Mechanical stretch enhances IL-8 production in pulmonary microvascular endothelial cells

Collagen Tubular Airway-on-Chip for Extended Epithelial Culture and Investigation of Ventilation Dynamics

The lower respiratory tract is a hierarchical network of compliant tubular structures that are made from extracellular matrix proteins with a wall lined by an epithelium. While microfluidic airway-on-a-chip models incorporate the effects of shear and stretch on the epithelium, week-long air-liquid-interface culture at physiological shear stresses, the circular cross-section, and compliance of native airway walls have yet to be recapitulated. To overcome these limitations, a collagen tube-based airway model is presented. The lumen is lined with a confluent epithelium during two-week continuous perfusion with warm, humid air while presenting culture medium from the outside and compensating for evaporation. The model recapitulates human small airways in extracellular matrix composition and mechanical microenvironment, allowing for the first time dynamic studies of elastocapillary phenomena associated with regular breathing and mechanical ventilation, as well as their impacts on the epithelium. A case study reveales increasing damage to the epithelium during repetitive collapse and reopening cycles as opposed to overdistension, suggesting expiratory flow resistance to reduce atelectasis. The model is expected to promote systematic comparisons between different clinically used ventilation strategies and, more broadly, to enhance human organ-on-a-chip platforms for a variety of tubular tissues.

Neutrophils are involved in early bone formation during midpalatal expansion

OBJECTIVE

Midpalatal expansion (MPE) is routinely employed to treat transverse maxillary arch deficiency. Neutrophils are indispensable for recruiting bone marrow stromal cells (BMSCs) at the initial stage of bone regeneration. This study aimed to explore whether neutrophils participate in MPE and how they function during bone formation under mechanical stretching.

MATERIALS AND METHODS

The presence and phenotype of neutrophils in the midpalatal suture during expansion were detected by flow cytometry and immunofluorescence staining. The possible mechanism of neutrophil recruitment and polarization was explored in vitro by exposing vascular endothelial cells (VECs) to cyclic tensile strain.

RESULTS

The number of neutrophils in the distracted suture peaked on Day 3, and N2-type neutrophils significantly increased on Day 5 after force application. The depletion of circulatory neutrophils reduced bone volume by 43.6% after 7-day expansion. The stretched VECs recruited neutrophils via a CXCR2 mechanism in vitro, which then promoted BMSC osteogenic differentiation through the VEGFA/VEGFR2 axis. Consistently, these neutrophils showed higher expression of canonical N2 phenotype genes, including CD206 and Arg1.

CONCLUSIONS

These results suggested that neutrophils participated in early bone formation during MPE. Based on these findings, we propose that stretched VECs recruited and polarized neutrophils, which, in turn, induced BMSC osteogenic differentiation.

Cell orientation under stretch: A review of experimental findings and mathematical modelling

The key role of electro-chemical signals in cellular processes had been known for many years, but more recently the interplay with mechanics has been put in evidence and attracted substantial research interests. Indeed, the sensitivity of cells to mechanical stimuli coming from the microenvironment turns out to be relevant in many biological and physiological circumstances. In particular, experimental evidence demonstrated that cells on elastic planar substrates undergoing periodic stretches, mimicking native cyclic strains in the tissue where they reside, actively reorient their cytoskeletal stress fibres. At the end of the realignment process, the cell axis forms a certain angle with the main stretching direction. Due to the importance of a deeper understanding of mechanotransduction, such a phenomenon was studied both from the experimental and the mathematical modelling point of view. The aim of this review is to collect and discuss both the experimental results on cell reorientation and the fundamental features of the mathematical models that have been proposed in the literature.

Inflammation Responses to Bone Scaffolds under Mechanical Stimuli in Bone Regeneration

Physical stimuli play an important role in one tissue engineering. Mechanical stimuli, such as ultrasound with cyclic loading, are widely used to promote bone osteogenesis; however, the inflammatory response under physical stimuli has not been well studied. In this paper, the signaling pathways related to inflammatory responses in bone tissue engineering are evaluated, and the application of physical stimulation to promote osteogenesis and its related mechanisms are reviewed in detail; in particular, how physical stimulation alleviates inflammatory responses during transplantation when employing a bone scaffolding strategy is discussed. It is concluded that physical stimulation (e.g., ultrasound and cyclic stress) helps to promote osteogenesis while reducing the inflammatory response. In addition, apart from 2D cell culture, more consideration should be given to the mechanical stimuli applied to 3D scaffolds and the effects of different force moduli while evaluating inflammatory responses. This will facilitate the application of physiotherapy in bone tissue engineering.

Construction and validation of a pulmonary complication score for patients after liver transplantation

PURPOSE

Identification of preoperative risk factors associated with pulmonary complications may benefit high-risk patients from more intense surveillance and earlier interventions in liver transplantation (LT). Our study aimed to identify risk factors for predicting pulmonary complications in LT patients.

MATERIALS AND METHODS

The discovery data set enrolled 208 patients who underwent orthotopic LT while the validation data set included 117 patients. Clinical data were collected from medical history retrospectively and risk factors were determined by logistic regression analyses. The pulmonary complication score (PCS-LT) was established and validated for predicting pulmonary complications after LT.

RESULTS

In the discovery data set, 47 (22.6%) participants experienced pulmonary complications following LT. Four independent risk factors for pulmonary complications were identified by multivariate logistic regression analysis, including preoperative abnormal pulmonary function (OR = 4.743, p < .001), elevated lymphocyte count (OR = 2.336, p = .027), hypoproteinemia (OR = 2.635, p = .030), and hypokalemia (OR = 5.257, p = .003), and PCS-LT based on these factors was established. ROC analyses showed PCS-LT could predict PC in both the discovery data set (area under curve [AUC] .752, 95% confidence interval [CI] .687-.809) and the validation data set (AUC .754, 95% CI, .666-.829). The PCS-LT demonstrated superior predictive value (AUC .735, 95% CI, .703-.799) to APACHE II score (AUC .653, 95% CI, .599-.705) in the combined data set (p = .032). Meanwhile, PCS-LT > 1 was used as the cut-off value and has prognostic significance in LT patients.

CONCLUSIONS

The PCS-LT score, consisting of abnormal pulmonary function, elevated lymphocyte count, hypoproteinemia, and hypokalemia, could predict pulmonary complications after LT.

Biomechanical and Mechanobiological Drivers of the Transition From PostCapillary Pulmonary Hypertension to Combined Pre-/PostCapillary Pulmonary Hypertension

Combined pre-/postcapillary pulmonary hypertension (Cpc-PH), a complication of left heart failure, is associated with higher mortality rates than isolated postcapillary pulmonary hypertension alone. Currently, knowledge gaps persist on the mechanisms responsible for the progression of isolated postcapillary pulmonary hypertension (Ipc-PH) to Cpc-PH. Here, we review the biomechanical and mechanobiological impact of left heart failure on pulmonary circulation, including mechanotransduction of these pathological forces, which lead to altered biological signaling and detrimental remodeling, driving the progression to Cpc-PH. We focus on pathologically increased cyclic stretch and decreased wall shear stress; mechanotransduction by endothelial cells, smooth muscle cells, and pulmonary arterial fibroblasts; and signaling-stimulated remodeling of the pulmonary veins, capillaries, and arteries that propel the transition from Ipc-PH to Cpc-PH. Identifying biomechanical and mechanobiological mechanisms of Cpc-PH progression may highlight potential pharmacologic avenues to prevent right heart failure and subsequent mortality.

Significance of Pulmonary Endothelial Injury and the Role of Cyclooxygenase-2 and Prostanoid Signaling

The endothelium plays a key role in the dynamic balance of hemodynamic, humoral and inflammatory processes in the human body. Its central importance and the resulting therapeutic concepts are the subject of ongoing research efforts and form the basis for the treatment of numerous diseases. The pulmonary endothelium is an essential component for the gas exchange in humans. Pulmonary endothelial dysfunction has serious consequences for the oxygenation and the gas exchange in humans with the potential of consecutive multiple organ failure. Therefore, in this review, the dysfunction of the pulmonary endothel due to viral, bacterial, and fungal infections, ventilator-related injury, and aspiration is presented in a medical context. Selected aspects of the interaction of endothelial cells with primarily alveolar macrophages are reviewed in more detail. Elucidation of underlying causes and mechanisms of damage and repair may lead to new therapeutic approaches. Specific emphasis is placed on the processes leading to the induction of cyclooxygenase-2 and downstream prostanoid-based signaling pathways associated with this enzyme.

