Extracellular matrix produced by osteoblasts cultured under low-magnitude, high-frequency stimulation is favourable to osteogenic differentiation of mesenchymal stem cells

Yoda1 Enhanced Low-Magnitude High-Frequency Vibration on Osteocytes in Regulation of MDA-MB-231 Breast Cancer Cell Migration

Low-magnitude (≤1 g) high-frequency (≥30 Hz) (LMHF) vibration has been shown to enhance bone mineral density. However, its regulation in breast cancer bone metastasis remains controversial for breast cancer patients and elder populations. Yoda1, an activator of the mechanosensitive Piezo1 channel, could potentially intensify the effect of LMHF vibration by enhancing the mechanoresponse of osteocytes, the major mechanosensory bone cells with high expression of Piezo1. In this study, we treated osteocytes with mono- (Yoda1 only or vibration only) or combined treatment (Yoda1 and LMHF vibration) and examined the further regulation of osteoclasts and breast cancer cells through the conditioned medium. Moreover, we studied the effects of combined treatment on breast cancer cells in regulation of osteocytes. Combined treatment on osteocytes showed beneficial effects, including increasing the nuclear translocation of Yes-associated protein (YAP) in osteocytes (488.0%, p < 0.0001), suppressing osteoclastogenesis (34.3%, p = 0.004), and further reducing migration of MDA-MB-231 (15.1%, p = 0.02) but not Py8119 breast cancer cells (4.2%, p = 0.66). Finally, MDA-MB-231 breast cancer cells subjected to the combined treatment decreased the percentage of apoptotic osteocytes (34.5%, p = 0.04) but did not affect the intracellular calcium influx. This study showed the potential of stimulating Piezo1 in enhancing the mechanoresponse of osteocytes to LMHF vibration and further suppressing breast cancer migration via osteoclasts.

Possible Mechanisms for the Effects of Sound Vibration on Human Health

This paper presents a narrative review of research literature to “map the landscape” of the mechanisms of the effect of sound vibration on humans including the physiological, neurological, and biochemical. It begins by narrowing music to sound and sound to vibration. The focus is on low frequency sound (up to 250 Hz) including infrasound (1–16 Hz). Types of application are described and include whole body vibration, vibroacoustics, and focal applications of vibration. Literature on mechanisms of response to vibration is categorized into hemodynamic, neurological, and musculoskeletal. Basic mechanisms of hemodynamic effects including stimulation of endothelial cells and vibropercussion; of neurological effects including protein kinases activation, nerve stimulation with a specific look at vibratory analgesia, and oscillatory coherence; of musculoskeletal effects including muscle stretch reflex, bone cell progenitor fate, vibration effects on bone ossification and resorption, and anabolic effects on spine and intervertebral discs. In every category research on clinical applications are described. The conclusion points to the complexity of the field of vibrational medicine and calls for specific comparative research on type of vibration delivery, amount of body or surface being stimulated, effect of specific frequencies and intensities to specific mechanisms, and to greater interdisciplinary cooperation and focus.

The effects of locomotion on bone marrow mesenchymal stem cell fate: insight into mechanical regulation and bone formation

Bone marrow mesenchymal stem cells (BMSCs) refer to a heterogeneous population of cells with the capacity for self-renewal. BMSCs have multi-directional differentiation potential and can differentiate into chondrocytes, osteoblasts, and adipocytes under specific microenvironment or mechanical regulation. The activities of BMSCs are closely related to bone quality. Previous studies have shown that BMSCs and their lineage-differentiated progeny (for example, osteoblasts), and osteocytes are mechanosensitive in bone. Thus, a goal of this review is to discuss how these ubiquious signals arising from mechanical stimulation are perceived by BMSCs and then how the cells respond to them. Studies in recent years reported a significant effect of locomotion on the migration, proliferation and differentiation of BMSCs, thus, contributing to our bone mass. This regulation is realized by the various intersecting signaling pathways including RhoA/Rock, IFG, BMP and Wnt signalling. The mechanoresponse of BMSCs also provides guidance for maintaining bone health by taking appropriate exercises. This review will summarize the regulatory effects of locomotion/mechanical loading on BMSCs activities. Besides, a number of signalling pathways govern MSC fate towards osteogenic or adipocytic differentiation will be discussed. The understanding of mechanoresponse of BMSCs makes the foundation for translational medicine.

