The instructive extracellular matrix of the lung: basic composition and alterations in chronic lung disease

Pulmonary Stretch and Lung Mechanotransduction: Implications for Progression in the Fibrotic Lung

Lung fibrosis results from the synergic interplay between regenerative deficits of the alveolar epithelium and dysregulated mechanisms of repair in response to alveolar and vascular damage, which is followed by progressive fibroblast and myofibroblast proliferation and excessive deposition of the extracellular matrix. The increased parenchymal stiffness of fibrotic lungs significantly affects respiratory mechanics, making the lung more fragile and prone to non-physiological stress during spontaneous breathing and mechanical ventilation. Given their parenchymal inhomogeneity, fibrotic lungs may display an anisotropic response to mechanical stresses with different regional deformations (micro-strain). This behavior is not described by the standard stress–strain curve but follows the mechano-elastic models of “squishy balls”, where the elastic limit can be reached due to the excessive deformation of parenchymal areas with normal elasticity that are surrounded by inelastic fibrous tissue or collapsed induration areas, which tend to protrude outside the fibrous ring. Increasing evidence has shown that non-physiological mechanical forces applied to fibrotic lungs with associated abnormal mechanotransduction could favor the progression of pulmonary fibrosis. With this review, we aim to summarize the state of the art on the relation between mechanical forces acting on the lung and biological response in pulmonary fibrosis, with a focus on the progression of damage in the fibrotic lung during spontaneous breathing and assisted ventilatory support.

Collagen VI as a driver and disease biomarker in human fibrosis

Fibrosis of visceral organs such as the lungs, heart, kidneys and liver remains a major cause of morbidity and mortality and is also associated with many other disorders, including cancer and metabolic disease. In this review, we focus upon the microfibrillar collagen VI, which is present in the extracellular matrix (ECM) of most tissues. However, expression is elevated in numerous fibrotic conditions, such as idiopathic pulmonary disease (IPF), and chronic liver and kidney diseases. Collagen VI is composed of three subunits α1, α2 and α3, which can be replaced with alternate chains of α4, α5 or α6. The C-terminal globular domain (C5) of collagen VI α3 can be proteolytically cleaved to form a biologically active fragment termed endotrophin, which has been shown to actively drive fibrosis, inflammation and insulin resistance. Tissue biopsies have long been considered the gold standard for diagnosis and monitoring of progression of fibrotic disease. The identification of neoantigens from enzymatically processed collagen chains have revolutionised the biomarker field, allowing rapid diagnosis and evaluation of prognosis of numerous fibrotic conditions, as well as providing valuable clinical trial endpoint determinants. Collagen VI chain fragments such as endotrophin (PRO-C6), C6M and C6Mα3 are emerging as important biomarkers for fibrotic conditions.

The critical role of collagen VI in lung development and chronic lung disease

Type VI collagen (collagen VI) is an obligate extracellular matrix component found mainly in the basement membrane region of many mammalian tissues and organs, including skeletal muscle and throughout the respiratory system. Collagen VI is probably most recognized in medicine as the genetic cause of a spectrum of muscular dystrophies, including Ullrich Congenital Myopathy and Bethlem Myopathy. Collagen VI is thought to contribute to myopathy, at least in part, by mediating muscle fiber integrity by anchoring myoblasts to the muscle basement membrane. Interestingly, collagen VI myopathies present with restrictive respiratory insufficiency, thought to be due primarily to thoracic muscular weakening. Although it was recently recognized as one of the (if not the) most abundant collagens in the mammalian lung, there is a substantive knowledge gap concerning its role in respiratory system development and function. A few studies have suggested that collagen VI insufficiency is associated with airway epithelial cell survival and altered lung function. Our recent work suggested collagen VI may be a genomic risk factor for chronic lung disease in premature infants. Using this as motivation, we thoroughly assessed the role of collagen VI in lung development and in lung epithelial cell biology. Here, we describe the state-of-the-art for collagen VI cell and developmental biology within the respiratory system, and reveal its essential roles in normal developmental processes and airway epithelial cell phenotype and intracellular signaling.

Collagen Biosynthesis, Processing, and Maturation in Lung Ageing

In addition to providing a macromolecular scaffold, the extracellular matrix (ECM) is a critical regulator of cell function by virtue of specific physical, biochemical, and mechanical properties. Collagen is the main ECM component and hence plays an essential role in the pathogenesis and progression of chronic lung disease. It is well-established that many chronic lung diseases, e.g., chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF) primarily manifest in the elderly, suggesting increased susceptibility of the aged lung or accumulated alterations in lung structure over time that favour disease. Here, we review the main steps of collagen biosynthesis, processing, and turnover and summarise what is currently known about alterations upon lung ageing, including changes in collagen composition, modification, and crosslinking. Recent proteomic data on mouse lung ageing indicates that, while the ER-resident machinery of collagen biosynthesis, modification and triple helix formation appears largely unchanged, there are specific changes in levels of type IV and type VI as well as the two fibril-associated collagens with interrupted triple helices (FACIT), namely type XIV and type XVI collagens. In addition, levels of the extracellular collagen crosslinking enzyme lysyl oxidase are decreased, indicating less enzymatically mediated collagen crosslinking upon ageing. The latter contrasts with the ageing-associated increase in collagen crosslinking by advanced glycation endproducts (AGEs), a result of spontaneous reactions of protein amino groups with reactive carbonyls, e.g., from monosaccharides or reactive dicarbonyls like methylglyoxal. Given the slow turnover of extracellular collagen such modifications accumulate even more in ageing tissues. In summary, the collective evidence points mainly toward age-induced alterations in collagen composition and drastic changes in the molecular nature of collagen crosslinks. Future work addressing the consequences of these changes may provide important clues for prevention of lung disease and for lung bioengineering and ultimately pave the way to novel targeted approaches in lung regenerative medicine.

Implications for Extracellular Matrix Interactions With Human Lung Basal Stem Cells in Lung Development, Disease, and Airway Modeling

The extracellular matrix (ECM) is not simply a quiescent scaffold. This three-dimensional network of extracellular macromolecules provides structural, mechanical, and biochemical support for the cells of the lung. Throughout life, the ECM forms a critical component of the pulmonary stem cell niche. Basal cells (BCs), the primary stem cells of the airways capable of differentiating to all luminal cell types, reside in close proximity to the basolateral ECM. Studying BC-ECM interactions is important for the development of therapies for chronic lung diseases in which ECM alterations are accompanied by an apparent loss of the lung's regenerative capacity. The complexity and importance of the native ECM in the regulation of BCs is highlighted as we have yet to create an in vitro culture model that is capable of supporting the long-term expansion of multipotent BCs. The interactions between the pulmonary ECM and BCs are, therefore, a vital component for understanding the mechanisms regulating BC stemness during health and disease. If we are able to replicate these interactions in airway models, we could significantly improve our ability to maintain basal cell stemness ex vivo for use in in vitro models and with prospects for cellular therapies. Furthermore, successful, and sustained airway regeneration in an aged or diseased lung by small molecules, novel compounds or via cellular therapy will rely upon both manipulation of the airway stem cells and their immediate niche within the lung. This review will focus on the current understanding of how the pulmonary ECM regulates the basal stem cell function, how this relationship changes in chronic disease, and how replicating native conditions poses challenges for ex vivo cell culture.

Breathing in vitro: Designs and applications of engineered lung models

The aim of this review is to provide a systematic design guideline to users, particularly engineers interested in developing and deploying lung models, and biologists seeking to identify a suitable platform for conducting in vitro experiments involving pulmonary cells or tissues. We first discuss the state of the art on lung in vitro models, describing the most simplistic and traditional ones. Then, we analyze in further detail the more complex dynamic engineered systems that either provide mechanical cues, or allow for more predictive exposure studies, or in some cases even both. This is followed by a dedicated section on microchips of the lung. Lastly, we present a critical discussion of the different characteristics of each type of system and the criteria which may help researchers select the most appropriate technology according to their specific requirements. Readers are encouraged to refer to the tables accompanying the different sections where comprehensive and quantitative information on the operating parameters and performance of the different systems reported in the literature is provided.

