Transcription upregulation via force-induced direct stretching of chromatin

A 3D micro-printed single cell micro-niche with asymmetric niche signals - An in vitro model for asymmetric cell division study

Intricate microenvironment signals orchestrate to affect cell behavior and fate during tissue morphogenesis. However, the underlying mechanisms on how specific local niche signals influence cell behavior and fate are not fully understood, owing to the lack of in vitro platform able to precisely, quantitatively, spatially, and independently manipulate individual niche signals. Here, microarrays of protein-based 3D single cell micro-niche (3D-SCμN), with precisely engineered biophysical and biochemical niche signals, are micro-printed by a multiphoton microfabrication and micropatterning technology. Mouse embryonic stem cell (mESC) is used as the model cell to study how local niche signals affect stem cell behavior and fate. By precisely engineering the internal microstructures of the 3D SCμNs, we demonstrate that the cell division direction can be controlled by the biophysical niche signals, in a cell shape-independent manner. After confining the cell division direction to a dominating axis, single mESCs are exposed to asymmetric biochemical niche signals, specifically, cell-cell adhesion molecule on one side and extracellular matrix on the other side. We demonstrate that, symmetry-breaking (asymmetric) niche signals successfully trigger cell polarity formation and bias the orientation of asymmetric cell division, the mitosis process resulting in two daughter cells with differential fates, in mESCs.

Sensing the squeeze: nuclear mechanotransduction in health and disease

The nucleus not only is a repository for DNA but also a center of cellular and nuclear mechanotransduction. From nuclear deformation to the interplay between mechanosensing components and genetic control, the nucleus is poised at the nexus of mechanical forces and cellular function. Understanding the stresses acting on the nucleus, its mechanical properties, and their effects on gene expression is therefore crucial to appreciate its mechanosensitive function. In this review, we examine many elements of nuclear mechanotransduction, and discuss the repercussions on the health of cells and states of illness. By describing the processes that underlie nuclear mechanosensation and analyzing its effects on gene regulation, the review endeavors to open new avenues for studying nuclear mechanics in physiology and diseases.

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.

Nucleocytoplasmic transport senses mechanical forces independently of cell density in cell monolayers

Cells sense and respond to mechanical forces through mechanotransduction, which regulates processes in health and disease. In single adhesive cells, mechanotransduction involves the transmission of force from the extracellular matrix to the cell nucleus, where it affects nucleocytoplasmic transport (NCT) and the subsequent nuclear localization of transcriptional regulators, such as YAP (also known as YAP1). However, if and how NCT is mechanosensitive in multicellular systems is unclear. Here, we characterize and use a fluorescent sensor of nucleocytoplasmic transport (Sencyt) and demonstrate that NCT responds to mechanical forces but not cell density in cell monolayers. Using monolayers of both epithelial and mesenchymal phenotype, we show that NCT is altered in response both to osmotic shocks and to the inhibition of cell contractility. Furthermore, NCT correlates with the degree of nuclear deformation measured through nuclear solidity, a shape parameter related to nuclear envelope tension. In contrast, YAP is sensitive to cell density, showing that the YAP response to cell-cell contacts is not via a mere mechanical effect of NCT. Our results demonstrate the generality of the mechanical regulation of NCT.

Mechanotransduction of the vasculature in Hutchinson-Gilford Progeria Syndrome

Hutchinson-Gilford Progeria Syndrome (HGPS) is a premature aging disorder that causes severe cardiovascular disease, resulting in the death of patients in their teenage years. The disease pathology is caused by the accumulation of progerin, a mutated form of the nuclear lamina protein, lamin A. Progerin binds to the inner nuclear membrane, disrupting nuclear integrity, and causes severe nuclear abnormalities and changes in gene expression. This results in increased cellular inflammation, senescence, and overall dysfunction. The molecular mechanisms by which progerin induces the disease pathology are not fully understood. Progerin's detrimental impact on nuclear mechanics and the role of the nucleus as a mechanosensor suggests dysfunctional mechanotransduction could play a role in HGPS. This is especially relevant in cells exposed to dynamic, continuous mechanical stimuli, like those of the vasculature. The endothelial (ECs) and smooth muscle cells (SMCs) within arteries rely on physical forces produced by blood flow to maintain function and homeostasis. Certain regions within arteries produce disturbed flow, leading to an impaired transduction of mechanical signals, and a reduction in cellular function, which also occurs in HGPS. In this review, we discuss the mechanics of nuclear mechanotransduction, how this is disrupted in HGPS, and what effect this has on cell health and function. We also address healthy responses of ECs and SMCs to physiological mechanical stimuli and how these responses are impaired by progerin accumulation.

The Myofibroblast Fate of Therapeutic Mesenchymal Stromal Cells: Regeneration, Repair, or Despair?

Mesenchymal stromal cells (MSCs) can be isolated from various tissues of healthy or patient donors to be retransplanted in cell therapies. Because the number of MSCs obtained from biopsies is typically too low for direct clinical application, MSC expansion in cell culture is required. However, ex vivo amplification often reduces the desired MSC regenerative potential and enhances undesired traits, such as activation into fibrogenic myofibroblasts. Transiently activated myofibroblasts restore tissue integrity after organ injury by producing and contracting extracellular matrix into scar tissue. In contrast, persistent myofibroblasts cause excessive scarring-called fibrosis-that destroys organ function. In this review, we focus on the relevance and molecular mechanisms of myofibroblast activation upon contact with stiff cell culture plastic or recipient scar tissue, such as hypertrophic scars of large skin burns. We discuss cell mechanoperception mechanisms such as integrins and stretch-activated channels, mechanotransduction through the contractile actin cytoskeleton, and conversion of mechanical signals into transcriptional programs via mechanosensitive co-transcription factors, such as YAP, TAZ, and MRTF. We further elaborate how prolonged mechanical stress can create persistent myofibroblast memory by direct mechanotransduction to the nucleus that can evoke lasting epigenetic modifications at the DNA level, such as histone methylation and acetylation. We conclude by projecting how cell culture mechanics can be modulated to generate MSCs, which epigenetically protected against myofibroblast activation and transport desired regeneration potential to the recipient tissue environment in clinical therapies.

Interplay of chromatin organization and mechanics of the cell nucleus

The nucleus of eukaryotic cells is constantly subjected to different kinds of mechanical stimuli, which can impact the organization of chromatin and, subsequently, the expression of genetic information. Experiments from different groups showed that nuclear deformation can lead to transient or permanent condensation or decondensation of chromatin and the mechanical activation of genes, thus altering the transcription of proteins. Changes in chromatin organization, in turn, change the mechanical properties of the nucleus, possibly leading to an auxetic behavior. Here, we model the mechanics of the nucleus as a chemically active polymer gel in which the chromatin can exist in two states: a self-attractive state representing the heterochromatin and a repulsive state representing euchromatin. The model predicts reversible or irreversible changes in chromatin condensation levels upon external deformations of the nucleus. We find an auxetic response for a broad range of parameters under small and large deformations. These results agree with experimental observations and highlight the key role of chromatin organization in the mechanical response of the nucleus.

