Articles in PresS. Am J Physiol Lung Cell Mol Physiol (October 12, 2012). doi:10.1152/ajplung.00279.2012
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Call for papers:
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“Real-time visualization of lung function: from micro to macro“
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Rory E. Morty1,2 and Sadis Matalon3
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Department of Lung Development and Remodelling, Max Planck Institute for Heart and
Lung Research, Bad Nauheim, Germany; 2Department of Internal Medicine (Pulmonology),
University Hospital Giessen and Marburg, Giessen, Germany; 3Department of
Anesthesiology, University of Alabama at Birmingham, AL 35294.
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Address for reprint requests and other correspondence: Rory E. Morty, Department of Lung
Development and Remodelling, Max Planck Institute for Heart and Lung Research,
Parkstrasse 1, 61231 Bad Nauheim, Germany (e-mail: [email protected]).
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Studies on normal physiological and pathological processes that take place in the lung are
hampered by the architecture and behaviour of a living, breathing lung with a very complex
three-dimensional structure that is constantly in motion. Not only do the airways and
vasculature constrict and relax, but the alveolar airspaces regularly and rapidly expand and
retract, appreciably changing the size and volume of the lung at regular intervals during
normal lung function. The development and function of the lung are dependent upon the
intactness and coordinated movement of the lung, making in vitro studies on intact lungs
difficult. Although the proximal regions of the intact, breathing lung are relatively accessible
for imaging studies via the trachea, the most distal regions of the lung, the alveolar units, are
relatively inaccessible (in terms of visualisation of lung function), being reachable only
through the tiny alveolar ducts which provide passage into the alveolar sacs. Recently, there
has been an explosion of interest in imaging physiological processes in the lung in real-time,
and several notable advances have been made, which have been facilitated by new
methodological approaches, novel microscopic and radiological imaging technologies, as
well as the development of genetically modified animal models.
One example of where real-time imaging of lung function has led to unexpected and
paradigm-shifting observations is the field of ion transport. Previously, physiological studies
on intact animals and isolated perfused lungs, as well as patch-clamp and Ussing chamber
studies on isolated alveolar epithelial cells and lung slices have demonstrated the presence
of amiloride-sensitive cation, as well as anion channels. However, vectorial Na+ transport has
been regarded as the predominant form of ion transport, with chloride transport by the
cystic fibrosis transmembrane conductance regulator playing an important role in enhancing
Copyright © 2012 by the American Physiological Society.
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Na+-transport. Recent work published in the pages of the Journal continues to underscore
the importance of patch-clamp and Ussing chamber studies to investigate fluid clearance
(7,8,16,21,23). However, elegant imaging studies have clearly demonstrated the presence of
chloride secretion in air-filled lungs (17). The isolated, ventilated and perfused lung model
has also been adapted to follow – in real-time – the transport of radioactive tracers (22Na
and [3H]mannitol for example), applied by ultrasonic nebulization to the alveolar airspaces,
into the vascular perfusate (10). Such technology has tremendous scope for extension to
chloride and other ions, as well as radioactive protein tracers. The isolated lung technology
has also lent itself to studies on the real-time assessment of channel function in lung
permeability (12), and indeed, real-time assessment of ventilator-induced lung damage (13).
Isolated lung studies are, by their nature, terminal experiments, which yield indirect
(although real-time) data about lung function. Most of the studies referred to above have
focused on ion transport in the lung epithelium. Studies on other lung cell types which
actively transport ions, such as vascular and airway smooth muscle, are sorely lacking.
Accordingly, manuscripts dealing with the real-time visualization of ion transport in cell
types other than the epithelium are particularly encouraged in the Call for Papers.