Extracellular Vesicle Mediated Tumor-Stromal Crosstalk Within an Engineered Lung Cancer Model

Tumor-stromal interactions within the tumor microenvironment (TME) influence lung cancer progression and response to therapeutic interventions, yet traditional in vitro studies fail to replicate the complexity of these interactions. Herein, we developed three-dimensional (3D) lung tumor models that mimic the human TME and demonstrate tumor-stromal crosstalk mediated by extracellular vesicles (EVs). EVs released by tumor cells, independent of p53 status, and fibroblasts within the TME mediate immunomodulatory effects; specifically, monocyte/macrophage polarization to a tumor-promoting M2 phenotype within this 3D-TME. Additionally, immune checkpoint inhibition in a 3D model that included T cells showed an inhibition of tumor growth and reduced hypoxia within the TME. Thus, perfused 3D tumor models incorporating diverse cell types provide novel insights into EV-mediated tumor-immune interactions and immune-modulation for existing and emerging cancer therapies.

Airspace Macrophages and Monocytes Exist in Transcriptionally Distinct Subsets in Healthy Adults

Rationale: Macrophages are the most abundant immune cell in the alveoli and small airways and are traditionally viewed as a homogeneous population during health. Whether distinct subsets of airspace macrophages are present in healthy humans is unknown. Single-cell RNA sequencing allows for examination of transcriptional heterogeneity between cells and between individuals. Understanding the conserved repertoire of airspace macrophages during health is essential to understanding cellular programing during disease.Objectives: We sought to determine the transcriptional heterogeneity of human cells obtained from BAL of healthy adults.Methods: Ten subjects underwent bronchoscopy with BAL. Cells from lavage were subjected to single-cell RNA sequencing. Unique cell populations and putative functions were identified. Transcriptional profiles were compared across individuals.Measurements and Main Results: We identify two novel subgroups of resident airspace macrophages-defined by proinflammatory and metallothionein gene expression profiles. We define subsets of monocyte-like cells and compare them with peripheral blood mononuclear cells. Finally, we compare global macrophage and monocyte programing between males and females.Conclusions: Healthy human airspaces contain multiple populations of myeloid cells that are highly conserved between individuals and between sexes. Resident macrophages make up the largest population and include novel subsets defined by inflammatory and metal-binding profiles. Monocyte-like cells within the airspaces are transcriptionally aligned with circulating blood cells and include a rare population defined by expression of cell-matrix interaction genes. This study is the first to delineate the conserved heterogeneity of airspace immune cells during health and identifies two previously unrecognized macrophage subsets.

Advanced single-cell technologies to guide the development of bioengineered lungs

Lung transplantation remains the only viable option for individuals suffering from end-stage lung failure. However, a number of current limitations exist including a continuing shortage of suitable donor lungs and immune rejection following transplantation. To address these concerns, engineering a decellularized biocompatible lung scaffold from cadavers reseeded with autologous lung cells to promote tissue regeneration is being explored. Proof-of-concept transplantation of these bioengineered lungs into animal models has been accomplished. However, these lungs were incompletely recellularized with resulting epithelial and endothelial leakage and insufficient basement membrane integrity. Failure to repopulate lung scaffolds with all of the distinct cell populations necessary for proper function remains a significant hurdle for the progression of current engineering approaches and precludes clinical translation. Advancements in 3D bioprinting, lung organoid models, and microfluidic device and bioreactor development have enhanced our knowledge of pulmonary lung development, as well as important cell-cell and cell-matrix interactions, all of which will help in the path to a bioengineered transplantable lung. However, a significant gap in knowledge of the spatiotemporal interactions between cell populations as well as relative quantities and localization within each compartment of the lung necessary for its proper growth and function remains. This review will provide an update on cells currently used for reseeding decellularized scaffolds with outcomes of recent lung engineering attempts. Focus will then be on how data obtained from advanced single-cell analyses, coupled with multiomics approaches and high-resolution 3D imaging, can guide current lung bioengineering efforts for the development of fully functional, transplantable lungs.

Chronic Obstructive Pulmonary Disease and the Cardiovascular System: Vascular Repair and Regeneration as a Therapeutic Target

Chronic obstructive pulmonary disease (COPD) is a major cause of morbidity and mortality worldwide and encompasses chronic bronchitis and emphysema. It has been shown that vascular wall remodeling and pulmonary hypertension (PH) can occur not only in patients with COPD but also in smokers with normal lung function, suggesting a causal role for vascular alterations in the development of emphysema. Mechanistically, abnormalities in the vasculature, such as inflammation, endothelial dysfunction, imbalances in cellular apoptosis/proliferation, and increased oxidative/nitrosative stress promote development of PH, cor pulmonale, and most probably pulmonary emphysema. Hypoxemia in the pulmonary chamber modulates the activation of key transcription factors and signaling cascades, which propagates inflammation and infiltration of neutrophils, resulting in vascular remodeling. Endothelial progenitor cells have angiogenesis capabilities, resulting in transdifferentiation of the smooth muscle cells via aberrant activation of several cytokines, growth factors, and chemokines. The vascular endothelium influences the balance between vaso-constriction and -dilation in the heart. Targeting key players affecting the vasculature might help in the development of new treatment strategies for both PH and COPD. The present review aims to summarize current knowledge about vascular alterations and production of reactive oxygen species in COPD. The present review emphasizes on the importance of the vasculature for the usually parenchyma-focused view of the pathobiology of COPD.

Biomimetic lipid Nanocomplexes incorporating STAT3-inhibiting peptides effectively infiltrate the lung barrier and ameliorate pulmonary fibrosis

Activation of signal transducer and activator of transcription 3 (STAT3) under conditions of inflammation plays a crucial role in the pathogenesis of life-threatening pulmonary fibrosis (PF), initiating pro-fibrotic signaling following its phosphorylation. While there have been attempts to interfere with STAT3 activation and associated signaling as a strategy for ameliorating PF, potent inhibitors with minimal systemic toxicity have yet to be developed. Here, we assessed the in vitro and in vivo therapeutic effectiveness of a cell-permeable peptide inhibitor of STAT3 phosphorylation, designated APTstat3-9R, for ameliorating the indications of pulmonary fibrosis. Our results demonstrate that APTstat3-9R formulated with biomimetic disc-shaped lipid nanoparticles (DLNPs) markedly enhanced the penetration of pulmonary surfactant barrier and alleviated clinical symptoms of PF while causing negligible systemic cytotoxicity. Taken together, our findings suggest that biomimetic lipid nanoparticle-assisted pulmonary delivery of APTstat3-9R may be a feasible therapeutic option for PF in the clinic, and could be applied to treat other fibrotic diseases.

High turnover of types III and VI collagen in progressive idiopathic pulmonary fibrosis

BACKGROUND AND OBJECTIVE

Prediction of idiopathic pulmonary fibrosis (IPF) progression is vital for the choice and timing of treatment and patient follow-up. This could potentially be achieved by prognostic blood biomarkers of extracellular matrix (ECM) remodelling.

METHODS

Neoepitope biomarkers of types III and VI collagen turnover (C3M, C6M, PRO-C3 and PRO-C6) were measured in 185 patients with newly diagnosed IPF. Disease severity at baseline and progression over 6 months was assessed by lung function tests and 6-min walk tests. All-cause mortality was assessed over a 3-year follow-up period.

