Cell mechanics and the cytoskeleton

Building on-chip cytoskeletal circuits via branched microtubule networks

Controllable platforms to engineer robust cytoskeletal scaffolds have the potential to create novel on-chip nanotechnologies. Inspired by axons, we combined the branching microtubule (MT) nucleation pathway with microfabrication to develop "cytoskeletal circuits." This active matter platform allows control over the adaptive self-organization of uniformly polarized MT arrays via geometric features of microstructures designed within a microfluidic confinement. We build and characterize basic elements, including turns and divisions, as well as complex regulatory elements, such as biased division and MT diodes, to construct various MT architectures on a chip. Our platform could be used in diverse applications, ranging from efficient on-chip molecular transport to mechanical nano-actuators. Further, cytoskeletal circuits can serve as a tool to study how the physical environment contributes to MT architecture in living cells.

Midline-1 regulates effector T cell motility in experimental autoimmune encephalomyelitis via mTOR/microtubule pathway

Background: Effector T cell activation, migration, and proinflammatory cytokine production are crucial steps in autoimmune disorders such as multiple sclerosis (MS). While several therapeutic approaches targeting T cell activation and proinflammatory cytokines have been developed for the treatment of autoimmune diseases, there are no therapeutic agents targeting the migration of effector T cells, largely due to our limited understanding of regulatory mechanisms of T cell migration in autoimmune disease. Here we reported that midline-1 (Mid1) is a key regulator of effector T cell migration in experimental autoimmune encephalomyelitis (EAE), a widely used animal model of MS. Methods: Mid1-/- mice were generated by Crispr-Cas9 technology. T cell-specific Mid1 knockout chimeric mice were generated by adoptive transfer of Mid1-/- T cells into lymphocyte deficient Rag2-/- mice. Mice were either immunized with MOG35-55 (active EAE) or received adoptive transfer of pathogenic T cells (passive EAE) to induce EAE. In vitro Transwell® assay or in vivo footpad injection were used to assess the migration of T cells. Results: Mid1 was significantly increased in the spinal cord of wild-type (Wt) EAE mice and disruption of Mid1 in T cells markedly suppressed the development of both active and passive EAE. Transcriptomic and flow cytometric analyses revealed a marked reduction in effector T cell number in the central nervous system of Mid1-/- mice after EAE induction. Conversely, an increase in the number of T cells was observed in the draining lymph nodes of Mid1-/- mice. Mice that were adoptively transferred with pathogenic Mid1-/- T cells also exhibited milder symptoms of EAE, along with a lower T cell count in the spinal cord. Additionally, disruption of Mid1 significantly inhibited T-cell migration both in vivo and in vitro. RNA sequencing suggests a suppression in multiple inflammatory pathways in Mid1-/- mice, including mTOR signaling that plays a critical role in cell migration. Subsequent experiments confirmed the interaction between Mid1 and mTOR. Suppression of mTOR with rapamycin or microtubule spindle formation with colcemid blunted the regulatory effect of Mid1 on T cell migration. In addition, mTOR agonists MHY1485 and 3BDO restored the migratory deficit caused by Mid1 depletion. Conclusion: Our data suggests that Mid1 regulates effector T cell migration to the central nervous system via mTOR/microtubule pathway in EAE, and thus may serve as a potential therapeutic target for the treatment of MS.

Machine learning interpretable models of cell mechanics from protein images

Cellular form and function emerge from complex mechanochemical systems within the cytoplasm. Currently, no systematic strategy exists to infer large-scale physical properties of a cell from its molecular components. This is an obstacle to understanding processes such as cell adhesion and migration. Here, we develop a data-driven modeling pipeline to learn the mechanical behavior of adherent cells. We first train neural networks to predict cellular forces from images of cytoskeletal proteins. Strikingly, experimental images of a single focal adhesion (FA) protein, such as zyxin, are sufficient to predict forces and can generalize to unseen biological regimes. Using this observation, we develop two approaches-one constrained by physics and the other agnostic-to construct data-driven continuum models of cellular forces. Both reveal how cellular forces are encoded by two distinct length scales. Beyond adherent cell mechanics, our work serves as a case study for integrating neural networks into predictive models for cell biology.

Molecular basis and current insights of atypical Rho small GTPase in cancer

Atypical Rho GTPases are a subtype of the Rho GTPase family that are involved in diverse cellular processes. The typical Rho GTPases, led by RhoA, Rac1 and Cdc42, have been well studied, while relative studies on atypical Rho GTPases are relatively still limited and have great exploration potential. With the increase in studies, current evidence suggests that atypical Rho GTPases regulate multiple biological processes and play important roles in the occurrence and development of human cancers. Therefore, this review mainly discusses the molecular basis of atypical Rho GTPases and their roles in cancer. We summarize the sequence characteristics, subcellular localization and biological functions of each atypical Rho GTPase. Moreover, we review the recent advances and potential mechanisms of atypical Rho GTPases in the development of multiple cancers. A comprehensive understanding and extensive exploration of the biological functions of atypical Rho GTPases and their molecular mechanisms in tumors will provide important insights into the pathophysiology of tumors and the development of cancer therapeutic strategies.

High-throughput single-cell assay for precise measurement of the intrinsic mechanical properties and shape characteristics of red blood cells

The intrinsic physical and mechanical properties of red blood cells (RBCs), including their geometric and rheological characteristics, can undergo changes in various circulatory and metabolic diseases. However, clinical diagnosis using RBC biophysical phenotypes remains impractical due to the unique biconcave shape, remarkable deformability, and high heterogeneity within different subpopulations. Here, we combine the hydrodynamic mechanisms of fluid-cell interactions in micro circular tubes with a machine learning method to develop a relatively high-throughput microfluidic technology that can accurately measure the shear modulus of the membrane, viscosity, surface area, and volume of individual RBCs. The present method can detect the subtle changes of mechanical properties in various RBC components at continuum scales in response to different doses of cytoskeletal drugs. We also investigate the correlation between glycosylated hemoglobin and RBC mechanical properties. Our study develops a methodology that combines microfluidic technology and machine learning to explore the material properties of cells based on fluid-cell interactions. This approach holds promise in offering novel label-free single-cell-assay-based biophysical markers for RBCs, thereby enhancing the potential for more robust disease diagnosis.

Liquid-like condensates mediate competition between actin branching and bundling

Cellular remodeling of actin networks underlies cell motility during key morphological events, from embryogenesis to metastasis. In these transformations, there is an inherent competition between actin branching and bundling, because steric clashes among branches create a mechanical barrier to bundling. Recently, liquid-like condensates consisting purely of proteins involved in either branching or bundling of the cytoskeleton have been found to catalyze their respective functions. Yet in the cell, proteins that drive branching and bundling are present simultaneously. In this complex environment, which factors determine whether a condensate drives filaments to branch or become bundled? To answer this question, we added the branched actin nucleator, Arp2/3, to condensates composed of VASP, an actin bundling protein. At low actin to VASP ratios, branching activity, mediated by Arp2/3, robustly inhibited VASP-mediated bundling of filaments, in agreement with agent-based simulations. In contrast, as the actin to VASP ratio increased, addition of Arp2/3 led to formation of aster-shaped structures, in which bundled filaments emerged from a branched actin core, analogous to filopodia emerging from a branched lamellipodial network. These results demonstrate that multi-component, liquid-like condensates can modulate the inherent competition between bundled and branched actin morphologies, leading to organized, higher-order structures, similar to those found in motile cells.

Atrial Proteomic Profiling Reveals a Switch Towards Profibrotic Gene Expression Program in CREM-IbΔC-X Mice with Persistent Atrial Fibrillation

Background

Overexpression of the CREM (cAMP response element-binding modulator) isoform CREM-IbΔC-X in transgenic mice (CREM-Tg) causes the age-dependent development of spontaneous AF.

