Preparation of hydrogel substrates with tunable mechanical properties

LPAR3 and COL8A1, as matrix stiffness-related biomarkers, promote nasopharyngeal carcinoma metastasis by triggering EMT and angiogenesis

Matrix stiffness affects the progression of nasopharyngeal carcinoma, but the underlying mechanism is still unknown. Here, we demonstrated that nasopharyngeal carcinoma tissues with distant metastasis contain large collagen deposits and strong matrix stiffness. First, we performed RNA-seq analysis of nasopharyngeal carcinoma cells cultured on polyacrylamide hydrogel systems and found that LPAR3 and COL8A1 are potential matrix stiffness markers. Based on in vivo and in vitro experiments, matrix stiffness mainly affected tumor metastasis rather than proliferation. Subsequently, we found that matrix stiffness triggers the formation of epithelial-mesenchymal transition by increasing the expression of LPAR3 in nasopharyngeal carcinoma, which is related to metastasis. In addition, matrix stiffness promotes the expression of COL8A1 secreted by nasopharyngeal carcinoma and is related to tumor angiogenesis. Simultaneous inhibition of LPAR3 and COL8A1 genes significantly reduced nasopharyngeal carcinoma invasion and metastasis. Based on the investigation, we confirmed that matrix stiffness governs the progression of nasopharyngeal carcinoma and that LPAR3 and COL8A1, as matrix stiffness related biomarkers, promote nasopharyngeal carcinoma metastasis by inducing epithelial-mesenchymal transition and angiogenesis. Overall, the in-depth exploration of matrix stiffness may provide a strategy for clinical treatment intervention and provide promising targets for clinical nasopharyngeal carcinoma treatment.

Stiffness regulates extracellular matrix synthesis in fibroblasts by DDR1-TGF-β/STAT3 mechanotransduction axis

For a long time, research on atherosclerosis (AS) has mainly focused on endothelial cells (ECs) and smooth muscle cells (SMCs) in blood vessels. Fibroblasts, however, being the major component in adventitia, little is known about their role. Fibroblasts are highly plastic cells, capable of undergoing phenotypic changes in response to various extracellular signals. Once activated, fibroblasts can promote fibrosis by altering the secretion of extracellular matrix (ECM). In this study, the effect of ECM stiffness on fibroblasts was investigated. Polyacrylamide (PA) gels with varying elastic moduli (1 kPa, 20 kPa and 100 kPa) were used as models for matrix stiffness. Human fibroblasts were cultured on these substrates, and their phenotypic and functional changes were examined. The data revealed that a collagen-binding receptor, Discoidin Domain Receptor 1 (DDR1), plays a central role in sensing mechanical stimuli from ECM. Matrix stiffness-induced phosphorylation of DDR1 suppresses the synthesis of ECM proteins in fibroblasts. The expression of ECM proteins on the 1 kPa substrate was significantly higher than that on the 20 kPa and 100 kPa substrates, while the phosphorylation level of DDR1 was notably reduced. After knocking out DDR1, the difference in ECM proteins expression among the three substrates with different stiffness levels disappeared. The signal transduction from DDR1 to ECM synthesis is mediated by the TGF-β/STAT3 signaling axis. Our study reveals how matrix stiffness regulates the synthesis of ECM in fibroblasts and paves the way for understanding the regulation of fibrotic process in the pathogenesis of AS.

Mechanomemory after short episodes of intermittent stresses induces YAP translocation via increasing F-actin

How forces and mechanics influence and regulate living cells remains elusive. Mechanomemory, the response to a mechanical perturbation that persists after the perturbation is removed, is believed to be a key to understanding the impact of forces and mechanics on cell functions. Recently, our lab has demonstrated the presence of mechanomemory that lasts for ∼30 min after applying external stress via integrins. Herein, we test the hypothesis that applications of short intermittent episodes of stress exert long-term effects on mechanomemory via the process of mechanotransduction. An Arginine-Glycine-Aspartic acid (RGD)-peptides-coated 4-μm magnetic bead was bound to the integrin receptors to apply stresses to the surface of a Chinese Hamster Ovary cell. At the same stress magnitude and frequency (15 Pa at 0.3 Hz), multiple cycles of externally applied intermittent 2 or 10 min stresses with 15 min intervals, 10 min stresses with 10 min intervals, or a 30 min stress plus a 30 min load-free interval increased nuclear translocation of YAP (Yes-Associated Protein) and Ctgf gene expression, like that by a 60 min continuous stress, but a 30 min continuous stress did not. Short durations of intermittent stresses increased F-actin in the cytoplasm, which coincided with the elevated YAP translocation. Inhibiting F-actin or actomyosin but not microtubules blocked stress-induced YAP translocation to the nucleus. Cells on soft substrates translocate more YAP than on stiff substrates after external load release. These results highlight the impact of multiple intermittent stresses-induced cytoplasmic mechanomemory on cell biological functions via YAP translocation.

A crosstalk between adhesion and phagocytosis integrates macrophage functions into their microenvironment

Phagocytosis is the process of actin-dependent internalization and degradation of large particles. Macrophages, which are professional phagocytes, are present in all tissues and are, thus, exposed to environments with different mechanical properties. How mechanical cues from macrophages' environment affect their ability to phagocytose and, in turn, how phagocytosis influences how phagocytic cells interact with their environment remain poorly understood. We found that the ability of macrophages to perform phagocytosis varied with the substrate stiffness. Using live traction force microscopy, we showed that phagocytosing macrophages applied more dynamic traction forces to their substrate. In addition, integrin-mediated phagocytosis triggered a transient loss of podosomes that was associated with decreased degradation of the extracellular matrix, concomitantly with RhoA activation and F-actin recruitment at phagocytic cups. Overall, these results highlight a crosstalk between macrophage phagocytosis and cell adhesion. Mechanical properties of the microenvironment influence phagocytosis, which, in turn, impacts how macrophages interact with their surroundings.

Piezo1-induced durotaxis of pancreatic stellate cells depends on TRPC1 and TRPV4 channels

Pancreatic stellate cells (PSCs) are primarily responsible for producing the stiff tumor tissue in pancreatic ductal adenocarcinoma (PDAC). Thereby, PSCs generate a stiffness gradient between the healthy pancreas and the tumor. This gradient induces durotaxis, a form of directional cell migration driven by differential stiffness. However, the molecular sensors behind durotaxis are still unclear. To investigate the role of mechanosensitive ion channels in PSC durotaxis, we established a two-dimensional stiffness gradient mimicking PDAC. Using pharmacological and genetic methods, we investigated the contribution of the ion channels Piezo1, TRPC1 and TRPV4 in PSC durotaxis. We found that PSC migration towards a stiffer substrate is diminished by altering Piezo1 activity. Moreover, disrupting TRPC1 along with TRPV4 abolishes PSC durotaxis even when Piezo1 is functional. Our results demonstrate that optimal PSC durotaxis requires an intermediary level of ion channel activity, which we simulated via a numerically discretized mathematical model. These findings suggest that mechanosensitive Piezo1 channels detect the differential stiffness microenvironment. The resulting intracellular signals are amplified by TRPV4 and TRPC1 channels to guide efficient PSC durotaxis.

Suppression of METTL3 expression attenuated matrix stiffness-induced vaginal fibroblast-to-myofibroblast differentiation and abnormal modulation of the extracellular matrix in pelvic organ prolapse

BACKGROUND

Fibrosis of the connective tissue in the vaginal wall predominates in pelvic organ prolapse (POP), which is characterized by excessive fibroblast-to-myofibroblast differentiation and abnormal deposition of the extracellular matrix (ECM). Our study aimed to investigate the effect of ECM stiffness on vaginal fibroblasts and to explore the role of methyltransferase 3 (METTL3) in the development of POP.

METHODS

Polyacrylamide hydrogels were applied to create an ECM microenvironment with variable stiffness to evaluate the effects of ECM stiffness on the proliferation, differentiation, and expression of ECM components in vaginal fibroblasts. METTL3 small interfering RNA and an overexpression vector were transfected into vaginal fibroblasts to evaluate the effects of METTL3 silencing and overexpression on matrix stiffness-induced vaginal fibroblast-to-myofibroblast differentiation and abnormal modulation of the ECM. Both procedures were detected by 5-ethynyl-2'-deoxyuridine (EdU) staining, Western blotting (WB), quantitative real-time polymerase chain reaction (RT-qPCR), and immunofluorescence (IF).

