Cell-extracellular matrix mechanotransduction in 3D

Perspectives on the extracellular matrix in inflammatory bowel disease and bowel decellularization protocols

The extracellular matrix (ECM) is a non-cellular three-dimensional structure present in all tissues that is essential for the intestinal maintenance, function and structure, as well as for providing physical support for tissue integrity and elasticity. ECM enables the regulation of various processes involved in tissue homeostasis, being vital for healing, growth, migration and cell differentiation. Structurally, ECM is composed of water, polysaccharides and proteins, such as collagen fibers and proteoglycans, which are specifically arranged for each tissue. In pathological scenarios, such as inflammatory bowel disease (IBD), the deposition and remodeling of the ECM can be altered in relation to the homeostatic composition. IBD, such as Ulcerative colitis and Crohn’s disease, can be differentiated according to ECM alterations, such as circulating levels of collagen, laminin and vimentin neoepitopes. In this context, ECM presents particularities in both physiological and pathological processes, however, exploring methods of tissue decellularization is emerging as a promising frontier for new therapeutic interventions and clinical protocols, promoting the development of new approaches to intestinal diseases.

Mechanisms of assembly and remodelling of the extracellular matrix

The extracellular matrix (ECM) is the complex meshwork of proteins and glycans that forms the scaffold that surrounds and supports cells. It exerts key roles in all aspects of metazoan physiology, from conferring physical and mechanical properties on tissues and organs to modulating cellular processes such as proliferation, differentiation and migration. Understanding the mechanisms that orchestrate the assembly of the ECM scaffold is thus crucial to understand ECM functions in health and disease. This Review discusses novel insights into the compositional diversity of matrisome components and the mechanisms that lead to tissue-specific assemblies and architectures tailored to support specific functions. The Review then highlights recently discovered mechanisms, including post-translational modifications and metabolic pathways such as amino acid availability and the circadian clock, that modulate ECM secretion, assembly and remodelling in homeostasis and human diseases. Last, the Review explores the potential of 'matritherapies', that is, strategies to normalize ECM composition and architecture to achieve a therapeutic benefit.

Physical effects of 3-D microenvironments on confined cell behaviors

Cell migration is a fundamental and functional cellular process, influenced by a complex microenvironment consisting of different cells and extracellular matrix. Recent research has highlighted that, besides biochemical cues from the microenvironment, physical cues can also greatly alter cellular behavior. However, due to the complexity of the microenvironment, little is known about how the physical interactions between migrating cells and surrounding microenvironment instructs cell movement. Here, we explore various examples of three-dimensional microenvironment reconstruction models in vitro and describe how the physical interplay between migrating cells and the neighboring microenvironment controls cell behavior. Understanding this mechanical cooperation will provide key insights into organ development, regeneration, and tumor metastasis.

Adaptive immunity of materials: Implications for tissue healing and regeneration

Recent cumulative findings signify the adaptive immunity of materials as a key agenda in tissue healing that can improve regenerative events and outcomes. Modulating immune responses, mainly the recruitment and functions of T and B cells and their further interplay with innate immune cells (e.g., dendritic cells, macrophages) can be orchestrated by materials. For instance, decellularized matrices have been shown to promote muscle healing by inducing T helper 2 (Th2) cell immunity, while synthetic biopolymers exhibit differential effects on B cell responses and fibrosis compared decellularized matrices. We discuss the recent findings on how implantable materials instruct the adaptive immune events and the subsequent tissue healing process. In particular, we dissect the materials' physicochemical properties (shape, size, topology, degradation, rigidity, and matrix dynamic mechanics) to demonstrate the relations of these parameters with the adaptive immune responses in vitro and the underlying biological mechanisms. Furthermore, we present evidence of recent in vivo phenomena, including tissue healing, cancer progression, and fibrosis, wherein biomaterials potentially shape adaptive immune cell functions and in vivo outcomes. Our discussion will help understand the materials-regulated immunology events more deeply, and offer the design rationale of materials with tunable matrix properties for accelerated tissue repair and regeneration.

Spatial Dimension Cues Derived From Fibrous Scaffolds Trigger Mechanical Activation to Potentiate the Paracrine and Regenerative Functions of MSCs via the FAK-PI3K/AKT Axis

Secretomes from mesenchymal stem cells (MSCs) have significant therapeutic potential and could be the basis for future MSCs treatments. Innovative design of the topology of biomaterials, which mechanically regulate cell behavior and function, can tremendously improve the efficacy of stem cell therapy. However, how spatial dimension cues derived from specific topology command cell mechanotransduction to regulate the paracrine function of MSCs remains unknown. In this study, the three-dimensional (3D) fibrous constructs with box-like pores and precise strand spacing from 150 μm down to only 40 μm were manufactured using melt electrowriting (MEW), which were used to systematically investigate the spatial dimension cues-triggered mechanotransduction of adipose-derived mesenchymal stem cells (Ad-MSCs) and their impact on the paracrine and regeneration function of Ad-MSCs. The results demonstrated that spatial instructions from the 3D fibrous constructs could influence the spatial reorganization of the cytoskeleton, resulting in cell elongation and augmented immunomodulatory and angiogenic paracrine effects of Ad-MSCs, which was most pronounced at a minimum strand spacing of 40 μm. Besides, mechanical activation of the FAK-PI3K/AKT axis significantly enhanced the paracrine function of Ad-MSCs. In vivo experiments demonstrated that the Ad-MSCs trained using well-defined 3D fibrous constructs with a strand spacing of 40 μm significantly promoted skin regeneration via paracrine signals. In conclusion, this study provides a new horizon for deciphering space dimension insights into the interactional mechanisms of mechanotransduction in regulating cell function, which has inspired innovations in biomaterials for improving tissue regeneration. STATEMENT OF SIGNIFICANCE: Designing cell-scale spatial dimension cues in engineered constructs potentiates the paracrine and regenerative functions of Ad-MSCs. FAK-PI3K/AKT signaling serves as the key mechanotransduction checkpoints for spatial dimension cues triggering mechanical activation. Paracrine signals of Ad-MSCs triggered by mechanical activation promotes skin repair and regeneration via the immunomodulation and angiogenesis.

Visualizing and quantifying dynamic cellular forces with photonic crystal hydrogels

Cellular forces play a crucial role in numerous biological processes, including tissue development, morphogenesis, and disease progression. However, existing methods for detecting cellular forces, such as traction force microscopy and atomic force microscopy, often face limitations in terms of high throughput, real-time monitoring, and applicability to complex biological systems. In this study, we utilized a novel Photonic Crystal Cellular Force Microscopy (PCCFM) system to visualize and quantify dynamic cellular forces. This system consists of a conventional optical microscope and a photonic crystal substrate formed by the periodic arrangement of silica nanoparticles within polyacrylamide hydrogels. Taking MDCK cells and BMSCs as examples, we found that PCCFM can capture dynamic cellular forces with high spatial and temporal resolution during the cell adhesion, spread, proliferation, and osteogenic differentiation. The application of this technique revealed distinct force patterns in different cellular stages, offering insights into the interplay between cellular forces and morphological changes. By investigating the migration of cells from MDCK cyst fragments, we could gain significant insights into tumour cell migration behaviours. The real-time, high-throughput analysis of cellular biomechanics from the PCCFM system offers valuable information on the mechanisms of tumour metastasis, potentially guiding therapeutic development and improving disease treatment strategies.

