A new lock-step mechanism of matrix remodelling based on subcellular contractile events

Exploring the role of dermal sheath cells in wound healing and fibrosis

Wound healing is a complex, dynamic process involving the coordinated interaction of diverse cell types, growth factors, cytokines, and extracellular matrix components. Despite emerging evidence highlighting their importance, dermal sheath cells remain a largely overlooked aspect of wound healing research. This review explores the multifunctional roles of dermal sheath cells in various phases of wound healing, including modulating inflammation, aiding in proliferation, and contributing to extracellular matrix remodelling. Special attention is devoted to the paracrine effects of dermal sheath cells and their role in fibrosis, highlighting their potential in improving healing outcomes, especially in differentiating between hairy and non-hairy skin sites. By drawing connections between dermal sheath cells activity and wound healing outcomes, this work proposes new insights into the mechanisms of tissue regeneration and repair, marking a step forward in our understanding of wound healing processes.

Fibroblast and myofibroblast activation in normal tissue repair and fibrosis

The term 'fibroblast' often serves as a catch-all for a diverse array of mesenchymal cells, including perivascular cells, stromal progenitor cells and bona fide fibroblasts. Although phenotypically similar, these subpopulations are functionally distinct, maintaining tissue integrity and serving as local progenitor reservoirs. In response to tissue injury, these cells undergo a dynamic fibroblast-myofibroblast transition, marked by extracellular matrix secretion and contraction of actomyosin-based stress fibres. Importantly, whereas transient activation into myofibroblasts aids in tissue repair, persistent activation triggers pathological fibrosis. In this Review, we discuss the roles of mechanical cues, such as tissue stiffness and strain, alongside cell signalling pathways and extracellular matrix ligands in modulating myofibroblast activation and survival. We also highlight the role of epigenetic modifications and myofibroblast memory in physiological and pathological processes. Finally, we discuss potential strategies for therapeutically interfering with these factors and the associated signal transduction pathways to improve the outcome of dysregulated healing.

The local mechanosensitive response of primary cardiac fibroblasts is influenced by the microenvironment mechanics

Cardiac fibroblasts (CFs) are essential for preserving myocardial integrity and function. They can detect variations in cardiac tissue stiffness using various cellular mechanosensors, including the Ca2+ permeable mechanosensitive channel Piezo1. Nevertheless, how CFs adapt the mechanosensitive response to stiffness changes remains unclear. In this work we adopted a multimodal approach, combining the local mechanical stimulation (from 10 pN to 350 nN) with variations of culture substrate stiffness. We found that primary rat CFs cultured on stiff (GPa) substrates showed a broad Piezo1 distribution in the cell with particular accumulation at the mitochondria membrane. CFs displayed a force-dependent behavior in both calcium uptake and channel activation probability, showing a threshold at 300 nN, which involves both cytosolic and mitochondrial Ca2+ mobilization. This trend decreases as the myofibroblast phenotype within the cell population increases, following a possible Piezo1 accumulation at focal adhesion sites. In contrast, the inhibition of fibroblasts to myofibroblasts transition with soft substrates (kPa) considerably reduces both mechanically- and chemically-induced Piezo1 activation and expression. Our findings shed light on how Piezo1 function and expression are regulated by the substrate stiffness and highlight its involvement in the environment-mediated modulation of CFs mechanosensitivity.

Impact of TRP Channels on Extracellular Matrix Remodeling: Focus on TRPV4 and Collagen

Disturbed remodeling of the extracellular matrix (ECM) is frequently observed in several high-prevalence pathologies that include fibrotic diseases of organs such as the heart, lung, periodontium, liver, and the stiffening of the ECM surrounding invasive cancers. In many of these lesions, matrix remodeling mediated by fibroblasts is dysregulated, in part by alterations to the regulatory and effector systems that synthesize and degrade collagen, and by alterations to the functions of the integrin-based adhesions that normally mediate mechanical remodeling of collagen fibrils. Cell-matrix adhesions containing collagen-binding integrins are enriched with regulatory and effector systems that initiate localized remodeling of pericellular collagen fibrils to maintain ECM homeostasis. A large cadre of regulatory molecules is enriched in cell-matrix adhesions that affect ECM remodeling through synthesis, degradation, and contraction of collagen fibrils. One of these regulatory molecules is Transient Receptor Potential Vanilloid-type 4 (TRPV4), a mechanically sensitive, Ca2+-permeable plasma membrane channel that regulates collagen remodeling. The gating of Ca2+ across the plasma membrane by TRPV4 and the consequent generation of intracellular Ca2+ signals affect several processes that determine the structural and mechanical properties of collagen-rich ECM. These processes include the synthesis of new collagen fibrils, tractional remodeling by contractile forces, and collagenolysis. While the specific mechanisms by which TRPV4 contributes to matrix remodeling are not well-defined, it is known that TRPV4 is activated by mechanical forces transmitted through collagen adhesion receptors. Here, we consider how TRPV4 expression and function contribute to physiological and pathological collagen remodeling and are associated with collagen adhesions. Over the long-term, an improved understanding of how TRPV4 regulates collagen remodeling could pave the way for new approaches to manage fibrotic lesions.

Direct investigation of cell contraction signal networks by light-based perturbation methods

Cell contraction plays an important role in many physiological and pathophysiological processes. This includes functions in skeletal, heart, and smooth muscle cells, which lead to highly coordinated contractions of multicellular assemblies, and functions in non-muscle cells, which are often highly localized in subcellular regions and transient in time. While the regulatory processes that control cell contraction in muscle cells are well understood, much less is known about cell contraction in non-muscle cells. In this review, we focus on the mechanisms that control cell contraction in space and time in non-muscle cells, and how they can be investigated by light-based methods. The review particularly focusses on signal networks and cytoskeletal components that together control subcellular contraction patterns to perform functions on the level of cells and tissues, such as directional migration and multicellular rearrangements during development. Key features of light-based methods that enable highly local and fast perturbations are highlighted, and how experimental strategies can capitalize on these features to uncover causal relationships in the complex signal networks that control cell contraction.

Response to Mechanical Properties and Physiological Challenges of Fascia: Diagnosis and Rehabilitative Therapeutic Intervention for Myofascial System Disorders

Damage to the fascia can cause significant performance deficits in high-performance sports and recreational exercise and may contribute to the development of musculoskeletal disorders and persistent potential pain. The fascia is widely distributed from head to toe, encompassing muscles, bones, blood vessels, nerves, and internal organs and comprising various layers of different depths, indicating the complexity of its pathogenesis. It is a connective tissue composed of irregularly arranged collagen fibers, distinctly different from the regularly arranged collagen fibers found in tendons, ligaments, or periosteum, and mechanical changes in the fascia (stiffness or tension) can produce changes in its connective tissue that can cause pain. While these mechanical changes induce inflammation associated with mechanical loading, they are also affected by biochemical influences such as aging, sex hormones, and obesity. Therefore, this paper will review the current state of knowledge on the molecular level response to the mechanical properties of the fascia and its response to other physiological challenges, including mechanical changes, innervation, injury, and aging; imaging techniques available to study the fascial system; and therapeutic interventions targeting fascial tissue in sports medicine. This article aims to summarize contemporary views.

