Nuclear Deformation Causes DNA Damage by Increasing Replication Stress

Effects of cell shape and nucleus shape on epithelial-mesenchymal transition revealed using chimeric micropatterns

Epithelial-mesenchymal transition (EMT) is a key phenotypic switch in cancer metastasis, leading to fatal consequences for patients. Under geometric constraints, the morphology of cancer cells changes in both cellular and subcellular levels, whose effects on EMT are, however, not fully understood. Herein, we designed and fabricated chimeric micropatterns of polystyrene (PS) with adhesion contrast to reveal the impacts of cell shapes and nuclear shapes on EMT in a decoupled way. Cell elongation was modulated via microwell aspect ratios (ARs), and nuclear deformation was generated through a micropillar array in the microwell. Human non-small cell lung cancer cells (A549) were cultured on the quasi-three dimensional micropatterned surfaces, and transforming growth factor-β1 (TGF-β1) was added to induce EMT. We found that chimeric micropatterns upregulated EMT with an increase of cellular AR and nuclear indentation under given TGF-β1. The subsequent assessment of the contractility and oriented assembly of microfilaments elucidated the key role of mechanotransduction in cell elongation and EMT, as proved by myosin inhibition, while it was obstructed by micropillars in the chimeric micropattern. Hence, the micropillar array possessed a nonmonotonic influence, enhancing the EMT of cells with AR of 1, but hindering the EMT with an impact more significant on microwells with large ARs due to the impeded cytoskeleton assembly. This fundamental research has illustrated the complex of cellular and subcellular geometries on cell behaviors including phenotype transition in cancer metastasis.

Nuclear envelope proteins, mechanotransduction, and their contribution to breast cancer progression

Breast cancer cells frequently exhibit changes in the expression of nuclear envelope (NE) proteins such as lamins and emerin that determine the physical properties of the nucleus and contribute to cellular mechanotransduction. This review explores the emerging interplay between NE proteins, the physical challenges incurred during metastatic progression, and mechanotransduction. Improved insights into the underlying mechanisms may ultimately lead to better prognostic tools and treatment strategies for metastatic breast cancer.

Tissue mechanics in tumor heterogeneity and aggression

Tumorigenesis ensues within a heterogeneous tissue microenvironment that promotes malignant transformation, metastasis and treatment resistance. A major feature of the tumor microenvironment is the heterogeneous population of cancer-associated fibroblasts and myeloid cells that stiffen the extracellular matrix. The heterogeneously stiffened extracellular matrix in turn activates cellular mechanotransduction and creates a hypoxic and metabolically hostile microenvironment. The stiffened extracellular matrix and elevated mechanosignaling also drive tumor aggression by fostering tumor cell growth, survival, and invasion, compromising antitumor immunity, expanding cancer stem cell frequency, and increasing mutational burden, which promote intratumor heterogeneity. Delineating the molecular mechanisms whereby tissue mechanics regulate these phenotypes should help to clarify the basis for tumor heterogeneity and cancer aggression and identify novel therapeutic targets that could improve patient outcome. Here, we discuss the role of the extracellular matrix in driving cancer aggression through its impact on tumor heterogeneity.

Learning via mechanosensitivity and activity in cytoskeletal networks

In this work we show how a network inspired by a coarse-grained description of actomyosin cytoskeleton can learn - in a contrastive learning framework - from environmental perturbations if it is endowed with mechanosensitive proteins and motors. Our work is a proof of principle for how force-sensitive proteins and molecular motors can form the basis of a general strategy to learn in biological systems. Our work identifies a minimal biologically plausible learning mechanism and also explores its implications for commonly occuring phenomenolgy such as adaptation and homeostatis.

The dilemma of nuclear mechanical forces in DNA damage and repair

Genomic stability, encompassing DNA damage and repair mechanisms, plays a pivotal role in the onset of diseases and the aging process. The stability of DNA is intricately linked to the chemical and mechanical forces exerted on chromatin, particularly within lamina-associated domains (LADs). Mechanical stress can induce DNA damage through the deformation and rupture of the nuclear envelope, leading to DNA bending and cleavage. However, DNA can evade such mechanical stress-induced damage by relocating away from the nuclear membrane, a process facilitated by the depletion of H3K9me3-marked heterochromatin and its cleavage from the lamina. When DNA double-stranded breaks occur, they prompt the rapid recruitment of Lamin B1 and the deposition of H3K9me3. Despite these insights, the precise mechanisms underlying DNA damage and repair under mechanical stress remain unclear. In this review, we explore the interplay between mechanical forces and the nuclear envelope in the context of DNA damage, elucidate the molecular pathways through which DNA escapes force-induced damage, and discuss the corresponding repair strategies involving the nuclear cytoskeleton. By summarizing the mechanisms of force-induced DNA damage and repair, we aim to underscore the potential for developing targeted therapeutic strategies to bolster genomic stability and alleviate the impacts of aging and disease.

Dynamic substrate topographies drive actin- and vimentin-mediated nuclear mechanoprotection events in human fibroblasts

BACKGROUND

Dynamic physical changes in the extracellular environment of living tissues present a mechanical challenge for resident cells that can lead to damage to the nucleus, genome, and DNA. Recent studies have started to uncover nuclear mechanoprotection mechanisms that prevent excessive mechanical deformations of the nucleus. Here, we hypothesized that dynamic topographical changes in the cellular environment can be mechanically transmitted to the nucleus and trigger nuclear mechanoprotection events. We tested this using a photoresponsive hydrogel whose surface topography can be reversibly changed on demand upon light illumination, allowing us to subject cells to recurring microscale topographical changes.

RESULTS

With each recurring topographical change, fibroblasts were found to increasingly compact and relocate their nuclei away from the dynamic regions of the hydrogel. These cell-scale reorganization events were accompanied by an increase of global histone acetylation and decreased methylation in cells on the dynamic topographies, resulting in a minimization of DNA strand breakage. We further found that these nuclear mechanoprotection events were mediated by both vimentin intermediate filaments and the actin cytoskeleton.

CONCLUSIONS

Together, these data reveal that fibroblasts actively protect their nuclei in the presence of dynamic topographical changes through cytoskeleton-mediated mechanisms. Broadly, these results stress the importance of gaining a deeper fundamental understanding of the cellular mechanoresponse under dynamically changing conditions.

Resilience in adversity: Exploring adaptive changes in cancer cells under stress

OBJECTIVE

Cancer cells undergo adaptive processes that favor their survival and proliferation when subjected to different types of cellular stress. These changes are linked to oncogenic processes such as genetic instability, tumor proliferation, therapy resistance, and invasion. Therefore, this study aimed to review studies that discuss possible morphological and genetic changes acquired by neoplastic cells under stressful conditions.

METHODS

The articles used in this integrative review were searched on PubMed, Web of Science, CAPES, BVS and Scopus. Studies that discussed how cells undergo morphogenetic changes as an adaptive response to stress in cancer were included.

RESULTS

This article reviewed 82 studies that highlighted multiple types of stress to which cancer can be subjected, such as oxidative, thermal and mechanical stress; glucose and other nutrients deficiency; hypoxia and chemotherapy. Neoplastic cells under stress can undergo adaptive changes that make it possible to overcome this obstacle. In this adaptive process, the acquisition of certain mutations implies cellular morphological changes such as Epithelial-Mesenchymal Transition, polyploidy, mitochondrial and cytoskeletal changes. These adaptive changes occur concomitantly with processes related to oncogenesis such as gene instability, tumor proliferation, resistance to therapy and invasion.