Inflammatory biomarkers and pendelluft magnitude in ards patients transitioning from controlled to partial support ventilation

The transition from controlled to partial support ventilation is a challenge in acute respiratory distress syndrome (ARDS) patients due to the risks of patient-self-inflicted lung injury. The magnitude of tidal volume (V_T) and intrapulmonary dyssynchrony (pendelluft) are suggested mechanisms of lung injury. We conducted a prospective, observational, physiological study in a tertiary academic intensive care unit. ARDS patients transitioning from controlled to partial support ventilation were included. On these, we evaluated the association between changes in inflammatory biomarkers and esophageal pressure swing (ΔP_es), transpulmonary driving pressure (ΔP_L), V_T, and pendelluft. Pendelluft was defined as the percentage of the tidal volume that moves from the non-dependent to the dependent lung region during inspiration, and its frequency at different thresholds (- 15, - 20 and - 25%) was also registered. Blood concentrations of inflammatory biomarkers (IL-6, IL-8, TNF-α, ANGPT2, RAGE, IL-18, Caspase-1) were measured before (T₀) and after 4-h (T₄) of partial support ventilation. Pendelluft, ΔP_es, ΔP_L and V_T were recorded. Nine out of twenty-four patients (37.5%) showed a pendelluft mean ≥ 10%. The mean values of ΔP_es, ΔP_L, and V_T were - 8.4 [- 6.7; - 10.2] cmH₂O, 15.2 [12.3-16.5] cmH₂O and 8.1 [7.3-8.9] m/kg PBW, respectively. Significant associations were observed between the frequency of high-magnitude pendelluft and IL-8, IL-18, and Caspase-1 changes (T₀/T₄ ratio). These results suggest that the frequency of high magnitude pendelluft may be a potential determinant of inflammatory response related to inspiratory efforts in ARDS patients transitioning to partial support ventilation. Future studies are needed to confirm these results.

Mechanistic Understanding of Lung Inflammation: Recent Advances and Emerging Techniques

Acute respiratory distress syndrome (ARDS) is a life-threatening lung injury characterized by an acute inflammatory response in the lung parenchyma. Hence, it is considered as the most appropriate clinical syndrome to study pathogenic mechanisms of lung inflammation. ARDS is associated with increased morbidity and mortality in the intensive care unit (ICU), while no effective pharmacological treatment exists. It is very important therefore to fully characterize the underlying pathobiology and the related mechanisms, in order to develop novel therapeutic approaches. In vivo and in vitro models are important pre-clinical tools in biological and medical research in the mechanistic and pathological understanding of the majority of diseases. In this review, we will present data from selected experimental models of lung injury/acute lung inflammation, which have been based on clinical disorders that can lead to the development of ARDS and related inflammatory lung processes in humans, including ventilation-induced lung injury (VILI), sepsis, ischemia/reperfusion, smoke, acid aspiration, radiation, transfusion-related acute lung injury (TRALI), influenza, Streptococcus (S.) pneumoniae and coronaviruses infection. Data from the corresponding clinical conditions will also be presented. The mechanisms related to lung inflammation that will be covered are oxidative stress, neutrophil extracellular traps, mitogen-activated protein kinase (MAPK) pathways, surfactant, and water and ion channels. Finally, we will present a brief overview of emerging techniques in the field of omics research that have been applied to ARDS research, encompassing genomics, transcriptomics, proteomics, and metabolomics, which may recognize factors to help stratify ICU patients at risk, predict their prognosis, and possibly, serve as more specific therapeutic targets.

Profiling Distinctive Inflammatory and Redox Responses to Hydrogen Sulfide in Stretched and Stimulated Lung Cells

Hydrogen sulfide (H2S) protects against stretch-induced lung injury. However, the impact of H2S on individual cells or their crosstalk upon stretch remains unclear. Therefore, we addressed this issue in vitro using relevant lung cells. We have explored (i) the anti-inflammatory properties of H2S on epithelial (A549 and BEAS-2B), macrophage (RAW264.7) and endothelial (HUVEC) cells subjected to cycling mechanical stretch; (ii) the intercellular transduction of inflammation by co-culturing epithelial cells and macrophages (A549 and RAW264.7); (iii) the effect of H2S on neutrophils (Hoxb8) in transmigration (co-culture setup with HUVECs) and chemotaxis experiments. In stretched epithelial cells (A549, BEAS-2B), the release of interleukin-8 was not prevented by H2S treatment. However, H2S reduced macrophage inflammatory protein-2 (MIP-2) release from unstretched macrophages (RAW264.7) co-cultured with stretched epithelial cells. In stretched macrophages, H2S prevented MIP-2 release by limiting nicotinamide adenine dinucleotide phosphate oxidase-derived superoxide radicals (ROS). In endothelial cells (HUVEC), H2S inhibited interleukin-8 release and preserved endothelial integrity. In neutrophils (Hoxb8), H2S limited MIP-2-induced transmigration through endothelial monolayers, ROS formation and their chemotactic movement. H2S induces anti-inflammatory effects in a cell-type specific manner. H2S limits stretch- and/or paracrine-induced inflammatory response in endothelial, macrophage, and neutrophil cells by maintaining redox homeostasis as underlying mechanism.

Mechanotransduction Regulates the Interplays Between Alveolar Epithelial and Vascular Endothelial Cells in Lung

Mechanical stress plays a critical role among development, functional maturation, and pathogenesis of pulmonary tissues, especially for the alveolar epithelial cells and vascular endothelial cells located in the microenvironment established with vascular network and bronchial-alveolar network. Alveolar epithelial cells are mainly loaded by cyclic strain and air pressure tension. While vascular endothelial cells are exposed to shear stress and cyclic strain. Currently, the emerging evidences demonstrated that non-physiological mechanical forces would lead to several pulmonary diseases, including pulmonary hypertension, fibrosis, and ventilation induced lung injury. Furthermore, a series of intracellular signaling had been identified to be involved in mechanotransduction and participated in regulating the physiological homeostasis and pathophysiological process. Besides, the communications between alveolar epithelium and vascular endothelium under non-physiological stress contribute to the remodeling of the pulmonary micro-environment in collaboration, including hypoxia induced injuries, endothelial permeability impairment, extracellular matrix stiffness elevation, metabolic alternation, and inflammation activation. In this review, we aim to summarize the current understandings of mechanotransduction on the relation between mechanical forces acting on the lung and biological response in mechanical overloading related diseases. We also would like to emphasize the interplays between alveolar epithelium and vascular endothelium, providing new insights into pulmonary diseases pathogenesis, and potential targets for therapy.

Organ-Specific Endothelial Cell Differentiation and Impact of Microenvironmental Cues on Endothelial Heterogeneity

Endothelial cells throughout the body are heterogeneous, and this is tightly linked to the specific functions of organs and tissues. Heterogeneity is already determined from development onwards and ranges from arterial/venous specification to microvascular fate determination in organ-specific differentiation. Acknowledging the different phenotypes of endothelial cells and the implications of this diversity is key for the development of more specialized tissue engineering and vascular repair approaches. However, although novel technologies in transcriptomics and proteomics are facilitating the unraveling of vascular bed-specific endothelial cell signatures, still much research is based on the use of insufficiently specialized endothelial cells. Endothelial cells are not only heterogeneous, but their specialized phenotypes are also dynamic and adapt to changes in their microenvironment. During the last decades, strong collaborations between molecular biology, mechanobiology, and computational disciplines have led to a better understanding of how endothelial cells are modulated by their mechanical and biochemical contexts. Yet, because of the use of insufficiently specialized endothelial cells, there is still a huge lack of knowledge in how tissue-specific biomechanical factors determine organ-specific phenotypes. With this review, we want to put the focus on how organ-specific endothelial cell signatures are determined from development onwards and conditioned by their microenvironments during adulthood. We discuss the latest research performed on endothelial cells, pointing out the important implications of mimicking tissue-specific biomechanical cues in culture.

Mechanobiology of Pulmonary Diseases: A Review of Engineering Tools to Understand Lung Mechanotransduction

Cells within the lung micro-environment are continuously subjected to dynamic mechanical stimuli which are converted into biochemical signaling events in a process known as mechanotransduction. In pulmonary diseases, the abrogated mechanical conditions modify the homeostatic signaling which influences cellular phenotype and disease progression. The use of in vitro models has significantly expanded our understanding of lung mechanotransduction mechanisms. However, our ability to match complex facets of the lung including three-dimensionality, multicellular interactions, and multiple simultaneous forces is limited and it has proven difficult to replicate and control these factors in vitro. The goal of this review is to (a) outline the anatomy of the pulmonary system and the mechanical stimuli that reside therein, (b) describe how disease impacts the mechanical micro-environment of the lung, and (c) summarize how existing in vitro models have contributed to our current understanding of pulmonary mechanotransduction. We also highlight critical needs in the pulmonary mechanotransduction field with an emphasis on next-generation devices that can simulate the complex mechanical and cellular environment of the lung. This review provides a comprehensive basis for understanding the current state of knowledge in pulmonary mechanotransduction and identifying the areas for future research.