MACC1-induced migration in tumors: Current state and perspective

Malignant tumors are still a global, heavy health burden. Many tumor types cannot be treated curatively, underlining the need for new treatment targets. In recent years, metastasis associated in colon cancer 1 (MACC1) was identified as a promising biomarker and drug target, as it is promoting tumor migration, initiation, proliferation, and others in a multitude of solid cancers. Here, we will summarize the current knowledge about MACC1-induced tumor cell migration with a special focus on the cytoskeletal and adhesive systems. In addition, a brief overview of several in vitro models used for the analysis of cell migration is given. In this context, we will point to issues with the currently most prevalent models used to study MACC1-dependent migration. Lastly, open questions about MACC1-dependent effects on tumor cell migration will be addressed.

Suggesting a mechanism for acupuncture as a global percutaneous needle fasciotomy that respects tensegrity principles for treating fibromyalgia

Acupuncture is a minimally invasive therapeutic method that uses small caliber needles while inserting them through the skin into various areas of the body. Some empirical studies find evidence to support the use of acupuncture as a treatment for certain medical conditions, however, this peculiar practice is widely considered as the domain of alternative and non-evidence-based medicine. Several mechanisms have been suggested in an attempt to explain the therapeutic action of acupuncture, but the way in which acupuncture alleviates chronic non-cancer pain or psychosomatic and psychiatric disorders is not fully understood. A recent study suggested a theoretical model (coined "Fascial Armoring") with a cellular pathway to help explain the pathogenesis of myofascial pain/fibromyalgia syndrome and functional psychosomatic syndromes. It proposes that these syndromes are a spectrum of a single medical entity that involves myofibroblasts with contractile activity in fascia and aberrant extracellular matrix (ECM) remodeling, which may lead to widespread mechanical tension and compression. This can help explain diverse psycho-somatic manifestations of fibromyalgia-like syndromes. Fascia is a continuous interconnected tissue network that extends throughout the body and has qualities of bio-tensegrity. Previous studies show that a mechanical action by needling induces soft tissue changes and lowers the shear modulus and stiffness in myofascial tissue. This hypothesis and theory paper offers a new mechanism for acupuncture therapy as a global percutaneous needle fasciotomy that respects tensegrity principles (tensegrity-based needling), in light of the theoretical model of "Fascial Armoring." The translation of this model to other medical conditions carries potential to advance therapies. These days opioid overuse and over-prescription are ubiquitous, as well as chronic pain and suffering.

The Role of Myofibroblasts in Physiological and Pathological Tissue Repair

Myofibroblasts are the construction workers of wound healing and repair damaged tissues by producing and organizing collagen/extracellular matrix (ECM) into scar tissue. Scar tissue effectively and quickly restores the mechanical integrity of lost tissue architecture but comes at the price of lost tissue functionality. Fibrotic diseases caused by excessive or persistent myofibroblast activity can lead to organ failure. This review defines myofibroblast terminology, phenotypic characteristics, and functions. We will focus on the central role of the cell, ECM, and tissue mechanics in regulating tissue repair by controlling myofibroblast action. Additionally, we will discuss how therapies based on mechanical intervention potentially ameliorate wound healing outcomes. Although myofibroblast physiology and pathology affect all organs, we will emphasize cutaneous wound healing and hypertrophic scarring as paradigms for normal tissue repair versus fibrosis. A central message of this review is that myofibroblasts can be activated from multiple cell sources, varying with local environment and type of injury, to either restore tissue integrity and organ function or create an inappropriate mechanical environment.

Macrophages-microenvironment crosstalk in fibrostenotic inflammatory bowel disease: from basic mechanisms to clinical applications

INTRODUCTION

Intestinal fibrosis is a common complication of Inflammatory Bowel Disease (IBD) with no available drugs. The current therapeutic principle is surgical intervention as the core. Intestinal macrophages contribute to both the progression of inflammation and fibrosis. Understanding the role of macrophages in the intestinal microenvironment could bring new hope for fibrosis prevention or even reversal.

AREAS COVERED

This article reviewed the most relevant reports on macrophage in the field of intestinal fibrosis. The authors discussed current opinions about how intestinal macrophages function and interact with surrounding mediators during inflammation resolution and fibrostenotic IBD. Based on biological mechanisms findings, authors summarized related clinical trial outcomes.

EXPERT OPINION

The plasticity of intestinal macrophages allows them to undergo dramatic alterations in their phenotypes or functions when exposed to gastrointestinal environmental stimuli. They exhibit distinct metabolic characteristics, secrete various cytokines, express unique surface markers, and transmit different signals. Nevertheless, the specific mechanism through which the intestinal macrophages contribute to intestinal fibrosis remains unclear. It should further elucidate a novel therapeutic approach by targeting macrophages, especially distinct mechanisms in specific subgroups of macrophages involved in the progression of fibrogenesis in IBD.

Wound Healing from an Actin Cytoskeletal Perspective

Wound healing requires a complex cascade of highly controlled and conserved cellular and molecular processes. These involve numerous cell types and extracellular matrix molecules regulated by the actin cytoskeleton. This microscopic network of filaments is present within the cytoplasm of all cells and provides the shape and mechanical support required for cell movement and proliferation. Here, an overview of the processes of wound healing are described from the perspective of the cell in relation to the actin cytoskeleton. Key points of discussion include the role of actin, its binding proteins, signaling pathways, and events that play significant roles in the phases of wound healing. The identification of cytoskeletal targets that can be used to manipulate and improve wound healing is included as an emerging area of focus that may inform future therapeutic approaches to improve healing of complex wounds.

Emergent Temporal Signaling in Human Trabecular Meshwork Cells: Role of TRPV4-TRPM4 Interactions

Trabecular meshwork (TM) cells are phagocytic cells that employ mechanotransduction to actively regulate intraocular pressure. Similar to macrophages, they express scavenger receptors and participate in antigen presentation within the immunosuppressive milieu of the anterior eye. Changes in pressure deform and compress the TM, altering their control of aqueous humor outflow but it is not known whether transducer activation shapes temporal signaling. The present study combines electrophysiology, histochemistry and functional imaging with gene silencing and heterologous expression to gain insight into Ca²⁺ signaling downstream from TRPV4 (Transient Receptor Potential Vanilloid 4), a stretch-activated polymodal cation channel. Human TM cells respond to the TRPV4 agonist GSK1016790A with fluctuations in intracellular Ca²⁺ concentration ([Ca²⁺]_i) and an increase in [Na⁺]_i. [Ca²⁺]_i oscillations coincided with monovalent cation current that was suppressed by BAPTA, Ruthenium Red and the TRPM4 (Transient Receptor Potential Melastatin 4) channel inhibitor 9-phenanthrol. TM cells expressed TRPM4 mRNA, protein at the expected 130-150 kDa and showed punctate TRPM4 immunoreactivity at the membrane surface. Genetic silencing of TRPM4 antagonized TRPV4-evoked oscillatory signaling whereas TRPV4 and TRPM4 co-expression in HEK-293 cells reconstituted the oscillations. Membrane potential recordings suggested that TRPM4-dependent oscillations require release of Ca²⁺ from internal stores. 9-phenanthrol did not affect the outflow facility in mouse eyes and eyes from animals lacking TRPM4 had normal intraocular pressure. Collectively, our results show that TRPV4 activity initiates dynamic calcium signaling in TM cells by stimulating TRPM4 channels and intracellular Ca²⁺ release. It is possible that TRPV4-TRPM4 interactions downstream from the tensile and compressive impact of intraocular pressure contribute to homeostatic regulation and pathological remodeling within the conventional outflow pathway.