Purpose

To identify key proteome signatures and biological processes accompanying the development of persistent AF through integrated proteomics and bioinformatics analysis.

Methods

Atrial tissue samples from three CREM-Tg mice and three wild-type littermates were subjected to unbiased mass spectrometry-based quantitative proteomics, differential expression and pathway enrichment analysis, and protein-protein interaction (PPI) network analysis.

Results

A total of 98 differentially expressed proteins were identified. Gene ontology analysis revealed enrichment for biological processes regulating actin cytoskeleton organization and extracellular matrix (ECM) dynamics. Changes in ITGAV, FBLN5, and LCP1 were identified as being relevant to atrial fibrosis and remodeling based on expression changes, co-expression patterns, and PPI network analysis. Comparative analysis with previously published datasets revealed a shift in protein expression patterns from ion-channel and metabolic regulators in young CREM-Tg mice to profibrotic remodeling factors in older CREM-Tg mice. Furthermore, older CREM-Tg mice exhibited protein expression patterns that resembled those of humans with persistent AF.

Conclusions

This study uncovered distinct temporal changes in atrial protein expression patterns with age in CREM-Tg mice consistent with the progressive evolution of AF. Future studies into the role of the key differentially abundant proteins identified in this study in AF progression may open new therapeutic avenues to control atrial fibrosis and substrate development in AF.

Deep Learning Image Recognition-Assisted Atomic Force Microscopy for Single-Cell Efficient Mechanics in Co-culture Environments

Atomic force microscopy (AFM)-based force spectroscopy assay has become an important method for characterizing the mechanical properties of single living cells under aqueous conditions, but a disadvantage is its reliance on manual operation and experience as well as the resulting low throughput. Particularly, providing a capacity to accurately identify the type of the cell grown in co-culture environments without the need of fluorescent labeling will further facilitate the applications of AFM in life sciences. Here, we present a study of deep learning image recognition-assisted AFM, which not only enables fluorescence-independent recognition of the identity of single co-cultured cells but also allows efficient downstream AFM force measurements of the identified cells. With the use of the deep learning-based image recognition model, the viability and type of individual cells grown in co-culture environments were identified directly from the optical bright-field images, which were confirmed by the following cell growth and fluorescent labeling results. Based on the image recognition results, the positional relationship between the AFM probe and the targeted cell was automatically determined, allowing the precise movement of the AFM probe to the target cell to perform force measurements. The experimental results show that the presented method was applicable not only to the conventional (microsphere-modified) AFM probe used in AFM indentation assay for measuring the Young's modulus of single co-cultured cells but also to the single-cell probe used in AFM-based single-cell force spectroscopy (SCFS) assay for measuring the adhesion forces of single co-cultured cells. The study illustrates deep learning imaging recognition-assisted AFM as a promising approach for label-free and high-throughput detection of single-cell mechanics under co-culture conditions, which will facilitate unraveling the mechanical cues involved in cell-cell interactions in their native states at the single-cell level and will benefit the field of mechanobiology.

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.

Two-phase kinetics and cell cortex elastic behavior in Xenopus gastrula cell-cell adhesion

Morphogenetic movements during animal development involve repeated making and breaking of cell-cell contacts. Recent biophysical models of cell-cell adhesion integrate adhesion molecule interactions and cortical cytoskeletal tension modulation, describing equilibrium states for established contacts. We extend this emerging unified concept of adhesion to contact formation kinetics, showing that aggregating Xenopus embryonic cells rapidly achieve Ca2+-independent low-contact states. Subsequent transitions to cadherin-dependent high-contact states show rapid decreases in contact cortical F-actin levels but slow contact area growth. We developed a biophysical model that predicted contact growth quantitatively from known cellular and cytoskeletal parameters, revealing that elastic resistance to deformation and cytoskeletal network turnover are essential determinants of adhesion kinetics. Characteristic time scales of contact growth to low and high states differ by an order of magnitude, being at a few minutes and tens of minutes, respectively, thus providing insight into the timescales of cell-rearrangement-dependent tissue movements.

Immunofluorescence study of cytoskeleton in endothelial cells induced with malaria sera

BACKGROUND

Endothelial cells (ECs) play a major role in malaria pathogenesis, as a point of direct contact of parasitized red blood cells to the blood vessel wall. The study of cytoskeleton structures of ECs, whose main functions are to maintain shape and provide strength to the EC membrane is important in determining the severe sequelae of Plasmodium falciparum malaria. The work investigated the cytoskeletal changes (microfilaments-actin, microtubules-tubulin and intermediate filaments-vimentin) in ECs induced by malaria sera (Plasmodium vivax, uncomplicated P. falciparum and complicated P. falciparum), in relation to the levels of pro-inflammatory cytokines.

METHODS

Morphology and fluorescence intensity of EC cytoskeleton stimulated with malaria sera were evaluated using immunofluorescence technique. Levels of tumour necrosis factor (TNF) and interferon (IFN)-gamma (γ) were determined using enzyme-linked immunosorbent assay (ELISA). Control experimental groups included ECs incubated with media alone and non-malaria patient sera. Experimental groups consisted of ECs incubated with malaria sera from P. vivax, uncomplicated P. falciparum and complicated P. falciparum. Morphological scores of cytoskeletal alterations and fluorescence intensity were compared across each experiment group, and correlated with TNF and IFN-γ.

RESULTS

The four morphological changes of cytoskeleton included (1) shrinkage of cytoskeleton and ECs with cortical condensation, (2) appearance of eccentric nuclei, (3) presence of "spiking pattern" of cytoskeleton and EC membrane, and (4) fragmentation and discontinuity of cytoskeleton and ECs. Significant damages were noted in actin filaments compared to tubulin and vimentin filaments in ECs stimulated with sera from complicated P. falciparum malaria. Morphological damages to cytoskeleton was positively correlated with fluorescence intensity and the levels of TNF and IFN-γ.

CONCLUSIONS

ECs stimulated with sera from complicated P. falciparum malaria showed cytoskeletal alterations and increased in fluorescence intensity, which was associated with high levels of TNF and IFN-γ. Cytoskeletal changes of ECs incubated with complicated P. falciparum malaria sera can lead to EC junctional alteration and permeability changes, which is mediated through apoptotic pathway. The findings can serve as a basis to explore measures to strengthen EC cytoskeleton and alleviate severe malaria complications such as pulmonary oedema and cerebral malaria. In addition, immunofluorescence intensity of cytoskeleton could be investigated as potential prognostic indicator for malaria severity.

Talin mechanotransduction in disease

Talin protein (Talin 1/2) is a mechanosensitive cytoskeleton protein. The unique structure of the Talin plays a vital role in transmitting mechanical forces. Talin proteins connect the extracellular matrix to the cytoskeleton by linking to integrins and actin, thereby mediating the conversion of mechanical signals into biochemical signals and influencing disease progression as potential diagnostic indicators, therapeutic targets, and prognostic indicators of various diseases. Most studies in recent years have confirmed that mechanical forces also have a crucial role in the development of disease, and Talin has been found to play a role in several diseases. Still, more studies need to be done on how Talin is involved in mechanical signaling in disease. This review focuses on the mechanical signaling of Talin in disease, aiming to summarize the mechanisms by which Talin plays a role in disease and to provide references for further studies.

