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The extracellular matrix is a fundamental, core component of all tissues and organs, and is essential for the existence of multicellular organisms. From the earliest stages of organism development until death, it regulates and fine-tunes every cellular process in the body. In cancer, the extracellular matrix is altered at the biochemical, biomechanical, architectural and topographical levels, and recent years have seen an exponential increase in the study and recognition of the importance of the matrix in solid tumours. Coupled with the advancement of new technologies to study various elements of the matrix and cell–matrix interactions, we are also beginning to see the deployment of matrix-centric, stromal targeting cancer therapies. This Review touches on many of the facets of matrix biology in solid cancers, including breast, pancreatic and lung cancer, with the aim of highlighting some of the emerging interactions of the matrix and influences that the matrix has on tumour onset, progression and metastatic dissemination, before summarizing the ongoing work in the field aimed at developing therapies to co-target the matrix in cancer and cancer metastasis.Alterations in the extracellular matrix at the biochemical, biomechanical, architectural and topographical levels contribute to the development and progression of solid tumours. Our increased understanding of matrix biology is leading to the development of new approaches that co-target the matrix in cancer, including in metastasis.

Chronic liver disease when accompanied by underlying fibrosis, is characterized by an accumulation of extracellular matrix (ECM) proteins and chronic inflammation. Although traditionally considered as a passive and largely architectural structure, the ECM is now being recognized as a source of potent damage-associated molecular pattern (DAMP)s with immune-active peptides and domains. In parallel, the ECM anchors a range of cytokines, chemokines and growth factors, all of which are capable of modulating immune responses. A growing body of evidence shows that ECM proteins themselves are capable of modulating immunity either directly ligation with immune cell receptors including integrins and TLRs, or indirectly through release of immunoactive molecules such as cytokines which are stored within the ECM structure. Notably, ECM deposition and remodeling during injury and fibrosis can result in release or formation of ECM-DAMPs within the tissue, which can promote local inflammatory immune response and chemotactic immune cell recruitment and inflammation. It is well described that the ECM and immune response are interlinked and mutually participate in driving fibrosis, although their precise interactions in the context of chronic liver disease are poorly understood. This review aims to describe the known pro-/anti-inflammatory and fibrogenic properties of ECM proteins and DAMPs, with particular reference to the immunomodulatory properties of the ECM in the context of chronic liver disease. Finally, we discuss the importance of developing novel biotechnological platforms based on decellularized ECM-scaffolds, which provide opportunities to directly explore liver ECM-immune cell interactions in greater detail.

The cardiac extracellular matrix (ECM) not only provides mechanical support, but also transduces essential molecular signals in health and disease. Following myocardial infarction, dynamic ECM changes drive inflammation and repair. Early generation of bioactive matrix fragments activates proinflammatory signaling. The formation of a highly plastic provisional matrix facilitates leukocyte infiltration and activates infarct myofibroblasts. Deposition of matricellular proteins modulates growth factor signaling and contributes to the spatial and temporal regulation of the reparative response. Mechanical stress due to pressure and volume overload and metabolic dysfunction also induce profound changes in ECM composition that contribute to the pathogenesis of heart failure. This manuscript reviews the role of the ECM in cardiac repair and remodeling and discusses matrix-based therapies that may attenuate remodeling while promoting repair and regeneration.

Pathological remodeling of the extracellular matrix (ECM) by fibroblasts leads to organ failure. Development of idiopathic pulmonary fibrosis (IPF) is characterized by a progressive fibrotic scarring in the lung that ultimately leads to asphyxiation; however, the cascade of events that promote IPF are not well defined. Here, we examined how the interplay between the ECM and fibroblasts affects both the transcriptome and translatome by culturing primary fibroblasts generated from IPF patient lung tissue or nonfibrotic lung tissue on decellularized lung ECM from either IPF or control patients. Surprisingly, the origin of the ECM had a greater impact on gene expression than did cell origin, and differences in translational control were more prominent than alterations in transcriptional regulation. Strikingly, genes that were translationally activated by IPF-derived ECM were enriched for those encoding ECM proteins detected in IPF tissue. We determined that genes encoding IPF-associated ECM proteins are targets for miR-29, which was downregulated in fibroblasts grown on IPF-derived ECM, and baseline expression of ECM targets could be restored by overexpression of miR-29. Our data support a model in which fibroblasts are activated to pathologically remodel the ECM in IPF via a positive feedback loop between fibroblasts and aberrant ECM. Interrupting this loop may be a strategy for IPF treatment.