Spatially Regulated Multiphenotypic Differentiation of Stem Cells in 3D via Engineered Mechanical Gradient

Within the osteochondral interface, cellular and extracellular matrix gradients provide a biomechanical and biochemical niche for homeostatic tissue functions. Postnatal joint loading is critical for the development of such tissue gradients, leading to the formation of functional osteochondral tissues composed of superficial, middle, and deep zones of cartilage, and underlying subchondral bone, in a depth-dependent manner. In this regard, a novel, variable core-shell electrospinning strategy was employed to generate spatially controlled strain gradients within three-dimensional scaffolds under dynamic compressive loading, enabling the local strain-magnitude dependent, multiphenotypic stem cell differentiation. Human mesenchymal stem cells (hMSCs) were cultured in electrospun scaffolds with a linear or biphasic mechanical gradient, which was computationally engineered and experimentally validated. The cell/scaffold constructs were subjected to various magnitudes of dynamic compressive strains in a scaffold depth-dependent manner at a frequency of 1 Hz for 2 h daily for up to 42 days in osteogenic media. Spatially upregulated gene expression of chondrogenic markers (ACAN, COL2A1, PRG4) and glycosaminoglycan deposition was observed in the areas of greater compressive strains. In contrast, osteogenic markers (COL1A1, SPARC, RUNX2) and calcium deposition were downregulated in response to high local compressive strains. Dynamic mechanical analysis showed the maintenance of the engineered mechanical gradients only under dynamic culture conditions, confirming the potent role of biomechanical gradients in developing and maintaining a tissue gradient. These results demonstrate that multiphenotypic differentiation of hMSCs can be controlled by regulating local mechanical microenvironments, providing a novel strategy to recapitulate the gradient structure in osteochondral tissues for successful regeneration of damaged joints in vivo and facile development of interfacial tissue models in vitro.

Combating osteoporosis and obesity with exercise: leveraging cell mechanosensitivity

Osteoporosis, a condition of skeletal decline that undermines quality of life, is treated with pharmacological interventions that are associated with poor adherence and adverse effects. Complicating efforts to improve clinical outcomes, the incidence of obesity is increasing, predisposing the population to a range of musculoskeletal complications and metabolic disorders. Pharmacological management of obesity has yet to deliver notable reductions in weight and debilitating complications are rarely avoided. By contrast, exercise shows promise as a non-invasive and non-pharmacological method of regulating both osteoporosis and obesity. The principal components of exercise - mechanical signals - promote bone and muscle anabolism while limiting formation and expansion of fat mass. Mechanical regulation of bone and marrow fat might be achieved by regulating functions of differentiated cells in the skeletal tissue while biasing lineage selection of their common progenitors - mesenchymal stem cells. An inverse relationship between adipocyte versus osteoblast fate selection from stem cells is implicated in clinical conditions such as childhood obesity and increased marrow adiposity in type 2 diabetes mellitus, as well as contributing to skeletal frailty. Understanding how exercise-induced mechanical signals can be used to improve bone quality while decreasing fat mass and metabolic dysfunction should lead to new strategies to treat chronic diseases such as osteoporosis and obesity.

The effects of dynamic compressive loading on human mesenchymal stem cell osteogenesis in the stiff layer of a bilayer hydrogel

Bilayer hydrogels with a soft cartilage-like layer and a stiff bone-like layer embedded with human mesenchymal stem cells (hMSCs) are promising for osteochondral tissue engineering. The goals of this work were to evaluate the effects of dynamic compressive loading (2.5% applied strain, 1 Hz) on osteogenesis in the stiff layer and spatially map local mechanical responses (strain, stress, hydrostatic pressure, and fluid velocity). A bilayer hydrogel was fabricated from soft (24 kPa) and stiff (124 kPa) poly (ethylene glycol) hydrogels. With hMSCs embedded in the stiff layer, osteogenesis was delayed under loading evident by lower OSX and OPN expressions, alkaline phosphatase activity, and collagen content. At Day 28, mineral deposits were present throughout the stiff layer without loading but localized centrally and near the interface under loading. Local strains mapped by particle tracking showed substantial equivalent strain (~1.5%) transferring to the stiff layer. When hMSCs were cultured in stiff single-layer hydrogels subjected to similar strains, mineralization was inhibited. Finite element analysis revealed that hydrostatic pressures ≥~600 Pa correlated to regions lacking mineralization in both hydrogels. Fluid velocities were low (~1-10 nm/s) in the hydrogels with no apparent correlation to mineralization. Mineralization was recovered by inhibiting ERK1/2, indicating cell-mediated inhibition. These findings suggest that high strains (~1.5%) combined with higher hydrostatic pressures negatively impact osteogenesis, but in a manner that depends on the magnitude of each mechanical response. This work highlights the importance of local mechanical responses in mediating osteogenesis of hMSCs in bilayer hydrogels being studied for osteochondral tissue engineering.

Efficacy of mechanical vibration in regulating mesenchymal stem cells gene expression

This study aimed at investigating the expression of osteoblast and chondrocyte-related genes in mesenchymal stem cells (MSCs), derived from rabbit adipose tissue, under mechanical vibration. The cells were placed securely on a vibrator's platform and subjected to 300 Hz of sinusoidal vibration, with a maximum amplitude of 10 μm, for 45 min per day, and for 14 consequent days, in the absence of biochemical reagents. The negative control group was placed in the conventional culture medium with no mechanical loading. The expression of osteoblast and chondrocyte-related genes was investigated using real-time polymerase chain reaction (real-time PCR). In addition, F-actin fiber structure and alignment with the help of actin filament fluorescence staining were evaluated, and the level of metabolic activity of MSCs was determined by the methyl thiazolyl tetrazolium assay. The real-time PCR study showed a significant increase of bone gene expression in differentiated cells, compared with MSCs (P < 0.05). On the other hand, the level of chondrocyte gene expression was not remarkable. Applying mechanical vibration enhanced F-actin fiber structure and made them aligned in a specific direction. It was also found that during the differentiation process, the metabolic activity of the cells increased (P < 0.05). The results of this work are in agreement with the well-accepted fact that the MSCs, in the absence of growth factors, are sensitive to low-amplitude, high-frequency vibration. Outcomes of this work can be applied in cell therapy and tissue engineering, when regulation of stem cells is required.

