Appreciating force and shape—the rise of mechanotransduction in cell biology

Multilayered hydrogel scaffold construct with native tissue matched elastic modulus: A regenerative microenvironment for urethral scar-free healing

The unsuitable deformation stimulus, harsh urine environment, and lack of a regenerative microenvironment (RME) prevent scaffold-based urethral repair and ultimately lead to irreversible urethral scarring. The researchers clarify the optimal elastic modulus of the urethral scaffolds for urethral repair and design a multilayered PVA hydrogel scaffold for urethral scar-free healing. The inner layer of the scaffold has self-healing properties, which ensures that the wound effectively resists harsh urine erosion, even when subjected to sutures. In addition, the scaffold's outer layer has an extracellular matrix-like structure that synergizes with adipose-derived stem cells to create a favorable RME. In vivo experiments confirm successful urethral scar-free healing using the PVA multilayered hydrogel scaffold. Further mechanistic study shows that the PVA multilayer hydrogel effectively resists the urine-induced inflammatory response and accelerates the transition of urethral wound healing to the proliferative phase by regulating macrophage polarization, thus providing favorable conditions for urethral scar-free healing. This study provides mechanical criteria for the fabrication of urethral tissue-engineered scaffolds, as well as important insights into their design.

Emerging biomedical technologies for scarless wound healing

Complete wound healing without scar formation has attracted increasing attention, prompting the development of various strategies to address this challenge. In clinical settings, there is a growing preference for emerging biomedical technologies that effectively manage fibrosis following skin injury, as they provide high efficacy, cost-effectiveness, and minimal side effects compared to invasive and costly surgical techniques. This review gives an overview of the latest developments in advanced biomedical technologies for scarless wound management. We first introduce the wound healing process and key mechanisms involved in scar formation. Subsequently, we explore common strategies for wound treatment, including their fabrication methods, superior performance and the latest research developments in this field. We then shift our focus to emerging biomedical technologies for scarless wound healing, detailing the mechanism of action, unique properties, and advanced practical applications of various biomedical technology-based therapies, such as cell therapy, drug therapy, biomaterial therapy, and synergistic therapy. Finally, we critically assess the shortcomings and potential applications of these biomedical technologies and therapeutic methods in the realm of scar treatment.

Mitochondrial mechanotransduction through MIEF1 coordinates the nuclear response to forces

Tissue-scale architecture and mechanical properties instruct cell behaviour under physiological and diseased conditions, but our understanding of the underlying mechanisms remains fragmentary. Here we show that extracellular matrix stiffness, spatial confinements and applied forces, including stretching of mouse skin, regulate mitochondrial dynamics. Actomyosin tension promotes the phosphorylation of mitochondrial elongation factor 1 (MIEF1), limiting the recruitment of dynamin-related protein 1 (DRP1) at mitochondria, as well as peri-mitochondrial F-actin formation and mitochondrial fission. Strikingly, mitochondrial fission is also a general mechanotransduction mechanism. Indeed, we found that DRP1- and MIEF1/2-dependent fission is required and sufficient to regulate three transcription factors of broad relevance-YAP/TAZ, SREBP1/2 and NRF2-to control cell proliferation, lipogenesis, antioxidant metabolism, chemotherapy resistance and adipocyte differentiation in response to mechanical cues. This extends to the mouse liver, where DRP1 regulates hepatocyte proliferation and identity-hallmark YAP-dependent phenotypes. We propose that mitochondria fulfil a unifying signalling function by which the mechanical tissue microenvironment coordinates complementary cell functions.

Mechano-adaptive meta-gels through synergistic chemical and physical information-processing

Global functional adaptation after local mechanical stimulation, as in mechanobiology and the mimosa plant, is fascinating and ubiquitous in nature. This is achieved by locally sensing mechanical deformation with precise thresholds, processing this information via biochemical circuits, followed by downstream actuation. The integration of such embodied intelligence allowing for mechano-to-chemo-to-function information-processing remains elusive in man-made systems. By merging the fields of chemical circuits and metamaterials, we introduce adaptive metamaterial hydrogels (meta-gels) that can accurately sense mechanical stimuli (local touch and global strain), transmit this information over long distances via reaction-diffusion signaling, and induce downstream mechanical strengthening by growing nanofibril networks, or soft robotic actuation through competitive swelling. All elements of the sensor-processor-actuator system are embedded in the device, functioning autonomously without external feeding reservoirs. Our concept enables designing advanced life-like materials systems that synergistically combine two worlds - chemical circuits for chemical information-processing and metamaterial unit cells for physical information-processing.

Overcoming Barriers in Photodynamic Therapy Harnessing Nanogenerators Strategies

Photodynamic therapy (PDT) represents a targeted approach for cancer treatment that employs light and photosensitizers (PSs) to induce the generation of reactive oxygen species (ROS). However, PDT faces obstacles including insufficient PS localization, limited light penetration, and treatment resistance. A potential solution lies in nanogenerators (NGs), which function as self-powered systems capable of generating electrical energy. Recent progress in piezoelectric and triboelectric NGs showcases promising applications in cancer research and drug delivery. Integration of NGs with PDT holds the promise of enhancing treatment efficacy by ensuring sustained PS illumination, enabling direct electrical control of cancer cells, and facilitating improved drug administration. This comprehensive review aims to augment our comprehension of PDT principles, explore associated challenges, and underscore the transformative capacity of NGs in conjunction with PDT. By harnessing NG technology alongside PDT, significant advancement in cancer treatment can be realized. Herein, we present the principal findings and conclusions of this study, offering valuable insights into the integration of NGs to overcome barriers in PDT.

Microbiology of human spaceflight: microbial responses to mechanical forces that impact health and habitat sustainability

SUMMARYUnderstanding the dynamic adaptive plasticity of microorganisms has been advanced by studying their responses to extreme environments. Spaceflight research platforms provide a unique opportunity to study microbial characteristics in new extreme adaptational modes, including sustained exposure to reduced forces of gravity and associated low fluid shear force conditions. Under these conditions, unexpected microbial responses occur, including alterations in virulence, antibiotic and stress resistance, biofilm formation, metabolism, motility, and gene expression, which are not observed using conventional experimental approaches. Here, we review biological and physical mechanisms that regulate microbial responses to spaceflight and spaceflight analog environments from both the microbe and host-microbe perspective that are relevant to human health and habitat sustainability. We highlight instrumentation and technology used in spaceflight microbiology experiments, their limitations, and advances necessary to enable next-generation research. As spaceflight experiments are relatively rare, we discuss ground-based analogs that mimic aspects of microbial responses to reduced gravity in spaceflight, including those that reduce mechanical forces of fluid flow over cell surfaces which also simulate conditions encountered by microorganisms during their terrestrial lifecycles. As spaceflight mission durations increase with traditional astronauts and commercial space programs send civilian crews with underlying health conditions, microorganisms will continue to play increasingly critical roles in health and habitat sustainability, thus defining a new dimension of occupational health. The ability of microorganisms to adapt, survive, and evolve in the spaceflight environment is important for future human space endeavors and provides opportunities for innovative biological and technological advances to benefit life on Earth.

