Mechanical strain and dexamethasone selectively
increase surfactant protein C and tropoelastin gene
expression
Tomohiko
Nakamura1,
Mingyao
Liu2,3,
Eric
Mourgeon2,
Art
Slutsky2,4, and
Martin
Post1,5,6
1 Lung Biology Program, Hospital for Sick
Children Research Institute, 2 Thoracic
Surgery Research Laboratory, The Toronto Hospital Research
Institute, and Departments of 5 Paediatrics,
6 Physiology, 4 Medicine,
and 3 Surgery, University of Toronto, Toronto,
Ontario, Canada M5G 1X8
 |
ABSTRACT |
Physical forces derived from fetal
breathing movements and hormones such as glucocorticoids are implicated
in regulating fetal lung development. To elucidate whether the
different signaling pathways activated by physical and hormonal factors
are integrated and coordinated at the cellular and transcriptional
levels, organotypic cultures of mixed fetal rat lung cells were
subjected to static culture or mechanical strain in the presence and
absence of dexamethasone. Tropoelastin and collagen type I were used as
marker genes for fibroblasts, whereas surfactant protein (SP) A and
SP-C were used as marker genes for distal epithelial cells. Mechanical
strain, but not dexamethasone, significantly increased SP-C mRNA
expression. Tropoelastin mRNA expression was upregulated by both
mechanical strain and dexamethasone. No additive or synergistic effect
was observed when cells were subjected to mechanical stretch in the presence of dexamethasone. Neither mechanical strain nor dexamethasone alone or in combination had any significant effect on the expression of
SP-A mRNA. Dexamethasone decreased collagen type I mRNA expression, whereas mechanical strain had no effect. The increases in tropoelastin and SP-C mRNA levels induced by mechanical strain and/or dexamethasone were accompanied by increases in their heterogeneous nuclear RNA. In
addition, the stretch- and glucocorticoid-induced alterations in
tropoelastin and SP-C mRNA expression were abrogated with 10 µg/ml
actinomycin D. These findings suggest that tropoelastin and SP-C genes
are selectively stimulated by physical and/or hormonal factors at the
transcriptional level in fetal lung fibroblasts and distal epithelial
cells, respectively.
glucocorticoids; gene transcription; fetal lung cells
 |
INTRODUCTION |
FETAL LUNG DEVELOPMENT requires coordinated lung growth
and maturation. This is a highly regulated process controlled by many factors including hormones and physical forces. The latter force derived from normal fetal breathing movements supports fetal lung growth, whereas an altered breathing pattern, e.g., reduced amplitude, may result in pulmonary hypoplasia (4). One of the most important markers of pulmonary maturation is the ability to produce surfactant, a
complex of lipids and protein that lines the alveolar surface of the
lung. Recent studies have shown that physical forces affect pulmonary
surfactant metabolism. A static stretch of adult type II cells
stimulated the release of surfactant phospholipids (31), whereas a
cyclic stretch of fetal type II cells increased the synthesis of
surfactant phospholipids (22). The effect of mechanical strain on
surfactant protein (SP) production by fetal lung cells is as yet
unknown. Antenatal glucocorticoid administration, however, has been
shown to increase SP expression by fetal type II cells (16, 18). The
importance of endogenous glucocorticoids for lung maturation is
demonstrated by the delayed pulmonary development of mice with targeted
mutation of the glucocorticoid receptor (2) or corticotropin-releasing
hormone (CRH) (10, 11) genes. The lungs of CRH-deficient mice exhibit
retarded lung maturation as indicated by delayed SP-A, SP-B, and fatty
acid synthetase expression as well as by increased cellular
proliferation (12). Additional features of morphological maturation of
the fetal lung include increased air space formation, vascularization,
and thinning of alveolar septa, leading to a mature blood-gas
interface. Lung elastogenesis is intimately associated with these
morphological processes. Moreover, tropoelastin expression in the fetal
lung coincides with the initiation of fetal breathing and the rise of
circulating glucocorticoids (15, 17). Both glucocorticoids (14, 36) and
mechanical strain (24) have been shown to stimulate tropoelastin
production in cultured mesenchyme-derived cells. Several other
extracellular matrix molecule genes, including collagen type I, have
been shown to be influenced by mechanical stress (33, 35) and
glucocorticoids (1). Thus it is evident that physical forces and
glucocorticoids influence the expression of a number of maturational
genes in the fetal lung; however, the interaction between physical
forces and hormonal factors in controlling fetal lung development is
unknown. The objective of this study was to elucidate whether the
signaling pathways induced by physical and hormonal factors during
development are integrated and coordinated at the cellular and
transcriptional levels.
 |
MATERIALS AND METHODS |
Preparation of organotypic cultures.