Pattern recognition in the nucleation kinetics of non-equilibrium self-assembly

Inspired by biology's most sophisticated computer, the brain, neural networks constitute a profound reformulation of computational principles1-3. Analogous high-dimensional, highly interconnected computational architectures also arise within information-processing molecular systems inside living cells, such as signal transduction cascades and genetic regulatory networks4-7. Might collective modes analogous to neural computation be found more broadly in other physical and chemical processes, even those that ostensibly play non-information-processing roles? Here we examine nucleation during self-assembly of multicomponent structures, showing that high-dimensional patterns of concentrations can be discriminated and classified in a manner similar to neural network computation. Specifically, we design a set of 917 DNA tiles that can self-assemble in three alternative ways such that competitive nucleation depends sensitively on the extent of colocalization of high-concentration tiles within the three structures. The system was trained in silico to classify a set of 18 grayscale 30 × 30 pixel images into three categories. Experimentally, fluorescence and atomic force microscopy measurements during and after a 150 hour anneal established that all trained images were correctly classified, whereas a test set of image variations probed the robustness of the results. Although slow compared to previous biochemical neural networks, our approach is compact, robust and scalable. Our findings suggest that ubiquitous physical phenomena, such as nucleation, may hold powerful information-processing capabilities when they occur within high-dimensional multicomponent systems.

Design of bio-scaffold conjugated with chitosan-PEG nano-carriers containing bio-macromolecules of Verbascum sinuatum L. to differentiate human adipose-derived stem cells into dermal keratinocytes

Regenerative medicine and drug delivery systems provide promising approaches for the treatment of skin lesions. However, the design of engineered substrates containing therapeutic agents for cell proliferation and its differentiation into skin cells, with skin-like patterns, is the major challenge. Here, to overcome this problem, a hybrid scaffold conjugated with nanoparticles containing the extract of Verbascum sinuatum L. flowers (HE) was designed. To this end, (chitosan-PEG)-based nanocarriers (Chi-PEG) were first prepared in the volume ratios of 90:10, 80:20, 70:30, and 50:50 v/v. The results indicated that the 70:30 ratio possessed better physical/morphologic properties along with more suitable stability than other nanoparticles (encapsulation-efficiency:86.34 %, zeta-potential:21.2 mV, and PDI:0.30). Afterward, PCL-collagen biologic scaffold (PCL-Coll) were prepared by the lyophilization method, then conjugated with selected nanoparticles(Chi-PEG70:30-HE). Notably, in addition to PCL-Coll/Chi-PEG-HE, two scaffolds of PCL-Coll and PCL-Coll/Chi-PEG were prepared to evaluate the role of conjugation in the release behavior of herbal bio-macromolecules. Based on the results, the conjugation process was led to a more stable release, compared to unconjugated nanoparticles. The mentioned process also created an integrated network along with better physicomechanical properties [modulus:12.31 MPa, tensile strength:4.44 MPa, smaller pore size(2 μm), and better swelling (100.27 %) with a symmetrical wettability on the surface]. PCL-Coll/Chi-PEG-HE scaffold was also resulted in higher expression levels of K10 and K14 keratinocytes with biomimetic patterns than PCL-Coll/Chi-PEG scaffold. This could be due to the active ingredients of V. sinuatum extract like alkaloids, flavonoids, and triterpenoids which imparts the wound healing (anti-inflammatory, anti-bacterial, anti-oxidant) properties to this scaffold. It seems that the use of bioactive materials like herbal extracts, in the form of encapsulated into polymeric nanocarriers, in the structure of engineered scaffolds can be a promising option for regenerating damaged skin without scarring. Hence, this study can provide innovative insights into the combination of two techniques of drug delivery and tissue engineering to design bio-scaffolds containing bioactive molecules with better therapeutic approaches.

Cellular assays combined with metabolomics highlight the dual face of phenolics: From high permeability to morphological cell damage

The Caco-2 cellular permeability of phenolic aqueous extracts from blackcurrant press cake (BC), Norway spruce bark (NS), scots pine bark (SP), and sea buckthorn leaves (SB) was evaluated by combining high-resolution mass spectrometry and atomic force microscopy. Besides, Caco-2 and HepG2 cells allowed the study of intracellular oxidative stress assessed in both apical and basolateral domains. Overall, BC and NS showed the highest total phenolic contents, 4.38 and 3.76 µg/mL, respectively. Multivariate statistics discriminated NS and BC from SP and SB extracts because of their phenolic profile. Polyphenols were classified as highly permeable, thus suggesting their potentially high bioavailability through the gastrointestinal tract. All the phenolic subclasses showed efflux ratio values < 1, except for BC flavonols, flavan-3-ols, and stilbenes. Regarding cellular damage, NS and BC extracts, when acting on the basolateral cellular side, caused epithelial leakage and morphological shape cell damage on Caco-2 cells associated with ROS production.

Single-Cell Transcriptome Atlas and Regulatory Dynamics in Developing Cotton Anthers

Plant anthers are composed of different specialized cell types with distinct roles in plant reproduction. High temperature (HT) stress causes male sterility, resulting in crop yield reduction. However, the spatial expression atlas and regulatory dynamics during anther development and in response to HT remain largely unknown. Here, the first single-cell transcriptome atlas and chromatin accessibility survey in cotton anther are established, depicting the specific expression and epigenetic landscape of each type of cell in anthers. The reconstruction of meiotic cells, tapetal cells, and middle layer cell developmental trajectories not only identifies novel expressed genes, but also elucidates the precise degradation period of middle layer and reveals a rapid function transition of tapetal cells during the tetrad stage. By applying HT, heterogeneity in HT response is shown among cells of anthers, with tapetal cells responsible for pollen wall synthesis are most sensitive to HT. Specifically, HT shuts down the chromatin accessibility of genes specifically expressed in the tapetal cells responsible for pollen wall synthesis, such as QUARTET 3 (QRT3) and CYTOCHROME P450 703A2 (CYP703A2), resulting in a silent expression of these genes, ultimately leading to abnormal pollen wall and male sterility. Collectively, this study provides substantial information on anthers and provides clues for heat-tolerant crop creation.

The Cytoskeleton and Its Binding Proteins as Mechanosensors, Transducers, and Functional Regulators of Cells

Due to its complement of diverse proteins, such as actin filaments, intermediate filaments, and microtubules, the cytoskeleton is essential not only for structural stability but also for regulating cellular signaling, intracellular transportation, and cell division [...].

Capsid-host interactions for HIV-1 ingress

The HIV-1 capsid, composed of approximately 1,200 copies of the capsid protein, encases genomic RNA alongside viral nucleocapsid, reverse transcriptase, and integrase proteins. After cell entry, the capsid interacts with a myriad of host factors to traverse the cell cytoplasm, pass through the nuclear pore complex (NPC), and then traffic to chromosomal sites for viral DNA integration. Integration may very well require the dissolution of the capsid, but where and when this uncoating event occurs remains hotly debated. Based on size constraints, a long-prevailing view was that uncoating preceded nuclear transport, but recent research has indicated that the capsid may remain largely intact during nuclear import, with perhaps some structural remodeling required for NPC traversal. Completion of reverse transcription in the nucleus may further aid capsid uncoating. One canonical type of host factor, typified by CPSF6, leverages a Phe-Gly (FG) motif to bind capsid. Recent research has shown these peptides reside amid prion-like domains (PrLDs), which are stretches of protein sequence devoid of charged residues. Intermolecular PrLD interactions along the exterior of the capsid shell impart avid host factor binding for productive HIV-1 infection. Herein we overview capsid-host interactions implicated in HIV-1 ingress and discuss important research questions moving forward. Highlighting clinical relevance, the long-acting ultrapotent inhibitor lenacapavir, which engages the same capsid binding pocket as FG host factors, was recently approved to treat people living with HIV.