Extracellular Matrix Components and Mechanosensing Pathways in Health and Disease

Glycosaminoglycans (GAGs) and proteoglycans (PGs) are essential components of the extracellular matrix (ECM) with pivotal roles in cellular mechanosensing pathways. GAGs, such as heparan sulfate (HS) and chondroitin sulfate (CS), interact with various cell surface receptors, including integrins and receptor tyrosine kinases, to modulate cellular responses to mechanical stimuli. PGs, comprising a core protein with covalently attached GAG chains, serve as dynamic regulators of tissue mechanics and cell behavior, thereby playing a crucial role in maintaining tissue homeostasis. Dysregulation of GAG/PG-mediated mechanosensing pathways is implicated in numerous pathological conditions, including cancer and inflammation. Understanding the intricate mechanisms by which GAGs and PGs modulate cellular responses to mechanical forces holds promise for developing novel therapeutic strategies targeting mechanotransduction pathways in disease. This comprehensive overview underscores the importance of GAGs and PGs as key mediators of mechanosensing in maintaining tissue homeostasis and their potential as therapeutic targets for mitigating mechano-driven pathologies, focusing on cancer and inflammation.

Principles and regulation of mechanosensing

Research over the past two decades has highlighted that mechanical signaling is a crucial component in regulating biological processes. Although many processes and proteins are termed 'mechanosensitive', the underlying mechanisms involved in mechanosensing can vary greatly. Recent studies have also identified mechanosensing behaviors that can be regulated independently of applied force. This important finding has major implications for our understanding of downstream mechanotransduction, the process by which mechanical signals are converted into biochemical signals, as it offers another layer of biochemical regulatory control for these crucial signaling pathways. In this Review, we discuss the different molecular and cellular mechanisms of mechanosensing, how these processes are regulated and their effects on downstream mechanotransduction. Together, these discussions provide an important perspective on how cells and tissues control the ways in which they sense and interpret mechanical signals.

The cytoskeleton dynamics-dependent LINC complex in periodontal ligament stem cells transmits mechanical stress to the nuclear envelope and promotes YAP nuclear translocation

BACKGROUND

Periodontal ligament stem cells (PDLSCs) are important seed cells in tissue engineering and clinical applications. They are the priority receptor cells for sensing various mechanical stresses. Yes-associated protein (YAP) is a recognized mechanically sensitive transcription factor. However, the role of YAP in regulating the fate of PDLSCs under tension stress (TS) and its underlying mechanism is still unclear.

METHODS

The effects of TS on the morphology and fate of PDLSCs were investigated using fluorescence staining, transmission electron microscopy, flow cytometry and quantitative real-time polymerase chain reaction (qRT-PCR). Then qRT-PCR, western blotting, immunofluorescence staining and gene knockdown experiments were performed to investigate the expression and distribution of YAP and its correlation with PDLSCs proliferation. The effects of cytoskeleton dynamics on YAP nuclear translocation were subsequently explored by adding cytoskeleton inhibitors. The effect of cytoskeleton dynamics on the expression of the LINC complex was proved through qRT-PCR and western blotting. After destroying the LINC complex by adenovirus, the effects of the LINC complex on YAP nuclear translocation and PDLSCs proliferation were investigated. Mitochondria-related detections were then performed to explore the role of mitochondria in YAP nuclear translocation. Finally, the in vitro results were verified by constructing orthodontic tooth movement models in Sprague-Dawley rats.

RESULTS

TS enhanced the polymerization and stretching of F-actin, which upregulated the expression of the LINC complex. This further strengthened the pull on the nuclear envelope, enlarged the nuclear pore, and facilitated YAP's nuclear entry, thus enhancing the expression of proliferation-related genes. In this process, mitochondria were transported to the periphery of the nucleus along the reconstructed microtubules. They generated ATP to aid YAP's nuclear translocation and drove F-actin polymerization to a certain degree. When the LINC complex was destroyed, the nuclear translocation of YAP was inhibited, which limited PDLSCs proliferation, impeded periodontal tissue remodeling, and hindered tooth movement.

CONCLUSIONS

Our study confirmed that appropriate TS could promote PDLSCs proliferation and periodontal tissue remodeling through the mechanically driven F-actin/LINC complex/YAP axis, which could provide theoretical guidance for seed cell expansion and for promoting healthy and effective tooth movement in clinical practice.

Trusting the forces of our cell lines

Cells isolated from their native tissues and cultured in vitro face different selection pressures than those cultured in vivo. These pressures induce a profound transformation that reshapes the cell, alters its genome, and transforms the way it senses and generates forces. In this perspective, we focus on the evidence that cells cultured on conventional polystyrene substrates display a fundamentally different mechanobiology than their in vivo counterparts. We explore the role of adhesion reinforcement in this transformation and to what extent it is reversible. We argue that this mechanoadaptation is often understood as a mechanical memory. We propose some strategies to mitigate the effects of on-plastic culture on mechanobiology, such as organoid-inspired protocols or mechanical priming. While isolating cells from their native tissues and culturing them on artificial substrates has revolutionized biomedical research, it has also transformed cellular forces. Only by understanding and controlling them, we can improve their truthfulness and validity.

Hydrogels: a promising therapeutic platform for inflammatory skin diseases treatment

Inflammatory skin diseases, such as psoriasis and atopic dermatitis, pose significant health challenges due to their long-lasting nature, potential for serious complications, and significant health risks, which requires treatments that are both effective and exhibit minimal side effects. Hydrogels offer an innovative solution due to their biocompatibility, tunability, controlled drug delivery capabilities, enhanced treatment adherence and minimized side effects risk. This review explores the mechanisms that guide the design of hydrogel therapeutic platforms from multiple perspectives, focusing on the components of hydrogels, their adjustable physical and chemical properties, and their interactions with cells and drugs to underscore their clinical potential. We also examine various therapeutic agents for psoriasis and atopic dermatitis that can be integrated into hydrogels, including traditional drugs, novel compounds targeting oxidative stress, small molecule drugs, biologics, and emerging therapies, offering insights into their mechanisms and advantages. Additionally, we review clinical trial data to evaluate the effectiveness and safety of hydrogel-based treatments in managing psoriasis and atopic dermatitis under complex disease conditions. Lastly, we discuss the current challenges and future opportunities for hydrogel therapeutics in treating psoriasis and atopic dermatitis, such as improving skin barrier penetration and developing multifunctional hydrogels, and highlight emerging opportunities to enhance long-term safety and stability.

Epidermal stem cells: skin surveillance and clinical perspective

The skin epidermis is continually influenced by a myriad of internal and external elements. At its basal layer reside epidermal stem cells, which fuels epidermal renovation and hair regeneration with powerful self-renewal ability, as well as keeping diverse signals that direct their activity under surveillance with quick response. The importance of epidermal stem cells in wound healing and immune-related skin conditions has been increasingly recognized, and their potential for clinical applications is attracting attention. In this review, we delve into recent advancements and the various physiological and psychological factors that govern distinct epidermal stem cell populations, including psychological stress, mechanical forces, chronic aging, and circadian rhythm, as well as providing an overview of current methodological approaches. Furthermore, we discuss the pathogenic role of epidermal stem cells in immune-related skin disorders and their potential clinical applications.

