Contribution of epithelial-derived fibroblasts to bleomycin-induced lung fibrosis.
BACKGROUND
Lung fibroblasts are key mediators of fibrosis resulting in accumulation of excessive interstitial collagen and extracellular matrix, but their origins are not well defined.


OBJECTIVE
We aimed to elucidate the contribution of lung epithelium-derived fibroblasts via epithelial-mesenchymal transition (EMT) in the intratracheal bleomycin model.


METHODS
Primary type II alveolar epithelial cells were cultured from Immortomice and exposed to transforming growth factor-beta(1) and epidermal growth factor. Cell fate reporter mice that permanently mark cells of lung epithelial lineage with beta-galactosidase were developed to study EMT, and bone marrow chimeras expressing green fluorescent protein under the control of the fibroblast-associated S100A4 promoter were generated to examine bone marrow-derived fibroblasts. Mice were given intratracheal bleomycin (0.08 unit). Immunostaining was performed for S100A4, beta-galactosidase, green fluorescent protein, and alpha-smooth muscle actin.


RESULTS
In vitro, primary type II alveolar epithelial cells undergo phenotypic changes of EMT when exposed to transforming growth factor-beta(1) and epidermal growth factor with loss of prosurfactant protein C and E-cadherin and gain of S100A4 and type I procollagen. In vivo, using cell fate reporter mice, approximately one-third of S100A4-positive fibroblasts were derived from lung epithelium 2 weeks after bleomycin administration. From bone marrow chimera studies, one-fifth of S100A4-positive fibroblasts were derived from bone marrow at this same time point. Myofibroblasts rarely derived from EMT or bone marrow progenitors.


CONCLUSIONS
Both EMT and bone marrow progenitors contribute to S100A4-positive fibroblasts in bleomycin-induced lung fibrosis. However, neither origin is a principal contributor to lung myofibroblasts.
Tanjore
Harikrishna
H
Division of Allergy, Pulmonary, and Critical Care Medicine, Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232-2650, USA.
Xu
Xiaochuan C
XC
Polosukhin
Vasiliy V
VV
Degryse
Amber L
AL
Li
Bo
B
Han
Wei
W
Sherrill
Taylor P
TP
Plieth
David
D
Neilson
Eric G
EG
Blackwell
Timothy S
TS
Lawson
William E
WE
D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000008:administration & dosage*; D001761:Bleomycin; D015153:Blotting, Western / Q000379:methods; D018929:Cell Culture Techniques; D004195:Disease Models, Animal; D004847:Epithelial Cells / Q000378:metabolism*; D004848:Epithelium / Q000378:metabolism; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism*; D008648:Mesoderm / Q000166:cytology / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D011650:Pulmonary Alveoli / Q000378:metabolism; D011658:Pulmonary Fibrosis / Q000139:chemically induced / Q000378:metabolism*
D000903:Antibiotics, Antineoplastic; D001761:Bleomycin