RESULTS

Vaginal fibroblasts from POP patients exhibited increased proliferation ability, increased expression of α-smooth muscle actin (α-SMA), decreased expression of collagen I/III, and significantly decreased expression of tissue inhibitors of matrix metalloproteinases (TIMPs) in the stiff matrix ( P <0.05). Compared with those from non-POP patients, vaginal wall tissues from POP patients demonstrated a significant increase in METTL3 content ( P <0.05). However, silencing METTL3 expression in vaginal fibroblasts with high ECM stiffness resulted in decreased proliferation ability, decreased α-SMA expression, an increased ratio of collagen I/III, and increased TIMP1 and TIMP2 expression. Conversely, METTL3 overexpression significantly promoted the process of increased proliferation ability, increased α-SMA expression, decreased ratio of collagen I/III and decreased TIMP1 and TIMP2 expression in the soft matrix ( P <0.05).

CONCLUSIONS

Elevated ECM stiffness can promote excessive proliferation, differentiation, and abnormal ECM modulation, and the expression of METTL3 plays an important role in alleviating or aggravating matrix stiffness-induced vaginal fibroblast-to-myofibroblast differentiation and abnormal ECM modulation.

Golgi Localized Arl15 Regulates Cargo Transport and Cell Adhesion

Arf-like GTPases (Arls) regulate membrane trafficking and cytoskeletal organization. Genetic studies predicted a role for Arl15 in type-2 diabetes, insulin resistance, adiposity, and rheumatoid arthritis. Cell biological studies implicated Arl15 in regulating various cellular processes, including magnesium homeostasis and TGFβ signaling. However, the role of Arl15 in vesicular transport is poorly defined. We evaluated the function of Arl15 using techniques to quantify cargo trafficking to mechanobiology. Fluorescence microscopy of stably expressing Arl15-GFP HeLa cells showed its localization primarily to the Golgi and cell surface. The depletion of Arl15 causes the mislocalization of selective Golgi cargo, such as caveolin-2 and STX6, in the cells. Consistently, expression of GTPase-independent dominant negative mutants of Arl15 (Arl15V80A,A86L,E122K and Arl15C22Y,C23Y) results in mislocalization of caveolin-2 and STX6 from the Golgi. However, the localization of Arl15 to the Golgi is dependent on its palmitoylation and Arf1-dependent Golgi integrity. At the cellular level, Arl15 depleted cells display enhanced cell spreading and adhesion strength. Traction force microscopy experiments revealed that Arl15 depleted cells exert higher tractions and generate multiple focal adhesion points during the initial phase of cell adhesion compared to control cells. Collectively, these studies implicate a functional role for Arl15 in regulating cargo transport from the Golgi to regulate cell surface processes.

Vinculin haploinsufficiency impairs integrin-mediated costamere remodeling on stiffer microenvironments

Vinculin (VCL) is a key adapter protein located in force-bearing costamere complexes, which mechanically couples the sarcomere to the ECM. Heterozygous vinculin frameshift genetic variants can contribute to cardiomyopathy when external stress is applied, but the mechanosensitive pathways underpinning VCL haploinsufficiency remain elusive. Here, we show that in response to extracellular matrix stiffening, heterozygous loss of VCL disrupts force-mediated costamere protein recruitment, thereby impairing cardiomyocyte contractility and sarcomere organization. Analyses of human pluripotent stem cell-derived cardiomyocytes (hPSC-CMs) harboring either VCL c.659dupA or VCL c.74del7 heterozygous VCL frameshift variants revealed that these VCL mutant hPSC-CMs exhibited heightened contractile strain energy, morphological maladaptation, and sarcomere disarray on stiffened matrix. Mechanosensitive recruitment of costameric talin 2, paxillin, focal adhesion kinase, and α-actinin was significantly reduced in vinculin variant cardiomyocytes. Despite poorly formed costamere complexes and sarcomeres, elevated expression of integrin β1 and cortical actin on stiff substrates may rescue force transmission on stiff substrates, an effect that is recapitulated in WT CMs by ligating integrin receptors and blocking mechanosensation. Together, these data support that heterozygous loss of VCL contributes to adverse cardiomyocyte remodeling by impairing adhesion-mediated force transmission from the costamere to the cytoskeleton. (191 words).

Local soft niches in mechanically heterogeneous primary tumors promote brain metastasis via mechanotransduction-mediated HDAC3 activity

Tumor cells with organ-specific metastasis traits arise in primary lesions with substantial variations of local niche mechanics owing to intratumoral heterogeneity. However, the roles of mechanically heterogeneous primary tumor microenvironment in metastatic organotropism remain an enigma. This study reports that persistent priming in soft but not stiff niches that mimic primary tumor mechanical heterogeneity induces transcriptional reprogramming reminiscent of neuron and promotes the acquisition of brain metastatic potential. Soft-primed cells generate brain metastases in vivo through enhanced transendothelial migration across blood-brain barrier and brain colonization, which is further supported by the findings that tumor cells residing in local soft niches of primary xenografts exhibit brain metastatic tropism. Mechanistically, soft niches suppress cytoskeleton-nucleus-mediated mechanotransduction, which promotes histone deacetylase 3 activity. Inhibiting histone deacetylase 3 abolishes niche softness-induced brain metastatic ability. Collectively, this study uncovers a previously unappreciated role of local niche softness within primary tumors in brain metastasis, highlighting the significance of primary tumor mechanical heterogeneity in metastatic organotropism.

PIEZO1-Mediated Calcium Signaling and Podocyte Injury in Diabetic Kidney Disease

Key Points

Background

Diabetic kidney disease (DKD) is characterized by progressive injury to glomerular podocytes due to sustained mechanical stress within the glomerulus. Piezo proteins, acting as cellular mechanosensors, play a pivotal role in mechanotransduction by sensing mechanical forces and regulating intracellular ion flux. This study investigates the role of Piezo1 in the progression of DKD and its mechanistic involvement in podocyte injury.

Methods

Podocyte-specific Piezo1 knockout mice were generated using the streptozotocin plus high-fat diet model of DKD. In vitro studies included the use of Piezo1 inhibitors to assess calcium influx, podocyte cytoskeletal rearrangement, and apoptosis under stiff matrix conditions. In addition, NF of activated T-cell cytoplasmic 1 (NFATc1) and transient receptor potential cation channel 6 (TRPC6) signaling pathways were explored to establish their role in Piezo1-mediated podocyte injury. Adeno-associated virus TRPC6 was used to overexpress TRPC6 in podocyte-specific Piezo1 knockout mice to assess the in vivo interaction between Piezo1 and TRPC6.

Results

Podocyte-specific deletion of Piezo1 significantly ameliorated the progression of DKD in diabetic mice. Inhibition of Piezo1 reduced calcium influx, cytoskeletal rearrangement, and podocyte apoptosis in vitro. Mechanistically, Piezo1 activation triggered a signaling loop involving NFATc1 and TRPC6, leading to increased calcium influx, perpetuating podocyte injury. TRPC6 overexpression in vivo counteracted the protective effects of Piezo1 deletion, confirming the critical role of the Piezo1/NFATc1/TRPC6 axis in DKD progression.

Conclusions

Piezo1 plays a key mechanosensory role in podocyte injury during DKD progression by mediating calcium influx and activating the NFATc1/TRPC6 signaling pathway.

Optical, contact-free assessment of brain tissue stiffness and neurodegeneration

Dementia affects a large proportion of the world's population. Approaches that allow for early disease detection and non-invasive monitoring of disease progression are desperately needed. Current approaches are centred on costly imaging technologies such as positron emission tomography and magnetic resonance imaging. We propose an alternative approach to assess neurodegeneration based on diffuse correlation spectroscopy (DCS), a remote and optical sensing technique. We employ this approach to assess neurodegeneration in mouse brains from healthy animals and those with prion disease. We find a statistically significant difference in the optical speckle decorrelation times between prion-diseased and healthy animals. We directly calibrated our DCS technique using hydrogel samples of varying Young's modulus, indicating that we can optically measure changes in the brain tissue stiffness in the order of 60 Pa (corresponding to a 1 s change in speckle decorrelation time). DCS holds promise for contact-free assessment of tissue stiffness alteration due to neurodegeneration, with a similar sensitivity to contact-based (e.g. nanoindentation) approaches.

