Cellular tensegrity: exploring how mechanical changes in the cytoskeleton regulate cell growth, migration, and tissue pattern during morphogenesis

From tensegrity to human organs-on-chips: implications for mechanobiology and mechanotherapeutics

The field of mechanobiology, which focuses on the key role that physical forces play in control of biological systems, has grown enormously over the past few decades. Here, I provide a brief personal perspective on the development of the tensegrity theory that contributed to the emergence of the mechanobiology field, the key role that crossing disciplines has played in its development, and how it has matured over time. I also describe how pursuing questions relating to mechanochemical transduction and mechanoregulation can lead to the creation of novel technologies and open paths for development of new therapeutic strategies for a broad range of diseases and disorders.

Type IV collagen reduces MUC5AC secretion in the lungs of ovalbumin-sensitized mice

Mucin 5AC (MUC5AC) is excessively secreted in the respiratory tract of patients with asthma. Suppressing this secretion is important for improving the air passages, which facilitates easy breathing. We have previously reported that the addition of type IV collagen, a typical extracellular matrix (ECM) protein, to the culture medium for human cell lines and primary cells reduced MUC5AC secretion. In this report, we further investigated the effect of type IV collagen on MUC5AC secretion in vivo. We employed ovalbumin (OVA)-sensitized mice to model of asthma and exposed them to type IV collagen to verify the reducing effect of MUC5AC in vivo. The amount of MUC5AC in bronchoalveolar lavage fluid was examined after nebulization of type IV collagen. Hypersecretion of MUC5AC of the OVA-sensitized mice was suppressed by type IV collagen exposure in a time- and dose-dependent manner. Furthermore, type IV collagen exposure to OVA-sensitized mice decreased integrin α2 and β1 expression in the lungs and increased the levels of Akt and extracellular signal-regulated kinase (ERK) phosphorylation in the trachea. These results suggest that type IV collagen suppresses MUC5AC hypersecretion via modulating integrin expression and Akt/ERK phosphorylation in the respiratory tract of the OVA-sensitized mice.

Mechanism of Lower Airway Hyperresponsiveness Induced by Allergic Rhinitis

Allergic rhinitis is a global illness that puzzles many researchers. Most patients with allergic rhinitis also have lower airway hyperresponsiveness, and an allergic rhinitis attack can increase lower airway hyperresponsiveness. However, the mechanism of the effect of allergic rhinitis on the lower airways is still unclear. In this paper, the effects of allergic rhinitis on the lower airways are studied in terms of epidemiology, anatomy, pathophysiology, nasal function loss, inflammation drainage, nasobronchial reflex, and whole-body circulatory flow to determine the mechanism involved and provide ideas for future diagnosis, treatment, and experiments.

ECM Mechanoregulation in Malignant Pleural Mesothelioma

Malignant pleural mesothelioma is a relatively rare, but devastating tumor, because of the difficulties in providing early diagnosis and effective treatments with conventional chemo- and radiotherapies. Patients usually present pleural effusions that can be used for diagnostic purposes by cytological analysis. This effusion cytology may take weeks or months to establish and has a limited sensitivity (30%-60%). Then, it is becoming increasingly urgent to develop alternative investigative methods to support the diagnosis of mesothelioma at an early stage when this cancer can be treated successfully. To this purpose, mechanobiology provides novel perspectives into the study of tumor onset and progression and new diagnostic tools for the mechanical characterization of tumor tissues. Here, we report a mechanical and biophysical characterization of malignant pleural mesothelioma cells as additional support to the diagnosis of pleural effusions. In particular, we examined a normal mesothelial cell line (Met5A) and two epithelioid mesothelioma cell lines (REN and MPP89), investigating how malignant transformation can influence cellular function like proliferation, cell migration, and cell spreading area with respect to the normal ones. These alterations also correlated with variations in cytoskeletal mechanical properties that, in turn, were measured on substrates mimicking the stiffness of patho-physiological ECM.

Multiscale Strain Transfer in Cartilage

The transfer of stress and strain signals between the extracellular matrix (ECM) and cells is crucial for biochemical and biomechanical cues that are required for tissue morphogenesis, differentiation, growth, and homeostasis. In cartilage tissue, the heterogeneity in spatial variation of ECM molecules leads to a depth-dependent non-uniform strain transfer and alters the magnitude of forces sensed by cells in articular and fibrocartilage, influencing chondrocyte metabolism and biochemical response. It is not fully established how these nonuniform forces ultimately influence cartilage health, maintenance, and integrity. To comprehend tissue remodelling in health and disease, it is fundamental to investigate how these forces, the ECM, and cells interrelate. However, not much is known about the relationship between applied mechanical stimulus and resulting spatial variations in magnitude and sense of mechanical stimuli within the chondrocyte’s microenvironment. Investigating multiscale strain transfer and hierarchical structure-function relationships in cartilage is key to unravelling how cells receive signals and how they are transformed into biosynthetic responses. Therefore, this article first reviews different cartilage types and chondrocyte mechanosensing. Following this, multiscale strain transfer through cartilage tissue and the involvement of individual ECM components are discussed. Finally, insights to further understand multiscale strain transfer in cartilage are outlined.

Biomechanics of cells and subcellular components: A comprehensive review of computational models and applications

Cells are a fundamental structural, functional and biological unit for all living organisms. Up till now, considerable efforts have been made to study the responses of single cells and subcellular components to an external load, and understand the biophysics underlying cell rheology, mechanotransduction and cell functions using experimental and in silico approaches. In the last decade, computational simulation has become increasingly attractive due to its critical role in interpreting experimental data, analysing complex cellular/subcellular structures, facilitating diagnostic designs and therapeutic techniques, and developing biomimetic materials. Despite the significant progress, developing comprehensive and accurate models of living cells remains a grand challenge in the 21st century. To understand current state of the art, this review summarises and classifies the vast array of computational biomechanical models for cells. The article covers the cellular components at multi-spatial levels, that is, protein polymers, subcellular components, whole cells and the systems with scale beyond a cell. In addition to the comprehensive review of the topic, this article also provides new insights into the future prospects of developing integrated, active and high-fidelity cell models that are multiscale, multi-physics and multi-disciplinary in nature. This review will be beneficial for the researchers in modelling the biomechanics of subcellular components, cells and multiple cell systems and understanding the cell functions and biological processes from the perspective of cell mechanics.

