A method for isolating contractile smooth muscle cells from cryopreserved tissue

Multiple techniques have been developed to isolate contractile smooth muscle cells (SMCs) from tissues with varying degrees of success. However, most of these approaches rely on obtaining fresh tissue, which poses logistical challenges. In the present study, we introduce a novel protocol for isolating contractile SMCs from cryopreserved smooth muscle (SM) tissue, thereby enhancing experimental efficiency. This protocol yields abundant viable, spindle-shaped, contractile SMCs that closely resemble those obtained from fresh samples. By analyzing the expression of contractile proteins, we demonstrate that both the isolated SMCs from cryopreserved tissue represent more accurately fresh SM tissue compared with cultured SMCs. Moreover, we demonstrate the importance of a brief incubation step of the tissue in culture medium before cell dissociation to achieve contractile SMCs. Finally, we provide a concise overview of our protocol optimization efforts, along with a summary of previously published methods, which could be valuable for the development of similar protocols for other species.NEW & NOTEWORTHY We report a successful protocol development for isolating contractile smooth muscle cells (SMCs) from cryopreserved tissue reducing the reliance on fresh tissues and providing a readily available source of contractile SMCs. Our findings suggest that SMCs isolated using our protocol maintain their phenotype better compared with cultured SMCs. This preservation of the cellular characteristics, including the expression of key contractile proteins, makes these cells more representative of fresh SM tissue.

Engineering dense tumor constructs via cellular contraction of extracellular matrix hydrogels

Physical characteristics of solid tumors such as dense internal microarchitectures and pathological stiffness influence cancer progression and treatment. While it is routine to engineer culture substrates and scaffolds with elastic moduli that approximate tumors, these models often fail to capture characteristic internal microarchitectures such as densely compacted concentric ECM fibers at the stromal interface. Contractile mesenchymal cells can solve this engineering challenge by deforming, contracting, and compacting extracellular matrix (ECM) hydrogels to decrease tissue volume and increase tissue density. Here we demonstrate that allowing human fibroblasts of varying origins to freely contract collagen type I-containing hydrogels co-seeded with carcinoma cell spheroids produces a tissue engineered construct with structural features that mimic dense solid tumors in vivo. Morphometry and mechanical testing were conducted in tandem with biochemical analysis of proliferation and viability to confirm that dense carcinoma constructs engineered using this approach capture relevant physical characteristics of solid carcinomas in a tractable format that preserves viability and is amenable to extended culture. The reported method is adaptable to the use of multiple mesenchymal cell types and the inclusion of fibrin in the ECM combined with seeding of endothelial cells to produce prevascularized constructs. The physical dense carcinoma constructs engineered using this approach may provide more clinically relevant venues for studying cancer pathophysiology and the challenges associated with the delivery of macromolecular drugs and cellular immunotherapies to solid tumors.

The fibrous character of pericellular matrix mediates cell mechanotransduction

Cells in solid tissues sense and respond to mechanical signals that are transmitted through extracellular matrix (ECM) over distances that are many times their size. This long-range force transmission is known to arise from strain-stiffening and buckling in the collagen fiber ECM network, but must also pass through the denser pericellular matrix (PCM) that cells form by secreting and compacting nearby collagen. However, the role of the PCM in the transmission of mechanical signals is still unclear. We therefore studied an idealized computational model of cells embedded within fibrous collagen ECM and PCM. Our results suggest that the smaller network pore sizes associated with PCM attenuates tension-driven collagen-fiber alignment, undermining long-range force transmission and shielding cells from mechanical stress. However, elongation of the cell body or anisotropic cell contraction can compensate for these effects to enable long distance force transmission. Results are consistent with recent experiments that highlight an effect of PCM on shielding cells from high stresses. Results have implications for the transmission of mechanical signaling in development, wound healing, and fibrosis.

Histone Modification of Osteogenesis Related Genes Triggered by Substrate Topography Promotes Human Mesenchymal Stem Cell Differentiation