In Vitro Measurements of Cellular Forces and their Importance in the Lung-From the Sub- to the Multicellular Scale

Throughout life, the body is subjected to various mechanical forces on the organ, tissue, and cellular level. Mechanical stimuli are essential for organ development and function. One organ whose function depends on the tightly connected interplay between mechanical cell properties, biochemical signaling, and external forces is the lung. However, altered mechanical properties or excessive mechanical forces can also drive the onset and progression of severe pulmonary diseases. Characterizing the mechanical properties and forces that affect cell and tissue function is therefore necessary for understanding physiological and pathophysiological mechanisms. In recent years, multiple methods have been developed for cellular force measurements at multiple length scales, from subcellular forces to measuring the collective behavior of heterogeneous cellular networks. In this short review, we give a brief overview of the mechanical forces at play on the cellular level in the lung. We then focus on the technological aspects of measuring cellular forces at many length scales. We describe tools with a subcellular resolution and elaborate measurement techniques for collective multicellular units. Many of the technologies described are by no means restricted to lung research and have already been applied successfully to cells from various other tissues. However, integrating the knowledge gained from these multi-scale measurements in a unifying framework is still a major future challenge.

Sodium Glucose Co-Transporter 2 Inhibitors Ameliorate Endothelium Barrier Dysfunction Induced by Cyclic Stretch through Inhibition of Reactive Oxygen Species

SGLT-2i's exert direct anti-inflammatory and anti-oxidative effects on resting endothelial cells. However, endothelial cells are constantly exposed to mechanical forces such as cyclic stretch. Enhanced stretch increases the production of reactive oxygen species (ROS) and thereby impairs endothelial barrier function. We hypothesized that the SGLT-2i's empagliflozin (EMPA), dapagliflozin (DAPA) and canagliflozin (CANA) exert an anti-oxidative effect and alleviate cyclic stretch-induced endothelial permeability in human coronary artery endothelial cells (HCAECs). HCAECs were pre-incubated with one of the SGLT-2i's (1 µM EMPA, 1 µM DAPA and 3 µM CANA) for 2 h, followed by 10% stretch for 24 h. HCAECs exposed to 5% stretch were considered as control. Involvement of ROS was measured using N-acetyl-l-cysteine (NAC). The sodium-hydrogen exchanger 1 (NHE1) and NADPH oxidases (NOXs) were inhibited by cariporide, or GKT136901, respectively. Cell permeability and ROS were investigated by fluorescence intensity imaging. Cell permeability and ROS production were increased by 10% stretch; EMPA, DAPA and CANA decreased this effect significantly. Cariporide and GKT136901 inhibited stretch-induced ROS production but neither of them further reduced ROS production when combined with EMPA. SGLT-2i's improve the barrier dysfunction of HCAECs under enhanced stretch and this effect might be mediated through scavenging of ROS. Anti-oxidative effect of SGLT-2i's might be partially mediated by inhibition of NHE1 and NOXs.

Simvastatin Mitigates Apoptosis and Transforming Growth Factor-Beta Upregulation in Stretch-Induced Endothelial Cells

Portal hypertension is a common clinical symptom of digestive disorders. With an increase in portal pressure, the portal vein will continue to dilate. We aimed to determine whether continuous stretch induced by portal hypertension may impair the function of endothelial cells (ECs) in the portal vein and aggravate the progress of portal hypertension and explore its mechanism. ECs were cultured on an elastic silicone membrane and subjected to continuous uniaxial stretch. Apoptosis and expression of TGF-β in ECs under stretch were measured. We found that sustained stretch induced the apoptosis of ECs in a stretch length-dependent manner. Compared with the control, continuous stretch increased the nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2) expression and damaged the mitochondria, resulting in an evident increase in reactive oxygen species (ROS) levels; pretreatment with gp91ds-tat or MitoTEMPO decreased the ROS level in the intracellular levels. N-acetyl-cysteine (NAC) treatment before stretch not only reduced ROS levels but also mitigated the apoptosis of ECs; simvastatin had similar effects through targeting NOX2 and mitochondria. During the stretch, the phosphorylation of p38 mitogen-activated protein kinase (P38MAPK), c-Jun N-terminal kinase (JNK), and nuclear factor-kappa B (NF-κB) was obviously increased; pretreatment with P38MAPK or JNK inhibitors decreased the phosphorylation of NF-κB and TGF-β expression. Pyrrolidine dithiocarbamate (PDTC) treatment before stretch also reduced TGF-β expression. After pretreatment with NAC, the phosphorylation of P38MAPK, JNK, and NF-κB and TGF-β expressions in ECs under stretch was suppressed; similar results were observed in simvastatin-treated ECs. This study demonstrated that simvastatin could mitigate EC apoptosis and TGF-β upregulation induced by continuous stretch by reducing the level of ROS.

Inhibition of calcineurin/NFATc4 signaling attenuates ventilator‑induced lung injury

Ventilator-induced lung injury (VILI) is a life-threatening condition caused by the inappropriate use of mechanical ventilation (MV). However, the precise molecular mechanism inducing the development of VILI remains to be elucidated. In the present study, it was revealed that the calcineurin/NFATc4 signaling pathway mediates the expression of adhesion molecules and proinflammatory cytokines essential for the development of VILI. The present results revealed that a high tidal volume ventilation (HV) caused lung inflammation and edema in the alveolar walls and the infiltration of inflammatory cells. The calcineurin activity and protein expression in the lungs were increased in animals with VILI, and NFATc4 translocated into the nucleus following calcineurin activation. Furthermore, the translocation of NFATc4 and lung injury were prevented by a calcineurin inhibitor (CsA). Thus, the present results highlighted the critical role of the calcineurin/NFATc4 signaling pathway in VILI and suggest that this pathway coincides with the release of ICAM-1, VCAM-1, TNF-α and IL-1β.

Ly-6Chigh inflammatory-monocyte recruitment is regulated by p38 MAPK/MCP-1 activation and promotes ventilator-induced lung injury

Lymphocyte antigen 6Chigh (Ly-6C^high) inflammatory monocytes, as novel mononuclear cells in the innate immune system, participate in infectious diseases. In this study, we investigated the potential role of these monocytes in ventilator-induced lung injury (VILI) and the possible mechanism involved in their migration to lung tissue. Our results showed that mechanical ventilation with high tidal volume (HTV) increased the accumulation of Ly-6C^high inflammatory monocytes in lung tissues and that blocking C‑C chemokine receptor 2 (CCR2) could significantly reduce Ly-6C^high inflammatory-monocyte migration and attenuate the degree of inflammation of lung tissues. In addition, inhibition of p38 mitogen-activated protein kinase (p38 MAPK) activity could decrease the secretion of monocyte chemoattractant protein 1 (MCP-1), which in turn decreased the migration of Ly-6C^high inflammatory monocytes into lung tissue. We also demonstrated that high ventilation caused Ly-6C^high inflammatory monocytes in the bone marrow to migrate into and aggregate in the lungs, creating inflammation, and that the mechanism was quite different from that of infectious diseases. Ly-6C^high inflammatory monocytes might play a pro-inflammatory role in VILI, and blocking their infiltration into lung tissue might become a new target for the treatment of this injury.