Impact of uniaxial cyclic stretching on matrix-associated endothelial cell responses

Uniaxial cyclic stretching plays a pivotal role in the fields of tissue engineering and regenerative medicine, influencing cell behaviors and functionality based on physical properties, including matrix morphology and mechanical stimuli. This study delves into the response of endothelial cells to uniaxial cyclic strain within the geometric constraints of micro-nano fibers. Various structural scaffold forms of poly(l-lactide-co-caprolactone) (PLCL), such as flat membranes, randomly oriented fiber membranes, and aligned fiber membranes, were fabricated through solvent casting and electrospinning methods. Our investigation focuses on the morphological variation of endothelial cells under diverse geometric constraints and the mechanical-dependent release of nitric oxide (NO) on oriented fibrous membranes. Our results indicate that while uniaxial cyclic stretching promotes endothelial cell spreading, the anisotropy of the matrix morphology remains the primary driving factor for cell alignment. Additionally, uniaxial cyclic stretching significantly enhances NO release, with a notably stronger effect correlated to the increasing strain amplitude. Importantly, this study reveals that uniaxial cyclic stretching enhances the mRNA expression of key proteins, including talin, vinculin, rac, and nitric oxide synthase (eNOS).

Fibroblast and myofibroblast activation in normal tissue repair and fibrosis

The term 'fibroblast' often serves as a catch-all for a diverse array of mesenchymal cells, including perivascular cells, stromal progenitor cells and bona fide fibroblasts. Although phenotypically similar, these subpopulations are functionally distinct, maintaining tissue integrity and serving as local progenitor reservoirs. In response to tissue injury, these cells undergo a dynamic fibroblast-myofibroblast transition, marked by extracellular matrix secretion and contraction of actomyosin-based stress fibres. Importantly, whereas transient activation into myofibroblasts aids in tissue repair, persistent activation triggers pathological fibrosis. In this Review, we discuss the roles of mechanical cues, such as tissue stiffness and strain, alongside cell signalling pathways and extracellular matrix ligands in modulating myofibroblast activation and survival. We also highlight the role of epigenetic modifications and myofibroblast memory in physiological and pathological processes. Finally, we discuss potential strategies for therapeutically interfering with these factors and the associated signal transduction pathways to improve the outcome of dysregulated healing.

Mechanomemory of nucleoplasm and RNA polymerase II after chromatin stretching by a microinjected magnetic nanoparticle force

Increasing evidence suggests that the mechanics of chromatin and nucleoplasm regulate gene transcription and nuclear function. However, how the chromatin and nucleoplasm sense and respond to forces remains elusive. Here, we employed a strategy of applying forces directly to the chromatin of a cell via a microinjected 200-nm anti-H2B-antibody-coated ferromagnetic nanoparticle (FMNP) and an anti-immunoglobulin G (IgG)-antibody-coated or an uncoated FMNP. The chromatin behaved as a viscoelastic gel-like structure and the nucleoplasm was a softer viscoelastic structure at loading frequencies of 0.1-5 Hz. Protein diffusivity of the chromatin, nucleoplasm, and RNA polymerase II (RNA Pol II) and RNA Pol II activity were upregulated in a chromatin-stretching-dependent manner and stayed upregulated for tens of minutes after force cessation. Chromatin stiffness increased, but the mechanomemory duration of chromatin diffusivity decreased, with substrate stiffness. These findings may provide a mechanomemory mechanism of transcription upregulation and have implications on cell and nuclear functions.

Bioengineered niches that recreate physiological extracellular matrix organisation to support long-term haematopoietic stem cells

Long-term reconstituting haematopoietic stem cells (LT-HSCs) are used to treat blood disorders via stem cell transplantation. The very low abundance of LT-HSCs and their rapid differentiation during in vitro culture hinders their clinical utility. Previous developments using stromal feeder layers, defined media cocktails, and bioengineering have enabled HSC expansion in culture, but of mostly short-term HSCs and progenitor populations at the expense of naive LT-HSCs. Here, we report the creation of a bioengineered LT-HSC maintenance niche that recreates physiological extracellular matrix organisation, using soft collagen type-I hydrogels to drive nestin expression in perivascular stromal cells (PerSCs). We demonstrate that nestin, which is expressed by HSC-supportive bone marrow stromal cells, is cytoprotective and, via regulation of metabolism, is important for HIF-1α expression in PerSCs. When CD34+ve HSCs were added to the bioengineered niches comprising nestin/HIF-1α expressing PerSCs, LT-HSC numbers were maintained with normal clonal and in vivo reconstitution potential, without media supplementation. We provide proof-of-concept that our bioengineered niches can support the survival of CRISPR edited HSCs. Successful editing of LT-HSCs ex vivo can have potential impact on the treatment of blood disorders.

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.

A Computational Model of Mechanical Stretching of Cultured Cells on a Flexible Membrane

Mechanical forces applied to cells are known to regulate a wide variety of biological processes. Recent studies have supported that mechanical forces can cause nuclear deformation, leading to significant alterations in the gene expression and chromatin landscape of the cell. While the stresses and strains applied to cells is it is often known or controlled experimentally on a macroscopic length scale, it is often unclear what the actual forces and displacements are at the microscopic level of the cell. In this work, we created a model of cell deformation during application of mechanical stretch to cultured cells growth on a flexible membrane. This configuration is commonly used is in experimental studies as a means to apply controlled mechanical strains to adherent cultured cells. The parameters used in the study were used for application of strain to a mesenchymal stem cell stretched on a membrane. computational model was created to simulate the stresses and strains within the cell under a variety of stain amplitudes, waveforms and frequencies of mechanical loading with the range of commonly used experimental systems. The results demonstrate the connection between mechanical loading parameters applied through the flexible membrane and the resulting stresses and strains within the cell and nucleus. Using a viscoelastic model of chromatin, we connected the results provide to a rough model of resulting deformation within chromatin from the forces applied to the nucleus. Overall, the model is useful in providing insight between experimentally applied mechanical forces and the actual forces within the cell to better interpret the results of experimental studies.

Statement of Significance

In this work, we created a computational model of the mechanical stretching of cell on a flexible membrane under cyclic mechanical loading. This model provides insight into the forces and displacements inside of cell that result from that application of stretch. As many experiments use this set up, our work is relevant to interpreting many studies that use mechanical stretch to stimulate mechanotransduction.