Revisiting tissue tensegrity: Biomaterial-based approaches to measure forces across length scales

Cell-generated forces play a foundational role in tissue dynamics and homeostasis and are critically important in several biological processes, including cell migration, wound healing, morphogenesis, and cancer metastasis. Quantifying such forces in vivo is technically challenging and requires novel strategies that capture mechanical information across molecular, cellular, and tissue length scales, while allowing these studies to be performed in physiologically realistic biological models. Advanced biomaterials can be designed to non-destructively measure these stresses in vitro, and here, we review mechanical characterizations and force-sensing biomaterial-based technologies to provide insight into the mechanical nature of tissue processes. We specifically and uniquely focus on the use of these techniques to identify characteristics of cell and tissue "tensegrity:" the hierarchical and modular interplay between tension and compression that provide biological tissues with remarkable mechanical properties and behaviors. Based on these observed patterns, we highlight and discuss the emerging role of tensegrity at multiple length scales in tissue dynamics from homeostasis, to morphogenesis, to pathological dysfunction.

Peripheral and central immune system crosstalk in Alzheimer disease - a research prospectus

Dysregulation of the immune system is a cardinal feature of Alzheimer disease (AD), and a considerable body of evidence indicates pathological alterations in central and peripheral immune responses that change over time. Considering AD as a systemic immune process raises important questions about how communication between the peripheral and central compartments occurs and whether this crosstalk represents a therapeutic target. We established a whitepaper workgroup to delineate the current status of the field and to outline a research prospectus for advancing our understanding of peripheral-central immune crosstalk in AD. To guide the prospectus, we begin with an overview of seminal clinical observations that suggest a role for peripheral immune dysregulation and peripheral-central immune communication in AD, followed by formative animal data that provide insights into possible mechanisms for these clinical findings. We then present a roadmap that defines important next steps needed to overcome conceptual and methodological challenges, opportunities for future interdisciplinary research, and suggestions for translating promising mechanistic studies into therapeutic interventions.

Integrin β1 subunit regulates cellular and secreted MUC5AC and MUC5B production in NCI-H292 human lung epithelial cells

The surface of the human respiratory tract is covered with a mucus layer containing mucin 5AC (MUC5AC) and mucin 5B (MUC5B) as the main components. This layer contributes to biological defense by eliminating irritants, but excessive MUC5AC secretion by the airway epithelial cells exacerbates asthma. Therefore, regulating mucin production is important for asthma treatment. In this study, the effects of integrin β1 subunit on MUC5AC and MUC5B production were examined in NCI–H292 human lung cancer epithelial cells. When integrin β1 was overexpressed, cellular and secreted MUC5AC levels were decreased, whereas cellular MUC5B production was increased. Conversely, integrin β1 depletion using siRNA increased cellular and secreted MUC5AC production, but decreased cellular MUC5B production. Further, the activity of extracellular signal-regulated kinase (ERK), which promotes MUC5AC production, was decreased by integrin β1 overexpression and increased by its depletion. These results suggest that integrin β1 suppresses MUC5AC production and promotes MUC5B production by downregulating ERK.

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We studied the regulation of MUC5AC and MUC5B production by integrin β1 subunit.

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Integrin β1 overexpression reduced MUC5AC, but increased MUC5B levels.

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Integrin β1 depletion increased MUC5AC production and ROS level, but decreased MUC5B production.

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Integrin β1 overexpression decreased ERK activity in NCI–H292 airway cells.

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Integrin β1 downregulates ERK to suppress MUC5AC & promote MUC5B production.

Application of 3D MAPs pipeline identifies the morphological sequence chondrocytes undergo and the regulatory role of GDF5 in this process

The activity of epiphyseal growth plates, which drives long bone elongation, depends on extensive changes in chondrocyte size and shape during differentiation. Here, we develop a pipeline called 3D Morphometric Analysis for Phenotypic significance (3D MAPs), which combines light-sheet microscopy, segmentation algorithms and 3D morphometric analysis to characterize morphogenetic cellular behaviors while maintaining the spatial context of the growth plate. Using 3D MAPs, we create a 3D image database of hundreds of thousands of chondrocytes. Analysis reveals broad repertoire of morphological changes, growth strategies and cell organizations during differentiation. Moreover, identifying a reduction in Smad 1/5/9 activity together with multiple abnormalities in cell growth, shape and organization provides an explanation for the shortening of Gdf5 KO tibias. Overall, our findings provide insight into the morphological sequence that chondrocytes undergo during differentiation and highlight the ability of 3D MAPs to uncover cellular mechanisms that may regulate this process.

Characterization of the Striatal Extracellular Matrix in a Mouse Model of Parkinson's Disease

Parkinson’s disease’s etiology is unknown, although evidence suggests the involvement of oxidative modifications of intracellular components in disease pathobiology. Despite the known involvement of the extracellular matrix in physiology and disease, the influence of oxidative stress on the matrix has been neglected. The chemical modifications that might accumulate in matrix components due to their long half-live and the low amount of extracellular antioxidants could also contribute to the disease and explain ineffective cellular therapies. The enriched striatal extracellular matrix from a mouse model of Parkinson’s disease was characterized by Raman spectroscopy. We found a matrix fingerprint of increased oxalate content and oxidative modifications. To uncover the effects of these changes on brain cells, we morphologically characterized the primary microglia used to repopulate this matrix and further quantified the effects on cellular mechanical stress by an intracellular fluorescence resonance energy transfer (FRET)-mechanosensor using the U-2 OS cell line. Our data suggest changes in microglia survival and morphology, and a decrease in cytoskeletal tension in response to the modified matrix from both hemispheres of 6-hydroxydopamine (6-OHDA)-lesioned animals. Collectively, these data suggest that the extracellular matrix is modified, and underscore the need for its thorough investigation, which may reveal new ways to improve therapies or may even reveal new therapies.

