Caspase 8 deletion causes infection/inflammation-induced bone marrow failure and MDS-like disease in mice.

Myelodysplastic syndromes (MDS) are a heterogeneous group of pre-leukemic hematopoietic disorders characterized by cytopenia in peripheral blood due to ineffective hematopoiesis and normo- or hypercellularity and morphologic dysplasia in bone marrow (BM). An inflammatory BM microenvironment and programmed cell death of hematopoietic stem/progenitor cells (HSPCs) are thought to be the major causes of ineffective hematopoiesis in MDS. Pyroptosis, apoptosis and necroptosis (collectively, PANoptosis) are observed in BM tissues of MDS patients, suggesting an important role of PANoptosis in MDS pathogenesis. Caspase 8 (Casp8) is a master regulator of PANoptosis, which is downregulated in HSPCs from most MDS patients and abnormally spliced in HSPCs from MDS patients with SRSF2 mutation. To study the role of PANoptosis in hematopoiesis, we generated inducible Casp8 knockout mice (Casp8-/-). Mx1-Cre-Casp8-/- mice died of BM failure within 10 days of polyI:C injections due to depletion of HSPCs. Rosa-ERT2Cre-Casp8-/- mice are healthy without significant changes in BM hematopoiesis within the first 1.5 months after Casp8 deletion. Such mice developed BM failure upon infection or low dose polyI:C/LPS injections due to the hypersensitivity of Casp8-/- HSPCs to infection or inflammation-induced necroptosis which can be prevented by Ripk3 deletion. However, impaired self-renewal capacity of Casp8-/- HSPCs cannot be rescued by Ripk3 deletion due to activation of Ripk1-Tbk1 signaling. Most importantly, mice transplanted with Casp8-/- BM cells developed MDS-like disease within 4 months of transplantation as demonstrated by anemia, thrombocytopenia and myelodysplasia. Our study suggests an essential role for a balance in Casp8, Ripk3-Mlkl and Ripk1-Tbk1 activities in the regulation of survival and self-renewal of HSPCs, the disruption of which induces inflammation and BM failure, resulting in MDS-like disease.

Distinct roles of hematopoietic cytokines in the regulation of leukemia stem cells in murine MLL-AF9 leukemia.

Lymphoid-primed multipotent progenitor (LMPP)-like and granulocyte-monocyte progenitor (GMP)-like leukemia stem cells (LSCs) co-exist in the blood of most patients with acute myeloid leukemia (AML). Complete elimination of both types of LSCs is required to cure AML. Using an MLL-AF9-induced murine AML model, we studied the role of hematopoietic cytokines in the survival of LMPP- and GMP-like LSCs. We found that SCF or FLT3L promotes the survival of LMPP-like LSCs by stimulating Stat5-mediated Mcl1 expression, whereas interleukin-3 (IL-3) or IL-6 induces the survival of GMP-like LSCs by stimulating Stat3/nuclear factor κB (NF-κB)-mediated Bcl2 expression. Functional study demonstrated that, compared to AML cells cultured in IL-3 and IL-6 medium, AML cells in SCF- or Flt3L-only culture are highly clonogenic in in vitro culture and are highly leukemogenic in vivo. Our study suggests that co-inhibition of both STAT5-MCL1 and STAT3/NF-κB-BCL2 signaling might represent an improved treatment strategy against AML, specifically AML cases with a monocytic phenotype and/or FLT3 mutations.

Biomarkers and molecular endotypes of sarcoidosis: lessons from omics and non-omics studies.

Sarcoidosis is a chronic granulomatous disorder characterized by unknown etiology, undetermined mechanisms, and non-specific therapies except TNF blockade. To improve our understanding of the pathogenicity and to predict the outcomes of the disease, the identification of new biomarkers and molecular endotypes is sorely needed. In this study, we systematically evaluate the biomarkers identified through Omics and non-Omics approaches in sarcoidosis. Most of the currently documented biomarkers for sarcoidosis are mainly identified through conventional "one-for-all" non-Omics targeted studies. Although the application of machine learning algorithms to identify biomarkers and endotypes from unbiased comprehensive Omics studies is still in its infancy, a series of biomarkers, overwhelmingly for diagnosis to differentiate sarcoidosis from healthy controls have been reported. In view of the fact that current biomarker profiles in sarcoidosis are scarce, fragmented and mostly not validated, there is an urgent need to identify novel sarcoidosis biomarkers and molecular endotypes using more advanced Omics approaches to facilitate disease diagnosis and prognosis, resolve disease heterogeneity, and facilitate personalized medicine.

