Effect of cyclic mechanical stimulation on the expression of osteogenesis genes in human intraoral mesenchymal stromal and progenitor cells

Regulation and mechanistic insights into tensile strain in mesenchymal stem cell osteogenic differentiation

Bone marrow mesenchymal stem cells (BMSCs) are integral to bone remodeling and homeostasis, as they are capable of differentiating into osteogenic and adipogenic lineages. This differentiation is substantially influenced by mechanosensitivity, particularly to tensile strain, which is a prevalent mechanical stimulus known to enhance osteogenic differentiation. This review specifically examines the effects of various cyclic tensile stress (CTS) conditions on BMSC osteogenesis. It delves into the effects of different loading devices, magnitudes, frequencies, elongation levels, dimensionalities, and coculture conditions, providing a comparative analysis that aids identification of the most conducive parameters for the osteogenic differentiation of BMSCs. Subsequently, this review delineates the signaling pathways activated by CTS, such as Wnt/β-catenin, BMP, Notch, MAPK, PI3K/Akt, and Hedgehog, which are instrumental in mediating the osteogenic differentiation of BMSCs. Through a detailed examination of these pathways, this study elucidates the intricate mechanisms whereby tensile strain promotes osteogenic differentiation, offering valuable guidance for optimizing therapeutic strategies aimed at enhancing bone regeneration.

Three-Dimensional Mechanical Microenvironment Rescued the Decline of Osteogenic Differentiation of Old Human Jaw Bone Marrow Mesenchymal Stem Cells

Resorption and atrophy of the alveolar bone, as two consequences of osteoporosis that remarkably complicate the orthodontic and prosthodontic treatments, contribute to the differentiated biological features and force-induced response of jaw bone marrow-derived mesenchymal stem cells (JBMSCs) in elderly patients. We isolated and cultured JBMSCs from adolescent and adult patients and then simulated the loading of orthodontic tension stress by constructing an in vitro three-dimensional (3D) stress loading model. The decline in osteogenic differentiation of aged JBMSCs was reversed by tensile stress stimulation. It is interesting to note that tension stimulation had a stronger effect on the osteogenic differentiation of elderly JBMSCs compared to the young ones, indicating a possible mechanism of aging rescue. High-throughput sequencing of microRNA (miRNAs) was subsequently performed before and after tension stimulation in all JBMSCs, followed by the comprehensive comparison of mechanically responsive miRNAs in the 3D strain microenvironment. The results suggested a significant reduction in the expression of miR-210-3p and miR-214-3p triggered by the 3D strain microenvironment in old-JBMSCs. Bioinformatic analysis indicated that both miRNAs participate in the regulation of critical pathways of aging and cellular senescence. Taken together, this study demonstrated that the 3D strain microenvironment efficiently rescued the cellular senescence of old-JBMSCs via modulating specific miRNAs, which provides a novel strategy for coordinating periodontal bone loss and regeneration of the elderly.

Mechanobiology-informed biomaterial and tissue engineering strategies for influencing skeletal stem and progenitor cell fate

Skeletal stem and progenitor cells (SSPCs) are the multi-potent, self-renewing cell lineages that form the hematopoietic environment and adventitial structures of the skeletal tissues. Skeletal tissues are responsible for a diverse range of physiological functions because of the extensive differentiation potential of SSPCs. The differentiation fates of SSPCs are shaped by the physical properties of their surrounding microenvironment and the mechanical loading forces exerted on them within the skeletal system. In this context, the present review first highlights important biomolecules involved with the mechanobiology of how SSPCs sense and transduce these physical signals. The review then shifts focus towards how the static and dynamic physical properties of microenvironments direct the biological fates of SSPCs, specifically within biomaterial and tissue engineering systems. Biomaterial constructs possess designable, quantifiable physical properties that enable the growth of cells in controlled physical environments both in-vitro and in-vivo. The utilization of biomaterials in tissue engineering systems provides a valuable platform for controllably directing the fates of SSPCs with physical signals as a tool for mechanobiology investigations and as a template for guiding skeletal tissue regeneration. It is paramount to study this mechanobiology and account for these mechanics-mediated behaviors to develop next-generation tissue engineering therapies that synergistically combine physical and chemical signals to direct cell fate. Ultimately, taking advantage of the evolved mechanobiology of SSPCs with customizable biomaterial constructs presents a powerful method to predictably guide bone and skeletal organ regeneration.

Potential of Oral Cavity Stem Cells for Bone Regeneration: A Scoping Review

Bone loss is a common problem that ranges from small defects to large defects after trauma, surgery, or congenital malformations. The oral cavity is a rich source of mesenchymal stromal cells (MSCs). Researchers have documented their isolation and studied their osteogenic potential. Therefore, the objective of this review was to analyze and compare the potential of MSCs from the oral cavity for use in bone regeneration.

METHODS

A scoping review was carried out following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) guidelines. The databases reviewed were PubMed, SCOPUS, Scientific Electronic Library Online (SciELO), and Web of Science. Studies using stem cells from the oral cavity to promote bone regeneration were included.

RESULTS

A total of 726 studies were found, of which 27 were selected. The MSCs used to repair bone defects were (I) dental pulp stem cells of permanent teeth, (II) stem cells derived from inflamed dental pulp, (III) stem cells from exfoliated deciduous teeth, (IV) periodontal ligament stem cells, (V) cultured autogenous periosteal cells, (VI) buccal fat pad-derived cells, and (VII) autologous bone-derived mesenchymal stem cells. Stem cells associate with scaffolds to facilitate insertion into the bone defect and to enhance bone regeneration. The biological risk and morbidity of the MSC-grafted site were minimal. Successful bone formation after MSC grafting has been shown for small defects with stem cells from the periodontal ligament and dental pulp as well as larger defects with stem cells from the periosteum, bone, and buccal fat pad.

