Department of Surgery, Division of Cardiothoracic Surgery, University of Colorado Anschutz Medical Center, Aurora, Colorado 80045, USA.
J Surg Res. 2011 Nov;171(1):e27-31. doi: 10.1016/j.jss.2011.06.033. Epub 2011 Jul 19.
Macrophage foam cells are central in the development of atherosclerosis, but the mechanism of foam cell formation is unclear. Toll-like receptor 4 (TLR4) signaling is known to participate in the pathogenesis of atherosclerosis. Further, oxidized low density lipoprotein (oxLDL) enhances TLR4 expression in macrophages. We hypothesized that TLR4 mediates macrophage differentiation to foam cells.
Peritoneal macrophages were isolated by lavage from TLR4 competent C3H/HeN mice and TLR4 defective C3H/HeJ mice. Cells were treated with oxLDL, lipopolysaccharide (LPS), or oxLDL plus LPS. Cells were also treated with a TLR4 blocking antibody before oxLDL treatment. Foam cells were identified by Oil red O staining for intracellular lipids. Percent macrophage differentiation into foam cells were compared between C3H/HeN and C3H/HeJ macrophages.
Following oxLDL treatment 29% of TLR4 competent macrophages differentiated into foam cells compared to 5.8% of TLR4 defective macrophages (P < 0.01). Pretreatment with a TLR4 blocking antibody decreased the differentiation of TLR4 competent cells to foam cells from 29% to 13% (P < 0.01). Stimulation of TLR4 with LPS in the presence of oxLDL increased differentiation of TLR4 competent cells to foam cells from 29% to 60% (P < 0.01). In addition, there was a pattern in the spatial relationship between foam cells that were consistently observed in clusters rather than as isolated cells.
TLR4 is necessary for oxLDL-induced macrophage differentiation to foam cells. Macrophage foam cell clustering may indicate an underlying intercellular signaling mechanism that facilitates foam cell formation. We conclude that TLR4 contributes to the pathogenesis of atherosclerosis by promoting foam cell formation.
泡沫细胞是动脉粥样硬化形成的关键，但其形成机制尚不清楚。已知 Toll 样受体 4（TLR4）信号参与动脉粥样硬化的发病机制。此外，氧化型低密度脂蛋白（oxLDL）增强了巨噬细胞中 TLR4 的表达。我们假设 TLR4 介导巨噬细胞分化为泡沫细胞。
用腹腔灌洗法从小鼠腹腔中分离出 TLR4 功能正常的 C3H/HeN 型和 TLR4 缺陷的 C3H/HeJ 型巨噬细胞。用 oxLDL、脂多糖（LPS）或 oxLDL+LPS 处理细胞。oxLDL 处理前，用 TLR4 阻断抗体处理细胞。用油红 O 染色法对细胞内脂质进行染色，鉴定泡沫细胞。比较 C3H/HeN 和 C3H/HeJ 巨噬细胞向泡沫细胞的分化百分比。
oxLDL 处理后，29%的 TLR4 功能正常的巨噬细胞分化为泡沫细胞，而 TLR4 缺陷的巨噬细胞只有 5.8%（P < 0.01）。用 TLR4 阻断抗体预处理可使 TLR4 功能正常的细胞向泡沫细胞的分化率从 29%降至 13%（P < 0.01）。在 oxLDL 存在的情况下，TLR4 激动剂 LPS 可使 TLR4 功能正常的细胞向泡沫细胞的分化率从 29%增加至 60%（P < 0.01）。此外，泡沫细胞之间存在一种聚集模式，这些细胞总是聚集在一起，而不是孤立存在。
TLR4 是 oxLDL 诱导巨噬细胞分化为泡沫细胞所必需的。巨噬细胞泡沫细胞的聚集可能表明存在促进泡沫细胞形成的细胞间信号机制。我们的结论是，TLR4 通过促进泡沫细胞形成而促进动脉粥样硬化的发病机制。