The organotypic culture of mixed fetal lung cells has been previously
described (6). Briefly, the rats were killed by an excess of diethyl
ether during the canalicular stage of fetal lung development at 19 days
of gestation (term = 22 days). The fetuses were aseptically removed,
and the fetal lungs were dissected out in cold Hanks' balanced salt
solution without calcium or magnesium (HBSS
) and cleared of
major airways and vessels. The lungs were washed twice in HBSS
,
minced, and suspended in HBSS
. The lung tissue was digested for
20 min in an enzymatic solution of 0.125% (wt/vol) trypsin and
0.4 mg/ml DNase. After filtration through 100-µm mesh nylon blotting
cloth, Eagle's minimum essential medium (MEM) with 10% (vol/vol)
fetal bovine serum (FBS) was added to the single-cell suspension to
neutralize trypsin activity, and the mixture was centrifugated at 300 g for 10 min. The pellet was resuspended in MEM plus 10% FBS
and inoculated onto 2 × 2 × 0.25-cm Gelfoam
sponges at a density of 1.6 × 106 cells/sponge. After
inoculation, the cells were incubated for 1 h before the addition of 3 ml of MEM plus 10% (vol/vol) FBS to the culture dish. After a 24-h
incubation, the sponges were washed three times with serum-free MEM and
then incubated in serum-free MEM for 24 h before treatment.
Exposure of mixed fetal rat lung cells to stretch and
dexamethasone.
The mechanical stretch device used in these studies has been
described in detail elsewhere (6). It consists of a programmable burst
timer, a control unit, a dual-regulated DC power supply, and a set of
solenoids. A culture dish with a Gelfoam sponge was placed in front of
each solenoid. One end of each sponge was glued to the bottom of the
dish. The other end was attached to a movable metal bar, which was
wrapped and sealed in plastic tubing. The strain of cells cultured on
sponges was driven by the magnetic force generated through the
solenoids. The sponges were subjected to a 5% elongation from their
original length at 60 cycles/min for 15 min/h, which optimally enhanced
DNA synthesis and cell division without cell injury (6). The cells were
incubated in MEM with and without dexamethasone (10
7
M) and subjected to static culture or intermittent strain for 24 h.
Northern analysis.
Total cellular RNA was isolated from organotypic cultures by lysing the
cells in 4 M guanidinium thiocyanate followed by centrifugation on a
5.7 M cesium chloride cushion to pellet RNA. Total RNA (15 µg) was
size-fractionated on 1% (wt/vol) agarose gel containing 3%
(wt/vol) formaldehyde, transferred to Hybond-N+ membranes, and
immobilized by ultraviolet (UV) cross-linking. Tropoelastin and
collagen type I cDNAs were labeled with
[
-32P]dCTP with the random-primer method.
Prehybridization and hybridization were performed in 50% (vol/vol)
formamide, 5× sodium chloride-sodium phosphate-EDTA, 0.5%
(wt/vol) SDS, 5× Denhardt's solution, and 100 µg/ml
denatured herring sperm DNA at 42°C. After hybridization, the blots
were washed with 2× saline-sodium citrate (SSC) containing 0.2%
(wt/vol) SDS at 42°C for 10 min, followed by 1× SSC
with 0.2% (wt/vol) SDS at 42°C for 10 min. The blots were
exposed to Kodak XAR-5 film at
80°C. The blots were then
stripped and rehybridized with radiolabeled rat
-actin cDNA for normalization.
RT-PCR and Southern blotting.
Steady-state mRNA levels of SP-A and SP-C and heterogeneous nuclear RNA
(hnRNA) levels of tropoelastin and SP-C were amplified by RT-PCR.
