SMOOTH MUSCLE CELLS AND GRAFT INTIMAL HYPERPLASIA

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The long-term goal of our research is to improve patency of prosthetic vascular grafts by controlling intimal hyperplasia. Intimal hyperplasia is characterized by smooth muscle cell (SMC) accumulation and matrix deposition, and is most severe adjacent to the anastomoses of prosthetic grafts. Our studies of endothelial cell (EC) seeded grafts demonstrate a time-dependent increase in production of platelet-derived growth factor (PDGF), which is associated with the appearance of SMC in the inner capsule of the graft. Preliminary in vitro studies suggest that graft SMC are significantly modified compared to aortic SMC; graft SMC produce high levels of PDGF, proliferative in minimal serum, and growth is less sensitive to inhibition by heparin compared to aortic SMC. We postulate that SMC that migrate to, and proliferate in, the inner capsule of the graft are modified to produce mitogens to which they respond in an autocrine fashion. Furthermore, we propose that the response of graft SMC to natural growth stimulators and inhibitors is altered, and that the most effective method to inhibit intimal hyperplasia is to block a common pathway between the multiple mitogen receptors and cell division. To test these hypotheses, production and response to growth regulators will be studied. Production of PDGF A-chain, B-chain, basic fibroblast growth factor (bFGF), and transforming growth factor beta (TGFBeta) a bi- directional growth regulator, will be compared in graft and aortic EC and SMC. To determine differences in the capacity of SMC to respond to mitogens, receptor number and affinity of binding of PDGF, bFGF, and TGFBeta will be studied in graft and aortic SMC. In addition, proliferative and migratory responses of graft and arterial SMC to PDGF- AA, AB, -BB; bFGF; TGFBeta; and heparin will be compared. If differences in mitogen or inhibitor production or response are identified between graft and artery SMC in vitro, the level of gene expression will be determined, and differences in mRNA related to variation in gene transcription rates or message stability. To determine if SMC proliferation on grafts can be inhibited by blocking a late common pathway of cell division, the efficacy of antisense to c-myb to inhibit SMC proliferation will be studied in vitro and in vivo. Production of mitogens by SMC lining the graft may be responsible for continued SMC migration and proliferation as well as matrix deposition causing neointimal hyperplasia of grafts. The proposed studies will lead to a better understanding of alterations in mitogen production and response by SMC lining prosthetic vascular grafts, and the ability to suppress proliferation by blocking the common pathway in cell division. Ultimately, this may lead to interventions to inhibit mitogenic responses and control the development of anastomotic intimal hyperplasia.