Development and Biocompatibility Assessment of Decellularized Porcine Uterine Extracellular Matrix-Derived Grafts

Biomaterials derived from biological matrices have been widely investigated due to their great therapeutic potential in regenerative medicine, since they are able to induce cell proliferation, tissue remodeling, and angiogenesis in situ. In this context, highly vascularized and proliferative tissues, such as the uterine wall, present an interesting source to produce acellular matrices that can be used as bioactive materials to induce tissue regeneration. Therefore, this study aimed to establish an optimized protocol to generate decellularized uterine scaffolds (dUT), characterizing their structural, compositional, and biomechanical properties. In addition, in vitro performance and in vivo biocompatibility were also evaluated to verify their potential applications for tissue repair. Results showed that the protocol was efficient to promote cell removal, and dUT general structure and extracellular matrix composition remained preserved compared with native tissue. In addition, the scaffolds were cytocompatible, allowing cell growth and survival. In terms of biocompatibility, the matrices did not induce any signs of immune rejection in vivo in a model of subcutaneous implantation in immunocompetent rats, demonstrating an indication of tissue integration after 30 days of implantation. In summary, these findings suggest that dUT scaffolds could be explored as a biomaterial for regenerative purposes, which is beyond the studies in the reproductive field.

The axis of tumor-associated macrophages, extracellular matrix proteins, and cancer-associated fibroblasts in oncogenesis

The extracellular matrix (ECM) is a complex, dynamic network of multiple macromolecules that serve as a crucial structural and physical scaffold for neighboring cells. In the tumor microenvironment (TME), ECM proteins play a significant role in mediating cellular communication between cancer-associated fibroblasts (CAFs) and tumor-associated macrophages (TAMs). Revealing the ECM modification of the TME necessitates the intricate signaling cascades that transpire among diverse cell populations and ECM proteins. The advent of single-cell sequencing has enabled the identification and refinement of specific cellular subpopulations, which has substantially enhanced our comprehension of the intricate milieu and given us a high-resolution perspective on the diversity of ECM proteins. However, it is essential to integrate single-cell data and establish a coherent framework. In this regard, we present a comprehensive review of the relationships among ECM, TAMs, and CAFs. This encompasses insights into the ECM proteins released by TAMs and CAFs, signaling integration in the TAM-ECM-CAF axis, and the potential applications and limitations of targeted therapies for CAFs. This review serves as a reliable resource for focused therapeutic strategies while highlighting the crucial role of ECM proteins as intermediates in the TME.

Structural extracellular matrix-mediated molecular signaling in wound repair and tissue regeneration

The extracellular matrix (ECM) is a complex, non-cellular network of molecules that offers structural support for cells and tissues. The ECM is composed of various structural components, including collagen, fibronectin, laminin, perlecan, nidogen, tenascin, and fibulin, which are capable of binding to each other and to cell-to-adhesion receptors, endowing the ECM with unique physical and biochemical properties that are essential for its function in maintaining health and managing disease. Over the past three decades, extensive research has shown that the core of the ECM can significantly impact cellular events at the molecular level. Structural modifications have also been strongly associated with tissue repair. Through interactions with cells, matrix proteins regulate critical processes such as cell proliferation and differentiation, migration, and apoptosis, essential for maintaining tissue homeostasis, formation, and regeneration. This review emphasizes the interlocking networks of ECM macromolecules and their primary roles in tissue regeneration and wound repair. Through studying ECM dynamics, researchers have discovered molecular signaling pathways that demonstrate how the ECM influences protein patterns and open up more possibilities for developing therapeutics that target the ECM to enhance wound repair and tissue regeneration.

Proteomic and Phosphoproteomic Profiling of Matrix Stiffness-Induced Stemness-Dormancy State Transition in Breast Cancer Cells

The dormancy of cancer stem cells is a major factor leading to drug resistance and a high rate of late recurrence and mortality in estrogen receptor-positive (ER+) breast cancer. Previously, we demonstrated that a stiffer matrix induces tumor cell dormancy and drug resistance, whereas a softened matrix promotes tumor cells to exhibit a stem cell state with high proliferation and migration. In this study, we present a comprehensive analysis of the proteome and phosphoproteome in response to gradient changes in matrix stiffness, elucidating the mechanisms behind cell dormancy-induced drug resistance. Overall, we found that antiapoptotic and membrane transport processes may be involved in the mechanical force-induced dormancy resistance of ER+ breast cancer cells. Our research provides new insights from a holistic proteomic and phosphoproteomic perspective, underscoring the significant role of mechanical forces stemming from the stiffness of the surrounding extracellular matrix as a critical regulatory factor in the tumor microenvironment.

Matrix stiffness regulates mitochondria-lysosome contacts to modulate the mitochondrial network, alleviate the senescence of MSCs

The extracellular microenvironment encompasses the extracellular matrix, neighbouring cells, cytokines, and fluid components. Anomalies in the microenvironment can trigger aging and a decreased differentiation capacity in mesenchymal stem cells (MSCs). MSCs can perceive variations in the firmness of the extracellular matrix and respond by regulating mitochondrial function. Diminished mitochondrial function is intricately linked to cellular aging, and studies have shown that mitochondria-lysosome contacts (M-L contacts) can regulate mitochondrial function to sustain cellular equilibrium. Nonetheless, the influence of M-L contacts on MSC aging under varying matrix stiffness remains unclear. In this study, utilizing single-cell RNA sequencing and atomic force microscopy, we further demonstrate that reduced matrix stiffness in older individuals leads to MSC aging and subsequent decline in osteogenic ability. Mechanistically, augmented M-L contacts under low matrix stiffness exacerbate MSC aging by escalating mitochondrial oxidative stress and peripheral division. Moreover, under soft matrix stiffness, cytoskeleton reorganization facilitates rapid movement of lysosomes. The M-L contacts inhibitor ML282 ameliorates MSC aging by reinstating mitochondrial network and function. Overall, our findings confirm that MSC aging is instigated by disruption of the mitochondrial network and function induced by matrix stiffness, while also elucidating the potential mechanism by which M-L Contact regulates mitochondrial homeostasis. Crucially, this presents promise for cellular anti-aging strategies centred on mitochondria, particularly in the realm of stem cell therapy.

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.

Exploring Mechanical Forces Shaping Self-Organization and Morphogenesis During Early Embryo Development

Embryonic development is a dynamic process orchestrated by a delicate interplay of biochemical and biophysical factors. While the role of genetics and biochemistry in embryogenesis has been extensively studied, recent research has highlighted the significance of mechanical regulation in shaping and guiding this intricate process. Here, we provide an overview of the current understanding of the mechanical regulation of embryo development. We explore how mechanical forces generated by cells and tissues play a crucial role in driving the development of different stages. We examine key morphogenetic processes such as compaction, blastocyst formation, implantation, and egg cylinder formation, and discuss the mechanical mechanisms and cues involved. By synthesizing the current body of literature, we highlight the emerging concepts and open questions in the field of mechanical regulation. We aim to provide an overview of the field, inspiring future investigations and fostering a deeper understanding of the mechanical aspects of embryo development.