CONCLUSIONS

This study reveals that adaptations to cellular stress promote morphological and functional changes that accompany or accelerate oncogenesis. It has been revised how epithelial-mesenchymal transition, polyploidy and mitochondrial dysfunctions not only reinforce the survival of tumor cells in adverse environments, but also increase therapeutic resistance and invasive capacity. Also noteworthy are the contributions on genomic instability associated with stress and the potential of senescent cells in tumor heterogeneity, both as factors of tumor resistance and progression. These insights suggest new therapeutic targets and prognostic biomarkers, expanding the possibilities for more effective strategies to combat cancer.

Regulation of cell migration by extracellular matrix mechanics at a glance

Cell migration occurs throughout development, tissue homeostasis and regeneration, as well as in diseases such as cancer. Cells migrate along two-dimensional (2D) surfaces or interfaces, within microtracks, or in confining three-dimensional (3D) extracellular matrices. Although the basic mechanisms of 2D migration are known, recent studies have elucidated unexpected migration behaviors associated with more complex substrates and have provided insights into their underlying molecular mechanisms. Studies using engineered biomaterials for 3D culture and microfabricated channels to replicate cell confinement observed in vivo have revealed distinct modes of migration. Across these contexts, the mechanical features of the surrounding microenvironment have emerged as major regulators of migration. In this Cell Science at a Glance article and the accompanying poster, we describe physiological contexts wherein 2D and 3D cell migration are essential, report how mechanical properties of the microenvironment regulate individual and collective cell migration, and review the mechanisms mediating these diverse modes of cell migration.

Arginase-II promotes melanoma and lung cancer cell growth by regulating Sirt3-mtROS axis

Background

Aberrant mitochondrial metabolism is a key source of massive mitochondrial reactive oxygen species (mtROS) in tumour cells. Arginase-II (Arg-II), a widely expressed mitochondrial metabolic enzyme, has recently been shown to enhance mtROS production and melanoma progression. However, how Arg-II enhances mtROS and whether mtROS is involved in stimulation of cancer cell proliferation and migration remain unclear.

Methods and results

Here, we show that ablation of arg-ii suppresses cell growth, migration, nuclear deformation, and DNA damage in melanoma cells. Vice versa, overexpression of arg-ii in melanoma cells promotes melanoma cell growth and migration accompanied by enhanced nuclear deformation and DNA damage. Ablation or overexpression of arg-ii reduces or enhances mtROS, respectively, accounting for the effects of Arg-II on melanoma growth, migration, and DNA damage. Further data demonstrate that Arg-II enhances mtROS through decreasing Sirtuin 3 (Sirt3) levels. Silencing sirt3 promotes melanoma growth, migration, nuclear deformation, and DNA damage through enhancing mtROS. In supporting of these findings, overexpression of sirt3 prevented Arg-II-induced mtROS production with concomitant prevention of Arg-II-induced cell growth, migration, nuclear deformation and DNA damage. Furthermore, we show that upregulation of Arg-II under hypoxia induces nuclear deformation and DNA damage through suppressing Sirt3. Similar results are obtained in A549 human lung carcinoma cells. In addition, analysis of publicly accessible datasets reveals that elevated arg-ii mRNA levels in human tumor samples including skin cutaneous melanoma and lung cancers associate with poorer prognosis.

Conclusion

Altogether, our findings demonstrate a critical role of Arg-II-Sirt3-mtROS cascade in promoting melanoma growth, migration, nuclear deformation, and DNA damage linking to melanoma progression and malignancy, which could be therapeutic targets for cancers such as melanoma and lung carcinoma.

SDC4 drives fibrotic remodeling of the intervertebral disc under altered spinal loading

Alterations in physiological loading of the spine are deleterious to intervertebral disc health. The caudal spine region Ca3-6 that experiences increased flexion, showed disc degeneration in young adult mice. Given the role of Syndecan 4 (SDC4), a cell surface heparan sulfate proteoglycan in disc matrix catabolism and mechanosensing, we investigated if deletion could mitigate this loading-dependent phenotype. Notably, at spinal levels Ca3-6, Sdc4- KO mice did not exhibit increased collagen fibril and fibronectin deposition in the NP compartment or showed the alterations in collagen crosslinks observed in wild-type mice. Similarly, unlike wild-type mice, NP cells in Sdc4 -KO mice retained transgelin (TGLN) expression and showed absence of COL X deposition, pointing to the preservation of their notochordal characteristics. Proteomic analysis revealed that NP tissues responded to the abnormal loading by increasing the abundance of proteins associated with extracellular matrix remodeling, chondrocyte development, and contractility. Similarly, downregulated proteins suggested decreased vesicle transport, autophagy-related pathway, and RNA quality control regulation. Notably, NP proteome from Sdc4 KO suggested that increased dynamin-mediated endocytosis, autophagy-related pathway, and RNA and DNA quality control may underscore the protection from increased flexion-induced degeneration. Our study highlights the important role of SDC4 in fine-tuning cellular homeostasis and extracellular matrix production in disc environment subjected to altered loading.

Actin-based deformations of the nucleus control mouse multiciliated ependymal cell differentiation

Ependymal cells (ECs) are multiciliated cells in the brain that contribute to cerebrospinal fluid flow. ECs are specified during embryonic stages but differentiate later in development. Their differentiation depends on genes such as GEMC1 and MCIDAS in conjunction with E2F4/5 as well as on cell-cycle-related factors. In the mouse brain, we observe that nuclear deformation accompanies EC differentiation. Tampering with these deformations either by decreasing F-actin levels or by severing the link between the nucleus and the actin cytoskeleton blocks differentiation. Conversely, increasing F-actin by knocking out the Arp2/3 complex inhibitor Arpin or artificially deforming the nucleus activates differentiation. These data are consistent with actin polymerization triggering nuclear deformation and jump starting the signaling that produces ECs. A player in this process is the retinoblastoma 1 (RB1) protein, whose phosphorylation prompts MCIDAS activation. Overall, this study identifies a role for actin-based mechanical inputs to the nucleus as controlling factors in cell differentiation.

Doxorubicin-induced phosphorylation of lamin A/C enhances DNMT1 and activates cardiomyocyte death via suppressing GATA-4 and Bcl-xL in rat heart

Cardiotoxic effect of Doxorubicin (Dox) limits its clinical application. Previously, we reported that Dox induces phosphorylation of lamin A/C (pS22 lamin A/C), increased nuclear size, damage to the nuclear membrane, and cell death. However, the activation of signalling pathway during this event remains elusive, and it is unclear whether increased phospho-lamin A/C activates the cell death pathway in heart. Here, we demonstrated that Dox-induced lamin A/C phosphorylation causes apoptotic cell death. Increased levels of reactive oxygen species (ROS), DNA methylation and apoptosis markers (Bax, Bid, caspase 3 and caspase 9) were observed in Dox-exposed H9c2 cells. Nuclear membrane damage due to increased pS22 lamin A/C causes increased DNMT1 and DNA methylation followed by reduced expression of GATA-4 and Bcl-xL in Dox-treated H9c2 cells and rat hearts. Further, increased mRNA expression of DNMT1 and reduced expression of GATA-4 and Bcl-xL was observed in H9c2 cells after knocking down of lamin A/C expression. Previously, we reported that N-acetylcysteine improves lamin A/C levels and maintain nuclear membrane integrity. Similarly, in this study Astaxanthin (Ast), a membrane-specific antioxidant, reduces the expression of DNMT1 and phospho-lamin A/C levels; increases mRNA expression of GATA-4 and Bcl-xL; reduces ROS levels and DNA leakage in Dox-treated H9c2 cells and rat hearts. Ast also improves the cardiac structure and function in Dox-treated rats. In conclusion, Dox exposure in cardiomyoblasts and hearts causes cell death by increasing the pS22 lamin A/C, DNA methylation and reducing the expression GATA-4 and Bcl-xL. This study provides a novel pathway for Dox-induced cardiotoxicity and a possible therapeutic approach to reduce it.