Mesenchymal stem cells lose the senescent phenotype under 3D cultivation

BACKGROUND

Three-dimensional (3D) cell culture is widely used in various fields of cell biology. In comparison to conventional two-dimensional (2D) cell culture, 3D cell culture facilitates a more accurate replication of the in vivo microenvironment, which is essential for obtaining more relevant results. The application of 3D cell culture techniques in regenerative medicine, particularly in mesenchymal stem cell (MSC)-based research, has been extensively studied. Many of these studies focus on the enhanced paracrine activity of MSCs cultured in 3D environments. However, few focus on the cellular processes that occur during 3D cultivation.

METHODS

In this work, we studied the changes occurring within 3D-cultured MSCs (3D-MSCs). Specifically, we examined the expression of numerous senescent-associated markers, the actin cytoskeleton structure, the architecture of the Golgi apparatus and the localization of mTOR, one of the main positive regulators of replicative senescence. In addition, we assessed whether the selective elimination of senescent cells occurs upon 3D culturing by using cell sorting based on autofluorescence.

RESULTS

Our findings indicate that 3D-MSCs were able to lose replicative senescence markers under 3D cell culture conditions. We observed changes in actin cytoskeleton structure, Golgi apparatus architecture and revealed that 3D cultivation leads to the nuclear localization of mTOR, resulting in a decrease in its active cytoplasmic form. Additionally, our findings provide evidence that 3D cell culture promotes the phenotypic reversion of senescent cell phenotype rather than their removal from the bulk population.

CONCLUSION

These novel insights into the biology of 3D-MSCs can be applied to research in regenerative medicine to overcome replicative senescence and MSC heterogeneity as they often pose significant concerns regarding safety and effectiveness for therapeutic purposes.

Rho GTPase activity crosstalk mediated by Arhgef11 and Arhgef12 coordinates cell protrusion-retraction cycles

Rho GTPases play a key role in the spatio-temporal coordination of cytoskeletal dynamics during cell migration. Here, we directly investigate crosstalk between the major Rho GTPases Rho, Rac and Cdc42 by combining rapid activity perturbation with activity measurements in mammalian cells. These studies reveal that Rac stimulates Rho activity. Direct measurement of spatio-temporal activity patterns show that Rac activity is tightly and precisely coupled to local cell protrusions, followed by Rho activation during retraction. Furthermore, we find that the Rho-activating Lbc-type GEFs Arhgef11 and Arhgef12 are enriched at transient cell protrusions and retractions and recruited to the plasma membrane by active Rac. In addition, their depletion reduces activity crosstalk, cell protrusion-retraction dynamics and migration distance and increases migration directionality. Thus, our study shows that Arhgef11 and Arhgef12 facilitate exploratory cell migration by coordinating cell protrusion and retraction by coupling the activity of the associated regulators Rac and Rho.

Molecular basis and cellular functions of vinculin-actin directional catch bonding

The ability of cells and tissues to respond differentially to mechanical forces applied in distinct directions is mediated by the ability of load-bearing proteins to preferentially maintain physical linkages in certain directions. However, the molecular basis and biological consequences of directional force-sensitive binding remain unclear. Vinculin (Vcn) is a load-bearing linker protein that exhibits directional catch bonding due to interactions between the Vcn tail domain (Vt) and filamentous (F)-actin. We developed a computational approach to predict Vcn residues involved in directional catch bonding and produced a set of associated Vcn variants with unaltered Vt structure, actin binding, or phospholipid interactions. Incorporation of the variants did not affect Vcn activation but reduced Vcn loading and altered exchange dynamics, consistent with the loss of directional catch bonding. Expression of Vcn variants perturbed the coordination of subcellular structures and cell migration, establishing key cellular functions for Vcn directional catch bonding.

Intravenous Injection of Na Ions Aggravates Ang II-Induced Hypertension-Related Vascular Endothelial Injury by Increasing Transmembrane Osmotic Pressure

Introduction

Extracellular protein nanoparticles (PNs) and ions perform synergistical functions in the control of transmembrane osmotic pressure (OP) under isotonic conditions. Intravenous injection may disrupt the ion balance and alter PN levels in blood plasma, changing transmembrane OP and damaging vascular endothelial cells.

Methods

Na ions were injected into AngII-induced HUVECs to simulate cell injury in vitro, and tail vein infusion of Na ions into hypertensive rats was performed to assess vascular damage. Optical measurements using an intermediate filament (IF) tension probe were conducted to detect indicators related to transmembrane OP. Immunofluorescence, Western blotting and small interfering RNA (siRNA) transfection were employed to investigate inflammasomes and the relationship between Abl2 and inflammation.

Results

Electrolyte injections with sodium ions (but not glucose and hydroxyethyl starch) induced the production of ASC and NLRP3 inflammasomes in Ang II-induced HUVECs; this in turn resulted in the disorder of calcium signals, and changes in transmembrane OP and cell permeability. Moreover, injection of Na ions into Ang II-induced HUVECs activated the mechanosensitive protein Abl2, involved in inflammation-induced transmembrane OP changes. A drug combination was identified that could induce OP recovery and block hyperpermeability induced by cytoplasmic inflammatory corpuscles in vivo and in vitro.

Conclusion

Changes in extracellular PNs and ions following chemical stimuli (Ang II) participate in the regulation of transmembrane OP. Furthermore, injection of Na ions causes vascular endothelial injury in Ang II-induced cells in vitro and hypertension rats in vivo, suggesting it is not safe for hypertensive patients, and we propose a new drug combination as a solution.

Mechanical positive feedback and biochemical negative feedback combine to generate complex contractile oscillations in cytokinesis

Contractile force generation by the cortical actomyosin cytoskeleton is essential for a multitude of biological processes. The actomyosin cortex behaves as an active material that drives local and large-scale shape changes via cytoskeletal remodeling in response to biochemical cues and feedback loops. Cytokinesis is the essential cell division event during which a cortical actomyosin ring generates contractile force to change cell shape and separate two daughter cells. Our recent work with active gel theory predicts that actomyosin systems under the control of a biochemical oscillator and experiencing mechanical strain will exhibit complex spatiotemporal behavior, but cytokinetic contractility was thought to be kinetically simple. To test whether active materials in vivo exhibit spatiotemporally complex kinetics, we used 4-dimensional imaging with unprecedented temporal resolution and discovered sections of the cytokinetic cortex undergo periodic phases of acceleration and deceleration. Quantification of ingression speed oscillations revealed wide ranges of oscillation period and amplitude. In the cytokinetic ring, activity of the master regulator RhoA pulsed with a timescale of approximately 20 seconds, shorter than that reported for any other biological context. Contractility oscillated with 20-second periodicity and with much longer periods. A combination of in vivo and in silico approaches to modify mechanical feedback revealed that the period of contractile oscillation is prolonged as a function of the intensity of mechanical feedback. Effective local ring ingression is characterized by slower speed oscillations, likely due to increased local stresses and therefore mechanical feedback. Fast ingression also occurs where material turnover is high, in vivo and in silico . We propose that downstream of initiation by pulsed RhoA activity, mechanical positive feedback, including but not limited to material advection, extends the timescale of contractility beyond that of biochemical input and therefore makes it robust to fluctuations in activation. Circumferential propagation of contractility likely allows sustained contractility despite cytoskeletal remodeling necessary to recover from compaction. Our work demonstrates that while biochemical feedback loops afford systems responsiveness and robustness, mechanical feedback must also be considered to describe and understand the behaviors of active materials in vivo .

Direct observation of oriented behavior of actin filaments interacting with desmin intermediate filaments

BACKGROUND

Associations between actin filaments (AFs) and intermediate filaments (IFs) are frequently observed in living cells. The crosstalk between these cytoskeletal components underpins cellular organization and dynamics; however, the molecular basis of filamentous interactions is not fully understood. Here, we describe the mode of interaction between AFs and desmin IFs (DIFs) in a reconstituted in vitro system.