Aligned fibrous scaffolds promote directional migration of breast cancer cells via caveolin-1/YAP-mediated mechanosensing

Tumorigenesis and metastasis are highly dependent on the interactions between the tumor and the surrounding microenvironment. In 3D matrix, the fibrous structure of the extracellular matrix (ECM) undergoes dynamic remodeling during tumor progression. In particular, during the late stage of tumor development, the fibers become more aggregated and oriented. However, it remains unclear how cancer cells respond to the organizational change of ECM fibers and exhibit distinct morphology and behavior. Here, we used electrospinning technology to fabricate biomimetic ECM with distinct fiber arrangements, which mimic the structural characteristics of normal or tumor tissues and found that aligned and oriented nanofibers induce cytoskeletal rearrangement to promote directed migration of cancer cells. Mechanistically, caveolin-1(Cav-1)-expressing cancer cells grown on aligned fibers exhibit increased integrin β1 internalization and actin polymerization, which promoted stress fiber formation, focal adhesion dynamics and YAP activity, thereby accelerating the directional cell migration. In general, the linear fibrous structure of the ECM provides convenient tracks on which tumor cells can invade and migrate. Moreover, histological data from both mice and patients with tumors indicates that tumor tissue exhibits a greater abundance of isotropic ECM fibers compared to normal tissue. And Cav-1 downregulation can suppress cancer cells muscle invasion through the inhibition of YAP-dependent mechanotransduction. Taken together, our findings revealed the Cav-1 is indispensable for the cellular response to topological change of ECM, and that the Cav-1/YAP axis is an attractive target for inhibiting cancer cell directional migration which induced by linearization of ECM fibers.

Variations in fluid chemical potential induce fibroblast mechano-response in 3D hydrogels

Mechanical deformation of skin creates variations in fluid chemical potential, leading to local changes in hydrostatic and osmotic pressure, whose effects on mechanobiology remain poorly understood. To study these effects, we investigate the specific influences of hydrostatic and osmotic pressure on primary human dermal fibroblasts in three-dimensional hydrogel culture models. Cyclic hydrostatic pressure and hyperosmotic stress enhanced the percentage of cells expressing the proliferation marker Ki67 in both collagen and PEG-based hydrogels. Osmotic pressure also activated the p38 MAPK stress response pathway and increased the expression of the osmoresponsive genes PRSS35 and NFAT5. When cells were cultured in two-dimension (2D), no change in proliferation was observed with either hydrostatic or osmotic pressure. Furthermore, basal, and osmotic pressure-induced expression of osmoresponsive genes differed in 2D culture versus 3D hydrogels, highlighting the role of dimensionality in skin cell mechanotransduction and stressing the importance of 3D tissue-like models that better replicate in vivo conditions. Overall, these results indicate that fluid chemical potential changes affect dermal fibroblast mechanobiology, which has implications for skin function and for tissue regeneration strategies.

Flow-on-repellent biofabrication of fibrous decellularized breast tumor-stroma models

On-the-fly biofabrication of reproducible 3D tumor models at a pre-clinical level is highly desirable to level-up their applicability and predictive potential. Incorporating ECM biomolecular cues and its complex 3D bioarchitecture in the design stages of such in vitro platforms is essential to better recapitulate the native tumor microenvironment. To materialize these needs, herein we describe an innovative flow-on-repellent (FLORE) 3D extrusion bioprinting technique that leverages expedited and automatized bioink deposition onto a customized superhydrophobic printing bed. We demonstrate that this approach enables the rapid generation of quasi-spherical breast cancer-stroma hybrid models in a mode governed by surface wettability rather than bioink rheological features. For this purpose, an ECM-mimetic bioink comprising breast tissue-specific decellularized matrix in the form of microfiber bundles (dECM-μF) and photocrosslinkable hyaluronan (HAMA), was formulated to generate triple negative breast tumor-stroma models. Leveraging on the FLORE bioprinting approach, a rapid, automated, and reproducible fabrication of physiomimetic breast cancer hydrogel beads was successfully demonstrated. Hydrogel beads size with and without dECM-μF was easily tailored by modelling droplet deposition time on the superhydrophobic bed. Interestingly, in heterotypic breast cancer-stroma beads a self-arrangement of different cellular populations was observed, independent of dECM-μF inclusion, with CAFs clustering overtime within the fabricated models. Drug screening assays showed that the inclusion of CAFs and dECM-μF also impacted the overall response of these living constructs when incubated with gemcitabine chemotherapeutics, with dECM-μF integration promoting a trend for higher resistance in ECM-enriched models. Overall, we developed a rapid fabrication approach leveraging on extrusion bioprinting and superhydrophobic surfaces to process photocrosslinkable dECM bioinks and to generate increasingly physiomimetic tumor-stroma-matrix platforms for drug screening.

Biomaterials Mimicking Mechanobiology: A Specific Design for a Specific Biological Application

Mechanosensing and mechanotransduction pathways between the Extracellular Matrix (ECM) and cells form the essential crosstalk that regulates cell homeostasis, tissue development, morphology, maintenance, and function. Understanding these mechanisms involves creating an appropriate cell support that elicits signals to guide cellular functions. In this context, polymers can serve as ideal molecules for producing biomaterials designed to mimic the characteristics of the ECM, thereby triggering responsive mechanisms that closely resemble those induced by a natural physiological system. The generated specific stimuli depend on the different natural or synthetic origins of the polymers, the chemical composition, the assembly structure, and the physical and surface properties of biomaterials. This review discusses the most widely used polymers and their customization to develop biomaterials with tailored properties. It examines how the characteristics of biomaterials-based polymers can be harnessed to replicate the functions of biological cells, making them suitable for biomedical and biotechnological applications.

Hydrogels with Independently Controlled Adhesion Ligand Mobility and Viscoelasticity Increase Cell Adhesion and Spreading

A primary objective in designing hydrogels for cell culture is recreating the cell-matrix interactions found within human tissues. Identifying the most important biomaterial features for these interactions is challenging because it is difficult to independently adjust variables such as matrix stiffness, stress relaxation, the mobility of adhesion ligands and the ability of these ligands to support cellular forces. In this work we designed a hydrogel platform consisting of interpenetrating polymer networks of covalently crosslinked poly(ethylene glycol) (PEG) and self-assembled peptide amphiphiles (PA). We can tailor the storage modulus of the hydrogel by altering the concentration and composition of each network, and we can tune the stress relaxation half-life through the non-covalent bonding in the PA network. Ligand mobility can be adjusted independently of the matrix mechanical properties by attaching the RGD cell adhesion ligand to either the covalent PEG network, the dynamic PA network, or both networks at once. Interestingly, our findings show that endothelial cell adhesion formation and spreading is maximized in soft, viscoelastic gels in which RGD adhesion ligands are present on both the covalent PEG and non-covalent PA networks. The dynamic nature of cell adhesion domains, coupled with their ability to exert substantial forces on the matrix, suggests that having different presentations of RGD ligands which are either mobile or are capable of withstanding significant forces are needed mimic different aspects of complex cell-matrix adhesions. By demonstrating how different presentations of RGD ligands affect cell behavior independently of viscoelastic properties, these results contribute to the rational design of hydrogels that facilitate desired cell-matrix interactions, with the potential of improving in vitro models and regenerative therapies.