RESULTS

High baseline levels of C3M, C6M, PRO-C3 and PRO-C6 were associated with more advanced disease at the time of diagnosis. Baseline levels of C6M and PRO-C3 were also associated with mortality over 3 years of follow-up (hazard ratio [HR]: 2.3, 95% CI: 1.3-3.9, p = 0.002 and HR: 1.8, 95% CI: 1.1-3.0, p = 0.03). Patients with several increased biomarkers at baseline, representing a high ECM remodelling phenotype, had more advanced disease at baseline, higher risk of progression or death at 6 months (OR: 1.4, 95% CI: 1.1-1.8, p = 0.002) and higher mortality over 3 years of follow-up (HR: 2.4, 95% CI: 1.3-4.5, p = 0.007).

CONCLUSION

Blood biomarkers of types III and VI collagen turnover, assessed at the time of diagnosis, are associated with several indices of disease severity, short-term progression and long-term mortality. These biomarkers can help to identify patients with a high ECM remodelling phenotype at high risk of disease progression and death.

Engineering Tissue-Informed Biomaterials to Advance Pulmonary Regenerative Medicine

Biomaterials intentionally designed to support the expansion, differentiation, and three-dimensional (3D) culture of induced-pluripotent stem cells (iPSCs) may pave the way to cell-based therapies for chronic respiratory diseases. These conditions are endured by millions of people worldwide and represent a significant cause of morbidity and mortality. Currently, there are no effective treatments for the majority of advanced lung diseases and lung transplantation remains the only hope for many chronically ill patients. Key opinion leaders speculate that the novel coronavirus, COVID-19, may lead to long-term lung damage, further exacerbating the need for regenerative therapies. New strategies for regenerative cell-based therapies harness the differentiation capability of human iPSCs for studying pulmonary disease pathogenesis and treatment. Excitingly, biomaterials are a cell culture platform that can be precisely designed to direct stem cell differentiation. Here, we present a closer look at the state-of-the-art of iPSC differentiation for pulmonary engineering, offer evidence supporting the power of biomaterials to improve stem cell differentiation, and discuss our perspective on the potential for tissue-informed biomaterials to transform pulmonary regenerative medicine.

Unmet needs in the management of exacerbations of chronic obstructive pulmonary disease

Exacerbations of chronic obstructive pulmonary disease (COPD) are episodes of acute worsening of respiratory symptoms that require additional therapy. These events play a pivotal role in the natural course of the disease and are associated with a progressive decline in lung function, reduced health status, a low physical activity level, tremendous health care costs, and increased mortality. Although most exacerbations have an infectious origin, the underlying mechanisms are heterogeneous and specific predictors of their occurrence in individual patients are currently unknown. Accurate prediction and early diagnosis of exacerbations is essential to develop novel targets for prevention and personalized treatments to reduce the impact of these events. Several potential biomarkers have previously been studied, these however lack specificity, accuracy and do not add value to the available clinical predictors. At present, microbial composition and host-microbiome interactions in the lung are increasingly recognized for their role in affecting the susceptibility to exacerbations, and may steer towards a novel direction in the management of COPD exacerbations. This narrative review describes the current challenges and unmet needs in the management of acute exacerbations of COPD. Exacerbation triggers, biological clusters, current treatment strategies, and their limitations, previously studied biomarkers and prediction tools, the lung microbiome and its role in COPD exacerbations as well as future directions are discussed.

Therapeutic targets in lung tissue remodelling and fibrosis

Structural changes involving tissue remodelling and fibrosis are major features of many pulmonary diseases, including asthma, chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF). Abnormal deposition of extracellular matrix (ECM) proteins is a key factor in the development of tissue remodelling that results in symptoms and impaired lung function in these diseases. Tissue remodelling in the lungs is complex and differs between compartments. Some pathways are common but tissue remodelling around the airways and in the parenchyma have different morphologies. Hence it is critical to evaluate both common fibrotic pathways and those that are specific to different compartments; thereby expanding the understanding of the pathogenesis of fibrosis and remodelling in the airways and parenchyma in asthma, COPD and IPF with a view to developing therapeutic strategies for each. Here we review the current understanding of remodelling features and underlying mechanisms in these major respiratory diseases. The differences and similarities of remodelling are used to highlight potential common therapeutic targets and strategies. One central pathway in remodelling processes involves transforming growth factor (TGF)-β induced fibroblast activation and myofibroblast differentiation that increases ECM production. The current treatments and clinical trials targeting remodelling are described, as well as potential future directions. These endeavours are indicative of the renewed effort and optimism for drug discovery targeting tissue remodelling and fibrosis.

Acinetobacter baumannii: An Ancient Commensal with Weapons of a Pathogen

Acinetobacter baumannii is regarded as a life-threatening pathogen associated with community-acquired and nosocomial infections, mainly pneumonia. The rise in the number of A. baumannii antibiotic-resistant strains reduces effective therapies and increases mortality. Bacterial comparative genomic studies have unraveled the innate and acquired virulence factors of A. baumannii. These virulence factors are involved in antibiotic resistance, environmental persistence, host-pathogen interactions, and immune evasion. Studies on host–pathogen interactions revealed that A. baumannii evolved different mechanisms to adhere to in order to invade host respiratory cells as well as evade the host immune system. In this review, we discuss current data on A. baumannii genetic features and virulence factors. An emphasis is given to the players in host–pathogen interaction in the respiratory tract. In addition, we report recent investigations into host defense systems using in vitro and in vivo models, providing new insights into the innate immune response to A. baumannii infections. Increasing our knowledge of A. baumannii pathogenesis may help the development of novel therapeutic strategies based on anti-adhesive, anti-virulence, and anti-cell to cell signaling pathways drugs.

NOX4-Derived ROS Promotes Collagen I Deposition in Bronchial Smooth Muscle Cells by Activating Noncanonical p38MAPK/Akt-Mediated TGF-β Signaling

Background

Airway smooth muscle (ASM) remodeling is a hallmark in chronic obstructive pulmonary disease (COPD). NADPH oxidase 4- (NOX4-) mediated reactive oxygen species (ROS) production plays a crucial role in cell differentiation and extracellular matrix (ECM) synthesis in ASM remodeling. However, the precise mechanisms underpinning its pathogenic roles remain elusive.

Methods

The expression of NOX4 and TGF-β₁ in the airway of the lung was measured in COPD patients and the control group. Cigarette smoke- (CS-) induced emphysema mice were generated, and the alteration of α-SMA, NOX4, TGF-β₁, and collagen I was accessed. The changes of the expression of ECM markers, NOX4, components of TGF-β/Smad, and MAPK/Akt signaling in human bronchial smooth muscle cells (HBSMCs) were ascertained for delineating mechanisms of NOX4-mediated ROS production on cell differentiation and remodeling in human ASM cells.

Results

An increased abundance of NOX4 and TGF-β₁ proteins in the epithelial cells and ASM of lung was observed in COPD patients compared with the control group. Additionally, an increased abundance expression of NOX4 and α-SMA was observed in the lungs of the CS-induced emphysema mouse model. TGF-β₁ displayed abilities to increase the oxidative burden and collagen I production, along with enhanced phosphorylation of ERK, p38MAPK, and p-Akt473 in HBSMCs. These effects of TGF-β₁ could be inhibited by the ROS scavenger N-acetylcysteine (NAC), siRNA-mediated knockdown of Smad3 and NOX4, and pharmacological inhibitors SB203580 (p38MAPK inhibitor) and LY294002 (Akt inhibitor).

Conclusions

NOX4-mediated ROS production alters TGF-β₁-induced cell differentiation and collagen I protein synthesis in HBSMCs in part through the p38MAPK/Akt signaling pathway in a Smad-dependent manner.

3D Cell Culture: Recent Development in Materials with Tunable Stiffness

It is widely accepted that three-dimensional cell culture systems simulate physiological conditions better than traditional 2D systems. Although extracellular matrix components strongly modulate cell behavior, several studies underlined the importance of mechanosensing in the control of different cell functions such as growth, proliferation, differentiation, and migration. Human tissues are characterized by different degrees of stiffness, and various pathologies (e.g., tumor or fibrosis) cause changes in the mechanical properties through the alteration of the extracellular matrix structure. Additionally, these modifications have an impact on disease progression and on therapy response. Hence, the development of platforms whose stiffness could be modulated may improve our knowledge of cell behavior under different mechanical stress stimuli. In this review, we have analyzed the mechanical diversity of healthy and diseased tissues, and we have summarized recently developed materials with a wide range of stiffness.

