The effect of ultrasound stimulation on the gene and protein expression of chondrocytes seeded in chitosan scaffolds

GelMA-glycol chitosan hydrogels for cartilage regeneration: The role of uniaxial mechanical stimulation in enhancing mechanical, adhesive, and biochemical properties

Untreated osteochondral defects are a leading cause of osteoarthritis, a condition that places a heavy burden on both patients and orthopedic surgeons. Although tissue engineering has shown promise for creating mechanically similar cartilage-like constructs, their integration with cartilage remains elusive. Therefore, a formulation of biodegradable, biocompatible biomaterial with sufficient mechanical and adhesive properties for cartilage repair is required. To accomplish this, we prepared biocompatible, photo-curable, mechanically robust, and highly adhesive GelMA-glycol chitosan (GelMA-GC) hydrogels. GelMA-GC hydrogels had a modulus of 283 kPa and provided a biocompatible environment (>70% viability of embedded chondrocytes) in long-term culture within a bovine cartilage ring. The adhesive strength of bovine chondrocyte-laden GelMA-GC hydrogel to bovine cartilage increased from 38 to 52 kPa over four weeks of culture. Moreover, intermittent uniaxial mechanical stimulation enhanced the adhesive strength to ∼60 kPa, indicating that the cartilage-hydrogel integration could remain secure and functional under dynamic loading conditions. Furthermore, gene expression data and immunofluorescence staining revealed the capacity of chondrocytes in GelMA-GC hydrogel to synthesize chondrogenic markers (COL2A1 and ACAN), suggesting the potential for tissue regeneration. The promising in vitro results of this work motivate further exploration of the potential of photo-curable GelMA-GC bioadhesive hydrogels for cartilage repair and regeneration.

Effects and mechanotransduction pathways of therapeutic ultrasound on healthy and osteoarthritic chondrocytes: a systematic review of in vitro studies

OBJECTIVE

To investigate the effects and mechanotransduction pathways of therapeutic ultrasound on chondrocytes.

METHOD

PubMed, EMBASE and Web of Science databases were searched up to 19^th September 2021 to identify in vitro studies exploring ultrasound to stimulate chondrocytes for osteoarthritis (OA) treatment. Study characteristics, ultrasound parameters, in vitro setup, and mechanotransduction pathways were collected. Risk of bias was judged using the Risk of Bias Assessment for Non-randomized Studies (RoBANS) tool.

RESULTS

Thirty-one studies were included comprising healthy and OA chondrocytes and explants. Most studies had high risk of performance, detection and pseudoreplication bias due to lack of temperature control, setup calibration, inadequate semi-quantitatively analyzes and independent experiments. Ultrasound was applied to the culture plate via acoustic gel, water bath or culture media. Regardless of the setup used, ultrasound stimulated the cartilage production and suppressed its degradation, although the effect size was nonsignificant. Ultrasound inhibited p38, c-Jun N-terminal kinases (JNK) and factor nuclear kappa B (NFκB) pathways in OA chondrocytes to reduce apoptosis, inflammation and matrix degradation, while triggered phosphoinositide-3-kinase/akt (PI3K/Akt), extracellular signal-regulated kinase (ERK), p38 and JNK pathways in healthy chondrocytes to promote matrix synthesis.

CONCLUSION

The included studies suggest that ultrasound application induces therapeutic effects on chondrocytes. However, these results should be interpreted with caution because high risk of performance, detection and pseudoreplication bias were identified. Future studies should explore the application of ultrasound on human OA chondrocytes cultures to potentiate the applicability of ultrasound towards cartilage regeneration of knee with OA.

Dual-frequency ultrasound enhances functional neuron differentiation from neural stem cells by modulating Ca2+ dynamics and the ERK1/2 signaling pathway

Our previous study demonstrated that ultrasound is able to promote differentiation on neural stem cells (NSCs), and dual-frequency ultrasound promotes this effect due to enhanced acoustic cavitation compared with single-frequency ultrasound. However, the underlying biological reasons have not been well disclosed. The purpose of this study was to investigate the underlying bioeffects, mechanisms and signaling pathways of dual-frequency ultrasound on NSC differentiation. The morphology, neurite outgrowth, and differentiation percentages were investigated under various dual-frequency simulation parameters with exposure periods varying from 5 to 15 min. Morphological observations identified that dual-frequency ultrasound stimulation promoted ultrasound dose-dependent neurite outgrowth. In particular, cells exposed for 10 min/2 days showed optimal neurite outgrowth and neuron differentiation percentages. In addition, live cell calcium images showed that dual-frequency ultrasound enhanced the internal calcium content of the cells, and calcium ions entering cells from the extracellular environment could be observed. Dual frequency ultrasound exposure enhanced extracellular calcium influx and upregulated extracellular signal-regulated kinases 1/2 (ERK1/2) expression. Observations from immunostaining and protein expression examinations also identified that dual-frequency ultrasound promoted brain-derived neurotrophic factor (BDNF) secretion from astrocytes derived from NSCs. In summary, evidence supports that dual-frequency ultrasound effectively enhances functional neuron differentiation via calcium channel regulation via the downstream ERK1/2 pathway and promotes BDNF secretion to serve as feedback to cascade neuron differentiation. The results may provide an alternative for cell-based therapy in brain injury.

Landscape of Cellular Bioeffects Triggered by Ultrasound-Induced Sonoporation

Sonoporation is the process of transient pore formation in the cell membrane triggered by ultrasound (US). Numerous studies have provided us with firm evidence that sonoporation may assist cancer treatment through effective drug and gene delivery. However, there is a massive gap in the body of literature on the issue of understanding the complexity of biophysical and biochemical sonoporation-induced cellular effects. This study provides a detailed explanation of the US-triggered bioeffects, in particular, cell compartments and the internal environment of the cell, as well as the further consequences on cell reproduction and growth. Moreover, a detailed biophysical insight into US-provoked pore formation is presented. This study is expected to review the knowledge of cellular effects initiated by US-induced sonoporation and summarize the attempts at clinical implementation.

