IN-SITU HYBRIDIZATION ANALYSIS OF RAT LUNG ALPHA(1)(I) AND ALPHA(2)(I) COLLAGEN GENE-EXPRESSION IN PULMONARY FIBROSIS INDUCED BY ENDOTRACHEAL BLEOMYCIN INJECTION
K. Zhang et al., IN-SITU HYBRIDIZATION ANALYSIS OF RAT LUNG ALPHA(1)(I) AND ALPHA(2)(I) COLLAGEN GENE-EXPRESSION IN PULMONARY FIBROSIS INDUCED BY ENDOTRACHEAL BLEOMYCIN INJECTION, Laboratory investigation, 70(2), 1994, pp. 192-202
BACKGROUND: Endotracheal bleomycin administration in rats and other an
imal species causes rapid development of pulmonary fibrosis, character
ized by a transiently increased number of contractile, filament-laden
parenchymal cells and increased lung collagen synthesis and deposition
. However, the identity and source of the cells that actively synthesi
ze collagen and other extracellular matrix and their relationship to t
he altered lung structure and function remain uncertain. EXPERIMENTAL
DESIGN: In this study, the cells expressing alpha(1)(I) and alpha(2)(I
) procollagen genes were identified and their localization analyzed in
control and bleomycin-treated rat lungs at different time points, by
in situ and Northern hybridization analyses. RESULTS: In control lungs
, only a few scattered fibroblasts with weak expression of the alpha(1
)(I) procollagen gene were localized exclusively in the adventitia of
the primary and tertiary bronchi, as well as major blood vessels. At d
ay 3 after bleomycin treatment, scattered interstitial cells with sign
ificantly increased alpha(1)(I) and alpha(2)(I) procollagen gene expre
ssion were observed in the adventitia of bronchioles, terminal brochio
les, and adjacent small blood vessels. At days 7 and 14, there was a d
ramatic increase in the number of interstitial cells expressing large
amounts of alpha(1)(I) procollagen messenger RNA in these areas and ex
tending to the lung parenchyma. This was followed on days 21 and 28 by
significant decreases in procollagen gene expression and the number o
f cells with increased collagen gene expression. Most of the cells wit
h enhanced collagen gene expression were arrayed in a disorganized fas
hion and were localized mainly around bronchioles, terminal bronchiole
s, and adjacent small blood vessels as well as in the irregularly dist
ributed fibrotic foci, some submesothelial areas, and injured parenchy
ma. Northern blot analysis was consistent with the above in situ hybri
dization observation of the kinetics of collagen gene expression. CONC
LUSIONS: The results indicate that in this rat fibrosis model, increas
ed numbers of the interstitial cells with high expression of type I pr
ocollagen genes are derived primarily from the fibroblasts in the adve
ntitia of bronchioles, terminal bronchioles, and adjacent blood vessel
s, as well as the submesothelial region. This then can result in furth
er expansion to adjacent parenchyma and alveolar areas.