scholarly journals The role of hypoxia-induced modulation of alveolar epithelial Na+- transport in hypoxemia at high altitude

2020 ◽  
Vol 10 (1_suppl) ◽  
pp. 50-58
Author(s):  
Emel Baloglu ◽  
Gabriel Nonnenmacher ◽  
Anna Seleninova ◽  
Lena Berg ◽  
Kalpana Velineni ◽  
...  
Keyword(s):  
Gas Exchange ◽  
High Altitude ◽  
Active Form ◽  
Alveolar Epithelium ◽  
Alveolar Epithelial Cells ◽  
Laboratory Animals ◽  
Apical Plasma Membrane ◽  
Alveolar Epithelial ◽  
Pulmonary Vasoconstriction

Reabsorption of excess alveolar fluid is driven by vectorial Na+-transport across alveolar epithelium, which protects from alveolar flooding and facilitates gas exchange. Hypoxia inhibits Na+-reabsorption in cultured cells and in-vivo by decreasing activity of epithelial Na+-channels (ENaC), which impairs alveolar fluid clearance. Inhibition also occurs during in-vivo hypoxia in humans and laboratory animals. Signaling mechanisms that inhibit alveolar reabsorption are poorly understood. Because cellular adaptation to hypoxia is regulated by hypoxia-inducible transcription factors (HIF), we tested whether HIFs are involved in decreasing Na+-transport in hypoxic alveolar epithelium. Expression of HIFs was suppressed in cultured rat primary alveolar epithelial cells (AEC) with shRNAs. Hypoxia (1.5% O2, 24 h) decreased amiloride-sensitive transepithelial Na+-transport, decreased the mRNA expression of α-, β-, and γ-ENaC subunits, and reduced the amount of αβγ-ENaC subunits in the apical plasma membrane. Silencing HIF-2α partially prevented impaired fluid reabsorption in hypoxic rats and prevented the hypoxia-induced decrease in α- but not the βγ-subunits of ENaC protein expression resulting in a less active form of ENaC in hypoxic AEC. Inhibition of alveolar reabsorption also caused pulmonary vasoconstriction in ventilated rats. These results indicate that a HIF-2α-dependent decrease in Na+-transport in hypoxic alveolar epithelium decreases alveolar reabsorption. Because susceptibles to high-altitude pulmonary edema (HAPE) have decreased Na+-transport even in normoxia, inhibition of alveolar reabsorption by hypoxia at high altitude might further impair alveolar gas exchange. Thus, aggravated hypoxemia might further enhance hypoxic pulmonary vasoconstriction and might subsequently cause HAPE.

Impairment of cation transport in A549 cells and rat alveolar epithelial cells by hypoxia

1997 ◽  
Vol 273 (4) ◽  
pp. L797-L806 ◽  
Author(s):  
Heimo Mairbäurl ◽  
Ralf Wodopia ◽  
Sigrid Eckes ◽  
Susanne Schulz ◽  
Peter Bärtsch
Keyword(s):  
Epithelial Cells ◽  
A549 Cells ◽  
Alveolar Epithelium ◽  
Cell Types ◽  
Cation Transport ◽  
Alveolar Epithelial Cells ◽  
Alveolar Type ◽  
Water Reabsorption ◽  
Alveolar Epithelial

A reduced cation reabsorption across the alveolar epithelium decreases water reabsorption from the alveoli and could diminish clearing accumulated fluid. To test whether hypoxia restricts cation transport in alveolar epithelial cells, cation uptake was measured in rat lung alveolar type II pneumocytes (AII cells) in primary culture and in A549 cells exposed to normoxia and hypoxia. In AII and A549 cells, hypoxia caused a[Formula: see text]-dependent inhibition of the Na-K pump, of Na-K-2Cl cotransport, and of total and amiloride-sensitive22Na uptake. Nifedipine failed to prevent hypoxia-induced transport inhibition in both cell types. In A549 cells, the inhibition of the Na-K pump and Na-K-2Cl cotransport occurred within ∼30 min of hypoxia, was stable >20 h, and was reversed by 2 h of reoxygenation. There was also a reduction in cell membrane-associated Na-K-ATPase and a decrease in Na-K-2Cl cotransport flux after full activation with calyculin A, indicating a decreased transport capacity. [14C]serine incorporation into cell proteins was reduced in hypoxic A549 cells, but inhibition of protein synthesis with cycloheximide did not reduce ion transport. In AII and A549 cells, ATP levels decreased slightly, and ADP and the ATP-to-ADP ratio were unchanged after 4 h of hypoxia. In A549 cells, lactate, intracellular Na, and intracellular K were unchanged. These results indicate that hypoxia inhibits apical Na entry pathways and the basolateral Na-K pump in A549 cells and rat AII pneumocytes in culture, indicating a hypoxia-induced reduction of transepithelial Na transport and water reabsorption by alveolar epithelium. If similar changes occur in vivo, the impaired cation transport across alveolar epithelial cells might contribute to the formation of hypoxic pulmonary edema.

