Matrix stiffness-modulated proliferation and secretory function of the airway smooth muscle cells

Synthesis and use of thermoplastic polymers for tissue engineering purposes

Thermoplastic polymers provide a versatile platform to mimic various aspects of physiological extracellular matrix properties such as chemical composition, stiffness, and topography for use in cell and tissue engineering applications. In this review, we provide a brief overview of the most promising thermoplastic polymers, and in particular the thermoplastic polyesters, such as poly(lactic acid), poly(glycolic acid), and polycaprolactone, and the thermoplastic elastomers, such as polyurethanes, polyhydroxyalkanoates, and poly(butyl cyanoacrylate). A particular focus has been made on the synthesis processes, the processability and the biocompatibility. We also discuss how these materials can be applied in tissue engineering, mimicking tissues' structure and function, and stimulate mesenchymal stem cells differentiation and mechanotransduction.

House dust mite allergens, store-operated Ca2+ channels and asthma

The house dust mite is the principal source of aero-allergen worldwide. Exposure to mite-derived allergens is associated with the development of asthma in susceptible individuals, and the majority of asthmatics are allergic to the mite. Mite-derived allergens are functionally diverse and activate multiple cell types within the lung that result in chronic inflammation. Allergens activate store-operated Ca2+ release-activated Ca2+ (CRAC) channels, which are widely expressed in multiple cell types within the lung that are associated with the pathogenesis of asthma. Opening of CRAC channels stimulates Ca2+-dependent transcription factors, including nuclear factor of activated T cells and nuclear factor-κB, which drive expression of a plethora of pro-inflammatory cytokines and chemokines that help to sustain chronic inflammation. Here, I describe drivers of asthma, properties of mite-derived allergens, how the allergens are recognized by cells, the signalling pathways used by the receptors and how these are transduced into functional effects, with a focus on CRAC channels. In vivo experiments that demonstrate the effectiveness of targeting CRAC channels as a potential new therapy for treating mite-induced asthma are also discussed, in tandem with other possible approaches.

Stiffness Mediated-Mechanosensation of Airway Smooth Muscle Cells on Linear Stiffness Gradient Hydrogels

In obstructive airway diseases such as asthma and chronic obstructive pulmonary disease (COPD), the extracellular matrix (ECM) protein amount and composition of the airway smooth muscle (ASM) is often remodelled, likely altering tissue stiffness. The underlying mechanism of how human ASM cell (hASMC) mechanosenses the aberrant microenvironment is not well understood. Physiological stiffnesses of the ASM were measured by uniaxial compression tester using porcine ASM layers under 0, 5 and 10% longitudinal stretch above in situ length. Linear stiffness gradient hydrogels (230 kPa range) were fabricated and functionalized with ECM proteins, collagen I (ColI), fibronectin (Fn) and laminin (Ln), to recapitulate the above-measured range of stiffnesses. Overall, hASMC mechanosensation exhibited a clear correlation with the underlying hydrogel stiffness. Cell size, nuclear size and contractile marker alpha-smooth muscle actin (αSMA) expression showed a strong correlation to substrate stiffness. Mechanosensation, assessed by Lamin-A intensity and nuc/cyto YAP, exhibited stiffness-mediated behaviour only on ColI and Fn-coated hydrogels. Inhibition studies using blebbistatin or Y27632 attenuated most mechanotransduction-derived cell morphological responses, αSMA and Lamin-A expression and nuc/cyto YAP (blebbistatin only). This study highlights the interplay and complexities between stiffness and ECM protein type on hASMC mechanosensation, relevant to airway remodelling in obstructive airway diseases.

Dynamic Hydrogels with Viscoelasticity and Tunable Stiffness for the Regulation of Cell Behavior and Fate

The extracellular matrix (ECM) of natural cells typically exhibits dynamic mechanical properties (viscoelasticity and dynamic stiffness). The viscoelasticity and dynamic stiffness of the ECM play a crucial role in biological processes, such as tissue growth, development, physiology, and disease. Hydrogels with viscoelasticity and dynamic stiffness have recently been used to investigate the regulation of cell behavior and fate. This article first emphasizes the importance of tissue viscoelasticity and dynamic stiffness and provides an overview of characterization techniques at both macro- and microscale. Then, the viscoelastic hydrogels (crosslinked via ion bonding, hydrogen bonding, hydrophobic interactions, and supramolecular interactions) and dynamic stiffness hydrogels (softening, stiffening, and reversible stiffness) with different crosslinking strategies are summarized, along with the significant impact of viscoelasticity and dynamic stiffness on cell spreading, proliferation, migration, and differentiation in two-dimensional (2D) and three-dimensional (3D) cell cultures. Finally, the emerging trends in the development of dynamic mechanical hydrogels are discussed.

Membrane adhesion junctions regulate airway smooth muscle phenotype and function

The local environment surrounding airway smooth muscle (ASM) cells has profound effects on the physiological and phenotypic properties of ASM tissues. ASM is continually subjected to the mechanical forces generated during breathing and to the constituents of its surrounding extracellular milieu. The smooth muscle cells within the airways continually modulate their properties to adapt to these changing environmental influences. Smooth muscle cells connect to the extracellular cell matrix (ECM) at membrane adhesion junctions that provide mechanical coupling between smooth muscle cells within the tissue. Membrane adhesion junctions also sense local environmental signals and transduce them to cytoplasmic and nuclear signaling pathways in the ASM cell. Adhesion junctions are composed of clusters of transmembrane integrin proteins that bind to ECM proteins outside the cell and to large multiprotein complexes in the submembranous cytoplasm. Physiological conditions and stimuli from the surrounding ECM are sensed by integrin proteins and transduced by submembranous adhesion complexes to signaling pathways to the cytoskeleton and nucleus. The transmission of information between the local environment of the cells and intracellular processes enables ASM cells to rapidly adapt their physiological properties to modulating influences in their extracellular environment: mechanical and physical forces that impinge on the cell, ECM constituents, local mediators, and metabolites. The structure and molecular organization of adhesion junction complexes and the actin cytoskeleton are dynamic and constantly changing in response to environmental influences. The ability of ASM to rapidly accommodate to the ever-changing conditions and fluctuating physical forces within its local environment is essential for its normal physiological function.

Effects of Elasticity on Cell Proliferation in a Tissue-Engineering Scaffold Pore

Scaffolds engineered for in vitro tissue engineering consist of multiple pores where cells can migrate along with nutrient-rich culture medium. The presence of the nutrient medium throughout the scaffold pores promotes cell proliferation, and this process depends on several factors such as scaffold geometry, nutrient medium flow rate, shear stress, cell-scaffold focal adhesions and elastic properties of the scaffold material. While numerous studies have addressed the first four factors, the mathematical approach described herein focuses on cell proliferation rate in elastic scaffolds, under constant flux of nutrients. As cells proliferate, the scaffold pores radius shrinks and thus, in order to sustain the nutrient flux, the inlet applied pressure on the upstream side of the scaffold pore must be increased. This results in expansion of the elastic scaffold pore, which in turn further increases the rate of cell proliferation. Considering the elasticity of the scaffold, the pore deformation allows further cellular growth beyond that of inelastic conditions. In this paper, our objectives are as follows: (i) Develop a mathematical model for describing fluid dynamics, scaffold elasticity and cell proliferation for scaffolds consist of identical nearly cylindrical pores; (ii) Solve the models and then simulate cellular proliferation within an elastic pore. The simulation can emulate real life tissue growth in a scaffold and offer a solution which reduces the numerical burdens. Lastly, our results demonstrated are in qualitative agreement with experimental observations reported in the literature.