DNA damage causes ATM-dependent heterochromatin loss leading to nuclear softening, blebbing, and rupture

The nucleus must maintain stiffness to preserve its shape and integrity to ensure proper function. Defects in nuclear stiffness caused from chromatin and lamin perturbations produce abnormal nuclear shapes common in aging, heart disease, and cancer. Loss of nuclear shape via protrusions called blebs lead to nuclear rupture that is well established to cause nuclear dysfunction, including DNA damage. However, it remains unknown how increased DNA damage affects nuclear stiffness, shape, and ruptures, which could create a feedback loop. To determine whether increased DNA damage alters nuclear physical properties, we treated mouse embryonic fibroblast cells with DNA damage drugs cisplatin and bleomycin. DNA damage drugs caused increased nuclear blebbing and rupture in interphase nuclei within a few hours and independent of mitosis. Micromanipulation force measurements reveal that DNA damage decreased chromatin-based nuclear mechanics but did not change lamin-based strain stiffening at long extensions relative to wild type. Immunofluorescence measurements of DNA damage treatments reveal the mechanism is an ATM-dependent decrease in heterochromatin leading to nuclear weaken, blebbing, and rupture which can be rescued upon ATM inhibition treatment. Thus, DNA damage drugs cause ATM-dependent heterochromatin loss resulting in nuclear softening, blebbing, and rupture.

Mechanical Forces, Nucleus, Chromosomes, and Chromatin

Individual cells and cells within the tissues and organs constantly face mechanical challenges, such as tension, compression, strain, shear stress, and the rigidity of cellular and extracellular surroundings. Besides the external mechanical forces, cells and their components are also subjected to intracellular mechanical forces, such as pulling, pushing, and stretching, created by the sophisticated force-generation machinery of the cytoskeleton and molecular motors. All these mechanical stressors switch on the mechanotransduction pathways, allowing cells and their components to respond and adapt. Mechanical force-induced changes at the cell membrane and cytoskeleton are also transmitted to the nucleus and its nucleoskeleton, affecting nucleocytoplasmic transport, chromatin conformation, transcriptional activity, replication, and genome, which, in turn, orchestrate cellular mechanical behavior. The memory of mechanoresponses is stored as epigenetic and chromatin structure modifications. The mechanical state of the cell in response to the acellular and cellular environment also determines cell identity, fate, and immune response to invading pathogens. Here, we give a short overview of the latest developments in understanding these processes, emphasizing their effects on cell nuclei, chromosomes, and chromatin.

Immune cells adapt to confined environments in vivo to optimise nuclear plasticity for migration

Cells navigating in complex 3D microenvironments frequently encounter narrow spaces that physically challenge migration. While in vitro studies identified nuclear stiffness as a key rate-limiting factor governing the movement of many cell types through artificial constraints, how cells migrating in vivo respond dynamically to confinement imposed by local tissue architecture, and whether these encounters trigger molecular adaptations, is unclear. Here, we establish an innovative in vivo model for mechanistic analysis of nuclear plasticity as Drosophila immune cells transition into increasingly confined microenvironments. Integrating live in vivo imaging with molecular genetic analyses, we demonstrate how rapid molecular adaptation upon environmental confinement (including fine-tuning of the nuclear lamina) primes leukocytes for enhanced nuclear deformation while curbing damage (including rupture and micronucleation), ultimately accelerating movement through complex tissues. We find nuclear dynamics in vivo are further impacted by large organelles (phagosomes) and the plasticity of neighbouring cells, which themselves deform during leukocyte passage. The biomechanics of cell migration in vivo are thus shaped both by factors intrinsic to individual immune cells and the malleability of the surrounding microenvironment.

Linking Metastatic Potential and Viscoelastic Properties of Breast Cancer Spheroids via Dynamic Compression and Relaxation in Microfluidics

The growth and invasion of solid tumors are associated with changes in their viscoelastic properties, influenced by both internal cellular factors and physical forces in the tumor microenvironment. Due to the lack of a comprehensive investigation of tumor tissue viscoelasticity, the relationship between such physical properties and cancer malignancy remains poorly understood. Here, the viscoelastic properties of breast cancer spheroids, 3D (in vitro) tumor models, are studied in relation to their metastatic potentials by imposing controlled, dynamic compression within a microfluidic constriction, and subsequently monitoring the relaxation of the imposed deformation. By adopting a modified Maxwell model to extract viscoelastic properties from the compression data, the benign (MCF-10A) spheroids are found to have higher bulk elastic modulus and viscosity compared to malignant spheroids (MCF-7 and MDA-MB-231). The relaxation is characterized by two timescales, captured by a double exponential fitting function, which reveals a similar fast rebound for MCF-7 and MCF-10A. Both the malignant spheroids exhibit similar long-term relaxation and display residual deformation. However, they differ significantly in morphology, particularly in intercellular movements. These differences between malignant spheroids are demonstrated to be linked to their cytoskeletal organization, by microscopic imaging of F-actin within the spheroids, together with cell-cell adhesion strength.

Feeling the force from within - new tools and insights into nuclear mechanotransduction

The ability of cells to sense and respond to mechanical signals is essential for many biological processes that form the basis of cell identity, tissue development and maintenance. This process, known as mechanotransduction, involves crucial feedback between mechanical force and biochemical signals, including epigenomic modifications that establish transcriptional programs. These programs, in turn, reinforce the mechanical properties of the cell and its ability to withstand mechanical perturbation. The nucleus has long been hypothesized to play a key role in mechanotransduction due to its direct exposure to forces transmitted through the cytoskeleton, its role in receiving cytoplasmic signals and its central function in gene regulation. However, parsing out the specific contributions of the nucleus from those of the cell surface and cytoplasm in mechanotransduction remains a substantial challenge. In this Review, we examine the latest evidence on how the nucleus regulates mechanotransduction, both via the nuclear envelope (NE) and through epigenetic and transcriptional machinery elements within the nuclear interior. We also explore the role of nuclear mechanotransduction in establishing a mechanical memory, characterized by a mechanical, epigenetic and transcriptomic cell state that persists after mechanical stimuli cease. Finally, we discuss current challenges in the field of nuclear mechanotransduction and present technological advances that are poised to overcome them.