Exploring the Role of Hormones and Cytokines in Osteoporosis Development

The disease of osteoporosis is characterized by impaired bone structure and an increased risk of fractures. There is a significant impact of cytokines and hormones on bone homeostasis and the diagnosis of osteoporosis. As defined by the World Health Organization (WHO), osteoporosis is defined as having a bone mineral density (BMD) that is 2.5 standard deviations (SD) or more below the average for young and healthy women (T score < -2.5 SD). Cytokines and hormones, particularly in the remodeling of bone between osteoclasts and osteoblasts, control the differentiation and activation of bone cells through cytokine networks and signaling pathways like the nuclear factor kappa-B ligand (RANKL)/the receptor of RANKL (RANK)/osteoprotegerin (OPG) axis, while estrogen, parathyroid hormones, testosterone, and calcitonin influence bone density and play significant roles in the treatment of osteoporosis. This review aims to examine the roles of cytokines and hormones in the pathophysiology of osteoporosis, evaluating current diagnostic methods, and highlighting new technologies that could help for early detection and treatment of osteoporosis.

Cell-cell communication: new insights and clinical implications

Multicellular organisms are composed of diverse cell types that must coordinate their behaviors through communication. Cell-cell communication (CCC) is essential for growth, development, differentiation, tissue and organ formation, maintenance, and physiological regulation. Cells communicate through direct contact or at a distance using ligand-receptor interactions. So cellular communication encompasses two essential processes: cell signal conduction for generation and intercellular transmission of signals, and cell signal transduction for reception and procession of signals. Deciphering intercellular communication networks is critical for understanding cell differentiation, development, and metabolism. First, we comprehensively review the historical milestones in CCC studies, followed by a detailed description of the mechanisms of signal molecule transmission and the importance of the main signaling pathways they mediate in maintaining biological functions. Then we systematically introduce a series of human diseases caused by abnormalities in cell communication and their progress in clinical applications. Finally, we summarize various methods for monitoring cell interactions, including cell imaging, proximity-based chemical labeling, mechanical force analysis, downstream analysis strategies, and single-cell technologies. These methods aim to illustrate how biological functions depend on these interactions and the complexity of their regulatory signaling pathways to regulate crucial physiological processes, including tissue homeostasis, cell development, and immune responses in diseases. In addition, this review enhances our understanding of the biological processes that occur after cell-cell binding, highlighting its application in discovering new therapeutic targets and biomarkers related to precision medicine. This collective understanding provides a foundation for developing new targeted drugs and personalized treatments.

Dynamic Responses of Human Skin and Fascia to an Innovative Stimulation Device-Shear Wave Stimulation

Exposure to mechanical stimuli such as pressure and stretching prompts the skin to undergo physiological adaptations to accommodate and distribute applied forces, a process known as mechanotransduction. Mechanotherapy, which leverages mechanotransduction, shows significant promise across various medical disciplines. Traditional methods, such as massage and compression therapy, effectively promote skin healing by utilizing this mechanism, although they require direct skin contact. This study introduces a novel contactless modality, Shear Wave Stimulation (SWS), and evaluates its efficacy compared to traditional massage in eliciting responses from human skin and fascia. Fifteen healthy volunteers received SWS, while another fifteen volunteers received massage. Tests of skin mechanical properties revealed significant enhancements in skin shear modulus for both methods, showing an increase of approximately 20%. Additionally, deformation analysis of ultrasound images showed distinct responses of the skin and fascia to the two stimuli. SWS induced extension in the dermis (∼18%), hypodermis (∼16%), and fascia (∼22%) along the X and Y axes. In contrast, massage compressed the skin layers, reducing the dermis by around 15% and the hypodermis by about 8%, while simultaneously stretching the superficial fascia by approximately 8%. The observed extension across the entire skin with SWS highlights its potential as a groundbreaking contactless approach for promoting skin healing. Furthermore, the differing responses in blood flow reaffirm the distinct stimulation modes of SWS and massage. These findings establish a foundation for future innovative skin therapy modalities.

Fibrosis-on-Chip: A Guide to Recapitulate the Essential Features of Fibrotic Disease

Fibrosis, which is primarily marked by excessive extracellular matrix (ECM) deposition, is a pathophysiological process associated with many disorders, which ultimately leads to organ dysfunction and poor patient outcomes. Despite the high prevalence of fibrosis, currently there exist few therapeutic options, and importantly, there is a paucity of in vitro models to accurately study fibrosis. This review discusses the multifaceted nature of fibrosis from the viewpoint of developing organ-on-chip (OoC) disease models, focusing on five key features: the ECM component, inflammation, mechanical cues, hypoxia, and vascularization. The potential of OoC technology is explored for better modeling these features in the context of studying fibrotic diseases and the interplay between various key features is emphasized. This paper reviews how organ-specific fibrotic diseases are modeled in OoC platforms, which elements are included in these existing models, and the avenues for novel research directions are highlighted. Finally, this review concludes with a perspective on how to address the current gap with respect to the inclusion of multiple features to yield more sophisticated and relevant models of fibrotic diseases in an OoC format.

Contactless mechanical stimulation of the skin using shear waves

The skin, the outermost organ of the human body, is vital for sensing and responding to stimuli through mechanotransduction. It is constantly exposed to mechanical stress. Consequently, various mechanical therapies, including compression, massage, and microneedling, have become routine practices for skin healing and regeneration. However, these traditional methods require direct skin contact, restricting their applicability. To address this constraint, we developed shear wave stimulation (SWS), a contactless mechanical stimulation technique. The effectiveness of SWS was compared with that of a commercial compression bioreactor used on reconstructed skin at various stages of maturity. Despite the distinct stimulus conditions applied by the two methods, SWS yielded remarkable outcomes, similar to the effects of the compression bioreactor. It significantly increased the shear modulus of tissue-engineered skin, heightened the density of collagen and elastin fibers, and resulted in an augmentation of fibroblasts in terms of their number and length. Notably, SWS exhibited diverse effects in the low- and high-frequency modes, highlighting the importance of fine-tuning the stimulus intensity. These results unequivocally demonstrated the capability of SWS to enhance the mechanical functions of the skin in vitro, making it a promising option for addressing wound healing and stretch mark recovery.

Mechanical state transitions in the regulation of tissue form and function

From embryonic development, postnatal growth and adult homeostasis to reparative and disease states, cells and tissues undergo constant changes in genome activity, cell fate, proliferation, movement, metabolism and growth. Importantly, these biological state transitions are coupled to changes in the mechanical and material properties of cells and tissues, termed mechanical state transitions. These mechanical states share features with physical states of matter, liquids and solids. Tissues can switch between mechanical states by changing behavioural dynamics or connectivity between cells. Conversely, these changes in tissue mechanical properties are known to control cell and tissue function, most importantly the ability of cells to move or tissues to deform. Thus, tissue mechanical state transitions are implicated in transmitting information across biological length and time scales, especially during processes of early development, wound healing and diseases such as cancer. This Review will focus on the biological basis of tissue-scale mechanical state transitions, how they emerge from molecular and cellular interactions, and their roles in organismal development, homeostasis, regeneration and disease.

Viscoelasticity in 3D Cell Culture and Regenerative Medicine: Measurement Techniques and Biological Relevance

The field of mechanobiology is gaining prominence due to recent findings that show cells sense and respond to the mechanical properties of their environment through a process called mechanotransduction. The mechanical properties of cells, cell organelles, and the extracellular matrix are understood to be viscoelastic. Various technologies have been researched and developed for measuring the viscoelasticity of biological materials, which may provide insight into both the cellular mechanisms and the biological functions of mechanotransduction. Here, we explain the concept of viscoelasticity and introduce the major techniques that have been used to measure the viscoelasticity of various soft materials in different length- and timescale frames. The topology of the material undergoing testing, the geometry of the probe, the magnitude of the exerted stress, and the resulting deformation should be carefully considered to choose a proper technique for each application. Lastly, we discuss several applications of viscoelasticity in 3D cell culture and tissue models for regenerative medicine, including organoids, organ-on-a-chip systems, engineered tissue constructs, and tunable viscoelastic hydrogels for 3D bioprinting and cell-based therapies.

