Fibronectin-bound α5β1 integrins sense load and signal to reinforce adhesion in less than a second

Improved Cell Adhesion on Self-Assembled Chiral Nematic Cellulose Nanocrystal Films

Chirality is ubiquitous in nature, and closely related to biological phenomena. Nature-originated nanomaterials such as cellulose nanocrystals (CNCs) are able to self-assemble into hierarchical chiral nematic CNC films and impart handedness to nano and micro scale. However, the effects of the chiral nematic surfaces on cell adhesion are still unknown. Herein, this work presents evidence that the left-handed self-assembled chiral nematic CNC films (L-CNC) significantly improve the adhesion of L929 fibroblasts compared to randomly arranged isotropic CNC films (I-CNC). The fluidic force microscopy-based single-cell force spectroscopy is introduced to assess the cell adhesion forces on the substrates of L-CNC and I-CNC, respectively. With this method, a maximum adhesion force of 133.2 nN is quantified for mature L929 fibroblasts after culturing for 24 h on L-CNC, whereas the L929 fibroblasts exert a maximum adhesion force of 78.4 nN on I-CNC under the same condition. Moreover, the instant SCFS reveals that the integrin pathways are involved in sensing the chirality of substrate surfaces. Overall, this work offers a starting point for the regulation of cell adhesion via the self-assembled nano and micro architecture of chiral nematic CNC films, with potential practical applications in tissue engineering and regenerative medicine.

Functional poly(ether-ketone-ketone) composite scaffold with enhanced cell-material interaction, anti-inflammatory and osteogenesis for facilitating osteointegration and bone regeneration

Bone defects resulting from trauma or disease remain a significant challenge in clinical practice, often requiring prolonged treatment. Poly(ether-ketone-ketone) (PEKK) is a commonly used implant material due to its excellent biocompatibility and mechanical properties, which are similar to those of bone. However, its biological inertness leads to poor anti-inflammatory and osteointegration properties, significantly hindering the bone repair process. In this study, a cryogel filled - PEKK/bioglass (BG) composite scaffold (SPBC) was prepared via 3D printing to provide immunomodulatory and bone integration performance. Compared with untreated PEKK, SPBC exhibited significant enhancements in surface properties, including higher hydrophilicity and roughness. Additionally, SPBC enhanced the adsorption of fibronectin and vitronectin on the scaffold surface and regulated the maturation of cytoskeleton and adhesion plaques by increasing the phosphorylation level of FAK at Y397, thereby promoting cell adhesion and spreading. Due to the release of bioactive ions, SPBC can significantly promote the polarization of RAW264.7 cells towards M2 and the secretion of anti-inflammatory cytokines, while also enhancing the proliferation and differentiation of rat mesenchymal stem cells (rMSCs) in vitro. Furthermore, the in vivo results confirmed the enhanced anti-inflammatory properties and the integration of SPBC with the host tissue. In summary, after surface modification and cryogel filling, SPBC demonstrated excellent anti-inflammatory and bone integration abilities, presenting potential for clinical application as an orthopedic implant scaffold.

Deciphering circulating tumor cells binding in a microfluidic system thanks to a parameterized mathematical model

The spread of metastases is a crucial process in which some questions remain unanswered. In this work, we focus on tumor cells circulating in the bloodstream, the so-called Circulating Tumor Cells (CTCs). Our aim is to characterize their trajectories under the influence of hemodynamic and adhesion forces. We focus on already available in vitro measurements performed with a microfluidic device corresponding to the trajectories of CTCs - without or with different protein depletions - interacting with an endothelial layer. A key difficulty is the weak knowledge of the fluid velocity that has to be reconstructed. Our strategy combines a differential equation model - a Poiseuille model for the fluid velocity and an ODE system for the cell adhesion model - and a robust and well-designed calibration procedure. The parameterized model quantifies the strong influence of fluid velocity on adhesion and confirms the expected role of several proteins in the deceleration of CTCs. Finally, it enables the generation of synthetic cells, even for unobserved experimental conditions, opening the way to a digital twin for flowing cells with adhesion.

Biochemical and structural bases for talin ABSs-F-actin interactions

Focal adhesions (FAs) are large intracellular macromolecular assemblies that play a critical role in cell polarization and migration. Talin serves as a direct connection between integrin receptor and actomyosin cytoskeleton within FAs. Talin contains three actin-binding sites (ABS1-3) that engage discreetly during the development of FAs, thus acting as a critical player in FA initiation and maturation. However, the molecular basis of the ABS-F-actin interactions remains unknown. Here, we explore interactions of ABSs with F-actin to understand the multivalent behavior of talin. Particularly, the cryo-EM structure of the F-actin-ABS3 complex at 2.9 Å shows ABS3 spanning through two actin monomers along the filament axis, each occupied by the R13 rod subdomain and the DD domain. The dimerization of ABS3 occurs through the DD domain where both protomers interact on the actin surface, and the dimerization of talin to the actin surface is necessary for the engagement to F-actin. The R13 helical bundle is distorted upon binding to F-actin and releases the H1 helix from the rest of the bundle. This phenomenon has also been observed with other tension-sensing proteins like vinculin and α-catenin, highlighting that unfolding is relevant for its force sensing activity. On the contrary, ABS2 (R4R8 subdomains), which is thought to be critical for the maintenance of mature FAs, had multiple F-actin-binding regions within ABS2 and the binding likely occurred by these subdomains running through the surface of F-actin, thus strengthening the interactions upon the maturation of FAs.

Zymogen granule protein 16B (ZG16B) is a druggable epigenetic target to modulate the mammary extracellular matrix

High tissue density of the mammary gland is considered a pro-tumorigenic factor, hence suppressing the stimuli that induce matrix buildup carries the potential for cancer interception. We found that in non-malignant mammary epithelial cells the combination of the chemopreventive agents bexarotene (Bex) and carvedilol (Carv) suppresses the zymogen granule protein 16B (ZG16B, PAUF) through an interaction of ARID1A with a proximal enhancer. Bex + Carv also reduced ZG16B levels in vivo in normal breast tissue and MDA-MB231 tumor xenografts. The relevance of ZG16B is underscored by ongoing clinical trials targeting ZG16B in pancreatic cancers, but its role in breast cancer development is unclear. In immortalized mammary epithelial cells, secreted recombinant ZG16B stimulated mitogenic kinase phosphorylation, detachment and mesenchymal characteristics, and promoted proliferation, motility and clonogenic growth. Highly concerted induction of specific laminin, collagen and integrin isoforms indicated a shift in matrix properties toward increased density and cell-matrix interactions. Exogenous ZG16B alone blocked Bex + Carv-mediated control of cell growth and migration, and antagonized Bex + Carv-induced gene programs regulating cell adhesion and migration. In breast cancer cells ZG16B induced colony formation and anchorage-independent growth, and stimulated migration in a PI3K/Akt-dependent manner. In contrast, Bex + Carv inhibited colony formation, reduced Ki67 levels, ZG16B expression and glucose uptake in MDA-MB231 xenografts. These data establish ZG16B as a druggable pro-tumorigenic target in breast cell transformation and suggest a key role of the matrisome network in rexinoid-dependent antitumor activity.

Tissue-engineered fibrillar fibronectin matrices are not only lovely, but also functional for regenerative medicines and in vitro model systems

Fibronectin is an ubiquitous extracellular matrix protein which comprises fibrous three-dimensional microenvironments in native tissues. Although its importance and fibrillogenesis in vivo has been considerably investigated, yet current in vitro tissue engineering platforms for fibrillar fibronectin pose major drawbacks such as low scalability, applicability, and reproducibility. Due to such platform limitations, understanding of spatiotemporal mechanobiology between cells and fibrillar fibronectin matrices largely remains unexplored. This article briefly underlines current tissue-engineering platforms and mechanobiological understanding of fibrillar fibronectin as well as suggests potential directions in future fibronectin researches.

