Age-dependent ventilator-induced lung injury: Mathematical modeling, experimental data, and statistical analysis

A variety of pulmonary insults can prompt the need for life-saving mechanical ventilation; however, misuse, prolonged use, or an excessive inflammatory response, can result in ventilator-induced lung injury. Past research has observed an increased instance of respiratory distress in older patients and differences in the inflammatory response. To address this, we performed high pressure ventilation on young (2-3 months) and old (20-25 months) mice for 2 hours and collected data for macrophage phenotypes and lung tissue integrity. Large differences in macrophage activation at baseline and airspace enlargement after ventilation were observed in the old mice. The experimental data was used to determine plausible trajectories for a mathematical model of the inflammatory response to lung injury which includes variables for the innate inflammatory cells and mediators, epithelial cells in varying states, and repair mediators. Classification methods were used to identify influential parameters separating the parameter sets associated with the young or old data and separating the response to ventilation, which was measured by changes in the epithelial state variables. Classification methods ranked parameters involved in repair and damage to the epithelial cells and those associated with classically activated macrophages to be influential. Sensitivity results were used to determine candidate in-silico interventions and these interventions were most impact for transients associated with the old data, specifically those with poorer lung health prior to ventilation. Model results identified dynamics involved in M1 macrophages as a focus for further research, potentially driving the age-dependent differences in all macrophage phenotypes. The model also supported the pro-inflammatory response as a potential indicator of age-dependent differences in response to ventilation. This mathematical model can serve as a baseline model for incorporating other pulmonary injuries.

Agent-based vs. equation-based multi-scale modeling for macrophage polarization

Macrophages show high plasticity and result in heterogenic subpopulations or polarized states identified by specific cellular markers. These immune cells are typically characterized as pro-inflammatory, or classically activated M1, and anti-inflammatory, or alternatively activated M2. However, a more precise definition places them along a spectrum of activation where they may exhibit a number of pro- or anti-inflammatory roles. To understand M1-M2 dynamics in the context of a localized response and explore the results of different mathematical modeling approaches based on the same biology, we utilized two different modeling techniques, ordinary differential equation (ODE) modeling and agent-based modeling (ABM), to simulate the spectrum of macrophage activation to general pro- and anti-inflammatory stimuli on an individual and multi-cell level. The ODE model includes two hallmark pro- and anti-inflammatory signaling pathways and the ABM incorporates similar M1-M2 dynamics but in a spatio-temporal platform. Both models link molecular signaling with cellular-level dynamics. We then performed simulations with various initial conditions to replicate different experimental setups. Similar results were observed in both models after tuning to a common calibrating experiment. Comparing the two models' results sheds light on the important features of each modeling approach. When more data is available these features can be considered when choosing techniques to best fit the needs of the modeler and application.

Using extracellular matrix derived from sugen-chronic hypoxia lung tissue to study pulmonary arterial hypertension

Pulmonary arterial hypertension has characteristic changes to the mechanical environment, extracellular matrix, and cellular proliferation. In order to develop a culture system to investigate extracellular matrix (ECM) compositional-dependent changes in pulmonary arterial hypertension, we decellularized and characterized protein and lipid profiles from healthy and Sugen-Chronic Hypoxia rat lungs. Significant changes in lipid profiles were observed in intact Sugen-Hypoxia lungs compared with healthy controls. Decellularized lung matrix retained lipids in measurable quantities in both healthy and Sugen-Chronic Hypoxia samples. Proteomics revealed significantly changed proteins associated with pulmonary arterial hypertension in the decellularized Sugen-Chronic Hypoxia lung ECM. We then investigated the potential role of healthy vs. Sugen-Chronic Hypoxia ECM with controlled substrate stiffness to determine if the ECM composition regulated endothelial cell morphology and phenotype. CD117+ rat lung endothelial cell clones were plated on the variable stiffness gels and cellular proliferation, morphology, and gene expression were quantified. Sugen-Chronic Hypoxia ECM on healthy stiffness gels produced significant changes in cellular gene expression levels of Bmp2, Col1α1, Col3α1 and Fn1. The signaling and cell morphology observed at low substrate stiffness suggests early changes to the ECM composition can initiate processes associated with disease progression. These data suggest that Sugen-Chronic Hypoxia ECM can be used to investigate cell-ECM interactions relevant to pulmonary arterial hypertension.