Mechanical regulation of lymphocyte activation and function

Mechanosensing, or how cells sense and respond to the physical environment, is crucial for many aspects of biological function, ranging from cell movement during development to cancer metastasis, the immune response and gene expression driving cell fate determination. Relevant physical stimuli include the stiffness of the extracellular matrix, contractile forces, shear flows in blood vessels, complex topography of the cellular microenvironment and membrane protein mobility. Although mechanosensing has been more widely studied in non-immune cells, it has become increasingly clear that physical cues profoundly affect the signaling function of cells of the immune system. In this Review, we summarize recent studies on mechanical regulation of immune cells, specifically lymphocytes, and explore how the force-generating cytoskeletal machinery might mediate mechanosensing. We discuss general principles governing mechanical regulation of lymphocyte function, spanning from the molecular scale of receptor activation to cellular responses to mechanical stimuli.

Perception and response of skeleton to mechanical stress

Mechanical stress stands as a fundamental factor in the intricate processes governing the growth, development, morphological shaping, and maintenance of skeletal mass. The profound influence of stress in shaping the skeletal framework prompts the assertion that stress essentially births the skeleton. Despite this acknowledgment, the mechanisms by which the skeleton perceives and responds to mechanical stress remain enigmatic. In this comprehensive review, our scrutiny focuses on the structural composition and characteristics of sclerotin, leading us to posit that it serves as the primary structure within the skeleton responsible for bearing and perceiving mechanical stress. Furthermore, we propose that osteocytes within the sclerotin emerge as the principal mechanical-sensitive cells, finely attuned to perceive mechanical stress. And a detailed analysis was conducted on the possible transmission pathways of mechanical stress from the extracellular matrix to the nucleus.

Ultimately Adaptive Fluid Interfacial Phospholipid Membranes Unveiled Unanticipated High Cellular Mechanical Work

Living cells actively interact biochemically and mechanically with the surrounding extracellular matrices (ECMs) and undergo dramatic morphological and dimensional transitions, concomitantly remodeling ECMs. However, there is no suitable method to quantitatively discuss the contribution of mechanical interactions in such mutually adaptive processes. Herein, a highly deformable "living" cellular scaffold is developed to evaluate overall mechanical energy transfer between cell and ECMs. It is based on the water-perfluorocarbon interface decorated with phospholipids bearing a cell-adhesive ligand and fluorescent tag. The bioinert nature of the phospholipid membranes prevents the formation of solid-like protein nanofilms at the fluid interface, enabling to visualize and quantify cellular mechanical work against the ultimately adaptive model ECM. A new cellular wetting regime is identified, wherein interface deformation proceeds to cell flattening, followed by its eventual restoration. The cellular mechanical work during this adaptive wetting process is one order of magnitude higher than those reported with conventional elastic platforms. The behavior of viscous liquid drops at the air-water interface can simulate cellular adaptive wetting, suggesting that overall viscoelasticity of the cell body predominates the emergent wetting regime and regulates mechanical output. Cellular-force-driven high-energy states on the adaptive platform can be useful for cell fate manipulation.

Single-cell topographical profiling of the immune synapse reveals a biomechanical signature of cytotoxicity

Immune cells have intensely physical lifestyles characterized by structural plasticity and force exertion. To investigate whether specific immune functions require stereotyped mechanical outputs, we used super-resolution traction force microscopy to compare the immune synapses formed by cytotoxic T cells with contacts formed by other T cell subsets and by macrophages. T cell synapses were globally compressive, which was fundamentally different from the pulling and pinching associated with macrophage phagocytosis. Spectral decomposition of force exertion patterns from each cell type linked cytotoxicity to compressive strength, local protrusiveness, and the induction of complex, asymmetric topography. These features were validated as cytotoxic drivers by genetic disruption of cytoskeletal regulators, live imaging of synaptic secretion, and in silico analysis of interfacial distortion. Synapse architecture and force exertion were sensitive to target stiffness and size, suggesting that the mechanical potentiation of killing is biophysically adaptive. We conclude that cellular cytotoxicity and, by implication, other effector responses are supported by specialized patterns of efferent force.

Impact of mechanical cues on key cell functions and cell-nanoparticle interactions

In recent years, it has been recognized that mechanical forces play an important regulative role in living organisms and possess a direct impact on crucial cell functions, ranging from cell growth to maintenance of tissue homeostasis. Advancements in mechanobiology have revealed the profound impact of mechanical signals on diverse cellular responses that are cell type specific. Notably, numerous studies have elucidated the pivotal role of different mechanical cues as regulatory factors influencing various cellular processes, including cell spreading, locomotion, differentiation, and proliferation. Given these insights, it is unsurprising that the responses of cells regulated by physical forces are intricately linked to the modulation of nanoparticle uptake kinetics and processing. This complex interplay underscores the significance of understanding the mechanical microenvironment in shaping cellular behaviors and, consequently, influencing how cells interact with and process nanoparticles. Nevertheless, our knowledge on how localized physical forces affect the internalization and processing of nanoparticles by cells remains rather limited. A significant gap exists in the literature concerning a systematic analysis of how mechanical cues might bias the interactions between nanoparticles and cells. Hence, our aim in this review is to provide a comprehensive and critical analysis of the existing knowledge regarding the influence of mechanical cues on the complicated dynamics of cell-nanoparticle interactions. By addressing this gap, we would like to contribute to a detailed understanding of the role that mechanical forces play in shaping the complex interplay between cells and nanoparticles.

DNA-based ForceChrono probes for deciphering single-molecule force dynamics in living cells

Understanding cellular force transmission dynamics is crucial in mechanobiology. We developed the DNA-based ForceChrono probe to measure force magnitude, duration, and loading rates at the single-molecule level within living cells. The ForceChrono probe circumvents the limitations of in vitro single-molecule force spectroscopy by enabling direct measurements within the dynamic cellular environment. Our findings reveal integrin force loading rates of 0.5-2 pN/s and durations ranging from tens of seconds in nascent adhesions to approximately 100 s in mature focal adhesions. The probe's robust and reversible design allows for continuous monitoring of these dynamic changes as cells undergo morphological transformations. Additionally, by analyzing how mutations, deletions, or pharmacological interventions affect these parameters, we can deduce the functional roles of specific proteins or domains in cellular mechanotransduction. The ForceChrono probe provides detailed insights into the dynamics of mechanical forces, advancing our understanding of cellular mechanics and the molecular mechanisms of mechanotransduction.

Microtubule-associated protein MAP7 promotes tubulin posttranslational modifications and cargo transport to enable osmotic adaptation

Cells remodel their cytoskeletal networks to adapt to their environment. Here, we analyze the mechanisms utilized by the cell to tailor its microtubule landscape in response to changes in osmolarity that alter macromolecular crowding. By integrating live-cell imaging, ex vivo enzymatic assays, and in vitro reconstitution, we probe the impact of cytoplasmic density on microtubule-associated proteins (MAPs) and tubulin posttranslational modifications (PTMs). We find that human epithelial cells respond to fluctuations in cytoplasmic density by modulating microtubule acetylation, detyrosination, or MAP7 association without differentially affecting polyglutamylation, tyrosination, or MAP4 association. These MAP-PTM combinations alter intracellular cargo transport, enabling the cell to respond to osmotic challenges. We further dissect the molecular mechanisms governing tubulin PTM specification and find that MAP7 promotes acetylation and inhibits detyrosination. Our data identify MAP7 in modulating the tubulin code, resulting in microtubule cytoskeleton remodeling and alteration of intracellular transport as an integrated mechanism of cellular adaptation.