Specifically, total lung RNA was treated with RNase-free DNase to
remove contaminating DNA. Total RNA (3 µg) in 5 µl of sterile water with 2.5 µM random hexanucleotide primer
(pdN6) was heated to 70°C for 10 min, quick-chilled on
ice, and then added to the reverse transcription reaction in
microcentrifuge tubes. Each reaction contained 4 µl of 5× PCR
buffer (100 mM Tris · HCl, pH 8.3, and 500 mM KCl),
0.2 µM 1,4-dithiothreitol, and 7.5 mM deoxynucleotide triphosphates
(dNTPs). After incubation at 37°C for 2 min, 200 U of Superscript
RT were added to a total volume of 20 µl. The samples were incubated
at 37°C for 60 min and heated to 70°C for 15 min, followed by
cooling at 5°C for 5 min. The cDNAs (5 µl) from the reverse
transcription reaction were then incubated with 5 µl of 10× PCR
buffer, 2.5 mM MgCl2, 10 mM dNTPs, 0.2 µM each primer,
and 2.5 U of Taq polymerase in a total volume of 50 µl at
95°C for 3 min. The samples were amplified for 15 (mRNA) and 25 (hnRNA) cycles, each consisting of 53°C annealing for 30 s,
72°C extension for 30 s, and denaturation for 30 s at 95°C.
Duration of the final elongation reaction was increased to 7 min at
72°C. For Southern blotting, amplified DNA (25 µl of total PCR)
was transferred to Hybond-N+ membranes and immobilized by UV
cross-linking. SP-A, SP-C, and
-actin probes for detection of
amplified mRNA were labeled by random priming with
[
-32P]dCTP. Tropoelastin and SP-C oligomer
probes for detection of amplified hnRNA were labeled with
[
-32P]ATP with T4 polynucleotide kinase.
After Southern hybridization, the blots were exposed to Kodak XAR-5
film for 6-12 h at
80°C. Autoradiographic signal was
quantified by densitometry and normalized to the relative amount of
-actin mRNA. No signals were detected after RNase treatment of
samples as well as after PCR without the initial addition of RT. The
oligonucleotide primer sequences are listed in Table
1, and PCR strategy is presented in Fig. 1.

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Fig. 1.
Schematic presentation of location of primers and probes used for
RT-PCR and Southern blotting. SP, surfactant protein; TE, tropoelastin;
hnRNA, heterogeneous nuclear RNA.
|
|
Statistical analysis.
Statistical significance was determined by one-way ANOVA followed by
assessment of differences with the Student-Newman-Keuls test for
nonpaired groups. Significance was defined as P < 0.05.
 |
RESULTS |
Mechanical strain selectively stimulated SP-C but not SP-A mRNA
expression.
To examine the effects of physical and hormonal factors on fetal lung
epithelial cell maturation, organotypic cultures of mixed fetal lung
cells incubated with and without 10
7 M dexamethasone
were subjected to either intermittent strain (60 cycles/min, 15 min/h,
5% elongation) or static culture for 24 h. Equal amounts of total RNA
(3 µg) were analyzed by low-cycle RT-PCR followed by Southern
hybridization with epithelium-specific SP-A and SP-C probes (5, 30,
32). Mechanical strain, but not dexamethasone treatment, significantly
increased the steady-state mRNA level of SP-C (Fig.
2). When the cells were subjected to both
mechanical strain and dexamethasone treatment, SP-C transcript levels
were not increased further (Fig. 2). In contrast, neither mechanical
strain nor dexamethasone affected steady-state mRNA levels of SP-A in
organotypic cultures of fetal rat lung cells (Fig. 2).


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Fig. 2.
Mechanical strain increased mRNA expression of SP-C, but not SP-A, in
organotypic cultures of fetal rat lung cells. Day 19 organotypic cultures of mixed lung cells incubated with and without
10 7 M dexamethasone (Dex) were subjected to a 24-h
intermittent strain regimen (60 cycles/min, 15 min/h, 5% elongation)
or static culture. Equal amounts of total RNA (3 µg) were analyzed by
RT-PCR followed by Southern hybridization with 32P-labeled
SP-A, SP-C, and -actin probes (A). Intensity of amplified
mRNA bands was quantified by densitometry (B). Results are
expressed as a ratio over -actin and normalized to control value.
Values are means ± SE of 3 separate experiments. * P < 0.05 vs. control.
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|
Mechanical strain and dexamethasone stimulated tropoelastin but not
collagen type I mRNA expression.
The effects of physical and hormonal factors on gene expression in
fetal lung mesenchymal cells were determined with the use of
tropoelastin and collagen type I as marker genes (19, 35, 36).
Mechanical strain did not affect mRNA expression of collagen type I
(Fig. 3), whereas dexamethasone treatment
showed a tendency to decrease the number of collagen type I
transcripts. In contrast, mechanical strain and dexamethasone treatment
alone significantly increased mRNA levels of tropoelastin. However,
when both mechanical strain and dexamethasone were applied to fetal
lung cells, no additive or synergistic effect on either collagen type I
or tropoelastin mRNA expression was observed (Fig. 3).