Electrosprayed Mesenchymal Stromal Cell Extracellular Matrix Nanoparticles Accelerate Cellular Wound Healing and Reduce Gram-Negative Bacterial Growth

Treatments for acute respiratory distress syndrome are still unavailable, and the prevalence of the disease has only increased due to the COVID-19 pandemic. Mechanical ventilation regimens are still utilized to support declining lung function but also contribute to lung damage and increase the risk for bacterial infection. The anti-inflammatory and pro-regenerative abilities of mesenchymal stromal cells (MSCs) have shown to be a promising therapy for ARDS. We propose to utilize the regenerative effects of MSCs and the extracellular matrix (ECM) in a nanoparticle. Our mouse MSC (MMSC) ECM nanoparticles were characterized using size, zeta potential, and mass spectrometry to evaluate their potential as pro-regenerative and antimicrobial treatments. The nanoparticles had an average size of 273.4 nm (±25.6) and possessed a negative zeta potential, allowing them to surpass defenses and reach the distal regions of the lung. It was found that the MMSC ECM nanoparticles are biocompatible with mouse lung epithelial cells and MMSCs, increasing the wound healing rate of human lung fibroblasts while also inhibiting the growth of Pseudomonas aeruginosa, a common lung pathogen. Our MMSC ECM nanoparticles display characteristics of healing injured lungs while preventing bacterial infection, which can increase recovery time.

Abstract 1991: Remodeling the microenvironment of osteosarcoma lung metastases with inhaled CSF-1Ri immunotherapy

Osteosarcoma (OS) metastasizes primarily and almost exclusively to the lungs. The survival rate decreases significantly for patients who develop OS lung metastasis (OSLM).

Purpose: To assess the safety and efficacy of colony-stimulating factor-1 receptor inhibitor (CSF-1Ri) (Pexidartinib; PLX) in shifting the OSLM tumor microenvironment (TME) to an anti-tumorigenic state upon local delivery to lungs of a syngeneic mouse model of OSLM.

Methods: The safety of PLX upon repeated pulmonary administration (9 doses, every other day at 2 mg/kg) in healthy BALB/c mice was assessed using health scoring, pulmonary mechanics, molecular and cellular composition of bronchoalveolar lavage fluid (BALF), blood count and plasma biochemistry, and H&E of lungs and liver. To establish the OSLM model, murine OS cells, expressing bioluminescent and fluorescent genes (K7M2-Luc-tdT), were used. Mice bearing OSLM were randomized into two groups (vehicle and PLX) and treated over 3 weeks. Tumor burden was evaluated using bioluminescent imaging (BLI) and lung weight. The treatment impact on the abundance and phenotype of tumor-associated macrophages (TAMs) and their CSF-1R expression as well as on the abundance of tumor-infiltrating lymphocytes and their expression to PD-1 were investigated using immunofluorescence, flow cytometry, and western blot.

Results: PLX is well tolerated upon local lung administration with all safety markers indicating no alteration compared to naïve and vehicle controls. Treatment did not affect health scores. We did not detect any functional or mechanical alteration on the lungs or systemically (including liver); no marked differences in pulmonary function parameters, proinflammatory cytokines, nor infiltrating differential cell count obtained from BALF were observed. Both total blood count and liver enzymes were within normal range. As a measure of efficacy, treatment with PLX via local lung administration reduced tumor burden, indicated by the in vivo BLI and lung weight. Notably, PLX significantly decreased the abundance of total TAMs, with a more pronounced effect on pro-tumorigenic alternatively-activated (M2-like) TAMs phenotype, thus leading to a 22-fold increase in M1/M2 ratio. PLX further led to a marked decrease in tumor-promoting T regulatory cells (Treg), increase in the CD8/Treg ratio, and decrease in PD-1+ percentage in CD8 T cells in the TME, indicating a shift to a more immunogenic tumor phenotype.

Conclusions: We demonstrated that repeated doses of PLX is safe upon local delivery to the lungs of murine model of OSLM, with no alternations in lungs or liver tissue. We further showed that PLX reduces tumor burden, which correlates with a change in the immune phenotype of the OSLM toward a more anti-tumorigenic profile. These results are clinically relevant as PLX has been approved by the FDA, thus opening opportunities for its repurposing to support standard of care therapy in OSLM.

