Spontaneous production of PDGF A-chain homodimer by rat lung fibroblasts in vitro.

Platelet-derived growth factor (PDGF) is considered a decisive mediator of fibroblast growth and phenotype within the lung. The cellular sources of PDGF within the lung remain undefined. The ability of lung fibroblasts themselves to produce PDGF in vitro was therefore investigated. Northern and Western blot analyses revealed the expression of PDGF-A mRNA and secretion of A-chain containing proteins by fibroblasts derived from adult and fetal rat lung. PDGF-A gene or protein expression were below the limits of detection in two human lung fibroblast lines examined in a similar manner. PDGF-B transcripts or proteins were not detected in any lung fibroblast line examined. Conditioned medium (CM) was collected from these same lung fibroblast lines and tested for its ability to promote cell growth using human fetal lung fibroblasts as targets. Both adult and fetal rat lung fibroblasts were found to produce a potent and efficacious stimulus for cell growth. Growth-promoting activity in rat fibroblast-derived CM functioned as a "competence" factor and was partially inhibited by anti-PDGF antibody. Thus rat lung fibroblasts in vitro produce potent growth factors of which at least one appears to be PDGF-AA. Differences in the expression of PDGF-AA between rat and human lung fibroblasts exist. Growth factor-producing fibroblasts may play a role in lung repair and remodeling through production PDGF-AA in vivo.