Substrate Rigidity Controls Activation and Durotaxis in Pancreatic Stellate Cells

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

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

Metabolism and bioenergetics in the pathophysiology of organ fibrosis

Fibrosis is the tissue scarring characterized by excess deposition of extracellular matrix (ECM) proteins, mainly collagens. A fibrotic response can take place in any tissue of the body and is the result of an imbalanced reaction to inflammation and wound healing. Metabolism has emerged as a major driver of fibrotic diseases. While glycolytic shifts appear to be a key metabolic switch in activated stromal ECM-producing cells, several other cell types such as immune cells, whose functions are intricately connected to their metabolic characteristics, form a complex network of pro-fibrotic cellular crosstalk. This review purports to clarify shared and particular cellular responses and mechanisms across organs and etiologies. We discuss the impact of the cell-type specific metabolic reprogramming in fibrotic diseases in both experimental and human pathology settings, providing a rationale for new therapeutic interventions based on metabolism-targeted antifibrotic agents.

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. 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 role 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. Hence, PSC durotaxis is optimal with an intermediary level of mechanosensitive channel activity, which we simulated using a numerically discretized mathematical model. Our findings suggest that mechanosensitive ion channels, particularly Piezo1, detect the mechanical microenvironment to guide PSC migration.

Positive and negative durotaxis - mechanisms and emerging concepts

Cell migration is controlled by the coordinated action of cell adhesion, cytoskeletal dynamics, contractility and cell extrinsic cues. Integrins are the main adhesion receptors to ligands of the extracellular matrix (ECM), linking the actin cytoskeleton to the ECM and enabling cells to sense matrix rigidity and mount a directional cell migration response to stiffness gradients. Most models studied show preferred migration of single cells or cell clusters towards increasing rigidity. This is referred to as durotaxis, and since its initial discovery in 2000, technical advances and elegant computational models have provided molecular level details of stiffness sensing in cell migration. However, modeling has long predicted that, depending on cell intrinsic factors, such as the balance of cell adhesion molecules (clutches) and the motor proteins pulling on them, cells might also prefer adhesion to intermediate rigidity. Recently, experimental evidence has supported this notion and demonstrated the ability of cells to migrate towards lower rigidity, in a process called negative durotaxis. In this Review, we discuss the significant conceptual advances that have been made in our appreciation of cell plasticity and context dependency in stiffness-guided directional cell migration.

A non local model for cell migration in response to mechanical stimuli

Cell migration is one of the most studied phenomena in biology since it plays a fundamental role in many physiological and pathological processes such as morphogenesis, wound healing and tumorigenesis. In recent years, researchers have performed experiments showing that cells can migrate in response to mechanical stimuli of the substrate they adhere to. Motion towards regions of the substrate with higher stiffness is called durotaxis, while motion guided by the stress or the deformation of the substrate itself is called tensotaxis. Unlike chemotaxis (i.e. the motion in response to a chemical stimulus), these migratory processes are not yet fully understood from a biological point of view. In this respect, we present a mathematical model of single-cell migration in response to mechanical stimuli, in order to simulate these two processes. Specifically, the cell moves by changing its direction of polarization and its motility according to material properties of the substrate (e.g., stiffness) or in response to proper scalar measures of the substrate strain or stress. The equations of motion of the cell are non-local integro-differential equations, with the addition of a stochastic term to account for random Brownian motion. The mechanical stimulus to be integrated in the equations of motion is defined according to experimental measurements found in literature, in the case of durotaxis. Conversely, in the case of tensotaxis, substrate strain and stress are given by the solution of the mechanical problem, assuming that the extracellular matrix behaves as a hyperelastic Yeoh's solid. In both cases, the proposed model is validated through numerical simulations that qualitatively reproduce different experimental scenarios.

Durotaxis and negative durotaxis: where should cells go?

Durotaxis and negative durotaxis are processes in which cell migration is directed by extracellular stiffness. Durotaxis is the tendency of cells to migrate toward stiffer areas, while negative durotaxis occurs when cells migrate toward regions with lower stiffness. The mechanisms of both processes are not yet fully understood. Additionally, the connection between durotaxis and negative durotaxis remains unclear. In this review, we compare the mechanisms underlying durotaxis and negative durotaxis, summarize the basic principles of both, discuss the possible reasons why some cell types exhibit durotaxis while others exhibit negative durotaxis, propose mechanisms of switching between these processes, and emphasize the challenges in the investigation of durotaxis and negative durotaxis.

Subcellular Force Imbalance in Actin Bundles Induces Nuclear Repositioning and Durotaxis

Durotaxis is a phenomenon in which cells migrate toward substrates of increasing stiffness. However, how cells assimilate substrate stiffness as a directional cue remains poorly understood. In this study, we experimentally show that mouse embryonic fibroblasts can discriminate between different substrate stiffnesses and develop higher traction forces at regions of the cell adhering to the stiffer pillars. In this way, the cells generate a force imbalance between adhesion sites. It is this traction force imbalance that drives durotaxis by providing directionality for cell migration. Significantly, we found that traction forces are transmitted via LINC complexes to the cell nucleus, which serves to maintain the global force imbalance. In this way, LINC complexes play an essential role in anterograde nuclear movement and durotaxis. This conclusion is supported by the fact that LINC complex-deficient cells are incapable of durotaxis and instead migrate randomly on substrates featuring a stiffness gradient.

A Large-format Polyacrylamide Gel with Controllable Matrix Mechanics for Mammalian Cell Culture and Conditioned Media Production

Tissue culture plastic has been used for routine cell culture and in vitro experiments for over 50 years. However, cells are mechanically responsive and behave differently on hard surfaces than they do on softer substrates. Polyacrylamide gels have become a popular hydrogel of choice for controlling surface stiffness and ligand density for cell adhesion. Many synthesis methods use coverslips and small gel surface areas for cell culture, which are amenable to microscopy-based experiments. However, none of the currently published methods can be scaled up to increase the surface area to accommodate conditioned media production, high volume analyte collection, or cell line expansion. To overcome this size limitation, we developed a protocol for synthesizing polyacrylamide in glass dishes using commercially available materials. This enables routine cell culture on soft surfaces and facilitates experiments that require large amounts of analyte, especially studies involving extracellular vesicles and secreted factors.

Forces exerted and transduced by cancer-associated fibroblasts during cancer progression

Although it is well-known that cancer-associated fibroblasts (CAFs) play a key role in regulating tumor progression, the effects of mechanical tissue changes on CAFs are understudied. Myofibroblastic CAFs (myCAFs), in particular, are known to alter tumor matrix architecture and composition, heavily influencing the mechanical forces in the tumor microenvironment (TME), but much less is known about how these mechanical changes initiate and maintain the myCAF phenotype. Additionally, recent studies have pointed to the existence of CAFs in circulating tumor cell clusters, indicating that CAFs may be subject to mechanical forces beyond the primary TME. Due to their pivotal role in cancer progression, targeting CAF mechanical regulation may provide therapeutic benefit. Here, we will discuss current knowledge and summarize existing gaps in how CAFs regulate and are regulated by matrix mechanics, including through stiffness, solid and fluid stresses, and fluid shear stress.