Mechanotransduction in stem cells

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

A molecular arm: the molecular bending-unbending mechanism of integrin

The balance of integrin activation and deactivation regulates its function and mediates cell behaviors. Mechanical force triggers the unbending and activation of integrin. However, how an activated and extended integrin spontaneously bends back is unclear. I performed all-atom molecular dynamics simulations on an integrin or its subunits to reveal the bending-unbending mechanism of integrin. According to the simulations, the integrin structure works like a human arm. The integrin α subunit serves as the bones, while the β leg serves as the bicep. The integrin extension results in the stretching of the β leg, and the extended integrin spontaneously bends as a consequence of the contraction of the β leg. This study provides new insights into the mechanism of how the integrin secures in the bent inactivated state and sheds light on how the integrin could achieve a stable extended state.

Nuclear curvature determines Yes-associated protein localization and differentiation of mesenchymal stem cells

Controlling mesenchymal stem cell (MSC) differentiation remains a critical challenge in MSCs' therapeutic application. Numerous biophysical and mechanical stimuli influence stem cell fate; however, their relative efficacy and specificity in mechanically directed differentiation remain unclear. Yes-associated protein (YAP) is one key mechanosensitive protein that controls MSC differentiation. Previous studies have related nuclear mechanics with YAP activity, but we still lack an understanding of what nuclear deformation specifically regulates YAP and its relationship with mechanical stimuli. Here, we report that maximum nuclear curvature is the most precise biophysical determinant for YAP mechanotransduction-mediated MSC differentiation and is a relevant parameter for stem cell-based therapies. We employed traction force microscopy and confocal microscopy to characterize the causal relationships between contractility and nuclear deformation in regulating YAP activity in MSCs. We observed that an increase in contractility compresses nuclei anisotropically, whereby the degree of asymmetric compression increased the bending curvature of the nuclear membrane. We then examined membrane curvature and tension using thin micropatterned adhesive substrate lines and an FRET-based tension sensor, revealing the direct role of curvature in YAP activity driven by both active and passive nuclear import. Finally, we employed micropatterned lines to control nuclear curvature and precisely direct MSC differentiation. This work illustrates that nuclear curvature subsumes other biophysical aspects to control YAP-mediated differentiation in MSCs and may provide a deterministic solution to some of the challenges in mesenchymal stem cell therapies.

Life at the crossroads: the nuclear LINC complex and vascular mechanotransduction

Vascular endothelial cells line the inner surface of all blood vessels, where they are exposed to polarized mechanical forces throughout their lifespan. Both basal substrate interactions and apical blood flow-induced shear stress regulate blood vessel development, remodeling, and maintenance of vascular homeostasis. Disruption of these interactions leads to dysfunction and vascular pathologies, although how forces are sensed and integrated to affect endothelial cell behaviors is incompletely understood. Recently the endothelial cell nucleus has emerged as a prominent force-transducing organelle that participates in vascular mechanotransduction, via communication to and from cell-cell and cell-matrix junctions. The LINC complex, composed of SUN and nesprin proteins, spans the nuclear membranes and connects the nuclear lamina, the nuclear envelope, and the cytoskeleton. Here we review LINC complex involvement in endothelial cell mechanotransduction, describe unique and overlapping functions of each LINC complex component, and consider emerging evidence that two major SUN proteins, SUN1 and SUN2, orchestrate a complex interplay that extends outward to cell-cell and cell-matrix junctions and inward to interactions within the nucleus and chromatin. We discuss these findings in relation to vascular pathologies such as Hutchinson-Gilford progeria syndrome, a premature aging disorder with cardiovascular impairment. More knowledge of LINC complex regulation and function will help to understand how the nucleus participates in endothelial cell force sensing and how dysfunction leads to cardiovascular disease.

Chromatin accessibility profiling reveals that human fibroblasts respond to mechanical stimulation in a cell-specific manner

Fibroblasts in the skin are highly heterogeneous, both in vivo and in vitro. One difference between follicular (dermal papilla fibroblasts [DP]) and interfollicular fibroblasts (papillary fibroblasts [PFi]) in vitro is their ability to differentiate in response to osteogenic media (OM), or mechanical stimulation. Here, we asked whether differences in the ability of DP and PFi to respond to differentiation stimuli are due to differences in chromatin accessibility. We performed chromatin accessibility and transcriptional profiling of DP and PFi in human skin, which arise from a common progenitor during development, yet display distinct characteristics in adult tissue and in vitro. We found that cells cultured in growth media had unique chromatin accessibility profiles; however, these profiles control similar functional networks. Upon introduction of a chemical perturbation (OM) to promote differentiation, we observed a divergence not only in the accessible chromatin signatures but also in the functional networks controlled by these signatures. The biggest divergence between DP and PFi was observed when we applied 2 perturbations to cells: growth in OM and mechanical stimulation (a shock wave [OMSW]). DP readily differentiate into bone in OMSW conditions, while PFi lack differentiation capability in vitro. In the DP we found a number of uniquely accessible promoters that controlled osteogenic interaction networks associated with bone and differentiation functions. Using ATAC-seq and RNA-seq we found that the combination of 2 stimuli (OMSW) could result in significant changes in chromatin accessibility associated with osteogenic differentiation, but only within the DP (capable of osteogenic differentiation). De novo motif analysis identified enrichment of motifs bound by the TEA domain (TEAD) family of transcription factors, and inter-cell comparisons (UpSet analysis) displayed large groups of genes to be unique to single cell types and conditions. Our results suggest that these 2 stimuli (OMSW) elicit cell-specific responses by modifying chromatin accessibility of osteogenic-related gene promoters.

Nuclear envelope dynamics in connection to chromatin remodeling

The nucleus is a central organelle of eukaryotic cells undergoing dynamic structural changes during cellular fundamental processes such as proliferation and differentiation. These changes rely on the integration of developmental and stress signals at the nuclear envelope (NE), orchestrating responses at the nucleo-cytoplasmic interface for efficient genomic functions such as DNA transcription, replication and repair. While in animals, correlation has already been established between NE dynamics and chromatin remodeling using last-generation tools and cutting-edge technologies, this topic is just emerging in plants, especially in response to mechanical cues. This review summarizes recent data obtained in this field with more emphasis on the mechanical stress response. It also highlights similarities/differences between animal and plant cells at multiples scales, from the structural organization of the nucleo-cytoplasmic continuum to the functional impacts of NE dynamics.

Microfluidic device featuring micro-constrained channels for multi-parametric assessment of cellular biomechanics and high-precision mechanical phenotyping of gastric cells

BACKGROUND

Cellular biomechanics plays a significant role in the regulation of cellular physiological and pathological processes. In recent years, multiple methods have been developed to evaluate cellular biomechanics, such as atomic force microscopy (AFM), micropipette aspiration, and magnetic tweezers. However, most of these methods only focus on a single parameter and cannot automate the process at a high-efficiency level. A novel microfluidic method is necessary to achieve the simultaneous multi-parametric measurement of cellular biomechanics and high-precision cellular mechanical phenotyping at high throughput.