Applying Spatiotemporal Modeling of Cell Dynamics to Accelerate Drug Development

Cells act as physical computational programs that utilize input signals to orchestrate molecule-level protein-protein interactions (PPIs), generating and responding to forces, ultimately shaping all of the physiological and pathophysiological behaviors. Genome editing and molecule drugs targeting PPIs hold great promise for the treatments of diseases. Linking genes and molecular drugs with protein-performed cellular behaviors is a key yet challenging issue due to the wide range of spatial and temporal scales involved. Building predictive spatiotemporal modeling systems that can describe the dynamic behaviors of cells intervened by genome editing and molecular drugs at the intersection of biology, chemistry, physics, and computer science will greatly accelerate pharmaceutical advances. Here, we review the mechanical roles of cytoskeletal proteins in orchestrating cellular behaviors alongside significant advancements in biophysical modeling while also addressing the limitations in these models. Then, by integrating generative artificial intelligence (AI) with spatiotemporal multiscale biophysical modeling, we propose a computational pipeline for developing virtual cells, which can simulate and evaluate the therapeutic effects of drugs and genome editing technologies on various cell dynamic behaviors and could have broad biomedical applications. Such virtual cell modeling systems might revolutionize modern biomedical engineering by moving most of the painstaking wet-laboratory effort to computer simulations, substantially saving time and alleviating the financial burden for pharmaceutical industries.

N-cadherin crosstalk with integrin weakens the molecular clutch in response to surface viscosity

Mesenchymal stem cells (MSCs) interact with their surroundings via integrins, which link to the actin cytoskeleton and translate physical cues into biochemical signals through mechanotransduction. N-cadherins enable cell-cell communication and are also linked to the cytoskeleton. This crosstalk between integrins and cadherins modulates MSC mechanotransduction and fate. Here we show the role of this crosstalk in the mechanosensing of viscosity using supported lipid bilayers as substrates of varying viscosity. We functionalize these lipid bilayers with adhesion peptides for integrins (RGD) and N-cadherins (HAVDI), to demonstrate that integrins and cadherins compete for the actin cytoskeleton, leading to an altered MSC mechanosensing response. This response is characterised by a weaker integrin adhesion to the environment when cadherin ligation occurs. We model this competition via a modified molecular clutch model, which drives the integrin/cadherin crosstalk in response to surface viscosity, ultimately controlling MSC lineage commitment.

Research progress on the immunological functions of Piezo1 a receptor molecule that responds to mechanical force

The human immune system is capable of defending against, monitoring, and self-stabilizing various immune cells. Differentiation, proliferation, and development of these cells are regulated by biochemical signals. Moreover, biophysical signals, such as mechanical forces, have been found to affect immune cell function, thus introducing a new area of immunological research. Piezo1, a mechanically sensitive ion channel, was awarded the Nobel Prize for Physiology and Medicine in 2021. This channel is present on the surface of many cells, and when stimulated by mechanical force, it controls calcium (Ca2+) inside the cells, leading to changes in downstream signals and thus regulating cell functions. Piezo1 is also expressed in various innate and adaptive immune cells and plays a major role in the immune function. In this review, we will explore the physiological functions and regulatory mechanisms of Piezo1 and its impact on innate and adaptive immunity. This may offer new insights into diagnostics and therapeutics for the prevention and treatment of diseases and surgical infections.

Mechanochemistry: Fundamental Principles and Applications

Mechanochemistry is an emerging research field at the interface of physics, mechanics, materials science, and chemistry. Complementary to traditional activation methods in chemistry, such as heat, electricity, and light, mechanochemistry focuses on the activation of chemical reactions by directly or indirectly applying mechanical forces. It has evolved as a powerful tool for controlling chemical reactions in solid state systems, sensing and responding to stresses in polymer materials, regulating interfacial adhesions, and stimulating biological processes. By combining theoretical approaches, simulations and experimental techniques, researchers have gained intricate insights into the mechanisms underlying mechanochemistry. In this review, the physical chemistry principles underpinning mechanochemistry are elucidated and a comprehensive overview of recent significant achievements in the discovery of mechanically responsive chemical processes is provided, with a particular emphasis on their applications in materials science. Additionally, The perspectives and insights into potential future directions for this exciting research field are offered.

Integrin mechanosensing relies on a pivot-clip mechanism to reinforce cell adhesion

Cells intricately sense mechanical forces from their surroundings, driving biophysical and biochemical activities. This mechanosensing phenomenon occurs at the cell-matrix interface, where mechanical forces resulting from cellular motion, such as migration or matrix stretching, are exchanged through surface receptors, primarily integrins, and their corresponding matrix ligands. A pivotal player in this interaction is the α5β1 integrin and fibronectin (FN) bond, known for its role in establishing cell adhesion sites for migration. However, upregulation of the α5β1-FN bond is associated with uncontrolled cell metastasis. This bond operates through catch bond dynamics, wherein the bond lifetime paradoxically increases with greater force. The mechanism sustaining the characteristic catch bond dynamics of α5β1-FN remains unclear. Leveraging molecular dynamics simulations, our approach unveils a pivot-clip mechanism. Two key binding sites on FN, namely the synergy site and the RGD (Arg-Gly-Asp) motif, act as active points for structural changes in α5β1 integrin. Conformational adaptations at these sites are induced by a series of hydrogen bond formations and breaks at the synergy site. We disrupt these adaptations through a double mutation on FN, known to reduce cell adhesion. A whole-cell finite-element model is employed to elucidate how the synergy site may promote dynamic α5β1-FN binding, resisting cell contraction. In summary, our study integrates molecular- and cellular-level modeling to propose that FN's synergy site reinforces cell adhesion through enhanced binding dynamics and a mechanosensitive pivot-clip mechanism. This work sheds light on the interplay between mechanical forces and cell-matrix interactions, contributing to our understanding of cellular behaviors in physiological and pathological contexts.

The M2 Macrophages Derived Migrasomes From the Surface of Titania Nanotubes Array as a New Concept for Enhancing Osteogenesis

As newly discovered substrate anchored extracellular vesicles, migrasomes (Migs) may bring a new opportunity for manipulating target cells bioactivities. In this study, the M2 macrophages derived Migs are obtained by titania nanotubes surface (NTs). Due to the benefits of nanostructuring, the NTs surface is not only able to induce RAW264.7 for M2 polarization but also to generate more Migs formation, which can be internalized by following seeded mesenchymal stem cells (MSCs). Then, the NTs surface induced Migs are collected by density-gradient centrifugation for MSCs treatment. As indicated by immunofluorescence staining, alkaline phosphatase activity, and alizarin red staining, the osteogenic differentiation capacity of MSCs is significantly enhanced by Migs treatment, in line with the dosage. By RNA-sequence analysis, the enhancement of osteogenic differentiation is correlated with PI3K-AKT pathway activation that may originate from the M2 polarization state of donor cells. Finally, the Migs are coated onto Ti surface for therapeutic application. Both the in vitro and in vivo analysis reveal that the Migs coated Ti implant shows significant enhancement of osteogenesis. In conclusion, this study suggests that the nanosurface may be a favorable platform for Migs production, which may bring a new concept for tissue regeneration.