MetaLP: An integrative linear programming method for protein inference in metaproteomics.

Metaproteomics based on high-throughput tandem mass spectrometry (MS/MS) plays a crucial role in characterizing microbiome functions. The acquired MS/MS data is searched against a protein sequence database to identify peptides, which are then used to infer a list of proteins present in a metaproteome sample. While the problem of protein inference has been well-studied for proteomics of single organisms, it remains a major challenge for metaproteomics of complex microbial communities because of the large number of degenerate peptides shared among homologous proteins in different organisms. This challenge calls for improved discrimination of true protein identifications from false protein identifications given a set of unique and degenerate peptides identified in metaproteomics. MetaLP was developed here for protein inference in metaproteomics using an integrative linear programming method. Taxonomic abundance information extracted from metagenomics shotgun sequencing or 16s rRNA gene amplicon sequencing, was incorporated as prior information in MetaLP. Benchmarking with mock, human gut, soil, and marine microbial communities demonstrated significantly higher numbers of protein identifications by MetaLP than ProteinLP, PeptideProphet, DeepPep, PIPQ, and Sipros Ensemble. In conclusion, MetaLP could substantially improve protein inference for complex metaproteomes by incorporating taxonomic abundance information in a linear programming model.

Stem cell therapy for COVID-19 and other respiratory diseases: Global trends of clinical trials.

Respiratory diseases, including coronavirus disease 2019 and chronic obstructive pulmonary disease (COPD), are leading causes of global fatality. There are no effective and curative treatments, but supportive care only. Cell therapy is a promising therapeutic strategy for refractory and unmanageable pulmonary illnesses, as proved by accumulating preclinical studies. Stem cells consist of totipotent, pluripotent, multipotent, and unipotent cells with the potential to differentiate into cell types requested for repair. Mesenchymal stromal cells, endothelial progenitor cells, peripheral blood stem cells, and lung progenitor cells have been applied to clinical trials. To date, the safety and feasibility of stem cell and extracellular vesicles administration have been confirmed by numerous phase I/II trials in patients with COPD, acute respiratory distress syndrome, bronchial dysplasia, idiopathic pulmonary fibrosis, pulmonary artery hypertension, and silicosis. Five routes and a series of doses have been tested for tolerance and advantages of different regimes. In this review, we systematically summarize the global trends for the cell therapy of common airway and lung diseases registered for clinical trials. The future directions for both new clinical trials and preclinical studies are discussed.

Ion transport mechanisms for smoke inhalation-injured airway epithelial barrier.

Smoke inhalation injury is the leading cause of death in firefighters and victims. Inhaled hot air and toxic smoke are the predominant hazards to the respiratory epithelium. We aimed to analyze the effects of thermal stress and smoke aldehyde on the permeability of the airway epithelial barrier. Transepithelial resistance (RTE) and short-circuit current (ISC) of mouse tracheal epithelial monolayers were digitized by an Ussing chamber setup. Zonula occludens-1 tight junctions were visualized under confocal microscopy. A cell viability test and fluorescein isothiocyanate-dextran assay were performed. Thermal stress (40 °C) decreased RTE in a two-phase manner. Meanwhile, thermal stress increased ISC followed by its decline. Na+ depletion, amiloride (an inhibitor for epithelial Na+ channels [ENaCs]), ouabain (a blocker for Na+/K+-ATPase), and CFTRinh-172 (a blocker of cystic fibrosis transmembrane regulator [CFTR]) altered the responses of RTE and ISC to thermal stress. Steady-state 40 °C increased activity of ENaCs, Na+/K+-ATPase, and CFTR. Acrolein, one of the main oxidative unsaturated aldehydes in fire smoke, eliminated RTE and ISC. Na+ depletion, amiloride, ouabain, and CFTRinh-172 suppressed acrolein-sensitive ISC, but showed activating effects on acrolein-sensitive RTE. Thermal stress or acrolein disrupted zonula occludens-1 tight junctions, increased fluorescein isothiocyanate-dextran permeability but did not cause cell death or detachment. The synergistic effects of thermal stress and acrolein exacerbated the damage to monolayers. In conclusion, the paracellular pathway mediated by the tight junctions and the transcellular pathway mediated by active and passive ion transport pathways contribute to impairment of the airway epithelial barrier caused by thermal stress and acrolein. Graphical abstract Thermal stress and acrolein are two essential determinants for smoke inhalation injury, impairing airway epithelial barrier. Transcellular ion transport pathways via the ENaC, CFTR, and Na/K-ATPase are interrupted by both thermal stress and acrolein, one of the most potent smoke toxins. Heat and acrolein damage the integrity of the airway epithelium through suppressing and relocating the tight junctions.