scholarly journals Alveolar Epithelial Cells in Mycobacterium tuberculosis Infection: Active Players or Innocent Bystanders?

2015 ◽  
Vol 8 (1) ◽  
pp. 3-14 ◽  
Author(s):  
Julia M. Scordo ◽  
Daren L. Knoell ◽  
Jordi B. Torrelles
Keyword(s):  
Mycobacterium Tuberculosis ◽  
Alveolar Epithelium ◽  
Alveolar Epithelial Cells ◽  
Mycobacterium Tuberculosis Infection ◽  
Alveolar Epithelial ◽  
Immune Balance ◽  
Global Threat ◽  
Cell Crosstalk

Tuberculosis (TB) is a disease that kills one person every 18 s. TB remains a global threat due to the emergence of drug-resistant Mycobacterium tuberculosis (M.tb) strains and the lack of an efficient vaccine. The ability of M.tb to persist in latency, evade recognition following seroconversion, and establish resistance in vulnerable populations warrants closer examination. Past and current research has primarily focused on examination of the role of alveolar macrophages and dendritic cells during M.tb infection, which are critical in the establishment of the host response during infection. However, emerging evidence indicates that the alveolar epithelium is a harbor for M.tb and critical during progression to active disease. Here we evaluate the relatively unexplored role of the alveolar epithelium as a reservoir and also its capacity to secrete soluble mediators upon M.tb exposure, which influence the extent of infection. We further discuss how the M.tb-alveolar epithelium interaction instigates cell-to-cell crosstalk that regulates the immune balance between a proinflammatory and an immunoregulatory state, thereby prohibiting or allowing the establishment of infection. We propose that consideration of alveolar epithelia provides a more comprehensive understanding of the lung environment in vivo in the context of host defense against M.tb.

Tight monolayers of rat alveolar epithelial cells: bioelectric properties and active sodium transport

1989 ◽  
Vol 256 (3) ◽  
pp. C688-C693 ◽  
Author(s):  
J. M. Cheek ◽  
K. J. Kim ◽  
E. D. Crandall
Keyword(s):  
Epithelial Cells ◽  
Sodium Transport ◽  
Short Circuit ◽  
Alveolar Epithelium ◽  
Alveolar Epithelial Cells ◽  
Active Sodium ◽  
Alveolar Epithelial ◽  
Active Sodium Transport ◽  
Complex Anatomy

Because the pulmonary alveolar epithelium separates air spaces from a fluid-filled compartment, it is expected that this barrier would be highly resistant to the flow of solutes and water. Investigation of alveolar epithelial resistance has been limited due to the complex anatomy of adult mammalian lung. Previous efforts to study isolated alveolar epithelium cultured on porous substrata yielded leaky monolayers. In this study, alveolar epithelial cells isolated from rat lungs and grown on tissue culture-treated Nucleopore filters resulted in tight monolayers with transepithelial resistance greater than 2,000 omega.cm2. Changes in bioelectric properties of these alveolar epithelial monolayers in response to ouabain, amiloride, and terbutaline are consistent with active sodium transport across a polarized barrier. 22Na flux measurements under short-circuit conditions directly confirm net transepithelial absorption of sodium by alveolar epithelial cells in the apical to basolateral direction, comparable to the observed short-circuit current (4.37 microA/cm2). The transport properties of these tight monolayers may be representative of the characteristics of the mammalian alveolar epithelial barrier in vivo.