Runx2-NLRP3 axis orchestrates matrix stiffness-evoked vascular smooth muscle cell inflammation

Arterial stiffening is a hallmark of chronic kidney disease (CKD)-related cardiovascular events and is primarily attributed to the elevated matrix stiffness. Stiffened arteries are accompanied by low-grade inflammation, but the causal effects of matrix stiffness on inflammation remain unknown. For analysis of the relationship between arterial stiffness and vascular inflammation, pulse-wave velocity (PWV) and aortic inflammatory markers were analyzed in an adenine-induced mouse model of CKD in chronological order. Compared with their control littermates, mice with CKD showed elevated arterial stiffness at the early stage of disease progression, which preceded the onset of vascular inflammation. Correspondingly, the increase of matrix stiffness induced vascular smooth muscle cells (VSMCs) to transdifferentiate into an inflammatory phenotype, as indicated by the increased expression and secretion of MCP-1, IL-6, IL-1β, and IL-18. RNA-sequencing analysis of stiff matrix-cultured VSMCs and bioinformatics analysis with the ChIP-Atlas database revealed the potential involvement of the transcription factor Runx2. The expression and the nuclear localization of Runx2 were significantly increased in stiff matrix-cultured VSMCs. High-throughput ChIP-sequencing and promoter luciferase assays further revealed that NLRP3 was directly transcriptionally regulated by Runx2. The inhibition of Runx2 or NLRP3 inflammasome abrogated the proinflammatory effect of matrix stiffening on VSMCs. Together, these data revealed that arterial stiffness precedes vascular inflammatory responses in CKD mice and that the Runx2-NLRP3 axis orchestrates matrix stiffness and the VSMC inflammatory phenotype, which may contribute to the pathogenic role in arterial stiffness-related vascular inflammation and CKD-related cardiovascular complications.NEW & NOTEWORTHY As a hallmark of chronic kidney disease (CKD), arterial stiffening is related to increased vascular inflammation and cardiovascular morbidity, whereas the underlying mechanism is unclear. The study demonstrates that increased arterial stiffness precedes the onset of vascular inflammation, and matrix stiffness stimulates the transdifferentiation of vascular smooth muscle cells (VSMCs) to an inflammatory phenotype via activating Runx2-NLRP3 signaling, which provides novel insights into CKD-related cardiovascular disorder treatment.

Cadherins and growth factor receptors - ligand-selective mechano-switches at cadherin junctions

This study investigated possible mechanisms underlying differences between heterophilic and homophilic cadherin adhesions that influence intercellular mechanics and multicellular organization. Results suggest that homophilic cadherin ligation selectively activates force transduction, such that resulting signaling and mechano-transduction amplitudes are independent of cadherin-binding affinities. Epithelial (E-) and neural (N-)cadherin cooperate with distinct growth factors to mechanically activate force transduction cascades. Prior results have demonstrated that E-cadherin and epidermal growth factor receptor form force-sensitive complexes at intercellular junctions. Here, we show that the reconstitution of N-cadherin force transduction requires the co-expression of N-cadherin and fibroblast growth factor receptor. Mechanical measurements further demonstrated that homophilic ligation initiates receptor tyrosine kinase-dependent force transduction cascades, but heterophilic cadherin ligands fail to activate signaling or generate stereotypical mechano-transduction signatures. The all-or-nothing contrast between mechano-transduction by heterophilic versus homophilic cadherin adhesions supersedes differences in cadherin adhesion strength. This mechano-selectivity impacts cell spreading and traction generation on cadherin substrates. Homophilic ligation appears to be a key that selectively unlocks cadherin mechano-transduction. These findings might reconcile the roles of cadherin recognition and cell mechanics in the organization of multicellular assemblies.

Enhancing Tribo-Rehydration in Hydrogel by Brush-Like Surface and Its Modulation

Synovial exudation, creeping, and lubrication failure in natural cartilage under a long-term normal loading can be counteracted by a tribo-rehydration (sliding-induced rehydration) phenomenon. Hydrogels, as porous materials, can also restore interfacial lubrication and overcome creep through this strategy. At appropriate sliding velocities, water molecules at the interface contact inlet are driven by hydrodynamic pressures into the porous network to resist creep extrusion. In this work, polyelectrolyte brushes were grafted onto the hydrogel surface to construct a loose, large-pore network structure and improve the interface hydration, enhancing the tribo-rehydration. Compared to the gel without grafted brushes, the grafted surface facilitated the water molecules flowing into the gel network, and the hydrated brushes effectively anchor water at the interface and increase their enrichment at the contact surface for enhancing the rehydration. Finally, the structure of the polymer brush was modulated by multivalent ions to explore the relationship between the rehydration and structure. These results indicate that constructing a loose, hydrated polymer brush layer on the gel surface significantly enhances its tribo-rehydration capability. This strategy can not only improve the load-bearing capacity and resistance to creep of the hydrogel but also effectively restore and maintain long-term lubrication.

Cell confinement by micropatterning induces phenotypic changes in cancer-associated fibroblasts

Recent advances in single-cell studies have revealed the vast transcriptomic heterogeneity of cancer-associated fibroblasts (CAFs), with each subset likely having unique roles in the tumor microenvironment. However, it is still unclear how different CAF subsets should be cultured in vitro to recapitulate their in vivo phenotype. The inherent plasticity of CAFs, or their ability to dynamically change their phenotype in response to different environmental stimuli, makes it highly challenging to induce and maintain a specific CAF state in vitro. In this study, we investigated how cell shape and confinement on two-dimensional culture substrates with different stiffnesses influence CAF transcriptomic profile and phenotype. Using micropatterning of polyacrylamide hydrogels to induce shape- and confinement-dependent changes in cell morphology, we observed that micropatterned CAFs exhibited phenotypic shifts towards more desmoplastic and inflammatory CAF subsets. Additionally, micropatterning enabled control over a range of CAF-specific markers and pathways. Lastly, we report how micropatterned and non-micropatterned CAFs respond differently to anti-cancer drugs, highlighting the importance of phenotype-oriented therapy that considers for CAF plasticity and regulatory networks. Control over CAF morphology offers a unique opportunity to establish highly robust CAF phenotypes in vitro, facilitating deeper understanding of CAF plasticity, heterogeneity, and development of novel therapeutic targets. STATEMENT OF SIGNIFICANCE: Cancer-associated fibroblasts (CAFs) are the dominant stromal cell type in many cancers, and recent studies have revealed that they are highly heterogeneous and comprise several subpopulations. It is still unclear how different subsets of CAFs should be cultured in vitro to recapitulate their in vivo phenotype. In this study, we investigated how cell shape and confinement affect CAF transcriptomic profile and phenotype. We report that micropatterned CAFs resemble desmoplastic and inflammatory CAF subsets observed in vivo and respond differently to anti-cancer drugs as compared to non-patterned CAFs. Control over CAF morphology enables the generation of highly robust CAF phenotypes in vitro, facilitating deeper understanding of CAF plasticity and heterogeneity.

Rapid Fabrication of Polyvinyl Alcohol Hydrogel Foams With Encapsulated Mesenchymal Stem Cells for Chronic Wound Treatment

Chronic wounds present a major healthcare challenge around the world, and significant hurdles remain in their effective treatment due to limitations in accessible treatment options. Mesenchymal stem cells (MSCs) with multifunctional differentiation and modulatory properties have been delivered to chronic wounds to enhance closure but have limited engraftment when delivered without a scaffold. In this study, hybrid porous hydrogel foams composed of modified polyvinyl alcohol and gelatin were developed that are suitable for rapid and facile MSC encapsulation, fully degradable, and supportive of wound healing. Rapid fabrication and encapsulation within porous foams was achieved using a cytocompatible gas blowing process. The hybrid hydrogels have tunable degradation rates based on chemistry, with complete mass loss achieved within 2-6 weeks, which is compatible with chronic wound closure rates. High encapsulated A375 epithelial cell and MSC viability with maintained cell functionality over 2 weeks reveals the potential of these hydrogels to serve as cell delivery systems for chronic wound treatment. An ex vivo porcine skin wound model demonstrated enhanced healing after application of cell-laden hydrogel foams. Overall, hybrid hydrogel foams with encapsulated therapeutic cells have the capacity for robust wound healing and are a promising platform for chronic wound dressings.