Low magnitude high frequency vibration promotes adipogenic differentiation of bone marrow stem cells via P38 MAPK signal

Low magnitude high frequency vibration (LMHFV) has been mainly reported for its influence on the musculoskeletal system, particularly the bone tissue. In the bone structure, osteogenic activity is the main focus of study with regards to LMHFV. However, adipogenesis, another important mode of differentiation in the bone marrow cavity that might be affected by LMHFV, is much less researched. Furthermore, the molecular mechanism of how LMHFV influences adipogenesis still needs to be understood. Here, we tested the effect of LMHFV (0.3g, 40 Hz, amplitude: 50μm), 15min/d, on multipotent stem cells (MSCs), which are the common progenitors of osteogenic, chondrogenic, adipogenic and myogenic cells. It is previously shown that LMHFV promotes osteogenesis of MSCs. In this study, we further revealed its effect on adipo-differentiation of bone marrow stem cells (BMSCs) and studied the underlying signaling pathway. We found that when treated with LMHFV, the cells showed a higher expression of PPARγ, C/EBPα, adiponectin and showed more oil droplets. After vibration, the protein expression of PPARγ increased, and the phosphorylation of p38 MAPK was enhanced. After treating cells with SB203580, a specific p38 inhibitor, both the protein level of PPARγ illustrated by immunofluorescent staining and the oil droplets number, were decreased. Altogether, this indicates that p38 MAPK is activated during adipogenesis of BMSCs, and this is promoted by LMHFV. Our results demonstrating that specific parameters of LMHFV promotes adipogenesis of MSCs and enhances osteogenesis, highlights an unbeneficial side effect of vibration therapy used for preventing obesity and osteoporosis.

Effect of the same mechanical loading on osteogenesis and osteoclastogenesis in vitro

PURPOSE

To investigate the influence of the same mechanical loading on osteogenesis and osteoclastogenesis in vitro.

METHODS

Primary osteoblasts, bone marrow-derived mesenchymal stem cells (BMSCs, cultured in osteoinductive medium) and RAW264.7 cells cultured in osteoclast inductive medium were all subjected to a 1000 μstrain (μs) at 1 Hz cyclic mechanical stretch for 30 min (twice a day).

RESULTS

After mechanical stimulation, the alkaline phosphatase (ALP) activity, osteocalcin protein level of the osteoblasts and BMSCs were all enhanced, and the mRNA levels of ALP and collagen type I increased. Additionally, extracellular-deposited calcium of both osteoblasts and BMSCs increased. At the same time, the activity of secreted tartrate-resistant acid phosphatase, the number of tartrate-resistant acid phosphatase-positive multinucleated cells, matrix metalloproteinase-9 protein levels of RAW264.7 cells and the extracellular calcium solvency all decreased.

CONCLUSION

The results demonstrated that 1000 μs cyclic mechanical loading enhanced osteoblasts activity, promoted osteoblastic differentiation of BMSCs and restrained osteoclastogenesis of RAW264.7 cells in vitro.

The extracellular microscape governs mesenchymal stem cell fate

Each cell forever interacts with its extracellular matrix (ECM); a stem cell relies on this interaction to guide differentiation. The stiffness, nanotopography, protein composition, stress and strain inherent to any given ECM influences stem cell lineage commitment. This interaction is dynamic, multidimensional and reciprocally evolving through time, and from this concerted exchange the macroscopic tissues that comprise living organisms are formed. Mesenchymal stem cells can give rise to bone, cartilage, tendon and muscle; thus attempts to manipulate their differentiation must heed the physical properties of incredibly complex native microenvironments to realize regenerative goals.