TRIM72 promotes alveolar epithelial cell membrane repair and ameliorates lung fibrosis.

BACKGROUND: Chronic tissue injury was shown to induce progressive scarring in fibrotic diseases such as idiopathic pulmonary fibrosis (IPF), while an array of repair/regeneration and stress responses come to equilibrium to determine the outcome of injury at the organ level. In the lung, type I alveolar epithelial (ATI) cells constitute the epithelial barrier, while type II alveolar epithelial (ATII) cells play a pivotal role in regenerating the injured distal lungs. It had been demonstrated that eukaryotic cells possess repair machinery that can quickly patch the damaged plasma membrane after injury, and our previous studies discovered the membrane-mending role of Tripartite motif containing 72 (TRIM72) that expresses in a limited number of tissues including the lung. Nevertheless, the role of alveolar epithelial cell (AEC) repair in the pathogenesis of IPF has not been examined yet. METHOD: In this study, we tested the specific roles of TRIM72 in the repair of ATII cells and the development of lung fibrosis. The role of membrane repair was accessed by saponin assay on isolated primary ATII cells and rat ATII cell line. The anti-fibrotic potential of TRIM72 was tested with bleomycin-treated transgenic mice. RESULTS: We showed that TRIM72 was upregulated following various injuries and in human IPF lungs. However, TRIM72 expression in ATII cells of the IPF lungs had aberrant subcellular localization. In vitro studies showed that TRIM72 repairs membrane injury of immortalized and primary ATIIs, leading to inhibition of stress-induced p53 activation and reduction in cell apoptosis. In vivo studies demonstrated that TRIM72 protects the integrity of the alveolar epithelial layer and reduces lung fibrosis. CONCLUSION: Our results suggest that TRIM72 protects injured lungs and ameliorates fibrosis through promoting post-injury repair of AECs.

Plasmin improves blood-gas barrier function in oedematous lungs by cleaving epithelial sodium channels.

BACKGROUND AND PURPOSE: Lung oedema in association with suppressed fibrinolysis is a hallmark of lung injury. Here, we have tested whether plasmin cleaves epithelial sodium channels (ENaC) to resolve lung oedema fluid. EXPERIMENTAL APPROACH: Human lungs and airway acid-instilled mice were used for analysing fluid resolution. In silico prediction, mutagenesis, Xenopus oocytes, immunoblotting, voltage clamp, mass spectrometry, and protein docking were combined for identifying plasmin cleavage sites. KEY RESULTS: Plasmin improved lung fluid resolution in both human lungs ex vivo and injured mice. Plasmin activated αßγENaC channels in oocytes in a time-dependent manner. Deletion of four consensus proteolysis tracts (αΔ432-444, γΔ131-138, γΔ178-193, and γΔ410-422) eliminated plasmin-induced activation significantly. Further, immunoblotting assays identified 7 cleavage sites (K126, R135, K136, R153, K168, R178, K179) for plasmin to trim both furin-cleaved C-terminal fragments and full-length human γENaC proteins. In addition, 9 new sites (R122, R137, R138, K150, K170, R172, R180, K181, K189) in synthesized peptides were found to be cleaved by plasmin. These cleavage sites were located in the finger and the thumb, particularly the GRIP domain of human ENaC 3D model composed of two proteolytic centres for plasmin. Novel uncleaved sites beyond the GRIP domain in both α and γ subunits were identified to interrupt the plasmin cleavage-induced conformational change in ENaC channel complexes. Additionally, plasmin could regulate ENaC activity via the G protein signal. CONCLUSION AND IMPLICATIONS: Plasmin can cleave ENaC to improve blood-gas exchange by resolving oedema fluid and could be a potent therapy for oedematous lungs.