Shaping the immune landscape: Multidimensional environmental stimuli refine macrophage polarization and foster revolutionary approaches in tissue regeneration

In immunology, the role of macrophages extends far beyond their traditional classification as mere phagocytes; they emerge as pivotal architects of the immune response, with their function being significantly influenced by multidimensional environmental stimuli. This review investigates the nuanced mechanisms by which diverse external signals ranging from chemical cues to physical stress orchestrate macrophage polarization, a process that is crucial for the modulation of immune responses. By transitioning between pro-inflammatory (M1) and anti-inflammatory (M2) states, macrophages exhibit remarkable plasticity, enabling them to adapt to and influence their surroundings effectively. The exploration of macrophage polarization provides a compelling narrative on how these cells can be manipulated to foster an immune environment conducive to tissue repair and regeneration. Highlighting cutting-edge research, this review presents innovative strategies that leverage the dynamic interplay between macrophages and their environment, proposing novel therapeutic avenues that harness the potential of macrophages in regenerative medicine. Moreover, this review critically evaluates the current challenges and future prospects of translating macrophage-centered strategies from the laboratory to clinical applications.

Principles and regulation of mechanosensing

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

Increased matrix stiffness in pituitary neuroendocrine tumors invading the cavernous sinus is activated by TAFs: focus on the mechanical signatures

PURPOSE

Pituitary neuroendocrine tumors (PitNETs) with invasion of the cavernous sinus (CS) are particularly challenging to treat. Tumor associated fibroblasts (TAFs) are recognized for their pivotal role in reprogramming extracellular matrix (ECM). Herein, we aimed to explore the potential involvement of TAFs in ECM reprogramming and elucidate the underlying mechanism involved.

METHODS

We applied dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) to measure tumor vessel permeability and applied atomic force microscopy (AFM) to measure the matrix stiffness of PitNETs located in both CS and sella turcica (ST). Western blotting, immunofluorescence, immunohistochemistry, and quantitative RT-PCR were utilized to analyze the ECM components. Proteomic biochemical analysis was utilized to uncover potential mechanisms governing ECM dynamics.

RESULTS

We found that PitNETs in the CS were stiffer than those in the ST. Increased ECM stiffness within the CS facilitated the acquisition of stem-like properties, enhanced proliferation, and induced epithelial-to-mesenchymal transition (EMT) of GH3 cells. Furthermore, the expression levels of lysyl oxidase (LOX), matrix metallopeptidase 2 (MMP2) and MMP9 in pituitary adenoma cells increased in the stiffer matrix. Proteomic analysis suggested TAFs were activated in the CS area and contributed enhanced matrix stiffness by secreting Col-1 and Col-3. Furthermore, mTOR pathway was activated under higher matrix stiffness and the migration and invasion of GH3 cells be repressed by mTOR inhibitor.

CONCLUSION

These findings demonstrated that activated TAFs contributed to stiffer matrix and increased ECM stiffness stimulating mTOR pathway in pituitary tumor cells. Our study indicated that mTOR inhibitor was a promising treatment strategy from the standpoint of PitNET biomechanical properties.

Well-Defined Synthetic Copolymers with Pendant Aldehydes Form Biocompatible Strain-Stiffening Hydrogels and Enable Competitive Ligand Displacement

Dynamic hydrogels are attractive platforms for tissue engineering and regenerative medicine due to their ability to mimic key extracellular matrix (ECM) mechanical properties like strain-stiffening and stress relaxation while enabling enhanced processing characteristics like injectability, 3D printing, and self-healing. Systems based on imine-type dynamic covalent chemistry (DCvC) have become increasingly popular. However, most reported polymers comprising aldehyde groups are based on either end-group-modified synthetic or side-chain-modified natural polymers; synthetic versions of side-chain-modified polymers are noticeably absent. To facilitate access to new classes of dynamic hydrogels, we report the straightforward synthesis of a water-soluble copolymer with a tunable fraction of pendant aldehyde groups (12-64%) using controlled radical polymerization and their formation into hydrogel biomaterials with dynamic cross-links. We found the polymer synthesis to be well-controlled with the determined reactivity ratios consistent with a blocky gradient microarchitecture. Subsequently, we observed fast gelation kinetics with imine-type cross-linking. We were able to vary hydrogel stiffness from ≈2 to 20 kPa, tune the onset of strain-stiffening toward a biologically relevant regime (σc ≈ 10 Pa), and demonstrate cytocompatibility using human dermal fibroblasts. Moreover, to begin to mimic the dynamic biochemical nature of the native ECM, we highlight the potential for temporal modulation of ligands in our system to demonstrate ligand displacement along the copolymer backbone via competitive binding. The combination of highly tunable composition, stiffness, and strain-stiffening, in conjunction with spatiotemporal control of functionality, positions these cytocompatible copolymers as a powerful platform for the rational design of next-generation synthetic biomaterials.

Comparison of vinculin tension in cellular monolayers and three-dimensional multicellular aggregates

Confocal frequency-domain fluorescence lifetime and Förster resonance energy transfer (FRET) microscopy of Chinese hamster ovary (CHO-K1) cells expressing the vinculin tension sensor (VinTS) is used to compare vinculin tension in three-dimensional (3D) multicellular aggregates and 2D cellular monolayers. In both 2D and 3D cultures, the FRET efficiency of VinTS is 5-6% lower than that of VinTL (p < 0.05), a tail-less control which cannot bind actin or paxillin. The difference between VinTS and VinTL FRET efficiency can be mitigated by treatment with the Rho-associated kinase inhibitor Y-27632, demonstrating that VinTS is under tension in both 2D and 3D cultures. However, there is an overall decrease in FRET efficiency of both VinTS and VinTL in the 3D multicellular aggregates compared with the 2D monolayers. Expression of VinTS in 2D and 3D cultures exhibits puncta consistent with cellular adhesions. While paxillin is present at the sites of VinTS expression in the 2D monolayers, it is generally absent from VinTS puncta in the 3D aggregates. The results suggest that VinTS experiences a modified environment in 3D aggregates compared with 2D monolayers and provide a basis for further investigation of molecular tension sensors in 3D tissue models.