Effect of endocytosis inhibitors on alveolar clearance of albumin, immunoglobulin G, and SP-A in rabbits

1994 ◽  
Vol 266 (5) ◽  
pp. L544-L552 ◽  
Author(s):  
R. H. Hastings ◽  
J. R. Wright ◽  
K. H. Albertine ◽  
R. Ciriales ◽  
M. A. Matthay
Keyword(s):  
Immunoglobulin G ◽  
Protein Transport ◽  
Protein A ◽  
Alveolar Epithelium ◽  
Alveolar Epithelial Cells ◽  
Capillary Endothelium ◽  
Alveolar Type ◽  
Protein Uptake ◽  
Alveolar Epithelial

Protein in the alveolar space may be cleared by endocytosis and degradation inside alveolar epithelial cells, by transcytosis across the alveolar epithelium, or by restricted diffusion through the epithelium. The relative contributions of these three pathways to clearance of large quantities of protein from the air spaces is not known. This study investigated the effects of monensin and nocodazole, agents which inhibit endocytosis in cell culture, on alveolar epithelial protein transport in anesthetized rabbits. There was evidence that monensin and nocodazole inhibited endocytosis by the alveolar epithelium in vivo. Nocodazole increased the number of vesicles in the alveolar epithelium and capillary endothelium. Monensin increased vesicle density in the endothelium. These results suggested that the inhibitors disrupted microtubules or interrupted cellular membrane traffic in the lung. Both inhibitors decreased lung parenchymal uptake of immunoreactive human albumin from the air spaces. Monensin and nocodazole inhibited albumin uptake in cultured alveolar type II cells. Monensin increased the amount of 125I-labeled surfactant protein A associated with the lungs, compared with the quantity remaining in the air space 2 h after instillation. Although the drugs decreased alveolar epithelial protein uptake, they did not decrease alveolar clearance of 125I-labeled immunoglobulin G or 131I-labeled albumin in anesthetized rabbits. Thus monensin- and nocodazole-sensitive protein-uptake pathways do not account for most alveolar protein clearance when the distal air spaces are filled with a protein solution.

scholarly journals Genome-wide integration of microRNA and transcriptomic profiles of differentiating human alveolar epithelial cells

2020 ◽  
Vol 319 (1) ◽  
pp. L173-L184 ◽  
Author(s):  
Alessandra Castaldi ◽  
Masafumi Horie ◽  
Megan E. Rieger ◽  
Mickael Dubourd ◽  
Mitsuhiro Sunohara ◽  
...  
Keyword(s):  
Gene Expression ◽  
Expression Profiles ◽  
Alveolar Epithelium ◽  
Alveolar Epithelial Cells ◽  
Cell Phenotype ◽  
Altered Expression ◽  
Alveolar Epithelial ◽  
Genome Wide ◽  
Glucocorticoid Signaling

The alveolar epithelium is comprised of two cell types, alveolar epithelial type 1 (AT1) and type 2 (AT2) cells, the latter being capable of self-renewal and transdifferentiation into AT1 cells for normal maintenance and restoration of epithelial integrity following injury. MicroRNAs (miRNAs) are critical regulators of several biological processes, including cell differentiation; however, their role in establishment/maintenance of cellular identity in adult alveolar epithelium is not well understood. To investigate this question, we performed genome-wide analysis of sequential changes in miRNA and gene expression profiles using a well-established model in which human AT2 (hAT2) cells transdifferentiate into AT1-like cells over time in culture that recapitulates many aspects of transdifferentiation in vivo. We defined three phases of miRNA expression during the transdifferentiation process as “early,” “late,” and “consistently” changed, which were further subclassified as up- or downregulated. miRNAs with altered expression at all time points during transdifferentiation were the largest subgroup, suggesting the need for consistent regulation of signaling pathways to mediate this process. Target prediction analysis and integration with previously published gene expression data identified glucocorticoid signaling as the top pathway regulated by miRNAs. Serum/glucocorticoid–regulated kinase 1 (SGK1) emerged as a central regulatory factor, whose downregulation correlated temporally with gain of hsa-miR-424 and hsa-miR-503 expression. Functional validation demonstrated specific targeting of these miRNAs to the 3′-untranslated region of SGK1. These data demonstrate the time-related contribution of miRNAs to the alveolar transdifferentiation process and suggest that inhibition of glucocorticoid signaling is necessary to achieve the AT1-like cell phenotype.

