Thrombin regulates PDGF expression in bovine glomerular endothelial cells

The proteolytic enzyme thrombin is produced during activation of the coagulation pathway. Intraglomerular fibrin deposition and thrombosis are common pathologic features of several glomerular diseases, including transplant rejection. The effect of thrombin on platelet-derived growth factor (PDGF) production and DNA synthesis in well characterized bovine glomerular endothelial cells (G/endo) was studied. DNA synthesis was measured as the amount of [3H]thymidine incorporated into acid-insoluble material. PDGF released in the supernatant was measured by Western blotting and by a radioreceptor assay. PDGF mRNA expression was analyzed by solution hybridization, using human genomic PDGF B-chain (c-sis) and A-chain cDNA probes. G/endo constitutively secrete PDGF activity in serum-free medium. Thrombin stimulates PDGF production and increases the expression of mRNA that hybridizes with labeled B-chain but not A-chain probe, whereas epidermal growth factor and transforming growth factor-alpha stimulate the expression of PDGF A-chain mRNA. In addition, thrombin stimulates DNA synthesis with a peak effect at 24 h. Unlike endothelial cells from other microvascular beds, G/endo did not respond to any of the three PDGF isoforms BB, AB, or AA. These data demonstrate that bovine G/endo produce PDGF and that thrombin stimulates de novo synthesis of PDGF from these cells. Because mesangial, but not bovine, G/endo express PDGF receptors, PDGF released by G/endo is likely to modulate mesangial cell functions such as proliferation and matrix production by means of a paracrine mechanism.