Low-magnitude, high-frequency vibration promotes the adhesion and the osteogenic differentiation of bone marrow-derived mesenchymal stem cells cultured on a hydroxyapatite-coated surface: The direct role of Wnt/β-catenin signaling pathway activation

The positive effect of low-magnitude, high‑frequency (LMHF) vibration on implant osseointegration has been demonstrated; however, the underlying cellular and molecular mechanisms remain unknown. The aim of this study was to explore the effect of LMHF vibration on the adhesion and the osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) cultured on hydroxyapatite (HA)-coated surfaces in an in vitro model as well as to elucidate the molecular mechanism responsible for the effects of LMHF vibration on osteogenesis. LMHF vibration resulted in the increased expression of fibronectin, which was measured by immunostaining and RT-qPCR. Stimulation of BMSCs by LMHF vibration resulted in the rearrangement of the actin cytoskeleton with more prominent F-actin. Moreover, the expression of β1 integrin, vinculin and paxillin was notably increased following LMHF stimulation. Scanning electron microscope observations revealed that there were higher cell numbers and more extracellular matrix attached to the HA-coated surface in the LMHF group. Alkaline phosphatase activity as well as the expression of osteogenic-specific genes, namely Runx2, osterix, collagen I and osteocalcin, were significantly elevated in the LMHF group. In addition, the protein expression of Wnt10B, β-catenin, Runx2 and osterix was increased following exposure to LMHF vibration. Taken together, the findings of this study indicate that LMHF vibration promotes the adhesion and the osteogenic differentiation of BMSCs on HA-coated surfaces in vitro, and LMHF vibration may directly induce osteogenesis by activating the Wnt/β‑catenin signaling pathway. These data suggest that LMHF vibration enhances the osseointegration of bone to a HA-coated implant, and provide a scientific foundation for improving bone-implant osseointegration through the application of LMHF vibration.

Vibrational stimulation induces osteoblast differentiation and the upregulation of osteogenic gene expression in vitro

Vibrational stimulation is an accepted non-invasive method used to improve bone remodeling. However, the underlying mechanisms of this phenomenon remain unclear. In this study, we developed a new vibration-loading system to apply vibrational stimulation to cells based on a previously reported in vivo study. We hypothesized that osteoblasts respond to vibrational strain by expressing osteogenic marker genes, such as alkaline-phosphatase (ALP), Runx2, and Osterix. To test our hypothesis, we developed a vibration-loading system to apply a precise vibrational force to an osteoblast culture on a silicone membrane. The system regulated frequency and acceleration of the vibration, and strain on the silicone membrane culture surface was measured using the strain gauge method. After vibrational stimulation, cellular gene expression was analyzed using real-time polymerase chain reaction. We obtained clear strain signals from the culture surface at vibrational ranges of 1.0-10 m/s² acceleration and frequencies of 30, 60, and 90 Hz, respectively. The strain increased in a linear fashion, depending on the acceleration magnitude. Vibrational stimulation also significantly upregulated expression of the osteogenic marker genes Runx2, Osterix, type I collagen, and ALP. In conclusion, we developed a new vibration-loading system that can precisely regulate frequency and acceleration, and we established the presence of dynamic cellular strain on a culture surface. Our findings suggest that vibrational stimulation may directly induce osteoblast differentiation.

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.

Vibration stimuli and the differentiation of musculoskeletal progenitor cells: Review of results in vitro and in vivo

Due to the increasing burden on healthcare budgets of musculoskeletal system disease and injury, there is a growing need for safe, effective and simple therapies. Conditions such as osteoporosis severely impact on quality of life and result in hundreds of hours of hospital time and resources. There is growing interest in the use of low magnitude, high frequency vibration (LMHFV) to improve bone structure and muscle performance in a variety of different patient groups. The technique has shown promise in a number of different diseases, but is poorly understood in terms of the mechanism of action. Scientific papers concerning both the in vivo and in vitro use of LMHFV are growing fast, but they cover a wide range of study types, outcomes measured and regimens tested. This paper aims to provide an overview of some effects of LMHFV found during in vivo studies. Furthermore we will review research concerning the effects of vibration on the cellular responses, in particular for cells within the musculoskeletal system. This includes both osteogenesis and adipogenesis, as well as the interaction between MSCs and other cell types within bone tissue.

Cell based advanced therapeutic medicinal products for bone repair: Keep it simple?

The development of cell based advanced therapeutic medicinal products (ATMPs) for bone repair has been expected to revolutionize the health care system for the clinical treatment of bone defects. Despite this great promise, the clinical outcomes of the few cell based ATMPs that have been translated into clinical treatments have been far from impressive. In part, the clinical outcomes have been hampered because of the simplicity of the first wave of products. In response the field has set-out and amassed a plethora of complexities to alleviate the simplicity induced limitations. Many of these potential second wave products have remained "stuck" in the development pipeline. This is due to a number of reasons including the lack of a regulatory framework that has been evolving in the last years and the shortage of enabling technologies for industrial manufacturing to deal with these novel complexities. In this review, we reflect on the current ATMPs and give special attention to novel approaches that are able to provide complexity to ATMPs in a straightforward manner. Moreover, we discuss the potential tools able to produce or predict 'goldilocks' ATMPs, which are neither too simple nor too complex.