What Are the Potential Roles of Nuclear Perlecan and Other Heparan Sulphate Proteoglycans in the Normal and Malignant Phenotype

The recent discovery of nuclear and perinuclear perlecan in annulus fibrosus and nucleus pulposus cells and its known matrix stabilizing properties in tissues introduces the possibility that perlecan may also have intracellular stabilizing or regulatory roles through interactions with nuclear envelope or cytoskeletal proteins or roles in nucleosomal-chromatin organization that may regulate transcriptional factors and modulate gene expression. The nucleus is a mechano-sensor organelle, and sophisticated dynamic mechanoresponsive cytoskeletal and nuclear envelope components support and protect the nucleus, allowing it to perceive and respond to mechano-stimulation. This review speculates on the potential roles of perlecan in the nucleus based on what is already known about nuclear heparan sulphate proteoglycans. Perlecan is frequently found in the nuclei of tumour cells; however, its specific role in these diseased tissues is largely unknown. The aim of this review is to highlight probable roles for this intriguing interactive regulatory proteoglycan in the nucleus of normal and malignant cell types.

Trends in Articular Cartilage Tissue Engineering: 3D Mesenchymal Stem Cell Sheets as Candidates for Engineered Hyaline-Like Cartilage

Articular cartilage defects represent an inciting factor for future osteoarthritis (OA) and degenerative joint disease progression. Despite multiple clinically available therapies that succeed in providing short term pain reduction and restoration of limited mobility, current treatments do not reliably regenerate native hyaline cartilage or halt cartilage degeneration at these defect sites. Novel therapeutics aimed at addressing limitations of current clinical cartilage regeneration therapies increasingly focus on allogeneic cells, specifically mesenchymal stem cells (MSCs), as potent, banked, and available cell sources that express chondrogenic lineage commitment capabilities. Innovative tissue engineering approaches employing allogeneic MSCs aim to develop three-dimensional (3D), chondrogenically differentiated constructs for direct and immediate replacement of hyaline cartilage, improve local site tissue integration, and optimize treatment outcomes. Among emerging tissue engineering technologies, advancements in cell sheet tissue engineering offer promising capabilities for achieving both in vitro hyaline-like differentiation and effective transplantation, based on controlled 3D cellular interactions and retained cellular adhesion molecules. This review focuses on 3D MSC-based tissue engineering approaches for fabricating “ready-to-use” hyaline-like cartilage constructs for future rapid in vivo regenerative cartilage therapies. We highlight current approaches and future directions regarding development of MSC-derived cartilage therapies, emphasizing cell sheet tissue engineering, with specific focus on regulating 3D cellular interactions for controlled chondrogenic differentiation and post-differentiation transplantation capabilities.

Biomechanical Characterization of Endothelial Cells Exposed to Shear Stress Using Acoustic Force Spectroscopy

Characterizing mechanical properties of cells is important for understanding many cellular processes, such as cell movement, shape, and growth, as well as adaptation to changing environments. In this study, we explore the mechanical properties of endothelial cells that form the biological barrier lining blood vessels, whose dysfunction leads to development of many cardiovascular disorders. Stiffness of living endothelial cells was determined by Acoustic Force Spectroscopy (AFS), by pull parallel multiple functionalized microspheres located at the cell-cell periphery. The unique configuration of the acoustic microfluidic channel allowed us to develop a long-term dynamic culture protocol exposing cells to laminar flow for up to 48 h, with shear stresses in the physiological range (i.e., 6 dyn/cm2). Two different Endothelial cells lines, Human Aortic Endothelial Cells (HAECs) and Human Umbilical Vein Endothelial Cells (HUVECs), were investigated to show the potential of this tool to capture the change in cellular mechanical properties during maturation of a confluent endothelial monolayer. Immunofluorescence microscopy was exploited to follow actin filament rearrangement and junction formation over time. For both cell types we found that the application of shear-stress promotes the typical phenotype of a mature endothelium expressing a linear pattern of VE-cadherin at the cell-cell border and actin filament rearrangement along the perimeter of Endothelial cells. A staircase-like sequence of increasing force steps, ranging from 186 pN to 3.5 nN, was then applied in a single measurement revealing the force-dependent apparent stiffness of the membrane cortex in the kPa range. We also found that beads attached to cells cultured under dynamic conditions were harder to displace than cells cultured under static conditions, showing a stiffer membrane cortex at cell periphery. All together these results demonstrate that the AFS can identify changes in cell mechanics based on force measurements of adherent cells under conditions mimicking their native microenvironment, thus revealing the shear stress dependence of the mechanical properties of neighboring endothelial cells.

Cytoskeleton systems contribute differently to the functional intrinsic properties of chondrospheres

Cytoskeleton systems, actin microfilaments, microtubules (MTs) and intermediate filaments (IFs) provide the biomechanical stability and spatial organization in cells. To understand the specific contributions of each cytoskeleton systems to intrinsic properties of spheroids, we've scrutinized the effects of the cytoskeleton perturbants, cytochalasin D (Cyto D), nocodazole (Noc) and withaferin A (WFA) on fusion, spreading on adhesive surface, morphology and biomechanics of chondrospheres (CSs). We confirmed that treatment with Cyto D but not with Noc or WFA severely affected CSs fusion and spreading dynamics and significantly reduced biomechanical properties of cell aggregates. Noc treatment affected spheroids spreading but not the fusion and surprisingly enhanced their stiffness. Vimentin intermediate filaments (VIFs) reorganization affected CSs spreading only. The analysis of all three cytoskeleton systems contribution to spheroids intrinsic properties was performed for the first time.