CONCLUSIONS

Stem cells of maxillofacial origin are a promising alternative to treat small and large craniofacial bone defects; however, an additional scaffold complement is required for stem cell delivery.

Effect of Static and Dynamic Stretching on Corneal Fibroblast Cell

A strain gradient was created by punching a hole in the center of a stretched elastic polydimethylsiloxane membrane to determine the effect of different strains on cultured human keratocytes (HK). In this study, two stretching methods were used: continuous stretching and cyclic stretching. Continuous stretching is relatively static, while acyclic stretching is relatively dynamic. These methods, respectively, represented the effects of high intraocular pressure and rubbing of the eyes on corneal cells. Image processing codes were developed to observe the effects of stress concentration, shear stress, continuous stretching, and cyclic stretching on HKs. The results demonstrate that stretching and shear stress are not conducive to the proliferation of corneal cells and instead cause cell death. A 10% strain had greater inhibitory effects than a 3% strain on cell proliferation. Cell survival rates for continuous stretching (static) were higher than those for cyclic stretching (dynamic). The stretching experiment revealed that cyclic stretching has a greater inhibitory effect on the growth and proliferation of corneal cells than continuous stretching. Accordingly, it shows that cyclic loading is more harmful than high intraocular pressure (static loading) to corneal cells.

Lamin A/C-Dependent Translocation of Megakaryoblastic Leukemia-1 and β-Catenin in Cyclic Strain-Induced Osteogenesis

Lamins are intermediate filaments that play a crucial role in sensing mechanical strain in the nucleus of cells. β-catenin and megakaryoblastic leukemia-1 (MKL1) are critical signaling molecules that need to be translocated to the nucleus for their transcription in response to mechanical strain that induces osteogenesis. However, the exact molecular mechanism behind the translocation of these molecules has not been fully investigated. This study used 10% cyclic strain to induce osteogenesis in the murine osteoblast precursor cell line (MC3T3). The translocation of β-catenin and MKL1 was studied by performing knockdown and overexpression of lamin A/C (LMNA). Cyclic strain increased the expression of osteogenic markers such as alkaline phosphatase (ALP), runt-related transcription factor 2 (RUNX2), and enhanced ALP staining after seven days of incubation. Resultantly, MKL1 and β-catenin were translocated in the nucleus from the cytoplasm during the stress-induced osteogenic process. Knockdown of LMNA decreased the accumulation of MKL1 and β-catenin in the nucleus, whereas overexpression of LMNA increased the translocation of these molecules. In conclusion, our study indicates that both MKL1 and β-catenin molecules are dependent on the expression of LMNA during strain-induced osteogenesis.

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.

Remote-Controlled 3D Porous Magnetic Interface toward High-Throughput Dynamic 3D Cell Culture

Mechanical stimuli have been shown to play a large role in cellular behavior, including cellular growth, differentiation, morphology, homeostasis, and disease. Therefore, developing bioreactor systems that can create complex mechanical environments for both tissue engineering and disease modeling drug screening is appealing. However, many of existing systems are restricted because of their bulky size with external force generators, destructive microenvironment control, and low throughput. These shortcomings have preceded to the utilization of magnetic stimuli responsive materials, given their untethered, fast, and tunable actuation potential at both the microscale and macroscale level, for seamless integration into cell culture wells and microfluidic systems. Nevertheless, magnetic soft materials for cell culture have been limited due to the inability to develop well-defined 3D structures for more complex and physiological relevant mechanical actuation. Herein, we introduce a facile fabrication process to develop magnetic-PDMS (polydimethylsiloxane) porous composite designs with both well-defined and controllable microlevel and macrolevel features to dynamically manipulate 3D cell-laden gel at the scale. The intrinsic stiffness of the magnetic-PDMS porous composites is also modulated to control the deformation potential to mimic physiological relevant strain levels, with 2.89-11% observed in magnetic actuation studies. High cell viability was achieved with the culturing of both human adipose stem cells (hADMSCs) and human umbilical cord mesenchymal stem cells (hUCMSCs) in 3D cell-laden gel interfaced with the magnetic-PDMS porous composite. Also, the highly interconnected porous network of the magnetic-PDMS composites facilitated free diffusion throughout the porous structure showcasing the potential of a multisurface contact 3D porous magnetic structure in both reservoir and 96-well plate insert designs for more complex dynamic mechanical actuation. In conclusion, these studies provide a means for establishing a biocompatible, tunable magnetic-PDMS porous composite with fast and programmable dynamic strain potential making it a suitable platform for high-throughput, dynamic 3D cell culture.

Functional assistance for stress distribution in cell culture membrane under periodically stretching

Dynamic cell cultures simulate the in vivo cell environment for a regular loading system with curtain strains. However, it is difficult to obtain strains that are suitable for cells without conducting multiple trials. This study develops a device that increases the strain gradient by changing the tensile section, in order to determine the effect of various cyclic strains on cultured human keratinocytes (HK) cells. This device is used to determine the effect of 3% and 5% cyclic strain and shear strain on cell proliferation and arrangement at 1 Hz. The results show that compared with static and 3% strain, a 5% cyclic strain better inhibits the proliferation of HK cells. Compared to the initial cell attachment when there is no specific directionality, the cells are aligned in the vertical stretching direction after cyclic stretching. This equipment increases the efficiency of the experiment and more intuitively maps the cell behavior and shape to the strain field and the response to the shear strain.

