Mechanism of Cyclic Tensile Stress in Osteogenic Differentiation of Human Periodontal Ligament Stem Cells

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.

Distinct and overlapping functions of YAP and TAZ in tooth development and periodontal homeostasis

Orthodontic tooth movement (OTM) involves mechanical-biochemical signal transduction, which results in tissue remodeling of the tooth-periodontium complex and the movement of orthodontic teeth. The dynamic regulation of osteogenesis and osteoclastogenesis serves as the biological basis for remodeling of the periodontium, and more importantly, the prerequisite for establishing periodontal homeostasis. Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are key effectors of the Hippo signaling pathway, which actively respond to mechanical stimuli during tooth movement. Specifically, they participate in translating mechanical into biochemical signals, thereby regulating periodontal homeostasis, periodontal remodeling, and tooth development. YAP and TAZ have widely been considered as key factors to prevent dental dysplasia, accelerate orthodontic tooth movement, and shorten treatment time. In this review, we summarize the functions of YAP and TAZ in regulating tooth development and periodontal remodeling, with the aim to gain a better understanding of their mechanisms of action and provide insights into maintaining proper tooth development and establishing a healthy periodontal and alveolar bone environment. Our findings offer novel perspectives and directions for targeted clinical treatments. Moreover, considering the similarities and differences in the development, structure, and physiology between YAP and TAZ, these molecules may exhibit functional variations in specific regulatory processes. Hence, we pay special attention to their distinct roles in specific regulatory functions to gain a comprehensive and profound understanding of their contributions.

Cyclic Stretching Triggers Cell Orientation and Extracellular Matrix Remodeling in a Periodontal Ligament 3D In Vitro Model

During orthodontic tooth movement (OTM), the periodontal ligament (PDL) plays a crucial role in regulating the tissue remodeling process. To decipher the cellular and molecular mechanisms underlying this process in vitro, suitable 3D models are needed that more closely approximate the situation in vivo. Here, a customized bioreactor is developed that allows dynamic loading of PDL-derived fibroblasts (PDLF). A collagen-based hydrogel mixture is optimized to maintain structural integrity and constant cell growth during stretching. Numerical simulations show a uniform stress distribution in the hydrogel construct under stretching. Compared to static conditions, controlled cyclic stretching results in directional alignment of collagen fibers and enhances proliferation and spreading ability of the embedded PDLF cells. Effective force transmission to the embedded cells is demonstrated by a more than threefold increase in Periostin protein expression. The cyclic stretch conditions also promote extensive remodeling of the extracellular matrix, as confirmed by increased glycosaminoglycan production. These results highlight the importance of dynamic loading over an extended period of time to determine the behavior of PDLF and to identify in vitro mechanobiological cues triggered during OTM-like stimulus. The introduced dynamic bioreactor is therefore a useful in vitro tool to study these mechanisms.

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.

Differential expression profiles and functional prediction of circRNA in mice with traumatic heterotopic ossification

Background

Traumatic heterotopic ossification (HO) is an intractable sequela incited by inflammatory insult. To date, the exact molecular mechanisms of traumatic HO formation remain unclear. Recent studies have indicated that circular RNAs (circRNAs) participate in various human skeletal diseases. Although the formation of HO recapitulates many programs during bone development and remodeling, few data are available concerning whether circRNAs could participate in this pathological osteogenesis.

Methods

To investigate the differentially expressed circRNAs (DE-circRNAs) in HO formation, microarray assay was performed to analyze the circRNA expression profile in four pairs of mice HO tissues and normal tissues. Then, qRT-PCR was applied to verify the microarray data. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed the biological functions of the differentially expressed circRNAs target genes. Cytoscape software was used to construct the circRNA-miRNA-mRNA network for circRNAs with different expression levels as well as the target genes.

Results

We demonstrated that 491 circRNAs were significantly differentially expressed in mouse HO tissues by a fold-change ≥ 2 and p-value ≤ 0.05. Among them, the expressions of 168 circRNAs were increased, while 323 were decreased. The expression levels of 10 selected circRNAs were verified successfully by qRT-PCR. GO analysis exhibited that these DE-circRNAs participated in a series of cellular processes. KEGG pathway analysis revealed that multiple upregulated and downregulated pathways were closely related to the DE-circRNAs in HO mice. The circRNA-miRNA-mRNA networks demonstrated that DE-circRNAs may be involved in the pathological osteogenesis of HO through the circRNA-targeted miRNA-mRNA axis.

Conclusion

Our study first demonstrated the expression profiles and predicted the potential functions of DE-circRNAs in mice traumatic HO, which may shed new light on the elucidation of mechanisms as well as provide novel potential peripheral biological diagnostic markers and therapeutic targets for traumatic HO.

Non-coding RNAs regulate the BMP/Smad pathway during osteogenic differentiation of stem cells

MicroRNAs (miRNAs), long non-coding RNAs (lncRNAs), and circular RNAs (circRNAs) are involved in the regulation of bone metabolism. The BMP/Smad pathway is a key signaling pathway for classical regulation of osteogenic differentiation. Non-coding RNAs (ncRNAs) and the BMP/Smad pathway both have important roles for osteogenic differentiation of stem cells, bone regeneration, and development of bone diseases. There is increasing evidence that ncRNAs interact with the BMP/Smad pathway to regulate not only osteogenic differentiation of stem cells but also progression of bone diseases, such as osteoporosis (OP), myeloma, and osteonecrosis of the femoral head (ONFH), by controlling the expression of bone disease-related genes. Therefore, ncRNAs that interact with BMP/Smad pathway molecules are potential targets for bone regeneration as well as bone disease diagnosis, prevention, and treatment. However, despite extensive studies on ncRNAs associated with the BMP/Smad pathway and osteogenic differentiation of stem cells, there is a lack of comparability. Moreover, some bone disease-associated ncRNAs with low abundance can be difficult to detect and there is a lack of mature delivery systems for their stable translocation to target sites, thus limiting their application. In this review, we summarize the research progress on interactions between ncRNAs and the BMP/Smad pathway during osteogenic differentiation of various stem cells and in the regulation of bone regeneration and bone diseases.