Concise Review: Therapeutic Potential of the Mesenchymal Stem Cell Derived Secretome and Extracellular Vesicles for Radiation-Induced Lung Injury: Progress and Hypotheses.

Radiation-induced lung injury (RILI) is a common complication in radiotherapy of thoracic tumors and limits the therapeutic dose of radiation that can be given to effectively control tumors. RILI develops through a complex pathological process, resulting in induction and activation of various cytokines, infiltration by inflammatory cells, cytokine-induced activation of fibroblasts, and subsequent tissue remodeling by activated fibroblasts, ultimately leading to impaired lung function and respiratory failure. Increasing evidence shows that mesenchymal stem cells (MSCs) may play a main role in modulating inflammation and immune responses, promoting survival and repair of damaged resident cells and enhancing regeneration of damaged tissue through soluble paracrine factors and therapeutic extracellular vesicles. Therefore, the use of the MSC-derived secretome and exosomes holds promising potential for RILI therapy. Here, we review recent progress on the potential mechanisms of MSC therapy for RILI, with an emphasis on soluble paracrine factors of MSCs. Hypotheses on how MSC derived exosomes or MSC-released exosomal miRNAs could attenuate RILI are also proposed. Problems and translational challenges of the therapies based on the MSC-derived secretome and exosomes are further summarized and underline the need for caution on rapid clinical translation. Stem Cells Translational Medicine 2019;8:344-354.

Flavonoids of Rosa roxburghii Tratt offers protection against radiation induced apoptosis and inflammation in mouse thymus.

The present study evaluated the protective effect of the natural compound flavonoids of Rosa roxburghii Tratt (FRT) against γ-radiation-induced apoptosis and inflammation in mouse thymus cells in vivo and in vitro. Thymus cells and mice were exposed to 60Co γ-ray at a dose of 6 Gy. The radiation treatment induced significant cell apoptosis and inflammation. Radiation increased the expressions of cleaved caspase 3/8-10, AIF, and PARP-1, and FRT could mitigate their activation and inhibit subsequent apoptosis in the thymus both in vitro or in vivo. Irradiation increased the mRNA expression of ICAM-1/VCAM-1, IL-1α/IL-6 and TNF-α/NF-κB. Our results also indicated that FRT alleviated gene expression of some inflammatory factors such as ICAM-1/VCAM-1, TNF-α/NF-κB, but not IL-1α/IL-6. Irradiation increased the protein expression levels of ICAM-1/VCAM-1, IL-1α/IL-6 and TNF-α/NF-Κb, and our results also indicated that FRT alleviated protein level expression of certain inflammatory factors such as ICAM-1, IL-1α/IL-6, TNF-α/NF-κB, but not VCAM-1. Our results suggested that FRT enhanced radioprotection at least partially by regulating caspase 3/8-10, AIF, and PARP-1 to reduce apoptosis and by regulating ICAM-1, IL-1α/IL-6, TNF-α/NF-κB to reduce inflammation.

Transepithelial Fluid and Salt Re-Absorption Regulated by cGK2 Signals.