scholarly journals Electron Microscopic Study of the Phagocytosis Process in Lung

1960 ◽  
Vol 7 (2) ◽  
pp. 357-366 ◽  
Author(s):  
H. E. Karrer
Keyword(s):  
Plasma Membrane ◽  
Alveolar Macrophages ◽  
Alveolar Epithelium ◽  
Alveolar Epithelial Cells ◽  
Electron Microscopic ◽  
Double Line ◽  
Alveolar Epithelial ◽  
Culture Cells ◽  
India Ink ◽  
Intracellular Vesicles

Diluted India ink was instilled into the nasal cavity of mice and the lungs of some animals were fixed with osmium tetroxide at various intervals after one instillation. The lungs of other animals were fixed after 4, 7, 9, 16, or 18 daily instillations. The India ink was found to be phagocytized almost exclusively by the free alveolar macrophages. A few particles are occasionally seen within thin portions of alveolar epithelium, within the "small" alveolar epithelial cells, or within occasional leukocytes in the lumina of alveoli. The particles are ingested by an invagination process of the plasma membrane resulting in the formation of intracellular vesicles and vacuoles. Ultimately large amounts of India ink accumulate in the cell, occupying substantial portions of the cytoplasm. The surfaces of phagocytizing macrophages show signs of intense motility. Their cytoplasm contains numerous particles, resembling Palade particles, and a large amount of rough surfaced endoplasmic reticulum. These structures are interpreted as indicative of protein synthesis. At the level of resolution achieved in this study the membranes of this reticulum appear as single dense "lines." On the other hand, the plasma membrane and the limiting membranes of vesicles and of vacuoles often exhibit the double-line structure typical of unit membranes (Robertson, 37). The inclusion bodies appear to be the product of phagocytosis. It is believed that some of them derive from the vacuoles mentioned above, and that they correspond to similar structures seen in phase contrast cinemicrographs of culture cells. Their matrix represents phagocytized material. Certain structures within this matrix are considered as secondary and some of these structures possess an ordered form probably indicative of the presence of lipid. The possible origin and the fate of alveolar macrophages are briefly discussed.

scholarly journals TRIM72 is required for effective repair of alveolar epithelial cell wounding

2014 ◽  
Vol 307 (6) ◽  
pp. L449-L459 ◽  
Author(s):  
Seong Chul Kim ◽  
Thomas Kellett ◽  
Shaohua Wang ◽  
Miyuki Nishi ◽  
Nagaraja Nagre ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Molecular Mechanisms ◽  
Striated Muscle ◽  
Alveolar Epithelial Cell ◽  
Alveolar Epithelial Cells ◽  
Lung Cells ◽  
Alveolar Epithelial ◽  
High Tidal Volume Ventilation

The molecular mechanisms for lung cell repair are largely unknown. Previous studies identified tripartite motif protein 72 (TRIM72) from striated muscle and linked its function to tissue repair. In this study, we characterized TRIM72 expression in lung tissues and investigated the role of TRIM72 in repair of alveolar epithelial cells. In vivo injury of lung cells was introduced by high tidal volume ventilation, and repair-defective cells were labeled with postinjury administration of propidium iodide. Primary alveolar epithelial cells were isolated and membrane wounding and repair were labeled separately. Our results show that absence of TRIM72 increases susceptibility to deformation-induced lung injury whereas TRIM72 overexpression is protective. In vitro cell wounding assay revealed that TRIM72 protects alveolar epithelial cells through promoting repair rather than increasing resistance to injury. The repair function of TRIM72 in lung cells is further linked to caveolin 1. These data suggest an essential role for TRIM72 in repair of alveolar epithelial cells under plasma membrane stress failure.

scholarly journals C3 Promotes Clearance of Klebsiella pneumoniae by A549 Epithelial Cells

2004 ◽  
Vol 72 (3) ◽  
pp. 1767-1774 ◽  
Author(s):  
Beatriz de Astorza ◽  
Guadalupe Cortés ◽  
Catalina Crespí ◽  
Carles Saus ◽  
José María Rojo ◽  
...  
Keyword(s):  
Epithelial Cells ◽  
Klebsiella Pneumoniae ◽  
Alveolar Epithelial Cells ◽  
Clinical Isolates ◽  
Complement Components ◽  
Innate Defense ◽  
Alveolar Epithelial