Matrix stiffness exacerbates the proinflammatory responses of vascular smooth muscle cell through the DDR1-DNMT1 mechanotransduction axis

Vascular smooth muscle cell (vSMC) is highly plastic as its phenotype can change in response to mechanical cues inherent to the extracellular matrix (ECM). VSMC may be activated from its quiescent contractile phenotype to a proinflammatory phenotype, whereby the cell secretes chemotactic and inflammatory cytokines, e.g. MCP1 and IL6, to functionally regulate monocyte and macrophage infiltration during the development of various vascular diseases including arteriosclerosis. Here, by culturing vSMCs on polyacrylamide (PA) substrates with variable elastic moduli, we discovered a role of discoidin domain receptor 1 (DDR1), a receptor tyrosine kinase that binds collagens, in mediating the mechanical regulation of vSMC gene expression, phenotype, and proinflammatory responses. We found that ECM stiffness induced DDR1 phosphorylation, oligomerization, and endocytosis to repress the expression of DNA methyltransferase 1 (DNMT1), very likely in a collagen-independent manner. The DDR1-to-DNMT1 signaling was sequentially mediated by the extracellular signal-regulated kinases (ERKs) and p53 pathways. ECM stiffness primed vSMC to a proinflammatory phenotype and this regulation was diminished by DDR1 inhibition. In agreement with the in vitro findings, increased DDR1 phosphorylation was observed in human arterial stiffening. DDR1 inhibition in mouse attenuated the acute injury or adenine diet-induced vascular stiffening and inflammation. Furthermore, mouse vasculature with SMC-specific deletion of Dnmt1 exhibited proinflammatory and stiffening phenotypes. Our study demonstrates a role of SMC DDR1 in perceiving the mechanical microenvironments and down-regulating expression of DNMT1 to result in vascular pathologies and has potential implications for optimization of engineering artificial vascular grafts and vascular networks.

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DDR1 is a mechanosensor in vSMC to perceive ECM stiffness in a collagen binding-independent way.

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Activation of DDR1 leads to repression of DNMT1 expression via the ERK-p53 pathway.

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The DDR1-DNMT1 axis mediates ECM stiffening-induced vascular inflammation.

The CaT stretcher: An open-source system for delivering uniaxial strain to cells and tissues (CaT)

Integration of mechanical cues in conventional 2D or 3D cell culture platforms is an important consideration for in vivo and ex vivo models of lung health and disease. Available commercial and published custom-made devices are frequently limited in breadth of applications, scalability, and customization. Herein we present a technical report on an open-source, cell and tissue (CaT) stretcher, with modularity for different in vitro and ex vivo systems, that includes the following features: 1) Programmability for modeling different breathing patterns, 2) scalability to support low to high-throughput experimentation, and 3) modularity for submerged cell culture, organ-on-chips, hydrogels, and live tissues. The strategy for connecting the experimental cell or tissue samples to the stretching device were designed to ensure that traditional biomedical outcome measurements including, but not limited to microscopy, soluble mediator measurement, and gene and protein expression remained possible. Lastly, to increase the uptake of the device within the community, the system was built with economically feasible and available components. To accommodate diverse in vitro and ex vivo model systems we developed a variety of chips made of compliant polydimethylsiloxane (PDMS) and optimized coating strategies to increase cell adherence and viability during stretch. The CaT stretcher was validated for studying mechanotransduction pathways in lung cells and tissues, with an increase in alpha smooth muscle actin protein following stretch for 24 h observed in independent submerged monolayer, 3D hydrogel, and live lung tissue experiments. We anticipate that the open-source CaT stretcher design will increase accessibility to studies of the dynamic lung microenvironment through direct implementation by other research groups or custom iterations on our designs.

Novel Lung Growth Strategy with Biological Therapy Targeting Airway Remodeling in Childhood Bronchial Asthma

Anti-inflammatory therapy, centered on inhaled steroids, suppresses airway inflammation in asthma, reduces asthma mortality and hospitalization rates, and achieves clinical remission in many pediatric patients. However, the spontaneous remission rate of childhood asthma in adulthood is not high, and airway inflammation and airway remodeling persist after remission of asthma symptoms. Childhood asthma impairs normal lung maturation, interferes with peak lung function in adolescence, reduces lung function in adulthood, and increases the risk of developing chronic obstructive pulmonary disease (COPD). Early suppression of airway inflammation in childhood and prevention of asthma exacerbations may improve lung maturation, leading to good lung function and prevention of adult COPD. Biological drugs that target T-helper 2 (Th2) cytokines are used in patients with severe pediatric asthma to reduce exacerbations and airway inflammation and improve respiratory function. They may also suppress airway remodeling in childhood and prevent respiratory deterioration in adulthood, reducing the risk of COPD and improving long-term prognosis. No studies have demonstrated a suppressive effect on airway remodeling in childhood severe asthma, and further clinical trials using airway imaging analysis are needed to ascertain the inhibitory effect of biological drugs on airway remodeling in severe childhood asthma. In this review, we describe the natural prognosis of lung function in childhood asthma and the risk of developing adult COPD, the pathophysiology of allergic airway inflammation and airway remodeling via Th2 cytokines, and the inhibitory effect of biological drugs on airway remodeling in childhood asthma.

Extracellular Matrix Stiffness in Lung Health and Disease

The extracellular matrix (ECM) provides structural support and imparts a wide variety of environmental cues to cells. In the past decade, a growing body of work revealed that the mechanical properties of the ECM, commonly known as matrix stiffness, regulate the fundamental cellular processes of the lung. There is growing appreciation that mechanical interplays between cells and associated ECM are essential to maintain lung homeostasis. Dysregulation of ECM-derived mechanical signaling via altered mechanosensing and mechanotransduction pathways is associated with many common lung diseases. Matrix stiffening is a hallmark of lung fibrosis. The stiffened ECM is not merely a sequelae of lung fibrosis but can actively drive the progression of fibrotic lung disease. In this article, we provide a comprehensive view on the role of matrix stiffness in lung health and disease. We begin by summarizing the effects of matrix stiffness on the function and behavior of various lung cell types and on regulation of biomolecule activity and key physiological processes, including host immune response and cellular metabolism. We discuss the potential mechanisms by which cells probe matrix stiffness and convert mechanical signals to regulate gene expression. We highlight the factors that govern matrix stiffness and outline the role of matrix stiffness in lung development and the pathogenesis of pulmonary fibrosis, pulmonary hypertension, asthma, chronic obstructive pulmonary disease (COPD), and lung cancer. We envision targeting of deleterious matrix mechanical cues for treatment of fibrotic lung disease. Advances in technologies for matrix stiffness measurements and design of stiffness-tunable matrix substrates are also explored. © 2022 American Physiological Society. Compr Physiol 12:3523-3558, 2022.

Pathobiology of Airway Remodeling in Asthma: The Emerging Role of Integrins

Airway remodeling is a complex clinical feature of asthma that involves long-term disruption and modification of airway architecture, which contributes significantly to airway hyperresponsiveness (AHR) and lung function decline. It is characterized by thickening of the airway smooth muscle layer, deposition of a matrix below the airway epithelium, resulting in subepithelial fibrosis, changes within the airway epithelium, leading to disruption of the barrier, and excessive mucous production and angiogenesis within the airway wall. Airway remodeling contributes to stiffer and less compliant airways in asthma and leads to persistent, irreversible airflow obstruction. Current asthma treatments aim to reduce airway inflammation and exacerbations but none are targeted towards airway remodeling. Inhibiting the development of airway remodeling or reversing established remodeling has the potential to dramatically improve symptoms and disease burden in asthmatic patients. Integrins are a family of transmembrane heterodimeric proteins that serve as the primary receptors for extracellular matrix (ECM) components, mediating cell-cell and cell-ECM interactions to initiate intracellular signaling cascades. Cells present within the lungs, including structural and inflammatory cells, express a wide and varying range of integrin heterodimer combinations and permutations. Integrins are emerging as an important regulator of inflammation, repair, remodeling, and fibrosis in the lung, particularly in chronic lung diseases such as asthma. Here, we provide a comprehensive summary of the current state of knowledge on integrins in the asthmatic airway and how these integrins promote the remodeling process, and emphasize their potential involvement in airway disease.