Tunable hybrid hydrogels with multicellular spheroids for modeling desmoplastic pancreatic cancer

The tumor microenvironment consists of diverse, complex etiological factors. The matrix component of pancreatic ductal adenocarcinoma (PDAC) plays an important role not only in physical properties such as tissue rigidity but also in cancer progression and therapeutic responsiveness. Although significant efforts have been made to model desmoplastic PDAC, existing models could not fully recapitulate the etiology to mimic and understand the progression of PDAC. Here, two major components in desmoplastic pancreatic matrices, hyaluronic acid- and gelatin-based hydrogels, are engineered to provide matrices for tumor spheroids composed of PDAC and cancer-associated fibroblasts (CAF). Shape analysis profiles reveals that incorporating CAF contributes to a more compact tissue formation. Higher expression levels of markers associated with proliferation, epithelial to mesenchymal transition, mechanotransduction, and progression are observed for cancer-CAF spheroids cultured in hyper desmoplastic matrix-mimicking hydrogels, while the trend can be observed when those are cultured in desmoplastic matrix-mimicking hydrogels with the presence of transforming growth factor-β1 (TGF-β1). The proposed multicellular pancreatic tumor model, in combination with proper mechanical properties and TGF-β1 supplement, makes strides in developing advanced pancreatic models for resembling and monitoring the progression of pancreatic tumors, which could be potentially applicable for realizing personalized medicine and drug testing applications.

Intracellular mechanics and TBX3 expression jointly dictate the spreading mode of melanoma cells in 3D environments

Cell stiffness and T-box transcription factor 3 (TBX3) expression have been identified as biomarkers of melanoma metastasis in 2D environments. This study aimed to determine how mechanical and biochemical properties of melanoma cells change during cluster formation in 3D environments. Vertical growth phase (VGP) and metastatic (MET) melanoma cells were embedded in 3D collagen matrices of 2 and 4 mg/ml collagen concentrations, representing low and high matrix stiffness. Mitochondrial fluctuation, intracellular stiffness, and TBX3 expression were quantified before and during cluster formation. In isolated cells, mitochondrial fluctuation decreased and intracellular stiffness increased with increase in disease stage from VGP to MET and increased matrix stiffness. TBX3 was highly expressed in soft matrices but diminished in stiff matrices for VGP and MET cells. Cluster formation of VGP cells was excessive in soft matrices but limited in stiff matrices, whereas for MET cells it was limited in soft and stiff matrices. In soft matrices, VGP cells did not change the intracellular properties, whereas MET cells exhibited increased mitochondrial fluctuation and decreased TBX3 expression. In stiff matrices, mitochondrial fluctuation and TBX3 expression increased in VGP and MET, and intracellular stiffness increased in VGP but decreased in MET cells. The findings suggest that soft extracellular environments are more favourable for tumour growth, and high TBX3 levels mediate collective cell migration and tumour growth in the earlier VGP disease stage but play a lesser role in the later metastatic stage of melanoma.

The Matrix Reloaded-The Role of the Extracellular Matrix in Cancer

As the core component of all organs, the extracellular matrix (ECM) is an interlocking macromolecular meshwork of proteins, glycoproteins, and proteoglycans that provides mechanical support to cells and tissues. In cancer, the ECM can be remodelled in response to environmental cues, and it controls a plethora of cellular functions, including metabolism, cell polarity, migration, and proliferation, to sustain and support oncogenesis. The biophysical and biochemical properties of the ECM, such as its structural arrangement and being a reservoir for bioactive molecules, control several intra- and intercellular signalling pathways and induce cytoskeletal changes that alter cell shapes, behaviour, and viability. Desmoplasia is a major component of solid tumours. The abnormal deposition and composition of the tumour matrix lead to biochemical and biomechanical alterations that determine disease development and resistance to treatment. This review summarises the complex roles of ECM in cancer and highlights the possible therapeutic targets and how to potentially remodel the dysregulated ECM in the future. Furthering our understanding of the ECM in cancer is important as the modification of the ECM will probably become an important tool in the characterisation of individual tumours and personalised treatment options.

The role of the Na+/Ca2+-exchanger (NCX) in cancer-associated fibroblasts

Cancer is characterized by uncontrolled growth, invasion, and metastasis. In addition to solid cancer cells, cancer-associated fibroblasts (CAFs) play important roles in cancer pathophysiology. They arise from "healthy" cells but get manipulated by solid cancer cells to supply them and develop a tumor microenvironment (TME) that protects the cancer cells from the immune defense. A wide variety of cell types can differentiate into CAFs, including fibroblasts, endothelial cells, and epithelial cells. Precise Ca²⁺ regulation is essential for each cell including CAFs. The electrogenic Na⁺/Ca²⁺ exchanger (NCX) is one of the ubiquitously expressed regulatory Ca²⁺ transport proteins that rapidly responds to changes of the intracellular ion concentrations. Its transport function is also influenced by the membrane potential and thereby indirectly by the activity of ion channels. NCX transports Ca²⁺ out of the cell (forward mode) or allows its influx (reverse mode), always in exchange for 3 Na⁺ ions that are moved into the opposite direction. In this review, we discuss the functional roles NCX has in CAFs and how these depend on the properties of the TME. NCX activity modifies migration and leads to a reduced proliferation and apoptosis. The effect of the NCX in fibrosis is still largely unknown.

Reprogramming of Activated Pancreatic Stellate Cells via Mechanical Modulation of Transmembrane Force-sensitive N-cadherin Receptor

Cancer has been the leading cause of death due mainly to tumor metastasis. The tumor microenvironment plays a key role in tumor metastasis. As the main stromal cells in tumor microenvironment originated from activated fibroblast, cancer-associated fibroblasts (CAFs) play a major role in promoting tumor metastasis. A promising therapeutic avenue is reprogramming of CAFs into tumor-restraining quiescence state. In this study, we observed that CAF-like active pancreatic stellate cells (PSCs) interact with each other via N-cadherin, a force-sensitive transmembrane receptor. Since N-cadherin ligation mediated mechanotransduction has been reported to restrict integrin mediated signalling, we thus hypothesized that the reprogramming of activated PSCs by mechanical modulation of N-cadherin ligation might be possible. To test this hypothesis, we grafted N-cadherin ligand (HAVDI peptide) onto soft polyethylene glycol hydrogel substrate prior to cell adhesion to mimic cell-cell interaction via N-cadherin ligation. We found that the activated PSCs could be reprogrammed to their original quiescent state when transferred onto the substrate with immobilized HAVDI peptide. These results reveal a key role of mechanosensing by intercellular transmembrane receptor in reprogramming of activated PSCs, and provide a potential way for designing novel therapeutic strategies for cancer treatment.