The clinical success of orthopedic implants is closely related to their integration in the bone tissue promoted by rough device surfaces. The biological response of precursor cells to their artificial microenvironments plays a critical role in this process. In this study, we elucidated the relation between cell instructivity and surface microstructure of polycarbonate (PC)-based model substrates. The rough surface structure (hPC) with an average peak spacing (Sm) similar to the trabecular spacing of trabecular bone improved osteogenic differentiation of human bone marrow mesenchymal stem cells (hBMSCs), as compared to the smooth surface (sPC) and the surface with a moderate Sm value (mPC). The hPC substrate promoted the cell adhesion and assembling of F-actin and enhanced cell contractile force by upregulating phosphorylated myosin light chain (pMLC) expression. The increased cell contractile force led to YAP nuclear translocation and the elongation of cell nuclei, presenting higher levels of active form of Lamin A/C. The nuclear deformation alternated the histone modification profile, particularly the decrease of H3K27me3 and increase of H3K9ac on the promoter region of osteogenesis related genes (ALPL, RUNX2, and OCN). Mechanism study using inhibitors and siRNAs elucidated the role of YAP, integrin, F-actin, myosin, and nuclear membrane proteins in such a regulatory process of surface topography on stem cell fate. These mechanistical insights on the epigenetic level give a new perspective in understanding of the interaction of substrate and stem cells as well as provide valuable criteria for designing bioinstructive orthopedic implants.

Elastomeric Pillar Cages Modulate Actomyosin Contractility of Epithelial Microtissues by Substrate Stiffness and Topography

Cell contractility regulates epithelial tissue geometry development and homeostasis. The underlying mechanobiological regulation circuits are poorly understood and experimentally challenging. We developed an elastomeric pillar cage (EPC) array to quantify cell contractility as a mechanoresponse of epithelial microtissues to substrate stiffness and topography. The spatially confined EPC geometry consisted of 24 circularly arranged slender pillars (1.2 MPa, height: 50 µm; diameter: 10 µm, distance: 5 µm). These high-aspect-ratio pillars were confined at both ends by planar substrates with different stiffness (0.15-1.2 MPa). Analytical modeling and finite elements simulation retrieved cell forces from pillar displacements. For evaluation, highly contractile myofibroblasts and cardiomyocytes were assessed to demonstrate that the EPC device can resolve static and dynamic cellular force modes. Human breast (MCF10A) and skin (HaCaT) cells grew as adherence junction-stabilized 3D microtissues within the EPC geometry. Planar substrate areas triggered the spread of monolayered clusters with substrate stiffness-dependent actin stress fiber (SF)-formation and substantial single-cell actomyosin contractility (150-200 nN). Within the same continuous microtissues, the pillar-ring topography induced the growth of bilayered cell tubes. The low effective pillar stiffness overwrote cellular sensing of the high substrate stiffness and induced SF-lacking roundish cell shapes with extremely low cortical actin tension (11-15 nN). This work introduced a versatile biophysical tool to explore mechanobiological regulation circuits driving low- and high-tensional states during microtissue development and homeostasis. EPC arrays facilitate simultaneously analyzing the impact of planar substrate stiffness and topography on microtissue contractility, hence microtissue geometry and function.

Cancer-Associated Fibroblasts in a 3D Engineered Tissue Model Induce Tumor-like Matrix Stiffening and EMT Transition

Simple Summary

The physical properties of a tumor, such as stiffness, are important drivers of tumor progression. However, current in vitro tumor models fail to recapitulate the full range of physical properties observed in solid tumors. Here, we proposed a 3D self-assembly engineered bladder model using cancer-associated fibroblasts in which stromal cells produce their extracellular matrix. We then proceeded to assess how our model recapitulates biological and mechanical features found in tumors. We confirmed that stroma assembled by cancer-associated fibroblasts have increased extracellular matrix content and display increased remodeling and higher stiffness. Moreover, normal urothelial cells seeded on the tumor model displayed a mechanotransduction response, increased cell proliferation, cell infiltration within stroma, and displayed features of the epithelial-to-mesenchymal transition. Altogether, we demonstrated that our cancer-associated fibroblast-derived tumor stroma recapitulates several biological and physical features expected from a tumor-like environment and, thus, provides the basis for more accurate cancer models.

Abstract

A tumor microenvironment is characterized by its altered mechanical properties. However, most models remain unable to faithfully recreate the mechanical properties of a tumor. Engineered models based on the self-assembly method have the potential to better recapitulate the stroma architecture and composition. Here, we used the self-assembly method based on a bladder tissue model to engineer a tumor-like environment. The tissue-engineered tumor models were reconstituted from stroma-derived healthy primary fibroblasts (HFs) induced into cancer-associated fibroblast cells (iCAFs) along with an urothelium overlay. The iCAFs-derived extracellular matrix (ECM) composition was found to be stiffer, with increased ECM deposition and remodeling. The urothelial cells overlaid on the iCAFs-derived ECM were more contractile, as measured by quantitative polarization microscopy, and displayed increased YAP nuclear translocation. We further showed that the proliferation and expression of epithelial-to-mesenchymal transition (EMT) marker in the urothelial cells correlate with the increased stiffness of the iCAFs-derived ECM. Our data showed an increased expression of EMT markers within the urothelium on the iCAFs-derived ECM. Together, our results demonstrate that our tissue-engineered tumor model can achieve stiffness levels comparable to that of a bladder tumor, while triggering a tumor-like response from the urothelium.