Scoping review and interpretation of myofascial pain/fibromyalgia syndrome: An attempt to assemble a medical puzzle

BACKGROUND

Myofascial Pain Syndrome (MPS) is a common, overlooked, and underdiagnosed condition and has significant burden. MPS is often dismissed by clinicians while patients remain in pain for years. MPS can evolve into fibromyalgia, however, effective treatments for both are lacking due to absence of a clear mechanism. Many studies focus on central sensitization. Therefore, the purpose of this scoping review is to systematically search cross-disciplinary empirical studies of MPS, focusing on mechanical aspects, and suggest an organic mechanism explaining how it might evolve into fibromyalgia. Hopefully, it will advance our understanding of this disease.

METHODS

Systematically searched multiple phrases in MEDLINE, EMBASE, COCHRANE, PEDro, and medRxiv, majority with no time limit. Inclusion/exclusion based on title and abstract, then full text inspection. Additional literature added on relevant side topics. Review follows PRISMA-ScR guidelines. PROSPERO yet to adapt registration for scoping reviews.

FINDINGS

799 records included. Fascia can adapt to various states by reversibly changing biomechanical and physical properties. Trigger points, tension, and pain are a hallmark of MPS. Myofibroblasts play a role in sustained myofascial tension. Tension can propagate in fascia, possibly supporting a tensegrity framework. Movement and mechanical interventions treat and prevent MPS, while living sedentarily predisposes to MPS and recurrence.

CONCLUSIONS

MPS can be seen as a pathological state of imbalance in a natural process; manifesting from the inherent properties of the fascia, triggered by a disrupted biomechanical interplay. MPS might evolve into fibromyalgia through deranged myofibroblasts in connective tissue ("fascial armoring"). Movement is an underemployed requisite in modern lifestyle. Lifestyle is linked to pain and suffering. The mechanism of needling is suggested to be more mechanical than currently thought. A "global percutaneous needle fasciotomy" that respects tensegrity principles may treat MPS/fibromyalgia more effectively. "Functional-somatic syndromes" can be seen as one entity (myofibroblast-generated-tensegrity-tension), sharing a common rheuma-psycho-neurological mechanism.

The people behind the papers – Donald Ready and Henry Chang

Coordinating contractility across tissues is key for maintaining the fidelity of morphogenetic processes. A new paper in Development explains how cytosolic calcium waves in the interommatidial cells, the pigment-secreting cells in the Drosophila eye, lead to remodelling of the retinal floor, by activating contraction of the basal actomyosin stress fibres. We caught up with the authors, Professor Donald Ready and Associate Professor Henry Chang, both from Purdue University, to find out more about this story.

Calcium waves facilitate and coordinate the contraction of endfeet actin stress fibers in Drosophila interommatidial cells

Actomyosin contraction shapes the Drosophila eye's panoramic view. The convex curvature of the retinal epithelium, organized in ∼800 close-packed ommatidia, depends upon a fourfold condensation of the retinal floor mediated by contraction of actin stress fibers in the endfeet of interommatidial cells (IOCs). How these tensile forces are coordinated is not known. Here, we discover a novel phenomenon: Ca2+ waves regularly propagate across the IOC network in pupal and adult eyes. Genetic evidence demonstrates that IOC waves are independent of phototransduction, but require inositol 1,4,5-triphosphate receptor (IP3R), suggesting these waves are mediated by Ca2+ releases from ER stores. Removal of IP3R disrupts stress fibers in IOC endfeet and increases the basal retinal surface by ∼40%, linking IOC waves to facilitating stress fiber contraction and floor morphogenesis. Further, IP3R loss disrupts the organization of a collagen IV network underneath the IOC endfeet, implicating ECM and its interaction with stress fibers in eye morphogenesis. We propose that coordinated cytosolic Ca2+ increases in IOC waves promote stress fiber contractions, ensuring an organized application of the planar tensile forces that condense the retinal floor.

The Role of Rho GTPases During Fibroblast Spreading, Migration, and Myofibroblast Differentiation in 3D Synthetic Fibrous Matrices

INTRODUCTION

Connective tissue repair and mechanosensing are tightly entwined in vivo and occur within a complex three-dimensional (3D), fibrous extracellular matrix (ECM). Typically driven by activated fibroblasts, wound repair involves well-defined steps of cell spreading, migration, proliferation, and fibrous ECM deposition. While the role of Rho GTPases in regulating these processes has been explored extensively in two-dimensional cell culture models, much less is known about their role in more physiologic, 3D environments.

METHODS

We employed a 3D, fibrous and protease-sensitive hydrogel model of interstitial ECM to study the interplay between Rho GTPases and fibrous matrix cues in fibroblasts during wound healing.

RESULTS

Modulating fiber density within protease-sensitive hydrogels, we confirmed previous findings that heightened fiber density promotes fibroblast spreading and proliferation. The presence of matrix fibers furthermore corresponded to increased cell migration speeds and macroscopic hydrogel contraction arising from fibroblast generated forces. During fibroblast spreading, Rac1 and RhoA GTPase activity proved crucial for fiber-mediated cell spreading and contact guidance along matrix fibers, while Cdc42 was dispensable. In contrast, interplay between RhoA, Rac1, and Cdc42 contributed to fiber-mediated myofibroblast differentiation and matrix contraction over longer time scales.

CONCLUSION

These observations may provide insights into tissue repair processes in vivo and motivate the incorporation of cell-adhesive fibers within synthetic hydrogels for material-guided wound repair strategies.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12195-021-00698-5.

Implant Fibrosis and the Underappreciated Role of Myofibroblasts in the Foreign Body Reaction

Body implants and implantable medical devices have dramatically improved and prolonged the life of countless patients. However, our body repair mechanisms have evolved to isolate, reject, or destroy any object that is recognized as foreign to the organism and inevitably mounts a foreign body reaction (FBR). Depending on its severity and chronicity, the FBR can impair implant performance or create severe clinical complications that will require surgical removal and/or replacement of the faulty device. The number of review articles discussing the FBR seems to be proportional to the number of different implant materials and clinical applications and one wonders, what else is there to tell? We will here take the position of a fibrosis researcher (which, coincidentally, we are) to elaborate similarities and differences between the FBR, normal wound healing, and chronic healing conditions that result in the development of peri-implant fibrosis. After giving credit to macrophages in the inflammatory phase of the FBR, we will mainly focus on the activation of fibroblastic cells into matrix-producing and highly contractile myofibroblasts. While fibrosis has been discussed to be a consequence of the disturbed and chronic inflammatory milieu in the FBR, direct activation of myofibroblasts at the implant surface is less commonly considered. Thus, we will provide a perspective how physical properties of the implant surface control myofibroblast actions and accumulation of stiff scar tissue. Because formation of scar tissue at the surface and around implant materials is a major reason for device failure and extraction surgeries, providing implant surfaces with myofibroblast-suppressing features is a first step to enhance implant acceptance and functional lifetime. Alternative therapeutic targets are elements of the myofibroblast mechanotransduction and contractile machinery and we will end with a brief overview on such targets that are considered for the treatment of other organ fibroses.

