Am. J. Respir. Cell Mol. Biol., Vol 12, No. 1, Jan 1995, 19-26.
In vivo hyperoxic exposure increases cultured lung fibroblast proliferation and c-Ha-ras expression
MD Kelleher, ET Naureckas, J Solway and MB Hershenson
Department of Pediatrics, University of Chicago, Illinois.
Exposure to hyperoxia has been demonstrated to alter the cell number of
lung fibroblasts in vivo. The precise mechanism of lung fibroblast
proliferation after hyperoxic exposure has not been elucidated, however. We
examined the growth characteristics of lung fibroblasts isolated from
21-day-old rats exposed to air or 100% O2 for 8 days. Cell proliferation
was assessed by hemocytometry, [3H]thymidine incorporation, and fractional
labeling with the thymidine analog bromodeoxyuridine. Under all conditions
tested, fibroblasts isolated from O2-exposed rats grew more rapidly than
those from air-exposed rats. Conditioned medium from fibroblasts isolated
from hyperoxia- exposed rats failed to increase the [3H]thymidine
incorporation of control cells to that observed in cells isolated from
hyperoxia-exposed animals, suggesting that an autocrine growth factor was
not responsible for the excess proliferation. Sensitivity to exogenous
growth factors was assessed by measuring the response to increasing
concentrations of insulin-like growth factor-1 (IGF-1). Relative to 1%
fetal bovine serum (FBS), concentrations of IGF-1 between 3 and 30 ng/ml
significantly increased the [3H]thymidine incorporation of fibroblasts
derived from hyperoxic animals, whereas control cells were unresponsive to
IGF-1 stimulation. The apparent sensitivity to IGF-1 led us to assess the
effect of in vivo hyperoxic exposure on the expression of c-Ha-ras, which
encodes a membrane-bound, GTP-binding/hydrolyzing protein essential for
progression through G1 in the cell cycle. ras mRNA levels in quiescent,
control cells were minimal but increased following serum stimulation. The
c-Ha-ras expression of lung fibroblasts from hyperoxia- exposed animals, on
the other hand, was substantial in quiescent cells and remained high after
serum exposure.(ABSTRACT TRUNCATED AT 250 WORDS)