Engineering fibronectin-templated multi-component fibrillar extracellular matrices to modulate tissue-specific cell response

Cells assemble fibronectin, the major extracellular matrix (ECM) protein, into fibrillar matrices, which serve as 3D architectural scaffolds to provide, together with other ECM proteins tissue-specific environments. Although recent approaches enable to bioengineer 3D fibrillar fibronectin matrices in vitro, it remains elusive how fibronectin can be co-assembled with other ECM proteins into complex 3D fibrillar matrices that recapitulate tissue-specific compositions and cellular responses. Here, we introduce the engineering of fibrillar fibronectin-templated 3D matrices that can be complemented with other ECM proteins, including vitronectin, collagen, and laminin to resemble ECM architectures observed in vivo. For the co-assembly of different ECM proteins, we employed their innate fibrillogenic mechanisms including shear forces, pH-dependent electrostatic interactions, or specific binding domains. Through recapitulating various tissue-specific ECM compositions and morphologies, the large scale multi-composite 3D fibrillar ECM matrices can guide fibroblast adhesion, 3D fibroblast tissue formation, or tissue morphogenesis of epithelial cells. In other examples, we customize multi-composite 3D fibrillar matrices to support the growth of signal propagating neuronal networks and of human brain organoids. We envision that these 3D fibrillar ECM matrices can be tailored in scale and composition to modulate tissue-specific responses across various biological length scales and systems, and thus to advance manyfold studies of cell biological systems.

Mechanotransduction in stem cells

Nowadays, it is an established concept that the capability to reach a specialised cell identity via differentiation, as in the case of multi- and pluripotent stem cells, is not only determined by biochemical factors, but that also physical aspects of the microenvironment play a key role; interpreted by the cell through a force-based signalling pathway called mechanotransduction. However, the intricate ties between the elements involved in mechanotransduction, such as the extracellular matrix, the glycocalyx, the cell membrane, Integrin adhesion complexes, Cadherin-mediated cell/cell adhesion, the cytoskeleton, and the nucleus, are still far from being understood in detail. Here we report what is currently known about these elements in general and their specific interplay in the context of multi- and pluripotent stem cells. We furthermore merge this overview to a more comprehensive picture, that aims to cover the whole mechanotransductive pathway from the cell/microenvironment interface to the regulation of the chromatin structure in the nucleus. Ultimately, with this review we outline the current picture of the interplay between mechanotransductive cues and epigenetic regulation and how these processes might contribute to stem cell dynamics and fate.

Novel tools to study cell-ECM interactions, cell adhesion dynamics and migration

Integrin-mediated cell adhesion is essential for cell migration, mechanotransduction and tissue integrity. In vivo, these processes are regulated by complex physicochemical signals from the extracellular matrix (ECM). These nuanced cues, including molecular composition, rigidity and topology, call for sophisticated systems to faithfully explore cell behaviour. Here, we discuss recent methodological advances in cell-ECM adhesion research and compile a toolbox of techniques that we expect to shape this field in future. We outline methodological breakthroughs facilitating the transition from rigid 2D substrates to more complex and dynamic 3D systems, as well as advances in super-resolution imaging for an in-depth understanding of adhesion nanostructure. Selected methods are exemplified with relevant biological findings to underscore their applicability in cell adhesion research. We expect this new "toolbox" of methods will allow for a closer approximation of in vitro experimental setups to in vivo conditions, providing deeper insights into physiological and pathophysiological processes associated with cell-ECM adhesion.

Fibronectin binds integrin α5β1 to regulate macular neovascularization through the Wnt/β-catenin signaling pathway

Age-related macular degeneration (AMD) is a progressive, degenerative disease of the macula. The formation of macular neovascularization (MNV) and subretinal fibrosis of AMD is the most classic cause of the loss of vision in older adults worldwide. While the underlying causes of MNV and subretinal fibrosis remain elusive, the common feature of many common retinal diseases is changes the proportions of protein deposition in extracellular matrix (ECM) when compared to normal tissue. In ECM, fibronectin (FN) is a crucial component and plays a pivotal part not only in fibrotic diseases but also in the process of angiogenesis. The study aims to understand the role of ligand FN and its common integrin receptor α5β1 on MNV, and to understand the molecular mechanism involved. To study this, the laser-induced MNV mouse model and the rhesus macaque choroid-retinal endothelial cell line (RF/6A) chemical hypoxia mode were established, and the FN-α5β1 expression levels were detected by immunohistochemistry (IHC) and quantitative real-time PCR analysis (qRT-PCR). Fibronectin expression was silenced using small interfering RNA (siRNA) targeting FN. The tube formation and vitro scratch assays were used to assess the ability to form blood vessels and cell migration. To measure the formation of MNV, immunofluorescence, and Western blot assays were used. These results revealed that the expressions of FN and integrin α5β1 were distinctly increased in the laser-induced MNV mouse model and in the RF/6A cytochemically induced hypoxia model, and the expression tendency was identical. After the use of FN siRNA, the tube formation and migration abilities of the RF/6A cells were lower, the ability of endothelial cells to proliferate was confined and the scope of damage caused by the laser in animal models was significantly cut down. In addition, FN gene knockdown dramatically inhibited the expression of Wnt/β-catenin signal. The interaction of FN with the integrin receptor α5β1 in the constructed model, which may act through the Wnt/β-catenin signaling pathway, was confirmed in this study. In conclusion, FN may be a potential new molecular target for the prevention and treatment of subretinal fibrosis and MNV.

Shaping Oncogenic Microenvironments: Contribution of Fibronectin

The extracellular matrix (ECM) is a complex network of proteins and glycans, dynamically remodeled and specifically tailored to the structure/function of each organ. The malignant transformation of cancer cells is determined by both cell intrinsic properties, such as mutations, and extrinsic variables, such as the mixture of surrounding cells in the tumor microenvironment and the biophysics of the ECM. During cancer progression, the ECM undergoes extensive remodeling, characterized by disruption of the basal lamina, vascular endothelial cell invasion, and development of fibrosis in and around the tumor cells resulting in increased tissue stiffness. This enhanced rigidity leads to aberrant mechanotransduction and further malignant transformation potentiating the de-differentiation, proliferation and invasion of tumor cells. Interestingly, this fibrotic microenvironment is primarily secreted and assembled by non-cancerous cells. Among them, the cancer-associated fibroblasts (CAFs) play a central role. CAFs massively produce fibronectin together with type I collagen. This review delves into the primary interactions and signaling pathways through which fibronectin can support tumorigenesis and metastasis, aiming to provide critical molecular insights for better therapy response prediction.

The role of fibronectin in mediating cell migration

Fibronectin (FN) is a major extracellular matrix (ECM) protein involved in a wide range of physiological processes, including cell migration. These FN-mediated cell migration events are essential to processes such as wound repair, cancer metastasis, and vertebrate development. This review synthesizes mainly current literature to provide an overview of the mechanoregulatory role of FN-mediated cell migration. Background on FN structure and role in mechanotransduction is provided. Cell migration concepts are introduced, including the general cell migration mechanism and classification of cell migration types. Then, FN-mediated events that directly affect cell migration are explored. Finally, a focus on FN in tissue repair and cancer migration is presented, as these topics represent a large amount of current research.

Mechanical stiffness promotes skin fibrosis via Piezo1-Wnt2/Wnt11-CCL24 positive feedback loop

Skin fibrosis is characterized by the excessive accumulation of extracellular matrix (ECM) caused by fibrotic disorders of the skin. In recent years, ECM stiffness has emerged as a prominent mechanical cue that precedes skin fibrosis and drives its progression by promoting fibroblasts activation. However, how stiffness influences fibroblasts activation for skin fibrosis progression remains unknown. Here, we report a positive feedback loop mediated by the mechanosensitive ion channel Piezo1 and aberrant tissue mechanics in driving skin fibrosis. Piezo1 is upregulated in fibrotic skin in both humans and mice. Piezo1 knockdown dermal fibroblasts lose their fibroproliferative phenotypes despite being grown on a stiffer substrate. We show that Piezo1 acts through the Wnt2/Wnt11 pathway to mechanically induce secretion of C-C motif chemokine ligand 24 (CCL24, also known as eotaxin-2), a potent cytokine associated with fibrotic disorders. Importantly, adeno-associated virus (AAV)-mediated Piezo1 knockdown ameliorated the progression of skin fibrosis and skin stiffness in mice. Overall, increased matrix stiffness promotes skin fibrosis through the inflammatory Piezo1-Wnt2/Wnt11-CCL24 pathway. In turn, a stiffer skin microenvironment increases Piezo1 expression to exacerbate skin fibrosis aggression. Therefore, targeting Piezo1 represents a strategy to break the positive feedback loop between fibroblasts mechanotransduction and aberrant tissue mechanics in skin fibrosis.