CD44/Integrin β1 Association Drives Fast Motility on Hyaluronic Acid Substrates

In addition to proteins such as collagen (Col) and fibronectin, the extracellular matrix (ECM) is enriched with bulky proteoglycan molecules such as hyaluronic acid (HA). However, how ECM proteins and proteoglycans collectively regulate cellular processes has not been adequately explored. Here, we address this question by studying cytoskeletal and focal adhesion organization and dynamics on cells cultured on polyacrylamide hydrogels functionalized with Col, HA and a combination of Col and HA (Col/HA). We show that fastest migration on HA substrates is attributed to the presence of smaller and weaker focal adhesions. Integrinβ $\beta $ 1 co-localization and its association with CD44-which is the receptor for HA, and insensitivity of cell spreading to RGD on HA substrates suggests that focal adhesions on HA substrates are formed via integrin association with HA bound CD44. Consistent with this, adhesion formation and cell motility were inhibited when CD44 was knocked out. Collectively, our results suggest that association of integrinβ $\beta $ 1 with CD44 drives fast motility on HA substrates.

ASMI: An automated, low-cost indenter for soft matter

The automated soft matter indenter (ASMI) is a platform for rapidly performing mechanical characterization of samples with elastic moduli in the range 7 kPa to 67 MPa with a sample acquisition time between 1 and 10 min. It is a low-cost system based upon open-source software, a modified mill, and an educational force sensor with a total bill of materials <$500. This system tests batches of up to 96 samples based on a standard well-plate sample holder without requiring any human intervention. Using the ASMI, users can obtain mechanical data in a programmable manner that enables high-throughput workflows, precisely testing time-dependent phenomena, and integration with other processing steps for closed-loop optimization.

Borg5 restricts contractility and motility in epithelial MDCK cells

The Borg (or Cdc42EP) family consists of septin-binding proteins that are known to promote septin-dependent stress fibers and acto-myosin contractility. We show here that epithelial Borg5 (also known as Cdc42EP1) instead limits contractility, cell-cell adhesion tension and motility, as is required for the acquisition of columnar, isotropic cell morphology in mature MDCK monolayers. Borg5 depletion inhibited the development of the lateral F-actin cortex and stimulated microtubule-dependent leading-edge lamellae as well as radial stress fibers and, independently of the basal F-actin phenotype, caused anisotropy of apical surfaces within compacted monolayers. We determined that Borg5 limits colocalization of septin proteins with microtubules, and that like septin 2, Borg5 interacts with the rod-domain of myosin IIA (herein referring to the MYH9 heavy chain). The interaction of myosin IIA with Borg5 was reduced in the presence of septins. Because septins also mediate myosin activation, we propose that Borg5 limits contractility in MDCK cells in part by counteracting septin-associated myosin activity.

Experimental & numerical investigations of ultra-high-speed dynamics of optically induced droplet cavitation in soft materials

Perfluorocarbon (PFC) droplets represent a novel class of phase-shift contrast agent with promise in applications in biomedical and bioengineering fields. PFC droplets undergo a fast liquid-gas transition upon exposure to acoustic or optical triggering, offering a potential adaptable and versatile tool as contrast agent in diagnostic imaging and localized drug delivery vehicles in therapeutics systems. In this paper, we utilize advanced imaging techniques to investigate ultra-high-speed inertial dynamics and rectified quasi-static (low-speed) diffusion evolution of optically induced PFC droplet vaporization within three different hydrogels, each of different concentrations, examining effects such as droplet size and PFC core on bubble dynamics and material viscoelastic properties. Gelatin hydrogels reveal concentration-dependent impacts on bubble expansion and material elasticity. Embedding PFC droplets in gelatin increases internal pressure, resulting in higher equilibrium radius and continuous bubble growth during quasi-static evolution. Similar trends are observed in fibrin and polyacrylamide matrices, with differences in bubble behavior attributed to matrix properties and droplet presence. Interestingly, droplet size exhibits minimal impact on bubble expansion during inertial dynamics but influences quasi-static evolution, with larger droplets leading to continuous growth beyond 60 s. Furthermore, the core composition of PFC droplets significantly affects bubble behavior, with higher boiling point droplets exhibiting higher maximum expansion and faster quasi-static dissolution rates. Overall, the study sheds light on the intricate interplay between droplet characteristics, matrix properties, and multi-timescale bubble dynamics, offering valuable insights into their behavior within biomimetic hydrogels.

Hydrogel models of pancreatic adenocarcinoma to study cell mechanosensing

Pancreatic adenocarcinoma (PDAC) is the predominant form of pancreatic cancer and one of the leading causes of cancer-related death worldwide, with an extremely poor prognosis after diagnosis. High mortality from PDAC arises partly due to late diagnosis resulting from a lack of early-stage biomarkers and due to chemotherapeutic drug resistance, which arises from a highly fibrotic stromal response known as desmoplasia. Desmoplasia alters tissue mechanics, which triggers changes in cell mechanosensing and leads to dysregulated transcriptional activity and disease phenotypes. Hydrogels are effective in vitro models to mimic mechanical changes in tissue mechanics during PDAC progression and to study the influence of these changes on mechanosensitive cell responses. Despite the complex biophysical changes that occur within the PDAC microenvironment, carefully designed hydrogels can very closely recapitulate these properties during PDAC progression. Hydrogels are relatively inexpensive, highly reproducible and can be designed in a humanised manner to increase their relevance for human PDAC studies. In vivo models have some limitations, including species-species differences, high variability, expense and legal/ethical considerations, which make hydrogel models a promising alternative. Here, we comprehensively review recent advancements in hydrogel bioengineering for developing our fundamental understanding of mechanobiology in PDAC, which is critical for informing advanced therapeutics.

Mechanical properties of soft hydrogels: assessment by scanning ion-conductance microscopy and atomic force microscopy

The growing interest in biomimetic hydrogels is due to their successful applications in tissue engineering, 3D cell culturing and drug delivery. The major characteristics of hydrogels include swelling, porosity, degradation rate, biocompatibility, and mechanical properties. Poor mechanical properties can be regarded as the main limitation for the use of hydrogels in tissue engineering, and advanced techniques for its precise evaluation are of interest. The current research aims to demonstrate the suitability of scanning ion conductance microscopy (SICM) for assessing the stiffness of various hydrogels - Fmoc-FF peptide hydrogel, polyacrylamide and gelatin, - which differ by two orders of magnitude in Young's modulus (E). We provide a direct comparison between SICM measurements and atomic force microscopy (AFM) data, the latter being a widely used method for assessing the mechanical properties of scaffolds. The results of these methods showed good agreement, however, for materials with various stiffness two SICM-based approaches - application of hydrostatic pressure and application of intrinsic force - should be used. For hydrogels with Young's modulus of more than 2.5 kPa the application of SICM using hydrostatic pressure is recommended, whereas for soft materials with E ∼ 200-400 Pa the technique using intrinsic force can also be applied. We have shown that SICM and AFM methods can be used for the evaluation of the mechanical properties of soft hydrogels with nanometer resolution, while SICM is a completely non-invasive method, which requires a minimum influence on the sample structure.

Chemomechanical regulation of EZH2 localization controls epithelial-mesenchymal transition

The methyltransferase enhancer of zeste homolog 2 (EZH2) regulates gene expression, and aberrant EZH2 expression and signaling can drive fibrosis and cancer. However, it is not clear how chemical and mechanical signals are integrated to regulate EZH2 and gene expression. We show that culture of cells on stiff matrices in concert with transforming growth factor (TGF)-β1 promotes nuclear localization of EZH2 and an increase in the levels of the corresponding histone modification, H3K27me3, thereby regulating gene expression. EZH2 activity and expression are required for TGFβ1- and stiffness-induced increases in H3K27me3 levels as well as for morphological and gene expression changes associated with epithelial-mesenchymal transition (EMT). Inhibition of Rho associated kinase (ROCK) proteins or myosin II signaling attenuates TGFβ1-induced nuclear localization of EZH2 and decreases H3K27me3 levels in cells cultured on stiff substrata, suggesting that cellular contractility, in concert with a major cancer signaling regulator TGFβ1, modulates EZH2 subcellular localization. These findings provide a contractility-dependent mechanism by which matrix stiffness and TGFβ1 together mediate EZH2 signaling to promote EMT.