Key Points Different tissues have unique and specialized extracellular matrix (ECM) components and organization, which enables each ECM to carry out tissue-specific roles, including structural support, the transmission of forces and macromolecular filtration. The architecture of the ECM is highly organized, which partly arises from the innate properties of its constituent molecules and their interactions and partly from the activities of the resident cells. The fibrous (collagens and elastin) and glycoprotein (fibronectin, proteoglycans and laminins) macromolecules that constitute the ECM have evolved structures and chemical properties that are particularly suited to their specific biological functions in their respective tissues. Each class of ECM molecule is designed to interact with another class to produce unique physical and signalling properties that support tissue structure, growth and function. Small, modular subunits form homopolymers and heteropolymers that become supramolecular assemblies with highly specialized organization. Collagens are the major proteins of the ECM. The structural hallmark of all collagens is the triple helix, which is a right-handed helix of three polypeptide α-chains (homotrimers and heterotrimers), each of which contains one or more regions that are characterized by the repeating amino acid motif Gly-X-Y, where X and Y can be any amino acid. The assembly of fibrillar collagen involves multiple complex intracellular and extracellular post-translational steps from the translational product to a fibrillar structure that is capable of withstanding tensile forces. The unique mechanical properties of fibrillar collagen are mainly controlled by the collagen structure, which shows the importance of the relationship between three-dimensional protein structure and the resulting ECM function. The primary biological function of proteoglycans derives from the biochemical and hydrodynamic characteristics of the glycosaminoglycan (GAG) components of the molecules, which are long, negatively charged, linear chains of disaccharide repeats that bind water to provide hydration and compressive resistance. Heparan sulphate proteoglycans (HSPGs) are a major part of the basement membrane and chondroitin sulphate proteoglycans (CSPGs) can be found in cartilage and in neural ECMs. The laminin family of large, mosaic glycoproteins are primarily located in basal lamina and some mesenchymal compartments, and they mediate interactions between cells via cell surface receptors (such as integrins and dystroglycan) and other components of the ECM through the modular domains within the laminin molecule. Similarly, many ECM proteins interact with cells through crucial connections with the multidomain protein fibronectin, which is secreted as a large glycoprotein that assembles via cell-mediated processes into fibrillar structures around cells. The production and assembly of the ECM follow different temporal and spatial patterns in various tissues, with load-bearing tissues such as tendons showing highly ordered, fibrillar structures and the continually evolving brain showing a less organized, GAG-rich ECM. Therefore, disruption of the relative abundance of ECM proteins or their interactions with one another has important consequences for the behaviour and the fate of cells within that tissue. The molecules that are associated with the extracellular matrix (ECM) in different tissues, including collagens, proteoglycans, laminins and fibronectin, and the manner in which they are assembled, determine the structure and the organization of the ECM. The resultant biochemical and biophysical properties of the ECM dictate its tissue-specific functions. The biochemical and biophysical properties of the extracellular matrix (ECM) dictate tissue-specific cell behaviour. The molecules that are associated with the ECM of each tissue, including collagens, proteoglycans, laminins and fibronectin, and the manner in which they are assembled determine the structure and the organization of the resultant ECM. The product is a specific ECM signature that is comprised of unique compositional and topographical features that both reflect and facilitate the functional requirements of the tissue.

Key Points The extracellular matrix (ECM) is a dynamic structure that is constantly remodelled to control tissue homeostasis. The ECM in mammals is composed of around 300 proteins, known as the core matrisome. Metalloproteinases are the main endopeptidases responsible for ECM degradation. These enzymes can also generate ECM fragments with different bioactive properties than their full-length proteins. These matrikines regulate many processes such as migration, adhesion and differentiation. ECM remodelling is important during organogenesis and development of the intestine, mammary and salivary glands and lung. Dysregulation of the ECM composition and structure and mutations in genes that affect ECM remodeling can lead to several severe human conditions, including fibrosis and cancer. ECM components and the proteins that regulate ECM remodelling represent promising therapeutic targets. Additional preclinical and clinical studies are required to fully understand the role of the ECM in human disease. The extracellular matrix (ECM) regulates many cellular functions, and its remodelling by enzymes such as metalloproteinases has a crucial role during development, as exemplified by intestinal, lung, mammary gland and submandibular gland morphogenesis. ECM structure and composition are important therapeutic targets, as their dysregulation contributes to conditions such as fibrosis and invasive cancer. The extracellular matrix (ECM) is a highly dynamic structure that is present in all tissues and continuously undergoes controlled remodelling. This process involves quantitative and qualitative changes in the ECM, mediated by specific enzymes that are responsible for ECM degradation, such as metalloproteinases. The ECM interacts with cells to regulate diverse functions, including proliferation, migration and differentiation. ECM remodelling is crucial for regulating the morphogenesis of the intestine and lungs, as well as of the mammary and submandibular glands. Dysregulation of ECM composition, structure, stiffness and abundance contributes to several pathological conditions, such as fibrosis and invasive cancer. A better understanding of how the ECM regulates organ structure and function and of how ECM remodelling affects disease progression will contribute to the development of new therapeutics.

