The complexity and rapid clearance mechanisms of lung tissue make it difficult to develop effective treatments for many chronic pathologies. We are investigating lung derived extracellular matrix (ECM) hydrogels as a novel approach for delivery of cellular therapies to the pulmonary system. The main objectives of this study include effective decellularization of porcine lung tissue, development of a hydrogel from the porcine ECM, and characterization of the material's composition, mechanical properties, and ability to support cellular growth. Our evaluation of the decellularized tissue indicated successful removal of cellular material and immunogenic remnants in the ECM. The self-assembly of the lung ECM hydrogel was rapid, reaching maximum modulus values within 3 min at 37°C. Rheological characterization showed the lung ECM hydrogel to have a concentration dependent storage modulus between 15 and 60 Pa. The purpose of this study was to evaluate our novel ECM derived hydrogel and measure its ability to support 3D culture of MSCs in vitro and in vivo delivery of MSCs. Our in vitro experiments using human mesenchymal stem cells demonstrated our novel ECM hydrogel's ability to enhance cellular attachment and viability. Our in vivo experiments demonstrated that rat MSC delivery in pre-gel solution significantly increased cell retention in the lung over 24 h in an emphysema rat model. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1922-1935, 2016.

Epithelial injury is a central event in the pathogenesis of many inflammatory and fibrotic lung diseases like acute respiratory distress syndrome, pulmonary fibrosis, and iatrogenic lung injury. Mechanical stress is an often underappreciated contributor to lung epithelial injury. Following injury, differentiated epithelia can assume a myofibroblast phenotype in a process termed epithelial to mesenchymal transition (EMT), which contributes to aberrant wound healing and fibrosis. We demonstrate that cyclic mechanical stretch induces EMT in alveolar type II epithelial cells, associated with increased expression of low molecular mass hyaluronan (sHA). We show that sHA is sufficient for induction of EMT in statically cultured alveolar type II epithelial cells and necessary for EMT during cell stretch. Furthermore, stretch-induced EMT requires the innate immune adaptor molecule MyD88. We examined the Wnt/␤-catenin pathway, which is known to mediate EMT. The Wnt target gene Wnt-inducible signaling protein 1 (wisp-1) is significantly up-regulated in stretched cells in hyaluronan-and MyD88-dependent fashion, and blockade of WISP-1 prevents EMT in stretched cells. In conclusion, we show for the first time that innate immunity transduces mechanical stress responses through the matrix component hyaluronan, and activation of the Wnt/␤-catenin pathway.Epithelial injury is now recognized as a primary event in the pathogenesis of lung disease (1). Alveolar cells consist of type I epithelia (AT1), 2 which serve gas exchange, and type II epithelia (AT2), which produce surfactant and are now recognized as the critical responders to lung injury. Although AT1 cells usually undergo cell death after critical injury, AT2 cells can present a variety of responses, including proinflammatory response, proliferation, differentiation to AT1 epithelia, or epithelial-tomesenchymal transition (EMT). The AT2 response to injury may ultimately lead to restoration of pulmonary architecture and function, or to dysregulated repair, fibrosis, and respiratory failure (2). The factors that promote regulated or pathological repair are incompletely understood. However, it is often forgotten that alveolar epithelia are not static cells. Alveolar epithelia undergo continuous cyclic stretch during ventilation; moreover, pathologically high levels of stretch are exerted on alveolar epithelia either as a consequence of injury (anatomical distortion from scarring) or iatrogenically (mechanical ventilation). The response of alveolar epithelia to injury must therefore be seen in the context of mechanical strain. The importance of stretch injury as a cause of lung disease is exemplified in the acute lung injury of critically ill patients, which is estimated at 200,000 cases in the United States annually (3). Mechanical ventilation is crucial for survival of these patients; however, it often leads to ventilator-induced lung injury (VILI) with pulmonary edema, inflammation, and fibrosis, leading to respiratory failure and death.Epithelial injury is central to the pa...

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Background and objectiveThe mortality rate for patients requiring mechanical ventilation is about 35% and this rate increases to about 53% for the elderly. In general, with increasing age, the dynamic lung function and respiratory mechanics are compromised, and several experiments are being conducted to estimate these changes and understand the underlying mechanisms to better treat elderly patients.Materials and methodsHuman tracheobronchial (G1 ~ G9), bronchioles (G10 ~ G22) and alveolar sacs (G23) geometric models were developed based on reported anatomical dimensions for a 50 and an 80-year-old subject. The aged model was developed by altering the geometry and material properties of the model developed for the 50-year-old. Computational simulations using coupled fluid-solid analysis were performed for geometric models of bronchioles and alveolar sacs under mechanical ventilation to estimate the airflow and lung function characteristics.FindingsThe airway mechanical characteristics decreased with aging, specifically a 38% pressure drop was observed for the 80-year-old as compared to the 50-year-old. The shear stress on airway walls increased with aging and the highest shear stress was observed in the 80-year-old during inhalation. A 50% increase in peak strain was observed for the 80-year-old as compared to the 50-year-old during exhalation. The simulation results indicate that there is a 41% increase in lung compliance and a 35%-50% change in airway mechanical characteristics for the 80-year-old in comparison to the 50-year-old. Overall, the airway mechanical characteristics as well as lung function are compromised due to aging.ConclusionOur study demonstrates and quantifies the effects of aging on the airflow dynamics and lung capacity. These changes in the aging lung are important considerations for mechanical ventilation parameters in elderly patients. Realistic geometry and material properties need to be included in the computational models in future studies.