Lamin B loss in nuclear blebs is rupture dependent while increased DNA damage is rupture independent

The nucleus houses genetic information and functions separate from the rest of the cell. Loss of nuclear shape results in nuclear ruptures. Nuclear blebs are deformations identified by decreased DNA density, while lamin B levels vary drastically. To determine if decreased lamin B levels are due to nuclear rupture, we used immunofluorescence to measure levels of lamin B and emerin, a nuclear envelope protein that enriches to sites of nuclear rupture. We observed that cell types that exhibit decreased levels of lamin B also show an enrichment of emerin in nuclear blebs. Oppositely, in other cell types, nuclear blebs display maintained levels of lamin B1 and showed no emerin enrichment. To determine how nuclear rupture affects DNA damage, we time lapse imaged nuclear rupture dynamics then fixed the same cells to conduct immunofluorescence of γH2AX and emerin. We find that DNA damage levels are higher in blebbed nuclei independent of nuclear rupture. Thus, we confirm that lamin B1 loss in nuclear blebs is due to nuclear rupture and blebbed nuclei have increased DNA damage that is independent of rupture.

Peripheral heterochromatin tethering is required for chromatin-based nuclear mechanical response

The cell nucleus is a mechanically responsive structure that governs how external forces affect chromosomes. Chromatin, particularly transcriptionally inactive heterochromatin, resists nuclear deformations through its mechanical response. However, chromatin also exhibits liquid-like properties, casting ambiguity on the physical mechanisms of chromatin-based nuclear elasticity. To determine how heterochromatin strengthens nuclear mechanical response, we performed polymer physics simulations of a nucleus model validated by micromechanical measurements and chromosome conformation capture data. The attachment of peripheral heterochromatin to the lamina is required to transmit forces directly to the chromatin and elicit its elastic response. Thus, increases in heterochromatin levels increase nuclear rigidity by increasing the linkages between chromatin and the lamina. Crosslinks within heterochromatin, such as HP1 α proteins, can also stiffen nuclei, but only if chromatin is peripherally tethered. In contrast, heterochromatin affinity interactions that may drive liquid-liquid phase separation do not contribute to nuclear rigidity. When the nucleus is stretched, gel-like peripheral heterochromatin can bear stresses and deform, while the more fluid-like interior euchromatin is less perturbed. Thus, heterochromatin's internal structure and stiffness may regulate nuclear mechanics via peripheral attachment to the lamina, while also enabling nuclear mechanosensing of external forces and external measurement of the nucleus' internal architecture.

At the nucleus of cancer: how the nuclear envelope controls tumor progression

Historically considered downstream effects of tumorigenesis-arising from changes in DNA content or chromatin organization-nuclear alterations have long been seen as mere prognostic markers within a genome-centric model of cancer. However, recent findings have placed the nuclear envelope (NE) at the forefront of tumor progression, highlighting its active role in mediating cellular responses to mechanical forces. Despite significant progress, the precise interplay between NE components and cancer progression remains under debate. In this review, we provide a comprehensive and up-to-date overview of how changes in NE composition affect nuclear mechanics and facilitate malignant transformation, grounded in the latest molecular and functional studies. We also review recent research that uses advanced technologies, including artificial intelligence, to predict malignancy risk and treatment outcomes by analyzing nuclear morphology. Finally, we discuss how progress in understanding nuclear mechanics has paved the way for mechanotherapy-a promising cancer treatment approach that exploits the mechanical differences between cancerous and healthy cells. Shifting the perspective on NE alterations from mere diagnostic markers to potential therapeutic targets, this review calls for further investigation into the evolving role of the NE in cancer, highlighting the potential for innovative strategies to transform conventional cancer therapies.

Mechanical Force-Induced cGAS Activation in Carcinoma Cells Facilitates Splenocytes into Liver to Drive Metastasis

Liver metastasis is the main cause of cancer-related mortality. During the metastasis process, circulating carcinoma cells hardly pass through narrow capillaries, leading to nuclear deformation. However, the effects of nuclear deformation and its underlying mechanisms on metastasis need further study. Here, it is shown that mechanical force-induced nuclear deformation exacerbates liver metastasis by activating the cGAS-STING pathway, which promotes splenocyte infiltration in the liver. Mechanical force results in nuclear deformation and rupture of the nuclear envelope with inevitable DNA leakage. Cytoplasmic DNA triggers the activation of cGAS-STING pathway, enhancing the production of IL6, TNFα, and CCL2. Additionally, splenocyte recruitment by the proinflammatory cytokines support carcinoma cell survival and colonization in the liver. Importantly, both intervening activity of cGAS and blocking of splenocyte migration to the liver efficiently ameliorate liver metastasis. Overall, these findings reveal a mechanism by which mechanical force-induced nuclear deformation exacerbates liver metastasis by regulating splenocyte infiltration into the liver and support targeting cGAS and blocking splenocyte recruitment as candidate therapeutic approaches for liver metastasis.

Micropillar-induced changes in cell nucleus morphology enhance bone regeneration by modulating the secretome

Nuclear morphology, which modulates chromatin architecture, plays a critical role in regulating gene expression and cell functions. While most research has focused on the direct effects of nuclear morphology on cell fate, its impact on the cell secretome and surrounding cells remains largely unexplored, yet is especially crucial for cell-based therapies. In this study, we fabricated implants with a micropillar topography using methacrylated poly(octamethylene citrate)/hydroxyapatite (mPOC/HA) composites to investigate how micropillar-induced nuclear deformation influences cell paracrine signaling for osteogenesis and cranial bone regeneration. In vitro, cells with deformed nuclei showed enhanced secretion of proteins that support extracellular matrix (ECM) organization, which promoted osteogenic differentiation in neighboring human mesenchymal stromal cells (hMSCs). In a mouse model with critical-size cranial defects, nuclear-deformed hMSCs on micropillar mPOC/HA implants elevated Col1a2 expression, contributing to bone matrix formation, and drove cell differentiation toward osteogenic progenitor cells. These findings indicate that micropillars not only enhance the osteogenic differentiation of human mesenchymal stromal cells (hMSCs) but also modulate the secretome, thereby influencing the fate of surrounding cells through paracrine effects.

Confinement-sensitive volume regulation dynamics via high-speed nuclear morphological measurements

Diverse tissues in vivo present varying degrees of confinement, constriction, and compression to migrating cells in both homeostasis and disease. The nucleus in particular is subjected to external forces by the physical environment during confined migration. While many systems have been developed to induce nuclear deformation and analyze resultant functional changes, much remains unclear about dynamic volume regulation in confinement due to limitations in time resolution and difficulty imaging in PDMS-based microfluidic chips. Standard volumetric measurement relies on confocal microscopy, which suffers from high phototoxicity, slow speed, limited throughput, and artifacts in fast-moving cells. To address this, we developed a form of double fluorescence exclusion microscopy, designed to function at the interface of microchannel-based PDMS sidewalls, that can track cellular and nuclear volume dynamics during confined migration. By verifying the vertical symmetry of nuclei in confinement, we obtained computational estimates of nuclear surface area. We then tracked nuclear volume and surface area under physiological confinement at a time resolution exceeding 30 frames per minute. We find that during self-induced entrance into confinement, the cell rapidly expands its surface area until a threshold is reached, followed by a rapid decrease in nuclear volume. We next used osmotic shock as a tool to alter nuclear volume in confinement, and found that the nuclear response to hypo-osmotic shock in confinement does not follow classical scaling laws, suggesting that the limited expansion potential of the nuclear envelope might be a constraining factor in nuclear volume regulation in confining environments in vivo.