RESULTS

To tackle the issue concerning the low-throughput and cellular single-parameter evaluation, we designed and fabricated a microfluidic chip featuring multiple micro-constrained channels structure, providing a simultaneous multi-parametric assessment of cellular biomechanics, including elastic modulus, recovery capability, and deformability. We compared the biomechanical properties of normal human gastric mucosal epithelial cells (GES-1) and human gastric cancer cells (AGS and MKN-45) by the chip. Results demonstrated that the elastic modulus of GES-1, AGS, and MKN-45 cells decreased sequentially, which was the opposite of their invasiveness and metastasis potential, suggesting the inverse correlation between cellular elastic modulus and malignancy. Meanwhile, the recovery capability and deformability of GES-1, AGS, and MKN-45 cells increased sequentially, demonstrating the positive correlation between cellular deformability and malignancy. Furthermore, multiple parameters were used to distinguish gastric cancer cells from normal gastric cells via machine learning. An accuracy of over 94.8% for identifying gastric cancer cells was achieved.

SIGNIFICANCE

This study provides a deep insight into the biophysical mechanism of gastric cancer metastasis at the single-cell level and possesses great potential to function as a valuable tool for single-cell analysis, thereby facilitating high-precision and high-throughput discrimination of cellular phenotypes that are not easily discernible through single-marker analysis.

Soft bioreactor systems: a necessary step toward engineered MSK soft tissue?

A key objective of tissue engineering (TE) is to produce in vitro funcional grafts that can replace damaged tissues or organs in patients. TE uses bioreactors, which are controlled environments, allowing the application of physical and biochemical cues to relevant cells growing in biomaterials. For soft musculoskeletal (MSK) tissues such as tendons, ligaments and cartilage, it is now well established that applied mechanical stresses can be incorporated into those bioreactor systems to support tissue growth and maturation via activation of mechanotransduction pathways. However, mechanical stresses applied in the laboratory are often oversimplified compared to those found physiologically and may be a factor in the slow progression of engineered MSK grafts towards the clinic. In recent years, an increasing number of studies have focused on the application of complex loading conditions, applying stresses of different types and direction on tissue constructs, in order to better mimic the cellular environment experienced in vivo. Such studies have highlighted the need to improve upon traditional rigid bioreactors, which are often limited to uniaxial loading, to apply physiologically relevant multiaxial stresses and elucidate their influence on tissue maturation. To address this need, soft bioreactors have emerged. They employ one or more soft components, such as flexible soft chambers that can twist and bend with actuation, soft compliant actuators that can bend with the construct, and soft sensors which record measurements in situ. This review examines types of traditional rigid bioreactors and their shortcomings, and highlights recent advances of soft bioreactors in MSK TE. Challenges and future applications of such systems are discussed, drawing attention to the exciting prospect of these platforms and their ability to aid development of functional soft tissue engineered grafts.

A microfluidic model to study the effects of arrhythmic flows on endothelial cells

Atrial fibrillation (AF) is the most common type of cardiac arrhythmia and an important contributor to morbidity and mortality. Endothelial dysfunction has been postulated to be an important contributing factor in cardiovascular events in patients with AF. However, how vascular endothelial cells respond to arrhythmic flow is not fully understood, mainly due to the limitation of current in vitro systems to mimic arrhythmic flow conditions. To address this limitation, we developed a microfluidic system to study the effect of arrhythmic flow on the mechanobiology of human aortic endothelial cells (HAECs). The system utilises a computer-controlled piezoelectric pump for generating arrhythmic flow with a unique ability to control the variability in both the frequency and amplitude of pulse waves. The flow rate is modulated to reflect physiological or pathophysiological shear stress levels on endothelial cells. This enabled us to systematically dissect the importance of variability in the frequency and amplitude of pulses and shear stress level on endothelial cell mechanobiology. Our results indicated that arrhythmic flow at physiological shear stress level promotes endothelial cell spreading and reduces the plasma membrane-to-cytoplasmic distribution of β-catenin. In contrast, arrhythmic flow at low and atherogenic shear stress levels does not promote endothelial cell spreading or redistribution of β-catenin. Interestingly, under both shear stress levels, arrhythmic flow induces inflammation by promoting monocyte adhesion via an increase in ICAM-1 expression. Collectively, our microfluidic system provides opportunities to study the effect of arrhythmic flows on vascular endothelial mechanobiology in a systematic and reproducible manner.

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.

Linking cell mechanical memory and cancer metastasis

Metastasis causes most cancer-related deaths; however, the efficacy of anti-metastatic drugs is limited by incomplete understanding of the biological mechanisms that drive metastasis. Focusing on the mechanics of metastasis, we propose that the ability of tumour cells to survive the metastatic process is enhanced by mechanical stresses in the primary tumour microenvironment that select for well-adapted cells. In this Perspective, we suggest that biophysical adaptations favourable for metastasis are retained via mechanical memory, such that the extent of memory is influenced by both the magnitude and duration of the mechanical stress. Among the mechanical cues present in the primary tumour microenvironment, we focus on high matrix stiffness to illustrate how it alters tumour cell proliferation, survival, secretion of molecular factors, force generation, deformability, migration and invasion. We particularly centre our discussion on potential mechanisms of mechanical memory formation and retention via mechanotransduction and persistent epigenetic changes. Indeed, we propose that the biophysical adaptations that are induced by this process are retained throughout the metastatic process to improve tumour cell extravasation, survival and colonization in the distant organ. Deciphering mechanical memory mechanisms will be key to discovering a new class of anti-metastatic drugs.

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.

Mechanotransduction and epigenetic modulations of chromatin: Role of mechanical signals in gene regulation

Mechanical forces may be generated within a cell due to tissue stiffness, cytoskeletal reorganization, and the changes (even subtle) in the cell's physical surroundings. These changes of forces impose a mechanical tension within the intracellular protein network (both cytosolic and nuclear). Mechanical tension could be released by a series of protein-protein interactions often facilitated by membrane lipids, lectins and sugar molecules and thus generate a type of signal to drive cellular processes, including cell differentiation, polarity, growth, adhesion, movement, and survival. Recent experimental data have accentuated the molecular mechanism of this mechanical signal transduction pathway, dubbed mechanotransduction. Mechanosensitive proteins in the cell's plasma membrane discern the physical forces and channel the information to the cell interior. Cells respond to the message by altering their cytoskeletal arrangement and directly transmitting the signal to the nucleus through the connection of the cytoskeleton and nucleoskeleton before the information despatched to the nucleus by biochemical signaling pathways. Nuclear transmission of the force leads to the activation of chromatin modifiers and modulation of the epigenetic landscape, inducing chromatin reorganization and gene expression regulation; by the time chemical messengers (transcription factors) arrive into the nucleus. While significant research has been done on the role of mechanotransduction in tumor development and cancer progression/metastasis, the mechanistic basis of force-activated carcinogenesis is still enigmatic. Here, in this review, we have discussed the various cues and molecular connections to better comprehend the cellular mechanotransduction pathway, and we also explored the detailed role of some of the multiple players (proteins and macromolecular complexes) involved in mechanotransduction. Thus, we have described an avenue: how mechanical stress directs the epigenetic modifiers to modulate the epigenome of the cells and how aberrant stress leads to the cancer phenotype.