Triple co-culture of human alveolar epithelium, endothelium and macrophages for studying the interaction of nanocarriers with the air-blood barrier

Predictive in vitro models are valuable alternatives to animal experiments for evaluating the transport of molecules and (nano)particles across biological barriers. In this work, an improved triple co-culture of air-blood barrier was set-up, being exclusively constituted by human cell lines that allowed to perform experiments at air-liquid interface. Epithelial NCI-H441 cells and endothelial HPMEC-ST1.6R cells were seeded at the apical and basolateral sides of a Transwell® membrane, respectively. Differentiated THP-1 cells were also added on the top of the epithelial layer to mimetize alveolar macrophages. Translocation and permeability studies were also performed. It was observed that around 14-18% of 50-nm Fluorospheres®, but less than 1% of 1.0 µm-Fluorospheres® could pass through the triple co-culture as well as the epithelial monoculture and bi-cultures, leading to the conclusion that both in vitro models represented a significant biological barrier and could differentiate the translocation of different sized systems. The permeability of isoniazid was similar between the epithelial monoculture and bi-cultures when compared with the triple co-culture. However, when in vitro models were challenged with lipopolysaccharide, the release of interleukin-8 increased in the bi-cultures and triple co-culture, whereas the NCI-H441 monoculture did not show any proinflammatory response. Overall, this new in vitro model is a potential tool to assess the translocation of nanoparticles across the air-blood barrier both in healthy state and proinflammatory state. STATEMENT OF SIGNIFICANCE: The use of in vitro models for drug screening as an alternative to animal experiments is increasing over the last years, in particular, models to assess the permeation through biological membranes. Cell culture models are mainly constituted by one type of cells forming a confluent monolayer, but due to its oversimplicity they are being replaced by three-dimensional (3D) in vitro models, that present a higher complexity and reflect more the in vivo-like conditions. Being the pulmonary route one of the most studied approaches for drug administration, several in vitro models of alveolar epithelium have been used to assess the drug permeability and translocation and toxicity of nanocarriers. Nevertheless, there is still a lack of 3D in vitro models that mimic the morphology and the physiological behavior of the alveolar-capillary membrane. In this study, a 3D in vitro model of the air-blood barrier constituted by three different relevant cell lines was established and morphologically characterized. Different permeability/translocation studies were performed to achieve differences/similarities comparatively to each monoculture (epithelium, endothelium, and macrophages) and bi-cultures (epithelial cells either cultured with endothelial cells or macrophages). The release of pro-inflammatory cytokines (namely interleukin-8) after incubation of lipopolysaccharide, a pro-inflammatory inductor, was also evaluated in this work.

Effect of Mechanical Stretch on the DNCB-induced Proinflammatory Cytokine Secretion in Human Keratinocytes

Skin is exposed to various physico-chemical cues. Keratinocytes, a major component of the skin epidermis, directly interact with the surrounding extracellular matrix, and thus, biochemical and biophysical stimulations from the matrix regulate the function of keratinocytes. Although it was reported that inflammatory responses of skin were altered by an applied mechanical force, understanding how the keratinocytes sense the mechanical stimuli and regulate a cytokine secretion remains unclear. Here, we designed a device that is able to apply chemo-mechanical cues to keratinocytes and assess their proinflammatory cytokine IL-6 production. We showed that when chemical stimuli were applied with mechanical stimuli simultaneously, the IL-6 production markedly increased compared to that observed with a single stimulus. Quantitative structural analysis of cellular components revealed that the applied mechanical stretch transformed the cell morphology into an elongated shape, increased the cell size, and dictated the distribution of focal adhesion complex. Our results suggest that the mechanical cue-mediated modulation of focal adhesion proteins and actin cytoskeleton translates into intracellular signaling associated with the IL-6 production particularly in skin sensitization. Our study can be applied to understand proinflammatory responses of skin under altered biophysical environments of the skin.

An in vitro investigation of the inflammatory response to the strain amplitudes which occur during high frequency oscillation ventilation and conventional mechanical ventilation

Children randomised in the neonatal period to high frequency oscillatory ventilation (HFOV) or conventional mechanical ventilation (CMV) in the United Kingdom Oscillation study (UKOS) had superior lung function at 11 to 14 years of age. During HFOV, much smaller tidal volumes, but a higher mean airway distending pressure is delivered, hence, a possible explanation for a volume dependent effect on long term lung function could be an increase in inflammation in response to higher tidal volumes and strains. We tested that hypothesis by assessing interleukin-6 (IL-6) and -8 (IL-8) release from A549 alveolar analogue cells following biaxial mechanical strain applied at 0.5 Hz occurring during conditions mimicking strain during CMV (5-20% strain) and conditions mimicking strain during HFOV (17.5% ± 2.5% strain) for up to 4 h. Cyclic strain of 5-20%, occurring during CMV, increased levels of both IL-6 and IL-8 compared to unstrained controls, while 17.5% ± 2.5% strain, occurring during HFOV, was associated with significantly lower levels of IL-6 (46.31 ± 2.66 versus 56.79 ± 3.73 pg/mL) and IL-8 (1340.2 ± 74.9 versus 2522 ± 248 pg/mL) secretion compared to conditions occurring during CMV at four hours. These results may provide a possible explanation for the superior lung function in 11-14-year-old children who had been supported in the neonatal period by HFOV.

Mechanosensing and Mechanoregulation of Endothelial Cell Functions

Vascular endothelial cells (ECs) form a semiselective barrier for macromolecules and cell elements regulated by dynamic interactions between cytoskeletal elements and cell adhesion complexes. ECs also participate in many other vital processes including innate immune reactions, vascular repair, secretion, and metabolism of bioactive molecules. Moreover, vascular ECs represent a unique cell type exposed to continuous, time-dependent mechanical forces: different patterns of shear stress imposed by blood flow in macrovasculature and by rolling blood cells in the microvasculature; circumferential cyclic stretch experienced by the arterial vascular bed caused by heart propulsions; mechanical stretch of lung microvascular endothelium at different magnitudes due to spontaneous respiration or mechanical ventilation in critically ill patients. Accumulating evidence suggests that vascular ECs contain mechanosensory complexes, which rapidly react to changes in mechanical loading, process the signal, and develop context-specific adaptive responses to rebalance the cell homeostatic state. The significance of the interactions between specific mechanical forces in the EC microenvironment together with circulating bioactive molecules in the progression and resolution of vascular pathologies including vascular injury, atherosclerosis, pulmonary edema, and acute respiratory distress syndrome has been only recently recognized. This review will summarize the current understanding of EC mechanosensory mechanisms, modulation of EC responses to humoral factors by surrounding mechanical forces (particularly the cyclic stretch), and discuss recent findings of magnitude-specific regulation of EC functions by transcriptional, posttranscriptional and epigenetic mechanisms using -omics approaches. We also discuss ongoing challenges and future opportunities in developing new therapies targeting dysregulated mechanosensing mechanisms to treat vascular diseases. © 2019 American Physiological Society. Compr Physiol 9:873-904, 2019.

p38 Inhibition Ameliorates Inspiratory Resistive Breathing-Induced Pulmonary Inflammation

Inspiratory resistive breathing (IRB), a hallmark of obstructive airway diseases, is associated with strenuous contractions of the inspiratory muscles and increased negative intrathoracic pressures that act as an injurious stimulus to the lung. We have shown that IRB induces pulmonary inflammation in healthy animals. p38 kinase is activated in the lung under stress. We hypothesized that p38 is activated during IRB and contributes to IRB-induced pulmonary inflammation. Anesthetized, tracheostomized rats breathed spontaneously through a two-way valve. Resistance was connected to the inspiratory port to provoke a peak tidal inspiratory pressure 50% of maximum. Following 3 and 6 h of IRB, respiratory system mechanics were measured and bronchoalveolar lavage (BAL) was performed. Phosphorylated p38, TNF-α, and MIP-2α were detected in lung tissue. Lung injury was estimated histologically. SB203580 (p38 inhibitor) was administered prior to IRB (1 mg kg^-1). Six hours of IRB increased phosphorylated p38 in the lung, compared with quietly breathing controls (p = 0.001). Six hours of IRB increased the numbers of macrophages and neutrophils (p = 0.01 and p = 0.005) in BAL fluid. BAL protein levels and lung elasticity increased after both 3 and 6 h IRB. TNF-α and MIP-2α increased after 6 h of IRB (p = 0.01 and p < 0.001, respectively). Increased lung injury score was detected at 6 h IRB. SB203580 administration blocked the increase of neutrophils and macrophages at 6 h IRB (p = 0.01 and p = 0.005 to 6 h IRB) but not the increase in BAL protein and elasticity. TNF-α, MIP-2α, and injury score at 6 h IRB returned to control. p38 activation contributes to IRB-induced pulmonary inflammation.

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.