Enhancing chondrogenic differentiation of mesenchymal stem cells through synergistic effects of cellulose nanocrystals and plastic compression in collagen-based hydrogel for cartilage formation

Collagen-based (COL) hydrogels could be a promising treatment option for injuries to the articular cartilage (AC) becuase of their similarity to AC native extra extracellular matrix. However, the high hydration of COL hydrogels poses challenges for AC's mechanical properties. To address this, we developed a hydrogel platform that incorporating cellulose nanocrystals (CNCs) within COL and followed by plastic compression (PC) procedure to expel the excessive fluid out. This approach significantly improved the mechanical properties of the hydrogels and enhanced the chondrogenic differentiation of mesenchymal stem cells (MSCs). Radially confined PC resulted in higher collagen fibrillar densities together with reducing fibril-fibril distances. Compressed hydrogels containing CNCs exhibited the highest compressive modulus and toughness. MSCs encapsulated in these hydrogels were initially affected by PC, but their viability improved after 7 days. Furthermore, the morphology of the cells and their secretion of glycosaminoglycans (GAGs) were positively influenced by the compressed COL-CNC hydrogel. Our findings shed light on the combined effects of PC and CNCs in improving the physical and mechanical properties of COL and their role in promoting chondrogenesis.

Single-molecule magnetic tweezers to probe the equilibrium dynamics of individual proteins at physiologically relevant forces and timescales

The reversible unfolding and refolding of proteins is a regulatory mechanism of tissue elasticity and signalling used by cells to sense and adapt to extracellular and intracellular mechanical forces. However, most of these proteins exhibit low mechanical stability, posing technical challenges to the characterization of their conformational dynamics under force. Here, we detail step-by-step instructions for conducting single-protein nanomechanical experiments using ultra-stable magnetic tweezers, which enable the measurement of the equilibrium conformational dynamics of single proteins under physiologically relevant low forces applied over biologically relevant timescales. We report the basic principles determining the functioning of the magnetic tweezer instrument, review the protein design strategy and the fluid chamber preparation and detail the procedure to acquire and analyze the unfolding and refolding trajectories of individual proteins under force. This technique adds to the toolbox of single-molecule nanomechanical techniques and will be of particular interest to those interested in proteins involved in mechanosensing and mechanotransduction. The procedure takes 4 d to complete, plus an additional 6 d for protein cloning and production, requiring basic expertise in molecular biology, surface chemistry and data analysis.

Transepithelial Electrical Impedance Increase Following Porous Substrate Electroporation Enables Label-Free Delivery

Porous substrate electroporation (PSEP) is a promising new method for intracellular delivery, yet fundamentals of PSEP are not well understood, especially the intermediate processes leading to delivery. PSEP is an electrical method, yet the relationship between PSEP and electrical impedance remains underexplored. In this study, a device capable of measuring impedance and performing PSEP is developed and the changes in transepithelial electrical impedance (TEEI) are monitored. These measurements show TEEI increases following PSEP, unlike other electroporation methods. The authors then demonstrate how cell culture conditions and electrical waveforms influence this response. More importantly, TEEI response features are correlated with viability and delivery efficiency, allowing prediction of outcomes without fluorescent cargo, imaging, or image processing. This label-free delivery also allows improved temporal resolution of transient processes following PSEP, which the authors expect will aid PSEP optimization for new cell types and cargos.

Biomechanical Activation of Keloid Fibroblasts Promotes Lysosomal Remodeling and Exocytosis

Keloids are a severe form of scarring for which the underlying mechanisms are poorly understood, and treatment options are limited or inconsistent. Although biomechanical forces are potential drivers of keloid scarring, the direct cellular responses to mechanical cues have yet to be defined. The aim of this study was to examine the distinct responses of normal dermal fibroblasts and keloid-derived fibroblasts (KDFs) to changes in extracellular matrix stiffness. When cultured on hydrogels mimicking the elasticity of normal or scarred skin, KDFs displayed greater stiffness-dependent increases in cell spreading, F-actin stress fiber formation, and focal adhesion assembly. Elevated actomyosin contractility in KDFs disrupted the normal mechanical regulation of extracellular matrix deposition and conferred resistance on myosin inhibitors. Transcriptional profiling identified mechanically regulated pathways in normal dermal fibroblasts and KDFs, including the actin cytoskeleton, Hippo signaling, and autophagy. Further analysis of the autophagy pathway revealed that autophagic flux was intact in both fibroblast populations and depended on actomyosin contractility. However, KDFs displayed marked changes in lysosome organization and an increase in lysosomal exocytosis, which was mediated by actomyosin contractility. Together, these findings demonstrate that KDFs possess an intrinsic increase in cytoskeletal tension, which heightens the response to extracellular matrix mechanics and promotes lysosomal exocytosis.

Structural anisotropy results in mechano-directional transport of proteins across nuclear pores

The nuclear pore complex regulates nucleocytoplasmic transport by means of a tightly synchronized suite of biochemical reactions. The physicochemical properties of the translocating cargos are emerging as master regulators of their shuttling dynamics. As well as being affected by molecular weight and surface-exposed amino acids, the kinetics of the nuclear translocation of protein cargos also depend on their nanomechanical properties, yet the mechanisms underpinning the mechanoselectivity of the nuclear pore complex are unclear. Here we show that proteins with locally soft regions in the vicinity of the nuclear-localization sequence exhibit higher nuclear-import rates, and that such mechanoselectivity is specifically impaired upon knocking down nucleoporin 153, a key protein in the nuclear pore complex. This allows us to design a short, easy-to-express and chemically inert unstructured peptide tag that accelerates the nuclear-import rate of stiff protein cargos. We also show that U2OS osteosarcoma cells expressing the peptide-tagged myocardin-related transcription factor import this mechanosensitive protein to the nucleus at higher rates and display faster motility. Locally unstructured regions lower the free-energy barrier of protein translocation and might offer a control mechanism for nuclear mechanotransduction.

Profiling native pulmonary basement membrane stiffness using atomic force microscopy

Mammalian cells sense and react to the mechanics of their immediate microenvironment. Therefore, the characterization of the biomechanical properties of tissues with high spatial resolution provides valuable insights into a broad variety of developmental, homeostatic and pathological processes within living organisms. The biomechanical properties of the basement membrane (BM), an extracellular matrix (ECM) substructure measuring only ∼100-400 nm across, are, among other things, pivotal to tumor progression and metastasis formation. Although the precise assignment of the Young's modulus E of such a thin ECM substructure especially in between two cell layers is still challenging, biomechanical data of the BM can provide information of eminent diagnostic potential. Here we present a detailed protocol to quantify the elastic modulus of the BM in murine and human lung tissue, which is one of the major organs prone to metastasis. This protocol describes a streamlined workflow to determine the Young's modulus E of the BM between the endothelial and epithelial cell layers shaping the alveolar wall in lung tissues using atomic force microscopy (AFM). Our step-by-step protocol provides instructions for murine and human lung tissue extraction, inflation of these tissues with cryogenic cutting medium, freezing and cryosectioning of the tissue samples, and AFM force-map recording. In addition, it guides the reader through a semi-automatic data analysis procedure to identify the pulmonary BM and extract its Young's modulus E using an in-house tailored user-friendly AFM data analysis software, the Center for Applied Tissue Engineering and Regenerative Medicine processing toolbox, which enables automatic loading of the recorded force maps, conversion of the force versus piezo-extension curves to force versus indentation curves, calculation of Young's moduli and generation of Young's modulus maps, where the pulmonary BM can be identified using a semi-automatic spatial filtering tool. The entire protocol takes 1-2 d.