Sliding-Induced Rehydration in Hydrogels for Restoring Lubrication and Anticreeping Capability

Fluid exudation in cartilage under normal loading can be counteracted by a sliding-induced rehydration phenomenon, which has a hydrodynamic origin related to a wedge effect at the contact inlet. Similar to cartilage, hydrogels also exhibit tribological rehydration properties, and we mimic this phenomenon to restore hydration lubrication and overcome creeping. It occurs within a specific velocity range and is mainly dependent on the applied load and hydrogel network structures. Crucially, a certain velocity in the mixed lubrication regime can produce a hydrodynamic pressure peak at the wedge and drive the rehydration inflow to overcome the extrusion. At lower sliding velocities in the boundary lubrication regime, inflows are insufficient to counteract fluid exudation, whereas at higher velocities in the hydrodynamic lubrication regime, the inlet wedge effect would diminish. These results suggest that tribological rehydration offers a novel approach to enhancing load-bearing capacity and maintaining lubrication in the hydrogels.

Understanding Comorbidities of Respiratory Models as Novel Platforms for Drug Discovery

Chronic respiratory diseases affect over 450 million people worldwide and result in 4 million deaths per year. The majority of lung diseases are treated with drugs delivered directly to the lungs. However, there is bidirectional crosstalk between the lung and other organs/tissues in health and disease. This crosstalk supports targeting of extrapulmonary sites in addition to the lung to improve the comorbidities associated with lung disease. However, new preclinical in vivo and in vitro assays that model the human pathophysiology are required. In this review, we showcase the latest knowledge of the bidirectional relationship between the respiratory system and organs affected by comorbidities such as obesity and atherosclerosis. We also discuss the impact of new cell culture systems, including complex 3D culture models that may be used as platforms to generate disease insights and for drug discovery. This review highlights work presented by Respiratory and Inflammation Special Interest Group researchers as part of the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists (ASCEPT) annual scientific meeting in 2023.

Piezo1-mediated mechanotransduction enhances macrophage oxidized low-density lipoprotein uptake and atherogenesis

Macrophages in the vascular wall ingest and clear lipids, but abundant lipid accumulation leads to foam cell formation and atherosclerosis, a pathological condition often characterized by tissue stiffening. While the role of biochemical stimuli in the modulation of macrophage function is well studied, the role of biophysical cues and the molecules involved in mechanosensation are less well understood. Here, we use genetic and pharmacological tools to show extracellular oxidized low-density lipoproteins (oxLDLs) stimulate Ca2+ signaling through activation of the mechanically gated ion channel Piezo1. Moreover, macrophage Piezo1 expression is critical in the transduction of environmental stiffness and channel deletion suppresses, whereas a gain-of-function mutation exacerbates oxLDL uptake. Additionally, we find that depletion of myeloid Piezo1 protects from atherosclerotic plaque formation in vivo. Together, our study highlights an important role for Piezo1 and its respective mutations in macrophage mechanosensing, lipid uptake, and cardiovascular disease.

Advancements of Biomacromolecular Hydrogel Applications in Food Nutrition and Health

Hydrogels exhibit remarkable degradability, biocompatibility and functionality, which position them as highly promising materials for applications within the food and pharmaceutical industries. Although many relevant studies on hydrogels have been reported in the chemical industry, materials, and other fields, there have been few reviews on their potential applications in food nutrition and human health. This study aims to address this gap by reviewing the functional properties of hydrogels and assessing their value in terms of food nutrition and human health. The use of hydrogels in preserving bioactive ingredients, food packaging and food distribution is delved into specifically in this review. Hydrogels can serve as cutting-edge materials for food packaging and delivery, ensuring the preservation of nutritional activity within food products, facilitating targeted delivery of bioactive compounds and regulating the digestion and absorption processes in the human body, thereby promoting human health. Moreover, hydrogels find applications in in vitro cell and tissue culture, human tissue repair, as well as chronic disease prevention and treatment. These broad applications have attracted great attention in the fields of human food nutrition and health. Ultimately, this paper serves as a valuable reference for further utilization and exploration of hydrogels in these respective fields.

Molecular and spatial signatures of human and rat corpus cavernosum physiopathological processes at single-cell resolution

The composition and cellular heterogeneity of the corpus cavernosum (CC) microenvironment have been characterized, but the spatial heterogeneity at the molecular level remains unexplored. In this study, we integrate single-cell RNA sequencing (scRNA-seq) and spatial transcriptome sequencing to comprehensively chart the spatial cellular landscape of the human and rat CC under normal and disease conditions. We observe differences in the proportions of cell subtypes and marker genes between humans and rats. Based on the analysis of the fibroblast (FB) niche, we also find that the enrichment scores of mechanical force signaling vary across different regions and correlate with the spatial distribution of FB subtypes. In vitro, the soft and hard extracellular matrix (ECM) induces the differentiation of FBs into apolipoprotein (APO)+ FBs and cartilage oligomeric matrix protein (COMP)+ FBs, respectively. In summary, our study provides a cross-species and physiopathological transcriptomic atlas of the CC, contributing to a further understanding of the molecular anatomy and regulation of penile erection.

Mechanical properties of intercellular tunneling nanotubes formed by different mechanisms

Tunneling nanotubes (TNTs) that connect cells have been recognized as a pathway for long-range intercellular transport of diverse cargoes, including viruses, lysosomes or other organelles, Ca2+ and electrical signals. TNTs can initially be formed from thin finger-like actin assembly-driven protrusions or cell contacts and dislodgment. However, it remains unclear whether the mechanical properties of TNTs formed by these two mechanisms are the same. Here, we developed novel microoperation methods to investigate the mechanical properties of TNTs in HEK293 cells, in which the TNTs form from thin finger-like actin assembly-driven protrusions and C2C12 cells, in which the TNTs form through contact and cell dislodgment. We found that TNTs formed by the two mechanisms represent elastic elements with similar tensile strength. In both the HEK and C2C12 cells, the tensile strength of TNTs exhibited a distinct size dependence on their lengths and diameters. Disturbing the cytoskeleton or removing extracellular Ca2+ also changed their tensile strength. In addition, the stiffening of the extracellular matrix (ECM) enhanced the length, diameter and tensile strength of TNTs both in both HEK and C2C12 cells. Finally, a theoretical model was established to reveal the changes in the TNT's mechanical properties with its length, diameter and individual tunneling nanotubes (iTNT) number. This work not only gains insights into the properties of TNTs but also helps understand the dynamics of various cells.

Nanoscale Surface Chemical Patterning of Soft Polyacrylamide with Elastic Modulus Similar to Soft Tissue

Nanometer-scale control over surface functionalization of soft gels is important for a variety of applications including controlling interactions with cells for in vitro cell culture and for regenerative medicine. Recently, we have shown that it is possible to transfer a nanometer-thick precision functional polymer layer to the surface of relatively stiff polyacrylamide gels. Here, we develop a fundamental understanding of the way in which the precision polymer backbone participates in the polyacrylamide radical polymerization and cross-linking process, which enables us to generate high-efficiency transfer to much softer hydrogels (down to 5 kPa) with stiffness similar to that of soft tissue. This approach creates hydrogel surfaces with exposed nanostructured functional arrays that open the door to controlled ligand presentation on soft hydrogel surfaces.

