Lamellar Bodies Form Solid Three-dimensional Films at the Respiratory Air-Liquid Interface

Ravasio, Andrea; Olmeda, Bárbara; Bertocchi, Cristina; Haller, Thomas; Pérez‐Gil, Jesús

doi:10.1074/jbc.m110.106518

Cited by 29 publications

(37 citation statements)

References 36 publications

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“…For instance, the ejection of intracellular LBs (which are dehydrated with respect to secreted LBs) into a relative diluted medium (like the epithelial lining fluid) could be favored by entropic changes caused by hydration. This hydration process could also play a role during the transformation of LBs after secretion into tubular myelin [20] or the spreading of these organelles at the alveolar interface [24]. Another biological example showing a similar entropy-driven process is the super-contraction of spider silk [44].…”

Section: Discussionmentioning

confidence: 99%

“…On the other hand, the mechanism for LBs adsorption into the air/water interphase has been carefully studied by Hobi et al [23]. These authors described how temperature, ionic strength, pH and other relevant physicochemical factors modulate their adsorption at the alveolar interphase [23], also suggesting the occurrence of “solid-like” domains in the surfactant monolayer formed upon adsorption of LBs to the air/water interphase [24]. Additionally, in a recent study these authors report that intracellular LBs membranes from rat ATII cells exist as crystalline-like highly ordered structures, with a high packed and dehydrated state relative to the pulmonary surfactant isolated from lung lavages [25].…”

Section: Introductionmentioning

confidence: 99%

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Spectral phasor analysis of LAURDAN fluorescence in live A549 lung cells to study the hydration and time evolution of intracellular lamellar body-like structures

Malacrida

Astrada

Briva

et al. 2016

Biochimica et Biophysica Acta (BBA) - Biomembranes

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Using LAURDAN spectral imaging and spectral phasor analysis we concurrently studied the growth and hydration state of subcellular organelles (Lamellar Body-like, LB-like) from live A549 lung cancer cells at different post-confluence days. Our results reveal a time dependent two-step process governing the size and hydration of these intracellular LB-like structures. Specifically, a first step (days 1 to 7) is characterized by an increase in their size, followed by a second one (days 7 to 14) where the organelles display a decrease in their global hydration properties. Interestingly, our results also show that their hydration properties significantly differ from those observed in well-characterized artificial lamellar model membranes, challenging the notion that a pure lamellar membrane organization is present in these organelles at intracellular conditions. Finally, these LB-like structures show a significant increase in their hydration state upon secretion, suggesting a relevant role of entropy during this process.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Spectral phasor analysis of LAURDAN fluorescence in live A549 lung cells to study the hydration and time evolution of intracellular lamellar body-like structures

Malacrida

Astrada

Briva

et al. 2016

Biochimica et Biophysica Acta (BBA) - Biomembranes

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“…Our inverted interface model was recently used to analyze calcium signals and surfactant adsorption at the IAL. For the details, we thus refer to these publications (8,33,57). In the present study, we used a specially designed, slightly different kind of chamber (200-m holes made in stainless steel, 45 holes/plate; see Fig.…”