Bone fracture healing: perspectives according to molecular basis

Fractures have a great impact on health all around the world and with fracture healing optimization; this problem could be resolved partially. To make a practical contribution to this issue, the knowledge of bone tissue, cellularity, and metabolism is essential, especially cytoskeletal architecture and its transformations according to external pressures. Special physical and chemical characteristics of the extracellular matrix (ECM) allow the transmission of mechanical stimuli from outside the cell to the plasmatic membrane. The osteocyte cytoskeleton is conformed by a complex network of actin and microtubules combined with crosslinker proteins like vinculin and fimbrin, connecting and transmitting outside stimuli through EMC to cytoplasm. Herein, critical signaling pathways like Cx43-depending ones, MAPK/ERK, Wnt, YAP/TAZ, Rho-ROCK, and others are activated due to mechanical stimuli, resulting in osteocyte cytoskeletal changes and ECM remodeling, altering the tissue and, therefore, the bone. In recent years, the osteocyte has gained more interest and value in relation to bone homeostasis as a great coordinator of other cell populations, thanks to its unique functions. By integrating the latest advances in relation to intracellular signaling pathways, mechanotransmission system of the osteocyte and bone tissue engineering, there are promising experimental strategies, while some are ready for clinical trials. This work aims to show clearly and precisely the integration between cytoskeleton and main molecular pathways in relation to mechanotransmission mechanism in osteocytes, and the use of this theoretical knowledge in therapeutic tools for bone fracture healing.

Mechanical stretch induces osteogenesis through the alternative activation of macrophages

For reconstructive surgeons, critically skeletal damage represents a major challenge. Growing evidence indicate that bone repair is dynamically regulated by the mesenchymal stem cell (MSC)-macrophage interaction. Mechanical strain plays a fundamental role in bone repair and regeneration by influencing MSCs differentiation. Recently, a few findings indicate that macrophages may be mechanically sensitive and their phenotype can be regulated, in part, by mechanical cues. However, how macrophages subjected mechanical stretch influence the osteogenic differentiation of MSCs remain unclear. Thus, the purpose of this study is to explore the effect of macrophages stimulated with mechanical stretch on MSCs osteogenesis. By using a coculture system, we discover that macrophages efficiently induce osteogenic differentiation of MSCs under specific stretch conditions. A synergy mechanism between M2 polarization and YAP/BMP2 axis are identified through molecular and genetic analyses. Macrophages are activated by cyclic stretch and polarized to M2 phenotype that produce anti-inflammatory cytokines such as IL-10 and TGF-β to regulate the local inflammatory microenvironment. Furthermore, mechanical stretch induces YAP activation and nuclear translocation, subsequently regulates downstream BMP2 expression to facilitate MSCs osteogenesis. These findings not only advance our understanding of the complex influence among the mechanical strain, macrophage inflammatory response as well as the osteogenic differentiation of MSCs, but also reveal a control system from mechanical signals to chemical response then to cell behaviors during bone repair and regeneration.

Mechanical loading and the control of stem cell behavior

OBJECTIVE

Mechanical stimulation regulates many cell responses. The present study describes the effects of different in vitro mechanical stimulation approaches on stem cell behavior.

DESIGN

The narrative review approach was performed. The articles published in English language that addressed the effects of mechanical force on stem cells were searched on Pubmed and Scopus database. The effects of extrinsic mechanical force on stem cell response was reviewed and discussed.

RESULTS

Cells sense mechanical stimuli by the function of mechanoreceptors and further transduce force stimulation into intracellular signaling. Cell responses to mechanical stimuli depend on several factors including type, magnitude, and duration. Further, similar mechanical stimuli exhibit distinct cell responses based on numerous factors including cell type and differentiation stage. Various mechanical applications modulate stemness maintenance and cell differentiation toward specific lineages.

CONCLUSIONS

Mechanical force application modulates stemness maintenance and differentiation. Modification of force regimens could be utilized to precisely control appropriate stem cell behavior toward specific applications.

Biofabrication and Signaling Strategies for Tendon/Ligament Interfacial Tissue Engineering

Tendons and ligaments (TL) have poor healing capability, and for serious injuries like tears or ruptures, surgical intervention employing autografts or allografts is usually required. Current tissue replacements are nonideal and can lead to future problems such as high retear rates, poor tissue integration, or heterotopic ossification. Alternatively, tissue engineering strategies are being pursued using biodegradable scaffolds. As tendons connect muscle and bone and ligaments attach bones, the interface of TL with other tissues represent complex structures, and this intricacy must be considered in tissue engineered approaches. In this paper, we review recent biofabrication and signaling strategies for biodegradable polymeric scaffolds for TL interfacial tissue engineering. First, we discuss biodegradable polymeric scaffolds based on the fabrication techniques as well as the target tissue application. Next, we consider the effect of signaling factors, including cell culture, growth factors, and biophysical stimulation. Then, we discuss human clinical studies on TL tissue healing using commercial synthetic scaffolds that have occurred over the past decade. Finally, we highlight the challenges and future directions for biodegradable scaffolds in the field of TL and interface tissue engineering.