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Fig. 3.
Mechanical strain and Dex increased mRNA expression of tropoelastin,
but not type I collagen, in organotypic cultures of fetal rat lung
cells. Day 19 organotypic cultures of mixed lung cells
incubated with and without 10 7 M Dex were subjected
to a 24-h intermittent strain regimen (60 cycles/min, 15 min/h, 5%
elongation) or static culture. Equal amounts of total RNA (10 µg)
were analyzed by Northern hybridization with 32P-labeled
tropoelastin, type I collagen, and -actin probes (A).
Intensity of amplified mRNA bands was quantified by densitometry
(B). Results are expressed as a ratio over -actin and
normalized to control value. Values are means ± SE of 3 separate
experiments. * P < 0.05 vs. control.
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Mechanical strain and dexamethasone increased SP-C and tropoelastin
gene expression at the transcriptional level.
To determine whether the increased mRNA levels of SP-C and tropoelastin
required new gene transcription, cells incubated with and without
dexamethasone were subjected to either mechanical strain or static
culture in the presence of 10 µg/ml actinomycin D, an inhibitor of
gene transcription. Actinomycin D abrogated mechanical strain-induced
SP-C and tropoelastin mRNA expression as well as the
dexamethasone-induced increase in tropoelastin mRNA (Fig.
4). Thus it appears that the upregulation
in SP-C and tropoelastin mRNA expression by mechanical strain and/or
dexamethasone is controlled primarily at the level of transcription. To
confirm that mechanical strain and/or dexamethasone treatment triggers transcriptional activation of the SP-C and tropoelastin genes, hnRNAs
of SP-C and tropoelastin were analyzed by RT-PCR followed by Southern
hybridization (25). In principle, hnRNA (or preprocessed mRNA) is a
complete copy of a DNA template, which contains both introns and exons.
After being spliced, intron sequences are removed and exons are linked
to mRNA. Because splicing is a rapid process, measurement of hnRNA
should estimate ongoing transcription. To measure hnRNA levels, PCR
primers were designed to include intron sequences of the gene of
interest, and the PCR products (SP-C, 643 bp; tropoelastin, 478 bp)
were detected by Southern hybridization with oligoprobes containing
SP-C- or tropoelastin-specific sequences (Fig. 1). Mechanical strain
significantly increased the level of SP-C hnRNA, whereas dexamethasone
alone had no effect (Fig. 5). The
combination of mechanical strain and dexamethasone also increased the
amount of SP-C hnRNA (Fig. 5). Stretch and dexamethasone alone as well
as the combined treatment significantly increased hnRNA expression of
tropoelastin (Fig. 6). These results
corroborate that the upregulation of SP-C gene expression by mechanical
strain and tropoelastin gene expression by mechanical strain and/or
dexamethasone are mainly due to an increase in the rate of
transcription.

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Fig. 4.
Increased SP-C and tropoelastin mRNA expression in organotypic cultures
of fetal rat lung cells subjected to mechanical strain and/or Dex were
blocked by actinomycin D. Day 19 organotypic cultures of mixed
lung cells incubated with and without 10 7 M Dex were
subjected to a 24-h intermittent strain regimen (60 cycles/min, 15 min/h, 5% elongation) or static culture in presence of 10 µg/ml
actinomycin D. Equal amounts of total RNA were analyzed by either
RT-PCR and Southern hybridization (SP-C) or by Northern hybridization
(TE). Intensity of amplified mRNA bands was quantified by densitometry.
Results are expressed as a ratio over -actin and normalized to
control value. Values are means ± SE of 3 separate experiments.
* P < 0.05 vs. control.
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Fig. 5.
Increased transcription of SP-C gene in organotypic cultures of fetal
rat lung cells subjected to mechanical strain. Day 19 organotypic cultures of mixed lung cells incubated with and without
10 7 M Dex were subjected to a 24-h intermittent
strain regimen (60 cycles/min, 15 min/h, 5% elongation) or static
culture. Amounts of hnRNA were analyzed by RT-PCR followed by Southern
hybridization (A; see Fig. 1). Intensity of amplified hnRNA
bands was quantified by densitometry (B). Results were
normalized to control value. Values are means ± SE of 3 separate
experiments. * P < 0.05 vs. control.
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Fig. 6.