Canonical and noncanonical regulatory roles for JAK2 in the pathogenesis of rheumatoid arthritis-associated interstitial lung disease and idiopathic pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) and rheumatoid arthritis-associated interstitial lung disease (RA-ILD) are two fibrotic interstitial lung diseases that share the usual interstitial pneumonia (UIP) injury pattern. Here, we report that RNA sequencing of lung biopsies from patients with RA-ILD and IPF revealed shared and distinct disease-causing pathways. Analysis of transcriptomic data identified a JAK2 related JAK/STAT signaling pathway gene signature that distinguishes RA-UIP from idiopathic UIP. This was further confirmed by immunohistostaining, which identified JAK2 phosphorylation with two distinct forms of activation: a cytoplasmic form of JAK2 activation in most IPF cases (13/20) and a nuclear form of p-JAK2 in RA-UIP (5/5) and a minority of IPF (6/20) cases. Further immunohistostaining identified STAT5A&B as the downstream transcriptional activator for JAK2-mediated canonical signal transduction and phosphorylation of Tyr41 on histone H3 (H3Y41ph) as the downstream epigenetic regulation site for JAK2-mediated noncanonical signal transduction. Gene Set Enrichment Analysis (GSEA) of the RNA-Seq data further supported this shared pathogenic mechanism for the two diseases with the enrichment of STAT5A&B target gene sets as well as the JAK2 regulated H3Y41ph target gene set. This regulatory role of JAK2 in the pathogenesis of pulmonary fibrosis was further demonstrated by the attenuation of bleomycin-induced murine pulmonary fibrosis using a JAK2-selective pharmacological inhibitor CEP33779. In vitro studies with normal and IPF derived lung fibroblasts revealed a central role for JAK2 as an essential intermediary molecule in TGF-β-mediated myofibroblast trans-differentiation, proliferation, and extracellular matrix protein production. These observations support a crucial role for JAK2 as an intermediary molecule in fibrotic lung disease development.

Lysyl oxidase-like 2 is increased in asthma and contributes to asthmatic airway remodelling

Background

Airway smooth muscle (ASM) cells are fundamental to asthma pathogenesis, influencing bronchoconstriction, airway hyperresponsiveness and airway remodelling. The extracellular matrix (ECM) can influence tissue remodelling pathways; however, to date no study has investigated the effect of ASM ECM stiffness and cross-linking on the development of asthmatic airway remodelling. We hypothesised that transforming growth factor-β (TGF-β) activation by ASM cells is influenced by ECM in asthma and sought to investigate the mechanisms involved.

Methods

This study combines in vitro and in vivo approaches: human ASM cells were used in vitro to investigate basal TGF-β activation and expression of ECM cross-linking enzymes. Human bronchial biopsies from asthmatic and nonasthmatic donors were used to confirm lysyl oxidase like 2 (LOXL2) expression in ASM. A chronic ovalbumin (OVA) model of asthma was used to study the effect of LOXL2 inhibition on airway remodelling.

Results

We found that asthmatic ASM cells activated more TGF-β basally than nonasthmatic controls and that diseased cell-derived ECM influences levels of TGF-β activated. Our data demonstrate that the ECM cross-linking enzyme LOXL2 is increased in asthmatic ASM cells and in bronchial biopsies. Crucially, we show that LOXL2 inhibition reduces ECM stiffness and TGF-β activation in vitro, and can reduce subepithelial collagen deposition and ASM thickness, two features of airway remodelling, in an OVA mouse model of asthma.

Conclusion

These data are the first to highlight a role for LOXL2 in the development of asthmatic airway remodelling and suggest that LOXL2 inhibition warrants further investigation as a potential therapy to reduce remodelling of the airways in severe asthma.

Novel role for matrix cross-linking enzyme LOXL2 in asthmatic airway remodelling: LOXL2 is increased in #asthma but LOXL2 inhibition reduces matrix stiffness in airway smooth muscle cells and reduces remodelling in vivohttps://bit.ly/3FnzGb3

Aging increases senescence, calcium signaling, and extracellular matrix deposition in human airway smooth muscle

Lung function declines as people age and their lungs become stiffer. With an increasing elderly population, understanding mechanisms that contribute to these structural and functional changes in the aging lung is important. Part of the aging process is characterized by thicker, more fibrotic airways, and senile emphysema caused by changes in lung parenchyma. There is also senescence, which occurs throughout the body with aging. Here, using human airway smooth muscle (ASM) cells from patients in different age groups, we explored senescence pathways and changes in intracellular calcium signaling and extracellular matrix (ECM) deposition to elucidate potential mechanisms by which aging leads to thicker and stiffer lungs. Senescent markers p21, γH2AX, and β-gal, and some senescence-associated secretory proteins (SASP) increased with aging, as shown by staining and biochemical analyses. Agonist-induced intracellular Ca2+ responses, measured using fura-2 loaded cells and fluorescence imaging, increased with age. However, biochemical analysis showed that expression of the following markers decreased with age: M3 muscarinic receptor, TRPC3, Orai1, STIM1, SERCA2, MMP2 and MMP9. In contrast, collagen III, and fibronectin deposition increased with age. These data show that senescence increases in the aging airways that is associated with a stiffer but surprisingly greater intracellular calcium signaling as a marker for contractility. ASM senescence may enhance fibrosis in a feed forward loop promoting remodeling and altered calcium storage and buffering.

The proprotein convertase furin inhibits IL-13-induced inflammation in airway smooth muscle by regulating integrin-associated signaling complexes

Furin is a proprotein convertase that regulates the activation and the inactivation of multiple proteins including matrix metalloproteinases, integrins, and cytokines. It is a serine endoprotease that localizes to the plasma membrane and can be secreted into the extracellular space. The role of furin in regulating inflammation in isolated canine airway smooth muscle tissues was investigated. The treatment of airway tissues with recombinant furin (rFurin) inhibited the activation of Akt and eotaxin secretion induced by IL-13, and it prevented the IL-13-induced suppression of smooth muscle myosin heavy chain expression. rFurin promoted a differentiated phenotype by activating β₁-integrin proteins and stimulating the activation of the adhesome proteins vinculin and paxillin by talin. Activated paxillin induced the binding of Akt to β-parvin IPP [integrin-linked kinase (ILK), PINCH, parvin] complexes, which inhibits Akt activation. Treatment of tissues with a furin inhibitor or the depletion of endogenous furin using shRNA resulted in Akt activation and inflammatory responses similar to those induced by IL-13. Furin inactivation or IL-13 caused talin cleavage and integrin inactivation, resulting in the inactivation of vinculin and paxillin. Paxillin inactivation resulted in the coupling of Akt to α-parvin IPP complexes, which catalyze Akt activation and an inflammatory response. The results demonstrate that furin inhibits inflammation in airway smooth muscle induced by IL-13 and that the anti-inflammatory effects of furin are mediated by activating integrin proteins and integrin-associated signaling complexes that regulate Akt-mediated pathways to the nucleus. Furin may have therapeutic potential for the treatment of inflammatory conditions of the lungs and airways.