Recent Advances in Mechanically Loaded Human Mesenchymal Stem Cells for Bone Tissue Engineering

Large bone defects are a major health concern worldwide. The conventional bone repair techniques (e.g., bone-grafting and Masquelet techniques) have numerous drawbacks, which negatively impact their therapeutic outcomes. Therefore, there is a demand to develop an alternative bone repair approach that can address the existing drawbacks. Bone tissue engineering involving the utilization of human mesenchymal stem cells (hMSCs) has recently emerged as a key strategy for the regeneration of damaged bone tissues. However, the use of tissue-engineered bone graft for the clinical treatment of bone defects remains challenging. While the role of mechanical loading in creating a bone graft has been well explored, the effects of mechanical loading factors (e.g., loading types and regime) on clinical outcomes are poorly understood. This review summarizes the effects of mechanical loading on hMSCs for bone tissue engineering applications. First, we discuss the key assays for assessing the quality of tissue-engineered bone grafts, including specific staining, as well as gene and protein expression of osteogenic markers. Recent studies of the impact of mechanical loading on hMSCs, including compression, perfusion, vibration and stretching, along with the potential mechanotransduction signalling pathways, are subsequently reviewed. Lastly, we discuss the challenges and prospects of bone tissue engineering applications.

Diffuse microdamage in bone activates anabolic response by osteoblasts via involvement of voltage-gated calcium channels

INTRODUCTION

Matrix damage sustained by bone tissue is repaired by the concerted action of bone cells. Previous studies have reported extracellular calcium ([Ca²⁺]_E) efflux to originate from regions of bone undergoing diffuse microdamage termed as "diffuse microdamage-induced calcium efflux" (DMICE). DMICE has also been shown to activate and increase intracellular calcium ([Ca²⁺]_I) signaling in osteoblasts via the involvement of voltage-gated calcium channels (VGCC). Past studies have assessed early stage (< 1 h) responses of osteoblasts to DMICE. The current study tested the hypothesis that DMICE has longer-term sustained effect such that it induces anabolic response of osteoblasts.

MATERIALS AND METHODS

Osteoblasts derived from mouse calvariae were seeded on devitalized bovine bone wafers. Localized diffuse damage was induced in the vicinity of cells by bending. The response of osteoblasts to DMICE was evaluated by testing gene expression, protein synthesis and mineralized nodule formation.

RESULTS

Cells on damaged bone wafers showed a significant increase in RUNX2 and Osterix expression compared to non-loaded control. Also, RUNX2 and Osterix expression were suppressed significantly when the cells were treated with bepridil, a non-selective VGCC inhibitor, prior to loading. Significantly higher amounts of osteocalcin and mineralized nodules were synthesized by osteoblasts on diffuse damaged bone wafers, while bepridil treatment resulted in a significant decrease in osteocalcin production and mineralized nodule formation.

CONCLUSION

In conclusion, this study demonstrated that DMICE activates anabolic responses of osteoblasts through activation of VGCC. Future studies of osteoblast response to DMICE in vivo will help to clarify how bone cells repair diffuse microdamage.

Expression of HIF‑1α in cycling stretch‑induced osteogenic differentiation of bone mesenchymal stem cells

During orthodontic treatment, mechanical force is applied to the teeth, and following a series of complex metabolism changes, the position of the teeth in the alveolar bone change. This process is closely associated with primitive bone mesenchymal stem cells (BMSCs), which may differentiate into osteoblasts precursor cell. A hypoxic microenvironment may be caused by orthodontic mechanical forces between the alveolar bone and the root. Hypoxia-inducible factor 1α (HIF-1α) is a specific receptor that adapts to a hypoxic environment. The present study was designed to investigate whether HIF-1α was involved in the osteoblastic differentiation of BMSCs induced by cyclic tensile stress. During this process, HIF-1α mRNA and protein expression were detected using a reverse transcription-quantitative polymerase chain reaction and western blotting. It was revealed that alkaline phosphatase activity increased in a time-dependent manner in three different stretching strength groups, which indicates that cyclic stretch promotes the osteogenic differentiation of BMSCs. The optimal force stage of osteogenesis was an unexpected discovery, which will provide theoretical guidance for selecting the most suitable orthodontic force for tooth movement in clinical orthodontic treatment. Most importantly, all experiments revealed that HIF-1α mRNA and protein were significantly increased following stretching treatment in BMSCs. It was therefore concluded that HIF-1α may be involved in BMSCs modulating osteogenic metabolism during exposure to cyclic stretch and a hypoxic microenvironment, which may prove useful for the reconstruction of a jaw during orthodontic treatment.

Mechanistic role of perfusion culture on bone regeneration

Bone tissue engineering (BTE) aims to develop engineered bone tissue to substitute conventional bone grafts. To achieve this, culturing the cells on the biocompatible three-dimensional (3D) scaffold is one alternative approach. The new functional bone tissue regeneration could be feasible by the synergetic combinations of cells, biomaterials and bioreactors. Although the field of biomaterial design/development for BTE applications attained reasonable success, development of suitable bioreactor remains still a major challenge. Tissue engineering bioreactors provide the microenvironment required for neo-tissue regeneration, and also can be used to study the physio-chemical cues effect on cell proliferation and differentiation in order to produce functional tissue. In this direction, various bioreactors have been developed and evaluated for the successful development of engineered bone tissue. Continues assessment of tissue development and limitations of the bioreactors lead to the progression of perfusion flow bioreactor system. Improvements in perfusion reactor system were able to yield multiple tissue engineered constructs with uniform cell distribution, easy to operate protocols and also effectively handled for the functional tissue development to meet the adequate supply of engineered graft for clinical application.