Revealing cytokine-induced changes in the extracellular matrix with secondary ion mass spectrometry

Cell-secreted matrices (CSMs), where extracellular matrix (ECM) deposited by monolayer cell cultures is decellularized, have been increasingly used to produce surfaces that may be reseeded with cells. Such surfaces are useful to help us understand cell-ECM interactions in a microenvironment closer to the in vivo situation than synthetic substrates with adsorbed proteins. We describe the production of CSMs from mouse primary osteoblasts (mPObs) exposed to cytokine challenge during matrix secretion, mimicking in vivo inflammatory environments. Time-of-flight secondary ion mass spectrometry data revealed that CSMs with cytokine challenge at day 7 or 12 of culture can be chemically distinguished from one another and from untreated CSM using multivariate analysis. Comparison of the differences with reference spectra from adsorbed protein mixtures points towards cytokine challenge resulting in a decrease in collagen content. This is supported by immunocytochemical and histological staining, demonstrating a 44% loss of collagen mass and a 32% loss in collagen I coverage. CSM surfaces demonstrate greater cell adhesion than adsorbed ECM proteins. When mPObs were reseeded onto cytokine-challenged CSMs they exhibited reduced adhesion and elongated morphology compared to untreated CSMs. Such changes may direct subsequent cell fate and function, and provide insights into pathological responses at sites of inflammation.

Acoustic-frequency vibratory stimulation regulates the balance between osteogenesis and adipogenesis of human bone marrow-derived mesenchymal stem cells

Osteoporosis can be associated with the disordered balance between osteogenesis and adipogenesis of bone marrow-derived mesenchymal stem cells (BM-MSCs). Although low-frequency mechanical vibration has been demonstrated to promote osteogenesis, little is known about the influence of acoustic-frequency vibratory stimulation (AFVS). BM-MSCs were subjected to AFVS at frequencies of 0, 30, 400, and 800 Hz and induced toward osteogenic or adipogenic-specific lineage. Extracellular matrix mineralization was determined by Alizarin Red S staining and lipid accumulation was assessed by Oil Red O staining. Transcript levels of osteogenic and adipogenic marker genes were evaluated by real-time reverse transcription-polymerase chain reaction. Cell proliferation of BM-MSCs was promoted following exposure to AFVS at 800 Hz. Vibration at 800 Hz induced the highest level of calcium deposition and significantly increased mRNA expression of COL1A1, ALP, RUNX2, and SPP1. The 800 Hz group downregulated lipid accumulation and levels of adipogenic genes, including FABP4, CEBPA, PPARG, and LEP, while vibration at 30 Hz supported adipogenesis. BM-MSCs showed a frequency-dependent response to acoustic vibration. AFVS at 800 Hz was the most favorable for osteogenic differentiation and simultaneously suppressed adipogenesis. Thus, acoustic vibration could potentially become a novel means to prevent and treat osteoporosis.

Low-magnitude high-frequency vibration enhances gene expression related to callus formation, mineralization and remodeling during osteoporotic fracture healing in rats

Low magnitude high frequency vibration (LMHFV) has been shown to improve anabolic and osteogenic responses in osteoporotic intact bones and during osteoporotic fracture healing; however, the molecular response of LMHFV during osteoporotic fracture healing has not been investigated. It was hypothesized that LMHFV could enhance osteoporotic fracture healing by regulating the expression of genes related to chondrogenesis (Col-2), osteogenesis (Col-1) and remodeling (receptor activator for nuclear factor- κ B ligand (RANKL) and osteoproteger (OPG)). In this study, the effects of LMHFV on both osteoporotic and normal bone fracture healing were assessed by endpoint gene expressions, weekly radiographs, and histomorphometry at weeks 2, 4 and 8 post-treatment. LMHFV enhanced osteoporotic fracture healing by up-regulating the expression of chondrogenesis-, osteogenesis- and remodeling-related genes (Col-2 at week 4 (p=0.008), Col-1 at week 2 and 8 (p<0.001 and p=0.008) and RANKL/OPG at week 8 (p=0.045)). Osteoporotic bone had a higher response to LMHFV than normal bone and showed significantly better results as reflected by increased expression of Col-2 and Col-1 at week 2 (p<0.001 for all), larger callus width at week 2 (p=0.001), callus area at week 1 and 5(p<0.05 for all) and greater relative area of osseous tissue (p=0.002) at week 8. This study helps to understand how LMHFV regulates gene expression of callus formation, mineralization and remodeling during osteoporotic fracture healing.

Gene expression responses to mechanical stimulation of mesenchymal stem cells seeded on calcium phosphate cement

INTRODUCTION

The aim of the study reported here was to investigate the molecular responses of human mesenchymal stem cells (MSC) to loading with a model that attempts to closely mimic the physiological mechanical loading of bone, using monetite calcium phosphate (CaP) scaffolds to mimic the biomechanical properties of bone and a bioreactor to induce appropriate load and strain.

METHODS

Human MSCs were seeded onto CaP scaffolds and subjected to a pulsating compressive force of 5.5±4.5 N at a frequency of 0.1 Hz. Early molecular responses to mechanical loading were assessed by microarray and quantitative reverse transcription-polymerase chain reaction and activation of signal transduction cascades was evaluated by western blotting analysis.