Dynamic Tuning of Viscoelastic Hydrogels with Carbonyl Iron Microparticles Reveals the Rapid Response of Cells to Three-Dimensional Substrate Mechanics

Current methods to dynamically tune three-dimensional hydrogel mechanics require specific chemistries and substrates that make modest, slow, and often irreversible changes in their mechanical properties, exclude the use of protein-based scaffolds, or alter the hydrogel microstructure and pore size. Here, we rapidly and reversibly alter the mechanical properties of hydrogels consisting of extracellular matrix proteins and proteoglycans by adding carbonyl iron microparticles (MPs) and applying external magnetic fields. This approach drastically alters hydrogel mechanics: rheology reveals that application of a 4000 Oe magnetic field to a 5 mg/mL collagen hydrogel containing 10 wt % MPs increases the storage modulus from approximately 1.5 to 30 kPa. Cell morphology experiments show that cells embedded within these hydrogels rapidly sense the magnetically induced changes in ECM stiffness. Ca²⁺ transients are altered within seconds of stiffening or subsequent softening, and slower but still dynamic changes occur in YAP nuclear translocation in response to time-dependent application of a magnetic field. The near instantaneous change in hydrogel mechanics provides new insight into the effect of changing extracellular stiffness on both acute and chronic changes in diverse cell types embedded in protein-based scaffolds. Due to its flexibility, this method is broadly applicable to future studies interrogating cell mechanotransduction in three-dimensional substrates.

Stiffening of the extracellular matrix is a sufficient condition for airway hyperreactivity

The current therapeutic approach to asthma focuses exclusively on targeting inflammation and reducing airway smooth muscle force to prevent the recurrence of symptoms. However, even when inflammation is brought under control, airways in an asthmatic can still hyperconstrict when exposed to a low dose of agonist. This suggests that there are mechanisms at play that are likely triggered by inflammation and eventually become self-sustaining so that even when airway inflammation is brought back under control, these alternative mechanisms continue to drive airway hyperreactivity in asthmatics. In this study, we hypothesized that stiffening of the airway extracellular matrix is a core pathological change sufficient to support excessive bronchoconstriction even in the absence of inflammation. To test this hypothesis, we increased the stiffness of the airway extracellular matrix by photo-crosslinking collagen fibers within the airway wall of freshly dissected bovine rings using riboflavin (vitamin B2) and Ultraviolet-A radiation. In our experiments, collagen crosslinking led to a twofold increase in the stiffness of the airway extracellular matrix. This change was sufficient to cause airways to constrict to a greater degree, and at a faster rate when they were exposed to 10^-5 M acetylcholine for 5 min. Our results show that stiffening of the extracellular matrix is sufficient to drive excessive airway constriction even in the absence of inflammatory signals.NEW & NOTEWORTHY Targeting inflammation is the central dogma on which current asthma therapy is based. Here, we show that a healthy airway can be made to constrict excessively and at a faster rate in response to the same stimulus by increasing the stiffness of the extracellular matrix, without the use of inflammatory agents. Our results provide an independent mechanism by which airway remodeling in asthma can sustain airway hyperreactivity even in the absence of inflammatory signals.

Coptisine, a protoberberine alkaloid, relaxes mouse airway smooth muscle via blockade of VDLCCs and NSCCs

Background/Aims: Recently, effective and purified ingredients of traditional Chinese medicine (TCM) were extracted to play crucial roles in the treatment of pulmonary diseases. Our previous research focused on TCM drug screening aimed at abnormal airway muscle contraction during respiratory diseases. Coptisine, an effective ingredient extracted from bitter herbs has shown a series of antioxidant, antibacterial, cardioprotective and neuroprotective pharmacological properties. In the current study, we questioned whether coptisine could also participate in asthma treatment through relaxing abnormal contracted mouse airway smooth muscle (ASM). The present study aimed to characterize the relaxant effects of coptisine on mouse ASM and uncover the underlying molecular mechanisms. Methods: To investigate the role of coptisine on pre-contracted mouse ASM, a series of biological techniques, including force measurement and patch-clamp experiments were employed. Results: Coptisine was found to inhibit high K⁺ or acetylcholine chloride (ACh)-induced pre-contracted mouse tracheal rings in a dose-dependent manner. Further research demonstrated that the coptisine-induced mouse ASM relaxation was mediated by alteration of calcium mobilization via voltage-dependent L-type Ca²⁺ channels (VDLCCs) and non-selective cation channels (NSCCs). Conclusion: Our data showed that mouse ASM could be relaxed by coptisine via altering the intracellular Ca²⁺ concentration through blocking VDLCCs and NSCCs, which suggested that this pharmacological active constituent might be classified as a potential new drug for the treatment of abnormal airway muscle contraction.

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.

Tools, techniques, and future opportunities for characterizing the mechanobiology of uterine myometrium

The myometrium is the smooth muscle layer of the uterus that generates the contractions that drive processes such as menstruation and childbirth. Aberrant contractions of the myometrium can result in preterm birth, insufficient progression of labor, or other difficulties that can lead to maternal or fetal complications or even death. To investigate the underlying mechanisms of these conditions, the most common model systems have conventionally been animal models and human tissue strips, which have limitations mostly related to relevance and scalability, respectively. Myometrial smooth muscle cells have also been isolated from patient biopsies and cultured in vitro as a more controlled experimental system. However, in vitro approaches have focused primarily on measuring the effects of biochemical stimuli and neglected biomechanical stimuli, despite the extensive evidence indicating that remodeling of tissue rigidity or excessive strain is associated with uterine disorders. In this review, we first describe the existing approaches for modeling human myometrium with animal models and human tissue strips and compare their advantages and disadvantages. Next, we introduce existing in vitro techniques and assays for assessing contractility and summarize their applications in elucidating the role of biochemical or biomechanical stimuli on human myometrium. Finally, we conclude by proposing the translation of "organ on chip" approaches to myometrial smooth muscle cells as new paradigms for establishing their fundamental mechanobiology and to serve as next-generation platforms for drug development.

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.

Regeneration of partially decellularized tracheal scaffolds in a mouse model of orthotopic tracheal replacement

Decellularized tracheal scaffolds offer a potential solution for the repair of long-segment tracheal defects. However, complete decellularization of trachea is complicated by tracheal collapse. We created a partially decellularized tracheal scaffold (DTS) and characterized regeneration in a mouse model of tracheal transplantation. All cell populations except chondrocytes were eliminated from DTS. DTS maintained graft integrity as well as its predominant extracellular matrix (ECM) proteins. We then assessed the performance of DTS in vivo. Grafts formed a functional epithelium by study endpoint (28 days). While initial chondrocyte viability was low, this was found to improve in vivo. We then used atomic force microscopy to quantify micromechanical properties of DTS, demonstrating that orthotopic implantation and graft regeneration lead to the restoration of native tracheal rigidity. We conclude that DTS preserves the cartilage ECM, supports neo-epithelialization, endothelialization and chondrocyte viability, and can serve as a potential solution for long-segment tracheal defects.

A novel method to make viscoelastic polyacrylamide gels for cell culture and traction force microscopy

Polyacrylamide hydrogels are commonly used in cell biology, notably to cultivate cells on soft surfaces. Polyacrylamide gels are purely elastic and well adapted to cell culture as they are inert and can be conjugated with adhesion proteins. Here, we report a method to make viscoelastic polyacrylamide gels with mechanical properties more closely resembling biological tissues and suitable for cell culture in vitro. We demonstrate that these gels can be used for traction force microscopy experiments. We also show that multiple cell types respond to the viscoelasticity of their substrate and that viscous dissipation has an influence on cell spreading, contractility, and motility. This new material provides new opportunities for investigating how normal or malignant cells sense and respond to viscous dissipation within the extra-cellular matrix.