Uniaxial Cyclic Tensile Stretching at 8% Strain Exclusively Promotes Tenogenic Differentiation of Human Bone Marrow-Derived Mesenchymal Stromal Cells

The present study was conducted to establish the amount of mechanical strain (uniaxial cyclic stretching) required to provide optimal tenogenic differentiation expression in human mesenchymal stromal cells (hMSCs) in vitro, in view of its potential application for tendon maintenance and regeneration. Methods. In the present study, hMSCs were subjected to 1 Hz uniaxial cyclic stretching for 6, 24, 48, and 72 hours; and were compared to unstretched cells. Changes in cell morphology were observed under light and atomic force microscopy. The tenogenic, osteogenic, adipogenic, and chondrogenic differentiation potential of hMSCs were evaluated using biochemical assays, extracellular matrix expressions, and selected mesenchyme gene expression markers; and were compared to primary tenocytes. Results. Cells subjected to loading displayed cytoskeletal coarsening, longer actin stress fiber, and higher cell stiffness as early as 6 hours. At 8% and 12% strains, an increase in collagen I, collagen III, fibronectin, and N-cadherin production was observed. Tenogenic gene expressions were highly expressed (p < 0.05) at 8% (highest) and 12%, both comparable to tenocytes. In contrast, the osteoblastic, chondrogenic, and adipogenic marker genes appeared to be downregulated. Conclusion. Our study suggests that mechanical loading at 8% strain and 1 Hz provides exclusive tenogenic differentiation; and produced comparable protein and gene expression to primary tenocytes.

Mechanical strain triggers differentiation of dental mesenchymal stem cells by activating osteogenesis-specific biomarkers expression

Dental stem cell biotechnology has been used as a potential method to treat the dental diseases. This study aimed to investigate effects of mechanical stimulation on osteogenic properties of rat dental mesenchymal stem cells (DMSCs). DMSCs were isolated from rat teeth root tissues and identified by detecting vimentin and keratin expression. Flexcell FX4K tension system that mediating cyclic strain was used to treat DMSCs. MTT assay was used to observe DMSCs viability. Alkaline phosphatase (ALP) staining and alizarin red staining were conducted. Osteogenesis-specific biomarkers, such as receptor activator for nuclear factor-kB ligand (RANKL), osteoprotegerin (OPG), dentin sialoprotein (DSP) and bone sialoprotein (BSP), were evaluated using RT-PCR, western blot and immunohistochemistry assay, respectively. Positive ALP staining and alizarin red staining confirmed DMSCs phenotype. There were no significant morphology differences between mechanical stimuli treated cells and normal control cells. MTT results showed no significant differences between normal control cells and mechanically stimulated DMSCs. RT-PCR, western blot and immunohistochemistry assay indicated that 10% cyclic strain could trigger an obvious change of mRNA and protein expression of RANKL, OPG, DSP and BSP, respectively. Mechanical stimulation could trigger relative higher levels of calcium deposition in DMSCs. Mechanical strain triggered bone formation mainly through activating RANKL gene expression. In conclusion, 10% cycle mechanical strain could stimulate higher amounts of ALP and calcium deposition by activating RNAKL, and could trigger dramatically changes of mRNA and protein expression of osteogenesis-specific biomarkers, such as OPG, BSP and DSP.

MicroRNA-129-1-3p regulates cyclic stretch-induced endothelial progenitor cell differentiation by targeting Runx2

Endothelial progenitor cells (EPCs) are vital to the recovery of endothelial function and maintenance of vascular homeostasis. EPCs mobilize to sites of vessel injury and differentiate into mature endothelial cells (ECs). Locally mobilized EPCs are exposed to cyclic stretch caused by blood flow, which is important for EPC differentiation. MicroRNAs (miRNAs) have emerged as key regulators of several cellular processes. However, the role of miRNAs in cyclic stretch-induced EPC differentiation remains unclear. Here, we investigate the effects of microRNA-129-1-3p (miR-129-1-3p) and its novel target Runt-related transcription factor 2 (Runx2) on EPC differentiation induced by cyclic stretch. Bone marrow-derived EPCs were exposed to cyclic stretch with a magnitude of 5% (which mimics physiological mechanical stress) at a constant frequency of 1.25 Hz for 24 hours. The results from a miRNA array revealed that cyclic stretch significantly decreased miR-129-1-3p expression. Furthermore, we found that downregulation of miR-129-1-3p during cyclic stretch-induced EPC differentiation toward ECs. Meanwhile, expression of Runx2, a putative target gene of miR-129-1-3p, was increased as a result of cyclic stretch. A 3'UTR reporter assay validated Runx2 as a direct target of miR-129-1-3p. Furthermore, small interfering RNA (siRNA)-mediated knockdown of Runx2 inhibited EPC differentiation into ECs and attenuated EPC tube formation via modulation of vascular endothelial growth factor (VEGF) secretion from EPCs in vitro. Our findings demonstrated that cyclic stretch suppresses miR-129-1-3p expression, which in turn activates Runx2 and VEGF to promote endothelial differentiation of EPCs and angiogenesis. Therefore, targeting miR-129-1-3p and Runx2 may be a potential therapeutic strategy for treating vessel injury.