Increased transcription of TE gene in organotypic cultures of fetal rat
lung cells subjected to mechanical strain and/or Dex. Day 19 organotypic cultures of mixed lung cells incubated with and without
10 7 M Dex were subjected to a 24-h intermittent
strain regimen (60 cycles/min, 15 min/h, 5% elongation) or static
culture. hnRNA expression was determined by RT-PCR followed by Southern
hybridization (A; see Fig. 1). Intensity of amplified hnRNA
bands was quantified by densitometry (B). Results were
normalized to control value. Values are means ± SE of 3 separate
experiments. * P < 0.05 from control.
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 |
DISCUSSION |
A variety of growth factors, hormones, and cytokines as well as
physical factors act as positive or negative regulators of lung growth
and development (27). Because fetal breathing movements and endogenous
hormones are concurrently present during lung development, it is
difficult to distinguish their relative contribution to the
maturational process. To elucidate the interactions between physical
and hormonal factors on fetal lung cell maturation at the cellular and
molecular levels, we exposed mixed fetal rat lung cells in organotypic
cultures to mechanical strain and dexamethasone alone or as a
combination. Marker gene analysis of this complex cellular model
allowed us to study the influence of mechanical strain and/or
glucocorticoids on the maturation of lung epithelial cells and
fibroblasts separately. We found that mechanical stress and
dexamethasone selectively stimulated gene expression in both epithelial
and mesenchymal cells. However, both stimulants appear not to form an
integrative signaling network during lung development.
Selective stimulation of SP-C gene expression by mechanical strain.
On the basis of previous in vivo (12, 21, 26) and in vitro (13, 28)
studies in fetal rats, we anticipated that glucocorticoids would
increase SP-A and SP-C mRNA expression. Our findings are not consistent
with these earlier observations. A possible explanation may be the
longer duration of exposure (>48 vs. 24 h) of the rat lung to
glucocorticoids in the previous studies (13, 21, 26, 28). Although
physical forces have been shown to affect pulmonary surfactant lipid
metabolism of fetal lung cells (22), to our knowledge, this is the
first demonstration that mechanical strain influences SP-C gene
expression by fetal lung epithelial cells. The observation that SP-C
and not SP-A mRNA expression is regulated by an intermittent mechanical
strain in vitro suggests that fetal breathing movements may
specifically contribute to SP-C gene expression during development.
Indeed, the appearance of SP-C mRNA in the fetal rat lung coincides
with the initiation of fetal breathing movements at 16-17 days of
gestation, whereas SP-A transcripts are first detectable at 18-19
days of gestation (20). Whether mechanical strain directly affects SP-C
expression in fetal epithelial cells remains to be elucidated. We used
an organotypic cell culture system in which mesenchymal-epithelial cell
interactions are preserved to mimic the cellular environment in vivo.
Because the developmental response to mechanical strain is determined
by the mesenchyme (34) and SP-C gene expression is controlled by
mesenchymal-epithelial interactions (3, 23), it is possible that a
mesenchyme-regulatory mechanism is involved in the mechanical
strain-induced SP-C gene expression.
Selective stimulation of tropoelastin gene expression by mechanical
strain and dexamethasone.
The physiological importance of elastic fibers lies in the unique
elastometric properties of elastin, which is the functional component
of the mature fiber. During fetal development, the lung is
characterized by the increase in collagenous and elastic matrices and
by the dynamic changes in the number and spatial relationship of
collagen- and elastin-producing cells. In this study, we demonstrated that mechanical force and glucocorticoids are important regulators of
gene expression of tropoelastin, the soluble precursor of elastin. The
induction of tropoelastin production coincides with the initiation of
fetal breathing movements (8, 17). Yee et al. (36) have previously reported that glucocorticoid-induced tropoelastin gene expression in fetal lung fibroblasts is mediated via transforming growth factor (TGF)-
3. Because mechanical strain has been found to
stimulate TGF-
gene expression in various cells (7, 37), it is
plausible that strain-induced tropoelastin gene expression in fetal
lung cells is mediated via TGF-
3. No significant additive or
synergistic effect in tropoelastin gene expression was noted when cells
were subjected to mechanical strain in the presence of dexamethasone.
This suggests that the signaling pathways activated by physiological
levels of mechanical strain and glucocorticoids in fetal lung
fibroblasts are probably not integrated or coordinated at the
transcriptional level. Alternatively, it is possible that this level of
mechanical strain and dexamethasone resulted in a maximal effect and
that suboptimal levels would have shown additive or synergistic effects.