The function of CD146 in human annulus fibrosus cells and mechanism of the regulation by TGF-β

The mouse outer annulus fibrosus (AF) was previously shown to contain CD146⁺ AF cells, while in vitro culture and exposure to transforming growth factor-beta (TGF-β) further increased the expression of CD146. However, neither the specific function of CD146 nor the underlying mechanism of TGF-β upregulation of CD146⁺ AF cells have been elucidated yet. In the current study, CD146 expression and its role in cultured human AF cells was investigated studying the cells' capacity for matrix contraction and gene expression of functional AF markers. In addition, TGF-β pathways were blocked by several pathway inhibitors and short hairpin RNAs (shRNAs) targeting SMAD and non-SMAD pathways to investigate their involvement in TGF-β-induced CD146 upregulation. Results showed that knockdown of CD146 led to reduction in AF cell-mediated collagen gel contraction, downregulation of versican and smooth muscle protein 22α (SM22α), and upregulation of scleraxis. TGF-β-induced CD146 upregulation was significantly blocked by inhibition of TGF-β receptor ALK5, and partially inhibited by shRNA against SMAD2 and SMAD4 and by an Protein Kinase B (AKT) inhibitor. Interestingly, the inhibition of extracellular signal-regulated kinases (ERK) pathway induced CD146 upregulation. In conclusion, CD146 was shown to be crucial to maintain the cell contractility of human AF cells in vitro. Furthermore, TGF-β upregulated CD146 via ALK5 signaling cascade, partially through SMAD2, SMAD4, and AKT pathway, whereas, ERK was shown to be a potential negative modulator. Our findings suggest that CD146 can potentially be used as a functional marker in AF repair strategies.

Protective effects of 18β-Glycyrrhetinic acid against myocardial infarction: Involvement of PI3K/Akt pathway activation and inhibiting Ca2+ influx via L-type Ca2+ channels

18β-Glycyrrhetinic acid (18β-GA) is a component extracted from licorice. This study aimed to evaluate the effects of 18β-GA on isoproterenol (ISO)-induced acute myocardial infarction in rats and mice. Two consecutive days of subcutaneous injection of ISO (85 mg/kg/day) resulted in acute myocardial infarction. We examined the pathological changes, oxidative stress, inflammatory response, and expression of apoptosis in mouse hearts. The expressions of phosphoinositol-3-kinase (PI3K), protein kinase B (Akt), and the phosphorylation levels of PI3K (p-PI3K) and Akt (p-Akt) were determined by western blotting. The whole-cell patch-clamp technique was applied to observe the L-type Ca2+ currents, and the Ion Optix detection system was used for cell contraction and Ca2+ transient in isolated rat cardiac ventricular myocytes. In ISO-induced myocardial infarction, the J-point, heart rate, creatine kinase, lactate dehydrogenase, superoxide dismutase, catalase, malondialdehyde, glutathion, and reactive oxygen species decreased in mice after 18β-GA treatment. 18β-GA improved ISO-induced morphologic pathology, inhibited the inflammatory pathway response and cardiomyocyte apoptosis, and inhibited PI3K/Akt signaling. 18β-GA could significantly inhibit ICa-L, myocardial contraction, and Ca2+ transient. This study demonstrates that 18β-GA has cardioprotective effects on acute myocardial infarction, which may be related to inhibiting oxidative stress, inflammation, apoptosis via the PI3K/Akt pathway, and reducing cell contractility and Ca2+ concentration via L-type Ca2+ channels.

An Outside-In Switch in Integrin Signaling Caused by Chemical and Mechanical Signals in Reactive Astrocytes

