Inhibitory Effects of Growth Factors on Proliferation of Porcine Smooth Muscle Cells in the Direct Co-culture System

Intimal hyperplasia (IH) is defined as the abnormal migration and proliferation of smooth muscle cells with associated deposition of extracellular matrix in the intimal layer. It is a natural response to endovascular injury induced by procedures such as angioplasty, stent implantation, or atherectomy. Research on the molecular pathways and mediators has led to the discovery of a variety of substances aimed to interrupt or attenuate IH. Heparin, low-molecular-weight heparin, aspirin, corticoids, angiotensin-converting enzyme inhibitors, cyclosporin, vascular endothelial growth factor (VEGF) and other agents have been investigated. However, none of these agents has been used with marked success at the clinical level. Therapeutic angiogenesis studies have demonstrated the potential of heparin binding angiogenic growth factors such as VEGF and basic fibroblast growth factor (bFGF/FGF-2) to treat ischemic heart diseases. Studies on endothelial nitric oxide synthase (eNOS) gene transfer in vivo showed attenuated IH caused by constitutive generation of nitric oxide (NO) via the NOS pathway. FGF-2 increased VEGF mRNA levels in single-cultures of rabbit smooth muscle cells (SMC) and also promoted NO production from endothelial cells (EC). Therefore, we hypothesize that FGF-2 mediates SMC inhibition through the NOS pathway. In order to elucidate the influence of these growth factors, we employed an appropriate SMC-EC co-culture system.Studies on SMC-EC interactions have been established in various in vitro co-culture systems. However, there exist only few co-culture systems in which the structure of a vessel wall is imitated. A direct co-culture model was used in this study to determine the effect of growth factors on the SMC and EC proliferation. In the following study we investigate the effects of VEGF, FGF-2 and FGF-2+VEGF on porcine aorta smooth muscle and endothelial cells. Addition of the higher concentrations (\u3e10 ng/ml) of FGF-2 to the SMC-EC direct co-culture greatly reduced smooth muscle cell numbers and cell cycle S-phase, as judged by propidium iodide DNA analysis using flow cytometry. We also observed that coadministration of FGF-2 with VEGF did not show any difference on SMC proliferation compared to control. These data demonstrate the potent regulatory capabilities of FGF-2 on smooth muscle cell inhibition. Nitric oxide which is generated by the enzyme NOS is hindered by the addition of NOS inhibitor, NG-Methyl-L-arginine acetate (L-NMMA). Utilizing L-NMMA we found that FGF-2 mediated smooth muscle cell inhibition does not follow the NOS pathway. This study is intended to understand the interactions of combination of therapeutic growth factors on vascular cells. The current study is a first step towards an overall goal of setting up an in vivo porcine model for clinical treatment of IH using FGF-2