Probing the effect of glycosaminoglycan depletion on integrin interactions with collagen I fibrils in the native extracellular matrix environment

Fibrillar collagen-integrin interactions in the extracellular matrix (ECM) regulate a multitude of cellular processes and cell signalling. Collagen I fibrils serve as the molecular scaffolding for connective tissues throughout the human body and are the most abundant protein building blocks in the ECM. The ECM environment is diverse, made up of several ECM proteins, enzymes, and proteoglycans. In particular, glycosaminoglycans (GAGs), anionic polysaccharides that decorate proteoglycans, become depleted in the ECM with natural aging and their mis-regulation has been linked to cancers and other diseases. The impact of GAG depletion in the ECM environment on collagen I protein interactions and on mechanical properties is not well understood. Here, we integrate ELISA protein binding assays with liquid high-resolution atomic force microscopy (AFM) to assess the effects of GAG depletion on the interaction of collagen I fibrils with the integrin α2I domain using separate rat tails. ELISA binding assays demonstrate that α2I preferentially binds to GAG-depleted collagen I fibrils in comparison to native fibrils. By amplitude modulated AFM in air and in solution, we find that GAG-depleted collagen I fibrils retain structural features of the native fibrils, including their characteristic D-banding pattern, a key structural motif. AFM fast force mapping in solution shows that GAG depletion reduces the stiffness of individual fibrils, lowering the indentation modulus by half compared to native fibrils. Together these results shed new light on how GAGs influence collagen I fibril-integrin interactions and may aid in strategies to treat diseases that result from GAG mis-regulation.

Extracellular matrix mechanobiology in cancer cell migration

The extracellular matrix (ECM) is pivotal in modulating tumor progression. Besides chemically stimulating tumor cells, it also offers physical support that orchestrates the sequence of events in the metastatic cascade upon dynamically modulating cell mechanosensation. Understanding this translation between matrix biophysical cues and intracellular signaling has led to rapid growth in the interdisciplinary field of cancer mechanobiology in the last decade. Substantial efforts have been made to develop novel in vitro tumor mimicking platforms to visualize and quantify the mechanical forces within the tissue that dictate tumor cell invasion and metastatic growth. This review highlights recent findings on tumor matrix biophysical cues such as fibrillar arrangement, crosslinking density, confinement, rigidity, topography, and non-linear mechanics and their implications on tumor cell behavior. We also emphasize how perturbations in these cues alter cellular mechanisms of mechanotransduction, consequently enhancing malignancy. Finally, we elucidate engineering techniques to individually emulate the mechanical properties of tumors that could help serve as toolkits for developing and testing ECM-targeted therapeutics on novel bioengineered tumor platforms. STATEMENT OF SIGNIFICANCE: Disrupted ECM mechanics is a driving force for transitioning incipient cells to life-threatening malignant variants. Understanding these ECM changes can be crucial as they may aid in developing several efficacious drugs that not only focus on inducing cytotoxic effects but also target specific matrix mechanical cues that support and enhance tumor invasiveness. Designing and implementing an optimal tumor mimic can allow us to predictively map biophysical cue-modulated cell behaviors and facilitate the design of improved lab-grown tumor models with accurately controlled structural features. This review focuses on the abnormal changes within the ECM during tumorigenesis and its implications on tumor cell-matrix mechanoreciprocity. Additionally, it accentuates engineering approaches to produce ECM features of varying levels of complexity which is critical for improving the efficiency of current engineered tumor tissue models.

Biomimetic virus-based soft niche for ischemic diseases

The essential therapeutic cues provided by a nanofibrous arginine-glycine-aspartic acid-engineered M13 phage were exploited as extracellular matrix (ECM)-mimicking niches, contributing to de novo soft tissue niche engineering. The interplay of biomimetic phage cues with surrounding organ tissues was identified, and cells were implanted between tissues to achieve an appropriate soft tissue niche that enables the proper functioning of the implanted stem cells at the injured site. With the polyacrylamide (PA) hydrogel mimicking the soft tissue organ stiffness ranges, it was found that biochemical and topological cues in conjunction with the ∼1-2 kPa elastic and mechanical cues of engineered phage nanofibers in soft tissues efficiently enhance the desired response of implanted stem cells. This phage cue with angiogenic and antioxidant functions overcomes the pathological environment to support implanted cells and surrounding soft tissues at the ischemic site, thereby successfully decreasing myogenic degeneration, minimizing fibrosis, and enhancing blood vessel regeneration with M2 macrophage polarization by improving the survival of the implanted endothelial progenitor cells (EPC) in an ischemic mouse model. These biomimetic phage nanofiber cues are considerably supportive of cell therapy, as they establish promising therapeutic extracellular de novo soft tissue niches for curing ischemic diseases.

Increased Stiffness Downregulates Focal Adhesion Kinase Expression in Pancreatic Cancer Cells Cultured in 3D Self-Assembling Peptide Scaffolds

The focal adhesion kinase (FAK) is a non-receptor tyrosine kinase that participates in integrin-mediated signal transduction and contributes to different biological processes, such as cell migration, survival, proliferation and angiogenesis. Moreover, FAK can be activated by autophosphorylation at position Y397 and trigger different signaling pathways in response to increased extracellular matrix stiffness. In addition, FAK is overexpressed and/or hyperactivated in many epithelial cancers, and its expression correlates with tumor malignancy and invasion potential. One of the characteristics of solid tumors is an over deposition of ECM components, which generates a stiff microenvironment that promotes, among other features, sustained cell proliferation and survival. Researchers are, therefore, increasingly developing cell culture models to mimic the increased stiffness associated with these kinds of tumors. In the present work, we have developed a new 3D in vitro model to study the effect of matrix stiffness in pancreatic ductal adenocarcinoma (PDAC) cells as this kind of tumor is characterized by a desmoplastic stroma and an increased stiffness compared to its normal counterpart. For that, we have used a synthetic self-assembling peptide nanofiber matrix, RAD16-I, which does not suffer a significant degradation in vitro, thus allowing to maintain the same local stiffness along culture time. We show that increased matrix stiffness in synthetic 3D RAD16-I gels, but not in collagen type I scaffolds, promotes FAK downregulation at a protein level in all the cell lines analyzed. Moreover, even though it has classically been described that stiff 3D matrices promote an increase in pFAK^Y397/FAK proteins, we found that this ratio in soft and stiff RAD16-I gels is cell-type-dependent. This study highlights how cell response to increased matrix stiffness greatly depends on the nature of the matrix used for 3D culture.

TRPC1 channels regulate the activation of pancreatic stellate cells through ERK1/2 and SMAD2 pathways and perpetuate their pressure-mediated activation

Pancreatic stellate cell (PSC) activation is a major event occurring during pancreatic ductal adenocarcinoma (PDAC) development. Up to now mechanisms underlying their activation by mechanical cues such as the elevated tissue pressure in PDAC remain poorly understood. Here we investigate the role of one potential mechano-transducer, TRPC1 ion channel, in PSC activation. Using pre-activated human siTRPC1 and murine TRPC1-KO PSCs, we show that TRPC1 promotes αSMA (α-smooth muscle actin) expression, the main activation marker, in cooperation with the phosphorylated SMAD2, under normal and elevated pressure. Functional studies following TRPC1 silencing demonstrate the dual role of TRPC1 in the modulation of PSC proliferation and IL-6 secretion through the activation of ERK1/2 and SMAD2 pathways. Moreover, pressurization changes the mechanical behavior of PSCs by increasing their cellular stiffness and emitted traction forces in a TRPC1-dependent manner. In summary, these results point to a role of TRPC1 channels in sensing and transducing the characteristic mechanical properties of the PDAC microenvironment in PSCs.

Modeling the mechanical stiffness of pancreatic ductal adenocarcinoma

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The PDAC stroma stiffness underlines its malignant behavior and drug resistance.