Mechanical Properties of Soft Biological Membranes for Organ-on-a-Chip Assessed by Bulge Test and AFM

Advanced in vitro models called "organ-on-a-chip" can mimic the specific cellular environment found in various tissues. Many of these models include a thin, sometimes flexible, membrane aimed at mimicking the extracellular matrix (ECM) scaffold of in vivo barriers. These membranes are often made of polydimethylsiloxane (PDMS), a silicone rubber that poorly mimics the chemical and physical properties of the basal membrane. However, the ECM and its mechanical properties play a key role in the homeostasis of a tissue. Here, we report about biological membranes with a composition and mechanical properties similar to those found in vivo. Two types of collagen-elastin (CE) membranes were produced: vitrified and nonvitrified (called "hydrogel membrane"). Their mechanical properties were characterized using the bulge test method. The results were compared using atomic force microscopy (AFM), a standard technique used to evaluate the Young's modulus of soft materials at the nanoscale. Our results show that CE membranes with stiffnesses ranging from several hundred of kPa down to 1 kPa can be produced by tuning the CE ratio, the production mode (vitrified or not), and/or certain parameters such as temperature. The Young's modulus can easily be determined using the bulge test. This method is a robust and reproducible to determine membrane stiffness, even for soft membranes, which are more difficult to assess by AFM. Assessment of the impact of substrate stiffness on the spread of human fibroblasts on these surfaces showed that cell spread is lower on softer surfaces than on stiffer surfaces.

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.

Eosinophil Responses at the Airway Epithelial Barrier during the Early Phase of Influenza A Virus Infection in C57BL/6 Mice

Eosinophils, previously considered terminally differentiated effector cells, have multifaceted functions in tissues. We previously found that allergic mice with eosinophil-rich inflammation were protected from severe influenza and discovered specialized antiviral effector functions for eosinophils including promoting cellular immunity during influenza. In this study, we hypothesized that eosinophil responses during the early phase of influenza contribute to host protection. Using in vitro and in vivo models, we found that eosinophils were rapidly and dynamically regulated upon influenza A virus (IAV) exposure to gain migratory capabilities to traffic to lymphoid organs after pulmonary infection. Eosinophils were capable of neutralizing virus upon contact and combinations of eosinophil granule proteins reduced virus infectivity through hemagglutinin inactivation. Bi-directional crosstalk between IAV-exposed epithelial cells and eosinophils occurred after IAV infection and cross-regulation promoted barrier responses to improve antiviral defenses in airway epithelial cells. Direct interactions between eosinophils and airway epithelial cells after IAV infection prevented virus-induced cytopathology in airway epithelial cells in vitro, and eosinophil recipient IAV-infected mice also maintained normal airway epithelial cell morphology. Our data suggest that eosinophils are important in the early phase of IAV infection providing immediate protection to the epithelial barrier until adaptive immune responses are deployed during influenza.

Fibronectin fibril alignment is established upon initiation of extracellular matrix assembly

The physical structure of the extracellular matrix (ECM) is tissue-specific and fundamental to normal tissue function. Proper alignment of ECM fibers is essential for the functioning of a variety of tissues. While matrix assembly in general has been intensively investigated, little is known about the mechanisms required for formation of aligned ECM fibrils. We investigated the initiation of fibronectin (FN) matrix assembly using fibroblasts that assemble parallel ECM fibrils and found that matrix assembly sites, where FN fibrillogenesis is initiated, were oriented in parallel at the cell poles. We show that these polarized matrix assembly sites progress into fibrillar adhesions and ultimately into aligned FN fibrils. Cells that assemble an unaligned meshwork matrix form matrix assembly sites around the cell periphery, but the distribution of matrix assembly sites in these cells could be modulated through micropatterning or mechanical stretch. While an elongated cell shape corresponds with a polarized matrix assembly site distribution, these two features are not absolutely linked, since we discovered that transforming growth factor beta (TGF-β1) enhances matrix assembly site polarity and assembly of aligned fibrils independent of cell elongation. We conclude that the ultimate orientation of FN fibrils is determined by the alignment and distribution of matrix assembly sites that form during the initial stages of cell–FN interactions.

Doxycycline aggravates granulomatous inflammation and lung microstructural remodeling induced by Schistosoma mansoni infection

Although doxycycline exhibits immunomodulatory properties, its effects on pulmonary infection by Schistosoma mansoni remain overlooked. Thus, we investigated the impact of this drug on lung granulomatous inflammation and microstructural remodeling in a murine model of schistosomiasis. Swiss mice were randomized in four groups: (i) uninfected, (ii) infected with S. mansoni and untreated, (iii) infected treated with praziquantel (Pzq; 200 mg/kg), and (iv) infected treated with Dox (50 mg/kg). Pz was administered in a single dose, and Dox for 60 days. S. mansoni induced marked granulomatous lung inflammation, which was associated to cytokines upregulation (IL-2, IL-4, IL-10, IFN-γ, TNF-α, and TGF-β), neutrophils and macrophages recruitment, alveolar collapse, lung fibrosis, and extensive depletion of elastic fibers. These parameters were attenuated by Pzq and aggravated by Dox. Exudative/productive granulomas were predominant in untreated and Dox-treated animals, while fibrotic granulomas were more frequent in Pzq-treated mice. The number and size of granulomas in Dox-treated animals was higher than untreated and Pzq-treated mice. Dox treatment inhibited the increase in MMP-1 and MMP-2 activity but upregulated myeloperoxidase and N-acetylglucosaminidase activity compared to untreated and Pzq-treated animals. Dox and Pzq exerted no effect on elastin depletion and upregulation of elastase activity. Together, our findings indicated that Dox aggravated granulomatous inflammation, accelerating lung microstructural remodeling by downregulating MMP-1 and MMP-2 activity without impair neutrophils and macrophages recruitment or elastase activity. Thus, Dox potentiates inflammatory damage associated with lung fibrosis, elastin depletion and massive alveolar collapse, profoundly subverting lung structure in S. mansoni-infected mice.

Second-generation lung-on-a-chip with an array of stretchable alveoli made with a biological membrane

The air-blood barrier with its complex architecture and dynamic environment is difficult to mimic in vitro. Lung-on-a-chips enable mimicking the breathing movements using a thin, stretchable PDMS membrane. However, they fail to reproduce the characteristic alveoli network as well as the biochemical and physical properties of the alveolar basal membrane. Here, we present a lung-on-a-chip, based on a biological, stretchable and biodegradable membrane made of collagen and elastin, that emulates an array of tiny alveoli with in vivo-like dimensions. This membrane outperforms PDMS in many ways: it does not absorb rhodamine-B, is biodegradable, is created by a simple method, and can easily be tuned to modify its thickness, composition and stiffness. The air-blood barrier is reconstituted using primary lung alveolar epithelial cells from patients and primary lung endothelial cells. Typical alveolar epithelial cell markers are expressed, while the barrier properties are preserved for up to 3 weeks.

Healing after COVID-19: are survivors at risk for pulmonary fibrosis?