Transepithelial fluid and salt re-absorption in epithelial tissues play an important role in fluid and salt homeostasis. In absorptive epithelium, fluid and salt flux is controlled by machinery mainly composed of epithelial sodium channels (ENaC), cystic fibrosis transmembrane conductance regulator (CFTR), Na⁺/H⁺ exchanger (NHE), aquaporin, and sodium potassium adenosine triphosphatase (Na⁺/K⁺-ATPase). Dysregulation of fluid and salt transport across epithelium contributes to the pathogenesis of many diseases, such as pulmonary edema and cystic fibrosis. Intracellular and extracellular signals, i.e., hormones and protein kinases, regulate fluid and salt turnover and resolution. Increasing evidence demonstrates that transepithelial fluid transport is regulated by cyclic guanosine monophosphate-dependent protein kinase (cGK) signals. cGK2 was originally identified and cloned from intestinal specimens, the presence of which has also been confirmed in the kidney and the lung. cGK2 regulates fluid and salt through ENaC, CFTR and NHE. Deficient cGK2 regulation of transepithelial ion transport was seen in acute lung injury, and cGK2 could be a novel druggable target to restore edematous disorder in epithelial tissues.

Gene editing as a promising approach for respiratory diseases.

Respiratory diseases, which are leading causes of mortality and morbidity in the world, are dysfunctions of the nasopharynx, the trachea, the bronchus, the lung and the pleural cavity. Symptoms of chronic respiratory diseases, such as cough, sneezing and difficulty breathing, may seriously affect the productivity, sleep quality and physical and mental well-being of patients, and patients with acute respiratory diseases may have difficulty breathing, anoxia and even life-threatening respiratory failure. Respiratory diseases are generally heterogeneous, with multifaceted causes including smoking, ageing, air pollution, infection and gene mutations. Clinically, a single pulmonary disease can exhibit more than one phenotype or coexist with multiple organ disorders. To correct abnormal function or repair injured respiratory tissues, one of the most promising techniques is to correct mutated genes by gene editing, as some gene mutations have been clearly demonstrated to be associated with genetic or heterogeneous respiratory diseases. Zinc finger nucleases (ZFN), transcription activator-like effector nucleases (TALEN) and clustered regulatory interspaced short palindromic repeats/CRISPR-associated protein 9 (CRISPR/Cas9) systems are three innovative gene editing technologies developed recently. In this short review, we have summarised the structure and operating principles of the ZFNs, TALENs and CRISPR/Cas9 systems and their preclinical and clinical applications in respiratory diseases.

A new and important relationship between miRNA-147a and PDPK1 in radiotherapy.

It was found that the expression level of miR-147a was significantly increased and the pathway of PI3K/AKT was dramatically inhibited after radiation. In view of the relationship between miRNA and target genes, we put forward the question, what is the relationship between PI3K/AKT and miR-147a? In order to find the answer to the question, we used bioinformatics techniques to analyze the relationship between miR-147 (a or b) and PI3K/AKT signaling pathway. miR-147a overexpression plasmid and PDPK1 3'UTR luciferase reporter gene plasmid were constructed. Dual luciferase reporter gene system validation experiments were carried out on miR-147a and PDPK1 relationship. The verification experiments were also carried out. Bioinformatics analysis showed that there is a miR-147a binding site in the non-coding region (3'UTR) of PDPK1. In the experimental groups transfected with wild type PDPK1 gene of 3'UTR plasmid, the luciferase activity decreased (or increased) significantly in miR-147a (or inhibitor) group compared with miR-NC (or anti-miR-NC); There was no significant difference between the miR-147a group (or inhibitor) and the miR-NC group (or anti-miR-NC) in the transfection of PDPK1-3'UTR-Mut gene vector. PDPK1 was a target gene for direct regulation of miR-147a downstream. Verifying test results showed that the expression of PDPK1 mRNA and protein was reduced after overexpression of miR-147a, which was up-regulated after silencing miR-147a in TC, and V79 cells. These results suggest that miR-147a could be involved in the regulation of PDPK1 transcription by binding to the target site in PDPK1 mRNA 3'UTR, and then regulated AKT.

Novel mechanisms for crotonaldehyde-induced lung edema.

