Mechanical stretch induces lung α-epithelial Na(+) channel expression

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.

Lysophosphatidic Acid Regulates Rho Family of GTPases in Lungs

The bio-active lipid, lysophosphatidic acid (LPA) interacts with various lysophosphatidic acid receptors (LPARs) to affect a variety of cellular functions, including proliferation, differentiation, survival, migration, morphogenesis and others. The Rho family of small GTPases, is well-known downstream signaling pathways activated by LPA. Among the Rho GTPases, RhoA, Rac1, and Cdc42 are best characterized and LPA-induced activation of the GTPases RhoA, Rac1, and Cdc42 influences a wide range of cellular processes and functions such as cell differentiation, contractile movements, cellular migration, or infiltration. In this review, we will briefly discuss the interplay between LPA and each of these three Rho family proteins, summarizing the main interactions between them. Our discussion will focus mainly on their interplay within lung endothelial and epithelial cells, drawing attention to how these interactions may contribute to pro-inflammatory processes.

Mechanical Strain-Mediated Tenogenic Differentiation of Mesenchymal Stromal Cells Is Regulated through Epithelial Sodium Channels

It has been suggested that mechanical strain may elicit cell differentiation in adult somatic cells through activation of epithelial sodium channels (ENaC). However, such phenomenon has not been previously demonstrated in mesenchymal stromal cells (MSCs). The present study was thus conducted to investigate the role of ENaC in human bone marrow-derived MSCs (hMSCs) tenogenic differentiation during uniaxial tensile loading. Passaged-2 hMSCs were seeded onto silicone chambers coated with collagen I and subjected to stretching at 1 Hz frequency and 8% strain for 6, 24, 48, and 72 hours. Analyses at these time points included cell morphology and alignment observation, immunocytochemistry and immunofluorescence staining (collagen I, collagen III, fibronectin, and N-cadherin), and gene expression (ENaC subunits, and tenogenic markers). Unstrained cells at similar time points served as the control group. To demonstrate the involvement of ENaC in the differentiation process, an ENaC blocker (benzamil) was used and the results were compared to the noninhibited hMSCs. ENaC subunits' (α, β, γ, and δ) expression was observed in hMSCs, although only α subunit was significantly increased during stretching. An increase in tenogenic genes' (collagen1, collagen3, decorin, tenascin-c, scleraxis, and tenomodulin) and proteins' (collagen I, collagen III, fibronectin, and N-cadherin) expression suggests that hMSCs underwent tenogenic differentiation when subjected to uniaxial loading. Inhibition of ENaC function resulted in decreased expression of these markers, thereby suggesting that ENaC plays a vital role in tenogenic differentiation of hMSCs during mechanical loading.

Quantitative Phosphoproteomics Reveals Cell Alignment and Mitochondrial Length Change under Cyclic Stretching in Lung Cells

Lung cancer is a leading cause of death. Most previous studies have been based on traditional cell-culturing methods. However, lung cells are periodically subjected to mechanical forces during breathing. Understanding the mechanisms underlying the cyclic stretching induced in lung cells may be important for lung cancer therapy. Here, we applied cyclic stretching to stimulate the continual contraction that is present under physiological conditions in lung cells. We first uncovered the stretching-induced phosphoproteome in lung cancer cell line A549 and fibroblast cell line IMR-90. We identified 2048 and 2604 phosphosites corresponding to 837 and 1008 phosphoproteins in A549 and IMR-90, respectively. Furthermore, we combined our phosphoproteomics and public gene expression data to identify the biological functions in response to cyclic stretching. Interestingly, cytoskeletal and mitochondrial reorganization were enriched. We further used cell imaging analysis to validate the profiling results and found that this physical force changed cell alignment and mitochondrial length. This study not only reveals the molecular mechanism of cyclic stretching but also provides evidence that cell stretching causes cellular rearrangement and mitochondrial length change.

Non-invasive respiratory support for the management of transient tachypnea of the newborn

BACKGROUND

Transient tachypnea of the newborn (TTN) is characterized by tachypnea and signs of respiratory distress. Transient tachypnea typically appears within the first two hours of life in term and late preterm newborns. Supportive management might be sufficient. Non-invasive (i.e. without endotracheal intubation) respiratory support may, however, be administered to reduce respiratory distress during TTN. In addition, non-invasive respiratory support might improve clearance of lung liquid thus reducing the effort required to breathe, improving respiratory distress and potentially reducing the duration of tachypnea.