Citation Format: Fatemah S. Sunbul, Sulaiman S. Alhudaithi, Rashed M. Almuqbil, Hanming Zhang, Raneem R. Aldaqqa, Shane Albin, Rebecca L. Heise, Valentina Robila, Matthew S. Halquist, Sarah W. Gordon, Paula D. Bos, Sandro R. da Rocha. Remodeling the microenvironment of osteosarcoma lung metastases with inhaled CSF-1Ri immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1991.

S1P lyase inhibition prevents lung injury following high pressure-controlled mechanical ventilation in aging mice

Ventilator-induced Lung Injury (VILI) is characterized by hypoxia, inflammatory cytokine influx, loss of alveolar barrier integrity, and decreased lung compliance. Aging influences lung structure and function and is a predictive factor in the severity of VILI; however, the mechanisms of aging that influence the progression or increased susceptibility remain unknown. Aging impacts immune system function and may increase inflammation in healthy individuals. Recent studies suggest that the bioactive sphingolipid mediator sphingosine-1-phosphate (S1P) and the enzyme that degrades it S1P lyase (SPL) may be involved in lung pathologies including acute lung injury. It is unknown whether aging influences S1P and SPL expression that have been implicated in lung inflammation, injury, and cell apoptosis. We hypothesized that aging and injurious mechanical ventilation synergistically impair S1P levels and enhance S1P lyase (SPL) expression that amplifies alveolar barrier damage and diminishes pulmonary function. Young (2-3 mo) and old (20-25 mo) C57BL/6 mice were mechanically ventilated for 2 h using pressure-controlled mechanical ventilation (PCMV) at 45 cmH2O and 35 cmH2O, respectively. We assessed the impact of aging and PCMV on several indications of acute lung injury, immune cell recruitment, S1P levels and SPL activity. Furthermore, we evaluated the protective effects of inhibiting SPL by tetrahydroxybutylimidazol (THI) administration on the negative outcomes associated with aging and mechanical injury. PCMV exacerbated lung injury in old mice and increased neutrophil influx that was further exacerbated due to aging. SPL expression increased in the young and old ventilated mice and the old nonventilated group. THI treatment reduced several of the indicators of lung injury and resulted in elevated S1P levels in lung tissue and plasma from mice that were injured from mechanical ventilation. CD80 and CD206 activation markers of alveolar and interstitial macrophages were also influenced by THI. SPL inhibition may be a viable therapeutic approach for patients requiring mechanical ventilation by preventing or regulating the exaggerated inflammatory response and reducing lung injury.

Computational, Ex Vivo, and Tissue Engineering Techniques for Modeling Large Airways

The large airways are a critical component of the respiratory tree serving both an immunoprotective role and a physiological role for ventilation. The physiological role of the large airways is to move a large amount of air to and from the gas exchange surfaces of the alveoli. This air becomes divided along the respiratory tree as it moves from the large airways to smaller airways, bronchioles, and alveoli. The large airways are incredibly important from an immunoprotective role as the large airways are an early line of defense against inhaled particles, bacteria, and viruses. The key immunoprotective feature of the large airways is mucus production and mucociliary clearance mechanism. Each of these key features of the lung is important from both a basic physiology perspective and an engineering perspective for regenerative medicine. In this chapter, we will cover the large airways from an engineering perspective to highlight existing models of the large airways as well as future directions for modeling and repair.