Astrocyte reactivity is associated with poor repair capacity after injury to the brain, where chemical and physical changes occur in the damaged zone. Astrocyte surface proteins, such as integrins, are upregulated, and the release of pro-inflammatory molecules and extracellular matrix (ECM) proteins upon damage generate a stiffer matrix. Integrins play an important role in triggering a reactive phenotype in astrocytes, and we have reported that α_Vβ₃ Integrin binds to the Thy-1 (CD90) neuronal glycoprotein, increasing astrocyte contractility and motility. Alternatively, α_Vβ₃ Integrin senses mechanical forces generated by the increased ECM stiffness. Until now, the association between the α_Vβ₃ Integrin mechanoreceptor response in astrocytes and changes in their reactive phenotype is unclear. To study the response to combined chemical and mechanical stress, astrocytes were stimulated with Thy-1-Protein A-coated magnetic beads and exposed to a magnetic field to generate mechanical tension. We evaluated the effect of such stimulation on cell adhesion and contraction. We also assessed traction forces and their effect on cell morphology, and integrin surface expression. Mechanical stress accelerated the response of astrocytes to Thy-1 engagement of integrin receptors, resulting in cell adhesion and contraction. Astrocyte contraction then exerted traction forces onto the ECM, inducing faster cell contractility and higher traction forces than Thy-1 alone. Therefore, cell-extrinsic chemical and mechanical signals regulate in an outside-in manner, astrocyte reactivity by inducing integrin upregulation, ligation, and signaling events that promote cell contraction. These changes in turn generate cell-intrinsic signals that increase traction forces exerted onto the ECM (inside-out). This study reveals α_Vβ₃ Integrin mechanoreceptor as a novel target to regulate the harmful effects of reactive astrocytes in neuronal healing.

[8]-Gingerol exerts anti-myocardial ischemic effects in rats via modulation of the MAPK signaling pathway and L-type Ca2+ channels

Myocardial ischemia (MI) remains the leading cause of mortality worldwide. Therefore, it is urgent to seek the treatment to protect the heart. [8]‐Gingerol (8‐Gin), one of the most active ingredients in ginger, has antioxidant, cardiotonic, and cardiovascular protective properties. The present study elucidated the cardioprotection effects and underlying mechanisms of 8‐Gin in isoproterenol (ISO)‐induced MI. ISO (85 mg/kg/d) was subcutaneously injected for 2 consecutive days to induce acute MI model in rats. Electrocardiography, oxidative stress levels, calcium concentrations, and apoptosis degree were observed. The effects of 8‐Gin on L‐type Ca²⁺ current (I_Ca‐L), contraction, and Ca²⁺ transients were monitored in rat myocytes via patch‐clamp and IonOptix detection systems. 8‐Gin decreased J‐point elevation and heart rate and improved pathological heart damage. Moreover, 8‐Gin reduced the levels of CK, LDH, and MDA, ROS production, and calcium concentrations in myocardial tissue, while increased the activities of SOD, CAT, and GSH. In addition, 8‐Gin down‐regulated Caspase‐3 and Bax expressions, while up‐regulated Bcl‐2 expression. 8‐Gin produced a marked decrease in the expression of p38, JNK, and ERK1/2 proteins. 8‐Gin inhibited I_Ca‐L, cell contraction, and Ca²⁺ transients in isolated rat myocytes. The results indicate that 8‐Gin could exert anti‐myocardial ischemic effects, which may be associated with oxidative stress reduction, cardiomyocytes apoptosis inhibition through MAPK signaling pathway, and Ca²⁺ homeostasis regulation via I_Ca‐L modulation.

TRPV4 integrates matrix mechanosensing with Ca2+ signaling to regulate extracellular matrix remodeling

In healthy connective tissues, mechanosensors trigger the generation of Ca²⁺ signals, which enable cells to maintain the structure of the fibrillar collagen matrix through actomyosin contractile forces. Transient receptor potential vanilloid type 4 (TRPV4) is a mechanosensitive Ca²⁺ -permeable channel that, when expressed in cell-matrix adhesions of the plasma membrane, regulates extracellular matrix (ECM) remodeling. In high prevalence disorders such as fibrosis and tumor metastasis, dysregulated matrix remodeling is associated with disruptions of Ca²⁺ homeostasis and TRPV4 function. Here, we consider that ECM polymers transmit cell-activating mechanical signals to TRPV4 in cell adhesions. When activated, TRPV4 regulates fibrillar collagen remodeling, thereby altering the mechanical properties of the ECM. In this review, we integrate functionally connected processes of matrix remodeling to highlight how TRPV4 in cell adhesions and matrix mechanics are reciprocally regulated through Ca²⁺ signaling.

Hydrogel Network Dynamics Regulate Vascular Morphogenesis

Matrix dynamics influence how individual cells develop into complex multicellular tissues. Here, we develop hydrogels with identical polymer components but different crosslinking capacities to enable the investigation of mechanisms underlying vascular morphogenesis. We show that dynamic (D) hydrogels increase the contractility of human endothelial colony-forming cells (hECFCs), promote the clustering of integrin β1, and promote the recruitment of vinculin, leading to the activation of focal adhesion kinase (FAK) and metalloproteinase expression. This leads to the robust assembly of vasculature and the deposition of new basement membrane. We also show that non-dynamic (N) hydrogels do not promote FAK signaling and that stiff D- and N-hydrogels are constrained for vascular morphogenesis. Furthermore, D-hydrogels promote hECFC microvessel formation and angiogenesis in vivo. Our results indicate that cell contractility mediates integrin signaling via inside-out signaling and emphasizes the importance of matrix dynamics in vascular tissue formation, thus informing future studies of vascularization and tissue engineering applications.

