Differential regulation of the genes encoding platelet-derived growth factor receptor and its ligand in rat lung during microvascular and alveolar wall remodeling in hyperoxia.

The growth factors that operate while the lung remodels in hyperoxia are not known. At the lung periphery, high oxygen levels cause cell hypertrophy and hyperplasia, and this results in a thickening of the alveolar-capillary membrane and the walls of its associated microvessels. The present study examines gene expression of platelet-derived growth factor (PDGF) receptor and its ligand in this region of the lung of rats breathing 87% oxygen and compares this with the levels of expression in normal lung. In similar peripheral lung tissue, the proliferative response of specific cell populations has been assessed by [3H]thymidine incorporation and autoradiography. Normal lung expresses PDGF alpha-receptor subunit transcripts of 6.5 and 4.7 kb and PDGF beta-receptor transcripts of 5.5 and 4.5 kb. PDGF A-chain transcripts of 2.9, 2.3, and 1.7 kb are also expressed, each being at 10-fold higher levels than the single 3.5-kb transcript detected for PDGF B-chain. Within hours of breathing high concentrations of oxygen, mRNA levels change rapidly for the PDGF receptor subunits. These levels return to normal after 1 day and then decline over the next 28 days of exposure. PDGF A-chain mRNA increases 12 to 18 h after exposure, but then returns to normal levels. It is the PDGF B-chain mRNA that responds most to hyperoxia by increasing 10-fold on day 3. This increase immediately precedes the proliferative response on day 4 of microvascular adventitial fibroblasts, precursor smooth muscle cells, and epithelial cells but not smooth muscle cells, which do not proliferate until day 28.