Am. J. Respir. Cell Mol. Biol., Vol 12, No. 3, 03 1995, 268-274.
Bronchoalveolar lavage fluid from immature rats with hyperoxia-induced airway remodeling is mitogenic for airway smooth muscle
ET Naureckas, MB Hershenson, MK Abe, MD Kelleher, C Florio, SI Heisler, M Absher, JN Evans, RW Samsel and J Solway
Department of Medicine, University of Chicago, Illinois 60637.
We previously demonstrated that hyperoxia-exposed immature rats develop
airway smooth muscle layer thickening; this remodeling appears partially
attributable to smooth muscle hyperplasia. In this study, we tested the
hypothesis that excess mitogenic activity for airway smooth muscle cells is
present within the lungs of hyperoxia-exposed immature rats. We assessed
the proliferative effect of bronchoalveolar lavage (BAL) fluid from air-
and O2-exposed animals on cultured rat tracheal smooth muscle cells. BAL
fluids from air- or O2-exposed immature rats increased DNA synthesis
([3H]-thymidine incorporation at 24 h of incubation) and cell number
(compared with DMEM-treated control cells, at 2 days of incubation), but
BAL fluid from O2-exposed animals had significantly greater mitogenic
effects. This excess mitogenic activity was lipid inextractable and was
ablated by trypsin digestion, indicating that at least one polypeptide
growth factor was responsible; molecular sieve fractionation demonstrated a
molecular weight of > 10 kD. Because platelet-derived growth factor
(PDGF) has been identified in other models of hyperoxia exposure, we tested
the further hypothesis that PDGF contributes to the observed excess
mitogenic activity. Addition of neutralizing anti-PDGF antibodies to
BAL-stimulated smooth muscle cultures did not reduce BAL fluid-induced
mitogenesis. These data indicate that the lungs of O2-exposed rats contain
excess mitogenic activity for airway smooth muscle, attributable to
non-PDGF polypeptide growth factors. It is conceivable that this abnormal
mitogenic activity contributes to O2-induced airway smooth muscle
remodeling observed in immature rats in vivo.