Nuclei as mechanical bumpers during epithelial remodeling

The morphogenesis of developing tissues relies on extensive cellular rearrangements in shape, position, and identity. A key process in reshaping tissues is cell intercalation-driven elongation, where epithelial cells align and intercalate along a common axis. Typically, analyses focus on how peripheral cortical forces influence cell shape changes. Less attention is given to how inhomogeneities in internal structures, particularly the nucleus, impact cell shaping. Here, we examine how pulsed contractile and extension dynamics interact with the nucleus in elongating Drosophila embryos. Our data show that tightly packed nuclei in apical layers hinder tissue remodeling/oscillatory behaviors. We identify two mechanisms for resolving internuclear tensions: nuclear deformation and dispersion. Embryos with non-deformable nuclei use nuclear dispersion to maintain near-normal extensile rates, while those with non-dispersible nuclei due to microtubule inhibition exhibit disruptions in contractile behaviors. Disrupting both mechanisms leads to severe tissue extension defects and cell extrusion. These findings highlight the critical role of nuclear shape and positioning in topological remodeling of epithelia.

Behind the stoNE wall: A fervent activity for nuclear lipids

The four main types of biomolecules are nucleic acids, proteins, carbohydrates and lipids. The knowledge about their respective interactions is as important as the individual understanding of each of them. However, while, for example, the interaction of proteins with the other three groups is extensively studied, that of nucleic acids and lipids is, in comparison, very poorly explored. An iconic paradigm of physical (and likely functional) proximity between DNA and lipids is the case of the genomic DNA in eukaryotes: enclosed within the nucleus by two concentric lipid bilayers, the wealth of implications of this interaction, for example in genome stability, remains underassessed. Nuclear lipid-related phenotypes have been observed for 50 years, yet in most cases kept as mere anecdotical descriptions. In this review, we will bring together the evidence connecting lipids with both the nuclear envelope and the nucleoplasm, and will make critical analyses of these descriptions. Our exploration establishes a scenario in which lipids irrefutably play a role in nuclear homeostasis.

Advances in mechanotransduction and sonobiology: effects of audible acoustic waves and low-vibration stimulations on mammalian cells

In recent decades, research on mechanotransduction has advanced considerably, focusing on the effects of audible acoustic waves (AAWs) and low-vibration stimulation (LVS), which has propelled the field of sonobiology forward. Taken together, the current evidence demonstrates the influence of these biosignals on key cellular processes, such as growth, differentiation and migration in mammalian cells, emphasizing the determining role of specific physical parameters during stimulation, such as frequency, sound pressure level/amplitude and exposure time. These mechanical waves interact with various cellular elements, including ion channels, primary cilia, cell-cell adhesion receptors, cell-matrix and extracellular matrix proteins, and focal adhesion complexes. These components connect with the cytoskeletal fibre network, enabling the transmission of mechanical stimuli towards the nucleus. The nucleus, in turn, linked to the cytoskeleton via the linkers of the nucleoskeleton and cytoskeleton complex, acts as a mechanosensitive centre, not only responding to changes in cytoskeletal stiffness and nuclear tension but also regulating gene expression through the transcriptional co-activator YAP/TAZ and interactions between chromatin and the nuclear envelope. This intricate chain of mechanisms highlights the potential of sonobiology in various fields, including dentistry, regenerative medicine, tissue engineering and cancer research. However, progress in these fields requires the establishment of standardized measurement methodologies and biocompatible experimental setups to ensure the reproducibility of results.

3D confinement alters smooth muscle cell responses to chemical and mechanical cues

Smooth muscle cell (SMC) phenotypic switching is a hallmark of many vascular diseases. Although prior work has established that chemical and mechanical cues contribute to SMC phenotypic switching, the impact of three-dimensional (3D) confinement on this process remains elusive. Yet, in vivo, arterial SMCs reside within confined environments. In this study, we designed a microfluidic assay to investigate the interplay between 3D confinement and different environmental stimuli in SMC function. Our results show that tightly, but not moderately, confined SMCs acquire a contractile phenotype when exposed to collagen I. Elevated compressive forces induced by hydrostatic pressure abolish this upregulation of the contractile phenotype and compromise SMC survival, particularly in tightly confined spaces. Transforming growth factor beta 1, which promotes the contractile state in moderate confinement, fails to enhance the contractility of tightly confined cells. Fibronectin and engagement of cadherin 2 suppress the contractile phenotype of SMCs regardless of the degree of confinement. In contrast, homophilic engagement of cadherin 11 upregulates SMC-specific genes and enhances contractility in both moderately and tightly confined cells. Overall, our work introduces 3D confinement as a regulator of SMC phenotypic responses to chemical and mechanical signals.

Chromatin compaction during confined cell migration induces and reshapes nuclear condensates

Cell migration through small constrictions during cancer metastasis requires significant deformation of the nucleus, with associated mechanical stress on the nuclear lamina and chromatin. However, how mechanical deformation impacts various subnuclear structures, including protein and nucleic acid-rich biomolecular condensates, is largely unknown. Here, we find that cell migration through confined spaces gives rise to mechanical deformations of the chromatin network, which cause embedded nuclear condensates, including nucleoli and nuclear speckles, to deform and coalesce. Chromatin deformations exhibit differential behavior in the advancing vs. trailing region of the nucleus, with the trailing half being more permissive for de novo condensate formation. We show that this results from increased chromatin heterogeneity, which gives rise to a shift in the binodal phase boundary. Taken together, our findings show how chromatin deformation impacts condensate assembly and properties, which can potentially contribute to cellular mechanosensing.

Microtubule forces drive nuclear damage in LMNA cardiomyopathy

Nuclear homeostasis requires a balance of forces between the cytoskeleton and nucleus. Mutations in the LMNA gene, which encodes the nuclear envelope proteins lamin A/C, disrupt this balance by weakening the nuclear lamina. This results in nuclear damage in contractile tissues and ultimately muscle disease. Intriguingly, disrupting the LINC complex that connects the cytoskeleton to the nucleus has emerged as a promising strategy to ameliorate LMNA-associated cardiomyopathy. Yet how LINC complex disruption protects the cardiomyocyte nucleus remains unclear. To address this, we developed an assay to quantify the coupling of cardiomyocyte contraction to nuclear deformation and interrogated its dependence on the nuclear lamina and LINC complex. We found that, surprisingly, the LINC complex was mostly dispensable for transferring contractile strain to the nucleus, and that increased nuclear strain in lamin A/C-deficient cardiomyocytes was not rescued by LINC complex disruption. Instead, LINC complex disruption eliminated the cage of microtubules encircling the nucleus. Disrupting microtubules was sufficient to prevent nuclear damage and rescue cardiac function induced by lamin A/C deficiency. We computationally simulated the stress fields surrounding cardiomyocyte nuclei and show how microtubule forces generate local vulnerabilities that damage lamin A/C-deficient nuclei. Our work pinpoints localized, microtubule-dependent force transmission through the LINC complex as a pathological driver and therapeutic target for LMNA-cardiomyopathy.