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3D in vitro cultures must model the PDAC stroma to effectively drug efficacy.

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PSCs are responsible for the stroma, and its activity is increased with TGF-β.

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Develop a 3D culture model of PDAC, which includes PSCs and TGF-β.

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Assess the mechanical stiffness, stain for collagen, and investigate gemcitabine efficacy.

Despite improvements in the understanding of disease biology, pancreatic ductal adenocarcinoma (PDAC) remains the most malignant cancer of the pancreas. PDAC constitutes ∼95% of all pancreatic cancers, and it is highly resistant to therapeutics. The increased tissue rigidity, which stems from the rich fibrotic stroma in the tumor microenvironment, is central to disease development, physiology, and resistance to drug perfusion. Pancreatic stellate cells (PSCs) are responsible for overproduction of extracellular matrix in the fibrotic stroma, and this is exacerbated by the overexpression of transforming growth factor-β (TGF-β). However, there are few in vitro PDAC models, which include both PSCs and TGF-β or mimic in vivo-like tumor stiffness. In this study, we present a three-dimensional in vitro PDAC model, which includes PSCs and TGF-β, and recapitulates PDAC tissue mechanical stiffness. Using oscillatory shear rheology, we show the mechanical stiffness of the model is within range of the PDAC tissue stiffness by day 21 of culture and highlight that the matrix environment is essential to adequately capture PDAC disease. PDAC is a complex, aggressive disease with poor prognosis, and biophysically relevant in vitro PDAC models, which take into account tissue mechanics, will provide improved tumor models for effective therapeutic assessment.

Mechanobiological Implications of Cancer Progression in Space

The human body is normally adapted to maintain homeostasis in a terrestrial environment. The novel conditions of a space environment introduce challenges that changes the cellular response to its surroundings. Such an alteration causes physical changes in the extracellular microenvironment, inducing the secretion of cytokines such as interleukin-6 (IL-6) and tumor growth factor-β (TGF-β) from cancer cells to enhance cancer malignancy. Cancer is one of the most prominent cell types to be affected by mechanical cues via active interaction with the tumor microenvironment. However, the mechanism by which cancer cells mechanotransduce in the space environment, as well as the influence of this process on human health, have not been fully elucidated. Due to the growing interest in space biology, this article reviews cancer cell responses to the representative conditions altered in space: microgravity, decompression, and irradiation. Interestingly, cytokine and gene expression that assist in tumor survival, invasive phenotypic transformation, and cancer cell proliferation are upregulated when exposed to both simulated and actual space conditions. The necessity of further research on space mechanobiology such as simulating more complex in vivo experiments or finding other mechanical cues that may be encountered during spaceflight are emphasized.

Stromal architecture directs early dissemination in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDA) is an extremely metastatic and lethal disease. Here, in both murine and human PDA, we demonstrate that extracellular matrix architecture regulates cell extrusion and subsequent invasion from intact ductal structures through tumor-associated collagen signatures (TACS). This results in early dissemination from histologically premalignant lesions and continual invasion from well-differentiated disease, and it suggests TACS as a biomarker to aid in the pathologic assessment of early disease. Furthermore, we show that pancreatitis results in invasion-conducive architectures, thus priming the stroma prior to malignant disease. Analysis in potentially novel microfluidic-derived microtissues and in vivo demonstrates decreased extrusion and invasion following focal adhesion kinase (FAK) inhibition, consistent with decreased metastasis. Thus, data suggest that targeting FAK or strategies to reengineer and normalize tumor microenvironments may have roles not only in very early disease, but also for limiting continued dissemination from unresectable disease. Likewise, it may be beneficial to employ stroma-targeting strategies to resolve precursor diseases such as pancreatitis in order to remove stromal architectures that increase risk for early dissemination.

Targeting Tumor-Stromal Interactions in Pancreatic Cancer: Impact of Collagens and Mechanical Traits

Pancreatic ductal adenocarcinoma (PDAC) has one of the worst outcomes among cancers with a 5-years survival rate of below 10%. This is a result of late diagnosis and the lack of effective treatments. The tumor is characterized by a highly fibrotic stroma containing distinct cellular components, embedded within an extracellular matrix (ECM). This ECM-abundant tumor microenvironment (TME) in PDAC plays a pivotal role in tumor progression and resistance to treatment. Cancer-associated fibroblasts (CAFs), being a dominant cell type of the stroma, are in fact functionally heterogeneous populations of cells within the TME. Certain subtypes of CAFs are the main producer of the ECM components of the stroma, with the most abundant one being the collagen family of proteins. Collagens are large macromolecules that upon deposition into the ECM form supramolecular fibrillar structures which provide a mechanical framework to the TME. They not only bring structure to the tissue by being the main structural proteins but also contain binding domains that interact with surface receptors on the cancer cells. These interactions can induce various responses in the cancer cells and activate signaling pathways leading to epithelial-to-mesenchymal transition (EMT) and ultimately metastasis. In addition, collagens are one of the main contributors to building up mechanical forces in the tumor. These forces influence the signaling pathways that are involved in cell motility and tumor progression and affect tumor microstructure and tissue stiffness by exerting solid stress and interstitial fluid pressure on the cells. Taken together, the TME is subjected to various types of mechanical forces and interactions that affect tumor progression, metastasis, and drug response. In this review article, we aim to summarize and contextualize the recent knowledge of components of the PDAC stroma, especially the role of different collagens and mechanical traits on tumor progression. We furthermore discuss different experimental models available for studying tumor-stromal interactions and finally discuss potential therapeutic targets within the stroma.

"Viscotaxis"- directed migration of mesenchymal stem cells in response to loss modulus gradient

Directed cell migration plays a crucial role in physiological and pathological conditions. One important mechanical cue, known to influence cell migration, is the gradient of substrate elastic modulus (E). However, the cellular microenvironment is viscoelastic and hence the elastic property alone is not sufficient to define its material characteristics. To bridge this gap, in this study, we investigated the influence of the gradient of viscous property of the substrate, as defined by loss modulus (G″) on cell migration. We cultured human mesenchymal stem cells (hMSCs) on a collagen-coated polyacrylamide gel with constant storage modulus (G') but with a gradient in the loss modulus (G″). We found hMSCs to migrate from high to low loss modulus. We have termed this form of directional cellular migration as "Viscotaxis". We hypothesize that the high loss modulus regime deforms more due to creep in the long timescale when subjected to cellular traction. Such differential deformation drives the observed Viscotaxis. To verify our hypothesis, we disrupted the actomyosin contractility with myosin inhibitor blebbistatin and ROCK inhibitor Y27632, and found the directional migration to disappear. Further, such time-dependent creep of the high loss material should lead to lower traction, shorter lifetime of the focal adhesions, and dynamic cell morphology, which was indeed found to be the case. Together, findings in this paper highlight the importance of considering the viscous modulus while preparing stiffness-based substrates for the field of tissue engineering. STATEMENT OF SIGNIFICANCE: While the effect of substrate elastic modulus has been investigated extensively in the context of cell biology, the role of substrate viscoelasticity is poorly understood. This omission is surprising as our body is not elastic, but viscoelastic. Hence, the role of viscoelasticity needs to be investigated at depth in various cellular contexts. One such important context is cell migration. Cell migration is important in morphogenesis, immune response, wound healing, and cancer, to name a few. While it is known that cells migrate when presented with a substrate with a rigidity gradient, cellular behavior in response to viscoelastic gradient has never been investigated. The findings of this paper not only reveal a completely novel cellular taxis or directed migration, it also improves our understanding of cell mechanics significantly.