ABSTRACT The airway epithelium represents a primary site for contact between microbes and their hosts. To assess the role of complement in this event, we studied the interaction between the A549 cell line derived from human alveolar epithelial cells and a major nosocomial pathogen, Klebsiella pneumoniae, in the presence of serum. In vitro, we found that C3 opsonization of poorly encapsulated K. pneumoniae clinical isolates and an unencapsulated mutant enhanced dramatically bacterial internalization by A549 epithelial cells compared to highly encapsulated clinical isolates. Local complement components (either present in the human bronchoalveolar lavage or produced by A549 epithelial cells) were sufficient to opsonize K. pneumoniae. CD46 could competitively inhibit the internalization of K. pneumoniae by the epithelial cells, suggesting that CD46 is a receptor for the binding of complement-opsonized K. pneumoniae to these cells. We observed that poorly encapsulated strains appeared into the alveolar epithelial cells in vivo but that (by contrast) they were completely avirulent in a mouse model of pneumonia compared to the highly encapsulated strains. Our results show that bacterial opsonization by complement enhances the internalization of the avirulent microorganisms by nonphagocytic cells such as A549 epithelial cells and allows an efficient innate defense.

Dome formation in primary cultured monolayers of alveolar epithelial cells

1982 ◽  
Vol 243 (1) ◽  
pp. C96-C100 ◽  
Author(s):  
B. E. Goodman ◽  
E. D. Crandall
Keyword(s):  
Epithelial Cells ◽  
Life Span ◽  
Fluid Balance ◽  
Alveolar Epithelial Cells ◽  
Type Ii ◽  
Transport Function ◽  
Dome Formation ◽  
Alveolar Epithelial ◽  
Free Air

We have observed the formation of domes by type II alveolar epithelial cells harvested from rat lungs. The cells were harvested using elastase and grew to confluence in 3-4 days after plating on plastic. Numerous domes were observed in the monolayers 4-18 days after plating, with peak dome density occurring at days 6-9. When trypsin was used instead of elastase as the harvesting enzyme, many fewer domes were formed by the monolayers, with peak dome density observed at day 5 and no domes seen after 8 days. The life span of an individual dome was about 3-4 h. The presence of domes indicates an intact active transport function of the cells in the monolayer, which may represent an important mechanism for the maintenance of fluid-free air spaces and normal alveolar fluid balance in mammalian lungs in vivo.

Mechanisms and sequelae of increased alveolar fluid clearance in hyperoxic rats

1997 ◽  
Vol 272 (3) ◽  
pp. L407-L412 ◽  
Author(s):  
G. Yue ◽  
S. Matalon
Keyword(s):  
Alveolar Epithelial Cells ◽  
Na Channels ◽  
Alveolar Fluid Clearance ◽  
Na Transport ◽  
Alveolar Epithelial ◽  
Lung Fluid ◽  
Isotonic Fluid ◽  
Epithelial Na Channels ◽  
Alveolar Edema

We instilled 4 ml isotonic fluid containing trace amounts of fluorescently labeled dextran (molecular mass 150 kDa) in the lungs of rats exposed to either 85% O(2) for 7 days or to 85% O(2) for 7 days and 100% O(2) for 3 days. We withdrew the fluid every hour for a 3-h period and calculated alveolar fluid clearance (AFC) from changes in dextran concentration. Postinstillation (3 h), AFC values in the control and the two hyperoxic groups were 51 +/- 1, 63 +/- 2, and 62 +/- 3 (SE), respectively (%instilled volume; n > or = 5; P < 0.05). Addition of either 1 mM amiloride or N-ethyl-N-isopropyl amiloride (EIPA) in the instillate decreased the AFC values in all groups 3 h later to approximately 30% of instilled volume. Instillation of phenamil, an irreversible blocker of epithelial Na+ channels into the lungs of rats exposed to 85% O(2) for 7 days and 100% O(2) for 2 days, resulted in a significant increase of their extravascular lung fluid volumes 24 h later. These results demonstrate the existence of EIPA-inhibitable Na+ channels in alveolar epithelial cells in vivo and indicate that an increase in Na+ transport plays an important role in limiting the amount of alveolar edema in O(2)-damaged lungs.

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