RESULTS

The maximum mechanical strain on cell/scaffolds was calculated at around 0.4%. After 2 h of loading, a total of 100 genes were differentially expressed. The largest cluster of genes activated with 2 h stimulation was the regulator of transcription, and it included FOSB. There were also changes in genes involved in cell cycle and regulation of protein kinase cascades. When cells were rested for 6 h after mechanical stimulation, gene expression returned to normal. Further resting for a total of 22 h induced upregulation of 63 totally distinct genes that were mainly involved in cell surface receptor signal transduction and regulation of metabolic and cell division processes. In addition, the osteogenic transcription factor RUNX-2 was upregulated. Twenty-four hours of persistent loading also markedly induced osterix expression. Mechanical loading resulted in upregulation of Erk1/2 phosphorylation and the gene expression study identified a number of possible genes (SPRY2, RIPK1, SPRED2, SERTAD1, TRIB1, and RAPGEF2) that may regulate this process.

CONCLUSION

The results suggest that mechanical loading activates a small number of immediate-early response genes that are mainly associated with transcriptional regulation, which subsequently results in activation of a wider group of genes including those associated with osteoblast proliferation and differentiation. The results provide a valuable insight into molecular events and signal transduction pathways involved in the regulation of MSC osteogenic differentiation in response to a physiological level of mechanical stimulation.

Impact of extracellular matrix derived from osteoarthritis subchondral bone osteoblasts on osteocytes: role of integrinβ1 and focal adhesion kinase signaling cues

INTRODUCTION

Our recent study indicated that subchondral bone pathogenesis in osteoarthritis (OA) is associated with osteocyte morphology and phenotypic abnormalities. However, the mechanism underlying this abnormality needs to be identified. In this study we investigated the effect of extracellular matrix (ECM) produced from normal and OA bone on osteocytic cells function.

METHODS

De-cellularized matrices, resembling the bone provisional ECM secreted from primary human subchondral bone osteoblasts (SBOs) of normal and OA patients were used as a model to study the effect on osteocytic cells. Osteocytic cells (MLOY4 osteocyte cell line) cultured on normal and OA derived ECMs were analyzed by confocal microscopy, scanning electron microscopy (SEM), cell attachment assays, zymography, apoptosis assays, qRT-PCR and western blotting. The role of integrinβ1 and focal adhesion kinase (FAK) signaling pathways during these interactions were monitored using appropriate blocking antibodies.

RESULTS

The ECM produced by OA SBOs contained less mineral content, showed altered organization of matrix proteins and matrix structure compared with the matrices produced by normal SBOs. Culture of osteocytic cells on these defective OA ECM resulted in a decrease of integrinβ1 expression and the de-activation of FAK cell signaling pathway, which subsequently affected the initial osteocytic cell's attachment and functions including morphological abnormalities of cytoskeletal structures, focal adhesions, increased apoptosis, altered osteocyte specific gene expression and increased Matrix metalloproteinases (MMP-2) and -9 expression.

CONCLUSION

This study provides new insights in understanding how altered OA bone matrix can lead to the abnormal osteocyte phenotypic changes, which is typical in OA pathogenesis.

Multiscale analysis of changes in an anisotropic collagen gel structure by culturing osteoblasts

Mimicking the complicated anisotropic structures of a native tissue is extremely important in tissue engineering. In a previous study, we developed an anisotropic collagen gel scaffold (ACGS) having a hierarchical structure and a properties gradient. In this study, our objective was to see how cells remodel the scaffolds through the cells-ACGS interaction. For this purpose, we cultured osteoblastic cells on ACGS, which we regarded as a model system for the cells-extracellular matrix (cell-ECM) interaction. Changes in the ACGS-cell composites structure by cell-ECM interactions was investigated from a macroscopic level to a microscopic level. Osteoblastic cells were also cultured on an isotropic collagen gel (ICGS) as a control. During the cultivation, mechanical stimuli were applied to collagen-cell composites for adequate matrix remodeling. Confocal laser scanning microscope (CLSM) was used to observe macroscopic changes in the ACGS-cell composite structure by osteoblastic cells. Small-angle X-ray scattering (SAXS) measurements were performed to characterize microscopic structural changes in the composites. Macroscopic observations using CLSM revealed that osteoblastic cells remained only in the diluted phase in ACGS and they collected collagen fibrils or formed a toroidal structure, depending on the depth from the ACGS surface in the tubular diluted phase. The cells were uniformly distributed in ICGS. SAXS analysis suggests that collagen fibrils were remodeled by osteoblastic cells, and this remodeling process would be affected by the structure difference between ACGS and ICGS. These results suggest that we directly regulate cell-ECM interaction by the unique anisotropic and hierarchical structure of ACGS. The cell-gel composite presented in this study would promise an efficient scaffold material in tissue engineering.