Biphasic regulation of epigenetic state by matrix stiffness during cell reprogramming

We investigate how matrix stiffness regulates chromatin reorganization and cell reprogramming and find that matrix stiffness acts as a biphasic regulator of epigenetic state and fibroblast-to-neuron conversion efficiency, maximized at an intermediate stiffness of 20 kPa. ATAC sequencing analysis shows the same trend of chromatin accessibility to neuronal genes at these stiffness levels. Concurrently, we observe peak levels of histone acetylation and histone acetyltransferase (HAT) activity in the nucleus on 20 kPa matrices, and inhibiting HAT activity abolishes matrix stiffness effects. G-actin and cofilin, the cotransporters shuttling HAT into the nucleus, rises with decreasing matrix stiffness; however, reduced importin-9 on soft matrices limits nuclear transport. These two factors result in a biphasic regulation of HAT transport into nucleus, which is directly demonstrated on matrices with dynamically tunable stiffness. Our findings unravel a mechanism of the mechano-epigenetic regulation that is valuable for cell engineering in disease modeling and regenerative medicine applications.

Lamins: The backbone of the nucleocytoskeleton interface

The nuclear lamina (NL) is a crucial component of the inner nuclear membrane (INM) and consists of lamin filaments and associated proteins. Lamins are type V intermediate filament proteins essential for maintaining the integrity and mechanical properties of the nucleus. In human cells, 'B-type' lamins (lamin B1 and lamin B2) are ubiquitously expressed, while 'A-type' lamins (lamin A, lamin C, and minor isoforms) are expressed in a tissue- and development-specific manner. Lamins homopolymerize to form filaments that localize primarily near the INM, but A-type lamins also localize to and function in the nucleoplasm. Lamins play central roles in the assembly, structure, positioning, and mechanics of the nucleus, modulating cell signaling and influencing development, differentiation, and other activities. This review highlights recent findings on the structure and regulation of lamin filaments, providing insights into their multifaceted functions, including their role as "mechanosensors", delving into the emerging significance of lamin filaments as vital links between cytoskeletal and nuclear structures, chromatin organization, and the genome.

Suppression of LPS-activated inflammatory responses and chromosomal histone modifications in macrophages by micropattern-induced nuclear deformation

Macrophages are important immune effector cells which participate various physiological and pathological conditions. Numerous studies have demonstrated the regulation of macrophage phenotype by micropatterns. It is well accepted that micropatterns affect cellular behaviors through changing cell shape and modulating the associated mechanical sensors on the plasma membrane and cytoskeleton. However, the role of nucleus, which serves as a critical physical sensing device, is often ignored. Herein, we found the nuclear deformation and the subsequently increased chromosomal histone methylation (H3K36me2) may contribute to the micropattern-induced suppression of macrophage inflammatory responses. Specifically, macrophages on micropatterned surfaces expressed lower levels of key inflammatory genes, compared with those on flat surfaces. Further investigation on macrophage nuclei showed that micropatterned surfaces cause shrinkage of nucleus volume and compaction of chromatin. Moreover, micropatterned surfaces elevated the methylation level of H3K36me2 in macrophages, while decreased the methylation level of H3K4me3. Our study provides new mechanistic insight into how micropatterns affect macrophage phenotype and highlights the importance of nuclear shape and chromatin histone modification in mediating micropattern-induced change in cell behaviors.

Coordinated in confined migration: crosstalk between the nucleus and ion channel-mediated mechanosensation

Cell surface and intracellular mechanosensors enable cells to perceive different geometric, topographical, and physical cues. Mechanosensitive ion channels (MICs) localized at the cell surface and on the nuclear envelope (NE) are among the first to sense and transduce these signals. Beyond compartmentalizing the genome of the cell and its transcription, the nucleus also serves as a mechanical gauge of different physical and topographical features of the tissue microenvironment. In this review, we delve into the intricate mechanisms by which the nucleus and different ion channels regulate cell migration in confinement. We review evidence suggesting an interplay between macromolecular nuclear-cytoplasmic transport (NCT) and ionic transport across the cell membrane during confined migration. We also discuss the roles of the nucleus and ion channel-mediated mechanosensation, whether acting independently or in tandem, in orchestrating migratory mechanoresponses. Understanding nuclear and ion channel sensing, and their crosstalk, is critical to advancing our knowledge of cell migration in health and disease.

Enhancing anti-tumor potential: low-intensity vibration suppresses osteosarcoma progression and augments MSCs' tumor-suppressive abilities

Rationale: Osteosarcoma (OS), a common malignant bone tumor, calls for the investigation of novel treatment strategies. Low-intensity vibration (LIV) presents itself as a promising option, given its potential to enhance bone health and decrease cancer susceptibility. This research delves into the effects of LIV on OS cells and mesenchymal stem cells (MSCs), with a primary focus on generating induced tumor-suppressing cells (iTSCs) and tumor-suppressive conditioned medium (CM). Methods: To ascertain the influence of vibration frequency, we employed numerical simulations and conducted experiments to determine the most effective LIV conditions. Subsequently, we generated iTSCs and CM through LIV exposure and assessed the impact of CM on OS cells. We also explored the underlying mechanisms of the tumor-suppressive effects of LIV-treated MSC CM, with a specific focus on vinculin (VCL). We employed cytokine array, RNA sequencing, and Western blot techniques to investigate alterations in cytokine profiles, transcriptomes, and tumor suppressor proteins. Results: Numerical simulations validated LIV frequencies within the 10-100 Hz range. LIV induced notable morphological changes in OS cells and MSCs, confirming its dual role in inhibiting OS cell progression and promoting MSC conversion into iTSCs. Upregulated VCL expression enhanced MSC responsiveness to LIV, significantly bolstering CM's efficacy. Notably, we identified tumor suppressor proteins in LIV-treated CM, including procollagen C endopeptidase enhancer (PCOLCE), histone H4 (H4), peptidylprolyl isomerase B (PPIB), and aldolase A (ALDOA). Consistently, cytokine levels decreased significantly in LIV-treated mouse femurs, and oncogenic transcript levels were downregulated in LIV-treated OS cells. Moreover, our study demonstrated that combining LIV-treated MSC CM with chemotherapy drugs yielded additive anti-tumor effects. Conclusions: LIV effectively impeded the progression of OS cells and facilitated the transformation of MSCs into iTSCs. Notably, iTSC-derived CM demonstrated robust anti-tumor properties and the augmentation of MSC responsiveness to LIV via VCL. Furthermore, the enrichment of tumor suppressor proteins within LIV-treated MSC CM and the reduction of cytokines within LIV-treated isolated bone underscore the pivotal tumor-suppressive role of LIV within the bone tumor microenvironment.