The Extracellular Matrix in Pancreatic Cancer: Description of a Complex Network and Promising Therapeutic Options

The stroma is a relevant player in driving and supporting the progression of pancreatic ductal adenocarcinoma (PDAC), and a large body of evidence highlights its role in hindering the efficacy of current therapies. In fact, the dense extracellular matrix (ECM) characterizing this tumor acts as a natural physical barrier, impairing drug penetration. Consequently, all of the approaches combining stroma-targeting and anticancer therapy constitute an appealing option for improving drug penetration. Several strategies have been adopted in order to target the PDAC stroma, such as the depletion of ECM components and the targeting of cancer-associated fibroblasts (CAFs), which are responsible for the increased matrix deposition in cancer. Additionally, the leaky and collapsing blood vessels characterizing the tumor might be normalized, thus restoring blood perfusion and allowing drug penetration. Even though many stroma-targeting strategies have reported disappointing results in clinical trials, the ECM offers a wide range of potential therapeutic targets that are now being investigated. The dense ECM might be bypassed by implementing nanoparticle-based systems or by using mesenchymal stem cells as drug carriers. The present review aims to provide an overview of the principal mechanisms involved in the ECM remodeling and of new promising therapeutic strategies for PDAC.

Molecular mechanisms of pancreatic myofibroblast activation in chronic pancreatitis and pancreatic ductal adenocarcinoma

Pancreatic fibrosis (PF) is an essential component of the pathobiology of chronic pancreatitis (CP) and pancreatic ductal adenocarcinoma (PDAC). Activated pancreatic myofibroblasts (PMFs) are crucial for the deposition of the extracellular matrix, and fibrotic reaction in response to sustained signaling. Consequently, understanding of the molecular mechanisms of PMF activation is not only critical for understanding CP and PDAC biology but is also a fertile area of research for the development of novel therapeutic strategies for pancreatic pathologies. This review analyzes the key signaling events that drive PMF activation including, initiating signals from transforming growth factor-β1, platelet derived growth factor, as well as other microenvironmental cues, like hypoxia and extracellular matrix rigidity. Further, we discussed the intracellular signal events contributing to PMF activation, and crosstalk with different components of tumor microenvironment. Additionally, association of epidemiologically established risk factors for CP and PDAC, like alcohol intake, tobacco exposure, and metabolic factors with PMF activation, is discussed to comprehend the role of lifestyle factors on pancreatic pathologies. Overall, this analysis provides insight into the biology of PMF activation and highlights salient features of this process, which offer promising therapeutic targets.

Mechanics of developmental migration

The ability to migrate is a fundamental property of animal cells which is essential for development, homeostasis and disease progression. Migrating cells sense and respond to biochemical and mechanical cues by rapidly modifying their intrinsic repertoire of signalling molecules and by altering their force generating and transducing machinery. We have a wealth of information about the chemical cues and signalling responses that cells use during migration. Our understanding of the role of forces in cell migration is rapidly evolving but is still best understood in the context of cells migrating in 2D and 3D environments in vitro. Advances in live imaging of developing embryos combined with the use of experimental and theoretical tools to quantify and analyse forces in vivo, has begun to shed light on the role of mechanics in driving embryonic cell migration. In this review, we focus on the recent studies uncovering the physical basis of embryonic cell migration in vivo. We look at the physical basis of the classical steps of cell migration such as protrusion formation and cell body translocation and review the recent research on how these processes work in the complex 3D microenvironment of a developing organism.

Self-Assembling Polypeptide Hydrogels as a Platform to Recapitulate the Tumor Microenvironment

Simple Summary

The tumor microenvironment is characterized by increased tissue stiffness, low (acidic) pH, and elevated temperature, all of which contribute to the development of cancer. Improving our in vitro models of cancer, therefore, requires the development of cell culture platforms that can mimic these microenvironmental properties. Here, we study a new biomaterial composed of short amino acid chains that self-assemble into a fibrous hydrogel network. This material enables simultaneous and independent tuning of substrate rigidity, extracellular pH, and temperature, allowing us to mimic both healthy tissues and the tumor microenvironment. We used this platform to study the effect of these conditions on pancreatic cancer cells and found that high substrate rigidity and low pH promote proliferation and survival of cancer cells and activate important signaling pathways associated with cancer progression.

Abstract

The tumor microenvironment plays a critical role in modulating cancer cell migration, metabolism, and malignancy, thus, highlighting the need to develop in vitro culture systems that can recapitulate its abnormal properties. While a variety of stiffness-tunable biomaterials, reviewed here, have been developed to mimic the rigidity of the tumor extracellular matrix, culture systems that can recapitulate the broader extracellular context of the tumor microenvironment (including pH and temperature) remain comparably unexplored, partially due to the difficulty in independently tuning these parameters. Here, we investigate a self-assembled polypeptide network hydrogel as a cell culture platform and demonstrate that the culture parameters, including the substrate stiffness, extracellular pH and temperature, can be independently controlled. We then use this biomaterial as a cell culture substrate to assess the effect of stiffness, pH and temperature on Suit2 cells, a pancreatic cancer cell line, and demonstrate that these microenvironmental factors can regulate two critical transcription factors in cancer: yes-associated protein 1 (YAP) and hypoxia inducible factor (HIF-1A).

Mechanosensitive Regulation of Fibrosis

Cells in the human body experience and integrate a wide variety of environmental cues. A growing interest in tissue mechanics in the past four decades has shown that the mechanical properties of tissue drive key biological processes and facilitate disease development. However, tissue stiffness is not only a potent behavioral cue, but also a product of cellular signaling activity. This review explores both roles of tissue stiffness in the context of inflammation and fibrosis, and the important molecular players driving such processes. During inflammation, proinflammatory cytokines upregulate tissue stiffness by increasing hydrostatic pressure, ECM deposition, and ECM remodeling. As the ECM stiffens, cells involved in the immune response employ intricate molecular sensors to probe and alter their mechanical environment, thereby facilitating immune cell recruitment and potentiating the fibrotic phenotype. This powerful feedforward loop raises numerous possibilities for drug development and warrants further investigation into the mechanisms specific to different fibrotic diseases.

Durotaxis: the mechanical control of directed cell migration

Directed cell migration is essential for cells to efficiently migrate in physiological and pathological processes. While migrating in their native environment, cells interact with multiple types of cues, such as mechanical and chemical signals. The role of chemical guidance via chemotaxis has been studied in the past, the understanding of mechanical guidance of cell migration via durotaxis remained unclear until very recently. Nonetheless, durotaxis has become a topic of intensive research and several advances have been made in the study of mechanically guided cell migration across multiple fields. Thus, in this article we provide a state of the art about durotaxis by discussing in silico, in vitro and in vivo data. We also present insights on the general mechanisms by which cells sense, transduce and respond to environmental mechanics, to then contextualize these mechanisms in the process of durotaxis and explain how cells bias their migration in anisotropic substrates. Furthermore, we discuss what is known about durotaxis in vivo and we comment on how haptotaxis could arise from integrating durotaxis and chemotaxis in native environments.