METHODS

AFs (rabbit skeletal muscle) and DIFs (chicken gizzard) were labeled with fluorescent dyes. DIFs were immobilized on a heavy meromyosin (HMM)-coated collodion surface. HMM-driven AFs with ATP hydrolysis was assessed in the presence of DIFs. Images of single filaments were obtained using fluorescence microscopy. Vector changes in the trajectories of single AFs were calculated from microscopy images.

RESULTS

AF speed transiently decreased upon contact with DIF. The difference between the incoming and outgoing angles of a moving AF broadened upon contact with a DIF. A smaller incoming angle tended to result in a smaller outgoing angle in a nematic manner. The percentage of moving AFs decreased with an increasing DIF density, but the speed of the moving AFs was similar to that in the no-desmin control. An abundance of DIFs tended to exclude AFs from the HMM-coated surfaces.

CONCLUSIONS

DIFs agitate the movement of AFs with the orientation. DIFs can bind to HMMs and weaken actin-myosin interactions.

GENERAL SIGNIFICANCE

The study indicates that apart from the binding strength, the accumulation of weak interactions characteristic of filamentous structures may affect the dynamic organization of cell architecture.

Mean-field theory approach to three-dimensional nematic phase transitions in microtubules

Microtubules are dynamic intracellular fibers that have been observed experimentally to undergo spontaneous self-alignment. We formulate a three-dimensional (3D) mean-field theory model to analyze the nematic phase transition of microtubules growing and interacting within a 3D space, then make a comparison with computational simulations. We identify a control parameter G_{eff} and predict a unique critical value G_{eff}=1.56 for which a phase transition can occur. Furthermore, we show both analytically and using simulations that this predicted critical value does not depend on the presence of zippering. The mean-field theory developed here provides an analytical estimate of microtubule patterning characteristics without running time-consuming simulations and is a step towards bridging scales from microtubule behavior to multicellular simulations.

Cellular consequences triggered by ketamine on exposure to human glioblastoma epithelial (LN-229) cells

Ketamine is generally a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist that interrelates with various other receptors, contributing to a wide range of actions. They are mainly approved as a general anesthetic, but a low dose of ketamine is applied for pain management, depression, and as analgesics. However, there is a significant concern regarding the long-term usage as antidepressants and as an abused drug. The study mainly aims to exhibit the possible long-term side effects of ketamine as an antidepressant and in recreational users. The study explores the in vitro cytotoxicity revealed on LN-229 cells in a dose-dependent manner. According to the cell viability assays, there is a dose-dependent response toward ketamine. Morphological and nuclear integrity was changed on exposure and assessed using Giemsa, Rhodamine phalloidin, 4',6-diamidino-2-phenylindole (DAPI), and Acridine orange staining. The apoptotic cell death marked by nuclear condensation, Lactate dehydrogenase leakage, pro-inflammatory cytokine (interleukin [IL]-β) release, and inhibition of cell migration was observed. The study highlights the importance of nonanesthetic usage of ketamine, which can lead to severe adverse side effects on long-term exposure rather than a single exposure as an anesthetic agent.

Bio-Inspired Far-From-Equilibrium Hydrogels: Design Principles and Applications

Inspired from dynamic living systems that operate under out-of-equilibrium conditions in biology, developing supramolecular hydrogels with self-regulating and autonomously dynamic properties to further advance adaptive hydrogels with life-like behavior is important. This review presents recent progress of bio-inspired supramolecular hydrogels out-of-equilibrium. The principle of out-of-equilibrium self-assembly for creating bio-inspired hydrogels is discussed. Various design strategies have been identified, such as chemical-driven reaction cycles with feedback control and physically oscillatory systems. These strategies can be coupled with hydrogels to achieve temporal and spatial control over structural and mechanical properties as well as programmable lifetime. These studies open up huge opportunities for potential applications, such as fluidic guidance, information storage, drug delivery, actuators and more. Finally, we address the challenges ahead of us in the coming years, and future possibilities and prospects are identified.

Non-Markovian Modeling of Nonequilibrium Fluctuations and Dissipation in Active Viscoelastic Biomatter

Based on a Hamiltonian that incorporates the elastic coupling between a tracer particle and the embedding active viscoelastic biomatter, we derive a generalized non-Markovian Langevin model for the nonequilibrium mechanical tracer response. Our analytical expressions for the frequency-dependent tracer response function and the tracer positional autocorrelation function agree quantitatively with experimental data for red blood cells and actomyosin networks with and without adenosine triphosphate over the entire frequency range and in particular reproduce the low-frequency violation of the fluctuation-dissipation theorem. The viscoelastic power laws, the elastic constants and effective friction coefficients extracted from the experimental data allow straightforward physical interpretation.

Meta-analysis of the Boyle van 't Hoff relation: Turgor and leak models explain non-ideal volume equilibrium

There has been much recent attention paid to the interaction of cell volume, its regulation, and the molecular biology of the cell. Cells are generally assumed to behave as linear osmometers, with their water volume linearly proportionate to the inverse of osmotic pressure as described by the Boyle van 't Hoff (BvH) relation. This study evaluates the generality of this and other long-standing assumptions about cell responses to anisotonic conditions. We present alternative models that account for osmoregulation including mechanical resistance to volumetric expansion (the turgor model) and ion-osmolyte leakage (the leak model). To evaluate the generality of the BvH relation and determine the suitability of alternative models, we performed a comprehensive survey of the literature and a careful analysis of the resulting data, and then we used these data to compare among models. We identified 137 articles published from 1964 to 2019 spanning 14 animal species and 26 cell types and determined the BvH relation is not an appropriate general model but is adequate when restricted to the hypertonic region. In contrast, models that account for either mechanical resistance or ion-osmolyte leakage fit well to almost all collected data. The leak model has fitted parameters that are in the same range as the current literature estimate, while the turgor model typically requires an elastic modulus value of one or multiple orders of magnitude larger than literature values. However, confirmation of the underlying mechanism of osmotic regulation is required at the cell-specific level and cannot be assumed a priori.

Coupling of static ultramicromagnetic field with elastic micropillar-structured substrate for cell response

Micropillars have emerged as promising tools for a wide range of biological applications, while the influence of magnetic fields on cell behavior regulation has been increasingly recognized. However, the combined effect of micropillars and magnetic fields on cell behaviors remains poorly understood. In this study, we investigated the responses of H9c2 cells to ultramicromagnetic micropillar arrays using NdFeB as the tuned magnetic particles. We conducted a comparative analysis between PDMS micropillars and NdFeB/PDMS micropillars to assess their impact on cell function. Our results revealed that H9c2 cells exhibited significantly enhanced proliferation and notable cytoskeletal rearrangements on the ultramicromagnetic micropillars, surpassing the effects observed with pure PDMS micropillars. Immunostaining further indicated that cells cultured on ultramicromagnetic micropillars displayed heightened contractility compared to those on PDMS micropillars. Remarkably, the ultramicromagnetic micropillars also demonstrated the ability to decrease reactive oxygen species (ROS) levels, thereby preventing F-actin degeneration. Consequently, this study introduces ultramicromagnetic micropillars as a novel tool for the regulation and detection of cell behaviors, thus paving the way for advanced investigations in tissue engineering, single-cell analysis, and the development of flexible sensors for cellular-level studies.