Synergistic Effects of Matrix Biophysical Properties on Gastric Cancer Cell Behavior via Integrin-Mediated Cell-ECM Interactions

The biophysical properties of the extracellular matrix (ECM) play a pivotal role in modulating cancer progression via cell-ECM interactions. However, the biophysical properties specific to gastric cancer (GC) remain largely unexplored. Pertinently, GC ECM shows significantly heterogeneous metamorphoses, such as matrix stiffening and intricate restructuring. By combining collagen I and alginate, this study designs an in vitro biomimetic hydrogel platform to independently modulate matrix stiffness and structure across a physiological stiffness spectrum while preserving consistent collagen concentration and fiber topography. With this platform, this study assesses the impacts of matrix biophysical properties on cell proliferation, migration, invasion, and other pivotal dynamics of AGS. The findings spotlight a compelling interplay between matrix stiffness and structure, influencing both cellular responses and ECM remodeling. Furthermore, this investigation into the integrin/actin-collagen interplay reinforces the central role of integrins in mediating cell-ECM interactions, reciprocally sculpting cell conduct, and ECM adaptation. Collectively, this study reveals a previously unidentified role of ECM biophysical properties in GC malignant potential and provides insight into the bidirectional mechanical cell-ECM interactions, which may facilitate the development of novel therapeutic horizons.

Matrix Viscoelasticity Tunes the Mechanobiological Behavior of Chondrocytes

In articular cartilage, the pericellular matrix acting as a specialized mechanical microenvironment modulates environmental signals to chondrocytes through mechanotransduction. Matrix viscoelastic alterations during cartilage development and osteoarthritis (OA) degeneration play an important role in regulating chondrocyte fate and cartilage matrix homeostasis. In recent years, scientists are gradually realizing the importance of matrix viscoelasticity in regulating chondrocyte function and phenotype. Notably, this is an emerging field, and this review summarizes the existing literatures to the best of our knowledge. This review provides an overview of the viscoelastic properties of hydrogels and the role of matrix viscoelasticity in directing chondrocyte behavior. In this review, we elaborated the mechanotransuction mechanisms by which cells sense and respond to the viscoelastic environment and also discussed the underlying signaling pathways. Moreover, emerging insights into the role of matrix viscoelasticity in regulating chondrocyte function and cartilage formation shed light into designing cell-instructive biomaterial. We also describe the potential use of viscoelastic biomaterials in cartilage tissue engineering and regenerative medicine. Future perspectives on mechanobiological comprehension of the viscoelastic behaviors involved in tissue homeostasis, cellular responses, and biomaterial design are highlighted. Finally, this review also highlights recent strategies utilizing viscoelastic hydrogels for designing cartilage-on-a-chip.

Neural Tissue-Like, not Supraphysiological, Electrical Conductivity Stimulates Neuronal Lineage Specification through Calcium Signaling and Epigenetic Modification

Electrical conductivity is a pivotal biophysical factor for neural interfaces, though optimal values remain controversial due to challenges isolating this cue. To address this issue, conductive substrates made of carbon nanotubes and graphene oxide nanoribbons, exhibiting a spectrum of conductivities from 0.02 to 3.2 S m-1, while controlling other surface properties is designed. The focus is to ascertain whether varying conductivity in isolation has any discernable impact on neural lineage specification. Remarkably, neural-tissue-like low conductivity (0.02-0.1 S m-1) prompted neural stem/progenitor cells to exhibit a greater propensity toward neuronal lineage specification (neurons and oligodendrocytes, not astrocytes) compared to high supraphysiological conductivity (3.2 S m-1). High conductivity instigated the apoptotic process, characterized by increased apoptotic fraction and decreased neurogenic morphological features, primarily due to calcium overload. Conversely, cells exposed to physiological conductivity displayed epigenetic changes, specifically increased chromatin openness with H3acetylation (H3ac) and neurogenic-transcription-factor activation, along with a more balanced intracellular calcium response. The pharmacological inhibition of H3ac further supported the idea that such epigenetic changes might play a key role in driving neuronal specification in response to neural-tissue-like, not supraphysiological, conductive cues. These findings underscore the necessity of optimal conductivity when designing neural interfaces and scaffolds to stimulate neuronal differentiation and facilitate the repair process.

Matrix stiffness regulates the triad communication of adipocytes/macrophages/endothelial cells through CXCL13

Adipose tissue remodeling and plasticity are dynamically regulated by the coordinated functions of adipocytes, macrophages, and endothelial cells and extracellular matrix (ECM) that provides stiffness networks in adipose tissue component cells. Inflammation and fibrosis are crucial exogenous factors that dysregulate adipose tissue functions and drastically change the mechanical properties of the ECM. Therefore, communication among the ECM and adipose tissue component cells is necessary to understand the multifaceted functions of adipose tissues. To obtain in vivo stiffness, we used genipin as a crosslinker for collagen gels. Meanwhile, we isolated primary adipocytes, macrophages, and endothelial cells from C57BL/6J mice and incubated these cells in the differentiation media on temperature-responsive culture dishes. After the differentiation, these cell sheets were transferred onto genipin-crosslinked collagen gels with varying matrix stiffness. We found that inflammatory gene expressions were induced by hard matrix, whereas antiinflammatory gene expressions were promoted by soft matrix in all three types of cells. Interestingly, the coculture experiments of adipocytes, macrophages, and endothelial cells showed that the effects of soft or hard matrix stiffness stimulation on adipocytes were transmitted to the distant adipose tissue component cells, altering their gene expression profiles under normal matrix conditions. Finally, we identified that a hard matrix induces the secretion of CXCL13 from adipocytes, and CXCL13 is one of the important transmitters for stiffness communication with macrophages and endothelial cells. These findings provide insight into the mechanotransmission into distant cells and the application of stiffness control for chronic inflammation in adipose tissues with metabolic dysregulation.

Fundamentals of redox regulation in biology

Oxidation-reduction (redox) reactions are central to the existence of life. Reactive species of oxygen, nitrogen and sulfur mediate redox control of a wide range of essential cellular processes. Yet, excessive levels of oxidants are associated with ageing and many diseases, including cardiological and neurodegenerative diseases, and cancer. Hence, maintaining the fine-tuned steady-state balance of reactive species production and removal is essential. Here, we discuss new insights into the dynamic maintenance of redox homeostasis (that is, redox homeodynamics) and the principles underlying biological redox organization, termed the 'redox code'. We survey how redox changes result in stress responses by hormesis mechanisms, and how the lifelong cumulative exposure to environmental agents, termed the 'exposome', is communicated to cells through redox signals. Better understanding of the molecular and cellular basis of redox biology will guide novel redox medicine approaches aimed at preventing and treating diseases associated with disturbed redox regulation.

Granulosa Cell-Layer Stiffening Prevents Escape of Mural Granulosa Cells from the Post-Ovulatory Follicle

Ovulation is vital for successful reproduction. Following ovulation, cumulus cells and oocyte are released, while mural granulosa cells (mGCs) remain sequestered within the post-ovulatory follicle to form the corpus luteum. However, the mechanism underlying the confinement of mGCs has been a longstanding mystery. Here, in vitro and in vivo evidence is provided demonstrating that the stiffening of mGC-layer serves as an evolutionarily conserved mechanism that prevents mGCs from escaping the post-ovulatory follicles. The results from spatial transcriptome analysis and experiments reveal that focal adhesion assembly, triggered by the LH (hCG)-cAMP-PKA-CREB signaling cascade, is necessary for mGC-layer stiffening. Disrupting focal adhesion assembly through RNA interference results in stiffening failure, mGC escape, and the subsequent development of an abnormal corpus luteum characterized by decreased cell density or cavities. These findings introduce a novel concept of "mGC-layer stiffening", shedding light on the mechanism that prevents mGC escape from the post-ovulatory follicle.