Interfacial Curvature in Confined Coculture Directs Stromal Cell Activity with Spatial Corralling of Pancreatic Cancer Cells

Interfacial cues in the tumor microenvironment direct the activity and assembly of multiple cell types. Pancreatic cancer, along with breast and prostate cancers, is enriched with cancer-associated fibroblasts (CAFs) that activate to coordinate the deposition of the extracellular matrix, which can comprise over 90% of the tumor mass. While it is clear that matrix underlies the severity of the disease, the relationship between stromal-tumor cell assembly and cell-matrix dynamics remains elusive. Micropatterned hydrogels deconstruct the interplay between matrix stiffness and geometric confinement, guiding heterotypic cell populations and matrix assembly in pancreatic cancer. Interfacial cues at the perimeter of microislands guide CAF migration and direct cancer cell assembly. Computational modeling shows curvature-stress dependent cellular localization for cancer and CAFs in coculture. Regions of convex curvature enhance edge stress that activates a myofibroblast phenotype in the CAFs with migration and increased collagen I deposition, ultimately leading to a central "corralling" of cancer cells. Inhibiting mechanotransduction pathways decreases CAF activation and the associated corralling phenotype. Together, this work reveals how interfacial biophysical cues underpin aspects of stromal desmoplasia, a hallmark of disease severity and chemoresistance in the pancreatic, breast, and prostate cancers, thereby providing a tool to expand stroma-targeting therapeutic strategies.

Hydrogel Models with Stiffness Gradients for Interrogating Pancreatic Cancer Cell Fate

Pancreatic ductal adenocarcinoma (PDAC) is the most common type of pancreatic cancer and has seen only modest improvements in patient survival rate over the past few decades. PDAC is highly aggressive and resistant to chemotherapy, owing to the presence of a dense and hypovascularized fibrotic tissue, which is composed of stromal cells and extracellular matrices. Increase deposition and crosslinking of matrices by stromal cells lead to a heterogeneous microenvironment that aids in PDAC development. In the past decade, various hydrogel-based, in vitro tumor models have been developed to mimic and recapitulate aspects of the tumor microenvironment in PDAC. Advances in hydrogel chemistry and engineering should provide a venue for discovering new insights regarding how matrix properties govern PDAC cell growth, migration, invasion, and drug resistance. These engineered hydrogels are ideal for understanding how variation in matrix properties contributes to the progressiveness of cancer cells, including durotaxis, the directional migration of cells in response to a stiffness gradient. This review surveys the various hydrogel-based, in vitro tumor models and the methods to generate gradient stiffness for studying migration and other cancer cell fate processes in PDAC.

Adhesion strength and contractility enable metastatic cells to become adurotactic

Significant changes in cell stiffness, contractility, and adhesion, i.e., mechanotype, are observed during a variety of biological processes. Whether cell mechanics merely change as a side effect of or driver for biological processes is still unclear. Here, we sort genotypically similar metastatic cancer cells into strongly adherent (SA) versus weakly adherent (WA) phenotypes to study how contractility and adhesion differences alter the ability of cells to sense and respond to gradients in material stiffness. We observe that SA cells migrate up a stiffness gradient, or durotax, while WA cells largely ignore the gradient, i.e., adurotax. Biophysical modeling and experimental validation suggest that differences in cell migration and durotaxis between weakly and strongly adherent cells are driven by differences in intra-cellular actomyosin activity. These results provide a direct relationship between cell phenotype and durotaxis and suggest how, unlike other senescent cells, metastatic cancer cells navigate against stiffness gradients.

A Perfusion Bioreactor for Longitudinal Monitoring of Bioengineered Liver Constructs

In the field of in vitro liver disease models, decellularised organ scaffolds maintain the original biomechanical and biological properties of the extracellular matrix and are established supports for in vitro cell culture. However, tissue engineering approaches based on whole organ decellularized scaffolds are hampered by the scarcity of appropriate bioreactors that provide controlled 3D culture conditions. Novel specific bioreactors are needed to support long-term culture of bioengineered constructs allowing non-invasive longitudinal monitoring. Here, we designed and validated a specific bioreactor for long-term 3D culture of whole liver constructs. Whole liver scaffolds were generated by perfusion decellularisation of rat livers. Scaffolds were seeded with Luc⁺HepG2 and primary human hepatocytes and cultured in static or dynamic conditions using the custom-made bioreactor. The bioreactor included a syringe pump, for continuous unidirectional flow, and a circuit built to allow non-invasive monitoring of culture parameters and media sampling. The bioreactor allowed non-invasive analysis of cell viability, distribution, and function of Luc⁺HepG2-bioengineered livers cultured for up to 11 days. Constructs cultured in dynamic conditions in the bioreactor showed significantly higher cell viability, measured with bioluminescence, distribution, and functionality (determined by albumin production and expression of CYP enzymes) in comparison to static culture conditions. Finally, our bioreactor supports primary human hepatocyte viability and function for up to 30 days, when seeded in the whole liver scaffolds. Overall, our novel bioreactor is capable of supporting cell survival and metabolism and is suitable for liver tissue engineering for the development of 3D liver disease models.

Ion Channels Orchestrate Pancreatic Ductal Adenocarcinoma Progression and Therapy

Pancreatic ductal adenocarcinoma is a devastating disease with a dismal prognosis. Therapeutic interventions are largely ineffective. A better understanding of the pathophysiology is required. Ion channels contribute substantially to the "hallmarks of cancer." Their expression is dysregulated in cancer, and they are "misused" to drive cancer progression, but the underlying mechanisms are unclear. Ion channels are located in the cell membrane at the interface between the intracellular and extracellular space. They sense and modify the tumor microenvironment which in itself is a driver of PDAC aggressiveness. Ion channels detect, for example, locally altered proton and electrolyte concentrations or mechanical stimuli and transduce signals triggered by these microenvironmental cues through association with intracellular signaling cascades. While these concepts have been firmly established for other cancers, evidence has emerged only recently that ion channels are drivers of PDAC aggressiveness. Particularly, they appear to contribute to two of the characteristic PDAC features: the massive fibrosis of the tumor stroma (desmoplasia) and the efficient immune evasion. Our critical review of the literature clearly shows that there is still a remarkable lack of knowledge with respect to the contribution of ion channels to these two typical PDAC properties. Yet, we can draw parallels from ion channel research in other fibrotic and inflammatory diseases. Evidence is accumulating that pancreatic stellate cells express the same "profibrotic" ion channels. Similarly, it is at least in part known which major ion channels are expressed in those innate and adaptive immune cells that populate the PDAC microenvironment. We explore potential therapeutic avenues derived thereof. Since drugs targeting PDAC-relevant ion channels are already in clinical use, we propose to repurpose those in PDAC. The quest for ion channel targets is both motivated and complicated by the fact that some of the relevant channels, for example, KCa3.1, are functionally expressed in the cancer, stroma, and immune cells. Only in vivo studies will reveal which arm of the balance we should put our weights on when developing channel-targeting PDAC therapies. The time is up to explore the efficacy of ion channel targeting in (transgenic) murine PDAC models before launching clinical trials with repurposed drugs.