The novel SARS-CoV-2 coronavirus, which is responsible for COVID-19 disease, was first reported in Wuhan, China, in December of 2019. The virus rapidly spread, and the World Health Organization declared a pandemic by March 2020. With millions of confirmed cases worldwide, there is growing concern and considerable debate regarding the potential for coronavirus infection to contribute to an appreciable burden of chronic respiratory symptoms or fibrotic disease among recovered individuals. Because the first case of COVID-19 was documented less than one year ago, data regarding long-term clinical outcomes are not yet available, and predictions for long-term outcome are speculative at best. However, due to the staggering number of cases and the severity of disease in many individuals, there is a critical need to consider the potential long-term implications of COVID-19. This review examines current basic and clinical data regarding fibrogenic mechanisms of viral injury in the context of SARS-CoV-2. Several intersecting mechanisms between coronavirus infection and fibrotic pathways are discussed to highlight factors and processes that may be targetable to improve patient outcome. Reports of post-infection sequelae from previous coronavirus outbreaks are presented toward the goal of improved recognition of potential contributing risk factors for fibrotic disease.

Lost in transition: biomarkers of remodeling in patients with asthma

PURPOSE OF REVIEW

'Biomarkers of remodeling' represent a loose collection of features referring to several biological adaptations of the lung to cope with stressing factors. In addition, remodel-'ing' infers a dynamic process that would require a spatiotemporal resolution. This review focuses on different aspects of remodeling in pediatric and adult care.

RECENT FINDINGS

This review will cover aspects of pediatric remodeling, adult remodeling and techniques and procedures to adequately assess remodeling across different age spectra. In pediatrics, the onset and first features of remodeling are discussed and the continuation into adolescence is addressed. For adults, this review addresses predominant features of remodeling throughout the adult life span and whether there are currently interventions available to treat or reverse remodeling.

SUMMARY

The term 'remodeling' is often referred to via biomarkers that reflect the endstage of a process, although it rather reflects a continuous process starting in childhood and progressing to all age-levels in patients with asthma. Hence, only few biomarkers or surrogates are able to 'capture' its spatiotemporal component, and hardly any are ready for routine use in clinical practice. Given the clinical impact of the remodeling processes, new biomarkers are needed to adequately treat patients with asthma and objectively monitor treatment response beyond symptom control and lung function.

Role of Collagen in Airway Mechanics

Collagen is the most abundant airway extracellular matrix component and is the primary determinant of mechanical airway properties. Abnormal airway collagen deposition is associated with the pathogenesis and progression of airway disease. Thus, understanding how collagen affects healthy airway tissue mechanics is essential. The impact of abnormal collagen deposition and tissue stiffness has been an area of interest in pulmonary diseases such as cystic fibrosis, asthma, and chronic obstructive pulmonary disease. In this review, we discuss (1) the role of collagen in airway mechanics, (2) macro- and micro-scale approaches to quantify airway mechanics, and (3) pathologic changes associated with collagen deposition in airway diseases. These studies provide important insights into the role of collagen in airway mechanics. We summarize their achievements and seek to provide biomechanical clues for targeted therapies and regenerative medicine to treat airway pathology and address airway defects.

Crosstalk between Mast Cells and Lung Fibroblasts Is Modified by Alveolar Extracellular Matrix and Influences Epithelial Migration

Mast cells play an important role in asthma, however, the interactions between mast cells, fibroblasts and epithelial cells in idiopathic pulmonary fibrosis (IPF) are less known. The objectives were to investigate the effect of mast cells on fibroblast activity and migration of epithelial cells. Lung fibroblasts from IPF patients and healthy individuals were co-cultured with LAD2 mast cells or stimulated with the proteases tryptase and chymase. Human lung fibroblasts and mast cells were cultured on cell culture plastic plates or decellularized human lung tissue (scaffolds) to create a more physiological milieu by providing an alveolar extracellular matrix. Released mediators were analyzed and evaluated for effects on epithelial cell migration. Tryptase increased vascular endothelial growth factor (VEGF) release from fibroblasts, whereas co-culture with mast cells increased IL-6 and hepatocyte growth factor (HGF). Culture in scaffolds increased the release of VEGF compared to culture on plastic. Migration of epithelial cells was reduced by IL-6, while HGF and conditioned media from scaffold cultures promoted migration. In conclusion, mast cells and tryptase increased fibroblast release of mediators that influenced epithelial migration. These data indicate a role of mast cells and tryptase in the interplay between fibroblasts, epithelial cells and the alveolar extracellular matrix in health and lung disease.

The role of integrins in inflammation and angiogenesis

Integrins are heterodimeric transmembrane cell adhesion molecules made up of alpha (α) and beta (β) subunits arranged in numerous dimeric pairings. These complexes have varying affinities to extracellular ligands. Integrins regulate cellular growth, proliferation, migration, signaling, and cytokine activation and release and thereby play important roles in cell proliferation and migration, apoptosis, tissue repair, as well as in all processes critical to inflammation, infection, and angiogenesis. This review presents current evidence from human and animal studies on integrin structure and molecular signaling, with particular emphasis on signal transduction in infants. We have included evidence from our own laboratory studies and from an extensive literature search in databases PubMed, EMBASE, Scopus, and the electronic archives of abstracts presented at the annual meetings of the Pediatric Academic Societies. To avoid bias in identification of existing studies, key words were short-listed prior to the actual search both from anecdotal experience and from PubMed's Medical Subject Heading (MeSH) thesaurus. IMPACT: Integrins are a family of ubiquitous αβ heterodimeric receptors that interact with numerous ligands in physiology and disease. Integrins play a key role in cell proliferation, tissue repair, inflammation, infection, and angiogenesis. This review summarizes current evidence from human and animal studies on integrin structure and molecular signaling and promising role in diseases of inflammation, infection, and angiogenesis in infants. This review shows that integrin receptors and ligands are novel therapeutic targets of clinical interest and hold promise as novel therapeutic targets in the management of several neonatal diseases.

Prenatal inflammation enhances antenatal corticosteroid-induced fetal lung maturation

Respiratory complicˆations are the major cause of morbidity and mortality among preterm infants, which is partially prevented by the administration of antenatal corticosteroids (ACS). Most very preterm infants are exposed to chorioamnionitis, but short- and long-term effects of ACS treatment in this setting are not well defined. In low-resource settings, ACS increased neonatal mortality by perhaps increasing infection. We report that treatment with low-dose ACS in the setting of inflammation induced by intraamniotic lipopolysaccharide (LPS) in rhesus macaques improves lung compliance and increases surfactant production relative to either exposure alone. RNA sequencing shows that these changes are mediated by suppression of proliferation and induction of mesenchymal cellular death via TP53. The combined exposure results in a mature-like transcriptomic profile with inhibition of extracellular matrix development by suppression of collagen genes COL1A1, COL1A2, and COL3A1 and regulators of lung development FGF9 and FGF10. ACS and inflammation also suppressed signature genes associated with proliferative mesenchymal progenitors similar to the term gestation lung. Treatment with ACS in the setting of inflammation may result in early respiratory advantage to preterm infants, but this advantage may come at a risk of abnormal extracellular matrix development, which may be associated with increased risk of chronic lung disease.

Precision 3D-Printed Cell Scaffolds Mimicking Native Tissue Composition and Mechanics

Cellular dynamics are modeled by the 3D architecture and mechanics of the extracellular matrix (ECM) and vice versa. These bidirectional cell-ECM interactions are the basis for all vital tissues, many of which have been investigated in 2D environments over the last decades. Experimental approaches to mimic in vivo cell niches in 3D with the highest biological conformity and resolution can enable new insights into these cell-ECM interactions including proliferation, differentiation, migration, and invasion assays. Here, two-photon stereolithography is adopted to print up to mm-sized high-precision 3D cell scaffolds at micrometer resolution with defined mechanical properties from protein-based resins, such as bovine serum albumin or gelatin methacryloyl. By modifying the manufacturing process including two-pass printing or post-print crosslinking, high precision scaffolds with varying Young's moduli ranging from 7-300 kPa are printed and quantified through atomic force microscopy. The impact of varying scaffold topographies on the dynamics of colonizing cells is observed using mouse myoblast cells and a 3D-lung microtissue replica colonized with primary human lung fibroblast. This approach will allow for a systematic investigation of single-cell and tissue dynamics in response to defined mechanical and bio-molecular cues and is ultimately scalable to full organs.