Transcriptional regulation of SP-C and tropoelastin by mechanical
strain and dexamethasone.
To assess the molecular mechanism by which physical force and
glucocorticoids control tropoelastin and SP-C mRNA expression, we first
inhibited transcription with actinomysin D. Because this treatment
blocked mechanical strain-induced SP-C mRNA expression as well as
mechanical strain- and/or dexamethasone-induced tropoelastin mRNA
expression, we examined transcriptional regulation by determining the
tropoelastin or SP-C hnRNA levels. Although this strategy does not
directly measure the transcriptional activity, hnRNA levels reflect the
rate of active, ongoing transcription (25). Compared with the commonly
used nuclear runoff assays, the hnRNA approach is more sensitive and
requires less material. A great advantage is that it can be combined
with regular RT-PCR to measure both mRNA and hnRNA from the same RT
products. In the present study, we found that hnRNA levels of both SP-C
and tropoelastin were increased by mechanical strain, whereas
dexamethasone also increased the amount of tropoelastin hnRNA. The
magnitude of changes in mRNA and hnRNA levels induced by either
mechanical strain or dexamethasone were in the same range, suggesting
that the elevation in mRNAs was mainly due to an increase in
transcription of the SP-C and tropoelastin genes. In contrast to
tropoelastin expression, Xu et al. (35) have recently found that
mechanical strain regulates the expression of various extracellular
matrix molecules in fetal lung cells by a posttranscriptional
mechanism. Mechanical strain increased soluble fibronectin content by
increasing protein synthesis and secretion of fibronectin while
decreasing fibronectin message levels (9). A similar effect of
mechanical stress was observed for collagen type I expression (35).
Mechanical strain of fetal lung cells has also been shown to increase
the secretion of proteoglycans and glycosaminonglycans without
affecting core protein expression (33, 35). Thus it appears that the
effects of mechanical forces on extracellular matrix remodeling during
fetal lung development are regulated at various levels depending on the
extracellular matrix molecule.
 |
ACKNOWLEDGEMENTS |
This study was supported by a Medical Research Council of Canada
Group Grant (to M. Post) and Operating Grant MT-13270 (to M. Liu) and
an operating grant from the James H. Cumming Foundation (to M. Liu).
 |
FOOTNOTES |
E. Mourgeon is a recipient of Fellowships from the Société
Française du Anesthesize et de Réanimation (SFAR) and the
Dean's Office, Faculty of Medicine, University of Toronto (Toronto,
Canada). M. Liu is a Scholar of the Medical Research Council of Canada.
The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement"
in accordance with 18 U.S.C. §1734 solely to indicate this fact.
Address for reprint requests and other correspondence: M. Post,
Lung Biology Program, Hospital for Sick Children, 555 University
Ave., Toronto, Ontario, Canada M5G 1X8 (E-mail: mppm{at}sickkids.on.ca).
Received 9 July 1999; accepted in final form 9 January 2000.
 |
REFERENCES |
1.
Beck, JC,
Mitzner W,
Johnson JW,
Hutchins GM,
Fiodart JM,
Lomdon WT,
Palmer AE,
and
Scott R.
Betamethasone and the rhesus fetus: effect on lung morphometry and connective tissue.
Pediatr Res
15:
235-240,
1981[Abstract].
2.
Cole, TJ,
Blendy JA,
Monaghan P,
Krieglstein K,
Schmid W,
Aguzzi A,
Fantuzzi Hummler E,
Unsicker K,
and
Schütz G.
Targeted disruption of the glucocorticoid receptor blocks adrenergic chromaffin cell development and severely retards lung maturation.
Genes Dev
9:
1611-1621,
1995.
3.
Deimling, J,
Thompson K,
Tseu I,
and
Post M.
Mesenchyme determines epithelial morphogenesis but not differentiation in lung recombinants at late fetal gestation (Abstract).
Am J Respir Crit Care Med
157:
A14,
1998.
4.
Harding, R,
and
Albuquerque C.
Pulmonary hypoplasia: role of mechanical factors in prenatal lung growth.
In: Lung Development, edited by Gaultier C,
Bourbon J,
and Post M.. Oxford, UK: Oxford University Press, 1999, p. 364-394.
5.
Kalina, M,
Mason RJ,
and
Shannon JM.
Surfactant protein C is expressed in alveolar type II cells but not in Clara cells of rat lung.
Am J Respir Cell Mol Biol
6:
594-600,
1992[ISI][Medline].
6.