The Role of Stellate Cells in Pancreatic Ductal Adenocarcinoma: Targeting Perspectives

Pancreatic ductal adenocarcinoma (PDAC) is a gastrointestinal malignancy with a dismal clinical outcome. Accumulating evidence suggests that activated pancreatic stellate cells (PSCs), the major producers of extracellular matrix (ECM), drive the severe stromal/desmoplastic reaction in PDAC. Furthermore, the crosstalk among PSCs, pancreatic cancer cells (PCCs) as well as other stroma cells can establish a growth-supportive tumor microenvironment (TME) of PDAC, thereby enhancing tumor growth, metastasis, and chemoresistance via various pathways. Recently, targeting stroma has emerged as a promising strategy for PDAC therapy, and several novel strategies have been proposed. The aim of our study is to give a profound review of the role of PSCs in PDAC progression and recent advances in stroma-targeting strategies.

Durotaxis: The Hard Path from In Vitro to In Vivo

Durotaxis, the process by which cells follow gradients of extracellular mechanical stiffness, has been proposed as a mechanism driving directed migration. Despite the lack of evidence for its existence in vivo, durotaxis has become an active field of research, focusing on the mechanism by which cells respond to mechanical stimuli from the environment. In this review, we describe the technical and conceptual advances in the study of durotaxis in vitro, discuss to what extent the evidence suggests durotaxis may occur in vivo, and emphasize the urgent need for in vivo demonstration of durotaxis.

Engineering of biomaterials for tumor modeling

Development of biomaterials mimicking tumor and its microenvironment has recently emerged for the use of drug discovery, precision medicine, and cancer biology. These biomimetic models have developed by reconstituting tumor and stroma cells within the 3D extracellular matrix. The models are recently extended to recapitulate the in vivo tumor microenvironment, including biological, chemical, and mechanical conditions tailored for specific cancer type and its microenvironment. In spite of the recent emergence of various innovative engineered tumor models, many of these models are still early stage to be adapted for cancer research. In this article, we review the current status of biomaterials engineering for tumor models considering three main aspects - cellular engineering, matrix engineering, and engineering for microenvironmental conditions. Considering cancer-specific variability in these aspects, our discussion is focused on pancreatic cancer, specifically pancreatic ductal adenocarcinoma (PDAC). In addition, we further discussed the current challenges and future opportunities to create reliable and relevant tumor models.

Recapitulating pancreatic tumor microenvironment through synergistic use of patient organoids and organ-on-a-chip vasculature

Tumor progression relies heavily on the interaction between the neoplastic epithelial cells and their surrounding stromal partners. This cell cross-talk affects stromal development, and ultimately the heterogeneity impacts drug efflux and efficacy. To mimic this evolving paradigm, we have micro-engineered a three-dimensional (3D) vascularized pancreatic adenocarcinoma tissue in a tri-culture system composed of patient derived pancreatic organoids, primary human fibroblasts and endothelial cells on a perfusable InVADE platform situated in a 96-well plate. Uniquely, through synergistic engineering we combined the benefits of cellular fidelity of patient tumor derived organoids with the addressability of a plastic organ-on-a-chip platform. Validation of this platform included demonstrating the growth of pancreatic tumor organoids by monitoring the change in metabolic activity of the tissue. Investigation of tumor microenvironmental behavior highlighted the role of fibroblasts in symbiosis with patient organoid cells, resulting in a six-fold increase of collagen deposition and a corresponding increase in tissue stiffness in comparison to fibroblast free controls. The value of a perfusable vascular network was evident in drug screening, as perfusion of gemcitabine into a stiffened matrix did not show the dose-dependent effects on tumor viability as those under static conditions. These findings demonstrate the importance of studying the dynamic synergistic relationship between patient cells with stromal fibroblasts, in a 3D perfused vascular network, to accurately understand and recapitulate the tumor microenvironment.

Force balancing ACT-IN the tumor microenvironment: Cytoskeletal modifications in cancer and stromal cells to promote malignancy

The tumor microenvironment is a complex milieu that dictates the growth, invasion, and metastasis of cancer cells. Both cancer and stromal cells in the tumor tissue encounter and adapt to a variety of extracellular factors, and subsequently contribute and drive the progression of the disease to more advanced stages. As the disease progresses, a small population of cancer cells becomes more invasive through a complex process known as epithelial-mesenchymal transition, and nearby stromal cells assume a carcinoma associated fibroblast phenotype characterized by enhanced migration, cell contractility, and matrix secretion with the ability to reorganize extracellular matrices. As cells transition into more malignant phenotypes their biophysical properties, controlled by the organization of cytoskeletal proteins, are altered. Actin and its associated proteins are essential modulators and facilitators of these changes. As the cells respond to the cues in the microenvironment, actin driven mechanical forces inside and outside the cells also evolve. Recent advances in biophysical techniques have enabled us to probe these actin driven changes in cancer and stromal cells and demarcate their role in driving changes in the microenvironment. Understanding the underlying biophysical mechanisms that drive cancer progression could provide critical insight on novel therapeutic approaches in the fight against cancer.

G Protein-Coupled Estrogen Receptor Regulates Actin Cytoskeleton Dynamics to Impair Cell Polarization

Mechanical forces regulate cell functions through multiple pathways. G protein-coupled estrogen receptor (GPER) is a seven-transmembrane receptor that is ubiquitously expressed across tissues and mediates the acute cellular response to estrogens. Here, we demonstrate an unidentified role of GPER as a cellular mechanoregulator. G protein-coupled estrogen receptor signaling controls the assembly of stress fibers, the dynamics of the associated focal adhesions, and cell polarization via RhoA GTPase (RhoA). G protein-coupled estrogen receptor activation inhibits F-actin polymerization and subsequently triggers a negative feedback that transcriptionally suppresses the expression of monomeric G-actin. Given the broad expression of GPER and the range of cytoskeletal changes modulated by this receptor, our findings position GPER as a key player in mechanotransduction.

RNA-seq reveals the diverse effects of substrate stiffness on epidermal ovarian cancer cells

Background: Increasing evidence has confirmed that ovarian cancer is a mechanically responsive tumor both in vivo and in vitro. However, an understanding of the complete molecular mechanism involved in the response to substrate stiffness is lacking, as the associated transcriptome-wide effects have not been mapped. This limited understanding has restricted the identification of potential mechanically responsive targets in ovarian cancer.

Results: To address these limitations, we used a polyacrylamide hydrogel system with a tunable Young’s modulus that broadly ranged from soft (1 kPa) to normal (6 kPa) and stiff (60 kPa) and investigated the effect of substrate rigidity on the morphology, spreading area, and cytoskeleton of SKOV-3 epidermal ovarian cancer (EOC) cells. RNA-seq analysis of these cells was then performed at appropriate timepoints to map the transcriptome-wide changes associated with stiffness sensing. We identified a large number of stiffness-sensing genes as well as many genes that were enriched in cancer-related pathways. Informed by these diverse expression results and based on bioinformatics analysis, we evaluated the hypothesis that PLEC and TNS2, which are located in focal adhesions and regulated by lnc-ZNF136, may play key roles in the EOC response to substrate stiffness.