Vimentin regulates nuclear segmentation in neutrophils

Granulocytes are indispensable for various immune responses. Unlike other cell types in the body, the nuclei of granulocytes, particularly neutrophils, are heavily segmented into multiple lobes. Although this distinct morphological feature has long been observed, the underlying mechanism remains incompletely characterized. In this study, we utilize cryo-electron tomography to examine the nuclei of mouse neutrophils, revealing the cytoplasmic enrichment of intermediate filaments on the concave regions of the nuclear envelope. Aided by expression profiling and immuno-electron microscopy, we then elucidate that the intermediate-filament protein vimentin is responsible for such perinuclear structures. Of importance, exogenously expressed vimentin in nonimmune cells is sufficient to form cytoplasmic filaments wrapping on the concave nuclear surface. Moreover, genetic deletion of the protein causes a significant reduction of the number of nuclear lobes in neutrophils and eosinophils, mimicking the hematological condition of the Pelger-Huët anomaly. These results have uncovered a new component establishing the nuclear segmentation of granulocytes.

The actin-bundling protein, PLS3, is part of the mechanoresponsive machinery that regulates osteoblast mineralization

Plastin-3 (PLS3) is a calcium-sensitive actin-bundling protein that has recently been linked to the development of childhood-onset osteoporosis. Clinical data suggest that PLS3 mutations lead to a defect in osteoblast function, however the underlying mechanism remains elusive. To investigate the role of PLS3 in bone mineralization, we generated MC3T3-E1 preosteoblast cells that are stably depleted of PLS3. Analysis of osteogenic differentiation of control and PLS3 knockdown (PLS3 KD) cells showed that depletion of PLS3 does not alter the first stage of osteoblast mineralization in which a collagen matrix is deposited, but severely affects the subsequent mineralization of that matrix. During this phase, osteoblasts heavily rely on mechanosensitive signaling pathways to sustain mineral deposition in response to increasing stiffness of the extracellular matrix (ECM). PLS3 prominently localizes to focal adhesions (FAs), which are intricately linked to mechanosensation. In line with this, we observed that depletion of PLS3 rendered osteoblasts unresponsive to changes in ECM stiffness and showed the same cell size, FA lengths and number of FAs when plated on soft (6 kPa) versus stiff (100 kPa) substrates in contrast to control cells, which showed an increased in each of these parameters when plated on 100 kPa substrates. Defective cell spreading of PLS3 KD cells on stiff substrates could be rescued by expression of wildtype PLS3, but not by expression of three PLS3 mutations that were identified in patients with early onset osteoporosis and that have aberrant actin-bundling activity. Altogether, our results show that actin-bundling by PLS3 is part of the mechanosensitive mechanism that promotes osteoblast mineralization and thus begins to elucidate how PLS3 contributes to the development of bone defects such as osteoporosis.

Cell-Based Modeling of Tissue Developing in the Scaffold Pores of Varying Cross-Sections

In this work, we present a mathematical model of cell growth in the pores of a perfusion bioreactor through which a nutrient solution is pumped. We have developed a 2-D vertex model that allows us to reproduce the microscopic dynamics of the microenvironment of cells and describe the occupation of the pore space with cells. In this model, each cell is represented by a polygon; the number of vertices and shapes may change over time. The model includes mitotic cell division and intercalation. We study the impact of two factors on cell growth. On the one hand, we consider a channel of variable cross-section, which models a scaffold with a porosity gradient. On the other hand, a cluster of cells grows under the influence of a nutrient solution flow, which establishes a non-uniform distribution of shear stresses in the pore space. We present the results of numerical simulation of the tissue growth in a wavy channel. The model allows us to obtain complete microscopic information that includes the dynamics of intracellular pressure, the local elastic energy, and the characteristics of cell populations. As we showed, in a functional-graded scaffold, the distribution of the shear stresses in the pore space has a complicated structure, which implies the possibility of controlling the growth zones by varying the pore geometry.

Activity-dependent glassy cell mechanics II: Nonthermal fluctuations under metabolic activity

The glassy cytoplasm, crowded with bio-macromolecules, is fluidized in living cells by mechanical energy derived from metabolism. Characterizing the living cytoplasm as a nonequilibrium system is crucial in elucidating the intricate mechanism that relates cell mechanics to metabolic activities. In this study, we conducted active and passive microrheology in eukaryotic cells, and quantified nonthermal fluctuations by examining the violation of the fluctuation-dissipation theorem. The power spectral density of active force generation was estimated following the Langevin theory extended to nonequilibrium systems. However, experiments performed while regulating cellular metabolic activity showed that the nonthermal displacement fluctuation, rather than the active nonthermal force, is linked to metabolism. We discuss that mechano-enzymes in living cells do not act as microscopic objects. Instead, they generate meso-scale collective fluctuations with displacements controlled by enzymatic activity. The activity induces structural relaxations in glassy cytoplasm. Even though the autocorrelation of nonthermal fluctuations is lost at long timescales due to the structural relaxations, the nonthermal displacement fluctuation remains regulated by metabolic reactions. Our results therefore demonstrate that nonthermal fluctuations serve as a valuable indicator of a cell's metabolic activities, regardless of the presence or absence of structural relaxations.

Arabidopsis MYB21 Negatively Regulates KTN1 to Fine-Tune the Filament Elongation

The growth process of the stamen filament is crucial for plant reproduction. However, the molecular mechanisms underlying the regulation of filament growth remain largely unclear. Our study has identified that MYB21 is involved in the regulation of filament growth in Arabidopsis. In comparison to the wild type, the cell length of the filaments is notably reduced in the myb21 mutant. Moreover, we found that KTN1, which encodes a microtubule-severing enzyme, is significantly upregulated in the myb21 mutant. Additionally, yeast one-hybrid assays demonstrated that MYB21 can bind to the promoter region of KTN1, suggesting that MYB21 might directly regulate the expression of KTN1. Finally, transcriptional activity experiments showed that MYB21 is capable of suppressing the driving activity of the KTN1 promoter. This study indicates that the MYB21-KTN1 module may play a precise regulatory role in the growth of Arabidopsis filament cells.

In situ quantification of osmotic pressure within living embryonic tissues

Mechanics is known to play a fundamental role in many cellular and developmental processes. Beyond active forces and material properties, osmotic pressure is believed to control essential cell and tissue characteristics. However, it remains very challenging to perform in situ and in vivo measurements of osmotic pressure. Here we introduce double emulsion droplet sensors that enable local measurements of osmotic pressure intra- and extra-cellularly within 3D multicellular systems, including living tissues. After generating and calibrating the sensors, we measure the osmotic pressure in blastomeres of early zebrafish embryos as well as in the interstitial fluid between the cells of the blastula by monitoring the size of droplets previously inserted in the embryo. Our results show a balance between intracellular and interstitial osmotic pressures, with values of approximately 0.7 MPa, but a large pressure imbalance between the inside and outside of the embryo. The ability to measure osmotic pressure in 3D multicellular systems, including developing embryos and organoids, will help improve our understanding of its role in fundamental biological processes.

Effect of substrate heterogeneity and topology on epithelial tissue growth dynamics

Tissue growth kinetics and interface dynamics depend on the properties of the tissue environment and cell-cell interactions. In cellular environments, substrate heterogeneity and geometry arise from a variety factors, such as the structure of the extracellular matrix and nutrient concentration. We used the CellSim3D model, a kinetic cell division simulator, to investigate the growth kinetics and interface roughness dynamics of epithelial tissue growth on heterogeneous substrates with varying topologies. The results show that the presence of quenched disorder has a clear effect on the colony morphology and the roughness scaling of the interface in the moving interface regime. In a medium with quenched disorder, the tissue interface has a smaller interface roughness exponent, α, and a larger growth exponent, β. The scaling exponents also depend on the topology of the substrate and cannot be categorized by well-known universality classes.