In contrast to isolated lung studies, radiological assessment of lung function both permits
the direct visualization of processes taking place within a live, working lung, and also allows
for the repetitive determinations to be made on the same animal, which represent two
important advances over isolated lung studies. Furthermore, radiological imaging will also
allow for lung measurements to be made at fixed levels of expansion, facilitating
standardization and comparison. The increasing use of radiological monitoring employing
magnetic resonance imaging (MRI) (20), positron emission tomography (PET) (4), and
computed axial tomography (CAT) (18) technologies has revealed the potential of these
approaches in the study of lung structure and physiology. The beauty of these techniques
includes the non-invasive and non-terminal nature of these assessments. While most
analyses of lung tissue rely on the extraction of the lung and subsequent processing for
microscopic or biochemical analysis, radiological analysis of lung structure and function
permits repetitive in vivo assessment of the living, breathing lung. The number of repeat
measurements is limited only by exposure to radiation, which applies largely to CAT studies.
Indeed, studies have reported the monitoring of post-natal pulmonary artery growth at
regular intervals for up to 160 days by phase-contrast (PC)-MRI (22), highlighting the
usefulness of non-invasive, non-terminal radiological approaches to study lung structure and
function. In terms of airway function, synchrotron radiation computed tomography (CT)
imaging has recently been very elegantly used to differentiate central versus peripheral
airway and lung parenchymal components of the response to airway provocation by
cigarette smoke (19); and single proton emission-computed tomography (SPECT) to quantify
clearance of intratracheally delivered 99mTc-diethylene triamine pentaacetic acid has been
used to assess airway barrier function (26). Optical coherence tomography is another
elegant approach that has been very successfully used to define (in real-time) neoplastic
morphological changes in bronchial microstructure (28), and this emerging technique can be
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potentially used, either alone, or in combination with confocal microscopy, to image subpleural alveoli.
Radiological approaches clearly also have their limitations, for example, the resolving power
of MRI, even in combination with hyperpolarized gases, to detect moderate alveolar edema
is currently poor. However, progress in the refinement and resolution of these radiological
approaches is on-going. Indeed, efforts have been made to quantify airspace fluid content by
X-ray fluoroscopy in live animals (6). Furthermore, dual-energy microCT can accurately
estimate vascular, tissue, and air fractions in rodent lungs (1), and high-resolution
echocardiography used together with MRI can determine cardiac output, pulmonary artery
pressure and right ventricle remodelling to a level of accuracy comparable to that of right
heart catheterization and autopsy, but at the same time permits serial monitoring (27).
In spite of the advantages of radiological approaches, the resolving power of these
approaches that is currently available to lung scientists is a major limitation, compared to
the phenomenal resolving power of microscopic approaches. Tremendous advances in
various forms of microscopy have literally opened a window into the living, breathing lung.
Outstanding recent work has given us a direct view of the microstructure of the bronchial
wall using fibered confocal fluorescence microscopy, where microscopic imaging of living
tissue can be generated through a 1-mm fiberoptic probe introduced into the working
channel of a bronchoscope (24). This methodology has been extended to the exploration of
the peripheral lung in vivo, revealing matrix structures and macrophage migration in the
expanding and contracting alveolus (25). This work was further extended by the
development of a new lung imaging technique based on endoscopic confocal fluorescence
microscopy, which provided cellular and structural assessment of living lung tissue using a
small confocal probe in direct contact with the visceral pleura. This allowed the visualization
of lung cell apoptosis, neutrophil tracking in the lung microcirculation and airspaces, and
edema formation (3). Furthermore, intravital microscopy has been refined for visual access
to the pulmonary microvasculature under closed-chest conditions using a variety of thoracic
window approaches (14), which has facilitated visualization of capillary recruitment, hypoxic
pulmonary vasoconstriction, and neutrophil margination in the pulmonary vasculature.
Real-time fluorescence imaging (RFI) approaches, with microscopic visualization of the
isolated, perfused lung, have taken lung imaging to the molecular level, and allowed the
study of lung cellular and molecular responses in situ. This approach has lent itself to the
study of intra- and inter-cellular signaling which involves calcium fluxes, nitric oxide, and
reactive oxygen species, in the pulmonary vasculature and the alveolus (15). Microscopic
approaches to the study of live lung cells in vitro in cell culture also continue to be
developed. For example, one recent report in the Journal has addressed the use of atomic
force microscopy to image surfactant insertion into lipid bilayers (9), while time-lapse optical
imaging has been refined to study mucus droplet formation (5). Real-time fluorescence
imaging, used in combination with new fluorescent tools such as Lifeact-GFP, continue to
facilitate advances in our understanding of cytoskeletal dynamics and actin remodelling, as
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recently demonstrated in the Journal for alveolar epithelial type I cell wound healing (11),
and hypoxia-induced contractile events in the pulmonary endothelium (2).