Conclusion: Overall, the results of the present study reveal previously unknown features of the EOC stiffness response and provide new insights into EOC metastasis in the clinic.

Concepts of extracellular matrix remodelling in tumour progression and metastasis

Tissues are dynamically shaped by bidirectional communication between resident cells and the extracellular matrix (ECM) through cell-matrix interactions and ECM remodelling. Tumours leverage ECM remodelling to create a microenvironment that promotes tumourigenesis and metastasis. In this review, we focus on how tumour and tumour-associated stromal cells deposit, biochemically and biophysically modify, and degrade tumour-associated ECM. These tumour-driven changes support tumour growth, increase migration of tumour cells, and remodel the ECM in distant organs to allow for metastatic progression. A better understanding of the underlying mechanisms of tumourigenic ECM remodelling is crucial for developing therapeutic treatments for patients.

Tumors are more than cancer cells — the extracellular matrix is a protein structure that organizes all tissues and is altered in cancer. Here, the authors review recent progress in understanding how the cancer cells and tumor-associated stroma cells remodel the extracellular matrix to drive tumor growth and metastasis.

Mechanical Cues Affect Migration and Invasion of Cells From Three Different Directions

Cell migration and invasion is a key driving factor for providing essential cellular functions under physiological conditions or the malignant progression of tumors following downward the metastatic cascade. Although there has been plentiful of molecules identified to support the migration and invasion of cells, the mechanical aspects have not yet been explored in a combined and systematic manner. In addition, the cellular environment has been classically and frequently assumed to be homogeneous for reasons of simplicity. However, motility assays have led to various models for migration covering only some aspects and supporting factors that in some cases also include mechanical factors. Instead of specific models, in this review, a more or less holistic model for cell motility in 3D is envisioned covering all these different aspects with a special emphasis on the mechanical cues from a biophysical perspective. After introducing the mechanical aspects of cell migration and invasion and presenting the heterogeneity of extracellular matrices, the three distinct directions of cell motility focusing on the mechanical aspects are presented. These three different directions are as follows: firstly, the commonly used invasion tests using structural and structure-based mechanical environmental signals; secondly, the mechano-invasion assay, in which cells are studied by mechanical forces to migrate and invade; and thirdly, cell mechanics, including cytoskeletal and nuclear mechanics, to influence cell migration and invasion. Since the interaction between the cell and the microenvironment is bi-directional in these assays, these should be accounted in migration and invasion approaches focusing on the mechanical aspects. Beyond this, there is also the interaction between the cytoskeleton of the cell and its other compartments, such as the cell nucleus. In specific, a three-element approach is presented for addressing the effect of mechanics on cell migration and invasion by including the effect of the mechano-phenotype of the cytoskeleton, nucleus and the cell's microenvironment into the analysis. In precise terms, the combination of these three research approaches including experimental techniques seems to be promising for revealing bi-directional impacts of mechanical alterations of the cellular microenvironment on cells and internal mechanical fluctuations or changes of cells on the surroundings. Finally, different approaches are discussed and thereby a model for the broad impact of mechanics on cell migration and invasion is evolved.

Mechanically stressed cancer microenvironment: Role in pancreatic cancer progression

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal solid malignancies in the world due to its insensitivity to current therapies and its propensity to metastases from the primary tumor mass. This is largely attributed to its complex microenvironment composed of unique stromal cell populations and extracellular matrix (ECM). The recruitment and activation of these cell populations cause an increase in deposition of ECM components, which highly influences the behavior of malignant cells through disrupted forms of signaling. As PDAC progresses from premalignant lesion to invasive carcinoma, this dynamic landscape shields the mass from immune defenses and cytotoxic intervention. This microenvironment influences an invasive cell phenotype through altered forms of mechanical signaling, capable of enacting biochemical changes within cells through activated mechanotransduction pathways. The effects of altered mechanical cues on malignant cell mechanotransduction have long remained enigmatic, particularly in PDAC, whose microenvironment significantly changes over time. A more complete and thorough understanding of PDAC's physical surroundings (microenvironment), mechanosensing proteins, and mechanical properties may help in identifying novel mechanisms that influence disease progression, and thus, provide new potential therapeutic targets.

Syndecan-4 tunes cell mechanics by activating the kindlin-integrin-RhoA pathway

Extensive research over the past decades has identified integrins to be the primary transmembrane receptors that enable cells to respond to external mechanical cues. We reveal here a mechanism whereby syndecan-4 tunes cell mechanics in response to localized tension via a coordinated mechanochemical signalling response that involves activation of two other receptors: epidermal growth factor receptor and β1 integrin. Tension on syndecan-4 induces cell-wide activation of the kindlin-2/β1 integrin/RhoA axis in a PI3K-dependent manner. Furthermore, syndecan-4-mediated tension at the cell-extracellular matrix interface is required for yes-associated protein activation. Extracellular tension on syndecan-4 triggers a conformational change in the cytoplasmic domain, the variable region of which is indispensable for the mechanical adaptation to force, facilitating the assembly of a syndecan-4/α-actinin/F-actin molecular scaffold at the bead adhesion. This mechanotransduction pathway for syndecan-4 should have immediate implications for the broader field of mechanobiology.

Double power-law viscoelastic relaxation of living cells encodes motility trends

Living cells are constantly exchanging momentum with their surroundings. So far, there is no consensus regarding how cells respond to such external stimuli, although it reveals much about their internal structures, motility as well as the emergence of disorders. Here, we report that twelve cell lines, ranging from healthy fibroblasts to cancer cells, hold a ubiquitous double power-law viscoelastic relaxation compatible with the fractional Kelvin-Voigt viscoelastic model. Atomic Force Microscopy measurements in time domain were employed to determine the mechanical parameters, namely, the fast and slow relaxation exponents, the crossover timescale between power law regimes, and the cell stiffness. These cell-dependent quantities show strong correlation with their collective migration and invasiveness properties. Beyond that, the crossover timescale sets the fastest timescale for cells to perform their biological functions.

Desmoplasia and Biophysics in Pancreatic Ductal Adenocarcinoma: Can We Learn From Breast Cancer?

Pancreatic ductal adenocarcinoma (PDAC) treatments have historically focused on targeting tumor cells directly. However, in pancreatic masses, the stroma encasing the malignant epithelial cells constitutes up to 80% to 90% of the tumor bulk. This extracellular matrix, which was previously neglected when designing cancer therapies, is now considered fundamental for tumor progression and drug delivery. Desmoplastic tissue is extensively cross-linked, resulting in tremendous tensile strength. This key pathological feature is procarcinogenic, linking PDAC and breast cancer (BC). Physical forces exerted onto cellular surfaces are detected intracellularly and transduced via biochemical messengers in a process called mechanotransduction. Mechanotransduction and tensional homeostasis are linked, with an integral role in influencing tumor growth, metastasis, and interactions with the immune system. It is essential to enhance our knowledge of these integral elements of parenchymal tumors. We aim to review the topic, with a special emphasis on desmoplastic processes and their importance in pancreatic and BC development and treatments, mindful that innovative diagnostic and therapeutic strategies cannot focus on biochemical pathways alone. We then focus on common therapeutic targets identified in both PDAC and BC models and/or patients, aiming to understand these treatments and draw similarities between the two tumors.