Small Rho GTPases and their associated RhoGEFs mutations promote immunological defects in primary immunodeficiencies

Primary immunodeficiencies (PIDs) are associated with deleterious mutations of genes that encode proteins involved in actin cytoskeleton reorganisation. This deficiency affects haematopoietic cells. PID results in the defective function of immune cells, such as impaired chemokine-induced motility, receptor signalling, development and maturation. Some of the genes mutated in PIDs are related to small Ras homologous (Rho) guanosine triphosphatase (GTPase), one of the families of the Ras superfamily. Most of these genes act as molecular switches by cycling between active guanosine triphosphate-bound and inactive guanosine diphosphate-bound forms to control multiple cellular functions. They are best studied for their role in promoting cytoskeleton reorganisation, cell adhesion and motility. Currently, only three small Rho GTPases, namely, Rac2, Cdc42 and RhoH, have been identified in PIDs. However, several other Rho small G proteins might also contribute to the deregulation and phenotype observed in PIDs. Their contribution in PIDs may involve their main regulator, Rho guanine nucleotide exchange factors such as DOCK2 and DOCK8, wherein mutations may result in the impairment of small Rho GTPase activation. Thus, this review outlines the potential contribution of several small Rho GTPases to the promotion of PIDs.

The relationship between crosslinking structure and silk fibroin scaffold performance for soft tissue engineering

Biologically active scaffolds with tunable mechano- and bio-performance remain desirable for soft tissue engineering. Previously, highly elastic and robust silk fibroin (SF) scaffolds were prepared via cryogelation. In order to get more insight into the role of ethylene glycol diglycidyl ether (EGDE) on the structure and properties of SF scaffolds, we investigated the fate of SF scaffolds with different usages of the crosslinking agent in vitro and in vivo. Although SF scaffolds with varied EGDE contents showed similar micro-morphology, increasing EGDE from 1 mmol/g to 5 mmol/g resulted in firstly increased and later decreased content of β-sheet conformation, and linearly increased tensile modulus and decreased elasticity. The dual-crosslinked SF scaffolds with EGDE up to 5 mmol/g did not show in vitro cytotoxicity for NIH3T3 fibroblasts. In vivo subcutaneous implantation of SF scaffolds with <3 mmol/g EGDE displayed excellent degradation behavior and tissue ingrowth after 28 days of implantation. However, with ≥3 mmol/g EGDE, SF scaffolds exhibited obvious post-implantation foreign body reactions, probably associated with slow degradation due to excess chemical crosslinks and less mechanical compatibility. These results suggest that an appropriate dosage of crosslinking agent was critical to achieve balanced mechanical properties, degradability in vivo and immuno-properties of the SF scaffold platform for soft tissue engineering.

Fibroblasts and macrophages: Collaborators in tissue homeostasis

Fibroblasts and macrophages are universal cell types across all mammalian tissues. These cells differ in many ways including their cellular origins; dynamics of renewal, recruitment, and motility within tissues; roles in tissue structure and secretion of signaling molecules; and contributions to the activation and progression of immune responses. However, many of the features that make these two cell types unique are not opposing, but instead complementary. This review will present cell-cell communication in this context and discuss how complementarity makes fibroblasts and macrophages highly compatible partners in the maintenance of tissue homeostasis.

In-Depth Characterization of Stromal Cells within the Tumor Microenvironment Yields Novel Therapeutic Targets

Simple Summary

This up-to-date and in-depth review describes fibroblast-derived cells and their role within the tumor microenvironment for tumor progression. Moreover, targets for future antitumor therapies are summarized and potential aspects for future translational research are outlined. Furthermore, this review discusses the challenges and possible obstacles related to certain treatment targets.

Abstract

Cells within the tumor stroma are essential for tumor progression. In particular, cancer-associated fibroblasts (CAF) and CAF precursor cells (resident fibroblasts and mesenchymal stromal cells) are responsible for the formation of the extracellular matrix in tumor tissue. Consequently, CAFs directly and indirectly mediate inflammation, metastasis, immunomodulation, angiogenesis, and the development of tumor chemoresistance, which is orchestrated by complex intercellular cytokine-mediated crosstalk. CAFs represent a strategic target in antitumor therapy but their heterogeneity hinders effective treatment regimes. In-depth understanding of CAF subpopulations and knowledge of specific functions in tumor progression will ultimately result in more specific and effective cancer treatments. This review provides a detailed description of CAFs and CAF precursor cells and summarizes possible treatment strategies as well as molecular targets of these cells in antitumor therapies.

Kindlin-2 Mediates Mechanical Activation of Cardiac Myofibroblasts

We identify the focal adhesion protein kindlin-2 as player in a novel mechanotransduction pathway that controls profibrotic cardiac fibroblast to myofibroblast activation. Kindlin-2 is co-upregulated with the myofibroblast marker α-smooth muscle actin (α-SMA) in fibrotic rat hearts and in human cardiac fibroblasts exposed to fibrosis-stiff culture substrates and pro-fibrotic TGF-β1. Stressing fibroblasts using ferromagnetic microbeads, stretchable silicone membranes, and cell contraction agonists all result in kindlin-2 translocation to the nucleus. Overexpression of full-length kindlin-2 but not of kindlin-2 missing a putative nuclear localization sequence (∆NLS kindlin-2) results in increased α-SMA promoter activity. Downregulating kindlin-2 with siRNA leads to decreased myofibroblast contraction and reduced α-SMA expression, which is dependent on CC(A/T)-rich GG(CArG) box elements in the α-SMA promoter. Lost myofibroblast features under kindlin-2 knockdown are rescued with wild-type but not ∆NLS kindlin-2, indicating that myofibroblast control by kindlin-2 requires its nuclear translocation. Because kindlin-2 can act as a mechanotransducer regulating the transcription of α-SMA, it is a potential target to interfere with myofibroblast activation in tissue fibrosis.

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.

Microengineered 3D pulmonary interstitial mimetics highlight a critical role for matrix degradation in myofibroblast differentiation

Fibrosis, characterized by aberrant tissue scarring from activated myofibroblasts, is often untreatable. Although the extracellular matrix becomes increasingly stiff and fibrous during disease progression, how these physical cues affect myofibroblast differentiation in 3D is poorly understood. Here, we describe a multicomponent hydrogel that recapitulates the 3D fibrous structure of interstitial tissue regions where idiopathic pulmonary fibrosis (IPF) initiates. In contrast to findings on 2D hydrogels, myofibroblast differentiation in 3D was inversely correlated with hydrogel stiffness but positively correlated with matrix fibers. Using a multistep bioinformatics analysis of IPF patient transcriptomes and in vitro pharmacologic screening, we identify matrix metalloproteinase activity to be essential for 3D but not 2D myofibroblast differentiation. Given our observation that compliant degradable 3D matrices amply support fibrogenesis, these studies demonstrate a departure from the established relationship between stiffness and myofibroblast differentiation in 2D, and provide a new 3D model for studying fibrosis and identifying antifibrotic therapeutics.

The myofibroblast at a glance

In 1971, Gabbiani and co-workers discovered and characterized the “modification of fibroblasts into cells which are capable of an active spasm” (contraction) in rat wound granulation tissue and, accordingly, named these cells ‘myofibroblasts’. Now, myofibroblasts are not only recognized for their physiological role in tissue repair but also as cells that are key in promoting the development of fibrosis in all organs. In this Cell Science at a Glance and the accompanying poster, we provide an overview of the current understanding of central aspects of myofibroblast biology, such as their definition, activation from different precursors, the involved signaling pathways and most widely used models to study their function. Myofibroblasts will be placed into context with their extracellular matrix and with other cell types communicating in the fibrotic environment. Furthermore, the challenges and strategies to target myofibroblasts in anti-fibrotic therapies are summarized to emphasize their crucial role in disease progression.