Dichotomous role of integrin-β5 in lung endothelial cells

Pulmonary arterial hypertension (PAH) is a progressive, devastating disease, and its main histological manifestation is an occlusive pulmonary arteriopathy. One important functional component of PAH is aberrant endothelial cell (EC) function including apoptosis-resistance, unchecked proliferation, and impaired migration. The mechanisms leading to and maintaining physiologic and aberrant EC function are not fully understood. Here, we tested the hypothesis that in PAH, ECs have increased expression of the transmembrane protein integrin-β5, which contributes to migration and survival under physiologic and pathological conditions, but also to endothelial-to-mesenchymal transition (EnMT). We found that elevated integrin-β5 expression in pulmonary artery lesions and lung tissue from PAH patients and rats with PH induced by chronic hypoxia and injection of CD117+ rat lung EC clones. These EC clones exhibited elevated expression of integrin-β5 and its heterodimerization partner integrin-αν and showed accelerated barrier formation. Inhibition of integrin-ανβ5 in vitro partially blocked transforming growth factor (TGF)-β1-induced EnMT gene expression in rat lung control ECs and less in rat lung EC clones and human lung microvascular ECs. Inhibition of integrin-ανβ5 promoted endothelial dysfunction as shown by reduced migration in a scratch assay and increased apoptosis in synergism with TGF-β1. In vivo, blocking of integrin-ανβ5 exaggerated PH induced by chronic hypoxia and CD117+ EC clones in rats. In summary, we found a role for integrin-ανβ5 in lung endothelial survival and migration, but also a partial contribution to TGF-β1-induced EnMT gene expression. Our results suggest that integrin-ανβ5 is required for physiologic function of ECs and lung vascular homeostasis.

A Two-Step Bioreactor for Decellularized Lung Epithelialization

Bioreactors for the reseeding of decellularized lung scaffolds have evolved with various advancements, including biomimetic mechanical stimulation, constant nutrient flow, multi-output monitoring, and large mammal scaling. Although dynamic bioreactors are not new to the field of lung bioengineering, ideal conditions during cell seeding have not been extensively studied or controlled. To address the lack of cell dispersal in traditional seeding methods, we have designed a two-step bioreactor. The first step is a novel system that rotates a seeded lung every 20 min at different angles in a sequence designed to anchor 20% of cells to a particular location based on the known rate of attachment. The second step involves perfusion-ventilation culture to ensure nutrient dispersion and cellular growth. Compared to statically seeded lungs, rotationally seeded lungs had significantly increased dsDNA content and more uniform cellular distribution after perfusion and ventilation had been administered. The addition of this novel seeding system before traditional culture methods will aid in recellularizing the lung and other geometrically complex organs for tissue engineering.

Cellular mitosis predicts vessel stability in a mechanochemical model of sprouting angiogenesis

Angiogenesis, the formation of new vessels, occurs in both developmental and pathological contexts. Prior research has investigated vessel formation to identify cellular phenotypes and dynamics associated with angiogenic disease. One major family of proteins involved in angiogenesis are the Rho GTPases, which govern function related to cellular elongation, migration, and proliferation. Using a mechanochemical model coupling Rho GTPase activity and cellular and intercellular mechanics, we investigate the role of cellular mitosis on sprouting angiogenesis. Mitosis-GTPase synchronization was not a strong predictor of GTPase and thus vessel signaling instability, whereas the location of mitotic events was predicted to alter GTPase cycling instabilities. Our model predicts that middle stalk cells undergoing mitosis introduce irregular dynamics in GTPase cycling and may provide a source of aberrant angiogenesis. We also find that cellular and junctional tension exhibit spatial heterogeneity through the vessel, and that tension feedback, specifically in stalk cells, tends to increase the maximum forces generated in the vessel.

Mathematical modeling of ventilator-induced lung inflammation

Respiratory infections, such as the novel coronavirus (SARS-COV-2) and other lung injuries, damage the pulmonary epithelium. In the most severe cases this leads to acute respiratory distress syndrome (ARDS). Due to respiratory failure associated with ARDS, the clinical intervention is the use of mechanical ventilation. Despite the benefits of mechanical ventilators, prolonged or misuse of these ventilators may lead to ventilation-associated/ventilation-induced lung injury (VILI). Damage caused to epithelial cells within the alveoli can lead to various types of complications and increased mortality rates. A key component of the immune response is recruitment of macrophages, immune cells that differentiate into phenotypes with unique pro- and/or anti-inflammatory roles based on the surrounding environment. An imbalance in pro- and anti-inflammatory responses can have deleterious effects on the individual's health. To gain a greater understanding of the mechanisms of the immune response to VILI and post-ventilation outcomes, we develop a mathematical model of interactions between the immune system and site of damage while accounting for macrophage polarization. Through Latin hypercube sampling we generate a virtual cohort of patients with biologically feasible dynamics. We use a variety of methods to analyze the results, including a random forest decision tree algorithm and parameter sensitivity with eFAST. Analysis shows that parameters and properties of transients related to epithelial repair and M1 activation and de-activation best predicted outcome. Using this new information, we hypothesize inter-ventions and use these treatment strategies to modulate damage in select virtual cases.