Fabrication of hyaline-like cartilage constructs using mesenchymal stem cell sheets

Cell and tissue engineering approaches for articular cartilage regeneration increasingly focus on mesenchymal stem cells (MSCs) as allogeneic cell sources, based on availability and innate chondrogenic potential. Many MSCs exhibit chondrogenic potential as three-dimensional (3D) cultures (i.e. pellets and seeded biomaterial scaffolds) in vitro; however, these constructs present engraftment, biocompatibility, and cell functionality limitations in vivo. Cell sheet technology maintains cell functionality as scaffold-free constructs while enabling direct cell transplantation from in vitro culture to targeted sites in vivo. The present study aims to develop transplantable hyaline-like cartilage constructs by stimulating MSC chondrogenic differentiation as cell sheets. To achieve this goal, 3D MSC sheets are prepared, exploiting spontaneous post-detachment cell sheet contraction, and chondrogenically induced. Results support 3D MSC sheets' chondrogenic differentiation to hyaline cartilage in vitro via post-contraction cytoskeletal reorganization and structural transformations. These 3D cell sheets' initial thickness and cellular densities may also modulate MSC-derived chondrocyte hypertrophy in vitro. Furthermore, chondrogenically differentiated cell sheets adhere directly to cartilage surfaces via retention of adhesion molecules while maintaining the cell sheets' characteristics. Together, these data support the utility of cell sheet technology for fabricating scaffold-free, hyaline-like cartilage constructs from MSCs for future transplantable articular cartilage regeneration therapies.

Cellular automata modeling suggests symmetric stem-cell division, cell death, and cell drift as key mechanisms driving adult spinal cord growth in teleost fish

Adult neurogenesis - the generation of neurons during adulthood - is intensively studied, yet little is known about its consequences at the tissue level. In the teleost fish Apteronotus leptorhynchus, morphometric analysis has revealed that the total number of cells in the spinal cord increases continuously throughout adulthood, driven by the activity of neurogenic stem/progenitor cells in both the ependymal layer at the central canal and in the radially located parenchyma. This net increase in cell numbers demonstrates cellular addition, as opposed to cellular turnover which appears to be the common outcome of adult neurogenesis in mammals. Grounded on a comprehensive set of quantitative data generated through high-resolution mapping of stem cells and their progeny, we constructed a cellular automata model of the stem-cell-driven growth of the spinal cord. Simulations based on this model suggest that three cellular mechanisms play a critical role for promoting sustained tissue growth and acquisition of correct form of the spinal cord, including the development of the ependymal layer and the parenchyma: the number of symmetric stem-cell divisions versus asymmetric divisions; the probability of the progeny of progenitor cells to undergo cell death; and the radial drifting of cells.

Elastic Tethers Between Separating Anaphase Chromosomes Regulate the Poleward Speeds of the Attached Chromosomes in Crane-Fly Spermatocytes

Elastic "tethers" connect separating anaphase chromosomes in most (or all) animal cells. We tested whether tethers are involved in coordinating movements of separating anaphase chromosomes in crane-fly spermatocytes. In these cells the coupled movements of separating chromosomes become uncoupled after the tethers are severed by laser microbeam irradiation of the interzone region between the chromosomes (Sheykhani et al., 2017). While this strongly suggests that tethers are involved with coordinating the poleward chromosome movements, the experiments are open to another interpretation: laser irradiations that cut the tethers also might damage something else in the interzone, and those non-tether components might regulate chromosome movements. In the experiments reported herein we distinguish between those two possibilities by disabling the tethers without cutting the interzone. We cut the arms from individual chromosomes, thereby severing the mechanical connection between separating chromosomes, disconnecting them, without damaging components in the interzone. Disabling tethers in this way uncoupled the movements of the separating chromosomes. We thus conclude that tethers are involved in regulating the speeds of separating anaphase chromosomes in crane-fly spermatocytes.

Immunostimulatory Potential of MoS2 Nanosheets: Enhancing Dendritic Cell Maturation, Migration and T Cell Elicitation

BACKGROUND

Due to their extraordinary physical and chemical properties, MoS2 nanosheets (MSNs) are becoming more widely used in nanomedicine. However, their influence on immune systems remains unclear.

MATERIALS AND METHODS

Two few-layered MSNs at sizes of 100-250 nm (S-MSNs) and 400-500 nm (L-MSNs) were used in this study. Bone marrow-derived dendritic cells (DCs) were exposed to both MSNs at different doses (0, 8, 16, 32, 64, 128 µg/mL) for 48 h and subjected to analyses of surface marker expression, cytokine secretion, lymphoid homing and in vivo T cell priming.

RESULTS

Different-sized MSNs of all doses did not affect the viability of DCs. The expression of CD40, CD80, CD86 and CCR7 was significantly higher on both S-MSN- and L-MSN-treated DCs at a dose of 128 μg/mL. As the dose of MSN increased, the secretion of IL-12p70 remained unchanged, the secretion of IL-1β decreased, and the production of TNF-α increased. A significant increase in IL-6 was observed in the 128 µg/mL L-MSN-treated DCs. In particular, MSN treatment dramatically improved the ex vivo movement and in vivo homing ability of both the local resident and blood circulating DCs. Furthermore, the cytoskeleton rearrangement regulated by ROS elevation was responsible for the enhanced homing ability of the MSNs. More robust CD4+ and CD8+ T cell proliferation and activation (characterized by high expression of CD107a, CD69 and ICOS) was observed in mice vaccinated with MSN-treated DCs. Importantly, exposure to MSNs did not interrupt LPS-induced DC activation, homing and T cell priming.

CONCLUSION

Few-layered MSNs ranging from 100 to 500 nm in size could play an immunostimulatory role in enhancing DC maturation, migration and T cell elicitation, making them a good candidate for vaccine adjuvants. Investigation of this study will not only expand the applications of MSNs and other new transition metal dichalcogenides (TMDCs) but also shed light on the in vivo immune-risk evaluation of MSN-based nanomaterials.