The pressing need for further advances in the development or refinement of experimental
approaches for the real-time assessment of lung structure and function, together with an
explosion of interest in this area of pre-clinical and clinical pulmonary research, has
prompted this Special Call for Papers on “Real-time Visualization of Lung Function: from
Micro to Macro” from the American Journal of Physiology - Lung Cellular and Molecular
Physiology. This Special Call for Papers aims to highlight novel methodological advances
which address how lung function may be visualized in real-time, both in the laboratory and
in a clinical setting, as well as the application of these methodologies in studies on lung
pathophysiology. Basic, translational and clinical research papers, as well as methodological
reports and reviews will be considered, particularly those focusing on the following specific
themes:
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Real-time visualisation of ion, protein, and water transport. The contribution of
transepithelial ion and protein transport to alveolar fluid dynamics remains
controversial and poorly understood. The development of new – or refinement of
existing – techniques which permit the real-time visualization of ion, protein, and
water transport in vivo, ex vivo, or in vitro, would do much to further our
understanding of these processes. Similarly, new methodologies to assess the
function, and indeed, monitor the efficiency of the mucocilliary escalator would
contribute much to studies on the epithelial function in the conducting airways.
Studies addressing the refinement of methodology to quantify airway surface liquid
volume and mucus transport rates by simple light refraction and confocal microscopy
would also be welcome.
Real-time radiological assessment of pulmonary structure and function. Novel or
refined radiological approaches such as CAT, MRI, PET, including microCT and
dynamic contrast-enhanced MRI, approaches to study and quantify lung structure
and pathological processes, including normal and aberrant lung vascularization. This
theme also spans the use of high-resolution synchrotron radiation X-ray tomographic
microscopy to assess lung micro-structure, for example, three-dimensional
visualisation of the alveolar capillary network; as well as the use of MRI and nuclear
magnetic resonance (NMR) to monitor inflammation, vascular remodelling, and
metabolism in the lung. Manuscripts reporting the development and use of
hyperpolarized gas MRI for the quantitative imaging of alveolar recruitment during
mechanical ventilation, and the quantitative assessment of alveolar edema, would be
very welcome, particularly comparative studies which evaluate radiological
approaches as alternatives to currently employed, more classical (but perhaps more
precise) assessments of extravascular lung water. Additionally, manuscripts reporting
the radiological monitoring of the delivery of genes and pharmacological agents to
the distal lung are also sought after.
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Real-time microscopic imaging of pulmonary structure and function. Manuscripts
reporting novel or refined intravital microscopic approaches to study lung function in
vivo, as well as functional fluorescence-based approaches to address signalling in situ
in living, breathing lungs, are particularly encouraged. The latter might include
photolytic uncaging to study cation signaling, optical-sectioning microscopy to study
cytoskeletal dynamics, and fluorescence energy transfer approaches to reveal
protein-protein interactions in situ. Manuscripts reporting the novel use of highspeed video and multiphoton microscopy to study large airway and cilia function, as
well as live-cell imaging in whole-lung sections, and darkfield and fluorescence
microscopy to study protein trafficking and secretion are encouraged. Quantum dot
single particle tracking studies would also be most welcome, addressing, for example,
nanoparticle distribution in the distal lung in vivo, as well as membrane protein
complex formation and trafficking within and on the surface of isolated cells in vitro.
Manuscripts that are submitted in these areas, in response to this call, will receive expedited
review. Submitting authors should indicate in their covering letter, as well as in the online
submission system under “Manuscript Type” that the submission is in response to a Special
Call for Papers. Submitted papers will be reviewed very promptly by members of the
Editorial Board as well as selected guest reviewers who are acknowledged experts in the
relevant areas of expertise. Accepted manuscripts will be published under a distinct
headline. Please direct any enquiries to Dr. Sadis Matalon, the Editor-in-Chief, via email at
[email protected].
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