Analysis of ceRNA networks during mechanical tension-induced osteogenic differentiation of periodontal ligament stem cells

The molecular mechanisms underlying osteogenic differentiation of periodontal ligament stem cells (PDLSCs) under mechanical tension remain unclear. This study aimed to identify a potential long non-coding ribonucleic acids (lncRNAs)/circular RNAs (circRNAs)-microRNAs (miRNAs)-messenger RNAs (mRNAs) network in mechanical tension-induced osteogenic differentiation of PDLSCs. PDLSCs were isolated from the healthy human periodontal ligament, identified, cultured, and exposed to tensile force. The expression of osteogenic markers was examined, and whole transcriptome sequencing was performed to identify the expression patterns of lncRNA, circRNA, miRNAs, and mRNAs. Enrichment analyses were also performed. Candidate targets of differentially expressed non-coding RNAs (ncRNAs) were predicted, and potential competitive endogenous RNA (ceRNA) networks were constructed by Cytoscape. We found that the osteogenic differentiation of PDLSCs was significantly enhanced under dynamic tension (magnitude: 12%, frequency: 0.7 Hz). Overall, 344 lncRNAs, 57 miRNAs, 41 circRNAs, and 70 mRNAs were differentially expressed in the tension group and the control group. Functional enrichment analysis showed that differentially expressed mRNAs were mainly enriched in osteogenesis-related and mechanical stress-related biological processes and signal transduction pathways (e.g., tumor necrosis factor [TNF] and Hippo signaling pathways). The lncRNA/circRNA-miRNA-mRNA networks were depicted, and potential key ceRNA networks were identified. Our findings may help to further explore the underlying regulatory mechanism of osteogenic differentiation of PDLSCs under mechanical tensile stress.

How the mechanical microenvironment of stem cell growth affects their differentiation: a review

Stem cell differentiation is of great interest in medical research; however, specifically and effectively regulating stem cell differentiation is still a challenge. In addition to chemical factors, physical signals are an important component of the stem cell ecotone. The mechanical microenvironment of stem cells has a huge role in stem cell differentiation. Herein, we describe the knowledge accumulated to date on the mechanical environment in which stem cells exist, which consists of various factors, including the extracellular matrix and topology, substrate stiffness, shear stress, hydrostatic pressure, tension, and microgravity. We then detail the currently known signalling pathways that stem cells use to perceive the mechanical environment, including those involving nuclear factor-kB, the nicotinic acetylcholine receptor, the piezoelectric mechanosensitive ion channel, and hypoxia-inducible factor 1α. Using this information in clinical settings to treat diseases is the goal of this research, and we describe the progress that has been made. In this review, we examined the effects of mechanical factors in the stem cell growth microenvironment on stem cell differentiation, how mechanical signals are transmitted to and function within the cell, and the influence of mechanical factors on the use of stem cells in clinical applications.

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.

Biophysical Stimuli as the Fourth Pillar of Bone Tissue Engineering

The repair of critical bone defects remains challenging worldwide. Three canonical pillars (biomaterial scaffolds, bioactive molecules, and stem cells) of bone tissue engineering have been widely used for bone regeneration in separate or combined strategies, but the delivery of bioactive molecules has several obvious drawbacks. Biophysical stimuli have great potential to become the fourth pillar of bone tissue engineering, which can be categorized into three groups depending on their physical properties: internal structural stimuli, external mechanical stimuli, and electromagnetic stimuli. In this review, distinctive biophysical stimuli coupled with their osteoinductive windows or parameters are initially presented to induce the osteogenesis of mesenchymal stem cells (MSCs). Then, osteoinductive mechanisms of biophysical transduction (a combination of mechanotransduction and electrocoupling) are reviewed to direct the osteogenic differentiation of MSCs. These mechanisms include biophysical sensing, transmission, and regulation. Furthermore, distinctive application strategies of biophysical stimuli are presented for bone tissue engineering, including predesigned biomaterials, tissue-engineered bone grafts, and postoperative biophysical stimuli loading strategies. Finally, ongoing challenges and future perspectives are discussed.

NEAT1 functions as a key mediator of BMP2 to promote osteogenic differentiation of renal interstitial fibroblasts

Aim: To clarify the mechanism of NEAT1, an aberrantly upregulated lncRNA in Randall's plaques (RP) similar to biomineralization, in mediating osteogenic differentiation of human renal interstitial fibroblasts. Materials & methods: A comprehensive strategy of bioinformatic analysis and experimental verification was performed. Results: BMP2 silence abolished the osteogenic differentiation of human renal interstitial fibroblasts promoted by NEAT1. Mechanically, NEAT1 not only induced the nucleolar translocation of EGR1 binding to BMP2 promotor, but also functioned as a sponge of miR-129-5p in the cytoplasm to promote BMP2 expression. Moreover, there was a positive correlation between NEAT1 and BMP2 expression in RP instead of normal renal papilla. Conclusion: NEAT1 acted as a key mediator of BMP2 to promote human renal interstitial fibroblast osteogenic differentiation, through which NEAT1 might be involved in RP formation.