Preconditioning of physiological cyclic stretch inhibits the inflammatory response induced by pathologically mechanical stretch in alveolar epithelial cells

The aim of the present study was to investigate the effects of preconditioning of physiological cyclic stretch (CS) on the overexpression of early pro-inflammatory cytokines [including tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-8] during the inflammatory response induced by pathologically mechanical stretch in lung epithelial cells, and to determine its molecular mechanism of action. Cells were subjected to 5% CS for various durations (0, 15, 30, 60 and 120 min) prior to 6 h treatment with pathological 20% CS. In a separate experiment, cells were preconditioned with physiological 5% CS or incubated with a nuclear factor (NF)-κB inhibitor, pyrroldine dithiocarbamate (PDTC). The expression levels of inflammatory mediators were measured using reverse transcription-quantitative polymerase chain reaction. NF-κB was quantified using western blot analysis. Preconditioning with physiological 5% CS for 30, 60 and 120 min was demonstrated to significantly attenuate the release of pathologically mechanical stretch-induced early pro-inflammatory cytokines (TNF-α, IL-1β and IL-8) in alveolar epithelial cells (P<0.05) and significantly reduce the expression of NF-κB (P<0.05). Peak suppression was observed in cells preconditioned for 60 min. In the second set of experiments, it was demonstrated that mechanical stretch-induced release of TNF-α, IL-1β and IL-8 was significantly inhibited by both PDTC pretreatment and 5% CS pretreatment alone (all P<0.05). Furthermore, significant inhibition was also observed when both 5% CS pretreatment and PDTC pretreatment was used on mechanical stretch-induced cells (P<0.05), which was markedly greater than the inhibition induced by either pretreatment alone. The present findings suggest that preconditioning with physiological 5% CS is able to inhibit the inflammatory response induced by pathologically mechanical stretch in alveolar epithelial cells. These anti-inflammatory effects are induced, at least in part, by suppressing the NF-κB signaling pathway.

miR-127 contributes to ventilator-induced lung injury

Although it is essential in critical care medicine, mechanical ventilation often results in ventilator‑induced lung injury (VILI). Treating mice with lipopolysaccharide has been reported to upregulate the expression of miR‑127, which has been implicated in the modulation of immune responses. However, the putative roles of miR‑127 during the development of VILI have yet to be elucidated. The present study demonstrated that challenging mice with mechanical ventilation for 6 h significantly upregulated the expression of miR‑127 in bronchoalveolar lavage fluid, serum and lung tissue samples. Conversely, following the downregulation of miR‑127 expression in vivo using an adenovirus delivery system, VILI‑associated pathologies, including alterations in the pulmonary wet/dry ratio, pulmonary permeability, lung neutrophil infiltration and levels of pro‑inflammatory cytokines, were significantly attenuated. In addition, miR‑127 knockdown inhibited the ventilation‑induced activation of nuclear factor (NF)‑κB and p38 mitogen‑activated protein kinase (MAPK). These findings suggested that the upregulation of miR‑127 expression may contribute to the development of VILI, through the modulation of pulmonary permeability, the induction of histopathological alterations, and the potentiation of inflammatory responses involving NF‑κB and p38 MAPK‑associated signaling pathways.

Real-time imaging of mechanically and chemically induced ATP release in human lung fibroblasts

Extracellular adenosine 5'-triphosphate (ATP) acts as an inflammatory mediator of pulmonary fibrosis. We investigated the effects of mechanical and chemical stimuli on ATP release from primary normal human lung fibroblasts. We visualized the ATP release from fibroblasts in real time using a luminescence imaging system while acquiring differential interference contrast cell images with infrared optics. Immediately following a single uniaxial stretch for 1s, ATP was released from a certain population of cells and spread to surrounding spaces. Hypotonic stress, which causes plasma membrane stretching, also induced the ATP release. Compared with the effects of mechanical stretch, ATP-induced release sites were homogeneously distributed. In contrast to the effects of mechanical stimuli, application of platelet-derived growth factor caused ATP release from small numbers of the cells. Our real-time ATP imaging demonstrates that there is a heterogeneous nature of ATP release from lung fibroblasts in response to mechanical and chemical stimuli.

PX-18 Protects Human Saphenous Vein Endothelial Cells under Arterial Blood Pressure

BACKGROUND

Arterial blood pressure-induced shear stress causes endothelial cell apoptosis and inflammation in vein grafts after coronary artery bypass grafting. As the inflammatory protein type IIA secretory phospholipase A₂ (sPLA₂-IIA) has been shown to progress atherosclerosis, we hypothesized a role for sPLA₂-IIA herein.

METHODS

The effects of PX-18, an inhibitor of both sPLA₂-IIA and apoptosis, on residual endothelium and the presence of sPLA₂-IIA were studied in human saphenous vein segments (n = 6) perfused at arterial blood pressure with autologous blood for 6 hrs.

RESULTS

The presence of PX-18 in the perfusion blood induced a significant 20% reduction in endothelial cell loss compared to veins perfused without PX18, coinciding with significantly reduced sPLA₂-IIA levels in the media of the vein graft wall. In addition, PX-18 significantly attenuated caspase-3 activation in human umbilical vein endothelial cells subjected to shear stress via mechanical stretch independent of sPLA₂-IIA.

CONCLUSIONS

In conclusion, PX-18 protects saphenous vein endothelial cells from arterial blood pressure-induced death, possibly also independent of sPLA₂-IIA inhibition.

Tanshinone IIA Induces Heme Oxygenase 1 Expression and Inhibits Cyclic Strain-Induced Interleukin 8 Expression in Vascular Endothelial Cells

Tanshinone IIA is the main effective component of Salvia miltiorrhiza, known as “Danshen,” which has been used in many therapeutic remedies in traditional Chinese medicine. However, the direct effects of tanshinone IIA on vascular endothelial cells have not yet been fully described. In the present study, we demonstrated that tanshinone IIA increased heme oxygenase-1 (HO-1) expression in human umbilical vein endothelial cells. Western blot analyses and experiments with specific inhibitors indicated tanshinone IIA enhanced HO-1 expression through the activation of phosphoinositide 3-kinase (PI3K)/Akt and the subsequent induction of nuclear factor erythroid 2-related factor 2 (Nrf2) nuclear translocation. In addition, tanshinone IIA inhibited cyclic strain induced interleukin-8 (IL-8) expression. HO-1 silencing significantly abrogated the repressive effects of tanshinone IIA on strain-induced IL-8 expression, which suggests HO-1 has a role in mediating the effects of tanshinone IIA. This study reports for the first time that tanshinone IIA inhibits cyclic strain-induced IL-8 expression via the induction of HO-1 in endothelial cells, providing valuable new insight into the molecular pathways that may contribute to the effects of tanshinone IIA.

Chronic high-magnitude cyclic stretch stimulates EC inflammatory response via VEGF receptor 2-dependent mechanism

Ventilator-induced lung injury (VILI) is associated with activated inflammatory signaling, such as cytokine production by endothelial and epithelial cells and macrophages, although the precise mechanisms of inflammatory activation induced by VILI-relevant cyclic stretch (CS) amplitude remain poorly understood. We show that exposure of human pulmonary endothelial cells (EC) to chronic CS at 18% linear distension (18% CS), but not at physiologically relevant 5% CS, induces "EC-activated phenotype," which is characterized by time-dependent increase in ICAM1 and VCAM1 expression. A preconditioning of 18% CS also increased in a time-dependent fashion the release of soluble ICAM1 (sICAM1) and IL-8. Investigation of potential signaling mechanisms of CS-induced EC inflammatory activation showed that 18% CS, but not 5% CS, induced time-dependent upregulation of VEGF receptor 2 (VEGFR2), as monitored by increased protein expression and VEGFR2 tyrosine phosphorylation. Both CS-induced VEGFR2 expression and tyrosine phosphorylation were abrogated by cotreatment with reactive oxygen species inhibitor, N-acetyl cysteine. Molecular inhibition of VEGFR2 expression by gene-specific siRNA or treatment with VEGFR2 pharmacological inhibitor SU-1498 attenuated CS-induced activation of ICAM1 and VCAM1 expression and sICAM1 release. Chronic EC preconditioning at 18% CS augmented EC inflammation and barrier-disruptive response induced by proinflammatory cytokine TNF-α. This effect of chronic 18% CS preconditioning was attenuated by siRNA-induced VEGFR2 knockdown. This study demonstrates for the first time a VEGFR2-dependent mechanism of EC inflammatory activation induced by pathological CS. We conclude that, despite the recognized role of VEGF as a prosurvival and angiogenic factor, excessive activation of VEGFR2 signaling by high-tidal-volume lung mechanical ventilation may contribute to ventilator-induced (biotrauma) lung inflammation and barrier dysfunction by augmenting cell response to VILI-associated inflammatory mediators.