The biophysics of cell motility through mechanochemically challenging environments

Challenging mechanochemical environments (i.e., with varied mechanical and adhesive properties) are now known to induce a wide range of adaptive phenomena in motile cells. For instance, confinement and low adhesion may trigger a phenotypic transition to fast amoeboid (leader bleb-based) migration. The molecular mechanisms that underly these phenomena are beginning to be understood. Due to its size, the mechanical properties of the nucleus have been shown to limit and facilitate cell migration. Additionally, the activity of various transient receptor potential (TRP) channels is now known to be integral to cell migration in response to a multitude of biophysical stimuli. How cells integrate signals from the nucleus and plasma membrane, however, is unclear. The development of therapeutics that suppress cancer or enhance immune cell migration for immuno-oncology applications, etc., will require additional work to completely understand the molecular mechanisms that enable cells to navigate mechanochemically challenging environments.

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.

Ultrack: pushing the limits of cell tracking across biological scales

Tracking live cells across 2D, 3D, and multi-channel time-lapse recordings is crucial for understanding tissue-scale biological processes. Despite advancements in imaging technology, achieving accurate cell tracking remains challenging, particularly in complex and crowded tissues where cell segmentation is often ambiguous. We present Ultrack, a versatile and scalable cell-tracking method that tackles this challenge by considering candidate segmentations derived from multiple algorithms and parameter sets. Ultrack employs temporal consistency to select optimal segments, ensuring robust performance even under segmentation uncertainty. We validate our method on diverse datasets, including terabyte-scale developmental time-lapses of zebrafish, fruit fly, and nematode embryos, as well as multi-color and label-free cellular imaging. We show that Ultrack achieves state-of-the-art performance on the Cell Tracking Challenge and demonstrates superior accuracy in tracking densely packed embryonic cells over extended periods. Moreover, we propose an approach to tracking validation via dual-channel sparse labeling that enables high-fidelity ground truth generation, pushing the boundaries of long-term cell tracking assessment. Our method is freely available as a Python package with Fiji and napari plugins and can be deployed in a high-performance computing environment, facilitating widespread adoption by the research community.

Mechanical stress during confined migration causes aberrant mitoses and c-MYC amplification

Confined cell migration hampers genome integrity and activates the ATR and ATM mechano-transduction pathways. We investigated whether the mechanical stress generated by metastatic interstitial migration contributes to the enhanced chromosomal instability observed in metastatic tumor cells. We employed live cell imaging, micro-fluidic approaches, and scRNA-seq to follow the fate of tumor cells experiencing confined migration. We found that, despite functional ATR, ATM, and spindle assembly checkpoint (SAC) pathways, tumor cells dividing across constriction frequently exhibited altered spindle pole organization, chromosome mis-segregations, micronuclei formation, chromosome fragility, high gene copy number variation, and transcriptional de-regulation and up-regulation of c-MYC oncogenic transcriptional signature via c-MYC locus amplifications. In vivo tumor settings showed that malignant cells populating metastatic foci or infiltrating the interstitial stroma gave rise to cells expressing high levels of c-MYC. Altogether, our data suggest that mechanical stress during metastatic migration contributes to override the checkpoint controls and boosts genotoxic and oncogenic events. Our findings may explain why cancer aneuploidy often does not correlate with mutations in SAC genes and why c-MYC amplification is strongly linked to metastatic tumors.

Multiple aspects of matrix stiffness in cancer progression

The biophysical and biomechanical properties of the extracellular matrix (ECM) are crucial in the processes of cell differentiation and proliferation. However, it is unclear to what extent tumor cells are influenced by biomechanical and biophysical changes of the surrounding microenvironment and how this response varies between different tumor forms, and over the course of tumor progression. The entire ensemble of genes encoding the ECM associated proteins is called matrisome. In cancer, the ECM evolves to become highly dysregulated, rigid, and fibrotic, serving both pro-tumorigenic and anti-tumorigenic roles. Tumor desmoplasia is characterized by a dramatic increase of α-smooth muscle actin expressing fibroblast and the deposition of hard ECM containing collagen, fibronectin, proteoglycans, and hyaluronic acid and is common in many solid tumors. In this review, we described the role of inflammation and inflammatory cytokines, in desmoplastic matrix remodeling, tumor state transition driven by microenvironment forces and the signaling pathways in mechanotransduction as potential targeted therapies, focusing on the impact of qualitative and quantitative variations of the ECM on the regulation of tumor development, hypothesizing the presence of matrisome drivers, acting alongside the cell-intrinsic oncogenic drivers, in some stages of neoplastic progression and in some tumor contexts, such as pancreatic carcinoma, breast cancer, lung cancer and mesothelioma.

Role of Moringa oleifera irrigation solution on the cell metabolism change of Streptococcus mutans

The principal etiological agent responsible for dental caries is Streptococcus mutans (S. mutans). The Moringa oleifera (M. oleifera) possesses antioxidant and antibacterial properties that function through the response to oxidative stress, which affects bacterial cell metabolism. This research examined M. oleifera impact on S. mutans growth, toxicity, glucan-binding protein (GBP) expression, and nucleic acid structure. Methods included spectrophotometry for growth analysis, enzyme-linked immunosorbent assay for GBP quantification, the (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) MTT assay for cytotoxicity, Fourier transform infrared for nucleic acid changes, and docking simulation for ligand-receptor affinity. Results showed that M. oleifera significantly inhibited S. mutans growth at all concentrations over 24 and 48 h (optical density <0.1), comparable to <300 CFU/mL. At 72 h, 6.25% and 3.125% concentrations were most effective, with chlorhexidine also showing stability at these times. A 3.125% concentration of M. oleifera notably reduced GBP production to below 15% and caused cell toxicity. Furthermore, 25% and 3.125% concentrations significantly altered S. mutans nucleic acids, and M. oleifera showed high binding affinity to the GBP gene receptor. Thus, M. oleifera can inhibit S. mutans growth and GBP production, cause nucleic acid deformation, and strongly bind to the GBP receptor, highlighting its potential in dental caries prevention.

Nuclear rupture induced by capillary constriction forces promotes differential effects on metastatic and normal breast cells

During metastatic dissemination, circulating tumour cells (CTCs) enter capillary beds, where they experience mechanical constriction forces. The transient and persistent effects of these forces on CTCs behaviour remain poorly understood. Here, we developed a high-throughput microfluidic platform mimicking human capillaries to investigate the impact of mechanical constriction forces on malignant and normal breast cell lines. We observed that capillary constrictions induced nuclear envelope rupture in both cancer and normal cells, leading to transient changes in nuclear and cytoplasmic area. Constriction forces transiently activated cGAS/STING and pathways involved in inflammation (NF-κB, STAT and IRF3), especially in the non-malignant cell line. Furthermore, the non-malignant cell line experienced transcriptional changes, particularly downregulation of epithelial markers, while the metastatic cell lines showed minimal alterations. These findings suggest that mechanical constriction forces within capillaries may promote differential effects in malignant and normal cell lines.

The impact of tumor microenvironment: unraveling the role of physical cues in breast cancer progression

Metastasis accounts for the vast majority of breast cancer-related fatalities. Although the contribution of genetic and epigenetic modifications to breast cancer progression has been widely acknowledged, emerging evidence underscores the pivotal role of physical stimuli in driving breast cancer metastasis. In this review, we summarize the changes in the mechanics of the breast cancer microenvironment and describe the various forces that impact migrating and circulating tumor cells throughout the metastatic process. We also discuss the mechanosensing and mechanotransducing molecules responsible for promoting the malignant phenotype in breast cancer cells. Gaining a comprehensive understanding of the mechanobiology of breast cancer carries substantial potential to propel progress in prognosis, diagnosis, and patient treatment.