Mechanical Factors Regulate Annulus Fibrosus (AF) Injury Repair and Remodeling: A Review

Low back pain is a common chronic disease that can severely affect the patient's work and daily life. The breakdown of spinal mechanical homeostasis caused by intervertebral disc (IVD) degeneration is a leading cause of low back pain. Annulus fibrosus (AF), as the outer layer structure of the IVD, is often the first affected part. AF injury caused by consistent stress overload will further accelerate IVD degeneration. Therefore, regulating AF injury repair and remodeling should be the primary goal of the IVD repair strategy. Mechanical stimulation has been shown to promote AF regeneration and repair, but most studies only focus on the effect of single stress on AF, and lack realistic models and methods that can mimic the actual mechanical environment of AF. In this article, we review the effects of different types of stress stimulation on AF injury repair and remodeling, suggest possible beneficial load combinations, and explore the underlying molecular mechanisms. It will provide the theoretical basis for designing better tissue engineering therapy using mechanical factors to regulate AF injury repair and remodeling in the future.

Rapid Regulation of Cardiomyocytes Adhesion on Substrates with Varied Modulus via Mechanical Cues

In-depth understanding of the mechanisms underlying the adhesion of myocardial cells holds significant importance for the development of effective therapeutic biomaterials aimed at repairing damaged or pathological myocardial tissues. Herein, we present evidence that myocardial cells (H9C2) exhibit integrin-based mechanosensing during the initial stage of adhesion (within the first 2 h), enabling them to recognize and respond to variations in substrate stiffnesses. Moreover, the bioinformatics analysis of RNA transcriptome sequencing (RNA-seq) reveals that the gene expressions associated with initial stage focal adhesion (Ctgf, Cyr61, Amotl2, Prickle1, Serpine1, Akap12, Hbegf, and Nedd9) are up-regulated on substrates with elevated Young's modulus. The fluorescent immunostaining results also suggest that increased substrate stiffness enhances the expression of Y397-phosphorylated focal adhesion kinase (FAK Y397), talin, and vinculin and the assembly of F-actin in H9C2 cells, thereby facilitating the adhesion of myocardial cells on the substrate. Next, we utilize fluidic force microscopy (FluidFM)-based single-cell force spectroscopy (SCFS) to quantitatively evaluate the impact of substrate stiffness on the cell adhesion force and adhesion work, thus providing novel insights into the biomechanical regulation of initial cell adhesion. Our findings demonstrate that the maximum adhesion forces of myocardial cells exhibit a rise from 23.6 to 248.0 nN when exposed to substrates with different moduli. It is worth noting that once the αvβ3 integrins are blocked, the disparities in the adhesion forces of myocardial cells on these substrates become negligible. These results exhibit remarkable sensitivity of myocardial cells to mechanical cues of the substrate, highlighting the role of αvβ3 integrin as a biomechanical sensor for the regulation of cell adhesion. Overall, this work offers a prospective approach for the regulation of cell adhesion via integrin mechanosensing with potential practical applications in the areas of tissue engineering and regenerative medicine.

Papain-Based Solubilization of Decellularized Extracellular Matrix for the Preparation of Bioactive, Thermosensitive Pregels

Solubilized, gel-forming decellularized extracellular matrix (dECM) is used in a wide range of basic and translational research and due to its inherent bioactivity can promote structural and functional tissue remodeling. The animal-derived protease pepsin has become the standard proteolytic enzyme for the solubilization of almost all types of collagen-based dECM. In this study, pepsin was compared with papain, α-amylase, and collagenase for their potential to solubilize porcine liver dECM. Maximum preservation of bioactive components and native dECM properties was used as a decisive criterion for further application of the enzymes, with emphasis on minimal destruction of the protein structure and maintained capacity for physical thermogelation at neutral pH. The solubilized dECM digests, and/or their physically gelled hydrogels were characterized for their rheological properties, gelation kinetics, GAG content, proteomic composition, and growth factor profile. This study highlights papain as a plant-derived enzyme that can serve as a cost-effective alternative to animal-derived pepsin for the efficient solubilization of dECM. The resulting homogeneous papain-digested dECM preserved its thermally triggered gelation properties similar to pepsin digests, and the corresponding dECM hydrogels demonstrated their enhanced bioadhesiveness in single-cell force spectroscopy experiments with fibroblasts. The viability and proliferation of human HepaRG cells on dECM gels were similar to those on pure rat tail collagen type I gels. Papain is not only highly effective and economically attractive for dECM solubilization but also particularly interesting when digesting human-tissue-derived dECM for regenerative applications, where animal-derived materials are to be avoided.

Thy-1 (CD90)-regulated cell adhesion and migration of mesenchymal cells: insights into adhesomes, mechanical forces, and signaling pathways

Cell adhesion and migration depend on the assembly and disassembly of adhesive structures known as focal adhesions. Cells adhere to the extracellular matrix (ECM) and form these structures via receptors, such as integrins and syndecans, which initiate signal transduction pathways that bridge the ECM to the cytoskeleton, thus governing adhesion and migration processes. Integrins bind to the ECM and soluble or cell surface ligands to form integrin adhesion complexes (IAC), whose composition depends on the cellular context and cell type. Proteomic analyses of these IACs led to the curation of the term adhesome, which is a complex molecular network containing hundreds of proteins involved in signaling, adhesion, and cell movement. One of the hallmarks of these IACs is to sense mechanical cues that arise due to ECM rigidity, as well as the tension exerted by cell-cell interactions, and transduce this force by modifying the actin cytoskeleton to regulate cell migration. Among the integrin/syndecan cell surface ligands, we have described Thy-1 (CD90), a GPI-anchored protein that possesses binding domains for each of these receptors and, upon engaging them, stimulates cell adhesion and migration. In this review, we examine what is currently known about adhesomes, revise how mechanical forces have changed our view on the regulation of cell migration, and, in this context, discuss how we have contributed to the understanding of signaling mechanisms that control cell adhesion and migration.

Free Energy Landscape of Type III Fibronectin Domain with Identified Intermediate State and Hierarchical Symmetry

The tenth domain of type III fibronectin (FNIII_{10}) mediates cell adhesion to the extracellular matrix. Despite its structural similarity to immunoglobulin domains, FNIII_{10} exhibits unique unfolding behaviors. We employed magnetic tweezers to investigate the unfolding and folding dynamics of FNIII_{10} under physiological forces (4-50 pN). Our results showed that FNIII_{10} follows a consistent transition pathway with an intermediate state characterized by detached A and G β strands. We determined the folding free energies and all force-dependent transition rates of FNIII_{10} and found that both unfolding rates from the native state to the intermediate state and from the intermediate state to the unfolded state deviate from Bell's model. We constructed a quantitative free energy landscape with well-defined traps and barriers that exhibits a hierarchical symmetrical pattern. Our findings provide a comprehensive understanding of FNIII_{10} conformational dynamics and demonstrate how free energy landscape of multistate biomolecules can be precisely mapped, illuminating the relationship between thermal stability, intermediate states, and folding rates in protein folding.