BACKGROUND: Crotonaldehyde is a highly noxious α,ß-unsaturated aldehyde in cigarette smoke that causes edematous acute lung injury. OBJECTIVE: To understand how crotonaldehyde impairs lung function, we examined its effects on human epithelial sodium channels (ENaC), which are major contributors to alveolar fluid clearance. METHODS: We studied alveolar fluid clearance in C57 mice and ENaC activity was examined in H441 cells. Expression of α- and γ-ENaC was measured at protein and mRNA levels by western blot and real-time PCR, respectively. Intracellular ROS levels were detected by the dichlorofluorescein assay. Heterologous αßγ-ENaC activity was observed in an oocyte model. RESULTS: Our results showed that crotonaldehyde reduced transalveolar fluid clearance in mice. Furthermore, ENaC activity in H441 cells was inhibited by crotonaldehyde dose-dependently. Expression of α- and γ-subunits of ENaC was decreased at the protein and mRNA level in H441 cells exposed to crotonaldehyde, which was probably mediated by the increase in phosphorylated extracellular signal-regulated protein kinases 1 and 2. ROS levels increased time-dependently in cells exposed to crotonaldehyde. Heterologous αßγ-ENaC activity was rapidly eliminated by crotonaldehyde. CONCLUSION: Our findings suggest that crotonaldehyde causes edematous acute lung injury by eliminating ENaC activity at least partly via facilitating the phosphorylation of extracellular signal-regulated protein kinases 1 and 2 signal molecules. Long-term exposure may decrease the expression of ENaC subunits and damage the cell membrane integrity, as well as increase the levels of cellular ROS products.

Serious adverse events of cell therapy for respiratory diseases: a systematic review and meta-analysis.

BACKGROUND: Cell therapy holds the most promising for acute and chronic deleterious respiratory diseases. However, the safety and tolerance for lung disorders are controversy. METHODS: We undertook a systematic review and meta-analyses of all 23 clinical studies of cell therapy. The outcomes were odds ratio (OR), risk difference (RD), Peto OR, relative risk, and mean difference of serious adverse events. RESULTS: 342 systemic infusions and 57 bronchial instillations (204 recipients) of cells were analyzed for acute respiratory distress syndrome (ARDS), bronchopulmonary dysplasia, pulmonary arterial hypertension, silicosis, sarcoidosis, extensively drug-resistant tuberculosis, chronic obstructive pulmonary diseases (COPD), and idiopathic pulmonary fibrosis. The frequency of death in adults from any causes was 71 and 177 per 1,000 for cell therapy and controls, respectively, with an OR of 0.31 (95% CI: 0.03, 3.76) and RD of -0.22 (95% CI: -0.53, 0.09). No significant difference was found for ARDS and COPD. The frequency of deaths and non-fatal serious adverse events of 17 open studies were similar to those of randomized controlled trials. Moreover, serious adverse events of allogenic cells were greater than autologous preparations, as shown by frequency, OR and RD. CONCLUSIONS: We conclude that either infusion or instillation of mesenchymal stem stromal or progenitor cells are well tolerated without serious adverse events causally related to cell treatment. Cell therapy has not been associated with significant changes in spirometry, immune function, cardiovascular activity, and the quality of life.

Formaldehyde impairs transepithelial sodium transport.

Unsaturated oxidative formaldehyde is a noxious aldehyde in cigarette smoke that causes edematous acute lung injury. However, the mechanistic effects of formaldehyde on lung fluid transport are still poorly understood. We examined how formaldehyde regulates human epithelial sodium channels (ENaC) in H441 and expressed in Xenopus oocytes and exposed mice in vivo. Our results showed that formaldehyde reduced mouse transalveolar fluid clearance in vivo. Formaldehyde caused a dose-dependent inhibition of amiloride-sensitive short-circuit Na+ currents in H441 monolayers and of αßγ-ENaC channel activity in oocytes. α-ENaC protein was reduced, whereas phosphorylation of the extracellular regulated protein kinases 1 and 2 (ERK1/2) increased significantly post exposure. Moreover, both α- and γ-ENaC transcripts were down-regulated. Reactive oxygen species (ROS) was elevated significantly by formaldehyde in addition to markedly augmented membrane permeability of oocytes. These data suggest that formaldehyde contributes to edematous acute lung injury by reducing transalveolar Na+ transport, through decreased ENaC activity and enhanced membrane depolarization, and by elevating ROS production over long-term exposure.

ENaC/DEG in Tumor Development and Progression.