Cell swelling, softening and invasion in a three-dimensional breast cancer model

Sculpting of structure and function of three-dimensional multicellular tissues depend critically on the spatial and temporal coordination of cellular physical properties, yet the organizational principles that govern these events, and their disruption in disease, remain poorly understood. Using a multicellular mammary cancer organoid model, here we map in three dimensions the spatial and temporal evolution of positions, motions, and physical characteristics of individual cells. Compared with cells in the organoid core, cells at the organoid periphery and the invasive front are found to be systematically softer, larger and more dynamic. These mechanical changes are shown to arise from supracellular fluid flow through gap junctions, suppression of which delays transition to an invasive phenotype. Together, these findings highlight the role of spatiotemporal coordination of cellular physical properties in tissue organization and disease progression.

Type IV collagen reduces mucin 5AC secretion in three-dimensional cultured human primary airway epithelial cells

Mucin 5AC (MUC5AC) hypersecretion induces airway narrowing in patients with asthma, which leads to breathing problems. We investigated the regulation of MUC5AC secretion by extracellular matrix (ECM) proteins in human primary airway epithelial cells from patients with asthma. The addition of type IV collagen to three-dimensional cultured human primary airway epithelial cells, which mimics the airway surface, reduced MUC5AC secretion in the medium, while the addition of laminin increased MUC5AC secretion. Furthermore, the addition of fibronectin did not affect MUC5AC secretion. In particular, the repeated addition of a low concentration of type IV collagen demonstrated a cumulative effect on the reduction in MUC5AC secretion. Human primary cells incubated with type IV collagen showed downregulated extracellular signal-regulated kinase (ERK) activity, which induced MUC5AC hypersecretion but did not affect Akt activity. These results suggest that the addition of type IV collagen to the apical surface of primary cells downregulates MUC5AC secretion and has a cumulative effect on MUC5AC secretion which might be effected via the ERK signaling pathway.

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We studied the regulation of MUC5AC secretion by extracellular matrix proteins.

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The addition of type IV collagen reduced MUC5AC secretion in primary airway cells.

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The repeated addition of a low concentration of collagen reduced MUC5AC secretion.

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Type IV collagen induced the downregulation of ERK which induces MUC5AC secretion.

Modelling Cell Origami via a Tensegrity Model of the Cytoskeleton in Adherent Cells

Cell origami has been widely used in the field of three-dimensional (3D) cell-populated microstructures due to their multiple advantages, including high biocompatibility, the lack of special requirements for substrate materials, and the lack of damage to cells. A 3D finite element method (FEM) model of an adherent cell based on the tensegrity structure is constructed to describe cell origami by using the principle of the origami folding technique and cell traction forces. Adherent cell models contain a cytoskeleton (CSK), which is primarily composed of microtubules (MTs), microfilaments (MFs), intermediate filaments (IFs), and a nucleoskeleton (NSK), which is mainly made up of the nuclear lamina and chromatin. The microplate is assumed to be an isotropic linear-elastic solid material with a flexible joint that is connected to the cell tensegrity structure model by spring elements representing focal adhesion complexes (FACs). To investigate the effects of the degree of complexity of the tensegrity structure and NSK on the folding angle of the microplate, four models are established in the study. The results demonstrate that the inclusion of the NSK can increase the folding angle of the microplate, indicating that the cell is closer to its physiological environment, while increased complexity can reduce the folding angle of the microplate since the folding angle is depended on the cell types. The proposed adherent cell FEM models are validated by comparisons with reported results. These findings can provide theoretical guidance for the application of biotechnology and the analysis of 3D structures of cells and have profound implications for the self-assembly of cell-based microscale medical devices.

Stochastic cellular automata model of neurosphere growth: Roles of proliferative potential, contact inhibition, cell death, and phagocytosis

Neural stem and progenitor cells isolated from the central nervous system form, under specific culture conditions, clonal cell clusters known as neurospheres. The neurosphere assay has proven to be a powerful in vitro system to study the behavior of such cells and the development of their progeny. However, the theory of neurosphere growth has remained poorly understood. To overcome this limitation, we have, in the present paper, developed a cellular automata model, with which we examined the effects of proliferative potential, contact inhibition, cell death, and clearance of dead cells on growth rate, final size, and composition of neurospheres. Simulations based on this model indicated that the proliferative potential of the founder cell and its progenitors has a major influence on neurosphere size. On the other hand, contact inhibition of proliferation limits the final size, and reduces the growth rate, of neurospheres. The effect of this inhibition is particularly dramatic when a stem cell becomes encapsulated by differentiated or other non-proliferating cells, thereby suppressing any further mitotic division - despite the existing proliferative potential of the stem cell. Conversely, clearance of dead cells through phagocytosis is predicted to accelerate growth by reducing contact inhibition. A surprising prediction derived from our model is that cell death, while resulting in a decrease in growth rate and final size of neurospheres, increases the degree of differentiation of neurosphere cells. It is likely that the cellular automata model developed as part of the present investigation is applicable to the study of tissue growth in a wide range of systems.

Bioreactors Design, Types, Influencing Factors and Potential Application in Dentistry. A Literature Review

Objectives:

A variety of bioreactors and related approaches have been applied to dental tissues as their use has become more essential in the field of regenerative dentistry and dental tissue engineering. The review discusses the various types of bioreactors and their potential application in dentistry.

Methods:

Review of the literature was conducted using keywords (and MeSH) like Bioreactor, Regenerative Dentistry, Fourth Factor, Stem Cells, etc., from the journals published in English. All the searched abstracts, published in indexed journals were read and reviewed to further refine the list of included articles. Based on the relevance of abstracts pertaining to the manuscript, full-text articles were assessed.

Results:

Bioreactors provide a prerequisite platform to create, test, and validate the biomaterials and techniques proposed for dental tissue regeneration. Flow perfusion, rotational, spinner-flask, strain and customize-combined bioreactors have been applied for the regeneration of bone, periodontal ligament, gingiva, cementum, oral mucosa, temporomandibular joint and vascular tissues. Customized bioreactors can support cellular/biofilm growth as well as apply cyclic loading. Center of disease control & dip-flow biofilm-reactors and micro-bioreactor have been used to evaluate the biological properties of dental biomaterials, their performance assessment and interaction with biofilms. Few case reports have also applied the concept of in vivo bioreactor for the repair of musculoskeletal defects and used customdesigned bioreactor (Aastrom) to repair the defects of cleft-palate.