A glitch in the matrix: Age-dependent changes in the extracellular matrix facilitate common sites of metastasis

People over 55 years old represent the majority of cancer patients and suffer from increased metastatic burden compared to the younger patient population. As the aging population increases globally, it is prudent to understand how the intrinsic aging process contributes to cancer progression. As we age, we incur aberrant changes in the extracellular matrix (ECM) of our organs, which contribute to numerous pathologies, including cancer. Notably, the lung, liver, and bone represent the most common sites of distal metastasis for all cancer types. In this review, we describe how age-dependent changes in the ECM of these organs influence cancer progression. Further, we outline how these alterations prime the premetastatic niche and why these may help explain the disparity in outcome for older cancer patients.

Extracellular matrix remodelling in COPD

The extracellular matrix (ECM) of the lung plays several important roles in lung function, as it offers a low resistant pathway that allows the exchange of gases, provides compressive strength and elasticity that supports the fragile alveolar-capillary intersection, controls the binding of cells with growth factors and cell surface receptors and acts as a buffer against retention of water.COPD is a chronic inflammatory respiratory condition, characterised by various conditions that result in progressive airflow limitation. At any stage in the course of the disease, acute exacerbations of COPD may occur and lead to accelerated deterioration of pulmonary function. A key factor of COPD is airway remodelling, which refers to the serious alterations of the ECM affecting airway wall thickness, resistance and elasticity. Various studies have shown that serum biomarkers of ECM turnover are significantly associated with disease severity in patients with COPD and may serve as potential targets to control airway inflammation and remodelling in COPD. Unravelling the complete molecular composition of the ECM in the diseased lungs will help to identify novel biomarkers for disease progression and therapy.

Interleukin-1β Modulation of the Mechanobiology of Primary Human Pulmonary Fibroblasts: Potential Implications in Lung Repair

Pro-inflammatory cytokines like interleukin-1β (IL-1β) are upregulated during early responses to tissue damage and are expected to transiently compromise the mechanical microenvironment. Fibroblasts are key regulators of tissue mechanics in the lungs and other organs. However, the effects of IL-1β on fibroblast mechanics and functions remain unclear. Here we treated human pulmonary fibroblasts from control donors with IL-1β and used Atomic Force Microscopy to unveil that IL-1β significantly reduces the stiffness of fibroblasts concomitantly with a downregulation of filamentous actin (F-actin) and alpha-smooth muscle (α-SMA). Likewise, COL1A1 mRNA was reduced, whereas that of collagenases MMP1 and MMP2 were upregulated, favoring a reduction of type-I collagen. These mechanobiology changes were functionally associated with reduced proliferation and enhanced migration upon IL-1β stimulation, which could facilitate lung repair by drawing fibroblasts to sites of tissue damage. Our observations reveal that IL-1β may reduce local tissue rigidity by acting both intracellularly and extracellularly through the downregulation of fibroblast contractility and type I collagen deposition, respectively. These IL-1β-dependent mechanical effects may enhance lung repair further by locally increasing pulmonary tissue compliance to preserve normal lung distension and function. Moreover, our results support that IL-1β provides innate anti-fibrotic protection that may be relevant during the early stages of lung repair.

Differential glycosylation of collagen modulates lung cancer stem cell subsets through β1 integrin-mediated interactions

In lung cancer, CD133+ cells represent the subset of cancer stem cells (CSC) able to sustain tumor growth and metastatic dissemination. CSC function is tightly regulated by specialized niches composed of both stromal cells and extracellular matrix (ECM) proteins, mainly represented by collagen. The relevance of collagen glycosylation, a fundamental post-translational modification controlling several biological processes, in regulating tumor cell phenotype remains, however, largely unexplored. To investigate the bioactive effects of differential ECM glycosylation on lung cancer cells, we prepared collagen films functionalized with glucose (Glc-collagen) and galactose (Gal-collagen) exploiting a neoglycosylation approach based on a reductive amination of maltose and lactose with the amino residues of collagen lysines. We demonstrate that culturing of tumor cells on collagen determines a glycosylation-dependent positive selection of CSC and triggers their expansion/generation. The functional relevance of CD133+ CSC increase was validated in vivo, proving an augmented tumorigenic and metastatic potential. High expression of integrin β1 in its active form is associated with an increased proficiency of tumor cells to sense signaling from glycosylated matrices (glyco-collagen) and to acquire stemness features. Accordingly, inhibition of integrin β1 in tumor cells prevents CSC enrichment, suggesting that binding of integrin β1 to Glc-collagen subtends CSC expansion/generation. We provide evidence suggesting that collagen glycosylation could play an essential role in modulating the creation of a niche favorable for the generation and selection/survival of lung CSC. Interfering with this crosstalk may represent an innovative therapeutic strategy for lung cancer treatment.

Regulation of cellular senescence by extracellular matrix during chronic fibrotic diseases

The extracellular matrix (ECM) is a complex network of macromolecules surrounding cells providing structural support and stability to tissues. The understanding of the ECM and the diverse roles it plays in development, homoeostasis and injury have greatly advanced in the last three decades. The ECM is crucial for maintaining tissue homoeostasis but also many pathological conditions arise from aberrant matrix remodelling during ageing. Ageing is characterised as functional decline of tissue over time ultimately leading to tissue dysfunction, and is a risk factor in many diseases including cardiovascular disease, diabetes, cancer, dementia, glaucoma, chronic obstructive pulmonary disease (COPD) and fibrosis. ECM changes are recognised as a major driver of aberrant cell responses. Mesenchymal cells in aged tissue show signs of growth arrest and resistance to apoptosis, which are indicative of cellular senescence. It was recently postulated that cellular senescence contributes to the pathogenesis of chronic fibrotic diseases in the heart, kidney, liver and lung. Senescent cells negatively impact tissue regeneration while creating a pro-inflammatory environment as part of the senescence-associated secretory phenotype (SASP) favouring disease progression. In this review, we explore and summarise the current knowledge around how aberrant ECM potentially influences the senescent phenotype in chronic fibrotic diseases. Lastly, we will explore the possibility for interventions in the ECM-senescence regulatory pathways for therapeutic potential in chronic fibrotic diseases.

Lung gene expression signatures suggest pathogenic links and molecular markers for pulmonary tuberculosis, adenocarcinoma and sarcoidosis

Previous reports have suggested a link between pulmonary tuberculosis (TB), which is caused by Mycobacterium tuberculosis (Mtb), and the development of lung adenocarcinoma (LUAD) and sarcoidosis. Furthermore, these lung diseases share certain clinical similarities that can challenge differential diagnosis in some cases. Here, through comparison of lung transcriptome-derived molecular signatures of TB, LUAD and sarcoidosis patients, we identify certain shared disease-related expression patterns. We also demonstrate that MKI67, an over-expressed gene shared by TB and LUAD, is a key mediator in Mtb-promoted tumor cell proliferation, migration, and invasion. Moreover, we reveal a distinct ossification-related TB lung signature, which may be associated with the activation of the BMP/SMAD/RUNX2 pathway in Mtb-infected macrophages that can restrain mycobacterial survival and promote osteogenic differentiation of mesenchymal stem cells. Taken together, these findings provide novel pathogenic links and potential molecular markers for better understanding and differential diagnosis of pulmonary TB, LUAD and sarcoidosis.

Previous work has suggested potential links between Mycobacterium tuberculosis infection and the development of both lung cancer and sarcoidosis, in addition to tuberculosis. Here, Qiyao Chai, Zhe Lu, Zhidong Liu and colleagues report a transcriptomic analysis of lung tissue from tuberculosis, lung adenocarcinoma, and sarcoidosis patients and find that while many disease-linked expression changes are shared between the three diseases, each also has distinct transcriptional signatures that could be useful as molecular markers.

