Vascular Endothelial Cells and Smooth Muscle Cells Differ in Expression of Fas and Fas Ligand and in Sensitivity to Fas Ligand–Induced Cell Death

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Abstract
—Fas ligand (FasL) is a death factor that induces apoptosis in cells bearing its receptor, Fas. Fas and FasL have been detected in the vessel wall, and it has been proposed that Fas-mediated apoptosis has a role in physiological and pathological cell turnover in the vasculature. Here, we evaluated the expression of Fas in the presence and absence of cytokines on both endothelial cells (ECs) and vascular smooth muscle cells (VSMCs). We also examined the sensitivity of ECs and VSMCs to Fas-mediated apoptosis induced by exposure to multiple Fas agonists: soluble FasL, anti-Fas antibody, and membrane-bound FasL resulting from transduction with a replication-defective adenovirus expressing FasL (Adeno-FasL). Cell-surface FasL expression was detected on human ECs with the use of 4 anti-FasL antibodies, whereas cell-surface FasL expression was not detected on VSMCs. Unstimulated ECs expressed relatively low levels of Fas, but expression was upregulated after treatment with tumor necrosis factor-α (TNF-α) or interferon gamma (IFN-γ). In contrast, VSMCs expressed relatively high levels of Fas, and treatment with TNF-α or IFN-γ induced little or no upregulation under the conditions of these assays. ECs were resistant to death after exposure to soluble FasL or agonist anti-Fas antibody and also after infection with Adeno-FasL in the presence or absence of cytokine treatment. In contrast, VSMCs remained viable in the presence of soluble FasL or agonist anti-Fas antibody, but they underwent apoptosis after infection with Adeno-FasL. IFN-γ enhanced Adeno-FasL-induced death of VSMCs, but TNF-α did not. These findings provide insights about the potential role of Fas-mediated apoptosis in the vessel wall and suggest strategies to treat proliferative vascular diseases by exploiting the differential sensitivity of ECs and VSMCs to FasL-induced cell death.