Phenotype transitions induced by mechanical stimuli in airway smooth muscle are regulated by differential interactions of parvin isoforms with paxillin and Akt

Mechanical tension and humoral stimuli can induce transitions in airway smooth muscle phenotype between a synthetic inflammatory state that promotes cytokine secretion and a differentiated state that promotes the expression of smooth muscle phenotype-specific proteins. When tissues are maintained under high tension, Akt activation and eotaxin secretion are suppressed, but expression of the differentiation marker protein, smooth muscle myosin heavy chain (SmMHC), is promoted. When tissues are maintained under low tension, Akt activation and eotaxin secretion are stimulated, and the differentiated phenotype is suppressed. We hypothesized that mechanical stimuli are differentially transduced to Akt-mediated signaling pathways that regulate phenotype expression by α-parvin and β-parvin integrin-linked kinase/PINCH/parvin (IPP) signaling complexes within integrin adhesomes. High tension or ACh triggered paxillin phosphorylation and the binding of phospho-paxillin to β-parvin IPP complexes. This inhibited Akt activation and promoted SmMHC expression. Low tension or IL-4 did not elicit paxillin phosphorylation and triggered the binding of unphosphorylated paxillin to α-parvin IPP complexes, which promoted Akt activation and eotaxin secretion and suppressed SmMHC expression. Expression of a nonphosphorylatable paxillin mutant or β-parvin depletion by siRNA promoted the inflammatory phenotype, whereas the depletion of α-parvin promoted the differentiated phenotype. Results demonstrate that phenotype expression is regulated by the differential interaction of phosphorylated and unphosphorylated paxillin with α-parvin and β-parvin IPP complexes and that these complexes have opposite effects on the activation of Akt. Our results describe a novel molecular mechanism for transduction of mechanical and humoral stimuli within integrin signaling complexes to regulate phenotype expression in airway smooth muscle.

Biomaterial-assisted scalable cell production for cell therapy

Cell therapy, the treatment of diseases using living cells, offers a promising clinical approach to treating refractory diseases. The global market for cell therapy is growing rapidly, and there is an increasing demand for automated methods that can produce large quantities of high quality therapeutic cells. Biomaterials can be used during cell production to establish a biomimetic microenvironment that promotes cell adhesion and proliferation while maintaining target cell genotype and phenotype. Here we review recent progress and emerging techniques in biomaterial-assisted cell production. The increasing use of auxiliary biomaterials and automated production methods provides an opportunity to improve quality control and increase production efficiency using standardized GMP-compliant procedures.

Impact of polypropylene prolapse mesh on vaginal smooth muscle in rhesus macaque

BACKGROUND

The use of polypropylene prolapse mesh to treat pelvic organ prolapse has been limited by mesh-related complications. Gynemesh PS mesh, implanted via sacrocolpopexy in rhesus macaques, had a negative impact on the vagina with thinning of vaginal muscularis and decreased vaginal smooth muscle contractility. The negative effect was attenuated when a bioscaffold derived from urinary bladder extracellular matrix was used as a composite with Gynemesh PS.

OBJECTIVE

The objective of the study was to further elucidate the impact of Gynemesh PS polypropylene mesh and MatriStem extracellular matrix bioscaffolds on the vaginal smooth muscle in terms of micromorphology of vaginal smooth muscle (muscle bundles and individual myocytes), innervation, and nerve-mediated contractile function following their implantations in a rhesus macaque model via sacrocolpopexy.

STUDY DESIGN

Thirty-two middle-aged rhesus macaques were randomized to undergo either a sham surgery (sham, n = 8), or the implantation of Gynemesh PS alone (n = 8) vs composite mesh comprised of Gynemesh PS plus 2-ply MatriStem (n = 8) vs 6-ply MatriStem alone (n = 8) via sacrocolpopexy. The graft-vagina complexes were harvested 3 months later. Histomorphometrics of smooth muscle bundles and myocytes were performed by immunofluorescent labeling of alpha smooth muscle actin, caveolin-3 (membrane protein), and cell nuclei followed by confocal imaging. The cross-sectional diameters of smooth muscle bundles and individual myocytes were quantified using images randomly taken in at least 5 areas of each section of sample. Contractile proteins alpha smooth muscle actin and smoothelin were quantified by Western immunoblotting. Nerve density was measured by immunohistochemical labeling of a pan-neuron marker, PGP9.5. Nerve-mediated smooth muscle contractility was quantified using electrical field stimulation. One-way analysis of variance and appropriate post hoc tests were used for statistical comparisons.

RESULTS

Compared with sham, the implantation of Gynemesh PS alone resulted in a disorganized smooth muscle morphology with the number of small muscle bundles (cross-sectional diameter less than 20 μm) increased 67% (P = .004) and the myocyte diameter decreased 22% (P < .001). Levels of contractile proteins were all decreased vs sham with alpha smooth muscle actin decreased by 68% (P = .009), low-molecular-weight smoothelin by 51% (P = .014), and high-molecular-weight smoothelin by 40% (P = .015). Nerve density was decreased by 48% (P = .03 vs sham) paralleled by a 63% decrease of nerve-mediated contractility (P = .02). Following the implantation of composite mesh, the results of measurements were similar to sham (all P > .05), with a 39% increase in the myocyte diameter (P < .001) and a 2-fold increase in the level of alpha smooth muscle actin relative to Gynemesh (P = .045). Following the implantation of MatriStem alone, the number of small muscle bundles were increased 54% vs sham (P = .002), while the other parameters were not significantly different from sham (all P > .05).

CONCLUSION

The implantation of Gynemesh PS had a negative impact on the structural and functional integrity of vaginal smooth muscle evidenced by atrophic macro- and microscopic muscle morphology, decreased innervation, and impaired contractile property, consistent with a maladaptive remodeling response. The extracellular matrix bioscaffold (MatriStem), when used with Gynemesh PS as a composite (2 ply), attenuated the negative impact of Gynemesh PS; when used alone (6 ply), it induced adaptive remodeling as evidenced by an increased fraction of small smooth muscle bundles with normal contractility.

Integrating structural heterogeneity, fiber orientation, and recruitment in multiscale ECM mechanics

Extracellular matrix (ECM) plays critical roles in establishing tissue structure-function relationships and controlling cell fate. However, the mechanisms by which ECM mechanics influence cell and tissue behavior remain to be elucidated since the events associated with this process span length scales from the tissue to molecular level. Entirely new methods are needed in order to better understand the multiscale mechanics of ECM. In this study, a multiscale experimental approach was established by integrating Optical Magnetic Twisting Cytometry (OMTC) with a biaxial tensile tester to study the microscopic (local) ECM mechanical properties under controlled tissue-level (global) loading. Adventitial layer of porcine thoracic artery was used as a collagen-based ECM. Multiphoton microscopy imaging was performed to capture the changes in ECM fiber structure during biaxial deformation. As visualized from multiphoton microscopy images, biaxial stretch induces gradual fiber straightening and the fiber families become evident at higher stretch levels. The OMTC measurements show that the local apparent storage and loss modulus increases with the global biaxial stretch, however there exists a complex interplay among local ECM mechanical properties, ECM structural heterogeneity, and fiber distribution and engagement. The phase lag does not change significantly with global biaxial stretch. Our results also show a much faster increase in global tissue tangent modulus compared to the local apparent complex modulus with biaxial stretch, indicating the scale dependency of ECM mechanics.

Profibrotic effect of IL-17A and elevated IL-17RA in idiopathic pulmonary fibrosis and rheumatoid arthritis-associated lung disease support a direct role for IL-17A/IL-17RA in human fibrotic interstitial lung disease

Interleukin (IL)-17 is a T helper 17 cytokine implicated in the pathogenesis of many autoimmune diseases, including rheumatoid arthritis (RA). Although IL-17A has a well-established role in murine pulmonary fibrosis models, its role in the tissue remodeling and fibrosis occurring in idiopathic pulmonary fibrosis (IPF) and RA-associated interstitial lung disease (RA-ILD) is not very well defined. To address this question, we utilized complimentary studies to determine responsiveness of human normal and pathogenic lung fibroblasts to IL-17A and used lung biopsies acquired from patients with IPF and RA-ILD to determine IL-17A receptor (IL-17RA) expression. Both normal and pathogenic IPF lung fibroblasts express functional IL-17RA and respond to IL-17A stimulation with cell proliferation, generation of extracellular matrix (ECM) proteins, and induction of myofibroblast transdifferentiation. Small interfering RNA (siRNA) silencing of IL-17RA attenuated this fibroblast response to IL-17A on ECM production. These fibroblast responses to IL-17A are dependent on NF-κB-mediated signaling. In addition, inhibiting Janus activated kinase (JAK) 2 by either siRNA or a selective pharmacological inhibitor, AZD1480-but not a JAK1/JAK3 selective inhibitor, tofacitinib-also significantly reduced this IL-17A-induced fibrogenic response. Lung biopsies of RA-ILD patients demonstrate significantly higher IL-17RA expression in areas of fibroblast accumulation and fibrosis, compared with either IPF or normal lung tissue. These observations support a direct role for IL-17A in lung fibrosis that may be particularly relevant in the context of RA-ILD.