[Hot Topics and Emerging Trends in Mechanobiology Research]

Mechanobiology focuses on a series of important physiopathological processes, such as how cells perceive different mechanomechanical stimuli, the process of intracellular mechanotransduction, and how mechanical signals determine the behavior and fate of cells. From the initial stage of embryogenesis, to developmental biology and regenerative medicine, or even through the whole life process, mechanical signaling cascades and cellular mechanical responses in mechanobiology are of great significance in biomedical research. In recent years, research in the field of mechanobiology has undergone remarkable development. Several scientific consortia around the world have been analyzing mechanobiological processes from different perspectives, aiming to gain insights into the regulatory mechanisms by which mechanical factors affect cell fate determination. In this article, we summarized and reviewed the topics that have attracted more research interests in recent years in the field of mechanobiology, for example, arterial blood vessels, stem cell, and ion channel. We also discussed the potential trends that may emerge, such as nuclear deformation, fibrous extracellular matrix, tumor mechanobiology, cellular mechanotransduction, and piezo ion channels. In addition, we put forward new ideas concerning the limitations of mechanism research and the importance of big data analysis and mining in this field, thereby providing objective support and a systematic framework for grasping the hot research topics and exploring new research directions in the field of mechanobiology.

Mechanosensitive genomic enhancers potentiate the cellular response to matrix stiffness

Epigenetic control of cellular transcription and phenotype is influenced by changes in the cellular microenvironment, yet how mechanical cues from these microenvironments precisely influence epigenetic state to regulate transcription remains largely unmapped. Here, we combine genome-wide epigenome profiling, epigenome editing, and phenotypic and single-cell RNA-seq CRISPR screening to identify a new class of genomic enhancers that responds to the mechanical microenvironment. These 'mechanoenhancers' could be active on either soft or stiff extracellular matrix contexts, and regulated transcription to influence critical cell functions including apoptosis, mechanotransduction, proliferation, and migration. Epigenetic editing of mechanoenhancers on rigid materials tuned gene expression to levels observed on softer materials, thereby reprogramming the cellular response to the mechanical microenvironment. These editing approaches may enable the precise alteration of mechanically-driven disease states.

Noncanonical Activity of Med4 as a Gatekeeper of Metastasis through Epigenetic Control of Integrin Signaling

Breast cancer metastatic relapse after a latency period, known as metastatic dormancy. Through genetic screening in mice, we identified the mediator complex subunit 4 (Med4) as a novel tumor-cell intrinsic gatekeeper in metastatic reactivation. Med4 downregulation effectively awakened dormant breast cancer cells, prompting macroscopic metastatic outgrowth in the lungs. Med4 depletion results in profound changes in nuclear size and three-dimensional chromatin architecture from compacted to relaxed states in contrast to the canonical function of the Mediator complex. These changes rewire the expression of extracellular matrix proteins, integrins, and signaling components resulting in integrin-mediated mechano-transduction and activation of YAP and MRTF. The assembly of stress fibers pulls on the nuclear membrane and contributes to reinforcing the overall chromatin modifications by Med4 depletion. MED4 gene deletions were observed in patients with metastatic breast cancer, and reduced MED4 expression correlates with worse prognosis, highlighting its significance as a potential biomarker for recurrence.

Extracellular Matrix Cues Regulate Mechanosensing and Mechanotransduction of Cancer Cells

Extracellular biophysical properties have particular implications for a wide spectrum of cellular behaviors and functions, including growth, motility, differentiation, apoptosis, gene expression, cell-matrix and cell-cell adhesion, and signal transduction including mechanotransduction. Cells not only react to unambiguously mechanical cues from the extracellular matrix (ECM), but can occasionally manipulate the mechanical features of the matrix in parallel with biological characteristics, thus interfering with downstream matrix-based cues in both physiological and pathological processes. Bidirectional interactions between cells and (bio)materials in vitro can alter cell phenotype and mechanotransduction, as well as ECM structure, intentionally or unintentionally. Interactions between cell and matrix mechanics in vivo are of particular importance in a variety of diseases, including primarily cancer. Stiffness values between normal and cancerous tissue can range between 500 Pa (soft) and 48 kPa (stiff), respectively. Even the shear flow can increase from 0.1-1 dyn/cm2 (normal tissue) to 1-10 dyn/cm2 (cancerous tissue). There are currently many new areas of activity in tumor research on various biological length scales, which are highlighted in this review. Moreover, the complexity of interactions between ECM and cancer cells is reduced to common features of different tumors and the characteristics are highlighted to identify the main pathways of interaction. This all contributes to the standardization of mechanotransduction models and approaches, which, ultimately, increases the understanding of the complex interaction. Finally, both the in vitro and in vivo effects of this mechanics-biology pairing have key insights and implications for clinical practice in tumor treatment and, consequently, clinical translation.

Cell stretching activates an ATM mechano-transduction pathway that remodels cytoskeleton and chromatin

Ataxia telangiectasia mutated (ATM) and ataxia telangiectasia and Rad3-related (ATR) DNA damage response (DDR) kinases contain elastic domains. ATM also responds to reactive oxygen species (ROS) and ATR to nuclear mechanical stress. Mre11 mediates ATM activation following DNA damage; ATM mutations cause ataxia telangiectasia (A-T). Here, using in vivo imaging, electron microscopy, proteomic, and mechano-biology approaches, we study how ATM responds to mechanical stress. We report that cytoskeleton and ROS, but not Mre11, mediate ATM activation following cell deformation. ATM deficiency causes hyper-stiffness, stress fiber accumulation, Yes-associated protein (YAP) nuclear enrichment, plasma and nuclear membrane alterations during interstitial migration, and H3 hyper-methylation. ATM locates to the actin cytoskeleton and, following cytoskeleton stress, promotes phosphorylation of key cytoskeleton and chromatin regulators. Our data contribute to explain some clinical features of patients with A-T and pinpoint the existence of an integrated mechano-response in which ATM and ATR have distinct roles unrelated to their canonical DDR functions.

Programmable and Reversible Integrin-Mediated Cell Adhesion Reveals Hysteresis in Actin Kinetics that Alters Subsequent Mechanotransduction

Dynamically evolving adhesions between cells and extracellular matrix (ECM) transmit time-varying signals that control cytoskeletal dynamics and cell fate. Dynamic cell adhesion and ECM stiffness regulate cellular mechanosensing cooperatively, but it has not previously been possible to characterize their individual effects because of challenges with controlling these factors independently. Therefore, a DNA-driven molecular system is developed wherein the integrin-binding ligand RGD can be reversibly presented and removed to achieve cyclic cell attachment/detachment on substrates of defined stiffness. Using this culture system, it is discovered that cyclic adhesion accelerates F-actin kinetics and nuclear mechanosensing in human mesenchymal stem cells (hMSCs), with the result that hysteresis can completely change how hMSCs transduce ECM stiffness. Results are dramatically different from well-known results for mechanotransduction on static substrates, but are consistent with a mathematical model of F-actin fragments retaining structure following loss of integrin ligation and participating in subsequent repolymerization. These findings suggest that cyclic integrin-mediated adhesion alters the mechanosensing of ECM stiffness by hMSCs through transient, hysteretic memory that is stored in F-actin.