In Vivo Disintegration and Bioresorption of a Nacre-Inspired Graphene-Silk Film Caused by the Foreign-Body Reaction

Graphene-based substrates are emerging as a promising functional platform for biomedical applications. Although dispersible graphene sheets have been demonstrated to be biodegradable, their assembled macroscopic architectures are biopersistent because of strong π-π interactions. In this study, we developed a nacre-inspired graphene-silk nanocomposite film by vacuum filtration with a subsequent green chemical reduction procedure. The "brick-and-mortar" architecture not only ensures the mechanical and electrical properties of the film but also endows it with disintegrable and bioresorbable properties following rat subcutaneous implantation. Furthermore, covalent cross-linking leads to the formation of graphene with decreased interlayer spacing, which effectively prolongs the residence time in vivo. We found that enzymatic treatment created microcracks on the film surface and that the foreign-body reaction was involved in the deformation, delamination, disintegration, and phagocytosis processes of the nanocomposite films. This bioinspired strategy paves the way for the development of high-performance graphene-based macroscopic biomaterials with tunable bioresorbability.

Bad Neighborhood: Fibrotic Stroma as a New Player in Melanoma Resistance to Targeted Therapies

Current treatments for metastatic cutaneous melanoma include immunotherapies and drugs targeting key molecules of the mitogen-activated protein kinase (MAPK) pathway, which is often activated by BRAF driver mutations. Overall responses from patients with metastatic BRAF mutant melanoma are better with therapies combining BRAF and mitogen-activated protein kinase kinase (MEK) inhibitors. However, most patients that initially respond to therapies develop drug resistance within months. Acquired resistance to targeted therapies can be due to additional genetic alterations in melanoma cells and to non-genetic events frequently associated with transcriptional reprogramming and a dedifferentiated cell state. In this second scenario, it is possible to identify pro-fibrotic responses induced by targeted therapies that contribute to the alteration of the melanoma tumor microenvironment. A close interrelationship between chronic fibrosis and cancer has been established for several malignancies including breast and pancreatic cancers. In this context, the contribution of fibrosis to drug adaptation and therapy resistance in melanoma is rapidly emerging. In this review, we summarize recent evidence underlining the hallmarks of fibrotic diseases in drug-exposed and resistant melanoma, including increased remodeling of the extracellular matrix, enhanced actin cytoskeleton plasticity, high sensitivity to mechanical cues, and the establishment of an inflammatory microenvironment. We also discuss several potential therapeutic options for manipulating this fibrotic-like response to combat drug-resistant and invasive melanoma.

Fibrosis and cancer: A strained relationship

Tumors are characterized by extracellular matrix (ECM) deposition, remodeling, and cross-linking that drive fibrosis to stiffen the stroma and promote malignancy. The stiffened stroma enhances tumor cell growth, survival and migration and drives a mesenchymal transition. A stiff ECM also induces angiogenesis, hypoxia and compromises anti-tumor immunity. Not surprisingly, tumor aggression and poor patient prognosis correlate with degree of tissue fibrosis and level of stromal stiffness. In this review, we discuss the reciprocal interplay between tumor cells, cancer associated fibroblasts (CAF), immune cells and ECM stiffness in malignant transformation and cancer aggression. We discuss CAF heterogeneity and describe its impact on tumor development and aggression focusing on the role of CAFs in engineering the fibrotic tumor stroma and tuning tumor cell tension and modulating the immune response. To illustrate the role of mechanoreciprocity in tumor evolution we summarize data from breast cancer and pancreatic ductal carcinoma (PDAC) studies, and finish by discussing emerging anti-fibrotic strategies aimed at treating cancer.

Evolving therapies for Peyronie's disease: how can we work towards new drugs?

Peyronie's disease (PD) is an idiopathic chronic fibrotic disease that causes a penile curvature (PC), subsequent erectile dysfunction (ED) and impaired sexual intercourse in patients. As of yet, there are no reliable non-surgical treatment options available. Intralesional injection with collagenase Clostridum Histolyticum has been FDA approved since 2013, but post-approval studies have not been unanimously positive. Moreover, it renders a curvature improvement of only 30% on average, usually still requiring surgical intervention to remedy PC. Therefore, there is a need for drugs which could prevent surgery altogether. Development of new drugs can either be through a target-based or phenotypic assay-based approach. The current in vivo model for PD is dependent on treatment of primary PD-derived fibroblasts with transforming growth factor-β1. Moreover, despite the existence of a genetic in vivo PD model, it does not allow for drug screening or testing. While some advances have been made in the past few years, new in vivo and in vivo systems and well-designed studies are urgently needed for the non-surgical treatment of PD.

Role of IL-24 in the mucosal remodeling of children with coeliac disease

BACKGROUND

Recently, involvement of IL-19, IL-20 and IL-24 has been reported in inflammatory diseases associated with tissue remodeling. However, their impact on the pathomechanism of coeliac disease (CD) is still completely unknown.

METHODS

Expression of IL19, IL20 and IL24 was measured by real-time RT-PCR, protein amount of IL-24, α smooth muscle actin (α-SMA) and fibronectin (FN) was determined by Western-blot analysis in the duodenal biopsies of therapy naive children with CD and controls. Localization of IL-24 and IL-20RB was investigated by immunofluorescent staining in the duodenal mucosa. Effect of recombinant IL-1β, TNF-α, TGF-β and IL-17 treatment on the expression of IL19, IL20, IL24 and their receptors was investigated by real-time RT-PCR in small intestinal epithelial cells (FHs74Int), in primary duodenal myofibroblasts (pdMFs) and in peripheral blood mononuclear cells (PBMCs). Effect of IL-24 on H₂O₂ treated FHs74Int cells and on pdMFs was measured by MTT, LDH, Annexin V assays, real-time RT-PCR and by fluorescent microscopy.

RESULTS

We found increased level of IL-24 (3.3×, p < 0.05), α-SMA (2.4×, p < 0.05) and FN (2.3×, p < 0.05) in the duodenal mucosa and increased expression of IL19 (3.6×, p < 0.05) and IL24 (5.2×, p < 0.05) in the PBMCs of children with CD compared to that of controls. IL-1β was a strong inducer of IL24 expression of FHs74Int cells (9.9×, p < 0.05), pdMFs (552.9×, p < 0.05) or PBMCs (17.2×, p < 0.05), as well. IL-24 treatment reduced the number of apoptotic cells (0.5×, p < 0.05) and decreased the expression of inflammatory factors, including IL1A, IL6 and TNF of H₂O₂-treated FHs74Int cells. IL-24 decreased the proliferation (0.6×, p < 0.05) of PDGF-B treated pdMFs. Moreover, IL-24 treatment altered the morphology of pdMFs by influencing the size of the angles between stress fibers and the longitudinal axis of the cells (2.0×, p < 0.05) and the expression of cytoskeletal components, including ACTA2, ACTB, VIM, SNAI1 and SNAI2.

CONCLUSION

Our results suggest that IL-24 plays a significant role in the maintenance of duodenal mucosal integrity in CD.

Direct Effects of Empagliflozin on Extracellular Matrix Remodelling in Human Cardiac Myofibroblasts: Novel Translational Clues to Explain EMPA-REG OUTCOME Results

BACKGROUND

Empagliflozin, an SGLT2 inhibitor, has shown remarkable reductions in cardiovascular mortality and heart failure admissions (EMPA-REG OUTCOME). However, the mechanism underlying the heart failure protective effects of empagliflozin remains largely unknown. Cardiac fibroblasts play an integral role in the progression of structural cardiac remodelling and heart failure, in part, by regulating extracellular matrix (ECM) homeostasis. The objective of this study was to determine if empagliflozin has a direct effect on human cardiac myofibroblast-mediated ECM remodelling.