Conclusions:

Bioreactors provide a sterile simulated environment to support cellular differentiation for oro-dental regenerative applications. Also, bioreactors like, customized bioreactors for cyclic loading, biofilm reactors (CDC & drip-flow), and micro-bioreactor, can assess biological responses of dental biomaterials by simultaneously supporting cellular or biofilm growth and application of cyclic stresses.

The application of stable-isotope tracers to study human musculoskeletal protein turnover: a tale of bag filling and bag enlargement

The nutritional regulation of protein and amino acid balance in human skeletal muscle carried out by the authors with Mike Rennie is reviewed in the context of a simple physiological model for the regulation of the maintenance and growth of skeletal muscle, the "Bag Theory". Beginning in London in the late 1970s the work has involved the use of stable isotopes to probe muscle protein synthesis and breakdown with two basic experimental models, primed-dose continuous tracer infusions combined with muscle biopsies and arterio-venous (A-V) studies across a limb, most often the leg, allowing both protein synthesis and breakdown as well as net balance to be measured. In this way, over a 30 year period, the way in which amino acids and insulin mediate the anabolic effect of a meal has been elaborated in great detail confirming the original concepts of bag filling within the muscle endomysial "bag", which is limited by the "bag" size unless bag enlargement occurs requiring new collagen synthesis. Finally we briefly review some new developments involving ² H₂ O labelling of muscle proteins.

AFM assessing of nanomechanical fingerprints for cancer early diagnosis and classification: from single cell to tissue level

Cancer development and progression are closely associated with changes both in the mechano-cellular phenotype of cancer and stromal cells and in the extracellular matrix (ECM) structure, composition, and mechanics. In this paper, we review the use of atomic force microscopy (AFM) as a tool for assessing the nanomechanical fingerprints of solid tumors, so as to be potentially used as a diagnostic biomarker for more accurate identification and early cancer grading/classification. The development of such a methodology is expected to provide new insights and a novel approach for cancer diagnosis. We propose that AFM measurements could be employed to complement standard biopsy procedures, offering an objective, novel and quantitative diagnostic approach with the properties of a blind assay, allowing unbiased evaluation of the sample.

Morphomechanical rules of embryonic development

We start by comparing two explicatory approaches, which we call law-centered and "instructivistic". Although the latter dominates in modern biology, we find it inappropriate for treating developmental problems, especially those related to morphogenesis. As an example of a law-centered approach we suggest a simple morphomechanical rule based upon the idea of the hyper-restoration of mechanical stresses. We show that this rule not only provides a general framework for morphogenesis, but can also reproduce, via parametric modulations, quite specific developmental events.

Professor Lev Beloussov and the birth of morphomechanics

The first explanations of the mechanisms of development of living organisms were proposed in antiquity. At that time two competing ideas existed, about the strict determination of embryonic structures (we call it the "Hippocrates line") and about the possible formation of structures from the unstructured condition ("Aristotle line"). We can trace the opposition between the "Hippocrates line" and "Aristotle line" from antiquity till the present time. At the end of the XIX century, experimental investigation of the mechanisms of integrity of development had started. In the XX century, the "Aristotle line" finds its expression in the Morphogenetic Field Theory of A.G. Gurwitsch, according to which cells of the organism are integrated in an organic whole. Since the 1970s, mechanical forces and tensions have been considered as integral factors of ontogenesis. One of the most productive scientific teams which worked in this area was the laboratory of Professor L.V. Beloussov from the Lomonossov Moscow State University, Russia. In the 1970s, Lev Beloussov and his colleagues discovered the presence of "passive" and "active" (i.e. metabolically-dependent) mechanical stresses in the tissues of developing organisms, their organization and stage-specific patterns. In 1980-1990 s, a lot of experimental data about the role of the patterns of mechanical stresses in morphogenesis and cell differentiation was accumulated. Based on the experimental data, Professor Beloussov and his colleagues developed a theory of the regulation of the development of living organisms on the basis of the interaction of passive and active mechanical stresses (Belousov-Mittenthal Theory), which forms the basis of a new science - morphomechanics.

Upper and lower airway remodelling mechanisms in asthma, allergic rhinitis and chronic rhinosinusitis: The one airway concept revisited

Allergic rhinitis (AR), chronic rhinosinusitis (CRS) and asthma often co-exist. The one airway model proposes that disease mechanisms occurring in the upper airway may mirror lower airway events. Airway remodelling is the term used to describe tissue structural changes that occur in a disease setting and reflect the dynamic process of tissue restructuring during wound repair. Remodelling has been long identified in the lower airways in asthma and is characterized by epithelial shedding, goblet cell hyperplasia, basement membrane thickening, subepithelial fibrosis, airway smooth muscle hyperplasia and increased angiogenesis. The concept of upper airway remodelling has only recently been introduced, and data so far are limited and often conflicting, an indication that more detailed studies are needed. Whilst remodelling changes in AR are limited, CRS phenotypes demonstrate epithelial hyperplasia, increased matrix deposition and degradation along with accumulation of plasma proteins. Despite extensive research over the past years, the precise cellular and molecular mechanisms involved in airway remodelling remain incompletely defined. This review describes our current rather limited understanding of airway remodelling processes in AR, CRS and asthma and presents mechanisms both shared and distinct between the upper and lower airways. Delineation of shared and disease-specific pathogenic mechanisms of remodelling between the sinonasal system and the lung may guide the rational design of more effective therapeutic strategies targeting upper and lower airways concomitantly and improving the health of individuals with inflammatory airway diseases.