Mechanical stretch-induced osteogenic differentiation of human jaw bone marrow mesenchymal stem cells (hJBMMSCs) via inhibition of the NF-κB pathway

Severe malocclusion can contribute to several serious dental and physical conditions, such as digestive difficulties, periodontal disease, and severe tooth decay. Orthodontic treatment is mainly used to treat malocclusion. Forces in orthodontic tooth results in bone resorption on the pressure side and bone deposition on the tension side. Osteoblasts have been considered as the key component in bone regeneration on the tension side. However, the underlying mechanisms remain unclear. In this study, we focus on how mechanical stretch regulates the osteogenesis during orthodontic treatment. Human jaw bone marrow mesenchymal stem cells (hJBMMSCs) were isolated from healthy adult donors and cultured in regular medium (control) or osteogenic medium (OS). Under OS culture, hJBMMSCs presented osteogenic differentiation potentials, as evidenced by increased mineralization, enhanced calcium deposition, and upregulated expression of osteogenesis markers (ALP, osterix, and Runx). What's more, the OS-induced osteogenesis of hJBMMSCs is associated with the dephosphorylation of IKK, activation of IKBα, and phosphorylation/nucleic accumulation of P65, which all indicated the inhibition of NF-κB activity. Overexpressing P65 in hJBMMSCs, which could constantly activate NF-κB, prevented the osteogenic differentiation in the OS. After that, we applied the Flexcell tension system, which could cause mechanical stretch on cultured hJBMMSCs to mimic the tension forces during tooth movement. Mechanical stretch resulted in 3.5-fold increase of ALP activity and 2.4-fold increase of calcium deposition after 7 days and 21 days treatment, respectively. The expression levels of ALP, Run×2, and Osterix were also significantly upregulated. In the meantime, applying mechanical stretch on OS-cultured hJBMMSCs also dramatically promoted the OS-induced osteogenesis. Both OS and mechanical stretch downregulated NF-κB activity. By overexpressing P65 in hJBMMSCs, neither OS nor mechanical stretch could induce their osteogenesis. These results indicated that, like OS induction, mechanical stretch-facilitated osteogenesis of hJBMMSCs by inhibiting NF-κB in the noninflammatory environments.

miR-208a-3p Suppresses Osteoblast Differentiation and Inhibits Bone Formation by Targeting ACVR1

Emerging evidence indicates that many microRNAs (miRNAs) are indispensable regulators of osteoblast differentiation and bone formation. However, the role of miRNAs in mechanotransduction of osteoblasts remains to be elucidated. This study aimed to identify a mechanosensitive miRNA that regulates Activin A receptor type I (ACVR1)-induced osteogenic differentiation. After 4 weeks of hindlimb unloading (HLU) suspension of 6-month-old male C57BL/6J mice, femurs and tibias were harvested to extract total bone RNAs. Elevated levels of miR-208a-3p correlated with a lower degree of bone formation in whole-bone samples of HLU mice. However, in vitro overexpression of miR-208a-3p inhibited osteoblast differentiation, whereas silencing of miR-208a-3p by antagomiR-208a-3p promoted expression of osteoblast activity, bone formation marker genes, and matrix mineralization under mechanical unloading condition. Bioinformatics analysis and a luciferase assay revealed that ACVR1 is a target gene of miR-208a-3p that negatively regulates osteoblast differentiation under mechanical unloading environment. Further, this study also demonstrates that in vivo pre-treatment with antagomiR-208a-3p led to an increase in bone formation and trabecular microarchitecture and partly rescued the bone loss caused by mechanical unloading. Collectively, these results suggest that in vivo, inhibition of miRNA-208a-3p by antagomiR-208a-3p may be a potential therapeutic strategy for ameliorating bone loss.

Deformation strain is the main physical driver for skeletal precursors to undergo osteogenesis in earlier stages of osteogenic cell maturation

Mesenchymal stem cells play a major role during bone remodelling and are thus of high interest for tissue engineering and regenerative medicine applications. Mechanical stimuli, that is, deformation strain and interstitial fluid-flow-induced shear stress, promote osteogenic lineage commitment. However, the predominant physical stimulus that drives early osteogenic cell maturation is not clearly identified. The evaluation of each stimulus is challenging, as deformation and fluid-flow-induced shear stress interdepend. In this study, we developed a bioreactor that was used to culture mesenchymal stem cells harbouring a strain-responsive AP-1 luciferase reporter construct, on porous scaffolds. In addition to the reporter, mineralization and vitality of the cells was investigated by alizarin red staining and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide. Quantification of the expression of genes associated to bone regeneration and bone remodelling was used to confirm alizarin red measurements. Controlled perfusion and deformation of the 3-dimensional scaffold facilitated the alteration of the expression of osteogenic markers, luciferase activity, and calcification. To isolate the specific impact of scaffold deformation, a computational model was developed to derive a perfusion flow profile that results in dynamic shear stress conditions present in periodically loaded scaffolds. In comparison to actually deformed scaffolds, a lower expression of all measured readout parameters indicated that deformation strain is the predominant stimulus for skeletal precursors to undergo osteogenesis in earlier stages of osteogenic cell maturation.

New Bioengineering Breakthroughs and Enabling Tools in Regenerative Medicine

PURPOSE OF REVIEW

In this review, we provide a general overview of recent bioengineering breakthroughs and enabling tools that are transforming the field of regenerative medicine (RM). We focus on five key areas that are evolving and increasingly interacting including mechanobiology, biomaterials and scaffolds, intracellular delivery strategies, imaging techniques, and computational and mathematical modeling.

RECENT FINDINGS

Mechanobiology plays an increasingly important role in tissue regeneration and design of therapies. This knowledge is aiding the design of more precise and effective biomaterials and scaffolds. Likewise, this enhanced precision is enabling ways to communicate with and stimulate cells down to their genome. Novel imaging technologies are permitting visualization and monitoring of all these events with increasing resolution from the research stages up to the clinic. Finally, algorithmic mining of data and soft matter physics and engineering are creating growing opportunities to predict biological scenarios, device performance, and therapeutic outcomes.