Liu, M,
Skinner SJM,
Xu J,
Han RNN,
Tanswell AK,
and
Post M.
Stimulation of fetal rat lung cell proliferation in vitro by mechanical strain.
Am J Physiol Lung Cell Mol Physiol
263:
L376-L383,
1992[Abstract/Free Full Text].
7.
Li, Q,
Muragaki Y,
Hatamura I,
Ueno H,
and
Ooshima A.
Stretch-induced collagen synthesis in cultured smooth muscle cells from rabbit aortic media and a possible involvement of angiotensin II and transforming growth factor-beta.
J Vasc Res
35:
93-103,
1998[ISI][Medline].
8.
Mariani, TJ,
and
Pierce RA.
Development of lung elastic matrix.
In: Lung Development, edited by Gaultier C,
Bourbon J,
and Post M.. Oxford, UK: Oxford University Press, 1999, p. 28-45.
9.
Mourgeon, E,
Xu J,
Tanswell AK,
Liu M,
and
Post M.
Mechanical strain-induced posttranscriptional regulation of fibronectin production in fetal lung cells.
Am J Physiol Lung Cell Mol Physiol
277:
L142-L149,
1999[Abstract/Free Full Text].
10.
Muglia, LJ,
Jenkins NA,
Gilbert DJ,
Copeland NG,
and
Majzoub JA.
Expression of the mouse corticotropin-releasing hormone gene in vivo and targeted inactivation in embryonic stem cells.
J Clin Invest
93:
2066-2072,
1994[ISI][Medline].
11.
Muglia, L,
Jacobson Dikkes P,
and
Majzoub JA.
Cortocotropin-releasing hormone deficiency reveals major fetal but not adult glucocorticoid need.
Nature
373:
427-432,
1995[ISI][Medline].
12.
Muglia, LJ,
Bae DS,
Brown TT,
Vogt SK,
Alvarez J,
Sunday ME,
and
Majzoub JA.
Proliferation and differentiation defects during lung development in corticotropin-releasing hormone-deficient mice.
Am J Respir Cell Mol Biol
20:
181-188,
1999[Abstract/Free Full Text].
13.
Nichols, KV,
Floros J,
Dynia DW,
Veletza SV,
Wilson CM,
and
Gross I.
Regulation of surfactant protein A mRNA by hormones and butyrate in cultured fetal rat lung.
Am J Physiol Lung Cell Mol Physiol
259:
L488-L495,
1990[Abstract/Free Full Text].
14.
Noguchi, A,
Fisching K,
Kursar JD,
and
Reddy R.
Developmental changes in tropoelastin synthesis by rat pulmonary fibroblasts and effect of dexamethasone.
Pediatr Res
28:
379-382,
1990[Abstract].
15.
Noguchi, A,
and
Samaha H.
Developmental changes in tropoelastin gene expression in the rat lung studied by in situ hybridization.
Am J Respir Cell Mol Biol
5:
571-578,
1991[ISI][Medline].
16.
Odom, MW,
and
Ballard PL.
Developmental and hormonal regulation of the surfactant system.
In: Lung Growth and Development, edited by McDonald J.. New York: Dekker, 1997, p. 495-575.
17.
Pierce, RA,
Mariencheck WI,
Sandefur S,
Crouch EC,
and
Parks WC.
Glucocorticoids upregulate tropoelastin expression during late stages of fetal lung development.
Am J Physiol Lung Cell Mol Physiol
268:
L491-L500,
1995[Abstract/Free Full Text].
18.
Post, M,
and
Smith BT.
Hormonal control of surfactant metabolism.
In: Pulmonary Surfactant: From Molecular Biology to Clinical Practice, edited by Robertson B,
van Golde LMG,
and Batenburg JJ.. Amsterdam: Elsevier, 1992, p. 379-424.
19.
Rolland, G,
Xu J,
Tanswell AK,
and
Post M.
Ontogeny of extracellular matrix related gene expression by rat lung cells at late fetal gestation.
Biol Neonate
73:
112-120,
1998[ISI][Medline].
20.
Schellhase, DE,
Emrie PA,
Fisher JH,
and
Shannon JM.
Ontogeny of surfactant proteins in the rat.
Pediatr Res
26:
167-174,
1989[Abstract].
21.
Schellhase, DE,
and
Shannon JM.
Effects of maternal dexamethasone on expression of SP-A, SP-B and SP-C in the fetal rat.
Am J Respir Cell Mol Biol
4:
304-312,
1991[ISI][Medline].