Section: Methodsmentioning

confidence: 99%

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

Hobi

Ravasio

Haller

2012

American Journal of Physiology-Lung Cellular and Molecular Phys

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.) showed that contact of alveolar epithelial type II cells with an air-liquid interface (I AL) leads to a paradoxical situation. It is a potential threat that can cause cell injury, but also a Ca 2ϩ -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 Ca 2ϩ was extracellular, and the transmembrane Ca 2ϩ 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. cell deformation; cell injury; mechanotransduction; microarray; stretch IN THE ALVEOLI, MECHANICAL forces are a constant modulator of tissue geometry and function (4). These forces arise from multiple sources, such as cyclic stretching and compression during respiration, changes in transcapillary pressure, or surface tension at the air-liquid interface (I AL ) (22). They are probably nonuniform in space and time (26,51,67) and impose either physiological responses of the cells, or pathological ones, depending on the type of tissue or the magnitude or abnormality of forces that are at work (reviewed in Refs. 18,66,69,72). In particular, tissue stretch (ϭ tensile strain) has already been shown to be an important determinant of surfactant secretion in alveolar type II (AT II) cells (2,15,36,47,71,73). Studies on single cells revealed that stretch induces an elevation of the intracellular Ca 2ϩ concentration ([Ca 2ϩ ] i ) (23, 73), perhaps via mechanosensitive ion channels like the wellcharacterized transient receptor potential (TRP) vanilloids (reviewed in Refs. 16,77). Recently, the panoply of mechanosensitive mechanisms was expanded by the finding that the I AL , the "normal" microenvironment of the AT II cells (6), may be a strong mechanical incentive as well. Two recent independent studies (55, 56) described a stimulating, but also harmful, effect of an I AL on the AT II cell function. Interestingly, interfacial contact is followed by an increase in [Ca 2ϩ ] i and release of ATP, both of which stimulate secretion (reviewed in Refs. 1, 44, 59). It has even been speculated that this response could act within a feedback loop to continuously monitor and to adjust the physical properties of the interface or the hypophase below.In addition...

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“…Details of the microscopic setup including the episcopic illumination are described (7,44). Briefly, we used a Zeiss 100 inverted microscope (Zeiss) equipped with a monochromator (Polychrom II, TILL Photonics) and a cooled CCD camera (Imago-SVGA; TILL Photonics), both controlled by TillVision software.…”

Section: Methodsmentioning

confidence: 99%

“…Further investigations along this are in progress; however, they require substantial technical improvements that allow modulating surface tension, even down to the minimum values observed in maximally compressed monolayers, while modulating the distance of the cells to the interface and monitoring interference in parallel. This task could not yet be solved in a sufficient way: Any addition of a surfactant (like Curosurf) led, due to strong light reflectivity at the I AL (44), to a concentration-dependent blurring and finally loss of interference signals. Thus Curosurf could only be used at such low concentrations (0.1 mg/ml) where its effect on reduction of surface tension was probably too small to eliminate a deforming stress (6).…”

Section: )mentioning

confidence: 99%

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

Ravasio

Hobi²,

Bertocchi³

et al. 2011

American Journal of Physiology-Cell Physiology

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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, Ca 2ϩ 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 Ca 2ϩ 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 I AL 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. mechanical stress; pneumocytes; strain; stretch; surfactant THE ALVEOLAR EPITHELIUM is covered by a thin and continuous layer of water (5). This aqueous layer, referred to as hypophase or alveolar lining fluid (ALF), introduces a considerable physical instability to the millions of alveolar invaginations, tending on overall to force the air out of the lungs. As a consequence, the great alveolar corner cells (or alveolar type II cells; AT II) synthesize and release surfactant into the ALF, from where it transits to the air-liquid interface (I AL ) and creates a highly surface-active coat (40). The importance of this protective coat is best demonstrated in the premature infant lung, where deficiency causes alveolar collapse with life-threatening consequences unless medicated by surfactant administration strategies (17).An important and almost unique aspect of the AT II cellspecific microenvironment is the presence of air. Not astonishingly, therefore, studies introducing such an I AL in AT II cell culture systems reported dramatic effects on cell function, morphology, protein expression, and ion channel activities (13,29). In general, the AT II cells have a higher phenotypic stability and seem to preserve characteristic cell functions for longer periods than compared with standard culture conditions. In particular, biosynthesis and secretion of surfactant is stable over several weeks. Furthermore, reculturing with exposure to air reverses the loss of differentiated AT II cell phenotype observed in submerged cultures (13). This effect of an I AL is indeed remarkable, though not readily intelligible. In particular, the phy...

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Lamellar Bodies Form Solid Three-dimensional Films at the Respiratory Air-Liquid Interface

Cited by 29 publications

References 36 publications

Spectral phasor analysis of LAURDAN fluorescence in live A549 lung cells to study the hydration and time evolution of intracellular lamellar body-like structures

Spectral phasor analysis of LAURDAN fluorescence in live A549 lung cells to study the hydration and time evolution of intracellular lamellar body-like structures

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

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

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