Regenerative Effect of Low-Intensity Pulsed Ultrasound and Platelet-Rich Plasma on the Joint Friction and Biomechanical Properties of Cartilage: A Non-traumatic Osteoarthritis Model in the Guinea Pig

This study was aimed at investigating the effects of platelet-rich plasma (PRP) and low-intensity pulsed ultrasound (LIPUS) on the joint friction parameters and biomechanical properties of articular cartilage in a non-traumatic knee osteoarthritis (OA) model. Fifty adult male Dunkin Hartley guinea pigs were randomly divided into five groups: control, OA60, OA + US, OA + PRP and OA + US + PRP). Non-traumatic knee OA was induced with a single dose of 3 mg of mono-iodoacetate (MIA) by intra-articular injection. Intra-articular PRP was injected twice in the OA + PRP and OA + US + PRP groups. LIPUS was delivered in 10 sessions in the OA + US and OA + US + PRP groups. By use of the pendulum free oscillation test, joint friction (coefficient of friction) was measured. In addition, the instantaneous elastic modulus and aggregate modulus were measured using the stress-relaxation test. MIA injection decreased cartilage thickness, instantaneous elastic modulus and aggregate modulus, and increased joint friction. The friction coefficients in the OA + US and OA + US + PRP groups reached near-normal values, and there was no significant difference compared with the control group (p = 0.232 and p = 0.459, respectively). The instantaneous elastic modulus and aggregate modulus in the OA + US group increased significantly compared with the OA + PRP group (p < 0.05). It seems that both LIPUS and PRP injection effectively improved joint lubrication, but LIPUS was superior to PRP in improving the mechanical properties of the articular cartilage.

The Challenge of Cartilage Integration: Understanding a Major Barrier to Chondral Repair

Articular cartilage defects caused by injury frequently lead to osteoarthritis, a painful and costly disease. Despite widely used surgical methods to treat articular cartilage defects and a plethora of research into regenerative strategies as treatments, long-term clinical outcomes are not satisfactory. Failure to integrate repair tissue with native cartilage is a recurring issue in surgical and tissue-engineered strategies, seeing eventual degradation of the regenerated or surrounding tissue. This review delves into the current understanding of why continuous and robust integration with native cartilage is so difficult to achieve. Both the intrinsic limitations of chondrocytes to remodel injured cartilage, and the significant challenges posed by a compromised biomechanical environment are described. Recent scaffold and cell-based techniques to repair cartilage are also discussed, and limitations of existing methods to evaluate integrative repair. In particular, the importance of evaluating the mechanical integrity of the interface between native and repair tissue is highlighted as a meaningful assessment of any strategy to repair this load-bearing tissue. Impact statement The failure to integrate grafts or biomaterials with native cartilage is a major barrier to cartilage repair. An in-depth understanding of the reasons cartilage integration remains a challenge is required to inform cartilage repair strategies. In particular, this review highlights that integration of cartilage repair strategies is frequently assessed in terms of the continuity of tissue, but not the mechanical integrity. Given the load-bearing nature of cartilage, evaluating integration in terms of interfacial strength is essential to assessing the potential success of cartilage repair methods.

Harnessing Mechanobiology for Tissue Engineering

A primary challenge in tissue engineering is to recapitulate both the structural and functional features of whole tissues and organs. In vivo, patterning of the body plan and constituent tissues emerges from the carefully orchestrated interactions between the transcriptional programs that give rise to cell types and the mechanical forces that drive the bending, twisting, and extensions critical to morphogenesis. Substantial recent progress in mechanobiology-understanding how mechanics regulate cell behaviors and what cellular machineries are responsible-raises the possibility that one can begin to use these insights to help guide the strategy and design of functional engineered tissues. In this perspective, we review and propose the development of different approaches, from providing appropriate extracellular mechanical cues to interfering with cellular mechanosensing machinery, to aid in controlling cell and tissue structure and function.

The Application of Bioreactors for Cartilage Tissue Engineering: Advances, Limitations, and Future Perspectives

Tissue engineering (TE) has brought new hope for articular cartilage regeneration, as TE can provide structural and functional substitutes for native tissues. The basic elements of TE involve scaffolds, seeded cells, and biochemical and biomechanical stimuli. However, there are some limitations of TE; what most important is that static cell culture on scaffolds cannot simulate the physiological environment required for the development of natural cartilage. Recently, bioreactors have been used to simulate the physical and mechanical environment during the development of articular cartilage. This review aims to provide an overview of the concepts, categories, and applications of bioreactors for cartilage TE with emphasis on the design of various bioreactor systems.

Biomaterial Stiffness Guides Cross-talk between Chondrocytes: Implications for a Novel Cellular Response in Cartilage Tissue Engineering

The exquisite cartilage architecture maintains an orderly dynamic equilibrium as a result of the interplay between chondrocyte functions and the unique extracellular matrix (ECM) microenvironment. Numerous studies have demonstrated that extracellular cues, including topological, mechanical, and biochemical properties of the underlying substrates, dictate the chondrocyte behaviors. Consequently, developing advanced biomaterials with the desired characteristics which could achieve the biointerface between cells and the surrounded matrix close to the physiological conditions becomes a great hotspot in bioengineering. However, how the substrate stiffness influences the intercellular communication among chondrocytes is still poorly reported. We used polydimethylsiloxane with varied stiffnesses as a cell culture substrate to elucidate a novel cell-to-cell communication in a collective of chondrocytes. First, morphological images collected using scanning electron microscopy revealed that the tunable substrate stiffnesses directed the changes in intercellular links among chondrocytes. Next, fibronectin, which played a vital role in the connection of ECM components or linkage of ECM to chondrocytes, was shown to be gathered along cell-cell contact areas and was changed with the tunable substrate stiffnesses. Furthermore, transmembrane junctional proteins including connexin 43 (Cx43) and pannexin 1 (Panx1), which are responsible for gap junction formation in cell-to-cell communication, were mediated by the tunable substrate stiffnesses. Finally, through a scrape loading/dye transfer assay, we revealed cell-to-cell communication changes in a living chondrocyte population in response to the tunable substrate stiffnesses via cell-to-cell fluorescent molecule transport. Taken together, this novel cell-to-cell communication regulated by biomaterial stiffness could help us to increase the understanding of cell behaviors under biomechanical control and may ultimately lead to refining cell-based cartilage tissue engineering.