22.
Scott, JE,
Yang S-Y,
Stanik E,
and
Anderson JE.
Influence of strain on [3H]thymidine incorporation, surfactant-related phospholopid synthesis, and cAMP levels in fetal type II alveolar cells.
Am J Respir Cell Mol Biol
8:
258-265,
1993[ISI][Medline].
23.
Shannon, JM.
Induction of alveolar type II cell differentiation in fetal tracheal epithelium by grafted distal lung mesenchyme.
Dev Biol
166:
600-614,
1994[ISI][Medline].
24.
Sutcliffe, MC,
and
Davidson JM.
Effect of static stretch on elastin production by porcine aortic smooth muscle cells.
Matrix
10:
148-153,
1990[ISI][Medline].
25.
Swee, MH,
Parks WC,
and
Pierce RA.
Developmental regulation of elastin production.
J Biol Chem
270:
14899-14906,
1995[Abstract/Free Full Text].
26.
Sweezey, N,
Mawdsley C,
Ghibu F,
Song L,
Buch S,
Moore A,
Antakly T,
and
Post M.
Differential regulation of glucocorticoid receptor expression in fetal rat lung cells.
Pediatr Res
38:
506-512,
1995[Abstract].
27.
Tanswell, AK,
Liu M,
and
Post M.
Bronchopulmonary dysplasia: strategies for therapeutic intervention.
In: Intensive Care in Childhood, edited by Tibboel D,
and van der Voort E.. Heidelberg, Germany: Springer-Verlag, 1996, vol. 25, p. 53-65.
28.
Vletza, SV,
Nichols KV,
Gross I,
Lu H,
Dynia DW,
and
Floros J.
Surfactant protein C: hormonal control of SP-C mRNA levels in vitro.
Am J Physiol Lung Cell Mol Physiol
262:
L684-L687,
1992[Abstract/Free Full Text].
29.
Wang, J,
Kuliszewski M,
Yee W,
Sedlackova L,
Xu J,
Tseu I,
and
Post M.
Cloning and characterization of glucocorticoid-induced genes in fetal rat lung fibroblasts: transforming growth factor
3.
J Biol Chem
270:
2722-2728,
1995[Abstract/Free Full Text].
30.
Wang, J,
Souza P,
Kuliszewski M,
Tanswell AK,
and
Post M.
Expression of surfactant proteins in embryonic rat lung.
Am J Respir Cell Mol Biol
10:
222-229,
1994[Abstract].
31.
Wirtz, HRW,
and
Dobbs LG.
Calcium mobilization and exocytosis after one mechanical strain of lung epithelial cells.
Science
250:
1266-1269,
1990[ISI][Medline].
32.
Wohlford-Lenane, CL,
and
Snyder LM.
Localization of surfactant-associated proteins SP-A and SP-B mRNA in rabbit fetal lung tissue by in situ hybridization.
Am J Respir Cell Mol Biol
7:
335-343,
1992[ISI][Medline].
33.
Xu, J,
Liu M,
Liu J,
Caniggia I,
and
Post M.
Mechanical strain induces constitutive and regulated secretion of glycosaminoglycans and proteoglycans in fetal lung cells.
J Cell Sci
109:
1605-1613,
1996[Abstract/Free Full Text].
34.
Xu, J,
Liu M,
Tanswell K,
and
Post M.
Mesenchymal determination of mechanical strain-induced fetal lung cell proliferation.
Am J Physiol Lung Cell Mol Physiol
275:
L545-L550,
1998[Abstract/Free Full Text].
35.
Xu, J,
Liu M,
and
Post M.
Differential regulation of expression of extracellular matrix molecules by mechanical strain of fetal lung cells.
Am J Physiol Lung Cell Mol Physiol
276:
L728-L735,
1999[Abstract/Free Full Text].
36.
Yee, W,
Wang J,
Liu J,
Tseu I,
Kuliszewski M,
and
Post M.
Glucocorticoid induced tropoelastin expression is mediated via transforming growth factor-
3.
Am J Physiol Lung Cell Mol Physiol
270:
L992-L1001,
1996[Abstract/Free Full Text].
37.
Zhuang, H,
Wang W,
Tahernia AD,
Levitz CL,
Luchetti WT,
and
Brighton CT.
Mechanical strain-induced proliferation of osteoblastic cell parallels increased TGF-beta 1 mRNA.
Biochem Biophys Res Commun
13:
449-453,
1996.
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