In response to myocardial infarction (MI), cardiac macrophages regulate inflammation and scar formation. We hypothesized that macrophages undergo polarization state changes over the MI time course and assessed macrophage polarization transcriptomic signatures over the first week of MI. C57BL/6 J male mice (3–6 months old) were subjected to permanent coronary artery ligation to induce MI, and macrophages were isolated from the infarct region at days 1, 3, and 7 post-MI. Day 0, no MI resident cardiac macrophages served as the negative MI control. Whole transcriptome analysis was performed using RNA-sequencing on n = 4 pooled sets for each time. Day 1 macrophages displayed a unique pro-inflammatory, extracellular matrix (ECM)-degrading signature. By flow cytometry, day 0 macrophages were largely F4/80highLy6Clow resident macrophages, whereas day 1 macrophages were largely F4/80lowLy6Chigh infiltrating monocytes. Day 3 macrophages exhibited increased proliferation and phagocytosis, and expression of genes related to mitochondrial function and oxidative phosphorylation, indicative of metabolic reprogramming. Day 7 macrophages displayed a pro-reparative signature enriched for genes involved in ECM remodeling and scar formation. By triple in situ hybridization, day 7 infarct macrophages in vivo expressed collagen I and periostin mRNA. Our results indicate macrophages show distinct gene expression profiles over the first week of MI, with metabolic reprogramming important for polarization. In addition to serving as indirect mediators of ECM remodeling, macrophages are a direct source of ECM components. Our study is the first to report the detailed changes in the macrophage transcriptome over the first week of MI.

Metastatic breast cancer cells disseminate to organs with a soft microenvironment. Whether and how the mechanical properties of the local tissue influence their response to treatment remains unclear. Here we found that a soft extracellular matrix empowers redox homeostasis. Cells cultured on a soft extracellular matrix display increased peri-mitochondrial F-actin, promoted by Spire1C and Arp2/3 nucleation factors, and increased DRP1- and MIEF1/2-dependent mitochondrial fission. Changes in mitochondrial dynamics lead to increased production of mitochondrial reactive oxygen species and activate the NRF2 antioxidant transcriptional response, including increased cystine uptake and glutathione metabolism. This retrograde response endows cells with resistance to oxidative stress and reactive oxygen species-dependent chemotherapy drugs. This is relevant in a mouse model of metastatic breast cancer cells dormant in the lung soft tissue, where inhibition of DRP1 and NRF2 restored cisplatin sensitivity and prevented disseminated cancer-cell awakening. We propose that targeting this mitochondrial dynamics- and redox-based mechanotransduction pathway could open avenues to prevent metastatic relapse. Romani et al. report that cells on soft extracellular matrix have increased mitochondrial fission, with subsequent production of mitochondrial reactive oxygen species and NRF2, which may increase resistance to reactive oxygen species-dependent chemotherapy drugs in breast cancer cells in vitro and in mouse lungs.

Extracellular matrix (ECM) is an extraordinarily complex and unique meshwork composed of structural proteins and glycosaminoglycans. The ECM provides essential physical scaffolding for the cellular constituents, as well as contributes to crucial biochemical signaling. Importantly, ECM is an indispensable part of all biological barriers and substantially modulates the interchange of the nanotechnology products through these barriers. The interactions of the ECM with nanoparticles (NPs) depend on the morphological characteristics of intercellular matrix and on the physical characteristics of the NPs and may be either deleterious or beneficial. Importantly, an altered expression of ECM molecules ultimately affects all biological processes including inflammation. This review critically discusses the specific behavior of NPs that are within the ECM domain, and passing through the biological barriers. Furthermore, regenerative and toxicological aspects of nanomaterials are debated in terms of the immune cells-NPs interactions.

Animal cells in tissues are supported by biopolymer matrices, which typically exhibit highly nonlinear mechanical properties. While the linear elasticity of the matrix can significantly impact cell mechanics and functionality, it remains largely unknown how cells, in turn, affect the nonlinear mechanics of their surrounding matrix. Here, we show that living contractile cells are able to generate a massive stiffness gradient in three distinct 3D extracellular matrix model systems: collagen, fibrin, and Matrigel. We decipher this remarkable behavior by introducing nonlinear stress inference microscopy (NSIM), a technique to infer stress fields in a 3D matrix from nonlinear microrheology measurements with optical tweezers. Using NSIM and simulations, we reveal large long-ranged cell-generated stresses capable of buckling filaments in the matrix. These stresses give rise to the large spatial extent of the observed cell-induced matrix stiffness gradient, which can provide a mechanism for mechanical communication between cells.