Chronic respiratory disease affects many people worldwide with little known about the intricate mechanisms driving the pathology, making it difficult to develop novel therapies. Improving the understanding of airway smooth muscle and extracellular matrix (ECM) interactions is key to developing treatments for this leading cause of death. With currently no relevant or controllable in vivo or in vitro models to investigate cell–ECM interactions in the small airways, the development of a biomimetic in vitro model with cell attachment, signaling, and organization is needed. The goal of this study was to create a biologically and structurally relevant in vitro model of small airway smooth muscle. In order to achieve this goal, a scaffold was engineered from synthetic poly-l-lactic acid (PLLA) and decellularized pig lung ECM (PLECM). PLECM scaffolds have improved physical characteristics over synthetic scaffolds, by exhibiting a significant decrease in the elastic modulus and an increase in hydrophilicity. Histological staining and SDS-PAGE showed that essential proteins or protein fragments found in natural ECM were present after processing. Human bronchial smooth muscle cells (HBSMCs) seeded onto PLECM 3D scaffolds formed confluent layers and maintained a contractile phenotype, as demonstrated by the organized arrangement of actin filaments within the cell and expected contractile protein expression of calponin 1. HBSMCs cultured on electrospun PLECM scaffold also increased alpha-1 type 1 collagen compared to those cultured on PLLA scaffolds. In summary, this research demonstrates that a PLLA/PLECM composite electrospun mat is a promising tool to produce an in vitro model of the airway with the potential for a better understanding of bronchiole smooth muscle behavior in diseased or normal states.

Cell migration, a fundamental physiological process in which cells sense and move through their surrounding physical environment, plays a critical role in development and tissue formation, as well as pathological processes, such as cancer metastasis and wound healing. During cell migration, dynamics are governed by the bidirectional interplay between cell-generated mechanical forces and the activity of Rho GTPases, a family of small GTP-binding proteins that regulate actin cytoskeleton assembly and cellular contractility. These interactions are inherently more complex during the collective migration of mechanically coupled cells because of the additional regulation of cell-cell junctional forces. In this study, we adapted a recent minimal modeling framework to simulate the interactions between mechanochemical signaling in individual cells and interactions with cell-cell junctional forces during collective cell migration. We find that migration of individual cells depends on the feedback between mechanical tension and Rho GTPase activity in a biphasic manner. During collective cell migration, waves of Rho GTPase activity mediate mechanical contraction/extension and thus synchronization throughout the tissue. Further, cell-cell junctional forces exhibit distinct spatial patterns during collective cell migration, with larger forces near the leading edge. Larger junctional force magnitudes are associated with faster collective cell migration and larger tissue size. Simulations of heterogeneous tissue migration exhibit a complex dependence on the properties of both leading and trailing cells. Computational predictions demonstrate that collective cell migration depends on both the emergent dynamics and interactions between cellular-level Rho GTPase activity and contractility and multicellular-level junctional forces. the direction of migration (5,6).At the level of an individual cell, although there are many signaling pathways that regulate the dynamics of lamellipodia and filopodia cellular extensions, Rho GTPases are key drivers of this process. Rho GTPases are small GTP-binding proteins that regulate essential cellular processes and functions, including cellular adhesion, shape, and proliferation.

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Successful approaches to tissue engineering smooth muscle tissues utilize biodegradable scaffolds seeded with autologous cells. One common problem in using biological scaffolds specifically is the difficulty of inducing cellular penetration and controlling de novo extracellular matrix deposition=remodeling in vitro. Our hypothesis was that small intestinal submucosa (SIS) exposed to specific mechanical stimulation regimes would modulate the synthesis of de novo collagen and elastin by bladder smooth muscle cells (BSMC) within the SIS matrix. We further hypothesized that the cytokines vascular endothelial growth factor (VEGF) and fibroblast growth factor-2 (FGF-2), two key growth factors involved in epithelial mesenchymal signaling, will promote the cellular penetration into SIS necessary for mechanical stimulation. BSMC were seeded at 0.5Â10 6 cells=cm 2 onto the luminal side of SIS specimens. VEGF (10 ng=mL) and FGF-2 (5 ng=mL) were added to each insert in the media every other day for up to 7 days in static culture. Following static culture, specimens were stretched stripbiaxially under 15% peak strain at either 0.5 or 0.1 Hz for an additional 7 days. Following the culture period, specimens were assayed histologically and biochemically for cellular penetration, proliferation, elastin, collagen, and protease activity. Histological analyses demonstrated that in standard culture media, BSMC remained on the surface of the SIS while both FGF-2 and VEGF profoundly promoted ingrowth of the BSMC into the SIS. The penetration of the cells in response to these cytokines was confirmed using a Transwell assay. Following cellular penetration, BSMC produced significant amounts of elastic fibers under cyclic mechanical stretching at 0.1 Hz under 15% stretch, as evidenced by colorimetric assay and histology using a Verhoeff-Van Gieson stain. Protease activity was assessed in the media and found to be statistically increased in static culture following FGF-2 treatment. These findings demonstrate, for the first time, the capability of BSMC to produce histologically apparent elastin fibers in vitro. Moreover, our results suggest that a strategy involving growth factors and controlled mechanical stimulation may be used to engineer functional, elastin-rich tissue replacements using decellularized biologically derived scaffolds.