Fibrillar adhesion dynamics govern the timescales of nuclear mechano-response via the vimentin cytoskeleton

The cell nucleus is continuously exposed to external signals, of both chemical and mechanical nature. To ensure proper cellular response, cells need to regulate not only the transmission of these signals, but also their timing and duration. Such timescale regulation is well described for fluctuating chemical signals, but if and how it applies to mechanical signals reaching the nucleus is still unknown. Here we demonstrate that the formation of fibrillar adhesions locks the nucleus in a mechanically deformed conformation, setting the mechanical response timescale to that of fibrillar adhesion remodelling (~1 hour). This process encompasses both mechanical deformation and associated mechanotransduction (such as via YAP), in response to both increased and decreased mechanical stimulation. The underlying mechanism is the anchoring of the vimentin cytoskeleton to fibrillar adhesions and the extracellular matrix through plectin 1f, which maintains nuclear deformation. Our results reveal a mechanism to regulate the timescale of mechanical adaptation, effectively setting a low pass filter to mechanotransduction.

Native extracellular matrix probes to target patient- and tissue-specific cell-microenvironment interactions by force spectroscopy

Atomic Force Microscopy (AFM) is successfully used for the quantitative investigation of the cellular mechanosensing of the microenvironment. To this purpose, several force spectroscopy approaches aim at measuring the adhesive forces between two living cells and also between a cell and an appropriate reproduction of the extracellular matrix (ECM), typically exploiting tips suitably functionalised with single components (e.g. collagen, fibronectin) of the ECM. However, these probes only poorly reproduce the complexity of the native cellular microenvironment and consequently of the biological interactions. We developed a novel approach to produce AFM probes that faithfully retain the structural and biochemical complexity of the ECM; this was achieved by attaching to an AFM cantilever a micrometric slice of native decellularised ECM, which was cut by laser microdissection. We demonstrate that these probes preserve the morphological, mechanical, and chemical heterogeneity of the ECM. Native ECM probes can be used in force spectroscopy experiments aimed at targeting cell-microenvironment interactions. Here, we demonstrate the feasibility of dissecting mechanotransductive cell-ECM interactions in the 10 pN range. As proof-of-principle, we tested a rat bladder ECM probe against the AY-27 rat bladder cancer cell line. On the one hand, we obtained reproducible results using different probes derived from the same ECM regions; on the other hand, we detected differences in the adhesion patterns of distinct bladder ECM regions (submucosa, detrusor, and adventitia), in line with the disparities in composition and biophysical properties of these ECM regions. Our results demonstrate that native ECM probes, produced from patient-specific regions of organs and tissues, can be used to investigate cell-microenvironment interactions and early mechanotransductive processes by force spectroscopy. This opens new possibilities in the field of personalised medicine.

The Mechanotransduction Signaling Pathways in the Regulation of Osteogenesis

Bones are constantly exposed to mechanical forces from both muscles and Earth's gravity to maintain bone homeostasis by stimulating bone formation. Mechanotransduction transforms external mechanical signals such as force, fluid flow shear, and gravity into intracellular responses to achieve force adaptation. However, the underlying molecular mechanisms on the conversion from mechanical signals into bone formation has not been completely defined yet. In the present review, we provide a comprehensive and systematic description of the mechanotransduction signaling pathways induced by mechanical stimuli during osteogenesis and address the different layers of interconnections between different signaling pathways. Further exploration of mechanotransduction would benefit patients with osteoporosis, including the aging population and postmenopausal women.

Optimal cell traction forces in a generalized motor-clutch model

Cells exert forces on mechanically compliant environments to sense stiffness, migrate, and remodel tissue. Cells can sense environmental stiffness via myosin-generated pulling forces acting on F-actin, which is in turn mechanically coupled to the environment via adhesive proteins, akin to a clutch in a drivetrain. In this "motor-clutch" framework, the force transmitted depends on the complex interplay of motor, clutch, and environmental properties. Previous mean-field analysis of the motor-clutch model identified the conditions for optimal stiffness for maximal force transmission via a dimensionless number that combines motor-clutch parameters. However, in this and other previous mean-field analyses, the motor-clutch system is assumed to have balanced motors and clutches and did not consider force-dependent clutch reinforcement and catch bond behavior. Here, we generalize the motor-clutch analytical framework to include imbalanced motor-clutch regimes, with clutch reinforcement and catch bonding, and investigate optimality with respect to all parameters. We found that traction force is strongly influenced by clutch stiffness, and we discovered an optimal clutch stiffness that maximizes traction force, suggesting that cells could tune their clutch mechanical properties to perform a specific function. The results provide guidance for maximizing the accuracy of cell-generated force measurements via molecular tension sensors by designing their mechanosensitive linker peptide to be as stiff as possible. In addition, we found that, on rigid substrates, the mean-field analysis identifies optimal motor properties, suggesting that cells could regulate their myosin repertoire and activity to maximize force transmission. Finally, we found that clutch reinforcement shifts the optimum substrate stiffness to larger values, whereas the optimum substrate stiffness is insensitive to clutch catch bond properties. Overall, our work reveals novel features of the motor-clutch model that can affect the design of molecular tension sensors and provide a generalized analytical framework for predicting and controlling cell adhesion and migration in immunotherapy and cancer.

SEMA7a primes integrin α5β1 engagement instructing fibroblast mechanotransduction, phenotype and transcriptional programming

Integrins are cellular receptors that bind the extracellular matrix (ECM) and facilitate the transduction of biochemical and biophysical microenvironment cues into cellular responses. Upon engaging the ECM, integrin heterodimers must rapidly strengthen their binding with the ECM, resulting in the assembly of force-resistant and force-sensitive integrin associated complexes (IACs). The IACs constitute an essential apparatus for downstream signaling and fibroblast phenotypes. During wound healing, integrin signaling is essential for fibroblast motility, proliferation, ECM reorganization and, ultimately, restoration of tissue homeostasis. Semaphorin 7A (SEMA7a) has been previously implicated in post-injury inflammation and tissue fibrosis, yet little is known about SEMA7a's role in directing stromal cell, particularly fibroblast, behaviors. We demonstrate that SEMA7a regulates integrin signaling through cis-coupling with active integrin α5β1 on the plasma membrane, enabling rapid integrin adhesion strengthening to fibronectin (Fn) and normal downstream mechanotransduction. This molecular function of SEMA7a potently regulates fibroblast adhesive, cytoskeletal, and migratory phenotype with strong evidence of downstream alterations in chromatin structure resulting in global transcriptomic reprogramming such that loss of SEMA7a expression is sufficient to impair the normal migratory and ECM assembly phenotype of fibroblasts resulting in significantly delayed tissue repair in vivo.

Engineered Biomimetic Fibrillar Fibronectin Matrices Regulate Cell Adhesion Initiation, Migration, and Proliferation via α5β1 Integrin and Syndecan-4 Crosstalk

Cells regulate adhesion to the fibrillar extracellular matrix (ECM) of which fibronectin is an essential component. However, most studies characterize cell adhesion to globular fibronectin substrates at time scales long after cells polarize and migrate. To overcome this limitation, a simple and scalable method to engineer biomimetic 3D fibrillar fibronectin matrices is introduced and how they are sensed by fibroblasts from the onset of attachment is characterized. Compared to globular fibronectin substrates, fibroblasts accelerate adhesion initiation and strengthening within seconds to fibrillar fibronectin matrices via α5β1 integrin and syndecan-4. This regulation, which additionally accelerates on stiffened fibrillar matrices, involves actin polymerization, actomyosin contraction, and the cytoplasmic proteins paxillin, focal adhesion kinase, and phosphoinositide 3-kinase. Furthermore, this immediate sensing and adhesion of fibroblast to fibrillar fibronectin guides migration speed, persistency, and proliferation range from hours to weeks. The findings highlight that fibrillar fibronectin matrices, compared to widely-used globular fibronectin, trigger short- and long-term cell decisions very differently and urge the use of such matrices to better understand in vivo interactions of cells and ECMs. The engineered fibronectin matrices, which can be printed onto non-biological surfaces without loss of function, open avenues for various cell biological, tissue engineering and medical applications.

