Proliferating Arterial Smooth Muscle Cells After Balloon Injury Express TNF-α but Not Interleukin-1 or Basic Fibroblast Growth Factor

Abstract

We have recently reported that balloon withdrawal injury to rabbit abdominal aortas induces sustained activation indicated by the expression of certain adhesion molecules such as vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 in regenerating endothelial cells and/or proliferating smooth muscle cells (SMCs). Local cytokine signaling may contribute to ongoing modulation of cellular functions and proliferation of intimal SMCs after acute vascular injury. We therefore studied the expression of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β), proinflammatory and SMC growth–promoting cytokines, and basic fibroblast growth factor (bFGF) in SMCs of rabbit aorta at 2 (n=4), 5 (n=4), and 10 days (n=6) after balloon injury. All animals were given bromodeoxyuridine (BrdU, 10 mg/kg per day) continuously to label proliferating SMCs. Frozen cross sections of injured vessels at each time point after balloon injury were examined by immunoperoxidase staining with monoclonal antibodies. As early as 2 days after injury, before intimal thickening begins, foci of medial SMCs expressed TNF-α, but not all TNF-α–positive medial SMCs had incorporated BrdU, suggesting that TNF-α expression by medial SMCs may precede their proliferation. At 5 days, TNF-α–bearing and BrdU-labeled medial SMCs increased in number. At 10 days after injury, when uniform intimal thickening occurred, almost all neointimal SMCs and foci of medial SMCs labeled with BrdU. Most of the BrdU-positive (proliferating) SMCs expressed immunoreactive TNF-α. Reverse transcription polymerase chain reaction showed increased TNF-α mRNA at 10 days after ballooning in the injured portion of the aorta. In contrast, regions of SMC proliferation showed inconsistent IL-1β expression, and bFGF, abundant in normal rabbit arteries, was not detected in areas of SMC replication. These data indicate that replication of arterial SMCs after balloon injury occurs in regions of TNF-α but not IL-1β expression and correlates inversely with the presence of bFGF. These results indicate that SMC-derived TNF-α serves as a marker of modulated SMC phenotype after acute vascular injury and may contribute to local cellular activation and proliferation of SMCs at sites of arterial injury.