SUMMARY

We have found that the development of these areas is not only leading to revolutionary technological advances but also enabling a conceptual leap focused on targeting regenerative strategies in a holistic manner. This approach is bringing us ever more closer to the reality of personalized and precise RM.

Intermittent parathyroid hormone (PTH) promotes cementogenesis and alleviates the catabolic effects of mechanical strain in cementoblasts

Background

External root resorption, commonly starting from cementum, is a severe side effect of orthodontic treatment. In this pathological process and repairing course followed, cementoblasts play a significant role. Previous studies implicated that parathyroid hormone (PTH) could act on committed osteoblast precursors to promote differentiation, and inhibit apoptosis. But little was known about the role of PTH in cementoblasts. The purpose of this study was to investigate the effects of intermittent PTH on cementoblasts and its influence after mechanical strain treatment.

Results

Higher levels of cementogenesis- and differentiation-related biomarkers (bone sialoprotein (BSP), osteocalcin (OCN), Collagen type I (COL1) and Osterix (Osx)) were shown in 1–3 cycles of intermittent PTH treated groups than the control group. Additionally, intermittent PTH increased alkaline phosphatase (ALP) activity and mineralized nodules formation, as measured by ALP staining, quantitative ALP assay, Alizarin red S staining and quantitative calcium assay. The morphology of OCCM-30 cells changed after mechanical strain exertion. Expression of BSP, ALP, OCN, osteopontin (OPN) and Osx was restrained after 18 h mechanical strain. Furthermore, intermittent PTH significantly increased the expression of cementogenesis- and differentiation-related biomarkers in mechanical strain treated OCCM-30 cells.

Conclusions

Taken together, these data suggested that intermittent PTH promoted cementum formation through activating cementogenesis- and differentiation-related biomarkers, and attenuated the catabolic effects of mechanical strain in immortalized cementoblasts OCCM-30.

Electronic supplementary material

The online version of this article (doi:10.1186/s12860-017-0133-0) contains supplementary material, which is available to authorized users.

Evidence of the Role of R-Spondin 1 and Its Receptor Lgr4 in the Transmission of Mechanical Stimuli to Biological Signals for Bone Formation

The bone can adjust its mass and architecture to mechanical stimuli via a series of molecular cascades, which have been not yet fully elucidated. Emerging evidence indicated that R-spondins (Rspos), a family of secreted agonists of the Wnt/β-catenin signaling pathway, had important roles in osteoblastic differentiation and bone formation. However, the role of Rspo proteins in mechanical loading-influenced bone metabolism has never been investigated. In this study, we found that Rspo1 was a mechanosensitive protein for bone formation. Continuous cyclic mechanical stretch (CMS) upregulated the expression of Rspo1 in mouse bone marrow mesenchymal stem cells (BMSCs), while the expression of Rspo1 in BMSCs in vivo was downregulated in the bones of a mechanical unloading mouse model (tail suspension (TS)). On the other hand, Rspo1 could promote osteogenesis of BMSCs under CMS through activating the Wnt/β-catenin signaling pathway and could rescue the bone loss induced by mechanical unloading in the TS mice. Specifically, our results suggested that Rspo1 and its receptor of leucine-rich repeat containing G-protein-coupled receptor 4 (Lgr4) should be a novel molecular signal in the transmission of mechanical stimuli to biological signal in the bone, and this signal should be in the upstream of Wnt/β-catenin signaling for bone formation. Rspo1/Lgr4 could be a new potential target for the prevention and treatment of disuse osteoporosis in the future.

MicroRNA-503-5p inhibits stretch-induced osteogenic differentiation and bone formation

Cyclical stretch-induced bone formation during orthodontic treatment is a complex biological process modulated by various factors including miRNAs and their targeted-gene network. However, the miRNA expression profile and their roles in osteogenic differentiation of bone mesenchymal stem cells (BMSCs) exposed to mechanical stretch remains unclear. Here, we use the miRNA microarray assay to screen for mechano-sensitive miRNAs during stretch-induced osteogenic differentiation of BMSCs and identified that nine miRNAs were differentially expressed between stretched and control BMSCs. Furthermore, miR-503-5p, which was markedly downregulated in both microarray assay and qRT-PCR assay were selected for further functional verification. We found that overexpression of miR-503-5p in BMSCs attenuated stretch-induced osteogenic differentiation while the effect was reversed by miR-503-5p inhibition treatment. In vivo studies, overexpression of miR-503-5p with specific agomir decreased Runx2, ALP mRNA, and protein expression, decreased osteoblast numbers and osteoblastic bone formation in the OTM tension sides. In conclusion, our study revealed that miR-503-5p functions as the mechano-sensitive miRNA and inhibits BMSCs osteogenic differentiation subjected to mechanical stretch and bone formation in OTM tension sides.