Receptor-Ligand Binding: Effect of Mechanical Factors

Gaining insight into the in situ receptor-ligand binding is pivotal for revealing the molecular mechanisms underlying the physiological and pathological processes and will contribute to drug discovery and biomedical application. An important issue involved is how the receptor-ligand binding responds to mechanical stimuli. This review aims to provide an overview of the current understanding of the effect of several representative mechanical factors, such as tension, shear stress, stretch, compression, and substrate stiffness on receptor-ligand binding, wherein the biomedical implications are focused. In addition, we highlight the importance of synergistic development of experimental and computational methods for fully understanding the in situ receptor-ligand binding, and further studies should focus on the coupling effects of these mechanical factors.

The Integrin Pathway Partially Mediates Stretch-Induced Deficits in Primary Rat Microglia

Stretch-injured microglia display significantly altered morphology, function and inflammatory-associated gene expression when cultured on a synthetic fibronectin substrate. However, the mechanism by which stretch induces these changes is unknown. Integrins, such as α5β1, mediate microglial attachment to fibronectin via the RGD binding peptide; following integrin ligation the integrin-associated signaling enzyme, focal adhesion kinase (FAK), autophosphorylates tyrosine residue 397 and mediates multiple downstream cellular processes. We therefore hypothesize that blocking the RGD binding/integrin pathway with a commercially available RGD peptide will mimic the stretch-induced morphological alterations and functional deficits in microglia. Further, we hypothesize that upregulation of stretch-inhibited downstream integrin signaling will reverse these effects. Using primary rat microglia, we tested the effects of RGD binding peptide and a FAK activator on cellular function and structure and response to stretch-injury. Similar to injured cells, RGD peptide administration significantly decreases media nitric oxide (NO) levels and iNOS expression and induced morphological alterations and migratory deficits. While stretch-injury and RGD peptide administration decreased phosphorylation of the tyrosine 397 residue on FAK, 20 nM of ZINC 40099027, an activator specific to the tyrosine 397 residue, rescued the stretch-induced decrease in FAK phosphorylation and ameliorated the injury-induced decrease in media NO levels, iNOS expression and inflammatory associated gene expression. Additionally, treatment alleviated morphological changes observed after stretch-injury and restored normal migratory behavior to control levels. Taken together, these data suggest that the integrin/FAK pathway partially mediates the stretch-injured phenotype in microglia, and may serve as a pathway to modulate microglial responses.

Ion-Pair-Enhanced Double-Click Driven Cell Adhesion and Altered Expression of Related Genes

Bio-orthogonal ligations that crosslink living cells with a substrate or other cells require high stability and rapid kinetics to maintain the nature of target cells. In this study, we report water-soluble cyclooctadiyne (WS-CODY) derivatives that undergo an ion-pair enhanced double-click reaction. The cationic side chain of WS-CODY accelerated the kinetics on the azide-modified cell surface due to proximity effect. Cationic WS-CODY was able to crosslink azide-modified, poorly adherent human lung cancer PC-9 cells not only to azide-grafted glass substrates but also to other cells within 5-30 min. We discovered that cell-substrate crosslinking induced the ITGA5 gene expression, whereas cell-cell crosslinking induced the CTNNA1 gene, according to the adhesion partner. Ion-pair-enhanced WS-CODY can be applied to a wide range of cells with established azide modifications and is expected to provide a powerful tool to regulate cell-substrate and cell-cell interactions.

Electrical charge on ferroelectric nanocomposite membranes enhances SHED neural differentiation

Stem cells from human exfoliated deciduous teeth (SHED) uniquely exhibit high proliferative and neurogenic potential. Charged biomaterials have been demonstrated to promote neural differentiation of stem cells, but the dose-response effect of electrical stimuli from these materials on neural differentiation of SHED remains to be elucidated. Here, by utilizing different annealing temperatures prior to corona poling treatment, BaTiO₃/P(VDF-TrFE) ferroelectric nanocomposite membranes with varying charge polarization intensity (d₃₃ ≈ 0, 4, 12 and 19 pC N⁻¹) were fabricated. Enhanced expression of neural markers, increased cell elongation and more prominent neurite outgrowths were observed with increasing surface charge of the nanocomposite membrane indicating a dose-response effect of surface electrical charge on SHED neural differentiation. Further investigations of the underlying molecular mechanisms revealed that intracellular calcium influx, focal adhesion formation, FAK-ERK mechanosensing pathway and neurogenic-related ErbB signaling pathway were implicated in the enhancement of SHED neural differentiation by surface electrical charge. Hence, this study confirms the dose-response effect of biomaterial surface charge on SHED neural differentiation and provides preliminary insights into the molecular mechanisms and signaling pathways involved.

•

Membrane surface charge can be precisely controlled by adjusting annealing temperature and corona poling parameters.

•

Both earlier and later neurogenic differentiation of SHED appear to be dose-dependently enhanced by surface charge.

•

Underlying molecular mechanisms may involve intracellular Ca2+ influx, focal adhesion formation, FAK-ERK and ErbB signaling.

Organization, dynamics and mechanoregulation of integrin-mediated cell-ECM adhesions

The ability of animal cells to sense, adhere to and remodel their local extracellular matrix (ECM) is central to control of cell shape, mechanical responsiveness, motility and signalling, and hence to development, tissue formation, wound healing and the immune response. Cell-ECM interactions occur at various specialized, multi-protein adhesion complexes that serve to physically link the ECM to the cytoskeleton and the intracellular signalling apparatus. This occurs predominantly via clustered transmembrane receptors of the integrin family. Here we review how the interplay of mechanical forces, biochemical signalling and molecular self-organization determines the composition, organization, mechanosensitivity and dynamics of these adhesions. Progress in the identification of core multi-protein modules within the adhesions and characterization of rearrangements of their components in response to force, together with advanced imaging approaches, has improved understanding of adhesion maturation and turnover and the relationships between adhesion structures and functions. Perturbations of adhesion contribute to a broad range of diseases and to age-related dysfunction, thus an improved understanding of their molecular nature may facilitate therapeutic intervention in these conditions.

Extracellular Matrix (ECM) and Fibrosis in Adipose Tissue: Overview and Perspectives

Fibrosis in adipose tissue is a major driver of obesity-related metabolic dysregulation. It is characterized by an overaccumulation of extracellular matrix (ECM) during unhealthy expansion of adipose tissue in response to over nutrition. In obese adipose-depots, hypoxia stimulates multiple pro-fibrotic signaling pathways in different cell populations, thereby inducing the overproduction of the ECM components, including collagens, noncollagenous proteins, and additional enzymatic components of ECM synthesis. As a consequence, local fibrosis develops. The result of fibrosis-induced mechanical stress not only triggers cell necrosis and inflammation locally in adipose tissue but also leads to system-wide lipotoxicity and insulin resistance. A better understanding of the mechanisms underlying the obesity-induced fibrosis will help design therapeutic approaches to reduce or reverse the pathological changes associated with obese adipose tissue. Here, we aim to summarize the major advances in the field, which include newly identified fibrotic factors, cell populations that contribute to the fibrosis in adipose tissue, as well as novel mechanisms underlying the development of fibrosis. We further discuss the potential therapeutic strategies to target fibrosis in adipose tissue for the treatment of obesity-linked metabolic diseases and cancer. © 2023 American Physiological Society. Compr Physiol 13:4387-4407, 2023.

