Expression and developmental control of platelet-derived growth factor A-chain and B-chain/Sis genes in rat aortic...

Cultured arterial smooth muscle cells (SMC) can produce platelet-derived growth factor (PDGF)-like molecules. This property raises the possibility that SMC-derived PDGFs function as autocrine/paracrine regulators in the formation and maintenance of the artery wall. In this study we have asked if levels of mRNAs directing synthesis of PDGF are modulated in aortic SMC during postnatal development. We report here that genes encoding PDGF A- and B-chain precursors are expressed at similar low levels in intact aortas from newborn and adult rats. Marked differences in regulation of transcript abundance of these genes were revealed when aortic SMC were grown in cell culture. PDGF B-chain transcripts accumulated in passaged newborn rat SMC but not adult rat SMC, whereas PDGF A-chain RNA was found in comparable amounts in SMC from both age groups. Similarly, SMC from newborn rats secreted at least 60-fold more PDGF-like activity into conditioned medium than did adult rat SMC. PDGF B-chain transcripts in newborn rat aortic SMC are short-lived and increased 5-fold by 3 hr after treatment with cycloheximide. In contrast, PDGF A-chain transcripts are more stable, and their constitutive levels were generally unaffected by cycloheximide. These results show that PDGF A- and B-chain genes are transcribed in the normal rat aorta and provide evidence for age-related change in the control of PDGF B-chain gene expression in aortic SMC. Independent regulation of transcript levels in cultured SMC leaves open the possibility that PDGFs of different composition (AA, AB, BB) play different roles in normal function of the artery wall.