The genetics of portal hypertension: Recent developments and the road ahead

Portal hypertension (PH), defined as a pathological increase in the portal vein pressure, has different aetiologies and causes. Intrahepatic PH is mostly secondary to the presence of underlying liver disease leading to cirrhosis, characterized by parenchymal changes with deregulated accumulation of extracellular matrix and vascular abnormalities; liver sinusoidal endothelial cells and hepatic stellate cells are key players in PH progression, able to influence each other. However, PH may also develop independently of parenchymal damage, as occur in portosinusoidal vascular disorder (PSVD), a group of clinical and histological entities characterized by portal vasculature dysfunctions. In this particular group of disorders, the pathophysiology of PH is still poorly understood. In the last years, several genetic studies, based on genome-wide association studies or whole-exome sequencing analysis, have highlighted the importance of genetic heritability in PH pathogenesis, both in cirrhotic and non-cirrhotic cases. The common PNPLA3 p.I148M variant, one of the main determinants of the susceptibility to steatotic liver disease, has also been associated with decompensation in patients with PH. Genetic variations at loci influencing coagulation, mainly the ABO locus, may directly contribute to the pathogenesis of PH. Rare genetic variants have been associated with familiar cases of progressive PSVD. In this review, we summarize the recent knowledges on genetic variants predisposing to PH development, contributing to better understand the role of genetic factors in PH pathogenesis.

Mechanobiology of portal hypertension

The interplay between mechanical stimuli and cellular mechanobiology orchestrates the physiology of tissues and organs in a dynamic balance characterized by constant remodelling and adaptative processes. Environmental mechanical properties can be interpreted as a complex set of information and instructions that cells read continuously, and to which they respond. In cirrhosis, chronic inflammation and injury drive liver cells dysfunction, leading to excessive extracellular matrix deposition, sinusoidal pseudocapillarization, vascular occlusion and parenchymal extinction. These pathological events result in marked remodelling of the liver microarchitecture, which is cause and result of abnormal environmental mechanical forces, triggering and sustaining the long-standing and progressive process of liver fibrosis. Multiple mechanical forces such as strain, shear stress, and hydrostatic pressure can converge at different stages of the disease until reaching a point of no return where the fibrosis is considered non-reversible. Thereafter, reciprocal communication between cells and their niches becomes the driving force for disease progression. Accumulating evidence supports the idea that, rather than being a passive consequence of fibrosis and portal hypertension (PH), mechanical force-mediated pathways could themselves represent strategic targets for novel therapeutic approaches. In this manuscript, we aim to provide a comprehensive review of the mechanobiology of PH, by furnishing an introduction on the most important mechanisms, integrating these concepts into a discussion on the pathogenesis of PH, and exploring potential therapeutic strategies.

Scaffold, mechanics and functions of nuclear lamins

Nuclear lamins are type-V intermediate filaments that are involved in many nuclear processes. In mammals, A- and B-type lamins assemble into separate physical meshwork underneath the inner nuclear membrane, the nuclear lamina, with some residual fraction localized within the nucleoplasm. Lamins are the major part of the nucleoskeleton, providing mechanical strength and flexibility to protect the genome and allow nuclear deformability, while also contributing to gene regulation via interactions with chromatin. While lamins are the evolutionary ancestors of all intermediate filament family proteins, their ultimate filamentous assembly is markedly different from their cytoplasmic counterparts. Interestingly, hundreds of genetic mutations in the lamina proteins have been causally linked with a broad range of human pathologies, termed laminopathies. These include muscular, neurological and metabolic disorders, as well as premature aging diseases. Recent technological advances have contributed to resolving the filamentous structure of lamins and the corresponding lamina organization. In this review, we revisit the multiscale lamin organization and discuss its implications on nuclear mechanics and chromatin organization within lamina-associated domains.

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.

Kids Mod PAH trial: A multicenter trial comparing mono- versus duo-therapy for initial treatment of pediatric pulmonary hypertension

Pulmonary hypertension (PH) is a significant health problem that contributes to high morbidity and mortality in diverse cardiac, pulmonary, and systemic diseases in children. Evidence-based advances in PH care have been challenged by a paucity of quality endpoints for assessing clinical course and the lack of robust clinical trial data to guide pharmacologic therapies in children. While the landmark adult AMBITION trial demonstrated the benefit of up-front combination PH therapy with ambrisentan and tadalafil, it remains unknown whether upfront combination therapy leads to more rapid and sustained clinical benefits in children with various categories of PH. In this article, we describe the inception of the Kids Mod PAH Trial, a multicenter Phase III trial, to address whether upfront combination therapy (sildenafil and bosentan vs. sildenafil alone) improves PH outcomes in children, recognizing that marked differences between the etiology and therapeutic response between adults and children exist. The primary endpoint of this study is WHO functional class (FC) 12 months after initiation of study drug therapy. In addition to the primary outcome, secondary endpoints are being assessed, including a composite measure of time to clinical worsening, WHO FC at 24 months, echocardiographic assessment of PH and quantitative assessment of right ventricular function, 6-min walk distance, and NT-proBNP levels. Exploratory endpoints include selected biomarkers, actigraphy, and assessments of quality of life. This study is designed to pave the way for additional clinical trials by establishing a robust infrastructure through the development of a PPHNet Clinical Trials Network.

The reversibility of cellular mechano-activation

The cellular microenvironment is highly heterogeneous and dynamic. Therefore, cells must be equipped with molecular tools to adapt and respond to constantly fluctuating inputs. One such input is mechanical force, which activates signalling and regulates cell behaviour in the process of mechanotransduction. Whereas the mechanisms activating mechanotransduction are well studied, the reversibility of this process, whereby cells disassemble and reverse force-activated signalling pathways upon cessation of mechanical stimulation is far less understood. In this review we will outline some of the key experimental techniques to investigate the reversibility of mechanical signalling, and key discoveries arising from them.