Tailoring the Sensitivity of Microcantilevers To Monitor the Mass of Single Adherent Living Cells

Microcantilevers are widely employed as mass sensors for biological samples, from single molecules to single cells. However, the accurate mass quantification of living adherent cells is impaired by the microcantilever's mass sensitivity and cell migration, both of which can lead to detect masses mismatching by ≫50%. Here, we design photothermally actuated microcantilevers to optimize the accuracy of cell mass measurements. By reducing the inertial mass of the microcantilever using a focused ion beam, we considerably increase its mass sensitivity, which is validated by finite element analysis and experimentally by gelatin microbeads. The improved microcantilevers allow us to instantly monitor at much improved accuracy the mass of both living HeLa cells and mouse fibroblasts adhering to different substrates. Finally, we show that the improved cantilever design favorably restricts cell migration and thus reduces the large measurement errors associated with this effect.

On the significance of membrane unfolding in mechanosensitive cell spreading: Its individual and synergistic effects

Mechanosensitivity of cell spread area to substrate stiffness has been established both through experiments and different types of mathematical models of varying complexity including both the mechanics and biochemical reactions in the cell. What has not been addressed in previous mathematical models is the role of cell membrane dynamics on cell spreading, and an investigation of this issue is the goal of this work. We start with a simple mechanical model of cell spreading on a deformable substrate and progressively layer mechanisms to account for the traction dependent growth of focal adhesions, focal adhesion induced actin polymerization, membrane unfolding/exocytosis and contractility. This layering approach is intended to progressively help in understanding the role each mechanism plays in reproducing experimentally observed cell spread areas. To model membrane unfolding we introduce a novel approach based on defining an active rate of membrane deformation that is dependent on membrane tension. Our modeling approach allows us to show that tension-dependent membrane unfolding plays a critical role in achieving the large cell spread areas experimentally observed on stiff substrates. We also demonstrate that coupling between membrane unfolding and focal adhesion induced polymerization works synergistically to further enhance cell spread area sensitivity to substrate stiffness. This enhancement has to do with the fact that the peripheral velocity of spreading cells is associated with contributions from the different mechanisms by either enhancing the polymerization velocity at the leading edge or slowing down of the retrograde flow of actin within the cell. The temporal evolution of this balance in the model corresponds to the three-phase behavior observed experimentally during spreading. In the initial phase membrane unfolding is found to be particularly important.

Spectral characterization of cell surface motion for mechanistic investigations of cellular mechanobiology

Understanding the specific mechanisms responsible for anabolic and catabolic responses to static or dynamic force are largely poorly understood. Because of this, most research groups studying mechanotransduction due to dynamic forces employ an empirical approach in deciding what frequencies to apply during experiments. While this has been shown to elucidate valuable information regarding how cells respond under controlled provocation, it is often difficult or impossible to determine a true optimal frequency for force application, as many intracellular complexes are involved in receiving, propagating, and responding to a given stimulus. Here we present a novel adaptation of an analytical technique from the fields of civil and mechanical engineering that may open the door to direct measurement of mechanobiological cellular frequencies which could be used to target specific cell signaling pathways leveraging synergy between outside-in and inside-out mechanotransduction approaches. This information could be useful in identifying how specific proteins are involved in the homeostatic balance, or disruption thereof, of cells and tissue, furthering the understanding of the pathogenesis and progression of many diseases across a wide variety of cell types, which may one day lead to the development of novel mechanobiological therapies for clinical use.

The glycocalyx affects the mechanotransductive perception of the topographical microenvironment

The cell/microenvironment interface is the starting point of integrin-mediated mechanotransduction, but many details of mechanotransductive signal integration remain elusive due to the complexity of the involved (extra)cellular structures, such as the glycocalyx. We used nano-bio-interfaces reproducing the complex nanotopographical features of the extracellular matrix to analyse the glycocalyx impact on PC12 cell mechanosensing at the nanoscale (e.g., by force spectroscopy with functionalised probes). Our data demonstrates that the glycocalyx configuration affects spatio-temporal nanotopography-sensitive mechanotransductive events at the cell/microenvironment interface. Opposing effects of major glycocalyx removal were observed, when comparing flat and specific nanotopographical conditions. The excessive retrograde actin flow speed and force loading are strongly reduced on certain nanotopographies upon strong reduction of the native glycocalyx, while on the flat substrate we observe the opposite trend. Our results highlight the importance of the glycocalyx configuration in a molecular clutch force loading-dependent cellular mechanism for mechanosensing of microenvironmental nanotopographical features.

In-situ growth of robust superlubricated nano-skin on electrospun nanofibers for post-operative adhesion prevention

It is a great challenge to achieve robustly bonded, fully covered, and nanoscaled coating on the surface of electrospun nanofibers. Herein, we develop a controllable, facile, and versatile strategy to in-situ grow superlubricated nano-skin (SLNS) on the single electrospun nanofiber. Specifically, zwitterionic polymer chains are generated from the nanofiber subsurface in an inside-out way, which consequently form a robust network interpenetrating with the polymeric chains of the nanofiber matrix. The nanofibers with SLNS are superlubricated with the coefficient of friction (COF) lower than 0.025, which is about 16-fold of reduction than the original nanofibers. The time-COF plot is very stable after 12, 000 cycles of friction test, and no abrasion is observed. Additionally, the developed nanofibrous membranes possess favorable tensile property and biocompatibility. Furthermore, the nanofibrous membranes with SLNS achieve prevention of post-operative adhesion, which is confirmed in both rat tendon adhesion model and abdominal adhesion model. Compared with clinically-used antiadhesive membranes such as Interceed and DK-film, our nanofibrous membranes are not only more effective but also have the advantage of lower production cost. Therefore, this study demonstrates a potential of the superlubricated nanofibrous membranes in-situ grown based on a SLNS strategy for achieving prevention of post-operative adhesion in clinics.

The interactions between integrin α5β1 of liver cancer cells and fibronectin of fibroblasts promote tumor growth and angiogenesis

Hepatocellular carcinoma (HCC) progression is closely related to pathological fibrosis, which involves heterotypic intercellular interactions (HIIs) between liver cancer cells and fibroblasts. Here, we studied them in a direct coculture model, and identified fibronectin from fibroblasts and integrin-α₅β₁ from liver cancer cells as the primary responsible molecules utilizing CRISPR/Cas9 gene-editing technology. Coculture led to the formation of 3D multilayer microstructures, and obvious fibronectin remodeling was caused by upregulated integrin-α₅β₁, which greatly promoted cell growth in 3D microstructures. Integrin-α₅ was more sensitive and specific than integrin-β₁ in this process. Subsequent mechanistic exploration revealed the activation of integrin-Src-FAK, AKT and ERK signaling pathways. Importantly, the growth-promoting effect of HIIs was verified in a xenograft tumor model, in which more blood vessels were observed in bigger tumors derived from the coculture group than that derived from monocultured groups. Hence, we conducted triculture by introducing human umbilical vein endothelial cells, which aligned to and differentiated along multilayer microstructures in an integrin-α₅β₁ dependent manner. Furthermore, fibronectin, integrin-α₅, and integrin-β₁ were upregulated in 52 HCC tumors, and fibronectin was related to microvascular invasion. Our findings identify fibronectin, integrin-α₅, and integrin-β₁ as tumor microenvironment-related targets and provide a basis for combination targeted therapeutic strategies for future HCC treatment.