Pathological Process of Prompt Connection between Host and Donor Tissue Vasculature Causing Rapid Perfusion of the Engineered Donor Tissue after Transplantation

The shortage of donors for transplantation therapy is a serious issue worldwide. Tissue engineering is considered a potential solution to this problem. Connection and perfusion in engineered tissues after transplantation is vital for the survival of the transplanted tissue, especially for tissues requiring blood perfusion to receive nutrients, such as the heart. A myocardial cell sheet containing an endothelial cell network structure was fabricated in vitro using cell sheet technology. Transplantation of the three-dimensional (3D) tissue by layering myocardial sheets could ameliorate ischemic heart disease in a rat model. The endothelial cell network in the 3D tissue was able to rapidly connect to host vasculature and begin perfusion within 24 h after transplantation. In this review, we compare and discuss the engineered tissue⁻host vasculature connection process between tissue engineered constructs with hydrogels and cell sheets by histological analysis. This review provides information that may be useful for further improvements of in vivo engineered tissue vascularization techniques.

Fabrication of thin-layer matrigel-based constructs for three-dimensional cell culture

Extracellular matrix-based hydrogels such as Matrigel are easy-to-use, commercially available, and offer environments for three-dimensional (3-D) cell culture that mimic native tissue. However, manipulating small volumes of these materials to produce thin-layer 3-D culture systems suitable for analysis is difficult because of air-liquid-substrate interfacial tension effects and evaporation. Here, we demonstrate two simple techniques that use standard liquid-handling tools and nontreated 96-well plates to produce uniform, thin-layer constructs for 3-D culture of cells in Matrigel. The first technique, the floating 3-D cell culture method, uses phase-separating polymers to form a barrier between the dispensed Matrigel, air, and cultureware surface to generate consistently thin hydrogels from volumes as low as 5 μL. These unanchored gels provide a useful assay for investigating airway smooth muscle cell contraction and may have future applications in studying asthma pathophysiology. The second technique, the fixed 3-D cell culture method, provides an anchored gel system for culturing noncontractile cells (e.g., neurons) where 20 μL of Matrigel is dispensed into the bottom of a well filled with culture medium to form a thin gel containing embedded cells. This technique has potential widespread applications as an accessible 3-D culture platform for high-throughput production of disease models for evaluation of novel drug therapies. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2733, 2019.

Cyclic stretch enhances reorientation and differentiation of 3-D culture model of human airway smooth muscle

Activation of airway smooth muscle (ASM) cells plays a central role in the pathophysiology of asthma. Because ASM is an important therapeutic target in asthma, it is beneficial to develop bioengineered ASM models available for assessing physiological and biophysical properties of ASM cells. In the physiological condition in vivo, ASM cells are surrounded by extracellular matrix (ECM) and exposed to mechanical stresses such as cyclic stretch. We utilized a 3-D culture model of human ASM cells embedded in type-I collagen gel. We further examined the effects of cyclic mechanical stretch, which mimics tidal breathing, on cell orientation and expression of contractile proteins of ASM cells within the 3-D gel. ASM cells in type-I collagen exhibited a tissue-like structure with actin stress fiber formation and intracellular Ca²⁺ mobilization in response to methacholine. Uniaxial cyclic stretching enhanced alignment of nuclei and actin stress fibers of ASM cells. Moreover, expression of mRNAs for contractile proteins such as α-smooth muscle actin, calponin, myosin heavy chain 11, and transgelin of stretched ASM cells was significantly higher than that under the static condition. Our findings suggest that mechanical force and interaction with ECM affects development of the ASM tissue-like construct and differentiation to the contractile phenotype in a 3-D culture model.

Cellular Mechanotransduction: From Tension to Function

Living cells are constantly exposed to mechanical stimuli arising from the surrounding extracellular matrix (ECM) or from neighboring cells. The intracellular molecular processes through which such physical cues are transformed into a biological response are collectively dubbed as mechanotransduction and are of fundamental importance to help the cell timely adapt to the continuous dynamic modifications of the microenvironment. Local changes in ECM composition and mechanics are driven by a feed forward interplay between the cell and the matrix itself, with the first depositing ECM proteins that in turn will impact on the surrounding cells. As such, these changes occur regularly during tissue development and are a hallmark of the pathologies of aging. Only lately, though, the importance of mechanical cues in controlling cell function (e.g., proliferation, differentiation, migration) has been acknowledged. Here we provide a critical review of the recent insights into the molecular basis of cellular mechanotransduction, by analyzing how mechanical stimuli get transformed into a given biological response through the activation of a peculiar genetic program. Specifically, by recapitulating the processes involved in the interpretation of ECM remodeling by Focal Adhesions at cell-matrix interphase, we revise the role of cytoskeleton tension as the second messenger of the mechanotransduction process and the action of mechano-responsive shuttling proteins converging on stage and cell-specific transcription factors. Finally, we give few paradigmatic examples highlighting the emerging role of malfunctions in cell mechanosensing apparatus in the onset and progression of pathologies.

Topographic distribution of idiopathic pulmonary fibrosis: a hybrid physics- and agent-based model

OBJECTIVE

Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal disease characterized by excessive deposition of collagen and associated stiffening of lung tissue. While it is known that inflammation and dysfunction of fibroblasts are involved in disease development, it remains poorly understood how cells and their microenvironment interact to produce a characteristic subpleural pattern of high and low tissue density variations, called honeycombing, on CT images of patients with IPF. Since the pleura is stiffer than the parenchyma, we hypothesized that local stiffness of the underlying extracellular matrix can influence fibroblast activation and consequently the deposition of collagen, which in turn influences tissue stiffness in a positive feedback loop.

APPROACH

We tested this hypothesis by developing a hybrid physics-based/agent-based computational model in which aberrant fibroblast activation is induced when cells migrate on stiff tissue. This activation then feeds back on itself via the altered mechanical environment that it creates by depositing collagen.

MAIN RESULTS

The model produces power law distributions of both low- and high-attenuation area clusters and predicts the development of honeycombing only when mechanical rupture is allowed to take place in highly strained normal tissue surrounded by stiff fibrotic tissue. These predictions compare well with histologic data computed from CT images of patients with IPF.

SIGNIFICANCE

We conclude that the clinical manifestation of subpleural honeycombing in IPF may result from fibroblasts entering into a positive feedback loop induced by the abnormally high tissue stiffness near the pleura.

Deterministic Encapsulation of Human Cardiac Stem Cells in Variable Composition Nanoporous Gel Cocoons To Enhance Therapeutic Repair of Injured Myocardium

Although cocooning explant-derived cardiac stem cells (EDCs) in protective nanoporous gels (NPGs) prior to intramyocardial injection boosts long-term cell retention, the number of EDCs that finally engraft is trivial and unlikely to account for salutary effects on myocardial function and scar size. As such, we investigated the effect of varying the NPG content within capsules to alter the physical properties of cocoons without influencing cocoon dimensions. Increasing NPG concentration enhanced cell migration and viability while improving cell-mediated repair of injured myocardium. Given that the latter occurred with NPG content having no detectable effect on the long-term engraftment of transplanted cells, we found that changing the physical properties of cocoons prompted explant-derived cardiac stem cells to produce greater amounts of cytokines, nanovesicles, and microRNAs that boosted the generation of new blood vessels and new cardiomyocytes. Thus, by altering the physical properties of cocoons by varying NPG content, the paracrine signature of encapsulated cells can be enhanced to promote greater endogenous repair of injured myocardium.

