Interfacial stress affects rat alveolar type II cell signaling and gene expression

Previous work from our group (Ravasio A, Hobi N, Bertocchi C, Jesacher A, Dietl P, Haller T. Am J Physiol Cell Physiol 300: C1456–C1465, 2011.) showed that contact of alveolar epithelial type II cells with an air-liquid interface (IAL) leads to a paradoxical situation. It is a potential threat that can cause cell injury, but also a Ca2+-dependent stimulus for surfactant secretion. Both events can be explained by the impact of interfacial tensile forces on cellular structures. Here, the strength of this mechanical stimulus became also apparent in microarray studies by a rapid and significant change on the transcriptional level. Cells challenged with an IAL in two different ways showed activation/inactivation of cellular pathways involved in stress response and defense, and a detailed Pubmatrix search identified genes associated with several lung diseases and injuries. Altogether, they suggest a close relationship of interfacial stress sensation with current models in alveolar micromechanics. Further similarities between IAL and cell stretch were found with respect to the underlying signaling events. The source of Ca2+ was extracellular, and the transmembrane Ca2+ entry pathway suggests the involvement of a mechanosensitive channel. We conclude that alveolar type II cells, due to their location and morphology, are specific sensors of the IAL, but largely protected from interfacial stress by surfactant release.

Download Full-text

Sublethal hydrogen peroxide inhibits alveolar type II cell surfactant phospholipid biosynthetic enzymes

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.1995.268.1.l129 ◽

1995 ◽

Vol 268 (1) ◽

pp. L129-L135 ◽

Cited By ~ 6

Author(s):

C. Crim ◽

W. J. Longmore

Keyword(s):

Cell Injury ◽

Phospholipid Metabolism ◽

Alveolar Type ◽

Type Ii Cells ◽

Reactive Oxygen Metabolites ◽

Type Ii ◽

Intracellular Atp ◽

Alveolar Type Ii Cell ◽

Atp Levels ◽

Type Ii Cell

Alveolar type II cell injury by phagocytic cell-derived reactive oxygen metabolites represents a potential mechanism for the altered surfactant metabolism found in patients with the adult respiratory distress syndrome (ARDS). Previous studies demonstrated altered surfactant phospholipid metabolism after sublethal oxidant exposure. In this study, we measured intracellular ATP levels and the activities of several enzymes involved in surfactant phospholipid biosynthesis after sublethal H2O2 exposure of cultured rat alveolar type II cells. Intracellular ATP levels were reduced by 46.6% after exposure to 75 microM H2O2. The activity of CTP:phosphorylcholine cytidyltransferase was unchanged after H2O2 exposure when measured in whole cell homogenates. However, when measured in the microsomal fraction, cytidyltransferase activity significantly fell after exposure of type II cells to 75 microM H2O2. Activity in the cytosolic fractions remained unchanged. Similarly, microsomal cholinephosphotransferase was reduced after H2O2 exposure. We conclude that H2O2 decreases surfactant phosphatidylcholine biosynthesis independently of its ability to deplete intracellular ATP content. These deleterious effects may partially explain the diminished alveolar surfactant observed in patients with ARDS.

Download Full-text

Interfacial sensing by alveolar type II cells: a new concept in lung physiology?

AJP Cell Physiology ◽

10.1152/ajpcell.00427.2010 ◽

2011 ◽

Vol 300 (6) ◽

pp. C1456-C1465 ◽

Cited By ~ 17

Author(s):

Andrea Ravasio ◽

Nina Hobi ◽

Cristina Bertocchi ◽

Alexander Jesacher ◽

Paul Dietl ◽

...

Keyword(s):