Recent progress in stem cell differentiation directed by material and mechanical cues

Stem cells play essential roles in tissue regeneration in vivo via specific lineage differentiation induced by environmental factors. In the past, biochemical signals were the focus of induced stem cell differentiation. As reported by Engler et al (2006 Cell 126 677-89), biophysical signal mediated stem cell differentiation could also serve as an important inducer. With the advancement of material science, it becomes a possible strategy to generate active biophysical signals for directing stem cell fate through specially designed material microstructures. In the past five years, significant progress has been made in this field, and these designed biophysical signals include material elasticity/rigidity, micropatterned structure, extracellular matrix (ECM) coated materials, material transmitted extracellular mechanical force etc. A large number of investigations involved material directed differentiation of mesenchymal stem cells, neural stem/progenitor cells, adipose derived stem cells, hematopoietic stem/progenitor cells, embryonic stem cells and other cells. Hydrogel based materials were commonly used to create varied mechanical properties via modifying the ratio of different components, crosslinking levels, matrix concentration and conjugation with other components. Among them, polyacrylamide (PAM) and polydimethylsiloxane (PDMS) hydrogels remained the major types of material. Specially designed micropatterning was not only able to create a unique topographical surface to control cell shape, alignment, cell-cell and cell-matrix contact for basic stem cell biology study, but also could be integrated with 3D bioprinting to generate micropattered 3D structure and thus to induce stem cell based tissue regeneration. ECM coating on a specific topographical structure was capable of inducing even more specific and potent stem cell differentiation along with soluble factors and mechanical force. The article overviews the progress of the past five years in this particular field.

Mechanical stretch inhibits mesenchymal stem cell adipogenic differentiation through TGFβ1/Smad2 signaling

Mesenchymal stem cells (MSCs) are the common precursors of several functionally disparate cell lineages. A plethora of chemical and physical stimuli contribute to lineage decisions and guidance, including mechanical stretch concomitant with physical movement. Here, we examined how stretch regulates MSC differentiation into adipocytes and the intracellular signaling pathways involved. MSCs were cultured under adipogenic conditions and divided into a control and an experimental group. Cultures in the experimental group were subjected to a sinusoidal stretch regimen delivered via flexible culture bottoms (5% magnitude, 10 times per min, 6h/day, 3 or 5 days). Expression levels of the adipocyte markers PPARγ-2, adiponectin, and C/EBPα were measured as indices of differentiation. Compared to controls, MSCs exposed to mechanical stretch exhibited downregulated PPARγ-2, adiponectin, and C/EBPα mRNA expression. Alternatively, stretch upregulated phosphorylation of Smad2. This stretch-induced increase in Smad2 phosphorylation was suppressed by pretreatment with the TGFβ1/Smad2 pathway antagonist SB-431542. Pretreatment with the TGFβ1/Smad2 signaling agonist TGFβ1 facilitated the inhibitory effect of stretch on the expression levels of PPARγ-2, adiponectin, and C/EBPα proteins, while pretreatment with SB-431542 reversed the inhibitory effects of subsequent stretch on the expression levels of these markers. These results strongly suggest that the anti-adipogenic effects of mechanical stretch on MSCs are mediated, at least in part, by activation of the TGFβ1/Smad2 signaling pathway.

Mechanobiology of mesenchymal stem cells: Perspective into mechanical induction of MSC fate

Bone marrow-derived mesenchymal stem and stromal cells (MSCs) are promising candidates for cell-based therapies in diverse conditions including tissue engineering. Advancement of these therapies relies on the ability to direct MSCs toward specific cell phenotypes. Despite identification of applied forces that affect self-maintenance, proliferation, and differentiation of MSCs, mechanisms underlying the integration of mechanically induced signaling cascades and interpretation of mechanical signals by MSCs remain elusive. During the past decade, many researchers have demonstrated that external applied forces can activate osteogenic signaling pathways in MSCs, including Wnt, Ror2, and Runx2. Besides, recent advances have highlighted the critical role of internal forces due to cell-matrix interaction in MSC function. These internal forces can be achieved by the materials that cells reside in through its mechanical properties, such as rigidity, topography, degradability, and substrate patterning. MSCs can generate contractile forces to sense these mechanical properties and thereby perceive mechanical information that directs broad aspects of MSC functions, including lineage commitment. Although many signaling pathways have been elucidated in material-induced lineage specification of MSCs, discovering the mechanisms by which MSCs respond to such cell-generated forces is still challenging because of the highly intricate signaling milieu present in MSC environment. However, bioengineers are bridging this gap by developing platforms to control mechanical cues with improved throughput and precision, thereby enabling further investigation of mechanically induced MSC functions. In this review, we discuss the most recent advances that how applied forces and cell-generated forces may be engineered to determine MSC fate, and overview a subset of the operative signal transduction mechanisms and experimental platforms that have emerged in MSC mechanobiology research. Our main goal is to provide an up-to-date view of MSC mechanobiology that is relevant to both mechanical loading and mechanical properties of the environment, and introduce these emerging platforms for tissue engineering use.

Mechanical strain regulates osteogenic and adipogenic differentiation of bone marrow mesenchymal stem cells

This study examined the effects of mechanical strain on osteogenic and adipogenic differentiation of cultured MSCs by stimulating MSCs cultured in general and adipogenic differentiation media using a mechanical strain device. Markers of osteogenic (Runx2, Osx, and I-collagen) and adipogenic (PPARγ-2, C/EBPα, and lipid droplets) differentiation were examined using real-time PCR, western blot, immunocytochemical, or histochemical stain analyses. Levels of Runx2 and Osx gradually increased in MSC groups in general medium subject to strain stimulation, as compared with in unstrained groups. After adding the stress signal, I-collagen protein levels of expression were obviously promoted in cells in comparison to the controls. The levels of PPARγ-2 and C/EBPα were decreased, and the emergence of lipid droplets was delayed in MSCs groups in adipogenic differentiation medium subject to strain stimulation, as compared with in unstrained groups. Mechanical strain can promote differentiation of MSCs into osteoblasts and can impede differentiation into adipocytes. These results clarify the mechanisms underlying the effects of exercise on bone repair and reconstruction and provide a more adequate scientific basis for the use of exercise therapy in the treatment of obesity and metabolic osteoporosis.