Continuous Low-Intensity Ultrasound Promotes Native-to-Native Cartilage Integration

Failure of the host/graft interface to integrate impedes the success of cartilage repair protocols. Continuous low-intensity ultrasound (cLIUS) at the resonant frequency of 5 MHz is proposed as a treatment modality for promoting native-to-native cartilage integration in vitro. Cylindrical incisions (4 mm) simulating chondral discontinuity were made in bovine cartilage and osteochondral explants, and maintained under cLIUS stimulation (14 kPa [5 MHz, 2.5 Vpp], 20 min, four times/day) for 28 days. Incised cartilage and osteochondral explants were categorized into three study groups; Group I: cLIUS was applied immediately upon incision; Group II: cLIUS was applied after 14 days following incision; Group-III: after 14 days following incision, explants were treated with 0.1% hyaluronidase and 30 U/mL collagenase VII. As a separate study group, incised osteochondral explants were treated immediately with cLIUS at a nonresonant frequency of 2 MHz (14 kPa [2 MHz, 6 Vpp], 20 min, four times/day). Cellular migration was analyzed by scratch assays, and by visualizing migrating cells into the hydrogel core of cartilage/hydrogel constructs. Explants under cLIUS (5 MHz) displayed higher percent apposition along with gap closures when compared with untreated controls and explants treated with cLIUS at 2 MHz. cLIUS (5 MHz)-treated explants were immunopositive for type II collagen. The strength of native-to-native cartilage integration was higher (p = 0.005) in cLIUS-treated cartilage explants at 0.19 ± 0.08 MPa as compared with 0.05 ± 0.03 MPa in untreated controls. Enhanced cartilage phenotype coupled with increased cellular migration were noted under cLIUS (5 MHz), alluding to the observed integration between cartilage interfaces. Collectively, cLIUS at cell resonant frequency promoted integrative cartilage repair, therefore, has the potential to improve cartilage repair outcomes. Impact Statement Lack of integration between the host and graft cartilage interfaces impedes the success of cartilage repair techniques. Continuous low-intensity ultrasound (cLIUS) is documented to induce chondrogenesis and chondrocyte phenotype. However, integrative cartilage repair under cLIUS has not been evaluated. Our results demonstrated integration between cartilage interfaces, increased percent apposition, increased strength of integration, and maintenance of cartilage phenotype under cLIUS (5 MHz). Integrative repair under cLIUS (5 MHz) stemmed from enhanced migration of cells and increased expression of cartilage-specific genes, namely SOX9 and COL2A1. Thus, cLIUS has the potential to improve the outcomes of grafting protocols for cartilage repair.

The matrix environmental and cell mechanical properties regulate cell migration and contribute to the invasive phenotype of cancer cells

The minimal structural unit of a solid tumor is a single cell or a cellular compartment such as the nucleus. A closer look inside the cells reveals that there are functional compartments or even structural domains determining the overall properties of a cell such as the mechanical phenotype. The mechanical interaction of these living cells leads to the complex organization such as compartments, tissues and organs of organisms including mammals. In contrast to passive non-living materials, living cells actively respond to the mechanical perturbations occurring in their microenvironment during diseases such as fibrosis and cancer. The transformation of single cancer cells in highly aggressive and hence malignant cancer cells during malignant cancer progression encompasses the basement membrane crossing, the invasion of connective tissue, the stroma microenvironments and transbarrier migration, which all require the immediate interaction of the aggressive and invasive cancer cells with the surrounding extracellular matrix environment including normal embedded neighboring cells. All these steps of the metastatic pathway seem to involve mechanical interactions between cancer cells and their microenvironment. The pathology of cancer due to a broad heterogeneity of cancer types is still not fully understood. Hence it is necessary to reveal the signaling pathways such as mechanotransduction pathways that seem to be commonly involved in the development and establishment of the metastatic and mechanical phenotype in several carcinoma cells. We still do not know whether there exist distinct metastatic genes regulating the progression of tumors. These metastatic genes may then be activated either during the progression of cancer by themselves on their migration path or in earlier stages of oncogenesis through activated oncogenes or inactivated tumor suppressor genes, both of which promote the metastatic phenotype. In more detail, the adhesion of cancer cells to their surrounding stroma induces the generation of intracellular contraction forces that deform their microenvironments by alignment of fibers. The amplitude of these forces can adapt to the mechanical properties of the microenvironment. Moreover, the adhesion strength of cancer cells seems to determine whether a cancer cell is able to migrate through connective tissue or across barriers such as the basement membrane or endothelial cell linings of blood or lymph vessels in order to metastasize. In turn, exposure of adherent cancer cells to physical forces, such as shear flow in vessels or compression forces around tumors, reinforces cell adhesion, regulates cell contractility and restructures the ordering of the local stroma matrix that leads subsequently to secretion of crosslinking proteins or matrix degrading enzymes. Hence invasive cancer cells alter the mechanical properties of their microenvironment. From a mechanobiological point-of-view, the recognized physical signals are transduced into biochemical signaling events that guide cellular responses such as cancer progression after the malignant transition of cancer cells from an epithelial and non-motile phenotype to a mesenchymal and motile (invasive) phenotype providing cellular motility. This transition can also be described as the physical attempt to relate this cancer cell transitional behavior to a T1 phase transition such as the jamming to unjamming transition. During the invasion of cancer cells, cell adaptation occurs to mechanical alterations of the local stroma, such as enhanced stroma upon fibrosis, and therefore we need to uncover underlying mechano-coupling and mechano-regulating functional processes that reinforce the invasion of cancer cells. Moreover, these mechanisms may also be responsible for the awakening of dormant residual cancer cells within the microenvironment. Physicists were initially tempted to consider the steps of the cancer metastasis cascade as single events caused by a single mechanical alteration of the overall properties of the cancer cell. However, this general and simple view has been challenged by the finding that several mechanical properties of cancer cells and their microenvironment influence each other and continuously contribute to tumor growth and cancer progression. In addition, basement membrane crossing, cell invasion and transbarrier migration during cancer progression is explained in physical terms by applying physical principles on living cells regardless of their complexity and individual differences of cancer types. As a novel approach, the impact of the individual microenvironment surrounding cancer cells is also included. Moreover, new theories and models are still needed to understand why certain cancers are malignant and aggressive, while others stay still benign. However, due to the broad variety of cancer types, there may be various pathways solely suitable for specific cancer types and distinct steps in the process of cancer progression. In this review, physical concepts and hypotheses of cancer initiation and progression including cancer cell basement membrane crossing, invasion and transbarrier migration are presented and discussed from a biophysical point-of-view. In addition, the crosstalk between cancer cells and a chronically altered microenvironment, such as fibrosis, is discussed including the basic physical concepts of fibrosis and the cellular responses to mechanical stress caused by the mechanically altered microenvironment. Here, is highlighted how biophysical approaches, both experimentally and theoretically, have an impact on classical hallmarks of cancer and fibrosis and how they contribute to the understanding of the regulation of cancer and its progression by sensing and responding to the physical environmental properties through mechanotransduction processes. Finally, this review discusses various physical models of cell migration such as blebbing, nuclear piston, protrusive force and unjamming transition migration modes and how they contribute to cancer progression. Moreover, these cellular migration modes are influenced by microenvironmental perturbances such as fibrosis that can induce mechanical alterations in cancer cells, which in turn may impact the environment. Hence, the classical hallmarks of cancer need to be refined by including biomechanical properties of cells, cell clusters and tissues and their microenvironment to understand mechano-regulatory processes within cancer cells and the entire organism.