Decoding Biomechanical Cues Based on DNA Sensors

Biological systems perceive and respond to mechanical forces, generating mechanical cues to regulate life processes. Analyzing biomechanical forces has profound significance for understanding biological functions. Therefore, a series of molecular mechanical techniques have been developed, mainly including single-molecule force spectroscopy, traction force microscopy, and molecular tension sensor systems, which provide indispensable tools for advancing the field of mechanobiology. DNA molecules with a programmable structure and well-defined mechanical characteristics have attached much attention to molecular tension sensors as sensing elements, and are designed for the study of biomechanical forces to present biomechanical information with high sensitivity and resolution. In this work, a comprehensive overview of molecular mechanical technology is presented, with a particular focus on molecular tension sensor systems, specifically those based on DNA. Finally, the future development and challenges of DNA-based molecular tension sensor systems are looked upon.

Pathological mechanisms of cold and mechanical stress in modulating cancer progression

Environmental temperature and cellular mechanical force are the inherent factors that participate in various biological processes and regulate cancer progress, which have been hot topics worldwide. They occupy a dominant part in the cancer tissues through different approaches. However, extensive investigation regarding pathological mechanisms in the carcinogenic field. After research, we found cold stress via two means to manipulate tumors: neuroscience and mechanically sensitive ion channels (MICHs) such as TRP families to regulate the physiological and pathological activities. Excessive cold stimulation mediated neuroscience acting on every cancer stage through the hypothalamus-pituitary-adrenocorticoid (HPA) to reach the target organs. Comparatively speaking, mechanical force via Piezo of MICHs controls cancer development. The progression of cancer depends on the internal activation of proto-oncogenes and the external tumorigenic factors; the above two means eventually lead to genetic disorders at the molecular level. This review summarizes the interaction of bidirectional communication between them and the tumor. It covers the main processes from cytoplasm to nucleus related to metastasis cascade and tumor immune escape.

The roles of Hippo/YAP signaling pathway in physical therapy

Cellular behavior is regulated by mechanical signals within the cellular microenvironment. Additionally, changes of temperature, blood flow, and muscle contraction also affect cellular state and the development of diseases. In clinical practice, physical therapy techniques such as ultrasound, vibration, exercise, cold therapy, and hyperthermia are commonly employed to alleviate pain and treat diseases. However, the molecular mechanism about how these physiotherapy methods stimulate local tissues and control gene expression remains unknow. Fortunately, the discovery of YAP filled this gap, which has been reported has the ability to sense and convert a wide variety of mechanical signals into cell-specific programs for transcription, thereby offering a fresh perspective on the mechanisms by which physiotherapy treat different diseases. This review examines the involvement of Hippo/YAP signaling pathway in various diseases and its role in different physical therapy approaches on diseases. Furthermore, we explore the potential therapeutic implications of the Hippo/YAP signaling pathway and address the limitations and controversies surrounding its application in physiotherapy.

Drug repurposing for cancer therapy

Cancer, a complex and multifactorial disease, presents a significant challenge to global health. Despite significant advances in surgical, radiotherapeutic and immunological approaches, which have improved cancer treatment outcomes, drug therapy continues to serve as a key therapeutic strategy. However, the clinical efficacy of drug therapy is often constrained by drug resistance and severe toxic side effects, and thus there remains a critical need to develop novel cancer therapeutics. One promising strategy that has received widespread attention in recent years is drug repurposing: the identification of new applications for existing, clinically approved drugs. Drug repurposing possesses several inherent advantages in the context of cancer treatment since repurposed drugs are typically cost-effective, proven to be safe, and can significantly expedite the drug development process due to their already established safety profiles. In light of this, the present review offers a comprehensive overview of the various methods employed in drug repurposing, specifically focusing on the repurposing of drugs to treat cancer. We describe the antitumor properties of candidate drugs, and discuss in detail how they target both the hallmarks of cancer in tumor cells and the surrounding tumor microenvironment. In addition, we examine the innovative strategy of integrating drug repurposing with nanotechnology to enhance topical drug delivery. We also emphasize the critical role that repurposed drugs can play when used as part of a combination therapy regimen. To conclude, we outline the challenges associated with repurposing drugs and consider the future prospects of these repurposed drugs transitioning into clinical application.

Role of mechanoregulation in mast cell-mediated immune inflammation of the smooth muscle in the pathophysiology of esophageal motility disorders

Major esophageal disorders involve obstructive transport of bolus to the stomach, causing symptoms of dysphagia and impaired clearing of the refluxed gastric contents. These may occur due to mechanical constriction of the esophageal lumen or loss of relaxation associated with deglutitive inhibition, as in achalasia-like disorders. Recently, immune inflammation has been identified as an important cause of esophageal strictures and the loss of inhibitory neurotransmission. These disorders are also associated with smooth muscle hypertrophy and hypercontractility, whose cause is unknown. This review investigated immune inflammation in the causation of smooth muscle changes in obstructive esophageal bolus transport. Findings suggest that smooth muscle hypertrophy occurs above the obstruction and is due to mechanical stress on the smooth muscles. The mechanostressed smooth muscles release cytokines and other molecules that may recruit and microlocalize mast cells to smooth muscle bundles, so that their products may have a close bidirectional effect on each other. Acting in a paracrine fashion, the inflammatory cytokines induce genetic and epigenetic changes in the smooth muscles, leading to smooth muscle hypercontractility, hypertrophy, and impaired relaxation. These changes may worsen difficulty in the esophageal transport. Immune processes differ in the first phase of obstructive bolus transport, and the second phase of muscle hypertrophy and hypercontractility. Moreover, changes in the type of mechanical stress may change immune response and effect on smooth muscles. Understanding immune signaling in causes of obstructive bolus transport, type of mechanical stress, and associated smooth muscle changes may help pathophysiology-based prevention and targeted treatment of esophageal motility disorders.NEW & NOTEWORTHY Esophageal disorders such as esophageal stricture or achalasia, and diffuse esophageal spasm are associated with smooth muscle hypertrophy and hypercontractility, above the obstruction, yet the cause of such changes is unknown. This review suggests that smooth muscle obstructive disorders may cause mechanical stress on smooth muscle, which then secretes chemicals that recruit, microlocalize, and activate mast cells to initiate immune inflammation, producing functional and structural changes in smooth muscles. Understanding the immune signaling in these changes may help pathophysiology-based prevention and targeted treatment of esophageal motility disorders.