Traction Forces Control Cell-Edge Dynamics and Mediate Distance Sensitivity during Cell Polarization

Traction forces are generated by cellular actin-myosin system and transmitted to the environment through adhesions. They are believed to drive cell motion, shape changes, and extracellular matrix remodeling [1-3]. However, most of the traction force analysis has been performed on stationary cells, investigating forces at the level of individual focal adhesions or linking them to static cell parameters, such as area and edge curvature [4-10]. It is not well understood how traction forces are related to shape changes and motion, e.g., forces were reported to either increase or drop prior to cell retraction [11-15]. Here, we analyze the dynamics of traction forces during the protrusion-retraction cycle of polarizing fish epidermal keratocytes and find that forces fluctuate together with the cycle, increasing during protrusion and reaching maximum at the beginning of retraction. We relate force dynamics to the recently discovered phenomenological rule [16] that governs cell-edge behavior during keratocyte polarization: both traction forces and probability of switch from protrusion to retraction increase with the distance from the cell center. Diminishing forces with cell contractility inhibitor leads to decreased edge fluctuations and abnormal polarization, although externally applied force can induce protrusion-retraction switch. These results suggest that forces mediate distance sensitivity of the edge dynamics and organize cell-edge behavior, leading to spontaneous polarization. Actin flow rate did not exhibit the same distance dependence as traction stress, arguing against its role in organizing edge dynamics. Finally, using a simple model of actin-myosin network, we show that force-distance relationship might be an emergent feature of such networks.

Targeting ROCK activity to disrupt and prime pancreatic cancer for chemotherapy

Pancreatic ductal adenocarcinoma (PDAC) is a devastating disease; the identification of novel targets and development of effective treatment strategies are urgently needed to improve patient outcomes. Remodeling of the pancreatic stroma occurs during PDAC development, which drives disease progression and impairs responses to therapy. The actomyosin regulatory ROCK1 and ROCK2 kinases govern cell motility and contractility, and have been suggested to be potential targets for cancer therapy, particularly to reduce the metastatic spread of tumor cells. However, ROCK inhibitors are not currently used for cancer patient treatment, largely due to the overwhelming challenge faced in the development of anti-metastatic drugs, and a lack of clarity as to the cancer types most likely to benefit from ROCK inhibitor therapy. In 2 recent publications, we discovered that ROCK1 and ROCK2 expression were increased in PDAC, and that increased ROCK activity was associated with reduced survival and PDAC progression by enabling extracellular matrix (ECM) remodeling and invasive growth of pancreatic cancer cells. We also used intravital imaging to optimize ROCK inhibition using the pharmacological ROCK inhibitor fasudil (HA-1077), and demonstrated that short-term ROCK targeting, or 'priming', improved chemotherapy efficacy, disrupted cancer cell collective movement, and impaired metastasis. This body of work strongly indicates that the use of ROCK inhibitors in pancreatic cancer therapy as 'priming' agents warrants further consideration, and provides insights as to how transient mechanical manipulation, or fine-tuning the ECM, rather than chronic stromal ablation might be beneficial for improving chemotherapeutic efficacy in the treatment of this deadly disease.

In vivo optochemical control of cell contractility at single-cell resolution

The spatial and temporal dynamics of cell contractility plays a key role in tissue morphogenesis, wound healing, and cancer invasion. Here, we report a simple optochemical method to induce cell contractions in vivo during Drosophila morphogenesis at single-cell resolution. We employed the photolabile Ca²⁺ chelator o-nitrophenyl EGTA to induce bursts of intracellular free Ca²⁺ by laser photolysis in the epithelial tissue. Ca²⁺ bursts appear within seconds and are restricted to individual target cells. Cell contraction reliably followed within a minute, causing an approximately 50% drop in the cross-sectional area. Increased Ca²⁺ levels are reversible, and the target cells further participated in tissue morphogenesis. Depending on Rho kinase (ROCK) activity but not RhoGEF2, cell contractions are paralleled with non-muscle myosin II accumulation in the apico-medial cortex, indicating that Ca²⁺ bursts trigger non-muscle myosin II activation. Our approach can be, in principle, adapted to many experimental systems and species, as no specific genetic elements are required.

