRNA and protein expression levels of collagen type II α1, aggrecan, SRY‑box 9 and matrix metalloproteinase 13 were detected by reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) and western blotting, respectively. Endplate chondrocytes exhibited degenerative alterations under mechanical conditions of 10% ICMT and 0.5 Hz at 8 h/day. Toluidine blue and phalloidin staining demonstrated that the cells in the peripheral region were more slender compared with cells in the central region, but RT‑qPCR and western blotting results demonstrated that the degree of cell degeneration between the two groups was not statistically differences. So that cell morphological alteration does not imply that cells have undergone degeneration.

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.

Role of Rho-specific guanine nucleotide dissociation inhibitor α regulation in cell migration

Cell migration is a vital process for many physiological and pathological events, and Rho GTPases have been confirmed as key factors in its regulation. The most studied negative regulator of Rho GTPases, Rho-specific guanine nucleotide dissociation inhibitor α (RhoGDIα), mediates cell migration through altering the overall expression and spatiotemporal activation of Rho GTPases. The RhoGDIα-Rho GTPases dissociation can be mediated by signal pathways targeting RhoGDIα directly. This review summarizes the research about the regulation of RhoGDIα during cell migration, which can be in a Rho GTPases association independent manner. Non-kinase proteins regulation, phosphorylation, SUMOylation and extracellular environmental factors are classified to discuss their direct signal regulations on RhoGDIα, which provide varied signal pathways for selective activation of Rho GTPases in cell migration.

Cyclic stretch promotes osteogenesis-related gene expression in osteoblast-like cells through a cofilin-associated mechanism

Osteoblasts have the capacity to perceive and transduce mechanical signals, and thus, regulate the mRNA and protein expression of a variety of genes associated with osteogenesis. Cytoskeletal reconstruction, as one of the earliest perception events for external mechanical stimulation, has previously been demonstrated to be essential for mechanotransduction in bone cells. However, the mechanism by which mechanical signals induce cytoskeletal deformation remains poorly understood. The actin‑binding protein, cofilin, promotes the depolymerization of actin and is understood to be important in the regulation of activities in various cell types, including endothelial, neuronal and muscle cells. However, to the best of our knowledge, the importance of cofilin in osteoblastic mechanotransduction has not been previously investigated. In the present study, osteoblast‑like MG‑63 cells were subjected to physiological cyclic stretch stimulation (12% elongation) for 1, 4, 8, 12 and 24 h, and the expression levels of cofilin and osteogenesis-associated genes were quantified with reverse transcription‑quantitative polymerase chain reaction, immunofluorescence staining and western blotting analyses. Additionally, knockdown of cofilin using RNA interference was conducted, and the mRNA levels of osteogenesis‑associated genes were compared between osteoblast‑like cells in the presence and absence of cofilin gene knockdown. The results of the present study demonstrated that cyclic stretch stimulates the expression of genes associated with osteoblastic activities in MG‑63 cells, including alkaline phosphatase (ALP), osteocalcin (OCN), runt‑related transcription factor 2 (Runx2) and collagen‑1 (COL‑1). Cyclic stretch also regulates the mRNA and protein expression of cofilin in MG‑63 cells. Furthermore, stretch‑induced increases in the levels of osteogenesis-associated genes, including ALP, OCN, Runx2 and COL‑1, were reduced following cofilin gene knockdown. Together, these results demonstrate that cofilin is involved in the regulation of mechanical load‑induced osteogenesis and, to the best of our knowledge, provides the first evidence demonstrating the importance of cofilin in osteoblastic mechanotransduction.

Mechanoresponsive musculoskeletal tissue differentiation of adipose-derived stem cells

Musculoskeletal tissues are constantly under mechanical strains within their microenvironment. Yet, little is understood about the effect of in vivo mechanical milieu strains on cell development and function. Thus, this review article outlines the in vivo mechanical environment of bone, muscle, cartilage, tendon, and ligaments, and tabulates the mechanical strain and stress in these tissues during physiological condition, vigorous, and moderate activities. This review article further discusses the principles of mechanical loading platforms to create physiologically relevant mechanical milieu in vitro for musculoskeletal tissue regeneration. A special emphasis is placed on adipose-derived stem cells (ADSCs) as an emerging valuable tool for regenerative musculoskeletal tissue engineering, as they are easily isolated, expanded, and able to differentiate into any musculoskeletal tissue. Finally, it highlights the current state-of-the art in ADSCs-guided musculoskeletal tissue regeneration under mechanical loading.

Cell Mechanosensitivity to Extremely Low-Magnitude Signals Is Enabled by a LINCed Nucleus

A cell's ability to recognize and adapt to the physical environment is central to its survival and function, but how mechanical cues are perceived and transduced into intracellular signals remains unclear. In mesenchymal stem cells (MSCs), high-magnitude substrate strain (HMS, ≥2%) effectively suppresses adipogenesis via induction of focal adhesion (FA) kinase (FAK)/mTORC2/Akt signaling generated at FAs. Physiologic systems also rely on a persistent barrage of low-level signals to regulate behavior. Exposing MSC to extremely low-magnitude mechanical signals (LMS) suppresses adipocyte formation despite the virtual absence of substrate strain (<0.001%), suggesting that LMS-induced dynamic accelerations can generate force within the cell. Here, we show that MSC response to LMS is enabled through mechanical coupling between the cytoskeleton and the nucleus, in turn activating FAK and Akt signaling followed by FAK-dependent induction of RhoA. While LMS and HMS synergistically regulated FAK activity at the FAs, LMS-induced actin remodeling was concentrated at the perinuclear domain. Preventing nuclear-actin cytoskeleton mechanocoupling by disrupting linker of nucleoskeleton and cytoskeleton (LINC) complexes inhibited these LMS-induced signals as well as prevented LMS repression of adipogenic differentiation, highlighting that LINC connections are critical for sensing LMS. In contrast, FAK activation by HMS was unaffected by LINC decoupling, consistent with signal initiation at the FA mechanosome. These results indicate that the MSC responds to its dynamic physical environment not only with "outside-in" signaling initiated by substrate strain, but vibratory signals enacted through the LINC complex enable matrix independent "inside-inside" signaling.

