Marianne Rouge

The Proliferative Response to Vascular Injury Is Suppressed by Angiotensin-Converting Enzyme Inhibition

Smooth muscle cell (SMC) proliferation and formation of extracellular matrix in the intima of muscular arteries are major processes that can lead to vascular stenosis in arteriosclerosis or after coronary angioplasty. These processes are also seen in the proliferative response to balloon catheter-induced vascular injury of the rat carotid artery, and result in marked neointima formation by 14 days after catheterization. We have shown recently that the angiotensin-converting enzyme (ACE) inhibitor cilazapril strongly suppressed this development of neointima. In this report, we show that the beneficial effects on neointima formation persist for at least 8 weeks after stopping treatment with cilazapril, and that continuous treatment may have additional inhibitory effects during the late phases of vascular remodeling after injury. To investigate further the possible mechanisms, we examined several vasoactive compounds in this model. Another ACE inhibitor of a different chemical class, captopril, reduced neointima formation as strongly as cilazapril (67 and 78%, respectively), but the calcium antagonist verapamil was not active as an inhibitor of neointima formation, despite similar lowering of blood pressure. Hydralazine and a new calcium antagonist, Ro 40-5967, partially suppressed neointima formation (36%, p less than 0.005 and 33%, p less than 0.05, respectively). In vitro, neither cilazapril nor its active metabolite, cilazaprilate, had any effect on SMC proliferation in response to serum or PDGF. To characterize further the role of angiotensin II (Ang II), we tested in cell culture the effects of Ang II and cilazaprilate on mRNA levels of several proteins potentially involved in regulating the SMC response.(ABSTRACT TRUNCATED AT 250 WORDS)

Conservation in sequence and affinity of human and rodent PDGF ligands and receptors

Platelet-derived growth factor (PDGF) consists of two chains, PDGF-A and -B, which activate as homo- or heterodimers two receptors, alpha and beta. To test PDGF function in vivo we have generated neutralizing monoclonal antibodies. When analyzed with rat PDGFs only antibodies raised against human PDGF-AA showed cross-species activity. This correlated with complete amino acid sequence conservation of PDGF-A whereas rat PDGF-B differed in six positions when cloned rat PDGF cDNAs were compared with their human homologs within the receptor binding region. Extracellular domains of cloned rat PDGF alpha- and beta-receptor cDNAs did not reflect this difference in cross-species ligand conservation. When rat extracellular domains were expressed as soluble proteins they bound human PDGF-BB with high affinity after immobilization of the purified proteins on solid phase. Dissociation constants were identical to those of their human homologs. Thus, high affinity binding of human PDGF-BB to extracellular domains does not depend on species origin but only on receptor type.

Human Vascular Smooth Muscle Cells Have at Least Two Distinct PDGF Receptors and Can Secrete PDGF-AA

Platelet-derived growth factor (PDGF), a potent mitogen and chemoattractant for smooth muscle cells and fibroblasts in culture, is believed to play an important role in the formation of proliferative lesions of arteriosclerosis. PDGF appears as three different dimeric isoforms: AA, AB, and BB. These were recently found to bind to two different receptors, the A/B receptor (which binds all three isoforms) and the B receptor (which binds only PDGF-BB). To find out whether these receptors exhibit functional differences, we have monitored the binding and mitogenic activities of PDGF-AA and -BB in human umbilical vein smooth muscle cells (HSMCs), human dermal fibroblasts (HFs), and Swiss mouse 3T3 cells. With each cell type, there was a good correlation between the maximal levels of DNA synthesis achieved by these isoforms and the numbers of the appropriate receptor present on the cell surface: HMSCs, which have at least 32,000 B receptors but only 8.000 A/B receptors, responded well to PDGF-BB but responded poorly to PDGF-AA; whereas Swiss 3T3 cells, which have about equal numbers of B and A/B receptors (70,000 and 90,000, respectively), responded equally well to both isoforms. PDGF-AB was a more efficacious mitogen of HSMCs and HFs than was PDGF-AA and inhibited [125I]-PDGF-BB binding to HSMCs more effectively than PDGF-AA. This indicates that there may exist a third PDGF receptor type to which PDGF-BB and -AB but not PDGF-AA can bind. These findings demonstrate that all three PDGF isoforms have mitogenic activity and that the responsiveness of a given cell to anyone of these isoforms is governed in part by the levels of the different receptors expressed. Finally, HSMCs secrete PDGF-AA-like activity. Thus, not only rat aortic SMCs and SMCs from diseased human arteries but also SMCs from healthy human vessels in vitro have the potential to regulate their growth in an autocrine and/or paracrine manner.