Differential response of MDA‑MB‑231 breast cancer and MCF10A normal breast cells to cytoskeletal disruption

Metastasis remains a major clinical problem in cancer diagnosis and treatment. Metastasis is the leading cause of cancer‑related mortality but is still poorly understood. Cytoskeletal proteins are considered potential therapeutic targets for metastatic cancer cells because the cytoskeleton serves a key role in the migration and invasion of these cells. Vimentin and F‑actin exhibit several functional similarities and undergo quantitative and structural changes during carcinogenesis. The present study investigated the effects of vimentin and F‑actin deficiency on the survival and motility of breast cancer cells. In metastatic breast cancer cells (MDA‑MB‑231) and breast epithelial cells (MCF10A), vimentin was knocked down by small interfering RNA and F‑actin was depolymerized by latrunculin A, respectively. The effect of reduced vimentin and F‑actin content on cell viability was analyzed using the MTT assay and the proliferative capacity was compared by analyzing the recovery rate. The effect on motility was analyzed based on two processes: The distance traveled by tracking the cell nucleus and the movement of the protrusions. The effects on cell elasticity were measured using atomic force microscopy. Separately reducing vimentin or F‑actin did not effectively inhibit the growth and motility of MDA‑MB‑231 cells; however, when both vimentin and F‑actin were simultaneously deficient, MDA‑MB‑231 cells growth and migration were severely impaired. Vimentin deficiency in MDA‑MB‑231 cells was compensated by an increase in F‑actin polymerization, but no complementary action of vimentin on the decrease in F‑actin was observed. In MCF10A cells, no complementary interaction was observed for both vimentin and F‑actin.

The formins inhibitor SMIFH2 inhibits the cytoskeleton dynamics and mitochondrial function during goat oocyte maturation

The cytoskeleton plays a crucial role in facilitating the successful completion of the meiotic maturation of oocytes. Its influence extends to the process of oocyte nuclear maturation and the proper functioning of various organelles during cytoplasmic maturation. The formin family of proteins plays a crucial role in the molecular regulation of cytoskeletal assembly and organization; however, its role in goat oocytes are not fully understood. Our study examined the inhibition of formins activity, which revealed its crucial role in the maturation of goat oocytes. We observed that the inhibition of formins resulted in meiotic defects in goat oocytes, as evidenced by the hindered extrusion of polar bodies and the expansion of cumulus cells. Additionally, the oocytes exhibited altered actin dynamics and compromised spindle/chromosome structure upon formins inhibition. The results of the transcriptomic analysis highlighted a noteworthy alteration in the mRNA levels of genes implicated in mitochondrial functions and oxidative phosphorylation in formins inhibited oocytes. Validation experiments provided evidence that the meiotic defects observed in these oocytes were due to the excessive early apoptosis induced by reactive oxygen species (ROS). Our findings demonstrate that the involvement of formins in sustaining the cytoskeletal dynamics and mitochondrial function is crucial for the successful meiotic maturation of goat oocytes.

Biophysics in tumor growth and progression: from single mechano-sensitive molecules to mechanomedicine

Evidence from physical sciences in oncology increasingly suggests that the interplay between the biophysical tumor microenvironment and genetic regulation has significant impact on tumor progression. Especially, tumor cells and the associated stromal cells not only alter their own cytoskeleton and physical properties but also remodel the microenvironment with anomalous physical properties. Together, these altered mechano-omics of tumor tissues and their constituents fundamentally shift the mechanotransduction paradigms in tumorous and stromal cells and activate oncogenic signaling within the neoplastic niche to facilitate tumor progression. However, current findings on tumor biophysics are limited, scattered, and often contradictory in multiple contexts. Systematic understanding of how biophysical cues influence tumor pathophysiology is still lacking. This review discusses recent different schools of findings in tumor biophysics that have arisen from multi-scale mechanobiology and the cutting-edge technologies. These findings range from the molecular and cellular to the whole tissue level and feature functional crosstalk between mechanotransduction and oncogenic signaling. We highlight the potential of these anomalous physical alterations as new therapeutic targets for cancer mechanomedicine. This framework reconciles opposing opinions in the field, proposes new directions for future cancer research, and conceptualizes novel mechanomedicine landscape to overcome the inherent shortcomings of conventional cancer diagnosis and therapies.

Molecular mechanocytometry using tension-activated cell tagging

Flow cytometry is used routinely to measure single-cell gene expression by staining cells with fluorescent antibodies and nucleic acids. Here, we present tension-activated cell tagging (TaCT) to label cells fluorescently based on the magnitude of molecular force transmitted through cell adhesion receptors. As a proof-of-concept, we analyzed fibroblasts and mouse platelets after TaCT using conventional flow cytometry.

Surface stress and shape relaxation of gelling droplets

Solidification is a heterogeneous transformation from liquid to solid, which usually combines transport, phase transition and mechanical strain. Predicting the shapes resulting from such a complex process is fascinating and has a wide range of implications from morphogenesis in biological tissues to industrial processes. For soft solids initially at equilibrium, elastic stresses, whether tensile or compressive, can be induced by heterogeneous volumetric deformations of the material. These stresses trigger surface instabilities leading to variations of curvature and shape of the solids. In this article, we study the shape evolution of elongated droplets of polymer and particle suspensions undergoing a solidification process caused by the inward diffusion of a gelling agent from the surface. We show experimentally and numerically that there appears a layer of gelled material growing at the surface. Due to volume contraction, this layer induces tensile stresses and drives a flow in the ungelled liquid core, resulting in the relaxation of the droplets toward spherical shapes. Over time, the thickness of this elastic membrane grows, hence the bending stiffness required to change its shape eventually balances the surface stresses, which arrests the relaxation process. These results provide general rules to understand the shape of solidifying materials combining both tension and bending driven deformations.

Unlocking Colchicine's Untapped Potential: A Paradigm Shift in Hepatocellular Carcinoma Prevention

Background: Liver cancer and notably hepatocellular carcinoma (HCC), results in significantly high mortality rates worldwide. Chronic hepatitis and fatty liver, recognized precursors, underscore the imperative need for effective preventive strategies. This study explores colchicine, traditionally acknowledged for its anti-inflammatory properties and investigates its potential in liver cancer prevention. Methods: Utilizing the iHi Data Platform of China Medical University Hospital, Taiwan, this study analyzed two decades of medical data, incorporating 10,353 patients each in the Colchicine and Non-Colchicine cohorts, to investigate the association between colchicine use and liver cancer risk. Results: The study identified that colchicine users exhibited a 19% reduction in liver cancer risk, with a multivariable-adjusted odds ratio of 0.81 after accounting for confounding variables. Additionally, the influence of gender and comorbidities like diabetes mellitus on liver cancer risk was identified, corroborating the existing literature. A notable finding was that the prolonged use of colchicine was associated with improved outcomes, indicating a potential dose-response relationship. Conclusions: This study proposes a potential new role for colchicine in liver cancer prevention, extending beyond its established anti-inflammatory applications. While the findings are promising, further research is essential to validate these results. This research may serve as a foundation for future studies, aiming to further explore colchicine's role via clinical trials and in-depth investigations, potentially impacting preventive strategies for liver cancer.

Mechanotransduction in tissue engineering: Insights into the interaction of stem cells with biomechanical cues

Stem cells in their natural microenvironment are exposed to biochemical and biophysical cues emerging from the extracellular matrix (ECM) and neighboring cells. In particular, biomechanical forces modulate stem cell behavior, biological fate, and early developmental processes by sensing, interpreting, and responding through a series of biological processes known as mechanotransduction. Local structural changes in the ECM and mechanics are driven by reciprocal activation of the cell and the ECM itself, as the initial deposition of matrix proteins sequentially affects neighboring cells. Recent studies on stem cell mechanoregulation have provided insight into the importance of biomechanical signals on proper tissue regeneration and function and have shown that precise spatiotemporal control of these signals exists in stem cell niches. Against this background, the aim of this work is to review the current understanding of the molecular basis of mechanotransduction by analyzing how biomechanical forces are converted into biological responses via cellular signaling pathways. In addition, this work provides an overview of advanced strategies using stem cells and biomaterial scaffolds that enable precise spatial and temporal control of mechanical signals and offer great potential for the fields of tissue engineering and regenerative medicine will be presented.