The potential benefits and inherent risks of vibration as a non-drug therapy for the prevention and treatment of osteoporosis

The delivery of mechanical signals to the skeleton using vibration is being considered as a non-drug treatment of osteoporosis. Delivered over a range of magnitudes and frequencies, vibration has been shown to be both anabolic and anti-catabolic to the musculoskeletal tissues, yet caution must be emphasized as these mechanical signals, particularly chronic exposure to higher intensities, is a known pathogen to many physiological systems. In contrast, accumulating preclinical and clinical evidence indicates that low intensity vibration (LIV) improves bone quality through regulating the activity of cells responsible for bone remodeling, as well as biasing the differentiation fate of their mesenchymal and hematopoietic stem cell progenitors. In vitro studies provide insights into the biologic mechanisms of LIV, and indicate that cells respond to these low magnitude signals through a distinct mechanism driven not by matrix strain but acceleration. These cell, animal, and human studies may represent the foundation of a safe, non-drug means to protect and improve the musculoskeletal system of the elderly, injured, and infirmed.

Stimulation of sub-sonic vibration promotes the differentiation of adipose tissue-derived mesenchymal stem cells into neural cells

AIMS

Adipose tissue-derived stem cells (AT-MSCs) have been proposed as a new source for nervous tissue damage due to their capacity of neural differentiation potential including neurons, oligodendrocytes and astrocytes. Recently, many studies have demonstrated that sub-sonic vibration (SSV) is an effective cell differentiation method but there have been no studies on the effect of SSV about AT-MSC differentiation into neural-like cells in vitro. Therefore, we examined the effect of SSV on AT-MSCs to investigate the differentiation potential of neural-like cells.

MAIN METHODS

We assessed the changes in AT-MSCs by SSV during 4 days at 10, 20, 30 and 40 Hz (1.0 V). After stimulation, they were analyzed by RT-PCR, Western blot and immunohistological analysis using neural cell type-specific genes and antibodies. Further, to confirm the neural differentiation, we investigated adipogenic genes for RT-PCR analysis. For a mechanism study, we analyzed activation levels in time course of ERK phosphorylation after SSV.

KEY FINDINGS

After 4-day SSV exposure, we observed morphological changes of AT-MSCs. Further, SSV induced gene/protein levels of neural markers while inhibiting adipogenesis and they were mainly upregulated at 30 Hz. In addition, phosphorylated ERK level was increased in a time-dependent manner upon 30 Hz SSV for 6h.

SIGNIFICANCE

These results demonstrated that SSV affects AT-MSCs differentiation potential and 30 Hz SSV affected neural differentiation on AT-MSCs.

The adhesion and proliferation of bone marrow-derived mesenchymal stem cells promoted by nanoparticle surface

This study's aim consists of evaluating the adhesion and proliferation of mesenchymal stem cells (MSCs) derived from rat bone marrow on nanoparticle Titanium (Ti) surface. Hence, passage 3 MSCs were, respectively, seeded on nanoparticle Ti and pure Ti surfaces and then cultured for 32 h. Cell morphology and viability were separately examined by scanning electron microscopy and 3-(4,5-dimethylthiazsol-2-yl)-2,5-diphenyltetrazolium bromide assay. Moreover, the mitotic rate of the attached MSCs was observed through immunocytochemistry. The real-time polymerase chain reaction was applied to determine the adhesion-associated messenger ribonucleic acid (mRNA), CD44 gene encoding variant isoform 6 (CD44 V6), and the integrinβ1 level. The results showed that MSCs performed better in faster extension on the nanoparticle Ti surface than on the pure Ti surface after culturing for 4 h, and were quicker in fusion patterns after 16 h. Furthermore, cell viability was significantly increased on the nanoparticle Ti surface compared to that of the pure Ti surface 16 h after initial seeding (p < 0.05), and the mitotic rate of attached MSCs on the nanoparticle Ti surface was higher than that on the pure Ti surface after 32 h (p < 0.05). More interestingly, the CD44 V6 and integrinβ1 mRNA in the nanoparticle Ti surface group expressed higher than that in the pure Ti surface group after 4 h (p < 0.05), and positive correlation between CD44 V6 and integrinβ1 was found through statistical analysis (correlation coefficient r (s) = 0.98, p < 0.05). Our study's result indicates that a nanoparticle Ti surface can significantly promote the adhesion and proliferation of MSCs, and also improve the bioactivity of Ti surface.

The differentiation of human adipose-derived stem cells (hASCs) into osteoblasts is promoted by low amplitude, high frequency vibration treatment

Several studies have demonstrated that tissue culture conditions influence the differentiation of human adipose-derived stem cells (hASCs). Recently, studies performed on SAOS-2 and bone marrow stromal cells (BMSCs) have shown the effectiveness of high frequency vibration treatment on cell differentiation to osteoblasts. The aim of this study was to evaluate the effects of low amplitude, high frequency vibrations on the differentiation of hASCs toward bone tissue. In view of this goal, hASCs were cultured in proliferative or osteogenic media and stimulated daily at 30Hz for 45min for 28days. The state of calcification of the extracellular matrix was determined using the alizarin assay, while the expression of extracellular matrix and associated mRNA was determined by ELISA assays and quantitative RT-PCR (qRT-PCR). The results showed the osteogenic effect of high frequency vibration treatment in the early stages of hASC differentiation (after 14 and 21days). On the contrary, no additional significant differences were observed after 28days cell culture. Transmission Electron Microscopy (TEM) images performed on 21day samples showed evidence of structured collagen fibers in the treated samples. All together, these results demonstrate the effectiveness of high frequency vibration treatment on hASC differentiation toward osteoblasts.