The Rho-mDia1 signaling pathway is required for cyclic strain-induced cytoskeletal rearrangement of human periodontal ligament cells

Tooth movement is the result of periodontal tissue reconstruction. The biomechanical effects produced by orthopedic forces can affect the cytoskeletal rearrangement of human periodontal ligament cells (hPDLCs). However, the mechanisms responsible for the cytoskeletal rearrangement are not completely understood. To analyze the effect, we investigated the role of the Rho-mDia1 signaling pathway in cyclic strain-induced cytoskeletal rearrangement of hPDLCs in detail. We cultured hPDLCs on collagen I-coated six-well Bioflex plates and then exposed them to cyclic strain with physiological loading (10%) at a frequency of 0.1Hz for 6 or 24h using a Flexercell Tension Plus system. Notably, the cells cultured on the Bioflex plates showed increased expression levels of RhoA-GTP, profilin-1 protein, and the combination of RhoA and mDia1, whereas the expression levels of Rho-GDIa were reduced compared with a static control group. Furthermore, the cytoskeletal rearrangement of cells was enhanced. However, profilin-1 protein expression and cytoskeletal reorganization under cyclic strain can decrease due to the overexpression of Rho-GDIa or mDia1-siRNA transfection, whereas Rho-GDIa siRNA transfection has the opposite effect on hPDLCs. Together, our results demonstrate that the Rho-mDia1 signaling pathway is involved in the cytoskeletal rearrangement of hPDLCs induced by cyclic strain. These observations may enable a more in-depth understanding of orthodontic tooth movement and the reconstruction of PDL and alveolar bone.

Rho is involved in periodontal tissue remodelling with experimental tooth movement in rats

OBJECTIVE

To characterise in vivo the close relationship between the Rho signalling pathway and periodontal tissue remodelling in experimental tooth movement in rats.

MATERIALS AND METHODS

In total, 24 male Sprague Dawley rats were divided randomly into four groups. Closed-coil springs were used to create a 40-g mesial force to move the right upper first molars in anaesthetised rats. The untreated contralateral side served as a control. On days 3, 7, 10, and 14 after force application, paraffin wax-embedded sections of the dissected maxilla were prepared for immunohistochemistry to localise Rho kinase (ROCK), LIM kinase (LIMK), and its downstream effector (cofilin). The immunoreactivity of the molecules investigated in the periodontal ligament area was converted into grey-scale values.

RESULTS

The expression of Rho and its signalling were detected mainly in the disto-coronal areas of the root in the periodontal ligament area of the control and loaded teeth. In contrast, ROCK-, LIMK-, and cofilin-positive cells were rare in the mesio-coronal areas. In the experimental group, the expression of ROCK, LIMK, and cofilin on the tension side (disto-coronal areas) increased significantly on days 7, 10, and 14, compared with those of untreated control teeth.

CONCLUSIONS

These data suggest that Rho is involved in periodontal tissue remodelling during orthodontic tooth movement, modulating ROCK, LIMK, and cofilin activity.

MicroRNA-21 regulates hTERT via PTEN in hypertrophic scar fibroblasts

BACKGROUND

As an important oncogenic miRNA, microRNA-21 (miR-21) is associated with various malignant diseases. However, the precise biological function of miR-21 and its molecular mechanism in hypertrophic scar fibroblast cells has not been fully elucidated.

METHODOLOGY/PRINCIPAL FINDINGS

Quantitative Real-Time PCR (qRT-PCR) analysis revealed significant upregulation of miR-21 in hypertrophic scar fibroblast cells compared with that in normal skin fibroblast cells. The effects of miR-21 were then assessed in MTT and apoptosis assays through in vitro transfection with a miR-21 mimic or inhibitor. Next, PTEN (phosphatase and tensin homologue deleted on chromosome ten) was identified as a target gene of miR-21 in hypertrophic scar fibroblast cells. Furthermore, Western-blot and qRT-PCR analyses revealed that miR-21 increased the expression of human telomerase reverse transcriptase (hTERT) via the PTEN/PI3K/AKT pathway. Introduction of PTEN cDNA led to a remarkable depletion of hTERT and PI3K/AKT at the protein level as well as inhibition of miR-21-induced proliferation. In addition, Western-blot and qRT-PCR analyses confirmed that hTERT was the downstream target of PTEN. Finally, miR-21 and PTEN RNA expression levels in hypertrophic scar tissue samples were examined. Immunohistochemistry assays revealed an inverse correlation between PTEN and hTERT levels in high miR-21 RNA expressing-hypertrophic scar tissues.

CONCLUSIONS/SIGNIFICANCE

These data indicate that miR-21 regulates hTERT expression via the PTEN/PI3K/AKT signaling pathway by directly targeting PTEN, therefore controlling hypertrophic scar fibroblast cell growth. MiR-21 may be a potential novel molecular target for the treatment of hypertrophic scarring.