Nanomechanical Characteristics of Cervical Cancer and Cervical Intraepithelial Neoplasia Revealed by Atomic Force Microscopy

Background

Understanding the biological features and developmental progress of cervical cancer is crucial for disease prevention. This study aimed to determine the nanomechanical signatures of cervical samples, ranging from cervicitis to cervical carcinomas, and to investigate the underlying mechanisms.

Material/Methods

Forty-five cervical biopsies at various pathological stages were subjected to atomic force microscopy (AFM) measurements. Cdc42 and collagen I were quantified using immunohistochemical staining to investigate their relationship with nanomechanical properties of cervical cancers and premalignant lesions.

Results

We found that the lower elasticity peaks (LEPs) in the high-grade squamous intraepithelial lesion (HSIL) group (21.24±3.83 kPa) and higher elasticity peaks (HEPs) in the cancer group (81.23±8.82 kPa) were upshifted compared with the control group (LEP at 8.51±0.18 kPa and HEP at 44.07±3.54 kPa). Furthermore, compared with the control [29.51±13.61 for cell division cycle 42 (Cdc42) expression and 28.61±17.65 for collagen I expression], immunohistochemical staining verified a significant increase of Cdc42 in the HSIL group (50.57±23.85) and collagen I (56.09±25.70) in the cancer group. In addition, using the Pearson correlation coefficient, Cdc42 expression tended to be positively correlated with LEP locations (r=0.63, P=0.012), while collagen I expression displayed a strong and positive correlation with HEP positions (r=0.88, P<0.001).

Conclusions

The nanomechanical properties of HSIL and cancer biopsies show unique features compared with controls, and these alterations are probably due to changes in cytoskeleton and extracellular matrix contents.

Fluid shear stress induces upregulation of COX-2 and PGI2 release in endothelial cells via a pathway involving PECAM-1, PI3K, FAK, and p38

Vascular endothelial cells play an important role in the regulation of vascular function in response to mechanical stimuli in both healthy and diseased states. Prostaglandin I₂ (PGI₂) is an important antiatherogenic prostanoid and vasodilator produced in endothelial cells through the action of the cyclooxygenase (COX) isoenzymes COX-1 and COX-2. However, the mechanisms involved in sustained, shear-induced production of COX-2 and PGI₂ have not been elucidated but are determined in the present study. We used cultured endothelial cells exposed to steady fluid shear stress (FSS) of 10 dyn/cm² for 5 h to examine shear stress-induced induction of COX-2/PGI₂ Our results demonstrate the relationship between the mechanosensor platelet endothelial cell adhesion molecule-1 (PECAM-1) and the intracellular mechanoresponsive molecules phosphatidylinositol 3-kinase (PI3K), focal adhesion kinase (FAK), and mitogen-activated protein kinase p38 in the FSS induction of COX-2 expression and PGI₂ release. Knockdown of PECAM-1 (small interference RNA) expression inhibited FSS-induced activation of α₅β₁-integrin, upregulation of COX-2, and release of PGI₂ in both bovine aortic endothelial cells (BAECs) and human umbilical vein endothelial cells (HUVECs). Furthermore, inhibition of the PI3K pathway (LY294002) substantially inhibited FSS activation of α₅β₁-integrin, upregulation of COX-2 gene and protein expression, and release of PGI₂ in BAECs. Inhibition of integrin-associated FAK (PF573228) and MAPK p38 (SB203580) also inhibited the shear-induced upregulation of COX-2. Finally, a PECAM-1^-/- mouse model was characterized by reduced COX-2 immunostaining in the aorta and reduced plasma PGI₂ levels compared with wild-type mice, as well as complete inhibition of acute flow-induced PGI₂ release compared with wild-type animals.NEW & NOTEWORTHY In this study we determined the major mechanotransduction pathway by which blood flow-driven shear stress activates cyclooxygenase-2 (COX-2) and prostaglandin I₂ (PGI₂) release in endothelial cells. Our work has demonstrated for the first time that COX-2/PGI₂ mechanotransduction is mediated by the mechanosensor platelet endothelial cell adhesion molecule-1 (PECAM-1).

3D Cell Culture in a Self-Assembled Nanofiber Environment

The development and utilization of three-dimensional cell culture platforms has been gaining more traction. Three-dimensional culture platforms are capable of mimicking in vivo microenvironments, which provide greater physiological relevance in comparison to conventional two-dimensional cultures. The majority of three-dimensional culture platforms are challenged by the lack of cell attachment, long polymerization times, and inclusion of undefined xenobiotics, and cytotoxic cross-linkers. In this study, we review the use of a highly defined material composed of naturally occurring compounds, hyaluronic acid and chitosan, known as Cell-Mate3DTM. Moreover, we provide an original measurement of Young's modulus using a uniaxial unconfined compression method to elucidate the difference in microenvironment rigidity for acellular and cellular conditions. When hydrated into a tissue-like hybrid hydrocolloid/hydrogel, Cell-Mate3DTM is a highly versatile three-dimensional culture platform that enables downstream applications such as flow cytometry, immunostaining, histological staining, and functional studies to be applied with relative ease.

The nanomechanical signature of liver cancer tissues and its molecular origin

Patients with cirrhosis are at higher risk of developing hepatocellular carcinoma (HCC), the second most frequent cause of cancer-related deaths. Although HCC diagnosis based on conventional morphological characteristics serves as the "gold standard" in the clinic, there is a high demand for more convenient and effective diagnostic methods that employ new biophysical perspectives. Here, we show that the nanomechanical signature of liver tissue is directly correlated with the development of HCC. Using indentation-type atomic force microscopy (IT-AFM), we demonstrate that the lowest elasticity peak (LEP) in the Young's modulus distribution of surgically removed liver cancer tissues can serve as a mechanical fingerprint to evaluate the malignancy of liver cancer. Cirrhotic tissues shared the same LEP as normal tissues. However, a noticeable downward shift in the LEP was detected when the cirrhotic tissues progressed to a malignant state, making the tumor tissues more prone to microvascular invasion. Cell-level mechanistic studies revealed that the expression level of a Rho-family effector (mDia1) was consistent with the mechanical trend exhibited by the tissue. Our findings indicate that the mechanical profiles of liver cancer tissues directly varied with tumor progression, providing an additional platform for the future diagnosis of HCC.