Magnetic Field Boosts the Transmembrane Transport Efficiency of Magnesium Ions from PLLA Bone Scaffold

In the system of magnesium-loaded scaffolds, the effect of magnesium ions (Mg2+ ) on the osteogenesis induction is restricted due to the low transmembrane transport efficiency of Mg2+ into the cell, which limits the application for bone defect repair. Inspired by the fact that magnetic field can regulate ion channel proteins on the cell membrane, magnetite nanoparticle is introduced into the poly (l-lactic acid) /magnesium oxide composite in this study, and a magnetic magnesium-loaded bone scaffold is prepared via selective laser sintering . Notably, the activities of the Mg2+ channel protein (MAGT1) on the membrane of bone marrow mesenchymal stem cells (rBMSCs) are enhanced via magnetic torque effect (via integrin αV β3/actin), under the action of static magnetic field (SMF), which promoted rBMSCs to capture Mg2+ in the microenvironment and induced osteogenesis. In vitro experiments showed that the magnetic magnesium-loaded scaffold, under the action of SMF, can accelerate the inflow of Mg2+ from surrounding microenvironment, which improved cellular activities, osteogenesis-related gene expression (ALP, Runx2, OCN, and OPN), and mineralization. Besides, in vivo skull defect repair experiments showed that the scaffolds possessed good ability to promote bone differentiation and new bone regeneration.

Acute downregulation of emerin alters actomyosin cytoskeleton connectivity and function

Fetal lung fibroblasts contribute dynamic infrastructure for the developing lung. These cells undergo dynamic mechanical transitions, including cyclic stretch and spreading, which are integral to lung growth in utero. We investigated the role of the nuclear envelope protein emerin in cellular responses to these dynamic mechanical transitions. In contrast to control cells, which briskly realigned their nuclei, actin cytoskeleton, and extracellular matrices in response to cyclic stretch, fibroblasts that were acutely downregulated for emerin showed incomplete reorientation of both nuclei and actin cytoskeleton. Emerin-downregulated fibroblasts were also aberrantly circular in contrast to the spindle-shaped controls and exhibited an altered pattern of filamentous actin organization that was disconnected from the nucleus. Emerin knockdown was also associated with reduced myosin light chain phosphorylation during cell spreading. Interestingly, emerin-downregulated fibroblasts also demonstrated reduced fibronectin fibrillogenesis and production. These findings indicate that nuclear-cytoskeletal coupling serves a role in the dynamic regulation of cytoskeletal structure and function and may also impact the transmission of traction force to the extracellular matrix microenvironment.

The spatiotemporal heterogeneity of the biophysical microenvironment during hematopoietic stem cell development: from embryo to adult

Hematopoietic stem cells (HSCs) with the ability to self-renew and differentiate are responsible for maintaining the supply of all types of blood cells. The complex and delicate microenvironment surrounding HSCs is called the HSC niche and can provide physical, chemical, and biological stimuli to regulate the survival, maintenance, proliferation, and differentiation of HSCs. Currently, the exploration of the biophysical regulation of HSCs remains in its infancy. There is evidence that HSCs are susceptible to biophysical stimuli, suggesting that the construction of engineered niche biophysical microenvironments is a promising way to regulate the fate of HSCs in vitro and ultimately contribute to clinical applications. In this review, we introduced the spatiotemporal heterogeneous biophysical microenvironment during HSC development, homeostasis, and malignancy. Furthermore, we illustrated how these biophysical cues contribute to HSC behaviors, as well as the possible mechanotransduction mechanisms from the extracellular microenvironment into cells. Comprehending the important functions of these biophysical regulatory factors will provide novel approaches to resolve clinical problems.

Fundamental insights into the correlation between chromosome configuration and transcription

Eukaryotic chromosomes exhibit a hierarchical organization that spans a spectrum of length scales, ranging from sub-regions known as loops, which typically comprise hundreds of base pairs, to much larger chromosome territories that can encompass a few mega base pairs. Chromosome conformation capture experiments that involve high-throughput sequencing methods combined with microscopy techniques have enabled a new understanding of inter- and intra-chromosomal interactions with unprecedented details. This information also provides mechanistic insights on the relationship between genome architecture and gene expression. In this article, we review the recent findings on three-dimensional interactions among chromosomes at the compartment, topologically associating domain, and loop levels and the impact of these interactions on the transcription process. We also discuss current understanding of various biophysical processes involved in multi-layer structural organization of chromosomes. Then, we discuss the relationships between gene expression and genome structure from perturbative genome-wide association studies. Furthermore, for a better understanding of how chromosome architecture and function are linked, we emphasize the role of epigenetic modifications in the regulation of gene expression. Such an understanding of the relationship between genome architecture and gene expression can provide a new perspective on the range of potential future discoveries and therapeutic research.

From the membrane to the nucleus: mechanical signals and transcription regulation

Mechanical forces drive and modulate a wide variety of processes in eukaryotic cells including those occurring in the nucleus. Relevantly, forces are fundamental during development since they guide lineage specifications of embryonic stem cells. A sophisticated macromolecular machinery transduces mechanical stimuli received at the cell surface into a biochemical output; a key component in this mechanical communication is the cytoskeleton, a complex network of biofilaments in constant remodeling that links the cell membrane to the nuclear envelope. Recent evidence highlights that forces transmitted through the cytoskeleton directly affect the organization of chromatin and the accessibility of transcription-related molecules to their targets in the DNA. Consequently, mechanical forces can directly modulate transcription and change gene expression programs. Here, we will revise the biophysical toolbox involved in the mechanical communication with the cell nucleus and discuss how mechanical forces impact on the organization of this organelle and more specifically, on transcription. We will also discuss how live-cell fluorescence imaging is producing exquisite information to understand the mechanical response of cells and to quantify the landscape of interactions of transcription factors with chromatin in embryonic stem cells. These studies are building new biophysical insights that could be fundamental to achieve the goal of manipulating forces to guide cell differentiation in culture systems.

Renin Cells, From Vascular Development to Blood Pressure Sensing

During embryonic and neonatal life, renin cells contribute to the assembly and branching of the intrarenal arterial tree. During kidney arteriolar development renin cells are widely distributed throughout the renal vasculature. As the arterioles mature, renin cells differentiate into smooth muscle cells, pericytes, and mesangial cells. In adult life, renin cells are confined to the tips of the renal arterioles, thus their name juxtaglomerular cells. Juxtaglomerular cells are sensors that release renin to control blood pressure and fluid-electrolyte homeostasis. Three major mechanisms control renin release: (1) β-adrenergic stimulation, (2) macula densa signaling, and (3) the renin baroreceptor, whereby a decrease in arterial pressure leads to increased renin release whereas an increase in pressure results in decrease renin release. Cells from the renin lineage exhibit plasticity in response to hypotension or hypovolemia, whereas relentless, chronic stimulation induces concentric arterial and arteriolar hypertrophy, leading to focal renal ischemia. The renin cell baroreceptor is a nuclear mechanotransducer within the renin cell that transmits external forces to the chromatin to regulate Ren1 gene expression. In addition to mechanotransduction, the pressure sensor of the renin cell may enlist additional molecules and structures including soluble signals and membrane proteins such as gap junctions and ion channels. How these various components integrate their actions to deliver the exact amounts of renin to meet the organism needs is unknown. This review describes the nature and origins of renin cells, their role in kidney vascular development and arteriolar diseases, and the current understanding of the blood pressure sensing mechanism.