Porcine Lung-Derived Extracellular Matrix Hydrogel Properties Are Dependent on Pepsin Digestion Time

Hydrogels derived from decellularized lungs are promising materials for tissue engineering in the development of clinical therapies and for modeling the lung extracellular matrix (ECM) in vitro. Characterizing and controlling the resulting physical, biochemical, mechanical, and biologic properties of decellularized ECM (dECM) after enzymatic solubilization and gelation are thus of key interest. As the role of enzymatic pepsin digestion in effecting these properties has been understudied, we investigated the digestion time-dependency on key parameters of the resulting ECM hydrogel. Using resolubilized, homogenized decellularized pig lung dECM as a model system, significant time-dependent changes in protein concentration, turbidity, and gelation potential were found to occur between the 4 and 24 h digestion time points, and plateauing with longer digestion times. These results correlated with qualitative scanning electron microscopy images and quantitative analysis of hydrogel interconnectivity and average fiber diameter. Interestingly, the time-dependent changes in the storage modulus tracked with the hydrogel interconnectivity results, while the Young's modulus values were more closely related to average fiber size at each time point. The structural and biochemical alterations correlated with significant changes in metabolic activity of several representative lung cells seeded onto the hydrogels with progressive decreases in cell viability and alterations in morphology observed in cells cultured on hydrogels produced with dECM digested for >12 and up to 72 h of digestion. These studies demonstrate that 12 h pepsin digest of pig lung dECM provides an optimal balance between desirable physical ECM hydrogel properties and effects on lung cell behaviors.

Excipient Enhanced Growth Aerosol Surfactant Replacement Therapy in an In Vivo Rat Lung Injury Model

Background: In neonatal respiratory distress syndrome, breathing support and surfactant therapy are commonly used to enable the alveoli to expand. Surfactants are typically delivered through liquid instillation. However, liquid instillation does not specifically target the small airways. We have developed an excipient enhanced growth (EEG) powder aerosol formulation using Survanta^®. Methods: EEG Survanta powder aerosol was delivered using a novel dry powder inhaler via tracheal insufflation to surfactant depleted rats at nominal doses of 3, 5, 10, and 20 mg of powder containing 0.61, 0.97, 1.73, and 3.46 mg of phospholipids (PL), whereas liquid Survanta was delivered via syringe instillation at doses of 2 and 4 mL/kg containing 18.6 and 34 mg of PL. Ventilation mechanics were measured before and after depletion, and after treatment. We hypothesized that EEG Survanta powder aerosol would improve lung mechanics compared with instilled liquid Survanta in surfactant depleted rats. Results and Conclusion: EEG Survanta powder aerosol at a dose of 0.61 mg PL significantly improved lung compliance and elastance compared with the liquid Survanta at a dose of 18.6 mg, which represents improved primary efficacy of the aerosol at a 30-fold lower dose of PL. There was no significant difference in white blood cell count of the lavage from the EEG Survanta group compared with liquid Survanta. These results provide an in vivo proof-of-concept for EEG Survanta powder aerosol as a promising method of surfactant replacement therapy.

Laminin-driven Epac/Rap1 regulation of epithelial barriers on decellularized matrix