The relationship between cancer and biomechanics

The onset, development, diagnosis, and treatment of cancer involve intricate interactions among various factors, spanning the realms of mechanics, physics, chemistry, and biology. Within our bodies, cells are subject to a variety of forces such as gravity, magnetism, tension, compression, shear stress, and biological static force/hydrostatic pressure. These forces are perceived by mechanoreceptors as mechanical signals, which are then transmitted to cells through a process known as mechanical transduction. During tumor development, invasion and metastasis, there are significant biomechanical influences on various aspects such as tumor angiogenesis, interactions between tumor cells and the extracellular matrix (ECM), interactions between tumor cells and other cells, and interactions between tumor cells and the circulatory system and vasculature. The tumor microenvironment comprises a complex interplay of cells, ECM and vasculature, with the ECM, comprising collagen, fibronectins, integrins, laminins and matrix metalloproteinases, acting as a critical mediator of mechanical properties and a key component within the mechanical signaling pathway. The vasculature exerts appropriate shear forces on tumor cells, enabling their escape from immune surveillance, facilitating their dissemination in the bloodstream, dictating the trajectory of circulating tumor cells (CTCs) and playing a pivotal role in regulating adhesion to the vessel wall. Tumor biomechanics plays a critical role in tumor progression and metastasis, as alterations in biomechanical properties throughout the malignant transformation process trigger a cascade of changes in cellular behavior and the tumor microenvironment, ultimately culminating in the malignant biological behavior of the tumor.

Substrate microtopographies induce cellular alignment and affect nuclear force transduction

Cellular physiology has been mainly studied by using two-dimensional cell culture substrates which lack in vivo-mimicking extracellular environment and interactions. Thus, there is a growing need for more complex model systems in life sciences. Micro-engineered scaffolds have been proven to be a promising tool in understanding the role of physical cues in the co-regulation of cellular functions. These tools allow, for example, probing cell morphology and migration in response to changes in chemo-physical properties of their microenvironment. In order to understand how microtopographical features, what cells encounter in vivo, affect cytoskeletal organization and nuclear mechanics, we used direct laser writing via two-photon polymerization (TPP) to fabricate substrates which contain different surface microtopographies. By combining with advanced high-resolution spectral imaging, we describe how the constructed grid and vertical line microtopographies influence cellular alignment, nuclear morphology and mechanics. Specifically, we found that growing cells on grids larger than 10 × 20 μm2 and on vertical lines increased 3D actin cytoskeleton orientation along the walls of microtopographies and abolished basal actin stress fibers. In concert, the nuclei of these cells were also more aligned, elongated, deformed and less flattened, indicating changes in nuclear force transduction. Importantly, by using fluorescence lifetime imaging microscopy for measuring Förster resonance energy transfer for a genetically encoded nesprin-2 molecular tension sensor, we show that growing cells on these microtopographic substrates induce lower mechanical tension at the nuclear envelope. To conclude, here used substrate microtopographies modulated the cellular mechanics, and affected actin organization and nuclear force transduction.

Bisphenol A is more potent than bisphenol S in influencing the physiological and pathological functions of lungs via inducing lung fibrosis and stimulating metastasis

Bisphenol A (BPA) is widely used in the production of plastics, food containers, and receipt ink globally. However, research has identified it as an endocrine disruptor, affecting the hormonal balance in living organisms. Bisphenol S (BPS), one of the alternative substances, was developed, but its effects on human health and the underlying mechanisms remain unclarified. Specifically, research on the effects of oral exposure to bisphenol on the lungs is lacking. We examined the potential differences in toxicity between these compounds in lung cells in vitro and in vivo. Our toxicity mechanism studies on MRC5 and A549 cells exposed to BPA or BPS revealed that BPA induced actin filament abnormalities and activated epithelial-mesenchymal transition (EMT). This finding suggests an increased potential for lung fibrosis and metastasis in lung cancer. However, given that BPS was not detected at the administered dose and under the specific experimental conditions, the probability of these occurrences is considered minimal. Additionally, animal experiments confirmed that oral exposure to BPA activates EMT in the lungs. Our study provides evidence that prolonged oral exposure to BPA can lead to EMT activation in lung tissue, similar to that observed in cell experiments, suggesting the potential to induce lung fibrosis. This research emphasizes the importance of regulating the use of BPA to mitigate its associated pulmonary toxicity. Furthermore, it is significant that within the parameters of our experimental conditions, BPS did not exhibit the toxicological pathways clearly evident in BPA.

Convergence of Calcium Channel Regulation and Mechanotransduction in Skeletal Regenerative Biomaterial Design

Cells are known to perceive their microenvironment through extracellular and intracellular mechanical signals. Upon sensing mechanical stimuli, cells can initiate various downstream signaling pathways that are vital to regulating proliferation, growth, and homeostasis. One such physiologic activity modulated by mechanical stimuli is osteogenic differentiation. The process of osteogenic mechanotransduction is regulated by numerous calcium ion channels-including channels coupled to cilia, mechanosensitive and voltage-sensitive channels, and channels associated with the endoplasmic reticulum. Evidence suggests these channels are implicated in osteogenic pathways such as the YAP/TAZ and canonical Wnt pathways. This review aims to describe the involvement of calcium channels in regulating osteogenic differentiation in response to mechanical loading and characterize the fashion in which those channels directly or indirectly mediate this process. The mechanotransduction pathway is a promising target for the development of regenerative materials for clinical applications due to its independence from exogenous growth factor supplementation. As such, also described are examples of osteogenic biomaterial strategies that involve the discussed calcium ion channels, calcium-dependent cellular structures, or calcium ion-regulating cellular features. Understanding the distinct ways calcium channels and signaling regulate these processes may uncover potential targets for advancing biomaterials with regenerative osteogenic capabilities.

Motor-free contractility of active biopolymer networks

Contractility in animal cells is often generated by molecular motors such as myosin, which require polar substrates for their function. Motivated by recent experimental evidence of motor-independent contractility, we propose a robust motor-free mechanism that can generate contraction in biopolymer networks without the need for substrate polarity. We show that contractility is a natural consequence of active binding-unbinding of crosslinkers that breaks the principle of detailed balance, together with the asymmetric force-extension response of semiflexible biopolymers. We have extended our earlier work to discuss the motor-free contraction of viscoelastic biopolymer networks. We calculate the resulting contractile velocity using a microscopic model and show that it can be reduced to a simple coarse-grained model under certain limits. Our model may provide an explanation of recent reports of motor-independent contractility in cells. Our results also suggest a mechanism for generating contractile forces in synthetic active materials.

Alterations induced by Bisphenol A on cellular organelles and potential relevance on human health

Bisphenol A (BPA) is a chemical partially soluble in water and exists in a solid state. Its structural similarity with estrogen makes it an endocrine-disrupting chemical. BPA can disrupt signaling pathways at very low doses and may cause organellar stress. According to in vitro and in vivo studies, BPA interacts with various cell surface receptors to cause organellar stress, producing free radicals, cellular toxicity, structural changes, DNA damage, mitochondrial dysfunction, cytoskeleton remodeling, centriole duplication, and aberrant changes in several cell signaling pathways. The current review summarizes the impact of BPA exposure on the structural and functional aspects of subcellular components of cells such as the nucleus, mitochondria, endoplasmic reticulum, lysosome, ribosome, Golgi apparatus, and microtubules and its consequent impact on human health.