Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065.
Vascular Biology Program, Boston Children's Hospital and Department of Surgery, Harvard Medical School, Boston, MA 02115.
J Lipid Res. 2017 Oct;58(10):1977-1987. doi: 10.1194/jlr.M076398. Epub 2017 Aug 16.
Macrophages use an extracellular, hydrolytic compartment formed by local actin polymerization to digest aggregated LDL (agLDL). Catabolism of agLDL promotes foam cell formation and creates an environment rich in LDL catabolites, including cholesterol and ceramide. Increased ceramide levels are present in lesional LDL, but the effect of ceramide on macrophage proatherogenic processes remains unknown. Here, we show that macrophages accumulate ceramide in atherosclerotic lesions. Using macrophages from sphingosine kinase 2 KO (SK2KO) mice to mimic ceramide-rich conditions of atherosclerotic lesions, we show that SK2KO macrophages display impaired actin polymerization and foam cell formation in response to contact with agLDL. C16-ceramide treatment impaired wild-type but not SK2KO macrophage actin polymerization, confirming that this effect is due to increased ceramide levels. We demonstrate that knockdown of RhoA or inhibition of Rho kinase restores agLDL-induced actin polymerization in SK2KO macrophages. Activation of RhoA in macrophages was sufficient to impair actin polymerization and foam cell formation in response to agLDL. Finally, we establish that during catabolism, macrophages take up ceramide from agLDL, and inhibition of ceramide generation modulates actin polymerization. These findings highlight a critical regulatory pathway by which ceramide impairs actin polymerization through increased RhoA/Rho kinase signaling and regulates foam cell formation.
巨噬细胞利用局部肌动蛋白聚合形成的细胞外水解隔室来消化聚集的 LDL（agLDL）。agLDL 的分解代谢促进泡沫细胞的形成，并产生富含 LDL 分解产物的环境，包括胆固醇和神经酰胺。病变 LDL 中存在神经酰胺水平升高，但神经酰胺对巨噬细胞前炎性过程的影响尚不清楚。在这里，我们表明巨噬细胞在动脉粥样硬化病变中积累神经酰胺。利用来自鞘氨醇激酶 2 KO（SK2KO）小鼠的巨噬细胞来模拟动脉粥样硬化病变中富含神经酰胺的条件，我们表明 SK2KO 巨噬细胞在与 agLDL 接触时表现出肌动蛋白聚合和泡沫细胞形成受损。C16-神经酰胺处理会损害野生型巨噬细胞但不会损害 SK2KO 巨噬细胞的肌动蛋白聚合，这证实了这种效应是由于神经酰胺水平升高所致。我们证明 RhoA 的敲低或 Rho 激酶的抑制恢复了 SK2KO 巨噬细胞中 agLDL 诱导的肌动蛋白聚合。巨噬细胞中 RhoA 的激活足以损害对 agLDL 的肌动蛋白聚合和泡沫细胞形成的反应。最后，我们确定在分解代谢过程中，巨噬细胞从 agLDL 摄取神经酰胺，并且神经酰胺生成的抑制调节肌动蛋白聚合。这些发现强调了一个关键的调节途径，即神经酰胺通过增加 RhoA/Rho 激酶信号传导来损害肌动蛋白聚合，并调节泡沫细胞的形成。