Engineered Biomaterials and Model Systems to Study YAP/TAZ in Cancer

The transcriptional coactivators yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are master regulators involved in a multitude of cancer types and a wide range of tumorigenic events, including cancer stem cell renewal, invasion, metastasis, tumor precursor emergence, and drug resistance. YAP/TAZ are known to be regulated by several external cues and stimuli, such as extracellular matrix stiffness, cell spreading, cell geometry, and shear stress. Therefore, there is a need in the field of cancer research to develop and design relevant in vitro models that can accurately reflect the complex biochemical and biophysical cues of the tumor microenvironment central to the YAP/TAZ signaling nexus. While much progress has been made, this remains a major roadblock to advancing research in this field. In this review, we highlight the current engineered biomaterials and in vitro model systems that can be used to advance our understanding of how YAP/TAZ shapes several aspects of cancer. We begin by discussing current 2D and 3D hydrogel systems that model the YAP/TAZ response to ECM stiffness. We then examine the current trends in organoid culture systems and the use of microfluidics to model the effects of cellular density and shear stress on YAP/TAZ. Finally, we analyze the ongoing pitfalls of the present models used and important future directions in engineering systems that will advance our current knowledge of YAP/TAZ in cancer.

Binary fabrication of decellularized lung extracellular matrix hybridgels for in vitro chronic obstructive pulmonary disease modeling

Limited treatments and a lack of appropriate animal models have spurred the study of scaffolds to mimic lung disease in vitro. Decellularized human lung and its application in extracellular matrix (ECM) hydrogels has advanced the development of these lung ECM models. Controlling the biochemical and mechanical properties of decellularized ECM hydrogels continues to be of interest due to inherent discrepancies of hydrogels when compared to their source tissue. To optimize the physiologic relevance of ECM hydrogel lung models without sacrificing the native composition we engineered a binary fabrication system to produce a Hybridgel composed of an ECM hydrogel reinforced with an ECM cryogel. Further, we compared the effect of ECM-altering disease on the properties of the gels using elastin poor Chronic Obstructive Pulmonary Disease (COPD) vs non-diseased (ND) human lung source tissue. Nanoindentation confirmed the significant loss of elasticity in hydrogels compared to that of ND human lung and further demonstrated the recovery of elastic moduli in ECM cryogels and Hybridgels. These findings were supported by similar observations in diseased tissue and gels. Successful cell encapsulation, distribution, cytotoxicity, and infiltration were observed and characterized via confocal microscopy. Cells were uniformly distributed throughout the Hybridgel and capable of survival for 7 days. Cell-laden ECM hybridgels were found to have elasticity similar to that of ND human lung. Compositional investigation into diseased and ND gels indicated the conservation of disease-specific elastin to collagen ratios. In brief, we have engineered a composited ECM hybridgel for the 3D study of cell-matrix interactions of varying lung disease states that optimizes the application of decellularized lung ECM materials to more closely mimic the human lung while conserving the compositional bioactivity of the native ECM. STATEMENT OF SIGNIFICANCE: The lack of an appropriate disease model for the study of chronic lung diseases continues to severely inhibit the advancement of treatments and preventions of these otherwise fatal illnesses due to the inability to recapture the biocomplexity of pathologic cell-ECM interactions. Engineering biomaterials that utilize decellularized lungs offers an opportunity to deconstruct, understand, and rebuild models that highlight and investigate how disease specific characteristics of the extracellular environment are involved in driving disease progression. We have advanced this space by designing a binary fabrication system for a ECM Hybridgel that retains properties from its source material required to observe native matrix interactions. This design simulates a 3D lung environment that is both mechanically elastic and compositionally relevant when derived from non-diseased tissue and pathologically diminished both mechanically and compositionally when derived from COPD tissue. Here we describe the ECM hybridgel as a model for the study of cell-ECM interactions involved in COPD.

Single-pericyte nanomechanics measured by contraction cytometry

Pericytes line the microvasculature throughout the body and play a key role in regulating blood flow by constricting and dilating vessels. However, the biophysical mechanisms through which pericytes transduce microenvironmental chemical and mechanical cues to mediate vessel diameter, thereby impacting oxygen and nutrient delivery, remain largely unknown. This knowledge gap is clinically relevant as numerous diseases are associated with the aberrant contraction of pericytes, which are unusually susceptible to injury. Here, we report the development of a high-throughput hydrogel-based pericyte contraction cytometer that quantifies single-cell contraction forces from murine and human pericytes in different microvascular microenvironments and in the presence of competing vasoconstricting and vasodilating stimuli. We further show that murine pericyte survival in hypoxia is mediated by the mechanical microenvironment and that, paradoxically, pre-treating pericytes to reduce contraction increases hypoxic cell death. Moreover, using the contraction cytometer as a drug-screening tool, we found that cofilin-1 could be applied extracellularly to release murine pericytes from hypoxia-induced contractile rigor mortis and, therefore, may represent a novel approach for mitigating the long-lasting decrease in blood flow that occurs after hypoxic injury.

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.

Biomaterial systems for evaluating the influence of ECM mechanics on anti-fibrotic therapeutic efficacy

Cardiac fibrosis is characterized by excessive accumulation and deposition of ECM proteins. Cardiac fibrosis is commonly implicated in a variety of cardiovascular diseases, including post-myocardial infarction (MI). We have previously developed a dual-delivery nanogel therapeutic to deliver tissue plasminogen activator (tPA) and Y-27632 (a ROCK inhibitor) to address MI-associated coronary artery occlusion and downregulate cell-contractility mediated fibrotic responses. Initial in vitro studies were conducted on glass substrates. The study presented here employs the use of polyacrylamide (PA) gels and microgel thin films to mimic healthy and fibrotic cardiac tissue mechanics. Soft and stiff polyacrylamide substrates or high and low loss tangent microgel thin films were utilized to examine the influence of cell-substrate interactions on dual-loaded nanogel therapeutic efficacy. In the presence of Y-27632 containing nanogels, a reduction of fibrotic marker expression was noted on traditional PA gels mimicking healthy and fibrotic cardiac tissue mechanics. These findings differed on more physiologically relevant microgel thin films, where early treatment with the ROCK inhibitor intensified the fibrotic related responses.

YAP/TAZ enhances P-body formation to promote tumorigenesis

The role of processing bodies (P-bodies) in tumorigenesis and tumor progression is not well understood. Here, we showed that the oncogenes YAP/TAZ promote P-body formation in a series of cancer cell lines. Mechanistically, both transcriptional activation of the P-body-related genes SAMD4A, AJUBA, and WTIP and transcriptional suppression of the tumor suppressor gene PNRC1 are involved in enhancing the effects of YAP/TAZ on P-body formation in colorectal cancer (CRC) cells. By reexpression of PNRC1 or knockdown of P-body core genes (DDX6, DCP1A, and LSM14A), we determined that disruption of P-bodies attenuates cell proliferation, cell migration, and tumor growth induced by overexpression of YAP5SA in CRC. Analysis of a pancancer CRISPR screen database (DepMap) revealed co-dependencies between YAP/TEAD and the P-body core genes and correlations between the mRNA levels of SAMD4A, AJUBA, WTIP, PNRC1, and YAP target genes. Our study suggests that the P-body is a new downstream effector of YAP/TAZ, which implies that reexpression of PNRC1 or disruption of P-bodies is a potential therapeutic strategy for tumors with active YAP.

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

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

miR-29a-3p orchestrates key signaling pathways for enhanced migration of human mesenchymal stem cells

BACKGROUND

The homing of human mesenchymal stem cells (hMSCs) is crucial for their therapeutic efficacy and is characterized by the orchestrated regulation of multiple signaling modules. However, the principal upstream regulators that synchronize these signaling pathways and their mechanisms during cellular migration remain largely unexplored.

METHODS

miR-29a-3p was exogenously expressed in either wild-type or DiGeorge syndrome critical region 8 (DGCR8) knockdown hMSCs. Multiple pathway components were analyzed using Western blotting, immunohistochemistry, and real-time quantitative PCR. hMSC migration was assessed both in vitro and in vivo through wound healing, Transwell, contraction, and in vivo migration assays. Extensive bioinformatic analyses using gene set enrichment analysis and Ingenuity pathway analysis identified enriched pathways, upstream regulators, and downstream targets.