Dual-Frequency Ultrasound Induces Neural Stem/Progenitor Cell Differentiation and Growth Factor Utilization by Enhancing Stable Cavitation

Neural stem/progenitor cells (NSPCs) have the potential to serve as the basic materials for treating severe neural diseases and injuries. Ultrasound exposure is an effective therapy for nonunion fractures and healing fresh wounds through an easy and noninvasive application. According to the results of our preliminary study, low-intensity ultrasound (LIUS) promotes the attachment and differentiation of NSPCs. However, the parameters of and mechanisms by which LIUS induces NSPC differentiation remain unclear. To the best of our knowledge, no published studies have reported and compared the biological effects of dual-frequency and single-frequency LIUS on NSPCs. The purpose of this study is to systematically compare several LIUS parameters, including single-frequency, single-transducer dual-frequency ultrasound, burst, and continuous cycling stimulation at several intensities. Furthermore, synergistic effects of single-/dual-frequency LIUS combined with neural growth factor addition on NSPCs were also evaluated. Based on the results of the cytotoxicity assay, low-intensity (40 kPa) ultrasound does not damage NSPCs compared with that observed in the control group. The morphology and immunostaining results show that all experimental groups exposed to ultrasound exhibit neurite outgrowth and NSPC differentiation. In particular, dual-frequency ultrasound promotes NSPCs differentiation to a greater extent than single-frequency ultrasound. In addition, more complicated and denser neural networks are observed in the dual-frequency group. Neural growth factor addition increased the percentage of neurons formed, particularly in the groups stimulated with ultrasound. Among these groups, the dual-frequency group exhibited significant differences in the percentage of differentiated neurons compared with the single-frequency group. This study may the first to prove that dual-frequency LIUS exposure further enhances NSPC differentiation and the utilization of growth factors than single-frequency LIUS. Moreover, the result also revealed that dual-frequency ultrasound generated higher calcium ion influx and extended the channel opening time. A potential explanation is that dual-frequency ultrasound generates more stable cavitation than single-frequency LIUS, which may stimulate cell membrane mechanochannels and enhance calcium ion influx but does not damage them. This in vitro study may serve as a useful alternative for ultrasound therapy.

Reactive Oxygen Species Mediate Therapeutic Ultrasound-Induced, Mitogen-Activated Protein Kinase Activation in C28/I2 Chondrocytes

Low-intensity pulsed ultrasound (LIPUS) has been used for the treatment of non-healing fractures because of its therapeutic properties of stimulating enhancing endochondral bone formation. However, its mechanism of action remains unclear. In this study, we hypothesized that LIPUS activates mitogen-activated protein kinases through generation of reactive oxygen species. C28/I2 cells were stimulated with LIPUS for 10 and 20 min, while the control group was treated using a sham LIPUS transducer. Through quantitative reverse transcription polymerase chain reaction and immunoblot analyses, we determined that LIPUS application increased reactive oxygen species generation and cell viability in C28/I2 cells. There were increases in the phosphorylation level of ERK1/2 and in expression of SOX9, COL2 A1 and ACAN genes. These effects were reversed when cells were treated with diphenylene iodonium, which is known to inhibit NADPH oxidase. It was concluded that exposure of chondrocytes to LIPUS led to reactive oxygen species generation, which activated MAPK signaling and further increased chondrocyte-specific gene markers involved in chondrocyte differentiation and extracellular matrix formation.

TGF-β1-induced chondrogenesis of bone marrow mesenchymal stem cells is promoted by low-intensity pulsed ultrasound through the integrin-mTOR signaling pathway

Background

Low-intensity pulsed ultrasound (LIPUS) is a mechanical stimulus that plays a key role in regulating the differentiation of bone marrow mesenchymal stem cells (BMSCs). However, the way in which it affects the chondrogenic differentiation of BMSCs remains unknown. In this study, we aimed to investigate whether LIPUS is able to influence TGF-β1-induced chondrogenesis of BMSCs through the integrin-mechanistic target of the Rapamycin (mTOR) signaling pathway.

Methods

BMSCs were isolated from rat bone marrow and cultured in either standard or TGF-β1-treated culture medium. BMSCs were then subjected to LIPUS at a frequency of 3 MHz and a duty cycle of 20%, and integrin and mTOR inhibitors added in order to analyze their influence on cell differentiation. BMSCs were phenotypically analyzed by flow cytometry and the degree of chondrogenesis evaluated through toluidine blue staining, immunofluorescence, and immunocytochemistry. Furthermore, expression of COL2, aggrecan, SOX9, and COL1 was assessed by qRT-PCR and western blot analysis.

Results

We found that LIPUS promoted TGF-β1-induced chondrogenesis of BMSCs, represented by increased expression of COL2, aggrecan and SOX9 genes, and decreased expression of COL1. Notably, these effects were prevented following addition of integrin and mTOR inhibitors.

Conclusions

Taken together, these results indicate that mechanical stimulation combined with LIPUS promotes TGF-β1-induced chondrogenesis of BMSCs through the integrin-mTOR signaling pathway.

Applications of Tissue Engineering in Joint Arthroplasty: Current Concepts Update

Research in tissue engineering has undoubtedly achieved significant milestones in recent years. Although it is being applied in several disciplines, tissue engineering's application is particularly advanced in orthopedic surgery and in degenerative joint diseases. The literature is full of remarkable findings and trials using tissue engineering in articular cartilage disease. With the vast and expanding knowledge, and with the variety of techniques available at hand, the authors aimed to review the current concepts and advances in the use of cell sources in articular cartilage tissue engineering.

Efficacy of extracorporeal shockwave therapy and low-intensity pulsed ultrasound in a rat knee osteoarthritis model: A randomized controlled trial

OBJECTIVE

This study aims to assess the efficacy of extracorporeal shockwave therapy (ESWT) and low-intensity pulsed ultrasound (LIPUS) on osteoarthritic rat knees.