A Se Nanoparticle/MgFe-LDH Composite Nanosheet as a Multifunctional Platform for Osteosarcoma Eradication, Antibacterial and Bone Reconstruction

Despite advances in treating osteosarcoma, postoperative tumor recurrence, periprosthetic infection, and critical bone defects remain critical concerns. Herein, the growth of selenium nanoparticles (SeNPs) onto MgFe-LDH nanosheets (LDH) is reported to develop a multifunctional nanocomposite (LDH/Se) and further modification of the nanocomposite on a bioactive glass scaffold (BGS) to obtain a versatile platform (BGS@LDH/Se) for comprehensive postoperative osteosarcoma management. The uniform dispersion of negatively charged SeNPs on the LDH surface restrains toxicity-inducing aggregation and inactivation, thus enhancing superoxide dismutase (SOD) activation and superoxide anion radical (·O2 -)-H2O2 conversion. Meanwhile, Fe3+ within the LDH nanosheets can be reduced to Fe2+ by depleting glutathione (GSH) in the tumor microenvironments (TME), which can catalyze H2O2 into highly toxic reactive oxygen species. More importantly, incorporating SeNPs significantly promotes the anti-bacterial and osteogenic properties of BGS@LDH/Se. Thus, the developed BGS@LDH/Se platform can simultaneously inhibit tumor recurrence and periprosthetic infection as well as promote bone regeneration, thus holding great potential for postoperative "one-stop-shop" management of patients who need osteosarcoma resection and scaffold implantation.

Quantitative atlas of collagen hydrogels reveals mesenchymal cancer cell traction adaptation to the matrix nanoarchitecture

Collagen-based hydrogels are commonly used in mechanobiology to mimic the extracellular matrix. A quantitative analysis of the influence of collagen concentration and properties on the structure and mechanics of the hydrogels is essential for tailored design adjustments for specific in vitro conditions. We combined focused ion beam scanning electron microscopy and rheology to provide a detailed quantitative atlas of the mechanical and nanoscale three-dimensional structural alterations that occur when manipulating different hydrogel's physicochemistry. Moreover, we study the effects of such alterations on the phenotype of breast cancer cells and their mechanical interactions with the extracellular matrix. Regardless of the microenvironment's pore size, porosity or mechanical properties, cancer cells are able to reach a stable mesenchymal-like morphology. Additionally, employing 3D traction force microscopy, a positive correlation between cellular tractions and ECM mechanics is observed up to a critical threshold, beyond which tractions plateau. This suggests that cancer cells in a stable mesenchymal state calibrate their mechanical interactions with the ECM to keep their migration and invasiveness capacities unaltered. STATEMENT OF SIGNIFICANCE: The paper presents a thorough study on the mechanical microenvironment in breast cancer cells during their interaction with collagen based hydrogels of different compositions. The hydrogels' microstructure were obtained using state-of-the-art 3D microscopy, namely focused ion beam-scanning electron microscope (FIB-SEM). FIB-SEM was originally applied in this work to reconstruct complex fibered collagen microstructures within the nanometer range, to obtain key microarchitectural parameters. The mechanical microenvironment of cells was recovered using Traction Force Microscopy (TFM). The obtained results suggest that cells calibrate tractions such that they depend on mechanical, microstructural and physicochemical characteristics of the hydrogels, hence revealing a steric hindrance. We hypothesize that cancer cells studied in this paper tune their mechanical state to keep their migration and invasiveness capacities unaltered.

3D Multispheroid Assembly Strategies towards Tissue Engineering and Disease Modeling

Cell spheroids (esp. organoids) as 3D culture platforms are popular models for representing cell-cell and cell-extracellular matrix (ECM) interactions, bridging the gap between 2D cell cultures and natural tissues. 3D cell models with spatially organized multiple cell types are preferred for gaining comprehensive insights into tissue pathophysiology and constructing in vitro tissues and disease models because of the complexities of natural tissues. In recent years, an assembly strategy using cell spheroids (or organoids) as living building blocks has been developed to construct complex 3D tissue models with spatial organization. Here, a comprehensive overview of recent advances in multispheroid assembly studies is provided. The different mechanisms of the multispheroid assembly techniques, i.e., automated directed assembly, noncontact remote assembly, and programmed self-assembly, are introduced. The processing steps, advantages, and technical limitations of the existing methodologies are summarized. Applications of the multispheroid assembly strategies in disease modeling, drug screening, tissue engineering, and organogenesis are reviewed. Finally, this review concludes by emphasizing persistent issues and future perspectives, encouraging researchers to adopt multispheroid assembly techniques for generating advanced 3D cell models that better resemble real tissues.

Mechanochemistry: Fundamental Principles and Applications

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

Tumoroids, a valid preclinical screening platform for monitoring cancer angiogenesis

In recent years, biologists and clinicians have witnessed prominent advances in in vitro 3D culture techniques related to biomimetic human/animal tissue analogs. Numerous data have confirmed that unicellular and multicellular (tumoroids) tumor spheroids with dense native cells in certain matrices are sensitive and valid analytical tools for drug screening, cancer cell dynamic growth, behavior, etc. in laboratory settings. Angiogenesis/vascularization is a very critical biological phenomenon to support oxygen and nutrients to tumor cells within the deep layer of solid masses. It has been shown that endothelial cell (EC)-incorporated or -free spheroid/tumoroid systems provide a relatively reliable biological platform for monitoring the formation of nascent blood vessels in micron/micrometer scales. Besides, the paracrine angiogenic activity of cells within the spheroid/tumoroid systems can be monitored after being treated with different therapeutic approaches. Here, we aimed to collect recent advances and findings related to the monitoring of cancer angiogenesis using unicellular and multicellular tumor spheroids. Vascularized spheroids/tumoroids can help us in the elucidation of mechanisms related to cancer formation, development, and metastasis by monitoring the main influencing factors.

Hydrogels: a promising therapeutic platform for inflammatory skin diseases treatment

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

Mechanical stress-induced autophagy is cytoskeleton dependent

The cytoskeleton is essential for mechanical signal transduction and autophagy. However, few studies have directly demonstrated the contribution of the cytoskeleton to mechanical stress-induced autophagy. We explored the role of the cytoskeleton in response to compressive force-induced autophagy in human cell lines. Inhibition and activation of cytoskeletal polymerization using small chemical molecules revealed that cytoskeletal microfilaments are required for changes in the number of autophagosomes, whereas microtubules play an auxiliary role in mechanical stress-induced autophagy. The intrinsic mechanical properties and special intracellular distribution of microfilaments may account for a large proportion of compression-induced autophagy. Our experimental data support that microfilaments are core components of mechanotransduction signals.