Activation of Vascular Endothelial Growth Factor (VEGF) Receptor 2 Mediates Endothelial Permeability Caused by Cyclic Stretch

High tidal volume mechanical ventilation and the resultant excessive mechanical forces experienced by lung vascular endothelium are known to lead to increased vascular endothelial leak, but the underlying molecular mechanisms remain incompletely understood. One reported mechanotransduction pathway of increased endothelial cell (EC) permeability caused by high magnitude cyclic stretch (18% CS) involves CS-induced activation of the focal adhesion associated signalosome, which triggers Rho GTPase signaling. This study identified an alternative pathway of CS-induced EC permeability. We show here that high magnitude cyclic stretch (18% CS) rapidly activates VEGF receptor 2 (VEGFR2) signaling by dissociating VEGFR2 from VE-cadherin at the cell junctions. This results in VEGFR2 activation, Src-dependent VE-cadherin tyrosine phosphorylation, and internalization leading to increased endothelial permeability. This process is also accompanied by CS-induced phosphorylation and internalization of PECAM1. Importantly, CS-induced endothelial barrier disruption was attenuated by VEGFR2 inhibition. 18% CS-induced EC permeability was linked to dissociation of cell junction scaffold afadin from the adherens junctions. Forced expression of recombinant afadin in pulmonary endothelium attenuated CS-induced VEGFR2 and VE-cadherin phosphorylation, preserved adherens junction integrity and VEGFR2·VE-cadherin complex, and suppressed CS-induced EC permeability. This study shows for the first time a mechanism whereby VEGFR2 activation mediates EC permeability induced by pathologically relevant cyclic stretch. In this mechanism, CS induces dissociation of the VE-cadherin·VEGFR2 complex localized at the adherens juctions, causing activation of VEGFR2, VEGFR2-mediated Src-dependent phosphorylation of VE-cadherin, disassembly of adherens junctions, and EC barrier failure.

Kinetic profiling of in vivo lung cellular inflammatory responses to mechanical ventilation

Mechanical ventilation, through overdistension of the lung, induces substantial inflammation that is thought to increase mortality among critically ill patients. The mechanotransduction processes involved in converting lung distension into inflammation during this ventilator-induced lung injury (VILI) remain unclear, although many cell types have been shown to be involved in its pathogenesis. This study aimed to identify the profile of in vivo lung cellular activation that occurs during the initiation of VILI. This was achieved using a flow cytometry-based method to quantify the phosphorylation of several markers (p38, ERK1/2, MAPK-activated protein kinase 2, and NF-κB) of inflammatory pathway activation within individual cell types. Anesthetized C57BL/6 mice were ventilated with low (7 ml/kg), intermediate (30 ml/kg), or high (40 ml/kg) tidal volumes for 1, 5, or 15 min followed by immediate fixing and processing of the lungs. Surprisingly, the pulmonary endothelium was the cell type most responsive to in vivo high-tidal-volume ventilation, demonstrating activation within just 1 min, followed by the alveolar epithelium. Alveolar macrophages were the slowest to respond, although they still demonstrated activation within 5 min. This order of activation was specific to VILI, since intratracheal lipopolysaccharide induced a very different pattern. These results suggest that alveolar macrophages may become activated via a secondary mechanism that occurs subsequent to activation of the parenchyma and that the lung cellular activation mechanism may be different between VILI and lipopolysaccharide. Our data also demonstrate that even very short periods of high stretch can promote inflammatory activation, and, importantly, this injury may be immediately manifested within the pulmonary vasculature.

Real-time imaging of ATP release induced by mechanical stretch in human airway smooth muscle cells

Airway smooth muscle (ASM) cells within the airway walls are continually exposed to mechanical stimuli, and exhibit various functions in response to these mechanical stresses. ATP acts as an extracellular mediator in the airway. Moreover, extracellular ATP is considered to play an important role in the pathophysiology of asthma and chronic obstructive pulmonary disease. However, it is not known whether ASM cells are cellular sources of ATP secretion in the airway. We therefore investigated whether mechanical stretch induces ATP release from ASM cells. Mechanical stretch was applied to primary human ASM cells cultured on a silicone chamber coated with type I collagen using a stretching apparatus. Concentrations of ATP in cell culture supernatants measured by luciferin-luciferase bioluminescence were significantly elevated by cyclic stretch (12 and 20% strain). We further visualized the stretch-induced ATP release from the cells in real time using a luminescence imaging system, while acquiring differential interference contrast cell images with infrared optics. Immediately after a single uniaxial stretch for 1 second, strong ATP signals were produced by a certain population of cells and spread to surrounding spaces. The cyclic stretch-induced ATP release was significantly reduced by inhibitors of Ca(2+)-dependent vesicular exocytosis, 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetraacetoxymethyl ester, monensin, N-ethylmaleimide, and bafilomycin. In contrast, the stretch-induced ATP release was not inhibited by a hemichannel blocker, carbenoxolone, or blockade of transient receptor potential vanilloid 4 by short interfering RNA transfection or ruthenium red. These findings reveal a novel property of ASM cells: mechanically induced ATP release may be a cellular source of ATP in the airway.

Differential and opposing effects of imatinib on LPS- and ventilator-induced lung injury

Endothelial dysfunction underlies the pathophysiology of vascular disorders such as acute lung injury (ALI) syndromes. Recent work has identified the Abl family kinases (c-Abl and Arg) as important regulators of endothelial cell (EC) barrier function and suggests that their inhibition by currently available pharmaceutical agents such as imatinib may be EC protective. Here we describe novel and differential effects of imatinib in regulating lung pathophysiology in two clinically relevant experimental models of ALI. Imatinib attenuates endotoxin (LPS)-induced vascular leak and lung inflammation in mice but exacerbates these features in a mouse model of ventilator-induced lung injury (VILI). We next explored these discrepant observations in vitro through investigation of the roles for Abl kinases in cultured lung EC. Imatinib attenuates LPS-induced lung EC permeability, restores VE-cadherin junctions, and reduces inflammation by suppressing VCAM-1 expression and inflammatory cytokine (IL-8 and IL-6) secretion. Conversely, in EC exposed to pathological 18% cyclic stretch (CS) (in vitro model of VILI), imatinib decreases VE-cadherin expression, disrupts cell-cell junctions, and increases IL-8 levels. Downregulation of c-Abl expression with siRNA attenuates LPS-induced VCAM-1 expression, whereas specific reduction of Arg reduces VE-cadherin expression in 18% CS-challenged ECs to mimic the imatinib effects. In summary, imatinib exhibits pulmonary barrier-protective and anti-inflammatory effects in LPS-injured mice and lung EC; however, imatinib exacerbates VILI as well as dysfunction in 18% CS-EC. These findings identify the Abl family kinases as important modulators of EC function and potential therapeutic targets in lung injury syndromes.

Ca2+ influx and ATP release mediated by mechanical stretch in human lung fibroblasts

One cause of progressive pulmonary fibrosis is dysregulated wound healing after lung inflammation or damage in patients with idiopathic pulmonary fibrosis and severe acute respiratory distress syndrome. The mechanical forces are considered to regulate pulmonary fibrosis via activation of lung fibroblasts. In this study, the effects of mechanical stretch on the intracellular Ca(2+) concentration ([Ca(2+)]i) and ATP release were investigated in primary human lung fibroblasts. Uniaxial stretch (10-30% in strain) was applied to fibroblasts cultured in a silicone chamber coated with type I collagen using a stretching apparatus. Following stretching and subsequent unloading, [Ca(2+)]i transiently increased in a strain-dependent manner. Hypotonic stress, which causes plasma membrane stretching, also transiently increased the [Ca(2+)]i. The stretch-induced [Ca(2+)]i elevation was attenuated in Ca(2+)-free solution. In contrast, the increase of [Ca(2+)]i by a 20% stretch was not inhibited by the inhibitor of stretch-activated channels GsMTx-4, Gd(3+), ruthenium red, or cytochalasin D. Cyclic stretching induced significant ATP releases from fibroblasts. However, the stretch-induced [Ca(2+)]i elevation was not inhibited by ATP diphosphohydrolase apyrase or a purinergic receptor antagonist suramin. Taken together, mechanical stretch induces Ca(2+) influx independently of conventional stretch-sensitive ion channels, the actin cytoskeleton, and released ATP.

Genetic and pharmacologic inhibition of Tpl2 kinase is protective in a mouse model of ventilator-induced lung injury

Background

Mechanical stress induced by injurious ventilation leads to pro-inflammatory cytokine production and lung injury. The extracellular-signal-regulated-kinase, ERK1/2, participates in the signaling pathways activated upon mechanical stress in the lungs to promote the inflammatory response. Tumor progression locus 2 (Tpl2) is a MAP3kinase that activates ERK1/2 upon cytokine or TLR signaling, to induce pro-inflammatory cytokine production. The role of Tpl2 in lung inflammation, and specifically in the one caused by mechanical stress has not been investigated. The aim of the study was to examine if genetic or pharmacologic inhibition of Tpl2 could ameliorate ventilator-induced lung injury.