MATERIAL AND METHODS

Twenty-four rats were divided into 3 groups: group 1-control (n=8), group 2-LIPUS (n=8) and group 3-ESWT (n=8). Cartilage degeneration was provided using mono-iodo-asetate (MIA). One milligram of MIA was delivered to the right knees in group 1 and both knees in group 2 and 3. A 0.09% saline solution was delivered to the left knees in group 1 for control. Twenty-four hours after the delivery, ESWT was applied once on the right knees in the group 2 rats to the medial tibia plateu with a 1 Hz frequency and 800 impulses. LIPUS was applied to the right knees in the group 2 rats to the medial tibia plateu with a 3 mHz frequency and 40 mW/cm2 intensity for 20 minutes over a period of 15 days. Pain scores were measured with a knee bend test. Bone mineral density measurements and scintigraphic bone scans were performed. Histopathological examination was done using a modified Mankin scale.

RESULTS

There was no difference among the right knee subchondral bone osteoblastic activities (p>0.05). The left knee osteoblastic activities in the LIPUS and extracorporeal shockwave therapy (ESWT) groups were higher than those in the control group (p<0.05), but there was no difference between the LIPUS and ESWT groups. There was no difference among the groups for both knee subchondral bone BMD values (p>0.05). The modified Mankin scores of both the right and left knees of the ESWT and LIPUS groups were lower than those of the control group (p<0.05), but there was no difference between the ESWT and LIPUS groups. The pain scores of both knees of the ESWT and LIPUS groups at day 7 were higher than those of the control group (p<0.05), but there was no difference between the ESWT and LIPUS groups. There was no difference among the pain scores of the right knees at day 14 (p<0.05).

CONCLUSION

ESWT and LIPUS have systemic proliferative and regenerative effects on cartilage and tissue.

Lipid Coated Microbubbles and Low Intensity Pulsed Ultrasound Enhance Chondrogenesis of Human Mesenchymal Stem Cells in 3D Printed Scaffolds

Lipid-coated microbubbles are used to enhance ultrasound imaging and drug delivery. Here we apply these microbubbles along with low intensity pulsed ultrasound (LIPUS) for the first time to enhance proliferation and chondrogenic differentiation of human mesenchymal stem cells (hMSCs) in a 3D printed poly-(ethylene glycol)-diacrylate (PEG-DA) hydrogel scaffold. The hMSC proliferation increased up to 40% after 5 days of culture in the presence of 0.5% (v/v) microbubbles and LIPUS in contrast to 18% with LIPUS alone. We systematically varied the acoustic excitation parameters-excitation intensity, frequency and duty cycle-to find 30 mW/cm2, 1.5 MHz and 20% duty cycle to be optimal for hMSC proliferation. A 3-week chondrogenic differentiation results demonstrated that combining LIPUS with microbubbles enhanced glycosaminoglycan (GAG) production by 17% (5% with LIPUS alone), and type II collagen production by 78% (44% by LIPUS alone). Therefore, integrating LIPUS and microbubbles appears to be a promising strategy for enhanced hMSC growth and chondrogenic differentiation, which are critical components for cartilage regeneration. The results offer possibilities of novel applications of microbubbles, already clinically approved for contrast enhanced ultrasound imaging, in tissue engineering.

Cell-based tissue engineering strategies used in the clinical repair of articular cartilage

One of the most important issues facing cartilage tissue engineering is the inability to move technologies into the clinic. Despite the multitude of current research in the field, it is known that 90% of new drugs that advance past animal studies fail clinical trials. The objective of this review is to provide readers with an understanding of the scientific details of tissue engineered cartilage products that have demonstrated a certain level of efficacy in humans, so that newer technologies may be developed upon this foundation. Compared to existing treatments, such as microfracture or autologous chondrocyte implantation, a tissue engineered product can potentially provide more consistent clinical results in forming hyaline repair tissue and in filling the entirety of the defect. The various tissue engineering strategies (e.g., cell expansion, scaffold material, media formulations, biomimetic stimuli, etc.) used in forming these products, as collected from published literature, company websites, and relevant patents, are critically discussed. The authors note that many details about these products remain proprietary, not all information is made public, and that advancements to the products are continuously made. Nevertheless, by understanding the design and production processes of these emerging technologies, one can gain tremendous insight into how to best use them and also how to design the next generation of tissue engineered cartilage products.

Cell-based tissue engineering strategies used in the clinical repair of articular cartilage

One of the most important issues facing cartilage tissue engineering is the inability to move technologies into the clinic. Despite the multitude of current research in the field, it is known that 90% of new drugs that advance past animal studies fail clinical trials. The objective of this review is to provide readers with an understanding of the scientific details of tissue engineered cartilage products that have demonstrated a certain level of efficacy in humans, so that newer technologies may be developed upon this foundation. Compared to existing treatments, such as microfracture or autologous chondrocyte implantation, a tissue engineered product can potentially provide more consistent clinical results in forming hyaline repair tissue and in filling the entirety of the defect. The various tissue engineering strategies (e.g., cell expansion, scaffold material, media formulations, biomimetic stimuli, etc.) used in forming these products, as collected from published literature, company websites, and relevant patents, are critically discussed. The authors note that many details about these products remain proprietary, not all information is made public, and that advancements to the products are continuously made. Nevertheless, by understanding the design and production processes of these emerging technologies, one can gain tremendous insight into how to best use them and also how to design the next generation of tissue engineered cartilage products.

Theoretical evaluation of the acoustic field in an ultrasonic bioreactor

Ultrasound-assisted bioreactors that provide mechanical conditioning to cells have broad applicability in tissue engineering, but biological experiments with ultrasound are very sensitive to environmental conditions. A mathematical model was developed to complement experimental measurements, as well as to describe ultrasonic fields existing in regions where measurements are impossible, specifically, within microporous tissue engineering scaffolds. The model uniquely combines Biot theory to predict the ultrasonic field in the scaffold with an electromechanical transducer model to couple the mechanical stimulation experienced by cells to the external electrical input. In the specific example examined here, cells immobilized on scaffolds are subjected to different forms of ultrasonic stimulation due to the formation of standing wave fields and vertical high-pressure bands. The model confirms the sensitivity of the supplied acoustic power to the liquid level in sonobioreactors and identifies the input electrical impedance as a method of detecting resonance effects.

Inhibition of interleukin-1beta-stimulated dedifferentiation of chondrocytes via controlled release of CrmA from hyaluronic acid-chitosan microspheres

Background

The previous studies indicated that CrmA could ameliorate the interleukin-1β induced osteoarthritis. In this study, we investigated the controlled-released cytokine response modifier A (CrmA) from hyaluronic acid (HA)-chitosan (CS) microspheres to improve interleukin-1β (IL-1β)-stimulated dedifferentiation of chondrocytes.