Matrix stiffness-dependent PD-L2 deficiency improves SMYD3/xCT-mediated ferroptosis and the efficacy of anti-PD-1 in HCC

INTRODUCTION

Heterogeneous tissue stiffening promotes tumor progression and resistance, and predicts a poor clinical outcome in patients with hepatocellular carcinoma (HCC). Ferroptosis, a congenital tumor suppressive mechanism, mediates the anticancer activity of various tumor suppressors, including immune checkpoint inhibitors, and its induction is currently considered a promising treatment strategy. However, the role of extracellular matrix (ECM) stiffness in regulating ferroptosis and ferroptosis-targeted resistance in HCC remains unclear.

OBJECTIVES

This research aimed to explore how extracellular matrix stiffness affects ferroptosis and its treatment efficacy in HCC.

METHODS

Ferroptosis analysis was confirmed via cell activity, intracellular ferrous irons, and mitochondrial pathology assays. Baseline PD-L2, SMYD3, and SLC7A11 (xCT) were evaluated in 67 sorafenib-treated patients with HCC (46 for non-responder and 21 for responder) from public data. The combined efficacy of shPD-L2, sorafenib, and anti-PD-1 antibody in HCC was investigated in vivo.

RESULTS

Here, we revealed that matrix stiffness-induced PD-L2 functions as a suppressor of xCT-mediated ferroptosis to promote cancer growth and sorafenib resistance in patients with HCC. Mechanically, matrix stiffening induced the expression of PD-L2 by activating SMYD3/H3K4me3, which acts as an RNA binding protein to enhance the mRNA stability of FTL and elevate its protein level. Knockdown of PD-L2 significantly promoted xCT-mediated ferroptosis induced by RSL3 or sorafenib on stiff substrate via FTL, whereas its overexpression abolished these upward trends. Notably, PD-L2 deletion in combination with sorafenib and anti-PD-1 antibody significantly sensitized HCC cells and blunted cancer growth in vivo. Additionally, we found the ferroptosis- and immune checkpoint-related prognostic genes that combined PD-L2, SLC7A11 and SYMD3 well predict the clinical efficacy of sorafenib in patients with HCC.

CONCLUSION

These findings expand our understanding of the mechanics-dependent PD-L2 role in ferroptosis, cancer progression and resistance, providing a basis for the clinical translation of PD-L2 as a therapeutic target or diagnostic biomarker.

Deciphering the dynamics: Exploring the impact of mechanical forces on histone acetylation

Living cells navigate a complex landscape of mechanical cues that influence their behavior and fate, originating from both internal and external sources. At the molecular level, the translation of these physical stimuli into cellular responses relies on the intricate coordination of mechanosensors and transducers, ultimately impacting chromatin compaction and gene expression. Notably, epigenetic modifications on histone tails govern the accessibility of gene-regulatory sites, thereby regulating gene expression. Among these modifications, histone acetylation emerges as particularly responsive to the mechanical microenvironment, exerting significant control over cellular activities. However, the precise role of histone acetylation in mechanosensing and transduction remains elusive due to the complexity of the acetylation network. To address this gap, our aim is to systematically explore the key regulators of histone acetylation and their multifaceted roles in response to biomechanical stimuli. In this review, we initially introduce the ubiquitous force experienced by cells and then explore the dynamic alterations in histone acetylation and its associated co-factors, including HDACs, HATs, and acetyl-CoA, in response to these biomechanical cues. Furthermore, we delve into the intricate interactions between histone acetylation and mechanosensors/mechanotransducers, offering a comprehensive analysis. Ultimately, this review aims to provide a holistic understanding of the nuanced interplay between histone acetylation and mechanical forces within an academic framework.

Exploiting Matrix Stiffness to Overcome Drug Resistance

Drug resistance is arguably one of the biggest challenges facing cancer research today. Understanding the underlying mechanisms of drug resistance in tumor progression and metastasis are essential in developing better treatment modalities. Given the matrix stiffness affecting the mechanotransduction capabilities of cancer cells, characterization of the related signal transduction pathways can provide a better understanding for developing novel therapeutic strategies. In this review, we aimed to summarize the recent advancements in tumor matrix biology in parallel to therapeutic approaches targeting matrix stiffness and its consequences in cellular processes in tumor progression and metastasis. The cellular processes governed by signal transduction pathways and their aberrant activation may result in activating the epithelial-to-mesenchymal transition, cancer stemness, and autophagy, which can be attributed to drug resistance. Developing therapeutic strategies to target these cellular processes in cancer biology will offer novel therapeutic approaches to tailor better personalized treatment modalities for clinical studies.

Matrix stiffness-dependent regulation of immunomodulatory genes in human MSCs is associated with the lncRNA CYTOR

Cell-matrix interactions in 3D environments significantly differ from those in 2D cultures. As such, mechanisms of mechanotransduction in 2D cultures are not necessarily applicable to cell-encapsulating hydrogels that resemble features of tissue architecture. Accordingly, the characterization of molecular pathways in 3D matrices is expected to uncover insights into how cells respond to their mechanical environment in physiological contexts, and potentially also inform hydrogel-based strategies in cell therapies. In this study, a bone marrow-mimetic hydrogel was employed to systematically investigate the stiffness-responsive transcriptome of mesenchymal stromal cells. High matrix rigidity impeded integrin-collagen adhesion, resulting in changes in cell morphology characterized by a contractile network of actin proximal to the cell membrane. This resulted in a suppression of extracellular matrix-regulatory genes involved in the remodeling of collagen fibrils, as well as the upregulation of secreted immunomodulatory factors. Moreover, an investigation of long noncoding RNAs revealed that the cytoskeleton regulator RNA (CYTOR) contributes to these 3D stiffness-driven changes in gene expression. Knockdown of CYTOR using antisense oligonucleotides enhanced the expression of numerous mechanoresponsive cytokines and chemokines to levels exceeding those achievable by modulating matrix stiffness alone. Taken together, our findings further our understanding of mechanisms of mechanotransduction that are distinct from canonical mechanotransductive pathways observed in 2D cultures.

Sustained Strain Applied at High Rates Drives Dynamic Tensioning in Epithelial Cells

Epithelial cells experience long lasting loads of different magnitudes and rates. How they adapt to these loads strongly impacts tissue health. Yet, much remains unknown about their stress evolution under sustained strain. Here, by subjecting cell pairs to sustained strain, we report a bimodal stress response, where in addition to the typically observed stress relaxation, a subset of cells exhibits a dynamic tensioning process with significant elevation in stress within 100s, resembling active pulling-back in muscle fibers. Strikingly, the fraction of cells exhibiting tensioning increases with increasing strain rate. The tensioning response is accompanied by actin remodeling, and perturbation to actin abrogates it, supporting cell contractility's role in the response. Collectively, our data show that epithelial cells adjust their tensional states over short timescales in a strain-rate dependent manner to adapt to sustained strains, demonstrating that the active pulling-back behavior could be a common protective mechanism against environmental stress.