RESULTS

The global depletion of microRNAs (miRNAs) due to DGCR8 gene silencing, a critical component of miRNA biogenesis, significantly impaired hMSC migration. The bioinformatics analysis identified miR-29a-3p as a pivotal upstream regulator. Its overexpression in DGCR8-knockdown hMSCs markedly improved their migration capabilities. Our data demonstrate that miR-29a-3p enhances cell migration by directly inhibiting two key phosphatases: protein tyrosine phosphatase receptor type kappa (PTPRK) and phosphatase and tensin homolog (PTEN). The ectopic expression of miR-29a-3p stabilized the polarization of the Golgi apparatus and actin cytoskeleton during wound healing. It also altered actomyosin contractility and cellular traction forces by changing the distribution and phosphorylation of myosin light chain 2. Additionally, it regulated focal adhesions by modulating the levels of PTPRK and paxillin. In immunocompromised mice, the migration of hMSCs overexpressing miR-29a-3p toward a chemoattractant significantly increased.

CONCLUSIONS

Our findings identify miR-29a-3p as a key upstream regulator that governs hMSC migration. Specifically, it was found to modulate principal signaling pathways, including polarization, actin cytoskeleton, contractility, and adhesion, both in vitro and in vivo, thereby reinforcing migration regulatory circuits.

Uncertainty-Aware Traction Force Microscopy

Traction Force Microscopy (TFM) is a versatile tool to quantify cell-exerted forces by imaging and tracking fiduciary markers embedded in elastic substrates. The computations involved in TFM are ill-conditioned, and data smoothing or regularization is required to avoid overfitting the noise in the tracked substrate displacements. Most TFM calculations depend critically on the heuristic selection of regularization (hyper)parameters affecting the balance between overfitting and smoothing. However, TFM methods rarely estimate or account for measurement errors in substrate deformation to adjust the regularization level accordingly. Moreover, there is a lack of tools to quantify how these errors propagate to the recovered traction stresses. These limitations make it difficult to interpret TFM readouts and hinder comparing different experiments. This manuscript presents an uncertainty-aware TFM technique that estimates the variability in the magnitude and direction of the traction stress vector recovered at each point in space and time of each experiment. In this technique, substrate deformation and its uncertainty are quantified using a non-parametric bootstrap PIV method by resampling the microscopy image pixels (PIV-UQ). This information is passed to a hierarchical Bayesian framework that automatically selects its hyperparameters to perform spatially adaptive regularization conditioned on image quality and propagates the uncertainty to the traction stress readouts (TFM-UQ). We validate the performance of PIV-UQ and TFM-UQ using synthetic datasets with prescribed image quality variations and demonstrate the application of PIV-UQ and TFM-UQ to experimental datasets. These studies show that TFM-UQ locally adapts the level of smoothing, outperforming traditional regularization methods. They also illustrate how uncertainty-aware TFM tools can be used to objectively choose key image analysis parameters like PIV-UQ interrogation window size. We anticipate that these tools will allow for decoupling biological heterogeneity from measurement variability and facilitate automating the analysis of large datasets by parameter-free, input data-based regularization.

Architecture design and advanced manufacturing of heart-on-a-chip: scaffolds, stimulation and sensors

Heart-on-a-chip (HoC) has emerged as a highly efficient, cost-effective device for the development of engineered cardiac tissue, facilitating high-throughput testing in drug development and clinical treatment. HoC is primarily used to create a biomimetic microphysiological environment conducive to fostering the maturation of cardiac tissue and to gather information regarding the real-time condition of cardiac tissue. The development of architectural design and advanced manufacturing for these "3S" components, scaffolds, stimulation, and sensors is essential for improving the maturity of cardiac tissue cultivated on-chip, as well as the precision and accuracy of tissue states. In this review, the typical structures and manufacturing technologies of the "3S" components are summarized. The design and manufacturing suggestions for each component are proposed. Furthermore, key challenges and future perspectives of HoC platforms with integrated "3S" components are discussed. Architecture design concepts of scaffolds, stimulation and sensors in chips.

Mechanobiological Modulation of In Vitro Astrocyte Reactivity Using Variable Gel Stiffness

After traumatic brain injury, the brain extracellular matrix undergoes structural rearrangement due to changes in matrix composition, activation of proteases, and deposition of chondroitin sulfate proteoglycans by reactive astrocytes to produce the glial scar. These changes lead to a softening of the tissue, where the stiffness of the contusion "core" and peripheral "pericontusional" regions becomes softer than that of healthy tissue. Pioneering mechanotransduction studies have shown that soft substrates upregulate intermediate filament proteins in reactive astrocytes; however, many other aspects of astrocyte biology remain unclear. Here, we developed a platform for the culture of cortical astrocytes using polyacrylamide (PA) gels of varying stiffness (measured in Pascal; Pa) to mimic injury-related regions in order to investigate the effects of tissue stiffness on astrocyte reactivity and morphology. Our results show that substrate stiffness influences astrocyte phenotype; soft 300 Pa substrates led to increased GFAP immunoreactivity, proliferation, and complexity of processes. Intermediate 800 Pa substrates increased Aggrecan+, Brevican+, and Neurocan+ astrocytes. The stiffest 1 kPa substrates led to astrocytes with basal morphologies, similar to a physiological state. These results advance our understanding of astrocyte mechanotransduction processes and provide evidence of how substrates with engineered stiffness can mimic the injury microenvironment.

Stiffness Mediated-Mechanosensation of Airway Smooth Muscle Cells on Linear Stiffness Gradient Hydrogels

In obstructive airway diseases such as asthma and chronic obstructive pulmonary disease (COPD), the extracellular matrix (ECM) protein amount and composition of the airway smooth muscle (ASM) is often remodelled, likely altering tissue stiffness. The underlying mechanism of how human ASM cell (hASMC) mechanosenses the aberrant microenvironment is not well understood. Physiological stiffnesses of the ASM were measured by uniaxial compression tester using porcine ASM layers under 0, 5 and 10% longitudinal stretch above in situ length. Linear stiffness gradient hydrogels (230 kPa range) were fabricated and functionalized with ECM proteins, collagen I (ColI), fibronectin (Fn) and laminin (Ln), to recapitulate the above-measured range of stiffnesses. Overall, hASMC mechanosensation exhibited a clear correlation with the underlying hydrogel stiffness. Cell size, nuclear size and contractile marker alpha-smooth muscle actin (αSMA) expression showed a strong correlation to substrate stiffness. Mechanosensation, assessed by Lamin-A intensity and nuc/cyto YAP, exhibited stiffness-mediated behaviour only on ColI and Fn-coated hydrogels. Inhibition studies using blebbistatin or Y27632 attenuated most mechanotransduction-derived cell morphological responses, αSMA and Lamin-A expression and nuc/cyto YAP (blebbistatin only). This study highlights the interplay and complexities between stiffness and ECM protein type on hASMC mechanosensation, relevant to airway remodelling in obstructive airway diseases.

The importance of 3D fibre architecture in cancer and implications for biomaterial model design

The need for improved prediction of clinical response is driving the development of cancer models with enhanced physiological relevance. A new concept of 'precision biomaterials' is emerging, encompassing patient-mimetic biomaterial models that seek to accurately detect, treat and model cancer by faithfully recapitulating key microenvironmental characteristics. Despite recent advances allowing tissue-mimetic stiffness and molecular composition to be replicated in vitro, approaches for reproducing the 3D fibre architectures found in tumour extracellular matrix (ECM) remain relatively unexplored. Although the precise influences of patient-specific fibre architecture are unclear, we summarize the known roles of tumour fibre architecture, underlining their implications in cell-matrix interactions and ultimately clinical outcome. We then explore the challenges in reproducing tissue-specific 3D fibre architecture(s) in vitro, highlighting relevant biomaterial fabrication techniques and their benefits and limitations. Finally, we discuss imaging and image analysis techniques (focussing on collagen I-optimized approaches) that could hold the key to mapping tumour-specific ECM into high-fidelity biomaterial models. We anticipate that an interdisciplinary approach, combining materials science, cancer research and image analysis, will elucidate the role of 3D fibre architecture in tumour development, leading to the next generation of patient-mimetic models for mechanistic studies and drug discovery.