MUC5B mucin production is upregulated by fibronectin and laminin in human lung epithelial cells via the integrin and ERK dependent pathway

MUC5B mucin is a principal component of airway mucus and plays a key role in biodefense. We investigated the regulation of MUC5B production using the signals from extracellular matrix (ECM) components in NCI-H292 human lung epithelial cells. We found that MUC5B production in NCI-H292 cells cultured on fibronectin or laminin increased by 4-5-fold, with the increase occurring in a dose- and time-dependent manner. In contrast, MUC5B production was unchanged on type-IV collagen. Inhibition of integrin β1 induced upregulation of MUC5B and MUC5AC; however, inhibition of p38 MAPK did not show any remarkable change in overproduced MUC5B. Inhibition of extracellular signal-regulated kinase (ERK) pathway or the transcription factor NF-κB induced the recovery of overproduced MUC5B on fibronectin and laminin. These results suggest that MUC5B production can be regulated by ECM components and that MUC5B is upregulated by fibronectin and laminin via the integrin, ERK, and NF-κB dependent pathway.

Macrophage adhesion on fibronectin evokes an increase in the elastic property of the cell membrane and cytoskeleton: an atomic force microscopy study

Interactions between cells and microenvironments are essential to cellular functions such as survival, exocytosis and differentiation. Cell adhesion to the extracellular matrix (ECM) evokes a variety of biophysical changes in cellular organization, including modification of the cytoskeleton and plasma membrane. In fact, the cytoskeleton and plasma membrane are structures that mediate adherent contacts with the ECM; therefore, they are closely correlated. Considering that the mechanical properties of the cell could be affected by cell adhesion-induced changes in the cytoskeleton, the purpose of this study was to investigate the influence of the ECM on the elastic properties of fixed macrophage cells using atomic force microscopy. The results showed that there was an increase (~50%) in the Young's modulus of macrophages adhered to an ECM-coated substrate as compared with an uncoated glass substrate. In addition, cytochalasin D-treated cells had a 1.8-fold reduction of the Young's modulus of the cells, indicating the contribution of the actin cytoskeleton to the elastic properties of the cell. Our findings show that cell adhesion influences the mechanical properties of the plasma membrane, providing new information toward understanding the influence of the ECM on elastic alterations of macrophage cell membranes.

Scaffold biomaterials for nano-pathophysiology

This review is intended to provide an overview of tissue engineering strategies using scaffold biomaterials to develop a vascularized tissue engineered construct for nano-pathophysiology. Two primary topics are discussed. The first is the biological or synthetic microenvironments that regulate cell behaviors in pathological conditions and tissue regeneration. Second is the use of scaffold biomaterials with angiogenic factors and/or cells to realize vascularized tissue engineered constructs for nano-pathophysiology. These topics are significantly overlapped in terms of three-dimensional (3-D) geometry of cells and blood vessels. Therefore, this review focuses on neovascularization of 3-D scaffold biomaterials induced by angiogenic factors and/or cells. The novel strategy of this approach in nano-pathophysiology is to utilize the vascularized tissue engineered construct as a tissue model to predict the distribution and subsequent therapeutic efficacy of a drug delivery system with different physicochemical and biological properties.

Akt induces down regulation of MUC5AC production in NCI-H292 human airway epithelial cells cultured on extracellular matrix

MUC5AC mucin overproduction is a key feature of asthma as contributes to airway obstruction. The production of MUC5AC is regulated in part by signals from extracellular matrix via integrin pathways, but it remains largely unclear. We investigated the role of Akt, a typical signal transducer in the integrin pathway, in the regulation of MUC5AC production. When NCI-H292 human airway epithelial cells were cultured on laminin or Matrigel, we found that the activity of Akt was suppressed, as compared to control cells with upregulated MUC5AC production. In contrast, Akt was activated in cells cultured on type IV collagen with downregulated MUC5AC production. The Akt inhibitor induced upregulation of MUC5AC. In contrast, overexpression of active Akt induced downregulation of MUC5AC production. These results suggest that a signal from laminin or Matrigel induces upregulation of MUC5AC by suppressing Akt activity, whereas a signal from type IV collagen induces downregulation of MUC5AC, mediated by Akt activation.

Bone tissue engineering and regenerative medicine: targeting pathological fractures

Patients with bone diseases have the highest risk of sustaining fractures and of suffering from nonunion bone healing due to tissue degeneration. Current fracture management strategies are limited in design and functionality and do not effectively promote bone healing within a diseased bone environment. Fracture management approaches include pharmaceutical therapy, surgical intervention, and tissue regeneration for fracture prevention, fracture stabilization, and fracture site regeneration, respectively. However, these strategies fail to accommodate the pathological nature of fragility fractures, leading to unwanted side effects, implant failures, and nonunions. To target fragility fractures, fracture management strategies should include bioactive bone substitutes designed for the pathological environment. However, the clinical outcome of these materials must be predictable within various disease environments. Initial development of a targeted treatment strategy should focus on simulating the physiological in vitro bone environment to predict clinical effectiveness of the engineered bone. An in vitro test system can facilitate reduction of implant failures and non-unions in fragility fractures.

Nanobiomechanics of living cells: a review

Nanobiomechanics of living cells is very important to understand cell-materials interactions. This would potentially help to optimize the surface design of the implanted materials and scaffold materials for tissue engineering. The nanoindentation techniques enable quantifying nanobiomechanics of living cells, with flexibility of using indenters of different geometries. However, the data interpretation for nanoindentation of living cells is often difficult. Despite abundant experimental data reported on nanobiomechanics of living cells, there is a lack of comprehensive discussion on testing with different tip geometries, and the associated mechanical models that enable extracting the mechanical properties of living cells. Therefore, this paper discusses the strategy of selecting the right type of indenter tips and the corresponding mechanical models at given test conditions.