GROWTH-REGULATION IN PRIMARY CULTURE OF RABBIT ARTERIAL SMOOTH-MUSCLE CELLS BY PLATELET-DERIVED GROWTH-FACTOR, INSULIN-LIKE GROWTH-FACTOR-I, AND EPIDERMAL GROWTH-FACTOR

Many studies have linked the proliferation of smooth muscle cells (SMC) to the development of atherosclerotic lesions. We examined the effects of platelet-derived growth factor (PDGF), insulin-like growth factor-I (IGF-I), and epidermal growth factor (EGF) on the regulation of SMC grown on type I collagen-coated dishes in serum-free primary culture. When added alone, PDGF (10 ng/ml), IGF-I (20 ng/ml), and EGF (10 ng/ml) produced minimal effects on BrdU (5-bromo-2'deoxyuridine) incorporation into cellular DNA and on cell growth. However, simultaneous addition of PDGF and IGF-I significantly stimulated DNA synthesis and cell growth. The combination of PDGF, IGF-I, and EGF synergistically stimulated DNA synthesis and cell proliferation. Flow cytometric analysis indicated that type I collagen alone promoted the phenotypic modulation and progression of the cells from the GO (contractile phenotype) to the G1A phase (intermediate phenotype), PDGF and IGF-I, together, stimulated the rate of cell transition from the G1A to the G1B and S phases (synthetic phenotype), and PDGF, IGF-I, and EGF together stimulated the rate of cell transition into the S and G2+M phases. In contrast, in quiescent secondary cultured SMC (G1B phase), PDGF alone was able to initiate DNA synthesis, although IGF-I and EGF were required to complete DNA synthesis. These results reveal that PDGF and IGF-I stimulate the cells to complete the G1A phase and proceed to the G1B phase and that EGF regulates the rate of entry into the S phase in rabbit SMC in primary culture. Furthermore, differences in the responsiveness to these growth factors between primary and secondary cultures reflected the varying phenotypic properties of vascular SMC. (C) 1994 Academic Press,Inc.