Introducing a Custom-Designed Volume-Pressure Machine for Novel Measurements of Whole Lung Organ Viscoelasticity and Direct Comparisons Between Positive- and Negative-Pressure Ventilation

Asthma, emphysema, COVID-19 and other lung-impacting diseases cause the remodeling of tissue structural properties and can lead to changes in conducting pulmonary volume, viscoelasticity, and air flow distribution. Whole organ experimental inflation tests are commonly used to understand the impact of these modifications on lung mechanics. Here we introduce a novel, automated, custom-designed device for measuring the volume and pressure response of lungs, surpassing the capabilities of traditional machines and built to range size-scales to accommodate both murine and porcine tests. The software-controlled system is capable of constructing standardized continuous volume-pressure curves, while accounting for air compressibility, yielding consistent and reproducible measures while eliminating the need for pulmonary degassing. This device uses volume-control to enable viscoelastic whole lung macromechanical insights from rate dependencies and pressure-time curves. Moreover, the conceptual design of this device facilitates studies relating the phenomenon of diaphragm breathing and artificial ventilation induced by pushing air inside the lungs. System capabilities are demonstrated and validated via a comparative study between ex vivo murine lungs and elastic balloons, using various testing protocols. Volume-pressure curve comparisons with previous pressure-controlled systems yield good agreement, confirming accuracy. This work expands the capabilities of current lung experiments, improving scientific investigations of healthy and diseased pulmonary biomechanics. Ultimately, the methodologies demonstrated in the manufacturing of this system enable future studies centered on investigating viscoelasticity as a potential biomarker and improvements to patient ventilators based on direct assessment and comparisons of positive- and negative-pressure mechanics.

Mechanical Feed-Forward Loops Contribute to Idiopathic Pulmonary Fibrosis

Idiopathic pulmonary fibrosis is a progressive scarring disease characterized by extracellular matrix accumulation and altered mechanical properties of lung tissue. Recent studies support the hypothesis that these compositional and mechanical changes create a progressive feed-forward loop in which enhanced matrix deposition and tissue stiffening contribute to fibroblast and myofibroblast differentiation and activation, which further perpetuates matrix production and stiffening. The biomechanical properties of tissues are sensed and responded to by mechanotransduction pathways that facilitate sensing of changes in mechanical cues by tissue resident cells and convert the mechanical signals into downstream biochemical signals. Although our understanding of mechanotransduction pathways associated with pulmonary fibrosis remains incomplete, recent progress has allowed us to begin to elucidate the specific mechanisms supporting fibrotic feed-forward loops. The mechanosensors discussed here include integrins, Piezo channels, transient receptor potential channels, and nonselective ion channels. Also discussed are downstream transcription factors, including myocardin-related transcription factor and Yes-associated protein/transcriptional coactivator with PDZ-binding motif. This review describes mechanosensors and mechanotransduction pathways associated with fibrosis progression and highlights promising therapeutic insights.

Airway mechanical compression: its role in asthma pathogenesis and progression

The lung is a mechanically active organ, but uncontrolled or excessive mechanical forces disrupt normal lung function and can contribute to the development of disease. In asthma, bronchoconstriction leads to airway narrowing and airway wall buckling. A growing body of evidence suggests that pathological mechanical forces induced by airway buckling alone can perpetuate disease processes in asthma. Here, we review the data obtained from a variety of experimental models, including in vitro, ex vivo and in vivo approaches, which have been used to study the impact of mechanical forces in asthma pathogenesis. We review the evidence showing that mechanical compression alters the biological and biophysical properties of the airway epithelium, including activation of the epidermal growth factor receptor pathway, overproduction of asthma-associated mediators, goblet cell hyperplasia, and a phase transition of epithelium from a static jammed phase to a mobile unjammed phase. We also define questions regarding the impact of mechanical forces on the pathology of asthma, with a focus on known triggers of asthma exacerbations such as viral infection.

Vascular and extracellular matrix remodeling by physical approaches to improve drug delivery at the tumor site

INTRODUCTION

Modern comprehensive studies of tumor microenvironment changes allowed scientists to develop new and more efficient strategies that will improve anticancer drug delivery on site. The tumor microenvironment, especially the dense extracellular matrix, has a recognized capability to hamper the penetration of conventional drugs. Development and co-applications of strategies aiming at remodeling the tumor microenvironment are highly demanded to improve drug delivery at the tumor site in a therapeutic prospect.

AREAS COVERED

Increasing indications suggest that classical physical approaches such as exposure to ionizing radiations, hyperthermia or light irradiation, and emerging ones as sonoporation, electric field or cold plasma technology can be applied as standalone or associated strategies to remodel the tumor microenvironment. The impacts on vasculature and extracellular matrix remodeling of these physical approaches will be discussed with the goal to improve nanotherapeutics delivery at the tumor site.

EXPERT OPINION

Physical approaches to modulate vascular properties and remodel the extracellular matrix are of particular interest to locally control and improve drug delivery and thus increase its therapeutic index. They are particularly powerful as adjuvant to nanomedicine delivery; the development of these technologies could have extremely widespread implications for cancer treatment.[Figure: see text].

Microfluidic lumen-based systems for advancing tubular organ modeling

Microfluidic lumen-based systems are microscale models that recapitulate the anatomy and physiology of tubular organs. These technologies can mimic human pathophysiology and predict drug response, having profound implications for drug discovery and development. Herein, we review progress in the development of microfluidic lumen-based models from the 2000s to the present. The core of the review discusses models for mimicking blood vessels, the respiratory tract, the gastrointestinal tract, renal tubules, and liver sinusoids, and their application to modeling organ-specific diseases. We also highlight emerging application areas, such as the lymphatic system, and close the review discussing potential future directions.

Normal Aging and Its Role in Cancer Metastasis

Metastasis is the most common cause of death, with treatments failing to provide a durable response. Aging is a key prognostic factor in many cancers. Emerging data suggest that normal age-related changes in the tumor microenvironment can contribute to metastatic progression. These changes encompass secreted factors, biophysical changes, and changes in both stromal and immune cell populations. These data also highlight the importance of conducting studies in preclinical models of appropriate age. Ultimately, therapies may also need to be tailored to reflect patient age, as markers of metastatic disease differ in young and aged populations. In this review, we will discuss some of the changes that occur during aging that increase the metastatic capacity of tumor cells.

Lung mechanics modifications facilitating metastasis are mediated in part by breast cancer-derived extracellular vesicles

Tumor microenvironment-mechanics greatly affect tumor-cell characteristics such as invasion and proliferation. We and others have previously shown that after chemotherapy, tumor cells shed more extracellular vesicles (EVs), leading to tumor growth and even spread, via angiogenesis and the mobilization of specific bone-marrow-derived cells contributing to metastasis. However, physical, mechanobiological and mechanostructural changes at premetastatic sites that may support tumor cell seeding, have yet to be determined. Here, we collected tumor-derived extracellular vesicles (tEV) from breast carcinoma cells exposed to paclitaxel chemotherapy, and tested their effects on tissue mechanics (eg, elasticity and stiffness) of likely metastatic organs in cancer-free mice, using shear rheometry. Cancer-free mice were injected with saline or with tEVs from untreated cells and lung tissue demonstrated widely variable, viscoelastic mechanics, being more elastic than viscous. Contrastingly, tEVs from chemotherapy-exposed cells induced more uniform, viscoelastic lung mechanics, with lower stiffness and viscosity; interestingly, livers were significantly stiffer than both controls. We observe statistically significant differences in softening of lung samples from all three groups under increasing strain-amplitudes and in their stiffening under increasing strain-frequencies; the groups reach similar values at high strain amplitudes and frequencies, indicating local changes in tissue microstructure. Evaluation of genes associated with the extracellular matrix and fibronectin protein-expression revealed potential compositional changes underlying the altered mechanics. Thus, we propose that tEVs, even without cancer cells, contribute to metastasis by changing microstructures at distant organs. This is done partially by altering the composition and mechanostructure of tissues to support tumor cell invasion and seeding.