OBJECTIVES

To assess benefits and harms of non-invasive respiratory support for the management of transient tachypnea of the newborn.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL; 2019, Issue 2), MEDLINE (1996 to 19 February 2019), Embase (1980 to 19 February 2019) and CINAHL (1982 to 19 February 2019). We applied no language restrictions. We searched clinical trial registries for ongoing studies.

SELECTION CRITERIA

Randomized controlled trials, quasi-randomized controlled trials and cluster trials on non-invasive respiratory support provided to infants born at 34 weeks' gestational age or more and less than three days of age with transient tachypnea of the newborn.

DATA COLLECTION AND ANALYSIS

For each of the included trials, two review authors independently extracted data (e.g. number of participants, birth weight, gestational age, duration of oxygen therapy, need for continuous positive airway pressure [CPAP] and need for mechanical ventilation, duration of mechanical ventilation, etc.) and assessed the risk of bias (e.g. adequacy of randomization, blinding, completeness of follow-up). The primary outcomes considered in this review were need for mechanical ventilation and pneumothorax. We used the GRADE approach to assess the certainty of evidence.

MAIN RESULTS

We included three trials (150 infants) comparing either CPAP to free-flow oxygen, nasal intermittent mandatory ventilation to nasal CPAP, or nasal high-frequency percussive ventilation versus nasal CPAP. Due to these different comparisons and to high clinical heterogeneity in the baseline clinical characteristics, we did not pool the three studies. The use of CPAP versus free oxygen did not improve the primary outcomes of this review: need for mechanical ventilation (risk ratio [RR] 0.30, 95% confidence interval [CI] 0.01 to 6.99; 1 study, 64 participants); and pneumothorax (not estimable, no cases occurred). Among secondary outcomes, CPAP reduced the duration of tachypnea as compared to free oxygen (mean difference [MD] -21.10 hours, 95% CI -22.92 to -19.28; 1 study, 64 participants). Nasal intermittent ventilation did not reduce the need for mechanical ventilation as compared with CPAP (RR 4.00, 95% CI 0.49 to 32.72; 1 study, 40 participants) or the incidence of pneumothorax (RR 1.00, 95% CI 0.07 to 14.90; 1 study, 40 participants); duration of tachypnea did not differ (MD 4.30, 95% CI -19.14 to 27.74; 1 study, 40 participants). In the study comparing nasal high-frequency ventilation to CPAP, no cases of mechanical ventilation of pneumothorax occurred (not estimable; 1 study, 46 participants); duration of tachypnea was reduced in the nasal high-frequency ventilation group (MD -4.53, 95% CI -5.64 to -3.42; 1 study, 46 participants). The quality of the evidence was very low due to the imprecision of the estimates and unclear risk of bias for detection bias and high risk of bias for reporting bias. Tests for heterogeneity were not applicable for any of the analyses as no studies were pooled. Two trials are ongoing.

AUTHORS' CONCLUSIONS

There is insufficient evidence to establish the benefit and harms of non-invasive respiratory support in the management of transient tachypnea of the newborn. Though two of the included trials showed a shorter duration of tachypnea, clinically relevant outcomes did not differ amongst the groups. Given the limited and low quality of the evidence available, it was impossible to determine whether non-invasive respiratory support was safe or effective for the treatment of transient tachypnea of the newborn.

IL-1 promotes α-epithelial Sodium Channel (α-ENaC) expression in murine lung epithelial cells: involvement of NF-κB