METHODS

Cardiac fibroblasts were isolated via explant culture from human atrial tissue obtained at open heart surgery. Collagen gel contraction assay was used to assess myofibroblast activity. Cell morphology and cell-mediated ECM remodelling was examined with the use of confocal microscopy. Gene expression of profibrotic markers was assessed with the use of reverse-transcription quantitative polymerase chain reaction.

RESULTS

Empagliflozin significantly attenuated transforming growth factor β1-induced fibroblast activation via collagen gel contraction after 72-hour exposure, with escalating concentrations (0.5 μmol/L, 1 μmol/L, and 5 μmol/L) resulting in greater attenuation. Morphologic assessment showed that myofibroblasts exposed to empagliflozin were smaller in size with shorter and fewer number of extensions, indicative of a more quiescent phenotype. Moreover, empagliflozin significantly attenuated cell-mediated ECM remodelling as measured by collagen fibre alignment index. Gene expression profiling revealed significant suppression of critical profibrotic markers by empagliflozin, including COL1A1, ACTA2, CTGF, FN1, and MMP-2.

CONCLUSIONS

We provide novel data showing a direct effect of empagliflozin on human cardiac myofibroblast phenotype and function by attenuation of myofibroblast activity and cell-mediated collagen remodelling. These data provide critical insights into the profound effects of empagliflozin as noted in the EMPA-REG OUTCOME study.

Oxidative stress-mediated senescence in mesenchymal progenitor cells causes the loss of their fibro/adipogenic potential and abrogates myoblast fusion

Sarcopenia is the age-related loss of skeletal muscle mass and function. Skeletal muscle comprises diverse progenitor cells, including mesenchymal progenitor cells (MPCs), which normally support myogenic cell function but cause a decline in skeletal muscle function after differentiating into fibrous/adipose tissue. Cellular senescence is a form of persistent cell cycle arrest caused by cellular stress, including oxidative stress, and is accompanied by the acquisition of senescence-associated secretory phenotype (SASP). Here, we found γH2AX⁺ senescent cells appeared in the interstitium in skeletal muscle, corresponding in position to that of MPCs. H₂O₂ mediated oxidative stress in 2G11 cells, a rat MPC clone previously established in our laboratory, successfully induced senescence, as shown by the upregulation of p21 and SASP factors, including IL-6. The senescent 2G11 cells lost their fibro/adipogenic potential, but, intriguingly, coculture of myoblasts with senescent 2G11 cells abrogated the myotube formation, which coincided with the downregulation of myomaker, a muscle-specific protein involved in myogenic cell fusion; however, forced expression of myomaker could not rescue this abrogation. These results suggest that senescent MPCs in aged rat skeletal muscle lose their fibro/adipogenic potential, but differ completely from undifferentiated progenitor cells in that senescent MPCs suppress myoblast fusion and thereby potentially accelerate sarcopenia.

Predictable fibroblast tension generation by measuring compaction of anchored collagen matrices using microscopy and optical coherence tomography

The anchored fibroblast-populated collagen matrix (aFPCM) is an appropriate model to study fibrocontractive disease mechanisms. Our goal was to determine if aFPCM height reduction (compaction) during development is sufficient to predict tension generation. Compaction was quantified daily by both traditional light microscopy and an optical coherence tomography (OCT) system. Contraction in aFPCM was revealed by releasing them from anchorage. We found that aFPCM contraction increase was correlated to the compaction increase. Cytochalasin D treatment reversibly inhibited compaction. Therefore, we demonstrated that aFPCM height reduction efficiently measures compaction, contraction, and relative maturity of the collagen matrix during development or treatment. In addition, we showed that OCT is suitable for effectively imaging the cross-sectional morphology of the aFPCM in culture. This study will pave the way for more efficient studies on the mechanisms of (and treatments that target) migration and contraction in wound healing and Dupuytren’s contracture in a tissue environment.

Active contractile properties of fascia

The ubiquitous network of fascial tissues in the human body is usually regarded as a passive contributor to musculoskeletal dynamics. This review aims to highlight the current understanding of fascial stiffness regulation. Notably the ability for active cellular contraction which may augment the stiffness of fascial tissues and thereby contribute to musculoskeletal dynamics. A related narrative literature search via PubMed and Google Scholar reveals a multitude of studies indicating that the intrafascial presence of myofibroblasts may enable these tissues to alter their stiffness. This contractile tissue behavior occurs not only in several pathological fibrotic contractures but has also been documented in normal fasciae. When viewed at time frames of seconds and minutes the force of such tissue contractions is not sufficient for exerting a significant effect on mechanical joint stability. However, when viewed in a time-window of several minutes and longer, such cellular contractions can impact motoneuronal coordination. In addition, over a time frame of days to months, this cellular activity can induce long-term and severe tissue contractures. These findings tend to question the common clear distinction between active tissues and passive tissues in musculoskeletal dynamics. Clin. Anat. 32:891-895, 2019. © 2019 Wiley Periodicals, Inc.

Dynamic fibroblast contractions attract remote macrophages in fibrillar collagen matrix

Macrophage (Mϕ)-fibroblast interactions coordinate tissue repair after injury whereas miscommunications can result in pathological healing and fibrosis. We show that contracting fibroblasts generate deformation fields in fibrillar collagen matrix that provide far-reaching physical cues for Mϕ. Within collagen deformation fields created by fibroblasts or actuated microneedles, Mϕ migrate towards the force source from several hundreds of micrometers away. The presence of a dynamic force source in the matrix is critical to initiate and direct Mϕ migration. In contrast, collagen condensation and fiber alignment resulting from fibroblast remodelling activities or chemotactic signals are neither required nor sufficient to guide Mϕ migration. Binding of α2β1 integrin and stretch-activated channels mediate Mϕ migration and mechanosensing in fibrillar collagen ECM. We propose that Mϕ mechanosense the velocity of local displacements of their substrate, allowing contractile fibroblasts to attract Mϕ over distances that exceed the range of chemotactic gradients.

Macrophages play an important role in wound healing but the guidance cues driving macrophages to sites of repair are still not clear. Here the authors discover that macrophages are attracted to contracting fibroblasts by responding to locally sensed displacements of collagen fibres.

The Cytoskeleton-A Complex Interacting Meshwork

The cytoskeleton of animal cells is one of the most complicated and functionally versatile structures, involved in processes such as endocytosis, cell division, intra-cellular transport, motility, force transmission, reaction to external forces, adhesion and preservation, and adaptation of cell shape. These functions are mediated by three classical cytoskeletal filament types, as follows: Actin, microtubules, and intermediate filaments. The named filaments form a network that is highly structured and dynamic, responding to external and internal cues with a quick reorganization that is orchestrated on the time scale of minutes and has to be tightly regulated. Especially in brain tumors, the cytoskeleton plays an important role in spreading and migration of tumor cells. As the cytoskeletal organization and regulation is complex and many-faceted, this review aims to summarize the findings about cytoskeletal filament types, including substructures formed by them, such as lamellipodia, stress fibers, and interactions between intermediate filaments, microtubules and actin. Additionally, crucial regulatory aspects of the cytoskeletal filaments and the formed substructures are discussed and integrated into the concepts of cell motility. Even though little is known about the impact of cytoskeletal alterations on the progress of glioma, a final point discussed will be the impact of established cytoskeletal alterations in the cellular behavior and invasion of glioma.

