INTRODUCTION: Inflammatory reactions following mechanical stress produce fibrosis and scarring of the ligament flavum(LF) that result in hypertrophy, a major pathological feature of spinal stenosis. To prove our hypothesis that activated LF, which was exposed to inflammation, induce angiogenesis, thus resulting in hypertrophy, we use coculture of human lumbar LF cells and activated macropage like THP‐1 cells.
METHODS: To determine their response to the inflammatory reaction, human LF cells were co‐cultured with phorbol myristate acetate‐stimulated macrophage‐like THP‐1 cells. The conditioned media were assayed for tumor necrosis factor (TNF)‐α, interleukin (IL)‐1β, IL‐6, IL‐8, vascular endothelial growth factor (VEGF), and transforming growth factor (TGF)‐β1. Naïve and macrophage‐exposed LF cells that responded to TNF‐α/IL‐1β were compared using the same outcome measures. Normal and hypertrophied LF tissues were compared using immunohistochemical staining with an endothelial cell marker (CD34) and TGF‐β1.
RESULTS: Larger quantities of IL‐6, IL‐8, and VEGF were secreted by co‐cultured cells than by macrophages or LF cells. Prior macrophage exposure increased the secretion of IL‐6, IL‐8, and VEGF in response to TNF‐α/IL‐1β stimulation, except for IL‐6 production in response to IL‐1β. More CD34‐positive stained endothelial cells were present in hypertrophied LF tissue than in normal tissue. TGF‐β1 expression was observed in endothelial cells, but not in LF cells.
DISCUSSION: LF cells interact with macrophage‐like cells to produce angiogenesisrelated factors. Hypertrophied LF showed many microvessels with CD34‐positive endothelial cells, which express TGF‐β1, suggesting that angiogenesis plays a major role in the pathomechanism of LF hypertrophy in lumbar spinal stenosis. Endothelial cells or blood‐borne factors from proliferated capillaries thus produce fibrosis and scarring as part of the hypertrophy mechanism.