Intra-amniotic exposure to proinflammatory cytokines such as interleukin-1 (IL-1) correlates with a decreased incidence of respiratory distress syndrome (RDS) in infants following premature birth. At birth, inadequate absorption of fluid from the fetal lung contributes to the onset RDS. Lung fluid clearance is coupled to Na⁺ transport via epithelial sodium channels (ENaC). In this study, we assessed the effects of IL-1 on the expression of ENaC, particularly the α-subunit which is critical for fetal lung fluid clearance at birth. Cultured mouse lung epithelial (MLE-12) cells were treated with either IL-1α or IL-1β to determine their effects on α-ENaC expression. Changes in IL-1-induced α-ENaC levels in the presence of IL-1 receptor antagonist (IL-1ra), cycloheximide, NF-κB inhibitor, and MAP kinase inhibitors were investigated. IL-1α and IL-1β independently induced a significant increase of α-ENaC mRNA and protein after 24 h compared to untreated cells. IL-1-dependent increases in α-ENaC protein were mitigated by IL-1ra and cycloheximide. IL-1 exposure induced NF-κB binding activity. Attenuation of IL-1-induced NF-κB activation by its inhibitor SN50 decreased α-ENaC protein abundance. Inhibition of ERK 1,2 MAPK significantly decreased both IL-1α and β-induced α-ENaC protein expression whereas inhibition of p38 MAPK only blocked IL-1β-induced α-ENaC protein levels. In contrast, IL-1-induced α-ENaC protein levels were unaffected by a c-Jun N-terminal kinase (JNK) inhibitor. Our results suggest that in MLE-12 cells, IL-1-induced elevation of α-ENaC is mediated via NF-κB activation and in part involves stimulation of the ERK 1,2 and p38 MAPK signaling pathways.

A New Role for the Mitochondrial Pro-apoptotic Protein SMAC/Diablo in Phospholipid Synthesis Associated with Tumorigenesis

The mitochondrial pro-apoptotic protein SMAC/Diablo participates in apoptosis by negatively regulating IAPs and activating caspases, thus encouraging apoptosis. Unexpectedly, we found that SMAC/Diablo is overexpressed in cancer. This paradox was addressed here by silencing SMAC/Diablo expression using specific siRNA (si-hSMAC). In cancer cell lines and subcutaneous lung cancer xenografts in mice, such silencing reduced cell and tumor growth. Immunohistochemistry and electron microscopy of the si-hSMAC-treated residual tumor demonstrated morphological changes, including cell differentiation and reorganization into glandular/alveoli-like structures and elimination of lamellar bodies, surfactant-producing organs. Next-generation sequencing of non-targeted or si-hSMAC-treated tumors revealed altered expression of genes associated with the cellular membrane and extracellular matrix, of genes found in the ER and Golgi lumen and in exosomal networks, of genes involved in lipid metabolism, and of lipid, metabolite, and ion transporters. SMAC/Diablo silencing decreased the levels of phospholipids, including phosphatidylcholine. These findings suggest that SMAC/Diablo possesses additional non-apoptotic functions related to regulating lipid synthesis essential for cancer growth and development and that this may explain SMAC/Diablo overexpression in cancer. The new lipid synthesis-related function of the pro-apoptotic protein SMAC/Diablo in cancer cells makes SMAC/Diablo a promising therapeutic target.

The role of stretch-activated ion channels in acute respiratory distress syndrome: finally a new target?

Mechanical ventilation (MV) and oxygen therapy (hyperoxia; HO) comprise the cornerstones of life-saving interventions for patients with acute respiratory distress syndrome (ARDS). Unfortunately, the side effects of MV and HO include exacerbation of lung injury by barotrauma, volutrauma, and propagation of lung inflammation. Despite significant improvements in ventilator technologies and a heightened awareness of oxygen toxicity, besides low tidal volume ventilation few if any medical interventions have improved ARDS outcomes over the past two decades. We are lacking a comprehensive understanding of mechanotransduction processes in the healthy lung and know little about the interactions between simultaneously activated stretch-, HO-, and cytokine-induced signaling cascades in ARDS. Nevertheless, as we are unraveling these mechanisms we are gathering increasing evidence for the importance of stretch-activated ion channels (SACs) in the activation of lung-resident and inflammatory cells. In addition to the discovery of new SAC families in the lung, e.g., two-pore domain potassium channels, we are increasingly assigning mechanosensing properties to already known Na(+), Ca(2+), K(+), and Cl(-) channels. Better insights into the mechanotransduction mechanisms of SACs will improve our understanding of the pathways leading to ventilator-induced lung injury and lead to much needed novel therapeutic approaches against ARDS by specifically targeting SACs. This review 1) summarizes the reasons why the time has come to seriously consider SACs as new therapeutic targets against ARDS, 2) critically analyzes the physiological and experimental factors that currently limit our knowledge about SACs, and 3) outlines the most important questions future research studies need to address.