Methods

A rat model of osteoarthritis (OA) in vitro was established using 10 ng/ml IL-1β as modulating and chondrocytes inducing agent. HA-CS-CrmA microspheres were added to the medium after IL-1β was co-cultured with freshly isolated rat chondrocytes for 48 hours. The chondrocytes viability and glycosaminoglycan (GAG) content were determined. The level of CrmA secreted was detected by Enzyme-Linked Immunosorbent Assay (ELISA). The protein levels of type II collagen, aggrecan, collagen I and IL-1β were detected using western blotting analyses.

Results

The CrmA release kinetics were characterized by an initial burst release, which was reduced to a linear release over ten days. The production of GAG and the expression of type II collagen, aggrecan significantly increased compared with the control group, while the expression of collagen I and IL-1β decreased.

Conclusions

This study demonstrated that HA-CS microspheres containing CrmA could attenuate the degeneration of articular cartilage by maintaining the phenotype of chondrocytes during culture expansion. The suppression of inflammatory cytokines activity within the joint might be one important mechanism of the action of the microspheres in the treatment of OA.

Application of an acoustofluidic perfusion bioreactor for cartilage tissue engineering

Cartilage grafts generated using conventional static tissue engineering strategies are characterised by low cell viability, suboptimal hyaline cartilage formation and, critically, inferior mechanical competency, which limit their application for resurfacing articular cartilage defects. To address the limitations of conventional static cartilage bioengineering strategies and generate robust, scaffold-free neocartilage grafts of human articular chondrocytes, the present study utilised custom-built microfluidic perfusion bioreactors with integrated ultrasound standing wave traps. The system employed sweeping acoustic drive frequencies over the range of 890 to 910 kHz and continuous perfusion of the chondrogenic culture medium at a low-shear flow rate to promote the generation of three-dimensional agglomerates of human articular chondrocytes, and enhance cartilage formation by cells of the agglomerates via improved mechanical stimulation and mass transfer rates. Histological examination and assessment of micromechanical properties using indentation-type atomic force microscopy confirmed that the neocartilage grafts were analogous to native hyaline cartilage. Furthermore, in the ex vivo organ culture partial thickness cartilage defect model, implantation of the neocartilage grafts into defects for 16 weeks resulted in the formation of hyaline cartilage-like repair tissue that adhered to the host cartilage and contributed to significant improvements to the tissue architecture within the defects, compared to the empty defects. The study has demonstrated the first successful application of the acoustofluidic perfusion bioreactors to bioengineer scaffold-free neocartilage grafts of human articular chondrocytes that have the potential for subsequent use in second generation autologous chondrocyte implantation procedures for the repair of partial thickness cartilage defects.

Effects of therapeutic ultrasound on the nucleus and genomic DNA

In recent years, data have been accumulating on the ability of ultrasound to affect at a distance inside the cell. Previous conceptions about therapeutic ultrasound were mainly based on compromising membrane permeability and triggering some biochemical reactions. However, it was shown that ultrasound can access deep to the nuclear territory resulting in enhanced macromolecular localization as well as alterations in gene and protein expression. Recently, we have reported on the occurrence of DNA double-strand breaks in different human cell lines exposed to ultrasound in vitro with some insight into the subsequent DNA damage response and repair pathways. The impact of these observed effects again sways between extremes. It could be advantageous if employed in gene therapy, wound and bone fracture-accelerated healing to promote cellular proliferation, or in cancer eradication if the DNA lesions would culminate in cell death. However, it could be a worrying sign if they were penultimate to further cellular adaptations to stresses and thus shaking the safety of ultrasound application in diagnosis and therapy. In this review, an overview of the rationale of therapeutic ultrasound and the salient knowledge on ultrasound-induced effects on the nucleus and genomic DNA will be presented. The implications of the findings will be discussed hopefully to provide guidance to future ultrasound research.

Enhanced depth-independent chondrocyte proliferation and phenotype maintenance in an ultrasound bioreactor and an assessment of ultrasound dampening in the scaffold

Chondrocyte-seeded scaffolds were cultured in an ultrasound (US)-assisted bioreactor, which supplied the cells with acoustic energy around resonance frequencies (~5.0 MHz). Polyurethane-polycarbonate (BM), chitosan (CS) and chitosan-n-butanol (CSB) based scaffolds with varying porosities were chosen and the following US regimen was employed: 15 kPa and 60 kPa, 5 min per application and 6 applications per day for 21 days. Non-stimulated scaffolds served as control. For BM scaffolds, US stimulation significantly impacted cell proliferation and depth-independent cell population density compared to controls. The highest COL2A1/COL1A1 ratios and ACAN mRNA were noted on US-treated BM scaffolds compared to controls. A similar trend was noted on US-treated cell-seeded CS and CSB scaffolds, though COL2A1/COL1A1 ratios were significantly lower compared to BM scaffolds. Expression of Sox-9 was also elevated under US and paralleled the COL2A1/COL1A1 ratio. As an original contribution, a simplified mathematical model based on Biot theory was developed to understand the propagation of the incident US wave through the scaffolds and the model analysis was connected to cellular responses. Scaffold architecture influenced the distribution of US field, with the US field being the least attenuated in BM scaffolds, thus coupling more mechanical energy into cells, and leading to increased cellular activity.

Tissue-engineered cartilage: the crossroads of biomaterials, cells and stimulating factors

Damage to cartilage represents one of the most challenging tasks of musculoskeletal therapeutics due to its limited propensity for healing and regenerative capabilities. Lack of current treatments to restore cartilage tissue function has prompted research in this rapidly emerging field of tissue regeneration of functional cartilage tissue substitutes. The development of cartilaginous tissue largely depends on the combination of appropriate biomaterials, cell source, and stimulating factors. Over the years, various biomaterials have been utilized for cartilage repair, but outcomes are far from achieving native cartilage architecture and function. This highlights the need for exploration of suitable biomaterials and stimulating factors for cartilage regeneration. With these perspectives, we aim to present an overview of cartilage tissue engineering with recent progress, development, and major steps taken toward the generation of functional cartilage tissue. In this review, we have discussed the advances and problems in tissue engineering of cartilage with strong emphasis on the utilization of natural polymeric biomaterials, various cell sources, and stimulating factors such as biophysical stimuli, mechanical stimuli, dynamic culture, and growth factors used so far in cartilage regeneration. Finally, we have focused on clinical trials, recent innovations, and future prospects related to cartilage engineering.

