Fibroblast Growth Factor Receptor-1 Expression is Associated with Neointimal Formation in Vitro

Neointimal formation was studied in a porcine aortic organ culture model that exhibits intimal smooth muscle cell accumulation after a brief time in culture. This in vitro model is dependent upon an intact endothelium, as removal of the endothelium at the time of harvesting results in the failure to develop a neointima. We previously showed that conditioned media from intact cultures induce neointimal formation in denuded aortic explants, and we speculated that basic fibroblast growth factor was the endothelial-derived factor in conditioned media promoting neointimal formation. However, the concentration of basic fibroblast growth factor in conditioned media from both intact and denuded explants, measured by an enzyme-linked immunosorbent assay, was not significantly different and, in fact, steadily decreased over the first 7 days of culture. Furthermore, the amount and intensity of immunoreactive basic fibroblast growth factor in tissue sections, also similar in both groups, decreased over the same time course. Nonetheless, exogenous basic fibroblast growth factor (1 ng/ml) induced neointimal formation in intact explants but was unable to do so in denuded explants. Western blot analysis of intimal lysates prepared from both intact and denuded explants showed a time-dependent increase in fibroblast growth factor receptor-1 expression over the first 7 days of culture, with higher levels seen in intimal lysates from intact explants at each time point examined. Immunoreactive fibroblast growth factor receptor-1 was detected in both endothelial cells and intimal smooth muscle cells of intact explant sections. These data indicate that, in the presence of the endothelium, neointimal formation may in part be mediated by upregulation of fibroblast growth factor receptor-1 in the intimal cells of porcine aortic explants.