Methods

Adult male wild-type and Tpl2-deficient mice were ventilated with normal or high tidal volume for 4 h. Additional wild-type mice were treated with a Tpl2 inhibitor either before or 30 min after initiation of high tidal ventilation. Non-ventilated mice of both genotypes served as controls. The development of lung injury was evaluated by measuring lung mechanics, arterial blood gases, concentrations of proteins, IL-6, and MIP-2 in bronchoalveolar lavage fluid (BALF) and by lung histology. Data were compared by Kruskal-Wallis non-parametric test and significance was defined as p < 0.05.

Results

Mechanical ventilation with normal tidal volume induced a mild increase of IL-6 in BALF in both strains. High tidal volume ventilation induced lung injury in wild-type mice, characterized by decreased lung compliance, increased concentrations of proteins, IL-6 and MIP-2 in BALF, and inflammatory cell infiltration on histology. All indices of lung injury were ameliorated in Tpl2-deficient mice. Wild-type mice treated with the Tpl2 inhibitor, either prior of after the initiation of high tidal volume ventilation were protected from the development of lung injury, as indicated by preserved lung compliance and lower BALF concentrations of proteins and IL-6, than similarly ventilated, untreated wild-type mice.

Conclusions

Genetic and pharmacologic inhibition of Tpl2 is protective in a mouse model of ventilator-induced lung injury, ameliorating both high-permeability pulmonary edema and lung inflammation.

Different mechanism of LPS-induced calcium increase in human lung epithelial cell and microvascular endothelial cell: a cell culture study in a model for ARDS

Acute respiratory distress syndrome (ARDS) is a contemporary term incorporating the historic 'acute lung injury' and the colloquial term 'shock lung'. ARDS remains a serious and enigmatic human disease, causing significant mortality. The mechanisms involved at the alveolar cell/capillary endothelial interface have been explored but to date we lack clarity on the role of intracellular calcium ([Ca(2+)]i) fluxes across this interface. To explore the mechanisms of Ca(2+) induced inflammatory reaction in epithelial cells and pulmonary microvascular endothelial cells (HMVEC) located at the two sides of blood-air barrier, lung epithelial A549 and HMVEC cells were treated with LPS. Our results demonstrated that LPS evoked the increase of [Ca(2+)]i, TNF-α and IL-8 in both cells types. The [Ca(2+)]i increases involved intracellular but not extracellular Ca(2+) sources in A549, but both intracellular and extracellular Ca(2+) sources in HMVEC cells. The effects of LPS on both cells types were completely inhibited by the combination of LPS and CaSR-targeted siRNA. Furthermore, LPS-inhibited cell proliferations were significantly reversed by the combined treatment. Therefore, LPS induced different mechanisms of [Ca(2+)]i increase during the activation of CaSR in A549 and HMVEC cells, which translates into functional outputs related to ARDS.

Excessive mechanical stress increases HMGB1 expression in human lung microvascular endothelial cells via STAT3

Ventilator-induced lung injury (VILI) occurs when the lung parenchyma and vasculature are exposed to repetitive and excessive mechanical stress via mechanical ventilation utilized as supportive care for the adult respiratory distress syndrome (ARDS). VILI induces gene expression and systemic release of inflammatory mediators that contribute to the multi-organ dysfunction and morbidity and mortality of ARDS. HMGB1, an intracellular transcription factor with cytokine properties, is a late mediator in sepsis and ARDS pathobiology, however, the role of HMGB1 in VILI remains poorly described. We now report HMGB1 expression in human lung microvessel endothelial cells (ECs) exposed to excessive, equibiaxial mechanical stress, an in vitro correlate of VILI. We determined that high amplitude cyclic stretch (18% CS) increased HMGB1 expression (2-4-fold) via a signaling pathway with critical involvement of the transcription factor, STAT3. Concomitant exposure to 18% CS and oxidative stress (H₂O₂) augmented HMGB1 expression (~13 fold increase) whereas lipopolysaccharide (LPS) challenge increased HMGB1 expression in static EC, but not in 18% CS-challenged EC. In contrast, physiologic, low amplitude cyclic stretch (5% CS) attenuated both oxidative H₂O₂- and LPS-induced increases in HMGB1 expression, suggesting that physiologic mechanical stress is protective. These results indicate that HMGB1 gene expression is markedly responsive to VILI-mediated mechanical stress, an effect that is augmented by oxidative stress. We speculate that VILI-induced HMGB1 expression acts locally to increase vascular permeability and alveolar flooding, thereby exacerbating systemic inflammatory responses and increasing the likelihood of multi-organ dysfunction.

Volutrauma, but not atelectrauma, induces systemic cytokine production by lung-marginated monocytes

OBJECTIVES

Ventilator-induced lung injury has substantive impact on mortality of patients with acute respiratory distress syndrome. Although low tidal volume ventilation has been shown to reduce mortality, clinical benefits of open-lung strategy are controversial. In this study, we investigated the impact of two distinct forms of ventilator-induced lung injury, i.e., volutrauma and atelectrauma, on the progression of lung injury and inflammation, in particular alveolar and systemic cytokine production.

DESIGN

Ex vivo study.

SETTING

University research laboratory.

SUBJECTS

C57BL/6 mice.

INTERVENTIONS

Isolated, buffer-perfused lungs were allocated to one of three ventilatory protocols for 3 hours: control group received low tidal volume (7 mL/kg) with positive end-expiratory pressure (5 cm H2O) and regular sustained inflation; high-stretch group received high tidal volume (30-32 mL/kg) with positive end-expiratory pressure (3 cm H2O) and sustained inflation; and atelectasis group received the same tidal volume as control but neither positive end-expiratory pressure nor sustained inflation.

MEASUREMENTS AND MAIN RESULTS

Both injurious ventilatory protocols developed comparable levels of physiological injury and pulmonary edema, measured by respiratory system mechanics and lavage fluid protein. High-stretch induced marked increases in proinflammatory cytokines in perfusate and lung lavage fluid, compared to control. In contrast, atelectasis had no effect on perfusate cytokines compared to control but did induce some up-regulation of lavage cytokines. Depletion of monocytes marginated within the lung microvasculature, achieved by pretreating mice with i.v. liposome-encapsulated clodronate, significantly attenuated perfusate cytokine levels, especially tumor necrosis factor, in the high-stretch, but not atelectasis group.

CONCLUSIONS

Volutrauma (high-stretch), but not atelectrauma (atelectasis), directly activates monocytes within the pulmonary vasculature, leading to cytokine release into systemic circulation. We postulate this as a potential explanation why open-lung strategy has limited mortality benefits in ventilated critically ill patients.

Integrating in vitro organ-specific function with the microcirculation

There is significant interest within the tissue engineering and pharmaceutical industries to create 3D microphysiological systems of human organ function. The interest stems from a growing concern that animal models and simple 2D culture systems cannot replicate essential features of human physiology that are critical to predict drug response, or simply to develop new therapeutic strategies to repair or replace damaged organs. Central to human organ function is a microcirculation that not only enhances the rate of nutrient and waste transport by convection, but also provides essential additional physiological functions that can be specific to each organ. This review highlights progress in the creation of in vitro functional microvessel networks, and emphasizes organ-specific functional and structural characteristics that should be considered in the future mimicry of four organ systems that are of primary interest: lung, brain, liver, and muscle (skeletal and cardiac).

Losartan attenuates microvascular permeability in mechanical ventilator-induced lung injury in diabetic mice

Mechanical ventilation can cause direct injury to the lungs, a type of injury known as ventilator-induced lung injury (VILI). VILI is associated with up-regulates angiotensinogen and AT1 receptor expression of in the lung. This work explored effects of losartan on VILI in diabetic mice. Ninty-six C57Bl/6 mice were randomly divided into six groups, control group (C group), diabetes group (D group), diabetes mechanical ventilation group (DV group), losartan control group (L + C group), losartan treatment group in diabetic mice (L + D group) and losartan treatment group in mechanical ventilation diabetic mice (L + DV group). Lung W/D, myeloperoxidase (MPO) activity, microvascular permeability, blood-gas analysis, Ang II concentrations and AT-1R protein expression were measured. Compared with D group, DV group increased Ang II concentrations, AT-1R protein expression, W/D ratio, MPO activity, and microvascular permeability. PaO2 were significantly lower in the DV group than D group or control group. Compared with DV group, L + DV group attenuates ventilator-induced lung injury in diabetic mice and prevented the increase Ang II concentrations, AT-1R protein expression and microvascular permeability caused by ventilation in diabetic mice. This study provides in vivo evidence that losartan attenuates microvascular permeability via down-regulates Ang II and AT-1R expression in mechanical ventilator-induced lung injury in diabetic mice.

