In vivo hyperoxic exposure increases cultured lung fibroblast proliferation and c-Ha-ras expression.

Abstract

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)

Apoptosis and proliferation in lungs of ventilated and oxygen-treated preterm infants

“…The mechanisms activating apoptosis and proliferation by physical forces remain to be investigated. Apoptosis following cyclic stretch has been shown in type II epithelial cells and fibroblasts [10,11]. Proliferation of rat lung fibroblasts, however, is inhibited by cyclic mechanical stretch [12], whereas, in a-smooth muscle cells, strain increases proliferation [13].…”

“…Proliferation of rat lung fibroblasts, however, is inhibited by cyclic mechanical stretch [12], whereas, in a-smooth muscle cells, strain increases proliferation [13]. Cellular reactions to hyperoxia in the lung have been investigated in animal models, and there exposure to hyperoxia has been shown to induce apoptosis and proliferation [1][2][3]11]. The present study of the effects of mechanical ventilation at elevated oxygen concentrations on apoptosis and proliferation in the lungs of preterm infants with RDS led to results which are in good agreement with the findings in animal models of hyperoxia.…”

“…Molecules such as p21 WAF/CIP1 and p53, which promote cell cycle arrest, are upregulated during hyperoxia [20] and the messenger ribonucleic acids (mRNAs) encoding the cell cycle proteins histone and thymidine kinase are not translated under hyperoxic conditions [19]. However, in rat lung and in lung explant cultures, under hyperoxic conditions, increased proliferation, especially of alveolar type II cells and fibroblasts, was observed [10,11]. This indicates that, in contrast to cell culture experiments, tissue cell proliferation is influenced by cell/cell interactions of different cell types.…”

Expression dynamics of caveolin-1 in fibroblasts of newborn rats with chronic lung disease and its impact on lung fibroblast proliferation

“…We followed the method reported by Kelleher et al 8 but with the following modifications. Wistar rats 2,3 were selected at random on days 3, 7 and 14 after the experiment had commenced.…”

Effect of covalent antithrombin-heparin complex on developmental mechanisms in the lung

“…During recovery in RDS patients, elevated cell proliferation leads to remodeling of the alveolar surface (18,37,50) that may assist in the evolution of BPD characterized by areas of increased fibroblast growth (fibrosis) (2,3,35) and generalized reticulogranular lung opacities (12). Indeed, for severely premature neonates, BPD/CLD shows progression towards impairment of alveolar septation from enhanced proteolysis of extracellular matrix components (30,77), coinciding with increased appearance of a number of enzymes such as neutrophil elastase and matrix metalloproteinase (MMP)-8 (20,77,79).…”