Matrix stiffness regulates microvesicle-induced fibroblast activation

Extracellular vesicles released by cancer cells have recently been implicated in the differentiation of stromal cells to their activated, cancer-supporting states. Microvesicles, a subset of extracellular vesicles released from the plasma membrane of cancer cells, contain biologically active cargo, including DNA, mRNA, and miRNA, which are transferred to recipient cells and induce a phenotypic change in behavior. While it is known that microvesicles can alter recipient cell phenotype, little is known about how the physical properties of the tumor microenvironment affect fibroblast response to microvesicles. Here, we utilized cancer cell-derived microvesicles and synthetic substrates designed to mimic the stiffness of the tumor and tumor stroma to investigate the effects of microvesicles on fibroblast phenotype as a function of the mechanical properties of the microenvironment. We show that microvesicles released by highly malignant breast cancer cells cause an increase in fibroblast spreading, α-smooth muscle actin expression, proliferation, cell-generated traction force, and collagen gel compaction. Notably, our data indicate that these phenotypic changes occur only on stiff matrices mimicking the stiffness of the tumor periphery and are dependent on the cell type from which the microvesicles are shed. Overall, these results show that the effects of cancer cell-derived microvesicles on fibroblast activation are regulated by the physical properties of the microenvironment, and these data suggest that microvesicles may have a more robust effect on fibroblasts located at the tumor periphery to influence cancer progression.

Cellular Control of Brain Capillary Blood Flow: In Vivo Imaging Veritas

The precise modulation of regional cerebral blood flow during neural activation is important for matching local energetic demand and supply and clearing brain metabolites. Here we discuss advances facilitated by high-resolution optical in vivo imaging techniques that for the first time have provided direct visualization of capillary blood flow and its modulation by neural activity. We focus primarily on studies of microvascular flow, mural cell control of vessel diameter, and oxygen level-dependent changes in red blood cell deformability. We also suggest methodological standards for best practices when studying microvascular perfusion, partly motivated by recent controversies about the precise location within the microvascular tree where neurovascular coupling is initiated, and the role of mural cells in the control of vasomotility.

Quantitative assessment of cell contractility using polarized light microscopy

Cell contractility regulates multiple cell behaviors which contribute to both normal and pathological processes. However, measuring cell contractility remains a technical challenge in complex biological samples. The current state of the art technologies employed to measure cell contractility have inherent limitations that greatly limit the experimental conditions under which they can be used. Here, we use quantitative polarization microscopy to extract information about cell contractility. We show that the optical retardance signal measured from the cell body is proportional to cell contractility in 2-dimensional and 3-dimensional platforms, and as such can be used as a straightforward, tractable methodology to assess cell contractility in a variety of systems. This label-free optical method provides a novel and flexible way to assess cellular forces of single cells and monolayers in several cell types, fixed or live, in addition to cells present in situ in mouse tumor tissue samples. This easily implementable and experimentally versatile method will significantly contribute to the cell mechanics field.

Ultrafast epithelial contractions provide insights into contraction speed limits and tissue integrity

By definition of multicellularity, all animals need to keep their cells attached and intact, despite internal and external forces. Cohesion between epithelial cells provides this key feature. To better understand fundamental limits of this cohesion, we study the epithelium mechanics of an ultrathin (∼25 μm) primitive marine animal Trichoplax adhaerens, composed essentially of two flat epithelial layers. With no known extracellular matrix and no nerves or muscles, T. adhaerens has been claimed to be the "simplest known living animal," yet is still capable of coordinated locomotion and behavior. Here we report the discovery of the fastest epithelial cellular contractions known in any metazoan, to be found in T. adhaerens dorsal epithelium (50% shrinkage of apical cell area within one second, at least an order of magnitude faster than other known examples). Live imaging reveals emergent contractile patterns that are mostly sporadic single-cell events, but also include propagating contraction waves across the tissue. We show that cell contraction speed can be explained by current models of nonmuscle actin-myosin bundles without load, while the tissue architecture and unique mechanical properties are softening the tissue, minimizing the load on a contracting cell. We propose a hypothesis, in which the physiological role of the contraction dynamics is to resist external stresses while avoiding tissue rupture ("active cohesion"), a concept that can be further applied to engineering of active materials.

Feeling Stress: The Mechanics of Cancer Progression and Aggression

The tumor microenvironment is a dynamic landscape in which the physical and mechanical properties evolve dramatically throughout cancer progression. These changes are driven by enhanced tumor cell contractility and expansion of the growing tumor mass, as well as through alterations to the material properties of the surrounding extracellular matrix (ECM). Consequently, tumor cells are exposed to a number of different mechanical inputs including cell–cell and cell-ECM tension, compression stress, interstitial fluid pressure and shear stress. Oncogenes engage signaling pathways that are activated in response to mechanical stress, thereby reworking the cell's intrinsic response to exogenous mechanical stimuli, enhancing intracellular tension via elevated actomyosin contraction, and influencing ECM stiffness and tissue morphology. In addition to altering their intracellular tension and remodeling the microenvironment, cells actively respond to these mechanical perturbations phenotypically through modification of gene expression. Herein, we present a description of the physical changes that promote tumor progression and aggression, discuss their interrelationship and highlight emerging therapeutic strategies to alleviate the mechanical stresses driving cancer to malignancy.