Contactless magnetically responsive injectable hydrogel for aligned tissue regeneration

Cellular alignment plays a pivotal role in several human tissues, including skeletal muscle, spinal cord and tendon. Various techniques have been developed to control cellular alignment using 3D biomaterials. However, the majority of 3D-aligned scaffolds require invasive surgery for implantation. In contrast, injectable hydrogels provide a non-invasive delivery method, gaining considerable attention for the treatment of diverse conditions, including osteochondral lesions, volumetric muscle loss, and traumatic brain injury. We engineered a biomimetic hydrogel with magnetic responsiveness by combining gellan gum, hyaluronic acid, collagen, and magnetic nanoparticles (MNPs). Collagen type I was paired with MNPs to form magnetic collagen bundles (MCollB), allowing the orientation control of these bundles within the hydrogel matrix through the application of a remote low-intensity magnetic field. This resulted in the creation of an anisotropic architecture. The hydrogel mechanical properties were comparable to those of human soft tissues, such as skeletal muscle, and proof of the aligned hydrogel concept was demonstrated. In vitro findings confirmed the absence of toxicity and pro-inflammatory effects. Notably, an increased fibroblast cell proliferation and pro-regenerative activation of macrophages were observed. The in-vivo study further validated the hydrogel biocompatibility and demonstrated the feasibility of injection with rapid in situ gelation. Consequently, this magnetically controlled injectable hydrogel exhibits significant promise as a minimally invasive, rapid gelling and effective treatment for regenerating various aligned human tissues.

Silk fibroin microgrooved zirconia surfaces improve connective tissue sealing through mediating glycolysis of fibroblasts

The use of zirconia has significantly enhanced the aesthetic outcomes of implant restorations. However, peri-implantitis remains a challenge to long-term functionality of implants. Unlike the perpendicularly arranged collagen fibers in periodontal tissue, those in peri-implant tissue lie parallel to the abutment surface and contain fewer fibroblasts, making them more prone to inflammation. Studies have shown that microgroove structures on implant abutments could improve surrounding soft tissue structure. However, creating precise microgrooves on zirconia without compromising its mechanical integrity is technically challenging. In this study, we applied inkjet printing, an additive manufacturing technique, to create stable silk fibroin microgroove (SFMG) coatings of various dimensions on zirconia substrates. SFMG significantly improved the hydrophilicity of zirconia and showed good physical and chemical stability. The SFMG with 90 μm interval and 10 μm depth was optimal in promoting the proliferation, alignment, and extracellular matrix production of human gingival fibroblasts (HGFs). Moreover, the in vitro results revealed that SFMG stimulated key glycolytic enzyme gene expression in HGFs via the PI3K-AKT-mTOR pathway. Additionally, the in vivo results of histological staining of peri-abutments soft tissue showed that SFMG promoted the vertical alignment of collagen fibers relative to the abutment surface, improving connective tissue sealing around the zirconia abutment. Our results indicated that SFMG on zirconia can enhance HGF proliferation, migration and collagen synthesis by regulating glycolysis though PI3K-AKT-mTor pathway, thereby improving connective tissue sealing.

Ultrasound-triggered three dimensional hyaluronic acid hydrogel promotes in vitro and in vivo reprogramming into induced pluripotent stem cells

Cellular reprogramming technologies have been developed with different physicochemical factors to improve the reprogramming efficiencies of induced pluripotent stem cells (iPSCs). Ultrasound is a clinically applied noncontact biophysical factor known for regulating various cellular behaviors but remains uninvestigated for cellular reprogramming. Here, we present a new reprogramming strategy using low-intensity ultrasound (LIUS) to improve cellular reprogramming of iPSCs in vitro and in vivo. Under 3D microenvironment conditions, increased LIUS stimulation shows enhanced cellular reprogramming of the iPSCs. The cellular reprogramming process facilitated by LIUS is accompanied by increased mesenchymal to epithelial transition and histone modification. LIUS stimulation transiently modulates the cytoskeletal rearrangement, along with increased membrane fluidity and mobility to increase HA/CD44 interactions. Furthermore, LIUS stimulation with HA hydrogel can be utilized in application of both human cells and in vivo environment, for enhanced reprogrammed cells into iPSCs. Thus, LIUS stimulation with a combinatorial 3D microenvironment system can improve cellular reprogramming in vitro and in vivo environments, which can be applied in various biomedical fields.

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

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

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.

Cancer Metastasis-on-a-Chip for Modeling Metastatic Cascade and Drug Screening

Microfluidic chips are valuable tools for studying intricate cellular and cell-microenvironment interactions. Traditional in vitro cancer models lack accuracy in mimicking the complexities of in vivo tumor microenvironment. However, cancer-metastasis-on-a-chip (CMoC) models combine the advantages of 3D cultures and microfluidic technology, serving as powerful platforms for exploring cancer mechanisms and facilitating drug screening. These chips are able to compartmentalize the metastatic cascade, deepening the understanding of its underlying mechanisms. This article provides an overview of current CMoC models, focusing on distinctive models that simulate invasion, intravasation, circulation, extravasation, and colonization, and their applications in drug screening. Furthermore, challenges faced by CMoC and microfluidic technologies are discussed, while exploring promising future directions in cancer research. The ongoing development and integration of these models into cancer studies are expected to drive transformative advancements in the field.

Molecular dynamics simulations reveal how vinculin refolds partially unfolded talin rod helices to stabilize them against mechanical force

Vinculin binds to specific sites of mechanically unfolded talin rod domains to reinforce the coupling of the cell's exterior to its force generation machinery. Force-dependent vinculin-talin complexation and dissociation was previously observed as contraction or extension of the unfolded talin domains respectively using magnetic tweezers. However, the structural mechanism underlying vinculin recognition of unfolded vinculin binding sites (VBSs) in talin remains unknown. Using molecular dynamics simulations, we demonstrate that a VBS dynamically refolds under force, and that vinculin can recognize and bind to partially unfolded VBS states. Vinculin binding enables refolding of the mechanically strained VBS and stabilizes its folded α-helical conformation, providing resistance against mechanical stress. Together, these results provide an understanding of a recognition mechanism of proteins unfolded by force and insight into the initial moments of how vinculin binds unfolded talin rod domains during the assembly of this mechanosensing meshwork.

Integrin signalling in joint development, homeostasis and osteoarthritis

Integrins are key regulators of cell-matrix interactions during joint development and joint tissue homeostasis, as well as in the development of osteoarthritis (OA). The signalling cascades initiated by the interactions of integrins with a complex network of extracellular matrix (ECM) components and intracellular adaptor proteins orchestrate cellular responses necessary for maintaining joint tissue integrity. Dysregulated integrin signalling, triggered by matrix degradation products such as matrikines, disrupts this delicate balance, tipping the scales towards an environment conducive to OA pathogenesis. The interplay between integrin signalling and growth factor pathways further underscores the multifaceted nature of OA. Moreover, emerging insights into the role of endocytic trafficking in regulating integrin signalling add a new layer of complexity to the understanding of OA development. To harness the therapeutic potential of targeting integrins for mitigation of OA, comprehensive understanding of their molecular mechanisms across joint tissues is imperative. Ultimately, deciphering the complexities of integrin signalling will advance the ability to treat OA and alleviate its global burden.