Cardiovascular Mechano-Epigenetics: Force-Dependent Regulation of Histone Modifications and Gene Regulation

The local mechanical microenvironment impacts on the cell behavior. In the cardiovascular system, cells in both the heart and the vessels are exposed to continuous blood flow, blood pressure, stretching forces, and changing extracellular matrix stiffness. The force-induced signals travel all the way to the nucleus regulating epigenetic changes such as chromatin dynamics and gene expression. Mechanical cues are needed at the very early stage for a faultless embryological development, while later in life, aberrant mechanical signaling can lead to a range of pathologies, including diverse cardiovascular diseases. Hence, an investigation of force-generated epigenetic alteration at different time scales is needed to understand fully the phenotypic changes in disease onset and progression. That being so, cardiovascular mechano-epigenetics emerges as an attractive field of study. Given the rapid advances in this emergent field of research, this short review aims to provide an analysis of the state of knowledge of force-induced epigenetic changes in the cardiovascular field.

Cell surface patching via CXCR4-targeted nanothreads for cancer metastasis inhibition

The binding of therapeutic antagonists to their receptors often fail to translate into adequate manipulation of downstream pathways. To fix this 'bug', here we report a strategy that stitches cell surface 'patches' to promote receptor clustering, thereby synchronizing subsequent mechano-transduction. The "patches" are sewn with two interactable nanothreads. In sequence, Nanothread-1 strings together adjacent receptors while presenting decoy receptors. Nanothread-2 then targets these decoys multivalently, intertwining with Nanothread-1 into a coiled-coil supramolecular network. This stepwise actuation clusters an extensive vicinity of receptors, integrating mechano-transduction to disrupt signal transmission. When applied to antagonize chemokine receptors CXCR4 expressed in metastatic breast cancer of female mice, this strategy elicits and consolidates multiple events, including interception of metastatic cascade, reversal of immunosuppression, and potentiation of photodynamic immunotherapy, reducing the metastatic burden. Collectively, our work provides a generalizable tool to spatially rearrange cell-surface receptors to improve therapeutic outcomes.

Shining Light in Mechanobiology: Optical Tweezers, Scissors, and Beyond

Mechanobiology helps us to decipher cell and tissue functions by looking at changes in their mechanical properties that contribute to development, cell differentiation, physiology, and disease. Mechanobiology sits at the interface of biology, physics and engineering. One of the key technologies that enables characterization of properties of cells and tissue is microscopy. Combining microscopy with other quantitative measurement techniques such as optical tweezers and scissors, gives a very powerful tool for unraveling the intricacies of mechanobiology enabling measurement of forces, torques and displacements at play. We review the field of some light based studies of mechanobiology and optical detection of signal transduction ranging from optical micromanipulation-optical tweezers and scissors, advanced fluorescence techniques and optogenentics. In the current perspective paper, we concentrate our efforts on elucidating interesting measurements of forces, torques, positions, viscoelastic properties, and optogenetics inside and outside a cell attained when using structured light in combination with optical tweezers and scissors. We give perspective on the field concentrating on the use of structured light in imaging in combination with tweezers and scissors pointing out how novel developments in quantum imaging in combination with tweezers and scissors can bring to this fast growing field.

Balancing competing effects of tissue growth and cytoskeletal regulation during Drosophila wing disc development

How a developing organ robustly coordinates the cellular mechanics and growth to reach a final size and shape remains poorly understood. Through iterations between experiments and model simulations that include a mechanistic description of interkinetic nuclear migration, we show that the local curvature, height, and nuclear positioning of cells in the Drosophila wing imaginal disc are defined by the concurrent patterning of actomyosin contractility, cell-ECM adhesion, ECM stiffness, and interfacial membrane tension. We show that increasing cell proliferation via different growth-promoting pathways results in two distinct phenotypes. Triggering proliferation through insulin signaling increases basal curvature, but an increase in growth through Dpp signaling and Myc causes tissue flattening. These distinct phenotypic outcomes arise from differences in how each growth pathway regulates the cellular cytoskeleton, including contractility and cell-ECM adhesion. The coupled regulation of proliferation and cytoskeletal regulators is a general strategy to meet the multiple context-dependent criteria defining tissue morphogenesis.

Diversity of Intercellular Communication Modes: A Cancer Biology Perspective

From the moment a cell is on the path to malignant transformation, its interaction with other cells from the microenvironment becomes altered. The flow of molecular information is at the heart of the cellular and systemic fate in tumors, and various processes participate in conveying key molecular information from or to certain cancer cells. For instance, the loss of tight junction molecules is part of the signal sent to cancer cells so that they are no longer bound to the primary tumors and are thus free to travel and metastasize. Upon the targeting of a single cell by a therapeutic drug, gap junctions are able to communicate death information to by-standing cells. The discovery of the importance of novel modes of cell-cell communication such as different types of extracellular vesicles or tunneling nanotubes is changing the way scientists look at these processes. However, are they all actively involved in different contexts at the same time or are they recruited to fulfill specific tasks? What does the multiplicity of modes mean for the overall progression of the disease? Here, we extend an open invitation to think about the overall significance of these questions, rather than engage in an elusive attempt at a systematic repertory of the mechanisms at play.

DNA-functionalized artificial mechanoreceptor for de novo force-responsive signaling

Synthetic signaling receptors enable programmable cellular responses coupling with customized inputs. However, engineering a designer force-sensing receptor to rewire mechanotransduction remains largely unexplored. Herein, we introduce nongenetically engineered artificial mechanoreceptors (AMRs) capable of reprogramming non-mechanoresponsive receptor tyrosine kinases (RTKs) to sense user-defined force cues, enabling de novo-designed mechanotransduction. AMR is a modular DNA-protein chimera comprising a mechanosensing-and-transmitting DNA nanodevice grafted on natural RTKs via aptameric anchors. AMR senses intercellular tensile force via an allosteric DNA mechano-switch with tunable piconewton-sensitive force tolerance, actuating a force-triggered dynamic DNA assembly to manipulate RTK dimerization and activate intracellular signaling. By swapping the force-reception ligands, we demonstrate the AMR-mediated activation of c-Met, a representative RTK, in response to the cellular tensile forces mediated by cell-adhesion proteins (integrin, E-cadherin) or membrane protein endocytosis (CI-M6PR). Moreover, AMR also allows the reprogramming of FGFR1, another RTK, to customize mechanobiological function, for example, adhesion-mediated neural stem cell maintenance.

Decoding the forces that shape muscle stem cell function

Skeletal muscle is a force-producing organ composed of muscle tissues, connective tissues, blood vessels, and nerves, all working in synergy to enable movement and provide support to the body. While robust biomechanical descriptions of skeletal muscle force production at the body or tissue level exist, little is known about force application on microstructures within the muscles, such as cells. Among various cell types, skeletal muscle stem cells reside in the muscle tissue environment and play a crucial role in driving the self-repair process when muscle damage occurs. Early evidence indicates that the fate and function of skeletal muscle stem cells are controlled by both biophysical and biochemical factors in their microenvironments, but much remains to accomplish in quantitatively describing the biophysical muscle stem cell microenvironment. This book chapter aims to review current knowledge on the influence of biophysical stresses and landscape properties on muscle stem cells in heath, aging, and diseases.