A trio of biological rhythms and their relevance in rhythmic mechanical stimulation of cell cultures

The primary aim of this article is to provide a biological rhythm model based on previous theoretical and experimental findings to promote more comprehensive studies of rhythmic mechanical stimulation of cell cultures, which relates to tissue engineering and regenerative medicine fields. Through an interdisciplinary approach where different standpoints from biology and musicology are combined, we explore some of the core rhythmic features of biological and cellular rhythmic processes and present them as a trio model that aims to afford a basic but fundamental understanding of the connections between various biological rhythms. It is vital to highlight such links since rhythmic mechanical stimulation and its effect on cell cultures are vastly underexplored even though the cellular response to mechanical stimuli (mechanotransduction) has been studied widely and relevant experimental evidence suggests mechanotransduction processes are rhythmic.

Thy-1-Integrin Interactions in cis and Trans Mediate Distinctive Signaling

Thy-1 is a cell surface glycosylphosphatidylinositol (GPI)-anchored glycoprotein that bears a broad mosaic of biological roles across various cell types. Thy-1 displays strong physiological and pathological implications in development, cancer, immunity, and tissue fibrosis. Quite uniquely, Thy-1 is capable of mediating integrin-related signaling through direct trans- and cis-interaction with integrins. Both interaction types have shown distinctive roles, even when interacting with the same type of integrin, where binding in trans or in cis often yields divergent signaling events. In this review, we will revisit recent progress and discoveries of Thy-1–integrin interactions in trans and in cis, highlight their pathophysiological consequences and explore other potential binding partners of Thy-1 within the integrin regulation/signaling paradigm.

Signaling Downstream of Focal Adhesions Regulates Stiffness-Dependent Differences in the TGF-β1-Mediated Myofibroblast Differentiation of Corneal Keratocytes

Following injury and refractive surgery, corneal wound healing can initiate a protracted fibrotic response that interferes with ocular function. This fibrosis is related, in part, to the myofibroblast differentiation of corneal keratocytes in response to transforming growth factor beta 1 (TGF-β1). Previous studies have shown that changes in the mechanical properties of the extracellular matrix (ECM) can regulate this process, but the mechanotransductive pathways that govern stiffness-dependent changes in keratocyte differentiation remain unclear. Here, we used a polyacrylamide (PA) gel system to investigate how mechanosensing via focal adhesions (FAs) regulates the stiffness-dependent myofibroblast differentiation of primary corneal keratocytes treated with TGF-β1. Soft (1 kPa) and stiff (10 kPa) PA substrata were fabricated on glass coverslips, plated with corneal keratocytes, and cultured in defined serum free media with or without exogenous TGF-β1. In some experiments, an inhibitor of focal adhesion kinase (FAK) activation was also added to the media. Cells were fixed and stained for F-actin, as well as markers for myofibroblast differentiation (α-SMA), actomyosin contractility phosphorylated myosin light chain (pMLC), focal adhesions (vinculin), or Smad activity (pSmad3). We also used traction force microscopy (TFM) to quantify cellular traction stresses. Treatment with TGF-β1 elicited stiffness-dependent differences in the number, size, and subcellular distribution of FAs, but not in the nuclear localization of pSmad3. On stiff substrata, cells exhibited large FAs distributed throughout the entire cell body, while on soft gels, the FAs were smaller, fewer in number, and localized primarily to the distal tips of thin cellular extensions. Larger and increased numbers of FAs correlated with elevated traction stresses, increased levels of α-SMA immunofluorescence, and more prominent and broadly distributed pMLC staining. Inhibition of FAK disrupted stiffness-dependent differences in keratocyte contractility, FA patterning, and myofibroblast differentiation in the presence of TGF-β1. Taken together, these data suggest that signaling downstream of FAs has important implications for the stiffness-dependent myofibroblast differentiation of corneal keratocytes.

Focal adhesion-mediated cell anchoring and migration: from in vitro to in vivo

Cell-extracellular matrix interactions have been studied extensively using cells cultured in vitro. These studies indicate that focal adhesion (FA)-based cell-extracellular matrix interactions are essential for cell anchoring and cell migration. Whether FAs play a similarly important role in vivo is less clear. Here, we summarize the formation and function of FAs in cultured cells and review how FAs transmit and sense force in vitro. Using examples from animal studies, we also describe the role of FAs in cell anchoring during morphogenetic movements and cell migration in vivo. Finally, we conclude by discussing similarities and differences in how FAs function in vitro and in vivo.

Arg-Gly-Asp peptide functionalized poly-amino acid/ poly (p-benzamide) copolymer with enhanced mechanical properties and osteogenicity

Poly-amino acid (PAA) is a promising biomaterial in biomedical engineering due to its similar amide bond structure to collagen and excellent biocompatibility, but the lack of osteogenic activity and inferior mechanical strength limit its long-term application in orthopedics. In this study, a poly-amino acid/poly (p-benzamide) (PAA-PBA) copolymer with high mechanical strength was designed and fabricated by the method of solution polymerization. The chain structures, thermal properties and mechanical properties of these polymers were evaluated and results showed that PBA greatly promoted the mechanical properties of PAA, and the copolymer performed the maximum mechanical strengths with compressive strength, bending strength and tensile strength of 123 MPa, 107 MPa and, 95 MPa, respectively. To increase the bioactivity of surface, a bioactive coating that consists of poly-(dopamine) (PDA) nanolayers and tripeptide Arginine-Glycine-Aspartic acid (RGD) on sulfonated PAA-PBA copolymer was created. A porous structure appeared on the surface after modification, the surface roughness and hydrophilicity of copolymer has been improved obviously after introducing PDA and RGD peptide coating. The in vitro bioactivity evaluation demonstrated that the RGD-functionalized sample showed a significantly improved ability to promote bone apatite mineralization, cell adhesion, proliferation and osteogenic differentiation. In a word, such a strategy of material synthesis and surface modification method shows a great potential for broadening the use of PAA in the application of load-bearing bone substitute biomaterials.

Engineering Photoresponsive Ligand Tethers for Mechanical Regulation of Stem Cells

Regulating stem cell functions by precisely controlling the nanoscale presentation of bioactive ligands has a substantial impact on tissue engineering and regenerative medicine but remains a major challenge. Here it is shown that bioactive ligands can become mechanically "invisible" by increasing their tether lengths to the substrate beyond a critical length, providing a way to regulate mechanotransduction without changing the biochemical conditions. Building on this finding, light switchable tethers are rationally designed, whose lengths can be modulated reversibly by switching a light-responsive protein, pdDronpa, in between monomer and dimer states. This allows the regulation of the adhesion, spreading, and differentiation of stem cells by light on substrates of well-defined biochemical and physical properties. Spatiotemporal regulation of differential cell fates on the same substrate is further demonstrated, which may represent an important step toward constructing complex organoids or mini tissues by spatially defining the mechanical cues of the cellular microenvironment with light.

Effects of forces on chromatin

Chromatin is a unique structure of DNA and histone proteins in the cell nucleus and the site of dynamic regulation of gene expression. Soluble factors are known to affect the chromatin structure and function via activating or inhibiting specific transcription factors. Forces on chromatin come from exogenous stresses on the cell surface and/or endogenous stresses, which are regulated by substrate mechanics, geometry, and topology. Forces on chromatin involve direct (via adhesion molecules, cytoskeleton, and the linker of nucleoskeleton and cytoskeleton complexes) and indirect (via diffusion and/or translocation processes) signaling pathways to modulate levels of chromatin folding and deformation to regulate transcription, which is controlled by histone modifications and depends on magnitude, direction, rate/frequency, duration, and modes of stresses. The rapid force transmission pathway activates multiple genes simultaneously, and the force may act like a "supertranscription factor." The indirect mechanotransduction pathways and the rapid force transmission pathway together exert sustained impacts on the chromatin, the nucleus, and cell functions.