The nexus of nuclear envelope dynamics, circular economy and cancer cell pathophysiology

The nuclear envelope (NE) is a critical component in maintaining the function and structure of the eukaryotic nucleus. The NE and lamina are disassembled during each cell cycle to enable an open mitosis. Nuclear architecture construction and deconstruction is a prime example of a circular economy, as it fulfills a highly efficient recycling program bound to continuous assessment of the quality and functionality of the building blocks. Alterations in the nuclear dynamics and lamina structure have emerged as important contributors to both oncogenic transformation and cancer progression. However, the knowledge of the NE breakdown and reassembly is still limited to a fraction of participating proteins and complexes. As cancer cells contain highly diverse nuclei in terms of DNA content, but also in terms of nuclear number, size, and shape, it is of great interest to understand the intricate relationship between these nuclear features in cancer cell pathophysiology. In this review, we provide insights into how those NE dynamics are regulated, and how lamina destabilization processes may alter the NE circular economy. Moreover, we expand the knowledge of the lamina-associated domain region by using strategic algorithms, including Artificial Intelligence, to infer protein associations, assess their function and location, and predict cancer-type specificity with implications for the future of cancer diagnosis, prognosis and treatment. Using this approach we identified NUP98 and MECP2 as potential proteins that exhibit upregulation in Acute Myeloid Leukemia (LAML) patients with implications for early diagnosis.

Insights into the mechanobiology of cancer metastasis via microfluidic technologies

During cancer metastasis, cancer cells will encounter various microenvironments with diverse physical characteristics. Changes in these physical characteristics such as tension, stiffness, viscosity, compression, and fluid shear can generate biomechanical cues that affect cancer cells, dynamically influencing numerous pathophysiological mechanisms. For example, a dense extracellular matrix drives cancer cells to reorganize their cytoskeleton structures, facilitating confined migration, while this dense and restricted space also acts as a physical barrier that potentially results in nuclear rupture. Identifying these pathophysiological processes and understanding their underlying mechanobiological mechanisms can aid in the development of more effective therapeutics targeted to cancer metastasis. In this review, we outline the advances of engineering microfluidic devices in vitro and their role in replicating tumor microenvironment to mimic in vivo settings. We highlight the potential cellular mechanisms that mediate their ability to adapt to different microenvironments. Meanwhile, we also discuss some important mechanical cues that still remain challenging to replicate in current microfluidic devices in future direction. While much remains to be explored about cancer mechanobiology, we believe the developments of microfluidic devices will reveal how these physical cues impact the behaviors of cancer cells. It will be crucial in the understanding of cancer metastasis, and potentially contributing to better drug development and cancer therapy.

DNA damage causes ATM-dependent heterochromatin loss leading to nuclear softening, blebbing, and rupture

The nucleus must maintain stiffness to protect the shape and integrity of the nucleus to ensure proper function. Defects in nuclear stiffness caused from chromatin and lamin perturbations produce abnormal nuclear shapes common in aging, heart disease, and cancer. Loss of nuclear shape via protrusions called blebs leads to nuclear rupture that is well-established to cause nuclear dysfunction, including DNA damage. However, it remains unknown how increased DNA damage affects nuclear stiffness, shape, and ruptures, which could create a negative feedback loop. To determine if increased DNA damage alters nuclear physical properties, we treated MEF cells with DNA damage drugs cisplatin and bleomycin. DNA damage drugs caused increased nuclear blebbing and rupture in interphase nuclei within a few hours and independent of mitosis. Micromanipulation force measurements reveal that DNA damage decreased chromatin-based nuclear mechanics but did not change lamin-based strain stiffening at long extensions relative to wild type. Immunofluorescence measurements of DNA damage treatments reveal the mechanism is an ATM-dependent decrease in heterochromatin leading to nuclear weaken, blebbing, and rupture which can be rescued upon ATM inhibition treatment. Thus, DNA damage drugs cause ATM-dependent heterochromatin loss resulting in nuclear softening, blebbing, and rupture.

Replication stress as a driver of cellular senescence and aging

Replication stress refers to slowing or stalling of replication fork progression during DNA synthesis that disrupts faithful copying of the genome. While long considered a nexus for DNA damage, the role of replication stress in aging is under-appreciated. The consequential role of replication stress in promotion of organismal aging phenotypes is evidenced by an extensive list of hereditary accelerated aging disorders marked by molecular defects in factors that promote replication fork progression and operate uniquely in the replication stress response. Additionally, recent studies have revealed cellular pathways and phenotypes elicited by replication stress that align with designated hallmarks of aging. Here we review recent advances demonstrating the role of replication stress as an ultimate driver of cellular senescence and aging. We discuss clinical implications of the intriguing links between cellular senescence and aging including application of senotherapeutic approaches in the context of replication stress.

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.

Targeting Nuclear Mechanics Mitigates the Fibroblast Invasiveness in Pathological Dermal Scars Induced by Matrix Stiffening

Pathological dermal scars such as keloids present significant clinical challenges lacking effective treatment options. Given the distinctive feature of highly stiffened scar tissues, deciphering how matrix mechanics regulate pathological progression can inform new therapeutic strategies. Here, it is shown that pathological dermal scar keloid fibroblasts display unique metamorphoses to stiffened matrix. Compared to normal fibroblasts, keloid fibroblasts show high sensitivity to stiffness rather than biochemical stimulation, activating cytoskeletal-to-nuclear mechanosensing molecules. Notably, keloid fibroblasts on stiff matrices exhibit nuclear softening, concomitant with reduced lamin A/C expression, and disrupted anchoring of lamina-associated chromatin. This nuclear softening, combined with weak adhesion and high contractility, facilitates the invasive migration of keloid fibroblasts through confining matrices. Inhibiting lamin A/C-driven nuclear softening, via lamin A/C overexpression or actin disruption, mitigates such invasiveness of keloid fibroblasts. These findings highlight the significance of the nuclear mechanics of keloid fibroblasts in scar pathogenesis and propose lamin A/C as a potential therapeutic target for managing pathological scars.

Chromatin organization and behavior in HRAS-transformed mouse fibroblasts

In higher eukaryotic cells, a string of nucleosomes, where long genomic DNA is wrapped around core histones, are rather irregularly folded into a number of condensed chromatin domains, which have been revealed by super-resolution imaging and Hi-C technologies. Inside these domains, nucleosomes fluctuate and locally behave like a liquid. The behavior of chromatin may be highly related to DNA transaction activities such as transcription and repair, which are often upregulated in cancer cells. To investigate chromatin behavior in cancer cells and compare those of cancer and non-cancer cells, we focused on oncogenic-HRAS (Gly12Val)-transformed mouse fibroblasts CIRAS-3 cells and their parental 10T1/2 cells. CIRAS-3 cells are tumorigenic and highly metastatic. First, we found that HRAS-induced transformation altered not only chromosome structure, but also nuclear morphology in the cell. Using single-nucleosome imaging/tracking in live cells, we demonstrated that nucleosomes are locally more constrained in CIRAS-3 cells than in 10T1/2 cells. Consistently, heterochromatin marked with H3K27me3 was upregulated in CIRAS-3 cells. Finally, Hi-C analysis showed enriched interactions of the B-B compartment in CIRAS-3 cells, which likely represents transcriptionally inactive chromatin. Increased heterochromatin may play an important role in cell migration, as they have been reported to increase during metastasis. Our study also suggests that single-nucleosome imaging provides new insights into how local chromatin is structured in living cells.