Extracellular matrix in lung development, homeostasis and disease

The lung's unique extracellular matrix (ECM), while providing structural support for cells, is critical in the regulation of developmental organogenesis, homeostasis and injury-repair responses. The ECM, via biochemical or biomechanical cues, regulates diverse cell functions, fate and phenotype. The composition and function of lung ECM become markedly deranged in pathological tissue remodeling. ECM-based therapeutics and bioengineering approaches represent promising novel strategies for regeneration/repair of the lung and treatment of chronic lung diseases. In this review, we assess the current state of lung ECM biology, including fundamental advances in ECM composition, dynamics, topography, and biomechanics; the role of the ECM in normal and aberrant lung development, adult lung diseases and autoimmunity; and ECM in the regulation of the stem cell niche. We identify opportunities to advance the field of lung ECM biology and provide a set recommendations for research priorities to advance knowledge that would inform novel approaches to the pathogenesis, diagnosis, and treatment of chronic lung diseases.

Unique mechanisms of connective tissue growth factor regulation in airway smooth muscle in asthma: Relationship with airway remodelling

Neovascularization, increased basal membrane thickness and increased airway smooth muscle (ASM) bulk are hallmarks of airway remodelling in asthma. In this study, we examined connective tissue growth factor (CTGF) dysregulation in human lung tissue and animal models of allergic airway disease. Immunohistochemistry revealed that ASM cells from patients with severe asthma (A) exhibited high expression of CTGF, compared to mild and non‐asthmatic (NA) tissues. This finding was replicated in a sheep model of allergic airways disease. In vitro, transforming growth factor (TGF)‐β increased CTGF expression both in NA‐ and A‐ASM cells but the expression was higher in A‐ASM at both the mRNA and protein level as assessed by PCR and Western blot. Transfection of CTGF promoter‐luciferase reporter constructs into NA‐ and A‐ASM cells indicated that no region of the CTGF promoter (−1500 to +200 bp) displayed enhanced activity in the presence of TGF‐β. However, in silico analysis of the CTGF promoter suggested that distant transcription factor binding sites may influence CTGF promoter activation by TGF‐β in ASM cells. The discord between promoter activity and mRNA expression was also explained, in part, by differential post‐transcriptional regulation in A‐ASM cells due to enhanced mRNA stability for CTGF. In patients, higher CTGF gene expression in bronchial biopsies was correlated with increased basement membrane thickness indicating that the enhanced CTGF expression in A‐ASM may contribute to airway remodelling in asthma.

Aging and anatomical variations in lung tissue stiffness

Lung function is inherently mechanical in nature and depends on the capacity to conduct air and blood to and from the gas exchange regions. Variations in the elastic properties of the human lung across anatomical compartments and with aging are likely important determinants of lung function but remain relatively poorly characterized. Here we applied atomic force microscopy microindentation to characterize human lung tissue from subjects ranging in age from 11 to 60 yr old. We observed striking anatomical variations in elastic modulus, with the airways (200- to 350-µm diameter) the stiffest and the parenchymal regions the most compliant. Vessels (diameter < 100 µm) represented an intermediate mechanical environment and displayed diameter-dependent trends in elastic modulus. Binning our samples into younger (11-30 yr old) and older (41-60 yr old) groups, we observed significant age-related increases in stiffness in parenchymal and vessel compartments, with the most pronounced changes in the vessels. To investigate cellular mechanisms that might contribute to vascular stiffening with aging, we studied primary human pulmonary artery smooth muscle cells from subjects ranging in age from 11 to 60 yr old. While we observed no change in the mechanical properties of the cells themselves, we did observe trends toward increases in traction forces and extracellular matrix deposition with aging. These results demonstrate age-related changes in tissue mechanical properties that likely contribute to impaired lung function with aging and underscore the potential to identify mechanisms that contribute to mechanical tissue remodeling through the study of human cells and tissues from across the aging spectrum.

Development of an electrospun biomimetic polyurea scaffold suitable for vascular grafting

The optimization of biomechanical and biochemical properties of a vascular graft to render properties relevant to physiological environments is a major challenge today. These critical properties of a vascular graft not only regulate its stability and integrity, but also control invasion of cells for scaffold remodeling permitting its integration with native tissue. In this work, we have synthesized a biomimetic scaffold by electrospinning a blend of a polyurea, poly(serinol hexamethylene urea) (PSHU), and, a polyester, poly-ε-caprolactone (PCL). Mechanical properties of the scaffold were varied by varying polymer blending ratio and electrospinning flow rate. Mechanical characterization revealed that scaffolds with lower PSHU content relative to PCL content resulted in elasticity close to native mammalian arteries. We also found that increasing electrospinning flow rates also increased the elasticity of the matrix. Optimization of elasticity generated scaffolds that enabled vascular smooth muscle cells (SMCs) to adhere, grow and maintain a SMC phenotype. The 30/70 scaffold also underwent slower degradation than scaffolds with higher PSHU content, thereby, providing the best option for in vivo remodeling. Further, Gly-Arg-Gly-Asp-Ser (RGD) covalently conjugated to the polyurea backbone in 30/70 scaffold resulted in significantly increased clotting times. Reducing surface thrombogenicity by the conjugation of RGD is critical to avoiding intimal hyperplasia. Hence, biomechanical and biochemical properties of a vascular graft can be balanced by optimizing synthesis parameters and constituent components. For these reasons, the optimized RGD-conjugated 30/70 scaffold electrospun at 2.5 or 5 mL/h has great potential as a suitable material for vascular grafting applications. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 278-290, 2018.

Matrix biomechanics and dynamics in pulmonary fibrosis

The composition and mechanical properties of the extracellular matrix are dramatically altered during the development and progression of pulmonary fibrosis. Recent evidence indicates that these changes in matrix composition and mechanics are not only end-results of fibrotic remodeling, but active participants in driving disease progression. These insights have stimulated interest in identifying the components and physical aspects of the matrix that contribute to cell activation and disease initiation and progression. This review summarizes current knowledge regarding the biomechanics and dynamics of the ECM in mouse models and human IPF, and discusses how matrix mechanical and compositional changes might be non-invasively assessed, therapeutically targeted, and biologically restored to resolve fibrosis.

Mechanosensation across borders: fibroblasts inside a macroporous scaffold sense and respond to the mechanical environment beyond the scaffold walls

In tissue defects, cells face distinct mechanical boundary conditions, but how this influences early stages of tissue regeneration remains largely unknown. Biomaterials are used to fill defects but also to provide specific mechanical or geometrical signals. However, they might at the same time shield mechanical information from surrounding tissues that is relevant for tissue functionalisation. This study investigated how fibroblasts in a soft macroporous biomaterial scaffold respond to distinct mechanical environments while they form microtissues. Different boundary stiffnesses counteracting scaffold contraction were provided via a newly developed in vitro setup. Online monitoring over 14 days revealed 3.0 times lower microtissue contraction but 1.6 times higher contraction force for high vs. low stiffness. This difference was significant already after 48 h, a very early stage of microtissue growth. The microtissue's mechanical and geometrical adaptation indicated a collective cellular behaviour and mechanical communication across scaffold pore walls. Surprisingly, the stiffness of the environment influenced cell behaviour even inside macroporous scaffolds where direct cell-cell contacts are hindered. Mechanical communication between cells via traction forces is essential for tissue adaptation to the environment and should not be blocked by rigid biomaterials. Copyright © 2017 John Wiley & Sons, Ltd.