Cell Damage ◽

Close Contact ◽

Alveolar Type ◽

Type Ii ◽

Potential Threat ◽

Paradoxical Situation ◽

Lung Physiology ◽

Physiological Relevance ◽

Interface Contact ◽

Air Liquid Interface

Alveolar type II (AT II) cells are in close contact with an air-liquid interface (IAL). This contact may be of considerable physiological relevance; however, no data exist to provide a satisfying description of this specific microenvironment. This is mainly due to the experimental difficulty to manipulate and analyze cell-air contacts in a specific way. Therefore, we designed assays to quantify cell viability, Ca2+ changes, and exocytosis in the course of interface contact and miniaturized IAL devices for direct, subcellular, and real-time analyses of cell-interface interactions by fluorescence microscopy or interferometry. The studies demonstrated that the sole presence of an IAL is not sensed by the cells. However, when AT II cells are forced into closer contact with it, they respond promptly with sustained Ca2+ signals and surfactant exocytosis before the occurrence of irreversible cell damage. This points to a paradoxical situation: a potential threat and potent stimulus for the cells. Furthermore, we found that the signalling mechanism underlying sensation of an IAL can be sufficiently explained by mechanical forces. These results demonstrate that the IAL itself can play a major, although so-far neglected, role in lung physiology, particularly in the regulatory mechanisms related with surfactant homeostasis. Moreover, they also support a general new concept of mechanosensation in the lung.

Download Full-text

Ascorbate deficiency and oxidative stress in the alveolar type II cell

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.1997.273.4.l782 ◽

1997 ◽

Vol 273 (4) ◽

pp. L782-L788 ◽

Cited By ~ 5

Author(s):

Lou Ann S. Brown ◽

Frank L. Harris ◽

Dean P. Jones

Keyword(s):

Oxidant Stress ◽

Alveolar Type ◽

Type Ii Cells ◽

Type Ii ◽

Partial Protection ◽

Alveolar Type Ii Cell ◽

A Cell ◽

Type Ii Cell ◽

The Impact ◽

And Oxidative Stress

The objective of this study was to determine the impact of limited ascorbate (Asc) availability on type II cell sensitivity to oxidant stress. Guinea pigs were fed diets with or without Asc for 18 days, and type II cells were isolated. Although lung Asc was decreased by 90% in deficient animals (scorbutic), type II cell Asc was decreased by 50%. Upon treatment with 250 μM H2O2, the necrotic injury was twofold greater in scorbutic cells compared with control cells. With 100 μM H2O2treatment, apoptotic injury was twofold greater in scorbutic cells compared with control cells. Although there was less necrotic injury in cells exposed to 95% O2, the scorbutic cells were more sensitive than control cells. Asc pretreatment protected against necrosis and apoptosis. The Asc analog isoascorbate provided partial protection and suggested that part of the protection was not chemical detoxification but was Asc specific. We conclude that limited Asc availability resulted in a functional type II cell but a cell more sensitive to oxidant-induced injury.

Download Full-text

Mechanical distension modulates pulmonary alveolar epithelial phenotypic expression in vitro

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.1998.274.2.l196 ◽

1998 ◽

Vol 274 (2) ◽

pp. L196-L202 ◽

Cited By ~ 27

Author(s):

Jorge A. Gutierrez ◽

Robert F. Gonzalez ◽

Leland G. Dobbs

Keyword(s):

Phenotypic Expression ◽

Alveolar Type ◽

Transcriptional Level ◽

Type I ◽

Type Ii Cells ◽

Type Ii ◽

Alveolar Type Ii Cells ◽

Alveolar Epithelial ◽

Mrna Content

The pulmonary alveolar epithelium is composed of two distinct types of cells, type I and type II cells, both of which are critical for normal lung function. On the basis of experiments of both nature and in vivo studies, it has been hypothesized that expression of the type I or type II phenotype is influenced by mechanical factors. We have investigated the effects of mechanical distension on the expression of specific markers for the type I and type II cell phenotypes in cultured alveolar type II cells. Rat alveolar type II cells were tonically mechanically distended in culture. Cells were analyzed for a marker for the type I phenotype (rTI40, an integral membrane protein specific for type I cells) and for markers for the type II phenotype [surfactant protein (SP) A, SP-B, and SP-C] as well as for glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Mechanical distension caused a 68 ± 25% ( n = 3) increase in mRNA content of rTI40 relative to undistended controls. In contrast, mechanical distension resulted in a decrease in mRNA content of SP-B to 35 ± 19% ( n = 3) and of SP-C to 20 ± 6.7% ( n = 3) of undistended controls. There was no effect on mRNA content of SP-A or GAPDH. The differences in mRNA content of SP-B and SP-C were found to be primarily due to changes at the transcriptional level by nuclear run-on assays. The effects on rTI40 appear to be due to posttranscriptional events. These data show that mechanical distension influences alveolar epithelial phenotypic expression in vitro, at least in part, at the transcriptional level.

Download Full-text