The epithelial Na+ channel/degenerin (ENaC/DEG) superfamily, including the acid-sensing ion channels (ASICs), is characterized by a high degree of similarity in structure but highly diverse in physiological functions. These ion channels have been shown to be important in several physiological functions of normal epithelial cells, including salt homeostasis, fluid transportation and cell mobility. There is increasing evidence suggesting that ENaC/DEG channels are critically engaged in cancer cell biology, such as proliferation, migration, invasion and apoptosis, playing a role in tumor development and progression. In this review, we will discuss recent studies showing the role of ENaC and ASIC channels in epithelial cells and its relationship to the oncogenesis.

Systematic review and meta-analysis of nasal potential difference in hypoxia-induced lung injury.

Nasal potential difference (NPD), a well-established in vivo clinical test for cystic fibrosis, reflects transepithelial cation and anion transport in the respiratory epithelium. To analyze whether NPD can be applied to diagnose hypoxic lung injury, we searched PubMed, EMBASE, Scopus, Web of Science, Ovid MEDLINE, and Google Scholar, and analyzed data retrieved from eleven unbiased studies for high altitude pulmonary edema (HAPE) and respiratory distress syndrome (RDS) using the software RevMan and R. There was a significant reduction in overall basal (WMD -5.27 mV, 95% CI: -6.03 to -4.52, P < 0.00001, I(2) = 42%), amiloride-sensitive (ENaC) (-2.87 mV, 95% CI: -4.02 to -1.72, P < 0.00001, I(2) = 51%), and -resistant fractions (-3.91 mV, 95% CI: -7.64 to -0.18, P = 0.04, I(2) = 95%) in lung injury patients. Further analysis of HAPE and RDS separately corroborated these observations. Moreover, SpO2 correlated with ENaC-associated NPD positively in patients only, but apparently related to CFTR-contributed NPD level inversely. These correlations were confirmed by the opposite associations between NPD values and altitude, which had a negative regression with SpO2 level. Basal NPD was significantly associated with amiloride-resistant but not ENaC fraction. Our analyses demonstrate that acute lung injury associated with systemic hypoxia is characterized by dysfunctional NPD.

Epithelial Sodium Channels in Pulmonary Epithelial Progenitor and Stem Cells.

Regeneration of the epithelium of mammalian lungs is essential for restoring normal function following injury, and various cells and mechanisms contribute to this regeneration and repair. Club cells, bronchioalveolar stem cells (BASCs), and alveolar type II epithelial cells (ATII) are dominant stem/progenitor cells for maintaining epithelial turnover and repair. Epithelial Na(+) channels (ENaC), a critical pathway for transapical salt and fluid transport, are expressed in lung epithelial progenitors, including club and ATII cells. Since ENaC activity and expression are development- and differentiation-dependent, apically located ENaC activity has therefore been used as a functional biomarker of lung injury repair. ENaC activity may be involved in the migration and differentiation of local and circulating stem/progenitor cells with diverse functions, eventually benefiting stem cells spreading to re-epithelialize injured lungs. This review summarizes the potential roles of ENaC expressed in native progenitor and stem cells in the development and regeneration of the respiratory epithelium.

Potential Roles of Amiloride-Sensitive Sodium Channels in Cancer Development.

The ENaC/degenerin ion channel superfamily includes the amiloride-sensitive epithelial sodium channel (ENaC) and acid sensitive ionic channel (ASIC). ENaC is a multimeric ion channel formed by heteromultimeric membrane glycoproteins, which participate in a multitude of biological processes by mediating the transport of sodium (Na(+)) across epithelial tissues such as the kidney, lungs, bladder, and gut. Aberrant ENaC functions contribute to several human disease states including pseudohypoaldosteronism, Liddle syndrome, cystic fibrosis, and salt-sensitive hypertension. Increasing evidence suggests that ion channels not only regulate ion homeostasis and electric signaling in excitable cells but also play important roles in cancer cell behaviors such as proliferation, apoptosis, invasion, and migration. Indeed, ENaCs/ASICs had been reported to be associated with cancer characteristics. Given their cell surface localization and pharmacology, pharmacological strategies to target ENaC/ASIC family members may be promising cancer therapeutics.