Fascia Is Able to Actively Contract and May Thereby Influence Musculoskeletal Dynamics: A Histochemical and Mechanographic Investigation

Fascial tissues form a ubiquitous network throughout the whole body, which is usually regarded as a passive contributor to biomechanical behavior. We aimed to answer the question, whether fascia may possess the capacity for cellular contraction which, in turn, could play an active role in musculoskeletal mechanics. Human and rat fascial specimens from different body sites were investigated for the presence of myofibroblasts using immunohistochemical staining for α-smooth muscle actin (n = 31 donors, n = 20 animals). In addition, mechanographic force registrations were performed on isolated rat fascial tissues (n = 8 to n = 18), which had been exposed to pharmacological stimulants. The density of myofibroblasts was increased in the human lumbar fascia in comparison to fasciae from the two other regions examined in this study: fascia lata and plantar fascia [H(2) = 14.0, p < 0.01]. Mechanographic force measurements revealed contractions in response to stimulation by fetal bovine serum, the thromboxane A2 analog U46619, TGF-β1, and mepyramine, while challenge by botulinum toxin type C3–used as a Rho kinase inhibitor– provoked relaxation (p < 0.05). In contrast, fascial tissues were insensitive to angiotensin II and caffeine (p < 0.05). A positive correlation between myofibroblast density and contractile response was found (r_s = 0.83, p < 0.001). The hypothetical application of the registered forces to human lumbar tissues predicts a potential impact below the threshold for mechanical spinal stability but strong enough to possibly alter motoneuronal coordination in the lumbar region. It is concluded that tension of myofascial tissue is actively regulated by myofibroblasts with the potential to impact active musculoskeletal dynamics.

Emission of Biophotons and Adjustable Sounds by the Fascial System: Review and Reflections for Manual Therapy

Every body structure is wrapped in connective tissue or fascia, creating a structural continuity that gives form and function to every tissue and organ. The fascial tissue is uniformly distributed throughout the body, enveloping, interacting with and permeating blood vessels, nerves, viscera, meninges, bones and muscles, creating various layers at different depths and forming a tridimensional metabolic and mechanical matrix. This article reviews the literature on the emission of biophotons and adjustable sounds by the fascial system, because these biological changes could be a means of local and systemic cellular communication and become another assessment tool for manual (therapy) practitioners. This is the first article that discusses these topics in a single text, attempting to bring such information into an area of application that is beneficial to osteopaths, chiropractors, and manual therapists.

TRPV4-mediated calcium signaling in mesenchymal stem cells regulates aligned collagen matrix formation and vinculin tension

Microarchitectural cues drive aligned fibrillar collagen deposition in vivo and in biomaterial scaffolds, but the cell-signaling events that underlie this process are not well understood. Utilizing a multicellular patterning model system that allows for observation of intracellular signaling events during collagen matrix assembly, we investigated the role of calcium (Ca²⁺) signaling in human mesenchymal stem cells (MSCs) during this process. We observed spontaneous Ca²⁺ oscillations in MSCs during fibrillar collagen assembly, and hypothesized that the transient receptor potential vanilloid 4 (TRPV4) ion channel, a mechanosensitive Ca²⁺-permeable channel, may regulate this signaling. Inhibition of TRPV4 nearly abolished Ca²⁺ signaling at initial stages of collagen matrix assembly, while at later times had reduced but significant effects. Importantly, blocking TRPV4 activity dramatically reduced aligned collagen fibril assembly; conversely, activating TRPV4 accelerated aligned collagen formation. TRPV4-dependent Ca²⁺ oscillations were found to be independent of pattern shape or subpattern cell location, suggesting this signaling mechanism is necessary for aligned collagen formation but not sufficient in the absence of physical (microarchitectural) cues that force multicellular alignment. As cell-generated mechanical forces are known to be critical to the matrix assembly process, we examined the role of TRPV4-mediated Ca²⁺ signaling in force generated across the load-bearing focal adhesion protein vinculin within MSCs using an FRET-based tension sensor. Inhibiting TRPV4 decreased tensile force across vinculin, whereas TRPV4 activation caused a dynamic unloading and reloading of vinculin. Together, these findings suggest TRPV4 activity regulates forces at cell-matrix adhesions and is critical to aligned collagen matrix assembly by MSCs.

TRP channels in cardiac and intestinal fibrosis

It is now widely accepted that advanced fibrosis underlies many chronic inflammatory disorders and is the main cause of morbidity and mortality of the modern world. The pathogenic mechanism of advanced fibrosis involves diverse and intricate interplays between numerous extracellular and intracellular signaling molecules, among which the non-trivial roles of a stress-responsive Ca²⁺/Na⁺-permeable cation channel superfamily, the transient receptor potential (TRP) protein, are receiving growing attention. Available evidence suggests that several TRP channels such as TRPC3, TRPC6, TRPV1, TRPV3, TRPV4, TRPA1, TRPM6 and TRPM7 may play central roles in the progression and/or prevention of fibroproliferative disorders in vital visceral organs such as lung, heart, liver, kidney, and bowel as well as brain, blood vessels and skin, and may contribute to both acute and chronic inflammatory processes involved therein. This short paper overviews the current knowledge accumulated in this rapidly growing field, with particular focus on cardiac and intestinal fibrosis, which are tightly associated with the pathogenesis of atrial fibrillation and inflammatory bowel diseases such as Crohn's disease.

Synchronized mechanical oscillations at the cell-matrix interface in the formation of tensile tissue

The formation of uniaxial fibrous tissues with defined viscoelastic properties implies the existence of an orchestrated mechanical interaction between the cytoskeleton and the extracellular matrix. This study addresses the nature of this interaction. The hypothesis is that this mechanical interplay underpins the mechanical development of the tissue. In embryonic tendon tissue, an early event in the development of a mechanically robust tissue is the interaction of the pointed tips of extracellular collagen fibrils with the fibroblast plasma membrane to form stable interface structures (fibripositors). Here, we used a fibroblast-generated tissue that is structurally and mechanically matched to embryonic tendon to demonstrate homeostasis of cell-derived and external strain-derived tension over repeated cycles of strain and relaxation. A cell-derived oscillatory tension component is evident in this matrix construct. This oscillatory tension involves synchronization of individual cell forces across the construct and is induced in each strain cycle by transient relaxation and transient tensioning of the tissue. The cell-derived tension along with the oscillatory component is absent in the presence of blebbistatin, which disrupts actinomyosin force generation of the cell. The time period of this oscillation (60-90 s) is well-defined in each tissue sample and matches a primary viscoelastic relaxation time. We hypothesize that this mechanical oscillation of fibroblasts with plasma membrane anchored collagen fibrils is a key factor in mechanical sensing and feedback regulation in the formation of tensile tissues.