Decellularized tissues offer a unique tool for developing regenerative biomaterials or in vitro platforms for the study of cell-extracellular matrix (ECM) interactions. One main challenge associated with decellularized lung tissue is that ECM components can be stripped away or altered by the detergents used to remove cellular debris. Without characterizing the composition of lung decellularized ECM (dECM) and the cellular response caused by the altered composition, it is difficult to utilize dECM for regeneration and specifically, engineering the complexities of the alveolar-capillary barrier. This study takes steps towards uncovering if dECM must be enhanced with lost ECM proteins to achieve proper epithelial barrier formation. To achieve this, the epithelial barrier function was assessed on dECM coatings with and without the systematic addition of several key basement membrane proteins. After comparing barrier function on collagen I, fibronectin, laminin, and dECM in varying combinations as an in vitro coating, the alveolar epithelium exhibited superior barrier function when dECM was supplemented with laminin as evidenced by trans-epithelial electrical resistance (TEER) and permeability assays. Increased barrier resistance with laminin addition was associated with upregulation of Claudin-18, E-cadherin, and junction adhesion molecule (JAM)-A, and stabilization of zonula occludens (ZO)-1 at junction complexes. The Epac/Rap1 pathway was observed to play a role in the ECM-mediated barrier function determined by protein expression and Epac inhibition. These findings revealed potential ECM coatings and molecular therapeutic targets for improved regeneration with decellularized scaffolds. STATEMENT OF SIGNIFICANCE: Efforts to produce a transplantable organ-scale biomaterial for lung regeneration has not been entirely successful to date, due to incomplete cell-cell junction formation, ultimately leading to severe edema in vivo. To fully understand the process of alveolar junction formation on ECM-derived biomaterials, this research has characterized and tailored decellularized ECM (dECM) to mitigate reductions in barrier strength or cell attachment caused by abnormal ECM compositions or detergent damage to dECM. These results indicate that laminin-driven Epac signaling plays a vital role in the stabilization of the alveolar barrier. Addition of laminin or Epac agonists during alveolar regeneration can reduce epithelial permeability within bioengineered lungs.

Mechanochemical Coupling and Junctional Forces during Collective Cell Migration

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.

Aging effects on airflow dynamics and lung function in human bronchioles

Background and objective

The 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 methods

Human 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.

Findings

The 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.

Conclusion

Our 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.

A novel role for primary cilia in airway remodeling

Primary cilia (PC) are solitary cellular organelles that play critical roles in development, homeostasis, and disease pathogenesis by modulating key signaling pathways such as Sonic Hedgehog and calcium flux. The antenna-like shape of PC enables them also to facilitate sensing of extracellular and mechanical stimuli into the cell, and a critical role for PC has been described for mesenchymal cells such as chondrocytes. However, nothing is known about the role of PC in airway smooth muscle cells (ASMCs) in the context of airway remodeling. We hypothesized that PC on ASMCs mediate cell contraction and are thus integral in the remodeling process. We found that PC are expressed on ASMCs in asthmatic lungs. Using pharmacological and genetic methods, we demonstrated that PC are necessary for ASMC contraction in a collagen gel three-dimensional model both in the absence of external stimulus and in response to the extracellular component hyaluronan. Mechanistically, we demonstrate that the effect of PC on ASMC contraction is, to a small extent, due to their effect on Sonic Hedgehog signaling and, to a larger extent, due to their effect on calcium influx and membrane depolarization. In conclusion, PC are necessary for the development of airway remodeling by mediating calcium flux and Sonic Hedgehog signaling.

Modeling the influence of acute changes in bladder elasticity on pressure and wall tension during filling

Tension-sensitive nerves in the bladder wall are responsible for providing bladder sensation. Bladder wall tension, and therefore nerve output, is a function of bladder pressure, volume, geometry and material properties. The elastic modulus of the bladder is acutely adjustable, and this material property is responsible for adjustable preload tension exhibited in human and rabbit detrusor muscle strips and dynamic elasticity revealed during comparative-fill urodynamics in humans. A finite deformation model of the bladder was previously used to predict filling pressure and wall tension using uniaxial tension test data and the results showed that wall tension can increase significantly during filling with relatively little pressure change. In the present study, published uniaxial rabbit detrusor data were used to quantify regulated changes in the elastic modulus, and the finite deformation model was expanded to illustrate the potential effects of elasticity changes on pressure and wall tension during filling. The model demonstrates a shift between relatively flat pressure-volume filling curves, which is consistent with a recent human urodynamics study, and also predicts that dynamic elasticity would produce significant changes in wall tension during filling. The model results support the conclusion that acute regulation of bladder elasticity could contribute to significant changes in wall tension for a given volume that could lead to urgency, and that a single urodynamic fill may be insufficient to characterize bladder biomechanics. The model illustrates the potential value of quantifying wall tension in addition to pressure during urodynamics.