Non-contact high-frequency ultrasound microbeam stimulation for studying mechanotransduction in human umbilical vein endothelial cells

We describe how contactless high-frequency ultrasound microbeam stimulation (HFUMS) is capable of eliciting cytoplasmic calcium (Ca(2+)) elevation in human umbilical vein endothelial cells. The cellular mechanotransduction process, which includes cell sensing and adaptation to the mechanical micro-environment, has been studied extensively in recent years. A variety of tools for mechanical stimulation have been developed to produce cellular responses. We developed a novel tool, a highly focused ultrasound microbeam, for non-contact cell stimulation at a microscale. This tool, at 200 MHz, was applied to human umbilical vein endothelial cells to investigate its potential to elicit an elevation in cytoplasmic Ca(2+) levels. It was found that the response was dose dependent, and moreover, extracellular Ca(2+) and cytoplasmic Ca(2+) stores were involved in the Ca(2+) elevation. These results suggest that high-frequency ultrasound microbeam stimulation is potentially a novel non-contact tool for studying cellular mechanotransduction if the acoustic pressures at such high frequencies can be quantified.

Towards the feasibility of using ultrasound to determine mechanical properties of tissues in a bioreactor

Our ultimate goal is to non-destructively evaluate mechanical properties of tissue-engineered (TE) cartilage using ultrasound (US). We used agarose gels as surrogates for TE cartilage. Previously, we showed that mechanical properties measured using conventional methods were related to those measured using US, which suggested a way to non-destructively predict mechanical properties of samples with known volume fractions. In this study, we sought to determine whether the mechanical properties of samples, with unknown volume fractions could be predicted by US. Aggregate moduli were calculated for hydrogels as a function of SOS, based on concentration and density using a poroelastic model. The data were used to train a statistical model, which we then used to predict volume fractions and mechanical properties of unknown samples. Young's and storage moduli were measured mechanically. The statistical model generally predicted the Young's moduli in compression to within <10% of their mechanically measured value. We defined positive linear correlations between the aggregate modulus predicted from US and both the storage and Young's moduli determined from mechanical tests. Mechanical properties of hydrogels with unknown volume fractions can be predicted successfully from US measurements. This method has the potential to predict mechanical properties of TE cartilage non-destructively in a bioreactor.

Effects of low-intensity pulsed ultrasound on integrin-FAK-PI3K/Akt mechanochemical transduction in rabbit osteoarthritis chondrocytes

The effect of low-intensity pulsed ultrasound (LIPUS) on extracellular matrix (ECM) production via modulation of the integrin/focal adhesion kinase (FAK)/phosphatidylinositol 3-kinase (PI3K)/Akt pathway has been investigated in previous studies in normal chondrocytes, but not in osteoarthritis (OA). Therefore, we investigated the LIPUS-induced integrin β1/FAK/PI3K/Akt mechanochemical transduction pathway in a single study in rabbit OA chondrocytes. Normal and OA chondrocytes were exposed to LIPUS, and mRNA and protein expression of cartilage, metalloproteinases and integrin-FAK-PI3K/Akt signal pathway-related genes was determined by quantitative reverse transcription polymerase chain reaction and Western blotting, respectively. Compared with levels in normal chondrocytes, expression levels of ECM-related genes were significantly lower in OA chondrocytes and those of metalloproteinase-related genes were significantly higher. In addition, integrin β1 gene expression and the phosphorylation of FAK, PI3K and Akt were significantly higher in OA chondrocytes. The expression of all tested genes was significantly increased except for that of metalloproteinase, which was significantly decreased in the LIPUS-treated OA group compared to the untreated OA group. LIPUS may affect the integrin-FAK-PI3K/Akt mechanochemical transduction pathway and alter ECM production by OA chondrocytes. Our findings will aid the future development of a treatment or even cure for OA.

Effects of low-intensity pulsed ultrasound and hyperbaric oxygen on human osteoarthritic chondrocytes

Background

Although the individual effects of hyperbaric oxygen (HBO) and low-intensity pulsed ultrasound (LIPUS) on osteoarthritic (OA) chondrocytes have been reported, the effects of HBO combined with LIPUS treatment are unknown.

Methods

OA chondrocytes were obtained from patients undergoing knee replacement surgery. RNA was isolated for real-time polymerase chain reaction (PCR) analysis of inducible nitric oxide synthase (iNOS), type-II collagen, and aggrecan gene expression. The protein levels of MMP-3 and TIMP-1 were quantified by enzyme-linked immunosorbent assay (ELISA) after LIPUS or HBO treatment. The data are given as mean ± standard deviation (SD) of the results from three independent experiments. A p value less than 0.05 was defined as statistically significant.

Results

Our data suggested that ultrasound and HBO treatment increased cell bioactivity of OA chondrocytes. Real-time PCR analysis showed that HBO treatment increased the mRNA of type-II collagen, aggrecan, and TIMP-1 but suppressed the iNOS expression of OA chondrocytes. LIPUS treatment increased the type-II collagen and iNOS expression of OA chondrocytes. ELISA data showed that HBO or LIPUS treatment increased TIMP-1 production of OA chondrocyte. MMP-3 production was suppressed by HBO treatment. HBO combined with LIPUS treatments resulted in additive effect in TIMP-1 production and compensatory effect in iNOS expression.

Conclusion

HBO combined with LIPUS treatment-induced increase of the anabolic factor (TIMP-1)/catabolic factor (MMP-3) ratio may provide an additive therapeutic approach to slow the course of OA degeneration.

Mechanotransduction of ultrasound is frequency dependent below the cavitation threshold

This study provides evidence that low-intensity ultrasound directly affects nuclear processes, and the magnitude of the effect varies with frequency. In particular, we show that the transcriptional induction of first load-inducible genes, which is independent of new protein synthesis, is frequency dependent. Bovine chondrocytes were exposed to low-intensity (below the cavitational threshold) ultrasound at 2, 5 and 8 MHz. Ultrasound elevated the expression of early response genes c-Fos, c-Jun and c-Myc, maximized at 5 MHz. The phosphorylated ERK inhibitor PD98059 abrogated any increase in c-series gene expression, suggesting that signaling occurs via the MAPPK/ERK pathway. However, phosphorylated ERK levels did not change with ultrasound frequency, indicating that processes downstream of ERK phosphorylation (such as nuclear transport and chromatin reorganization) respond to ultrasound with frequency dependence. A quantitative, biphasic mathematical model based on Biot theory predicted that cytoplasmic and nuclear stress is maximized at 5.2 ± 0.8 MHz for a chondrocyte, confirming experimental measurements.