Blockade of Rho-associated protein kinase (ROCK) inhibits the contractility and invasion potential of cancer stem like cells

Recent studies have implicated the roles of cancer stem like cells (CSCs) in cancer metastasis. However, very limited knowledge exists at the molecular and cellular level to target CSCs for prevention of cancer metastasis. In this study, we examined the roles of contractile dynamics of CSCs in cell invasion and delineated the underlying molecular mechanisms of their distinct cell invasion potential. Using de-adhesion assay and atomic force microscopy, we show that CSCs derived from melanoma and breast cancer cell lines exhibit increased contractility compared to non-CSCs across all tumor types. In addition, CSCs possess increased ECM remodeling capacity as quantified by collagen degradation assay. More importantly, pharmacological blockade of Rho-associated protein kinase completely abolished the contractility and collagen degradation capacity of both CSCs and non-CSCs. In conclusion, our study demonstrates the importance of cell contractility in regulating invasiveness of CSCs and suggests that pharmacological targeting of ROCK pathway represents a novel strategy for targeting both CSCs and bulk population for the treatment of cancer metastasis.

Patterned cortical tension mediated by N-cadherin controls cell geometric order in the Drosophila eye

Adhesion molecules hold cells together but also couple cell membranes to a contractile actomyosin network, which limits the expansion of cell contacts. Despite their fundamental role in tissue morphogenesis and tissue homeostasis, how adhesion molecules control cell shapes and cell patterns in tissues remains unclear. Here we address this question in vivo using the Drosophila eye. We show that cone cell shapes depend little on adhesion bonds and mostly on contractile forces. However, N-cadherin has an indirect control on cell shape. At homotypic contacts, junctional N-cadherin bonds downregulate Myosin-II contractility. At heterotypic contacts with E-cadherin, unbound N-cadherin induces an asymmetric accumulation of Myosin-II, which leads to a highly contractile cell interface. Such differential regulation of contractility is essential for morphogenesis as loss of N-cadherin disrupts cell rearrangements. Our results establish a quantitative link between adhesion and contractility and reveal an unprecedented role of N-cadherin on cell shapes and cell arrangements.

DOI:http://dx.doi.org/10.7554/eLife.22796.001

Multiscale model predicts increasing focal adhesion size with decreasing stiffness in fibrous matrices

We describe a multiscale model that incorporates force-dependent mechanical plasticity induced by interfiber cross-link breakage and stiffness-dependent cellular contractility to predict focal adhesion (FA) growth and mechanosensing in fibrous extracellular matrices (ECMs). The model predicts that FA size depends on both the stiffness of ECM and the density of ligands available to form adhesions. Although these two quantities are independent in commonly used hydrogels, contractile cells break cross-links in soft fibrous matrices leading to recruitment of fibers, which increases the ligand density in the vicinity of cells. Consequently, although the size of focal adhesions increases with ECM stiffness in nonfibrous and elastic hydrogels, plasticity of fibrous networks leads to a departure from the well-described positive correlation between stiffness and FA size. We predict a phase diagram that describes nonmonotonic behavior of FA in the space spanned by ECM stiffness and recruitment index, which describes the ability of cells to break cross-links and recruit fibers. The predicted decrease in FA size with increasing ECM stiffness is in excellent agreement with recent observations of cell spreading on electrospun fiber networks with tunable cross-link strengths and mechanics. Our model provides a framework to analyze cell mechanosensing in nonlinear and inelastic ECMs.