Tunable Hydrogels from Pulmonary Extracellular Matrix for 3D Cell Culture

Here we present a method for establishing multiple component cell culture hydrogels for in vitro lung cell culture. Beginning with healthy en bloc lung tissue from porcine, rat, or mouse, the tissue is perfused and submerged in subsequent chemical detergents to remove the cellular debris. Histological comparison of the tissue before and after processing confirms removal of over 95% of double stranded DNA and alpha galactosidase staining suggests the majority of cellular debris is removed. After decellularization, the tissue is lyophilized and then cryomilled into a powder. The matrix powder is digested for 48 hr in an acidic pepsin digestion solution and then neutralized to form the pregel solution. Gelation of the pregel solution can be induced by incubation at 37 °C and can be used immediately following neutralization or stored at 4 °C for up to two weeks. Coatings can be formed using the pregel solution on a non-treated plate for cell attachment. Cells can be suspended in the pregel prior to self-assembly to achieve a 3D culture, plated on the surface of a formed gel from which the cells can migrate through the scaffold, or plated on the coatings. Alterations to the strategy presented can impact gelation temperature, strength, or protein fragment sizes. Beyond hydrogel formation, the hydrogel stiffness may be increased using genipin.

Conservative fluid management prevents age-associated ventilator induced mortality

BACKGROUND

Approximately 800 thousand patients require mechanical ventilation in the United States annually with an in-hospital mortality rate of over 30%. The majority of patients requiring mechanical ventilation are over the age of 65 and advanced age is known to increase the severity of ventilator-induced lung injury (VILI) and in-hospital mortality rates. However, the mechanisms which predispose aging ventilator patients to increased mortality rates are not fully understood. Ventilation with conservative fluid management decreases mortality rates in acute respiratory distress patients, but to date there has been no investigation of the effect of conservative fluid management on VILI and ventilator associated mortality rates. We hypothesized that age-associated increases in susceptibility and incidence of pulmonary edema strongly promote age-related increases in ventilator associated mortality.

METHODS

2month old and 20month old male C57BL6 mice were mechanically ventilated with either high tidal volume (HVT) or low tidal volume (LVT) for up to 4h with either liberal or conservative fluid support. During ventilation, lung compliance, total lung capacity, and hysteresis curves were quantified. Following ventilation, bronchoalveolar lavage fluid was analyzed for total protein content and inflammatory cell infiltration. Wet to dry ratios were used to directly measure edema in excised lungs. Lung histology was performed to quantify alveolar barrier damage/destruction. Age matched non-ventilated mice were used as controls.

RESULTS

At 4h, both advanced age and HVT ventilation significantly increased markers of inflammation and injury, degraded pulmonary mechanics, and decreased survival rates. Conservative fluid support significantly diminished pulmonary edema and improved pulmonary mechanics by 1h in advanced age HVT subjects. In 4h ventilations, conservative fluid support significantly diminished pulmonary edema, improved lung mechanics, and resulted in significantly lower mortality rates in older subjects.

CONCLUSION

Our study demonstrates that conservative fluid alone can attenuate the age associated increase in ventilator associated mortality.

Development and characterization of a naturally derived lung extracellular matrix hydrogel

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.

From Here to There, Progenitor Cells and Stem Cells Are Everywhere in Lung Vascular Remodeling

The field of stem cell biology, cell therapy, and regenerative medicine has expanded almost exponentially, in the last decade. Clinical trials are evaluating the potential therapeutic use of stem cells in many adult and pediatric lung diseases with vascular component, such as bronchopulmonary dysplasia (BPD), chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF), or pulmonary arterial hypertension (PAH). Extensive research activity is exploring the lung resident and circulating progenitor cells and their contribution to vascular complications of chronic lung diseases, and researchers hope to use resident or circulating stem/progenitor cells to treat chronic lung diseases and their vascular complications. It is becoming more and more clear that progress in mechanobiology will help to understand the various influences of physical forces and extracellular matrix composition on the phenotype and features of the progenitor cells and stem cells. The current review provides an overview of current concepts in the field.