Blood flow-bearing physical forces, endothelial glycocalyx, and liver enzyme mobilization: A hypothesis

Numerous elements involved in shear stress-induced signaling have been identified, recognizing their functions as mechanotransducing ion channels situated at cellular membranes. This form of mechanical signaling relies on transmembrane proteins and cytoplasmic proteins that restructure the cytoskeleton, contributing to mechanotransduction cascades. Notably, blood flow generates mechanical forces that significantly impact the structure and remodeling of blood vessels. The primary regulation of blood vessel responses occurs through hemodynamic forces acting on the endothelium. These mechanical events intricately govern endothelial biophysical, biochemical, and genetic responses. Endothelial cells, positioned on the intimal surface of blood vessels, have the capability to express components of the glycocalyx. This endothelial structure emerges as a pivotal factor in mechanotransduction and the regulation of vascular tone. The endothelial glycocalyx assumes diverse roles in both health and disease. Our findings propose a connection between the release of specific enzymes from the rat liver and variations in the hepatic blood flow/mass ratio. Importantly, this phenomenon is not correlated with liver necrosis. Consequently, this review serves as an exploration of the potential involvement of membrane proteins in a hypothetical mechanotransducing phenomenon capable of controlling the release of liver enzymes.

Hypertensive Pressure Mechanosensing Alone Triggers Lipid Droplet Accumulation and Transdifferentiation of Vascular Smooth Muscle Cells to Foam Cells

Arterial Vascular smooth muscle cells (VSMCs) play a central role in the onset and progression of atherosclerosis. Upon exposure to pathological stimuli, they can take on alternative phenotypes that, among others, have been described as macrophage like, or foam cells. VSMC foam cells make up >50% of all arterial foam cells and have been suggested to retain an even higher proportion of the cell stored lipid droplets, further leading to apoptosis, secondary necrosis, and an inflammatory response. However, the mechanism of VSMC foam cell formation is still unclear. Here, it is identified that mechanical stimulation through hypertensive pressure alone is sufficient for the phenotypic switch. Hyperspectral stimulated Raman scattering imaging demonstrates rapid lipid droplet formation and changes to lipid metabolism and changes are confirmed in ABCA1, KLF4, LDLR, and CD68 expression, cell proliferation, and migration. Further, a mechanosignaling route is identified involving Piezo1, phospholipid, and arachidonic acid signaling, as well as epigenetic regulation, whereby CUT&Tag epigenomic analysis confirms changes in the cells (lipid) metabolism and atherosclerotic pathways. Overall, the results show for the first time that VSMC foam cell formation can be triggered by mechanical stimulation alone, suggesting modulation of mechanosignaling can be harnessed as potential therapeutic strategy.

Tensile Stress-Activated and Exosome-Transferred YAP/TAZ-Notch Circuit Specifies Type H Endothelial Cell for Segmental Bone Regeneration

The Ilizarov technique has been continuously innovated to utilize tensile stress (TS) for inducing a bone development-like regenerative process, aiming to achieve skeletal elongation and reconstruction. However, it remains uncertain whether this distraction osteogenesis (DO) process induced by TS involves the pivotal coupling of angiogenesis and osteogenesis mediated by type H endothelial cells (THECs). In this study, it is demonstrated that the Ilizarov technique induces the formation of a metaphysis-like architecture composed of THECs, leading to segmental bone regeneration during the DO process. Mechanistically, cell-matrix interactions-mediated activation of yes-associated protein (YAP)/transcriptional co-activator with PDZ-binding motif (TAZ) transcriptionally upregulates the expression of Notch1 and Delta-like ligand 4, which act as direct positive regulators of THECs phenotype, in bone marrow endothelial cells (BMECs) upon TS stimulation. Simultaneously, the Notch intracellular domain enhances YAP/TAZ activity by transcriptionally upregulating YAP expression and stabilizing TAZ protein, thus establishing the YAP/TAZ-Notch circuit. Additionally, TS-stimulated BMECs secrete exosomes enriched with vital molecules in this positive feedback pathway, which can be utilized to promote segmental bone defect healing, mimicking the therapeutic effects of Ilizarov technique. The findings advance the understanding of TS-induced segmental bone regeneration and establish the foundation for innovative biological therapeutic strategies aimed at activating THECs.

A Hierarchical Mechanotransduction System: From Macro to Micro

Mechanotransduction is a strictly regulated process whereby mechanical stimuli, including mechanical forces and properties, are sensed and translated into biochemical signals. Increasing data demonstrate that mechanotransduction is crucial for regulating macroscopic and microscopic dynamics and functionalities. However, the actions and mechanisms of mechanotransduction across multiple hierarchies, from molecules, subcellular structures, cells, tissues/organs, to the whole-body level, have not been yet comprehensively documented. Herein, the biological roles and operational mechanisms of mechanotransduction from macro to micro are revisited, with a focus on the orchestrations across diverse hierarchies. The implications, applications, and challenges of mechanotransduction in human diseases are also summarized and discussed. Together, this knowledge from a hierarchical perspective has the potential to refresh insights into mechanotransduction regulation and disease pathogenesis and therapy, and ultimately revolutionize the prevention, diagnosis, and treatment of human diseases.

Squishy matters - Corneal mechanobiology in health and disease

The cornea, as a dynamic and responsive tissue, constantly interacts with mechanical forces in order to maintain its structural integrity, barrier function, transparency and refractive power. Cells within the cornea sense and respond to various mechanical forces that fundamentally regulate their morphology and fate in development, homeostasis and pathophysiology. Corneal cells also dynamically regulate their extracellular matrix (ECM) with ensuing cell-ECM crosstalk as the matrix serves as a dynamic signaling reservoir providing biophysical and biochemical cues to corneal cells. Here we provide an overview of mechanotransduction signaling pathways then delve into the recent advances in corneal mechanobiology, focusing on the interplay between mechanical forces and responses of the corneal epithelial, stromal, and endothelial cells. We also identify species-specific differences in corneal biomechanics and mechanotransduction to facilitate identification of optimal animal models to study corneal wound healing, disease, and novel therapeutic interventions. Finally, we identify key knowledge gaps and therapeutic opportunities in corneal mechanobiology that are pressing for the research community to address especially pertinent within the domains of limbal stem cell deficiency, keratoconus and Fuchs' endothelial corneal dystrophy. By furthering our understanding corneal mechanobiology, we can contextualize discoveries regarding corneal diseases as well as innovative treatments for them.

Interplay between the plasma membrane and cell-cell adhesion maintains epithelial identity for correct polarised cell divisions

Polarised epithelial cell divisions represent a fundamental mechanism for tissue maintenance and morphogenesis. Morphological and mechanical changes in the plasma membrane influence the organisation and crosstalk of microtubules and actin at the cell cortex, thereby regulating the mitotic spindle machinery and chromosome segregation. Yet, the precise mechanisms linking plasma membrane remodelling to cell polarity and cortical cytoskeleton dynamics to ensure accurate execution of mitosis in mammalian epithelial cells remain poorly understood. Here, we manipulated the density of mammary epithelial cells in culture, which led to several mitotic defects. Perturbation of cell-cell adhesion formation impairs the dynamics of the plasma membrane, affecting the shape and size of mitotic cells and resulting in defects in mitotic progression and the generation of daughter cells with aberrant architecture. In these conditions, F- actin-astral microtubule crosstalk is impaired, leading to mitotic spindle misassembly and misorientation, which in turn contributes to chromosome mis-segregation. Mechanistically, we identify S100 Ca2+-binding protein A11 (S100A11) as a key membrane-associated regulator that forms a complex with E-cadherin (CDH1) and the leucine-glycine-asparagine repeat protein LGN (also known as GPSM2) to coordinate plasma membrane remodelling with E-cadherin-mediated cell adhesion and LGN-dependent mitotic spindle machinery. Thus, plasma membrane-mediated maintenance of mammalian epithelial cell identity is crucial for correct execution of polarised cell divisions, genome maintenance and safeguarding tissue integrity.