Modeling the two-way feedback between contractility and matrix realignment reveals a nonlinear mode of cancer cell invasion

Cancer cell invasion from primary tumors is mediated by a complex interplay between cellular adhesions, actomyosin-driven contractility, and the physical characteristics of the extracellular matrix (ECM). Here, we incorporate a mechanochemical free-energy-based approach to elucidate how the two-way feedback loop between cell contractility (induced by the activity of chemomechanical interactions such as Ca2+ and Rho signaling pathways) and matrix fiber realignment and strain stiffening enables the cells to polarize and develop contractile forces to break free from the tumor spheroids and invade into the ECM. Interestingly, through this computational model, we are able to identify a critical stiffness that is required by the matrix to break intercellular adhesions and initiate cell invasion. Also, by considering the kinetics of the cell movement, our model predicts a biphasic invasiveness with respect to the stiffness of the matrix. These predictions are validated by analyzing the invasion of melanoma cells in collagen matrices of varying concentration. Our model also predicts a positive correlation between the elongated morphology of the invading cells and the alignment of fibers in the matrix, suggesting that cell polarization is directly proportional to the stiffness and alignment of the matrix. In contrast, cells in nonfibrous matrices are found to be rounded and not polarized, underscoring the key role played by the nonlinear mechanics of fibrous matrices. Importantly, our model shows that mechanical principles mediated by the contractility of the cells and the nonlinearity of the ECM behavior play a crucial role in determining the phenotype of the cell invasion.

AGE-modified basement membrane cooperates with Endo180 to promote epithelial cell invasiveness and decrease prostate cancer survival

Biomechanical strain imposed by age-related thickening of the basal lamina and augmented tissue stiffness in the prostate gland coincides with increased cancer risk. Here we hypothesized that the structural alterations in the basal lamina associated with age can induce mechanotransduction pathways in prostate epithelial cells (PECs) to promote invasiveness and cancer progression. To demonstrate this, we developed a 3D model of PEC acini in which thickening and stiffening of basal lamina matrix was induced by advanced glycation end-product (AGE)-dependent non-enzymatic crosslinking of its major components, collagen IV and laminin. We used this model to demonstrate that antibody targeted blockade of CTLD2, the second of eight C-type lectin-like domains in Endo180 (CD280, CLEC13E, KIAA0709, MRC2, TEM9, uPARAP) that can recognize glycosylated collagens, reversed actinomyosin-based contractility [myosin-light chain-2 (MLC2) phosphorylation], loss of cell polarity, loss of cell-cell junctions, luminal infiltration and basal invasion induced by AGE-modified basal lamina matrix in PEC acini. Our in vitro results were concordant with luminal occlusion of acini in the prostate glands of adult Endo180(Δ) (Ex2-6/) (Δ) (Ex2-6) mice, with constitutively exposed CTLD2 and decreased survival of men with early (non-invasive) prostate cancer with high epithelial Endo180 expression and levels of AGE. These findings indicate that AGE-dependent modification of the basal lamina induces invasive behaviour in non-transformed PECs via a molecular mechanism linked to cancer progression. This study provides a rationale for targeting CTLD2 in Endo180 in prostate cancer and other pathologies in which increased basal lamina thickness and tissue stiffness are driving factors. © 2014 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Decoupling cell and matrix mechanics in engineered microtissues using magnetically actuated microcantilevers

A novel bio-magnetomechanical microtissue system is described for magnetic actuation of arrays of 3D microtissues using microcantilevers. This system enables both in situ measurements of fundamental mechanical properties of engineered tissue, such as contractility and stiffness, as well as dynamic stimulation of the microtissues. Using this system, cell and extracellular matrix contributions to the tissue mechanical properties are decoupled for the first time under both static and dynamic loading conditions.

Focal contacts as mechanosensors: externally applied local mechanical force induces growth of focal contacts by an mDia1-dependent and ROCK-independent mechanism

The transition of cell-matrix adhesions from the initial punctate focal complexes into the mature elongated form, known as focal contacts, requires GTPase Rho activity. In particular, activation of myosin II-driven contractility by a Rho target known as Rho-associated kinase (ROCK) was shown to be essential for focal contact formation. To dissect the mechanism of Rho-dependent induction of focal contacts and to elucidate the role of cell contractility, we applied mechanical force to vinculin-containing dot-like adhesions at the cell edge using a micropipette. Local centripetal pulling led to local assembly and elongation of these structures and to their development into streak-like focal contacts, as revealed by the dynamics of green fluorescent protein-tagged vinculin or paxillin and interference reflection microscopy. Inhibition of Rho activity by C3 transferase suppressed this force-induced focal contact formation. However, constitutively active mutants of another Rho target, the formin homology protein mDia1 (Watanabe, N., T. Kato, A. Fujita, T. Ishizaki, and S. Narumiya. 1999. Nat. Cell Biol. 1:136-143), were sufficient to restore force-induced focal contact formation in C3 transferase-treated cells. Force-induced formation of the focal contacts still occurred in cells subjected to myosin II and ROCK inhibition. Thus, as long as mDia1 is active, external tension force bypasses the requirement for ROCK-mediated myosin II contractility in the induction of focal contacts. Our experiments show that integrin-containing focal complexes behave as individual mechanosensors exhibiting directional assembly in response to local force.