Bronchial epithelial injury in the context of alloimmunity promotes lymphocytic bronchiolitis through hyaluronan expression

Epithelial injury is often detected in lung allografts, however, its relation to rejection pathogenesis is unknown. We hypothesized that sterile epithelial injury can lead to alloimmune activation in the lung. We performed adoptive transfer of mismatched splenocytes into recombinant activating gene 1 (Rag1)-deficient mice to induce an alloimmune status and then exposed these mice to naphthalene to induce sterile epithelial injury. We evaluated lungs for presence of alloimmune lung injury, endoplasmic reticulum (ER) stress, and hyaluronan expression, examined the effect of ER stress induction on hyaluronan expression and lymphocyte trapping by bronchial epithelia in vitro, and examined airways from patients with bronchiolitis obliterans syndrome and normal controls histologically. We found that Rag1-deficient mice that received mismatched splenocytes and naphthalene injection displayed bronchial epithelial ER stress, peribronchial hyaluronan expression, and lymphocytic bronchitis. Bronchial epithelial ER stress led to the expression of lymphocyte-trapping hyaluronan cables in vitro. Blockade of hyaluronan binding ameliorated naphthalene-induced lymphocytic bronchitis. ER stress was present histologically in >40% of bronchial epithelia of BOS patients and associated with subepithelial hyaluronan deposition. We conclude that sterile bronchial epithelial injury in the context of alloimmunity can lead to sustained ER stress and promote allograft rejection through hyaluronan expression.

Analysis for stress environment in the alveolar sac model

Better understanding of alveolar mechanics is very important in order to avoid lung injuries for patients undergoing mechanical ventilation for treatment of respiratory problems. The objective of this study was to investigate the alveolar mechanics for two different alveolar sac models, one based on actual geometry and the other an idealized spherical geometry using coupled fluid-solid computational analysis. Both the models were analyzed through coupled fluid-solid analysis to estimate the parameters such as pressures/velocities and displacements/stresses under mechanical ventilation conditions. The results obtained from the fluid analysis indicate that both the alveolar geometries give similar results for pressures and velocities. However, the results obtained from coupled fluid-solid analysis indicate that the actual alveolar geometry results in smaller displacements in comparison to a spherical alveolar model. This trend is also true for stress/strain between the two models. The results presented indicate that alveolar geometry greatly affects the pressure/velocities as well as displacements and stresses/strains.

Mechanical stretch induces epithelial-mesenchymal transition in alveolar epithelia via hyaluronan activation of innate immunity

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/β-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/β-catenin pathway.

Ex vivo deformations of the urinary bladder wall during whole bladder filling: contributions of extracellular matrix and smooth muscle

As the complete understanding of urinary bladder function requires knowledge of organ level deformations, we conducted ex vivo studies of surface strains of whole bladders during controlled filling. The surface strains derived from displacements of surface markers applied to the posterior surface of excised rat bladders were tracked under slow filling with pressure and volume simultaneously recorded in the passive and completely inactivated states (i.e. with and without smooth muscle tone, respectively). Bladders evaluated in the passive state exhibited spontaneous contractions and larger average peak pressures (16.7 mm Hg compared to 6.4 mm Hg in the inactive state). Overall, the bladders exhibited anisotropic deformations and were stiffer in the circumferential direction, with average peak stretch values of approximately 2.3 and approximately 1.9 in the longitudinal and circumferential directions, respectively, for both states. Although bladders in the passive state were stiffer, they had similar average peak areal stretches of 4.3 in both states. However, differences early in the filling process as a result of a loss in smooth muscle tone in the inactive state resulted in longitudinal lengthening of 36%. Idealizing the bladder as a prolate spheroid, we estimated the wall stress-strain relation during filling and demonstrated that the intact bladder exhibited the classic stress-stretch relation, with a significantly protracted low stress region and peak stresses of 36 and 51 kPa in the longitudinal and circumferential directions, respectively. The present study fills a major gap in the urinary bladder biomechanics literature, wherein knowledge of the pressure-volume-wall stress-wall strain relation was explored for the first time in a functioning organ ex vivo.

New syndrome in three affected siblings

A previously undescribed syndrome is reported. Major features include: (1) poorly mineralized calvarium, (2) dysmorphic facies (cleft lip and palate, micrognathia, upturned nares, apparent ocular hypertelorism), and (3) extracranial and musculoskeletal anomalies (absence of cervical vertebrae and clavicles, talipes equilnorvarus, and soft tissue syndactyly). Autosomal recessive inheritance is the most likely mode of transmission. Prenatal diagnosis via ultrasonography wa successful in two fetuses at risk.