A high-content screen reveals new regulators of nuclear membrane stability

Nuclear membrane rupture is a physiological response to multiple in vivo processes, such as cell migration, that can cause extensive genome instability and upregulate invasive and inflammatory pathways. However, the underlying molecular mechanisms of rupture are unclear and few regulators have been identified. In this study, we developed a reporter that is size excluded from re-compartmentalization following nuclear rupture events. This allows for robust detection of factors influencing nuclear integrity in fixed cells. We combined this with an automated image analysis pipeline in a high-content siRNA screen to identify new proteins that both increase and decrease nuclear rupture frequency in cancer cells. Pathway analysis identified an enrichment of nuclear membrane and ER factors in our hits and we demonstrate that one of these, the protein phosphatase CTDNEP1, is required for nuclear stability. Analysis of known rupture determinants, including an automated quantitative analysis of nuclear lamina gaps, are consistent with CTDNEP1 acting independently of actin and nuclear lamina organization. Our findings provide new insights into the molecular mechanism of nuclear rupture and define a highly adaptable program for rupture analysis that removes a substantial barrier to new discoveries in the field.

Compartment specific responses to contractility in the small intestinal epithelium

Tissues are subject to multiple mechanical inputs at the cellular level that influence their overall shape and function. In the small intestine, actomyosin contractility can be induced by many physiological and pathological inputs. However, we have little understanding of how contractility impacts the intestinal epithelium on a cellular and tissue level. In this study, we probed the cell and tissue-level effects of contractility by using mouse models to genetically increase the level of myosin activity in the two distinct morphologic compartments of the intestinal epithelium, the crypts and villi. We found that increased contractility in the villar compartment caused shape changes in the cells that expressed the transgene and their immediate neighbors. While there were no discernable effects on villar architecture or cell polarity, even low levels of transgene induction in the villi caused non-cell autonomous hyperproliferation of the transit amplifying cells in the crypt, driving increased cell flux through the crypt-villar axis. In contrast, induction of increased contractility in the proliferating cells of the crypts resulted in nuclear deformations, DNA damage, and apoptosis. This study reveals the complex and diverse responses of different intestinal epithelial cells to contractility and provides important insight into mechanical regulation of intestinal physiology.

Multiscale transport and 4D time-lapse imaging in precision-cut liver slices (PCLS)

Background

Monitoring cellular processes across different levels of complexity, from the cellular to the tissue scale, is important for understanding tissue structure and function. However, it is challenging to monitor and estimate these structural and dynamic interactions within three-dimensional (3D) tissue models.

Objective

The aim of this study was to design a method for imaging, tracking, and quantifying 3D changes in cell morphology (shape and size) within liver tissue, specifically a precision-cut liver slice (PCLS). A PCLS is a 3D model of the liver that allows the study of the structure and function of liver cells in their native microenvironment.

Methods

Here, we present a method for imaging liver tissue during anisosmotic exposure in a multispectral four-dimensional manner. Three metrics of tissue morphology were measured to quantify the effects of osmotic stress on liver tissue. We estimated the changes in the volume of whole precision cut liver slices, quantified the changes in nuclei position, and calculated the changes in volumetric responses of tissue-embedded cells.

Results

During equilibration with cell-membrane-permeating and non-permeating solutes, the whole tissue experiences shrinkage and expansion. As nuclei showed a change in position and directional displacement under osmotic stress, we demonstrate that nuclei could be used as a probe to measure local osmotic and mechanical stress. Moreover, we demonstrate that cells change their volume within tissue slices as a result of osmotic perturbation and that this change in volume is dependent on the position of the cell within the tissue and the duration of the exposure.

Conclusion

The results of this study have implications for a better understanding of multiscale transport, mechanobiology, and triggered biological responses within complex biological structures.

Nuclear shape is affected differentially by loss of lamin A, lamin C, or both lamin A and C

Lamin intermediate filaments form a peripheral meshwork to support nuclear shape and function. Knockout of the LMNA gene that encodes for both lamin A and C results in an abnormally shaped nucleus. To determine the relative contribution of lamin A and C to nuclear shape, we measured nuclear blebbing and circular deviation in separate lamin A and lamin C knockdown and LMNA-/- stable cells. Lamin A knockdown increased nuclear blebbing while loss of lamin A, C, or both increased circular deviation. Overall, loss of lamin A, lamin C or both lamin A/C affect nuclear shape differentially.

Actin contraction controls nuclear blebbing and rupture independent of actin confinement

The nucleus is a mechanically stable compartment of the cell that contains the genome and performs many essential functions. Nuclear mechanical components chromatin and lamins maintain nuclear shape, compartmentalization, and function by resisting antagonistic actin contraction and confinement. Studies have yet to compare chromatin and lamins perturbations side-by-side as well as modulated actin contraction while holding confinement constant. To accomplish this, we used nuclear localization signal green fluorescent protein to measure nuclear shape and rupture in live cells with chromatin and lamin perturbations. We then modulated actin contraction while maintaining actin confinement measured by nuclear height. Wild type, chromatin decompaction, and lamin B1 null present bleb-based nuclear deformations and ruptures dependent on actin contraction and independent of actin confinement. Actin contraction inhibition by Y27632 decreased nuclear blebbing and ruptures while activation by CN03 increased rupture frequency. Lamin A/C null results in overall abnormal shape also reliant on actin contraction, but similar blebs and ruptures as wild type. Increased DNA damage is caused by nuclear blebbing or abnormal shape which can be relieved by inhibition of actin contraction which rescues nuclear shape and decreases DNA damage levels in all perturbations. Thus, actin contraction drives nuclear blebbing, bleb-based ruptures, and abnormal shape independent of changes in actin confinement.

Biophysical Control of the Glioblastoma Immunosuppressive Microenvironment: Opportunities for Immunotherapy

GBM is the most aggressive and common form of primary brain cancer with a dismal prognosis. Current GBM treatments have not improved patient survival, due to the propensity for tumor cell adaptation and immune evasion, leading to a persistent progression of the disease. In recent years, the tumor microenvironment (TME) has been identified as a critical regulator of these pro-tumorigenic changes, providing a complex array of biomolecular and biophysical signals that facilitate evasion strategies by modulating tumor cells, stromal cells, and immune populations. Efforts to unravel these complex TME interactions are necessary to improve GBM therapy. Immunotherapy is a promising treatment strategy that utilizes a patient's own immune system for tumor eradication and has exhibited exciting results in many cancer types; however, the highly immunosuppressive interactions between the immune cell populations and the GBM TME continue to present challenges. In order to elucidate these interactions, novel bioengineering models are being employed to decipher the mechanisms of immunologically "cold" GBMs. Additionally, these data are being leveraged to develop cell engineering strategies to bolster immunotherapy efficacy. This review presents an in-depth analysis of the biophysical interactions of the GBM TME and immune cell populations as well as the systems used to elucidate the underlying immunosuppressive mechanisms for improving current therapies.