Mechanical induction of group V phospholipase A(2) causes lung inflammation and acute lung injury

Ventilation at high tidal volume may cause lung inflammation and barrier dysfunction that culminates in ventilator-induced lung injury (VILI). However, the mechanisms by which mechanical stimulation triggers the inflammatory response have not been fully elucidated. This study tested the hypothesis that onset of VILI is triggered by activation of secretory group V phospholipase A(2) (gVPLA2) in pulmonary vascular endothelium exposed to excessive mechanical stretch. High-magnitude cyclic stretch (18% CS) increased expression and surface exposure of gVPLA2 in human pulmonary endothelial cells (EC). CS-induced gVPLA2 activation was required for activation of ICAM-1 expression and polymorphonuclear neutrophil (PMN) adhesion to CS-preconditioned EC. By contrast, physiological CS (5% CS) had no effect on gVPLA2 activation or EC-PMN adhesion. CS-induced ICAM-1 expression and EC-PMN adhesion were attenuated by the gVPLA2-blocking antibody (MCL-3G1), general inhibitor of soluble PLA2, LY311727, or siRNA-induced EC gVPLA2 knockdown. In vivo, ventilator-induced lung leukocyte recruitment, cell and protein accumulation in the alveolar space, and total lung myeloperoxidase activity were strongly suppressed in gVPLA2 mouse knockout model or upon administration of MCL-3G1. These results demonstrate a novel role for gVPLA2 as the downstream effector of pathological mechanical stretch leading to an inflammatory response associated with VILI.

Cyclic stretch augments production of neutrophil chemokines and matrix metalloproteinases-1 (MMP-1) from human decidual cells, and the production was reduced by progesterone

PROBLEM

The purpose of this study was to evaluate the impact of mechanical stretch caused by uterine contraction and progesterone (P₄) on decidual cells (DC), neutrophil chemokines, and MMP-1 expression.

METHOD OF STUDY

DC were cultured, and cyclic stretch was applied using a computer-operated cell stretch system. Interleukin (IL)-8, growth-regulated oncogene (GRO) α, matrix metalloproteinase (MMP)-1, and mRNA and/or protein expression/activity was measured using RT-PCR and ELISA. Neutrophil chemotactic activity in conditioned media was evaluated using migration assays. The effect of P₄ was also studied.

RESULTS

Cyclic mechanical stretch increased IL-8, GROα, mRNA and protein, and MMP-1 production and activity level. Supernatant from stretched cells induced neutrophil chemotactic activity significantly. P₄ suppressed the effect of stretch.

CONCLUSION

The current study demonstrates that cyclic mechanical stretch stimulates the production of neutrophil chemokines and MMP-1 from human decidual cells, and the production was reduced by progesterone. These findings suggest that decidual cells are responding to mechanical and endocrine signals and induce biochemical factors and thereby contribute to the regulation of human labor.

Neuroprotective effect of gadolinium: a stretch-activated calcium channel blocker in mouse model of ischemia-reperfusion injury

The present study was designed to investigate the potential of gadolinium, a stretch-activated calcium channel blocker in ischemic reperfusion (I/R)-induced brain injury in mice. Bilateral carotid artery occlusion of 12 min followed by reperfusion for 24 h was given to induce cerebral injury in male Swiss mice. Cerebral infarct size was measured using triphenyltetrazolium chloride staining. Memory was assessed using Morris water maze test and motor incoordination was evaluated using rota-rod, lateral push, and inclined beam walking tests. In addition, total calcium, thiobarbituric acid reactive substance (TBARS), reduced glutathione (GSH), and acetylcholinesterase (AChE) activity were also estimated in brain tissue. I/R injury produced a significant increase in cerebral infarct size. A significant loss of memory along with impairment of motor performance was also noted. Furthermore, I/R injury also produced a significant increase in levels of TBARS, total calcium, AChE activity, and a decrease in GSH levels. Pretreatment of gadolinium significantly attenuated I/R-induced infarct size, behavioral and biochemical changes. On the basis of the present findings, we can suggest that opening of stretch-activated calcium channel may play a critical role in ischemic reperfusion-induced brain injury and that gadolinium has neuroprotective potential in I/R-induced injury.

Differential regulation of airway smooth muscle cell migration by E-prostanoid receptor subtypes

Migration of airway smooth muscle (ASM) cells plays an important role in the pathophysiology of airway hyperresponsiveness and remodeling in asthma. It has been reported that prostaglandin (PG)E2 inhibits migration of ASM cells. Although PGE2 regulates cellular functions via binding to distinct prostanoid EP receptors, the role of EP receptor subtypes in mechanisms underlying cell migration has not been fully elucidated. We investigated the role of EP receptors in the inhibitory effects of PGE2 on the migration of human ASM cells. Migration induced by platelet-derived growth factor (PDGF)-BB (10 ng/ml, 6 h) was assessed by a chemotaxis chamber assay. PDGF-BB-induced cell migration was inhibited by PGE2, the specific EP2 agonist ONO-AE1-259-01, the specific EP4 agonist ONO-AE1-329, and cAMP-mobilizing agents. The inhibition of cell migration by PGE2 was significantly reversed by a blockade of EP2 and EP4 receptors using antagonists or transfection with siRNAs. Moreover, PGE2, the EP2 agonist, and the EP4 agonist significantly increased phosphorylation of small heat shock protein 20, one of the protein substrates for protein kinase A (PKA), with depolymerization of actin. In contrast, the EP3 agonist ONO-AE-248 significantly promoted baseline cell migration without affecting PDGF-BB-induced cell migration. In summary, activation of EP2 and EP4 receptors and subsequent activation of the cAMP/PKA pathway are the main mechanisms of inhibition of ASM cell migration by PGE2. HSP20 phosphorylation by PKA is possibly involved in this mechanism. Conversely, EP3 is potent in promoting cell migration. EP receptor subtypes may be novel therapeutic target molecules in airway remodeling and asthma.

Low tidal volume protects pulmonary vasomotor function from "second-hit" injury in acute lung injury rats

Background

Sepsis could induce indirect acute lung injury(ALI), and pulmonary vasomotor dysfunction. While low tidal volume is advocated for treatment of ALI patients. However, there is no evidence for low tidal volume that it could mitigate pulmonary vasomotor dysfunction in indirect ALI. Our study is to evaluate whether low tidal volume ventilation could protect the pulmonary vascular function in indirect lipopolysaccharide (LPS) induced acute lung injury rats.

Methods

An indirect ALI rat model was induced by intravenous infusion of LPS. Thirty rats (n = 6 in each group) were randomly divided into (1)Control group; (2) ALI group; (3) LV group (tidal volume of 6mL/kg); (4) MV group (tidal volume of 12mL/kg); (5)VLV group (tidal volume of 3mL/kg). Mean arterial pressure and blood gas analysis were monitored every 2 hours throughout the experiment. Lung tissues and pulmonary artery rings were immediately harvested after the rats were bled to be killed to detect the contents of endothelin-1 (ET-1), endothelial nitric oxide synthase (eNOS) and TNF-α. Acetylcholine (Ache)-induced endothelium-dependent and sodium nitroprusside (SNP)-induced endothelium-independent relaxation of isolated pulmonary artery rings were measured by tensiometry.

Results

There was no difference within groups concerning blood pressure, PaCO₂ and SNP-induced endothelium-independent relaxation of pulmonary artery rings. Compared with MV group, LV group significantly reduced LPS-induced expression of ET-1 level (113.79 ± 7.33pg/mL vs. 152.52 ± 12.75pg/mL, P < 0.05) and TNF-α (3305.09 ± 334.29pg/mL vs.4144.07 ± 608.21pg/mL, P < 0.05), increased the expression of eNOS (IOD: 15032.05 ± 5925.07 vs. 11454.32 ± 6035.47, P < 0.05). While Ache (10^-7mol/L-10^-4mol/L)-induced vasodilatation was ameliorated 30% more in LV group than in MV group.

Conclusions

Low tidal volume could protect the pulmonary vasodilative function during indirect ALI by decreasing vasoconstrictor factors, increasing expressions of vasodilator factors in pulmonary endothelial cells, and inhibiting inflammation injuries.