Hippo-PKCζ-NFκB signaling axis: A druggable modulator of chondrocyte responses to mechanical stress

Recent studies have implicated a crucial role of Hippo signaling in cell fate determination by biomechanical signals. Here we show that mechanical loading triggers the activation of a Hippo-PKCζ-NFκB pathway in chondrocytes, resulting in the expression of NFκB target genes associated with inflammation and matrix degradation. Mechanistically, mechanical loading activates an atypical PKC, PKCζ, which phosphorylates NFκB p65 at Serine 536, stimulating its transcriptional activation. This mechanosensitive activation of PKCζ and NFκB p65 is impeded in cells with gene deletion or chemical inhibition of Hippo core kinases LATS1/2, signifying an essential role of Hippo signaling in this mechanotransduction. A PKC inhibitor AEB-071 or PKCζ knockdown prevents p65 Serine 536 phosphorylation. Our study uncovers that the interplay of the Hippo signaling, PKCζ, and NFκB in response to mechanical loading serves as a therapeutic target for knee osteoarthritis and other conditions resulting from mechanical overloading or Hippo signaling deficiencies.

Solo regulates the localization and activity of PDZ-RhoGEF for actin cytoskeletal remodeling in response to substrate stiffness

Recent findings indicate that Solo, a RhoGEF, is involved in cellular mechanical stress responses. However, the mechanism of actin cytoskeletal remodeling via Solo remains unclear. Therefore, this study aimed to identify Solo-interacting proteins using the BioID, a proximal-dependent labeling method, and elucidate the molecular mechanisms of function of Solo. We identified PDZ-RhoGEF (PRG) as a Solo-interacting protein. PRG colocalized with Solo in the basal area of cells, depending on Solo localization, and enhanced actin polymerization at the Solo accumulation sites. Additionally, Solo and PRG interaction was necessary for actin cytoskeletal remodeling. Furthermore, the purified Solo itself had little or negligible GEF activity, even its GEF-inactive mutant directly activated the GEF activity of PRG through interaction. Moreover, overexpression of the Solo and PRG binding domains, respectively, had a dominant-negative effect on actin polymerization and actin stress fiber formation in response to substrate stiffness. Therefore, Solo restricts the localization of PRG and regulates actin cytoskeletal remodeling in synergy with PRG in response to the surrounding mechanical environment.

Bone morphogenetic protein signaling inhibitor improves differentiation and function of 3D muscle construct fabricated using C2C12

Functional tissue-engineered artificial skeletal muscle tissue has great potential for pharmacological and academic applications. This study demonstrates an in vitro tissue engineering system to construct functional artificial skeletal muscle tissues using self-organization and signal inhibitors. To induce efficient self-organization, we optimized the substrate stiffness and extracellular matrix (ECM) coatings. We modified the tissue morphology to be ring-shaped under optimized self-organization conditions. A bone morphogenetic protein (BMP) inhibitor was added to improve overall myogenic differentiation. This supplementation enhanced the myogenic differentiation ratio and myotube hypertrophy in two-dimensional cell cultures. Finally, we found that myotube hypertrophy was enhanced by a combination of self-organization with ring-shaped tissue and a BMP inhibitor. BMP inhibitor treatment significantly improved myogenic marker expression and contractile force generation in the self-organized tissue. These observations indicated that this procedure may provide a novel and functional artificial skeletal muscle for pharmacological studies.

Directed biomechanical compressive forces enhance fusion efficiency in model placental trophoblast cultures

The syncytiotrophoblast is a multinucleated structure that arises from fusion of mononucleated cytotrophoblasts, to sheath the placental villi and regulate transport across the maternal-fetal interface. Here, we ask whether the dynamic mechanical forces that must arise during villous development might influence fusion, and explore this question using in vitro choriocarcinoma trophoblast models. We demonstrate that mechanical stress patterns arise around sites of localized fusion in cell monolayers, in patterns that match computational predictions of villous morphogenesis. We then externally apply these mechanical stress patterns to cell monolayers and demonstrate that equibiaxial compressive stresses (but not uniaxial or equibiaxial tensile stresses) enhance expression of the syndecan-1 and loss of E-cadherin as markers of fusion. These findings suggest that the mechanical stresses that contribute towards sculpting the placental villi may also impact fusion in the developing tissue. We then extend this concept towards 3D cultures and demonstrate that fusion can be enhanced by applying low isometric compressive stresses to spheroid models, even in the absence of an inducing agent. These results indicate that mechanical stimulation is a potent activator of cellular fusion, suggesting novel avenues to improve experimental reproductive modelling, placental tissue engineering, and understanding disorders of pregnancy development.

Extracellular Matrix Stiffness-Induced Mechanotransduction of Capillarized Liver Sinusoidal Endothelial Cells

The mechanobiological response mechanism of the fenestrae of liver sinusoidal endothelial cells (LSECs) to the physical stiffness of the extracellular matrix (ECM) remains unclear. We investigated how the mechanical properties of their substrates affect the LSECs' fenestrae by the nitric oxide (NO)-dependent pathway and how they relate to the progression of hepatic sinus capillarization during liver fibrosis. We detected different stiffnesses of ECM in the progress of liver fibrosis (LF) and developed polyacrylamide hydrogel (PAM) substrates to simulate them. Softer stiffness substrates contributed to LSECs maintaining fenestrae phenotype in vitro. The stiffness of liver fibrosis tissue could be reversed in vivo via treatment with anti-ECM deposition drugs. Similarly, the capillarization of LSECs could be reversed by decreasing the ECM stiffness. Our results also indicate that the NO-dependent pathway plays a key regulatory role in the capillarization of ECM-LSECs. Our study reveals ECM-induced mechanotransduction of capillarized LSECs through a NO-dependent pathway via a previously unrevealed mechanotransduction mechanism. The elucidation of this mechanism may offer precise biomechanics-specific intervention strategies targeting liver fibrosis progression.

Regulation of AMPK activation by extracellular matrix stiffness in pancreatic cancer

The adenosine monophosphate (AMP)-activated protein kinase (AMPK) sits at a central node in the regulation of energy metabolism and tumor progression. AMPK is best known to sense high cellular ADP or AMP levels, which indicate the depletion of energy stores. Previous studies have shown that the low expression of phosphorylated AMPK is associated with a poor prognosis of pancreatic cancer. In this study, we report that AMPK is also highly sensitive to extracellular matrix (ECM) stiffness. We found that AMPK is activated in cells when cultured under low ECM stiffness conditions and is functionally required for the metabolic switch induced by ECM stiffness. This regulation of AMPK requires the Hippo kinases but not LKB1/CaMKKβ. Hippo kinases directly phosphorylate AMPKα at Thr172 to activate AMPK at low ECM stiffness. Furthermore, we found AMPK activity is inhibited in patients with pancreatic ductal adenocarcinoma (PDAC) with high ECM stiffness and is associated with a poor survival outcome. The activation of Hippo kinases by ROCK inhibitor Y-27632 in combination with the mitochondrial inhibitor metformin synergistically activates AMPK and dramatically inhibits PDAC growth. Together, these findings establish a novel model for AMPK regulation by the mechanical properties of ECMs and provide a rationale for simultaneously targeting the ECM stiffness-Hippo kinases-AMPK signaling and low glucose-LKB1-AMPK signaling pathways as an effective therapeutic strategy against PDAC.

Self-Degrading Multifunctional PEG-Based Hydrogels-Tailormade Substrates for Cell Culture

The use of PEG-based hydrogels as cell culture matrix to mimic the natural extracellular matrix (ECM) has been realized using a range of well-defined, tunable, and dynamic scaffolds, although they require cell adhesion ligands such as RGDS-peptide (Arg-Gly-Asp-Ser) to promote cell adhesion. Herein the synthesis of ionic and degradable hydrogels is demonstrated for cell culture by crosslinking [PEG-SH]4 with the zwitterionic crosslinker N,N-bis(acryloxyethyl)-N-methyl-N-(3-sulfopropyl) ammonium betaine (BMSAB) and the cationic crosslinker N,N-bis(acryloxyethyl)-N,N-dimethyl-1-ammonium iodide (BDMAI). Depending on the amount of ionic crosslinker used in gel formation, the hydrogels show tunable gelation time and stiffness. At the same time, the ionic groups act as catalysts for hydrolytic degradation, thereby allowing to define a stability window. The latter could be tailored in a straightforward manner by introducing the non-degradable crosslinker tri(ethylene glycol) divinyl ether. In addition, both ionic crosslinkers favor cell attachment in comparison to the pristine PEG hydrogels. The degradation is examined by swelling behavior, rheology, and fluorescence correlation spectroscopy indicating degradation kinetics depending on diffusion of incorporated fluorescent molecules.