Stereological analysis of subchondral angiogenesis induced by chitosan and coagulation factors in microdrilled articular cartilage defects

OBJECTIVE

Cartilage repair elicited by bone marrow stimulation can be enhanced by a chitosan-glycerol phosphate (GP)/blood implant, through mechanisms involving therapeutic inflammatory angiogenesis. The implant is formed by in situ coagulation, which can be accelerated by adding coagulation factors. We hypothesized that coagulation factors enhance acute subchondral angiogenesis in repairing drilled defects.

DESIGN

Full-thickness cartilage defects were created bilaterally in 12 skeletally mature rabbit knee trochlea, microdrilled, then allowed to bleed as a control (N = 6) or treated with chitosan-GP/blood implant (N = 6), or implant solidified with thrombin (IIa), tissue factor (TF) with recombinant human factor VIIa (rhFVIIa), or rhFVIIa alone (N = 4 each condition). At 3 weeks post-operative, quantitative stereology was used to obtain blood vessel length (L(V)), surface (S(V)), and volume (V(V)) density at systematic depths in two microdrill holes per defect. Collagen type I, type II and glycosaminoglycan (GAG) percent stain in non-mineralized repair tissue were analysed by histomorphometry.

RESULTS

All drill holes were healing, and showed a depth-dependent increase in granulation tissue blood vessel density (Lv, Sv, and Vv, P < 0.005). Residual chitosan implant locally suppressed blood vessel ingrowth into the granulation tissue, whereas holes completely cleared of chitosan amplified angiogenesis vs microdrill-only (P = 0.049), an effect enhanced by IIa. Chitosan implant suppressed strong Col-I, Col-II, and GAG accumulation that occurred spontaneously in drill-only bone defects (P < 0.005) and coagulation factors did not alter this effect.

CONCLUSIONS

Subchondral angiogenesis is promoted by chitosan implant clearance. Chitosan implant treatment suppresses fibrocartilage scar tissue formation, and promotes bone remodeling, which allows more blood vessel migration and woven bone repair towards the cartilage lesion area.

Integrin-mediated mechanotransduction pathway of low-intensity continuous ultrasound in human chondrocytes

Chondrocytes are mechanosensitive cells that require mechanical stimulation for proper growth and function in in vitro culture systems. Ultrasound (US) has emerged as a technique to deliver mechanical stress; however, the intracellular signaling components of the mechanotransduction pathways that transmit the extracellular mechanical stimulus to gene regulatory mechanisms are not fully defined. We evaluated a possible integrin/mitogen-activated protein kinase (MAPK) mechanotransduction pathway using Western blotting with antibodies targeting specific phosphorylation sites on intracellular signaling proteins. US stimulation of chondrocytes induced phosphorylation of focal adhesion kinase (FAK), Src, p130 Crk-associated substrate (p130Cas), CrkII and extracellular-regulated kinase (Erk). Furthermore, pre-incubation with inhibitors of integrin receptors, Src and MAPK/Erk kinase (MEK) reduced US-induced Erk phosphorylation levels, indicating integrins and Src are upstream of Erk in an US-mediated mechanotransduction pathway. These findings suggest US signals through integrin receptors to the MAPK/Erk pathway via a mechanotransduction pathway involving FAK, Src, p130Cas and CrkII.

Ultrasonic bioreactor as a platform for studying cellular response

The need for tissue-engineered constructs as replacement tissue continues to grow as the average age of the world's population increases. However, additional research is required before the efficient production of laboratory-created tissue can be realized. The multitude of parameters that affect cell growth and proliferation is particularly daunting considering that optimized conditions are likely to change as a function of growth. Thus, a generalized research platform is needed in order for quantitative studies to be conducted. In this article, an ultrasonic bioreactor is described for use in studying the response of cells to ultrasonic stimulation. The work is focused on chondrocytes with a long-term view of generating tissue-engineered articular cartilage. Aspects of ultrasound (US) that would negatively affect cells, including temperature and cavitation, are shown to be insignificant for the US protocols used and which cover a wide range of frequencies and pressure amplitudes. The bioreactor is shown to have a positive influence on several factors, including cell proliferation, viability, and gene expression of select chondrocytic markers. Most importantly, we show that a total of 138 unique proteins are differentially expressed on exposure to ultrasonic stimulation, using mass-spectroscopy coupled proteomic analyses. We anticipate that this work will serve as the basis for additional research which will elucidate many of the mechanisms associated with cell response to ultrasonic stimulation.

The effect of ultrasound stimulation on the cytoskeletal organization of chondrocytes seeded in three-dimensional matrices

The impact of low-intensity diffuse ultrasound (LIDUS) stimulation on the cytoskeletal organization of chondrocytes seeded in three-dimensional (3D) scaffolds was evaluated. Chondrocytes seeded on 3D chitosan matrices were exposed to LIDUS at 5.0 MHz (approx. 15 kPa, 51 s, 4 applications/day) in order to study the organization of actin, tubulin and vimentin. The results showed that actin presented a punctate cytosolic distribution and tubulin presented a quasiparallel organization of microtubules, whereas vimentin distribution was unaffected. Chondrocytes seeded on 3D scaffolds responded to US stimulation by the disruption of actin stress fibers and were sensitive to the presence of Rho-activated kinase (ROCK) inhibitor (Y27632). The gene expression of ROCK-I, a key element in the formation of stress fibers and mDia1, was significantly upregulated under the application of US. We conclude that the results of both the cytoskeletal analyses and gene expression support the argument that the presence of punctate actin upon US stimulation was accompanied by the upregulation of the RhoA/ROCK pathway.

Remodeling of chromatin under low intensity diffuse ultrasound

A variety of mechanotransduction pathways mediate the response of fibroblasts or chondrocytes to ultrasound stimulation. In addition, regulatory pathways that co-ordinate stimulus-specific cellular responses are likely to exist. In this study, analysis was confined to the hypothesis that ultrasound stimulation (US) influences the chromatin structure, and that these changes may reflect a regulatory pathway that connects nuclear architecture, chromatin structure and gene expression. Murine fibroblasts seeded on tissue culture plates were stimulated with US (5.0 MHz (14 kPa), 51-s per application) and the thermal denaturation profiles of nuclei isolated from fibroblasts were assessed by dynamic scanning calorimetry (DSC). When compared to the thermal profiles obtained from the nuclei of non-stimulated cells, the nuclei obtained from stimulated cells showed a change in peak profiles and peak areas, which is indicative of chromatin remodeling. Independently, US was also observed to impact the histone (H1):chromatin association as measured indirectly by DAPI staining. Based on our work, it appears plausible that US can produce a remodeling of chromatin, thus triggering signal cascade and other intracellular mechanisms.