Measured pulmonary arterial tissue stiffness is highly sensitive to AFM indenter dimensions

The mechanical properties of pulmonary tissues are important in normal function and the development of diseases such as pulmonary arterial hypertension. Hence it is critical to measure lung tissue micromechanical properties as accurately as possible in order to gain insight into the normal and pathological range of tissue stiffness associated with development, aging and disease processes. In this study, we used atomic force microscopy (AFM) micro-indentation to characterize the Young's modulus of small human pulmonary arteries (vessel diameter less than 100µm), and examined the influence of AFM tip geometry and diameter, lung tissue section thickness and the range of working force applied to the sample on the measured modulus. We observed a significant increase of the measured Young's modulus of pulmonary vessels (one order of magnitude) associated with the use of a pyramidal sharp AFM tips (20nm radius), compared to two larger spherical tips (1 and 2.5µm radius) which generated statistically indistinguishable results. The effect of tissue section thickness (ranging from 10 to 50 μm) on the measured elastic modulus was relatively smaller (<1-fold), but resulted in a significant increase in measured elastic modulus for the thinnest sections (10 μm) relative to the thicker (20 and 50 μm) sections. We also found that the measured elastic modulus depends modestly (again <1-fold), but significantly, on the magnitude of force applied, but only on thick (50 μm) and not thin (10 μm) tissue sections. Taken together these results demonstrate a dominant effect of indenter shape/radius on the measured elastic modulus of pulmonary arterial tissues, with lesser effects of tissue thickness and applied force. The results of this study highlight the importance of AFM parameter selection for accurate characterization of pulmonary arterial tissue mechanical properties, and allow for comparison of literature values for lung vessel tissue mechanical properties measured by AFM across a range of indenter and indentation parameters.

Pro-fibrotic pathway activation in trabecular meshwork and lamina cribrosa is the main driving force of glaucoma

While primary open-angle glaucoma (POAG) is a leading cause of blindness worldwide, it still does not have a clear mechanism that can explain all clinical cases of the disease. Elevated IOP is associated with increased accumulation of extracellular matrix (ECM) proteins in the trabecular meshwork (TM) that prevents normal outflow of aqueous humor (AH) and has damaging effects on the fine mesh-like lamina cribrosa (LC) through which the optic nerve fibers pass. Applying a pathway analysis algorithm, we discovered that an elevated level of TGFβ observed in glaucoma-affected tissues could lead to pro-fibrotic pathway activation in TM and in LC. In turn, activated pro-fibrotic pathways lead to ECM remodeling in TM and LC, making TM less efficient in AH drainage and making LC more susceptible to damage from elevated IOP via ECM transformation in LC. We propose pathway targets for potential therapeutic interventions to delay or avoid fibrosis initiation in TM and LC tissues.

Simultaneously Targeting Myofibroblast Contractility and Extracellular Matrix Cross-Linking as a Therapeutic Concept in Airway Fibrosis

Fibrosis after solid organ transplantation is considered an irreversible process and remains the major cause of graft dysfunction and death with limited therapies. This remodeling is characterized by aberrant accumulation of contractile myofibroblasts that deposit excessive extracellular matrix (ECM) and increase tissue stiffness. Studies demonstrate, however, that a stiff ECM itself promotes fibroblast-to-myofibroblast differentiation, stimulating further ECM production. This creates a positive feedback loop that perpetuates fibrosis. We hypothesized that simultaneously targeting myofibroblast contractility with relaxin and ECM stiffness with lysyl oxidase inhibitors could break the feedback loop, reversing established fibrosis. To test this, we used the orthotopic tracheal transplantation (OTT) mouse model, which develops robust fibrotic airway remodeling. Mice with established fibrosis were treated with saline, mono-, or combination therapies. Although monotherapies had no effect, combining these agents decreased collagen deposition and promoted re-epithelialization of remodeled airways. Relaxin inhibited myofibroblast differentiation and contraction in a matrix-stiffness-dependent manner through prostaglandin E₂ (PGE₂ ). Furthermore, the effect of combination therapy was lost in PGE₂ receptor knockout and PGE₂ -inhibited OTT mice. This study revealed the important synergistic roles of cellular contractility and tissue stiffness in the maintenance of fibrotic tissue and suggests a new therapeutic principle for fibrosis.

Directional preference of airway smooth muscle mass increase in human asthmatic airways

Airway smooth muscle (ASM) orientation and morphology determine the ability of the muscle to constrict the airway. In asthma, ASM mass is increased, but it is unknown whether ASM orientation and morphology are altered as well or whether the remodeling at the source of the mass increase is ongoing. We dissected human airway trees from asthmatic and control lungs. Stained, intact airway sections were imaged in axial projection to show ASM bundle orientation, whereas cross-sectional histological slides were used to assess ASM area, bundle thickness, and ASM bundle-to-basement membrane distance. We also used these slides to assess cell size, proliferation, and apoptosis. We showed that ASM mass increase in cartilaginous airways is primarily the result of an increase of ASM bundle thickness (as measured radially in an airway cross section) and coincides with an increased distance of the ASM bundles to the airway perimeter. ASM orientation was unchanged in all airways. Apoptosis markers and cell size did not show differences between asthmatics and controls. Our findings show that ASM mass increase likely contributes to the airway-constricting capacity of the muscle. Both the increased bundle thickness and increased thickness of the airway wall inwards of the ASM bundles could further enhance this capacity. Turnover of ASM appears to be the same in airways and biopsies, but the lack of correlation between different markers of proliferation casts doubt on the specificity of markers generally used to assess proliferation.

The Critical Role of Pulmonary Arterial Compliance in Pulmonary Hypertension

The normal pulmonary circulation is a low-pressure, high-compliance system. Pulmonary arterial compliance decreases in the presence of pulmonary hypertension because of increased extracellular matrix/collagen deposition in the pulmonary arteries. Loss of pulmonary arterial compliance has been consistently shown to be a predictor of increased mortality in patients with pulmonary hypertension, even more so than pulmonary vascular resistance in some studies. Decreased pulmonary arterial compliance causes premature reflection of waves from the distal pulmonary vasculature, leading to increased pulsatile right ventricular afterload and eventually right ventricular failure. Evidence suggests that decreased pulmonary arterial compliance is a cause rather than a consequence of distal small vessel proliferative vasculopathy. Pulmonary arterial compliance decreases early in the disease process even when pulmonary artery pressure and pulmonary vascular resistance are normal, potentially enabling early diagnosis of pulmonary vascular disease, especially in high-risk populations. With the recognition of the prognostic importance of pulmonary arterial compliance, its impact on right ventricular function, and its contributory role in the development and progression of distal small-vessel proliferative vasculopathy, pulmonary arterial compliance is an attractive target for the treatment of pulmonary hypertension.

Emerging concepts in smooth muscle contributions to airway structure and function: implications for health and disease

Airway structure and function are key aspects of normal lung development, growth, and aging, as well as of lung responses to the environment and the pathophysiology of important diseases such as asthma, chronic obstructive pulmonary disease, and fibrosis. In this regard, the contributions of airway smooth muscle (ASM) are both functional, in the context of airway contractility and relaxation, as well as synthetic, involving production and modulation of extracellular components, modulation of the local immune environment, cellular contribution to airway structure, and, finally, interactions with other airway cell types such as epithelium, fibroblasts, and nerves. These ASM contributions are now found to be critical in airway hyperresponsiveness and remodeling that occur in lung diseases. This review emphasizes established and recent discoveries that underline the central role of ASM and sets the stage for future research toward understanding how ASM plays a central role by being both upstream and downstream in the many interactive processes that determine airway structure and function in health and disease.