Section of Experimental Atherosclerosis, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, USA.
J Lipid Res. 2012 Jan;53(1):34-42. doi: 10.1194/jlr.M018887. Epub 2011 Nov 4.
Accumulation of cholesterol by macrophage uptake of LDL is a key event in the formation of atherosclerotic plaques. Previous research has shown that granulocyte-macrophage colony-stimulating factor (GM-CSF) is present in atherosclerotic plaques and promotes aortic lipid accumulation. However, it has not been determined whether murine GM-CSF-differentiated macrophages take up LDL to become foam cells. GM-CSF-differentiated macrophages from LDL receptor-null mice were incubated with LDL, resulting in massive macrophage cholesterol accumulation. Incubation of LDL receptor-null or wild-type macrophages with increasing concentrations of ¹²⁵I-LDL showed nonsaturable macrophage LDL uptake that was linearly related to the amount of LDL added, indicating that LDL uptake was mediated by fluid-phase pinocytosis. Previous studies suggest that phosphoinositide 3-kinases (PI3K) mediate macrophage fluid-phase pinocytosis, although the isoform mediating this process has not been determined. Because PI3Kγ is known to promote aortic lipid accumulation, we investigated its role in mediating macrophage fluid-phase pinocytosis of LDL. Wild-type macrophages incubated with LDL and the PI3Kγ inhibitor AS605240 or PI3Kγ-null macrophages incubated with LDL showed an ∼50% reduction in LDL uptake and cholesterol accumulation compared with wild-type macrophages incubated with LDL only. These results show that GM-CSF-differentiated murine macrophages become foam cells by fluid-phase pinocytosis of LDL and identify PI3Kγ as contributing to this process.
巨噬细胞摄取 LDL 导致胆固醇积累是动脉粥样硬化斑块形成的关键事件。先前的研究表明，粒细胞-巨噬细胞集落刺激因子（GM-CSF）存在于动脉粥样硬化斑块中，并促进主动脉脂质积累。然而，尚未确定鼠 GM-CSF 分化的巨噬细胞是否摄取 LDL 成为泡沫细胞。用 LDL 孵育 LDL 受体缺失小鼠的 GM-CSF 分化的巨噬细胞，导致大量巨噬细胞胆固醇积累。用递增浓度的 ¹²⁵I-LDL 孵育 LDL 受体缺失或野生型巨噬细胞显示非饱和的巨噬细胞 LDL 摄取，与添加的 LDL 量呈线性相关，表明 LDL 摄取是由液相胞吞作用介导的。先前的研究表明，磷酸肌醇 3-激酶（PI3K）介导巨噬细胞液相胞吞作用，尽管尚未确定介导该过程的同工酶。由于已知 PI3Kγ 促进主动脉脂质积累，我们研究了它在介导巨噬细胞 LDL 液相胞吞作用中的作用。用 LDL 孵育野生型巨噬细胞和 PI3Kγ 抑制剂 AS605240 或用 LDL 孵育 PI3Kγ 缺失巨噬细胞，与仅用 LDL 孵育的野生型巨噬细胞相比，LDL 摄取和胆固醇积累减少约 50%。这些结果表明，GM-CSF 分化的鼠巨噬细胞通过 LDL 的液相胞吞作用成为泡沫细胞，并确定 PI3Kγ 参与了这一过程。