Developmental changes in haemocyte morphology in response to Staphylococcus aureus and latex beads in the beetle Tenebrio molitor L

The evolutionary success of insects is undoubtedly related to a well-functioning immune system. This is especially apparent during insect development by the adaptation of individuals to the changing risk of infection. In addition, current studies show that the insect immune system is characterized by some specificity in response to natural pathogens (for example, bacteria, viruses or fungi) and artificial challengers (for example, latex beads or nylon filaments). However, developmental changes and the specificity of immune system reactions simultaneously have not been analysed. Thus, the aim of the present research was to determine changes in haemocyte morphology in response to attenuated Staphylococcus aureus and latex beads across each developmental stage of the beetle Tenebrio molitor. The results of the present research clearly showed differences in the morphology of T. molitor haemocytes during development. The haemocytes of larvae and 4-day-old adult males were characterized by the highest adhesion ability, which was expressed as the largest average surface area, filopodia length and number of filopodia. In contrast, the haemocytes of pupae and 30-day-old adult males had a significantly lower value for these morphological parameters, which was probably related to metamorphosis (pupae) and immunosenescence (30-day-old adults). The haemocytes of the tested individuals reacted differently to the presence of S. aureus and latex beads. The presence of S. aureus led to a significant decrease in all previously mentioned morphological parameters in larvae and in both groups of adult individuals. In these groups, incubation of haemocytes with latex beads caused only a slight decrease in surface area and filopodia length and number. This morphological response of haemocytes to biotic and artificial challengers might be related to an increase in the migration abilities of haemocytes during infection. However, the differences in haemocyte reactivity towards S. aureus and latex beads might be explained by differences in pathogen recognition. Conversely, increased adhesive abilities of pupal haemocytes were also observed, which might be related to the specificity of metamorphosis and the hormonal titre during this developmental stage.

The third path of tubulointerstitial fibrosis: aberrant endothelial secretome

The secretome, defined as a portion of proteins secreted by specific cells to the extracellular space, secures a proper microenvironmental niche not only for the donor cells, but also for the neighboring cells, thus maintaining tissue homeostasis. Communication via secretory products exists between endothelial cells and fibroblasts, and this local mechanism maintains the viability and density of each compartment. Endothelial dysfunction, apart from obvious cell-autonomous defects, leads to the aberrant secretome, which predisposes fibroblasts to acquire a myofibroblastic fibrogenic phenotype. In our recent profiling of the secretome of such dysfunctional profibrogenic renal microvascular endothelial cells, we identified unique profibrogenic signatures, among which we detected ligands of Notch and Wnt-β-catenin pathways. Here, we stress the role of reprogramming cues in the immediate microenvironment of (myo)fibroblasts and the contribution of the endothelial secretome to the panoply of instructive signals in the vicinity of fibroblasts. We hope that this brief overview of endothelial-fibroblast communication in health and disease will lead to eventual unbiased proteomic mapping of individual secretomes of glomerular and tubular epithelial cells, pericytes, and podocytes through reductionist approaches to allow for the synthetic creation of a complex network of secretomic signals acting as reprogramming factors on individual cell types in the kidney. Knowledge of profibrogenic and antifibrogenic signatures in the secretome may garner future therapeutic efforts.

Matrix Remodeling in Pulmonary Fibrosis and Emphysema

Pulmonary fibrosis and emphysema are chronic lung diseases characterized by a progressive decline in lung function, resulting in significant morbidity and mortality. A hallmark of these diseases is recurrent or persistent alveolar epithelial injury, typically caused by common environmental exposures such as cigarette smoke. We propose that critical determinants of the outcome of the injury-repair processes that result in fibrosis versus emphysema are mesenchymal cell fate and associated extracellular matrix dynamics. In this review, we explore the concept that regulation of mesenchymal cells under the influence of soluble factors, in particular transforming growth factor-β1, and the extracellular matrix determine the divergent tissue remodeling responses seen in pulmonary fibrosis and emphysema.

Calcium oscillations in wounded fibroblast monolayers are spatially regulated through substrate mechanics

The maintenance of tissue integrity is essential for the life of multicellular organisms. Healing of a skin wound is a paradigm for how various cell types localize and repair tissue perturbations in an orchestrated fashion. To investigate biophysical mechanisms associated with wound localization, we focus on a model system consisting of a fibroblast monolayer on an elastic substrate. We find that the creation of an edge in the monolayer causes cytosolic calcium oscillations throughout the monolayer. The oscillation frequency increases with cell density, which shows that wound-induced calcium oscillations occur collectively. Inhibition of myosin II reduces the number of oscillating cells, demonstrating a coupling between actomyosin activity and calcium response. The spatial distribution of oscillating cells depends on the stiffness of the substrate. For soft substrates with a Young's modulus E ~ 360 Pa, oscillations occur on average within 0.2 mm distance from the wound edge. Increasing substrate stiffness leads to an average localization of oscillations away from the edge (up to ~0.6 mm). In addition, we use traction force microscopy to determine stresses between cells and substrate. We find that an increase of substrate rigidity leads to a higher traction magnitude. For E  <  ~2 kPa, the traction magnitude is strongly concentrated at the monolayer edge, while for E  >  ~8 kPa, traction magnitude is on average almost uniform beneath the monolayer. Thus, the spatial occurrence of calcium oscillations correlates with the cell-substrate traction. Overall, the experiments with fibroblasts demonstrate a collective, chemomechanical localization mechanism at the edge of a wound with a potential physiological role.

Characterization and Standardization of Cultured Cardiac Fibroblasts for Ex Vivo Models of Heart Fibrosis and Heart Ischemia

A full understanding of cardiac fibroblast (cFB) biology is essential to study the adverse cardiac remodeling and recovery of myocardium infarction. However, compared to cardiac myocytes, cFBs are less well characterized. Important questions, including the variability introduced by cell age (neonatal vs. adult), culture conditions (passage, plate coating, and culture medium), and responses to stimuli (e.g., hypoxia and drug treatments), have not been well addressed and standardization of techniques is lacking. This variability invites inconsistency and the confounding of study conclusions. Thus, we here focus on characterizing cell responses and standardizing procedures for cFB isolation and culture conditions to provide reliable platforms to address important questions about cFB proliferation, activation, collagen matrix formation, and responses to relevant stimuli. Thirty litters of 1-3-day pups and 30 female (240-330 g) Sprague-Dawley rats were used to isolate neonatal and adult cFBs. We detail and validate procedures to isolate cFBs for the use of culture or direct analysis. We characterize the differences between neonatal and adult cFBs, define the changes of cFBs during serial passage, and identify the response of cFBs to different culture conditions. We have also established models for the functional screening of profibrotic and antifibrotic drugs based on cFB proliferation, myofibroblast activation, and pericellular collagen matrix formation, and models of hypoxia/reoxygenation with appropriate time course and media conditions to achieve consistent cell injury. Our standardized procedures will ensure consistency in assessing cFB function. This original contribution provides a valid platform for the ex vivo investigation of the role of cFBs in cardiac ischemia and fibrosis.

Transient mechanical strain promotes the maturation of invadopodia and enhances cancer cell invasion in vitro

Cancer cell invasion is influenced by various biomechanical forces found within the microenvironment. We have previously found that invasion is enhanced in fibrosarcoma cells when transient mechanical stimulation is applied within an in vitro mechano-invasion assay. This enhancement of invasion is dependent on cofilin (CFL1), a known regulator of invadopodia maturation. Invadopodia are actin-rich structures present in invasive cancer cells that are enzymatically active and degrade the surrounding extracellular matrix to facilitate invasion. In this study, we examine changes in gene expression in response to tugging on matrix fibers. Interestingly, we find that integrin β3 expression is downregulated and leads to an increase in cofilin activity, as evidenced by a reduction in its Ser3 phosphorylation levels. As a result, invadopodia lengthen and have increased enzymatic activity, indicating that transient mechanical stimulation promotes the maturation of invadopodia leading to increased levels of cell invasion. Our results are unique in defining an invasive mechanism specific to the invasive process of cancer cells that is triggered by tugging forces in the microenvironment, as opposed to rigidity, compression or stretch forces.