SLIT2/ROBO1-signaling inhibits macropinocytosis by opposing cortical cytoskeletal remodeling

Macropinocytosis is essential for myeloid cells to survey their environment and for growth of RAS-transformed cancer cells. Several growth factors and inflammatory stimuli are known to induce macropinocytosis, but its endogenous inhibitors have remained elusive. Stimulation of Roundabout receptors by Slit ligands inhibits directional migration of many cell types, including immune cells and cancer cells. We report that SLIT2 inhibits macropinocytosis in vitro and in vivo by inducing cytoskeletal changes in macrophages. In mice, SLIT2 attenuates the uptake of muramyl dipeptide, thereby preventing NOD2-dependent activation of NF-κB and consequent secretion of pro-inflammatory chemokine, CXCL1. Conversely, blocking the action of endogenous SLIT2 enhances CXCL1 secretion. SLIT2 also inhibits macropinocytosis in RAS-transformed cancer cells, thereby decreasing their survival in nutrient-deficient conditions which resemble tumor microenvironment. Our results identify SLIT2 as a physiological inhibitor of macropinocytosis and challenge the conventional notion that signals that enhance macropinocytosis negatively regulate cell migration, and vice versa.

Role of metalloproteinases and TNF-α in obesity-associated asthma in mice

Numerous population studies conducted worldwide indicate that the prevalence of asthma is higher in obese versus lean individuals. It has been reported that sensitized lean mice has a better recovery of lung inflammation in asthma. Extracellular matrix (ECM) plays an essential role in the structural support of the lungs regulating the airways diameter, thus preventing its collapse during expiration. ECM renewal by metalloproteinase (MMPs) enzymes is critical for pulmonary biology. There seems to be an imbalance of MMPs activity in asthma and obesity, which can impair the lung remodeling process. In this study, we characterized the pulmonary ECM of obese and lean mice, non-sensitized and sensitized with ovalbumin (OVA). Pharmacological intervention was performed by using anti-TNF-α, and MMP-8 and MMP-9 inhibitors in obese and lean sensitized mice. Activity of MMPs was assessed by gelatinase electrophorese, western blotting and zymogram in situ. Unbalance of MMP-2, MMP-8, MMP-9 and MMP-12 was detected in lung tissue of OVA-sensitized obese mice, which was accompanied by high degradation, corroborating an excessive deposition of types I and III collagen in pulmonary matrix of obese animals. Inhibitions of TNF-α and MMP-9 reduced this MMP imbalance, clearly suggesting a positive effect on pulmonary ECM. Obese and lean mice presented diverse phenotype of asthma regarding the ECM compounds and the inhibition of MMPs pathway could be a good alternative to regulate the activity in ECM lungs of asthmatic obese individuals.

Liver Matrix in Benign and Malignant Biliary Tract Disease

The extracellular matrix is a highly reactive scaffold formed by a wide array of multifunctional molecules, encompassing collagens and noncollagenous glycoproteins, proteoglycans, glycosaminoglycans, and polysaccharides. Besides outlining the tissue borders, the extracellular matrix profoundly regulates the behavior of resident cells by transducing mechanical signals, and by integrating multiple cues derived from the microenvironment. Evidence is mounting that changes in the biostructure of the extracellular matrix are instrumental for biliary repair. Following biliary damage and eventually, malignant transformation, the extracellular matrix undergoes several quantitative and qualitative modifications, which direct interactions among hepatic progenitor cells, reactive ductular cells, activated myofibroblasts and macrophages, to generate the ductular reaction. Herein, we will give an overview of the main molecular factors contributing to extracellular matrix remodeling in cholangiopathies. Then, we will discuss the structural alterations in terms of biochemical composition and physical stiffness featuring the "desmoplastic matrix" of cholangiocarcinoma along with their pro-oncogenic effects.

Endotrophin, an extracellular hormone, in combination with neoepitope markers of von Willebrand factor improves prediction of mortality in the ECLIPSE COPD cohort

BACKGROUND

Lung epithelial damage, activation of the wound healing cascade, and remodeling of the extracellular matrix (ECM) play a major role in chronic obstructive pulmonary disease (COPD). The pro-peptide of type VI collagen has been identified as the hormone endotrophin. Endotrophin has been shown to promote fibrosis and inflammation, whereas von Willebrand factor (VWF) is a crucial part of wound healing initiation. Here, we assessed the released and activated form of VWF and endotrophin, the pro-peptide of type VI collagen, serologically to investigate their association with mortality in COPD subjects alone or in combination.

METHODS

One thousand COPD patients with 3 years of clinical follow-up from the Evaluation of COPD Longitudinally to Identify Predictive Surrogate Endpoints (ECLIPSE) cohort were included. Serum and heparin plasma were collected at 6 months and 1 year, respectively. Competitive ELISA utilizing specific monoclonal antibodies assessed endotrophin/type VI collagen formation (PRO-C6), VWF release (VWF-N), and activated VWF (VWF-A). Biomarker levels were dichotomized into high and low as defined by receiver operating characteristic (ROC) curves based on mortality data. Kaplan-Meier analysis was used to determine hazard ratios for all-cause mortality for biomarkers alone or in combination.

RESULTS

High levels of PRO-C6, VWF-A, and VWF-N have previously been shown to be individually associated with a higher risk of mortality with hazard ratios of 5.6 (95% CI 2.4-13.1), 3.7 (1.8-7.6), and 4.6 (2.2-9.6), respectively. The hazard ratios increased when combining the biomarkers: PRO-C6*VWFA 8.8 (2.8-27.7) and PRO-C6*VWFN 13.3 (5.6-32.0). Notably, PRO-C6*VWF-N increased more than 2-fold.

CONCLUSION

We demonstrated that by combining two pathological relevant aspects of COPD, tissue remodeling, and wound healing, the predictive value of biomarkers for mortality increased notably.

Prospects for RNAi Therapy of COVID-19

COVID-19 caused by the SARS-CoV-2 virus is a fast emerging disease with deadly consequences. The pulmonary system and lungs in particular are most prone to damage caused by the SARS-CoV-2 infection, which leaves a destructive footprint in the lung tissue, making it incapable of conducting its respiratory functions and resulting in severe acute respiratory disease and loss of life. There were no drug treatments or vaccines approved for SARS-CoV-2 at the onset of pandemic, necessitating an urgent need to develop effective therapeutics. To this end, the innate RNA interference (RNAi) mechanism can be employed to develop front line therapies against the virus. This approach allows specific binding and silencing of therapeutic targets by using short interfering RNA (siRNA) and short hairpin RNA (shRNA) molecules. In this review, we lay out the prospect of the RNAi technology for combatting the COVID-19. We first summarize current understanding of SARS-CoV-2 virology and the host response to viral entry and duplication, with the purpose of revealing effective RNAi targets. We then summarize the past experience with nucleic acid silencers for SARS-CoV, the predecessor for current SARS-CoV-2. Efforts targeting specific protein-coding regions within the viral genome and intragenomic targets are summarized. Emphasizing non-viral delivery approaches, molecular underpinnings of design of RNAi agents are summarized with comparative analysis of various systems used in the past. Promising viral targets as well as host factors are summarized, and the possibility of modulating the immune system are presented for more effective therapies. We place special emphasis on the limitations of past studies to propel the field faster by focusing on most relevant models to translate the promising agents to a clinical setting. Given the urgency to address lung failure in COVID-19, we summarize the feasibility of delivering promising therapies by the inhalational route, with the expectation that this route will provide the most effective intervention to halt viral spread. We conclude with the authors' perspectives on the future of RNAi therapeutics for combatting SARS-CoV-2. Since time is of the essence, a strong perspective for the path to most effective therapeutic approaches are clearly articulated by the authors.