Different effects of intermittent and continuous fluid shear stresses on osteogenic differentiation of human mesenchymal stem cells

A reasonable mechanical microenvironment similar to the bone microenvironment in vivo is critical to the formation of engineering bone tissues. As fluid shear stress (FSS) produced by perfusion culture system can lead to the osteogenic differentiation of human mesenchymal stem cells (hMSCs), it is widely used in studies of bone tissue engineering. However, effects of FSS on the differentiation of hMSCs largely depend on the FSS application manner. It is interesting how different FSS application manners influence the differentiation of hMSCs. In this study, we examined the effects of intermittent FSS and continuous FSS on the osteogenic differentiation of hMSCs. The phosphorylation level of ERK1/2 and FAK is measured to investigate the effects of different FSS application manners on the activation of signaling molecules. The results showed that intermittent FSS could promote the osteogenic differentiation of hMSCs. The expression level of osteogenic genes and the alkaline phosphatase (ALP) activity in cells under intermittent FSS application were significantly higher than those in cells under continuous FSS application. Moreover, intermittent FSS up-regulated the activity of ERK1/2 and FAK. Our study demonstrated that intermittent FSS is more effective to induce the osteogenic differentiation of hMSCs than continuous FSS.

The effects of vibration loading on adipose stem cell number, viability and differentiation towards bone-forming cells

Mechanical stimulation is an essential factor affecting the metabolism of bone cells and their precursors. We hypothesized that vibration loading would stimulate differentiation of human adipose stem cells (hASCs) towards bone-forming cells and simultaneously inhibit differentiation towards fat tissue. We developed a vibration-loading device that produces 3g peak acceleration at frequencies of 50 and 100 Hz to cells cultured on well plates. hASCs were cultured using either basal medium (BM), osteogenic medium (OM) or adipogenic medium (AM), and subjected to vibration loading for 3 h d(-1) for 1, 7 and 14 day. Osteogenesis, i.e. differentiation of hASCs towards bone-forming cells, was analysed using markers such as alkaline phosphatase (ALP) activity, collagen production and mineralization. Both 50 and 100 Hz vibration frequencies induced significantly increased ALP activity and collagen production of hASCs compared with the static control at 14 day in OM. A similar trend was detected for mineralization, but the increase was not statistically significant. Furthermore, vibration loading inhibited adipocyte differentiation of hASCs. Vibration did not affect cell number or viability. These findings suggest that osteogenic culture conditions amplify the stimulatory effect of vibration loading on differentiation of hASCs towards bone-forming cells.

Decellularized matrices for tissue engineering

IMPORTANCE OF THE FIELD

Biomimetic scaffolds and substrates of extracellular matrices (ECMs) play an important role in the regulation of cell function and in the guidance of new tissue regeneration, as an ECM has the intrinsic cues necessary to communicate with and dictate to cells.

AREAS COVERED IN THIS REVIEW

This paper reviews the latest developments in ECM scaffolds and substrates obtained from decellularized tissues, organs or cultured cells and their application in tissue engineering. The ECM composition, structure, interaction with surrounding cells, preparation method and usage in the regeneration of various tissues and organs are summarised.

WHAT THE READER WILL GAIN

The advantages and challenges of decellularized matrices are highlighted.

TAKE HOME MESSAGE

Similarity in the composition, microstructure and biomechanical properties of the decellularized scaffolds and substrates to those of the native tissues and organs maximizes the promotion effect in the regeneration of both structural and functional tissues and organs. Simple tissues as well as complicated organs have been decellularized and decellularization methods have been optimized to completely remove the cellular components while keeping the ECM intact.

The effects of mechanical loading on mesenchymal stem cell differentiation and matrix production

Mesenchymal stem cells or stromal cells (MSCs) have the potential to be used therapeutically in tissue engineering and regenerative medicine to replace or restore the function of damaged tissues. Therefore, considerable effort has been ongoing in the research community to optimize culture conditions for predifferentiation of MSCs. All mesenchymal tissues are subjected to mechanical forces in vivo and all fully differentiated mesenchymal lineage cells respond to mechanical stimulation in vivo and in vitro. Therefore, it is not surprising that MSCs are highly mechanosensitive. We present a summary of current methods of mechanical stimulation of MSCs and an overview of the outcomes of the different mechanical culture techniques tested. Tissue engineers and stem cell researchers should be able to harness this mechanosensitivity to modulate MSC differentiation and matrix production; however, more research needs to be undertaken to understand the complex interactions between the mechanosensitive and biochemically stimulated differentiation pathways.